Full-scale OFDR-based distributed strain sensing with enhanced measurement accuracy.

In this Letter, we propose a method to improve strain sensing accuracy across the full-scale distance at the 100 m level in optical frequency domain reflectometry (OFDR) by minimizing residual phase noise (RPN), which significantly degrades strain accuracy. We derive a quantitative relationship between RPN variance and interferometer delay and design a coded delay fiber module (OPEM) that dynamically provides delay fibers of optimal length. By quantitatively analyzing RPN and guiding the output configuration of the OPEM to suppress RPN at the hardware level, we achieved strain sensing with a spatial resolution of 2 mm and a strain accuracy better than 1.5 με (2σ) across the full-scale distance at the 100 m level, approaching the theoretical accuracy limited by optical shot noise.