Optically pumped rare-earth-doped Al₂O₃ distributed-feedback lasers on silicon [Invited]

This paper reviews recent progress in the field of optically pumped rare-earth-doped channel waveguide lasers, with a focus on operation utilizing distributed-feedback resonators on silicon wafers. Rare-earth-doped amorphous aluminum oxide thin films have been deposited onto silicon wafers by RF reactive co-sputtering from metallic Al and rare-earth targets, the spectroscopy and optical gain of Er³⁺, Yb³⁺, Nd³⁺, and Tm³⁺ ions has been investigated, and the near-infrared laser transitions near 1 μm in Yb³⁺, 1.5 μm in Er³⁺, and 2 μm in Tm³⁺ and Ho³⁺ have been demonstrated. Output power between a few μW and hundreds of mW have been achieved in different waveguide geometries, and ultranarrow-linewidth laser operation has been demonstrated.