Efficient Precoding Scheme for Dual-Polarization Multi-Soliton Spectral Amplitude Modulation

Soliton pulses are special waveforms to account for nonlinearity in fiber optical communication. They can be represented in a nonlinear spectrum by eigenvalues and spectral amplitudes which have simple transformation equations along the ideal link. This motivates to encode data in the nonlinear spectrum. In this paper, we consider dual-polarization modulation of spectral amplitudes, and show that they become highly correlated during propagation along a noisy fiber link. Thus, joint equalization is generally needed for detection at the receiver. We propose a simple precoding scheme that almost removes these correlations. This allows to significantly improve the detection performance even without any complex equalization. The spectral amplitudes are transformed into pairs of common and differential information part. We show that the differential part is almost preserved along the link, even in the presence of noise. Thus, it can be directly detected from the received spectral amplitudes with high reliability. Exploiting the differential gain of the precoding allows much higher bit rates at comparable error rates. We analyze our precoding scheme and verify its performance gain in split-step-Fourier simulations by comparing it to the conventional independent modulation of spectral amplitudes for first and second order solitons.