Raman study of protonated H : LiNbO3 thin film waveguides

Multimode proton exchanged waveguides HxLi1-xNbO3 have been formed in congr uent z-cut substrates using benzoic acid for proton source. The H concentra tion was changed by annealing, applying two different rates of cooling - qu ick (q) and slow (s). The samples were characterized by measuring their ext raordinary refractive index profiles and waveguide Raman scattering. At hig h proton concentrations (x > 0.56), where the beta(i) phases are supposed t o be existing the s- (equilibrium beta(2)/beta P-1 combination) and q- (met astable beta(1) phase) type of samples show very different Raman spectra, b eing also different from the scattering of the pure substrate. This is an e vidence for lattice transformations probably related to the large differenc es in the electrooptic and nonlinear properties of the phases. (C) 1999 Els evier Science B.V. All rights reserved.