Asynchronous secure communication scheme using a new modulation of message on optical chaos

An asynchronous secure communication scheme of modulation of message on optical chaos, combining (6, 3) linear block codes (LBC) with majority decoding, is proposed. In this scheme, a semiconductor laser (SL) with electro-optical phase feedback is used to generate an optical chaotic carrier with high complexity. We calculate the sum of the absolute values at adjacent three moments in the chaotic sequence, and divide interval between its maximum and minimum into eight different segments, which are used as the key for generating a new chaotic sequence according to a certain rule. Introducing (6, 3) LBC to encode the message, and using dispersion-compensating fiber (DCF) to eliminate the effect of dispersion induced by single mode fiber (SMF), and then using majority decoding to demodulate the original message at receiving end, we demonstrate that the performance of the bit error rate (BER) in a channel with noise is well improved, and the distortion is greatly reduced. Moreover, our system can realize communication between transmitter and receiver without chaotic synchronization by negotiating these keys through a secret channel.