Hearing the Sounds of Aquatic Life Using Optical Fiber Microtip-Based Hydrophone

For marine bioacoustics applications, the sounds by aquatic animals must be recorded with a high precision and minimal noise in order to extract valuable information. For such marine applications, we propose and demonstrate an optical fiber microtip-based hydrophone. The hydrophone design consists of an extrinsic Fabry-Perot interferometer, which utilizes fiber microtip and processed aluminum foil as two partially reflecting mirrors. The packaged optical fiber hydrophone of dimensions 1.4 cm x 1.4 cm x 2 cm, with a microtip diameter of 31.23 mu m and natural rubber diaphragm of 6 mm diameter, shows a high sensitivity of 8.94 nm/mPa or -41.42-dB re 1 nm/mu Pa at 1 kHz. The hydrophone shows an excellent signal-to-noise ratio, and the noise-limited minimum detectable pressure is as low as 0.388 mu Pa/root Hz at 1 kHz. The linear working range of the hydrophone is 0-3950 Hz. The experimental results show that the proposed optical fiber hydrophone can very accurately detect the click trains produced by dolphins for echolocation. Furthermore, depending on the applications, the performance parameters of the proposed hydrophone can be tailored by changing the diaphragm thickness and diameter, thus opening a new platform to study the marine environment.