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Chaos Synchronization Of Semiconductor Lasers Subject To Optical Feedback And Its Applications In Secure Communication

Posted on:2009-09-06Degree:MasterType:Thesis
Country:ChinaCandidate:L XuFull Text:PDF
GTID:2178360242996901Subject:Optics
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With the wide use of the computer and various communication networks, secret communication becomes a new researching focus in the science fields of computer communication, network, application mathematics, microelectronics and so on. Chaotic motion is a complex nonlinear motion. Chaotic signals are ergodicity, aperiodie, uncorrelated, broadband and noise-like and have been proved to be useful for secure communication. Therefore, chaotic synchronization and its application have received and growing research interest. Semiconductor laser (SL), as the best optical resource in the optical communication, which can redize large band-width (about several GHz) and hyper-dimension chaos signal (with some positive enthuse Lyapunov exponents) through feedback or injection, has been enthusiastically studied. In this paper, the chaotic characteristic and synchronized principle based on SL subject to optical feedback and its application to secure communication have been investigated.Firstly, the dissertation discusses systematically basic concepts of chaos and chaos synchronization: (definition, main feature, the way to chaos and how to judge chaos synchronization); and the chaos synchronization subject to feedback is also introduced.Secondly, the paper discussed the chaos of SL. There are two feedback ways leading the laser to chaos: optoelectronic feedback and optical feedback, where the optical feedback includes coherent optical feedback and incoherent optical feedback.Coherent optical feedback synchronization system can be divided into two categories: complete synchronization and injection-locking synchronization. Complete synchronization has high secrecy, but is sensitive to the parameters mismatch. If there exists small oscillating frequency detuning or parameters mismatch between the emitting laser and receiving laser, the synchronized performance will greatly decrease Therefore complete synchronization is hardly realized in practice. As for injection-locking synchronization, it has good tolerance to parameters mismatch. However, the sensitivity lowering to parameter mismatch will lead to the security decline.Unlike coherent optical feedback, the synchronization system subject to incoherent optical feedback acts only on the carrier density in the laser rather than the optical field, so it does not depend on locking of optical carrier frequency. In this paper, based on the theoretical mode of the incoherent optical feedback system, the influence of the internal parameter mismatch on the synchronized characteristics of the chaotic system has been investigated. Comparing with two styles of chaotic system with coherent optical feedback, the chaotic system with incoherent optical feedback is not only easier to put into practice than the complete synchronized coherent optical feedback system but also has higher security than injection-locking synchronization coherent optical feedback system. Using encoding of chaos shift keying, the message can be hidden efficiently during the transmission and decoded easily in the receiver.Finally, based on the theoretical mode of the incoherent feedback system, message encoding and decoding of the incoherent optical feedback synchronization system are studied numerically. The results demonstrate that the message can be hidden efficiently during the transmission for all encryption schemes; For the bit rate is 250Mb/s, the message can be decoded easily in the receiver with CSK (chaos shift keying) and CMS (chaos masking); when the bit rate increases to 2.5Gb/s, the message can not be decoded with CSK, the quality of decoding message with CMS becomes bad; furthermore, when the frequency increases to 12.5Gb/s, the message can not decoded with both CSK and CMS but can be decoded easily with ACM (additive chaos modulation).
Keywords/Search Tags:Semiconductor laser, Chaos, Chaotic synchronization, Secure communication, Coherent optical feedback, Incoherent optical feedback
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