In a recent paper in Optics Letters, we demonstrate a chip-integrated optical parametric oscillator in the 2 um wavelength band, through use of a photonic crystal microring resonator. We further show theoreticall that straightforward modifications to the geometry can provide significant spectral coverage in the mid-infrared.
Lu, X., A. Chanana, F. Zhou, M. Davanço, and K. Srinivasan, "Kerr optical parametric oscillation in a photonic crystal microring for accessing the infrared", Optics Letters, vol. 47, pp. 3331–3334, 2022.