Extrinsic optical-fiber interferometric sensor that uses multimode optical fibers: system and sensing-head design for low-noise operation.

We report an extrinsic Fabry-Perot-type optical-fiber interferometric sensor system constructed by using multimode optical fibers. The intermodal noise produced by the multimode optical fibers was suppressed by the use of optical-fiber white-light interferometry and by the consideration given to the sensor-head design. Both a theoretical analysis and an experimental investigation were carried out, and a system signal-to-noise ratio of 45 dB was demonstrated.