Analysis of a Polarization-Maintaining Optical Fiber Interferometer for Simultaneous Measurement of Acoustic Pressure and Temperature

An all polarization-maintaining fiber Mach-Zehnder interferometer for simultaneous measurement of acoustic pressure and temperature is examined. Measurements by Farahi et al. (1990) indicate that the cross-sensitivity between temperature and axial strain may be significant for a polarization-maintaining fiber Fabry-Perot interferometer; however, no one has examined the significance of cross-sensitivity for the Mach-Zehnder case. Sensitivities to acoustic pressure and temperature, and the cross-sensitivity generated by simultaneous disturbances are determined both analytically and numerically. The fiber’s relatively high temperature sensitivity compared with its acoustic pressure sensitivity suggests that a short length of sensing fiber is sufficient for use as a temperature sensor with little or no interference from acoustic pressure. To measure acoustic pressure, however, a straight length of the fiber examined in this study is not sufficient. In practice, this sensing fiber could be coiled around a compliant cylinder or into a small diameter sensing element to enhance longitudinal strain and thus sensitivity. Results show that in either case, the cross-sensitivity is extremely small and can be ignored.