Fast and reliable random number generation (RNG) is a key requirement for, e.g., secure telecommunication or quantum simulations. This has driven the development of physical random number generators to replace deterministic, pseudo-random number generators. Semiconductor lasers exhibiting chaotic dynamics induced for example by optical feedback [1] can provide up to 1 Tbit/s, but their speed is ultimately limited by the time scales of the laser dynamics. Parallel RNG via spatial or spectral multiplexing can further increase the speed but previous demonstrations were limited by low intrinsic speed or a small number of channels.
Fast and reliable random number generation (RNG) is a key requirement for, e.g., secure telecommunication or quantum simulations. This has driven the development of physical random number generators to replace deterministic, pseudo-random number generators. Semiconductor lasers exhibiting chaotic dynamics induced for example by optical feedback [1] can provide up to 1 Tbit/s, but their speed is ultimately limited by the time scales of the laser dynamics. Parallel RNG via spatial or spectral multiplexing can further increase the speed but previous demonstrations were limited by low intrinsic speed or a small number of channels.
Random numbers have great application value in the fields of secure communications, which are commonly used as secret keys to encrypt the information. To guarantee that the information is absolutely secure in the current high-speed communication, the applied random keys should possess a generation speed not less than the encrypted data rate, according to one-time pad theory found by Shannon (Shannon C E 1949 Bell.Syst.Tech.J. 28 656) Pseudo-random numbers generated by algorithm may easily reach a fast speed, but a certain periodicity makes them difficult to meet the aforementioned demand of information security. Utilizing physical stochastic phenomena can provide reliable random numbers, called physical random number generators (RNGs). However, limited by the bandwidth of the conventional physical sources such as electronic noise, frequency jitter of oscillator and quantum randomness, the traditional physical RNG has a generation speed at a level of Mb/s typically. Therefore, real-time and ultrafast physical random number generation is urgently required from the view of absolute security for high-speed communication today. With the advent of wideband photonic entropy sources, in recent years lots of schemes for high-speed random number generation are proposed. Among them, chaotic laser has received great attention due to its ultra-wide bandwidth and large random fluctuation of intensity. The real-time speed of physical RNG based on chaotic laser is now limited under 5 Gb/s, although the reported RNG claims that an ultrafast speed of Tb/s is possible in theory. The main issues that restrict the real-time speed of RNG based on chaotic laser are from two aspects. The first aspect is electrical jitter bottleneck confronted by the electrical analog-to-digital converter (ADC). Specifically, most of the methods of extracting random numbers are first to convert the chaotic laser into an electrical signal by a photo-detector, then use an electrical ADC driven by radio frequency (RF) clock to sample and quantify the chaotic signal in electronic domain. Unfortunately, the response rate of ADC is below Gb/s restricted by the aperture jitter (several picoseconds) of RF clock in the sample and hold circuit. The second aspect comes from the complex post-processes, which are fundamental in current RNG techniques to realize a good randomness. The strict synchronization among post-processing components (e.g., XOR gates, memory buffers, high-order difference) is controlled by an RF clock. Similarly, it is also an insurmountable obstacle to achieve an accurate synchronization due to the electronic jitter of the RF clock. In this paper, we propose a method of ultrafast multi-bit physical RNG based on chaotic laser without any post-process. In this method, a train of optical pulses generated by a GHz mode-locked laser with low temporal jitter at a level of fs is used as an optical sampling clock. The chaotic laser is sampled in the optical domain through a low switching energy and high-linearity terahertz optical asymmetric demultiplexer (TOAD) sampler, which is a fiber loop with an asymmetrical nonlinear semiconductor optical amplifier. Then, the peak amplitude of each sampled chaotic pulse is digitized by a multi-bit comparator (i.e., a multi-bit ADC without sample and hold circuit) and converted into random numbers directly. Specifically, a proof-of-principle experiment is executed to demonstrate the aforementioned proposed method. In this experiment, an optical feedback chaotic laser is used, which has a bandwidth of 6 GHz. Through setting a sampling rate to be 5 GSa/s and selecting 4 LSBs outputs of the 8-bit comparator, 20 Gb/s (=5 GSa/s4 LSBs) physical random number sequences are obtained. Considering the ultrafast response rate of TOAD sampler, the speed of random numbers generated by this method has the potential to reach several hundreds of Gb/s as long as the used chaotic laser has a sufficient bandwidth.
Real-time and ultrafast random number generators (RNGs) based on physical randomness sources are of paramount importance for cryptography and secure communications, where they are used as cryptographic keys to protect the privacy of data transmission. Since 2008, laser chaos has been viewed as the most promising source of randomness for fast RNGs because of its high bandwidth and large fluctuation. However, most of physical RNGs based on laser chaos did their random number extraction in the electrical domain, and thus their real-time rates suffered from the limitation of electronic bottleneck. Combing the chaotic laser with photonic signal processing techniques, we proposed and developed an innovative real-time methodology for ultrafast physical RNGs. Different with previous reports on RNGs, our fully photonic method do the random number extraction in the optical domain, so it efficiently circumvents the electronic bottleneck and has the potential to reach a real-time rate at the level of Tb/s. In this paper, we review our representative works on this topic of fully photonics based physical RNGs and some possible development orientations in the future are discussed.
Absolutely secure communication should be implemented only through the ‘one-time pad' proposed by Shannon, requires that physical random numbers with rates matched with the associated communication systems be used as secret keys. With the wide application of the WDM technology in optical communication, the single channel rate of the current digital communication system has exceeded 10 Gb/s and developed towards 100 Gb/s. To ensure the absolute security of such a large capacity communication, a large number of real-time, and secure random numbers are needed.#br#Secure random numbers are commonly produced through utilizing physical random phenomena, called physical random number generators. However, conventional physical random number generators are limited by the low bandwidth of the applied entropy sources such as thermal noise, photon-counting and chaotic electrical circuits, and thus have typical low bit rates of the order of Mb/s.#br#In recent years, chaotic lasers attracted wide attention due to their generation of secure, reliable and high-speed random number sequences, and so due to their coherent merits such as high bandwidth, large amplitude fluctuation and ease of integration. There have been lots of schemes based on laser chaos for high-speed random number generation, but most of them execute the random number extractions from the associated laser chaos in the electrical domain and thus their generation rates are faced with the well-known ‘electrical bottleneck'. On the other hand, all-optical random number generation (AO-RNG) methods are all signal processes in the optical domain, so they can efficiently overcome this rate limitation and have a great potential in generating ultrafast random numbers of several dozens or hundreds of Gb/s. However, there is no experimental report on its realization of AO-RNG. One of the obstacles in the way for the AO-RNG achievement is to implement the fast and real-time all-optical sampling of the entropy signals (i.e., laser chaos).#br#In this paper, we present a principal experimental demonstration of the feasibility in the all-optical sampling of the chaotic light signal through constructing a TOAD-based all-optical sampler with a polarization-independent semiconductor optical amplifier (SOA). Specifically, we experimentally generate chaotic laser signals using an optical feedback semiconductor laser and finally complete a 5 GSa/s real-time and high-fidelity all-optical sampling of the chaotic laser with a bandwidth of 6.4 GHz. Further experimental results show that whether the optical sampling period is proportional to the external cavity feedback time or not has a great effect on the weak periodic suppression of the chaotic signal: only when both of them are out of proportion, can the weak periodicity of the original chaotic signal be effectively eliminated; and this is favorable for the generation of high-quality physical random numbers. To the best of our knowledge, it is the first time to realize all-optical sampling of chaotic signal in experiments.
Abstract Random number generators (RNGs) are an essential ingredient of modern cryptographic systems. Particular attention is paid today to a special class of RNGs – quantum RNGs, which are attracting close attention of researchers due to the explosive development of quantum key distribution systems, where the use of quantum randomness is a necessary security requirement. A large number of various quantum entropy sources have been proposed over the last 10-15 years. Most of them are based on the use of different quantum optics phenomena, particularly, on the effects occurring in semiconductor lasers. This choice is due to the relatively low cost and ease of use of such devices and the high random bit generation rate available with optical QRNGs. Motivated by these reasons, we study in the present research the QRNG based on variations of light polarization in a vertical-cavity surface-emitting laser (VCSEL). The scheme we propose allows creating an extremely compact and fast optical QRNG, consisting essentially of only a laser and a polarizing beam splitter. We revealed that it is possible to ensure the pulsed operation of a VCSEL in a bistable regime, which is characterized by random switch of light polarization. We show, however, that probabilistic properties of such laser pulses significantly depend on the internal laser parameters as well as on its operating mode. Understanding these properties is fundamentally important for the correct assessment of the quantum noise contribution and, consequently, for the subsequent post-processing of digitized random sequences.
True random numbers with high security originate from non-deterministic physical processes. Random laser with random feedback arising from multiple elastic scattering in a highly disordered structure is an ideal physical entropy source theoretically. In this work, a secure optical ultrafast random number generator based on random laser spectra was demonstrated. Unlike the usual method of recording laser intensity over time, the random laser spectrum under each pump pulse was recorded and converted into random numbers through post-processing. Approaches in three different dimensions—space, spectrum and time were used to increase the rate of random number generation. The randomness of resulting random bit streams was verified by the NIST statistics tests. Experimental results showed that an instantaneous bit rate of 810 terabits per second with off-line post-processing could be theoretically reached with an ideal experimental condition. This novel technique has big advantages in secure communications and promises to further increase the speed of random number generators to the lever of petabits per second or even higher.
We demonstrate for the first time, to the best of our knowledge, a high-speed physical random bit generator at gigabits/second without the time-delay signature based on chaotic power fluctuations of a random fiber laser. The random fiber laser is configured using a ring structure with semiconductor optical amplifiers as the optical gain and a fiber random grating as the random feedback medium. The long-length ring cavity provides a large number of densely spaced cavity modes that co-exist within the gain bandwidth tailored by the optical filter. Unlike fixed cavity modes in conventional fiber ring lasers, these modes are less phase-correlated due to the random distributed feedback from the fiber random grating fabricated by a plane-by-plane inscription technique without phase control, leading to intensified lasing output fluctuations with high-dimensional chaotic dynamic natures without specific cavity features, when the random fiber laser is operated slightly above the lasing threshold. Random bit generation at a bit rate up to ∼1.6 Gbps is achieved with verified randomness through standard tests. Different from the previously reported schemes requiring offline post-processing procedures, this physical random number generator can function in real time, offering high-quality randomness and security assurance for pertinent applications.