Light control apparatus

Abstract

A display system is provided. The display system includes a replicator arranged to receive the spatially modulated light and replicate the spatially modulated light to form a plurality of replicas of the spatially modulated light through a waveguide between a reflective surface and a transflective surface. The transflective surface forms an output surface of a plurality of replicas of spatially modulated light. The display system also includes a light control device located downstream of the output surface of the replicator in the optical path of the plurality of replicas of spatially modulated light. The light control device is arranged to provide a first compensation for the curvature of the curved optical component downstream of the light control device. The first compensation is a function of the position on the output surface and is arranged to only partially cancel the curvature of the optical component and preserve some distortions in the curvature of the optical component of at least one replica compared to another replica.

Description

Technical Field

[0001] The present disclosure relates to a display system including a light control device. The present disclosure also relates to a light control device such as a thin film and a method of compensating for the curvature of an optical combiner such as a vehicle windshield. Some embodiments relate to holographic projectors, picture generation units, or head-up displays. Background Art

[0002] Light scattered from an object contains amplitude and phase information. This amplitude and phase information can be captured, for example, on a photosensitive plate by well-known interference techniques to form a holographic record or "hologram" including interference fringes. The hologram can be reconstructed by illuminating it with suitable light to form a two-dimensional or three-dimensional holographic reconstruction or replay image representing the original object.

[0003] Computer-generated holography can numerically simulate the interference process. Computer-generated holograms can be calculated by techniques based on mathematical transforms such as the Fresnel or Fourier transform. These types of holograms can be referred to as Fresnel / Fourier transform holograms or simply Fresnel / Fourier holograms. A Fourier hologram can be considered a Fourier domain / plane representation of an object or a frequency domain / plane representation of an object. For example, computer-generated holograms can also be calculated by coherent ray tracing or point cloud techniques.

[0004] Computer-generated holograms can be encoded on a spatial light modulator arranged to modulate the amplitude and / or phase of incident light. For example, electro-addressable liquid crystals, optically addressable liquid crystals, or micromirrors can be used to achieve light modulation.

[0005] Spatial light modulators typically include a plurality of individually addressable pixels, which can also be referred to as cells or elements. The light modulation scheme can be binary, multi-level, or continuous. Alternatively, the device can be continuous (i.e., not including pixels), so that light modulation can be continuous across the device. Spatial light modulators can be reflective, meaning that the modulated light is output by reflection. Spatial light modulators can equally be transmissive, meaning that the modulated light is output by transmission.

[0006] Using the systems described herein can provide holographic projectors. Such projectors have been applied in head-up displays "HUDs". Summary of the Invention

[0007] Aspects of the present disclosure are defined in the appended independent claims.

[0008] Broadly speaking, a light control device or glare mitigation device for displaying light is provided, which is arranged to compensate for the curvature of a curved optical component on the optical path of the display light. In an embodiment, the light control device or glare mitigation device is for the display light of a display system. In an embodiment, the curved optical component is located on the optical path of the display system. In some embodiments, the curved optical component is an optical combiner, such as a vehicle windshield, which is arranged to redirect the display light from a display device to an observation window or a so-called eyebox. The optical component may have a first curvature in a first direction and a second curvature in a second direction perpendicular to the first direction. The first and / or second curvature may be non-linear. The optical component has a complex curvature, which introduces complex distortions when used in a display system, especially a holographic projection-based display system.

[0009] The display light may be spatially modulated light. The display system may be arranged to relay the spatially modulated light to an observation plane or an eyebox. In some embodiments, the display system is a holographic display system, and the spatially modulated light is light spatially modulated according to a hologram. The spatially modulated light may be referred to as a holographic wavefront. In other embodiments, the display system is an image or picture display system (e.g., part of a conventional picture generation unit), and the spatially modulated light is light spatially modulated according to an image or picture. In these embodiments, the spatially modulated light may be referred to as an image or picture wavefront. The picture wavefront may be received from a screen or a diffuser. Thus, the picture wavefront may be diffuse and / or contain a range of ray angles. The light control device of the present disclosure provides means for controlling the reflection of ambient light to prevent or suppress glare from reaching the observation plane while allowing the spatially modulated light to reach the observation plane. For example, the display device may include an optical component comprising a reflective surface. In the absence of a light control device, the ambient light may be reflected by the reflective surface towards the observation plane / eyebox of the display device, thereby forming glare. The light control device of the present disclosure is arranged to suppress such reflection.

[0010] As described above, the light control device of the present disclosure is also arranged to compensate for the curvature of a curved optical component on the optical path of a display system. A curved optical component on the optical path of a display system can mean that spatially modulated light propagating through the display system can be incident on the curved optical component, reflected by the curved optical component, transmitted through the curved optical component, or otherwise interact with the curved optical component. As will be understood by those skilled in the art, the curvature of an optical component can change the divergence or convergence of spatially modulated light and its angle. For example, if the spatially modulated light is substantially collimated upstream of the curved optical component (before interacting with the optical component), the spatially modulated light can be non-parallel (e.g., converging or diverging) downstream of the curved optical component (after interacting with the optical component). In other words, the curved optical component can have a lens effect on the spatially modulated light incident thereon. If the curvature of the curved optical component is non-uniform, the lens effect may be non-uniform. For example, different portions of the curved optical component can have different radii of curvature and thus can have different lens effects on the spatially modulated light incident thereon. In some embodiments, the curved optical component is the windshield or windscreen of a vehicle. The windshield or windscreen can have a complex curvature and can have a complex lens effect on the display light incident thereon.

[0011] The inventors have discovered a number of problems associated with the lens effect of a curved optical component. One problem is that the lens effect may distort the display light (of a display system). For example, the display light may render a picture observable at an observation plane. For example, the display light may be spatially modulated according to a hologram of the picture or simply according to the picture. The lens effect of the curved optical component may distort the picture observable at the observation plane. This may adversely affect the viewing experience of the display system. Another problem discovered by the inventors is specific to a display system including a duplicator upstream of the curved optical component. The duplicator may be arranged to duplicate the spatially modulated light to form a plurality of copies of the spatially modulated light. For example, if the spatially modulated light is a holographic wavefront, the duplicator may be arranged to form a plurality of copies of the holographic wavefront. In an embodiment, as described below, the duplicator may be a waveguide. For example, the waveguide may include an input port arranged to receive the spatially modulated light. The waveguide may include a pair of surfaces arranged to guide therebetween the spatially modulated light received at the input. The first surface of the pair of surfaces may be partially transmissive and partially reflective. The first surface may be arranged to form a plurality of copies of the spatially modulated light. It can be said that at least a portion of the first surface forms an output port of the duplicator / waveguide. The duplicator may be arranged such that the plurality of copies are relayed towards the curved optical component. The display system may also be arranged such that the plurality of copies are relayed towards the observation plane / eyebox of the display system. The inventors have found that the spacing of the copies of the spatially modulated light (at the observation plane) is important for ensuring a good viewing experience. Through simulation and experimentation, the inventors have also found that the spacing of the copies is affected by the lens effect of the curved optical component. For example, the spacing of the copies at the observation plane may be increased or decreased. This may have an adverse effect on the viewing experience. For example, if the spacing of the copies is decreased, a so-called ghosting effect may become more pronounced, in which copies of the intended picture or image content are displayed slightly offset from the intended picture or image content. If the curved optical component has a concave shape, such as the inner surface of a windshield or a windscreen, the spacing of the copies may be decreased. As used herein, the spacing of the copies refers to the spacing or distance between the centers of adjacent copies.

[0012] Light control devices / anti-glare devices for reflection / glare suppression have been previously disclosed, for example in UK Patent GB2607672 and UK Patent Application GB2303536.3 (published as GB2627988A). Light control devices for compensating for the curvature of a curved optical component have also been disclosed in UK Patent Applications 2317637.3 and 2401627.1. These applications are hereby incorporated by reference.

[0013] However, the problem that the inventors have addressed is that, as described in these applications, using only physical lenses to mitigate the lensing effect of a curved optical component requires different lenses for any change in the curved optical component. For example, if the curved optical component is the windshield of a vehicle, different lenses would have to be used for each different vehicle line that the system needs to be assembled into. If the lens is not fine-tuned or optimized to the curvature of the curved optical component, then elements of the above problems may still exist. This requires a significant amount of additional development time and cost because the fine-tuning / optimization process for the lenses for each vehicle line must be completed, as well as additional manufacturing complexity because any production facility must handle multiple different lenses for use with various curved optical components.

[0014] According to a first aspect of the present disclosure, a display system is provided. The display system includes a replicator arranged to receive spatially modulated light and replicate the spatially modulated light to form multiple replicas of the spatially modulated light through a waveguide between a reflective surface and a transmissive-reflective surface. The transmissive-reflective surface forms an output surface for the multiple replicas of the spatially modulated light. The display system further includes a light control device in the optical path of the multiple replicas of the spatially modulated light downstream of the output surface of the replicator. The light control device is arranged to provide a first compensation for the curvature of a curved optical component downstream of the light control device. The first compensation is a function of a position (or location) on the output surface (or the light control device) and is arranged to only partially counteract the curvature of the optical component. In other words, the first compensation is not constant or varies with the position on the output surface or the light control device.

[0015] That is, for each position on the output surface of the replicator, the corresponding point of the light control device provides compensation for the curvature of the corresponding point of the curved optical component. The "corresponding" points are the points on the light control device or the curved optical component that will interact with the replica emitted from any given point on the output surface of the replicator - that is, the points on the light control device, the curved optical component, and the output surface of the replicator that are connected by the same replica when the light ray traces the replica through the system. The compensation provided by the light control device to the replica emitted from a given point on the output surface can vary compared to the compensation provided to the replica emitted from an adjacent point on the output surface, and likewise, the first compensation varies over the output surface (i.e., is a function of the position on the output surface). In other words, for an output surface having first and second dimensions, replicas are emitted from the output surface in the first and second dimensions (of an array), and the compensation provided by the light control device to any replica will depend on the position of the corresponding point on the output surface in the first and second dimensions from which the replica is emitted. That is, the compensation is a function of at least one dimension (e.g., x or y) of the component. Although the discussion here refers to "points" on the output surface, the light control device, and the curved optical component, those skilled in the art should understand that this may be purely illustrative. It may be the case that instead of corresponding finite "points", a "region" of the light control device provides the required compensation for the curvature of the corresponding region of the curved optical component.

[0016] The term "partial compensation" used here reflects that the first compensation is arranged to retain some distortion from the curvature of the optical component. This distortion can be the distortion of at least one replica compared to another replica. The magnitude of the first compensation reduces the (wavefront) distortion caused by the curvature of the optical component but does not completely eliminate it. That is, although the light control device has a partial correction effect, some (wavefront) distortion is still retained. In other words, the (wavefront) distortion with the first (partial) compensation is smaller (has a lower magnitude) than when there is no first (partial) compensation, but not as low as if there were complete compensation.

[0017] In other words, a projector is provided that includes a replicator and a light control device. The replicator is arranged to receive spatially modulated light and replicate the spatially modulated light to form multiple replicas of the spatially modulated light through a waveguide between a reflective surface and a transmissive-reflective surface. The transmissive-reflective surface forms the output surface of the multiple replicas of the spatially modulated light. The light control device (e.g., implemented as a lens of a thin film) is located in the optical path of the multiple replicas of the spatially modulated light downstream of the output surface of the replicator and is arranged to provide a first partial compensation (e.g., a first negative optical power) for the curvature of a curved optical combiner (e.g., having a positive optical power) that is used in cooperation with the projector (e.g., receives the light of the projector). The first partial compensation is a function of the position on the output surface that does not completely cancel the curvature of the optical combiner.

[0018] Similarly, the inventors have found that purposefully selecting a light control device that only partially compensates for the curvature of a curved optical component allows for fine-tuning the system in other ways to accommodate a particular curved optical component. This allows the same system and light control device to be used with a variety of curved optical components, eliminating the additional development and manufacturing time and cost described above.

[0019] Compensation or alternative correction can address any optical effects (such as wavefront distortion, aberration, or differences) imparted to any or all replicas by the curvature of the curved optical component. In other words, the purpose of (partial) compensation is that, after interaction with the curved optical component, at least one optical property or characteristic (such as size, shape, aspect ratio, etc.) of at least one replica is closer to the expected optical property or characteristic than when the compensation is not in place. In summary, the compensation is to reduce the (wavefront) distortion of the replicas relative to each other, where the distortion is the change in the optical property relative to its expected value.

[0020] The spatially modulated light can be a holographic wavefront, and the replicator can be arranged to form multiple replicas of the holographic wavefront. In this way, the system can be used with a holographic projector. In other embodiments, the spatially modulated light is the wavefront of a picture.

[0021] The light control device can include a lens or a lens function, optionally including a Fresnel structure having a lens effect. The physical lens can be a film, optionally having a thickness of less than 5 mm, such as less than 2 mm, 1 mm, or 0.5 mm. The device provides the required compensation / correction while minimizing the space it occupies in the system, reducing packaging constraints.

[0022] The first compensation can have a lens effect opposite to that of the curved optical component. For the avoidance of doubt, the term "opposite" used here is related to direction but not necessarily to magnitude. That is, the opposite lens effect has the opposite direction, not necessarily the same magnitude. The first compensation can be a negative optical power. The curved optical component can be a positive optical power. Thus, the compensation provides a corresponding optical power to address the optical power of the curved optical component.

[0023] The display system can also include a processor arranged to determine the hologram and lens function of an image, and the lens function provides a second compensation for the curvature of the curved optical component downstream of the light control device. The second compensation is arranged to only partially cancel the curvature of the optical component. The second compensation can also be arranged to retain some distortion (such as at least some distortion) of the curvature of the optical component of at least one replica compared to another replica. The display system can also include a display device arranged to spatially modulate light according to a diffraction pattern displayed thereon. The diffraction pattern includes the hologram and the lens function.

[0024] In other words, the system (or projector) may also include a processor arranged to determine a hologram of the picture and a (pixelated) lens function that provides a second part of the compensation (e.g., a second negative optical power) for the curvature of a curved optical combiner (e.g., having a positive optical power) used in conjunction with the projector (e.g., receiving light from the projector). The system (or projector) may also include a display device arranged to spatially modulate light according to a diffraction pattern displayed thereon, where the diffraction pattern includes the hologram and the lens function (e.g., their superposition or sum).

[0025] In some embodiments, the combination of the light control device (providing hardware compensation / correction) and the lens function of the processor (providing software compensation / correction) allows for complete correction or compensation of any curvature of the curved optical component without changing the hardware used for each different curved optical component. That is, most of the correction / compensation is done by the light control device, while the fine-tuning is performed by the software of the processor. This allows for the use of a set / fixed "one size fits all" (hardware) system regardless of the curvature of the curved optical component, thus reducing the development and manufacturing time associated with producing a new light control device for any new curved optical component to be used in conjunction with the system.

[0026] In other words, the light control device is a passive component (i.e., a component that cannot be changed as needed during use). Thus, in order to increase the degree of freedom for correction / compensation of the curvature of the curved optical component, the light control device does not precisely compensate the optical power of the curved optical component. Instead, the light control device compensates for low-order optical powers (e.g., defocus and astigmatism), while software-based compensation is used for fine-tuning.

[0027] This combination of hardware and software compensation / correction has more advantages than correction using a pure hardware or software solution. As described above, using pure hardware correction / compensation would result in having to install a new piece of hardware for each curvature of the curved optical component to be used with the system. The advantages of a pure software solution are discussed below.

[0028] Depth information of the virtual image (i.e., the image observed or perceived by the observer) is encoded in the replica wavefront emitted from the output surface of the replicator. When the wavefront is reflected by the curved optical component, due to the curvature of the component, a positive optical power is added to the wavefront, which pushes the image further away and increases the virtual image distance (the distance at which the observer observes the virtual image). This may result in the virtual image being too far away to be clearly observed by the observer or being in the wrong position relative to the observer's environment. In order for the observer to perceive the correct virtual image distance, the wavefront needs to be pre-distorted with an opposite optical power (i.e., a negative optical power) before hitting the curved optical component.

[0029] The intuitive way to increase the negative optical power is to apply a negative software lens "on top" of the hologram by the processor responsible for generating the hologram. While this does bring the virtual image back to its nominal distance, the inventors have found that as the distance between the virtual image and the display device decreases, significant ghosting artifacts are introduced. The more curved the curved optical component, the stronger the optical power that needs to be added to the hologram, and the more ghosting effects have been observed.

[0030] Therefore, the inventors have found a better way to correct the virtual image distance is to add negative optical power after the replicator. Adding such a negative light control device brings the virtual image closer to the observer, which results in the correct virtual image distance. However, as mentioned above, using only a hardware solution is suboptimal in terms of development and manufacturing time and cost, so a software solution (with more complementary capabilities) is included to fine-tune the compensation / correction. In other words, the optical power of the hardware lens will be similar to the defocus and astigmatism of the curved optical component, while the software correction will be a fine-tuning depending on the actual curved optical component and system parameters (such as the field of view). There may be a large number of terms (i.e., Zernike polynomials) in the software correction. In addition, the inventors have found that using only a hardware solution cannot fully restore the image quality of the curved optical component. However, during the calculation of the hologram, the remaining ghosting artifacts can be removed by software-based anti-ghosting techniques known to the inventors.

[0031] The inventors have found that there are two key planes in designing such a display system: the plane where the display is located and the plane where the virtual image is located. The optical power of the curved optical component will push these two planes further apart, so the virtual image will appear too far from the expected distance to the observer. Using a negative software lens will bring the virtual image closer, but the display device remains at the same distance, so the spacing between the virtual image and the display device will be reduced (introducing more ghosting). Adding a hardware lens between the display device and the observer, because this will bring the virtual image and the display device closer, so the spacing between them remains long enough to avoid ghosting. In summary, the software lens can only affect the virtual image and not the display device, while the hardware lens can affect both.

[0032] For optimal performance, a thin negative lens made of high-quality optical glass is preferred. However, in some embodiments, a Fresnel structure such as a Fresnel lens is used to reduce the overall volume and weight of the unit. It can be said that the Fresnel structure has a lens effect or optical power. Alternatively, it can be said that the light control device includes a Fresnel structure or a phase wrapping structure.

[0033] The lens function can be a pixelated lens function. The second compensation can be negative optical power. The diffraction pattern can include the superposition or sum of the hologram and the lens function. In this way, the software part of the correction / compensation is included as part of the replica reflected by the curved optical component.

[0034] The display system may also include an observer tracking system arranged to determine a position within the eyebox and correlate the position with positions on a sub-region of the curved optical component and on the output surface of the replicator. The first and second compensations may compensate for the curvature of the sub-region of the curved optical component.

[0035] Generally speaking, a hybrid software-hardware approach for compensating the curvature of a curved optical component, such as a combiner, e.g., a windshield, is disclosed herein. The first and second compensations may together provide full compensation for the curvature of the curved optical component. In other words, in the present disclosure, through the sum of the corrections / compensations provided by the software and hardware solutions, the corrections / compensations previously provided by a customized hardware solution for each different curved optical component are achieved.

[0036] The first compensation may be 2 to 10 times the second compensation. Alternatively, the first compensation may provide a virtual image shift correction in the range of 75% to 99%, and the second compensation may provide a virtual image shift correction in the range of 1% to 25%. In other words, the main / most corrections / compensations are achieved by the hardware solution, while the fine-tuning of the corrections / compensations is achieved by the software solution. Those skilled in the art will understand how the optical power associated with the curved optical component causes a change in the image distance. Thus, the virtual image shift may be a distance. Therefore, the virtual image shift correction is the percentage change in the image distance.

[0037] The magnitude of the first and / or second compensations may be such that the spacing of each of the plurality of replicas at the viewing plane of the display system may be at least half of the human pupil size.

[0038] Also, according to a second aspect of the present disclosure, a display system is provided. The display system includes a replicator arranged to receive spatially modulated light and replicate the spatially modulated light to form a plurality of replicas of the spatially modulated light through a waveguide between a reflective surface and a transmissive-reflective surface. The transmissive-reflective surface forms an output surface of the plurality of replicas of the spatially modulated light. The display system also includes a light control device in the optical path of the plurality of replicas of the spatially modulated light downstream of the output surface of the replicator. The light control device is arranged to provide compensation for the curvature of a curved optical component downstream of the light control device. The compensation is a function of the position on the output surface. The magnitude of the first and / or second compensations is such that the spacing of each of the plurality of replicas at the viewing plane of the display system may be at least half of the human pupil size.

[0039] To generate a complete image for an observer, their eyes must be tracked to ensure that the correct replicas pass through their pupils to their retinas (and are thus seen by the observer), and optionally a 3D display is provided. If one or more of the correct replicas do not pass through the pupil, the observer may miss at least a portion of the intended image, or crosstalk issues may occur. Similarly, if multiple conflicting replicas reach the eye, ghosting of (other) images may occur. This is particularly problematic in the presence of curved optical components, which cause multiple replicas to reach the observer at different phases (due to the curvature of the component imparting different phases to different replicas), resulting in a distorted image seen by the observer. Accordingly, a significant amount of computational power can be used to track the eyes of an observer within an eye box to ensure that such distortion and ghosting are minimized or eliminated.

[0040] By increasing the spacing between replicas, the chance that multiple conflicting replicas simultaneously pass through the observer's pupil and cause the above-mentioned image distortion is reduced. This reduces the requirements on the eye tracking system, as the chance of allowing multiple conflicting replicas through the observer's pupil is reduced. In this way, the requirements on the eye tracking system can be relaxed.

[0041] The inventors have found that this can be achieved using the hardware correction described above. The hardware correction effectively moves the display device closer to the eye box, which in turn effectively increases the spacing between replicas and thus allows for a greater tolerance in eye tracking.

[0042] The inventors have found that optimally, compensation for the curvature of the curved optical component can be such that the coverage area of the viewing pupil on the display device contains at least 50 pixels of the display device, optionally 50 to 75 pixels, or alternatively 100 pixels. Compensation for the curvature of the curved optical component can be such that the coverage area of the viewing pupil on the display device is substantially symmetric. Compensation for the curvature of the curved optical component can be such that the coverage area of the viewing pupil on the display device has an aspect ratio in the range of 1:1 to 1:1.25.

[0043] Similarly, according to a third aspect of the present disclosure, a display system is provided. The display system includes a duplicator arranged to receive spatially modulated light and duplicate the spatially modulated light to form multiple replicas of the spatially modulated light through a waveguide between a reflective surface and a transmissive-reflective surface. The transmissive-reflective surface forms an output surface for the multiple replicas of the spatially modulated light. The display system further includes a light control device in an optical path of the multiple replicas of the spatially modulated light downstream of the output surface of the duplicator. The light control device is arranged to provide compensation for the curvature of a curved optical component downstream of the light control device. The compensation is a function of the position on the output surface. The display system also further includes a display device arranged to spatially modulate light. The compensation for the curvature of the curved optical component can cause the coverage area of the viewing pupil on the display device to include at least 50 pixels of the display device, optionally 50 to 75 pixels or alternatively 100 pixels. Alternatively, the compensation for the curvature of the curved optical component can cause the coverage area of the viewing pupil on the display device to be substantially symmetric. Alternatively, the compensation for the curvature of the curved optical component can cause the coverage area of the viewing pupil on the display device to have a region with an aspect ratio in the range of 1:1 to 1:1.25.

[0044] By ray-tracing the optical path of the replicas back through the system to the display device, the inventors have found that the distortion of the curved optical component also reduces the area on the display device that is responsible for a particular point of the image perceived by the observer. For example, if the area on the display device is circular or approximately / essentially circular, the distortion caused by the curved optical component may cause the area to become elliptical. That is, the width of the circular area in a first direction may remain the same, but it decreases in a second direction perpendicular to the first direction. In summary, the distortion eliminates the symmetry of the area, reduces its size, and increases its aspect ratio. The quality of each point in the reconstructed image depends largely on how many pixels contribute to that point and how those pixels are distributed.

[0045] By using the compensation described in the present disclosure, the inventors have found that the area on the display device can be at least partially restored to the shape and size it would have had if the distortion had not occurred. That is, the width of the area in the second direction can be closer to the width in the first direction. In other words, the compensation increases the symmetry of the area, increases its size, and decreases its aspect ratio. The increase in the area of the display device responsible for each point of the image perceived by the observer means that the image can be presented with greater / finer detail (in other words, at a higher resolution). The inventors have found that using this method can improve the perceived image quality, such as resolution.

[0046] The display system may further include a curved optical component downstream of the light control device. The curved optical component can be an optical combiner. The curved optical component can be the windshield of a vehicle.

[0047] The light control device may also include the function of "rotating the film" (i.e., the light control device can act as a rotating film). That is to say, the light control device can provide "overall rotation" (i.e., providing an equal and minimum amount of rotation to each replica), which moves the position of the eyebox / viewing window to a position that is more comfortable and / or more accessible to the observer / user. In other words, the first compensation function may have a (static) coefficient such that each position on the light control device provides a minimum amount of rotation.

[0048] According to a fourth aspect of the present disclosure, a method of processing spatially modulated light is provided. The method includes receiving spatially modulated light at a replicator, the replicator having a reflective surface and a transmissive-reflective surface. The transmissive-reflective surface forms an output surface. The method further includes replicating the spatially modulated light by waveguiding the spatially modulated light between the reflective surface and the transmissive-reflective surface to form a plurality of replicas of the spatially modulated light. The plurality of replicas of the spatially modulated light are output from the replicator at the output surface. The method further includes receiving the plurality of replicas at a light control device. Finally, the method includes providing a first compensation for the curvature of a curved optical component downstream of the light control device via the light control device. The first compensation is a function of the position on the output surface and is arranged to only partially cancel the curvature of the optical component.

[0049] In this way, a method is provided that provides the benefits of partial compensation, as discussed above with respect to the first aspect of the present disclosure.

[0050] The method may further include determining, by a processor, a hologram of an image and a lens function that provides a second compensation for the curvature of a curved optical component downstream of the light control device. The second compensation is arranged to only partially cancel the curvature of the optical component. The method may further include spatially modulating light on a display device according to a diffraction pattern displayed on the display device. The diffraction pattern includes the hologram and the lens function.

[0051] The magnitude of the first and / or second compensation may be such that the spacing of each of the plurality of replicas at the viewing plane of the display system is at least half of the size of the human pupil. The compensation for the curvature of the curved optical component may be such that the coverage area of the viewing pupil on the display device includes at least 50 pixels of the display device, optionally 50 to 75 pixels or alternatively 100 pixels.

[0052] It should be understood that the features discussed above in relation to the display system of the first aspect of the present disclosure may also be features of the display systems of the second and third aspects of the present disclosure and / or the method of the fourth aspect of the present disclosure, and vice versa.

[0053] In the present disclosure, the term "replica" is only used to reflect that the spatially modulated light is split such that the complex light field is directed along multiple different optical paths. The term "replica" is used to refer to each occurrence or instance of the complex light field after a replication event - such as partial reflection - transmission by a pupil expander. Each replica propagates along a different optical path. Some embodiments of the present disclosure relate to the propagation of light encoded with holograms rather than images - i.e., spatially modulated light using holograms of images rather than the images themselves. Thus, it can be said that multiple replicas of the hologram are formed. Those skilled in the art of holography will understand that the complex light field associated with the propagation of light encoded with a hologram will vary with the propagation distance. The term "replica" used herein is independent of the propagation distance, and thus two optical branches or paths associated with a replication event are still referred to as "replicas" of each other, even if the branches have different lengths such that the complex light field evolves differently along each path. That is, according to the present disclosure, even if two complex light fields are associated with different propagation distances, they are still considered "replicas" - assuming they originate from the same replication event or series of replication events.

[0054] A "diffraction light field" according to the present disclosure is a light field formed by diffraction. A diffraction light field can be formed by irradiating a corresponding diffraction pattern. Examples of diffraction patterns according to the present disclosure are holograms, and examples of diffraction light fields are holographic light fields or light fields of holographic reconstructions forming images. A holographic light field forms a (holographic) reconstruction of an image in a replay plane. The holographic light field propagating from a hologram to a reproduction plane can be said to include light encoded with the hologram or light in the holographic domain. The diffraction light field is characterized by a diffraction angle determined by the minimum feature size of the diffraction structure and the wavelength of the light (of the diffraction light field). According to the present disclosure, it can also be said that a "diffraction light field" is a light field in which a reconstruction is formed in a plane spatially separated from the corresponding diffraction structure. An optical system for propagating a diffraction light field from a diffraction structure to an observer is disclosed herein. The diffraction light field can form an image.

[0055] The term "hologram" is used to refer to a record containing amplitude information or phase information about an object or some combination thereof. The term "holographic reconstruction" is used to refer to the optical reconstruction of an object formed by illuminating the hologram. The systems disclosed herein are described as "holographic projectors" because the holographic reconstruction is a real image and is spatially separated from the hologram. The term "replay field" is used to refer to a 2D region within which the holographic reconstruction is formed and is fully focused. If the hologram is displayed on a spatial light modulator including pixels, the replay field will repeat in the form of multiple diffraction orders, where each diffraction order is a replica of the zero-order replay field. The zero-order replay field typically corresponds to the preferred or primary replay field because it is the brightest replay field. Unless otherwise explicitly stated, the term "replay field" shall be considered to refer to the zero-order replay field. The term "replay plane" is used to refer to the plane in space that contains all the replay fields. The terms "image", "replay image", and "image region" refer to the region of the replay field illuminated by the light of the holographic reconstruction. In some embodiments, an "image" may include discrete points, which may be referred to as "image points" or, for convenience only, as "image pixels".

[0056] The terms "encoding", "writing", and "addressing" are used to describe the process of providing a respective plurality of control values to a plurality of pixels of an SLM that respectively determine the modulation level of each pixel. It can be said that the pixels of the SLM are configured to "display" a light modulation distribution in response to receiving the plurality of control values. Thus, it can be said that the SLM "displays" the hologram, and the hologram can be considered an array of light modulation values or levels.

[0057] It has been found that a holographic reconstruction of acceptable quality can be formed from a "hologram" that contains only phase information related to the Fourier transform of the original object. Such a holographic record may be referred to as a phase-only hologram. Embodiments relate to phase-only holograms, but the present disclosure is equally applicable to amplitude-only holography.

[0058] The present disclosure is also equally applicable to using amplitude and phase information related to the Fourier transform of the original object to form a holographic reconstruction. In some embodiments, this is achieved by using complex modulation of a so-called fully complex hologram that contains amplitude and phase information related to the original object. Since the value (gray level) assigned to each pixel of the hologram has both an amplitude and a phase component, such a hologram may be referred to as a fully complex hologram. The value (gray level) assigned to each pixel can be represented as a complex number having an amplitude and a phase component. In some embodiments, fully complex computer-generated holograms are calculated.

[0059] The phase value, phase component, phase information, or simply the phase of a pixel of a computer-generated hologram or a spatial light modulator can be referred to as "phase delay" for short. That is, any phase value described actually represents a number (e.g., in the range of 0 to 2π) that represents the amount of phase delay provided by that pixel. For example, a pixel of a spatial light modulator described as having a phase value of π / 2 will delay the phase of the received light by π / 2 radians. In some embodiments, each pixel of the spatial light modulator can operate in one of a plurality of possible modulation values (e.g., phase delay values). The term "gray level" can be used to refer to the plurality of available modulation levels. For example, the term "gray level" can be used for convenience to refer to only the plurality of available phase levels in a phase modulator, even if the different phase levels do not provide different shades of gray. For convenience, the term "gray level" can also be used to refer to the plurality of available complex modulation levels in a complex modulator.

[0060] Accordingly, a hologram includes an array of gray levels, i.e., an array of light modulation values, such as an array of phase delay values or complex modulation values. A hologram is also considered a diffraction pattern because it is a pattern that causes diffraction when displayed on a spatial light modulator and illuminated with light having a wavelength relative to (usually less than) the pixel pitch of the spatial light modulator. In this document, reference is made to combining a hologram with other diffraction patterns, such as diffraction patterns used as lenses or gratings. For example, a diffraction pattern used as a grating can be combined with a hologram to translate the replay field on a replay plane, or a diffraction pattern used as a lens can be combined with a hologram to focus the holographic reconstruction on a replay plane in the near field.

[0061] Although different embodiments and groups of embodiments can be separately disclosed in the following detailed description, any feature of any embodiment or group of embodiments can be combined with any other feature or combination of features of any embodiment or group of embodiments. That is, all possible combinations and permutations of the features disclosed in this disclosure are contemplated. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] The following drawings are referred to, and specific embodiments are described by way of example only:

[0063] Figure 1 is a schematic diagram showing a reflective SLM that produces a holographic reconstruction on a screen;

[0064] Figure 2 shows an image for projection, including eight image regions / components V1 to V8, and a cross-section of the corresponding hologram channels H1 - H8;

[0065] Figure 3 shows a hologram displayed on an LCOS that directs light to a plurality of discrete regions;

[0066] Figure 4 shows including a display asFigure 2 and 3 A system of a display device for a computed hologram shown;

[0067] Figure 5A A perspective view of a first exemplary two-dimensional pupil expander including two replicators, each replicator including a pair of stacked surfaces;

[0068] Figure 5B A perspective view of a first exemplary two-dimensional pupil expander including two replicators, each replicator being in the form of a solid waveguide;

[0069] Figure 6 A schematic diagram of a system according to the prior art;

[0070] Figure 7 A schematic diagram of a system according to an embodiment of the present disclosure;

[0071] Figure 8A A schematic diagram of an LCOS in an ideal system;

[0072] Figure 8B A schematic diagram of an LCOS in a system according to the prior art; and

[0073] Figure 8C A schematic diagram of an LCOS in a system according to an embodiment of the present disclosure.

[0074] In all the figures, the same reference numerals will be used to refer to the same or similar parts. Detailed Description of the Invention

[0075] The present invention is not limited to the embodiments described below, but extends to the full scope of the appended claims. That is, the present invention can be implemented in different forms and should not be construed as limited to the described embodiments, which are set forth for illustrative purposes.

[0076] Unless otherwise specified, terms in the singular form may include the plural form.

[0077] A structure described as being formed on the upper / lower part of another structure or above / below another structure should be construed to include cases where the structures are in contact with each other, and in addition, cases where a third structure is provided between them.

[0078] When describing temporal relationships, such as when the chronological order of events is described as "after", "subsequently", "next", "before", etc., the present disclosure should be considered to include both continuous and discontinuous events, unless otherwise specified. For example, the description should be considered to include discontinuous cases unless terms such as "just", "adjacent", or "direct" are used.

[0079] Although terms such as "first" and "second" may be used herein to describe various elements, these elements are not limited by these terms. These terms are only used to distinguish between individual elements. For example, without departing from the scope of the appended claims, the first element may be referred to as the second element, and similarly, the second element may be referred to as the first element.

[0080] The features of different embodiments may be coupled or combined with each other partially or wholly, and may interoperate with each other differently. Some embodiments may be executed independently of each other, or may be executed together in a relationship of mutual dependence.

[0081] In the present disclosure, the term "substantially" when applied to a structural unit of a device may be interpreted as the technical features of the structural unit produced within the technical tolerances of the method used to manufacture it.

[0082] Conventional optical configuration of holographic projection

[0083] Figure 1 An embodiment is shown in which a computer-generated hologram is encoded on a single spatial light modulator. The computer-generated hologram is the Fourier transform of the object to be reconstructed. Thus, it can be said that the hologram is a representation of the object in the Fourier domain or frequency domain or spectral domain. In this embodiment, the spatial light modulator is a reflective liquid crystal on silicon "LCOS" device. The hologram is encoded on the spatial light modulator, and a holographic reconstruction is formed at a replay field such as a light receiving surface such as a screen or a diffuser.

[0084] A light source 110, such as a laser or a laser diode, is arranged to irradiate the SLM 140 via a collimating lens 111. The collimating lens makes a substantially planar wavefront of light incident on the SLM. In Figure 1 , the direction of the wavefront is off-normal (e.g., two or three degrees away from the plane truly orthogonal to the transparent layer). However, in other embodiments, a substantially planar wavefront is provided incident normally, and a beam splitter arrangement is used to separate the input and output optical paths. In Figure 1 The embodiment shown, the arrangement is such that light from the light source is reflected from the mirror back surface of the SLM and interacts with the light modulation layer to form an outgoing wavefront 112. The outgoing wavefront 112 is applied to an optical device including a Fourier transform lens 120, and the focal point of the Fourier transform lens 120 is located at the screen 125. More specifically, the Fourier transform lens 120 receives the modulated light beam from the SLM 140 and performs a frequency-space transformation to produce a holographic reconstruction at the screen 125.

[0085] It is worth noting that in this type of hologram, each pixel of the hologram contributes to the overall reconstruction. There is no one-to-one correlation between a specific point (or image pixel) on the replay field and a specific light modulation element (or holographic image pixel). In other words, the modulated light leaving the light modulation layer is distributed over the entire replay field.

[0086] In these embodiments, the position of the holographic reconstruction in space is determined by the diopter (focus) of the Fourier transform lens. In Figure 1 the illustrated embodiment, the Fourier transform lens is a physical lens. That is, the Fourier transform lens is an optical Fourier transform lens and performs a Fourier transform optically. Any lens can act as a Fourier transform lens, but the performance of the lens will limit the accuracy of the Fourier transform it performs. A person skilled in the art understands how to use a lens to perform an optical Fourier transform. In some embodiments of the present disclosure, the lens of the observer's eye performs the conversion of the hologram to an image.

[0087] Hologram calculation

[0088] In some embodiments, the computer-generated hologram is a Fourier transform hologram, or simply a Fourier hologram or a Fourier-based hologram, where the image is reconstructed in the far field by utilizing the Fourier transform property of a positive lens. The Fourier hologram is calculated by Fourier-transforming the desired light field in the replay plane back to the lens plane. A Fourier transform can be used to calculate the computer-generated Fourier hologram. By way of example only, the embodiments relate to Fourier holography and the Gerchberg-Saxton type algorithm. The present disclosure is equally applicable to Fresnel holography and Fresnel holograms that can be calculated by similar methods. In some embodiments, the hologram is a phase or pure-phase hologram. However, the present disclosure is also applicable to holograms calculated by other techniques, such as techniques based on point cloud methods.

[0089] In some embodiments, the hologram engine is arranged to exclude the contribution of light blocked by the limiting aperture of the display system from the hologram calculation. UK Patent Application 2101666.2, filed on 5 February 2021 and incorporated herein by reference, discloses a first method of hologram calculation, where eye tracking and ray tracing are used to identify sub-regions of the display device for calculating a point cloud hologram that eliminates ghost images. The sub-regions of the display device correspond to the apertures of the present disclosure and are used to exclude the optical paths from the hologram calculation. UK Patent Application 2112213.0, filed on 26 August 2021 and incorporated herein by reference, discloses a second method based on an improved Gerchberg-Saxton type algorithm, which includes the step of performing light field clipping according to the pupil of the optical system during the hologram calculation. The clipping of the light field corresponds to the determination of the limiting aperture of the present disclosure. UK Patent Application 2118911.3, filed on 23 December 2021 and also incorporated herein by reference, discloses a third method of calculating a hologram, which includes the step of determining the region of a so-called extended modulator formed by the hologram duplicator. According to the present disclosure, the region of the extended modulator is also an aperture.

[0090] In some embodiments, a real-time engine is provided that is arranged to receive image data and compute holograms in real time using an algorithm. In some embodiments, the image data is a video comprising a sequence of image frames. In other embodiments, the holograms are pre-computed, stored in a computer memory and retrieved as needed for display on an SLM. That is, in some embodiments, a repository of predetermined holograms is provided.

[0091] Large field of view using a small display device

[0092] Broadly speaking, the present disclosure relates to image projection. It relates to methods of image projection and image projectors comprising a display device. The present disclosure also relates to projection systems comprising an image projector and an observation system, wherein the image projector projects or relays light from the display device to the observation system. The present disclosure is equally applicable to monocular and binocular observation systems. The observation system may comprise one or more eyes of an observer. The observation system includes an optical element having a focal power (such as the lens of a human eye) and an observation plane (such as the retina of a human eye). The projector may be referred to as a "light engine". The display device and the image formed (or perceived) using the display device are spatially separated from each other. The observer forms or perceives the image on a display plane. In some embodiments, the image is a virtual image and the display plane may be referred to as a virtual image plane. In other examples, the image is a real image formed by holographic reconstruction and the image is projected or relayed to the observation plane. In these other examples, the spatially modulated light of an intermediate holographic reconstruction formed in free space or on a screen or other light-receiving surface between the display device and the observer is propagated to the observer. In both cases, the image is formed by illuminating a diffraction pattern (such as a hologram or a kinoform) displayed on the display device.

[0093] The display device includes pixels. The pixels of the display may display a diffraction pattern or structure of diffracted light. The diffracted light may form an image on a plane that is spatially separated from the display device. According to well-known optical principles, the magnitude of the maximum diffraction angle is determined by the size of the pixels and other factors such as the wavelength of light.

[0094] In an embodiment, the display device is a spatial light modulator, such as a liquid crystal on silicon ("LCOS") spatial light modulator (SLM). Light propagates from the LCOS to an observing entity / system such as a camera or an eye within a range of diffraction angles (e.g., from zero to the maximum diffraction angle). In some embodiments, magnification techniques may be used to increase the range of available diffraction angles beyond the conventional maximum diffraction angle of the LCOS.

[0095] In some embodiments, light from the hologram itself propagates to the eye. For example, the spatially modulated light of the hologram (which has not been fully converted to a holographic reconstruction, i.e., an image) - which can be informally referred to as being "encoded" with / by the hologram - propagates directly to the observer's eye. The observer can perceive a real or virtual image. In these embodiments, no intermediate holographic reconstruction / image is formed between the display device and the observer. Sometimes it is said that in these embodiments, the lens of the eye performs the conversion or transformation of the hologram to an image. The projection system or light engine can be configured such that the observer effectively looks directly at the display device.

[0096] The "light field" mentioned here is a "complex light field". The term "light field" simply means a light pattern having a finite size in at least two orthogonal spatial directions such as x and y. The term "light field" simply means a light pattern having a finite dimension in at least two orthogonal spatial directions (x and y). The term "complex" used here simply means that the light at each point in the light field can be defined by an amplitude value and a phase value, and thus can be represented by a complex number or a pair of values. For the purpose of hologram calculation, the complex light field can be a two-dimensional array of complex numbers, where the complex numbers define the light intensity and phase at multiple discrete positions within the light field.

[0097] According to well-known optical principles, the angular range of light propagating from the display device that can be observed by the eye or other observing entity / system varies with the distance between the display device and the observing entity. For example, at an observation distance of 1 meter, only a small angular range from an LCOS can propagate through the pupil of the eye to form an image on the retina at a given eye position. The angular range of the light rays propagating from the display device determines the portion of the image that is "visible" to the observer, which can successfully propagate through the pupil of the eye to form an image on the retina at a given eye position. In other words, not all parts of the image are visible from any point on the observation plane (e.g., any eye position within an observation window such as an eye box).

[0098] In some embodiments, the image perceived by the observer is a virtual image that appears upstream of the display device, that is, the observer perceives the image to be farther from them than the display device. Thus, conceptually, it can be considered that the observer is observing the virtual image through a "display-device-sized window", which can be very small, e.g., 1 centimeter in diameter, and at a relatively large distance, e.g., 1 meter. And the user will observe the display-device-sized window through the pupil of their eye, which can also be very small. Thus, at any given time, the field of view is reduced, and the specific angular range that can be seen depends strongly on the eye position.

[0099] The pupil expander solves the problem of how to increase the angular range of light propagating from the display device, and this light can successfully propagate through the pupil of the eye to form an image. The display device is typically (relatively) small and the projection distance is (relatively) large. In some embodiments, the projection distance is at least one order of magnitude larger than the diameter or width of the entrance pupil and / or aperture of the display device (i.e., the size of the pixel array), for example at least two orders of magnitude.

[0100] The use of a pupil expander laterally increases the viewing area (i.e., the user's eyebox), thus enabling some movement of the eye while still enabling the user to see the image. As those skilled in the art will understand, in an imaging system, the viewing area (the user's eyebox) is the area where the observer's eye can perceive the image. The present disclosure includes a non-infinite virtual image distance - i.e., a near-field virtual image.

[0101] Traditionally, a two-dimensional pupil expander includes one or more one-dimensional optical waveguides, each formed using a pair of opposing reflective surfaces, where the output light from the surfaces forms a viewing window or eyebox. The light received from the display device (e.g., spatially modulated light from an LCOS) is replicated by the waveguide or each waveguide in order to increase the field of view (or viewing area) in at least one dimension. In particular, the waveguide expands the viewing window because additional light rays or "copies" are generated by dividing the amplitude of the incident wavefront.

[0102] The display device can have an active or pixel display area, and this active or display area has a first dimension of less than 10 cm, for example less than 5 cm or less than 2 cm. The propagation distance between the display device and the viewing system can be greater than 1 m, for example greater than 1.5 m or greater than 2 m. The optical propagation distance within the waveguide can be up to 2 m, for example up to 1.5 m or up to 1 m. The method is capable of receiving an image and determining a corresponding hologram of sufficient quality within less than 20 ms, such as less than 15 ms or less than 10 ms.

[0103] In some embodiments described by way of example of only diffraction or holographic light fields in accordance with the present disclosure, the hologram is configured to route light into a plurality of channels, each channel corresponding to a different part (i.e., sub-region) of the image. The channels formed by the diffraction structure are referred to herein as "hologram channels" merely to reflect that they are light channels encoded by a hologram with image information. It can be said that the light of each channel is in the holographic domain rather than in the image or spatial domain. In some embodiments, the hologram is a Fourier or Fourier transform hologram, and thus the holographic domain is the Fourier or frequency domain. The hologram can equally be a Fresnel or Fresnel transform hologram. The hologram can also be a point cloud hologram. The hologram is described herein as routing light into a plurality of hologram channels to reflect that the image reconstructable from the hologram has a finite size and can be arbitrarily divided into a plurality of image sub-regions, where each hologram channel will correspond to each image sub-region. Importantly, the hologram of this example is characterized by how it distributes the image content when illuminated. Specifically and uniquely, the hologram divides the image content by angle. That is, each point on the image is associated with a unique ray angle in the spatially modulated light formed by the hologram when illuminated - at least a unique pair of angles since the hologram is two-dimensional. For the avoidance of doubt, this hologram behavior is not conventional. When illuminated, the spatially modulated light formed by this special type of hologram can be divided into a plurality of hologram channels, where each hologram channel is defined by a certain range of ray angles (in two dimensions). From the above, it can be understood that any hologram channel (i.e., sub-range of ray angles) that can be considered in the spatially modulated light will be associated with a corresponding part or sub-region of the image. That is, all the information required to reconstruct that part or sub-region of the image is contained within the angular sub-range of the spatially modulated light formed by the hologram of the image. When observing the spatially modulated light as a whole, there may not necessarily be any evidence of multiple discrete light channels.

[0104] Nevertheless, the hologram can still be recognized. For example, if only a continuous portion or sub-region of the spatially modulated light formed by the hologram is reconstructed, only a sub-region of the image should be visible. If different continuous portions or sub-regions of the spatially modulated light are reconstructed, different sub-regions of the image should be visible. Another identifying feature of this type of hologram is that the shape of the cross-section of any hologram channel substantially corresponds to (i.e., is substantially the same as) the shape of the entrance pupil, although the size may be different - at least at the correct plane of the computer-generated hologram. Each light / hologram channel propagates from the hologram at a different angle or angular range. While these are example ways of characterizing or identifying this type of hologram, other ways may also be used. In summary, the holograms disclosed herein are characterized and identified by how the image content is distributed within the light encoded by the hologram. Additionally, for the avoidance of any doubt, references herein to holograms configured to direct light or angularly divide an image into multiple hologram channels are for example only, and the present disclosure is equally applicable to any type of holographic light field or even the pupil expansion of any type of diffractive or diffracted light field.

[0105] The system can be provided in a compact and streamlined physical form. This makes the system suitable for a wide range of practical applications, including those with limited space and high asset value. For example, it can be implemented in a head-up display (HUD), such as a vehicle or automotive HUD.

[0106] According to the present disclosure, a pupil expander for diffracted light is provided, which can include a diverging light beam. The diffractive light field can be defined by a "light cone". Thus, the size of the diffractive light field (as defined in a two-dimensional plane) increases with the propagation distance from the corresponding diffractive structure (i.e., the display device). It can be said that the pupil expander replicates the hologram or forms at least one replica of the hologram to convey that the light transmitted to the observer is spatially modulated according to the hologram.

[0107] In some embodiments, two one-dimensional waveguide pupil expanders are provided, each one-dimensional waveguide pupil expander arranged to effectively increase the size of the system's exit pupil by forming multiple replicas or copies of the exit pupil (or the light of the exit pupil) of the spatial light modulator. The exit pupil can be understood as the physical region of the light output by the system. It can also be said that each waveguide pupil expander is arranged to expand the size of the system's exit pupil. It can also be said that each waveguide pupil expander is arranged to expand / increase the size of the eyebox within which the observer's eye can be located in order to see / receive the light output by the system.

[0108] Optical channel

[0109] Holograms formed according to some embodiments angularly divide the image content to provide a plurality of hologram channels, which may have a cross-sectional shape defined by the aperture of the optical system. The holograms are calculated to provide such guidance of the diffracted light field. In some embodiments, as described above, this is achieved by considering the aperture (virtual or real) of the optical system during hologram calculation.

[0110] Figure 2 and 3 An example of this type of hologram is shown, which can be used in combination with the pupil expander disclosed herein. However, this example should not be construed as a limitation of the present disclosure.

[0111] Figure 2 An image 252 for projection is shown, including eight image regions / components V1 to V8. By way of example only, Figure 2 eight image components are shown, and the image 252 can be divided into any number of components. Figure 2 An encoded light pattern 254 (i.e., a hologram) is also shown, which can reconstruct the image 252 - for example, when converted by the lens of a suitable viewing system. The encoded light pattern 454 includes first to eighth sub-holograms or components H1 to H8, corresponding to the first to eighth image components / regions V1 to V8. Figure 2 It further shows how the hologram angularly decomposes the image content. Thus, the hologram is characterized by its guidance of light. This is shown in Figure 3 . Specifically, the hologram in this example directs light into a plurality of discrete regions. In the example shown, the discrete regions are disks, but other shapes can also be contemplated. After propagation through the waveguide, the optimal size and shape of the disks can be related to the size and shape of the aperture of the optical system (e.g., the entrance pupil of the viewing system).

[0112] Figure 4 A system 400 is shown, including a display device that displays the hologram calculated as shown in Figure 2 and 3 .

[0113] The system 400 includes a display device, which in this arrangement includes an LCOS 402. The LCOS 402 is arranged to display a modulation pattern (or "diffraction pattern") including the hologram and project the light that has been holographically encoded onto an eye 405, which includes a pupil acting as an aperture 404, a lens 409, and a retina (not shown) acting as a viewing plane. There is a light source (not shown) arranged to illuminate the LCOS 402. The lens 409 of the eye 405 performs the conversion of the hologram to an image. The light source can be of any suitable type. For example, it can include a laser source.

[0114] The viewing system 400 also includes a waveguide 408 located between the LCOS 402 and the eye 405. The presence of the waveguide 408 enables all angular content from the LCOS 402 to be received by the eye, even at the relatively large projection distances shown. This is because the waveguide 408 acts as a pupil expander in a well-known manner and is therefore only briefly described here.

[0115] In short, Figure 4 the waveguide 408 shown includes a generally elongated structure. In this example, the waveguide 408 includes an optical plate of refractive material, but other types of waveguides are also well-known and may be used. The waveguide 408 is positioned to intersect a light cone (i.e., a diffracted light field) projected from the LCOS 402, for example at an oblique angle. In this example, the size, position, and orientation of the waveguide 408 are configured to ensure that light from each of the eight light beams within the light cone enters the waveguide 408. Light from the light cone enters the waveguide 408 via a first planar surface of the waveguide 408 (the surface closest to the LCOS 402 in position) and is guided at least partially along the length of the waveguide 408 before being emitted via a second planar surface of the waveguide 408 that is generally opposite the first surface (the surface closest to the eye in position). It is readily understood that the second planar surface is partially reflective and partially transmissive. In other words, when each ray of light propagates within the waveguide 408 from the first planar surface and impinges on the second planar surface, some light will transmit out of the waveguide 408 and some light will be reflected back to the first planar surface by the second planar surface. The first planar surface is reflective such that all light impinging on it from within the waveguide 408 will be reflected back to the second planar surface. Thus, some light can simply refract between the two planar surfaces of the waveguide 408 before being transmitted, while other light can be reflected and thus can undergo one or more reflections (or "bounces") between the planar surfaces of the waveguide 408 before being transmitted.

[0116] Figure 4 A total of nine "bounce" points B0 to B8 along the length of the waveguide 408 are shown. Although as Figure 2 shown, light associated with all points of the image (V1 - V8) is transmitted out of the waveguide at each "bounce" from the second planar surface of the waveguide 408, only light from one angular portion of the image (e.g., light from one of V1 to V8) has a trajectory that enables it to reach the eye 405 from each corresponding "bounce" point B0 to B8. Additionally, light from different angular portions (V1 to V8) of the image reaches the eye 405 from each corresponding "bounce" point. Thus, in Figure 4 the example, each angular channel of the encoded light reaches the eye from the waveguide 408 only once.

[0117] The waveguide 408 forms multiple replicas of a hologram at corresponding "bounce" points B1 to B8 along its length, corresponding to the direction of pupil expansion. AsFigure 4 As shown, multiple replicas can be linearly extrapolated back to the corresponding multiple replicas or virtual display device 402'. This process corresponds to the step of "unfolding" the optical path within the waveguide such that the light rays of the replicas are extrapolated back to a "virtual surface" without internal reflection within the waveguide. Thus, the light expanding the exit pupil can be considered to originate from a virtual surface (also referred to herein as an "expanded modulator") including the display device 402 and the replicated display device 402'.

[0118] Although virtual images have been generally discussed herein and a virtual image requires the eye to transform the received modulated light to form a perceived image, the methods and apparatuses described herein can be applied to real images.

[0119] Two-dimensional pupil expansion

[0120] While Figure 4 the arrangement shown includes a single waveguide providing pupil expansion in one dimension, pupil expansion can be provided in more than one dimension, such as in two dimensions. Additionally, while Figure 4 the example in

[0121] Figure 5A uses holograms that have been calculated to create optical channels, each corresponding to a different part of the image, the present disclosure and the systems described below are not limited to this type of hologram.

[0122] In Figure 5A system 500, the first replicator 504 includes a first pair of surfaces stacked parallel to each other and arranged to provide replication or pupil expansion in a manner similar to Figure 4 waveguide 408 of Figure 5A . The first pair of surfaces are similar in size and shape to each other (identical in some cases) and are substantially elongated in one direction. The collimated beam 502 is directed to the input on the first replicator 504. Due to the internal reflection process between the two surfaces and the partial transmission of the light from each of the multiple output points on one of the surfaces (the upper surface, as

[0123] The second replicator 506 includes a second pair of surfaces stacked parallel to each other and arranged to receive each collimated beam of the first plurality of beams 508, and further arranged to provide replication or pupil expansion by expanding each of these beams in a second direction that is substantially orthogonal to the first direction. The first pair of surfaces are similar in size and shape to each other (identical in some cases) and are substantially rectangular. The second replicator is implemented with a rectangular shape so that it has a length along the first direction to receive the first plurality of beams 508 and a length along the second orthogonal direction to provide replication in the second direction. Due to the internal reflection process between the two surfaces and the partial transmission of light from each of the plurality of output points on one of the surfaces (such as the upper surface as shown in Figure 5A ), the light of each beam within the first plurality of beams 508 is replicated in the second direction. Thus, a second plurality of beams 510 are emitted from the second replicator 506, where the second plurality of beams 510 includes replicas of the input beam 502 along each of the first and second directions. Thus, the second plurality of beams 510 can be regarded as including a two-dimensional grid or array of replica beams.

[0124] Thus, it can be said that Figure 5A the first and second replicators 504, 505 combine to provide a two-dimensional replicator (or "two-dimensional pupil expander"). Thus, the replicated beams 510 can be emitted along the optical path to an expanded eye box of a display system, such as a head-up display.

[0125] In Figure 5A the system, the first replicator 504 is a waveguide including a pair of elongated straight reflective surfaces stacked parallel to each other. Similarly, the second replicator 504 is a waveguide including a pair of rectangular reflective surfaces stacked parallel to each other. In other systems, the first replicator can be a solid elongated straight waveguide, and the second replicator can be a solid planar rectangular waveguide, where each waveguide includes an optically transparent solid material, such as glass. In this case, the pair of parallel reflective surfaces are formed by a pair of opposing main sidewalls, optionally including respective reflective and reflection-transmissive surface coatings, which are familiar to those skilled in the art.

[0126] Figure 5B A perspective view of a system 500 is shown, which includes two replicators 520, 540 arranged for replicating a beam 522 in a two-dimensional space, where the first replicator is a solid elongated waveguide 520 and the second replicator is a solid planar waveguide 540.

[0127] In Figure 5BIn the system, the first replicator / waveguide 520 is arranged such that a pair of its elongated parallel reflective surfaces 524a, 524b are perpendicular to the plane of the second replicator / waveguide 540. Accordingly, the system includes an optical coupler arranged to couple light from the output port of the first replicator 520 to the input port of the second replicator 540. In the illustrated arrangement, the optical coupler is a planar / folding mirror 530, which is arranged to fold or redirect the optical path of the light to achieve the desired optical coupling from the first replicator to the second replicator. As Figure 5B shown, the mirror 530 is arranged to receive light from the output port / reflection-transmission surface 524a of the first replicator / waveguide 520, including a one-dimensional array of replicas extending in a first dimension. The mirror 530 is tilted so as to redirect the received light at an angle onto the optical path of the input port in the (total) reflection surface of the second replicator 540 to provide waveguide and replica formation along its length in a second dimension. It should be understood that the mirror 530 is one example of an optical element capable of redirecting light in the manner shown, and one or more other elements may alternatively be used to perform this task.

[0128] In the illustrated arrangement, the (partial) reflection-transmission surface 524a of the first replicator 520 is adjacent to the input port of the first replicator / waveguide 520 that receives the input beam 522 at an angle to provide waveguide and replica formation along its length in the first dimension. Accordingly, the input port of the first replicator / waveguide 520 is located at its input end, on the same surface as the reflection-transmission surface 524a. The skilled reader will understand that the input port of the first replicator / waveguide 520 can be in any other suitable location.

[0129] Accordingly, Figure 5B the arrangement enables the first replicator 520 and the mirror 530 to be provided as part of a first relatively thin layer in the first and third dimensions (shown as the x-z plane). Specifically, the size or “height” of the first planar layer (in which the first replicator 520 is located) is reduced in the second dimension (shown as the y dimension). The mirror 530 is configured to direct light out of the first layer / plane (i.e., “the first planar layer”) in which the first replicator 520 is located and direct it to the second layer / plane (i.e., “the second planar layer”) in which the second replicator 540 is located, which is located above and substantially parallel to the first layer / plane. Accordingly, the overall size or “height” of the system—in the first and third dimensions (illustrated as the x-z plane)—in the second dimension (illustrated as the y dimension)—of the first and second replicators 520, 540 and the mirror 530 located in the stacked first and second planar layers—is compact. The skilled reader will understand that many variations to the Figure 5B arrangement for implementing the present disclosure are possible and contemplated.

[0130] An image projector can be arranged to project a diverging or diffracted light field. In some embodiments, the light field is encoded with a hologram. In some embodiments, the diffracted light field includes diverging light beams. In some embodiments, the image formed by the diffracted light field is a virtual image.

[0131] In some embodiments, the first pair of parallel / complementary surfaces are elongated or slender surfaces that are relatively long along a first dimension and relatively short along a second dimension, e.g., relatively short along each of two other dimensions, each dimension being substantially orthogonal to each of the corresponding other dimensions. The process of light reflecting / transmitting between / from the first pair of parallel surfaces is arranged such that the light propagates within the first waveguide pupil expander, and the general direction of light propagation is the relatively long direction of the first waveguide pupil expander (i.e., in its "elongated" direction).

[0132] A system is disclosed herein that uses diffracted light to form an image and provides an eye box size and field of view suitable for real-world applications - e.g., in the automotive industry via a head-up display. The diffracted light is the light holographically reconstructed from a diffractive structure to form an image - e.g., a hologram such as a Fourier or Fresnel hologram. Using diffraction and diffractive structures requires a high-density display device with very small pixels (e.g., 1 micron) - which in practice means a small display device (e.g., 1 cm). The inventors have solved the problem of how to provide a diffracted light field for 2D pupil expansion, e.g., a diffracted light including a diverging (non-collimated) light beam.

[0133] In some embodiments, the display system includes a display device - such as a pixelated display device, e.g., a spatial light modulator (SLM) or a liquid crystal on silicon (LCoS) SLM - that is arranged to provide or form a diffracted or diverging light. In these aspects, the aperture of the spatial light modulator (SLM) is the limiting aperture of the system. That is, the aperture of the spatial light modulator - more specifically, the size of the region defining the array of light modulation pixels contained within the SLM - determines the size (e.g., spatial extent) of the light beam that can exit the system. According to the present disclosure, it is stated that by using at least one pupil expander, the exit pupil of the system is expanded such that the exit pupil of the system (which is limited by a small display device having a pixel size for light diffraction) becomes larger in spatial extent.

[0134] The diffracted or diverging light field can be said to have a "light field size" that is defined in a direction substantially orthogonal to the propagation direction of the light field. Since the light is diffracted / diverged, the light field size increases with the propagation distance.

[0135] In some embodiments, the diffracted light field is spatially modulated according to the hologram. In other words, in these aspects, the diffracted light field includes a "holographic light field". The hologram can be displayed on a pixelated display device. The hologram can be a computer-generated hologram (CGH). It can be a Fourier hologram or a Fresnel hologram or a point cloud hologram or any other suitable type of hologram. Optionally, the hologram can be calculated so as to form channels of holographic light, each channel corresponding to a different part of the image that the observer wishes to view (or perceive, if it is a virtual image). The pixelated display device can be configured to display a plurality of different holograms continuously or sequentially. Each aspect and embodiment disclosed herein can be applied to the display of multiple holograms.

[0136] The output port of the first waveguide pupil expander can be coupled to the input port of the second waveguide pupil expander. The second waveguide pupil expander can be arranged to direct the diffracted light field (including some, preferably most, preferably all replicas of the light field output by the first waveguide pupil expander) from its input port to the corresponding output port by means of internal reflection between a third pair of parallel surfaces of the second waveguide pupil expander.

[0137] The first waveguide pupil expander can be arranged to provide pupil expansion or replication in a first direction, while the second waveguide pupil expander can be arranged to provide pupil expansion or replication in a different second direction. The second direction can be substantially orthogonal to the first direction. The second waveguide pupil expander can be arranged to maintain the pupil expansion provided by the first waveguide pupil expander in the first direction and to expand (or replicate) some, preferably most, preferably all replicas that it receives from the first waveguide pupil expander in the different second direction. The second waveguide pupil expander can be arranged to receive the light field directly or indirectly from the first waveguide pupil expander. One or more other elements can be provided along the propagation path of the light field between the first and second waveguide pupil expanders.

[0138] The first waveguide pupil expander can be substantially elongated, and the second waveguide pupil expander can be substantially planar. The elongated shape of the first waveguide pupil expander can be defined by a length along a first dimension. The planar or rectangular shape of the second waveguide pupil expander can be defined by a length along the first dimension and a width or breadth along a second dimension that is substantially orthogonal to the first dimension. The dimension or length of the first waveguide pupil expander along its first dimension can respectively correspond to the length or width of the second waveguide pupil expander along its first dimension or second dimension. The first surface of a pair of parallel surfaces of the second waveguide pupil expander that includes its input port can be shaped, sized, and / or positioned to correspond to the area defined by the output port on the first surface of a pair of parallel surfaces on the first waveguide pupil expander, such that the second waveguide pupil expander is arranged to receive each replica output by the first waveguide pupil expander.

[0139] The first and second waveguide pupil expanders can jointly provide pupil expansion in a first direction and a second direction perpendicular to the first direction. Optionally, the plane containing the first and second directions is substantially parallel to the plane of the second waveguide pupil expander. In other words, the first and second dimensions that respectively define the length and width of the second waveguide pupil expander can be parallel to the first and second directions (or parallel to the second and first directions respectively), where the waveguide pupil expander provides pupil expansion. The combination of the first waveguide pupil expander and the second waveguide pupil expander is generally referred to as a "pupil expander".

[0140] It can be said that the expansion / replication provided by the first and second waveguide expanders has the effect of expanding the exit pupil of the display system in each of the two directions. The region defined by the expanded exit pupil can in turn define an expanded eye box region from which an observer can receive light of an input diffracted or diverging light field. It can be said that the eye box region lies in or defines the viewing plane.

[0141] The two directions of the exit pupil expansion can be coplanar or parallel to the first and second directions in which the first and second waveguide pupil expanders provide replication / expansion. Alternatively, in an arrangement including other elements such as an optical combiner, for example, the windshield of a vehicle, the exit pupil can be considered as the exit pupil from such other element, such as from the windshield. In such an arrangement, the exit pupil can be non-coplanar and non-parallel to the first and second directions in which the first and second waveguide pupil expanders provide replication / expansion. For example, the exit pupil can be substantially perpendicular to the first and second directions in which the first and second waveguide pupil expanders provide replication / expansion.

[0142] The viewing plane and / or the eye box region can be non-coplanar or non-parallel to the first and second directions in which the first and second waveguide pupil expanders provide replication / expansion. For example, the viewing plane can be substantially perpendicular to the first and second directions in which the first and second waveguide pupil expanders provide replication / expansion.

[0143] To provide suitable emission conditions for achieving internal reflection within the first and second waveguide pupil expanders, the elongated dimension of the first waveguide pupil expander can be inclined with respect to the first and second dimensions of the second waveguide pupil expander.

[0144] Combiner shape compensation

[0145] The advantage of projecting a hologram onto an eyebox is that the optical compensation can be encoded in the hologram (see, for example, European Patent 2936252, which is incorporated herein by reference). The present disclosure is compatible with holograms that compensate for the complex curvature of an optical combiner that is part of a projection system. In some embodiments, the optical combiner is the windshield of a vehicle. All the details of this method are provided in European Patent 2936252 and are not repeated here because the detailed features of these systems and methods are not necessary for the new teachings of this disclosure herein and are merely examples of configurations that benefit from the teachings of this disclosure.

[0146] Control device

[0147] The present disclosure is also compatible with an optical configuration that includes a control device (such as a light shutter device) to control the transfer of light from a light-channel hologram to an observer. The holographic projector may also include a control device arranged to control the transfer of an angular channel to an eyebox position. UK Patent Application 2108456.1, filed on June 14, 2021 and incorporated herein by reference, discloses at least one waveguide pupil expander and a control device. The reader will understand from at least this prior disclosure that the optical configuration of the control device is based substantially on the user's eyebox position and is compatible with any hologram calculation method for implementing the light channels described herein. It can be said that the control device is a light shutter or aperture device. The light shutter device may include a 1D array of apertures or windows, where each aperture or window can be independently switched between a light-transmissive and light-opaque state to control the transfer of the hologram light channels and their replicas to the eyebox. Each aperture or window may include a plurality of liquid crystal cells or pixels.

[0148] Duplicate distortion and spacing

[0149] Figure 6 is a schematic diagram of a part of a display system 600, showing the effect of a curved optical component 608 (in this case, the windshield of a vehicle) on multiple replicas 602 of spatially modulated light.

[0150] The multiple replicas 602 are generated by spatially modulated light from a display device (such as the LCOS described above, not shown) passing through a duplicator or waveguide (also not shown), such as the duplicator or waveguide described above with respect to Figures 4 to 5B the duplicator or waveguide. Those skilled in the art will understand that although Figure 6 is a side cross-sectional (two-dimensional) view of the system 600, the multiple replicas 602 will also extend into the third dimension.

[0151] In this example, multiple replicas are equally spaced apart at a first distance 604. The spacing of the replicas 602 allowed by the first distance 604 can be arranged (by design) to ensure that conflicting replicas 602 cannot enter the observer's pupil simultaneously, which would cause the observer to see double images. Thus, the observer's eye tracking is utilized to track the observer's eye within the eye box, so that it can be derived which replicas 602 the observer's pupil will receive. This allows the display device to change the spatially modulated light that is generated (to form the replicas 602) to ensure that conflicting replicas 602 do not enter the observer's eye and cause the aforementioned double images. It should be understood that the closer the spacing of the replicas 602, the more precise the eye tracking must be, because a smaller movement of the observer (and by extension, the aperture of their pupil) has a greater chance of moving into the paths of more replicas. In other words, for their pupil, allowing different replicas 602 (which could cause the aforementioned double images) would require a smaller movement of the observer. The higher the precision required for eye tracking, the higher the computational power and complexity required to implement it. Thus, at least this spacing should be maintained to preserve the image quality observed by the observer and to reduce the computational power required to achieve said image quality.

[0152] Multiple replicas 602 interact with a curved optical component 608. In this case, the curved optical component 608 is a vehicle windshield that acts as an optical combiner. Some of the light of the replicas 602 is reflected by the curved optical component 608 towards the user at a generally (but not exactly, as will be discussed further below) perpendicular angle. It should be understood that although Figure 6 only the paths of the replicas 602 that are of concern to the present disclosure are shown, some of the light of the replicas 602 will take paths different from the shown paths. For example, some light can pass through the curved optical component 608 rather than being reflected by it.

[0153] Due to the curvature of the curved optical component 608, the reflection angles of the reflected light are not exactly perpendicular and actually vary across the surface of the curved optical component 608. As Figure 6 shown, this has the effect of tilting the paths of each of the multiple replicas 602 towards each other. This causes the multiple replicas 602 to be spaced apart at a second distance 616 that is much shorter than the first distance 602. In other words, the curved optical component 608 compresses the spacing of the multiple replicas 602. Although the multiple replicas 602 travel parallel to each other before interacting with the curved optical component 608, after said interaction, they instead converge towards each other. In summary, the curved optical component 608 applies a positive optical power to the multiple replicas 602. As will be described below, this positive optical power causes many problems.

[0154] As described above, the spacing of the replicas 602 must be maintained such that as few replicas 602 as possible enter the pupil simultaneously to prevent the observer from seeing double images. The positive optical power of the curved optical component 608 compresses the spacing of the replicas 602 and thus contributes to double images in this way.Figure 6 The first imaginary pupil diameter 610 is shown at a first length 611 away from the curved optical component 608. At this first length 611, it is possible to guide only one of the replicas 602 through the aperture 610. Thus, if an observer is positioned such that the distance of their eyes from the length of the curved optical component 608 is similar to the first length 611, they will not perceive ghosting from the replicas 602. However, a second imaginary pupil diameter 612 is shown at a second length 613 away from the curved optical component 608, and the second length 613 is longer than the first length 611. It can be seen that due to the spacing of the multiple replicas 602 being compressed by the curved optical component 608, the replicas overlap such that multiple replicas 602 will always pass through the second aperture 612. Thus, if an observer is positioned such that the distance of their eyes from the length of the curved optical component 608 is similar to the second length 613, they will likely perceive ghosting from the replicas 602. Thus, the observer must move closer to the curved optical component 608 (from the second length 613 to the first length 611) or may experience a ghosting effect. Moving the observer in this way is not possible in many cases, such as when the curved optical component 608 is the windshield of a vehicle and the observer cannot move closer due to the dashboard and driving position.

[0155] The positive optical power of the curved optical component 608 also pushes the virtual image distance (i.e., the distance beyond the curved optical component 608 at which the observer sees the image carried by the replica 602). This can cause problems with the observer's perception of the target image - either the target image is too small for them to see clearly, or the observer perceives the target image to be in the wrong location (e.g., away from any surrounding objects where the target image might draw attention).

[0156] Finally, the curvature of the curved optical component 608 effectively applies different phase delays to each replica 602 during the aforementioned interactions. This delay causes the different replicas 602 to reach the observer at different times, which can cause the image to appear distorted.

[0157] Hardware correction

[0158] Figure 7 is a schematic diagram of a part of the display system 700, showing how the light control device 706 can be used to overcome the effects of the curved optical component 608 on the multiple replicas 602 of spatially modulated light.

[0159] As Figure 6 shown, the multiple replicas 602 are generated by spatially modulated light from a display device (such as the LCOS described above, not shown) passing through a duplicator or waveguide (also not shown), for example as described above with respect to Figures 4 to 5BThe replicator or waveguide described above. Due to the aforementioned replicator / waveguide, multiple replicas are equally spaced apart at a first distance 604. Those skilled in the art will understand that although Figure 7 is a side cross-sectional (two-dimensional) view of system 700, the multiple replicas 602 will also extend into the third dimension.

[0160] However, different from Figure 6 , the multiple replicas 602 interact with the light control device 706 before interacting with the curved optical component 608. In Figure 7 , the light control device 706 is represented by a curved mirror, however other suitable devices are possible, such as Fresnel lenses, and the devices disclosed in the aforementioned UK patent applications 2317637.3 and 2401627.1.

[0161] The light control device 706 applies a negative optical power to the multiple replicas 602. That is, as light travels between the light control device 706 and the curved optical component 608, the spacing between the replicas 602 increases. As a result, when the replicas 602 interact with the curved optical component 608, the corresponding negative optical power from the curvature of the curved optical component 608 is canceled by the positive optical power from the light control device 706. In other words, the light control device 706 diverges the multiple replicas 602 by the same amount as the curved optical component 608 converges the multiple replicas 602.

[0162] As a result, the multiple replicas 602 that arrive at the light control device 706 parallel to each other remain parallel to each other after interacting with the curved optical component 608. In this way, the light pupil diameters 710, 712, 714 can be placed at any length from the curved optical component 608 along the path of the replicas 602, and placed in such a way that only one replica 602 is allowed to pass through. Therefore, the observer can be located anywhere along the path of the replicas 602 and still see the image at the correct virtual image distance without the aforementioned ghosting caused by replica overlap. Additionally, since (due to its diverging nature caused by the negative optical power of the light control device 706) the replicas 602 are spaced apart at a second distance 716 greater than the first distance 602, the computational power required for eye tracking is reduced. This is because the greater spacing between the replicas 602 allows the observer to have a greater degree of freedom of movement before their eyes may encounter conflicting replicas 602 (which, as described above, can cause ghosting). In other words, as the replicas 602 are spaced farther apart, the observer can move a greater distance before encountering conflicting replicas 602 that may cause ghosting. In this way, the eye tracking can be less precise, resulting in a need for less computational power.

[0163] Similarly, the phase delay of the replicas caused by the curved optical component 608 relative to each other can also be mitigated by causing a corresponding phase delay by the optical control device 706, such that each replica 602 is in the same phase. This ensures that after interacting with the curved optical component 608 and receiving the phase delay, each replica 602 still reaches the observer in the same phase, thereby reducing image distortion. This correction by the optical control device 706 can be applied to any optical property imparted to the replicas 602 by the curved optical component 608.

[0164] However, the details of the optical control device 706 (such as the exact curvature and phase delay provided at each point on its surface) must be tuned to the corresponding properties of the curved optical component 608. That is, if the first replica 602i is reflected by a point Ai of the curved optical component 608, and the point Ai applies a optical power +Pi and a phase delay +Di, then the optical control device 706 must have a corresponding point Bi, where the first replica 602i is also reflected, and the point Ai applies an optical power -Pi and a phase delay -Di. Similarly, if the second replica 602ii is reflected by a point Aii of the curved optical component 608, and the point Aii applies an optical power +Pii and a phase delay +Dii, then the optical control device 706 must have a corresponding point Bii, where the second replica 602ii is also reflected, and the point Aii applies an optical power -Pii and a phase delay -Dii. For each replica 602, this must continue for each point on the curved optical component 608 and the corresponding points on the optical control device 706. Those skilled in the art will understand that for each point on the curved optical component 608, other properties in addition to the optical power and phase delay must also be adjusted. Thus, the time spent developing and manufacturing the optical control device 706 for each curved optical component 608 is long because each point on the optical control device 706 must be finely tuned in this way.

[0165] Hardware and software correction

[0166] The inventors have found that pre-adjusting each replica 602 with a software lens can resolve any minor differences between the properties of the optical control device 706 and the curved optical component 608. That is, while most of the optical power and phase delay (and other properties) caused by the curved optical component 608 are cancelled out by the corresponding opposite properties of the corresponding points of the optical control device 706, a smaller correction of the properties of the curved optical component 608 can be achieved using the software lens. When describing such an optical control device that purposefully applies only partial correction / compensation, the reference numeral 706' will be used.

[0167] To use the above example, the first replica 602i is reflected by the point Ai of the bending optical component 608, and the point Ai applies an optical power +Pi and a phase delay +Di. As described above, the optical control device 706' has a corresponding point B1' where the first replica 6021 is reflected. However, in this case, the point Bi' applies an optical power -Pi' and a phase delay -Di'. The optical power -Pi' and the phase delay -Di' are different from the above optical power -Pi and phase delay -Di. The sum of the optical power -Pi' of the optical control device 706' and the optical power +Pi of the bending optical component 608 is not zero, and there will be a remaining optical power +Pi of the bending optical component 608. The same is true for the phase delay -Di' of the optical control device 706' and the opposite phase delay +Di of the bending optical component 608 (as well as any other characteristics of the bending optical component 608 corrected by the optical control device 706').

[0168] Conversely, there is a correction of the optical power +Pi* and the phase delay +Di* (as well as any other characteristics) provided by the software lens. In this case, the sum of the optical power -Pi of the bending optical component 608 and the combination of the optical power +Pi' of the optical control device 706' and the optical power +Pi* of the software lens is zero. The same is true for the combination of the phase delay -Di of the bending optical component 608 and the phase delay +Di' of the optical control device 706' and the phase delay +Di* of the software lens (as well as any other characteristics of the bending optical component 608 that need to be corrected or compensated). This process is repeated for each replica 602, at each point on the bending optical component 608 and the corresponding point of the optical control device 706'.

[0169] Although the discussion has involved the complete correction of the bending optical component 608 (i.e., the sum of the values related to the bending optical component 608, the optical control device 706', and the software lens is zero), the present disclosure also involves the compensation of the bending optical component 608. That is, when the sum of the values related to the bending optical component 608, the optical control device 706', and the software lens is close to zero, an improved image is generated for the observer.

[0170] Although the inventors found that using a pure software lens solution would produce significant image ghosting, especially in the case where the curvature of the bending optical component 608 increases (which requires a more powerful software lens), the combination of the hardware solution of the optical control device 706' and the software lens is a positive compromise. Most of the correction / compensation is achieved by the hardware solution of the optical control device 706', and the fine-tuning is achieved by the software solution of the software lens.

[0171] LCOS pixel control

[0172] It has also been found that the negative correction using the curved optical component 608 can improve the image quality by increasing the pixel area available for creating an image on the LCOS. By tracing the path of each replica 602 from the observer back to the LCOS (through various optical components such as the curved optical component 608, the light control devices 706, 706', and the duplicator / waveguide), the inventors have found that only a relatively small number of pixels on the LCOS control the appearance of each point of the image visible to the observer.

[0173] Figure 8A FIG. 4 is a schematic diagram of a region of the LCOS 800a in the display system, where the optical combiner is flat (i.e., a flat optical component rather than the curved optical component 608). In this ideal system (a system without the distortion caused by the curvature of the curved optical component 608), the area of the pixels 802a is responsible for the appearance of the imaginary point of the expected image from the observer's perspective. It can be seen that there is a relatively large number of pixels (because the area of the pixels 802a is large and symmetric), which means that the imaginary associated point of the image can be presented in good detail.

[0174] Figure 8B FIG. 5 is a schematic diagram of a similar region of the LCOS 800b but for Figure 6 the system 600 shown (i.e., a system with the curved optical component 608 but without proper correction). Due to the distortion caused by the curvature of the curved optical component 608 (as described above), the area of the pixels 802b responsible for the appearance of the imaginary point of the expected image has shrunk and become distorted. That is, the area 802b is now less symmetric and has an increased aspect ratio (where the length of the area 802b from the upper left to the lower right of the figure is less than the length of the area 802b from the lower left to the upper right). As such, there are fewer pixels available to present the imaginary point of the image, resulting in the point being presented with less detail (lower quality) than Figure 8A the ideal system.

[0175] By optically correcting the distortion caused by the curvature of the curved optical component 608 using the system 700, the region of the LCOS 800c as shown in Figure 8C FIG. 6 is achieved. It can be seen that the area of the pixels 802c is larger and more symmetric than the area of Figure 8B the uncorrected system 600. That is, the area 802c is more symmetric than the area 802b and has an aspect ratio closer to that of the area 802a. As such, there are more pixels in the area 802c, and thus the imaginary point of the image can be presented to the observer in more detail.

[0176] Additional features

[0177] The methods and processes described herein can be embodied on a computer-readable medium. The term "computer-readable medium" includes media arranged to store data temporarily or permanently, such as random access memory (RAM), read-only memory (ROM), buffer memory, flash memory, and cache memory. The term "computer-readable medium" should also be considered to include any medium or combination of media capable of storing instructions for execution by a machine such that when the instructions are executed by one or more processors, the machine performs, wholly or in part, any of the one or more methods described herein.

[0178] The term "computer-readable medium" also encompasses cloud-based storage systems. The term "computer-readable medium" includes, but is not limited to, one or more tangible and non-transitory data repositories (e.g., data volumes) in the form of examples such as solid-state storage chips, optical discs, magnetic disks, or any suitable combination thereof. In some example embodiments, the instructions for execution can be conveyed by a carrier medium. Examples of such carrier media include transient media (e.g., a propagated signal that conveys instructions).

[0179] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the scope of the appended claims. The present disclosure covers all modifications and variations within the scope of the appended claims and their equivalents.

Claims

1. A display system, comprising: a replicator arranged to receive the spatially modulated light and replicate the spatially modulated light to form a plurality of copies of the spatially modulated light through a waveguide between a reflective surface and a transflective surface, the transflective surface forming an output surface of the plurality of copies of the spatially modulated light; as well as A light control device is located in the optical path of the multiple copies of the spatially modulated light, downstream of the output surface of the replicator, and is arranged to provide a first compensation for the curvature of the curved optical component downstream of the light control device, wherein the first compensation is a function of the position on the output surface and is arranged to only partially offset the curvature of the optical component.

2. The display system according to claim 1, wherein: The spatially modulated light is a holographic wavefront and the replicator is arranged to form multiple copies of the holographic wavefront.

3. The display system according to claim 1 or 2, wherein: The light control device comprises a lens, optionally a Fresnel lens, further optionally wherein the lens is a film, optionally having a thickness less than 5 mm, such as less than 2 mm, less than 1 mm or less than 0.5 mm.

4. A display system as claimed in any preceding claim, wherein: The first compensation has an opposite lens effect to the curved optical component.

5. A display system as claimed in any preceding claim, wherein: The first compensation is a negative optical power, and / or wherein the curved optical component has a positive optical power.

6. A display system as claimed in any preceding claim, further comprising: a processor arranged to determine a hologram of the image and a lens function, the lens function providing a second compensation for the curvature of a curved optical component downstream of the light control device, wherein the second compensation is arranged to only partially cancel the curvature of the optical component; as well as A display device arranged to spatially modulate light according to a diffraction pattern displayed thereon, wherein the diffraction pattern comprises a hologram and a lens function.

7. The display system according to claim 6, wherein: The lens function is a pixelated lens function.

8. The display system according to claim 6 or 7, wherein: The second compensation is a negative optical power.

9. The display system according to any one of claims 6 to 8, wherein: The diffraction pattern comprises a superposition or sum of the hologram and a lens function.

10. A display system as claimed in any one of claims 6 to 9, further comprising an observer tracking system arranged to determine a position within an eye box and to relate the position to a sub-region of the curved optical component and a position on an output surface of the replicator, wherein the first and second compensations compensate for the curvature of the sub-region of the curved optical component.

11. The display system according to any one of claims 6 to 10, wherein: The first compensation and the second compensation together provide full compensation for the curvature of the curved optical component.

12. The display system according to any one of claims 6 to 11, wherein: The first compensation is 2 to 10 times greater than the second compensation.

13. The display system according to any one of claims 6 to 11, wherein: The first compensation provides a virtual image shift correction in the range of 75% to 99%, and the second compensation provides a virtual image shift correction in the range of 1% to 25%.

14. The display system according to any one of claims 6 to 13, wherein: The magnitude of the first and / or second compensation is such that a spacing of each of the plurality of replicas at a viewing plane of the display system is at least half the size of a human pupil.

15. The display system according to claim 14, wherein: The spacing is controlled at least in part by each compensation of the curvature of the curved optical component.

16. The display system according to claim 14 or 15, wherein: The spacing between each of the plurality of replicas is greater than or approximately equal to the size of a human pupil.

17. The display system according to any one of claims 6 to 16, wherein: Compensation for the curvature of the curved optical component is such that the footprint of the viewing pupil on the display device encompasses at least 50 pixels, optionally 50 to 75 pixels, or alternatively optionally 100 pixels of the display device.

18. The display system according to any one of claims 6 to 17, wherein: Compensation for the curvature of the curved optical component is such that the footprint of the viewing pupil on the display device is substantially symmetrical.

19. The display system according to any one of claims 6 to 18, wherein: Compensation for the curvature of the curved optical component is such that the footprint of the viewing pupil on the display device has an area with an aspect ratio in the range of 1:1 to 1:1.

25.

20. A method of processing spatially modulated light, the method comprising: receiving the spatially modulated light at a replicator having a reflective surface and a transflective surface, the transflective surface forming an output surface; replicating the spatially modulated light to form a plurality of copies of the spatially modulated light by waveguiding the spatially modulated light between the reflective surface and the transflective surface, the plurality of copies of the spatially modulated light being output from the replicator at the output surface; receiving a plurality of copies at a light control device; as well as A first compensation for the curvature of the curved optical component downstream of the light control device is provided via the light control device, wherein the first compensation is a function of the position on the output surface and is arranged to only partially cancel the curvature of the optical component.

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