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Accepted papers to appear in an upcoming issue

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Two dimensional photon-electronic spectroscopy for excited state population detection

Long Xu, Hui Dong, and Libin Fu

Doc ID: 344938 Received 05 Sep 2018; Accepted 19 Oct 2018; Posted 19 Oct 2018  View: PDF

Abstract: Atomic excitation to excited states in strong laser field is the key to high-order harmonic generation below ionization threshold, yet remains unclear mainly due to the lack of proper detection methods. We propose a two-dimensional photon-electron spectroscopy technique to reconstruct population of excited states with the second delayed laser pulse. The technique utilizes Fourier transformation to separate ionization from different excited states to different position on the spectrum. With the advantage of the separation, we provide a scheme to reconstruct populations on different excited states after the first pulse. The scheme is validated by high-precision population reconstruction of helium and hydrogen atoms.

All-optical non-volatile tuning of AMZI-coupled ring resonator with GST phase-change material

ZAHNG HANYU, Linjie Zhou, jian xu, Liangjun Lu, Jianping Chen, and Azizur Rahman

Doc ID: 346886 Received 28 Sep 2018; Accepted 18 Oct 2018; Posted 18 Oct 2018  View: PDF

Abstract: We present a Ge2Sb2Te5(GST)-integrated ring resonator with the tuning enabled by all-optical phase change of GST using a sequence of optical pulses. The tuning is non-volatile and repeatable, with no static power consumption due to the “self-holding” feature of the GST phase-change material. The 2-m-long GST can be partially crystallized by controlling the number of pulses, increasing the tuning freedom. The coupling between the ring resonator and the bus waveguide is based on an asymmetric Mach-Zehnder interferometer. The coupling strength is wavelength-dependent so that an optimal wavelength can be selected for the probe light to get more than 20 dB transmission contrast between the amorphous and crystalline GST states. © 2018 Optical Society of America

Cavity induced tunable perfect infrared absorption in imprinted coupled complementary hole-disk array

alireza safaei, Sushrut Modak, Abraham Vázquez-Guardado, Daniel Franklin, and Debashis Chanda

Doc ID: 344258 Received 29 Aug 2018; Accepted 17 Oct 2018; Posted 17 Oct 2018  View: PDF

Abstract: Photonic microcavity coupling of a subwavelength hole-disk array, a two-element metal/dielectric composite structure with enhanced extraordinary transmission, leads to 100% coupling of incident light to the cavity system and subsequent absorption. This light-funneling process arises from the temporal and spatial coupling of the broadband localized surface plasmon resonance on the coupled hole-disk array and the photonic modes of the optical cavity, which induces spectral narrowing of the perfect absorption of light. A simple nanoimprint lithography-based large area fabrication process paves the path towards practical implementation of plasmonic cavity-based devices and sensors.

Generation of 3.9-cycle pulses from the coherent synthesis of two cw injection seeded optical parametric amplifiers

Ming-lie Hu, Jintao Fan, CHENGLIN Gu, Haosen Shi, Jun Zhao, Bo Liu, Lu Chai, and Chingyue Wang

Doc ID: 342569 Received 17 Aug 2018; Accepted 16 Oct 2018; Posted 16 Oct 2018  View: PDF

Abstract: High repetition rate, few-cycle light pulse is of great importance due to its potential for a variety of applications including two-dimensional infrared spectroscopy and time-resolved imaging of molecular structures which are benefit from its ultrabroadband spectrum and ultrashort pulse duration. The generation of an ultrabroadband coherent spectrum is one of the frontiers of ultrafast optics and accessing such few cycle pulses is presently under active exploration. Here, we demonstrate a simple, yet effective pulse synthesizer. It is based on two cw injection seeded high repetition rate optical parametric amplification (OPA) systems and the following self-phase-modulation (SPM) dominated spectra broadening processes. The combined spectrum spans from 1250 nm to 1670 nm, and a near Fourier-transform-limited 3.9-cycle (19.2 fs) synthesized pulse with a central wavelength of 1470 nm is obtained accordingly.

Cascaded downconversion interface to convert single-photon-level signals at 650 nm to the telecom band

Vahid Esfandyarpour, Carsten Langrock, and Martin Fejer

Doc ID: 342897 Received 28 Aug 2018; Accepted 15 Oct 2018; Posted 16 Oct 2018  View: PDF

Abstract: We present a device for two-step downconversion of single-photon-level signals at 650 nm to the 1.5-μm band with low excess noise and low required pump power as a quantum interface between matter-qubit-based nodes and low-loss photonic channels for quantum communication networks. The required pump power for this interface is around 60% of that for a comparable conventional single-pass device, which reduces the demand on the pump laser and yields a corresponding reduction in dark counts due to inelastic pump scattering. The single-photon-level signal at 649.7 nm is downconverted to the telecom band using a fiber-coupled reverse proton exchange (RPE) periodically poled lithium niobate waveguide and a 2.19-μm pump laser. We achieved 99% depletion efficiency for each stage, corresponding to an internal conversion efficiency of 63% at the optimum pump power for the complete cascaded process.

Efficient design of random metasurfaces

Hadiseh Nasari, Matthieu Dupre, and Boubacar Kante

Doc ID: 343216 Received 27 Aug 2018; Accepted 15 Oct 2018; Posted 16 Oct 2018  View: PDF

Abstract: Random media introduce large degrees of freedom in device design and can thus address challenges in manipulating optical waves. Wave shaping with metasurfaces has mainly utilized periodic or quasi-periodic grids, and, the potential of random arrangement of particles for devices has only come under investigation recently. The main difficulty in pursuing random metasurfaces is the identification of the degrees of freedom that optimize their efficiencies and functions. They can also encode information using the statistics of particles distribution. We propose a phase-map that accounts for the statistical nature of random media. The method takes into account effects of random near-field couplings that introduce phase errors by affecting the phase shift of elements. The proposed approach increases the efficiency of our random metasurface devices by up to ~20%. This work paves the way towards the efficient design of random metasurfaces with potential applications in highly secure optical cryptography and information encoding.

Efficient Perfectly Vertical Grating Coupler for Multi-Core Fibers Fabricated with 193-nm DUV Lithography

Yeyu Tong, Wen Zhou, and Hon Tsang

Doc ID: 345258 Received 07 Sep 2018; Accepted 15 Oct 2018; Posted 16 Oct 2018  View: PDF

Abstract: We proposed a novel high-efficiency, low-reflection and fabrication-tolerant perfectly vertical grating coupler (PVGC) with a minimum feature size >200 nm to allow for fabrication using the 193-nm deep-ultraviolet (DUV) lithography. The structural parameters of PVGC were optimized by a genetic optimization algorithm. Simulations predicted the coupling efficiency to be −2.0 dB (63.0%) and the back reflections less than −20 dB in the wavelength range of 1532 nm to 1576 nm. The design was fabricated in a multi-project wafer (MPW) run for silicon photonics and a coupling efficiency of −2.7dB (53.7%) with a 1-dB bandwidth of 33 nm is experimentally demonstrated. The measured back reflection is less than −16 dB over the C-band. The PVGC occupies a compact footprint of 30×24 µm2 and can be interfaced with the multi-core fibers for future space-division-multiplexing networks.

Thickness dependent surface plasmon of silver film detected by nitrogen vacancy centers in diamond

Dengfeng Li, Cuihong Li, Leiming Zhou, Yu Zheng, Bowen Zhao, Shen Li, Nan Zhao, Xiangdong Chen, Guang-can Guo, and Fang-Wen Sun

Doc ID: 345551 Received 13 Sep 2018; Accepted 15 Oct 2018; Posted 16 Oct 2018  View: PDF

Abstract: Precise detection of surface plasmon was crucial for the research of nanophotonics and quantum optics. In this work, we used a single nitrogen vacancy center in diamond as a probe to detect the surface plasmon that was tuned by the thickness of metallic film. The fluorescence intensity and lifetime of nitrogen vacancy center were measured to obtain the information of local light-matter interaction. A nonlinear thickness dependent change of surface plasmon was observed, with the maximum at the thickness of approximate 30 nm. The results proved that this system can quantitatively detect the light-matter interaction at nanoscale. And it provided an approach to enhance the fluorescence intensity of quantum emitter.

Static degradation of mode and polarization in dualpass rod-type fiber amplifier

Jean-francois Lupi, METTE JOHANSEN, Mattia Michieletto, and Jesper Laegsgaard

Doc ID: 346384 Received 20 Sep 2018; Accepted 15 Oct 2018; Posted 15 Oct 2018  View: PDF

Abstract: This paper describes an experimental realization of adouble-pass amplifier using rod-type fiber. In this device,the gain reaches 26 dB amplifying a 300mW, 20 ps,20 MHz seed up to 120 W, with an optical to optical efficiencyof 50 % and excellent beam quality. In addition,by design the output of the amplifier has a polarizationextinction ratio of 33 dB. Beside these good performances,we report a marginal degradation of modequality and degree of polarization followed by the socalledtransverse mode instability who occurs at 120 Wsignal power. The first degradation is static, and by analyzingits two polarizations, we conclude it is causedby a coupling between modes due to the formation of astatic thermal Long-Period Grating, which in turn initiatesthe dynamic instability.

Depth-Resolved Speckle-Correlations Imaging through Scattering Layers

Ofer Salhov, Ori Katz, and Gil Weinberg

Doc ID: 342111 Received 13 Aug 2018; Accepted 14 Oct 2018; Posted 15 Oct 2018  View: PDF

Abstract: Recently, novel imaging techniques based on the 'memory-effect' speckle-correlations have enabled diffraction-limited imaging through scattering layers and around corners. These techniques, however, are currently limited to imaging only small planar objects that are contained within the angular and axial range of the memory effect. In addition, they do not provide depth information or depth sectioning capability.Here, we extend speckle-correlation imaging to include high-resolution depth-sectioning capability in reflection-mode, by combining it with coherence-gating via low coherence holography. We demonstrate depth measurements of hidden targets through a scattering layer, and speckle-correlation imaging using coherence-gated scattered light.

High power 266 nm laser generation with NaSr3Be3B3O9F4 crystal

lijuan Liu, Zhanyu Hou, Zhi Fang, Lei Yang, Dexian Yan, Xiao Wang, Degang Xu, and Chuangtian Chen

Doc ID: 346332 Received 19 Sep 2018; Accepted 14 Oct 2018; Posted 19 Oct 2018  View: PDF

Abstract: We demonstrate a 266 nm ultraviolet (UV) picosecond (ps) laser by fourth harmonic generation (FOHG) of an Nd: YAG laser with a 5.4 mm thick NaSr3Be3B3O9F4 (NSBBF) crystal. A maximum output power at 266nm exceeding 1 watt (the highest output power being 1.6 W) has been successfully obtained, corresponding to a conversion efficiency of 10.3%. Stability research on NSBBF crystal with a fluctuation of 3.34% at 200 mw within 1 hour indicates that it is a promising UV nonlinear optical (NLO) material for practice applications. In addition, we firstly measured the effective nonlinear coefficient of NSBBF crystal at 266 nm compared with BBO crystal.

Enhanced Absorption by Coherent Conrol in a Photonic Crystal Resonator Coupled with a Microfiber

Jihoon Choi and Heeso Noh

Doc ID: 344386 Received 31 Aug 2018; Accepted 13 Oct 2018; Posted 18 Oct 2018  View: PDF

Abstract: We demonstrate enhanced absorption in a photonic crystal resonator (PCR) coupled with an optical microfiber. Enhanced absorption is based on coherent perfect absorption (CPA) that is time-reversed lasing. PCR is fabricated on a silicon membrane with optimized parameters obtained from a numerical simulation. In an experiment, we observed 72% of absorption for the PCR with the optimized parameters. We also verified numerically that the absorption required for CPA can be tuned by changing the distance between the PCR and the optical microfiber.

Real-time SPR imaging based on large area beam from a wavelength-swept laser

Seongjin Bak, Gyeong Hun Kim, Hansol Jang, Jeonghyo Kim, Jaebeom Lee, and Chang-Seok Kim

Doc ID: 341529 Received 03 Aug 2018; Accepted 13 Oct 2018; Posted 15 Oct 2018  View: PDF

Abstract: We demonstrate a real-time surface plasmon resonance imaging (SPRi) system based on wavelength-swept laser in near-infrared (NIR) region. Compared with conventional spectral modulation SPRi system with white light and spectral filter, the proposed SPRi system with wavelength-swept laser has a higher scan-rate to detect rapid change of refractive index and a higher output power for large area illumination. This SPRi system is capable of scan-rate over 12 Hz and simultaneously finds dip position of SPR curve for full-field over 12 mm × 12 mm illumination region. With wavelength-swept laser, 2-dimensional (2D) biomolecular array imaging can be acquired with high dynamic detection range of 7.67×10^-3 refractive index unit (RIU). Sensitivity and resolution are also obtained to 6501 nm/RIU and 1.89×10^-6 RIU, respectively.

High Speed Random Access Optical Scanning Using ALinear MEMS Phased Array

Stephen Hamann, Andrew Ceballos, Joseph Landry, and Olav Solgaard

Doc ID: 344825 Received 05 Sep 2018; Accepted 11 Oct 2018; Posted 12 Oct 2018  View: PDF

Abstract: We demonstrate a high speed linear MEMS phasemodulator capable of random access scanning at 350 kHz,such that any state can be accessed in 2.9 µs from anyother state. 670 scan lines with a .87 degree field of view(FOV) are demonstrated in a Fourier regime, with aprojected far field response of 660 lines with an 18 degreeFOV after magnification.

Light curve measurements with superconducting nanowire single-photon detector.

Tang feng, Zhulian Li, Yuqiang Li, Xiao Pi, Rongwang Li, Xiaoli Su, Haitao Zhang, Dongsheng Zhai, and Honglin Fu

Doc ID: 345828 Received 14 Sep 2018; Accepted 11 Oct 2018; Posted 12 Oct 2018  View: PDF

Abstract: The superconducting nanowire single-photon detector (SNSPD) is used to detect the sunlight reflected by the artificial satellite and space debris, and their light curves are successfully measured. In 2017, a space-debris laser ranging system with four-element SNSPD is developed by Yunnan Observatories in China. During the ranging experiments, the detector works in a freely detecting state. It can detect photons not only of the laser echo but also of the sunlight reflected by the target. After separating the data triggered by background light from the whole detected data set, the light curves of satellites including Topex, and several debris are acquired. The apparent rotation rate of satellite Topex is determined by analyzing the light curves by Fourier transform and phase dispersion minimization (PDM). On the basis of laser ranging system using SNSPD, the simultaneous measurement of the laser ranging and light curves of some space targets without any additional equipment is realized for the first time.

Sub-100 fs pulses generation from Kerr-lens mode-locked Yb:Lu₂O₃ ceramic thin-disk laser

Shotaro Kitajima, Akira Shirakawa, Hideki Yagi, and Takagimi Yanagitani

Doc ID: 346139 Received 17 Sep 2018; Accepted 11 Oct 2018; Posted 12 Oct 2018  View: PDF

Abstract: The first Kerr-lens mode-locked (KLM) ceramic thin-disk laser was demonstrated. Ceramic laser gain media has many advantages for high power laser such as high fracture toughness, size scalability and low cost, short time fabrication. By using the Yb:Lu2O3 ceramic thin disk, the pulse duration of 98 fs with the output power of 3.7 W was demonstrated. The shortest pulse duration was 86 fs with the decreased output power of 0.36 W. From our results, it was proved that KLM thin-disk laser with ceramic gain media can become a new option of high power, sub-100 fs pulse laser sources.

Efficiency increase of distributed feedback Raman fiber lasers by dynamic control of the phase shift

Sébastien Loranger and Raman Kashyap

Doc ID: 340668 Received 27 Jul 2018; Accepted 11 Oct 2018; Posted 12 Oct 2018  View: PDF

Abstract: Π-phase-shifted distributed feedback (DFB), ultra-long fiber Bragg gratings (FBG) with Raman gain have been shown to be excellent ultra-narrow single-frequency (SF) lasers which can be operated at any wavelength. However, these lasers have shown unusually low slope-efficiency (1-10 %), while theoretical simulations predict a much higher (30-60 %) number. We believe this poor performance is due to a thermally induced phase shift inside the FBG due to absorption of the high intensity of the signal oscillating in the cavity. To compensate for this, a thermally controlled dynamic phase-shift is proposed to increase efficiency, after lasing first occurs. We show here an increase in the slope efficiency of a factor of 4 and an increase in the total output efficiency by a factor of 6.5 with 6 Ws of pump power by reducing the phase shift once the laser begins oscillating.

Observation of crossover from intraband to interband nonlinear terahertz optics

XIN CHAI, xavier ropagnol, Andrey Ovchinnikov, Oleg Chefonov, Alexander Ushakov, Carlos Garcia-Rosas, elchin isgandarov, M.B. Agranat, Tsuneyuki Ozaki, and Andrei Savel'ev

Doc ID: 341934 Received 16 Aug 2018; Accepted 11 Oct 2018; Posted 12 Oct 2018  View: PDF

Abstract: We investigate the nonlinear effects of extremely intense few-cycle terahertz (THz) pulses (generated from the organic crystal 4-𝑁N, 𝑁N-dimethylamino-4′4′-𝑁′N′-methyl-stilbazolium 2, 4, 6 trimethylbenzenesulfonate (DSTMS), with peak electrical fields of a few MV/cm) on the carrier dynamics in n-doped semiconductor In0.53Ga0.47As. By performing open-aperture Z-scan measurements and recording the transmitted THz energy through semiconductor sample, we observed a strong THz absorption bleaching effect at high fields, followed by an absorption enhancement at even higher fields. We attribute our observations to a crossover from pure intraband carrier dynamics to an interplay between intraband carrier heating and interband carrier generations.

Super Contrast-Enhanced Darkfield Imaging of Nano Objects through Null Ellipsometry

Seongkeun Cho, Janghwi Lee, Hyungu Kim, Seulgi Lee, Akinori Ohkubo, Jungchul Lee, Taehyun Kim, Sangwoo Bae, and Wondon Joo

Doc ID: 342860 Received 23 Aug 2018; Accepted 11 Oct 2018; Posted 15 Oct 2018  View: PDF

Abstract: We rediscover the null ellipsometry principle as for an outstanding image-contrast enhancement method for darkfield imaging. Simply by adding polarizers, compensators and a PD sensor to a conventional dark-field imaging system and applying null principle, Si nano-cylinder structures as small as D20nm (H20nm) on non-patterned wafer and gap defects as small as 14.6nm and bridge defects as small as 21.9nm in size on 40nm Line and 40nm Space pattern (H40nm) which are invisible in conventional darkfield imaging can be distinguished from scattered noise. As far as we are concerned, no method has been successful for identifying such small non-metal (silicon) nanoscale-objects with such low magnification (X20) optics.

Electrical conductance of near-infrared femtosecond air filaments in the multi-filament regime

Milos Burger, Patrick Skrodzki, John Nees, and Igor Jovanovic

Doc ID: 345433 Received 10 Sep 2018; Accepted 11 Oct 2018; Posted 15 Oct 2018  View: PDF

Abstract: Electrical conductive properties of femtosecond laser filaments are of significant interest for applications such as remote arc suppression and discharge guiding. We transmitted electrical current through a DC-biased air plasma channel formed in the wake of an energetic femtosecond laser pulse and observed an increased rate of change of the charge transmitted through the ionized channel with laser energy when crossing from the single- to the multi-filament regime. This behavior is attributed to the confluent effects of greater electron density and increased cross-sectional area of the multi- filament plasma structures. As the laser energy is in- creased, the formation of additional conductive channels in the multi-filamentation regime becomes a significant contributor to the rapid increase of conductivity. These observations suggest a potential path to attractive applications such as efficient energy transfer in air mediated by femtosecond laser-produced filaments.

Vector beam generation from vertical cavity surface emitting lasers

Yuichi Kozawa, Yuki Nara, Naoto Jikutani, Yasuhiro Higashi, and Shunichi Sato

Doc ID: 346630 Received 24 Sep 2018; Accepted 11 Oct 2018; Posted 15 Oct 2018  View: PDF

Abstract: Radially and azimuthally polarized beams in a single transverse mode are generated from a commercially available VCSEL in an external cavity with a birefringent rutile lens, of which c-axis is parallel to the optical axis of the cavity, to select favorable polarization. In addition, a vector Bessel-Gaussian beam is generated from a VCSEL, which is fabricated to oscillate with a linear polarization in a fixed direction in free-running, in the same way using the external cavity. These results clearly show potential ability of VCSELs to generate vector beams, which will be essential to the space-division multiplexing in the future optical communication.

Broadband main OPCPA amplifier at 808 nm wavelength in high deuterated DKDP crystals

Xiao Liang, Xinglong Xie, Cheng Zhang, Jun Kang, Qingwei Yang, Ping Zhu, Ailin Guo, Haidong Zhu, Shunhua Yang, Ziruo Cui, Meizhi Sun, and Jianqiang Zhu

Doc ID: 346732 Received 27 Sep 2018; Accepted 10 Oct 2018; Posted 15 Oct 2018  View: PDF

Abstract: The optical aperture of ultrashort extreme intensity laser facilities, which reach 10 Petawatt, will be beyond several hundred millimeters. DKDP is by now the only nonlinear crystal that can be grown to such diameter and used in the main Optical Parametric Chirped Pulse Amplification (OPCPA) amplifier of such laser system. Here, at the signal wavelength of 808 nm for the first time, we experimentally present a broadband OPCPA system which consists of a pre-amplifier in BBO crystals and a main OPCPA amplifier in two 95% deuterated DKDP crystals. The final amplified spectrum exceeding 50 nm and the compressed pulse duration of 27 fs have been proved. The conversion efficiency of main OPCPA amplifier reached 24 % and a net signal gain of 13 was obtained. For high energy OPCPA amplifier, the influence due to partial absorption on the idler pulses in DKDP crystal is theoretically analyzed. The results indicate the potential utilization of high deuterium DKDP for the main OPCPA amplifiers in multi-Petawatt laser system at 808 nm wavelength.

Supercritical focusing coherent anti-Stokes Raman scattering microscopy for high-resolution vibrational imaging

Li Gong, Jian Lin, Chenglong hao, Wei Zheng, Steve Wu, Jinghua Teng, Chengwei Qiu, and Zhiwei Huang

Doc ID: 346741 Received 26 Sep 2018; Accepted 10 Oct 2018; Posted 19 Oct 2018  View: PDF

Abstract: We report the development of a novel supercritical focusing coherent anti-Stokes Raman scattering (SCF-CARS) microscopy for high resolution vibrational imaging. Two optimized phase patterns with a combination of concentric rings with alternative 0 and π phase is generated by using a spatial light modulator and applied to the pump beam for minimizing its focal spot size. One of the phase patterns is for both lateral and axial resolution enhancement, the other can further improve the lateral resolution but sacrifice axial resolution to some extent. We demonstrate this high-resolution SCF-CARS microscopy technique by imaging the PMMA nano-cylinder on microscope slide and glass-air interface, as well as biomedical samples, e.g. tooth.

Flipping interferometry with doubled imaging area

Noa Nativ, Nir Turko, and Natan Shaked

Doc ID: 344950 Received 10 Sep 2018; Accepted 10 Oct 2018; Posted 10 Oct 2018  View: PDF

Abstract: We present a new external off-axis holographic module that doubles the acquired complex wavefront field of view, based on using both flipping and holographic multiplexing. In contrast to previous designs, this design does not require spatial filtering (no pinhole and lenses) to create the reference beam externally. In addition, the overlap area between the fields of view as well as the off-axis angle between the sample and reference beams can be fully controlled. As we demonstrate experimentally, this approach is useful for quantitative phase microscopy of extended stationary and dynamic samples, such as cancer cells during rapid flow and beating cardiomyocytes.

Dielectric metamaterials with electric response

Ekaterian Maslova, Mikhail Limonov, and M Rybin

Doc ID: 344351 Received 27 Aug 2018; Accepted 10 Oct 2018; Posted 12 Oct 2018  View: PDF

Abstract: Dielectric metamaterials are usually studied as low-loss media with magnetic response. However, the control over the electric response is more promising for applications in photonics. Here we report an all-dielectric metamaterial with the electric response. The structure consists from high-index dielectric rods arranged in a square lattice. We present a phase diagram that includes regions of metamaterials with magnetic and electric response. A metamaterial behavior is demonstrated for homogeneous ε-near zero modes, which are observed regardless of a lattice orientation and a structure boundary. The ε-near zero modes make it possible to enhance electric field intensity by two orders of magnitude that can be used for applications exploiting light-matter interactions.

Acousto-optic tunable bandpass filter based on acoustic flexural wave induced fiber birefringence

Ligang Huang, Wending Zhang, Yujia Li, Haonan Han, Xiaoting Li, Pengfa Chang, Feng Gao, Guoquan Zhang, Lei Gao, and Tao Zhu

Doc ID: 347113 Received 01 Oct 2018; Accepted 09 Oct 2018; Posted 10 Oct 2018  View: PDF

Abstract: An acousto-optic tunable bandpass filter (AOTBF) was proposed and fabricated based on the acoustic flexural wave induced single-mode fiber birefringence via coupling the core mode to a single cladding vector mode. In the experiment, the resonant wavelength and insertion loss could be electrically tuned with span of nearly 100 nm and the lowest insertion loss of -1.7 dB. The structure gains advantages of large tuning range, fast speed, easy fabrication, low insertion loss and zero frequency shift.

Detection and perfect fitting of 13.2 dB squeezed vacuum states by considering green light-induced infrared absorption

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

Doc ID: 346185 Received 17 Sep 2018; Accepted 09 Oct 2018; Posted 09 Oct 2018  View: PDF

Abstract: We report on a high-level squeezed vacuum state with maximum quantum noise reduction of 13.2 dB directly detected at the pump power of 180 mW. The pump power dependence of squeezing factor is experimentally exhibited. When only considering the loss and phase fluctuation, the fitting results have a large deviation from the measurement value near the threshold. By integrating the green light-induced infrared absorption (GLIIRA) loss together, the squeezing factor can be perfectly fitted in the whole pump power range. The result indicates that the GLIIRA loss should be thoroughly considered and quantified in the generation of high-level squeezed states.

Whispering gallery mode excitation in a microsphere by use of an etched cavity on multimode fiber end

Dongning Wang and xueqian bai

Doc ID: 342385 Received 14 Aug 2018; Accepted 09 Oct 2018; Posted 12 Oct 2018  View: PDF

Abstract: In this paper, we demonstrate a whispering-gallery-mode microsphere resonator. The device is fabricated by fusion splicing of a section of no-core fiber with multi-mode fiber and single-mode fiber at its two ends. The open end of multimode fiber is etched to create an arc shaped cavity, with a microsphere glued at its bottom. When the arc of the cavity bottom and microsphere surface is tangent, part of the incident light is coupled into the microsphere and travels exactly one circle before being directed back to the multimode fiber core along the tangent line and exciting whispering-gallery-mode. The device has a Q-factor of 1.21×〖10〗^4, is robust in structure and of low cost.

In-situ surface-enhanced Raman scattering sensing with soft and flexible polymer optical fiber probes

Jingjing Guo, Yuqing Luo, Changxi Yang, and Lingjie Kong

Doc ID: 341221 Received 31 Jul 2018; Accepted 09 Oct 2018; Posted 12 Oct 2018  View: PDF

Abstract: Surface enhanced Raman scattering (SERS) fiber sensors have shown great potential in sensitive biosensing and medical diagnostics. However, current SERS fiber probes are most commonly based on stiff silica fibers, which unfortunately are not mechanically compliant with soft biological tissues. In addition, the poor biocompatibility of the silica fibers sets another barrier that hindered their developments for biomedical applications. Here, we present the first demonstration of soft polymer optical fibers based SERS (SPOF-SERS) probes with physio-mechanical properties suitable for implantation, and demonstrate their potential applications for in-situ detection of bioanalysts. The SPOFs are made from porous hydrogel materials that are soft, elastic and biocompatible. The three-dimensional porous structures of the hydrogels enable high loading of metal nanoparticles to provide a large amount of SERS “hot spots” for high sensitivity. We tested the SPOF-SERS sensor for detection and discrimination of Rhodamine 6G and 4-mercaptopyridine in situ with the detection limit of 10-7 M and 10-8 M, respectively. We also demonstrated the capability of the SPOF-SERS probes in multiplexing detection. The soft, biocompatible and highly sensitive SERS probe is promising for bioanalytical and implantable biomedical applications.

Thermal Coupling Impact on MMW Carrier Generated using Two Free Running DFB Lasers on Glass

NISRINE ARAB, Lionel Bastard, Julien Poette, Jean-Emmanuel Broquin, and Beatrice Cabon

Doc ID: 340145 Received 23 Jul 2018; Accepted 09 Oct 2018; Posted 09 Oct 2018  View: PDF

Abstract: In this letter, the impact of thermal coupling between two glass laser cavities on heterodyned signal for millimeter wave frequency generation is presented. In addition to a narrow heterodyne linewidth estimated to be lower than 1kHz, the frequency drift is reduced down to ±16.5ppm/7s. The signal quality is also evaluated by performing data transmission respecting communication standards at 60GHz using complex modulation formats.

Forward Brillouin scattering acoustic impedance sensor using thin polyimide coated fiber

Desmond Chow and Luc Thevenaz

Doc ID: 341756 Received 06 Aug 2018; Accepted 09 Oct 2018; Posted 09 Oct 2018  View: PDF

Abstract: The standard single-mode fiber has been demonstrated as opto-mechanical sensor recently to measure the acoustic impedances of surrounding liquids by means of the generation and detection of forward stimulated Brillouin scattering (FSBS). FSBS allows the mechanical properties of an external material to be probed directly through the interaction of guided light and transverse sound waves that occurs entirely inside the fiber structure. In this technique, having a low loss interface between the fiber bulk and the external medium is essential for precise measurement, however it leads to the necessary but impractical removal of the thick polymer fiber coating in most reported methods. Here, we use a commercially available 80 μm-diameter optical fiber coated with 8 μm-thickness polyimide coating layer to measure the acoustic impedances of the surrounding liquids, showing accurate measurement results while retaining the mechanical strength of the fiber.

Generation of broadband chaos with perfect time delay signature suppression by using self-phase-modulated feedback and microsphere resonator

Ning Jiang, Anke Zhao, Shiqin Liu, Chenpeng Xue, Boyang Wang, and Kun Qiu

Doc ID: 342079 Received 10 Aug 2018; Accepted 09 Oct 2018; Posted 09 Oct 2018  View: PDF

Abstract: We propose and experimentally demonstrate a broadband chaos generation scheme by introducing self-phase modulation (SPM) in the feedback loop of external-cavity semiconductor laser and propagating the chaos through a microsphere resonator (MPR). Four chaos generation cases: conventional optical feedback (COF), COF+MPR, individual SPM optical feedback (SPMOF), and the proposed SPMOF+MPR, are experimentally discussed. The experimental results demonstrate that with respect to the other three cases, in the proposed scheme with the joint effects of SPMOF and MPR, the relaxation oscillation effect in chaos can be eliminated and a flat RF spectrum with much more significant bandwidth enhancement can be achieved. Simultaneously, the time delay signature (TDS) in the chaos can be perfectly suppressed at a very low level close to 0, in a wide operation range of feedback. This work shows a novel scheme to generate broadband chaos with flat spectrum and perfect TDS suppression.

Performance enhancement of an optically-injected-semiconductor-laser-based optoelectronic oscillator by subharmonic microwave modulation

Shilong Pan, Pei Zhou, Fangzheng Zhang, and Daocheng Zhang

Doc ID: 342313 Received 14 Aug 2018; Accepted 09 Oct 2018; Posted 09 Oct 2018  View: PDF

Abstract: An approach to enhancing the performance of an optically-injected-semiconductor-laser-based optoelectronic oscillator (OEO) is proposed by subharmonic microwave modulation. In this system, a free-running OEO is first established based on period-one (P1) dynamics of an optically injected semiconductor laser. The oscillation frequency can be tuned in the range of 8.87 to 18.41 GHz by controlling the optical injection strength, but the output signal suffers from high side modes and poor frequency stability. To address these problems, subharmonic microwave modulation technique is applied to the injected semiconductor laser. In the experiment, microwave modulation with 1/2, 1/4 and 1/6 subharmonics is demonstrated. The side mode suppression ratio is improved by over 40 dB. The phase noise at 1-kHz offset is reduced by about 18 dB. Furthermore, the frequency drift in 20 minutes, which characterizes the long-term stability, is reduced from 8.7 kHz to less than 1 Hz, indicating a significant reduction of over three orders.

Single-camera, Single-shot, Time-resolved Laser-induced Incandescence Decay Imaging

Yi Chen, Emre Cenker, Daniel Richardson, Sean Kearney, Benjamin Halls, Scott Skeen, Christopher Shaddix, and Daniel Guildenbecher

Doc ID: 342531 Received 28 Aug 2018; Accepted 09 Oct 2018; Posted 09 Oct 2018  View: PDF

Abstract: Knowledge of soot particle sizes is important for understanding soot formation and heat transfer in combustion environments. Soot primary particle sizes can be estimated by measuring the decay of time-resolved laser-induced incandescence (TiRe-LII) signals. Existing methods for making planar TiRe-LII measurements require either multiple cameras or time-gate sweeping with multiple laser pulses, making these techniques difficult to apply in turbulent or unsteady combustion environments. Here we report a technique for planar soot particle sizing using a single high-sensitivity, ultra-high-speed 10 MHz camera with a 50 ns gate and no intensifier. With this method, we demonstrate measurements of background flame luminosity, prompt LII, and TiRe-LII decay signals for particle sizing in a single laser shot. The particle sizing technique is first validated in a laminar non-premixed ethylene flame. Then, the method is applied to measurements in a turbulent ethylene jet flame.

Further Emission Efficiency Improvement of a Commercial-quality Light-emitting Diode through Surface Plasmon Coupling

Chun-Han Lin, Chia-Ying Su, Yu-Feng Yao, Ming-Yen Su, Hsin-Chun Chiang, Meng-Che Tsai, Wei-Heng Liu, Charng-Gan Tu, Yean-woei Kiang, Chih-Chung Yang, Feng-Wen Huang, Chi-Ling Lee, and Ta-Cheng Hsu

Doc ID: 337912 Received 04 Jul 2018; Accepted 09 Oct 2018; Posted 15 Oct 2018  View: PDF

Abstract: It is usually believed that surface plasmon (SP) coupling is practically useful only for improving the performance of a light-emitting diode (LED) with a low intrinsic internal quantum efficiency (IQE). In this letter, we demonstrate that the performance of a commercial-quality blue LED with a high IQE (>80 %) can still be significantly improved through SP coupling based on a surface Ag nanoparticle (NP) structure. The performance improvement of such an LED is achieved by increasing the Mg doping concentration in its p-AlGaN electron blocking layer to enhance the hole injection efficiency such that the p-GaN layer thickness can be significantly reduced without sacrificing its electrical property. In this situation, the distance between surface Ag NPs and quantum wells is decreased and hence SP coupling strength is increased. By reducing the distance between the surface Ag NPs and the top quantum well to 66 nm, the IQE can be increased to almost 90 % (an ~11 % enhancement) and the electroluminescence intensity can be enhanced by ~24 %.

Sensing at terahertz frequency domain using sapphirewhispering gallery mode resonator

Cijy Mathai, Ravikumar Jain, Venu Gopal Achanta, Siddartha P. Duttagupta, Dipa Ghindani, Niraj Joshi, Richard Pinto, and Shriganesh Prabhu

Doc ID: 344629 Received 30 Aug 2018; Accepted 08 Oct 2018; Posted 09 Oct 2018  View: PDF

Abstract: In this letter, we experimentally demonstrate a terahertz(THz) whispering gallery mode (WGM) sensorbased on sapphire WGM resonator. The fundamentalmode at 129.49 GHz with a Q factor of 4.63 103 isused to study its sensitivity to adsorbed molecules. Theefficiency of our sensor to detect Rhodamine 6G dyemolecule in polyvinyl alcohol matrix at room temperaturehas been manifested and a detection sensitivityof 25 parts per million has been achieved. Also, wereport an analytical approach based on coupled modetheory between the waveguide mode and the sphericalresonator mode to evaluate the absorption coefficient ofthe adsorbed molecule on the resonator. The model ismodified to evaluate optical constants of materials. Theresults obtained have been verified by continuous waveTHz transmission results. The results are of importancein sensing, metrology and material characterization.

Diode-pumped Q-switched Alexandrite Laser in single longitudinal mode operation with Watt level output power

Alexander Munk, Michael Strotkamp, Martin Walochnik, Bernd Jungbluth, Martin Traub, Dieter Hoffmann, Reinhart Poprawe, Josef Höffner, and Franz-Josef Lübken

Doc ID: 345138 Received 06 Sep 2018; Accepted 08 Oct 2018; Posted 09 Oct 2018  View: PDF

Abstract: We present significantly improved performance data of a diode-pumped Q-switched Alexandrite laser operating in single longitudinal mode and developed as a beam source for resonance lidar systems. The average output power of the laser – operating at the potassium resonance at 770 nm with a linewidth below 10 MHz – could be increased by a factor of five to the Watt level by means of an optimized resonator design and pump scheme. The pulse energy is 1.7 mJ with a beam quality of M2 ≤ 1.1 in both spatial directions at a repetition rate of 500 Hz.

Quantitative phase imaging with increased spatial coherence based on Fourier filtering

J. Martinez-Carranza and Tomasz Kozacki

Doc ID: 337855 Received 04 Jul 2018; Accepted 08 Oct 2018; Posted 10 Oct 2018  View: PDF

Abstract: This work reports a method for tuning the degree of spatial coherence in an optical microscope. The method employs an amplitude Spatial Light Modulator (aSLM) that is placed in the Fourier plane of the microscope. The aSLM displays a set of binary filters that blocks specific frequencies of the Fourier spectrum of the complex object field. It is shown that numerical processing of these filtered fields provides a final intensity with increased spatial coherence. The coherence tuning is used in a new hybrid phase reconstruction algorithm that employs the Transport of Intensity Equation and an iterative phase retrieval technique. It is validated experimentally that this hybrid approach is able to retrieve the phase information with high resolution, and effective artifact noise suppression when employing as minimum two symmetrical defocused intensities and large sources.

Brillouin optical time-domain analysis via compressed sensing

Da-Peng Zhou, Wei Peng, Liang Chen, and Xiaoyi Bao

Doc ID: 341687 Received 07 Aug 2018; Accepted 08 Oct 2018; Posted 10 Oct 2018  View: PDF

Abstract: A compressed sensing technique based Brillouin optical time-domain analysis is proposed. Brillouin spectrum has a sparse representation in its discrete cosine transform domain, which can be successfully recovered from far fewer measurements with high probability through orthogonal matching pursuit algorithm. This work shows both empirically and experimentally that the amount of frequency acquisitions needed is only 30% of those required by a conventional distributed Brillouin fiber-optic sensing system with 1 MHz frequency increment in the acquisition process to obtain Brillouin spectra along an optical fiber; therefore, the number of acquisitions and the amount of data storage/transfer are greatly reduced. Moreover, the proposed method does not need any hardware modification in an existing sensing system, and can also be adopted by Brillouin optical time-domain reflectometry.

Ultra-broadband tunable continuous phase masks using optical aberrations

Dimitris Papazoglou and Dimitris Mansour

Doc ID: 341550 Received 03 Aug 2018; Accepted 08 Oct 2018; Posted 09 Oct 2018  View: PDF

Abstract: We show that through the use of optical aberrations, a reflective cylindrical beam expander can be properly adjusted to preform as a tunable ultra-broadband continuous phase modulation device. We demonstrate the effectiveness of such a device for the case of a net cubic phase modulation that is used to generate ultra-broadband white light 2D-Airy beams. In this case, the nature of our device enables all spectral components to co-propagate, following the same accelerating trajectory. The scalability of our approach, both in respect of input power and bandwidth, makes it possible to be used in any part of the electromagnetic spectrum.

Trapped modes with extremely high quality factor in a circular array of dielectric nanorods

Hailong Han, He Li, Haibin Lü, and Xiaoping Liu

Doc ID: 334952 Received 13 Jun 2018; Accepted 08 Oct 2018; Posted 09 Oct 2018  View: PDF

Abstract: In this paper, we investigate the formation of trapped modes with near zero group velocities in a ring chain composed of dielectric nanorods. Two kinds of bounded modes are successfully identified: the regular BCR modes formed at the band edge and importantly the quasi-BIC trapped modes (similar to the bound states in the continuum in the equivalent infinite linear chain). The lowest-order trapped mode possesses the highest Q factor, which scales exponentially with the number of nanorods N as Q~exp(0.325N) for the BCR and Q~exp(0.662N) for the quasi-BIC. Interestingly, a moderate high Q factor ~105 can be obtained for the quasi-BIC mode even with a very small N=8. This suggests that our nanorod-based ring resonator possesses a clear advantage over the linear chain for the same N. Our findings greatly expand the application scope of BIC-based phenomena.

Long distance distribution of telecom band intensity difference squeezing generated in a fiber optical parametric amplifier

Yuhong Liu, Nan Huo, Jiamin Li, and Xiaoying Li

Doc ID: 335820 Received 31 Jul 2018; Accepted 08 Oct 2018; Posted 09 Oct 2018  View: PDF

Abstract: Using an all fiber source of pulsed twin beams, with the record intensity difference squeezing of 6.1 ± 0.15 dB for fiber optical parametric amplifiers, we experimentally distribute the pulsed continuous variable quantum state over long distance. After separating the signal and idler twin beams apart by 26 km single mode fibers, the measured intensity difference noise is still below the shot noise limit by 2 dB.The result shows the distribution process is only affected by the vacuum noise originated from fiber transmission loss. Extra noise contributed by the acoustic wave Brillouin scattering and Raman scattering in 26 km transmission fiber has not been observed. The investigation is beneficial for studying long distance continuous variable quantum communication.

Gold nanostars as a Q-switcher for the mid-infrared erbium-doped fluoride fiber laser

Lingling Yang, Zhe Kang, Bin Huang, Jie Li, Lili Miao, Pinghua Tang, Chujun Zhao, Guanshi Qin, and Shuangchun Wen

Doc ID: 341888 Received 10 Aug 2018; Accepted 08 Oct 2018; Posted 12 Oct 2018  View: PDF

Abstract: We demonstrated passively Q-switched mid-infrared erbium-doped fiber lasers by using gold nanostars (GNSs) as the Q-switcher. The nonlinear optical responses of the GNSs synthesized via the seed-mediated method have been characterized via Z-scan technique, and the modulation depth and saturation intensity of the GNSs are measured to be 25% and 15.75 kW/cm², respectively. The Q-switched fiber laser can deliver a maximum average power of 454 mW with corresponding pulse energy of 3.6 μJ and pulse duration of 536 ns at a repetition rate of 125 kHz under the incident pump power 3.5 W. To the best of our knowledge, this is the first report that the GNSs can act as a Q-switcher for the mid-infrared erbium-doped ZBLAN fiber lasers. This work can deepen the understanding of the nonlinear optical behavior of the gold nanomaterials, and may make inroads for the excellent mid-infrared optoelectronic devices.

All-optical generation of magnetization with arbitrary three-dimensional orientations

Sicong Wang, Jianjun Luo, Zhu Zhu, Yao-Yu Cao, Haiwei Wang, Changsheng Xie, and Xiangping Li

Doc ID: 341678 Received 06 Aug 2018; Accepted 08 Oct 2018; Posted 15 Oct 2018  View: PDF

Abstract: In this Letter, all-optical generation of magnetization with arbitrary three-dimensional (3D) orientations is numerically demonstrated through the inverse Faraday effect (IFE) by using a reversing calculation method. The IFE-induced magnetization with an expected 3D orientation is initially conceived by coherently configuring two orthogonally arranged electric dipoles with a phase difference of π/2 in the focal region of a to-be-determined incident light field. Based on the dipole antenna theory, this required incident light field can be deduced analytically according to the orientations of the electric dipoles. By utilizing this field as illumination and reversing the field propagation, magnetization with the expected orientation can be obtained in the focal region through the IFE. Moreover, this method showcases a high magnetization orientation purity (greater than 93%) within the focal volume defined by the full width at half maximum when the numerical aperture of the focal lens is 0.95. This result demonstrates extended flexibility of magnetization manipulations in an all-optical fashion and possesses great potentials in spintronics and all-optical magnetic recording.

Discrimination of incoherent vortex states of light

Jun Chen and Yao Li

Doc ID: 346263 Received 18 Sep 2018; Accepted 08 Oct 2018; Posted 12 Oct 2018  View: PDF

Abstract: Coherence vortex (CV) states provide a new way for optical manipulation and communication. As a promising option for increasing the data-transmission capacity, CV multiplexing warrants investigation. However, few studies have focused on discriminating and sorting CV states with different topological charges. In this work, we examine the cross-spectral density (CSD) of a CV state embedded in an incoherent light field and so-called incoherent vortex (ICV). We demonstrate a mechanism to generate a multiplexed ICV and propose a method to recognize the constituting single ICVs therein. Our analytical results, which are derived according to the coherence theory and the paraxial propagation law and are given in analytical forms, show that the CSD can reveal the topological charge spectrum of a multiplexed incoherent Laguerre-Gaussian mode. This proposal can be used for free-space communication and remote sensing where light fields with low coherence are preferable to completely coherent beams.

Thermally tunable ultra-compact Fano resonator on a silicon photonic chip

Jianping Yao and Weifeng Zhang

Doc ID: 344267 Received 28 Aug 2018; Accepted 07 Oct 2018; Posted 10 Oct 2018  View: PDF

Abstract: A thermally tunable ultra-compact Fano resonator on a silicon photonic chip is reported. The Fano resonator is implemented by using an add-drop microdisk resonator (MDR) with the through and drop ports connected by two waveguides and combined via an adiabatic 2 × 2 3-dB coupler, to form a Mach-Zehnder interferometer (MZI). Thanks to the resonant mode interference between the MDR and the MZI, a Fano resonance with an asymmetric line shape is resulted. A p-type doped micro-heater is incorporated in the MDR to achieve thermal tuning. By tuning the DC voltage applied to the micro-heater, the Fano resonance is tuned. The proposed Fano resonator is designed, fabricated and characterized. Measurement results show a Fano resonance with an extinction ratio of 30.2 dB and a slope rate of 41 dB/nm is achieved. When the micro-heater is tuned by tuning the DC voltage with a power from 0 to 22.9 mW, the Fano line shape is largely tuned with the Fano parameter q tuned from negative to positive and a maximum wavelength shifting as large as 15.97 nm. Thanks to its ultra-compact configuration, and strong and fast tunability with low power consumption, the integrated Fano resonator holds a high potential for applications such as in on-chip optical switching and sensing. © 2018 Optical Society of America

Tunable size selectivity and nanoparticle immobilization on a photonic-crystal optical trap

Aravind Krishnan, Michelle Povinelli, and Shao-Hua Wu

Doc ID: 341770 Received 07 Aug 2018; Accepted 07 Oct 2018; Posted 08 Oct 2018  View: PDF

Abstract: We harness residual thermal effects in a low-absorptivity system to manipulate parallel optical trapping of particles on the nanoscale. A photonic crystal is used to generate a 2D array of optical traps. We show that the size selectivity of the trap can be tuned by adding a non-ionic surfactant to the solution, altering the thermophoretic effect that delivers nanoparticles to trapping sites. We further show that particles can be permanently immobilized on the photonic crystal via photo-polymerization of the trapping medium.

Fast Raman spectral mapping of highly fluorescing samples by time-gated spectral multiplexed detection

Christopher Corden, Dustin Shipp, Pavel Matousek, and Ioan Notingher

Doc ID: 335878 Received 11 Sep 2018; Accepted 07 Oct 2018; Posted 16 Oct 2018  View: PDF

Abstract: We present a time-gated Raman micro-spectroscopy technique suitable for fast Raman mapping of samples eliciting large laser-induced fluorescence backgrounds. To achieve the required time resolution for effective fluorescence rejection, a pico-second pulsed laser and a single photon avalanche diode were used. A module consisting of a spectrometer, digital micromirror device (DMD) and two prisms was used for high-resolution spectral filtering and multiplexing, required for a high chemical specificity and short integration times. With this instrument, we demonstrated time-gated Raman imaging of highly fluorescent samples, achieving acquisition times as short as 3 minutes for 40x40 pixels resolution images.

A general way to obtain multiple defect modes in multiple photonic quantum-well structures

Liming Zhao, Yun-Song Zhou, and Ai-Hua Wang

Doc ID: 341062 Received 30 Jul 2018; Accepted 06 Oct 2018; Posted 08 Oct 2018  View: PDF

Abstract: It is a facile method to obtain and describe the multiple interface states in a cascaded heterostructuredue to the topological robustness, as the equally important defect modes, it is also an interesting and important issue to obtain and describe the multiple defect modes.In this letter, we got a general way to generate multiple defect modes in multiple photonic quantum-well structure $[(AB)_mC]_n(AB)_m$. It is found that a laconic and unifying-expression can be used to describe the energy levels of both the interface modes and defect modes. The internal mechanism to determine the related parameters is revealed. We believe that these findings can be used to provide a direct guidance for practical application

Interferometric Spatial Frequency Modulation Imaging

Nathan Worts, Jeffrey Field, Randy Bartels, Jason Jones, Jeff Broderick, and Jeffrey Squier

Doc ID: 341508 Received 03 Aug 2018; Accepted 06 Oct 2018; Posted 08 Oct 2018  View: PDF

Abstract: Interferometric spatial frequency modulation for imaging (I-SPIFI) is demonstrated for the first time. Significantly, this imaging modality can be seamlessly combined with nonlinear SPIFI imaging and operates through single element detection, making it compatible for use in scattering specimens. Imaging dynamic processes with sub-micrometer axial resolution through long working distance optics is shown, as well as high contrast images compared to traditional wide-field microscopy images. Finally, enhanced lateral resolution is achieved in I-SPIFI. To our knowledge this is the first single platform that enables multimodal linear and nonlinear imaging, with enhanced resolution, all of which can be performed simultaneously.

Laser speckle contrast imaging of blood flow in deep brain using microendoscopy

Ming Chen, Wen Dong, songlin huang, shen gui, Zhihong Zhang, Jinling Lu, and Pengcheng Li

Doc ID: 338725 Received 13 Jul 2018; Accepted 06 Oct 2018; Posted 09 Oct 2018  View: PDF

Abstract: Dysfunctions of blood flow circulation locating in deep brain below the cortex may be involved in many brain diseases. However, the limitation of light penetration hinders detection of blood flow in deep brain tissue in vivo. Therefore, we present a gradient index (GRIN) lens based laser speckle contrast imaging system to perform time-lapse blood flow detection in deep brain. Hemodynamic changes in thalamus of the mouse models of acute hypoxia and transient middle cerebral artery occlusion (tMCAo) were conducted as validation.

Sensing performance optimization of the Bloch surface wavebiosensor based on the Bloch impedance matching method

Ji Ma, xiu-bao kang, and Zhi-Guo Wang

Doc ID: 344768 Received 04 Sep 2018; Accepted 06 Oct 2018; Posted 08 Oct 2018  View: PDF

Abstract: We propose a novel strategy to optimize the sensing performance of the Bloch surface wave biosensor. First of all, the one-dimensional photonic crystal with an omnidirectional photonic bandgap is designed. Except for sustaining the Bloch surface wave, the omnidirectional photonic bandgap guarantees a tiny full width at half maximum (FWHM=0.84 nm) for the reflection dip induced by the BSW resonance. Then, the specific dependence of wavelength sensitivity on incident angle is obtained by the Bloch impedance matching method. Study shows that the wavelength sensitivity increases with the decreases of incident angle (larger than the critical angle). At the same time, when the incident angle approaches the critical angle (θ=67.5 deg), the wavelength sensitivity increases rapidly (S_λ=1570 nm/RIU). Moreover, the theoretical research reveals that the biosensor sensitivity can also be further enhanced by the other system parameters. Combining the tiny FWHM of reflection dip and the large wavelength sensitivity, the figure of merit of the optimized biosensor can reach as high as 1869 〖RIU〗^(-1). These results enable the design of biosensors with high-performance in a predictable manner.

Photoluminescence spectra of the Mn2+ d-d multiplets transitions of zinc-blende MnTe epitaxial films: laser and deuterium lamp excitation study

Xuanting Zhu, Qin Lian, Pengzhan Zhang, Wei Bai, Kai Tang, Liangqing Zhu, Jing Yang, Yuanyuan Zhang, xiaodong tang, and Junhao Chu

Doc ID: 341866 Received 10 Aug 2018; Accepted 05 Oct 2018; Posted 09 Oct 2018  View: PDF

Abstract: The luminescences of zinc-blende MnTe epitaxial films are respectively excited by a laser and deuterium lamp to study Mn2+ d-d multiplets transitions. Besides the inclusion of the band gap, all other excited states related to Mn2+ d-d transitions including 4T1(4G), 4T2(4G), 4A1[4E(4G)], 4T2(4D), 4E(4D) and 2T2(2I) are observed. The shift and broadening of the 4T1(4G) and 4T2(4G) lines with increasing temperature are described by the electron-phonon coupling. Step-like energy and intensity shifts for the 4A1[4E(4G)], 4T2(4D), 4E(4D) and 2T2(2I) transitions occur in the vicinity of Néel point, which can be ascribed to the different spin-ordering induced energy relaxation in ground and excited states of Mn2+ d-d multiplets, and these transitions show temperature independence and weak quenching.

Widely-tunable, continuous-wave, intra-cavity optical parametric oscillator based on an Yb-doped fiber laser

Ye Li, Zhenwen Ding, Pei Liu, Guanhua Chen, and Zhaowei Zhang

Doc ID: 344765 Received 31 Aug 2018; Accepted 05 Oct 2018; Posted 10 Oct 2018  View: PDF

Abstract: We report an optical parametric oscillator (OPO) intra-cavity-pumped by an Yb-doped fiber laser. In comparison to an intra-cavity OPO based on a solid-state laser gain medium, the benefits of using a fiber-based scheme include a superior beam-quality of the generated mid-infrared idler light at high power-levels, a more efficient process of nonlinear frequency conversion, and the prospect of scaling to higher power. In a preliminary experiment, we obtained a slope-efficiency of the down-converted power of as high as 66% with respect to the absorbed LD power. To the best of our knowledge, this is the first demonstration of an intra-cavity OPO based on a fiber laser.

Highly Flexible Organic/Inorganic Hybrid Perovskite Light-Emitting Devices Based on An Ultrathin Au Electrode

Hong-Bo Sun, Yu-Shan Liu, Shuang Guo, fang-shun yi, and Jing Feng

Doc ID: 342988 Received 22 Aug 2018; Accepted 05 Oct 2018; Posted 12 Oct 2018  View: PDF

Abstract: Organic/inorganic hybrid perovskite materials have been paid much attention in light-emitting applications during the past several years. The commonly used indium tin oxide (ITO) electrodes in perovskite light-emitting devices (PeLEDs) have unavoidable drawbacks of increasing cost and incompatibility with flexible devices, which limit the development of the PeLEDs. Here, high-performance and ITO-free flexible PeLEDs utilizing an ultrathin Au electrode have been achieved and exhibit high brightness (>10000 cdm¯²). The ultrathin Au film with thickness of 7 nm exhibits an excellent surface morphology with a root-mean-square roughness value of 0.307 nm, outstanding optical properties with a transparency of 83% at the wavelength of 550 nm, and favorable conductivity with a sheet resistance of 13 Ω sq¯¹ by introducing a MoO₃/SU-8 modification layer. High mechanical robustness and flexibility have been obtained for the flexible PeLEDs by surviving 1000 bending cycles. The flexible PeLEDs reported here have exhibited tremendous potential for its commercial applications.

Broad-range self-sweeping single-frequency linearly polarized Tm-doped fiber laser

Ivan Lobach, Sergey Kablukov, Budarnykh Artem, and Anastasia Vladimirskaya

Doc ID: 344762 Received 31 Aug 2018; Accepted 05 Oct 2018; Posted 05 Oct 2018  View: PDF

Abstract: We experimentally demonstrate a linearly-polarized Tm-doped fiber laser with sweeping range up to 26 nm in the region of 1.92 µm. The main feature of the laser is generation of periodic microsecond pulses where each of them contains practically only single longitudinal mode radiation. The laser frequency changes from pulse to pulse with high linearity by one intermode beating frequency of the laser ~8 MHz. The developed source is applied to measure spectrum of water absorption lines in air.

Free-beam spectral self-compression at supercritical peak powers

Alexander Mitrofanov, Maxim Nazarov, Aleksandr Voronin, Dmitry Sidorov-Biryukov, Vladislav Panchenko, and Aleksei Zheltikov

Doc ID: 335567 Received 18 Jun 2018; Accepted 05 Oct 2018; Posted 05 Oct 2018  View: PDF

Abstract: We demonstrate free-beam spectral self-compression of ~100-GW femtosecond laser pulses due to self-phase modulation (SPM) in a transparent dielectric. While all the earlier studies of SPM-induced spectral narrowing have been performed using optical fibers, experiments and simulations presented in this paper show that this type of spectral transformation can be implemented as a part of a full three-dimensional field-waveform dynamics and can be extended to peak powers ~10^5 times higher than the critical power of self-focusing. With a properly chosen initial chirp, spectral self-compression is accompanied by pulse compression, providing spectral--temporal mode self-compression as a whole.

Experimental utilization of repeated spatial-mode shifting for achieving discrete delays in a free-space recirculating loop

Ahmed Almaiman, Zhe Zhao, Yinwen Cao, Guodong Xie, Amirhossein Mohajerin Ariaei, Fatemeh Alishahi, Peicheng Liao, Changjing Bao, Ahmad Fallahpour, Bishara Shamee, Youichi Akasaka, Shlomo Zach, Nadav Cohen, Moshe Tur, and Alan Willner

Doc ID: 342595 Received 17 Aug 2018; Accepted 05 Oct 2018; Posted 05 Oct 2018  View: PDF

Abstract: We demonstrate an optical recirculating delay loop by shifting the spatial mode order of orbital-angular-momentum (OAM) beams in the free-space. The desired delay can be selected at the loop output by exploiting the orthogonality of the OAM modes. When sending a 20-Gbaud quadrature-phase-shift-keyed (QPSK) signal through the delay system, three recirculations are demonstrated, each with an additional delay of 2.2 ns. Around 0.5 dB and 2 dB system penalties are measured for the second and third recirculations, respectively. We also simulate the performance of our approach under different scenarios.

Cavity enhanced Thomson scattering measurements of electron density and temperature in a hollow cathode discharge

Adam Friss and Azer Yalin

Doc ID: 342849 Received 21 Aug 2018; Accepted 04 Oct 2018; Posted 05 Oct 2018  View: PDF

Abstract: A cavity enhanced Thomson scattering (CETS) diagnostic has been developed to perform electron density and temperature measurements in low-density weakly-ionized discharges. The diagnostic approach is based upon generating a high-power beam in an optical build-up cavity and using the beam as a light source for Thomson scattering from a plasma housed within the cavity. In our setup, a high-power (~5 W) fiber laser at 1064 nm allows an intra-cavity power of 11.7 kW in a two-mirror cavity for measurements in the plume of a BaO hollow cathode discharge. A study of plasma density and temperature was performed at various operating conditions. Electron densities and temperatures in the range of ~10¹² cm-³ and ~3 eV were measured, respectively. Based on a SNR of 1100, the CETS technique has a lower detection limit of ~3x10⁹ cm-³ and should extend current LTS diagnostic capabilities.

Deterministic Aperiodic Photonic Crystal Nanobeam Supporting Adjustable Multiple Mode-matched Resonances

Jingxuan Wei, Fujun Sun, Bowei Dong, Yiming Ma, Yuhua Chang, Huiping Tian, and Chengkuo Lee

Doc ID: 345484 Received 10 Sep 2018; Accepted 04 Oct 2018; Posted 05 Oct 2018  View: PDF

Abstract: We investigate nanocavities in deterministic aperiodic photonic crystal (PhC) nanobeams. We reveal that even a single nanocavity can support multiple mode-matched resonances, which show almost perfect field overlap in cavity region. The unique property is enabled by the existence of adjustable multiple bandgaps in deterministic aperiodic PhC nanobeams. Our investigation may inspire related studies on low threshold lasers, integrated nonlinear devices, optical filters and on-chip sensors.

Digital hologram for data augmentation in learning-based pattern classification

Chau-Jern Cheng, KUANG-CHE CHANG CHIEN, and Yu-Chih Lin

Doc ID: 340708 Received 26 Jul 2018; Accepted 04 Oct 2018; Posted 04 Oct 2018  View: PDF

Abstract: This study proposes a novel data augmentation method based on numerical focusing of digital holography to boost the performance of learning-based pattern classification. To conduct digital holographic data augmentation (DHDA), a complex pattern diffraction approach is used to provide the least separation of confusion in the effective diffraction regime to access the full-field wavefront information of a target sample. By using DHDA, the accessible amount of labeled data is increased to complement the data manifold, and to provide various three-dimensional diffraction characteristics for improving the performance of learning-based pattern classification. Experimental results demonstrated that overall accuracy of pattern classification with DHDA (95.1%) was higher than that without DHDA (90.9%).

Three-photon light-sheet fluorescence microscopy

Adrià Escobet-Montalbán, Federico Gasparoli, Jonathan Nylk, Pengfei Liu, Zhengyi Yang, and Kishan Dholakia

Doc ID: 342675 Received 23 Aug 2018; Accepted 04 Oct 2018; Posted 08 Oct 2018  View: PDF

Abstract: We present the first demonstration of three-photon excitationlight-sheet fluorescence microscopy. Light-sheetfluorescence microscopy in single- and two-photonmodes has emerged as a powerful wide-field, lowphoto-damage technique for fast volumetric imagingof biological samples. We extend this imaging modalityto the three-photon regime enhancing its penetrationdepth. Our present study uses a standard conventionalfemtosecond pulsed laser at 1000 nm wavelengthfor the imaging of 450μm diameter cellularspheroids. In addition, we show, experimentally andthrough numerical simulations, the potential advantagesin three-photon light-sheet microscopy of usingpropagation-invariant Bessel beams in preference toGaussian beams.

Dispersion Engineering and Thermo-Optic Tuning in Mid-Infrared Photonic Crystal Slow Light Waveguides on Silicon-on-Insulator

Yiming Ma, Bowei Dong, Bo Li, Kah-Wee Ang, and Chengkuo Lee

Doc ID: 346261 Received 19 Sep 2018; Accepted 04 Oct 2018; Posted 09 Oct 2018  View: PDF

Abstract: In this paper, the design, fabrication, and characterization of slow light devices using photonic crystal waveguides (PhCWs) in the mid-infrared wavelength range of 3.9-3.98 µm are demonstrated. The PhCWs are built on the silicon-on-insulator platform without undercut to leverage its well-developed fabrication process and strong mechanical robustness. Lattice shifting and thermo-optic tuning methods are utilized to manipulate the slow light region for potential spectroscopy sensing applications. Up to 20 nm wavelength shift of the slow light band edge is demonstrated. Normalized delay-bandwidth products of 0.084-0.112 are obtained as a result of dispersion engineering. From the thermo-optic characterization results, the slow light enhancement effect of thermo-optic tuning efficiency is verified by the proportional relationship between the phase shift and the group index. This work serves as a proof-of-concept that slow light effect can strengthen light-matter interaction and thereby improve device performance in sensing and nonlinearity applications.

Dynamic Switching of a Packaged Photonic Integrated Network on Chip using an FPGA Controller

Stefano Faralli, Fabrizio Gambini, Isabella Cerutti, Odile Liboiron-Ladouceur, and Nicola Andriolli

Doc ID: 345695 Received 12 Sep 2018; Accepted 03 Oct 2018; Posted 08 Oct 2018  View: PDF

Abstract: A packaged photonic integrated network-on-chip (NoC) based on multi-microrings with a controller and scheduler implemented in FPGA is demonstrated under dynamic packet-switched traffic. Multiple transmission scenarios have been investigated, comprising up to three interfering signals at the same wavelength. The dynamic switching exhibits a power penalty of approximately 0.5 dB at a BER of 10-9. The presence of up to three interferers induces a power penalty below 1 dB.

Polarization determination based on the longitudinal field of a converging terahertz wave

SHANG JIE, Xinke Wang, wenfeng sun, Peng Han, yue yu, Shengfei Feng, Jia-Sheng Ye, and Yan Zhang

Doc ID: 344530 Received 29 Aug 2018; Accepted 03 Oct 2018; Posted 05 Oct 2018  View: PDF

Abstract: Based on coherently measuring the longitudinal field of a converging terahertz (THz) wave, a polarization determination method to the THz radiation is proposed. By utilizing the method, the arbitrary uniform polarization state of a THz field can be effectively identified in a single measurement. By using the vector diffraction integral, the principle of the method is theoretically discussed in detail. The feasibility of the method is validated experimentally by measuring a THz wire grating polarizer and a THz quarter wave plate. The method offers a powerful technical support for developing the THz polarization spectroscopy.

Temporal Localized Structures in mode-locked Vertical External-Cavity Surface-Emitting Lasers

patrice camelin, Christian Schelte, A VERSCHELDE, Arnaud Garnache, Grégoire Beaudoin, ISABELLE SAGNES, Guillaume Huyet, Julien Javaloyes, Svetlana Gurevich, and Massimo Giudici

Doc ID: 342824 Received 21 Aug 2018; Accepted 02 Oct 2018; Posted 02 Oct 2018  View: PDF

Abstract: Temporal Localized States (TLSs) are individually addressable structures traveling in optical resonators. They can be used as bit of information and to generate frequency combs with tunable spectral density. We show that a pair of specially designed nonlinear mirrors, a \textonehalf{} Vertical-Cavity Surface-Emitting Laser and a Semiconductor Saturable Absorber, coupled in self-imaging conditions, can lead to the generation of such TLSs. Our results indicate how a conventional passive mode-locking scheme can be adapted to provide a robust and simple system emitting TLSs and it paves the way towards the observation of three dimensions confined states, the so-called light bullets.

Rapid prototyping of all-polymer AWGs for FBG readout using direct laser lithography

Elke Pichler, Konrad Bethmann, Christian Kelb, and Wolfgang Schade

Doc ID: 341175 Received 01 Aug 2018; Accepted 02 Oct 2018; Posted 03 Oct 2018  View: PDF

Abstract: This letter describes the design, production and characterization of a 1x2 AWG for FBG readout, centered at 850 nm, with a channel spacing of 1 nm. The employed manufacturing process is laser direct lithography, a low cost, rapid-prototyping capable, maskless method that allows for short iteration cycles and simple migration of successful design to mask-based high throughput methods. We also consider the achievable AWG performance if used for strain or temperature measurements with FBG sensors.

An Effective Strategy for Visible-Infrared Compatible Camouflage: Surface Graphical One-dimension Photonic Crystal

Dong Qi, Fu Chen, Xian Wang, Hui Luo, Yongzhi Cheng, Xiaoyan Niu, and Rongzhou Gong

Doc ID: 342768 Received 22 Aug 2018; Accepted 02 Oct 2018; Posted 03 Oct 2018  View: PDF

Abstract: Herein, a novel design concept of surface graphical photonic crystal (SGPC) has been proposed as an effective strategy to achieve angle-insensitive visible-infrared compatible stealth. The SGPC, designed as a quasi-periodic Ge/ZnS photonic crystal following an arithmetic sequence in the physical thickness for each period, possesses a functionalized ZnS surface consisting of lithography-fabricated mosaic patterns. Our experiment data demonstrate the excellent infrared stealth capability of SGPC with a high average reflectance 92.7% (surface emissivity ε = 0.07) in 8-14 μm, and related simulations further reveal the satisfying angle-insensitive reflection characteristic with a maximum effective relative photonic bandgap δBW = 91.3% in 0° ≤ θ ≤ 60°. Besides, owing to the irregular shape design, the patterns with various etching depth form colorful digital camouflages which is of outstanding optical stealth property without distinct angle dependency (dominant wavelength shift δλd ≤ 2.33% ).

Exceptional points and quantum interference

Stefano Longhi

Doc ID: 344308 Received 27 Aug 2018; Accepted 02 Oct 2018; Posted 03 Oct 2018  View: PDF

Abstract: Exceptional points (EPs), i.e. branch point singularitiesof non-Hermitian Hamiltonians, are ubiquitous in optics. So far, the signatures of EPs have been mostly studied assuming classical light. In the passive parity-time ($\mathcal{PT}$) optical coupler, a fingerprint of EPs resulting from the coalescence of two resonance modes is a qualitative change of the photon decay law, from damped Rabi-like oscillations to transparency, as the EP is crossed by increasing the loss rate. However, when probed by non-classical states of light, quantum interference can hide EPs. Here it is shown that, under excitation with polarization-entangled two-photon states, EP phase transition is smoothed until to disappear as the effective particle statistics is changed from bosonic to fermionic.

Highly Sensitivity Fabry–Perot Interferometer Temperature Sensor Probe Based on Liquid Crystal and Vernier Effect

yongjun liu, feiru wang, Yuelan Lu, Lingli Zhang, Ji Ma, Lei Wang, and Weimin Sun

Doc ID: 341956 Received 09 Aug 2018; Accepted 02 Oct 2018; Posted 04 Oct 2018  View: PDF

Abstract: A novel high sensitivity Fabry–Perot interferometer temperature sensor based on liquid crystals (LCs) and Vernier effect is proposed and demonstrated in this paper. This sensor is prepared by inserting two cleaved single mode fibers (SMFs) into a section of a capillary tube to generate a Fabry–Perot cavity. The cavity is filled with LCs, which induces a Vernier effect due to the birefringence of LCs. The refractive indices of the ordinary and extraordinary light have different responses to the temperature changes. As a result, the temperature sensitivity is significantly improved by detecting the peak shifts of a periodic envelope. Experimental results show that the proposed sensor can provide a high-temperature sensitivity of 19.55 nm/°C. This sensor offers key features and advantages of the Fabry–Perot interferometer including low cost and good fringe visibility. Furthermore, such a sensor probe can meet different requirements of temperature sensing in various application areas by using different kinds of LCs.

All-optical tunable sub-kHz single-mode fiber laser based on a hybrid microbottle resonator

Ruilong Ma, Shixing Yuan, Song Zhu, Lei Shi, and Xinliang Zhang

Doc ID: 345569 Received 11 Sep 2018; Accepted 02 Oct 2018; Posted 04 Oct 2018  View: PDF

Abstract: We experimentally demonstrated an all-optical tunable sub-kHz single-mode fiber laser based on an ultrahigh-quality (Q)-factor hybrid microbottle resonator. The wavelength tunability is a very important function for fiber lasers, and the all-optical tuning method has rarely been proposed. Here, we use the iron-oxide-nanoparticle-coated silica microbottle resonator with a Q factor of 1.8×10^8 as the feedback element of the fiber ring laser and suppress the higher-order modes of the microresonator to achieve single-mode lasing with a linewidth of ~500 Hz and a signal-to-noise ratio of 49 dB. Iron oxide nanoparticles are coated on the tapered area of the microbottle resonator and the control light is fed through the axial direction of the microbottle. So the lasing wavelength of the fiber laser can be all-optically and linearly tuned with a range of 2.7 nm due to the strong photothermal effect of iron oxide nanoparticles. With such an excellent tunability and a narrow linewidth, this single-mode fiber laser has great potential in applications such as optical spectroscopy, sensing and signal processing.

Electroluminescence from two I-III-VI quantum dots of A-Ga-S (A=Cu, Ag)

Jong-Hoon Kim, Suk-Young Yoon, Kyung-Hye Kim, Han-Byul Lim, Hwi-Jae Kim, and Heesun Yang

Doc ID: 345226 Received 06 Sep 2018; Accepted 30 Sep 2018; Posted 04 Oct 2018  View: PDF

Abstract: Together with III–V InP, chalcopyrite I–III–VI metal chalcogenides particularly with the compositions of A–B–S (A=Cu+, Ag+, B=In3+, Ga3+) are regarded as an emerging non-Cd class for synthesis of visible-emitting colloidal quantum dots (QDs) and the following fabrication of QD-light-emitting diode (QLED). To date, the composition of I–III–VI QDs which were exploited for QLED fabrication remains highly limited, with most devices demonstrated from Cu–In–S-based ones. Herein, we explore synthesis of two Ga-based I–III–VI QDs of Ag–Ga–S (AGS) and Cu–Ga–S (CGS) QDs and their application to QLED fabrication. Using cyan AGS/ZnS and azure CGS/ZnS core/shell QDs, all-solution-processed, multilayered QLEDs with a hybrid combination of organic hole transport layer and inorganic electron transport layer are fabricated and compared. We observe that CGS QLED by far outperforms in luminance and efficiency AGS counterpart, which is ascribable to the differences in both electronic band structure and core/shell structure between two comparative QDs.

Dispersion Engineering in Unidirectional Excitation of Surface Wave of Photonic Crystal

Bing Hu, Shengnan Tian, Yizhou Yang, Songlin Zhuang, and Hanming Guo

Doc ID: 344357 Received 27 Aug 2018; Accepted 30 Sep 2018; Posted 01 Oct 2018  View: PDF

Abstract: The discovery of transverse spin angular momentum (SAM) of evanescent and guided modes presents a novel spin-orbit interaction (SOI), i.e., transverse SOI, to affect and control the intensity distribution and propagation path of light. In the present letter, we first theoretically verify the transverse SAM property of surface wave of Photonic Crystal (PhC) slab. Then, we realize the polarization-controllable unidirectional excitation of such (forward) surface wave by means of transverse SOI. Furthermore, taking advantage of dispersion engineering of PhC we design another PhC slab capable of sustaining backward surface wave, and find that compared to forward surface wave, backward surface wave is related to inverse unidirectional excitation with incident of circularly polarized beam. In other words, dispersion engineering of PhC provides another route to control excitation direction of surface modes. The combination of dispersion engineering and transverse SOI will facilitate the design of functional devices based on PhC in the field of nanophotonics and nanoplasmonics.

Improving the dynamic range of InGaAs-based THz detectors by localized beryllium doping: Up to 70 dB at 3 THz

Robert Kohlhaas, Roman Dietz, Steffen Breuer, Simon Nellen, Lars Liebermeister, Martin Schell, and Björn Globisch

Doc ID: 340463 Received 24 Jul 2018; Accepted 29 Sep 2018; Posted 01 Oct 2018  View: PDF

Abstract: In this letter, we report on photoconductive THz detectors for 1550 nm excitation based on a low-temperature-grown InGaAs/InAlAs superlattice with a localized beryllium doping profile. With this approach, we address the inherent lifetime-mobility tradeoff, which arises since trapping centers also act as scattering sites for photo-excited electrons. The localized doping of the InAlAs barrier only leads to faster electron trapping for a given mobility. As a result, we obtain THz detectors with more than 6 THz bandwidth and 70 dB dynamic range at 3 THz and 55 dB dynamic range at 4 THz. To the best of our knowledge, this is the highest dynamic range for photoconductive THz-TDS systems published so far.

Image reversal reactive immersion lithography improves the detection limit of focal molography

Andreas Frutiger, Yves Blickenstrofer, Cla Tschannen, Andreas Reichmuth, Christof Fattinger, and Janos Vörös

Doc ID: 341991 Received 04 Sep 2018; Accepted 29 Sep 2018; Posted 01 Oct 2018  View: PDF

Abstract: Focal molography is a label-free optical biosensing method that relies on a coherent pattern of binding sites for biomolecular interaction analysis. Reactive immersion lithography (RIL) is central to the patterning molographic chips but has potential for improvements. Here, we show that applying the idea of image reversal to RIL enables the fabrication of coherent binding patterns of increased quality (i.e., higher analyte efficiency). Thereby the detection limit of focal molography in biological assays can be improved.

Spatiotemporal filtering of high-order harmonics in solids

Mette Gaarde, Christopher Abadie, and Mengxi Wu

Doc ID: 342362 Received 14 Aug 2018; Accepted 28 Sep 2018; Posted 01 Oct 2018  View: PDF

Abstract: We study the macroscopic spatial and temporal properties of harmonic radiation generated by a model solid in the interaction with a intense, focused laser beam. We show that different temporal contributions to the harmonic yield can be separated in the spatial domain because they lead to radiation with different divergences, similar to what is observed in gas-phase harmonic generation. We show that applying a spatial filter in the far field results in a temporal separation of the two contributions upon refocusing, which yields spatially collimated harmonics, a spectrum with well-resolved peaks, and a sub-cycle time profile of the harmonic radiation with only one burst per half-cycle.

Flexible and rapid fabrication of silver microheaters with spatial modulated multifoci by femtosecond laser multiphoton reduction

DongDong Qian, Liang Yang, Yachao Zhang, Chen Xin, Zhijiang Hu, Kai Hu, Yulong Wang, Deng Pan, Jiawen Li, Dong Wu, Yanlei Hu, and Jiaru Chu

Doc ID: 344352 Received 28 Aug 2018; Accepted 28 Sep 2018; Posted 01 Oct 2018  View: PDF

Abstract: In this Letter, parallel writing of silver microwire (AgMW) arrays based on femtosecond laser multiphoton reduction (MPR) is realized by modulating femtosecond laser beam into multifoci pattern with a spatial light modulator (SLM). Arbitrarily distributed multifoci are generated with pre-designed holograms loaded on SLM for multiphoton reduction. The experimental parameters for desired AgMWs fabrication with multifoci are systematically investigated and optimized. On this basis, different AgMW patterns are dynamically and simultaneously fabricated by loading different holograms onto high frequency refreshed SLM in sequence. The quantity and distribution of multifoci can be controlled dynamically by SLM in the fabrication process, even the intensity of individual focus is dynamically modulated by the control of gray level of holograms. Finally, the potential application of this flexible and rapid AgMW fabrication method in microheater fabrication is demonstrated. The microheaters exhibit controllable temperature gradient after energized.

High-order harmonic generation from a solid-surface plasma by relativistic-intensity sub-100-fs mid-infrared pulses

Alexander Mitrofanov, Dmitry Sidorov-Biryukov, Mikhail Rozhko, Sergey Ryabchuk, Aleksandr Voronin, and Aleksei Zheltikov

Doc ID: 341566 Received 06 Aug 2018; Accepted 28 Sep 2018; Posted 28 Sep 2018  View: PDF

Abstract: High-order harmonic generation (HHG) in plasmas induced by ultrashort, relativistic-intensity laser pulses on solid surfaces promises an efficient source of attosecond pulses and bright x rays and opens routes toward new regimes of laser--matter interactions, laser particle acceleration, and relativistic nonlinear optics. The λ-2 scaling of the driver field intensity needed to achieve the relativistic regime of HHG with a driver of wavelength λ provides a strong motivation for short-pulse laser-plasma HHG studies in the mid-infrared. However, the generation of relativistic-intensity sub-100-fs pulses in this spectral range remains one of the greatest challenges of laser technologies. Experiments reported here aim to confront this challenge. We present the first, to the best of our knowledge, laser-plasma HHG studies using ultrashort mid-infrared relativistically intense driver pulses. In these experiments, 80-fs, 3.9-μm pulses delivered by an optical parametric chirped-pulse amplifier are focused to a beam diameter less than 20 μm to achieve a field intensity above 1017 W/cm2, thus providing relativistic values of the normalized vector potential. When focused on the surface of a solid target, such driver pulses induce a laser plasma, which radiates bright coherent high-order optical harmonics. High-order harmonics with signature plateaus in their spectra are observed in this regime with both p- and s-polarized driver fields, suggesting the relativistic mechanism of HHG as a possible interpretation.

Auto-modulation versus breathers in the nonlinear stage of modulational instability

Matteo Conforti, Gino Biondini, Stefano Trillo, and Sitai Li

Doc ID: 342934 Received 22 Aug 2018; Accepted 27 Sep 2018; Posted 28 Sep 2018  View: PDF

Abstract: The nonlinear stage of modulational instability in optical fibers induced by a wide and easily accessible class of localized perturbations is studied using the nonlinear Schrödinger equation. It is showed that the development of associated spatio-temporal patterns is strongly affected by the shape and the parameters of the perturbation.Different scenarios are presented that involve an auto-modulation developing in a characteristic wedge, possibly coexisting with breathers which lie inside or outside the wedge.

Optical event horizon based complete transformation and control of dark solitons

Zhixiang Deng, yu chen, Jun Liu, Chujun Zhao, and Dianyuan Fan

Doc ID: 338101 Received 06 Jul 2018; Accepted 27 Sep 2018; Posted 01 Oct 2018  View: PDF

Abstract: We propose a manipulation approach to vary the wave speed as well as the grayness of dark solitons under the optical event horizon arising from the interaction between a dark soliton and a probe wave. The optical event horizon effect is demonstrated, for the first time to be capable of inducing a reversible conversion between a black soliton and a gray one. This reversible soliton transformation and control process originates from the intrinsic competition between the probe-induced nonlinear phase shift and the internal phase of the dark soliton. In a cascaded system consisting of two optical event horizons, we also observe the new optical soliton tunneling phenomena where a dark soliton can be reset longitudinally purposely. The results may find applications in information cloaking such as effectively hiding the presence of intermediate fiber section to the receiver.

How anomalous is my Faraday filter?

Ilja Gerhardt

Doc ID: 345263 Received 11 Sep 2018; Accepted 26 Sep 2018; Posted 01 Oct 2018  View: PDF

Abstract: The Macaluso-Corbino effect describes the optical rotation of light in the spectral proximity to an atomic resonance. One use of this effect is narrow-band optical filtering. So-called Faraday filters utilize the difference of the two components of the refractive indices which are split by the Zeeman effect in a longitudinal magnetic field. This allows for a net rotation of a linearly polarized input beam, such that a second analyzing polarizer can be passed - far off resonant light is simply crossed out by the polarizer. Since any resonant spectrum implies anomalous dispersion on resonance these filters are often characterized as being based on this anomalous dispersion. This paper analyses to what extent the anomalous dispersion and the anomalous rotation is relevant for Faraday filters. Considering the sign of the anomalous rotation introduces a strict criterion if the filter is operated in the line-center or in the spectral wing of an atomic resonance.

Multiplexed single-shot ptychography

BING KUAN CHEN, Pavel Sidorenko, Oren Lahav, Or Peleg, and Oren Cohen

Doc ID: 346625 Received 24 Sep 2018; Accepted 26 Sep 2018; Posted 01 Oct 2018  View: PDF

Abstract: We demonstrate experimentally multiplexed single-shot ptychography. Specifically, we present a polarization-resolved single-shot ptychographic microscope, where the s- and p-polarized amplitudes and phases of a polarization-sensitive object are reconstructed from a ptychographic data recorded in a single CCD exposure. Moreover, the s- and p-polarized amplitudes and phases of the probe beam are also recovered. That is, altogether we decipher eight images from the single-shot ptychographic data. This work is an important step towards the experimental demonstration of time-resolved imaging by multiplexed ptychography.

Microwave photonic multiband filter with independently tunable passband spectral properties

Qidi Liu, Mable Fok, and Jia Ge

Doc ID: 336395 Received 27 Jun 2018; Accepted 26 Sep 2018; Posted 26 Sep 2018  View: PDF

Abstract: Multiband RF filters with independently controllable passbands are an essential component in dynamic multiband RF communications. Unfortunately, even a fixed multiband RF filter without the capability to adjust the passband properties individually is very difficult to achieve using either RF electronics or microwave photonic technologies. In microwave photonic approaches, the critical limitation is the close relationship between passbands – the tuning of one passband will lead to a change in another, hindering the ability to independently control each passband. In this article, a programmable microwave photonic multiband filter with full control of amplitude, frequency, bandwidth, group delay slope, and spectral shape of each passband has been experimentally demonstrated. A multiband filter design algorithm has also been developed, which considers each RF passband as an individual, then uses inverse Fourier transform and filter design rule to determine the corresponding optical parameters, and combines a series of shaped cosine functions to achieve the desired RF properties.

An optical method to extract the reduced scattering coefficient from tissue: theory and experiments

Dror Fixler, Inbar Yariv, and Hamootal Duadi

Doc ID: 335532 Received 18 Jun 2018; Accepted 24 Sep 2018; Posted 01 Oct 2018  View: PDF

Abstract: Tissues are considered challenging in terms of structure and composition analysis due to their tendency to multiple scatter the incident light. One of the most common theories for extracting optical properties in tissue is diffusion reflection (DR). This paper presents the relation between the tissue reduced scattering coefficient and the reflected light phase. The technique is a modified DR theory, where the phase is calculated by the product of the wavenumber and the effective pathlength. This theory is supported by the reconstructed phase of tissue-like phantom experiments using an iterative algorithm.

Slice-illuminated optical projection tomography

Samuel Davis, Laura Wisniewski, Sunil Kumar, Teresa Correia, Simon Arridge, Paul Frankel, James McGinty, and Paul French

Doc ID: 343033 Received 23 Aug 2018; Accepted 24 Sep 2018; Posted 01 Oct 2018  View: PDF

Abstract: To improve the imaging performance of optical projection tomography (OPT) in live samples, we have explored a parallelized implementation of semi-confocal line illumination and detection to discriminate against scattered photons. Slice-illuminated OPT (sl-OPT) improves reconstruction quality in scattering samples by reducing interpixel crosstalk at the cost of increased acquisition time. For in vivo imaging, this can be ameliorated through the use of compressed sensing on angularly undersampled OPT data sets. Here we demonstrate sl-OPT applied to 3D imaging of bead phantoms and live adult zebrafish.

Normal-dispersion fiber optical parametric chirped-pulse amplification

Walter Fu and Frank Wise

Doc ID: 337816 Received 24 Jul 2018; Accepted 22 Sep 2018; Posted 24 Sep 2018  View: PDF

Abstract: We demonstrate a fiber optical parametric chirped-pulse amplifier pumped in the normally-dispersive regime. This approach is readily scalable, offering a route to microjoule-level, femtosecond pulses at new wavelengths. As a first demonstration, by pumping with broadband, stretched pulses at 1.03 μm and seeding with a continuous-wave beam at 0.85 μm, we are able to generate femtosecond-scale idler pulses at 1.3 μm with durations as short as 210 fs or energies as high as 180 nJ.

3D Stimulation and Imaging-based Functional Optical Microscopy (SIFOM) of Biological Cells

Xiangyu Quan, Manoj Kumar, Osamu Matoba, Yasuhiro Awatsuji, Yoshio Hayasaki, Satoshi Hasegawa, and Hiroaki Wake

Doc ID: 341699 Received 08 Aug 2018; Accepted 19 Sep 2018; Posted 24 Sep 2018  View: PDF

Abstract: A new type of functional optical microscope system called three-dimensional (3D) stimulation and imaging-based functional optical microscopy (SIFOM) is proposed. SIFOM can precisely stimulate user-defined targeted biological cells and can simultaneously record the volumetric fluorescence distribution in a single acquisition. Precise and simultaneous stimulation of fluorescent-labeled biological cells is achieved by multiple 3D spots generated by digital holograms displayed on a phase-mode spatial light modulator. Single-shot 3D acquisition of the fluorescence distribution is accomplished by common-path off-axis incoherent digital holographic microscopy in which a diffraction grating with a focusing lens is displayed on another phase-mode spatial light modulator. The effectiveness of the proposed functional microscope system was verified in experiments using fluorescent microbeads and human lung cancer cells located at various defocused positions. The system can be used for manipulating the states of cells in optogenetics.

High resolution air-clad imaging fibers

Harry Wood, Kerrianne Harrington, Tim Birks, Jonathan Knight, and James Stone

Doc ID: 335944 Received 25 Jun 2018; Accepted 15 Sep 2018; Posted 17 Sep 2018  View: PDF

Abstract: We present a coherent fiber bundle comprising over 11,000 doped silica cores separated by an air-filled cladding. The fiber is characterized and its imaging quality is shown to be a substantial improvement over the commercial state of the art, with comparable resolution over an unparalleled spectral range.

Dielectric Properties of Conductively LoadedPolyimides in the Far Infrared

Kyle Helson, Edward Wollack, Karwan Rostem, Kevin Miller, and Manuel Quijada

Doc ID: 337884 Received 05 Jul 2018; Accepted 30 Aug 2018; Posted 30 Aug 2018  View: PDF

Abstract: The dielectric properties of selected conductively loadedpolyimide samples are characterized in microwavethrough far infrared wavebands. These materials,belonging to the Vespel® family, are more readilyformed by direct machining than their ceramicloaded epoxy counterparts and present an interestingsolution for realizing absorptive optical control structures.Measurements spanning a spectral range from 1to 600 cm¯¹ (0.03 to 18 THz) were preformed and usedin parametrization of the media’s dielectric function atfrequencies below ~3 THz.

InGaN/GaN microdisks enabled by nanoporous GaN cladding

Ge Yuan, Cheng Zhang, Kanglin Xiong, and Jung Han

Doc ID: 336213 Received 17 Jul 2018; Accepted 07 Aug 2018; Posted 19 Oct 2018  View: PDF

Abstract: The fabrication of nanoporous (NP) GaN is proposed as a generic technique to create out-of-plane index guiding for nitride microcavities. Compared to conventional undercut technique, the proposed technique forms uniformly a low index NP-GaN layer beneath the entire microcavity. It therefore supports all cavity modes (with different cavity geometries) while the undercut technique only supports the modes that reside at the circumference of a circular microcavity. As a proof of concept, GaN microdisk cavities were fabricated with the NP-GaN as the bottom low index medium. Cold cavity with Q > 2,000 was reported under continuous wave pumping. Lasing was demonstrated with threshold optical pumping power Pth ~ 60 kW/cm2 for the r = 10 µm microdisk and Pth ~ 7 kW/cm2 for r = 50 µm microdisk. Rate equation analysis was performed to estimate the spontaneous coupling factor β ~ 1E-3, which was one order of magnitude higher than the previous report of nitride microdisk laser with InGaN quantum well active region. NP GaN was therefore proven to be a suitable replacement of the undercut technique for future nitride microcavities applications.

Photonics in highly dispersive media: The exact modal expansion

Frederic Zolla, Andre Nicolet, and Guillaume Demesy

Doc ID: 338174 Received 09 Jul 2018; Accepted 28 Jul 2018; Posted 30 Jul 2018  View: PDF

Abstract: We present exact modal expansions for photonic systems including highly dispersive media. The formulas, based on a simple version of the Keldysh theorem, are very general since both permeability and permittivity can be dispersive, anisotropic, and even possibly non reciprocal. A simple dispersive test case where both plasmonic and geometrical resonances strongly interact exemplifies the numerical efficiency of our approach.

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