All-Fiber Vortex Laser Generated With Few-Mode Long-Period Gratings

We report a simple method for generating optical vortex beams (OVB) from an all-fiber laser. An intracavity mode converter based on few-mode fiber long-period gratings was used to enable the OVB operation. The intensity profiles and the wavefront helicity of the output laser beams were characterized by analyzing the spatial intensity profiles of the laser emission and its self-interference. Selection of the wavefront handedness can be achieved simply by adjusting the intracavity polarization controller. The laser achieved ~50 mW of output power for both first-order and second-order vortex modes generation with the corresponding slope efficiencies of 8.12% and 7.91%, respectively. The corresponding mode conversion efficiency of 98% and 99.5% are for the LP11 mode and LP21 mode, individually. The linearly polarized orbital angular momentum beams with $l=\pm 1$ were characterized experimentally by adjusting a polarizer at the laser output.