High refractive index low-loss aluminium oxide waveguides

A high refractive index (n~1.715 at 633 nm of wavelength) aluminium oxide slab waveguide has been developed, which exhibits very low losses from the near-UV to the near infrared wavelength range. Slab waveguide losses as low as 1.8 dB/cm at 407 nm and less than 0.1 dB/cm at 1550 nm of wavelength have been experimentally characterized. Such low losses are limited by surface scattering. The layer was deposited by reactive sputter coating with an aluminium target, a set substrate temperature of 700 C and an oxidation state of the target of 5 %. The very high optical quality of this material, in combination with rare-earth ion doping, could pave the way towards high-gain on-chip amplifiers in different wavelength ranges, on-chip lasers and non-linear applications