Abstract

Crossing may occur when two short pulses of different central frequencies are propagated in an optical fiber. In the anomalous-dispersion range, the pulse with the higher frequency propagates faster and may catch up with the one with lower frequency. During crossing, the two pulses interact through cross-phase modulation. For picosecond-range solitons, the effects of cross-phase modulation in the first-half crossing cancel those in the second-half, so that the individual solitons remain unchanged after a complete crossing. However, for femtosecond-range or ultrashort solitons, individual solitons change owing to higher-order dispersion, shock effects and Raman scattering. In particular, Raman scattering results in energy redistribution between the two solitons. The peak gain of the Raman spectrum in optical fibers is at 440/cm frequency shift, corresponding to a delay time of 75 fs in the Raman response function. Hence, when any two femtosecond-range solitons are separated by a lime period shorter than 75 fs, Raman scattering occurs. In our research, the dependence of the energy redistribution on several input parameters, such as frequency separation, temporal separation, relative phase, and relative intensity, are investigated. A modified beam-propagation method is used for numerical study.

© 1990 Optical Society of America