Study Of Chaotic Secure Communication Method On Erbium-doped Fiber Lasers

The progress of communication technology is the deveplement of the national economy. Now almost all the carrier wave of opticommunication is the sine wave with special parameters or other special signal. Any company or person can produce the equipment of opticommunication to realize the aim of transmitting information, only if they know the communication protocols. But in the national defence, the transmitting mode is easy to be leaked out. The theory of chaos has no use in the latter half of 20 century when it is discovered and researched. But since American scientists Pecora and Carroll discovered the chaotic synchronization in 1990, the chaotic system became a potential carrier waver for the secure communication. Because of the potential application values and especially the successful invention of the single mode fiber which can operate on the low decay wavelength, the research of the chaos/superchaos and the chaotic synchronization on the erbium-doped fiber laser provide the foundation of favorable theory and experiment for the applications on the optical secure communication.Firstly, the characteristic of the nonlinear chaotic system is put forward. And then the methods of researching nonlinear chaotic system are provided. A method of changing the single ring erbium-doped fiber laser to chaotic system is proposed, and the nonlinear characteristic is discussed. We research the chaotic/superchaotic synchronization of single ring and dual-ring erbium-doped fiber lasers. At last, we research the applications on the chaotic secure communication of the single ring and the dual ring erbium-doped fiber lasers. The thesis can be divided four parts.1. The conception of chaos is proposed. In the past decades years, the conception of chaos has many descriptions. Here we explain the Li-Yorke Conception and the rigorous mathematical definition, which indicate the basic characteristic of chaos. Then we show the definition of chaos and enumerate the chaotic methods. There have been many chaotic methods, which have the same aim. The signals output from the driving system are injected into the response system to obtain the chaotic synchronization between the systems. All these results supply the important theoretical evidence for the chaotic synchronization on the optical laser systems, which is universal. Finally, we show the research course on characteristics of the optical laser systems. We also retrospect the research of nonlinear and chaotic synchronization of the CO₂ laser, He-Ne laser, Nd:YVO₄ laser, Nd:YAG laser and the erbium-doped fiber laser.2. With the erbium-doped fiber laser system, we first discussed the chaos method of modulating pump parameter. And propose a new chaos method-optical delay feedback injection, which is effective and reliable. The dynamic characteristic has infinite degrees of freedom, which increase the system's complexity. Based on the dynamics, we discuss the nonlinear characteristic. The numerical analysis indicates that the system has complicated nonlinear and chaotic characteristic, and it also may appear the superchaotic phenomenon under the certain parameters. Finally we research the superchaotic synchronization on the two single-ring erbium-doped fiber laser systems. In the master-slave scheme, the whole system can achieve the synchronization if the signal's amplitude is small enough. But in the coupling scheme, the transmitter system and the receiver system is controlled each other, which can achieve the synchronization with the parameter varies in a wide field. The successful simulations of these two schemes provide the perfect theoretical foundation for the chaotic secure communication on the single-ring erbium-doped fiber laser systems.3. Firstly, we review the dynamical characteristics on the dual-ring erbium-doped fiber laser system, and provide the bifurcation and Lyapunov exponent in the first time, which indicate that the system can be superchaos with specific parameters. Based on the parameter-modulating method and the general synchronization method, we propose the nonlinear feedback parameter-modulating methods and the general synchronization method on the single-ring system driving the dual-ring system. In this method, the decay rate is modulated by the difference of master system and slave system, and we obtain the synchronization between these two systems, on the suitable parameters. On the further research, we discover that the synchronization has phase-vagueness. But the phase-vagueness can be canceled automatically by designing the circuit in the laser synchronization system, and obtain the identical synchronization. In order to strengthen the security on the chaos correspondence we propose for the first time the general synchronization of single-ring system driving the dual-ring system, and confirm the condition of general synchronization by the Maximal Condition Lyapunov Exponent. To indicating the process of general synchronization, we make the numerical simulation by the assistant system method. We obtain the relationship between output laser signals of the driving system and the response system, which prove that the different systems can also be synchronized. All these results provide the new roads for identical synchronization of many laser systems.4. We show the modulation scheme for chaotic secure communication. The signal-masking scheme can transmit the analog signals and the numerical signals, but the amplitude cannot be too great. The shift-keying scheme is suitable for the numerical signals. The signal with great amplitude is feat for the wide-frequency modulation. And then numerically analyze the method for chaotic secure communication on the single-ring erbium-doped fiber laser system. In the single-ring erbium-doped fiber laser system, the analog signal is mixed with the chaotic carrier wave by message-masking scheme. With the sine wave message, the message can be demodulated successfully. When the message is digital signal, we modulate the parameters of the driving system by the digital signal, and also the message can be demodulated. But the speed is low because of the transient time, and it can become higher with the application of new materials. In the scheme of chaotic secure communication on the dual-ring erbium-doped fiber lasers, we realized the analog and digital signals effectively transmitted with the general synchronization method and message-masking scheme. Because the driving signal and the message signal are transmitted respectively, the whole systems are more steady and the demodulated message is more accurater. Finally, we analized the robustness of the chaotic secure communication on these two kinds of erbium-doped fiber laser systems, and we find that the system has good robustness and is transplantable.The numerical research of the chaotic/superchaotic synchronization and the chaotic secure communication on the erbium-doped fiber lasers must supply the theoretical and experimental foundation for its application on the optical secure communication.