A Miniature Fiber-Optic Silicon Cantilever-Based Acoustic Sensor Using Ultra-High Speed Spectrum Demodulation

Abstract

A silicon cantilever-based fiber-optic acoustic sensor (FOAS) is presented in this work. A rectangular cantilever is fabricated upon a silicon-on-insulator (SOI) wafer using a micro-electro-mechanical system (MEMS). The length, width and thickness of the silicon cantilever are 530 μm, 200 μm and 3 μm, respectively. The resonant frequency of the silicon cantilever is 14820 Hz with a sensitivity of 950 nm/Pa. An ultra-high speed absolute cavity length demodulation method is adopted using a complementary metal oxide semiconductor (CMOS) spectrometer and an 850 nm superluminescent light emitting diode (SLED). A modified Buneman frequency estimation and total phase demodulation algorithm is adopted. The frequency response curve shows a relatively flat trend from 20 Hz to 13 kHz. The sensor exhibits good linearities at different frequencies while the applied acoustic pressure is increased from 0 Pa to 2.5 Pa. Experimental results indicate that the minimum detectable pressure (MDP) of the proposed FOAS is calculated to be 25.68 μPa/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> at the frequency of 13 kHz. The silicon cantilever-based FOAS achieves broad operating bandwidth, high sensitivity, small size, and good stability.