Photorefractive screening solitons of high and low intensity

We analyze self-trapping of optical beams in photorefractive media for low irradiances that are typical of cw lasers and high irradiances that are typical of short-pulse lasers and obtain bright and dark soliton solutions in one transverse dimension. Whereas in the low-intensity regime photorefractive screening solitons are trapped by the refractive-index change that is related to the electric field associated with ionized donors or accepters, in the high-intensity regime the index is related to the field that is also associated with free carriers. Since the time necessary to form the soliton scales inversely with the intensity, one expects a very fast response time in the high-intensity regime, and this suggests attractive applications in optical switching and reconfigurable optical waveguides. We show that throughout the entire intensity range dark solitons require lower voltages and less energy per pulse for applications than do bright solitons. (C) 1996 Optical Society of America