Nonlinear interaction between non-orthogonally polarization-multiplexed signals in fiber transmission with polarization-dependent loss

Abstract

Polarization-division-multiplexing (PDM) is widely used in fiber transmission systems, wherein fiber nonlinearity is a crucial issue to be considered. Conventionally, the Manakov equation has been used to analyze the nonlinear propagation properties of PDM signal lights, which describes the nonlinear interaction between orthogonally polarized lights. However, because the polarization states of PDM signals are not necessarily orthogonal in transmission systems with polarization-dependent loss (PDL), it is not certain if the Manakov equation is applicable to such systems. Therefore, this study presents a wave equation that describes the nonlinear interaction between non-orthogonally polarized PDM signal lights. We derive a formula that considers the nonorthogonality resulting from PDL. Calculation based on the formula is carried out, the result of which shows that the nonlinear wave equation assuming orthogonal PDM signals results in negligible errors in effect when treating nonorthogonal PDM signals.