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Fiber Optics and Optical Communications|458 Article(s)
Photonics-assisted 200 Gb/s 2 × 2 MIMO THz wireless system over 200 m links at 300 GHz utilizing iterative pruning 2D CNN-based nonlinear equalization
Jingwen Lin, Wen Zhou, Qihang Wang, Sicong Xu, Jie Zhang, Jingtao Ge, Siqi Wang, Zhihang Ou, Yuan Ma, Tong Wang, Hanyu Zhang, Yuancheng Cai, Mingzheng Lei, Junjie Ding, Bingchang Hua, Jiao Zhang, Min Zhu, and Jianjun Yu
We demonstrate a 200 m outdoor 2 × 2 multiple-input multiple-output (MIMO) terahertz (THz) communication system operating at 300 GHz with 200 Gb/s polarization-division multiplexed quadrature phase-shift keying (PDM-QPSK) transmission. We propose an iteratively pruned two-dimensional convolutional neural network (2D CNN) equalizer that adaptively captures polarization crosstalk and temporal nonlinearities through 2D convolution kernels. The system achieves a bit error rate (BER) below the hard-decision forward error correction (HD-FEC) threshold at a lower power of 6 dBm, while reducing the computational complexity by 30.2% compared to the iteratively pruned one-dimensional (1D) CNN approach. This enables high-capacity and energy-efficient operation in long-distance THz links. We demonstrate a 200 m outdoor 2 × 2 multiple-input multiple-output (MIMO) terahertz (THz) communication system operating at 300 GHz with 200 Gb/s polarization-division multiplexed quadrature phase-shift keying (PDM-QPSK) transmission. We propose an iteratively pruned two-dimensional convolutional neural network (2D CNN) equalizer that adaptively captures polarization crosstalk and temporal nonlinearities through 2D convolution kernels. The system achieves a bit error rate (BER) below the hard-decision forward error correction (HD-FEC) threshold at a lower power of 6 dBm, while reducing the computational complexity by 30.2% compared to the iteratively pruned one-dimensional (1D) CNN approach. This enables high-capacity and energy-efficient operation in long-distance THz links.
Chinese Optics Letters
- Publication Date: Sep. 01, 2025
- Vol. 23, Issue 9, 090604 (2025)
Analysis and brief review on noise processing for phase-extracted signals in coherent Φ-OTDR
Zhen Zhong, Xuping Zhang and Ningmu Zou
This review begins by elucidating the rationale for selecting phase optical time domain reflectometry (Φ-OTDR) based on coherent detection as the subject of study, underscoring the necessity and significance of analyzing noise suppression methodologies. With the aid of in-phase/quadrature (I/Q) demodulation process for phase extraction, the review analyzes the impact of noise on phase-extracted results in coherent Φ-OTDR. Subsequently, nine specific implementable pathways to mitigate noise effects are explored within three categories: amplitude signal, phase signal, and the data itself. For each pathway, the review summarizes the advancements in noise suppression research, providing a typical implementation case to deepen the reader’s understanding of noise processing principles and techniques. Finally, the review not only identifies the shortcomings but also provides insights into noise processing in coherent Φ-OTDR, underlining the current limitations and suggesting potential avenues for future investigation. This review begins by elucidating the rationale for selecting phase optical time domain reflectometry (Φ-OTDR) based on coherent detection as the subject of study, underscoring the necessity and significance of analyzing noise suppression methodologies. With the aid of in-phase/quadrature (I/Q) demodulation process for phase extraction, the review analyzes the impact of noise on phase-extracted results in coherent Φ-OTDR. Subsequently, nine specific implementable pathways to mitigate noise effects are explored within three categories: amplitude signal, phase signal, and the data itself. For each pathway, the review summarizes the advancements in noise suppression research, providing a typical implementation case to deepen the reader’s understanding of noise processing principles and techniques. Finally, the review not only identifies the shortcomings but also provides insights into noise processing in coherent Φ-OTDR, underlining the current limitations and suggesting potential avenues for future investigation.
Chinese Optics Letters
- Publication Date: Sep. 08, 2025
- Vol. 23, Issue 9, 090603 (2025)
On-fiber dielectric metasurface for dynamic polarization manipulation
Zhongyue Luo, Tingting Sun, Haozhe Lü, Xiaowen Jiang, Yang Wang, Wentao Zhang, Libo Yuan, and Hongchang Deng
Dynamic polarization control remains a major challenge in fiber-integrated metasurfaces, with most research focusing on static polarization. Herein, we propose a dynamic polarization metasurface (DP-MS) integrated at the end of a large-mode fiber. The DP-MS decouples orthogonal polarization states, enabling precise rotation of focal spots in response to changes in the polarization direction of incident quasi-plane waves. Simulations show that the DP-MS can generate single, vortex, and multi-focal spots. By optimizing signal functions, multi-focal spots with precise control over number, position, distance, and synchronized rotation are achieved. This study has potential applications in optical manipulation and beam shaping. Dynamic polarization control remains a major challenge in fiber-integrated metasurfaces, with most research focusing on static polarization. Herein, we propose a dynamic polarization metasurface (DP-MS) integrated at the end of a large-mode fiber. The DP-MS decouples orthogonal polarization states, enabling precise rotation of focal spots in response to changes in the polarization direction of incident quasi-plane waves. Simulations show that the DP-MS can generate single, vortex, and multi-focal spots. By optimizing signal functions, multi-focal spots with precise control over number, position, distance, and synchronized rotation are achieved. This study has potential applications in optical manipulation and beam shaping.
Chinese Optics Letters
- Publication Date: Aug. 18, 2025
- Vol. 23, Issue 9, 090602 (2025)
Demonstration of high-capacity WDM long-haul transmission based on a long-span nested antiresonant nodeless fiber
Hui Chen, Xu Zhang, Siyue Jin, Honglin Ji, Qibing Wang, Lei Zhang, Jie Luo, Lei Wang, Yingjun Zhou, Junwen Zhang, Zhixue He, Nan Chi, and Shaohua Yu
We experimentally demonstrate low-latency, high-capacity, and long-haul coherent transmission, recirculated through a self-fabricated, low-loss, and long-span 20 km nested antiresonant nodeless fiber (NANF) in the C-band. By leveraging wavelength division multiplexing (WDM), polarization multiplexing, probabilistic amplitude shaping technology, and low-complexity receiver-side digital signal processing (DSP), we achieve a record-breaking transmission capacity of 16.763 Tb/s over 1000 km for the first time, to the best of our knowledge. This achievement represents a significant step forward in high-capacity and long-haul optical communication based on NANF. We experimentally demonstrate low-latency, high-capacity, and long-haul coherent transmission, recirculated through a self-fabricated, low-loss, and long-span 20 km nested antiresonant nodeless fiber (NANF) in the C-band. By leveraging wavelength division multiplexing (WDM), polarization multiplexing, probabilistic amplitude shaping technology, and low-complexity receiver-side digital signal processing (DSP), we achieve a record-breaking transmission capacity of 16.763 Tb/s over 1000 km for the first time, to the best of our knowledge. This achievement represents a significant step forward in high-capacity and long-haul optical communication based on NANF.
Chinese Optics Letters
- Publication Date: Aug. 13, 2025
- Vol. 23, Issue 9, 090601 (2025)
Channel modeling for underwater scattered light communication based on Gaussian and Bessel beams
Yi Gao, Zhitong Huang, Jie Xu, Hongcheng Qiu, Yan Jia, and Yuefeng Ji
Underwater scattered light communication (USLC) utilizes the strong scattering properties of seawater to achieve a non-line-of-sight (NLOS) communication channel, which is a promising solution to the stringent alignment requirements and random transmission path blocking in underwater wireless optical communication. In this Letter, we model the channel for USLC based on Gaussian and Bessel beams, in which we comprehensively explore the effects of different water types and transceiver configurations on USLC and simulate the photon propagation in seawater by Monte Carlo (MC) method. Specifically, we analyze the fluctuation in received signal strength as a function of the communication distance across three distinct water types, in which the model considers the influence of different optical wavelengths and spatial modes at the transmitter as well as various optical lens configurations at the receiver. Modeling and experiments validate blue Gaussian beams for short-range, low-turbidity cases; green Bessel beams for long-range, high-turbidity conditions; and the receiver antenna’s utility which is restricted to short-range applications. The conclusion obtained can be used for the selection of transceiver devices in USLC systems. Underwater scattered light communication (USLC) utilizes the strong scattering properties of seawater to achieve a non-line-of-sight (NLOS) communication channel, which is a promising solution to the stringent alignment requirements and random transmission path blocking in underwater wireless optical communication. In this Letter, we model the channel for USLC based on Gaussian and Bessel beams, in which we comprehensively explore the effects of different water types and transceiver configurations on USLC and simulate the photon propagation in seawater by Monte Carlo (MC) method. Specifically, we analyze the fluctuation in received signal strength as a function of the communication distance across three distinct water types, in which the model considers the influence of different optical wavelengths and spatial modes at the transmitter as well as various optical lens configurations at the receiver. Modeling and experiments validate blue Gaussian beams for short-range, low-turbidity cases; green Bessel beams for long-range, high-turbidity conditions; and the receiver antenna’s utility which is restricted to short-range applications. The conclusion obtained can be used for the selection of transceiver devices in USLC systems.
Chinese Optics Letters
- Publication Date: May. 30, 2025
- Vol. 23, Issue 6, 060606 (2025)
Active coherent beam combining of 1.55 µm pulsed fiber lasers based on intrapulse sampling
Zhen Liu, Yongke Zhang, Qihao Shen, Xingkai He, Dingfu Zhou, Liangyou Duan, and Siyin Liu
This study presents active coherent beam combining (CBC) of a pulsed laser based on sampling the intrapulse evaluation function. By precisely controlling the trigger sequence of an analog-to-digital converter, the fixed time point of the pulse light is sampled as an evaluation function for CBC. The active CBC of two fiber amplifiers with a 500 ns pulse width and a 10 kHz repetition rate is experimentally demonstrated by applying a hill-climbing algorithm. The residual phase error is approximately λ/27. A coherent Doppler wind lidar (CDWL) based on CBC light source is verified. The experimental results verify the feasibility of using the pulsed CBC to improve the pulse energy of a CDWL without degrading performance. This study presents active coherent beam combining (CBC) of a pulsed laser based on sampling the intrapulse evaluation function. By precisely controlling the trigger sequence of an analog-to-digital converter, the fixed time point of the pulse light is sampled as an evaluation function for CBC. The active CBC of two fiber amplifiers with a 500 ns pulse width and a 10 kHz repetition rate is experimentally demonstrated by applying a hill-climbing algorithm. The residual phase error is approximately λ/27. A coherent Doppler wind lidar (CDWL) based on CBC light source is verified. The experimental results verify the feasibility of using the pulsed CBC to improve the pulse energy of a CDWL without degrading performance.
Chinese Optics Letters
- Publication Date: May. 30, 2025
- Vol. 23, Issue 6, 060605 (2025)
30 Gbps visible light communication in rainy environments based on laser diodes|Editors' Pick
Yang Xiao, Jiakang Ai, Xiangyang Chen, Xugao Cui, and Pengfei Tian
Rain has a strong attenuation effect on light, which can impact the performance of visible light communication (VLC). In this paper, we addressed the crucial challenge of implementing high-speed VLC systems in rainy environments by focusing on the performance of different wavelengths under varying rain conditions. By analyzing the attenuation characteristics of four laser diodes at different wavelengths under various artificial rain environments, we developed a high-speed VLC system optimized for rainy channel high-speed visible light communication by employing the orthogonal frequency-division multiplexing modulation scheme. By integrating channel-adaptive pre-equalization and bit-loading algorithms, our system optimized signal transmission in rainy channels, enabling an aggregated data rate exceeding 30 Gbps, which was the highest reported data rate for VLC in rainy channels, to the best of our knowledge. Rain has a strong attenuation effect on light, which can impact the performance of visible light communication (VLC). In this paper, we addressed the crucial challenge of implementing high-speed VLC systems in rainy environments by focusing on the performance of different wavelengths under varying rain conditions. By analyzing the attenuation characteristics of four laser diodes at different wavelengths under various artificial rain environments, we developed a high-speed VLC system optimized for rainy channel high-speed visible light communication by employing the orthogonal frequency-division multiplexing modulation scheme. By integrating channel-adaptive pre-equalization and bit-loading algorithms, our system optimized signal transmission in rainy channels, enabling an aggregated data rate exceeding 30 Gbps, which was the highest reported data rate for VLC in rainy channels, to the best of our knowledge.
Chinese Optics Letters
- Publication Date: May. 23, 2025
- Vol. 23, Issue 6, 060604 (2025)
Magnetic actuation of paramagnetic liquids for optical beam steering in high-speed optical wireless communications
Mithilesh K. Mane, Amjad Ali, Riffat Tehseen, Arfan Mahmood, and Jing Xu
This study examines paramagnetic liquids for optical beam steering in optical wireless communication (OWC) systems. By employing magnetic actuation, effective optical beam control was achieved for both free-space optics (FSO) and underwater wireless optical communication (UWOC). Experimental findings revealed that dysprosium nitrate provided the highest beam steering angles of 5.99° in the ±X direction and 5.73° in the ±Y direction. Additionally, power loss analysis indicated minimal absorption and scattering for dysprosium nitrate and gadolinium nitrate. The system achieved high-speed data rates of 2.1 Gbps for FSO and 1.9 Gbps for UWOC systems, showcasing the promise of this technology. This study examines paramagnetic liquids for optical beam steering in optical wireless communication (OWC) systems. By employing magnetic actuation, effective optical beam control was achieved for both free-space optics (FSO) and underwater wireless optical communication (UWOC). Experimental findings revealed that dysprosium nitrate provided the highest beam steering angles of 5.99° in the ±X direction and 5.73° in the ±Y direction. Additionally, power loss analysis indicated minimal absorption and scattering for dysprosium nitrate and gadolinium nitrate. The system achieved high-speed data rates of 2.1 Gbps for FSO and 1.9 Gbps for UWOC systems, showcasing the promise of this technology.
Chinese Optics Letters
- Publication Date: May. 20, 2025
- Vol. 23, Issue 6, 060603 (2025)
Highly robust and hardware-efficient frame synchronization and carrier recovery via pilot-only approaches for short-reach optical interconnections
Chenchen Wang, Zhipei Li, Ze Dong, Junyuan Song, Ran Gao, Dong Guo, Huan Chang, Lei Zhu, Xiaolong Pan, Tianle Mai, Shanting Hu, and Xiangjun Xin
We propose a cost-effective scheme relying exclusively on pilot symbols for robust frame synchronization and high-precision, wide-range carrier recovery in short-reach optical interconnects. Our method mitigates phase offsets and enhances phase tracking by strategically placing dual-polarization pilot symbols, both aligned and misaligned, within the frame. Compared to traditional carrier recovery schemes, our approach offers a broader frequency offset estimation range, higher carrier recovery accuracy, and significantly lower computational complexity. Experimental results show a 0.7 dB sensitivity improvement at the soft decision forward error correction threshold, outperforming Fourier transform-based frequency offset estimation combined with blind phase search. We propose a cost-effective scheme relying exclusively on pilot symbols for robust frame synchronization and high-precision, wide-range carrier recovery in short-reach optical interconnects. Our method mitigates phase offsets and enhances phase tracking by strategically placing dual-polarization pilot symbols, both aligned and misaligned, within the frame. Compared to traditional carrier recovery schemes, our approach offers a broader frequency offset estimation range, higher carrier recovery accuracy, and significantly lower computational complexity. Experimental results show a 0.7 dB sensitivity improvement at the soft decision forward error correction threshold, outperforming Fourier transform-based frequency offset estimation combined with blind phase search.
Chinese Optics Letters
- Publication Date: May. 19, 2025
- Vol. 23, Issue 6, 060602 (2025)
Machine vision-based intelligent turbulence perception for underwater wireless optical communication
Yan Jia, Zhitong Huang, Jie Xu, Hongcheng Qiu, Yi Gao, and Yuefeng Ji
Turbulence induced by thermohaline gradient and air bubbles poses a significant challenge to the robustness of underwater wireless optical communication (UWOC) systems. It is imperative to accurately measure the turbulence intensity of the channel to guide the design of adaptive UWOC systems. However, current measurements based on pilot information consume additional spectral resources. We propose a machine vision-based intelligent turbulence perception (MV-ITP) mechanism to measure the turbulence intensity of the underwater channel. The MV-ITP mechanism utilizes the spatiotemporal intrinsic coupling correlation between optical imaging and optical communication to establish a precise quantitative relationship between the pixel intensity variation of the beam images and the scintillation index. We conduct experiments under different turbulence conditions induced by temperature, salinity, as well as air bubbles, and the experimental results demonstrate that the proposed mechanism can accurately measure the intensity of turbulence. Turbulence induced by thermohaline gradient and air bubbles poses a significant challenge to the robustness of underwater wireless optical communication (UWOC) systems. It is imperative to accurately measure the turbulence intensity of the channel to guide the design of adaptive UWOC systems. However, current measurements based on pilot information consume additional spectral resources. We propose a machine vision-based intelligent turbulence perception (MV-ITP) mechanism to measure the turbulence intensity of the underwater channel. The MV-ITP mechanism utilizes the spatiotemporal intrinsic coupling correlation between optical imaging and optical communication to establish a precise quantitative relationship between the pixel intensity variation of the beam images and the scintillation index. We conduct experiments under different turbulence conditions induced by temperature, salinity, as well as air bubbles, and the experimental results demonstrate that the proposed mechanism can accurately measure the intensity of turbulence.
Chinese Optics Letters
- Publication Date: May. 16, 2025
- Vol. 23, Issue 6, 060601 (2025)
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