Selective-area doping of porous solgel films for integrated optics.

A technique for doping of porous films by surface adsorption of ions from aqueous solution is demonstrated. Fabrication of the films by use of the solgel technique gives a nanometer-scale porosity, which provides high doping levels and homogeneity. Doping through a masking layer patterned by photolithography is thus possible. With Pb as a dopant, lead silicate films with refractive indices of 1.46 to 1.55 were obtained, with submicrometer patterning resolution. Linear control of the refractive index is achieved through variation of the solution pH. Applications of this technique in integrated optics and optical elements are proposed.