Frequency response of fiber-optic multilayer hydrophones: experimental investigation and finite element simulation

The frequency response of a fiber-optic hydrophone that uses a dielectric multilayer system as the sensing element for ultrasound detection is investigated. A primary interferometric calibration technique is applied to determine by experiment the frequency-dependent pressure-voltage transfer function up to 45 MHz. The interaction between an incident pressure wave and the fiber end is analyzed by finite element methods. The simulation yields the response of the sensor to a short Gaussian impulse in the time domain from which the transfer function is calculated. The results of the model simulations allowed the transfer function obtained to be interpreted as the result of the superposition of longitudinal, edge diffraction and lateral waves with a resonant vibration mode of the fiber body representing an elastic rod.