This paper investigates the resonantly enhanced nonlinearity in active-medium densely doped composite materials the interparticle collective effects due to the high concentration of dopants significantly enhances the nonlinear index of refraction and results in a density- dependent distortion of the dispersive spectra. Two types of active composite materials, organically modified silicate (ORMOSIL) incorporated with perylimide dye molecules and silica incorporated with erbium ions, which represent, respectively, molecular and atomic nonlinear system, are examined. Perylimide dye doped ORMOSILs exhibit more obvious collective effects at a relative lower doping level than erbium ions in silica. The enhancement of nonlinear index of refraction in active-medium densely doped composites provides a new possibility for the low-intensity operation of switching devices and self-guiding nonlinear devices. The gain properties are also studied.
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