Abstract

We have observed experimentally, and modelled both analytically and numerically, the appearance of oscillations in the output spectrum after a reshaped optical soliton has propagated over a few tens of soliton periods in an optical fiber. An optical pulse with sufficient intensity will reshape into a fundamental soliton after propagating a few soliton periods by stripping off the non-soliton part of its energy, which will propagate radiatively in the fiber. This radiative field has a spectrum that is overlapped with the output soliton spectrum, and the phase difference between the two spectra is both frequency and distance dependent. Thus the interference between the two fields will cause a modulation of the output field spectrum, with peaks at discrete frequencies that depend on the distance of propagation. An analytical study, based on the analysis in Ref. ¹, gives results in good agreement with the observed spectra. This study, carried for hyperbolic secant-shaped input pulses for which the soliton part of the asymptotic solution of the nonlinear Schrödinger equation is exactly known,² allows the calculation of the non-soliton field after several soliton periods of propagation, and therefore the spectrum of the total output field. In addition, numerical results obtained by a split-step Fourier transform technique show good agreement with the analytical results.

© 1992 Optical Society of America