Study of anomalous behaviour of LiTaO3 during the annealed proton exchange process of optical waveguide´s formation - comparison with LiNbO3

This paper deals with detailed study of changes that lithium tantalate (LT) and lithium niobate (LN) single crystals undergo during the APE (Annealed Proton Exchange) process of optical waveguides´ formation. It is a well-known fact that several cases of anomalous behaviour are connected to the APE:LT samples, bringing thus serious limitations for the practical utilization of the APE:LT waveguides. As the LT crystal posseses even better optical properties than the LN (e.g., it is less susceptible to optical damage), it is highly desirable to provide research focused on its behaviour during the APE in order to get a control over fabrication of the APE:LT devices.
Neutron Depth Profiling (NDP), Elastic Recoil Detection Analysis (ERDA) and High Ion Energy ERDA (HIERDA) were performed to study changes in the surface of the LT and LN Z-cut wafers caused by the APE treatment and to determine the concentration depth profiles of the exchanged ions (lithium and hydrogen). Information on modifications of the crystals during the APE were obtained using X-Ray Diffraction (XRD) analysis. Optical/waveguiding properties of the samples were obtained by means of the standard mode spectroscopy at 633 nm.
The experiments proved that the LT is significantly less affected by the APE process compared to the LN and that most characteristics of the APE:LT layers are relatively easily restored back towards that of the virgin crystal by the annealing process.