All-in-fiber method of generating orbital angular momentum with helically symmetric fibers.

An all-in-fiber method of generating orbital angular momentum (OAM) is proposed. A simple device composed with a section of helically symmetric fiber and another section of regular fiber is designed to convert input light to optical vortices. Finite element method calculation of first- and second-order OAM generation based on the coordinates transformation technique is taken to show that the eigenmodes of the helically symmetric fiber structures carry orbital and spin angular momentum. Simulation using the self-developed beam propagation method algorithm is also performed to verify the orbital angular momentum generation and evaluate the performance of the OAM generator.