Diffusion structure of the light source

Abstract

The present invention relates to a diffuser (3) opposite to a light source (1), which comprises a transmission layer (10) and a diffusing layer (22, 23) that scatters the light emitted by the light source. The diffuser is characterized in that the diffusing layer comprises a plurality of metal structures (200, 200a, 200b) called metal nanostructures, the size of which is smaller than the wavelength of the emitted light; the metal nanostructures have various sizes and are distributed in the diffusing layer such that the distance between adjacent metal nanostructures varies and is preferably smaller than the wavelength of the emitted light. The diffuser (3) according to the present invention enables the optimization of the scattering of the light emitted by the light source (preferably a point light source). The present invention also relates to a method for manufacturing such a diffuser, and a display system comprising such a diffuser.

Description

Technical Field

[0001] The present invention relates to the field of optics. Particularly advantageous applications have been found in improving the scattering rate of pixelated light sources such as light emitting diodes (LEDs). Background Art

[0002] A light source can be an extended light source or a point light source.

[0003] A point light source, also known as a pixelated light source, can be used in visualization or display systems. In particular, multiple adjacent point light sources can form the pixels of a screen. Such a point light source can have a size on the order of several tens of micrometers. Light emitting diodes (LEDs) can advantageously form these point light sources.

[0004] LEDs generally have a relatively small emission angle. It is characterized by strong directivity.

[0005] However, in some applications, a point light source with weak directivity and a large emission angle may be required. This is the case for 3D display screens, for example.

[0006] One solution to reduce the directivity of an LED includes adding a diffusion structure to the LED so that the light emitted by the LED is diffused in all directions.

[0007] In a known manner, such a diffusion structure can be in the form of a dielectric diffusion film including random dielectric corrugations ( Figure 1A ). The pseudo-period and / or size of these corrugations can reach several micrometers, or even several tens of micrometers ( Figure 1A ). In particular, they are larger than the emission wavelength of the LED.

[0008] Therefore, the operation of such a dielectric diffusion film is not directly based on the light scattering phenomenon. As Figure 1B shown, in this case, the dielectric diffusion film produces multiple refractions of light on the surfaces of the corrugations with different inclinations. Therefore, the light is refracted by the diffusion film, which is called a refractive diffusion film, in multiple different directions.

[0009] Through the averaging effect, the statistical refraction phenomenon of this light reproduces the isotropic diffusion phenomenon in all directions. This type of refractive diffusion film is very effective for large light sources.

[0010] However, for pixelated light sources, especially for pixelated light sources with a size less than or equal to 15 μm, this type of refractive diffusion film cannot reproduce the isotropic diffusion phenomenon for each light source.

[0011] Such a pixelated light source arranged opposite to this type of refractive diffusion film is no longer associated with multiple corrugations respectively.

[0012] Therefore, the average effect obtained with an extended light source can no longer be obtained with a point light source. In this case, the light emitted by the point light source is refracted in a limited direction, or even in one direction only. Therefore, the diffusion phenomenon cannot be well reproduced. This refraction is even particularly anisotropic. A point light source, such as an LED forming a pixel on a display screen, still has a strong directivity with respect to this type of refractive diffusion film.

[0013] In this case, the direction of refraction also varies with the pixel. Therefore, for a screen of LEDs that emit light of the same light intensity for all pixels, depending on the viewing direction, a change in the light intensity caused by the refractive diffusion film on the screen can be perceived, which is naturally very strongly undesirable.

[0014] The present invention aims to at least partially overcome some of the above-mentioned drawbacks.

[0015] In particular, the object of the present invention is to provide a diffuser or a diffuser film that enables the optimization of the scattering of light emitted by a light source (preferably a point light source).

[0016] Another object of the present invention is to provide a method for manufacturing such a diffuser.

[0017] Another object of the present invention is to provide a system that includes at least one such diffuser and at least one pixelated light source that cooperate with each other.

[0018] By reading the following description and the drawings, other objects, features, and advantages of the present invention will become apparent. It is understood that other advantages can be combined. Summary of the Invention

[0019] To achieve the above object, one aspect of the present invention relates to a diffuser for receiving light emitted by a visible light source. The diffuser includes a transmissive layer that is transparent to the emitted light and a diffusing layer (couche de diffusion) that is intended to diffuse the light emitted by the light source and is preferably at least partially supported by the transmissive layer.

[0020] Advantageously, the diffusing layer includes a plurality of metal nanostructures. The projection of each metal nanostructure in the main extension plane has a first and a second dimension in a first direction and a second orthogonal direction of the main extension plane, respectively. The first and second dimensions are less than 650 nm.

[0021] These metal nanostructures are distributed within the diffusing layer such that there is a varying separation distance between adjacent metal nanostructures. The dimensions of these metal nanostructures are further determined such that they have various dimensions between the first dimension and the second dimension.

[0022] Thus, the diffuser according to the present invention comprises a plurality of nanostructures, each nanostructure having at least two dimensions less than 650 nm, preferably less than 500 nm, more preferably less than 400 nm. Thus, the first and second dimensions of the nanostructures are less than at least a portion of the wavelength spectrum of visible light. Different from the refractive diffuser described above, such a diffusion phenomenon of the light can be obtained.

[0023] Furthermore, these first and second dimensions are intercepted along two orthogonal axes in the main extension plane. This makes it possible to obtain such a diffusion phenomenon in at least two directions, which, on average, can best cover the observation plane where the observer is located. The relative orthogonal arrangement corresponds to the best possible compromise between two directions. This improves the isotropy of the scattering.

[0024] These nanostructures are made of a metallic material. The refractive index of this metallic material is at least twice that of the transmission layer, which is transparent to the emitted light. Different from the refractive diffuser introduced above, this makes it possible to obtain a significant scattering phenomenon. The diffusion efficiency is improved.

[0025] The nanostructures preferably form a single layer of particles on the transmission layer. Thus, the light incident through this single layer at normal or near-normal incidence is slightly attenuated. Thus, almost all the incident light can be effectively scattered.

[0026] Furthermore, these nanostructures, especially adjacent nanostructures, have varying sizes and spacing distances between them. This makes it possible to prevent the light from scattering in a specific direction through the lattice effect. This improves the isotropy of the scattering. The nanostructures are preferably irregular or disordered.

[0027] Thus, the present invention provides for integrating metallic nanostructures into a diffusing layer that not only diffuses light but also makes such scattering effective and isotropic.

[0028] Improvements made within the scope of the present invention show that the combination of the characteristics of these nanostructures makes it possible to obtain a synergistic effect, thereby optimizing the diffusion, especially for point light sources or pixelated light sources.

[0029] As an alternative solution (although different from the solution adopted in the context of the present invention but also achievable), it consists of a diffuser that includes a transmission layer and a diffusing layer based on dielectric nanostructures, such as Figure 3A shown.

[0030] This alternative solution is not retained in the context of the present invention because it has been determined that dielectric nanostructures impede the effective diffusion of light. The performance of this alternative solution is introduced in detail below through simulation results.

[0031] Thus, the improvements leading to the present invention show that a diffusive layer based on metal nanostructures must be provided.

[0032] Another aspect of the present invention relates to a diffuser for receiving light emitted by a visible light source, the diffuser comprising a transmissive layer transparent to the emitted light and a diffusive layer for diffusing the emitted light. The diffusive layer comprises at least one metal nanostructure, the projection of which in the main extension plane has a first dimension and a second dimension less than 650 nm in a first direction and a second orthogonal direction of the main extension plane, respectively.

[0033] Advantageously, the diffuser further comprises a focusing layer configured to focus the emitted light on at least one metal nanostructure. This increases the angular diffusion profile.

[0034] The following gives advantageous effects related to diffusers according to various aspects of the present invention.

[0035] The present invention also relates to a method of manufacturing a diffuser comprising at least one diffusive layer intended to diffuse light emitted by a visible light source and comprising a plurality of metal nanostructures.

[0036] The process comprises the following steps:

[0037] - providing a support in a transparent material and having a support surface,

[0038] - forming a plurality of metal nanostructures or at least one metal nanostructure on the support surface, each metal nanostructure having protrusions in a first and a second orthogonal direction of the main extension plane of the support surface parallel to a first dimension and a second dimension, the first and second dimensions being less than 650 nm.

[0039] The metal nanostructures of the plurality of metal nanostructures are distributed on a carrier such that adjacent metal nanostructures have a varying separation distance between them. The dimensions of these metal nanostructures are further determined such that they have various dimensions between the first dimension and the second dimension.

[0040] The present invention also relates to a system comprising at least one diffuser according to the present invention and a plurality of pixelated light sources arranged side by side with each other. The at least one diffuser is configured to cooperate with the at least one point light source to diffuse the light emitted from the point light source.

[0041] Such a system can advantageously be used in the production of display screens, in particular 3D screens. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments of the present invention with reference to the accompanying drawings.

[0043] Figure 1A is a scanning electron microscope image of a dielectric diffusion film according to the prior art.

[0044] Figure 1B schematically shows in a sectional view Figure 1A the operation of the dielectric diffusion film.

[0045] Figure 2A schematically shows a diffuser including only a transmissive layer.

[0046] Figure 2B shows the electromagnetic field map of light transmitted through Figure 2A the diffuser shown.

[0047] Figure 2C shows the angular diagram of light passing through Figure 2A the diffuser shown.

[0048] Figure 3A schematically shows a diffuser according to an alternative determined during the research and development process of the present invention, which includes a transmissive layer and a diffusive layer based on a disordered dielectric nanostructure.

[0049] Figure 3B shows the electromagnetic field map of light transmitted through Figure 3A the diffuser shown.

[0050] Figure 3C shows the angular diagram of light passing through Figure 3A the diffuser shown.

[0051] Figure 4A schematically shows a diffuser according to an embodiment of the present invention, which includes a transmissive layer and a diffusive layer based on a disordered metal nanostructure.

[0052] Figure 4B shows the mapping of the electromagnetic field obtained by simulating light transmitted through Figure 4A the diffuser.

[0053] Figure 4C shows the angular diagram of light passing through Figure 4A the diffuser shown.

[0054] Figure 5A schematically shows a diffuser including a transmissive layer and a focusing layer.

[0055] Figure 5B shows the electromagnetic field map of light transmitted through Figure 5A the diffuser.

[0056] Figure 5CShows the light obtained through simulation passing through Figure 5A The angular diagram of the diffuser shown.

[0057] Figure 6A Schematically shows a diffuser including a transmissive layer, a focusing layer, and a diffusive layer based on metal nanostructures according to an embodiment of the present invention.

[0058] Figure 6B Shows the light transmission obtained through simulation through Figure 6A The electromagnetic field diagram of the diffuser shown.

[0059] Figure 6C Shows the light obtained through simulation passing through Figure 6A The angular diagram of the diffuser shown.

[0060] Figure 7A Schematically shows a diffuser including a transmissive layer, a focusing layer, a reflective layer, and a diffusive layer based on metal nanostructures according to an embodiment of the present invention.

[0061] Figure 7B Shows the light transmission obtained through simulation through Figure 7A The electromagnetic field diagram of the diffuser.

[0062] Figure 7C Shows the light transmission obtained through simulation through Figure 7A The angular diagram of the diffuser shown.

[0063] Figure 8A Schematically shows a diffuser including a transmissive layer, a focusing layer, a reflective layer, and a diffusive layer based on multiple metal nanostructures according to an embodiment of the present invention.

[0064] Figure 8B Shows the light transmission obtained through simulation through Figure 8A The electromagnetic field diagram of the diffuser.

[0065] Figure 8C Shows the light obtained through simulation passing through Figure 8A The angular diagram of the diffuser shown.

[0066] Figure 9A Schematically shows in cross-section a diffuser according to an embodiment of the present invention, the diffuser including a transmissive layer and a diffusive layer based on multiple metal nanostructures.

[0067] Figure 9B Schematically shows in a top view a diffuser according to Figure 9A The embodiment of.

[0068] Figure 10AA diffuser according to an embodiment of the present invention is schematically shown in cross-section. The diffuser includes a transmissive layer, a focusing layer, and a diffusive layer based on metal nanostructures.

[0069] Figure 10B A diffuser according to another embodiment of the present invention is schematically shown in cross-section. The diffuser includes a transmissive layer, a focusing layer, and a diffusive layer based on metal nanostructures.

[0070] Figures 10C to 10E Schematically shown in a top view are different focusing layers of a diffuser according to Figure 10B an embodiment.

[0071] Figure 11 A diffuser according to an embodiment of the present invention is schematically shown in cross-section. The diffuser includes a transmissive layer, a focusing layer, a reflective layer, and a diffusive layer based on metal nanostructures.

[0072] Figure 12 A diffuser according to an embodiment of the present invention is schematically shown in cross-section. The diffuser includes a transmissive layer, a focusing layer, a reflective layer, and a diffusive layer based on multiple metal nanostructures.

[0073] Figure 13A Schematically shown is a diffuser according to an embodiment of the present invention, which includes a transmissive layer, a focusing layer, a reflective layer, and a diffusive layer based on metal nanostructures, and is irradiated with light having a wavelength λ = 450 nm.

[0074] Figure 13B Shown is the electromagnetic field pattern of light having a wavelength λ = 450 nm transmitted through the Figure 13A diffuser shown.

[0075] Figure 13C Shown is the angular pattern of light having a wavelength λ = 450 nm passing through the Figure 13A diffuser shown.

[0076] Figure 14A Schematically shown is a diffuser according to an embodiment of the present invention, which includes a transmissive layer, a focusing layer, a reflective layer, and a diffusive layer based on metal nanostructures, and is irradiated with light having a wavelength λ = 550 nm.

[0077] Figure 14B Shown is the electromagnetic field pattern of light having a wavelength λ = 550 nm transmitted through the Figure 14A diffuser shown.

[0078] Figure 14C Shown is the electromagnetic field pattern of light having a wavelength λ = 550 nm transmitted through the Figure 14A diffuser shown.

[0079] Figure 15A Schematically shown is a diffuser including a transmissive layer, a focusing layer, a reflective layer, and a diffusive layer based on metal nanostructures according to an embodiment of the present invention, and irradiated with light of wavelength λ = 650 nm.

[0080] Figure 15B Shown is the electromagnetic field map of light with wavelength λ = 650 nm transmitted through the Figure 15A diffuser shown.

[0081] Figure 15C Shown is the angular map of light with wavelength λ = 650 nm transmitted through the Figure 15A diffuser shown.

[0082] Figure 16A Schematically shown is a diffuser including a transmissive layer, a focusing layer, a reflective layer, and a diffusive layer based on metal nanostructures according to an embodiment of the present invention with an ideal structure, and irradiated in an ideal manner.

[0083] Figure 16B Schematically shown is a diffuser according to an embodiment of the present invention with a non-ideal configuration, which includes a transmissive layer, a focusing layer, a reflective layer, and a diffusive layer based on metal nanostructures, and is irradiated ideally.

[0084] Figure 16C Shown is the angular map of light transmitted through the Figure 16B diffuser shown, where the distance between the reflective layer and the diffusive layer is d = 3 μm, and the distance between the reflective layer and the focusing layer is H = 12 μm.

[0085] Figure 16D Shown is the angular map of light transmitted through the Figure 16B diffuser shown, where the distance between the reflective layer and the diffusive layer is d = 7 μm, and the distance between the reflective layer and the focusing layer is H = 8 μm.

[0086] Figure 17A Schematically shown is a diffuser according to an embodiment of the present invention with an ideal structure, which includes a transmissive layer, a focusing layer, a reflective layer, and a diffusive layer based on metal nanostructures, and is irradiated in an ideal manner.

[0087] Figure 17B Schematically shown is a diffuser according to an embodiment of the present invention with an ideal structure, which includes a transmissive layer, a focusing layer, a reflective layer, and a diffusive layer based on metal nanostructures. And irradiated in a non-ideal manner.

[0088] Figure 17C Shown is the light transmitted through obtained by simulation Figure 17BAngular diagram of the diffuser shown, where the distance between the reflective layer and the diffusive layer is d = 3 μm, and the distance between the reflective layer and the focusing layer is H = 12 μm.

[0089] Figure 17D Shows the light transmission obtained through simulation through Figure 17B Angular diagram of the diffuser shown, where the distance d between the reflective layer and the diffusive layer is 7 μm, and the distance H between the reflective layer and the focusing layer is 8 μm.

[0090] Figures 18A to 18D Schematically shows the steps of a method for manufacturing a diffuser according to an embodiment of the present invention.

[0091] Figures 19A to 19C Schematically shows the steps of a method for manufacturing a diffuser according to an embodiment of the present invention, the diffuser including a diffusive layer based on metal nanostructures, a transmissive layer, and a focusing layer including microlenses.

[0092] Figures 20A to 20G Schematically shows the steps of forming microlenses for a diffuser according to an embodiment of the present invention, the diffuser including a diffusive layer based on a plurality of metal nanostructures, a transmissive layer, a reflective layer, and a focusing layer including microlenses.

[0093] Figures 21A to 21F Schematically shows the steps of a method for manufacturing a diffuser according to an embodiment of the present invention, the diffuser including a diffusive layer based on a plurality of metal nanostructures, a transmissive layer, a reflective layer, and a focusing layer including microlenses.

[0094] Figures 22A to 22E Schematically shows the steps of forming a Fresnel lens for a diffuser according to an embodiment of the present invention, the diffuser including a diffusive layer based on a plurality of metal nanostructures, a transmissive layer, a reflective layer, and a focusing layer including a Fresnel lens.

[0095] Figure 23 Shows the arrangement of a plurality of diffusers according to an embodiment of the present invention.

[0096] Figure 24 Shows a system according to an embodiment of the present invention, the system including a plurality of diffusers arranged with a plurality of LEDs.

[0097] Figure 25 Shows a system configured for a 3D display, the 3D display including a high-resolution screen associated with a microlens array.

[0098] Figure 26 Shows a system configured for a 3D display, the 3D display including a plurality of micro-screens associated with a plurality of projection systems and at least one diffuser and a microlens array.

[0099] Figure 27 shows a Figure 26 projection system of the 3D display system shown.

[0100] Figure 28 shows Figure 26 the dimensions of a part of the 3D display system shown.

[0101] Figure 29 shows a Figure 26 3D display system including a plurality of diffusers according to an embodiment of the present invention.

[0102] The accompanying drawings are given by way of example and do not limit the present invention. They constitute schematic diagrams of the principles intended to facilitate the understanding of the present invention and are not necessarily within the scope of actual applications. In particular, the dimensions and structures of the different layers of the diffuser do not represent the actual. For the sake of clarity, it is not necessary to add the same set of reference numerals applicable to the drawings of the same series to all the drawings of that series. It should be understood that in order to identify the elements of the drawings in a particular series, the reader may refer to other drawings in that series. A series of drawings typically includes drawings with the same numerical markings associated with alphabetical characters. Detailed Description

[0103] Before beginning a detailed description of the embodiments of the present invention, it should be recalled that the present invention particularly includes the following optional features, which may be used in combination or selectively. Unless there is any incompatibility, it should be understood that according to the various aspects of the diffuser, the manufacturing process and the display system (plus necessary modifications) include the following features:

[0104] According to one example, adjacent metal nanostructures are spaced at different distances from each other.

[0105] According to one example, at least some adjacent metal nanostructures have a separation distance of less than 500 nm, and at least some of the other adjacent metal nanostructures have a separation distance of greater than 600 nm.

[0106] According to one example, the separation distance between two adjacent metal nanostructures varies by up to 200%, preferably up to 300%, and preferably up to 500% within the diffuser layer.

[0107] In one example, the spacing distance between adjacent metal nanostructures is less than the wavelength of interest of the emitted light.

[0108] According to one example, the first and second dimensions of the metal nanostructures are between 100 nm and 500 nm.

[0109] According to one example, for the same nanostructure, the first dimension and the second dimension of the metal nanostructure are substantially equal to each other.

[0110] According to one example, for at least some of the plurality of metal nanostructures, the various dimensions taken from the first and second dimensions are less than 250 nm, and for at least some other metal nanostructures of the plurality of nanostructures, the various dimensions of the first and second dimensions are both greater than 350 nm.

[0111] In one example, within the diffusive layer, the variation in the various dimensions with respect to the first and second dimensions is up to 200%, preferably up to 300%, and preferably up to 500%.

[0112] According to one example, within the diffusive layer, both the first dimension and the second dimension vary. Alternatively, within the diffusive layer, only the first dimension or only the second dimension varies.

[0113] According to one example, the first dimension varies proportionally to the second dimension.

[0114] According to one example, in the projection in the main extension plane, the metal nanostructures all have surfaces, and the surfaces of the metal nanostructures are not equal or at least not all equal. The variation in the surface of the metal nanostructures within the diffusive layer can be such that Smax≥x*Smin, where Smax and Smin are the maximum and minimum surfaces within the diffusive layer respectively, and x = 2, preferably x = 3, and most preferably x = 5.

[0115] According to one example, the diffuser further includes a focusing layer configured to focus the emitted light onto at least one of the plurality of metal nanostructures. The focusing layer is preferably located on the transmissive layer, on the side opposite to the side of the transmissive layer that supports the diffusive layer.

[0116] In one example, the focusing layer includes one of a refractive microlens and a Fresnel lens.

[0117] According to one example, the diffuser further includes a reflective layer located within the transmission layer, between the diffusive layer and the focusing layer, the reflective layer having at least one opening facing the metal nanostructures, and the emitted light is focused onto the metal nanostructures. The reflective layer is preferably parallel to the diffusive layer.

[0118] According to one example, the opening presents a main extension dimension W in the projection in the main extension plane, such that: W≥(D.d) / (H + d), where D is the main extension dimension of the diffuser, d is the distance between the diffusive layer and the reflective layer, and H is the distance between the reflective layer and the focusing layer.

[0119] According to one example, the diffuser has a projection between 5 μm and 30 μm in the main extension plane of the main extension dimension D.

[0120] According to one example, the refractive index of the metal nanostructure is at least twice the refractive index of the transmissive layer.

[0121] According to one example, the thickness h of the diffusive layer in a direction perpendicular to the main extension plane is between 100 nm and 500 nm.

[0122] According to one example, at least a part of the metal nanostructure is made of at least one metal selected from aluminum, tungsten, copper, silver, and gold.

[0123] According to one example, the display system includes:

[0124] - A screen, preferably a very high-resolution screen, including a plurality of micro-screens, each micro-screen containing a plurality of pixels,

[0125] - A plurality of projection systems associated with the plurality of micro-screens,

[0126] - A plurality of diffusers, each diffuser associated with at least one pixel of the plurality of pixels of the micro-screen, and

[0127] - A microlens matrix associated with the plurality of diffusers.

[0128] According to one example, the method further includes the steps of: depositing a material transparent to the emitted light on the plurality of metal nanostructures and surrounding the metal nanostructures. According to one example, the method further includes a step of planarizing the plurality of metal nanostructures, the step being configured to form a composite diffusive layer including the material transparent to the emitted light surrounding the metal nanostructures such that the composite diffusive layer has a planarized surface.

[0129] According to one example, the method further includes forming a transmissive layer on the planarized surface, the transmissive layer having a transmissive surface opposite to and facing the light source with respect to the planarized surface.

[0130] According to one example, the method further includes forming a focusing layer extending on the transmissive surface, the focusing layer focusing the emitted light on at least one of the plurality of metal nanostructures.

[0131] According to one example, the focusing layer is formed by refractive microlenses, in particular refractive microlenses made of a material transparent to the emitted light.

[0132] According to one example, the focusing layer is formed by a Fresnel lens.

[0133] According to one example, the method further includes forming a reflective layer within the transmissive layer, between the diffusive layer and the focusing layer, the reflective layer having at least one opening facing at least one metal nanostructure, and the emitted light is focused thereon by the focusing layer. The reflective layer is preferably parallel to the diffusive layer.

[0134] In the present patent application, reference is made to the main extension plane. The main extension plane is the xy plane of the orthogonal coordinate system shown in the figure.

[0135] In the present patent application, the preferred thickness of the layer and the preferred height of the device will be discussed. The thickness and height are taken in the z direction perpendicular to the main extension plane.

[0136] The term "nanostructure" particularly refers to a solid whose at least one dimension is nanoscale, i.e., much less than 1 μm. In the context of the present invention, the projections of one or more nanostructures on the main extension plane respectively have two nanosizes, less than a few hundred nanometers or less than the wavelength of the emitted light of interest.

[0137] The term "size" of a nanostructure should be understood as:

[0138] - The maximum distance between two points of the nanostructure obtained in a plane parallel to the main extension plane, called the critical dimension,

[0139] - The projected area of the nanostructure on the main extension plane,

[0140] - Or the volume of the nanostructure.

[0141] Thus, the size of the nanostructure corresponds to one or more dimensions representing the nanostructure. The size of a spherical nanostructure can, for example, correspond to the diameter of the sphere.

[0142] The term "separation distance" between two adjacent nanostructures should be understood to mean the minimum projected distance by which two adjacent nanostructures are separated in the main extension plane xy. Two adjacent nanostructures 200 i and 200 j The separation distance by which they are separated is denoted as d ij , where i and j are natural numbers.

[0143] In the context of the present invention, the nanostructures have various sizes and / or distances between them. This means that the sizes of these nanostructures and / or the distances between these nanostructures are not all equal. For example, there needs to be at least a 15% standard deviation in the sizes of these nanostructures and / or the distances between these nanostructures.

[0144] In the present invention, the diffuser is particularly suitable for being arranged together with a point light source, in particular an LED.

[0145] A point light source refers to a light source whose size projected on the main extension plane is less than several tens of micrometers, especially less than 30 micrometers, and preferably less than or equal to 15 micrometers.

[0146] However, the present invention can be more widely applied to different light sources, such as extended light sources.

[0147] The point light source or surface light source can be multi - colored or monochromatic. The light emitted by these light sources is preferably visible light.

[0148] In the case of a multi - colored light source, the wavelength of interest of the light emitted by the light source may be the minimum wavelength emitted by the light source. In the case where certain light rays are intentionally or unintentionally filtered out by an intermediate element (such as a filter or even the transmission layer itself) between the light source and the diffusing layer, it can optionally be the minimum wavelength emitted by the light source and received by the diffusing layer. It can also be understood to refer to a wavelength range of several tens of nanometers, such as approximately 100 nm or less.

[0149] In the case of a monochromatic or quasi - monochromatic light source, the wavelength of interest is the single wavelength emitted by the light source or the wavelength mainly emitted by the light source.

[0150] Unless otherwise explicitly stated, in the context of the present invention, the relative arrangement of the third layer inserted between the first layer and the second layer does not necessarily mean that the layers are in direct contact with each other, but may mean that the third layer is either in direct contact with the first and second layers or is separated from them by at least one other layer or at least one other element.

[0151] The formation steps of different layers and regions are understood in a broad sense: they can be carried out in several sub - steps that are not necessarily strictly continuous.

[0152] A substrate, layer, or device “based on” material M refers to a substrate, layer, or device that includes only the material M or only the material M and may include other materials (such as alloying elements, impurities, or doping elements). Thus, a diffusing layer based on metal nanostructures can, for example, include nanostructures made of tungsten (W) or nanostructures made of tungsten (W) and aluminum (Al), or also nanostructures made of tungsten (W) nanostructures and a transparent encapsulating material.

[0153] A layer or material “transparent to the emitted light or the wavelength of interest” should be understood to mean a layer or material that allows at least 90% of the luminous intensity of light having the wavelength of interest to pass through.

[0154] The terms “substantially”, “about”, “approximately” mean “within 10%”, or when referring to an angular orientation, mean “within 10°”. Thus, a direction substantially orthogonal to a plane refers to a direction at an angle of 90 ± 10° with respect to the plane.

[0155] To determine the geometry of the diffuser and the composition of the different layers, optical microscopy or scanning electron microscopy (SEM) analysis can be performed.

[0156] Well-known EDX or X-EDS methods can be used to determine the chemical composition of the different layers or regions, which is an acronym for "Energy Dispersive X-ray Spectrometer" and means "Energy Dispersive Analysis of X-photons".

[0157] This method is very suitable for analyzing the composition of small-sized structures (such as metal nanostructures). It can be implemented on metallurgical cuts of a scanning electron microscope (SEM).

[0158] As described in the present invention, these techniques make it possible to specifically determine whether the diffuser includes a diffusing layer that includes at least one metal nanostructure or a plurality of metal structures.

[0159] The diffuser according to various aspects of the present invention is intended to diffuse visible light emitted by a light source (preferably a point light source). Depending on the situation, the light emitted by this light source can in particular be transmitted, focused, diffused, backscattered, reflected or extracted by the diffuser. Before detailing the structural features and manufacturing of the diffuser, certain functional aspects of the diffuser are illustrated below by the results obtained from simulations of various embodiments of the diffuser.

[0160] Figures 2A - 2C , Figures 3A - 3C and Figures 4A - 4C Shows the simulation results obtained by the method of finite-difference time-domain (FDTD, abbreviated as "finite-difference time-domain") calculations, aiming to determine which is a part of the transmitted light (specular transmission at Φ = 0°) and a part of the scattered light (non-specular transmission for Φ ≠ 0°) received by a diffuser from a light source 1. For each simulation, the diffuser and the light source 1 are shown in the cross-section of Figure xA (x = 2...4). The electromagnetic field map of the diffuser is shown in Figure xB (x = 2...4). The angular diagrams of these diffusers are shown in Figure xC (x = 2...4).

[0161] Taking Figures 2A - 2C as a reference, the visible light transmission ( Figure 2A ) through a diffuser that only includes a transmission layer 10 ( Figure 2B ) is shown. The angular diagram shows that the light from the light source 1 is transmitted only in a specular manner ( Figure 2C ) in this case. Therefore, the "diffuser" shown here is strictly speaking not a device for diffusing the light emitted by the light source. This case is presented to provide a first reference that can be used to compare the diffusion performance of different embodiments of the diffusers introduced below.

[0162] Figures 3A - 3C Shows the visible light transmission through the diffuser (Figure 3B ),the diffuser includes a transmissive layer 10 and a diffusive layer 21 based on a disordered dielectric nanostructure Figure 3A ). The angular diagram shows that the light emitted by the light source 1 is mainly transmitted in a specular manner in this case. The proportion of scattered light is low Figure 3C ).

[0163] Therefore, such a diffuser is a solution capable of diffusing the light emitted by a point light source. However, this solution cannot effectively scatter light and is not the subject of the present invention.

[0164] Figures 4A - 4C The transmission of visible light through a diffuser according to the present invention is shown Figure 4B ), the diffuser includes a transmissive layer 10 and a diffusive layer 22 based on a disordered metal nanostructure Figure 4A ). It can be seen from the angular diagram that in this case, compared with the previous diffuser, the proportion of scattered light has increased significantly Figure 4C ).

[0165] Metal nanostructures allow the scattering of visible light, which is much more effective than dielectric nanostructures. This is especially due to the contrast in refractive index between the metal nanostructures and the transmissive layer, which is usually based on a transparent dielectric material.

[0166] Preferably but optionally, the diffuser further includes a focusing layer configured to focus the emitted light on the metal nanostructures of a plurality of metal nanostructures. This increases the proportion of light scattered by the diffuser. Therefore, the light emitted by the light source, especially a point light source, is focused at the level of the nanostructures (preferably a single nanostructure). The focusing causes the divergence of the light outside the nanostructures. This divergence increases the proportion of light transmitted in a non-specular manner.

[0167] Figures 5A - 5C , Figures 6A - 6C , Figures 7A - 7C and Figures 8A - 8C shows other results of the simulations performed by FDTD for different embodiments of a diffuser including a focusing layer. For each simulation, the diffuser and the light source 1 are shown in the cross-section of FIG. xA (x = 5... 8). The electromagnetic field diagram of the diffuser is shown in FIG. xB (x = 5... 8). The angular diagrams of these diffusers are shown in FIG. xC (x = 5... 8).

[0168] Figures 5A - 5C The light transmission through the diffuser is shown Figure 5B ), the diffuser includes a transmissive layer 10 and a focusing layer 30 Figure 5A ). It can be seen from the angular diagram Figure 5C ) that, compared with Figures 2A - 2CCompared with the reference situation shown, in this case the portion of the light transmitted in a non-specular manner is greatly increased. However, strictly speaking, the "diffuser" shown here is not a device that enables the light emitted by the light source 1 to be diffused. This situation is provided in a way that provides a second reference that can be used to compare the diffusion performance of different diffuser embodiments including a focusing layer, as shown below.

[0169] In the case where the diffuser includes a diffusing layer based on one or more metal nanostructures, the light is focused on only a few nanostructures, or even on a single nanostructure, such that any lattice effects can be avoided, thus facilitating the isotropic diffusion of light.

[0170] According to Figure 6A one possibility shown, the diffusing layer 23 of the diffuser can be based on one or at least one metal nanostructure.

[0171] Figures 6A - 6C The transmission of light ( Figure 6B ) through such a diffuser is shown, which diffuser includes a transmission layer 10, a focusing layer 30, and a diffusing layer 23 ( Figure 6A ) based on metal nanostructures. The angular diagram ( Figure 6C ) shows that, compared with the Figures 4A - 4C situation shown, the portion of the scattered light is increased. The diagram is also symmetric, reflecting the isotropic nature of this diffusion.

[0172] According to one possibility, the diffusing layer of the diffuser can be based on a plurality of metal nanostructures. In this case, after the light is focused, only a few metal nanostructures are effectively illuminated. In this case, the lattice effects are strictly limited or even eliminated.

[0173] Preferably but optionally, the diffuser further includes a reflective layer that is located between the diffusing layer and the focusing layer within the transmission layer, parallel to the diffusing layer and having at least one opening through which the metal nanostructures can be seen, on which the emitted light is focused. This increases the total transmittance of the diffuser.

[0174] The total transmittance of the diffuser corresponds to the portion of the light that an observer can perceive as seeing the light source through the diffuser.

[0175] The diffusion of the metal nanostructures occurs in multiple directions, partly in the same direction as the emitted light (the light that the observer can perceive as transmitted and scattered), and partly in the direction opposite to the emitted light (the backscattered light that the observer cannot perceive).

[0176] The reflective layer advantageously enables a portion of the backscattered light to be reflected in the direction of the observer. Thus, the total transmittance of the diffuser is improved.

[0177] According toFigure 7A A possibility as shown, the diffuser layer 23 of the diffuser including the reflective layer 40 can be based on one or at least one metal nanostructure.

[0178] Figures 7A - 7C The light transmission through such a diffuser is shown ( Figure 7B ), the diffuser including a transmissive layer 10, a focusing layer 30, a reflective layer 40, and a diffuser layer 23 based on metal nanostructures. ( Figure 7A ). The angular diagram shows that, compared with the Figures 6A - 6C previous case as shown, the total transmittance proportional to the integral of the function defining the curve in Figure 7C has increased. Thus, the total transmittance of the diffuser can reach about 50% of the light emitted in the previous case, and can thus be increased to about 70% of the light emitted.

[0179] According to Figure 8A a possibility as shown, the diffuser layer 22 of the diffuser including the reflective layer 40 can be based on multiple metal nanostructures. This advantageously makes it possible to promote the so-called grazing part of the light backscattered by the metal nanostructures at the focus.

[0180] The grazing part of the backscattered light includes light rays whose propagation direction forms an angle with the diffuser layer that is less than the total internal reflection angle of the transmissive layer. Thus, in the absence of singularities at one and / or the other of these interfaces, these rays are trapped within the transmissive layer between the diffuser layer and the reflective layer. The presence of multiple metal nanostructures in the diffuser layer makes it possible to generate singularities, facilitating the extraction of these light rays from the transmissive layer in the direction of the observer. Thus, the total transmittance is increased.

[0181] Figures 8A - 8C The light transmission through the diffuser is shown ( Figure 8B ), the diffuser including a transmissive layer 10, a focusing layer 30, a reflective layer 40, and a diffuser layer 22 based on multiple metal nanostructures ( Figure 8A ). Compared with the Figures 7A to 7C previous case as shown, the total transmittance of this diffuser can be deduced from the angular diagram ( Figure 8C ), and has increased by about 5%.

[0182] Furthermore, the angular diagram of this diffuser is enlarged and the light diffusion is optimized.

[0183] Now, a first embodiment of a diffuser according to the present invention will be described with reference to Figure 9A , 9B.

[0184] According to this first embodiment, the diffuser includes a transmissive layer 10 made of a material that is transparent in at least a part of the visible light wavelength range, in particular at the wavelength of the light to be transmitted.

[0185] The transparent material may be based on silicon oxide, silicon nitride, or sapphire.

[0186] The transmissive layer 10 in particular forms a transparent support for the diffuser layer 22 of the diffuser.

[0187] The diffuser layer 22 includes a plurality of metal nanostructures 200, also referred to as metal structures 200 or particles 200. These metal nanostructures 200 are different from each other and may resemble metal particles. They are spaced apart from each other by a certain distance. Thus, two metal nanostructures 200 are separated by a material different from the metal material that constitutes the metal nanostructures 200. Typically, two metal nanostructures 200 are separated by the material forming the transmissive layer 10.

[0188] The metal nanostructures 200 may have a height h between 100 nm and 500 nm ( Figure 9A ).

[0189] In the projection of these nanostructures 200 onto the main extension plane xy, they have a first and a second dimension L1, L2 that are less than 650 nm. These dimensions, referred to as the main extension dimensions, are in particular less than the wavelength of the light to be diffused that is of interest.

[0190] The nanostructures 200 may have main extension dimensions L1, L2 between 100 nm and 500 nm, preferably between 100 nm and 400 nm. These dimensions L1, L2 are in two directions of the xy plane that are orthogonal to each other, for example the x and y directions. This helps to promote isotropic light scattering.

[0191] In Figure 9B the example shown, for all the metal nanostructures 200, the first dimension L1 extends in a first direction parallel to the x-axis of the reference xyz, and the second dimension L2 extends in a second direction parallel to the y-axis of the xyz coordinate system. This example is not restrictive, and according to another possibility, the first directions along which the first dimension L1 extends are not all parallel to each other, and necessarily, the second directions along which the second dimension L2 extends and that are orthogonal to the first directions are not all parallel to each other.

[0192] The main extension dimensions may be L1 = L2. This also helps to promote isotropic light scattering.

[0193] The projection of the nanostructures onto the main extension plane xy may have different shapes, such as Figure 9B the square shown, or be circular, or exhibit a certain degree of symmetry to facilitate isotropic scattering. The nanostructures 200 preferably have an n-fold axis of symmetry perpendicular to the main extension plane xy, where n ≥ 3. Thus, they exhibit invariance with a rotation angle of 2π / n.

[0194] They preferably have various sizes. The sizes of the nanostructures 200, such as their critical sizes or the projected surface areas in the xy plane, preferably exhibit significant variations, for example, the difference between the smallest nanostructure 200 and the largest nanostructure 200 in the diffusive layer is on the order of about 200%, or even 300%, or even 500%. The multiple between the smallest nanostructure and the largest nanostructure is 2, or even 3, or even 5, so that a relatively wide range of sizes can be obtained.

[0195] Therefore, the variation in the surface area of the metal nanostructures can be such that Smax≥x*Smin, where Smax and Smin are the largest surface area and the smallest surface area within the diffusive layer, respectively, and x = 2, preferably x = 3, preferably x = 5.

[0196] Therefore, the variation in the critical size of the metal nanostructures can be such that Tmax≥x*Tmin, where Tmax and Tmin are the largest and smallest critical sizes within the diffusive layer, respectively, and x = 2, preferably x = 3, and more preferably x = 5.

[0197] The size variation of the metal nanostructures 200 can involve only the size L1 or can involve only the size L2, or can involve both the size L1 and the size L2.

[0198] In addition, it is preferred that the size distribution of the nanostructures is sufficiently dispersed within this size range.

[0199] In the case where the size distribution of the nanostructures is narrow or is a Gaussian size distribution, it is indeed beneficial for the formation of an ordered lattice of the nanostructures. The high order of this ordered lattice is beneficial for certain interactions with the incident light emitted by the light source (e.g., through resonance). This will be referred to as the "lattice effect" hereinafter. As a result, light is extracted only in certain specific directions by this ordered lattice. In this case, the scattering is not isotropic.

[0200] On the contrary, a distributed size distribution of the nanostructures is beneficial for the formation of a disordered lattice of the nanostructures. The lower order of this disordered lattice limits the lattice effect. As a result, light is extracted through this disordered lattice in a more isotropic manner. The angular diffusion pattern is improved ( Figure 4C the case shown).

[0201] According to a favorable possibility, the size distribution of the nanostructures 200, for example according to the critical size or according to the average size (L1 + L2) / 2, is preferably in the range of 100 nm to 500 nm or as dispersed as possible within this range. For example, in the range of 100 nm to 400 nm, within the diffuse layer 22 among a plurality of metal nanostructures 200, at least some metal nanostructures (for example at least 10, preferably at least 20) have a main extension size less than 250 nm. At least some metal nanostructures (for example at least 10, preferably at least 20) have a main extension size greater than 350 nm.

[0202] Preferably, the metal nanostructures 200 are also dispersed or distributed randomly or disorderly on the transmission layer 10. The metal nanostructures 200 especially have a plurality of separation distances d between adjacent nanostructures ij ( Figure 9B )。

[0203] These separation distances d ij , also called the inter-particle distance, are preferably in the range of 100 nm to 1000 nm.

[0204] Preferably, the separation distance shows a significant variation between the minimum distance and the maximum separation distance of two adjacent nanostructures. For example, the difference between the minimum separation distance and the maximum separation distance of two adjacent nanostructures in the diffuse layer 22 is about 200%, or even 300%, or even 500%. The multiple between the minimum and the maximum separation distance is 2, or even 3, or even 5, so that a relatively wide range of distances can be obtained.

[0205] In addition, preferably the distribution of the inter-particle distances is sufficiently dispersed within this range.

[0206] In the case where the inter-particle distance distribution is narrow or has a Gaussian distribution, it is beneficial to form an ordered lattice with highly ordered nanostructures.

[0207] On the contrary, the dispersion of the inter-particle distance distribution is beneficial to the formation of a disordered nanostructure network with low order.

[0208] According to a favorable possibility, the distribution of the inter-particle distances of the nanostructures 200 is preferably as much as possible in the range of 100 nm to 1000 nm. This helps to limit the network effect.

[0209] To obtain a scattered inter-particle distance distribution, at least some adjacent metal nanostructures can have a separation distance less than 500 nm, and at least some other adjacent metal nanostructures can have a separation distance greater than 600 nm. According to Figure 9BIn the example shown, for the nanostructure 2001 surrounded by eight closely adjacent nanostructures 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, the inter-particle distances d12, d13, d14, d15, d16, d17, d18, d19 are preferably different from each other and preferably sufficiently different such that a part of said distances, such as d12, d14, d16, is less than 500 nm and another part of said distances, such as d13, d17, d18, d19, is greater than 600 nm.

[0210] According to another example not shown, the inter-particle distances between the nanostructure 2001 and each of its adjacent nanostructures 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 are different from each other.

[0211] The production of such a diffuser layer 22 can advantageously be accomplished by standard planar techniques of microelectronics (deposition, lithography, etching), as will be explained later in the specification.

[0212] Alternatively, it can be carried out by the simple step of depositing metal nanoparticles having the above-described size characteristics. This deposition can be done by gravity deposition and / or by well-known electrodeposition or electrophoresis techniques from commercially available colloidal solutions of nanoparticles.

[0213] Other embodiments of the diffuser according to the present invention can be envisaged. Only the unique features of the first embodiment are described below, and the other features not described are considered to be the same as those of the first embodiment.

[0214] Now reference will be made to Figures 10A to 10E Describe a second embodiment of the diffuser according to the present invention.

[0215] According to this second embodiment, the diffuser includes a transmission layer 10, a diffuser layer 23 including at least one metal nanostructure 201, 200a, and a focusing layer 30. The transmission layer 10 is interposed between the diffuser layer 23 and the focusing layer 30.

[0216] The diffuser layer 23 can include a single metal nanostructure 201. Instead, a diffuser layer 22 including a plurality of metal nanostructures 200 can be used.

[0217] The focusing layer 30 can have material continuity with the transmission layer 10. In the drawings, the focusing layer 30 and the transmission layer 10 are shown in brackets. Even if they may not be structurally distinct, this can at least functionally distinguish these different layers.

[0218] The focusing layer 30 is configured to focus the light emitted by the source onto the nanostructure 201, or onto the nanostructures 200a of the plurality of metallic nanostructures 200, or onto several of the nanostructures 200a of the plurality of metallic nanostructures 200, for example from 2 to 10.

[0219] The light emitted by the light source (e.g., a plane incident wave arriving at the focusing layer 30) thus propagates to the nanostructures 201, 200a at the apex of an illumination cone.

[0220] Thus, the focusing layer 30 makes it possible to improve the diffusion (non-specular transmission) of the diffuser. The combination of this focusing layer 30 with a single metallic nanostructure 201 or with only several nanostructures 200a can also improve the isotropic nature of the scattering ( Figure 6C as shown).

[0221] According to Figure 10A one possibility shown, the focusing layer 30 is in the form of a lens, also known as a microlens, and is, for example, refractive. This microlens 300 generally forms a bulge on the side of the transmission layer 10 opposite to the side on which its diffusing support layer 23 is located.

[0222] The width or diameter D of such a microlens taken in a plane parallel to the main extension plane corresponds to the width of the diffuser. It is preferably between 5 μm and 30 μm, for example approximately 15 μm.

[0223] The focal length of this microlens 300 essentially corresponds to the thickness H' of the transmission layer 10, generally on the order of a few micrometers, for example 8 ≤ H’ ≤ 12 μm, up to the order of several hundred micrometers, for example, for a glass substrate, H' ≈ 700 μm.

[0224] According to Figure 10B one possibility shown, the focusing layer 30 is in the form of a Fresnel lens 303.

[0225] Such a Fresnel lens can include, in a plane parallel to the main extension plane, geometric patterns 300, 301, 302 made of a material having a relatively high refractive index compared to the surrounding transparent material. The principle of such a Fresnel lens 303 is well known.

[0226] Thus, the different geometric patterns 300, 301, 302 can allow the focusing of light onto the nanostructures 201, 200.

[0227] For example, these reasons may include:

[0228] parallel bands 320, the width of which decreases gradually from the center of the lens ( Figure 10C ),

[0229] squares or disks 321, the width or diameter of which decreases gradually from the center of the lens ( Figure 10D ),

[0230] Concentric rings 322 ([[]] Figure 10E ) that gradually decrease in width starting from the center of the lens.

[0231] Such a focusing layer including a Fresnel lens can be advantageously fabricated by standard planar techniques in microelectronics (deposition, lithography, etching), as described later in the specification.

[0232] Compared with a diffuser including refractive microlenses, the overall size of a diffuser including a Fresnel lens can be reduced. In particular, the height of the diffuser can be reduced.

[0233] Now, reference will be made to Figure 11 and Figure 12 to describe a third embodiment of a diffuser according to the present invention.

[0234] According to this third embodiment, the diffuser includes a transmissive layer 10, a diffusive layer 23 including at least one metal nanostructure 201 or a diffusive layer 22 including a plurality of metal nanostructures 200a, 200b, a focusing layer 30, and a reflective layer 40. As in the previous example, the focusing layer 30 can be formed by microlenses continuous with the transmissive layer 10.

[0235] The reflective layer 40 is interposed between the diffusive layers 22, 23 and the focusing layer 30. The reflective layer 40 can be disposed within the transmissive layer 10, at a distance d from the diffusive layers 22, 23 and at a distance H from the focusing layer 30.

[0236] The reflective layer 40 is configured to reflect a portion of the light backscattered by the metal nanostructures 201, 200a on which the emitted light is focused. The propagation direction of the backscattered light is opposite to the propagation direction of the light scattered toward the observer. The reflective layer 40 reflects a portion of this backscattered light toward the direction of the observer.

[0237] Therefore, this reflective layer 40 improves the total transmittance of the diffuser.

[0238] The reflective layer 40 has an opening 400 that is approximately at the center of the metal nanostructures 201, 200a of the diffusive layers 23, 22. The opening 400 has a width dimension or opening diameter W. The opening W preferably satisfies the following relationship:

[0239] [Mathematical formula 1]

[0240]

[0241] where D is the diameter of the focusing lenses 300, 303, d is the distance by which the diffusive layers 22, 23 are separated from the reflective layer 40 (d can be obtained between the opposing surfaces of the relevant layers or between the centers of the relevant layers), and H is the distance by which the reflective layer 40 is separated from the focusing layer 30 (Figure 11 )。

[0242] In fact, for a glass substrate, a typical value of H can be 700 μm, and for a lens, a typical value of D can be 15 μm.

[0243] For a non-planar incident wave, for example, for light emitted by an LED having low divergence and forming a light-emitting cone, it is advantageous to reduce the value of H. This makes it possible to limit the transmission loss of light. The incident angle is close to the edge of the LED light-emitting cone.

[0244] It is also particularly advantageous to maximize the value of d to maximize the aperture W400. This allows increasing the angular aperture for backscattered light.

[0245] In fact, typical values of d obtainable by standard microelectronic planar technology are between 1 μm and 20 μm.

[0246] For a given value of d, for example, d = 3 μm, or d = 7 μm, the above relation [mathematical formula 1] can optimize the size of the opening W.

[0247] If then some of the light emitted by the light source does not reach the nanostructures 201, 200a.

[0248] If a part of the light backscattered by the nanostructures 201, 200a outside the illumination cone is not reflected.

[0249] According to Figure 11 one possibility shown, the diffuser layer 23 can include a single metal nanostructure 201.

[0250] The light rays backscattered by the nanostructure 201 and then reflected by the reflector layer 40 towards the observer can enhance the non-specular diffusion of the diffuser.

[0251] Furthermore, the angular diffusion of the diffuser is completely isotropic ( Figure 7C the case shown).

[0252] According to Figure 12 another possibility shown, the diffuser layer 22 can include a plurality of metal nanostructures 200a, 200b.

[0253] In the latter case, only one or a few of the nanostructures 200a are directly irradiated by the illumination cone formed by the focusing layer 30.

[0254] The metal nanostructures 200b advantageously make it possible to facilitate the extraction of the so-called grazing part backscattered by the metal nanostructure or the plurality of nanostructures 200a at the focus in the direction of the observer.

[0255] This grazing part particularly includes light rays whose propagation direction forms an angle with the diffusing layer 22, and this angle is smaller than the total reflection angle at the interface 1022 between the transmissive layer 10 and the diffusing layer 22. During their propagation, these grazing light rays are successively reflected at the interface 1022 and then successively reflected at the interface 1040 between the transmissive layer 10 and the reflective layer 40. Therefore, these grazing light rays are trapped within the transmissive layer 10 and are not transmitted in the direction of the observer.

[0256] Advantageously, the metal nanostructures 200b form singularities at the interface 1022. These singularities are conducive to extracting the grazing light rays from the transmissive layer 10 in the direction of the observer. The total transmittance of the diffuser increases.

[0257] Compared with the light rays directly scattered by the nanostructures 200a, the grazing light rays scattered by the nanostructures 200b exhibit relatively higher scattering angles.

[0258] Therefore, the angular spread of the diffuser becomes wider ( Figure 8C as shown in the case).

[0259] Hereinafter, the diffuser shown in Figure 7A and 11 is evaluated for non-optimal production or operating conditions.

[0260] Specifically, the scattering efficiency is evaluated:

[0261] For incident light of different wavelengths emitted by the light source 1 ("wavelength" case), then

[0262] For a diffuser whose opening 400 is eccentric with respect to the nanostructure 201 ("deviation" case), then

[0263] For a diffuser, whose illumination cone is not perpendicular to the reflective layer 40 and the diffusing layer 23 ("incident angle" case).

[0264] Wavelength

[0265] The diffuser evaluated by FDTD simulation below includes a transmissive layer 10, a focusing layer 30, a reflective layer 40, and a diffusing layer 23 based on metal nanostructures 201.

[0266] The diameter D of the focusing lens is equal to 15 μm here. The distance d between the diffusing layer 23 and the reflective layer 40 is equal to 3 μm here. The distance H between the reflective layer 40 and the focusing layer 30 is equal to 12 μm here. The diameter of the opening 400 in the reflective layer 40 is equal to 1.36 μm here.

[0267] The light emitted by the light source 1 is an incident plane wave.

[0268] Figure 13A and 13B shows light with a wavelength λ = 450 nm (Figure 13B ) Transmission through such a diffuser ( Figure 13A ).

[0269] The angular diagrams obtained under these implementation and irradiation conditions are as Figure 13C shown.

[0270] Figure 14A and 14B show the transmission of light with a wavelength λ = 550 nm ( Figure 14B ) through such a diffuser ( Figure 14A ). The angular diagrams obtained under these production and irradiation conditions are as Figure 14C shown.

[0271] Figure 15A and 15B show the transmission of light with a wavelength λ = 650 nm ( Figure 15B ) through such a diffuser ( Figure 15A ). The angular diagrams obtained under these production and irradiation conditions are as Figure 15C shown.

[0272] By comparing Figure 13C , the angular scattering diagrams of 14C and 15C, it seems that the transmission level (far-field intensity) of the diffuser is approximately constant regardless of the wavelength.

[0273] Independent of the wavelength, the width of the angular scattering pattern is also relatively wide and constant.

[0274] Therefore, the change in the wavelength of the light emitted by the light source has a negligible effect on the scattering efficiency of the diffuser, at least for the visible spectrum from 450 nm to 650 nm.

[0275] From this, it is conceivable to use this diffuser for pixels of different colors on a display screen.

[0276] Therefore, an observer can observe such a display screen within a wide viewing angle range relative to the normal direction of the screen without feeling any fluctuations in parasitic intensity.

[0277] Deviation

[0278] The diffuser evaluated in this section shows an X deviation between the nanostructure 201 and the center of the opening 400 parallel to the diffuser layer. This X deviation is shown in Figure 16A (nanostructure aligned with the opening, as a reference) and Figure 16B (nanostructure not aligned with the opening).

[0279] This X deviation may be due to, for example, unregulated technical manufacturing steps. The opening 400 has a diameter W.

[0280] In this case, the light transmittance T of the diffuser is given by the following relation:

[0281] [Mathematical formula 2]

[0282]

[0283] Figure 16C A graph of the light transmittance T versus the deviation (offset) X is shown for the following parameters:

[0284] The diameter D of the focusing lens is equal to 15 μm here. The distance d between the diffuser layer 23 and the reflector layer 40 is equal to 3 μm here. The distance H between the reflector layer 40 and the focusing layer 30 is equal to 12 μm here. The diameter of the opening 400 in the reflector layer 40 is equal to 1.36 μm here.

[0285] Under these conditions, an X deviation of less than approximately ±1 μm allows for retaining more than 70% of the light transmitted by the diffuser.

[0286] This tolerance of the order of ±1 μm is much higher than the positioning accuracy of different layers or levels relative to each other in standard microelectronic technology.

[0287] Figure 16D A graph of the transmittance T versus the deviation X is shown for the following parameters:

[0288] The diameter D of the focusing lens is equal to 15 μm here. The distance d between the diffuser layer 23 and the reflector layer 40 is equal to 7 μm here. The distance H between the reflector layer 40 and the focusing layer 30 is equal to 8 μm here. The diameter of the opening 400 in the reflector layer 40 is equal to 7 μm here.

[0289] Under these conditions, an X deviation of less than about ±2 μm allows for retaining more than 70% of the light transmitted by the diffuser.

[0290] This tolerance of ±2 μm is much greater than the positioning accuracy of different layers or levels relative to each other in standard microelectronic technology.

[0291] These construction conditions are even more favorable for the robustness of the diffuser in case of misalignment.

[0292] Angle of incidence

[0293] The diffuser evaluated in this section is irradiated by an illumination cone having an angle of incidence β with respect to the direction perpendicular to the reflector layer 40 of the diffuser reflector.

[0294] The center of the illumination cone is offset by a distance X from the center of the opening 400 aligned with the nanostructure 201 at the intersection with the opening 400.

[0295] At Figure 17A (normal angle of incidence, as a reference) andFigure 17B (Angle of incidence β) shows such an illumination situation.

[0296] The angle of incidence β may be due to, for example, the divergence of the light-emitting cone of the light source 1, or due to improper control of the setting of the diffuser relative to the light source. The opening 400 has a diameter W.

[0297] In this case, the light transmittance T of the diffuser is given by the following relationship:

[0298] [Mathematical formula 3]

[0299]

[0300] Figure 17C The relationship between the transmittance T and the angle of incidence β of the following parameters is shown:

[0301] The diameter D of the focusing lens is equal to 15 μm here. The distance d between the diffuser layer 23 and the reflective layer 40 is equal to 3 μm here. The distance H between the reflective layer 40 and the focusing layer 30 is equal to 12 μm here. The diameter of the opening 400 in the reflective layer 40 is equal to 1.36 μm here.

[0302] Under these conditions, an angle of incidence β less than approximately ±5° can retain more than 60% of the light transmitted by the diffuser.

[0303] This tolerance of ±5° is much better than the assembly accuracy in standard microelectronics technology.

[0304] Figure 17D The relationship between the transmittance T and the angle of incidence β of the following parameters is shown:

[0305] The diameter D of the focusing lens is equal to 15 μm here. The distance d between the diffuser layer 23 and the reflective layer 40 is equal to 7 μm here. The distance H between the reflective layer 40 and the focusing layer 30 is equal to 8 μm here. The diameter of the opening 400 in the reflective layer 40 is equal to 7 μm here.

[0306] Under these conditions, an angle of incidence β less than about ±20° can retain more than 60% of the light transmitted by the diffuser.

[0307] Compared with Figure 17C the previous situation shown, here the sensitivity of the diffuser to the angle of incidence of the light-emitting cone is reduced.

[0308] These implementation conditions are more favorable for the efficiency of the diffuser under illumination conditions.

[0309] Standard GaN LEDs emit light at a maximum angle of ±25° in the light-emitting cone. In addition, the light emission of the LED within this angular range is Lambertian and favors the normal angle of incidence.

[0310] Therefore, diffusers with such parameters (especially when H is close to d) are very suitable for diffusing the light emitted by standard GaN LEDs.

[0311] Example of production method

[0312] The present invention also relates to a method for manufacturing a diffuser as described in the previous embodiments.

[0313] Advantageously, standard microelectronic manufacturing devices can be implemented.

[0314] On the surface 110 of a substrate 11 made of, for example, glass, which is transparent at least in at least a part of the visible range, preferably throughout the visible range ( Figure 18A ), a metal layer 12 ( Figure 18B ) is deposited.

[0315] The thickness of the metal layer 12 is preferably on the order of 100 nm to 500 nm.

[0316] The metal layer 12 can be made of aluminum. Such a layer is advantageously compatible with CMOS technology.

[0317] Then the aluminum layer is structured in a known manner by lithography (UV or electron beam) and etching (e.g., RIE).

[0318] This makes it possible to form nanostructures 200 of various sizes distributed in a disordered manner on the substrate 11 ( Figure 18C ). The diffusing layer 22 of the diffuser is thus formed in a simple and minimal number of process steps.

[0319] In addition, aluminum exhibits low absorption losses. The total transmittance of the diffuser based on aluminum nanostructures is optimized.

[0320] Optionally, a planarization step can also be performed.

[0321] A transparent layer made of, for example, silicon dioxide can be deposited around the nanostructures 200, especially between the nanostructures 200, to encapsulate them ( Figure 18D ). Such a composite diffusing layer 22 has improved mechanical strength.

[0322] For example, polishing can also be performed, e.g., by CMP (chemical mechanical polishing), to expose the tops of the nanostructures 200 of the composite diffusing layer 22. This makes it possible to obtain a composite diffusing layer 22 with a planarized surface 220 having surface conditions compatible with possible subsequent process steps.

[0323] Figures 19A - 19C The structure of a diffuser including metal nanostructures 201 and refractive microlenses 300 is illustrated.

[0324] As before, a diffuser layer 23 including a single metal nanostructure 201 is generated and planarized by lithography / etching ( Figure 19A ).

[0325] A transmissive layer 10 of silica is deposited on the planarized surface 230 of the diffuser layer 23, with a thickness of H' ( Figure 19B ).

[0326] Then, a silica microlens 300 is formed on the transmissive layer 10 ( Figure 19C ).

[0327] Figures 20A to 20G An example of the formation of such a microlens 300 is shown in more detail.

[0328] These examples relate to embodiments of a diffuser that includes a diffuser layer 22 based on a plurality of nanostructures, a transmissive layer 10, a reflective layer 40, and a focusing layer 30 including microlenses. These examples of the formation of the microlens 300 can be modified as necessary in detail to suit other embodiments of the diffuser, particularly those suitable for a diffuser including a diffuser layer 23 based on a single nanostructure and / or a diffuser without a reflective layer 40.

[0329] To produce the silica microlens 300 on the surface 100 of the transmissive layer 10 ( Figure 20A ), a silica layer 301 having a thickness corresponding to the height of the microlens can be pre-deposited on the surface 100. Then, a focusing layer is formed from the silica layer 301.

[0330] According to one example, a photosensitive resin layer 31 having a thickness approximately equal to the height of the microlens to be produced is then deposited on the silica layer 301 ( Figure 20B ). The photosensitive resin 31 is intended to form a microlens pattern, which is then transferred into the underlying silica layer 301.

[0331] The thickness of the resin to be deposited can vary according to the etching conditions used to transfer the microlens pattern into the silica layer 301.

[0332] First, the photosensitive resin layer 31 is structured by lithography ( Figure 20C ) to obtain a resin portion 310 centered with respect to the opening 400 of the reflective layer 40.

[0333] The width of this portion 310 is approximately equal to the width of the microlens 300.

[0334] Then, heat treatment of this portion 310 can enable the generation of a microlens pattern 311 ( Figure 20E ). This heat treatment can be adjusted according to the viscosity and / or surface tension properties of the photosensitive resin.

[0335] Then, anisotropic etching is performed in a direction perpendicular to the silica layer 301 to transfer the microlens pattern 311 into the silica layer 301.

[0336] The microlens 300 is thus formed in the silica layer 301 ( Figure 20G ).

[0337] This etching can advantageously exhibit a selectivity of 1:1 between the resin and the silica. Thus, the pattern 311 is directly transferred into the silica layer 301. Therefore, the initial curvature of the resin pattern 311 can be faithfully reproduced on the microlens 300. The height of the microlens 300 is substantially the same as the height of the pattern 311.

[0338] The silicon nitride (SiN) microlens 300 can also be made from a SiN layer 301 according to the same principle. Depending on the required refractive index contrast between the microlens and the surrounding medium, other materials can be used to form the microlens 300.

[0339] According to another example, the pattern 311 can be formed by locally dispensing resin on the hydrophilic surface 302.

[0340] According to this alternative, a mask 312 is formed on the surface 302 of the silica layer 301 before dispensing the resin ( Figure 20D ). This mask 312 allows restricting the diffusion of the resin to the level of the pattern 311.

[0341] The thickness of the mask 312 is preferably at least less than half of the height of the pattern 311 and preferably at least less than one-fifth of the height of the pattern 311. This allows avoiding capillary effects at the edges of the pattern 311, such as a change in the curvature of the pattern 311.

[0342] In this example, the surface 302 is functionally hydrophilized. This allows changing the surface tension between the surface 302 and the resin, thereby obtaining the desired curvature of the pattern 311 ( Figure 20F ).

[0343] Then, as described above, the pattern 311 is transferred into the silica layer 301 by etching.

[0344] The microlens 300 is thus formed in the silica layer 301 ( Figure 20G ).

[0345] Figures 21A to 21F The construction of a diffuser is shown, which includes at least one metal nanostructure, a reflective layer open to the at least one nanostructure, and a refractive microlens conjugated with the at least one nanostructure.

[0346] As described above, a diffusive layer 22 including at least one nanostructure 200a or a plurality of metal nanostructures 200a, 200b is produced on a flat substrate 11 by lithography / etching. Figure 21A )

[0347] A first portion 10a of the silica transmissive layer 10 is deposited on the plane of the diffusive layer 22 with a thickness of d. Figure 21B )

[0348] A metal layer 41 (such as aluminum) is deposited on the first portion 10a of the transmissive layer 10. The thickness of the metal layer 41 is preferably between 50 nm and 300 nm.

[0349] An opening 400 aligned with at least one nanostructure 200a is formed in the metal layer 41 by lithography and etching. Figure 21D ) The opening 400 has a diameter W.

[0350] Thereby, a reflective layer 40 is formed.

[0351] Then, silica deposition is performed to fill the opening 400 and form a second portion 10b of the transmissive layer 10. Figure 21E )

[0352] The second portion 10b has a thickness H.

[0353] Thereby, a transmissive layer 10 including the reflective layer 40 is formed.

[0354] Then, a focusing layer 30 including a microlens 300 is fabricated as described above. Figure 21F )

[0355] Figures 22A to 22E The fabrication of a diffuser is shown, which includes at least one metal nanostructure 200a, a reflective layer 40 open to at least one nanostructure 200a, and a Fresnel lens 303 combined with at least one nanostructure 200a.

[0356] As previously described, a diffusive layer 22 and a transmissive layer 10 including a reflective layer 40 therein are formed. Figure 22A )

[0357] A metal layer 302 (such as aluminum) is deposited on the exposed surface of the transmissive layer 10. The thickness of the metal layer 302 is preferably between 50 nm and 300 nm. Figure 22B )

[0358] Preferably, a Fresnel lens pattern 320, 321, 322 is formed in the metal layer 302 by lithography / etching, thereby forming a focusing layer 30. Figure 22C )

[0359] Optionally, a planarization step including silica deposition and / or polishing between units 320, 321, 322 can also be performed ( Figure 22D ). Thereby, the focusing layer 30 is protected and the mechanical strength is increased.

[0360] In Figure 22E such a Fresnel lens 303 is shown, which includes a pattern 322 of concentric rings, for example, with a width decreasing from the center.

[0361] The width of the rings and the spacing between the rings are selected to obtain a desired focal length, which substantially corresponds to the thickness H + d of the transmissive layer 10.

[0362] Thus, the Fresnel lens can be advantageously manufactured by standard planar techniques (deposition, lithography, etching) in microelectronics.

[0363] Such a focusing layer 30 is easy to manufacture.

[0364] System example

[0365] The present invention also relates to a system associating at least one light source, preferably a plurality of point light sources, with a plurality of diffusers, as described by the foregoing exemplary embodiments. The following refers to Figure 23 and 24 to describe such a system.

[0366] Such a system includes a plurality of diffusers 3 adjacent to each other. These diffusers 3 extend in a plane parallel to the main extension plane xy. According to the above-described construction and method, the plurality of diffusers 3 can be manufactured by standard planar techniques in microelectronics.

[0367] The plurality of diffusers 3 can, for example, include diffusers, each diffuser including a transparent support 11, a transmissive layer 10, a reflective layer 40, a diffusive layer 22 based on at least one metal nanostructure, and a focusing layer 30 including refractive microlenses ( Figure 23 ).

[0368] According to a possibility not shown, the refractive microlenses can be made of SiN and protected by a planarized silica layer.

[0369] Then the plurality of diffusers 3 can be arranged opposite to the point light source 1, for example, an LED ( Figure 24 ).

[0370] The LEDs 1 can be separated from each other by a structure 2 for insulation and / or electrical injection.

[0371] Preferably, the LEDs 1 are controlled independently of each other by integrating a control matrix 1000, for example, a CMOS (Complementary Metal Oxide Semiconductor) component.

[0372] These LEDs 1 form pixels or sub - pixels of, for example, a display screen.

[0373] The assembly between the plurality of diffusers 3 and the plurality of point light sources 12 can be accomplished by conventional coupling, for example, using a bonder called "Die - to - wafer". The cohesion of the components is ensured, for example, by an adhesive whose refractive index does not interfere with the operation of the lenses of the focusing layer. The adhesive can be, for example, a UV glue.

[0374] According to one possibility, spacers can be arranged between the plurality of diffusers 3 and the plurality of point light sources 12 to fix the spacing distance between the two facing parts 3, 12.

[0375] The system according to the invention for associating a plurality of point light sources with a plurality of diffusers finds an advantageous application in the production of three - dimensional (3D) display screens.

[0376] Such a 3D display screen is designed to display slightly different images according to the viewing angle. In particular, in order to provide the observer O with a three - dimensional perception, his two eyes O1, O2 must see two slightly different images (for example, in terms of brightness and / or color) Figure 25 )

[0377] As Figure 25 shown, a 3D screen can be generated by combining a matrix of microlenses 4 and a super - high - resolution screen 51. In this configuration, the observer O sees the high - resolution screen 51 through the microlens array 4. In particular, the observer's first eye O1 sees a first series of small regions of the high - resolution screen through the microlens array, thus forming a first image. The observer's second eye O2 sees a second series of small regions of the high - resolution screen through the microlens array, forming a second image. These first and second series are intertwined in the high - resolution screen 51.

[0378] In order to enable the observer O to place himself arbitrarily at a given position in front of the 3D screen, the system generates different images for a plurality of viewpoints adjacent to each other. These viewpoints are generally referred to as "views". At a given position relative to the 3D screen, the observer's eyes O1, O2 select two different views, which, when combined, provide the observer with a three - dimensional perception. When the observer moves his head relative to the 3D screen, this selection changes, thus further enhancing the 3D perception.

[0379] In fact, different series of small regions correspond to the pixels of a very high-resolution screen 51. These pixels form point light sources. For example, they can include one or more LEDs 1. In the case of application to 3D displays, the number of pixels of an ultra-high-resolution screen is the number of micro-lens 4 arrays (corresponding to the nominal resolution of the 3D screen perceived by the observer) multiplied by the number of views (corresponding to the possible positions of the observer relative to the 3D screen). Thus, for the same nominal resolution, due to the number of views, the number of pixels required to make a 3D screen is much larger than that of a 2D screen. Therefore, such a system needs to use a very high-resolution internal screen 51 in order to finally obtain the desired nominal resolution in 3D displays. The high-resolution screen 51 typically has a pixel density greater than or equal to 500 ppi (abbreviation for "pixels per inch" or in French "pixels par pouce"), and / or a pixel pitch less than or equal to 50 μm. The high-resolution screen 51 typically has a number of pixels greater than or equal to 10 MP (mégapixel, i.e., 10 6 pixels).

[0380] A very high-resolution internal screen 51 that mixes together a plurality of images associated with the required number of views can be implemented or replaced by a plurality of internal micro-screens 52, each of which diffuses a part of the required image. In this case, each micro-screen 52 is associated with a projection system 6. Figure 26 Such a system is shown, which combines a micro-screen 52 and a projection system 6. For the sake of clarity, only two micro-screens 52 are shown in this Figure 26 and two projection systems 6 are shown.

[0381] In order to direct the light from the edges of the micro-screen 52 towards the direction of the observer O, a diffuser 3 must be placed in the image plane I conjugate to the plane in which the micro-screen 52 is located.

[0382] Such a diffuser 3 must be effective within the range of the pixels of the high-resolution screen 51 or the pixels of the plurality of micro-screens 52. The size of these pixels is typically about 15 μm. The diffuser 3 protected by the present invention advantageously makes it possible to obtain the required efficiency for 3D displays in the context of the present application.

[0383] Thus, the system according to the present invention includes:

[0384] - An ultra-high-resolution screen 51 composed of a plurality of micro-screens 52, each micro-screen 52 including a plurality of pixels,

[0385] - A plurality of projection systems 6 associated with the plurality of micro-screens 52,

[0386] - The plurality of diffusers 3 as described in the present invention, each diffuser 3 being associated with each pixel of the plurality of pixels of the micro screen 52, and

[0387] - The array of microlenses 4,

[0388] The above system is particularly advantageous for 3D displays.

[0389] The following describes non-limiting examples of the dimensions of such a system.

[0390] For a 3D screen size of 195 mm x 150 mm diagonal 246 mm (9.6 inches), a display resolution of 1300 x 1000, the pitch perceived by the user is 150 μm (corresponding to the size of the microlenses 4 of the microlens array). To obtain a 10 x 10 view, the ultra-high resolution screen 51 must have 13,000 x 10,000 pixels at a pitch of 15 μm. Thus, the size of each pixel is approximately 15 μm.

[0391] In fact, a very high resolution screen 51 can be achieved by assembling 5 x 5 micro screens 52 each having 2600 x 2000 pixels. Such micro screens 52 are sold, for example, by microOLED.

[0392] It can be manufactured according to Figure 27 the optical design shown. For example, it can form an image of the micro screen 52 on the image plane I at a distance of 110 mm from the micro screen 52. In this case, the maximum angle of incidence β with respect to the normal of the image plane I is approximately 20°. As described above, the diffuser 3 according to the present invention can effectively transmit the incident light into a luminous cone having such an angle of incidence of approximately 20°.

[0393] Then, the image formed on the image plane I is diffused by the diffuser 3 and then focused by the array of microlenses 4.

[0394] As Figure 28 shown, for a screen of width L and for an observer at a distance D with the eyes of the observer spaced apart by A, the maximum angle α allowed by the microlenses 4 can be approximately determined as:

[0395] [Mathematical formula 4]

[0396]

[0397] That is, for L = 195 mm (typical width of a tablette), D = 50 cm (typical viewing distance of a tablette) and A = 10 cm, α ≈ 21.5°.

[0398] The angles α and β have opposite signs. Thus, the diffuser 3 is configured to present an angular pattern with a maximum diffusion angle of approximately 40°. As shown above, the diffuser 3 according to the invention makes it possible to obtain such an angular pattern.

[0399] Thus, as Figure 29 shown, thanks to the diffuser 3 described in the present invention, a functionally efficient 3D display system can be advantageously produced.

[0400] The present invention is not limited to the above embodiments, but extends to all embodiments covered by the claims.

Claims

1. A diffuser (3) for receiving light emitted by a visible light source (1), comprising a transmissive layer (10) transparent to the emitted light and a diffusive layer (22, 23) for scattering the emitted light, wherein the diffusive layer (22, 23) of the diffuser (3) comprises a plurality of metal nanostructures (200, 200a, 200b), each metal nanostructure having a projection in a main extension plane (xy), the projection having a first dimension (L1) and a second dimension (L2) in a first direction (y) and a second direction (x) orthogonal to the main extension plane (xy) respectively, the first dimension (L1) and the second dimension (L2) being less than 650 nm, the metal nanostructures (200, 200a, 200b) being distributed above the transmissive layer (10), and adjacent metal nanostructures (200 i , 200 j ) having a varying spacing distance (d ij ), the dimensions of the metal nanostructures (200, 200a, 200b) being determined such that they have the varying first dimension (L1) and the varying second dimension (L2), The diffuser (3) further comprises: at least one focusing layer (30) configured to focus the emitted light onto at least one of the plurality of metal nanostructures (200a); and at least one reflective layer (40) located within the transmissive layer (10) between the diffusive layer (22) and the focusing layer (30), the reflective layer (40) having at least one opening (400) facing the at least one metal nanostructure (200a), the emitted light being focused onto the at least one metal nanostructure.

2. The diffuser (3) according to claim 1, wherein, At least some adjacent metal nanostructures (200 i , 200 j ) have a spacing distance (d ij ) of less than 500 nm, and at least some of the other adjacent metal nanostructures (200 i , 200j) have a spacing distance (d ij ) of greater than 600 nm.

3. The diffuser (3) according to claim 1, wherein, Within the diffusing layer (22, 23), the spacing distance (d ij ) varies by at most 200%.

4. The diffuser (3) according to claim 1, wherein, Within the diffusing layer (22, 23), the spacing distance (d ij ) varies by at most 300%.

5. The diffuser (3) according to claim 1, wherein, Within the diffusing layer (22, 23), the spacing distance (d ij ) varies by at most 500%.

6. The diffuser (3) according to claim 1, wherein, For the same nanostructure, the first dimension (L1) and the second dimension (L2) are substantially equal to each other.

7. The diffuser (3) according to claim 1, wherein, The first dimension (L1) and the second dimension (L2) of the metal nanostructure (200) are between 100 nm and 500 nm.

8. The diffuser (3) according to claim 1, wherein for at least some of the metal nanostructures (200), the variation in the first dimension (L1) and the second dimension (L2) is less than 250 nm, and for at least some of the other metal nanostructures, the variation in the first dimension (L1) and the second dimension (L2) is greater than 350 nm.

9. The diffuser (3) according to claim 1, wherein, Within the diffusive layer (22), the variation in the first dimension (L1) and the second dimension (L2) varies by up to 200%.

10. The diffuser (3) according to claim 1, wherein, Within the diffusive layer (22), the variation in the first dimension (L1) and the second dimension (L2) varies by up to 300%.

11. The diffuser (3) according to claim 1, wherein, Within the diffusive layer (22), the variation in the first dimension (L1) and the second dimension (L2) varies by up to 500%.

12. The diffuser (3) according to claim 1, wherein, Within the diffusive layer (22), both the first dimension (L1) and the second dimension (L2) vary.

13. The diffuser (3) according to claim 1, wherein, Within the diffusive layer (22), the first dimension (L1) varies proportionally to the second dimension (L2).

14. The diffuser (3) according to claim 1, wherein, The focusing layer (30) comprises at least one of a refractive microlens (300) and a Fresnel lens (303).

15. The diffuser (3) according to claim 1, wherein, The opening exhibits a main extension dimension W in the projection in the main extension plane such that: where D is the main extension dimension of the diffuser (3), d is the distance between the diffusive layer (22, 23) and the reflective layer (40), and H is the distance between the reflective layer (40) and the focusing layer (30).

16. The diffuser (3) according to claim 15, having a main extension dimension D in the projection in the main extension plane (xy) sized between 5 μm and 30 μm.

17. The diffuser (3) according to claim 1, wherein, At least a portion of the metal nanostructures (200, 200a, 200b) is made of at least one metal selected from aluminum, tungsten, copper, silver, gold.

18. A display system, comprising: At least one diffuser (3) according to any one of claims 1 - 17 and at least one point light source (1), wherein the at least one diffuser (3) is configured to cooperate with the at least one point light source (1) to scatter the light emitted therefrom.

19. The display system according to claim 18, comprising: - having a resolution with a number of pixels greater than or equal to 10 6 a screen (51), including a plurality of micro-screens (52), each micro-screen including a plurality of pixels, - A plurality of projection systems (6) associated with a plurality of micro-screens (52), - A plurality of diffusers (3) according to any one of claims 1-17, each diffuser (3) being associated with at least one of the plurality of pixels of the micro-screen (52), and - A matrix of microlenses (4) associated with the plurality of diffusers (3).

20. A method of manufacturing a diffuser (3) comprising at least one diffusing layer (22) for diffusing light emitted by a visible light source (1) and comprising a plurality of metal nanostructures (200), the method comprising at least the steps of: - Providing a support (11) made of a material transparent to the emitted light, the support having a support surface (110), - Form a plurality of metal nanostructures (200) on the support surface (110), the projection of each metal nanostructure in the main extension plane (xy) parallel to the support surface (110) having a first dimension (L1) and a second dimension (L2) in the first direction (y) and the second direction (x) orthogonal to the main extension plane (xy), respectively, the first dimension and the second dimension being less than 650 nm, the metal nanostructures (200) being distributed above the support (11) such that adjacent metal nanostructures (200 i , 200 j ) have different spacing distances (d ij ) from each other, and the dimensions of the metal nanostructures (200, 200a, 200b) are determined such that they have a varying first dimension (L1) and a varying second dimension (L2), - Depositing a material transparent to the emitted light on the plurality of metal nanostructures (200) and surrounding the metal nanostructures (200), and - A planarization step configured to form a composite diffusing layer (22) comprising the material transparent to the emitted light surrounding the metal nanostructures (200), the composite diffusing layer (22) having a planarized surface (220), The method further comprises: Forming a transmissive layer (10) on the planarized surface (220), the transmissive layer (10) having a transmissive surface (100) opposite and facing the light source (1); Forming a focusing layer (30) extending on the transmissive surface (100), the focusing layer (30) being configured to focus the emitted light onto at least one of the plurality of metal nanostructures (200a); and Forming a reflective layer (40) within the transmissive layer (10) between the diffusing layer (22) and the focusing layer (30), the reflective layer (40) having at least one opening (400) facing at least one of the metal nanostructures (200a), the emitted light being focused onto the at least one metal nanostructure by the focusing layer (30).

21. The method according to claim 20, wherein, The focusing layer (30) is formed by at least one of a refractive microlens (300) and a Fresnel lens (303).

Images