Sensitivity improved fiber Bragg grating strain sensor based on the microwave-photonic enhanced Vernier effect.

This work demonstrates a fiber Bragg grating strain sensor system by utilizing the enhanced microwave-photonic Vernier effect, which is generated from two parallel fiber rings inserted with linear chirped fiber Bragg gratings (FR-LCFBGs). The two LCFBGs are configured in forward and backward orientations, enabling the external strain-induced center wavelength shift of the FBG sensor to be converted into frequency shifts in opposite directions within two microwave resonant rings. As a result, the enhanced Vernier effect can be constructed, which greatly improves the strain sensitivity of the system. The experimental results reveal that the sensor based on parallel FR-LCFBGs achieves the strain measurement sensitivity of 102.8 kHz/με with the help of the enhanced Vernier effect, being 175.4 times that in the single FR-LCFBG. Therefore, the proposed device may have potential applications in weak strain measurement.