Design criterion of polarization-time codes for optical fiber channels

Coherent detection with Polarization Multiplexing (PolMux) is the most promising technique for future optical fiber transmission systems. However, the optical channel suffers from non-unitary impairments known as Polarization Dependent Loss (PDL). Space-Time coding, originally designed for wireless Rayleigh fading channels, was proven to be capable of mitigating PDL. Coding gains of ST codes were evaluated through simulations and experiments that showed differences in their performance on the optical channel and on the wireless channel. In this paper, we derive an upper bound of the pairwise error probability of an optical channel considering the PDL effect. This upper bound explains the performance of ST codes used to mitigate PDL and yields the design criterion that a code should satisfy in order to completely mitigate PDL.