One million quality factor integrated ring resonators in the mid-infrared

We report ring resonators on a silicon germanium on silicon platform operating in the mid-infrared wavelength range around 3.5-4.6 µm with quality factors reaching up to one million. Advances in fabrication technology enable us to demonstrate such high Q-factors, which put silicon germanium at the forefront of mid-infrared integrated photonic platforms. The achievement of high Q is attested by the observation of degeneracy lifting between clockwise (CW) and counter-clockwise (CCW) resonances, as well as optical bistability due to an efficient power buildup in the rings.