Orbital angular momentum division multiplexing in optical fibre

We investigate the feasibility of the orbital angular momentum division multiplexing in optical fibre. Two optical vortices carrying well-definite values of orbital angular momentum, with topological charges equal to 0 and 1, respectively, are multiplexed in a few-mode fibre and then demultiplexed after a propagation of 200 m. The two vortices are discriminated by means of a Mach-Zehnder interferometer with mutually 90°-rotated Dove prisms in the two different arms, showing an inter-modal crosstalk lower than -10 dB. This demultiplexing scheme can be generalized to a higher number of vortices and it is all-optical, without the need of electronic post-processing. The proposed orbital angular momentum division multiplexing technique is very promising for increasing the capacity of the fibre-optic transmission systems in an energy-saving efficient way.