Ultrasonic hydrophone based on distributed Bragg reflector fiber laser

We demonstrate a novel fiber-optic hydrophone that uses a dual polarization distributed Bragg reflector (DBR) fiber laser as sensing element. The operation principle is based on the modulation of the birefringence of the fiber laser by high-frequency ultrasound. By measuring the amplitude and frequency of the sidebands as well as the polarization beat frequency of the output of the fiber laser using a photodetector and a radio-frequency spectrum analyzer, the amplitude and frequency of the acoustic pressure, and temperature can be determined simultaneously. The DBR fiber laser hydrophone has a linear response to acoustic pressure and can detect acoustic frequency up to at least 40 MHz.