线宽增强因子对光反馈半导体激光器混沌信号生成随机数性能的影响

摘要

基于光反馈半导体激光器产生的宽带混沌信号作为物理熵源生成物理随机数已得到广泛研究.线宽增强因子的存在会导致半导体激光器出现大量不稳定动态特性,因此,本文着重研究半导体激光器的线宽增强因子对生成随机数性能的影响.数值仿真结果表明:随着线宽增强因子的增加,光反馈半导体激光器输出混沌信号的延时峰值逐渐减小、最大李雅普诺夫指数逐渐增大.基于不同线宽增强因子下产生的混沌信号提取随机数,并利用NIST SP 800-22软件对生成随机数的性能进行测试.测试结果表明,选取线宽增强因子较大的半导体激光器产生混沌信号作为物理熵源易于生成性能良好的随机数.%Random numbers play an important role in many fields, including information security, testing and engineering practice. Especially in information security, generation of secure and reliable random numbers, they have a significant influence on national security, financial stability, trade secrets and personal privacy. Generally, random number generators can be classified as two main types: pseudo random number generators and physical random number generators. Pseudo random numbers with high speed are generated by software algorithms, but the inherent periodicity will cause serious hidden dangers when they are used in information security. Random numbers based on physical entropy sources (such as electronic thermal noise, frequency jitter of oscillator, quantum randomness) can produce reliable random numbers. However, due to the limitation of traditional physical source bandwidth, their generation speeds are at a level of Mbit/s typically, which cannot meet the needs of the current high-speed and large-capacity communication. In 2008, Uchida et al. (2008 Nat. Photon. 2728) realized the physical random number of 1.7 Gbit/s by using a wideband chaotic laser for the first time. The emergence of wideband physical entropy sources such as chaotic laser greatly promote the rapid development of the physical random number generators. As far as we know, a semiconductor laser can generate wideband chaotic signals under external disturbances such as optical feedback, optical injection or photoelectric feedback. However, compared with the structures of other two lasers, the structure of the optical feedback semiconductor laser is simple and easy to integrate. Therefore, chaotic signals have received great attention to produce high-speed physical random number extracted from the optical feedback semiconductor laser. In the reported schemes, a variety of post-processing methods are used to improve the speed and randomness of random numbers. Besides, optimizing the chaotic entropy source can also improve the performance of random number. So far, the influence of internal parameters on the dynamic characteristics of semiconductor lasers has attracted wide attention. The linewidth enhancement factor is one of the key parameters for a semiconductor laser. The values of linewidth enhancement factor are different, depending on the type of semiconductor laser. The existence of linewidth enhancement factor results in a large number of unstable dynamic characteristics of semiconductor lasers. Therefore, it is of great significance for studying the influence of the linewidth enhancement factor on performance of random numbers. In this paper, we focus on the influence of the linewidth enhancement factor on the randomness of the obtained random numbers. The time delay characteristics and complexity are two important parameters to measure the quality of chaotic signals. The simulation results show that with the increase of the linewidth enhancement factor, the time delay characteristic peak of the chaotic signal from an optical feedback semiconductor laser decreases gradually, meanwhile, the maximum Lyapunov exponent of chaotic signal increases gradually. The randomness of random numbers, generated by the chaotic signal from the optical feedback semiconductor laser under different linewidth enhancement factors, is tested by NIST SP 800-22. The test results show that semiconductor laser with larger linewidth enhancement factor is chosen as a physical entropy source to generate random numbers with high quality.