Photonic-crystal-diaphragm-based fiber-tip hydrophone optimized for ocean acoustics

We report a miniature fiber hydrophone that consists of a Fabry-Perot interferometer made of a photonic-crystal reflector embedded on a compliant silicon diaphragm placed at the tip of a single-mode fiber. A model was developed to show that after proper optimization to ocean acoustics, this sensor has a minimum detectable pressure that follows the minimum ambient noise of the ocean (reaching a minimum of ~10 μPa/Hz^1/2 at ~30 kHz) in the bandwidth of 1 Hz-100 kHz. By placing several such sensors with different acoustic power ranges within a single hydrophone head, the hydrophone is able of exhibiting a dynamic range in the excess of 200 dB. A prototype was fabricated, assembled, and tested that confirmed this high sensitivity and bandwidth.