Vehicle lighting device comprising a surface light guide with a metal lens

Abstract

The invention relates to a lighting device (1) comprising: - a light source (10) configured to emit light (R), - a surface light guide (11) comprising a body (110) in the form of a light-guiding sheet configured to propagate said light (R) emitted by said light source (10), characterized in that said light guide (11) further comprises: - a metal lens (111) configured to receive said light (R) and modify the propagation phase (φ) of said light (R) so that it is guided in the body (110) of said light guide (11) in a given propagation direction (P). Figure for the abstract: Figure 1

Description

Title of the invention: Vehicle lighting device comprising a surface light guide with a metal lens

[0001] The present invention relates to a lighting device. The invention also relates to a lighting assembly comprising such a lighting device. It finds a particular, but not limiting, application in motor vehicles.

[0002] In the field of motor vehicles, a lighting device known to those skilled in the art comprises: - a light source configured to emit light, - a surface light guide comprising a body in the form of a light guide sheet configured to propagate said light emitted by the light source.

[0003] The light source is arranged on one side of the light guide mat.

[0004] One drawback of this prior art is that the light guiding sheet The light source has a very thin profile, and the size of the light source is too large compared to the thickness of the light guide mat. Consequently, a significant portion of the light emitted by the light source does not enter the light guide; only about 15% of the light generated by the light source is coupled to the surface light guide. The luminous efficacy of the surface light guide is therefore low.

[0005] In this context, the present invention aims to provide a lighting device that makes it possible to resolve the aforementioned drawback.

[0006] To this end, the invention proposes a lighting device comprising: - a light source configured to emit light, - a surface light guide comprising a body in the form of a light-guiding sheet configured to propagate said light emitted by said light source, characterized in that said light guide further comprises: -a meta-lens configured to receive said light and modify the propagation phase of said light so that it is guided in the body of said light guide in a given propagation direction.

[0007] According to non-limiting embodiments, the lighting device may further comprise one or more additional features taken alone or in all technically possible combinations, from among the following.

[0008] According to a non-limiting embodiment, said light source is monochromatic.

[0009] According to a non-limiting embodiment, said light guide body is formed in one piece or is composed of a core and two sheaths distributed on either side of said core and of a refractive index lower than a refractive index of said body.

[0010] According to a non-limiting embodiment, the refractive index of each sheath has a minimum index difference of 0.09 with respect to the refractive index of said body

[0011] According to a non-limiting embodiment, said light emitted by the light source covers a wavelength range between 400 nanometers and 780 nanometers.

[0012] According to a non-limiting embodiment, said meta-lens comprises a substrate disposed on the surface of said light guide mat of the light guide and nano-pillars disposed on said substrate and defined by a radius, a height and a pitch between two nano-pillars.

[0013] According to a non-limiting embodiment, said nano-pillars are made of Silicon Nitride.

[0014] According to a non-limiting embodiment, the substrate is made of glass and is glued onto said light guide mat of the light guide.

[0015] According to a non-limiting embodiment, the nano-pillars have different radii and the same height.

[0016] According to a non-limiting embodiment, said light device further comprises a collimator disposed between the light source and the metal lens.

[0017] According to a non-limiting embodiment, the direction of propagation is defined by an angle between 20 degrees and 47 degrees.

[0018] According to a non-limiting embodiment, said angle is less than a critical angle of total reflection.

[0019] A vehicle lighting assembly is also proposed, characterized in that said lighting assembly comprises said lighting device according to any one of the preceding characteristics.

[0020] According to a non-limiting embodiment, said lighting assembly: - is a front or rear face of said vehicle, or a headlight or rear light of said vehicle, or - is part of an element of the passenger compartment of said vehicle.

[0021] The invention and its various applications will be better understood upon reading the following description and examining the accompanying figures:

[0022] [Fig. 1] illustrates a lighting device according to a first non- limiting, said luminous device comprising a light source, a light guide comprising a body and a metal lens;

[0023] [Fig.2] illustrates a lighting device according to a second non-limiting embodiment, said lighting device comprising a light source, a light guide comprising a body and a metal lens, and a collimator;

[0024] [Fig.3a] illustrates the body of the light guide as a single block according to a first non-limiting embodiment,

[0025] [Fig.3b] illustrates the body of the light guide, said body comprising a core and two sheaths according to a second non-limiting embodiment,

[0026] [Fig.4] a representation of the meta-lens of the light guide of Figure 1 or of Figure 2 according to a non-limiting embodiment, the meta-lens comprising a substrate and nano-pillars;

[0027] [Fig.5] is an enlarged view of a plurality of nano-pillars of the metal lens of the light guide of Figure 1 or Figure 2 according to a first non-limiting embodiment,

[0028] [Fig.6] illustrates a highly magnified view of a single nano-pillar of the metal lens of the light guide in Figure 1 or Figure 2,

[0029] [Fig.7] illustrates the nano-pillars of Figure 5 and the direction of propagation of the light emitted by the light source of the luminous device of Figure 1 or Figure 2 when they pass through said nano-pillars,

[0030] [Fig.8a] illustrates a first curve indicating a phase variation as a function of the radius of a nano-pillar of the metal-lens of the light guide of Figure 1 or Figure 2,

[0031] [Fig.8b] illustrates a second curve indicating a variation in light transmission as a function of the radius of a nano-pillar of the metal lens of the light guide in Figure 1 or Figure 2,

[0032] [Fig.9a] illustrates very schematically a lighting assembly for a vehicle according to a first non-limiting embodiment, said lighting assembly comprising said lighting device of figure 1,

[0033] [Fig.9b] illustrates very schematically a lighting assembly for a vehicle according to a first non-limiting embodiment, said lighting assembly comprising said lighting device of [Fig.1].

[0034] Identical elements, by structure or by function, appearing on different figures retain, unless otherwise specified, the same references.

[0035] The lighting device 1 according to the invention is described with reference to Figures 1 to 9b. The lighting device 1 is configured to produce static or animated patterns implemented in a lighting assembly 3.

[0036] In a non-limiting embodiment, the lighting device 1 is a lighting device of a vehicle 2 (illustrated in Figures 9a and 9b). In a mode of In this non-limiting embodiment, vehicle 2 is a motor vehicle. A motor vehicle is defined as any type of motorized vehicle. This embodiment is taken as a non-limiting example in the following description. In the remainder of the description, vehicle 2 is thus also referred to as motor vehicle 2. In a non-limiting variant embodiment, vehicle 2 is a combustion engine, electric, or hybrid vehicle.

[0037] The lighting device 1 is part of a lighting assembly 3 illustrated in Figures 9a and 9b. In non-limiting embodiments, the lighting assembly 3 is a front or rear face of the motor vehicle 2, or a front or rear headlight of the motor vehicle 2. In one non-limiting embodiment, the front headlight is configured to perform a projection and / or signaling function. In the non-limiting example of [Fig. 9a], the lighting assembly 3 is the front face of the motor vehicle 2.

[0038] In another non-limiting embodiment, the lighting assembly 3 is part of an element 21 of the passenger compartment 20 of the motor vehicle 2. In non-limiting variants, the element 21 is: - the dashboard, or - part of a door of motor vehicle 2, or - a decorative element of the ceiling of motor vehicle 2, or - an interior lighting element. In the non-limiting example of [Fig.9b], element 21 is a decorative element of the ceiling of motor vehicle 2.

[0039] The non-limiting embodiment of the front face is taken as a non-limiting example in the rest of the description.

[0040] As illustrated in Figures 1 and 2, the lighting device 1 comprises: - a light source 10, and - a light guide 11 comprising a body 110 and a meta-lens 111.

[0041] As illustrated in figures 1 and 2, the light device 1 has a first direction D and a second direction D' opposite to the first direction D and parallel to the first direction D. The first direction D is longitudinal to the body 110 of the light guide 11.

[0042] When the light assembly 3 comprising the light device 1 is positioned on the motor vehicle 2, the first direction D and the second direction D' are perpendicular to the vehicle axis Ox (illustrated in figures 9a and 9b).

[0043] The elements of the lighting device 1 are described in detail below.

[0044] The light source 10 is configured to emit light R. As illustrated in Figures 1 and 2, it is positioned opposite the metal lens 111 of the light guide 11 such that its light R forms a light beam Fx which enters the light guide 11 via the metal lens 111. In a non- limiting, the light R arrives at normal incidence on the meta-lens 111. In the following description, the light beam Fx will otherwise be called the incoming light beam Fx.

[0045] In a non-limiting embodiment, the light source 10 is a semiconductor light source. In other non-limiting embodiments, the semiconductor light source is a light-emitting diode (LED) or a laser diode. The term "light-emitting diode" includes any type of LED, including, but not limited to, LEDs (Light Emitting Diodes), OLEDs (Organic LEDs), AMOLEDs (Active-Matrix Organic LEDs), and FOLEDs (Flexible OLEDs). In another non-limiting embodiment, the light source 10 is a laser light source. It should be noted that some laser light sources are not semiconductor light sources. It should also be noted that some laser light sources can be naturally collimated.

[0046] In a non-limiting embodiment, the light source 10 is a monochromatic source. In other non-limiting embodiments, it is a monochromatic R (red), G (green), or B (blue) source. As a reminder, for a monochromatic source: - B: the wavelength of X-ray light is 455 nanometers (nm), - G: the wavelength of X-ray light is 535 nanometers, - R: the wavelength of X-ray light is 621 nanometers.

[0047] Due to the monochromatic light source 10, the light beam Fx is monochromatic.

[0048] The light guide 11 is surface-based. A surface-based light guide is defined as an optical guiding element in which one dimension is much smaller than the other two dimensions in space, for example, smaller by one or more orders of magnitude. Here, the thickness el of the light guide 11 is much smaller than its length 11 and its width (not shown).

[0049] When the light guide 11 is surface-based, its body 110 is in the form of a light-guiding sheet. The body 110 is thus also called the light-guiding sheet 110. In a non-limiting embodiment, the light-guiding sheet 110 has a thickness el of between 50 and 1000 µm (micrometers). In a non-limiting variant of the embodiment, the thickness el is between 50 and 500 µm. The light guide 11 is thus very thin. As is known to those skilled in the art, the light-guiding sheet 110 comprises one or more regions with one or more light-emitting zones. In a non-limiting embodiment, the light-emitting zone(s) form all or part of a decoupling pattern (not shown). The decoupling pattern is thus illuminated by the light generated by the light source 10 which emerges from the light guide 11. This makes it possible to create a static or animated pattern in the light assembly 3 comprising the light device 1. In the case of an animated pattern, several light guides with several light sources each with its own metal-lens structure can be used, or a single light guide with a plurality of light sources each with its own metal-lens structure.

[0050] In a non-limiting embodiment, the light guide 11 is a flexible light guide. Flexible means that it can bend without being damaged or breaking. Because it is flexible, it can adapt to flat or curved surfaces.

[0051] The light guide 11 is transparent. The term transparent indicates that the material composing it allows visible light to pass through, at least partially, and in particular the light emitted by the light source 10.

[0052] In a non-limiting embodiment, the light guide 11 is made of polycarbonate (PC), polymethyl methacrylate (PMMA), thermoplastic polyurethane (TPU), or polyethylene terephthalate (PET). Such materials allow for the production of a transparent light guide 11.

[0053] The light guide 11 comprises a first surface 11.1 and a second surface 11.2 opposite the first surface 11.1.

[0054] The body 110 of the light guide 11 is configured to propagate the light R emitted by the light source 10. It has a refractive index of light nl.l, otherwise more simply called the refractive index nl.l. The body 110 is surrounded by air of index n0=l.

[0055] In a first, non-limiting embodiment illustrated in [Fig. 3a], the body 110 of the light guide 11 is formed from a single block. That is, there is a bare core 110.1. In a non-limiting example, the body 110 is made of PC (polycarbonate).

[0056] In a second, non-limiting embodiment illustrated in [Fig. 3b], the body 110 of the light guide 11 is composed of a core 110.1 and two sheaths 110.2, 110.3 distributed on either side of said core 110.1. In this case, in a non-limiting embodiment, the two sheaths 110.2, 110.3 have the same light refractive index ni.2 (otherwise more simply called refractive index ni.2) which is lower than the refractive index nl.l of the body 110. This first embodiment is easy to realize because in this case, the two sheaths 110.2, 110.3 can be made of the same material. In another non-limiting embodiment, the two sheaths 110.2, 110.3 are made of different materials having different refractive indices and lower than the refractive index nl.l of the body 110.

[0057] In a non-limiting embodiment, the refractive index ni.2 of each sheath 110.2, 110.3 has a minimum index difference of 0.09 with respect to the index The refractive index nl.l of body 110 is given by nl.l - nl.2 > 0.09. The greater the difference in refractive index, the more easily light is guided into the core 110.1. In a non-limiting example, if nl.1 = 1.586 when the core 110.1 is made of PC, nl.2 = 1.49 when the sheaths 110.2 and 110.3 are made of PMMA. This allows light to be guided by optically isolating the core 110.1 from another material with which the light guide 11 is overmolded or a material bonded to it, without affecting light propagation. Otherwise, the contacting material would absorb or scatter the light. In a non-limiting embodiment, the core 110.1 is made of PC and the sheaths of PMMA or silicone.

[0058] The metal lens 111 is disposed on the surface of the light guide 11. In a non-limiting embodiment illustrated in Figures 1 and 2, it is disposed on the first surface 11.1. In non-limiting embodiments, the metal lens 111 is glued to the surface of the light guide 11 or it can be directly created on the light guide 11 by ablation or by a nano-etching or nanoprinting process, the latter being called in English "nano-imprint".

[0059] The meta-lens 111 is configured to receive the light R emitted by the light source 10 and modify its propagation phase q> so that it is deflected and guided within the body 110 of said light guide 11 in a given propagation direction P (illustrated in Figures 1 and 2). In other words, the meta-lens 111 is configured to create a phase shift that deflects the propagation direction of the light R so as to trap the light R within the light guide 11. In the following description, the propagation phase q> of the light R and the propagation phase q> of the light beam Fx formed by the light R will be used interchangeably. In the following description, the propagation phase q> is otherwise referred to as phase q>. As will be seen later, the meta-lens 111 creates a phase mask.

[0060] The meta-lens 111 has a light refractive index n2 (illustrated in [Fig.4]) for the nano-pillars 111.2 (described later), otherwise more simply called the refractive index n2. In a non-limiting embodiment, the light R used to illuminate the meta-lens 111 covers a wavelength range X from 400 to 780 nm, and the material used for the meta-lens 111 (i.e. for the nano-pillars 111.2) has different values ​​of refractive index n2 depending on the wavelength X.

[0061] In a non-limiting embodiment, the R light may also cover a wavelength in the infrared or near-infrared.

[0062] Thus, in non-limiting examples: - n2 = 2.1 for X = 631 nm (red), - n2 = 2.47 for X = 450 nm (blue), - n2 = 2.38 for X = 550 nm (green), - n2 = 2.35 for X = 621 nm (red) and 632 nm (super red).

[0063] As illustrated in Figure 4, the meta-lens 111 comprises: - a substrate 111.1, and - a plurality of nano-pillars 111.2.

[0064] The substrate 111.1 is disposed on the surface of the light-guiding mat 110 of the light guide 11. It comprises a thickness E and a length L. In a non-limiting embodiment, the substrate 111.1 is made of glass. In a non-limiting embodiment, the substrate 111.1 is bonded to the light-guiding mat 110.

[0065] The nano-pillars 111.2 are arranged on the substrate 111.1. They are defined by parameters including: - a radius r (illustrated in figure 6), - a height h (illustrated in figure 6), - a ps step between two nano-pillars 111.2. The ps step (illustrated in Figure 5) represents the repetition frequency of the nano-pillars 111.2, - a material with a refractive index n2 which is the refractive index of the metal-lens 111, - a bs base (illustrated in [Fig.6]).

[0066] It should be noted that the pitch ps is defined between the two longitudinal axes (illustrated by dashed lines in [Fig. 5]) of two adjacent nano-pillars 111.2. In a non-limiting embodiment illustrated in [Fig. 6], the nano-pillars 111.2 have a disc-shaped base bs.

[0067] In a non-limiting embodiment, the nano-pillars 111.2 are made of Silicon Nitride (SiN). This material is easy to work with and pollutes less in terms of dust compared to other materials that can be used for the nano-pillars 111.2 such as, in non-limiting examples, Titanium Dioxide (TiO2) or Hafnium Oxide (HfO2).

[0068] Thus, in a non-limiting embodiment example, on a substrate 111.1 of thickness E=5 millimeters which is glued onto the light guide mat 110, a 70 nanometer layer of siN can be deposited and the siN layer etched to obtain the nanopillars 111.2.

[0069] The nano-pillars 111.2 modify the propagation phase q of the light R passing through them. In other words, they add a phase delay. The result is that the light is deflected in a direction that traps it by total internal reflection in the light guide 11, thus giving it a path in a desired propagation direction P so as to obtain an emergent light beam (not shown).

[0070] The propagation direction P is defined by an angle θ defined with respect to a surface of the light guide 11. The propagation direction P is equal to 2ir*sinθ / X, where θ is expressed in radians. As illustrated in Figures 1 and 2, the angle θ is the angle between the propagation direction P and the inner wall of the body 110 of the light guide 11 opposite the second surface 11.2.

[0071] In a non-limiting embodiment, the angle 0 is between 20 degrees and 47 degrees, i.e., between 0.35 radians and 0.82 radians. In a non-limiting example, for a body 110 with a bare core 110.1 made of PC, 0 = 45°.

[0072] The angle θ is less than a critical angle of total internal reflection [3 (illustrated in Figures 1 and 2). Beyond this angle, the light exits the light guide 11 perpendicularly to the surface of the light guide 1L. In this case, there is no reflection and no propagation of light within the body 110 of the light guide 11. It should be noted that the exit angle of the light depends on the angle θ according to Snell's law of refraction, which is known to those skilled in the art.

[0073] In a non-limiting example, for a body 110 with a bare core 110.1 made in PC, [3 = 51°, we have [3 in radians = (ir / 2-asin(n0 / nl)) with n0=l the index of air.

[0074] In a non-limiting example, for a body 110 with a core 110.1 and cladding 110.2, we have [3 in radians = (ir / 2 - asin(nl.2 / nl.l)), with nl.l the refractive index of the core 110.1 and nl.2 the refractive index of the cladding nl.2. It should be noted that the critical angle [3] decreases as the difference in index between the cladding 110.2 and the core 110.1 decreases, and less light manages to propagate in the light guide 11. It is therefore necessary to decrease the angle 0 for the light to propagate correctly.

[0075] It will be noted that the angle 0 and therefore the direction of propagation P is readjusted according to whether the body 110 is composed solely of a bare core 110.1, or of a core 110.1 and sheaths 110.2.

[0076] To adjust the angle 0 and therefore the direction of propagation P, the gradient of the phase change q> of the light R emitted by the light source 10 is controlled. This is done by means of the nano-pillars 111.2.

[0077] To this end, in a non-limiting embodiment illustrated in [Fig. 5], the nanopillars 111.2 have different radii r and the same height h. For the sake of clarity in the figure, only one height ha and one radius ra have been referenced. It should be noted that the smaller the radius r, the less material a nanopillar 111.2 contains, which results in a minimal change in the phase q>, leading to a small phase delay. Conversely, when the radius r is larger, the more material a nanopillar 111.2 contains, which results in a more significant change in the phase q>, leading to a larger phase delay.

[0078] As illustrated in [Fig. 5], the nano-pillars 111.2 have a radius r that increases from left to right. Each nano-pillar 111.2 will induce a different phase delay q> compared to its neighbor. The larger the radius r, the greater the phase delay q>. The radius r thus acts on the phase q> of the light beam Fx from the light source 10. Since the radii r are smaller on the left, the phase delays on the left are smaller, and the light will be less delayed on the left than on the right. It should be noted that the greater the delay, the more the wavefront is distorted and the more the resulting light beam is deflected.

[0079] As a reminder, light, forming a beam, always propagates perpendicularly to the wavefront. Classically, there is zero phase delay along the same line of the wavefront. As can be seen in Figure 7, the incoming wavefront Fo at the entrance of the meta-lens 111 (also called the incident wavefront Fo) is planar and perpendicular to the substrate 111.1 of the meta-lens 111.

[0080] Each nano-pillar 111.2 introduces a phase delay q> different from its neighbor, because they all have a different diameter, this differential phase delay then causes a deformation of the wavefront.

[0081] As can be seen in [Fig.7], the emerging wavefront Fo' is deformed, which therefore results in a deviation of the emerging beam Fx'.

[0082] Thus, at the exit of the metal lens 111, the light, which always propagates perpendicularly to the wavefront—here the emergent wavefront Fo', which is inclined—will be oriented along a given propagation direction P. Consequently, the light is oriented along a propagation direction P that has changed due to the phase shift of the light, namely 0 = 45° in the non-limiting example of Figures 1 and 2.

[0083] It will be noted that the emergent wavefront Fo' has been delayed progressively and linearly. Each nano-pillar 111.2 is configured to produce a linearly evolving phase change q> of the light, namely a linear phase shift. This makes it possible to obtain a planar emergent wavefront Fo'. It will be noted that a phase shift between 0 and 2ir is equivalent. It is therefore not necessary to create a linear phase shift along the entire length of the input wavefront Fo to obtain a continuous deflection. A phase shift between 0 and 2ir can be performed as many times as necessary. Thus, a linear phase shift between 0 and 10ir is equivalent to five linear phase shifts between 0 and 2ir.

[0084] It should be noted that the phase q is modulated between 0 and 2ir. It should be noted that with a phase q = 0, there is no delay. With q = ji, there is a delay of X / 2. From the point of view of the meta-lens 111, as soon as 9 = 2ir, we return to a radius r of a nano-pillar 111.2 corresponding to 0, and therefore to the same nano-pillar 111.2 to avoid having too large differences between the radii r. Thus, the meta-lens 111 comprises several 111.2 nano-pillar assemblies defined so as to obtain a phase shift of light with a phase modulated between 0 and 2ir.

[0085] The height h of the nano-pillars 111.2 allows the phase q> to be controlled for a given wavelength X. With the correct height h defined, all phase changes between 0 and 2ir can be performed.

[0086] In a non-limiting example, to obtain 0= 45°, for X=630 nm, the radius r of the nano-pillars 111.2 varies between 60 and 140 nm and the height h = 800 nm and the pitch ps = 400 nm.

[0087] As explained previously, the radius r allows control of the phase q> of the light beam Fx.

[0088] The other parameters, namely the height h, the pitch ps, and the material of the nano-pillars 111.2, are defined to maximize the transmission rate of light through the nano-pillars 111.2. Maximizing the transmission rate amounts to minimizing the absorption of light by the material of the nano-pillar 111.2. Thus, these other parameters are determined to obtain minimum absorption over the range where the radius r is varied to obtain a phase shift (also called phase difference) between 0 and 2ir.

[0089] By calculation, for a nano-pillar 111.2, a given height h and a given pitch ps are fixed, and its material is Silicon Nitride SiN with a refractive index n2 = 2.04. In the non-limiting example shown, h = 1.35 μm and ps = 0.450 μm. Working at a constant height h facilitates the fabrication of the nano-pillars 111.2. With a constant height h, the design of the nano-pillars 111.2 must be adapted to obtain a phase shift between 0 and 2μ and, at the same time, the highest possible light transmission to retain a maximum amount of light.

[0090] For a fixed height h and a fixed step size ps, the light transmission curves as a function of the radius r, and the phase shift curves as a function of the radius r, are established. Curves 8a and 8b illustrate the phase shift and light transmission for the best compromise for the chosen constant height h and for a given wavelength X. It should be noted that this compromise changes if the wavelength X changes.

[0091] In Figure 8a, in a non-limiting example, for a height h=1.35pm (micrometers), we can thus observe the phase variation q> in radians (on the ordinates) between 0 and 9 as a function of the radius r (on the abscissas) of the nano-pillars 111.2 which varies between 0.04 and 0.15 qm, for a given wavelength X, here for X=590nm in the illustrated non-limiting example.

[0092] In Figure 8b, in a non-limiting example, for a height h=1.35pm, a variation in light transmission Tx (on the ordinate) between 0 and 1 can be observed as a function of the radius r (on the abscissa) of the nano-pillars 111.2, which varies between 0.04 and 0.15 pm, for the given wavelength X, here 590nm. At a value of 0 for transmission, no light passes. At a value of 1 for transmission, all light passes.

[0093] With these two curves, it is therefore possible to determine the height h and radius r of the 111.2 nano-pillars that allow for phase shift control dynamics while maximizing light transmission through the 111.2 nano-pillars, and while remaining manufacturable. The values ​​of all the parameters of a 111.2 nano-pillar can thus be found to obtain the possible phase shift and transmission values, and in particular a transmission rate close to 1 for a given X wavelength. It should be noted that if the results are not satisfactory, the procedure can be repeated by setting a different value for the height h.

[0094] In a non-limiting embodiment illustrated in [Fig. 1], the light source 10 is natively collimated. In this case, the incident wavefront Fo of the light emitted R by the light source 10 is planar and the light R arrives at normal incidence on said metal lens 111.

[0095] In another non-limiting embodiment illustrated in Figure 2, the light source 10 is not natively collimated and, in addition to the light source 10 and the light guide 11, the lighting device 1 further comprises a collimator 12 disposed between the light source 10 and the metal lens 111. The collimator 12 is positioned opposite the metal lens 111 between the light source 10 and the metal lens 111. This allows the light emitted R by the light source 10 to be collimated and the light R to arrive at normal incidence on the metal lens 111. It should be noted that collimating light means making its wavefront planar.

[0096] Of course, the description of the invention is not limited to the embodiments and the domain described above. Thus, in other non-limiting embodiments, the base bs of the nano-pillars 111.2 is oblong or elliptical in shape. Thus, in another non-limiting embodiment, the nano-pillars 111.2 are configured to perform a collimation function to collimate the light emitted R by the light source 10, which is not natively collimated. It should be noted that a light source that is not natively collimated has a spherical incident wavefront Fos. In this case, the phase shift induced by the metal lens 111 compensates for the curvature of the spherical incident wavefront F0 to make it planar. In this case, the nano-pillars 111.2 have different radii r and different heights h. Thus, in another non-limiting embodiment, the nano-pillars 111.2 have the same radius r and different heights h.

[0097] Thus, the described invention has, in particular, the following advantages: - It increases the efficiency of light collection at the input of the light guide 11 and therefore the overall efficiency of the light guide. Thus, according to experiments, an input efficiency of up to approximately 67% is obtained. namely 67% of the light emitted by the light source 10 enters the light guide 11, - It reduces light loss and is therefore more efficient than a lighting device that would include a surface light guide with a light-guiding sheet and folded light injection elements, known to those skilled in the art, forming a stack through which the light from the light source enters. Indeed, in the case of folded light injection elements, which include a fold, the light rays from the light source that reach this fold are not reflected back towards the light-guiding sheet, resulting in a loss of luminous efficiency. - it therefore allows for a more efficient lighting system 1, - it allows for a more compact lighting device 1 with a limited light guide thickness compared to direct coupling via the edge of the light guide, - It allows for the same decorative patterns as other prior art forms while being more efficient in light coupling, - and it consumes less energy. Indeed, as the light coupling efficiency improves, so does the overall efficiency. Greater optical efficiency means less light flux is needed at the source to obtain the same amount of light at the output, therefore the light source consumes less electricity.

Claims

Demands

1. A lighting device (1) comprising: - a light source (10) configured to emit light (R), - a surface light guide (11) comprising a body (110) in the form of a light guide sheet configured to propagate said light (R) emitted by said light source (10), characterized in that said light guide (11) further comprises: - a meta-lens (111) configured to receive said light (R) and modify the propagation phase (q>) of said light (R) so that it is guided in the body (110) of said light guide (11) in a given propagation direction (P).

2. Light device (1) according to claim 1, characterized in that said light source (10) is monochromatic.

3. Light-guided light-guide device (1) according to any one of the preceding claims, characterized in that said body (110) of the light guide (11) is formed in one piece or is composed of a core (110.1) and two sheaths (110.2, 110.3) distributed on either side of said core (110.1) and of refractive index (nl.2) lower than a refractive index (nl.1) of said body (110).

4. Light device (1) according to the preceding claim, characterized in that the refractive index (nl.2) of each sheath (110.2, 110.3) has a minimum index difference of 0.09 with respect to the refractive index (nl.l) of said body (110).

5. Light device (1) according to any one of the preceding claims, characterized in that said light (R) emitted by the light source (10) covers a wavelength range (X) between 400 nanometers and 780 nanometers.

6. Light-up device (1) according to any one of the preceding claims, characterized in that said meta-lens (111) comprises a substrate (111.1) disposed on the surface of said light-guide mat (110) of the light guide (11) and nano-pillars (111.2) disposed on said substrate (111.1) and defined by a radius (r), a height (h) and a pitch (p) between two nano-pillars (111.2).

7. Light device (1) according to claim 6, characterized in that said nano-pillars (111.2) are made of Silicon Nitride (SiN).

8. Light device (1) according to claim 6 or claim 7, characterized in that the substrate (111.1) is made of glass and is glued onto said light guide mat (110) of the light guide (11).

9. Light device (1) according to any one of the preceding claims 6 to 8, characterized in that the nano-pillars (111.2) have different radii (r) and the same height (h).

10. Light device (1) according to any one of the preceding claims, characterized in that said light device (1) further comprises a collimator (12) disposed between the light source (10) and the metal lens (111).

11. A light device (1) according to any one of the preceding claims, characterized in that the direction of propagation (P) is defined by an angle (0) between 20 degrees and 47 degrees.

12. A luminous device (1) according to the preceding claim, characterized in that said angle (0) is less than a critical angle of total reflection (|3).

13. Light assembly (3) of vehicle (2), characterized in that said light assembly (3) comprises said light device (1) according to any one of the preceding claims.

14. Light assembly (3) according to the preceding claim, characterized in that said light assembly (3): - is a front face or a rear face of said vehicle (2), or a projector or a rear light of said vehicle (2), or - is part of an element (21) of the passenger compartment (20) of said vehicle (2).

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