Keywords: 
• 半导体激光器 /
• 混沌激光 /
• 多位量化 /
• 物理随机数

Abstract: Real-time high-speed physical random numbers are crucial for a broad spectrum of applications in cryptography, communications as well as numerical computations and simulations. Chaotic laser is promising to construct high-speed physical random numbers in real time benefitting from its complex nonlinear dynamics. However, the real-time generation rate of physical random numbers by using single-bit extraction is confronted with a bottleneck because of the bandwidth limitation caused by laser relaxation, which dominates the laser chaos and then limits the effective bandwidth only to a few GHz. Although some bandwidth-enhanced methods have been proposed to increase the single-bit generation rate, the potential is very limited, and meanwhile the defects of system complexity will be introduced. An alternative method is to construct high-speed physical random numbers by using the multi-bit extraction. In this method, each sampling point is converted to N digital bits by using multi-bit analog-to-digital converter (ADC) and their M (M ≤ N) least significant bits are retained as an output of random bits, where N and M are the numbers of ADC bits and retained bits, respectively. The generation rate of random numbers is thus equal to M times sampling rate and can be greatly increased. Whereas, in the multi-bit extraction demonstrations, the intensity output of chaotic laser is usuallydigitized by the commercial oscilloscope and then processed with least-significant-bit retention followed by other post-processing methods such as derivative, exclusive-OR, and bit-order reversal. These followed post-processing operations have to be implemented off-line and thus cannot support the real-time generation of random numbers. Resultantly, it is still an ongoing challenge to develop high-speed generation schemes of physical random numbers with the capability of real-time output. In this paper, a real-time high-speed generation method of physical random numbers by using multi-bit quantization of chaotic laser is proposed and demonstrated experimentally. In the proposed generation scheme, an external-cavity feedback semiconductor laser is utilized as a source of chaotic laser. Through quantizing the chaotic laser with 6-bit ADC, which is triggered by a clock at a sampling rate of 7 GHz, a binary sequence with six significant bits can be achieved. After the selection of the two least-significant bits and self-delayed exclusive-OR operation in the field-programmable gate array (FPGA), a real-time 14-Gb/s binary stream is finally achieved. This binary stream has good uniformity and independence, and has passed the industry-standard statistical test suite provided by the National Institute of Standards and Technology (NIST), showing a good statistical randomness. It is believed that this work provides an alternative method of generating the real-time high-speed random numbers and promotes its applications in the field of information security.