Abstract

We have explored the power dependence of dark optical solitons in both infinite and finite-width background pulses through numerical solutions of the nonlinear Schrodinger equation. The dark optical soliton is found to have a critical power for the formation of the high (unity) contrast fundamental soliton; at higher powers additional soliton pairs of lower contrast are generated. At all powers examined, the fundamental soliton retains its unity contrast and maintains a velocity identical to that of the background pulse. Subsequent experiments showed good agreement with these results at low and moderate powers but deviated at powers significantly higher than the soliton power. At the highest powers the fundamental soliton lost contrast and developed a velocity different from that of the background pulse. This suggested a Raman-induced self-frequency shift. The effect of stimulated Raman scattering was modeled by incorporating an experimentally determined time-dependent Raman response function into our description of the nonlinear susceptibility. Using this model we found essentially no change in dark soliton propagation at moderate power and reproduced the experimentally observed self-frequency shift and loss of contrast at high power. Further studies of dark soliton propagation influenced by Raman scattering and other higher-order nonlinear effects are discussed.

© 1988 Optical Society of America