Measurement of polarization-mode dispersion in single-mode fibers with random mode coupling

A simple frequency-domain technique for measuring polarization-mode dispersion in single-mode fibers with random mode coupling is used to give what is to my knowledge the first direct experimental demonstration of the transition of the dispersion from a linear length dependence to a square-root-of-length dependence. Sensitivity to external perturbations is demonstrated by an order-of-magnitude increase in dispersion when the fiber is removed from a conventional spool and placed on a large-diameter drum. An expression for the length-dependent probability density function that describes the dispersion for highly coherent sources is also presented and confirmed experimentally.