High-contrast Kerr frequency combs

Optical microresonators are attractive for frequency comb generation due to their small size compared to fiber loops or free space cavities. However, most microresonator “Kerr combs” have strong harmonic at the optical pump frequency, undesirable for applications. We theoretically and experimentally investigate Kerr frequency combs with the depressed pump harmonic. This result is achieved in a MgF2 photonic belt resonator having reduced density of modes in its spectrum and configured with the add–drop optical couplers. The Kerr combs with the depressed pump harmonic will be useful for future optical communications and advanced spectroscopy.