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Nonlinear optical materials are essential components of functional photonic devices for optical communications, in particular, all-optical switching devices. Nonlinear switching devices can be based on optical waveguide structures which provide strong beam confinement in prescribed patterns. In these devices, the intensity of an optical signal is used as the parameter that causes switching between two output channels, thus performing logic operations. In the last few years, composite glasses formed by embedding semiconductor or metal nanoclusters in glass have attracted much attention as promising materials in this research area [1]. In particular, metal nanocluster-doped glasses, i. e., glasses which contain crystallites of metals, show an enhanced third-order susceptibility [2], whose real part is related to the intensity-dependent refractive index. The technological interest is strengthened by the general interest in strongly quantum-confined electronic systems which exhibit several effects deriving from the increased electronic density of states near the conduction-band edges. This suggested the introduction for metal nanoclusters-doped composites of the term metal quantum-dot composites (MQDC), in analogy to multiple-quantum-well devices [3]. Nonlinear optical materials based on glasses are intrinsically attractive for photonic-device applications owing to their high transparency, ease of fabrication, durability and thermomechanical stability. Moreover, it should be mentioned the compatibility of materials and fabrication processes with silicon-based electronic materials. |
