Broadband Dispersive-Wave Emission Coupled with Two-Stage Soliton Self-Compression in Gas-Filled Anti-Resonant Hollow-Core Fibers

We studied the underlying mechanism of broadband dispersive-wave emission within a resonance band of gas-filled anti-resonant hollow-core fiber. Both numerical and experimental results unveiled that the pump pulse with a soliton order of ~3, launched into the hollow-core fiber, experienced two stages of pulse compression, resulting in a multi-peak structure of the emitted dispersive-wave spectrum. Over the first-stage pulse compression, a sharp increase of the pulse peak power triggered the first time of dispersive-wave emission, and simultaneously caused the soliton frequency blue-shift due to soliton-plasma interactions. As the central frequency of the blue-shifting soliton approached to a resonance band of the hollow-core fiber, it experienced a fast-decreasing dispersion value in the fiber waveguide, resulting in the second stage of pulse compression. The second-stage pulse compression triggered the second time of dispersive-wave emission with a phase-matched frequency slightly lower than that at the first stage. Multi-peak spectra of the output dispersive-waves and their formation dynamics can be understood using a delicate and unique coupling mechanism among three nonlinear effects including multi-stage soliton compression, soliton-plasma interaction and phase-matched dispersive-wave emission. The output broadband dispersive-wave, exhibiting good coherence and stability, could be potentially compressed to sub-30 fs duration using precise chirp-compensation technique.