Nonlinear fourier transform in optical communications

Abstract

Information traffic demands have increased dramatically in recent years, leading to the so called “Capacity Crunch” in optical fiber. There are two possible ways to solve this problem. The first is using Space Division Multiplexing to increase the capacity. This requires setting up a completely new infrastructure with multimode fibers. The second is to improve the capacity of the current infrastructure with novel transmission techniques. A promising approach for the second solution is Nonlinear Frequency Division Multiplexing (NFDM) [1], see also 2] for an overview. This approach improves on Wavelength Division Multiplexing (WDM) [3] by replacing the Fourier transform by the Nonlinear Fourier Transform (NFT). The NFT hinges on the crucial observation that a linear operator exists which is associated with the propagation equation and whose spectrum is invariant under propagation. In NFDM, information is encoded in the spectrum of this operator. In the absence of noise, the nonlinear fiber channel is decomposed into parallel independent scalar channels in the nonlinear Fourier domain. As a result, inter-symbol interference (ISI) is absent with nonlinear multiplexing. Previously, encouraging results have been found for normal dispersion fibers [4]. We present achievable rates for NFDM in standard fibers with anomalous dispersion.