Cross polarization interference cancellation for fiber optic systems

One method of improving the bandwidth efficiency of a fiber optic communication system is to use polarization multiplexing, where independent signals are transmitted with orthogonal polarizations. A receiver can reconstruct both signals without interference by tracking their polarizations as long as they remain orthogonal. Since orthogonality is lost to some extent during propagation through an optical fiber, a polarization tracking system will incur a signal crosstalk penalty. A new and practical method using cross polarization interference cancellation (XPIC) is proposed to correct for the loss of orthogonality incurred during propagation through an optical fiber. The system optimally reconstructs both signals at the receiver and eliminates the need for conventional polarization tracking. XPI cancellation uses fewer lasers than conventional polarization interleave multiplexing and can also mitigate effects that currently limit link performance such as chromatic and polarization mode dispersion (PMD).