Abstract: An optical communication system is disclosed. The optical communication system comprises an optical transmitter and a substantially circular multi-mode optical fiber. The optical transmitter comprises a generator of at least two free space circular vortices and comprises an optical element configured to receive the at least two free space circular vortices and to couple them to an input facet of the optical fiber. The optical fiber is configured to receive at the input facet the at least two free space circular vortices and is configured to generate therefrom at least two corresponding guided circular vortices having respective propagation constants, wherein the values of the propagation constants at a defined frequency are different each other.