Fiber-optical acoustic sensor based on a photonic-crystal diaphragm

This paper reports on a highly sensitive fiber-optical acoustic sensor. The miniature acoustic sensor consists of a Fabry-Perot interferometer made of a photonic-crystal reflector embedded on a compliant silicon diaphragm placed at the tip of a single-mode fiber. A high-reflectivity multilayer dielectric mirror is deposited on the tip of the single-mode fiber. When combined with the high reflection from the photonic-crystal mirror, this second mirror forms a Fabry-Perot with a relatively high finesse (~15), giving rise to a high pressure sensitivity over the 10-50 kHz range. A minimum detectable pressure of 30 muPa/Hz¹² at 15 kHz is reported.