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https://www.readbyqxmd.com/read/30499956/dynamic-mode-switchable-optical-vortex-beams-using-acousto-optic-mode-converter
#1
Jiafeng Lu, Linghao Meng, Fan Shi, Xiaomin Liu, Zhengqian Luo, Peiguang Yan, Liangjin Huang, Fufei Pang, Tingyun Wang, Xianglong Zeng, Pu Zhou
We propose a dynamic scheme to realize mode-switchable generation of LP11a/b modes and ±1-order orbital angular momentum (OAM) modes simultaneously, which are induced by an acoustically induced fiber grating driven by radio frequency modulation. LP11a/b mode degeneration in a few-mode fiber is induced by the geometric irregularity of optical fibers. A dual-wavelength resonance of mode coupling from LP01 to LP11a/b modes is found based on the combined effects of optical and acoustic birefringence. Within the configuration of continuous-wave intra-cavity laser output, we experimentally demonstrate a fast-switchable generation of LP11a/b modes and optical vortex beams with ±1-order OAM at a switching speed up to 4...
December 1, 2018: Optics Letters
https://www.readbyqxmd.com/read/30470001/performance-of-mode-diversity-reception-of-a-polarization-division-multiplexed-signal-for-free-space-optical-communication-under-atmospheric-turbulence
#2
Manabu Arikawa, Toshiharu Ito
We investigated the performance of mode diversity reception of a polarization-division-multiplexed (PDM) signal with few-mode-fiber (FMF) coupling for high-speed free-space optical communications under atmospheric turbulence. Optical propagation through eigenmodes of a FMF yields coupling between different linearly polarized (LP) modes in orthogonal polarizations, which causes power imbalance and loss of the orthogonality of multiplexed signals within each individual LP mode. Due to this phenomenon, the architecture of mode diversity combining affects the receiver performance...
October 29, 2018: Optics Express
https://www.readbyqxmd.com/read/30469672/few-mode-fiber-true-time-delay-lines-for-distributed-radiofrequency-signal-processing
#3
Rubén Guillem, Sergi García, Javier Madrigal, David Barrera, Ivana Gasulla
We report, for the first time to our knowledge, distributed radiofrequency signal processing built upon true time delay operation on a step-index few-mode fiber. Two 3-sample configurations with different time delay properties are implemented over the same 60-meter 4-LP-mode fiber link. The inscription of a long period grating at a specific fiber position converts part of the LP01 mode into the LP02 , permitting sample time delay engineering. Delay line performance is experimentally demonstrated when applied to radiofrequency signal filtering, example of fiber-distributed processing functionality exhibiting one order or magnitude gain in terms of compactness...
October 1, 2018: Optics Express
https://www.readbyqxmd.com/read/30469642/distributed-acoustic-sensor-based-on-a-two-mode-fiber
#4
Mengmeng Chen, Ali Masoudi, Francesca Parmigiani, Gilberto Brambilla
A distributed optical fiber dynamic strain sensor also known as a distributed acoustic sensor (DAS) based on two-mode fiber is demonstrated. By using φ-OTDR interrogation technique, the backscattered light from higher order modes can be used to fully quantify vibrations along the sensing fiber. In addition, by combining the results obtained from different modes, 2.52dB improvement in noise floor is achieved. These results confirm that few-mode fibers can be used for DAS applications.
September 17, 2018: Optics Express
https://www.readbyqxmd.com/read/30469617/dynamic-characteristics-of-stimulated-raman-scattering-in-high-power-fiber-amplifiers-in-the-presence-of-mode-instabilities
#5
Rumao Tao, Hu Xiao, Hanwei Zhang, Jinyong Leng, Xiaolin Wang, Pu Zhou, Xiaojun Xu
Impact of mode instability on dynamic characteristics of stimulated Raman scattering in high power fiber amplifiers has been studied for the first time, which reveals another characterization of mode instability from the aspect of optical spectrum. It shows that, after the onset of mode instability, the measured light spectrums, especially the Raman light spectrums, are different from those without mode instability, which become burr-like. As mode instability evolves into different stages, the intensity of stimulated Raman scattering effects as laser power increasing also behaves differently...
September 17, 2018: Optics Express
https://www.readbyqxmd.com/read/30462019/coupling-ultrafast-laser-pulses-into-few-mode-optical-fibers-a-numerical-study-of-the-spatiotemporal-field-coupling-efficiency
#6
Zhe Guang, Yani Zhang
Few-mode optical fibers have been widely used in applications such as data transmission and laser amplification. The coupling of laser beams into such fibers is important because it determines the fiber mode contents, which influence the beam quality, laser amplification efficiency, and appropriate distortion control methods. Ultrafast lasers, as a widely used type of laser source for intense-field applications, can generate pulses with broad spectra and varying phases, adding complexity to the fiber mode coupling problem...
November 20, 2018: Applied Optics
https://www.readbyqxmd.com/read/30461876/simultaneous-measurement-of-mode-dependent-loss-and-mode-coupling-in-few-mode-fibers-by-analyzing-the-rayleigh-backscattering-amplitudes
#7
Feng Liu, Guijun Hu, Congcong Song, Weicheng Chen, Cuiguang Chen, Jiake Chen
In this paper, we propose and experimentally demonstrate a nondestructive method for simultaneously measuring the mode-dependent loss (MDL) and mode coupling (MC) in few-mode fibers (FMFs). The method is based on analyzing the Rayleigh backscattering amplitudes obtained with an optical time domain reflectometer (OTDR). The experimental results show that, in about 4 km six-mode FMF, the MDL and MC values are 0.132 dB and -23.13  dB/km between LP01 and LP11a , 0.176 dB and -23.73  dB/km between LP01 and LP11b , 0...
October 20, 2018: Applied Optics
https://www.readbyqxmd.com/read/30417035/highly-parallel-interferometric-diffusing-wave-spectroscopy-for-monitoring-cerebral-blood-flow-dynamics
#8
Wenjun Zhou, Oybek Kholiqov, Shau Poh Chong, Vivek J Srinivasan
Light-scattering methods are widely used in soft matter physics and biomedical optics to probe dynamics in turbid media, such as diffusion in colloids or blood flow in biological tissue. These methods typically rely on fluctuations of coherent light intensity, and therefore cannot accommodate more than a few modes per detector. This limitation has hindered efforts to measure deep tissue blood flow with high speed, since weak diffuse light fluxes, together with low single-mode fiber throughput, result in low photon count rates...
2018: Optica
https://www.readbyqxmd.com/read/30411714/few-layer-bismuthene-for-femtosecond-soliton-molecules-generation-in-er-doped-fiber-laser
#9
Chong Wang, Lu Wang, Xiaohui Li, Wenfeng Luo, Tianci Feng, Ying Zhang, Penglai Guo, Yanqi Ge
Bismuthene, a mono-elemental two-dimensional material with a novel kind of few-layer structure purely consisting of bismuth, has been predicted to have a prominent optical response and enhanced stability in theory. In this paper, few-layer bismuthene is employed as the saturable absorber. The mode-locker is fabricated by dropping bismuthene on a microfiber in a passively mode-locked, Er-doped fiber laser. The single pulse can be obtained at 122.1 mW, with 621.5 fs pulse duration at 1557.5 nm central wavelength, 10...
January 11, 2019: Nanotechnology
https://www.readbyqxmd.com/read/30325397/2d-bismuthene-fabricated-via-acid-intercalated-exfoliation-showing-strong-nonlinear-near-infrared-responses-for-mode-locking-lasers
#10
Qi-Qi Yang, Rui-Tong Liu, Chao Huang, Yi-Fan Huang, Lin-Feng Gao, Bing Sun, Zhi-Peng Huang, Lei Zhang, Chen-Xia Hu, Ze-Qi Zhang, Chun-Lin Sun, Qiang Wang, Yu-Long Tang, Hao-Li Zhang
The rediscovery of black phosphorus (BP) has expanded the 2D family into Group 15 (Nitrogen Group) elements, among which bismuthene is the latest member with extraordinary opto-electronic, catalytic and biocompatible properties and potential as a 2D topological insulator. However, bulk Bi is not easily mechanically exfoliated as its counterpart of BP. Thus, to date, the reports on 2D Bi fabrication are rare, and investigations on its nonlinear optical properties are even less. Herein, we rationally designed a new strategy combining acid-interaction and liquid exfoliation to successfully transform metal bulk Bi into few-layer semiconductor, which resulted in unseen opto-electronic properties, such as tunable nonlinear responses all the way to the near-infrared (NIR) region...
December 7, 2018: Nanoscale
https://www.readbyqxmd.com/read/30272737/theory-of-thermo-optic-instabilities-in-dual-core-fiber-amplifiers
#11
Jesper Lægsgaard, Federica Poli, Annamaria Cucinotta, Stefano Selleri
A coupled-mode theory for nonlinear mode coupling by the thermo-optic effect, originally developed for single-core fiber amplifiers, is applied to the case of dual-core amplifiers. It is shown that a non-phase-matched coupling term, which is usually irrelevant in single-core amplifiers, can strongly affect the mode stability when the coupling length between supermodes exceeds a few centimeters. The phase-mismatched coupling can lead to a strongly reduced instability threshold and static deformation effects for a range of intermediate coupling lengths...
October 1, 2018: Optics Letters
https://www.readbyqxmd.com/read/30258667/beyond-backscattering-optical-neuroimaging-by-brad
#12
Pablo Eugui, Antonia Lichtenegger, Marco Augustin, Danielle J Harper, Martina Muck, Thomas Roetzer, Andreas Wartak, Thomas Konegger, Georg Widhalm, Christoph K Hitzenberger, Adelheid Woehrer, Bernhard Baumann
Optical coherence tomography (OCT) is a powerful technology for rapid volumetric imaging in biomedicine. The bright field imaging approach of conventional OCT systems is based on the detection of directly backscattered light, thereby waiving the wealth of information contained in the angular scattering distribution. Here we demonstrate that the unique features of few-mode fibers (FMF) enable simultaneous bright and dark field (BRAD) imaging for OCT. As backscattered light is picked up by the different modes of a FMF depending upon the angular scattering pattern, we obtain access to the directional scattering signatures of different tissues by decoupling illumination and detection paths...
June 1, 2018: Biomedical Optics Express
https://www.readbyqxmd.com/read/30213047/passive-q-switching-by-cr-4-yag-saturable-absorber-of-buried-depressed-cladding-waveguides-obtained-in-nd-doped-media-by-femtosecond-laser-beam-writing
#13
Gabriela Croitoru Salamu, Nicolaie Pavel
We report on laser performances obtained in Q-switch mode operation from buried depressed-cladding waveguides of circular shape (100 μm diameter) that were inscribed in Nd:YAG and Nd:YVO₄ media by direct writing with a femtosecond laser beam. The Q-switch operation was realized with a Cr4+ :YAG saturable absorber, aiming to obtain laser pulses of moderate (few μJ) energy at high (tens to hundreds kHz) repetition rate. An average power of 0.52 W at 1.06 μm consisting of a train of pulses of 7.79 μJ energy at 67 kHz repetition rate, was obtained from a waveguide realized in a 4...
September 12, 2018: Materials
https://www.readbyqxmd.com/read/30211908/experimental-demonstration-of-a-few-mode-raman-amplifier-with-a-flat-gain-covering-1530-1605-nm
#14
Jiaxiong Li, Lulu Wang, Jiangbing Du, Shoulin Jiang, Lin Ma, Chengkun Cai, Long Zhu, Andong Wang, Ming-Jun Li, Hao Chen, Jian Wang, Zuyuan He
We design and experimentally demonstrate a few-mode Raman amplifier over the C+L band with a flat on-off gain of ∼4  dB, for the first time, to the best of our knowledge. A state-of-the-art gain bandwidth of 75 nm (1530-1605 nm) is achieved. The wavelength-dependent gain for both LP01 and LP11 modes is about 0.6 dB, and the maximum mode-dependent gain is less than 0.3 dB. Mode-division multiplexed optical transmissions are performed over 75 km few-mode fiber assisted by the proposed Raman amplifier...
September 15, 2018: Optics Letters
https://www.readbyqxmd.com/read/30208634/experimental-study-on-shear-behavior-of-steel-fiber-reinforced-concrete-beams-with-high-strength-reinforcement
#15
Jun Zhao, Jingchao Liang, Liusheng Chu, Fuqiang Shen
Many researchers have performed experimental and theoretical studies on the shear behavior of steel fiber reinforced concrete (SFRC) beams with conventional reinforcement; few studies involve the shear behavior of SFRC beams with high-strength reinforcement. In this paper, the shear test of eleven beams with high-strength reinforcement was carried out, including eight SFRC beams and three reinforced concrete (RC) beams. The load-deflection curve, concrete strain, stirrup strain, diagonal crack width, failure mode and shear bearing capacity of the beams were investigated...
September 11, 2018: Materials
https://www.readbyqxmd.com/read/30184930/sub-200-fs-soliton-mode-locked-fiber-laser-based-on-bismuthene-saturable-absorber
#16
Bo Guo, Shi-Hao Wang, Zhi-Xin Wu, Ze-Xin Wang, Da-He Wang, Hao Huang, Feng Zhang, Yan-Qi Ge, Han Zhang
Few-layer bismuthene is an emerging two-dimensional material in the fields of physics, chemistry, and material science. However, its nonlinear optical property and the related photonics device have been seldom studied so far. Here, we demonstrate a sub-200 fs soliton mode-locked erbium-doped fiber laser (EDFL) using a microfiber-based bismuthene saturable absorber for the first time, to the best of our knowledge. The bismuthene nanosheets are synthesized by the sonochemical exfoliation method and transferred onto the taper region of a microfiber by the optical deposition method...
September 3, 2018: Optics Express
https://www.readbyqxmd.com/read/30160764/mode-interference-induced-oscillation-in-propagation-speed-of-fiber-fuse-in-few-mode-fibers
#17
Shoulin Jiang, Lin Ma, Shuai Wang, Xinyu Fan, Zuyuan He
We investigated the fiber fuse propagation speed in different kinds of few-mode fibers (FMFs) by combining heterodyne detection and time-frequency analysis. The periodic speed oscillation due to mode interference was observed, and we confirm that the characteristic length Lc (defined as the optical discharge propagation distance within a period of speed oscillation) is independent of the launched power, which is different from that observed in single-mode fibers. Moreover, we believe that the optical field modulation with enough intensity led to the variation of the optical discharge center position...
September 1, 2018: Optics Letters
https://www.readbyqxmd.com/read/30160744/transverse-mode-switchable-all-fiber-brillouin-laser
#18
Xiaobo Heng, Jiulin Gan, Zhishen Zhang, Jiong Li, Muqiao Li, Hua Zhao, Qi Qian, Shanhui Xu, Zhongmin Yang
A transverse mode switchable all-fiber Brillouin laser architecture is proposed. This laser architecture consists mainly of an optical switch, a set of cascaded mode selection couplers (MSCs), and a few-mode fiber ring cavity. By switching the output signal of the optical switch, specific transverse modes generated by MSCs can be coupled into the ring cavity to excite the corresponding Brillouin scattering light. Based on the Brillouin nonlinear effect, the desired mode resonant amplification is guaranteed, and a transverse mode switchable laser beam is obtained...
September 1, 2018: Optics Letters
https://www.readbyqxmd.com/read/30129578/link-optimized-few-mode-fiber-raman-distributed-temperature-sensors
#19
Chen Yang, Meng Wang, Ming Tang, Hao Wu, Can Zhao, Tongqing Liu, Songnian Fu, Weijun Tong
A link optimized few-mode fiber-based Raman distributed temperature sensor is proposed to enhance the temperature resolution of the long-distance sensing system. Comprehensive theoretical analysis and experimental validation in contrast with the traditional single-mode fiber-based sensing link have been conducted to reveal the benefits provided by the optimization scheme. The temperature resolutions are about 3.8°C for the proposed fiber link at 20 km distance, leading to about 6.2°C improvement compared with the single-mode fiber (SMF) link...
August 20, 2018: Applied Optics
https://www.readbyqxmd.com/read/30119554/all-fiber-stable-orbital-angular-momentum-beam-generation-and-propagation
#20
Xiaobo Heng, Jiulin Gan, Zhishen Zhang, Jiong Li, Muqiao Li, Hua Zhao, Qi Qian, Shanhui Xu, Zhongmin Yang
An all-fiber scheme for stable orbital angular momentum (OAM) beam generation and propagation is proposed and demonstrated. This scheme is based on a self-designed and manufactured graded-index few mode fiber (GI-FMF) and compatible mode selection coupler (MSC). The MSC, which consists of a conventional single mode fiber (SMF) and the GI-FMF, can effectively couple the fundamental mode in the SMF to the desired OAM mode in the GI-FMF based on phase matching condition. Meanwhile, the GI-FMF breaks the degeneracy between the desired eigenmodes and neighboring vector modes, thereby allowing the preservation and propagation of the selectively excited OAM modes...
June 25, 2018: Optics Express
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