Acoustic Localization With an Optical Fiber Silicon Microphone System

We develop a wavelength-multiplexed system of optical fiber-based photonic-crystal microphones for acoustic source localization. Our microphones use $392 \mu \text{m}$ wide and 450 nm thick photonic-crystal silicon diaphragms that we fabricate on the wafer scale and mount to an optical fiber with a simplified groove-based alignment. Our microphones have a bandwidth of acoustic sensitivity from 150 Hz to 50 kHz and an average minimum detectable pressure of $2 \mu Pa/ \sqrt {Hz}$ on resonance. The consistency of our microphone fabrication and assembly allows us to interrogate the pressure-sensitive Fabry-Pérot cavities using wavelength-sliced channels from the spontaneous emission of a C-band optical amplifier. Using our compact wavelength-multiplexed sensor system composed of standard fiber-optic communications hardware, we can localize acoustic sources in the environment to within 5 cm by a time-difference of arrival method.