Theoretical analysis of a mid-infrared Kerr frequency comb in a graphene-on-silicon micro-resonator

Mid-infrared (Mid-IR) Kerr frequency combs have great application potential in sensing and spectroscopy. To generate a Kerr frequency comb, a continuous-wave, wavelength-tunable, narrow-linewidth, low-noise laser is normally utilized to pump a high-nonlinearity micro-resonator to emit a large number of coherent and equally spaced modes. However, chip-based pump lasers in the mid-IR band, namely, quantum cascade lasers and interband cascade lasers, are usually challenging to develop with both high output powers and good wavelength tunability based on a single diode. To overcome the limitation, we theoretically study a mid-IR Kerr frequency comb generation technique based on a graphene-on-silicon micro-resonator by using a monochromatic mid-IR laser. The approach is based on the exploration of an electric-field-assisted resonance scanning technique and graphene-enhanced silicon Kerr nonlinearity. Our result shows that a soliton Kerr frequency comb with a spectral range of 3.23-5.26 mu m, 3-dB bandwidth of similar to 550 nm, and frequency spacing of 140 GHz could be generated under a pump wavelength of 4 mu m. The study paves a promising way toward developing monolithically chip-integrated mid-IR Kerr frequency combs with cost efficiencies and ultrafast tuning speeds.