Frequency-Domain Joint Monitoring of Differential Group Delay and Dependent Loss of Optical Singleand Few-Mode Fiber Channels Based on CAZAC Sequences

Linsheng Fan; Gao Ye; Zhongliang Sun; Lingguo Cao; Hao Shi; Jianwei Tang; Shunfeng Wang; Hengying Xu; Chenglin Bai; Jian Zhao; Weisheng Hu; Jinlong Wei

arXiv · 2505.24589

Frequency-Domain Joint Monitoring of Differential Group Delay and Dependent Loss of Optical Singleand Few-Mode Fiber Channels Based on CAZAC Sequences

Linsheng Fan·Gao Ye·Zhongliang Sun·Lingguo Cao·Hao Shi·Jianwei Tang·Shunfeng Wang·Hengying Xu·Chenglin Bai·Jian Zhao·Weisheng Hu·Jinlong Wei

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Abstract

This paper addresses the challenges of monitoring optical-fiber channels subject to complex, multidimensional impairments-such as dynamic interference across polarization or modal dimensions-where conventional methods suffer from high equipment costs, poor impairment discrimination and limited scalability. We propose an in-service, frequency-domain joint monitoring scheme based on constant-amplitude zero-autocorrelation (CAZAC) sequences. Exploiting their flat spectra and ideal autocorrelation, we model the channel as a multi-input multi-output (MIMO) system and estimate its frequency response to extract both differential group delay (DGD) and dimension-dependent loss (DL) regardless of dimensionality. Experimental validation in polarization-division-multiplexing (PDM) and mode-division-multiplexing (MDM) scenarios demonstrates robust performance: in a 2x2 PDM setup, polarization-dependent loss (PDL) error stays below 0.3 dB and polarization-mode dispersion (PMD) accuracy is 0.3 ps; in a 4x4 MDM system, mode-dependent loss (MDL) and differential mode-group delay (DMGD) errors remain around 0.3 dB and 0.3 ps, respectively. Fully compatible with existing coherent DSP without additional hardware, the scheme enables continuous, cost-effective, real-time monitoring of multidimensional optical channels.

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Linsheng Fan, Gao Ye, Zhongliang Sun, Lingguo Cao, Hao Shi, Jianwei Tang, Shunfeng Wang, Hengying Xu, Chenglin Bai, Jian Zhao, Weisheng Hu, Jinlong Wei. 2025-05-30. Frequency-Domain Joint Monitoring of Differential Group Delay and Dependent Loss of Optical Singleand Few-Mode Fiber Channels Based on CAZAC Sequences. https://arxiv.org/abs/2505.24589

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