Sol-gel derived La-doped PbTiO₃ waveguides

PbTi03-based ferroelectric films are attractive materials for passive and active waveguides due to their high refractive indices (> 2.0), small attenuation losses (1-6 dB/cm) and low processing temperatures (< 600C). A series of solgel derived La-doped PbTiO3 waveguides was prepared on Coming 7059 glasses. 0.5M precursor solutions of Pb1-x/100 Lax/100Ti1-x/400O3 with x = 0, 5,10,15, 20, 25,28,30 and 32 were spincoated on the substrates and fired to 400C, 500C and 600C for 30 mins. XRD was used to determine the phase assembly present in the films as a funcion of La stoichiometry and firing temperature. The presence of La seemed to aid in achieving the formation of single-phase perovskite films. Transmission spectra obtained using a UV-Vis spectrometer provided information on band gap energies; and the spectra were used to calculate the refarctive indices and extinction coefficients based on the envelope method. The refractive index decreased and band gap increased with increasing La content in the films. The waveguiding properties and optical attenuation were studied by prism coupling using a HeNe laser and rutile prism. The optical losses are discussed with regard to composition (especially La content), phase assembly and inicrostmcture of the films. Crystalline PLT 28 films exhibit attenuation loss as low as 1.4 dB/cm, which represent the lowest reported value for any solgel or sputtered PLZT film.