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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.

Planar lightwave circuits (PLCs) provide various important devices for optical wavelength division multiplexing (WDM), time division multiplexing (TDM) systems, subscriber networks and etc. This paper reviews the recent progress and future prospects of PLC technologies including arrayed-waveguide grating (AWG) wavelength filters, optical add/drop multiplexers (ADM), strictly non-blocking matrix switches, programmable dispersion equalizers and hybrid optoelectronics integration technologies.

Direct measurement of the ultimate limit of the polarization cross talk of the birefringent fibers caused by anisotropic Rayleigh scattering (ARS) is presented theoretically and experimentally by using polarization optical time-domain reflectometry (POTDR). With POTDR, ARS appears as the bias existing in the backscattered power ratio between the cross-coupled and excited modes. A value twice that of the bias corresponds to the depolarization ratio representing the anisotropy of the fiber core material. The biases measured by birefringent polarization-maintaining fibers are all within 3% of the mean value 0.048.