Distributed bragg reflector high-Q cavities and lasers in Al2O3 on silicon

The Bragg grating technology was used to fabricate a DBR waveguide laser with two 3.75-mm long Bragg reflectors, which were separated by 2.5 mm, in ytterbium-doped Al₂O₃. The laser was pumped at 976 nm and had a threshold of 10 mW launched pump power. It produced a maximum output power of 47 mW at a launched pump power of 91.5 mW, which resulted in a slope efficiency of 67% (Fig. la). No saturation of the output power was observed and further power scaling was only limited by the available pump power. The laser operated at the Bragg wavelength of 1021.2 nm (TE polarized) and the laser emission peak had a signal-to noise ratio of more than 45 dB. The measured optical linewidth was limited by the 0.1 nm resolution of the optical spectrum analyzer. This is, to our knowledge, the first Al₂O₃ DBR waveguide laser and also the highest efficiency of any rare-earth-ion-doped waveguide laser on a silicon chip.