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Mode division multiplexed transmission of WDM signals over 100-km single-span OAM fiber

Junwei Zhang, Junyi Liu, Lei Shen, Zhang Lei, Jie Luo, Jie Liu, and Siyuan Yu

DOI: 10.1364/PRJ.394864 Received 09 Apr 2020; Accepted 26 May 2020; Posted 26 May 2020  View: PDF

Abstract: We experimentally demonstrate mode-division multiplexed transmission using 8 orbital angular momentum (OAM) modes over a single span of 100-km low-attenuation and low-crosstalk ring-core fiber (RCF). Each OAM mode channel carries 10 WDM signal channels in the C-band, with each WDM channel in turn transmitting 16-GBaud QPSK signal. An aggregate capacity of 2.56 Tbit/s and an overall spectral efficiency of 10.24 bit/s/Hz are realized. The capacity-distance product of 256 Tbit/s·km is the largest reported so far for OAM fiber communications systems to the best of our knowledge. Exploiting the low crosstalk between the OAM mode groups in the RCF, the scheme only requires the use of modular 4×4 MIMO processing, therefore can be scaled up in the number of MDM channels without increasing the complexity of signal processing.

Multitask deep-learning-based design of chiral plasmonic metamaterials

Eric Ashalley, Kingsley Acheampong, Lucas Vázquez, Peng Yu, Arup Neogi, Alexander O Govorov, and Zhiming Wang

DOI: 10.1364/PRJ.388253 Received 13 Jan 2020; Accepted 26 May 2020; Posted 26 May 2020  View: PDF

Abstract: Chiral plasmonics has registered considerable progress with Machine-Learning (ML)-mediated metamaterials prototyping, drawing from the success of ML frameworks in other data-related applications such as pattern and image recognition. Here, we present an end-to-end functional bi-directional deep-learning (DL) model for three-dimensional chiral metamaterials design and optimization. This ML model utilizes multitask joint learning features to recognize, generalize and explore the non-trivial relationship between the metamaterials’ geometry and their chiroptical response in fine detail, eliminating the need of auxiliary networks or equivalent approaches to stabilize the physical output. The model efficiently realizes both forward and inverse retrieval tasks with great precision, offering a promising tool for iterative computational design tasks in complex physical systems. Finally, we explore the behavior of a sample ML-optimized structure in a practical application, assisting the sensing of biomolecular enantiomers. Other potential applications of our metastructure include photodetectors, polarization-resolved imaging and CD spectroscopy, with our ML framework being applicable to a wider range of physical problems.

Unidirectional reflection from an integrated “taiji” microresonator

Allegra Calabrese, Fernando Ramiro-Manzano, Hannah Price, Stefano Biasi, Martino Bernard, Mher Ghulinyan, Iacopo Carusotto, and Lorenzo Pavesi

DOI: 10.1364/PRJ.393070 Received 18 Mar 2020; Accepted 26 May 2020; Posted 29 May 2020  View: PDF

Abstract: We study light transmission and reflection from an integrated microresonator device, formed by a circular microresonator coupled to a bus waveguide, with an embedded S-shaped additional crossover waveguide element that selectively couples counter-propagating modes in a propagation-direction-dependent way. The overall shape of the device resembles a ``taiji' symbol, hence its name. While Lorentz reciprocity is preserved in transmission, the peculiar geometry allows us to exploit the non-Hermitian nature of the system to obtain high-contrast unidirectional reflection with negligible reflection for light incident in one direction and a significant reflection in the opposite direction.

Plasmonic resonance-linewidth shrinkage to boost biosensing

Min Gao, Wei Min Yang, Zhengying Wang, Shaowei Lin, Jinfeng Zhu, and Yang Zhi-Lin

DOI: 10.1364/PRJ.390343 Received 12 Feb 2020; Accepted 25 May 2020; Posted 26 May 2020  View: PDF

Abstract: Unique surface plasmon resonance (SPR) mode with a narrow linewidth has found wide applications in photovoltaics, photocatalysis, ultrahigh-resolution spectroscopy, and medical biosensing. Inspired by the physics of plasmon hybridization, we reveal an abrupt linewidth-shrinking effect in 2D gold nanohole arrays at the Γ-M direction arising from the interference of two degenerate SPR modes. We further demonstrate the biosensing capability under various excitation conditions for detecting the critical molecular biomarker of prostatic carcinoma, and achieve the maximum sensitivity at the Γ-M direction. Our study not only enhances the understanding toward plasmonic resonance-linewidth shrinking, but also provides a promising strategy to greatly improve biosensing performance by light manipulation on plasmonic nanostructures.

Triple cation perovskite solar cells for visible light communications

Natalie Mica, Rui Bian, Pavlos Manousiadis, Lethy Jagadamma, Iman Tavakkolnia, Harald Haas, Graham Turnbull, and Ifor D. Samuel

DOI: 10.1364/PRJ.393647 Received 03 Apr 2020; Accepted 25 May 2020; Posted 26 May 2020  View: PDF

Abstract: Hybrid perovskite materials are widely researched due to their high absorptivity, inexpensive synthesis, and promise in photovoltaic devices. These materials are also of interest as highly-sensitive photodetectors. In this study their potential for use in visible light communication (VLC) is explored in a configuration that allows for simultaneous energy and data harvesting. Using a triple cation material and appropriate device design, a new record data rate for perovskite photodetectors of 56 Mbps and power conversion efficiencies above 25% under red illumination are achieved. With this device design the -3 dB bandwidth is increased by minimizing the dominating time constant of the system. This correlation between the bandwidth and time constant is proved using measurements of time resolved photo-luminescence, transient photocurrent, and device resistance.

Real-time observation of vortex mode switching in a narrow-linewidth mode locked fiber laser

JIAFENG LU, Fan Shi, Linghao Meng, longkun zhang, Linping Teng, Zhengqian Luo, Peiguang Yan, Fufei Pang, and Xianglong Zeng

DOI: 10.1364/PRJ.386954 Received 06 Jan 2020; Accepted 25 May 2020; Posted 26 May 2020  View: PDF

Abstract: Physical systems with energy oscillation possess resonant modes that mainly include temporal and spatial domains. In the laser field, enormous progress has been made toward controlling the interactions of many longitudinal modes and locking them to form temporal mode locking, which paves the way for diverse applications. Recently, it has evolved from a curiosity to the mode locking mechanism of spatial modes that reveals the new effects of spatial modes interactions in the mode locking formation process. In this paper the first observation of vortex mode switching and the corresponding pulse evolution dynamics in a narrow-linewidth mode locked fiber laser has been demonstrated. The vortex mode switching dynamics has four stages prior to the final mode locking of another vortex mode including quiet-down, relaxation oscillation, quasi-mode locking and energy recovery. The wavelength shifting evolution dynamics has been observed via time-stretch dispersion Fourier transform method. The spatial mode competition through optical nonlinearity induces energy fluctuation on the time scale of ultrashort pulses, which plays an essential role in the mode switching dynamic process. This investigation is performed by making use of a dual-resonant acousto-optic mode converter. The result has great implications in mode locking mechanism study and ultrashort laser applications.

All-optical PtSe₂ silicon photonic modulator with ultra-high stability

Jianji Dong, Han Zhang, Xinliang Zhang, Kangkang Wei, Delong Li, Zhitao Lin, Zhao Cheng, Yuhan Yao, Jia Guo, Yunzheng Wang, and Yupeng Zhang

DOI: 10.1364/PRJ.392512 Received 12 Mar 2020; Accepted 21 May 2020; Posted 21 May 2020  View: PDF

Abstract: All-optical modulator based on the photothermal effect of two-dimensional (2D) material shows great promise for all-optical signal processing and communication. In this work, an all-optical modulator with 2D PtSe₂-on-silicon structure based on microring resonator (MRR) is proposed and demonstrated. A tuning efficiency of 0.0040 nm mW-1 is achieved, and the 10-90% rise and decay times are 304 μs and 284 μs, respectively. The fabricated device exhibits a long-term air stability of more than three months. The experimental results prove that 2D PtSe₂ has great potential for optical modulation on silicon photonic platform.

A Low-loss Hybrid Plasmonic TM-pass Polarizer using Polarization Dependent Mode Conversion

Ruixuan Chen, Bowen Bai, and Zhiping Zhou

DOI: 10.1364/PRJ.392654 Received 13 Mar 2020; Accepted 21 May 2020; Posted 21 May 2020  View: PDF

Abstract: A low-loss hybrid plasmonic transverse magnetic (TM)-pass polarizer has been demonstrated utilizing polarization dependent mode conversion. Taking advantage of the silicon hybrid plasmonic slot waveguide, the unwanted transverse electric (TE) fundamental mode can be efficiently converted to TM first higher order mode and then be suppress by a power combiner, while the retained TM fundamental mode can pass through with negligible influence. Through eigenmode expansion and mode overlap analysis, the optimized insertion loss of the device is as low as 0.4 dB. At the wavelength of 1550nm, the extinction ratio is 28.3 dB with a moderate footprint of 2.38 × 10 µm2. For the entire C band, the average reflection of TE mode is suppressed below -14 dB and the extinction ratio is over 18.6 dB. This work provides another more efficient and effective approach for better on-chip polarizers.

Wavelength-Selective 2×2 Optical Switch Based on a GST-Assisted Microring

Changping Zhang, Ming Zhang, Yiwei Xie, Yaocheng Shi, Rajesh Kumar, Roberto Panepucci, and Daoxin Dai

DOI: 10.1364/PRJ.393513 Received 25 Mar 2020; Accepted 21 May 2020; Posted 21 May 2020  View: PDF

Abstract: A novel wavelength-selective 2×2 optical switch based on a Ge₂Sb₂Te₅ (GST)-assisted microring-resonator (MRR) is proposed. The present GST-assisted MRR consists of two access optical waveguides, an MRR coupled with a bent GST-loaded silicon photonic waveguide. The 2×2 optical switch is switched ON or OFF by modifying the GST state to be crystalline or amorphous. In particular, the microring waveguide and the bent GST-loaded waveguide are designed to satisfy the phase-matching condition when the GST is crystalline. As a result, the MRR becomes highly lossy and the resonance peak is depressed significantly. On the other hand, when it is off, there is little coupling due to the significant phase-mismatching. Consequently, one has a low-loss transmission at the drop port for the resonance wavelength. In this paper, the simulation using the three-dimensional finite-difference (3D-FDTD) method shows the extinction ratio of the designed photonic switch is ~20 dB at the resonance wavelength while the excess losses at the through- and drop-ports are 0.9 dB and 2 dB. In particular, the resonance wavelength changes little between the ON and OFF states, which makes it suitable for multi-channel wavelength-division-multiplexing systems.

Ultra-low quantum defect Raman laser based on boson peak in phosphosilicate fiber

Yang Zhang, Xu Jiangming, Jun Ye, Jiaxin Song, Tianfu Yao, and Pu Zhou

DOI: 10.1364/PRJ.390950 Received 21 Feb 2020; Accepted 19 May 2020; Posted 19 May 2020  View: PDF

Abstract: Quantum defect (QD) has always been a key factor of thermal effect in high power fiber lasers. Lots of researches of low QD fiber lasers have been reported in the past decades, but most of them are based on active fibers. However, Raman fiber lasers based on stimulated Raman scattering effect in passive fiber, is also becoming an important kind of high power fiber laser for its unique advantages, such as significant broader wavelength tunable range and free of photon darkening. In this letter, we demonstrate an ultra-low QD Raman fiber laser based on phosphosilicate fiber. There’s a strong boson peak located at a frequency shift of 3.65 THz in the Raman gain spectrum of the phosphosilicate fiber we employed. By utilizing this boson peak to provide Raman gain and adopting an amplified spontaneous emission source operating at 1066 nm as pump source, 1080 nm Stokes light is generated, corresponding to a QD of 1.3%. The spectral purity of the 1080 nm Stokes light component can be up to 96.03%, and the output power is 12.5 W, corresponding to a conversion efficiency of 67.2%. To the best of our knowledge, this is the lowest QD ever reported for Raman fiber lasers. Our work proposes a promising way of achieving high power, high efficiency Raman fiber lasers.

Sub-wavelength thick ultrahigh-Q terahertz disc microresonators

Dominik Vogt, Angus Jones, Thomas Haase, and Rainer Leonhardt

DOI: 10.1364/PRJ.392288 Received 11 Mar 2020; Accepted 19 May 2020; Posted 19 May 2020  View: PDF

Abstract: Artificial structures that exhibit narrow resonance features are key to a myriad of scientific advances and technologies. In particular, exploration of the terahertz spectrum - the final frontier of the electromagnetic spectrum - would greatly benefit from high quality resonant structures. Here we present a new paradigm of terahertz silicon disc microresonators with sub-wavelength thickness. Experimental results utilising continuous wave THz spectroscopy establish quality factors in excess of 120,000 at 0.6THz. Reduction of the disc thickness to a fraction of the wavelength reduces the losses from the silicon substrate, and paves the way to unparalleled possibilities for light-matter interaction in the THz frequency range

Polarization-independent highly efficient generation of Airy optical beams with dielectric metasurfaces

Binbin Yu, Jing Wen, Lei Chen, Zhang Leihong, Yulong Fan, Bo Dai, Saima Kanwal, Dangyuan Lei, and Dawei Zhang

DOI: 10.1364/PRJ.390202 Received 11 Feb 2020; Accepted 18 May 2020; Posted 19 May 2020  View: PDF

Abstract: Airy optical beams have emerged to hold enormous theoretical and experimental research interests due to their outstanding characteristics. Conventional approaches and the newly developed metasurfaces based generators suffer from one or several constraints such as bulky and costly systems, poor phase discretization, polarization dependence and low generation efficiency. Here, we experimentally demonstrate a polarization-independent silicon dielectric metasurface for generation of high-efficiency Airy optical beams. In our implementation, rather than synchronous manipulation of the amplitude and phase by plasmonic or Huygens’ metasurfaces, we employ and impose a 3/2 phase-only manipulation to the dielectric metasurface, consisting of an array of silicon nano-pillars with an optimized transmission efficiency as high as 97%. The resultant Airy optical beams possess extraordinarily large defection angles and relatively narrow beam widths. Our validated scheme will open up a fascinating doorway to broaden the application scenarios of Airy optical beams on ultra-compact photonic platforms.

High-sensitivity high-spatial-resolution distributed strain sensing based on poly(methyl methacrylate) chirped fiber Bragg grating

Xin Cheng, Chengang Lyu, Hwa Yaw Tam, Ziqi Liu, Chunfeng Ge, and ziqiang huo

DOI: 10.1364/PRJ.391160 Received 24 Feb 2020; Accepted 12 May 2020; Posted 13 May 2020  View: PDF

Abstract: In this study, a high-sensitivity high-spatial-resolution distributed strain-sensing approach based on a poly(methyl methacrylate) chirped fiber Bragg grating (CFBG) is proposed and experimentally demonstrated. Linearly chirped FBGs in a polymer optical fiber provide an alternative to the silica fiber owing to the lower Young’s modulus, which can yield a higher stress sensitivity under the same external force. According to the spatial wavelength-encoded characteristic of the CFBG, a fully distributed strain measurement can be achieved by optical frequency-domain reflectometry. Through time/space-resolved short-time Fourier transform, the applied force can be located by the beat frequency originated from the space-induced time delay and measured by the differential frequency offset originated from the strain-induced dispersion time delay. In a proof-of-concept experiment, a high spatial resolution of 1 mm over a gauge length of 40 mm and strain resolution of 0.491 Hz/με are achieved.

Reconfigurable nano-kirigami metasurfaces by pneumatic pressure

Shanshan Chen, Wei Wei, Zhiguang Liu, Xing Liu, shuai feng, Honglian Guo, and Jiafang Li

DOI: 10.1364/PRJ.393333 Received 27 Mar 2020; Accepted 10 May 2020; Posted 13 May 2020  View: PDF

Abstract: Tunable/reconfigurable metasurfaces that can actively control electromagnetic waves upon external stimuli are of great importance for the practical applications of metasurfaces. Here we demonstrate a reconfigurable nano-kirigami metasurface driven by the pneumatic pressure operating in the near-infrared wavelength region. The metasurfaces consist of combined Archimedean spirals and are fabricated in a free-standing gold/silicon nitride nanofilm by employing focused ion beam (FIB) lithography. The deformable spirals are instantly transformed from two dimensions (2D) to three dimensions (3D) by the FIB-based nano-kirigami process. The 2D-to-3D transformation induces a dramatic irreversible change of the plasmonic quadruple modes and results in significant modulation in reflection by 137%. The suspended porous nano-kirigami metasurface is further integrated with an optofluidics device, with which the optical resonance is reversibly modulated by the pneumatic pressure. This work provides a novel strategy for tunable/reconfigurable metasurfaces, which are useful to build a promising lab-on-a-chip platform for microfluidics, biological diagnostics, chemical sensing, pressure monitoring, etc.

Multi-Photon Synthetic Lattices in Multi-Port Waveguide Arrays: Synthetic Atoms and Fock Graphs

Konrad Tschernig, Roberto Leon Montiel, Armando Perez Leija, and Kurt Busch

DOI: 10.1364/PRJ.382831 Received 11 Nov 2019; Accepted 05 May 2020; Posted 07 May 2020  View: PDF

Abstract: Activating transitions between internal states of physical systems has emerged as an appealing approach to create lattices and complex networks. In such a scheme, the internal states or modes of a physical system are regarded as lattice sites or network nodes in an abstract space whose dimensionality may exceed the systems' apparent (geometric) dimensionality. This introduces the notion of synthetic dimensions, thus providing entirely novel pathways for fundamental research and applications. Here, we analytically show that the propagation of multi-photon states through multi-port waveguide arrays gives rise to synthetic dimensions where a single waveguide system generates a multitude of synthetic lattices. Since these synthetic lattices exist in photon-number space, we introduce the concept of pseudo-energy and demonstrate its utility for studying multi-photon interference processes. Specifically, the spectrum of the associated pseudo-energy operator generates a unique ordering of the relevant states. Together with generalized pseudo-energy ladder operators, this allows for representing the dynamics of multi-photon states by way of pseudo-energy term diagrams that are associated with a synthetic atom. As a result, the pseudo-energy representation leads to concise, analytical expressions for the eigensystem of N photons propagating through M nearest-neighbor coupled waveguides. In the regime where N>2 and M>2, non-local coupling in Fock space gives rise to hitherto unknown quasi-bound states which display intriguing non-trivial dynamics.

64Gbps Low-Voltage Waveguide Si-Ge Avalanche Photodiodes with Distributed Bragg Reflectors

Binhao Wang, Zhihong Huang, Yuan Yuan, Di Liang, Xiaoge Zeng, Marco Fiorentino, and Raymond Beausoleil

DOI: 10.1364/PRJ.390339 Received 13 Feb 2020; Accepted 04 May 2020; Posted 04 May 2020  View: PDF

Abstract: We demonstrate low-voltage waveguide Si-Ge APDs integrated with distributed Bragg reflectors (DBRs). The internal quantum efficiency is improved from 60% to 90% at 1550 nm assisted with DBRs while still achieving a 25 GHz bandwidth. A low breakdown voltage of 10 V and a gain bandwidth product (GBP) of near 500 GHz are obtained. APDs with DBRs at a data rate of 64 Gb/s pulse amplitude modulation with four levels (PAM4) show 30%-40% increase in optical modulation amplitude (OMA) compared to APDs with no-DBR. A sensitivity of around -13 dBm at a data rate of 64 Gb/s PAM4 and a bit error rate (BER) of 2.4E-4 is realized for APDs with DBRs, which improves the sensitivity by ~2 dB compared to APDs with no-DBR.

White Light Color Conversion with Red/Green/Violet-mLDs and Yellow-LED Mixing for 30 Gbps Visible Lighting Communication

Wei-Chun Wang, Chih-Hsien Cheng, Huai-Yung Wang, and Gong-Ru Lin

DOI: 10.1364/PRJ.391431 Received 25 Feb 2020; Accepted 03 May 2020; Posted 04 May 2020  View: PDF

Abstract: The visible wavelength division multiplexing (VWDM) optical wireless communication (OWC) beyond 30 Gbit/s with a white-light beam mixed by red/green/violet (R/G/V) LDs and yellow (Y) LED is demonstrated via 32-level QAM discrete multitone modulation. To faciliate both high-quality indoor lighting and high-speed optical wireless communication, the R/G/V-LD white-light module incorporates with a Y-LED to provide high color rendering index (CRI) and encapsulates with a frosted glass to enlarge its divergent angle. By respectively encoding the R/G/V LDs with the filtered 16-quadrature amplitude modulation discrete multi-tone (16-QAM DMT) data in back-to-back case, the total raw data rate as high as 34.8 Gbit/s is achieved by encoded R/G/V LDs with respective VWDM data rates of 18/7.2/9.6 Gbit/s. To fulfill the demanded CRI and correlated color temperature (CCT) for indoor white-lighting, the yellow LED contributes the yellowish-orange luminescence with flexible CCT and CRI varying from 3952K to 3031K and from 0 to 45.9, respectively. Cold white-light carrier at CCT of 4852K, CRI of 71.6 and CIE of (0.3652, 0.4942) is also approached with attenuating the red LD power, such a cold white-light spot with illuminance of 6800 lux and divergent solid angle (Ω) of 0.89 steradian (sr) can support VWDM data transmission at 28.4 Gbit/s.

Distance-controllable and direction-steerable opto-conveyor for targeting delivery

Zhen Che, Wenguo Zhu, Yaoming Huang, Yu Zhang, Lin Zhuo, Pengpeng Fan, Zhibin Li, Huadan Zheng, wenjin long, Wentao Qiu, Yunhan Luo, Jun Zhang, Jinghua Ge, JianHui Yu, and Zhe Chen

DOI: 10.1364/PRJ.388106 Received 17 Jan 2020; Accepted 03 May 2020; Posted 04 May 2020  View: PDF

Abstract: Opto-conveyors have attracted widespread interest in various fields because of their non-invasive and non-contact delivery of micro/nanoparticles. However, the flexible control of the delivery distance and the dynamic steering of the delivery direction, although very desirable in all-optical manipulation, have not yet been achieved by opto-conveyors. Here, using a simple and cost-effective scheme of an elliptically focused laser beam obliquely irradiated on a substrate, a direction-steerable and distance-controllable opto-conveyor for the targeting delivery of microparticles is implemented. Theoretically, in the proposed scheme of the opto-conveyor, the transverse and longitudinal resultant forces of the optical gradient force and the optical scattering force result in the transverse confinement and the longitudinal transportation of microparticles, respectively. In this study, it is experimentally shown that the proposed opto-conveyor is capable of realizing the targeting delivery for microparticles. Additionally, the delivery distance of microparticles can be flexibly and precisely controlled by simply adjusting the irradiation time. By simply rotating the cylindrical lens, the proposed opto-conveyor is capable of steering the delivery direction flexibly within a large range of azimuthal angles, from −75° to 75°. This study also successfully demonstrated the real-time dynamic steering of the delivery direction from −45° to 45° with the dynamical rotation of the cylindrical lens. Owing to its simplicity, flexibility, and controllability, the proposed method is capable of creating new opportunities in bioassays as well as in drug assembly and delivery.

Phase Demodulation Method Based on Dual-Identical-Chirped-Pulse and Weak Fiber Bragg Gratings for Distributed Acoustic Sensing

guanhua Liang, Junfeng Jiang, Kun Liu, Wang Shuang, Tianhua Xu, Wenjie Chen, Zhe Ma, Zhenyang Ding, Xuezhi Zhang, Zhang Yongning, and T. Liu

DOI: 10.1364/PRJ.389400 Received 30 Jan 2020; Accepted 29 Apr 2020; Posted 29 Apr 2020  View: PDF

Abstract: A phase demodulation method for distributed acoustic sensing (DAS) systems based on dual-identical-chirped-pulse and weak fiber Bragg gratings (WFBGs) is proposed. Compared to the use of Rayleigh backscattering (RBS) light in optical fibers, the implementation of WFBGs can contribute to obtaining an optical signal with a higher signal-to-noise ratio (SNR). The dual-identical-chirped-pulse is generated by a time-delay fiber, and the sinusoidal carrier is generated by the interference between the two chirped pulses reflected by adjacent WFBGs. The phase of sinusoidal carrier represents the dynamic strain change posed on the sensing fiber. Discrete Fourier transform (DFT) is used to directly retrieve the phase information. The performance of the phase demodulation from interference signals under different sinusoidal carrier frequencies and SNRs is numerically investigated. The PZT is employed to emulate the sound in the experiment to verify the effectiveness of our method. It is shown that the dynamic strain can be well reconstructed at the end of a 101.64 km fiber when the signal SNR is down to 3. 4 dB. Our proposed method enables the application of the long distance sensing in DAS systems.

MXene-Based High-Performance All-Optical Modulators for Actively Q-Switched Pulse Generation

Qing Wu, Yunzheng Wang, Weichun Huang, Wang Cong, Zheng Zheng, Meng Zhang, and Han Zhang

DOI: 10.1364/PRJ.391911 Received 03 Mar 2020; Accepted 28 Apr 2020; Posted 29 Apr 2020  View: PDF

Abstract: Q-switched fiber lasers are integral tools in science, industry and medicine due to their advantages of flexibility, compactness and reliability. All-optical strategies to generate ultrashort pulses have obtained considerable attentions as they can modulate the intracavity Q-factors without employing costly and complex electrically-drive devices. Here, we propose a high-performance all-optical modulator for actively Q-switched pulse generation based on a microfiber knot resonator deposited with V2CTx MXene. Experimental results show that the obtained Q-switching pulses exhibit a wide adjustment range of repetition rate from 1 kHz-20 kHz, a high signal-to-background contrast ratio of ~ 55 dB and a narrow pulse width of 8.82 μs, indicating great potentials of providing a simple and viable solution in photonic applications.

Phosphor-free Single Chip GaN-based white light emitting diodes with moderate color rendering index and significantly enhanced communications bandwidth

Rongqiao Wan, Xiang Gao, Liancheng Wang, shuo zhang, Xiongbin Chen, Zhiqiang Liu, Xiaoyan Yi, junxi wang, Junhui Li, Wenhui Zhu, and jinmin li

DOI: 10.1364/PRJ.392046 Received 04 Mar 2020; Accepted 28 Apr 2020; Posted 29 Apr 2020  View: PDF

Abstract: To achieve high quality lighting and visible light communication (VLC) simultaneously, GaN based white light emitting diodes (WLEDs) oriented for lighting in VLC has attracted great interest. However, the overall bandwidth of conventional phosphor converted WLEDs is limited by long lifetime of phosphor, slow stokes transfer process, resistance-capacitance (RC) time delay and quantum-confined Stark effect (QCSE). Here by adopting self-assembled InGaN quantum dots (QDs) structure, we have fabricated phosphor-free single chip WLEDs with tunable correlated color temperature (CCT, from CCT = 1600 K to = 6000 K) , broadband spectrum, moderate color rendering index (CRI) of 75 and significantly improved modulation bandwidth (maximum of 150 MHz) at low current density of 72 A/cm2. The broadband spectrum and high modulation bandwidth are ascribed to capture of carriers by different localized states of InGaN QDs with alleviative QCSE as compared to the traditional InGaN/GaN quantum wells (QWs) structures. We believe the approach reported in this work will find its potential application in GaN WLEDs, and advance the development of semiconductor lighting-communication integration.

Research Progresses in Large-area Perovskite Solar Cells

Yang Zhao, Fei Ma, Feng Gao, Zhigang Yin, Xing-Wang Zhang, and Jingbi You

DOI: 10.1364/PRJ.392996 Received 19 Mar 2020; Accepted 21 Apr 2020; Posted 21 Apr 2020  View: PDF

Abstract: The record power conversion efficiency of small-area perovskite solar cells has impressively exceeds 25%. For practical application, large area device is the necessary step. Recently, significant progresses have been achieved in fabricating efficient large-area perovskite solar cells. In this review, we will summarize recent achievement in large-area perovskite solar cells including the deposition method, growth control of large area, high quality of perovskite layer and also the charge transport layer. Finally, we will give our insight into large-area perovskite solar cells.

Great enhancement of image details with high-fidelity in a scintillator imager using an optical coding method

Yanqing Wu, Huijuan Xia, Lei Zhang, Yuanhe Sun, Zhongyang Wang, and Renzhong Tai

DOI: 10.1364/PRJ.391605 Received 27 Feb 2020; Accepted 19 Apr 2020; Posted 20 Apr 2020  View: PDF

Abstract: High resolution lens-coupled indirect X-ray scintillator imagers are required by many imaging applications. However, the severe weakening of image details prevents its further performance improvement. Through our research, this image degradation is attributed to the broadband loss of the high spatial frequency information caused by the high refractive index. And a technique, known as high-spatial frequency spectrum enhanced reconstruction, is thus proposed to retrieve these information. A two-dimensional high-density array is covered on the scintillator’s exit surface, and operates as an encoder based on which high-frequency information can be shifted to the low-frequency region to improve the signal-to-noise ratio. The experimental results show that the middle–high frequency signal intensities can be increased by an order of magnitude or more. Therefore the image details can be effectively enhanced to breakthrough the performance bottleneck of such widely used X-ray imagers for synchrotron radiation facilities or table-top X-ray tubes.

Ultrapure and Highly Efficient Green Light Emitting Devices Based on Ligand-modified CsPbBr3 Quantum Dots

Dongdong Yan, Shuangyi Zhao, Huaxin Wang, and Zhigang Zang

DOI: 10.1364/PRJ.391703 Received 02 Mar 2020; Accepted 18 Apr 2020; Posted 20 Apr 2020  View: PDF

Abstract: All inorganic CsPbBr3 perovskite quantum dots (QDs) have been recognized as the promising optical materials to fabricate the green light emission devices because of their excellent optical performance. However, the regular CsPbBr3 QDs with oleic acid (OA) ligand show poor stability, limiting their practical application. Herein, CsPbBr3 QDs with 2-hexyldecanoic acid (DA) ligand by replacing the OA ligand in the synthesis show better optical properties than that of the regular CsPbBr3 QDs (CsPbBr3-OA QDs). Due to the strong binding energy between DA ligand and QDs, the ligand modified CsPbBr3 QDs (CsPbBr3-DA QDs) show a high photoluminescence quantum yield (PLQY) of 96%, while the PLQY of CsPbBr3-OA QDs is 84%. Subsequently, the CsPbBr3 QDs coated on the blue light-emitting diodes (LEDs) chips as green phosphors are demonstrated. The color conversion from blue to pure green is achieved by adding the CsPbBr3-OA QDs solution up to 60 μL, while the pure green emission devices only need 18 μL CsPbBr3-DA QDs solution under the same concentration. The ultrapure and highly efficient green light-emitting devices based on CsPbBr3-DA QDs exhibit a luminous efficiency of 43.6 lm/W with a CIE (0.2086, 0.7635) under 15.3 mA driving current. In addition, the green emission wavelength of the devices based on CsPbBr3-DA QDs almost has no shift even under high injection current. These results highlight the promise of the DA ligand modified CsPbBr3 QDs for light-emitting devices and enrich the application field of the ligand modified CsPbBr3 QDs.

Ultra-broadband and sensitive cavity optomechanical magnetometry

Beibei Li, George Brawley, Hamish Greenall, Stefan Forstner, Eoin Sheridan, Halina Rubinsztein-Dunlop, and Warwick Bowen

DOI: 10.1364/PRJ.390261 Received 11 Feb 2020; Accepted 10 Apr 2020; Posted 10 Apr 2020  View: PDF

Abstract: Magnetostrictive optomechanical cavities provide a new optically-readout approach to room temperature magnetometry. Here we report ultrasensitive and ultrahigh bandwidth cavity optomechanical magnetometers constructed by embedding a grain of the magnetostrictive material Terfenol-D within a high quality (Q) optical microcavity on a silicon chip. By engineering their physical structure, we achieve a peak sensitivity of 26 pT/Hz^1/2 comparable to the best cryogenic microscale magnetometers, along with a 3 dB bandwidth as high as 11.3 MHz. Two classes of magnetic response are observed, which we postulate arise from the crystallinity of the Terfenol-D. This allows single- and poly-crystalline grains to be distinguished at the level of a single particle. Our results may enable applications such as lab-on-chip nuclear magnetic spectroscopy and magnetic navigation.

Computational 4D imaging of light-in-flight with relativistic effects

Mingjie Sun, Yue Zheng, Zhi-Guan Wang, and Daniele Faccio

DOI: 10.1364/PRJ.390417 Received 18 Feb 2020; Accepted 10 Apr 2020; Posted 10 Apr 2020  View: PDF

Abstract: Light-in-flight imaging enables the visualization and characterization of light propagation, which provides essential information for the study of the fundamental phenomena of light. A camera images an object by sensing the light emitted or reflected from it, and interestingly, when a light pulse itself is to be imaged, the relativistic effects, caused by the fact that the distance a pulse travels between consecutive frames is of the same scale of the distance that scattered photons travel from the pulse to the camera, must be accounted for to acquire accurate space-time information of the light pulse. Here, we propose a computational light-in-flight imaging scheme, which records the projection of light-in-flight on a transverse x-y plane using a single-photon avalanche diode camera, calculates z and t information of light-in-flight via an optical model, and therefore reconstructs its accurate (x, y, z, t) four-dimensional information. The proposed scheme compensates the temporal distortion in the recorded arrival time to retrieve the accurate time of a light pulse with respect to its corresponding spatial location, without performing any extra measurements. Experimental light-in-flight imaging in a three-dimensional space of 375mm×75mm×50mm is performed, showing that the position error is 1.75mm, and the time error is 3.84ps, despite the fact that the camera time resolution is 55ps, demonstrating the feasibility of the proposed scheme. This work provides a method to expand the recording and measuring of repeatable transient events with extremely weak scattering to four-dimensions and can be applied to observe optical phenomena with ps temporal resolution.

Widely all-parameter-tunable ultra-narrow-linewidth dissipative soliton generation at telecom band

Chang Kyun Ha, Kisang Lee, Dohyeon Kwon, and Myeongsoo Kang

DOI: 10.1364/PRJ.389080 Received 24 Jan 2020; Accepted 30 Mar 2020; Posted 01 May 2020  View: PDF

Abstract: Ultra-narrow-linewidth mode-locked lasers having wide wavelength tunability can be versatile light sources for a variety of newly emergent applications. However, it is very challenging to achieve the stable mode-locking of substantially long, anomalously dispersive fiber laser cavities employing a narrowband spectral filter at the telecom band. Here, we show that an almost dispersion-insensitive dissipative mode-locking regime can be accessed through a subtle counterbalance among significantly narrowband spectral filtering, sufficiently deep saturable absorption, and moderately strong in-fiber Kerr nonlinearity. This achieves ultra-narrow-linewidth (a few gigahertz) nearly transform-limited self-starting stable dissipative soliton generation at low repetition rates (a few megahertz) without cavity dispersion management over a broad tuning range of wavelengths covering the entire telecom C-band. This unique laser may have immediate application as an idealized pump source for high-efficiency nonlinear frequency conversion and nonclassical light generation in dispersion-engineered tightly light-confining micro/nano-photonic systems.

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