High-Resolution Long-Reach Brillouin Distributed Fiber Sensing with Reduced Acquisition Time
Abstarct: Brillouin scattering-based distributed fiber sensing is a technology by which a standard telecom single-mode fiber is turned into many thousands of temperature or strain sensors. The principle is known in research for 25 years. The most widely employed configuration for these measurements is Brillouin optical time domain analysis (B-OTDA), in which pump pulses are used to amplify a continuous-wave signal and the output signal power is monitored as a function of time. A typical commercial B-OTDA interrogator can provide a measurement sensitivity of 1 °C or 20 µe (micro-strain), over a range of 50 km, with a spatial resolution of 2-3 m and an acquisition time of ten minutes. Over the last 15 years, continuous monitoring systems based on the B-OTDA technique had been commercialized and deployed in variety of applications: pipeline integrity monitoring, subsea monitoring of umbilical cords in rigs, electrical power line cable monitoring and more.
In this work, I propose, analyze and experimentally demonstrate a new scheme for distributed Brillouin sensing. The technique combines between time-domain and Brillouin optical correlation-domain analysis (B-OCDA) principles. Using the proposed scheme, the Brillouin gain spectra was experimentally mapped along a 1700 m-long fiber under test with a spatial resolution of 2 cm, representing over 80,000 resolution points, with only 127 scans per choice of frequency offset between pump and signal. Compared with previous B-OCDA protocols developed by our group, with equal range and resolution, the acquisition time is reduced by a factor of over 600. The measurement sensitivity is 1.7 °C or 35 µe. The method is routinely being employed by our group in the analysis of the mechanical properties of composite material parts.
* This M. Sc. work was carried out under the supervision of Prof. Avi Zadok, Faculty of Engineering, Bar-Ilan University