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 β_L is the dominant birefringence in the fiber, such that the circular birefringence β_C can be ignored, allowing the PMD due to β_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 β_C will have a considerable influence on the POTDR output and can lead to an overestimate of the fiber´s PMD.