Optical system comprising a laser emitter and a translucent filter

Abstract

The invention relates to an optical projection system (1) comprising a laser emitter (3) configured to emit at least one light beam (Fx), an oscillating mirror device (4), a first optical assembly (6), a second optical assembly (7) and a translucent filter (8), interposed between the first optical assembly (6) and the second optical assembly (7).

Description

Optical system comprising a laser transmitter and a translucent screen

[0001] The invention relates to an optical system comprising a laser emitter and a translucent screen. The invention also relates to a method of using such an optical system. Finally, it relates to a motor vehicle equipped with an optical system according to the invention.

[0002] Laser light sources typically emit a directional beam of light, allowing for greater efficiency than LED light sources. However, the high brightness of laser light sources makes them susceptible to damage to an observer's eye if viewed directly, making them dangerous if used improperly or unsafely.

[0003] As a result of such a disadvantage, the integration of laser light sources, particularly in the automotive sector, is regulated and limited. For example, the power of laser light sources integrated into vehicle headlights, enabling the lighting and / or visibility of the vehicle, or in information display systems inside or outside the vehicle, is greatly limited. As a consequence, the level of contrast and detail permitted in the context of the use of such laser light sources is limited, making them poorly suited to the projection of information onto projection surfaces, particularly in broad daylight.

[0004] Conventionally, it is known to integrate an oscillating mirror device into such optical systems. The angular size of the image projected onto said device is then, for example, of the order of the dimension of the oscillating mirror device as long as the latter is operating and oscillating. The accommodation of the eye of an observer is then carried out at the oscillating mirror device and the permitted light power of the laser light beam is directly linked to the size of said device. In this way, the larger the oscillating mirror device, the larger the light spot projected onto said device and the higher the brightness of the laser light beam can be while remaining safe for an observer.However, currently existing oscillating mirror devices are unsuitable due to their insufficient resonant frequency and / or their large size which would make their use complex in automotive applications.

[0005] The invention falls within this context and aims to propose an alternative to known optical systems allowing the secure integration of laser light sources, in particular with a view to integration into a motor vehicle.

[0006] To this end, the invention relates to an optical projection system, in particular for a motor vehicle, comprising a laser transmitter configured to emit at least one light beam, an oscillating mirror device configured to reflect the at least one light beam, the at least one light beam forming a light spot on the oscillating mirror device, and an optical projection device, arranged downstream of the oscillating mirror device in a direction of propagation of the at least one light beam.The optical device comprises a first optical assembly, a second optical assembly, and a translucent screen, interposed between the first optical assembly and the second optical assembly, and:- the translucent screen comprises an input face facing the first optical assembly and an output face, opposite the input face, and facing the second optical assembly;- an image focus of the first optical assembly is arranged on the output face of the translucent screen or at a distance less than or equal to 1.00 mm or even less than or equal to 500 µm, or even less than or equal to 300 µm from the output face of the translucent screen, such that the first optical assembly is configured to form an intermediate image of the light spot on the output face of the translucent screen; and- the second optical assembly is configured to project an image of the intermediate image onto a projection surface.

[0007] For example, the first optical assembly may comprise one or more lenses, called primary lenses.

[0008] Optionally, the second optical assembly may comprise at least one projection lens and / or at least one mirror. The projection lens(es) may be referred to as secondary projection lens(es). For example, the second optical assembly may comprise a lens, referred to as a secondary projection lens. The mirror(s) may be referred to as secondary mirror(s). For example, the second optical assembly may comprise a plurality of secondary mirrors, at least one of which is a deflecting mirror.

[0009] According to an exemplary embodiment, the object focus of the second optical assembly is separated from the image focus of the first optical assembly by a distance less than or equal to 5.00 mm, or even less than or equal to 1 mm.

[0010] According to an exemplary embodiment, the object focus of the second optical assembly can be confused with the image focus of the first optical assembly. The light beam projected by the second optical assembly then comprises parallel rays.

[0011] According to an alternative embodiment, the object focus of the second optical assembly is located at a non-zero distance from the image focus of the first optical assembly. In particular, the object focus of the second optical assembly may be located between the image focus of the first optical assembly and the second optical assembly. For example, the object focus of the second optical assembly may be separated from the image focus of the first optical assembly by a distance less than or equal to 5.00 mm, or even less than or equal to 1 mm. Thus, the rays of the light beam converge at the output of the projection system, which makes it possible to project an image at a given distance. Such an image is advantageously sharper than in the case of projection with parallel rays of the light beam.

[0012] In particular, the translucent screen is defined by an optical blur greater than or equal to 15% and a transmission coefficient greater than or equal to 80%.

[0013] According to one embodiment, at least the output face of the translucent screen is curved.

[0014] According to another exemplary embodiment, the second optical assembly comprises a free-form lens or a free-form mirror.

[0015] Optionally, the translucent screen includes a non-uniform heterogeneous structure.

[0016] For example, the heterogeneous structure comprises microstructures comprising at least one of:- graining arranged at all or part of the output face; and / or- an irregular heterogeneous holographic pattern; and / or- a plurality of microscopic prisms.

[0017] According to yet another exemplary embodiment, the translucent screen is configured so as to comprise a plurality of zones each having a diffusion angle specific to them, at least two zones having a distinct diffusion angle, inversely proportional to a distance separating the zone considered from the translucent screen from the projection surface. In particular, the projection surface is then inclined or substantially inclined relative to at least a portion of the translucent screen.

[0018] According to an exemplary embodiment, the at least one light beam is configured so that a main direction of said beam is inclined relative to at least one face of the translucent screen, in particular relative to the input face of the translucent screen, the translucent screen being configured to deflect the at least one light beam so as to direct it towards the projection surface when it is in an operational state.

[0019] In particular, such a system further comprises a safety device configured to detect a failure of the translucent screen during which the at least one light beam is not deflected by the translucent screen.

[0020] Optionally, the optical system comprises a correction device configured to modify the at least one emitted light beam so as to correct noise generated by the translucent screen, in particular the at least one output face of the translucent screen.

[0021] The invention may extend to a method for projecting a light beam in such an optical system, equipped with a correction device, comprising: - the determination, by the correction device, of a correction to be applied to the at least one light beam so as to reduce, or even eliminate, noise generated by the translucent screen, in particular the output face of the translucent screen; and - the projection of the at least one light beam, via the laser transmitter, to which said determined correction is applied.

[0022] The invention also relates to a vehicle comprising an optical projection system according to the invention.

[0023] Other details, characteristics and advantages will emerge more clearly on reading the detailed description given below, for informational and non-limiting purposes, in relation to the various exemplary embodiments illustrated in the following figures: This is a general schematic representation of an optical system according to the invention. This is a general schematic representation of an alternative of the optical system according to the invention. This is a schematic representation of a first embodiment applied to a part of the optical system. This is a schematic representation of a second embodiment applied to a part of the optical system. This is a schematic representation of the variation in the size of a retinal image as a function of the illumination surface of a second optical assembly. This is a schematic representation of a third embodiment applied to a part of the optical system.This is a schematic representation of a fourth embodiment applied to a part of the optical system. This is a schematic representation of an example of image projection onto an inclined projection surface without specific arrangement of the optical system. This is a schematic representation of an example of image projection onto an inclined projection surface in the context of a fifth embodiment. This is a schematic representation of a sixth embodiment of the optical system.

[0024] Figures 1a to 7 schematically illustrate exemplary embodiments of an optical system 1 according to the invention. In particular, the optical system 1 may be included in a motor vehicle. According to a non-limiting exemplary embodiment, the optical system 1 is included in a projector, in particular a front projector, of the vehicle so as to implement lighting and / or the projection of specific information onto a projection surface 2 defined on the roadway. According to an alternative exemplary embodiment, the optical system 1 is included in an information display system arranged in a passenger compartment of the vehicle, such as a head-up display system or a display system projecting information onto a projection surface 2 included in a stand framing a windshield of the vehicle, a projection screen, the windshield or onto a dashboard of the passenger compartment.

[0025] By convention in the description below, the terms "first" and "second" or "primary" and "secondary" are intended to distinguish similar elements and not to define a hierarchy within said elements. Also, the terms "upstream" and "downstream" refer to a direction of propagation of a light beam considered.

[0026] Generally, the optical system 1 according to the invention comprises a laser transmitter 3, an oscillating mirror device 4 and an optical device 5.

[0027] The laser emitter 3 is configured to emit at least one light beam Fx towards the oscillating mirror device 4 and through the optical device 5. Optionally but preferably, the laser emitter 3 comprises a plurality of laser light sources. For example, said sources comprise red, green and / or blue laser light sources. In the case where the laser emitter 3 comprises at least one red laser light source, one green laser light source and one blue laser light source, the laser emitter 3 is then an “RGB laser emitter”, making it possible to emit a light beam Fx of the desired color. Each laser light source of the laser emitter 3 then emits a primary light beam, and these primary light beams are combined to form the light beam Fx. The light beam Fx is then directed towards a reflective surface of the oscillating mirror device 4.In particular, the different laser light sources are controlled independently of each other.

[0028] The oscillating mirror device 4 is configured to reflect the at least one light beam Fx emitted by the laser transmitter 3 towards the optical device 5. The at least one light beam Fx forms a light spot Tx on the oscillating mirror device 4. The oscillating mirror device 4 notably comprises, in a conventional manner, a mobile scanning mirror, which reflects the at least one light beam Fx according to an angle of rotation in which it is arranged. The scanning mirror can be of any known type and driven according to conventional drive methods. For example, the oscillating mirror device 4 comprises a mechanical device for oscillating the mirror along a fast axis and a slow axis, extending perpendicular to the fast axis.In particular, the fast axis corresponds to the axis around which the oscillating mirror device 4 is in resonance and oscillates while the slow axis is linked to a mechanical detachment of the oscillating mirror device 4. The oscillating mirror device 4 is thus configured to take a plurality of different angular orientations and to pass from one to the other of these angular orientations at very high frequency.

[0029] For example, the oscillating mirror device 4 is of the MEMS type, from the English “Micro Electro Mechanical Systems” meaning “micro-electromechanical system”, making it possible to orient each of the incident light beams according to a plurality of angular orientations over time. According to a non-limiting, non-detailed conventional embodiment, the oscillating mirror device 4 is configured to implement a sequential two-dimensional scanning along lines to form an image on the projection surface 2 also known under the English names “raster scan” or “raster scanning”.

[0030] For each position of the oscillating mirror device 4, the light beam Fx emitted by the laser transmitter 3 forms a light spot Tx on the oscillating mirror device, and the oscillating mirror device 4 reflects this light spot Tx in a given direction. This light spot Tx is then projected by the optical device 5, and forms a primary image on the projection surface 2. The image projected by the optical projection system 1, inside the vehicle or outside the vehicle, is then formed by the superposition of all the primary images formed. Indeed, due to the retinal persistence of the observer, the latter does not distinguish the primary images, but perceives the image resulting from the superposition of the primary images.

[0031] The optical projection device 5 is arranged downstream of the oscillating mirror device 4 in a direction of propagation of the at least one light beam Fx. Optionally, the optical system 1 is configured so that the light beam Fx, when it arrives at the optical projection device 5, is collimated. Generally, the optical device 5 comprises a first optical assembly 6, a second optical assembly 7 and a translucent screen 8, interposed between the first optical assembly 6 and the second optical assembly 7. In particular, the translucent screen 8 is arranged so that an input face 81 of said screen is turned towards the first optical assembly 6 while an output face 82 of said screen, opposite the input face 81, is turned towards the second optical assembly 7.

[0032] Preferably, the first optical assembly 6 comprises a lens called a primary lens or a plurality of lenses, called primary lenses. The first optical assembly 6 is interposed between the oscillating mirror device 4 and the translucent screen 8 so that it is configured to form an intermediate image Ix of the light spot Tx, projected onto the oscillating mirror device 4, on the output face 82 of the translucent screen 8. Note that, due to the scanning carried out by the oscillating mirror device 4, the latter notably reflects the at least one light beam Fx onto a portion of the first optical assembly 6, for example of the primary lens, for each position of said device.

[0033] The second optical assembly 7 is configured to project, or image, the intermediate image Ix onto a projection surface 2 so as to form a final image Ifx there. As explained above, according to non-limiting exemplary embodiments, the projection surface 2 is a portion of the roadway, for example extending to the front of a vehicle, a glazed surface, such as a windshield or a screen, or a portion of the passenger compartment, such as a leg supporting the windshield or the dashboard. As further explained below, the projection surface 2 is a flat and / or inclined surface relative to the second optical assembly 7 and / or relative to the translucent screen 8.

[0034] According to an exemplary embodiment, the second optical assembly 7 comprises at least one secondary projection lens. Alternatively, the second optical assembly 7 comprises at least one secondary mirror. For example, the second optical assembly 7 comprises a plurality of secondary mirrors, at least one of which is a deflecting mirror.

[0035] The translucent screen 8 is arranged within the optical device 5 so as to be interposed between the first optical assembly 6 and the second optical assembly 7. Consequently, the translucent screen 8 is interposed between the second optical assembly 7 and the oscillating mirror device 4. In this way, when the eye of an observer observes the optical system 1 according to the invention, it perceives the at least one light beam Fx at the second optical assembly 7 and / or the intermediate image Ix projected at the translucent screen 8 instead of directly perceiving the light spot Tx projected at the oscillating mirror device 4, regardless of whether the eye is at rest or in the accommodation phase, also referred to as focusing.

[0036] In particular, the translucent screen 8 is arranged so that an image focus F1i of the first optical assembly 6 is arranged on the output face 82 of the translucent screen 8. Alternatively, the position of the image focus F1i of the first optical assembly 6 is located less than 1.00 mm, i.e. ±1.00 mm, or even less than 500 µm, i.e. ±500 µm or even less than 300 µm, i.e. ±300 µm from the output face 82 of the translucent screen 8.

[0037] Optionally, the translucent screen 8 is arranged so that an object focus F2o of the second optical assembly 7 is arranged at the exit face 82 of the translucent screen 8, in particular so as to be merged with the image focus F1i of the first optical assembly 6. The optical device 5 is then afocal. Such a principle can in particular be implemented when the at least one light beam Fx is collimated. Rays forming the at least one light beam exiting the second optical assembly 7 then extend parallel or substantially parallel to each other, as illustrated in.

[0038] Alternatively, as shown in , the translucent screen 8 is arranged so that the object focus F2o of the second optical assembly 7 extends between the exit face 82 of the translucent screen 8 and the second optical assembly 7. More particularly, the object focus F2o of the second optical assembly 7 is arranged between the image focus F1i of the first optical assembly 6 and the second optical assembly 7. For example, the object focus F2o of the second optical assembly 7 is separated from the image focus F1i of the first optical assembly 6 by a distance less than or equal to 5.00 mm, or even less than or equal to 1 mm. Such a principle can in particular be implemented in the case where it is desired that the light beam Fx projected by the optical system 1 be convergent downstream of the exit face 82 of the translucent screen 8 according to the direction of propagation of the at least one light beam Fx.Such a principle is implemented in particular in the case of projection of information onto a projection surface 2 located at a given, predefined distance. Rays of the at least one light beam Fx emerging from the second optical assembly 7 then converge towards each other. Such a principle makes it possible to minimize the size of the intermediate image Ix projected onto the intermediate screen in order to optimize its resolution and sharpness while ensuring the ocular safety of an observer due to the presence of the translucent screen 8 by preventing the accommodation of the eye on the oscillating mirror device 4.

[0039] Thus, for example, the object focus F2o of the second optical assembly 7 is separated from the image focus F1i of the first optical assembly 6 by a distance less than or equal to 1.00 mm, or even less than or equal to 300 µm, such a distance being zero when said foci are merged, as indicated above, and not zero when said foci are distinct.

[0040] In particular, a distance separating the output face 82 of the translucent screen 8 from the second optical assembly 7, for example from a surface of the secondary projection lens or from a reflective surface of the secondary mirror of the second optical assembly 7, is defined by the following relationship: Where: De_opt2 is the distance separating the output face 82 of the translucent screen 8 from the second optical assembly 7; df2 is the focal length of the second optical assembly 7, in particular of the secondary projection lens; dpj is the distance between the second optical assembly 7, for example at the surface of the secondary lens or the reflective surface of the secondary mirror, and the projection surface 2.

[0041] The translucent screen 8 has in particular the function of diffuser, that is to say that it allows in part to diffuse or to burst the light beam Fx and to modify, particularly to increase, the angular size and the size of the retinal image of the final image Ifx in relation to the size of the light spot Tx projected on the oscillating mirror device 4. Indeed, an external observer observes an image formed by several intermediate images Ix projected and juxtaposed on the translucent screen 8, thanks to retinal persistence. This image thus becomes the point of accommodation of the eye of the observer, for accommodation to infinity of the eye or even for the eye at rest, instead of the light spot Tx projected on the oscillating mirror device 4, and this image is larger than the light spot Tx.

[0042] Thus, the first optical assembly 6 creates, on the translucent screen 8, an intermediate image Ix of the light spot Tx projected onto the oscillating mirror device 4 while the second optical assembly 7 reproduces the intermediate image Ix on the projection surface 2. Advantageously, the second optical assembly 7 makes it possible to increase the dimension of the final image Ifx, projected onto the target projection surface 2 relative to a dimension of the intermediate image Ix. The size of the at least one light beam Fx is thus greater at the output of the optical system 1, i.e. downstream of the second optical assembly 7, than at the input thereof, i.e. upstream of the oscillating mirror device 4.

[0043] In the absence of the translucent screen 8, as is the case in the optical systems of the prior art, the observer's eye directly perceives the light spot Tx projected onto the oscillating mirror device 4 and the apparent angle of the projected image, and consequently the retinal image, is smaller. It is therefore necessary to limit the brightness, in other words, the illuminance, of the laser emitter 3 in order to ensure the ocular safety of any observer present. The integration of the translucent screen 8 makes it possible to overcome such a limitation since the observer can no longer directly perceive the light spot Tx formed by the laser emitter 3 on the oscillating mirror device 4.The observer's eye focuses on the translucent screen 8 without the possibility of focusing on the oscillating mirror device 4, thus focusing on a plurality of juxtaposed intermediate images Ix which are themselves projected by the second optical assembly 7.

[0044] The optical system 1 according to the invention thus makes it possible to overcome the constraints conventionally applied in order to ensure eye safety. The oscillation, or scanning, frequency of the oscillating mirror device 4 is thus not defined as a function of the brightness of the laser emitter 3. For example, such an oscillation frequency may be of the order of 25 kHz. According to a particular, non-limiting example, the oscillation frequency is of the order of 30 kHz to 40 kHz to produce a line along the slow axis and of the order of 60 kHz along the fast axis.

[0045] According to exemplary embodiments, the translucent screen 8 is made of a material selected from glass, plastic, such as polycarbonate or even ceramic. For example, the translucent screen 8 is obtained by injection, overmolding and / or photolithography. It is, for example, dimensioned so as to have a surface greater than or equal to a surface of the first optical assembly 6, for example of the primary lens, and / or greater than or equal to a reflective surface of the oscillating mirror device 4.

[0046] Preferably, the translucent screen 8 has a transmission coefficient greater than or equal to 80%. In particular, the transmission coefficient is measured in a conventional manner by flux measurement with an integrating sphere, the flux measurement being carried out with passage through the translucent screen, then without passage through the translucent screen 8. The two measurements are then compared.

[0047] The translucent screen 8 also has an at least partial obstruction function by preventing direct visibility of the oscillating mirror device 4, and particularly of the light spot Tx projected onto it. In particular, preferably, the translucent screen 8 is defined by a level of optical blur greater than or equal to 15%. “Optical blur” means a veil, also called reflection mist or “haze” in English. “Optical blur level” means the percentage of light dispersed outside a 2.5° cone centered on an optical axis of the optical system 1. In this way, the at least one light beam Fx is able to propagate through the translucent screen 8 but the accommodation of the eye of an observer on the oscillating mirror device 4 is not possible.

[0048] According to exemplary embodiments, the translucent screen 8 has an optical blur of the surface, volume or holographic type.

[0049] A translucent screen 8 of surface type has a mist at least arranged on one of the faces of the translucent screen 8, in particular at least on the exit face 82 thereof. Preferably, such a translucent screen 8 has a level of optical blur greater than or equal to 15%.

[0050] A translucent screen 8 of the volume type has a haze over all or part of a thickness of the translucent screen 8, corresponding to the dimension between the entry face 81 and the exit face 82. Preferably, the translucent screen 8 then has a level of optical blur greater than or equal to 20%, or even 22%.

[0051] A translucent screen 8 of holographic type comprises patterns or microstructures, optionally combined with a mist, in particular at the exit face 82. In particular, said patterns or microstructures have a regular periodicity. Said patterns are of the order of a micrometer and are arranged so as to diffuse the at least one light beam in a preferred field of vision, as explained below. Preferably, the translucent screen 8 then has a level of optical blur greater than or equal to 25%, or even 27%.

[0052] Figures 2 to 7 illustrate different embodiments of the optical system 1 according to the invention.

[0053] According to a first embodiment, illustrated in , the translucent screen 8 is curved. In particular, at least the output face 82 of the translucent screen 8 is curved. According to an alternative example, not shown, the input face 81 is also curved. Such a principle aims to correct a possible field curvature, also called Petzval field curvature, resulting from the combination of the first optical assembly 6 and the second optical assembly 7.

[0054] Indeed, due to the geometric aberrations generated by these optical assemblies, the object focal plane Pf2o of the second optical assembly 7, in particular, of the secondary projection lens, is curved. As a result, a portion of the final image Ifx imaged from a portion of the intermediate image Ix located at the edges of the translucent screen 8 has reduced sharpness.

[0055] It should be noted that, in such an embodiment, the oscillating mirror device 4 reflects, optionally but preferentially, the at least one light beam Fx onto a limited portion of the first optical assembly 6 for each possible position of the oscillating mirror device 4, three examples of which are illustrated in the, so that the rays of the at least one light beam Fx converge towards a specific area of ​​the translucent screen 8 for each position of the oscillating mirror device 4. As a result, the aberrations generated by the first optical assembly 6 can at least partly be corrected by known conventional means, for example by adapting the asphericity parameters.

[0056] On the other hand, such a correction is more complex to implement for the second optical assembly 7, particularly when the at least one light beam Fx is projected onto the majority of the surface of said second optical assembly 7, i.e. a surface of the at least one secondary mirror or of the secondary projection lens, at a given instant t. Here, the term "most" means at least 50% of a surface of a component of the second optical assembly 7 considered. In particular, as illustrated, the entire surface of the component of the second optical assembly 7 considered is optionally illuminated at a given instant.Such a principle makes it possible in particular to ensure the projection of the at least one light beam Fx onto a larger surface area of ​​the second optical assembly 7 so that the projected image has a larger retinal size Trx and a larger apparent size, as illustrated in FIGS. 3a and 3b, thus ensuring the ocular safety of an observer at all times, even in the event of the oscillating mirror device 4 being blocked.

[0057] The integration of a translucent screen 8 of which at least the output face 82 is curved advantageously makes it possible to correct field curvature aberrations of the second optical assembly 7 without intervening on the latter directly. The constraints applied to the optical system 1 are thus alleviated since it is not necessary to optimize the different optical assemblies simultaneously. The translucent screen 8 then advantageously makes it possible to limit, or even entirely correct, the field curvature induced by the optical assemblies.

[0058] In particular, the curvature of the output face 82 of the translucent screen 8 is at least partly identical to a curvature of the object focal plane Pf2o of the second optical assembly 7. Preferably, the curvature of the output face 82 is essentially similar to the curvature of said object focal plane of the second optical assembly 7. Here, the term "essentially" means at least 50% of the surface area of ​​the output face 82. Preferably, the curvature of the output face 82 as a whole is similar, or substantially similar, to the curvature of the focal plane of the second optical assembly 7 and coincides with it. In other words, the curve of the output face 82 of the translucent screen 8 matches the shape of the object focal plane of the second optical assembly 7.

[0059] Figures 3a and 3b illustrate a second embodiment, in which the translucent screen 8 comprises a heterogeneous, i.e. non-uniform, structure. In other words, at least two distinct zones of the translucent screen 8 have different structures. Note that the second embodiment and the first embodiment can be combined without constraint so that the translucent screen 8 comprises a heterogeneous structure and is curved as described above.

[0060] Such heterogeneity aims to optimize the ocular safety of an observer by increasing the angular size and the apparent size of the image perceived by the observer at the level of the second optical assembly 7, independently of the position of the intermediate image Ix on the output face 82 of the translucent screen 8 and independently of the proximity of the observer with the second optical assembly 7. In other words, the integration of such a translucent screen 8 makes it possible to increase the illuminated surface of the component of the second optical assembly 7 considered, for example the surface of the secondary projection lens or of the secondary mirror, by dispersing, or diffusing, the at least one light beam Fx.

[0061] For example, optionally but preferably, the translucent screen 8 comprising a heterogeneous structure is configured so that the at least one light beam Fx is projected onto the majority of the surface of said second optical assembly 7, i.e. a surface of the at least one secondary mirror or of the secondary projection lens, at a given instant t. The description given in relation to the first embodiment applies here mutatis mutandis, the term "most of it" meaning that at least 50% of a surface of the second optical assembly 7 is illuminated, i.e. 50% of the surface of the secondary projection lens or of the reflective surface of the secondary mirror of the second optical assembly 7 for example. Figures 3a and 3b illustrate different examples of projection onto at least 50% of the surface of the second optical assembly 7.Similar to what has been described above, optionally, the structure of the translucent screen 8 is configured so that the entire surface of the component of the second optical assembly 7 considered is illuminated at a given instant.

[0062] In particular, at least the exit face 82 of the translucent screen 8 has a heterogeneous structure. Optionally, all or part of the thickness of the translucent screen 8, between the entry face 81 and the exit face 82, has a heterogeneous structure.

[0063] In particular, the heterogeneous structure of the translucent screen 8 comprises a plurality of microstructures 83 selected from: - heterogeneous graining arranged at the level of all or part of the output face 82; and / or - a plurality of microscopic prisms; and / or - an irregular heterogeneous holographic pattern.

[0064] The heterogeneous structure of the translucent screen 8 thus depends on its texturing.

[0065] The term “graining” means that the translucent screen 8, in particular the exit face 82, comprises a plurality of grains. The heterogeneity of the structure is then obtained by heterogeneity of shapes, dimensions, refractive index of said grains and / or heterogeneity of distribution, or density, of said grains within the translucent screen 8. For example, the grains have dimensions of the order of 1 to 10 µm.

[0066] The term “microscopic prisms” means that the translucent screen 8, in particular the exit face 82, comprises a plurality of polyhedra whose dimensions may be of the order of 1 to 10 µm. The heterogeneity of the structure is then obtained by heterogeneity of shapes, dimensions, refractive index, and / or distribution, or density, of said prisms within the translucent screen 8.

[0067] The term “holographic pattern” means that the translucent screen 8, in particular the output face 82, comprises a plurality of holograms corresponding to microstructures with a regular period, in particular with a characteristic size of the order of 10 µm. The heterogeneity of the structure is then obtained by heterogeneity of shapes, dimensions, inclination, refractive index, and / or distribution, or density, of said holograms within the translucent screen 8.

[0068] Optionally but preferably, the heterogeneity, or non-uniformity, of the structure of the translucent screen 8 is defined from a transmission function depending on the position and the distance of a point considered on the translucent screen 8, in particular its exit face 82, relative to a center of said screen. For example, a central zone of the translucent screen 8 comprises microstructures 83 ensuring the diffusion of the light beam Fx while zones distant from it also ensure the deflection of the light beam Fx towards a predefined portion of the second optical assembly 7. The microstructures 83 are then configured so that the further the zone considered is from the central zone of the translucent screen 8, the greater the deflection of the at least one light beam. Such an evolution can thus be radial relative to the center of the translucent screen 8.The heterogeneous structure of the translucent screen 8 can thus be at least partly symmetrical, in particular according to a radial symmetry centered on the center of the translucent screen 8 and / or according to a planar symmetry in which a plane of symmetry passes through the center of said screen and / or comprises the optical axis of the optical system 1.

[0069] Illustrates an example of a third embodiment, in which the translucent screen 8 has another example of a heterogeneous, i.e. non-uniform, structure. Note that the third embodiment can here be combined with the first and / or the second embodiment without constraint.

[0070] In such an embodiment, the projection surface 2 is particularly inclined relative to at least a portion of the translucent screen 8 and relative to the image focal plane Pf2i of the second optical assembly 7. As a result, different portions of the output face 82 of the translucent screen 8 are arranged at different distances from the projection surface 2, said distances being evaluated along the same direction, here a first direction 100. The same applies to distances separating the projection surface 2 from the second optical assembly 7. Without specific arrangement, the projection of information onto an inclined surface is accompanied by a variation in the sharpness of the final image Ifx and in the size of the final image Ifx as a function of the area of ​​the translucent screen 8, and consequently of the projection surface 2, illuminated by the at least one light beam Fx.Indeed, the sharpness of the final image Ifx is directly linked to the depth of field of the at least one light beam Fx and, consequently, to a diffusion angle β of the translucent screen 8, in particular of the zone of the translucent screen 8 considered. Thus, the lower the diffusion angle β, the greater the depth of field and vice versa.

[0071] In the present embodiment, the translucent screen 8 is configured so as to comprise a plurality of zones having distinct diffusion angles β. Such heterogeneity of diffusion angles makes it possible to obtain depths of field, illustrated schematically by a rectangle, which vary depending on the illuminated zone of the translucent screen 8. In particular, the translucent screen 8 is configured so that each zone is defined by a diffusion angle β which is specific to it and which is inversely proportional to a distance separating the zone considered of the translucent screen 8 from the projection surface 2, said distance being defined along the first direction 100. In other words, the further the zone of the translucent screen 8 considered is from the projection surface 2, the lower the diffusion angle β thereof and, consequently, the greater the depth of field thereof.In particular, the diffusion angles β of the different zones of the translucent screen 8 considered are adapted so that the size of the final image Ifx is equal, or substantially equal, independently of the zone of the translucent screen 8 illuminated.

[0072] In particular, the translucent screen 8 illustrated in comprises at least a first zone Z1 and a second zone Z2, distinct from the first zone Z1. It is understood that such a configuration is in no way limiting and that the translucent screen 8 may comprise more distinct zones. The first zone Z1 is defined by a first diffusion angle β1 and configured to be arranged at a first distance from the projection surface 2 along the first direction 100. The second zone Z2 is defined by a second diffusion angle β2 and configured to be arranged at a second distance from the projection surface 2, strictly greater than the first distance along the first direction 100, the first diffusion angle β1 being strictly greater than the second diffusion angle β2 of the second zone Z2.

[0073] Such a principle makes it possible to obtain a variable depth of field, particularly greater for the areas of the translucent screen 8 furthest from the projection surface 2, depending on the area of ​​the translucent screen 8 illuminated. In this way, the final image Ifx is clear regardless of the area of ​​said screen illuminated. The variation in size of the final image Ifx, and in particular the deformation of the final image Ifx observed when the areas of the translucent screen 8 furthest from the projection surface 2 are illuminated, is thus reduced, or even eliminated.

[0074] Preferably, the variation in diffusion angle β from one zone considered to another of the translucent screen 8 is obtained by means of a plurality of microstructures 83 as described previously with reference to the second embodiment, in particular arranged at the level of the exit face 82, selected from: - a heterogeneous graining arranged at the level of all or part of the exit face 82; and / or - an irregular heterogeneous holographic pattern; and / or - a plurality of microscopic prisms.

[0075] Also, the preceding description relating to such microstructures 83 applies mutatis mutandis.

[0076] Optionally but preferably, in such an embodiment, the intermediate image Ix, and therefore the surface of the translucent screen 8, illuminated by the at least one light beam Fx at a given instant t is projected onto a surface less than or equal to 50% of a face of the second optical assembly 7, for example a face of the secondary lens or a reflecting face of the secondary mirror.

[0077] Illustrates an example of a fourth embodiment. The fourth embodiment can be combined with the various embodiments set out above.

[0078] In the present embodiment, the at least one light beam Fx incident relative to the translucent screen 8 is configured so that a main direction Dx of said beam is inclined relative to the optical axis of the optical system 1, here represented by the axis Ox. Here, the term "main direction" means the mean axis of the rays forming the at least one light beam Fx or an axis on which said beam is centered. The at least one incident light beam Fx is then in particular inclined relative to the entry face 81 of the translucent screen 8. Optionally, the translucent screen 8 is also inclined relative to the first optical assembly 6, in particular relative to at least one surface of the first optical assembly 6, and / or relative to the second optical assembly 7, in particular relative to the surface of the secondary projection lens or to the reflective surface of the secondary mirror of the second optical assembly 7.

[0079] In such an embodiment, when the translucent screen is in an operational state, it is configured to deflect the at least one light beam Fx so as to direct it towards the projection surface 2 in addition to its diffusion function as described previously. In other words, the at least one light beam Fx exiting the translucent screen 8 is refracted relative to the at least one incident light beam Fx, i.e. arriving at the level of the entry face 81 of the screen. Light rays forming the at least one light beam Fx are thus deflected from their incident trajectory, corresponding to the direction of propagation of the light ray considered upstream of the translucent screen 8. In particular, the translucent screen 8 is configured to deflect the at least one light beam Fx according to a deflection angle μ1, as illustrated in. In particular, the deviation angle µ1 may be less than or equal to 150° and / or greater than or equal to 70°.Here, the term “deviation angle” is understood to mean the angle measured between the direction of a light ray considered from the at least one incident light beam Fx and the direction of this same ray within the light beam Fx emerging from the translucent screen 8.

[0080] For example, the deflection angle µ1 of the translucent screen 8 is obtained by means of a plurality of microstructures, not shown, as described previously with reference to the second embodiment, in particular arranged at the level of the entry face 81. Optionally but preferably, said microstructures comprise a plurality of microscopic prisms.

[0081] Therefore, the previous description relating to such microstructures applies mutatis mutandis.

[0082] In this way, when the translucent screen 8 is functional, that is to say that it operates without problem or defect, the at least one light beam Fx is deflected in order to be directed towards the projection surface 2. On the other hand, in the event of a failure of the optical system 1 located at the level of the translucent screen 8, the at least one light beam Fx is not deflected and all or part of the light rays forming the at least one light beam Fx continue to propagate along the same direction, or substantially along the same direction. The at least one light beam Fx, or part thereof, is then not sent towards the projection surface 2.Such a principle makes it possible to ensure the safety of a user in various cases of failure of the translucent screen 8, for example in the event of it falling, damage due to its breakage, its melting or a burn which may result from the blocking of the at least one oscillating mirror device 4 in the same position for a prolonged period.

[0083] Optionally, the optical projection system 1 further comprises a safety device 9 configured to detect a failure of the translucent screen 8 during which the at least one light beam Fx is not deflected. To this end, the safety device 9 is arranged in the continuity of the trajectory of at least one light ray of the incident light beam Fx arriving at the level of the translucent screen 8.

[0084] According to a first alternative embodiment, which is not limiting, said safety device 9 comprises a beam trap, also referred to as a light trap. For example, said trap is configured to absorb the at least one non-deflected light beam Fx or to disperse said beam in the event of failure of the translucent screen 8 so as to make it non-dangerous for a possible observer. Optionally, the safety device 9 further comprises at least one sensor configured to detect that the at least one light beam Fx reaches the beam trap, i.e. that said beam is not deflected. In particular, according to non-limiting examples, said sensor is a light sensor, a photodiode or even a thermistor.Optionally again, in combination with the at least one sensor, the safety device 9 comprises a control means 91 of the laser transmitter 3 capable of interrupting the operation of the laser transmitter 3 and the emission of the at least one light beam Fx when it is detected that the at least one light beam Fx reaches the safety device 9. Thus, when said sensor detects a failure of the translucent screen 8, it transmits the information to the control means 91 which interrupts the operation of the laser transmitter 3.

[0085] According to a second alternative embodiment, the security device 9 comprises the at least one sensor and the control means 91 described previously but is devoid of a beam trap.

[0086] The invention relates to a fifth embodiment in which the second optical assembly 7 comprises a freeform lens 71, also known as a "freeform lens" in English, or a freeform mirror. The invention is described here with reference to a secondary projection lens being a freeform lens 71 but extends, mutatis mutandis, to a freeform mirror. The freeform lens 71 has a suitable shape, configured so as to have a variable focal length depending on the area of ​​the illuminated lens so as to allow variable focusing and, consequently, ensure the sharpness of the final image Ifx independently of the area of ​​the projection surface 2 over which it extends.In other words, distinct areas of the free-form lens 71 are defined by distinct focal lengths and form a non-regular and / or non-parallel image focal plane Pfi2 relative to an output face of the free-form lens 71. The same applies to a free-form mirror relative to a reflective surface of said mirror.

[0087] Similar to what was previously explained with reference to the third embodiment, in the present embodiment, the projection surface 2 is inclined relative to at least a portion of the translucent screen 8 and relative to the second optical assembly 7. In this case, the projection surface 2 is inclined relative to the secondary projection lens. As a result, without specific arrangement, as illustrated in the, the second optical assembly 7 has an image focal plane Pfix inclined relative to the projection surface 2 and the projection of information onto an inclined surface is accompanied by a stretching of the final image Ifx as well as a reduction in the sharpness and level of detail of the final image Ifx with the increase in the distance separating the projection surface 2 from the second optical assembly 7 and / or from the translucent screen 8.

[0088] The secondary projection lens being free-form, it is non-uniform and is optimized to ensure the sharpness and resolution of the image over the entire projection surface 2, regardless of the distance separating it from the second optical assembly 7, in order to have the same level of detail in the near field and in the far field. In particular, it is optimized so that the rays of the at least one light beam Fx converge at an intersection zone, with the projection surface 2 regardless of the illuminated zone of the second optical assembly 2.

[0089] Optionally but preferably, in such an embodiment, the intermediate image Ix, and therefore the surface of the translucent screen 8, illuminated by the at least one light beam Fx at a given instant t is projected onto a surface less than or equal to 50% of the surface of the second optical assembly 7, for example the surface of the secondary lens or the reflecting surface of the secondary mirror.

[0090] Such an embodiment can advantageously be combined with the first embodiment, with the third embodiment and / or with the fourth embodiment set out above. In the case where this embodiment is combined with the first embodiment, the third embodiment and / or the fourth embodiment, a compromise may then have to be found on the portion of the surface of the second optical assembly 7 which is illuminated. The more a small portion is illuminated, the clearer the image will be on the projection surface, and the more a large portion is illuminated, the more eye safety will be ensured.

[0091] Illustrates an exemplary embodiment of a sixth embodiment in which the optical projection system 1 further comprises a correction device 10 configured to modify the at least one light beam Fx emitted so as to correct noise generated by the translucent screen 8, in particular by the output face 82 of the translucent screen 8. This embodiment can be combined with the different embodiments set out above.

[0092] Here, “noise” is understood to mean a parasitic fluctuation or degradation that the final projected image Ifx undergoes due to the translucent screen 8, in particular due to defects, irregularities, microstructures 83 described previously or a structural granularity of the translucent screen 8.

[0093] The correction device 10 is thus able to control and drive the laser transmitter 3 in order to compensate, at least partially, for the noise induced by the translucent screen 8 so that it is not visible in the final image Ifx. Such a principle allows processing of the projected image as soon as the at least one light beam Fx is emitted, ensuring smoothing of the final image Ifx projected onto the projection surface 2 so as to optimize its quality and details.

[0094] For example, the processing of the projected image includes: - smoothing of a reference image, also called "white page", pre-recorded or recorded and used for each image projected in real time; - calculating a background image with "rolling ball" type processing; - removing said background image from each image projected in real time and removing the reference image.

[0095] For example, the correction device 10 comprises a memory element on which is pre-recorded or recorded at least one reference image representative of the noise generated by the translucent screen 8, for example an image of the irregularities of the output face 82. Additionally or alternatively, the correction device 10 comprises a camera capable of capturing an image representative of the noise generated by the translucent screen 8, for example an image of the irregularities of the output face 82. Additionally, the correction device 10 comprises a processing unit, capable of defining a correction to be applied, and a means 91 for controlling the laser emitter 3.

[0096] The invention also extends to a method of using an optical projection system 1 as defined in the sixth embodiment. It is understood that the above description, relating to the sixth embodiment, applies here mutatis mutandis. The method comprises, in a first step, the determination, by the correction device 10, of a correction to be applied to the at least one light beam Fx so as to reduce, or even eliminate, noise generated by the translucent screen 8, in particular by the output face 82 of the translucent screen 8. Such a determination can be carried out from at least one pre-recorded image representative of the noise generated by the translucent screen 8 or from an image captured, in real time or at regular time intervals, by the correction device 10 as described above.

[0097] Then, the method comprises the projection of the at least one light beam Fx, via the laser transmitter 3, to which the determined correction is applied so as to obtain a final image Ifx, projected onto the projection surface 2, optimized in which the noise generated by the translucent screen 8 is attenuated, or even eliminated.

[0098] Thus, the present invention provides an optical system comprising a laser transmitter for ensuring the eye safety of potential observers. The integration of the translucent screen prevents the accommodation of the observer's eye directly onto the oscillating mirror device, the latter then accommodating onto the surface of the translucent screen or onto the second optical element, arranged downstream of the translucent screen. The translucent screen also makes it possible to increase the apparent angle of the projected image, which reduces the eye risk. The optical system thus allows the projection of an image with a higher light intensity while remaining compliant with eye safety standards, which allows for better illumination and optimized contrast of the image, even during the day.

[0099] The invention is advantageously suited to a cluttered environment, particularly for integration into a vehicle. The invention is also capable of optimizing the quality of the final image projected onto various projection surfaces.

[0100] The present invention cannot, however, be limited to the means and configurations described and illustrated here and it also extends to any equivalent means or configuration and to any technically operative combination of such means insofar as they ultimately fulfill the functionalities described and illustrated in the present document.

Claims

Optical projection system (1), in particular for a motor vehicle, comprising a laser transmitter (3) configured to emit at least one light beam (Fx), an oscillating mirror device (4) configured to reflect the at least one light beam (Fx), the at least one light beam (Fx) forming a light spot (Tx) on the oscillating mirror device (4), and an optical projection device (5), arranged downstream of the oscillating mirror device (4) in a direction of propagation of the at least one light beam (Fx), characterized in that the optical device (5) comprises a first optical assembly (6), a second optical assembly (7), and a translucent screen (8), interposed between the first optical assembly (6) and the second optical assembly (7), and in that: - the translucent screen (8) comprises an entry face (81) facing the first optical assembly (6) and an exit face (82), opposite the entry face (81),and facing the second optical assembly (7);- an image focus (F1i) of the first optical assembly (6) is arranged on the output face (82) of the translucent screen (8) or at a distance less than or equal to 1.00 mm, or even less than or equal to 500 µm, or even less than or equal to 300 µm from the output face (82) of the translucent screen (8), so that the first optical assembly (6) is configured to form an intermediate image (Ix) of the light spot (Tx) on the output face of the translucent screen (8); and- the second optical assembly (7) is configured to project an image of the intermediate image (Ix) onto a projection surface (2)., Optical projection system (1) according to the preceding claim, in which an object focus (F2o) of the second optical assembly (7) is located at a non-zero distance from the image focus (F1i) of the first optical assembly (6). Optical projection system (1) according to one of the preceding claims, in which an object focus (F2o) of the second optical assembly (7) is separated from the image focus (F1i) of the first optical assembly (6) by a distance less than or equal to 5.00 mm, or even less than or equal to 1 mm. Optical projection system (1) according to one of the preceding claims, in which the translucent screen (8) is defined by an optical blur greater than or equal to 15% and a transmission coefficient greater than or equal to 80%. Optical projection system (1) according to one of the preceding claims, in which at least the exit face (82) of the translucent screen (8) is curved Optical projection system (1) according to one of the preceding claims, wherein the second optical assembly (7) comprises a free-form lens or a free-form mirror. Optical projection system (1) according to one of claims 1 to 5, in which the translucent screen (8) comprises a non-uniform heterogeneous structure. Optical projection system (1) according to the preceding claim in which the heterogeneous structure comprises microstructures (83) comprising at least one of: - graining arranged at the level of all or part of the output face (82); and / or - an irregular heterogeneous holographic pattern; and / or - a plurality of microscopic prisms. Optical projection system (1) according to one of claims 7 or 8, in which the translucent screen (8) is configured so as to comprise a plurality of zones each having a diffusion angle (β) which is specific to them, at least two zones (Z1, Z2) having a distinct diffusion angle (β, β1, β2), inversely proportional to a distance separating the zone considered from the translucent screen (8) from the projection surface (2). Optical projection system (1) according to one of the preceding claims, the at least one light beam (Fx) is configured so that a main direction (Dx) of said beam is inclined relative to at least one face of the translucent screen (81), in particular relative to the entry face (81) of the translucent screen (8), the translucent screen (8) being configured to deflect the at least one light beam (Fx) so as to direct it towards the projection surface (2) when it is in an operational state. Optical projection system (1) according to the preceding claim, further comprising a safety device (9) configured to detect a failure of the translucent screen (8) during which the at least one light beam (Fx) is not deflected by the translucent screen (8). Optical projection system (1) according to one of the preceding claims, comprising a correction device configured to modify the at least one light beam (Fx) emitted so as to correct noise generated by the translucent screen (8), in particular the at least one exit face (82) of the translucent screen (8). Method for projecting a light beam (Fx) in an optical system (1) according to claim 12 onto a projection surface (2) comprising:- the determination, by the correction device, of a correction to be applied to the at least one light beam (Fx) so as to reduce, or even eliminate, noise generated by the translucent screen (8), in particular the exit face (82) of the translucent screen (8); and- the projection of the at least one light beam (Fx), via the laser emitter (3), to which said determined correction is applied.

Images