Ultra-wideband all-fiber microphone enabled by micro-beam and diaphragm structure

We propose an all-fiber microphone based on a micro-beam and diaphragm structure, achieving ultra-wideband frequency response through efficient coupling of acousto-optic signals. The microphone is constructed by an optical fiber, a diaphragm and a micro-beam, which is located between the fiber and the diaphragm and serves as an optical transmission waveguide. Under acoustic pressure, the micro-beam and diaphragm undergo deformation. The refractive index of the micro-beam periodically varies due to the photo-elastic effect, which further broadens its frequency response. Changes in beam length and refractive index collectively introduce variation in optical path, which is further probed interferometrically with light delivered by optical fiber. The all-fiber microphone is fabricated by picosecond laser irradiation followed by a chemical etching process. Experimental results show that the microphone presents an acoustic pressure sensitivity of up to 139.89 mV/kPa@80 kHz, and its frequency response covers the range of 40 to 1600 kHz. High temperature working point up to 1000 °C and low temperature crosstalk are achieved. With compact structure, ultra-wide frequency range, and high temperature survivability, the proposed microphone is attractive for harsh environment applications.