Tunable telecom to mid-infrared optical parametric oscillation via microring-based $\chi^{(3)}$ nonlinearities.

Optical parametric oscillation (OPO) with far-shifted frequency sidebands has attracted significant interests in precision spectroscopy and quantum information processing. Microresonator based OPO sources hold the advantages of miniaturized footprint and versatile dispersion engineering. Here we demonstrate large-frequency-shifted $\chi^{(3)}$-based OPO from crystalline aluminum nitride microrings pumped at $\sim$2 $\mu$m in the normal dispersion regime. OPO in the telecom and mid-infrared bands with a frequency separation of 65.5 THz is achieved. The OPO frequency can be agilely tuned in the ranges of 10, 1 and 0.1 THz respectively by tailoring the microring dimensions, shifting the pump wavelength, and controlling the chip temperature. At high intracavity pump powers, the OPO sidebands further evolve into localized frequency comb lines. Such telecom to mid-infrared OPO with flexible wavelength tunability will lead to enhanced chip-scale light sources.