Optical microphone based on a modulated diffractive lens

The authors present an optical microphone based on a diffractive lens. The distance between the diffractive lens and a reflecting microphone membrane determines the light intensity at the focal point of the lens. With this design, an integrated micromachined microphone transducer can be mass produced at low cost. They describe the sensing principle, calculate the intensity at the focal point, and show how it depends on the membrane position. The authors present results from measurements with a prototype setup which proves the measurement principle and has excellent properties when compared to an expensive condenser microphone.