Intracavity Pumped Tunable Low Threshold Mid-IR Kerr Comb at 2 μm

Compact low-threshold 2 μm (Mid-IR) optical frequency combs are important for applications ranging from sensing of gases like CO2 and CO, optical communications, LIDAR, and gravitational wave detection. Development of low-loss waveguides and high-Q microresonators with anomalous dispersion, and availability of tunable narrow linewidth 1.55 μm lasers has enabled realization of small footprint soliton combs and low-threshold Kerr combs in this wavelength region. However, such developments are lacking in the 2 μm wavelength region, making the realization of microresonator Kerr combs challenging. Here, we harness a novel intracavity pumping scheme to demonstrate a low-threshold (< 100 mW) 2 μm Kerr comb. We exploit Brillouin lasing in a silica microsphere to create an intracavity pump thereby exciting a ∼170 nm wide Kerr comb in the generated Stokes direction. We demonstrate the tolerance of comb generation scheme to microsphere dimensions and input pump wavelength, by achieving Kerr comb generation in microspheres of diameters ranging from 300 to 325 μm and also, at different input pump wavelengths for a particular microsphere diameter. Intracavity pumping opens up opportunities for the development of soliton combs and low-threshold Kerr combs in the Mid-IR for applications such as dual-comb spectroscopy, LIDAR and optical communications.