Study Of The Chaos Synhcronization Systems Based On Mutual Coupling Semiconductor Lasers

Optical chaos signals generated by semiconductor lasers (SLs) have attracted great interests in all-optical secure communications for their broad bandwidth and intrinsic privacy characteristics. The chaos synchronization system based on semiconductor lasers has been applied in the fields of all-optical secure communication, private key negotiation, and public channel cryptography etc. At the same time, along with the development of the innovations in the methods and technologies, the research and application about the chaos synchronization system based on the semiconductor lasers are facing new opportunities and challenges. Against the important requirements and research situations of the optical communications and secure communications, the study and application of the chaos synchronization system based on mutual coupling semiconductor lasers (MCSLs) are chosen as the topic of this dissertation, which is supported by the by the National Natural Science Foundation of China, the Key Project of the Science and Technology Research Fund of Ministry of Education, the Specialized Research Fund for the Doctoral Program of Higher Education of China, the Applied Basic Research Foundation of Sichuan Province, and the Doctoral Innovation Talent Foundation of Southwest Jiaotong University. The aims are to explore new theory and methods for the achievement of chaos synchronization, to design some novel and practical chaos communication and secure communication schemes, to enhance the security of chaos communication, and to expand the applications of semiconductor laser chaos synchronization system, which has important theoretical significance and practical value.Against the above-mentioned background, an indepth study on the chaos synchronization properties and communication applications of different MCSL systems and their expansion systems is performed in this dissertation. From the theoretical perspective, the synchronization conditions, synchronization distribution, and chaos communication security of the mutual coupling semiconductor lasers subject to external optical feedback (EOF-MCSLs) are thoroughly studied. By introducing injection-locking mechanism into the MCSL systems, a chaos synchronization scheme based on the MCSLs subject to external optical injection (EOI-MCSLs) is proposed, which can efficiently overcome the restrictive problems of demanding synchronization conditions, disappointing robustness, and restricted communication performance in EOF-MCSL systems. From the point of application expansion, the isochronal chaos synchronization properties and multichannel communication application in the multiple time-delayed mutual coupling external-cavity semiconductor lasers (MTDMC-ECSLs) that work in a high-frequency chaotic regime are explored, a chaos synchronization and multicharmel communication scheme based on the multiple time-delayed mutual coupling semiconductor lasers subject to external optical injection (EOI-MTDMCSLs) is proposed for the first time, and moreover, a multiaccess chaos communication scheme and a network-type SL chaos synchronization system on the basis of the EOI-MCSLs are designed.The investigations on the chaos synchronization properties of the MCSL systems and their expansion systems are performed on the basis of the rate equation model of SLs. The theoretical conditions for the chaos synchronization are obtained by analyzing the rate equation model. The numerical studies on the synchronization distribution, robustness etc., are carried out by the Rung-Kutta algorithm. On the other hand, the research about the communication applications of the systems is concentrated on the designs of the novel and practical chaos communication scheme, high-privacy encryption scheme and the security-improved method exploration. The availability and advantages of the novel methods and schemes are confirmed by establishing the simulation models with the Simulink toolbox of Matlab2007. The main innovative work and results of this dissertation are presented in the following. During the period of working for PhD degree, eleven academic journal papers have been published with N. Jiang listed as the first author, and nine of them are indexed by SCI and one is indexed by El. Four papers were published in the second division of SCI journal. Moreover, one national invention patent in which N. Jiang is list as the first inventor has been applied (publicized).Taking the mutual coupling external cavity semiconductor lasers and the mutual coupling semiconductor lasers with a partially transparent mirror in between for instance, an indepth study on the chaos synchronization properties of the EOF-MCSL system and the exploration for enhancing the security of bidirectional chaos communication are presented. Firstly, with the synchronization mechanism for conventional mutual coupling systems, i.e. the symmetric operation mechanism, the theoretical conditions for the chaos synchronization in the EOF-MCSL system is derived, which indicates that there are two types of chaos synchronization, namely the isochronal chaos synchronization (ICS) and the leader/laggard chaos synchronization (LLCS) exist in the EOF-MCSL system. The former requires the feedback parameters and mutual coupling parameters of the MCSLs are respectively identical, while the latter occurs when the feedback strength of each MCSL is identical to the strength of the coupling that they injects into the counterparts, and the sum of the feedback delays equals to two times of the mutual coupling delay. Secondly, a systematical investigation on the synchronization distribution, robustness, and communication performance of the ICS and LLCS is performed. The results indicate that stable high-quality ICS appears in the region where the feedback strengths are close to the coupling strengths, while the synchronization operation region for the LLCS is wider and the synchronization lag is determined by the difference of the feedback delays. With respect to the ICS, the LLCS shows a wider operation region, a stronger robustness, more obvious chaos pass filtering effects and a better synchronization communication performance. In addition, with regard to the security drawbacks of the synchronization communication between EOF-MCSLs, several security-enhanced methods, i.e., properly increasing the message bit rate, adopting asymmetric bit rate transmission, monitoring the quality and lag time of chaos synchronization, and encrypting messages with the internal modulation technology etc. are proposed. In this sub-topic, the chaos synchronization properties and synchronization communication performances have been revealed thoroughly. Three academic papers have been published with N. Jiang listed as the first author, i.e.,[Physical Review E,2010,81(066217)],[Optics Communications,2009,282(2217)], and [Chinese Optics Letters,2008,6(517)].By introducing the injection-locking mechanism into achieving chaos synchronization in the MCSL systems, a chaos synchronization scheme based on the EOI-MCSLs is proposed. In the scheme, the MCSLs are subjected to unidirectional injection from a chaotic driver semiconductor laser named as DSL. The injection-locking effect induced by the external optical injection weakens the demanding requirements in the symmetry and guarantees the stability of the chaos synchronization. As long as the external chaotic injection is sufficiently strong, stable high-quality chaos synchronization can always be achieved between the MCSLs, which not only overcomes the problem of stringent synchronization conditions in the EOF-MCSL system, but also can provide a wider synchronization region and a stronger robustness. Meanwhile, the efficient bandwidth of chaotic carrier is enhanced by the external optical injection, thus the EOI-MCSL system affords high-speed bidirectional chaos communication. The proposed scheme shows several advantages, such as convenient synchronization conditions, strong robustness and good communication performance, and moreover, the performances of chaos synchronization and communication can be further improved by increasing the external optical injection strength. This sub-topic has developed the theory of chaos synchronization in MCSL systems, and proposed a much practical chaos synchronization scheme for mutual coupling semiconductor laser system. One academic paper has been published with N. Jiang listed as the first author, i.e.,[IEEE/OSA Journal of Lightwave Technology,2010,28(13):1978-1986], which also gets the "IEEE excellent student paper award" in2010.The isochronal chaos synchronization properties and its multichannel synchronization communication application in the high-frequency chaotic MTDMC-ECSL system is explored. The MTDMC-ECSL system is established by extending the conventional mutual coupling external-cavity semiconductor laser system. An in-depth investigation on the distribution and robustness of the isochronal chaos synchronization is carried out, and the isochronal chaos synchronization is used to achieve multichannel chaos communication. Obviously different from the complicated requirements in the relationship between the feedback delay and mutual coupling delay in the low-frequency fluctuation systems, the stable high-quality isochronal chaos synchronization in the high-frequency MTDMC-ECSL system only requires that one of the mutual coupling time delays equals to the feedback delay. The high-quality isochronal chaos synchronization shows relatively strong robustness to the mismatches of internal parameter and injection current, but is much sensitive to the frequency detuning. With proper selection of the feedback and couplings, In messages can be simultaneously transmitted through n (n>1) bidirectional public links, and the performance is much good. In this sub-topic, the chaos synchronization conditions that are obviously different from those of the low frequency fluctuation systems of the high-frequency MTDMC-ECSLs is uncovered, and a high-performance multichannel chaos synchronization communication is achieved, which has been reported in the following published paper with N. Jiang listed as the first author, i.e.,[Journal of Optical Society of America B,2011.28(5):1139-1145].A chaos synchronization and multichannel communication scheme based on the EOI-MTDMCSLs is proposed for the first time. The multiple time-delayed mutual coupling semiconductor lasers'outputs are driven to evolve toward a same track by the injection-locking effect induced by the external optical injection. The chaos synchronization distribution and multichannel communication performance are studied systematically. The results show that, as long as the external injection is properly strong, stable high-quality chaos synchronization that is independent with the injection delay and coupling delays can always be achieved. The stronger the external optical injection is, the wider the operation region for stable chaos synchronization is, and the stronger the synchronization robustness is. With the chaos modulation encryption technology and its corresponding decryption methods, a high-speed multichannel chaos communication can be achieved, in manner of achieving simultaneous bidirectional message transmissions on each link. This sub-topic proposes a new practical chaos synchronization and multichannel communication scheme, in which the performances are greatly better than those of the MTDMC-ECSL system. One academic paper has been published with N. Jiang listed as the first author, i.e.,[IEEE Journal of Selected Topics in Quantum Electronics,2011,17(5):1220-1227], and one national invention patent in which N. Jiang is listed as the first inventor has been applied, i.e.,[application number:201110236861.6; publication number:CN102347832A].The compound chaos synchronization regularity of the EOI-MCSL system is uncovered, with which a multiaccess chaos communication scheme and a network-type SL chaos synchronization system are designed. An intensive investigation on the cross correlations between the SLs in the EOI-MCSL system is carried out, which indicates that, along with the achievement of the high quality isochronal chaos synchronization between the MCSLs, an unidirectional complete synchronization or general synchronization between the DSL and MCSLs can be achieved simultaneously. With this compound synchronization property, a broadcasting synchronization communication from the DSL to the MCSLs and a bidirectional chaos communication between the MCSLs can be simultaneously achieved. Based on this case, a high-security encryption chaos communication scheme that adopting the broadcasting message as the encryption/decryption key for the encryption chaos communication between the MCSLs is firstly proposed, which can greatly enhance the security of the bidirectional synchronization communication. This work has been published in the following academic paper, i.e.,[IEEE Photonics Technology Letters,2010,22(10):676-678], where Ning Jiang is listed as the first author. On the other hand, by further expanding the EOI-MCSL system, a network-type SLs chaos synchronization system is designed, in which a DSL drives multiple cascade-configurated MCSLs (CC-MCSLs) with unidirectional optical injections. In this system, any two MCSLs can communicate with each other bidirectionally, and a broadcasting synchronization communication from the DSL to the CC-MCSLs can be carried out simultaneously. This work has been submitted to the journal of Science China Information Sciences. The multi-access chaos communication scheme and network-type SLs chaos synchronization system can greatly expand the novel applications of MCSLs, which is much beneficial to the realism of chaos communication networks.