Highly Sensitive Distributed Strain Sensor Based on φ-OTDR with Ultraweak Fiber Bragg Grating

A distributed sensing system was proposed for quantitative of strain measurement based on phase-sensitive optical time-domain reflectometry (φ-OTDR) , The coherent detection principle and I/Q demodulation method are adopted to demodulate the distributed strain. Compared with the traditional φ-OTDR system, this scheme uses ultra-weak fiber Bragg grating (UWFBG) to enhance the reflective Rayleigh scattering signal, which can effectively improve the signal-to-noise ratio. In addition, a polarizer is added to reduce the impact of polarization fading. Using PZT as a strain sensor, the position and phase of the strain signal are successfully demodulated by φ-OTDR. The experiment results show that the demodulated phase difference has a linear response to the strain generated by PZT. Due to the enhanced reflective signal by UWFBG, a high strain sensitivity of 2.11 rad/nε was obtained. This scheme has the advantages of low cost, simple sensing structure, no need for amplifiers, and high sensitivity.