Red reflective module for a motor-vehicle part, and associated system

Abstract

The invention relates to a reflective module (1) for a motor-vehicle part comprising a multilayer stack (13) configured to receive an incident light beam (2) and reflect a reflected light beam (2') having a determined wavelength, and a waveguide mounted on the multilayer stack (13) and configured to transmit, to the multilayer stack (13), a light beam (2'') generated by a remote light source (31), the multilayer stack (13) comprising at least one layer forming a metal mirror, a polymer layer mounted on the mirror and configured to form the reflected light beam (2') via a Fabry-Pérot effect, and having a maximum reflectivity in a wavelength range between 480 nm and 650 nm, a partially transparent metal bilayer being mounted on the polymer layer. The reflective module improves the reflectivity of the perceived red colour.

Description

Red reflective module for automotive parts, and associated system

[0001] The present invention relates to the field of reflective multilayer modules. Its application is particularly advantageous in the field of vehicle bodywork or signaling, especially for red signaling of rear vehicle parts. STATE OF THE ART

[0002] It is common to feature a design or visual element on a vehicle part, either for decoration or for signaling purposes. For rear vehicle signaling, there are red reflectors or reflective modules configured to reflect a beam of red light. A red color rendering is highly desirable in automotive applications, but in practice, it is quite difficult to achieve reliably and in a way that meets the specific requirements of these applications.

[0003] These reflective modules generally include rigid and brittle materials, making them unsuitable for adaptation to curved surfaces as may be required in automotive applications.

[0004] These reflective modules use light sources, typically light-emitting diodes (LEDs) with wavelengths between 420 nm and 680 nm. These LEDs are generally subjected to high currents, which raises their operating temperature. This increase in operating temperature typically leads to wavelength drift and a loss of light beam emission efficiency. Consequently, this impacts the reflective module's light output, both in terms of perceived color and reflected light intensity.

[0005] An object of the present invention is therefore to propose a solution improving the reflectivity of the perceived red color of a reflective module, and in particular to make it more compatible with an application in automotive parts.

[0006] The other objects, features, and advantages of the present invention will become apparent from an examination of the following description and accompanying drawings. It is understood that other advantages may be incorporated. SUMMARY

[0007] To achieve this objective, according to a first aspect, a reflective module for an automotive part is planned, comprising: a substrate, a multilayer stack arranged on the substrate and configured to receive an incident light beam and reflect a reflected light beam having a determined wavelength, the multilayer stack comprising at least one layer forming a metallic mirror,

[0008] Advantageously, the module further comprises a waveguide above the multilayer stack, the waveguide being configured to transmit to the multilayer stack a light beam from a light source located away from the multilayer stack, and in that the multilayer stack further comprises: a layer comprising at least one polymer above the metallic mirror, and configured to form by the Fabry-Pérot effect the reflected light beam, said layer being configured to exhibit maximum reflectivity in a wavelength range between 480 nm and 650 nm, a partially transparent metallic bilayer comprising a first metallic layer based on a first metal, and a second metallic layer based on a second metal distinct from the first metal, the metallic bilayer above the layer comprising at least one polymer.

[0009] The polymer layer forms a Fabry-Pérot cavity with the metallic bilayer and the mirror, which together close the Fabry-Pérot cavity. This multilayer stacking, through the Fabry-Pérot effect, filters the wavelength of the light beam from the light source to obtain a stable red color over time, even with potential wavelength drift from the source.

[0010] The metallic bilayer deposited on the polymer layer also forms a broadband absorber that absorbs a portion of the visible light spectrum. This absorbed radiation will not be reflected by the reflective module and therefore will not contribute to the perceived color. The reflected radiation, synergistically with the Fabry-Pérot cavity, will have a reduced wavelength range between 480 nm and 650 nm. The perceived red color will therefore be more vivid and pronounced.

[0011] Finally, the waveguide allows the light source to be positioned away from the multilayer stack that reflects its light. This makes it possible to use a larger but more efficient heat dissipation device at the light source than in existing solutions, such as using the vehicle's sheet metal. The wavelength and emission efficiency of the source can therefore be better maintained over time.

[0012] Through the synergistic interaction of these elements, it becomes clear that the reflective module enhances the perceived reflectivity of the red color. Furthermore, the multilayer stacking, utilizing a polymer Fabry-Pérot cavity, makes the reflective module lighter, more flexible, and therefore better suited for application in automotive parts.

[0013] A second aspect concerns a reflective system for an automotive part comprising at least one reflective module according to the first aspect, and at least one light source located away from the reflective module, the light source being configured to emit the light beam for its transmission to the waveguide.

[0014] In one example, the light source is configured to emit the light beam with a wavelength between 610 nm and 650 nm, preferably between 620 nm and 631 nm.

[0015] A second aspect concerns a motor vehicle part comprising a reflective module according to the first aspect or a reflective system according to the second aspect. BRIEF DESCRIPTION OF THE FIGURES

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

[0017] Larepresents a cross-sectional view of the principle of the reflective module and the associated system, according to an example of implementation.

[0018] Larepresents an automotive part including a reflective system, according to an example of implementation

[0019] Figures 3 to 5 represent a schematic cross-sectional view of the reflective module and associated system, according to several embodiment examples.

[0020]

[0021] Figures 6A and 6B show a cross-sectional view of the optical patterns of a light input or output grating, according to two embodiments. Figure 6A is a perspective view of the optical patterns illustrated in Figure 6.

[0022]

[0023] Figures 7A and 7B show a cross-sectional view of the optical patterns of a light input or output grating, according to two other embodiments. Figure 1 is a perspective view of the optical patterns illustrated in Figure 2.

[0024] Figures 8A and 8B represent a cross-sectional view of the multilayer stacking according to two embodiment examples.

[0025] The drawings are provided by way of example and are not intended to limit the invention. They are schematic representations of principle intended to facilitate understanding of the invention and are not necessarily to scale with practical applications. In particular, the relative dimensions of the substrates and layers, the waveguide, and the thickness of a layer or substrate relative to its other dimensions are not representative of reality. DETAILED DESCRIPTION

[0026] Before beginning a detailed review of embodiments of the invention, optional features that may be used in combination or alternatively are stated below.

[0027] In one example, the light source is configured to emit a light beam with a wavelength exhibiting a peak intensity at 631 nm.

[0028] According to one example, the layer comprising at least one polymer having an optical index n1 and a thickness of 15 , the optical index n1 and the thickness d 15 are configured together so that said layer exhibits maximum reflectivity in the wavelength range between 480 nm and 650 nm. As an example, this wavelength range has a peak intensity at 631 nm.

[0029] In one example, the optical index n1 is between 1.4 and 1.8 and the thickness of 15is between 100 nm and 250 nm. The polymer layer is therefore particularly well-suited for reflection in the wavelength range between 480 nm and 650 nm. Furthermore, the polymer layer has an optical index that can be more easily matched to that of the waveguide. The optical coupling between the waveguide and the Fabry-Pérot cavity is thus improved, further increasing the reflectivity of the perceived red color by the reflective module.

[0030] According to one example, the waveguide comprises: a light input grating intended to receive the light beam from the light source and comprising a plurality of optical patterns inclined at a first angle of inclination, so as to optically couple by diffraction the light beam from the light source for its propagation in the waveguide, and / or a light output grating surmounting the multilayer stack and comprising a plurality of optical patterns inclined at a second angle of inclination, so as to optically couple by diffraction the light beam propagating in the waveguide for its transmission to the multilayer stack.

[0031] The first and / or second angle of inclination is more specifically taken with respect to the main extension direction of the waveguide.

[0032] The light-input grating thus allows for better coupling of the beam emitted by the light source to the waveguide, thereby improving the proportion of the beam transmitted by the waveguide. Furthermore, this optical diffraction coupling enables additional wavelength filtering at the input grating, which further enhances the red rendering of the reflective module.

[0033] The light output grating allows for better coupling of the beam propagating through the waveguide to the multilayer stack, thus improving the proportion of the beam transmitted to the stack. Furthermore, this optical diffraction coupling enables additional wavelength filtering at the output grating, which further enhances the red rendering of the reflective module.

[0034] As an example, the first and / or second inclination angle is between 40° and 50°, preferably approximately 45°. This angle is particularly well-suited to waveguide manufacturing using industrial roll-to-plate processes, which are compatible with waveguide fabrication over large areas. These processes generally constrain the geometry of patterns that can be produced on large surfaces, particularly in terms of pattern angle.

[0035] As an example, the optical patterns of at least one of the light input and light output gratings have a triangular cross-section and a height greater than or equal to 500 nm, preferably greater than or equal to 550 nm, and preferably substantially equal to 565 nm. This shape allows for optical coupling greater than 50%, while remaining simple to shape and robust in use.

[0036] As an example, the optical patterns of at least one of, and where applicable, the other of, the light input and light output gratings have a parallelogram-shaped cross-section and a height greater than or equal to 300 nm, preferably greater than or equal to 350 nm, and preferably approximately 364 nm. This shape allows for optimized optical coupling greater than 90%, thus ensuring better reflection by the reflecting module.

[0037] According to one example, the optical patterns of one of the light input grating and the light output grating have a triangular cross-section and a height greater than or equal to 500 nm, preferably greater than or equal to 550 nm and preferably substantially equal to 565 nm, and the optical patterns of the other of the light input grating and the light output grating have a parallelepiped cross-section and a height greater than or equal to 300 nm, preferably greater than or equal to 350 nm and preferably substantially equal to 364 nm.

[0038] For example, in a layer comprising at least one polymer with an optical index n1, the waveguide comprises, and preferably is made of, a material with an optical index n2 such that the ratio n1 / n2 is between 0.90 and 1.1, preferably at the wavelength of the beam emitted by the source. The optical coupling between the waveguide and the multilayer stack is thus improved, enhancing light reflection by the reflecting module.

[0039] For example, in a metallic bilayer, the first metallic layer is gold-based and the second metallic layer is chromium-based. The use of these two metals in the metallic bilayer allows for broadband absorption across the visible spectrum.

[0040] For example, the first gold-based metal layer is placed on top of the base layer, and the second chromium-based metal layer is placed on top of the first metal layer. This improves the chemical stability of the stacked materials.

[0041] As an example, the metallic bilayer has a non-zero thickness of less than or equal to 10 nm. The transparency of the metallic bilayer is thus improved.

[0042] As an example, in the metallic bilayer, the first metallic layer has a non-zero thickness substantially less than 10 nm, preferably substantially less than or equal to 7 nm, preferably substantially less than or equal to 5 nm. As another example, the first metallic layer has a non-zero thickness substantially greater than or equal to 3 nm, preferably a thickness substantially equal to 3 nm.

[0043] As an example, in the metallic bilayer, the second metallic layer has a non-zero thickness substantially less than 10 nm, preferably substantially less than or equal to 7 nm, preferably substantially less than or equal to 5 nm. As another example, the second metallic layer has a non-zero thickness substantially greater than or equal to 3 nm, preferably a thickness substantially equal to 3 nm.

[0044] As an example, in a metallic bilayer, at least one of the first and second metallic layers has a plurality of nanometer-sized holes along the main extension plane of the metallic bilayer. Thus, the module presents these nanometer-sized holes close to the surface that receives and re-emits light. The extraction of reflected light is therefore improved, increasing the module's light reflection efficiency.

[0045] In one example, each of the first and second metallic layers exhibits a plurality of nanometer-sized holes along the principal extension plane of the metallic bilayer. In another example, the holes are continuous between the first and second metallic layers of the bilayer.

[0046] According to one example, the layer comprising at least one polymer includes at least one polymer chosen from the group consisting of polyethers, polycarbonates, polyesters, polynitriles, polyalcohols, polyamines, polysiloxanes, fluoropolymers, biopolymers and their derivatives.

[0047] According to one example, the layer comprising at least one polymer comprises, and preferably is made of, polymethyl methacrylate and has a thickness of 15 between 200 and 250 nm, preferably approximately equal to 200 nm.

[0048] As an example, a layer containing at least one polymer has a transmittance greater than or equal to 80%. This transmittance further improves the transmission of the reflected beam away from the module.

[0049] In one example, the multilayer stack is topped with a second substrate. This substrate protects the reflective module, which is particularly advantageous for automotive applications.

[0050] Preferably, the first, and if necessary the second, substrate are flexible substrates. This further minimizes the risk of poor electronic contact between the electrode substrates and the polymer layer, and thus limits the risk of colorless areas appearing in the polymer layer, even under the application of a potential difference.

[0051] Preferably, the first and, where applicable, the second substrate are based on polyethylene terephthalate or its derivatives.

[0052] A substrate or layer "based" on species A is understood to be a substrate or layer comprising only that species A or that species A and possibly other species.

[0053] Several embodiments of the invention implementing successive manufacturing process steps are described below. Unless explicitly stated, the adjective "successive" does not necessarily imply, although this is generally preferred, that the steps follow each other immediately; intermediate steps may separate them.

[0054] Furthermore, the term "step" refers to the completion of a part of the process, and can designate a set of sub-steps.

[0055] Furthermore, the term "step" does not necessarily imply that the actions carried out during a step are simultaneous or immediately successive. Some actions in a first step may be followed by actions related to a different step, and other actions from the first step may be repeated later. Thus, the term "step" does not necessarily refer to unitary actions that are inseparable in time and in the sequence of phases of the process.

[0056] It is specified that, within the framework of the present invention, the thickness of a layer or substrate is measured along a direction perpendicular to the surface along which this layer or substrate has its maximum extent. The thickness is thus taken along a direction perpendicular to the principal faces of the substrate on which the different layers rest.

[0057] It is specified that, within the scope of the present invention, the terms "on," "overcomes," "covers," "underlying," "opposite," and their equivalents do not necessarily mean "in contact with." Thus, for example, the deposition, transfer, bonding, assembly, or application of a first layer onto a second layer does not necessarily mean that the two layers are directly in contact with each other, but rather means that the first layer at least partially covers the second layer, either by being directly in contact with it or by being separated from it by at least one other layer or element. "In contact" is understood to mean that a thin interface may exist, for example, due to manufacturing variability.

[0058] In the detailed description that follows, terms such as "longitudinal," "transverse," "upper," and "lower" may be used. These terms should be interpreted relatively in relation to the position of the elements of the reflective module or system once assembled, with the direction normal to the principal extension plane of the stacking layers being considered the vertical direction. A lateral or transverse dimension is understood as a dimension in a plane parallel to or coinciding with the principal extension plane of the stacking layers.

[0059] By "juxtaposed" elements we mean here that these elements are arranged side by side according to their main extension plane or arranged one above the other according to the direction of stacking, this direction being perpendicular to the main extension plane.

[0060] A parameter that is "approximately equal to / greater than / less than" a given value means that the parameter is equal to / greater than / less than the given value, within ±10% of that value. A parameter that is "approximately between" two given values ​​means that the parameter is at least equal to the smaller of the two given values, within ±10% of that value, and at most equal to the larger of the two given values, within ±10% of that value.

[0061] By "nanometric", and more specifically "nanometric thickness" or "nanometric size", we mean a dimension, for example a thickness, greater than or equal to 1 nm and strictly less than 1 µm.

[0062] Within the framework of the invention, the visible domain, or spectrum, corresponds to the range of wavelengths between 350 and 900 nm, and preferably between 400 and 800 nm.

[0063] Generally, a material or layer is considered flexible if it can bend without being damaged or breaking, and more specifically if the mechanical and electrical properties of the film remain unchanged even under a significant stress of 2.5% with a concave and convex radius of curvature of 0.5 mm. The deformation (flexibility) of the reflective modulus 1 can be evaluated using the following equation: deformation = (ts - tp - tf ) / (2.rc), where: ts is the thickness of the layer of the substrate(s) 10, 11; tp is the total thickness of the layers of the stack 13; tf is the total thickness of the electrode layers 12, 13; rc is the radius of curvature.

[0064] The expression "A and / or B" means (A), (B), or (A and B). The expression "A, B and / or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C).

[0065] The multilayer reflective module 1 and the reflective system 3 comprising it are now described according to several embodiment examples.

[0066] As illustrated, for example, the reflective module 1 comprises a first substrate 10, also referred to as substrate 10, on which a multilayer stack 13 is deposited. The substrate 10 has a lower surface 10a and an upper surface 10b. The stack 13 can be arranged on the upper surface 10b. The multilayer stack 13 is configured to receive an incident light beam 2, 2'' and reflect a reflected light beam 2'. The incident beam 2 can, in particular, be a beam of ambient light. The incident light beam 2 has a wavelength spectrum, for example, that of visible light. The reflective system 3 comprises a light source 31 configured to emit a light beam 2''. For the multilayer stack 13, it is understood that the light beams 2 and 2'' can be considered as incident beams.The reflective module 1 can achieve an ambient light reflectivity greater than or equal to 80%, for example greater than or equal to 90%.

[0067] According to one example, the light source 31 is a semiconductor light source. In a non-limiting embodiment, the semiconductor light source is an LED. By LED, we mean any type of light-emitting diode, whether in non-limiting examples LEDs (Light Emitting Diode), OLEDs (Organic LED), AMOLEDs (Active-Matrix-Organic LED), or FOLEDs (Flexible OLED).

[0068] The light source 31 is preferably configured to emit the 2'' beam with a wavelength between 610 nm and 650 nm, for example the source 31 is a monochromatic LED of 620 nm or 631 nm.

[0069] Note that the term "a wavelength", for example for the 2'' beam and / or the reflected 2' beam, is not limited to an isolated or monochromatic wavelength but can designate a range of wavelengths.

[0070] Due to the Fabry-Pérot effect, a portion of the wavelength spectra of beams 2 and 2'' will be transmitted by constructive interference and then reflected by a metallic mirror 14 to form the reflected beam 2'. Furthermore, the multilayer stack 13 is configured to exhibit maximum reflectivity in the wavelength range between 480 and 650 nm, corresponding to a perceived color of amber-red to red, and preferably between 586 nm and 680 nm. It is therefore understood that the wavelength spectrum of the reflected light beam 2' can be distinct, and preferably shorter, compared to the spectrum of the incident beam 2. The reflecting module 1 thus enables the conversion of ambient light to reflect a light beam with a perceived red color.The wavelength spectrum of the reflected light beam 2' can be distinct, and preferably reduced, in wavelength, compared to the spectrum of the beam 2'' emitted by the light source 31, particularly in the case of a chromatic deviation of the beam 2'' following an increase in the temperature of the light source 31.

[0071] Typically, a wavelength shift of approximately 30 nm per 100°C can be observed as a function of temperature for a "RED" AlInGaP LED, compared to a blue InGaN LED for which this shift is approximately 6 nm per 100°C. At high temperatures, the efficiency (in terms of luminous flux) of the aforementioned RED LED decreases by 0.6% / °C compared to the 0.2% / °C generally observed for blue and green LEDs.

[0072] The reflective module 1 can thus use sunlight to reflect a beam of perceived red color. The light source 31 can enhance the red component during the day as needed, and illuminates the multilayer stack 13 at night to obtain the reflected beam 2. In the following, it is assumed, for the sake of completeness, that the multilayer stack 13 receives an incident beam 2 of ambient light and a beam 2'' emitted by the light source 31.

[0073] According to an example, the system 3 can comprise a plurality of reflective modules 1 juxtaposed along at least one direction called "of juxtaposition", parallel to or coincident with a principal extension direction of these modules 1. Preferably, the reflective modules 1 are juxtaposed along at least two directions called "of juxtaposition" of a plane parallel to or coincident with a principal extension plane of these modules 1.

[0074] The light source 31 is offset from the multilayer stack 13. The light source 31 can be placed in a location in the vehicle different from that of the multilayer stack 13. This can be a lateral light source for example in relation to the multilayer stack.

[0075] In order to transmit the 2" beam emitted by the light source 31 to the multilayer stack 13, the module 1 may further include a waveguide 12. The waveguide 12 may be configured to transmit the 2" light beam from the light source 31 to one or more reflective modules 1. For this purpose, the waveguide 32 may include internal total reflection elements configured to conduct the 2" light beam from the light source 31.

[0076] Depending on the angle of reflection of the beam 2" in the waveguide 12, the beam 2" from the source 31 can be transmitted to a reflecting module 1 or continue propagating within the waveguide 12. For example, and as detailed later, the waveguide 12 can include optical patterns configured to modify the optical path of a portion of the beam 2" from the source 31 to direct it to the corresponding reflecting module 1. Those skilled in the art can design a waveguide suitable for the arrangement of one or more reflecting modules 1. These optical patterns can, for example, be arranged at regular intervals along the waveguide 12, according to the arrangement of the reflecting modules 1. A single waveguide 12 can be shared by several reflecting modules 1. Other structures can be provided as alternatives or complements to optical patterns by those skilled in the art, for example, suspended particles.

[0077] The reflective module 1 may further comprise a second substrate 11 above the multilayer stack 13, for example above the waveguide 12. The second substrate 11 has a lower surface 11a and an upper surface 11b. The waveguide 12 may be arranged on the lower surface 11a. The multilayer stack 13, for example with the waveguide, can thus be enclosed by the first 10 and second 11 substrates. The second substrate 11 can form an entrance diopter for the incident light beam 2 and an exit diopter for the reflected beam 2'. The second substrate 11 is therefore preferably configured to allow these beams 2, 2' to pass through. The substrate 11 preferably has a transmittance greater than or equal to 75%, and preferably approximately equal to 80%.

[0078] The reflective module 1, and the system 3 comprising it, can be incorporated into parts such as vehicle parts, for example, car parts. The illustration shows, as an example, a rear car body panel comprising reflective systems 3 in the center and on the sides. The reflective module or reflective system 3 can be incorporated into other parts, for example, inside the passenger compartment or on other body parts.

[0079] To enable reflection by the Fabry-Pérot effect, and with reference to Figures 3 to 5 and 8A, 8B, the multilayer stack 13 comprises at least one reflective metallic mirror 14 and a layer comprising at least one polymer 15, equivalently designated as the polymer layer. This polymer layer 15 is configured to allow a specific wavelength to emerge by the Fabry-Pérot effect through constructive interference.

[0080] The Fabry-Pérot effect is first presented. The polymer layer 15, nanometric in thickness and typically on the order of one or several hundred nanometers, forms a Fabry-Pérot cavity in which the 2, 2'' beams are confined. This cavity produces, from the light it receives, interferences of a specific wavelength. These interferences result in multiple reflections of rays of a given wavelength propagating inside the cavity.

[0081] To improve the reflective properties of the reflective module 1, the module further includes a partially transparent metallic bilayer 18. The metallic bilayer 18 is positioned above the polymer layer 15. The metallic bilayer 18 can therefore be placed between the polymer layer 15 and the waveguide 12. The metallic bilayer 18 acts as a broadband absorber to absorb a portion of the light beams 2, 2'' to perform an initial selection of the wavelengths reaching the polymer layer 15.

[0082] Synergistically, between the Fabry-Pérot effect and the broadband absorption of the metallic bilayer 18, the wavelengths in the visible range of the incident beam 2, and of the beam 2'' emitted by the light source 31, are selected to reduce the range of wavelengths of the reflected beam 2'. The resulting perceived red color is therefore brighter and appears more intense.

[0083] According to an example, the reflective module 1 has a reflection rate of an incident light beam 2 greater than 50%, for example between 90% and 95%.

[0084] Specific examples of system 3 are now described with reference to figures 3 to 8B.

[0085] The waveguide 12 is first described in more detail. As illustrated, for example, by Figures 3 to 5, the waveguide 12 comprises a body 122 through which the beam from the light source 31 propagates. The waveguide 12 may further comprise a diffraction grating 120 for light entry and / or a diffraction grating 121 for light exit. The diffraction grating 120 for light entry is referred to as the light entry grating 120 or simply the entry grating 120 in the following description. The diffraction grating 121 for light exit is also referred to as the light exit grating 121 or simply the exit grating 121 in the following description.

[0086] The light-input grating 120 is configured to optically couple, by diffraction, the light beam from the source 31 in order to orient it so as to propagate into the body 122. The light-input grating 120 is configured to optically couple, by diffraction, the light beam that has propagated into the body 122 in order to orient it so as to transmit it to the multilayer stack 13. For this purpose, each grating 120, 121 comprises periodic optical patterns 1200, 1210. By periodic, it is understood that the patterns are repeated along at least one dimension of the grating at a distance designated as the "period" P. The light-input grating 120 and the light-output grating 112 are preferably 1D gratings, that is to say, the patterns are repeated, along one dimension of the grating, with the period P.

[0087] As illustrated in Figure 1, the light source 31 can be arranged so as to directly inject the emitted beam 2" without requiring a light input array 120. As illustrated in Figures 4 and 5, the light source 31 can be arranged opposite the light input array 120 so that the emitted beam 2" enters the light input array 111. It is possible to provide that the light source 31 is offset from the light input array and that the emitted beam 2" is routed to the light input array 120, for example via an optical fiber.

[0088] As an example, light guide 11 is a rod-shaped light guide. It can be expected to have a round or square cross-section.

[0089] In another limiting example, the light guide 11 is a surface light guide. A surface light guide is defined as an optical guiding element in which one dimension is much smaller than the other two spatial dimensions, for example, smaller by one or more orders of magnitude. Here, the thickness of the waveguide 12 is much smaller than its length and width. In a non-limiting embodiment, the waveguide 12 has a thickness between 125 and 2000 micrometers. The waveguide 12 is thus very thin.

[0090] As an example, waveguide 12 is a flexible waveguide. Because it is flexible, it can adapt to flat or curved surfaces.

[0091] The waveguide 12 is preferably at least partially transparent. The term transparent indicates that the material from which it is made allows visible light to pass through, and in particular the light emitted by the light source 31.

[0092] As an example, the waveguide 12 is based on, and preferably made of, polycarbonate (PC) with a refractive index of 1.58, polymethyl methacrylate (PMMA), thermoplastic polyurethane (TPU), or polyethylene terephthalate (PET). Such materials allow for the production of a transparent waveguide 12.

[0093] The waveguide material 12 preferably has an optical index n2 less than 1.8. This allows the light generated by the light source 31 to be reflected and propagated in a perfectly suitable manner within the body 120 of the waveguide 12. For example, the waveguide material is configured to have an optical index n2 that is compatible with the light source 31 and the polymer layer 15. For instance, if the polymer layer 15 has an optical index n1, the waveguide material 12 can have an optical index n2 such that the ratio n1 / n2 is between 0.90 and 1.1. For example, if the light source 31 is made of a material with an optical index n3, the waveguide material 12 can have an optical index n2 such that the ratio n1 / n3 is between 0.90 and 1.1.It can be predicted that the body 122 of the waveguide exhibits an optical index gradient between a portion of coupling with the light source 31 and another portion of coupling with the multilayer stack 13.

[0094] As an example, the body 122 has a thickness chosen to prevent total internal reflection of light within the body 122, thus preventing light from exiting through the light-entry grating 120. The waveguide 12 can have a thickness greater than or equal to 125 µm, for example, approximately 500 µm. In this way, the light is diffracted within the body 122 at a diffraction angle θ of approximately 45°.

[0095] The light input grating 111 and the light output grating 112 are typically surrounded by air, with a refractive index n = 1.

[0096] As illustrated in Figures 3 to 6C, each input 120 or output 121 grating comprises a plurality of optical patterns 1200, 1210 which are diffractive optical patterns inclined at an angle of inclination α, α' and repeated periodically over a period P.

[0097] The beam emitted 2" by the source 31 can thus be coupled to the light-entry grating 120. The beam 2" is diffracted in the material of the waveguide 12 by means of the patterns 1200, then when the beam 2" encounters a wall of the waveguide 12 beyond the light-entry grating 120, it is reflected by reflection into the body 122 of the waveguide 12, which achieves the guiding effect in said body 122. Thanks to the optical patterns 1200, the light-entry grating 120 allows the light to be sent into the body 110 of the waveguide with a diffraction angle θ of approximately 45°.

[0098] The 2'' beam which propagated by reflection in the body 122 of the waveguide 12 is coupled at output with the light output grating 121. The 2'' beam is diffracted in the material of the waveguide 12 by means of the patterns 1210 and thus emerges as a 2'' light beam in a direction at least oblique, and preferably substantially normal, to the main extension plane of the layers of the multilayer stack 13.

[0099] The optical patterns 1200, 1210 have a cross-section in a plane substantially parallel to the beam propagation direction 2" in the waveguide body 122, this section having at least one side with an inclination angle α, α' relative to the principal extension direction of the waveguide 12. Preferably, the inclination angle α, α' of the optical patterns 1200, 1210 is between 40° and 50°, preferably approximately 45°. The inclination angle may be distinct between the optical patterns 1200 of the input grating 120 and the optical patterns 1210 of the output grating 121 and 1210, or preferably substantially equal between them.

[0100] Other pattern shape parameters can be chosen from the angle of inclination.

[0101] The period P can, for example, be chosen according to the wavelength λ that we wish to reflect 2' by the reflecting module 1, for example 620 nm or 631 nm, the tilt angle, and the refractive index of the waveguide 12. We can, for example, have P = λ / (n2*sin(α or α')). Thus, the optical patterns 1200, 1210 are optimized to diffract the beam 2'' at the chosen wavelength. Optical motifs 1200, 1210 thus act as a wavelength filter, which further improves the perceived red color of the beam reflected 2' by module 1. As an alternative or in addition, the light source 31 may include a wavelength filter, for example a bandpass filter centered at the desired wavelength, for example at 620 nm or 631 nm.

[0102] The dimensions of the cross-section of each motif 1200, 1210, and in particular the height H and the length L, can be optimized by simulation in order to identify the values ​​increasing the optical coupling for the desired wavelength.

[0103] The optical patterns 1200, 1210 can preferably be formed in the constitutive material of the waveguide 12. It can be foreseen that the optical patterns are formed in protrusion from a surface 12a of the body 122 of the waveguide 12, as illustrated in Figures 6A and 7A, or in depression from this surface 12a, as illustrated in Figures 6B and 7B.

[0104] As illustrated in Figures 6A to 6C, the optical motifs 1200 and 1210 have a triangular cross-section. These motifs preferably have a height between 500 and 600 nm, and more preferably 565 nm. A coupling efficiency of 56% was thus observed for a polycarbonate waveguide 12 with an optical index of 1.58 and a tilt angle of 45°.

[0105] According to an example illustrated in Figures 7A to 7C, the optical patterns 1200, 1210 can have a parallelogram-shaped cross-section. The patterns 1200, 1210 are preferably repeated at a period of approximately 565 nm. The patterns 1200, 1210 preferably have a height approximately between 350 nm and 400 nm, preferably approximately 364 nm, and a width L between 200 nm and 230 nm, preferably approximately 210 nm. The fill factor can then be equal to L / P, and therefore here to 0.371. A coupling efficiency of 94% was thus observed for a polycarbonate waveguide 12 with an optical index of 1.58, with a tilt angle of 45°.

[0106] Since the input network 120 and / or the output network 121 is preferably a 1D network, its shape can be seen in a 3D view illustrated in figures 6C and 7C.

[0107] Recall that the wavelength λ = ct = c / f, where t is the time period, f is the frequency, and c is the speed of light. Light with a given wavelength λ arrives at a light input grating 120, which has a period P close to its time period t. Thus, it can resonate with the grating, enabling coupling of the light with the input grating 120. The period P is very close to the time period t. In a non-limiting embodiment, the period P differs from the time period t by 5% to 10%.

[0108] The period P of the output grating 121 is preferably equal to the period P of the input grating 120. Thus, the light output grating 121 has the same periodicity as the light input grating 120. This simplifies the manufacturing process. The diffraction of the light exiting the waveguide 12 will therefore also be very efficient since the period P of the output grating 121 is also very close to the time period t corresponding to the wavelength λ of the light generated by the light source 31.

[0109] According to the example illustrated in Figures 3 and 4, optical motifs 1200 and optical motifs 1210 have the same cross-section. This allows for a simpler manufacturing process than if they were of different shapes. However, it is possible to adapt optical motifs 1200 and 1210 so that they have different cross-sections between the input grating 120 and the output grating 121, as illustrated for example in Figure 3.

[0110] As illustrated in Figures 3 to 5, the inlet grating 120 and the outlet grating 121 can be arranged on different surfaces, and in particular on opposite surfaces, of the waveguide 12. Thus, the coupling of the light entering the waveguide 12 with the inlet grating 120 occurs on a different side than the coupling of the light exiting the waveguide 12 with the outlet grating 121. It can be assumed that they are arranged on the same surface. We then have |α'+α| = 180°. The first optical motifs 1110 are inclined in one direction and the second optical motifs 1120 are inclined in the other direction.

[0111] The person skilled in the art is perfectly capable of considering the manufacturing techniques of the 1200, 1210 patterns, and for example: electron beam lithography, or laser engraving, or near-infrared lithography.

[0112] The multilayer stack 13 is now described in more detail with reference to Figures 8A and 8B. Examples of the dimensions of the reflective module 1 are now given. Each module 1 can extend along a plane parallel to the main extension plane of the layers of the stack 13. Each reflective module 1 can, in this plane, have lateral dimensions, in directions perpendicular to each other, in the range of values ​​on the order of a few millimeters for small areas, or even a few meters for large areas. The thickness of the multilayer stack 13 can be substantially greater than or equal to 100 micrometers (µm), and substantially less than or equal to 300 micrometers (µm). It is therefore understood that the reflective module 1 is compact and thus more easily integrated into existing parts, for example, automotive parts, particularly compared to existing solutions using liquid electrolytes.

[0113] The first 10 and / or the second 11 substrates can extend along at least one direction of the main extension plane of the layers of the stack 13, over a distance d1 less than or equal to 5 mm, preferably 3 mm, relative to the layers of the stack 18.

[0114] The reflective module 1 is now written in more detail element by element.

[0115] The first substrate 10 and / or the second substrate 11 are preferably flexible substrates. This facilitates the incorporation of the reflective modules into existing parts and increases the mechanical strength of the reflective module 1.

[0116] For example, substrate 10 and / or the second substrate 11 are manually deformable without tools. For example, the first substrate 10 and / or the second substrate 11 are polymer-based or made of polymer. More specifically, the first substrate 10 and / or the second substrate 11 are polymer-based or made of polyethylene terephthalate (PET), PMMA, or their derivatives. Note that other polymers may be considered.

[0117] In the case of a plurality of juxtaposed reflective modules 1, the first 10 and / or the second 11 substrates may be common to a plurality of modules 1. Alternatively, it may be provided that each module includes its own substrate(s), distinct between different modules 1.

[0118] The metallic mirror 14 can be formed of at least one metallic layer 140, for example based on or made of aluminum. Good reflection of the incident beam 2 is thus obtained. The metallic mirror 14 may also include layers that improve chemical compatibility with the polymer layer 15. For this purpose, the metallic mirror 14 may include a layer based on or made of gold 142. The gold layer 142 can thus be in contact with the polymer layer 15 without risking degradation of this layer or of the metallic mirror 14. It should be noted that several metallic mirrors 14 can be used in the stack 13, or even in the reflective module 1. For example, one or more substrates 10 and one or more mirrors 14 can be superimposed. In order to adhere the gold layer 142 to the aluminum layer 140, the mirror 14 may include an adhesion layer based on or made of chromium 141 between these layers 140 and 142.The metallic mirror 14 is preferably of micrometer thickness, that is, between 1 µm and 1000 µm, strictly excluded. For example, the aluminum layer 140 may have a thickness d140 approximately between 100 and 300 µm, and preferably approximately 200 µm. The chromium layer may have a thickness d141 approximately 100 nm. The gold layer may have a thickness d142 approximately 3 nm.

[0119] As an example, the Young's modulus of the polymer layer 15 is approximately between 0.2 and 4 MPa. The elongation at break can be approximately greater than or equal to 100%, for example, approximately between 150% and 160%. The reflective modulus 1 thus exhibits a long service life despite the stresses that may be exerted on the modulus. Preferably, the polymer layer 15 has a transmittance greater than or equal to 80%.

[0120] The polymer layer 15 may be based on at least one polymer selected from polyethers, polycarbonates (for example polybutylene glutarate abbreviated PBG), polyesters (for example polymethyl methacrylate abbreviated PMMA), polynitriles (for example polyacrylonitrile abbreviated PAN), polyalcohols (for example polyvinyl alcohol abbreviated PVA), polyamines (for example polyethyleneimine abbreviated PEI), polysiloxanes (for example polydimethylsiloxane abbreviated PDMS), fluoropolymers (for example polyvinylidene fluoride abbreviated PVDF, and poly(vinylidene fluoride-co-hexafluoropropylene), abbreviated P(VDF-co-HFP)), biopolymers (for example lignin, chitosan and cellulose) and their derivatives. the polymer layer 15 may for example include a copolymer of which at least one of the monomer motifs corresponds to the polymers mentioned above.

[0121] The polymer layer 15 preferably has a thickness of 15between 100 and 250 nm, preferably between 200 nm and 220 nm. This thickness is particularly advantageous for a polymer layer 15 based on or made of PMMA, for the reflection of the red color.

[0122] The metallic bilayer 18 is now described in more detail. The metallic bilayer 18 comprises a first metallic layer 180 and a second metallic layer 181. The first 180 and second 181 layers are preferably in contact with each other. The first layer 180 is preferably in contact, and preferably in direct contact, with the polymer layer 15.

[0123] For example, the first metallic layer 180 is gold-based or made of gold, and the second metallic layer 181 is chromium-based or made of chromium, or vice versa. Chromium exhibits a peak absorption in the blue region and little in the red, while gold exhibits a peak absorption in the red region and little in the blue. Using these two metals in the metallic bilayer 18 provides a broadband absorber function distributed across the visible spectrum. Other metals could be considered, such as silver.

[0124] Preferably, the first metallic layer 180 is gold-based or made of gold. Gold exhibits better chemical compatibility with the polymer layer 15.

[0125] The thickness of the metallic layers 180 and 181 is chosen so as to partially absorb the incident light radiation 2 while being sufficiently transparent to allow good reflection by the reflective module 1. In order to allow the unabsorbed part of the incident radiation 2 to pass through, the metallic bilayer 18 preferably has a transmittance greater than or equal to 75%, preferably substantially equal to 80%.

[0126] For this reason, the first 180 and second 181 metallic layers have a non-zero thickness, preferably greater than or equal to 3 nm. To maintain good transparency, as illustrated for example by Figures 1A and 1B, the first 180 and second 181 metallic layers may each have a thickness of 180 , d 181preferably less than 10 nm, preferably substantially less than or equal to 7 nm, preferably substantially less than or equal to 5 nm, and preferably substantially equal to 3 nm. The metallic bilayer 18 may have a total thickness substantially less than or equal to 20 nm, preferably substantially less than or equal to 10 nm.

[0127] According to an example, illustrated by the figure, the metallic bilayer 18 is free of nanometer-sized holes 182. The metallic bilayer 18 can be continuous without interruption.

[0128] As illustrated, for example, the metallic bilayer 18 can alternatively include nanometer-sized holes 182. This improves the extraction of radiation reflected by modulus 1, as this radiation passes through fewer layers at the level of these holes 182. For example, their largest dimension in the principal extension plane of the metallic bilayer 18 is nanometer-sized. This dimension can be their diameter.

[0129] At least one of, and preferably each of, the first 180 and second 181 metallic layers have these holes 182. These holes 182 can traverse at least 90%, and preferably substantially 100%, of the layer 180, 181 in question, and preferably both layers 180, 181, in a direction substantially perpendicular to the main extension plane of the bilayer 18.

[0130] According to one example, the 192 holes represent, in projection onto the surface of the layer considered, 20% to 40% of the surface of the corresponding layer(s).

[0131] These holes 182 may have a circular cross-section, this cross-section being more particularly taken in the principal extension plane of the metallic bilayer 18. The distribution of these holes 182 in the corresponding layer(s) is preferably regular, at the center and at the four corners of squares subdividing these layers. Each of the squares, for example, has a side with a length of 600 nm. The diameter of each of the holes 192 may be approximately 200 nm.

[0132] As illustrated, for example, the reflective module 1, and preferably each reflective module 1, can include a mask 111 configured to partially block the transmission of the incident beams 2 and reflected beams 2'. This mask 111 can, according to an example not shown, be placed on the upper surface 11b of the second substrate 11. In a direction normal to the multilayer stack 13, the mask 11 can span the waveguide 12, or span the metallic bilayer 18 by being positioned below the waveguide 12, as shown in the example. The mask 111 can define areas 111 blocking light transmission and areas 111a allowing the incident beams 2 and reflected beams 2' to pass through. For a reflective module 1, the mask 111 thus creates a pattern. Note that this mask 111 can be shared by several juxtaposed reflective modules 1.

[0133] Reflective module 1 can be manufactured according to the example described below. Note that the process can include any step required to obtain the characteristics of reflective module 1 described above. Specific manufacturing recipe examples are also provided. The deposition parameters and techniques can be configured to obtain the thicknesses described previously.

[0134] The process may include a formation of the multilayer stack 13 as introduced above.

[0135] To achieve this, the process may include depositing the metallic mirror 14 onto the first substrate 10. As previously mentioned, the mirror 14 may consist of several successive layers of metal. These layers 140, 141, 142 can be formed by any physical deposition technique, for example, sputtering, electron beam evaporation, flash evaporation, or induction evaporation.

[0136] On the formed metallic mirror 14, the process may include the deposition of the polymer layer 15. Alternatively, the polymer layer 15 may be deposited on the metallic bilayer 18. Numerous deposition techniques can be used for this purpose, depending in particular on the nature of the polymer. Deposition can be carried out by droplet deposition, by slide deposition, or by centrifugation (generally referred to by the English term spin-coating). For example, the deposition of the polymer layer may involve the deposition of a precursor solution to form a preliminary layer. This deposited layer 15' can then form the polymer layer 15 through heat treatment and / or UV radiation and / or drying.

[0137] Preferably, the reflective module 1 is fabricated in two sub-modules 1' and 1'', which can be more easily assembled. The formation of the polymer layer 15 is thus decoupled from the formation of either the mirror 14 or the metallic bilayer 18, depending on which layer the layer 15 is deposited onto. In this example, following the deposition of the polymer layer 15, a first sub-module 1' is obtained. A second sub-substrate 1'' is then fabricated for their subsequent assembly.

[0138] Note that, as an alternative, the reflective module 1 could be formed layer by layer, starting from the first substrate 10, by successively stacking the layers to be deposited to form the reflective module 1, using the same techniques described. However, this risks damaging the polymer layer 15 during the deposition of the mirror 14 or the metallic bilayer 18, which would then be placed over the polymer layer 15.

[0139] The fabrication of the second 1" sub-module is now described. The second substrate 11 can be supplied. The process may include a fabrication deposition step for the waveguide 12, for example as previously described.

[0140] Depending on the example in which one or both of the metallic layers 180, 181 of the bilayer include nanometric holes 182, the holes 182 can be produced, for example, by colloidal lithography or by electron beam lithography (more commonly known in English as "e-beam lithography"). These techniques offer good precision and regularity in creating a homogeneous distribution of holes 182 in a material, eliminating the need for a mask.

[0141] The reflective module 1 can then be obtained by assembling, or equivalently transferring, the sub-modules 1' and 1''. In order to join the sub-modules 1', 1'', it can for example be provided that this assembly is carried out when the polymer layer 15 is not entirely solidified, this solidification being finalized after the assembly of the sub-modules 1', 1''.

[0142] The manufacturing process for the reflective system 3 may include, for each module, the manufacturing steps described above. The manufacturing process for the reflective substrate 3 may further include the electrical connection of the light source 21 to the waveguide 12. This process may also include assembly steps for additional system components, for example, the mask 111.

[0143] In a 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 description, vehicle 2 is thus also referred to as motor vehicle 2. In a non-limiting variant of this embodiment, vehicle 2 is a combustion engine vehicle, an electric vehicle, or a hybrid vehicle.

[0144] The present invention is not limited to the examples described above. Many other embodiments are possible, for example by combining features described above, without departing from the scope of the invention. Furthermore, the features described with respect to one aspect of the invention can be combined with another aspect of the invention.

Claims

A reflective module (1) for an automotive part (4) comprising: a substrate (10), a multilayer stack (13) disposed on the substrate (10) and configured to receive an incident light beam (2, 2'') and reflect a reflected light beam (2') having a determined wavelength, the multilayer stack (13) comprising at least one layer forming a metallic mirror (14), characterized in that the module (1) further comprises a waveguide (12) surmounting the multilayer stack (13), the waveguide (12) being configured to transmit to the multilayer stack (13) a light beam (2'') from a remote light source (31) of the multilayer stack (18), and in that the multilayer stack (13) further comprises: a layer comprising at least one polymer (15) surmounting the metallic mirror (14), and configured to form, by the Fabry-Pérot effect, the reflected light beam (2'),said layer (15) being configured to exhibit maximum reflectivity in a wavelength range between 480 nm and 650 nm, a partially transparent metallic bilayer (18) comprising a first metallic layer (180) based on a first metal, and a second metallic layer (181) based on a second metal distinct from the first metal, the metallic bilayer (18) overlying the layer comprising at least one polymer (15). reflective module (1) according to the preceding claim, wherein, the layer comprising at least one polymer (15) having an optical index n1 and a thickness d15, the optical index n1 and the thickness d15 are configured together such that said layer (15) exhibits a maximum reflectivity in the wavelength range between 480 nm and 650 nm. reflective module (1) according to the preceding claim, wherein the optical index n1 is between 1.4 and 1.8 and the thickness d15 is between 100 nm and 250 nm. Reflective module (1) according to any one of the preceding claims, wherein the waveguide (12) comprises: an input light grating (120) for receiving the light beam (2'') from the light source (31) and comprising a plurality of optical patterns (1200) inclined at a first angle of inclination (α), so as to optically couple by diffraction the light beam (2'') from the light source (31) for its propagation in the waveguide (12), and / or an output light grating (121) above the multilayer stack (13) and comprising a plurality of optical patterns (1210) inclined at a second angle of inclination (α'), so as to optically couple by diffraction the light beam (2'') propagating in the waveguide (12) for its transmission to the multilayer stack (13). Reflective module (1) according to the preceding claim, wherein the first angle of inclination (α) and / or the second angle of inclination (α') is between 40° and 50°, preferably substantially equal to 45°. Reflective module (1) according to any one of the two preceding claims, wherein the optical patterns (1200, 1210) of at least one of the light input grating (120) and the light output grating (121) have a triangular cross-section and a height (H) greater than or equal to 500 nm. Reflective module (1) according to any one of claims 4 to 6, wherein the optical patterns (1200, 1210) of at least one of, where applicable, the other of, the light input grating (120) and the light output grating (121) have a parallelogram cross-section and a height (H) greater than or equal to 300 nm, preferably greater than or equal to 350 nm and preferably substantially equal to 364 nm. Module (1) according to any one of the preceding claims, wherein the layer comprising at least one polymer (15) having an optical index n1, the waveguide (12) comprises a material having an optical index n2 such that the ratio n1 / n2 is between 0.90 and 1.

1. Module (1) according to any one of the preceding claims, wherein, in the metallic bilayer (18), the first metallic layer (180) is gold-based and the second metallic layer (181) is chromium-based. Module (1) according to any one of the preceding claims, wherein the metallic bilayer (18) has a non-zero thickness less than or equal to 10 nm. Module (1) according to any one of the preceding claims, wherein the layer comprising at least one polymer (15) comprises at least one polymer selected from the group consisting of polyethers, polycarbonates, polyesters, polynitriles, polyalcohols, polyamines, polysiloxanes, fluoropolymers, biopolymers and their derivatives. Module (1) according to any one of the preceding claims, wherein the layer comprising at least one polymer (15) comprises, and preferably is made of, polymethyl methacrylate and has a thickness of 15 between 200 and 250 nm, preferably approximately equal to 200 nm. Reflective system (3) for an automotive part comprising at least one reflective module (1) according to any one of the preceding claims, and at least one light source (31) remote from the reflective module (1), the light source being configured to emit the light beam (2'') for its transmission to the waveguide (12). Reflective system (3) according to the preceding claim, wherein the light source (31) is configured to emit the light beam (2'') of wavelength between 610 nm and 650 nm, preferably between 620 nm and 631 nm. Motor vehicle part (4) comprising a reflective module (1) according to any one of claims 1 to 12 or a reflective system (3) according to any one of claims 13 and 14.

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