Visible-Wavelength All-Fiber Mode-Locked Vortex Laser

We report, to the best of our knowledge, the first visible-wavelength all-fiber passively mode-locked vortex laser by a figure-9 cavity in combination with $\sim$ 635 nm mode selective coupler, which can deliver picosecond optical vortex pulses with topological charges of OAM $_{\pm 1}$ . The mode-locked vortex laser emits stable rectangular pulses with pulse duration tunable range from 85 to 510 ps and a 0.16-nm narrow linewidth at 634.36 nm. The maximum output power of the vortex laser reaches 1.3 mW with a high purity $\sim 97.2\%$ . This work demonstrated the generation of picosecond pulsed vortex in visible passively mode-locked fiber laser, showing their potential for applications in particle trapping, optical tweezers, and high-resolution microscopy.