Optical vortex fiber laser based on modulation of transverse modes in two mode fiber

Optical vortices, characterized by helical phase fronts, are usually generated outside the laser cavity using passive modulation methods. Here, we demonstrate an all-fiber laser to directly deliver mode-locked and continuous-wave vortex beams based on modulation of transverse modes in the two mode fiber. The mode couplers and reflectors for three schemes are long period fiber grating (LPFG) and fiber mirror, fiber taper and fiber Bragg grating, and LPFG and fiber Bragg grating, respectively. The laser is switchable between ±1 order vortex operations by tuning the intracavity polarization controller, and the optical vortex can directly work as an optical tweezer to manipulate rhenium diselenide nanosheets. The pulse duration at the mode-locked state is tunable from subpicoseconds to several picoseconds by spectral filters, and the maximum output power at the continuous-wave state exceeds 35 mW. The cost-effective all-fiber vortex laser is quite attractive for research of micromanipulation, spatiotemporal soliton, and optical communication.