FR3046830A1 - LIGHTING DEVICE WITH COHERENT AND DIRECTIVE PHOTON SENSING BY DICKE SUPER-RADIANCE - Google Patents

Abstract

A lighting device (DE) comprises a light source (SL) comprising a substrate (SD), a first electrode (E1) firmly fixed on one side of the substrate (SD), a network of nano-antennas (NA), a second electrode (E2), an electroluminescent structure (SE) interposed between the first (E1) and second (E2) electrodes, and clean, when a current flows between the first (E1) and second (E2) electrodes, generating coherent photons propagating in a general direction by a so-called "super-Dicke radiance" effect induced by a first optical coupling between the electroluminescent structure (SE) and the nano-antennas (NA).

Description

The invention relates to lighting devices that are capable of delivering a coherent and directional light beam.

In what follows, the term "lighting device" a device for illuminating in a directive manner and / or to participate in a directive signaling function, whether indoors or outdoors. Consequently, such a lighting device can generate beams intended either to restore a hologram inscribed in a holographic plate (possibly for a human / machine interface), or to participate in a directional photometric function.

Most holographic lighting devices comprise a laser source and so-called "free space" optical elements, such as lenses and a beam collimator, which make it possible to shape a laser beam and direct it to the laser beam. surface of a holographic plate. Such a lighting device is quite bulky, and therefore difficult to integrate in a small space and / or congested, such as for example a motor vehicle, it has been proposed (particularly in the patent document FR 1350105) to replace all the elements. optics by a plate comprising a network of optical guides including nano-antennas. These define coherent emission points capable of redirecting light from a laser source to the holographic plate. However, the coupling of the photons of the laser source with the optical guide array plate is relatively difficult to achieve.

A large number of internal or external lighting devices providing a directive photometric function comprise a light-emitting diode (or LEDs), possibly of organic type (or OLED), and at least one lens intended to confer the directivity of the photons emitted by the light source. The presence of such a lens makes the lighting device quite cumbersome.

Furthermore, no coherent and directional light beam lighting device can provide illumination over a large area, without significant increase in size and cost. The purpose of the invention is in particular to improve the situation.

In particular, it proposes for this purpose a lighting device comprising a source of light capable of generating photons and comprising: a substrate, a first electrode fixedly affixed to one side of the substrate, a network of nano-antennas, second electrode, an electroluminescent structure interposed between the first and second electrodes and clean, when a current flows between the first and second electrodes, to generate coherent photons propagating in a general direction by a so-called "super" effect; -Dicke radiance induced by a first optical coupling between the electroluminescent structure and the nano-antennas. The spontaneous emission generated in the electroluminescent structure by recombination of charges (or electric carriers) is exalted and synchronized thanks to at least the interaction with the nano-antennas. Consequently, this spontaneous emission becomes dominant in front of other de-energizing processes, and the synchronization (which induces the coherence of the photons) can be established over a large area by close coupling of the nano-antennas.

Such a lighting device is very compact and can advantageously serve as a source of holographic restitution and / or coherent and directional lighting source, possibly for a large lighting surface.

The lighting device according to the invention may comprise other characteristics that can be taken separately or in combination, and in particular: the super-radiance effect of Dicke can be induced by the first optical coupling between the electroluminescent structure and the nano-antennas and a second optical coupling between the nano-antennas; the general direction may be parallel to a stacking direction of the substrate, the first electrode, the electroluminescent structure and the second electrode. In this case, the first electrode is transparent to photons; the substrate may be transparent to photons and / or the second electrode may be transparent to photons; The substrate may be made of a material chosen from (at least) a glass, a polymer, and a crystal; The first electrode can be made of a combination of indium and tin oxide (or ITO) or graphene; the first electrode may, for example, comprise the nano-antenna network; the electroluminescent structure may comprise an active layer capable of emitting photons when it is fed with charges, and at least one substructure capable of supplying this active layer with charges; the electroluminescent structure may comprise an organic layer defining the active layer and interposed between first and second substructures each defining a heterojunction; The organic layer can be made of Zn (PPI) 2: IR (MDQ) 2 (acac); The first substructure (or heterojunction) may comprise an N PB layer and a MoO 3 layer and the second substructure (or heterojunction) may comprise a LiF layer and a TpBi layer; the substrate can be flexible; the second electrode may be made of aluminum; the nano-antennas may have dimensions of between 50 nm and 500 nm; the nano-antennas may have an annular shape. The invention also proposes a vehicle optical unit, possibly of automobile type, and comprising at least one lighting device of the type of that presented above. The invention also proposes a vehicle, possibly of automobile type, and comprising at least one lighting device of the type of the one presented above or at least one optical block of the type of that presented above. Other features and advantages of the invention will appear on examining the detailed description below, and the accompanying drawings, in which: - Figure 1 illustrates schematically and functionally, in a sectional view, an embodiment. 2 schematically illustrates, in a perspective view, an exemplary embodiment of a nano-antenna, and FIG. 3 schematically illustrates, in a view from above, of a lighting device according to the invention. the directional and coherent emission mechanism of photons occurring in a lighting device according to the invention. The invention aims in particular to provide a lighting device DE capable of delivering a coherent and directional light beam, while having, in particular, a (very) small footprint.

In what follows, it is considered, by way of non-limiting example, that the lighting device DE is intended to be part of a vehicle optical unit, possibly of automotive type. For example, this optical unit can be a front projector or a rear light. But the invention is not limited to this application. Indeed, a lighting device DE, according to the invention, can be an independent equipment of an optical unit. In this case, it has its own housing, and can, for example, be installed in different systems, devices or installations, indoors and outdoors. In general, a lighting device DE, according to the invention, can be part of any type of vehicle, land, sea (or fluvial), or air, or any type of installation (including industrial), or any type of building.

Moreover, a lighting device DE, according to the invention, may be intended to illuminate in a directive and coherent manner and / or to participate in a signaling function, whether indoors or outdoors. Therefore, it can generate lighting beams for rendering a hologram inscribed in a holographic plate (possibly for a man / machine interface) and / or to participate in a directive and coherent photometric function. Therefore, a lighting device DE, according to the invention, can also equip any type of device having display capabilities, such as for example a computer (fixed or portable), a smartphone (or "smartphone") , an electronic tablet, or an appliance.

FIG. 1 shows schematically and functionally a nonlimiting exemplary embodiment of a lighting device DE according to the invention.

As illustrated in FIG. 1, a lighting device DE according to the invention comprises at least one light source SL.

The light source SL is arranged to generate directional and coherent photons. It comprises for this purpose an SD substrate, first E1 and second E2 electrodes, a network of nano-antennas NA and an electroluminescent structure SE. The substrate SD, the first electrode E1, the electroluminescent structure SE and the second electrode E2 constitute a stack of layers in a first direction d1, each layer comprising two opposite faces contained in planes parallel to a plane defined by second d2 and third d3 directions perpendicular to each other and perpendicular to the first direction d1.

The term "nano-antenna" is used here to mean a nanostructure defining an interface between a confined (or guiding) medium and free space, like a radio antenna, and having dimensions smaller than the wavelength photons generated by the electroluminescent structure SE. The nano-antennas NA may therefore be discrete elements of very small dimensions and arranged in a network, not necessarily periodic, or interconnected elements by defining a large structure. In general, any nano-element subwavelength, two-dimensional (surface) or three-dimensional (possibly a nano-hole), may constitute a nano-antenna.

For example, and as illustrated nonlimitingly in FIG. 2, the nano-antennas NA may have an annular shape. But, as mentioned above, they can have many other forms (including hollow (nano-holes)). Their shape and dimensions may in particular depend on the application requirements in terms of radiation pattern and / or efficiency and / or gain, for example. In general, these nano-antennas NA may have dimensions of between 50 nm and 500 nm.

In the example shown non-limitatively in FIG. 1, the network of nano-antennas NA is part of the first electrode E1. But this is not obligatory. Indeed, the nano-antennas NA may be placed at different locations, and especially above the first electrode E1, or in the middle of the electroluminescent structure SE, or in one of the first E1 and second E2 electrodes. It will be noted that these nano-antennas NA may even constitute one of the first E1 and second E2 electrodes for use in the injection of carriers. In the latter case, the nano-antennas NA must be connected to each other for electrical injection.

It will be noted that the realization of the nano-antennas NA in the first electrode E1 can be done by different techniques, in the space dedicated to the latter (E1), but before its constitution. For example, it will be possible to use an electronic lithography technique, or a nanoprinting technique (or "nano-imprint") or a self-assembly technique (chemical process). Once the nano-antennas NA made, we can then perform around them a deposit of a selected material intended to immerse them.

It will be noted that the realization of the NA nano-antennas can be done by different techniques. For example, it will be possible to use an electronic lithography technique, or a nano-imprint technique or a self-assembly technique (chemical process). Once the nano-antennas NA made, we can then perform around them a deposit of a selected material intended to immerse them.

It will also be noted that the material in which the nano-antennas NA are produced is not necessarily the same as that in which the layer (or structure) of which they form part is formed (here the first electrode E1 by way of example) . By way of example, the nano-antennas NA can be made of highly doped metallic or semiconductor materials, or high index dielectrics (the important thing being that they constitute sublongeur wave optical resonators). But, as will be seen later, they could also be made of a combination of indium and tin oxide (or ITO) or graphene, just like the first electrode E1, especially when the latter (E1) must be transparent to the wavelengths of the photons generated by the electroluminescent structure SE.

The network of nano-antennas NA can advantageously (and possibly) extend over great distances so as to allow lighting on (very) large areas, adaptable as needed. It should be noted that such a network may not have periodicity. The nano-antennas NA can therefore be defined with respect to each other at potentially variable distances and / or in possibly variable orientations depending on the optical coupling that is to be obtained between them (phase effect). Such optical coupling may be zero or non-zero. As will be seen below, the optical coupling (non-zero) between nanowires NA is likely to favor an effect called "super-radiance of Dicke >> described below.

The first electrode E1 is firmly fixed on one side of the substrate SD.

The electroluminescent structure SE is interposed fixedly between the first E1 and second E2 electrodes. It (SE) is thus secured to one side of the first electrode E1, opposite to the substrate SD, and to one side of the second electrode E2. This electroluminescent structure SE is clean, when a current flows between the first E1 and second electrodes E2, to generate coherent photons and propagating in a general direction dg (see Figure 3) by a so-called effect of "super-radiance Dicke Induced by a first optical coupling between the electroluminescent structure SE and the nano-antennas NA, and possibly a second optical coupling between the nano-antennas NA (described above).

The current flowing between the first E1 and second electrodes E2 (due to the voltage V between their terminals) provides the electroluminescent structure SE charges (or electrical carriers) which recombine in the latter (SE) by generating a spontaneous emission of photons. This spontaneous emission is exalted and synchronized thanks to the interaction with the nano-antennas NA, and possibly to the mutual coupling of the latter (NA).

The primary role of the nano-antennas NA is to promote the synchronization of the emitters of the electroluminescent structure SE by introducing an additional coupling force into the emitter system. Moreover, the nano-antennas NA accelerate the photon emission rate, which ensures that these are emitted before the loss of quantum coherence emitters of the electroluminescent structure SE. Finally, the nano-antennas NA can also establish the synchronization of the emitters of the electroluminescent structure SE over a large area by close-coupled coupling of the nano-antennas NA. This synchronization between transmitters is what is called the super-radiance of Dicke. The coherent double coupling is accompanied by a selectivity of the direction of emission, which allows the light source SL to become directive (according to the general direction dg).

In the example shown non-limitatively in FIG. 1, the light source SL is arranged to emit coherent photons in a general direction dg which is parallel to the stacking direction d1. Consequently, the photons exit from the light source SL perpendicular to its substrate SD and / or perpendicularly to its second electrode S2. In this case, the first electrode E1 must be transparent to the photons produced by the electroluminescent structure SE.

It should be noted that an output of photons on one side can significantly increase the intensity of coherent and directional lighting. In this case, the layer (SD or E2) which is not transparent may, for example, be fixedly affixed to a support plate, such as for example a printed circuit board, possibly PCB type ("Printed Circuit Board" ), rigid or flexible ("type" Flex ").

When the first electrode E1 must be transparent, it may, for example, be made of a combination of indium oxide and tin (or ITO) or graphene, as mentioned above.

In order for the coherent and directive photons to emerge from the light source SL perpendicularly to its substrate SD, the latter must be transparent to the photons. Similarly, for coherent and directive photons to emerge from the light source SL perpendicularly to its second electrode E2, the latter must be transparent to the photons.

When the SD substrate must be transparent, it can be made of glass, polymer or a crystal, for example.

When the second electrode E2 should not be transparent, it can be made of aluminum or gold or a mixture of platinum and gold, for example. However, when it must be transparent, it can be realized in a combination of indium oxide and tin (or ITO) or graphene, for example.

For example, and as illustrated in non-limiting manner in FIG. 1, the electroluminescent structure SE may comprise an active layer CA capable of emitting photons when it is fed with charges and at least one substructure HJ1, HJ2 capable of supplying charges. this active layer CA.

As illustrated without limitation in FIG. 1, the active layer CA can be sandwiched between first HJ1 and second HJ2 substructures which each define a heterojunction. This gives a multilayer structure with double heterojunction and PIN type. This type of multilayer structure is particularly advantageous compared to a simple heterojunction combined with an active layer, because it allows the charge carriers (electrons and holes) to be trapped in the active layer CA, where they are almost all forced to annihilate in pairs by creating each time a photon. This confinement effect in the AC active layer therefore makes it possible to significantly increase the efficiency of the electrical pumping and therefore the number of photons produced. However, in an alternative embodiment, the electroluminescent structure SE could comprise only an active layer CA bonded to a single heterojunction, thus constituting a PN-type multilayer structure. By way of example, the active layer CA may be an organic layer and the first HJ1 and second HJ2 substructures may also be organic layers. A purely organic electroluminescent SE structure is thus obtained, of the OLED ("Organic Light-Emitting Diode" - organic electroluminescent diode) type.

In this case, the organic layer CA may, for example, be made of Zn (PPI) 2: IR (MDQ) 2 (acac), the first substructure (or heterojunction) HJ1 may, for example, comprise a layer of NPB and an M0O3 layer, and the second substructure (or heterojunction) HJ2 may comprise a LiF layer and a TpBi layer. This embodiment is adapted to an emission wavelength of 633 nm. The use of a dual heterojunction and OLED organic multilayer structure provides improved radiative emission efficiency (because singlet states are exalted and triplet states become radiative) compared to a standard OLED structure (where singlets are radiative but triplets are non-radiative).

It will be noted that in an alternative embodiment, the organic AC active layer could be replaced by a structure comprising colloidal quantum dots. In general, the double heterojunction and PIN SE multilayer structure can be exclusively organic, or exclusively non-organic or hybrid (organic and inorganic).

The respective thicknesses and materials of each layer of the electroluminescent structure SE are chosen so as to produce the desired macroscopic effect. These thicknesses are between a few angstroms and a few microns. By way of example in the electroluminescent structure SE illustrated in FIG. 1, the first heterojunction HJ1 may comprise a 60 nm SC1 layer of M0O3 and a 10 nm SC2 layer of NPB, the organic layer CA may be made of Zn ( PPI) 2: IR (MDQ) 2 (acac) and have a thickness of 30 nm, and the second heterojunction HJ2 may comprise a SC3 layer of 30 nm of TpBi and a SC4 layer of 1 nm of LiF. In this case, the first electrode E1 may have a thickness of 30 nm of tin-doped indium oxide with nano-antennas NA having a diameter of 200 nm and a hollow core having a diameter of 100 nm. As indicated above, this embodiment is adapted to an emission wavelength of 633 nm.

It will be noted that the light source SL is monochromatic. But it is possible to combine within the same lighting device several sources of SL lights producing photons of different colors, for example a red light source, a green light source and a blue light source. This allows the lighting device DE to deliver a coherent light, directional and variable color, or even white, and therefore to use it within a very thin (or flat) and large color screen. It should be noted that the substrate SD may be possibly flexible so that the light source SL is flexible and thus can equip a flexible screen.

It is also possible to add to the lighting device DE, near its light source SL, a holographic plate. In this case, the directivity and the coherence of the beam produced by the light source SL advantageously makes it possible to restore the hologram inscribed on the holographic plate.

Moreover, in the above detailed description, the pumping of the active layer CA is done electrically through the first E1 and second E2 electrodes. But in an alternative embodiment this pumping could be done optically, without strong optical alignment constraints. Such optical pumping can be done by injecting a beam by the slice or global illumination of the surface, above or below. The invention offers several advantages, among which: - a great compactness, - a possibility of ensuring a large coherent and directive lighting surface, - a reduced manufacturing cost thanks to the use of low-cost materials and the lack of optical alignment, - low power consumption, - adaptability to many configurations, including flexibility.

Claims (10)

A lighting device (DE) comprising a light source (SL) capable of generating photons, characterized in that said light source (SL) comprises i) a substrate (SD), ii) a first electrode (E1 ) fixedly fixed on one side of said substrate (SD), iii) a network of nano-antennas (NA), iv) a second electrode (E2), and v) an electroluminescent structure (SE) interposed between said first (E1) and second (E2) electrodes, and clean, when a current flows between said first (E1) and second (E2) electrodes, to generate coherent photons and propagating in a general direction by an effect called "super-radiance of Dicke "induced by a first optical coupling between said electroluminescent structure (SE) and said nano-antennas (NA). 2. Device according to claim 1, characterized in that said super-radiance effect of Dicke is induced by said first optical coupling between said electroluminescent structure (SE) and said nano-antennas (NA) and a second optical coupling between said nano -antennes (NA). 3. Device according to one of claims 1 and 2, characterized in that said general direction is parallel to a stacking direction of said substrate (SD), said first electrode (E1), said electroluminescent structure (SE) and said second electrode (E2), and said first electrode (E1) is transparent to said photons. 4. Device according to claim 3, characterized in that said substrate (SD) is transparent to said photons and / or said second electrode (E2) is transparent to said photons. 5. Device according to claim 4, characterized in that said substrate (SD) is made of a material selected from a group comprising a glass, a polymer, and a crystal. 6. Device according to one of claims 4 and 5, characterized in that said first electrode (E1) is made of a combination of indium oxide and tin or graphene. 7. Device according to one of claims 1 to 6, characterized in that said first electrode (E1) comprises said network of nano-antennas (NA). 8. Device according to one of claims 1 to 7, characterized in that said electroluminescent structure (SE) comprises an active layer (CA) capable of emitting photons when it is fed with charges and at least one substructure ( HJ1, HJ2) capable of supplying said active layer (CA) with charges. 9. Device according to claim 8, characterized in that said electroluminescent structure (SE) comprises an organic layer defining said active layer (CA) and interposed between first (HJ1) and second (HJ2) substructures each defining a heterojunction. 10. Vehicle optical unit, characterized in that it comprises at least one lighting device (DE) according to one of the preceding claims.