  A scanning white light interferometer is developed to measure the distributed
polarization coupling (DPC) in high birefringence polarization maintaining
fibers (PMFs). Traditionally, this technique requests only one polarization
mode to be excited or both polarization modes to be excited with equal
intensity in the PMF. Thus, an accurate alignment of the polarization direction
with the principal axis in PMF is strictly required, which is not facilely
realized in practical measurement. This paper develops a method to measure the
spatial distribution of polarization mode coupling with random modes excited
using a white light Michelson interferometer. The influence of incident
polarization extinction ratio (PER) on polarization coupling detection is
evaluated theoretically and experimentally. It is also analyzed and validated
in corresponding measurement that the sensitivity of the polarization coupling
detection system can be improved more than 100 times with the rotation of the
analyzer.
