Temperature sensing using single-mode fibers has been demonstrated using both Michelson and Mach-Zehnder fiber interferometers and by polarization mode interference in a single-fiber polarimetric configuration.1,3 In the latter approach the sensitivity is a function of the dependence of the fiber birefringence on temperature, which, for thermally stressed high-birefringence fibers, can be strong. In general, however, the overall sensitivity of the polarimetric approach is less than that exhibited by the interferometric configurations. Due to this high sensitivity, the intrinsic unambiguous sensing range of the interferometric technique is small. A range of demodulation techniques, such as pseudoheterodyne detection, has been developed in recent years, which allows the total phase excursion of the interferometer to be electronically tracked. The use of such processing techniques, however, only partially alleviates the ambiguity problem associated with the interferometric transfer function as the absolute measurand value cannot be determined when the sensor is initialized.
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