Secure OCDM Transmission Using a Planar Multiport Encoder/Decoder

We present different optical secure point-to-point transmission schemes using a planar multiport encoder/decoder. We consider both bit- and block-cipher cryptography: in the first case, each bit (both mark and space) from each user is encoded in a two-key optical code-division multiplexing signal. Block-cipher cryptography encodes a stream of n bits into a single code and corresponds to optical M-ary transmission. We demonstrate that block-ciphers are more secure with respect to bit-ciphers schemes and also against known-plaintext and chosen-plaintext attacks.