Investigation On Analog-Digital Hybrid Electro-Optic Chaotic Systems And Their Applications In Secure Communication

With the widespread application of communication technology,optical network security has become a serious concern.Conventional algorithm-based information security techniques pin hopes on the difficulty of solving specific mathematical problems.And their security becomes weak with the rapid development of softwar e and hardware technologies.Chaotic optical communications systems utilize chaos synchronization mechanism to encrypt and decrypt messages,which has the potential to achieve information-theoretic security.It can cope with the challenges faced by conventional algorithm-based information security technologies and has received more and more attention in recent years.High-quality chaotic laser systems and robust chaos synchronization methods are the fundaments for guaranteeing the security of these secure communication systems.Since most of existing chaotic optical communications schemes are based on pure analog chaotic laser systems,the inevitable channel impairments in fiber optic links limit the transmission distance of these secure communication systems.Besides,the delay signature problem that is common in pure analog chaotic laser systems has a negative impact on its security.Analog-digital hybrid electro-optic chaotic systems could integrate the advantages of analog and digital chaos systems,is compatible with digital synchronization strategy.And the time delay signature problem of pure analog chaotic laser systems is avoided.Two analog-digital hybrid electro-optic chaotic systems with good chaotic characteristics and robustness are proposed.Subsequently,their applications in secure communication are explored.Researches have significant value for further improving the practicality of chaotic optical communication and meeting the growing demand for secure communication.The main results are as follows:(1)Aiming at the problem of complex structure and limited synchronization range of existing chaotic systems,an analog-digital hybrid electro-optical chaotic system based on external modulation is proposed.The system consists of nonlinear convers ion,sample quantization,and digital feedback.By using an equivalent process made by general devices,the system simplifies the implementation of nonlinear conversion.Analyses show that the system can output high dynamic complexity broadband optical chaotic signals.In addition,the system is compatible with digital synchronization strategy.With mature digital signal optical transmission technologies,the impact of channel impairments on chaos synchronization is greatly reduced.The system also guarantees its robustness,overcomes the time delay signature problem of analog chaos systems and the degradation of characteristics of digital chaotic systems.(2)In order to further reduce the implementation complexity and cost of the analog-digital hybrid electro-optical chaotic system,an analog-digital hybrid electro-optical chaotic system based on semiconductor laser is proposed.By introducing a semiconductor laser with self-feedback and external injection,the scheme further simplifies nonlinear conversion.The problem that the existing systems require complicated optic-electro-optic signal transformation process is overcome.Compared with the external modulation system,the chaotic signal bandwidth generated by the scheme is relatively limited and can be applied to applications where the rate requirement is relatively low.(3)Using the robust long-distance digital synchronization strategy,a "one-time-pad" secure transmission scheme based on the analog-digital hybrid electro-optic chaotic system is proposed.The scheme generates synchronized random number sequences with the synchronized analog output signal of the chaotic system and then performs data encryption and decryption operation in exclusive OR operations.Based on analog delay difference and digital high-order differential,a post-processing algorithm is proposed to ensure the randomness of the generated sequence.A dual threshold quantization agreement method is used to improve the synchronism of generated sequences.Taking image data as an example,the ability of the scheme to achieve high-speed long-distance "one-time-one-secret" secure transmission of Gb/s-level communication rate is demonstrated.(4)Aiming at the problem of how to achieve the highest possible secure transmission rate under the condition of limited bandwidth of chaotic signals,using high-order modulation techniques,an OFDM secure transmission scheme based on the analog-digital hybrid electro-optic chaotic system is proposed.The scheme converts the analog output signal of the synchronized analog-digital hybrid electro-optical chaotic systems into the digital domain,and then performs phase masking and unmasking on the subcarriers to achieve the data encryption and decryption operation.The applicability of the proposed analog-digital hybrid electro-optical chaotic source to the chaotic optical communication using a high-order modulation format is demonstrated.The scheme alleviates the system's calculation speed pressure and simultaneously improves the transmission security.(5)Aiming at the problem of limited distribution distance of existing chaotic key distribution systems,using robust long-haul digital synchronization strategy,a key distribution scheme based on the analog-digital hybrid electro-optic chaotic system is proposed.By exchanging the random control parameters,the scheme determines the time slots where the chaotic systems are synchronized.And then the keys are generat ed based on the synchronized analog chaotic signals.A post-processing method based on analog delay difference is used to obtain unbiased analog chaotic signals and enhance the security of the system.This scheme can robustly distribute secure keys at high speed in long-haul digital communication networks.