Keywords: 
• 混沌激光 /
• 物理随机数 /
• 光采样 /
• 延时比较

Abstract: Random numbers are used to encrypt the information in the field of secure communications. According to"one-time pad" theory found by Shannon, the absolute security of the high-speed communication requires the ultrafast reliable random numbers to be generated in real-time.Using complex algorithms can generate pseudorandom numbers, but they can be predicted due to their periodicity. Random numbers based on physical stochastic phenomena (such as electronic noise, frequency jitter of oscillator) can provide reliable random numbers. However, their generation rates are at a level of Mbit/s typically, limited by the bandwidth of traditional physical sources.In recent years, high-speed physical random number generation based on chaotic laser has attracted much attention. Common methods of extracting random numbers are to sample and quantitate the chaotic signal in electronic domain with a 1-bit or multi-bit analog-to-digital converter (ADC) triggered by an RF clock and then post-process the original binary sequences into random numbers. However, the large jitter of the RF clock severely restricts the speed of ADC. Moreover, the existence of the subsequent post-processing process put a huge challenge to how the synchronization is kept among all the devices (e.g., XOR gates, memory buffers, parallel serial converters) by using an RF clock. Thus, to our knowledge, the fastest real-time speed of the reported physical random number generator is less than 5 Gbit/s.In this paper, we propose a novel method of generating the real-time physical random numbers by utilizing chaotic laser pulses. Through sampling the chaotic laser in all-optical domain by using a mode-locked pulsed laser, chaotic laser pulse sequences can be obtained. Then, real-time physical random numbers are obtained directly by self-delay comparing the chaotic pulse sequences with no need of RF clock nor any post-processing.Furthermore, a proof-of-principle experiment is carried out, in which an optical feedback chaotic semiconductor laser is employed as an entropy source. Experimental results show that the real-time random number sequences at rates of up to 7 Gbit/s can be achieved. The real-time speed is mainly limited by the bandwidth of the applied chaotic signal. If the chaotic laser with a higher bandwidth is adopted, the real-time generation rate can be further enhanced.