High-dimensional encoding based on classical nonseparability.

Based on the formal analogy between classical nonseparability and quantum entanglement, we present a multi-ary encoding protocol exploiting the nonseparability of orbital angular momentum (OAM) and polarization for a hybrid vector beam. Such an encoding can be realized in high-dimensional state space by transforming OAM of the vector beam under the assistance of polarization, which is called "high-dimensional" encoding. It is shown that N-ary encoding using N-dimensional non-separable basis can be obtained by manipulating N/2 different OAM modes, which is equivalent to encoding log2N bits of information. It is also shown that the decoding of vector beams can be realized with very low cross talk. Compared with the encoding protocol transforming OAM modes of scalar beams, our encoding scheme, based on classical nonseparability of vector beams, can encode much more information. This is of great benefit to the optical communication.