Optical coupler for a lighting system, in particular for a vehicle passenger compartment

Abstract

One aspect of the invention relates to an optical coupler (22) having a longitudinal centre axis X, the optical coupler (22) comprising first (221), second (222) and third (223) portions in which: • the first portion (221) comprises a shell (221') having the shape of an ellipsoid of revolution having an axis X, which shell is truncated along a section through a plane perpendicular to the longitudinal axis X, having a polygonal cross-section (S1), the area of the cross-section (S1) increasing gradually along the longitudinal axis X, between an entrance section (SE) and a first intermediate section (SI1); • the third portion (223) comprises a shell (222') having the shape of a right prism, having a constant-are polygonal cross-section (S3) between a second intermediate section (SI2) and a first exit section (SS1), the area of the first intermediate section (SI1) being greater than the area of the second intermediate section (SI2); • the second portion (222) being a transitional portion arranged between the first portion (221) and the third portion (223), the second portion (222) comprising a shell (222') having a cross-section (S2) whose area gradually decreases along the longitudinal axis X, the second portion (222) comprising: • a first connecting section for connecting to the first portion (221), the first connecting section being the first intermediate section (SI1); • a second connecting section for connecting to the second portion (222), the second connecting section being the second intermediate section (SI2).

Description

Description Title of the invention: optical coupler for a lighting system, in particular for vehicle interiors. TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of optical coupling.

[0002] The present invention relates to an optical coupler and an optical lighting system, particularly for a vehicle interior. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] The passenger compartment of a vehicle may include several lighting systems, including backlighting, for functional as well as aesthetic purposes, contained within trim panels.

[0004] Patent EP2145796A2 presents, for example, an interior trim panel for a motor vehicle having a backlit area, the panel comprising a rigid support layer, a coating on the support layer defining a visible face of the panel and a lighting device allowing to illuminate an area of ​​the reverse of the support layer, the support layer and the coating being adapted to allow the light from the lighting device to pass through so that it is visible on the panel.

[0005] A trim panel may, for example, feature bright coloured patterns chosen by the user or vehicle manufacturer, depending on the nature of the lighting system.

[0006] US patent 2016229338A1 describes a cladding panel comprising a textile covering, a transparent base, and a lighting device including a light source, such as an LED (light-emitting diode), and light guides, with the light source positioned in front of the light guide. When the light guide is illuminated by the light source, colorimetric effects can be achieved through the colors of the light-transmitting threads in the covering.

[0007] US patent 2014211498A1 describes an interior trim panel for a motor vehicle, comprising: a backing layer, which defines the outline of the interior trim panel; a cover layer, which is applied to the front side of the backing layer; and a light-emitting layer, which is applied to the rear side of the backing layer, in which the backing component and the cover layer are transparent. The light-emitting layer is a fabric in which a bundle of optical fibers is woven, the optical fibers being twisted into a connector, to which a light source, for example, can be connected. The bundle of optical fibers guides light waves. visible on the trim panel, the light waves can be of any color chosen by the vehicle user or the manufacturer.

[0008] However, when an RGB (red green blue) LED (light-emitting diode) light source is used, it is sometimes difficult to obtain uniform illumination for each color at the input of each optical fiber, resulting in a non-uniform luminous flux and a non-homogeneous distribution of colors in each optical fiber.

[0009] Patent EP0562873B1 describes a constant polygonal cross-section optical coupling device used with a high-intensity light source. The polygonal cross-section allows for improved light mixing, resulting in uniform illumination for each color at the coupler's output. The optical coupler can be used to couple the light source to a fiber optic bundle via a connector.

[0010] However, the cross-section of a fiber optic bundle connector depends on the number and type of stranded fibers and may be smaller than the surface area of ​​the light source at the input of a coupler, thus making the use of a constant cross-section coupler, such as the one presented in patent EP0562873B1, less efficient due to significant losses of luminous flux, the coupler not being adapted to both the sizes of the light source and the surface area of ​​the connector.

[0011] Thus, there is a need to transmit a light beam, especially a colored one emitted by a light source, to a bundle of optical fibers, via a connector with a cross-section smaller than the surface area of ​​the light source, while minimizing light flux losses and having homogeneous illumination for each color, at the connector input. Summary of the invention

[0012] The invention offers a solution to the problems mentioned above, by allowing a light source with a larger surface area to be coupled to the surface of a connector linking a bundle of optical fibers, while minimizing the losses of luminous flux between a light source and a bundle of optical fibers.

[0013] One aspect of the invention relates to an optical coupler having a central longitudinal axis X, said optical coupler comprising a first, a second and a third part and in which: • said first part comprises an envelope following the shape of an ellipsoid of revolution with axis X, truncated according to a section of plane perpendicular to the longitudinal axis X, of polygonal cross section, making said section increasing progressively along the longitudinal axis X, between an entry section and a first intermediate section; • said third part comprises an envelope in the form of a right prism, with a polygonal cross-section of constant area between a second intermediate section and a first output section; the area of ​​the first intermediate section being greater than the area of ​​the second intermediate section; • Said second part being a transitional part disposed between the first part and the third part, said second part comprising an envelope having a cross-section whose size gradually decreases along the longitudinal axis X, said second part comprising: • a first connecting section to the first part, the first connecting section being the first intermediate section, • a second connecting section to the second part, the second connecting section being the second intermediate section.

[0014] Thanks to the invention, it is possible to receive a light beam through an input section larger than the first output section, thus enabling the coupling of a light source with a cross-section larger than the cross-section of a connector in a set of optical fibers. The envelope of the first section is shaped to collect a maximum of light, with each light ray arriving at the envelope of the first section having an incident angle that allows for total internal reflection. The envelope of the second section is shaped to connect the first and third sections and is designed to minimize light leakage and therefore flux loss. The polygonal shape of the first and third sections breaks down the propagation modes of rays of different colors, resulting in uniform illumination for each color at the coupler's output.

[0015] In addition to the characteristics mentioned in the preceding paragraph, the optical coupler according to one aspect of the invention may have one or more complementary characteristics from among the following, considered individually or in all technically possible combinations: • said optical coupler has a full configuration; • The optical coupler comprises a fourth part having an envelope of constant cross-sectional area, along the longitudinal axis X, between the first output section and a second output section. Advantageously, the fourth part allows the shape of the second output section to be adapted in order to emit a light beam towards a light receiver, for example, the optical fiber beam connector, whose input section does not have the same shape as the first output section of the third part of the optical coupler. • The section of the envelope of the first part, and / or the section of the envelope of the third part are respectively polygons of order n, n being a natural number between 4 and 10. Advantageously, a section in the form of a polygon of order n between 4 and 10 allows for better homogenization of the propagation of light rays of different colors within the optical coupler and therefore to break the modes of propagation of each light ray. • The section of the envelope of the second part is a polygon of order n. This characteristic allows a seamless transition at the level of the first connecting section and the second connecting section. • n is equal to 6. Advantageously, the hexagonal shape of the section of the first part and the third part is the optimal shape to homogenize the propagation of light rays of different colors in order to obtain uniform illumination for each group of light rays of the same color. • Said optical coupler is formed from a transparent optical material such as polycarbonate (PC), polymethyl methacrylate (PMMA), glass or silicone. • the envelope of the first part has a first focus and a second focus, the first focus being located outside the optical coupler.

[0016] Another aspect of the invention relates to an optical lighting system comprising: • A light source; • An optical coupler according to the invention • A bundle of optical fibers;

[0017] In addition to the characteristics mentioned in the preceding paragraph, the optical lighting system according to one aspect of the invention may have one or more additional characteristics from among the following, considered individually or in all technically possible combinations: • the light source is a monochromatic, bi-chromatic or trichromatic light source. • The light source is placed at the conjugate focus of the first focus through the entrance surface. Advantageously, this characteristic allows all rays entering the coupler via the entrance section to be focused at the second focus after their total or partial reflection. • The optical fiber bundle comprises a plurality of optical fibers; each optical fiber in the plurality of optical fibers is formed from polymethyl methacrylate. Polymethyl methacrylate is a advantageous material enabling the production of a set of flexible and fine optical fibers that can be woven into a textile included in a trim panel for vehicle interiors.

[0018] Another aspect of the invention relates to a trim panel for vehicle interior comprising the lighting system according to the invention.

[0019] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0020] The figures are presented for illustrative purposes only and are in no way limiting to the invention.

[0021] Unless otherwise specified, the same element appearing on different figures has a unique reference.

[0022] Fig. 1 is a diagram representing an optical lighting system according to the invention.

[0023] Fig. 2 is a detailed diagram of an optical coupler according to the invention included in an optical lighting system according to the invention.

[0024] Fig. 3 is a diagram representing the respective paths of two light rays from a light source to the first part of the optical coupler according to the invention. DETAILED DESCRIPTION

[0025] An optical lighting system 2 according to the invention is schematically represented in [Fig. 1],

[0026] The optical lighting system 2 comprises a light source 21, an optical coupler 22 according to the invention and a bundle of optical fibers 23.

[0027] Figure [Fig. 2] shows in detail the optical coupler 22.

[0028] The optical coupler 22 has a central longitudinal axis X.

[0029] The optical coupler 22 comprises a first 221, a second 222 and a third 223 parts

[0030] The optical coupler 22 may further comprise a fourth part 224.

[0031] The first part 221 comprises an envelope 221' following the shape of an ellipsoid of revolution with axis X, truncated along a plane section perpendicular to the longitudinal axis X.

[0032] The envelope 221' of the first part 221, being ellipsoidal in shape with longitudinal axis X, is defined by two foci located on the longitudinal axis X: the envelope 221' of the first part 221 has a first focus Fl and a second focus F2. The envelope 221' of the first part 221 is truncated such that the first focus Fl is located outside the first part 221 and outside the optical coupler 22. The envelope 221' of the first part 221 is truncated so that the second focus F2 is located outside the first part 221, but inside the optical coupler 22.

[0033] The envelope 221' of the first part 221 has a regular polygonal cross-section SI. The cross-sectional area SI of the envelope 221' of the first part increases gradually and continuously along the longitudinal axis X, between an entry section SE and a first intermediate section SU. The area of ​​the entry section SE is less than that of the first intermediate section SU. In other words, the envelope 221' is formed by a continuous succession of increasing polygonal sections.

[0034] Preferably, the SE inlet section should completely cover a square surface with an area greater than or equal to 9 mm 2 .

[0035] For example, making the SE polygonal inlet section completely cover a square surface with an area of ​​16 mm 2 .

[0036] For example, the diameter of the circle inscribed in the polygonal SE input section is greater than or equal to 3mm.

[0037] For example, the diameter of the circle inscribed in the inlet section SE is equal to 4 mm.

[0038] For example, the diameter of the circle inscribed in the first intermediate section SU polygonal is between 6mm and 10mm.

[0039] Preferably, the diameter of the circle inscribed in the first intermediate section SU polygonal is equal to 6.698 mm.

[0040] Thus, the envelope 221' of the first part 221 is delimited at its ends by the entrance section SE and the first intermediate section SU.

[0041] The SE inlet section is adapted to receive a beam of light.

[0042] Preferably, the envelope 221' of the first part 221 is designed so that the focus Fl is located at a predetermined distance D, along the longitudinal axis X, from the inlet section SE

[0043] The SI section of the envelope of the first part 221 is a regular convex polygon of order n, the number n being a natural number preferably between 4 and 10. The order of a polygon is the number of its edges and / or the number of its vertices.

[0044] Thus, the SI cross-section of the envelope of the first part 221 can be a quadrilateral, for example a square, a pentagon, a hexagon, a heptagon, an octagon, a nonagon or a decagon.

[0045] Preferably, the SI cross-section of the envelope of the first part 221 is a polygon of order 6 and is therefore a hexagon.

[0046] The third part 223 comprises an envelope 223' in the form of a right prism whose central axis is the longitudinal axis X. A right prism is a geometric solid delimited by two polygons, the two polygons being connected to each other by parallelograms.

[0047] The envelope 223' of the third part 223 has a continuous constant polygonal cross section S3 between a second intermediate section SI2 and a first exit section SSL. Thus, the envelope 223' of the third part 223 is formed by a continuous succession of constant polygonal sections.

[0048] According to a first embodiment, the first output section SS1 is adapted to emit a beam of light.

[0049] Thus, the 223' envelope of the third part 223 is delimited at its extremities by the second intermediate section SI2 and the first SSL output section

[0050] The envelope 223' of the third part following a right prism shape, the cross section S3 of the envelope of the third part 223 is thus polygonal.

[0051] According to a preferred embodiment, the cross-section S3 of the envelope 223' of the third part 223 is a polygon of order n, the number n being defined previously. Thus, the cross-section S3 of the envelope 223' of the third part 223 can be a quadrilateral, for example a square or a rectangle, a pentagon, a hexagon, a heptagon, an octagon, a nonagon, or a decagon. Therefore, the envelope 223' of the third part 223 has n planar faces.

[0052] According to one embodiment, the cross section S3 of the envelope 223' of the third part 223 is a polygon of order k, k being a natural number other than n. k is preferably between 4 and 10.

[0053] Preferably, section S3 of the envelope of the third part 223 is a polygon of order 6 and is therefore a hexagon.

[0054] Preferably, the first polygonal SS1 exit section should completely cover a circular surface with an area less than or equal to 9 mm². 2 .

[0055] Preferably, the diameter of the circle inscribed in the first SS1 polygonal output section is less than or equal to 3mm.

[0056] For example, the diameter of the circle inscribed in the first SS1 polygonal output section is equal to 2 mm.

[0057] The second part 222 is a transitional part arranged between the first part 221 and the third part 223.

[0058] The second part 222 is connected to the first part 221 via a first connecting section, the first connecting section being the first intermediate section SU. Thus, the first intermediate section SU is common to the first part 221 and to the second part 222, forming a first end section.

[0059] The second part 222 is connected to the third part 233 via a second connecting section, the second connecting section being the second intermediate section SI2. Thus, the second intermediate section SI2 is common to the second part 222, forming its second end section, and to the Part three 223.

[0060] Thus the second part 222 is delimited at its ends by the first intermediate section SU and the second intermediate section SI2.

[0061] The second part 222 comprises an envelope 222' of section S2 with decreasing area along the longitudinal axis X, the section S2 of the envelope 222' of the second part 222 decreasing continuously.

[0062] According to the embodiment in which the natural number n is equal to the natural number k, the cross-section S2 of the envelope 222' of the second part 222 is preferably a polygon of order n and envelope 222' of the second part 222 is formed by a continuous succession of increasing polygonal sections.

[0063] According to an embodiment in which the optical coupler 22 comprises the fourth part 224, the fourth part 224 has an envelope 224' of constant cross-section S4 continuous along the longitudinal axis X, between the first output section SS1, which forms a first end section of the fourth part 224, and a second output section SS2, which forms a second end section of the fourth part 224, adapted to emit a beam of light.

[0064] Thus, the first outlet section SS1 is common to the third part 223 and the fourth part 224. Preferably, the second outlet section SS2 is circular. Preferably, the diameter of the second outlet section SS2 is less than 3 mm, and is, for example, between 2 mm and 3 mm. Preferably, the dimensions of the first outlet section SS1 and the second outlet section SS2 are identical.

[0065] Therefore, making the SE input section superior to making the first SSL output section

[0066] Thus, making the input section SE is superior to making the second output section SS2.

[0067] The optical coupler 22 does not have a discontinuity between the first part 221 and the second part 222.

[0068] The optical coupler 22 does not have a discontinuity between the second part 222 and the third part 223.

[0069] The optical coupler 22 does not have a discontinuity between the third part 223 and the fourth part 224.

[0070] The optical coupler 22 can be formed from at least one material, the material can be a transparent optical material such as PC (polycarbonate), PMMA (polymethyl methacrylate), for example extruded PMMA, glass or silicone, or any other transparent optical material.

[0071] The optical coupler 22 can be made of a reflective metal, for example.

[0072] According to a preferred embodiment in which the optical coupler 22 is made of a transparent optical material, said optical coupler 22 is preferably made of full configuration, therefore it does not exhibit extrusion.

[0073] According to an embodiment in which the optical coupler 22 is formed of a reflective metal, the optical coupler 22 is of hollow configuration.

[0074] The material forming the optical coupler 22 has an index n c , the index n c which can vary depending on the wavelength.

[0075] When the optical coupler 22 is formed from PMMA, the index of the optical coupler 22 can be n c = 1.49.

[0076] When the optical coupler 22 is formed from the PC, the index of the optical coupler 22 can be n c = 1.586 .

[0077] When the optical coupler 22 is formed from the glass, the index of the optical coupler 22 can be n c = 1.5 .

[0078] Thus, the SE inlet section is a diopter.

[0079] According to a first embodiment in which the optical coupler 22 comprises three parts, the first output section SS1 is a diopter.

[0080] According to a second embodiment in which the optical coupler 22 comprises the fourth part 224, the second output section SS2 is a diopter.

[0081] The total length of the optical coupler 22 along the longitudinal axis X is, for example, 25 mm. Preferably, the lengths of the first part 221, the second part 222, and the third part 223, along the longitudinal axis X, are equal. Preferably, the length of the fourth part 224 is much shorter than the lengths of the first part 221, the second part 222, and the third part 223.

[0082] The optical coupler 22 can receive a light beam, via the input section SE, emitted by the light source 21.

[0083] A beam of light is a collection of light rays originating from the same light source. The collection of rays propagates preferably in all directions within a solid angle equal to 2ir steradians.

[0084] According to one embodiment, the light source 21 can be monochromatic or polychromatic.

[0085] A monochromatic light source 21 emits a light beam having a single wavelength.

[0086] The polychromatic light source 21 can emit a light beam whose electromagnetic spectrum is extended over the visible range, the light source 21 being, for example, a white source.

[0087] The polychromatic light source 21 can, in particular, be a trichromatic light source emitting a light beam resulting from the superposition of three light beams having three wavelengths respectively, each wavelength corresponding to a different primary color; the intensity of each light beam can be different. The three primary colors are red, green and blue.

[0088] According to one embodiment, the light source 21 can be a laser.

[0089] In one embodiment, the light source 21 comprises at least one monochromatic LED (light-emitting diode). A monochromatic LED produces a monochromatic beam of light. The monochromatic beam of light can be red, green, or blue, for example. The intensity of the light emitted by each monochromatic LED can be varied.

[0090] In one embodiment, the light source 21 preferably comprises an RGB (red green blue) LED. An RGB LED is a package containing three monochromatic LEDs, each emitting monochromatic beams of light in red, green, and blue, respectively. The package may be clear.

[0091] According to the previous embodiment, when the case is clear, the RGB LED simultaneously emits three light beams, respectively of distinct red, green and blue color.

[0092] According to the previous embodiment, when the housing is diffusing, the RGB LED emits a beam of light whose color corresponds to the synthesis of the three colors: red, green and blue.

[0093] In one embodiment, the light source 21 is placed in the plane perpendicular to the longitudinal axis X and comprising the conjugate focus F'1 of the first focus Fl by the entrance section SE. The conjugate focus F'1 is located on the longitudinal axis X. In other words, the light source 21 is placed on the conjugate focus F'1 such that the image of the light source 21, formed by the entrance surface, is located at the first focus FL. The conjugate focus F'1 is located at a distance D' from the entrance section SE. Descartes' law of conjugation allows us to find the conjugate focus F'1.

[0094] Preferably, the light source 21 is centered on the longitudinal axis X.

[0095] Thus, according to the previous embodiment, the light source 21 is located at a distance D' from the inlet section SE.

[0096] According to the preceding embodiment, the distance D is chosen such that the distance D' is preferably greater than or equal to 0.5 mm. For example, the distance D' may be equal to 1 mm. A distance D' greater than or equal to 0.5 mm limits the risk of damage to the input section SE due to the increase in heat caused by receiving the light beam emitted by the light source 23. A distance D' greater than or equal to 0.5 mm also provides a spacing tolerance between the light source 21 and the input section SE, so that the light source 21 is never in contact with the optical coupler 22.

[0097] According to the preceding embodiment, in which the light source 21 emits a monochromatic or polychromatic light beam towards the entrance section SE, the light rays of the light beam entering the entrance section SE are totally reflected by the envelope 221' of the first part 221 and are partially reflected by the envelope of the second part 222 according to their respective angle of incidence and the index of the material of the optical coupler 22.

[0098] Let n air and 0 the angle of incidence of a light ray from a light beam emitted by the light source 21. The ellipsoidal shape of the envelope of the first part 221 is designed such that each light ray incident towards the envelope of the first part 221 is totally reflected towards the focus F2. Thus, according to Descartes' law, each light ray incident towards the envelope of the first part 221 has an angle of incidence satisfying the following condition:

[0099] Sin(0) > ^ , the sine of the angle of the incident light ray is greater than the ratio between the refractive index of air nair and the refractive index of the coupler n c.

[0100] According to the previous embodiment, in which the light source 21 emits a monochromatic or polychromatic light beam towards the inlet section SE, the envelope 222' of the second part 222 is designed to minimize the leakage of incident light rays towards the envelope 222' of the second part 222, in order to minimize the losses in brightness and intensity of the light rays.

[0101] the light source 21 being located at the conjugate focus F'1, each light ray reflected totally or partially by the envelope 221' of the first part 221 or the envelope 222' of the second part 222 is focused at the focus F2, included in the third part 223.

[0102] Figure [Fig.3] represents the path of two light rays emitted by the light source 21 and being reflected by the envelope 221' of the first part 221 towards the focus F2.

[0103] It is possible that some light rays, of wavelength X, are focused at the focus F2, located on the longitudinal axis X, less than one millimeter from the focus F2, and not directly at the focus F2, due to chromatic aberration.

[0104] According to an embodiment in which the light source 21 is an RGB LED emitting a light beam comprising red, green, and blue rays towards the input surface SE, all reflected light rays are focused at the focal point F2 and then propagate respectively into the third part 223 by reflecting off the n flat faces of the envelope 223' of the third part 223. Advantageously, the polygonal section 23 of the third part 223 makes it possible to break the propagation modes of each red, green, and blue ray due to the multiple reflections on each of the n faces of the third part 223, and to obtain a uniform distribution of light intensity and a homogeneous and optimal color mixing at the output of the third part 223, at the level of the third inter- section. median SI3.

[0105] According to the preceding embodiment, in which the optical coupler 22 comprises the fourth part 224, the fourth part 224 enables the conduction of light rays of uniform intensity and homogeneous color from the third intermediate section to the optical fiber bundle 23.

[0106] The optical fiber bundle 23 (called Bundle in English), 23 comprises a connector 231 and at least one optical fiber 232, preferably a plurality of optical fibers, the plurality of optical fibers being threaded into the connector 213. Preferably, the optical fibers of the plurality of optical fibers are identical.

[0107] The 231 connector can have a circular cross-section.

[0108] Preferably, the optical fiber bundle 23 has a linear configuration. In a linear configuration, all the optical fibers of the plurality of optical fibers are parallel and lie in the same plane.

[0109] In the embodiment in which the optical coupler 22 comprises the fourth part 224 and in which the second output section SS2 is circular, the connector 213 has a transverse diameter equal to the diameter of the second output section SS2 of the fourth part 224 of the optical coupler 22.

[0110] Each optical fiber 232 of the optical fiber bundle 23 is multimode.

[0111] Each optical fiber 232 of the optical fiber bundle 23 preferably has an outside diameter equal, for example, to 0.5mm or 0.25mm.

[0112] According to one embodiment, in which the plurality of optical fibers of the optical fiber bundle 23 are woven directly into a decorative fabric, it is preferable to use optical fibers of respective diameter equal to 0.25 mm, this allows for better weaving fineness and finer patterns.

[0113] According to one embodiment, in which the plurality of optical fibers of the optical fiber bundle 23 are woven into a technical fabric, covered with a decorative material, it is preferable to use optical fibers of respective diameter of 0.5 mm.

[0114] Each optical fiber 232 of the optical fiber bundle 23 is preferably formed, for example, from glass or preferably from plastic, for example from PMMA (Polymethyl methacrylate).

[0115] According to one embodiment, each optical fiber 232 of the optical fiber bundle 23 does not include a sheath.

[0116] In one embodiment, each optical fiber 232 of the optical fiber bundle 23 comprises a cladding of fluorinated polymer and a core of PMMA.

[0117] Each optical fiber 232 of the optical fiber bundle 23 is adapted to conduct light rays.

[0118] According to one embodiment, in which the optical coupler 22 is formed of PC, the connector 231 is glued to optical coupler 22 via the SS output section, using a transparent optical quality adhesive of type OCA for "Optical Clear Adhesive" according to English terminology.

[0119] According to one embodiment, in which the optical coupler 22 comprises the fourth part 224, the connector 231 is located at a distance D c from the second output section SS2 of the fourth part of the optical coupler 22.

[0120] The optical lighting system 2 can be included in a trim panel for the vehicle interior.

[0121] Several simulations were performed to evaluate the efficiency of the optical coupler 22, according to the embodiment in which the coupler 22 includes the fourth part. Efficiency is defined as the ratio between the luminous flux (in lumens) at the second output section SS2, for the {light source 21 + optical coupler 22} assembly, and the luminous flux (in lumens, denoted Lm) emitted by the light source 21. In the simulations, the light source 21 is an RGB LED. Efficiency is measured for an optical coupler 22 made from PC and for an optical coupler 22 made from PMMA. Several cross-sectional diameters of the second output section SS2 were simulated.

[0122] The following simulations were carried out according to an embodiment in which the optical coupler 22 is glued to the fiber strand by means of a transparent adhesive, via the second output SS2, to the optical fiber bundle 23 with a transparent optical-grade adhesive:

[0123] [Tables 1]

[0124] The chosen LED emits a light beam with a flux of 4.39 lm. According to In previous simulations, the luminous flux output of the {LED + optical coupler 22} assembly, with the optical coupler 22 made from PC, shows greater efficiency compared to the {LED + optical coupler 22} assembly with the optical coupler 22 made from PMMA. In this embodiment, the efficiency is better when the coupler is made of PC because the refractive index of PC is higher than the refractive index of PMMA.

[0125] The following simulations were performed according to an embodiment in which the coupler is not attached to the optical fiber bundle:

[0126] [Tables 2]

[0127] Thus, when the optical coupler 22 is not glued to the optical fiber bundle 23, the efficiency decreases by 14% for an optical coupler 22 formed from PMMA and decreases by 17% for an optical coupler 22 formed from PC.

Claims

Demands

1. Optical coupler (22) having a longitudinal central axis X, said optical coupler (22) comprising a first (221), a second (222) and a third (223) part and wherein: - said first part (221) comprises an envelope (221') following the shape of an ellipsoid of revolution with axis X, truncated according to a plane section perpendicular to the longitudinal axis X, of polygonal cross section (SI), the area of ​​said cross section (SI) increasing progressively along the longitudinal axis X, between an entry section (SE) and a first intermediate section (SU); - said third part (223) comprises an envelope (222') in the form of a right prism, with a polygonal cross-section (S3) of constant area between a second intermediate section (SI2) and a first output section (SS1) making the first intermediate section (SU) greater than making the second intermediate section (SI2), - Said second part (222) being a transition part disposed between the first part (221) and the third part (223), said second part (222) comprising an envelope (222') having a transverse section (S2) which gradually decreases along the longitudinal axis X, said second part (222) comprising: • a first connecting section to the first part (221), the first connecting section being the first intermediate section (SU), • a second connecting section to the second part (222), the second connecting section being the second intermediate section (SI2).

2. Optical coupler (22) according to the preceding claim characterized in that said optical coupler (22) has a full configuration.

3. Optical coupler (22) according to any one of the preceding claims in that said optical coupler (22) comprises a fourth part (224) having an envelope (224') of cross-section (S4) of constant area, along the longitudinal axis X, between the first outlet section (SS1) and a second outlet section (SS2).

4. Optical coupler (22) according to any one of the preceding claims characterized in that the cross section (SI) of the envelope (221') of the first part (221) and / or the cross section (S3) of the envelope (223') of the third part (223) are respectively polygons of order n, n being a natural number between 4 and 10.

5. Optical coupler (22) according to the preceding claim characterized in that n is equal to 6.

6. Optical coupler (22) according to any one of the preceding claims characterized in that said optical coupler (22) is formed from the following material: polycarbonate, polymethyl methacrylate, glass or silicone.

7. Optical coupler (22) according to any one of the preceding claims characterized in that the envelope (221') of the first part (221) has a first focus (F1) and a second focus (F2), the first focus (F1) being located outside the optical coupler (22).

8. Optical lighting system (2) comprising: - A light source (21); - An optical coupler (22) according to any one of claims 1 to 7; - A bundle of optical fibers (23).

9. Optical lighting system (2) according to claim 8 wherein the light source (21) is placed at the conjugate focus (F'1) of the first focus (Fl) by the entrance surface (SE).

10. Optical lighting system (2) according to any one of claims 8 to 9 wherein the optical fiber bundle (23) comprises a plurality of optical fibers, each optical fiber of the plurality of optical fibers being formed of Polymethyl Methacrylate.

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