FR3124865A1 - Spatial light modulator for holographic image projection device - Google Patents

Abstract

The present invention relates to a spatial light modulator (32) intended to be illuminated by coherent light sources to form a holographic image, said modulator comprising:- a substrate on which is formed at least one lattice of waveguides defining a holographic image resolution; and- at each intersection between two waveguides of a lattice, are deposited two chains of nanoparticles of a plasmonic material and nano-drops of a material with optically controllable index change, each of said chains of nanoparticles being aligned in the direction of one of the two waveguides of the intersection and said nano-drops being deposited above said chains of nanoparticles. Figure for abstract: Figure 6

Description

Spatial light modulator for holographic image projection device

The present invention lies in the general field of dynamic holography, applicable to holographic image projection devices such as 3D displays or augmented reality systems embedded in vehicles, in particular autonomous vehicles.

Technology background

Holography is a method of restoring a 3D (three-dimensional) image based on interference figures (commonly called holograms) and diffraction phenomena to reconstruct in 3D a wave front emitted from an object towards an observer. . The use of holography for 3D image reconstruction and visualization is a possible solution because it does not cause headaches or other discomfort that other 3D technologies can cause.

Augmented reality, known as AR (Augmented Reality), which is increasingly found in the automotive field, is a technological evolution of Head Up Display (HUD) systems. ). Essentially, a VTH system includes a Picture Generation Unit (PGU) that generates an image. The VTH system also includes an optical system formed by several mirrors, possibly adjustable, and adapted so that an observer sees the image in a zone located beyond the windshield at a projection distance (approximately 2 meters in front of the driver) and at a certain angle relative to the horizontal by an optical system. A “VTH” system makes it possible to display, for example, speed information, pictograms or even information on the vehicle in the field of vision of the driver of the vehicle when the latter is driving this vehicle.

Augmented reality in the automotive field takes the form of one or more virtual images projected at a distance of approximately 7 meters in front of the windshield (see more). Virtual reality images can be superimposed on images from a HUD system to, for example, highlight road events, virtually illuminate a GPS track, etc. There illustrates an example of superimposition of an image from a VTH system (image 1) superimposed with an image from an AR system (image 2).

Current AR systems adapted for the automotive field are based on the integration of several image generation units (or a single unit divided into two) and two optical paths implemented by refractive optic mirrors: one for the propagation of an image of a VTH system and the other for the propagation of an image of an AR system.

The main defect of current systems is their size: AR systems entirely based on conventional optics have minimum volumes approaching 20 liters while VTH systems have a volume of around 5 liters. Current VTH and AR systems are difficult to integrate without reducing their size.

3D displays for the automotive sector are one of the vehicle trends of the future for integration in the cockpit (combined, central screen) but also for integration as a conversational assistant. Human-Machine interfaces would then be more intuitive because the interaction with 3D interfaces is more intuitive compared to an interaction with classic 2D interfaces.

Existing 3D displays are based on autostereoscopy (with or without eye tracking) which produces a different image for the left eye and for the right eye of an observer or include multiple screens layers (in English "multilayer") which are equipped with several LCD panels to produce several image planes at different depths.

Autostereoscopic 3D displays suffer from the "vergence/accommodation" conflict, i.e. the observer focuses on the screen but the 3D content springs in front of this screen. The 3D experience can be degraded or even “denied” by the observer. As for multilayer systems, they only allow a display on several discrete planes in depth or in gush.

Spatial light modulators, commonly called SLM (Spatial Light Modulator) can also be used as a holographic image display of an AR system or as a 3D display.

The modulation mechanism of a spatial light modulator is based on a method that changes the properties of the modulating material and how the spatial field of an incident light beam is changed. Various methods including mechanical, electro-optical, thermo-optical and magneto-optical effects can be used to modify the properties of the modulating material of a spatial light modulator which interacts with incident light and transforms its spatial field distribution. One of the most commonly used modulation mechanisms today is the electro-optical spatial light modulator containing liquid crystals as modulating material (LC-SLM from the English “Liquid Crytal Spatial Light Modulator”). These LC-SLM type modulators are based on a liquid crystal pixel array which, by modulating the phase of coherent light, generates a hologram at any time to produce a 2D or 3D video at the output of an optical system. The current silicon/liquid crystal technologies of this type of modulator today make it possible to obtain pixel sizes of 1 to 4 μm, and image resolutions of up to 4160×2464 pixels.

State-of-the-art AR systems that use spatial light modulators do not have sufficient resolution to allow democratization of “dynamic” holography, that is to say driven by a control unit, in particular in the automotive field.

Indeed, on the one hand, the visual field of a holographic image, due to a diffraction angle of the hologram, is linked to the size of a pixel of the modulator and the number and the size of the pixels play a role. on the resolution of the holographic image. Moreover, the product of the size of the image by the field of view is proportional to the number of pixels of the modulator. Thus, to obtain a hologram of pixels, which would make it possible to obtain a correct resolution of a holographic image, a field of view of 60° and an image of 50 cm are necessary. However, current modulators only allow visual fields of approximately 20°, which induces insufficient resolutions of the holographic images.

There is a need for spatial light modulators that provide high resolution holographic images and provide fields of view beyond those produced today by spatial light modulators.

Summary of the present invention

An object of the present invention is to increase the resolution of spatial light modulators.

Another object of the present invention is to improve holographic image projection devices.

According to a first aspect, the present invention relates to a spatial light modulator intended to be illuminated by coherent light sources to form a holographic image, said modulator comprising:
- A substrate on which is formed at least one lattice of waveguides defining a resolution of the holographic image; And
- at each intersection between two waveguides of a lattice, are deposited two chains of nanoparticles of a plasmonic material and nano-drops of a material with optically controllable index change, each of said chains of nanoparticles being aligned in the direction of one of the two waveguides of the intersection and said nano-drops being deposited above said chains of nanoparticles.

According to a particular and non-limiting embodiment, the optically controllable index change material is a liquid crystal.

According to a particular and non-limiting embodiment, the optically controllable index change material is a photostrictive or phase loading material.

According to a particular and non-limiting embodiment, the plasmonic material is gold, silver, copper or aluminum.

According to a particular and non-limiting embodiment, the core-shell structure of the plasmonic material is of the metal-dielectric type.

According to a particular and non-limiting embodiment, the waveguides are formed from a dielectric material.

According to a particular and non-limiting embodiment, the waveguides of a trellis are structured to form a geometric pattern.

According to a second aspect, the present invention relates to a method for generating a holographic image implemented by a spatial light modulator according to the first aspect of the present invention. The method comprises the following steps to activate a pixel of the holographic image: obtaining information concerning the activation of a pair of light sources associated with two waveguides relating to an intersection of a lattice of waveguides 'wave ; emission of a first near-infrared light wave by a light source associated with one of the two waveguides, this wave propagating in said waveguide and exciting chains of nanoparticles deposited in the same direction as said guide wave: and emission of a second near-infrared light wave by a light source associated with the other of the two waveguides, said wave propagating in said other waveguide and exciting chains of nanoparticles deposited in the same direction as this other waveguide.

According to a third aspect, the present invention relates to a holographic image projection device comprising at least one spatial light modulator according to the first aspect of the present invention.

According to a fourth aspect, the present invention relates to a vehicle comprising at least one spatial light modulator according to the first aspect of the present invention.

Brief description of figures

Other characteristics and advantages of the present invention will emerge from the description of the particular and non-limiting examples of embodiments of the present invention below, with reference to the appended FIGS. 1 to 9, in which:

schematically illustrates the projection of images by an augmented reality system and a head-up system of a vehicle, according to the state of the art;

schematically illustrates the projection of images in a vehicle 10, according to a particular and non-limiting embodiment of the present invention;

schematically illustrates the field of vision associated with a driving position of the vehicle 10, according to a particular and non-limiting embodiment of the present invention;

schematically illustrates a holographic image projection device for a vehicle 10, according to a particular and non-limiting embodiment of the present invention.

schematically illustrates a control unit configured to provide the information necessary for the generation of one or more holographic images to a spatial light modulator, according to a particular and non-limiting embodiment of the present invention;

schematically illustrates a spatial light modulator 32 according to a particular and non-limiting embodiment of the present invention;

schematically illustrates an addressing of the pixels by a spatial light modulator 32 according to a particular and non-limiting embodiment of the present invention;

schematically illustrates the implementation of a hologram function by a spatial light modulator 32 according to a particular and non-limiting embodiment of the present invention; And

illustrates a flowchart of the different steps of a holographic image projection method, according to a particular embodiment of the present invention.

Description of the examples of realization

A spatial light modulator, a holographic image projection method and device will now be described in the following with reference in conjunction to FIGS. 1 to 9. The same elements are identified with the same reference signs throughout the description that follows.

According to a particular and non-limiting embodiment, the present invention relates to a very high resolution spatial light modulator which, once illuminated by laser sources, can be integrated as a 3D holographic screen for a 3D display application or inserted into a AR system for example for automotive. The spatial light modulator comprises a substrate on which is formed at least one lattice of waveguides defining a resolution of the holographic image; and at each intersection between two waveguides of a lattice, are deposited two chains of nanoparticles of a plasmonic material and nano-drops of a material with optically controllable index change, each of said chains of nanoparticles being aligned in the direction of one of the two waveguides of the intersection and said nano-drops being deposited above said chains of nanoparticles.

The addressing of the pixels is carried out by the chains of nanoparticles while the phase modulation (the “hologram” function) is carried out by the nano-drops deposited above the nanoparticles.

The use of chains of nanoparticles of a plasmonic material and nano-drops of a material with an optically controllable index change, makes it possible to significantly increase the number of pixels and therefore the resolution of the projected holographic image without one might as well have to increase the size of the optical part of a holographic image projection device such as an RA or VTH system or a 3D display. On the other hand, the integration of such a spatial light modulator in a current AR system allows to improve the resolution of the projected holographic images without the need for additional refractive optics. Their integration can also induce a reduction in the size of the optical part of such a system because the size related to the enlargement of the projected image is less.

In addition, the use of holographic technology for the 3D image display provides comfort for observation compared to other 3D technologies.

Typically, the present invention makes it possible to obtain spatial light modulators having pixel sizes of less than one micrometer, whereas the size of the pixels of current spatial modulators is of the order of 1 to 4 μm.

schematically illustrates the projection of images in a vehicle 10, according to a particular and non-limiting embodiment of the present invention.

There presents a view of the interior of a vehicle 10, in particular of the front part of the passenger compartment of the vehicle 10 comprising in particular the steering wheel, the dashboard, and the windshield 100 of the vehicle 10.

The vehicle 10 corresponds for example to a vehicle with a combustion engine, with electric motor(s) or else a hybrid vehicle with a combustion engine and one or more electric motors. The vehicle 1 thus corresponds for example to a land vehicle, for example an automobile, a truck, a bus.

The vehicle 10 embeds for example a set of sensors configured to obtain data on the environment of the vehicle 10, these data or a part of them being used in particular for driving in autonomous mode of the vehicle 10. This or these sensors correspond for example to sensors of one or more systems for detecting objects in the environment of the vehicle 10, the data obtained from this or these sensors making it possible, for example, to detect objects in the environment of the vehicle 10, for example in front of the vehicle 10. This or these object detection systems are for example associated with or included in one or more driving assistance systems, called ADAS systems (from the English “Advanced Driver-Assistance System” or in French “Advanced driver assistance system”).

The sensor(s) associated with these object detection systems correspond, for example, to one or more of the following sensors:

- one or more millimetric wave radars arranged on the vehicle 10, for example at the front, at the rear, on each front/rear corner of the vehicle; each radar is adapted to emit electromagnetic waves and to receive the echoes of these waves returned by one or more objects, with the aim of detecting obstacles and their distances vis-à-vis the vehicle; and or

- one or more LIDAR (s) (from the English "Light Detection And Ranging", or "Detection and estimation of the distance by light" in French), a LIDAR sensor corresponding to an optoelectronic system composed of a transmitter device laser, a receiver device comprising a light collector (to collect the part of the light radiation emitted by the emitter and reflected by any object located on the path of the light rays emitted by the emitter) and a photodetector which transforms the light collected as an electrical signal; a LIDAR sensor thus makes it possible to detect the presence of objects located in the light beam emitted and to measure the distance between the sensor and each object detected; and or

- one or more cameras (associated or not with a depth sensor) for acquiring one or more images of the environment around the vehicle located in the field of vision of the camera(s).

The vehicle 10 also embeds, for example, a navigation system, which uses, for example, geolocation information provided by a satellite positioning system such as the GPS system (from the English “Global Positioning System” or in French “Système mondial de positioning”) or the Galileo system. This geolocation information is combined with mapping data, in particular road data, to display the route of the route on a map obtained from the mapping data.

The vehicle 10 advantageously embeds a holographic image projection device.

The holographic image projection device comprises for example one or more projectors integrated for example in the dashboard. Such a device for projecting a holographic image or graphic content corresponds, for example, to a 3D display or to an RA or VTH system, which allows the embedding of virtual objects in the driver's field of vision, for example on the windshield. -breeze of the vehicle 10, so as to superimpose the virtual objects on the real road scene. The projection of the holographic image is for example controlled by one or more computers of the on-board system of the vehicle 10, for example by the computer of the infotainment system, called the IVI computer (from the English "In-Vehicle Infotainment" or in French “On-board infotainment”) of the vehicle 10.

The holographic image is advantageously displayed on a surface 101 by projection of the image data in the form of a light beam emitted by a spatial light modulator 32. The surface 101 corresponds for example to an opaque strip arranged on the board of edge of the vehicle 10, for example above and behind the steering wheel with respect to a point of view corresponding to the point of view according to which a driver is supposed to look at the road in front of him when driving the vehicle 10.

The holographic image advantageously comprises a set of graphical objects each representative of a parameter or an operating state of the vehicle 10. By way of example, the set of graphical objects represents parameters or operating state of the vehicle 10 corresponding to all or part of the following information, in any possible combination:

- information representative of instantaneous speed; and or

- information representative of the rotation of an engine shaft (also called tachometer information); and or

- information representative of a mileage travelled; and or

- information representing a fuel level or the state of charge of the battery in the case of an electric vehicle; and or

- information representing the temperature of an engine coolant; and or

- at least one item of information representative of a warning light (for example battery charge indicator, engine oil pressure indicator, engine oil or coolant temperature indicator, brake failure indicator, etc.), corresponding for example to a pictogram displayed or taking on a specific color in the event of an alert; and or

- at least one piece of information representative of a warning light (for example engine oil level light, air bag light (also called airbag), brake pad wear light, etc.), corresponding for example to a pictogram displayed or taking on a determined color in the event of a warning; and or

- at least one item of information representative of an on-board system operating indicator light (positioning, dipped or main beam indicator light, hazard warning light indicator light, rear window demisting indicator light, etc.), corresponding for example to a pictogram displayed or taking on a determined color in the event of the on-board system being put into operation.

the set of graphic objects can also represent contextual or environmental information of the vehicle 10 correspond to all or part of the following information, according to any possible combination:

- information representative of the map of the environment of the vehicle 10, for example obtained from a navigation system on board the vehicle or from a navigation system installed on a mobile communication device (for example a smart telephone (of the "smartphone") connected in wireless communication with the vehicle 10, or more specifically with the on-board system of the vehicle 10 comprising the computer(s) in charge of controlling the projection of the first image and of the second image; and/or

- information representative of the navigation of the vehicle, for example a plot of the route to be followed by the vehicle, the current position of the vehicle, the instantaneous speed of the vehicle, the speed limit applicable on the portion of road on which the vehicle is traveling 10; this information is for example obtained from the navigation system on board the vehicle or from the navigation system installed on a mobile communication device; and or

- information representative of an object detected in the environment, for example the presence of a vehicle preceding the vehicle 10, the presence of a pedestrian or an animal on the roadway in front of the vehicle 10, the presence of a road sign, the presence of a stationary object on the roadway, the presence of a tunnel entrance, etc. ; this or this information is for example obtained from one or more object detection sensors on board the vehicle 10 and for example associated with one or more ADAS systems of the vehicle 10; according to a variant, this information is received from another vehicle or from the infrastructure connected to the vehicle 10 in wireless communication according to a vehicle-to-everything communication mode, called V2X (from the English “vehicle-to- everything”) comprising vehicle-to-vehicle, known as V2V (vehicle-to-vehicle) communication modes, vehicle-to-V2I infrastructure (vehicle-to-infrastructure) and/or vehicle-to-pedestrian V2P; and or

- information representative of an event detected in the environment, for example information on a disturbance on the road, for example an accident, a traffic jam, information on particular climatic conditions and able to disturb traffic (snow, fog, rain, ice); this or this information is for example obtained from one or more object detection sensors on board the vehicle 10 and for example associated with one or more ADAS systems of the vehicle 10; according to a variant, this information is received from another vehicle or from the infrastructure connected to the vehicle 10 in wireless communication according to a vehicle-to-everything communication mode, called V2X (from the English “vehicle-to- everything”) comprising vehicle-to-vehicle, known as V2V (vehicle-to-vehicle) communication modes, vehicle-to-V2I infrastructure (vehicle-to-infrastructure) and/or vehicle-to-pedestrian V2P; according to another variant, this information is received from one or more servers of the “cloud” (or “cloud” in French) via a cellular wireless network of the 4G or 5G type.

Of course, the list of information displayed via the holographic image is given by way of example and is not limited to the examples above.

schematically illustrates a field of vision associated with a driving position of the vehicle 10, according to a particular and non-limiting embodiment of the present invention.

There illustrates the front part of the vehicle 10 in a top view. The field of vision 210 is associated with a point of view 21 which corresponds to the point of view according to which a driver is supposed to look at the road in front of him when driving the vehicle 10. This point of view 21 is for example positioned in the middle of the driver's seat (front left in the direction of travel of the vehicle 10 according to the particular example of the , at the location of the driver's head if the driver was seated in the driver's seat. The point of view 21 is for example positioned in the center of a headrest resting on the driver's seat when the seat is equipped with such a headrest.

The field of vision 210 extends for example around a main axis of vision 211, and covers an area between an upper vertical limit (forming for example an angle of 15° with the axis 211 from the point of view 21) , a lower vertical limit (forming for example an angle of 15° with the axis 211 from the point of view 21), a right lateral limit (forming for example an angle of 20 or 25° with the axis 211 from the point of view 21) and a left lateral limit (forming for example an angle of 25 or 30° with the axis 211 from the viewpoint 21).

A graphic object 2100 corresponding to an element of the holographic image is advantageously projected or displayed inside the field of vision 210, to ensure that the driver looks at the road or the environment in front of the vehicle 10 according to this field of vision. view 210.

The graphic object 2100 depends for example on the type of information projected on the surface 101. The graphic object 2100 corresponds for example to a representation of a warning sign, of a vehicle, for example automobile, or of a pedestrian, an arrow indicating the direction to follow. The graphic object 2100 is for example semi-transparent to allow the driver to see the road environment through this graphic object 2100.

When the projection of the holographic image is intended to alert the driver of the vehicle 10 to a potential danger, the graphic object is for example displayed at the location of an object detected in front of the vehicle 10, to attract the driver's attention to this detected object. The graphic object 2100 corresponds to a virtual element added by embedding or superimposing this virtual element on an element of the real world.

The movement of the graphical object 2100 follows, for example, the movement of an object detected in front of the vehicle 10, the movement of the detected object corresponding, for example, to the movement of the detected object, where applicable, relative to the movement of the vehicle 10. According to a variant, the graphic object 2100 is initially displayed in a first position before following the movement of the detected object.

schematically illustrates a holographic image projection device for a vehicle 10, according to a particular and non-limiting embodiment of the present invention.

The holographic image projection device 3 comprises a control unit 31 configured for the processing of data received from sensors of the vehicle 10 and/or from systems on board the vehicle 10 and/or from remote devices connected to the vehicle 10. The control unit 31 is advantageously configured to supply information necessary for the generation of one or more holographic images from the data received.

The holographic image projection device 3 comprises a spatial light modulator 32 ( ) configured to generate a light beam representative of a holographic image from information coming from the control unit 31.

The holographic image projection device 3 comprises at least one coherent light source (for example laser) 34 formed, for example of RGB laser diode (from the English “Red, Green, Blue”, in French Rouge, Vert Bleu ).

According to a particular and non-limiting embodiment, the light sources are suitable for emitting near-infrared light waves (700 nm to 1600 nm).

The holographic image projection device 3 also comprises a reflective device 33 associated with the spatial light modulator 32. The reflective device 33 is configured to direct the light beam emitted by the spatial light modulator 32 towards the surface 101 for display of the holographic image in the field of view of viewpoint 21.

According to a variant, the holographic image projection device 3 does not include such reflective device(s), the spatial light modulator 32 then being arranged so as to project the light beam directly onto the surface 101.

According to an optional variant embodiment, the holographic image projection device 3 further comprises optical means (for example an arrangement of optical lenses not shown) configured to focus the holographic image in the image plane.

The holographic image projection device 3 is for example configured for the implementation of the operations described with regard to FIGS. 6, 7 and 8 and/or of the steps of the method described with regard to the .

schematically illustrates a control unit 31 configured to provide the information necessary for the generation of one or more holographic images to the spatial light modulator 32, according to a particular and non-limiting embodiment of the present invention.

The control unit 31 corresponds for example to a device on board the vehicle 10, for example a computer.

The control unit 31 is for example configured for the implementation of all or part of the operations described with regard to FIGS. 6, 7 and 8 and/or the steps of the method described with regard to the . Examples of such a control unit 31 include, but are not limited to, on-board electronic equipment such as a vehicle's on-board computer, an electronic computer such as an ECU (“Electronic Control Unit”). The elements of the control unit 31, individually or in combination, can be integrated in a single integrated circuit, in several integrated circuits, and/or in discrete components. The control unit 31 can be made in the form of electronic circuits or software (or computer) modules or else a combination of electronic circuits and software modules.

The control unit 31 comprises one (or more) processor(s) 40 configured to execute instructions for carrying out the steps of the method and/or for executing the instructions of the software or software embedded in the control unit 31 The processor 40 may include integrated memory, an input/output interface, and various circuits known to those skilled in the art. The control unit 31 further comprises at least one memory 41 corresponding for example to a volatile and/or non-volatile memory and/or comprises a memory storage device which may comprise volatile and/or non-volatile memory, such as EEPROM , ROM, PROM, RAM, DRAM, SRAM, flash, magnetic or optical disk.

The computer code of the on-board software or software comprising the instructions to be loaded and executed by the processor is for example stored on the memory 41.

According to different particular embodiments, the control unit 31 is coupled in communication with other similar devices or systems and/or with communication devices, for example a TCU (from the English “Telematic Control Unit” or in French "Telematic Control Unit"), for example via a communication bus or through dedicated input/output ports.

According to a particular and non-limiting embodiment, the control unit 31 comprises a block 42 of interface elements for communicating with external devices, for example a remote server or the "cloud", other nodes of the network ad hoc. Block 42 interface elements include one or more of the following interfaces:

- RF radio frequency interface, for example of the Bluetooth® or Wi-Fi® type, LTE (from English "Long-Term Evolution" or in French "Evolution à long terme"), LTE-Advanced (or in French LTE-advanced );

- USB interface (from the English "Universal Serial Bus" or "Universal Serial Bus" in French);

- HDMI interface (from the English “High Definition Multimedia Interface”, or “Interface Multimedia Haute Definition” in French);

- LIN interface (from English “Local Interconnect Network”, or in French “Réseau interconnecté local”).

According to another particular embodiment, the control unit 31 comprises a communication interface 43 which makes it possible to establish communication with other devices (such as other computers of the on-board system) via a communication channel 430. The communication interface 43 corresponds for example to a transmitter configured to transmit and receive information and/or data via the communication channel 430. The communication interface 43 corresponds for example to a CAN-type wired network (of the 'English "Controller Area Network" or in French "Réseau de Contrôleurs"), CAN FD (from English "Controller Area Network Flexible Data-Rate" or in French "Réseau de Contrôleurs à Flow de Data Flexible"), FlexRay ( standardized by ISO 17458) or Ethernet (standardized by ISO/IEC 802-3).

According to an additional particular embodiment, the control unit 31 can provide output signals to one or more external devices, such as a display screen 440, one or more loudspeakers 450 and/or other peripherals 460 (for example the spatial light modulator 32) respectively via output interfaces 44, 45 and 46. According to a variant, one or the other of the external devices is integrated into the control unit 31.

schematically illustrates a spatial light modulator 32 according to a particular and non-limiting embodiment of the present invention.

The spatial light modulator 32 is intended to be illuminated by the light sources 34 to form a holographic image. These light sources 34 are controlled (activated/deactivated) by information coming from the control unit 31 to form a holographic image. The holographic image corresponds to a set of pixels very often organized in the form of a trellis, with each pixel being associated with information, for example gray levels coded on 8, 10 or 12 bits for each color channel of a given color space. , for example RGB.

The holographic image is for example generated to graphically represent information on the operating state of the vehicle 10 or on the context or the environment in which the vehicle 10 is moving. This information is for example received from sensors and/or systems embedded in the vehicle and measuring vehicle control parameters 10.

The holographic image from the spatial light modulator 32 is projected in the form of a light beam onto the surface 101 by reflecting device 33 ( ).

Of course, the generation and the projection is not limited to a single image but extends to the generation and the projection of a sequence of images, for example at a frame rate equal to for example 24, 30 or 60 frames per second.

The spatial light modulator 32 comprises a substrate, for example made of silica (S _i 0 ₂ ), on which is formed at least one lattice of waveguides defining a resolution of the holographic image.

By waveguide lattice, we mean a set of waveguides organized to form at least one intersection between two waveguides.

For example, the width of each waveguide is of the order of 500 nm and the spacing between the waveguides is of the order of 500 nm.

According to a particular non-limiting embodiment, the waveguides are formed from a dielectric material, for example silica (S _i 0 ₂ ).

According to a particular example of non-limiting embodiment, the waveguides of a trellis are structured to form a geometric pattern.

According to a variant, as illustrated in the , a waveguide lattice forms a matrix of parallel rows and columns of waveguide. Each intersection of two waveguides then corresponds to a pixel of the holographic image. On the example of the , 4 intersections are shown of a waveguide matrix. Each intersection corresponds to a pixel of the holographic image.

Alternatively, a waveguide lattice forms a triangular or hexagonal pattern of waveguides.

According to the present invention, at each intersection between two waveguides of a lattice, are deposited two chains of nanoparticles (nanostructures with a dimension of the order of a nanometer) of a plasmonic material and nano-drops (drops with a dimension of the order of a nanometer) of a material with an optically controllable index change. Each chain of nanoparticles is aligned in the direction of one of the two waveguides of an intersection and the nano-drops are deposited above the chains of nanoparticles as illustrated in the .

For example, nanoparticles have a size of 100 to 250 nm.

The spatial light modulator 32 makes it possible to obtain pixel sizes of less than 500 nm leading to fields of view of more than 60° and to very high holographic image resolution, much higher than those of current holographic images.

In a first operation, information is obtained from the control unit 31 concerning the activation of a pair of light sources 34 associated with two waveguides associated with an intersection of a lattice of waveguides .

In a second operation, a near-infrared light wave is emitted by a light source 34, this wave propagates in a waveguide and interacts with the nanoparticles. The chains of nanoparticles along this waveguide are then said to be excited and then behave like light concentrators at a sub-wavelength scale. A pixel is said to be activated, i.e. it concentrates enough light energy, if and only if two chains of nanoparticles at an intersection are excited simultaneously.

The individual addressing of the pixels of the holographic image is controlled by injection or not of light into the two waveguides of each intersection of a lattice of waveguides, at the appropriate wavelengths, i.e. that is to say corresponding to the respective resonances of the chains of nanoparticles.

According to an example, illustrated in FIG. 7, 4 waveguides are represented forming 4 intersections. Pixel addressing is implemented here by referencing columns x1 and x2 and rows y1 and y2. Two light sources are associated with each waveguide: light sources are associated with lines y1 and y2 and light sources are associated with columns x1 and x2. According to the example, two pixels are activated: a first pixel corresponding to the intersection between column x1 and line y2 and a second pixel corresponding to column x2 and line y1. The first pixel is activated when the light source of line y2 and the light source of column x1 emit a light wave, and the second pixel is activated when the light source of line y1 and the light source of column x2 emit a light wave.

The light sources are controlled using information from the control unit 31.

Note that according to this example, pixel addressing is illustrated with a single waveguide lattice but pixel addressing can also be implemented for multiple overlapping waveguide lattices.

Modulator 32 also implements a so-called hologram function. This function is performed by the nano-drops which provide phase modulation of the visible incident light wave. Indeed, when a pixel is activated, the optical field generated by the chains of nanoparticles exerts on the molecules of the nano-drops (made of a material with controllable change of index) located nearby, an optical couple which has the effect to vary their orientation as shown in . This orientation varies continuously with the optical power, and induces a variation in the index of the material of these nano-drops, in particular along the axis perpendicular to the surface of the substrate. With a sufficient thickness of material with controllable index change and a controlled range of "deposited" power, each pixel can induce a phase shift to a wave reflected on its sub-wavelength surface varying continuously from 0 to 2π.

According to a particular and non-limiting embodiment, the plasmonic material is gold (Au), silver (Al), copper (Cu) or aluminum (Al).

According to a particular and non-limiting example of embodiment, the nano-drops are structured in meso-structured matrices.

According to a particular and non-limiting embodiment, the optically controllable index change material is a liquid crystal.

According to a particular and non-limiting embodiment, the optically controllable index change material is a photostrictive or phase change material.

According to a particular and non-limiting embodiment, the core-shell structure of the plasmonic material is of the metal-dielectric type.

illustrates a flowchart of the different steps of a holographic image projection method, according to a particular and non-limiting embodiment of the present invention. The method is for example implemented by the holographic projection device 3 of the .

In a first step 51, information is obtained from the control unit 31 concerning the activation of a pair of light sources 34 associated with two waveguides associated with an intersection of a lattice of waveguides. wave.

In a second step 52, a first near-infrared light wave is emitted by a light source 34 associated with one of the two waveguides, this wave propagates in this waveguide and excites the chains of nanoparticles deposited in the same direction as this waveguide.

In a third step 53, a second near-infrared light wave is emitted by a light source 34 associated with the other of the two waveguides, this wave propagates in this other waveguide and excites the chains of nanoparticles deposited in the same direction as this other waveguide.

Of course, the present invention is not limited to the embodiments described above but extends to a spatial light modulator which would include secondary elements without thereby departing from the scope of the present invention.

The present invention also relates to a vehicle, for example automobile or more generally an autonomous land motor vehicle, comprising the spatial light modulator of the .

Claims (10)

A spatial light modulator (32) intended to be illuminated by coherent light sources to form a holographic image, said modulator comprising:
- A substrate on which is formed at least one lattice of waveguides defining a resolution of the holographic image; And
- at each intersection between two waveguides of a lattice, are deposited two chains of nanoparticles of a plasmonic material and nano-drops of a material with optically controllable index change, each of said chains of nanoparticles being aligned in the direction of one of the two waveguides of the intersection and said nano-drops being deposited above said chains of nanoparticles. A spatial light modulator according to claim 1, wherein the optically controllable index changing material is a liquid crystal. A spatial light modulator according to claim 1, wherein the optically controllable index change material is a photostrictive or phase loading material. Spatial light modulator according to one of Claims 1 to 3, in which the plasmonic material is gold, silver, copper or aluminium. Spatial light modulator according to one of Claims 1 to 3, in which the core-shell structure of the plasmonic material is of the metal-dielectric type. Spatial light modulator according to one of Claims 1 to 5, in which the waveguides are formed from a dielectric material. Spatial light modulator according to one of Claims 1 to 6, in which the waveguides of a trellis are structured to form a geometric pattern. Method for generating a holographic image implemented by a spatial light modulator according to one of claims 1 to 7, said method comprising the following steps for activating a pixel of the holographic image:
- obtaining information concerning the activation of a pair of light sources associated with two waveguides relating to an intersection of a lattice of waveguides;
- emission of a first near-infrared light wave by a light source associated with one of the two waveguides, this wave propagating in said waveguide and exciting chains of nanoparticles deposited in the same direction as said waveguide: and
- emission of a second near-infrared light wave by a light source associated with the other of the two waveguides, said wave propagating in said other waveguide and exciting chains of nanoparticles deposited in the same direction as this other waveguide. Holographic image projection device comprising at least one spatial light modulator according to one of Claims 1 to 6. Vehicle comprising at least one spatial light modulator according to one of Claims 1 to 7.