Abstract

Recently, there has been an increasing interest in studying the properties of annealed proton-exchanged (APE) structures in LiTaO₃ due to its large electro-optical and nonlinear coefficients, as well as a higher optical damage threshold than that of LiNbO₃. Previous studies have indicated the anomalies of waveguides formed in LiTaO₃ [1–5], in particular, an increase of the extraordinary index increment upon annealing [1]. The feasibility of obtaining buried profiles in just a single-step diffusion has also been suggested [2,5], however, could not be verified due to the lack of data from direct measurements of refractive-index profiles. On the other hand, the presence of buried profiles would seriously undermine the adequacy of previous theoretical studies most of which relied on the inverse WKB procedure and monotonically decreasing depth profiles [2]. As for the ordinary index, very scarce information was available on its negative change on account of the absence of guided modes for this polarization and, as a consequence, inapplicability of conventional profile reconstruction methods. Overall, most of the previous studies have been based on indirect approaches, with associated, sometimes questionable, assumptions to deduce information of the actual index profile. Therefore, the importance of direct optical characterization of index profiles for developing and examining theoretical models is quintessential.

© 1996 Optical Society of America