Optical and x-ray characterization of HxLi1−xNbO3 phases in proton-exchanged LiNbO3 optical waveguides

Abstract

Infrared reflection, attenuated total reflection, prism coupling, and x-ray diffraction methods were used to characterize seven crystallographic HxLi1−xNbO3 phases in proton-exchanged Z-cut LiNbO3 waveguides. Drastic changes of the crystal lattice parameters and the lattice vibrational spectrum at the phase boundaries were observed. The LO–TO splitting, which is proportional to the width of the main band ranging from 580 to 900 cm−1, was demonstrated to vary significantly from phase to phase. Strong decrease of the LO–TO splitting for the polar mode attributed to NbO6 octahedra vibrations (800–900 cm−1) was detected. It was shown that the HxLi1−xNbO3 phases are organized as individual layers.

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

“…10 In similarity with the phases of PE LiNbO 3 , each phase of PE LiTaO 3 has a specific dependence of refractive index on proton concentration and crystal lattice parameters. [10][11][12] Furthermore, as is expected to be the case with H x Li 1Ϫx TaO 3 , substantial variations of chemical bonding 13 as well as electro-optical 13 and nonlinear 14 properties are observed among the H x Li 1Ϫx NbO 3 phases.…”

“…The application of these methods for wave guide characterization has recently been demonstrated in PE/APE LiNbO 3 . 13 In addition, Raman and IR-reflection measurements can provide direct information about the phonon spectrum related to the structure and chemical bonds of a given crystalline phase. Such information may be useful for correct identification of both phase composition and the microscopic mechanisms responsible for the observed alteration of properties from phase to phase.…”

Infrared spectra of proton-exchanged waveguides in LiNbO3 and LiTaO3

“…According to [9], the presence of ␤ i -phases significantly affects the spectra in the range of 800-1000 cm −1 where new bands appear which are absent in the cases of virgin or ␣-phase PE-LiNbO 3 . The characteristic changes are at 975 cm −1 for ␤ 1 -phase, at 980 cm −1 for ␤ 2 and ␤ 3 and at 970 cm −1 for ␤ 4 [9]. Thus, looking at the spectra of Fig.…”

“…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].…”

“…Since the penetration depth depends on the angle of incidence, at smaller angles (closer to the normal incidence) deeper penetration takes place and the spectra measured are affected by the presence of the various phases forming the waveguiding layer. It was established [9] that at 70 • the spectrum of the surface layer is separated from those of deeper situated layers in multiphase guides. This way only the surface phase could contribute to the reflection spectra of multiphase waveguides.…”