Low-loss Al₂O₃ waveguides produced by pulsed laser deposition at room temperature

Abstract

Al₂O₃ waveguides have been produced at room temperature by pulsed laser deposition on Si substrates covered by a SiO₂ buffer layer. The dependence of the refractive index and the losses on both the laser energy density and the gas used during deposition (either reactive (O₂) or inert (Ar)) are discussed in terms of densification processes, surface roughness, and oxygen-related defects. Amorphous waveguides with refractive indices >1.66 and losses below 10 dB cm^-1 were produced under a wide range of experimental conditions, the best results being achieved with low laser energy densities and gas oxygen pressures. Losses as low as ≈2.5 dB cm^-1, which are close to the resolution limit, were achieved under optimized conditions, even when the waveguide had a thickness inhomogeneity along the propagation direction of at least 10%.