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Accepted papers to appear in an upcoming issue

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Terahertz Spectrum Splitting by Graphene-Covered Array of Rectangular Grooves

Mohammad Reza Tavakol, Amirhossein Saba, Amir Jafargholi, and Amin Khavasi

Doc ID: 304014 Received 08 Aug 2017; Accepted 19 Oct 2017; Posted 19 Oct 2017  View: PDF

Abstract: We propose a bi-directional terahertz (THz) spectrum splitter using a practically simple metamaterial structure consisting of rectangular grooves covered by graphene. Thanks to the graphene optoelectronic tunability and by adjusting the grooves width, this structure provides nearly $2\pi$ phase shift. At the same time, the reflection efficiency is acceptable throughout the phase shifts. We design each meta-atoms using a circuit model, then we synthesize the final super-cell based on the generalized Snell's law so that the structure reflects different frequency waves to totally different directions. The full-wave simulations demonstrate the beam splitting with a remarkable efficiency of around 80\%.

Ultracompact, high extinction ratio polarization beam splitter-rotator based on hybrid plasmonic-dielectric directional coupling

Bowen Bai, Lu Liu, and Zhiping Zhou

Doc ID: 307121 Received 15 Sep 2017; Accepted 17 Oct 2017; Posted 19 Oct 2017  View: PDF

Abstract: A polarization beam splitter-rotator based on asymmetry directional coupling is demonstrated. Ultrashort cross-polarization coupling length of 7.7 μm is achieved by manipulating the optical field distribution via plasmonic effect, which is the shortest one reported so far. At the wavelength of 1.55 μm, the extinction ratios are as high as 50.9 dB and 28.2 dB for fundamental TM and TE polarizations, respectively and the corresponding insertion losses are 1.545 dB and 0.037 dB. In addition, the TM0-to-TE0 polarization conversion efficiency is higher than 95% within a bandwidth of 70nm.

Narrowband silicon waveguide Bragg reflector achieved by highly-ordered graphene oxide gratings

Yung-Jr Hung, Ya Ching Liang, Chia-Wei Huang, Jyun-Fu Shih, SHIH HU, Tzu-Hsiang Yen, CHIA-WEI Kao, and CHUN-HU Chen

Doc ID: 307347 Received 18 Sep 2017; Accepted 17 Oct 2017; Posted 19 Oct 2017  View: PDF

Abstract: Graphene oxide (GO) ultrathin film can be wafer-scale deposited by spin-coating, can be patterned by laser interference lithography and oxygen plasma etching, can be thinned atomically (0.26 nm/min) and oxidized by ozone treatment, and is a relatively transparent and low-refractive-index material compared to pristine graphene. All those unique properties prompt us to realize a low-loss (~5 dB/cm), high-extinction-ratio (19 dB), and narrowband (0.425 nm) GO/silicon hybrid waveguide Bragg reflector by transferring 7-nm-thick GO gratings (n = 1.58) atop a silicon strip waveguide. Unlike sidewall-corrugated strip waveguide Bragg reflector that generally exhibits distorted corrugation profiles and is sensitive to fabrication errors, as-realized GO-grating-covered strip waveguide Bragg reflector exhibits stable reflecting wavelength and controllable reflection bandwidth which can be well predicted by numerical simulations.

Experimental realization of narrowband four-photon Greenberger-Horne-Zeilinger state in single cold atomic ensemble

Ming-Xin Dong, Wei Zhang, Zhi-Bo Hou, Yi-Chen Yu, Shuai Shi, Dong-Sheng Ding, and Bao-Sen Shi

Doc ID: 305098 Received 18 Aug 2017; Accepted 17 Oct 2017; Posted 17 Oct 2017  View: PDF

Abstract: Multi-photon entangled states not only play a crucial role in researching on quantum physics but also have many applications in quantum information field such as quantum computation, quantum communication and quantum metrology. To fully exploit the multi-photon entangled states, it is important to establish the interaction between entangled photons and matter, which requires photons having narrow bandwidth. Here we report on the experimental generation of narrowband four-photon Greenberger-Horne-Zeilinger state with a fidelity of 64.9% through multiplexing two spontaneously four-wave mixings in a cold 85Rb atomic ensemble. The generated photons have the bandwidth of 50 MHz matching the atoms effectively, which are very suitable for building up quantum computation and quantum communication network based on atomic ensembles.

Bose-Hubbard hopping due to Resonant Rayleigh Scattering

Andrey Matsko and Lute Maleki

Doc ID: 303029 Received 21 Jul 2017; Accepted 17 Oct 2017; Posted 18 Oct 2017  View: PDF

Abstract: We show theoretically that dynamic behavior of light confined in modes of a nonlinear optical ring cavity characterized with resonant Rayleigh scattering can be described using the Bose-Hubbard model. Nonlinear interaction between clockwise and counterclockwise optical modes results in instability and inter-mode hopping occurring at a rate defined by the frequency separation of the Rayleigh doublet harmonics. The hopping may lead to an instability and breathing behavior of a Kerr frequency comb observed in the cavity.

Enhancement of Raman scattering of gaseous medium near the surface of silver holographic grating

Dmitry Petrov, alexey zaripov, and Nikita Toropov

Doc ID: 308875 Received 11 Oct 2017; Accepted 16 Oct 2017; Posted 17 Oct 2017  View: PDF

Abstract: The letter demonstrates a possibility to enhance Raman scattering of gaseous medium due to enhanced electromagnetic field caused by the excitation of the propagating surface plasmon-polaritons (PSPP) on silver holographic grating. Efficiency is studied of collinear and noncollinear schemes of PSPP excitation on metal-gaseous medium interface. When using a collinear scheme, we registered an 8-fold enhancement of Raman scattering of atmospheric nitrogen and oxygen herewith average gain near PSPP-active surface was ~4×10³.

Third-order nonlinearity OPO: Schmidt Mode Decomposition And Tripartite Entanglement

Carlos González Arciniegas, Nicolas Treps, and Paulo Nussenzveig

Doc ID: 306089 Received 04 Sep 2017; Accepted 16 Oct 2017; Posted 17 Oct 2017  View: PDF

Abstract: We investigate quantum properties of light in optical parametric oscillators (OPOs) based on four-wave mixing gain in media with third-order non-linearities. In spite of other competing χ(3) effects, such as phase modulation, bipartite and tripartite entanglement are predicted above threshold. These findings are relevant for recent implementations of CMOS-compatible on-chip OPOs

Passively Q-switched Pr:YLF laser with Co2+:MgAl2O4 saturable absorber

Maxim Demesh, Daniel-Timo Marzahl, Anatol Yasukevich, Viktor Kisel, Guenter Huber, Nikolai Kuleshov, and Christian Kraenkel

Doc ID: 306266 Received 01 Sep 2017; Accepted 16 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: We report on a 2ω-OPSL pumped passively Q-switched Pr3+:LiYF4 laser operating at the wavelengths 5 nm, 607 nm and 640 nm. For this we utilized a Co2+ doped MgAl2O4 (MALO) crystal as a saturable absorber in the visible range for the first time. In the green spectral region the pulse duration was 210 ns with a pulse energy of 3.6 μJ and repetition rate of 125 kHz. The minimum pulse duration of 87 ns at the highest pulse energy of 8.6 μJ was obtained at a repetition rate of 110 kHz at 607 nm. The highest Q-switched average laser power of 1.4 W was obtained at an absorbed cw pump power of 3.3 W with a slope efficiency of 47% at 640 nm. Absorption saturation measurements with Co:MALO were performed and ground and excited state absorption cross sections in the visible spectral range were determined.

Fiber-format dual-comb coherent Raman spectrometer

Nicola Coluccelli, Christopher Howle, Kenneth McEwan, Yuchen Wang, Toney Fernandez, Alessio Gambetta, Paolo Laporta, and Gianluca Galzerano

Doc ID: 306477 Received 05 Sep 2017; Accepted 16 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: We demonstrate a fiber-format system for dual-comb coherent anti-Stokes Raman scattering spectroscopy. The system is based on two ytterbium fiber femtosecond lasers at repetition frequencies of 94 MHz, a ytterbium fiber amplifier, and a photonic crystal fiber for spectral broadening and generation of pulses with central wavelength of 1040 nm and durations in the sub-20 fs regime. We observed Raman spectra of acetonitrile and ethyl acetate with spectral coverage from 100 to 1300 cm^-1, resolution of 8 cm^-1, and signal-to-noise ratio around 100, when averaging over 10 acquisitions. The design is suitable for implementing portable dual-comb coherent Raman spectrometers.

Direct imaging of tunable photonic nanojets from a self-assembled liquid crystal microdroplet

Tatsunosuke Matsui and Kazuya Tsukuda

Doc ID: 307747 Received 25 Sep 2017; Accepted 16 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: We report the direct experimental observation of electrically tunable photonic nanojets (PNJ) generated from self-assembled liquid crystal (LC) microdroplets formed by dispersing nematic LCs in polymer matrix. Optical measurements were performed with a home-built laser-scanning confocal microscope (LSCM) system. PNJs with subwavelength beam waist were successfully obtained from LC microdroplets of 5 m diameter similar to those from SiO2 microsphere of the same size. By applying external voltage of a few Volts some of major properties of PNJs such as beam length and brightness are tuned. Electro-tunable PNJs from self-assembled LC microdroplets may open the way for the development of novel micro-optical devices.

Atom-mediated spontaneous parametric down-conversion in periodic waveguides

Sina Saravi, Alexander Poddubny, Thomas Pertsch, Frank Setzpfandt, and Andrey Sukhorukov

Doc ID: 305349 Received 29 Aug 2017; Accepted 16 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: We propose the concept of atom-mediated spontaneous parametric down-conversion (SPDC), where photon-pair generation can only take place in the presence of a single 2-level emitter, relying on the bandgap evanescent modes of a nonlinear periodic waveguide. Using a guided signal mode, an evanescent idler mode, and an atom-like emitter with idler's transition frequency embedded in the structure, we find a heralded excitation mechanism, where the detection of a signal photon outside the structure heralds the excitation of the embedded emitter. We use a rigorous Green's function quantization method to model this heralding mechanism in a 1D periodic waveguide and determine its robustness against losses.

Scattering of Waves by A Half-space of Periodic Scatterers Using Broadband Green's Function

Shurun Tan and Leung Tsang

Doc ID: 307989 Received 26 Sep 2017; Accepted 15 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: An efficient full-wave solution for planewave scattering from a half-space of two-dimensional (2D) periodic scatterers is derived using broadband Green's function. The Green's function is constructed using band solutions of the infinite periodic structure, and it satisfies boundary conditions on all the scatterers. A low wavenumber extraction technique is applied to the Green's function to accelerate the convergence of the modal expansion. This facilitates the Green's function with low wavenumber extraction (BBGFL) to be evaluated over a broadband as the modal solutions are independent of wavenumber. Coupled surface integral equations (SIE) are constructed using the BBGFL and the free-space Green's function respectively for the two half-spaces with unknowns only on the interface. The method is distinct from the effective medium approach which represents the periodic scatters with an effective medium. This new approach provides accurate near field solutions around the interface with localized field patterns useful for surface plasmon polaritons and topological edge states examinations.

Multi-wavelength filtering with waveguide integratedphase-modulated Bragg grating

Somnath Paul, Toni Saastamoinen, Seppo Honkanen, Matthieu Roussey, and Markku Kuittinen

Doc ID: 306267 Received 05 Sep 2017; Accepted 15 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: We are presenting a multi-wavelength band-rejection filter on a titanium dioxide coated silicon-on-insulator platform. The concept rests upon the use of a finely tuned waveguide-based Bragg gratingfor which the periods are slightly varied from one to another. This quasi-random Bragg grating enablesprecise customization of integrated waveguide filters. The number of rejection bands and the center tocenter separation between themare tailored by dividing the grating into several super-periods and codingan optimal phase function onto each super-period. The optimal phase function is obtained by employingan iterative Fourier transform algorithm. The design is supported by an experimental demonstration.

Experimental evidence for partial spatial coherence in imaging Mueller polarimetry

Razvigor Ossikovski, Oriol Arteaga, SangHyuk YOO, Enric Garcia-Caurel, and Kurt Hingerl

Doc ID: 307153 Received 14 Sep 2017; Accepted 15 Oct 2017; Posted 18 Oct 2017  View: PDF

Abstract: We demonstrate experimentally the validity of the partial spatial coherence formalism in Mueller polarimetry and show that, in a finite spatial resolution experiment, the measured response is obtained through convolving the theoretical one with the instrument function. The reported results are of primary importance for Mueller imaging systems.

Gaussian beams diffracting in time

Miguel Porras

Doc ID: 307334 Received 18 Sep 2017; Accepted 14 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: We show how to transform the mathematical expression of any monochromatic paraxial light beam into the expression of a pulsed beam whose diffraction is switched from the axial direction to its temporal structure. We exemplify this transformation with time-diffracting Gaussian beams. The conditions for the obtained diffraction-free wave to be physically meaningful are discussed.

Design of optical wavelength demultiplexer based on off-axis meta-lens

Yi Zhou, Rui Chen, and Yungui Ma

Doc ID: 307583 Received 20 Sep 2017; Accepted 14 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: We propose an off-axis meta-lens based optical wavelength demultiplexer. The performance of the device initially proposed with four output channels (1527-1596 nm, channel spacing nm) composed of an optical fiber array is analyzed by both scalar diffraction theory and ray tracing method. The results show that the fiber energy coupling efficiency of the demultiplexer could be larger than 89% and the channel bandwidth is about 9 nm. Influences of the two key parameters, focal length f and off-axis angle α, are also investigated. We find that the minimum spectral linewidth of the channel is inversely proportional to the sine of α and nearly independent on f for meta-lens with large F-number (F>5), while the effective spectral range is negatively (positively) dependent on α (f). These results are of the significant in guiding us to build thin and compact demultiplexing devices for optical telecommunication.

Rotational control of computer generated holograms

Daryl Preece and Halina Rubinsztein-Dunlop

Doc ID: 305228 Received 21 Aug 2017; Accepted 13 Oct 2017; Posted 19 Oct 2017  View: PDF

Abstract: We develop a basis for three-dimensional rotation of arbitrary light fields created by computer-generated holograms. By adding an extra phase function into the kinoform any light field or holographic image can be tilted in the focal plane with minimized distortion. We present two different approaches to rotate an arbitrary hologram: the Scheimpflug method and a novel coordinate transformation method. Experimental results are presented to demonstrate the validity of both proposed methods.

Phase-shifting digital holographic microscopy by using a multi-camera setup

Carlos Trujillo and Jorge Garcia-Sucerquia

Doc ID: 303697 Received 01 Aug 2017; Accepted 12 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: In this letter, the use of two-coupled Mach-Zehnder interferometers to obtain four π/2 phase-shifted interferograms is introduced. Multi-camera systems in phase-shifting interferometry have been reported in the past to obtain phase-shifted interferograms without using any active shifter device, but these proposals make use of polarizers, diffracting gratings or other optical elements that increase the complexity of the setup. In this proposal, a simple multi-camera setup using no more than beam splitters and mirrors is implemented to obtain in a single shot the needed phase-shifted interferograms in the different output channels of the setup. This proposal is validated in digital holographic microscopy to visualize a biological sample of onion cells.

Optimized Optical Coupling to Silica-Clad Photonic Crystal Waveguide

Yosuke Terada, Kenji Miyasaka, Keisuke Kondo, Norihiro Ishikura, Takuya Tamura, and Toshihiko Baba

Doc ID: 308115 Received 27 Sep 2017; Accepted 12 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: Silica-clad silicon photonic crystal waveguides (PCWs) are promising components for various applications because of their simple fabrication and generation of slow light. However, an optical loss higher than 4 dB occurs when they are simply coupled to input/output silicon wire waveguides. To reduce the optical loss, we proposed a junction structure in which light in the waveguide is first coupled to a high-group-velocity radiation mode at an expanded core and subsequently converted to the slow-light mode in a tapered core of the PCW. The coupling loss at a junction is calculated to be 0.28 dB at its minimum and less than 0.5 dB for the wavelength range of 12 nm. We measured a coupling loss of 0.46 dB for the device fabricated by the silicon photonics process. This low-loss junction well supports the practical use of PCWs.

The origination of the temperature induced red shift of the charge transfer band of GdVO₄

Shaoshuai Zhou, Changkui Duan, and Mei Wang

Doc ID: 308306 Received 29 Sep 2017; Accepted 12 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: The charge transfer band (CTB) of the VO₄³- groups in vanadates shifts to longer wavelength with increasing temperature. The origination of this temperature induced red shift was explored by studying the temperature dependent excitation and emission spectra of GdVO₄ ranging from 300 to 480 K. The influences of the thermal population and the decline of the charge transfer gap on the spectral shift were analyzed using the configurational coordinate diagram. We conclude that the thermal population of vibrational sublevels of the ground electronic energy level dominates the temperature induced red shift of the CTB. Taking advantage of the red shift and the thermal quenching, a novel ratiometric temperature sensing strategy was proposed. Drastic temperature dependence was achieved, indicating a promising candidate for optical thermometer with high sensing performance.

Self-referenced octave-wide subharmonic GaP optical parametric oscillator centered at 3 µm and pumped by an Er-fiber laser

Qitian Ru, Zachary Loparo, Xiaosheng Zhang, Sean Crystal, Subith Vasu, Peter Schunemann, and Konstantin Vodopyanov

Doc ID: 307987 Received 02 Oct 2017; Accepted 12 Oct 2017; Posted 17 Oct 2017  View: PDF

Abstract: We report an octave-wide mid-IR spectrum (2.3-4.8 µm) obtained from a subharmonic optical parametric oscillator (OPO) based on a newly-developed nonlinear crystal, orientation-patterned gallium phosphide (OP-GaP) that was synchronously pumped by a femtosecond 1560-nm fiber laser. We proved that the octave-wide output is in the form of a single frequency comb. The observed f-to-2f frequency beats, originating directly from the OPO, can be used for self-referencing and phase locking of the pump laser comb with no need for supercontinuum generation. With an average output power of ~ 30 mW, this setup might be beneficial for a variety of spectroscopic applications in the mid-IR.

On Sagnac frequency splitting in a solid state ring Raman laser

Wei Liang, Anatoliy Savchenkov, Vladimir Ilchenko, Robert Griffith, Edwin De Cuir, Steven Kim, Andrey Matsko, and Lute Maleki

Doc ID: 308631 Received 05 Oct 2017; Accepted 12 Oct 2017; Posted 17 Oct 2017  View: PDF

Abstract: We report on an accurate measurement of the frequency splitting of an optical rotating ring microcavity made out of calcium fluoride. By measuring the frequencies of the clockwise and counterclockwise coherent Raman emission confined in the cavity modes we show that the frequency splitting is inversely proportional to the refractive index of the cavity host material. The measurement has an accuracy of 1% and unambiguously confirms the classical theoretical prediction based on special theory of relativity. The study also demonstrates usefulness of the ring Raman microlaser for rotation measurements.

Carrier-envelope offset stabilization of a GHz repetition rate femtosecond laser using opto-optical modulation of a SESAM

SARGIS HAKOBYAN, Valentin Wittwer, Kutan Gurel, Aline Sophie Mayer, Stephane Schilt, and Thomas Sudmeyer

Doc ID: 306876 Received 14 Sep 2017; Accepted 12 Oct 2017; Posted 13 Oct 2017  View: PDF

Abstract: We demonstrate the first carrier-envelope offset (CEO) frequency stabilization of a GHz femtosecond laser based on opto-optical modulation (OOM) of a semiconductor saturable absorber mirror (SESAM). The 1.05-GHz laser is based on an Yb:CALGO gain crystal and emits sub 100 fs pulses with 2.1-W average power at a center wavelength of 1055 nm. The SESAM plays two key roles: it starts and stabilizes the modelocking operation and is simultaneously used as an actuator to control the CEO frequency. This second functionality is implemented by pumping the SESAM with a continuous-wave 980-nm laser diode in order to slightly modify its nonlinear reflectivity. We use the standard f-to-2f method for detection of the CEO frequency, which is stabilized by applying a feedback signal to the current of the SESAM pump diode. We compare the SESAM-OOM stabilization with the traditional method of gain modulation via control of the pump power of the Yb:CALGO gain crystal. While the bandwidth for gain modulation is intrinsically limited to ~250 kHz by the laser cavity dynamics, we show that the OOM provides a feedback bandwidth above 500 kHz. Hence, we were able to obtain a residual integrated phase noise of 430 mrad for the stabilized CEO beat, which represents an improvement of more than 30 % compared to gain modulation stabilization.

Performance optimization of hollow-core fibre photothermal gas sensors

Yuechuan LIN, Wei Jin, Fan Yang, Yanzhen Tan, and HOI LUT HO

Doc ID: 303737 Received 31 Jul 2017; Accepted 12 Oct 2017; Posted 13 Oct 2017  View: PDF

Abstract: We report performance optimization of hollow-core photonic bandgap fibre (HC-PBF) photothermal (PT) gas sensors. The PT phase modulation efficiency of a C₂H₂ filled HC-PBF (HC-1550-02) is found independent of the pump modulation frequency for up to ~330 kHz, but starts to drop quickly to 10% of the maximum value at a couple of MHz. With a 1.1-m-long HC-PBF gas cell with angle-cleaved SMF/HC-PBF joints to reduce reflection, and a modified 3×3 Sagnac interferometer with balanced detection for phase demodulation, a noise equivalent concentration of ~67 ppb C₂H₂ is achieved with 1s time constant, and it goes down to ~18 ppb with 145s integration time. The system has good long term stability and exhibits signal fluctuations of <1% over a ~5 hours period.

Extended ellipticity control for attosecond pulses by high harmonic generation

Nikolai Zhavoronkov and Misha Ivanov

Doc ID: 305442 Received 25 Aug 2017; Accepted 12 Oct 2017; Posted 13 Oct 2017  View: PDF

Abstract: Attosecond (1 as=10(-18)s) pulses produced through highharmonic generation (HHG) is a basis for studies ofelectron dynamics during light-matter interaction onelectron´s natural time-scale. An extensively exploitedby attophysics HHG technology has, however, a fewunsolved problems, where producing of circularly polarizedor chiral attosecond pulses is belong them. Wehave demonstrated experimentally a way to controlthe ellipticity of attosecond pulse trains produced viahigh harmonic generation in two-color, bi-circular laserfields. We show that the combination of nonlinearmedium position and the intensities of the two-colordriving laser fields create an effective helicity dependentfilter. Based on this approach, we report generationof chiral spectra providing potential to produce attosecondpulses with polarization tuned from the rotating,but linear to highly elliptic with ellipticity as machas e = 0.75. This new way to create a chiral sensitive elementoffer a simple and practical knob to control polarizationfor combined harmonics field in a smooth andpredictable manner.

Analytical registration of vertical image drifts in parallel beam tomographic data

Malte Storm, Felix Beckmann, and Christoph Rau

Doc ID: 304177 Received 09 Aug 2017; Accepted 12 Oct 2017; Posted 12 Oct 2017  View: PDF

Abstract: Reconstructing tomographic images of high resolution, as in X-ray microscopy or transmission electron microscopy, is often limited by the stability of stages or sample drifts, which requires an image alignment prior to reconstruction. Feature--based image registration is routinely used to align images, but this technique relies on strong features in the sample or the application of for example gold tracer particles. In this letter, we present an analytic approach for achieving the vertical registration based on the inherent properties of the data acquired for tomographic reconstruction. It is computationally cheap to implement and can be easily integrated into existing reconstruction pipelines.

Physical significance of backscattering phase measurements

Chenfei Hu and Gabriel Popescu

Doc ID: 305623 Received 25 Aug 2017; Accepted 11 Oct 2017; Posted 11 Oct 2017  View: PDF

Abstract: Quantitative phase imaging of transparent objects in transmission allows for a direct interpretation of the results: the phase shift measured is linear in the refractive index contrast and object thickness. However, the same measurement in a backscattering geometry yields fundamentally different results because the incident field component is absent from the detected field. As a result, the relationship between the measured phase and the object properties is obscure. We derived analytical expressions for the propagating fields under the first-order Born approximation and studied the interpretation of the measured phase shifts in backscattering vs. transmission geometries. Our analysis shows that the backscattering phase shift is the result of the plane wave superposition originating at various depths in the object, which makes it impossible to infer quantitative morphology or topography information of 3D transparent samples from a reflection phase measurement alone.

Second-order moments of Schell-model beams with non-conventional correlation functions in atmospheric turbulence

Guo Zheng, Jue Wang, Lin Wang, Muchun Zhou, Yu Xin, and MinMin Song

Doc ID: 305796 Received 29 Aug 2017; Accepted 11 Oct 2017; Posted 11 Oct 2017  View: PDF

Abstract: The general formulae for second-order moments of Schell-model beams with non-conventional correlation functions in atmospheric turbulence are derived and validated by the Bessel-Gaussian Schell-model beams. Our finding shows that the second-order moments of partially coherent Schell-model beams are related to the second-order partial derivatives of source spectral degree of coherence at the origin. The formulae we provide are much more convenient to analyze and research propagation problems in turbulence.

Performance evaluation of underwater optical communications using spatial modes subjected to bubbles and obstructions

Yifan Zhao, Andong Wang, Long Zhu, Weichao Lv, Jing Xu, Shuhui Li, and Jian Wang

Doc ID: 305947 Received 29 Aug 2017; Accepted 11 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: Spatial modes have attracted increasing interest in free-space and fiber-based optical communications. Underwater wireless optical communication is becoming a promising technique in marine exploration. Here we investigate the underwater wireless optical communications using different spatial modes, i.e. traditional Gaussian mode, orbital angular momentum (OAM) mode having helical phasefront, and diffraction-free and obstruction-tolerant Bessel mode. We evaluate the underwater transmission performance of three spatial modes subjected to dynamic bubbles, which cause similar power fluctuations regardless of spatial modes. We also demonstrate an underwater transmission link subjected to static obstructions using three spatial modes carrying 1.4-Gbaud orthogonal frequency division multiplexing (OFDM) 16-ary quadrature amplitude modulation (16-QAM) signals. The Bessel mode shows the best performance against obstructions.

Q-switch pumped supercontinuum for ultra-high resolution optical coherence tomography

Michael MARIA, Iván Bravo Gonzalo, Thomas Feuchter, Mark Denninger, Peter Moselund, Lasse Leick, Ole Bang, and Adrian Podoleanu

Doc ID: 307518 Received 20 Sep 2017; Accepted 11 Oct 2017; Posted 18 Oct 2017  View: PDF

Abstract: In this report, we investigate the possibility of using a commercially available Q-switch pumped Supercontinuum (QS-SC) source, operating in the kHz regime, for ultra-high resolution optical coherence tomography (UHR-OCT) in the 1300 nm region. We show that by ensuring sufficient pulses per readout of the camera in the spectrometer, good quality images can be achieved. The QS-SC source proves to be more intrinsically stable from pulse to pulse than a mode-locked based SC (ML-SC) source while at the same time is less expensive. However, its pumping rate is lower than that used in ML-SC sources. Therefore, we investigate here specific conditions to make such a source useable for OCT. We compare images acquired with the QS-SC source and with a current state of the art SC source used for imaging.

Whispering gallery modes in liquid-filled hollow glass microsphere

Shuangqiang Liu, bojian shi, Yan Wang, lugui cui, Jun Yang, Weimin Sun, and Hanyang Li

Doc ID: 307124 Received 14 Sep 2017; Accepted 10 Oct 2017; Posted 13 Oct 2017  View: PDF

Abstract: We develop an HF etching process to open a microhole on the hollow glass microsphere (HGM). The typical whispering gallery mode (WGM) resonance was observed by coupling the HGM with a tapered fiber. Dioctyl phthalate was filled into the HGM, the resonance wavelength decreased at elevated temperatures. We analyzed the WGM resonance properties inside the liquid-filled HGM with higher or lower refractive index in comparison against the HGM wall. Four different liquids were also injected into the HGM to investigate the influence of the thermo-optic coefficient on the temperature sensitivity. Size-dependent experiments further showed that HGMs with varying size have varying temperature sensitivity. The maximum temperature sensitivity observed was 334.3 pm/°C.

Improving the sensitivity of velocity measurements in laser speckle contrast imaging using a noise correction method

yang wang, wenzhi lv, Xiao Chen, Jinling Lu, and Pengcheng Li

Doc ID: 305659 Received 25 Aug 2017; Accepted 10 Oct 2017; Posted 11 Oct 2017  View: PDF

Abstract: We demonstrate that noise is an important factor contributing to the decline of sensitivity and linear response range of velocity measurements for laser speckle contrast imaging. We propose to use a noise correction method to improve the sensitivity of velocity measurements. For a kind of cameras in which the mean values of the dark noise have been subtracted and negative counts have been set to zero, we propose a method to estimate the true dark noise based on the maximum likelihood estimation, which expands the application scope of the noise correction method.

All-optimized integrated RF photonic notch filter

Yang Liu, Jason Hotten, Amol Choudhary, Benjamin Eggleton, and David Marpaung

Doc ID: 306513 Received 20 Sep 2017; Accepted 10 Oct 2017; Posted 12 Oct 2017  View: PDF

Abstract: We report a silicon nitride chip-based radio-frequency photonic notch filter with an unprecedented performance including an RF gain of 8 dB, a record-low noise figure of 15.6 dB, and a spurious-free dynamic range of 116 dB.Hz2/3, with a stopband rejection of 50 dB. This level of performance is achieved by using on-chip resonators’ unique phase responses, and thorough optimizations of the photonic link. These record results will potentially stimulate future implementations of integrated microwave photonic subsystems for real-world applications.

Output power enhancement of self-frequency-doubled laser by selective excitation of inequivalent active centers in La2CaB10O19 (Nd:LCB) crystal

Qiannan Fang, Haohai Yu, Huaijin Zhang, Guochun Zhang, Jiyang Wang, and Yicheng Wu

Doc ID: 307037 Received 13 Sep 2017; Accepted 10 Oct 2017; Posted 12 Oct 2017  View: PDF

Abstract: We demonstrate the enhancement of the self-frequency-doubled laser with the Nd3+ doped lanthanum calcium borate La2CaB10O19 (Nd:LCB) crystals by selective excitation of its inequivalent activge centers. When the Nd3+ ions located in the Ca2+ sites were excited in the Nd:LCB crystal, the fundamental laser at the wavelength of 1066 nm was successfully realized which can keep the self-frequency-doubled wavelength away from the self-absorption peak of Nd3+ ions at about 5 nm. By optimizing the key parameters, the maximum output power of 801 mW was achieved with the frequency-doubling at the wavelength of 533 nm and the enhancement of output power was about 7.8 times compared with the results by excitation of Nd3+ ions in the La3+ sites. Up to now, this output power of self-frequency-doubled laser represents for the highest one in the Nd:LCB crystal and the efficient emission at 533 nm should have promising applications in the visible range, such as laser displays, optical data storage, laser printing, etc.. Meanwhile, the selective excitation of inequivalent active ions and the enhancement of self-frequency-doubled laser may provide some inspirations for the investigation of multi-functional materials.

A novel method to retrieve the nocturnal aerosol optical depth with a CCD Laser Aerosol Detective System

Yuxuan Bian, Wanyun Xu, Nan Ma, Jiangchuan Tao, Ye Kuang, Gang Zhao, Hongjian Liu, and ChunSheng Zhao

Doc ID: 308172 Received 29 Sep 2017; Accepted 10 Oct 2017; Posted 12 Oct 2017  View: PDF

Abstract: Aerosol optical depth (AOD) is a crucial parameter in describing the atmospheric pollution and analyzing the influences of aerosol on the radiative equilibrium. Currently, there is no method that can measure the nocturnal AOD precisely and continuously. In this study, a novel method was developed to retrieve the nocturnal AOD based on a remote sensing instrument named charge-coupled device-laser aerosol detective system (CCD-LADS). CCD-LADS consists of a CCD camera, a continuous laser, a fisheye lens and related filters. The AOD can be calculated by integrating the aerosol extinction coefficient profile retrieved from CCD-LADS measurements. The retrieved AOD was validated with AERONET and MODIS datasets. The comparison shows good agreement.

Retina-simulating phantom produced by photolithography

Denise dos Santos and Brian Vohnsen

Doc ID: 297304 Received 05 Jun 2017; Accepted 10 Oct 2017; Posted 10 Oct 2017  View: PDF

Abstract: Cone photoreceptors have a narrow acceptance angle well matched to the size of the eye pupil that dampens the visual impact of aberrations and scattering. However, the structure of the human retina is not replicated in existing eye models used to test refractive designs or retinal implants that restore partial vision to the blind. Here, we report on an artificial waveguide-based retinal phantom manufactured by photolithography in photoresist film with dimensions and refractive index contrast similar to the retinal receptor layer. The optical performance of the waveguide array is analysed in terms of angular coupling efficiency and it is experimentally verified that the structure leads to improved resolution and contrast of optical images transmitted through the layer when defocus is present.

Optical Voice Encryption based on Digital Holography

Sudheesh Rajput and Osamu Matoba

Doc ID: 302598 Received 07 Aug 2017; Accepted 09 Oct 2017; Posted 10 Oct 2017  View: PDF

Abstract: We propose an optical voice encryption scheme based on digital holography (DH). An off-axis DH is employed to acquire voice information by obtaining phase retardation occurred in the object wave due to sound wave propagation. The acquired hologram including voice information is encrypted using optical image encryption. The DH reconstruction and decryption with all correct parameters can retrieve original voice. The scheme has capability to record human voice in holograms and encrypt it directly. These aspects make the scheme suitable for other security applications and help to use voice as a potential security tool. We present experimental and some part of simulation results.

The filtering characteristics of a three-lens slit spatial filter for high power lasers

Han Xiong, Tiancheng Yu, Gao Fan, Zhang Xiang, and Xiao Yuan

Doc ID: 305787 Received 29 Aug 2017; Accepted 09 Oct 2017; Posted 10 Oct 2017  View: PDF

Abstract: Aiming to a three-lens slit spatial filtering system with excellent performances in inhibition of pinhole closure, improvement of beam quality, compactness of the system and lowering the requirement of vacuum, the filtering characteristics and image relay of the slit spatial filter are demonstrated. The results show that the beam quality is greatly improved, and the system has a good property in image relay, which has potential applications in high power lasers.

Detection of stably bright squeezed light with the quantum noise reduction of 12.6 dB by mutually compensating the phase fluctuations

Wenhai Yang, Shaoping Shi, Yajun Wang, Weiguang Ma, Yaohui Zheng, and Kunchi Peng

Doc ID: 306701 Received 07 Sep 2017; Accepted 09 Oct 2017; Posted 10 Oct 2017  View: PDF

Abstract: We present a mutual compensation scheme of three phase fluctuations, originating from the residual amplitude modulation (RAM) in the phase modulation process, in the bright squeezed light generation system. The influence of the RAM on each locking loop is harmonized by using one electro-optic modulator (EOM), and the direction of the phase fluctuation is manipulated by positioning the photodetector (PD) that extracts the error signal before or after the optical parametric amplifier (OPA). Therefore a bright squeezed light with non-classical noise reduction of 12.6 ± 0.2 dBis obtained. By fitting the squeezing and antisqueezing measurement results, we confirm that the total phase fluctuation of the system is around 3.1 mrad. The fluctuation of the noise suppression is 0.2 dB for 3 hours.

Bi-hyperbolic isofrequency surface in a magnetic-semiconductor superlattice

Vladimir Tuz, Illia Fedorin, and Volodymyr Fesenko

Doc ID: 305173 Received 18 Aug 2017; Accepted 09 Oct 2017; Posted 09 Oct 2017  View: PDF

Abstract: Topology of isofrequency surfaces of a magnetic-semiconductor superlattice influenced by an external static magnetic field is studied. In particular, in the given structure, topology transitions from standard closed forms of sphere and ellipsoid to open ones of Type I and Type II hyperboloids as well as bi-hyperboloid were revealed and analyzed. In the latter case, it is found out that a complex of ellipsoid and bi-hyperboloid in isofrequency surfaces appears as a simultaneous effect of both ratio between magnetic and semiconductor filling factors and magnetic field influence. It is proposed to consider the obtained bi-hyperbolic isofrequency surface as a new topology class of the wave dispersion.

Compact narrow-linewidth integrated laser based on low-loss silicon nitride ring resonator

Brian Stern, Xingchen Ji, Avik Dutt, and Michal Lipson

Doc ID: 307092 Received 19 Sep 2017; Accepted 09 Oct 2017; Posted 09 Oct 2017  View: PDF

Abstract: We design and demonstrate a compact, narrow-linewidth integrated laser based on low-loss silicon nitride waveguides coupled to a III-V gain chip. By using a highly confined optical mode, we simultaneously achieve compact bends and ultra-low loss. We leverage the narrowband backreflection of a high-Q microring resonator to act as a cavity output mirror, a single-mode filter, and a propagation delay all in one. This configuration allows the ring to provide feedback and obtain a laser linewidth of 13 kHz with 1.7 mW output power around 1550 nm. This demonstration realizes a compact sub-mm silicon nitride laser cavity with narrow linewidth.

The response of an erbium-doped dual-polarization fiber laser to a perpendicular gradient magnetic field

Tianfang Zhang, Jun Zhang., Linghao Cheng, Yizhi Liang, Long Jin, Hao Liang, and Bai-Ou Guan

Doc ID: 306369 Received 04 Sep 2017; Accepted 09 Oct 2017; Posted 13 Oct 2017  View: PDF

Abstract: Direct interaction between fiber lasers and magnetic field is useful but seldom explored because fiber is known as magnetic field insensitive. In this paper, the response of an erbium-doped dual-polarization fiber laser to a perpendicular gradient magnetic field is investigated. Measured as beat note frequency change, significant response greater than 500 MHz has been observed, which is within theoretical expectation and translates to a birefringence change of about 4 × 10-6 and a very high response to magnetic field of about 12.8 pT/Hz. The response can be further enhanced by increasing the gradient of the gradient magnetic field.

Demonstration of a CW diode pumped Ar metastable laser operating at 4W

Jiande Han, Michael Heaven, Paul Moran, Greg Pitz, Eric Guild, Carl Sanderson, and Brett Hokr

Doc ID: 304191 Received 21 Aug 2017; Accepted 08 Oct 2017; Posted 10 Oct 2017  View: PDF

Abstract: Optically pumped rare gas lasers are being investigated as potential high-energy, high beam quality systems. The lasing medium consists of rare gas atoms (Rg=Ne, Ar, Kr or Xe) that have been electric discharge excited to the metastable np⁵(n+1)s ³P₂ state. Following optical excitation, Helium at pressures of 200 – 1000 Torr is used as the energy transfer agent to create a population inversion. The primary technical difficulty for this scheme is the discharge production of sufficient Rg* metastables in the presence of >200 Torr of He. In this study we describe a pulsed discharge that yields >10¹³ cm¯³ Ar* in the presence at He pressures up to 730 Torr. Using this discharge, a diode pumped Ar* laser providing 4.1 W has been demonstrated

Photoacoustic endomicroscopy (PAEM) based on a MEMS scanning mirror

Guo Heng, Chaolong Song, Huikai Xie, and Lei Xi

Doc ID: 305381 Received 22 Aug 2017; Accepted 07 Oct 2017; Posted 09 Oct 2017  View: PDF

Abstract: In this letter, we present a high-resolution photoacoustic endomicroscopy (PAEM) probe based on a microelectromechanical systems (MEMS) scanning mirror. The built-in optical assembly consists of a 0.7 mm graded-index (GRIN) lens for light focusing and a ∅1 mm MEMS mirror to reflect and scan the beam. A miniaturized unfocused ultrasound transducer with a center frequency of 10 MHz is used for photoacoustic detection. Sharp blades, carbon fibers and black tapes were utilized to evaluate the performance of the system. In vivo mouse ears and resected rectums were imaged to further demonstrate the feasibility of this probe for potential biological and clinical applications.

Hybrid system for in vivo epifluorescence and 4D optoacoustic imaging

Zhenyue Chen, Xose Luis Dean Ben, Sven Gottschalk, and Daniel Razansky

Doc ID: 303932 Received 08 Aug 2017; Accepted 07 Oct 2017; Posted 09 Oct 2017  View: PDF

Abstract: Epifluorescence is the most widely used imaging modality in cell and molecular biology due to its excellent sensitivity, contrast and ease of implementation. Optoacoustic imaging has been shown to deliver a highly complementary and unique set of capabilities, such as high spatial resolution in deep tissue observations, fast volumetric imaging capacity and spectrally enriched imaging contrast. In this work, we report on a hybrid system combining planar fluorescence and real-time volumetric (4D) optoacoustic imaging by means of a fiberscope integrated within a handheld hemispherical ultrasound detection array. The in vivo imaging performance is demonstrated by non-invasive visualization of fast contrast agent perfusion through the mouse brain. The proposed synergistic combination of fluorescence and optoacoustic imaging can benefit numerous studies looking at multi-scale in vivo dynamics, such as functional neuroimaging, visualization of organ perfusion and contrast agent uptake, cell tracking, pharmacokinetic and bio-distribution analysis.

A scanning system for angle-resolved low-coherence interferometry

Zachary Steelman, Derek Ho, Kengyeh Chu, and Adam Wax

Doc ID: 304220 Received 08 Aug 2017; Accepted 06 Oct 2017; Posted 09 Oct 2017  View: PDF

Abstract: Angle-resolved low-coherence interferometry (a/LCI) detects precancer by enabling depth-resolved measurements of nuclear morphology in vivo. A significant limitation of a/LCI is the point-probe nature of the method, sampling <0.5 mm² before probe relocation is necessary. In this work, we demonstrate a scanning method capable of assessing an area >100 mm² without repositioning. By utilizing a reflection-only three-optic rotator (ROTOR) prism and two-axis scanning mirror, we demonstrate radial scans of a sample with a linear range of 12 mm and a full rotational range of 180°. Use of this design will improve the diagnostic utility of a/LCI for wide-area screening of tissue health.

Growth, spectroscopy and laser characterisation of Er:KGdxYbyY1-x-y(WO4)2 epitaxial layers

Sergey Kurilchik, Olga Dernovich, Konstantin Gorbachenya, Viktor Kisel, Irina Kolesova, Andrey Kravtsov, Sergey Guretsky, and Nikolai Kuleshov

Doc ID: 305326 Received 24 Aug 2017; Accepted 06 Oct 2017; Posted 06 Oct 2017  View: PDF

Abstract: We report on composition of Er-doped KGdxYbyY1-x-y(WO4)2 layers to be grown onto undoped KY(WO4)2 substrate characterized by fine lattice matching and high refractive index contrast with the substrate, fabrication of high optical quality Er(1at.%):KGd0.2Yb0.15Y0.65(WO4)2 epitaxial layers with thickness up to 180 μm, evaluation of their absorption and luminescence properties, as well as, for the first time to our knowledge, laser action under direct in-band pumping in a non-waveguide configuration. Maximum output power of 16 mW with slope efficiency of 64% was achieved at 1606 nm.

Switchable generation of rectangular noise-like pulse and dissipative soliton resonance in a fiber laser

Zhuo-Shuang Deng, Guan-Kai Zhao, Jia-Qi Yuan, Jin-Ping Lin, hongjie chen, Hongzhan Liu, Aiping Luo, Hu Cui, Zhi-Chao Luo, and Wen-Cheng Xu

Doc ID: 305416 Received 23 Aug 2017; Accepted 06 Oct 2017; Posted 06 Oct 2017  View: PDF

Abstract: We report on the switchable generation of a rectangular noise-like pulse (NLP) and a dissipative soliton resonance (DSR) in a fiber laser with highly nonlinear effect at very low pump power. The NLP centered at 1530.5 nm emerges a new characteristic that its profile evolves gradually from rectangular shape to Gaussian-like shape with the increasing pump power. By appropriately manipulating the polarization controller (PC), the laser switches to emit DSR pulse centered at 1551.3 nm. The duration of the DSR could broaden from 17.4 ns to the cavity round trip time as the raise of the pump power, while keeping the pulse profile and the intensity unaltered. This type of fiber laser may not only facilitate further investigating the characteristics of NLP and DSR, but also serve as a multifunctional optical source for potential applications.

Point-spread function engineering enhances digital Fourier microscopy

Ryan McGorty and Devynn Wulstein

Doc ID: 305541 Received 25 Aug 2017; Accepted 06 Oct 2017; Posted 06 Oct 2017  View: PDF

Abstract: While numerous optical methods exist to probe the dynamics of biological or complex fluid samples, in recent years digital Fourier microscopy techniques, like differential dynamic microscopy, have emerged as ways to efficiently combine elements of imaging and scattering methods. Here, we demonstrate, through experiments and simulations, how point-spread function engineering can be used to extend the reach of differential dynamic microscopy.

Highly Efficient and Broadband Mid-Infrared Metamaterial Thermal Emitter for Optical Gas Sensing

Yongkang Gong, Zuobin Wang, Kang Li, Leshan Uggalla, jungang huang, Nigel Copner, yang zhou, dun qiao, and jiuyuan zhu

Doc ID: 306182 Received 01 Sep 2017; Accepted 05 Oct 2017; Posted 06 Oct 2017  View: PDF

Abstract: Development of novel cost-effective and high efficiency mid-infrared light source has been a major scientific and technological goal in the research field of optical gas sensing. We proposed and investigated a mid-infrared metamaterial thermal emitter based on microstructured Chromium thin film. Our results demonstrated that the proposed thermal light source supports broadband and wide angular absorption for both TE- and TM-polarized light, giving rise to broadband thermal radiation with averaged emissivity of ~0.94 in mid-infrared atmospheric window of 8 um-14 um. The proposed microphotonic concept provides a promising alternative mid-infrared source and pays a way towards novel optical gas sensing platforms for many applications

Tunable 30-fs light pulses at 1-W power level from an Yb-pumped optical parametric oscillator

Nicola Coluccelli, Daniele Viola, Vikas Kumar, Antonio Perri, Marco Marangoni, Giulio Cerullo, and Dario Polli

Doc ID: 304023 Received 03 Aug 2017; Accepted 05 Oct 2017; Posted 09 Oct 2017  View: PDF

Abstract: We report on an Yb-pumped optical parametric oscillator (OPO) that delivers 30-fs pulses with spectral coverage from 680 to 910 nm and an average output power up to 1.1 W. The resulting peak power is ~0.5 MW, which is, to the best of our knowledge, the highest ever demonstrated in a femtosecond OPO. The intensity noise remains at a level of 0.2 % rms and rapid wavelength tuning is obtained by simply scanning the resonator length. The performances of the OPO are promising for a variety of applications in nonlinear microscopy and ultrafast spectroscopy.

Electron induced Photon Emission above the Quantum Cut Off due to Time-Energy Uncertainty

Ebru Ekici, Philip Kapitza, Christian Bobisch, and Rolf Moeller

Doc ID: 307978 Received 25 Sep 2017; Accepted 05 Oct 2017; Posted 10 Oct 2017  View: PDF

Abstract: The light emission from a tunneling junction induced by tunneling electrons has been studied around the cut off at hν=eVt . The emitted photons are found to exceed the excitation energy provided by the energy of the tunneling electrons. The experiments have been performed by a low temperature scanning tunneling microscope at 80K for a Ag(111) surface and a Ag covered PtIr tip. A detailed analysis of the emission spectra reveals that the findings cannot be explained by the thermal broadening of the electrons Fermi distribution alone. However, a correct description is found if a finite lifetime of the excited states in the range of 30 fs to 80 fs is included.

All-fiber mode converter based on long-period fiber gratings written in few-mode fiber

Yunhe Zhao, Yunqi Liu, Chenyi Zhang, Liang Zhang, Guangjun Zheng, Chengbo Mou, Jianxiang Wen, and Tingyun Wang

Doc ID: 305227 Received 21 Aug 2017; Accepted 05 Oct 2017; Posted 13 Oct 2017  View: PDF

Abstract: We investigated an all-fiber mode converter based on long-period fiber gratings (LPFGs) written in few-mode fiber (FMF). Mode conversion between the fundamental core mode and different higher-order core modes (LP11, LP21, and LP02 modes) can be realized via single LPFG with an efficiency of 99% at the resonance wavelength. Moreover, optimized mode conversion between the LP01 and LP21 modes can be realized by cascading two LPFGs with different grating pitches. The maximum conversion efficiency is estimated to be ~99.5% at 1553 nm. The orbital angular momentum states with different topological charges (±1,±2) are demonstrated experimentally. The all-fiber LPFG mode converters could have promising applications in the mode division multiplexing optical communications.

All-fiber Sixth Harmonic Generation of Deep UV

YUN WANG, Timothy Lee, Francesco De Lucia, Muhammad Abdul Khudus, Pier Sazio, Martynas Beresna, and Gilberto Brambilla

Doc ID: 303284 Received 04 Aug 2017; Accepted 05 Oct 2017; Posted 06 Oct 2017  View: PDF

Abstract: We simulate and experimentally demonstrate deep UV generation from a 1550 nm laser source in a fully fiberized system by cascading second and third harmonic generation using a periodically poled silica fiber and an optical sub-micron diameter fiber. Harmonic generation is achieved harnessing intermodal phase matching in optical microfibers and a permanent χ(2) induced via thermal poling. As a result, efficient non-linear processes can be observed despite a low third-order nonlinear susceptibility of silica glass.

Watt-level single-frequency tunable Neodymium MOPA fiber laser operating at 915-937 nm

sergio rota-rodrigo, benoit gouhier, Mathieu Laroche, jian zhao, Benjamin Canuel, Andrea Bertoldi, Philippe Bouyer, Nicholas Traynor, benoit cadier, thierry Robin, and GIORGIO SANTARELLI

Doc ID: 303487 Received 31 Jul 2017; Accepted 05 Oct 2017; Posted 06 Oct 2017  View: PDF

Abstract: We have developed a Watt-level single-frequency tunable fiber laser in the 915-937 nm spectral window. The laser is based on a neodymium-doped fiber master oscillator power amplifier architecture, with two amplification stages using a 20 mW extended cavity diode laser as seed. The system output power is higher than 2 W from 921 to 933 nm, with a stability better than 1.4% and a low relative intensity noise.

Enhancing the resolution of a near-eye display with Pancharatnam−Berry phase deflector

Yun-Han Lee, Tao Zhan, and Shin-Tson Wu

Doc ID: 307169 Received 18 Sep 2017; Accepted 05 Oct 2017; Posted 18 Oct 2017  View: PDF

Abstract: We demonstrate a simple method to enhance the resolution of a display device based on fast-switching Pancharatnam−Berry phase deflector (PBD). The PBD has a switching time less than 1 ms. Through synchronizing and computational factorization, we are able to double the display resolution for reducing the screen door effect. Such a thin and lightweight PBD image shifter can be easily integrated into wearable display devices. Its potential application for virtual reality and augmented reality is emphasized.

All-optical digital-to-analog converter based on cross-phase modulation with temporal integration

Deming Kong, Zihan Geng, Benjamin Foo, Valery Rozental, Bill Corcoran, and Arthur Lowery

Doc ID: 303340 Received 03 Aug 2017; Accepted 04 Oct 2017; Posted 05 Oct 2017  View: PDF

Abstract: We propose and experimentally demonstrate an all-optical digital-to-analog converter (DAC) based on cross-phase modulation (XPM) with temporal integration. The scheme is robust to driving signal noise due to the low-pass filtering feature of the temporal integrator. The proof-of-concept experiment demonstrates the generation of pulse-amplitude modulation (PAM) sequences up to 8 levels. The performance of random PAM~2 and PAM~4 signals with different optical signal-to-noise ratios (OSNRs) of the binary driving signal is also investigated. The scheme is scalable for high-speed operation with appropriate dispersion profile of the nonlinear medium.

3D point cloud based apparent magnitude model of space objects

Yang Wang and Xiaoping Du

Doc ID: 307926 Received 28 Sep 2017; Accepted 04 Oct 2017; Posted 09 Oct 2017  View: PDF

Abstract: A new 3D point cloud based model is presented for calculating the apparent magnitude of space objects. This model does not consider topological relations of space objects, and it can accurately describe the shape of a space object and calculate its apparent magnitude. Once a 3D point cloud of a space object and its material parameters under a certain wavelength are obtained, the apparent magnitude can be solved. Through this model, the apparent magnitude of space objects with different shapes and the wrinkled surface can be calculated easily. Simulation results show that the increase in the number of points can improve the accuracy of this model.

Bound States in the Continuum on Periodic Structures: Perturbation Theory and Robustness

Lijun Yuan and Ya Yan Lu

Doc ID: 302570 Received 18 Jul 2017; Accepted 04 Oct 2017; Posted 06 Oct 2017  View: PDF

Abstract: On periodic structures, a bound state in the continuum (BIC) is astanding or propagating Bloch wave with a frequency in the radiationcontinuum. Some BICs (e.g., antisymmetric standing waves) aresymmetry-protected, since they have incompatible symmetry withoutgoing waves in the radiation channels. The propagating BICs do nothave this symmetry mismatch, but they still depend crucially on thesymmetry of the structure. In this Letter, a perturbation theory isdeveloped for propagating BICs on two-dimensional periodic structures.The study shows that these BICs are robust against structuralperturbations that preserve the symmetry, indicating that these BICsare in fact implicitly protected by symmetry.

Fourier Processing with Partially Coherent Fields

Taco Visser, Govind Agrawal, and Peter Milonni

Doc ID: 305456 Received 24 Aug 2017; Accepted 04 Oct 2017; Posted 06 Oct 2017  View: PDF

Abstract: We describe how Fourier signal processing techniques can be generalized to partially coherent fields. Using standard coherence theory we first show that focusing of a partially coherent beam by a lens modifies its coherence properties. We then consider a 4f imaging system composed of two lenses and discuss how spatial filtering in the Fourier plane allows one to tune the coherence properties of the beam. This in turn provides control over the beam's directionality, spectrum, and degree of polarization.

Purified frequency modulation of quantum cascade laser with an all-optical approach

Chen Peng, haijun zhou, Li-Guo Zhu, Tao Chen, QIAO LIU, Detian Wang, Jiang Li, Qixian Peng, Gang Chen, and Ze-Ren Li

Doc ID: 305406 Received 24 Aug 2017; Accepted 03 Oct 2017; Posted 05 Oct 2017  View: PDF

Abstract: Purified frequency modulation is demonstrated in a standard middle-infrared quantum cascade laser by illuminating its front facet with two near-infrared lasers. A 2 mW laser at 1550 nm is utilized to modulate the amplitude and frequency of quantum cascade laser, and the associated amplitude modulation is suppressed by a 1.85 mW laser at 850 nm. Due to the hot carrier effect and the increment of electron temperature, the amplitude modulation has been decreased. In addition, the free carrier concentration increases in the active region due to the two near infrared illuminations, which enhance the frequency modulation. Purified frequency modulation is beneficial in improving the signal fidelity for free space optical communication and high speed frequency modulation spectroscopy.

Tunable optical properties of amorphous Tantala layers in a quantizing structure

Thomas Willemsen, Marco Jupé, Laurent Gallais, Dominic Tetzlaff, and Detlev Ristau

Doc ID: 304631 Received 17 Aug 2017; Accepted 03 Oct 2017; Posted 03 Oct 2017  View: PDF

Abstract: Plasma deposition techniques like Ion-Beam-Sputtering (IBS) are state of the art to manufacture high quality optical components for laser applications. Beside the well optimized process and monitoring systems, the selection of coating material is of major importance to achieve optimum optical performances. Applying the IBS technology, an approach is presented to create novel materials by the direct application of binary oxides in a quantizing structure. By reducing the physical thickness of the high refractive index material to a few nm within a classical high low index stack the electron confinement can be changed. Optical characterizations of the manufactured samples with decreasing quantum well thicknesses result in an increasing blue shift of the absorption gap and offer amethod to approximate the effective mass of the high refractive index material in conjunction with theoretical models. Laser induced damage threshold tests of coating samples prepared with different well thickness indicate an increase of the measured threshold values with optical gap energy.

Morphological-adaptive photoacoustic tomography with flexible transducer and flexible orientation light

xin wang, Zhong Ji, Sihua Yang, and Da Xing

Doc ID: 302896 Received 19 Jul 2017; Accepted 03 Oct 2017; Posted 05 Oct 2017  View: PDF

Abstract: Although conventional photoacoustic tomography (PAT) provides high optical contrast and high ultrasound resolution in depth, its fixed-energy-distribution laser and unchangeable-shape detector hinder its implementations on clinical routine breast screening. In this Letter, for the first time, we present a fully-flexible photoacoustic coupling system (FPACS) that integrates optical fiber bundles and flexible ultrasonic transducer for morphological-adaptive breast detection. The experimental results show that the system has better resolution and higher energy utilization rate than traditional PAT systems even at the edge of imaging region. Moreover, the system can achieve morphological adaption, suggesting that FPACS provides the potential for clinical routine breast screening.

Transmissive Terahertz Metalens with Full Phase Control Based on Dielectric Metasurface

Delin Jia, Yuan Tian, Wei Ma, Xiaofeng Gong, Jiayi Yu, Guozhong Zhao, and Xiaomei Yu

Doc ID: 304354 Received 17 Aug 2017; Accepted 03 Oct 2017; Posted 03 Oct 2017  View: PDF

Abstract: In this paper, we report a transmissive terahertz (THz) metalens based on a dielectric metasurface which consists of periodically arranged sub-wavelength silicon cross resonators with a spatially hyperboloidal phase profile. By varying arm lengths of the cross resonators, we obtain a full 2π phase coverage with high transmission at target frequency. The fabricated metalens was experimentally demonstrated to focus a continuous THz beam to a spot with a full width at half maximum (FWHM) of 630 μm at a focal length of 28 mm, which agrees well with the theoretical calculation. This device has potential for applications in THz imaging and communications, and our work can also easily be extended in the design of other planar THz components like beam deflectors or vortex plates.

Microresonator-based high-resolution gas spectroscopy

Mengjie Yu, Yoshitomo Okawachi, Austin Griffith, Michal Lipson, and Alexander Gaeta

Doc ID: 302293 Received 14 Jul 2017; Accepted 02 Oct 2017; Posted 03 Oct 2017  View: PDF

Abstract: In recent years, microresonator-based optical frequency combs have created up opportunities for developing a spectroscopy laboratory on a chip due to its broadband emission and high comb power. However, with mode spacings typically in the range of 10 - 1000 GHz, the realization of a chip-based high-resolution spectrometer suitable for gas-phase spectroscopy has proven to be difficult. Here, we show mode-hop-free tuning of a microresonator-based frequency comb over 16 GHz by simultaneously tuning both the pump laser and the cavity resonance. We illustrate the power of this scanning technique by demonstrating gas-phase molecular fingerprinting of acetylene with a high-spectral-resolution of < 80 MHz over a 45-THz optical bandwidth in the mid-IR. Our technique represents a significant step towards on-chip gas sensing with an ultimate spectral resolution given by the comb linewidth.

Portable optical resolution photoacoustic microscopy (pORPAM) for human oral imaging

Tian Jin, Guo Heng, Huabei Jiang, bowen ke, and Lei Xi

Doc ID: 303243 Received 28 Aug 2017; Accepted 02 Oct 2017; Posted 03 Oct 2017  View: PDF

Abstract: Optical resolution photoacoustic microscopy (ORPAM) represents one of the fastest evolving optical microscopic techniques. However, due to the bulky size and complicated system configuration of conventional ORPAMs, they are largely limited to small animal experiments. In this letter, we present the design and evaluation of a portable optical resolution photoacoustic microscopy (pORPAM) with a high spatiotemporal resolution and a large field of view. In this system, we utilize a rotatory scanning mechanism instead of the conventional raster scanning to achieve translationless of the imaging probe/samples, making it accessible to the human oral lip and tongue. After phantom evaluation, we applied this system to monitor longitudinal neo-angiogenesis of tumor growth, and for the first time image the oral vascular network of humans to show its potential in clinical detection of early-stage oral cancer.

Coherent Combination of Ultrashort Pulse Beams Using Two Diffractive Optics

Tong Zhou, Tyler Sano, and Russell wilcox

Doc ID: 306672 Received 08 Sep 2017; Accepted 02 Oct 2017; Posted 02 Oct 2017  View: PDF

Abstract: A novel coherent beam combiner, capable of combining large numbers of femtosecond pulse beams using two diffractive optics, is presented. The diffractive optic pair cancels pulse front tilt, while uncorrected dispersions are minimized. An example using four beams is modeled numerically and tested experimentally, demonstrating 120fs pulses combined without degradation of pulse width. Scaling the concept, we show analytically that combining loss due to uncorrected dispersions is only a few percent for ~200 beams with 130fs pulses.

Electromagnetically induced transparency in vacuum and buffer gas potassium cells probed via electro-optic frequency combs

David Long, Adam Fleisher, David Plusquellic, and Joseph Hodges

Doc ID: 306812 Received 11 Sep 2017; Accepted 02 Oct 2017; Posted 02 Oct 2017  View: PDF

Abstract: Electromagnetically induced transparency (EIT) in 39K and 41K was probed using electro-optic frequency combs generated by applying chirped waveforms to a phase modulator. The carrier tone of the frequency comb served as the pump beam and induced the necessary optical cycling. Comb tooth spacings as narrow as 20 kHz were used to probe potassium in both buffer gas and evacuated cells at elevated temperatures. Atomic absorption features as narrow as 33(5) kHz were observed allowing for the 39K lower state hyperfine splitting to be optically measured with a fit uncertainty of 2 kHz. Due to the ultranarrow width of the EIT features, long-lived optical free induction decays were also observed which allowed for background-free detection.

Strongly enhanced molecular fluorescence with ultra-thin optical magnetic mirror metasurfaces

Jian Qin, Ding Zhao, Si Luo, Wei Wang, Jun Lu, Min Qiu, and Qiang Li

Doc ID: 305389 Received 29 Aug 2017; Accepted 02 Oct 2017; Posted 03 Oct 2017  View: PDF

Abstract: As a kind of two-dimensional metamaterials, metasurfaces can modify the amplitude, phase and polarization of the transmitted or reflected electromagnetic wave, and thereby can be used for enhancing the light-matter interactions. Based on this notion, an optical magnetic mirror metasurface featuring periodic nanoscale grooves is designed to confine the strong electric field near the metal surface by magnetic responses. As a result, fluorescence from an ultra-thin layer of fluorescent polymer blend (~15 nm) on the mirror surface can be strongly enhanced (by 45-fold in experiment). The fluorescence emission can be controlled by the polarization of excitation light since the responses of the magnetic mirror are polarization-sensitive. This kind of magnetic mirror metasurface is potentially useful in biological monitors, optical sources and chemical sensors.

Optical memory based on quantized atomic center-of-mass motion

Jesús Pavón López, Allan Almeida, Daniel Barbosa, and Jose Tabosa

Doc ID: 306293 Received 05 Sep 2017; Accepted 02 Oct 2017; Posted 03 Oct 2017  View: PDF

Abstract: We report a new type of optical memory using a pure two-level system of cesium atoms cooled by the magnetically assisted Sisyphus effect. The optical information of a probe field is stored in the coherence between quantized vibrational levels of the atoms in the potential wells of a 1-D optical lattice. The retrieved pulse shows Rabi oscillations with a frequency determined by the reading beams intensity and are qualitatively understood in terms of a simple theoretical model. Exploration of the external degrees of freedom of an atom may add another capability in the design of quantum-information protocols using light.

Coherent, directional supercontinuum generation

Yoshitomo Okawachi, Mengjie Yu, Jaime Cardenas, Xingchen Ji, Michal Lipson, and Alexander Gaeta

Doc ID: 304733 Received 15 Aug 2017; Accepted 02 Oct 2017; Posted 03 Oct 2017  View: PDF

Abstract: We demonstrate a novel approach to producing coherent, directional supercontinuum via cascaded dispersive wave generation. By pumping in the normal group-velocity dispersion regime, pulse compression of the first dispersive wave results in the generation of a second dispersive wave, resulting in an octave-spanning supercontinuum generated primarily to one side of the pump spectrum. We theoretically investigate the dynamics and show that the generated spectrum is highly coherent. We experimentally confirm this dynamical behavior and the coherence properties in silicon nitride waveguides by performing direct detection of the carrier-envelope-offset frequency of our femtosecond pump source using an f-2f interferometer. Our technique offers a path towards a stabilized, high-power, integrated supercontinuum source with low noise and high coherence, with applications including direct comb spectroscopy.

Physical mechanism of order between electric and magnetic dipole in spoof plasmonic structures

Hongwei Wu, Yi-Zeng Han, Hua-Jun Chen, Yu Zhou, Xue-Chao Li, Juan Gao, and Zong-Qiang Sheng

Doc ID: 307528 Received 19 Sep 2017; Accepted 02 Oct 2017; Posted 06 Oct 2017  View: PDF

Abstract: It has been recently shown that a solid textured metal cylinder can supports electric and magnetic dipolar resonances simultaneously [Physical Review X 4, 021003 (2014)] which are almost degenerate in two-dimension and non-degenerate in three-dimension structure, and with the magnetic dipole appearing at higher frequency. They are described as spoof localized plasmonic modes analogous to localized plasmonic resonances in optical frequencies. Here, we consider a hollow metal cylinder corrugated by periodic cut-through slits. Our results indicate that the magnetic dipole can be separated from electric dipole in two-dimension structure, and magnetic dipolar resonance appears at lower frequency rather than electric resonance both in two- and three-dimension structure. In order to clarify the physical mechanism behind the abnormal phenomenon, we study the influence of the core material on the electric- and magnetic-dipole modes based on theoretical analysis and numerical simulation. It is discovered that there is a threshold of imaginary part of permittivity for switching the order between the electric and magnetic dipole. These results may provide fundamental understanding and physical insight for spoof plasmonic modes supported in designer structure.

Ns-duration transient Bragg gratings in silica fibers

Avishay Shamir, Aviran Halstuch, Yonatan Sivan, and Amiel Ishaaya

Doc ID: 301848 Received 06 Jul 2017; Accepted 02 Oct 2017; Posted 18 Oct 2017  View: PDF

Abstract: We demonstrate, for the first time to our knowledge, fast all-optical switching in standard silica fibers, based on a transient Bragg grating. The grating is implemented in the fiber using an immunization photo-pretreatment process, followed by side illumination with fs laser pulses through a suitable phase mask. Each pulse is nonlinearly absorbed, creating a thermal grating that is washed out by thermal diffusion. Reflections measured from such gratings are characterized by a very fast rise time, ns duration, and a high extinction ratio.

Micro-pulse polarization lidar at 1.5 μm using a single superconducting nanowire single photon detector

Jiawei Qiu, Haiyun Xia, Mingjia Shangguan, Xiankang Dou, Manyi Li, Chong Wang, Xiang Shang, Shengfu Lin, and Jianjiang Liu

Doc ID: 306260 Received 04 Sep 2017; Accepted 01 Oct 2017; Posted 02 Oct 2017  View: PDF

Abstract: An all-fiber, eye-safe and micro-pulse polarization lidar is demonstrated with polarization-maintaining structure, incorporating a single superconducting nanowire single-photon detector at 1.5 μm. Time-division multiplexing technique is used to achieve a calibration-free optical layout. A single piece of detector is used to detect the backscatter signals at two orthogonal states in an alternative sequence. Thus, regular calibration of the two detectors in traditional polarization lidars is avoided. The signal to noise ratio of the lidar is guaranteed by using a superconducting nanowire single-photon detector, providing high detection efficiency and low dark count noise. The linear depolarization ratio (LDR) of the urban aerosol is observed horizontally over 48 hours in Hefei [N31°50’37”, E117°15’54”], when a serious air pollution is spreading from the north to the central east of China. Phenomenon of LDR bursts is detected at a location where a building is under construction. The lidar results show good agreement with the data detected from a sun photometer, a visibility sensor and the weather forecast information.

Asymmetry parameter for anomalous scattering of light in nanostructured glasses

Mikhail Shepilov

Doc ID: 305084 Received 23 Aug 2017; Accepted 01 Oct 2017; Posted 05 Oct 2017  View: PDF

Abstract: An approach is proposed for evaluation of asymmetry parameter for anomalous scattering of light in nanostructured glasses from the experimental wavelength dependence of scattering coefficient. This dependence observed for phase-separated glasses and glass-ceramics is described by the power law with the constant exponent (-p) where p is greater than 4. The material is modelled by identical Rayleigh scatterers distributed in a homogeneous matrix. We use this model, the interference approximation for scattering coefficient and its experimental wavelength dependence and express asymmetry parameter in terms of p. The results can be applied to simulation of multiple light scattering in nanomaterials.

UVA light-emitting diode grown on Si substrate with enhanced electron and hole injections

Zi Hui Zhang, luping Li, Ching-Hsueh Chiu, Tien-Chang Lu, Chunshuang Chu, Yonghui Zhang, Kangkai Tian, Mengqiang Fang, Qian Sun, Hao-chung Kuo, and Wengang (Wayne) Bi

Doc ID: 305642 Received 28 Aug 2017; Accepted 30 Sep 2017; Posted 05 Oct 2017  View: PDF

Abstract: In this work, III-nitride based ~ 370 nm UVA light-emitting diodes (LEDs) grown on Si substrates are demonstrated. We also reveal the impact of the AlN composition in the AlGaN quantum barrier on the carrier injection for the studied LEDs. We find that, by properly increasing the AlN composition, both the electron and hole concentrations in the multiple quantum wells (MQWs) are enhanced. We attribute the increased electron concentration to the better electron confinement within the MQW region when increasing the AlN composition for the AlGaN barrier. The improved hole concentration in the MQW region is ascribed to the reduced hole blocking effect by the p-type electron blocking layer (p-EBL), since the density of the polarization induced positive charges at the AlGaN last quantum barrier (LB)/p-EBL interface decreases which correspondingly suppresses the surface depletion at the AlGaN LB/p-EBL interface and decreases the valence band barrier height for the p-EBL. As a result, the optical power is improved.

Photon ensemble correlation spectroscopy enables decorrelation-rate-limited ultrafast measurement of diffusive particle dynamics

Peng Li, Shanshan Yang, Zhihua Ding, and Pei Li

Doc ID: 303537 Received 01 Aug 2017; Accepted 30 Sep 2017; Posted 06 Oct 2017  View: PDF

Abstract: In contrast to conventional dynamic light scattering measurement via a single sampling volume (SV) observation over a long time span, we propose a novel technique named “photon ensemble correlation spectroscopy” for ultrafast characterization of diffusive particle dynamics through decorrelation analysis of complex-valued dynamic light scattering signals from an ensemble of independent SVs. We confirm that the ensemble analysis provides a decorrelation-rate-limited ultrafast measurement, and demonstrate the feasibility of imaging spatially resolved particle dynamics. Moreover, the use of complex-valued signals gives additional superiority in terms of reliability.

Using a Complex Optical Orbital-Angular-Momentum Spectrum to Measure Object Parameters

Guodong Xie, haoqian song, Zhe Zhao, Giovanni Milione, Yongxiong Ren, Cong Liu, Runzhou Zhang, Changjing Bao, Long Li, Zhe Wang, Kai Pang, Dmitry Starodubov, Brittany Lynn, Moshe Tur, and Alan Willner

Doc ID: 304920 Received 17 Aug 2017; Accepted 30 Sep 2017; Posted 03 Oct 2017  View: PDF

Abstract: Light beams can be characterized by their complex spatial profiles in both intensity and phase. Analogous to time signals, which can be decomposed into multiple orthogonal frequency functions, a light beam can also be decomposed into a set of spatial modes that are taken from an orthogonal basis. Such a decomposition can potentially provide a tool for spatial spectrum analysis, which may enable stable, accurate, and robust extraction of physical object information that may not be readily achievable using traditional approaches. As a proof-of-concept example, we measure an object’s opening angle using orbital angular momentum (OAM) based complex spectrum, achieving a >15 dB signal-to-noise-ratio. Moreover, the dip (i.e., notch) positions of the OAM intensity spectrum are dependent on an object’s opening angle but independent of the opening’s angular orientation, whereas the slope of the OAM phase spectrum is dependent on the opening’s orientation but independent on the opening angle.

High contrast wide-field evanescent wave illuminated sub-diffraction imaging

Chenlei Pang, xiaowei liu, Minghua Zhuge, Xu Liu, Michael Somekh, Yiying Zhao, Di Jin, Weidong Shen, Haifeng Li, Lan Wu, Changhua Wang, Cuifang Kuang, and Qing Yang

Doc ID: 306289 Received 04 Sep 2017; Accepted 29 Sep 2017; Posted 11 Oct 2017  View: PDF

Abstract: In this letter, we show how to obtain high contrast wide-field evanescent wave illuminated sub-diffraction imaging through controlling nanoscale light-matter interaction. The light coupling, propagation and far-field imaging processes show strong polarization selectivity and film quality dependence, which is used to improve the image contrast to noise ratio (CNR) and to enlarge the field of view (FOV). We demonstrate experimentally high CNR sub-diffraction imaging with lateral resolution of 122 nm and FOV of thousands of micrometer square.

In-fiber refractive index sensor based on single eccentric hole-assisted dual-core fiber

jing Yang, Chunying Guan, peixuan tian, Tingting yuan, zheng zhu, ping li, Jin-hui Shi, Jun Yang, and Libo Yuan

Doc ID: 305251 Received 21 Aug 2017; Accepted 28 Sep 2017; Posted 03 Oct 2017  View: PDF

Abstract: We propose a novel and simple in-fiber refractive index sensor based on resonant coupling, constructed by a short section of single eccentric hole-assisted dual-core fiber (SEHADCF) spliced between two single mode fibers (SMFs). The coupling characteristics of the SEHADCF are calculated numerically. The strong resonant coupling occurs when the fundamental mode of the center core phase-matches to that of the suspended core in the air-hole. The effective refractive index of the fundamental mode of the suspended core can be obviously changed by injecting solution into the air-hole. The responses of the proposed devices to the refractive index and temperature are experimentally measured. The refractive index sensitivity is 627.5 nm/RIU in the refractive index range of 1.335 ~ 1.395, more importantly the sensor is insensitive for temperature change in the range of 30 ~ 90 °C. The proposed refractive index sensor has outstanding advantages, such as simple fabrication, good mechanical strength and excellent microfluidic channel, and will be of importance in biological detection, chemical analysis and environment monitoring.

Fiber in-line Mach-Zehnder interferometer based on femtosecond laser inscribed waveguides

Weiwei Li, Weiping Chen, Dongning Wang, Zhaokun Wang, and Ben Xu

Doc ID: 307089 Received 13 Sep 2017; Accepted 27 Sep 2017; Posted 02 Oct 2017  View: PDF

Abstract: A new type of Mach-Zehnder interferometer device based on in-fiber optical waveguides, fabricated by direct femtosecond laser pulse inscription in single mode fiber has been demonstrated and successfully employed for temperature and strain measurement. The in-fiber waveguide can couple the light out from the fiber core, guide it along the cladding region before directing it back into the fiber core. Such an inner structured interferometer device is compact and robust, can be constructed in a flexible and precisely controlled manner, and hence is expected to have many potential applications.

Critical Phenomenon in Tapered Dielectric Structures

Adi Hanuka and Levi Schachter

Doc ID: 301666 Received 06 Jul 2017; Accepted 27 Sep 2017; Posted 28 Sep 2017  View: PDF

Abstract: We demonstrate the existence of a critical behavior of a single electromagnetic mode propagating in a tapered dielectric structure. This behavior is conveniently described in terms of a critical phase velocity in case of an adiabatic tapering. In the vicinity of this critical phase velocity, the tapered structure no longer confines the radiation and a significant fraction of the power escapes transversely.

Nano-ablation of Silica by Plasmonic Surface Wave at Low Fluence

Lei Wang, Xiao-Wen Cao, Muhammad Irfan Abid, Qian-Kun Li, Wen-Jing Tian, Qi-Dai Chen, Saulius Juodkazis, and Hong-Bo Sun

Doc ID: 306256 Received 01 Sep 2017; Accepted 26 Sep 2017; Posted 28 Sep 2017  View: PDF

Abstract: Formation of ripples by ablation of surfaces of laser irradiated materials is an example of ultrafast energy delivery. Herein we report on fs-laser optical imprinting of periodic nano-grooves on silica substrate at only 25% of the laser ablation threshold via an interface plasmonic light localization at the ZnS film (top) interface with silica (bottom) by plasmonic surface wave. The nano-grooves were formed on silica below between the nanogratings on the film with the same period and directions. Based on detailed account of the multiple photon and avalanche ionization using Drude model, laser induced plasmonic ablation describes quantitatively the energy deposition from the top ZnS to the substrate of silica.

Lumped Rayleigh reflectors

Haniel Gabai, Itai Shpatz, and Avishay Eyal

Doc ID: 304018 Received 07 Aug 2017; Accepted 26 Sep 2017; Posted 05 Oct 2017  View: PDF

Abstract: Distributed acoustic sensing (DAS) via optical fibers makes use of Rayleigh backscattering for detection of acoustic waves which interact with the fiber along its entire length. The random nature of Rayleigh backscattering leads to non-uniform performance along the fiber and occasionally to complete signal fading. In addition, distance-dependent SNR degradation is always present due to propagation loss. In contrast, using arrays of discrete reflectors (such as weak FBGs with equal center wavelengths) offers deterministic performance which can be designed to be uniform along the fiber. Here we describe an approach for implementing Rayleigh-based discrete reflectors which can offer enhanced detection performance in selected regions. It is based on enclosing sections of the fiber in acoustically insulated boxes to create Lumped Rayleigh Reflectors (LRRs). Besides diminishing the randomness in detection sensitivity, the method enables increasing the detection SNR far beyond the typical value for Rayleigh-based DAS and obtaining sensitivities comparable with discrete reflectors. The proposed method was successfully tested via both simulation and experiment.

Single-shot optical recorder with sub-picosecond resolution and scalable record length on a semiconductor wafer

Ryan Muir and John Heebner

Doc ID: 301313 Received 04 Aug 2017; Accepted 25 Sep 2017; Posted 02 Oct 2017  View: PDF

Abstract: We demonstrate a novel, single-shot recording technology for transient optical signals. A resolution of 0.4 ps over a record length of 54 ps was demonstrated. Here, a pump pulse crossing through a signal samples a diagonal “slice” of space-time enabling a camera to record spatially the time content of the signal. Unlike related (2) based cross-correlation techniques, here the signal is sampled through optically-pumped carriers that modify the refractive index of a silicon wafer. Surrounding the wafer with birefringent retarders enables two time-staggered, orthogonally-polarized signal copies to probe the wafer. Recombining the copies at a final crossed polarizer destructively interferes them except during the brief stagger window where a differential phase shift is incurred. This enables the integrating response of the rapidly excited but persistent carriers to be optically differentiated. This sampling mechanism has several advantages that enable scaling to long record lengths, including making use of large, inexpensive semiconductor wafers, eliminating the need for phase matching, broad insensitivity to the spectral and angular properties of the pump, and overall hardware simplicity.

Multiple Frequency-Spaced Flat Optical Comb Generation Using Multiple-Parallel Phase Modulator

Takahide Sakamoto and Akito Chiba

Doc ID: 304921 Received 21 Aug 2017; Accepted 25 Sep 2017; Posted 26 Sep 2017  View: PDF

Abstract: We propose multiple frequency-spaced flat optical comb generation using an electro-optic (EO) multiple-parallel phase modulator. We formulate and clarify the operating conditions, where we can generate optical combs adding the two important functionalities of spectral shaping: (1) multiplication of frequency spacing and (2) spectral flattening. The frequency spacing of the generated comb is enhanced much higher than the EO modulation bandwidth. The spectral shaping is achieved fully through EO modulation process, without relying on any optical filters. This filter-less configuration is advantageous for flexible tuning of wavelength and frequency spacing of the generated combs. The concept is numerically verified, focusing on N×25-GHz-spaced comb generation.

Precursors propagation in inhomogeneous broadened media: Experiment and Numerical Simulation

Federico Tommasi, Emilio Ignesti, Lorenzo Fini, and Stefano Cavalieri

Doc ID: 304549 Received 11 Aug 2017; Accepted 25 Sep 2017; Posted 03 Oct 2017  View: PDF

Abstract: We report experimental results on the propagation temporal characteristics of the precursor in an inhomogeneous sample. The transient behavior of step-like pulse in an atomic hot medium is two order of magnitude faster than the radiative broadened case up to now presented in literature. Moreover we show the dependence on the resonant or non-resonant condition. Numerical simulations compare favorable to experimental results.

Optical vector network analyzer based on double-sideband modulation

wen jun, Ling Wang, Chengwu Yang, Ming Li, Ninghua Zhu, Jin-Jin Guo, Liangming Xiong, and Wei Li

Doc ID: 305494 Received 24 Aug 2017; Accepted 22 Sep 2017; Posted 02 Oct 2017  View: PDF

Abstract: We report an optical vector network analyzer (OVNA) based on double-sideband (DSB) modulation using a dual-parallel Mach-Zehnder modulator (DPMZM). A device-under-test (DUT) is measured twice with dif-ferent modulation schemes. By post-processing the measurement results, the response of the DUT can be obtained accurately. Since DSB modulation is used in our approach, the measurement range is doubled compared with conventional single-sideband (SSB) modulation-based OVNA. Moreover, the measurement accuracy is improved by eliminating the even-order sidebands. The key advantage of the proposed scheme is that the measurement of a DUT with band-pass response can also be simply realized, which is a big challenge for the SSB-based OVNA. The proposed method is theoretically and experimentally demon-strated.

Highly efficient, high peak-power, narrow linewidth fiber gas Raman amplifier operating at 1.9 μm

Zefeng Wang, Bo Gu, Yubin Chen, Xiaoming Xi, and zhixian li

Doc ID: 305571 Received 24 Aug 2017; Accepted 22 Sep 2017; Posted 22 Sep 2017  View: PDF

Abstract: We demonstrate here, to the best of our knowledge, the first 1.9 μm fiber gas Raman amplifier based on SRS in a H2-filled anti-resonance hollow-core fiber. A CW seed fiber laser near 1908 nm is amplified by the 1st vibrational Stokes wave of hydrogen molecules while pumping with a pulsed 1064 nm microchip laser. The seed significantly enhances the vibrational SRS and suppresses the rotational SRS, resulting in a record optical-to-optical conversion efficiency of ~41% and a corresponding quantum efficiency of ~73.5% for such H2 vibrational Raman experiments in hollow-core fibers, with 1.4 meter fiber and only 2 bar H2, which is more preferable in applications. The maximum average Stokes power of 74.2 mW with linewidth about 1 GHz (~12pm) is obtained, which also makes a record peak power of ~150 kW for sub-nanosecond 2μm- band fiber lasers of gigahertz-level linewidth. This paper provides a suitable laser source for the generation of supercontinuum and lasers at mid-infrared wavelength.

Acceleratating two-dimensional infrared spectroscopywhile preserving lineshapes using GIRAF

Ipshita Bhattacharya, Jonathan Humston, Christopher Cheatum, and Mathews Jacob

Doc ID: 304846 Received 16 Aug 2017; Accepted 14 Sep 2017; Posted 15 Sep 2017  View: PDF

Abstract: We introduce a computationally efficient structuredlow rank algorithm for the reconstruction of twodimensionalinfrared (2D IR) spectroscopic data fromfew measurements. The signal is modeled as a combinationof exponential lineshapes, which are annihilatedby appropriately chosen filters. The annihilationrelations result in a low-rank constraint on a Toeplitzmatrix constructed from the signal samples, which is exploitedto recover the unknown signal samples. Quantitativeand qualitative studies on simulated and experimental2D IR data demonstrate that the algorithm outperformsdiscrete compressed sensing algorithm, bothin the uniform and non-uniform sampling settings.

Efficient wavelength conversion with low operation power in Ta₂O₅ based micro-ring resonator

Chung-Lun Wu, Jen-Yang Huang, Ding-Hsin Ou, Ting-Wei Liao, Yi-jen Chiu, Min-Hsiung Shih, YuanYao Lin, Ann-Kuo Chu, and Chao-Kuei Lee

Doc ID: 302655 Received 17 Jul 2017; Accepted 12 Sep 2017; Posted 14 Sep 2017  View: PDF

Abstract: The Ta₂O₅ based micro-ring resonator with unloaded quality factor of ~182000 has been demonstrated to realize efficient nonlinear wavelength generation. The propagation loss of Ta₂O₅ based micro-ring resonator is 0.5/cm, and the buildup factor of ring resonator is estimated to be ~50. With a high buildup factor of ring structure, the four-wave-mixing (FWM) conversion efficiency of -30dB is achieved in the Ta₂O₅ based micro-ring resonator with pump power of 6mW. Based on a power-dependent FWM results, the nonlinear refractive index of Ta₂O₅ is estimated to be 1.4E-14 cm²/W at wavelength of ~1550nm. The demonstration of enhanced FWM process in the Ta₂O₅ based micro-ring cavity implies the possibility of realizing FWM based optical parametric oscillation in Ta₂O₅ based micro-ring resonator.

Near-infrared Persistent Luminescence of Yb3+ in Perovskite Phosphor

Zehua Zou, Chen Wu, Xiaodong Li, Jiachi Zhang, Huihui Li, Deyin Wang, and Yu Wang

Doc ID: 305592 Received 28 Aug 2017; Accepted 08 Sep 2017; Posted 05 Oct 2017  View: PDF

Abstract: Here we reported the observation of near-infrared Persistent luminescence (NIR PersL) of Yb3+ in perovskite CaTiO3. Sensitized by the Bi3+ codopant, it exhibits intense NIR PersL of Yb3+ at about 1000 nm. Also, this phosphor can be excited by the near ultraviolet and even visible light, and the PersL signals can be recorded for more than 80 h. The PersL enhancement by Bi3+ is revealed to be due to the suitable Bi3+ induced deeper traps and the possible PersL quantum cutting. The results suggest that the NIR PersL of the CaTiO3:Yb3+,Bi3+ phosphor has the potential applications for the biomedical imaging in the second biological window.

Six-pack off-axis holography

Moran Rubin, Gili Dardikman, Simcha Mirsky, Nir Turko, and Natan Shaked

Doc ID: 302445 Received 21 Jul 2017; Accepted 05 Sep 2017; Posted 05 Oct 2017  View: PDF

Abstract: We present a new holographic concept, named six-pack holography (6PH), in which we compress six off-axis holograms into a multiplexed off-axis hologram without loss of magnification or resolution. The multiplexed hologram contains straight off-axis fringes with six different orientations, and can be generated optically or digitally. We show that since the six different complex wave fronts do not overlap in the spatial-frequency domain, they can be fully reconstructed. 6PH allows more than 50% improvement in the spatial bandwidth consumption when compared to the best multiplexing method proposed so far. We expect the 6PH concept to be useful for a variety of applications, such as field of view multiplexing, wavelength multiplexing, temporal multiplexing, multiplexing for super-resolution imaging, and others.

A system of broadband polarization beam splitter for edge-coupling-enabled silicon photonics

Junrong Ong, Thomas Ang, Ezgi Sahin, Bryan Pawlina, George Feng Rong Chen, Dawn Tan, Soon LIM, and Ching Eng Png

Doc ID: 303629 Received 31 Jul 2017; Accepted 31 Aug 2017; Posted 25 Sep 2017  View: PDF

Abstract: We report on the design and experimental demonstration of high-performance silicon polarization beam splitter (PBS) with extinction ratio (ER) ≥ ~ 30 dB. This is achieved using a bend PBS with a bridge waveguide. By optimizing the bridge waveguide, a measured ER of ~25 dB for the quasi-TE mode, and ~20 to ~30 dB for the quasi-TM mode was realized across the measured bandwidth of 90 nm (C and L bands). The insertion loss (IL) varies from –0.2 dB to ~ –1 dB (–0.2 dB to ~ –2 dB) for the quasi-TE (quasi-TM) mode. By using a cascaded PBS system, the ER was enhanced to ~40 dB for the quasi-TE state, with IL of ~–0.2 to –2 dB and bandwidth of 90nm. To the best of our knowledge, this is the first PBS system with a high ER of ~40 dB that is experimentally realized on edge-coupling-enabled silicon photonics platform.

Single Silicon CMOS platform for multi-spectral detection from THz to X-rays

Mostafa Shalaby, Carlo Vicario, and Christoph Hauri

Doc ID: 295247 Received 12 May 2017; Accepted 11 Aug 2017; Posted 24 Aug 2017  View: PDF

Abstract: Charge coupled devices (CCDs) is a well-established imaging concept in the visible and x-ray frequency ranges. However, the small quantum photon energies of terahertz (THz) radiation have hindered the use of this mature semiconductor technological platform in this frequency range, leaving THz imaging totally dependent on low-resolution bolometer technologies. Recently, it was shown that silicon CCDs can detect THz photons under special conditions but the detection sensitivity was limited. Here we show that silicon CMOS technology offers enhanced detection sensitivity of almost two orders of magnitude compared to CCDs. Our findings allow us to extend the low frequency THz cut off to less than 2 THz nearly closing the technological gap with electronic imagers operating up to 1 THz. Furthermore, with the CMOS technology being sensitive to mid infrared (midIR) and the x-ray ranges, we demonstrate multispectral detection with a single detector from 1 Exahertz to 2 THz. This overcomes the present challenge in spatially overlapping THz/midIR pump and x-ray probe radiation at facilities like free electron lasers, synchrotron and laser-based x-ray sources.

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