Real-time Optical Sampling Of Chaotic Laser For All-optical Physical Random Number Generator

Random numbers have been widely used in Monte-Carlo simulation,spread spectrum communication, optical fiber sensing, radar ranging，electroniccommerce and other fields. Especially, in the field of secure communications,with the rapid development of computer and network technology, how to ensureinformation security is particularly important. Shannon information theory hasproved that in order to ensure the absolute safety of information, we need toadopt one-time pad security mechanism. Therefore, how to producehigh-speed physical random numbers has a vital significance for informationsecurity.Random numbers are divided into pseudo random numbers and physicalrandom numbers. Pseudo random numbers are usually generated by a certainalgorithm with an initial seed, which often can produce several Gbit/s randomnumbers. While the pseudo random numbers are difficult to meet the demand ofinformation security due to the certain predictability and periodicity. On the contrary, the physical random numbers are based on the random phenomena ofphysical entropy source in the nature. They are completely unpredictable and notrenewable. There are some commonly-used physical entropy sources, such asthermal noise of electronic circuit, radioactive decay, frequency noise ofelectronic oscillator, chaotic circuit and so on. However, limited to thebandwidth of these sources, the bit rate of true random numbers is difficult toachieve up to Gbit/s.Chaotic laser has some unique features, such as the ultra-broadbandbandwidth, random fluctuation of intensity, sensitive to initial value and so on,which is an ideal entropy source to extract the physical random numbers. For theparticular entropy source, now a common extraction method is to convert thechaotic laser to electrical signals by photoelectric detector firstly, then tocomplete the sampling, quantization and coding of chaos with an analog-digitalconverter in the electric field. The optoelectronic techniques can producephysical random numbers, but the bit rate is bound to be limited by thebandwidth bottleneck of electronic components, so the real-time bit rate has notreached to5Gbit/s at present. For the disadvantage, we put forward toprocessing the chaotic laser directly in the optical domain to achieve high-speedall-optical physical random numbers, and to satisfy the demands of modernhigh-speed optical communication.In order to generate high-speed all-optical physical random numbers fromthe chaotic laser, we need to complete all-optical sampling of chaotic laser firstly. For the goal, we put forward to building an all-optical sampler using aterahertz optical asymmetric multiplexer (TOAD) to complete all-opticalsampling of the chaotic laser which generated by optical feedback to the DFBsemiconductor laser diode. Specific work is as follows:1. Firstly, the research significance and present development of randomnumbers is summarized, and the importance of studying all-optical physicalrandom numbers is illustrated. In addition, the high-speed all-optical physicalrandom numbers generator of using the wideband chaotic entropy sourcecombined with all-optical sampler and all-optical comparator proposed by ourresearch group is introduced.2. The present all-optical sampling techniques and their advantages anddisadvantages are investigated. For the random fluctuation of polarization andthe poor coherence of chaotic laser, we proposed to build an all-optical samplerbased on TOAD using a polarization-insensitive semiconductor opticalamplifier. The influence of some parameters related to the TOAD onperformance of the all-optical sampler is analyzed experimentally. Meanwhilethe switching energy and linearity of TOAD sampler is studied and we achievethe best performance parameters of the sampler. In addition, we completeall-optical sampling of500-MHz sinusoidal optical signal to verify thefeasibility of the TOAD sampler.3. The5-GS/s all-optical sampling of6.4-GHz chaotic laser based on theTOAD sampler under the best performance parameters is realized. In addition, for the all-optical physical random number generator, the influence of opticalsampling period proportional to the chaotic laser period or not on extracting thephysical random numbers is studied.