Phase unwrapping algorithm based on phase diversity wavefront reconstruction and virtual Hartmann-Shack technology

Ying Zhang, Hua Bao, Naiting Gu, Shuqi Li, Yiqun Zhang, and Changhui Rao

DOI: 10.1364/OL.515821 Received 13 Dec 2023; Accepted 24 Apr 2024; Posted 24 Apr 2024  View: PDF

Abstract: Phase unwrapping algorithms play a crucial role in various phase measurement techniques. Traditional algorithms cannot work well in strong noise environments, which makes it very difficult to obtain the accurate absolute phase from the noisy wrapped phase. In this paper, we proposed a novel phase unwrapping algorithm based on phase diversity (PD) wavefront reconstruction and virtual Hartmann-Shack (VHS) technology, called PD-VHS, which coped well with the large-scale noise in the wrapped phase. In simulation experiments, hundreds of random noise wrapped phases, containing the first 45 Zernike polynomials and the wavefront RMS= 0.5λ, 1λ,are used to compare the classical quality-map guided algorithm, the VHS algorithm with decent noise immunity and our PD-VHS algorithm. When SNR drops to just 2dB, the mean RMSEs of residual wavefront between the unwrapped result and the absolute phase of quality-map guided algorithm and VHS algorithm are up to 3.99λ, 0.44λ and 4.29λ, 0.85λ respectively, but our algorithm's are low to 0.11λ and 0.17λ. Simulation results demonstrated that the PD-VHS algorithm significantly outperforms the quality-map guided algorithm and the VHS algorithm under strong noise conditions.

Surface relief VCSELs at 670nm with integrated polymer microlens for highly collimated fundamental-mode emission

Lena Engel, Farnaz Khamseh, Michael Zimmer, Michael Jetter, and Peter Michler

DOI: 10.1364/OL.524493 Received 21 Mar 2024; Accepted 24 Apr 2024; Posted 24 Apr 2024  View: PDF

Abstract: We demonstrate the integration of a wet-chemically etched surface relief on a VCSEL emitting in the red spectral range for higher-order mode suppression. With this relief, fundamental-mode emission is achieved over the entire power range from threshold beyond thermal rollover. For collimation of the emitted beam, we implement polymer microlenses fabricated on-chip by thermal reflow technique. We reduce the angle of divergence for all injected currents to a maximum of 2°. By measuringhigh-resolution spectra, we show that Gaussian beam profiles correspond to pure fundamental-mode emission which is preserved after implementation of the polymer microlens onto the etched relief, proving the compatibility of the two processes.

Channel modeling for NLoS visible light networks with integrated sensing and communication

Pinpin Zhang, Jiacheng Wu, Zixian Wei, Yimao Sun, Rui Deng, and Yanbing Yang

DOI: 10.1364/OL.520129 Received 30 Jan 2024; Accepted 24 Apr 2024; Posted 24 Apr 2024  View: PDF

Abstract: Inspired by the advanced integrated sensing and communication (ISAC), in this Letter, we explore the non-line-of-sight (NLoS) optical channels formed by reflections from the ground or objects to establish an integrated channel model for simultaneous communication and sensing. The integrated channel model can, on the one hand, perceive the changes in the surrounding environment in time; on the other hand, determine whether these changes positively or negatively affect the quality of communication simultaneously. To validate the effectiveness of the proposed model, from the sensing perspective, we analyze the impact of various floor materials and objects on the integrated channel; from the communication perspective, we characterize the influence of perceived environmental changes on communication performance by calculating throughput. Simulation results confirm the capability of the derived model, which can support the design and deployment of visible light-based ISAC networks.

Light Field Image Super-Resolution Based on Dual Learning and Deep Fourier Channel Attention

Jian Ma, Zhipeng Li, Cheng Jin, Ping An, Dong Liang, and Linsheng Huang

DOI: 10.1364/OL.522701 Received 29 Feb 2024; Accepted 24 Apr 2024; Posted 24 Apr 2024  View: PDF

Abstract: Light Field (LF) imaging has gained significant attention in the field of computational imaging due to its unique capability to capture both spatial and angular information of a scene. In recent years, super-resolution (SR) techniques based on deep learning have shown considerable advantages in enhancing LF image resolution. However, the inherent challenges of obtaining rich structural information and reconstructing complex texture details persist, particularly in scenarios where spatial and angular information are intricately interwoven. This Letter introduces a novel approach for Disentangling LF Image SR Network (DLISN) by leveraging the synergy of dual learning and Fourier channel attention (FCA) mechanisms. Dual learning strategies are employed to enhance reconstruction results, addressing limitations in model generalization caused by the difficulty in acquiring paired datasets in real-world LF scenarios. The integration of FCA facilitates the extraction of high-frequency information associated with different structures, contributing to improved spatial resolution. Experimental results consistently demonstrate superior performance in enhancing the resolution of LF images.

High-sensitivity vector magnetic field sensor based on V-shaped multimode-no-core-multimode fiber structure

yu ji, Shengli Pu, Weinan Liu, Chen Zhang, Jiaqi Fu, shufei han, Simiao Duan, yang Huang, and Mahieddine Lahoubi

DOI: 10.1364/OL.522928 Received 06 Mar 2024; Accepted 24 Apr 2024; Posted 24 Apr 2024  View: PDF

Abstract: This work proposes and investigates a bent multimode-no-core-multimode optical fiber structure for vector magnetic field sensing applications. The bent no-core fiber (NCF) serves as the sensing area, and the gold film is deposited on its surface to excite the surface plasmon resonance effect. Due to the strong evanescent field of the unclad and bent NCF, the as-fabricated sensor exhibits a high sensitivity of 5630 nm/RIU in the refractive index range of 1.36-1.39. Magnetic fluid is employed as the magneto-sensitive material for magnetic field sensing, exhibiting a high magnetic field intensity sensitivity of 5.74 nm/mT and a high magnetic field direction sensitivity of 0.22 nm/°. The proposed sensor features a simple structure, low cost, point sensing, and excellent mechanical performance.

Self-healing propagation of longitudinally varying vector optical beam for distance measurement

Ji-Xiang Guo, Jin-Song Li, Yulei Wang, Jia-Qi Lv, and Zhiwei Lv

DOI: 10.1364/OL.524158 Received 19 Mar 2024; Accepted 23 Apr 2024; Posted 23 Apr 2024  View: PDF

Abstract: Based on the longitudinal manipulation of polarization, special vector optical beam (VOB) with customized polarization variation in propagation direction can be generated, whose properties and applications remain to be studied. Here, the self-healing propagation behaviors of the longitudinally varying VOB after an opaque object are investigated, and the localized polarization responses on the object distance are revealed. On this basis, characteristic parameters are defined to measure the distance of object, achieving a minimum relative error of 0.63% in a longitudinal range of 300 mm. Besides, the correlations and uncoupling methods of object distance and size are discussed. Our studies open new ways to use the structural properties of VOB, and may be instructive for laser measurement.

Simulation of diffraction and scattering using the Wigner Distribution Function

Emilie Pietersoone, Jean Michel Letang, Simon Rit, and Max Langer

DOI: 10.1364/OL.523608 Received 19 Mar 2024; Accepted 23 Apr 2024; Posted 23 Apr 2024  View: PDF

Abstract: X-ray phase-contrast imaging enhances soft tissue visualization by leveraging the phase shift of X-rays passing through materials. It permits to minimize radiation exposure due to high contrast, as well as high resolution imaging limited by the wavelength of the X-rays. Phase retrieval extracts the phase shift computationally, but simulated images fail to recreate low-frequency noise observed in experimental images. To this end, we propose a new method to simulate phase contrast images using the Wigner Distribution Function. This permits the simulation of wave and particle effects simultaneously and simulates images photon by photon. Here, we give a first demonstration of the method by simulating the Gaussian double-slit experiment. It has the potential for realistic simulation of low-dose imaging.

Defocus-integration interferometric scattering microscopy for speckle suppression and enhancing nanoparticle detection on substrate

Nanfang Jiao, Shupei Lin, Delong Feng, Yong He, and Xuewen Chen

DOI: 10.1364/OL.519263 Received 17 Jan 2024; Accepted 23 Apr 2024; Posted 23 Apr 2024  View: PDF

Abstract: Direct optical detection and imaging of single nanoparticles on substrate in wide field underpin vast applications across different research fields. However, the speckles originating from the unavoidable random surface undulations of the substrate ultimately limit the size of the decipherable nanoparticles by the current optical techniques, including the ultrasensitive interferometric scattering microscopy (iSCAT). Here we report a defocus-integration iSCAT to suppress the speckle noise and to enhance the detection and imaging of single nanoparticles on ultra-flat glass substrate and silicon wafer. In particular, we discover distinct symmetry properties of the scattering phase between the nanoparticle and the surface undulations that cause the speckles. Consequently, we develop the defocus-integration technique to suppress the speckles.We experimentally achieve an enhancement of the signal to noise ratio by 6.9 dB for the nanoparticle detection. We demonstrate that the technique is generally applicable for nanoparticles of various materials and for both low and high refractive-index substrates.

Beam swinging coherent Doppler wind lidar utilizing wavelength switching through a single telescope

Hidenobu Tsuji, Nobuki Kotake, Shumpei Kameyama, Toshiyuki Ando, and Eisuke Haraguchi

DOI: 10.1364/OL.523674 Received 13 Mar 2024; Accepted 22 Apr 2024; Posted 23 Apr 2024  View: PDF

Abstract: We have developed a new beam-swinging coherent Doppler wind lidar (BS-CDWL) by employing wavelength switching method using mass-produced components for wavelength division multiplexing (WDM) optical communication systems. This BS-CDWL also has a single and position-to-angle conversion telescope for multiple LOS measurement which contributes to cost-effectiveness. Preliminary wind sensing result is shown with measurable range of up to 350 m.

Enabling Endogenous Distributed Acoustic Sensing in Digital Subcarrier Coherent Transmission System

Zihe Hu, Ming-Ming Zhang, Yuqi Li, Junda Chen, Weihao Li, Yuxuan Xiong, Luming Zhao, Can Zhao, and Ming Tang

DOI: 10.1364/OL.524132 Received 19 Mar 2024; Accepted 22 Apr 2024; Posted 23 Apr 2024  View: PDF

Abstract: To monitor the health of the fiber network and its ambient environment in densely populated access/metro network areas, in this letter, an endogenous distributed acoustic sensing (DAS) has been proposed and achieved in a coherent digital subcarrier multiplexing (DSCM) system. Rather than specially-allocating sensing probe in general integrated communication and sensing schemes, the fractional Fourier transformed (FrFT) training sequence (TS) designated for time/frequency synchronization in DSCM coherent communications has been repurposed for sensing. While achieving excellent synchronization performance of communication, the FrFT-based TS can also be concurrently utilized to perform distributed vibration sensing. Experimental results demonstrate that the FrFT-based timing/frequency synchronization sequence is repurposed to achieve a DAS sensitivity of 70 pε·Hz-½ at a spatial resolution of 5 m, along with 100-Gb/s 16 quadrature amplitude modulation (QAM) DSCM transmission, without a loss of spectral efficiency.

Optically synchronized unidirectional optical amplifiers based coherent optical fiber links

Ziang Qiu, Rong Li, Liang Hu, Guiling Wu, and Jianping Chen

DOI: 10.1364/OL.524886 Received 27 Mar 2024; Accepted 22 Apr 2024; Posted 24 Apr 2024  View: PDF

Abstract: We report on the realization of a unidirectional transmission based bidirectional erbium-doped fiber amplifier (UTB-EDFA) for the coherent optical fiber links. By applying an optical phase-locked loop (OPLL) between the two unidirectional EDFAs (Ui-EDFAs) paths, the annoying uncorrelated phase noise between the two paths can be largely suppressed. Promisingly, we can independently optimize the gains of the UTB-EDFAs for bidirectional transmissions, resulting in the higher net gain acquired compared with the conventional single-path bidirectional EDFAs (SPBAs) based ones. We demonstrate that the fractional frequency instability of the UTB-EDFAs based scheme can be decreased by 26.3 % over the most asymmetrical 100 km two-way optical frequency comparison (TWC) system compared with the SPBAs based ones and, more importantly, can acquire higher net gain for unevenly distributed sub-links over ultra-long fiber links, such as 1,000 km, by independently optimizing the gains. This technique paves the way for the applications of the large-scale fiber networks.

Vortex phase-based Adaptive Moiré technique accommodating micro displacement measurement of freeform surfaces

Zhang Lei and aoxin Wang

DOI: 10.1364/OL.524170 Received 19 Mar 2024; Accepted 22 Apr 2024; Posted 22 Apr 2024  View: PDF

Abstract: The traditional displacement measurement interferometer (DMI) provides elegant performance by straight interference fringe movement counting to convert phase calculation into image motion calculation. However, it cannot be applied to curve surface displacement measurement. The counting of the movement of irregular fringes is not achievable. We provide an adaptive Moiré technique with a vortex phase to realize micro displacement measurement of a freeform surface with any continuous shape. The technique produces straight Moiré fringes that rotate in a circle, regardless of the shape of interference fringes and tested surface shapes. The vortex phase is used to record only one interferogram before measurement for subsequent data processing, and then no longer participates in the displacement measurement process. Therefore, this technology can be employed to remold traditional DMIs. Simulations and experiments validating the method are presented.

Dual-key-based adaptive watermark embedding for light field 3D images

Qiming Wu, JunFeng Guo, Yu Kou, Shouxin Liu, Changjian Shang, and xiaowei Li

DOI: 10.1364/OL.521288 Received 08 Feb 2024; Accepted 21 Apr 2024; Posted 22 Apr 2024  View: PDF

Abstract: The existing methods fail to effectively utilize the viewpoint information of light field 3D images based on integral imaging for watermark embedding which results in a serious decrease in both invisibility and robustness of the watermarking network. In this regard, we propose a novel approach called the light field 3D dual-key-based watermarking network. Our method employs a pixel mapping algorithm to obtain the disparity sub-image of the light field 3D image and generates an encoding key. Adaptive watermark embedding is then performed on the disparity sub-image and a steganographic key is generated. Finally, the light field 3D image with the embedded watermark is reconstructed. During decoding, the watermark information is obtained by combining the two keys. Compared with previous approaches, our method reasonably utilizes the viewpoint information of light field 3D images, resulting in significantly improved invisibility and robustness of the watermark, while also reducing the algorithm's device requirements.

Tilted Bragg grating in a glycerol-infiltrated specialty optical fiber for temperature and strain measurements

Xuehao Hu, yang liu, Heming Wei, Chuanxin Teng, Qianqing Yu, Zhijun luo, Zhenggang Lian, Hang Qu, and Christophe Caucheteur

DOI: 10.1364/OL.521797 Received 20 Feb 2024; Accepted 21 Apr 2024; Posted 22 Apr 2024  View: PDF

Abstract: In this Letter, we propose an in-line tilted fiber Bragg grating sensor for temperature and strain measurements. The grating is inscribed in a specialty optical fiber using tightly-focused femtosecond laser pulses and the line-by-line direct writing method. Beside the central core in which the grating is produced, a hollow channel filled with glycerol aqueous solution significantly improves the sensitivity of the fiber cladding modes due to its high thermo-optic coefficient. We show that the temperature sensitivity of the core mode is 9.8 pm/°C , while the one of the cladding modes is strongly altered and can reach ‒24.3 pm/°C, in the investigated range of 20-40 °C. For strain measurement, sensitivities of the core mode and the cladding modes are similar (~0.60 pm/με) between 0 and 2400 με. The significative difference of temperature sensitivity between the two modes facilitates the discrimination of the dual parameters in simultaneous measurements.

RF E-field enhanced sensing based on Rydberg-atom-based superheterodyne receiver

Wenguang yang, Mingyong Jing, Hao Zhang, Linjie Zhang, Liantuan Xiao, and Suotang Jia

DOI: 10.1364/OL.522466 Received 26 Feb 2024; Accepted 21 Apr 2024; Posted 22 Apr 2024  View: PDF

Abstract: We present enhanced sensing of radio frequency (RF) electric field (E-field) by the combined polarizability of Rydberg atoms and the optimized local oscillator (LO) field of superheterodyne receiving. Our modified theoretical model reveals the dependencies of the sensitivity of E-field amplitude measurement on the polarizability of Rydberg states and the strength of the LO field. The enhanced sensitivities of megahertz (MHz) E-field are demonstrated at the optimal LO field for three different Rydberg states 43D5/2, 60S1/2, and 90S1/2. The sensitivity of 63 MHz for the 90S1/2 state reaches 9.6×10^-5 V/m/Hz½, which is approximately an order of magnitude higher than those already published. This result closely approaches the theoretical sensitivity limit of RF dipole antennas and indicates the potential for exceeding the limit in measuring sub-MHz E-field. This atomic sensor based on the Rydberg Stark effect with heterodyne technique is expected to boost an alternative solution to electric dipole antennas.

Photonic random walks with traps

Stefano Longhi

DOI: 10.1364/OL.522686 Received 29 Feb 2024; Accepted 21 Apr 2024; Posted 22 Apr 2024  View: PDF

Abstract: Random walks behave very differently for classical and quantum particles. Here we unveil a ubiquitous distinctive behavior of random walks of a photon in a one-dimensional lattice in the presence of a finite number of traps, at which the photon can be destroyed and the walk terminates. While for a classical random walk the photon is unavoidably destroyed by the traps, for a quantum walk the photon can remain alive and the walk continues for ever. Such an intriguing behavior is illustrated by considering photonic random walks in synthetic mesh lattices with controllable decoherence, which enables to switch from quantum to classical random walks.

Quasi-distributed quartz enhanced photoacoustic spectroscopy sensing based on hollow waveguide micropores

Weipeng Chen, Shunda Qiao, Ying He, Jie Zhu, Kang Wang, Limin Xiao, and Yufei Ma

DOI: 10.1364/OL.525188 Received 29 Mar 2024; Accepted 21 Apr 2024; Posted 22 Apr 2024  View: PDF

Abstract: In this article, a quasi-distributed quartz enhanced photoacoustic spectroscopy (QEPAS) gas sensing based on hollow waveguide micropores (HWGMP) was reported for the first time. Three micropores were developed on the HWG to achieve distributed detection units. Three self-designed quartz tuning fork (QTFs) with low resonant frequency of 8.7 kHz were selected as the acoustic wave traducer to improve the detection performance. Compared with micro-nano fiber evanescent wave (FEW) QEPAS, HWGMP-QEPAS sensor has advantages such as strong anti-interference ability, low loss and cost. Acetylene (C2H2) was selected as the target gas to verify the characteristics of the reported sensor. The experimental results showed that the three QTFs almost had the same sensing ability and possessed an excellent linear concentration response to C2H2. The minimum detection limits (MDL) for the three QTFs were determined as 68.90 ppm, 68.31 ppm, and 66.62 ppm, respectively. Allan deviation analysis indicated that the system had good long-term stability and the MDL can be improved below 3 ppm in an average time of 1000 s.

Receiver IQ skew tolerant baud-rate timing recovery scheme for short-reach coherent optical interconnection

siyu gong, Yanfu Yang, Qian Xiang, Linsheng Fan, chen cheng, Qun Zhang, and Tianjian Zuo

DOI: 10.1364/OL.523842 Received 14 Mar 2024; Accepted 20 Apr 2024; Posted 22 Apr 2024  View: PDF

Abstract: A baud-rate sampling timing recovery (TR) scheme with receiver IQ skew tolerance is proposed and experimentally demonstrated. The proposed scheme performs independent TR for the in-phase and quadrature (IQ) tributary signals, thereby tracking the sampling phase error while naturally compensating for receiver IQ skew. The robustness of the IQ-independent TR to frequency offset (FO) and phase noise is theoretically analyzed. To address IQ misalignment caused by the IQ-independent TR, the use of pseudo-noise (PN) sequences for IQ frame synchronization is proposed. The proposed scheme achieves accurate timing recovery with hardware-efficient baud-rate sampling in the presence of receiver IQ skew, laying the foundation for stable performance of subsequent baud-rate equalization. The performance of the scheme is validated in a 56 GBaud polarization division multiplexed (PDM) 16QAM coherent experimental system. Experimental results demonstrate that the proposed scheme achieves similar BER performance as the modified Gardner + RVMIMO (@2SPS) scheme. Moreover, the proposed scheme exhibits robustness to arbitrary IQ skew compared to the ABSPD + RVMIMO (@1SPS) scheme.

Confidential MIMO optical camera communication aided by two-dimensional pilot

Shanshan Hu, xuefen chi, Fenglei Ji, Shaoqi Chen, and Gaoyang Hu

DOI: 10.1364/OL.524542 Received 22 Mar 2024; Accepted 20 Apr 2024; Posted 22 Apr 2024  View: PDF

Abstract: Optical camera communication (OCC), as a novel network technique for the Sixth-Generation (6G), attracts increasing attention for its inherent security advantage. However, there still exists the risk of eavesdropping on the broadcasting channel of OCC. To achieve confidential communication, we propose the confidentiality-interference dual LEDs communication (CIDLC) scheme at the transmitter (TX) and elimination of interference (EI) scheme at the receiver (RX). Meanwhile, the interference signals refer to the bits shift of confidential signals. Further, we propose the two-dimensional pilot-aided channel estimation (2D-PACE) scheme to enhance the reliability of MIMO OCC. \hl{Experiment results validate the effectiveness of our schemes, which guarantee confidentiality while performing well at 2 m non-line-of-sight (NLOS) distance.} Finally, the communication-illumination integration OCC is constructed via the energy equalization coding (EEC) scheme.

A compact supermode switch for photonic matrix processing

Jiapeng Luan, Yue Qin, Zelu Wang, Shuqi Xiao, and Hon Tsang

DOI: 10.1364/OL.524988 Received 27 Mar 2024; Accepted 19 Apr 2024; Posted 22 Apr 2024  View: PDF

Abstract: A 2×2 switch based on differential effective thermo-optic (TO) coefficients of waveguide supermodes is proposed and experimentally demonstrated as a more compact alternative to Mach-Zehnder interferometer (MZI) based switches used in coherent photonic matrix processing networks. The total waveguide width of the device is 1.335μm. Using a novel wideband 3-dB supermode coupler, the switch was engineered to have on-off extinction ratios (ERs) ranging from 24.1dB to 38.9dB for the two output ports over a 135nm bandwidth. Insertion losses (ILs) of less than 0.3dB and 0.4dB over the 100nm bandwidth were measured for bar and cross transmission, respectively. The waveguide width-error tolerance is +/-30nm. The proposed device has the potential to improve the scalability of programmable coherent mesh for matrix processing by increasing the integration density without sacrificing the overall accuracy or limiting the operational wavelength range of the mesh.

Optical coherence elastography under homolateral parallel acoustic radiation force excitation for ocular elasticity quantification

Chongyang Wang, Fan Fan, Jiawei Ma, Zongqing Ma, xiaochen meng, and Jiang Zhu

DOI: 10.1364/OL.523215 Received 06 Mar 2024; Accepted 19 Apr 2024; Posted 23 Apr 2024  View: PDF

Abstract: Alteration in the elastic properties of biological tissues may indicate changes in the structure and components. Acoustic radiation force optical coherence elastography (ARF-OCE) can assess the elastic properties of the ocular tissues non-invasively. However, coupling the ultrasound beam and the optical beam remains challenging. In this paper, we proposed an OCE method incorporating homolateral parallel ARF excitation for measuring the elasticity of the ocular tissues. An acoustic-optic coupling unit was established to reflect the ultrasound beam while transmitting the light beam. The ARF excited the ocular tissue in the direction parallel to the light beam from the same side of the light beam. We demonstrated the method on the agar phantoms, the porcine cornea, and the porcine retina. The results show that the ARF-OCE method can measure the elasticity of the cornea and the retina, resulting in higher detection sensitivity and a more extensive scanning range.

Method to overlay an interference field over a grating using only the grating’s profile symmetry

Lifeng Li, Keqiang Qiu, and Huoyao Chen

DOI: 10.1364/OL.519122 Received 18 Jan 2024; Accepted 18 Apr 2024; Posted 22 Apr 2024  View: PDF

Abstract: We theoretically present and experimentally validate a method to overlay the interference field (for making straight-line holographic gratings) with a real grating and a derived method to measure the lateral shift between two real gratings. The methods rely only on the real gratings’ profile symmetry and they are robust against variations of the real gratings’ profile parameters.

Optical single-sideband (OSSB) Raman laser system based on atomic filter for atom gravimeters

Cong Yi, Yang Zhao, Wei Zhuang, Jingbiao Chen, Tian Shi, and Xiaomin Qin

DOI: 10.1364/OL.523729 Received 13 Mar 2024; Accepted 18 Apr 2024; Posted 22 Apr 2024  View: PDF

Abstract: Phase-modulator-generated laser for Raman transition is widely used in atom gravimeters to simplify system and improve robustness. However, the induced additional sidebands (ASBs) lead to systematic errors in gravity measurement. This work presents a novel method to generate optical single-sideband (OSSB) laser for Raman transition through phase modulation based on Faraday anomalous dispersion atomic filter (FADOF). The experimental result indicates that it can reduce the additional sidebands with a signal-to-noise ratio (SNR, the intensity ratio of carrier and unwanted sidebands) of better than 50 dB, and the phase shift caused by ASBs is demonstrated to be effectively suppressed from 358.8 mrad to 2.2 mrad. Furthermore, this system has already applied on atom gravimeter to achieve primary gravity measurement. It shows that FADOF-based Raman laser system is a new scheme for a compact atom absolute gravimeter.

Deep learning based inverse design of multi-functional metasurface absorbers

Yikun Huang, Xiaoshan Liu, Mulin Liu, Jing Chen, Wei Du, and Zhengqi Liu

DOI: 10.1364/OL.518786 Received 12 Jan 2024; Accepted 18 Apr 2024; Posted 18 Apr 2024  View: PDF

Abstract: A novel approach—integrating a simulated annealing (SA) algorithm with deep learning (DL) acceleration—is presented for the rapid and accurate development of terahertz perfect absorbers through forward prediction and backward design. The forward neural network (FNN) effectively deduces the absorption spectrum based on metasurface geometry, resulting in an 80,000-fold increase in computational speed compared to a full-wave solver. Furthermore, the absorber's structure can be precisely and promptly derived from the desired response. The incorporation of SA algorithm significantly enhances design efficiency. We successfully designed low-frequency, high-frequency, and broadband absorbers spanning the 4 THz to 16 THz range with an error margin below 0.02 and a remarkably short design time of only 10 minutes. The proposed model in this letter introduces a novel method for metasurface design at terahertz frequencies.

Optical-parametric-amplification-enhanced background-free spectroscopy

Mingchen Liu, Robert Gray, Arkadev Roy, Luis Ledezma, and Alireza Marandi

DOI: 10.1364/OL.520848 Received 15 Feb 2024; Accepted 18 Apr 2024; Posted 19 Apr 2024  View: PDF

Abstract: Traditional absorption spectroscopy has fundamental difficulty in resolving small absorbance from strong background due to the instability of laser sources. Existing background-free methods in broadband vibrational spectroscopy help to alleviate this problem but face challenges in realizing either low extinction ratios or time-resolved field measurements. Here, we introduce optical-parametric-amplification-enhanced background-free spectroscopy, in which the excitation background is first suppressed by an interferometer and then the free-induction decay that carries molecular signatures is selectively amplified. We show that this method can improve the limit of detection in linear interferometry by order(s) of magnitude without requiring lower extinction ratios or time-resolved measurement, which can benefit sensing applications in detecting trace species.

Spin injection enhancement in CW VECSEL at room temperature using push-pull optical pumping

Alexandre Joly, Ghaya Baili, Jean-marie George, Isabelle Sagnes, Daniel Dolfi, and Mehdi Alouini

DOI: 10.1364/OL.522095 Received 22 Feb 2024; Accepted 17 Apr 2024; Posted 18 Apr 2024  View: PDF

Abstract: We report the enhancement of spin injection efficiency in an external cavity VCSEL based on a non-resonant pumping coupled with a polarized optical resonant illumination. This double pumping scheme allows both the injection of spin polarized electrons in the conduction band and the selection of the spin orientation for the electron/hole recombination laser process. Experimentally, a flip of the polarization state of the laser is achieved with an ellipticity of +31° (spin down) and -33° (spin up), so an increase of about 50% of the ellipticity in comparison to an optical non-resonant pumping alone.

In-fiber chirped Fabry-Perot cavity for temperature sensing

Zhe Zhang, Min Zhou, Qingdian Lin, Yu Jun, Xiaoyang Guo, Cangtao Zhou, and Shuangchen Ruan

DOI: 10.1364/OL.525506 Received 03 Apr 2024; Accepted 17 Apr 2024; Posted 18 Apr 2024  View: PDF

Abstract: Measurement resolution and dynamic range of conventional optical fiber sensors are often mutually restricted. In this work, an in-fiber chirped Fabry-Perot cavity (interferometer) is proposed for the first time to our knowledge, to resolve the conflict between the resolution and dynamic range. The chirped Fabry-Perot interferometer is constructed by two chirped fiber Bragg gratings inscribed in the opposite directions, resulting in a gradually varied (i. e. chirp) cavity length for different reflection wavelength. As such, the interference spectrum exhibits high Figure of Merit (FOM) and large Free Spectrum Range (FSR) at long and short wavelength regions, respectively, enabling high resolution and large dynamic range measurement simultaneously. Temperature tests are then carried out to confirm the validity of the solution. The proposed sensing schema may be developed further and find vital applications in biomedicine fields such as endosomatic temperature monitoring of living bodies. The proposed concept of chirped Fabry-Perot interferometer can provide breakout ideas for other sensing scenarios where high resolution and large dynamic range are both demanded and can be further generalized to other measurands or even free-space interference metrologies.

Algebra of optical dislocations with plasmonic nanostructures

Pasha Goz, Andre Yaroshevsky, and Yuri Gorodetski

DOI: 10.1364/OL.521949 Received 20 Feb 2024; Accepted 17 Apr 2024; Posted 17 Apr 2024  View: PDF

Abstract: Plasmonic structures with physical and the Berry-type dislocation are shown to produce vortices with phase singularity according to the system and the illumination parameters. We demonstrate that by combining the two types of the dislocations in one structure the manipulation with the topological charge of the emerging vortex beams can be controlled in an intriguing way. As a result, the plasmonic field in the near-field can be conveniently modified and selectively excited.

Amplification-free GW-level, 150 W, 14 MHz and 8 fs, thin-disk laser oscillator

Semyon Goncharov, Kilian Fritsch, and Oleg Pronin

DOI: 10.1364/OL.524513 Received 21 Mar 2024; Accepted 16 Apr 2024; Posted 17 Apr 2024  View: PDF

Abstract: We report an amplification-free thin-disk laser oscillatory system delivering 0.9 GW peak power. The 120 fs pulses at 14 MHz containing 12.8 μJ delivered by thin-disk oscillator were compressed by factor 15 down to 8.0 fs with 148 W average output power and overall 82% efficiency. Additionally, we showed that even a sub-two-cycle operation with 6.2 fs can be reached with this technology. The system will be a crucial part of XUV frequency comb being developed and unique high-repetition rate driver for attosecond pulse generation.

Controlling the Bandwidth of High Harmonic Emission Peaks with the Spectral Polarization of the Driver

Eldar Ragonis, Eran Ben Arosh, lev merensky, and Avner Fleischer

DOI: 10.1364/OL.522237 Received 26 Feb 2024; Accepted 16 Apr 2024; Posted 17 Apr 2024  View: PDF

Abstract: We demonstrate a High-Harmonic-Generation scheme which offers control over the bandwidth of the spectral peaks. The scheme uses a vectorial two-color driver with close central frequencies, generated by spectrally splitting a linearly-polarized input femtosecond-duration laser pulse and subsequent recombining the two halves after their polarizations are made cross-elliptical and counter-rotating. This results in the generation of new emission channels which coalesce into broad odd-integer HHG peaks, the bandwidth of each being proportional to the frequency difference between the two colors, to the harmonic order and inversely-proportional to the driver fields' ellipticities. Peak-broadening to the extent that a supercontinuum is formed is also demonstrated. This source will find use in HHG applications benefiting from high-flux broadband extreme ultra-violet radiation, such as attosecond transient absorption spectroscopy.

Polarization-engineered photon statistics and its tomography via optomagnonic interaction

Zhu Liang, Ying Wu, and Li Jiahua

DOI: 10.1364/OL.523989 Received 15 Mar 2024; Accepted 16 Apr 2024; Posted 17 Apr 2024  View: PDF

Abstract: Cavity optomagnonics have received considerable research interests in recent years, due to the coherent magnetic Brillioun light scattering in the ferromagnetic material. Here, we theoretically propose and numerically verify a feasible scheme for the full polarization tomography on photon statistics in an optomagnonic whispering-gallery-mode microresonator system in the weak-coupling regime. By performing the polarization pre- and post-selections to manipulate the polarization states of the input and output photons, we find that the rich sub- and super-Poissonian photon statistics can be selectively generated, thanks to quantum interferences. In the parameter space of phase delay, the evolution from photon bunching to antibunching indicates the change from phase to amplitude squeezing. Our obtained result has potential applications in tunable quantum polarized light source based on cavity optomagnonic platform in micro-nano scale. It also offers a deeper understanding for full quantum cavity optomagnonics.

Synchronous mode-locking of solid-state lasers by difference frequency generation

Ole Jensen, Anders Hansen, Mingjun Chi, and Peter Tidemand-Lichtenberg

DOI: 10.1364/OL.523991 Received 18 Mar 2024; Accepted 16 Apr 2024; Posted 17 Apr 2024  View: PDF

Abstract: This letter introduces a novel method for achieving mode-locking and synchronization of mode-locked output pulses from two lasers. The proposed technique leverages parametric gain from difference frequency generation. Specifically, a Nd:YAG laser is mode-locked by single-pass mode-locked pulses from a mode-locked Ti:sapphire laser using an intracavity nonlinear crystal. When the continuous-wave laser is not actively pumped, the system functions as a synchronously pumped optical parametric oscillator. This novel approach has the potential to enable new devices, especially for pump-probe applications or for generation of mode-locked pulses in spectral regions where conventional mode-locked devices are typically not available.

Simultaneous deep ultraviolet transmission and scattering microscopy for virtual histology

Brendyn Cikaluk, Mohammad Masoumi, Brendon Restall, Matthew Martell, Nathaniel Haven, and Roger Zemp

DOI: 10.1364/OL.514077 Received 23 Nov 2023; Accepted 16 Apr 2024; Posted 17 Apr 2024  View: PDF

Abstract: In recent years, the emergence of a variety of novel opticalmicroscopy techniques has enabled the generationof virtual optical stains of unlabelled tissue specimens,which have the potential to transform existing clinicalhistopathology workflows. In this work, we present a simultaneousdeep ultraviolet transmission and scatteringmicroscopy system that can produce virtual histologyimages that show good concordance to conventionalgold-standard histological processing techniques. Theresults of this work demonstrate the system’s diagnosticpotential for characterizing unlabelled thin tissuesections and streamlining histological workflows.

5 µm CW Ce3+-doped chalcogenide glass fiber laser with 17% slope efficiency

Vasiliy Koltashev, M. Frolov, Stanislav Leonov, Sergei Sverchkov, Boris Galagan, Yuriy Korostelin, Yan Skasyrsky, Gennady Snopatin, Maxim Sukhanov, Alexander Velmuzhov, Vladimir Kozlovsky, Boris Denker, and Victor Plotnichenko

DOI: 10.1364/OL.521495 Received 13 Feb 2024; Accepted 15 Apr 2024; Posted 17 Apr 2024  View: PDF

Abstract: Efficient room temperature mid-infrared laser action in a Ce3+-doped chalcogenide fiber was demonstrated. The fiber had a doped selenide glass core in an undoped sulfide glass cladding. The pump source was a CW Fe2+:ZnSe laser emitting at 4.14 µm. The optimized fiber length allowed to obtain up to 7 mW of 5.06 µm output with 17% slope efficiency at room temperature.

Manipulation of large, irregular-shape particles using contour-tracking optical tweezers

Ryohei Omine, Shuzo Masui, Shotaro Kadoya, Masaki Michihata, and Satoru Takahashi

DOI: 10.1364/OL.524424 Received 21 Mar 2024; Accepted 15 Apr 2024; Posted 16 Apr 2024  View: PDF

Abstract: While optical tweezers technique is a promising tool for manipulation of microparticles, its application to large (>50 µm) particles and irregular-shape ones is still a hard task. In this Letter, we propose a novel concept of contour-tracking optical tweezers (CTOTs), which extract the contour of the objective particle to form the illumination pattern of the trapping laser into the contour shape in real time. We demonstrated trapping of polystyrene particles of irregular shape with the size of over 100 µm with CTOTs. Our approach has potential to open the way for expanding the applicability of optical tweezers by enabling manipulation of a variety of samples.

3D drift correction for super-resolution imaging with a single laser light

Yunze Li, Yingchuan He, Ke Fang, Lulu Zhou, Zhen Wang, Wei Shi, and Yiming Li

DOI: 10.1364/OL.519290 Received 24 Jan 2024; Accepted 15 Apr 2024; Posted 16 Apr 2024  View: PDF

Abstract: Single-molecule localization microscopy (SMLM) enables three-dimensional (3D) super-resolution imaging of nanoscale structures within biological samples. However, prolonged acquisition introduces drift between the sample and the imaging system, resulting in artifacts in the reconstructed super-resolution image. Here, we present a novel 3D drift correction method that utilizes both the reflected and scattered light from the sample. Our method employs the reflected light of a near-infrared (NIR) laser for focus stabilization while synchronously capturing speckle images to estimate lateral drift. This approach combines high-precision active compensation in the axial direction with lateral post-processing compensation, achieving the abilities of the 3D drift correction with a single laser light. Compared to the popular localization events-based cross-correlation method, our approach is much more robust, especially for datasets with sparse localization points.

Efficient sum-frequency generation of yellow laser in a thin-film lithium niobate waveguide

you wu, Junjie Wei, Cheng Zeng, and Jinsong Xia

DOI: 10.1364/OL.522924 Received 05 Mar 2024; Accepted 15 Apr 2024; Posted 16 Apr 2024  View: PDF

Abstract: Yellow laser with high efficiency and safety plays an essential role in many applications such as biomedicine. Here, we demonstrate the sum-frequency generation (SFG) of yellow light on a periodically poled thin-film lithium niobate (PP-TFLN) waveguide. Taking advantage of large χ(2) nonlinearity, a high normalized conversion efficiency of 10097%/(W·cm²) is obtained with pump wavelengths of 1317.7nm and 1064nm. An absolute conversion efficiency of 20.67% is recorded with on-chip pump powers of 10.4dBm (1317.7nm) and 14.5dBm (1064nm).

SpatiotemporalAiryprimeComplex-variable-function wavepacketsinastronglynonlocalnonlinearmedium

Chidao Chen, Liping Zhang, Shuo Yang, Shuyu Li, and Dongmei Deng

DOI: 10.1364/OL.523374 Received 11 Mar 2024; Accepted 15 Apr 2024; Posted 16 Apr 2024  View: PDF

Abstract: A type of circular Airyprime Function of Complex-Variable Gaussian vortex (AFCGV) wave packets in a strongly nonlocal nonlinear medium is introduced numerically, combining the properties of helicity states and abrupt autofocusing. We investigate the effects of the chirp factor, distribution parameter, and decay factor on the AFCGV wave packets in the strongly nonlocal nonlinear medium. Interestingly, by adjusting the distribution parameter, the AFCGV wave packets can exhibit stable rotational motions in various shapes, such as symmetric lobes and doughnuts. Meanwhile, the Poynting vector and the gradient force of the AFCGV wave packets are also discussed. Our research not only elucidates a sophisticated theoretical propagation model for multi-dimensionally controllable AFCGV wave packets but also significantly promotes the progressive advancement of fundamental research on self-bending and autofocusing structured light fields.

Imaging Micrometer Sized Aerosol Particles with Digital Holography

Matthew Berg, Justin Jacquot, Jeremy Harris, and Xiaoli Shen

DOI: 10.1364/OL.521772 Received 19 Feb 2024; Accepted 15 Apr 2024; Posted 15 Apr 2024  View: PDF

Abstract: Small particles that are trapped, deposited, or otherwise fixed can be imaged by digital holography with a resolution approaching that of optical microscopy. However, when such particles are in motion, a comparable resolution is challenging to achieve. Using a simplified bi-telecentric lens system, we demonstrate that one micrometer free-flowing aerosol particles can be imaged at the single-particle level using digital in-line holography. The imaging is demonstrated with an aerosol of one-micrometer polystyrene latex microspheres and further illustrated by a single ragweed pollen aerosol.

Optical chaos synchronisation in a cascaded injection experiment

Jules Mercadier, Yaya Doumbia, Stefan Bittner, and Marc Sciamanna

DOI: 10.1364/OL.522576 Received 27 Feb 2024; Accepted 14 Apr 2024; Posted 15 Apr 2024  View: PDF

Abstract: We experimentally study the synchronization of chaos generated by semiconductor lasers in a cascade injection configuration, i.e., a tunable master laser is used to generate chaos by optical injection in a transmitter laser that injects light into a receiver laser. Chaos synchronization between the transmitter and the receiver lasers is achieved with a correlation coefficient of 90% for a measurement bandwidth up to 35 GHz. Two parameter regions of good synchronization are found, corresponding to the alignment of the oscillation frequencies of the receiver laser with either the transmitter laser or the master laser.

Statistical properties for an optically injected chaotic semiconductor laser with a high-pass filter

Shiyu Liang, Pu Li, Qiang Cai, Qizhi Li, Jianguo Zhang, Yuwen Qin, and Yuncai Wang

DOI: 10.1364/OL.522908 Received 04 Mar 2024; Accepted 14 Apr 2024; Posted 15 Apr 2024  View: PDF

Abstract: Chaotic waveforms with Gaussian distributions are significant for laser-chaos-based applications such as random number generation. By exploring the injection parameter space of the optical injection semiconductor lasers, we numerically investigate the associated probability density functions of the generated chaotic waveforms when different high-pass filters with different cutoff frequencies are used. Our results demonstrate that the chaotic waveforms with Gaussian probability density functions can be obtained once the cutoff frequency of the high-pass filter is larger than the laser relaxation resonance frequency. Especially, we find that the Gaussian probability density function can reach a superhigh coefficient of determination R² ≥ 99.5% in a large parameter space by jointly controlling the injection parameter and cutoff frequency.

Octave-spanning supercontinuum generation in a CMOS-compatible thin Si3N4 waveguide coated with highly nonlinear TeO2

Hamidu Mbonde, Neetesh Singh, Bruno Segat Frare, Milan Sinobad, Pooya Torab Ahmadi, Batoul Hashemi, Dawson Bonneville, Peter Mascher, Franz Kaertner, and Jonathan Bradley

DOI: 10.1364/OL.503820 Received 24 Aug 2023; Accepted 14 Apr 2024; Posted 17 Apr 2024  View: PDF

Abstract: Supercontinuum generation (SCG) is an important nonlinear optical process enabling broadband light sources for many applications, for which silicon nitride (Si3N4) has emerged as a leading on-chip platform. To achieve suitable group velocity dispersion and high confinement for broadband SCG the Si3N4 waveguide layer used is typically thick (>~700 nm), which can lead to high stress and cracks unless specialized processing steps are used. Here, we report on efficient octave-spanning SCG in a thinner moderate-confinement 400-nm Si3N4 platform using a highly nonlinear tellurium oxide (TeO2) coating. An octave-spanning supercontinuum is achieved at a low peak power of 258 W using a 100-fs laser centered at 1565 nm. Our numerical simulations agree well with the experimental results showing an increase of waveguide’s nonlinear parameter by 2.5× when coating the Si3N4 waveguide with TeO2 film. This work demonstrates highly efficient SCG via effective dispersion engineering and an enhanced nonlinearity in a CMOS-compatible hybrid TeO2-Si3N4 waveguides and a promising route to monolithically integrated nonlinear, linear, and active functionalities on a single silicon photonic chip

Full-band compatible coherent reception method for dual-band phased array radar

Defu Zhou, Na Qian, Bowen Ma, zhenbin lv, lu wenbin, and Weiwen Zou

DOI: 10.1364/OL.522973 Received 05 Mar 2024; Accepted 13 Apr 2024; Posted 15 Apr 2024  View: PDF

Abstract: Receiving signals across different frequency bands with devices in separate bands negatively affects the size, cost, and inter-band coherence of phased array radar. This paper proposes a full-band compatible reception method for dual-band phased array radar. The method employs optical pulses to achieve dual-band frequency conversion, phase shifting, and digitization over a large bandwidth using a single suite of devices. The proposed reception method eliminates the differences between devices in different frequency bands and maintains inter-band coherence. Based on this full-band compatible coherent reception method, a four-channel phased array antenna (PAA) receiver is built. Using the PAA receiver, we successfully conduct beamforming and reception of dual-band signals in the X- and Ku-band with a beam direction range of -45° to 60°. Due to the high inter-band coherence, data fusion is processed without additional complex algorithmic corrections. After fusing the dual-band data, the pulse compression results in all directions revealed a doubled improvement in range resolution.

Foveated pancake lens design for improved optical performance and eye rotation support

Youngmo Jeong, Myongjo Choi, JongChul Choi, and Kyusub Kwak

DOI: 10.1364/OL.523675 Received 14 Mar 2024; Accepted 13 Apr 2024; Posted 15 Apr 2024  View: PDF

Abstract: We propose a novel approach to address the limitations of traditional pancake lenses for virtual reality headsets, such as low image contrast and poor performance when eyes rotate. The design leverages the foveated nature of human vision, achieving superior modulation transfer function in the foveal area to enhance optical performance significantly. Furthermore, the pancake lens design is presented that considers the rotation of the user's pupil position, maintaining optimal image quality even when the user's eye rotates. The proposed method presents the parameters and optimization of a novel pancake lens that utilizes the characteristics of the human visual system and accounts for the rotation of the pupil position of the user, leading to improvements in image quality and user experience. The lens design and image simulation results are presented to demonstrate the effectiveness of the approach.

Evaluation and correction of laser scattering-based particle size measurements at high obscurations using the Monte Carlo method

Geyi Su, Cunjin Sun, Shiwei Zhang, Fengxian Fan, and Mingxu Su

DOI: 10.1364/OL.515911 Received 14 Dec 2023; Accepted 13 Apr 2024; Posted 15 Apr 2024  View: PDF

Abstract: High turbidity and its associated multiple scattering phenomena can often lead to an underestimation of the particle size for the laser scattering method. To investigate the light scattering characteristics and evaluate the effect of high-obscuration particle systems, a Monte Carlo model has been developed based on Mie's theory. A compact setup was utilized to perform a series of experiments on three certified reference materials (CRM) at different concentrations. Both the scattered light energy distribution and the obscuration were measured simultaneously. The inversion results of particle size indicate a continuous increase in deviation from the nominal value as the obscuration rises. According to the conventional single scattering model, the inversion errors fall within 5% for obscuration levels ranging from 0.15 to 0.2. However, for a higher obscuration, the error can reach approximately 15%. Thus, a correction method has been proposed by introducing an improved model matrix that included the multiple scattering contribution for the data inversion, which exhibited a significant enhancement in the accuracy of particle size measurements under high obscuration conditions. For all three types of particles being studied, the error was successfully reduced to within 5.0%.

Quantifying changes in oxygen saturation of the internal jugular vein in vivo using deep neuron networks and subject-specific three-dimensional Monte Carlo models

Chin-Hsuan Sun, Hao-Wei Lee, Ya-Hua Tasi, Jia-Rong Luo, and Kung-Bin Sung

DOI: 10.1364/OL.517960 Received 09 Jan 2024; Accepted 13 Apr 2024; Posted 16 Apr 2024  View: PDF

Abstract: Central venous oxygen saturation (ScvO2) is an important parameter for assessing global oxygen usage and guiding clinical interventions. However, measuring ScvO2 requires invasive catheterization. As an alternative, we aim to non-invasively and continuously measure changes in oxygen saturation of the internal jugular vein (SijvO2) by a multi-channel near-infrared spectroscopy system. The relation between the measured reflectance and changes in SijvO2 is modeled by Monte Carlo simulations and used to build a prediction model using deep neural networks. The prediction model is tested with simulated data to show robustness to individual variations in tissue optical properties. The proposed technique is promising to provide a non-invasive tool for monitoring the stability of brain oxygenation in broad patient populations.

Optofluidic SERS based on Ag nanocubes with high sensitivity for detecting prevalent water pollutant

Na Ran, Xing Wang, Yuan Gan, and Jie Zhang

DOI: 10.1364/OL.524709 Received 25 Mar 2024; Accepted 13 Apr 2024; Posted 16 Apr 2024  View: PDF

Abstract: To enhance the integration and practical applicability of the Raman detection system, silver nanocubes (Ag NCs) were synthesized using a polyol method. A liquid-liquid interface approach was employed to transfer a monolayer of Ag NCs "film" onto a silicon wafer substrate, resulting in the fabrication of a highly sensitive and uniform surface enhanced Raman scattering (SERS) substrate denoted as "Ag@SiO2". The electromagnetic field distribution of various dimers on the Ag@SiO2 was analyzed using finite difference time domain (FDTD) software. The results reveal that the electromagnetic enhancement effect is most pronounced in cube-cube dimers, indicating that Ag NCs exhibit superior localized surface plasmon resonance (LSPR) response due to their well-defined geometric regularity and sharp geometric angles. For Rhodamine 6G (R6G) probe molecules, the Ag@SiO2 shows ultra-high sensitivity, with the limit of detection (LOD) of 10^−12 mol/L, and the enhancement factor (EF) can reach 1.4×10^10. The relative standard deviation (RSD) at the main characteristic peaks is below 10%, demonstrating good consistency in substrate performance. In addition, the Ag@SiO2 modified with hexanethiol exhibits high sensitivity, uniformity, and repeatability in detecting for pyrene, with the LOD of 10^−8 mol/L and a minimum RSD of 6.09% at the main characteristic peak, effective recognition capabilities for pyrene and anthracene in mixed solutions. Finally, chemisorption and physisorption strategies were prepared in microfluidic channels and experimentally compares, and a real-time detection of pyrene solutions can also be achieved. This method can achieve rapid detection and precise differentiation of polycyclic aromatic hydrocarbons in water pollutant.

Effects of system parameters on single-beam synthetic gradiometer with dual-cell structure

Wu ZiNan, Zhang Jialong, Chen Wei, Zhonghua Ou, Huimin Yue, cheng chunyue, and YONG LIU

DOI: 10.1364/OL.518697 Received 11 Jan 2024; Accepted 13 Apr 2024; Posted 18 Apr 2024  View: PDF

Abstract: We report a single-beam synthetic gradiometer operated in the spin-exchange-relaxation free (SERF) regime, using the structure of two separate atomic vapor cells spaced 2cm apart. To improve the capability of the gradiometer in suppressing the common-mode magnetic field noise, we are aiming at investigating the effects of the system parameters on the gradiometer common-mode rejection ratio (CMRR). The mathematical expression for the relationship between the gradiometer CMRR and the two variables including the linewidth ratio and the pumping factor ratio are constructed for the first time. This means that the CMRR can be optimized by controlling the linewidth and the pumping factor, which is easy to implement in the operation process. As a result, a CMRR of 18.5 is achieved and a gradiometer sensitivity of 4.5fT/cm/Hz1/2 is also measured. This method is very useful for performance optimization of a gradiometer, which can be tuned to a desired state by simply controlling the linewidth and the incident light intensity.

Time-domain full-field optical coherence tomography with digital defocus correction

Austeja Treciokaite, Karolis Adomavicius, and Egidijus Auksorius

DOI: 10.1364/OL.520911 Received 05 Feb 2024; Accepted 12 Apr 2024; Posted 12 Apr 2024  View: PDF

Abstract: Time-Domain Full-Field Optical Coherence Tomography (TD-FF-OCT) is an interferometric technique capable of acquiring high-resolution en face OCT images deep within biomedical tissue, utilizing an incoherent white light source. However, optical aberrations, such as sample defocus, can degrade image quality, thereby limiting the achievable imaging depth. In this study, we demonstrate that sample defocus within a highly scattering medium can be digitally corrected over a wide defocus range. This correction is feasible after the optical path lengths in the sample and reference arms are matched. We showcase the application of digital defocus correction on both reflective and scattering samples, effectively compensating digitally for up to 1 mm of defocus.

A high-fidelity single logical qubit encoding scheme assisted by single-sided quantum dot-cavity systems

Xiao-Ming Xiu, Xin-Ying Wang, Si-Tong Liu, Liu Lv, Zi-Lin Zhao, Zi-Qing Yuan, Zi-Long Yang, Yanqiang Ji, and Li Dong

DOI: 10.1364/OL.516989 Received 27 Dec 2023; Accepted 12 Apr 2024; Posted 15 Apr 2024  View: PDF

Abstract: We present an encoding scheme of a single logical qubit with single-sided quantum dot (QD)-cavity systems, which is immune to the collective decoherence. By adjusting the Purcell factor to satisfy the balanced reflection condition, the detrimental effects of unbalanced reflection between the coupled and uncoupled QD-cavity systems can be effectively suppressed. Furthermore, the fidelity of each step can be increased to unity regardless of the strong coupling regime and the weak coupling regime of cavity quantum electrodynamics (QED) with the assistance of the waveform correctors. The scheme requires QD-cavity systems and simple linear optical elements, which can be implemented with the currently experimental techniques.

Design of an ultrafast plasmonic nanolaser for high-intensity broadband emission operating at room temperature

peng zhou, Lei Jin, Kun Liang, Xiongyu Liang, Li Junqiang, Xuyan Deng, Wang yilin, Guo Jiaqi, Li Yu, and Jiasen Zhang

DOI: 10.1364/OL.518240 Received 09 Jan 2024; Accepted 12 Apr 2024; Posted 12 Apr 2024  View: PDF

Abstract: We propose a plasmonic nanolaser based on Metal-Insulator-Semiconductor-Insulator-Metal (MISIM) structure, which effectively confines light on a subwavelength scale (~λ/14). As the pump power increases, the proposed plasmonic nanolaser exhibits broadband output characteristics of 20nm and the maximum output power can reach 20uW. Furthermore, the carrier lifetime at the upper energy level in our proposed structure is measured to be about 400 fs using a double pump-probe excitation. The ultrafast characteristic is attributed to the inherent Purcell effect of plasmon systems. Our work paves the way toward deep-subwavelength mode confinement and ultrafast femtoseconds plasmonic laser in Spaser-based interconnects，eigenmode engineering of plasmonic nanolasers, Nano-LEDs, spontaneous emission control.

Emission behaviors from ZnO nanowire pumped CsPbBr3 perovskite microwire

Xinyu Zhang, Jing Lv, Shuangyang Zou, DeNan Kong, Yujing Zhao, and ruibin liu

DOI: 10.1364/OL.520575 Received 22 Feb 2024; Accepted 12 Apr 2024; Posted 12 Apr 2024  View: PDF

Abstract: Perovskite semiconductor materials have attracted significant attention in the fields of photovoltaics and luminescence due to their excellent photoelectric properties, such as high carrier mobility, high absorption coefficient, and high fluorescence quantum yield. In particular, low-dimensional metal-halide perovskite microcrystalline materials have been reported to exhibit low-dimensional lasing phenomena and laser devices due to their high gain and widely tunable band gap. In this work, one-dimensional (1 D) ZnO nanowires with its ultraviolet lasing emission is utilized as an excitation source to pump CsPbBr3 microwires on a hybrid ZnO-CsPbBr3 microscale structures. At higher excitation, the amplified spontaneous emission (ASE) behaviors from CsPbBr3 nanowire are realized with ultralow threshold by indirect pumping from ZnO lasing emission for the first time. In comparison, the ASE behaviors from CsPbBr3 nanowire directly pumped by Nd:YAG Q-switched laser and continuous wave laser are also performed at room temperature. There are also no multimode lasing behaviors observed. The paper provides a new method to achieve low threshold on-chip nanolaser by high-quality perovskite nanostructures.

Bistable response and quasi-periodicity excitation of the internal dynamics of soliton molecules

Defeng Zou, Guizhen Xu, Runmin Liu, Aoyan Zhang, Jinna Chen, Hong Dang, Ming-lie Hu, Youjian Song, and Perry Shum

DOI: 10.1364/OL.520785 Received 02 Feb 2024; Accepted 11 Apr 2024; Posted 12 Apr 2024  View: PDF

Abstract: Soliton molecules, a frequently observed phenomenon in most mode-locked lasers, have intriguing characteristics comparable to their matter molecule counterparts. However, there are rare explorations of the deterministic control of the underlying physics within soliton molecules. Here, we demonstrate the bistable response of intramolecular motion to external stimuli and identify a general approach to excite their quasi-periodic oscillations. By introducing frequency-swept gain modulation, the intrinsic resonance frequency of the soliton molecule is observed in the simulation model. Applying stronger modulation, the soliton molecule exhibits divergent response susceptibility to up and down sweeping, accompanied by a jump phenomenon. Quasi-periodic intramolecular oscillations appear at the red-shifted resonance frequency. Given the leading role of bistability and quasi-periodic dynamics in nonlinear physics, our research provides insights into the complex nonlinear dynamics within dissipative soliton molecules. It may pave the way to related experimental studies on synchronization and chaos at ultrafast timescale.

Realization of the Pascal based on Argon using a Fabry-Pérot refractometer

Isak Silander, Johan Zakrisson, Ove Axner, and Martin Zelan

DOI: 10.1364/OL.523293 Received 11 Mar 2024; Accepted 11 Apr 2024; Posted 12 Apr 2024  View: PDF

Abstract: Based on a recent experimental determination of the static polarizability and a first-principles calculation of the frequency-dependent dipole polarizability of argon, this work presents, by use of a Fabry-Pérot refractometer operated at 1550 nm, a realization of the SI unit of pressure, the pascal, for pressures up to 100 kPa, with an uncertainty of [(0.98 mPa)^2+(5.8x10 ^(−6)P)^2+(26×10^(−12)P^2)^2]^(1/2). The work also presents a value of the molar polarizability of N_2 at 1550 nm of 4.396572(26) × 10^-6 m^3/mol, which agrees well with previously determined ones in the literature.

Longitudinal Manipulation of Local Nonseparability in Vector Beams

Zhiming QING, Wenxiang Yan, Xian Long, Zheng Yuan, Zhi-Cheng Ren, Xi-Lin Wang, Jianping Ding, and Hui-Tian Wang

DOI: 10.1364/OL.524647 Received 26 Mar 2024; Accepted 11 Apr 2024; Posted 12 Apr 2024  View: PDF

Abstract: The inherent nonseparability of vector beams presents a unique opportunity to explore novel optical functionalities, expanding new degrees of freedom for optical information processing. In this letter, we introduce a novel method for tailoring the local nonseparability along the propagation axis of vector beams. Employing higher-order Bessel vector beams, the longitudinal control over the local nonseparability is achieved through targeted amplitude modulation of constituent orthogonal polarization components within the main ring region. Experimental demonstrations of diverse longitudinal nonseparability profiles corroborate the efficacy and versatility of our approach, opening avenues for further exploration of the nonseparability manipulation in vector beams.

Cross-Domain Heterogeneous Metasurface Inverse Design Based on Transfer-Learning Method

Fan Gao, Zhihao Ou, Chenchen Yang, Juan Deng, and Bo Yan

DOI: 10.1364/OL.514212 Received 29 Nov 2023; Accepted 11 Apr 2024; Posted 12 Apr 2024  View: PDF

Abstract: In this paper, a transfer learning method is proposed to complete design tasks on heterogeneous metasurface datasets with distinct functionalities. Through fine-tuning the inverse design network and freezing the parameters of hidden layers, we successfully transfer the metasurface inverse design knowledge from the electromagnetic-induced transparency (EIT) domain to three target domains of EIT (different design), absorption, and phase-controlled metasurface. Remarkably, only 5% of the target domain samples are required to complete the training process in comparison to the source domain datasets. This work presents a significant solution to lower the data threshold for inverse design process and provides the possibility of knowledge transfer between different domain metasurface datasets.

Propagation Constant-Based Diameter Measurement Technique for Sub-micrometer Scale Optical Fiber

Yushen Liu, Shotaro Kadoya, Masaki Michihata, and Satoru Takahashi

DOI: 10.1364/OL.521545 Received 13 Feb 2024; Accepted 11 Apr 2024; Posted 15 Apr 2024  View: PDF

Abstract: Diameter is a critical parameter for determining the physical properties of a submicrometer optical fiber and requires accurate measurement. In this study, we propose a novel diameter measurement technique derived from the waveguide theory and utilize the pitch of a standing wave near-field light generated by two counter-propagating lights within the submicrometer optical fiber. In a submicrometer optical fiber, the propagating light extends into the surrounding air as near-field light, existing within a range approximately equivalent to one wavelength from the surface of the fiber. By generating standing wave near-field light via the incident light from both ends of the fiber, the pitch of standing wave near-field light can be measured by scanning along the central axis of the fiber using a scanning near-field optical microscopy probe. The fiber diameter is subsequently acquired by solving the optical fiber eigenvalue equation. Based on the feasibility verification experiment, a high-precision measurement of approximately 500 nm was realized for the diameter of the optical fiber diameter.

Optimizing focus: Switchable modes and sub-diffraction spots in inverse circular Airy beams

Lai Chen, Chengjian Tao, and Li-Gang Wang

DOI: 10.1364/OL.524686 Received 26 Mar 2024; Accepted 11 Apr 2024; Posted 15 Apr 2024  View: PDF

Abstract: We report an experimental investigation into the tight-focusing characteristics of linearly polarized inverse circular Airy beams (ICABs). Our study reveals that tightly focused ICABs exhibit Bessel-like, needle-like, or dual foci profiles depending on whether the main-ring's radius is smaller than, equal to, or larger than the critical radius. The emergence of the dual foci structure is attributed to the constrained entrance aperture of the microscope objective. In contrast to traditional Gaussian beams, ICABs demonstrate remarkable advantages in terms of focal spot size. Notably, we observe a focal spot with a size of 245 nm, representing a 26.4% reduction compared to the diffraction limit. These unique properties open up promising avenues for potential applications in optical multi-plane particle trapping, conveying, and super-resolution optical imaging.

Generation of optical vortex beams with bandwidth exceeding 550 nm using a helical fiber needle exhibiting strong mode coupling

Chengliang Zhu, Chengfeng Tang, Xinyue Meng, Jinming Chang, Tonglei Cheng, and Yong Zhao

DOI: 10.1364/OL.513883 Received 21 Nov 2023; Accepted 11 Apr 2024; Posted 11 Apr 2024  View: PDF

Abstract: A strong-coupling helical fiber needle (HFN) is proposed and demonstrated for the realization of bandwidth-enhanced broadband optical vortex beam (OVB) generation. The HFN is based on a single mode fiber and operates at the dispersion-turning-point (DTP) of the lowest radial order of the cladding mode (i.e., LP11) but with a remarkably high mode coupling efficiency. By utilizing this novel HFN, successful generation of the first-order OVB with an impressive bandwidth up to 556 nm at -10 dB and a center wavelength of ~1570 nm has been achieved. To the best of our knowledge, this represents the broadest bandwidth demonstrated among all fiber grating-based OVB generators to date. The proposed HFN-based OVB generator exhibits relatively compact size, ultra-wide bandwidth, and customizable center wavelength, making it highly promising for applications in optical vortex-based endoscopic imaging as well as particle detection and manipulation.

Multiple-access ultrastable frequency dissemination based on optical frequency combs via fiber link

Yixuan Zheng, xing chen, bing xu, Yinan Chen, Bin Luo, and Song Yu

DOI: 10.1364/OL.518781 Received 12 Jan 2024; Accepted 11 Apr 2024; Posted 11 Apr 2024  View: PDF

Abstract: We demonstrate an optical fiber-based, multiple-access frequency transmission using two optical frequency combs. The experimental results using Allan deviation analysis show that with the phase compensation technique, the frequency instabilities at the remote site are 8.7 × 10⁻¹⁵/1 s and 1.0 × 10⁻¹⁷/10³ s, and the accessing node along the fiber link, frequency instabilities are 6.9 × 10⁻¹⁵/1s and 1.1 × 10⁻¹⁷/10³ s. Similarly, the power spectral density of phase noise was analyzed in the frequency domain. These experimental results demonstrate that the compensation scheme improved performance by two to three orders of magnitude compared to the uncompensated transmission. Thus, the proposed frequency transmission technique has potential application for disseminating ultra-stable frequency references in the optical fiber network.

Synchronous time multiplexing for non-line-of-sight MIMO optical camera communications

Shaoqi Chen and xuefen chi

DOI: 10.1364/OL.522540 Received 27 Feb 2024; Accepted 11 Apr 2024; Posted 11 Apr 2024  View: PDF

Abstract: In typical multiple-input multiple-output (MIMO) optical camera communication (OCC) systems, the spatial correlation of MIMO channels is large. Optical signals between light sources can easily interfere with each other, negatively impacting the overall transmission performance. In this work, we propose a time-multiplexing integral modulation scheme for non-line-of-sight MIMO OCC system, where each LED transmits different signals to improve both the data rate and security of the system. A genetic algorithm (GA)-based adaptive multi-threshold scheme is designed to demodulate the blurred fringes in multi-level pulse amplitude modulation. The experimental results show that at a distance of 2.5m, a data rate of 16.4kb/s can reach with the BER performance of 3.01 × 10e-3, which validates the superiority and reliability of our proposed schemes.

A linear-space-variant model for Fourier ptychographic microscopy

Tianci Feng, Aiye Wang, Zhiping Wang, Terry Liao, and An Pan

DOI: 10.1364/OL.522745 Received 29 Feb 2024; Accepted 11 Apr 2024; Posted 11 Apr 2024  View: PDF

Abstract: Fourier ptychographic microscopy (FPM) has to realize well-accepted reconstruction by image segmentation and discarding problematic data due to artifacts caused by vignetting. However, the imaging results have long been suffering from uneven color blocks and the consequent digital stitching artifacts, failing to bring satisfying experiences to researchers and users over the past decade since the invention of FPM. In fact, the fundamental reason for vignetting artifacts lies in that the acquired data does not match the adopted linear-space-invariant (LSI) forward model, that is, the actual object function is modulated by a quadratic phase factor during data acquisition, which has been neglected in the advancement of FPM. In this letter, we rederive a linear-space-variant (LSV) model for FPM and design the corresponding loss function for FPM, termed LSV-FPM. Utilizing LSV-FPM for optimization enables the efficient removal of wrinkle artifacts caused by vignetting in the reconstruction results, without the need of segmenting or discarding images. The effectiveness of LSV-FPM is validated through data acquired in both 4f and finite conjugate single-lens systems.

InSb all-dielectric metasurface for ultra-highly efficient Si-based mid-infrared detection

Shengyi Wang, qiu wang, Hao Luo, Hua Ge, xiang li, and BO WEN JIA

DOI: 10.1364/OL.519664 Received 31 Jan 2024; Accepted 10 Apr 2024; Posted 11 Apr 2024  View: PDF

Abstract: Mid-infrared (MIR) Si-based optoelectronics have wide potential applications and their design requires simultaneous consideration of device performance optimization and the feasibility of heterogeneous integration. The emerging interest in all-dielectric metasurfaces for optoelectronic applications stems from their exceptional ability to manipulate light. In this letter, we present our research on an InSb all-dielectric metasurface designed to achieve ultra-high absorptivity within the 5-5.5 µm wavelength range. By integrating InSb nanodisk array layer on Si platform using wafer bonding and heteroepitaxial growth, we demonstrate three kinds of metasurface with high absorptivity of 98.36%, 99.28%, and 99.18%. The enhanced absorption is mainly contributed to the Kerker effect and the anapole state, and the peak, with the added flexibility of tuning both the peak and bandwidth of absorption by altering the metasurface parameters. Our finds provide an alternative scheme to develop high performance detectors and absorbers for MIR silicon photonics.

Non-resonant Bragg scattering four-wave-mixing at near visible wavelengths in low-confinement silicon nitride waveguides

Nicholas Jaber, Scott Madaras, Andrew Starbuck, Andrew Pomerene, Christina Dallo, Douglas Trotter, Michael Gehl, and Nils Otterstrom

DOI: 10.1364/OL.519793 Received 25 Jan 2024; Accepted 10 Apr 2024; Posted 11 Apr 2024  View: PDF

Abstract: Quantum state coherent frequency conversion processes—such as Bragg scattering four wave mixing (BSFWM)—hold promise as a flexible technique for networking heterogeneous and distant quantum systems. In this letter, we demonstrate BSFWM within an extended (1.2-m) low-confinement silicon nitride waveguide and show that this system has the potential for near unity quantum coherent frequency conversion in visible and near-visible wavelength ranges. Using sensitive heterodyne laser spectroscopy at low optical powers, we characterize the Kerr coefficient (∼1.55 W^{−1}m^{−1}) and linear propagation loss (∼0.0175 dB/cm) of this non-resonant waveguide system, revealing a record-high nonlinear figure of merit (NFM = γ/α ≈ 3.85 W^{−1}) for BSFWM of near visible light in non-resonant silicon nitride waveguides. We demonstrate how, at high yet achievable on-chip optical powers, this NFM would yield a comparatively large frequency conversion efficiency, opening the door to near-unity flexible frequency conversion without cavity enhancement and resulting bandwidth constraints.

Real-time FPGA prototyping of Doppler frequency shift compensation using DSP-assisted automatic frequency control

Xinpei Tang, Yan Li, Jingwei Song, Hongxiang Guo, Xiaobin Hong, Jifang Qiu, Zhisheng Yang, and Jian Wu

DOI: 10.1364/OL.518629 Received 16 Jan 2024; Accepted 10 Apr 2024; Posted 10 Apr 2024  View: PDF

Abstract: This letter presents a real-time coherent receiver using digital signal processing (DSP) assisted automatic frequency control (AFC) to compensate for Doppler frequency shift (DFS). DFS compensation range of ±8GHz and the frequency change rate of 33 MHz/s are demonstrated in an FPGA-based 2.5Gbaud QPSK coherent optical system. The experimental results indicate that the scheme achieves a sensitivity of -47dBm at a bit error rate (BER) of 2E-4. The power penalty induced by DFS compensation is less than 1dB.

Using quasi-BIC in all-dielectric metasurface array to enhance terahertz fingerprint sensing

Yue Wang, Wenshuo Chen, Zijian Cui, Guangchen Sun, and Kuang Zhang

DOI: 10.1364/OL.522765 Received 29 Feb 2024; Accepted 10 Apr 2024; Posted 10 Apr 2024  View: PDF

Abstract: The terahertz absorption fingerprint spectrum is crucial for qualitative spectral analysis, revealing the rotational or vibrational energy levels of numerous biological macromolecules and chemicals within the THz frequency range. However, conventional sensing in this band is hindered by weak interactions with trace analytes, leading to subtle signals. In this work, an all-dielectric metasurface array is proposed to enhance the absorption fingerprint spectrum using quasi-BIC resonance. The observable quasi-BIC resonance is achieved by breaking the symmetry of the C₂v structure. The periodic dimensions of the structure are adjusted to excite quasi-BIC resonances at different frequencies, thereby enhancing the fingerprint spectra of four different substances. By exploiting the correlation between the Q-factor and absorption across different frequencies, calibration of the molecular absorption fingerprint spectrum obtained through metasurface sensing yields precise enhanced absorption fingerprint spectra for various substances within the 0.55-1.6 THz range. Our work introduces a novel strategy for trace sensing in the THz frequency range, demonstrating the promising potential for enhanced absorption fingerprint spectrum sensing.

Polarization switching in a mid-infrared Er:YAlO3 laser

Florent Cassouret, Ahmed Nady, Pavel Loiko, Simone Normani, Alain BRAUD, Weidong Chen, Valentin Petrov, Dunlu Sun, Peixiong Zhang, Bruno viana, Ammar Hideur, and Patrice Camy

DOI: 10.1364/OL.523010 Received 13 Mar 2024; Accepted 10 Apr 2024; Posted 10 Apr 2024  View: PDF

Abstract: We report on a polarization-resolved study of mid-infrared emission properties of Er3+-doped orthorhombic yttrium aluminum perovskite YAlO3 single crystal. For the 4I11/2→4I13/2 Er3+ transition, the stimulated emission cross-section is 0.20×10-20 cm² at 2919 nm for light polarization E ‖ c. Pumped by an Yb-fiber laser at 976 nm, the 10 at.% Er:YAlO3 laser delivered 1.36 W at 2919 nm with a slope efficiency of 31.4%, very close to the Stokes limit, a laser threshold as low as 33 mW and a linear polarization. Pump-induced polarization switching between E || b and E || c eigen states was observed and explained by excited-state absorption from the terminal laser level.

Achieving Bi-anisotropic Coupling through Uniform Temporal Modulations without Inversion Symmetry Disruption

Neng Wang, Fanghu Feng, and Guo Ping Wang

DOI: 10.1364/OL.518816 Received 17 Jan 2024; Accepted 10 Apr 2024; Posted 10 Apr 2024  View: PDF

Abstract: Temporal modulations provide a new approach for realizing metamaterials. In this study, through the imposition of uniform temporal modulations, we achieve two types of reciprocal bi-anisotropic metamaterials. Notably, these achievements do not rely on any spatial modulation, preserving inversion symmetry at any instantaneous time. This stands in sharp contrast to the scenario of traditional bi-anisotropic metamaterials, where the disruption of inversion symmetry by spatial arrangements is necessary. The conditions for realizing nonzero bi-anisotropic coupling are discussed and verified through full wave simulations. Our work will stimulate research in the field of temporal bi-anisotropic metamaterials, as well as the application of temporal modulations in manipulating photonic spin angular momentum.

Active control of nonreciprocal near-field radiative heat transfer with a drift-current biased graphene/α-MoO3 heterostructure

Qijun Ma, Qisen Xiong, Xue Chen, Leyong Jiang, and Yuanjiang Xiang

DOI: 10.1364/OL.519609 Received 24 Jan 2024; Accepted 10 Apr 2024; Posted 12 Apr 2024  View: PDF

Abstract: The interaction between the drift current biased graphene plasmonics and the hyperbolic phonon polaritons (HPPs) of α-MoO3 provides a promising way to manipulate near-field radiation heat transfer (NFRHT). Based on the drift-biased graphene/α-MoO3 heterostructure, it is found that the drift currents applied to the graphene surface can effectively promote photon tunneling, and hence it can dynamically modulate the coupling effect of the two excitations, providing a reliable pathway for the modulation of NFRHT. Furthermore, the influencing mechanism of vacuum gaps on nonreciprocal NFRHT with different drift current rates is revealed, and it is discovered that the vacuum gaps can filter the nonreciprocal surface plasmon polaritons with high nonreciprocity. Our findings make it possible to manipulate nanoscale thermal rectification and noncontact thermal modulation.

Ultra-high extinction ratio and low power silicon thermo-optic switch

Jin Wang, shangqing shi, Hongsheng Niu, Suzhe Gao, Bo Yang, Shihao Zhang, Cheng Wei, Yifei Chen, Chen Guo, Wanghua Zhu, Guohua Hu, Yiping Cui, and Bin Yun

DOI: 10.1364/OL.520209 Received 31 Jan 2024; Accepted 10 Apr 2024; Posted 12 Apr 2024  View: PDF

Abstract: The silicon thermo-optic switch (TOS) is one of the most fundamental and crucial blocks in large-scale silicon photonics integrated circuits (PICs). An energy-efficient silicon TOS with ultra-high extinction ratio can effectively mitigate crosstalk and reduce power consumption in optical systems. In this letter, we demonstrate a silicon TOS based on cascading Mach-Zehnder interferometers (MZIs) with spiral thermo-optic phase shifters. The experimental results show that an ultra-high extinction ratio of 58.8 dB is obtained, and the switching power consumption is as low as 2.32 mW/ without silicon air trench. The rise time and fall time of the silicon TOS are about 10.8 s and 11.2 s, respectively. Particularly, the figure of merit (FOM) has been improved compared with previously reported silicon TOS. The proposed silicon TOS may find potential applications in optical switch arrays, on-chip optical delay lines, etc.

A K-means non-uniform-quantization digital-analog radio-over-fiber scheme for THz-band photonics-aided wireless fronthaul

mingxu wang, Jianjun Yu, xianming zhao, chengzhen bian, Wen Zhou, and KAIHUI WANG

DOI: 10.1364/OL.521380 Received 14 Feb 2024; Accepted 10 Apr 2024; Posted 19 Apr 2024  View: PDF

Abstract: We propose a non-uniform-quantization digital-analog radio-over-fiber (NUQ-DA-RoF) scheme based on an advanced K-means NUQ algorithm and demonstrate it experimentally in a 2-m 300-GHz photonics-aided wireless fronthaul system. Results show that the NUQ-DA-RoF scheme achieves a SNR gain of ~1.9 dB compared to digital-analog radio-over-fiber (DA-RoF) at an equivalent Common Public Radio Interface equivalent data rate (CPRI-EDR). Remarkably, the NUQ-DA-RoF scheme exhibits an ∼1.6-dB power sensitivity enhancement over DA-RoF at the 256-QAM EVM threshold. These findings highlight the advantages of the NUQ-DA-RoF scheme over DA-RoF in terms of power budget and SNR improvement, suggesting promising prospects for future radio access networks and wireless fronthaul.

Compact light couplers for lateral III-V membrane devices grown on SOI platforms

Zhaojie Ren and Yu Han

DOI: 10.1364/OL.524405 Received 21 Mar 2024; Accepted 10 Apr 2024; Posted 16 Apr 2024  View: PDF

Abstract: Compact light couplers between III-V devices and Si waveguides are crucial for advancing the scalability of Si photonics. Here, we present a compact light coupling strategy for lateral III-V membrane lasers and PDs directly grown on SOI platforms. Benefiting from the coplanar configuration of epitaxial III-V membrane and Si device layer, we designed novel butt couplers to achieve both small footprint and high efficiency coupling. We employed sub-wavelength grating structures to gradually bridge the effective refractive index between III-V membrane and Si waveguide and obtained a coupling loss of less than 0.5 dB across the entire telecom band in a length of less than 10 μm. Our work here offers a fresh perspective for future densely-integrated Si-photonics.

A hybrid BOFDA/BOCDA system for distributed static and dynamic strain measurements

Raffaele Vallifuoco, Luigi Zeni, and Aldo Minardo

DOI: 10.1364/OL.523252 Received 06 Mar 2024; Accepted 09 Apr 2024; Posted 12 Apr 2024  View: PDF

Abstract: We present a distributed optical fiber sensor based on a hybrid Brillouin optical frequency/correlation domain analysis (BOFDA/BOCDA) configuration, for both static and dynamic strain measurements. Distributed static strain (or temperature) measurements are realized using the conventional BOFDA method, i.e., acquiring the baseband transfer function of the fiber through a vector network analyzer (VNA). With little modifications, the same setup can perform dynamic, position-selective measurements synthetizing a correlation peak through a frequency modulation of the laser source, while operating the VNA at a single modulation frequency. Experimental tests, carried out at a sampling frequency up to 40 Hz and a spatial resolution of ~ 5 cm, demonstrate the validity of the proposed approach.

1.7 W holmium-doped fluoroindate fiber laser at 3920 nm

Tommy Boilard, Vincent Fortin, Maxime Lemieux-Tanguay, Pascal Paradis, Paul Du Teilleul, Jean-Yves Carrée, Real Vallee, and Martin Bernier

DOI: 10.1364/OL.522233 Received 23 Feb 2024; Accepted 09 Apr 2024; Posted 10 Apr 2024  View: PDF

Abstract: A monolithic fiber laser emitting 1.7 W at 3920 nm is experimentally demonstrated in a Ho3+:InF3 fiber. The cavity comprises a pair of highly reflective fiber Bragg gratings written in the active fiber with the femtosecond phase-mask scanning technique, and is spliced to the pump diode with a robust silica-to-fluoride fiber splice. This work is an important step towards high-power all-fiber laser operating in the vicinity of 4 μm.

Lightweight W-band Wireless IM-DD PAM-4 Data Transmission with Compact Photonics Integrated Circuits and Envelope Detection

Shi Jia, Mu-Chieh Lo, Deming Kong, Guillermo Carpintero, and Hao Hu

DOI: 10.1364/OL.523301 Received 07 Mar 2024; Accepted 09 Apr 2024; Posted 11 Apr 2024  View: PDF

Abstract: Wireless data traffic is expected to exponentially increase in the future, and meeting this demand will require high data rate photonic-wireless links operating in the W-band (75-110 GHz). For this purpose, pulse-amplitude-modulation with four levels (PAM-4)-based intensity modulation and direct detection (IM-DD) photonic-wireless systems are preferred due to their simplified configuration. To further enhance integration, chip-based light sources can be employed. In this paper, we experimentally demonstrate an IM-DD PAM-4 photonic-wireless link in the W-band using a monolithic dual-laser photonic chip. The chip is injection-locked by an optical comb to generate a W-band wireless signal through photo-mixing with a photodiode. The use of the comb allows for injection-locking of the two modes of the chip, resulting in a phase-stabilized beat note. The integration of the chip-based phase-locked light source and the utilization of an envelope detector (ED) mark notable features of our experimental setup. The monolithic dual-laser photonic chip significantly enhances integration, while the envelope detector plays a crucial role in the simplified configuration, contributing to the overall decrease in size, weight, power, and complexity of the system. PAM-4 signal modulation is then applied to the two coherent optical carriers simultaneously to improve the signal-to-noise ratio. Our experiments have successfully transmitted 5 GBaud and 10 GBaud PAM-4 W-band wireless signals, achieving a line data rate of up to 20 Gbit/s. The experimental results demonstrate the potential of implementing fully integrated photonic-wireless transmitters using this scheme.

Highly stable power control for chip-based continuous-variable quantum key distribution system

Yiming Bian, Yang Li, Xuesong Xu, Tao Zhang, Yan Pan, Wei Huang, Song Yu, Lei Zhang, Yichen Zhang, and Bing-Jie Xu

DOI: 10.1364/OL.522320 Received 26 Feb 2024; Accepted 09 Apr 2024; Posted 10 Apr 2024  View: PDF

Abstract: Quantum key distribution allows secret key generation with information theoretical security. It can be realized with photonic integrated circuits to benefit the tiny footprints and the large-scale manufacturing capacity. Continuous-variable quantum key distribution is suitable for chip-based integration due to its compatibility with mature optical communication devices. However, the quantum signal power control compatible with the mature photonic integration process faces difficulties on stability, which limits the system performance and causes the overestimation of secret key rate that opens practical security loopholes. Here, a highly stable chip-based quantum signal power control scheme based on a biased Mach-Zehnder interferometer structure is proposed, theoretically analyzed and experimentally implemented with standard silicon photonic techniques. Simulations and experimental results show that the proposed scheme significantly improves the system stability, where the standard deviation of the secret key rate is suppressed by an order of magnitude compared with the system using traditional designs, showing a promising and practicable way to realize highly stable continuous-variable quantum key distribution system on chip.

Polymer-based cascaded waveguide Bragg grating for blood glucose sensing

Ruina Zhao, Hongqiang Li, MING Han, Mingjun Ding, Licheng Zuo, Lizhen Zhang, shanshan zhang, Wentao Meng, Fanglin Xie, Shuai Ma, Lu Cao, Feng Ren, Enbang Li, and Juan Daniel Prades Garcia

DOI: 10.1364/OL.523504 Received 11 Mar 2024; Accepted 09 Apr 2024; Posted 10 Apr 2024  View: PDF

Abstract: Waveguide Bragg grating (WBG) blood glucose sensing, as a biological sensing technology with broad application prospects, plays an important role in the fields of health management and medical treatment. In this work, a polymer-based cascaded WBG is applied to glucose detection. We investigated photonic devices with two different grating structures cascaded, a crossed grating and a bilateral grating, and analyzed the effects of the crossed grating period, the bilateral grating period, and number of grating periods on the sensing performance of the glucose sensor. Finally, the reflectance spectral characteristics, response time and sensing specificity of the cascaded WBG were evaluated. The experimental results show that the glucose sensor has a sensitivity of 190 pm/(mg/ml) in the glucose concentration range of 0-2 mg/ml and has the advantages of high integration, a narrow bandwidth and low cost.

Supercontinuum Generation in a Graded-Index Multimode Tellurite Fiber

Ekaterina Krutova, lauri SALMELA, Zahra Eslami, Tanvi Karpate, Mariusz Klimczak, Ryszard Buczynski, and Goëry Genty

DOI: 10.1364/OL.521639 Received 14 Feb 2024; Accepted 08 Apr 2024; Posted 08 Apr 2024  View: PDF

Abstract: We report a near two-octave spanning supercontinuum (SC) from 790 nm to 2900 nm in a nanostructured tellurite graded-index multimode fiber with a nanostructured core. We study the SC dynamics in different dispersion regimes and observe near-single mode spatial intensity distribution at high input energy values. Numerical simulations of the (3+1)D generalized nonlinear Schrödinger equation are in good agreement with our experiments. Our results open a new avenue for the generation of high-power mid-infrared SC sources in soft glass fibers.

High-Precision Frequency-Controlled Optical Phase Shifter with Acousto Optic Devices

Eduardo Esquivel Ramírez, Leonardo Uhthoff-Rodriguez, Edgar Giovanni Alonso-Torres, Alberto Hernández-López, Carlos Gardea-Flores, and Asaf Paris-Mandoki

DOI: 10.1364/OL.522688 Received 04 Mar 2024; Accepted 08 Apr 2024; Posted 08 Apr 2024  View: PDF

Abstract: A fundamental parameter to determine how electromagnetic waves interfere is their relative phase and achieving a fine control over it enables a wide range of interferometric applications. Existing phase control methods rely on modifying the optical path length by either changing the path followed by the light or by altering the thickness or index of refraction of an optical element in the setup. In this work we present a novel method, based on acousto-optic modulators (AOM), which allows adjusting the phase by shifting the frequency of the light in a segment of its path. Since the amount of phase-shift depends on the length of the segment, an optical fiber is used to realize a 2π shift. Two experimental implementations are described which deal with different sources of phase fluctuations. The first addresses fluctuations resulting from the optical fiber while the second also tackles unwanted variations originating from the AOMs.

Spatial-temporal optical vortices pendulum on a curved surface

Weifeng Ding and Zhaoying Wang

DOI: 10.1364/OL.523573 Received 11 Mar 2024; Accepted 08 Apr 2024; Posted 08 Apr 2024  View: PDF

Abstract: Spatial-temporal optical vortices (STOV) have recently become the focus of new structured optical fields. In this paper, the propagation on a 2D curved surface called the constant Gaussian curvature surface (CGCS) is studied. Under the paraxial approximation, we obtain the analytical solution of the STOV propagation on CGCS by using the matrix optics method. Different from the propagation on the flat surface, the spatiotemporal distribution direction of STOV light intensity swings as a pendulum throughout the evolution, allowing for one way of making timers. Meanwhile, this swing stops when the curvature radius of the curved surface equals the Rayleigh distance of light, which can give a new scheme for the designing and manufacturing of non-Euclidetic photonic devices. Besides, the transverse orbital angular momentum is deduced, we find that the intrinsic and extrinsic OAM periodically exchange, but the total transverse OAM is always zero during the propagation on CGCS. It aids in controlling the transverse extrinsic orbital angular momentum of STOV in nontrivial space.

Helical hollow channel waveguide fabricated by femtosecond laser enhanced wet etching

jie Wu, Yixiao Xu, Yue Li, Fangjie Wang, Yangliu Zhai, Deng Guoliang, and Shouhuan Zhou

DOI: 10.1364/OL.523400 Received 12 Mar 2024; Accepted 08 Apr 2024; Posted 09 Apr 2024  View: PDF

Abstract: Three-dimensional optical waveguides with hollow channels have many advantages such as strong mode confinement and excellent dispersion control ability. Femtosecond laser enhanced wet etching is widely used to fabricate hollow channel waveguides in transparent dielectric materials. We propose a method for fabricating hollow channel waveguides using femtosecond laser enhanced wet etching with a simpler fabrication process and shorter etching time compared with the previous work. After 90 hours of etching, a series of helical hollow channel waveguides with a length of 5 mm and a radius of 32 μm were successfully fabricated. At a pitch of 3 μm, the waveguide exhibited a loss (including coupling loss and transmission loss) as low as 1.37 dB/cm at 1030 nm. The helical hollow channel waveguide also exhibited exceptional isotropic light confinement capability and remarkable supercontinuum-generating properties. Moreover, helical hollow channel waveguides with a radius of 2 μm were successfully fabricated. According to simulations, waveguides of such size can effectively control dispersion. Our work presents a novel approach to fabricating hollow channel waveguides with arbitrary lengths using femtosecond laser enhanced wet etching.

High-power Raman lasing and efficient anti-Stokes generation in mm-sized glass disk resonators

Atul Bhadkamkar, Steven Carpenter, David Gold, Matthew Beede, Randall Goldsmith, Daniel van der Weide, and Deniz Yavuz

DOI: 10.1364/OL.519399 Received 18 Jan 2024; Accepted 07 Apr 2024; Posted 09 Apr 2024  View: PDF

Abstract: We have previously experimentally observed highpower Stokes and second-order Stokes output from amm-sized CaF2 disk using stimulated Raman scattering.A pump laser at a wavelength of 1.06 μm was coupledvia a tapered fiber to the whispering gallery modes ofthe disk. In this paper, we extend this work and demon-strate the production of the first anti-Stokes sideband atpower levels as high as 60 μW in near continuous-wave(CW) operation. The result is a four-component Ramancomb at the output, with a wavelength range coveringfrom 1.0 μm to 1.14 μm. We discuss the threshold de-pendence of the observed Raman lines on the crystalorientation and provide experimental validation. Theseadvances enable the use of such mm-sized resonators ascompact, efficient sources for terahertz level frequencymodulation.

All-optical Einstein-Podolsky-Rosen steering swapping

QIWU HU, Jiabin Wang, Shengshuai Liu, and Jietai Jing

DOI: 10.1364/OL.520036 Received 26 Jan 2024; Accepted 07 Apr 2024; Posted 09 Apr 2024  View: PDF

Abstract: Einstein-Podolsky-Rosen (EPR) steering, an important resource in quantum information, describes the ability of one party to influence the state of another party through local measurements. It differs from Bell nonlocality and entanglement due to its asymmetric property. EPR steering swapping allows two spatially independent parties to present EPR steering without a direct interaction. Here, we theoretically propose an all-optical EPR steering swapping (AOSS) scheme based on four-wave mixing (FWM) processes. A low-noise parametric amplifier is utilized to implement the function of Bell-state measurement without detection, avoiding the optic-electro and electro-optic conversions. After AOSS, one-way and two-way EPR steering between two independent optical modes can be obtained. Our scheme provides a guidance for the construction of a measurement-free, all-optical broadband quantum network utilizing EPR steering swapping.

Event-triggered background-oriented schlieren: High- frequency visualization of heated jet flow

Zhen Lyu, Weiwei Cai, and yingzheng liu

DOI: 10.1364/OL.515700 Received 13 Dec 2023; Accepted 06 Apr 2024; Posted 11 Apr 2024  View: PDF

Abstract: This letter reports a novel event-triggered background-oriented schlieren (EBOS) technique using a combination of an event-triggered camera and pulsed laser speckle projection. The BOS images are reconstructed using the event data generated by the pulsed laser speckle projection and then processed to obtain the density and temperature distribution of the flow. This technique enables continuous visualization and recording of flows at kFPS frame rates with a very low cost, breaking through the short operating times of existing high-frame-rate BOS. To examine the event-triggered BOS technique, tests are conducted on a hot air gun. The measured temperature distribution coincides with the thermocouple data with an error of no more than 10.8%. Measurements taken during the startup of the hot air gun demonstrate that the presented technique can measure the evolution of the jet temperature for at least 150 s, as well as capture the localized unsteady turbulent structure in the heated jet flow.

Time-domain Slicing Optical Frequency Domain Reflectometry

Qing Bai, Zhen Shen, Luxuan Wu, Changshuo Liang, Yu Wang, Xin Liu, and baoquan Jin

DOI: 10.1364/OL.520850 Received 05 Feb 2024; Accepted 06 Apr 2024; Posted 08 Apr 2024  View: PDF

Abstract: A time-domain slicing (TDS) optical frequency domain reflectometry is proposed for large strain sensing with high spatial resolution. Compared with the conventional frequency domain slicing (FDS) method, the TDS with Burg spectrum estimation is capable of enhancing the similarity of local spectrum under large strain and mostly suppressing the fake peaks during the strain resolving. The experimental results demonstrated that it enables measurements of strain ranging from 600με to 4200με with a spatial resolution of 2.4 mm and a narrow optical frequency scanning range of only 10 nm. Moreover, the measurement accuracy is improved by six times by decreasing the root-mean-square error from 8.6611 με to 1.3396 με without any hardware modification.

Bias-drift insensitive full-field frequency response characterization of thin-film lithium niobate-based intensity modulator

Xiaobao Li, Wu Ruitao, Jilong Li, Heyun Tan, Meng Xiang, Songnian Fu, Xinlun Cai, and Yuwen Qin

DOI: 10.1364/OL.519329 Received 17 Jan 2024; Accepted 05 Apr 2024; Posted 10 Apr 2024  View: PDF

Abstract: We propose a rapid and precise scheme for characterizing the full-field frequency response of thin-film lithium niobate-based intensity modulator (TFLN-IM), via a specially designed multi-tone microwave signal. Our proposed scheme remains insensitive to the bias-drift of IM. Experimental verification is implemented with a self-packaged TFLN-IM with a 3 dB bandwidth of 30 GHz. In comparison with the vector network analyzer (VNA) characterization results, the deviation values of the amplitude-frequency response (AFR) and phase-frequency response (PFR) within the 50 GHz bandwidth are below 0.3 dB and 0.15 rad, respectively. When the bias is drifted within the 90% of V_π range , the deviation fluctuation values of AFR and PFR are less than 0.3 dB and 0.05 rad, respectively. With the help of the full-field response results, we can pre-compensate the TFLN-IM for the 64 Gbaud PAM-4 signals under the back-to-back (B2B) transmission, achieving a received optical power (ROP) gain of 2.3 dB. The versatility of our proposed full-field response characterization scheme can extend to various optical transceivers, offering the advantage of low cost, robust operation, and flexible implementation.

Large-scale high-quality full-color computer-generated volume hologram fabricated by stacking and tiling technique

Shunsuke Fujiki, Hirohito Nishi, and Kyoji Matsushima

DOI: 10.1364/OL.521515 Received 13 Feb 2024; Accepted 05 Apr 2024; Posted 16 Apr 2024  View: PDF

Abstract: A technique is presented to produce very high-quality full-color holographic 3D images in large-scale computer holography, which uses over a billion pixels. In this technique, three large-scale computer-generated holograms, printed using laser lithography, are transferred to three computer-generated volume holograms (CGVH) using a method called tiling contact-copy. Then, the full-color holographic image is created by stacking the three CGVHs. We demonstrate a 10-cm square stacked CGVH that reconstructs full-parallax full-color 3D images at high quality with a viewing angle of more than 35°.

Tightly focusing metalens based on high order Bessel function

zhaojin guo, Xuanguang Wu, Liang Zhou, Yanke Li, Bingyan Wei, Dandan Wen, Peng Li, Jianlin Zhao, and Sheng Liu

DOI: 10.1364/OL.517256 Received 28 Dec 2023; Accepted 04 Apr 2024; Posted 10 Apr 2024  View: PDF

Abstract: Fabrication of a high numerical aperture (NA) metalens is always a major challenge. The traditional metalens based on the hyperboloidal phase can achieve a near-unity NA. In this paper, by referring to the tightly autofocusing beam, we propose a new type of metalens of which the phase profile is extracted from the higher-order Bessel function. A light beam passing through this metalens would focus along the circular trajectory and produces a tightly-focusing field. Utilizing the phase binarization, we provide a method to design the geometric-phase dielectric metasurface both for phase and polarization modulations, which reduces the demand for phase gradient. We demonstrate two metalenses for circularly and radially polarized output beams at 633nm, with the measured 0.737λ and 0.616λ focal spots, respectively. Theoretically, it can realize a super-diffraction-limit spot (0.38λ). This work can extend the way of realizing tightly focused optical devices.

Terahertz fan-beam computed tomography

Sishi Shen, Congjing Hao, Bin Liang, Jinsong Liu, Zhengang Yang, and Kejia Wang

DOI: 10.1364/OL.523116 Received 06 Mar 2024; Accepted 04 Apr 2024; Posted 10 Apr 2024  View: PDF

Abstract: A terahertz (THz) fan-beam computed tomography (CT) system using a 0.3 THz continuous-wave sheet beam is proposed. The diffraction-free sheet beam expands in a fan shape in only one direction and provides propagation-invariant focal lines and extended depth of field. The fan-beam CT based on this beam is the second-generation THz CT. It breaks the conventional 4-f symmetric structure of THz CT using the parallel beam. The fan-beam THz CT allows for use with a linear array detector, which reduces the time required to collect data. To demonstrate its feasibility for three-dimensional(3D) imaging, the 3D structure of a metal rod packed in a carton is reconstructed with the support of the system. The results show that the object's internal structure can be obtained by this new THz CT system while retaining the geometrically magnified features of the cross-sectional structure. The results of our research provide a template for the second-generation THz CT system, which provides an additional method for nondestructive testing.

Broadband frequency comb generation through cascaded quadratic nonlinearity in thin-film lithium niobate microresonators

chao tang, Mingming Nie, Jiayang Chen, Zhaohui Ma, zhan li, Yijun Xie, Yong Meng Sua, Shu-Wei Huang, and Yuping Huang

DOI: 10.1364/OL.523920 Received 14 Mar 2024; Accepted 04 Apr 2024; Posted 09 Apr 2024  View: PDF

Abstract: Broadband frequency comb generation through cascaded quadratic nonlinearity remains experimentally untapped in free-space cavities with bulk χ(2) materials mainly due to the high threshold power and restricted ability of dispersion engineering. Thin-film lithium niobate (LN) is a good platform for nonlinear optics due to the tight mode confinement in a nano-dimensional waveguide, the ease of dispersion engineering, large quadratic nonlinearities, and flexible phase matching via periodic poling. Here we demonstrate broadband frequency comb generation through dispersion engineering in a thin-film LN microresonator. Bandwidths of 150 nm (80 nm) and 25 nm (12 nm) for center wavelengths at 1560 nm and 780 nm are achieved, respectively, in a cavity-enhanced second-harmonic generation (doubly resonant optical parametric oscillator). Our demonstration paves the way for pure quadratic soliton generation, which is a great complement to dissipative Kerr soliton frequency combs for extended interesting nonlinear applications.

Dynamically manipulating long-wave infrared polarized thermal radiation by vanadium dioxide metasurface

Qianlong Kang, Kai Guo, Xizheng Zhang, Wei Wang, and Zhongyi Guo

DOI: 10.1364/OL.523161 Received 05 Mar 2024; Accepted 04 Apr 2024; Posted 08 Apr 2024  View: PDF

Abstract: Dynamically manipulating the spectra and polarization properties of thermal radiation is the key to counter infrared polarization imaging system (IPIS) under the different background environments. In this letter, we propose a phase-change metasurface thermal emitter (PCMTE) composed of vanadium dioxide (VO2) dipole antenna arrays to dynamically manipulate polarized radiation spectra in the long-wave infrared (LWIR) region of 8-14μm. During the thermally-induced and reversible insulator-to-metal transition (IMT) in VO2, by simulating the LWIR images at different polarization angles for the PCMTE and background plates, the PCMTE can realize dynamically tunable LWIR camouflage, then their degree of linear polarization (DoLPs) can be calculated, which can demonstrate that the PCMTE can also achieve dynamically tunable LWIR polarization camouflage at the specific radiation angles and backgrounds. Our proposed PCMTE provides an effective scheme for adaptive IR polarization camouflage.

Cross-Waveband Optical Computing Imaging

Shu-Hang Bie, Jintao Xie, joyce zhang, ming-fei li, Wen-Kai Yu, and Xi-Hao Chen

DOI: 10.1364/OL.515730 Received 12 Dec 2023; Accepted 03 Apr 2024; Posted 04 Apr 2024  View: PDF

Abstract: A novel cross-spectral optical computing imaging experiment has been achieved through a single exposure of a charge-coupled device. The experimental setup integrates single-pixel imaging (SPI) with ghost imaging (GI) through a photoelectric conversion circuit and a synchronous modulation system. The experimental process involves modulation in one wavelength band (in SPI) and demodulation using GI algorithm in another. Significantly, our approach utilizes optical computing demodulation, a departure from the conventional electronic demodulation in GI (SPI), which involves the convolution between the bucket optical signals and the modulated patterns on the digital micromirror device. A proof-of-concept cross-band imaging experiment from near-infrared to visible light has been carried out. The results highlight the system's ability to capture images at up to 20 frames per second using near-infrared illumination, which are then reconstructed in the visible light spectrum. This success not only validates the feasibility of our approach but also expands the potential applications in the SPI or GI fields, particularly in scenarios where two-dimensional detector arrays are either unavailable or prohibitively expensive in certain electromagnetic spectra such as x-ray and terahertz.

Deep-learning enhanced high-quality imaging in metalens-integrated camera.

Yanxiang Zhang, Yue Wu, Chunyu Huang, Zi-Wen Zhou, Muyang Li, zaichen zhang, and Ji Chen

DOI: 10.1364/OL.521393 Received 09 Feb 2024; Accepted 03 Apr 2024; Posted 09 Apr 2024  View: PDF

Abstract: Benefitting from the characteristics of ultra-light, ultra-thin and flexibility in design, metalenses exhibit significant potential in the development of highly integrated cameras. However, the performances of metalens-integrated camera are constrained by their fixed architectures. Here we proposed a high-quality imaging method based on deep learning to overcome this constraint. We employed a multi-scale convolutional neural network (MSCNN) to train an extensive paired of high-quality and low-quality images obtained from convolutional imaging model. Through our method, the imaging resolution, contrast, and distortion have all been improved, resulting in a noticeable overall image quality with SSIM over 0.9 and an improvement in PSNR over 3dB. Our approach enables cameras to combine the advantages of high integration with enhanced imaging performances, revealing tremendous potential for future groundbreaking imaging technology.

Macroscopic entanglement between ferrimagnetic magnons and atoms via crossed optical cavity

Ke Di, Xi Wang, Yinxue Zhao, Yu Liu, Huarong Xia, Anyu Cheng, and Jiajia Du

DOI: 10.1364/OL.520039 Received 02 Feb 2024; Accepted 03 Apr 2024; Posted 10 Apr 2024  View: PDF

Abstract: We consider a two-dimensional opto-magnomechanical (OMM) system including two optical cavity modes, a magnon mode, a phonon mode, and a collection of two-level atoms. In this study, we demonstrate the methodology for generating stationary entanglement between two-level atoms and magnons, which are implemented using two optical cavities inside the setup. Additionally, we probe the entanglement transformation efficiency of switching from atom-phonon entanglement to atom-magnon entanglement. Furthermore, this improvement is found to be resistant to changes in temperature. The entanglement between atoms and magnons plays a crucial role in the construction of hybrid quantum networks.

Extending the Coverage of User-diversified IM-DD PON by FDM: A Mathematical Model with Experimental Verification

Peiji Song, Yuan Liu, Zhouyi Hu, Calvin C. K. Chan, and Di Che

DOI: 10.1364/OL.514370 Received 29 Nov 2023; Accepted 03 Apr 2024; Posted 03 Apr 2024  View: PDF

Abstract: Future passive optical networks (PONs) call for more flexibility to support diversified users with various rate demands and link qualities. Using the traditional time-division multiplexing (TDM), the concept of flexible-rate PON was proposed to accommodate more users with link diversity by rate adaptation. In this letter, we reveal the PON coverage can be further extended through frequency division multiplexing (FDM) in the presence of multiuser diversity, namely, (i) there exist users with frequency-dependent link conditions, and (ii) the link conditions exhibit disparity among users. We build a mathematical model and propose an optimization algorithm based on the binary tree search to optimize the diversity gain. We experimentally verify its feasibility by studying the diversity gain concerning chromatic dispersion, differential optical path loss, and SNR variation in a 200G-class intensity-modulation direct-detection (IM-DD) system.

Experimental demonstration of optical waveform transmission with multiple-eigenvalue 16-APSK modulation

Tao Huang, Li Jianping, Yuwen Qin, Xinkuo Yu, Jianqing He, Gai Zhou, Jianbo Zhang, and Songnian Fu

DOI: 10.1364/OL.520537 Received 16 Feb 2024; Accepted 03 Apr 2024; Posted 03 Apr 2024  View: PDF

Abstract: The multi-eigenvalue multiplexing based discrete spectrum modulated nonlinear frequency division multiplexed (DS-NFDM) system with higher-order modulation format has been demonstrated experimentally. After designing and optimizing the coefficients of the multiplexed eigenvalue set and the constellation points distribution of 16 amplitude phase shift keying (16-APSK), the realizations of 14-, 30- and 46-eigenvalue multiplexed DS-NFDM signals have been implemented. The results show that 46-eigenvalue and 30-eigenvalue multiplexed DS-NFDM signals can transmit 50km and 400km over non-zero dispersion shift fiber (NZDSF) under SD-FEC threshold of 2.4E-2, respectively. To the best of our knowledge, this demonstration shows record for multiplexed eigenvalue number and data rate of multiple-eigenvalue based DS-NFDM system.

Dissemination of UTC(NIST) over 20 km of commercial optical fiber with active phase stabilization

Jacob VanArsdale, Matthew Deutch, Michael Lombardi, Glenn Nelson, Jeff Sherman, James Spicer, William Yates, Dylan Yost, and Samuel Brewer

DOI: 10.1364/OL.521175 Received 07 Feb 2024; Accepted 03 Apr 2024; Posted 03 Apr 2024  View: PDF

Abstract: We demonstrate the transfer of a cesium frequency standard steered to UTC(NIST) over 20 km of dark telecom optical fiber. Our dissemination scheme uses an active stabilization technique with a phase-locked voltage-controlled oscillator. Out-of-loop characterization of the optical fiber link performance is done with dual-fiber and single-fiber transfer schemes. We observe a fractional frequency instability of $1.5 \times 10^{-12}$ and $2 \times 10^{-15}$ at averaging intervals of 1 s and $10^5$ s, respectively, for the link. Both schemes are sufficient to transfer the cesium clock reference without degrading the signal, with nearly an order of magnitude lower fractional frequency instability than the cesium clocks over all time scales. The simplicity of the two-fiber technique may be useful in future long-distance applications where higher stability requirements are not paramount, as it avoids technical complications involved with the single-fiber scheme.

Sorting infrared optical vortices with a nonlinear angular lens

Weiqian Shu, Xiaodong Qiu, yuan ren, Wuhong Zhang, and Lixiang Chen

DOI: 10.1364/OL.522430 Received 26 Feb 2024; Accepted 03 Apr 2024; Posted 03 Apr 2024  View: PDF

Abstract: Analogous to the regular lens, which spatially maps plane waves in the space domain to distinct points in the Fourier domain, the angular lens establishes the mapping relations between angular mode and angular position. Thus, providing an effective toolkit for detecting optical vortex. However, using angular lens to sort infrared optical vortex modes via nonlinear optical processes remains relatively unexplored. Here, we design a nonlinear optical version of the angular lens to map the various infrared optical vortex modes to different angular positions in the visible region. We successfully sort nine infrared optical vortex modes of different topological charges with a visible camera, showing the cost-effective ability to sort infrared vortices compared to a relatively expensive infrared camera. Our scheme holds promise for infrared remote sensing, infrared vortex-encoded optical communications, and so on.

Chirped flicker optoretinography for in vivo characterization of human photoreceptors' frequency response to light.

Slawomir Tomczewski, Piotr Wegrzyn, Maciej Wojtkowski, and Andrea Curatolo

DOI: 10.1364/OL.514637 Received 29 Nov 2023; Accepted 02 Apr 2024; Posted 03 Apr 2024  View: PDF

Abstract: Over the years, flicker based, scotopic electroretinography (ERG) has served as a valuable objective tool for investigating retinal physiological function through the measurement of electrical signals originating from retinal neurons in response to light stimulation. To date, an optical and non-invasive counterpart to the ERG method has not been developed. In this letter, we present findings obtained from the application of a novel, in vivo method - scotopic, flicker optoretinography (f-ORG). Specifically, it focuses on the measurement of retinal photoreceptor response to a flicker stimulus with chirped frequency. In contrast to measurements performed at discrete frequencies, this technique enables a significantly accelerated and more streamlined characterization of photoreceptor optical pathlength modulation amplitudes in the nanometer range as a function of stimulus frequency.

Spiral scanning improves subject fixation in widefield retinal imaging

Franklin Wei, Claire Li, KRISTEN HAGAN, Sandra Stinnett, Anthony Kuo, Joseph Izatt, and Al-Hafeez Dhalla

DOI: 10.1364/OL.517088 Received 02 Jan 2024; Accepted 02 Apr 2024; Posted 03 Apr 2024  View: PDF

Abstract: Point scanning retinal imaging modalities, including confocal scanning light ophthalmoscopy (cSLO) and optical coherence tomography, often suffer from fixational motion artifacts. Traditional fixation targets, though effective at reducing these artifacts, may not be acceptable in certain circumstances (particularly handheld devices) due to their bulk and cost. In this letter, we report on a cSLO device that instead leverages a spiral scan pattern under pseudo-visible illumination to function as a virtual fixation target. A human imaging study of 14 volunteers was conducted to compare the fixational performance of this technique to that of traditional raster scanning, with and without a fixation target. Image registration was used to quantify subject eye motion under each scan type. A strip-wise registration method was used for raster scans, and we developed a novel ring-based method for spiral scans. Results indicate a statistically significant reduction in eye motion by the use of spiral scanning as compared to raster scanning without a fixation target.

Multiple topological states within a common bandgap of two non-trivial photonic crystals

Dongyang Liu, Peng Peng, Xiaoya Lu, Aoqian Shi, Yuchen Peng, Yizhou Wei, and Jianjun Liu

DOI: 10.1364/OL.520866 Received 07 Feb 2024; Accepted 02 Apr 2024; Posted 02 Apr 2024  View: PDF

Abstract: Topological photonic crystals (PCs) provide an effective method for controlling how light propagates and concentrates through their topological states. However, it remains unclear whether topological states can be obtained by combining two different two-dimensional (2D) PCs with topological non-trivial states. In this Letter, two types of 2D Penrose-square (P-S) PCs are proposed. These PCs can generate topological edge states (TESs) and topological corner states (TCSs) within the low-frequency part of the bandgap. Moreover, by combining these two non-trivial PCs, a total of two groups of TESs and four groups of TCSs can be realized in both the high-frequency and low-frequency parts of the common bandgap. The two proposed P-S PCs offer a new platform for investigating topological photonics and related devices, providing novel approaches and perspectives for achieving topological states in 2D PCs.

Charge-transfer-driven ultrasensitive SERS sensing in two-dimensional titanium carbonitride MXene

leilei lan, Caiye Zhao, Xiao Tang, Juan Gao, Guoqun Li, Hanyong Cai, Sen Yang, Jin Liu, Zhongwei Qu, Xingce Fan, and Teng Qiu

DOI: 10.1364/OL.522183 Received 23 Feb 2024; Accepted 02 Apr 2024; Posted 02 Apr 2024  View: PDF

Abstract: Two-dimensional (2D) MXenes stand out as promising platforms for surface-enhanced Raman scattering (SERS) sensing owing to their metallic feature, various compositions, high surface area, compatibility with functionalization, and ease of fabrication. In this work, we report a high-performance 2D titanium carbonitride (Ti3CN) MXene SERS substrate. We reveal that the abundant electronic density of states near the Fermi level of Ti3CN MXene boosts the efficiency of photoinduced charge transfer at the interface of Ti3CN/molecule, resulting in significant Raman enhancement. The SERS sensitivity of Ti3CN MXene is further promoted through a 2D morphology regulation and molecular enrichment strategies. Moreover, prohibited drugs are detectable on this substrate, presenting the potential of trace amount analysis on Ti3CN MXene. This work provides a deep insight of the SERS mechanisms of Ti3CN MXene, and broadens the practical application of transition metal carbonitride MXene SERS substrates.

Statistical mechanics and pressure of composite multimoded weakly nonlinear optical systems

Nikolaos Efremidis and Demetrios Christodoulides

DOI: 10.1364/OL.511787 Received 08 Nov 2023; Accepted 02 Apr 2024; Posted 03 Apr 2024  View: PDF

Abstract: Statistical mechanics can provide a versatile theoretical framework for investigating the collective dynamics of weakly nonlinear waves-settings that can be utterly complex to describe otherwise. In optics, composite systems arise due to interactions between different frequencies and/or polarizations. The purpose of this work is to develop a thermodynamic theory that takes into account the synergistic action of multiple components. We find that the type of the nonlinearity involved can have important implications in the thermalization process and, hence, can lead to different thermal equilibrium conditions. Importantly, we derive closed-form expressions for the actual optomechanical pressure that is exerted on the system. In particular, the total optomechanical pressure is the sum of the partial pressures due to each component. Our results can be applied to a variety of weakly nonlinear optical settings such as multimode fibers, bulk waveguides, photonic lattices, and coupled microresonators. We present two specific examples, where two colors interact in a one- waveguide array with either a cubic or quadratic nonlinearity.

High-efficiency and broadband tunable Raman fiber laser in a chalcogenide fiber based on Fresnel reflection

Yingying Wang, Shixun Dai, Lingling Yang, Duanduan Wu, Peiqing Zhang, Lei Zhang, and Zhaolong Liao

DOI: 10.1364/OL.521472 Received 16 Feb 2024; Accepted 02 Apr 2024; Posted 03 Apr 2024  View: PDF

Abstract: A high-efficiency and broadband tunable chalcogenide fiber Raman laser with Fabry–Perot cavity formed by Fresnel reflection was established. A maximum average power slope efficiency of around 43% and a maximum output peak power of about 2.9 W at 2148 nm were demonstrated by using a 2 μm nanosecond pump source, and the experimental results were in good agreement with numerical simulations. The Raman-dominated spike had a broadened pump with a full width half maximum of 674 ns and a pulse duration of 561 ns. A broadband tunable central wavelength from 2100 to 2186 nm was obtained. The Raman Fabry–Perot cavity constituted by the Fresnel reflection from the chalcogenide fiber endfaces can operate at any wavelength without the aid of any additional optical feedback element. This will facilitate the realization of fiber lasers with excellent performance and compact system, especially in the mid-infrared region.

Monolayer directional metasurface for all-optical image classifier doublet

Rui Xia, Lin Wu, Jin Tao, Ming Zhao, and Zhen Yu Yang

DOI: 10.1364/OL.520642 Received 02 Feb 2024; Accepted 02 Apr 2024; Posted 04 Apr 2024  View: PDF

Abstract: Diffractive deep neural networks, known for their passivity, high scalability, and high efficiency, offer great potential in holographic imaging, target recognition, and object classification. However, previous endeavors have been hampered by spatial size and alignment challenges. To address these issues, this study introduces a monolayer directional metasurface, aimed at reducing spatial constraints and mitigating alignment issues. and eliminate the effects of alignment. Utilizing this methodology, we reveal that the metasurface trained by the diffractive deep neural network can achieve excellent digital classification results, and the classification accuracy of ideal phase mask plates and metasurface can reach 84.73% and 84.85%, respectively. Despite a certain loss of degrees of freedom compared to multi-layer phase mask plates, the single-layer metasurface is easier to fabricate and alignment, thereby improving spatial utilization efficiency.

Bragg-like microcavity formed by collision of single-cycle self-induced transparency light pulses in a resonant medium

Rostislav Arkhipov, Anton Pakhomov, Olga Diachkova, Mikhail Arkhipov, and Nikolay Rosanov

DOI: 10.1364/OL.521645 Received 15 Feb 2024; Accepted 02 Apr 2024; Posted 08 Apr 2024  View: PDF

Abstract: The coherent interaction of extremely short light pulses with a resonant medium can result in formation of population difference gratings. Such gratings have been created by pulses that are π/2 or smaller. This paper demonstrates that a microcavity with Bragg-like mirrors can be formed by colliding two single-cycle attosecond self-induced transparency pulses in the center of a two-level medium. The parameters of this structure can be quickly adjusted by increasing the number of collisions, which showcases the ability to control the dynamic properties of the medium on a sub-cycle time scale by using attosecond pulses.

Cross-connection of multiplexed cylindrical vector beams using off-axis spin-decoupled metasurfaces

Zhiqiang Xie, Junmin Liu, Wang Xinrou, Haisheng Wu, Chuangxin Xie, Qingji Zeng, Huapeng Ye, Xinxing Zhou, Dianyuan Fan, and Shuqing Chen

DOI: 10.1364/OL.520388 Received 15 Feb 2024; Accepted 02 Apr 2024; Posted 10 Apr 2024  View: PDF

Abstract: Cylindrical vector beam (CVB) multiplexing communication demands effective mode cross-connection techniques to establish communication networks. While methods like polarized grating and coordinate transformation have been developed for (de)multiplexing CVB modes, challenges persist in the cross-connection of these multiplexed mode channels, including multi-mode conversion and inhomogeneous polarization control. Herein, we present an independent off-axis spin-orbit interaction strategy utilizing spin-decoupled metasurfaces. Cross-connection is achieved by encoding conjugated Dammann optical vortex grating phases onto the two orthogonal circularly polarized components of CVBs. Experimental results demonstrate the successful interconversion of four CVB modes (CVB+1 and CVB-2, CVB+2 and CVB-4) using a Si-based metasurface with a polarization conversion efficiency exceeding 85%. This facilitates the cross-connection of 200 Gbit/s quadrature phase-shift keying signals with bit-error-rates below 10-6. Offering advantages such as ultra-compact device size, flexible control of CVB modes, and multi-mode parallel processing, this approach shows promise in advancing the networking capabilities of CVB mode multiplexing communication networks.

Time-gated single pixel imaging of Cherenkov emission from a medical linear accelerator

Mengyu Jia, zhaoqi wei, Feng Gao, Mingfeng Jiang, wei wang, zhiyong yuan, and Brian Pogue

DOI: 10.1364/OL.518624 Received 11 Jan 2024; Accepted 01 Apr 2024; Posted 04 Apr 2024  View: PDF

Abstract: Cherenkov imaging is an ideal tool for real-time in vivo verification of radiation therapy dose. Given that radiation is pulsed from medical linear accelerator (LINAC) together with the weak Cherenkov emissions, time-gated high-sensitivity imaging is required for robust measurements. Instead of using an expensive camera system with limited efficiency of detection in each pixel, a single pixel imaging (SPI) approach could be used to maintain outstanding sensitivity over the entire spectral band, and provide a low-cost and viable alternative. A prototype SPI system was developed and demonstrated here for the first time, in Cherenkov imaging of LINAC dose delivery to a water tank. Validation experiments were performed using four regular fields and an intensity-modulated radiotherapy (IMRT) delivery plan. The Cherenkov image-based projection percent depth dose curves (pPDDs) were compared to pPDDs simulated by the treatment planning system (TPS), with an overall average error of 0.48%, 0.42%, 0.65%, and 1.08% for the 3, 5, 7, and 9 cm square beams, respectively. The composite image of the IMRT plan achieved 85.9% pass rate using 3%/3 mm gamma index criteria, in comparing Cherenkov intensity and TPS dose. By taking the specific advantages of SPI, Cherenkov imaging could be further enhanced with additional temporal and spectral information with significantly higher signal capture than with current camera systems.

Photonic convolution accelerator based on hybrid integrated multi-wavelength laser array by photonic wire bonding for real-time image classification

Yuxin Ma, Kaifei Tang, Jun LU, Zhenxing Sun, Yuxin yao, Yuxin wang, zhenzhen Xu, Mi Li, Xin Wang, Rulei Xiao, Yu Xin, Jiahui Liu, Xiang Ji, Wei Jiang, Yuechun Shi, and Xiangfei Chen

DOI: 10.1364/OL.518837 Received 15 Jan 2024; Accepted 01 Apr 2024; Posted 04 Apr 2024  View: PDF

Abstract: We propose and experimentally demonstrate a compact and efficient photonic convolution accelerator based on hybrid integrated multi-wavelength DFB laser array by photonic wire bonding. The photonic convolution accelerator operates at 60.12 GOPS for one 3×3 kernel with a convolution window vertical sliding stride of 1 and generates 500 images of real-time image classification. Furthermore, real-time image classification on the MNIST database of handwritten digits with a prediction accuracy of 93.86 % is achieved. This work provides a novel compact hybrid integration platform to realize the optical convolutional neural networks.

Validated enhancement and temperature modulated absorbance of WS2 monolayer based on planar structure

Xueyong Yuan, Guangsheng jiang, Pingwei Liu, Qiang Fu, Zhi Zhang, Tianqi Liu, Yuru Jiang, weiwei zhao, wenhui wang, Bei Zhao, Zejun Li, Dan Liu, Zhenhua Ni, and Junpeng Lu

DOI: 10.1364/OL.522089 Received 23 Feb 2024; Accepted 01 Apr 2024; Posted 02 Apr 2024  View: PDF

Abstract: Transition-metal dichalcogenides (TMDC), as emerging optoelectronic materials, necessitate the establishment of an experimentally viable system to study their interaction with light. In this study, we propose andanalyze a WS2/PMMA/Ag planar Fabry-Perot (F-P) cavity, enabling the direct experimental measurement of WS2 absorbance. By optimizing the structure, the absorbance of A exciton of WS2 up to 0.546 can be experimentally achieved, which matches well with the theoretical calculations. Through temperature and the thermal expansion strain induced by temperature, the absorbance of the A exciton can be tuned in situ. Furthermore, temperature-dependent photocurrent measurementsconfirmed the consistent absorbance of the A exciton under varying temperatures. This WS2/PMMA/Ag planar structure provides a straightforward and practical platform for investigating light interaction in TMDCs, laying a solid foundation for future developments of TMDC-based optoelectronic devices.

Capacity Enhancement through Entropy Loading with Probabilistically Shaped Signals in Frequency Comb Based Transmission System

Ziyue Zhang, Yuanfei Zhang, Qiulin Zhang, and Chester C.T. Shu

DOI: 10.1364/OL.519159 Received 16 Jan 2024; Accepted 01 Apr 2024; Posted 01 Apr 2024  View: PDF

Abstract: We demonstrate a multichannel entropy loading mechanism in an optical frequency comb based coherent communication system. In high-capacity wavelength division multiplexing communications, the individual laser sources can be replaced by an optical frequency comb, thus reducing the complexity and energy consumption of the transmitter. However, the power variation among different comb lines will lead to performance discrepancies. Spectral flattening filters can be adopted to suppress the variation at the expense of additional system loss. Alternatively, by applying probabilistic shaping, we have implemented multichannel entropy loading to facilitate continuous adaptation of the source entropy. The data rate can be dynamically allocated according to the performance of each channel. Through the loading scheme, the non-uniform performances across the channels are effectively mitigated, achieving a capacity enhancement of 34.91 Gbit/s.

Spatial photoluminescence and lifetime mappings of Purcell-enhanced quasi-2D perovskites with non-local dielectric metasurface

Hai Bui, Tuyet Doan, Nhan Luong, Khue Luu, Ha Do, Linh Chu, Duong Pham, Oanh Vu, Son Tung Bui, Thuat Nguyen-Tran, Xuan Khuyen Bui, Lam Vu, Hai-Son Nguyen, Son Tung Ha, and Quynh Le-Van

DOI: 10.1364/OL.517100 Received 29 Dec 2023; Accepted 01 Apr 2024; Posted 03 Apr 2024  View: PDF

Abstract: Light-matter interaction between quantum emitters and optical cavities plays a vital role in fundamental quantum photonics and the development of optoelectronics. Resonant metasurfaces are proven to be an efficient platform for tailoring the spontaneous emission (SP) of the emitters. In this work, we study the interplay between quasi-2D perovskites and dielectric TiO2 metasurfaces. The metasurface, designed as an open cavity, enhances electric fields near its plane, shaping the perovskite's emissions. This is verified through angle-resolved photoluminescence (PL) studies. We also conducted reflectivity measurements and numerical simulations to validate the coupling between the quasi-2D perovskites and photonic modes. Notably, our work introduces a spatial mapping approach to study Purcell enhancement. Using Fluorescence Lifetime Imaging Microscopy (FLIM), we directly link the PL and lifetimes of the quasi-2D perovskites in spatial distribution when positioned on the metasurface. This correlation provides unprecedented insights into emitter distribution and emitter-resonator interactions. The methodology paves the way for applications in quantum optics, optoelectronics, and medical imaging by enabling spatial mapping of both PL intensity and lifetime.

A high-performance Ge/GeSi multi-quantum wells photodetector on a Ge-buffered Si substrate

wang he, kong zhenzhen, Xinguang Tan, SU JIALE, Junhao Du, Hongxiao Lin, li ben, wang yijie, ZIWEI ZHOU, MIAO YUANHAO, Zhao xuewei, Hu qin, and Henry Radamson

DOI: 10.1364/OL.521237 Received 14 Feb 2024; Accepted 01 Apr 2024; Posted 03 Apr 2024  View: PDF

Abstract: This work demonstrates a high-performance photodetector with a 4-cycle Ge/Ge0.84Si0.16 multi-quantum wells (MQWs) structure grown by reduced pressure chemical vapor deposition techniques on a Ge-buffered Si (100) substrate. At -1V bias, the dark current density of the fabricated PIN mesa devices is as low as 3 mA/cm2, and the optical responsivities are 0.51 and 0.17 A/W at 1310 and 1550 nm, respectively, corresponding to the cutoff wavelength of 1620nm. At the same time, the device has good high-power performance and continuous repeatable light response. On the other hand, the temperature coefficient of resistance (TCR)of the device is as high as -5.18%/K, surpassing all commercial thermal detectors. These results indicate that the CMOS-compatible and low-cost Ge/Ge0.84Si0.16 multilayer structure is promising for short-wave infrared and uncooled infrared imaging.

Application of femtosecond mode-locked SnTe thin films and generation of bound state solitons

Chen Yueqian, zhitao wu, Peiyao xiao, wende xiao, and Wen Liu

DOI: 10.1364/OL.519940 Received 29 Jan 2024; Accepted 31 Mar 2024; Posted 02 Apr 2024  View: PDF

Abstract: In the realm of ultrafast laser technology, the exploration of two-dimensional materials as saturable absorbers (SA) has garnered significant research interest. Our research investigates the characteristics of SnTe thin films, a topological crystalline insulator material, as a potential saturable absorber for ultrafast lasers. Using the molecular beam epitaxy (MBE) technique, we analyze the films’ morphology and composition through atomic force microscopy (AFM) and successfully deposit SnTe epilayers on Au(111)/Mica substrates. Through the utilization of SnTe-SA, an erbium-doped fiber laser is fabricated, demonstrating a pulse output with a width of 276 fs and a center wavelength of 1560 nm, highlighting the potential of SnTe films in manufacturing ultrafast optical devices. Additionally, tightly bound solitons with a soliton interval of 1.01 ps are observed, contributing to the exploration of soliton nonlinear dynamics.

Instantaneous thermometry imaging using two-photon laser-induced fluorescence

Mehdi Stiti, Vassily Kornienko, Elias Kristensson, Guillaume Castanet, and Edouard Berrocal

DOI: 10.1364/OL.516775 Received 21 Dec 2023; Accepted 31 Mar 2024; Posted 01 Apr 2024  View: PDF

Abstract: Measuring temperature in complex two-phase flows is crucial for understanding the dynamics of heat and mass transfer. In this letter, we introduce a novel optical approach based on using two-photon Laser-Induced Fluorescence (2p-LIF) imaging with two-Color Laser-Induced Fluorescence (2CLIF) for instantaneous temperature mapping of complex liquid media. Using Kiton Red and Rhodamine 560 as temperature probes, a temperature ranging from 15°C to 80°C with a sensitivity of 1.54 %/°C has been achieved. The application of this 2p-2CLIF technique allows the observation of the temperature dynamics occurring during the heating and degassing of water. This new approach contributes to the toolkit of optical temperature measurement techniques, providing a robust solution for studying complex, transient, high-speed two-phase flows.

High Efficiency Vertically Emitting Grating Coupler Facilitated by Three Wave Interactions

Carson Valdez, Sunil Pai, Payton Broaddus, and Olav Solgaard

DOI: 10.1364/OL.517492 Received 26 Jan 2024; Accepted 31 Mar 2024; Posted 01 Apr 2024  View: PDF

Abstract: We design a grating coupler optimized for normal inci-dence and we numerically demonstrate near unity cou-pling in a standard 220 nm thick silicon-on-insulatortechnology. Our design breaks the vertical symmetrywithin the grating region by implementing three scatter-ing sites per local period. This technique removes theneed for bottom reflectors or additional material layersand can be realized using only two lithography masks.Using adjoint method-based optimization we can en-gineer the coupling spectrum of the grating, balancingthe trade-off between peak efficiency and bandwidth.Using this technique, we simulate three devices withpeak coupling efficiencies ranging between 93.4% (-0.3dB) and 98.6% (-0.06 dB) with corresponding 1dB band-widths between 48 nm and 8 nm all centered around1550 nm

Polarization-insensitive and high-efficiency edge coupler for thin-film lithium niobate

Zehao Guo, weixi liu, Chengfeng Wen, lijia song, Liu Liu, Daoxin Dai, and Yaocheng Shi

DOI: 10.1364/OL.520812 Received 02 Feb 2024; Accepted 31 Mar 2024; Posted 09 Apr 2024  View: PDF

Abstract: In this paper, we propose and demonstrate a fiber-to-chip edge coupler (EC) on x-cut thin film lithium niobate (TFLN) for polarization-insensitive (PI) coupling. The EC consists of three width-tapered full-etched waveguides with silica cladding and matches well with single mode fiber (SMF). The measured results show that the minimum coupling loss for TE0/TM0 modes remain to be 0.9 dB/1.1 dB per facet and polarization dependent loss (PDL) is <0.5 dB over the wavelength range from 1260 nm to 1340 nm. Moreover, the EC features large misalignment tolerance of ±2 μm in Z direction and ±1.5 μm in X direction for both polarizations for 1 dB penalty. To the best of our knowledge, this is the first realized O-band edge coupler on TFLN with SMF. The proposed device shows promising potential for integration into TFLN polarization diversity devices.

Disorder effects on flatbands in moiré superlattices

Xiaoshuang Xia, Qian Liu, bingsuo zou, Peilong Hong, and Yi Liang

DOI: 10.1364/OL.522215 Received 26 Feb 2024; Accepted 29 Mar 2024; Posted 01 Apr 2024  View: PDF

Abstract: Plenty of exotic phenomena in moiré superlattices arise from the emergence of flatbands, but their significance could be diminished by structural disorders that will significantly alter flatbands. Thus, unveiling the effects of disorder on moiré flatbands is crucial. In this work, we explore the disorder effects on two sets of flatbands in silicon-based mismatched moiré superlattices, where the level of disorder is controlled by varying the magnitude of random perturbations of the locations of silicon strips. The results reveal that, after ensemble averaging, the average spectral positions of the four flat bands exhibit stability despite variations in the degree of disorder. However, the δ-like density of states (DOS) related to flatbands in the perfect superlattice evolves into a finite-width envelope of high DOS. By increasing the level of disorder, the width of the DOS envelope increases accordingly. Particularly, we observe a fascinating contrast: the width of bandgap flatbands saturates after intial growing, while the width of dispersive-band-crossed flatbands exhibits a linear increase versus disorder. This unveils fundamental differences in how flatbands respond to structural imperfections, offering crucial insights into their perturbation characteristics within moiré superlattices. Our work offers new perspectives on flatbands in partially disordered moiré superlattices.

Controlling ultrafast laser writing in silica glass by pulse temporal contrast

Yuhao Lei, Huijun Wang, Gholamreza Shayeganrad, Yuri Svirko, and Peter Kazansky

DOI: 10.1364/OL.522307 Received 26 Feb 2024; Accepted 29 Mar 2024; Posted 02 Apr 2024  View: PDF

Abstract: We demonstrate that the temporal contrast of femtosecond light pulses is a critical parameter in laser writing inside transparent dielectrics, allowing different material modifications. In particular, anisotropic nanopores in silica glass are produced by high-contrast of 107 femtosecond Yb: KGW laser pulses rather than low-contrast of 103 Yb fiber laser pulses. The difference originates in the fiber laser storing third of its energy in a post-pulse of 200 ps duration. The absorption of this low-intensity fraction of the pulse by laser-induced transient defects with relatively long lifetime and low excitation energy, such as self-trapped holes, drastically changes the kinetics of energy deposition and type of material modification. We also demonstrate that low-contrast pulses are effective in creating lamellar birefringent structures, possibly driven by quadrupole nonlinear current.

Reference-free dual-comb spectroscopy with inbuilt coherence

Mikhail Roiz, Santeri Larnimaa, Touko Uotila, Mikko Narhi, and Markku Vainio

DOI: 10.1364/OL.521866 Received 21 Feb 2024; Accepted 28 Mar 2024; Posted 01 Apr 2024  View: PDF

Abstract: We demonstrate a simple system for dual-comb spectroscopy based on two inherently coherent optical frequency combs generated via seeded parametric down-conversion. The inbuilt coherence is established by making the two combs share a common comb line. We show that the inbuilt coherence makes it possible to use a simple numerical post-processing procedure to compensate for small drifts of the repetition rate and the phase between the two combs.

Programmable hyperspectral coherent anti-Stokes Raman scattering microscopy

Janet Sorrells, Lingxiao Yang, Rishyashring Iyer, Eric Chaney, Carlos Renteria, and Stephen Boppart

DOI: 10.1364/OL.521864 Received 28 Feb 2024; Accepted 28 Mar 2024; Posted 01 Apr 2024  View: PDF

Abstract: Hyperspectral (HS) coherent Raman scattering microscopy provides a significant improvement in acquisition time compared to spontaneous Raman scattering, yet still suffers from the time required to sweep through individual wavenumbers. To address this, we present the use of a pulse shaper consisting of a 2D spatial light modulator (SLM) for phase- and amplitude-based shaping of the Stokes beam to create programmable spectrally-tailored excitation envelopes. This enables collection of useful spectral information in a more rapid and efficient manner.

High Power of a Self-Q-Switched Tm:YAP Laser

Zhaoyu Ma, Qianqian Hao, Huanli Wang, Xudong Sun, and Linjun Li

DOI: 10.1364/OL.518655 Received 22 Jan 2024; Accepted 28 Mar 2024; Posted 28 Mar 2024  View: PDF

Abstract: For the first time, the output performance of a self-Q-switched Tm:YAP laser has been controlled by adjusting the cavity length. By using a concise concave-flat cavity, a pulsed laser emitting at 1993.08 nm is produced without any additional modulation device. Under a stable self-Q-switched mode, the maximum average output power of 9.76 W is achieved from the laser when the incident pump power is 28.78 W, corresponding to a slope efficiency of 36.86% and an optical-to-optical conversion efficacy of 33.91%. Also, the narrowest pulse width of 485 ns at 48.97 kHz is obtained from the laser with a single pulse energy of 199.31 µJ. As far as we know, this laser has the highest average power and narrowest pulse width compared to other self-Q-switched Tm:YAP lasers.

Efficient single-scattering look-up table for lidar and polarimeter phytoplankton studies

Eduard Chemyakin, Snorre Stamnes, James Allen, Sharon Burton, Johnathan Hair, Chris Hostetler, Jacek Chowdhary, Bastiaan van Diedenhoven, and Brian Cairns

DOI: 10.1364/OL.513735 Received 21 Nov 2023; Accepted 27 Mar 2024; Posted 01 Apr 2024  View: PDF

Abstract: Coupled atmosphere and ocean remote sensing retrievals of aerosol, cloud, and oceanic phytoplankton microphysical properties, such as those carried out by the NASA Plankton, Aerosol, Cloud, ocean Ecosystem mission, involve single scattering calculations that are time consuming. Look-up tables exist to speed up these calculations for aerosol and water droplets in the atmosphere. In our new Lorenz-Mie look-up table we tabulate the single scattering by an ensemble of coated isotropic spheres representing oceanic phytoplankton at wavelengths from 0.355 μm. The look-up table covers phytoplankton particles with radii in the range of 0.15-100 μm at an increase of up to 10^4 in computational speed compared to the single scattering calculations. The allowed complex refractive indices range from 1.05 to 1.24 for the shell's real part, from 10^-7 to 0.3 for the shell's imaginary part, from 0 to 0.001 for the core's imaginary part, and equal to 1.02 for the core's real part. We show that we precisely compute inherent optical properties for the phytoplankton size distributions ranging up to 5 μm for the effective radius and up to 0.6 for the effective variance. We test wavelengths from 0.355 to 1.065 μm and find that all the inherent optical properties of interest agree with the single scattering calculations to within 1% for 99.9% of cases. We also provide an example of using the look-up table to reproduce the phytoplankton optical datasets listed in the PANGAEA Database for synthetic hyperspectral algorithm development. The table together with C++, Fortran, MATLAB, and Python codes to apply different complex refractive indices and phytoplankton size distributions are freely available online.

Spatial resolution limit of single pixel imaging of complex light fields

Dennis Scheidt and Pedro Quinto-Su

DOI: 10.1364/OL.519587 Received 25 Jan 2024; Accepted 26 Mar 2024; Posted 27 Mar 2024  View: PDF

Abstract: Complex light fields with arbitrary amplitudes and phases can be measured by sampling them with an orthogonal basis (i.e. canonical, Hadamard) and performing single pixel interferometric measurements of the focused modes. In this work we show that when the spatial resolution of the sampling basis is coarser than the spatial resolution of the phase in the complex field, the measured reconstructed amplitude exhibits crosstalk with the phase, that is, phase information appears in the amplitude. To demonstrate this phenomenon, we encode an arbitrary amplitude and phase with a spatial light modulator and compare measurements with simulations.

Noninvasive holographic imaging through dynamically scattering media

Naoki Matsuda, Jun Tanida, Makoto Naruse, and Ryoichi Horisaki

DOI: 10.1364/OL.516083 Received 21 Dec 2023; Accepted 26 Mar 2024; Posted 26 Mar 2024  View: PDF

Abstract: We present a noninvasive method for quantitative phase imaging through dynamically scattering media. A complex amplitude object, illuminated with coherent light, is captured through a dynamically scattering medium and a variable coded aperture, without the need for interferometric measurements or imaging optics. The complex amplitude of the object is computationally retrieved from intensity images that use multiple coded aperture patterns, employing a stochastic gradient descent algorithm. We demonstrate the proposed method both numerically and experimentally.

Partially coherent Pearcey-Gauss source of the spatial spectrum with hyperbolic sine correlation

JingHuan Huang, Yanghong Li, Yejin Liu, jingyi shi, YingJun Luo, Yongzheng Yang, Peiwen Peng, Shigen Ouyang, and Dongmei Deng

DOI: 10.1364/OL.519074 Received 18 Jan 2024; Accepted 25 Mar 2024; Posted 26 Mar 2024  View: PDF

Abstract: By designing the intricate coherence structure, we are able to create a desired beam profile and trajectory with exceptional beam quality and flexible propagation characteristics even in different conditions. Our research focus lies on the Fourier plane, specifically emphasizing the coherence of spatial frequencies, and we find it can be seen as a constant system response. A theoretical framework is developed and experimental studies are conducted to generate a light field of the spatial spectrum with a complex correlation model using the pseudo-modes superposition method. We successfully produce partially coherent Pearcey-Gauss beams whose spatial spectrum is hyperbolic sine correlational. Interestingly, these beams maintain the distinctive propagation properties of the Pearcey pattern while simultaneously exhibiting the remarkable ability to split the mainlobe into two separate lobes.

Direct generation of 635nm red random lasers based on praseodymium(Pr)-doped ZBLAN fiber

zhipeng dong, yongjia yao, mingyue he, xinyun yang, Wencheng Jia, Hang Wang, and Zhengqian Luo

DOI: 10.1364/OL.519425 Received 18 Jan 2024; Accepted 23 Mar 2024; Posted 25 Mar 2024  View: PDF

Abstract: Visible random fiber lasers have garnered significant attention due to their unique emission properties and potential applications in various fields. We first demonstrated, to the best of our knowledge, a compact all-fiber structure, red wavelength, random fiber laser (RFL) based on double-clad Pr-doped ZBLAN fiber. The simple half-open cavity consists of a high-reflectivity fiber pigtail mirror and the Pr-doped ZBLAN fiber. The Pr-doped ZBLAN fiber not only served as a gain medium but also offered random backward scattering. We investigated the effects of different lengths on output power and slope efficiency of the RFL. For 21 meters Pr-doped fiber, the RFL emitted a maximum output power of 208.50 mW with a slope efficiency of 11.09%. For 15 meters Pr-doped fiber, the maximum power decreased to 120.18 mW with the slope efficiency of 7.27%. We are also numerical simulating the output power versus pump power at different fiber lengths based on power steady-state light propagation equations. This novel RFL has the potential for broad applications in fields such as display technology, spectroscopy, biomedical imaging, and optical sensing due to its unique properties and simple all-fiber structure.

All-Optical High-Contrast Femtosecond Switching using Nonlinearity from Epsilon-Near-Zero effect in Plasmonic Metamaterials

TANMAY BHOWMIK, BODHAN CHAKRABORTY, and Debabrata Sikdar

DOI: 10.1364/OL.521075 Received 07 Feb 2024; Accepted 22 Mar 2024; Posted 27 Mar 2024  View: PDF

Abstract: Metamaterials opened a new realm to control light–matter interactions at sub-wavelength scale by engineering meta-atoms. Recently, the integration of several emerging nonlinear materials with metamaterial structures enables ultrafast all-optical switching at the nanoscale and thus, brings enormous possibilities to realize next-generation optical communication systems. This letter presents a novel design of plasmonic metamaterial for high-contrast femtosecond all-optical switching. We leverage magnetic plasmon (MP) resonance combined with the nonlinear effects of epsilon-near-zero (ENZ) material. The proposed design comprises a periodic array of two closely-spaced Au-nanograting deposited on an optically thick Au-substrate to excite MP-resonance. To enable dynamically tunable resonance, the nanogrooves in meta-atoms are filled with an ENZ-material, cadmium-oxide (CdO). The intraband transition-induced optical nonlinearities in the ENZ-medium are studied using two-temperature model. We observe that the pump-induced refractive index change in CdO-layer causes red-shift of the MP-resonance dip wavelength in the reflectance spectrum leading to a high modulation depth of 0.83 at 1.55 µm. With ultrafast response time of 776 fs while maintaining a low pump-fluence requirement of 75 µJ/cm², the proposed metamaterial could help in realizing switches for next-generation optical computation systems.

Polarization insensitive multimode interference coupler based on subwavelength grating structure

Ruoran Liu, weike zhao, Zejie Yu, and Daoxin Dai

DOI: 10.1364/OL.522246 Received 23 Feb 2024; Accepted 21 Mar 2024; Posted 10 Apr 2024  View: PDF

Abstract: A multimode interference (MMI) coupler is one of the basic components for photonic integrated circuits. However, MMI couplers realized by conventional waveguides are polarization sensitive which is undesired for many applications such as optical switches and communications. In this paper, we propose a polarization-insensitive MMI coupler on a 220-nm silicon-on-insulator platform by constructing different effective interference lengths for TE and TM modes assisted with subwavelength grating structures. The designed MMI coupler shows an excess loss of <0.24(0.43) dB, and a power imbalance of <0.6(0.5) dB for the TE(TM) mode over the wavelength range of 1.5-1.6 μm in theory. Experimentally, the fabricated MMI exhibits low excess loss <0.64(0.53) dB and power imbalance <1(0.85) dB for the TE(TM) mode over a wavelength range of 1.55-1.61 μm.

Super-resolution radial fluctuations microscopy for optimal resolution and fidelity

yanru li, Selene Roberts, Lixin Liu, and Lin Wang

DOI: 10.1364/OL.514964 Received 11 Dec 2023; Accepted 20 Mar 2024; Posted 21 Mar 2024  View: PDF

Abstract: Fluorescence fluctuations super-resolution microscopy (FF-SRM) has emerged as a promising method for fast, low-cost, and uncomplicated imaging of biological specimens beyond the diffraction limit. Among the FF-SRM techniques, super-resolution radial fluctuations (SRRF) microscopy is a popular technique but is prone to artifacts, resulting in low fidelity, especially under conditions of high-density fluorescence. In this paper, we propose a novel approach, namely VeSRRF, that combines intensity and gradient variance reweighted radial fluctuations (VRRF) and enhanced-SRRF (eSRRF) algorithms, leveraging the enhanced resolution achieved through intensity and gradient variance analysis in VRRF and the improved fidelity obtained from the radial gradient convergence transform in eSRRF. Our method is validated using microtubules in mammalian cells as a standard biological model system. Our results demonstrate that VeSRRF consistently achieves the highest resolution and fidelity compared to those obtained from other algorithms in both single molecule localization microscopy and fluorescence fluctuations microscopy. Moreover, we have developed the VeSRRF software package that is freely available on the open-source ImageJ/Fiji software platform, to facilitate the use of VeSRRF in the broader community of biomedical researchers.

Non-telecentric photoacoustic microscopy for multi-scale imaging

Yujie Wang, Linyang Li, Weizhi Qi, Wei Qin, Tian Jin, Tingting Li, Lei Xi, and Pavel Subochev

DOI: 10.1364/OL.519330 Received 31 Jan 2024; Accepted 19 Mar 2024; Posted 12 Apr 2024  View: PDF

Abstract: Optical-resolution photoacoustic microscopy (OR-PAM) excels in precisely imaging biological tissue based on absorption contrast. However, existing OR-PAMs are confined by fixed compromises between spatial resolution and field of view (FOV), preventing the integration of large FOV and local high-resolution within one system. Here, we present a non-telecentric OR-PAM (nTC-PAM) that empowers efficient adaptation of FOV and spatial resolution to match the multiscale requirement of diverse biological imaging. Our method allows for a large-scale transformation in FOV, and even surpassing the nominal FOV of the objective with minimal marginal degradation of the lateral resolution. We demonstrate the advantage of nTC-PAM through multi-scale imaging of the leaf phantom, mouse ear and cortex. The results reveal that nTC-PAM can switch the FOV and spatial resolution to meet the requirements of different biological tissues, such as large-scale imaging of the whole cerebral cortex and high-resolution imaging of microvascular structures in local brain regions.

Pump-power-controlled L-band wavelength-tunable mode-locked fiber laser utilizing all polarization maintaining nonlinear polarization rotation

Guanyu YE, Bowen Liu, Maolin Dai, Yifan Ma, Takuma Shirahata, Shinji Yamashita, and Sze Set

DOI: 10.1364/OL.518882 Received 15 Jan 2024; Accepted 15 Mar 2024; Posted 15 Mar 2024  View: PDF

Abstract: For the first time, we present the pump power-controlled wavelength-tunable mode-locked fiber laser in the L-band (1565 nm to 1625 nm), achieved by all-polarization maintaining (all-PM) nonlinear polarization rotation (NPR). The wavelength of the laser can be tuned over 20 nm, from 1568.2 nm to 1588.9 nm simply by controlling the pump power from 45 mW to 115 mW. In contrast to conventional wavelength tuning mechanisms such as optical bandpass filters, our tuning method is non-mechanical and electrically controllable, featuring simplicity and cost-effectiveness in a superior all-fiber design.

Optical Snake States in Photonic Graphene

Olha Bahrova, Sergei Koniakhin, Anton Nalitov, and Evgenia Cherotchenko

DOI: 10.1364/OL.519717 Received 25 Jan 2024; Accepted 11 Mar 2024; Posted 12 Mar 2024  View: PDF

Abstract: We propose an optical analogue of electron snake states based on artificial gauge magnetic field in photonic graphene implemented by varying distance between cavity pillars.We develop an intuitive and exhaustive continuous model based on tight-binding approximation and compare it with numerical simulations of a realistic photonic structure.The allowed lateral propagation direction is shown to be strongly coupled to the valley degree of freedom and the proposed photonic structure may be used a valley filter.

Comparative study of the multiple wavelength lasing of nitrogen ions: the role of vibrational level-dependent photoionization

Siyu Qin, Chaohui Zhou, Haicheng Mei, Qi Lu, Kailu Wang, Zixiang Jiang, Xiao jing Liu, peng peng, Liang Xu, and Yi Liu

DOI: 10.1364/OL.517496 Received 08 Jan 2024; Accepted 09 Mar 2024; Posted 04 Apr 2024  View: PDF

Abstract: We report on optical amplification and energy threshold of the two most prominent emission lines, 391.4 nm and 427.8 nm, of the cavity-less lasing of nitrogen ions pumped by femtosecond laser pulses. It was found the two transitions both show optical amplification under low gas pressure condition, while the 391.4 nm emission is barely amplified under high gas pressure. Moreover, the 427.8 nm emission presents a significant lower pump laser energy threshold and a larger gain factor than the 391.4 nm emission. Numerical simulations based on three-state coupling model suggest that the smaller ionization Franck-Condon factor from the ground state of N2 to the vibrational level ν = 1 in X state of N2+ favors the formation of population inversion corresponding to the 427.8 nm emission. Meanwhile, the competition between strong field ionization and excitation induced by the pumping laser requires higher laser intensity to acquire the population inversion for 391.4 nm radiation, leading to a corresponding larger energy threshold.

Pulse pattern manipulation of dichromatic soliton complexes by a twistable tapered fiber filter

Bowen Liu, Shinji Yamashita, and Sze Set

DOI: 10.1364/OL.517054 Received 15 Jan 2024; Accepted 06 Mar 2024; Posted 14 Mar 2024  View: PDF

Abstract: Soliton complexes highlight the particle-like dynamics of dissipative pulse motions. Whereas simple and reliable manipulation of bound solitons remains challenging. Here, we report controllable pulse patterns of robustly coexisting dichromatic soliton complexes in an all-polarization-maintaining fiber laser based on a twistable tapered fiber filter. According to the twist angle, dichromatic pulses are switched between different patterns. Components at each wavelength can also be independently manipulated depending on the twist direction, enabling extended encoding formats from the time to frequency domain. To the best of our knowledge, it is the first experimental demonstration of dual-wavelength soliton complexes that different bound pulse patterns coexist at separated wavebands.

Off-plane quartz-enhanced photoacoustic spectroscopy

Huijian Luo, Junming Li, Haohua Lv, Jiabao Xie, Chenglong Wang, Haoyang Lin, Ruobin Zhuang, Wenguo Zhu, Yongchun Zhong, Ruifeng Kan, JianHui Yu, and Huadan Zheng

DOI: 10.1364/OL.506650 Received 25 Sep 2023; Accepted 01 Jan 2024; Posted 31 Jan 2024  View: PDF

Abstract: In this work, we developed off-plane quartz-enhanced photoacoustic spectroscopy (OP-QEPAS). In the OP-QEPAS the light beam neither went through the prong spacing of the quartz tuning fork (QTF), nor in the QTF plane. The light beam is in parallel with the QTF with an optimal distance, resulting in low background noise. A radial-cavity (RC) resonator was coupled with the QTF to enhance the photoacoustic signal by radial resonance mode. By offsetting both the QTF and the laser position from the central axis, we enhance the effect of acoustic radial resonance and prevent the noise generated by direct laser irradiation of the QTF. Compared to IP-QEPAS based on a bare QTF, the developed OP-QEPAS with a RC resonator showed a >10× signal-to-noise ratio (SNR) enhancement. The OP-QEPAS system has great advantages in the use of light emitting devices (LEDs), long-wavelength laser sources such as mid-infrared quantum cascade lasers, and terahertz sources. When employing a LED as excitation source, the noise level was suppressed by ~2 orders of magnitude. Furthermore, the radial and longitudinal resonance modes can be combined to further improve the sensor performance.

Extreme-value statistics in nonlinear optics

Aleksei Zheltikov

DOI: 10.1364/OL.510419 Received 26 Oct 2023; Accepted 27 Dec 2023; Posted 13 Feb 2024  View: PDF

Abstract: We show that, although nonlinear optics may give rise to a vast multitude of statistics, all these statistics converge, in their extreme-value limit, to one of a few universal extreme-value statistics. Specifically, in the class of polynomial nonlinearities, such as those found in the Kerr effect, weak-field harmonic generation, and multiphoton ionization, the statistics of the nonlinear-optical output converges, in the extreme-value limit, to the exponentially tailed, Gumbel distribution. Exponentially growing nonlinear signals, on the other hand, such as those induced by parametric instabilities and stimulated scattering, are shown to reach their extreme-value limits in the class of the Fréchet statistics, giving rise to extreme-value distributions with heavy, manifestly nonexponential tails, thus favoring extreme-event outcomes and rogue-wave buildup.