Dispersion properties of aluminum nitride as measured by an optical waveguide technique

An aluminum nitride thin film on sapphire substrate was prepared by metal–organic chemical-vapor deposition for optical waveguide study. A rutile prism coupler was employed to display the waveguide modes ($N$ lines) with wavelengths of 632.8, 532.1, 514.5, and 488.0 nm. The refractive index and thickness of the waveguide material were obtained by prism–coupler measurement. The parameters in the dispersion equation were determined by curve fitting. The attenuation in the waveguide was evaluated by scattering loss measurements using a fiber probe. The attenuation coefficient α is in the range of $\text{1.5–2.1\hspace{0.17em}}{\mathrm{cm}}^{\mathrm{-1}}$ $\text{(5.4–7.6\hspace{0.17em}}{\mathrm{dB\hspace{0.17em}cm}}^{\mathrm{-1}}\mathrm{),}$ depending on the surface roughness of the sample and different orders of waveguide modes.