Research On Physical Layer Encryption Scheme Based On Digital Polarization State Perturbation In CO-PDM System

From the ascendant of the Internet of Things,VR,and AR earlier,to the proposal of new concepts such as 5G,Metaverse,and Artificial Intelligence in recent years,the global Internet business has entered the fast track to development,and the scale of the total data is also growing exponentially.The growth rate of the level,which puts forward new requirements for communication technology,requires better communication technologies such as speed,bandwidth and other performance to support the transmission of network data and meet the needs of the Internet business.Coherent Optical Polarization Division Multiplexing(CO-PDM)technology has the characteristics of high spectrum utilization,large capacity,and convenient use of digital signal processing(DSP)technology for damage equalization at the receiving end,and has become one of the main technologies of optical fiber transmission system.With the rapid increase in data volume,data security issues have also followed.In recent years,large-scale corporate and government sensitive data leakage incidents have occurred from time to time,creating huge hidden dangers for the smooth development of the digital economy.In previous schemes to improve data security,most of them focused on encrypting the upper layer of the communication network.However,from the perspective of complexity and encrypted data coverage,encrypting the communication system at the physical layer is a more secure and economical way.Therefore,this paper mainly studies the physical layer encryption technology of CO-PDM system.Encrypting communication systems at the physical layer is diverse and flexible.After investigating other optical physical layer encryption methods and development trends,combined with the relevant characteristics of CO-PDM system,this paper chooses to use a matrix of digital polarization devices to perturb the signal in the electrical domain to realize data encryption,and adopt a symmetric encryption structure,which is easy to implement,flexible and low cost.Based on the detailed study of the basic principles and structure of CO-PDM system,we use digital polarization disturbance technology to encrypt the data of CO-PDM system,so as to improve the system security.The main research work is as follows:(1)Using the sensitivity of the CO-PDM system to polarization effect,the CO-PDM system is encrypted by using polarization as a new encryption dimension,which effectively scrambles the signal constellation diagram.Since the CO-PDM system uses the polarization dimension of the optical signal,the modulated optical signal will be affected by damage such as Rotation of State of Polarization(RSOP),and the traditional constant modulus algorithm(CMA)has limited compensation ability for RSOP,only 2-3Mrad/s.The encryption scheme proposed in this paper uses this feature to use digital polarization devices in the electrical domain to perturb the signal,due to the approximate linear modulation characteristics of the modulator,that is,the introduction of artificially controllable high-speed RSOP in the modulated optical signal,in which the RSOP speed can be as high as 50Mrad/s,which increases the difficulty of illegal receivers to obtain effective information and improves the security of the system.(2)In this paper,three different encryption modes and corresponding parameter sequence generation schemes are designed,and digital polarization devices are used to encrypt and perturbate signals in the electrical domain.The construction of a 40Gbps PDM-QPSK coherent optical communication simulation system verifies the feasibility of the encryption scheme,and the bit error rate of the illegal receiver in the three encryption modes of the receiving end is about 0.5,which indicates that the data is successfully encrypted in these encryption modes.(3)The transmission performance and encryption performance analysis of the three encryption modes are carried out.The results show that for the legal receiver,when the Optical Signal Noise Ratio(OSNR)of the system is greater than 9.5 dB,the BER in the three modes is less than the forward error correction threshold under the hard decision.The maximum transmission distance without relay of the encryption system is about 140km.Due to the small key space of the three encryption modes,which may not be able to withstand exhaustive attacks by eavesdroppers,this paper introduces a chaotic system in the process of generating parameter sequences to optimize the encryption scheme,so that the key space of the encryption scheme reaches more than 1052 to ensure the security of information transmission.