Optical cryptography by phase modulation of a chaotic carrier

Optical chaotic cryptography is a hardware technique for secure transmission based on a pair of lasers routed to chaos, usually by delayed optical feedback with an external cavity. The basic scheme makes use of two chaotic lasers, one at the transmitter (the master), where chaos is added to the message, and one at the receiver (the slave), where chaos is subtracted to recover the message. Chaos cancellation at the receiver relies on synchronization between master and slave, i.e., on the generation of the same chaotic waveform at both ends of the channel is based on direct observation of the synchronized slave output, which, under suitable operating conditions, can transduce the phase modulation into amplitude modulation.