Optical system for detecting obstacles

Abstract

The invention relates to an optical system (100) comprising: - a photon emitter (121, 122) emitting a high-frequency coded light signal (s1) within a wavelength range; - a photon receiver (321, 322, 323) and means for filtering the reflected light signal (s2), reflected by an obstacle and contained in light heading towards the photon receiver; - obstacle detection means (40) comprising means for calculating a distance to the obstacle according to a demodulation of the reflected light signal (s2) and the light signal (s1) emitted by the photon emitter (121, 122), wherein the filtering means comprises wavelength conversion means (4) capable of shifting a portion of the light heading towards the photon receiver (321, 322, 323) away from the wavelength range.

Description

Optical system for obstacle detection

[0001] The present invention relates to the fields of optics and electronics, and finds a particular application in the automotive field. It relates more specifically to an optical system integrating an obstacle detection function, which can be installed in a vehicle.

[0002] In recent vehicles, light-emitting diode assemblies are commonly used to create external lighting devices such as dipped headlights or signaling lights. These diode assemblies allow energy savings while providing vehicles with light signatures specific to each brand, and are expected to be future means of vehicle communication with each other or with road infrastructure, thanks to optical communication technology such as VLC (for "Visible Light Communication") for example.

[0003] Indeed, the bandwidth of a white light-emitting diode with a side of one millimeter is approximately 2 MHz (MegaHertz), and can therefore be sufficient to enable light communication between vehicles or between a vehicle and a road infrastructure. However, this bandwidth is not suitable for obstacle detection applications. Such an application is generally carried out optically in certain vehicles using LiDAR (Light Detection And Ranging) technology based on an infrared laser transmitter allowing analysis of the reflected signal over a bandwidth of the order of several tens of MegaHertz, or even a few hundred MegaHertz. LiDAR systems on board vehicles are nevertheless very expensive.

[0004] The inventors have, however, discovered that such an obstacle detection application is possible by using light-emitting diodes that emit light in the visible spectrum, by increasing their bandwidth, either by equalization techniques, or by using diodes smaller than 300 micrometers, or by combining these techniques. This application may require the use of a specific type of light-emitting diode driver such as a high-speed driver or a laser driver. The light-emitting diodes used for this application are also blue-light light-emitting diodes adapted to emit white light.

[0005] Thanks to this discovery, the inventors have made it possible to replace the expensive LiDAR technology in a vehicle with specific optical systems based on light-emitting diodes, which perform an obstacle detection function and also carry out regulatory signaling or lighting functions.

[0006] The operation of such an optical obstacle detection system 1 is now represented. The obstacle detection uses, on the face of the vehicle integrating this function, a plurality 12 of photonic emitters, for example in each optical unit of the vehicle when the optical system is intended to detect frontal obstacles, and a plurality of photonic receivers 32, also present in this example in each optical unit of the vehicle. The plurality 12 of photonic emitters comprises for example two blue light-emitting diodes 121, 122, adapted to emit white light.

[0007] The light-emitting diodes 121, 122 each comprise, for example, a layer of Galium-Indium Nitride (InGaN) on which is deposited a light color conversion layer generally called phosphor in the bibliography. Thus, they are suitable for producing a light beam of a daytime running light.

[0008] The plurality 32 of photonic receivers is for example a sensor consisting of a matrix of photon avalanche photodiodes or SPAD photodiodes (from the English "Single-Photon Avalanche Diode") for increasing the reception gain, such as the SPAD photodiodes referenced 321, 322. Of course, lane only comprises two light-emitting diodes and two photodiodes for simplicity. Many more photodiodes are preferentially used, and the daytime running lights can use many more diodes.

[0009] The plurality 12 of light-emitting diodes is capable of emitting a high-frequency coded light signal s1 towards the exterior of the vehicle, and the plurality 32 of photodiodes is capable of receiving a corresponding reflected light signal s2, arriving from the exterior of the vehicle.

[0010] In order to form the high-frequency coded light signal s1, each optical block comprises a source 10 of electrical signals in voltage square waves and a control unit 3, connected upstream of the light-emitting diodes 121, 122. To send the light signal s1, the source 10 provides a square wave signal whose width l of the square waves is, in an exemplary embodiment, approximately 10ns (nanoseconds), the frequency of the signal being 50MHz. The duty cycle of the signal is, in this example, less than or equal to 50%.

[0011] To enable the transmission of this signal having such a high frequency level, the control unit 3 comprises for example a pre-equalization stage, possibly associated with an amplifier stage. It is therefore an electronic device. Instead of or in addition, the light-emitting diodes 121, 122 are chosen to be smaller than 300 micrometers so as to naturally have a cut-off frequency greater than 50 MHz.

[0012] The light signal s1 sent by the diodes 121, 122 encodes a specific sequence of "slots" or light peaks of width l of 10ns, this sequence repeating cyclically. In other words, the light signal s1 is modulated according to a specific data sequence, called modulating. This sequence is defined so as to easily evaluate a time shift between its transmission and its reception as explained below.

[0013] The reflection of the light signal s1 on an obstacle 6 gives rise to the reflected light signal s2 of sufficient light power to be captured by the photodiodes 321, 322.

[0014] The receiving means comprise, in addition to the photodiodes 321, 322, a blue light filter 8 for filtering the light of the reflected light signal s2 so as to allow only the blue component of this light to pass, and a lens 9 focusing this component towards the photodiodes 321, 322. The blue light emitted by the diodes 121, 122 generally has a light intensity lower than that of the illumination of the sun, but approaches it for wavelengths close to 460 nm (nanometers). The modulation of the reflected signal s2 makes it possible to distinguish it from external light pollution in the process of demodulation of this reflected light signal s2.

[0015] More precisely, the photodiodes 321, 322 capture the blue components of the reflected light signal s2 and of the ambient light, for example sunlight, and provide an electrical signal to an electronic control device 13 which amplifies it and provides it to demodulation means 38. The electronic control device 13 optionally comprises, in addition to an amplifier stage, a post-equalization stage. The photodiodes 321 and 322 being SPAD photodiodes, the electrical signal that they provide is equivalent to a count Nb of the photons received as a function of time t by each of the photodiodes 321, 322. Thresholding means 34 adjust the detection level of these photodiodes so as to separate in the intensity of the light signal received by the photodiodes 321, 322, the portion of light intensity due to sunlight.This thresholding corresponds to keeping in the counting signal Nb as a function of time t, only the values ​​extending beyond a number of photons corresponding to the luminous intensity of the blue component of sunlight, which gives rise to a thresholded light signal s3. Such thresholding makes it possible to remove the component due to sunlight from the received electrical signal. Of course, the thresholded light signal is actually an electrical or digital signal corresponding to the thresholding of the received reflected light signal s2.

[0016] The demodulation means 38 comprise the thresholding means 34 which are produced in software or analog manner from a non-thresholded electrical signal from the photodiodes 321, 322.

[0017] The demodulation means 38 also comprise means 36 for correlating the thresholded light signal s3 once demodulated, with the light signal s1 sent by the diodes 121, 122. These correlation means 36 determine a time shift τ between the demodulated thresholded light signal s3 and the light signal s1 sent, and transmit this time shift τ to obstacle detection means 40 of the vehicle. The obstacle detection means 40 convert this time shift τ into a distance relative to the obstacle 6, and therefore make it possible to detect this obstacle. Described otherwise, the demodulation means 38, from the reflected light signal 2 received by the photodiodes 321, 322, are capable of providing the obstacle detection means 40 with at least one value representative of a time shift τ between, on the one hand, the reflected light signal s2 and, on the other hand, the light signal s1 emitted by the photonics 121, 122.

[0018] However, for this optical system to work well under all ambient light conditions, especially during the day and at night, the system elements must be sized accordingly. Especially during the day, to distinguish the reflected light signal s2 from sunlight, the diodes must be slightly oversized to emit strong light peaks.

[0019] Photodiodes must also be sized according to the intensity of these light peaks and sunlight. Indeed, when the light intensity they receive is too high, SPAD photodiodes saturate, being constantly subject to a dead time during which they can no longer emit a signal, this dead time immediately following the arrival of a photon. In other words, they can no longer allow the counting of photons during these dead times and therefore no longer have a linear response according to the light intensity they receive. In this case, obstacle detection no longer works correctly, the signal-to-noise ratio being too low.

[0020] It is therefore also necessary to oversize the photodiodes to avoid their saturation when the vehicle is driving under intense sunlight, and to ensure the obstacle detection function by the optical system whatever the ambient light conditions, which significantly increases the cost of the optical system.

[0021] The present invention aims to remedy at least in part the aforementioned drawbacks by providing an optical system integrating an obstacle detection function, which reduces the parasitic action of the intensity of the sun on the reception by photodiodes of the optical system, of a light signal having been reflected on an obstacle, in a predefined range of wavelengths of this light signal.

[0022] To this end, the invention proposes an optical system, the optical system comprising:- light emitting means comprising at least one photonic emitter capable of emitting a high-frequency coded light signal, said light signal being included at least in a predefined range of wavelengths,- light receiving means comprising at least one photonic receiver capable of receiving a reflected light signal contained in light heading towards the photonic receiver, said light comprising the reflected light signal and uncoded light, the reflected light signal originating from a reflection on an obstacle, of the light signal emitted by the light emitting means, and- means for filtering the light heading towards the photonic receiver,capable of increasing the signal-to-noise ratio between the reflected light signal contained in the light heading towards the photonic receiver and the uncoded light heading towards the photonic receiver,- means for demodulating the reflected light signal received by the photonic receiver, and- obstacle detection means comprising means for calculating a distance to the obstacle as a function of a demodulated signal supplied by the demodulation means and the light signal emitted by the photonic transmitter.According to the invention, the filtering means further comprise wavelength conversion means, capable of absorbing part of the light heading towards the photonic receiver, and re-emitting it in light whose wavelengths are outside the predefined range of wavelengths.,

[0023] By "uncoded light" we of course mean the part of the light heading towards the photonic receiver which does not include the high-frequency coded reflected light signal.

[0024] The predefined wavelength range is a useful range in which the light signal is received for decoding and corresponds, for example, to wavelengths for which the signal-to-noise ratio is most favorable, whereby the light signal may also be present outside the predefined wavelength range.

[0025] When the optical system is mounted in a vehicle, the light signal is emitted by the emitting means towards the exterior of the vehicle, and the receiving means are configured to receive such a light signal having been reflected and arriving from the exterior of the vehicle.

[0026] Furthermore, the filtering means of the optical system other than the wavelength conversion means are, for example, wavelength filtering means, such as, for example, a blue light filter.

[0027] Thanks to the invention, under conditions of high light intensity, the quantity of photons arriving at the photonic receiver, in the predefined range of wavelengths of the high-frequency coded light signal, is reduced homogeneously as a function of time, which allows the photonic receiver to saturate less and to perceive the variations in this quantity of photons due to the high-frequency coded light signal. In other words, the invention improves the signal-to-noise ratio over the predefined range of wavelengths of the reflected light signal received by the photonic receiver when the ambient light is strong. This makes it possible to have a high-performance optical obstacle detection system regardless of the ambient light conditions, by choosing SPAD photodiodes with a longer response time and therefore less expensive.

[0028] The photonic receiver is preferably a photon avalanche photodiode, but of course other types of photonic receiver can be used as alternatives, such as PIN (positive-intrinsic-negative) photodiodes or simple PN (positive-negative) junction photodiodes.

[0029] According to an optional and advantageous characteristic of the invention, the reception means comprise a device for focusing the light directed towards the photonic receiver, upstream of the filtering means. Here, the term “upstream” is defined in relation to the direction of propagation of the light signals directed towards the photonic receiver. The focusing device is, for example, a lens allowing the photonic receiver to cover a larger detection field than it would without this focusing device.

[0030] According to another optional and advantageous characteristic of the invention, the filtering means further comprise a high-pass filter with a cut-off wavelength greater than or equal to the upper limit of the predefined range of wavelengths, and a low-pass filter with a cut-off wavelength less than or equal to the lower limit of the predefined range of wavelengths.

[0031] The high-pass filter allows very little passage of light components with wavelengths shorter than its cutoff wavelength, and the low-pass filter allows very little passage of light components with wavelengths longer than its cutoff wavelength.

[0032] Alternatively, the filtering means comprise a bandpass filter whose high cut-off length is greater than or equal to the upper limit of the predefined wavelength range and whose low cut-off length is less than or equal to the lower limit of the predefined wavelength range. However, such filtering means require several optical devices and are complex to implement.

[0033] In one embodiment of the invention, the wavelength conversion means comprise at least one phosphor element.

[0034] Preferably, the phosphor comprises a phosphorescent material. This material is hereinafter referred to as a “phosphor” in the sense that it is a material having a phosphorescence property. A phosphor is preferably chosen whose decay time or relaxation time is greater than or equal to one millisecond, for example equal to 10 ms. The wavelength conversion means therefore consist, for example, of a phosphor layer K2SiF6:Mn4+, GdAlO3:Mn4+, SrTiO3:Mn4+ or Y2Sn2O7:Mn4+.

[0035] The predefined wavelength range in which the light signal is included is, for example, between 420 and 460 nanometers. The light signal can of course be demodulated in a predefined, narrower wavelength range, for example, between 420 and 450 nm or between 420 and 445 nm (nanometers).

[0036] In the embodiment using a phosphor, the high-pass filter is then preferably located between the focusing device and the wavelength conversion means, the low-pass filter being located between the wavelength conversion means and the photonic receiver. Thus, the ultraviolet rays are filtered before the light passes through the phosphor, in order to be able to excite it only with the blue components of the incident light, then the green, yellow or red light present in the light initially received and in the light converted by the phosphor is filtered. Alternatively, for example if the conversion means deflect the light towards the ultraviolet, the low-pass filter can be located upstream of the conversion means.

[0037] Preferably, the receiving means comprise several photonic receivers and the wavelength conversion means comprise several phosphor elements of different densities and / or thicknesses, arranged side by side so as to form a surface for transmitting light towards the photonic receivers, the phosphor elements of different densities and / or thicknesses being capable of each transmitting, to a separate set of one or more photonic receivers, a light in which the signal-to-noise ratio between the reflected light signal contained in the transmitted light and the uncoded light contained in the transmitted light is a function of the density and / or the thickness of the phosphor element.

[0038] In particular, each phosphor element may be in the form of a layer having a defined thickness. The phosphor elements may be distinct and separated by a non-zero distance. Alternatively, the phosphor elements are integral with each other so as to form a continuous phosphor layer.

[0039] For example, the phosphor has four elements of different thicknesses facing four SPAD photodiodes, each thickness transmitting the incident light to a different photodiode. In another example, the phosphor has four elements of different thicknesses facing seventeen SPAD photodiodes, sets of four or five SPAD photodiodes each receiving the light having passed through an element of different thickness of the phosphor.

[0040] Preferably, one of the phosphor elements of the transmission surface is of zero thickness or density, that is to say that one of the distinct sets of one or more photonic receivers directly receives the light transmitted by the high-pass filter.

[0041] Each distinct set of one or more photonic receptors is therefore associated with a single phosphor element even though they may possibly receive some stray photons from other phosphor elements.

[0042] Preferably, however, the receiving means are configured so that a beam of light rays, transmitted from one of the phosphor elements to a distinct set of one or more photonic receivers corresponding to this element, is distinct from a beam of light rays transmitted from another of the phosphor elements to another distinct set of one or more photonic receivers corresponding to this other element.

[0043] For example, the focusing device brings the light rays orthogonally to the filters, the phosphor elements and the receiving surface of the photonic receivers, the filters being able to be glued to the phosphor elements and the low-pass filter also glued to the receiving surface of the photonic receivers. In another example, anti-crossing means are implemented to prevent interference of a beam of light rays transmitted by a phosphor element, by another beam of light rays transmitted by another phosphor element.

[0044] According to an optional and advantageous characteristic of the optical system according to the invention, the means for demodulating the received light signal generate a reception matrix, each element of which is associated with a group of photonic receivers receiving the light transmitted by a group of phosphor elements comprising all of the different densities or thicknesses of phosphor elements of the wavelength conversion means. In other words, the group of photonic receivers comprises several of the distinct sets of one or more photonic receivers mentioned above. For example, if the conversion means comprise N different phosphor densities, the group comprises N distinct sets each associated with an element of a different density.An element of the reception matrix corresponds, for example, after processing the electrical signals received from the group of photonic receivers, to a pixel of an obstacle detection rendering image, generated by the detection means of the optical system.

[0045] The reception means comprise, for example, means for summing the signals received by the photonic receivers of said group of photonic receivers.

[0046] Thus, the photons counted by the different photonic receivers of the group are added together, which allows for a good signal-to-noise ratio regardless of the ambient light conditions. Indeed, when the ambient light intensity is high, the matrix element will include at least one photon count representative of the light signal having passed through the thickest phosphor element, while when the ambient light intensity is low, the matrix element will include at least one photon count representative of the light signal having passed through the thinnest or least dense phosphor element, the latter possibly being of zero thickness or density.

[0047] The different densities and / or thicknesses of the phosphor elements are also each preferentially adapted to receiving the light signal under different ambient light conditions. The different ambient light conditions correspond, for example, to mid-day ambient light, early-day ambient light, late-day ambient light, and night-time ambient light.

[0048] Furthermore, since the optical system is preferably intended to be installed in a vehicle, the emission means are capable of forming a lighting beam and / or fulfilling a signaling function.

[0049] The invention also relates to a vehicle comprising an optical system according to the invention. The vehicle according to the invention has advantages similar to those of the optical system according to the invention.

[0050] Other characteristics and advantages of the invention will become apparent from the following description on the one hand, and from several examples of embodiment given for informational and non-limiting purposes with reference to the attached schematic drawings on the other hand, in which:

[0051] already commented on in relation to the prior art, represents an optical system for a vehicle integrating an obstacle detection function,

[0052] represents an optical system according to the invention integrating an obstacle detection function, in one embodiment of the invention,

[0053] functionally represents the processing carried out by filtering means on light arriving at photodiodes of the optical system of the,

[0054] is another representation of the means of filtering the light arriving on the photodiodes of the optical system of the, and

[0055] is an explanatory diagram of the filtering carried out by one of the filtering means of the.

[0056] According to an embodiment of the invention shown, an optical system 100 according to the invention comprises elements identical to those of the and referenced in the same way. These elements are therefore not excessively re-detailed, the emphasis being placed on the new elements.

[0057] In particular, the optical system 100 comprises light emission means comprising the plurality 12 of photonic emitters, present for example in each optical unit of a vehicle, and comprising the two blue light-emitting diodes 121, 122, adapted to emit white light. The light-emitting diodes 121, 122 are capable of emitting the high-frequency coded light signal s1 towards the outside of the vehicle, the light signal being included in a predefined range of wavelengths 420 to 430nm.

[0058] The light emission means also comprise the source 10 of electrical signals in voltage square waves and the control unit 3, connected upstream of the light-emitting diodes 121, 122. To send the light signal s1, the source 10 provides a square wave signal whose width l of the square waves is, in this exemplary embodiment of the invention, approximately 10ns (nanoseconds), the frequency of the signal being 50MHz. The duty cycle of the signal is, in this example, less than or equal to 50%. This duty cycle may vary in particular depending on the signaling or lighting function provided by the light-emitting diodes 121, 122.

[0059] As explained previously, the control unit 3 is an electronic device which may include a component called a “bias tee” to bias the light-emitting diodes, and a pre-equalization stage.

[0060] The reflection of the light signal s1 on the obstacle 6 gives rise to the reflected light signal s2 of sufficient light power to be captured by light receiving means of the optical system 100, comprising the lens 9 which focuses the incident light towards the plurality of photonic receivers 32, also present in each optical unit of the vehicle, and comprising at least the SPAD photodiodes 321, 322, 323, 324 (the latter being referenced). The plurality 32 of photonic receivers comprises a matrix of SPAD photodiodes, the output electrical signals of which are managed by the electronic control device 13 which amplifies it and supplies it to demodulation means 39.

[0061] The electronic control device 13 optionally comprises, in addition to an amplifier stage, a post-equalization stage. Unlike the optical system 1 of the, the demodulation means 39 of the optical system 100 do not comprise thresholding means.

[0062] Indeed, the reception means comprise, in addition to the lens 9, SPAD photodiodes and the electronic control device 13, filtering means 2, 4 and 7, capable of increasing the signal-to-noise ratio between the light signal s2 contained in the light heading from the lens 9 towards the SPAD photodiodes, and the uncoded light contained in this light.

[0063] These filtering means, shown in more detail, make it possible to obtain at the input of the SPAD photodiodes a light representative of the light signal s2 despite the sunlight which interferes with this light signal s2.

[0064] For this, the first filtering means, downstream of the lens 9, is a high-pass filter 2 with a cut-off wavelength of the order of 420 nm, made for example from a layer of tinted resin. This high-pass filter 2 filters the majority of the components of the light at the output of the lens 9, which are of wavelengths lower than 420 nm, that is to say that it prevents ultraviolet rays from passing and allows the other components of the light, including those of the light signal s2, to pass in the direction of the SPAD photodiodes. The gain of this high-pass filter 2 is represented in percentages (up to 100%) on the, as a function of the wavelength.

[0065] This high-pass filtering therefore makes it possible to exclude very energetic components of sunlight, which we do not want to excite the second filtering means downstream of the lens 9, which consists of conversion means 4 into the wavelength of the incident light.

[0066] These conversion means 4 consist of deposits of a phosphorescent material, for example deposits of manganese-doped potassium fluorosilicate ceramic (K2SiF6:Mn 4+), on a support placed between the high-pass filter 2 and a third filtering means which is a low-pass filter 7 downstream of the conversion means 4 on the path of the light heading from the lens 9 towards the SPAD photodiodes. The low-pass filter 7 is made for example of a layer of tinted resin. Each deposit corresponding to a phosphor element has a layer of uniform thickness on its support.

[0067] These phosphorus deposits convert some of the blue light passing through them into yellow or red components of light, while the wavelengths of the other part of the blue light passing through them are not changed.

[0068] The light having passed through the conversion means 4 therefore comprises the blue light converted into yellow or red light, the unconverted blue light and the non-blue components of the sun, having been neither filtered by the high-pass filter 2, nor modified when passing through the conversion means 4.

[0069] The low-pass filter 7 then makes it possible to remove the non-blue components of the light having passed through the conversion means 4. The gain of this low-pass filter 7 is represented in percentages (up to 100%) on the, depending on the wavelength. The cut-off wavelength of the low-pass filter 7 is 430nm, so that the light arriving at the SPAD photodiodes is light within the predefined wavelength range 420 to 430nm of the light signal s2.

[0070] In addition, this light has been lightened by a continuous component of blue light thanks to the conversion means 4, which allows the SPAD photodiodes to be less easily saturated and therefore to perceive more easily the light peaks contained in the light signal s2.

[0071] In order to adapt the conversion means 4 to different light intensities that may correspond to different ambient light conditions, the conversion means 4 comprise different phosphor elements of different densities. Thus, the quantity of blue light converted into yellow or red light upon passing through the conversion means 4 depends on the density of the phosphor element through which the blue light passes, these densities each being adapted to different ambient light conditions, as is now explained in relation to the. The phosphor elements are deposits of phosphorescent material each having the same thickness, so as to be able to control the quantity of light converted by each of them. Alternatively, these phosphor elements are deposits of a phosphorescent material of the same density but each having different thicknesses on their support.

[0072] Lamontre shows a portion of the light focused by the lens 9 towards four SPAD photodiodes 321 to 324 forming a surface then treated as a single pixel by the demodulation means 39. Each of these SPAD photodiodes is arranged opposite a phosphor element of different density. Thus:

[0073] - the first SPAD photodiode 321 is opposite a phosphor element 41 of a first density D1, and only receives the light having passed through this phosphor element of first density D1,

[0074] - the second SPAD photodiode 322 is opposite a phosphor element 42 of a second density D2, and only receives the light having passed through this phosphor element of second density D2,

[0075] - the third photodiode SPAD 323 is opposite a phosphor element 43 of a third density D3, and only receives the light having passed through this phosphor element of third density D3, and

[0076] - the fourth SPAD photodiode 324 is opposite a portion of the conversion means 4 devoid of phosphorus deposit and only receives the light having passed through this portion of the conversion means.

[0077] In order to avoid crossings of light rays between the different light channels formed by the different phosphor layers, opaque partitions 51, 53, 55, 57 delimit these channels between the conversion means 4 and the low-pass filter 7, and other opaque partitions 52, 54, 56, 58 delimit these channels between the low-pass filter 7 and the SPAD photodiodes 321, 322, 323, 324 each corresponding to the outlet of one of the channels.

[0078] These opaque partitions are not necessary in the case where the light rays arriving at the SPAD photodiodes 321, 322, 323, 324 are parallel to each other and where the filtering means 2, 4, 7 are glued to each other and to the SPAD photodiodes.

[0079] Depending on the sizing of the SPAD 321, 322, 323, 324 photodiodes, it may even be useful to replace these opaque partitions with a system for mixing the light at the output of the light channels before they arrive at the SPAD 321, 322, 323, 324 photodiodes.

[0080] This configuration of phosphor elements and SPAD photodiodes is reproduced over the entire reception surface of the reception means of the optical system 100, that is to say that each set of four SPAD photodiodes corresponding to a pixel is located opposite four phosphor elements of different densities, one of the densities being zero. These different densities correspond to different ambient light conditions.

[0081] Opaque partitions are possibly present between, on the one hand, the light channels going from a set of phosphor elements to a set of SPAD photodiodes corresponding to a pixel, and on the other hand the light channels going from another set of phosphor elements to another set of SPAD photodiodes corresponding to another pixel, depending on the configuration of the filtering means with respect to the SPAD photodiodes and the sizing of the latter.

[0082] The second density D2 corresponds to ambient brightness in the middle of the day, D2 being strictly greater than the first density D1 which corresponds for example to ambient brightness at the start of the day, and which is strictly greater than the third density D3 which corresponds to ambient brightness at the end of the day.

[0083] In the middle of the day, as shown, the light arriving at the fourth SPAD 324 photodiode is light filtered only by filters 2 and 7 and therefore corresponds to blue light, but which saturates the fourth SPAD 324 photodiode by its intensity. The fourth SPAD 324 photodiode is therefore almost always in a dead time period and therefore does not count all the photons arriving on its surface.

[0084] The light arriving at the first and third SPAD photodiodes 321 and 323 is blue light in the predefined wavelength range 420 to 430nm and of which a DC component has been suppressed by the first and third density phosphor elements D1 and D3. However, in the middle of the day, this blue light is so intense that it saturates the first and third SPAD photodiodes 321 and 323.

[0085] In contrast, the light arriving at the second SPAD 322 photodiode, which is blue light in the predefined wavelength range 420 to 430nm, is not very intense due to the wavelength conversion performed by the second density phosphor element D2, which has removed a substantial DC component of this blue light. As a result, the second SPAD 322 photodiode is not saturated and provides at the output a signal representative of the reflected light signal s2.

[0086] Similarly, at the beginning of the day, only the third and fourth photodiodes 323 and 324 are saturated, and the second photodiode 322 will receive very little blue light. Only the first photodiode 321 will receive blue light of an intensity allowing a photon count representative of the reflected light signal s2.

[0087] At the end of the day, only the fourth photodiode 324 will be saturated, and the first and second photodiodes 321, 322 will receive very little blue light. Only the third photodiode 323 will receive blue light of an intensity allowing a photon count representative of the reflected light signal s2.

[0088] Finally, in ambient light conditions at night, only the fourth photodiode 324 will receive blue light of an intensity allowing a photon count representative of the reflected light signal s2, the other photodiodes 321, 322, and 323 receiving only very few photons.

[0089] It is therefore understood that each group of SPAD photodiodes corresponding to a pixel comprises at least one SPAD photodiode capable of emitting an output signal representative of the reflected light signal s2, whatever the ambient light conditions.

[0090] Lamontre shows the effects of the conversion means 4 on the luminous intensity, in Watts per square meter (W / m²), of the blue light arriving at these conversion means 4. We place ourselves at the level of a phosphorus element of homogeneous density.

[0091] This light intensity corresponds to a quantity of light Q, varying over time due to the presence of light peaks due to the light signal s2.

[0092] The phosphor element of homogeneous density converts a constant portion Q1 of this luminous quantity as a function of time t, into yellow or red light.

[0093] We therefore obtain a quantity Q2 = Q – Q1 of blue light, varying over time like the light signal s2, with a continuous component much weaker than in the blue light arriving upstream of the conversion means 4.

[0094] Returning to the, the demodulation means 39 sum, for each set of four SPAD photodiodes corresponding to a pixel, the output signals of these pixels. These summing means make it possible to obtain a signal close to that of the reflected light signal s2, whatever the ambient light conditions. Thanks to the conversion means 4, the light peaks corresponding to the blue light of the reflected signal s2 are sufficiently large to make it possible to carry out a demodulation of the reflected signal s2 without using thresholding means, as in the prior art, and to obtain a demodulated signal s4 after demodulation of the electrical signal supplied by the photodiodes. This demodulation can use means for suppressing parasitic coded signals from other vehicles.

[0095] Then the demodulation means 39 use the correlation means 36 to determine a time shift τ of the demodulated signal s4 relative to the emitted light signal s1. This time shift τ is then sent by the demodulation means 39 to the obstacle detection means 40 of the optical system 100, which deduce therefrom a distance from the obstacle 6 to the vehicle integrating the optical system 100.

[0096] Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention. In particular, the emission frequency of the light signal s1 can be different, for example 20 MHz, the width of a slot then being 25 ns.

[0097] Furthermore, the invention is not limited to the use of light-emitting diodes capable of emitting blue light, the high-frequency coded light signal being able to be decoded in another predefined range of wavelengths, the filtering means then being adapted to this other predefined range of wavelengths at reception. In this case, the transmission frequency of the signal is also adapted to this other predefined range of wavelengths of the emitted light.

[0098] Finally, the characteristics of the different variant embodiments of the invention envisaged in this application can be combined to achieve the invention, to the extent that these variants are not incompatible with each other.

Claims

Optical system (100), the optical system (100) comprising:- light emitting means comprising at least one photonic emitter (121, 122) capable of emitting a high-frequency coded light signal (s1), said light signal (s1) being included at least in a predefined range of wavelengths,- light receiving means comprising at least one photonic receiver (321, 322, 323) capable of receiving a reflected light signal (s2) contained in light heading towards the photonic receiver (321, 322, 323), said light comprising the reflected light signal (s2) and uncoded light, the reflected light signal (s2) originating from a reflection on an obstacle (6), of the light signal (s1) emitted by the light emitting means, and- means for filtering the light heading towards the photonic receiver (321, 322, 323),capable of increasing the signal-to-noise ratio between the reflected light signal (s2) contained in the light heading towards the photonic receiver (321, 322, 323) and the uncoded light heading towards the photonic receiver (321, 322, 323),-,- means for demodulating (39) the reflected light signal (s2) received by the photonic receiver (321, 322, 323), and- obstacle detection means (40) comprising means for calculating a distance to the obstacle as a function of a demodulated signal supplied by the demodulation means (39) and the light signal emitted (s1) by the photonic transmitter (121, 122),the optical system (100) being characterized in that the filtering means further comprise wavelength conversion means (4), capable of absorbing part of the light heading towards the photonic receiver (321, 322, 323). 322, 323), and to re-emit it in light whose wavelengths are outside the predefined range of wavelengths. The optical system (100) of claim 1, wherein the photonic receiver (321, 322, 323) is a photon avalanche photodiode. Optical system (100) according to claim 1 or 2, in which the receiving means comprise a device (9) for focusing the light heading towards the photonic receiver (321, 322, 323), upstream of the filtering means. Optical system (100) according to any one of claims 1 to 3, wherein the filtering means further comprises a high-pass filter (2) with a cut-off wavelength greater than or equal to the upper limit of the predefined range of wavelengths, and a low-pass filter (7) with a cut-off wavelength less than or equal to the lower limit of the predefined range of wavelengths. Optical system (100) according to claims 3 and 4 together, wherein the high-pass filter (2) is located between the focusing device (9) and the wavelength conversion means (4), the low-pass filter (7) being located between the wavelength conversion means (4) and the photonic receiver (321, 322, 323). Optical system (100) according to any one of claims 1 to 5, wherein the wavelength conversion means (4) comprise at least one phosphor element. The optical system (100) of claim 6, wherein the phosphor comprises a phosphorescent material. An optical system (100) according to any one of claims 1 to 7, wherein the predefined range of wavelengths is between 420 and 460 nanometers. Optical system (100) according to any one of claims 1 to 6 and claims 7 and 8 taken in dependence on claim 6, in which the receiving means comprise several photonic receivers (321, 322, 323) and in which the wavelength conversion means (4) comprise several phosphor elements (41, 42, 43) of different densities (D1, D2, D3) and / or thicknesses, arranged side by side so as to form a surface for transmitting light towards the photonic receivers (321, 322, 323), the phosphor elements of different densities (D1, D2, D3) and / or thicknesses being capable of transmitting each to a separate set of one or more photonic receivers (321, 322, 323), a light in which the signal-to-noise ratio between the reflected light signal (s2) contained in the transmitted light and the uncoded light contained in the transmitted light is a function of the density (D1, D2,D3) and / or the thickness of the phosphor element., An optical system (100) according to claim 9, wherein the receiving means (32) are configured so that a beam of light rays transmitted from one of the phosphor elements to a distinct set of one or more photonic receivers (321, 322, 323) corresponding to that element, is distinct from a beam of light rays transmitted from another of the phosphor elements to another distinct set of one or more photonic receivers (321, 322, 323) corresponding to that other element. Optical system (100) according to claim 9 or 10, in which the means for demodulating (39) the received light signal (s2) generate a reception matrix, each element of which is associated with a group of photonic receivers (321, 322, 323) receiving the light transmitted by a group of phosphor elements comprising all of the different densities (D1, D2, D3) or thicknesses of phosphor elements of the wavelength conversion means (4). Optical system (100) according to claim 11, wherein the receiving means (32) comprise means for summing the signals received by the photonic receivers (321, 322, 323) of said group of photonic receivers (321, 322, 323). Optical system (100) according to any one of claims 9 to 12, wherein the different densities (D1, D2, D3) and / or thicknesses of the phosphor elements (41, 42, 43) are each adapted to reception of the reflected light signal (s2) under distinct ambient light conditions. Optical system (100) according to any one of claims 1 to 13, in which the emission means are capable of forming an illumination beam and / or of fulfilling a signaling function. Vehicle comprising an optical system (100) according to any one of claims 1 to 14.

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