TECHNICAL FIELD

The present disclosure relates to a vehicular signalling system and method, and particularly, but not exclusively, to a holographic signalling system for a vehicle. Aspects of the invention relate to a hologram projection system, to a method of generating a holographic image for use in a vehicle, and to a vehicle comprising a hologram projection system.

BACKGROUND

Currently, road worthy vehicles are provided with a selection of signalling systems to communicate a driving intention and/or action to nearby vehicles. These signalling systems typically comprise a visual indicator in the form of coloured lights located on the exterior of the vehicle that are visible to nearby vehicles when activated. An example of signalling systems are the brake lights, typically affixed above the rear spoiler of a vehicle, and often also located in the rear windshield. The brake lights are activated when the brakes of the vehicle are engaged by the driver depressing the brake pedal. The purpose of the brake lights is to warn trailing vehicles that the leading vehicle is decelerating, and to provide them with sufficient time to decelerate and/or take other mitigating action to avoid a collision. The brake lights are typically coloured red.

Other examples of existing signalling systems are turn indicators, which are activated to inform nearby vehicles of a vehicle's intention to change direction of travel. The turn indicators are typically in the form of a blinking amber coloured light. Each vehicle typically comprises at least two different turn indicators, which are configured to be selectively activated to indicate the intended direction of change of travel. Hazard lights are yet a further example of an existing signalling system, used to warn nearby vehicles of a potential hazard. The hazard lights are typically comprised of a plurality of simultaneously flashing lights.

One shortcoming of existing signalling systems is that their efficacy is proportional to the ease with which they are perceivable by the drivers of trailing and/or nearby vehicles. Ambient lighting conditions can significantly impact the ease with which the signalling systems can be perceived. For example, in bright sunny conditions it becomes more difficult to distinguish an activated brake light from a deactivated brake light, since the contrast between the activated brake light state and the deactivated state is less prominent. In contrast, at night, the contrast between an activated brake light state and a deactivated brake light state is significant, which in turns means that it is easier to identify the activated state. Similarly, adverse weather conditions such as fog also have a large impact on the ease with which an activated brake light is perceived.

A further shortcoming of existing signalling systems is their lack of versatility. Only the most essential driving intentions (e.g. braking, hazards, and change of direction) are catered for using conventional lighting solutions. Since each different lighting system on the exterior of the vehicle is used to communicate a different intention, the number of different driving intentions is dependent on the number of different available lighting systems. However, increasing the number of different available lighting systems present on the exterior of a vehicle is counterproductive, since the efficacy of such systems relies on a driver recognising the meaning of each lighting system, which becomes more difficult the greater the number of different available lighting systems present on a vehicle. Accordingly, to address this issue, the prior art prioritises a small number of lighting systems used to communicate only the most essential driving intentions.

It is an object of the present invention to address at least some of the shortcomings of the prior art, and in particular to provide a solution which is more versatile and effective than the prior art.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a hologram projection system for a vehicle, a vehicle comprising such hologram projection system and a method of generating a holographic image for projection to an exterior of the vehicle as claimed in the appended claims.

According to an aspect of the invention there is provided a hologram projection system for a vehicle. The system comprises a holographic optical structure configured to generate a holographic image when illuminated; an illumination source arranged to illuminate the holographic optical structure when activated; and a controller arranged to activate the illumination source in dependence on a vehicle signal, such that a holographic image is projected from the holographic optical structure, the image being selected in dependence on a characteristic of the vehicle signal. An advantage of using a holographic image is that this is more readily perceivable by a driver of a trailing vehicle in a variety of different weather conditions. The illumination source may comprise an illumination source, which may optionally relate to a coherent illumination source arranged to emit coherent light.

The vehicle signal may comprise a vehicle sensor signal generated by a sensor of the vehicle, and the controller may be arranged to activate the illumination source in dependence on the vehicle sensor signal.

The vehicle signal may comprise a control system signal generated by an electrical and/or mechanical control system of the vehicle, and the controller may be arranged to activate the illumination source in dependence on the vehicle sensor signal. In certain embodiments the holographic optical structure comprises an interference pattern etched on to a screen, and the interference pattern is arranged to diffract incident illumination to generate the holographic image at a predetermined distance from the screen. The screen may form a holographic screen layer and the holographic optical structure may comprise a glass layer disposed adjacent to the holographic screen layer. In an embodiment, the glass layer is a wedged glass layer.

Light from the illumination source may be transmitted from an edge of the glass layer, and propagated through the glass layer to light the hologram.

The holographic screen may be comprised in at least a part of the rear windshield of the vehicle, and the holographic image may be formed at an exterior of the vehicle, at the predetermined distance from the rear windshield. This configuration enables a trailing vehicle to readily see the generated holographic image, as the holographic image is generated behind the leading vehicle in a space between the leading vehicle and the trailing vehicle. In one embodiment, the glass layer of the holographic optical structure may comprise or consist of at least a portion of the rear windshield of the vehicle. In an embodiment the holographic screen may be comprised of the rear windshield of a vehicle. When the holographic screen and/or the holographic optical structure extends to cover the whole surface area of rear windshield, a better resolution of the holographic images is achieved. The holographic optical structure may comprise a plurality of different interference patterns etched on to a screen. Each interference pattern may be arranged to diffract incident illumination to generate a different holographic image. In this way, different holographic images may be generated using the same holographic optical structure. This increases the versatility of the holographic optical structure in communicating with adjacent and trailing vehicles, since a plurality of different holographic images of indicia representative of different driving intentions may be generated. The number of different holographic images that may be generated is proportional to the number of different interference patterns etched on to the screen.

The hologram projection system may comprise a plurality of different illumination sources, and the holographic optical structure may be configured as a multiplexed holographic optical structure arranged to generate a different holographic image when illuminated with a different one of the plurality of illumination sources.

Each one of the plurality of different illumination sources may be configured to emit light having a different wavelength or frequency of light. The holographic optical structure may be configured to simultaneously generate two different holographic images when illuminated with two different illumination sources. This improves the versatility of the hologram projection system, by increasing the amount of information that can be communicated to trailing vehicles. In certain embodiments the holographic optical structure may be configured as a spatially multiplexed structure, and comprises a plurality of different portions, each portion being arranged to generate a different holographic image when illuminated. Each one of the plurality of illumination sources may be configured to illuminate a different portion of the holographic optical structure.

The holographic optical structure may be configured as an angular multiplexed structure. Each one of the plurality of illumination sources may be positioned such that light emitted from each one of the plurality of illumination sources is incident on the holographic optical structure at a different relative angle of incidence. In this way, different holographic images may be generated by selectively activating one or more different illumination sources. The multiplexed holographic optical structure may be configured as an edge-lit optical structure, and the plurality of illumination sources may be arranged at an edge of the multiplexed holographic optical structure. The controller may be arranged to activate one or more of the plurality of different illumination sources in dependence on the characteristic of one or more vehicle signals.

The vehicle signal may be a proximity sensor signal generated by a proximity sensor of the vehicle, and the controller may be arranged to activate the illumination source in dependence on the proximity sensor signal being indicative that an object is located within a threshold distance of the vehicle. In this way, the generation of the holographic image may be used to warn trailing vehicles that they are not maintaining a safety distance of separation, when the vehicle sensor signal is indicative of the trailing vehicle being at a distance less than the recommended safety distance for the vehicle's current speed of travel. Similarly, a holographic image may be generated if the proximity sensor signal is indicative of a trailing vehicle or a bicycle approaching the leading vehicle's blind spot, to warn the trailing vehicle or bicycle that they are approaching the leading vehicle's blind spot. Similarly, when the leading vehicle's turn indicator is activated, the holographic image may be generated to warn a trailing vehicle or bicycle detected by the leading vehicle's proximity sensor that the leading vehicle intends to change its direction of travel.

The vehicle signal may comprise a brake signal generated when the brakes of the vehicle are engaged.

The vehicle signal may comprise an acceleration signal generated by an accelerometer of the vehicle, and the controller may be arranged to activate the illumination source in dependence on the acceleration signal being indicative that the vehicle is decelerating at a rate that is greater than or equal to a predetermined deceleration rate. This is particularly helpful at warning trailing vehicles of the severity with which a leading vehicle is braking, and helps to reduce the risk of collisions resulting from trailing vehicles underestimated the rate of deceleration of the leading vehicle.

The vehicle signal may be a fault signal indicative of an electrical and/or mechanical fault present in the vehicle. The vehicle signal may be generated by a driver assistance system comprised in the vehicle.

The vehicle signal may be an indication of the drivers intended turning. For example, the vehicle signal may be a turn indicator signal generated when the a turn indicator of the vehicle is activated.

In certain embodiments the controller may comprise a control system of the vehicle. This reduces the amount of apparatus that is required to be fitted to a vehicle configured with the hologram projection system, since an existing control system of the vehicle can be used to control operation of the hologram projection system. For example, the control system may comprise an electronic control unit (ECU) of the vehicle. An aspect of the invention relates to apparatus for a vehicle, arranged to generate a holographic image of an indicium. The apparatus comprises a holographic screen configured to generate the holographic image, when illuminated. The apparatus also comprises an illumination source, in the form of an LED (light emitting diode) and/or a laser, arranged to illuminate the holographic screen when activated; and a controller, comprising a processor, arranged to activate the illumination source in dependence on a vehicle signal, such that a holographic image is projected from the holographic screen. The holographic image is selected in dependence on a characteristic of the vehicle signal. A further aspect of the invention relates to a vehicle comprising a hologram projection system as previously described.

Yet a further aspect of the invention relates to a method, for use in a vehicle, of generating a holographic image for projection to an exterior of the vehicle. The method comprises receiving a signal from the vehicle, and illuminating a holographic optical structure with an illumination source to generate a holographic image at an exterior of the vehicle, the holographic image being associated with the received signal. The holographic optical structure may comprise a plurality of different interference patterns, each interference pattern being arranged to generate a different holographic image when illuminated with an associated illumination source, and the method comprises identifying an image from a plurality of available images associated with the received signal. An illumination source is selected to be activated from a plurality of available illumination sources, the selected illumination source being associated with the identified image, and illuminating the holographic optical structure with the selected illumination source to generate a holographic image of the identified image.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a perspective illustration of a holographic image projected from a rear windshield of a lead vehicle in the space between the lead vehicle and a trailing vehicle, in accordance with an embodiment of the invention;

Figure 2 is a schematic illustration of a holographic projection system used to project holographic images from a vehicle as illustrated in Figure 1 ;

Figure 3 is a process flow chart outlining the method carried out by the holographic projection system of Figure 2, in generating a holographic image of an indicium;

Figure 4a is a perspective illustration of the rear windshield of a vehicle, the rear windshield comprising a multiplexed holographic optical structure, in accordance with an embodiment;

Figure 4b is a side view of the vehicle of Figure 4a, and shows the illumination sources being fitted within the passenger compartment area;

Figure 4c is a rear view of the vehicle of Figure 4a, and shows a holographic image of a hazard warning indicium being projected from the rear windshield of the vehicle; Figure 4d is a perspective view of the vehicle shown in Figure 4c, generating a holographic image of the hazard warning indicium; Figure 5 is a perspective illustration of a vehicle projecting a holographic image representing a turn indicator indicium, in accordance with an embodiment of the invention;

Figure 6a is an illustration of a holographic optical structure, in accordance with an embodiment of the invention; and

Figure 6b is an illustration of a holographic optical structure, in accordance with another embodiment of the invention.

DETAILED DESCRIPTION

A non-limiting illustrative example of a holographic image being projected from a vehicle configured with a holographic projection system in accordance with an aspect of the present invention, is illustrated in Figure 1 . A leading vehicle 1 , comprising a hologram projection system (not shown in Figure 1 ) is configured to generate a holographic image 3 formed externally from and at the rear of the leading vehicle 1 in the space present between the leading vehicle 1 and a trailing vehicle 5. The holographic image 3 represents a 'stop' indicium that may be automatically generated in dependence upon the generation of one or more vehicle signals. For example, in the illustrated embodiment the holographic image 3 of the 'stop' indicium may be generated in dependence upon the generation of a brake signal generated when the brakes are activated by the driver. Generation of the holographic image of the 'stop' indicium may complement activation of existing brake lights, and provides an improved means of warning to the trailing vehicle 5 that the leading vehicle 1 is braking. The holographic projection system may be configured to project images of different indicia in dependence upon receipt of different vehicle signals at the holographic projection system. For example, and as will be discussed in further detail below, in certain embodiments holographic images of turn indicator indicia may be generated in response to activation by the vehicle driver of the turn indicators. Similarly, a holographic image of a hazard warning indicium may be generated, in dependence upon activation of the hazard lights by the vehicle driver. Embodiments of the present invention can be used to generate a plurality of different holographic images, as will become clearer from the below description. In certain embodiments the hologram projection system is configured to project one or more different images, each holographic image being associated with a different indicium, and being selected for projection in dependence upon the characteristics of the received vehicle signal.

Figure 2 is a schematic system overview of the hologram projection system 7 that may be configured within a vehicle, for example within the leading vehicle 1 of Figure 1 . The hologram projection system 7 comprises a controller 9, operatively coupled illumination sources 1 1 , and a holographic optical structure 13 arranged to generate one or more holographic images 3 when illuminated. Within the context of the present disclosure, and for the avoidance of confusion, the holographic optical structure 13 relates to any means for generating a holographic image, such as, but not limited to, an optical element arranged to generate a holographic image. Such holographic optical structures are often referred to as 'holograms' within the known art. Further non-limiting examples of such holographic optical structures may relate to an optical element such as a lens, a diffraction grating, a filter or a beam splitter. The optical elements may be transmissive or reflective. The holographic optical structure 13 of Figure 2 is transmissive, although it could equally be reflective in alternative embodiments. In a transmissive holographic optical structure, an incident light field 15 interacts with the optical structure 13, and a modulated light field 17 is transmitted from the holographic optical structure 13, forming the holographic image 3. The holographic optical structure 13 may be generated using methods of manufacture known in the art, and such methods are beyond the scope of the present disclosure but will be known to the reader skilled in the field of holography.

The holographic optical structure 13 may be configured with a diffractive optical structure dimensioned proportional to the wavelength or frequency of the incident illuminating light that is modulated to generate the required holographic image. The holographic optical structure 13 may be configured with a plurality of different component optical structures of different dimensions and each being responsive to different wavelengths or frequencies of incident light. In this way a single holographic optical structure 13 may be used to generate a plurality of different holographic images using a plurality of illumination sources of differing wavelengths or frequencies. For example, where the holographic optical structure 13 comprises a diffractive grating structure, the distance of separation between adjacent gratings is configured to be proportional to the wavelength or frequency of the illumination source. Different component grating structures having different distances of separation between adjacent gratings may be comprised in the holographic optical structure 13. Each different component grating structure may be configured to generate a different holographic image when illuminated with the appropriate wavelength or frequency of light, and may therefore be associated with a different illumination source.

Similarly, the holographic optical structure 13 may relate to a multiplexed holographic optical structure, in which a plurality of different interference patterns are embedded within the multiplexed holographic optical structure. The required holographic image is generated by illuminating the multiplexed holographic optical structure with the appropriate wavelength, or frequency of light. Again, different holographic images are generated by illuminating the optical structure with different wavelengths or frequencies of light. The multiplexed holographic optical structure may be either spatially multiplexed or angularly multiplexed. In a spatially multiplexed holographic optical structure, different holographic images are generated by illuminating different portions of the optical structure. In contrast, in an angularly multiplexed holographic optical structure, different holographic images are generated by varying the relative position of the illuminating light source relative to the optical structure - in other words, by varying the angle of illumination.

The multiplexed holographic optical structure may relate to an edge-multiplexed holographic optical structure, in which different holographic images are generated by illuminating different edges of the optical structure.

In alternative embodiments, the holographic optical structure 13 may comprise a spatial light modulator (SLM) (not shown) comprising a variable optical structure arranged to generate a plurality of different interference patterns. Using an operatively coupled processor (not shown), the structure of the SLM may be varied to generate different interference patterns, which when illuminated generate different holographic images. In such embodiments, a single light source may be used in place of the plurality of illumination sources 1 1 of Figure 2, since the different holographic images are generated by varying the optical structure of the SLM.

The hologram projection system 7 is operatively coupled to any one or more of: one or more vehicle sensors 19; one or more different mechanical control systems 21 of the vehicle 1 ; one or more different electrical control systems 23 of the vehicle 1 . In the embodiment illustrated in Figure 2, the controller 9 is operatively coupled to a plurality of different vehicle sensors 19, to a plurality of different mechanical control systems 21 , and to a plurality of different electrical control systems 23 present within the vehicle 1 . Within the present context, by operatively coupled is intended any means enabling data communication between two devices, whether directly or via a proxy. Such means may relate to a data communication channel enabling data to be transmitted from the one or more vehicle sensors 19, the one or more mechanical control systems 21 , the one or more electrical control systems 23 of the vehicle 1 , to the controller 9. The data communication channel may be a direct communication channel or an indirect communication channel, wherein data signals are transmitted between the one or more vehicle sensors 19 and the controller 9 via a proxy. The communication channel may comprise a bus, which bus may relate to a CAN bus (controller area network bus).

The controller 9 may comprise, or otherwise be operatively communicable with an electronic database 25, comprising one or more lookup tables 27. The one or more lookup tables 27 comprise information associating the one or more different vehicle signals receivable by the controller 9 from any one or more of the operatively coupled vehicle sensors 19, and/or control systems 21 ,23, with one or more different images that are projectable by the hologram projection system 7. Each one of the operatively coupled vehicle sensors 19, and/or control systems 21 , 23 is configured to generate one or more different signals. Such signals may be electronic or optical. For example, a mechanical control system 21 such as a mechanical braking control system may be configured to generate an electronic signal when the brakes of a vehicle are activated. Similarly, an electronic control system such as an Anti-lock braking system (ABS) may be configured to generate an electronic signal when the ABS system is engaged to maintain tractive contact with the road surface during braking. Vehicle sensors 19 may relate to any sensor configured to measure or determine a characteristic of the vehicle's environs. Non-limiting examples of vehicle sensors 19 are: proximity sensors; radar sensors; remote sensing sensors (e.g. LIDAR); ambient lighting sensors; biometric sensors; climate sensors (e.g. temperature and weather sensors). Figure 3 is a process flow chart outlining a method carried out by the hologram projection system 7 of Figure 2, for generating a holographic image of an indicium in dependence upon receipt of a signal from the vehicle 1 , in accordance with an embodiment of the present invention.

A vehicle signal is received at the controller 9, at step 29. The vehicle signal may originate from any one of the operatively coupled control systems 21 , 23 and/or vehicle sensors 19. The indicium requiring holographic projection that is associated with the received vehicle signal is identified, at step 31 . This may comprise the controller 9 accessing the operatively coupled database 25 and performing a lookup action within the one or more lookup tables 27. The lookup tables 27 comprise a list of vehicle signals receivable by the controller 9, and the indicium associated with each vehicle signal. In this way, on the basis of the received vehicle signal, the controller 9 is able to determine the indicium requiring holographic projection. The controller 9 subsequently determines which one of the illumination sources 1 1 requires activation in order to generate the required holographic image, at step 33. This may also be achieved via a lookup action in the lookup tables 27. For example, the lookup tables 27 may also associate each available indicium with a specific illumination source requiring activation in order to generate the required holographic image of the desired indicium. The controller 9 subsequently activates the specific illumination source associated with the required indicium from the available illumination sources 1 1 , at step 35. The activated illumination source illuminates the holographic optical structure to generate the required holographic image of the desired indicium, at step 37. Accordingly, each indicium, and by virtue of association, each projectable holographic image is associated with a different illumination source and with a different component of the holographic optical structure. Different holographic images are generated by selectively activating different illumination sources.

The illumination sources 1 1 may relate to any plurality of illumination sources, such as light emitting diodes (LEDs), lasers, or conventional light bulbs. The use of substantially coherent illumination sources may improve the quality of the generated holographic images, although it is not a necessary requirement, and any type of light source may be used. The different illumination sources are each characterised by having a different wavelength or frequency. The holographic projection system 7 of Figure 2 may be configured to generate a plurality of different holographic images simultaneously using a single holographic optical structure 13. This is achievable, for example, by using a multiplexed holographic optical structure and by simultaneously illuminating it with different illumination sources, each source characterised by having a different wavelength or frequency. Each wavelength or frequency of illuminating light interacts with and is modulated by its associated component optical structure comprised within the holographic optical structure 13. Since each component optical structure is responsive to a different wavelength or frequency of light, the different generated holographic images are invariably of a different colour in this embodiment. In this way, a plurality of holographic images may be simultaneously generated and projected to the exterior of a vehicle.

In certain embodiments, the hologram projection system 7 comprises three different illumination sources - e.g. the primary colours red, blue and green. Generating different colours of images is possible by combining the colours of light emitted by the illumination sources and mixing them accordingly to obtain the desired colour. For example, by mixing any of the available primary colours. It is possible to generate holographic images which appear to have a composite colour by illuminating a multiplexed holographic optical structure configured to diffract incident light of different colours (and hence of different wavelengths) to form holographic images at the same point in image space. For example, to obtain a yellow coloured holographic image using three illumination sources emitting the primary colours red, blue and green, requires illuminating the holographic optical structure with both red and green light. If the holographic optical structure is configured with an interference pattern arranged to diffract incident red and green light to form a supposition of two holographic images, respectively red and green in colour, at the same position in image space, the human eye will perceive these superposed images as a single yellow image. In this way, it is possible to generate a plurality of different holographic images of different colours, the number of different colours being greater than the number of available illumination sources. It is to be appreciated that this method of generating multi-coloured holographic images works equally well with alternative colour models, and such alternatives fall within the scope of the present invention. For example, the illumination sources could be selected in accordance with the CMYK (Cyan, Magenta, Yellow and Black) colour model.

The holographic optical structure 13 may be comprised within the rear windshield 39 of a vehicle 41 , as illustrated in Figures 4a and 4b, in accordance with an embodiment. Figure 4a is a perspective view of the rear of the vehicle 41 . The holographic optical structure 13 may be etched to the surface of the rear windshield 39, and may relate to a multiplexed holographic optical structure as previously described. Figure 4b is a cross-sectional side profile view of the rear windshield 41 , and shows the illumination sources 1 1 being configured within the passenger compartment 43, and mounted to the underside of the roof of the vehicle 41 at a distance from the rear windshield 39. The illumination sources 1 1 are configured to enable the entirety of the holographic optical structure 13 to be illuminated as required. One or more holographic images 3 are generated as described in relation to the preceding embodiments. In alternative embodiments the illumination sources 1 1 may be mounted at different locations within the passenger compartment 43. For example, the illumination source 1 1 may be mounted behind the rear passenger seats. In alternative embodiments adopting edge-lit holographic optical structures, the optical sources may be configured on the edges of the rear windshield.

In another embodiment, the holographic optical structure 13 comprises a holographic screen layer 60 and a glass layer 62. The holographic screen layer 60 and the glass layer 62 are disposed adjacent to each other. As shown in Figure 6a the holographic screen layer 60 is a transmission hologram and provides an external surface such that the holographic screen layer is a proximal layer to a generated holographic image 45. The glass layer 62 provides a channel which may be edge lit by the illumination source 1 1 and having a surface from which light can be emitted to illuminate the holographic optical structure 13. In this manner the glass layer 62 acts as an optical slab waveguide. In an embodiment, the glass layer is wedged. The wedged shape of the glass provides a mechanism for the light to illuminate in a more uniform manner extending to the spread of the wedged glass layer by distributing the light substantially equally. Such a layered structure having the light travelled through a layer of the structure allows the use of whole surface of the rear windshield. Such a layered structure provides total internal reflection of the light. The light source 1 1 is capable of producing a specific light wavelength such as LED or LASER.

A holographic image 45, 47 is produced in the mid-air when a light source is active to emit a specific light wavelength through the glass. In an alternative embodiment, the holographic optical structure 13 comprises a glass layer 62 which is located on top of the holographic screen layer 61 . The glass layer 62 provides an external surface as shown in Figure 6b. The glass layer 62 is a proximal to a generated holographic image 45, 47 when the hologram is activated. In this embodiment the holographic screen layer 61 uses Bragg grating so that the recording angle of reflection hologram is the same as the critical angle of waveguide for the total internal reflection in glass. The holographic screen layer 61 is a reflection hologram. A plurality of light sources 1 1 emit the light with specific wavelengths to illuminate the edge of the glass layer 62 and to propagate the emitted light there through. The light is subsequently emitted from the surface of the glass layer 62 to illuminate the holographic optical structure 13. In this manner the glass layer 62 acts as an optical slab waveguide. For an example, a multiple LED lights are used. Then multiple images 45, 47 corresponding to each of the wavelengths as emitted by different LEDs are produced. The plurality of light source is positioned at the edge of the glass layer 62. As described above the glass layer 62 may be wedged.

The precise location of the optical sources relative to the holographic optical structure 13 is immaterial provided that it is able to illuminate the holographic optical structure to generate holographic images, and alternative configurations satisfying this requirement are envisaged.

Since the holographic optical structure is a nano-structure it is not perceivable to the naked eye, and does not interfere with the driver's ability to see through the rear windshield. Accordingly, the driver is able to see through the rear windshield either directly or via the rear view mirror (not shown), even whilst a holographic image is being projected through the rear windshield. Figure 4c is rear view of the vehicle 41 of Figures 4a and 4b. A holographic image of a hazard warning indicium 45 is shown being projected from the holographic optical structure 13, and forming at a distance from the rear of the vehicle 41 . The precise distance at which the holographic image is formed is dependent on the characteristics of the holographic optical structure, and is configurable during manufacture of the holographic optical structure. In the illustrated embodiment of Figure 4c, the holographic image is formed approximately one meter from the rear windshield 39. Figure 4d is a perspective view of the embodiment of Figure 4c, and shows the holographic image of the hazard warning indicium 45 being projected from the rear of the vehicle 41 .

In embodiments of the present invention, the controller 9 may be configured within an existing electronic control unit (ECU) of the vehicle. It is to be understood that the controller described herein can comprise a control unit or computational device having one or more electronic processors (e.g., a microprocessor, a microcontroller, an application specific integrated circuit (ASIC), etc.). The system may comprise a single control unit or controller or alternatively different functions of the controller may be embodied in, or hosted in, different control units or controllers. As used herein, the term "control unit" will be understood to include both a single control unit or controller and a plurality of control units or controllers collectively operating to provide the required control functionality. A set of instructions could be provided which, when executed, cause the controller to implement the control techniques described herein (including some or all of the functionality or methodologies described herein). The set of instructions could be embedded in the one or more electronic processors. Alternatively, the set of instructions could be provided as software to be executed in the controller. A first controller may be implemented in software run on one or more processors. One or more other controllers may be implemented in software run on one or more processors, optionally the same one or more processors as the first controller. Other arrangements are also useful. The controller 9 may comprise an electronic processor (not shown) having one or more electrical inputs and one or more electrical outputs. The controller 9 further includes an electronic memory device (not shown) that is part of or electrically connected to the processor, and that is accessible by the processor. In an embodiment, the memory device (not shown) has stored therein or thereon instructions for software, firmware, programs, algorithms, scripts, applications, information etc. that may govern all or part of the methodologies described herein, and that may be executed and/or used by the processor to carry out or perform some or all of the functionality and methodologies describe herein. Alternatively, some or all of the aforementioned instructions may be embedded in a computer-readable storage medium (e.g. a non-transitory or non-transient storage medium) that may comprise any mechanism for storing information in a form readable by a machine or electronic processors/computational devices, including, without limitation: a magnetic storage medium (e.g. floppy diskette); optical storage medium (e.g. CD-ROM); magneto optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g. EPROM ad EEPROM); flash memory; or electrical or other types of medium for storing such information/instructions. Additionally, the controller 9 may also be electronically connected to other components of the vehicle 1 , 41 via suitable communications (e.g. CAN bus, SMBus, a proprietary communication link, or through some other arrangement known in the art) and can interact with them when or as required. Non-limiting examples of the different applications in which the hologram projection system 7 and associated method may be put to use are described below, to complement the reader's understanding of the invention.

In an embodiment where the vehicle sensor 19 relates to proximity sensor, and/or the hologram projection system 7 is operatively coupled to an electronic control system 23 of a vehicle proximity sensor, the hologram projection system may be configured to generate a holographic image in dependence on a proximity sensor signal, generated when an object, such as another vehicle, is detected within a threshold distance. The indicium selected for projection as a holographic image may be dependent on the characteristics of the proximity sensor signal. For example, where the proximity sensor signal is indicative of a trailing vehicle at a distance less than the required safety distance of separation for a given speed, an indicium warning the driver of the trailing vehicle to "stay back" and/or "maintain safety distance" may be generated.

Similarly, if it is determined from the proximity sensor signal that a trailing vehicle is approaching the leading vehicle with the likely intention of overtaking the leading vehicle, and it is also determined that the leading vehicle has engaged its indicators to change lanes into the lane of the approaching leading vehicle, then a holographic image of the indicium "Do Not Pass" may be projected in combination with an arrow indicating the direction in which the leading vehicle intends to turn. This embodiment may be particularly useful for reducing accidents between automotive vehicles and bicycles. A significant number of accidents between bicycles and automotive vehicles occur when bicyclists overtake or undertake vehicles that are turning. In accordance with this embodiment, as the approach of the cyclist relative to the turning vehicle is detected in combination with an activated turn indicator, a holographic image of the warning indicium "Do Not Pass - Vehicle Turning" may be generated. The holographic warning indicium may be generated at a height that falls within the cyclist's direct line of sight, and is therefore more readily perceivable by the cyclist, compared to a turn indicator, which may fall within the periphery of the cyclist's field of view. Figure 5 is a perspective illustration of a vehicle 41 projecting a holographic image of a "Do Not Pass" turn indicator indicium 47, in accordance with this embodiment.

The hologram projection system and the herein described methods may be used in conjunction with driver assistance systems, for example with an Intelligent Emergency Braking System (IEBS). In such a system the brakes may be automatically engaged to reduce the likelihood of impact, if it is determined that the rate of deceleration between a leading vehicle and a trailing vehicle is likely to result in an impact unless the trailing vehicle engages its breaks immediately. A holographic image of a hazard warning sign may be generated upon activation of the IEBS to alert any other trailing vehicles of the potential danger.

Similarly, the hologram projection system may be configured to automatically generate a holographic image of the hazard warning indicium if a very sharp deceleration is determined on the basis of a vehicle velocity sensor signal.

As mentioned previously, the hologram projection system may be configured to automatically generate a holographic image of a "stop" or "brake" indicium in dependence on a brake signal, which is generated when the brakes are engaged. Furthermore, the size, brightness and colour of the generated holographic image may be varied on the basis of how firmly the brakes are engaged. For example, if the brake pedal is depressed rapidly, and with force, such as is likely in the event of an emergency engagement of the brakes (e.g. a hard stop), a larger image may be generated. For example, this is achievable using a multiplexed holographic optical structure, as described previously. Furthermore, a sequence of progressively brighter and larger holographic images may be generated in sequence in dependence on the force with which the brake pedal is depressed, which may appear to the driver of a trailing vehicle as a sequence of moving images. The displayed holographic images may also vary in colour, such that a relatively light depression of the brake pedal results in a yellow hazard warning indicium, whilst a violent engagement may be associated with a red coloured hazard warning indicium. In this way the colour also informs the driver of a trailing vehicle of the likely severity of braking of the leading vehicle. The size and colour of the generated holographic image may also be dependent on a vehicle speed sensor. For example, it may be dependent on a measured decoration. A very rapid deceleration may be associated with the generation of a very large and red coloured holographic image of a hazard warning indicium, whilst a lower rate of measured deceleration may be associated with a smaller and more neutrally coloured indicium - e.g. a yellow coloured hazard warning indicium.

The hologram projection system may be configured to generate holographic images of turn indicators, which are generated in dependence upon an indicator signal. For example, when the driver activates a turn indicator, the hologram projection system may be configured to automatically generate a holographic image of an arrow arranged to point in the direction that the vehicle intends to turn. This may complement the traditional turn indicator light.

The hologram projection system may be configured to generate holographic images in dependence on a biometric signal associated with a driver's vital statistic. For example, if the driver suffers a heart attack or similar ailment whilst driving, the hologram projection system can generate a suitable holographic image of a warning indicium informing the drivers of trailing vehicles that the driver of the leading vehicle is unwell. It is envisaged that this embodiment could be complementary to the aforementioned IEBS, in which the IEBS is simultaneously activated to bring the vehicle to rest if the driver is unwell. The hologram projection system may be configured to generate holographic images in dependence on a major mechanical and/or electrical fault of the vehicle being detected.

The above described aspects and embodiments are presented for illustrative purposes only, and are not be construed as limiting. Alternative embodiments are envisaged in which the above described embodiments, and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible, and such alternatives fall within the scope of the present invention.