Shannon's theory in nonlinear systems

An exponential growth in the capacity of optical networks has taken place over the last decade, but the extent to which future capacity growth can continue is limited by physical laws governing signal propagation through optical fibres. While the classic theory of communication developed by Claude Shannon allows the analytical calculation of information spectral density limits for linear channels with white additive Gaussian noise, the nonlinear nature of optical fibres makes these limits much more difficult to determine for long-haul optical transmission. Accurately predicting the ultimate limits has been the focus of much recent research. This paper describes the sources of linear and nonlinear signal impairments, reviews progress on extending Shannon's theory to the case of nonlinear signal propagation, and discusses new optical and electronic signal processing techniques that may be used to approach the Shannon limit in future networks.