Metal Quantum Dot – Glass Composites as Nonlinear Optical Materials for Photonic Applications

Technology has made great developments in electronic device speed, but optical devices operate in the time-domain unreachable to electronics. Optical devices have no competition in the time domain less than 1 picosecond. Photonic devices can switch and process light signals without converting them into electronic form. Major advantages of these devices are speed and conservation of bandwidth. Switching is performed through changes in refractive index of the material that are proportional to the light intensity. This particular feature is the result of third-order dielectric susceptibility, χ (3) , or “optical Kerr susceptibility”, which is related to the nonlinear part of the total refractive index. Future prospects in photonic switching and information processing critically depend on the progress towards improved photonic materials with significantly enhanced Kerr susceptibilities. Optically isotropic materials like silica glasses that have inversion symmetry intrinsically possess some third-order optical nonlinearities at λ = 1.06 µm. This, combined with extremely low absorption coefficient of silica glasses, allows all-optical switching between two waveguides embedded in a silica fiber simply by controlling the optical pulse intensity. Plasmonic nanoparticles in dielectric media lead to the generation of surface-plasmons in the neighborhood of dielectric surfaces, resulting in a local evanescent field that experiences dielectric confinement. This field affects the coherent oscillation of dipoles in the conduction band thus enhancing the effective third-order nonlinearity. The strength of the nonlinearity is influenced by controlling the “surface plasmon resonance” (SPR) band by tuning the size and shape of the nanomaterials. The incorporation of metal nanoclusters in glasses have been found to induce desired third-order optical non-linearities in the composite at wavelengths very close to that of the characteristic SPR of the metal clusters. Ion implantation is a potential method for inducing colloid formation at a high local concentration unachievable by chemical doping or melt-glass fabrication process and for confining the nonlinearities to specific regions in various host matrices. Metal-ion induced colloid generation in bulk silica glasses has shown that these nanocluster–glass composites under favorable circumstances have significant enhancement of χ (3) with picosecond to femtosecond temporal responses. The extraordinary achievements in developing such novel photonic materials have opened the way for advances in photonic devices, such as all-optical switching, coupled waveguides as a directional coupler, etc.