Phonon spectra and electro-optic properties of crystalline phases in proton-exchanged LiTaO3 wave guides

Abstract

Annealed proton-exchanged wave guides in X-cut LiTaO 3 were characterized by infrared reflection and Raman scattering spectroscopy. The measured spectra were related to the multiple crystalline phases of H x Li 1Ϫx TaO 3 as identified by direct wave guide index profiling. Unique relationships were found to exist between the crystalline phases and corresponding spectra, which thus can be used to identify phase contents in a given wave guide. Vibrational bands of the studied spectra were correlated with the electro-optic properties of H x Li 1Ϫx TaO 3 phases. Phase-dependent anisotropy of protonic conductivity was predicted based on the observed polarization dependence of OH libration bands. Finally, the electro-optic coefficient r 33 was theoretically estimated for all phases and compared with previously reported experimental data.

Phase composition and stress in LiTaO 3 proton-exchanged optical waveguides

“…According to [10], the changes observed at 899, 952 and 985 cm −1 could be assigned to the β and γ phases, and the change at about 1000 cm −1 , to the δ-phase, respectively. As seen in fig.…”

Infrared spectra of proton-exchanged waveguides in LiNbO3 and LiTaO3

“…This way only the surface phase could contribute to the reflection spectra of multiphase waveguides. The IR reflection spectra contain new bands within the range 890-1010 cm −1 and each phase has its own reflection spectrum [9,10].…”

“…They were compared to the spectra of X-cut PE-LiTaO 3 given in [10] and some correlations with lattice deformations and reflection minimums were made in order to assign the spectral changes to a definite phase. According to [10], the changes observed at 899, 952 and 985 cm −1 in IR-reflection spectra of all samples could be assigned to the ␤-phase, and the change at about 1000 cm −1 to the ␦-phase, correspondingly. Since the second perturbation is much stronger, we should conclude that the surface phase of the waveguides investigated is ␦.…”

Interface and thickness dependent domain switching and stability in Mg doped lithium niobate

“…[50][51][52][53] The original lines of the substrate are still present, but broadened and changed in intensity (Figure 6(a)). A characteristic phonon frequency of 680 cm À1 originated in distortion of Nb 5þ octahedra towards non polar states [52][53][54] exhibits a high intensity in exposed PE areas. Only the edge of a PE band 53 located at 69 cm À1 is visible within the measured spectral range.…”

“…A new peak at 960 cm À1 appears and is assigned to OH -librational bands that are strongly dependent on the proton exchange phase. 54,55 Having assigned spectral characteristics, it is possible to monitor the influence of PE across the sample as well as strains indicated by peak broadening and position shift. 30 In Raman spectra (Figure 6(a)), extracted at different positions on the sample (red: 20 lm thick Mg:LN; blue: exposed PE area; green: 14.1 lm thick Mg:LN above 5.9 lm PE, as also approximately indicated by colored crosses in the intensity map, Figure 6(b)), this peak is unexpectedly visible as a shoulder on the Mg:LN stripe and is even more pronounced above the PE channel (spectral area of interest shaded in light blue).…”