Engineering an optical microphone for consumer electronics

Between the years 2010–2015, a small start-up in Austin, TX was focused on commercializing an optical MEMS microphone to address high-volume consumer electronics applications. The motivation for the optical approach was to achieve a higher signal-to-noise ratio (SNR) than capacitive MEMS microphones. Similar to other commercial MEMS microphone offerings, the product was required to be small size, relatively low-cost, and surface-mountable. This presentation will focus on the challenges faced in engineering an optical microphone to meet these requirements. The particular approach used a diffractive optical element fabricated directly into the backplate of an otherwise conventional microphone die. Vertical-cavity surface emitting lasers (VCSELs) resided inside the die's etched cavity. Completed pilot-scale samples proved capable of demonstrating high SNR, but ultimately the company made a pivot to focus engineering and business-development resources on a similar product line—ground-motion sensors and seismometers. The company has been manufacturing and selling seismometers 2015–present.