Mid-infrared broadband optical frequency comb generated in MgF_2 resonators

Microresonator-based optical frequency combs are broadband light sources consisting of equally spaced and coherent narrow lines,which are extremely promising for applications in molecular spectroscopy and sensing in the mid-infrared(MIR)spectral region.There are still great challenges in exploring how to improve materials for microresonator fabrication,extend spectral bandwidth of parametric combs,and realize fully stabilized soliton MIR frequency combs.Here,we present an effective scheme for broadband MIR optical frequency comb generation in a MgF_(2) crystalline microresonator pumped by the quantum cascade laser.The spectral evolution dynamics of the MIR Kerr frequency comb is numerically investigated,revealing the formation mechanism of the microresonator soliton comb via scanning the pump-resonance detuning.We also experimentally implement the modulation instability state MIR frequency comb generation in MgF_(2) resonators covering from 3380 nm to 7760 nm.This work proceeds microresonator-based comb technology toward a miniaturization MIR spectroscopic device that provides potential opportunities in many fields such as fundamental physics and metrology.