Research On Optical Transmission And Encryption Technology Based On Constellation Transform

With the emergence of new Internet services and the advent of the intelligent era of interconnection of all things,the total amount of network traffic in the world has skyrocketed.Hence,new technologies based on cloud computing and data centers continue to be presented,which brings new challenges to the communication system between data centers.The communication system between the inter-data center is a direct detection optical communication system with the advantages of low cost and simple equipment.And the current communication network environment puts forward higher and higher requirements for the performance of the direct detection optical communication system.Most optical fiber communication systems are actually power limited,especially low-cost short-distance optical fiber transmission systems,which is one of the focus of this article.In addition,the rich services of the Internet and smart Internet of Things applications bring convenience to people,but also threaten people’s privacy.The traditional security technology of upper-layer network protocols and algorithms can no longer cope with the increased speed of powerful computing power.Then the physical layer encryption technology stands out with its high speed,low latency,and high reliability.How to design a physical layer encryption scheme with higher adaptability,reliable security performance,and low complexity is also the main research point of this article.This article mainly focuses on the short-distance direct detection system of the Kramers-Kronig(KK)receiver based on constellation map transformation and the physical layer encryption of the optical communication system,and conducts in-depth research on how to improve the system performance and design a new physical layer encryption scheme.And through the establishment of multiple communication simulation systems to verify the feasibility of the program,its main work and innovation are:(1)The principle of direct detection of the main components of the optical communication system is explained,and the principle of the KK receiving algorithm and several ways of single-sideband signal generation are introduced in detail.In order to reduce the system’s demand for optical signal noise ratio(OSNR),and after explaining the mechanism of geometric shaping(GS)and probabilistic shaping(PS),we introduced it into the direct detection system based on the KK receiver.The simulation results show that the introduction of hybrid probabilistic-geometric shaping can reduce the OSNR requirement by 0.6dB compared with the traditional uniform distribution.And the introduction of geometric shaping for the 64 quadrature amplitude modulation(QAM)modulation format can reduce the OSNR requirement by 0.5dB compared with the uniform distribution.(2)On the basis of introducing several common physical layer encryption schemes,a phase modulator-based constellation diagram rotation physical layer encryption scheme is designed from multiple generation methods of high-order modulation formats.In order to verify the feasibility of the solution,we introduced the encryption solution into differential phase shift keying(DPSK)communication system.The simulation showed that the eavesdropper could not get the transmitted signal correctly and the error rate of the signal received by the legal receiver was negligible compared with the unencrypted signal.In the DPSK modulation format,this scheme is equivalent to the realization of optical XOR logic operation.At the same time,we also briefly introduced the basic principles of coherent optical communication systems,and different rotation angles and Quadrature Phase Shift Keying(QPSK)modulation formats and higher-order 16QAM modulation formats were adopted for analysis and comparison.The constellation diagram received by the eavesdroppers is more confusing when the rotation angle of higher-order modulation formats is larger.Inspired by the encryption scheme of the rotating constellation,we proposed to use geometric shaping as an encryption technology.The KK receiver based on geometric shaping directly detects the optical communication system for verification and the criterion is mutual information(MI),and the eavesdropper get the wrong MI value.