The Nd:YAG laser is a solid state laser that has many applications in the industry, science and medicine. We in this paper use a continuous wave (CW) Nd:YAG laser emitting light at 1064 nm to generate random numbers. We first give a recipe of an experimental setup that is capable of measuring and recording the vacuum fluctuations with the help of our cw Nd:YAG laser. The basic scheme simply involves the Nd:YAG laser, detectors and some radio frequency electronic components. The laser source used in the demonstration provides us with a quantum noise limited CW at a radio frequency sideband of 14 MHz. The final data obtained after appropriate electronic signal processing are digitized voltage fluctuations that correspond to the vacuum fluctuations in the optical domain. The data randomly lies above or below zero due to its quantum mechanical probabilistic nature. We assign a '1' to the data that is positive and a '0' to the data that is negative, hence we are able to generate a random bit sequence by using a cw Nd:YAG laser. This result adds yet another interesting application to the many number of broad applications of the Nd:YAG laser system.
The Nd:YAG laser is a solid state laser that has many applications in the industry, science and medicine. We in this paper use a continuous wave (CW) Nd:YAG laser emitting light at 1064 nm to generate random numbers. We first give a recipe of an experimental setup that is capable of measuring and recording the vacuum fluctuations with the help of our cw Nd:YAG laser. The basic scheme simply involves the Nd:YAG laser, detectors and some radio frequency electronic components. The laser source used in the demonstration provides us with a quantum noise limited CW at a radio frequency sideband of 14 MHz. The final data obtained after appropriate electronic signal processing are digitized voltage fluctuations that correspond to the vacuum fluctuations in the optical domain. The data randomly lies above or below zero due to its quantum mechanical probabilistic nature. We assign a '1' to the data that is positive and a '0' to the data that is negative, hence we are able to generate a random bit sequence by using a cw Nd:YAG laser. This result adds yet another interesting application to the many number of broad applications of the Nd:YAG laser system.
Lasers are recently being used more frequently in random number generators. The world record in random number generation was broken by the help of lasers. The world's fastest quantum random number generators utilize lasers to tap into the random fluctuations in order to extract true random bit sequences. We investigate a system based on a Nd:YAG laser that potentially generates true random bits at Gbit/s rates. As photonic on chip technologies progress we foresee laser based high speed random number generators integrated on chips. Such a photonic chip will create a revolution in the technology of security devices that employ quantum cryptography techniques for secure communication.
Random number generation is an enabling technology for fields as varied as Monte Carlo simulations and quantum information science. An important application is a secure quantum key distribution (QKD) system; here, we propose and demonstrate an approach to random number generation that satisfies the specific requirements for QKD. In our scheme, vacuum fluctuations of the electromagnetic-field inside a laser cavity are sampled in a discrete manner in time and amplified by injecting current pulses into the laser. Random numbers can be obtained by interfering the laser pulses with another independent laser operating at the same frequency. Using only off-the-shelf opto-electronics and fibre-optics components at 1.5 μm wavelength, we experimentally demonstrate the generation of high-quality random bits at a rate of up to 1.5 GHz. Our results show the potential of the new scheme for practical information processing applications.
We describe a method of generating physical random numbers by means of a diode laser that has an extremely wide-band frequency-noise profile. Fluctuations in the laser frequency affect the intensity of the light transmitted through the optical frequency discriminator, detected thereafter as random fluctuations. This allows us to simultaneously generate 8 random bit streams, due to the parallel processing of 8-digit binary numbers sampled by an 8-bit analog-to-digital converter. Finally, we generated physical random numbers at a rate of 3 Gbit/s, by combining one data stream with another stream that is delayed by 2 ms, by exclusive-OR.
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.
Randomness is essential ingredient for applications in cryptography, stochastic simulation, and fundamental science experiments [American Scientist 89, 4 (2001); PRL 115, 25 (2015)]. Common practice is to generate random numbers from mathematical algorithm using Pseudo-random number generators. We are interested in tackling this problem with quantum technology. Phase diffusion in spontaneous emission events is a quantum phenomena with inherent randomness [Opt. Express 19, 21 (2011)]. Implementations of this scheme using pulsed lasers can yield high-speed quantum random number generation (QRNG) [Opt. Express 22, 2 (2014)]. The general interest in the laser phase diffusion QRNG setup has been mainly focused on and motivated by the speed of the random number generations. Little has been stated about the performance of quantum phase noise as a randomness source in QRNG, from the perspective of the physics involved. We reanalyze the process of phase diffusion based QRNG and give an intuitive explaining picture of the underlying physics. Our findings show that a pulsed process is beneficial over the continuous-wave approach and give a upper bound of maximum random bit rate for a given experimental setting. In detail, the output of a semiconductor laser contains fluctuations in intensity and phase. This was originally studied first by Charles Henry in 1982 [J. Lightwave Techn. 4, 3 (1986)]. Based on that one can identify two phenomena contributing to the phase noise, which takes the form of a random walk. First, there will be phase changes due to the carrier-induced change in refractive index in the semiconductor laser. Second, spontaneous emission events take place in the active medium [Opt. Express 19, 21 (2011)]. Naturally, taking spontaneous emission events into account necessitates the application of stochastic laser rate equations for theoretical description. We solve these equations numerically be a Monte-Carlo simulation and investigate several random walk scenarios. One of our essential findings is that the phase fluctuation becomes much larger in the pulsed laser regime than in the continuous-wave mode. Additionally, there is a natural limit on the maximum pulse repetition rate for a given pulse width, since the phase jumps become smaller for shorter pulse distances. Since phase measurement is not a feasible procedure for optical signals, the phase fluctuation needs to be converted to an observable macroscopic parameter such as the optical intensity. This can be done by using an interferometer setup. The whole experimental setting is shown in Fig. 2 (left). An DFB laser diode is modulated using gain-switching technique to generate uniform amplitude signals with random phases. Each signal interferes with neighboring pulses through an unbalanced Mach-Zehnder interferometer. The delay in one arm was set to equal to the pulse repetition rate. With this setup we investigate the influence of several parameters on the shape of the probability distribution determining the quality of QRNG. The theoretical as well as experimental findings can help to find physical standards for QRNG verification rather than the ones based on classical statistical information theory.
Abstract An effective approach to obtain a single-frequency laser with low intensity noise is presented in this paper, which is implemented by employing a gain medium with the small stimulated-emission cross section (SECS). When the adopted Nd:YAP (Nd:YAlO 3 ) gain medium with SECS of 4.6×10 −19 cm 2 is replaced by Nd:CYA (Nd:CaYAlO 4 ) gain medium with SECS of 1.04×10 −19 cm 2 , the frequency of measured intensity noise reached shot noise limit obviously reduces from 2.49 to 1.5 MHz, which agrees well with the theoretical predictions. On this basis, a single-frequency continuous-wave (CW) Nd:CYA laser with low intensity noise is first achieved. The attained output power of the Nd:CYA laser is 1.12 W. The achieved single-frequency CW 1080 nm laser will satisfy the requirements of the squeezed and entangled light generation.