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All-optical XOR gate for quantum ciphertext in optical communications

Cryptography in communications is of increasing importance and several sophisticated cryptographic algorithms have been developed. Quantum mechanical principles have been employed yielding cryptographic keys to generate ciphertext, especially applicable to optical communications, and which are believed to be unbreakable. In optical communications, the quantum ciphertext is the bit-by-bit exclusive-Or (XOR) operation of the quantum key and the text. Thus, an all-optical XOR gate is required at the transmitter, which for compactness and efficiency it should be simple and monolithically integrable. In this paper we review the quantum ciphertext generation, and we present a novel XOR gate that requires a single wavelength, in contrast to other solutions that require additional optical signals for control and synchronization. Simulation results support the viability of our novel all-optical XOR gate at data rates up to 40 Gbps.