Light beam receiving device and lighting system for a motor vehicle incorporating such a device

Abstract

Light beam receiving device and lighting system for motor vehicle comprising such a device. One aspect of the invention relates to a light beam receiving device (200), said light beam (L) comprising a continuous component of ambient light and a light signal modulated by means of a high-frequency light code, said receiving device comprising: - a photodiode-based light sensor (210), adapted to detect the light beam, and - an active optical filter (220), positioned upstream of the light sensor and adapted to dynamically control a power of the light beam (L) received by the light sensor (210) in order to highlight the modulated light signal with respect to the continuous component of the ambient light.Another aspect of the invention relates to a lighting system (100) such as a lighting system (110) or a signaling system (120) for a motor vehicle comprising such a device for receiving a light beam. Figure to be published with the abbreviation: Figure 2.

Description

Title of the invention: Light beam receiving device and lighting system for a motor vehicle comprising such a device. TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a light beam receiving device equipped with a technology that prevents saturation of the light sensor. The invention also relates to a lighting system, such as a lighting and / or signaling system, equipped with such a light beam receiving device.

[0002] The invention finds applications in the field of land vehicles and in particular automobiles, to enable the vehicle's lighting and / or signaling systems to integrate, in addition to their lighting and / or signaling function, a distance detection function. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] It is well known that automobile manufacturers are constantly striving to make vehicles increasingly safer, both for passengers inside the vehicle and for third parties in the vicinity. To this end, vehicles are continually being improved to give them greater autonomy. To improve vehicle autonomy, it is important that vehicles be able to detect, in the near or far environment, the presence of objects or pedestrians (referred to interchangeably as objects) and determine the distance to these objects. To this end, and to avoid a high detection rate and / or false positives, the standard requires complementary technologies on the vehicle with the integration of three redundant detection devices.

[0004] Thus, a vehicle can incorporate, for example, one or more devices using Lidar technology (for "Light Detection and Ranging"), which is based on analyzing the properties of a laser beam emitted by a specific light source and reflected by the object or pedestrian. With Lidar technology, the distance between the light source and the object is measured from the time lag between the emission of a laser pulse and the reception of the reflected pulse. Such an object detection device, however, requires specific equipment to emit the infrared signal and to receive the reflected signal.

[0005] A vehicle may also incorporate one or more cameras adapted to determine the distance to objects. However, these cameras, like Lidar devices, require a specific location on the vehicle. Adding a third detection device has the disadvantage of overloading an area of ​​the vehicle that is already heavily used in terms of space requirements. Indeed, like cameras and Lidars, all distance detection devices considered by car manufacturers must be positioned in strategic locations on the vehicle, and these locations are relatively limited and already crowded.

[0006] To address space constraints, object detection was considered using the vehicle's existing lighting, such as the vehicle's front lighting systems or rear signaling systems. This involved integrating a distance detection sensor within the vehicle's lighting and / or signaling system, which utilizes the light sources of the lighting or signaling systems—generally LEDs (or light-emitting diodes)—and modulating the light beam emitted by these LEDs. The modulation of the light beam consists of high-frequency coding performed by a coding unit (called a "driver" in Anglo-Saxon terminology).The coded light signals generated by the LEDs are transmitted through the protective glass of the lighting or signaling system to the road scene (which may contain an object), either in front of or behind the vehicle. If the road scene contains an object, the coded light signals are reflected back to the lighting or signaling system and received by a receiver unit housed within said system. The receiver unit typically includes a distance detection sensor, specifically a light sensor (containing, for example, photodiodes), coupled with a processing unit.

[0007] The coded light signals returned to the lighting or signaling system are called return light signals. Coded light signals generated by LEDs emit, in accordance with the automotive standard, what is called "white" light. For this reason, the light emitted by the LEDs has a yellow color spectrum and a blue light peak. The blue light peak, also called the blue peak, constitutes the region of interest in the spectrum of the return light signals. However, the distance sensor within the lighting or signaling system receives not only the return light signals but also an ambient light flux, such as sunlight. Since the sunlight flux has a broad spectrum with a continuous component, not only does its spectrum encompass the blue light peak of the return light signal, but its intensity also saturates the distance sensor.When saturated, the distance sensor can no longer distinguish the blue light peak. For example, when the distance sensor has photodiodes with a relatively wide sensitivity that covers almost the entire visible spectrum, then only a portion of the ambient light spectrum is sufficient to saturate the distance sensor. Even when a bandpass filter is added to the distance sensor to limit the width of the received spectrum to the width of the area of ​​interest, the intensity remains insufficient. The energy of the light beam from the sun prevents the distance sensor from distinguishing the peak of blue light.

[0008] There is therefore a real need for a technology that limits the influence of ambient light flux on the presence sensor. Summary of the invention

[0009] To address the aforementioned problems of saturation of the distance detection sensor, the applicant proposes a light beam receiving device comprising an active optical filter, located upstream of the distance detection sensor and whose opacity can vary according to the energy intensity of the received light beam.

[0010] According to a first aspect, the invention relates to a device for receiving a light beam, said light beam comprising a continuous component of ambient light and a light signal modulated by means of a high-frequency light code, said receiving device comprising: • a photodiode-based light sensor, suitable for detecting the light beam, and • an active optical filter, positioned upstream of the light sensor and adapted to dynamically control an energy intensity of the light beam received by the light sensor in order to highlight the light signal modulated with respect to the continuous component of the ambient light.

[0011] This light beam receiving device (more simply called the receiving device) has the advantage of being able to increase or decrease the transmittance of the active optical filter in order to optimize the proportion of the modulated light signal in the light beam reaching the light sensor, the transmittance being maximum when the proportion of the continuous component of ambient light is low in intensity in the light beam (for example at night) or, on the contrary, minimum when the proportion of the continuous component of ambient light in the light beam is high (for example in the presence of sunlight).

[0012] Those skilled in the art will understand from the following description that the invention aims to control the transmittance of the active optical filter located upstream of the light sensor. The filter's transmittance corresponds to a state of opacity of the filter, or state of occultation of the filter, and indicates the filter's capacity to allow more or less light rays from the light beam to pass through. The filter's transmittance is high when the filter allows a maximum of light rays to pass through and, conversely, low when the filter absorbs a large part of the light beam and allows a minimum of light rays to pass through. The filter's opacity is high when the filter absorbs a large part of the light beam and allows a minimum of light rays to pass through, and is low when it does not. The filter's opacity state is defined as the state of transparency where the filter allows maximum light transmission. It can be any state of opacity or blackout between a transparent or nearly transparent level, where the filter allows maximum light transmission, and an opaque level where the majority of light is absorbed by the filter, allowing a minimum amount of light to pass through. As explained later, the filter's opacity state is related to the transmittance and / or bias voltage applied to the filter.

[0013] By "high frequency" is meant a pulsed signal at more than 1 MHz, i.e. a signal consisting of pulses of less than ips. Preferably, the signal is encoded using pulses of duration less than 200ns, preferably less than 50ns, preferably 10 or 20ns.

[0014] Advantageously, the light sensor includes at least one single-photon avalanche diode (known to those skilled in the art by the Anglo-Saxon abbreviation SPAD) which allows the detection of photons with high temporal resolution.

[0015] Advantageously, the sensor comprises a substrate on which the photodiodes are arranged, preferably arranged in an orthogonal matrix arrangement.

[0016] Preferably, the diodes of the light sensor are arranged to form acquisition modules comprising at least one photodiode, preferably a plurality of photodiodes, for example 15 or more. The acquisition modules may have an equal or variable number of diodes, for example, a variable number depending on the positioning of the acquisition module within the light sensor. It is understood that a light sensor equipped with a plurality of acquisition modules makes it possible to associate an energy intensity received by the acquisition module with spatial data, for example angular data, corresponding to a light beam reaching the acquisition module. This light beam itself corresponds to an area of ​​the scene seen by the detection device.

[0017] It is understood that increasing the number of acquisition modules implies reducing the number of photodiodes per acquisition module, unless the sensor area is increased, thus increasing costs and size, which requires using a reduced number of photodiodes. In this respect, it should be noted that reducing the number of photodiodes per acquisition module increases the risk of saturation of the acquisition modules in bright light and decreases the chances of detecting photons. The sensor's dynamic range, that is, its ability to generate useful information in both extreme situations of low and high received energy intensity, is therefore dependent on this reduction. The present invention aims to allow the sensor's sensitivity to be adapted to distant extreme situations, which is particularly relevant for a sensor with a large number of acquisition modules.

[0018] In addition to the characteristics mentioned in the preceding paragraph, the light beam receiving device according to one aspect of the invention may have one or more additional characteristics from among the following, considered individually or in all technically possible combinations: • The active optical filter comprises a layer of an active material having a variable opacity depending on a bias voltage applied to said layer of active material. • The active material layer comprises several independent cells, each forming a pixel controlled by a pixel-specific bias voltage. • The active material layer comprises several cells grouped into sectors, each sector being controlled by a sector-specific bias voltage. • The active material layer consists of several cells, with the bias voltage controlling all the cells. • The active material layer is an electrowetting layer formed of cells, each containing a droplet of an electrically conductive liquid that expands or contracts under the effect of a bias voltage applied via electrodes. • The active material layer is a layer of electrochromic material made up of at least one electrolyte and ions ensuring a color change under the effect of a bias voltage applied by electrodes. • The active material layer is a layer of a crystalline material liquids made up of at least two polarizing filters and liquid crystals whose orientation changes under the effect of a polarizing voltage applied by electrodes. • It includes a convergence device positioned upstream of the light sensor to converge the light beam towards said light sensor. • The active optical filter is positioned directly on the front face of the light sensor. • The active optical filter is fixed to a protective wall of the light sensor by means of a protective layer of silicone material. • The silicone material has an optimal refractive index (n), suitable for both the active optical filter and the light sensor. • The active optical filter is positioned at a distance from the light sensor, between two elements of the convergence device. • The bias voltage applied to the active material layer of the active optical filter is controlled by servo control from temperature information provided by the light sensor. • The bias voltage applied to the active material layer of the active optical filter is controlled by servo control from temperature information provided by an external sensor.

[0019] When the filter comprises pixels and the light sensor comprises a plurality of acquisition modules, several embodiments offer particular advantages: • In one embodiment, at least one first pixel of the filter is arranged to correspond to a first acquisition module of the light sensor; that is, substantially all the light filtered by the first pixel is received by the first acquisition module, and the first acquisition module receives only light filtered by the first pixel. It is understood that, according to the teachings of the invention, it is thus possible to individually control the energy intensity of the light beam received by the first acquisition module, in order to highlight the light signal modulated with respect to the continuous component of the ambient light.This allows, in particular, for consideration of situations in which the light beam received by the first acquisition module originates from areas of the scene seen by the light sensor. These areas are illuminated by ambient lighting in a disparate manner, for example, particularly dark or particularly bright compared to the rest of the scene, such that the energy intensity related to the ambient lighting received by the light sensor is particularly low or particularly high. It is clear that filtering adapted to the rest of the scene is then not suitable for the area in question. Thus, it is possible to take into account the disparities in energy intensity depending on the acquisition module. • In another embodiment, a second pixel of the filter corresponds to a plurality of second acquisition modules; that is, substantially all the light filtered by the second pixel is received by the plurality of second acquisition modules, and the plurality of second acquisition modules receives only light filtered by the second pixel. This configuration can be advantageous when the number of pixels available on the filter differs from the number of acquisition modules available on the light sensor, for example, when, due to the filter technology, the filter's transmittance decreases as the density of the pixels increase. This results in a receiving device whose filtering allows it to take into account disparate ambient lighting, moderating the detriment to optical reception performance, while maintaining a high angular resolution for the acquisition modules. In another embodiment, a plurality of third pixels of the filter correspond to the same third acquisition module. This embodiment is particularly relevant when the pixels of the active filter have only a limited number of states, each corresponding to a given opacity level. It is then possible to obtain a higher opacity resolution by activating only a portion of the third pixels corresponding to the third acquisition module. Alternatively, by controlling a portion of the third pixels to block the light received from that portion by the third acquisition module, it becomes possible to reduce the angular field of the light beam reaching the third acquisition module.In this way, it becomes possible to perform light acquisitions in which the light beam reaching the third acquisition module corresponds to a more precise area of ​​the scene, thus improving the accuracy of the spatial data generated by the third acquisition module. If applicable, the third pixels controlled to transmit light preferably have controlled opacity to highlight the modulated light signal against the continuous component of the ambient light. Even more preferably, the third pixels transmitting light have contiguous angular fields in the light beam received by the acquisition module, so that it is possible to discriminate the origin of the received signal. Alternatively, the third pixels form a sector of cells. In another embodiment, a plurality of fourth pixels of the filter corresponds to a plurality of fourth acquisition modules. Depending on the number of fourth pixels and fourth acquisition modules, those skilled in the art will be able to derive the applicable advantages from the embodiments in this list. All or part of these embodiments can be combined within the same receiving device, for example when the angular field of the light beam covered by the acquisition modules is variable and the angular field of the light beam covered by the filter pixels is fixed. Conversely, it is possible that all pixels and all acquisition modules are arranged according to only one of these embodiments.

[0020] According to a second aspect, the invention relates to a lighting system such as a lighting system or a signaling system for a motor vehicle, comprising at least one light module emitting pulsed visible light, modulated by means of a high-frequency light code, characterized in that it further comprises a device for receiving a light beam according to any one of the preceding claims.

[0021] A third aspect of the invention relates to a driving assistance system for a motor vehicle, characterized in that it comprises at least one lighting system according to the preceding claim, combined with at least one other detection device for the detection of an object.

[0022] The term "object" is to be interpreted very generally as any physical object, human being, animal, or any other element that may be found on or near the road or path on which the vehicle is traveling. BRIEF DESCRIPTION OF FIGURES

[0023] Other advantages and features of the invention will become apparent from the following description, illustrated by the figures in which:

[0024] Fig. 1 schematically represents an example of a vehicle equipped with lighting systems according to the invention.

[0025] Fig. 2 schematically represents an example of a light beam receiving device according to the invention.

[0026] Fig. 3A and Fig. 3B schematically represent examples of the receiving device of Fig. 2 in the cases, respectively, of a light beam when the filter transmittance is high and of a light beam when the filter transmittance is low.

[0027] Fig. 4A, Fig. 4B and Fig. 4C schematically represent each an embodiment of the active material layer of the active optical filter of the receiving device of Fig. 2.

[0028] Fig. 5A and Fig. 5B schematically represent two distinct embodiments of the receiving device of Fig. 2.

[0029] Fig. 6 schematically represents several views of a manufacturing method by electrowetting of the active material layer of the active optical filter.

[0030] Fig. 7 schematically represents a method of manufacturing the active material layer of the active optical filter by electrochromism.

[0031] Fig. 8 schematically represents a method of manufacturing the active material layer of the active optical filter using liquid crystals.

[0032] Fig. 9 schematically represents examples of curves of the detection rate and the false detection rate by the light sensor, as a function of the bias voltage applied to the filter and the filter transmittance.

[0033] Fig.1OA, Fig.1OB and Fig.1OC represent, in the form of functional blocks, different examples of tests implemented within the receiving device of Fig.2.

[0034] Figure 11 functionally represents an example of a servo control method for the opacity state of the active optical filter of the receiving device of Figure 2.

[0035] In the figures, identical elements are identified by identical reference numerals. For the sake of readability, the size scales between represented elements are not respected. DETAILED DESCRIPTION

[0036] An example of an embodiment of a light beam receiving device equipped with an active optical filter and an example of an embodiment of a lighting system comprising such a receiving device are described in detail below, with reference to the accompanying drawings. These examples illustrate the features and advantages of the invention. It should be noted, however, that the invention is not limited to these examples.

[0037] An example of a motor vehicle 10 equipped with lighting systems 100, such as lighting systems 110 and signaling systems 120, is shown in [Fig. 1]. The lighting systems 110, for example daytime running lights, are mounted at the front of the vehicle and illuminate the road scene SR in front of the vehicle. The signaling systems 120, for example reversing lights, are mounted at the rear of the vehicle to signal the vehicle's presence to other drivers and / or to illuminate the road scene behind the vehicle when the vehicle is reversing. The example in [Fig. 1] shows a pedestrian 20 in the road scene SR in front of the vehicle 10; this pedestrian 20 may, for example, be walking on the road or crossing the road in front of the vehicle 10.The 100 lighting systems can be integrated into a vehicle driver assistance system, an assistance system enabling the detection of objects in front of and / or behind the vehicle. These objects can be road signs, safety barriers, sidewalks, etc., but also human beings or animals. In the example of [Fig. 1], the object considered is a pedestrian 20 located in the road scene SR in front of the vehicle 100.

[0038] The lighting system 100 according to the invention can be any basic lighting or signaling system present on a vehicle. The lighting system 100 can, for example, be a daytime running light, a position light, a signal light, a side light strip, a front light grille, or any other An external lighting system, usually integrated on a vehicle to enable its visibility on the road. The lighting system of the invention has a dual function, namely its basic function, which is lighting or signaling, and a function of detecting objects in the vehicle's external environment, particularly the road scene or the roadside.

[0039] Whatever the light system 100, it comprises at least one light module emitting pulsed visible light, modulated by means of a high-frequency light code. This light code is a binary cyclic code composed of a succession of 1s and 0s, the 1s corresponding to a pulse, the 0s to no light emission. This light code is used to modulate the light beam emitted by the LEDs contained in the light module. The LEDs thus emit a succession of light pulses at a high frequency, that is, at a rate of approximately 10 to 20 ns. This modulation by light code is imperceptible to the human eye; it is invisible to humans. The light beam thus modulated at a high frequency and perceived as a continuous light beam by humans can be used for object detection and, therefore, constitute one of the three means of redundancy for object detection.

[0040] The high-frequency modulated light beam is sent by the light module towards the road scene and, when it encounters an object, it is reflected back to the light system, which contains a light beam receiver 200, an example of which is shown in [Fig. 2]. This light beam receiver 200, more simply called the receiver, includes a light sensor 210 adapted to receive the light beam. This light sensor 210 includes one or more photodiodes designed to capture the light radiation and convert it into an electrical signal. The light sensor 210 can be a SPAD (Single-Photon Avalanche Diode) type photodetector comprising one or more single-photon avalanche diodes, the particularity of which is, in particular, to detect single photons providing short-duration trigger pulses.

[0041] The light sensor 210 of the receiving device 200 shown in [Fig. 2] comprises a sensor chip 214 and a protective wall 213 to protect the sensor chip 214. The protective wall may be, for example, a protective glass or a protective film. The sensor chip 214 and the protective wall 213 are separated by an intermediate layer 212, for example, an air layer or any other transparent layer having an optimal refractive index that prevents any light reflection between the protective wall 213 and the sensor chip 214. The entire set of elements of the light sensor 210 (namely the sensor chip 214, the protective wall 213 and the intermediate layer 212) are encapsulated in an encapsulation material 211 to form a single sensor.

[0042] According to the invention, the receiving device 200 comprises an active optical filter 220 positioned upstream of the light sensor 210, the upstream position being defined along the direction of the light beam L as shown in Figures 3A and 3B. The active optical filter 220, more simply called the filter, comprises a layer of an active material 221 having variable opacity. The dimensions (length and width) of the active material layer 221 are substantially equal to those of the sensor chip 214. The opacity of the active material layer 221, and consequently of the filter, varies according to the bias voltage applied to this active material layer. The applied bias voltage is determined, as explained below, as a function of the energy intensity (i.e., the radiometric energy flux per unit solid angle) of the light beam L received by the receiving device 200.

[0043] According to an example shown in [Fig. 3A], when the energy intensity of the light beam L is relatively low, i.e., below a predetermined threshold, then the bias voltage applied to the filter 220 is chosen so that the active material layer 221 of the filter is only slightly opaque, i.e., as transparent as possible, so that a maximum of the light beam reaches the sensor chip 214 and, thus, the modulated light signal is as high as possible. According to another example shown in [Fig.[3B] when the energy intensity of the light beam L1 is relatively high, i.e. above a predetermined threshold, then the bias voltage applied to the filter 220 is chosen so that the active material layer 221 of the filter is opaque, i.e. with low transmittance, and that, consequently, only the L2 part of the light beam reaches the sensor chip 214, the L2 part of the light beam containing the modulated light signal.

[0044] The variable opacity active material layer 221 can be produced using several technologies, explained below, which are known technologies but for applications in technical fields different from that of vehicle lighting systems. Regardless of the technology chosen, the active material layer 221 can be formed of several cells 222, controlled independently or not. The number of cells 222 constituting the active material layer 221 can vary according to several criteria such as, for example, the dimensions of the light sensor 210, the dimensions of the sensor chip 214, the technology chosen for the active material layer 221, the properties and / or accuracy required for the receiving device, etc.

[0045] In an embodiment shown in [Fig. 4A], the cells 222n are independent and each forms a pixel; each cell is controlled independently of the others by its own bias voltage. Each cell 222n1, 222n2, 222n3, etc., also called a pixel, can thus exhibit a different opacity from that of the neighboring cells 222n4, 222n5, etc.

[0046] In another embodiment, shown in [Fig. 4B], the cells 222 of the active material layer 221 are grouped into sectors 223; each sector 223 is controlled independently of neighboring sectors by a sector-specific bias voltage. In other words, in the embodiment of [Fig. 4B], all the cells 222 of the same sector 223, for example cells 222a, 222b, 222c, and 222d, have the same opacity, but the cells 222e, 222f, 222g, and 222h of another sector may have a different opacity than cells 222a, 222b, 222c, and 222d.

[0047] In yet another embodiment, shown in [Fig. 4C], all the cells 222i of the active material layer 221 are controlled by the same bias voltage. Thus, all the cells 222i of the active material layer 221 exhibit the same opacity. The filter 220 then has a uniform opacity over its entire surface.

[0048] As shown in [Fig. 2], the filter 220 of the receiving device 200 is positioned upstream of the light sensor 210, i.e., in front of the light sensor 210. In one embodiment, the filter 220 can be positioned directly on the front face of the light sensor 210, i.e., it is attached to the protective wall 213 of said light sensor. The filter can then be fixed to the light sensor, for example, by means of a layer of silicone material 230 deposited between the protective wall 213 of the light sensor and said filter 220. The layer of silicone material 230, also called the fixing layer, is made of silicone material having an optimal refractive index n, suitable for both the filter 220 and the light sensor 210.In other words, the silicone material is chosen so as to limit, and preferably avoid, internal light reflections (i.e. between the filter and the protective wall) so as not to pollute the light beam received by the sensor chip 214.

[0049] According to certain embodiments of the invention (Figures 5A and 5B), the receiving device 200 comprises a light beam convergence device 240, positioned upstream of the light sensor 210 so as to converge the light beam L entering the lighting system towards the light sensor 210 and, in particular, towards the sensor chip 214. In one of these embodiments, shown in [Fig. 5A], the convergence device 240 comprises a single convergence element 241, for example a converging lens, positioned upstream of the "filter 220 and light sensor 210" assembly, at a predefined distance d1. This embodiment has the advantage of being compact and space-saving. In another embodiment, shown in [Fig. 5B], the filter 220 is positioned at a distance d2 from the light sensor 210; it is therefore not attached to the protective wall 213 of the light sensor. In this embodiment of [Fig. 5B], the convergence device 240 comprises two convergence elements 241, 243, for example converging lenses, and one divergence element 242, for example a diverging lens. The light sensor 210 is positioned downstream of the convergence device 240, and the filter 220 is positioned between the convergence elements 241, 243 and the divergence element 242.More specifically, the filter 220 is positioned between the first convergence element 243 and the divergence element 242, and the second convergence element 241 is positioned between the divergence element 242 and the light sensor 210. This embodiment has the advantage of separating the filter 220 from the light sensor 210 and thus avoiding the layer of silicone material between the filter and the protective wall of the light sensor.

[0050] As explained previously, the active optical filter 220 comprises a layer of an active material 221 having variable opacity, depending on the bias voltage applied to said layer of active material. Several technologies can be used to produce the layer of active material. In one embodiment, shown in [Fig. 6], the layer of active material 221 is an electrowetting layer formed of cells 224, each containing a droplet 224 of an electrically conductive liquid that expands or contracts under the effect of a bias voltage applied via an electrode. This electrowetting technology is based on modifying the wetting properties of a generally hydrophobic surface by applying an electrical voltage between a solid and a conductive liquid.For this purpose, electrowetting cells 224 are arranged against each other to form an electrowetting layer. Each cell 224 is made of a transparent hydrophobic material 224b and contains within it a droplet of conductive fluid 224a, more simply called a droplet. The conductive fluid can be, for example, an electrically conductive oil.

[0051] When an electrical voltage is applied to an electrowetting cell 224, via an electrode, the droplet 224a expands or contracts. Indeed, depending on the fluid used, two configurations can occur: • Either the droplet 224a is dilated in its natural state and contracts when subjected to an electrical voltage, • Either the droplet 224a is contracted in its natural state and when subjected to an electrical voltage it expands.

[0052] Regardless of the configuration, examples of retracted and expanded droplet 224a are shown in [Fig. 6]. Drawings A1, B1, and C2 show a retracted droplet 224a, while drawings A2, B2, and C1 show an expanded droplet 224a. In particular, drawings A1 and A2 show a single retracted and expanded droplet 224a, respectively. Drawings B1 and B2 show several electrowetting cells 224 when the droplet 224a is retracted and expanded, respectively. Drawings C1 and C2 show a portion of an active material layer 221 of the electrowetting layer type containing an electrowetting cell 224 when the droplet 224a of the cell is expanded and retracted, respectively.Drawings C1 and C2 show in particular that an electrowetting cell 224 is formed between two horizontal walls 224d and two vertical walls 224c, each made of a transparent film, a glass plate, or any other transparent material. Several cells 224 are positioned side by side in the same plane and form an electrowetting layer, or active material layer 221. Thus, when the droplets 224a are contracted, the active material layer 221 is transparent to the light beam, and when the droplets 224a are expanded, the active material layer 221 is opaque and filters the light beam.

[0053] In other words, in the embodiment of the invention where the active material layer is an electrowetting layer 224, said electrowetting layer is opaque when a bias voltage is applied to the filter 220 and this same electrowetting layer is transparent when the bias voltage is zero; alternatively the transparent or opaque effect of the electrowetting layer can be reversed depending on the fluid chosen for the droplets of the electrowetting layer.

[0054] According to one embodiment, the droplets 224a of the electrowetting layer can be tinted in a predefined color, allowing the filtering to be adapted to certain wavelengths of the light beam. For example, it is advantageous for the droplets to be tinted blue, so that they do not allow the light from the blue light peak to pass through.

[0055] In one embodiment, shown in [Fig. 7], the active material layer 221 is a layer of an electrochromic material 225 formed of at least one electrolyte and ions ensuring a color change under the effect of the bias voltage applied by an electrode. An electrochromic material has the advantage of changing color reversibly when an electrical pulse is applied to it, the color change being reversible by reversing the polarity of the bias voltage. An example of an electrochromic material layer 225 is represented in drawing A of [Fig. 7]. This electrochromic layer 225 is in the form of a sandwich structure made up of several sublayers such as: • two transparent support substrates 225e, positioned parallel to each other on either side of the electrochromic assembly to ensure the mechanical stability of the assembly, • two transparent electrodes 225a, each positioned along one of the support substrates 225e, to apply the bias voltage to the electrochromic assembly, • two 225b ion storage layers, each positioned along one of the electrodes and made from the same ionic chemical compound or from different ionic chemical compounds (e.g., nickel oxide and / or tungsten oxide), the ions of these compounds ensuring the movement of the chemical species responsible for the color change, and • an electrolyte, positioned at the center of the sandwich structure to allow the passage of electric current by movement of ions but without movement of electrons.

[0056] An example of an electrochromic material layer, used in a glazing application, is shown in Drawing B of [Fig. 7] to illustrate examples of opacity that can be obtained using this electrochromic technique. In the embodiment of the invention where the active material layer is an electrochromic material layer 225, said electrochromic material layer is opaque when a bias voltage is applied to the filter 220 and this same electrochromic material layer is transparent when the polarity of the bias voltage is reversed.

[0057] In another embodiment, shown in [Fig. 8], the active material layer 221 is a layer of liquid crystal material 226 comprising a first polarizing filter 226a, a second polarizing filter 226b, and a liquid crystal layer 226c positioned between the first and second polarizing filters 226a and 226b. The liquid crystal layer 226c comprises two transparent plates 226d enclosing liquid crystals 226e. The two polarizing filters 226a and 226b are arranged parallel to one of the transparent plates 226d and each has a polarization direction perpendicular to the polarization direction of the other polarizing filter.The inner faces of the transparent plates 226d each have an array of transparent electrodes 226f allowing the application of a potential difference, causing a change in the orientation of the liquid crystals and thus a variation in the transparency of the liquid crystal material layer. Drawing A in [Fig. 8] shows a liquid crystal material layer 226 in the case where the bias voltage V, applied to the filter 220, is less than . a predefined threshold voltage Vseuii: the liquid crystals then form a helical structure causing a rotation of the polarization of the light beam L passing through the liquid crystal layer; the liquid crystal material layer 226 is then transparent to the light L. Drawing B of [Fig.8] shows the liquid crystal material layer 226 in the case where the bias voltage V, applied to the filter 220, is greater than the predefined threshold voltage Vseuii: the liquid crystals are then aligned and the polarization remains unchanged.Since one of the polarizing filters has a polarization direction extending in a first plane, for example a horizontal plane xz, and the other polarizing filter has a polarization direction extending in a second plane perpendicular to the first plane xz, for example a vertical plane yz, the light beam L is transmitted only when the liquid crystals form a helical structure, modifying the polarization direction of the light beam L. Thus, in the embodiment of the invention where the active material layer is a liquid crystal material layer 226, said liquid crystal material layer is transparent when the bias voltage applied to the filter 220 is less than a predefined threshold voltage and opaque when the bias voltage applied to the filter 220 is greater than this same threshold voltage.

[0058] As explained previously, the light signals received by the receiving device 200 comprise both white light, which is emitted by the LEDs of the lighting or signaling system and reflected by the object, and ambient light. In particular, the receiving device 200 receives the blue peak constituting the region of interest in the spectrum of the returning light signals, as well as a continuous component of the ambient light flux. The filter 220 of the detection device is intended to filter the light flux L reaching the light sensor 210: • Either by reducing its transmittance to avoid saturation of the light sensor, for example during the day when the ambient light flux is high due to the sun; indeed, a light beam that is too high leads to saturation of the light sensor and the generation of false detections (called "Dark count" in Anglo-Saxon terminology); • Either by increasing its transmittance so that the light sensor receives a maximum of photons contained in the light flux L, for example at night when the light flux reflected by the object is relatively low; indeed, a light beam that is too weak leads to a poor signal-to-noise ratio and the generation of false detections.

[0059] The 220 filter is controlled by means of a bias voltage applied to said filter. This bias voltage is controlled automatically and dynamically so as to control in real time the opacity state of the filter and therefore the amount of light beam reaching the light sensor of the device. Reception 200. Dynamic control of the bias voltage can be achieved by means of a feedback loop, or control loop. This feedback loop is based on determining the temperature within the device to estimate the optimal opacity state of the filter 220. For this purpose, the feedback loop can incorporate a temperature sensor or a light sensor, either internal or external to the sensing device 200. In one variant, the feedback loop sensor includes one or more photodiodes already present in the vehicle's lighting or signaling system, such as, for example, the photodiodes used for the daytime running lights or night lights activation function.In another variant, the feedback loop sensor is the light sensor 210 of the detection device 200; indeed, the temperature reading of the light sensor 210 allows the optimal opacity state of the filter 220 to be estimated and, consequently, the bias voltage to be applied to it.

[0060] Examples of signal response curves are shown in [Fig. 9] which illustrate the signal detected by the feedback loop sensor, i.e., the photon detection rate, and the false detection rate. In particular, drawing A of [Fig. 9] shows a curve S representing the detected signal (and therefore the photon detection rate) and a curve FD representing the false detection rate, as a function of the bias voltage applied to the filter 220 of the device. Detection 200. Diagram B in [Fig. 9] shows a curve S representing the detected signal and a curve FD representing the false detection rate, as a function of the transmittance Φ of filter 220, or the opacity of said filter. These curves S and FD in [Fig. 9] thus show the relationship between the bias voltage and the sensitivity of the light sensor 210, that is, the photon detection rate: if the light beam L received by the detection device 200 is too intense, it is advantageous to decrease the bias voltage to decrease the sensitivity of the light sensor 210; conversely, if the light beam L received by the detection device 200 is too weak, it is advantageous to increase the transmittance of filter 220 to increase the rate of photons detected by the light sensor 210.

[0061] Examples of feedback loop implementation are shown in Figures 10A, 10B, and 10C. These figures 10A, 10B, and 10C functionally represent different examples of determining the opacity to be applied to the active optical filter 220 of the receiving device 200. Figure 10A shows a first example of a feedback loop 510 in which it is observed that the false detection rate DC is greater than the photon rate <e>multiplied by n, which is the target ratio between the false detection rate and the photon rate (step 511). In this case, the bias voltage Vpoiarisation is reduced (step 512). A test (step 513) is then implemented to verify if the photon rate <e>is less than the minimum photon rate Omin (step 513). If the photon rate <e>is less than the minimum photon rate Omin, then the filter transmittance Tfltee is increased (step 514).

[0062] Figure 10B shows a second example of a feedback loop 520 in which it is found that the light sensor 210 is saturated (step 521). A test (step 522) is then implemented to verify whether the false detection rate DC is less than or equal to the photon rate <e>multiplied by the target ratio N between the false detection rate and the photon rate. If this is the case (yes), then the filter transmittance Tfilter is decreased (step 523); if this is not the case (no), then the bias voltage VpoiaHsation is reduced (step 524).

[0063] Figure 10C shows a third example of a 530 feedback loop in which it is found that the photon rate <e>is less than the minimum photon rate Omin (step 531). The bias voltage VpoiaHsation is then increased (step 532) and then a test (step 533) is implemented to verify if the DC false detection rate is less than or equal to the photon rate <e>multiplied by the target ratio N between the false detection rate and the photon rate. If this is not the case (no), then the bias voltage VpoiariSatiOnest is reduced (step 534) and the filter transmittance is increased (step 535).

[0064] Figure 11 shows an example of the servo control method for the detection device 200, in the form of a flowchart 500. This flowchart 500 includes all the steps implemented to control the detection device 200 of the invention. It therefore incorporates some of the implementation examples from Figures 10A, 10B, and 10C and places them in relation to each other within an overall context. This flowchart 500 includes a first step 501 for starting up the method. It then includes a step 502 for obtaining the temperature TSPAd of the light sensor 210, followed by a step 503 for calculating the false detection rate DC. In parallel with steps 502 and 503, the method performs a step 504 for obtaining the photon rate ¢. A step 505 then consists of verifying whether the photon rate <t>is greater than a maximum photon rate <t>max allowed in the detection device 200. If so, then the process 500 continues with steps 522, 523 and 524 identical to those described for [Fig. 1OB], namely a test 522 to verify whether the false detection rate DC is less than or equal to the photon rate <t>multiplied by the target ratio N between the false detection rate and the photon rate, and if "yes", then the filter transmittance Tfl is reduced, and if "no", then the bias voltage Vpoiansation is reduced. Whether it is the filter transmittance Tfl or the bias voltage Vp that has been decreased, the process then includes a step 506 of obtaining the new photon rate. The process then continues with a test 507 in which it is verified whether the photon rate <t>East lower than a minimum photon rate <e>min. If the test result is "yes", then the procedure continues with steps 532, 533, 534 and 535 already described for [Fig. 1OC], namely an increase in the bias voltage Vp (step 532) followed by a test (533) to verify whether the DC false detection rate is less than or equal to the photon rate <h multiplié par le rapport cible n entre taux de fausses détections et photons et, si la réponse au test 533 est « non », alors une réduction tension polarisation         (étape 534) puis augmentation transmittance of the filter (step 535).

[0065] If the response to test 505 of photon rate value <h est « non », alors le procédé se poursuit par test 507 décrit ci-dessus. si la réponse à ce oui les étapes 532, 533 et ou 534, 535 déjà décrites. au si » une fois l’étape d’augmentation de transmittance tf^ exécutée, reboucle début du procédé, c'est-à-dire qu’il réitère partir des 502 504. autrement dit, 500 réitéré en continu depuis 504 jusqu’aux 507, afin d’adapter l’état d’opacité filtre 210 faisceau lumineux l reçu dispositif détection 200 donc d’ajuster aux variations cours temps.

[0066] Although described through a number of examples, variants and embodiments, the light beam receiving device and the lighting system integrating this detection device include various variants, modifications and improvements which will be obvious to a person skilled in the art, it being understood that these variants, modifications and improvements are part of the scope of the invention.< / h> < / h> < / e> < / t> < / t> < / t> < / t> < / e> < / e> < / e> < / e> < / e> < / e>

Claims

Demands

1. A device (200) for receiving a light beam, said light beam (L) comprising a continuous component of ambient light and a light signal modulated by means of a high-frequency light code, said receiving device comprising: - a light sensor (210) based on photodiodes, adapted to detect the light beam, and - an active optical filter (220), positioned upstream of the light sensor and adapted to dynamically control an energy intensity of the light beam (L) received by the light sensor (210) in order to highlight the modulated light signal with respect to the continuous component of the ambient light.

2. Light beam receiving device according to claim 1, characterized in that the light sensor (210) comprises at least one single-photon avalanche diode.

3. Light beam receiving device according to claim 1 or 2, characterized in that the active optical filter (220) comprises a layer of an active material (221) having a variable opacity depending on a bias voltage (Vp;,^^^) applied to said layer of active material.

4. Light beam receiving device according to claim 3, characterized in that the active material layer (221) comprises several independent cells (222n), each forming a pixel controlled by a pixel-specific bias voltage.

5. Light beam receiving device according to claim 3, characterized in that the active material layer (221) comprises several cells (222) grouped into sectors (223), each sector being controlled by a sector-specific bias voltage.

6. Light beam receiving device according to claim 3, characterized in that the active material layer (221) comprises several cells (222i), the bias voltage controlling all the cells.

7. A light beam receiving device according to any one of claims 3 to 6, characterized in that the active material layer (221) is an electrowetting layer (224) formed of cells, each containing a droplet (224a) of a electrically conductive liquid that expands or contracts under the effect of a bias voltage applied via electrodes.

8. Light beam receiving device according to any one of claims 3 to 6, characterized in that the active material layer (221) is a layer of an electrochromic material (225) formed of at least one electrolyte (225d) and ions ensuring a color change under the effect of a bias voltage applied by electrodes.

9. Light beam receiving device according to any one of claims 3 to 6, characterized in that the active material layer (221) is a layer of liquid crystal material (226) formed of at least two polarizing filters (226b) and liquid crystals (226e) whose orientation changes under the effect of a polarizing voltage applied by electrodes.

10. Light beam receiving device according to any one of claims 1 to 9, characterized in that it comprises a convergence device (240) positioned upstream of the light sensor (210) to converge the light beam (L) towards said light sensor.

11. Light beam receiving device according to any one of claims 1 to 10, characterized in that the active optical filter (220) is positioned directly on a front face of the light sensor (210).

12. Light beam receiving device according to claim 11, characterized in that the active optical filter (220) is fixed on a protective wall of the light sensor by means of a protective layer of silicone material (230).

13. Light beam receiving device according to any one of claims 1 to 10, characterized in that the active optical filter (220) is positioned at a distance from the light sensor (210), between two elements (242, 243) of the convergence device (240).

14. A light beam receiving device according to any one of claims 3 to 13, characterized in that the bias voltage (VpOiarisation) applied to the active material layer (221) of the active optical filter is controlled by servo control from from a temperature information provided by the light sensor (210).

15. Light beam receiving device according to any one of claims 3 to 13, characterized in that the bias voltage (Vpoiarisation) applied to the active material layer (221) of the active optical filter is controlled by servo control from temperature information provided by an external sensor.

16. A lighting system (100) such as a lighting system (110) or a signaling system (120) for a motor vehicle, comprising at least one light module emitting pulsed visible light, modulated by means of a high-frequency light code, characterized in that it further comprises a receiving device (200) for a light beam (L) according to any one of the preceding claims.

17. A motor vehicle driving assistance system, characterized in that it comprises at least one light system (100) according to the preceding claim, combined with at least one other detection device for the detection of an object.

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