Capacity of fiber: nonlinear propagation and information theory

This talk summarises recent information theoretic developments in the context of the optical fiber communication channel. While it has been appreciated for a long time that nonlinearities can degrade information transmission through optical fiber, it has been difficult to systematically apply information theoretic methods to the fiber channel. Rather than tackle this problem head on, the approach we have taken in our work is to treat simplified channel models that retain some of the essential features of the original propagation equations, but are more tractable from an information theoretic perspective. We have also applied perturbation theory to directly compute the channel capacity in the case of weak nonlinearities. Based on this work, the sources of nonlinear impairments of channel capacity can be categorized into three broad classes: out of band power loss, nonlinear crosstalk between channels and noise amplification. The relevant mechanisms have been previously identified in specific contexts, but the emphasis here is to unify a number of seemingly disparate phenomena from the point of view of channel capacity.