Optical Microphone Structures Fabricated for Broad Bandwidth and Low Noise

A micromachined optical microphone structure using a grating based interferometer has been presented previously and is undergoing continued development (JASA, vol. 118, pp 3000-3009, November 2005). Two advantages of the approach that have been highlighted in prior work are high displacement resolving capability of the microphone diaphragm vibration (2 pm rms over the audio bandwidth) and a flexible mechanical design space for achieving broad bandwidth and low thermal noise designs. Here, we summarize a variety of structures we are fabricating using Sandia National Laboratories silicon-based microfabrication technology to explore this versatile design space. These structures are being packaged to resemble instrumentation-type microphones with approximately 1 cm² form factor in order to facilitate rigorous acoustic evaluation in the Micromachined Sensors and Transducers Laboratory (MiST) and anechoic test facilities at Georgia Tech.