Visible continuous emission from a silica microphotonic device by third-harmonic generation

Nonlinear harmonic generation is widely used to extend the emission wavelength of laser sources. These devices typically require high peak powers to generate sufficient nonlinear optical response. Here, we demonstrate experimentally and analyse theoretically continuous-wave, visible emission from a silica microresonator on a silicon chip by third-harmonic generation. Emission is observed with pump powers of less than 300 mu W, and is verified to scale cubically with pump power. We also observe third-order sum-frequency generation and mixing of the pump with a concomitant Raman laser within the same structure, giving rise to emission of various colours. In addition to providing low-power operation, this result opens the possibility of silicon microphotonic emitters spanning all the way down to the ultraviolet and operating continuously.