Fibre-coupled photonic crystal hydrophone

Many applications, including medical diagnostics, sonar and navigation rely on the detection of acoustic waves. Photonic hydrophones demonstrate comparable sensitivity to piezoelectric-based hydrophones, but with significantly reduced size, weight and power requirements. In this paper we demonstrate a micron-sized free-standing silicon photonic hydrophone. We demonstrate sensitivity on the order of $\sim$mPa/$\sqrt{\textrm{Hz}}$ from 10-200 kHz, with a minimum detectable pressure of 145 $\mu$Pa/$\sqrt{\textrm{Hz}}$ at 22 kHz. We also deployed our hydrophone in a wave flume to evaluate its suitability for underwater measurement and communication. Our hydrophone matches the sensitivity of commercial hydrophones, but is many orders of magnitude smaller in volume, which could enable high spatial resolution imaging of micron-sized acoustic features (i.e., living cell vibrations). Our hydrophone could also be used in underwater communication and imaging applications.