Orbital angular momentum transition of light using a cylindrical vector beam

We demonstrate that using a single cylindrical vector (CV) beam in two-mode fibers, the orbital angular momentum of light can be switched among -1, 0, and 1. The input CV beam can be a conventional radial and azimuthal polarization distribution or a generalized CV beam, and we first use and verify that a rocking-long period fiber grating generates the tunable generalized CV beam. Because of using a single CV beam as the light source, this approach not only provides an increased stability compared to the conventional superposed eigenmodes method, but also builds a bridge between the polarization singularity beams and the phase singularity beams.