Optronic device and associated driver monitoring system

Abstract

An optronic device (1) comprises a light source (10) emitting light rays (101), an optical sensor (11) configured to image a field of view (110), and a window (13) having a refractive index of n1, and comprising an inner face (130) oriented towards the optical sensor and the light source. This inner face has an illuminated area (14) through which the light rays pass and an imaged area (15) within the field of view. The optronic device includes an overlayer (16) on an area (17) of the inner face, between the illuminated area and the imaged area. The overlayer has a refractive index of n2, such that the intensity Fresnel coefficient R = at a reflection at an interface between the window and the overlayer is strictly less than 3%. A driver monitoring system comprising such an optronic device is also described. Figure for the abstract: Fig. 1

Description

Title of the invention: Optronic device and associated driver monitoring system technical field

[0001] The present invention relates to an optronic device comprising both an optical sensor and a light source.

[0002] In particular, the present invention relates to an optronic device that can be included in a driver monitoring system, the optronic device comprising an overlay that attenuates unwanted reflections within the device. Technological background

[0003] Driver monitoring systems are now fitted to many motor vehicles to increase occupant safety. Indeed, through sensors, primarily located at the front of the vehicle's passenger compartment to target the driver, the driver's behavior can be monitored. Signs of drowsiness, inattention, or markers of intoxication, or any other indicators of inappropriate driving behavior, can thus be detected. An alert can then be triggered if necessary.

[0004] For example, an optronic imaging device, generally comprising an optical sensor, or image sensor, and a light source, makes it possible to monitor the driver's behavior through visual information. This information is acquired via the image sensor and analyzed, for example, by a dedicated image processing unit.

[0005] In order to meet a need for compactness, but also aesthetic criteria, it is preferable to have driver monitoring systems whose various elements are integrated within an enclosure, such as a box for example, ideally, with a neutral appearance and compact shape.

[0006] Thus, the various elements of the driver monitoring system, some of which are oriented to illuminate and image the driver, are generally masked by a glass panel that appears opaque to the human eye but is nevertheless transparent to the wavelengths emitted and received by the light source and the image sensor, respectively. This glass panel also protects the device's components, which are arranged in a relatively confined space.

[0007] The integration of the optical sensor and the light source, taking into account the aforementioned constraints, therefore constitutes a technical difficulty for car manufacturers.

[0008] In particular, the propagation of stray light rays from the light source to the detector is a recurring problem.

[0009] The solutions usually implemented by manufacturers to mitigate these parasitic radiations detected by the optical sensor and which degrade image quality, complicate the design and manufacturing processes.

[0010] For example, it is known in the prior art for driver monitoring system windows to have a textured surface in part designed to trap these stray radiations. This solution is therefore not easily transferable from one model to another and represents additional manufacturing costs.

[0011] Similarly, solutions involving an injection-molded plastic part, intended to form a physical boundary between the optical sensor and the light source and positioned perpendicular to the glass, generate additional manufacturing steps. Furthermore, the contact between the injection-molded plastic part and the glass adds constraints to manufacturing tolerances, with the risk of image quality degradation if the part were to press against the glass. Summary of the invention

[0012] In this context, an optronic device is proposed, in which a coating having a refractive index close to that of the glass is deposited directly in contact with it, in order to reduce or even cancel the Fresnel coefficient in intensity.

[0013] More particularly, the invention proposes an optronic device, comprising a housing, sheltering a light source emitting light rays, and an optical sensor configured to image a field of view, the housing having a window, the window having a refractive index equal to ni, and having an inner face oriented towards the optical sensor and the light source as well as an outer face oriented opposite to the inner face, the inner face comprising an illuminated area which is traversed by said light rays and an imaged area which is included in the field of view of the optical sensor, in which a topcoat is provided, this topcoat being in contact with an area of ​​the inner face of the window, the area being placed between the illuminated area and the imaged area, the topcoat having a refractive index equal to n2,the refractive index n2 being such that the Fresnel coefficient in intensity R = j2 \nl+n2 7 during a reflection at an interface between the glass and the coating is strictly less than 3%.

[0014] Thus, thanks to the invention, any unwanted reflections that might propagate from the light source to the optical sensor, by propagating within the glass, are eliminated. Indeed, the addition of the overcoat locally minimizes these reflections. The Fresnel coefficient in intensity R means that light rays incident on the inner face of the glass continue their propagation, instead of being reflected off the glass.

[0015] Thus, the duly chosen refractive index overlayer prevents the propagation by multiple reflection of these parasitic light rays.

[0016] The design and manufacture of the windows is advantageously uncorrelated with the problem of eliminating unwanted reflections.

[0017] Moreover, the proposed technical solution is simple, inexpensive, and easily transferable to any other window model.

[0018] Other advantageous and non-limiting features of the process according to the invention, taken individually or in all technically possible combinations, are as follows: - The Fresnel coefficient in intensity R is strictly less than 0.3%. - The Fresnel coefficient in intensity R is strictly less than 0.03%. - The light source emits light rays contained within a beam luminous presenting an angular extent equal to an illumination angle 0, the glass has a thickness el, a distance between the light source and the inner face of the glass is equal to e2, a center of the area where the overcoat is located is at least 2.el.tan[asin(sin(^) / nl)]+e2.tan(0) from a center of the illuminated area. - The overlayer is composed of an optical adaptation gel, the gel being a thixotropic gel, with an apparent viscosity at 25° Celsius greater than or equal to 11000 poises, measured according to a NYE CTM measurement standard. - The overlayer is composed of an optical adhesive. - The overlayer has an absorption rate for a wavelength of said light rays emitted by the light source greater than or equal to 80%. - The overcoat is dyed throughout using ink. - The top layer has an absorption rate of 20% or less for a wavelength of the radiation emitted by the light source. - A wall having an absorption rate greater than or equal to 80% for a wavelength of the light rays emitted by the light source, is interposed between the overlayer and a support plate, the optical sensor and the light source being arranged on said support plate.

[0019] The invention also proposes a driver monitoring system comprising an optronic device as described.

[0020] Of course, the different features, variants and embodiments of the invention can be combined with each other in various ways insofar as they are not incompatible or mutually exclusive. Detailed description of the invention

[0021] In addition, various other features of the invention become apparent from the attached description made with reference to the drawings which illustrate non-limiting embodiments of the invention and where:

[0022] [Fig.1] schematically represents an optronic device according to a first embodiment.

[0023] [Fig.2] represents a second embodiment of the optronic device of [Fig.1].

[0024] [Fig.3] illustrates a third embodiment of the optronic device according to the invention.

[0025] It should be noted that in these figures the structural and / or functional elements common to the different variants may have the same references.

[0026] Various other modifications may be made to the invention within the scope of the annexed claims.

[0027] Figure 1 shows a portion of an optronic device 1. An optronic device 1 is understood to be a device comprising both optical and electronic components. Here, this optronic device 1 is integrated into an occupant monitoring system, more specifically a driver monitoring system for a motor vehicle. Such a driver monitoring system is typically located in the passenger compartment of a motor vehicle and uses sensors, such as optical sensors, including image sensors, to detect and report any potential lack of vigilance on the part of the driver.

[0028] This optronic device 1 comprises a light source 10, adapted to emit light beams 101 towards the vehicle's passenger compartment, more particularly towards the driver. This light source 10 is thus configured to illuminate a region of interest, emitting the light beams 101 in a beam of light, this beam being subtended by an illumination angle 102. This illumination angle 102 thus describes an angular extent of the light beams 101 included in the illumination beam emitted by the light source 10.

[0029] The light source 10 corresponds for example to a light-emitting diode (commonly referred to as an LED, or LED, according to the Anglo-Saxon designation) of any type, or to a vertical cavity laser diode emitting from the surface (referred to as a VCSEL, according to the Anglo-Saxon designation), or any other light source 10 deemed suitable.

[0030] Here, in [Fig. 1], the light source 10 shown corresponds to a light-emitting diode. Such a light source 10 has an illumination angle 102 typical of 60 degrees, measured between an optical axis 103 and an edge of the light beam.

[0031] The light rays 101 emitted by the light source 10 usually have a central wavelength within a spectral range corresponding to the infrared, in particular the near-infrared range, if the optronic device 1 is integrated into an occupant monitoring system. Indeed, the infrared range, and more specifically the near-infrared range, has the advantage of being invisible to the human eye, thus avoiding dazzling and / or distracting the driver. However, a light source 10 emitting in a visible spectral range is also possible.

[0032] In the embodiment shown, the light rays 101 are considered to have a central wavelength in the infrared range, that is, between 700 nanometers and 2000 nanometers. In particular, this is the near-infrared range. For example, the light source 10 emits radiation with a central wavelength of 850 nanometers, or 950 nanometers.

[0033] Furthermore, the light source 10 can emit radiation considered monochromatic, with a spectral width of a few tens of nanometers around the central wavelength. However, a polychromatic light source 10 is also conceivable within the framework of this description.

[0034] The optronic device 1 also includes an optical sensor or image sensor 11. This image sensor 11, also referred to as the "camera", includes a photosensitive pixel array, and imaging optics, adapted to image the area of ​​interest, which is illuminated by the light source 10, on the pixel array which is located downstream with respect to the imaging optics.

[0035] Imaging optics refer, for example, to a camera lens, possibly associated with bandpass optical filters designed to eliminate any unwanted light rays emitted outside a spectral range of interest.

[0036] The photosensitive pixel matrix corresponds to an arrangement of photosensitive pixels in the form of an array, which may be rectangular. The pixels are sensitive to a spectral range that at least partially overlaps the spectral range emitted by the light source 10. Thus, as stated previously, the pixels of the pixel matrix are sensitive to a spectral range corresponding to the infrared range, in particular, the near-infrared range, and especially to light rays 101 having a central wavelength of 850 nanometers or 950 nanometers.

[0037] This image sensor 11 makes it possible, in particular, to acquire images of the area of ​​interest, here, of a region around the driver, the image sensor 11 presenting a field of view 110, which is schematically represented in [Fig. 1]. This field of view 110 angularly delimits a region of space that can be imaged by the imaging optics on the photosensitive pixel matrix.

[0038] The images acquired using the image sensor 11 are then analyzed in order to trigger an alert if necessary.

[0039] The elements of the optronic device, in particular the image sensor 11 and the light source 10, are fixed on a support plate 12. This is, for example, an electronic board, and the aforementioned elements can be soldered to it.

[0040] The support plate 12, the image sensor 11 and the light source 10 are then placed in an enclosure, for example a housing. This is not shown in the figures.

[0041] This housing has, on one of its faces, a window 13, through which the light rays 101 emitted by the light source 10 are transmitted, and through which the image sensor 11 collects the image of the region of interest. The dimensions of the window 13 are specifically designed so as not to obstruct either the emitted light beam or the field of view 110.

[0042] This glass 13 is also adapted to transmit light rays 101 from the spectral range emitted by the light source 10. In particular, in the case of a monochromatic light source 10, the glass 13 is adapted to transmit the central wavelength emitted by the light source 10. In other words, the glass 13 is transparent to the central wavelength of the light rays 101 emitted and received by the optical device, and has, for example, an absorption rate of less than 20% for this central wavelength.

[0043] However, the window 13 is also configured to be opaque to the human eye, for reasons of discretion and / or aesthetics. Thus, the window 13 is designed to absorb radiation in a spectral range corresponding to the visible spectrum. The window 13 absorbs light rays 101 with a central wavelength between 400 nanometers and 800 nanometers. For example, the window 13 exhibits an absorption rate greater than 80% for wavelengths between 400 nanometers and 800 nanometers.

[0044] Alternatively, a reflective coating can cover the glass 13, so as to reflect radiation having a central wavelength in the visible range, between 400 nanometers and 800 nanometers.

[0045] The window 13 can be made of a plastic material, that is to say, the window 13 can be composed of a polymer. Here, for example, a polycarbonate window 13 is considered. However, a window 13 composed of any material exhibiting suitable thermal and mechanical resistances may also be suitable.

[0046] The glass 13 can then be tinted, for example throughout its mass, in order to meet the aforementioned criteria. It is also possible to deposit a thin anti-reflective coating on it.

[0047] Here, in the embodiment presented, the window 13, made of polycarbonate, has an optical refractive index, or refractive index, of 1.591. This refractive index associated with the window 13 is denoted ni.

[0048] This glass 13 has a thickness denoted el, where el varies between a few hundred micrometers and a few tens of millimeters, for example, el = 1 millimeter, and has two faces, opposite each other, an inner face 130 and an outer face 131. The inner face 130 is oriented towards the image sensor 11 and the light source 10, while the outer face 131 is oriented towards the passenger compartment of the motor vehicle.

[0049] In other words, the inner face 130 is turned towards the inside of the case, while the outer face 131 is turned towards the outside of the case.

[0050] According to [Fig. 1], the light rays 101 from the light source 10 pass through the glass 13. The light rays 101 therefore intercept the glass 13. A surface on the inner face 130 of the glass 13 that is traversed by the light rays 101 from the light source 10 is called the illuminated area 14 in the following description. Thus, the illuminated area 14 corresponds to an intersection between the inner face 130 of the glass 13 and the illuminating light beam.

[0051] The shape and dimensions of this illuminated area 14 on the inner face 130 of the glass 13 are determined as a function of an emission indicator of the light source 10 considered. The emission indicator corresponds to a distribution of a luminous intensity as a function of the directions in space.

[0052] Here, it is considered that the light rays 101 from the light source 10 are contained in a cone centered around the optical axis of the light source 10. The light beam is therefore incident on the inner face 130 along an illuminated area 14 which is considered to be circular in shape, and whose dimensions, i.e. here the radius, are determined in particular as a function of the illumination angle 102 of the light source 10, and of a distance between the light source 10 and the inner face 130, measured vertically from the light source 10. This distance is noted e2 on [Fig.1].

[0053] Similarly, an imaged area 15 is defined on the surface of the inner face 130, and corresponds to an area within the field of view 110 of the image sensor 11. In other words, light rays emanating from the passenger compartment and passing through the imaged area 15 on the inner face 130 of the window 13 are collected by the imaging optics. They are then focused onto the photosensitive pixel array to produce an image.

[0054] A shape and dimension of the imaged area 15 on the glass 13 are determined according to the optical properties of the imaging optics and the dimensions of the photosensitive pixels of the matrix.

[0055] To avoid saturation of the matrix pixels and / or degradation of the image quality of the image sensor 11, the illuminated area 14 and the imaged area 15 are spatially distinct from each other. Thus, the arrangement of the light source 10 and the image sensor 11 is such that the image sensor 11 does not image the light rays 101 coming directly from the light source 10, but rather collects reflected light rays 101 from the vehicle's interior.

[0056] However, stray light rays 104 are likely to propagate from the light source 10 to the image sensor 11. This has the effect of degrading the quality of the images acquired by the image sensor 11.

[0057] These parasitic light rays 104, or simply parasitic light rays 104, are for example produced by unwanted light reflections at interfaces, in particular planar interfaces, of the optronic device 1.

[0058] In particular, as shown in [Fig. 1], stray light rays 104 are likely to propagate by multiple reflections within the glass 13 from the source to the image sensor 11, the glass 13 then acting as a waveguide. The light radiation from the light source 10 is then reflected at an air / inner face interface and an outer face / air interface.

[0059] At each of these interfaces, a proportion of the incident light intensity that is reflected by the interface is determined as a function of the intensity Fresnel coefficient R, which is formulated here as follows:

[0060] d _ / ni-n0 Ÿ

[0061] Where R is the intensity Fresnel coefficient, ni corresponds to the optical refractive index of a first interface medium, here, the glass, and nO corresponds to the optical refractive index of the second interface medium. Here, the intensity Fresnel coefficient is represented as a percentage, using the symbol %.

[0062] Considering the glass 13 as the first medium with optical refractive index ni, whose optical refractive index is close to 1.591 and the ambient air as the second medium whose optical index is close to 1, then the Fresnel coefficient in intensity R for the reflection of a light ray 101 at this interface is equal to R = 5.20%.

[0063] Thus, a non-negligible proportion of the intensity of the light radiation emitted by the light source 10 (here, 5.20% of an incident light intensity) is likely to propagate from the illuminated area 14 to the imaged area 15 of the window 13.

[0064] Moreover, the luminous intensity of the parasitic light rays 104 is greater than the luminous intensity of the light rays 101 propagating to the area of ​​interest, i.e. here the passenger compartment of the vehicle, before being backscattered towards the image sensor 11.

[0065] This has the effect of degrading the image quality of the image sensor 11.

[0066] It is proposed within the framework of the invention to locally reduce the coefficient Fresnel intensity R. For this, as illustrated in [Fig.1], a coating 16 with an appropriate optical refractive index is applied to the glass 13, in particular to the inner face 130 of the glass 13. The refractive index of the coating 16 is denoted n2.

[0067] Advantageously, this localized decrease in the Fresnel coefficient reduces the proportion of stray light rays 104 likely to be collected by the image sensor 11.

[0068] Moreover, the localized application of this overcoat 16 on the glass 13 makes it an inexpensive, flexible solution that can be used downstream of the design and manufacturing process, since it can be applied to any type of glass 13.

[0069] Thus, the constraints related to the design and manufacture of the windows 13 of the optronic devices 1, in particular those integrated within driver monitoring systems, are reduced. Indeed, they are then decoupled from the constraints related to the elimination of stray light rays 104.

[0070] Fig. 1 illustrates a first embodiment.

[0071] In this first embodiment, a coating 16 with an appropriate refractive index is deposited on the inner face 130 of the glass 13, so as to cover an area 17 located between the area illuminated 14 by the light source 10, and the area imaged 15 by the image sensor 11.

[0072] For example, the zone 17 is positioned here so as to intercept light rays 101 coming from an outer end of the light beam, in particular, light rays 101 passing through the illuminated zone 14 at its end closest spatially to the imaged zone 15.

[0073] Indeed, these light rays 101 located at the outer end of the light beam are likely to propagate to the illuminated area 14 with a minimum number of reflections on the air / inner face 130 and outer face / air interfaces due to a high angle of incidence and a certain geographical proximity to the illuminated area 14. Now, at each reflection on one of the two interfaces that the glass 13 presents, a proportion of the incident light is reflected, while the rest is transmitted, according to the Fresnel coefficient established previously.

[0074] Thus, the intensity or luminous power of a parasitic light ray 104 is decreasing as a function of the number of reflections on the interfaces.

[0075] These parasitic light rays 104 from the outer end then have a greater luminous intensity than other parasitic light rays 104, resulting from reflections at the interfaces of more central light rays 101 within the light beam.

[0076] For example, a distance between the optical axis 103 and a geometric center of the zone 17 on which the overlay 16 is applied is, for example:

[0077] D = 2.el.tan[asin(sin(^) / nl)]+e2.tan(^);

[0078] where D is equal to the distance sought, el is equal to the thickness of the glass 13, e2 to a distance between the support plate and the glass, S corresponds to the illumination angle 102, and ni to the optical refractive index of the glass 13.

[0079] Similarly, a dimension and / or shape of the area 17 covered by the overlayer 16 can be chosen so as to minimize the size of the overlayer 16, while maximizing an attenuation of the light intensity of the stray light rays 104 likely to propagate to the image sensor 11. For example, a dimension and / or shape of the area 17 is such that, geometrically, all the stray light rays 104, that is to say, light rays 101 propagating within the glass 13 by reflection on the air / inner face and outer face / air interfaces, are incident on the area 17.

[0080] The overlayer 16 is applied to the area in such a way as to have a substantially uniform thickness, varying between one hundred micrometers and ten millimeters, over its entire surface. Here, the overlayer 16 has, for example, a thickness of 0.5 millimeters.

[0081] Such a deposit is illustrated in [Fig.1].

[0082] The optical refractive index n2 of the overlayer 16 is chosen so as to decrease the value of the intensity Fresnel coefficient R calculated for a reflection at the interface between the glass 13 and the overlayer 16.

[0083] To this end, the optical refractive index n2 of the overlayer 16 is chosen to be close to the optical refractive index ni of the glass 13, at the wavelengths emitted by the light source 10. In particular, here, a monochromatic light source 10 is considered, emitting in a spectral range corresponding to the near-infrared. Specifically, the light source 10 emits light radiation around 850 nanometers, or around 950 nanometers.

[0084] An optical refractive index n2 of the overlayer 16 is chosen to obtain a Fresnel coefficient in intensity R lower than that between the glass / ambient air interface. This means, equivalently, that in absolute value, a difference in optical refractive index between the overlayer 16 and the glass 13 is chosen to be strictly less than a difference in optical refractive index between the glass 13 and the ambient air.

[0085] The window 13 described in the first embodiment is made of polycarbonate. The window 13 then has an optical refractive index of n2 = 1.591.

[0086] The value of the Fresnel coefficient in intensity R is, as a reminder, R = 5.20% for a reflection at the glass / ambient air interface.

[0087] Thus, the refractive index n2 of the overcoat 16 is chosen so that the value of the intensity Fresnel coefficient R is strictly less than 5.20%.

[0088] For example, the refractive index n2 of the overcoat 16 is such that the intensity Fresnel coefficient R for a reflection at the overcoat / glass interface is within a range of values ​​from 0% to 3%, the range of values ​​including the following values ​​and any interval between these values: 3%; 2%; 1%; 0.9%; 0.8%; 0.7%; 0.6%; 0.5%; 0.4%; 0.3%; 0.2%; 0.1%; 0.09%; 0.08%; 0.07%; 0.06%; 0.05%; 0.04%; 0.03%; 0.02%; 0.01%; 0.009%; 0.008%; 0.007%; 0.006%; 0.005%; 0.004%; 0.003%; 0.002%; 0.001%; ​​0%.

[0089] Preferably, the refractive index n2 of the coating 16 is chosen to minimize the intensity Fresnel coefficient R for reflection at the coating / glass interface. Thus, the intensity Fresnel coefficient R for reflection at such an interface is preferably strictly less than 3%, or even strictly less than 0.3%, or even strictly less than 0.003%.

[0090] Thus, in the first embodiment, in which the window 13 is made of polycarbonate, the optical refractive index of the overcoat 16 is within a range of values ​​from 1.2 to 1.59, the range of values ​​comprising the following values ​​and any interval between these values: 1.20; 1.30; 1.31; 1.32; 1.33; 1.34; 1.35; 1.36; 1.37; 1.38; 1.39; 1.40; 1.41; 1.42; 1.43; 1.44; 1.45; 1.46; 1.47; 1.48; 1.49; 1.50; 1.51; 1.52; 1.53; 1.54; 1.55; 1.56; 1.57; 1.58; 1.59.

[0091] Preferably, the difference between the optical refractive index of the overlayer 16 and the glass 13 is minimized. The optical refractive index of the overlayer 16 is chosen to be as close as possible to the optical refractive index of the glass 13, for example in a range of values ​​from 1.43 to 1.59.

[0092] These refractive indices n2 of the overlayer 16 are considered at the wavelength of the light emitted by the light source 10. In particular, in the first embodiment, the light source 10 emits in a spectral range corresponding to the near-infrared. Thus, the optical refractive indices n2 described for the overlayer 16 are evaluated in this spectral range, in particular, for light with a wavelength of 850 nanometers or 950 nanometers.

[0093] Furthermore, in the first embodiment illustrated in [Fig. 1], the overlayer 16 is transparent to the wavelengths emitted by the light source 10, thus allowing the light radiation emitted by the light source 10 to pass through. By "transparent," it is understood that the overlayer 16 has an absorption rate of the light intensity less than 50%, or even less than 10%, or even less than 1% for the wavelengths emitted by the light source 10. Here, this means an absorption rate of less than 10% for radiation emitted at 850 nanometers, or at 950 nanometers over the thickness of the overlayer 16.

[0094] In particular in the first embodiment, the overlayer 16 has an optical absorption (or linear absorption rate) of between 1% per micron of thickness, and 10% per micron of thickness.

[0095] The overlayer 16 is for example made of a material called optical matching, or, according to the Anglo-Saxon term, ddndex-matching, as known to the person skilled in the art.

[0096] Such an optical matching material corresponds, for example, to a gel, or to an optical glue or adhesive, commonly known to those skilled in the art as an "optical cement" or "optical adhesive," having a controlled refractive index. In particular, these optical matching materials have controlled refractive indices, so as to be close to the optical refractive indices of conventional optical materials, for specified wavelength ranges.

[0097] For example, by optical matching gel, it is understood that an optical matching gel is such as is frequently used in the field of fiber optics.

[0098] For the purposes of this description, a gel is understood to be a material that can be described as semi-solid or quasi-solid, that is, exhibiting a state between solid and liquid, capable of maintaining a defined shape and supporting its own weight, while remaining malleable when pressure is applied. In other words, a gel is understood here to be a material that can be described as soft and ductile under certain conditions, and that can potentially harden under other conditions.

[0099] Such gels result in particular from the dilution of solids in a solvent, this solvent being in particular water, oil, air, or any other suitable solvent.

[0100] Solids generally diluted for obtaining such optical adaptation gels are, for example, macromolecules, such as polymers.

[0101] Some of these gels can also be described as colloids, or colloidal systems, where a dispersion of at least one substance in the form of particles of dimensions less than a micrometer is carried out in a solvent.

[0102] In the embodiment described herein, the optical adaptation gel considered is a thixotropic gel, comprising in particular a mixture of silica in colloidal form, and 2,6-di-tert-butyl-p-cresol.

[0103] The optical adaptation gel used in this first embodiment, also described as a lubricant by the manufacturer, has an optical refractive index of 1.4454 at 980 nanometers.

[0104] This optical refractive index value is measured, in a non-limiting manner, according to the standardized method ASTM D-1218, which corresponds to the standard test method for a refractive index and for a dispersion of the refractive index of hydrocarbon liquids, according to the English name Standard Test Method for Refractive Index and Refractive Dispersion of Hydrocarbon Liquids.

[0105] The optical refractive index of the gel considered varies between 1.4647 at 589.3 nanometers and 1.4372 at 1550 nanometers, and is in particular 1.4617 at 589.3 nanometers. These values ​​are measured according to the standardized method ASTM D-1218.

[0106] The optical adaptation gel also has an apparent viscosity at 25°C measured at 11000 poises, according to the NYE CTM test method, and an evaporation at 24 hours at 100°C measured as being less than 0.2% according to the ASTM D-972 test method.

[0107] These various parameters, of composition, refractive index, apparent viscosity, etc., are described in a non-limiting manner, and the choice of an optical matching gel or an optical matching material suitable in view of the necessary specifications is left to the discretion of the person skilled in the art.

[0108] The application of such an optical adaptation gel in the first embodiment as an overcoat 16 on the glass 13, more specifically on the area 17 on the inner face 130 described previously allows, for a light source 10 emitting at 980 nanometers, to reduce the intensity Fresnel coefficient R for a reflection, to R = 0.223%.

[0109] Alternatively, the overlayer 16 can be formed by an optical adhesive or optical cement. Such an adhesive is frequently used in applications in the field of optics, for example, to bond i.e., cement two optical lenses without a demarcation of refractive index.

[0110] The optical matching material may be, for example, a resin, such as an epoxy, epoxy adhesive, or epoxy resin. Such a resin initially has a semi-solid form before being hardened by polymerization. Thus, the epoxy adhesive has a typical refractive index between 1.50 and 1.59 for the wavelength ranges considered.

[0111] The overlayer 16 is therefore applied to the inner face 130 of the glass 13 of the optronic device, ideally in a localized manner, so as to reduce the intensity Fresnel coefficient R for a reflection at the level of the overlayer 16.

[0112] Due to the reduction of the Fresnel coefficient in intensity, the light rays 101 are therefore transmitted through the overlayer 16 at the interface between the overlayer 16 and the glass 13.

[0113] In other words, the application of a refractive index matching material via an overlayer 16 makes it possible to reduce a difference in refractive index perceived by light rays 101. In the idealized case of a zero refractive index difference, the interface is not perceptible to the light rays 101, which therefore continue to propagate along a straight optical path. The propagation of such a light ray 105 is shown in [Fig. 1].

[0114] Here, it is considered that a proportion greater than 97% of the light rays 101 incident on the glass / overcoat interface are transmitted through the overcoat 16.

[0115] In order to block the propagation of these stray light rays 104, a wall 18 is inserted extending in a direction perpendicular to the surface of the glass 13.

[0116] This wall 18 has an extent in the direction perpendicular to the surface of the glass 13 of dimension strictly less than a distance between the glass 13 and the support plate 12, on which the light source 10 and the image sensor 11 are fixed. The extent of the wall 18 in this direction is therefore less than the distance e2.

[0117] This wall 18 is therefore configured to be inserted into an available space between the glass 13 and the support plate 12, without exerting any mechanical stress on the glass 13.

[0118] The wall 18 therefore has two main surfaces, extending in the direction perpendicular to the surface of the glass 13, a base, in contact with the support plate 12, and a top 180, located at an opposite end with respect to the base.

[0119] The apex 180 of the wall 18 is placed in contact with the overlayer 16, without being in contact with the inner face 130 of the window 13.

[0120] For example, the various elements can be put in place while the overlay 16 exhibits a certain ductility, particularly in the case of an epoxy adhesive. Thus, the gap between the apex 180 of the wall 18 and the overlay 16 is made zero, without risking exerting mechanical stress on the glass 13.

[0121] The apex 180 of the wall 18 here has dimensions and a shape substantially similar to the dimensions and shape of the area on which the overlayer 16 is applied.

[0122] Thus, the stray light rays 104 transmitted through the overlayer 16 are incident on the top 180 of the wall, as illustrated in [Fig.1].

[0123] The wall 18 therefore has an absorption rate greater than or equal to 80% for wavelengths emitted by the light source 10. It is therefore considered that the wall 18 has an absorption rate greater than or equal to 80% for light rays 101 in the infrared, in particular, for light rays 101 in the near-infrared range, for example, for light rays 101 at 850 nanometers or 950 nanometers.

[0124] To achieve this, the wall 18 is dyed throughout, using a pigment or ink with a suitable absorption spectrum. The ink is chosen so as to exhibits an absorption rate greater than or equal to 80% for the wavelengths of light radiation considered.

[0125] Here, in the first embodiment, the wall 18 is made of polycarbonate. In particular, the wall 18 can be made by injection molding of polycarbonate. Here, it is assumed that the polycarbonate has been dyed throughout beforehand, using ink or pigment.

[0126] Alternatively, the wall 18 is, for example, painted on at least part of its surface, this part including the top 180 of the wall. An ink or paint having a suitable absorption spectrum will also be chosen.

[0127] By combining the overlayer 16 and the wall, stray light rays 104 propagating within the glass 13 are considered to be eliminated. A light intensity emanating from the light source 10, and likely to reach the image sensor 11, is therefore reduced.

[0128] Furthermore, the insertion of the wall 18 intended to absorb stray light radiation does not exert any mechanical stress on the glass 13, which helps to preserve its optical performance.

[0129] The design and manufacture of the window 13 are thus uncorrelated with the constraints related to the attenuation of parasitic radiation.

[0130] A second embodiment is shown in [Fig.2].

[0131] According to this second embodiment, just as in the first embodiment of [Fig.1], a coating 16 is applied to a localized area 17 of the inner face 130 of the glass 13 of the optronic device.

[0132] This overlay 16 can have most of the characteristics and their possible variations, as previously described. In particular, the overlay 16 has an optical refractive index n2 chosen so as to reduce the intensity Fresnel coefficient R for a reflection of a light ray from the light source 10. In other words, the refractive index n2 of the overlay 16 is chosen to be as close as possible to the refractive index of the glass 13.

[0133] However, unlike the embodiment described above, the overlayer 16 has an absorption rate greater than 50%, or even greater than 80%, or even greater than 90%, for the wavelengths emitted by the light source 10. Here, the light source 10 emits in a spectral range corresponding to the infrared range, more specifically to the near-infrared range. In particular, the light source 10 emits at 850 nanometers or 950 nanometers.

[0134] Thus, the overlayer 16 ideally exhibits an absorption rate greater than 80% for light radiation at 850 nanometers or 950 nanometers. The overlayer 16 absorbs the light radiation emitted at the aforementioned wavelengths. The propagation of these stray light rays 104 within the device housing Optronics 1 is blocked by the overlayer 16. Indeed, due to the optical refractive index chosen for the overlayer 16, the light rays 101 incident on the area are mostly transmitted through the glass / overlayer interface. These stray light rays 104 are transmitted into the overlayer 16 and absorbed within its thickness.

[0135] The overlayer 16, which, as a reminder, consists of an optical matching material, for example an optical matching gel or an optical matching adhesive, is colored throughout in the second embodiment. For this purpose, the optical matching material is colored throughout prior to its application to the area of ​​the inner face 130 of the glass 13.

[0136] An ink or pigment absorbing light rays 101 in the aforementioned wavelength ranges, which correspond to the wavelength ranges emitted by the light source 10, is used to dye the optical matching material composing the overcoat 16.

[0137] Ideally, the ink or pigment is chosen to have a sufficiently high absorption rate for these wavelength ranges, so as to absorb, for example, at least 80% of the incident light intensity. Even more advantageously, the ink or pigment chosen to tint the overcoat 16 has a sufficiently high absorption rate, so as to absorb at least 90% of the incident light intensity.

[0138] In this second embodiment, a thickness of the overlayer 16 is determined as a function of a linear absorption rate of the material composing the overlayer 16.

[0139] In the second embodiment, the presence of a wall 18, as described in the first embodiment, is therefore optional.

[0140] A third embodiment is illustrated in [Fig.3].

[0141] This third embodiment combines elements of the first embodiment of implementation, as well as elements of the second embodiment previously detailed in this description. Thus, features described for the first and second embodiments are included in the third embodiment.

[0142] In this embodiment, a tinted overlayer 16 is associated with a wall 18.

[0143] The overlayer 16 has an optical refractive index n2 chosen so as to be as close as possible to the optical refractive index of the glass 13, as described above.

[0144] The overcoat 16 is dyed throughout to provide an absorption rate for the wavelength ranges emitted by the light source 10 of at least 80%, ideally greater than 90%. To achieve this, a suitable ink or pigment is mixed with the overcoat 16 before its application to the glass 13.

[0145] A wall 18, as described above, is also inserted between the glass 13 and the support plate 12, in contact with the overlay 16, via a vertex 180 of the wall. The dimensions of this wall 18 in a direction perpendicular to the surface of the glass 13 are chosen so that the wall 18 does not exert mechanical pressure within the housing. The dimensions of the wall 18 in this direction are less than e2.

[0146] This wall 18, like the overlayer 16, is configured to absorb at least 80%, or even at least 90%, of the incident light intensity, for stray light radiation in a spectral range emitted by the light source 10.

[0147] For this purpose, the wall 18 is, for example, dyed throughout before being shaped. In the case where the wall 18 is made by injection molding of polycarbonate, an ink is, for example, mixed with the polycarbonate beads.

[0148] According to one variant, wall 18 is painted on its surface.

[0149] The combination of a tinted overlayer 16 and a wall 18 ensures significant attenuation of stray light radiation. In particular, the light intensity likely to interfere with the performance of the image sensor 11 is substantially reduced.

[0150] Of course, the preceding description has been given by way of example only and does not limit the scope of the invention, which would not be exceeded by replacing the various elements with any other equivalents. Furthermore, the different features, variants, and / or embodiments of the present invention can be combined with one another in various ways.

Claims

Demands

1. An optronic device (1) comprising a housing containing a light source (10) emitting light rays (101), and an optical sensor (11) configured to image a field of view (110), said housing having a window (13), said window (13) having a refractive index of ni, and having an inner face (130) oriented towards said optical sensor (11) and said light source (10), said inner face (130) comprising an illuminated area (14) through which said light rays (101) pass and an imaged area (15) contained within the field of view (110) of said optical sensor (11), said optronic device (1) being characterized in that the optronic device (1) comprises an overlayer (16), this overlayer (16) being in contact with an area (17) of the inner face (130) of the window (13), said area (17) extending at least between the illuminated area (14) and imaged area (15), said overlayer (16) having a refractive index equal to n2,said refractive index n2 being such that the Fresnel coefficient in intensity R = / \2 during a reflection \«1+h2 / at an interface between the glass 13 and the overcoat 16 is strictly less than 3%.,

2. Device according to claim 1, wherein said intensity Fresnel coefficient R is strictly less than 0.3%.

3. Device according to claim 1, wherein said intensity Fresnel coefficient R is strictly less than 0.03%.

4. Device according to any one of claims 1 to 3, wherein the light source (10) emits light rays (101) contained in a light beam having an angular extent equal to an illumination angle 6 (102), the glass (13) has a thickness el, a distance between said light source (10) and the inner face (130) of the glass (13) is equal to e2, a center of the zone (17) where the overcoat (16) is located is at least 2.el.tan[asin(sin(^) / nl)]+e2.tan(#) from a center of the illuminated zone (14).

5. Device according to any one of claims 1 to 4, wherein the overlayer (16) is composed of an optical adapting gel, the gel being a thixotropic gel, of an apparent viscosity at 25° Celsius greater than or equal to 11000 poises, measured according to a NYE CTM measurement standard.

6. Device according to any one of claims 1 to 4, wherein the overlayer (16) is composed of an optical adhesive.

7. A device according to any one of claims 1 to 6, wherein the overlayer (16) has an absorption rate for a wavelength of said light rays (101) emitted by the light source (10) greater than or equal to 80%

8. Device according to claim 7, wherein the overcoat (16) is dyed in mass using an ink.

9. Device according to any one of claims 1 to 6, wherein the overcoat (16) has an absorption rate less than or equal to 20% for a wavelength of the radiation emitted by the light source (10).

10. Device according to any one of claims 1 to 9, wherein a wall (18), having an absorption rate greater than or equal to 80% for a wavelength of the light rays (101) emitted by the light source (10), is intercalated between the overlayer (16) and a support plate (12), the optical sensor (11) and the light source (10) being arranged on said support plate (12).

11. Driver monitoring system comprising an optronic device (1) according to any one of claims 1 to 10.

Images