All-optical low noise fiber Bragg grating microphone

We present an all-fiber design for a microphone using a fiber Bragg grating Fabry-Perot resonator attached to a diaphragm transducer. We analytically model and verify the fiber-diaphragm mechanical interaction, using the Hänsch-Couillaud readout technique to provide necessary sensitivity. We achieved a noise-equivalent strain sensitivity of 7.1×10-12 ϵ/Hz, which corresponds to a sound pressure of 74 μPa/Hz at 1 kHz limited by laser frequency noise and yielding a signal-to-noise ratio of 47±2 dB with a 1 Pa drive at 1 kHz, in close agreement with modeled results.