Phase Chaos Synchronization In Open-loop Unidirectional Coupling Semiconductor Laser

Today,the society has entered the era of big data,and people's demands for the speed and security of communication systems are also increasing.Traditional secure communications are usually encrypted using algorithms,such as symmetric encryption and asymmetric encryption,and its security depends largely on the complexity of the algorithm.With the rapid development of computer operation speed,there is a risk that algorithm encryption technology will be cracked in principle.Therefore,the secure communication technology based on the physical layer has always received much research attention.Quantum key distribution is a physical layer secret technology,which uses the principle of quantum non-cloning and uncertainty to achieve the secure distribution of encryption keys.However,this technology urgently needs to break through bottlenecks such as key distribution rate limitation and compatibility with traditional communication networks.Over the past two decades,chaotic laser secret communication has received extensive research attention due to its advantages of high speed and compatibility with existing communication systems.The rate of chaotic laser secret communication essentially depends on the bandwidth of the chaotic carrier.Due to the simple structure and easy integration,chaotic transceivers mostly use the structure of optical feedback semiconductor lasers.Its chaotic carrier bandwidth is limited by the relaxation oscillation frequency of the laser,which in turn limits the communication rate to only a few Gbps,and still cannot meet the security requirements of current high-speed optical communication.Many methods to enhance the bandwidth of chaotic signals have been proposed one after another,but they usually increase the complexity of the chaotic transceiver system and increase the difficulty of high-quality chaotic synchronization.Another way to increase the information rate is multi-dimensional higher-order modulation,such as optical quadrature amplitude modulation.However,in order to hide higher-order modulation signals,chaotic lasers not only need intensity chaotic synchronization,but also phase chaotic synchronization.At present,the research on phase synchronization of semiconductor lasers is limited to theoretical numerical research.Therefore,to explore the phase synchronization characteristics of the laser from an experimental point of view is of great significance for exploring a high-order signal chaotic secret transmission scheme.This paper focuses on the phase chaos synchronization of the open-loop unidirectional coupling system of semiconductor lasers,and carries out the following two main tasks:(1)Using the Hilbert transform to extract the phase,the experiment observes the phase chaos synchronization based on the DFB laser open-loop unidirectional coupling system.And we further analyze the influence of injection intensity and frequency detuning on the cross-correlation and synchronization error of phase synchronization.The results show that the phase synchronization can reach more than 0.95 in the parameter range of injection intensity greater than 0.8 and frequency detuning in the range of-11 GHz to4GHz.It is also found that phase synchronization has a larger synchronization range than intensity synchronization.(2)The experiment found that there is an unstable phenomenon of phase chaos synchronization between the master and slave lasers.Combining theory,the duration and transition value of the phase difference between the master and slave lasers are statistically analyzed,and the effects of feedback parameters and injection parameters on the phase synchronization in the synchronization system are studied.Causes of phase difference jump.The results show that the master-slave lasers are synchronized under a large number of statistical characteristics,but there will be 2? and non-2? transitions at the instantaneous characteristics,which leads to unstable phase synchronization,which is not conducive to hiding information based on phase synchronization.How to stabilize phase synchronization or explore other methods of phase synchronization has important guiding role for chaotic secret optical communication based on higher-order modulation.