Anomalous refractive index change and recovery of electro-optic coefficient r 33 in proton-exchanged LiTaO3 optical waveguides after annealing

An increase of surface refractive index and a recovery of the r33 electro-optic coefficient have been observed for proton-exchanged LiTaO3 optical waveguides after annealing. On the basis of the results of nuclear reaction analysis, x-ray rocking curve analysis, and infrared-absorption spectroscopy, a qualitative model to explain these phenomena is proposed. The evolutions of the index profile and the r33 coefficient after proton exchange and annealing are considered to be caused by the movement of protons in the crystal lattice and the interdiffusion of protons and Li ions. The condition required for the fabrication of waveguides with good electro-optic performance is also shown.