In this paper, a chaotic secure communication system based on single feedback phase modulation is designed, in which phase modulation of feedback light is carried out by using random square wave as communication key, and chaotic light with wide spectrum and no delay signature is generated. Message is modulated into chaotic carrier at transmitter end, through chaotic synchronization and comparison, original message is successfully demodulated at receiver end. In addition, two kinds of message encryption methods, chaos modulation and chaos masking, are studied by comparing synchronization and bit error rate under different channel signal-to-noise rate.

A novel bidirection secure communication scheme based on the digital key and chaotic random optical feedback is proposed and numerically verified. Digital sequence is used as a key to control random variation of external cavity optical feedback, and under the operation of this random feedback, high-dimensional chaotic light is generated with complex dynamics. It is proved that chaotic time delay signature is effectively suppressed and key space increases significantly, which enhances the security of chaotic secure communication. Meanwhile, the bidirection chaotic secure communication is successfully implemented with the message rate of 10 Gb/s. In addition, simulation results show that the proposed scheme increases system synchronization and reduces the bit-error rate of the transmitted message.