Raman gap solitons

Summary form only given. The phenomena predicted to occur in nonlinear periodic structures include optical bistability, self-pulsation, pulse compression, Bragg soliton propagation, and the formation of gap solitons. Most of these phenomena have been observed recently in fiber Bragg gratings. One notable exception is the stationary gap soliton which has not been observed. The problem is that a periodic structure is highly reflective at frequencies within the band gap. Thus it is extremely difficult to couple enough light into the structure to shift the band gap and create gap solitons. In fact the grating transmissivity is proportional to the velocity of the gap soliton which implies that an attempt to launch a zero-velocity gap soliton in the middle of the stop band would result in the reflection of the entire input pulse. We show that it is possible to launch gap solitons by exciting a grating with an intense pulse so far detuned from the Bragg frequency that it does not interact with the grating. Because of this detuning the pump pulse is not reflected, making it possible to couple most of its energy into the medium.