Artificial Cnoidal Wave Breathers in Optical Microresonators

Yiran Gao, Jian Dai, Zhonghan Wu, Junqiu Liu, tian zhang, Wei Sun, Anni Liu, and Kun Xu

DOI: 10.1364/PRJ.519666 Received 20 Feb 2024; Accepted 01 May 2024; Posted 02 May 2024  View: PDF

Abstract: Breathers are localized structures that undergo a periodic oscillation in their duration and amplitude. Optical microresonators, benefiting from their high-quality factor, provide an ideal test bench for studying breathing phenomena. In a monochromatically pumped microresonator system, intrinsic breathing instabilities are widely observed in the form of temporal dissipative Kerr solitons which only exist in the effectively red-detuned regime. Here, we demonstrate a novel bichromatic pumping scheme to create compulsive breathing microcombs via respectively distributing two pump lasers at the effectively blue- and red- detuned sides of a single resonance. We experimentally discover the artificial cnoidal wave breathers and molecular crystal-like breathers in a photonic chip-based silicon nitride microresonator, and theoretically describe their intriguing temporal dynamics based on the bichromatic pumping Lugiato-Lefever equation. In particular, the corresponding breathing microcombs exhibit diverse comb line spacing ranging from 2 to 17 times the free spectral range of the microresonator. Our discovery not only provides a simple yet robust method to harness microcombs with reconfigurable comb line spacing, but also reveals a new class of breathing waves in driven dissipative nonlinear systems.

Line-scanning microscopy with laterally symmetric imaging using simultaneous cross-line-illumination

Dan Shen, Yafeng Li, Meng Wang, Yutong Han, Bolin Lu, Hui Gong, Qingming Luo, and Jing Yuan

DOI: 10.1364/PRJ.521819 Received 23 Feb 2024; Accepted 01 May 2024; Posted 02 May 2024  View: PDF

Abstract: Using an on-the-fly scanning scheme, line confocal microscopy can obtain complex structures of large biological tissues with high throughput. Yet, it suffers from lateral imaging asymmetry and thus sacrifices the detection accuracy of the observation results. Here, we propose cross-line illumination microscopy (cLIM) that acquires the imaging data of two perpendicular directions simultaneously through the same objective lens in a line scanning and utilizes two-direction deconvolution (De2dir) fusion to achieve lateral symmetric imaging performance. Imaging fluorescence beads indicates that cLIM reduces lateral resolution asymmetry from 46.1% to 2.5% and improves lateral resolution by 31.0%, compared with traditional line-scanning imaging. Compared with commercial point-confocal microscopy, the cLIM has a 25.84× increase in imaging speed and 1.93× better background-suppressing ability by imaging an 11,306 × 7,783 × 100 μm3 mouse kidney slice. We also show the advantages of the cLIM in observing direction-sensitive texture features by imaging a muscular tissue slice. cLIM offers a novel solution to achieve laterally symmetric line scanning imaging with simple modifications while maintaining high throughput and accuracy for imaging large-scale samples.

Patterned Microsphere-Lens Projection Lithography Using Electrohydrodynamic Jet Printing-Assisted Assembly

Ya Zhong, Haibo Yu, Peilin Zhou, Hongji Guo, Tianming Zhao, Hao Luo, Yangdong Wen, Xiaoduo Wang, and Lianqing Liu

DOI: 10.1364/PRJ.520479 Received 05 Feb 2024; Accepted 30 Apr 2024; Posted 02 May 2024  View: PDF

Abstract: Microlens arrays have been widely used in the fields of micro-optics and micro- and nanofabrication. Traditional preparation methods utilize commercial photoresists and thermosetting materials, thereby restricting the optical properties of microlenses. In recent years, significant advancements have been achieved in near-field super-resolution imaging by utilizing microspheres and forming arrays of microsphere lenses via self-assembly. However, self-assembly approaches lack flexibility in terms of pattern selection. This study proposes a method that utilizes electrohydrodynamic jet (E-jet) printing to code ultraviolet (UV)-curable adhesives and assist in the assembly of patterned microsphere-lens arrays. Simulation results demonstrate that the UV-curable adhesive has little impact on the optical properties of the microsphere lens. Moreover, the microsphere lens exhibits a superior imaging resolution compared with traditional microlenses. A projection-lithography system is developed to achieve an accurate alignment between the focal plane of the microsphere lenses and the plane of the photoresist, facilitating the fabrication of patterned nanostructures. The lithographic nanostructures have a minimum feature size of 850 nm. This method enables the fabrication of arrays of microsphere-lens with arbitrary patterns and presents an inexpensive and simple strategy for fabricating micro- and nanostructure arrays with submicrometer features.

Liquid crystal immunosensors for the selective detection of Escherichia coli with a fast analysis tool

Sandro Oliveira, Simone Soares, Barbara goncalves, Andreia rodrigues, Amadeu Soares Soares, rita sobral, Nuno Santos, Jan Nedoma, Pedro Almeida, and Carlos Marques

DOI: 10.1364/PRJ.524660 Received 26 Mar 2024; Accepted 27 Apr 2024; Posted 29 Apr 2024  View: PDF

Abstract: The consumption of contaminated food can cause very serious illnesses, but traditional methods of Escherichia coli detection are still associated with long waiting times and high costs given the need to transport samples to specialized laboratories. There is a need to develop new technologies that allow cheap, fast, and direct monitoring at the site of interest. Thus, in this work, we developed optical immunosensors for the specific detection of E. coli, based on liquid crystal technology, whose molecules can align in different manners depending on the boundary conditions (such as substrates) as well as the environment that they experience. Each glass substrate was functionalized with anti-E. coli antibody using cysteamine as an intermediate, and a vertical alignment was imposed on the liquid crystal molecules by using DMOAP during functionalization. The presence of bacteria disrupts the alignment of the liquid crystal molecules, changing the intensity of light emerging between cross polarizers, measured using a polarized optical microscope and a monochromator. It was possible to detect E. coli in suspensions in the concentration range from 2.8 cells/mL to 2.8×109 cells/mL. Selectivity was also evaluated, and the sensors were used to analyze contaminated water samples. A prototype was also developed to allow faster, in-situ and easier analysis avoiding bulky instruments.

Frequency Stabilisation of C-band Semiconductor Lasers through SiN Photonic Integrated Circuit

Alessandro Brugnoni, Ali Kaplan, Valerio Vitali, Kyle Bottrill, Michele Re, Periklis Petropoulos, Cosimo Lacava, and Ilaria Cristiani

DOI: 10.1364/PRJ.516588 Received 21 Dec 2023; Accepted 23 Apr 2024; Posted 24 Apr 2024  View: PDF

Abstract: Integrated semiconductor lasers represent essential building blocks for integrated optical components and circuits and their stability in frequency is fundamental for the developments of numerous frontier applications and engineering development tasks.When dense optical circuits are considered, the stability of integrated laser sources can be impaired by the thermal cross-talk generated by the action of neighbouring components, leading to a deterioration of the long-term system performance (in the scale of seconds).In this work we show the design and the experimental characterization of a silicon nitride photonic integrated circuit (PIC) that is able to frequency stabilize 16 semiconductor lasers, simultaneously. A stabilised 50 GHz-spaced 2-channel system is demonstrated through the detection of the related beating note and the stability of the resulting waveform was characterized via the use of artificially induced thermal cross-talk stimuli.

Dual-curvilinear beam enabled simultaneous and tunable manipulation of light- and dark- seeking particles

Zheng Yuan, Chenchen Zhang, Yuan Gao, Wenxiang Yan, Xian Long, Zhi-Cheng Ren, Xi-Lin Wang, Jianping Ding, and Hui-Tian Wang

DOI: 10.1364/PRJ.520425 Received 01 Feb 2024; Accepted 23 Apr 2024; Posted 24 Apr 2024  View: PDF

Abstract: We present an innovative approach for the agile manipulation of light- and dark-seeking particles. Our method involves introducing a dual-curvilinear optical vortex beam (DC-OVB) generated by superimposing a pair of curved beams. The proposed DC-OVB provides customizable motion paths and velocities for both dark-seeking and light-seeking particles. Each curve of the DC-OVB can support a distinct orbital flow density (OFD), enabling the application of torques to light- and dark-seeking particles, guiding them to orbit along specified trajectories. We conduct experimental manipulations on light- and dark-seeking particles, prompting them to execute various curvilinear motions simultaneously, including linear movement, revolution, and rotation.

Spectral interferometry-based diff-iteration for high precision micro-dispersion measurement

Wei Du, Jingsheng Huang, yang wang, Maozhong Zhao, Juan Li, Juntao He, Jindong Wang, Wenfu Zhang, and Tao Zhu

DOI: 10.1364/PRJ.523314 Received 07 Mar 2024; Accepted 22 Apr 2024; Posted 22 Apr 2024  View: PDF

Abstract: Precise measurement of micro-dispersion for optical devices (optical fiber, lens, etc.) holds paramount significance across domains such as optical fiber communication, dispersion interference ranging. However, due to its complex system, complicated process and low reliability, the traditional dispersion measurement methods (interference, phase shift, or time delay methods) are not suitable for the accurate measurement of micro-dispersion in a wide spectral range. Here, we propose spectral interferometry-based diff-iteration (SiDi) method for achieving accurate wide-band micro-dispersion measurements. Using an optical frequency comb, based on the phase demodulation of dispersion interference spectrum, by employing the carefully designed SiDi method to solve the dispersion curve at any position and any order. Our approach is proficient in precisely measuring micro-dispersion across a broadband spectrum, without the need for cumbersome wavelength scanning processes or reliance on complex high-repetition-rate combs, while enabling adjustable resolution. The efficacy of the proposed method is validated through simulations and experiments. We employed a chip-scaled soliton microcomb (SMC) to compute the dispersion curves of a 14 m single-mode fiber (SMF) and a 0.05m glass, respectively. Compared to a laser interferometer or the theoretical value given by manufacturer, the average relative error of refractive index measurement for SMF reaches 2.8×10-6 and for glass reaches 3.8×10-6. The approach ensures high precision, while maintaining a simple system structure, with realizing adjustable resolution, thereby propelling the practical implementation of precise measurement and control-dispersion.

Detector-integrated vertical-cavity surface-emitting laser with a movable high-contrast grating mirror

Minglu Wang, HONGLING PENG, Chenxi Hao, Xuyan Zhou, Wan-hua Zheng, and Anjin Liu

DOI: 10.1364/PRJ.519679 Received 22 Jan 2024; Accepted 22 Apr 2024; Posted 22 Apr 2024  View: PDF

Abstract: In this paper, we present a detector-integrated vertical-cavity surface-emitting laser (VCSEL) with a movable high-contrast grating (HCG) mirror in an n-i-p-i-n manner. The detector-integrated VCSEL with a movable HCG can achieve three functions, including wavelength tuning, power monitoring, and resonant-cavity-enhanced (RCE) photon detection. Currently, the device can achieve a tuning range of 27 nm at room temperature when the suspended HCG is driven by the reverse bias voltage. The n-i-p structure located at the upper part of the device can serve as an intra-cavity photodiode to monitor the output power due to the defect absorption. The RCE photon detection function of the detector-integrated VCSEL with a movable HCG is measured, and it has a peak responsivity at about 926 nm. This detector-integrated VCSEL with a movable HCG will be useful for sensing and imaging.

Gbps key rate passive-state-preparation continuous-variable quantum key distribution within access-network area

FeiYu Ji, Peng Huang, Tao Wang, Xueqin Jiang, and Guihua Zeng

DOI: 10.1364/PRJ.519909 Received 25 Jan 2024; Accepted 22 Apr 2024; Posted 22 Apr 2024  View: PDF

Abstract: The conventional Gaussian-modulated coherent-state quantum key distribution (QKD) protocol requires the sender to perform active modulations based on true random number generator. Compared with it, the passive-state-preparation (PSP) continuous-variable quantum key distribution (CVQKD) equivalently performs modulations passively by exploring the intrinsic field fluctuations of a thermal source, which offers the prospect of chip integration QKD with low cost. In this paper, we propose and experimentally demonstrate a high-rate PSP-CVQKD scheme within access-network area using high-bandwidth detectors with continuous wave encoding and decoding way. By proposing effective methods for suppressing the noises during the PSP process and polarization multiplexing to decrease the photon leakage noises, we realize the high-intensity local oscillator transmission, thereby achieving coherent detection with high efficient, low noise and high bandwidth. The secure key rate over transmission distances of 5.005 km with and without consideration of finite-size effect are 273.25 Mbps and 1.09 Gbps. The use of PSP method boosts the asymptotic secret key rate of CVQKD to Gbps level for the first time within the range of the access network, which provides an effective and secure key distribution strategy for high-speed quantum cryptography access communication.

High Capacity, Low Power, Short Reach Integrated Silicon Photonic Interconnects

Andrew Netherton, Mario Dumont, Zach Nelson, Jahyun Koo, Jinesh Jhonsa, Alice Mo, David McCarthy, Skylar Deckoff-Jones, Yun Gao, Noah pestana, Jordan Goldstein, Ren Shiue, Christopher Poulton, MJ Kennedy, Mark Harrington, Bozhang Dong, Jock Bovington, Michael Frankel, Luke Theogarajan, Michael Watts, Daniel Blumenthal, and John Bowers

DOI: 10.1364/PRJ.520203 Received 29 Jan 2024; Accepted 21 Apr 2024; Posted 22 Apr 2024  View: PDF

Abstract: The architecture and component technology of low power, high capacity, short-reach optical interconnect are detailed. Techniques for operating such a system in the presence of changing ambient temperature are addressed. Experiments on a 1 Tbps design are conducted with an optical link experiment indicating sub-pJ/bit energy consumption at scale.

Ultra-high NA graphene oxide flat lens on fiber facet with near diffraction-limited focusing

xiaoke Chen, Lin Ma, Zuyuan He, Guiyuan Cao, Han Lin, and Baohua Jia

DOI: 10.1364/PRJ.521005 Received 08 Feb 2024; Accepted 20 Apr 2024; Posted 22 Apr 2024  View: PDF

Abstract: Realizing high numerical aperture (NA) fiber lens is critical to achieve high imaging resolution of endoscope and enable subwavelength operation in optical tweezers and high efficiency coupling between optical fibers and photonic chips. But it remains challenging with conventional design and fabrication. Here we propose an ultra-thin (400 𝑛𝑚) graphene oxide (GO) film lens in-situ fabricated on a standard single-mode fiber facet using the femtosecond laser direct writing technique. Extremely high NA of 0.89 has been realized with near diffraction-limited focal spot (FWHM=0.68 λ), which has been verified theoretically and experimentally.The diameter of the fabricated fiber GO lens is as small as 12 𝜇𝑚 with no beam expansion structure. The proposed fiber GO lens is promising in applications such as super-resolution imaging, compact optical tweezers, medical endoscopes and on-chip integration.

Burst-mode pulse generation in passively mode-locked all-fiber green/orange lasers at 543 nm and 602 nm

Qiujun Ruan, Jinhai Zou, chunna feng, Tingting Chen, hang wang, zhipeng dong, and Zhengqian Luo

DOI: 10.1364/PRJ.520141 Received 31 Jan 2024; Accepted 17 Apr 2024; Posted 18 Apr 2024  View: PDF

Abstract: We report on the experimental realization of, to the best of our knowledge, the first green and orange passively mode-locked all-fiber lasers. Stable mode-locking in the burst-pulse status is achieved at the wavelengths of 543.3 nm and 602.5 nm, respectively. The figure-9 cavity comprises the fiber end-facet mirror, gain fiber (Ho3+: ZBLAN fiber or Pr3+/Yb3+: ZBLAN fiber) and fiber loop mirror (FLM). The FLM with long 460 HP fiber is not only used as an output mirror, but also acts as a nonlinear optical loop mirror for initiating visible-wavelength mode-locking. The green/orange mode-locked fiber lasers with the fundamental repetition rates of 3.779/5.662 MHz produce long bursts containing ultrashort pulses with the 0.85/0.76 GHz intra-burst repetition rates, respectively. The ultrashort intra-burst pulses are stemmed from the dissipative four-wave-mixing effect in the highly nonlinear FLM as well as the intracavity Fabry-Perot filtering. Long bursts of 22.2/11.6 ns with ultrashort pulses of 87/62 ps are obtained in our experiment. The visible-wavelength passively mode-locked lasers in all-fiber configuration and burst-mode would represent an important step towards miniaturized ultrafast fiber laser and may contribute to the applications in ablation-cooling micromachining, bio-medicine imaging and scientific research.

Instantaneous preparation of gold-carbon dot nanocomposites for on-site SERS identification of pathogens in diverse interfaces

Yanxian Guo, Ye Liu, Chaocai Luo, Yue Zhang, Yang Li, Fei Zhou, Zhou Guo, Zhengfei Zhuang, and ZhinMing Liu

DOI: 10.1364/PRJ.522216 Received 26 Feb 2024; Accepted 15 Apr 2024; Posted 15 Apr 2024  View: PDF

Abstract: Herein, a facile and instantaneous synthetic route was firstly developed for grown Au core in molybdenum-doped gallic acid-derived carbon dots (Au@MCDs) shell without extrinsic reductant. The nanocomposites exhibited exceptional surface-enhanced Raman scattering (SERS) activity towards common organic pollutants by the synergistic effect of electromagnetic enhancement and charge transfer. The approach further enables the sensitive and reproducible foodborne pathogen detection in practical samples with anisotropic surfaces with a significant reduction in on-site detection time (within 5 min). Finally, the molecular fingerprint analysis and 3D PCA analysis of foodborne pathogen based on Au@MCDs was also completed, indicating the promising potential for widespread applications in biomedical research and clinical diagnostics.

Superconducting single photon detector with speed of 5 GHz and photon number resolution of 61

Tianzhu Zhang, Jia Huang, XINGYU ZHANG, ChaoMeng Ding, Huiqin Yu, Xiao You, ChaoLin Lv, Xiaoyu Liu, Zhen Wang, Lixing YOU, Xiaoming Xie, and Hao Li

DOI: 10.1364/PRJ.522714 Received 05 Mar 2024; Accepted 15 Apr 2024; Posted 15 Apr 2024  View: PDF

Abstract: Rapid detection and discrimination of single photons are pivotal in various applications, such as deep-space laser communication, high-rate quantum key distribution, and optical quantum computation. However, conventional single-photon detectors (SPDs), including semiconducting and recently developed superconducting detectors, have limited detection speed and photon number resolution (PNR), which pose significant challenges in practical applications. In this paper, we present an efficient, fast SPD with good PNR, which has 64 paralleled, sandwiched superconducting nanowires fabricated on a distributed Bragg reflector. The detector is operated in a compact Gifford–McMahon cryocooler that supports 64 electrical channels and has a minimum working temperature of 2.3 K. The combined detector system shows a functional nanowire yield of 61/64, a system detection efficiency of 90% at 1550 nm, and a maximum count rate of 5.2 GHz. Additionally, it has a maximum PNR of 61, corresponding to the operating nanowires. This SPD signifies a substantial improvement in quantum detector technology, with potential applications in deep-space laser communication, high-speed quantum communication, and fundamental quantum optics experiments.

Dual-objective two-photon microscope for volumetric imaging of dense scattering biological samples by bidirectional excitation and collection

Muyue Zhai, Jing Yu, Yanhui Hu, Hang Yu, Beichen Xie, Yi Yu, Dawei Li, Aimin Wang, and Heping Chen

DOI: 10.1364/PRJ.516824 Received 28 Dec 2023; Accepted 14 Apr 2024; Posted 15 Apr 2024  View: PDF

Abstract: Full view observation throughout entire specimens over a prolonged period is crucial when exploring the physiological functions and system-level behaviors. Multi-photon microscopy (MPM) has been widely employed for such purposes owing to its deep penetration ability. However, the current MPM struggles with balancing the imaging depth and quality while avoiding photodamage for the exponential increasement of excitation power with the imaging depth. Here, we present a dual objective two-photon microscope (Duo-2P), characterized by bidirectional two-photon excitation and fluorescence collection, for long-duration volumetric imaging of dense scattering samples. Duo-2P effectively doubles the imaging depth, reduces the total excitation energy by an order of magnitude for samples with a thickness five times the scattering length, and enhances the signal-to-noise ratio up to 1.4 times. Leveraging these advantages, we acquired volumetric images of a 380-μm suprachiasmatic nucleus slice for continuous 4-hour recording at a rate of 1.67 seconds/volume, visualized the calcium activities over 4000 neurons, and uncovered their state-switching behavior. We conclude that Duo-2P provides an elegant and powerful means to overcome the fundamental depth limit while mitigating photodamages for deep tissue volumetric imaging.

Grating-free autofocus for single-pixel microscopic imaging

Guan Wang, Huaxia Deng, Yu Cai, Mengchao Ma, Xiang Zhong, and xinglong gong

DOI: 10.1364/PRJ.519876 Received 01 Feb 2024; Accepted 14 Apr 2024; Posted 15 Apr 2024  View: PDF

Abstract: As a computational technology, single-pixel microscopic imaging (SPMI) transfers the target's spatial information into a temporal dimension. The traditional focusing method of imaging before evaluation is not applicable to the SPMI system. We propose a grating-free autofocus strategy derived from the physical mechanism of optical defocus. Maximizing the amplitude information of just one high-frequency point in the spectrum is all that is needed to achieve fast autofocus with the SPMI system. Accordingly, only 4 patterns need to be cyclically projected, enabling efficient localization of the focal plane based on the measurement data. We demonstrate SPMI autofocus experiments at micrometer and even nanometer depths of the field. The proposed method can be extended to achieve SMPI autofocus with invisible optical pattern illumination.

An integrated bound-state-in-continuum quantum photon-pair source

Fan Ye, Yue Qin, Chenfei Cui, Xiankai Sun, and Hon Tsang

DOI: 10.1364/PRJ.521058 Received 07 Feb 2024; Accepted 14 Apr 2024; Posted 15 Apr 2024  View: PDF

Abstract: Integrated photon-pair sources based on spontaneous parametric down conversion (SPDC) in novel high-χ(2) materials are used in quantum photonic systems for quantum information processing, quantum metrology and quantum simulations. However, the need for extensive fabrication process development and optimization of dry etching processes significantly impedes the rapid exploration of different material platforms for low-loss quantum photonic circuits. Recently, bound states in the continuum (BICs) have emerged as a promising approach for realizing ultralow-loss integrated photonic circuits without requiring the development of etching process specific to that material. Previous realizations of BIC photonic circuits have however been primarily limited to the classical regimes. Here, we explore the BIC phenomena in the quantum regime, and show that the etchless BIC platform is suitable for use in integrated entangled photon-pair sources based on SPDC process in high-χ(2) materials. Using lithium niobate as an example, we demonstrate photon-pair generation at telecommunication wavelengths, attaining a maximum internal generation rate of 3.46 MHz, a coincidence-to-accidental ratio of 5773, and an experimental two‐photon interference visibility of 94%. Our results demonstrate that the BIC platform may be used for quantum photonic circuits, and this will enable the rapid exploration of different emerging χ(2) materials for possible use in integrated quantum photonics in the future.

Manipulation of Low-refractive-index Particles Using Customized Dark Traps

Ming Lei, Minru He, Yansheng Liang, XUE YUN, Shaowei Wang, Tianyu Zhao, Linquan Guo, Xinyu Zhang, Shiqi Kuang, and Jinxiao Chen

DOI: 10.1364/PRJ.523874 Received 15 Mar 2024; Accepted 12 Apr 2024; Posted 12 Apr 2024  View: PDF

Abstract: Low-refractive-index particles play significant roles in physics, drug delivery, biomedical science, and other fields. However, they haven’t attained sufficient utilization in active manipulation due to the repulsive effect of light. In this work, the establishment of customized dark traps is demonstrated, to fulfill the demands of versatile manipulation of low-refractive-index particles. The customized dark traps are generated by assembling generalized perfect optical vortices based on the free lens modulation method, by which the beams' shape, intensity, and position can be elaborately designed with size independent of topological charge. Using the customized dark traps with high quality and high efficiency, rotation along arbitrary trajectories with controllable speed, parallel manipulation, and sorting of low-refractive-index particles by size can be realized. With unprecedented flexibility and quality, the customized dark traps provide tremendous potential in optical trapping, lithography, and biomedicine.

Flexible incidence angle scanning surface plasmon resonance microscopy for morphology detection with enhanced contrast

lingke wang, Jingyu Mi, Shuqi Wang, Wenrui Li, Ju Tang, Jiwei Zhang, jiawei zhang, and Jianlin Zhao

DOI: 10.1364/PRJ.519727 Received 23 Jan 2024; Accepted 09 Apr 2024; Posted 10 Apr 2024  View: PDF

Abstract: Surface plasmon resonance microscopy (SPRM) has been massively applied for near-field optical measurement, sensing, and imaging because of its high sensitivity, non-destructive, non-invasive, wide-field, and label-free imaging capabilities. However, the transverse propagation characteristic of the surface plasmon wave generated during surface plasmon resonance (SPR) leads to the notable “tail” patterns in the SPR image which severely deteriorates the image quality. Here, we propose an incidence angle scanning method in SPRM to obtain resonance angle image with exceptional contrast which significantly mitigates the adverse effects of “tail” patterns. The resonance angle image provides the complete morphology of the analyzed samples and enables two-dimensional quantification which is incapable in conventional SPRM. The effectiveness of the method was experimentally verified using photoresist square samples with different sizes and two-dimensional materials with various geometric shapes. The edges of samples were fully reconstructed and a maximum five-fold increase in image contrast has been achieved. Our method offers a convenient way to enhance the SPRM imaging capabilities with low cost and stable performance, which greatly expands the application of SPRM in label-free detection, imaging, and quantification.

Broadband Intelligent Programmable Metasurface with Polarization-Modulated Self-Adaptively Electromagnetic Functionality Switching

Ximing Li, Rui Xu, XiaoFeng Sun, Yuan Zhao, Zhao Yang, and GuoHong Du

DOI: 10.1364/PRJ.520779 Received 09 Feb 2024; Accepted 09 Apr 2024; Posted 10 Apr 2024  View: PDF

Abstract: Programmable metasurfaces have received a great deal of attention due to their ability to dynamically manipulate electromagnetic (EM) waves. Despite the rapid growth, most of the existing metasurfaces require manual control to switch among different functionalities, which poses severe limitations on practical applications. Here, we put forth an intelligent metasurface that has self-adaptively EM functionality switching in broadband without human participation. It is equipped with polarization discrimination antennas (PDAs) and feedback components to automatically adjust functionalities for the different incident polarization information. The PDAs module can first perceive the polarization of incident EM waves, e.g., linear or circular polarization, and then provide the feedback signal to the controlling platform for switching the EM functionality. As exemplary demonstrations, a series of functionalities in 9-22 GHz bands have been realized, including beam scanning for x-polarization, specular reflection for y-polarization, diffuse scattering for left-handed circular polarization (LCP), and vortex beam generation for right-handed circular polarization (RCP) wave. Experiments verify the good self-adaptive reaction capability of the intelligent metasurface and are in good agreement with the designs. Our strategy provides an avenue toward future unmanned devices that are consistent with the ambient environment.

Screening COVID-19 from Chest X-ray Images by Optical Diffractive Neural Network with the Optimized F number

JiaLong Wang, Shouyu Chai, Wenting Gu, Boyi Li, Xue Jiang, Yunxiang Zhang, Hongen Liao, Xin liu, and Dean Ta

DOI: 10.1364/PRJ.513537 Received 20 Nov 2023; Accepted 07 Apr 2024; Posted 08 Apr 2024  View: PDF

Abstract: The COVID-19 pandemic continues to significantly impact people’s lives worldwide, emphasizing the critical need for effective detection methods. Many existing deep learning-based approaches for COVID-19 detection offer high accuracy but demand substantial computing resources, time, and energy. In this study, we introduce an optical diffraction neural network (ODNN-COVID) that distinguish itself with low power consumption, efficient parallelization, and fast computing speed for COVID-19 detection. Our system achieves an impressive overall accuracy of 92.64% in binary-classification and 88.89% in three-classification diagnosis tasks. In addition, we explore how the physical parameters of ODNN-COVID affect its diagnostic performance. We identify the F number as a key parameter for evaluating the overall detection capabilities. Through an assessment of the connectivity of the diffraction network, we established an optimized range of F numbers, offering guidance for constructing optical diffraction neural networks. Both simulations and experiments validate that our proposed optical diffractive neural network serve as a passive optical processor for effective COVID-19 diagnosis, featuring low power consumption, high parallelization, and fast computing capabilities. Furthermore, ODNN-COVID exhibits versatility, making it adaptable to various image analysis and object classification tasks related to medical fields owing to its general architecture.

High-resolution mid-infrared single-photon upconversion ranging

Shuhong Jiang, Kun Huang, Tingting Yu, Jianan Fang, Ben Sun, Yan Liang, Qiang Hao, E Wu, Ming Yan, and Heping Zeng

DOI: 10.1364/PRJ.522253 Received 23 Feb 2024; Accepted 06 Apr 2024; Posted 08 Apr 2024  View: PDF

Abstract: Single-photon laser ranging has widespread applications in remote sensing and target recognition. However, highly-sensitive light detection and ranging (LiDAR) has long been restricted in visible or near-infrared bands. An appealing quest is to extend the operation wavelength into the mid-infrared (MIR) region, which calls for an infrared photon counting system at high detection sensitivity and precise temporal resolution. Here, we devise and demonstrate a MIR upconversion LiDAR based on nonlinear asynchronous optical sampling. Specifically, the infrared probe is interrogated in a nonlinear crystal by a train of pump pulses at a slightly different repetition rate, which favors for a temporal optical scanning at a picosecond timing resolution and a kilohertz refreshing rate over ~50 ns. Moreover, the cross-correlation upconversion trace is temporally stretched by a factor of 2×10⁴, which can thus be recorded by a low-bandwidth silicon detector. In combination with time-correlated photon-counting technique, the achieved effective resolution is about two orders of magnitude better than the timing jitter of the detector itself, which facilitates a ranging precision of 4 μm under a low detected flux of 8×10¯⁵ photons per pulse. The presented MIR time-of-flight range finder is featured with single-photon sensitivity and high positioning resolution, which would be particularly useful in infrared sensing and imaging in photon-starved scenarios.

Dynamic 3D holographic projection of vectorial images with a multimode fiber

jinghan zhuang, Panpan Yu, Yifan Liu, yijing wu, Ziqiang Wang, Yinmei Li, and Lei Gong

DOI: 10.1364/PRJ.514689 Received 01 Dec 2023; Accepted 04 Apr 2024; Posted 08 Apr 2024  View: PDF

Abstract: An optical multimode fiber (MMF) is capable of delivering structured light modes or complex images with high flexibility. Here, we present a holographic approach to enable the MMF as a 3D holographic projector with the capability of complete polarization control. By harnessing the strong coupling of the spatial and polarization degrees of freedom of light propagating through MMFs, our approach realizes active control of the output intensity and polarization in 3D space by shaping only the wavefront of the incident light. In this manner, we demonstrate MMF-based holographic projection of vectorial images on multiple planes via a phase-only hologram. Particularly, dynamic projection of polarization-multiplexed grayscale images is presented with an averaged Pearson correlation coefficient of up to 0.92. Our work will benefit fiber-based holographic displays, optical imaging and manipulation.

Experimental demonstration of quantum downstream access network in continuous variable quantum key distribution with a local local oscillator

Dengke Qi, Xiangyu Wang, Zhenghua Li, Jiayu Ma, Ziyang Chen, Yueming Lu, and Song Yu

DOI: 10.1364/PRJ.519140 Received 16 Jan 2024; Accepted 04 Apr 2024; Posted 04 Apr 2024  View: PDF

Abstract: Quantum networks provide opportunities and challenges across a range of intellectual and technical frontiers, including quantum computation, communication and others. Unlike traditional communication networks, quantum networks utilize quantum bits rather than classical bits to store and transmit information. Quantum key distribution (QKD) relying on the principles of quantum mechanics is a key component in quantum networks enables two parties to produce a shared random secret key, thereby ensuring the security of data transmission. In this work, we propose a cost-effective quantum downstream access network structure in which each user can get their corresponding key information through terminal distribution. Based on this structure, we demonstrate the first four-end-users quantum downstream access network in continuous variable QKD with a local local oscillator. In contrast to point-to-point continuous variable QKD, the network architecture reevaluates the security of each user and accounts for it accordingly, and each user has a lower tolerance for excess noise as the overall network expands with more users. Hence, the feasibility of the experiment is based on the analysis of theoretical model, noise analysis, and multiple techniques such as particle filtering and adaptive equalization algorithm used to suppress excess noise. The results show that each user can get a low level of excess noise and can achieve secret key rate of 546 kbps, 535 kbps, 522.5 kbps and 512.5 kbps under transmission distance of 10 km, respectively with the finite-size block of 1×10⁸. This not only verifies the good performance but also provides the foundation for the future multi-users quantum downstream access network.

Ka-band thin film Lithium Niobate photonic integrated optoelectronics oscillator

Rui Ma, ZIJUN HUANG, Shengqian Gao, Jingyi Wang, XICHEN WANG, xian zhang, PENG HAO, Steve Yao, and Xinlun Cai

DOI: 10.1364/PRJ.521301 Received 09 Feb 2024; Accepted 03 Apr 2024; Posted 04 Apr 2024  View: PDF

Abstract: Photonics integration of an optoelectronic oscillator (OEO) on a chip is attractive for fabricating low cost, compact, low power consumption, and highly reliable microwave sources, which has been demonstrated recently in silicon on insulator (SOI) and indium phosphide (InP) platforms at X-band around 8 GHz. Here we demonstrate the first integration of OEOs on the thin film Lithium Niobate (TFLN) platform, which has the advantages of lower Vπ, no chirp, wider frequency range, and less sensitivity to temperature. We have successfully realized two different OEOs operating at Ka-band, with phase noises even lower than those of the X-band OEOs on SOI and InP platforms. One is a fixed frequency OEO at 30 GHz realized by integrating a Mach-Zehnder modulator (MZM) with an add-drop microring resonator (MRR), and the other is a tunable frequency OEO at 20-35 GHz realized by integrating a phase modulator (PM) with a notch MRR. Our work marks a first step of using TFLN to fabricate integrated OEOs with high frequency, small size, low cost, wide range tenability and potentially low phase noise.

Experimental demonstration of non-reciprocity effects on satellite-based two-way time-frequency transfer links

ting zeng, Qi Shen, Yuan Cao, Jian-Yu Guan, Meng-Zhe Lian, Jin-Jian Han, lei hou, jian lu, xinxin peng, Min Li, WeiYue Liu, Jincai Wu, yong wang, Juan Yin, Ji-Gang Ren, Hai-Feng Jiang, Qiang Zhang, Cheng-Zhi Peng, and Jian-Wei Pan

DOI: 10.1364/PRJ.511141 Received 06 Nov 2023; Accepted 02 Apr 2024; Posted 02 Apr 2024  View: PDF

Abstract: Future optical clock networks will require high-precision optical time-frequency transfer between satellites and ground stations. However, the standard two-way time transfer's time-of-flight reciprocity breaks down due to the spatio-temporal displacement caused by point-ahead effects and delay effects between the satellite and ground. Here, we experimentally demonstrate the impact of spatio-temporal displacement on high-precision optical time-frequency transfer between two stationary terminals located 113 km apart. We implement optical transceiver in each terminal with separate transmitting and receiving paths using an orthogonal polarization scheme, and construct a separate two-way atmospheric link with an asymmetric distance of 174 mm which is a consequence of point-ahead effects. Additionally, the delay effect is simulated by shifting the time labels of one side with the experimental data. Our experiment show that the impact of spatio-temporal displacement on the link instability is less than 2.3 ×10^{-19} at 10000 s. This indicates that when the link instability of satellite-ground optical time-frequency transfer is on the order of 10^{-19}, it is not necessary to consider non-reciprocal point-ahead effects and delay effects.

Ionic-Gated Perovskite Quantum Dots/Graphene Heterojunction Synaptic Transistor with Bipolar Photoresponse for Neuromorphic Computing

Xiaoying He, Minghao Xu, Shilin Liu, Kun Wang, Bowen Cao, Lan Rao, and Xiangjun Xin

DOI: 10.1364/PRJ.516207 Received 19 Dec 2023; Accepted 28 Mar 2024; Posted 29 Mar 2024  View: PDF

Abstract: By combining good charge transport property of graphene and excellent photo-carrier’s generation characteristic of perovskite quantum dots (PQDs), we propose and demonstrate an ionic-gated synaptic transistor based on CsPbBr3 QDs/graphene heterojunction for bipolar photoresponse. Controlling potential barrier of the CsPbBr3 QDs/graphene heterojunction can promote the separation of photogenerated carrier pairs and effectively retard their recombination. Using the ionic-gate-tunable Fermi level of the graphene and the pinning effect of PQDs, bipolar photocurrents response corresponding to the excitatory and inhibitory short-term and long-term plasticity are realized by adjusting the negative gate bias. A series of synaptic functions including logic operation, Morse code decoding, the optical memory and electrical erasure effect, and light-assisted re-learning have also been demonstrated in an optoelectronic collaborative pathway. Furthermore, the excellent optical synaptic behaviors also contribute to the handwritten font recognition accuracy of ~ 95% in artificial neural network simulations. The results pave the way for the fabrication of the bipolar photoelectric synaptic transistors and bolster new directions in the development of future integrated human retinotopic vision neuromorphic system.

Two-dimensional flow vector measurement based on all-fiber laser feedback frequency-shifted multiplexing technology

Lei Zhang, Jialiang Lv, Yunkun Zhao, Jie Li, Keyan Liu, Qi Yu, Hongtao Li, Benli Yu, and liang lu

DOI: 10.1364/PRJ.516560 Received 21 Dec 2023; Accepted 28 Mar 2024; Posted 29 Mar 2024  View: PDF

Abstract: The decomposition and identification of signals are crucial for flow vector acquisition in a multi-dimensional measurement. Here, we proposed a two-dimensional (2D) flow vector measurement system based on all-fiber laser feedback frequency-shifted multiplexing technology. The reliable performance of the system is characterized by experimental verification and numerical simulation. An orthogonal dual-beam structure is employed to eliminate the impact of an unknown incident angle in the practical application. Meanwhile, the vector velocity signals in 2D can be decomposed into one-dimensional (1D) scalar signals by adopting the frequency-shifted multiplexing, which makes it easy to obtain the vector information and velocity distribution of fluid motion through the self-mixing interference frequency spectrum. Moreover, the measured flow rates present a high linearity with syringe pump speeds ranging from 200 - 2000 μL/min, and the velocity information of the different incidence angles is easily obtained with high precision. This work may pave the way for the acquisition and processing of multi-dimensional flow vector signals, with potential applications in biomedical monitoring and microflow velocity sensing.

Picotesla fiberized diamond-based AC magnetometer

Zhang Shaochun, Yong Liu, Long-Kun Shan, Xue-Dong Gao, Jiaqi Geng, Cui Yu, Yang Dong, Xiangdong Chen, Guang-can Guo, and Fang-Wen Sun

DOI: 10.1364/PRJ.522062 Received 23 Feb 2024; Accepted 27 Mar 2024; Posted 29 Mar 2024  View: PDF

Abstract: Portable quantum sensors are crucial for developing practical quantum sensing and metrology applications. Fiberized nitrogen-vacancy (NV) centers in diamonds have emerged as one of the most promising candidates for compact quantum sensors. Nevertheless, due to the difficulty of coherently controlling the ensemble spin and noise suppression in a large volume, it often faces problems such as reduced sensitivity and narrowed bandwidth in integrated lensless applications. Here, we propose a fluorescence signal treatment method for NV spin ensemble manipulation by the exponential fitting of spin polarization processes, instead of integrating the photon emission. This enables spin state readout with a high signal-to-noise ratio and applies to the pulse sensing protocols for large-volume NV spins. Based on this, we further developed a fiberized diamond-based AC magnetometer. With XY8-N dynamical decoupling pulse sequence, we demonstrated a $T_2$-limited sensitivity of 8 pT$\rm{/\sqrt{Hz}}$ and $T_1$-limited frequency resolution of 90 Hz over a wide frequency band from 100 kHz to 3 MHz. This integrated diamond sensor leverages quantum coherence to achieve enhanced sensitivity in detecting AC magnetic fields, making it suitable for implementation in a compact, and portable endoscopic sensor.

Towards ultrafast 3D imaging scanning LiDAR system: a review

Zhi Li, Yaqi Han, Lican Wu, Zihan Zang, Maolin Dai, Sze Set, Shinji Yamashita, Qian Li, and Hongyan Fu

DOI: 10.1364/PRJ.509710 Received 15 Nov 2023; Accepted 27 Mar 2024; Posted 29 Mar 2024  View: PDF

Abstract: Light detection and ranging (LiDAR), as a hot imaging technology in both industry and academia, has undergone rapid innovation and evolution. The current mainstream direction is towards system miniaturization and integration. There are many metrics that can be used to evaluate the performance of a LiDAR system, such as lateral resolution, ranging accuracy, stability, size, and price. Until recently, with the continuous enrichment of LiDAR application scenarios, the pursuit of imaging speed has attracted tremendous research interest. Particularly, for autonomous vehicles running on motorways or industrial automation applications, the imaging speed of LiDAR systems is a critical bottleneck. In this review, we will focus on discussing the upper speed limit of the LiDAR system. Based on the working mechanism, the limitation of optical parts on the maximum imaging speed is analyzed. The beam scanner has the greatest impact on imaging speed. We provide the working principle of current popular beam scanners used in LiDAR systems and summarize the main constraints on the scanning speed. Especially, we highlight the spectral scanning LiDAR as a new paradigm of ultrafast LiDAR. Additionally, to further improve the imaging speed, we then review the parallel detection methods which includes multiple-detector schemes and multiplexing technologies. Furthermore, we summarize the LiDAR systems with the fastest point acquisition rate reported nowadays. In the outlook, we address the current technical challenges for ultrafast LiDAR systems from different aspects and give a brief analysis of the feasibility of different approaches.

Advancing large-scale thin-film PPLN nonlinear photonics with segmented tunable micro-heaters

Xiaoting LI, Haochuan Li, zhenzheng wang, Zhaoxi CHEN, Fei Ma, Ke ZHANG, wenzhao sun, and Cheng Wang

DOI: 10.1364/PRJ.516180 Received 15 Dec 2023; Accepted 27 Mar 2024; Posted 29 Mar 2024  View: PDF

Abstract: Thin-film periodically poled lithium niobate (TF-PPLN) devices have recently gained prominence forefficient wavelength conversion processes in both classical and quantum applications. However, thepatterning and poling of TF-PPLN devices today are mostly performed at chip scales, presenting a significantbottleneck for future large-scale nonlinear photonic systems that require the integration of multiplenonlinear components with consistent performance and low cost. Here, we take a pivotal step towards thisgoal by developing a wafer-scale TF-PPLN nonlinear photonic platform, leveraging ultraviolet stepperlithography and an automated poling process. To address the inhomogeneous broadening of the quasiphasematching (QPM) spectrum induced by film thickness variations across the wafer, we propose anddemonstrate segmented thermal optic tuning modules that can precisely adjust and align the QPM peakwavelengths in each section. Using the segmented micro-heaters, we show the successful realignment ofinhomogeneously broadened multi-peak QPM spectra with more than doubled peak second-harmonicgeneration efficiency. The advanced fabrication techniques and segmented tuning architectures presentedherein pave the way for wafer-scale integration of complex functional nonlinear photonic circuits withapplications in quantum information processing, precision sensing and metrology, and low-noise-figureoptical signal amplification.

On-chip Source-Device-Independent Quantum Random Number Generator

Lang Li, minglu cai, Tao Wang, Zicong Tan, Peng Huang, Kan Wu, and Guihua Zeng

DOI: 10.1364/PRJ.506960 Received 29 Sep 2023; Accepted 26 Mar 2024; Posted 01 Apr 2024  View: PDF

Abstract: Quantum resources offer intrinsic randomness that is valuable for applications such as cryptography, scientific simulation, and computing. Silicon-based photonics chips present an excellent platform for the cost-effective deployment of next-generation quantum systems on a large scale, even at room temperature. Nevertheless, the potential susceptibility of these chips to hacker control poses a challenge in ensuring security for on-chip quantum random number generation, which is crucial for enabling extensive utilization of quantum resources. Here, we introduce and implement an on-chip source-device-independent quantum random number generator (SDI-QRNG). The randomness of this generator is achieved through distortion-free on-chip detection of quantum resources, effectively eliminating classical noise interference. The security of the system is ensured by employing on-chip criteria for estimating security entropy in a practical chip environment. By incorporating a photoelectric package, the SDI-QRNG chip achieves a secure bit rate of 146.2 Mbps and a bare chip rate of 248.47 Gbps, with all extracted secure bits successfully passing the randomness test. Our experimental demonstration of this chip-level SDI-QRNG shows significant advantages in practical applications, paving the way for the widespread and cost-effective implementation of room-temperature secure QRNG, which marks a milestone in the field of QRNG chips.

Addressable structured light system using metasurface optics and individually addressable VCSEL array

Chenyang Wu, Xuanlun Huang, Yipeng Ji, Tingyu Cheng, Jiaxing Wang, Nan Chi, Shaohua Yu, and Connie Chang-Hasnain

DOI: 10.1364/PRJ.516942 Received 08 Jan 2024; Accepted 26 Mar 2024; Posted 29 Mar 2024  View: PDF

Abstract: Structured-light (SL) based 3D sensors have been widely used in many fields. Speckle SL is the most widely deployed among all SL sensors due to its light weight, compact size, fast video rate and low cost. The transmitter (known as the dot projector) consists of a randomly patterned vertical-cavity surface-emitting lasers (VCSEL) array multiplicated by a Diffractive Optical Element (DOE) with a fixed repeated pattern. The receiver is a CMOS image sensor placed at a fixed distance from the dot projector. The randomness of speckles is used to identify the two-dimensional x-y coordinates of a given pair of speckles. The depth information associated with this x-y coordinate is derived from the deformed speckle images deviated from the pair’s known separation based on triangulation principle. Based on matching deformed speckle images reflected from the detected target with a known speckle reference image, the 3D image is obtained. Given that the separation of any two speckles is only one known and fixed number (albeit random), there are no other known scales to calibrate or average. Hence, typical SL sensors require extensive in-factory calibrations, and the depth resolution is limited to 1mm at ~60 cm distance. In this paper, we propose a novel dot projector and a new addressable SL (ASL) 3D sensor by using a regularly spaced, individually addressable VCSEL array, multiplicated by a metasurface-DOE (MDOE) into a random pattern of the array. The randomness of the MDOE enables the determination of the x-y coordinates of the VCSEL array. Dynamically turning on or off the VCSELs in the array provides multiple known distances between neighboring speckles, which is used as a “built-in caliper” to achieve higher accuracy of the depth. Serving as a precise "vernier caliper", the addressable VCSEL array enables fine control over speckle positions and high detection precision. We experimentally demonstrated the proposed method can result in sub-hundred microns level precision. This new concept opens new possibilities for applications such as 3D computation, facial recognition and wearable devices.

Self-aligned Dual-beam Superresolution Laser Direct Writing with Polarization Engineered Depletion Beam

Guoliang Chen, Dewei Mo, Jian Chen, and Qiwen Zhan

DOI: 10.1364/PRJ.518734 Received 12 Jan 2024; Accepted 25 Mar 2024; Posted 25 Mar 2024  View: PDF

Abstract: A fiber-based, self-aligned dual-beam laser direct writing system with a polarization-engineered depletion beam is designed, constructed, and tested. This system employs a vortex fiber to generate a donut-shaped, cylindrically polarized depletion beam while simultaneously allowing the fundamental mode excitation beam to pass through. This results in a co-axially self-aligned dual-beam source, enhancing stability and mitigating assembly complexities. The size of the central dark spot of the focused cylindrical vector depletion beam can be easily adjusted using a simple polarization rotation device. With a depletion wavelength of 532 nm and an excitation wavelength of 800 nm, the dual-beam laser direct writing system has demonstrated a single linewidth of 63 nm and a minimum line spacing of 173 nm. Further optimization of this system may pave the way for practical super-resolution photolithography that surpasses the diffraction limit.

Optical manipulation of ratio-designable Janus microspheres

Yulu Chen, Cong Zhai, Xiaoqing Gao, Han Wang, Zuzeng Lin, Xiaowei Zhou, and Chunguang Hu

DOI: 10.1364/PRJ.517601 Received 04 Jan 2024; Accepted 22 Mar 2024; Posted 25 Mar 2024  View: PDF

Abstract: Angular optical trapping based on Janus microspheres has been proven to be a novel method to achieve controllable rotation. In contrast to natural birefringent crystals, Janus microspheres are chemically synthesized of two compositions with different refractive indices. Thus, their structures can be artificially regulated, which brings excellent potential for fine and multi-degree-of-freedom manipulation in the optical field. However, it is a considerable challenge to model the interaction of heterogeneous particles with the optical field, and there has also been no experimental study on the optical manipulation of microspheres with such designable refractive index ratios. How the specific structure affects the kinematic properties of Janus microspheres remains unknown. Here, we report systematic research on the optical trapping and rotating of various ratio-designable Janus microspheres. We employ an efficient T-matrix method to rapidly calculate the optical force and torque on Janus microspheres to obtain their trapped postures and rotational characteristics in the optical field. We have developed a robust microfluidic-based scheme to prepare Janus microspheres. Our experimental results demonstrate the relationship between the microspheres’ kinematic characteristics and refractive index distributions. The trapped postures vary linearly within a specific ratio range, which is of great importance in guiding the design of Janus microspheres, and their orientations flip at a particular ratio, all consistent with the simulations. Our work provides a reliable theoretical analysis and experimental strategy for studying the interaction of heterogeneous particles with the optical field and further expands the diverse manipulation capabilities of optical tweezers.

A low-phase-noise K-band signal generation using polarization diverse single-soliton integrated microcomb

Alwaleed Aldhafeeri, Hsiao-Hsuan Chin, Tristan Melton, Allen Chu, Wenting Wang, Mingbin Yu, Patrick Lo, Dim-Lee Kwong, and Chee Wei Wong

DOI: 10.1364/PRJ.521282 Received 13 Feb 2024; Accepted 20 Mar 2024; Posted 25 Mar 2024  View: PDF

Abstract: Frequency microcombs with microwave and millimeter-wave repetition rates provide a compact solution for coherent communication and information processing. The implementation of these microcombs using a CMOS-compatible platform further paves the way for large-scale photonic integration and modularity. Here we demonstrate free-running soliton microcombs with K-band repetition rates with very low phase noise over a 4 GHz pump detuning range reaching −117(-1 )dBc/Hz at 10kHz offset for a 19.7(10) GHz carrier without active pump stabilization, exceeding commercial electronic microwave oscillators at frequency offsets above 40 kHz. The minimum laser noise to soliton microwave signal transduction factor observed is -73 dB. This noise performance is achieved using a hybridized dual-mode for soliton generation to achieve passive thermal stabilization and minimal soliton spectrum shift from prior Raman scattering and dispersive wave formation. We further examine the locking of the repetition rate to an external ultra-stable photonic oscillator to illustrate the feasibility of phase noise suppression below the thermorefractive noise limits of microresonator frequency combs.

Transient long-range distance measurement by a Vernier spectral interferometry

Chi Zhang, Liang Xu, Kun Wang, Chen Liu, Wenying Chen, and Xinliang Zhang

DOI: 10.1364/PRJ.515112 Received 05 Dec 2023; Accepted 19 Mar 2024; Posted 19 Mar 2024  View: PDF

Abstract: Rapid and long-range distance measurements are essential in various industrial and scientific applications, and among them, the dual-comb ranging system attracts great attention due to its high precision. However, the temporal asynchronous sampling results in the tradeoff between frame rate and ranging precision, and the non-ambiguity range (NAR) is also limited by the comb cycle, which hinders the further advancement of the dual-comb ranging system. Given this constraint, we introduce a Vernier spectral interferometry to improve the frame rate and NAR of the ranging system. First, leveraging the dispersive time-stretch technology, the dual-comb interferometry becomes spectral interferometry. Thus, its asynchronous time step is greatly enlarged, and the frame rate is improved to 100 kHz. Second, dual-wavelength bands are introduced to implement a Vernier spectral interferometry, whose NAR is enlarged from 1.5 m to 1.5 km. Moreover, this fast and long-range system also demonstrated high precision, with a 22.91-nm Allan deviation over 10-ms averaging time. As a result, the proposed Vernier spectral interferometry ranging system is promising for diverse applications that necessitate rapid and extensive distance measurement.

Asymmetric frequency multiplexing topological devices based on floating edge band

Jiajun Ma, Chunmei Ouyang, Yuting Yang, Dongyang Wang, hongyi li, Li Niu, Yi Liu, Quan Xu, Yanfeng Li, Zhen tian, Jiaguang Han, and Weili Zhang

DOI: 10.1364/PRJ.518426 Received 12 Jan 2024; Accepted 19 Mar 2024; Posted 20 Mar 2024  View: PDF

Abstract: Topological photonics provide a platform for robust energy transport regardless of sharp corners and defects. Recently, the frequency multiplexing topological devices have attracted much attention due to the ability to separate optical signals by wavelength and hence the potential application in optical communication systems. The existing frequency multiplexing topological devices are generally based on the slow light effect. However, the group velocity of such the resulting static spatial local mode or finely-tuned flat band is zero, making it difficult for both experimental excitation and channel out-coupling. Here, we propose and experimentally demonstrate an alternative prototype of asymmetric frequency multiplexing devices including topological rainbow and frequency router based on floating topological edge mode (instead of localized ones), hence the multiple wavelength channels can be collectively excited with a point source and efficiently routed to separate output ports. The channel separation in our design is achieved by the gradually tuned bandgap truncation on a topological edge band covering a wide range of frequencies. Wherein, a crucial feature lies in that the topological edge band is detached from bulk states and floating within the upper and lower photonic band gaps. More interestingly, due to the sandwiched morphology of the edge band, the top and bottom band gaps will each truncate into transport channels that support topological propagation towards opposite directions, and the asymmetrical transportation is first-time realized for the frequency multiplexing topological devices.

High-speed GaN-based laser diode with modulation bandwidth exceeding 5 GHz for 20 Gbps visible light communication

Junfei Wang, Junhui Hu, Chaowen Guan, Yuqi Hou, Zengyi Xu, Leihao Sun, Yue Wang, Yuning Zhou, Boon Ooi, Jianyang Shi, Ziwei Li, Junwen Zhang, Nan Chi, Shaohua Yu, and Chao Shen

DOI: 10.1364/PRJ.516829 Received 03 Jan 2024; Accepted 18 Mar 2024; Posted 19 Mar 2024  View: PDF

Abstract: Visible light communication (VLC) based on laser diodes demonstrates great potential for high data rate maritime, terrestrial, and aerial wireless data links. Here, we design and fabricate high-speed blue laser diodes (LDs) grown on c-plane gallium nitride (GaN) substrate. This was achieved through active region design and miniaturization towards a narrow ridge waveguide, short cavity length, single longitudinal mode Fabry-Perot laser diode. The fabricated mini-LD has a low threshold current of 31 mA, and slope efficiency of 1.02 W/A. A record modulation bandwidth of 5.9 GHz (-3 dB) was measured from the mini-LD. Using the developed mini-LD as a transmitter, the VLC link exhibits a high data transmission rate of 20.06 Gbps adopting the bit and power loading discrete multitone (DMT) modulation technique. The corresponding bit error rate is 0.003, satisfying the forward error correction standard. The demonstrated GaN-based mini-LD has significantly enhanced data transmission rates, paving the path for energy-efficient VLC systems and integrated photonics in the visible regime.

Short-term prediction for chaotic time series based on photonic reservoir computing using VCSEL with feedback loop

Xingxing Guo, Hanxu Zhou, shui xiang, Qian Yu, YAHUI ZHANG, Yanan Han, Tao Wang, and Yue Hao

DOI: 10.1364/PRJ.517275 Received 03 Jan 2024; Accepted 18 Mar 2024; Posted 19 Mar 2024  View: PDF

Abstract: Chaos, occurring in a deterministic system, has permeated various fields such as mathematics, physics, and life science. Consequently, the prediction of chaotic time series has received widespread attention and made significant progress. However, many problems, such as high computational complexity and difficulty in hardware implementation, could not be solved by existing scheme. To overcome the problems, we employ the chaotic system of VCSEL mutual coupling network to generate chaotic time series through optical system simulation and experimentation in this paper. Furthermore, a photonic reservoir computing based on VCSEL, along with feedback loop, is proposed for the short-term prediction of the chaotic time series. The relationship between the prediction difficulty of the RC computing system and the difference in complexity of the chaotic time series has been studied with emphasis. Additionally, the attention coefficient of injection strength and feedback strength, prediction duration and other factors on system performance are considered in both simulation and experiment. The use of RC system to predict the chaotic time series generated by actual chaotic systems is significant for expanding the practical application scenarios of the RC.

Demonstration of acousto-optical modulation based on thin-film AlScN photonic platform

Kewei Bian, Zhenyu Li, Yushuai Liu, Sumei Xu, Xingyan Zhao, yang qiu, Yuan Dong, Qize Zhong, Tao Wu, Shaonan Zheng, and Ting Hu

DOI: 10.1364/PRJ.517719 Received 12 Jan 2024; Accepted 15 Mar 2024; Posted 15 Mar 2024  View: PDF

Abstract: Acousto-optic (AO) modulation technology holds significant promise for applications in microwave and optical signal processing. Thin-film scandium-doped aluminum nitride (AlScN), with excellent piezoelectric properties and a wide transparency window, is a promising candidate for achieving on-chip AO modulation with a fabrication process compatible with complementary metal-oxide-semiconductor (CMOS) technology. This study presents the first demonstration of AO modulators with surface acoustic wave generation and photonic waveguides monolithically integrated on a 400-nm-thick film of AlScN on an insulator. The intramodal AO modulation is realized based on an AlScN straight waveguide, and the modulation efficiency is significantly enhanced by 12.3 dB through the extension of the AO interaction length and the utilization of bidirectional acoustic energy. The intermodal AO modulation and non-reciprocity are further demonstrated based on a multi-mode spiral waveguide, achieving a high non-reciprocal contrast (>10 dB) across an optical bandwidth of 0.48 nm. This research marks a significant stride forward, representing an advancement in the realization of microwave photonic filters, magnet-free isolators, and circulators based on the thin-film AlScN photonic platform.

Interdigitated Terahertz Metamaterial Sensors: Design with the Dielectric Perturbation Theory

Lei Cao, Fanqi Meng, Esra Özdemir, Yannik Loth, Merle Richter, Anna Wigger, Maira Perez, Alaa Jumaah, Shihab Al-Daffaie, Peter Haring Bolivar, and Hartmut Roskos

DOI: 10.1364/PRJ.516228 Received 15 Dec 2023; Accepted 04 Mar 2024; Posted 04 Mar 2024  View: PDF

Abstract: Designing terahertz sensors for highly sensitive detection of nanoscale thin films and a few biomolecules poses a substantial challenge, but is crucial for unlocking their full potential in scientific research and advanced applications. This work presents a strategy for optimizing metamaterial sensors in detecting small amounts of dielectric materials.The amount of frequency shift depends on intrinsic properties (electric field distribution, Q-factor, and mode volume) of the bare cavity, as well as the overlap volume of its high-electric-field zone(s) and the analyte. Guided by the simplified dielectric perturbation theory, interdigitated electric split-ring resonators (ID-eSRR) are devised to significantly enhance detection sensitivity compared to eSRRs without interdigitated fingers. ID-eSRR's fingers redistribute the electric field, creating strongly localized enhancements that boost analyte interaction. The periodic change of the inherent anti-phase electric field reduces radiation loss, leading to a higher Q-factor. Experiments with ID-eSRR sensors operating at around 300 GHz demonstrate a remarkable 33.5 GHz frequency shift upon depositing a 150 nm SiO2 layer as an analyte simulant, with a figure of merit (FOM) improvement of over 50 times compared to structures without interdigitated fingers. This rational design offers a promising avenue for highly sensitive detection of thin films and trace biomolecules.

Diffractive Neural Networks with Improved Expressive Power for Grayscale Image Classification

Minjia Zheng, wenzhe liu, Lei Shi, and Jian Zi

DOI: 10.1364/PRJ.513845 Received 29 Nov 2023; Accepted 29 Feb 2024; Posted 20 Mar 2024  View: PDF

Abstract: In order to harness diffractive neural networks (DNNs) for tasks that better align with real-world computer vision requirements, the incorporation of grayscale is essential. Currently, DNNs is not powerful to accomplish grayscale image processing tasks due to limitations in their expressive power. In our work, we elucidate the relationship between the improvement in the expressive power of DNNs and the increase in the number of phase modulation layers, as well as the optimization of the Fresnel number, which can describe the diffraction process. To demonstrate this point, we numerically trained a double-layer DNN, addressing the prerequisites for intensity-based grayscale image processing. Furthermore, we experimentally constructed this double-layer DNN based on digital micromirror devices and spatial light modulators, achieving 8-level intensity-based grayscale image classification for the MNIST and Fashion-MNIST datasets for the first time. This optical system achieved the maximum accuracies of 95.10% and 80.61%, respectively.

Probing Phase Transition of Band Topology via Radiation Topology

Chang-Yin Ji, Wenze Lan, Peng Fu, Gang Wang, Changzhi Gu, Yeliang Wang, Jiafang Li, Yugui Yao, and Baoli Liu

DOI: 10.1364/PRJ.500575 Received 17 Jul 2023; Accepted 09 Jan 2024; Posted 09 Jan 2024  View: PDF

Abstract: Topological photonics has received extensive attention from researchers because it provides brand new physical principles to manipulate light. Band topology is characterized using the Berry phase defined by Bloch states. Until now, the scheme for experimentally probing the topological phase transition of band topology has always been relatively lacking in topological physics. Moreover, radiation topology can be aroused by the far-field polarization singularities of Bloch states, which is described by the Stokes phase. Although such two types of topologies are both related to Bloch states on the band structures, it is rather surprising that their development is almost independent. Here, in optical analogs of the quantum spin Hall effects (QSHEs) and Su-Schrieffer-Heeger model, we reveal the correlation between the phase transition of band topology and radiation topology and then demonstrate that the radiation topology can be employed to study the band topological transition. We experimentally demonstrate such an intriguing phenomenon in optical analogs of QSHEs. Our findings not only provide an insightful understanding of band topology and radiation topology, but also can serve as a novel route to manipulate the light.