Theoretical Investigation Of The Effects Of Fiber Channel On Optical Chaotic Secure Communication

Chaotic communication has been cared more and more extensively for potential application in secure communication. Theoretical and experimental investigations show that the chaotic carrier with wide bandwidth and high dimension is very easily generated by semiconductor laser subject to optical feedback or optical injection. Thus, chaotic optical communication based on semiconductor laser becomes a hot issue in current research. It is of a higher value in application that chaotic optical communication can achieve long-distance secure transmission of high-frequency messages by combining with the existing optical fiber links. Focusing on the influences of fiber channel on optical chaotic secure communication, this thesis is mainly summarized in the following:1. A theoretical model for optical chaotic secure communication system by coupling chaotic laser synchronization system and fiber channel is presented. The influences of dispersion, nonlinear effects, and the combination of dispersion and nonlinear effects on synchronization performance and the extracted messages of optical chaotic secure communication system are numerically investigated based on the nonlinear Schrodinger equation. We find that the transmitter-receiver synchronization progressively degrades and the signal-to-noise ratio of the recovered messages deteriorates owing to fiber dispersion which leads to the widening of chaotic carrier and nonlinear effects which gives rise to an intensity-dependent phase shift. When fiber dispersion together with nonlinear effects acts on optical chaotic secure communication system, the quality of the recovered messages can be optimized in the anomalous-dispersion fiber because SPM decreases the broadening rate imposed on the pulse by the GVD alone.2. The influence of fiber dispersion on chaotic carrier is further quantitatively investigated by introducing two physical parameters of the root-mean-square widthσand the peak-to-peak value V_p-p. The effects of normal-dispersion and anomalous-dispersion on chaotic carrier are also compared. The results show that fiber dispersion has a less influence on the system's synchronization and the extracted messages when the anomalous-dispersion fiber is considered as transmission channel. To overcome the downgrading of the system performance and improve the quality of the recovered messages, we especially proposed a symmetrical dispersion compensation scheme to compensate the dispersion in optical chaotic fiber secure communication system.3. Wavelength division multiplexed transmission of chaotic optical communication and current optical communication is numerically confirmed and analyzed. For a 100GHz channel span, a 1-Gb/s digital message extraction is achieved in chaotic optical communication system and a 2.5-Gb/s digital signal is decoded in current optical communication system. We find that when the peak power of digital signal in current communication is less than threshold power 14dBm regulated by ITU-T, chaotic communication can realize long-haul transmission of 100km without inter-channel crosstalk. In addition, the quality of the decoded signal in current communication is hardly interfered by chaotic communication and the opening of the corresponding eye diagram keeps nearly invariable as the transmission distance increases.