Compact diaphragm-based optical accelerometers with µg/√Hz resolution

A compact fiber accelerometer that meets the resolution requirement for aircraft navigation is reported. It detects extremely weak acceleration-induced vibrations of a spring-loaded diaphragm using a two-wave interferometer with a π / 2 biasing step micro-fabricated on the diaphragm. A single-mode fiber provides a laser beam that interrogates the interferometer. This sensor has a measured flat-band sensitivity with a bandwidth of 10.7 kHz, and a resolution limited by thermo-mechanical noise of 13 µ g / √ H z at 100 Torr, and 712 n g / √ H z at 20 mTorr.