SOLITONS NEAR THE ZERO DISPERSION WAVELENGTH OF SINGLE-MODE FIBERS.

The propagation characteristics of nonlinear pulses in the vicinity of the zero dispersion wavelength are studied. It is found that immediately after the pulse is launched, part of it is shifted toward the anomalous dispersion regime, while the other part is shifted toward the normal dispersion regime. That is, the frequency spectrum evolves into a two-peak structure with a peak on either side of the zero dispersion point. It is found that the peak in the normal regime corresponds to a dispersive wave, while that in the anomalous regime represents a soliton. The soliton and dispersive wave have different group velocities. Hence they separate from each other. For those cases where the initial pulses are launched at the zero dispersion point, on the average approx. 60% of the initial energy goes into the solitons. This proportion increases if the initial carrier frequency is inside the anomalous regime. However, for the same width, the energy required for a soliton increases with wavelength because of the increase in dispersion. Hence, for a given pulse width, there is an optimal operating wavelength at which the power needed to produce a soliton is minimum. The effect of the Raman frequency downshift on these solitons is also discussed.