Metasurface device

Description

[0001] The field of the invention is that of metasurface devices, for example metasurface antennas. The invention applies to microwave devices.

[0002] Such devices can be used in various applications such as radar applications in avionics and aerospace, high-speed communication, and space telecommunications.

[0003] Patent application WO2019219708 discloses an antenna device comprising a substrate, a ground plane formed on a rear surface of the substrate, and an antenna element formed on the front surface of the substrate. The antenna element comprises a first array of conductive pads separated by switches arranged between the conductive pads. The antenna device includes an electromagnetic wave source configured and arranged to generate a surface wave on the front face of the substrate. The surface wave is transformed by the two-dimensional array of conductive pads into leakage waves emitted in a direction having a component perpendicular to the front surface of the substrate. The electrical connection of some of the conductive pads to each other allows the formation of an array of interconnected pad groups.This solution allows, without using phase shifters, control of the main direction of the antenna's emission pattern and therefore the realization of low-cost electronically scanned antennas.

[0004] There is a need to offer such metasurface devices with good temporal accuracy so as, for example, to allow distances to be measured with good accuracy when the metasurface device is used in radar.

[0005] One aim of the invention is to provide a metasurface antenna device that enables good temporal accuracy.

[0006] To this end, the invention relates to a metasurface device comprising: a substrate having a rear surface and a front surface; a transmitting and / or receiving device capable of transmitting and / or receiving an electromagnetic wave, configured and arranged so that the wave is capable of propagating as a surface wave on the front surface of the substrate, an antenna element comprising a two-dimensional array of conductive pads arranged on the front surface of the substrate, spaced apart and having dimensions smaller than the operating wavelength of the transmitting and / or receiving device, the substrate comprising a mass structure capable of functioning as a ground plane, the mass structure being capable of being alternately in an insulating state in which it prevents the propagation of the surface wave on the front surface of the substrate, from the transmitting and / or receiving device to the conductive pads, or vice versa, and in a conductive state in which the mass structure functions as a ground plane allowing the propagation of the surface wave on the front surface of the substrate, from the transmitting and / or receiving device to the conductive pads, or vice versa,The mass structure is capable of switching from an insulating state to a conductive state by illuminating the mass structure at a wavelength known as the switching wavelength.

[0007] When the mass structure has a ground plane allowing the surface wave to propagate from the transmitting / receiving device to the conductive pads or vice versa, the antenna element is capable of reflecting or transforming the surface wave to radiate in a direction having a component perpendicular to the front surface of the substrate (in transmit mode) or of reflecting or transforming a wave received on the front surface of the substrate to transform it into a surface wave (in receive mode).

[0008] Advantageously, the metasurface device includes a switching source capable of switching from a state in which it does not illuminate the mass structure so that the mass structure is in the insulating state, to a state in which it illuminates the mass structure so that the mass structure is in the conducting state.

[0009] In a first embodiment, the substrate comprises a ground layer and an intermediate layer insulating the ground plane of the conductive pads when the ground structure has the function of a ground plane, the ground structure comprising a central photoconductive part and a peripheral conductive part surrounding the central photoconductive part, the central photoconductive part being in an insulating state, when not illuminated, in which it prevents the propagation of the surface wave from the transmitting and / or receiving device to the conductive pads, or conversely, the central photoconductive part being able to be in a conductive state, when illuminated at the switching wavelength, in which the central photoconductive part is conductive so that the ground structure has the function of a ground plane.

[0010] In a first example, the mass structure is a mass layer, with the intermediate layer being interposed between the conductive pellets and the mass layer.

[0011] In a second example, the intermediate layer is made of a photoconductive semiconductor material capable of being in a conductive state when illuminated at the switching wavelength, the intermediate layer being interposed between the conductive pads and the conductive peripheral part, the central photoconductive part comprising a central part of a back face of the intermediate layer, the back face of the intermediate layer being in direct physical contact with the conductive peripheral part.

[0012] In one particular example, the device includes several switching sources, the mass structure comprising several photoconductive central parts and a switch allowing to selectively illuminate only one of the photoconductive central parts taken from among the photoconductive central parts and / or allowing to simultaneously selectively illuminate several photoconductive central parts.

[0013] In a second embodiment, the bulk structure is a first photoconductive layer made of a single photoconductive semiconductor material, the photoconductive material being insulating when not illuminated and conductive when illuminated at the switching wavelength.

[0014] Advantageously, the photoconductive semiconductor material forming the first photoconductive layer is chosen such that the first photoconductive layer has a penetration depth less than the thickness of the first photoconductive layer at the switching wavelength, so that when an entire back face of the first photoconductive layer is illuminated at the switching wavelength by the switching source, the first photoconductive layer comprises: a conductive portion forming the ground plane and extending from the back face of the semiconductor layer over a thickness less than the thickness of the first semiconductor layer and, an insulating portion extending over the remainder of the thickness of the semiconductor layer so that the conductive portion is insulated from the conductive pellets by the insulating portion.

[0015] Advantageously, the metasurface device includes a semiconducting intermediate layer, the metasurface device including an optical reconfiguration device comprising a so-called reconfiguration source emitting an optical beam and a diffractive optical device capable of illuminating a set of at least one area, called the illuminated area, of the intermediate layer so that the intermediate layer is conductive only in the set of at least one illuminated area, so as to electrically connect two by two the separate metal pellets of the antenna element connected by a continuous area of ​​the intermediate layer located totally in an illuminated area of ​​the set of at least one illuminated area to form at least one group of electrically connected conductive pellets (4).

[0016] Advantageously, the intermediate layer is interposed between the ground layer and the conductive pads. Alternatively, the intermediate layer is the ground layer.

[0017] The metasurface device according to the invention has the advantage of providing optical control for generating the ground plane. This control is therefore independent of the control of the electromagnetic wave source used to excite the metasurface (or the antenna element) and thus of the signal radiated by the metasurface device.

[0018] The temporal accuracy of optical control is better than that of electrical control. This solution therefore allows for very high temporal accuracy at the instant the metasurface device is switched on or off, and thus at the instant electromagnetic radiation is emitted. Indeed, the antenna only radiates when the ground structure is illuminated in such a way as to create the ground plane.

[0019] This temporal precision allows for accurate measurements, for example, in radar or telecommunications applications. It enables, for instance, high accuracy in measuring the round-trip travel time of the emitted wave to the illuminated object.

[0020] Optical control of the ground plane can also be uncorrelated with another optical control to ensure the selective electrical connection of the conductive pads of the metasurface to configure the antenna element, for example, to adjust the scale of the metasurface, i.e. the pitch of the antenna elements of the metasurface.

[0021] Other features, details and advantages of the invention will become apparent from the description provided with reference to the accompanying drawings given by way of example, which represent, respectively: [ Fig.1 ] there figure 1 schematically illustrates, from a top view, a first example of a metasurface device according to a first embodiment of the invention, [ Fig.2 ] there figure 2 illustrates schematically, in a more precise manner, a part of the antenna element of the device. figure 1 , top view, a first example of a metasurface device according to a first mode, [ Fig.3 ] there figure 3 illustrates schematically, another example of an antenna element, [ Fig.4 ] there figure 4 schematically illustrates, in cross-section, the device of the figure 1 , [ Fig.5 ] there figure 5 schematically illustrates, from a bottom view, the device of the figure 1 , [ Fig.6 ] there figure 6 illustrates schematically, in cross-section, a second example of the device according to the first embodiment of the invention, [ Fig.7 ] there figure 7 illustrates schematically, in cross-section, a third example of the device according to the first embodiment of the invention, [ Fig.8 ] there figure 8 schematically illustrates, in cross-section, a metasurface device according to a second embodiment, [ Fig.9 ] there figure 9 schematically illustrates, in exploded view, the metasurface device of the figure 8 .

[0022] From one figure to another, the same elements are identified by the same references.

[0023] In the rest of the text, by conductor we mean electrically conductive and by insulator we mean electrically insulating.

[0024] An optical beam is understood to be a beam whose wavelength is located in the optical range including infrared, ultraviolet and visible light.

[0025] There figure 1 schematically illustrates, in top view, a metasurface device 1 according to the invention.

[0026] The metasurface device 1 comprises a stacking E of layers stacked along a stacking axis z perpendicular to the plane of the figure 1 The stack comprises a substrate 2, a central conductive ring CM, and an antenna element 3 formed around the central conductive ring CM. The central conductive ring CM is separated from a central channel O and from the antenna element 3.

[0027] The antenna element 3 comprises a two-dimensional periodic array of conductive pellets 4 (or conductive patches) arranged on the front surface of the substrate.

[0028] The conductive pads 4 are spaced apart. The conductive pads 4 are separated by openings 5. The antenna element 3 forms a metasurface.

[0029] The conductive pads 4 are, for example, metallic pads or indium-tin oxide or ITO just like the CM metallic ring.

[0030] The conductive pads 4 and the apertures 5 are substantially self-complementary. Unlike a metasurface composed of strictly self-complementary conductive pads 4 and apertures 5, the conductive pads 4 of the antenna element 3 are spaced apart from each other, as can be seen in the figure 2 representing a part of the antenna element or metasurface 3.

[0031] In other words, the closest points of two adjacent conductive pads 4 are separated by an interval 6. The openings 5 ​​are therefore larger than the conductive pads 4.

[0032] The antenna element 3 therefore includes intervals 6 separating adjacent pads by their adjacent vertices.

[0033] In the non-limiting example of the figure 1 The antenna element 3 has a substantially checkerboard structure. The openings 5 ​​and the conductive pads 4 are substantially square in shape.

[0034] The conductive pellets 4 may have a strictly square shape or a substantially square shape with clipped or flattened vertices. They may have a different shape, such as an oval or rounded shape.

[0035] The conductive pellets 4 have sides or dimensions that are sub-wavelength. The same is true for the grating pitch.

[0036] Advantageously, the conductive pellets 4 have dimensions or sides of lengths less than or equal to λ / 50 and preferably between λ / 50 and λ / 100. λ is the operating wavelength of the metasurface device, i.e. of the wave radiated by the antenna element 3.

[0037] The size of the interval 6, that is to say the minimum distance between two adjacent pads which can be the distance between two vertices of two adjacent conductive pads 4, is between λ / 1000 and λ / 2000. For an antenna operating at the frequency of 30 GHz, the wavelength is about 10 mm in air, the sides of the pads have a length between 100 and 200 µm and the distance between adjacent pads 4 by their vertices is between 5 and 10 µm.

[0038] Other metasurfaces comprising conductive pellets 4 and substantially self-complementary apertures 5 are conceivable. The pellets 4 and / or the apertures 5 may, for example, have shapes resembling equilateral triangles, crosses, or ovals. Thus, the conductive pellets are arranged in rows and columns. The columns may or may not be perpendicular to the columns.

[0039] In the example of the figure 1 The four conductive pads all have the same orientation in a two-dimensional coordinate system linked to the front face of the substrate. Alternatively, the conductive pads may have different orientations in a two-dimensional coordinate system linked to the front face of the substrate.

[0040] In the example of the figure 1 The four conductive pads all have the same shape and dimensions. Alternatively, some conductive pads have different shapes and / or different dimensions.

[0041] In figure 3 A metasurface 30 is shown, in which the conductive pellets 40 are approximately oval in shape. The conductive pellets are not all identical. Some conductive pellets differ from others in their shapes and orientations, using a two-dimensional coordinate system linked to the front face of the substrate.

[0042] The selective electrical connection between conductive pads 4 makes it possible to form a reconfigurable antenna element 3, that is, one capable of exhibiting different radiation patterns from the same excitation. It allows, for example, obtaining a multi-scale antenna element that can comprise a two-dimensional array of electrically isolated conductive pads or a two-dimensional array of groups of electrically connected conductive pads, as we will see later.

[0043] There figure 4 schematically illustrates in cross-section the metasurface device 1 of the figure 1 constituting a first example of a metasurface device according to a first embodiment of the invention. The figure 5 is a schematic rear view of the same device.

[0044] The metasurface device includes a source S for emitting electromagnetic waves (not visible in figure 1 ) and configured and arranged so as to generate surface waves on the front surface 22 of the substrate 2.

[0045] The source is, advantageously, isotropic.

[0046] The source advantageously allows the emission of spherical or cylindrical electromagnetic waves. The source includes, for example, a monopole.

[0047] Electromagnetic waves are preferably microwaves, preferably high frequencies. The metasurface device is, for example, a microwave antenna.

[0048] The metasurface device 1 includes a channel O traversing the stack E along the z-axis.

[0049] The source S includes, for example, a coaxial cable C comprising a conductive central core A, surrounded by a dielectric material MD itself surrounded by a shield B. The source S also includes an electrical source SE capable of generating a microwave electrical signal transmitted by the coaxial cable C to an end ED of the central core A.

[0050] The bare end ED passes through substrate 2 and extends opposite the metallic crown CM.

[0051] The portion of the exposed end ED extending opposite the antenna element 3 constitutes a monopole that radiates an electromagnetic wave, the essential part of which is scattered towards the antenna element 3 and propagates along the front face of the substrate 2 as a surface wave. The remainder of the wave emitted by the exposed end ED is transmitted into free space.

[0052] The antenna element 3, regardless of its scale, reflects or transforms the surface wave emitted on the front surface 22 of the substrate 2 to radiate, at the wavelength of the electromagnetic wave, in a direction with a component perpendicular to the front surface 22 of the substrate 2, i.e., it has a component along the z-axis. The total wave radiated by the antenna element results from a recombination of the leakage waves reflected or transformed by the different conductive pads, regardless of the antenna element's scale, i.e., even when the conductive pads 4 are electrically isolated from each other. The interference between the leakage waves radiated by the different conductive pads is radiated in a direction with a component along the z-axis.

[0053] Advantageously, the central CM ring is configured and arranged to optimize the coupling ratio between the wave generated by the antenna element 3 and the ED monopole. The configuration of the central CM ring depends on the frequency of the wave generated by the ED monopole.

[0054] The antennas are classically circular, as on the figure 1 but they can have another geometric shape, such as, for example, a rectangular shape, for example a square.

[0055] The substrate 2 includes a mass layer 7 suitable for having a ground plane function.

[0056] The mass layer 7 is continuous and extends along the entire length of the antenna element 3.

[0057] The mass layer 7 is capable of being in an insulating state in which it prevents the propagation of the surface wave (generated by the source S) on the front surface 22 or front face of the substrate 2 so as to prevent the antenna element 3 from radiating.

[0058] The mass layer 7 is also capable of being in a conductive state in which the mass layer 7 has a ground plane function enabling the transmission of the surface wave on the front surface 22 of the substrate 2, from the source to the conductive pads 4, i.e. to the antenna element 3, so that the antenna element 3 radiates in a direction having a component perpendicular to the front surface 22 of the substrate 20, i.e. a component along the z-axis.

[0059] The mass layer 7 is capable of switching from an insulating state to a conductive state by illuminating the mass layer 7 at a wavelength called the switching wavelength λc. It is also capable of remaining in the conductive state when the illumination is maintained.

[0060] Thus, by optically controlling the mass layer 7, to make it pass from the insulating state to the conductive state, we make the antenna element 3 pass from an off state, in which it is unable to radiate under the effect of the radiation from the source S, to an on state, in which it is able to radiate under the effect of the radiation from the source S.

[0061] In order to optically control the ground layer 7, the metasurface device 1 advantageously includes a switching source 8 capable of switching from a state in which it does not illuminate the ground layer so that the ground layer 7 is in the insulating state to a state in which it illuminates the ground layer 7 so that the ground layer 7 switches from the insulating state to the conducting state.

[0062] We will now describe in more detail the first example of the first embodiment of the invention shown below figures 4 And 5 . There figure 4 schematically illustrates in cross-section the device according to the invention.

[0063] The substrate 2 comprises a stack of several layers including the ground layer 7 and an intermediate layer 9 interposed between the conductive pellets and the ground layer 7. The intermediate layer 9 has the function of electrically isolating the ground layer 7 from the conductive pellets 4.

[0064] In the specific realization of the figure 4 , the intermediate layer 9 is insulating regardless of the state (first state or second state of the source 8).

[0065] The intermediate layer 9 is, for example, made of an insulating semiconductor when illuminated at the switching wavelength λc. It is, for example, made of silicon or gallium arsenide.

[0066] The intermediate layer 9 comprises the front surface 22 of the substrate 2. The front surface 22 of the substrate 2 is in direct physical contact with the conductive pellets 4.

[0067] The intermediate layer 9 includes a back face 23 on which the mass layer 7 is formed, i.e. in direct physical contact with the mass layer 7.

[0068] The mass layer 7 comprises the back face 21 of the substrate 2.

[0069] The ground layer 7 is advantageously electrically connected to the coaxial cable C and, more particularly, to the shield B.

[0070] There figure 5 represents a rear view of stack E and coaxial cable C. For clarity, mirror 82 is not shown.

[0071] The ground layer 7 comprises a central photoconductive part PC surrounding the O channel and a peripheral conductive part PF surrounding the central photoconductive part PC.

[0072] The central photoconductive part PC has a crown shape surrounding and delimiting the O channel.

[0073] The peripheral conductive part PF has a crown shape surrounding the central photoconductive part PC.

[0074] The peripheral conductive part PF is attached to the central photoconductive part PC.

[0075] The central photoconductive PC part is capable of being alternately in an insulating state and in a conductive state.

[0076] The central photoconductive PC part is in the insulating state when not illuminated.

[0077] The central photoconductive part PC is capable of switching into the conductive state, in which it is totally conductive, when illuminated at the switching wavelength λc by photoconductivity.

[0078] The central photoconductive part PC is made of a semiconductor material such as, for example, Silicon, gallium arsenide GaAs or a two-dimensional material such as, for example, a transition metal dichalcogenide or TMD, acronym for the Anglo-Saxon expression "Transition metal dichalcogenide" or an organic semiconductor material.

[0079] The peripheral conductive part PF is, for example, metallic or indium tin oxide or ITO for the English name "Indium tin oxide") which is transparent in the visible spectrum.

[0080] When the central photoconductive part PC is in the insulating state, it prevents the propagation of the surface wave on the front surface 22 of substrate 2 from the source to the antenna element or the conductive pads 4.

[0081] When the central photoconductive part PC is in the conductive state, the ground layer 7 is substantially fully conductive. It is substantially continuously conductive with respect to the entire antenna element 3, or metasurface. The ground layer 7 therefore functions as a ground plane, enabling the transmission of the surface wave onto the front surface 22 of the substrate 2. The antenna element 3 reflects or transforms the surface wave. The antenna element 3 radiates in a direction that includes a component perpendicular to the upper surface 22.

[0082] Thus, by optically controlling the central photoconductive part PC to make it switch from the insulating state to the conductive state, we switch the metasurface device from an off state in which the antenna element 3 is unable to radiate under the effect of the radiation from the source S to an on state in which the metasurface device is able to radiate under the effect of the radiation from the source S.

[0083] To optically control the central photoconductive part PC, the metasurface device advantageously includes a switching source 8, capable of illuminating the central photoconductive part PC at the switching wavelength λc so as to switch the central photoconductive part PC from an insulating state to a conductive state in which the central photoconductive part PC is substantially totally conductive or totally conductive. When the illumination of the central photoconductive part is maintained, the central photoconductive part remains in the conductive state.

[0084] Advantageously, the switching source 8 is arranged and configured so as to allow the emission of a light beam illuminating substantially totally the rear face 25 of the central photoconductive part PC at the switching wavelength λc so as to bring or maintain the central photoconductive part PC in the conductive state in which it is totally conductive.

[0085] The rear face 25 of the central photoconductive part PC means the face of the central photoconductive part PC that is opposite the intermediate layer 9. The front face 26 of the central photoconductive part faces the intermediate layer 9.

[0086] The switching source 8 includes, for example, a laser source 81, for example a vertical cavity surface-emitting laser diode or VCSEL, an acronym for the Anglo-Saxon expression "vertical cavity surface-emitting laser diode", or a light-emitting diode.

[0087] The switching source 8 includes, for example, a mirror 82, to deflect the optical beam emitted by the laser source 81 so that the optical beam illuminates the desired surface. The optical source includes, for example, an optical lens for collimating the beam from the laser source.

[0088] The metasurface device 1 advantageously includes a DC control device for controlling the switching source 8 so as to switch it from an on state in which it illuminates the central photoconductive part PC, so that the ground layer 7 is in the conductive state, to an off state in which it does not illuminate the central photoconductive part PC, and vice versa.

[0089] There figure 6 schematically represents, in cross-section, a second example of the first embodiment according to the invention.

[0090] In the realization of the figure 6 , the metasurface device 101 differs from that of the figure 4 in that the substrate 122 comprises two channels O1, O2 and in that the metasurface device 101 comprises two sources of electromagnetic waves.

[0091] Each source of electromagnetic waves includes a bare end ED1, ED2 or monopole, passing through one of the two channels O1, O2, visible in figure 6 , and being opposite the conductive pads 4 and is configured and arranged so as to generate surface waves on the front surface 22 of the substrate 2.

[0092] Each exposed end belongs to a core of a coaxial cable not shown in figure 6 for clarity, just like the SE source.

[0093] Each channel O1, O2 is surrounded by a central conductive ring CM1, CM2.

[0094] Antenna element 103 of the figure 6 differs from that of the figure 4 in that it is formed around the two channels O1, O2. The two spherical wave sources ED1, ED2 are capable of radiating waves of the same frequency or of different frequencies and / or of the same amplitude and / or of different amplitudes.

[0095] Thus, the metasurface device 101 is capable of radiating a microwave wave resulting from the recombination of two microwave waves, each generated by the propagation of a surface wave generated by one of the two sources ED1 or ED2 on the front surface 22 of the substrate 2.

[0096] The 107 mass layer differs from the mass layer of the figure 4 in that it comprises two central photoconductive parts PC1, PC2 semiconductors separated from each other and each surrounding one of the two channels O1, O2. The ground layer 107 also comprises a peripheral conductive part PF1 surrounding the central photoconductive parts PC1, PC2.

[0097] The central photoconductive parts PC1, PC2 each have a crown shape surrounding and delimiting one of the two respective channels O1 and O2.

[0098] The metasurface device 101 advantageously includes an optical switch COM allowing the metasurface device 101 to be switched from a first state in which the antenna element 103 is able to radiate under the effect of the radiation from the first spherical wave source S1 only, to a second state in which the antenna element 103 is able to radiate under the effect of the radiation from the second spherical wave source S2 only.

[0099] For this purpose, the metasurface device 101 includes, for example, a single switching source 108 generating an optical beam, the optical switch COM being able to deflect this optical beam so that it selectively illuminates only one of the central photoconductive parts among the central photoconductive parts PC1 and PC2 so that the illuminated central photoconductive part is conductive and the ground layer 107 has a ground plane function.

[0100] This allows transmission in different directions, which makes it possible, for example, to track an object.

[0101] Alternatively, or in addition, the COM switch is capable of being in a state in which it selectively illuminates several central photoconductive zones simultaneously, here the two central photoconductive parts PC1 and PC2, so that each illuminated central photoconductive zone is fully conductive. The total wave emitted by the source results from the recombination of waves emitted under the effect of radiation by the different electromagnetic wave sources ED1 and ED2.

[0102] The illumination of the photoconductive parts can be done either on the rear side or on the front. figure 6 or on the front panel.

[0103] It should be noted that the metasurface device could, alternatively, include more than two sources of electromagnetic waves intended to propagate as surface waves on the surface of the substrate and more than two central photoconductive parts each being associated with one of the spherical wave sources.

[0104] There figure 7 represents a variant of the 301 metasurface device. The 301 metasurface device differs from that of the figure 4 by its substrate 302 which differs from substrate 2 of the figure 4 by the ground layer 370, which lacks the central PC portion, and by the intermediate layer 290, which is made of a photoconductive semiconductor material chosen such that, when the source 8 illuminates the central portion 292 of the rear face 291 of the intermediate layer 290 at the switching wavelength λc, this central portion 292 becomes conductive and the ground layer 370 functions as a ground plane. The ground layer 370 comprises the rear face 221 of the substrate 302.

[0105] The rear face 291 of the intermediate layer 290 is attached to the mass layer 370.

[0106] The central part 292 connects the O channel to the peripheral part PF.

[0107] The device therefore includes a mass structure comprising the mass layer 370; comprising only the peripheral part PF, and the central part 292 of the rear face 291 of the intermediate layer 290. The thickness EP of the intermediate layer 290 is greater than the penetration depth of the material which forms it so that the intermediate layer 290 ensures electrical insulation between the ground plane and the conductive pads 4.

[0108] There figure 8 The figure schematically represents, in cross-section, a metasurface device according to a second embodiment of the invention. To simplify this figure, only the stripped end ED of the coaxial cable is shown.

[0109] The second embodiment of the invention differs from the first embodiment in that the ground layer is entirely made of a single photoconductive semiconductor material. This photoconductive material is insulating when not illuminated and conductive when illuminated at the switching wavelength λc.

[0110] The photoconductive semiconductor material is, for example, of the same type as the materials given as examples for the central conductive part PC.

[0111] More specifically, the 201 metasurface device of the figure 8 differs from the realization of the figure 4 in that the substrate 202 comprises a first photoconductive layer 212 corresponding to a single layer of a single photoconductive semiconductor material. In other words, the first photoconductive layer 212 is homogeneous. The semiconductor layer 212 is the ground layer.

[0112] Advantageously, the metasurface device includes an intermediate photoconductive layer 213 of semiconductor material interposed between the conductive pellets 4 and the first photoconductive layer 212.

[0113] For example, the first semiconductor layer 212 includes a front face 224, attached to the photoconductive intermediate layer 213 comprising the front face 22 of the substrate 202, and a back face 225 opposite the photoconductive intermediate layer 213.

[0114] An insulating layer 214 is formed on the back side 225 of the first photoconductive layer 212. The insulating layer 214 is transparent at the switching wavelength λc. For example, the insulating layer 214 is transparent to optical beams. The insulating layer 214 is, for example, made of glass, such as silicon dioxide or borosilicate, which have the advantage of growing easily on silicon.

[0115] In the rest of the text, the thickness of a part of the device means its dimension along the z-axis of the stacking.

[0116] The photoconductive semiconductor material of the first photoconductive layer 212 is chosen such that the first photoconductive layer 212 has a penetration depth denoted E1 less than the thickness Ep of the first photoconductive layer 212 at the switching wavelength λc, so that when the entire back face 225 of the first photoconductive layer 212 is illuminated at the switching wavelength λc, the first photoconductive layer 212 comprises: a conductive portion 215 forming the ground plane and extending from the rear face 225 of the semiconducting layer 212 over a thickness of the conductive portion less than the thickness Ep of the first semiconducting layer 212 and, an insulating portion 216 extending over the remainder of the thickness Ep so that the conductive portion 215 is insulated from the conductive pellets 4 by the insulating portion 216.

[0117] The penetration depth of a material at a predetermined wavelength is equal to the inverse of the absorption coefficient of that material at the same wavelength.

[0118] Advantageously, as can be seen in figure 9 , the metasurface device 201 includes, in addition to the source S and the switching source 8, visible in figure 8 and not represented in figure 9 For clarity, an optical reconfiguration device DR of antenna element 3 allowing optical reconfiguration of antenna element 3.

[0119] The reconfiguration device DR of the antenna advantageously includes a reconfiguration source SR capable of emitting an optical beam at the reconfiguration wavelength λr and a diffractive device DIFF capable of illuminating a set of at least one area, called illuminated area ZE, of the intermediate layer 213 such that the intermediate layer 213 is conductive only in the set of at least one illuminated area ZE, so as to electrically connect two by two the separate metal pellets 4 of the antenna element connected by a continuous area of ​​the intermediate layer 213 located totally in an illuminated area ZE of the set of at least one illuminated area ZE to form at least one group G of electrically connected conductive pellets 4.

[0120] It should be noted that, for clarity, only the 4 electrically connected pads are shown in figure 9 The white areas separating the G groups of electrically connected 4 conductive pads include 4 conductive pads that are electrically insulated from each other.

[0121] Advantageously, the reconfiguration device DR comprises a single reconfiguration optical source SR. The reconfiguration source SR is configured to emit an optical beam at the reconfiguration wavelength λr.

[0122] The metasurface device 1 further includes a diffractive optical device DIFF which, from the optical beam emitted by the source SR, by diffraction, illuminates the whole of at least one illuminated area ZE of the connection layer at the reconfiguration wavelength λr.

[0123] Advantageously, as in the example of the figure 5 The diffractive device DIFF illuminates, at the reconfiguration wavelength λr, a network of continuous illuminated zones ZE (or spots) of layer 213. The illuminated zones ZE are spaced apart and separated by an unilluminated zone ZNE of layer 213, such that layer 213 is conductive only in the illuminated zones ZE. The light spots formed on layer 213 by the optical diffractive device DIFF, i.e., the illuminated zones ZE, are rounded in shape in the non-limiting example of the figure 9 but could very well take different forms.

[0124] The illuminated areas (ZE) of layer 213 are separated by an unilluminated area (ZNE). The illuminated areas (ZE) are spaced apart. This allows for the creation of groups of electrically connected conductive pads, with the groups being electrically isolated from each other.

[0125] The network can alternatively comprise a set of at least illuminated zones delimiting a network of unlit zones. The illuminated zones are spaced apart. This allows for the creation of groups of electrically connected conductive pads, with the groups being electrically connected to each other.

[0126] The network may alternatively include at least one lit area completely surrounded by an unlit area and at least one unlit area completely surrounded by a lit area.

[0127] a step corresponding to a multiple of the step of the network of conductive pads 3.

[0128] In the specific realization of the figure 9 , each illuminated zone ZE comprises several intervals 6 and / or openings 5, i.e. comprises a group of more than 2 metal pads 4 so that the illumination of the illuminated zone ZE ensures the electrical connection, between them, of all the metal pads 4 of the antenna element 3 located in the illuminated zone ZE.

[0129] Alternatively, the DIFF diffractive device is configured so that each illuminated zone comprises a single interval 6 or a single aperture 5, thus allowing only two adjacent pads to be connected. The solution of the figure 7 However, it is easier to implement.

[0130] When the reconfiguration device is off, the antenna element 4 consists of the conductive pad elements 4 isolated from each other.

[0131] The solution of the figure 2 This allows the antenna's radiation pattern to be modified by changing the frequency and / or orientation of the wave radiated by the antenna element. Modifying the orientation of the radiated wave is equivalent to a spatial sweep of the beam radiated by the antenna.

[0132] In the realization of the figure 9 , the DR reconfiguration device is configured to illuminate the rear face 21 of the substrate 202.

[0133] The layer 212 is advantageously made of photoconductive material transparent at the reconfiguration wavelength λr different from the switching wavelength λc and the intermediate layer 213 is made of a material transparent at the switching wavelength λc.

[0134] It is advantageous to choose transparent materials at wavelengths that are far apart, for example a material that is transparent at 800 nm and has a high absorption coefficient at 1.5 micrometers and another material that is substantially transparent at 1.5 micrometers and has a high absorption coefficient at 800 nm.

[0135] For example, one can choose a bulk layer of the AsGa type and an intermediate layer of two-dimensional semiconductor material.

[0136] Alternatively, the DR reconfiguration device is configured to illuminate the EE stack on its front face. The layer 213 advantageously has a thickness such that the optical beams illuminating the front face 22 of the substrate 20 at wavelength λr are totally absorbed by the layer 213, thus allowing the layer 212 to be made of absorbing material at wavelength λr.

[0137] Therefore, the thickness of layer 213 is advantageously chosen so as to be greater than the depth of penetration of light at wavelength λr.

[0138] Optical reconfiguration of the antenna element uses photoconductivity to make the substrate conductive at the intervals 6 between the conductive pads 4. This optical control has the advantage of being contactless and potentially rapid. The reconfiguration speed depends primarily on the characteristics of the semiconductor material used and the laser source employed. It can vary from a few milliseconds to a few pixels.

[0139] Furthermore, the proposed solution has the advantage of using a single optical source to reconfigure the antenna by selectively controlling the substrate areas located opposite the gaps between the conductive pads, thus allowing the selective connection of adjacent conductive pads in pairs. It is relatively simple to implement since it uses only one optical source to reconfigure the antenna. It is also more reliable than a solution that would require a separate optical source for each spot created on the intermediate layer.

[0140] This optical control ensures independence between the antenna reconfiguration function and the antenna radiation function, with the emission of the spherical wave being electrically controlled).

[0141] Alternatively, the metasurface device of the figure 8 is devoid of the intermediate photoconductive layer. It is possible to reconfigure the metasurface device by the reconfiguration device DR by front-facing illumination when the switching source 8 illuminates the substrate on the rear face by choosing the wavelengths λr and λc and the thickness of the conductive layer 212 so that the first photoconductive layer 212 includes an insulating portion electrically insulating the illuminated ZE areas made conductive by the reconfiguration device DR and the conductive area 216 made conductive by the switching source 8.

[0142] It should be noted that it is possible to add to the device the figure 4 or of the figure 6 Or 7, a semiconducting photoconductive layer between the intermediate layer 9 and the antenna element 3 such that the semiconducting photoconductive layer has the same function as layer 213 and a DR reconfiguration device like that of the figure 9 in order to allow reconfiguration of the metasurface device.

[0143] There are many diffractive optical devices (DIFF) that allow for the illumination of a network of illuminated areas, such as diffractive optical elements (DOE), referring to the English expression "Diffractive Optical Elements," or optical devices based on a matrix of micromirrors (DMD), referring to the English expression "digital micromirror device."

[0144] Such diffractive optical devices (DIFFs) allow the generation, through diffraction, of a one-dimensional or two-dimensional grating of illuminated or unilluminated areas. The grating can be regular or irregular.

[0145] The DIFF optical diffractive device can be configured to be able to illuminate, from the beam radiated by the source, a unique set of illuminated areas of the conductive layer such as, for example, a DIFF optical diffractive device based on a DOE diffractive optical element located at a fixed distance from the SR source and the 213 layer.

[0146] The DIFF optical diffractive device can be configured to allow the illumination, from the beam radiated by the source, SR alternately, of different networks of illuminated areas of layer 213, each network of illuminated areas being different from the other sets of illuminated areas.

[0147] This is, for example, the case of a diffractive optical device DIFF comprising a micro-mirror matrix or DMD, a control device and a set of actuators allowing, on control of the actuator, to move each of the mirrors individually between a first position in which it reflects the light towards a diffusion lens and a second position in which it reflects the light towards an absorbing surface so that the micro-mirror matrix illuminates, from the beam radiated by the reconfiguration source SR, a network of groups of conductive pellets 4 connected together taken from a set of predetermined networks.

[0148] The control device includes, for example, a memory storing a set of networks of groups of 4 interconnected conductive pads taken from a set of predetermined networks and associating with each of these networks the position taken from the first position and the second position, which must be occupied by each of the micro-mirrors so that the micro-mirror matrix illuminates the network in question from the beam radiated by the reconfiguration source.

[0149] The continuous illuminated areas (ZE) or unilluminated areas may differ, for example, in their shape and / or size and / or orientation in a coordinate system linked to the antenna element. Each of the arrays of electrically connected pellet groups may be one-dimensional or two-dimensional, periodic or aperiodic.

[0150] Other types of reconfiguration devices for metasurface devices are of course conceivable. For example, it is possible to arrange the switches in the intervals 6 as described in patent application WO2019219708 A1.

[0151] Each switch is configured to allow two adjacent pads 4 separated by an interval 6 to be electrically connected together.

[0152] These switches can be of the electrically controlled type, such as microelectromechanical systems or MEMS (micro-electro-mechanical systems), or of the type comprising a phase change material.

[0153] However, the control of unitary switches poses a complex problem of electrical control signal distribution which leads to electromagnetic disturbances, induced by the supply wires, on the radiation pattern of the metasurface device.

[0154] Switching and / or reconfiguration wavelengths are, for example, located in the infrared range. They are, for instance, between 800 nm and 1500 nm, which allows the use of conventional semiconductor materials such as silicon and gallium arsenide (GaAs). Switching and reconfiguration wavelengths can also be located throughout the optical range. They can, for example, be in the ultraviolet or visible range. Two-dimensional semiconductor materials or gallium nitride (GaN) can be used, for instance.

[0155] In the realization of the figure 4 The metasurface device includes an electromagnetic wave emission source S such that the metasurface device is capable of radiating an electromagnetic wave. More generally, applicable to all examples and embodiments, the metasurface device includes a transmitting and / or receiving device capable of transmitting and / or receiving an electromagnetic wave, the transmitting and / or receiving device being configured and arranged so that the electromagnetic wave it emits or receives is capable of propagating as a surface wave on the front surface of the substrate. In the case of a receiving device, the antenna element is capable of reflecting or transforming a wave propagating in a direction that includes a non-zero component along the x-axis into a wave propagating on the front surface of the substrate and being received by the receiving device, which may include a coaxial cable as shown in figure 4 The device then includes means for processing the signal received by the coaxial cable. The transmitting and / or receiving device is designed to operate at a specific wavelength.

Claims

1. Metasurface device comprising: - a substrate (2) having a rear surface (21) and a front surface (22), - a transmission and / or receiving device which is capable of transmitting and / or receiving an electromagnetic wave, the transmission and / or receiving device being configured and arranged so that the wave is capable of being propagated in the form of a surface wave on the front surface (22) of the substrate (2), - an antenna element (3) which comprises a two-dimensional network (2) of conductive wafers which are arranged on the front surface of the substrate remote from each other and which have dimensions less than the operating wavelength of the transmission and / or receiving device, - the substrate (2) comprising an earthing structure (7) which is capable of being in an insulating state in which the earthing structure prevents the propagation of the surface wave on the front surface of the substrate, from the transmission and / or receiving device as far as the conductive wafers, in order to prevent the antenna element (3) from radiating, or vice versa, and in a conductive state, in which the earthing structure acts as an earthing plane which enables the propagation of the surface wave on the front surface of the substrate, from the transmission and / or receiving device as far as the conductive wafers, the earthing structure being capable of changing from the insulating state to the conductive state by means of illumination of the earthing structure at a wavelength called the commutation wavelength.

2. Metasurface device according to the preceding claim, comprising a commutation source (8) which is capable of changing from a state in which it does not illuminate the earthing structure (7), so that the earthing structure (7) is in the insulating state, to a state in which it illuminates the earthing structure (7) so that the earthing structure acts as an earthing plane.

3. Metasurface device according to claim 2, wherein the substrate (2) comprises an earthing layer (7) and an intermediate layer (9) which insulates the earthing plane of the conductive wafers when the earthing structure (7) acts as an earthing plane, the earthing structure (7) comprising a photo-conductive central portion (PC) and a conductive peripheral portion (PF) which surrounds the photo-conductive central portion (PC), the photo-conductive central portion (PC) being in an insulating state when it is not illuminated, in which it prevents the propagation of the surface wave from the transmission and / or receiving device as far as the conductive wafers (4) or, vice versa, the photo-conductive central portion (PC) being capable of being in a conductive state when it is illuminated at the commutation wavelength, in which the photo-conductive central portion (PC) is conductive so that the earthing structure acts as an earthing plane.

4. Metasurface device according to claim 3, wherein, the earthing structure (7) being an earthing layer, the intermediate layer (9) being interposed between the conductive wafers (4) and the earthing layer (7).

5. Metasurface device according to claim 3, wherein the intermediate layer is a photo-conductive semi-conductor material which is capable of being in a conductive state when it is illuminated at the commutation wavelength , the intermediate layer being interposed between the conductive wafers (4) and the conductive peripheral portion, the conductive central portion comprising a central portion of a rear face of the intermediate layer, the rear face of the intermediate layer being in direct physical contact with the conductive peripheral portion.

6. Metasurface device according to any one of claims 3 to 5, comprising several commutation sources, the earthing structure (7) comprising several photo-conductive central portions and a commutator (COM) which allows only one of the photo-conductive central portions from the photo-conductive central portions to be selectively illuminated and / or which allows several photo-conductive central portions to be selectively illuminated simultaneously.

7. Metasurface device according to either claim 1 or 2, wherein the earthing structure is a first photo-conductive layer (212) which is made from a single photo-conductive semi-conductor material, the photo-conductive material being insulating when it is not illuminated and conductive when it is illuminated at the commutation wavelength.

8. Metasurface device according to the preceding claim, wherein the photo-conductive semi-conductor material which forms the first photo-conductive layer (212) is selected in such a manner that the first photo-conductive layer (212) has a penetration depth less than the thickness of the first photo-conductive layer (212) at the commutation wavelength so that, when the whole of a rear face of the first photo-conductive layer (212) is illuminated at the commutation wavelength by the commutation source (8), the first photo-conductive layer (212) comprises: - a conductive portion (215) which forms the earthing plane and which extends from the rear face (225) of the semi-conductor layer (212) over a thickness less than the thickness of the first semi-conductor layer (212) and - an insulating portion (216) which extends over the remainder of the thickness of the semi-conductor layer so that the conductive portion (215) is insulated from the conductive wafers (4) by the insulating portion (216).

9. Metasurface device according to any one of the preceding claims, comprising an intermediate semi-conductor layer (213), the metasurface device comprising an optical reconfiguration device (DR) comprising a source called the reconfiguration source (SR) which transmits an optical beam and a diffractive optical device (DIFF) which is capable of illuminating a group of at least one zone, called the illumination zone, of the intermediate layer (213) so that the intermediate layer (213) is conductive only in the group of at least one illuminated zone (ZE) so as to electrically connect in pairs the metal wafers of the antenna element which are separated and connected by a continuous zone of the semi-conductor intermediate layer (213) which is located completely in an illuminated zone (ZE) of the group of at least one illuminated zone (ZE) in order to form at least one group (G) of conductive wafers (4) which are electrically connected to each other.

10. Metasurface device according to the preceding claim, wherein the intermediate layer is interposed between the conductive wafers (4) and the earthing layer or wherein the intermediate layer is the earthing layer.

Images