Contents 2 Issue (s), 37 Article (s)

Vol.10, Iss.6—Jun.1, 2022 • pp: 1325-1471 Spec. pp: A82-A96

Vol.10, Iss.5—May.1, 2022 • pp: 1146-1324 Spec. pp: A66-A81

Export citation format
Research ArticlesVol.10, Iss.6-Jun..1,2022
Fiber Optics and Optical Communications
Multiphoton ionization of standard optical fibers
M. Ferraro, F. Mangini, Y. Sun, M. Zitelli, A. Niang, M. C. Crocco, V. Formoso, R. G. Agostino, R. Barberi, A. De Luca, A. Tonello, V. Couderc, S. A. Babin, and S. Wabnitz
Atoms ionization by the simultaneous absorption of multiple photons has found applications in fiber optics, where it leads to unique nonlinear phenomena. To date, studies of the ionization regime have been limited to gas-filled hollow-core fibers. Here, we investigate multiphoton ionization of standard optical fibers, where intense laser pulses ionize the atoms constituting the fiber structure itself, instead of that of the filling gas. We characterize material modifications produced by optical breakdown. Their formation affects laser beam dynamics over hours long temporal scales. The damage features are studied by means of optical microscopy and X-ray microtomography. In the framework of glass photonics, our results pave the way for a novel glass waveguide micromachining technique.
Photonics Research
  • Publication Date: May. 12, 2022
  • Vol.10 Issue, 6 06001394 (2022)
Instrumentation and Measurements
Coherent-detection-based distributed acoustic impedance sensing enabled by a chirped fiber Bragg grating array
Zhou Zheng, Zhengying Li, Xuelei Fu, and Xin Gui
Distributed optical fiber sensing exploring forward stimulated Brillouin scattering (FSBS) has received wide attention, as it indicates a new sensing method to measure the liquid property surrounding an optical fiber. In the existing techniques, backward stimulated Brillouin scattering is adopted for detection of the sensing signal, which requires time-consuming signal acquisition and post-processing. In this work, an approach that distributedly measures FSBS spectra is proposed and demonstrated based on coherent detection. While an excitation pulse with single-frequency amplitude modulation is used to induce a guided acoustic mode in the fiber, a following pulse is adopted to probe the induced phase modulation. Using a chirped fiber Bragg grating array, an enhanced-backward-propagating sensing signal is generated from the probe pulse. Heterodyne coherent-detection-based phase demodulation is then realized by mixing the sensing signal with a local oscillator. The FSBS spectra can then be reconstructed from the beat signals with only one round of frequency sweeping. With significantly accelerated signal acquisition and simplified post-processing, the proposed distributed acoustic sensing system has achieved spatial resolution of 5 m over a 500-m sensing range.
Photonics Research
  • Publication Date: May. 06, 2022
  • Vol.10 Issue, 6 06001325 (2022)
Instrumentation and Measurements
Single-shot terahertz polarization detection based on terahertz time-domain spectroscopy
Qinggang Lin, Xinming Yuan, Xuanke Zeng, Yatao Yang, Yi Cai, Xiaowei Lu, Maijie Zheng, Congying Wang, Wenhua Cao, and Shixiang Xu
This paper presents a novel design for single-shot terahertz polarization detection based on terahertz time-domain spectroscopy (THz-TDS). Its validity has been confirmed by comparing its detection results with those of the THz common-path spectral interferometer through two separate measurements for the orthogonal components. Our results also show that its detection signal-to-noise ratios (SNRs) are obviously superior to those of the 45° optical bias THz-TDS by electro-optical sampling due to its operation on common-path spectral interference rather than the polarization-sensitive intensity modulation. The setup works without need of any optical scan, which does not only save time, but also efficiently avoids the disturbances from the fluctuations of the system and environment. Its single-shot mode allows it to work well for the applications with poor or no repeatability.
Photonics Research
  • Publication Date: May. 12, 2022
  • Vol.10 Issue, 6 06001374 (2022)
Integrated Optics
Heterogeneous integrated phase modulator based on two-dimensional layered materials
Hao Chen, Zexing Zhao, Ziming Zhang, Guoqing Wang, Jiatong Li, Zhenyuan Shang, Mengyu Zhang, Kai Guo, Junbo Yang, and Peiguang Yan
Silicon nitride, with ultralow propagation loss and a wide transparency window, offers an exciting platform to explore integrated photonic devices for various emerging applications. It is appealing to combine the intrinsic optical properties of two-dimensional layered materials with high-quality optical waveguides and resonators to achieve functional devices in a single chip. Here we demonstrate a micro-ring resonator-based phase modulator integrated with few-layer MoS2. The ionic liquid is employed directly on the surface of MoS2 to form a capacitor configuration. The effective index of the composite MoS2SiN waveguide can be modulated via adjusting bias voltages to achieve different charged doping induced electro-refractive responses in MoS2 film. The maximum effective index modulation of the composite MoS2SiN waveguide can be achieved to 0.45×10-3. The phase tuning efficiency is measured to be 29.42 pm/V, corresponding to a VπL of 0.69 V·cm. Since the micro-ring resonator is designed near the critical coupling regime, the coupling condition between the bus waveguide and micro-ring resonator can also be engineered from under-coupling to over-coupling regime during the charged doping process. That can be involved as a degree of freedom for the coupling tailoring. The ability to modulate the effective index with two-dimensional materials and the robust nature of the heterostructure integrated phase modulator could be useful for engineering reliable ultra-compact and low-power-consumption integrated photonic devices.
Photonics Research
  • Publication Date: May. 16, 2022
  • Vol.10 Issue, 6 06001401 (2022)
Medical Optics and Biotechnology
High-axial-resolution optical stimulation of neurons in vivo via two-photon optogenetics with speckle-free beaded-ring patterns
Cheng Jin, Chi Liu, and Lingjie Kong
Two-photon optogenetics has become an indispensable technology in neuroscience, due to its capability in precise and specific manipulation of neural activities. A scanless holographic approach is generally adopted to meet the requirement of stimulating neural ensembles simultaneously. However, the commonly used disk patterns fail in achieving single-neuron resolution, especially in axial dimension, and their inherent speckles decrease stimulation efficiency. Here, we propose a novel speckle-free, beaded-ring pattern for high-axial-resolution optical stimulation of neurons in vivo. Using a dye pool and a fluorescent thin film as samples, we verify that, compared to those with disk patterns, higher axial resolution and better localization ability can be achieved with beaded-ring patterns. Furthermore, we perform two-photon based all-optical physiology with neurons in mouse S1 cortex in vivo, and demonstrate that the axial resolution obtained by beaded-ring patterns can be improved by 24% when stimulating multiple neurons, compared to that of disk patterns.
Photonics Research
  • Publication Date: May. 12, 2022
  • Vol.10 Issue, 6 06001367 (2022)
Nanophotonics and Photonic Crystals
Broadband high-efficiency polymerized liquid crystal metasurfaces with spin-multiplexed functionalities in the visible
Xinjian Lu, Xiaoyin Li, Yinghui Guo, Mingbo Pu, Jiangyu Wang, Yaxin Zhang, Xiong Li, Xiaoliang Ma, and Xiangang Luo
Traditional optical components are usually designed for a single functionality and narrow operation band, leading to the limited practical applications. To date, it is still quite challenging to efficiently achieve multifunctional performances within broadband operating bandwidth via a single planar optical element. Here, a broadband high-efficiency polarization-multiplexing method based on a geometric phase polymerized liquid crystal metasurface is proposed to yield the polarization-switchable functionalities in the visible. As proofs of the concept, two broadband high-efficiency polymerized liquid crystal metalenses are designed to obtain the spin-controlled behavior from diffraction-limited focusing to sub-diffraction focusing or focusing vortex beams. The experimental results within a broadband range indicate the stable and excellent optical performance of the planar liquid crystal metalenses. In addition, low-cost polymerized liquid crystal metasurfaces possess unique superiority in large-scale patterning due to the straightforward processing technique rather than the point-by-point nanopatterning method with high cost and low throughput. The high-efficiency liquid crystal metasurfaces also have unrivalled advantages benefiting from the characteristic with low waveguide absorption. The proposed strategy paves the way toward multifunctional and high-integrity optical systems, showing great potential in mobile devices, optical imaging, robotics, chiral materials, and optical interconnections.
Photonics Research
  • Publication Date: May. 12, 2022
  • Vol.10 Issue, 6 06001380 (2022)
Optical and Photonic Materials
3D printing of optical materials by processes based on photopolymerization: materials, technologies, and recent advances
Emma Geisler, Maxime Lecompère, and Olivier Soppera
3D printing technologies have expanded beyond the research laboratories where they were used solely for prototyping and have become widely used in several industries. The production of custom 3D objects has significant potential in optical applications. However, this necessitates extremely specific material properties, such as transparency, homogeneity, birefringence, and surface finish. Currently, the majority of optical objects are manufactured using plastics. Moreover, the 3D printing processes using polymers to produce optical objects have significant advantages, such as limited wastage, short manufacturing time, and easy customization. However, despite extensive efforts, no technology has achieved the production of objects perfectly suited for optical applications. The objective of this review is to summarize recent advances in the field of 3D printing for optics, with an emphasis on specific developments for dedicated applications, and to explore new candidate processes.
Photonics Research
  • Publication Date: May. 12, 2022
  • Vol.10 Issue, 6 06001344 (2022)
Optical and Photonic Materials
Wideband diffusion metabsorber for perfect scattering field reduction
Zicheng Song, Pingping Min, Jiaqi Zhu, Lei Yang, and Feng Han Lin
Both absorption and diffuse reflection can effectively suppress microwave backward reflection. However, the challenge of designing wideband absorptive elements with anti-phase reflection hinders the simultaneous working of the two principles. With aid of the wideband characteristic of bilateral complementary structure, we propose a strategy to design wideband absorptive elements with large reflection phase differences. For proof of concept, the proposed elements are arranged in a rectangular grid by optimizing scattering field distribution. The proposed diffusion metabsorber achieves over 20-dB scattering field reduction in the range of 8.5–20.3 GHz with good polarization stability and high angular insensitivity of up to ±40°, which has been verified by real experiments. Furthermore, the proposed design strategy exhibits the potential to further reduce electromagnetic wave reflection, and the optical transparent characteristic is promising for window applications.
Photonics Research
  • Publication Date: May. 12, 2022
  • Vol.10 Issue, 6 06001361 (2022)
Optical and Photonic Materials
Passivation of degradation path enables high performance perovskite nanoplatelet lasers with high operational stability
Guohui Li, Huihui Pi, Yanfu Wei, Bolin Zhou, Ya Gao, Rong Wen, Yuying Hao, Han Zhang, Beng S. Ong, and Yanxia Cui
MAPbI3 perovskite has attracted widespread interests for developing low-cost near infrared semiconductor gain media. However, it faces the instability issue under operation conditions, which remains a critical challenge. It is found that the instability of the MAPbI3 nanoplatelet laser comes from the thermal-induced degradation progressing from the surface defects towards neighboring regions. By using PbI2 passivation, the defect-initiated degradation is significantly suppressed and the nanoplatelet degrades in a layer-by-layer way, enabling the MAPbI3 laser to sustain for 4500 s (2.7×107 pulses), which is nearly three times longer than that of the nanoplatelet laser without passivation. Meanwhile, the PbI2 passivated MAPbI3 nanoplatelet laser with the nanoplatelet cavity displays a maximum quality factor up to 7800, the highest reported for all MAPbI3 nanoplatelet cavities. Furthermore, a high stability MAPbI3 nanoplatelet laser that can last for 8500 s (5.1×107 pulses) is demonstrated based on a dual passivation strategy, by retarding the defect-initiated degradation and surface-initiated degradation simultaneously. This work provides in-depth insights for understanding the operating degradation of perovskite lasers, and the dual passivation strategy paves the way for developing high stability near infrared semiconductor laser media.
Photonics Research
  • Publication Date: May. 20, 2022
  • Vol.10 Issue, 6 06001440 (2022)
Optical Devices
Evanescent waveguide lab-on-chip for optical biosensing in food quality control
Alessio Buzzin, Rita Asquini, Domenico Caputo, and Giampiero de Cesare
Optical biosensing systems are commonly developed assembling a source, a light–sample interaction area, and a detector as distinct stand-alone elements. We present a compact, inexpensive, and easy-to-use glass chip that monolithically integrates both the interaction and detection elements in a 1 cm2 overall surface. The device working principle is based on evanescent wavelight interaction with the complex refractive index of a liquid mixture, being the index influenced by the mixture’s physical and chemical features. We describe the manufacture of a prototype able to perform investigations on food quality and subsequent tests on the detection of fat content in milk. Theoretical investigations are reported as well as measurements performed on samples in the green spectrum. A sensitivity of about 139 fA/(g/dL) and a limit of detection of 14 ppm have been achieved, better than those of current commercial devices.
Photonics Research
  • Publication Date: May. 20, 2022
  • Vol.10 Issue, 6 06001453 (2022)
Optical Devices
Neural network-based surrogate model for inverse design of metasurfaces
Guoqing Jing, Peipei Wang, Haisheng Wu, Jianjun Ren, Zhiqiang Xie, Junmin Liu, Huapeng Ye, Ying Li, Dianyuan Fan, and Shuqing Chen
Metasurfaces composed of spatially arranged ultrathin subwavelength elements are promising photonic devices for manipulating optical wavefronts, with potential applications in holography, metalens, and multiplexing communications. Finding microstructures that meet light modulation requirements is always a challenge in designing metasurfaces, where parameter sweep, gradient-based inverse design, and topology optimization are the most commonly used design methods in which the massive electromagnetic iterations require the design computational cost and are sometimes prohibitive. Herein, we propose a fast inverse design method that combines a physics-based neural network surrogate model (NNSM) with an optimization algorithm. The NNSM, which can generate an accurate electromagnetic response from the geometric topologies of the meta-atoms, is constructed for electromagnetic iterations, and the optimization algorithm is used to search for the on-demand meta-atoms from the phase library established by the NNSM to realize an inverse design. This method addresses two important problems in metasurface design: fast and accurate electromagnetic wave phase prediction and inverse design through a single phase-shift value. As a proof-of-concept, we designed an orbital angular momentum (de)multiplexer based on a phase-type metasurface, and 200 Gbit/s quadrature-phase shift-keying signals were successfully transmitted with a bit error rate approaching 1.67×10-6. Because the design is mainly based on an optimization algorithm, it can address the “one-to-many” inverse problem in other micro/nano devices such as integrated photonic circuits, waveguides, and nano-antennas.
Photonics Research
  • Publication Date: May. 20, 2022
  • Vol.10 Issue, 6 06001462 (2022)
Optoelectronics
Optically pumped low-threshold microdisk lasers on a GeSn-on-insulator substrate with reduced defect density
Yongduck Jung, Daniel Burt, Lin Zhang, Youngmin Kim, Hyo-Jun Joo, Melvina Chen, Simone Assali, Oussama Moutanabbir, Chuan Seng Tan, and Donguk Nam
Despite the recent success of GeSn infrared lasers, the high lasing threshold currently limits their integration into practical applications. While structural defects in epitaxial GeSn layers have been identified as one of the major bottlenecks towards low-threshold GeSn lasers, the effect of defects on the lasing threshold has not been well studied yet. Herein, we experimentally demonstrate that the reduced defect density in a GeSn-on-insulator substrate improves the lasing threshold significantly. We first present a method of obtaining high-quality GeSn-on-insulator layers using low-temperature direct bonding and chemical–mechanical polishing. Low-temperature photoluminescence measurements reveal that the reduced defect density in GeSn-on-insulator leads to enhanced spontaneous emission and a reduced lasing threshold by 10 times and 6 times, respectively. Our result presents a new path towards pushing the performance of GeSn lasers to the limit.
Photonics Research
  • Publication Date: May. 12, 2022
  • Vol.10 Issue, 6 06001332 (2022)
Optoelectronics
High-performance modified uni-traveling carrier photodiode integrated on a thin-film lithium niobate platform
Xiangwen Guo, Linbo Shao, Lingyan He, Kevin Luke, Jesse Morgan, Keye Sun, Junyi Gao, Ta-Ching Tzu, Yang Shen, Dekang Chen, Bingtian Guo, Fengxin Yu, Qianhuan Yu, Masoud Jafari, Marko Lončar, Mian Zhang, and Andreas Beling
Lithium niobate on insulator (LNOI) has become an intriguing platform for integrated photonics for applications in communications, microwave photonics, and computing. Whereas, integrated devices including modulators, resonators, and lasers with high performance have been recently realized on the LNOI platform, high-speed photodetectors, an essential building block in photonic integrated circuits, have not been demonstrated on LNOI yet. Here, we demonstrate for the first time, heterogeneously integrated modified uni-traveling carrier photodiodes on LNOI with a record-high bandwidth of 80 GHz and a responsivity of 0.6 A/W at a 1550-nm wavelength. The photodiodes are based on an n-down InGaAs/InP epitaxial layer structure that was optimized for high carrier transit time-limited bandwidth. Photodiode integration was achieved using a scalable wafer die bonding approach that is fully compatible with the LNOI platform.
Photonics Research
  • Publication Date: May. 12, 2022
  • Vol.10 Issue, 6 06001338 (2022)
Quantum Optics
Spectrally multiplexed indistinguishable single-photon generation at telecom-band
Hao Yu, Chenzhi Yuan, Ruiming Zhang, Zichang Zhang, Hao Li, You Wang, Guangwei Deng, Lixing You, Haizhi Song, Zhiming Wang, Guang-Can Guo, and Qiang Zhou
Heralded single-photon source (HSPS) intrinsically suffers from the trade-off between the heralded single-photon rate and the single-photon purity. To break through this trade-off, one can apply multiplexing technology in different degrees of freedom that significantly improves the performance of the HSPS. Here, we propose a 1.5 μm chip-scale HSPS on lithium niobate on insulator by employing spectral multiplexing and active feed-forward spectral manipulating, and we demonstrate a proof-of-principle experiment with discrete fiber-based components. With continuous-wave laser pumping and three spectral modes multiplexed, our experimental results show that the spectral multiplexing improves the heralded single-photon rate by near threefold while keeping the g(2)(0) as low as 0.0006±0.0001 at a measured single-photon rate of 3.1 kHz. By measuring the joint spectral intensity, we show that the spectral multiplexing and feed-forward control effectively erase the frequency correlation of photon pairs. Moreover, we implement the Hong–Ou–Mandel interference between the spectrally multiplexed single photons and photons from an independent weak coherence source, which indicates that the multiplexed single photons are highly indistinguishable after the spectral manipulation. Our results pave a way for on-chip scalable and high-performance HSPS with spectral multiplexing toward deterministic single-photon emission.
Photonics Research
  • Publication Date: May. 20, 2022
  • Vol.10 Issue, 6 06001417 (2022)
Quantum Optics
Experimental quantum simulation of dynamic localization on curved photonic lattices
Hao Tang, Tian-Yu Wang, Zi-Yu Shi, Zhen Feng, Yao Wang, Xiao-Wen Shang, Jun Gao, Zhi-Qiang Jiao, Zhan-Ming Li, Yi-Jun Chang, Wen-Hao Zhou, Yong-Heng Lu, Yi-Lin Yang, Ruo-Jing Ren, Lu-Feng Qiao, and Xian-Min Jin
Dynamic localization, which originates from the phenomena of particle evolution suppression under an externally applied AC electric field, has been simulated by suppressed light evolution in periodically curved photonic arrays. However, experimental studies on their quantitative dynamic transport properties and application for quantum information processing are rare. Here we fabricate one-dimensional and hexagonal two-dimensional arrays both with sinusoidal curvatures. We successfully observe the suppressed single-photon evolution patterns, and for the first time, to the best of our knowledge, measure the variances to study their transport properties. For one-dimensional arrays, the measured variances match both the analytical electric-field calculation and the quantum walk Hamiltonian engineering approach. For hexagonal arrays as anisotropic effective couplings in four directions are mutually dependent, the analytical approach suffers, whereas quantum walk conveniently incorporates all anisotropic coupling coefficients in the Hamiltonian and solves its exponential as a whole, yielding consistent variances with our experimental results. Furthermore, we implement a nearly complete localization to show that it can preserve both the initial injection and the wave packet after some evolution, acting as a memory of a flexible time scale in integrated photonics. We demonstrate a useful quantum simulation of dynamic localization for studying their anisotropic transport properties and a promising application of dynamic localization as a building block for quantum information processing in integrated photonics.
Photonics Research
  • Publication Date: May. 20, 2022
  • Vol.10 Issue, 6 06001430 (2022)
Research ArticlesVol.10, Iss.5-May..1,2022
Fiber Optics and Optical Communications
Electrically induced dynamic Fano-like resonance in a graphene-coated fiber grating
Biqiang Jiang, Xiaoming Zhang, Ailun Li, Yueguo Hou, Zhen Hao, Xuetao Gan, and Jianlin Zhao
We created an all-fiber solution for fast, continuous, and controllable tuning of Fano-like resonance. By embedding a graphene-coated fiber Bragg grating into one arm of a Mach–Zehnder interferometer, the narrow Bragg resonance interacts with a broad interference spectrum, forming a sharp asymmetric Fano-like resonance line shape. With the application of an electrical voltage over the graphene layer, the generated Joule heating shifts the Bragg resonance and consequently tunes the asymmetric Fano-like resonance line shape to a symmetric dip or electromagnetically induced transparency-like peak. Further, by exploiting two modulated states with reversed Fano-like resonance line shapes, an optical switch can operate with an extinction ratio of 9 dB. The well-engineered Fano-like resonance in an all-fiber structure opens up new horizons for applications of fiber gratings in optical signal processing, slow-light lasing, and fiber sensing.
Photonics Research
  • Publication Date: Apr. 14, 2022
  • Vol.10 Issue, 5 05001238 (2022)
Imaging Systems, Microscopy, and Displays
Improving signal-to-background ratio by orders of magnitude in high-speed volumetric imaging in vivo by robust Fourier light field microscopy
Jiazhen Zhai, Ruheng Shi, and Lingjie Kong
Fourier light field microscopy (FLFM) shows great potential in high-speed volumetric imaging of biodynamics. However, due to the inherent disadvantage of wide-field illumination, it suffers from intense background, arising from out of the depth-of-field signal and tissue scattered noise. The background will not only deteriorate the image contrast, making quantitative measurement difficult, but also introduce artifacts, especially in functional imaging of the neuronal network activity in vivo. Here, we propose the robust Fourier light field microscopy (RFLFM), which suppresses the background in FLFM by introducing structured illumination and computational reconstruction based on HiLo. The superior performance of RFLFM is verified by volumetric imaging of biological dynamics in larval zebrafish and mouse in vivo, at a volumetric imaging rate up to 33.3 Hz. The statistical results show that the fluorescence background can be significantly depressed, with the signal-to-background ratio improved by orders of magnitude and the whole image contrast improved by as much as 10.4 times. Moreover, we stress that, in functional imaging of neuronal network activity in turbid brain tissues, our system can avoid artifacts resulting from background fluctuations, while conventional light field microscopy fails. As a simple but powerful tool, we anticipate our technique to be widely adopted in robust, high-contrast, high-speed volumetric imaging.
Photonics Research
  • Publication Date: Apr. 21, 2022
  • Vol.10 Issue, 5 05001255 (2022)
Imaging Systems, Microscopy, and Displays
Polarization microwave-induced thermoacoustic imaging for quantitative characterization of deep biological tissue microstructures
Yujing Li, Shanxiang Zhang, Linghua Wu, Zhongwen Cheng, Zhenhui Zhang, Haohao Wang, Shuxiang Zhao, Mingyang Ren, Sihua Yang, Da Xing, and Huan Qin
Polarization optical imaging can be used to characterize anisotropy in biological tissue microstructures and has been demonstrated to be a powerful tool for clinical diagnosis. However, the approach is limited by an inability to image targets deeper than 1 mm due to strong optical scattering in biological tissues. As such, we propose a novel polarization microwave-induced thermoacoustic imaging (P-MTAI) technique to noninvasively detect variations in deep tissue by exploiting the thermoacoustic signals induced by four pulsed microwaves of varying polarization orientations. The proposed P-MTAI method overcomes the penetration limits of conventional polarization optical imaging and provides submillimeter resolution over depths of several centimeters. As part of the paper, the structural characteristics of tissues were quantified using a new parameter, the degree of microwave absorption anisotropy. P-MTAI was also applied to the noninvasive detection of morphological changes in cardiomyocytes as they transitioned from ordered to disordered states, providing a potential indication of myocardial infarction.
Photonics Research
  • Publication Date: Apr. 29, 2022
  • Vol.10 Issue, 5 05001297 (2022)
Imaging Systems, Microscopy, and Displays
Miniaturized structured illumination microscopy with diffractive optics
Guoxuan Liu, Ning Xu, Huaidong Yang, Qiaofeng Tan, and Guofan Jin
Structured illumination microscopy (SIM) is an advanced microscope system that provides superresolution capability with excellent imaging speed, which has become a practical tool for live-cell imaging. However, the bulky size is blocking the application of SIM in wider study fields and scenarios. Here, we developed a miniaturized SIM (Mini SIM) system that provided periodic illumination using a diffractive optical element (DOE) for the first time. This optimized phase-only DOE generated the two-dimensional sinusoidal illumination by optical Fourier transform with an illuminating objective lens, which substantially simplified and miniaturized the illumination system. We built up a Mini SIM prototype and demonstrated lateral superresolution imaging of fluorescence beads and A549 cell slides. The proposed Mini SIM greatly simplifies the experimental setup and may lead to important applications in bio-imaging.
Photonics Research
  • Publication Date: Apr. 29, 2022
  • Vol.10 Issue, 5 05001317 (2022)
Instrumentation and Measurements
Measurement of sub-fm/Hz1/2 displacement spectral densities in ultrahigh-Q single-crystal microcavities with hertz-level lasers
Yoon-Soo Jang, Jinkang Lim, Wenting Wang, Seung-Woo Kim, Anatoliy Savchenkov, Andrey B. Matsko, and Chee Wei Wong
Tracing a resonance frequency of a high quality factor (Q) optical cavity facilitates subpicometer displacement measurements of the optical cavity via Pound–Drever–Hall (PDH) locking scheme, tightly synchronizing a laser frequency to the optical cavity. Here we present observations of subfemtometer displacements on a ultrahigh-Q single-crystal MgF2 whispering-gallery-mode microcavity by frequency synchronization between a 1 Hz cavity-stabilized laser and a resonance of the MgF2 cavity using PDH laser-cavity locking. We characterize not only the displacement spectral density of the microcavity with a sensitivity of 1.5×10-16 m/Hz1/2 over the Fourier offset frequency ranging from 15 mHz to 100 kHz but also a 1.77 nm displacement fluctuation of the microcavity over 4500 s. Such measurement capability not only supports the analysis of integrated thermodynamical and technical cavity noise but allows for minute displacement measurements using laser-cavity locking for ultraprecise positioning, metrology, and sensing.
Photonics Research
  • Publication Date: Apr. 14, 2022
  • Vol.10 Issue, 5 05001202 (2022)
Instrumentation and Measurements
Intensity diffusion: a concealed cause of fringe distortion in fringe projection profilometry
Zheng Sun, Minghui Duan, Yabing Zheng, Yi Jin, Xin Fan, and Jinjin Zheng
Fringe projection profilometry (FPP) is widely used in optical three-dimensional (3D) measurements because of its high stability. In FPP, fringe distortion is an inevitable and highly complex systematic error that significantly reduces the 3D measurement accuracy. At this point, the existing causes of fringe distortion represented by gamma distortion, high-order harmonics, and image saturation have been effectively analyzed and compensated to restore high-quality fringe images. In this paper, we innovatively reveal a concealed cause of fringe distortion, i.e., intensity diffusion across pixels, which is induced by photocarrier diffusion between photodiodes. To the best of our knowledge, intensity diffusion has not been studied in the field of fringe restoration. Based on the motion of photocarrier diffusion, we theoretically analyze the mechanism of how the intensity diffusion affects FPP. Subsequently, an intensity diffusion model is established for quantifying the diffused intensity in each pixel, and an intensity diffusion correction algorithm is presented to remove the diffused intensity from the fringe images and correct the fringe distortion. Experiments demonstrate the impact of intensity diffusion on FPP, and the 3D measurement results prove the effectiveness of the proposed methods on improving the 3D measurement accuracy by correcting the fringe distortion.
Photonics Research
  • Publication Date: Apr. 14, 2022
  • Vol.10 Issue, 5 05001210 (2022)
Integrated Optics
Machine-learning-empowered multispectral metafilm with reduced radar cross section, low infrared emissivity, and visible transparency
Ruichao Zhu, Jiafu Wang, Jinming Jiang, Cuilian Xu, Che Liu, Yuxiang Jia, Sai Sui, Zhongtao Zhang, Tonghao Liu, Zuntian Chu, Jun Wang, Tie Jun Cui, and Shaobo Qu
For camouflage applications, the performance requirements for metamaterials in different electromagnetic spectra are usually contradictory, which makes it difficult to develop satisfactory design schemes with multispectral compatibility. Fortunately, empowered by machine learning, metamaterial design is no longer limited to directly solving Maxwell’s equations. The design schemes and experiences of metamaterials can be analyzed, summarized, and learned by computers, which will significantly improve the design efficiency for the sake of practical engineering applications. Here, we resort to the machine learning to solve the multispectral compatibility problem of metamaterials and demonstrate the design of a new metafilm with multiple mechanisms that can realize small microwave scattering, low infrared emissivity, and visible transparency simultaneously using a multilayer backpropagation neural network. The rapid evolution of structural design is realized by establishing a mapping between spectral curves and structural parameters. By training the network with different materials, the designed network is more adaptable. Through simulations and experimental verifications, the designed architecture has good accuracy and robustness. This paper provides a facile method for fast designs of multispectral metafilms that can find wide applications in satellite solar panels, aircraft windows, and others.
Photonics Research
  • Publication Date: Apr. 06, 2022
  • Vol.10 Issue, 5 05001146 (2022)
Integrated Optics
Topological protection of partially coherent lightEditors' Pick
Konrad Tschernig, Gabriel Martinez-Niconoff, Kurt Busch, Miguel A. Bandres, and Armando Perez-Leija
Topological physics exploits concepts from geometry and topology to implement systems capable of guiding waves in an unprecedented fashion. These ideas have led to the development of photonic topological insulators, which are optical systems whose eigenspectral topology allows the creation of light states that propagate along the edge of the system without any coupling into the bulk or backscattering even in the presence of disorder. Indeed, topological protection is a fully coherent effect, and it is not clear to what extent topological effects endure when the wavefronts become partially coherent. Here, we study the interplay of topological protection and the degree of spatial coherence of classical light propagating in disordered photonic topological insulators. Our results reveal the existence of a well-defined spectral window in which partially coherent light is topologically protected. This opens up the design space to a wider selection of light sources, possibly yielding smaller, cheaper, and more robust devices based on the topological transport of light.
Photonics Research
  • Publication Date: Apr. 14, 2022
  • Vol.10 Issue, 5 05001223 (2022)
Integrated Optics
Soliton frequency comb generation in CMOS-compatible silicon nitride microresonators
Yaozu Xie, Jiaqi Li, Yanfeng Zhang, Zeru Wu, Shihao Zeng, Shuqing Lin, Zhaoyang Wu, Wenchao Zhou, Yujie Chen, and Siyuan Yu
The monolithic integration of soliton microcomb devices with active photonic components and high-frequency electronics is highly desirable for practical applications. Among many materials, silicon nitride (SiNx) waveguide layers prepared by low-pressure chemical vapor deposition (LPCVD) have been the main platform for on-chip optical frequency comb generation. However, the high temperatures involved in LPCVD render it incompatible as a back-end process with complementary metal oxide semiconductor (CMOS) or active III-V compound semiconductor fabrication flows. We report the generation of coherent soliton frequency combs in micro-ring resonators fabricated in deuterated silicon nitride (SiNx:D) waveguides with a loss of 0.09 dB/cm. Deposited at 270°C by an inductance-coupled plasma chemical vapor deposition (ICP-CVD) process, the material preparation and fabrication flow are fully CMOS-compatible. These results enable the integration of silicon-nitride-based optical combs and photonic integrated circuits (PICs) on prefabricated CMOS and/or III-V substrates, therefore marking a major step forward in SiNx photonic technologies.
Photonics Research
  • Publication Date: Apr. 29, 2022
  • Vol.10 Issue, 5 05001290 (2022)
Lasers and Laser Optics
Four-wave mixing in 1.3 μm epitaxial quantum dot lasers directly grown on siliconEditors' Pick
Jianan Duan, Bozhang Dong, Weng W. Chow, Heming Huang, Shihao Ding, Songtao Liu, Justin C. Norman, John E. Bowers, and Frédéric Grillot
Photonics Research
  • Publication Date: Apr. 21, 2022
  • Vol.10 Issue, 5 05001264 (2022)
Lasers and Laser Optics
High-performance distributed feedback quantum dot lasers with laterally coupled dielectric gratings
Zhuohui Yang, Zhengqing Ding, Lin Liu, Hancheng Zhong, Sheng Cao, Xinzhong Zhang, Shizhe Lin, Xiaoying Huang, Huadi Deng, Ying Yu, and Siyuan Yu
The combination of grating-based frequency-selective optical feedback mechanisms, such as distributed feedback (DFB) or distributed Bragg reflector (DBR) structures, with quantum dot (QD) gain materials is a main approach towards ultrahigh-performance semiconductor lasers for many key novel applications, as either stand-alone sources or on-chip sources in photonic integrated circuits. However, the fabrication of conventional buried Bragg grating structures on GaAs, GaAs/Si, GaSb, and other material platforms has been met with major material regrowth difficulties. We report a novel and universal approach of introducing laterally coupled dielectric Bragg gratings to semiconductor lasers that allows highly controllable, reliable, and strong coupling between the grating and the optical mode. We implement such a grating structure in a low-loss amorphous silicon material alongside GaAs lasers with InAs/GaAs QD gain layers. The resulting DFB laser arrays emit at pre-designed 0.8 THz local area network wavelength division multiplexing frequency intervals in the 1300 nm band with record performance parameters, including sidemode suppression ratios as high as 52.7 dB, continuous-wave output power of 26.6 mW (room temperature) and 6 mW (at 55°C), and ultralow relative intensity noise (RIN) of <-165 dB/Hz (2.5–20 GHz). The devices are also capable of isolator-free operating under very high external reflection levels of up to -12.3 dB while maintaining high spectral purity and ultralow RIN qualities. These results validate the novel laterally coupled dielectric grating as a technologically superior and potentially cost-effective approach for fabricating DFB and DBR lasers free of their semiconductor material constraints, which are thus universally applicable across different material platforms and wavelength bands.
Photonics Research
  • Publication Date: Apr. 29, 2022
  • Vol.10 Issue, 5 05001271 (2022)
Lasers and Laser Optics
Ultra-broadband flat-top quantum dot comb lasersSpotlight on Optics
Jing-Zhi Huang, Zi-Tao Ji, Jia-Jian Chen, Wen-Qi Wei, Jia-Le Qin, Zi-Hao Wang, Zhi-Yuan Li, Ting Wang, Xi Xiao, and Jian-Jun Zhang
A quantum dot (QD) mode-locked laser as an active comb generator takes advantage of its small footprint, low power consumption, large optical bandwidth, and high-temperature stability, which is an ideal multi-wavelength source for applications such as datacom, optical interconnects, and LIDAR. In this work, we report a fourth-order colliding pulse mode-locked laser (CPML) based on InAs/GaAs QD gain structure, which can generate ultra-stable optical frequency combs in the O-band with 100 GHz spacing at operation temperature up to 100°C. A record-high flat-top optical comb is achieved with 3 dB optical bandwidth of 11.5 nm (20 comb lines) at 25°C. The average optical linewidth of comb lines is measured as 440 kHz. Single-channel non-return-to-zero modulation rates of 70 Gbit/s and four-level pulse amplitude modulation of 40 GBaud/s are also demonstrated. To further extend the comb bandwidth, an array of QD-CPMLs driven at separate temperatures is proposed to achieve 36 nm optical bandwidth (containing 60 comb lines with 100 GHz mode spacing), capable of a total transmission capacity of 4.8 Tbit/s. The demonstrated results show the feasibility of using the QD-CPML as a desirable broadband comb source to build future large-bandwidth and power-efficient optical interconnects.
Photonics Research
  • Publication Date: Apr. 29, 2022
  • Vol.10 Issue, 5 05001308 (2022)
Nanophotonics and Photonic Crystals
Higher-order valley vortices enabled by synchronized rotation in a photonic crystal
Rui Zhou, Hai Lin, Yanjie Wu, Zhifeng Li, Zihao Yu, Y. Liu, and Dong-Hui Xu
Synchronized rotation of unit cells in a periodic structure provides a novel design perspective for manipulation of band topology. We then design a two-dimensional version of higher-order topological insulator (HOTI) by such rotation in a triangular photonic lattice with C3 symmetry. This HOTI supports the hallmark zero-dimensional corner states and, simultaneously, the one-dimensional edge states. We also find that our photonic corner states carry chiral orbital angular momenta locked by valleys, whose wave functions are featured by the phase vortex (singularity) positioned at the maximal Wyckoff points. Moreover, when excited by a fired source with various frequencies, the valley topological states of both one-dimensional edges and zero-dimensional corners emerge simultaneously. Extendable to higher or synthetic dimensions, our paper provides access to a chiral vortex platform for HOTI realizations in the terahertz photonic system.
Photonics Research
  • Publication Date: Apr. 21, 2022
  • Vol.10 Issue, 5 05001244 (2022)
Optical and Photonic Materials
Broadband NIR-emitting Te cluster-doped glass for smart light source towards night-vision and NIR spectroscopy applications
Linling Tan, Yanqing Fu, Shiliang Kang, Lothar Wondraczek, Changgui Lin, and Yuanzheng Yue
Broadband near-infrared (NIR)-emitting materials are crucial components of the next generation of smart NIR light sources based on blue light-emitting diodes (LEDs). Here, we report a Te cluster-doped borate glass, which exhibits ultra-broadband emission around 980 nm with a full-width at half-maximum (FWHM) of 306 nm under blue light excitation. We propose adjustments of glass chemistry and processing condition as a means for topo-chemical tailoring of the NIR photoemission characteristics in such materials. Through implementing strongly reducing conditions during glass melting, Te clusters with broad NIR photoluminescence can be generated and stabilized once the melt is vitrified to the glassy state. Tunability of the NIR emission peak over the wavelength range of 904 to 1026 nm is possible in this way, allowing for fine adjustments of spectral properties relative to the stretching vibrations of common chemical bonds, for example, in water, proteins, and fats. This potentially enables high sensitivity in NIR spectroscopy. We further demonstrate potential application of glass-converted LEDs in night vision.
Photonics Research
  • Publication Date: Apr. 14, 2022
  • Vol.10 Issue, 5 05001187 (2022)
Optical Devices
Continuous-wave operation of 405 nm distributed Bragg reflector laser diodes based on GaN using 10th-order surface gratings
J. H. Kang, H. Wenzel, E. Freier, V. Hoffmann, J. Fricke, O. Brox, M. Matalla, and S. Einfeldt
Single longitudinal mode continuous-wave operation of GaN-based distributed Bragg reflector (DBR) laser diodes with 10th-order surface gratings is demonstrated. The DBR consists of periodic V-shaped grooves on a 2 μm wide ridge waveguide fabricated by using electron-beam lithography and plasma etching. The effect of different lengths of the DBR section and the gain section on the device performance has been studied. Periodic mode hops to the adjacent longitudinal Fabry–Perot resonator mode at shorter wavelength have been observed when increasing the operation current. Between the mode hops, single longitudinal mode emission at around 405 nm is achieved with a full width at half-maximum of 0.03 nm. A linear redshift of the emission wavelength with increasing temperature of 0.019 nm/K was derived.
Photonics Research
  • Publication Date: Apr. 08, 2022
  • Vol.10 Issue, 5 05001157 (2022)
Optoelectronics
Demonstration of electrically injected vertical-cavity surface-emitting lasers with post-supported high-contrast gratingsOn the Cover
Jing Zhang, Chenxi Hao, Wanhua Zheng, Dieter Bimberg, and Anjin Liu
We experimentally demonstrate for the first time to our knowledge electrically injected vertical-cavity surface-emitting lasers (VCSELs) with post-supported high-contrast gratings (HCGs) at 940 nm. The HCG-VCSELs have two posts to support the air-suspended HCGs, which are realized by simple fabrication without critical point drying. The HCG-VCSEL achieves a threshold current of about 0.65 mA and a side-mode suppression ratio of 43.6 dB under continuous-wave operation at 25°C. Theoretically the HCG-VCSEL with a λ/2-cavity for the transverse magnetic polarization has a smaller effective mode length of 1.38·(λ/n). Thus, the relaxation resonance frequency can be increased by 16% compared with that of the conventional VCSEL. The modulation speed of 100 Gbit/s for the HCG-VCSEL is expected in the on–off keying modulation format. Our easy design of HCG-VCSELs has great potential for applications in optical interconnects, sensing, illumination, and so on.
Photonics Research
  • Publication Date: Apr. 14, 2022
  • Vol.10 Issue, 5 05001170 (2022)
Optoelectronics
Epitaxial indium antimonide for multiband photodetection from IR to millimeter/terahertz wave
Jinchao Tong, Heng Luo, Fei Suo, Tianning Zhang, Dawei Zhang, and Dao Hua Zhang
Conventional photodetection converts light into electrical signals only in a single electromagnetic waveband. Multiband detection technology is highly desirable because it can handle multispectral information discrimination, identification, and processing. Current epitaxial solid-state multiband detection technologies are mainly within the IR wave range. Here, we report epitaxial indium antimonide on gallium arsenide for IR and millimeter/terahertz wave multiband photodetection. The photoresponse originates from interband transition in optoelectrical semiconductors for IR wave, and surface plasmon polaritons induced nonequilibrium electrons for a millimeter/terahertz wave. The detector shows a strong response for an IR wave with a cutoff wavelength of 6.85 μm and a blackbody detectivity of 1.8×109 Jones at room temperature. For a millimeter/terahertz wave, the detector demonstrates broadband detection from 0.032 THz (9.4 mm) to 0.330 THz (0.9 mm); that is, from Ka to the W and G bands, with a noise equivalent power of 1.0×10-13 W Hz-1/2 at 0.270 THz (1.1 mm) at room temperature. The detection performance is an order of magnitude better while decreasing the temperature to 170 K, the thermoelectric cooling level. Such detectors, capable of large scale and low cost, are promising for advanced uncooled multiband detection and imaging systems.
Photonics Research
  • Publication Date: Apr. 14, 2022
  • Vol.10 Issue, 5 05001194 (2022)
Optoelectronics
Dissipative microwave photonic solitons in spontaneous frequency-hopping optoelectronic oscillators
Tengfei Hao, Hao Ding, Wei Li, Ninghua Zhu, Yitang Dai, and Ming Li
Dissipative solitons relying on the double balance between nonlinear and linear effects as well as cavity loss and gain have attracted increasing attention in recent years, since they give rise to novel operating states of various dissipative nonlinear systems. An optoelectronic oscillator (OEO) is a dissipative nonlinear microwave photonic system with a high quality factor that has been widely investigated for generating ultra-low noise single-frequency microwave signals. Here, we report a novel operating state of an OEO related to dissipative solitons, i.e., spontaneous frequency hopping related to the formation of dissipative microwave photonic solitons. In this operating state, dissipative microwave photonic solitons occur due to the double balance between nonlinear gain saturation and linear filtering as well as cavity loss and gain in the OEO cavity, creating spontaneous frequency-hopping microwave signals. The generation of wideband tunable frequency-hopping microwave signals with a fast frequency-hopping speed up to tens of nanoseconds is observed in the experiment, together with the corresponding soliton sequences. This work reveals a novel mechanism between the interaction of nonlinear and linear effects in an OEO cavity, extends the suitability and potential applications of solitons, and paves the way for a new class of soliton microwave photonic systems for the generation, processing, and control of microwave and RF signals.
Photonics Research
  • Publication Date: Apr. 29, 2022
  • Vol.10 Issue, 5 05001280 (2022)
Silicon Photonics
Discretization of annular-ring diffraction pattern for large-scale photonics beamformingEditors' Pick
Aroutin Khachaturian, Reza Fatemi, Artsroun Darbinian, and Ali Hajimiri
A solid-state active beamformer based on the annular-ring diffraction pattern is demonstrated in an integrated photonic platform. Such a circularly symmetric annular-ring aperture achieves a radiating element limited field of view. Furthermore, it is demonstrated that a multi-annular-ring aperture with a fixed linear density of elements maintains the beam efficiency for larger apertures while reducing the beamwidth and side-lobe level. A 255-element multi-annular-ring optical phased array with active beamforming is implemented in a standard photonics process. A total of 510 phase and amplitude modulators enable beamforming and beam steering using this aperture. A row–column drive methodology reduces the required electrical drivers by more than a factor of 5.
Photonics Research
  • Publication Date: Apr. 14, 2022
  • Vol.10 Issue, 5 05001177 (2022)
Surface Optics and Plasmonics
Multidimensional trapping by dual-focusing cylindrical vector beams with all-silicon metalens
Jia-Lu Zhu, Ren-Chao Jin, Li-Li Tang, Zheng-Gao Dong, Jia-Qi Li, and Jin Wang
Dual-focusing effect with a cylindrical vector-light characteristic (i.e., radial and azimuthal polarizations) is theoretically proposed and numerically demonstrated by spin-decoupled phase control with all-silicon metalens. Attributed to the polarization dependence, the pair of focusing cylindrical vector beams can be interchanged by orthogonally switching the polarization of incident light. We demonstrate the unique contributions of focused radial and azimuthal vector beams to longitudinal and transverse optical forces on glass spheres, respectively, by calculations based on the Maxwell stress tensor. This paper presents the use of all-silicon metalens with highly-compact vector beams, promising for applications such as multidimensional optical trapping.
Photonics Research
  • Publication Date: Apr. 08, 2022
  • Vol.10 Issue, 5 05001162 (2022)