Generation controllable orbital angular momentum beams in fiber laser system

Abstract

A method to generate controllable orbital angular momentum (OAM) beams is demonstrated in this paper. Both simulation and experiment show that the controllability originates from simultaneous superposition of four linearly polarized (LP) modes. A linear fiber laser is built, in which offset splicing is used to achieve the LP11 mode excitation and two-mode fiber Bragg grating is employed as a mode splitter to improve the mode purity. As a result, first-order optical vortex beams with controllable OAM are realized in the Yb-doped fiber laser system, and the topological charge can be tuned from −l to +l.