The principle of fiber optic microphones works with a transmitting and a receiving optical fiber and a mirrored micro- diaphragm. According to the method, a laser beam is projected through the transmitting optical fiber onto the micro-diaphragm, which reflects the light beam into the receiving optical fiber. The micromembrane moves with the incident acoustic pressure, causing more or less incident light to be reflected into the receiving optical fiber. The brightness of the received light beam thus varies in rhythm with the sound pressure. The changing sound pressure is thus converted into changes in brightness, which is amplified and used for audio reproduction.