Strain-induced channel waveguiding in bulk sapphire substrates

We report on the two-dimensional confinement of light in the channel region of a bulk sapphire substrate, which was formed by utilizing the photoelastic effect in sapphire induced by a sputter-deposited SiO2 film. The experimental result, combined with the simulation results, shows that the sputter-deposited SiO2 films are compressively stressed up to 10 GPa level and that a 1.0-μm-thick film, for example, induces an index change of 5×10−3 in sapphire in the vertical direction. This amount of index change is found sufficient to support a fundamental mode at wavelengths of 1.54 μm or below.