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Fiber Optics and Optical Communications|437 Article(s)
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)
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)
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)
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)
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)
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)
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)
Tunable erbium-doped fiber lasers based on modulatable hollow-core anti-resonant fiber filters
Weiqian Shi, Yifei Zhao, Ziwei Fang, Yuheng Zhang, Ting Yang, Guiyao Zhou, and Changming Xia
In this paper, we demonstrate and experimentally verify a tunable, multi-wavelength switchable ring-cavity erbium-doped fiber laser (EDFL). The hollow-core anti-resonant fiber (HC-ARF) filters, which are based on polarization interference, are fabricated using a bent HC-ARF. These filters were incorporated into a ring-cavity EDFL, achieving a tunable laser output ranging from 1547 to 1561 nm with a tuning step of 3.5 nm, and all measured optical signal-to-noise ratios (OSNRs) exceeded 35 dB. Additionally, the laser system supports switching from single-wavelength to three-wavelength operation near the 1560 nm region. In this paper, we demonstrate and experimentally verify a tunable, multi-wavelength switchable ring-cavity erbium-doped fiber laser (EDFL). The hollow-core anti-resonant fiber (HC-ARF) filters, which are based on polarization interference, are fabricated using a bent HC-ARF. These filters were incorporated into a ring-cavity EDFL, achieving a tunable laser output ranging from 1547 to 1561 nm with a tuning step of 3.5 nm, and all measured optical signal-to-noise ratios (OSNRs) exceeded 35 dB. Additionally, the laser system supports switching from single-wavelength to three-wavelength operation near the 1560 nm region.
Chinese Optics Letters
- Publication Date: Dec. 11, 2024
- Vol. 23, Issue 3, 030603 (2025)
Three-dimensional dynamic probabilistic shaping high-security transmission scheme based on dual physical layer encryption for seven-core fibers
Yaya Mao, Bo Liu, Jingrui Huang, Jianxin Ren, Shuaidong Chen, Xiangyu Wu, Yongfeng Wu, Xiumin Song, Zhipeng Qi, and Jie Cui
In this paper, a carrier-less amplitude and phase modulation passive optical network (CAP-PON) scheme is proposed based on dynamic probabilistic shaping (DPS) and Rubik’s cube encryption in optical access networks. The key is generated from a novel five-dimensional entangled chaos model for dynamic probabilistic shaping and Rubik’s cube encryption. To verify the performance of the encryption scheme, an experimental demonstration of 70 Gb/s (7 × 10 Gb/s) encrypted DPS-3D-CAP signal transmission over 2 km weakly coupled 7-core fiber is performed. The key space of the new five-dimensional entangled chaos model reaches 10173, and the interference level reaches 100%. Experimental results show that the receiver sensitivity increases by 1.47 dB compared to the conventional uniform 3D-CAP due to the introduction of dynamic probabilistic shaping. In this paper, a carrier-less amplitude and phase modulation passive optical network (CAP-PON) scheme is proposed based on dynamic probabilistic shaping (DPS) and Rubik’s cube encryption in optical access networks. The key is generated from a novel five-dimensional entangled chaos model for dynamic probabilistic shaping and Rubik’s cube encryption. To verify the performance of the encryption scheme, an experimental demonstration of 70 Gb/s (7 × 10 Gb/s) encrypted DPS-3D-CAP signal transmission over 2 km weakly coupled 7-core fiber is performed. The key space of the new five-dimensional entangled chaos model reaches 10173, and the interference level reaches 100%. Experimental results show that the receiver sensitivity increases by 1.47 dB compared to the conventional uniform 3D-CAP due to the introduction of dynamic probabilistic shaping.
Chinese Optics Letters
- Publication Date: Mar. 31, 2025
- Vol. 23, Issue 3, 030602 (2025)
High-security three-dimensional CAP modulation technique integrating end-to-end constellation optimization and four-level masking
Juntao Zhang, Bo Liu, Jianxin Ren, Yaya Mao, Xiangyu Wu, Rahat Ullah, Jie Cui, Yilan Ma, Jianye Zhao, Dongdong Xu, Shuaidong Chen, and Shuyu Zhou
In this paper, a high-security three-dimensional carrierless amplitude and phase (3D-CAP) modulation technique is proposed, integrating deep learning with four-level masking. The 3D constellation geometry is optimized using an autoencoder (AE) with an additive white Gaussian noise (AWGN) channel model, reducing complexity by 40% compared to a variational autoencoder (VAE). Experimental validation on a 2 km seven-core fiber intensity modulation/direct detection (IM/DD) system shows a 1 dB improvement in receiver sensitivity. A 3D chaotic oscillator model is used for chaotic selective mapping, polynomial-like masking, constellation rotation, and subcarrier masking. The encrypted 3D-CAP signal achieves a key space of up to 10103, with strong anti-noise and confidentiality performance. In this paper, a high-security three-dimensional carrierless amplitude and phase (3D-CAP) modulation technique is proposed, integrating deep learning with four-level masking. The 3D constellation geometry is optimized using an autoencoder (AE) with an additive white Gaussian noise (AWGN) channel model, reducing complexity by 40% compared to a variational autoencoder (VAE). Experimental validation on a 2 km seven-core fiber intensity modulation/direct detection (IM/DD) system shows a 1 dB improvement in receiver sensitivity. A 3D chaotic oscillator model is used for chaotic selective mapping, polynomial-like masking, constellation rotation, and subcarrier masking. The encrypted 3D-CAP signal achieves a key space of up to 10103, with strong anti-noise and confidentiality performance.
Chinese Optics Letters
- Publication Date: Mar. 31, 2025
- Vol. 23, Issue 3, 030601 (2025)
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