Journals >Chinese Optics Letters
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2023
Volume: 21 Issue 6
15 Article(s)
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Research Articles
Atmospheric, Oceanic, Space, and Environmental Optics
Target-independent dynamic wavefront sensing method based on distorted grating and deep learning
Xinlan Ge, Licheng Zhu, Zeyu Gao, Ning Wang, Wang Zhao, Hongwei Ye, Shuai Wang, and Ping Yang
A real-time wavefront sensing method for arbitrary targets is proposed, which provides an effective way for diversified wavefront sensing application scenarios. By using a distorted grating, the positive and negative defocus images are simultaneously acquired on a single detector. A fine feature, which is independent of the target itself but corresponding to the wavefront aberration, is defined. A lightweight and efficient network combined with an attention mechanism (AM-EffNet) is proposed to establish an accurate mapping between the features and the incident wavefronts. Comparison results show that the proposed method has superior performance compared to other methods and can achieve high-accuracy wavefront sensing in varied target scenes only by using the point target dataset to train the network well.A real-time wavefront sensing method for arbitrary targets is proposed, which provides an effective way for diversified wavefront sensing application scenarios. By using a distorted grating, the positive and negative defocus images are simultaneously acquired on a single detector. A fine feature, which is independent of the target itself but corresponding to the wavefront aberration, is defined. A lightweight and efficient network combined with an attention mechanism (AM-EffNet) is proposed to establish an accurate mapping between the features and the incident wavefronts. Comparison results show that the proposed method has superior performance compared to other methods and can achieve high-accuracy wavefront sensing in varied target scenes only by using the point target dataset to train the network well..
Chinese Optics Letters
- Publication Date: Jun. 07, 2023
- Vol. 21, Issue 6, 060101 (2023)
Fiber Optics and Optical Communications
Optical scrambler using WGM micro-bottle cavity
Pengfa Chang, Chen Wang, Tao Jiang, Longsheng Wang, Tong Zhao, Hua Gao, Zhiwei Jia, Yuanyuan Guo, Yuncai Wang, and Anbang Wang
An optical scrambler using a whispering-gallery-mode (WGM) micro-bottle cavity to scramble a complex optical signal to generate an uncorrelated output is proposed. We experimentally demonstrated this micro-cavity scrambler by using chaotic laser light as the incident signal and studied the influence of the coupling state. Experiments achieved full scrambling with a low cross correlation of 0.028 between the output and the input. Results indicate that the scrambling effect originates from the interference among numerous WGMs in the bottle cavity. It is believed that the micro-bottle cavity with an efficient scrambling function can become a promising candidate for encryption.An optical scrambler using a whispering-gallery-mode (WGM) micro-bottle cavity to scramble a complex optical signal to generate an uncorrelated output is proposed. We experimentally demonstrated this micro-cavity scrambler by using chaotic laser light as the incident signal and studied the influence of the coupling state. Experiments achieved full scrambling with a low cross correlation of 0.028 between the output and the input. Results indicate that the scrambling effect originates from the interference among numerous WGMs in the bottle cavity. It is believed that the micro-bottle cavity with an efficient scrambling function can become a promising candidate for encryption..
Chinese Optics Letters
- Publication Date: Jun. 06, 2023
- Vol. 21, Issue 6, 060601 (2023)
Security enhanced underwater visible light communication system based on chaotic phase scrambling and conjugate frequency hopping
Zhilan Lu, Chao Shen, Jianyang Shi, and Nan Chi
We propose an encryption technique for underwater visible light communication (UVLC) based on chaotic phase scrambling (PS) and conjugate frequency hopping (CFH). The technique is experimentally tested using an 8-level pulse amplitude modulation (PAM-8) and a 1.2 m underwater link. The security key of the phase scrambling code is generated according to a logistic map, and the frequency hopping is achieved by adding the same zero frequency points to the signal spectrum. The maximum transmission rate of 2.1 Gbit/s is measured with bit-error-rate (BER) below 7% the hard-decision forward error correction (HD-FEC) threshold of 3.8×10-3.We propose an encryption technique for underwater visible light communication (UVLC) based on chaotic phase scrambling (PS) and conjugate frequency hopping (CFH). The technique is experimentally tested using an 8-level pulse amplitude modulation (PAM-8) and a 1.2 m underwater link. The security key of the phase scrambling code is generated according to a logistic map, and the frequency hopping is achieved by adding the same zero frequency points to the signal spectrum. The maximum transmission rate of 2.1 Gbit/s is measured with bit-error-rate (BER) below 7% the hard-decision forward error correction (HD-FEC) threshold of
Chinese Optics Letters
- Publication Date: Jun. 13, 2023
- Vol. 21, Issue 6, 060602 (2023)
Quasiperiodic photonic crystal fiber [Invited] | Fast Track , On the Cover
Exian Liu, and Jianjun Liu
In the fields of light manipulation and localization, quasiperiodic photonic crystals, or photonic quasicrystals (PQs), are causing an upsurge in research because of their rotational symmetry and long-range orientation of transverse lattice arrays, as they lack translational symmetry. It allows for the optimization of well-established light propagation properties and has introduced new guiding features. Therefore, as a class, quasiperiodic photonic crystal fibers, or photonic quasicrystal fibers (PQFs), are considered to add flexibility and richness to the optical properties of fibers and are expected to offer significant potential applications to optical fiber fields. In this review, the fundamental concept, working mechanisms, and invention history of PQFs are explained. Recent progress in optical property improvement and its novel applications in fields such as dispersion control, polarization-maintenance, supercontinuum generation, orbital angular momentum transmission, plasmon-based sensors and filters, and high nonlinearity and topological mode transmission, are then reviewed in detail. Bandgap-type air-guiding PQFs supporting low attenuation propagation and regulation of photonic density states of quasiperiodic cladding and in which light guidance is achieved by coherent Bragg scattering are also summarized. Finally, current challenges encountered in the guiding mechanisms and practical preparation techniques, as well as the prospects and research trends of PQFs, are also presented.In the fields of light manipulation and localization, quasiperiodic photonic crystals, or photonic quasicrystals (PQs), are causing an upsurge in research because of their rotational symmetry and long-range orientation of transverse lattice arrays, as they lack translational symmetry. It allows for the optimization of well-established light propagation properties and has introduced new guiding features. Therefore, as a class, quasiperiodic photonic crystal fibers, or photonic quasicrystal fibers (PQFs), are considered to add flexibility and richness to the optical properties of fibers and are expected to offer significant potential applications to optical fiber fields. In this review, the fundamental concept, working mechanisms, and invention history of PQFs are explained. Recent progress in optical property improvement and its novel applications in fields such as dispersion control, polarization-maintenance, supercontinuum generation, orbital angular momentum transmission, plasmon-based sensors and filters, and high nonlinearity and topological mode transmission, are then reviewed in detail. Bandgap-type air-guiding PQFs supporting low attenuation propagation and regulation of photonic density states of quasiperiodic cladding and in which light guidance is achieved by coherent Bragg scattering are also summarized. Finally, current challenges encountered in the guiding mechanisms and practical preparation techniques, as well as the prospects and research trends of PQFs, are also presented..
Chinese Optics Letters
- Publication Date: May. 03, 2023
- Vol. 21, Issue 6, 060603 (2023)
Vector bending sensor based on chirped long-period grating with off-axis micro-helix taper
Jian Zhou, Xuelan He, Hongzhou Chen, Ziyang Xiong, Jing Yang, Chunying Guan, and Libo Yuan
Vector bending sensing has been consistently growing in many fields. A low-cost and high sensitivity vector bending sensor based on a chirped long-period fiber grating (LPFG) with an off-axis micro helix taper is proposed and experimentally demonstrated. The grating is composed of several sections of single-mode fiber with gradually larger lengths, and the off-axis micro helix tapers with fixed lengths when they are fabricated by using the arc discharge technology. The large refractive index modulation in the micro-helix taper greatly reduces the sensor size. The total length of the sensor is only 4.67 mm. The micro-helix taper-based LPFG can identify the bending direction due to the asymmetric structure introduced by the micro helix. The experimental results show that the transmission spectra of the sensor have distinct responses for different bending directions, and the maximum bending sensitivity is 14.08 nm/m-1 in the range from 0.128 m-1 to 1.28 m-1. The proposed bending sensor possesses pronounced advantages, such as high sensitivity, small size, low cost, and orientation identification, and offers a very promising method for bend measurement.Vector bending sensing has been consistently growing in many fields. A low-cost and high sensitivity vector bending sensor based on a chirped long-period fiber grating (LPFG) with an off-axis micro helix taper is proposed and experimentally demonstrated. The grating is composed of several sections of single-mode fiber with gradually larger lengths, and the off-axis micro helix tapers with fixed lengths when they are fabricated by using the arc discharge technology. The large refractive index modulation in the micro-helix taper greatly reduces the sensor size. The total length of the sensor is only 4.67 mm. The micro-helix taper-based LPFG can identify the bending direction due to the asymmetric structure introduced by the micro helix. The experimental results show that the transmission spectra of the sensor have distinct responses for different bending directions, and the maximum bending sensitivity is 14.08 nm/m-1 in the range from 0.128 m-1 to 1.28 m-1. The proposed bending sensor possesses pronounced advantages, such as high sensitivity, small size, low cost, and orientation identification, and offers a very promising method for bend measurement..
Chinese Optics Letters
- Publication Date: Jun. 05, 2023
- Vol. 21, Issue 6, 060604 (2023)
Imaging Systems and Image Processing
Compact in situ microscope for photoelectron spectroscopy via two-mirror reflection
Chenyang Yue, Hong Jiang, Tianzhi Li, Siyan Yao, Shengyue Zeng, Xiaojun Xu, and Chaofan Zhang
Photoelectron spectroscopy is a powerful tool in characterizing the electronic structure of materials. To investigate the specific region of interest with high probing efficiency, in this work we propose a compact in situ microscope to assist photoelectron spectroscopy. The configuration of long objective distance of 200 mm with two-mirror reflection has been introduced. Large magnification of 5× to 100×, lateral resolution of 4.08 µm, and longitudinal resolution of 4.49 µm have been achieved. Meanwhile, the testing result shows larger focal depth of this in situ optical microscope. Similar configurations could also be applied to other electronic microscopes to improve their probing capability.Photoelectron spectroscopy is a powerful tool in characterizing the electronic structure of materials. To investigate the specific region of interest with high probing efficiency, in this work we propose a compact in situ microscope to assist photoelectron spectroscopy. The configuration of long objective distance of 200 mm with two-mirror reflection has been introduced. Large magnification of
Chinese Optics Letters
- Publication Date: Jun. 05, 2023
- Vol. 21, Issue 6, 061101 (2023)
Simulation for embedded-defects foam terahertz images of active bifocal terahertz imaging system at 0.22 THz based on geometric optics
Hui Wang, Deliang Zhou, Yan Wang, Runfeng Su, Shaohe Li, Xuecou Tu, Xiaoqing Jia, Lin Kang, Biaobing Jin, Huabing Wang, Jian Chen, and Peiheng Wu
We simulate the measurements of an active bifocal terahertz imaging system to reproduce the ability of the system to detect the internal structure of foams having embedded defects. Angular spectrum theory and geometric optics tracing are used to calculate the incident and received electric fields of the system and the scattered light distribution of the measured object. The finite-element method is also used to calculate the scattering light distribution of the measured object for comparison with the geometric optics model. The simulations are consistent with the measurements at the central axis of the horizontal stripe defects.We simulate the measurements of an active bifocal terahertz imaging system to reproduce the ability of the system to detect the internal structure of foams having embedded defects. Angular spectrum theory and geometric optics tracing are used to calculate the incident and received electric fields of the system and the scattered light distribution of the measured object. The finite-element method is also used to calculate the scattering light distribution of the measured object for comparison with the geometric optics model. The simulations are consistent with the measurements at the central axis of the horizontal stripe defects..
Chinese Optics Letters
- Publication Date: May. 23, 2023
- Vol. 21, Issue 6, 061102 (2023)
Passive non-line-of-sight imaging for moving targets with an event camera
Conghe Wang, Yutong He, Xia Wang, Honghao Huang, Changda Yan, Xin Zhang, and Hongwei Chen
Non-line-of-sight (NLOS) imaging is an emerging technique for detecting objects behind obstacles or around corners. Recent studies on passive NLOS mainly focus on steady-state measurement and reconstruction methods, which show limitations in recognition of moving targets. To the best of our knowledge, we propose a novel event-based passive NLOS imaging method. We acquire asynchronous event-based data of the diffusion spot on the relay surface, which contains detailed dynamic information of the NLOS target, and efficiently ease the degradation caused by target movement. In addition, we demonstrate the event-based cues based on the derivation of an event-NLOS forward model. Furthermore, we propose the first event-based NLOS imaging data set, EM-NLOS, and the movement feature is extracted by time-surface representation. We compare the reconstructions through event-based data with frame-based data. The event-based method performs well on peak signal-to-noise ratio and learned perceptual image patch similarity, which is 20% and 10% better than the frame-based method.Non-line-of-sight (NLOS) imaging is an emerging technique for detecting objects behind obstacles or around corners. Recent studies on passive NLOS mainly focus on steady-state measurement and reconstruction methods, which show limitations in recognition of moving targets. To the best of our knowledge, we propose a novel event-based passive NLOS imaging method. We acquire asynchronous event-based data of the diffusion spot on the relay surface, which contains detailed dynamic information of the NLOS target, and efficiently ease the degradation caused by target movement. In addition, we demonstrate the event-based cues based on the derivation of an event-NLOS forward model. Furthermore, we propose the first event-based NLOS imaging data set, EM-NLOS, and the movement feature is extracted by time-surface representation. We compare the reconstructions through event-based data with frame-based data. The event-based method performs well on peak signal-to-noise ratio and learned perceptual image patch similarity, which is 20% and 10% better than the frame-based method..
Chinese Optics Letters
- Publication Date: May. 26, 2023
- Vol. 21, Issue 6, 061103 (2023)
Integrated Optics
Photonic and phononic interface states based on sunflower-type crystals [Invited]
Zixian Guo, Bei Yan, and Jianjun Liu
Interface states are widely applied in waveguide devices. However, previous studies failed to achieve photonic and phononic interface states independent of each other in the same crystal structure depending on the behavior of the crystal structure, i.e., photonic or phononic crystals, making the function of interface states single. In this study, straight-line and circular photonic and phononic interface states were realized independently in sunflower-type crystals. In addition, with a defect and a metal barrier, interface states could remain almost undamaged. The results have the potential to achieve multi-function devices and reduce the cost of engineering applications.Interface states are widely applied in waveguide devices. However, previous studies failed to achieve photonic and phononic interface states independent of each other in the same crystal structure depending on the behavior of the crystal structure, i.e., photonic or phononic crystals, making the function of interface states single. In this study, straight-line and circular photonic and phononic interface states were realized independently in sunflower-type crystals. In addition, with a defect and a metal barrier, interface states could remain almost undamaged. The results have the potential to achieve multi-function devices and reduce the cost of engineering applications..
Chinese Optics Letters
- Publication Date: Jun. 05, 2023
- Vol. 21, Issue 6, 061301 (2023)
Lasers, Optical Amplifiers, and Laser Optics
Sideband-free dispersion-managed Yb-doped mode-locked fiber laser with Gires–Tournois interferometer mirrors | Editors' Pick
Aoran Feng, Bowen Liu, Dongyu Yan, Genyu Bi, Youjian Song, and Minglie Hu
High-order dispersion introduced by Gires–Tournois interferometer mirrors usually causes spectral sidebands in the near-zero dispersion region of mode-locked fiber lasers. Here, we demonstrate a sideband-free Yb-doped mode-locked fiber laser with dispersion-compensating Gires–Tournois interferometer mirrors. Both the simulation and the experiment demonstrate that the wavelength and energy of the sidebands can be tuned by changing the transmission coefficient of the output mirror, the pump power, and the ratio of the net cavity dispersion to the net third-order dispersion in the cavity. By optimizing these three parameters, the laser can generate a sideband-free, Gaussian-shaped spectrum with a 13.56-nm bandwidth at -0.0232 ps2 net cavity dispersion, which corresponds to a 153-fs pulse duration.High-order dispersion introduced by Gires–Tournois interferometer mirrors usually causes spectral sidebands in the near-zero dispersion region of mode-locked fiber lasers. Here, we demonstrate a sideband-free Yb-doped mode-locked fiber laser with dispersion-compensating Gires–Tournois interferometer mirrors. Both the simulation and the experiment demonstrate that the wavelength and energy of the sidebands can be tuned by changing the transmission coefficient of the output mirror, the pump power, and the ratio of the net cavity dispersion to the net third-order dispersion in the cavity. By optimizing these three parameters, the laser can generate a sideband-free, Gaussian-shaped spectrum with a 13.56-nm bandwidth at
Chinese Optics Letters
- Publication Date: Jun. 06, 2023
- Vol. 21, Issue 6, 061401 (2023)
Wavelength-tunable dissipative soliton from Yb-doped fiber laser with nonlinear amplifying loop mirror
Yangyang Li, Man Jiang, Lei Hou, Jianing Tao, Pengye Song, Baole Lu, and Jintao Bai
We report a Yb-doped mode-locked fiber laser based on a nonlinear amplifying loop mirror (NALM), which is all-normal-dispersion (ANDi), and allows the output wavelength to be tunable. The laser can generate a stable femtosecond dissipative soliton with a maximum output power of 196 mW. Its repetition rate is 112.4 MHz, and the final pulse duration is 236 fs. By adjusting the angle of the reflective diffraction grating, the mode-locked fiber laser was realized to tune the output with a tuning range of 54 nm from 1011.8 nm to 1065.6 nm. To the best of our knowledge, this is the widest tuning range of an ANDi Yb-doped mode-locked fiber laser based on NALM.We report a Yb-doped mode-locked fiber laser based on a nonlinear amplifying loop mirror (NALM), which is all-normal-dispersion (ANDi), and allows the output wavelength to be tunable. The laser can generate a stable femtosecond dissipative soliton with a maximum output power of 196 mW. Its repetition rate is 112.4 MHz, and the final pulse duration is 236 fs. By adjusting the angle of the reflective diffraction grating, the mode-locked fiber laser was realized to tune the output with a tuning range of 54 nm from 1011.8 nm to 1065.6 nm. To the best of our knowledge, this is the widest tuning range of an ANDi Yb-doped mode-locked fiber laser based on NALM..
Chinese Optics Letters
- Publication Date: Jun. 06, 2023
- Vol. 21, Issue 6, 061402 (2023)
Light-matter Interaction
Effects of laser waveform on the generation of fast electrons in laser–solid interactions
Xiaomei Dong, Yuhan Du, Miaohua Xu, Yutong Li, Zhe Zhang, and Yingjun Li
In the scheme of fast ignition of inertial confinement fusion, the fuel temperature mainly relies on fast electrons, which act as an energy carrier, transferring the laser energy to the fuel. Both conversion efficiency from the laser to the fast electron and the energy spectrum of the fast electron are essentially important to achieve highly effective heating. In this study, a two-dimensional particle in cell simulation is applied to study the generation of fast electrons from solid-density plasmas with different laser waveforms. The results have shown that the slope of the rising edge has a significant effect on fast electron generation and energy absorption. For the negative skew pulse with a relatively slow rising edge, the J×B mechanism can most effectively accelerate the electrons. The overall absorption efficiency of the laser energy is optimized, and the fast electron yield in the middle- and low-energy range is also improved.In the scheme of fast ignition of inertial confinement fusion, the fuel temperature mainly relies on fast electrons, which act as an energy carrier, transferring the laser energy to the fuel. Both conversion efficiency from the laser to the fast electron and the energy spectrum of the fast electron are essentially important to achieve highly effective heating. In this study, a two-dimensional particle in cell simulation is applied to study the generation of fast electrons from solid-density plasmas with different laser waveforms. The results have shown that the slope of the rising edge has a significant effect on fast electron generation and energy absorption. For the negative skew pulse with a relatively slow rising edge, the
Chinese Optics Letters
- Publication Date: Jun. 06, 2023
- Vol. 21, Issue 6, 063801 (2023)
Nonlinear Optics
400 Gb/s physical random number generation based on deformed square self-chaotic lasers
Jiancheng Li, Yali Li, Yunxiao Dong, Yuede Yang, Jinlong Xiao, and Yongzhen Huang
A circular-sided square microcavity laser etched a central hole has achieved chaos operation with a bandwidth of 20.8 GHz without external optical feedback or injection, in which the intensity probability distribution of a chaotic signal with a two-peak pattern was observed. Based on the self-chaotic microlaser, physical random numbers at 400 Gb/s were generated by extracting the four least significant bits without other complex post-processing methods. The solitary chaos laser and minimal post-processing have predicted a simpler and low-cost on-chip random number generator in the future.A circular-sided square microcavity laser etched a central hole has achieved chaos operation with a bandwidth of 20.8 GHz without external optical feedback or injection, in which the intensity probability distribution of a chaotic signal with a two-peak pattern was observed. Based on the self-chaotic microlaser, physical random numbers at 400 Gb/s were generated by extracting the four least significant bits without other complex post-processing methods. The solitary chaos laser and minimal post-processing have predicted a simpler and low-cost on-chip random number generator in the future..
Chinese Optics Letters
- Publication Date: Jun. 06, 2023
- Vol. 21, Issue 6, 061901 (2023)
On-chip ultraviolet second-harmonic generation in lithium-tantalate thin film microdisk | Fast Track , Editors' Pick
Miao Xue, Xiongshuo Yan, Jiangwei Wu, Rui Ge, Tingge Yuan, Yuping Chen, and Xianfeng Chen
The compact and reliable ultraviolet (UV) source has attracted remarkable attention for its potential use in optical measurement systems, high-density optical storage, and biomedical applications. We demonstrate ultraviolet generation by frequency doubling in a lithium-tantalate-on-insulator (LTOI) microdisk via modal phase matching. The 50-µm-diameter microdisk was milled by a focused ion beam (FIB) and followed by chemo-mechanical polishing (CMP) to smooth the disk surface and edge, and the Q-factor reaches 2.74×105 in the visible band. On-chip UV coherent light with a wavelength of 384.3 nm was achieved, which shows great promise for using LTOIs in integrated ultraviolet source platforms.The compact and reliable ultraviolet (UV) source has attracted remarkable attention for its potential use in optical measurement systems, high-density optical storage, and biomedical applications. We demonstrate ultraviolet generation by frequency doubling in a lithium-tantalate-on-insulator (LTOI) microdisk via modal phase matching. The 50-µm-diameter microdisk was milled by a focused ion beam (FIB) and followed by chemo-mechanical polishing (CMP) to smooth the disk surface and edge, and the Q-factor reaches
Chinese Optics Letters
- Publication Date: Apr. 19, 2023
- Vol. 21, Issue 6, 061902 (2023)
Optical Materials
Environmentally stable, spectral-shape-controllable, GHz femtosecond Yb-doped fiber laser
Kefeng Chen, Lina Gan, Yingge Tao, Weilin Shao, Wei Yu, Haowei Lin, Zhiping Cai, and Huihui Cheng
We demonstrate an all-polarization-maintaining (PM) passively mode-locked Yb3+-doped fiber laser (YDFL) with a fundamental repetition rate of 1.3 GHz. The optical spectra of a linearly polarized soliton exhibit different shapes by rotating the fast axis of the fiber optical pigtail of a dispersive dielectric mirror. The oscillator provides a series of laser performance, such as a threshold pump power for continuous wave laser oscillation of 3.1 mW, an optical-to-optical efficiency for mode-locking of 29%, and an integrated relative intensity noise of 0.08%. To the best of our knowledge, this is the first report of >1 GHz ultrafast all-fiber YDFL with PM architecture.We demonstrate an all-polarization-maintaining (PM) passively mode-locked
Chinese Optics Letters
- Publication Date: Jun. 06, 2023
- Vol. 21, Issue 6, 061601 (2023)
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