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Multi-point fiber-optic laser-ultrasound generation along a fiber based on core-offset splicing fibers

Xiaolong Dong, Shimin Gao, Jiajun Tian, and Yong Yao

Doc ID: 292588 Received 13 Apr 2017; Accepted 16 May 2017; Posted 17 May 2017  View: PDF

Abstract: Fiber-optic laser-ultrasound generation is being used in an increasing number of applications, including medical diagnosis, material characterization, and structural health monitoring. However, most currently used fiber-optic ultrasonic transducers allow effective ultrasound generation at only a single location, i.e., at the fiber tip, although there have been a few limited proposals for achieving multi-point ultrasound generation along a fiber. Here we present a novel fiber-optic ultrasound transducer that uses the core-offset splicing of fibers to effectively generate ultrasound at multiple locations along the fiber. The proposed laser-ultrasonic transducer can produce a balanced-strength signal between each ultrasonic generation point by reasonably controlling the offsets of the fibers. The proposed transducer has other outstanding characteristics, including high photoacoustic conversion efficiency, and is simple and inexpensive to fabricate.

Stable single-mode operation of distributed feedback quantum cascade laser integrated with distributed Bragg reflector

fengmin cheng, Zhiwei Jia, jinchuan zhang, Ning Zhuo, Shenqiang Zhai, lijun wang, Junqi Liu, Shuman Liu, Liu Fengqi, and Zhanguo Wang

Doc ID: 290896 Received 21 Mar 2017; Accepted 15 May 2017; Posted 17 May 2017  View: PDF

Abstract: We report a novel index-coupled distributed feedback (DFB) quantum cascade laser (QCL) by employing an equivalent phase shift (EPS) of quarter-wave (λ/4) integrated with distributed Bragg reflector (DBR) at λ ~ 5.03 μm. The EPS is fabricated through extending one sampling period by 50% in the center of a sampled Bragg grating. The key EPS and DBR pattern are fabricated by conventional holographic exposure combined with the optical photolithography technology, which lead to improved flexibility, repeatability, and cost-effectiveness. Stable single-mode emission can be obtained by changing the injection current or heat sink temperature even under the condition of large driving pulse width.

A fiber laser with random-access pulse train profiling for a photoinjector driver

Konstantin Yushkov, Ekaterina Gacheva, Anatoly Poteomkin, Sergey Mironov, Victor Zelenogorsky, Efim Khazanov, Vladimir Molchanov, and Alexander Chizhikov

Doc ID: 286501 Received 24 Feb 2017; Accepted 07 May 2017; Posted 09 May 2017  View: PDF

Abstract: We report design and performance of a fiber laser system with adaptive acousto-optic macropulse control for a novel photocathode laser driver with 3D ellipsoidal pulse shaping. The laser system incorporates a three-stage fiber amplifier with an integrated acousto-optical modulator. A digital electronic control system combines the functions of the arbitrary pulse selection and envelope correction of the macropulse with feedback. As a benefit, a narrow temporal transparency window of the modulator comparably to laser pulse repetition period provides effective laser noise suppression. In experiments, we demonstrated rectangular profiling of laser pulse train at the output of a three-cascade ytterbium fiber amplifier with stability of intensity better than 10%.

Characterization of geometry and depleting carrier dependence of active silicon waveguide in tailoring optical properties

Md. Rezwanul Haque Khandokar, Masuduzzaman Bakaul, Md Asaduzzaman, Efstratios Skafidas, and Ampalavanapilla Nirmalathas

Doc ID: 281253 Received 05 Jan 2017; Accepted 06 May 2017; Posted 09 May 2017  View: PDF

Abstract: Changes in refractive index and the corresponding changes in the characteristics of an optical waveguide in enabling propagation of light are the basis for many modern silicon photonic devices. Optical properties of these active nano-scale waveguides are sensitive to the little changes in geometry, external injection/ biasing and doping profiles, and can be crucial in the design and manufacturing processes. This paper brings the active silicon waveguide for a complete characterization of various distinctive guiding parameters including perturbation in real and imaginary refractive index, mode loss, group velocity dispersion, and bending loss that can be instrumental in developing optimal design specifications for various application centric active silicon waveguides.

Amplification assisted different frequency generation for efficient mid-infrared conversion based on monolithic tandem lithium niobate superlattice

Tao Chen, Hao Liu, Wei Kong, and Shu Rong

Doc ID: 286845 Received 15 Feb 2017; Accepted 05 May 2017; Posted 09 May 2017  View: PDF

Abstract: We report the investigation on the performance of an amplification assisted difference frequency generation (AA-DFG) system driven by pulsed pump and continuous-wave primary signal lasers. A monolithic tandem lithium (LN) niobate superlattice was employed as the nonlinear crystal with a uniform grating section for the DFG process followed by a chirp section for the OPA process, respectively. The impacts of pump pulse shape, primary signal power, input beam diameter and crystal structure on the pump-to-idler conversion efficiency of the AA-DFG system were comprehensively studied by numerically solving the coupled wave equations. It is concluded that square pump pulse and high primary power are beneficial to high pump-to-idler conversion efficiency. Besides, tighter input beam focus and smaller DFG’s length proportion could redeem the reduction of conversion efficiency resulted from wider acceptance bandwidths for the input lasers. To the best of our knowledge, this is the first numerical investigation on the performance of tandem LN superlattice based AA-DFG systems with certain input acceptance bandwidths under shaped pulse pumping

Numerical investigations of an optical switch based on silicon stripe waveguide embedded with vanadium dioxide layers

Lei Chen, Han Ye, Yumin Liu, dong wu, Rui Ma, and Zhongyuan Yu

Doc ID: 288086 Received 06 Mar 2017; Accepted 04 May 2017; Posted 04 May 2017  View: PDF

Abstract: We propose a novel scheme for the optical switch based on a standard silicon (Si) photonic stripe waveguide inserted with a section of hyperbolic metamaterial (HMM) consisting of 20-pair alternating vanadium dioxide (VO2)/Si thin layers. Finite-element-method simulation results show that with the help of a HMM with size of 400nm × 220nm × 200nm (width × height × length), the ON/OFF switching for fundamental TE mode propagation in Si waveguide can be characterized by modulation depth (MD) of 5.6dB and insertion loss (IL) of 1.25dB. It also allows for a relatively wide operating bandwidth of 215nm maintaining MD > 5dB and IL< 1.25dB. Furthermore, we discuss that the tungsten-doped VO2 layers could be useful for reducing metal-insulator-transition temperature and thus promoting switching performance. In general, our findings may provide some useful ideas for optical switch design and application in on-chip all-optical communication system with demanding integration level.

Exploiting a metal wire grating in total internal reflection geometry to achieve achromatic polarisation conversion

Xudong Liu, Xuequan Chen, Edward Parrott, and Emma Pickwell-MacPherson

Doc ID: 290680 Received 16 Mar 2017; Accepted 04 May 2017; Posted 04 May 2017  View: PDF

Abstract: We demonstrate how a metal wire grating can work as a 45° polarization converter, a quarter wave retarder and a half wave retarder over a broadband terahertz range when set up in total internal reflection geometry. Classical electromagnetic theory is applied to understand the mechanism and equations to calculate the polarization state of reflected light are derived. We use a metal grating with period of 20 µm and width of 10 µm on fused silica surface: linearly-polarized terahertz light incident from fused silica with supercritical incident angle of 52° is totally reflected by the metal grating and air. The polarization of the terahertz light is rotated by 45°, 90° and circularly-polarized by simply rotating the wire grating. The performance is achromatic over the measured range of 0.1-0.7 THz and comparable to commercial visible light wave retarders.

Two-color Laser Diode for 54-Gbit/s Fiber-wired and 16-Gbit/s MMW Wireless OFDM Transmissions

Chung-Yu Lin, Yu-Chieh Chi, Cheng-Ting Tsai, Hsiang-Yu Chen, and Gong-Ru Lin

Doc ID: 286701 Received 15 Feb 2017; Accepted 02 May 2017; Posted 04 May 2017  View: PDF

Abstract: A two-color laser diode based full-duplex fiber-wired and MMW-wireless OFDM transmission link is performed. With the modal control on the two-color laser diode, a single-wavelength optical carrier is used as down- and up-stream transmitters to replace the dual-mode one for optical baseband, which effectively suppresses the chromatic dispersion occurred in single-mode fiber (SMF). The proposed system demonstrates a carrier-reused full-duplex 28-GHz MMW dense wavelength division multiplexing passive optical network (DWDM-PON) system, providing OFDM transmission with 54-Gbit/s down-stream, 36-Gbit/s up-stream and 16-Gbit/s wireless data rates. The single-wavelength optical carrier transmits data from optical line terminal (OLT) to remote node (RN) and then transfers into a dual-wavelength carrier for optically heterodyne beating a MMW carrier, which further wireless transmits the data to optical network unit (OUN). In addition, the up-stream data is carried by another slave colorless laser diode injection-locked by reusing the down-stream carrier without the need of data-erasing, which avoids the wavelength selection problem occurred from identifying or addressing up- and down-stream channels. Among three laser transmitters with different cavity lengths, the 600-μm long one embedded MMW wireless carrier can provide the lowest BER after 25-km SMF and 1.6-m free-space transmissions at 16 Gbit/s, because its highest external quantum efficiency supports the optimization on self-heterodyne transferring the MMW carrier to enable the low-noise and long-distance wireless transmission.

Efficient separating orbital angular momentum mode with radial varying phase

cheng li and Shengmei Zhao

Doc ID: 284360 Received 09 Jan 2017; Accepted 30 Apr 2017; Posted 04 May 2017  View: PDF

Abstract: It is shown that orbital angular momentum (OAM) is a new promising resource in future classical and quantum communications. However,the separation of OAM modes is a still big challenge. In this paper, we propose a simple and efficient separation method with a radial varying phase.In the method, specific radial varying phases are designed and modulated for different OAM modes.%Then, the OAM modes beams are superposed and propagated in the optical free space channel.The resultant beam is focused to the spots with different horizontal and vertical positions after a convex lens,when the coordinate transformation, including two optical elements with coordinatetransformation phase and correct phase, operates on the received beam.The horizontal position of the spot is determined by the vortex phases, and the vertical position of the spot is depended on the radial varying phases.The simulation and experimental results show that the proposed method is feasible both for two OAM modes separation and three OAM modes separation.The proposed separation method is available in principle for any neighboring OAM modes because the radial varying phase is controlled. Additionally,there is no extra instruments are introduced, and there is no diffraction and narrowing process limitation for the separation.

Fabrication and Near-infrared Optical Responses of 2D Periodical Au/ITO Nanocomposite Arrays

Long Zhang, Zhengyuan Bai, Guiju Tao, Yuanxin Li, Jin He, Kangpeng Wang, Gaozhong Wang, Xiongwei Jiang, Werner Blau, and Jun Wang

Doc ID: 290311 Received 08 Mar 2017; Accepted 29 Apr 2017; Posted 04 May 2017  View: PDF

Abstract: Two dimensional periodical Au and indium tin oxide (ITO) nanocomposite arrays have been fabricated based on a self-assembled nanosphere lithography technique. The button-shaped Au nanoparticle was formed on each hollow hemisphere-shaped ITO shell. Importantly, the underlying formation mechanism during the thermal treatment has been thoroughly discussed through comparing the structure resulted from different deposition conditions in detail. Compared to the Au nanoparticle arrays without ITO shells, the Au/ITO nanocomposite arrays showed a stronger localized surface plasmon resonance effect and higher absorption in near-infrared region, benefiting from the free-electron interaction enhancement between Au and ITO. The nonlinear optical properties were investigated by a modified femtosecond intensity-scan system, and the results demonstrated Au/ITO nanocomposite arrays with a remarkable two-photon absorption saturation effect for femtosecond pulses at 1030 nm. The versatile near-infrared optical responses imply the great potential of the elaborately prepared two dimensional periodical Au/ITO nanocomposite arrays in many applications such as solar cell, photocatalysis and novel nano optoelectronic devices.

Polarization-maintaining few mode fiber composed of a central circular-hole and an elliptical-ring core

Jiajia Zhao, Ming Tang, Kyunghwan Oh, Zhenhua Feng, Can Zhao, Liao Ruolin, Songnian Fu, Perry Ping Shum, and Deming Liu

Doc ID: 290365 Received 09 Mar 2017; Accepted 20 Apr 2017; Posted 26 Apr 2017  View: PDF

Abstract: We propose a novel waveguide design of polarization-maintaining few mode fiber (PM-FMF) supporting ≥10 non-degenerate modes, utilizing a central circular air hole, and a circumjacent elliptical ring core. The structure endows a new degree of freedom to adjust the birefringence of all the guided modes including the fundamental polarization mode. Numerical simulations demonstrate that by optimizing the air-hole and elliptical ring core, a PM-FMF supporting 10 distinctive polarization modes has been achieved, and the effective index difference Δneff between the adjacent guided modes could be kept larger than 1.32 × 10-4 over the whole C+L band. The proposed fiber structure can flexibly tailored to support even larger number of modes in PM-FMF (14-mode PM-FMF has been demonstrated as an example), which can be readily applicable to a scalable mode division multiplexing system.

A fiber laser for on-demand modes in 1550 nm band

Chenghui Tian, Song Yu, Shanyong Cai, Mingying Lan, and Wanyi Gu

Doc ID: 283714 Received 28 Dec 2016; Accepted 18 Apr 2017; Posted 26 Apr 2017  View: PDF

Abstract: Transverse mode characteristics of laser is related to many interesting applications. The on-demand mode solid laser is proposed in 1064 nm band. In this article, we provide a fiber laser for on-demand modes in 1550nm band to prescribe the pure and high quality emission of higher-order transverse laser mode, based on a simple construction with one space light modulator (SLM) and single-mode Erbium-Doped Fiber (SM-EDF). The SLM is designated to generate the desired higher-order mode and separate the higher-order mode and the fundamental mode. The fundamental mode is oscillated in the fiber ring laser, and therefore the SM-EDF can be pumped with single-mode 980 nm laser, no matter what the higher-order mode is prescribed. In the proof-of-principle experiment, high quality higher-order modes are observed from LP01 to LP105. The stable emission and real-time switching between modes can be easily realized by altering the phase on SLM. The propagation of LP01, LP11, LP21 and LP02 modes from the fiber laser is also demonstrated in a 4-modes few mode fiber (FMF).

Effects of Gain Non-linearities in an Optically-Injected Gain Lever Semiconductor Laser

Jean-Maxime SARRAUTE, kevin Shires, Sophie LaRochelle, and Frederic Grillot

Doc ID: 286300 Received 08 Feb 2017; Accepted 15 Apr 2017; Posted 26 Apr 2017  View: PDF

Abstract: The effects of gain compression on the modulation dynamics of an optically-injected gain lever semiconductor laser are studied. Calculations unveil that the gain compression is not necessarily a drawback affecting the laser dynamics. With a practical injection strength, a high gain lever effect and a moderate compression value allow totheoretically predict a modulation bandwidth as high as 85 GHz, which is of paramount importance for the development of directly-modulated broadband optical sources compatiblewith short reach communication links.

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