• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    The invention is based on a method and a device for generating random numbers by means of a quantum random number generation method, the method comprising the steps of operating a laser diode (LD) in single-mode operation and high modulation bandwidth by means of an electrical pulse generator (PD), transforming the phase-randomized ones optical pulses into random-amplitude optical pulses, and detecting these resulting random-amplitude signals by means of a fast photodiode (PIN). The numbers generated in this way are really random.
    公开号:CH705137B1
    申请号:CH01283/12
    申请日:2012-08-06
    公开日:2016-12-15
    发明作者:Pruneri Valerio；Curty Alonso Marcos；Morgan Mitchel；Jofre Cruanyes Marc
    申请人:Fundació Inst De Ciències Fotòniques；Institució Catalana De Recerca I Estudis Avançats；Univ Vigo；
    IPC主号:
    专利说明:

    Field of the invention
    The present invention relates to random number generators (RNGs), in particular to such generators based on the intrinsic randomness of quantum observables.
    State of the art
    Random numbers form sequences of numbers or symbols that lack any pattern and that appear random. A random number generator (RNG) is a computational or physical device designed to generate random numbers. RNGs can be classified into pseudo-RNGs (PRNGs), computer algorithms, and real RNGs (TRNGs). TRNGs are physical devices designed to generate number or symbol sequences lacking any pattern. In addition, RNGs implemented in physical devices can be classified into classical RNGs (CRNGs) based on classical hardware devices with unpredictable behavior, as well as quantum RNGs (QRNGs) based on quantum effects [1, 2, 3].
    Current commercial RNG devices rely on: quantum single-photon detector arrays [4], CMOS metastability, noise signal using the stochastic physical phenomenon of electrons trapped in the silicon nitride layer of a transistor, arrival time of the photons of a continuous wave (cw) laser , reverse-biased semiconductor junction, thermal or Johnson noise, and transistor noise. Various documents describe such devices: a light beam illuminating a quantum detector array [5], wave diffraction using a high-order diffraction grating [6], photon detection as random events [7], photon coupling to a single-mode coupler [8], electrical noise [ 9, 10], single-photon laser beam splitting using homodyne detection [11].
    The publication "High-speed quantum random number generation by measuring phase noise of a single-mode laser" by Bing Qi et al. [12] describes a QRNG based on quantum phase noise measurement of a single-mode semiconductor laser. The phase noise of the laser comes from amplified spontaneous emission (ASE) when the laser is operated very close to its threshold. The system has a 500 Mbps random number generation rate, which is limited by the system's ability to increase the ASE bandwidth to reduce the coherence time. A phase modulator is used to reduce the influence of periodic drifts that limit the length of the generated random sequence. However, apart from being an additional element, the phase modulator itself is intrinsically subject to drift behavior if electro-optic materials such as LiNbO3 are used. In addition, the fact that the laser is operated very close to its threshold makes it difficult to avoid classical noise, which reduces the proportion of quantum randomness associated with ASE.
    Accordingly, there is a need for a higher rate QRNG source that shortens coherence time, avoids the use of a phase modulator, and greatly reduces the impact of classical noise.
    Summary of the invention
    The object of the present invention is to provide a QRNG with which the limitations of the prior art are overcome. The object of the invention is achieved by a method according to claim 1 and an apparatus according to claim 6. The method comprises the steps of: operating a single mode and high modulation bandwidth laser diode by means of an electrical pulse generator to generate phase-randomized optical pulses, transforming the phase-randomized optical pulses into random-amplitude optical pulses, and detecting these resulting random amplitudes by means of a fast photodiode (PIN) , The laser is operated well below the threshold prior to generating phase-randomized optical pulses and passed over the threshold during optical pulse generation to increase the field in the laser cavity to macroscopic values. To ensure single mode operation and high modulation bandwidth, the laser is a laser diode and the pulse generator is operated such that the duration of the electrical pulses is less than 50% of the optical pulse repetition period. There are two ways to transform the pulse: by passing through a Mach-Zehnder interferometer or by combining it with the optical signal of another laser before detecting it. In the first case, the signals can optionally be optically isolated in order to avoid the reflection of optical power into the laser cavity. A possible device for carrying out the method according to the invention is likewise provided. Such a device comprises a laser diode for generating random-phase optical pulses, a Mach-Zehnder interferometer equipped with two polarization-maintaining couplers, a polarization-maintaining fiber, an electric pulse generator for the laser diode, and a fast photodiode for detecting the output signals of the interferometer. An optical isolator located between the laser diode and the interferometer, designed to prevent back-reflected optical power into the cavity, may also be provided.
    Brief description of the drawings
    To complete the description, a set of drawings will be presented for better understanding of the invention. Said drawings illustrate preferred embodiments of the invention, which should not be construed as limiting the scope of the invention, but merely as an example of how the invention may be practiced.<Tb> FIG. Fig. 1 shows a first arrangement for practicing a first method according to the invention, in which a laser diode generates optical pulses with random phase, which pass through a Mach-Zehnder interferometer, optically interfere and are then electrically detected.<Tb> FIG. Fig. 2 shows a second arrangement for practicing a second method according to the invention, in which the phase of the random-phase pulses of the first laser diode is combined with the signal of a second laser.
    Description of the invention
    The invention is based on the transformation of random-phase laser pulses into random-amplitude pulses which can be detected with a fast photodiode and the use of an electrical pulse generator. In the first embodiment of the invention (Fig. 1), this is achieved by using a single-mode laser source in which an optical pulse train is emitted with the aid of an electric generator for a given period, whereupon the optical pulse train is split into two equivalent optical pulse trains and one of the both trains are delayed by at least one period, the pulses are recombined and finally the resulting exit intensities are detected. In the second embodiment (Figure 2) of the present invention, instead of splitting and delaying the laser pulses, one can combine the latter with another laser source and then detect the exit intensities.
    Referring to Fig. 1, a system for realizing the method of the present invention includes a laser diode (LD) as an oscillator, resulting in a single-mode operation and a high modulation bandwidth. A single-mode LD is directly modulated by a train of sufficiently short electrical pulses. The duration of the electrical pulses should be less than 50% of the repetition period of the generated pulse train. A polarization-maintaining single-fiber Mach-Zehnder unbalanced interferometer (MZI) is a stable single-mode interferometer. The interferometer consists of an input coupler which distributes the incoming optical pulses with equal power to the two arms. The long arm allows the stream of copied pulses to be delayed by one period from the pulses in the short arm. In the output coupler, the two currents interfere coherently. In Fig. 1, PD denotes the electric pulse generator for directly modulating the laser, LD the laser diode, Ol an optical isolator which prevents back-reflected optical power in the cavity of the LD, PMF a polarization-maintaining fiber for stability in polarization along the interferometer Φ0-3 are the optical phases of several successive pulses, PMC is a polarization-maintaining coupler, Φloop is the phase introduced by the long arm, which corresponds to an appropriate time delay, and finally PIN is a fast photodiode. The random phase of the various input pulses causes the output signals to acquire random amplitudes.
    The laser source is first operated with a current of at least 30% below the threshold, which at the same time produces a strong attenuation of the Kavitätsfeldes and a high ASE. This attenuates any pre-existing coherence to a negligible level, while the ASE resulting from vacuum fluctuations contributes a masking field with a truly random phase. The laser is then briefly transposed above the threshold to rapidly increase the cavity field to a macroscopic value, typically to several tens of mW peak power. The gain is pumped electrically and is therefore independent of the optical phase. Due to a saturated gain, the resulting field has a predictable amplitude but a truly random phase. The cycle is repeated, producing a sequence of identical random-phase optical pulses.
    By interference of successive pulses the phase sensitivity is converted into a strong amplitude modulation with random intensity, which is detected directly by means of a conventional fast photodiode and then digitized.
    A second embodiment (Figure 2) comprises two laser sources (LD1, LD2). Similar to the laser source of Fig. 1, at least one of the two sources (LD1) emits random-phase pulses generated by means of an electrical pulse generator. The laser beams of the same wavelength originating from LD1 and LD2 are then combined together, for example by using a beam splitter (BS). In this way, the random phase of the pulses emitted by at least LD1 generates random amplitudes in the output signal. Compared with the scheme of Fig. 1, the scheme of Fig. 2 makes it possible to dispense with the use of the input coupler and the time delay line, and thus the interferometric structure, thus simplifying the requirements for controlling the system. The power of the source (LD2), which can operate in either a pulsed or continuous wave mode, can achieve higher power levels and thus produce higher energy pulses at the output, thereby enabling the extraction of more random bits per pulse.
    It will be understood that one of ordinary skill in the art could use any of the above-mentioned embodiments using fiber geometry (FIG. 1), free space geometry (FIG. 2), waveguide geometry, or hybrid geometry (ie, a combination of these three geometries ) can realize. In the case of the waveguide geometry, which is also known as integrated optical geometry, the optical fiber elements (divider, delay, coupler, etc.) of Figure 1 are replaced by optical waveguide elements. The laser sources and the photodiode may also be integrated into the same waveguide chip or integrated by hybrid integration techniques known to those skilled in the art.
    A specific example of the implementation of the system of Fig. 1 is given below:
    LD1 is an approximately 852 nm emitting laser diode operated at 25 mA DC, well below its threshold of 36 mA. It is electrically modulated at 100 MHz with electrical pulses of approximately 1 ns duration. Phase randomized coherent optical pulses of 400 ps duration and 3.5 mW peak power are generated. A 30-dB optical isolator (OI) is placed directly after the laser diode LD1 to prevent back reflections into the oscillator cavity of the laser diode LD1. Subsequently, the linearly polarized optical pulses are split in terms of power by means of a polarization-maintaining coupler (PMC) according to a fixed coupling ratio. To one of the output terminals of the PMC is connected a 2 m polarization maintaining fiber (PMF) patch cable which is approximately equivalent to the equivalent pulse repetition period length of approximately 10 ns between successive pulses. Finally, both arms of the interferometer are connected to a second PMC, where the interference between pulses takes place. The total interferometer arrangement has power coupling rates of 49.8% and 40.3% and a polarization isolation of 23.98 dB and 25.23 dB for the two arms measured at the output thereof. Connected to one of the output ports of the interferometer is a 150 MHz photodiode which serves to detect the various output-generated interfering optical pulses which are processed by a fast oscilloscope. The oscilloscope operates on a 200 MHz bandwidth on the input channel, which is triggered by the system clock reference.The time delay difference of the interferometer is set by tuning the pulse repetition frequency (PRF) at 97.6 MHz.
    The parameter φloop is controlled by implementation of a reduced tuning range by fine tuning the propagation characteristics in the long arm of the interferometer. For example, by changing the temperature of the optical fiber, a change in the refractive index and a thermal expansion corresponding to an equivalent shift of one wavelength (852 nm) over a temperature range of 0.03 ° C may be effected.
    Otherwise, the parameter Φloop can be controlled as explained below by implementing a tuning over the entire range. The interferometer is temperature-stabilized to 0.01 ° to keep the parameter Φloopkonstant. Disregarding the pulse repetition frequency corresponds to a change in the period between successive optical pulses, allowing a transient temporal adjustment of the pulse overlap in the two arms of the interferometer. A detuning at 200 KHz corresponds to a change in the period of the train of optical pulses Δt = 20 ps. Since the duration of the optical pulses is 400 ps, there is no longer time overlap of the pulses at Δt = 400 ps.
    Thanks to the use of optical pulses of macroscopic intensity can be coded with moderate signal powers (mW) numerous bits per pulse (12-18 bits). The achieved random number generation rate is 1.11 Gbps. Higher generation rates of up to 100 Gbps can be achieved by simply increasing the direct LD modulation frequency and by increasing the coded number of bits per pulse. The emission wavelength can also be chosen to improve the electro-optic performance as well as the integration value and to reduce costs, for example, by using telecommunications accessories at a wavelength around 1550 nm.The proposed QRNGs scheme includes a low complexity detection system based on standard photodiodes and a conventional electronic detection system, which allows for the achievement of high random number generation rates. In addition, its calibration procedure can be easily automated, allowing it a long service life. The invention, by virtue of its working principle, can generate high rates of true random numbers using commercially available optical and electronic accessories, offering a low cost integrated solution.
    In the present text, the term "include" and its derivatives (such as "comprehensive" etc.) is not to be understood in an exclusive sense, that is, these terms should not be interpreted so that the possibility that the described here and Defined also could include other elements and steps, etc., is excluded.On the other hand, obviously, the invention is not limited to the specific embodiment (s) described herein, but also includes any modifications that might be considered by any person skilled in the art (eg, with regard to the choice of components, configuration etc.), as far as it is within the general scope of the invention according to the claim definition.
    references
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    [0021] H. Guo, W. Tang, Y. Liu, and W. Wei, "Truly random number generation based on measurement of phase noise of a laser," Physical Review E, vol. 81, p. 051 137, 2010.
    [0022] C. Gabriel, C. Wittmann, D. Sych, R. Dong, W. Mauerer, UL Andersen, C. Marquardt, and G. Leuchs, "A generator for unique quantum random numbers based on vacuum states , »Natura Photonics, vol. 4, pp. 711-715, 2010.
    [4] "Random number generation using quantum physics," ID Quantique White Paper, 2010. [Online]. Available: http://www.idquantique.com/images/stories/PDF/quantis-random-generator/quantis-whitepaper.pdf
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    W. Gunawan and M. Berhad, "Quantum Random Number Generator Based on Diffraction of High-order Grating," International Patent WO 2010 062 161, 2010.
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    权利要求:
    Claims (7)
    [1]
    A method of generating random numbers using a quantum random number generator, the method comprising the steps of:- a) operating a first laser (LD) in single mode operation and with sufficient modulation bandwidth by means of an electrical pulse generator (PD) for generating phase-randomized optical pulsesB) transforming the phase-randomized optical pulses generated in a) into random-amplitude optical pulses, andC) detecting the resulting signals of said random-amplitude optical pulses by means of a fast photodiode (PIN) so that the random numbers generated thereby are based on the random-amplitude signals, the first laser (LD) for ensuring single-mode operation and sufficient modulation bandwidth is a laser diode and wherein the first laser (LD) is operated well below the threshold prior to generating phase-randomized optical pulses and generating phase-randomized optical pulses above the threshold to amplify the field in the laser cavity to macroscopic values.
    [2]
    2. The method according to claim 1, characterized in that the pulse generator is operated such that the duration of the electrical pulses is shorter than 50% of the repetition period of the phase-randomized optical pulse.
    [3]
    3. The method according to any one of claims 1 or 2, characterized in that the phase-randomized optical pulses generated in a) are transformed by passage through a Mach-Zehnder interferometer (MZI).
    [4]
    4. The method according to any one of claims 1 or 2, characterized in that the phase-randomized optical pulses generated in a) are transformed by their combination with the optical signal of a second laser (LD2) before their detection.
    [5]
    A method according to any one of claims 1 or 2, comprising a step of optically isolating the signals to avoid reflection of optical power into the laser cavity.
    [6]
    6. A device for carrying out the method according to one of claims 1 to 3, wherein the device comprises a diode laser for generating random-phase input signals and a polarization-maintaining fibers (PMF) and polarization-maintaining couplers (PMC) equipped Mach-Zehnder interferometer (MZI) characterized in that it further comprises an electric pulse generator (PD) for the laser (LD) and a fast photodiode (PIN) for detecting the amplitude of the output signals of the interferometer (MZI).
    [7]
    Apparatus according to claim 6, characterized in that it further comprises an optical isolator located between the laser (LD) and the interferometer (MZI) and configured to prevent back-reflected optical power into the cavity.
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