The Generation of Ultrahigh Repetition-Rate OAM Frequency Combs in Dual-Concentric Germania-Doped Ring-Core Fiber

We theoretically demonstrate, for the first time to the best of our knowledge, the orbital angular momentum (OAM) frequency combs induced by dissipative Faraday instability (DFI) mechanism in a 2-μm waveband Mamyshev oscillator. Dual-concentric Germania-doped ring-core fibers are specially designed with flat normal dispersion curves for different OAM modes, inhibiting the Benjamin-Feir instability and facilitating phase matching conditions for broadband frequency comb generation. The frequency comb tooth spacing scales up to ∼100 GHz, which matches well with the Floquet linear stability analysis by Ikeda map. Our investigations might benefit the development of OAM frequency combs for a variety of further applications including communication.