Temperature-insensitive Fabry–Perot interferometer for microseism sensing based on hollow core photonic crystal fibres

Abstract

This study proposes an inline temperature-insensitive Fabry–Perot interferometer (TI-FPI) for coal mine microseism sensing based on a cantilever structure. The sensor is fabricated by splicing a section of hollow core photonic crystal fibre (HC-PCF) between a lead-in polarisation-maintaining fibre (PMF) and a multi-mode fibre (MMF) using a CO2 laser splicer. The HC-PCF and MMF are employed as a cantilever beam. An air cavity of the TI-FPI formed by the HC-PCF is modulated via external vibration, leading to a variation in the length. Sensors with air cavities of 407 μm, 698 μm, and 1069 μm are demonstrated. The experimental results show that the lowest temperature response is −0.04 pm/°C. The flat frequency band of the acceleration response can be adjusted by the cantilever beam's length, and the best average sensitivity and resolution of the sensors are 3.45 mV/g and 0.26 mg/√Hz (g is gravity of 9.8 m/s2), respectively. The minimum resolution is 5.04 μg/√Hz at a resonance frequency of 1500 Hz. The sensor is anticipated to have wide application prospects in microseism monitoring in coal mines.