The per-sample capacity of zero-dispersion optical fibers

The capacity of the channel defined by the stochastic nonlinear Schrödinger equation, which includes the effects of the Kerr nonlinearity and amplified spontaneous emission noise, is considered in the case of zero dispersion. For the first time, the exact capacity subject to peak and average power constraints is numerically quantified using dense multiple ring modulation formats. It is shown that, for a fixed noise power, the per-sample capacity grows unbounded with input signal power. A distribution with a half-Gaussian profile on amplitude and uniform phase is shown to provide a lower bound to the capacity which is simple and asymptotically optimal at high SNRs.