  Higher-order solitons inherently possess a spatial periodicity along the
propagation axis. The pulse expands and compresses in both, frequency and time
domain. This property is exploited for a bandwidth-limited receiver by sampling
the optical signal at two different distances. Numerical simulations show that
when pure solions are transmitted and the second (i.e., further propagated)
signal is also processed, a significant gain in terms of required receiver
bandwidth is obtained. Since all pulses propagating in a nonlinear optical
fiber exhibit solitonic behavior given sufficient input power and propagation
distance, the above concept can also be applied to spectrally efficient Nyquist
pulse shaping and higher symbol rates. Transmitter and receiver are trainable
structures as part of an autoencoder, aiming to learn a suitable predistortion
and post-equalization using both signals to increase the spectral efficiency.
