Fundamental Limitations of Digital Back Propagation due to Polarization Mode Dispersion

Performance limits in optical communications due to fiber nonlinearity

“…Conceptually it is readily argued that a polarization adjustment should ideally be applied at around half the polarization walk off length, with an increased frequency increasing the accuracy at the expense of complexity. For practical purposes, the ratio of polarization rotations to nonlinear steps should be a rational number, and whilst initial progress has been made by making this ratio an integer [264] or even unity [265] further optimization is required. In the case of OPC based links, it may be argued that provided the OPCs are spaced at less than half of the polarization walk off length, each adjacent segment between OPCs will have approximately identical polarization distributions for the channels, enabling effective nonlinearity compensation since the degree of random polarization rotation experienced by the signals before they are compensated is significantly reduced [245].…”

Digital backpropagation accounting for polarization-mode dispersion

“…Several variations of DBP have been proposed and demonstrated including transmitter- [9], receiver-side [10], and both transmitterand receiver-side [11] compensation. Having exact knowledge of the fiber parameters, it is believed that the deterministic nonlinear signal-signal interactions are completely removed using DBP and that the performance of a fiber-optical system is limited by the uncompensated stochastic effects, such as amplified spontaneous emission noise, which leads to signal-noise interactions [12], and PMD, leading to polarization-dependent nonlinear interactions [13][14][15][16][17], which considerably undermine the effectiveness of DBP. In order to account for the signal-noise interactions, a modified DBP algorithm [18] has been proposed that takes into account the additive noise, getting the performance of the optical fiber channel closer to the fundamental limits.…”

Modified Digital Backpropagation Accounting for Polarization-Mode Dispersion

“…DBP compensates for the deterministic fiber nonlinear impairments by solving the nonlinear propagation equation using the split-step Fourier (SSF) method and backpropagating the received optical field with inverted channel parameters. It is believed that the deterministic nonlinear signal-signal interactions are completely removed using DBP and that the performance of a fiber-optical system is limited by the uncompensated stochastic effects, such as amplified spontaneous emission noise, which leads to signal-noise interactions, and PMD leading to polarization-dependent nonlinear interactions [2][3][4].…”