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

TL;DR

This paper introduces a frequency-domain joint monitoring method using CAZAC sequences for optical fiber channels, enabling real-time, cost-effective detection of complex impairments like DGD and DL in multi-dimensional systems.

Contribution

It presents a novel in-service, frequency-domain monitoring scheme based on CAZAC sequences that accurately estimates DGD and DL in multidimensional optical channels without extra hardware.

Findings

Achieves polarization-dependent loss error below 0.3 dB

Attains polarization-mode dispersion accuracy of 0.3 ps

Maintains mode-dependent loss and differential mode-group delay errors around 0.3 dB and 0.3 ps

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.