Structural and optical properties of annealed proton-exchanged waveguides in z-cut LiTaO3

Abstract

Diffusion characteristics and waveguiding properties of protonexchanged and annealed LiNbO3 channel waveguidesThe structural properties of annealed proton-exchanged waveguides in Z-cut LiTaO, have been investigated. Observations made in a polarizing microscope together with infrared-absorption measurements indicate the formation of monoclinic L4,-,,H,TaO, after proton exchange in pure pyrophosphoric acid. This monoclinic phase disappears after annealing at 300 "C. High-resolution x-ray diffraction shows that the c lattice parameter is 0.57% larger in the exchanged layer than in the bulk. During annealing the c parameter relaxes and in addition there appears a second diffraction peak in the x-ray rocking curves. This peak is attributed to a-phase Li,, -X,H,TaO,. A model for the increase of the refractive index is suggested. It shows that the main reason for the difference in index increase between proton-exchanged waveguides in LiTa03 and LiNbO, is the stronger spontaneous polarization of LiNb03. The model predicts an increase of the refractive index of LiTaO, after annealing which is experimentally observed. A short-term postannealing index decrease is suggested to be related to a ferroelectric domain reversal. 0 199.5 American Institute of Physics.

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

“…4͒ spectra of unexchanged LiTaO 3 appear to confirm the claim of Ref. 24. Indeed, we observed all of the three A modes that were previously reported 25 for the range 590-870 cm Ϫ1 , which is related to the intrinsic vibrations of TaO 6 octahedra.…”

“…At the same time, nine IR-and Raman-active c-polarized A modes, corresponding to the C 3 point group symmetry, were observed in Ref. 24 where it was established that a small intrinsic distortion of the unit cell reduces the crystal's symmetry from C 3v to C 3 . Our IR-reflection ͑Figs.…”

Channeling Study of Proton-Exchanged LiNbO3 Optical Waveguides

“…Large refractive index changes and decrease of nonlinear optical coefficients are found in PELN waveguide layers [4,5], which has been attributed mainly to the decrease of spontaneous polarization in waveguide layers [6]. The spontaneous polarization in LN crystal is mainly caused by the ordered displacement of Li atoms and Nb atoms in the c-direction from the oxygen planes [7].…”

Optical and structural properties of waveguides in LiNbO 3 fabricated by ultrashort laser pulses

“…The combination of volume change and decrease of spontaneous polarization was deemed responsible for the observed index changes caused by proton exchange 34 and ion implantation. 35,36 However, quantitative predictions were impossible due to the simple nature of the model.…”