We employed the atomic layer deposition technique to grow ${\mathrm{Al}}_2{\mathrm{O}}_3$ films with nominal thicknesses of 400, 300, and $200\mathrm{nm}$ on silicon and soda lime glass substrates. The optical properties of the films were investigated by measuring reflection spectra in the $400–1800\mathrm{nm}$ wavelength range, followed by numerical fitting assuming the Sellmeier formula for the refractive index of ${\mathrm{Al}}_2{\mathrm{O}}_3$ . The films grown on glass substrates possess higher refractive indices as compared to the films on silicon. Optical waveguiding is demonstrated, confirming the feasibility of high-index contrast planar waveguides fabricated by atomic layer deposition.