Fabrication and characterisation of a CdS-doped silica-on-silicon planar waveguide

A planar silica-titania waveguide doped with CdS nanocrystallites has been fabricated on a silicon substrate. A passive nanoporous host layer and a pure silica buffer layer, of thickness 2.2 and 7.5 mu m, respectively, were deposited by the sol-gel technique. Crystallites were then precipitated in the porous matrix by soaking in a CdF2 solution followed by reaction in H2S gas, and a sputtered layer of silica was used to seal the structure. The absorption spectrum of an equivalent film indicates crystallites with radii up to similar to 26 Angstrom, while energy dispersion spectroscopy indicates a dopant concentration of similar to 0.5 volume%. The third order optical nonlinearity (Kerr effect) was measured using an m-line technique, yielding a value of -5 x 10(-9) cm(2)/kW.