Numerical Analysis on Ultrasonic Sensing Mechanism of Fiber Gratings and their frequency Responses

Fiber grating has the advantages of small size, light weight, strong to electromagnetic interference, which has been a research focus in the field of ultrasonic sensing. Grating devices include fiber Bragg grating (FBG) and phase-shifting fiber Bragg grating (PS-FBG). Due to different refractive index distribution of the two gratings, they have different sensing characteristics for ultrasonic sensing. In this paper, an analysis method of fiber grating ultrasonic sensing mechanism was proposed, and the frequency response of fiber grating was studied. Results showed that the frequency response bandwidth of PS-FBG is wider than that of FBG when the optical parameters is the same. The frequency response of FBG is affected mainly by grating length, but for PS-FBG, the frequency response is affected by refractive index modulation depth and grating length together.