Accepted papers to appear in an upcoming issue
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Multiple plasmonic-photonic couplings in the Au nanobeaker arrays: enhanced robustness and wavelength tunability
- received 03/18/2015; accepted 04/11/2015; posted 04/13/2015; Doc. ID 236389
- [full text: PDF (1983) KB)]
- Abstract: Diffractive coupling in the plasmonic nanoparticle arrays introduces the collective plasmon resonances with high scattering efficiency and narrow linewidth. However, the collective behavior is often limited to the arrays embedded in a homogeneous refractive index environment. The collective plasmon resonances can be suppressed when the arrays are supported on the solid-state substrates with different superstrates, as required for many applications, because of the different dispersion relations between the substrate and the superstrate. Herein, we develop a general concept, which seeks to synergize the sub-nanoparticle engineering of “hot spots” with the far-field coupling behavior, for the versatile control of plasmonic-photonic couplings in an asymmetric environment. To demonstrate our concept, we choose as an example the Au nanobeaker arrays (NBAs), which are the conformally coated Au thin layers on the interior sidewalls and bottoms of nanohole arrays in SiO2 substrates. Using the finite-difference time-domain simulations, we show that engineering the plasmonic “hot spots” in the NBAs by simply controlling the depth-to-diameter aspect ratio of individual units enables multiple plasmonic-photonic couplings in an asymmetric environment. These couplings are robust with a wide range of resonance wavelengths from visible to infrared. Furthermore, the angle-dependent transmission spectra of the arrays reveal a transition from band-edge to propagating state for the orthogonal coupling and a splitting of diffraction waves in the parallel coupling. The proposed NBAs will find enhanced applications in plasmonic lasers and bio-sensing.
- (240.6680) Optics at surfaces : Surface plasmons
- (260.3910) Physical optics : Metal optics
- (260.5740) Physical optics : Resonance
- (160.4236) Materials : Nanomaterials
Enhanced spectral response of π-phase shifted fiber Bragg gratings in closed-loop configuration
- received 02/17/2015; accepted 04/11/2015; posted 04/13/2015; Doc. ID 234919
- [full text: PDF (645) KB)]
- Abstract: By integrating a π-shifted fiber Bragg grating (π-FBG) in a ring resonator, a spectral feature shows in the transmission spectrum in correspondence of the Bragg wavelength, that is much sharper than the π-FBG resonance. This feature can be detected with a simple integrated cavity output technique. The resolution of any sensor based on the fitting of the π-FBG spectral profile can thus be largely improved at no additional fabrication costs and without altering the sensor robustness. A theoretical model shows that the resolution improvement attainable in the closed-loop geometry depends on the grating symmetry and the ring resonator quality factor. With a commercial grating in a medium-finesse ring, a spectral feature 12 times sharper than the π-FBG resonance is experimentally demonstrated. A much larger enhancement is expected in an optimized, low-loss setup.
- (060.2370) Fiber optics and optical communications : Fiber optics sensors
- (060.3735) Fiber optics and optical communications : Fiber Bragg gratings
- (230.4555) Optical devices : Coupled resonators
Self-induced transparency and coherent population trapping of ⁸⁷Rb vapor in a mode-locked laser
- received 02/11/2015; accepted 04/11/2015; posted 04/13/2015; Doc. ID 234389
- [full text: PDF (431) KB)]
- Abstract: Simultaneous self-induced transparency and a dark line resonance are observed inside a mode-locked laser. The circulating pulse, tuned to the 795 nm optical resonance of intracavity rubidium, has sufficient intensity to create at each passage a population inversion — return to ground state, typical of self-induced transparency. A drop in fluorescence (dark line resonance), is observed as the repetition rate is tuned to a submultiple of the hyperfine ground-state splitting.
- (020.1670) Atomic and molecular physics : Coherent optical effects
- (020.2930) Atomic and molecular physics : Hyperfine structure
- (320.5390) Ultrafast optics : Picosecond phenomena
- (320.7120) Ultrafast optics : Ultrafast phenomena
Turbulence Compensation of an Orbital-Angular-Momentum and Polarization Multiplexed Link Using a Data-Carrying Beacon on a Separate Wavelength
- received 02/27/2015; accepted 04/11/2015; posted 04/13/2015; Doc. ID 233828
- [full text: PDF (620) KB)]
- Abstract: We investigate sensing of a data-carrying Gaussian beacon on a separate wavelength as a means to provide the information needed to compensate for the effects of atmospheric turbulence on orbital angular momentum (OAM) and polarization multiplexed beams in a free-space optical link. The influence of the Gaussian beacon's wavelength on the compensation of OAM beams at 1560 nm is studied experimentally. It is found that the compensation performance degrades slowly with the increase in the beacon's wavelength offset, in the 1520-1590 nm band, from the OAM beams. Using this scheme, we experimentally demonstrate a 1-Tbit/s OAM-and polarization-multiplexed link through emulated dynamic turbulence with a data-carrying beacon at 1550 nm. Experimental results show that turbulence effects on all 10 data channels each carrying a 100-Gbit/s signal, are mitigated efficiently and the power penalties after compensation are below 5.9 dB for all channels. The results of work might be helpful to the future implementation of a high-capacity OAM, polarization and wavelength multiplexed free-space optical link affected by atmospheric turbulence.
- (010.1080) Atmospheric and oceanic optics : Active or adaptive optics
- (010.1330) Atmospheric and oceanic optics : Atmospheric turbulence
- (060.4230) Fiber optics and optical communications : Multiplexing
- (060.2605) Fiber optics and optical communications : Free-space optical communication
Microwave controlled efficient Raman sub-harmonic generation
- received 01/19/2015; accepted 04/11/2015; posted 04/14/2015; Doc. ID 232628
- [full text: PDF (665) KB)]
- Abstract: We propose a novel scheme for efficient Raman sub-harmonic generation in a system of homogeneously broadened atomic vapor with atoms in a closed three level -configuration. The key feature of our scheme is the microwave induced atomic coherence of the two lower level metastable states. We show explicitly that by manipulating these coherence via the amplitude and phase of the microwave field, we can control the generation of different Raman sub-harmonics. Our scheme is viable in currently available atomic vapour cells thereby opening the way for efficient sub-harmonic generation in standard experimental setups.
- (020.1670) Atomic and molecular physics : Coherent optical effects
- (190.0190) Nonlinear optics : Nonlinear optics
- (190.4223) Nonlinear optics : Nonlinear wave mixing
Flexible compensation of dispersion-induced power fading for multi-service RoF links based on phase-coherent orthogonal lightwave generator
- received 03/18/2015; accepted 04/11/2015; posted 04/14/2015; Doc. ID 236292
- [full text: PDF (1335) KB)]
- Abstract: A novel technique to simultaneously compensate dispersion-induced power fading for multi-service radio-over-fiber (RoF) links is proposed. At the central office (CO), phase-coherent orthogonal lightwave generator (POLG) consisting of a polarization rotator (PR) and a single-driver Mach-Zehnder modulator (MZM) is used. By adjusting a polarization controller (PC) in the base station (BS), the phase difference between the orthogonal polarization carrier and two sidebands can be controlled, and the frequency response can be flexibly shifted for individual radio frequency (RF) service. We experimentally shift the destructive interference to the constructive interference at various frequencies for 25-km and 30-km fiber links. The performances of two services carrying 1-Gb/s on-off keying (OOK) data at 9 GHz and 16.6 GHz over 30-km fiber in the proposed system show receiver sensitivity improvement of ~12-dB at the bit error rate (BER) of 10−3 compared with the conventional double sideband (DSB) modulation case.
- (060.2360) Fiber optics and optical communications : Fiber optics links and subsystems
- (350.4010) Other areas of optics : Microwaves
- (060.5625) Fiber optics and optical communications : Radio frequency photonics
- (130.4110) Integrated optics : Modulators
Ground-plane-less bidirectional terahertz absorber based on omega resonators
- received 03/12/2015; accepted 04/11/2015; posted 04/13/2015; Doc. ID 236100
- [full text: PDF (1595) KB)]
- Abstract: We present a new ultrathin metamaterial which acts as a frequency-selective absorber of terahertz radiation. The absorber is a square array of pairs of omega-shaped micro-resonators made of high ohmic loss metal. The metamaterial provides significant suppression of transmitted and reflected radiation in a bidirectional regime (that is, for both forward and backward propagating radiation). The absorber is efficient in a wide range of angles of incidence. The absence of a ground plane makes the absorber unique in comparison with numerous analogs with a ground plane that operate in a unidirectional regime. The novel metamaterial potentially enables controllable transmission of terahertz radiation in imaging systems. Analytical calculations as well as finite-element electromagnetic modeling are presented for an exemplary case with peak absorption at ~3 THz.
- (350.2450) Other areas of optics : Filters, absorption
- (160.3918) Materials : Metamaterials
- (170.6795) Medical optics and biotechnology : Terahertz imaging
Beam deformation within an acousto-optic lens
- received 03/02/2015; accepted 04/11/2015; posted 04/16/2015; Doc. ID 235374
- [full text: PDF (729) KB)]
- Abstract: The acousto-optic lens (AOL) is becoming a popular tool in the neuroscience field. Here we analyzed the deformation of the diffraction beam after passage through an AOL consisting of a pair of acousto-optic deflectors using both theoretical and experimental data. The results showed that, because of the high sensitivity of optical spatial frequencies of acousto-optic deflectors, the boundary strength of the diffraction beam of the AOL decreases significantly. When the focal length of AOL diminishes, the deformation of the diffraction beam becomes more serious with a smaller beam size. This deformation of the diffraction beam finally leads to a decreased illuminative numerical aperture, which worsens the image’s spatial resolution.©
- (070.4790) Fourier optics and signal processing : Spectrum analysis
- (120.5800) Instrumentation, measurement, and metrology : Scanners
- (170.1065) Medical optics and biotechnology : Acousto-optics
In situ study of two interacting femtosecond filaments in sapphire
- received 02/02/2015; accepted 04/10/2015; posted 04/13/2015; Doc. ID 232577
- [full text: PDF (1618) KB)]
- Abstract: Interaction dynamics of two co-propagating femtosecond light filaments in sapphire crystal is studied by means of time-resolved off-axis digital holographic and shadowgraphic microscopy with 22 fs temporal and 1 μm spatial resolution. In particular, we demonstrate that filament interaction originates from instantaneous modification of the refractive index resulting from Kerr effect. Fusion, splitting and even suppression of the resulting plasma channels induced by interacting filaments was observed by varying time delay between the input pulses. Free electron channels were reconstructed in the form of the time-lapse movie with unprecedented spatial and temporal resolution.
- (190.3270) Nonlinear optics : Kerr effect
- (190.7110) Nonlinear optics : Ultrafast nonlinear optics
- (320.7100) Ultrafast optics : Ultrafast measurements
- (350.5400) Other areas of optics : Plasmas
- (100.0118) Image processing : Imaging ultrafast phenomena
- (090.1995) Holography : Digital holography
Molecular decay rate near nonlocal plasmonic particles
- received 01/28/2015; accepted 04/10/2015; posted 04/10/2015; Doc. ID 233146
- [full text: PDF (386) KB)]
- Abstract: When the size of metal nanoparticles is smaller than typically 10 nm, their optical response becomes sensitive to both spatial dispersion and quantum size effects associated with the confinement of the conduction electrons inside the particle. In this Letter, we propose a nonlocal scheme able to compute molecular decay rates near spherical nanoparticles which includes the electron--electron interactions through a simple model of electronic polarizabilities. The plasmonic particle is schematized by a dynamic dipolar polarizability and the quantum system is characterized by a two--level--system. In this scheme, the light--matter interaction is described in term of classical field--susceptibilities. This theoretical framework could be extended to address the influence of nonlocality on the dynamics of quantum systems placed in the vicinity of nano-objects of arbitrary morphologies.
- (000.6800) General : Theoretical physics
- (250.5403) Optoelectronics : Plasmonics
- (050.6624) Diffraction and gratings : Subwavelength structures
Visible-to-near-infrared octave spanning supercontinuum generation in a silicon nitride waveguide
- received 02/25/2015; accepted 04/10/2015; posted 04/17/2015; Doc. ID 234835
- [full text: PDF (2158) KB)]
- Abstract: The generation of an octave spanning supercontinuum covering 488 nm to 978 nm (at -30 dB) is demonstrated for the first time on-chip. This result is achieved by dispersion engineering a 1 cm long Si₃N₄ waveguide and pumping it with an 100 fs Ti:Sapphire laser emitting at 795 nm. This work offers a bright broadband source for biophotonic applications and frequency metrology.
- (190.4390) Nonlinear optics : Nonlinear optics, integrated optics
- (320.6629) Ultrafast optics : Supercontinuum generation
Effect of Blood Vessels on Light Distribution on Optogenetic Stimulation of Cortex
- received 12/17/2014; accepted 04/09/2015; posted 04/17/2015; Doc. ID 230883
- [full text: PDF (4728) KB)]
- Abstract: In this article, the impact of blood vessels on light distribution during photostimulation of cortical tissue in small rodents is investigated. Brain optical properties were extracted using a double-integrating sphere setup and optical coherence tomography was used to image cortical vessels and capillaries to generate three-dimensional angiogram of the cortex. By combining these two datasets, a complete volumetric structure of the cortical tissue was developed and linked to a Monte Carlo code which simulates light propagation in this inhomogeneous structure and illustrates the effect of blood vessels on the penetration depth and pattern preservation in optogenetic stimulation.
- (000.1430) General : Biology and medicine
- (110.4500) Imaging systems : Optical coherence tomography
Ultracompact and broadband polarization beam splitter based on polarization dependent critical guiding condition
- received 02/11/2015; accepted 04/09/2015; posted 04/10/2015; Doc. ID 234489
- [full text: PDF (1214) KB)]
- Abstract: An ultracompact and broadband polarization beam splitter (PBS) based on the polarization dependent critical guiding condition of an asymmetrical directional coupler is proposed. The device consists of a pair of silicon waveguides with different height and width. Due to the different cutoff conditions for the TE and TM polarization modes, it is possible to have the TM mode guided in one waveguide, while the TE mode is supported in both. Therefore, only the phase-matching condition for the cross-coupling of TE mode needs to be considered. This approach not only simplifies the design procedures, but also significantly improves device performance, with smaller total length and larger bandwidth. Finally, regardless of the contribution of S-bend waveguides, our proposed PBS has a coupling region as short as 0.2µm, which is the shortest reported until now. The simulation result shows that the extinction ratios for TE and TM polarization are 13.5dB and 16.6dB at their respective output ports, and their insertion losses are 0.29dB and 0.13dB, respectively. Numerical simulations also show that the device offers a very large bandwidth (~140nm) with large extinction ratio (>10dB) and low insertion loss (<1dB).
- (130.3120) Integrated optics : Integrated optics devices
- (230.7370) Optical devices : Waveguides
- (130.5440) Integrated optics : Polarization-selective devices
Imaging and characterizing shear wave and shear modulus under orthogonal acoustic radiation force excitation using OCT Doppler variance method
- received 02/19/2015; accepted 04/09/2015; posted 04/10/2015; Doc. ID 234982
- [full text: PDF (654) KB)]
- Abstract: We report on a system for imaging and quantifying shear wave and shear modulus under orthogonal acoustic radiation force (ARF) excitation using optical coherence tomography (OCT) Doppler variance method. The ARF perpendicular to the OCT beam is produced by a remote ultrasonic transducer. A shear wave induced by ARF excitation propagates parallel to the OCT beam. The OCT Doppler variance method, which is sensitive to the transverse vibration, is used to measure the ARF induced vibration. For analysis of the shear modulus, the Doppler variance method is utilized to visualize shear wave propagation instead of Doppler OCT method and the propagation velocity of the shear wave is measured at different depths of one location with the M scan. In order to quantify shear modulus beyond the OCT imaging depth, we move ARF to a deeper layer at a known step and measure the time delay of the shear wave propagating to the same OCT imaging depth. We also quantitatively map the shear modulus of a cross-section in a tissue-equivalent phantom after employing the B scan.
- (120.0120) Instrumentation, measurement, and metrology : Instrumentation, measurement, and metrology
- (170.4500) Medical optics and biotechnology : Optical coherence tomography
- (170.7170) Medical optics and biotechnology : Ultrasound
- (170.6935) Medical optics and biotechnology : Tissue characterization
Diamagnetic Cavitization of laser produced barium plasma in transverse magnetic field
- received 03/04/2015; accepted 04/09/2015; posted 04/10/2015; Doc. ID 235592
- [full text: PDF (679) KB)]
- Abstract: Influence of uniform transverse magnetic field and ambient Ar pressure on the plasma plume produced by Nd:YAG laser ablation of barium has been investigated by time-of-flight optical emission spectroscopy. Experiments were carried out with laser pulse energy of 150 mJ and 0.45 Tesla magnetic field. The time-of-flight profiles showed ambient pressure independent behaviour at 6 mm distance from the target which is attributed to the diamagnetic behavior of the laser plasma. We have explained the compression of temporal profiles of ionic lines using a theoretical model and correlated to estimated magnetic diffusion time.
- (300.6500) Spectroscopy : Spectroscopy, time-resolved
- (350.5400) Other areas of optics : Plasmas
- (280.5395) Remote sensing and sensors : Plasma diagnostics
- (300.6365) Spectroscopy : Spectroscopy, laser induced breakdown
Concept for a transmissive, large angle, light steering device with high efficiency
- received 01/12/2015; accepted 04/09/2015; posted 04/09/2015; Doc. ID 232106
- [full text: PDF (1145) KB)]
- Abstract: A device concept is presented to allow very large angle deflection of light passing through a transmissive device. Deflection of light, switchable between angles larger than +-60 degrees, is shown to be possible with efficiency approaching 100%
- (230.0250) Optical devices : Optoelectronics
- (230.1950) Optical devices : Diffraction gratings
- (230.3720) Optical devices : Liquid-crystal devices
- (230.5440) Optical devices : Polarization-selective devices
On the rewriting of ultrashort pulse induced nanogratings
- received 03/19/2015; accepted 04/08/2015; posted 04/08/2015; Doc. ID 236212
- [full text: PDF (2602) KB)]
- Abstract: In this study we report on the erasure and rewriting of nanogratings by femtosecond laser pulses in the bulk of fused silica. To map the structural processes during rewriting, a combination of optical retardance (OR) measurement, small angle X-ray scattering (SAXS) and scanning electron microscopy (SEM) was used. The results reveal that already few pulses lead to erasure and formation of anisotropic structures. Repetitive rewriting favors the formation of nanoscopic pores which increases the optical retardance of nanogratings.
- (140.3390) Lasers and laser optics : Laser materials processing
- (320.2250) Ultrafast optics : Femtosecond phenomena
- (220.4241) Optical design and fabrication : Nanostructure fabrication
Beyond the current noise limit in imaging through turbulent medium
- received 02/11/2015; accepted 04/07/2015; posted 04/08/2015; Doc. ID 230482
- [full text: PDF (1603) KB)]
- Abstract: Shift-and-add is an approach employed to mitigate the phenomenon of resolution degradation in images acquired through a turbulent medium. Using this technique, a large number of consecutive short exposures is registered below the coherence time of the atmosphere or other blurring medium. The acquired images are shifted to the position of the brightest speckle and stacked together to obtain high-resolution and high signal-to-noise frame. In this Letter, we present a highly efficient method for determination of frames shifts, even if in a single frame the object cannot be distinguished from the background noise. The technique utilizes our custom genetic algorithm, which iteratively evolves a set of image shifts. We used the maximal energy of stacked images as an objective function for shifts estimation and validate the efficiency of the method on simulated and real images of simple and complex sources. Obtained results validated, that our proposed method allows for the recovery of spatial distribution of objects even only 2% brighter than their background. The presented approach extends significantly current limits of image reconstruction with the use of shift-and-add method. The applications of our algorithm include both the optical and the infrared imaging. Our method may be also employed as a digital image stabilizer in extremely low light level conditions in professional and consumer applications.
- (010.7060) Atmospheric and oceanic optics : Turbulence
- (100.2000) Image processing : Digital image processing
- (100.3010) Image processing : Image reconstruction techniques
All-fiber bidirectional optical parametric oscillator for precision sensing
- received 12/19/2014; accepted 04/07/2015; posted 04/08/2015; Doc. ID 231175
- [full text: PDF (469) KB)]
- Abstract: We present the design and operation of an all-fiber, synchronously pumped, bidirectional optical parametric oscillator (OPO) for precision sensing applications. The fiber-based OPO (FOPO) generates two frequency combs with identical repetition rates but different carrier offset frequencies. A narrow beatnote was observed with full-width-half-maximum (FWHM) linewidth of <10Hz when the two frequency combs were overlapped on a photodetector. The all-fiber design removes the need for free-space alignment and adjustment. In addition, an external delay line to overlap the two pulse trains in time on the detector is not needed since our unique design provides automatic delay compensation. We expect the novel FOPO to find important applications in precision measurements including rotation sensing with ultra-large sensing area and sensitivity.
- (140.3370) Lasers and laser optics : Laser gyroscopes
- (140.3510) Lasers and laser optics : Lasers, fiber
- (140.7090) Lasers and laser optics : Ultrafast lasers
Background-free 3D chemical imaging based on polarization coherent Raman holography
- received 01/05/2015; accepted 04/07/2015; posted 04/08/2015; Doc. ID 231548
- [full text: PDF (474) KB)]
- Abstract: We report on a holographic coherent anti-Stokes Raman scattering imaging by using polarization discrimination for non-resonant background suppression. With reduced polarization scrambling effect under weakly focused excitation, non-resonant background free coherent Raman imaging is demonstrated. A fast chemically selective imaging is achieved in a three-dimensional volume of 70um x70um x100um in 2 seconds.
- (190.4380) Nonlinear optics : Nonlinear optics, four-wave mixing
- (090.1995) Holography : Digital holography
- (180.4315) Microscopy : Nonlinear microscopy