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January


Experimental analysis of distributed pump absorption and refractive index changes in Yb-doped fibers using acousto-optic interaction

  • Antonio Diez, Erica Alcusa-Sáez, and Miguel Andrés
  • received 10/10/2014; accepted 01/19/2015; posted 01/21/2015; Doc. ID 224690
  • [full text: PDF (634) KB)]
  • Abstract: In fiber acousto-optic interaction is used to characterize the refractive index changes at the C band in a single-mode ytterbium-doped optical fiber under 980 nm pumping. The transmission notch created by the acoustic-induced coupling between the core mode and a cladding mode shifts to longer wavelengths when the pump is delivered to the fiber. The electronic contribution to the refractive index change is quantified from the wavelength shift. Using a time-resolved acousto-optic method, we investigate the distribution of pump absorption, and the resulting refractive index change profile, along sections of ytterbium-doped fiber exceeding 1 m long under different pump power levels.

Keywords (OCIS):

  • (060.2270) Fiber optics and optical communications : Fiber characterization
  • (230.1040) Optical devices : Acousto-optical devices
  • (060.3510) Fiber optics and optical communications : Lasers, fiber

Estimation of particle size variations for laser speckle rheology of materials

  • Zeinab Hajjarian and Seemantini Nadkarni
  • received 12/18/2014; accepted 01/19/2015; posted 01/21/2015; Doc. ID 231092
  • [full text: PDF (2611) KB)]
  • Abstract: Laser Speckle Rheology (LSR) is an optical technique for assessing the viscoelastic properties of materials with several industrial, biological, and medical applications. In LSR, the viscoelastic modulus, G*(ω), of a material is quantified by analyzing the temporal fluctuations of speckle patterns. However, the size of scattering particles within the material also influences the rate of speckle fluctuations, independent of sample mechanical properties, and complicates the accurate estimation of G*(ω). Here, we demonstrate that the average particle size may be retrieved from the azimuth-angle dependence of time-averaged speckle intensities, permitting the accurate quantification of the viscoelastic moduli of materials with unknown particle size distribution using LSR.

Keywords (OCIS):

  • (110.6150) Imaging systems : Speckle imaging
  • (170.3880) Medical optics and biotechnology : Medical and biological imaging
  • (290.4020) Scattering : Mie theory
  • (290.5850) Scattering : Scattering, particles
  • (290.5855) Scattering : Scattering, polarization

Long-range surface plasmon resonance sensor based on dielectric/silver coated hollow fiber with enhanced figure of merit

  • Xiao-Song ZHU, Binghong Liu, Yongxiang Jiang, Xiaoli Tang, and Yi-Wei Shi
  • received 10/22/2014; accepted 01/18/2015; posted 01/21/2015; Doc. ID 225373
  • [full text: PDF (773) KB)]
  • Abstract: A long-range surface plasmon resonance (LRSPR) sensor based on dielectric/silver coated hollow fiber (HF) is proposed. It can detect the refractive index (RI) of sensed liquid filled in the hollow core of the sensor. A HF LRSPR sensor with 90nm thick silver layer and 260nm thick OC300 layer is fabricated. Experiments are taken to evaluate the performance of the sensor by measuring the transmission spectra. Theoretical analysis based on a ray model is also taken and the results agree well with the experimental results. The proposed sensor has similar sensitivity but much smaller SPR dip width than the silver coated HF SPR sensor. Thus figure of merit of the sensor are enhanced approximately five times. The stability of the sensor is also improved because the dielectric layer acts as a protection layer for the damageable silver layer.

Keywords (OCIS):

  • (060.2280) Fiber optics and optical communications : Fiber design and fabrication
  • (060.2370) Fiber optics and optical communications : Fiber optics sensors
  • (240.6680) Optics at surfaces : Surface plasmons

Thermal stress modification in regenerated fiber Bragg grating via manipulation of glass transition temperature based on CO2 laser annealing

  • Kok-Sing Lim, Man-Hong Lai, Dinusha Gunawardena, Harith Ahmad, Wu Yi Chong, and Hang-Zhou Yang
  • received 11/06/2014; accepted 01/18/2015; posted 01/21/2015; Doc. ID 226431
  • [full text: PDF (639) KB)]
  • Abstract: In this work, we have demonstrated thermal stress relaxation in regenerated fiber Bragg gratings (RFBGs) by using direct CO2 laser annealing technique. After the isothermal annealing and slow cooling process, the Bragg wavelength of the RFBG has been red-shifted. This modification is reversible by re-annealing and rapid cooling. It is repeatable with different cooling process in the subsequent annealing treatments. This phenomenon can be attributed to the thermal stress modification in the fiber core by means of manipulation of glass transition temperature with different cooling rates. This finding in this investigation is important for accurate temperature measurement of RFBG in dynamic environment.

Keywords (OCIS):

  • (060.2280) Fiber optics and optical communications : Fiber design and fabrication
  • (060.2370) Fiber optics and optical communications : Fiber optics sensors
  • (060.3735) Fiber optics and optical communications : Fiber Bragg gratings

Optical phase cloning by an integrated dual-parallel Mach-Zehnder modulator

  • Marco Marangoni, Johannes Burkart, Tommaso Sala, KASSI Samir, and Daniele Romanini
  • received 11/13/2014; accepted 01/16/2015; posted 01/21/2015; Doc. ID 222450
  • [full text: PDF (641) KB)]
  • Abstract: The use of a dual-parallel Mach-Zehnder modulator in a feed-forward configuration is shown to serve the purpose of cloning the optical phase of a master oscillator on a Distributed-Feed-Back (DFB) slave laser exhibiting a multi-MHz-wide frequency noise spectrum. A residual phase error of 113 mrad is obtained together with an unprecedented control bandwidth of hundreds of megahertz and a gigahertz-level capture and tuning range. Besides offering a dramatic improvement over feedback loops, this approach is susceptible of hybrid integration in a cost-effective compact device benefiting from the wide tunability of DFB lasers, now available from the visible to the mid-infrared.

Keywords (OCIS):

  • (120.3930) Instrumentation, measurement, and metrology : Metrological instrumentation
  • (250.7360) Optoelectronics : Waveguide modulators
  • (140.3425) Lasers and laser optics : Laser stabilization

Universal Axial Fluctuations in Optical Tweezers

  • Felix Ritort, Anna Alemany, and Marco Ribezzi-Crivellari
  • received 12/08/2014; accepted 01/16/2015; posted 01/21/2015; Doc. ID 229174
  • [full text: PDF (755) KB)]
  • Abstract: Optical tweezers allow the measurement of fluctuations at the nano-scale, in particular fluctuations in the end-to-end distance in single molecules. Fluctuation spectra can yield valuable information, but they can easily be contaminated by instrumental effects. We identify axial fluctuations, i.e. fluctuations of the trapped beads in the direction of light propagation, as one of these instrumental effects. Remarkably, axial fluctuations occur on a characteristic timescale similar to that of conformational (folding) transitions, which may lead to misinterpretation of the experimental results. We show that a precise measurement of the effect of force on both axial and conformational fluctuations is crucial to disentangle them. Our results on axial fluctuations are captured by a simple and general formula valid for all optical tweezers setups and provide experimentalists with a general strategy to distinguish axial fluctuations from conformational transitions.

Keywords (OCIS):

  • (070.4790) Fourier optics and signal processing : Spectrum analysis
  • (140.7010) Lasers and laser optics : Laser trapping
  • (170.4520) Medical optics and biotechnology : Optical confinement and manipulation
  • (230.0230) Optical devices : Optical devices
  • (350.4855) Other areas of optics : Optical tweezers or optical manipulation

An electrically actuated liquid iris

  • Hongwen Ren, Miao Xu, and Yi-Hsin Lin
  • received 12/17/2014; accepted 01/16/2015; posted 01/21/2015; Doc. ID 230826
  • [full text: PDF (413) KB)]
  • Abstract: We report an adaptive iris using dielectric liquids and a radial-interdigitated electrode. A black liquid is confined by a circular gasket with a donut shape. The surrounding of the black liquid is filled with an immiscible liquid. In the relaxing state, the black liquid obtains the largest clear aperture. By applying a voltage, the surface of the black liquid is stretched to expand by the generated dielectric force, leading its aperture to decrease. For the demonstrated iris, the diameter of its aperture can be tuned from ~4.7 mm to ~1.2 mm when the applied voltage is varied from 0 to 70 Vrms. The aperture ratio is ~ 94%. Owing to the radial-interdigitated electrode, the aperture of the iris can be largely tuned with a reasonably fast response time. The optical switch is polarization-insensitive. Our iris has potential applications in light shutters, optical attenuators, biomimicry, and wearable devices.

Keywords (OCIS):

  • (120.4610) Instrumentation, measurement, and metrology : Optical fabrication
  • (230.0230) Optical devices : Optical devices
  • (230.2090) Optical devices : Electro-optical devices
  • (250.0250) Optoelectronics : Optoelectronics
  • (250.6715) Optoelectronics : Switching
  • (220.1080) Optical design and fabrication : Active or adaptive optics

Optical bistability of localized Josephson surface plasmons in cuprate superconductors

  • Filippo Alpeggiani
  • received 12/03/2014; accepted 01/16/2015; posted 01/22/2015; Doc. ID 228894
  • [full text: PDF (507) KB)]
  • Abstract: Microparticles made of high-Tc cuprate superconductors are characterized by localized plasmonic excitations known as Josephson surface plasmons, whose electromagnetic response is intrinsically nonlinear, giving rise to yet unexplored optical phenomena. In this work bistability effects in the near-resonance excitation of Josephson surface plasmons of dipolar symmetry are investigated for spheroidal superconducting particles. The threshold for the incident intensity is estimated and experimental probing strategies are discussed. The system can be of interest in view of terahertz light switching and detection.

Keywords (OCIS):

  • (190.1450) Nonlinear optics : Bistability
  • (300.6495) Spectroscopy : Spectroscopy, teraherz

Tailoring between network rigidity and nanosecond transient absorption in a-GexAs35-xSe65 thin films

  • KV Adarsh, Pritam Khan, and Tarun Saxena
  • received 01/14/2015; accepted 01/15/2015; posted 01/21/2015; Doc. ID 232490
  • [full text: PDF (1285) KB)]
  • Abstract: In this letter, we report the first observation of dramatic decrease in nanosecond (ns) pulsed laser induced transient absorption (TA) in a-GexAs35-xSe65 thin films by tuning the amorphous network from floppy to rigid. Our results provide the direct experimental evidence of a self trapped exciton mechanism, where trapping of the excitons occurs through bond rearrangements. Taken together, a rigid amorphous network with more constraints than degrees of freedom, are unable to undergo any such bond rearrangements and results in weaker TA. However, we also demonstrate that excitation fluence can be effectively utilized as a simple tool to lift up enough constraints to introduce large TA even in rigid networks. Apart from this, we also show that TA is tunable with network rigidity as it blueshift when the mean coordination is increased from 2.35 to 2.6.

Keywords (OCIS):

  • (160.2750) Materials : Glass and other amorphous materials
  • (310.6860) Thin films : Thin films, optical properties
  • (160.5335) Materials : Photosensitive materials

Nonlocal study of ultimate plasmon hybridization

  • Søren Raza, Martijn Wubs, Sergey Bozhevolnyi, and N. Asger Mortensen
  • received 10/27/2014; accepted 01/15/2015; posted 01/16/2015; Doc. ID 214449
  • [full text: PDF (544) KB)]
  • Abstract: Within our recently proposed generalized nonlocal optical response (GNOR) model, where nonlocal response is included by taking into account both convective and diffusive currents of the conduction electrons, we revisit the fundamental problem of an optically excited plasmonic dimer. We consider the transition from separated dimers via touching dimers to finally overlapping dimers. In particular, we focus on the touching case, showing a fundamental limit on the hybridization of the bonding plasmon modes due to nonlocality. Using transformation optics we determine a simple analytical equation for the resonance energies of the bonding plasmon modes of the touching dimer.

Keywords (OCIS):

  • (240.6680) Optics at surfaces : Surface plasmons
  • (290.5850) Scattering : Scattering, particles

High magneto-optical properties of visible-infrared Faraday rotator based on the cerium doped terbium gallium garnet

  • zhe chen, Yin Hang, jun wang, Xianyong Wang, Peixiong Zhang, qi hong, jun shi, qi wang, and Lei Yang
  • received 11/18/2014; accepted 01/15/2015; posted 01/16/2015; Doc. ID 226697
  • [full text: PDF (982) KB)]
  • Abstract: High optical quality (Tb(1-x)Cex)3Ga5O12(TCGG) has been grown by the Czochralski(Cz)method. The optical and magneto-optical properties of the TCGG crystal were analyzed in detailed and compared with the undoped Tb3Ga5O12 crystal. TCGG presented a very high transmittance, particularly in the visible region, and its Verdet constant is obviously larger than that of TGG in the visible-infrared region. The figure of merit and optical features point out the superior characteristics of TCGG respect to TGG.

Keywords (OCIS):

  • (160.3820) Materials : Magneto-optical materials
  • (160.4670) Materials : Optical materials

Spectral and spatial full-bandwidth correlation analysis of bulk-generated supercontinuum in the mid-infrared

  • Aymeric van de Walle, Nicolas Forget, Patrick Georges, Marc Hanna, Florent Guichard, Yoann Zaouter, and Alexandre Thai
  • received 12/12/2014; accepted 01/15/2015; posted 01/16/2015; Doc. ID 230541
  • [full text: PDF (619) KB)]
  • Abstract: We report the measurement of spectral and spatial correlations in supercontinua generated by focusing µJ pulses from a femtosecond ytterbium-doped fiber amplifier laser in bulk YAG. The measurement is full-bandwidth at a repetition rate of 1 MHz owing to the use of time-stretch dispersive Fourier transform technique. In contrast with fiber-based supercontinuum generation, our results show an excellent stability of the spectral and spatial properties of the output supercontinuum, with an essentially correlated behavior in the 1.4 µm – 1.7 µm wavelength range. These results provide strong ground for the development of supercontinuum-seeded ultrafast optical parametric amplifier systems in the mid-infrared using ytterbium lasers as pump sources.

Keywords (OCIS):

  • (140.3070) Lasers and laser optics : Infrared and far-infrared lasers
  • (140.7090) Lasers and laser optics : Ultrafast lasers
  • (190.7110) Nonlinear optics : Ultrafast nonlinear optics
  • (320.6629) Ultrafast optics : Supercontinuum generation

Electrically-driving Bandwidth Tunable Subwavelength Optical Filter Based on a Twisted Nematic Liquid Crystal Polarization Rotator

  • Linyong Qian, Dawei Zhang, Bo Dai, Yuanshen Huang, Ruijin Hong, Chunxian Tao, and Songlin Zhuang
  • received 12/03/2014; accepted 01/14/2015; posted 01/16/2015; Doc. ID 228606
  • [full text: PDF (2438) KB)]
  • Abstract: A novel bandwidth-tunable filter is proposed based on non-polarizing guided-mode resonance effect. The compact, electrically-driving bandwidth-tunable optical filter is realized by taking advantage of the effect of bandwidth-to-polarization sensitivity, and using a twisted nematic liquid crystal polarization rotator for simple and precise polarization control. The operation principle and the design of the device are presented. The center wavelength is fixed at 623.1 nm with a relatively symmetric line shape. The full width at half maximum bandwidth is tuned from 12 nm to 44.8 nm by controlling the voltage in the polarization rotator.

Keywords (OCIS):

  • (050.1950) Diffraction and gratings : Diffraction gratings
  • (120.2440) Instrumentation, measurement, and metrology : Filters
  • (260.5740) Physical optics : Resonance
  • (310.6628) Thin films : Subwavelength structures, nanostructures

Ultra-small and tunable wavelength splitters in a subwavelength plasmonic waveguide

  • Jianjun Chen, chengwei Sun, Hongyun Li, and Qihuang Gong
  • received 10/07/2014; accepted 01/14/2015; posted 01/16/2015; Doc. ID 224533
  • [full text: PDF (3225) KB)]
  • Abstract: Miniaturizing optical devices beyond the diffraction limit is of great importance for the high-integration photonic circuits. By directly fabricating a double-slit aperture structure of different sizes in a subwavelength plasmonic waveguide, an ultra-small plasmonic wavelength splitter is realized experimentally. Due to the different slit widths, the SPPs in the opposite directions exhibit anti-phase interferences. As a result, the SPPs excited at different wavelengths can be split to propagate in the opposite directions along the subwavelength plasmonic waveguide. The plasmonic wavelength splitter only occupies a footprint of about 1.4 μm2 on the metal surface, and the splitting wavelengths and their separations can be easily tuned by adjusting the structural parameters. This makes it have important applications in the areas of the optical modulating, sensing, and computing networks in highly integrated plasmonic circuits.

Keywords (OCIS):

  • (230.1360) Optical devices : Beam splitters
  • (230.7370) Optical devices : Waveguides
  • (240.6680) Optics at surfaces : Surface plasmons
  • (260.3160) Physical optics : Interference

Pump-bleaching of Tm-doped fiber with 793nm pump source

  • Nengli Dai, Ying Xing, Hong Huang, Nan Zhao, Lei Liao, and Li yan
  • received 09/02/2014; accepted 01/13/2015; posted 01/16/2015; Doc. ID 222339
  • [full text: PDF (813) KB)]
  • Abstract: We demonstrate, for the first time to our knowledge, the strong recovery of the optical-optical slope efficiency of the gamma-ray irradiated Tm-doped fiber under 793 nm LD pumping. The fiber optical-optical slope efficiency, the fiber cladding absorption spectra, and the fluorescence spectra of the Tm-doped fiber before and after 500Gy gamma-ray irradiation have been measured for comparison. It is found that the fiber optical-optical slope efficiency had significant degradation from 56.3% to 26.7% after irradiation and recovered to 40.8% after 15 hours pump-bleaching. Based on the comparative analysis of fiber cladding absorption spectra among the pristine, irradiation and bleaching, the reasons for the strong recovery have also been discussed.

Keywords (OCIS):

  • (140.3510) Lasers and laser optics : Lasers, fiber
  • (160.5690) Materials : Rare-earth-doped materials
  • (350.5610) Other areas of optics : Radiation

100kHz-Mueller polarimeter in reflection configuration

  • Matthieu DUBREUIL, Aymeric Le Gratiet, Sylvain Rivet, and Yann LE GRAND
  • received 11/26/2014; accepted 01/13/2015; posted 01/14/2015; Doc. ID 228522
  • [full text: PDF (914) KB)]
  • Abstract: A new setup is proposed to perform high speed Mueller polarimetry by spectral coding of polarization in a reflection configuration. The system uses a swept laser source and a photodiode, which results in a simple optical setup allowing to measure Mueller matrices at 100kHz repetition rate. A special focus is made on the influence of the cube beamsplitter polarimetric response, essential to measurements in a reflection configuration. The instrument is first validated on reference samples for single-point measurements and the effect of a proper system calibration is also demonstrated on polarimetric images. The device is intended to be implemented within a laser scanning microscope to perform multimodal imaging (confocal/multiphoton and Mueller polarimetry).

Keywords (OCIS):

  • (120.5410) Instrumentation, measurement, and metrology : Polarimetry
  • (260.5430) Physical optics : Polarization
  • (110.5405) Imaging systems : Polarimetric imaging

Extraordinary optical extinctions through dual metallic gratings

  • Grégory Vincent, Clément Tardieu, Thomas Estruch, Julien Jaeck, Nathalie Bardou, Stéphane Collin, and Riad Haidar
  • received 12/03/2014; accepted 01/13/2015; posted 01/14/2015; Doc. ID 228580
  • [full text: PDF (1827) KB)]
  • Abstract: We report on multiple extraordinary optical extinction (EOE) phenomena through encapsulated dual metallic gratings. They are evidenced in TM polarization by angularly and spectrally resolved transmission measurements in the mid-infrared wavelength range. We show that EOE can be achieved on both sides of extraordinary optical transmission (EOT) resonance, leading to pass-band filters with improved rejection rate.

Keywords (OCIS):

  • (240.0310) Optics at surfaces : Thin films
  • (310.6188) Thin films : Spectral properties
  • (050.6624) Diffraction and gratings : Subwavelength structures
  • (310.6628) Thin films : Subwavelength structures, nanostructures
  • (130.7408) Integrated optics : Wavelength filtering devices

Lens-free digital inline holographic microscopy through layers of different refractive index

  • Mario Kanka
  • received 12/04/2014; accepted 01/13/2015; posted 01/21/2015; Doc. ID 228995
  • [full text: PDF (1352) KB)]
  • Abstract: Digital inline holographic microscopy is applied for lens-free imaging with high lateral resolution. Microfluidic chambers for imaging of cells in water-like or native solutions, e.g. thick layers of glass and other materials with different refractive index, cause aberrations which limit the spatial resolution and change the magnification scale. In the paper, a fast reconstruction technique considering parallel layer systems of different refractive indices is presented. In experiments, properly scaled images of micro-beads and red human blood cells with an optical resolution corresponding to a numerical aperture of about 0.62 were reconstructed.

Keywords (OCIS):

  • (180.6900) Microscopy : Three-dimensional microscopy
  • (090.1995) Holography : Digital holography
  • (110.3010) Imaging systems : Image reconstruction techniques

Multidimensional coherent pulse addition of ultrashort laser pulses

  • Marco Kienel, Michael Müller, Arno Klenke, Tino Eidam, Jens Limpert, and Andreas Tünnermann
  • received 09/17/2014; accepted 01/13/2015; posted 01/14/2015; Doc. ID 223366
  • [full text: PDF (1857) KB)]
  • Abstract: Spatially and temporally separated amplification and subsequent coherent addition of femtosecond pulses is a promising performance-scaling approach for ultrafast laser systems. Herein we demonstrate for the first time the application of this multidimensional scheme in a scalable architecture. Applying actively controlled divided-pulse amplification producing up to four pulse replicas that are amplified in two ytterbium-doped step-index fibers (6 µm core), pulse energies far beyond the damage threshold of the single fiber have been achieved. In this proof-of-principle experiment, high system efficiencies are demonstrated at both high pulse energies (i.e. in case of strong saturation) and high accumulated nonlinear phases.

Keywords (OCIS):

  • (140.3280) Lasers and laser optics : Laser amplifiers
  • (140.7090) Lasers and laser optics : Ultrafast lasers
  • (140.3298) Lasers and laser optics : Laser beam combining

Suppression of cross-coupling in an external resonator for a diode laser bar with 19 single emitters

  • Sarah Klein, Stefan Hengesbach, Thomas Westphalen, Dieter Hoffmann, and Martin Traub
  • received 10/10/2014; accepted 01/13/2015; posted 01/14/2015; Doc. ID 224535
  • [full text: PDF (5300) KB)]
  • Abstract: We present an external cavity in a Quasi-Littrow configuration for a diode laser bar with 19 single emitters and the individual spectral stabilization, ranging from wavelengths between 970 nm and 980 nm corresponding to each emitter. The imaging of the vertical waveguide mode onto a blazed grating acting as diffractive optical element is realized with a beam transformation system that swaps the vertical and lateral axes. Along with a feedback intensity of < 10%, the reduction of the divergence due to a beam expander results in high losses for cross-coupling-modes. We demonstrate the possibility to suppress cross-coupling and that even a process-related small smile error has a positive effect on the quality of the spectral stabilization in a Quasi-Littrow configuration.

Keywords (OCIS):

  • (050.1950) Diffraction and gratings : Diffraction gratings
  • (140.2010) Lasers and laser optics : Diode laser arrays
  • (140.3410) Lasers and laser optics : Laser resonators
  • (140.3425) Lasers and laser optics : Laser stabilization

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