Transmission of chaotically encrypted signals over an optical channel

The important problems of the contemporary information transmission systems are privacy and security. Traditional cryptosystems are based on software techniques where a short secret parameter defined as the key is used, or the message is encoded directly. A novel approach to encryption is based on a hardware communication system where the encryption is directly applied to the physical layer of the communication system. Chaos communication is a direct encoding and decoding scheme of a message system in a communication system. Optical communication with chaotic laser system attracted a wide interest. Optical-fiber communication systems using chaotic semiconductor lasers have been investigated both theoretically and experimentally. The advantages of the chaotic communications are following: (i) Efficient use of the bandwidth of the communication channel; (ii) Utilization of the intrinsic nonlinearities in communication devices such as semiconductor diode lasers; (iii) Large-signal modulation for efficient use of carrier-power; (iv) Reduced number of components in a communication system; (v) Security of communication based on chaotic encryption. Typically, generation of chaotic signals can be achieved by introduction of the delayed all-optical or electro-optical feedback into diode lasers. We propose a novel system of the coupled lasers synchronization based on the master and slave lasers both in the transmitter and in the receiver. We carried out the numerical simulations of the optical communication channel containing such a transmitter and a receiver. We investigated theoretically the influence of optical fiber dispersion and nonlinearity on the chaotically encoded signal transmission efficiency. The numerical simulations show that the efficient transmission of the chaotically modulated waveform over the optical channel of a 100 km distance and the following decoding are possible.