Laser optical system and manufacturing method

Abstract

The invention relates to an optical projection system (1) for a motor vehicle, the system having an optical axis (X), and a light beam output (13), the system comprising a laser emitter (10) and an optical scattering device (12) configured to distribute the beam originating from the laser emitter to the light beam output, characterised in that the system also comprises a prism (120) which comprises an input face (121), at least one reflection face (122) and a scattering face (123), the reflection face being separate from the scattering face.

Description

Laser optical system and manufacturing process

[0001] The invention relates to an optical system for a motor vehicle comprising a laser emitter and a diffuser device. The invention also relates to a method for manufacturing such an optical system.

[0002] Preferred applications of the invention include the projection of light or images inside or outside a motor vehicle.

[0003] Examples of applications of the invention relating to the projection of images outside the vehicle include the emission of luminous images to communicate with people outside the vehicle by emitting light indications to these people, and the emission of light from the vehicle to the ground to help the driver or passengers get into the vehicle.

[0004] Examples of applications of the invention relating to the projection of images inside the vehicle include dashboard lighting, or the projection of luminous information to replace screens inside the vehicle. STATE OF THE ART

[0005] Laser light sources typically emit a directional beam of light, offering greater efficiency than LED (light-emitting diode) light sources. However, the high brightness of laser light sources makes them susceptible to eye damage if viewed directly. This makes laser light sources dangerous if used improperly or unsafely, which is a limitation.

[0006] This limitation means that the integration of laser light sources, particularly in the automotive sector, is regulated and restricted. For example, the power of laser light sources integrated into vehicle headlights, used for vehicle illumination and / or visibility, or in interior or exterior vehicle information display systems, is significantly limited. Consequently, the level of contrast and detail achievable with such laser light sources is also limited – one example of this limitation is that using such light sources to project information onto projection surfaces, especially in bright daylight, is problematic.

[0007] In order to avoid dazzling an observer who would directly observe the laser beam which comes from a laser source, and damaging their eye, it is known to interpose a diffuser between the laser source and the output of the light beam to the outside of the optical system.

[0008] More specifically, it is known to produce this diffuser in the form of a transmitting diffuser screen that allows light from the laser source to pass through it and transmits this light by diffusing it outwards from the system. Lamontre thus demonstrates a diffuser 30, interposed between a laser emitter 10' and projection means 14'.

[0009] These known systems thus make it possible to protect the eye of an observer by eliminating the risk of the observer being able to focus directly on the laser source.

[0010] However, a drawback of these known systems is that if the diffuser screen is damaged, there is a risk that the laser beam could directly strike an observer's eye, allowing them to focus on the source. The energy density on the observer's retina would then be abnormally high, potentially causing eye injury.

[0011] The invention aims to overcome this drawback.

[0012] The invention also aims to enable the creation of a simple system that does not require any special treatment of light aberrations. SUMMARY

[0013] To achieve these objectives, the invention proposes an optical projection system for a motor vehicle, said system having an optical axis and a light beam output, said system comprising: a laser emitter configured to emit at least one light beam, an oscillating mirror device configured to reflect the at least one light beam from the laser emitter, an optical diffusion device disposed downstream of the oscillating mirror device in the direction of propagation of the at least one light beam and configured to distribute the at least one light beam towards the light beam output, characterized in that the system comprises a prism having an entrance face, at least one reflection face and a diffusion face, the reflection face being distinct from the diffusion face, the prism being configured to: receive the light emitted by the laser source through the entrance face of the prism,said light emitted by the laser source entering the prism with an entry direction into the prism, reflect the light emitted by the laser source and which has entered the prism, with the reflecting face of the prism, and return the reflected light in a reflection direction towards the diffusion face of the prism, and distribute the reflected light as it passes through the diffusion face of the prism.

[0014] Preferred but not limiting aspects of this system are as follows: the scattering face of the prism is oriented substantially perpendicular to the optical axis of the system; the scattering face of the prism is oriented perpendicular to the optical axis of the system; said direction of reflection is substantially perpendicular to the scattering face of the prism; said direction of reflection is perpendicular to the scattering face of the prism; said direction of reflection is substantially parallel to the optical axis of the system; said direction of reflection is parallel to the optical axis of the system; the reflecting face is inclined at 45 degrees to the optical axis of the system; the prism comprises three faces: the entrance face, a single reflecting face, and the scattering face; the length of the projection of said reflecting face into the plane comprising the direction of reflection and the direction of entry into the prism.is greater than the lengths of the projections of the other faces of the prism projected onto the same plane; the system includes an optical projection device configured to project at least one light beam along the optical axis of the system, onto a projection surface so as to form a final image on said projection surface.

[0015] The invention also proposes a method for manufacturing such an optical system, comprising manufacturing the prism by forming a layer of vitreous material on the diffusion face of the prism by a solution-gelation process, and molding a light-diffusing structure on said layer of vitreous material.

[0016] The invention also proposes a method for manufacturing an optical system as mentioned above, comprising manufacturing the prism by laminating or gluing a sheet comprising a diffusing structure onto the diffusion face of the prism. BRIEF DESCRIPTION OF THE FIGURES

[0017] The aims, objects, features and advantages of the invention will become clearer from the detailed description of an embodiment thereof, which is illustrated by the following accompanying drawings in which:

[0018] This schematically represents a known optical system which has been discussed above.

[0019] The diagram schematically represents an optical system according to the invention.

[0020] This represents manufacturing steps for a first embodiment of a prism that can be used in an optical system according to the invention.

[0021] This represents manufacturing steps for a second embodiment of a prism that can be used in an optical system according to the invention.

[0022] The drawings are given as examples and are not limiting to the invention. They constitute schematic representations of principle intended to facilitate understanding of the invention and are not necessarily to scale with practical applications. DETAILED DESCRIPTION

[0023] The diagram schematically represents an optical system according to the invention.

[0024] This figure shows an optical projection system 1 for a motor vehicle. The system 1 has an optical axis X which is the axis of propagation of light out of the system, and a light beam output 13, through which a light beam exits to be projected onto a projection surface 2.

[0025] According to one non-limiting embodiment, the optical system 1 is included in a projector, in particular a front projector, of the vehicle so as to implement the projection of specific information onto a projection surface 2 defined on the roadway.

[0026] According to an alternative embodiment, the optical system 1 is included in an information display system located in a vehicle cabin, such as a head-up display system or a display system projecting information onto a projection surface 2 included in a stand framing a vehicle windshield, a projection screen, the windshield or onto a dashboard of the cabin.

[0027] System 1 includes at least one laser emitter 10. The example shown includes four laser emitters 10a, 10b, 10c and 10d.

[0028] System 1 also includes an oscillating mirror device 11 which is configured to reflect at least one light beam from the laser emitter.

[0029] The laser emitter is configured to emit at least one light beam towards the oscillating mirror device 11. Optionally, but preferably, and as shown in the embodiment illustrated in the figure, the laser emitter comprises a plurality of laser light sources. For example, said sources comprise red, green, and / or blue laser light sources.

[0030] In the case where the laser emitter comprises at least one red laser light source, one green laser light source, and one blue laser light source, the laser emitter is then an "RGB laser emitter," each source emitting a respective light beam of the desired color. Each laser light source in the laser emitter emits a primary light beam, and these primary light beams are combined by a device 100 to form the light beam Fx. The at least one light beam Fx is then directed onto a reflective surface of the oscillating mirror device 11, after being collimated. Notably, the different laser light sources are controlled independently of each other.

[0031] The oscillating mirror device 11 is configured to reflect the light beam Fx emitted by at least one laser emitter 10 towards an optical scattering device 12, which is also part of the optical system 1.

[0032] The light beam Fx forms a luminous image on the oscillating mirror device 11. The oscillating mirror device 11 includes, in particular, a movable scanning mirror that reflects the light beam Fx according to a rotational angle at which it is positioned. The scanning mirror can be of any known type and driven using conventional drive methods.

[0033] For example, the oscillating mirror device 11 is of the MEMS type, from the English "Micro Electro Mechanical Systems," meaning "micro-electromechanical system," allowing the light beam Fx to be oriented according to a plurality of angular orientations over time. According to a known, non-limiting embodiment, not detailed here, the oscillating mirror device 11 is configured to implement a sequential two-dimensional scan along lines to form an image on the projection surface 2 – such a sequential two-dimensional scan is also known by the English names "raster scan" or "raster scanning." Alternatively, the oscillating mirror device 11 is configured to implement a so-called "vector" scan or a "Lissajous" scan, known from the prior art.

[0034] The system also includes an optical condensation device 15 to converge the beam reflected by the oscillating mirror device 11 towards the optical diffusion device 12.

[0035] The optical diffusion device 12 is arranged downstream of the oscillating mirror device 11 and the condensation device 15, according to the direction of propagation of the light beam.

[0036] This optical diffusion device 12 is configured to distribute the light beam towards the light beam output 13.

[0037] In this text, "distributing light" means diffusing or diffracting light, and more generally, distributing light according to a desired pattern (for example: plateau distribution, or Gaussian distribution, etc.). This allows, in particular, for the distributed light to be safely observed by a user located between output 13 and projection surface 2.

[0038] Distributing the light "towards the light beam output 13" means in this text that the distributed light is directed towards the light beam output 13, along the optical axis of the system.

[0039] In general, system 1 also includes a prism 120 which has an entrance face 121, at least one reflection face 122 and a diffusion face 123.

[0040] The reflecting face is separate from the scattering face. The prism is preferably made of glass or polymer.

[0041] In the representation, the faces of the prism extend perpendicularly to the plane of the figure.

[0042] The prism is configured to: receive the light emitted by the laser source and reflected by the device 11 through the entrance face 121 of the prism, said light emitted by the laser source entering the prism with an entry direction (E) into the prism, reflect with the reflection face 122 of the prism the light emitted by the laser source and which has entered the prism, and return the reflected light along a reflection direction R towards the diffusion face 123 of the prism, and distribute the reflected light as it passes through the diffusion face 123 of the prism.

[0043] It is the scattering face 123 of the prism that produces the light distribution; the prism, with its scattering face, thus constitutes the optical scattering device of the system. An intermediate image is therefore formed on the surface of the scattering face 123, from the luminous image formed on the oscillating mirror device 11 with the light from the beam Fx.

[0044] The intermediate image formed on the diffusion face 123, is produced by scanning the light from the image formed on the oscillating mirror device 11. The light beam that formed this image is directed after passing through the diffusion face of the prism along the reflection direction R, towards the outlet 13.

[0045] Preferably the reflecting face is inclined at 45 degrees with respect to the optical axis X of the system.

[0046] Generally, the reflecting face is oriented relative to the direction in which the beam enters the prism, at an angle that produces total internal reflection of the beam within the prism. This angle can be 45 degrees.

[0047] Projection means 14 (typically lenses) are located between the prism and the outlet 13, in the path of the beam whose light has been distributed by the diffusion face of the prism. These projection means project the desired image onto the surface 2.

[0048] Thus the light beam that is projected out of the optical system 1 towards the projection surface 2 comes from a distributed light.

[0049] It is noted that if the prism were to be damaged, there would be no risk of an observer receiving light from the laser emitter. Indeed, the light from the beam Fx, generated by device 11, follows a prism entrance direction E that is not directed towards the output 13. It should be specified that all the system elements shown in diagram A are contained within a housing B, the walls of which would receive the light from the beam Fx if this light were not reflected and distributed by the prism.

[0050] This is advantageous for system safety, and allows for the selection of a high light output from the laser emitter (for example, a power of around 150 lumens or more), while preventing any risk of this high-power light being projected outside the system.

[0051] This is not the case with a known system such as the one schematically represented in Figure 1, in which the diffuser 30 is interposed between a laser emitter 10' and a projection device 14'. In such a known system, the laser passes through the diffuser without the direction of the beam from the laser emitter changing. Therefore, if the diffuser 30 is damaged, it is possible for the light from the laser emitter to exit the system directly without being distributed and reach an observer who could then focus on the beam upstream of the diffuser and potentially directly on the laser source(s).

[0052] The scattering face of the prism is preferably perpendicular to the optical axis of the system. It should be noted that in the optical system according to the invention, light is distributed by passing through a surface (the scattering face of the prism) which is substantially perpendicular, and preferably perpendicular, to the direction of propagation of this light, which is the direction of reflection R. It should also be noted that the direction of reflection R is substantially parallel, and preferably parallel, to the optical axis X of the system.

[0053] This prevents the generation of optical aberrations during the light distribution. Indeed, in the system according to the invention, the surface that reflects the beam is different from the surface that distributes the beam. And the surface 123 that distributes the beam is positioned perpendicular to the beam rays, which avoids aberrations because these rays arrive at the beam distribution surface perpendicular to it.

[0054] The prism shown comprises three faces: the entrance face, a single reflection face, and the diffusion face. This corresponds to a preferred embodiment of the invention.

[0055] It is also possible to consider other variants of the invention, in which the prism has several reflection faces – in this case the beam of light is reflected more than once inside the prism, after entering the prism through the entrance face, the last internal reflection in the prism directing the beam towards the diffusion face of the prism which in all cases constitutes an exit face.

[0056] In all cases, preferably the scattering face of the prism is substantially perpendicular to the optical axis of the system and to the direction of the last reflection from the prism.

[0057] We define plane P as the plane that is perpendicular to the direction of the optical axis of the system, and to the faces of the prism. This plane is the plane in which the light extends.

[0058] The length of the projection of the reflection face in this plane P is greater than the lengths of the projections of the other faces of the prism projected in the same plane.

[0059] The scattering face 123 of the prism distributes the light that passes through it. Generally, the scattering face of the prism is translucent and unpolished, so it is impossible for an observer looking at this face to see through it by focusing.

[0060] The light distribution produced by the prism's diffusion face generates a distribution (for example, a plateau or "top hat" distribution, or a Gaussian distribution) with a diffusion angle that must be large enough to effectively distribute the light passing through the diffusion face. This angle is preferably at least 30 degrees.

[0061] To distribute the light, the diffusion face 123 is associated with a diffusing structure. The diffusing structure thus covers the surface of face 123 through which the beam passes.

[0062] The diffusing structure consists of raised patterns (engravings, grains or others) whose characteristic size (engraving width, or grain diameter for example) allows the light of the beam that passes through the diffusion face to be distributed.

[0063] This diffusing structure is not reimaged outside the system. Therefore, the size of the patterns (grains or other features) in the diffusing structure is small enough to be below the resolution of an observer's vision. Generally, an observer cannot discern an optical pattern smaller than one arcminute (0.0017 degrees). The pattern size of the diffusing structure is preferably less than 40 microns. This size may vary depending on the focal length characteristics of the projection equipment.

[0064] In an alternative embodiment not shown in the figures, it is possible to arrange the prism so that the light having passed through the diffusion face of the prism is directed under the laser source(s).

[0065] In this variant, compared to the illustration, the prism would be rotated 180 degrees around the direction of light entering the prism, the entrance face of the prism would be in the same position as on the illustration, the reflection face of the prism would be oriented so as to reflect the light entering from the direction E still along the direction R, but in the opposite direction to that shown on the illustration, and the diffusion face of the prism would be on the left of the prism and not on its right as shown on the illustration.

[0066] In this variant, the means 14 and the output 13 would be positioned below the laser source(s) (the "top" being defined here as the top of the). This variant would further increase the compactness of the device.

[0067] The manufacture of the prism with its diffusion face can be carried out in different ways.

[0068] In general, the diffractive structure is made of material with the diffusion face of the prism, or is made solid to the diffusion face of the prism.

[0069] We will give below three non-limiting examples of prism fabrication. These examples all use a prism made of glass or polymer.

[0070] According to a first example, the face of a prism is engraved (typically with a laser), or this face is subjected to electro-erosion, to constitute the diffractive structure in the mass of the prism on the face chosen to be the diffusion face of the prism.

[0071] According to a second example shown in Figure 1, a diffusion layer made of a polymer in a soft state (i.e., not fully hardened) is applied to the diffusion face of the prism, and a mold with a three-dimensional pattern is pressed onto this soft polymer layer to transfer the pattern into the material of the soft polymer layer. The soft polymer is then hardened—for example, by exposure to ultraviolet radiation—to create the prism with its diffusion face.

[0072] The polymer used for the diffusion layer 1231 can be an inorganic material such as a sol-gel glass obtained by a solution-gelation process and made solid to a prism 1201. Once this diffusion layer 1200 is formed on the face of the prism which is to be its diffusion face, a mold M whose surface has a three-dimensional pattern M1 is pressed against said diffusion layer to obtain as shown on the right of the figure a prism having on one face a diffusing structure 12310.

[0073] According to a third example illustrated on laon, a diffusion sheet 1232 is created first, which can be transparent, and on which a diffusing structure 12320 is created by lamination or gluing this structure onto the sheet 1232. The sheet with its diffusing structure is then assembled with a prism 1202, as shown on the right side of this figure.

[0074] The invention is not limited to the embodiments previously described and extends to all embodiments covered by the invention.

Claims

Optical projection system (1) for a motor vehicle, said system having an optical axis (X), and a light beam output (13), said system comprising: a laser emitter (10) configured to emit at least one light beam, an oscillating mirror device (11) configured to reflect the at least one light beam from the laser emitter, an optical diffusion device (12) disposed downstream of the oscillating mirror device in the direction of propagation of the at least one light beam and configured to distribute the at least one light beam towards the light beam output, characterized in that the system comprises a prism (120) having an entrance face (121), at least one reflection face (122) and a diffusion face (123), the reflection face being distinct from the diffusion face, the prism being configured to: receive the light emitted by the laser source through the entrance face of the prism,said light emitted by the laser source entering the prism with an entry direction (E) into the prism, reflect the light emitted by the laser source and which has entered the prism, with the reflection face (122) of the prism, and return the reflected light along a reflection direction (R) towards the diffusion face (123) of the prism, and distribute the reflected light as it passes through the diffusion face of the prism. Optical system according to claim 1, characterized in that the diffusion face of the prism is oriented perpendicular to the optical axis of the system. Optical system according to any one of the preceding claims, characterized in that said direction of reflection is perpendicular to the diffusion face of the prism. Optical system according to any one of the preceding claims, characterized in that said direction of reflection is parallel to the optical axis of the system. Optical system according to any one of the preceding claims, characterized in that the reflecting face is inclined at 45 degrees with respect to the optical axis of the system. Optical system according to one of the preceding claims, characterized in that the prism comprises three faces: the entrance face, a single reflection face, the diffusion face. Optical system according to any one of the preceding claims, characterized in that the length of the projection of said reflection face in the plane (P) comprising the direction of reflection and the direction of entry into the prism, is greater than the lengths of the projections of the other faces of the prism projected in the same plane. An optical system according to any one of the preceding claims, characterized in that the system comprises an optical projection device (14) configured to project at least one light beam along the optical axis of the system, onto a projection surface (2) so as to form a final image on said projection surface. Method of manufacturing an optical system according to one of the preceding claims, comprising manufacturing the prism by forming on the diffusion face (123) of the prism a layer of vitreous material (1231) by a solution-gelation process, and molding a light-diffusing structure (12310) on said layer of vitreous material. Method of manufacturing an optical system according to any one of claims 1 to 11, comprising manufacturing the prism by laminating or gluing onto the diffusion face of the prism a sheet (1232) comprising a diffusing structure (12320).

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