Wavelength-tunable vortex fiber lasers that could generate beams carrying
orbital angular momentum (OAM) hold great interest in large-capacity optical
communications. The wavelength tunability of conventional vortex fiber lasers
is however limited by the range of 35 nm due to narrow bandwidth and/or
insertion loss of mode conversion components. Optical metasurfaces apart from
being compact planar components can flexibly manipulate light with high
efficiency in a broad wavelength range. Here, we propose and demonstrate for
the first time, to the best of our knowledge, a metasurface-assisted vortex
fiber laser that can directly generate OAM beams with changeable topological
charges. Due to the designed broadband gap-surface plasmon metasurface,
combined with an intracavity tunable filter, the laser enables OAM beam with
center wavelength continuously tunable from 1015 nm to 1075 nm, nearly twice of
other vortex fiber lasers ever reported. The metasurface can be designed at
will to satisfy requirements for either low pump threshold or high slope
efficiency of the laser. Furthermore, the cavity-metasurface configuration can
be extended to generate higher-order OAM beams or more complex structured beams
in different wavelength regions, which greatly broadens the possibilities for
developing low-cost and high-quality structured-beam laser sources