Optronic device and associated driver monitoring system

Abstract

The invention relates to an optronic device (1) comprising a light source (10) that emits light rays (101), an optical sensor (11) configured to image a field of view (110) and a window (13) having a refractive index equal to n1, and comprising an inner face (130) oriented towards the optical sensor and the light source, this inner face having an illuminated zone (14) through which the light rays pass and an imaged zone (15) included in the field of view. The optronic device comprises an overlayer (16) in a zone (17) of the inner face, between the illuminated zone and the imaged zone, the overlayer having a refractive index equal to n2, such that the intensity Fresnel coefficient (formula A) during 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.

Description

Optronic device and associated driver monitoring system

[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 attenuating parasitic reflections within the device. Technological background

[0003] Driver monitoring systems are now standard equipment in many vehicles, designed to enhance occupant safety. Sensors, primarily positioned at the front of the vehicle's cabin to target the driver, monitor their behavior. Signs of drowsiness, inattention, or signs of intoxication, as well as other indicators of inappropriate driving behavior, can be detected. An alert can then be triggered if necessary.

[0004] For example, an optronic imaging device, typically comprising an optical sensor, or image sensor, and a light source, allows for monitoring driver 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 the need for compactness, but also aesthetic criteria, it is preferable to have driver monitoring systems whose different elements are integrated within an enclosure, such as a box for example, ideally, with a neutral appearance and compact shape.

[0006] Thus, the various components of the driver monitoring system, some of which are positioned to illuminate and image the driver, are generally concealed behind a glass panel that appears opaque to the human eye but is nonetheless 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 otherwise 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 that have a textured surface to trap stray radiation. This solution is therefore difficult to transfer from one model to another and represents additional manufacturing costs.

[0011] Similarly, solutions involving an injection-molded plastic part, positioned perpendicular to the glass to create a physical boundary between the optical sensor and the light source, 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.

[0012] In this context, we propose an optronic device in which a coating with 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 specifically, the invention proposes an optronic device comprising a housing containing a light source emitting light rays and an optical sensor configured to image a field of view. The housing has a window, the window having a refractive index of n1, and an inner face oriented towards the optical sensor and the light source, and an outer face oriented opposite to the inner face. The inner face comprises an illuminated area through which the light rays pass and an imaged area within the field of view of the optical sensor. The sensor is provided with a topcoat in the lens, this topcoat being in contact with an area of ​​the inner face of the window, the area being located between the illuminated area and the imaged area. The topcoat has a refractive index of n2, the refractive index n2 being such that the intensity Fresnel coefficient R = during a reflection at an interface between the glass and the overlay 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 traveling through the glass, are eliminated. Indeed, the addition of the coating, which locally minimizes the intensity of the Fresnel coefficient R, causes light rays incident on the inner surface of the glass to continue propagating instead of being reflected off the glass.

[0015] Thus, the carefully chosen refractive index overlayer prevents the propagation of these stray light rays by multiple reflections.

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

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

[0018] Other advantageous and non-limiting features of the method according to the invention, taken individually or in any technically possible combination, are as follows: The intensity Fresnel coefficient R is strictly less than 0.3%. The intensity Fresnel coefficient R is strictly less than 0.03%. The light source emits light rays contained within a beam having an angular extent equal to an illumination angle. , the glass has a thickness e1, a distance between the light source and the inner face of the glass is equal to e2, a center of the area where the coating is located is at least 2.e1.tan[asin(sin( ) / n1)]+e2.tan( ) of a center of the illuminated area. The overlay is composed of an optical matching gel, the gel being a thixotropic gel, with an apparent viscosity at 25° Celsius greater than or equal to 11,000 poises, measured according to a NYE CTM measurement standard. The overlay is composed of an optical adhesive. The overlay has an absorption rate for a wavelength of said light rays emitted by the light source greater than or equal to 80%. The overlay is dyed throughout using an ink. The overlay has an absorption rate less than or equal to 20% for a wavelength of radiation emitted by the light source. A wall having an absorption rate greater than or equal to 80% for a wavelength of light rays emitted by the light source is interposed between the overlay 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 as long as they are not incompatible or mutually exclusive. Detailed description of the invention

[0021] Furthermore, 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] schematically represents an optronic device according to a first embodiment.

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

[0024] 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 attached claims.

[0027] Figure 1 shows a portion of an optronic device. An optronic device is defined as a device comprising both optical and electronic components. Here, this optronic device is integrated into an occupant monitoring system, 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 driver inattention.

[0028] This optronic device 1 includes a light source 10, adapted to emit light beams 101 towards the vehicle's interior, more specifically 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 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 VCSEL, according to the Anglo-Saxon designation), or any other light source 10 deemed suitable.

[0030] Here, in the figure, the light source 10 shown corresponds to a light-emitting diode. Such a light source 10 has a typical illumination angle 102 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 the 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 a "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 of the imaging optics.

[0035] Imaging optics refers, 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 allows, in particular, the acquisition of images of the area of ​​interest, here, a region around the driver. The image sensor 11 has a field of view 110, which is schematically represented in the figure. This field of view 110 angularly delimits a region of space that can be imaged by the imaging optics on the photosensitive pixel array.

[0038] The images acquired using 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 to 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 glass pane 13 is also designed to be opaque to the human eye, for reasons of discretion and / or aesthetics. Thus, the glass pane 13 is made to absorb radiation in a spectral range corresponding to the visible spectrum. The glass pane 13 absorbs light rays 101 with a central wavelength between 400 nanometers and 800 nanometers. For example, the glass pane 13 has an absorption rate greater than 80% for wavelengths between 400 nanometers and 800 nanometers.

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

[0045] The window 13 can be made of a plastic material, meaning it can be composed of a polymer. Here, for example, a polycarbonate window 13 is considered. However, a window 13 made of any material with suitable thermal and mechanical resistance is also acceptable.

[0046] The glass 13 can then be tinted, for example throughout, to meet the aforementioned criteria. It is also possible to apply a thin anti-reflective coating to 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 n1.

[0048] This glass 13 has a thickness denoted e1, where e1 varies between a few hundred micrometers and a few tens of millimeters, for example, e1 = 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] Put another way, 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 the diagram, 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 under consideration. The emission indicator corresponds to a distribution of 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 above the light source 10. This distance is noted e2 on the.

[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 array of photosensitive pixels 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 results in degrading the quality of the images acquired by the image sensor 11.

[0057] These stray light rays 104, or simply stray 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 Figure 1, stray light rays 104 are likely to propagate by multiple reflections within the glass 13 from the source to the image sensor 11, with 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]

[0061] Where R is the Fresnel coefficient for intensity, n1 corresponds to the optical refractive index of the first interface medium, here the glass, and n0 corresponds to the optical refractive index of the second interface medium. Here, the Fresnel coefficient for intensity is represented as a percentage, using the symbol %.

[0062] Considering the window 13 as the first medium with optical refractive index n1, 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 light intensity of the stray light rays 104 is greater than the light 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 results in a degradation of the image quality of image sensor 11.

[0066] It is proposed within the framework of the invention to locally reduce the Fresnel coefficient in intensity R. For this purpose, as illustrated in the figure, 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] Furthermore, 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 optronic devices 1, in particular those integrated within driver monitoring systems, are eased. Indeed, they are then decoupled from the constraints related to the elimination of stray light rays 104.

[0070] This illustrates a first method of implementation.

[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, 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. However, at each reflection on one of the two interfaces presented by the glass 13, 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 decreases 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.e1.tan[asin(sin( ) / n1)]+e2.tan( ) ;

[0078] where D is equal to the distance sought, e1 is equal to the thickness of the glass pane 13, e2 to a distance between the support plate and the glass pane, corresponds to the illumination angle 102, and n1 the optical refractive index of the glass 13.

[0079] Similarly, a dimension and / or shape of the area 17 covered by the overlay 16 can be chosen so as to minimize the size of the overlay 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 16 overlay is applied to the area to ensure a relatively uniform thickness, varying between one hundred micrometers and ten millimeters, across its entire surface. Here, for example, the 16 overlay has a thickness of 0.5 millimeters.

[0081] Such a deposit is illustrated on the.

[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 achieve this, the optical refractive index n2 of the overlayer 16 is chosen to be close to the optical refractive index n1 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 for 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, the difference in optical refractive index between the overlayer 16 and the glass 13 is chosen to be strictly less than the 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, within 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, specifically for light with a wavelength of 850 nanometers or 950 nanometers.

[0093] Furthermore, in the first embodiment illustrated by the figure, 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 of 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 overlay 16 is for example made of a material called optical adaptation, or, according to the Anglo-Saxon term, index-matching, as known to the person skilled in the art.

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

[0097] For example, optical matching gel is understood to be an optical matching gel 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, existing in a state between solid and liquid, capable of maintaining a defined shape and supporting its own weight, while remaining malleable under pressure. In other words, a gel is understood here to be a material that can be described as soft and ductile under certain conditions, and capable of becoming rigid 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] The 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 smaller than a micrometer is achieved 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 refractive index dispersion 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 in question varies between 1.4647 at 589.3 nanometers and 1.4372 at 1550 nanometers, and is notably 1.4617 at 589.3 nanometers. These values ​​are measured according to the standardized ASTM D-1218 method.

[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 adapting gel or an optical adapting 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 optical applications, for example, to bond, i.e., cement, two optical lenses together without a refractive index demarcation.

[0110] The optical matching material can 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, epoxy adhesive typically has a 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, applying a refractive index matching material via an overlayer 16 reduces the difference in refractive index perceived by the 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 the figure.

[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 eliminated, without risking exerting mechanical stress on the glass 13.

[0121] The summit 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 by the.

[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, wall 18 is dyed throughout, using a pigment or ink with a suitable absorption spectrum. The ink is specifically chosen to have an absorption rate greater than or equal to 80% for the wavelengths of light radiation considered.

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

[0126] Alternatively, 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 with 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. The light intensity emanating from the light source 10, and potentially reaching 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 window 13 are thus uncorrelated with the constraints related to the attenuation of parasitic radiation.

[0130] A second embodiment is shown on the.

[0131] According to this second embodiment, just as in the first embodiment of the, a layer 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 exhibit most of the characteristics and their possible variations, as previously described. In particular, the overlay 16 has an optical refractive index n2 chosen 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 previously, the overlayer 16 exhibits an absorption rate exceeding 50%, even exceeding 80%, or even exceeding 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 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 housing of the optronic device 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 adaptation material, for example an optical adaptation gel or an optical adaptation adhesive, is colored throughout in the second embodiment. For this purpose, the optical adaptation 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 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 on the.

[0141] This third embodiment combines elements of the first embodiment, as well as elements of the second embodiment previously detailed in this description. Thus, features described for the first and second embodiments are repeated 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 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 ensure 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 previously, 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, wall 18 is, for example, dyed throughout before being shaped. In the case where 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 overlay 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 considerably reduced.

[0150] Of course, the preceding description is given by way of example only and does not limit the scope of the invention, which would remain open even if its various elements were replaced by any other equivalents. Furthermore, the different features, variants, and / or embodiments of the present invention can be combined in various ways.

Claims

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 equal to n1, 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) which is included in 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 area illuminated (14) and the 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 =, during a reflection at an interface between the glass 13 and the overlay 16 is strictly less than 3%. Device according to claim 1, wherein said intensity Fresnel coefficient R is strictly less than 0.3%. Device according to claim 1, wherein said intensity Fresnel coefficient R is strictly less than 0.03%. A 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 angle of illumination (102), the glass (13) has a thickness e1, 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 overlayer (16) is located is at least 2.e1.tan[asin(sin( ) / n1)]+e2.tan( ) of a center of the illuminated area (14). Device according to any one of claims 1 to 4, wherein the overlayer (16) is composed of an optical adaptation 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. Device according to any one of claims 1 to 4, wherein the overlayer (16) is composed of an optical adhesive. 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% Device according to claim 7, wherein the overcoat (16) is dyed in mass using an ink. Device according to any one of claims 1 to 6, wherein the overlayer (16) has an absorption rate less than or equal to 20% for a wavelength of the radiation emitted by the light source (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). Driver monitoring system comprising an optronic device (1) according to any one of claims 1 to 10.

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