A high performance distributed optical fiber sensor based on Φ-OTDR for dynamic strain measurement

Abstract

A high-performance distributed optical fiber sensor based on phase-sensitive optical time-domain reflectometry (Φ-OTDR) for dynamic strain measurement has been proposed. In this newly designed system, ultraweak fiber Bragg gratings (UWFBGs) are sparsely embedded in the sensing fiber. Through an unbalanced 3 × 3 coupler structure, the reflected lights from two adjacent UWFBGs would be mixed with each other and then split into three parts for phase demodulation. Then, a novelty table-look-up scheme is introduced to precisely demodulate the frequency, amplitude, and phase of dynamic strain. Rayleigh back-scattering light is utilized to identify and locate the accurate position of vibration event between two adjacent UWFBGs. The experimental results show that the proposed system is capable of reconstructing the vibration with a linear intensity response of R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 0.9986 and a fiber length variation sensitivity of 117 pm/(Hz) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> . Meanwhile, a wide frequency response band from 50 to 2075 Hz is achieved with high signal-to-noise ratio above 56 dB.