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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.

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.

Target-Adaptive Optical Phased Array LiDAR

Yunhao Fu, Baisong Chen, Wenqiang Yue, Min Tao, Haoyang Zhao, Yingzhi Li, Xuetong Li, Huan Qu, xueyan li, Xiaolong Hu, and Junfeng Song

DOI: 10.1364/PRJ.514468 Received 28 Nov 2023; Accepted 26 Feb 2024; Posted 26 Feb 2024  View: PDF

Abstract: LiDAR based on the optical phased array (OPA) and frequency-modulated continuous wave (FMCW) technology, stands out in automotive applications due to its all-solid-state design, high reliability, and remarkable resistance to interference. However, while FMCW coherent detection enhances interference resistance capabilities, it concurrently results in a significant increase in distance resolution computation, becoming a primary constraint for improving point-cloud density in such perception systems. To address this challenge, this study introduces a novel LiDAR solution leveraging the flexible scanning characteristics of OPA. The proposed system categorizes target types within the scene based on RGB images and 3D coarse-scan point clouds. Subsequently, it performs scans with varying angular resolutions depending on the importance of the targets. Experimental results demonstrate that, compared to high-resolution scans across the entire field of view, this solution reduces the number of points in a single frame by 75% while maintaining the resolution of key targets. Conversely, with an equivalent number of points in a single frame, the proposed approach increases the point-cloud density of critical targets by 4 times.

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.

Complex transmission matrix retrieval for highly scattering medium via regional phase differentiation

Qiaozhi He, Rongjun Shao, Yuan Qu, Linxian Liu, Chunxu Ding, and Jiamiao Yang

DOI: 10.1364/PRJ.513519 Received 17 Nov 2023; Accepted 25 Feb 2024; Posted 26 Feb 2024  View: PDF

Abstract: Accurately measuring the complex transmission matrix (CTM) of the scattering medium (SM) holds critical significance for applications in anti-scattering optical imaging, phototherapy, and optical neural networks. Non-interferometric approaches, utilizing phase retrieval algorithms, can robustly extract the CTM from the speckle patterns formed by multiple probing fields traversing the SM. However, in cases where an amplitude-type spatial light modulator is employed for probing field modulation, the absence of phase control frequently results in the convergence towards a local optimum, undermining the measurement accuracy. Here, we propose a high-accuracy CTM retrieval (CTMR) approach based on regional phase differentiation (RPD). It incorporates a sequence of additional phase masks into the probing fields, imposing a priori constraints on the phase retrieval algorithms. By distinguishing the variance of speckle patterns produced by different phase masks, the RPD-CTMR can effectively direct the algorithm towards a solution that closely approximates the CTM of the SM. We built a prototype of a digital micromirror device modulated RPD-CTMR. By accurately measuring the CTM of diffusers, we achieved an enhancement in the peak-to-background ratio of anti-scattering focus by a factor of 3.6, alongside a reduction in the bit error rate of anti-scattering image transmission by a factor of 24, respectively. Our proposed approach aims to facilitating precise modulation of scattered optical fields, thereby fostering advancements in diverse fields including high-resolution microscopy, biomedical optical imaging, and optical communications.

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.

A high Q-factor 3D meta-absorbing chip for terahertz sensing based on two-photon polymerization printing

Xueer Chen, Longfang Ye, and Daquan Yu

DOI: 10.1364/PRJ.519652 Received 23 Jan 2024; Accepted 21 Feb 2024; Posted 26 Feb 2024  View: PDF

Abstract: The narrowband meta-absorbers exhibit significantly enhanced electromagnetic confinement capabilities, showcasing broad application prospects in sensing field. They can be applied for biomarker detection, chemical composition analysis, and monitoring of specific gas in the environments. In this work, we propose a new 3D meta-absorber of out-of-plane plasma mechanism based on two-photon printing system. Compared to the conventional fabrication of metal-insulator-metal 2D meta-absorber, the 3D absorber is composed of metal layer and resin layer from top to bottom, its manufacturing process is simpler, only including two-photon printing and magnetron sputtering deposition. A noticeable absorbing resonance appears in 0.3142 THz with perfect absorbance with a high Q-factor of 104.67. The theoretical sensitivity to refractive index of the sensor reaches up to 172.5 GHz/RIU, with a figure of merit (FOM) of 19.56. In the experiments, it was validated as a meta-absorber with high sensitivity for doxycycline (DCH). As the DCH concentration increase from 0 to 4 mg/mL, the absorption intensity decreases around 49%, while the resonant frequency shift around 70 GHz. It reflects the real-time residual content of DCH, and potentially applied in trace antibiotic detection. The results showcase perfect narrowband absorption capability with strong electromagnetic confinement in the terahertz spectrum, along with high-Q sensing characteristics of DCH. Compared to 2D metamaterials, the diversity of 3D metamaterial significantly expands, and intrduced additional effects provide greater flexibility in manipulating electromagnetic waves. The novel 3D devic offers opportunities for the application of terahertz biochemical sensing.

A Broadband High-Efficiency Plasmonic Metalens with Negative Dispersion Characteristic

Liu Yong-qiang, Yong Zhu, Hongcheng Yin, jinhai Sun, Yan Wang, and Yongxing Che

DOI: 10.1364/PRJ.513990 Received 22 Nov 2023; Accepted 20 Feb 2024; Posted 21 Feb 2024  View: PDF

Abstract: Controlling the dispersion characteristic of metasurfaces (or metalenses) along broad bandwidth is of great importance to develop high-performance broadband meta-devices. Different from traditional lenses rely on material refractive index along light trajectory, metasurfaces or metalenses provide new regime of dispersion control via sub-wavelength meta-structure, which is known as negative chromatic dispersion. However, broadband metalenses design with high-performance focusing especially with a reduced device dimension is a significant challenge in the society. Here, we design, fabricate and demonstrate a broadband high-performance diffractive-type plasmonic metalens based on a circular split ring resonator metasurface with a relative working bandwidth of 28.6%. The metalens thickness is only 0.09λ0 (λ0 is at central wavelength), which is much thinner than previous broadband all-dielectric metalenses. The full-wave simulation results show that both high transmissive efficiency above 80% (the maximum is even above 90%) and high average focusing efficiency above 45% (the maximum is 56%) are achieved within the entire working bandwidth of 9-12GHz. Moreover, an average high numerical aperture of 0.7 (NA=0.7) of high-efficiency microwave metalens is obtained in the simulations. The broadband high-performance metalens is also fabricated and experimental measurements verify its much higher average focusing efficiency of 55% (the maximum is above 65% within the broad bandwidth) and a moderate high NA of 0.6. The proposed plasmonic metalens can facilitate the development of wavelength-dependent broadband diffractive devices and is also meaningful to further studies on arbitrary dispersion control in diffractive optics based on plasmonic metasurfaces.

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.

Strong light-matter interactions based on excitons and the abnormal all-dielectric anapole mode with both large field enhancement and low loss

Yan-Hui Deng, Yuwei Lu, Houjiao Zhang, zhonghong Shi, Zhangkai Zhou, and Xue-Hua Wang

DOI: 10.1364/PRJ.514576 Received 30 Nov 2023; Accepted 14 Feb 2024; Posted 15 Feb 2024  View: PDF

Abstract: The room-temperature strong coupling between the photonic modes of micro/nano-cavities and quantum emitters (QEs) can bring ahout promising advantages for fundamental and applied physics. Improving the electric fields (EF) by the plasmonic modes or reducing their losses by the dielectric nanocavities are widely employed to achieve the room-temperature strong coupling. However, the ideal photonic modes with both large EF and low loss have been lacking. Herein, we propose the abnormal anapole mode (AAM), showing both strong EF enhancements of ~70-fold (comparable to plasmonic modes) and low loss of 34 meV (much smaller than previous records of isolated all-dielectric nanocavities). Besides its advatages for realizing of strong coupling, we further show that by replaceing the normal anaple mode to the AAM, the lasing threshold of the AAM coupled QEs can be reduced by one order of magnitude, implying a vital step toward the creation of on-chip integration of nanophotonic devices.

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.

Deep correlated speckles: suppressing correlation fluctuation and optical diffraction

Xiaoyu Nie, Haotian Song, Wenhan Ren, Zhedong Zhang, Tao Peng, and Marlan Scully

DOI: 10.1364/PRJ.504327 Received 18 Sep 2023; Accepted 12 Feb 2024; Posted 13 Feb 2024  View: PDF

Abstract: The generation of speckle patterns via random matrices, statistical definitions, or apertures may not always result in optimal outcomes. Issues such as correlation fluctuations in low ensemble numbers and diffraction in long-distance propagation can arise. Our solution is catching deep correlations of patterns with the framework, Speckle-Net, which is universally applicable to various systems. We demonstrate this in computational ghost imaging (CGI) and structured illuminating microscope (SIM). In CGI with extremely low ensemble number, it minimizes correlation fluctuations in illuminating patterns and achieves higher-quality images. It also creates non-Rayleigh nondiffracting speckle patterns only through a phase mask modulation, which overcomes the power loss in the traditional ring aperture method. Our approach provides new insights into the non-trivial speckle patterns and has great potential for a variety of applications including dynamic SIM, x-ray and photo-acoustic imaging, and disorder physics.

Highly Efficient Nonuniform Finite Difference Method for Three-Dimensional Electrically Stimulated Liquid Crystal Photonic Devices

Zhenghao Guo, Mengjun Liu, ZIJIA CHEN, RUIZHI YANG, Peiyun Li, xia da, Dong Yuan, Guofu Zhou, Lingling Shui, and Huapeng Ye

DOI: 10.1364/PRJ.516364 Received 21 Dec 2023; Accepted 10 Feb 2024; Posted 15 Feb 2024  View: PDF

Abstract: Liquid crystal (LC) photonic devices have attracted intensive attention in recent decade, due to the merits of tunability, cost-effectiveness and high efficiency. However, the precise and efficient simulation of large-scale three-dimensional electrically-stimulated LC photonic devices remains challenging and resources consuming. Here we report a straightforward nonuniform finite difference method (NFDM) for efficiently simulating large-scale LC photonic devices by employing spatially nonuniform mesh grid. We show that the NFDM can be further accelerated by approximate 504 times by using the improved successive over-relaxation method (by 12 times), the symmetric boundary (by 4 times), the momentum gradient descent algorithm (by 3.5 times), and the multigrid (by 3 times). We experimentally fabricated the large-scale electrically-stimulated LC photonic device, and the measured results demonstrate the effectiveness and validity of the proposed NFDM. The NFDM allocates more grids to the core area with steep electric field gradient, thus reducing the distortion of electric field and the truncation error of calculation, rendering it more precise than finite element method and traditional finite difference method with similar computing resource. This study demonstrates an efficient and highly reliable method to simulate the large-scale electrically-stimulated LC photonic device, and paves the way for customizing large-scale LC photonic device with designable functionalities.

On-chip spiking neural networks based on add-drop ring microresonators and electrically reconfigurable phase-change materials photonic switches

Qiang Zhang, Ning Jiang, Yiqun Zhang, Anran Li, Huanhuan Xiong, Gang Hu, Yongsheng Cao, and Kun Qiu

DOI: 10.1364/PRJ.507178 Received 29 Sep 2023; Accepted 08 Feb 2024; Posted 09 Feb 2024  View: PDF

Abstract: We propose and demonstrate a photonic computing primitive designed for integrated spiking neural networks (SNNs) based on add-drop ring microresonators (ADRMRs) and electrically reconfigurable phase-change materials (PCMs) photonic switches. In this neuromorphic system, the passive silicon-based ADRMR equipped with power-tunable auxiliary light effectively demonstrates nonlinear-induced dual neural dynamics encompassing spiking response and synaptic plasticity, capable of generating single-wavelength optical neural spikes with synaptic weight. By cascading these ADRMRs with different resonant wavelengths, weighted multiple-wavelength spikes can be feasibly outputted from the ADRMRs-based hardware arrays when external wavelength-addressable optical pulses are injected, and subsequently, the cumulative power of these weighted output spikes is utilized to ascertain the activation status of the reconfigurable PCMs photonic switches. Moreover, the reconfigurable mechanism driving the interconversion of the PCMs between resonant-bonded crystalline states and covalent-bonded amorphous states is achieved through precise thermal modulation. Drawing from the thermal properties, an innovative thermodynamic leaky-integrate-and-firing (TLIF) neuron system is proposed. With the TLIF neuron system as the fundamental unit, a fully-connected SNN is constructed to complete a classic deep learning task: the recognition of handwritten digit patterns. The simulation results reveal that the exemplary SNN is capable of recognizing ten numbers directly in the optical domain by employing the surrogate gradient algorithm. The implementation of our innovative architecture paves a whole new perspective way for integrated photonic SNNs, holding potential promise for advancing the field of neuromorphic photonic systems and enabling more efficient spiking information processing.

Synergic action of linear dispersion, second and third-order nonlinearity in shaping the spectral profile of femtosecond pulse transporting in lithium-niobate crystal

Hong Lihong, Liu Yuanyuan, and Zhiyuan Li

DOI: 10.1364/PRJ.516105 Received 15 Dec 2023; Accepted 07 Feb 2024; Posted 09 Feb 2024  View: PDF

Abstract: We present a detailed theoretical and numerical analysis upon the temporal-spectral-spatial evolution of high-peak-power femtosecond laser pulse in two sets of systems: a pure lithium niobate (LN) plate and a periodic-poled lithium niobate (PPLN) plate. We develop a modified unidimensional pulse propagation model that considers all the prominent linear and nonlinear processes and carry out the simulation process based on an improved spilt-step Fourier transformation method. We theoretically analyze the synergic action of the linear dispersion effect, second-order nonlinear (2nd-NL) second-harmonic generation (SHG) effect and the third-order nonlinear (3rd-NL) self-phase modulation (SPM) effects, and clarify the physical mechanism underlying the peculiar and diverse spectral broadening patterns previously reported in the LN and PPLN thin plate experiments. Such an analysis and discussion would provide a deeper insight into the synergetic contribution of these linear and nonlinear effects brought about by the interaction of femtosecond laser pulse with the LN nonlinear crystal, and help to draw a picture for fully understanding these fruitful optical physical processes, phenomena, and laws.

High speed GeSn resonance cavity enhanced photodetectors for 50 Gbps Si-based 2 µm band communication system

Cui Jinlai, Jun Zheng, Yupeng Zhu, Xiangquan Liu, Yiyang Wu, Qinxing Huang, Yazhou Yang, Zhipeng Liu, zhi Liu, Yuhua Zuo, and Buwen Cheng

DOI: 10.1364/PRJ.514764 Received 01 Dec 2023; Accepted 05 Feb 2024; Posted 06 Feb 2024  View: PDF

Abstract: Expanding the optical communication band is one of the most effective methods of overcoming the nonlinear Shannon capacity limit of single fiber. In this study, GeSn resonance cavity enhanced (RCE) photodetectors (PDs) with an active layer Sn component of 9~10.8% were designed and fabricated on an SOI substrate. The GeSn RCE PDs present a responsivity of 0.49A/W@2µm and a 3-dB bandwidth of approximately 40 GHz@2µm. Consequently, Si-based 2 µm band optical communication with a transmission rate of 50 Gb/s was demonstrated for the first time by using a GeSn RCE detector and Si modulator. This work demonstrates the considerable potential of the Si-based 2µm band photonics in future high-speed and high-capacity optical communication.

Flexible 2x2 Multiple Access Visible Light Communication System Based on an Integrated Parallel GaN/InGaN Micro-Photodetector Array Module

Zengyi Xu, Xianhao Lin, Zhiteng Luo, Qianying Lin, Jianli Zhang, Guang Wang, Xiaolan Wang, Ziwei Li, Jianyang Shi, Junwen Zhang, Chao Shen, and Nan Chi

DOI: 10.1364/PRJ.517212 Received 28 Dec 2023; Accepted 04 Feb 2024; Posted 06 Feb 2024  View: PDF

Abstract: In recent studies, visible light communication (VLC) is predicted to be a prospective technique in the future 6G communication system. To suit the trend of exponentially growing connectivity, researchers have intensively studied techniques that enable multiple access (MA) in VLC systems, such as the MIMO system based on LED devices to support potential applications in the Internet of Things (IoT) or edge computing in the next-generation access network. However, their transmission rate is limited due to the intrinsic bandwidth of LED. Unfortunately, the majority of Visible light laser communication (VLLC) research with beyond 10Gb/s data rates concentrates on point-to-point links, or using discrete photodetector (PD) devices instead of integrated array PD. In this paper, we demonstrated an integrated PD array device fabricated with Si-substrated GaN/InGaN multi-quantum-well (MQW) structure, which has a 4x4 array of 50μm x 50μm micro-PD units with common cathode and anode. This single-integrated array successfully provides access for two different transmitters simultaneously in the experiment, implementing a 2x2 MIMO-VLLC link at 405nm. The highest transmission rate achieved is 13.2Gb/s, using 2.2GHz bandwidth and superposed PAM signals. Furthermore, we assess the Huffman-coded coding scheme, which brings a fine-grain adjustment in access capacity, and enhances the overall data throughput when the user signal power varies drastically due to distance, weather, or other challenges in the channel condition. As far as we know, this is the first demonstration of multiple visible light laser source access based on a single integrated GaN/InGaN receiver module.

Dielectric Metasurface Evolution from Bulk to Monolayer by Strong Coupling of Quasi-BICs for Second Harmonic Boosting

Yinong Xie, Qianting Chen, Jin Yao, Xueying Liu, zhaogang dong, and Jinfeng Zhu

DOI: 10.1364/PRJ.514140 Received 27 Nov 2023; Accepted 04 Feb 2024; Posted 06 Feb 2024  View: PDF

Abstract: 2D materials are promising candidates as nonlinear optical components for on-chip devices due to their ultrathin structure. In general, their nonlinear optical responses are inherently weak due to the short interaction thickness with light. Recently, there has been great interest in using quasi-bound states in the continuum (q-BICs) of dielectric metasurfaces, which are able to achieve remarkable optical near-field enhancement for elevating the second harmonic generation (SHG) emission from 2D materials. However, most studies focus on the design of combining bulk dielectric metasurfaces with unpatterned 2D materials, which suffers considerable radiation loss and limits near-field enhancement by high-quality q-BIC resonances. Here, we investigate the dielectric metasurface evolution from bulk silicon to monolayer molybdenum disulfide (MoS2), and discover the critical role of meta-atom thickness design on enhancing near-field effects of two q-BIC modes. We further introduce the strong-coupling of the two q-BIC modes by oblique incidence manipulation, and enhance the localized optical field on monolayer MoS2 dramatically. In the ultraviolet and visible region, the MoS2 SHG enhancement factor of our design is 105 times higher than that from conventional bulk metasurfaces, leading to an extremely high nonlinear conversion efficiency of 5.8%. Our research will provide an important theoretical guide for the design of high-performance nonlinear devices based on 2D materials.

Aberration correction for deformable mirror based remote focusing enables high-accuracy whole-cell super-resolution imaging

Wei Shi, Yingchuan He, Jianlin Wang, Lulu Zhou, Jianwei Chen, Liwei Zhou, Zeyu Xi, Zhen Wang, Ke Fang, and Yiming Li

DOI: 10.1364/PRJ.514414 Received 04 Dec 2023; Accepted 01 Feb 2024; Posted 01 Feb 2024  View: PDF

Abstract: Single-molecule localization microscopy (SMLM) enables three-dimensional (3D) investigation of nanoscale structures in biological samples, offering unique insights into their organization. However, traditional 3D super-resolution microscopy using high numerical aperture (NA) objectives is limited by imaging depth of field (DOF), restricting their practical application to relatively thin biological samples. Here, we developed a unified solution for thick sample super-resolution imaging using a deformable mirror (DM) which was served for fast remote focusing, optimized point spread function (PSF) engineering and accurate aberration correction. By effectively correcting the system aberrations introduced during remote focusing and sample aberrations at different imaging depths, we achieved high-accuracy, large DOF imaging of the whole-cell organelles [i.e. nuclear pore complex (NPC), microtubules, and mitochondria] with a nearly uniform resolution of approximately 30 nm across the entire cellular volume.

Faster structured illumination microscopy using complementary encoding-based compressive imaging

Zhengqi Huang, Yunhua Yao, Yilin He, Yu He, Chengzhi Jin, Mengdi Guo, Dalong Qi, Lianzhong Deng, Zhenrong Sun, Zhiyong Wang, and shi zhang

DOI: 10.1364/PRJ.515895 Received 13 Dec 2023; Accepted 30 Jan 2024; Posted 01 Feb 2024  View: PDF

Abstract: Structured illumination microscopy (SIM) has been widely applied to investigate the intricate biological dynamics due to its outstanding super-resolution imaging speed. Incorporating compressive sensing into SIM brings the possibility to further improve the super-resolution imaging speed. Nevertheless, the recovery of the super-resolution information from the compressed measurement remains challenging in experiments. Here, we report a structured illumination microscopy with complementary encoding-based compressive imaging (i.e., CECI-SIM) to realize a faster super-resolution imaging. Compared to nine measurements to obtain a super-resolution image in conventional SIM, CECI-SIM can achieve a super-resolution image by three measurements, and therefore a three-fold improvement in the imaging speed can be acquired. This faster imaging ability in CECI-SIM is experimentally verified by observing tubulin and actin in mouse embryonic fibroblast cells. This work provides a feasible solution for high-speed super-resolution imaging, which would bring significant applications in biomedical research.

Intensity-based polarization manipulation by tunable polarization holographic grating

Hong Chen, Ziyao Lyu, and Changshun Wang

DOI: 10.1364/PRJ.502730 Received 10 Aug 2023; Accepted 30 Jan 2024; Posted 30 Jan 2024  View: PDF

Abstract: Polarization holography has been extensively applied in many fields, such as optical science, metrology and biochemistry, due to its property of polarization modulation. However, the modulated polarization state of diffracted light corresponds strictly to that of incident light one by one. Here, a kind of tunable polarization holographic grating has been designed in terms of Jones matrices, and intensity-based polarization manipulation has been realized experimentally. The proposed tunable polarization holographic grating is recorded on an azobenzene liquid-crystalline film by a pair of coherent light beams with orthogonal polarization states and asymmetrically controlled intensities. It is found that the diffracted light can be actively manipulated from linearly to circularly polarized based on the light intensity of the recording holographic field when the polarization state of incident light keeps constant. Our work could enrich the field of light manipulation and holography.

High-speed impulsive stimulated Brillouin microscopy

Jiarui Li, Taoran Le, Hongyuan Zhang, Haoyun Wei, and Yan Li

DOI: 10.1364/PRJ.509922 Received 20 Oct 2023; Accepted 30 Jan 2024; Posted 01 Feb 2024  View: PDF

Abstract: Brillouin microscopy, which maps elastic modulus from the frequency shift of scattered light, has evolved to a faster speed for the investigation of rapid biomechanical changes. Impulsive stimulated Brillouin scattering (ISBS) spectroscopy has the potential to speed up measurement through the resonant amplification interaction from pulsed excitation and time-domain continuous detection. However, significant progress has not been achieved due to the limitation in signal-to-noise ratio (SNR) and the corresponding need for excessive averaging to maintain high spectral precision. Moreover, the limited spatial resolution also hinders its application in mechanical imaging. Here, by scrutinizing the SNR model, we design a high-speed ISBS microscope through multi-parameter optimization including phase, reference power, and acquisition time. Leveraging this, with the further assistance of the Matrix Pencil method for data processing, three-dimensional mechanical images are mapped under multiple contrast mechanisms for a millimeter-scale polydimethylsiloxane pattern immersed in methanol, enabling the identification of these two transparent materials without any contact or labeling. Our experimental results demonstrate the capability to maintain high spectral precision and resolution at a sub-millisecond integration time for one pixel. With a two-order improvement in the speed and a tenfold improvement in the spatial resolution over the state-of-the-art systems, this method makes it possible for ISBS microscopes to sensitively investigate rapid mechanical changes in time and space.

Frequency-comb-linearized, widely tunable lasers for coherent ranging

Baoqi Shi, Yi-Han Luo, Wei Sun, Yue Hu, Jinbao Long, Xue Bai, Anting Wang, and Junqiu Liu

DOI: 10.1364/PRJ.510795 Received 31 Oct 2023; Accepted 29 Jan 2024; Posted 30 Jan 2024  View: PDF

Abstract: Tunable lasers, with the ability to continuously adjust their emission wavelengths, have found widespread applications across various fields such as biomedical imaging, coherent ranging, optical communications, and spectroscopy. In these applications, a wide chirp range is advantageous for large spectral coverage and high frequency resolution. Besides, the frequency accuracy and precision also depend critically on the chirp linearity of the laser. While extensive efforts have been made on the development of many kinds of frequency-agile, widely tunable, narrow-linewidth lasers, wideband yet precise methods to characterize and linearize laser chirp dynamics are also demanded. Here we present an approach to characterize laser chirp dynamics using an optical frequency comb. The instantaneous laser frequency is tracked over terahertz bandwidth at 1 MHz intervals. Using this approach we calibrate the chirp performance of twelve tunable lasers from Toptica, Santec, New Focus, EXFO, and NKT that are commonly used in fiber optics and integrated photonics. In addition, with acquired knowledge of laser chirp dynamics, we demonstrate a simple frequency-linearization scheme that enables coherent ranging without any optical or electronic linearization unit. Our approach not only presents a novel wideband, high-resolution laser spectroscopy, but is also critical for sensing applications with ever-increasing requirements on performance.

Microscopic nonlinear optical activities and ultrafast carrier dynamics in layered AgInP2S6

Zixin Wang, Ningning Dong, Yu Mao, Chenduan Chen, Xin Chen, Chang Xu, Zhouyuan Yan, and Jun Wang

DOI: 10.1364/PRJ.510142 Received 27 Oct 2023; Accepted 23 Jan 2024; Posted 24 Jan 2024  View: PDF

Abstract: Since the emergence of graphene, transition metal dichalcogenides, and black phosphorus, two-dimensional materials have attracted significant attention and have driven the development of fundamental physics and optoelectronic devices. Metal phosphorous trichalcogenides (MPX3), due to their large bandgap of 1.3-3.5 eV, enable the extension of optoelectronic applications to visible and ultraviolet (UV) wavelengths. Micro-Z/I-scan (µ-Z/I-scan) and micro-pump-probe (µ-pump-probe) setups were used to systematically investigate the third-order nonlinear optical properties and ultrafast carrier dynamics of the representative material AgInP2S6. UV-visible absorption spectra and density functional theory (DFT) calculations revealed a quantum confinement effect, in which the bandgap decreased with increasing thickness. Two-photon absorption (TPA) effect is exhibited under the excitation of both 520 and 1040 nm femtosecond pulses, where the TPA coefficient decreases as the AgInP2S6 thickness increases. In contrast, the TPA saturation intensity exhibits the opposite behavior that the TPA saturation is more likely to occur under visible excitation. After the valence band electrons undergo photon transitions to the conduction band, the non-equilibrium carriers relax through non-radiative and defect-assisted recombination. These findings provide a comprehensive understanding of the optical response process of AgInP2S6 and a valuable reference for the development of optoelectronic devices.

Lensless opto-electronic neural network with quantum dots nonlinear activation

Wanxin Shi, Xi Jiang, Zheng Huang, Xue Li, Yuyang Han, Sigang Yang, Haizheng Zhong, and Hongwei Chen

DOI: 10.1364/PRJ.515349 Received 08 Dec 2023; Accepted 23 Jan 2024; Posted 24 Jan 2024  View: PDF

Abstract: With the swift advancement of neural networks and their expanding applications in many fields, optical neural networks have gradually become a feasible alternative to electrical neural networks due to their parallelism, high speed, low latency and power consumption. Nonetheless, the optical nonlinearity is hard to realize in free-space optics, which restrict the potential of the architecture. To harness the benefits of optical parallelism while ensuring compatibility with natural light scenes, it becomes essential to implement two-dimensional spatial nonlinearity within an incoherent light environment. Here, we demonstrate a lensless opto-electrical neural network that incorporates optical nonlinearity, capable of performing convolution calculations and achieving nonlinear activation via a quantum dot film, all without an external power supply. Through simulation and experiments, the proposed nonlinear system can enhance the accuracy of image classification tasks, yielding a maximum improvement of 3.75% over linear models. The scheme shows a facile implementation of passive incoherent two-dimensional nonlinearities, paving the way for the applications of multi-layer incoherent optical neural networks in the future.

Simplistic framework of single-pixel-programmable metasurfaces integrated with capsuled LED array

Yuxi Li, Jiafu Wang, Sai Sui, Ruichao Zhu, Yajuan Han, Hongya Chen, Xinmin Fu, Shaojie Wang, Cunqian Feng, and Shaobo Qu

DOI: 10.1364/PRJ.506044 Received 15 Sep 2023; Accepted 22 Jan 2024; Posted 24 Jan 2024  View: PDF

Abstract: Coding metasurfaces can manipulate electromagnetic wave in real time with high degree of freedom, the fascinating properties of which enrich the metasurface design with a wide range of application prospects. However, most of the coding metasurfaces are designed based on external excitation framework with the wired electrical or wireless light control devices, thus inevitably causing the interference with electromagnetic wave transmission and increasing the complexity of the metasurface design. In this work, a simplistic framework of single-pixel-programmable metasurfaces integrated with capsuled LED array is proposed to dynamically control electromagnetic wave. The framework fully embeds the photoresistor in the meta-atom, controls LED array to directly illuminate the photoresistor to modulate the phase response. With this manner, the complex biasing network is transformed to the universal LED array, which means physical control framework can be transformed to software framework, and thus the functions of the metasurface can be freely manipulated by encoding the capsuled LED array avoiding mutual coupling of adjacent meta-atoms in real time. All the results verify that the far-field scattering pattern can be customized with this single-pixel-programmable metasurface. Encouragingly, this work provides an universal framework for coding metasurface design, which lays the foundation for metasurface intelligent perception and adaptive modulation.

Photonic crystal nanolasers in polydimethylsiloxane thin film for sensing quantities leading to strain

Tsan-Wen Lu, Kuang-Ming Lin, Zhen-Yu Wang, and Po-Tsung Lee

DOI: 10.1364/PRJ.506148 Received 15 Sep 2023; Accepted 22 Jan 2024; Posted 24 Jan 2024  View: PDF

Abstract: In this report, we propose and demonstrate a 1D photonic crystal (PhC) nanocavity laser embedded in a polydimethylsiloxane (PDMS) thin film. This thin film can be reattached to different surfaces or integrated into various configurations, enabling the detection of various physical quantities that induce strain in the film. In our experiments, the proposed nanocavity exhibits a significant optical wavelength response to strain, allowing us to use it as a sensor for detecting temperature variations and bending degrees by attaching it to a temperature-controllable or bendable plate, respectively. Moreover, we utilize the PDMS thin film as a diaphragm of a chamber to demonstrate its potential as a highly sensitive pressure gauge and chemical sensor. By adjusting the thickness of the PDMS thin film and the position of the PhC nanocavity, we achieve a minimum detectable gas pressure variation of 0.1 kPa, which is comparable to leading high-sensitivity pressure gauges in the market. Furthermore, we use the same configuration to sense the swelling of the PDMS thin film induced by different organic solvents. In our experiments, the different wavelength shift rates of the PhC nanocavity over time caused by different organic solvent vapors can be used to identify specific organic vapors within the chamber. Based on our experimental results and the film's versatility in reattaching to different objects or configurations, we believe that our proposed PhC nanocavity laser in PDMS thin film holds significant potential as a highly sensitive mechanical and chemical sensor.

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.

High-performance, low-power and flexible ultraviolet photodetector based on crossed ZnO microwires p-n homojunction

Shulin Sha, Kai Tang, Maosheng Liu, Peng Wan, Chenyang Zhu, Daning Shi, Caixia Kan, and Mingming Jiang

DOI: 10.1364/PRJ.505839 Received 13 Sep 2023; Accepted 09 Jan 2024; Posted 09 Jan 2024  View: PDF

Abstract: Low-power, flexible and integrated photodetectors have attracted ever-increasing attentions due to their potential applications of photosensing, astronomy, communications, wearable electronics, etc. Herein, the samples of ZnO microwires exhibiting p-type (Sb-doped ZnO, ZnO:Sb) and n-type (Ga-doped ZnO, ZnO:Ga) conduction properties were synthesized individually. Sequentially, p-n homojunction vertical structure photodiode involving a single ZnO:Sb microwire crossed with ZnO:Ga microwire was constructed, which can detect ultraviolet light signals. When exposed under 360 nm light illumination at -0.1 V, the proposed photodiode revealss pronounce photodetection features, including a largest On/Off ratio of $\sim$ 10$^5$, responsivity of $\sim$ 2.3 A/W, specific detectivity of $\sim$ 6.5$\times$10$^{13}$ Jones, noise equivalent power of $\sim$ 4.8$\times$10$^{-15}$ W Hz$^{-1/2}$, and superior photo-electron conversion efficiency of $\sim$ 7.8\%. The photodiode also exhibits a fast response/recovery time of 0.48 ms/9.41 ms. Further, we propose a facile and scalable construction scheme to integrate a p-ZnO:Sb$\bigotimes$n-ZnO:Ga MWs homojunction component into a flexible, array-type detector, which manifests significant flexibility and electrical stability with insignificant degradation. Moreover, the as-constructed array unit can be integrated into a practical photoimaging system, which demonstrates remarkable high-resolution single-pixel imaging capability. The results represented in this work may supply a workable approach for developing low-dimensional ZnO-based homojunction optoelectronic devices with low-consumption, flexible and integrated characteristics.

Varifocal occlusion in optical see-through near-eye display with single phase-only liquid crystal on silicon

Woongseob Han, Jae-Won Lee, Jung-Yeop Shin, Myeong-ho Choi, Hak Rin Kim, and Jae-Hyeung Park

DOI: 10.1364/PRJ.509948 Received 20 Oct 2023; Accepted 01 Jan 2024; Posted 03 Jan 2024  View: PDF

Abstract: We propose a novel near-eye display optics that supports three-dimensional mutual occlusion. By exploiting the polarization-control properties of the phase-only liquid crystal on silicon (LCoS), we achieve real see-through scene masking as well as virtual digital scene imaging using a single LCoS. Dynamic depth control of the real scene mask and virtual digital image is also achieved by using a focus tunable lens (FTL) pair of opposite curvatures. The proposed configuration using a single LCoS and opposite curvature FTL pair enables the self-alignment of the mask and image at arbitrary depth without distorting the see-through view of the real scene. We verified the feasibility of the proposed optics using two optical benchtop setups: one with two off-the-shelf FTLs for continuous depth control, and the other with a single Pancharatnam-Berry phase type FTL for the improved form factor.

Universal Silicon Ring Resonator for Error Free Transmission Links

Weiwei Zhang, junbo zhu, Ke Li, Bharat Pant, MARTIN EBERT, Xingzhao Yan, Mehdi Banakar, Denh Tran, Callum Littlejohns, Fuwan Gan, Graham Reed, and David Thomson

DOI: 10.1364/PRJ.509237 Received 13 Oct 2023; Accepted 21 Dec 2023; Posted 22 Dec 2023  View: PDF

Abstract: We report the design, fabrication, and characterization of a universal silicon p-n junction ring resonator for C band error-free communication links operated up to 50 Gb/s with co-designed optical modulation and detection performance. The universal p-n junction ring device shows co-designed detection responsivity up to 0.84 A/W, and in conjunction with a modulation efficiency of ~4 Vmm and >8 dB optical modulation extinction ratio (ER), enabling C band 50-Gb/s NRZ communication link with bit error rate (BER) ≤ 3×10-12. Individually, the speed of modulation and detection is measured up to 112 Gb/s and 80 Gb/s, respectively. The principle of co-designing PN junction ring modulator and detector performance required for error-free communication links can significantly ease the fabrication yield challenges of ring structures by reducing the number of types of devices. The principle can also be applied to O band wavelengths. To the best of our knowledge, for the first time, a device of this type has achieved both error-free modulation and detection operation up to 50 Gb/s in the C band individually or in conjugation as an error free communication link, which paves the way to realize a >1.6 Tb/s all-silicon WDM based error free optical transceiver link in future and is essential for future programmable photonics circuits.

Entanglement quantification via weak measurements assisted by deep learning

Mu Yang, Ya Xiao, Ze-Yan Hao, Yu-wei Liao, Jia-He Cao, Kai Sun, Enhui Wang, Zheng-Hao Liu, Yutaka Shikano, Jin-Shi Xu, Chuanfeng Li, and Guang-can Guo

DOI: 10.1364/PRJ.498498 Received 30 Jun 2023; Accepted 07 Dec 2023; Posted 11 Dec 2023  View: PDF

Abstract: Entanglement has been recognized as being crucial when implementing various quantum information tasks. Nevertheless, quantifying entanglement for an unknown quantum state requires non-physical operations or post-processing measurement data. For example, evaluation methods via quantum state tomography require vast amounts of measurement data and likelihood estimation. Although a direct entanglement determination has been reported for the unknown pure state, it is still tricky for the mixed state. In this work, assisted by weak measurement and deep learning technology, we directly detect the entanglement, namely, the concurrence, of a class two-photon polarization-entangled mixed states both theoretically and experimentally according to the local photon spatial distributions after weak measurement.