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, in which the active medium is densely doped, by considering the interparticle interaction between the nearest neighboring active particles. A model is presented to describe the nonlinear modulation induced by interparticle collective effects and upconversion in the resonantly enhanced nonlinearity and its response to an input optical signal in such a densely doped composite. The results show that the nonlinear refractive index can be greatly increased with unchanged or slightly reduced transient response time. This is expected to have potential in lowering the critical switching intensity of bistable switching devices without sacrificing switching speed. We examined two typical composites: rare-earth densely doped silica and perylimide-dye densely doped polymer/glass composites. It is found that perylimide-dye densely doped polymer/glass composite is more suitable for the switching application due to its large nonlinear refractive index and fast response time at relatively low optical intensity