Visible blue-to-red 10 GHz frequency comb via on-chip triple-sum frequency generation

A broadband visible blue-to-red, 10 GHz repetition rate frequency comb is generated by combined spectral broadening and triple-sum frequency generation in an on-chip silicon nitride waveguide. Ultra-short pulses of 150 pJ pulse energy, generated via electro-optic modulation of a 1560 nm continuous-wave laser, are coupled to a silicon nitride waveguide giving rise to a broadband near-infrared supercontinuum. Modal phase matching inside the waveguide allows direct triple-sum frequency transfer of the near-infrared supercontinuum into the visible wavelength range covering more than 250 THz from below 400 nm to above 600 nm wavelength. This scheme directly links the mature optical telecommunication band technology to the visible wavelength band and can find application in astronomical spectrograph calibration as well as referencing of continuous-wave lasers.