Photonic circuit and device for generating random numbers comprising such photonic circuit

Abstract

The present invention relates to a photonic circuit (10, 100, 200), comprising: - at least one solid-state light emitter (20a, 220a) configured to emit a light radiation (R); - at least one solid-state optical sensor (30a) configured to detect the incidence of a photon of the aforesaid light radiation (R). It should be noted that this circuit (10, 100, 200) also comprises a plate (11) of a semiconductor material whose thickness is defined by at least a first layer (20, 220) on which the emitter (20a, 220a) is obtained and by at least a second layer (30) on which the sensor (30a) is obtained.

Description

[0001] PHOTONIC CIRCUIT AND DEVICE FOR GENERATING RANDOM NUMBERS COMPRISING SUCH PHOTONIC CIRCUIT.

[0002] DESCRIPTION

[0003] The invention relates to a photonic circuit, as well as a device for generating random numbers comprising such a photonic circuit.

[0004] Photonic integrated circuits A are now known, for example the one shown in figure 1 , comprising:

[0005] - at least one solid-state light emitter B obtained on the surface of a plate of semiconductor material and configured to emit light radiation;

[0006] - at least one solid-state optical sensor C obtained on the surface of the aforesaid plate adjacent to the emitter B and configured to detect the incidence of a photon of such light radiation.

[0007] Such a photonic circuit A is typically, but not exclusively, employed in the generation of random numbers (QRNG) through the actuation of one or more detection steps.

[0008] In particular, each of these detection steps typically provides for the activation of the light radiation by the emitter B at an initial instant.

[0009] The detection step continues with waiting for a detection of the incidence of a photon of the light radiation by the sensor C at a final instant.

[0010] Finally, always with reference to this example, the calculation of a detection time defined as the difference between the aforesaid final instant and the aforesaid initial instant is envisaged.

[0011] The detection times thus defined are then used to determine one or more random numbers.

[0012] A similar photonic circuit A, although known and appreciated, however, has some important limitations due to the fact that both the emitter B and the sensor C are both obtained on the surface of a plate of semiconductor material as described above.

[0013] In particular, a first limit is due to the fact that the emitter B and the sensor C are inevitably separated from each other by a portion D of semiconductor material for reasons of constraint of the photonic circuit A.

[0014] This disadvantageously entails that the light radiation component Ri emitted by the emitter B directly towards the sensor C is strongly subject to the absorption of the photons that compose it by the aforesaid portion D.

[0015] Furthermore, although a metal layer M can be arranged to cover the surface of the plate so that the reflection of a second component of light radiation R2 is favoured, an important component of such light radiation R3 is dispersed by such a photonic circuit A.

[0016] Yet another disadvantage is related to unwanted phenomena of electrical coupling between the emitter B and the sensor C due to the construction characteristics of this photonic circuit A.

[0017] The task of the present invention is to develop a photonic circuit capable of obviating the mentioned drawbacks and limitations of the prior art.

[0018] In particular, it is an object of the present invention to realize a photonic circuit whose optical coupling between emitter and sensor entails a lower absorption and a lower dispersion of photons compared to similar photonic circuits of known type.

[0019] Furthermore, it is an object of the present invention to realize a photonic circuit that minimizes the undesired phenomena of electrical coupling between the emitter and the sensor.

[0020] The above task and objects are achieved by a photonic circuit according to claim 1.

[0021] Further features of the photonic circuit according to claim 1 are described in the dependent claims.

[0022] The aforesaid task and objects, together with the advantages that will be mentioned hereinafter, are highlighted by the description of an embodiment of the invention, which is given by way of non-limiting example with reference to the attached drawings, where:

[0023] - figure 1 represents a schematic view of a photonic circuit of known type;

[0024] - figure 2 represents a schematic view of the photonic circuit of figure 1 according to a first embodiment of the invention;

[0025] - figure 3 represents a schematic view of the photonic circuit of figure 1 according to a second embodiment of the invention;

[0026] - figure 4 represents a schematic view of the photonic circuit of figure 1 according to a third embodiment of the invention.

[0027] With reference to figures 2, 3 and 4, three examples of photonic circuits according to the invention are indicated as a whole with the numbers 10, 100 and 200.

[0028] Each of these circuits 10, 100 and 200 comprises:

[0029] - at least one solid-state light emitter 20a, 220a configured to emit a light radiation R;

[0030] - at least one solid-state optical sensor 30a configured to detect the incidence of a photon of the aforesaid light radiation R.

[0031] It should be noted that each of the aforesaid photonic circuits 10, 100 and 200 comprises a plate 11 of a semiconductor material whose thickness is defined by at least a first layer 20, 220 on which the emitter 20a, 220a is obtained and by at least a second layer 30 on which the sensor 30a is obtained.

[0032] Furthermore, the circuit 10, 100, 200 comprises an insulation layer 40, 140, 240 of the aforesaid semiconductor material interposed between the first layer 20, 220 and the second layer 30.

[0033] This insulation layer 40, 140, 240 guarantees an electrical insulation between the first layer 20, 220 and the second layer 30 while remaining permeable to light radiation R.

[0034] Therefore, the interposition of this insulation layer 40, 140, 240 does not hinder the passage of photons of the light radiation R, but advantageously allows to prevent the phenomenon of “charge injection” on the sensor 30a by the emitter 20a, 220a

[0035] By obtaining the emitter 20a, 220a and the sensor 30a on different layers, respectively the first layer 20, 220 and the second layer 30, an at least partial alignment of the emitter 20a, 220a and of the sensor 30a in parallel to a normal axis Z to the plate 11 is guaranteed.

[0036] It is thereby meant that the main propagation axis P of the emitter 20a, 220a forms an angle of incidence comprised between 0° and 90° with the sensitive surface S of the sensor 30a.

[0037] It is therefore clear that the optical coupling between the emitter 20a, 220a and the sensor 30a just defined and clearly visible in figures 2, 3 and 4 entails a lower absorption by the plate 11 and a lower dispersion of photons compared to similar photonic circuits of known type, such as the one schematized in figure 1 , which typically have this angle of incidence substantially equal to 0° since both the emitter 20a, 220a and the sensor 30a are obtained adjacent on the surface of a plate of semiconductor material.

[0038] Therefore, each photon belonging to the light radiation R emitted by the emitter 20a, 220a has a higher probability of reaching the sensor 30a and being detected by the sensor itself compared to similar photonic circuits of known type and under the same other conditions. It is important to emphasize that, in the context of this patent, a plate 11 can be intended as a monolithic element or an element composed of a plurality of layers superimposed on each other and permanently connected.

[0039] In particular, the photonic circuits 10, 100 and 200 are made directly on the plate 11 thus obtaining a monolithic circuit.

[0040] However, it is not excluded that these circuits 10, 100 and 200 are made using the 3d-stacking technique.

[0041] It can be observed that the first layer 20, 220 is defined at a main surface of the plate 11.

[0042] It is thereby simply meant that a surface of the first layer 20, 220 coincides with a main surface of the plate 11 itself.

[0043] In addition, a metal layer M is arranged to cover the plate 11 at the first layer 20, 220 so that the reflection of the light radiation R towards the sensor 30a is favoured.

[0044] This favours an even lower dispersion of the photons in the optical coupling between the emitter 20a, 220a and the sensor 30a, but it is not excluded that the first layer 20, 220 is defined in a different position in relation to the thickness of the plate 11 and that the metal layer M is absent.

[0045] The emitter 20a, 220a and the sensor 30a are aligned in parallel along the aforesaid normal development axis Z to the plate 11.

[0046] It is thereby meant that the main propagation axis P of the emitter 20a, 220a forms an angle of incidence substantially equal to 90° with the sensitive surface S of the sensor 30a.

[0047] It is therefore clear that the optical coupling between the emitter 20a, 220a and the sensor 30a thus defined entails an even lower absorption by the plate 11 and a lower dispersion of photons compared to similar photonic circuits of known type, thus speeding up the time necessary for the actuation of a detection step. This also allows to reduce the sizes of the circuit 10, 100, 200, but it is not excluded that the aforesaid alignment is not present in other embodiments of the invention.

[0048] Furthermore, the sensor 30a is a SPAD (Single-Photon Avalanche Diode) whose sensitive surface S is therefore sensitive to a single photon.

[0049] It is not excluded, however, that the emitter 20a, 220a as well as the sensor 30a are different from what has just been described.

[0050] With reference to a first embodiment of the invention indicated as a whole with the number 10 and clearly visible in figure 2, the first layer 20 is made of silicon, the emitter 20a obtained on said first layer 20 is a p-n junction and the aforesaid insulation layer 40 is defined by a p-n junction diode configured to electrically isolate the first layer 20 from the second layer 30. However, it is not excluded that, in the present embodiment of the invention, the aforesaid first layer 20 is made of polycrystalline silicon.

[0051] In a second embodiment of the invention, schematically represented in figure 3 and indicated with the number 100, the lamination of the plate 11 is made by means of a FD-SOI (Fully Depleted Silicon-On-lnsulator) process, but it is not excluded that a different technique for making the plate 11 and layers thereof can be used.

[0052] The resulting insulation layer 140 is a free-charge-depleted oxide layer that guarantees an electrical insulation between the first layer 20 and the second layer 30 that remains permeable to light radiation R.

[0053] In a third embodiment of the invention, schematically represented in figure 4 and indicated with the number 200, the first layer 220 is made of polycrystalline silicon, the emitter 220a obtained on said first layer 220 is a p-i-n junction and the insulation layer 240 is still a free-charge-depleted oxide layer.

[0054] However, it is not excluded that, in the present embodiment of the invention, the aforesaid first layer 220 is simply made of silicon.

[0055] This advantageously allows better control over the flow of photons emitted by the emitter 220a, which is proportional to the current that runs through this p-i-n junction.

[0056] Furthermore, the use of this technology makes it possible to optimise the power consumption of the emitter 220a.

[0057] It is not excluded, however, that this insulation layer 240 is defined by a p-n junction as previously described.

[0058] It should be specified that the emitters described in the three embodiments of the invention just presented are all semiconductor emitters based on “indirect bandgap”, but it is not excluded that the emitters used are different from what has just been presented.

[0059] As anticipated above, a device for generating random bits comprising a circuit 10, 100, 200 as described above is also an object of the present invention.

[0060] This device comprises a control unit operatively connected to the circuit 10, 100, 200 and configured to generate at least one random bit as a function of the signals generated by the circuit 10, 100, 200.

[0061] Specifically, the control unit is configured to generate the random bit by implementing the following steps in sequence: a) initiating a detection step by activating the emission of light radiation R by the emitter 20a, 220a at an initial instant; b) waiting for a detection of the incidence of a photon of the light radiation R by the sensor 30a at a final instant; c) calculating a detection time defined as the difference between the aforesaid final instant and the aforesaid initial instant; d) defining the random bit as a function of the detection time.

[0062] Even more precisely, the control unit is configured to generate the random bit by implementing the following steps in sequence: ai-ci) actuating steps a) to c) in a first detection step so as to calculate a first detection time; a2-C2) actuating steps a) to c) in a second detection step so as to calculate a second detection time.

[0063] Furthermore, during the aforesaid step d) the random bit is defined as a function of the first detection time and the second detection time.

[0064] In particular, in the present embodiment of the invention, if the first detection time is greater than the second detection time, the bit defined during step d) is equivalent to “0”.

[0065] Conversely, if the first detection time is less than the second detection time, the bit defined during step d) is equivalent to “1”.

[0066] It is not excluded, however, that a different method for defining a bit can be implemented or that the aforesaid photonic circuit 10 can be used in different contexts from QRNG.

[0067] Practically, it has been established that the invention achieves the intended task and objects.

[0068] In particular, with the invention, a photonic circuit has been developed whose optical coupling between emitter and sensor involves a lower absorption and a lower dispersion of photons compared to similar photonic circuits of known type.

Claims

CLAIMS1 ) Photonic circuit (10, 100, 200), comprising:- at least one solid-state light emitter (20a, 220a) configured to emit a light radiation (R);- at least one solid-state optical sensor (30a) configured to detect the incidence of a photon of said light radiation (R);- a plate (11 ) of a semiconductor material whose thickness is defined by at least a first layer (20, 220) on which said emitter (20a, 220a) is obtained and by at least a second layer (30) on which said sensor (30a) is obtained, characterized in that it comprises an insulation layer (40, 140, 240) of said semiconductor material interposed between said first layer (20, 220) and said second layer (30) and configured to electrically insulate said first layer (20, 220) from said second layer (30).2) Circuit (10, 100, 200) according to claim 1 , characterized in that said first layer (20, 220) is defined at a main surface of said plate (11 ).3) Circuit (10, 100, 200) according to claim 2, characterized in that it comprises a metal layer (M) covering said plate (11 ) at said first layer (20, 220).4) Circuit (10, 100, 200) according to any one of the preceding claims, characterized in that said emitter (20a, 220a) and said sensor (30a) are aligned in parallel along a normal development axis (Z) to said plate (11 ).5) Circuit (10, 100, 200) according to any one of the preceding claims, characterized in that said sensor (30a) is a SPAD.6) Circuit (10, 100, 200) according to any one of the preceding claims, characterized in that said first layer (20, 220) is polycrystalline silicon.7) Circuit (10) according to any one of the preceding claims, characterized in that said insulation layer (40) is defined by a p-n junction diode.8) Circuit (100, 200) according to any one of claims 1 to 6, characterized in that said insulation layer (140, 240) is a free-charge-depleted oxide layer.9) Circuit (10, 100) according to any one of the preceding claims, characterized in that said emitter (20a) is a p-n junction.10) Circuit (200) according to any one of claims 1 to 8, characterized in that said emitter (220a) is a p-i-n junction.11 ) Device for the generation of random bits, characterized in that it comprises a circuit (10, 100, 200) according to any one of the preceding claims, said device comprising a control unit operatively connected to said circuit(10, 100, 200) and configured to generate at least one random bit as a function of the signals generated by said circuit (10, 100, 200).12) Device according to claim 11 , characterized in that said control unit is configured to generate said random bit by implementing the following steps in sequence: a) initiating a detection step by activating the emission of said light radiation (R) by said emitter (20a, 220a) at an initial instant; b) waiting for a detection of the incidence of a photon of said light radiation (R) by said sensor (30a) at a final instant; c) calculating a detection time defined as the difference between said final instant and said initial instant; d) defining said random bit as a function of said detection time.13) Device according to claim 12, characterized in that said control unit is configured to generate said random bit by implementing the following steps in sequence: ai-ci) actuating said steps a) to c) in a first detection step so as to calculate a first detection time; a2-C2) actuating said steps a) to c) in a second detection step so as to calculate a second detection time; said step d) defining said random bit as a function of said first detection time and said second detection time.

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