Sensitivity-Improved Fiber Bragg Grating Temperature Sensor Based on Microwave-Photonic Enhanced Vernier Effect

This paper reports a highly sensitive fiber Bragg grating (FBG) temperature sensor system based on microwave-photonic interrogation and the enhanced Vernier effect. A low-coherent system-based microwave-photonic three-beam interferometer is constructed using three parallel-arranged FBGs with different Bragg wavelengths and different lead-in fiber lengths. One FBG is used as the sensing device, and the other two are considered as the reference device. Changes in the Bragg wavelength difference between the sensing FBG and the reference FBGs induced by temperature variations are encoded into spectral shifts of the Vernier envelope in the magnitude spectrum of the system in the microwave domain. By carefully designing the Bragg wavelength differences and the lead-in fiber length differences, the enhanced Vernier effect can be realized. A remarkable temperature sensitivity of -40.89 MHz/°C is successfully demonstrated based on the three-FBG sensor system based on the enhanced Vernier effect.