Separation of temperature and strain measurement in photon-counting BOTDR

This paper introduces a photon-counting Brillouin Optical Time-Domain Reflectometry (ν-BOTDR) system designed to separate the effects of temperature and strain along an optical fiber. Based on measurements taken at different working points of a fiber Bragg grating (FBG), the system’s sensitivity to strain and temperature variations can be tuned accordingly. The main advantage of BOTDR is that it allows temperature or strain information to be recovered from the Brillouin frequency shift. However, when a Single Photon Avalanche Detector (SPAD) is used to improve the signal-to-noise ratio and range of these sensors, information on the frequency of the scattered signal is lost. In this paper, we present a new technique that enables frequency shifts to be measured unaffected by optical losses or intensity variations caused by Brillouin gain, while benefiting from the high sensitivity of SPADs. This paper outlines the methodology and presents experimental results that distinguish strain and temperature variations over distances exceeding 50 km, with a spatial resolution of 2 m using standard single-mode fiber.