Optical quantum random number generator

Abstract

To continuously improve the performance of a quantum random number generator (QRNG) that is based on a gain-switched laser.SOLUTION: A quantum random number generator (QRNG) 1 comprises: a semiconductor laser 3 configured to emit a stream of phase randomized pulses; an optical amplifier 9 (e.g., a semiconductor optical amplifier) which is an intensity controller for modulating pairs of pulses in the stream of phase randomized pulses; a time delay interferometer 11 which serves as a phase measuring element configured to convert the phase difference between the modulated pairs of pulses into intensity modulation at the output of the phase measuring element; and an optical detector assembly optically coupled to the output of the phase measuring element and comprising optical detectors D1 and D2.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The embodiments described herein relate to quantum random number generators, and more particularly to optical quantum random number generators. [Background technology]

[0002] Random numbers are used in a variety of applications, including cryptography, numerical simulations, and lotteries. Random numbers can be generated from quantum random number generators (QRNGs). In QRNGs, the source of randomness is physical and relies on the unpredictability of measurement, particularly its quantum mechanical properties. QRNGs can be implemented using gain-switched diode lasers. In gain-switched diode lasers, the lasing threshold is governed by spontaneous emission, a quantum mechanical process, and therefore the phase of the emitted pulses is random. By repeatedly switching the diode laser on and off, a stream of optical pulses, each with a random phase, can be generated. A sequence of random numbers can be obtained by measuring the random phase of each optical pulse in the stream.

[0003] The performance of QRNG based on gain-switched lasers needs to be continuously improved.

[0004] Next, embodiments of the present invention will be described simply as examples with reference to the attached schematic diagrams. [Brief explanation of the drawing]

[0005] [Figure 1] Figure 1 is a schematic diagram of QRNG using a comparative example. [Figure 2] Figure 2 is a schematic diagram of an exemplary QRNG according to one embodiment. [Figure 3] Figure 3 shows the digitization and processing of the output of a differential amplifier for obtaining random numbers. [Figure 4]Figure 4 is a schematic diagram of the laser pulse intensity profile. [Figure 5] Figure 5 is a schematic diagram of a further exemplary QRNG according to an embodiment. [Figure 6] Figure 6 is a schematic diagram of a further exemplary QRNG according to an embodiment. [Figure 7A] Figure 7A shows the experimental data. [Figure 7B] Figure 7B shows the experimental data. [Figure 7C] Figure 7C shows the experimental data. [Figure 7D] Figure 7D shows the experimental data. [Figure 8] Figure 8 shows the experimental data. [Modes for carrying out the invention]

[0006] To avoid unnecessary repetition, the same reference number is used to indicate similar features in the figures.

[0007] In one embodiment, a novel and useful optical quantum random number generator (QRNG) is provided that at least partially overcomes the problems of conventional devices. For example, a conventional optical QRNG may employ a gain-switched semiconductor laser to generate phase-randomized optical pulses. Two of these phase-randomized optical pulses are then interfered to generate interference pulses of random intensity. The intensity of the interference pulses is converted by a photodiode to provide an analog voltage signal, which is then digitized by an analog-to-digital converter (ADC) for further processing to generate random numbers. The problem with conventional optical QRNGs is that (for example, when the device operates at high repetition rates and / or when the device is implemented as a photonic integrated circuit) the voltage pulses provided by the photodiode are often too small to optimally utilize the dynamic range of the ADC (unless significantly large electronic amplification is used, resulting in undesirable classical noise). This reduces the achievable random number generation rate. To this end, the Disclosure proposes a QRNG that uses an optical amplifier to amplify the intensity of a phase-randomized optical pulse (i.e., before the phase-randomized optical pulse is interfered with) so that the interference pulse becomes a voltage signal by a photodiode that makes optimal use of the dynamic range of the ADC. Another problem with conventional optical QRNGs employing gain-switched lasers is that each of the generated phase-randomized pulses contains a reduced coherence initial portion (as described in more detail below). In practice, this means that this portion of the pulse does not affect the desired interference signal, but instead adds undesirable classical noise to the photodiode signal. To this end, the Disclosure proposes a QRNG that blocks (or at least reduces the relative intensity of the initial portion of the pulse compared to the later "useful portion" of the pulse) the initial (or "leading") portion of the pulse to which the phase-randomized optical pulse is involved before it is interfered with.Another problem with conventional optical QRNGs is that the generated photodiode signal is often "contaminated" by classical noise (such as electrical crosstalk from the laser drive signal), which introduces undesirable correlations into the raw output. For this purpose, the present disclosure proposes a QRNG employing two photodetectors configured to detect complementary interference pulses. In this case, crosstalk and classical noise are suppressed by taking the difference between the outputs of the two photodetectors and generating a random number from this difference.

[0008] In one embodiment, a quantum random number generator (QRNG) is provided. The QRNG comprises a laser configured to emit a stream of multiple phase-randomized pulses, an intensity controller configured to modulate (e.g., amplify or attenuate) pairs of pulses from the stream of multiple phase-randomized pulses, a phase measurement element configured to convert the phase difference between the modulated pulse pairs into intensity modulation at the output of the phase measurement element, and an optical detector optically coupled to the output of the phase measurement element.

[0009] In one embodiment, the intensity controller may be configured to modulate pairs of pulses from a stream of multiple phase-randomized pulses such that, for each pulse in the pair, the intensity of the leading portion of the pulse is reduced compared to the intensity of the trailing portion of the pulse.

[0010] In one embodiment, the intensity controller may include an optical amplifier (e.g., a semiconductor optical amplifier) ​​configured to amplify the intensity of a pair of pulses.

[0011] In one embodiment, the optical amplifier may be configured to amplify the intensity of the trailing portion of the pulse more strongly than the intensity of the leading portion of the pulse.

[0012] In one embodiment, the intensity controller may be configured to modulate each emitted pulse by attenuating the intensity of the leading portion of the pulse more strongly than the intensity of the trailing portion of the pulse.

[0013] In one embodiment, the intensity controller element may comprise an electroabsorption modulator, a Mach-Zehnder modulator, or an optical switch.

[0014] In one embodiment, the phase measurement element may be a time-delay interferometer configured to direct light from an optical amplifier towards two arms, at least one arm of which comprises an interferometer delay. Light from the two arms may interfere with each other and be directed to the output of the phase measurement element.

[0015] In one embodiment, the interferometer delay may be set to allow the time-delay interferometer to interfere with a pair of modulated pulses (for example, the interferometer delay may be equal to an integer multiple of the temporal separation between a plurality of pulses in an emitted stream of pulses, or the interferometer delay may be equal to the temporal separation between a plurality of pulses in an emitted stream of pulses such that successive plurality of optical pulses are interfered by the time-delay interferometer).

[0016] In one embodiment, the QRNG may further comprise: an optical detector assembly coupled to a first output port and a second output port of the time-delay interferometer, the optical detector assembly being configured to generate, as an output signal, an analog signal indicating a difference between an intensity at the first output port of the time-delay interferometer and an intensity at the second output port of the time-delay interferometer; and processing circuitry configured to generate a plurality of random numbers based on the output signal of the optical detector assembly.

[0017] In one embodiment, the optical detector assembly may comprise a plurality of balanced photodetectors for generating an analog signal indicative of a difference between the intensity at a first output port and the intensity at a second output port of a time-delay interferometer. Alternatively, the optical detector assembly may comprise a first optical detector and a second optical detector respectively coupled to the first output port and the second output port of the time-delay interferometer, and a differential amplifier configured to receive the analog signal provided by the first optical detector and the analog signal provided by the second optical detector as a plurality of input signals, and generate an analog signal indicative of a difference between the plurality of input signals as an output signal.

[0018] In one embodiment, the QRNG may further comprise a semiconductor substrate, and the plurality of components of the QRNG may be integrated on the semiconductor substrate to form a photonic integrated circuit.

[0019] In one embodiment, the laser may be further configured to emit a plurality of phase-randomized pulses at a repetition rate between 1 GHz and 2 GHz, and each emitted pulse may have a pulse duration between 200 ps and 500 ps.

[0020] In one embodiment, a quantum random number generator (QRNG) is provided. The QRNG comprises a laser configured to emit a stream of a plurality of phase-randomized pulses, a phase measurement element configured to convert a phase difference between two pulses from the stream of the plurality of phase-randomized pulses into intensity modulation at a first output port and a second output port of the phase measurement element, an optical detector assembly coupled to the first output port and the second output port of the phase measurement element and configured to generate, as an output signal, an analog signal indicative of a difference between the intensity at the first output port and the intensity at the second output port of the phase measurement element, and processing circuitry configured to generate a plurality of random numbers based on the output signal of the optical detector assembly.

[0021] In one embodiment, the optical detector assembly may comprise a plurality of balanced photodetectors for generating an analog signal indicating the difference between the intensity at a first output port and the intensity at a second output port of a phase measuring element. Alternatively, the optical detector assembly may comprise a first optical detector and a second optical detector coupled to the first and second output ports of a phase measuring element, respectively, and a differential amplifier configured to receive the analog signals provided by the first optical detector and the analog signals provided by the second optical detector as a plurality of input signals, and to generate an analog signal indicating the difference between the plurality of input signals as an output signal.

[0022] Before describing further proposed embodiments relating to quantum random number generators (QRNGs), the design of an optical QRNG will now be described in detail with reference to Figure 1. This design employs a laser that emits optical pulses into the input port of a time-delay interferometer (also known as an asymmetric Mach-Zehnder interferometer (AMZI)). More specifically, Figure 1 shows a portion of a conventional optical QRNG, comprising a pulsed laser P1 driven at a fixed repetition rate by a controller P2 to output a stream of pulses. When the repetition rate is sufficiently low, each pulse from the stream of pulses may have a random phase. The pulses are coupled to a time-delay interferometer P3 via an input coupler P4. The time-delay interferometer P3 comprises a short arm and a long arm. The long arm of the time-delay interferometer P3 comprises a delay element P7 that delays pulses by a time D relative to pulses traveling in the short arm. In this QRNG device, the delay element P7 is configured such that the resulting delay D is such that each delayed pulse temporally overlaps with the previous reference pulse in the reference arm. The delayed pulse and the reference pulse interfere in the 2x2 coupler P5 (or beam splitter) of the time-delay interferometer P3, and the interference pulse is sent to a single photodetector P6 that converts the random intensity of the interference pulse into a voltage pulse of random intensity. This electrical signal corresponding to the intensity of the interference pulse has random values ​​because the phases of the reference pulse and the delayed pulse are random. Random numbers (e.g., a sequence of bits with random values) can be generated from the random intensity of the interfered pulse by digitizing the electrical signal from the photodetector P6 using a digitizer P8.

[0023] Figure 2 shows an exemplary optical quantum random number generator (QRNG) 1 according to one embodiment. Generally, the QRNG 1 is configured to generate (and output) random numbers from the random intensity of an interfering optical pulse. The QRNG 1 is generally provided (and described below) as an integrated device, i.e., the components of device 1 are integrated on a common semiconductor substrate (or on multiple semiconductor substrates assembled / connected as appropriate). However, in other embodiments, the QRNG 1 may also be implemented using discrete (optical fiber pigtailed or free-space) components.

[0024] The optical device 1 comprises a semiconductor laser 3 (e.g., a distributed feedback (DFB) laser, a Fabry-Perot laser diode, etc.) and a controller 5 for controlling the operation of the semiconductor laser 3. The semiconductor laser 3 is operable to emit coherent light. The semiconductor laser 3 is operated in pulsed mode (i.e., to emit a stream of optical pulses, e.g., nanosecond or picosecond pulses). When operating in pulsed mode, the semiconductor laser 3 has a clearly defined pulse duration and a clearly defined regular time interval (where the time interval between subsequent emitted pulses is Δ laserThe semiconductor laser 3 can be driven (by the controller 5) at a fixed repetition rate (for example, at a fixed repetition rate selected from the range of 1 to 2 GHz) to output a stream of pulses (as shown). More specifically, the semiconductor laser 3 may be a gain-switched semiconductor laser driven to output a stream of phase-randomized pulses (i.e., each pulse from the stream of pulses may have a random phase). Generally, a gain-switched laser produces light when the laser is switched above the laser oscillation threshold and produces little light when the laser is switched below the laser oscillation threshold. Therefore, the controller 5 can control the modulation of the gain of the laser 3 by modulating the electrically driven current applied to the laser 3 in a time-varying manner (as shown by reference numeral 7 in Figure 2). For example, the semiconductor laser 3 can be periodically switched above and below the laser oscillation threshold by the application of a time-varying current. In this way, the laser produces light pulses. It should be understood that the controller 5 may have (or be connected to) a suitable drive circuit for generating and applying such a time-varying current.

[0025] QRNG1 further comprises an intensity controller configured to receive phase-randomized pulses emitted by laser 3 and modulate (e.g., amplify or attenuate) the optical intensity of the received pulses. More specifically, in the embodiment of Figure 2, the intensity controller is an optical amplifier 9 (e.g., a semiconductor optical amplifier). The optical amplifier 9 may be optically coupled to laser 3 via an optical waveguide, via an optical free-space path, etc. The optical amplifier 9 is further configured to amplify the intensity of the received pulses and to output “amplified pulses”. The amplifier 9 may operate in different modes, as will be described in more detail below. Generally, the controller 5 may be further configured to control the operation of the amplifier 9.

[0026] The optical device 1 further comprises a time delay interferometer 11 configured to receive the output of the amplifier 9. The time delay interferometer 11 functions as a phase measurement element that converts the phase difference between two received pulses into intensity modulation. The time delay interferometer 11 comprises an input coupler 13, a short arm 15, a long arm 17, and an output coupler 21. The input coupler 13 is configured to direct light from the amplifier 9 towards the short arm 15 and the long arm 17. The long arm 17 is configured to delay an optical pulse propagating in the long arm 17 by a delay time Δ relative to an optical pulse propagating in the short arm 15 delay , and comprises a delay element (e.g., a delay line). The delay time Δ delay is selected such that the delay time Δ delay is an integer multiple of the time interval Δ laser (for example, the time interval Δ laser may be equal to the delay time Δ delay , or the delay time Δ delay may be twice the time interval Δ laser , etc.). In this way, a pulse propagating through the long arm 17 is delayed by the delay element such that it interferes at the output coupler 21 with an undelayed pulse propagating through the short arm 15. The phases of the delayed pulse and the undelayed pulse are random (since these pulses are generated in different cycles), and therefore the intensity of the interfered pulses at the two output ports of the output coupler 21 has a random value. A random number can be generated from the random intensity of the interfered pulses.

[0027] QRNG1 further comprises an optical detector assembly coupled to the output port of the output coupler 21. Generally, the optical detector assembly is configured to produce an analog signal as an output signal, which represents the difference between light intensities at the output port of the output coupler 21 (and thus a random number can be generated from this output signal of the optical detector assembly). In the embodiment of Figure 2, the optical detector assembly comprises photodetectors D1 and D2, each optically coupled to a different output port of the output coupler 21. Photodetectors D1 and D2 are configured to convert the random intensity of the interfered light pulse into an electrical signal (e.g., a voltage pulse). The electrical signals provided by their detectors are generally analog signals (rather than, for example, the binary "click" signals associated with single-photon detectors). Photodetectors D1 and D2 may be InP-based on-chip photodiodes.

[0028] It should be understood that the two detectors D1 and D2 are configured to detect "complementary" interference pulses, since they are coupled to different outputs of the time-delay interferometer 11. For example, interference of a particular pair of phase-randomized pulses may result in an increased-intensity interference pulse at detector D1 (due to primarily constructive interference at the corresponding output port coupled to detector D1) and a correspondingly decreased-intensity interference pulse at detector D2 (due to primarily destructive interference at the corresponding output port coupled to detector D2).

[0029] QRNG1 further comprises a processing circuit configured to generate random numbers from analog signals provided by photodetectors D1 and D2. In particular, the processing circuit may be configured to generate random numbers based on the difference between the analog signal provided by photodetector D1 and the analog signal provided by photodetector D2. For this purpose, QRNG1 comprises a differential amplifier 23 that receives the analog signals provided by photodetectors D1 and D2 and determines the difference between these signals. The differential amplifier 23 may further amplify the determined difference by a predetermined gain. The differential amplifier 23 then outputs the (amplified) difference between the analog signals to a digitizer circuit 25 configured to digitize the received signals and extract random numbers from the digitized signals.

[0030] One embodiment of the digitizer circuit 25 is shown in Figure 3. The digitizer circuit 25 may include an analog-to-digital converter (ADC) 27 that converts the (amplified) difference between photodetector signals into a digital signal. The ADC 27 is coupled to a post-processor 29. The digital signal generated by the ADC 27 is provided to the post-processor 29, which processes the digital signal using a randomness extractor algorithm and outputs a sequence of random numbers 31 having a uniform probability distribution.

[0031] Advantageously, extracting random numbers from the difference between the analog signals provided by photodetectors D1 and D2 can result in the suppression of undesirable crosstalk and classical noise (e.g., classical noise introduced by amplifier 9), as will be further explained below with reference to Figure 7.

[0032] It should be understood that other embodiments may not include the differential amplifier 23. In these embodiments, the photodetectors D1 and D2 of the optical detector assembly may be configured as balanced photodetectors to directly generate analog signals indicating the difference between light intensities at the output ports of the output coupler 21 (for example, the photodetectors D1 and D2 are configured so that the currents produced by them are (directly) subtracted). The outputs of the balanced photodetectors may be supplied to the digitizer circuit 25 (for example, directly, or the outputs of the balanced photodetectors may be electrically amplified and the amplified signal may be supplied to the digitizer circuit 25).

[0033] Next, the operation of amplifier 9 will be described in more detail. Amplifier 9 can operate in "continuous mode" or "pulse mode". For example, in "continuous mode", amplifier 9 is operated such that the intensity of an incoming pulse is amplified over the entire pulse duration. In this case, amplifier 9 can be continuously switched "on". The amplification provided by amplifier 9 can increase the intensity of the phase randomization pulse such that the amplitude of the analog signals produced by detectors D1 and D2 is increased. More specifically, the gain of amplifier 9 can be selected so that the dynamic range of ADC 27 (i.e., the range of signal amplitudes that ADC 27 can resolve) is used optimally (or at least better). In other words, the gain of amplifier 9 can be selected such that the distribution of amplitude values ​​of the analog signals produced by detectors D1 and D2 (i.e., the distribution of amplitude values ​​formed by the amplitude values ​​of a number of interfered pulses) substantially matches the distribution of difference values ​​provided by differential amplifier 23 to the dynamic range of ADC 27. By utilizing the full dynamic range of the ADC27, a wider (i.e., finer-grained) distribution of the digitized difference values ​​is generated (by the ADC27), which increases the random number generation rate. In some embodiments, the gain of the optical amplifier 9 may be at least 10 dB, at least 20 dB, or at least 30 dB in "continuous mode". Providing the amplifier 9 is particularly advantageous when the QRNG1 is implemented as a photonic integrated circuit (in such an implementation, high losses in the waveguide can result in weak signals in the photodetectors D1 and D2 that do not utilize the full dynamic range of the ADC).

[0034] Next, the operation of amplifier 9 in "pulse mode" will be explained with reference to Figure 4, which shows the temporal intensity profile of a typical optical pulse 41 generated by gain switching of laser 3. The pulse 41 generally has a pulse duration t between 200 ps and 500 ps. pulse It holds.

[0035] Generally, the optical output produced by a gain-switched laser does not simply follow the shape of the electrically driven signal (typically a rectangular or Gaussian pulse). Instead, the temporal characteristics of the light emission depend on the interaction between photons in the laser cavity and electrically injected carriers, and carriers in semiconductor lasers generally have a lifetime of nanosecond duration. When a large current is initially applied to the laser, carriers may accumulate rapidly, temporarily overshooting the carrier density threshold. This results in a large emission of photons, which subsequently depletes the carriers. The resulting interaction between photons and carriers induces damped oscillations (and corresponding phase fluctuations) known as "relaxation oscillations." These relaxation oscillations gradually decay to reach a steady state. Therefore, gain-switched lasers generally produce rectangular-shaped pulses with an initial overshoot (as shown in Figure 4). Therefore, the pulse 41 can be considered to have a front portion 43 (also called the "leading portion") and an end portion 45 (also called the "trailing portion"), and the front portion 43 of the pulse 41 may have lower temporal coherence than the end portion 45. The front portion 43 extends from the leading edge of the pulse 41 to the midpoint of the pulse 41. The end portion 45 extends from its midpoint to the trailing edge of the pulse 41.

[0036] As described above, the pre-pulse portion 43 comprises the leading edge of the pulse 41, i.e., the initial "unsteady state" phase of the pulse 41. Therefore, the pre-pulse portion 43 may have a large, sharp intensity peak caused by relaxation oscillations. In particular, the pre-pulse portion 43 may have decaying oscillations of the light intensity at the beginning of the pulse. The pre-pulse portion 43 of the pulse generally exhibits frequency chirps due to changes in refractive index in the laser cavity with respect to the changing carrier density. As a result of the frequency chirps, the pre-pulse portion 43 has reduced coherence and therefore produces a reduced (or completely suppressed) interference signal. In other words, the pre-pulse portion of a phase-randomized pulse does not (significantly) affect the interference signal from which random numbers can be extracted. Instead, the pre-pulse portion 43 of the pulse 41 affects undesirable (classical) noise to the photodetector signal. The duration of the pre-pulse portion 43 generally depends on the details of the laser and drive current, but in many cases, the pre-pulse portion 43 lasts for at least 50 ps (e.g., between 50 ps and 200 ps). In one embodiment, the duration of the front portion 43 can be within the range of 10% to 40% of the total duration of the pulse 41.

[0037] The trailing portion 45 comprises a “steady state” phase following the pulse 41 (i.e., the trailing portion 45 comprises the remainder of the pulse 41, following the trailing portion 43). The intensity in the trailing portion 45 is generally constant. Importantly, the optical frequency of the pulse 41 is generally constant in the trailing portion 45, and therefore these trailing portions of the pulse produce the desired random interference signal from which random numbers can be extracted as described above.

[0038] In "pulse mode," the amplifier 9 is operated to amplify only the latter portion 45 of the pulse 41 (or to amplify the latter portion 45 (significantly) more strongly than the former portion 43). For this purpose, the controller 5 may appropriately synchronize the operation of the amplifier 9 with the drive current pulse supplied to the laser 3. In other words, the controller may control the amplifier 9 such that the gain provided by the amplifier 9 is significantly higher during the latter portion of the received pulse than during the former portion. In some embodiments, the gain of the optical amplifier 9 during the latter portion 45 of the pulse 41 may be at least 10 dB, at least 20 dB, or at least 30 dB higher than during the former portion 43 of the pulse 41.

[0039] This time-selective amplification effectively reduces the relative influence of the initial "non-steady state" portion of the pulse on the signals detected by photodetectors D1 and D2 compared to the influence of the subsequent "steady state" portion of the pulse. As a result, the signals generated by photodetectors D1 and D2 exhibit less classical noise. Furthermore, amplification in "pulse mode" can produce a desirable broadening of the distribution of values ​​generated by the differential amplifier 23, which better matches the dynamic range of the ADC 27 as described above with respect to the "continuous mode" of amplifier 9.

[0040] Although not shown in Figure 2, it should be understood that QRNG1 may be equipped with additional elements, such as an (adjustable) attenuator, to compensate for the difference in accumulated optical loss in the short arm 15 and the long arm 17 (to ensure that delayed and non-delayed pulses of substantially the same intensity enter the output coupler 21).

[0041] As an addition or alternative, the input coupler 13 may have an adjustable composite ratio (i.e., the composite ratio may be changed during use, i.e., by employing electro-optic or thermo-optic effects in general). In one embodiment, the input coupler 13 may be equipped with a tunable Mach-Zehnder interferometer for adjusting the composite ratio.

[0042] Figure 5 shows a modified form of the QRNG in Figure 2 (similar reference numbers are used to indicate similar features to avoid unnecessary repetition). The QRNG51 in Figure 5 has the same components as the QRNG1 in Figure 2 and operates in substantially the same way, except that the QRNG51 in Figure 5 has an intensity modulator 53 instead of an optical amplifier 9 as the intensity controller.

[0043] The intensity modulator 53 is configured to receive pulses emitted by the laser 3, modulate the intensity of the received pulses, and provide the modulated pulses to the time-delay interferometer 11. Similar to the amplifier 9 described above (when operating in “pulse mode”), the intensity modulator 53 modulates each emitted pulse such that the intensity of the leading portion 43 of the pulse 41 is reduced compared to the intensity of the trailing portion 45. The intensity modulator 53 achieves this by attenuating the intensity of the leading portion 43 of the pulse 41 more strongly than the intensity of the trailing portion 45. In other words, the intensity modulator 53 “carves” the received pulses so as to block unwanted optical signals from reaching the photodetectors D1, D2. For this purpose, the controller 5 may be configured to synchronize the attenuation provided by the intensity modulator 53 with the electrically driven signal provided to the laser 3. In embodiments, the intensity modulator may be implemented as an electric absorption modulator, a Mach-Zehnder modulator, or an optical switch. In some embodiments, the optical attenuation of the intensity modulator 53 during the preceding portion 43 of the pulse 41 may be at least 10 dB, at least 15 dB, or at least 20 dB higher than during the following portion 45 of the pulse 41.

[0044] This selective attenuation effectively reduces the relative influence of the initial "transient state" portion of the pulse on the signals detected by photodetectors D1 and D2 compared to the influence of the subsequent "steady state" portion of the pulse. As a result, the signals generated by photodetectors D1 and D2 exhibit less classical noise.

[0045] In another variant (shown in Figure 6), the QRNG61 may include an intensity modulator 53 (as described with reference to Figure 5) in addition to the amplifier 9 (as described with reference to Figure 2). In this case, the amplifier 9 may operate in "continuous mode" (as described above), and the intensity modulator 53 "forms" the leading portion of the pulse (as described above). The intensity modulator may be upstream or downstream of the amplifier. Although shown as individual components in Figure 6, in some embodiments, the amplifier 9 and the modulator 53 may be provided as an integrated component.

[0046] Figures 7A–7D show experimental data acquired by the first exemplary QRNG (the first exemplary device is configured as described above with reference to Figure 2, and in particular, the first exemplary QRNG is implemented as an (unpackaged) photonic integrated circuit with a semiconductor optical amplifier operating in continuous or pulsed mode). Figure 7A shows the accumulated oscilloscope trace 73 generated by a (single) photodiode detecting an optical pulse produced by gain-switching laser 3. As described above with reference to Figure 4, the optical pulse 73 includes an initial portion with a large, sharp intensity peak and a later steady-state portion. Figure 7B shows the accumulated oscilloscope trace 75 of the optical pulse after the intensity modulator 53 attenuated the leading edge of the pulse (as described above with reference to Figure 5). It can be seen that the resulting pulse 75 no longer has the (unwanted) initial transient phase, but the (desired) steady-state portion remains essentially unchanged (i.e., unattenuated). Histograms 77 and 79 of the voltage values ​​corresponding to pulses 73 and 75 are shown in Figures 7C and 7D. It can be seen that both histograms 77 and 79 generally follow an arcsine distribution, as expected for interference pulses generated by pulses with randomly uniformly distributed phases.

[0047] Figure 8 shows further experimental data acquired by a second exemplary QRNG, which is configured similarly to the first exemplary QRNG used to acquire the data in Figure 7, but unlike the first exemplary device, is implemented as a packaged photonic integrated circuit. The top row of Figure 8 shows a heatmap 81 of the signal generated by a single photodetector (e.g., photodetector D1) that detects interference pulses generated by the interference of two phase-randomized pulses emitted by laser 3 (in the experimental data shown in Figure 8, the amplifier was operated in continuous mode (i.e., not pulsed mode)). In addition to the signal caused by the interference pulses, the generated signal 83 includes the effect of large crosstalk from the electric laser drive signal. This crosstalk is significantly stronger in the packaged photonic integrated circuit than in the unpackaged photonic integrated circuit (Figures 7A-7D) because the electric wires / wires carrying the laser drive current and the electric wires / wires carrying the photodetector signal are necessarily closer to each other than in the unpackaged first exemplary device. The top row of Figure 8 also shows a histogram 87 corresponding to the heatmap 81. It can be seen that the two peaks in histogram 87 are not sufficiently resolved.

[0048] The bottom row of Figure 8 shows a heatmap 89 of the signal generated by the differential amplifier 23 (i.e., heatmap 89 shows the difference between the signals of photodetectors D1 and D2). It can be seen that the crosstalk described above is strongly suppressed by the differential amplifier 23 by amplifying the difference between the two photodetector outputs. Thus, undesirable crosstalk, which is particularly pronounced in highly integrated devices, can be significantly reduced by using the difference between the two photodetector outputs. The signal 91 corresponding to the interference pulse shows the expected random distribution of values. Advantageously, the width of the corresponding histogram 93 is significantly wider than that of histogram 87 (which reduces the need for further electrical amplification), and the two peaks in histogram 93 are much more clearly resolved.

[0049] While several embodiments have been described, these embodiments are presented merely as examples and do not limit the scope of the invention. In fact, the novel devices and methods described herein may be embodied in various other forms, and furthermore, various omissions, substitutions, and modifications of the forms of devices, methods, and products described herein may be made without departing from the spirit of the invention. The appended claims and their equivalents are intended to encompass such forms or modifications so as to fall within the scope and spirit of the invention.

Claims

1. A laser configured to emit a stream of multiple phase-randomized pulses, An intensity controller configured to modulate a pair of pulses from a stream of multiple phase-randomized pulses, comprising an optical amplifier configured to amplify the intensity of the pair of pulses, A phase measuring element configured to convert the phase difference between the modulated pulse pair into intensity modulation at the output of the phase measuring element, An optical detector optically coupled to the output of the phase measurement element Equipped with, The optical amplifier is configured to amplify the intensity of the trailing portion of each pulse in the pair to a stronger degree than the intensity of the leading portion of the pulse, and is a quantum random number generator (QRNG).

2. The quantum random number generator according to claim 1, wherein the intensity controller comprises a semiconductor optical amplifier.

3. The quantum random number generator according to claim 1, wherein the intensity controller is configured to modulate each emitted pulse by attenuating the intensity of the leading portion of the pulse more strongly than the intensity of the trailing portion of the pulse.

4. The quantum random number generator according to claim 3, wherein the intensity controller comprises an electric field absorption modulator, a Mach-Zehnder modulator, or an optical switch.

5. The quantum random number generator according to claim 1, wherein the phase measuring element is a time-delay interferometer configured such that light from the optical amplifier is directed toward two arms, one of which has an interferometer delay, and wherein the light from the two arms interferes with each other and is directed toward the output of the phase measuring element.

6. The quantum random number generator according to claim 5, wherein the interferometer delay is set to allow the time-delay interferometer to interfere with the modulated pulse pair.

7. The quantum random number generator according to claim 6, wherein the interferometer delay is equal to an integer multiple of the temporal separation between the multiple pulses in the stream of emitted pulses.

8. The quantum random number generator according to claim 7, wherein the interferometer delay is equal to the temporal separation between the multiple pulses in the stream of emitted pulses so that the multiple consecutive optical pulses are interfered with by the time-delay interferometer.

9. An optical detector assembly is coupled to the first and second output ports of the time-delay interferometer and configured to generate an analog signal as an output signal that indicates the difference between the intensity at the first output port and the intensity at the second output port of the time-delay interferometer. A processing circuit configured to generate a plurality of random numbers based on the output signal of the optical detector assembly. The quantum random number generator according to claim 5, further comprising:

10. The quantum random number generator according to claim 9, wherein the optical detector assembly comprises a plurality of balanced photodetectors for generating the analog signal indicating the difference between the intensity at the first output port and the intensity at the second output port of the time-delay interferometer.

11. The quantum random number generator according to claim 9, wherein the optical detector assembly comprises a first optical detector and a second optical detector coupled to the first output port and the second output port of the time-delay interferometer, respectively, and a differential amplifier configured to receive the analog signals provided by the first optical detector and the analog signals provided by the second optical detector as a plurality of input signals, and to generate an analog signal indicating the difference between the plurality of input signals as an output signal.

12. The quantum random number generator according to claim 1, further comprising a semiconductor substrate, wherein a plurality of components of the QRNG are integrated on the semiconductor substrate to form a photonic integrated circuit.

13. The quantum random number generator according to claim 1, wherein the laser is further configured to emit the plurality of phase randomization pulses at a repetition rate between 1 and 2 GHz, wherein each emitted pulse has a pulse duration between 200 ps and 500 ps.

14. A laser configured to emit a stream of multiple phase-randomized pulses, A phase measuring element configured to convert the phase difference between two pulses from a stream of multiple phase-randomized pulses into intensity modulation at a first output port and a second output port of the phase measuring element, the phase measuring element being a time-delay interferometer in which at least one arm has an interferometer delay and light from the two arms interferes with each other, An optical detector assembly is coupled to the first output port and the second output port of the phase measurement element and configured to generate an analog signal as an output signal that indicates the difference between the intensity at the first output port and the intensity at the second output port of the phase measurement element. A processing circuit configured to generate a plurality of random numbers based on the output signal of the optical detector assembly, Semiconductor substrate and A quantum random number generator (QRNG) comprising a plurality of QRNG components integrated on a semiconductor substrate to form a photonic integrated circuit.

15. The quantum random number generator according to claim 14, wherein the optical detector assembly comprises a plurality of balanced photodetectors for generating the analog signal indicating the difference between the intensity at the first output port and the intensity at the second output port of the phase measuring element.

16. The quantum random number generator according to claim 14, wherein the optical detector assembly comprises a first optical detector and a second optical detector coupled to the first output port and the second output port of the phase measurement element, respectively, and a differential amplifier configured to receive an analog signal provided by the first optical detector and an analog signal provided by the second optical detector as a plurality of input signals, and to generate an analog signal indicating the difference between the plurality of input signals as an output signal.

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