Frequency comb up- and down-conversion in synchronously driven χ optical microresonators.

Optical frequency combs are key to optical precision measurements. While most frequency combs operate in the near-infrared (NIR) regime, many applications require combs at mid-infrared (MIR), visible (VIS), or even ultra-violet (UV) wavelengths. Frequency combs can be transferred to other wavelengths via nonlinear optical processes; however, this becomes exceedingly challenging for high-repetition-rate frequency combs. Here it is demonstrated that a synchronously driven high-Q microresonator with a second-order optical nonlinearity can efficiently convert high-repetition-rate NIR frequency combs to VIS, UV, and MIR wavelengths, providing new opportunities for microresonator and electro-optic combs in applications including molecular sensing, astronomy, and quantum optics.