Luminous module including a field-correcting optical element

Abstract

A field-correcting optical element configured to be arranged in an adaptive lighting device crosswise to light rays emitted by a plurality of light sources includes an entrance face through which light rays enter and an exit face through which these light rays exit. At least one segment of the entrance face is covered with an antireflection coating that is able to increase the transmittance of light rays through the optical element.

Claims

1. A motor-vehicle luminous module comprising: primary light sources that are configured to emit light rays from a common emission plane that is orthogonal to an optical axis of the luminous module; a primary optical element that includes a front segment forming a lens and a back segment that includes a plurality of light guides, each light guide including an entrance face through which light rays emitted by a primary light source enter and an exit face through which these light rays exit in the direction of the front segment forming said lens; and a projecting optic that is able to project an image of the exit faces in order to form an overall adaptive light beam, a field-correcting optical element being arranged on the optical axis of the luminous module between the primary optical element and the projecting optic, the entrance face, which is at least partially covered with an antireflection coating, being turned towards the primary optical element, the field-correcting optical element including an entrance face through which light rays enter, and an exit face through which these light rays exit, wherein at least one segment of the entrance face is covered with an antireflection coating that is able to decrease the reflection of some of the light rays by this entrance face.

2. The motor-vehicle luminous module according to claim 1, wherein a dioptric interface formed between the entrance face of the field-correcting optical element and its antireflection coating is configured to have a transmittance at least equal to 97%.

3. The motor-vehicle luminous module according to claim 1, wherein at least one segment of the exit face of the field-correcting optical element is covered with an antireflection coating.

4. The motor-vehicle luminous module according to claim 1, wherein the antireflection coating is a monolayer coating of low-refractive-index material, preferably magnesium fluoride MgF.sub.2.

5. The motor-vehicle luminous module according to claim 1, wherein the antireflection coating has a thickness of 101 nm.

Description

(1) Other features and advantages of the invention will become more clearly apparent on reading the detailed description of embodiments of the invention, which is given below by way of nonlimiting illustrative example and with reference to the appended figures, in which:

(2) FIG. 1 is a cross-sectional view, in a cross-sectional plane comprising the longitudinal optical axis (A) of the projecting optic, of a luminous module that is able to provide an ADB adaptive high-beam function in a motor-vehicle signalling or lighting device, the luminous module including a field-correcting optical lens L2 according to the invention; and

(3) FIG. 2 is a detail view in vertical transverse cross section along a longitudinal orientation L of the longitudinal optical axis (A) of a field-correcting optical lens L2 according to the invention, said lens configured to be arranged in a pixelated optical system including a plurality of light guides.

(4) It will firstly be noted that although the figures illustrate the invention in a detailed way with regard to implementation thereof, they may of course serve to better define the invention where appropriate. Likewise, it will be recalled that, in all the figures, elements that are the same have been referenced with the same references. It will also be understood that the embodiments of the invention that are illustrated in the figures are given by way of nonlimiting example.

(5) It will also be recalled that, in the following description, the term front refers to the direction of the final light beam emitted longitudinally frontwards, i.e. as output from the luminous module according to the invention.

(6) The invention has an application in a motor vehicle equipped with a lighting device that is able to produce an ADB adaptive lighting function. This lighting device in particular includes a luminous module such as will be described with reference to FIG. 1, and wherein it is noteworthy that a field-correcting optical element is at least partially covered with an antireflection coating.

(7) FIG. 1 illustrates a luminous module 1 equipped with a field-correcting optical element 20 according to the invention, and more particularly in a case where the field-correcting optical element is formed by a lens L2.

(8) The luminous module 1 has a longitudinal optical axis (A) and it is configured to emit an adaptive final light beam longitudinally frontwards in order to provide what is called an ADB adaptive high-beam function in a motor-vehicle signalling or lighting device.

(9) Along the longitudinal direction L of the optical axis, the module includes, from back to front, a matrix 16 of primary light sources that are here formed by light-emitting diodes each of which is able to emit a primary elementary beam from a common emission plane that is orthogonal to the optical axis, then a primary optical element 10 that is arranged following the matrix 16 of light-emitting diodes 12 in order to modify the distribution of the emitted light rays, then the field-correcting optical element 20 and a projecting optic 30, the field-correcting optical element being intended to correct the path of the rays output from the primary optical element to the projecting optic 30 in order to achieve a clear projection to infinity of the whole of the adaptive final light beam.

(10) The matrix 16, which lies in a plane that is orthogonal to the longitudinal direction L, is here equipped with two transverse rows of 17 light-emitting diodes 12 that are borne by the front face of a printed circuit board 15 and that are arranged one above the other, as may be seen in FIG. 2. Each light-emitting diode 12 may be controlled individually via control electronics and the printed circuit board 15. With a view to creating an adaptive beam, i.e. an overall light beam including a dark zone therein, each transverse row of light-emitting diodes 12 may be controlled to form at least one set of successive turned-on diodes and at least one or at least one set of successive turned-off diodes.

(11) The primary optical element 10 here includes a back first segment 17, which is formed from a plurality of light guides 11 and which is turned towards the matrix 16 of primary light sources, and a front second segment 18 for shaping the light beams emitted by the secondary light sources, so as to form a lens L1.

(12) In the back first segment 17 of the primary optical element, one light guide 11 is placed facing each light-emitting diode 12, so that, in the illustrated embodiment, two rows of light guides are arranged one above the other, though it will be understood that, without departing from the context of the invention, there could be a different number of rows and for example a single row of diodes and of light guides, or a system comprising three rows. Each light guide 11 extends along a longitudinal principal axis from an entrance face 13, which is placed facing the corresponding light-emitting diode 12 so that most of the light rays emitted by each diode 12 enters into the associated light guide 11, and passes to a front end face, or exit face 14 for the light rays. Each light guide 11 is designed to guide, via successive internal reflections, the rays entering via the entrance face 13 to the exit face 14.

(13) The light exiting via the exit face 14 emerges into the front second segment 18, which forms a lens L1 for shaping the light rays in order to direct them towards the projecting optic 30 via the field-correcting optical element 20. The lens L1 formed by the front second segment 18 is here placed in the direct extension of the light guides 11, the latter and the front second segment 18 being integrally formed and made of the same material in order to form a single-piece primary optical element. As a result, the shape of the light rays which is imparted by the exit face 14 of a light guide generates a secondary light source. In the illustrated example, the exit faces 14 of the light guides form a matrix of two rows each of 17 secondary light sources.

(14) The field-correcting optical element 20 here has the shape of a lens comprising an entrance face 21 through which the light rays emitted by each diode enter, which face is placed facing the primary optical element 10 and which is concave, and an exit face 22 through which these corrected rays exit, which face is placed facing the projecting optic 30 and which is convex.

(15) According to the invention, at least one segment of one of the faces 21, 22 of the lens L2, i.e. the concave entrance face and the convex exit face, respectively, is covered with an antireflection coating AR1, AR2 that is able to increase the transmittance of incident light rays coming from the lens L1 of the primary optical element 10 and that are initially emitted by the turned-on light-emitting diodes 12.

(16) The field-correcting optical element and the antireflection coating that is provided to at least partially cover this field-correcting optical element, and in particular its entrance face, through which the rays emitted by the light sources penetrate into the field-correcting optical element, will now be described in more detail.

(17) FIG. 2 illustrates in cross section a portion of the primary optical element 10, allowing two light guides, which are arranged one above the other so as to face two light-emitting diodes, which are shown schematically, and a portion of a lens L2 forming the field-correcting optical element 20 according to the invention, to be seen.

(18) In the illustrated example, a first antireflection-coating layer AR1 has been partially deposited on the entrance face 21 through which the rays enter, and a second antireflection-coating layer AR2 has been partially deposited on the exit face 22 through which the incident light rays exit, and it will be understood that the thickness of these coating layers has here been exaggerated in order to allow them to be seen in the figure.

(19) Such as may have been specified above, each of these coating layers has the effect of increasing the transmittance of at least one incident light ray. Thus, the amount of light rays liable to be reflected by the entrance face 21 of the rays in the direction of the primary optical element with a transverse shift such that the ray issued from a secondary light source passes, on return, into the zone dedicated to a neighbouring secondary light source, and therefore the amount of light rays liable to decrease the clearness of the dark zone formed by the turned-off light sources, is decreased.

(20) It will be understood that the definition of an antireflection-coating zone AR1, AR2 on at least one face 21, 22 of the lens L2 forming the field-correcting element is dependent on the arrangement of the primary optical element 10 and more particularly of at least one light guide 11 including an entrance face 13 that is positioned longitudinally directly opposite and in proximity to an associated light-emitting diode 12 and an exit face 14 that forms a secondary light source. In particular, the minimum area (S) of the segment of a face 21, 22 of this lens L2 that is covered by an antireflection coating AR1, AR2 depends on the distance (D) between the entrance face 13 of a light guide 11 and the face 21, 22 in question of the lens L2, on the length (d) of said light guide 11, i.e. its longitudinal dimension between the entrance face 13 and the exit face 14, and on the vertical or transverse dimension of the exit face 14, in the dimension of the minimum coating area that it is desired to define.

(21) By way of example, in FIG. 2, the dimensions to be taken into account to define the height H1 and the height H2, i.e. the dimension in a first direction perpendicular to the optical axis, and here the vertical dimension, defined by the coordinate system shown in FIG. 2, of the antireflection-coating zones AR1, AR2, have been illustrated. Such as described above, the distance (D) between the entrance face of the light guide and the face to be coated, and the length (d) of the light guide are used to calculate them using the formulae:
H1=D1*H/d
H2=D2*H/d,

(22) where H is the height, i.e. the dimension aligned with the vertical dimension, of the exit face 14 of the light guide 11 in question.

(23) It is necessary that the antireflection coating be placed so as to cover one and/or the other of the faces of the lens L2 forming the field-correcting optical element, at least over this height H1, H2. It will thus be possible to use a minimum amount of antireflection coating and to limit the cost of obtaining the final product. Of course, if the process used to produce the coverage is made easier when the corresponding face is completely covered, it is advantageous not to seek to limit the coverage to its strict minimum.

(24) According to the invention, at least one face of the field-correcting optical element 20, and more particularly at least the concave entrance face 21 directly facing the primary optical element 10, includes an antireflection coating. Provision will possibly be made for a single antireflection-coating zone AR1 to cover at least one segment of this concave entrance face 21.

(25) According to one preferred embodiment of the invention, the antireflection coatings, AR1 and AR2, cover at least one segment of the concave entrance face 21 and at least one segment of the convex exit face 22 of the field-correcting optical lens L2, respectively.

(26) The presence of this at least one antireflection-coating layer allows a transmittance of light rays through a dioptric interface of the lens L2 forming the field-correcting optical element that is comprised between 97% and 99% to be obtained. The increase in this transmittance, measured at normal incidence, with respect to a standard transmittance of 95%, measured in an equivalent way for a dioptric interface made of polycarbonate, allows the amount of rays that are redirected towards the primary optical element and that may thus decrease the clearness of the contrast between the dark zone and the light zone of the projected overall light beam, to be drastically decreased.

(27) The type of antireflection coating used on one and/or the other of the faces of the lens L2 forming the field-correcting optical element will now be described in more detail. It should be noted that the material used in the antireflection coating must be transparent in the range of wavelengths employed by the light sources.

(28) The antireflection coating of the faces of the lens L2 may be a multilayer or monolayer coating.

(29) In the case of a monolayer antireflection coating AR, the low-refractive-index material used may in particular consist of a magnesium fluoride monolayer MgF.sub.2 of a minimum thickness (e) of 101 nm for a refractive index n=1.36 centred on a wavelength of 550 nm. If it is desired to modify the centrepoint of the filter for a known refractive index, it is enough to change the thickness of the deposited layer. A contrario, the modification of the thickness of the coating may allow the centrepoint of the antireflection to be shifted: increasing the thickness leads to a shift in the centrepoint towards the red, and decreasing this thickness shifts this centrepoint towards the blue.

(30) It is also possible, by way of example, to provide a hybrid monolayer within which are dispersed a plurality of hybrid particles each including at least two elements of different natures and refractive indices. In this case, each hybrid particle consists of a first element of refractive index n1 surrounded by a second element of refractive index n2 forming a coating layer, the first and second elements possibly being of polymer and/or inorganic and/or organic nature. Preferably, the first element is made of at least one mineral alkoxide.

(31) In the case of a multilayer antireflection coating, a coating consisting of at least two layers of different refractive indices and in which the thickness of a layer depends on the refractive index will possibly be preferred. Preferably, the multilayer coating is composed of an alternation of at least one layer of a high-refractive-index material and of at least one layer of a low-refractive-index material.

(32) Among low-refractive-index materials, materials having a refractive index lower than 1.6 at a wavelength of 550 nm, such as SiO.sub.2, MgF.sub.2, LiF, CaF.sub.2, NaF, ZrF.sub.4, AlF.sub.3, Na.sub.5Al.sub.3F.sub.14 and Na.sub.3AlF.sub.6, employed alone or in a mixture, will be preferred. Among high-refractive-index materials, materials having a refractive index higher than 1.7 at a wavelength of 550 nm, such as ZrO.sub.2, TiO.sub.2, Ta.sub.2O.sub.5, Na.sub.2O.sub.5, SnO.sub.2, ZnO, ZnS, HfO.sub.2, Pr.sub.2O.sub.3, PrTiO.sub.3, La.sub.2O.sub.3, Dy.sub.2O.sub.5, In.sub.2O.sub.3, Nb.sub.2O.sub.5, Yb.sub.2O.sub.3, Si.sub.3N.sub.4 and AlN, employed alone or in a mixture, will be preferred.

(33) It will be understood that the nature (monolayer, multilayer) and composition (choice of the material that is transparent in the visible domain) of the antireflection coating may in particular depend on the deposition technique employed to carry out the surface treatment on the substrate formed by at least one face 21, 22 of the field-correcting optical lens L2.

(34) The process for manufacturing a lens L2 forming the field-correcting optical element according to the invention, which includes at least one step of applying an antireflection coating AR, will now be described.

(35) In a first embodiment of this process, the applying step consists in depositing at least one antireflection-coating layer AR using a vacuum process, preferably a physical vapour deposition (PVD) based on an evaporating method consisting in heating the antireflection-coating material so that it evaporates in the direction of the substrate and condenses on its surface to form the desired layer.

(36) In the case of a monolayer antireflection coating AR obtained in a PVD operation, a low-refractive-index material, preferably magnesium fluoride MgF.sub.2 (refractive index 1.36), is deposited in a vacuum chamber in which the pressure is about 10.sup.4 mbar. By thermal evaporation in the vacuum chamber, what is meant is that the material, placed in a molybdenum crucible, is heated, via a tungsten filament, until its evaporation temperature is reached. The material then deposits on the substrate, here the entrance face and/or exit face of the lens L2, in a single layer. The thickness of the layer is continuously measured via a quartz balance so as to stop the deposition when the thickness required to obtain a monolayer antireflection effect centred on the desired wavelength is reached. By way of example, the antireflection coating may be a monolayer of MgF.sub.2 centred on 550 nm. The minimum reflection being achieved at a quarter wavelength, the required thickness value is 101 nm with a refractive index of 1.36 at 550 nm.

(37) The same type of process may be used in the case of a multilayer antireflection coating, the various materials used being evaporated in succession, provided that a layer of sufficient thickness is obtained.

(38) In a second embodiment of this process, the applying step consists in depositing at least one antireflection-coating layer AR using a so-called sol-gel process and a wet deposition technique implemented at atmospheric pressure and at room temperature, which technique may be a dip-coating deposition technique, a spin-coating deposition technique, a spray-coating deposition technique or even a laminar-flow coating technique.

(39) The dip-coating deposition technique, which consists in submerging the lens forming the field-correcting optical element in the sol-gel solution, then in removing this substrate at constant speed, will in particular possibly be preferred. This technique has the advantage of simultaneously depositing a coating layer on each face 21, 22 of the lens L2 forming the substrate. This dip-coating deposition technique allows a hybrid antireflection-coating monolayer to be obtained, the thickness of which may be varied depending on the centrepoint desired for the antireflection. In particular, if the obtained hybrid monolayer has a refractive index comprised between 1.32 and 1.36, its thickness, for a centrepoint of 550 nm, may be comprised between 101 and 110 nm. More generally, provision will possibly be made, by way of example, for a coating thickness comprised between 10 nanometres and 10 microns.

(40) In one preferred embodiment of the invention, the dip-coating depositing step is carried out at a room temperature of 20 to 25 C., under a relative humidity of 30 to 60% at 22 C. Under these conditions, the recommended speed of removal is 1.6 mm/s. Advantageously, the substrate covered with the antireflection coating is placed, after the gelification, in an oven in order to receive a drying heat treatment, preferably at 90 C. for 2 hours.

(41) The application of an antireflection coating AR to at least one face of the lens L2 forming the field-correcting optical element has the effect of decreasing the amount of light not transmitted by at least half for a given wavelength of 450 nm and/or 550 nm.

(42) The above description clearly explains how the invention makes it possible to achieve the objectives that were set therefor and in particular to provide a field-correcting optical lens in a luminous module configured to form an adaptive beam, and in particular a lens the concavity of the face of which being arranged facing the light sources creates a problem with the redirection of rays emitted by a zone corresponding to turned-on light sources towards a zone corresponding to turned-off light sources, which is covered with an antireflection coating.

(43) Such as was possibly mentioned above, variants are possible and the invention is not limited to the embodiments specifically given in this document by way of nonlimiting example, and encompasses in particular any equivalent means and any technically employable combination of these means.