| Optical fiber communication has outstanding advantages such as high speed,low loss and large capacity,which has gradually become the main communication method for long-distance transmission today,carrying more than 90%of the world's communication services.With the development of various optical fiber eavesdropping technologies,the security of optical fiber communication is facing severe technical challenges.The chaotic signal based on external cavity semiconductor laser can be used not only as an optical carrier for encrypting optical signals at the physical layer,but also as a physical entropy source for high-speed key generation,because of its advantages of wide spectrum and noise-like waveform.The chaos generated by external cavity semiconductor laser(ECSL)has been a research hotspot in the last two decades.However,the problems of insufficient bandwidth and complexity of ECSL-based chaos limit the speed and security of chaotic optical communication and key distribution systems.In order to improve the practical application ability of chaotic laser,this dissertation studies the following three aspects.1.broadband complex chaos generationAiming at the limited bandwidth of chaotic signals generated by optical feedback ECSL and the existence of time delay signature,this dissertation studies the optimization technology of chaotic laser.(1)A chaotic laser optimization scheme based on self-feedback phase modulation and dispersion is proposed.The bandwidth broadening and time-delay signature suppression are realized by utilizing the optical spectrum spreading effect of chaotic phase modulation and the phase-to-intensity conversion effect of dispersion.In this scheme,chaotic signal with bandwidth up to 100GHz can be produced,and TDS can be unrecognizable in the feedback strength range of 20 d B.(2)A chaotic bandwidth and TDS optimization scheme is proposed,in which a phase modulator driven by self-delayed signal and a time-delayed interference are introduced into the feedback loop.The experimental and numerical results show that chaotic signals with flat spectrum and suppressed TDS can be generated.(3)Two multi-channel broadband complex chaos generation schemes are proposed and experimentally verified.On the one hand,another laser source and mutual injection are introduced into the structure of optical feedback ECSL.On the other hand,optoelectronic hybrid feedback and parallel filtering are introduced after the output of optical feedback ECSL.In those two schemes,multiple chaotic outputs with high bandwidth,TDS suppression and low correlation are simultaneously obtained.2.broadband chaos synchronization and physical random number generationChaos synchronization is the basis for the application of chaotic laser in the field of secure communication.In order to solve the problem of limited bandwidth and complexity of the existing experimental chaos synchronization systems,this dissertation studies the broadband complex chaos synchronization technology.(1)Two broadband complex chaos synchronization schemes are proposed,which adopt a one-way master-slave injection structure and a common phase noise injection structure,respectively.Under the condition that the device parameters of both communication sides are matched,the experimental results have verified that the synchronization of chaotic signals with bandwidth exceeding 20GHz and TDS suppression can be achieved.(2)A chaos synchronization optimization scheme is proposed,in which generative adversarial network is introduced to improve the initial synchronized chaotic signals.In this scheme,the TDS suppression of chaotic signal,the improvement of amplitude distribution symmetry and the enhancement of synchronization privacy are realized.(3)The experimentally obtained broadband complex chaotic laser is applied as the physical entropy source to the random number generator.Single-channel and multi-channel random bit sequences with a rate of hundreds of Gbps are verified through simple offline post-processing.(4)The generation of high-speed synchronized physical random numbers is verified.Double-threshold quantization is used to extract synchronized random bit sequences with a rate up to Gbps and a bit error rate lower than 10-3 from synchronized broadband chaotic entropy source.3.chaos-based secure optical communicationAiming at the problem of insufficient speed and security of chaotic optical communication,this dissertation studies high-speed physical layer secure optical communication technology.(1)A secure optical communication scheme based on broadband complex chaotic carrier is proposed.The sender uses the broadband complex chaos as the optical carrier to hide information,and the receiver decrypts the information through the synchronized chaotic signal.In the experiment,high-speed secure optical communication with a rate of over 10Gbps is realized.The results prove that the information can be encrypted and decrypted at a high rate and an appropriate concealment coefficient.The encryption performance and maximum transmission rate of the system are investigated by simulation,and the security of the communication system as well as the key space of hardware parameters are discussed.(2)An encryption scheme based on chaotic phase disturbance is proposed,which is different from the traditional chaotic optical carrier encryption.In the scheme,the synchronized chaotic signals are used as the dynamic control signals of encryption and decryption,and directly converts the high-speed optical information signal of the physical layer into noise-like signal.The numerical results show that the maximum transmission rate of the system is as high as 100Gbps under the OOK modulation format.In the experiment,the secure optical transmissions of a 10Gbps OOK signal and a 25Gbps QPSK signal are verified.(3)A multi-channel aliasing encryption scheme based on chaotic phase disturbance is proposed.In the experiment,4 channels are used to verify the WDM secure optical transmission with a rate of 50Gbps.The numerical results further verified that channels with different modulation formats can be encrypted at the same time. |
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