RF amplitude modulated fiber optic acoustic sensing

A novel acoustic sensor based on combined techniques of optical fiber microbending and radio frequency (RF) modulation techniques is described. The experimental measurements were conducted with the aid of an optical network analyzer developed from an RF network analyzer coupled to a laser/detector system. The device under test consists of the laser, fiber sensor, photodetector, and external acoustic source. The sensor can, in addition, form a closed optical loop coupled to the optical path between the laser and detector. This results in a resonant condition in the loop corresponding to a Fabry-Perot cavity at an RF resonance. The principal source of signal modulation for the sensor is obtained from microbending amplitude modulation, whereas phase modulation is absent.<>