Microseismic wave detection in coal mines using differential optical power measurement

Microseismic wave detection is important to avoid major disaster in coal mines. Here, a scheme of differential power measurement is proposed that can detect microseismic waves by converting minimal wavelength shift detected by a fiber Bragg grating interrogation system into corresponding variation in optical power. The Bragg-reflected signals are phase modulated by 500-MHz RF signal and detected by differential arrangement circuit consisting of photodetectors (PDs). The differential power at the PD is calculated theoretically and verified through simulation experiment. The variation of differential power with applied strain is nonlinear with the threshold at 100 mu epsilon. The sensitivity of the present system is 0.041 dB/mu epsilon below the threshold and increases to 0.598 dB/mu epsilon above the threshold with the system resolution of 16.72 n epsilon. (C) 2019 Society of Photo-Optical Instrumentation Engineers (SPIE)