Capacity analysis of signaling on the continuous spectrum of nonlinear optical fibers

This paper investigates the capacity of signaling on the continuous spectrum (CS) of optical fibers as defined by the nonlinear Fourier transform (NFT). The channel model of such NFT-based optical fiber communication systems is studied based on the behavior of the propagated optical signal in the time domain for an asymptotically long fiber length. The derived channel model is validated using simulation for different scenarios of practical interest. An important characteristic of the channel in the nonlinear spectral domain is the strong dependence of noise to signal. A variance normalizing transform is applied as a tool to obtain an estimate on the capacity of the underlying channel. The results predict a remarkable capacity for signaling on CS, which can be utilized as an extra degree of freedom along with discrete spectrum (i.e., soliton transmission). It is further observed that the channel capacity of signaling on CS saturates at high signal power despite the linearizing capability of the NFT.