Ultrahigh Sensitivity Fiber-Optic Fabry–Perot Interferometric Acoustic Sensor Based on Silicon Cantilever

Abstract

Detection of weak acoustic signals is of great significance. To achieve ultrahigh sensitivity acoustic detection, a silicon cantilever-based fiber-optic acoustic sensor (FOAS) formed by a Fabry–Perot interferometric structure is proposed in this work. Theoretical analysis and finite element analysis are used to assist the sensor design. The cantilever is fabricated by the microelectro-mechanical system (MEMS) processing technology on a silicon-on-insulator (SOI) wafer. A white light interference (WLI) demodulation system based on an amplified spontaneous emission (ASE) source is used to demodulate the cavity length of the sensor. The acoustic pressure sensitivity of the sensor was measured to be <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.753~\mu \text{m}$ </tex-math></inline-formula> /Pa at a frequency of 1 kHz and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$28.75~\mu \text{m}$ </tex-math></inline-formula> /Pa at the resonance frequency of the cantilever. Experimental results indicated that the minimum detectable pressure (MDP) level of the fabricated sensor was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.21~\mu $ </tex-math></inline-formula> Pa/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> at 1 kHz, which is the lowest reported value. The silicon-based FOAS proposed in this article demonstrates its ability to detect ultraweak acoustic signals due to its extremely high sensitivity.