Optical waveguiding in LiNbO3 single-crystal film grown by the EGM technique

We report optical waveguiding in LiNbO3 single-crystal film grown onto a LiTaO3 substrate by the epitaxial-growth-by-melting (EGM) technique. Studies on the x-ray rocking curve and waveguide mode indices have indicated that the film has a graded refractive-index distribution. We have estimated the index profile on the basis of the WKB method, and have found that the index profile is approximated by a linear distribution. Light propagation loss has been measured to be about 1 dB/cm for the film with the surface flatness of λ/10. Poling of the film has been achieved by the field-cooling technique using a newly developed setup.