Optoelectronic device with controlled light emission profile

Abstract

Title: Optoelectronic Device with Controlled Light Emission Profile The invention relates to an optoelectronic device (1) comprising an assembly (10) of photonic crystals (100, 200, 300, 400) for emitting a light beam having predominantly a wavelength λ. This assembly comprises at least one first elementary photonic crystal (100) comprising an assembly of first nanowires (101) and configured to emit a first elementary light beam having predominantly the wavelength λ, and a second elementary photonic crystal (200) comprising an assembly of second nanowires (201) and configured to emit a second elementary light beam having predominantly the wavelength λ. The elementary photonic crystals (100, 200) have distinct structures, so as to impart to the elementary light beams at least one distinct optical characteristic.The light beam emitted by the set of photonic crystals can be formed by the first elementary light beam and / or the second elementary light beam. Figure for the abbreviation: Fig. 2A.

Description

Title of the invention: Optoelectronic device with controlled light emission profile technical field

[0001] The present invention relates in particular to the field of microelectronics and optoelectronics technologies. It finds a particularly advantageous, but not limiting, application in LED (Light-Emitting Diode) display systems. STATE OF THE ART

[0002] Light-emitting diodes (LEDs) are used in a wide variety of fields, from display screens to street lighting. Depending on the intended application, it is necessary to modulate the angular emission profile of the device. However, the light emitted by an LED is generally Lambertian. The light profile generated by conventional Lambertian LEDs is suitable for only a few industrial applications. Many applications require uniform illumination at a given distance. For example, street lighting requires uniform illumination at ground level. In backlit display applications (commonly referred to as "Back Light Unit" or "BLU"), uniform illumination is desired across the screen to illuminate each pixel homogeneously. Examples of ideal angular emission profiles for BLU applications are illustrated in Figures IA and IB. [Fig.[Fig. 1A] corresponds to a situation in which the LEDs are located 5 mm from the pixels and are spaced 5 mm apart, while [Fig. 1B] corresponds to a situation in which the LEDs are located 3 mm from the pixels and are spaced 10 mm apart. These profiles deviate significantly from the emission profile of Lambertian LEDs, and it is clear that to obtain uniform pixel illumination, it is necessary to modulate the profile emitted by the LEDs.

[0003] Depending on the intended applications, it may also be necessary to modulate the polarization of the light emitted by the device.

[0004] An existing solution for modulating the emission profile is to integrate optical elements configured to modify the direction of the beam emitted by the LEDs. These optical elements can notably consist of lenses, reflectors, diffusers, or even micro- or nano-structured films, or a combination of these different elements. Similarly, to control the polarization of the emitted light, it is possible to integrate polarizing filters into the devices. The integration of these However, combining these various elements is complex, costly, time-consuming, and energy-inefficient. This solution, though widely used today, is therefore not optimal.

[0005] There is therefore a need for a solution to control the optical properties of optoelectronic devices. Preferably, the proposed solution will allow control of the emission profile of the optoelectronic devices. Preferably, the proposed solution will allow control of the polarization of the light emitted by the optoelectronic devices. SUMMARY

[0006] To achieve this objective, a first aspect of the invention relates to an optoelectronic device comprising an array of photonic crystals intended to emit a light beam having primarily a wavelength X, the array of photonic crystals comprising at least, juxtaposed in a principal plane: • a first elementary photonic crystal comprising a set of first nanowires and configured to be able to emit a first elementary light beam exhibiting mainly the X wavelength, • a second elementary photonic crystal comprising an array of second nanowires and configured to be able to emit a second elementary light beam exhibiting mainly the X wavelength, • the first elementary photonic crystal and the second elementary photonic crystal having distinct structures, so as to impart to the first elementary light beam and the second elementary light beam at least one distinct optical characteristic, • the light beam emitted by the set of photonic crystals that can be formed by the first elementary light beam and / or the second elementary light beam.

[0007] By exploiting the properties of different elementary light beams, it is possible to emit an overall beam at wavelength X having optical characteristics that are difficult to access and / or control with the prior art. These optical characteristics relate in particular to the angular emission profile and the polarization of the emitted beam.

[0008] In particular, it is possible to obtain an angular emission profile of the overall beam which would not have been possible to obtain, or only at the cost of long and expensive processes, by transforming the emission of conventional Lambertian LEDs by optical elements.

[0009] By modulating the photonic characteristics of elementary crystals, it is possible to generate an infinite number of different emission profiles.

[0010] The present invention therefore makes it possible to control the emission profile of devices integrating LEDs.

[0011] Another advantage of the invention is that the desired emission profile is directly generated by the nanowires. Therefore, it is not necessary to add optical elements to modulate the emission. This significantly reduces the size of the optoelectronic device. Even if it were still desired to integrate optical elements to further improve the emission profile, the size would be very small compared to prior art devices. Indeed, fewer optical elements would be required. In the specific example of a homogeneous target profile, the more uniform the illumination generated by the LED itself, the simpler and therefore thinner the stacking of optical elements needed to modulate the emission profile. Thus, the invention makes it possible to limit or even eliminate the size due to optical elements for correcting the emission profile.

[0012] Furthermore, the decomposition into elementary photonic crystals allows, during the use of the optoelectronic device, for the selection in time or space of optical characteristics, and in particular the angular emission profile and polarization. It is indeed possible to independently power the nanowires of the different elementary photonic crystals. Thus, it is possible to choose which elementary photonic crystals are active at any given time. This can be exploited to simultaneously display several types of content (images, videos) from the same optoelectronic device in several angular directions or with different polarizations, or to offer different display modes such as a private viewing mode and a public viewing mode for a computer or phone screen.

[0013] A second aspect of the invention relates to a lighting system comprising the optoelectronic device according to the first aspect of the invention, the lighting system being taken from: an urban lighting system, an automotive lighting system, an aeronautical lighting system.

[0014] A third aspect of the invention relates to a method for dimensioning the optoelectronic device according to the first aspect of the invention, comprising: • the provision of information on the theoretical emission intensity of at least a first theoretical photonic crystal and a second theoretical photonic crystal as a function of an emission direction, • the provision of a target emission profile, • based on said target emission profile and said information, a deduction of a first coefficient to be applied to a given parameter of the first theoretical photonic crystal and a second coefficient to be applied to said given parameter of the second theoretical photonic crystal so that the superposition of a first theoretical elementary light beam emitted by said first theoretical photonic crystal and a second theoretical elementary light beam emitted by said second theoretical photonic crystal approaches the target emission profile, the given parameter being taken from the following parameters: i. a surface in the principal plane, ii. a theoretical power supply per photonic crystal, iii. a power supply ratio between the first theoretical photonic crystal and the second theoretical photonic crystal • use the first coefficient and the second coefficient respectively for the dimensioning of the first elementary photonic crystal and the second elementary photonic crystal.

[0015] The advantages provided by the device according to the first aspect of the invention apply mutatis mutandis to the other aspects of the invention. BRIEF DESCRIPTION OF THE FIGURES

[0016] The aims, objects, features and advantages of the invention will become clearer from the detailed description of an embodiment thereof, which is illustrated by the following accompanying drawings in which:

[0017] [Fig.1A][Fig.1B] Figures IA and IB represent ideal angular emission diagrams for SSB applications using the principle of local dimming of the backlight.

[0018] [Fig. 2A] [Fig. 2B] Figures 2A and 2B illustrate two examples of the device according to the invention. [Fig. 2A] illustrates a case in which the LED comprises four elementary photonic crystals. [Fig. 2B] illustrates a case in which the LED comprises sixteen elementary photonic crystals.

[0019] [Fig.2C] The [Fig.2C] is a cross-sectional view of nanowires belonging to two adjacent photonic crystals.

[0020] [Fig.3A][Fig.3B] Figures 3A and 3B illustrate how the principal direction of a beam can be located in space.

[0021] [Fig.4A] [Fig.4B] [Fig.4C] [Fig.4D] Figures 4A to 4D illustrate the variation of the principal emission direction of a photonic crystal as a function of its filling factor.

[0022] [Fig.5A] [Fig.5B] [Fig.5C] Figures 5A to 5C illustrate how it is possible to dimension elementary photonic crystals so that they emit elementary light beams whose superposition approaches a target emission profile.

[0023] [Fig. 6A][Fig. 6B][Fig. 6C] Figure 6A illustrates examples of emission profiles that can be assigned to the public and private viewing modes of a display device. Figures 6B and 6C illustrate examples of emission profiles that can be assigned to the simultaneous broadcasting of different content by the same display device.

[0024] [Fig.7A][Fig.7B] Figures 7A and 7B are optical band diagrams of a photonic crystal, showing emission bands corresponding respectively to s and p polarizations.

[0025] The drawings are given by way of example and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate understanding of the invention and are not necessarily to scale with practical applications. In particular, the dimensions are not representative of reality. DETAILED DESCRIPTION

[0026] Before proceeding with a detailed review of embodiments of the invention, optional features that may be used in combination or alternatively are listed below:

[0027] According to one embodiment, the first elementary photonic crystal has a first nanowire filling factor, denoted Fb, and the second elementary photonic crystal has a second nanowire filling factor, denoted F2, with F^Fo. Advantageously, Fi > 1.1*F2, and preferably Fi > 1.2*F2.

[0028] According to one embodiment, the first nanowires have first diameters having a value substantially equal to a first target diameter di and the second nanowires have second diameters having a value substantially equal to a second target diameter d2, with di^d2.

[0029] Advantageously, di>l,l*d2, and preferably di>l,2*d2.

[0030] According to one embodiment, the first nanowires are arranged within the first elementary photonic crystal according to a first period pl and the second nanowires are arranged within the second elementary photonic crystal according to a second period p2, with pi^p2. Advantageously, pi>l,l*p2, and preferably pi>l,2*p2.

[0031] According to one embodiment, the first elementary photonic crystal and the second elementary photonic crystal extend respectively in the principal plane on a first surface Si and on a second surface S2, with Si^S2. Advantageously, Si>1.5*S2, and preferably Si>2*S2.

[0032] According to one embodiment, the first photonic crystal has a first effective index neff 1 and the second photonic crystal has a second effective index neff2, with neffi^neff2. Advantageously, neffi>l,l*neff2, and preferably neffl>l,2*neff2.

[0033] According to one embodiment: • The first elementary photonic crystal is configured so that the first elementary light beam is directed primarily along a first direction. • the second elementary photonic crystal is configured so that the second elementary light beam is directed mainly along a second direction distinct from the first direction.

[0034] According to one embodiment: • The first elementary photonic crystal is configured so that the first elementary light beam exhibits a first polarization, • the second elementary photonic crystal is configured so that the second elementary light beam exhibits a second polarization distinct from the first polarization.

[0035] According to one example, the first nanowires and the second nanowires are based on the same material.

[0036] According to a preferred example, the first nanowires and the second nanowires are light-emitting diodes and each have an active emitting region, the active regions of the first nanowires and the second nanowires being configured to emit at the wavelength X.

[0037] According to one example, within each nanowire, the active emitting region is substantially transverse to said nanowire, and is preferably located at a non-zero height within said nanowire, the height within the nanowire being considered along a longitudinal direction perpendicular to the principal plane.

[0038] According to one embodiment, the photonic crystal assembly further comprises a third elementary photonic crystal comprising a third set of nanowires and configured to emit a third elementary light beam having mainly the wavelength X, the third elementary photonic crystal having a structure distinct from that of the first elementary photonic crystal and from that of the second elementary photonic crystal, so as to confer on the third elementary light beam at least one optical characteristic distinct from the first and second elementary light beams.

[0039] According to one embodiment, the third photonic crystal is configured so that the third elementary light beam is directed mainly along a third direction, distinct from the first direction and the second direction.

[0040] According to one embodiment, the superposition of all the elementary light beams gives a target emission profile. The target emission profile is, for example, taken from: • a profile enabling homogeneous illumination at a given distance, for example for lighting applications (urban lighting, backlighting of a screen, etc.), • a profile exhibiting at least two distinct principal components, for example for the diffusion by the optoelectronic device of two different contents (images, videos) in two different directions, • a specific emission profile corresponding to a particular architecture (typically when one wants to highlight different elements, for example paintings displayed in a museum).

[0041] According to one embodiment, the target light beam makes it possible to obtain substantially uniform illumination over a given angular range.

[0042] Depending on the distance between the source and the size of the area of ​​interest, different angular emission ranges are involved. Preferably, the given angular range extends over more than 10°, preferably over 20°, preferably over 50°. This angular range is identified by the angle 0 measured relative to the longitudinal direction Z. Typically, when referring to a given angular range [0min; 0max], the effective emission is considered between two cones of revolution around the direction Z, with respective angular apertures 0min and 0max with respect to the direction Z. By "the angular range extends over a°", it is meant that 0max - 0min = a°.

[0043] According to one embodiment, at least two of the elementary photonic crystals are electrically powered independently. Preferably, all the elementary photonic crystals are electrically powered independently of each other. This allows control of the LED's emission profile during operation. This provides control over the emission profile after the device has been manufactured and once the elementary photonic crystals have been sized and fabricated.

[0044] In this patent application, the terms "light-emitting diode", "LED" or simply "diode" are used synonymously. An "LED" may also be understood to mean a "micro-LED".

[0045] A wire or nanowire is understood to be a 3D structure elongated along its longitudinal direction. The longitudinal dimension of the 3D structure, along the Z axis in the figures, is greater, and preferably much greater, than the transverse dimensions of the 3D structure in the principal XY plane in the figures. The longitudinal dimension is, for example, at least five times, and preferably at least ten times, greater than the transverse dimensions. In the present application, and unless otherwise specified, the wires or nanowires are light-emitting 3D structures. As will be described later, each nanowire has an active emitting region designed to emit a beam of light at a given wavelength. Each nanowire thus forms a Light-emitting diode (LED), or micro-LED. The photonic crystals mentioned in the application are each formed by a plurality of such emitting nanowires.

[0046] The diameter refers to the largest transverse dimension of the nanowire. In the present invention, the 3D structures do not necessarily have a circular cross-section. In particular, in the case of GaN-based 3D structures, this cross-section may be hexagonal. The diameter then corresponds to the distance between two opposite vertices of the hexagonal section. Alternatively, the diameter may correspond to an average diameter calculated from the diameter of a circle inscribed in the polygon of the cross-section and the diameter of a circumcircle of this polygon.

[0047] 3D structures may also have a hexagonal or polygonal cross-section.

[0048] A substrate, layer, or device "based on" a material M is understood to mean a substrate, layer, or device comprising only that material M or that material M and optionally other materials, for example, alloying elements, impurities, or dopant elements. Thus, a 3D structure based on gallium nitride (GaN) may, for example, comprise gallium nitride (GaN or GaN-i) or doped gallium nitride (GaN-p, GaN-n). An active region based on gallium-indium nitride (InGaN) may, for example, comprise gallium aluminum nitride (AlGaN) or gallium nitride with varying aluminum and indium content (GalnAIN). In the context of the present invention, the material M is generally crystalline.

[0049] A "light beam exhibiting predominantly a wavelength X" is understood to be a beam whose peak spectral wavelength is at wavelength X. The beam spectrum typically follows a Gaussian distribution. The peak of the spectrum is then understood to be the maximum value of the Gaussian distribution.

[0050] The term "light beam emitted mainly along a direction d" means a beam whose maximum luminous intensity is located in the axis defining the direction d.

[0051] In the following, we refer to the effective refractive index of photonic crystals. This index is defined for each photonic crystal based on the materials forming the nanowires contained within that crystal, as well as the materials adjacent to these nanowires, including the materials of the filling layer(s) extending between the nanowires, the materials of the electrical contacts ensuring the electrical connection of the nanowires, and the materials of any surrounding spacers. The effective refractive index is equal to the ratio of the speed of light c (speed of light in a vacuum) to the speed of light propagation in the photonic crystal.

[0052] To determine the geometry of the 3D structures and the compositions of the different elements (wire, active region, collar for example) of these 3D structures, one can carry out analyses of Scanning Electron Microscopy (SEM) or Transmission Electron Microscopy (TEM or TEM for the English acronym for "Transmission Electron Microscopy") or even Scanning Transmission Electron Microscopy (STEM) (English acronym for "Scanning Transmission Electron Microscopy").

[0053] TEM or STEM are particularly well suited to the observation and identification of quantum wells – whose thickness is generally on the order of a few nanometers – in the active region. Various techniques, listed below in a non-exhaustive manner, can be implemented: dark-field and bright-field imaging, weak beam imaging, and high-angle annular dark field (HAADF) diffraction.

[0054] The chemical compositions of the different elements can be determined using the well-known EDX or X-EDS method, an acronym for "energy dispersive x-ray spectroscopy" which means "energy dispersive analysis of X-ray photons".

[0055] This method is well suited for analyzing the composition of small optoelectronic devices such as 3D emitting structures. It can be implemented on metallurgical sections within a Scanning Electron Microscope (SEM) or on thin sections within a Transmission Electron Microscope (TEM).

[0056] The optical properties of the different elements, and in particular the principal emission wavelengths of the axial emitting nanowires based on GaN and / or the active regions based on InGaN, can be determined by spectroscopy.

[0057] Cathodoluminescence (CL) and photoluminescence (PL) spectroscopies are well suited to optically characterize the 3D structures described in the present invention.

[0058] A coordinate system, preferably orthonormal, comprising the x, y, z axes is shown in the attached figures.

[0059] The terms "approximately," "about," and "in the order of" mean, when referring to a value, "to the nearest 10%," preferably "to the nearest 5%," of that value, or, when referring to an angular orientation, "to the nearest 10°," preferably "to the nearest 5°," of that orientation. Thus, a direction substantially normal to a plane means a direction having an angle of 90+10°, preferably 90+5°, with respect to the plane.

[0060] The optoelectronic device 1 according to the present invention will now be described in more detail with reference to the figures.

[0061] As illustrated in Figures 2A and 2B, the device 1 according to the invention comprises a plurality of elementary photonic crystals, and at a minimum a first elementary photonic crystal 100 and a second elementary photonic crystal 200. It is understood, however, that it may comprise more. By way of example, [Fig. 2A] illustrates a set of four elementary photonic crystals 100, 200, 300, 400 and [Fig. 2B] a set of sixteen elementary photonic crystals 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600.

[0062] The elementary photonic crystals are juxtaposed to each other in a principal XY plane. In particular, the first elementary photonic crystal 100 and the second elementary photonic crystal 200 are preferably adjacent.

[0063] The elementary photonic crystals are each formed of a plurality of nanowires. In particular: • the first elementary photonic crystal 100 comprises a plurality of nanowires designated as first nanowires 101, • the second elementary photonic crystal 200 comprises a plurality of nanowires designated second nanowires 201.

[0064] In the example of [Fig.2A], we also have: • the third elementary photonic crystal 300 comprises a plurality of nanowires designated third nanowires 301, • the fourth elementary photonic crystal 400 comprises a plurality of nanowires designated fourth nanowires 401.

[0065] Nanowires 101, 201, 301, 401 are typically based on a semiconductor material such as GaN.

[0066] As illustrated in [Fig. 2C], the nanowires 101, 201, 301, 401 typically extend from a substrate 2 on which they have been conventionally fabricated. The substrate 2 can be in the form of a stack comprising, along the longitudinal direction Z: a ​​support 21, a nucleation layer 22, and a masking layer 23. The support 21 can be made of sapphire, in particular, to limit lattice parameter mismatch with GaN, or of silicon to reduce costs and for technological compatibility reasons. In the latter case, it can be in the form of a wafer with a diameter of 200 mm or 300 mm.

[0067] A filling layer based on one or more filling material(s) can also be formed between the nanowires (not shown in [Fig.2C]).

[0068] The nanowires 101, 201, 301, 401 preferably all have a diameter, measured in projection onto the principal XY plane, less than or equal to the emission wavelength of the device in the effective index of the photonic crystal to which the nanowires belong, preferably less than or equal to this same emission wavelength divided by 2. Each nanowire 101, 201, 301, 401 comprises a region active region 11 is typically electrically connected. The active region 11 of the nanowire is the site of radiative electron-hole pair recombination, resulting in light radiation with a principal wavelength. The active region 11 typically comprises a plurality of quantum wells, for example, formed by emissive layers based on GaN, InN, InGaN, AlGaN, AIN, AlInGaN, GaP, AlGaP, AlInGap, AlGaAs, GaAs, InGaAs, AlIlAs, or a combination of several of these materials.

[0069] Nanowires 101, 201, 301, 401 each form a micro-LED.

[0070] Within the same set 10 of photonic crystals, all the elementary photonic crystals are configured to emit mainly at the same wavelength denoted X. Thus, all the sets of nanowires in the same set 10 are configured to emit mainly at the wavelength X. In the example of [Fig. 2A], the sets of first nanowires 101, second nanowires 201, third nanowires 301 and fourth nanowires 401 are all configured to emit mainly at the same wavelength X.

[0071] In particular: • The first set of nanowires 101 is configured to emit a first elementary light beam exhibiting mainly the wavelength X, • the set of second nanowires 201 emit a first elementary light beam exhibiting mainly the wavelength X.

[0072] Thus, the set 10 of photonic crystals itself emits a light beam whose main wavelength is X.

[0073] The set of photonic crystals can, for example, correspond to a sub-pixel of a display screen pixel. Indeed, within a pixel, each sub-pixel is designed to emit a given color corresponding to a principal wavelength (for example, red, blue, green).

[0074] The present description details the structure and dimensions of a single set 10 of photonic crystals, but it is understood that the optoelectronic device 1 according to the invention may comprise a plurality of sets 10 of photonic crystals. Each set may emit a light beam having a distinct principal wavelength. The device 1 may, in particular, comprise a plurality of pixels, each formed of at least two sets of photonic crystals, preferably three, each emitting at a distinct principal wavelength. Each set will then comprise at least two elementary photonic crystals as described, configured so that the superposition—or addition—of their elementary beams can produce the desired beam for said LED (i.e., for the sub-pixel).

[0075] The various elementary photonic crystals 100, 200, 300, 400 are juxtaposed to form an assembly 10. Preferably, the elementary photonic crystals 100, 200, 300, 400 are in contact with each other. In particular, the first elementary photonic crystal 100 and the second elementary photonic crystal 200 are preferably in contact. By "contact between two photonic crystals" is meant the contact at the substrate level between the implantation zones defining the boundaries in the principal XY plane of each of the elementary photonic crystals. There is typically no physical contact between the nanowires 101, 201, 301, 401 forming the various photonic crystals.

[0076] The elementary photonic crystals 100, 200, 300, 400 are distinguished from one another by at least one optical characteristic resulting for each crystal from its structure.

[0077] Elementary photonic crystals can, for example, be distinguished from one another by the direction in which their nanowires emit the elementary beams. According to this embodiment, within an assembly 10, at least two elementary photonic crystals emit in distinct directions. In particular: • The first elementary light beam, emitted by the set of first nanowires 101 of the first elementary photonic crystal 100, is emitted in a first direction, • The second elementary light beam, emitted by the set of second nanowires 201 of the second elementary photonic crystal 200, is emitted in a second direction.

[0078] In the case where the assembly 10 comprises more than two elementary photonic crystals, it is possible that some crystals emit in the same direction. However, it is preferable to multiply the emission directions. Preferably, all the elementary photonic crystals emit in distinct directions.

[0079] The emission direction of an elementary beam can be identified by two angles, commonly denoted θ and θ, as illustrated in Figures 3A and 3B. θ identifies the orientation of the principal beam direction in the principal XY plane and is typically between 0° and 360°. θ identifies the inclination of the principal beam direction with respect to the third direction Z perpendicular to the principal XY plane. θ is typically between -90° and 90°.

[0080] According to another embodiment that can be implemented separately or in combination with the preceding one, the elementary photonic crystals can be distinguished from one another by the polarization of the beams they emit. According to this embodiment, within an assembly 10, at least two elementary photonic crystals emit beams with distinct polarizations. In particular: • The first elementary light beam, emitted by the set of first nanowires 101 of the first elementary photonic crystal 100, is emitted according to a first polarization, • The second elementary light beam, emitted by the set of second nanowires 201 of the second elementary photonic crystal 200, is emitted according to a second polarization.

[0081] Figures 7A and 7B are band diagrams illustrating how the same photonic crystal can emit according to distinct polarizations. Each of these figures comprises two parts: • a first part, corresponding to negative angles (according to a convention without physical meaning), obtained experimentally by measuring the effective polarization of a beam emitted by a fabricated photonic crystal, and • a second part, corresponding to positive angles, obtained by numerical simulation.

[0082] Comparison of experimental and theoretical results shows a good correlation between the two, which proves in particular that it is possible to carry out upstream sizing work before manufacturing using numerical simulations.

[0083] A band of emission corresponding to a polarization can be identified in [Fig.7A] s of the beam emitted by the photonic crystal, and on [Fig. 7B] an emission band corresponding to a p-polarization. For example, for a wavelength marked by the line with the reference 7a, it is possible to emit an s-polarized beam. For a wavelength marked by the line with the reference 7b, it is possible to emit a p-polarized beam.

[0084] The height of the emission bands of the s and p polarizations can be modulated according to the structure of the photonic crystal. It is thus possible to dimension two distinct photonic crystals so that for a given wavelength, one emits a p-polarized beam, and the other an s-polarized beam.

[0085] In order to modulate the emission direction and / or the polarization of an elementary photonic crystal, it is possible to manipulate several characteristics, alone or in combination. These characteristics include, in particular: • The dimensions of the nanowires of the elementary photonic crystal and in particular their diameter. • The period according to which the nanowires are arranged within the elementary photonic crystal. The period can also be referred to as the "pitch." Several periods can potentially be defined, depending on the type of lattice in which the nanowires are arranged (hexagonal, square, etc.). The / The directions in which the period(s) are measured also depend on the type of network. • The nanowire filling factor within the elementary photonic crystal, which is a function of the period and dimensions of the nanowires. The filling factor can also be referred to as the filling ratio, openness ratio, or density. It is generally between 10 and 90%. • The surface area occupied by the nanowires in the principal XY plane within the elementary photonic crystal. It is notably a function of the period and dimensions of the nanowires. • The refractive indices of the materials used, mainly the index of the nanowire material(s) and that of the filling material(s). • The position of the emission zone (quantum wells) inside the nanowires.

[0086] Thus, the first elementary photonic crystal 100 and the second elementary photonic crystal 200 are distinguished by at least one of the above parameters. This allows the emission of the first and second elementary beams in distinct directions and / or with distinct polarizations.

[0087] For example, in Figures 2A and 2B, the period in which the nanowires are arranged is substantially the same from one elementary photonic crystal to another, but all the elementary photonic crystals have nanowires of distinct diameters. Consequently, the filling factor and the surface area occupied by the nanowires also differ from one elementary photonic crystal to another.

[0088] Figures 4A to 4D illustrate how the photonic properties of different periodic crystals can be modulated by manipulating the characteristics described above. Figures 4A, 4B, and 4C are simulation results obtained for photonic crystals with the same period but different filling factors. These graphs illustrate the intensity of light emission from the photonic crystal as a function of the emission wavelength and the emission angle. Considering an emission wavelength of 550 nm, the following principal emission ranges are observed: • Photonic crystal no. 1, [Fig. 4A]: emission range Ai from approximately 0° to 5°, • Photonic crystal no. 2, [Fig. 4B]: emission range A2 from approximately 16° to 18°, • Photonic crystal no. 3, [Fig.4C]: emission range A3 ranging from approximately 21° to 22°.

[0089] Fig. 4D is the emission diagram corresponding to the results obtained above. The emission intensity peaks at angles of approximately 0°, 18° and 22° are clearly visible, respectively for the photonic crystals of Figures 4A (reference 41), 4B (reference 42) and 4C (reference 43).

[0090] These figures illustrate the possibility of dimensioning elementary photonic crystals so that they emit elementary beams along distinct principal directions.

[0091] The elementary beams are superimposed to give the beam emitted by the assembly 10. By superimposing distinct elementary beams, it is possible to generate a beam that cannot be generated by a single photonic crystal, and which previously could only be obtained by integrating optical elements to transform the native beam. It is thus possible to size the elementary photonic crystals so as to obtain an overall light beam whose profile approximates a target emission profile, which could also be called a theoretical emission profile.

[0092] The greater the number of elementary photonic crystals emitting in distinct directions, the closer one gets to the target emission profile. This explains the advantage of increasing the number of elementary photonic crystals, and preferably that these all emit in distinct directions.

[0093] Figures 5A to 5C illustrate how such dimensioning can be carried out.

[0094] Figure 5A is a graph showing a set of emission profiles 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, each corresponding to a theoretical photonic crystal that emits light along a distinct principal direction. Specifically, the theoretical photonic crystals shown emit light along principal angles of 0°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°, and 90°, respectively. This set of curves constitutes a nomogram for sizing elementary photonic crystals.

[0095] Curve 60 corresponds to the target emission profile, that is, the profile that we want the LED to emit. By superimposing the target emission profile and the theoretical profiles, it is possible to determine the elementary photonic crystals to be integrated into the LED and the weight to be assigned to each of these elementary crystals within the LED. It is thus possible to establish coefficients to be assigned to each of the photonic crystals (for example: the first elementary photonic crystal should cover approximately twice the surface area of ​​the second elementary photonic crystal, or the first elementary photonic crystal should be supplied with a current twice that of the second elementary photonic crystal). Here, it appears that it is necessary to integrate the LED 10 of the photonic crystals corresponding to curves 50, 51, 52, 53 and 54. It also appears that the elementary photonic crystal of curve 54 should be about twice as extensive as the elementary photonic crystal of curve 51.

[0096] The graph in [Fig. 5A] has, for example, allowed us to establish the following coefficients to be assigned to each of the elementary photonic crystals: [Tables 1] Main direction of crystal emission Coefficient 0° 1 10° 1.02 20° 1.18 30° 1.49 40° 2.27 50° 0 60° 0 70° 0 80° 0 90° 0

[0097] The determined coefficients are then used in the fabrication of the photonic crystals. [Fig. 5B] shows the areas 50', 51', 52', 53', 54' assigned to each of the elementary photonic crystals of the curves 50, 51, 52, 53, 54. The relative areas of each of these areas follow the coefficients in Table 1.

[0098] An LED was simulated following the sizing protocol described above, and the emission profile 70 of the light beam emitted by this diode was compared to the target emission profile 60 (see [Fig. 5C]). It can be observed that the experimental emission profile closely approximates the target emission profile 60.

[0099] Fig. 5B illustrates areas assigned to the different elementary photonic crystals arranged concentrically, but it is understood that these areas could very well be juxtaposed, as in Figures 2A and 2B.

[0100] In the example shown above, the dimensioning was carried out on the basis of ten photonic crystals whose respective principal emission directions ranged in 10° increments. It is understood that more or fewer photonic crystals can be used, that the spacing between principal directions can be different (for example, in 5° increments), and that this spacing is not necessarily regular. For example, it may be advantageous to use several photonic crystals exhibiting main emission directions close together within a range of the emission profile that we want to be particularly well defined.

[0101] The paragraphs above describe assigning different weights to the photonic crystals by giving them different surface areas on the substrate, but it is also possible to assign them different weights by varying their respective power supplies. It is thus possible to supply the different elementary photonic crystals with a different current. Several embodiments are conceivable: • individually controlling the supply current of each of the elementary photonic crystals, which would allow total and dynamic control of the emission pattern (this example is similar to the embodiment described below for the independent electrical control of the photonic crystals), • define an electronic regulation circuit (e.g., current divider bridge) which allows, from a single current source, to power the elementary photonic crystals with predefined current ratios and thus obtain the desired emission diagram.

[0102] Several embodiments can therefore be implemented to give distinct weights to the different photonic crystals present.

[0103] According to an advantageous embodiment of the invention, at least some of the elementary photonic crystals of the same assembly 10 are electrically powered independently. By powering only some of the elementary photonic crystals, an emission profile of the assembly 10 is obtained that is distinct from that obtained if all the crystals were powered. Thus, it is possible to control the overall polarization and emission profile of the assembly 10 during its use, that is, even after the fabrication of the elementary photonic crystals.

[0104] In this embodiment, the light emission profile and the polarization of the assembly 10 can therefore be described as dynamic.

[0105] This embodiment has several particularly advantageous applications. First, it is possible to implement this embodiment to allow switching from a public to a private viewing mode of a computer screen. Figure

[0105] illustrates examples of emission profiles that can be attributed to each of these viewing modes. As illustrated, a public viewing mode typically has a wide emission profile (profile with reference numeral 81): the screen can be viewed over a large angular range. To enter this viewing mode, it is possible to electrically power a plurality of elementary photonic crystals, the superposition or addition of whose elementary light beams will produce an emission profile of this type. Conversely, a private viewing mode has a narrow emission profile (profile (Reference 82): it is only possible to see what the screen displays by positioning oneself directly in front of the screen, that is, by observing the screen from a direction perpendicular to it. To achieve this viewing mode, it is possible to feed a small number of elementary photonic crystals, typically a single elementary photonic crystal. This will produce a profile with a reduced angular range of intense emission.

[0106] This same application can be obtained by exploiting different emission polarizations: the content of the public mode is emitted with a p polarization, and the content of the private mode with an s polarization. A polarizing filter is placed in front of the screen to switch from the public mode to the private mode.

[0107] Preferably, we play on both the directivity and the polarization: for example, the content of the private mode can be emitted according to a very directive profile, in s polarization, and the content of the public mode according to a broader, even Lambertian, profile, in p polarization.

[0108] In this first example (public mode / private mode), the two emission profiles are used successively. It is also possible to use two emission profiles simultaneously. A second example concerns the simultaneous display of two images or videos on the same screen, in different directions. Figures 6B and 6C illustrate examples of emission profiles that can be assigned to the display of different content (image, video). In [Fig. 6B], each piece of content is considered to be emitted by a single photonic crystal (see profiles 91, 92, showing a reduced angular aperture). In [Fig. 6C], each piece of content is considered to be emitted by a plurality of photonic crystals (see profiles 91', 92', showing a larger angular aperture, characteristic of the superposition of several elementary photonic crystals).In both cases, the emission profiles of the different content do not overlap, or only very slightly.

[0109] By broadcasting the two streams in different directions, two users can use the same device to watch two different streams. For example, the same display screen can be used to watch two different streams from two different viewing positions. More than two streams can, of course, be broadcast simultaneously.

[0110] This same application can be achieved by exploiting different emission polarizations: the first content (image, video) is emitted with p-polarization, and the second content with s-polarization. Each user wears glasses, each polarized in the same way on both eyes. In this way, each user views different content.

[0111] Another application of this example is that of glasses-free three-dimensional (3D) display. 3D display can be rendered by projecting two images in two different directions.

[0112] In the preceding example, the profiles are typically static, meaning that content is broadcast according to the same emission profile throughout the observation period (for example, throughout the films). However, it is possible to broadcast content according to a variable emission profile. For example, an image or video can be broadcast so that it is visible from different viewing positions over time. This is possible by successively feeding elementary photonic crystals with distinct principal emission directions. This principle can be implemented for several pieces of content simultaneously. An advantageous application is, for example, an advertising screen displaying an advertisement whose display direction follows the movement of a pedestrian, with the possibility of broadcasting an advertisement to each pedestrian in the vicinity of the advertising screen.

[0113] It is also possible to exploit the emission with different polarizations in the field of 3D televisions viewed with glasses. To do this, it is possible to emit the image corresponding to the right eye with s-polarization, and the image corresponding to the left eye with p-polarization (or vice versa). The glasses used will present different polarizers in front of each eye, allowing the user to view the image in 3D.

[0114] Modules controlling the power supply to the nanowires of the different photonic crystals will be configured according to the intended applications. By integrating separate electrical connection elements for each elementary photonic crystal, the range of display possibilities based on the present invention is very broad.

[0115] In view of the different embodiments described above, it appears that the invention offers an effective solution to enable the emission of a light beam with a particular emission profile, depending on the applications intended.

[0116] The invention is not limited to the embodiments previously described and extends to all embodiments covered by the invention.

Claims

Demands

1. An optoelectronic device (1) comprising an assembly (10) of photonic crystals (100, 200, 300, 400) for emitting a light beam having predominantly a wavelength of X, the assembly of photonic crystals (100, 200, 300, 400) comprising at least, juxtaposed in a principal (XY) plane: • a first elementary photonic crystal (100) comprising an assembly of first nanowires (101) and configured to be able to emit a first elementary light beam having predominantly a wavelength of X, • a second elementary photonic crystal (200) comprising an assembly of second nanowires (201) and configured to be able to emit a second elementary light beam having predominantly a wavelength of X, the first elementary photonic crystal (100) and the second elementary photonic crystal (200) having distinct structures,in order to impart to the first elementary light beam and the second elementary light beam at least one distinct optical characteristic, the light beam emitted by the set (10) of photonic crystals that can be formed by the first elementary light beam and / or the second elementary light beam.

2. Optoelectronic device (1) according to the preceding claim in which the first elementary photonic crystal (100) has a first nanowire filling factor (101), denoted FH and the second elementary photonic crystal (200) has a second nanowire filling factor (201), denoted F2, with Fi^F2.

3. Optoelectronic device (1) according to any one of the preceding claims wherein the first nanowires (101) have first diameters having a value substantially equal to a first target diameter di and the second nanowires (201) have second diameters having a value substantially equal to a second target diameter d2, with di^d2.

4. Optoelectronic device (1) according to any one of the preceding claims wherein the first nanowires (101) are arranged within the first elementary photonic crystal (100) according to a first period pi and the second nanowires (201) are arranged within the second elementary photonic crystal (200) according to a second period p2, with pi^p2.

5. An optoelectronic device (1) according to any one of the preceding claims, wherein the first photonic crystal (10) has a first effective index neffi and the second photonic crystal (200) has a second effective index neff 2, with neffl^neff 2-

6. Optoelectronic device (1) according to any one of the preceding claims wherein: • the first elementary photonic crystal (100) is configured so that the first elementary light beam is directed mainly along a first direction, • the second elementary photonic crystal (200) is configured so that the second elementary light beam is directed mainly along a second direction distinct from the first direction.

7. Optoelectronic device (1) according to any one of the preceding claims wherein: • the first elementary photonic crystal (100) is configured so that the first elementary light beam has a first polarization, • the second elementary photonic crystal (200) is configured so that the second elementary light beam has a second polarization distinct from the first polarization.

8. Optoelectronic device (1) according to any one of the preceding claims wherein the first nanowires (101) and the second nanowires (201) are based on the same material.

9. An optoelectronic device (1) according to any one of the preceding claims, wherein the first nanowires (101) and the second nanowires (201) are light-emitting diodes and each comprise an active emitting region (11), the regions active (11) of the first nanowires (101) and of the second nanowires (201) being configured to emit at the X wavelength.

10. Optoelectronic device (1) according to the preceding claim in which, within each nanowire (101, 201), the emitting active region (11) is substantially transverse to said nanowire (101, 201), and is preferably located at a non-zero height within said nanowire (101, 201), the height within the nanowire (101, 201) being considered along a longitudinal direction (Z) perpendicular to the principal plane (XY).

11. Optoelectronic device (1) according to any one of the preceding claims wherein the set (10) of photonic crystals (100, 200, 300, 400) further comprises a third elementary photonic crystal (300) comprising a set of third nanowires (301) and configured to emit a third elementary light beam having mainly the wavelength X, the third elementary photonic crystal (300) having a structure distinct from that of the first elementary photonic crystal (100) and from that of the second elementary photonic crystal (200), so as to impart to the third elementary light beam at least one optical characteristic distinct from the first and second elementary light beams.

12. Optoelectronic device (1) according to the preceding claim in which the third photonic crystal (300) is configured so that the third elementary light beam is directed mainly in a third direction, distinct from the first and second directions.

13. Optoelectronic device (1) according to claim 6 alone or in combination with any of the preceding claims wherein the superposition of all the elementary light beams gives a target emission profile.

14. Optoelectronic device (1) according to the preceding claim in which the target light beam makes it possible to obtain substantially uniform illumination over a given angular range.

15. Optoelectronic device (1) according to any one of the preceding claims wherein at least two of the elementary photonic crystals (100, 200, 300, 400) are electrically powered independently.

16. Lighting system comprising the optoelectronic device (1) according to any one of the preceding claims, the lighting system being taken from: an urban lighting system, an automotive lighting system, an aeronautical lighting system.

17. A method for dimensioning the optoelectronic device (1) according to any one of claims 1 to 15 comprising: • providing information on a theoretical emission intensity of at least a first theoretical photonic crystal and a second theoretical photonic crystal as a function of an emission direction, • providing a target emission profile, • as a function of said target emission profile and said information, deducing a first coefficient to be applied to a given parameter of the first theoretical photonic crystal and a second coefficient to be applied to said given parameter of the second theoretical photonic crystal so that the superposition of a first theoretical elementary light beam emitted by said first theoretical photonic crystal and a second theoretical elementary light beam emitted by said second theoretical photonic crystal approximates the target emission profile,The given parameter being taken from among the following parameters: i. a surface area in the principal (XY) plane, ii. a theoretical power supply per photonic crystal, • A power supply ratio between the first theoretical photonic crystal and the second theoretical photonic crystal, using the first coefficient and the second coefficient respectively for the dimensioning of the first elementary photonic crystal (100) and the second elementary photonic crystal (200).

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