Metasurface device

Abstract

A metasurface device comprising: - an antenna element (3) formed on the front surface of a substrate (20), said antenna element comprising a two-dimensional array of electrically conductive tabs (4) spaced apart from one another and having dimensions smaller than the operating wavelength of a transmission and / or reception device, the antenna element (3) being able to radiate in a direction having a component perpendicular to the front surface of the substrate (4) when the ground structure has a ground plane function, the substrate (20) comprising a layer, called connection layer (80), made of photoconductive semiconductor material, in direct physical contact with the conductive tabs (4), the semiconductor material being insulating when it is not illuminated and able to be conductive when it is illuminated at a reconfiguration wavelength.

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] This patent application proposes placing electrically controlled switches, such as MEMS or diodes, between adjacent conductive pads to allow for selective electrical connection of these pads. However, this solution has several drawbacks. In particular, it generates electromagnetic interference that distorts the radiation pattern of the metasurface device. Furthermore, the switching response may be too slow.

[0005] One aim of the invention is to limit at least one of the aforementioned disadvantages.

[0006] To this end, the invention relates to a metasurface device comprising: a substrate having a rear surface and a front surface, the substrate comprising a mass structure capable of functioning as a ground plane, 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 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 electrically conductive pellets arranged on the front surface of the substrate, being spaced apart and having dimensions smaller than the operating wavelength of the transmitting and / or receiving device, the antenna element being capable of radiating, under the effect of the propagation of a surface wave on the front surface of the substrate,along a direction having a component perpendicular to the front surface of the substrate when the mass structure has a ground plane function, the substrate comprising a layer, called the connection layer, of photoconductive semiconductor material, in direct physical contact with the conductive pads, the semiconductor material being insulating when not illuminated and capable of being conductive when illuminated at a wavelength called the reconfiguration wavelength.

[0007] Advantageously, the metasurface device includes an optical reconfiguration device capable of illuminating a set of at least one area, called the illuminated area, of the connection layer, so that the connection layer is conductive only in the set of at least one illuminated area, so as to electrically connect two by two the separate metal pads of the antenna element connected by a continuous area of ​​the connection 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 pads.

[0008] Advantageously, the optical reconfiguration device comprises a single optical reconfiguration source capable of emitting an optical beam at the reconfiguration wavelength and a diffractive optical device enabling, from the optical beam, by diffraction, the entirety of at least one area illuminated at the reconfiguration wavelength.

[0009] Advantageously, the diffractive device allows for the illumination of a network of continuous illuminated areas of the connection layer, separated by areas of the connection layer or a set of at least one illuminated area delimiting areas of the connection layer not illuminated by the diffractive device.

[0010] Alternatively, the set of at least one illuminated area comprises a single illuminated area.

[0011] Advantageously, the diffractive device is capable of alternately illuminating different sets of at least one illuminated area of ​​the connection layer.

[0012] Advantageously, the metasurface device includes a mass structure capable of having a ground plane function, 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 has a ground plane function 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 layer being capable of switching from the insulating state to the conductive state by illuminating the mass layer with an optical beam at a so-called switching wavelength.

[0013] The reconfiguration device can be configured and arranged to illuminate the substrate from the rear or front side.

[0014] In the case of front-facing illumination, the diffractive device can be mounted on a cover of the metasurface device, the cover being positioned opposite the antenna element at a distance from the antenna element, or be in the form of a substantially flat plate extending in a plane substantially perpendicular to the surface or front face of the substrate.

[0015] 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, in top view, a metasurface device according to 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, [ 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, in exploded view, the device of the figure 1 , [ Fig.6 ] there figure 6 schematically illustrates, in cross-section, a first variant of the device in which the stack is illuminated from the front, [ Fig.7 ] there figure 7 schematically illustrates, in cross-section, a second variant of the device in which the stack is illuminated from the front, [ Fig.8 ] there figure 8 schematically illustrates, in cross-section, a third variant of the metasurface device, [ Fig.9 ] there figure 9 schematically illustrates, in cross-section, a fourth variant of the metasurface device [ Fig.10 ] there figure 10 schematically illustrates, in cross-section, a fifth variant of the metasurface device.

[0016] In the rest of the text, by conductor we mean electrically conductive and by insulator we mean electrically insulating.

[0017] An optical beam is understood to be a beam whose wavelength is located in the optical range including infrared, ultraviolet and visible light.

[0018] There figure 1 schematically illustrates, in top view, a metasurface device 1 according to the invention.

[0019] 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.

[0020] The substrate 20 comprises a front surface 22 and a rear face 21. The front and rear faces of the different layers of the stack E are defined along a z-axis going in the direction from back to front.

[0021] The antenna element 3 comprises a two-dimensional periodic array of conductive pads 4 (or conductive patches) arranged on the front surface 22 of the substrate 20 and spaced apart. The conductive pads 4 are separated by openings 5. The antenna element 3 constitutes a metasurface.

[0022] The conductive pads 4 are, for example, metallic pads or indium-tin oxide or ITO just like the CM metallic ring.

[0023] 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.

[0024] 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.

[0025] The antenna element 3 therefore includes intervals 6 separating adjacent pads by their adjacent vertices.

[0026] 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.

[0027] 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.

[0028] The conductive pellets 4 have sides or dimensions that are sub-wavelength. The same is true for the grating pitch.

[0029] 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.

[0030] 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.

[0031] Other metasurfaces comprising conductive pellets 4 and substantially self-complementary apertures 5 are conceivable. The pellets 4 and / or the apertures 5 can, 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] There figure 4 schematically illustrates partially, in cross-section, the metasurface device 1 of the figure 1 .

[0037] 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.

[0038] The source allows, for example, the emission of spherical or cylindrical electromagnetic waves.

[0039] Source S is, for example, isotropic.

[0040] Electromagnetic waves are preferably microwaves, preferably high frequencies. The metasurface device is, for example, a microwave antenna.

[0041] The metasurface device 1 includes a channel O traversing the stack E along the z-axis.

[0042] 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.

[0043] The bare end ED passes through substrate 2 and extends opposite the metallic crown CM.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] The substrate 20 comprises a stack of several layers including the mass layer 70, a connection layer 80 and an intermediate layer 90.

[0049] The mass layer 70 is continuous and extends along the entire length of the antenna element 3.

[0050] The mass layer 70 is suitable for having a ground plane function allowing the transmission of the surface wave on the front surface 22, from the bare end ED to the conductive pads 4, i.e. to the antenna element 3, or vice versa, 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.

[0051] The mass layer 70 is advantageously metallic or made of a transparent conductive oxide (TCO) or transparent conductive oxide (TCO), such as indium tin oxide (ITO). Transparent conductive oxides (TCOs) have the characteristic of being simultaneously electrically conductive and optically transparent.

[0052] In the non-limiting example of the figure 4 , the mass layer 70 includes the back face 21 of the substrate 20.

[0053] The ground layer 70 is electrically connected to the coaxial cable C and more specifically to the coaxial cable shield B.

[0054] The intermediate layer 90 has the function of electrically isolating the ground layer 70 from the connection layer 80.

[0055] The intermediate layer 90 is, for example, made of glass, for example silicon dioxide or borosilicate, which has the advantage of growing easily on silicon.

[0056] The connection layer 80 is a layer made of photoconductive semiconductor material. The connection layer 80 is in direct physical contact with the conductive pads 4. In other words, the connection layer 80 comprises the front face 22 of the substrate 20.

[0057] The semiconductor material is insulating when not illuminated and is capable of becoming conductive when illuminated at a reconfiguration wavelength λr. The semiconductor material transitions from the insulating state to the conductive state through photoconductivity.

[0058] Thus, by illuminating a region of the connection layer 80 in an illuminated area, the semiconductor material becomes conductive only in the illuminated area. By illuminating a region of the connection layer 80, only the metal pads 4 of the antenna element 3 can be electrically connected in pairs. These pads are separated and connected by a continuous region of the connection layer located in the illuminated area, linking the conductive pads 4 and thus forming a group of electrically connected conductive pads 4.

[0059] The optical reconfiguration of the antenna element 3 uses photoconductivity to make the connecting layer 80 conductive at the intervals 6 between the conductive pads 4. This optical control has the advantage of being contactless and fast. The reconfiguration speed depends mainly on the characteristics of the semiconductor material used to form the connecting layer and the laser source used. It can vary from a few milliseconds to a few pixels.

[0060] The antenna element 3 can thus be reconfigured by going from an antenna element 3 forming a checkerboard of conductive pads 4 electrically isolated from each other, when the connection layer 80 is not illuminated at the reconfiguration wavelength λr, to an antenna element comprising one or more groups of conductive pads electrically connected to each other and, possibly, pads electrically isolated from all other pads, when the connection layer 80 is illuminated at the reconfiguration wavelength λr.

[0061] The proposed configuration therefore allows optical modification of the radiation law of the antenna element 3 by selectively illuminating one or more areas of the connection layer 80 at the reconfiguration wavelength λr.

[0062] The proposed metasurface device can therefore exhibit different radiation laws without any physical modification to the E stack or the network of conductive pellets 4. It is sufficient to provide an optical lighting device capable of illuminating the connecting layer appropriately to the desired radiation law. The metasurface device can thus be used for various applications.

[0063] Furthermore, optical control helps to limit electromagnetic interference. Optical control is also uncorrelated with the electrical control of the source S. It ensures independence between the antenna reconfiguration function and the antenna radiation function, with the emission of the spherical wave being electrically controlled.

[0064] The proposed solution is relatively simple to implement since it uses a single optical source to reconfigure the antenna. It is more reliable than a solution that would require a separate optical source for each spot created on the connection layer to achieve the desired radiation pattern.

[0065] On the figure 5 , a schematic exploded view of the metasurface device according to the invention has been represented when it further includes an optical reconfiguration device DR allowing the antenna element 3 to be optically reconfigured.

[0066] For the sake of simplicity, channel O and source S are not shown on the figure 5 .

[0067] The antenna reconfiguration device DR is capable of illuminating a set of at least one area, called illuminated area ZE, of the connection layer 80 so that the connection layer is conductive only in the set of at least one illuminated area ZE, so as to electrically connect two by two only the metal pads 4 of the antenna element separated and connected by continuous areas of the connection layer 80 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 conductive pads 4 electrically connected to each other.

[0068] 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.

[0069] 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.

[0070] 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 the connection layer 80. The illuminated zones ZE are spaced apart and separated by an unilluminated zone ZNE of the connection layer 80, such that the connection layer 80 is conductive only in the illuminated zones ZE. The light spots formed on the connection layer 80 by the optical diffractive device DIFF, i.e., the illuminated zones ZE, are rounded in shape in the non-limiting example of the figure 5 but could very well take different forms. Source S is not shown in this figure for clarity.

[0071] The illuminated areas (ZE) of layer 80 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.

[0072] 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.

[0073] 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.

[0074] The network of illuminated zones ZE corresponds to the image projected by the reconfiguration device DR onto the front face 22 of the substrate 20. The front face 22 of the substrate 20 is the image plane of the reconfiguration device DR.

[0075] The white areas of antenna element 3 of the figure 5 represent the areas in which the conductive pads 4 are electrically disconnected from each other and the checkered areas represent the groups G of conductive pads 4 electrically connected to each other.

[0076] The DR reconfiguration device may include an assembly of at least one focusing lens to focus the image formed by the diffractive device DIFF onto the front face 22 of the substrate 20.

[0077] The proposed solution allows to connect electrically, two by two only the metal pads 4 of the antenna element 3 which are separated and connected a continuous area of ​​the connection layer 80 located totally in a lit area of ​​the whole of at least one lit area to form a group G network of conductive pads 4 electrically connected to each other.

[0078] This solution allows, for example, by choosing the appropriately selected diffractive optical device DIFF, to obtain a multi-scale antenna element 3 capable of presenting unit patterns corresponding to the conductive pellets and a pitch equal to that of the conductive pellet array 4. The antenna element is also capable of presenting unit patterns corresponding to groups of electrically connected conductive pellets and therefore a pitch corresponding to a multiple of the pitch of the conductive pellet array 3.

[0079] In the specific realization of the figure 5 , each illuminated area ZE of the connection layer 80 comprises several intervals 6 and apertures 5. Indeed, each illuminated area ZE comprises a group of more than 2 metal pellets 4 so that the illumination of the illuminated area ZE at the wavelength λr ensures the electrical connection between all the metal pellets 4 of the antenna element 3 located in the illuminated area.

[0080] Alternatively, the diffractive optical device DIFF is capable of illuminating a single interval 6 or a single continuous zone connecting two adjacent pads 4. Each illuminated zone allows only two adjacent pads to be connected. The solution of the figure 5 However, it is easier to implement.

[0081] There are many diffractive optical devices (DIFF) that can illuminate a network of lit areas, such as diffractive optical elements (DOEs), or optical devices based on a micromirror array (DMDs). digital micromirror device ».

[0082] 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.

[0083] 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 connecting layer.

[0084] 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 the connection layer 80, each network of illuminated areas being different from the other sets of illuminated areas.

[0085] 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.

[0086] 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.

[0087] The continuous illuminated areas (ZE) or the continuous 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 groups of pellets may be one-dimensional or two-dimensional, periodic or aperiodic.

[0088] The proposed solution therefore allows the antenna's radiation pattern to be modified by changing the frequency, for example by modifying the spacing of the conductive pad array, and / or the direction of the antenna radiation, for example by changing the orientation of the interconnected cell groups. Modifying the direction of the antenna radiation is equivalent to a spatial scan of the beam radiated by the antenna.

[0089] In the realization of the figure 5 The reconfiguration device DR is configured to illuminate the substrate 20 or the stack E on its rear face. In other words, at least one beam projected onto the stack E is projected from the front face 22 to the rear face 21 of the substrate. The ground layer 70 is advantageously made of a material transparent at the reconfiguration wavelength λr so as not to absorb the beam projected by the reconfiguration device DR onto the substrate, thereby making the connecting layer 90 conductive in the illuminated areas to interconnect conductive pads.

[0090] In a variant of the 100 metasurface device, shown in figure 6 , the reconfiguration device DR is configured to illuminate the stack E on the front face, i.e. the set of at least one radiation projected onto the stack E is projected in the direction of the front face 22 towards the rear face 21 of the substrate 20.

[0091] This embodiment is less restrictive and can be less expensive than rear-facing illumination 21 because the ground layer does not obscure the connection layer. The choice of material for the ground layer is more extensive. The ground layer can be made as described previously or from a material that absorbs radiation at the reconfiguration wavelength λr. For example, it could be an inexpensive metallic layer.

[0092] On the figure 6 The diffractive device DIFF is mounted opposite antenna element 3. For simplicity, channel O and source S are not shown on the diagrams. figures 6 And 7 The diffractive device DIFF, for example, has substantially a flat plate shape substantially parallel to the front face 21 of the substrate 20.

[0093] The diffractive device DIFF is, for example, mounted on a protective cover CP of the metasurface or radome. This cover CP has a plate shape substantially parallel to the front face 21 of the substrate 20 and is positioned at a distance from the antenna element 3 along the z-axis. The cover CP is advantageously transparent in the optical range, at least at the reconfiguration wavelength λr, which allows the optical diffractive device DIFF to be positioned on the front face AV of the cover without interfering with the reconfiguration of the antenna element 3.

[0094] The diffractive device illuminates the illuminated areas ZE included in a global area Z.

[0095] Alternatively, the DIFF diffractive device is mounted on a rear face AR of the CP cover, this rear face AR being opposite the antenna element 3.

[0096] The SR source may include a remote laser L and an optical fiber transmitting the radiation emitted by the SR source to one end of the optical fiber FO positioned opposite the diffractive optical device DIFF. The end of the optical fiber FO is held opposite the diffractive optical device DIFF by a support.

[0097] In the variant shown in figure 7 , the DIFF diffractive device of the metasurface device 1001 is mounted on a CA frame holding a CP protective cover away from the antenna element 3.

[0098] The diffractive device DIFF has, for example, substantially a flat plate shape substantially perpendicular to the front face 22 of the substrate 20. The front face 22 is then illuminated grazingly.

[0099] This configuration helps to limit the masking of the antenna element by the diffractive optical device DIFF.

[0100] There figure 8 represents a variant of the 201 metasurface device. The 201 metasurface device differs from that of the figure 4 by substrate 200 and, more specifically, in that the ground layer 212 is a photoconductive semiconductor material. For the sake of simplicity, the coaxial cable and the SE power source are not shown on the figure 8 .

[0101] Advantageously, the metasurface device comprises the connection layer 280 and the ground layer 212, the connection layer 280 being interposed between the antenna element 3 and the ground layer 212. The connection layer 280 is disposed on the front face 224 of the ground layer 212.

[0102] The substrate S also includes an insulating layer 214 formed on the back face 225 of the ground layer 212. The insulating layer 214 is transparent at a switching wavelength λc.

[0103] For example, the insulating layer is transparent to optical beams. The insulating layer 214 is, for example, made of glass, for example silicon dioxide or borosilicate, which has the advantage of growing easily on silicon.

[0104] Advantageously, the mass layer 212 is capable of being in an insulating state in which it prevents the propagation of the surface wave on the front surface 22 of substrate 20, so as to prevent the antenna element

[0105] For example, the mass layer 212 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 of substrate 20, from the transmitting and / or receiving device to the conductive pads 4, or vice versa, which prevents the antenna element 3 from radiating at the wavelength of the electromagnetic wave, in a direction having a non-zero component along the z-axis.

[0106] The mass layer 212 is also capable of being in a conductive state in which the mass layer 212 has a ground plane function allowing the propagation of the surface wave on the front surface 22 of the substrate 20. Thus the antenna element 3 transforms or reflects the surface wave and radiates an electromagnetic wave in a direction having a component perpendicular to the front surface 22 of the substrate 20, that is to say a component along the z-axis.

[0107] The mass layer 212 is capable of switching from an insulating state to a conductive state by photoconductivity under the effect of illumination of the mass layer 212 by an optical beam at a wavelength called the switching wavelength λc. It is also capable of being maintained in the conductive state when the illumination is maintained.

[0108] Thus, by optically controlling the mass layer 212, to make it pass from the insulating state to the conductive state, we pass the metasurface device 201 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.

[0109] In order to optically control the mass layer 212, the metasurface device 201 advantageously includes a switching source 8 capable of switching from a state in which it does not illuminate the mass layer so that the mass layer 212 is in the insulating state to a state in which it illuminates the mass layer 7 at the switching wavelength so that it switches from the insulating state to the conducting state.

[0110] The metasurface device 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 ground layer, so that the ground layer is in the conductive state, to an off state in which it does not illuminate the ground layer, and vice versa.

[0111] Thus, the control of the mass layer 212 is independent of the control of the electromagnetic wave source generating the spherical excitation wave of the metasurface and therefore of the signal radiated by the metasurface device.

[0112] 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.

[0113] 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.

[0114] In the rest of the text, the thickness of a part of the device means its dimension along the z-axis of the stacking.

[0115] The photoconductive semiconductor material of the ground layer 212 is chosen such that the ground layer 212 has a penetration depth E1 less than the thickness E of the ground layer 212 at the switching wavelength λc, so that when the entire back face 225 of the ground layer 212 is illuminated at the switching wavelength λc, the ground layer 212 comprises: a conductive portion 215 forming the ground plane and extending, from the rear face 225, over a thickness of the conductive portion less than the thickness E of the ground layer 212 and, an insulating portion 216 extending over the remainder of the thickness E so that the conductive portion 215 is insulated from the antenna element 3 by the insulating portion 216 when the connection layer 280 is conductive.

[0116] In the realization of the figure 8 , the DR reconfiguration device is configured to illuminate the rear face 22 of the substrate 202.

[0117] The ground layer 212 is advantageously made of photoconductive material transparent at the reconfiguration wavelength λr different from the switching wavelength λc and the connecting layer is made of a material transparent at the switching wavelength λc.

[0118] 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.

[0119] For example, one can choose a mass layer of the AsGa type and a connection layer of two-dimensional semiconductor material.

[0120] Alternatively, the DR reconfiguration device is configured to illuminate the EE stack on the front face. The connecting layer 280 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 connecting layer 280, thus allowing the ground layer to be made of absorbing material at wavelength λr.

[0121] Therefore, the thickness of the connecting layer is advantageously chosen so as to be greater than the penetration depth of light at wavelength λr.

[0122] Alternatively, the ground layer is the connection 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 back face by choosing the wavelengths λr and λc and the thickness of the connection layer so that the ground layer includes an insulating portion electrically insulating the illuminated ZE areas made conductive by the reconfiguration device DR and the conductive area made conductive by the switching source 8.

[0123] There figure 9 represents a variant of the 301 metasurface device. The 301 metasurface device differs from that of the figure 4 by the substrate 300 and, more particularly, in that the mass layer 370 is capable of switching from an insulating state to a conductive state by photoconductivity under the effect of illuminating the mass layer 370 by a source 8 at the switching wavelength λc.

[0124] The 370 ground layer comprises a central photoconductive PC portion surrounding the O channel and a peripheral conductive PF portion surrounding the central photoconductive PC portion.

[0125] The central photoconductive PC part made of semiconductor material has a crown shape surrounding and delimiting the O channel.

[0126] The peripheral conductive part PF has a crown shape surrounding the central photoconductive part PC.

[0127] The peripheral conductive part PF is attached to the central photoconductive part PC.

[0128] The central photoconductive PC part is capable of being alternately in an insulating state and in a conductive state.

[0129] The central photoconductive PC part is in the insulating state when not illuminated.

[0130] 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.

[0131] 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.

[0132] The conductive peripheral part PF is, for example, metallic or indium tin oxide or ITO for the English term " Indium tin oxide which is transparent in the visible spectrum.

[0133] When the central photoconductive part PC is in the insulating state, it prevents the propagation of the surface wave generated by the source S on the front surface 22 of substrate 300 from the source to the antenna element 3 i.e. to the conductive pads 4, or vice versa.

[0134] When the central photoconductive part PC is in the conductive state, the ground layer 370 is substantially fully conductive. It is 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 a total wave at the wavelength of the electromagnetic wave in a direction that includes a component perpendicular to the upper surface 22.

[0135] The switching source 8 includes, for example, a laser source, for example a surface-emitting vertical cavity laser diode or VCSEL, an acronym for the Anglo-Saxon expression "surface-emitting vertical cavity laser diode", or a light-emitting diode.

[0136] The switching source 8 includes, for example, a mirror, to deflect the optical beam emitted by the laser source so that the optical beam illuminates the desired surface.

[0137] The central photoconductive part PC is advantageously made of photoconductive material transparent at the reconfiguration wavelength λr different from the switching wavelength λc and the connection layer 80 is made of a material transparent at the switching wavelength λc.

[0138] There figure 10 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 470, which lacks the central PC portion, and by the intermediate layer 290, which is made of a photoconductive semiconductor material selected 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 470 functions as a ground plane. The ground layer 470 comprises the rear face 221 of the substrate 302.

[0139] The rear face 291 of the intermediate layer 290 is attached to the mass layer 470.

[0140] The central part 292 connects the O channel to the peripheral part PF.

[0141] The device therefore includes a mass structure comprising the mass layer 470; 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.

[0142] Advantageously the material forming the intermediate layer 290 is transparent to the reconfiguration wavelength λr different from the switching wavelength λc and the connecting layer 80 is in a material transparent to the switching wavelength λc.

[0143] 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.

[0144] 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 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 4The 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 (20) having a rear surface (21) and a front surface (22), the substrate (20) comprising an earthing structure (70) capable of having an earthing plane function, - a transmission and / or receiving device capable of transmitting and / or receiving an electromagnetic wave, the transmission and / or receiving device being configured and disposed, such that the wave is capable of being propagated in the form of a surface wave on the front surface of the substrate, - an antenna element (3) comprising a two-dimensional network of electrically conductive wafers (4) disposed on the front surface of the substrate (20), distant from one another and having smaller dimensions than the operating wavelength of the transmission and / or receiving device, the antenna element (3) being capable of radiating, under the effect of the propagation of a surface wave on the front surface of the substrate, in a direction having a component perpendicular to the front surface of the substrate, when the earthing structure (270) has an earthing plane function, the substrate (20) comprising a so-called connection layer (80) made of photoconductive semiconductor material, in direct physical contact with the conductive wafers (4), the semiconductor material being insulating when it is not illuminated, electrically insulating the conductive wafers between them, that are not connected by a continuous illuminated zone of the connection layer, and capable of being conductive when it is illuminated at a so-called reconfiguration wavelength, electrically connecting only the conductive wafers to one another, that are connected by a continuous illuminated zone of the connection layer.

2. Metasurface device according to the preceding claim, comprising an optical reconfiguration device (DR), capable of illuminating a set of at least one zone, called the illuminated zone, of the connection layer (80), so that the connection layer (80) is conductive only in the set of at least one illuminated zone, so as to electrically connect in pairs the metal wafers (4) of the antenna element, which are separated and connected by a continuous zone of the connection layer (80), which is located completely in an illuminated zone (ZE) of the set 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 one another.

3. Metasurface device (1) according to the preceding claim, wherein the optical reconfiguration device (DR) comprises one single optical reconfiguration source (DIFF) capable of transmitting an optical beam to the reconfiguration wavelength and an optical diffractive device (DIFF) making it possible, from the optical beam, by diffraction, to illuminate the set of at least one illuminated zone (ZE) at the reconfiguration wavelength.

4. Metasurface device (1) according to the preceding claim, wherein the diffractive device (DIFF) makes it possible to illuminate a network of illuminated zones (ZE), of the connection layer (80) or a set of at least one illuminated zone delimiting zones of the connection layer, not illuminated by the diffractive device (DIFF).

5. Metasurface device according to the preceding claim, wherein the diffractive device (DIFF) is capable of alternatively illuminating differently at least one illuminated zone of the connection layer (80).

6. Metasurface device according to any one of the preceding claims, comprising a earthing structure (370) capable of having an earthing plane function, the earthing structure (370) being capable of being alternatively in an insulating state, wherein it prevents the propagation of the surface wave on the front surface (22) of the substrate (2), from the transmission and / or receiving device as far as the conductive wafers (4), or vice versa, and in a conductive state, wherein the earthing structure (370) has an earthing plane function, enabling the propagation of the surface wave on the front surface (22) of the substrate (2), from the transmission and / or receiving device as far as the conductive wafers, or vice versa, the earthing layer (7) being capable of changing from the insulating state to the conductive state by means of illumination of the earthing layer (7) by an optical beam at a so-called commutation wavelength.

7. Metasurface device according to any one of claims 2 to 6, wherein the reconfiguration device (DR) is configured and disposed to illuminate the substrate on the rear face.

8. Metasurface device according to any one of claims 2 to 7, wherein the reconfiguration device (DR) is capable of illuminating the substrate on the front face.

9. Metasurface device according to claim 8, wherein the diffractive device (DIFF) is mounted on a cover of the metasurface device, the cover being disposed facing the antenna element (3) at a distance from the antenna element (3).

10. Metasurface device according to claim 8, wherein the diffractive device (DIFF) has a substantially flat plate shape, substantially perpendicular to the front surface (22).

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