A fiber-optic microphone

Abstract A fiber-optic microphone is a device in which the incident sound waves modulate the light guided in optical fibers without the help of electricity. One possible modulation technique is intensity modulation by beam deflection at a moving membrane. Several approaches to realize such a microphone are presented, including multi-mode and single-mode solutions as well as an integrated-optical implementation. With a set-up consisting of two single-mode fibers and a gradient index lens mounted in front of a reflecting membrane, a noise equivalent pressure level of 42 dB(A) is achieved. The first membrane resonance of this device lies at a frequency of 4.3 kHz.