CN109828745B - Quantum random number generator - Google Patents

Abstract

The invention discloses a quantum random number generator. The optical beam splitting component has n output ports, the optical beam combining component has n input ports, the output port 1 of the optical beam splitting component is connected to the input port 1 of the optical beam combining component via the optical switch component 1; the output port 2 of the optical beam splitting component is connected to the input port 2 of the optical beam combining component via the optical delay component 1 and the optical switch component 2; the output port 3 of the optical beam splitting component is connected to the input port 3 of the optical beam combining component via the optical delay component 2 and the optical switch component 3; by analogy, the delay difference between any two input light beams of the optical beam combining component is greater than the coherence time of the light source; the optical signal output end of the optical beam combining component is connected to the optical signal input end of the optical detection component; wherein n≥3. By controlling the working sequence of the optical switch component, the light fields with different delay differences can be interfered in a time-division manner, the maximum sampling rate can be increased, and the extracted random numbers can be guaranteed to have the maximum possible entropy value.

Description

A quantum random number generator

Technical Field

The present invention relates to the technical field of random number generating devices, and in particular to a quantum random number generator.

Background Art

With the explosive growth of information, information security has begun to attract more and more attention. Random numbers play an irreplaceable role in the information encryption process. The quantum random number generator based on light source phase noise can generate true random numbers due to its inherent quantum random characteristics, thus ensuring the absolute security of information transmission.

In a quantum random number generator (QRNG) based on light source phase noise, an interferometer structure is generally used to interfere two or more light beams with relative delay differences. Therefore, the coherence of the light source itself will affect the performance of the random number generator. The temporal coherence of the light source means that only light waves with a delay difference within a certain range have a relatively fixed phase difference, so that stable interference can occur. This time range is called the coherence time. From a statistical point of view, it can be considered that two light beams with a delay difference less than the coherence time are correlated, that is, they are not independent of each other. In the extreme case, when the delay difference between the two light beams is zero, their phases are exactly the same, and the correlation coefficient at this time is "1". As the delay difference between the two light beams increases, their correlation coefficient gradually decreases. When the delay difference is much larger than the coherence time, it can be considered that the two light beams are independent of each other. At this time, the amplitude noise distribution extracted by interference is approximately uniformly distributed, and the generated random numbers have the maximum possible entropy value (uniformly distributed random numbers have the greatest disorder). In the current QRNG scheme based on light source phase noise, most of them achieve high-rate random number generation by increasing the sampling rate (i.e. reducing the sampling interval). However, the potential problem brought by this method is that reducing the sampling interval is actually equivalent to reducing the delay difference between the two beams involved in the interference, which increases the correlation between the interfering beams. This will bring three adverse effects: 1) the dynamic range of the converted amplitude noise is reduced, which is very unfavorable for the subsequent quantization process; 2) the probability distribution of the extracted data becomes a Gaussian distribution, reducing the entropy value of the generated random numbers; 3) the interferometer must increase feedback control to avoid random drift of the bias point caused by environmental factors. Therefore, considering the above-mentioned limitation of the coherence time of the light source, the maximum sampling rate required to generate true random numbers is limited by the coherence time of the light source, that is:

Among them, _vs,max is the maximum sampling rate; Ts _,min is the minimum sampling interval; _τc is the coherence time of the light source.

Summary of the invention

The present invention provides a quantum random number generator, thereby achieving the technical effect that the maximum sampling rate is not limited by the coherence time of the light source.

The present invention provides a quantum random number generator, comprising: an optical beam splitting component, an optical delay component 1 to n-1, an optical switch component 1 to n, a photosynthetic component and a light detection component; the optical beam splitting component has n output ports, the photosynthetic component has n input ports, the output port 1 of the optical beam splitting component is connected to the input port 1 of the photosynthetic component via the optical switch component 1; the output port 2 of the optical beam splitting component is connected to the input port 2 of the photosynthetic component via the optical delay component 1 and the optical switch component 2; the output port 3 of the optical beam splitting component is connected to the input port 3 of the photosynthetic component via the optical delay component 2 and the optical switch component 3; and so on, the delay difference between any two input light beams of the photosynthetic component is greater than the coherence time of the light source; the optical signal output end of the photosynthetic component is connected to the optical signal input end of the light detection component; wherein n≥3.

Furthermore, it also includes: an analog-to-digital conversion component; the electrical signal input end of the analog-to-digital conversion component is electrically connected to the electrical signal output end of the light detection component.

Furthermore, it also includes: a light-emitting component; the optical signal output end of the light-emitting component is connected to the optical signal input end of the optical beam splitting component.

Furthermore, the light emitting component is a semiconductor laser, a fiber laser or a solid laser.

Furthermore, the optical delay component is a fiber delay device, a waveguide delay device or a free space delay device.

Furthermore, the optical switch component is an electro-optical optical switch, a magneto-optical optical switch or a semiconductor optical amplifier optical switch, and the switching time reaches nanosecond level.

Furthermore, the light detection component is a photomultiplier tube, an avalanche photodiode or a PIN photodiode.

One or more technical solutions provided in the present invention have at least the following technical effects or advantages:

The output light of the light source is split into n parts with equal power by an optical beam splitting component, and enters branches with different delays respectively. Each branch has an optical switch component to determine whether the light field of this branch participates in the interference process. At the same time, only two optical switch components among the n branches are in the on state. The two branches in the on state are coupled and interfered in the optical beam combining component, and the phase noise is converted into amplitude noise. This amplitude noise is converted into an electrical signal in the optical detection component, which can realize the extraction of quantum phase noise of different time windows of the light source. Among them, the delay difference between the two beams of light participating in the interference is always greater than the coherence time of the light source. Therefore, the correlation between the two beams of light participating in the interference in the present invention is small, and the extracted laser phase noise has the characteristics of uniform distribution, and the random number generated has the maximum possible entropy value. On the other hand, thanks to the fact that the delay difference between the two beams of light participating in the interference is always greater than the coherence time of the light source, the present invention has the advantage of not requiring feedback control compared with the existing scheme with a smaller effective delay difference. By reasonably setting the delay amount of each branch, it can be made that for two adjacent sampling points, the time difference between the previous field points or the next field points in the two field points participating in the interference is greater than the coherence time, so that the correlation of the data of the adjacent sampling points can be minimized without limiting the sampling interval. In addition, in the present invention, the random number generation rate can be increased by directly increasing the number of branches, so it has the advantage of easy upgrade. Theoretically, the sampling rate can be infinite, and the increase in the generation rate will not sacrifice the randomness of the random number. Therefore, the maximum sampling rate of the present invention is not limited by the coherence time of the light source.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the structure of a quantum random number generator provided in an embodiment of the present invention.

FIG. 2 is a schematic diagram comparing the principles of the solution of the present invention and a common two-path interference solution.

FIG3 is a schematic diagram of the principle of reducing the correlation of adjacent sampling point data in a quantum random number generator provided by an embodiment of the present invention.

FIG4 is a schematic structural diagram of an optical quantum random number generator having a three-branch interference structure based on a quantum random number generator provided in an embodiment of the present invention.

FIG. 5 is a control timing diagram of each optical switch in a working cycle and a corresponding interference time window diagram in the embodiment of FIG. 4 .

FIG6 is a diagram showing the relationship between the field points involved in interference and the key time parameters corresponding to each sampling point in the embodiment of FIG4 and the coherence time of the light source and the conduction time of the optical switch.

DETAILED DESCRIPTION

The present invention provides a quantum random number generator, thereby achieving the technical effect that the maximum sampling rate is not limited by the coherence time of the light source.

The technical solution in the present invention is to achieve the above technical effects, and the overall idea is as follows:

The output light of the light source is split into n parts with equal power by an optical beam splitting component, and enters branches with different delays respectively. Each branch has an optical switch component to determine whether the light field of this branch participates in the interference process. At the same time, only two optical switch components among the n branches are in the on state. The two branches in the on state are coupled and interfered in the optical beam combining component, and the phase noise is converted into amplitude noise. This amplitude noise is converted into an electrical signal in the optical detection component, which can realize the extraction of quantum phase noise of different time windows of the light source. Among them, the delay difference between the two beams of light participating in the interference is always greater than the coherence time of the light source. Therefore, the correlation between the two beams of light participating in the interference in the present invention is small, and the extracted laser phase noise has the characteristics of uniform distribution, and the random number generated has the maximum possible entropy value. On the other hand, thanks to the fact that the delay difference between the two beams of light participating in the interference is always greater than the coherence time of the light source, the present invention has the advantage of not requiring feedback control compared with the existing scheme with a smaller effective delay difference. By reasonably setting the delay amount of each branch, it can be made that for two adjacent sampling points, the time difference between the previous field points or the next field points in the two field points participating in the interference is greater than the coherence time, so that the correlation of the data of the adjacent sampling points can be minimized without limiting the sampling interval. In addition, in the present invention, the random number generation rate can be increased by directly increasing the number of branches, so it has the advantage of easy upgrade. Theoretically, the sampling rate can be infinite, and the increase in the generation rate will not sacrifice the randomness of the random number. Therefore, the maximum sampling rate of the present invention is not limited by the coherence time of the light source.

In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

Referring to Figure 1, the quantum random number generator provided by the present invention includes: an optical beam splitting component, an optical delay component 1~n-1, an optical switch component 1~n, a photosynthetic component and a light detection component; the optical beam splitting component has n output ports, the photosynthetic component has n input ports, the output port 1 of the optical beam splitting component is connected to the input port 1 of the photosynthetic component via the optical switch component 1; the output port 2 of the optical beam splitting component is connected to the input port 2 of the photosynthetic component via the optical delay component 1 and the optical switch component 2; the output port 3 of the optical beam splitting component is connected to the input port 3 of the photosynthetic component via the optical delay component 2 and the optical switch component 3; and so on, the delay difference between any two input light beams of the photosynthetic component is greater than the coherence time of the light source; the optical signal output end of the photosynthetic component is connected to the optical signal input end of the light detection component; wherein n≥3, such as 3, 4, 5, 6, etc.

The structure of the quantum random number generator provided by the present invention is specifically described, and also includes: an analog-to-digital conversion component; the electrical signal input end of the analog-to-digital conversion component is electrically connected to the electrical signal output end of the light detection component.

The structure of the quantum random number generator provided by the present invention is further described, and further includes: a light-emitting component; an optical signal output end of the light-emitting component is connected to an optical signal input end of the optical beam splitting component.

In this embodiment, the light-emitting component is a semiconductor laser, a fiber laser or a solid-state laser, etc., which operates near the threshold and slightly above the threshold, and the operating wavelength of the light-emitting component matches the response wavelength of the photoelectric conversion component. The optical delay components 1 to n-1 are optical fiber delay devices, waveguide delay devices or free space delay devices, etc., and each optical delay component can be the same or different. The optical switch components 1 to n are high-speed optical switches such as electro-optical optical switches, magneto-optical optical switches or semiconductor optical amplifier optical switches, and the switching time can reach the nanosecond level. The number of branches n can be 3, 4, 5, ..., etc. For the same light-emitting component (same coherence time), when n increases, the switching time of the optical switch is required to decrease according to the law of ∝1/(n(n-1)). Each optical switch component can be the same or different. The optical detection component is a photomultiplier tube, an avalanche photodiode, a PIN photodiode or a photodetector, etc. The optical beam splitting component is an optical beam splitter that realizes the beam splitting function, etc. The optical beam combining component is an optical beam combiner that realizes the beam combining function, etc. The analog-to-digital conversion component is an A/D converter, etc.

As shown in Figure 1, _τc is the coherence time of the light source; _ti is the delay time of the optical delay device i (i = 1, 2, ..., n-1, n = 3, 4, 5, ...); the optical beam splitter is an optical coupler that realizes n-way beam splitting; the optical beam combiner is an optical coupler that realizes n-way beam combining. The optical beam splitter is used to divide the light from the light source into n beams with equal power, and enters n branches respectively. The delay introduced on each branch is different, and the delay difference between any two branches in the n branches is greater than the coherence time of the light source to ensure that the extracted noise obeys uniform distribution. Any branch has an optical switch to realize the conduction and closing of this branch. By controlling the optical switch, only the optical switches on two branches can be turned on at the same time, thereby realizing the selection of the relative delay amount of the two light waves participating in the interference. Thanks to this selectivity, interference between light waves with different delay differences can be realized in a time-sharing manner, so as to extract phase noise in different time windows. The comparison between the scheme shown in Figure 1 and the ordinary dual-beam interference scheme can be simply given by Figure 2. Among them, the solid line is the interference time window of the ordinary double-beam interference scheme, and the dotted line is the different interference time window used in the embodiment of the present invention. If A, B, C, D, and E are the time positions of five consecutive sampling points, then under the limit conditions required for generating true random numbers, the interval _Ts between two adjacent points should be equal to the delay difference _Td of the interferometer and equal to the coherence time _τc of the light source. The ordinary double-beam interference scheme only extracts the quantum phase information of two adjacent time points (such as A and B, B and C, C and D, D and E), while the quantum phase information of two non-adjacent time points (such as A and C, A and D, A and E, B and D, B and E) cannot be extracted. The embodiment of the present invention can interfere with two branches with different delay differences in different time windows by controlling the optical switch, so as to realize the time-sharing extraction of quantum phase noise, thereby breaking through the theoretical maximum sampling rate determined by formula (1), and ensuring that the amplitude noise distribution extracted by interference is approximately uniform. When the number of branches is n, as long as the delay of each branch and the switch-on sequence are set reasonably, an infinite sampling rate can be achieved in theory. Considering that there are n(n-1)/2 possible choices for selecting two of the n switches to be turned on, and the delay difference between any two branches is greater than the coherence time of the light source, it is required that:

Where _Tk is the on-time of the optical switch, and Δt _i,j is the relative delay difference between any two branches. This means that if the sampling time _Ts is equal to the on-time _Tk of the optical switch, the actual sampling rate can be n(n-1)/2 times the theoretical maximum value, so when n approaches infinity, it also means that an infinite sampling rate can be achieved. At this time, the sampling time limit in the embodiment of the present invention is given by the following inequality:

T _s ≥T _k ≥T _r (3)

Wherein, _Tr is the response time of the photoelectric conversion component.

The greatest innovation of the embodiment of the present invention is that it gets rid of the limitation of the light source coherence time on the sampling time in the ordinary double-beam interference scheme (Formula (1)). By distinguishing different time windows, the coherence time of the light source only affects the setting of the delay difference of each branch, but does not affect the sampling time, and the sampling time is only limited by the conduction time of the optical switch. The sample value sampled in the ordinary double-beam interference scheme depends only on the interference results at both ends of the time window (the width is equal to the delay difference between the two arms of the interferometer). The reason why the embodiment of the present invention allows the sampling time to be less than the light source coherence time is that the interference results of two beams of light with different delay differences are used to fill the original coherence time window at equal intervals. This time-divided interference makes it possible to extract phase noise inside the time window where phase noise could not be extracted originally.

In addition, as shown in FIG3 , since the phase noise information extracted from each sampling point depends on the interference result of two field points whose time interval is equal to the delay difference, if for two adjacent sampling points, the time difference _TS between the previous field points (such as A and C) or the time difference _Td between the next field points (such as B and D) participating in the interference (respectively connected by arcs) is greater than the coherence time, the correlation of the data of adjacent sampling points can be minimized without affecting the sampling time, thereby obtaining the maximum entropy.

The embodiment of the present invention selects n=3, that is, the case of three branches.

The three-branch time-division interference structure is shown in Figure 4. Among them, the light source is a distributed feedback (DFB) semiconductor laser with a line width of 10MHz, and the coherence time of the light source is _τc = 31.84ns; the optical switch adopts a high-speed lithium niobate electro-optical switch; the delay device is two standard single-mode optical fibers (G.652) with lengths of 8.5 meters and 19.5 meters respectively; the optical beam splitter is a 1×3 directional coupler; the optical beam combiner is a 3×1 directional coupler; the photodetector is a PIN photodetector with a bandwidth of 10GHz. The delay difference between any two branches of the three branches is greater than the coherence time _τc of the light source, ensuring that the light waves participating in the interference are independent of each other, so that the interference results obey a uniform distribution and the random numbers generated have the maximum possible entropy value. Only two of the three optical switches are in the on state at the same time, thereby realizing the alternating interference of the three optical paths. By controlling the switch, the selection of the optical path participating in the interference can be realized. Theoretically, the maximum sampling rate will depend on the switching speed of the optical switch, and will not be restricted by the coherence time of the light source. The optical switch control process in one timing cycle in the embodiment of FIG4 is: 1) k1 and k3 are turned on, k2 is turned off, and sampling point _S1 is obtained; 2) k1 and k2 are turned on, k3 is turned off, and sampling point _S2 is obtained; 3) k2 and k3 are turned on, k1 is turned off, and sampling point _S3 is obtained; 4) _S4 is the first sampling point of the next cycle, and its corresponding optical switch state is the same as _S1 , k1 and k2 are turned on, k3 is turned off; and so on. FIG5 shows the control timing diagram of the optical switch in one timing cycle in the embodiment of FIG4 and the corresponding interference time window. Among them, _S1 ~ _S3 correspond to the time position of the sampling point respectively; the delay time _t1 >_τc; _t2 - _t1 > _τc . FIG6 shows the field points participating in the interference corresponding to each sampling point in the embodiment of FIG4, as well as the relationship between the key time parameters and the coherence time of the light source and the optical switch on time. Among them, τ _c is the coherence time of the light source; delay time t ₁ >τ _c ; t ₂ -t ₁ >τ _c ; T _k is the on-time of the optical switch; AL corresponds to the light field at different times, and each line connects the field points involved in the interference determined by the delay difference; S ₁ ~ S ₆ correspond to the time position of the sampling point. In order to make the generated data meet the uniform distribution and reduce the correlation of adjacent sampling points without being affected by the coherence time of the light source, the relationship between the time parameters in Figure 6 must satisfy the following inequalities:

AG: 3T _k ＞τ _c (5)

EC: t ₁ -T _k ＞τ _c (6)

CD: t ₂ -t ₁ > τ _c (7)

HF: t ₂ -t ₁ -T _k >τ _c (8)

DH: t ₂ -t ₁ -2T _k >τ _c (9)

IF：t ₂ -t ₁ -2T _k >τ _c (10)

DL: 4T _k ＞τ _c (11)

There are three ways to select two out of three branches at the same time, which means that the optimal timing period is 3T _k , which leads to inequality (5). Among the four optical field points C, D, E and F, the time difference between D and F is T _k , which is obviously less than the coherence time. Therefore, the time difference between the two optical fields E and C must be greater than the coherence time to ensure that the sampling points S ₂ and S ₃ have the minimum correlation, thus deriving equation (6). Similarly, equations (7)-(11) can be derived. Combining equations (5)-(11), the constraints on the time parameters of the optical switch and optical delay device in this structure can be deduced as follows:

t ₂ ＞3τ _c (14)

From formula (12), we can see that if the AD converter is 3-bit sampling, the maximum sampling rate that can be achieved by this scheme is It is the theoretical maximum sampling speed of the ordinary double-beam interference scheme 3 times.

In summary, the embodiments of the present invention get rid of the limitation of the light source coherence time on the sampling time in the ordinary dual-beam interference scheme, and transfer this limitation to the limitation on the branch delay, as shown in equations (13) and (14).

It should be noted that the embodiments of the present invention can be implemented directly in free space by discrete devices, or part or all of the devices therein can be replaced by integrated optoelectronic devices.

【Technical Effect】

The output light of the light source is split into n parts with equal power by an optical beam splitting component, and enters branches with different delays respectively. Each branch has an optical switch to determine whether the light field of this branch participates in the interference process. At the same time, only two optical switches among the n branches are in the on state. The two branches in the on state perform coupling interference in the optical beam combining component, converting the phase noise into amplitude noise. This amplitude noise is converted into an electrical signal in the optical detection component, which can realize the extraction of quantum phase noise of different time windows of the light source. Among them, the delay difference between the two beams of light participating in the interference is always greater than the coherence time of the light source. Therefore, the correlation between the two beams of light participating in the interference in the embodiment of the present invention is much smaller, and the extracted laser phase noise has the characteristics of uniform distribution, and the random number generated thereby has the maximum possible entropy value. Thanks to the fact that the delay difference between the two beams of light participating in the interference is always greater than the coherence time of the light source, the embodiment of the present invention has the advantage of not requiring feedback control compared with the existing ordinary dual-beam interference scheme with a smaller effective delay difference. By reasonably setting the delay amount of each branch, it can be made that for two adjacent sampling points, the time difference between the previous field points or the next field points in the two field points involved in the interference is greater than the coherence time, so that the correlation of the data of adjacent sampling points can be minimized without limiting the sampling interval. In addition, in the embodiment of the present invention, the maximum generation rate of random numbers can be increased by directly increasing the number of branches, so it has the advantage of easy upgrade. Theoretically, the sampling rate can be infinite, and the increase in the generation rate will not be at the expense of the entropy value of random numbers. Therefore, the maximum sampling rate of the embodiment of the present invention is not limited by the coherence time of the light source. If the switching time of the optical switch is small enough, when there are n branches, a sampling rate of n(n-1)/2 times the theoretical maximum value can be achieved. The currently commercialized optical switches can achieve a switching speed of 1ns, so it can be assumed that the conduction time of the optical switch is 2ns. Assuming that the AD converter is 3-bit sampling, the line width of the light source is Then the maximum sampling speed that can be achieved with the ordinary MZI solution in theory is: The maximum sampling speed that can be achieved by the quantum random number generator provided by the embodiment of the present invention is: This is 16 times the theoretical maximum value.

In summary, the embodiment of the present invention can extract quantum phase information of different time windows (i.e., time-sharing extraction) by selectively acting on branches with optical switches, allowing light fields with different delay differences to interfere in a time-sharing manner, thereby breaking through the theoretical maximum sampling rate of the ordinary double-beam interference scheme, while ensuring that the sampled data obeys a uniform distribution and the correlation between adjacent sampling points is minimal, thereby ensuring that the extracted random number has the maximum possible entropy value. In addition, in this scheme, there is no need to feedback control the bias point of the interferometer, which simplifies the system design. The greatest significance of the scheme proposed in the embodiment of the present invention is that, without affecting the sampling time, a uniformly distributed random number is obtained (thereby obtaining the maximum possible entropy value), and the correlation between adjacent sampling points is minimized to the greatest extent, thereby achieving a breakthrough in the theoretical maximum sampling rate of the ordinary double-beam interference scheme, and this scheme also has the advantages of simple upgrade method (directly increasing the number of branches) and huge room for rate improvement (theoretically, the sampling rate can be infinite).

Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims (7)

1. A quantum random number generator, comprising: the optical delay device comprises an optical beam splitting component, optical delay components 1-n-1, optical switch components 1-n, an optical beam combining component and an optical detection component; the optical beam splitting component is provided with n output ports, the optical beam combining component is provided with n input ports, and the output port 1 of the optical beam splitting component is connected with the input port 1 of the optical beam combining component through the optical switch component 1; the output port 2 of the optical beam splitting component is connected with the input port 2 of the optical beam combining component through the optical delay component 1 and the optical switch component 2; the output port 3 of the optical beam splitting component is connected with the input port 3 of the optical beam combining component through the optical delay component 2 and the optical switch component 3; similarly, the delay difference of any two beams of input light of the light combining component is larger than the coherence time of the light source; the optical signal output end of the optical beam combining component is connected with the optical signal input end of the optical detection component; wherein n is more than or equal to 3; the optical switch is used for carrying out interference on light fields with different delay differences in a time-sharing mode through the selective action of the optical switch on the branch, and quantum phase information of different time windows is extracted, so that the maximum sampling rate in the theory of a common double-beam interference scheme is broken through, sampling data is guaranteed to be subjected to uniform distribution, the correlation between adjacent sampling points is minimum, and the extracted random number is guaranteed to have the maximum possible entropy value.

2. The quantum random number generator of claim 1, further comprising: an analog-to-digital conversion section; the electric signal input end of the analog-digital conversion component is electrically connected with the electric signal output end of the light detection component.

3. The quantum random number generator of claim 1, further comprising: a light emitting member; the optical signal output end of the light emitting component is connected with the optical signal input end of the light splitting component.

4. A quantum random number generator according to claim 3, wherein the light emitting means is a semiconductor laser, a fibre laser or a solid state laser.

5. The quantum random number generator of claim 1 wherein the optical delay element is a fiber optic delay, a waveguide delay, or a free space delay.

6. The quantum random number generator of claim 1 wherein the optical switching element is an electro-optic optical switch, a magneto-optic optical switch or a semiconductor optical amplifier optical switch, the switching time being on the order of nanoseconds.

7. The quantum random number generator of claim 1 wherein the light detecting component is a photomultiplier tube, an avalanche photodiode, or a PIN photodiode.