Study for Broad-Band Chaotic Generator Using Semiconductor Lasers in Secure Optical Communications

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Recently, it has been discovered that the modulation bandwidth of semiconductor laser is greatly enhanced by a strong optical injection from a different laser. In chaotic secure communication systems using semiconductor lasers, the maximum chaotic carrier frequency plays an important role for data transmission rate. The chaotic carrier frequency is closely related to the modulation bandwidth of semiconductor lasers. Therefore the usage of semiconductor lasers with high modulation bandwidth is essential in chaotic secure optical communications. However, little study has been performed for the mechanism of the enhancement of the modulation bandwidth. In this study, we performed an extensive research for the mechanism for the modulation bandwidth in semiconductor lasers with strong optical injection. Also, we developed a broad-band chaotic generators using chaotic semiconductor lasers with strong optical injection for the purpose of hardware-dependent secure optical secure communications … More with high data-transmission rate.We have proposed the model for the chaotic generator of semiconductor lasers with optical feedback and formulated the systems by the rate equations. By the numerical simulations, the cut-off chaotic carrier frequency of 2.7 GHz without strong optical injection to a semiconductor laser is expanded to 7.0 GHz by the introduction of strong optical injection to the laser. Based on the theoretical investigation, we have developed a chaotic generator consisting of a MQW semiconductor laser with strong optical injection. The injection ratio was over 30 % of the solitary laser output power. In this system, we could obtain 9 GHz bandwidth for the solitary chaotic carrier frequency of 3 GHz. For the case of a DFB semiconductor laser, the chaotic generator frequency of 3 GHz without optical injection is expanded up to 14 GHz. Based on this research, we have done numerical study for chaos synchronization in the broadband chaotic generators. According to this numerical study, we have successfully performed chaos synchronization between the broadband chaotic generators. Also we have numerically succeeded a message transmission over the solitary chaotic carrier frequency. Less