Polarization effects and performance of fiber optic recirculating loops

Polarization effects such as PMD and PDL in a straight-line optical fiber communication system are random due to the random birefringence of optical fiber. However, since there is periodicity in a fiber recirculating loop, the polarization effects are quite different than in a straight line. Theoretically and experimentally we analyze the polarization effects in a loop and their effect on performance and the evolution of the state of polarization of a channel. Using this analysis, we are able to better understand the physical impact of the evolution of the state of polarization of a channel on performance. We show that loop-synchronous polarization scrambling is an effective way of breaking this periodicity in an attempt to make the recirculating loop perform more like a straight-line system.