Extrinsic Fabry-Perot interferometer fiber-optic microphone

In this paper we describe a new fiber-optic microphone developed as a passive acoustic sensor for traffic monitoring and vehicle classification. It is based on a fiber-optic extrinsic Fabry–Perot (FP) microinterferometer coupled to an external membrane for modulating the FP cavity length and a low coherent superluminescent diode as light source. The frequency characteristic as compared with a standard condenser microphone exhibits a sensitivity range of more than 80 dB between 100 Hz and 15 kHz. Initial results are presented demonstrating acoustic monitoring of aircraft via their characteristic noise spectra using downleads of km length.