Ultrasensitive all-fiber microphone with in-line beam and 45° tilted optical fiber fabricated by laser micromachining

We present an in-fiber microphone utilizing a 45° tilted optical fiber and in-line beam structure, featuring exceptionally high sensitivity, ultra-compact structure and high temperature survivability. The sensor is fabricated through picosecond laser micromachining assisted with a fiber polishing process. Under acoustic excitation, in-line beam deflection is probed interferometrically with light delivered by the tilted optical fiber endface. Experimental results demonstrate highly-sensitive response within the frequency range of 60.0-95.0 kHz, with sensitivity reaching 2667.6 mV/kPa at 82.0 kHz, which is two orders of magnitude higher than that of all-fiber sensors previously reported. The temperature working point is up to 350 °C. Benefiting from ultrahigh sensitivity, biocompatibility, all-fiber structure, and high temperature survivability, the microphone offers significant potential for diverse applications including hydrophones, photoacoustic spectroscopy and optical endoscopic imaging.