Measurement of spatial distribution of mode coupling in birefringent polarization-maintaining fiber with new detection scheme.

We present a new detection scheme for measuring the spatial distribution of mode coupling in birefringent, polarization-maintaining fibers. The new method canl improve the signal-to-noise ratio by a factor of 100 compared with the previously reported heterodyne-detection scheme. As a result, origin of the mode coupling in a low-cross-talk, birefringent fiber is clarified.