Free-space orbital angular momentum division multiplexing with Bessel beams

We present an apparatus for multiplexing and demultiplexing free-space beams carrying different values of orbital angular momentum (OAM), at a wavelength of 633 nm. We have considered nondiffracting Bessel beams of order from 0 to 3, produced by means of suitable binary-amplitude computer-generated holograms and carrying an OAM per photon directly proportional to the beam order. The effectiveness of the OAM division multiplexing technique has been experimentally verified by monitoring the output ports of a demultiplexing interferometer with rotated Dove prisms in the arms. This interferometer is capable of discriminating the even-order Bessel beams from the odd-order ones.