Thulium-doped tellurite distributed Bragg reflector waveguide laser on a silicon nitride chip

We show a distributed Bragg reflector laser operating at 1875 nm, using a hybrid silicon nitride photonic chip coated with thulium-doped tellurite glass. The passive laser cavity consists of nominally 50 nm wide sidewall Bragg gratings directly patterned in a 1.2 µm wide, 0.2 µm thick, and 22 mm long silicon nitride waveguide on a thermally-oxidized silicon substrate, fabricated using a standard foundry process. A 0.39 µm thick thulium-doped tellurium dioxide optical gain layer was deposited onto the chip by reactive radio frequency magnetron co-sputtering. The resulting hybrid laser includes 6 and 4 mm long gratings separated by an 11 mm gap to form an asymmetrical cavity and promote directional lasing off the shorter reflector. We obtain a maximum on-chip output power of 4.5 mW and a lasing threshold of 20 mW when pumping at 1610 nm. A total slope efficiency of 5% was achieved, as well as a thermal tunability of the laser wavelength of 32.3 pm/°C. These results are a step toward simple, compact, and high-power on-chip thulium-based tellurite lasers for silicon-based photonic integrated circuits.