A Sensitivity Enhanced Microdisplacement Sensing Method Improved Using Slow Light in Fiber Bragg Grating

Fiber Bragg grating (FBG) sensors have been widely used in all industrial fields due to their advantages of small size, corrosion resistance, strong antijamming capability, and easy to reuse. Traditional FBG sensors can measure microdisplacement, but low sensitivity and resolution limit its applications in the field of precision measurement. There are sidelobes near the FBG bandgap whose transmittivity changes with wavelength, and the transmitted light has a huge group delay time due to the light here transmitting back and forth numerous times. This paper proposes and demonstrates a sensitivity enhanced microdisplacement sensor using slow light in FBGs through numerical simulations and experiments. A theoretical model of gratings is established by the coupled mode theory and transfer matrix method, and the mechanism of slow light generated in FBG is studied theoretically and also by numerical simulation analysis. This paper determined the set structure parameters of FBG by studying the slow light characteristics of different types of gratings with different structure parameters and influences of structure parameters on the FBG slow light characteristics. A microdisplacement sensing system is designed and built, and finally a sensitivity of 15.0786 mW/mm and a resolution of 66 nm are reached in the range of 0-60 μm, which is 13 times more than the traditional grating sensing with light intensity demodulation.