Mode-division multiplexing in fibre-optic communications based on orbital angular momentum

The possibility of using optical vortices with different values of topological charge l, and hence with different values of the orbital angular momentum (OAM), for mode-division multiplexing in optical fibres is here investigated. Two OAM modes with l equal to 0 and 1, respectively, are multiplexed in a few-mode fibre and then demultiplexed after a fibre propagation of 200 m. Such modes are spatially separated at the two output ports of a Mach–Zehnder interferometer with mutually 90°-rotated Dove prisms in the two arms. It is also shown how to generalize this demultiplexing scheme, which is all-optical, passive and in principle without splitting losses, in order to deal with a higher number of vortices propagating in the fibre. Therefore the proposed mode-division multiplexing technique based on OAM modes is very promising for increasing the capacity of fibre-optic transmission systems in an energy-saving efficient way, without the high power consumption of modal demultiplexing exploiting real-time electronic post-processing.