An Optical Acoustic Detection System Based on Fabry Pérot Etalon Stability Structure

The optical acoustic detection system based on the Fabry Pérot Etalon (FPE) with high quality-factor (High Q) and stability structure is described and tested. The FPE contains two high-reflectivity Plano-Concave lenses, achieving high fineness and stability. The protective structure of the confocal stabilized FPE is composed of an invar tube, copper sheath, Bakelite sheath and aluminum housing to protect the sensor from the effects of ambient temperature and vibration. The audio signal is injected into the cavity through the sound hole located in the center of the cavity. Acoustic waves induce the vibration of the medium in the cavity, which leads to a simultaneous change in the FPE optical path and a shift of the interference spectrum. The acoustic detection system is built, and the frequency of the laser is locked on the resonant frequency points of the FPE by using phase modulation technology, so as to detect acoustic signals of different frequencies and amplitudes. In addition, the sensitivity of the proposed sensor exceeds 34.49 mV/Pa in the range of 20 Hz-20 kHz. A Signal-to-Noise Ratio (SNR) of 37 dB can be achieved at 20 Hz. Acoustic signal detection technology based on the FPE stability model is used to test the theoretical feasibility of the future high sensitivity Fabry Pérot Interferometric (FPI) acoustic sensors.