Generation of orbital angular momentum mode using a single cylindrical vector mode based on mode selective coupler

Abstract

Abstract We deduce theoretically that arbitrary lth order cylindrical vector (CV) mode in few-mode fiber can be seen as linear combination of a left-handed and a right-handed circularly polarized orbital angular momentum (CP-OAM) modes with the opposite l, where l is the topological charge (l ≥ 1). And these two CP-OAM modes can be stimulated by a combination of a quarter-wave plate (QWP) and a polarizer with an angle ±π/4. Thus, using a single CV mode, the orbital angular momentum of light can be switched among –l, 0, l. As an example, the generations of σ+OAM±l and σ−OAM±l (l = 1, 2) beams are demonstrated and verified by theoretical simulation and experiment. Compared to the conventional combination of eigenmodes pairs to generate OAM beams, this approach not only provides an increased stability, but also builds a bridge between polarization singularities mode and phase singularities mode, due to using a single CV mode as the light source.