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Review of exceptional point-based sensors [Invited]

Jan Wiersig

DOI: 10.1364/PRJ.396115 Received 29 Apr 2020; Accepted 27 Jun 2020; Posted 30 Jun 2020  View: PDF

Abstract: Exceptional points are spectral singularities in open quantum and wave systems which exhibit a giant spectral response to perturbations. This feature can be exploited for a new generation of sensors. This paper explains the basic mechanism and comprehensively reviews the recent developments. In particular, it highlights the influence of classical noise and fundamental limitations due to quantum noise.

Linear and nonlinear photophysical properties of ZnSe/CdS/ZnS core/shell/shell type II nanocrystals

Xin Qiu, Fuli Zhao, Shuyu Xiao, Junzi Li, Yang Gao, Xiaodong Lin, Rui Chen, and Tingchao He

DOI: 10.1364/PRJ.387099 Received 02 Jan 2020; Accepted 26 Jun 2020; Posted 30 Jun 2020  View: PDF

Abstract: In this work, one kind of type II ZnSe/CdS/ZnS core/shell/shell nanocrystals (NCs) are synthesized and their linear and nonlinear photophysical properties are investigated. Through the measurements of the temperature dependent photoluminescence spectra of NCs, their excitonic properties, including the coefficient of the bandgap change, coupling strength of exciton acoustic phonons and exciton longitudinal optical (LO) phonons, and LO-phonon energy, are revealed. Femtosecond transient absorption spectroscopy was employed to obtain insight into ultrafast processes occurring at the interface of ZnSe and CdS, such as those involving the injection of photoinduced electrons into the CdS shell and photoinduced holes into the ZnSe core as well as their subsequent relaxation rates. At the end, their multiphoton absorption spectra were determined by using the Z-scan technique, which yielded a maximum two-photon absorption cross-section of 3717 GM at 820 nm and three-photon absorption cross-section up to 3.9 × 10-77 cm6 s2 photon-2 at 1220 nm, respectively. The photophysical properties presented here may be important for exploiting their relevant applications in optoelectronic devices and deep-tissue bioimaging.

LT-GaAs based plasmonic photoconductive THz detector with gold nano-islands

Hironaru Murakami, Masayoshi Tonouchi, and Tomoya Takarada

DOI: 10.1364/PRJ.395517 Received 21 Apr 2020; Accepted 26 Jun 2020; Posted 30 Jun 2020  View: PDF

Abstract: A low-temperature grown GaAs (LT-GaAs) based photoconductive antenna is one of the useful devices for terahertz (THz) applications with a femtosecond pulsed laser (fs-laser) excitation, but it cannot be not effectively used in the THz systems with a fs-laser source with a wavelength longer than 800 nm. On the other hand, it is well known that the localized surface plasmon resonance (LSPR) effect can localize the light field and significantly enhance the performance of optical devices. Therefore, we tried to develop a high-sensitivity LT-GaAs photoconductive detector (PCD) which can be used over a wide wavelength range by utilizing the LSPR effects. For this purpose, gold nano-islands with various sizes were deposited on the dipole gap region of the PCD, and the sensitivity was improved by 29% and 40% in the amplitude of observed THz pulse for the excitation lasers with the wavelengths of 800 nm and 1560 nm, respectively.

Saturable and Reverse Saturable Absorption in Molybdenum Disulfide Dispersion and Film by Defect Engineering

Hongwen Xuan, Chunhui Lu, Yixuan Zhou, Xinlong Xu, Qiyi Zhao, and Jintao Bai

DOI: 10.1364/PRJ.395870 Received 22 Apr 2020; Accepted 23 Jun 2020; Posted 24 Jun 2020  View: PDF

Abstract: Understanding and controlling defect in two-dimensional materials is important for both linear and nonlinear optoelectronic devices, especially in terms of tuning nonlinear optical absorption. Taking advantage of atomic defect formed easily by smaller size, molybdenum disulfide (MoS2) nanosheet is prepared successfully with different size by gradient centrifugation. Interestingly, size-dependent sulfur vacancies are observed by high-resolution X-ray photoelectron spectroscopy, atomic force microscopy, and transmission electron microscopy. The defect effect on nonlinear absorption is investigated by Z-scan measurement at the wavelength of 800 nm. The results suggest the transition from saturable absorption to reverse saturable absorption can be observed in both dispersions and films. First principle calculations suggest that sulfur vacancies act as the trap state to capture the excited electrons. Moreover, an energy-level model with the trap state is put forward to explain the role of the sulfur vacancy defect in nonlinear optical absorption. The results suggest that saturable and reverse saturable absorption originate from the competition between the excited, defect state and ground state absorption. Our finding provides a way to tune the nonlinear optical performance of optoelectronic devices by defect engineering.

Impact of carrier transport on the CW performance ofQD lasers on silicon: a drift-diffusion approach

Marco Saldutti, Alberto Tibaldi, Federica Cappelluti, and Mariangela Gioannini

DOI: 10.1364/PRJ.394076 Received 03 Apr 2020; Accepted 23 Jun 2020; Posted 23 Jun 2020  View: PDF

Abstract: The operation of quantum dot lasers epitaxially grown on silicon is investigated through a quantum correctedPoisson-drift-diffusion model. This in-house developed simulation framework completesthe traditional rate equation approach, that models the intersubband transitions involved into simultaneousground-state and excited-state lasing, with a physics-based description of carrier transport andelectrostatic effects. The code is applied to look into the main detrimental mechanisms for lasing operationsuch as threading dislocations and carrier transport asymmetries, and to pinpoint the benefits/contraindications of p-type modulation doping, revealing the fundamental role of an accurate electrostatic/carrier transport picture.

High- responsivity, self-driven photodetectors based on monolayer WS₂/GaAs heterojunction

Kuilong Li, Wenjia Wang, Jianfei Li, Wenxin Jiang, Min Feng, and Yang He

DOI: 10.1364/PRJ.396880 Received 12 May 2020; Accepted 21 Jun 2020; Posted 23 Jun 2020  View: PDF

Abstract: Constructing two-dimensional (2D) layered materials with traditional three-dimensional (3D) semiconductors into complex heterostructures has opened a new platform for the development of optoelectronic devices. Herein, large area high performance self-driven photodetectors based on monolayer WS₂/GaAs heterostructures were successfully fabricated with a wide response spectrum band ranging from ultraviolet to near-infrared region. The detector exhibits an overall high performance, including high photoresponsivity of 65.58 A/W at 365 nm and 28.50 A/W at 880 nm, low noise equivalent power of 1.97×10¯¹⁵ W/Hz^½, high detectivity of 4.47×10¹² Jones, and a fast response speed of 30/10 ms. This work suggests that the WS₂/GaAs heterostructure is promising in future novel optoelectronic device applications, and also provides a low-cost, easy-to-process method for the preparation of 2D/3D heterojunction based devices.

Structural color switching with a doped indium-gallium-zinc-oxide semiconductor

Inki Kim, Juyoung Yun, Trevon Badloe, Hyuk Park, Taewon Seo, Younghwan Yang, Juhoon Kim, Yoonyoung Chung, and Junsuk Rho

DOI: 10.1364/PRJ.395749 Received 21 Apr 2020; Accepted 21 Jun 2020; Posted 22 Jun 2020  View: PDF

Abstract: Structural coloration techniques have improved display science due to their high durability in terms of resistance to bleaching and abrasion, and low energy consumption. However, it is not easy to achieve in electronics applications because of the need for the control in geometry of the nanostructure or in phase of the material, which is limited by materials or even impossible to change after fabrication. Here, we propose and demonstrate an all solid-state, large-area, lithography-free color filter that can switch structural color based on a doped semiconductor. Particularly, an indium gallium zinc oxide (IGZO) thin film is used as an active index-changing layer. The refractive index of the IGZO layer is tuned by controlling the charge carrier concentration; a hydrogen (H2) plasma treatment was used to control the conductivity of the IGZO layer. In this paper, we have verified the color modulation using finite difference time domain (FDTD) simulations and experiments. The IGZO based color filter technology proposed in this study will pave the way for charge-controlled tunable color filters displaying wide visible colors on demand.

Experimental free-space quantum secure direct communication and its security analysis

Gui Lu Long, Dong Pan, Zaisheng Lin, Liuguo Yin, Jiawei Wu, Zhen Sun, and Dong Ruan

DOI: 10.1364/PRJ.388790 Received 22 Jan 2020; Accepted 20 Jun 2020; Posted 22 Jun 2020  View: PDF

Abstract: We report an experimental implementation of free-space quantum secure direct communication based on single photons. The quantum communication scheme uses phase encoding, and the asymmetric Mach-Zehnder interferometer is optimized so as to automatically compensate phase drift of the photons during their transitions over the free-space medium. An information transmission rate of 500 bps over a 10-meter free space with a mean quantum bit error rate of 0.49%±0.27% is achieved. The security is analyzed under the scenario that Eve performs collective attack and photon number splitting collective attack. Our results show that quantum secure direct communication is feasible in free space.

High gain amplification for femtosecond optical vortex with mode-control regenerative cavity

Shuiqin Zheng, Zhenkuan Chen, QINGGANG LIN, Yi Cai, Xiaowei Lu, Yanxia Gao, Shixiang Xu, and Dianyuan Fan

DOI: 10.1364/PRJ.390963 Received 24 Feb 2020; Accepted 19 Jun 2020; Posted 22 Jun 2020  View: PDF

Abstract: Ultra-intense femtosecond vortex pulses can provide an opportunity to investigate the new phenomena with orbital angular momentum (OAM) involved under extreme cases. This paper reports a high gain optical vortex amplifier for intense femtosecond vortex pulses generation. Traditional regeneration amplifiers can offer high gain for Gaussian mode pulses but cannot to amplify optical vortex pulses with maintaining the phase singularity because of mode competition. To solve this problem, we design a regeneration amplifier with a ring-shaped pump. By controlling the radius of the pump, the system can realize the motivation of LG0,1(-1) mode and the suppression of Gaussian mode. Without a seeding, the amplifiers have a donut-shaped output containing two opposite OAM simultaneously, as our prediction by simulation. But by seeding by a pulse with the topologic charge of 1 or -1, the system will output an amplified LG0,1(-1) mode pulse with the same topologic charge to the seed. To our knowledge, this amplifier can offer the highest gain as 1.45×106 for optical vortex amplification. Finally, we obtain a 1.8 mJ, 51 fs compressed optical vortex seeded from a 2 nJ optical vortex.

Frequency stabilization and tuning of breathing soliton in Si₃N₄ microresonators

Shuai Wan, Rui Niu, Zheng-Yu Wang, Jin-Lan Peng, Ming Li, Jin Li, Guang-can Guo, Chang-Ling Zou, and Chunhua Dong

DOI: 10.1364/PRJ.397619 Received 14 May 2020; Accepted 19 Jun 2020; Posted 22 Jun 2020  View: PDF

Abstract: Dissipative Kerr soliton offers broadband coherent and low-noise frequency comb and stable temporal pulse train, having shown great potential applications in spectroscopy, communications, and metrology. Breathing soliton is a particular dissipative Kerr soliton that the pulse duration and peak intensity show periodic oscillation. Here, we have investigated the breathing dissipative Kerr solitons in silicon nitride (Si3N4) microrings, while the breathing period shows uncertainties around MHz in both simulation and experiments. This instability is the main obstacle for future applications. By applying a modulated signal to the pump laser, the breathing frequency can be injection-locked to the modulation frequency and tuned over tens of MHz with frequency noise significantly suppressed. Our demonstration offers an alternative knob for the control of soliton dynamics in microresonator and paves a new avenue towards practical applications of breathing soliton.

Electrical properties and microstructure formation of V/Al-based n-contacts on high Al mole fraction n-AlGaN layers

Luca Sulmoni, Frank Mehnke, Anna Mogilatenko, Martin Guttmann, Tim Wernicke, and M Kneissl

DOI: 10.1364/PRJ.391075 Received 21 Feb 2020; Accepted 18 Jun 2020; Posted 18 Jun 2020  View: PDF

Abstract: The electrical and structural properties of V/Al-based n-contacts on n-AlxGa1-xN with an Al mole fraction x ranging from x = 0.75 to x = 0.95 are investigated. Ohmic n-contacts are obtained up to x = 0.75 with a contact resistivity of 5.7×10¯⁴ Ωcm² whereas for higher Al mole fraction the IV characteristics are rectifying. Transmission electron microscopy reveals a thin crystalline AlN layer formed at the metal/semiconductor interface upon thermal annealing. Compositional analysis confirmed an Al enrichment at the interface. The interfacial nitride-based layer in n-contacts on n-Al0.9Ga0.1N is partly amorphous and heavily contaminated by oxygen. The role and resulting limitations of Al in the metal stack for n-contacts on n-AlGaN with very high Al mole fraction are discussed. Finally, UVC LEDs grown on n-Al0.87Ga0.13N and emitting at 2 nm are fabricated with an operating voltage of 7.3 V and an emission power of 120 μW at 20 mA in cw operation.

Reconfigurable time stretched swept laser source with up to 100 MHz swept rate, 100 nm bandwidth and 100 mm OCT imaging depth

Dongmei HUANG, Feng Li, Shang Chao, Zihao Cheng, and Ping Kong Wai

DOI: 10.1364/PRJ.390076 Received 07 Feb 2020; Accepted 17 Jun 2020; Posted 18 Jun 2020  View: PDF

Abstract: The repetition rate, sweeping range and coherence length of swept sources respectively determine the acquisition rate, axial resolution and imaging depth of optical coherence tomography (OCT). In this paper, we demonstrate a reconfigurable high speed and broadband swept laser by time stretching of a flat spectrum femtosecond pulse train with over 100 nm bandwidth and a repetition rate of 100 MHz. By incorporating an optical modulator and utilizing appropriate dispersive modules, swept sources with swept rates of 25 and 2.5 MHz are also demonstrated. The imaging depth of the 2.5 MHz swept source reaches >100 mm with 6 dB sensitivity roll off. It is the first time that ultrafast swept sources for OCT with 100 MHz swept rate and with >100 mm imaging depth are demonstrated. Compared with other swept sources, the imaging depth has been improved by more than one order of magnitude. The ultrafast swept source with ultralong coherence length will greatly extend the potential applications of swept source optical coherence tomography (SS-OCT).

Fast structured illumination microscopy via deep learning

Chang Ling, Chonglei Zhang, MINGQUN WANG, Fanfei Meng, Luping Du, and Xiaocong Yuan

DOI: 10.1364/PRJ.396122 Received 11 May 2020; Accepted 15 Jun 2020; Posted 15 Jun 2020  View: PDF

Abstract: This study shows that convolutional neural networks (CNNs) can be used to improve the performance of wide-field structured illumination microscopy (SIM) to enable it to reconstruct a super-resolution image using three (3_SIM) instead of nine raw frames (9_SIM), which is the standard number of frames required to this end. This allows for gentler super-resolution imaging at higher speeds and weakens phototoxicity in the imaging process. Owing to the isotropy of the fluorescence group, the correlation between the high frequency information in each direction of the spectrum is obtained by training the CNN. A high-precision super-resolution image can thus be reconstructed using accurate data from three image frames in one direction (1d_SIM). The performance of the proposed approach was verified through simulations and experiments on the reconstruction of super-resolution images.

Graphene metalens for integrated particle nanotracking

Xueyan Li, Shibiao Wei, Guiyuan Cao, Han Lin, Yuejin Zhao, and Baohua Jia

DOI: 10.1364/PRJ.397262 Received 11 May 2020; Accepted 15 Jun 2020; Posted 15 Jun 2020  View: PDF

Abstract: Particle nanotracking (PNT) is highly desirable in lab-on-a-chip systems for flexible and convenient multiparameter measurement. Ultrathin flat lens is the preferred imaging device in such a system with the advantage of high focusing performance and compactness. However, PNT using ultrathin flat lenses has not been demonstrated so far because PNT requires the clear knowledge of the relationship between the object and image in the imaging system. While, such relationship still remains elusive in ultrathin flat lens-based imaging systems because they operate based on diffraction rather than refraction. In this paper, we experimentally reveal the imaging relationship of a graphene metalens using nanohole arrays with micrometer spacing. The distance relationship between the object and image as well as the magnification ratio is acquired with nanometer accuracy. The measured imaging relationship agrees well with the theoretical prediction and is expected to be applicable to other ultrathin flat lenses based on diffraction principle. By analyzing the high-resolution images from the graphene lens using the imaging relationship, 3D trajectories of particles with high accuracy in PNT have been achieved. The revealed imaging relationship for metalenses is essential in designing different types of integrated optical systems, including digital camera, microfluidic devices, virtual reality devices, telescope and eyeglasses, thus will find broad applications.

Laser-driven Self-exfoliation of Graphene Oxide Layers on Fiber Facet for Q-switching of an Er-doped Fiber Laser at the longest wavelength

Kyunghwan Oh, Seongjin Hong, Jaedeok Park, Yong Soo Lee, Dong-Il Yeom, and Byungjoo Kim

DOI: 10.1364/PRJ.396566 Received 01 May 2020; Accepted 12 Jun 2020; Posted 12 Jun 2020  View: PDF

Abstract: A new method to make an all-fiber nonlinear optic device for laser pulse generation is developed by depositing multi-layer graphene oxide (GO) selectively onto the core of the cleaved fiber facet by combining the electrical arc discharge and the laser-driven self-exfoliation. Using the GO colloid droplet with sub-nanoliter volume, we obtained GO bulk-layer deposited on a fiber facet in the order of milliseconds (ms) by using an electric arc. The prepared fiber facet was then included in an Er-doped fiber laser (EDFL) cavity and we obtained a few layers of GO having a nonlinear optic 2-dimensional (2-D) characteristics selectively on the fiber core by the laser-driven self-exfoliation. The 2-D GO layers on the fiber core served as a stable and efficient saturable absorber enabling robust pulse train generation at λ=1600.5 nm, the longest Q-switched laser wavelength in EDFLs. Pulse characteristics were analyzed as we varied the pump power at λ=980nm from 149.3mW to 371.3mW, to obtain the maximum repetition rate of 17.8kHz and the maximum output power of 2.3mW with the minimum pulse duration of 7.8μs. The proposed method could be further applied to other novel inorganic 2-D materials opening a window to explore their novel nonlinear optic laser applications.

A Self-powered, Flexible and Ultra-broadband, UV-THz Photodetector based on Laser Reduced Graphene Oxide/CsPbBr3 Composite

Yifan Li, Yating Zhang, Zhiliang Chen, Qingyan Li, Tengteng Li, Mengyao Li, Hongliang Zhao, Quan Sheng, Wei Shi, and Jian-Quan Yao

DOI: 10.1364/PRJ.395090 Received 13 Apr 2020; Accepted 10 Jun 2020; Posted 12 Jun 2020  View: PDF

Abstract: Self-powered and flexible ultra-broadband photodetectors (PDs) are desirable in a wide applications. The current PDs based on photothermoelectric (PTE) effect have realized broadband photodetection. However, most of them express low photoresponse and lack of flexible. In this work, high performance, self-powered and flexible PTE PDs based on laser rGO/CsPbBr3 are developed. The comparison experiment with laser rGO PD and fundamental electric properties show that the laser rGO/CsPbBr3 device exhibits enhanced ultra-broadband photodetection performance covering ultraviolet (UV) to terahertz (THz) range with high photoresponsivity of 100 mA/W for 405 nm and 10 mA/W for 118 μm at zero bias voltage, respectively. A fast response time of 18 ms and flexible experiment are also acquired at room temperature. Moreover, PTE effect is fully discussed in the laser rGO/CsPbBr3 device. This work demonstrates that laser rGO/CsPbBr3 is a promising candidate for construction of high-performance, flexible and self-powered ultra-broadband PDs at room temperature.

Vortex Smith-Purcell Radiation Generation with Holographic Grating

Mengxuan Wang, Fang Liu, Yuechai Lin, Kaiyu Cui, Xue Feng, Wei Zhang, and Yidong Huang

DOI: 10.1364/PRJ.394136 Received 13 Apr 2020; Accepted 05 Jun 2020; Posted 08 Jun 2020  View: PDF

Abstract: Smith-Purcell radiation (SPR) is the electromagnetic wave generated by free electrons passing above a diffraction grating, which has played an important character in free electron light sources and particle accelerators. Orbital angular momentum (OAM) is a new degree of freedom which can significantly promote the capacity of information carried by an electro-magnetic beam. In this paper, we propose an integratable method for generating vortex Smith-Purcell radiation (VSPR), namely SPR carrying OAM, by having free electron bunches pass on planar holographic gratings. The VSPR generated by different electron energy, with different topological charge of OAM, radiation angles, and frequencies are demonstrated numerically. It is also found that, for high order radiation, its topological charge of the OAM wave will be multiplied by the radiation order. This work introduces a new way to generate SPR with OAM and provides a method to achieve an integratable and tunable free-electron OAM wave source at different frequency.

Pulse-width-induced polarization enhancement of optically-pumped N-V electron spin in diamond

Yumeng Song, Yu Tian, Zhiyi Hu, Feifei Zhou, Tengteng Xing, Dawei Lu, Bing Chen, Ya Wang, Nanyang Xu, and Jiangfeng Du

DOI: 10.1364/PRJ.386983 Received 08 Jan 2020; Accepted 03 Jun 2020; Posted 04 Jun 2020  View: PDF

Abstract: The nitrogen-vacancy (N-V) center in diamond is a widely-used platform for quantum information processing and metrology. The electron-spin state of N-V center could be initialized and readout optically, and manipulated by resonate microwave fields. In this work, we analyze the dependence of electron-spin initialization on widths of laser pulses. We build a numerical model to simulate this process and verify the simulation results in experiment. Both simulations and experiments reveal a fact that shorter laser pulses are helpful to the electron-spin polarization. We therefore propose to use extremely-short laser pulses for electron-spin initialization. In this new scheme, the spin-state contrast could be improved about 10% in experiment by using laser pulses as short as 4 ns in width. Furthermore, we provide a mechanism to explain this effect which is due to the occupation time in the meta-stable spin-singlet states of N-V center. Our new scheme is applicable in a broad range of NV-based applications in the future.

Design of micron-long superconducting nanowire perfect absorber for efficient high speed single-photon detection

Risheng Cheng, Sihao Wang, Chang-Ling Zou, and Hong Tang

DOI: 10.1364/PRJ.390945 Received 20 Feb 2020; Accepted 02 Jun 2020; Posted 03 Jun 2020  View: PDF

Abstract: Despite very efficient superconducting nanowire single-photon detectors (SNSPDs) reported recently, combining their other performance advantages such as high speed and ultra-low timing jitter in a single device still remains challenging. In this work, we present a perfect absorber model and corresponding detector design based on a micron-long NbN nanowire integrated with a 2D-photonic crystal cavity of ultra-small mode volume, which promises simultaneous achievement of near-unity absorption, gigahertz counting rates and broadband optical response with a 3 dB bandwidth of 71 nm. Compared to previous stand-alone meandered and waveguide-integrated SNSPDs, this perfect absorber design addresses the trade space in size, efficiency, speed and bandwidth for realizing large on-chip single-photon detector arrays.

Second harmonic generation and manipulation in Lithium Niobate slab waveguides by grating metasurfaces

Bin Fang, Hanmeng Li, Shining Zhu, and Tao Li

DOI: 10.1364/PRJ.391850 Received 11 Mar 2020; Accepted 01 Jun 2020; Posted 03 Jun 2020  View: PDF

Abstract: Nonlinear optical processes in waveguides play important roles in compact integrated photonics, while efficient coupling and manipulations inside the waveguides still remain challenging. In this work, we propose a new scheme for second harmonic generation as well as beam shaping in lithium niobate (LN) slab waveguides with the assistance of well-designed grating metasurfaces at λ=1064 nm. By encoding the amplitude and phase into the holographic gratings, we further demonstrate strong functionalities of nonlinear beam shaping by the metasurface design, including dual focusing and Airy beam generation. Our approach would inspire new designs in the miniaturization and integration of compact multifunctional nonlinear light sources on chip.

Geometric-phase-induced arbitrary polarization and orbital angular momentum generation in helically twisted birefringent photonic crystal fiber

Takeshi Fujisawa and Kunimasa Saitoh

DOI: 10.1364/PRJ.393255 Received 19 Mar 2020; Accepted 01 Jun 2020; Posted 03 Jun 2020  View: PDF

Abstract: The evolutions of polarization and orbital angular momentum (OAM) states of light in helically twisted birefringent photonic crystal fibers (TB-PCFs) are analyzed. It is shown that a circular polarization (CP) component (S3 of Stokes parameter) is periodically excited, when usual linearly polarized (LP) modes of PCF is launched. The excitation is originating from a geometric phase in TB-PCFs. The S3 excitation is larger for larger birefringence for fixed twisting rate. If the birefringence is large enough, a CP filtering behavior can be seen in addition to the S3 excitation. From the analytical consideration of the sign of the geometric phase, TB-PCFs with periodical inversion of twisting is proposed to generate arbitrary polarization state on Poincare sphere. Next, an OAM state generation in multimode TB-PCFs is shown for higher-order LP mode input. By observing a far field interference pattern (FFIP) from TB-PCF mixed with LP01 mode, a vortex associated with the OAM state can be seen. Similar to the single mode case, by using periodical twisting inversion, efficient OAM generation is possible. These results indicate that by simply launching fiber’s LP mode into TB-PCF, arbitrary polarization and OAM states can be generated, leading to novel mechanism for the manipulation of the spatial state of the light.

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.

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.

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.

All-fiber generation of arbitrary cylindrical vector beams on the first-order Poincaré sphere

Yan Li, lipeng feng, Sihan Wu, Chen Yang, Weijun Tong, Wei Li, Jifang Qiu, Xiaobin Hong, Yong Zuo, Hongxiang Guo, Jian Wu, Xun Guan, and Erhu Chen

DOI: 10.1364/PRJ.385007 Received 04 Dec 2019; Accepted 03 May 2020; Posted 04 Jun 2020  View: PDF

Abstract: We propose an all-fiber approach to generate arbitrary cylindrical vector (CV) beams and realize its polarization evolution on the first-order Poincaré sphere (FOPS) based on the four-dimension complex Jones matrices in the fiber in terms of the linearly-polarized (LP) mode bases. In the experiment, through the combination of a mode converter and two-segment cascaded few-mode fibers with stresses of different directions and amplitudes, it is possible to convert a fundamental mode with homogeneous polarization state into a vector mode with cylindrically-symmetric polarization distribution on the FOPS. The Stokes parameters of the output light are measured to verify our scheme, which shows good agreement with the theoretical prediction. The method may provide a convenient way to generate CV beams and evolve the polarization states in any path on the FOPS, which is expected to have potential applications in encoding information and quantum computation.

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