A MODIFIED SPLIT-STEP FOURIER SCHEME FOR FIBER-OPTIC COMMUNICATION SYSTEMAND ITS APPLICATION TO FORWARD AND BACKWARD PROPAGATION

Abstract

<p>In the passed half century, great improvements have been achieved to make fiber-optic communication systems overweigh other traditional transmission systems such as coaxial systems in many applications. However, the physical features including optic fiber losses, group velocity dispersion (GVD) and nonlinear effects lead to significant system impairments in fiber-optic communications. The nonlinear Schrödinger equation (NLSE) governs the pulse propagation in the nonlinear dispersive media such as an optical fiber. A large number of analytical and numerical techniques can be used to solve this nonlinear partial differential equation (PDE). One of theses techniques that has been extensively used is split-step Fourier scheme (SSFS) which employs the fast Fourier transform (FFT) algorithm to increase the computational speed.<br />In this thesis, we propose a novel lossless SSF scheme in which the fast decay of the optical field due to fiber losses is separated out using a suitable transformation and the resulting lossless NLSE is solved using the symmetric SSF scheme with some approximations. The various symmetric SSF schemes in terms of accuracy for the<br />given computational cost are compared. Our results show that the proposed scheme could lead to one or two orders of magnitude reduction in error as compared to the<br />conventional symmetric SSFS when the computational cost is fixed. The proposed<br />scheme can be also used as an effective algorithm for digital backward propagation<br />(BP) too. Our numerical simulation of quadrature amplitude modulation-16 (QAM-16)<br />coherent fiber-optic transmission system with digital BP has shown that the bit error<br />rate (BER) obtained using the proposed scheme is much lower than that obtained<br />using the conventional SSF schemes.</p>