Random number generator equipped with a vertical cavity surface emitting laser

Abstract

A random number generator comprising a vertical cavity surface emitting laser, a mode separator, and a photodetector, further comprising a power supply for driving the vertical cavity surface emitting laser in a direct modulation mode, the vertical cavity surface emitting laser being configured to emit laser light having two different laser modes of random relative intensities that may propagate in a propagation direction away from the emitter into a space outside the vertical cavity surface emitting laser cavity, the mode separator being disposed between the photodetector and the vertical cavity surface emitting laser in the propagation direction, the mode separator being disposed to separate the two different laser modes from each other and send one of the two different laser modes to the photodetector.

Description

Technical Field

[0001] The present invention relates to a random number generator comprising a vertical cavity surface emitting laser (VCSEL) according to claim 1, and a method for generating a random number using a random number generator comprising a vertical cavity surface emitting laser according to claim 9.

Background Art

[0002] Vertical cavity surface emitting lasers (hereinafter referred to as "VCSELs") are widely known in communication technology. A VCSEL is a type of semiconductor laser diode that emits a laser beam or laser pulse vertically from one of its upper surfaces. This is different from normal laser oscillation in which a laser beam is emitted from the end face of a semiconductor laser.

[0003] In a VCSEL, the laser resonator typically includes two distributed Bragg reflectors parallel to a structure including an active region such as quantum dots or quantum wells. These Bragg reflectors are provided with layers having different refractive indices arranged alternately, and these layers usually have a thickness of 1 / 4 of the laser wavelength in the material of the reflector, whereby high-intensity reflectivity is obtained.

[0004] VCSELs typically include a mode suppression element. This mode suppression element is incorporated into the cavity of the VCSEL or into the VCSEL itself, so that only one mode of the laser beam or laser pulse emitted from the VCSEL to the surrounding environment, i.e., outside the VCSEL, is obtained. The reason for making the mode single in this way is that in communication technology, it is necessary to make the mode of the VCSEL used single, and it is preferable that the intensity of the laser beam in one mode accumulates. This can be achieved, for example, by applying a dedicated mode suppression element.

[0005] VCSELs are known to operate at high frequencies of 1 MHz or more or up to several GHz, and such operating frequencies are particularly advantageous in communication technology. This is because high frequencies are required in information transmission.

[0006] Currently, VCSELs are used in the fields of gigabit Ethernet and fiber channel technology, providing link bandwidths ranging from 1 GB / s to over 400 GB / s, thereby achieving high transmission rates.

[0007] From the above, a fairly large amount of information can be generated and output in a short time.

[0008] In recent years, in the field of physical random number generators, developments have been made to generate true random numbers by utilizing the physical characteristics of systems. Laser diodes are also used in this field. This is because the quality of the emitted laser pulses depends on the quantum physical characteristics of the laser. Since these are truly unpredictable, the random numbers and random bit sequences obtained by the above technologies have high reliability and can be used, for example, in the encryption of security-related data, computing applications, or gaming.

[0009] When constructing a physical random number generator, the integration level, quality, and actual operating speed are important. In this regard, there are applications where it is difficult to obtain random numbers (or generally entropy) at a sufficiently high speed or rate, especially in applications where it is necessary to make the size very small and keep the cost low. SUMMARY OF THE INVENTION

[0010] In view of the above, the problem to be solved by the present invention is to provide a random number generator that achieves a high output of entropy (i.e., random numbers) per unit time, and preferably has a relatively high cost-effectiveness in manufacturing, and preferably has a small size and specific advantages in terms of quality.

[0011] The above problem is solved by a random number generator comprising a vertical cavity surface emitting laser according to independent claim 1, and a method for generating random numbers using a random number generator comprising a vertical cavity surface emitting laser according to independent claim 9. Further preferred embodiments of the present invention are described in the dependent claims.

[0012] This random number generator includes a vertical cavity surface emitting laser (VCSEL), a mode separator, and a light receiving element, and further includes a power supply for driving the VCSEL in a direct modulation mode. The VCSEL is configured to emit laser light having two different laser modes with random relative intensities that can propagate in a propagation direction away from the emission part from the emission part to a space outside the VCSEL cavity. The mode separator is disposed between the light receiving element and the VCSEL in the propagation direction, and the mode separator is arranged to separate the two different laser modes from each other and send one of the two different laser modes to the light receiving element.

[0013] In the present invention, the mode separator is understood as all physical entities having the ability to separate a first mode emitted from the VCSEL from a second mode emitted from the VCSEL. For example, the mode separator can include a filter or a polarization filter, etc. This is particularly relevant to a VCSEL that emits a plurality of separated different laser modes (e.g., laser modes rotated by about 90°, spatially separated laser modes, etc.). Other mode separation modes, such as separating modes by frequency, etc. are also included. The present invention is not limited to a specific type of mode separator.

[0014] The direct modulation mode includes emitting a pulse from the VCSEL by driving the VCSEL alternately below and above the laser oscillation threshold. The durations of driving the VCSEL below and above the laser oscillation threshold are not limited in the present invention and can be changed according to requirements. To obtain a sufficient number of laser pulses to obtain random numbers or random bits, the frequency of driving the VCSEL above the laser oscillation threshold to emit laser pulses can be set, for example, above 1 Hz or above 1 GHz. However, the present invention is not limited to a specific pulse frequency (number of pulses per second), and all allowed frequencies or all frequencies at which the VCSEL can operate can be used.

[0015] Preferably, the output power of the laser of each pulse can be made substantially the same as each other, but the relative intensities of a plurality of different laser modes generated in the cavity are random. By blocking one of the above modes, the intensity of the other light also becomes random. Then, using this random intensity, "random" bits of information can be obtained from the signal detected by the light receiving element. For example, when the intensity of the other laser mode transmitted to the light receiving element without being separated and removed by the mode separator is less than the detection threshold of the light receiving element, no signal is generated in the light receiving element, and later, the fact that this signal was not generated can be converted into a "0" bit at this point. When the intensity of the other laser mode exceeds the detection threshold of the light receiving element, a "1" bit can be generated. Thus, the random number generator of the present invention can efficiently generate a random bit sequence of values "0" and "1" while making its implementation relatively cost-effective.

[0016] In one embodiment, the random number generator further includes a digital conversion unit connected to the light receiving element, and the digital conversion unit is configured to digitally convert the signal from the light receiving element so that when the signal obtained from the light receiving element exceeds a threshold, a first value is output, and when the signal of the light receiving element is below the threshold, a second value different from the first value is output.

[0017] According to such an embodiment, the signal detected by the light receiving element can be converted into a digital signal that can be further processed by, for example, a subsequent arithmetic entity that encrypts communication. As the digital conversion unit, a digital conversion unit that can digitally convert a signal at a sufficiently high frequency so as to fully utilize the capabilities of the VCSEL can be selected.

[0018] In a more specific embodiment, the digital conversion unit is an analog-to-digital converter. The analog-to-digital converter can convert an analog signal into a digital signal with high efficiency and high processing speed. As a result, while utilizing all random values in the digital conversion process, it is possible to drive the random number generator of the above embodiment at a high frequency.

[0019] In another embodiment, the vertical cavity surface emitting laser cavity does not include a mode suppression element that suppresses one of the two different laser modes. By not providing a mode suppression element, both of the two different laser modes can be emitted from the VCSEL into the space outside the VCSEL cavity. As a result, using the mode separator provided subsequently above, either one of the modes can be used to separate the two modes and generate a signal with a light receiving element.

[0020] Also, it is possible to configure the threshold value to have a value corresponding to at least 90%, or at least 75%, or at least 50%, or at least 25% of the maximum energy that can be output by the vertical cavity surface emitting laser. It should be understood that the threshold value used in the digital conversion unit can be a voltage value or a current value. Here, the phrase "the threshold value corresponds to a certain percentage of the maximum energy that can be output by the vertical cavity surface emitting laser" is understood to refer to the voltage value or current value of the threshold value that corresponds to a certain percentage of the voltage value or current value generated by the light receiving element when receiving a laser pulse of the maximum energy that can be output by the vertical cavity surface emitting laser. With the above configuration, highly reliable digital conversion of the signal output from the light receiving element can be realized.

[0021] In another embodiment, the vertical cavity surface emitting laser includes quantum dots or quantum wells as an active medium for generating the laser light.

[0022] Further, the mode separator may include a polarization beam splitter, a filter, or a polarization-dependent optical isolator. The above specific configuration of the mode separator can advantageously be embodied according to the circumstances and according to the mode of separating the different laser modes from each other. For example, when it is more efficient to separate both modes based on the relative polarization of the two modes, a grating or a polarization-dependent optical isolator can be used. When the frequencies constituting both modes are different, but the relative polarization between the two modes is not at a large angle (e.g., 90° etc.), separation based on frequency may be more suitable.

[0023] In another embodiment, an optical isolator is disposed between the mode separator and the emission part of the vertical cavity surface emitting laser and / or between the mode separator and the light receiving element. According to such an embodiment, noise that can affect signal generation and the light receiving element can be suppressed.

[0024] In a method for generating a random number using the random number generator of the present invention, the random number generator includes a vertical cavity surface emitting laser, a mode separator, and a light receiving element, and the random number generator further includes a power source for driving the vertical cavity surface emitting laser in a direct modulation mode. The vertical cavity surface emitting laser emits laser light having two different laser modes with random relative intensities propagating in a propagation direction away from the emission part into the space outside the vertical cavity surface emitting laser cavity from the emission part. The mode separator is disposed between the light receiving element and the vertical cavity surface emitting laser in the propagation direction. The mode separator separates the two different laser modes from each other and sends one of the two different laser modes to the light receiving element. The light receiving element outputs a signal corresponding to the intensity of the laser light received at the light receiving element from the vertical cavity surface emitting laser via the mode separator.

[0025] By the above method, entropy can be generated at high speed while reducing costs, and thus random numbers can be generated at high speed.

[0026] In one embodiment, the random number generator further includes a digital conversion unit connected to the light receiving element. The digital conversion unit outputs a first value when the signal output from the light receiving element exceeds a threshold value, and outputs a second value different from the first value when the signal of the light receiving element is below the threshold value, so as to digitally convert the signal of the light receiving element. According to this embodiment, high-efficiency digital conversion of the analog signal of the light receiving element is realized.

[0027] In another embodiment, the threshold value has a value corresponding to at least 90%, or at least 75%, or at least 50%, or at least 25% of the maximum energy that can be output by the vertical cavity surface emitting laser. By setting the threshold value used in the digital conversion unit to a value as described above, the reliability of the random bits generated by the digital conversion unit can be improved.

[0028] In another embodiment, the control unit adjusts the frequency of the direct modulation mode according to the number of random numbers generated per unit time. Here, the "number of random numbers" can be understood as the number of random bits generated per unit time. For example, when generating 40 GB of random bits per second, the frequency of the direct modulation mode can be adjusted to 40 GHz. Since the VCSEL can be used at a high frequency, the value of the frequency driving the direct modulation mode can be set to almost any value. Specifically, in some embodiments of the present invention, frequencies in the range from several Hz to up to several tens of GHz are assumed. Any frequency between the above upper and lower limit values can be realized and is also included in the disclosure of the present application.

[0029] In one embodiment, the system of the above embodiment is mounted on a chip. With such a system, the random number generator of the above embodiment can be used as an integrated circuit in a computer system such as a personal computer or a smartphone.

[0030] In another embodiment, a plurality of random number generators of any of the above embodiments are arranged in an array, and one mode separator is provided for all the random number generators, or one mode separator is provided for each of the random number generators, and / or, one optical isolator is provided for all the random number generators, or one optical isolator is provided for each of the random number generators.

[0031] According to the above embodiment, it is possible to increase the number of random bits generated per unit time while suppressing the structural complexity of providing a plurality of random number generators. In addition, since the number of required separate components is reduced, the cost can be reduced.

Brief Description of the Drawings

[0032]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0033] FIG. 1 is a schematic diagram of a random number generator 100 according to an embodiment of the present invention.

[0034] The random number generator basically includes four components. As will be described in detail below, the random number generator 100 includes a vertical cavity surface emitting laser (VCSEL) 101, a mode separator 102, a light receiving element 103, and a power supply 105.

[0035] As is known to those skilled in the art, the VCSEL 101 includes at least one laser cavity 111, and an active region 113 is provided in this laser cavity 111. On both sides of the laser cavity 111 (the left and right sides in FIG. 1), and necessarily, in a plane parallel to the laser cavity 111, a plurality of mirrors 114 that can form a Bragg reflector are arranged. Due to such mirrors 114 and the Bragg reflector, internal reflection of the generated light can be caused to finally output a laser beam.

[0036] Furthermore, a confinement structure 112 that can condense the laser light 120 emitted from the active region of the VCSEL can also be provided. The VCSEL further includes an emission portion 115 through which the laser light generated by the VCSEL actually exits from the VCSEL to the external space. The above-mentioned external space can be, for example, an optical isolator or free space where the laser light is incident, or a glass fiber or (transparent) polymer fiber, or any other medium such as an "optical" fiber capable of internally propagating an optical signal such as a laser pulse.

[0037] In the structure of a VCSEL in the conventionally known technology, a mode suppression element that suppresses any one of the modes of the laser light generated by the VCSEL is provided. When the VCSEL is driven in a specific manner, the mode suppression element prevents the one mode from exiting the VCSEL. Specifically, the total energy output output from the VCSEL is provided almost entirely by only one of the two modes, and this one mode exits the VCSEL.

[0038] As is known to those skilled in the art, the VCSEL generates laser light in two different laser modes. The relative intensities between these two laser modes are random, but both laser modes propagate in the same direction or substantially the same direction.

[0039] By suppressing one of the two modes described above, the emission section 115 of the VCSEL emits only the laser beam of one mode having the total energy output of the VCSEL. The recognition in the present invention is that the mode suppression as described above inside the VCSEL in a typical VCSEL has been preventing the use of the VCSEL in the field of random number generation technology.

[0040] Therefore, in a preferred embodiment of the present invention, as shown in Graph 141, it is assumed that the emission section 115 is configured to emit laser light having two different laser modes M1 and M2. This is achieved by configuring the VCSEL not to include a mode suppression element. The two modes emitted from the emission section 115 can be, for example, polarization modes. In that case, the first mode M1 is polarized with respect to the second mode M2 at, for example, 90° or 60° or any other arbitrary angle. Alternatively or additionally, the two modes M1 and M2 each have different frequencies, or different ratios of the same frequency, or have a time delay, or can have any other arbitrary physical quantity that can identify that the two modes are different from each other but belong to the same laser pulse. Due to the quantum mechanical characteristics of the VCSEL, the relative intensities of the two different modes emitted from the emission section 115 of the VCSEL are arbitrary, and thus random for each laser pulse.

[0041] Here, it should be noted that in a "perfect" system that does not exhibit a non-linear effect that affects the two modes when competing in the VCSEL cavity, only one of the two modes M1 and M2 is actually emitted from the VCSEL, and this one mode emits with all the energy of the laser pulse. However, an actual VCSEL usually cannot avoid non-linearities such as relaxation oscillations and carrier dynamics, so some energy transfer can occur between the two modes when competing in the VCSEL cavity. Such energy transfer can result in both modes being emitted from the cavity. Usually, one of the two modes carries some energy, and most of the energy is carried by the other mode.

[0042] When applying mode switching to drive a VCSEL, the above-mentioned competition between the two modes occurs within the VCSEL for each laser pulse. As a result, which of the two modes actually emits with the majority of the energy is unknown until the pulse is emitted and is truly random.

[0043] In view of the above, the recognition in the present invention is that when two modes M1 and M2 compete within the VCSEL, a physically digital signal is obtained (only one mode wins and either M1 or M2 emits from the VCSEL), and the signal thus obtained already provides all of its energy (or substantially all of its energy) in the first mode or all of its energy (or substantially all of its energy) in the second mode. Also in the present invention, it is recognized that by utilizing the above recognition together with a mode separator, random bits can be generated in a simple digital conversion process (the reason being that the signal is already digital or substantially digital and there is no noise added by an analog-to-digital converter).

[0044] Also in the present invention, it is recognized that with the above configuration, random numbers can be generated by other means and procedures described below.

[0045] A mode separator 102 is arranged in the propagation direction (indicated by the arrow) of the laser pulse emitted from the emission unit 115.

[0046] In the most general sense, this mode separator 102 is configured to separate two different laser modes from each other and allow only one of the two modes to further propagate in the direction of the arrow toward the light receiving element 103 downstream of the mode separator 102. This is shown in graph 142, which includes only laser mode M1 and not laser mode M2, or at least most of laser mode M2 is suppressed. Preferably, the mode separator suppresses the propagation of the second laser mode to such an extent that at least 10% or at least 45% or at least 75% or at least 90% of the energy provided by the second laser mode does not propagate in the same direction as the first laser mode M1.

[0047] The manner in which the mode separator achieves the separation between laser modes M1 and M2 is not limited and can be realized in any suitable manner. Of course, the manner in which the mode separator 102 can actually act on the laser modes M1 and M2 that reach the mode separator 102 after being emitted from the emission unit 115 depends on the physical characteristics and differences of these different laser modes M1 and M2.

[0048] In one embodiment, the plurality of different laser modes described above have different polarization states along different axes. For example, one of the different laser modes can be polarized in the x direction while the other of the different laser modes can be polarized in the y direction.

[0049] This is shown in coordinate diagram 144. The propagation direction of the laser pulse is indicated by the k direction, and the polarization axes X and Y are in a plane perpendicular to the propagation direction K.

[0050] For easier explanation, assume that the first mode M1 is polarized along the x - direction for example with respect to the electric - field component, and the other mode M2 is polarized along the y - direction for example with respect to the electric - field component. In such a case, a suitable mode separator 102 can be a filter or a grating arranged so as to allow the mode M1 to pass through but not the mode M2. In the case as described above, since the angle between the polarization direction of the first mode M1 and the polarization direction of the second mode M2 is 90°, the mode separator 102 can (substantially) completely eliminate the second mode M2, or block the passage of the second mode M2, and the first mode M1 can pass through the mode separator 102 with (substantially) the original intensity.

[0051] Other embodiments of the mode separator are similarly possible.

[0052] Specifically, the mode separator can be realized as a polarization beam splitter and configured to separate the first mode M1 and the second mode M2 without actually suppressing either mode. Thereby, it becomes possible to redirect the second mode M2 in another propagation direction. Alternatively, a polarization - dependent optical isolator that allows the first mode M1 to pass through and blocks the second mode M2 can also be used.

[0053] However, the present invention is not limited to how the mode separator is actually realized, and any realization mode is possible as long as it can separate different laser modes M1 and M2 from each other. Preferably, the above separation is a complete or substantially complete separation such that one mode is completely separated from the other mode.

[0054] A light - receiving element 103 is arranged downstream of the mode separator 102 in the propagation direction of the laser light. Regardless of the realization mode of the mode separator 102, depending on how the mode separator 102 actually separates the two modes, only one of the modes M1 or M2 is sent in the direction of the light - receiving element 103 and is intended to actually enter the light - receiving element 103.

[0055] In a more practical case, the mode separator does not perfectly separate modes M1 and M2 from each other. Even in such a case, the intensity of modes M1 and M2 can always be distinguished by the mode separator (such as a filter or the like). Therefore, even when the mode separation is not perfect, after both modes pass through the mode separator, it becomes possible to distinguish one mode from the other mode.

[0056] Furthermore, in many cases as described above, substantially all of the energy of the laser pulse is carried by one of modes M1 or M2. Even when the mode separator does not perfectly separate the modes, in some embodiments, a detectable signal exists at the light receiving element only when the mode that can pass through the mode separator 102 carries most of the pulse energy. Correspondingly, when the mode that should be separated and removed by the mode separator 102 and should not enter the light receiving element carries most of the pulse energy, no signal exists. This automatic digital conversion already described above can be appropriately used together with the mode separator to actually generate random bits (specifically, for example, 1 when the mode carrying most of the pulse energy passes through the mode separator, and 0 when the mode carrying most of the pulse energy does not pass through the mode separator). The reason is that the mode separated and removed by the mode separator does not generate a detectable signal at the light receiving element (this is the same even when the filtering or separation is not perfect), and a signal is generated at the light receiving element when the mode passing through the mode separator carries a large proportion of the pulse energy. This also applies when the mode separator does not operate perfectly, that is, when the mode separator does not affect the other mode and separates one mode without completely separating the modes.

[0057] Based on the above configuration and the fact that the relative intensities of the first mode M1 and the second mode M2 of each laser pulse emitted from the VCSEL are governed by the laws of quantum mechanics, thereby becoming truly random, the intensity of the mode reaching the light-receiving element becomes unpredictable, and thus truly random. As a result, the light-receiving element arbitrarily detects an optical signal depending on the intensity of the mode actually hitting the light-receiving element.

[0058] Accordingly, by using the output of the light-receiving element as an indication of the randomly obtained mode M1, random numbers can be generated.

[0059] However, in some embodiments, it may be advantageous to obtain a random bit sequence or bit stream (a plurality of 0s and 1s). This makes the subsequent processing of the random values generated by the random number generator more convenient when using random numbers in a computing environment.

[0060] In view of the above, the random number generator can further include a digital conversion unit 104 connected to the light-receiving element 103. This digital conversion unit 104 can be configured to digitally convert the signal received from the light-receiving element and can be implemented, for example, as an analog-to-digital converter.

[0061] The signal output from the light-receiving element and processed by the digital conversion unit generally or typically takes a current value or a voltage value that can be any value between a minimum value corresponding to the noise of the light-receiving element and a maximum value corresponding to at least the maximum energy output per pulse of the VCSEL. To digitally convert such a signal, the digital conversion unit can be configured to compare the signal received from the light-receiving element (e.g., a voltage value or a current value) with a reference signal. When the signal received from the light-receiving element exceeds the above reference signal, the output of the digital conversion unit can be set to 1. When the signal of the light-receiving element is below the above reference signal, the output of the digital conversion unit can be set to 0. Of course, the reverse is also possible.

[0062] Accordingly, the digital conversion unit 104 performs digital conversion of the signal received from the light receiving element by means of a comparison operation. A preferred embodiment of the digital conversion unit can be an analog-to-digital converter. This is because such a converter is cost-effective and can convert an analog signal (such as a current signal received from the light receiving element, etc.) into digital values (0 and 1) at a high frequency. Thereby, all the entropy (that is, all the respective values output from the light receiving element) can be converted into digital values.

[0063] The reference signal input to or used by the digital conversion unit may be referred to as a "threshold value" or a "threshold signal". This reference signal can basically have any value. However, in some embodiments, the threshold value is set based on the VCSEL output energy per laser pulse.

[0064] For example, for the first laser pulse, 50% of the total energy output can be provided in the first mode M1, and the remaining 50% can be provided in the second mode M2. Assuming that the mode separator 102 perfectly separates the first mode M1 from the second mode M2 and allows only the first mode to pass through and further propagate in the direction of the light receiving element 103, the mode M1 having an energy equal to 50% of the total output of the VCSEL hits the light receiving element 103, and a signal can be generated here. This signal can be converted into a current, and then input into a digital conversion unit. In this digital conversion unit, the current is compared with a reference signal, and in some embodiments, the signal is thereby digitally converted. Considering the second laser pulse, assume that in this laser pulse, more than 50%, for example 90%, of the total energy output of the VCSEL is provided in the second mode M2, and only 10% of the energy is provided in the first mode M1. However, the mode separator separates the second mode M2 from the first mode M1, and only 10% of the total output energy of the VCSEL is provided in the first mode M1 and hits the light receiving element 103. Thereafter, this signal is similarly converted into an electrical signal (such as a current signal) by the light receiving element 103, input into the digital conversion unit, and digitally converted. Preferably, the digital conversion unit can digitally convert the signal reaching the light receiving element such that, according to a signal indicating that most of the energy is carried by one mode, the signal obtained by the light receiving element is digitally converted to 1 or 0 depending on which mode carries more energy.

[0065] In the recognition in the present invention, in most cases, almost all the energy of the laser pulse is carried by one of the two modes (see above). This recognition is advantageously used when selecting the threshold of the digital conversion unit. Therefore, by setting the reference signal to a value corresponding to at least 25% or at least 50% or at least 75% or 90% of the maximum energy output by the VCSEL (also referred to as the "threshold"), only the signal of the light receiving element 103 indicating that the mode passing through the mode separator 102 carries almost all the energy of the pulse emitted from the VCSEL is counted as the first digital value (for example, 1), and digital conversion is realized such that all signals below the above threshold are determined to be the second digital value (for example, 0).

[0066] Normally, even when the light receiving element is shielded together with the VCSEL and the mode separator, the light receiving element not only receives the mode M1 of any intensity but also receives other signals from the surrounding environment. The cause is, for example, thermal fluctuations, etc., and the above other signals are known as "noise" or as "untrusted signals" with respect to random number generation by a trusted process (such as the VCSEL operation described in the present invention).

[0067] However, the present invention is not limited to the threshold values in the above examples, and it is also possible to set other values. The threshold can correspond to, for example, exactly 90% or 95% of the maximum energy that can be output by the VCSEL, thereby ensuring that a signal is generated only when the mode M1 carries almost all of the energy output by the VCSEL to the laser part. Specifically, since the energy distribution in one of the modes usually approaches 100% (that is, in most pulses, almost all the energy is provided by one or the other mode), there are also embodiments where it may be advantageous to use a high threshold.

[0068] To drive the VCSEL 101 to generate laser pulses, the random number generator 100 can further include a power supply 105 for driving the VCSEL in a direct modulation mode. To drive the VCSEL in this direct modulation mode, the power supply 105 can be configured to generate a current signal as shown in graph 143 of FIG. 1. In graph 143, the current I varies between a maximum value I1 that exceeds the laser oscillation threshold of the VCSEL labeled L in graph 143 and a minimum value I2 that is below the laser oscillation threshold of the VCSEL, such that the laser oscillation period and the non-oscillation period alternate.

[0069] The power supply 105 is preferably configured to vary the frequency for driving the VCSEL in a direct modulation mode. For example, the power supply can be configured to vary the frequency reaching the laser oscillation threshold from less than 10 Hz to several tens of GHz or several hundreds of GHz. Depending on requirements, any number of random numbers or random bit sequences can be generated with the above configuration. Furthermore, unnecessary entropy is no longer generated, thereby reducing the stress on the VCSEL.

[0070] In FIG. 1, other components 131 and 132 are provided. These components 131 and 132 are merely optional and are optical isolators. The optical isolator 131 is disposed between the emission part 115 of the VCSEL and the mode separator 102 and is within the propagation region of the laser part 120.

[0071] The optical isolator 131 can prevent scattered light from the outside from entering the system and can improve the efficiency and reliability of generating random numbers. Specifically, by applying the optical isolator 131 as described above, noise with respect to the random signal obtained by the light receiving element can be suppressed.

[0072] As shown in FIG. 1, it is not always necessary to dispose an optical isolator between the emission unit 115 and the mode separator 102. Instead of this, or in addition to this, an optical isolator 132 can also be disposed between the mode separator 102 and the light receiving element 103. Since the mode separator 102 preferably passes only one mode without passing scattered light, the noise level has already been reduced at this point. Therefore, it may be necessary to further reduce noise only between the mode separator 102 and the light receiving element 103.

[0073] As described above, the system of FIG. 1 has been described without specifically referring to the dimensions and actual arrangements of the unique components of the system of FIG. 1.

[0074] Preferably, the random number generator 100 is provided by being integrated on a chip. Specifically, the VCSEL and other components, particularly the light receiving element, the digital conversion unit, and the power supply are arranged on the chip and are advantageously miniaturized to a size of less than 1 cm. However, the present invention is not limited to such dimensions, and a large-scale implementation mode on the order of several centimeters for the entire system is also possible.

[0075] One advantage of the embodiment of the present invention is that the frequency for generating random bits of a random signal (emitted from the light receiving element) can be adjusted substantially arbitrarily within a wide frequency range. However, in some applications, it may be necessary to further increase the number of random numbers generated per unit time.

[0076] The second mode separated by the mode separator can basically be propagated to the second light receiving element. However, in the above case, the second mode cannot be used because this mode only represents redundant information. The reason is that if the first mode is detected, the second mode will not provide any additional entropy. If the second mode M2 separated by the mode separator 102 is not completely eliminated, it can be used as a control signal. However, since the second mode M2 does not provide additional randomness, it does not constitute actual entropy. However, in some embodiments, it is also possible to detect the second mode by using, for example, the second light receiving element and, optionally, other digital conversion units provided for the light receiving element. Such embodiments can be advantageous when evaluating the reliability of the random values obtained by the digital conversion unit. For example, it is possible to determine whether the proportion of the pulse energy carried by the second mode is actually less than 50%. The bit generated by the digital conversion unit 104 can be further used or output only when the sum of the value of the bit generated by the digital conversion unit 104 and the value of the bit generated by the digital conversion unit that digitally converts the signal of the second mode is equal to 1.

[0077] To increase the rate of generating random numbers using a VCSEL, a mode separator, and a light receiving element, an integrated configuration is shown in FIGS. 2a to 2c, which shows a system with multiple random number generators.

[0078] In the embodiment of FIG. 2a, the system 201 includes four random number generators 261 to 264.

[0079] In order for each of these four random number generators to generate true random numbers, each random number generator includes a separate or distinct VCSEL 211 to 214, and each VCSEL 211 to 214 generates only the laser beam or laser pulse related to each random number generator. Further, each random number generator includes its own light receiving element 251 to 254.

[0080] Although not shown here, in some embodiments, all random number generators share one power supply and the one power supply is connected to each random number generator, so that all random number generators receive the same current signal simultaneously and at the same frequency, and can be configured to synchronize the generation of laser pulses. In some embodiments, instead of providing the same current signal, the current signal supplied to a specific VCSEL can be adjusted. For example, the current (i.e., the amount of current) supplied to a specific VCSEL among a plurality of VCSELs can be adjusted while maintaining the relationship between the timing and frequency at which the current signal is emitted unchanged. Thereby, for at least one of the VCSELs, the actually supplied current is different from the current supplied to other VCSELs, while the current signal is supplied to all VCSELs simultaneously and at the same frequency. Such a configuration also includes a configuration in which the current supplied to each VCSEL is different from the current supplied to each other VCSEL. Further, in some embodiments, the current or current signal supplied to the VCSEL can be adjusted independently of the current supplied to other VCSELs for one pulse train or for one pulse.

[0081] In the above configuration, the relative intensities of the first mode and the second mode output from each VCSEL of each random number generator are completely arbitrary, and the relative intensity of the mode of the laser pulse output from VCSEL211 is almost always different from the relative intensity of the mode of the laser pulse output simultaneously by VCSEL212, so that it does not prevent the generation of random numbers of the mode. Accordingly, the signals detected by the light receiving elements 251 to 254 are usually different from each other.

[0082] As shown in the embodiment of FIG. 2a, each random number generator includes its own mode separators 231 to 234, and optional corresponding optical isolators 221 to 224 and / or 241 to 244. These multiple different random number generators can be integrated on one chip, and one digital conversion unit can be provided for each random number generator to enable highly reliable digital conversion of each signal. However, it is also possible to provide one digital conversion unit for all the random number generators. When only one digital conversion unit is provided, it may be preferable to first collect the outputs of all the light receiving elements and then supply the collected output to the digital conversion unit. When the VCSELs are driven at different frequencies or timings so that the VCSELs do not emit pulses simultaneously, it becomes unnecessary to collect the outputs of the light receiving elements, and each light receiving element may be connected to the input port of the digital conversion unit. Only one signal from only one light receiving element reaches the digital conversion unit at a specific point in time, thereby ensuring clear signal separation. Since the digital conversion unit does not need to know or grasp which light receiving element actually output the one signal, this can result in a highly cost-effective implementation without adversely affecting random number generation.

[0083] Although four random number generators are shown in FIGS. 2a, 2b, and 2c, the present embodiment is not limited in this regard, and any other arbitrary number of random number generators can be provided. In this regard, for example, a VCSEL array with a maximum of 20, or a maximum of 50, or a maximum of 100 VCSELs per array can be provided (along with corresponding components such as optical isolators, mode separators, light receiving elements, etc.).

[0084] In the embodiment of FIG. 2b, the system 202 includes four random number generators 261 to 264. The structures of these random number generators are basically the same as those described with reference to FIG. 2a, but this embodiment includes one mode separator 230 for all the random number generators. For example, the above one mode separator can be realized by a grating or a filter or a polarization-dependent optical isolator in the region where the laser pulses of the VCSELs of all the random number generators travel in the directions of the respective light receiving elements 251 to 254.

[0085] According to such an embodiment, the number of individual components that need to be used can be reduced, and the integration of the system can be facilitated.

[0086] In the embodiment of FIG. 2c, further, in addition to having one mode separator 230, for all the random number generators, one optical isolator 220 or 240 is provided as the optical isolator 220 and / or the optical isolator 240. Thereby, the number of separate independent components that require adjustment and relative arrangement with respect to other components is further reduced.

[0087] In some embodiments, instead of the light receiving elements 251 to 254, only one light receiving element is provided for all the VCSELs or for at least a group of VCSELs where the number of VCSELs is more than 1 and less than the total number of VCSELs.

[0088] The signal output from the VCSEL can be guided to and detected by the above one light receiving element using, for example, (one or more) mode separators.

[0089] This embodiment is particularly advantageous when driving the VCSELs at the same frequency but with a slight time delay to eliminate signals emitted simultaneously from a plurality of different VCSELs so that the separated signals can be separated in the light receiving element and / or the corresponding digital conversion unit.

[0090] In an embodiment where there is one light-receiving element for a plurality of VCSELs, or in other embodiments described herein (specifically, embodiments in which a plurality of light-receiving elements are provided), it is also possible to provide a multi-bit digital conversion unit, preferably a multi-bit analog-to-digital converter, for converting the (one or more) signals received from the (one or more) light-receiving elements.

Claims

1. A random number generator comprising a vertical cavity surface emitting laser, a mode separator, and a light receiving element, further comprising a power supply for driving the vertical cavity surface emitting laser in a direct modulation mode, wherein the vertical cavity surface emitting laser is configured to emit laser light having two different laser modes with random relative intensities that can propagate in a propagation direction away from the emission part into a space outside the vertical cavity surface emitting laser cavity from the emission part, the mode separator is disposed between the light receiving element and the vertical cavity surface emitting laser in the propagation direction, and the mode separator is arranged to separate the two different laser modes from each other and send one of the two different laser modes to the light receiving element. A random number generator characterized by the above.

2. further comprising a digital conversion unit connected to the light receiving element, wherein the digital conversion unit is configured to digitally convert the signal from the light receiving element so that a first value is output when the signal obtained from the light receiving element exceeds a threshold value, and a second value different from the first value is output when the signal of the light receiving element is below the threshold value. The random number generator according to claim 1.

3. The digital conversion unit is an analog-to-digital converter. The random number generator according to claim 2.

4. The vertical cavity surface emitting laser cavity does not include a mode suppression element that suppresses one of the two different laser modes. The random number generator according to any one of claims 1 to 3.

5. The threshold value has a value corresponding to at least 90%, or at least 75%, or at least 50%, or at least 25% of the maximum energy that can be output by the vertical cavity surface emitting laser. The random number generator according to claim 2.

6. The vertical cavity surface emitting laser includes quantum dots or quantum wells as an active medium for generating the laser light. The random number generator according to any one of claims 1 to 5.

7. The mode separator includes a polarization beam splitter or a filter or a polarization-dependent optical isolator. The random number generator according to any one of claims 1 to 6.

8. An optical isolator is disposed between the mode separator and the emission part of the vertical cavity surface emitting laser and / or between the mode separator and the light receiving element. The random number generator according to any one of claims 1 to 7.

9. A method for generating a random number using a random number generator including a vertical cavity surface emitting laser, a mode separator, and a light receiving element, wherein the random number generator further includes a power source for driving the vertical cavity surface emitting laser in a direct modulation mode, the vertical cavity surface emitting laser emits laser light having two different laser modes with random relative intensities propagating in a propagation direction away from the emission part from the emission part to a space outside the vertical cavity surface emitting laser cavity, the mode separator is disposed between the light receiving element and the vertical cavity surface emitting laser in the propagation direction, the mode separator separates the two different laser modes from each other and sends out one of the two different laser modes to the light receiving element, the light receiving element outputs a signal corresponding to the intensity of the laser light received by the light receiving element from the vertical cavity surface emitting laser via the mode separator characterized in that.

10. the random number generator further includes a digital conversion unit connected to the light receiving element, the digital conversion unit digitally converts the signal of the light receiving element so that when the signal output from the light receiving element exceeds a threshold value, a first value is output, and when the signal of the light receiving element is below the threshold value, a second value different from the first value is output, The method according to claim 9.

11. the threshold value has a value corresponding to at least 90%, or at least 75%, or at least 50%, or at least 25% of the maximum energy output by the vertical cavity surface emitting laser, The method according to claim 10.

12. The frequency of the direct modulation mode is adjusted by a control unit according to the number of random numbers generated per unit time, The method according to any one of claims 9 to 11.

13. A system including the random number generator according to any one of claims 1 to 8, characterized in that it is mounted on a chip.

14. A system including an array of a plurality of random number generators according to any one of claims 1 to 8, one mode separator is provided for all the random number generators, or one mode separator is provided for each of the random number generators, and / or One optical isolator is provided for all of the random number generators, or one optical isolator is provided for each of the random number generators. A system characterized by this.

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