Micromachined Fabry-Perot Interferometer for Motion Detection

The monolithic integration of a Fabry-Perot interferometer and a (100) silicon photodiode is reported for use as a highly sensitive transduction method in the detection of minute displacements of a proof mass attached to a spring. The combination results in a compact device with active transistor-like amplification and minimal parasitic elements, The transducer is fabricated using standard surface micromachining techniques. The finesse of the optical cavity, incident optical power, and geometry of the mirror and support structure control the sensitivity of the transducer. A transduction of more than 2285 A/m, percent change in transmission with displacement of 3%/nm, small-signal voltage amplification of 460 V/V output resistance of 100 M-OMEGA and transconductance of 1 mA/V have been obtained thus far for a single device without amplification. Pub. in Applied Physics Letters, v81 n18, 28 Oct 2002.