Analysis of fiber Bragg gratings reflective spectrum under ultrasonic excitation

The optical spectrum of fiber Bragg gratings (FBG) under ultrasonic excitation during damage detection is analyzed in detail in this paper. First, the strain transferring equation from host material to fiber under ultrasonic excitation in structure detection is presented. On this basis, the optical spectrum of FBG under ultrasonic excitation is simulated with the Transmission Matrix method. The influences of FBG length and ultrasonic power on the FBG spectrum distribution are discussed, and the FBG center wavelength change under a continuous ultrasonic wave is given. Numerical results prove that the FBG can be used to detect ultrasonic signal in structure detection when the length of the FBG is shorter than a half of ultrasound wavelength with proper energy.