Message Filtering Characteristics Of Semiconductor Laser As Receiver In Optical Chaos Communication

With the achievement of the chaos synchronization, more and more attentions are paid to the chaotic cryptographic communication, in which the carrier's chaotic signal with good cryptic function, unpredictability, high complexity. The quality of chaotic optical cryptographic communication is not only depended on the quality of chaos synchronization but also on the filtering characteristics of the receiver. As the transmitter and receiver, semiconductor lasers have particular advantages because they are small in size, reasonably efficient, readily available, and widely employed in conventional optical communication systems.The closed-loop type of semiconductor laser chaos synchronization system for the research is used in this paper. Focusing on Message filtering characteristics of semiconductor laser as receiver in optical chaos communication, this thesis mainly includes that: 1. Focusing on the closed-loop scheme of chaotic communication system, using rate equations which consider the semiconductor laser with optical feedback to describe the dynamics of chaos system, we educe the response function of the receiver by small-signal analysis.2. The filtering properties of semiconductor laser with modulation message of different frequencies and amplitudes are numerically simulated. The frequency of transmission signal is limited by the relaxation oscillation frequency of the receiver laser, and the signal to noise rate will be decreased when the amplitude of message is too big or too small.3. Based on the research of filtering characteristics of the receiver, we improve the primary closed-loop scheme by enhancing the response peak value of the receiver with optical injection. The transmission of high frequency message is realized, which break through the limit of relaxation oscillation frequency of the receiver.4. The effect of parameter mismatches of system on the filtering characteristics of the receiver is numerically simulated. We analyze the effect by two encryption method, chaos masking and chaos shift key. The result is that the filtering characteristics of receiver will be depressed greatly with the increasing of frequency detune between the transmitter and the receiver, and the message cannot be recovered when frequency detune up to 9.5GHz. The mismatches of parameter gain coefficient and carrier lifetime play an important role on the filtering characteristics of the receiver, because these two parameters have direct effect on the relaxation oscillation frequency of the semiconductor laser.