Metastable phases in HxLi1-xTaO3 waveguide layers and pure LiTaO3

Abstract

The formation of high-temperature phases in low-doped H:LiTaO3 waveguide layers in Z-cut LiTaO3 has been observed both by refractive-index and IR-spectra measurements. This permits us to correlate the index jumps to the changes of the OH bonds in the crystal lattice. Reversible phase transitions were detected in the temperature interval T=50–200 °C over a wide range of hydrogen content including as-grown LiTaO3. The high-temperature phases are metastable close to room temperature. This was demonstrated by tracing the time evolution of the refractive-index change. It was shown that the high-temperature phases are responsible for the long-term refractive-index instabilities in both H:LiTaO3 waveguides and virgin LiTaO3.