Journals >Chinese Optics Letters
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2025
Volume: 23 Issue 4
27 Article(s)
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Research Articles
Biophotonics
Method for measuring retinal capillary blood flow velocity by encoded OCTA
Shujiang Chen, Kaixuan Hu, Wei Yi, Fuwang Wu, Yi Wan, Lei Zhang, Jianmei Li, Aiqun Wang, and Weiye Song
The quantification of microvascular blood flow velocity is pivotal in elucidating the characteristics of retinal microcirculation, and it plays a vital role in the early detection of numerous ophthalmic pathologies. However, non-invasive technology with a large field of view for directly measuring retinal capillary blood flow velocity is lacking. In this study, a novel imaging modality called encoding optical coherence tomography angiography (En-OCTA) is presented, utilizing retinal optical coherence tomography angiography (OCTA) encoding to accurately measure the absolute blood flow velocity in retinal capillaries. En-OCTA employs a scanning speed of 250 kHz to capture multiple OCTA images at two different locations on the same unbranched capillary. As red blood cells (RBCs) slowly flow through capillaries in a single file, intermittent light and dark changes can be observed on OCTA images. Analyzing the correlation of light and dark patterns in chronologically coded images of the capillary region allows for the determination of the lag time in RBC movement between two points. Combining this lag time with the distance between scan points allows the absolute blood flow velocity in the capillaries to be accurately calculated. Animal experiments demonstrate that the method can accurately measure capillary blood flow velocity and detect changes in velocity over the duration of anesthesia.The quantification of microvascular blood flow velocity is pivotal in elucidating the characteristics of retinal microcirculation, and it plays a vital role in the early detection of numerous ophthalmic pathologies. However, non-invasive technology with a large field of view for directly measuring retinal capillary blood flow velocity is lacking. In this study, a novel imaging modality called encoding optical coherence tomography angiography (En-OCTA) is presented, utilizing retinal optical coherence tomography angiography (OCTA) encoding to accurately measure the absolute blood flow velocity in retinal capillaries. En-OCTA employs a scanning speed of 250 kHz to capture multiple OCTA images at two different locations on the same unbranched capillary. As red blood cells (RBCs) slowly flow through capillaries in a single file, intermittent light and dark changes can be observed on OCTA images. Analyzing the correlation of light and dark patterns in chronologically coded images of the capillary region allows for the determination of the lag time in RBC movement between two points. Combining this lag time with the distance between scan points allows the absolute blood flow velocity in the capillaries to be accurately calculated. Animal experiments demonstrate that the method can accurately measure capillary blood flow velocity and detect changes in velocity over the duration of anesthesia..
Chinese Optics Letters
- Publication Date: Apr. 23, 2025
- Vol. 23, Issue 4, 041701 (2025)
Diffraction, Gratings, and Holography
Phong shading approximation of computer-generated holography based on fully analytical triangle meshes
Xi Zou, Qingyang Fu, Yan Liu, Min Yang, Pin Wang, Yaping Zhang, and Ting-Chung Poon
We propose a Phong shading approximation, which gives the amplitude of each point inside the triangle through linear interpolation within the framework of self-similarity segmentation and affine transformation in polygon-based computer-generated holography. Shading is important as it reflects the geometric properties of the objects. To accurately represent the geometric properties of objects in three-dimensional space, the method involves calculating the amplitude distribution on each triangle and maintaining a complete analytical framework, with the edges of the reconstructed polygons nearly unobservable. Numerical simulations and optical reconstructions demonstrate that the proposed method successfully addresses the issue of edge discontinuity on polygonal surfaces.We propose a Phong shading approximation, which gives the amplitude of each point inside the triangle through linear interpolation within the framework of self-similarity segmentation and affine transformation in polygon-based computer-generated holography. Shading is important as it reflects the geometric properties of the objects. To accurately represent the geometric properties of objects in three-dimensional space, the method involves calculating the amplitude distribution on each triangle and maintaining a complete analytical framework, with the edges of the reconstructed polygons nearly unobservable. Numerical simulations and optical reconstructions demonstrate that the proposed method successfully addresses the issue of edge discontinuity on polygonal surfaces..
Chinese Optics Letters
- Publication Date: Apr. 16, 2025
- Vol. 23, Issue 4, 040501 (2025)
Single-frame multiwavelength coherent diffraction imaging using extreme ultraviolet high-harmonic comb sources | Editors' Pick
Huixiang Lin, Jin Niu, Kui Li, Pengju Sheng, Angyi Lin, Jianfeng You, Jie Li, Xiaoshi Zhang, and Fucai Zhang
Coherent diffraction imaging (CDI) enables diffraction-limited high-resolution imaging without using high-quality lenses. It will be desirable to combine it with multiple spectral light sources to achieve chemically resolved imaging capability. Here, we demonstrate a single-frame multiwavelength CDI approach that can provide complex transmittance images of a sample at multiple wavelengths. The superior performance of our method in terms of rapid convergence and improved image quality over current methods has been validated through high-harmonic extreme ultraviolet experiments. The feasibility of our method for single-frame chemical imaging is also demonstrated by the simulation. This work can pave the way for implementing in situ chemical imaging with tabletop high-harmonic generation extreme ultraviolet sources.Coherent diffraction imaging (CDI) enables diffraction-limited high-resolution imaging without using high-quality lenses. It will be desirable to combine it with multiple spectral light sources to achieve chemically resolved imaging capability. Here, we demonstrate a single-frame multiwavelength CDI approach that can provide complex transmittance images of a sample at multiple wavelengths. The superior performance of our method in terms of rapid convergence and improved image quality over current methods has been validated through high-harmonic extreme ultraviolet experiments. The feasibility of our method for single-frame chemical imaging is also demonstrated by the simulation. This work can pave the way for implementing in situ chemical imaging with tabletop high-harmonic generation extreme ultraviolet sources..
Chinese Optics Letters
- Publication Date: Apr. 10, 2025
- Vol. 23, Issue 4, 040502 (2025)
Fiber Optics and Optical Communications
Detection of center wavelength of jittery spectrum of uwCFBG based on correlation coefficient solution
Yandong Pang, Su Wu, Cong Liu, Su Zhang, Qing Ji, Junbin Huang, Hongcan Gu, and Zhiqiang Zhang
In this paper, we propose a method for detecting the center wavelength of ultra-weak chirped fiber Bragg grating (uwCFBG) with a jittery spectrum, based on the solution of the correlation coefficient. We establish a mathematical model for uwCFBG by superimposing segmented step Gaussian functions with noise. Then, we analyze the variation trajectory of the correlation coefficient under different relative positions through simulation. Finally, we conduct a comparative analysis of the 284-element uwCFBGs. The experimental results show that the extreme difference of the center wavelength calculation is 0.19 nm and the variance is 0.08, which proves that the proposed algorithm process is simpler and the results are more robust.In this paper, we propose a method for detecting the center wavelength of ultra-weak chirped fiber Bragg grating (uwCFBG) with a jittery spectrum, based on the solution of the correlation coefficient. We establish a mathematical model for uwCFBG by superimposing segmented step Gaussian functions with noise. Then, we analyze the variation trajectory of the correlation coefficient under different relative positions through simulation. Finally, we conduct a comparative analysis of the 284-element uwCFBGs. The experimental results show that the extreme difference of the center wavelength calculation is 0.19 nm and the variance is 0.08, which proves that the proposed algorithm process is simpler and the results are more robust..
Chinese Optics Letters
- Publication Date: Apr. 11, 2025
- Vol. 23, Issue 4, 040601 (2025)
Joint frequency offset estimation and adaptive equalization for a coherent passive optical network
Yiyang Feng, Zhengxuan Li, Chenyu Liu, Bingyao Cao, Lilin Yi, and Yingxiong Song
Coherent optics are emerging as promising solutions for future passive optical networks. However, upstream burst-mode coherent detection faces challenges due to the need for fast digital signal processing and its susceptibility to laser wavelength drift. To address these issues, we propose an algorithm capable of rapid channel equalization and frequency offset estimation (FOE). The feasibility of the proposed scheme is experimentally verified through 128-Gbit/s 16QAM signal transmission systems. Consequently, integrating a fine FOE tap into the adaptive equalization allows for rapid convergence and accurate frequency offset estimates within ∼±0.5 times the symbol rate while maintaining low complexity.Coherent optics are emerging as promising solutions for future passive optical networks. However, upstream burst-mode coherent detection faces challenges due to the need for fast digital signal processing and its susceptibility to laser wavelength drift. To address these issues, we propose an algorithm capable of rapid channel equalization and frequency offset estimation (FOE). The feasibility of the proposed scheme is experimentally verified through 128-Gbit/s 16QAM signal transmission systems. Consequently, integrating a fine FOE tap into the adaptive equalization allows for rapid convergence and accurate frequency offset estimates within ∼±0.5 times the symbol rate while maintaining low complexity..
Chinese Optics Letters
- Publication Date: Apr. 23, 2025
- Vol. 23, Issue 4, 040602 (2025)
Tunable mode-locked fiber laser using multifunctional long-period grating
Chen Jiang, Zhiqiang Wang, Ying Wan, Ling Yun, Yuehui Ma, Siyu Chen, Bing Sun, Qianqian Huang, Chengbo Mou, Yunqi Liu, and Zuxing Zhang
A laser has been demonstrated to achieve tunable mode-locked operation using a multifunctional long-period fiber grating (LPFG). By introducing an LPFG with a relatively high polarization-dependent loss of up to 21 dB into the laser cavity, a stable fundamental frequency mode-locked operation was achieved at 1546.26 nm. We also have achieved a wavelength-tunable 40th-harmonic mode-locked laser with a tuning range of nearly 10 nm through simple thermal tuning, based on the tunable attenuation characteristics of the grating. The results indicate that the LPFG can simultaneously act as a polarization-selective and wavelength-selective element in mode-locked lasers.A laser has been demonstrated to achieve tunable mode-locked operation using a multifunctional long-period fiber grating (LPFG). By introducing an LPFG with a relatively high polarization-dependent loss of up to 21 dB into the laser cavity, a stable fundamental frequency mode-locked operation was achieved at 1546.26 nm. We also have achieved a wavelength-tunable 40th-harmonic mode-locked laser with a tuning range of nearly 10 nm through simple thermal tuning, based on the tunable attenuation characteristics of the grating. The results indicate that the LPFG can simultaneously act as a polarization-selective and wavelength-selective element in mode-locked lasers..
Chinese Optics Letters
- Publication Date: Apr. 10, 2025
- Vol. 23, Issue 4, 040603 (2025)
Radiation-resistant polycrystalline fibers: from production technologies to property studies
Anastasia Yuzhakova, Alexander Lvov, Dmitrii Salimgareev, Ivan Yuzhakov, Polina Pestereva, and Liya Zhukova
We propose clad and unclad infrared polycrystalline fibers based on photo- and radiation-resistant single crystals of the AgCl0.25Br0.75-TlCl0.74Br0.26 and AgCl0.25Br0.75-TlBr0.54I0.46 systems, and we demonstrate the widest transmission range (3.5–28 µm) among currently existing optical fibers. The optical losses in the fibers reach 0.2 dB/m at a wavelength range of 11–17 µm, which is an excellent value for polycrystalline fibers. The developed infrared (IR) fibers open up opportunities for creating fiber-optic equipments of the mid- and far-IR up to 28 µm, including those operating at a high level of radiation background.We propose clad and unclad infrared polycrystalline fibers based on photo- and radiation-resistant single crystals of the AgCl0.25Br0.75-TlCl0.74Br0.26 and AgCl0.25Br0.75-TlBr0.54I0.46 systems, and we demonstrate the widest transmission range (3.5–28 µm) among currently existing optical fibers. The optical losses in the fibers reach 0.2 dB/m at a wavelength range of 11–17 µm, which is an excellent value for polycrystalline fibers. The developed infrared (IR) fibers open up opportunities for creating fiber-optic equipments of the mid- and far-IR up to 28 µm, including those operating at a high level of radiation background..
Chinese Optics Letters
- Publication Date: Apr. 23, 2025
- Vol. 23, Issue 4, 040604 (2025)
In-orbit intersatellite laser communication experiment based on compound-axis tracking
Hanghua Yu, Shaowen Lu, Qiong Hu, Yongbo Fan, Funan Zhu, Haowei Xia, Jiawei Li, Jianfeng Sun, Xia Hou, Weibiao Chen, and Huijie Liu
We have designed a beaconless laser communication terminal based on intensity modulation and direct detection (IM/DD). In this terminal, a compound-axis tracking system composed of a coarse tracking loop based on a large aperture mirror driven by a stepper motor and a fine tracking loop based on a fast steering mirror (FSM) driven by piezoelectric ceramics is used to realize wide-range and high-precision beam tracking. By optimizing the control loop delay and control parameters, the -3 dB tracking bandwidth of the system is 50 Hz, which can effectively suppress the deterioration of communication performance caused by platform micro-vibration. When the terminal operates in orbit, the tracking error (3σ) is 2.8 µrad. With Reed–Solomon [RS (255,223)] error correction coding, a sensitivity of -40.5 dBm is achieved while the bit error rate (BER) is below 10-7at 10 Gbps. The bidirectional-link experiment has been repeated 45 times, and the results show that the acquisition success ratio is 93%. The methods proposed in this paper are analyzed and verified by the GMS-β satellite in orbit.We have designed a beaconless laser communication terminal based on intensity modulation and direct detection (IM/DD). In this terminal, a compound-axis tracking system composed of a coarse tracking loop based on a large aperture mirror driven by a stepper motor and a fine tracking loop based on a fast steering mirror (FSM) driven by piezoelectric ceramics is used to realize wide-range and high-precision beam tracking. By optimizing the control loop delay and control parameters, the -3 dB tracking bandwidth of the system is 50 Hz, which can effectively suppress the deterioration of communication performance caused by platform micro-vibration. When the terminal operates in orbit, the tracking error (3σ) is 2.8 µrad. With Reed–Solomon [RS (255,223)] error correction coding, a sensitivity of -40.5 dBm is achieved while the bit error rate (BER) is below 10-7at 10 Gbps. The bidirectional-link experiment has been repeated 45 times, and the results show that the acquisition success ratio is 93%. The methods proposed in this paper are analyzed and verified by the GMS-β satellite in orbit..
Chinese Optics Letters
- Publication Date: Apr. 23, 2025
- Vol. 23, Issue 4, 040605 (2025)
Single-frequency narrow-linewidth fiber laser based on whispering gallery resonators and dynamic population gratings
Ziyun Wang, Fangxing Zhang, Ziyu Lei, Jiwen Cui, and Jiubin Tan
Whispering gallery mode resonators (WGMRs) are used as excellent optical feedback components of narrow-linewidth fiber lasers, applied from distributed fiber sensing to optical fiber communication. However, WGMRs lead to output of a few microwatts and serious multi-modes in lasers. In this Letter, we fabricated the specially designed WGMR with an over-coupling structure, and its quality (Q) factor was over 109. It improved laser output power significantly. Based on that, dynamic population gratings were applied successfully in the laser. Finally, a single-frequency WGMR fiber laser was realized. Its linewidth was less than 1.07 kHz, its output power was over 0.107 mW, and its spectral signal-to-noise ratio (SNR) was nearly 50 dB. Our research offers a new scheme of a single-frequency narrow-linewidth WGMR fiber laser.Whispering gallery mode resonators (WGMRs) are used as excellent optical feedback components of narrow-linewidth fiber lasers, applied from distributed fiber sensing to optical fiber communication. However, WGMRs lead to output of a few microwatts and serious multi-modes in lasers. In this Letter, we fabricated the specially designed WGMR with an over-coupling structure, and its quality (Q) factor was over 109. It improved laser output power significantly. Based on that, dynamic population gratings were applied successfully in the laser. Finally, a single-frequency WGMR fiber laser was realized. Its linewidth was less than 1.07 kHz, its output power was over 0.107 mW, and its spectral signal-to-noise ratio (SNR) was nearly 50 dB. Our research offers a new scheme of a single-frequency narrow-linewidth WGMR fiber laser..
Chinese Optics Letters
- Publication Date: Apr. 22, 2025
- Vol. 23, Issue 4, 040606 (2025)
Heptagonal core anti-resonant hollow-core fiber for laser beam mode shapers
Yang Wang, Xiaobei Zhang, Wei Chen, Qi Zhang, Yong Yang, Maochun Li, Miao Yan, and Tingyun Wang
We report a novel anti-resonant hollow-core fiber (ARF) with a heptagonal core surrounded by connected cladding tubes, which is employed as a laser beam mode shaper. Cladding nodes are formed between each pair of adjacent cladding tubes, which efficiently enhances the mode coupling, thus significantly suppressing higher-order modes (HOMs) within a short fiber length. Numerical investigation and simulation for variations in the curvature of each node are conducted, through which an optimized structure of cladding nodes is obtained. Experimental results demonstrate that for a 1-m-long ARF-based mode shaper, the output beam quality M2 is enabled, and the near-diffraction-limit beam quality is 1.03. The ARF presents a maximum average transmission power of 600 mW, achieving a total coupling efficiency of approximately 85%. Moreover, it is maintained for one hour without inducing any damage while maintaining beam quality. These results highlight the great potential of the mode shaper in applications such as laser surgery, precision welding, and laser writing.We report a novel anti-resonant hollow-core fiber (ARF) with a heptagonal core surrounded by connected cladding tubes, which is employed as a laser beam mode shaper. Cladding nodes are formed between each pair of adjacent cladding tubes, which efficiently enhances the mode coupling, thus significantly suppressing higher-order modes (HOMs) within a short fiber length. Numerical investigation and simulation for variations in the curvature of each node are conducted, through which an optimized structure of cladding nodes is obtained. Experimental results demonstrate that for a 1-m-long ARF-based mode shaper, the output beam quality M2 is enabled, and the near-diffraction-limit beam quality is 1.03. The ARF presents a maximum average transmission power of 600 mW, achieving a total coupling efficiency of approximately 85%. Moreover, it is maintained for one hour without inducing any damage while maintaining beam quality. These results highlight the great potential of the mode shaper in applications such as laser surgery, precision welding, and laser writing..
Chinese Optics Letters
- Publication Date: Apr. 18, 2025
- Vol. 23, Issue 4, 040607 (2025)
Imaging Systems and Image Processing
Feature fusion and variational autoencoder based deep coded aperture design for a CUP-VISAR diagnostic system
Miao Li, Chenyan Wang, Xi Wang, Lingqiang Zhang, Chaorui Chen, Zhaohui Guo, and Xueyin Zhao
In this Letter, a coding aperture design framework is introduced for data sampling of a CUP-VISAR system in laser inertial confinement fusion (ICF) research. It enhances shock wave velocity fringe reconstruction through feature fusion with a convolutional variational auto-encoder (CVAE) network. Simulation and experimental results indicate that, compared to random coding aperture, the proposed coding matrices exhibit superior reconstruction quality, achieving more accurate fringe pattern reconstruction and resolving coding information aliasing. In the experiments, the system signal-to-noise ratio (SNR) and reconstruction quality can be improved by increasing the light transmittance of the encoding matrix. This framework aids in diagnosing ICF in challenging experimental settings.In this Letter, a coding aperture design framework is introduced for data sampling of a CUP-VISAR system in laser inertial confinement fusion (ICF) research. It enhances shock wave velocity fringe reconstruction through feature fusion with a convolutional variational auto-encoder (CVAE) network. Simulation and experimental results indicate that, compared to random coding aperture, the proposed coding matrices exhibit superior reconstruction quality, achieving more accurate fringe pattern reconstruction and resolving coding information aliasing. In the experiments, the system signal-to-noise ratio (SNR) and reconstruction quality can be improved by increasing the light transmittance of the encoding matrix. This framework aids in diagnosing ICF in challenging experimental settings..
Chinese Optics Letters
- Publication Date: Apr. 10, 2025
- Vol. 23, Issue 4, 041101 (2025)
Compressed sensing reflection matrix optical coherent tomography
Kang Liu, Jia Wu, Jing Cao, Rusheng Zhuo, Kun Li, Xiaoxi Chen, Qiang Zhou, Pinghe Wang, and Guohua Shi
The reflection matrix optical coherence tomography (RM-OCT) method has made significant progress in extending imaging depth within scattering media. However, the current method of measuring the reflection matrix (RM) through uniform sampling results in relatively long data collection time. This study demonstrates that the RM in scattering media exhibits sparsity. Consequently, a compressed sensing (CS)-based technique for measuring the RM is proposed and applied to RM-OCT images. Experimental results show that this method requires less than 50% of the traditional sampling data to recover target information within scattering media, thereby significantly reducing data acquisition time. These findings not only expand the theory of the RM but also provide a more efficient measurement approach. This advancement opens up broader applications for CS techniques in RM-OCT and holds great potential for improving imaging efficiency in scattering media.The reflection matrix optical coherence tomography (RM-OCT) method has made significant progress in extending imaging depth within scattering media. However, the current method of measuring the reflection matrix (RM) through uniform sampling results in relatively long data collection time. This study demonstrates that the RM in scattering media exhibits sparsity. Consequently, a compressed sensing (CS)-based technique for measuring the RM is proposed and applied to RM-OCT images. Experimental results show that this method requires less than 50% of the traditional sampling data to recover target information within scattering media, thereby significantly reducing data acquisition time. These findings not only expand the theory of the RM but also provide a more efficient measurement approach. This advancement opens up broader applications for CS techniques in RM-OCT and holds great potential for improving imaging efficiency in scattering media..
Chinese Optics Letters
- Publication Date: Apr. 11, 2025
- Vol. 23, Issue 4, 041102 (2025)
High-resolution single-pixel holography for biological specimens
Zhiyong Wang, Yazhen Wang, Yuecheng Shen, Dalong Qi, Yunhua Yao, Lianzhong Deng, Zhenrong Sun, and Shian Zhang
Single-pixel imaging (SPI) is a computational imaging technique that is able to reconstruct high-resolution images using a single-pixel detector. However, most SPI demonstrations have been mainly focused on macroscopic scenes, so their applications to biological specimens are generally limited by constraints in space-bandwidth-time product and spatial resolution. In this work, we further enhance SPI’s imaging capabilities for biological specimens by developing a high-resolution holographic system based on heterodyne holography. Our SPI system achieves a space-bandwidth-time product of 41,667 pixel/s and a lateral resolution of 4–5 μm, which represent state-of-the-art technical indices among reported SPI systems. Importantly, our SPI system enables detailed amplitude imaging with high contrast for stained specimens such as epithelial and esophageal cancer samples, while providing complementary phase imaging for unstained specimens including molecular diagnostic samples and mouse brain tissue slices, revealing subtle refractive index variations. These results highlight SPI’s versatility and establish its potential as a powerful tool for advanced biomedical imaging applications.Single-pixel imaging (SPI) is a computational imaging technique that is able to reconstruct high-resolution images using a single-pixel detector. However, most SPI demonstrations have been mainly focused on macroscopic scenes, so their applications to biological specimens are generally limited by constraints in space-bandwidth-time product and spatial resolution. In this work, we further enhance SPI’s imaging capabilities for biological specimens by developing a high-resolution holographic system based on heterodyne holography. Our SPI system achieves a space-bandwidth-time product of 41,667 pixel/s and a lateral resolution of 4–5
Chinese Optics Letters
- Publication Date: Apr. 17, 2025
- Vol. 23, Issue 4, 041103 (2025)
Instrumentation, Measurement, and Optical Sensing
Compact optical frequency standard based on a miniature cell using modulation transfer spectroscopy
Jiqing Lian, Qiaohui Yang, Tianyu Liu, Duo Pan, Jie Miao, Zhendong Chen, Jingming Chen, Jiang Chen, Lina Bai, Zhidong Liu, and Jingbiao Chen
This study investigates the application of miniature quantum references within small-scale optical atomic frequency standards, utilizing a diminutive 87Rb glass cell, dimensions of 6 mm × 6 mm × 6 mm, to establish a quantum frequency standard. By employing the transition spectrum from 52S1/2 F = 2 to 52P3/2 F′=3, this study successfully demonstrates the development of a compact rubidium atomic optical frequency standard via modulation transfer spectroscopy (MTS). Subsequent to frequency stabilization, the 780 nm clock laser exhibits a linewidth of 6.9 kHz, and its out-of-loop short-term stability reaches 4.1 × 10-13@ 1 s, as confirmed through beat frequency analysis. This research not only provides a practical blueprint for the development of small optical atomic frequency standards but also lays down essential groundwork for future advancements in chip-level optical frequency standard technologies.This study investigates the application of miniature quantum references within small-scale optical atomic frequency standards, utilizing a diminutive 87Rb glass cell, dimensions of 6 mm × 6 mm × 6 mm, to establish a quantum frequency standard. By employing the transition spectrum from 52S1/2 F = 2 to 52P3/2 F′=3, this study successfully demonstrates the development of a compact rubidium atomic optical frequency standard via modulation transfer spectroscopy (MTS). Subsequent to frequency stabilization, the 780 nm clock laser exhibits a linewidth of 6.9 kHz, and its out-of-loop short-term stability reaches 4.1 × 10-13@ 1 s, as confirmed through beat frequency analysis. This research not only provides a practical blueprint for the development of small optical atomic frequency standards but also lays down essential groundwork for future advancements in chip-level optical frequency standard technologies..
Chinese Optics Letters
- Publication Date: Apr. 22, 2025
- Vol. 23, Issue 4, 041201 (2025)
All-fiber high-accuracy reconstructive spectrometer based on differential polarization division multiplexing
Junrui Liang, Jiangming Xu, Junhong He, Xiaoya Ma, Jun Ye, Jun Li, Jinyong Leng, and Pu Zhou
This study introduced a differential polarization division multiplexing (DPDM) scheme for all-fiber high-accuracy spectral measurement. Launching two orthogonal linearly polarized light beams into multimode fibers, the DPDM elegantly reconstructs the input spectra from the differential speckle, which is more comprehensive spectral-to-spatial encoding with fewer noises and better contrast. A spectral measurement with 2 pm resolution and 2000 channels was achieved. Compared with traditional transmission matrix and polarization division multiplexing schemes, the proposed DPDM approach reduced the spectral reconstruction error by 77% and 69%, respectively, offering a simple and effective solution for highly accurate spectral measurements.This study introduced a differential polarization division multiplexing (DPDM) scheme for all-fiber high-accuracy spectral measurement. Launching two orthogonal linearly polarized light beams into multimode fibers, the DPDM elegantly reconstructs the input spectra from the differential speckle, which is more comprehensive spectral-to-spatial encoding with fewer noises and better contrast. A spectral measurement with 2 pm resolution and 2000 channels was achieved. Compared with traditional transmission matrix and polarization division multiplexing schemes, the proposed DPDM approach reduced the spectral reconstruction error by 77% and 69%, respectively, offering a simple and effective solution for highly accurate spectral measurements..
Chinese Optics Letters
- Publication Date: Apr. 10, 2025
- Vol. 23, Issue 4, 041202 (2025)
Integrated Optics
Experimental demonstration of a performance-enhanced optical quantizer based on adjoint shape optimization
Yijun He, Jifang Qiu, Bowen Zhang, Qiuyan Li, Suping Jiao, Yan Li, and Jian Wu
We propose and demonstrate a performance-enhanced optical quantizer by inverse design. An adjoint shape co-optimization method is used to optimize the boundaries of the optical quantizer, aiming to reduce the insertion loss (IL), improve the uniformity, and increase the bandwidth of the effective number of bits (ENOB). Meanwhile, the optimized shape maintains its deep ultraviolet (DUV) photolithography fabrication capability. We fabricate the device on a commercial silicon-on-insulator (SOI) platform. Measurement results show that the IL is reduced from 0.85 to 0.35 dB, and the uniformity is optimized from 1.21 to 0.24 dB at 1550 nm. The maximum ENOB increases to 3.31 bit, which is very close to the ideal value of 3.32 bit, and the bandwidth of the ENOB > 3 bit is expanded to more than 50 nm.We propose and demonstrate a performance-enhanced optical quantizer by inverse design. An adjoint shape co-optimization method is used to optimize the boundaries of the optical quantizer, aiming to reduce the insertion loss (IL), improve the uniformity, and increase the bandwidth of the effective number of bits (ENOB). Meanwhile, the optimized shape maintains its deep ultraviolet (DUV) photolithography fabrication capability. We fabricate the device on a commercial silicon-on-insulator (SOI) platform. Measurement results show that the IL is reduced from 0.85 to 0.35 dB, and the uniformity is optimized from 1.21 to 0.24 dB at 1550 nm. The maximum ENOB increases to 3.31 bit, which is very close to the ideal value of 3.32 bit, and the bandwidth of the ENOB > 3 bit is expanded to more than 50 nm..
Chinese Optics Letters
- Publication Date: Apr. 23, 2025
- Vol. 23, Issue 4, 041301 (2025)
Lasers, Optical Amplifiers, and Laser Optics
Issues of few-mode operation in high-power semiconductor lasers at a wavelength of 1550 nm
Yulia Kirichenko (Bobretsova), Dmitriy Veselov, Andrey Lyutetsky, Sergey Slipchenko, Nikita Pikhtin, Artem Rizaev, Andrey Leshko, Alexander Klimov, Vladimir Svetogorov, Yuriy Ryaboshtan, Maksim Ladugin, and Alexander Marmalyuk
Studies have been conducted of emission characteristics directly related to the mode composition of radiation such as the spatial distribution of radiation and generation spectra of lasers with a radiation aperture of 20 µm and different cavity lengths, made on the basis of an AlGaInAs/InP heterostructure with an ultra-narrow waveguide. It is shown that there are two ranges of pump currents in which the laser characteristics behave differently. The first range of currents corresponds to operation in a few-mode lasing mode and switching between modes. The characteristics of every individual sample have a strong influence on mode competition, which leads to a spread of characteristics between identical samples in this region. In the second range, the laser operates in a multimode lasing mode, and the spread of characteristics between samples practically degenerates.Studies have been conducted of emission characteristics directly related to the mode composition of radiation such as the spatial distribution of radiation and generation spectra of lasers with a radiation aperture of 20 µm and different cavity lengths, made on the basis of an AlGaInAs/InP heterostructure with an ultra-narrow waveguide. It is shown that there are two ranges of pump currents in which the laser characteristics behave differently. The first range of currents corresponds to operation in a few-mode lasing mode and switching between modes. The characteristics of every individual sample have a strong influence on mode competition, which leads to a spread of characteristics between identical samples in this region. In the second range, the laser operates in a multimode lasing mode, and the spread of characteristics between samples practically degenerates..
Chinese Optics Letters
- Publication Date: Apr. 22, 2025
- Vol. 23, Issue 4, 041401 (2025)
Flip-chip bonded 8-channel DFB laser array with highly uniform 400 GHz spacing and high output power for optical I/O technology
Jie Zhao, Zhenxing Sun, Pan Dai, Jin Zhang, Yanqiu Xu, Yue Zhang, Zhuoying Wang, Jiaqiang Nie, Wenxuan Wang, Rulei Xiao, and Xiangfei Chen
In this paper, we proposed and experimentally demonstrated an 8-channel O-band distributed feedback (DFB) laser array with highly uniform 400 GHz spacing and high output power for optical input/output (I/O) technology. The grating phase is precisely controlled, and an equivalent π phase shift is implemented in the laser cavity via the reconstruction equivalent chirp (REC) technology. Anti-reflection (AR) and high-reflection (HR) films are coated on the front and rear facets, respectively, to enhance output power. The equivalent π phase shift is strategically placed near the HR film facet to improve the yield of the single longitudinal mode. Operating with a 400 GHz wavelength spacing, the proposed DFB laser array meets the continuous wave-wavelength division multiplexing multi-source agreement (CW-WDM MSA) specifications. The proposed DFB laser array is flip-chip bonded to a thin-film circuit with an aluminum nitride (AlN) submount to reduce the thermal resistance and enhance the output power. Compared to the p-side-up structure, the flip-chip bonding design significantly reduces junction temperature by 28% and increases maximum output power by approximately 20%. This design effectively lowers the thermal resistance of the chip and enhances its heat dissipation properties. At a bias current of 110 mA, the laser demonstrates wavelength deviations below 1.579 GHz and side-mode suppression ratios above 50 dB. The far-field divergence is measured at 25.8° × 30.1°, and the Lorentzian linewidth is 3.28 MHz. Increasing the bias current to 250 mA results in a laser output power exceeding 80 mW. Furthermore, the relative intensity noise (RIN) for all 8 channels is below -135.3 dB/Hz. The proposed flip-chip bonded 8-channel high-power DFB laser array demonstrates uniform wavelength spacing, high output power, and stable single longitudinal mode performance, making it a promising candidate for multiple wavelength laser sources in optical I/O technology.In this paper, we proposed and experimentally demonstrated an 8-channel O-band distributed feedback (DFB) laser array with highly uniform 400 GHz spacing and high output power for optical input/output (I/O) technology. The grating phase is precisely controlled, and an equivalent π phase shift is implemented in the laser cavity via the reconstruction equivalent chirp (REC) technology. Anti-reflection (AR) and high-reflection (HR) films are coated on the front and rear facets, respectively, to enhance output power. The equivalent π phase shift is strategically placed near the HR film facet to improve the yield of the single longitudinal mode. Operating with a 400 GHz wavelength spacing, the proposed DFB laser array meets the continuous wave-wavelength division multiplexing multi-source agreement (CW-WDM MSA) specifications. The proposed DFB laser array is flip-chip bonded to a thin-film circuit with an aluminum nitride (AlN) submount to reduce the thermal resistance and enhance the output power. Compared to the p-side-up structure, the flip-chip bonding design significantly reduces junction temperature by 28% and increases maximum output power by approximately 20%. This design effectively lowers the thermal resistance of the chip and enhances its heat dissipation properties. At a bias current of 110 mA, the laser demonstrates wavelength deviations below 1.579 GHz and side-mode suppression ratios above 50 dB. The far-field divergence is measured at 25.8° × 30.1°, and the Lorentzian linewidth is 3.28 MHz. Increasing the bias current to 250 mA results in a laser output power exceeding 80 mW. Furthermore, the relative intensity noise (RIN) for all 8 channels is below -135.3 dB/Hz. The proposed flip-chip bonded 8-channel high-power DFB laser array demonstrates uniform wavelength spacing, high output power, and stable single longitudinal mode performance, making it a promising candidate for multiple wavelength laser sources in optical I/O technology..
Chinese Optics Letters
- Publication Date: Apr. 10, 2025
- Vol. 23, Issue 4, 041402 (2025)
280 W near-diffraction-limited picosecond amplifier system with two-segmented doped Nd:YVO4 crystals
Yiwen Jin, Zhibin Ye, Xiang Zhang, Yang Liu, Xiaoyan Qiu, Yuhong Shen, Yichao Peng, Miao Hu, Chong Liu, and Dong Liu
A multistage amplifier system based on high-power end-pumped two-segmented Nd:YVO4 is developed, which realizes the effective beam quality management in high-power lasers. Because of the severe thermal effect caused by high-power end pumping, both the appropriate crystal and beam filling factor (the ratio of the laser beam radius to the pump beam radius) are important in the amplifier. The multisegmented doped crystal is controlled in cooperation with the beam filling factor to realize high output power and maintain good beam quality. To study the thermal effect in the end-pumped crystal, the temperature distributions of end-pumped single-segmented and two-segmented Nd:YVO4 are theoretically calculated. In the experiment, a probe laser is employed to measure the spherical aberration coefficient and the beam quality of the laser at the rear end of the two end-pumped crystals, respectively, and the experimental results are in good agreement with the theoretical results. In the power amplification, a seed laser is employed in the experiment. The appropriate gain medium and beam filling factor are determined by considering the spherical aberration coefficient, beam quality, and power extraction efficiency. Based on the reasonable layout of the power amplification for each stage amplifier, the multistage amplifier system outputs a 280.2 W picosecond laser with the beam quality factors of Mx2 = 1.28 and My2 = 1.32.A multistage amplifier system based on high-power end-pumped two-segmented Nd:YVO4 is developed, which realizes the effective beam quality management in high-power lasers. Because of the severe thermal effect caused by high-power end pumping, both the appropriate crystal and beam filling factor (the ratio of the laser beam radius to the pump beam radius) are important in the amplifier. The multisegmented doped crystal is controlled in cooperation with the beam filling factor to realize high output power and maintain good beam quality. To study the thermal effect in the end-pumped crystal, the temperature distributions of end-pumped single-segmented and two-segmented Nd:YVO4 are theoretically calculated. In the experiment, a probe laser is employed to measure the spherical aberration coefficient and the beam quality of the laser at the rear end of the two end-pumped crystals, respectively, and the experimental results are in good agreement with the theoretical results. In the power amplification, a seed laser is employed in the experiment. The appropriate gain medium and beam filling factor are determined by considering the spherical aberration coefficient, beam quality, and power extraction efficiency. Based on the reasonable layout of the power amplification for each stage amplifier, the multistage amplifier system outputs a 280.2 W picosecond laser with the beam quality factors of Mx2 = 1.28 and My2 = 1.32..
Chinese Optics Letters
- Publication Date: Apr. 17, 2025
- Vol. 23, Issue 4, 041403 (2025)
Time transfer over a 2061 km telecommunication fiber-optic network with single-fiber and two-wavelength approach | On the Cover
Xinxing Guo, Bo Liu, Shaoshao Yu, Qian Jing, Jiang Chen, Lin Wu, Tao Liu, Ruifang Dong, and Shougang Zhang
In this paper, we demonstrate the single-fiber and two-wavelength time transfer (SFTWTT) over a 2061 km field fiber loop-back link network with a synchronous wavelength-division and time-division multiplexing access (WD-TDMA). This system utilizes wavelength-division multiplexing to avoid the impact of backscatter. In order to achieve high-precision time transfer, time-division multiplexing access is employed. This approach facilitates multiple bidirectional comparisons between local and remote devices. A digital phase-locked loop (PLL), which matches the bandwidth of the transfer system, and precision temperature control technology have been proposed to enhance the high stability of the fiber-optic time and frequency transfer system. The first on-site high-precision fiber-optic time transfer system exceeding 2000 km has been validated. Experimental results show that the stabilities of 5.6 ps@1 s and 3.1 ps@40,000 s can be achieved. The precision of time transfer over a 2061 km fiber-optic network, employing a single-fiber and two-wavelength approach, has been significantly enhanced. This study presents an average time difference of 52 ps across the distance, with a system uncertainty budgeted at 41.8 ps. This achievement signifies a substantial advancement in the realms of stability and reach for optical fiber time transfer, facilitating the development of a high-precision ground-based time service system.In this paper, we demonstrate the single-fiber and two-wavelength time transfer (SFTWTT) over a 2061 km field fiber loop-back link network with a synchronous wavelength-division and time-division multiplexing access (WD-TDMA). This system utilizes wavelength-division multiplexing to avoid the impact of backscatter. In order to achieve high-precision time transfer, time-division multiplexing access is employed. This approach facilitates multiple bidirectional comparisons between local and remote devices. A digital phase-locked loop (PLL), which matches the bandwidth of the transfer system, and precision temperature control technology have been proposed to enhance the high stability of the fiber-optic time and frequency transfer system. The first on-site high-precision fiber-optic time transfer system exceeding 2000 km has been validated. Experimental results show that the stabilities of 5.6 ps@1 s and 3.1 ps@40,000 s can be achieved. The precision of time transfer over a 2061 km fiber-optic network, employing a single-fiber and two-wavelength approach, has been significantly enhanced. This study presents an average time difference of 52 ps across the distance, with a system uncertainty budgeted at 41.8 ps. This achievement signifies a substantial advancement in the realms of stability and reach for optical fiber time transfer, facilitating the development of a high-precision ground-based time service system..
Chinese Optics Letters
- Publication Date: Apr. 10, 2025
- Vol. 23, Issue 4, 041404 (2025)
Nanophotonics, Metamaterials, and Plasmonics
Coherent coupling in a WS2/graphene van der Waals heterostructure integrated with an Au nanoantenna
Liping Hou, Qifa Wang, Huan Luo, Chenyang Li, Xuetao Gan, Fajun Xiao, and Jianlin Zhao
Coherent interactions between excitons strongly coupled to plasmons are vital for quantum information devices. For practical applications, suppressing the incoherent dissipation pathways in the hybrid system is essential. Here, we report on a strong plasmon–exciton coupling in a monolayer WS2/graphene van der Waals heterostructure (WS2/Gr vdWhs) integrated with an Au nanocube (Au NC). The presence of graphene effectively suppresses the nonradiative decay pathway of neutral excitons in the vdWhs, resulting in a narrower photoluminescence (PL) linewidth. The further integration of the WS2/Gr vdWhs with the Au NC enables coherent interaction between the in-plane exciton and a tilted plasmonic dipole, delivering a Rabi splitting energy of 120 meV and an incoherent coupling strength of 1 meV. Our findings possess the potential to facilitate the advancement of quantum nanophotonic devices.Coherent interactions between excitons strongly coupled to plasmons are vital for quantum information devices. For practical applications, suppressing the incoherent dissipation pathways in the hybrid system is essential. Here, we report on a strong plasmon–exciton coupling in a monolayer WS2/graphene van der Waals heterostructure (WS2/Gr vdWhs) integrated with an Au nanocube (Au NC). The presence of graphene effectively suppresses the nonradiative decay pathway of neutral excitons in the vdWhs, resulting in a narrower photoluminescence (PL) linewidth. The further integration of the WS2/Gr vdWhs with the Au NC enables coherent interaction between the in-plane exciton and a tilted plasmonic dipole, delivering a Rabi splitting energy of 120 meV and an incoherent coupling strength of 1 meV. Our findings possess the potential to facilitate the advancement of quantum nanophotonic devices..
Chinese Optics Letters
- Publication Date: Apr. 09, 2025
- Vol. 23, Issue 4, 043601 (2025)
Evolution of multipeak spectral features in SERS reveals atomic-scale structural fluctuations in plasmonic nanocavities
Wenjin Zhou, Lei Xi, Min Yang, Guofeng Zhang, Chengbing Qin, Jianyong Hu, Yao Zhang, Ruiyun Chen, Liantuan Xiao, and Suotang Jia
In this study, we investigate the intensity and spectral fluctuations in surface-enhanced Raman scattering (SERS) signals from individual plasmonic nanocavities. Extremely long-duration blinking components lasting up to minutes are observed in the SERS intensity fluctuation at room temperature, which can be characterized by successive and random appearance and eventual disappearance of multiple vibrational modes at different frequencies. Theoretical simulations show that multiple hotspots acting on different molecular sites are required to explain these multipeak features, suggesting that the source of long-duration blinking events is multiple atomic-scale protrusions interacting simultaneously with different sites of individual molecules or each with a different molecule.In this study, we investigate the intensity and spectral fluctuations in surface-enhanced Raman scattering (SERS) signals from individual plasmonic nanocavities. Extremely long-duration blinking components lasting up to minutes are observed in the SERS intensity fluctuation at room temperature, which can be characterized by successive and random appearance and eventual disappearance of multiple vibrational modes at different frequencies. Theoretical simulations show that multiple hotspots acting on different molecular sites are required to explain these multipeak features, suggesting that the source of long-duration blinking events is multiple atomic-scale protrusions interacting simultaneously with different sites of individual molecules or each with a different molecule..
Chinese Optics Letters
- Publication Date: Apr. 10, 2025
- Vol. 23, Issue 4, 043602 (2025)
Bending-switchable terahertz metamaterial with a single layer based on laser-induced graphene
Abdul Jalal, Yan Dong, Bowen Deng, Muhammad Qasim, Mojtaba Moghaddasi, Ubaid Ur Rahman Qureshi, Zongyuan Wang, Xudong Wu, Chenjie Xiong, and Bin Hu
We propose a fast-printable and function-switchable metamaterial based on laser-induced graphene for terahertz (THz) wave modulation in the reflection mode. The design can modulate the linear polarization of the incoming wave fronts to its cross-polarization from 0.27 to 0.41 THz and linear polarization to circular polarization from 0.48 to 0.62 THz. The function of the device can also be switched from a polarization converter to an absorber by bending it with an angle of 57°. Experimental results showed a good agreement with those of the simulation. The proposed polarization converter may find its application in THz polarization control systems and sensing.We propose a fast-printable and function-switchable metamaterial based on laser-induced graphene for terahertz (THz) wave modulation in the reflection mode. The design can modulate the linear polarization of the incoming wave fronts to its cross-polarization from 0.27 to 0.41 THz and linear polarization to circular polarization from 0.48 to 0.62 THz. The function of the device can also be switched from a polarization converter to an absorber by bending it with an angle of 57°. Experimental results showed a good agreement with those of the simulation. The proposed polarization converter may find its application in THz polarization control systems and sensing..
Chinese Optics Letters
- Publication Date: Apr. 16, 2025
- Vol. 23, Issue 4, 043603 (2025)
Nonlinear Optics
Nonlinear Cherenkov radiation in rotatory nonlinear optics
Zhongmian Zhang, Dazhi Lu, Haohai Yu, Huaijin Zhang, and Yicheng Wu
Nonlinear Cherenkov radiation is a phenomenon of light first observed in 1970 that can be manipulated by phase matching conditions. However, under a rotatory symmetry, the nonlinear Cherenkov radiation was still untouched, where the rotation parameters in optics would introduce an additional phase to the beam, change the phase velocity of the electromagnetic wave, and lead to novel optical phenomena. Here, we introduce rotation as a new freedom and study the nonlinear Cherenkov radiation in optically rotatory crystals in theory. With a quartz crystal as the representative, we derive theoretical variations, which show that the phase velocity of the crystal-coupled wave is found to be accelerated or decelerated by the rotational angular velocity, corresponding to the change of the Cherenkov radiation angle. In addition, the variation on the effective nonlinear coefficient of quartz crystals with rotational polarization direction is analyzed theoretically and used to simulate the Cherenkov ring distribution in rotatory nonlinear optics. This work introduces the rotation parameter into the non-collinear phase matching process and may inspire the development of modern photonics and physics in rotatory frames.Nonlinear Cherenkov radiation is a phenomenon of light first observed in 1970 that can be manipulated by phase matching conditions. However, under a rotatory symmetry, the nonlinear Cherenkov radiation was still untouched, where the rotation parameters in optics would introduce an additional phase to the beam, change the phase velocity of the electromagnetic wave, and lead to novel optical phenomena. Here, we introduce rotation as a new freedom and study the nonlinear Cherenkov radiation in optically rotatory crystals in theory. With a quartz crystal as the representative, we derive theoretical variations, which show that the phase velocity of the crystal-coupled wave is found to be accelerated or decelerated by the rotational angular velocity, corresponding to the change of the Cherenkov radiation angle. In addition, the variation on the effective nonlinear coefficient of quartz crystals with rotational polarization direction is analyzed theoretically and used to simulate the Cherenkov ring distribution in rotatory nonlinear optics. This work introduces the rotation parameter into the non-collinear phase matching process and may inspire the development of modern photonics and physics in rotatory frames..
Chinese Optics Letters
- Publication Date: Apr. 16, 2025
- Vol. 23, Issue 4, 041901 (2025)
Cascaded optical parameter oscillator within lithium tantalate microdisk based on two periodically poled structures | Editors' Pick
Kun Zhang, Yifan Chen, Chongyang Xu, Hongquan Yao, Jian Ning, Xinjie Lü, Gang Zhao, Peng Zhan, Zhenda Xie, and Shining Zhu
The whispering gallery resonator (WGR) represents a promising avenue for the miniaturization of optical devices, while cascaded optical parameter oscillator (OPO) processes have not been realized in the WGR, to the best of our knowledge. We present a microdisk with quality factors up to 3.2 × 107, then embed two quasi-phase-matching structures inside it to demonstrate cascaded OPO. The cascaded OPO exhibits the same idler light output with the threshold of 32.7 mW at 36°C (1063.8 nm → 1566.6 nm + 3314.6 nm/1566.6 nm → 2970.4 nm + 3314.6 nm), while the operating threshold of OPO without cascade process is 4.32 mW. Moreover, diverse cascaded processes are observed, with the longest output wavelength reaching 4802.9 nm. Our results suggest the potential for a low-threshold cascade OPO based on WGR.The whispering gallery resonator (WGR) represents a promising avenue for the miniaturization of optical devices, while cascaded optical parameter oscillator (OPO) processes have not been realized in the WGR, to the best of our knowledge. We present a microdisk with quality factors up to 3.2 × 107, then embed two quasi-phase-matching structures inside it to demonstrate cascaded OPO. The cascaded OPO exhibits the same idler light output with the threshold of 32.7 mW at 36°C (1063.8 nm → 1566.6 nm + 3314.6 nm/1566.6 nm → 2970.4 nm + 3314.6 nm), while the operating threshold of OPO without cascade process is 4.32 mW. Moreover, diverse cascaded processes are observed, with the longest output wavelength reaching 4802.9 nm. Our results suggest the potential for a low-threshold cascade OPO based on WGR..
Chinese Optics Letters
- Publication Date: Apr. 10, 2025
- Vol. 23, Issue 4, 041902 (2025)
Quantum Optics and Quantum Information
Ten-channel Hong–Ou–Mandel interference between independent optical combs | Fast Track
Wenhan Yan, Yang Hu, Yifeng Du, Kai Wang, Yan-Qing Lu, Shining Zhu, and Xiao-Song Ma
The dissipative Kerr soliton (DKS) frequency comb exhibits broad and narrow-linewidth frequency modes, which make it suitable for quantum communication. However, a scalable quantum network based on multiple independent combs is still a challenge due to fabrication-induced frequency mismatches. This limitation becomes critical in measurement-device-independent quantum key distribution, which requires high visibility of Hong–Ou–Mandel interference between multiple frequency channels. Here, we experimentally demonstrate two independent DKS combs with 10 spectrally aligned lines without any frequency locking system. The visibility for individual comb-line pairs reaches up to 46.72% ± 0.63% via precision frequency translation, establishing a foundation for deploying DKS combs in multi-user quantum networks.The dissipative Kerr soliton (DKS) frequency comb exhibits broad and narrow-linewidth frequency modes, which make it suitable for quantum communication. However, a scalable quantum network based on multiple independent combs is still a challenge due to fabrication-induced frequency mismatches. This limitation becomes critical in measurement-device-independent quantum key distribution, which requires high visibility of Hong–Ou–Mandel interference between multiple frequency channels. Here, we experimentally demonstrate two independent DKS combs with 10 spectrally aligned lines without any frequency locking system. The visibility for individual comb-line pairs reaches up to 46.72% ± 0.63% via precision frequency translation, establishing a foundation for deploying DKS combs in multi-user quantum networks..
Chinese Optics Letters
- Publication Date: Apr. 24, 2025
- Vol. 23, Issue 4, 042701 (2025)
X-ray Optics
Optical characterization of X-ray polymer refractive lenses using a microfocus X-ray grating interferometer
Dongxu Qin, Lian Xue, Yifan Ding, Ziwen Huang, Lei Yang, Zhaofeng Kang, Keyi Wang, and Shuai Zhao
Two-photon polymerization lithography is a technique that provides hundreds of nanometer resolution and full geometric freedom. Several X-ray polymer refractive lenses created by this technique were characterized using differential phase contrast imaging (DPCI) with a microfocus X-ray grating interferometer. The beam deflection angle and wavefront phase shift of the X-ray beam through the lens were obtained. Comparative tests using synchrotron radiation sources showed that the system could measure the surface shape of X-ray refractive lenses with an accuracy of 0.4 µm. This study is important for improving the fabrication process and focusing performance of X-ray refractive lenses.Two-photon polymerization lithography is a technique that provides hundreds of nanometer resolution and full geometric freedom. Several X-ray polymer refractive lenses created by this technique were characterized using differential phase contrast imaging (DPCI) with a microfocus X-ray grating interferometer. The beam deflection angle and wavefront phase shift of the X-ray beam through the lens were obtained. Comparative tests using synchrotron radiation sources showed that the system could measure the surface shape of X-ray refractive lenses with an accuracy of 0.4 µm. This study is important for improving the fabrication process and focusing performance of X-ray refractive lenses..
Chinese Optics Letters
- Publication Date: Apr. 10, 2025
- Vol. 23, Issue 4, 043401 (2025)
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