Enhancing performance of coherent OTDR systems with polarization diversity complementary codes

TL;DR

This paper introduces a novel polarization-diversity coding technique using Golay complementary sequences to improve the sensitivity and bandwidth of coherent OTDR systems for fiber sensing applications.

Contribution

It presents a new probing method employing orthogonal Golay pairs in polarization to achieve perfect fiber response estimation and enhance system performance.

Findings

Achieved perfect channel response estimation under specific conditions.

Enhanced sensitivity and bandwidth up to 18 kHz.

Demonstrated linear response with a 10 FBG sensor array.

Abstract

Monitoring the optical phase change in a fiber enables a wide range of applications where fast phase variations are induced by acoustic signals or vibrations in general. However, the quality of the estimated fiber response strongly depends on the method used to modulate the light sent to the fiber and capture the variations of the optical field. In this paper, we show that distributed optical fiber sensing systems can advantageously exploit techniques from the telecommunication domain, as those used in coherent optical transmission, to enhance their performance in detecting mechanical events, while jointly offering a simpler setup than widespread pulse-cloning or spectral-sweep based schemes with acousto-optic modulators. We periodically capture an overall fiber Jones matrix estimate thanks to a novel probing technique using two mutually orthogonal complementary (Golay) pairs of binary sequences applied simultaneously in phase and quadrature on two orthogonal polarization states. A perfect channel response estimation of the sensor array is achieved, subject to conditions detailed in the paper, thus enhancing the sensitivity and bandwidth of coherent phase-OTDR systems. High sensitivity, linear response, and bandwidth coverage up to 18 kHz are demonstrated with a sensor array composed of 10 fiber Bragg gratings (FBGs).