Mid-Infrared chalcogenide all-solid Kagome fiber with large mode field area and high beam quality

Mid-infrared (MIR) high-power fiber lasers have advanced rapidly, but further power scaling requires fibers with enlarged mode-field areas while maintaining near-diffraction-limited beam quality. In conventional step-index large-mode-area (LMA) fibers, increasing the core size inevitably excites higher-order modes that compete with the fundamental mode for gain, leading to a pronounced deterioration in beam quality. Here, we introduce a node-free, all-solid chalcogenide Kagome fiber (AS-KF), in which the suppression of higher-order modes is effectively achieved, ensuring stable broadband single-mode guidance. Both numerical simulations and experiments reveal a nearly perfect Gaussian near-field intensity at 1.55 µm and 4.5 µm, with an average mode-field area exceeding 1400 µm² across the MIR band. These results demonstrate that AS-KFs offer exceptional potential for high-brightness MIR power delivery while preserving outstanding beam quality.