Ultra-compact and low-threshold thulium microcavity laser monolithically integrated on silicon.

We demonstrate an ultra-compact and low-threshold thulium microcavity laser that is monolithically integrated on a silicon chip. The integrated microlaser consists of an active thulium-doped aluminum oxide microcavity beside a passive silicon nitride bus waveguide, which enables on-chip pump-input and laser-output coupling. We observe lasing in the wavelength range of 1.8-1.9 μm under 1.6 μm resonant pumping and at varying waveguide-microcavity gap sizes. The microlaser exhibits a threshold as low as 773 μW (226 μW) and a slope efficiency as high as 24% (48%) with respect to the pump power coupled into the silicon nitride bus waveguide (microcavity). Its small footprint, minimal energy consumption, high efficiency, and silicon compatibility demonstrate that on-chip thulium lasers are promising light sources for silicon microphotonic systems.