A Wavelength-Diversity Method for Complete Spatial Polarization Profiling in Optical Fibers

Fully distributed optical-fiber sensing (FDOFS) systems are developing rapidly and offering significant advantages for measurement functions in a variety of industrial applications. Polarization techniques are well established in FDOFS and the analysis of polarization-mode dispersion (PMD) for optical-fiber telecommunications. However, a major problem has been of determining, from one end of the fiber, the complete spatial distribution of the full polarization properties of a monomode optical fiber, along its length, with some specified spatial resolution (~1 m). This paper will present the theoretical framework for provision of this full polarization-profile information and thus for measuring the spatial distribution of any parameter, external to the fiber, which can modify its polarization behavior, such as strain. The techniques comprise a wavelength-diverse extension of polarization-optical time-domain reflectometry and necessitate on-line processing. Details of the physical principles and the polarimetry will be presented. The practical techniques can be extended, importantly for the oil and gas industries, to the distributed measurement of fluid pressure. Extensions also are possible to electric and magnetic field distributions. Finally, it is possible fully to characterize the PMD profile of a telecommunications fiber and, in particular, to identify any sections with anomalously large values of PMD.