Linear Least Squares Estimation of Fiber-Longitudinal Optical Power Profile

TL;DR

This paper introduces a linear least squares method for accurately estimating fiber-longitudinal optical power profiles, enabling high-resolution detection of loss anomalies using coherent receivers.

Contribution

It proposes a novel least squares approach for PPE that achieves high accuracy and spatial resolution, including a fundamental limit analysis of estimation stability.

Findings

Achieves RMS error of 0.18 dB in PPE

Detects loss anomalies as small as 0.77 dB

Validates effectiveness under WDM conditions

Abstract

This paper presents a linear least squares method for fiber-longitudinal power profile estimation (PPE), which estimates an optical signal power distribution throughout a fiber-optic link at a coherent receiver. The method finds the global optimum in least square estimation of longitudinal power profiles, thus closely matching true optical power profiles and locating loss anomalies in a link with high spatial resolution. Experimental results show that the method achieves accurate PPE with an RMS error from OTDR of 0.18 dB. Consequently, it successfully identifies a loss anomaly as small as 0.77 dB, demonstrating the potential of a coherent receiver in locating even splice and connector losses. The method is also evaluated under a WDM condition with optimal system fiber launch power, highlighting its feasibility for use in operations. Furthermore, a fundamental limit for stable estimation and spatial resolution of least-squares-based PPE is quantitatively discussed in relation to the ill-posedness of PPE by evaluating the condition number of a nonlinear perturbation matrix.