Optical Back Propagation With Optimal Step Size for Fiber Optic Transmission Systems

An optical back propagation scheme consisting of an optical phase conjugator, fiber Bragg gratings (FBGs), and highly nonlinear fibers (HNLFs) is investigated. Transmission fiber dispersion is compensated by the FBGs and the nonlinearity is compensated by HNLFs. Several sections of FBGs and HNLFs are concatenated in a way analogous to the split-step Fourier scheme used for solving the nonlinear Schrödinger equation. The optimum accumulated dispersion of each section of the FBG and the optimum nonlinear phase shift of the each section of the HNLF are calculated by minimizing the mismatch between the area under the exponentially increasing nonlinearity profile and its stepwise approximation. The method of Lagrange multipliers is used for optimization. The proposed optimization technique leads to significant performance improvement and/or reach enhancement as compared to uniformly spaced sections, for the given number of sections.