Bright optical spatial solitons in a photovoltaic photorefractive waveguide exhibiting the two photon photorefractive effect

We investigate for the first time, photorefractive solitons in a two photon photorefractive waveguide which also exhibits the bulk photovoltaic effect. The dynamical evolution equation of such solitons has been obtained under the paraxial ray approximation along with the Wentzel-Kramers-Brilluoin Jefferys (WKBJ) approximation. The existence curve for the solitons is derived and four distinct regions of power have been identified in the absence of waveguiding depending upon the threshold power for self trapping. Bistable states have been observed to be present. We have studied the effect of the planar waveguide and found that it enhances the self trapping nonlinearity and hence results in a reduction of the threshold power required for formation of the soliton. The propagation of the light beam is studied for various different strengths of the waveguide. A beam which would not have normally been self trapped can now become a soliton by virtue of the planar waveguide structure. Finally, we investigate the linear stability of these solitons by both, the Lyapunov method and numerical simulations.