Design and Fabrication of Monolithic Photonic Crystal Fiber Acoustic Sensor

Single-crystal silicon is an excellent optical and mechanical material, but its properties are compromised by the incorporation of other materials required for functionality or structural support. Here, we describe a monolithic silicon acoustic sensor based on a sensing diaphragm with an integrated photonic crystal (PC) mirror. Diaphragm deflection is measured in a Fabry–Perot resonator formed between the PC mirror and a gold coated single-mode fiber. The sensors are fabricated on standard silicon wafers by standard CMOS processing technologies, yielding monolithic, low-stress sensing diaphragms. The packaged sensor exhibits a minimum detectable pressure of $10~\mathrm {\mu }$ Pa/ $\mathrm {\sqrt {Hz}}$ in the 8–17-kHz frequency range.