Guided-wave optical properties of sol-gel ferroelectric films

Abstract

Sol-gel processing methods have been used to prepare thin films of lead titanate, Pb(Zr,Ti)O3, and Pb(Mg1/3Nb2/3)O3 on sapphire and single-crystal strontium titanate substrates. These films have been characterized using x-ray diffraction, optical waveguiding measurements at 633 nm wavelength, and optical transmission measurements. The films, in general, contain a mixture of perovskite and pyrochlore phases, with perovskite formation being favored by higher processing temperatures, by use of the SrTiO3 substrates, and by the addition of excess lead precursor compound to the starting solutions. The films have refractive indices close to, but lower than, those of the corresponding bulk materials. The reduction of the refractive indices from the bulk values is believed to result primarily from incomplete densification. Transmission measurements show that the optical dispersion in the PbTiO3 films is similar to that in the bulk crystal. Although all films showed scattering losses, waveguiding over distances up to 1 cm was observed in some films. For multimode waveguides, conformity of the mode indices to those expected for a uniform guide is suggested as one test of film uniformity as a function of depth.