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.

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.

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.

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.

Highly-efficient fiber to Si-waveguide free-form coupler for foundry-scale silicon photonics

Luigi Ranno, Jia Xu Brian Sia, Cosmin-Constantin Popescu, Drew Weninger, Samuel Serna Otálvaro, Shaoliang Yu, Lionel Kimerling, Anuradha Agarwal, Tian Gu, and Juejun Hu

DOI: 10.1364/PRJ.514999 Received 13 Dec 2023; Accepted 17 Mar 2024; Posted 18 Mar 2024  View: PDF

Abstract: As silicon photonics transitions from research to commercial deployment, packaging solutions that efficiently couple light into highly-compact and functional sub-micron silicon waveguides are imperative but remain challenging. The 220 nm silicon-on-insulator (SOI) platform, poised to enable large-scale integration, is the most widely adopted by foundries, resulting in established fabrication processes and extensive photonic component libraries. The development of a highly-efficient, scalable and broadband coupling scheme for this platform is therefore of paramount importance. Leveraging two-photon polymerization (TPP) and a deterministic free-form micro-optics design methodology based on the Fermat's principle, this work demonstrates an ultra-efficient and broadband 3-D coupler interface between standard SMF-28 single-mode fibers and silicon waveguides on the 220 nm SOI platform. The coupler achieves a low coupling loss of 0.8 dB for fundamental TE mode, along with 1-dB bandwidth exceeding 180 nm. The broadband operation enables diverse bandwidth-driven applications ranging from communications to spectroscopy. Furthermore, the 3-D free-form coupler also enables large tolerance to fiber misalignments and manufacturing variability, thereby relaxing packaging requirements towards cost reduction capitalizing on standard electronic packaging process flows.

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.

Enriched endogenous photosensitizer for deep-seated tumors photodynamic therapy

Hongrui Shan, Xueqian Wang, Qiheng Wei, Hailang Dai, and Xianfeng Chen

DOI: 10.1364/PRJ.515233 Received 07 Dec 2023; Accepted 14 Mar 2024; Posted 15 Mar 2024  View: PDF

Abstract: Photodynamic therapy (PDT) is an innovative approach that utilizes photochemical reactions for non-invasive disease treatment. Conventional PDT is limited by the low penetration depth of visible light required for activation. Herein, we employed upconversion nanoparticles (UCNPs) to extend the activation wavelength of photosensitizers into the infrared range, enabling a treatment depth of over 10 mm. Furthermore, we also used the abundant amino groups of polyethyleneimine (PEI) to enhance the loading capacity of the protoporphyrin (PPIX) at the UCNPs, and ultimately improved tumor clearance rates in deep-seated. Moreover, we achieved tumor-specific treatment by utilizing folic acid (FA) targeting and active enrichment of PPIX. According to cellular experimental results, we demonstrated the remarkable ROS generation capability of the material and ultra-low dark toxicity. Additionally, we investigated the apoptosis mechanism and demonstrated that synthetized nanoparticle stimulates the up-regulation of apoptosis-associated proteins Bax/Bcl-2 and Cyto c. In vivo experiments involving intravenous injection in mouse tails, we investigated the anticancer efficacy of the nanoparticle, confirming its excellent PDT therapeutic effects. This research provides a promising avenue for future non-invasive treatment of deep-seated tumors, offering a way to the treatment and management of specific cancers.

Nonlinear generation of vector beams by using compact nonlinear fork grating

Qian Yang, Yangfeifei Yang, Hao Li, Haigang Liu, and Xianfeng Chen

DOI: 10.1364/PRJ.515731 Received 12 Dec 2023; Accepted 14 Mar 2024; Posted 15 Mar 2024  View: PDF

Abstract: Vectorial beams have attracted great interests due to their broad applications in optical micromanipulation, optical imaging, optical micromachining, and optical communication. Nonlinear frequency conversion is an effective technique to expand the frequency range of the vectorial beams. However, the scheme of existing methods to generate nonlinear vector beams are in lack of compactness in the experiment. Here, we introduce a new way to realize the generation of nonlinear vector beams by using nonlinear fork grating to solve such problem. We examine the properties of generated second-harmonic (SH) vector beams by using Stokes parameters, which agree well with theoretical predictions. Then we demonstrate that linearly polarized vector beams with arbitrary topological charge can be achieved by adjusting the optical axis direction of the half-wave plate (HWP). Finally, we measure the nonlinear conversion efficiency of such method. The proposed method provides a new way to generate nonlinear vector beams by using microstructure of nonlinear crystal, which may also be applied in other nonlinear processes and promote all optical waveband applications of such vector beams.

Silicon photonic spectrometer with multiple customized wavelength-bands

long zhang, Xiaolin Yi, Dajian Liu, Shihan Hong, Gaopeng wang, Hengzhen Cao, Yaocheng Shi, and Daoxin Dai

DOI: 10.1364/PRJ.520543 Received 31 Jan 2024; Accepted 12 Mar 2024; Posted 13 Mar 2024  View: PDF

Abstract: A silicon photonic spectrometer with multiple customized wavelength-band is developed by introducing multiple channels of wideband optical filters based on multimode waveguide gratings (MWGs) for pre-filtering and the corresponding thermally-tunable narrowband filter for high resolution. For these multiple customized wavelength-bands, the central wavelengths, bandwidths and resolutions are designed flexibly as desired, so that the system is simplified and the footprint is minimized for the real applications of e.g. gas sensing. As an example, a customized silicon photonic spectrometer is designed and demonstrated experimentally with four wavelength-bands centered around 1310 nm, 1560 nm, 1570 nm, and 1930 nm, which is the first on-chip spectrometer available for sensing multiple gas components like HF, CO, H2S, and CO2, to the best of our knowledge. The spectral resolutions of the four wavelength-bands are 0.11 nm, 0.08 nm, 0.08 nm, 0.37 nm, respectively. Such a customized silicon photonic spectrometer shows great potential for various applications, including gas monitors, wearable biosensors, portable spectral-domain optical coherence tomography and more.

On-chip ultra-high rejection and narrow bandwidth filter based on coherency-broken cascaded cladding-modulated gratings

Jinzhao Wang, ting li, Yang Feng, Jiewen Li, Wanxin Li, Luwei Ding, Yong Yao, Jianan Duan, Wei Liu, Feng He, Yi Zou, and Xiaochuan Xu

DOI: 10.1364/PRJ.510899 Received 03 Nov 2023; Accepted 08 Mar 2024; Posted 11 Mar 2024  View: PDF

Abstract: Bragg filters are of essential importance for chip-scale photonic systems. However, the implementation of filters with sub-nanometer bandwidth and rejection beyond 70 dB is hindered by the high index contrast of the silicon-on-insulator platform, which makes filters prone to fabrication imperfections. In this paper, we propose to combine coherency-broken cascading architecture and cladding modulation to circumvent the intrinsic limitation. The cascading architecture effectively prevents the accumulation of phase-errors, while the cladding modulation offers additional design freedom to reduce the coupling coefficient. A bimodal Bragg filter with a testing equipment-limited rejection level of 74 dB and a 40 dB bandwidth of 0.44 nm is experimentally demonstrated. The minimum feature size is 90 nm, which significantly relieves the fabrication constrains.

Optical trapping-enhanced probes designed by deep learning approach

Miao Peng, Guangzong Xiao, Xinlin Chen, Te Du, Tengfang Kuang, Xiang Han, Wei Xiong, Gangyi Zhu, Junbo Yang, Zhongqi Tan, Kaiyong Yang, and hui luo

DOI: 10.1364/PRJ.517547 Received 03 Jan 2024; Accepted 08 Mar 2024; Posted 11 Mar 2024  View: PDF

Abstract: Realizing optical trapping enhancement is crucial in biomedicine, fundamental physics, and precision measurement. Taking the metamaterials with artificially engineered permittivity as photonic force probes in optical tweezers will offer unprecedented opportunities for optical trap enhancement. However, it usually involves multi-parameter optimization and requires lengthy calculations, thereby remaining little studies despite decades of research on optical tweezers. Here, we introduce a deep learning (DL) model to attack this problem. The DL model can efficiently predict the maximum axial optical stiffness of Si/Si3N4 (SSN) multilayer metamaterial nanoparticles and reduce the design duration by about one order of magnitude. We experimentally demonstrate that the designed SSN nanoparticles show more than twofold and fivefold improvement in the lateral (kx and ky) and the axial (kz) optical trap stiffness on the high refractive index amorphous TiO2 microsphere. Incorporating the DL model in optical manipulation systems will expedite the designation and optimization processes, providing a means for developing various photonic force probes with specialized functional behaviors.

Silicon-based Optical Phased Array with Reconfigurable Aperture for “Gaze” Scanning of LiDAR

heming hu, yafang he, Baisong Chen, Ziming Wang, Yingzhi Li, Qijie Xie, Quanxin Na, Zihao Zhi, Xuetong Li, Huan Qu, Patrick Lo, and Junfeng Song

DOI: 10.1364/PRJ.515496 Received 11 Dec 2023; Accepted 07 Mar 2024; Posted 07 Mar 2024  View: PDF

Abstract: Light detection and ranging (LiDAR) serves as one of the key components in the fields of autonomous driving, surveying mapping and environment detection. Conventionally, dense points cloud are pursued by LiDAR system to provide high-definition 3D images. However, the LiDAR is typically used to produce abundant yet redundant data for scanning the homogeneous background of scenes, resulting in power waste and excessive processing time. Hence, it is highly desirable for a LiDAR system to “gaze” at the target of interest by dense scanning and rough sparse scan on the uninterested areas. Here, we propose a novel LiDAR structure based on optical phased array (OPA) with reconfigurable apertures to achieve such gaze scanning function. By virtue of the cascaded optical switch integrated on the OPA chip, with 64-, or 128-, or 192- or 256-channels antenna can be selected discretionarily to construct an aperture with variable size. The corresponding divergence angle for the far-field beam are 0.32°, 0.15°, 0.10° and 0.08°, respectively. The reconfigurable-aperture OPA enables the LiDAR system to perform rough scan via the large beam spots prior to fine scan of the target by using the tiny beam spots. In this way, the OPA-based LiDAR can perform “gaze” function and achieve full-range scanning efficiently. The scanning time and power consumption can be reduced by 1/4 while precise details of the target are maintained. Finally, we embed the OPA into a frequency-modulated continuous-wave (FMCW) system to demonstrate the “gaze” function in beam scanning. Experiment results show that the number of precise scanning points can be reduced by 2/3 yet able to obtain the reasonable outline of the target. The reconfigurable-aperture OPA (RA-OPA) can be a promising candidate for the applications of rapid recognition, like car navigation and robot vision.

Ultrafast Modulable 2DEG Huygens’ Metasurface

Hongxin Zeng, Xuan Cong, Shiqi Wang, Sen Gong, Ling Huang, Lan Wang, Huajie Liang, Feng Lan, Haoyi Cao, Zheng Wang, Weipeng Wang, Shixiong Liang, Zhihong Feng, Ziqiang Yang, yaxin zhang, and Tie Jun Cui

DOI: 10.1364/PRJ.517350 Received 05 Jan 2024; Accepted 07 Mar 2024; Posted 07 Mar 2024  View: PDF

Abstract: Huygens metasurfaces have demonstrated remarkable potential in perfect transmission and precise wavefront modulation through the synergistic integration of electric resonance and magnetic resonance. However, prevailing active or reconfigurable Huygens metasurfaces, based on all-optical systems, encounter formidable challenges associated with the intricate control of bulk dielectric using laser equipment and the presence of residual thermal effects, leading to limitations in continuous modulation speeds. Here, we present an ultrafast electrically driven terahertz Huygens metasurface that comprises an artificial microstructure layer featuring a two-dimensional electron gas (2DEG) provided by an AlGaN/GaN heterojunction, as well as a passive microstructure layer. Through precise manipulation of the carrier concentration within the 2DEG layer, we effectively govern the current distribution on the metasurfaces, inducing variations in electromagnetic resonance modes to modulate terahertz waves. This modulation mechanism achieves high efficiency and contrast for terahertz wave manipulation. Experimental investigations demonstrate continuous modulation capabilities of up to 6 GHz, a modulation depth of 90%, a transmission efficiency of 91%, and a remarkable relative operating bandwidth of 55.5%. These significant advancements substantially enhance the performance of terahertz metasurface modulators. Importantly, our work not only enables efficient amplitude modulation but also introduces a novel approach for the development of high-speed and efficient intelligent transmissive metasurfaces.

Kilowatt cladding-pumped low quantum defect Raman fiber amplifier

Yang Zhang, Xu Jiangming, junrui Liang, Sicheng Li, Jun Ye, Xiao Ma, Tianfu Yao, Zhiyong Pan, Jinyong Leng, and Pu Zhou

DOI: 10.1364/PRJ.510057 Received 02 Nov 2023; Accepted 06 Mar 2024; Posted 06 Mar 2024  View: PDF

Abstract: Heat generated by the quantum defect (QD) in optically pumped lasers can result in detrimental effects such as mode instability, frequency noise and even catastrophic damage. Previously, we demonstrated that boson peak-based Raman fiber lasers have great potential in low QD laser generation. But their power scalability and heat load characteristics have yet to be investigated. Here, we demonstrate a boson peak-based Raman fiber amplifier (RFA) with kilowatt-level output and a QD of 1.3%. The low heat generation characteristics of this low QD RFA are demonstrated. Both experimental and simulation results show that under kilowatt output power, the heat load of the low QD RFA is significantly lower than that of the conventional RFA with a QD of 4.8%. Thanks to its low heat generation characteristics, the proposed phosphosilicate fiber-based low QD RFA provides an effective solution for the intractable thermal issue in optically pumped lasers, which is of significance in reducing the laser’s noise, improving the laser’s stability and safety, and solve the challenge of heat removing.

An on-chip integrated few-mode erbium-ytterbium co-doped waveguide amplifier

He Xiwen, Deyue Ma, Chen Zhou, mingyue xiao, Weibiao Chen, and Zhiping Zhou

DOI: 10.1364/PRJ.516242 Received 20 Dec 2023; Accepted 05 Mar 2024; Posted 07 Mar 2024  View: PDF

Abstract: We propose for the first time an on-chip integrated few-mode erbium-ytterbium co-doped waveguide amplifier (FM-EYCDWA) based on an 800 nm thick Si3N4 platform, which demonstrates high amplification gains and low differential modal gains (DMGs) simultaneously. An eccentric waveguide structure and a co-propagating pumping scheme are adopted to balance the gain of each mode. A hybrid mode/polarization/wavelength-division-(de) multiplexer with low insertion losses (ILs) and crosstalks (CTs) is used for multiplexing and demultiplexing in two operation wavebands centered on 1550 nm and 980 nm, where the light in these two bands serves as the signal light and pump light of the amplifier, respectively. The results demonstrate that with an input signal power of 0.1 mW, TE0 mode pump power of 300 mW, and TE1 mode pump power of 500 mW, the three signal modes (TE0/TM0/TE1) all exhibit amplification gains exceeding 30 dB, while maintaining a DMG of less than 0.1 dB.

Perovskite quantum laser with enhanced population inversion driven by plasmon-induced hot electron transfer under potential shift polarization conditions

Yong Pan, Lijie Wu, Yuan Zhang, Yihao Zhang, Jie Xu, Haixia Xie, and Jianguo Cao

DOI: 10.1364/PRJ.515120 Received 14 Dec 2023; Accepted 04 Mar 2024; Posted 06 Mar 2024  View: PDF

Abstract: The hot electron transfer resulting fluorescence enhancement has the significant meaningful for theory and experiment of photoelectric devices studying. However, the laser emission based on hot electron transfer directly is difficult to realize because of the low transfer efficiency. To achieve laser with new generation mechanism base on hot-electron transfer, the photo-electric co-excitation are proposed for improving the efficiency of hot electron transfer. The lasing behavior at 532 nm are realized with a threshold of 5 kw cm-2&1 μA, which can be considered as the hot e transfer resulting population inversion enhancement. For details, number of hot electrons transfer process were described via transient absorption spectrum according to the improved ground state bleaching and excited state absorption signal in device ON. Through comparing to optical pump only, the quantum efficiencies of hot electron generation (HEG) and hot electron transfer (HET) were increased by this method about 31% and 31% (about 2.2 and 3.5 times), respectively. Most importantly, a triple gain mode coupling device including local surface plasmon, hot-e transfer and array oscillation was presented in experiment and simulation. Finally, two modes of population inversion enhancement are proposed, including hot electron occupancy mode and ground state absorption enhancement mode. This study can provide theoretical and experimental reference for the research of hot electron lasers and device.

Dead-zone-free magnetometer based on hybrid Poincare beams

Ke Tian, Weifeng Ding, and Zhaoying Wang

DOI: 10.1364/PRJ.519409 Received 18 Jan 2024; Accepted 04 Mar 2024; Posted 04 Mar 2024  View: PDF

Abstract: In this paper, we present the experiment and the theory scheme of the light-atom interaction in atomic magnetometers by using a hybrid Poincare beam (HPB) to solve an annoying problem, named “Dead zone”. This kind of magnetometer can be sensitive to arbitrary directions of the external magnetic fields. The HPB has a complex polarization distribution, consisting of a vector radially polarized beam and a scalar circularly polarized beam in our experiment. These two kinds of beams have different directions of dead zones of the external magnetic fields, thereby the atom magnetometer with a HPB can avoid the non-signal area when the direction of the external magnetic field is in the plane perpendicular to the light polarization plane. Furthermore, the optical magnetic resonance (OMR) signal using a HPB is still no dead zones even when the direction of the external magnetic field is in the plane parallel to the polarization plane in our scheme. Our work has the potential to simplify and optimize the dead-zone-free atomic magnetometers.

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.

On-Chip Terahertz Orbital Angular Momentum Demultiplexer

Xiaohan Jiang, Wanying Liu, Quan Xu, Yuanhao Lang, Yikai Fu, Fan Huang, Haitao Dai, Yanfeng Li, Xueqian Zhang, Jianqiang Gu, Jiaguang Han, and Weili Zhang

DOI: 10.1364/PRJ.519701 Received 24 Jan 2024; Accepted 03 Mar 2024; Posted 04 Mar 2024  View: PDF

Abstract: The terahertz regime is widely recognized as a fundamental domain with significant potential to address the demands of next generation wireless communications. In parallel, mode division multiplexing based on orbital angular momentum (OAM) shows promise in enhancing the bandwidth utilization, thereby expanding the overall communication channel capacity. In this study, we present both theoretical and experimental demonstrations of an on-chip terahertz OAM demultiplexer. This device effectively couples and steers seven incident terahertz vortex beams into distinct high-quality focusing surface plasmonic beams, and the focusing directions can be arbitrarily designated. The proposed design strategy integrates space-to-chip mode conversion, OAM recognition, and on-chip routing in a compact space with subwavelength thickness, exhibiting versatility and superior performance.

Miniaturized and highly-sensitive fiber-optic Fabry-Pérot sensor for mHz infrasound detection based on Cr-Ag-Au composite diaphragm and MEMS spiral micro-flow hole

Peijie Wang, Yufeng Pan, Ping Lu, jiangshan zhang, Jie Zhai, and Deming Liu

DOI: 10.1364/PRJ.519946 Received 25 Jan 2024; Accepted 02 Mar 2024; Posted 04 Mar 2024  View: PDF

Abstract: Infrasound detection is important in natural disasters monitoring, military defense, underwater acoustic detection, and other domains. Fiber-optic Fabry-Pérot (FP) acoustic sensors have the advantages of small structure size, long-distance detection, immune to electromagnetic interference, and so on. The size of a FP sensor depends on the transducer diaphragm size and the back cavity volume. However, a small transducer diaphragm size means a low sensitivity. Moreover, a small back cavity volume will increase the low cut-off frequency of the sensor. Hence, it is difficult for fiber-optic FP infrasound sensors to simultaneously achieve miniaturization, high sensitivity, and extremely low detectable frequency. In this work, we proposed and demonstrated a miniaturized and highly-sensitive fiber-optic FP sensor for mHz infrasound detection by exploiting Cr-Ag-Au composite acoustic-optic transducer diaphragm and MEMS technique-based spiral micro-flow hole. The use of spiral micro-flow hole as the connecting hole greatly reduced the volume of the sensor and decreased the low-frequency limit, while the back cavity volume was not increased. Combined with the Cr-Ag-Au composite diaphragm, a detection sensitivity of -1 .19 dB re rad/μPa@5 Hz and a minimum detectable pressure (MDP) of 1.2 mPa/Hz½@5 Hz were achieved. The low detectable frequency can reach to 0.01 Hz and the flat response range was from 0.01 Hz to 2500 Hz with a sensitivity fluctuation of ±1.5 dB. Moreover, the size of the designed sensor was only 12 mm × Φ 12.7 mm. These excellent characteristics make the sensor have great practical application prospects.

Ultrafast optical modulation of the fluorescence from a single-photon emitter in silicon carbide

Mengting He, Yujing Cao, Junjie Lin, Zhiping Ju, Botao Wu, and E Wu

DOI: 10.1364/PRJ.517734 Received 09 Jan 2024; Accepted 02 Mar 2024; Posted 04 Mar 2024  View: PDF

Abstract: Based on nonlinearities in single atoms or molecules, the quest for operating an optical transistor at room temperature is attracting a lot of attention. In this work, a single-photon emitter in cubic silicon carbide is verified that can run as an optical switch at room temperature under pulsed green laser illumination. We demonstrated an ultrafast and reversible optical modulation with a fluorescence intensity suppression rate reaching up to 97.9% and a time response of less than 287.9 ± 5.7 ps. The current development provides new insights for high-precision and ultrafast optical switches, with possibilities for integration with emerging electronic installations to realize more intelligent photoelectric integrated devices.

High-performance portable grating-based surface plasmon resonance sensor using a tunable laser at normal incidence

Duc Le, Anni Ranta-Lassila, Teemu Sipola, Mikko Karppinen, Jarno Petäjä, Minna Kehusmaa, Sanna Aikio, Tianlong Guo, Matthieu Roussey, Jussi Hiltunen, and Alexey Popov

DOI: 10.1364/PRJ.517895 Received 11 Jan 2024; Accepted 29 Feb 2024; Posted 01 Mar 2024  View: PDF

Abstract: Surface plasmon resonance (SPR) sensors are among the most sensitive sensors. In such devices, a grating is a compelling alternative to a prism for the excitation of surface plasmon, especially in the development of sensors for point-of-care applications. It yields compactness and cost-effective fabrication, although it often goes with low robustness and limited performance. Here, we present a high-performance portable grating-based SPR sensor using a tunable laser. The tunable laser working at normal incidence replaces spectral and moving components, while also simplifying the optical setup. Normal incidence is conventionally avoided due to the complexity of the control of degenerated SPR modes. We investigate, both computationally and experimentally, the splitting of the SPR modes at small non-zero incidences, which is lacking in previously reported studies. By optimizing the grating configuration, we were able to diminish the SPR mode splitting phenomenon when the excitation was feasible with normal incidence configuration. The fabricated sensor showed a high sensitivity of 1181.6 nm/RIU. Notably, the figure of merit (FOM) of the sensor, defined as the ratio between the sensitivity and bandwidth of SPR resonance dip, was 246.2. The experimental results were consistent with the simulation results. We also demonstrate its capability for detecting low concentrations of glucose and creatinine with the limit of detection of 14.2 mM and 19.1 mM, respectively.

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.

Reliable intracavity reflection for self-injection locking laser and microcomb generation

Bitao Shen, xuguang zhang, Yimeng Wang, Zihan Tao, Haowen Shu, Huajin Chang, Wencan Li, Yan Zhou, Zhangfeng Ge, Ruixuan Chen, Bowen Bai, Lin Chang, and Xingjun Wang

DOI: 10.1364/PRJ.511627 Received 09 Nov 2023; Accepted 26 Feb 2024; Posted 26 Feb 2024  View: PDF

Abstract: Self-injection locking has emerged as a crucial technique for coherent optical sources, spanning from narrow linewidth lasers to the generation of localized microcombs. This technique involves key components, namely a laser diode and a high-quality cavity that induces narrow-band reflection back into the laser diode. However, in prior studies, the reflection mainly relied on the random intracavity Rayleigh backscattering, rendering it unpredictable and unsuitable for large-scale production and wideband operation. In this work, we present a simple approach to achieve reliable intracavity reflection for self-injection locking to address this challenge by introducing a sagnac loop into the cavity. This method guarantees robust reflection for every resonance within a wide operational band without compromising the quality factor or adding complexity to the fabrication process. As a proof of concept, we showcase the robust generation of narrow linewidth lasers and localized microcombs locked to different resonances within a normal-dispersion microcavity. Furthermore, the existence and generation of localized pattern in a normal-dispersion cavity with broadband forward-backward field coupling is first proved, as far as we know, both in simulation and in experiment. Our research offers a transformative approach to self-injection locking and holds great potential for large-scale production.

Wide-Angle Digital Holography with large multi-object and aliasing-free recording

Rafał Kukołowicz, Izabela Gerej, and Tomasz Kozacki

DOI: 10.1364/PRJ.512314 Received 16 Nov 2023; Accepted 25 Feb 2024; Posted 26 Feb 2024  View: PDF

Abstract: High-quality wide-angle (WA) holographic content is at the heart of the success of the near eye display technology. This work proposes the first digital holographic (DH) system enabling recording (i) WA scenes that are assembled from (ii) multiple objects larger than the setup field of view (FOV) and can be (iii) directly replied without 3D deformation in the near-eye display. The DH system contains two parts: free space and Fourier Transform (FT), which are connected by a rectangular aperture. In the first part, the object wave propagates away from the object, while in the second part, it propagates through the single lens toward the camera plane. The rectangular aperture can take two sizes, depending on which DH operates in single-shot or multi-shot recording mode. An integral part of the DH solution is a numerical reconstruction algorithm consisting of two elements: fringe processing for object wave recovery and wide-angle propagation to the object plane. The second element simulates propagation through both parts of the experimental system. The free space part is a space-limited angular spectrum compact space algorithm, while for propagation through the lens, the multi-FT algorithm with Petzval curvature compensation is proposed. In the experimental part of the article, we present the WADH system with FOV 25°×19°, which allows high-quality recording and reconstruction of a large multi-object scene.

Butler Matrix Enabled Multi-Beam Optical Phased Array for Two-Dimensional Beam-Steering and Ranging

zuoyu zhou, Weihan Xu, chuxin Liu, Reyang Xu, chen zhu, Xinhang Li, Liangjun Lu, Jianping Chen, and Linjie Zhou

DOI: 10.1364/PRJ.509595 Received 18 Oct 2023; Accepted 25 Feb 2024; Posted 26 Feb 2024  View: PDF

Abstract: Based on the wavelength transparency of the Butler matrix (BM) beamforming network, we demonstrate a multi-beam optical phased array (MOPA) with an emitting aperture composed of grating couplers at a 1.55-um-pitch for wavelength-assisted two-dimensional beam-steering. The device is capable of simultaneous multi-beam operation in a field of view (FOV) of 60° by 8° in the phased-array scanning axis and the wavelength-tuning scanning axis, respectively. The typical beam divergence is about 4° on both axes. Using multiple linearly chirped lasers, multi-beam frequency-modulated continuous wave (FMCW) ranging is realized with an average ranging error of 4 cm. A C-shaped target is imaged for proof-of-concept 2-D scanning and ranging.

High-speed PGC demodulation model and method with subnanometer displacement resolution in fiber-optic micro-probe laser interferometer

Yisi Dong, Wenwen Li, Jinran Zhang, Wenrui Luo, Haijin Fu, Xu Xing, Peng-Cheng Hu, Yong Kang Dong, and Jiubin Tan

DOI: 10.1364/PRJ.513576 Received 20 Nov 2023; Accepted 15 Feb 2024; Posted 15 Feb 2024  View: PDF

Abstract: We present a high-speed phase-generated carrier (PGC) demodulation model to achieve subnanometer displacement measurement accuracy in fiber-optic micro-probe laser interferometer (FMI). This model includes an equivalent resolution analysis method and an analysis of the demodulation error mechanism. Utilizing this model, the failure issues regarding the PGC demodulation method under high speed and large range are addressed for the first time. Furthermore, a high-precision PGC demodulation algorithm with delay dynamic adaptive regulation is proposed to enable high-speed and wide-range displacement precision measurement. In this paper, the proposed high-speed and high-precision demodulation model and algorithm are validated through simulation and experimental tests. The results demonstrate a displacement resolution of 0.1nm with a standard deviation of less than 0.5 nm when measuring at a high velocity of 1.5 m/s.

Optical Magnetic Field Enhancement using Ultrafast Azimuthally Polarized Laser Beams and Tailored Metallic Nanoantennas

Rodrigo Martín Hernández, Lorenz Grünewald, Luis Sánchez-Tejerina, Luis Plaja, Enrique Conejero Jarque, Carlos Hernandez-Garcia, and Sebastian Mai

DOI: 10.1364/PRJ.511916 Received 13 Nov 2023; Accepted 14 Feb 2024; Posted 15 Feb 2024  View: PDF

Abstract: Structured light provides unique opportunities to spatially tailor the electromagnetic field of laser beams. This includes the possibility of a sub-wavelength spatial separation of their electric and magnetic fields, which would allow isolating interactions of matter with pure magnetic (or electric) fields. This could be particularly interesting in molecular spectroscopy, as excitations due to electric and—usually very weak—magnetic transition dipole moments can be disentangled. In this work, we show that the use of tailored metallic nanoantennas drastically enhances the strength of the longitudinal magnetic field carried by an ultrafast azimuthally polarized beam (by a factor of ∼65), which is spatially separated from the electric field by the beam’s symmetry. Such enhancement is due to favorable phase-matching of the magnetic field induced by the electronic current loops created in the antennas. Our particle-in-cell simulation results demonstrate that the interaction of moderately intense (~10^11 W/cm^2) and ultrafast azimuthally polarized laser beams with conical, parabolic, Gaussian, or logarithmic metallic nanoantennas provide spatially isolated magnetic field pulses of several tens of Tesla.

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.