Microfabricated optical interference microphone for high signal-to-noise ratio up to 70.2 dB

Optical transduction-enabled acoustic sensing stands out as a promising substitute for conventional capacitive sensing in MEMS microphones, especially for ultra-low-noise applications. Here, we demonstrate a prototype optical MEMS microphone sensor with optimized photonic-mechanical coupling. The sensor is fabricated through a standard micro-manufacturing process, wherein the diaphragm is made of polysilicon material with low bending stiffness and compatibility with the MEMS process. The sensor enables measurement within a frequency bandwidth of 200 Hz to 6.1 kHz. A sensitivity of 89.2 mV/Pa is obtained within the sound pressure measurement range of 0.1 to 1 Pa with a maximum nonlinearity error of 2.97% and a repetitive error of 1.11%. The signal-to-noise ratio of the sensor is 70.2 dB based on the balanced differential method. Moreover, the total harmonic distortion of the sensor is 0.08% within the pressure range. The sensor demonstrates significant application potential in high-performance acoustic detection, such as medical auscultation and machine condition monitoring.