On-chip diamond Raman laser

Synthetic single-crystal diamond has recently emerged as a promising platform for Raman lasers at exotic wavelengths due to its giant Raman shift, large transparency window, and excellent thermal properties yielding a greatly enhanced figure of merit compared to conventional materials. To date, diamond Raman lasers have been realized using bulk plates placed inside macroscopic cavities, requiring careful alignment and resulting in high threshold powers (W–kW range). Here we demonstrate an on-chip Raman laser based on fully integrated, high-quality-factor, diamond racetrack microresonators embedded in silica. Pumping at telecom wavelengths, we show Stokes output discretely tunable over a ∼100  nm bandwidth around 2 μm with output power >250 μW, extending the functionality of diamond Raman lasers to an interesting wavelength range at the edge of the mid-infrared spectrum. Continuous-wave operation with only ∼85  mW pump threshold power in the feeding waveguide is demonstrated along with continuous, mode-hop-free tuning over ∼7.5  GHz in a compact, integrated-optics platform.