Abstract

The method of epitaxial growth by melting was first applied by Ballman¹ to grow 6Bi₂O₃:1TiO₂ on Bi₁₂GeO₂₀. It was later used by Miyazawa² and by Ballman and Tien³ for growing single-crystal LiNbO₃ waveguides on LiTaO₃ substrates. The method has since earned a special position in integrated optics on the following accounts: First, for the method to apply the material used for the film must have a melting point lower than that for the substrate. It turns out that the material which has a lower melting point has also a larger refractive index. Therefore, the condition of waveguiding that requires the film to have a refractive index larger than the substrate is automatically satisfied. Secondly, the film grown by this method has a broad transition region in which the material varies slowly from the film composition to the substrate composition. The transition minimizes any effect due to mismatch in lattice between the film and the substrate. Finally, the refractive-index profile of the film follows roughly a Fermi function which is somewhere between the step function of the uniform waveguides and the exponential function of the diffused waveguides. There appears to be no difficulty in forming a single-mode waveguide.

© 1976 Optical Society of America