CH(2) frequency comb generation based on optical parametric oscillation in a lithium niobate microresonator

Microresonator frequency combs have rapidly evolved in the last years and have become a hot topic in integrated photonics. These combs are typically generated relying on the CH(3) nonlinearity via degenerate and non-degenerate four wave mixing. More recently, the idea of comb generation based on the CH(2) nonlinearity has also started to be explored as it might provide new potential benefits like accesing new wavelength ranges. In this direction, we investigate the generation of CH(2) frequency combs based on optical parametric oscillation in a lithium niobate whispering gallery resonator. By pumping at 532 nm and driving the optical parametric oscillation to degeneracy at 1064 nm, we observe two 1-THz-wide combs centered around these wavelengths. This scheme can directly be transferred to other materials to generate combs in the mid-IR region by pumping at telecom wavelengths.