High-Capacity Optical Secure Communication Technology Based On Constellation Shaping

Fiber optic communication is the cornerstone of modern communication networks and an indispensable structure for the information society.With the advance of the digital era,various high-bandwidth applications,new network products and novel network concepts continuously emerge.The entire optical communication network carries an enormous amount of network traffic,and information exchange between countries,organizations,and individuals heavily reliant on fiber optic communications.Thus,future optical communication systems require high-capacity and high-security requirements.Currently,the backbone network and the data center require urgent expansion.Submarine cable transmission,which involves national security,and short-range interconnection for personal and enterprise security,face the threat of fiber optic eavesdropping.The development of optical communication systems poses three major challenges:further capacity expansion of the backbone network,low-cost high-capacity solution for the short-reach interconnect,and refinement of the physical layer security transmission.This thesis tends to address these challenges,by using probabilistic constellation shaping technology and self-homodyne coherence technology.Moreover,by combining these new techniques,high-capacity high-security chaotic encryption optical communication systems are proposed with new encryption dimensions and sensitive parameters.The main innovative research outcomes are summarized as follows.（1）To achieve high-throughput low-complexity probabilistic shaping,simplified bit-level distribution matching（SBL-DM）is proposed.Experimental results confirm that SBL-DM achieves receiver sensitivity gains of up to 0.11 d B and 0.89 d B in comparison with SL-PAS and PDM,respectively.SBL-DM achieves low complexity and high throughput while retaining considerable shaping gain,providing a better choice for the practical applications of probabilistic shaping（PS）.（2）Optimum enumerative sphere shaping（OESS）is proposed as an optimized version of enumerative sphere shaping（ESS）,which can always achieve the lowest average energy at any blocklength.Numerical analysis shows that OESS leads to better energy efficiency,as well as more Maxwell-Boltzmann-like distributions compared with ESS,decreasing rate loss of up to 0.031 bits/amp at the blocklength of 20.In the 75km transmission of a discrete multi-tone（DMT）system,OESS achieves receiver sensitivity gains of 0.24 d B and 5.61 d B compared with ESS and CCDM,respectively.Moreover,a chaotic ESS for digital-layer encryption is proposed.In the experimental verification in a 3-dimention digital chaotic encryption DMT system,60.79Gbit/s PS 64-ary quadrature amplitude modulation（QAM）signals are transmitted over 75km standard single mode fiber.The digital key space is larger than 10⁷⁴,yielding relable security performance.（3）A cost-efficient bi-directional polarization-multiplexed self-homodyne coherent system is proposed and experimentally verified through 120Gbit/s 16QAM transmission,achieving a transmission distance of 5 km and a polarization rotation tolerance of up to 45rad/s.Based on the polarization-multiplexed self-homodyne coherent system,the feasibility of the optical-layer encryption enabled time mismatch beween the signal and local oscillator is verified.In the 160Gbit/s 16QAM experimental verification,time mismatches of more than 1 symbol interval can introduce severe phase noise,which provides enough key space for the security of the system and realize the real-time encryption of physical-layer transmission as well.（4）By combining constellation shaping and self-homodyne coherent,A chaoptic security system is proposed which includes optical-layer encryption and digital-layer encryption.With a hyperchaotic system,chaotic sequences are generated and used for the exclusive or operation,chaotic constant composition distribution matching,phase disturbance,and optical-layer time-delay disturbance.Moreover,64-ary circular quadrature amplitude modulation（64CQAM）format is adopted for transmission due to its advantages of sensitivity to phase noise,immunity to conventional digital signal processing,and ability of time-mismatch masking.Last,we conduct an experimental verification in a 1.8km 20GBaud probabilistically shaped 64CQAM system.With a large-linewidth laser source,optical-layer security can be protected by time mismatches up to 60ps.The joint encryption of digital and optical domains greatly reduces the risk of information leakage caused by the system crack.This thesis aims to apply the current advanced optical communication technology to secure optical communication,expanding the operational dimension of encryption and improving the physical layer security transmission mechanism.These efforts have the potential to contribute to the development of the cause of cyberspace security.