Volume: 9 Issue 11
18 Article(s)

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Research Articles
Imaging Systems, Microscopy, and Displays
Ten-mega-pixel snapshot compressive imaging with a hybrid coded aperture
Zhihong Zhang, Chao Deng, Yang Liu, Xin Yuan, Jinli Suo, and Qionghai Dai
High-resolution images are widely used in our everyday life; however, high-speed video capture is more challenging due to the low frame rate of cameras working at the high-resolution mode. The main bottleneck lies in the low throughput of existing imaging systems. Toward this end, snapshot compressive imaging (SCI) was proposed as a promising solution to improve the throughput of imaging systems by compressive sampling and computational reconstruction. During acquisition, multiple high-speed images are encoded and collapsed to a single measurement. Then, algorithms are employed to retrieve the video frames from the coded snapshot. Recently developed plug-and-play algorithms made the SCI reconstruction possible in large-scale problems. However, the lack of high-resolution encoding systems still precludes SCI’s wide application. Thus, in this paper, we build, to the best of our knowledge, a novel hybrid coded aperture snapshot compressive imaging (HCA-SCI) system by incorporating a dynamic liquid crystal on silicon and a high-resolution lithography mask. We further implement a PnP reconstruction algorithm with cascaded denoisers for high-quality reconstruction. Based on the proposed HCA-SCI system and algorithm, we obtain a 10-mega-pixel SCI system to capture high-speed scenes, leading to a high throughput of 4.6 × 109 voxels per second. Both simulation and real-data experiments verify the feasibility and performance of our proposed HCA-SCI scheme.
Photonics Research
  • Publication Date: Oct. 25, 2021
  • Vol.9 Issue, 11 11002277 (2021)
Instrumentation and Measurements
Dispersion engineering and measurement in crystalline microresonators using a fiber ring etalon
Xiaobao Zhang, Guoping Lin, Tang Sun, Qinghai Song, Guangzong Xiao, and Hui Luo
Dispersion engineering and measurement are significant for nonlinear photonic applications using whispering gallery mode microresonators. Specifically, the Kerr microresonator frequency comb as an important example has attracted a great amount of interest in research fields due to the potential capability of full integration on a chip. A simple and cost-efficient way for dispersion measurements is thereby in high demand for designing such a microcomb device. Here, we report a dispersion measurement approach using a fiber ring etalon reference. The free spectral range of the etalon is first measured through sideband modulation, and the dispersion of the etalon is inferred by binary function fitting during the dispersion measurement. This method is demonstrated on two MgF2 disk resonators. Experimental results show good agreement with numerical simulations using the finite element method. Dispersion engineering on such resonators is also numerically investigated.
Photonics Research
  • Publication Date: Oct. 19, 2021
  • Vol.9 Issue, 11 11002222 (2021)
Integrated Optics
Polarization-insensitive interferometer based on a hybrid integrated planar light-wave circuit
Guo-Wei Zhang, Yu-Yang Ding, Wei Chen, Fang-Xiang Wang, Peng Ye, Guan-Zhong Huang, Shuang Wang, Zhen-Qiang Yin, Jun-Ming An, Guang-Can Guo, and Zheng-Fu Han
Interferometers are essential elements in classical and quantum optical systems. The strictly required stability when extracting the phase of photons is vulnerable to polarization variation and phase shift induced by environment disturbance. Here, we implement polarization-insensitive interferometers by combining silica planar light-wave circuit chips and Faraday rotator mirrors. Two asymmetric interferometers with temperature controllers are connected in series to evaluate the single-photon interference. Average interference visibility over 12 h is above 99%, and the variations are less than 0.5%, even with active random polarization disturbance. The experiment results verify that the hybrid chip is available for high-demand applications like quantum key distribution and entanglement measurement.
Photonics Research
  • Publication Date: Oct. 09, 2021
  • Vol.9 Issue, 11 11002176 (2021)
Coherent self-control of free-space optical beams with integrated silicon photonic meshes | Spotlight on Optics
Maziyar Milanizadeh, Fabio Toso, Giorgio Ferrari, Tigers Jonuzi, David A. B. Miller, Andrea Melloni, and Francesco Morichetti
In technologies operating at light wavelengths for wireless communication, sensor networks, positioning, and ranging, a dynamic coherent control and manipulation of light fields is an enabling element for properly generating and correctly receiving free-space optical (FSO) beams even in the presence of unpredictable objects and turbulence in the light path. In this work, we use a programmable mesh of Mach–Zehnder (MZI) interferometers to automatically control the complex field radiated and captured by an array of optical antennas. The implementation of local feedback control loops in each MZI stage, without global multivariable optimization techniques, enables an unlimited scalability. Several functionalities are demonstrated, including the generation of perfectly shaped beams with nonperfect optical antennas, the imaging of a desired field pattern through an obstacle or a diffusive medium, and the identification of an unknown obstacle inserted in the FSO path. Compared to conventional devices used for the manipulation of FSO beams, such as spatial light modulators, our programmable device can self-configure through automated control strategies and can be integrated with other functionalities implemented onto the same photonic chip.
Photonics Research
  • Publication Date: Oct. 15, 2021
  • Vol.9 Issue, 11 11002196 (2021)
Thermally enhanced responsivity in an all-silicon optical power monitor based on defect-mediated absorption
Qikai Huang, Hui Yu, Qiang Zhang, Yan Li, Weiwei Chen, Yuehai Wang, and Jianyi Yang
We demonstrate a high responsivity all-silicon in-line optical power monitor by using the thermal effect to enhance the quantum efficiency of defect-mediated absorption at 1550 nm. The doping compensation technique is utilized to increase the density of lattice defects responsible for the sub-bandgap absorption and suppress the detrimental free carrier absorption. The 200-μm-long device presents a propagation loss as low as 2.9 dB/cm. Its responsivity is enhanced from 12.1 mA/W to 112 mA/W at -9 V bias by heating the optical absorption region. With this device, we build an optical power monitoring system that operates in the sampling mode. The minimal detectable optical power of the system is below -22.8 dBm, while the average power consumption is less than 1 mW at a sampling frequency of 10 Hz. Advantages of this scheme in terms of high responsivity, low insertion loss, and low power consumption lend itself to implement the feedback control of advanced large-scale silicon photonic integrated circuits.
Photonics Research
  • Publication Date: Oct. 19, 2021
  • Vol.9 Issue, 11 11002205 (2021)
Nonlinear Optics
Synchronization in PT-symmetric optomechanical resonators
Chang-Long Zhu, Yu-Long Liu, Lan Yang, Yu-Xi Liu, and Jing Zhang
Synchronization has great impacts in various fields such as self-clocking, communication, and neural networks. Here, we present a mechanism of synchronization for two mechanical modes in two coupled optomechanical resonators with a parity-time (PT)-symmetric structure. It is shown that the degree of synchronization between the two far-off-resonant mechanical modes can be increased by decreasing the coupling strength between the two optomechanical resonators due to the large amplification of optomechanical interaction near the exceptional point. Additionally, when we consider the stochastic noises in the optomechanical resonators by working near the exceptional point, we find that more noises can enhance the degree of synchronization of the system under a particular parameter regime. Our results open up a new dimension of research for PT-symmetric systems and synchronization.
Photonics Research
  • Publication Date: Oct. 09, 2021
  • Vol.9 Issue, 11 11002152 (2021)
Optical and Photonic Materials
Tuning the luminous properties and optical thermometry of Cs2SnCl6 phosphor microcrystals via Bi and Sb codoping
Shunfa Gong, Ruirui Wu, Sen Yang, Lifang Wu, Minmin Zhang, Qiuju Han, and Wenzhi Wu
The toxicity and instability of lead halide perovskite seriously limit its commercial application in lighting, although it has high photoluminescence (PL) efficiency and adjustable emission. Here, lead-free bismuth (Bi) and antimony (Sb) codoped Cs2SnCl6 (BSCSC) microcrystals (MCs) are prepared successfully by a solvothermal method. The PL spectrum is composed of dual emission bands with the peak at 485 and 650 nm, of which relative intensity can be tunable through the change of Bi and Sb feeding contents, respectively. Because of the phonon–electron interaction, the PL intensity is enhanced as the temperature rises within the range of 80–260 K. Then, the nonradiative transition is intensified until 380 K, which results in decrease in PL intensity. Simultaneously, combining with time-resolved PL, it is concluded that the emission peak at 485 nm is attributed to the [BiSn+VCl] as the luminescent centers with the lifetime of hundreds of nanoseconds, and the emission peak at 650 nm is attributed to microsecond-timescale self-trapped excitons. The maximum values of relative sensitivity (SR) and absolute sensitivity (SA) values obtained are 3.82% K-1 and 5.11 ns ·K-1, which for the first time to our knowledge demonstrate that BSCSC MCs can be novel luminescent materials for developing better optical thermometry. White-light-emitting diodes (WLEDs) are constructed using BSCSC MCs only combined with an LED chip, the Commission Internationale de L’Eclairage color coordinates of which are (0.30, 0.37). It provides a novel scheme for the lighting field to realize WLEDs without adding additional commercial phosphors.
Photonics Research
  • Publication Date: Oct. 14, 2021
  • Vol.9 Issue, 11 11002182 (2021)
Control of phase, polarization, and amplitude based on geometric phase in a racemic helix array
Chao Wu, Quan Li, Zhihui Zhang, Song Zhao, and Hongqiang Li
The Pancharatnam–Berry geometric phase has attracted great interest due to the elegant phase control strategy via geometric transformation of optical elements. The commonly used geometric phase is associated with circular polarization states. Here, we show that by exploiting the geometric phase associated with the two elliptical eigen-polarization states in a racemic metallic helix array, exotic features including full range phase modulation for linear polarization states, diverse polarization conversion, and full complex amplitude modulation can be obtained with rotation of the helices. As a proof of concept, several devices for implementing polarization conversion, vortex beam generating, and lateral dual focusing are built with a racemic helix array in the microwave regime. The calculated and experimental results validate our proposals, which can stimulate various advanced metadevices.
Photonics Research
  • Publication Date: Oct. 25, 2021
  • Vol.9 Issue, 11 11002265 (2021)
Optical Devices
Control of angular dispersion in dielectric gratings for multifunctional wavefront shaping and dynamic polarization conversion
Yiwu Yuan, Jierong Cheng, Fei Fan, Xianghui Wang, and Shengjiang Chang
Compared with traditional optical elements, metasurfaces have shown unique advantages in multifunctionality encoded in different frequencies, polarization states, and orbital angular momentums. However, the study of metasurfaces with well-controlled functions under different incident angles is still in its infancy. Here we propose a general method to tailor the angular dispersion over the simplest binary dielectric grating in the transmission mode. We demonstrate that the angular response is strongly related to the number of waveguide modes inside the grating, so one can intentionally reduce or enhance the angular dispersion by controlling the number of waveguide modes. Independent phase manipulation over incident angles is experimentally demonstrated by a metalens with angle-dependent focus. The angular dispersion in orthogonal polarization states is further utilized to demonstrate angle-insensitive and angle-multiplexed wave plates. These devices with simple configuration and clear physics offer a general platform to expand the scope of beam manipulation over metasurfaces.
Photonics Research
  • Publication Date: Oct. 14, 2021
  • Vol.9 Issue, 11 11002190 (2021)
Enhanced performance of a fast GaAs-based terahertz modulator via surface passivation
Yulian He, Yuansheng Wang, Qinghui Yang, Huaiwu Zhang, and Qiye Wen
Surface-modified semiconductors show enormous potential for opto-terahertz (THz) spatial modulation due to their enhanced modulation depth (MD) along with their inherent broad bandwidth. Taking full advantage of the surface modification, a performance-enhanced, all-optical, fast switchable THz modulator was achieved here based on the surface-passivated GaAs wafer. With a decreased surface recombination rate and prolonged carrier lifetime induced by passivation, S-passivated GaAs was demonstrated as a viable candidate to enhance THz modulation performance in MD, especially at low photodoping levels. Despite a degraded modulation rate owing to the longer carrier lifetime, this passivated GaAs modulator simultaneously realizes a fast modulation at a 69-MHz speed and as high an MD as ∼94% in a spectral wideband of 0.2–1.2 THz. The results demonstrated a new strategy to alleviate the tradeoff between high MD and speed in contrast to bare surfaces or heterogeneous films/unusual geometry on semiconductors including Si, Ge, and GaAs.
Photonics Research
  • Publication Date: Oct. 19, 2021
  • Vol.9 Issue, 11 11002230 (2021)
High-efficiency and large light-receiving area superconducting nanowire single-photon detector integrated with high-contrast grating
Chen Wei, Wencong Wang, Dongmei Liu, Min Gu, and Xianqiu Wu
By using a high-contrast grating (HCG, high transmittance >90%) to control the phase shift of incident light, we theoretically designed a novel-structured HCG-integrated superconducting nanowire single-photon detector (HCG-SNSPD) with a high-efficiency and large light-receiving area. Without enlarging the typical single-pixel SNSPD nanowire area (10 μm×10 μm), the effective detection area is expanded to 115 μm, while the absorption efficiency of the nanowire reaches 84.9% at a wavelength of 1550 nm. The effective detection area of HCG-SNSPD is increased by 11.5 times compared to that of conventional single-pixel SNSPDs. Moreover, the absorption efficiencies of HCG-SNSPD exceed 70% at wavelengths ranging from 1460 nm to 1650 nm, indicating high-efficiency broadband detection. This study promotes new possibilities for the application of SNSPDs.
Photonics Research
  • Publication Date: Oct. 25, 2021
  • Vol.9 Issue, 11 11002253 (2021)
Highly stable full-color display device with VLC application potential using semipolar μLEDs and all-inorganic encapsulated perovskite nanocrystal | On the Cover
Tingzhu Wu, Yue Lin, Yu-Ming Huang, Meng Liu, Konthoujam James Singh, Wansheng Lin, Tingwei Lu, Xi Zheng, Jianyang Zhou, Hao-Chung Kuo, and Zhong Chen
A promising approach for the development of effective full-color displays is to combine blue microLEDs (μLEDs) with color conversion layers. Perovskite nanocrystals (PNCs) are notable for their tolerance to defects and provide excellent photoluminescence quantum yields and high color purity compared to metal chalcogenide quantum dots. The stability of PNCs in ambient conditions and under exposure to blue light can be improved using a SiO2 coating. This study proposes a device that could be used for both display and visible light communication (VLC) applications. The semipolar blue μLED array fabricated in this study shows a negligible wavelength shift, indicating a significant reduction in the quantum confined Stark effect. Owing to its shorter carrier lifetime, the semipolar μLED array exhibits an impressive peak 3 dB bandwidth of 655 MHz and a data transmission rate of 1.2 Gb/s corresponding to an injection current of 200 mA. The PNC–μLED device assembled from a semipolar μLED array with PNCs demonstrates high color stability and wide color-gamut features, achieving 127.23% and 95.00% of the National Television Standards Committee standard and Rec. 2020 on the CIE 1931 color diagram, respectively. These results suggest that the proposed PNC–μLED device is suitable for both display-related and VLC applications.
Photonics Research
  • Publication Date: Oct. 09, 2021
  • Vol.9 Issue, 11 11002132 (2021)
Ultrabroadband and multiband infrared/terahertz photodetectors with high sensitivity
Jiaqi Zhu, He Zhu, Mengjuan Liu, Yao Wang, Hanlun Xu, Nasir Ali, Huiyong Deng, Zhiyong Tan, Juncheng Cao, Ning Dai, and Huizhen Wu
Broadband response is pursued in both infrared (IR) and terahertz (THz) detection technologies, which find their applications in both terrestrial and astronomical realms. Herein, we report an ultrabroadband and multiband IR/THz detector based on blocked-impurity-band detecting principle. The detectors are prepared by implanting phosphorus into germanium (Ge:P), where photoresponses with a P impurity band, a self-interstitial defect band, and a vacancy-P (V-P) pair defect band are realized simultaneously. The response spectra of the detectors show ultrabroad and dual response bands in a range of 3–28 μm (IR band) and 40–165 μm (THz band), respectively. Additionally, a tiny mid-IR (MIR) band within 3–4.2 μm is embedded in the IR band. The THz band arises from the P impurity band, whereas the IR and the MIR bands are ascribed to the two defect bands. At 150 mV and 4.5 K, the peak detectivities of the three bands are obtained as 2.9×1012 Jones (at 3.9 μm), 6.8×1012 Jones (at 16.3 μm), and 9.9×1012 Jones (at 116.5 μm), respectively. The impressive coverage and sensitivity of the detectors are promising for applications in IR and THz detection technologies.
Photonics Research
  • Publication Date: Oct. 09, 2021
  • Vol.9 Issue, 11 11002167 (2021)
Physical Optics
Off-axis optical levitation and transverse spinning of metallic microparticles
Yansheng Liang, Shaohui Yan, Zhaojun Wang, Baoli Yao, and Ming Lei
Photonics Research
  • Publication Date: Oct. 09, 2021
  • Vol.9 Issue, 11 11002144 (2021)
Sculpturing spatiotemporal wavepackets with chirped pulses | Editors' Pick
Qian Cao, Jian Chen, Keyin Lu, Chenhao Wan, Andy Chong, and Qiwen Zhan
Pulse shaping has become a powerful tool in generating complicated ultrafast optical waveforms to meet specific application needs. Traditionally, pulse shaping focuses on the temporal waveform synthesis. Recent interests in structuring light in the spatiotemporal domain rely on Fourier analysis. A space-to-time mapping technique allows us to directly imprint complex spatiotemporal modulation through taking advantage of the relationship between frequency and time of chirped pulses. The concept is experimentally verified through the generation of spatiotemporal optical vortex (STOV) and STOV lattice. The power of this method is further demonstrated by STOV polarity reversal, vortex collision, and vortex annihilation. Such a direct mapping technique opens tremendous potential opportunities for sculpturing complex spatiotemporal waveforms.
Photonics Research
  • Publication Date: Oct. 25, 2021
  • Vol.9 Issue, 11 11002261 (2021)
Quantum Optics
Submegahertz spectral width photon pair source based on fused silica microspheres | Editors' Pick
Erasto Ortiz-Ricardo, Cesar Bertoni-Ocampo, Mónica Maldonado-Terrón, Arturo Garcia Zurita, Roberto Ramirez-Alarcon, Hector Cruz Ramirez, R. Castro-Beltrán, and Alfred B. U’Ren
High-efficiency submegahertz bandwidth photon pair generators will enable the field of quantum technology to transition from laboratory demonstrations to transformational applications involving information transfer from photons to atoms. While spontaneous parametric processes are able to achieve high-efficiency photon pair generation, the spectral bandwidth tends to be relatively large, as defined by phase-matching constraints. To solve this fundamental limitation, we use an ultrahigh quality factor (Q) fused silica microsphere resonant cavity to form a photon pair generator. We present the full theory for the spontaneous four-wave mixing (SFWM) process in these devices, fully taking into account all relevant source characteristics in our experiments. The exceptionally narrow (down to kilohertz-scale) linewidths of these devices result in a reduction in the bandwidth of the photon pair generation, allowing submegahertz spectral bandwidth to be achieved. Specifically, using a pump source centered around 1550 nm, photon pairs with the signal and idler modes at wavelengths close to 1540 and 1560 nm, respectively, are demonstrated. We herald a single idler-mode photon by detecting the corresponding signal photon, filtered via transmission through a wavelength division multiplexing channel of choice. We demonstrate the extraction of the spectral profile of a single peak in the single-photon frequency comb from a measurement of the signal–idler time of emission distribution. These improvements in device design and experimental methods enabled the narrowest spectral width (Δν=366 kHz) to date in a heralded single-photon source based on SFWM.
Photonics Research
  • Publication Date: Oct. 19, 2021
  • Vol.9 Issue, 11 11002237 (2021)
Adiabaticity in state preparation for spin squeezing of large atom ensembles
Shenchao Jin, Han Bao, Junlei Duan, Xingda Lu, Mingfeng Wang, Kai-Feng Zhao, Heng Shen, and Yanhong Xiao
Photonics Research
  • Publication Date: Oct. 27, 2021
  • Vol.9 Issue, 11 11002296 (2021)
Silicon Photonics
Ultrawide-band silicon microring avalanche photodiode with linear photocurrent-wavelength response
Yang Ren, and Vien Van
Photonics Research
  • Publication Date: Oct. 27, 2021
  • Vol.9 Issue, 11 11002303 (2021)