Optical properties of epitaxial PLZT thin films fabricated by a sol-gel method

The composition dependence near the morphotropic phase boundary (MPB) composition of refractive index and electric-optic (EO) coefficient of the epitaxial (Pb_1-x, La_x)(Zr_1-y, Ti_y)_1-x4/O₃ [PLZT] thin films were investigated. PLZT films were fabricated on Nb doped SrTiO₃ [Nb-STO] (100) substrates by a sol-gel method. The TE- and TM-mode of optical properties were measured separately. Depending on La content the refractive index were varied up to 2 %. This is adequate for fabrications of waveguide structures. Birefringence became small from 4×10^-3 to 1×10^-3 as the crystal structure became close to cubic. The EO coefficient of PLZT (9/65/35) thin films was 45 pm/V, and only a small polarization dependence of the EO coefficient was observed. PLZT optical waveguide that was structured changing PLZT compositions was fabricated on Nb-STO substrate. TE- and TM-modes have similar EO coefficients of 41-42 pm/V.