Experimental study of high-order soliton propagation in optical fibers

Abstract

In the context of nonlinear fiber-optic propagation, It is important to investigate the validity range of the nonlinear Schrodinger (NLS) equation for high input powers; possible applications to optical transmissions have also been foreseen In this regime.1 To this end, we experimentally studied high-order soliton propagation, which shows in a spectacular way the effect of Kerr nonlinearity; existing data2 are not completely clear above N = 3, especially regarding the optical spectrum. The pulses, 14-ps FWHM, were produced by a color center laser tuned around 1.5 µm, and launched into a 1360-m optical fiber, corresponding to about one-sixth of the soliton period. The output autocorrelation trace shows an increasing number of well-resolved peaks with the increase of the input power. Detailed features of the spectral shape, like a central dip and several lateral maxima, over a few nanometers span, are clearly resolved in the experimental data. Both autocorrelation and spectrum are in surprisingly good agreement with theory compared with previous results. Solitons until N = 8 are well identified, while for greater input powers the NLS equation seems to break; the output pulse is always a sharp peak (500 fs) with a polarization-dependent pedestal; the spectrum shifts toward lower frequencies, presumably because of the Raman effect.