Optical fiber ring horn Fabry-Perot ultra-thin film acoustic sensor by two-photon polymerization 3D printing

This paper presents a miniaturized fiber-optic FP acoustic sensor with an integrated annular horn structure. The proposed sensor features a 2-μm-thick diaphragm and an 80-μm-long FP cavity, which was directly fabricated on the fiber end face via two-photon polymerization technology. Wavelength demodulation method and intensity demodulation method are used to detect the audible sound waves of the sensor in low, medium and high frequency bands, and the sound pressure response ability is tested. The sensor shows good linearity in low, medium and high frequency bands. The sound pressure sensitivity is 0.271 V/Pa@200 Hz for acoustic pressures between 75 dB and 95 dB. At 85 dB SPL and 200 Hz frequency, this sensor demonstrates a minimum detectable pressure (MDP) of 0.652 mPa/Hz^1/2, outperforming conventional fiber-optic detectors. Under the condition of a sound pressure of 0.63 Pa at 200 Hz, the sensor exhibited a time-domain response peak of 0.47 mV, which is 1.47 times higher than the mid-frequency signal (0.19 mV at 2500 Hz) and 4.88 times greater than the high-frequency signal (0.08 mV at 14 kHz), indicating the most pronounced time-domain response at 200 Hz. Both wavelength demodulation and intensity demodulation methods confirmed that the sensor achieves optimal frequency response performance at 200 Hz, with a normalized peak frequency response value of 0.55. In the sound pressure response experiment, when the sound pressure was 0.36 Pa, the sensor achieved the highest signal-to-noise ratio and the minimum detectable sound pressure, demonstrating its superior performance in detecting weak acoustic signals. Owing to its superior frequency response characteristics and exceptional acoustic detection sensitivity, the proposed sensor demonstrates significant potential for applications in marine biological monitoring and industrial non-destructive testing.