| The Optical Fiber Infrasound Sensor (OFIS) is an interferometric pressure transducer consisting of a pair of optical fibers helically wrapped about a compliant tube. While the OFIS has been successfully deployed for nearly a decade, its performance has been plagued by downtime due to polarization fading (resulting from no interference fringe intensity) and a nearly continuous change in its pressure sensitivity. This thesis explores the use of very expensive polarization maintaining fiber and inexpensive Faraday mirrors, both of which solve the polarization fading issue. Laboratory measurements of the thermal behavior of the pressure sensitivity are found to confirm field tests, but measurements of the temperature dependence of the tube's elastic modulus does not appear to adequately describe the observed behavior. Therefore, a crude analytic mechanical and optical model is explored to help investigate potential causes, however, the simple theory of compound thick cylinders was found to be problematic as a realistic model for the OFIS. |
