Theoretical analysis and measurement of the effect of fiber twist on the polarization OTDR of optical fibers

With the growing interest in polarization-mode dispersion (PMD), the technique of polarization optical time domain reflectometry (POTDR) has received attention because of its ability to measure birefringence characteristics along a fiber. PMD measurements using POTDR normally assume that the linear birefringence /spl beta//sub L/ is the dominant birefringence in the fiber, such that the circular birefringence /spl beta//sub C/ can be ignored, allowing the PMD due to /spl beta//sub L/ to be inferred from the periodicity of the POTDR output. In this paper we induce circular birefringence by fiber twist and show that even small values of /spl beta//sub C/ will have a considerable influence on the POTDR output and can lead to an overestimate of the fiber's PMD.