Ultra-broadband 2000-nm acousto-optic first-order azimuthal mode conversion for dynamic fiber-optic vortex generation

The practical adoption of orbital angular momentum (OAM) in technologies ranging from high-capacity communications to quantum information science has been severely hindered by the lack of integrated devices capable of dynamic OAM manipulation across broad bandwidths. Existing solutions, particularly in optical fiber, are fundamentally constrained to narrowband operation by wavelength-specific phase-matching conditions. Here, we break this long-standing paradigm by demonstrating a fiber-optic vortex converter that achieves an ultra-broad bandwidth exceeding 2000 nm, spanning from the deep ultraviolet to the short-wave infrared. This unprecedented performance is enabled by a novel mechanism—equivalent continuously phase-modulated acousto-optic interaction in a customized graded-index few-mode fiber. This approach effectively decouples the OAM mode-conversion process from wavelength-dependent constraints. Our device simultaneously delivers dynamic tunability and high conversion efficiency, establishing a versatile platform that unlocks the full potential of OAM in ultrahigh-capacity communications, chiral photonics, ultrafast optics, and quantum information processing. The demonstrated >2000-nm bandwidth corresponds to the first-order azimuthal LP01 → LP11 mode-conversion process as directly verified by bar-transmission measurements. Subsequent high-purity OAM generation is achieved via a polarization-interference scheme and experimentally verified at 633 nm and across the 1480–1640 nm range as representative of the visible and near-infrared bands, with the phase-control principle supporting operation across the full bandwidth. The present demonstration is limited to the first-order azimuthal mode conversion; extension to higher-order modes would require cascaded conversion stages.