Long-range interference effects of soliton reshaping in optical fibers

We report the observation of spectral oscillations at the output of an optical fiber after the propagation of a reshaped optical soliton over several soliton periods. The experimental results are in good agreement with the results of an analytical study that permits the calculation of the radiated field associated with a hyperbolicsecant- shaped input pulse, after a few soliton periods of propagation. For a nonsoliton input we show that the spectra of the asymptotic soliton and of the radiated field, which is stripped from the input pulse, remain overlapped during propagation, and the phase difference between the two fields is both distance and frequency dependent. This causes an interference that gives rise to the observed oscillations. Furthermore, a numerical simulation that uses a split-step Fourier-transform technique gives results that agree well with the experimental observations.