FR3101391A1 - Optical system - Google Patents

Abstract

Title: Optical system for a light module The invention relates to a projection optical system which comprises: - an input optical group (10) with a first lens (11) and a second lens (12), receiving light rays coming from 'a light source (1) and making them converge; - an intermediate optical group (20) comprising a lens (21), the intermediate optical group (20) receiving rays from the input optical group (10) to make them diverge; - an output optical group (30) comprising at least one lens (31), the output optical group (30) receiving light rays from the intermediate optical group (20) to make them converge. Figure for the abstract: Fig. 1

Description

Optical system

The present invention relates in particular to an optical projection system and to a light module for a vehicle.

A preferred application concerns the automotive industry, for vehicle equipment, in particular for the production of devices capable of emitting light beams, also called lighting and/or signaling functions, generally complying with regulations. For example, the invention can allow the production of a light beam of the segmented type, in particular for participation in lighting functions at the front of a vehicle and/or possibly signalling.

The invention can in particular make it possible to generate an additional main beam (associated with a base beam totally or at least mainly projected below a horizontal cut-off line of the type used for the dipped beam function, the road complement adding to the base beam so as to complete it above the cut-off line); advantageously, this additional main beam is adaptive to switch on or off certain parts of the overall projected beam, for example for anti-dazzle functions. The invention can also be applied to writing functionalities on the road, or even to light projections of welcome scenarios for which lighting is generated in particular when the user is approaching his vehicle.

In the automobile sector, devices capable of emitting light beams, also called lighting and/or signaling functions, are known, generally complying with regulations.

Recently, technologies have been developed to produce a segmented beam, also called pixelated, to perform advanced lighting functions. This is particularly the case for a lighting function of the "highway complement" type generally based on a plurality of lighting units each comprising a light-emitting diode, these diodes being able to be controlled individually.

The beam, resulting from the different beam segments from the diodes, is projected by means of a projection optical system generally comprising one or more lenses. For example, an additional driving beam can be produced, associated with a base beam totally or at least mainly projected below a horizontal cut-off line of the type used for the dipped headlight function, the additional driving beam adding to the basic beam so as to complete it above the cut-off line; advantageously, this additional main beam is adaptive to switch on or off certain parts of the overall projected beam, for example for anti-dazzle functions. The acronym ADB (for Adaptive Driving Beam) is used for this type of function.

It will be noted that the invention is in no way limited to the beams of the ADB type mentioned above but finds an application in the projection of all beams having a segmentation for which imaging is preferably sufficiently precise while keeping a large aperture. These may be beams with more or less segments, which may be arranged in whole or in part above a cut line or below. Certain functionalities, in particular dynamic adaptation of beam directions in the event of bends, for example the function known by the acronym DBL (Dynamic Bending Light, for dynamic lighting in curves).

In the present description, the term segmented beam refers to a beam whose projection forms an image composed of beam segments, each segment being able to be lit independently. A pixelated light source can be used to form these segments. Such a source comprises a plurality of selectively activatable emissive zones.

For reasons of cost price and size, optical systems should be optimized for automotive implementations; however, specialized applications such as the production of an ADB beam require sufficient sharpness, in particular to properly isolate the segments of the beam to be extinguished, so as to achieve precise shaping of the dark zone without however penalize the general illumination, which itself requires a large numerical aperture.

An object of the present invention is therefore to provide an optical system which achieves a compromise between the complexity and the optical efficiency, in particular in terms of aperture and sharpness, of the optical system.

The other objects, features and advantages of the present invention will become apparent from a review of the following description and the accompanying drawings. It is understood that other benefits may be incorporated.

SUMMARY

To achieve this objective, according to one embodiment, an optical projection system is provided, in particular for a vehicle light module, comprising:
- an optical input group comprising at least a first lens and a second lens, the optical input group being adapted to receive light rays from a light source and to make them converge;
- an intermediate optical group comprising at least one lens, the intermediate optical group receiving light rays from the input optical group and being configured to make them diverge;
- an output optical group comprising at least one lens, the output optical group receiving light rays from the intermediate optical group and being configured to make them converge.

Thanks to this arrangement, the light emitted by the source is successively processed by the three optical groups of the invention. The sequence of a convergent group, a divergent group and a convergent group as proposed ensures high definition without making it necessary to multiply the lenses. In particular, the invention may be limited to four or five lenses for all the groups considered. Advantageously, there is no need for an additional projection lens.

Compared to a triplet optical system typically used, the presence of several lenses, and preferably two lenses, in the input group ensures an increase in the numerical aperture of the projection optical system.

In a preferred embodiment, the output optical group also has several lenses, and in particular two, so that the sharpness is increased, to obtain a better resolution.

Advantageously, the angular field of projection can be greater than 30°, which is particularly well suited to producing an ADB type beam.

Preferably, only spherical components are used, which ensures a reduced manufacturing cost. It is also possible to space the lenses by air gaps so that lens bonding is not necessary.

Another aspect relates to a light module, in particular for a motor vehicle, comprising the optical system, and a pixelated light source comprising a plurality of selectively activatable emissive zones. The light module is advantageously configured to produce or participate in producing an ADB beam.

Another aspect relates to a vehicle equipped with at least one module according to the present invention.

The aims, objects, as well as the characteristics and advantages of the invention will emerge better from the detailed description of an embodiment of the latter which is illustrated by the following accompanying drawings in which:

Figure 1 shows a schematic view of a module in a first indicative embodiment.

Figure 2 shows a schematic view of a module in a second indicative embodiment.

The drawings are given by way of examples and do not limit the invention. They constitute schematic representations of principle intended to facilitate understanding of the invention and are not necessarily scaled to practical applications.

Unless specifically indicated otherwise, technical characteristics described in detail for a given embodiment may be combined with technical characteristics described in the context of other embodiments described by way of example and not limitation.

Here we introduce options that can be implemented, either separately or in any possible combination:
- the distance separating the exit diopter of the optical input group 10 and the entry diopter of the intermediate optical group 20, measured at the level of the edge of said diopters, is less than or equal to 3 mm;
- the distance separating the output diopter of the intermediate optical group 20 and the input diopter of the output optical group 30, measured at the level of the edge of said diopters, is less than or equal to 3 mm;
- the optical input group 10, the intermediate optical group 20 and the optical output group 30 are configured so that the system is more open numerically than F/0.9, and preferably more open than F/0.75;
- all the lenses at least of the optical input group 10 and of the optical output group 20 are made of optical glass with a refractive index greater than or equal to 1.7;
- all the lenses of the input optical group 10, of the intermediate optical group 20 and of the output optical group 30 have a ratio "thickness at the center of the lens / useful diameter of the lens" which does not exceed 1/4 or 0.25 , which means that the useful diameter is at least four times greater than the thickness at the center; the useful surface is the part of the lens in which all the rays contributing to the performance of the system pass. In the present case, it is typically a circle, because everything is advantageously rotationally symmetrical; this useful diameter is generally different from the mechanical diameter: a width of a few millimeters is typically left around the useful diameter to hold the lens or facilitate manufacture; the exact value of the mechanical diameter does not matter from an optical point of view.
- The intermediate optical group 20 comprises a single lens 21;
- The single lens 21 is bi-concave;
- the optical output group 30 consists of a first lens 31 and a second lens 32;
- the optical input group 10 consists of the first lens 11 and the second lens 12;
- All the lenses of the optical input group 10, of the intermediate optical group 20 and of the optical output group 30 are successively spaced by an air gap;
- the minimum distance separating the light source 1 and the input dioptre of the input optical group 10 is greater than or equal to 5 mm.
- the entry face of the first lens of the entry group is flat or concave; a concave surface increases the resolution;
- the second lens the input group is preferably of biconvex shape;
- the entry face of the first lens of the exit group is flat or concave;
- the input face of the second lens of the output group is flat or convex;
- at least a part of the optical surfaces is covered by an antireflection coating;
- the light source is centered on the optical axis of the optical system;
- At least part of the optical surfaces may be microstructured (presence of relief patterns, the dimensional scale of which is micrometric or nanometric);
- the optical system is included in a housing whose inner surface has a black diffusive texture;
- all the dioptres of all the lenses of the input optical group, of the intermediate optical group and of the output optical group are spherical.

Motor vehicle headlamps are often provided with one or more light modules arranged in a housing closed by a glass so as to obtain one or more lighting and/or signaling beams at the exit of the headlamp. In a simplified way, a light module of the housing comprises in particular a light source which emits a light beam, an optical system comprising one or more lenses and, in certain cases, an optical element, for example a reflector, to direct the light rays coming from light sources, in order to form the output light beam of the optical module. The situation is the same for the rear lights.

The invention can take part in a main beam function which is used to illuminate the scene facing the vehicle over a wide area, but also over a substantial distance, typically about two hundred meters. This light beam, due to its lighting function, is located mainly above the horizon line. It may have a slightly upward illumination optical axis, for example. In particular, it can be used to generate a lighting function of the "highway complement" type which forms a portion of a main beam complementary to that produced by a near-field beam, the main beam seeking in whole or at least mainly to illuminate above the horizon line while the near field beam (which may have the specificities of a dipped beam) seeks to illuminate entirely or at least mainly below the horizon line.

The device can also be used to form other lighting functions via or apart from those described previously in relation to the adaptive beams. Notably, a writing function on the ground, especially at the front of the vehicle is another potential use. Any other type of beam and any other lighting or signaling function may be affected by the module of the invention.

The module of the invention incorporates at least one light source 1 making it possible to generate a segmented type beam to be projected via the optical system.

As shown schematically in FIG. 1, the light module according to the invention may successively comprise a light source 1 and an optical system comprising, and preferably consisting of, three groups of lenses, namely an input optical group 10, an optical group intermediate optics 20 and an output optical group 30. Rays 2 emitted by source 1 are processed by the optical system so as to produce projected rays 4. The entire optical system can be organized along an optical axis 3, and source 1 is preferably centered on the latter.

The light source 1 can in particular be designed in the form of a matrix of emissive elements in the activation can be driven individually, to turn off or turn on any of the emissive elements. The shape of the resulting beam is thus varied with a very wide flexibility. For purely illustrative purposes, it is possible to implement a matrix of nine emissive elements, forming nine pixels, arranged in three rows and three columns.

In a manner known per se, the present invention can use light sources of the light-emitting diode type also commonly called LEDs. It may possibly be organic LED(s). In particular, these LEDs can be equipped with at least one chip using semiconductor technology and capable of emitting light. Furthermore, the term light source here means a set of at least one elementary source such as an LED capable of producing a flux leading to the generation at the output of the module of the invention at least one light beam. In an advantageous mode, the output face of the source is of rectangular section, which is typical for LED chips.

Preferably, the light-emitting source comprises at least one matrix of monolithic light-emitting elements, also called monolithic matrix. In a monolithic matrix, the light-emitting elements are grown from a common substrate and are electrically connected so as to be selectively activatable, individually or by subset of light-emitting elements. The substrate may mainly be made of semiconductor material. The substrate may comprise one or more other materials, for example non-semiconductors. Thus each electroluminescent element or group of electroluminescent elements can form a luminous pixel and can emit light when its or their material is supplied with electricity. The configuration of such a monolithic matrix allows the arrangement of selectively activatable pixels very close to each other, compared to conventional light-emitting diodes intended to be soldered on printed circuit boards. The monolithic matrix within the meaning of the invention comprises light-emitting elements of which a main dimension of elongation, namely the height, is substantially perpendicular to a common substrate, this height being at most equal to one micrometer.

Advantageously, the monolithic matrix(es) capable of emitting light rays can be coupled to a light emission control unit of the pixelated source. The control unit can thus control (we can also say drive) the generation and/or the projection of a pixelated light beam by the light device. The control unit can be integrated into the lighting device. The control unit can be mounted on one or more of the matrices, the assembly thus forming a light module. The control unit may comprise a central processing unit coupled with a memory on which is stored a computer program which includes instructions allowing the processor to carry out steps generating signals allowing control of the light source. The control unit can thus, for example, individually control the light emission of each pixel of a matrix. Further, the luminance obtained by the plurality of light emitting elements is at least 60Cd/mm2, preferably at least 80Cd/mm2.

The control unit can form an electronic device capable of controlling the light-emitting elements. The control unit may be an integrated circuit. An integrated circuit, also called an electronic chip, is an electronic component reproducing one or more electronic functions and able to integrate several types of basic electronic components, for example in a small volume (i.e. on a small plate). This makes the circuit easy to implement. The integrated circuit may for example be an ASIC or an ASSP. An ASIC (acronym for “Application-Specific Integrated Circuit”) is an integrated circuit developed for at least one specific application (that is to say for a customer). An ASIC is therefore a specialized integrated circuit (microelectronics). In general, it bundles a large number of unique or tailor-made features. An ASSP (acronym for “Application Specific Standard Product”) is an integrated electronic circuit (microelectronics) grouping together a large number of functions to satisfy a generally standardized application. An ASIC is designed for a more particular (specific) need than an ASSP. The monolithic matrices are supplied with electricity via the electronic device, itself supplied with electricity using, for example, at least one connector connecting it to a source of electricity. The source of electricity can be internal or external to the device according to the invention. The electronic device supplies the light source with electricity. The electronic device is thus able to control the light source.

According to the invention, the light source preferably comprises at least one monolithic matrix whose light-emitting elements extend projecting from a common substrate from which they have respectively grown. Different arrangements of light-emitting elements can meet this definition of monolithic matrix, provided that the light-emitting elements have one of their main dimensions of elongation substantially perpendicular to a common substrate and that the spacing between the pixels, formed by a or several light-emitting elements grouped together electrically, is small in comparison with the spacings imposed in known arrangements of flat square chips soldered on a printed circuit board.

In particular, the light source according to one aspect of the invention may comprise a plurality of light-emitting elements distinct from the others and which are grown individually from the substrate, being electrically connected to be selectively activatable, if necessary by sub- sets in which rods can be activated simultaneously.

According to an embodiment not shown, the monolithic matrix comprises a plurality of light-emitting elements, of sub-millimeter dimensions, which are arranged projecting from a substrate so as to form rods of hexagonal section. The light-emitting rods extend parallel to the optical axis of the light module when the light source is in position in the housing.

These light-emitting rods are grouped together, in particular by electrical connections specific to each set, in a plurality of portions which can be selectively activated. The light-emitting rods originate on a first face of a substrate. Each electroluminescent rod, here formed by using gallium nitride (GaN), extends perpendicularly, or substantially perpendicularly, projecting from the substrate, here made from silicon, other materials such as silicon carbide being able to be used without depart from the context of the invention. By way of example, the light-emitting rods could be made from an alloy of aluminum nitride and gallium nitride (AlGaN), or from an alloy of aluminum phosphides, indium and gallium (AlInGaP). Each electroluminescent rod extends along an axis of elongation defining its height, the base of each rod being arranged in a plane of the upper face of the substrate.

The light-emitting rods of the same monolithic matrix advantageously have the same shape and the same dimensions. They are each delimited by an end face and by a circumferential wall which extends along the axis of elongation of the rod. When the light-emitting rods are doped and subjected to biasing, the resulting light at the output of the semiconductor source is emitted essentially from the circumferential wall, it being understood that light rays can also come out from the face terminal. As a result, each light-emitting rod acts as a single light-emitting diode and the luminance of this source is improved on the one hand by the density of the light-emitting rods present and on the other hand by the size of the illuminating surface defined by the circumferential wall. and which therefore extends over the entire circumference, and the entire height, of the rod. The height of a rod can be between 2 and 10 μm, preferably 8 μm; the largest dimension of the end face of a rod is less than 2 μm, preferably less than or equal to 1 μm.

It is understood that, during the formation of the light-emitting rods, the height can be modified from one zone of the light source to another, so as to increase the luminance of the corresponding zone when the average height of the rods constituting it is increased. Thus, a group of light-emitting rods can have a height, or heights, different from another group of light-emitting rods, these two groups being constitutive of the same semiconductor light source comprising light-emitting rods of sub-millimeter dimensions. The shape of the light-emitting rods can also vary from one monolithic matrix to another, in particular on the section of the rods and on the shape of the terminal face. The rods have a generally cylindrical shape, and they may in particular have a polygonal section shape, and more particularly hexagonal. It is understood that it is important for light to be able to be emitted through the circumferential wall, whether the latter has a polygonal or circular shape.

Furthermore, the end face may have a substantially planar shape perpendicular to the circumferential wall, so that it extends substantially parallel to the upper face of the substrate, or it may have a rounded or pointed shape at its center. , so as to multiply the directions of emission of the light emerging from this end face.

The light-emitting rods are arranged in a two-dimensional array. This arrangement could be such that the sticks are staggered. In general, the rods are arranged at regular intervals on the substrate and the separation distance of two immediately adjacent electroluminescent rods, in each of the dimensions of the matrix, must be at least equal to 2 μm, preferably between 3 μm and 10 µm, so that the light emitted from the circumferential wall of each rod can exit the array of light-emitting rods. Furthermore, it is expected that these separation distances, measured between two axes of elongation of adjacent rods, are not greater than 100 μm.

According to another embodiment not shown, the monolithic matrix may comprise light-emitting elements formed by layers of epitaxial light-emitting elements, in particular a first n-doped GaN layer and a second p-doped GaN layer, on a single substrate, by example of silicon carbide, and which is cut (by grinding and/or ablation) to form a plurality of pixels respectively originating from the same substrate. The result of such a design is a plurality of light-emitting blocks all derived from the same substrate and electrically connected to be selectively activatable from each other.

In an exemplary embodiment according to this other mode, the substrate of the monolithic matrix may have a thickness of between 100 μm and 800 μm, in particular equal to 200 μm; each block can have a width and width, each being between 50 μm and 500 μm, preferably between 100 μm and 200 μm. Alternatively, the length and the width are equal. The height of each block is less than 500 μm, preferably less than 300 μm. Finally, the exit surface of each block can be made via the substrate on the side opposite to the epitaxy. The separation distance between two pixels. The distance of the contiguous pixels can be less than 1 μm, in particular less than 500 μm, and it is preferably less than 200 μm.

Regarding monolithic chips with light-emitting blocks:

- The number of pixels can be between 250 and several thousand. A typical value being around a thousand pixels.

- Their overall shape is usually square, and can also be rectangular. Aspect ratio usually between 1:1 and 1:5.

- The size of a unit pixel (square in all known cases, perhaps rectangular) is between 100 and 300 µm in the current state of the art.

According to another embodiment not shown, both with light-emitting rods extending respectively projecting from the same substrate, as described above, and with light-emitting blocks obtained by cutting out superimposed light-emitting layers on the same substrate, the monolithic matrix may further comprise a layer of a polymer material in which the light-emitting elements are at least partially embedded. The layer can thus extend over the entire extent of the substrate or only around a determined group of light-emitting elements. The polymer material, which may in particular be based on silicone, creates a protective layer which makes it possible to protect the light-emitting elements without hindering the diffusion of the light rays. In addition, it is possible to integrate in this layer of polymer material wavelength conversion means, and for example phosphors, able to absorb at least part of the rays emitted by one of the elements and to convert at least a part of said excitation light absorbed into emission light having a wavelength different from that of the excitation light. It is possible to provide either that the phosphors are embedded in the mass of the polymer material, or that they are arranged on the surface of the layer of this polymer material. The light source may further comprise a coating of reflective material to deflect the light rays towards the output surfaces of the pixelated source.

The light-emitting elements of sub-millimeter dimensions define in a plane, substantially parallel to the substrate, a determined output surface. It is understood that the shape of this output surface is defined according to the number and arrangement of the light-emitting elements which compose it. It is thus possible to define a substantially rectangular shape of the emission surface, it being understood that the latter can vary and take any shape without departing from the context of the invention.

The embodiment presented in FIG. 1 has five lenses arranged downstream of a light source 1 whose emissive surface is represented by a plane from which rays 2 leave in the direction of an entry face of a first lens 11 of an optical input group 10 of lenses.

It will be seen that FIG. 2 presents a variant with four lenses.

Advantageously, an optical glass having a refractive index at least equal to 1.7 is used to produce the lenses, and at least those of the optical input group 10 and of the optical output group 30. The shapes of the faces of the lenses are described below in more detail, it being generally considered that they are advantageously of circular cross-section. Furthermore, it is preferred that the faces of the lenses, forming diopters with the surrounding air, be of a spherical nature.

In the case of FIG. 1, the optical input group 10 comprises a first lens 11 having an input face (or diopter) (advantageously concave, but which can also be planar) and a convex output face. As represented by the path of the light rays, this lens 11 ensures a first convergence.

This convergence is completed by a second lens 12 of the optical input group 10, the latter being biconvex. The constringency of the input optical group 10 is advantageously high, and at least higher than that of the intermediate optical group 20 described below.

The light rays leaving the input optical group 10 reach, advantageously directly, a second group, called the intermediate optical group 20. Preferably, it consists of a biconcave lens 21. The useful edge of the input face of the lens 21 is preferably spaced by at most 3 mm from that of the lens which precedes it, that is to say the last lens of the optical input group 10; this limited spacing is favorable to the optical resolution and, the preservation of a space between the lenses facilitates the assembly of the optical system, in particular by sparing collages.

The intermediate optical group 20 diverges the light rays in the direction of a third group, called output optical group 30. The latter, like the first, has a convergent function. It comprises a first lens 31 of a convergent nature, having an entrance face which is either flat, concave or convex and whose exit face is convex. Preferably, as described in relation to the input optical group 10, the spacing between the intermediate optical group 20 and the output optical group 30 is limited, in particular to 3 mm at the useful edge of the adjacent lenses of the two groups.

In the embodiment represented in FIG. 1, the optical output group 30 comprises a second lens 32, the input face of which can be flat or convex and the output face of which is convex.

After this path, the rays 4 leaving the system can be projected, advantageously directly, towards the outside of the vehicle.

FIG. 2 presents a variant embodiment with four lenses. The first group, input optical group 10, always has two lenses. Likewise, the intermediate optical group 20 here always consists of a lens with two concave faces. However, the output optical group 30 then only comprises a single lens 31. Obviously, the sharpness obtained is lower than the previous case, but so is the size. Depending on the optical and size requirements of the application, one or the other of these two embodiments may be used, which are not, however, limiting of the invention.

Thanks to the invention, it is possible to obtain a sharp projection, preferably with a numerical aperture greater than or equal to F/0.9 or even F/0.75 and over an angular sector advantageously greater than or equal to 30°.

The invention is not limited to the embodiments previously described

Claims (13)

Projection optical system, in particular for a vehicle light module, characterized in that it comprises:
- an input optical unit (10) comprising at least a first lens (11) and a second lens (12), the input optical unit (10) being able to receive light rays from a light source ( 1) and make them converge;
- an intermediate optical group (20) comprising at least one lens (21), the intermediate optical group (20) receiving light rays from the input optical group (10) and being configured to make them diverge;
- an output optical group (30) comprising at least one lens (31), the output optical group (30) receiving light rays from the intermediate optical group (20) and being configured to make them converge. System according to the preceding claim, in which the distance separating the output diopter of the input optical group (10) and the input diopter of the intermediate optical group (20), measured at the level of the edge of the said diopters, is less than or equal at 3mm. System according to any one of the preceding claims, in which the distance separating the output diopter of the intermediate optical group (20) and the input diopter of the output optical group (30), measured at the level of the edge of the said diopters, is less than or equal to 3 mm. A system according to any preceding claim, wherein the input optical group (10), the intermediate optical group (20) and the output optical group (30) are configured such that the system is more digitally open than F /0.9, and preferably more open than F/0.75. A system according to any preceding claim, wherein all the lenses of at least the input optical group (10) and the output optical group (20) are formed from optical glass with an index of refraction greater than or equal to 1 ,7. A system according to any preceding claim, wherein all of the lenses of the input optical group (10), the intermediate optical group (20) and the output optical group (30) have a "lens center thickness /lens effective diameter" which does not exceed 0.25. A system according to any preceding claim, wherein the intermediate optical group (20) comprises a single lens (21). System according to the preceding claim, in which the single lens (21) is bi-concave. A system according to any preceding claim, wherein the output optical group (30) consists of a first lens (31) and a second lens (32). A system according to any preceding claim, wherein the input optical group (10) consists of the first lens (11) and the second lens (12). System according to any one of the preceding claims, in which all the lenses of the input optical group (10), of the intermediate optical group (20) and of the output optical group (30) are successively spaced apart by an air gap . Light module, in particular for a motor vehicle, comprising a system according to any one of the preceding claims and a pixelated light source (1) comprising a plurality of selectively activatable emissive zones. Light module according to the preceding claim, in which the minimum distance separating the light source (1) and the input dioptre of the input optical group (10) is greater than or equal to 5 mm.