Contents 1 Issue (s), 29 Article (s)

Vol. 12, Iss.6—Jun.1, 2024 • pp: 1107-1370 Spec. pp:

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Research ArticlesVol. 12, Iss.6-Jun..1,2024
Image Processing and Image Analysis
Diffractive neural networks with improved expressive power for gray-scale image classification
Minjia Zheng, Wenzhe Liu, Lei Shi, and Jian Zi
In order to harness diffractive neural networks (DNNs) for tasks that better align with real-world computer vision requirements, the incorporation of gray scale is essential. Currently, DNNs are not powerful enough to accomplish gray-scale 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 gray-scale image processing. Furthermore, we experimentally constructed this double-layer DNN based on digital micromirror devices and spatial light modulators, achieving eight-level intensity-based gray-scale image classification for the MNIST and Fashion-MNIST data sets. This optical system achieved the maximum accuracies of 95.10% and 80.61%, respectively.
Photonics Research
  • Publication Date: May. 27, 2024
  • Vol. 12, Issue 6, 1159 (2024)
Imaging Systems, Microscopy, and Displays
Flexible incidence angle scanning surface plasmon resonance microscopy for morphology detection with enhanced contrast
Lingke Wang, Jingyu Mi, Shuqi Wang, Wenrui Li, Ju Tang, Jiawei Zhang, Jiwei Zhang, and Jianlin Zhao
Surface plasmon resonance microscopy (SPRM) has been massively applied for near-field optical measurement, sensing, and imaging because of its high detection sensitivity, nondestructive, noninvasive, 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 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 a resonance angle image with exceptional contrast that 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 fivefold increase in the 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 applications of SPRM in label-free detection, imaging, and quantification.
Photonics Research
  • Publication Date: May. 31, 2024
  • Vol. 12, Issue 6, 1213 (2024)
Imaging Systems, Microscopy, and Displays
Grating-free autofocus for single-pixel microscopic imaging
Guan Wang, Huaxia Deng, Yu Cai, Mengchao Ma, Xiang Zhong, and Xinglong Gong
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 four 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 field. The proposed method can be extended to achieve SMPI autofocus with invisible optical pattern illumination.
Photonics Research
  • Publication Date: May. 31, 2024
  • Vol. 12, Issue 6, 1313 (2024)
Imaging Systems, Microscopy, and Displays
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
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 0.91. Our work is expected to benefit fiber-based holographic displays, data transmission, optical imaging, and manipulation.
Photonics Research
  • Publication Date: May. 31, 2024
  • Vol. 12, Issue 6, 1344 (2024)
Imaging Systems, Microscopy, and Displays
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 Cheng
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-h recording at a rate of 1.67 s/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.
Photonics Research
  • Publication Date: May. 31, 2024
  • Vol. 12, Issue 6, 1351 (2024)
Instrumentation and Measurements
Transient long-range distance measurement by a Vernier spectral interferometry
Liang Xu, Kun Wang, Chen Liu, Wenying Chen, Chi Zhang, and Xinliang Zhang
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, the asynchronous time step is unlimited, 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.
Photonics Research
  • Publication Date: May. 07, 2024
  • Vol. 12, Issue 6, 1107 (2024)
Instrumentation and Measurements
Measurement of atmospheric non-reciprocity effects for satellite-based two-way time-frequency transfer
Ting Zeng, Qi Shen, Yuan Cao, Jian-Yu Guan, Meng-Zhe Lian, Jin-Jian Han, Lei Hou, Jian Lu, Xin-Xin Peng, Min Li, Wei-Yue Liu, Jin-Cai Wu, Yong Wang, Juan Yin, Ji-Gang Ren, Hai-Feng Jiang, Qiang Zhang, Cheng-Zhi Peng, and Jian-Wei Pan
Future optical clock networks will require high-precision optical time-frequency transfer between satellites and ground stations. However, due to atmospheric turbulence, satellite motion and time delay between the satellite–ground transmission links will cause spatial and temporal variations, respectively, resulting in the breakdown of the time-of-flight reciprocity on which optical two-way time-frequency transfer is based. Here, we experimentally simulate the atmospheric effects by two-way spatio-temporally separated links between two stationary terminals located 113 km apart and measure the effects for optical two-way time-frequency transfer. Our experiment shows that the effect on the link instability is less than 2.3×10-19 at 10,000 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 the atmospheric non-reciprocity effects.
Photonics Research
  • Publication Date: May. 31, 2024
  • Vol. 12, Issue 6, 1274 (2024)
Instrumentation and Measurements
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
Precise measurement of micro-dispersion for optical devices (optical fiber, lenses, etc.) holds paramount significance across domains such as optical fiber communication and 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 a 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 the dispersion interference spectrum, we employ 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 0.05 m glass. Compared to a laser interferometer or the theoretical value given by manufacturers, the average relative error of refractive index measurement for single-mode fiber (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.
Photonics Research
  • Publication Date: May. 31, 2024
  • Vol. 12, Issue 6, 1362 (2024)
Integrated Optics
Demonstration of acousto-optical modulation based on a 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
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, to the best of our knowledge, 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.
Photonics Research
  • Publication Date: May. 17, 2024
  • Vol. 12, Issue 6, 1138 (2024)
Integrated Optics
Integrated bound-state-in-the-continuum photon-pair source
Fan Ye, Yue Qin, Chenfei Cui, Xiankai Sun, and Hon Ki Tsang
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 an etching process. Previous realizations of BIC photonic circuits have, however, been limited primarily to the classical regime. 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 the 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 can 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.
Photonics Research
  • Publication Date: May. 31, 2024
  • Vol. 12, Issue 6, 1322 (2024)
Lasers and Laser Optics
Short-term prediction for chaotic time series based on photonic reservoir computing using VCSEL with a feedback loop
Xingxing Guo, Hanxu Zhou, Shuiying Xiang, Qian Yu, Yahui Zhang, Yanan Han, Tao Wang, and Yue Hao
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 schemes. To overcome the problems, we employ the chaotic system of a vertical-cavity surface-emitting laser (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 a feedback loop, is proposed for the short-term prediction of the chaotic time series. The relationship between the prediction difficulty of the reservoir computing (RC) 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 the RC system to predict the chaotic time series generated by actual chaotic systems is significant for expanding the practical application scenarios of the RC.
Photonics Research
  • Publication Date: May. 31, 2024
  • Vol. 12, Issue 6, 1222 (2024)
Lasers and Laser Optics
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
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. 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 stem 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 an all-fiber configuration and burst-mode would represent an important step towards miniaturized ultrafast fiber lasers and may contribute to the applications in ablation-cooling micromachining, biomedicine imaging, and scientific research.
Photonics Research
  • Publication Date: May. 31, 2024
  • Vol. 12, Issue 6, 1231 (2024)
Nanophotonics and Photonic Crystals
Self-aligned dual-beam superresolution laser direct writing with a polarization-engineered depletion beam
Guoliang Chen, Dewei Mo, Jian Chen, and Qiwen Zhan
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 superresolution photolithography that surpasses the diffraction limit.
Photonics Research
  • Publication Date: May. 27, 2024
  • Vol. 12, Issue 6, 1194 (2024)
Nonlinear Optics
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
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 the 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 an 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 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 the 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.
Photonics Research
  • Publication Date: May. 31, 2024
  • Vol. 12, Issue 6, 1294 (2024)
Optical and Photonic Materials
Optical manipulation of ratio-designable Janus microspheres
Yulu Chen, Cong Zhai, Xiaoqing Gao, Han Wang, Zuzeng Lin, Xiaowei Zhou, and Chunguang Hu
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 distributions. 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 that within a specific ratio range, the rotation radii of microspheres vary linearly and the orientations of microsphere are always aligned with the light polarization direction. This 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.
Photonics Research
  • Publication Date: May. 31, 2024
  • Vol. 12, Issue 6, 1239 (2024)
Optical Devices
Interdigitated terahertz metamaterial sensors: design with the dielectric perturbation theory
Lei Cao, Fanqi Meng, Esra Özdemir, Yannik Loth, Merle Richter, Anna Katharina Wigger, Maira Beatriz Pérez Sosa, Alaa Jabbar Jumaah, Shihab Al-Daffaie, Peter Haring Bolívar, and Hartmut G. Roskos
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 quantities 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-eSRRs) are devised to significantly enhance the detection sensitivity compared with eSRRs without interdigitated fingers. ID-eSRR’s fingers redistribute the electric field, creating strongly localized enhancements, which boost analyte interaction. The periodic change of the inherent antiphase 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 improvement of over 50 times compared with structures without interdigitated fingers. This rational design offers a promising avenue for highly sensitive detection of thin films and trace biomolecules.
Photonics Research
  • Publication Date: May. 17, 2024
  • Vol. 12, Issue 6, 1115 (2024)
Optical Devices
Side ionic-gated perovskite/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
By combining the good charge transport property of graphene and the excellent photo-carrier generation characteristic of perovskite nanocrystal, we propose and demonstrate an ionic-gated synaptic transistor based on CsPbBr3/graphene heterojunction for bipolar photoresponse. Controlling the potential barrier of the CsPbBr3/graphene heterojunction by the ionic-gate of the electrical double-layer effect can promote the separation of photogenerated carriers and effectively retard their recombination. Using the ionic-gate-tunable Fermi level of graphene and the pinning effect of perovskite nanocrystal, the bipolar photocurrent responses 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 coding, 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 bipolar photoelectric synaptic transistors and bolster new directions in the development of future integrated human retinotopic vision neuromorphic systems.
Photonics Research
  • Publication Date: May. 27, 2024
  • Vol. 12, Issue 6, 1167 (2024)
Optical Devices
Superconducting single-photon detector with a speed of 5 GHz and a photon number resolution of 61
Tianzhu Zhang, Jia Huang, Xingyu Zhang, Chaomeng Ding, Huiqin Yu, You Xiao, Chaolin Lv, Xiaoyu Liu, Zhen Wang, Lixing You, Xiaoming Xie, and Hao Li
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.
Photonics Research
  • Publication Date: May. 31, 2024
  • Vol. 12, Issue 6, 1328 (2024)
Optoelectronics
Addressable structured light system using metasurface optics and an individually addressable VCSEL array
Chenyang Wu, Xuanlun Huang, Yipeng Ji, Tingyu Cheng, Jiaxing Wang, Nan Chi, Shaohua Yu, and Connie J. Chang-Hasnain
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 laser (VCSEL) array multiplicated by a diffractive optical element (DOE) with a fixed repeated pattern. 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 1 mm at 60 cm distance. In this paper, to the best of our knowledge, 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. 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 depth. Serving as a precise “vernier caliper,” the addressable VCSEL array enables fine control over speckle positions and high detection precision. We experimentally demonstrated that the proposed method can result in sub-hundred-micron level precision. This new concept opens new possibilities for applications such as 3D computation, facial recognition, and wearable devices.
Photonics Research
  • Publication Date: May. 17, 2024
  • Vol. 12, Issue 6, 1129 (2024)
Optoelectronics
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 S. Ooi, Jianyang Shi, Ziwei Li, Junwen Zhang, Nan Chi, Shaohua Yu, and Chao Shen
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 toward a narrow ridge waveguide, short cavity length, and 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.
Photonics Research
  • Publication Date: May. 27, 2024
  • Vol. 12, Issue 6, 1186 (2024)
Optoelectronics
Ka-band thin film lithium niobate photonic integrated optoelectronic oscillator
Rui Ma, Zijun Huang, Shengqian Gao, Jingyi Wang, Xichen Wang, Xian Zhang, Peng Hao, X. Steve Yao, and Xinlun Cai
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 the first step of using TFLN to fabricate integrated OEOs with high frequency, small size, low cost, wide range tunability, and potentially low phase noise.
Photonics Research
  • Publication Date: May. 31, 2024
  • Vol. 12, Issue 6, 1283 (2024)
Physical Optics
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
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 route to manipulate light.
Photonics Research
  • Publication Date: May. 17, 2024
  • Vol. 12, Issue 6, 1150 (2024)
Physical Optics
Manipulation of low-refractive-index particles using customized dark traps
Minru He, Yansheng Liang, Xue Yun, Shaowei Wang, Tianyu Zhao, Linquan Guo, Xinyu Zhang, Shiqi Kuang, Jinxiao Chen, and Ming Lei
Low-refractive-index particles play significant roles in physics, drug delivery, biomedical science, and other fields. However, they have not 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.
Photonics Research
  • Publication Date: May. 31, 2024
  • Vol. 12, Issue 6, 1334 (2024)
Quantum Optics
Picotesla fiberized diamond-based AC magnetometer
Shao-Chun Zhang, Yong Liu, Long-Kun Shan, Xue-Dong Gao, Jia-Qi Geng, Cui Yu, Yang Dong, Xiang-Dong Chen, Guang-Can Guo, and Fang-Wen Sun
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 an XY8-N dynamical decoupling pulse sequence, we demonstrated a T2-limited sensitivity of 8 pT/Hz and T1-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.
Photonics Research
  • Publication Date: May. 31, 2024
  • Vol. 12, Issue 6, 1250 (2024)
Quantum Optics
Experimental demonstration of a 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
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 and 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 the theoretical model, noise analysis, and multiple techniques such as the particle filter 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 rates of 546 kbps, 535 kbps, 522.5 kbps, and 512.5 kbps under a 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-user quantum downstream access networks.
Photonics Research
  • Publication Date: May. 31, 2024
  • Vol. 12, Issue 6, 1262 (2024)
Silicon Photonics
Low phase noise K-band signal generation using polarization diverse single-soliton integrated microcombs
Alwaleed Aldhafeeri, Hsiao-Hsuan Chin, Tristan Melton, Dong IL Lee, Allen Chu, Wenting Wang, Mingbin Yu, Patrick Guo-Qiang Lo, Dim-Lee Kwong, and Chee Wei Wong
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 (-123) dBc/Hz at 10 kHz 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 ultrastable photonic oscillator to illustrate the feasibility of phase noise suppression below the thermorefractive noise limits of microresonator frequency combs.
Photonics Research
  • Publication Date: May. 27, 2024
  • Vol. 12, Issue 6, 1175 (2024)
Spectroscopy
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, Zhouyi Guo, Zhengfei Zhuang, and Zhiming Liu
Rapid detection of pathogens present on contaminated surfaces is crucial for food safety and public health due to the high morbidity and mortality of bacterial infections. Herein, a sensitive and efficient method for on-site identification of foodborne pathogens on anisotropic surfaces was developed by using an in situ instantaneously prepared surface-enhanced Raman scattering (SERS) platform. To achieve this, molybdenum-doped gallic acid-derived carbon dots (MCDs) are utilized as the reductant for synthesizing Au@MCDs nanohybrids within just 3 s at ambient temperature. The synergistic effect of the electromagnetic enhancement and charge transfer of Au@MCDs enables excellent SERS performance 10 times stronger than bare Au NPs. The bioassay platform requires less than 5 min to complete the quantitative detection of foodborne pathogens on various microbial-contaminated interfaces with a sensitivity of 10 CFU/mL. This innovative strategy breaks the long-standing limitations of SERS substrates in practical use, such as the time-consuming process, interference of residual surfactants, poor surface stability, and few application scenarios, providing a promising tool for widespread applications in biomedical research and clinical diagnostics.
Photonics Research
  • Publication Date: May. 31, 2024
  • Vol. 12, Issue 6, 1303 (2024)
Surface Optics and Plasmonics
Asymmetric frequency multiplexing topological devices based on a 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
Topological photonics provides 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. Existing frequency multiplexing topological devices are generally based on the slow light effect. However, the resulting static local spatial mode or finely tuned flat band has zero-group velocity, 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 a 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 gradually tuning the band gap truncation on a topological edge band over a wide range of frequencies. 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 realized for the frequency multiplexing topological devices.
Photonics Research
  • Publication Date: May. 31, 2024
  • Vol. 12, Issue 6, 1201 (2024)