Directional optical mircophone

摘要

An optical microphone having enhanced sensitivity only along a specified axis and free from the effect of ambient noises. The optical microphone comprises a diaphragm (2) vibrating with sound pressure, a light source (3) for irradiating the diaphragm (2) with a light beam, a photodetector (5) for receiving a fraction of the light reflected from the diaphragm (2) and outputting a signal corresponding to the vibration of the diaphragm (2), and a light source driving circuit (13) for driving the light source (3) by supplying a specified current. The optical microphone is additionally provided with a negative feedback circuit (100) for supplying the light source driving circuit (13) with a part of the output signal from the photodetector (5) as a negative feedback signal.