Light guide for a luminous device with which a motor vehicle is intended to be equipped

Abstract

Disclosed is a light guide (2) for a luminous device for a motor vehicle (1), the light guide being intended to be illuminated by at least one light source (4) configured to produce a monochromatic or polychromatic light beam (F), the light guide (2) being characterized in that it comprises a waveguide (6) comprising a transparent material having a first refractive index (n1), and characterized in that it comprises at least one meta-lens (15), the meta-lens (15) being configured to modify at least one property of the wavefront of the light beam (F) produced by the light source (4) and passing through the light guide (2).

Description

Light guide for a light device intended to equip a motor vehicle

[0001] The present invention relates to a light guide for a light device. The invention also relates to a motor vehicle equipped with a light device comprising such a light guide.

[0002] Some automotive lighting devices are equipped with a light guide to provide signaling functions and / or functions for projecting light signals into the environment of the motor vehicle. A light guide is an optical device used to transport light from a light source to a location where the light is needed. A light guide generally offers great flexibility in light distribution and thus allows the position of the lighting to be changed without changing the location of the light source. Such a light guide can guide light from a polychromatic or monochromatic light source.

[0003] In the case where the light source is polychromatic, the light produced by this source is for example included in the visible spectrum and the light may appear white. A light guide configured to transport the light produced by a polychromatic source may comprise at least one diffraction grating, such as an optical device composed of a series of parallel slits or reflective stripes, which makes it possible to divide the incident light into several beams by diffraction, which has the effect of propagating the light of different wavelengths in different directions.

[0004] The objective of the present invention is to propose a less bulky and lighter light guide which makes it possible to regulate the light transported in the guide so as to select rays having a precise wavelength or to focus this light at a given location or to direct the light in a certain direction of propagation. In other words, the objective of the present invention is to multiply the functionalities of a light guide while minimizing its size to allow better integration of said light guide in a lighting device for a motor vehicle in order to provide signaling functions and / or for projecting light signals in the environment of the motor vehicle with the same light guide.

[0005] Thus, an object of the invention is a light guide offering good optical quality and high luminous efficiency while being more compact, more robust and lighter; which is simple to use and easily integrated into a motor vehicle.

[0006] The invention therefore relates to a light guide for a light device for a motor vehicle, the light guide being intended to be illuminated by at least one light source configured to produce a monochromatic or polychromatic light beam, the light guide being characterized in that it comprises a waveguide comprising a transparent material having a first refractive index and characterized in that it comprises at least one meta-lens, the meta-lens being configured to modify at least one property of the wavefront of the light beam produced by the light source and passing through the light guide.

[0007] According to a particular embodiment, the waveguide is surrounded by a layer comprising another transparent material having a second refractive index which is lower than the first refractive index of the waveguide material.

[0008] In this same particular embodiment, the meta-lens is arranged at the interface between the waveguide and the layer.

[0009] According to a particular embodiment, the meta-lens comprises at least one nanostructure comprising an arrangement of nanopillars on the surface and the nanopillars are configured to modify the intensity and / or the phase and / or the orientation of the light beam at the exit of the meta-lens.

[0010] According to a particular embodiment, the nanopillars have a third refractive index.

[0011] According to a particular embodiment, the third refractive index of the nanopillars is greater than the first refractive index of the waveguide material.

[0012] According to a particular embodiment, the third refractive index of the nanopillars is greater than the second refractive index of the layer.

[0013] According to a particular embodiment, the light source is a monochromatic source, and the light guide comprises an element comprising phosphor, said element being intended to receive a light beam from the meta-lens, said element being configured to produce a polychromatic light beam.

[0014] According to a particular embodiment, the element comprising phosphorus has a fourth refractive index greater than the third refractive index of the nanopillars of the meta-lens.

[0015] The invention also relates to a light device for a motor vehicle characterized in that it comprises at least one such light guide and at least one light source configured to produce a monochromatic or polychromatic light beam, the at least one light source being juxtaposed with the light guide so that the light beam passes through the light guide.

[0016] According to a particular embodiment, the light source of said light device emits a monochromatic light of blue color having a wavelength between 435 nm and 450 nm. Presentation of figures

[0017] These objects, characteristics and advantages of the present invention will be explained in detail in the following description of different particular embodiments made without limitation in relation to the attached figures among which:

[0018] This is a schematic view of a light guide according to one embodiment of the invention.

[0019] This is a detailed view of a nanostructure of a meta-lens.

[0020] This is another schematic detail view of a nanostructure of a meta-lens.

[0021] This is a schematic view of a light guide according to another embodiment of the invention. Detailed description

[0022] A first embodiment of a light guide 2 according to the invention is described below with reference to the. A second embodiment of a light guide 2 according to the invention is described below with reference to the. These two embodiments aim to provide a solution to the problems identified with the known embodiment of the prior art by remedying the drawbacks described above and by proposing an improved light guide.

[0023] For each of the two embodiments, the light guide 2 is configured to be integrated into a lighting device which is itself intended to equip a motor vehicle. Throughout the description, the motor vehicle is a motor vehicle of any type, in particular a passenger vehicle, a utility vehicle, a truck or even a bus.

[0024] For each of the two embodiments, the light guide 2 is intended to be juxtaposed with a light source 4 so that a light beam F produced by the light source 4 enters the light guide 2.

[0025] In the case of the first embodiment of the light guide 2, the light source 4 is configured to emit a polychromatic light beam F, that is to say a light beam F of white color.

[0026] In the case of the second embodiment of the light guide 2, the light source 4 is configured to emit a monochromatic light beam F. The light from such a light source 4 comprises only rays of a single wavelength, that is to say it comprises only light rays having a specific color. In the second embodiment, the light source 4 preferably emits a monochromatic light of blue color having a wavelength between 435 nm and 450 nm.

[0027] For each of the two embodiments, the light guide 2 comprises a waveguide 6 comprising a transparent material having a first refractive index n1. This first refractive index n1 is for example between 1.4 and 1.8. According to a preferred embodiment, this first refractive index n1 is more particularly equal to 1.5.

[0028] The waveguide 6 of the light guide 2 may optionally be surrounded by a protective layer 8 comprising another transparent material having a second refractive index n2 which is lower than the first refractive index n1 of the waveguide 6, but higher than the refractive index of air. By surrounding the waveguide 6 comprising a transparent material having a first refractive index n1 with a layer 8 of transparent material having a lower second refractive index n2, this ensures the propagation of the light rays of the light beam F inside the waveguide 6 of the light guide 2.

[0029] For each of the two embodiments, the light guide 2 comprises at least one meta-lens 15 configured to modify at least one optical property of the wavefront of the light beam F produced by the light source 4 and passing through the waveguide 6 of the light guide 2. More particularly, the at least one meta-lens 15 is arranged on the surface of the waveguide 6 or at the interface between the waveguide 6 and the protective layer 8 surrounding this waveguide 6.

[0030] Generally speaking, meta-lenses 15 have the advantage of being flat, extremely thin, very light and compact, which greatly facilitates their integration into lighting devices in general and into light guides in particular.

[0031] A meta-lens 15 has for example the shape of a flat cylinder, comparable to a wafer. The diameter of such a meta-lens 15 is for example a few millimeters, it is for example less than 15 mm. Alternatively, a meta-lens 15 can have a quadrilateral shape and more particularly a square shape, a rectangular shape or even a diamond shape. Since the integration of one or more meta-lenses 15 is relatively easy and these meta-lenses 15 have a minimal bulk, a wide variety of designs can thus be imagined for the light guide 2.

[0032] A meta-lens 15 generally comprises a nanostructure 16 configured to regulate the shape of the wavefront of the light beam F produced by the light source 4 and passing through said meta-lens 15. A meta-lens 15 may more particularly be configured to modify the amplitude and therefore the intensity and / or the phase and therefore the direction of propagation of the light beam F.

[0033] The nanostructure 16 of the meta-lens 15 may comprise an arrangement of nanopillars 17 on its surface. These nanopillars 17 are generally fabricated by nanostructuring, i.e., by electron beam lithography or by nanoimprint lithography in thin layers and arranged in the form of periodic arrays. These nanometer-sized nanopillars 17 may comprise dielectric materials with a high refractive index, for example, a refractive index greater than two.

[0034] The nanopillars 17 may have a third refractive index n3 which is higher than the first refractive index n1 of the material of the waveguide 6. The third refractive index n3 of the nanopillars 17 may also be higher than the second refractive index n2 of the layer 8. Such a higher third refractive index n3 makes it possible to promote the passage of the light beam F through the meta-lens 15. According to a particular example, the third refractive index n3 of the nanopillars 17 is 2.5.

[0035] The nanopillars 17 are for example placed on the waveguide 6. The material of the waveguide 6 is flexible and is chosen to provide suitable structural support and to allow a majority of the light passing through it to pass through.

[0036] More particularly, the nanostructure 16 may comprise a periodic array of nanopillars 17. By "periodic" is meant here that the nanopillars within the nanostructure 16 are placed at more or less regular intervals from one another. For example, the nanopillars 17 of a nanostructure 16 may be placed at intervals of between 100 nm and 900 nm.

[0037] The optical properties of a meta-lens 15 are mainly defined by the wavelength of the light source 4 used, by the third refractive index n3 of the material used for the nanopillars 17, by the dimensions of the nanopillars 17 and by their distribution within the nanostructure 16. In other words, the density of material in the nanostructure 16 of the meta-lens 15 defines the effect that the meta-lens 15 has on the light beam F which passes through it.

[0038] In general, the nanopillars 17 may have cross-sections of different sizes from one another. Indeed, the shape and size of the cross-section of a nanopillar 17 of the nanostructure 16 may have an impact on the propagation speed of the light beam F which passes through said nanopillar 17, thus modifying the optical properties of the wavefront of said light beam F which passes through the meta-lens 15.

[0039] The nanopillars 17 may in particular have a cylindrical shape; in this case, they may comprise a circular-shaped base, as illustrated in the. The diameter may vary from one nanopillar 17 to another. Alternatively, the shape of the base could be different from a circular shape, for example a polygonal base, in particular square or rectangular.

[0040] Furthermore, the nanopillars 17 of a meta-lens 15 may have the same height configured to modify a phase of the light beam F produced by the light source 4 and passing through this meta-lens 15.

[0041] The distribution of the nanopillars 17 within the nanostructure 16 of the meta-lens 15 can be optimized to contribute to a change in the direction of propagation of the light beam. In other words, the distribution of the nanopillars 17 within the nanostructure 16 can be specifically configured to influence the direction of propagation of the light beam F in order to modify the orientation of the light beam at the exit of the meta-lens 15.

[0042] More generally, a meta-lens 15 comprises a periodic array of nanopillars 17 having different diameters so as to influence the speed of propagation of light through the nanopillars 17 so as to modify the properties of the wavefront of the light beam F which passes through the meta-lens 15. Indeed, for two nanopillars 17 having the same height and different diameters, the nanopillar having a larger diameter will slow down the propagation of the light which passes through it more than the nanopillar with a smaller diameter, as illustrated in the. This makes it possible in particular to orient the light beam F at the exit of the light device 2.

[0043] Thus, in the case where the nanostructure 16 of the meta-lens 15 comprises on its surface an arrangement of nanopillars 17 all having the same specific height, this nanostructure 16 of the meta-lens 17 makes it possible to introduce a phase shift of the light beam F with a specific wavelength which passes through the meta-lens 15, thus modifying the phase of the wavefront of said light beam F. An example of an arrangement of nanopillars 17 of cylindrical shape with a determined height and different diameters is illustrated in the.

[0044] In the case of the first embodiment of the light guide 2, the latter may comprise several meta-lenses 15 with nanostructures 16 that differ from one meta-lens 15 to another. More particularly, the third refractive index of the material used for the nanopillars 17, the dimensions of the nanopillars 17 and their distribution within the nanostructure 16 may be different from one meta-lens 15 to another.

[0045] Thus, thanks to the materials, the height and the diameters of the nanopillars 17 and thanks to their arrangement at the level of the nanostructure 16, it is possible to obtain light beams having distinct properties in terms of wavelength, phase, orientation and amplitude at the output of each of the meta-lenses 15 which equip this light guide 2. This is more particularly illustrated on the.

[0046] In the first embodiment of the light guide 2 illustrated in the, it comprises three meta-lenses 15 having properties distinct from each other.

[0047] More particularly, a first meta-lens 15 comprises a nanostructure 16 with nanopillars 17 configured to let a red light beam F pass through, this beam F being oriented perpendicular to the surface of the meta-lens 15 and perpendicular to the surface of the waveguide 6 on which the meta-lens 15 is arranged.

[0048] A second meta-lens 15 comprises a nanostructure 16 with nanopillars 17 configured to let through a green light beam F, this beam F being inclined relative to the surface of the meta-lens 15 and inclined relative to the surface of the waveguide 6 on which the meta-lens 15 is arranged. The nanopillars 17 and the nanostructure 16 of this second meta-lens 15 are therefore different from the nanopillars 17 and the nanostructure 16 of the first meta-lens 15.

[0049] A third meta-lens 15 comprises a nanostructure 16 with nanopillars 17 configured to let a blue-colored light beam F pass through, this beam F being convergent so as to be focused on an element 19 comprising phosphorus which is arranged directly on the surface of the waveguide 6 or on the layer 8 surrounding the waveguide 6.

[0050] According to a particular embodiment, the element 19 comprising phosphorus has a fourth refractive index n4 greater than the third refractive index n3 of the nanopillars 17. Furthermore, the fourth refractive index n4 of the element 19 comprising phosphorus may be greater than the first refractive index n1 of the material of the waveguide 6 and, in this case, also be greater than the second refractive index n2 of the material of the layer 8 surrounding the waveguide 6. According to a particular example, the fourth refractive index n4 of the element 19 comprising phosphorus is equal to 4.

[0051] Thus, the same light guide 2 illuminated by a single light source 4 producing polychromatic light and equipped with a multitude of meta-lenses 15 which allow light beams F with different wavelengths to pass through can be used to produce lighting with several colors and / or with different intensities and / or with different orientations.

[0052] In the case of the second embodiment of the light guide 2, it may comprise several meta-lenses 15 with nanostructures 16 that differ from one meta-lens 15 to another. However, these nanostructures 16 are specifically configured for a light beam F comprising monochromatic light, i.e. light with a specific wavelength or a wavelength within a specific range, which may further contribute to a high transmission rate. Thus, for monochromatic light having a given wavelength, the ideal height of the nanopillars 17 can be determined to obtain the highest possible transmission rate.

[0053] Thus, the transmission rate through a light guide 2 comprising a meta-lens 15 with a monochromatic light beam F is for example greater than 75% and in particular greater than 80%, in particular greater than 90%. Thanks to this high transmission rate, it is thus possible to use a less powerful and more energy-efficient light source 4 for a result just as satisfactory as that observed for the prior art. The use of such a light source 4 can also make it possible to avoid heating of said light source 4 and its environment.

[0054] In this second embodiment of the waveguide 2, the distribution of the nanopillars 17 of the different nanostructures 16 of the different meta-lenses 15 can be specifically configured for such a monochrome light beam F, in particular to increase the efficiency of the optical result.

[0055] In this case, the nanopillars 17 of the nanostructure 16 are more particularly configured to obtain light beams having distinct properties in terms of phase, therefore of orientation and / or in terms of intensity and therefore of amplitude at the output of each of the meta-lenses 15 which equip this light guide 2 according to the second embodiment.

[0056] Thus, the light guide 2 according to the second embodiment comprises three meta-lenses 15 having properties distinct from each other.

[0057] More particularly, a first meta-lens 15 comprises a nanostructure 16 with nanopillars 17 configured to let through a light beam F oriented perpendicular to the surface of the meta-lens 15 and perpendicular to the surface of the waveguide 6 on which the meta-lens 4 is arranged.

[0058] The light beam F then passes through an element 19 comprising phosphor which is arranged directly on the surface of the waveguide 6 or on the layer 8 surrounding the waveguide 6. This element 19 comprising phosphor is intended to receive a light beam F coming from the meta-lens 15 and it is configured to produce a polychromatic light beam at the output of the light guide 2.

[0059] For example, in the case where the light source 4 is a monochromatic light source which emits blue light having a wavelength between 435 nm and 450 nm, the element 19 comprising phosphorus can make it possible to color a portion of the blue light into white light, optionally with a yellow tint or a more or less pronounced blue tint. Such an element 19 comprising phosphorus is in particular arranged directly on the surface of the waveguide 6 or on the layer 8 surrounding the waveguide 6.

[0060] A second meta-lens 15 comprises a nanostructure 16 with nanopillars 17 configured to let through a light beam F inclined relative to the surface of the meta-lens 15 and inclined relative to the surface of the waveguide 6 on which the meta-lens 4 is arranged. The nanopillars 17 and the nanostructure 16 of this second meta-lens 15 are therefore different from the nanopillars 17 and the nanostructure 16 of the first meta-lens 15. The light beam F then passes through an element 19 comprising phosphorus.

[0061] A third meta-lens 15 comprises a nanostructure 16 with nanopillars 17 configured to let a convergent light beam F pass through so as to be focused on the element 19 comprising phosphor which is arranged directly on the surface of the waveguide 6 or on the layer 8 surrounding the waveguide 6.

[0062] Such a light guide 2 can be used to provide exterior lighting and / or signaling functions for day and / or night. It is therefore possible to design a more compact, lighter and more robust light guide 2 which can be easily integrated into a motor vehicle 1.

[0063] Such a light guide 2 according to the invention can be illuminated by a single light source 4 and offer, thanks to the meta-lenses 15 which equip this light guide 2, light beams having properties distinct from each other at the exit points of said light guide 2.

[0064] Such a light guide 2 according to the invention is not susceptible to, or only slightly to, possible shocks and / or vibrations generated by the use of the motor vehicle in which said light guide 2 is integrated and therefore offers a more robust, more reliable and more versatile alternative than the light guides known from the state of the art.

Claims

Light guide (2) for a light device for a motor vehicle (1), the light guide being intended to be illuminated by at least one light source (4) configured to produce a monochromatic or polychromatic light beam (F), the light guide (2) being characterized in that it comprises a waveguide (6) comprising a transparent material having a first refractive index (n1), and characterized in that it comprises at least one meta-lens (15), the meta-lens (15) being configured to modify at least one property of the wavefront of the light beam (F) produced by the light source (4) and passing through the light guide (2). Light guide according to the preceding claim, characterized in that the waveguide (6) is surrounded by a layer (8) comprising another transparent material having a second refractive index (n2) which is lower than the first refractive index (n1) of the material of the waveguide (6), and characterized in that the meta-lens (15) is arranged at the interface between the waveguide (6) and the layer (8). Light guide according to one of the preceding claims, characterized in that the meta-lens (15) comprises at least one nanostructure (16) comprising an arrangement of nanopillars (17) on the surface and in that the nanopillars (17) are configured to modify the intensity and / or the phase and / or the orientation of the light beam (F) at the exit of the meta-lens (15). Light guide according to the preceding claim, characterized in that the nanopillars (17) have a third refractive index (n3). Light guide according to the preceding claim, characterized in that the third refractive index (n3) of the nanopillars (17) is greater than the first refractive index (n1) of the material of the waveguide (6). Light guide according to claim 2 and according to one of claims 4 or 5, characterized in that the third refractive index (n3) of the nanopillars (17) is greater than the second refractive index (n2) of the layer (8). Light guide according to one of the preceding claims, characterized in that the light source (4) is a monochromatic source, and in that the light guide (2) comprises an element (19) comprising phosphor, said element (19) being intended to receive a light beam (F) coming from the meta-lens (15), said element (19) being configured to produce a polychromatic light beam. Light guide according to the preceding claim, characterized in that the element (19) comprising phosphorus has a fourth refractive index (n4) greater than the third refractive index (n3) of the nanopillars (17) of the meta-lens (15). Lighting device for a motor vehicle (1) characterized in that it comprises at least one light guide (2) according to one of the preceding claims and at least one light source (4) configured to produce a monochromatic or polychromatic light beam (F), the at least one light source (4) being juxtaposed with the light guide (2) so that the light beam (F) passes through the light guide (2). Luminous device according to the preceding claim, characterized in that the light source (4) emits a monochromatic light of blue color having a wavelength between 435 nm and 450 nm.

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