Electromagnetic modes and prism-film coupling in anisotropic planar waveguides of epitaxial (101) rutile thin films

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Abstract
We report optical waveguiding in single‐crystal, epitaxial (101) oriented rutile (TiO2) thin films grown on (112̄0) sapphire (α‐Al2O3) substrates using the metal‐organic chemical vapor deposition technique. The electromagnetic field distributions and propagation constants for asymmetric planar waveguides composed of an anisotropic dielectric media applicable to these films are derived. Modifications to the prism‐film coupling theory for this anisotropic case are also discussed. By application of this model to (101) oriented rutile thin films, we directly obtain values of the ordinary and extraordinary refractive indexes, n0 and ne, of the rutile thin films as well as film thicknesses. We obtain typical values of the refractive indexes (n0=2.5701±0.0005; ne=2.934±0.001) near to those for bulk rutile single crystals indicating the exceptional quality of these films.