LARGE REFRACTIVE-INDEX AND INTERPARTICLE-INTERACTION-INDUCED NONLINEAR MODULATION IN DENSELY DOPED COMPOSITE-MATERIALS

We have performed a study of the population dynamics in a composite, i n which the active medium is densely doped, by considering the interpa rticle interaction between the nearest neighboring active particles. A model is presented to describe the nonlinear modulation induced by in terparticle collective effects and upconversion in the resonantly enha nced nonlinearity and its response to an input optical signal in such a densely doped composite. The results show that the nonlinear refract ive index can be greatly increased with unchanged or slightly reduced transient response time. This is expected to have potential in lowerin g the critical switching intensity of bistable switching devices witho ut sacrificing switching speed. We examined two typical composites: fa re-earth densely doped silica and perylimide-dye densely doped polymer /glass composites. It is found that perylimide-dye densely doped polym er/glass composite is more suitable for the switching application due to its large nonlinear refractive index and fast response time at rela tively low optical intensity.