Underwater Acoustic Wave Detection Based on Packaged Optical Microbubble Resonator

Abstract

We demonstrate an optical underwater acoustic sensor with high sensitivity and broad bandwidth (10 Hz to 100 kHz), based on the packaged optical microbubble whispering gallery mode resonator, for the first time. The underwater acoustic pressure sensitivity level is as high as −159.3 dB re 1 V/μPa at 1 kHz that benefits from the high optical Q-factor and low refractive index (RI) polymer cladding. The corresponding noise equivalent pressure (NEP) is 66.8 dB re 1 μPa/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> , which is equivalently 2.2 mPa/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> . The sensitivity is hardly affected by the changes of static pressure and temperature in practical applications. The wide underwater acoustic response directivity is measured and the angular responses have – 6 dB angle range of 75.6° and 105.5° in two orthogonal directions, respectively. This work provides a potential miniature optical acoustic sensor for the broadband underwater acoustic wave detection.