High-Resolution Strain/Temperature Sensing System Based on a High-Finesse Fiber Cavity and Time-Domain Wavelength Demodulation

A high-resolution strain/temperature sensing system based on a fiber Bragg grating-Fabry-Perot cavity (FBG-FPC) and a wavelength-swept single-longitudinal-mode laser diode (modulated by a sawtooth signal) is proposed. The high-finesse (~627) FBG-FPC formed by two uniform FBGs of high reflectivity (~99.5%) is used both as a strain/temperature sensor and a FPC with ultranarrow (~0.12 pm) transmission bands. Using a photodetector to detect the transmissive light of the laser diode through the FBG-FPC, wavelength demodulation is achieved by mapping wavelength measurement to time measurement. Both strain sensing and temperature sensing with a resolution of 0.11 muepsiv and 0.014degC, respectively, have been demonstrated.