Design of a MEMS Optical Microphone Transducer Based on Light Phase Modulation

Acoustic sensing through optical transduction represents a promising alternative to the conventional capacitive sensing used in MEMS microphones, especially when aiming at ultralow-noise applications. In fact, the traditional acoustic to electrical transduction stages are decoupled by the intermediate conversion of the signal into the optical domain. As a result, the mechanical design of the sensor has no direct influence on the electrical readout performance, and this allows for a significant reduction of the MEMS transducer noise through aggressive acoustically semi-transparent stator designs that represent one of the limits of the standard capacitive technologies. This article reports the design and the modeling of the sensing elements of a MEMS optical microphone. The basic transduction mechanism is presented, and the main design parameters and challenges are explained and analyzed with advanced modeling techniques; the measurement results are finally compared to the expected performance.