Demonstration of an All-Optical OCDMA Encryption and Decryption System With Variable Two-Code Keying

We demonstrate the first all-optical optical code-division multiple-access (OCDMA) encryption and decryption system with variable two-code keying. The nonlinear optical loop mirror (NOLM)-based exclusive or (xor) employed in encryption utilizes the shortest length silica-based nonlinear fiber element to date, enabling a compact architecture. Fiber Bragg grating arrays create wavelength-hopping time-spreading OCDMA codes from broadband pulses at output ports of the xor resulting in variable two-code keying, a code-switching modulation format characterized by a random alternation in bit representation and immunity to differential analysis unlike fixed two-code keying. The terahertz optical asymmetric demultiplexer employed in decryption shows mutual compatibility of nonlinear fiber-based and semiconductor optical amplifier-based NOLM configurations. Our architecture can potentially perform one-time pad encryption and decryption for unconditional security.