Light control device

Abstract

To provide a display system.SOLUTION: A display system comprises 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 by waveguiding between a reflective surface and a transmissive-reflective surface. The transmissive-reflective surface forms an output surface for the plurality of replicas of the spatially modulated light. The display system further comprises a light control device that is arranged in an 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 configured so as to provide a first compensation for a curvature of a curved optical component downstream of the light control device. The first compensation is a function of a position on the output surface, and is configured to cancel the curvature of the optical component only partially, and hold a distortion to some extent from the curvature of the optical component of at least one replica in comparison with other replicas.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a display system including an optical control device. The present invention also relates to an optical control device such as a thin film and a method for correcting the curvature of an optical combiner such as a front glass of a vehicle. Some embodiments relate to a holographic projector, an image generation unit, or a head-up display.

Background Art

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

[0003] Computer-generated holography numerically simulates the interference process. Computer-generated holograms can be calculated by methods based on mathematical transforms such as Fresnel transform and Fourier transform. These types of holograms may be referred to as Fresnel / Fourier transform holograms, or simply Fresnel / Fourier holograms. Fourier holograms can be regarded as the Fourier domain / plane representation of an object, or the frequency domain / plane representation of an object. Computer-generated holograms can also be calculated by, for example, coherent ray tracing or point cloud methods.

[0004] Computer-generated holograms may be encoded on a spatial light modulator arranged to modulate the amplitude and / or phase of the incident light. The optical modulation can be realized using, for example, electrically addressable liquid crystals, optically addressable liquid crystals, or micromirrors.

[0005] A spatial light modulator typically consists of a plurality of individually addressable pixels, often referred to as cells or elements. The light modulation method can be binary, multi-level, or continuous. Alternatively, the device may be continuous (i.e., not composed of pixels), in which case the light modulation is continuous across the entire device. The spatial light modulator may be reflective, in which case the modulated light is reflected and output. The spatial light modulator may similarly be transmissive, in which case the modulated light is transmitted and output.

[0006] Using the system described herein, a holographic projector can be provided. Such projectors are applied to head-up displays (HUDs).

SUMMARY OF THE INVENTION

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

[0008] Generally speaking, there is provided a light control device or glare reduction device for display light configured to correct the curvature of a curved optical component in the optical path of the display light. In an embodiment, the light control device or glare reduction device is for the display light of a display system. In an embodiment, the curved optical component is in the optical path of the display system. In some embodiments, the curved optical component is an optical combiner such as a vehicle windshield configured to redirect 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 that causes complex distortion, especially when used in a display system based on holographic projection.

[0009] The represented light may be spatially modulated light. The display system may be configured to relay the spatially modulated light to an observation surface 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 an image display system (e.g., part of a conventional image generation unit), and the spatially modulated light is light spatially modulated according to an image or an image. In these embodiments, the spatially modulated light may be referred to as an image or an image wavefront. The image wavefront may be received from a screen or a diffuser. Thus, the image wavefront may be diffused and / or may include a range of light 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 surface while allowing the spatially modulated light to reach the observation surface. For example, the display device may include an optical component including a reflective surface. Without the light control device, ambient light may be reflected by the reflective surface toward the viewing surface / eyebox of the display device, resulting in glare. The light control device of the present disclosure is configured to suppress such reflection.

[0010] As described above, the light control device of the present disclosure is further configured to correct the curvature of a curved optical component on the optical path of the display system. The fact that a curved optical component is on the optical path of the display system means that the spatially modulated light propagating through the display system may be incident on the curved optical component, reflected by the curved optical component, transmitted through the curved optical component, or interact with the curved optical component. As can be understood by those skilled in the art, the curvature of the optical component may change the divergence or convergence of the 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 may become 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 may 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 also be non-uniform. For example, different portions of the curved optical component may have different radii of curvature, and thus may have different lens effects on the spatially modulated light incident thereon. In some embodiments, the curved optical component is the front windshield or windshield of a vehicle. The front windshield or windshield may have a complex curvature with a complex lens effect on the display light incident thereon.

[0011] The inventors have identified several problems related to the lens effect of a curved optical component. One problem is that the display light (of a display system) may be distorted by the lens effect. For example, the display light may be light such that an image is visible on the display surface. For example, the display light may be spatially modulated according to a hologram of an image or simply according to an image. Due to the lens effect of the curved optical component, the image visible on the display surface may be distorted. This may have an adverse effect on the viewing experience of the display system. Another problem identified by the inventors is specific to a display system having a replicator upstream of a curved optical component. The replicator can be arranged to replicate spatially modulated light to form a plurality of replicas of the spatially modulated light. For example, when the spatially modulated light is a holographic wavefront, the replicator can be arranged to form a plurality of replicas of the holographic wavefront. In an embodiment, the replicator may be a waveguide, as described below. For example, the waveguide may comprise an input port arranged to receive spatially modulated light. The waveguide may comprise a pair of surfaces arranged to guide the spatially modulated light received at the input. The first of the pair of surfaces may be partially transmissive and partially reflective. The first surface may be arranged to form a plurality of replicas of the spatially modulated light. At least a portion of the first surface can be said to form an output port of the replicator / waveguide. The replicator may be arranged such that a plurality of replicas are relayed towards the curved optical component. The display system may be further arranged such that a plurality of replicas are relayed towards the display surface / eyebox of the display system. The inventors have discovered that the pitch (on the display surface) of the replicas of the spatially modulated light is important for ensuring a good viewing experience. Through simulations and experiments, the inventors have further discovered that the pitch of the replicas may be affected by the lens effect of the curved optical component. For example, the pitch of the replicas on the display surface may increase or decrease. This may have an adverse effect on the viewing experience.For example, as the pitch of the replicas decreases, the so-called ghost effect, where a copy of the intended image or image content is displayed slightly shifted from the intended image or image content, may become more prominent. When the curved optical component is in a concave shape, such as in the case of a front glass or the inner surface of a front glass, the pitch of the replicas may decrease. The pitch of the replicas used here refers to the separation or distance between the centers of adjacent replicas.

[0012] Light control devices / anti-glare devices for reflection / glare suppression are disclosed, for example, in UK Patent No. GB2607672 and UK Patent Application No. GB2303536.3 (Publication No. GB2627988A). Light control devices for correcting the curvature of curved optical components are also disclosed in UK Patent Applications 2317637.3 and 2401627.1. These applications are incorporated herein by reference.

[0013] However, the inventors have addressed the problem that, as described in these applications, reducing the lens effect of a curved optical component with only physical lenses requires different lenses for each change in the curved optical component. For example, if the curved optical component is the front glass of a vehicle, different lenses need to be used for each different vehicle line on which the system needs to be installed. If the lens is not finely adjusted or optimized to match the curvature of the curved optical component, elements of the above problem may still remain. This not only requires significant additional development time and cost to complete the process of finely adjusting / optimizing the lens for all vehicle lines, but also increases the manufacturing complexity as the production facility needs to handle multiple different lenses used in combination 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 replication device configured to receive spatially modulated light and replicate the spatially modulated light to form a plurality of replicas of the spatially modulated light by guiding the spatially modulated light 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 further includes a light control device disposed in an optical path of the plurality of replicas of the spatially modulated light downstream of the output surface of the replication device. The light control device is configured to provide a first correction to a curvature of a curved optical component downstream of the light control device. The first correction is a function of a position (or location) on the output surface (or on the light control device) and is configured to only partially cancel the curvature of the optical component. In other words, the first correction is not constant or varies across the position of 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 optical control device corrects the curvature of the corresponding point of the curved optical component. The "corresponding" points are the points on the optical control device or the curved optical component that interact with the replica emitted from an arbitrary point on the output surface of the replicator, that is, the optical control device, the curved optical component, and the points on the output surface of the replicator that are connected by the same replica when ray-tracing the replica through the system. The correction provided by the optical control device for a replica emitted from a specific point on the output surface may vary compared to the correction provided by the optical control device for a replica emitted from an adjacent point on the output surface, and thus, the first correction varies across the output surface (i.e., is a function of the position on the output surface). In other words, in the case of an output surface having a first dimension and a second dimension, replicas are emitted from the output surface in the first dimension and the second dimension (array), and the correction provided by the optical control device to any of the replicas depends on the position of the corresponding point on the output surface in the first dimension and the second dimension from which the replica is emitted. That is, the correction is a function of at least one dimension of a component such as x or y. Although the description herein refers to "points" of the output surface, the optical control device, and the curved optical component, it will be understood by those skilled in the art that this is merely illustrative. In some cases, instead of corresponding finite "points", a "region" of the optical control device provides the correction necessary for the curvature of the corresponding region of the curved optical component.

[0016] Here, the expression "partial correction" is used to reflect that the first correction is configured to retain some of the distortion due to the curvature of the optical component. This distortion may be the distortion of at least one of the replicas compared to other replicas. The first correction has a magnitude that reduces the (wavefront) distortion caused by the curvature of the optical component, but does not completely remove it. That is, despite the partial correction effect of the optical control device, some (wavefront) distortion is retained. In other words, in the presence of the first (partial) correction, the (wavefront) distortion is smaller (has a lower magnitude) than in the absence of the first (partial) correction, but is not as low as in the case of complete correction.

[0017] In other words, a projector including a replicator and an optical control device is provided. The replicator is arranged to receive spatially modulated light and form a plurality of replicas of the spatially modulated light by guiding it between a reflective surface and a transmissive-reflective surface. The transmissive-reflective surface forms the output surfaces of the plurality of replicas of the spatially modulated light. The optical control device (e.g., a lens embodied as a thin film) is arranged in the optical paths of the plurality of replicas of the spatially modulated light downstream of the output surface of the replicator and is arranged to provide a first partial correction (e.g., a first negative refractive power) with respect to the curvature of a curved optical combiner (e.g., having a positive refractive power) used in cooperation with the projector (e.g., to receive the light of the projector). The first partial correction is a function of the position on the output surface that does not completely cancel the curvature of the optical combiner.

[0018] Therefore, the inventors have discovered that by intentionally selecting an optical control device that only partially corrects the curvature of a curved optical component, the system can be fine-tuned in other ways to fit a particular curved optical component. This allows the same system and optical control device to be used with various curved optical components, reducing the aforementioned additional development and manufacturing time and costs.

[0019] Compensation, or correction, can take into account the optical effects (such as wavefront distortion, aberration, or parallax, etc.) imparted to any or all of the replicas by the curved optical component (its curvature). In other words, the purpose of (partial) correction is that at least one of the optical properties or features (such as size, shape, aspect ratio, etc.) of at least one of the replicas after interacting with the curved optical component is closer to the intended optical property or feature than if no correction were performed. In summary, correction is to reduce the (wavefront) distortion of the replicas compared to each other. Distortion is the change in an optical property compared to the intended value.

[0020] Spatially modulated light is 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 an image.

[0021] The light control device can include a lens or a lens function, and optionally a Fresnel structure with a lens effect. The physical lens can be a film, and optionally, it can have a thickness of less than 5 mm, such as less than 2 mm, 1 mm, or 0.5 mm. This device provides the necessary correction / modification while minimizing the space occupied within the system and reducing the packaging constraints.

[0022] The first correction may have a lens effect opposite to that of the curved optical component. To avoid misunderstanding, here the term "opposite" is used in relation to direction and not necessarily in relation to magnitude. That is, the opposite lens effect has the opposite direction but not necessarily the opposite magnitude. The first correction may be a negative refractive power. The curved optical component may have a positive refractive power. Therefore, considering the refractive power of the curved optical component, the corresponding refractive power is provided by the correction.

[0023] The display system may further include a processor arranged to determine a hologram of an image, and a lens function that provides a second correction for the curvature of a curved optical component downstream of the light control device. The second correction is arranged to only partially cancel out the curvature of the optical component. The second correction may be arranged to retain distortion (such as at least some of the distortion) from the curvature of at least one replica of the optical component as compared to other replicas. The display system may further 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 include a processor arranged to determine a hologram of an image, and a (pixelated) lens function that provides a second partial correction (such as a second negative refractive power) for the curvature of a curved light combiner (such as having a positive refractive power) used in conjunction with the projector (such as to receive 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. The diffraction pattern includes the hologram and the lens function (such as their superposition or sum).

[0025] In some embodiments, the combination of the light control device (providing hardware correction / modification) and the lens function of the processor (providing software correction / modification) can fully correct or compensate for the curvature of the curved optical component without changing the hardware used for each of the different curved optical components. That is, most of the correction / modification is completed by the light control device, and 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 shortening the development and manufacturing time associated with the production of a new light control device for a new curved optical component with which the system is used in combination.

[0026] In other words, the optical control device is a passive component (i.e., a component that cannot be changed as needed during use). Therefore, in order to add degrees of freedom for correcting / modifying the curvature of the curved optical component, the optical control device does not exactly compensate for the refractive power of the curved optical component. Rather, the optical control device compensates for low-order refractive powers (such as focus shift and astigmatism), and software-based compensation is used for fine-tuning.

[0027] This combination of hardware and software correction / modification has more advantages than corrections using purely hardware or software solutions. As explained above, using purely hardware correction / modification requires installing new hardware for each curvature of the curved optical components used in the system. The advantages over purely software solutions are explained below.

[0028] The depth information of the virtual image (i.e., the image observed or perceived by the observer) is encoded in the wavefront of the replica emitted from the output surface of the replication device. When the wavefront is reflected by a curved optical component, the curvature of that component adds a positive refractive power to the wavefront, causing the image to move further away and increasing the virtual image distance (the distance at which the observer observes the virtual image). As a result, the virtual image may be too far away to be clearly visible to the observer or may be in the wrong position relative to the observer's surroundings. In order for the observer to perceive the correct virtual image distance, it is necessary to pre-correct the aberration with an inverse refractive power (i.e., a negative refractive power) before the wavefront hits the curved optical component.

[0029] An intuitive way to add negative refractive power is to apply a negative software lens "on top of" the hologram via the processor responsible for generating the hologram. This can bring the virtual image back to the nominal distance, but the inventors have discovered that significant ghost artifacts occur when the distance between the virtual image and the display device is short. The greater the curvature of the curved optical component, the stronger the optical power that needs to be added to the hologram, and the greater the ghost effect.

[0030] Therefore, the inventors have discovered that a better way to correct the distance of the virtual image is to add negative refractive power after the replicator. Adding such a negative light control device brings the virtual image closer to the viewer and generates the correct virtual image distance. However, as explained above, using only the hardware solution is not optimal in terms of development and manufacturing time and cost, so a software solution is incorporated (with more complementary capabilities) to fine-tune the correction / modification. In other words, the power of the hardware lens is similar to the focus shift and aberration of the curved optical component, but the software correction is fine-tuned according to the actual curved optical component and system parameters such as the field of view. There may be multiple terms (such as Zernike polynomials) in the software correction. Furthermore, the inventors have discovered that the image quality from the curved optical component is not fully restored even when using only the hardware solution. However, the residual ghost artifacts can be removed by software-based anti-ghost techniques known to the inventors during the calculation of the hologram.

[0031] When designing such a display system, the inventors discovered that there are two important planes: the plane where the display is located and the plane where the virtual image is located. Due to the optical power of the curved optical component, these two planes are further apart, so the virtual image appears too far from the intended distance to the viewer. Using a negative software lens makes the virtual image closer, but the display device remains at the same distance, so the distance between the virtual image and the display device becomes shorter (ghosting increases). A hardware lens is added between the display device and the viewer. This makes both the virtual image and the display device closer, and the distance between them is kept long enough to avoid ghosting. In summary, the software lens only affects the virtual image and does not affect the display device, while the hardware lens can affect both.

[0032] To obtain the best performance, a thin negative lens made of high-quality optical glass is desirable. However, in some embodiments, a Fresnel structure such as a Fresnel lens is used to reduce the overall volume and weight of the unit. The Fresnel structure can be said to have a lens effect or optical power. Alternatively, it can be said that the light control device has a Fresnel structure or a phase wrap structure.

[0033] The lens function may be a pixelated lens function. The second correction may be a negative optical power. The diffraction pattern is composed of the superposition or sum of a hologram and the lens function. Thus, the software part of the correction / modification is included as part of the replica reflected by the curved optical component.

[0034] The display system may further include a viewer tracking system configured to determine the position within the eyebox and correlate that position with the position on the output surface of the sub-region of the curved optical component and the replicator. The first and second corrections may correct the curvature of the sub-region of the curved optical component.

[0035] Briefly, here we disclose an approach that combines software and hardware to correct the curvature of a curved optical component, such as a combiner for a windshield. By combining a first correction and a second correction, the curvature of the curved optical component can be fully corrected. In other words, the correction / modification that was heretofore provided by a custom hardware solution for each different curved optical component is, in the present disclosure, achieved by summing the correction / modification provided by a software solution and a hardware solution.

[0036] The first correction can be from two to ten times the second correction. Alternatively, the first correction can provide virtual image offset correction in the range of 75% to 99%, and the second correction can provide virtual image offset correction in the range of 1% to 25%. In other words, most of the correction / compensation is achieved by the hardware solution, and the fine-tuning of the correction / compensation is achieved by the software solution. One skilled in the art can understand the mechanism by which the optical power associated with a curved optical component causes a change in the image distance. Therefore, the virtual image offset is a distance. Therefore, the virtual image offset correction is a percentage change in the image distance.

[0037] The size can be such that the spacing between each of the plurality of replicas on the display surface of the display system is at least half the size of the human pupil.

[0038] Similarly, according to a second aspect of the present disclosure, a display system is provided. The display system includes a replication device configured to receive spatially modulated light and replicate the spatially modulated light by guiding it between a reflective surface and a transmissive-reflective surface to form a plurality of replicas of the spatially modulated light. The transmissive-reflective surface forms an output surface of the plurality of replicas of the spatially modulated light. The display system further includes a light control device disposed in an optical path of the plurality of replicas of the spatially modulated light downstream of the output surface of the replication device. The light control device is configured to correct the curvature of a curved optical component downstream of the light control device. The correction is a function of the position on the output surface. The magnitude of the first and / or second correction is such that the spacing between each of the plurality of replicas on the display surface of the display system is at least half the size of a human pupil.

[0039] In order to provide a complete image to the viewer, it is necessary to track the viewer's eyes so that the correct replica passes through the pupil and reaches the retina (visible to the viewer), and optionally enable 3D display. If the correct replica does not pass through the pupil, at least a part of the intended image may not reach the viewer, or a crosstalk problem may occur. Similarly, when multiple conflicting replicas reach the eye, ghosts of (other) images may be displayed. This is particularly problematic when there is a curved optical component. With a curved optical component, multiple replicas may reach the viewer with different phases (because different phases are given to different replicas due to the curvature of the component), and the image will appear distorted to the viewer. Therefore, in order to minimize or eliminate this kind of distortion and ghosting, a large amount of computing power can be used to track the viewer's eyes within the eyebox.

[0040] By increasing the spacing between the replicas, the possibility that multiple conflicting replicas pass through the viewer's pupil simultaneously and cause the aforementioned image distortion is reduced. This reduces the likelihood that multiple conflicting replicas pass through the viewer's pupil, thus reducing the requirements on the eye tracking system. Therefore, the requirements on the eye tracking system can be relaxed.

[0041] The inventors have discovered that this can be achieved using the above hardware correction. The hardware correction causes the display device to approach the eye box, effectively increasing the separation between replicas and expanding the tolerance range of eye tracking.

[0042] The inventors have discovered that the correction of the curvature of the curved optical component is optimally performed such that the footprint of the observation pupil on the display device encompasses at least 50 pixels, optionally 50 to 75 pixels, or optionally 100 pixels of the display device. The correction of the curvature of the curved optical component is performed such that the footprint of the observation pupil on the display device is substantially symmetric. The correction of the curvature of the curved optical component is performed such that the footprint of the observation 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 replication device configured to receive spatially modulated light and form a plurality of replicas of the spatially modulated light by guiding the spatially modulated light 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 further includes an optical control device disposed in the optical paths of the plurality of replicas of the spatially modulated light downstream of the output surface of the replication device. The optical control device is configured to correct the curvature of a curved optical component downstream of the optical control device. The correction is a function of the position on the output surface. The display system further includes a display device configured to spatially modulate light. The correction of the curvature of the curved optical component can be performed such that the footprint of the observation pupil on the display device encompasses at least 50 pixels, optionally 50 to 75 pixels, or optionally 100 pixels of the display device. Alternatively, the correction of the curvature of the curved optical component can be performed such that the footprint of the observation pupil on the display device is substantially symmetric. Alternatively, the correction of the curvature of the curved optical component can be performed such that the footprint of the observation pupil on the display device has an aspect ratio in the range of 1:1 to 1:1.25.

[0044] The inventors have discovered that by ray tracing the optical paths of the replicas that return to the display device through the system, the distortion of the curved optical component also reduces and distorts the area on the display device related to a particular point of the image perceived by the observer. For example, if the area on the display device is circular or approximately circular, the distortion caused by the curved optical component can cause the area to become elliptical. That is, the width in the first direction of the circular area remains the same, but the width can be narrower in the second direction perpendicular to the first direction. In summary, the distortion causes the symmetry of the area to be lost, the size of the area to be reduced, and the aspect ratio to increase. The quality of each point of the reconstructed image depends greatly on the number of pixels contributing to that point and the way those pixels are distributed.

[0045] By using the corrections described in this disclosure, the inventors have discovered that regions on the display device can be restored, at least in part, to their shape and size as if no distortion had occurred. That is, the width of the region in the second direction may approach the width in the first direction. In other words, the correction increases the symmetry of the region, increases its size, and decreases its aspect ratio. This increase in the area of the display device corresponding to each point of the image perceived by the viewer means that the image can be rendered in more detail (in other words, at a higher resolution). The inventors have discovered that by using this approach, the perceived image quality, such as resolution, can be improved.

[0046] The display system may further include a curved optical component disposed downstream of the light control device. The curved optical component may be a light coupler. The curved optical component may be the front windshield of a vehicle.

[0047] The light control device can further include the function of a "rotating film" (i.e., the light control device can function as a rotating film). That is, the light control device can provide a "global rotation" that moves the position of the eye box / display window to a more comfortable and / or accessible position for the viewer / user (i.e., provides a minimum rotation amount equal for each replica). In other words, the first correction function can have a (static) coefficient such that each position on the light control device provides a minimum rotation amount.

[0048] According to a fourth aspect of the present disclosure, a method for processing spatially modulated light is provided. The method includes receiving the spatially modulated light with 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 forming a plurality of replicas of the spatially modulated light by guiding the spatially modulated light between the reflective surface and the transmissive-reflective surface to replicate the spatially modulated light. The plurality of replicas of the spatially modulated light are output from the replicator at the output surface. The method also includes receiving the plurality of replicas with an optical control device. Finally, the method includes providing, via the optical control device, a first correction to the curvature of a curved optical component downstream of the optical control device. The first correction is a function of a 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 offers the advantages of using partial correction as described above in connection with the first aspect of the present disclosure.

[0050] The method can further include determining, via a processor, a hologram of an image and a lens function that provides a second correction to the curvature of a curved optical component downstream of the optical control device. The second correction is configured to only partially cancel the curvature of the optical component. The method can also include spatially modulating the light on the 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 correction can be such that the spacing between each of the plurality of replicas at the display surface of the display system is at least half the size of the human pupil. The correction of the curvature of the curved optical component can be such that the footprint of the display pupil on the display device includes at least 50 pixels, optionally 50 - 75 pixels, or optionally 100 pixels of the display device.

[0052] It will be understood that the above features regarding 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 used only to reflect that spatially modulated light is split and the composite light field is directed along a plurality of different optical paths. The word "replica" is used to refer to each occurrence or instance of the composite light field after a replication event such as partial reflective transmission by a pupil expander. Each replica moves along a different optical path. Some embodiments of the present disclosure relate to the propagation of light encoded by a hologram rather than an image, i.e., to spatially modulated light by a hologram of an image rather than the image itself. Thus, it can be said that a plurality of replicas of the hologram are formed. Those skilled in the art of holography will understand that the composite light field associated with the propagation of light encoded by a hologram changes with the propagation distance. The use of the term "replica" here is independent of the propagation distance, and thus two optical branches or paths associated with a replication event are still called each other's "replicas" even if the lengths of the branches are different. As a result, the composite light field evolves in different forms along each path. That is, two composite light fields are still regarded as "replicas" according to the present disclosure even if they are associated with different propagation distances, provided that they are generated from the same replication event or a series of replication events.

[0054] The "diffraction light field" or "diffracted light field" according to the present disclosure is a light field formed by diffraction. The diffraction light field can be formed by irradiating the corresponding diffraction pattern. According to the present disclosure, an example of the diffraction pattern is a hologram, and an example of the diffraction light field is a light field that forms a holographic light field or a holographic reconstruction of an image. The holographic light field forms a (holographic) reconstruction of the image on the reproduction plane. It can be said that the holographic light field propagating from the hologram to the reproduction plane includes the light encoded by the hologram or the light within the hologram region. 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 the "diffraction light field" is a light field that forms a reconstruction on a plane spatially separated from the corresponding diffraction structure. An optical system for propagating the diffraction light field from the diffraction structure to the observer is disclosed herein. The diffraction light field can form an image.

[0055] The term "hologram" is used to refer to a record that contains amplitude information or phase information about an object, or a combination thereof. The term "holographic reconstruction" is used to refer to the optical reconstruction of an object formed by irradiating a hologram. The system disclosed herein is described as a "holographic projector". This is 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 where the holographic reconstruction is formed and is fully focused. When a hologram is displayed on a spatial light modulator that includes pixels, the replay field is repeated in the form of multiple diffraction orders, and each diffraction order is a replica of the zero-order replay field. Since the zero-order replay field is the brightest replay field, it generally corresponds to the priority or primary replay field. Unless explicitly stated otherwise, the term "replay field" is construed to refer to the zero-order replay field. The term "replay plane" is used to refer to a plane in space that includes all replay fields. The terms "image", "replay image", and "image region" refer to a region of the replay field illuminated by the light of the holographic reconstruction. In some embodiments, an "image" is composed of individual spots called "image spots" or, for convenience, "image pixels".

[0056] The terms "encode", "write", or "address" are used to describe a process of providing a plurality of control values that respectively determine the modulation levels of a plurality of pixels of an SLM. 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. Accordingly, the SLM is said to "display" a hologram, and the hologram can be regarded as an array of light modulation values or levels.

[0057] It has been found that acceptable quality holographic reconstruction can be formed from a "hologram" that contains only the phase information associated with the Fourier transform of the original object. Such a holographic record is sometimes 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 equally applicable to forming holographic reconstruction using the amplitude and phase information associated with the Fourier transform of the original object. In some embodiments, this is achieved by complex modulation using a so-called full complex hologram that includes both the amplitude and phase information associated with the original object. Such a hologram is sometimes referred to as a full complex hologram because the value (gray level) assigned to each pixel of the hologram has both amplitude and phase components. The value (gray level) assigned to each pixel can be represented as a complex number having both amplitude and phase components. In some embodiments, a full complex computer-generated hologram is calculated.

[0059] The phase of a pixel of a computer-generated hologram or a spatial light modulator, referred to as a phase value, phase component, phase information, or simply phase, may be referred to as an abbreviation for "phase delay". That is, the phase value being described is actually a numerical value (e.g., in the range from 0 to 2π) representing 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 delays the phase of the received light by π / 2 radians. In some embodiments, each pixel of the spatial light modulator is operable with one of a plurality of possible modulation values (e.g., phase delay values). The term "gray level" may be used to refer to a plurality of available modulation levels. For example, the term "gray level" may be used to refer to a plurality of phase levels available in a phase-only modulator, even if different phase levels do not provide different shades of gray. The term "gray level" may also be used, for convenience, to refer to a plurality of complex modulation levels available in a complex modulator.

[0060] Thus, a hologram is composed of an array of gray levels, i.e., an array of optical modulation values such as an array of phase delay values or complex modulation values. Since a hologram is a pattern that is displayed on a spatial light modulator and causes diffraction when irradiated with light having a wavelength comparable to (usually shorter than) the pixel pitch of the spatial light modulator, it can also be considered a diffraction pattern. Here, mention is made of combining a hologram with other diffraction patterns such as a diffraction pattern that functions as a lens or a grating. For example, a diffraction pattern that functions as a grating can be combined with a hologram to transform a reproduction field on a reproduction plane, or a diffraction pattern that functions as a lens can be combined with a hologram to focus holographic reconstruction on a near-field reproduction plane.

[0061] In the following detailed description, different embodiments and groups of embodiments may be disclosed separately, but 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 envisioned.

Brief Description of the Drawings

[0062] Specific embodiments are described by way of example only with reference to the following figures.

Figure 1

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[0063] The present invention is not limited to the embodiments described below, but extends to the entire scope of the appended claims. That is, the present invention can be implemented in different forms and should not be construed as being limited to the embodiments described for the purpose of explanation.

[0064] The singular terms may include the plural unless otherwise specified.

[0065] Structures described as being formed on top of / below other structures, or on / under other structures, are to be construed as including cases where the structures are in contact with each other, and further cases where a third structure is disposed therebetween.

[0066] When describing the relationship of time, for example, when the chronological order of events is described as "after", "subsequent", "next", "before", etc., unless otherwise specified, the present disclosure should be construed to include both continuous events and discontinuous events. For example, unless words such as "exactly", "immediately", "directly" are used, the description should be construed to include cases where it is not continuous.

[0067] In this specification, terms such as "first", "second", etc. may be used to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of the appended claims, the first element can also be called the second element, and similarly, the second element can also be called the first element.

[0068] The features of different embodiments can be combined or combined with each other partially or wholly, and can be interoperated with each other in various forms. Depending on the embodiment, they can be executed independently of each other or executed together in an interdependent relationship.

[0069] In the present disclosure, when applied to the structural unit of the device, the term "substantially" can be construed such that the technical features of the structural unit are generated within the technical tolerance range of the method used to manufacture it.

[0070] Conventional optical configuration of holographic projection FIG. 1 shows an embodiment in which a computer-generated hologram is encoded in a single spatial light modulator. The computer-generated hologram is the Fourier transform of the object for reconstruction. Therefore, it can be said that the hologram is a Fourier domain, frequency domain, or spectral domain representation of the object. In this embodiment, the spatial light modulator is a reflective liquid crystal on silicon (LCOS) device. The hologram is encoded in the spatial light modulator, and a holographic reconstruction is formed on a light receiving surface such as a screen or a diffuser, for example, a reproduction field.

[0071] A light source 110, such as a laser or a laser diode, is arranged to illuminate an SLM 140 via a collimating lens 111. The collimating lens makes an approximately planar wavefront of light incident on the SLM. In FIG. 1, the direction of the wavefront is not perpendicular (e.g., it is 2 or 3 degrees away from true orthogonality with respect to the plane of the transparent layer). However, in other embodiments, an approximately planar wavefront is provided with normal incidence, and a beam splitter arrangement is used to separate the input optical path and the output optical path. In the embodiment shown in FIG. 1, the light from the light source is reflected by the mirror back surface of the SLM and is arranged to interact with the light modulation layer to form an outgoing wavefront 112. The outgoing wavefront 112 is applied to an optical system including a Fourier transform lens 120 focused on a screen 125. More specifically, the Fourier transform lens 120 receives the beam of modulated light from the SLM 140, performs a frequency space conversion, and generates a holographic reconstruction on the screen 125.

[0072] In particular, in this type of holography, 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 reproduction field and a specific light modulation element (or hologram pixel). In other words, the modulated light emerging from the light modulation layer is dispersed throughout the reproduction field.

[0073] In these embodiments, the position of the holographic reconstruction in space is determined by the refractive power (focusing power) of the Fourier transform lens. In the embodiment shown in FIG. 1, the Fourier transform lens is a physical lens. That is, the Fourier transform lens is an optical Fourier transform lens, and the Fourier transform is performed optically. Any lens can function as a Fourier transform lens, but the performance of the lens limits the accuracy of the Fourier transform performed. Those skilled in the art understand how to perform an optical Fourier transform using a lens. In some embodiments of the present disclosure, the lens of the observer's eye performs the conversion from the hologram to the image.

[0074] Hologram calculation In some embodiments, the computer-generated hologram is a Fourier transform hologram, or simply a Fourier hologram, or a Fourier-based hologram, and the image is reconstructed in the far-field by utilizing the Fourier transform characteristics of a positive lens. The Fourier hologram is calculated by a Fourier transform that returns the desired light field of the playback surface to the lens surface. The computer-generated Fourier hologram can be calculated using a Fourier transform. Embodiments relate, by way of example only, to Fourier holography and Gerchberg-Saxton type algorithms. The present disclosure is equally applicable to Fresnel holography and Fresnel holograms that can be calculated in a similar manner. In some embodiments, the hologram is a phase or phase-only hologram. However, the present disclosure is also applicable to holograms calculated by other techniques such as those based on the point cloud method.

[0075] In some embodiments, the hologram engine is configured 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 February 5, 2021 and incorporated herein by reference, discloses a first hologram calculation method that uses ray tracing and ray tracing to identify sub-areas of a display device for the calculation of point cloud holograms that eliminate ghost images. The sub-areas of the display device correspond to the apertures of the present disclosure and are used to exclude optical paths from the hologram calculation. UK Patent Application 2112213.0, filed on August 26, 2021 and incorporated herein by reference, discloses a second method based on a modified Gerchberg-Saxton type algorithm that includes the step of cropping the light field according to the pupil of the optical system during hologram calculation. The cropping of the light field corresponds to the determination of the limiting aperture of the present disclosure. UK Patent Application 2118911.3, filed on December 23, 2021 and incorporated herein by reference, discloses a third method of calculating a hologram that includes the step of determining the area of a so-called extended modulator formed by a hologram replicator. According to this disclosure, the area of the extended modulator is also an aperture.

[0076] In some embodiments, a real-time engine is provided that is configured to receive image data and calculate holograms in real time using an algorithm. In some embodiments, the image data is a video comprising a series of image frames. In other embodiments, the holograms are pre-calculated, stored in computer memory, and called as needed for display on the SLM. That is, in some embodiments, a repository of predetermined holograms is provided.

[0077] Wide field of view using a small display device Broadly speaking, the present disclosure relates to image projection. The present disclosure relates to a method of image projection and an image projector including a display device. The present disclosure also relates to a projection system including an image projector and a display system. In this projection system, the image projector projects or relays light to the display system from the display device. The present disclosure is equally applicable to both monocular and binocular display systems. The display system can include the eyes of a viewer or multiple eyes. The display system includes an optical element having an optical power (e.g., the lens of a human eye) and a display surface (e.g., the retina of a human eye). The projector may be referred to as an "optical engine". The display device and the image formed (or perceived) using the display device are spatially separated from each other. The image is formed on the display surface or perceived by the viewer. In some embodiments, the image is a virtual image, and the display surface 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 onto the display surface. In these other examples, spatially modulated light of an intermediate holographic reconstruction formed on a free space or a screen or other light receiving surface between the display device and the viewer propagates to the viewer. In either case, the image is formed by irradiating a diffraction pattern (e.g., a hologram or a kinoform) displayed on the display device.

[0078] The display device is composed of pixels. The pixels of the display can display a diffraction pattern or structure that diffracts light. The diffracted light forms an image on a plane spatially separated from the display device. According to well-known optics, the magnitude of the maximum diffraction angle is determined by other factors such as the size of the pixel and the wavelength of light.

[0079] 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 towards a display entity / system such as a camera or an eye over a range of diffraction angles (e.g., from zero to a maximum diffraction angle). In some embodiments, an expansion technique can be used to expand the range of available diffraction angles beyond the conventional maximum diffraction angle of the LCOS.

[0080] In some embodiments, the light of the hologram itself reaches the eye. For example, the spatially modulated light of the hologram (holographic reconstruction, i.e., not yet fully converted into an image) can be said to be "encoded" by the hologram informally, but it reaches the viewer's eye directly. The viewer can perceive a real or virtual image. In these embodiments, no intermediate holographic reconstruction / image is formed between the display device and the viewer. In these embodiments, the eye lens is sometimes said to perform the conversion or transformation from the hologram to an image. The projection system or the light engine can be configured such that the viewer effectively sees the display device directly.

[0081] The specification refers to a "light field", which is a "complex light field". The term "light field" only indicates a pattern of light having a finite size in at least two orthogonal spatial directions, e.g., x and y. The term "complex" is used in this specification only to indicate that the light at each point within the light field is defined by an amplitude value and a phase value and can thus be represented by a complex number or a pair of values. For the purpose of hologram calculation, a complex light field is a two-dimensional array of complex numbers, where the complex numbers define the intensity and phase of the light at a plurality of discrete positions within the light field.

[0082] According to well-known optical principles, the range of angles of light propagated from a display device that can be observed by an eye or other observation target / system varies depending on the distance between the display device and the observation target. For example, at an observation distance of 1 meter, only a very small portion of the angles from an LCOS passes through the pupil of the eye and can form an image on the retina at a specific eye position. The range of angles of the light rays propagated from the display device is the range that can pass through the pupil of the eye and form an image on the retina, and determines the portion of the image that is "visible" to the observer. In other words, not all parts of the image are visible from any one point on the observation plane (for example, any one eye position within an observation window such as an eyebox).

[0083] In some embodiments, the image perceived by the viewer is a virtual image displayed upstream of the display device. That is, the viewer perceives the image to be farther away than the display device. Conceptually, the viewer can think of looking through a very small "window the size of the front display device", such as 1 cm in diameter, at a relatively large distance, for example 1 meter, to view the virtual image. Also, the user will be looking through a very small pupil of the eye at the window the size of the display device. Therefore, the field of view is narrow, and the specific angular range that can be seen depends greatly on the eye position at any given time.

[0084] The pupil expander addresses the problem of how to expand the range of angles of the light rays propagated from the display device and successfully pass through the pupil of the eye to form an image. The display device is generally (relatively) small, and the projection distance is (relatively) large. In some embodiments, the projection distance is at least one order of magnitude, for example at least two orders of magnitude, larger than the diameter or width of the entrance pupil and / or aperture of the display device (that is, the size of the pixel array).

[0085] When a pupil expander is used, the viewing area (i.e., the user's eye box) expands horizontally, allowing the user to move their eyes while still being able to view the image. As will be understood by those skilled in the art, in an image system, the viewing area (the user's eye box) is the area where the observer's eyes can recognize the image. The present disclosure is directed to a non-infinite virtual image distance, i.e., a near-field virtual image.

[0086] Conventionally, a two-dimensional pupil expander is composed of one or more one-dimensional optical waveguides each formed using a pair of opposing reflecting surfaces, and the output light from the surface forms a display window or an eye box. The light received from the display device (e.g., spatially modulated light from an LCOS) is replicated by the waveguide or each waveguide such that the viewing field (or display area) is expanded in at least one dimension. In particular, the waveguide expands the display window by generating additional light rays or "replicas" by splitting the amplitude of the incident wavefront.

[0087] It may have an active area or display area 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 display system may be more than 1 m, for example more than 1.5 m or more than 2 m. The optical propagation distance in the waveguide may be up to 2 m, for example up to 1.5 m or up to 1 m. This method can receive an image and determine a corresponding hologram of sufficient quality in less than 20 ms, for example less than 15 ms or less than 10 ms.

[0088] In some embodiments, although described only as an example of a diffractive light field or a holographic light field according to the present disclosure, the hologram is configured to route light into a plurality of channels, each channel corresponding to a different portion (i.e., sub-area) of the image. The channels formed by the diffractive structure are herein simply referred to as "hologram channels" to reflect that they are channels of light encoded by the hologram with image information. The light of each channel can be said to be in the hologram region rather than in the image or spatial region. In some embodiments, the hologram is a Fourier or Fourier transform hologram, and thus the hologram region is the Fourier or frequency domain. The hologram may similarly be a Fresnel or Fresnel transform hologram. The hologram may be a point cloud hologram. In this specification, the hologram is described as routing light into a plurality of hologram channels to reflect that the image that can be reconstructed from the hologram has a finite size and can be arbitrarily divided into a plurality of image sub-regions, each hologram channel corresponding to each image sub-region. Importantly, the hologram of this example is characterized by how it distributes the image content when illuminated. Specifically, 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, since the hologram is two-dimensional, it is a pair of unique angles. To avoid ambiguity, the operation of this hologram is different from the conventional one. The spatially modulated light formed by this special type of hologram, when illuminated, is divided into a plurality of hologram channels, each hologram channel being defined by a range of ray angles (two-dimensional). From the foregoing, it is understood that the hologram channels that may be considered in the spatially modulated light (i.e., sub-ranges of ray angles) are associated with respective portions or sub-regions of the image. That is, all the information necessary to reconstruct that portion or sub-region of the image is contained within the sub-range of angles of the spatially modulated light formed from the hologram of the image.When spatially modulated light is observed as a whole, evidence of multiple individual optical channels does not necessarily exist.

[0089] Nevertheless, the hologram can be identified. 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. A further distinguishing feature of this type of hologram is that the shape of the cross-sectional area of the hologram channel, at least in the correct plane in which the hologram was calculated, may be of different sizes but substantially corresponds to (i.e., is substantially the same as) the shape of the entrance pupil. Each light / hologram channel propagates from the hologram at a different angle or angular range. These are exemplary ways to characterize or identify this type of hologram, but other methods can also be used. In summary, the holograms disclosed herein are characterized by how image content is dispersed within the light encoded by the hologram and are distinguishable. Again, for the sake of avoiding doubt, the references herein to holograms configured to direct light or angularly divide an image into multiple hologram channels are for illustrative purposes only, and this disclosure is equally applicable to any type of holographic optical field, and further to any type of diffractive optical field or pupil expansion of a diffractive optical field.

[0090] This system can be provided in a compact and rationalized physical form. This enables the realization of a system suitable for various practical applications, such as when space is limited and real estate values are high. For example, it can be implemented in a head-up display (HUD) such as those in vehicles or automobiles.

[0091] According to the present disclosure, pupil dilation is provided for diffracted light or diffracted light including a diverging light beam. The diffracted light field is defined by a "light cone". Therefore, the size of the diffracted light field (defined on a two-dimensional plane) increases with the propagation distance from the corresponding diffraction structure (i.e., the display device). It can be said that the pupil expander replicates a hologram or forms a replication of at least one hologram, and conveys that the light reaching the viewer is spatially modulated according to the hologram.

[0092] In some embodiments, two one-dimensional waveguide pupil expanders are provided, and each one-dimensional waveguide pupil expander is arranged to effectively expand the size of the system's exit pupil by forming a plurality of replicas or copies of the exit pupil (or the light of the exit pupil) of the spatial light modulator. It can be understood that the exit pupil is the physical area where light is output by the system. Also, it can be said that each waveguide pupil expander is arranged to expand the size of the system's exit pupil. Also, it can be said that each waveguide pupil expander is arranged to expand / increase the size of the eye box where the observer's eye can be located to view / receive the light output by the system.

[0093] Light channeling The hologram formed according to some embodiments can provide a plurality of hologram channels that angularly divide the image content and have a cross-sectional shape defined by the aperture of the optical system. The hologram is calculated to provide this channeling of the diffracted light field. In some embodiments, this is achieved during hologram calculation by considering the aperture (virtual or real) of the optical system as described above.

[0094] Figures 2 and 3 show examples of this type of hologram that can be used in combination with the pupil dilation device disclosed herein. However, this example should not be considered limiting with respect to the present disclosure.

[0095] Figure 2 shows a projection image 252 that includes eight image regions / components V1 through V8. Figure 2 shows eight image components as an example, and image 252 can be divided into any number of components. Figure 2 also shows an encoded light pattern 254 (i.e., a hologram) that can reconstruct image 252 when converted by the lens of a suitable display system. The encoded light pattern 254 is composed of first through eighth sub-holograms or components H1 through H8 that correspond to the first through eighth image components / regions V1 through V8. Figure 2 further shows how the hologram decomposes image content by angle. Thus, the hologram is characterized by the channelling of light that it performs. This is shown in Figure 3. Specifically, the hologram in this example directs light into a plurality of individual regions. The individual regions are disks in the example shown, although other shapes are envisioned. The optimal disk size and shape may be related to the size and shape of the aperture of an optical system such as the entrance pupil of the observation system after propagation through the waveguide.

[0096] Figure 4 shows a system 400 that includes a display device that displays a hologram calculated as shown in Figures 2 and 3.

[0097] System 400 includes a display device that includes an LCOS 402 in this arrangement. The LCOS 402 displays a modulation pattern (or "diffraction pattern") that includes a hologram and projects holographically encoded light toward an eye 405 that includes a pupil that functions as an aperture 404, a lens 409, and a retina (not shown) that functions as a field plane. There is a light source (not shown) arranged to illuminate the LCOS 402. The lens 409 of the eye 405 performs the conversion from the hologram to an image. The light source may be of any suitable type. For example, it may be a laser light source.

[0098] The visual system 400 further includes a waveguide 408 disposed between the LCOS 402 and the eye 405. Due to the presence of the waveguide 408, all angular content from the LCOS 402 is received by the eye even at the relatively long projection distances shown in the figure. This is because the waveguide 508 functions as a pupil expander. This method is well known and will only be briefly described here.

[0099] Briefly speaking, the waveguide 408 shown in FIG. 4 is substantially composed of an elongated structure. In this example, the waveguide 408 is composed of an optical slab of a refractive material, but other types of waveguides are also well known and may be used. The waveguide 408 is arranged, for example, at an oblique angle so as to intersect the light cone (i.e., the diffracted light field) projected from the LCOS 402. In this example, the size, location, and position of the waveguide 408 are configured such that light from each of the eight light bundles within the light cone enters the waveguide 408. The light from the light cone enters the waveguide 408 through the first planar surface (closest to the LCOS 402) of the waveguide 408, and after being at least partially guided along the length of the waveguide 408, is emitted through the second planar surface (closest to the eye) substantially opposite the first surface. As is well understood, the second plane is partially reflective and partially transmissive. In other words, when each ray of light moves from the first plane into the waveguide 408 and hits the second plane, part of the light is transmitted through the waveguide 408, and part is reflected by the second plane and returns to the first plane. The first plane is reflective, and all light hitting the first plane from within the waveguide 408 is reflected to the second plane. Therefore, some of the light is refracted and then transmitted between the two planes of the waveguide 408, while other light is reflected and transmitted after undergoing one or more reflections (or "bounces") between the planes of the waveguide 408.

[0100] FIG. 4 shows a total of nine "reflection" points B0 to B8 along the length of the waveguide 408. As shown in FIG. 2, the light associated with all points (V1-V8) of the image is transmitted from the waveguide at each "reflection" from the second plane of the waveguide 408, but only the light from one angular portion of the image (e.g., the light from any of V1 to V8) has a trajectory that can reach the eye 405 from each "reflection" point B0 to B8. Further, the light from different angular portions V1 to V8 of the image reaches the eye 405 from each "reflection" point. Thus, in the example of FIG. 4, each angular channel of the encoded light reaches the eye only once from the waveguide 408.

[0101] The waveguide 408 forms a plurality of replicas of the hologram at each "reflection" point B1 to B8 along its length corresponding to the direction of pupil dilation. As shown in FIG. 4, the plurality of replicas are linearly extrapolated to the corresponding plurality of replicas or virtual display devices 402'. This process corresponds to the step of "unfolding" the optical path within the waveguide, and the light rays of the replicas are extrapolated to the "virtual surface" without internal reflection within the waveguide. Thus, the light of the enlarged exit pupil is considered to originate from a virtual surface (also referred to herein as an "expansion modulator") that includes the display device 402 and the replica display device 402'.

[0102] In this specification, virtual images have been generally described for which the eye needs to convert the received modulated light to form a perceived image, but the methods and configurations described herein are also applicable to real images.

[0103] Two-dimensional pupil expansion The arrangement shown in FIG. 4 includes a single waveguide that provides pupil dilation in one dimension, but pupil dilation can be provided in multiple dimensions such as two dimensions. Further, in the example of FIG. 4, holograms calculated to create channels of light corresponding to different portions of the image are used, but the present disclosure and the systems described below are not limited to such types of holograms.

[0104] FIG. 5A shows a perspective view of a system 500 including two replicators 504, 506 arranged to expand a light beam 502 two-dimensionally.

[0105] In the system 500 of FIG. 5A, the first replicator 504 is composed of a first pair of surfaces that are stacked parallel to each other and arranged to provide replication (or pupil expansion) similar to the waveguide 408 of FIG. 4. The first pair of surfaces have similar (in some cases identical) sizes and shapes to each other and are substantially elongated in one direction. The collimated light beam 502 is directed towards the input of the first replicator 504. As is well known to those skilled in the art, due to the internal reflection process between the two surfaces and the partial transmission of light from each of the multiple output points of one of the surfaces (the upper surface as shown in FIG. 5A), the light of the light beam 502 is replicated in the first direction along the length of the first replicator 504. Accordingly, a first plurality of replica light rays 508 are radiated from the first replicator 504 towards the second replicator 506.

[0106] The second replication device 506 includes a second pair of surfaces stacked parallel to each other and is arranged to receive each of the collimated light rays of the first plurality of light rays 508. Further, it is arranged to provide replication, i.e., pupil expansion, by expanding each of those light rays in a second direction substantially orthogonal to the first direction. The first pair of surfaces are of similar (and in some cases identical) size and shape and are substantially rectangular. The second replication device is implemented in a rectangular shape in order to have a length along the first direction to receive the first plurality of light rays 508, have a length along the second orthogonal direction, and provide replication in the second direction. By the process of internal reflection between the two surfaces and the partial transmission of light from each of a plurality of output points on one of the surfaces (the upper surface as shown in FIG. 5A), the light of each light ray within the first plurality of light rays 508 is replicated in the second direction. Accordingly, a second plurality of light beams 510 are emitted from the second replication device 506, and the second plurality of light beams 510 include replicas of the input light beam 502 along each of the first and second directions. Accordingly, the second plurality of light beams 510 can be regarded as including a two-dimensional grid or array of replica light beams.

[0107] Accordingly, it can be said that combining the first and second replicators 504, 505 of FIG. 5A provides a two-dimensional replicator (or “two-dimensional pupil expander”). Accordingly, the replica light beams 510 may be emitted along the optical path to an expanded eye box of a display system such as a head-up display.

[0108] In the system of FIG. 5A, the first replicator 504 is a waveguide including a pair of elongated straight reflective surfaces stacked parallel to each other, and 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 is a solid elongated straight waveguide, and the second replicator is a solid planar rectangular waveguide, and 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 major sidewalls that optionally include reflective and reflection-transmission surface coatings, respectively, which are well known to those skilled in the art.

[0109] FIG. 5B shows a perspective view of a system 500 including two replication devices 520, 540 arranged to replicate an optical beam 522 in two dimensions, where the first replication device is a solid elongated waveguide 520 and the second replication device is a solid planar waveguide 540.

[0110] In the system of FIG. 5B, the first replicator / waveguide 520 is arranged such that its pair of 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 / bent mirror 530 arranged to bend and rotate the optical path of the light to achieve the required optical coupling from the first replicator to the second replicator. As shown in FIG. 5B, the mirror 530 is arranged to receive light including a one-dimensional array of replicas extending in the first dimension from the output port / reflection-transmission surface 524a of the first replicator / waveguide 520. The mirror 530 is tilted to redirect the received light into the optical path to the input port of the (total) reflection surface of the second replicator 540 at an angle that provides waveguiding and replica formation along the length of the second dimension. The mirror 530 is an example of an optical element that can redirect light in the manner illustrated, and it is understood that one or more other elements can be used instead to perform this task.

[0111] In the illustrated arrangement, the (partially) reflective transmissive surface 524a of the first replicator 520 is adjacent to the input port of the first replicator / waveguide 520, receives the input beam 522 at an angle, and guides and forms replicas along the length of the first dimension. Thus, the input port of the first replicator / waveguide 520 is disposed at the input end of the same surface as the reflective transmissive surface 524a. A skilled reader will understand that the input port of the first replicator / waveguide 520 may be disposed at other suitable locations.

[0112] Thus, with the arrangement of FIG. 5B, the first replicator 520 and the mirror 530 can be provided as part of a relatively thin first layer in the plane of the first and third dimensions (illustrated as the xz plane). In particular, the size or "height" of the first planar layer in which the first replicator 520 is disposed is reduced in the second dimension (illustrated as the y dimension). The mirror 530 is configured to direct light away from the first layer / plane (i.e., the "first planar layer") in which the first replicator 520 is disposed, and above the first layer / plane and substantially parallel to the first layer / plane, and direct the light to the second layer / plane (i.e., the "second planar layer") in which the second replicator 540 is disposed. Thus, the overall size or "height" of the system including the first and second replicators 520, 540 and the mirror 530 disposed in the stacked first and second planar layers of the first and third dimensions (illustrated as the xz plane) is compact in the second dimension (illustrated as the y dimension). A skilled reader will understand that many variations of the arrangement of FIG. 5B for implementing the present disclosure are possible and have been considered.

[0113] The 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 a diverging light beam. In some embodiments, the image formed by the diffracted light field is a virtual image.

[0114] In some embodiments, the pair of first parallel / complementary surfaces are relatively long along a first dimension and relatively short along a second dimension, e.g., relatively short along each of the other two dimensions, with each dimension being substantially orthogonal to each of the other dimensions, and are elongated or slender surfaces. The process of reflection / transmission of light between the pair of first parallel surfaces is configured such that light propagates within the first waveguide pupil expander, and the general direction of light propagation is the direction in which the first waveguide pupil expander is relatively long (i.e., its "elongated" direction).

[0115] Disclosed herein is a system that uses diffracted light to form an image and provides an eyebox size and field of view suitable for an actual application (e.g., a head-up display in the automotive industry). Diffracted light is light that forms a holographic reconstruction of an image from a diffraction structure (e.g., a hologram such as a Fourier or Fresnel hologram). The use of diffraction and diffraction structures requires a high-density display device with very small pixels (e.g., 1 μm), which in practice means a small display device (e.g., 1 cm). The inventors have addressed the problem of a method for providing 2D pupil expansion using a diffracted light field (e.g., diffracted light including a diverging (non-parallel) light beam).

[0116] In some embodiments, the display system includes a pixelated display device configured to provide or form diffracted light or divergent light, such as a spatial light modulator (SLM) or a liquid crystal on silicon (LCoS) SLM. In such an aspect, the aperture of the spatial light modulator (SLM) is the system's limiting aperture. That is, the size of the aperture of the spatial light modulator, more specifically, the region delimiting the array of light modulation pixels included within the SLM, determines the size (e.g., spatial extent) of the light beam that can exit the system. According to this disclosure, the system's exit pupil is stated to be enlarged to reflect that the system's exit pupil (which is limited by a small display device having a pixel size for light diffraction) is made larger or larger or larger in spatial extent by the use of at least one pupil expander.

[0117] It can be said that the diffracted or divergent light field has a "light field size" defined in a direction substantially orthogonal to the propagation direction of the light field. Since light diffracts / diverges, the light field size increases with the propagation distance.

[0118] In some embodiments, the diffracted light field is spatially modulated according to a hologram. In other words, in such an aspect, the diffracted light field includes a "holographic light field". The hologram may be displayed on a pixelated display device. The hologram may be a computer-generated hologram (CGH). This may be a Fourier hologram, a Fresnel hologram, a point cloud hologram, or any other suitable type of hologram. Optionally, the hologram may be calculated to form channels of holographic light. Each channel corresponds to a different respective portion of the image intended for the viewer to see (or, in the case of a virtual image, to perceive). The pixelated display device may be configured to display a plurality of different holograms continuously or in sequence. Each of the aspects and embodiments disclosed herein may be applied to the display of a plurality of holograms.

[0119] The output port of the first waveguide pupil expander may be coupled to the input port of the second waveguide pupil expander. The second waveguide pupil expander may be arranged to direct a diffracted optical field including a part, preferably a majority, preferably all of the replica of the optical field output by the first waveguide pupil expander, by means of internal reflection between a pair of third parallel planes of the second waveguide pupil expander, from its input port to respective output ports.

[0120] The first waveguide pupil expander can be arranged to provide pupil expansion or replication in a first direction, and the second waveguide pupil expander can be arranged to provide pupil expansion or replication in a second different 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 expand (or replicate) a part, preferably a majority, preferably all of the replica received from the first waveguide pupil expander in the second different direction. The second waveguide pupil expander can be arranged to receive the optical field directly or indirectly from the first waveguide pupil expander. One or more other elements can be provided along the propagation path of the optical field between the first and second waveguide pupil expanders.

[0121] The first waveguide pupil expander may be substantially elongated and the second waveguide pupil expander may be substantially planar. The elongated shape of the first waveguide pupil expander may be defined by a length along a first dimension. The plane, i.e., rectangular shape, of the second waveguide pupil expander may be defined by a length along a first dimension and a width, i.e., breadth, along a second dimension substantially orthogonal to the first dimension. The size, i.e., length, of the first waveguide pupil expander along the first dimension corresponds respectively to the length, i.e., width, of the second waveguide pupil expander along the first dimension or the second dimension. Of the pair of parallel planes of the second waveguide pupil expander, the first surface including the input port may be shaped, sized, and / or arranged to correspond to the region defined by the output port on the first surface of the pair of parallel planes of the first waveguide pupil expander. Thereby, the second waveguide pupil expander is arranged to receive each replica output by the first waveguide pupil expander.

[0122] 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 including 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 defining the length and width of the second waveguide pupil expander, respectively, can be parallel to the first and second directions (or the second and first directions) in which the waveguide pupil expander provides pupil expansion. The combination of the first waveguide pupil expander and the second waveguide pupil expander is sometimes generally referred to as a "pupil expander".

[0123] 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 two directions. The region defined by the expanded exit pupil defines an expanded eyebox region from which a viewer can receive light from the input diffraction or diverging light field. The eyebox region can be said to be disposed on or to define the display surface.

[0124] The two directions in which the exit pupil is expanded may be in the same plane 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 (or windscreen) of a vehicle, the exit pupil may be regarded as the exit pupil from other elements such as the windshield. In such an arrangement, the exit pupil may not be in the same plane and parallel to the first and second directions in which the first and second waveguide pupil expanders provide replication / expansion. For example, the exit pupil may be substantially perpendicular to the first and second directions in which the first and second waveguide pupil expanders provide replication / expansion.

[0125] The field of view surface and / or the eyebox region may be non-coplanar or non-parallel with respect to the first and second directions in which the first and second waveguide pupil expanders provide duplication / expansion. For example, the field of view surface may be substantially perpendicular to the first and second directions in which the first and second waveguide pupil expanders provide duplication / expansion.

[0126] To provide appropriate emission conditions for realizing internal reflection within the first and second waveguide pupil expanders, the elongated dimension of the first waveguide pupil expander may be inclined with respect to the first and second dimensions of the second waveguide pupil expander.

[0127] Combiner shape correction The advantage of projecting a hologram onto the eyebox is that optical compensation can be encoded into the hologram (see, for example, European Patent No. 2936252 incorporated herein). The present disclosure is compatible with holograms that compensate for the complex curvature of an optical combiner used as part of a projection system. In some embodiments, the optical combiner is the windshield of a vehicle. Details of this approach are described in European Patent No. 2936252, and the detailed features of those systems and methods are not essential to the novel teachings of the present disclosure and are merely exemplary configurations that benefit from the teachings of the present disclosure, and thus will not be repeated here.

[0128] Control device The present disclosure is also compatible with an optical configuration including a control device (e.g., an optical shutter device) for controlling the delivery of light from an optical channeling hologram to a viewer. The holographic projector may further comprise a control device arranged to control the delivery of angular channels to the eye box position. UK Patent Application 2108456.1, filed on 14 June 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 basically based on the user's eye box position and is compatible with any hologram calculation method for realizing the optical channeling described herein. The control device can be said to be an optical shutter or an aperture device. The optical shutter device comprises a 1D array of apertures or windows, each of which can be independently switched between a light-transmissive state and a light-non-transmissive state in order to control the delivery of the hologram optical channels and their replicas to the eye box. Each aperture or window may comprise a plurality of liquid crystal cells or pixels.

[0129] Distortion and spacing of replicas FIG. 6 is a schematic view showing a part of the display system 600, and shows the influence exerted by the curved optical component 608 (in this case, the windshield of a vehicle) on a plurality of replicas 602 of spatially modulated light.

[0130] The plurality of replicas 602 are generated from spatially modulated light from a display device (not shown, such as the aforementioned LCOS) passing through a replicator or waveguide (not shown) as described above in connection with FIGS. 4 to 5B. Although FIG. 6 is a side cross-sectional view (2D) of the system 600, it will be understood by those skilled in the art that the plurality of replicas 602 are also extended in three dimensions.

[0131] In this example, a plurality of replicas 602 are arranged at equal intervals over a first distance 604. The spacing between replicas 602 allowed by this first distance 604 can be arranged (by design) such that competing replicas 602 do not enter the viewer's pupil simultaneously. If they compete, the viewer will see ghosts. Therefore, the viewer's eye is tracked within the viewer's line-of-sight box to derive which replica 602 the viewer's pupil receives using the viewer's eye tracking. Thereby, the display device can change the spatially modulated light (forming the replicas 602) generated so that competing replicas 602 do not enter the viewer's eye and the aforementioned ghosts do not occur. It will be understood that the smaller the spacing between replicas 602, the higher the accuracy of eye tracking needs to be. This is because the smaller the viewer's movement (and thus the pupil opening), the higher the likelihood of entering the paths of more replicas. In other words, to enable the viewer's pupil to recognize different replicas 602, it is necessary to reduce the viewer's movement (which may cause the aforementioned ghosts). The higher the required accuracy of eye tracking, the greater the amount of computing power and complexity required to achieve it. Therefore, this spacing needs to be maintained at least to maintain the quality of the image observed by the viewer and to reduce the computing power required to achieve that image quality.

[0132] The plurality of replicas 602 interact with a curved optical component 608. In this case, the curved optical component 608 is the front windshield of a vehicle that functions as an optical combiner. A portion of the light of the replicas 602 is reflected by the curved optical component 608 towards the user at a substantially perpendicular angle (although not exactly perpendicular as will be further explained below). FIG. 6 shows only the paths of the replicas 602 relevant to the present disclosure, but it will be understood that a portion of the light of the replicas 602 may take paths different from those shown. For example, some light may pass through the curved optical component 608 instead of being reflected by it.

[0133] Due to the curvature of the curved optical component 608, the reflection angle of the reflected light is not exactly perpendicular and varies across the surface of the curved optical component 608. This has the effect of tilting the respective paths of the plurality of replicas 602 towards each other, as can be seen in FIG. 6. As a result, the plurality of replicas 602 can be spaced apart over a second distance 616 that is much shorter than the first distance 602. In other words, the curved optical component 608 compresses the spacing between the plurality of replicas 602. The plurality of replicas 602 move parallel to each other before interacting with the curved optical component 608, but converge towards each other after the interaction. In summary, the curved optical component 608 applies a positive refractive force to the plurality of replicas 602. This positive refractive force causes several problems, as will be explained below.

[0134] As described above, in order to prevent the ghost from being visible to the observer, it is essential to maintain the spacing of the replicas 602 such that as few replicas 602 as possible enter the pupil at one time. The positive optical power of the curved optical component 608 compresses the spacing of the replicas 602 and thus contributes to the generation of ghosts in this way. FIG. 6 shows a first virtual pupil aperture 610 that is separated from the curved optical component 608 by a first length 611. At this first length 611, only one of the replicas 602 can pass through the aperture 610. Thus, when the observer is positioned such that the eyes are at the same length as the first length 611 from the curved optical component 608, ghosts from the replicas 602 are not perceived. However, the second virtual pupil aperture 612 is shown at a second length 613 from the curved optical component 608, which is longer than the first length 611. Since the spacing of the plurality of replicas 602 is compressed by the curved optical component 608, it can be seen that the replicas overlap and a plurality of replicas 602 always pass through the second aperture 612. Thus, when the observer is positioned such that the eyes are at the same length as the first length 611 from the curved optical component 608, ghosts from the replicas 602 are not perceived. When the curved optical component 608 is similar to the second length 613, the observer is likely to recognize ghosts from the replicas 602. Therefore, the observer is likely to approach the curved optical component 608 (from the second length 613 to the first length 611) and experience the ghost effect. Moving the observer in this way may not be possible in many situations. For example, when the curved optical component 608 is the front windshield of a vehicle and the observer cannot be brought closer due to the dashboard or the driving position.

[0135] The positive optical power of the curved optical component 608 also pushes up the virtual image distance (i.e., the distance beyond the curved optical component 608 where the viewer sees the image carried by the replica 602). This can cause problems in the viewer's recognition of the target image. For example, the target image may be too small to be clearly visible, or it may be recognized by the viewer as being in the wrong place (e.g., away from the surrounding objects that the target image may be likely to be focused on).

[0136] Finally, due to the curvature of the curved optical component 608, different phase delays are effectively applied to each replica 602 during the aforementioned interaction. This delay causes the different replicas 602 to reach the viewer at different times, and the image may appear distorted.

[0137] Hardware correction FIG. 7 is a schematic diagram showing a part of the display system 700, and shows how the optical control device 706 can be used to suppress the influence of the curved optical component 608 on a plurality of replicas 602 of spatially modulated light.

[0138] Similar to FIG. 6, the plurality of replicas 602 are generated from spatially modulated light from a display device (not shown, such as the aforementioned LCOS) that passes through a replicator or waveguide (not shown) as described above in relation to FIGS. 4 to 5B. By the aforementioned replicator / waveguide, the plurality of replicas are arranged at equal intervals over a first distance 604. Although FIG. 7 is a side cross-sectional view (two-dimensional) of the system 700, it will be understood by those skilled in the art that the plurality of replicas 602 also extend in the third dimension.

[0139] However, unlike FIG. 6, the plurality of replicas 602 interact with the optical control device 706 before interacting with the curved optical component 608. In FIG. 7, the optical control device 706 is represented by a curved mirror, but other suitable devices can also be used, such as a Fresnel lens or the devices disclosed in the aforementioned UK Patent Applications 2317637.3 and 2401627.1.

[0140] The optical control device 706 applies a negative refractive force to the plurality of replicas 602. That is, the spacing between the replicas 602 increases as light travels between the optical control device 706 and the curved optical component 608. As a result, when the replicas 602 interact with the curved optical component 608, the corresponding negative refractive force from the curvature of the curved optical component 608 is canceled out by the positive refractive force from the optical control device 706. In other words, the optical control device 706 diverges the plurality of replicas 602 by the same amount that the curved optical component 608 converges the plurality of replicas 602.

[0141] As a result, the plurality of replicas 602 that arrive at the optical control device 706 parallel to each other remain parallel to each other after interacting with the curved optical component 608. Therefore, the pupil apertures 710, 712, 714 can be arranged along the path of the replicas 602 at any distance from the curved optical component 608 and arranged so that only one replica 602 can pass through. Thus, no matter where the observer is along the path of the replicas 602, there is no ghosting as described above caused by replica overlap, and the observer can view the image at the correct virtual image distance. Further, (due to the diverging characteristics caused by the negative refractive force of the optical control device 706) the replicas 602 are arranged with a spacing at a second distance 716 greater than the first distance 602, reducing the computational power required for gaze tracking. This is because the wider the spacing between the replicas 602, the more freely the viewer can move before encountering replicas 602 that the viewer's eyes would compete with (which can cause ghosting as described above). In other words, the wider the spacing between the replicas 602, the farther the viewer can move before encountering competing replicas 602 that cause ghosting. Therefore, even if the accuracy of gaze tracking is low, less computational power is required.

[0142] Similarly, the phase delay between replicas caused by the curved optical component 608 is also mitigated by the optical control device 706, resulting in a corresponding phase delay such that each replica 602 is in the same phase. As a result, after interacting with the curved optical component 608 and undergoing the phase delay, each replica 602 reaches the viewer in the same phase, reducing image distortion. This correction by the optical control device 706 can be applied to any optical characteristics imparted by the curved optical component 608 to the replicas 602.

[0143] However, the details of the optical control device 706 (e.g., the exact curvature and phase delay provided by each point on its surface) need to be finely adjusted according to the corresponding characteristics of the curved optical component 608. That is, if the first replica 602i is reflected by a point Ai on the curved optical component 608, and the point Ai exhibits a refractive power +Pi and a phase delay +Di, the optical control device 706 requires a corresponding point Bi where the first replica 602i is also reflected, and the point Ai exhibits a refractive power -Pi and a phase delay -Di. Similarly, if the second replica 602ii is reflected at a point Aii on the curved optical component 608, and the point Aii exerts a refractive power +Pii and a phase delay +Dii, the optical control device 706 needs to have a corresponding point Bii where the second replica 602ii is also reflected, and the point Aii needs to exert a refractive power -Pii and a phase delay -Dii. This must be continued for each replica 602 at each point of the curved optical component 608 and the corresponding points of the optical control device 706. Those skilled in the art will understand that other characteristics besides refractive power and phase delay also need to be adjusted for each point on the curved optical component 608. Thus, due to the requirement of having to finely adjust each point of the optical control device 706 in this way, the time required to develop and manufacture the optical control device 706 for each curved optical component 608 is long.

[0144] Hardware and software corrections The inventors have discovered that by pre-adjusting each replica 602 using a software lens, the slight differences between the characteristics of the optical control device 706 and the curved optical component 608 can be compensated for. That is, most of the refractive power and phase delay (and other characteristics) caused by the curved optical component 608 are canceled out by the corresponding opposite characteristics of the corresponding points of the optical control device 706, but by using a software lens, the characteristics of the curved optical component 608 can be further slightly corrected. When describing this optical control device that intentionally applies only partial correction / compensation, the reference number 706' is used.

[0145] Using the above example, the first replica 602i is reflected by the point Ai of the curved optical component 608, and the point Ai exhibits a refractive power of +Pi and a phase delay of +Di. As before, there is a corresponding point Bi' on the optical control device 706' where the first replica 602i is reflected. However, in this case, the point Bi' exhibits a refractive power of -Pi' and a phase delay of -Di'. The refractive power -Pi' and the phase delay -Di' are not the same as the above refractive power -Pi and phase delay -Di. The refractive power -Pi' of the optical control device 706' does not sum to zero even when added to the refractive power +Pi of the curved optical component 608. The remainder of the refractive power +Pi of the curved optical component 608 remains. The same is true for the phase delay -Di' of the optical control device 706' and the opposite phase delay +Di of the curved optical component 608 (and other characteristics of the curved optical component 608 corrected by the optical control device 706').

[0146] Instead, the refractive power +Pi* and the phase delay +Di* (and other characteristics) provided by the software lens are corrected. In this case, the refractive power -Pi of the curved optical component 608 is zero in total as a combination of the refractive power +Pi' of the optical control device 706' and the refractive power +Pi* of the software lens. The same applies to the phase delay -Di of the curved optical component 608, which is a combination of the phase delay +Di' of the optical control device 706' and the phase delay +Di* of the software lens (and other characteristics of the curved optical component 608 that require correction or compensation). This is repeated for each replica 602 at each point of the curved optical component 608 and the corresponding point of the optical control device 706'.

[0147] This description relates to the complete correction of the curved optical component 608 (i.e., the sum of the values associated with the curved optical component 608, the optical control device 706', and the software lens being zero), but the present disclosure also relates to the correction of the curved optical component 608. That is, the sum of the values associated with the curved optical component 608, the optical control device 706', and the software lens approaches zero, and an improved image is generated for the viewer.

[0148] The inventors have discovered that when using a purely software lens solution, image ghosting becomes prominent, especially in situations where the curvature of the curved optical component 608 increases (requiring a more powerful software lens), but using a 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 adjustment is achieved by the software solution of the software lens.

[0149] LCOS pixel control Furthermore, it has also been found that using the negative correction of the curved optical component 608 expands the area of pixels that can be used to create an image on the LCOS, improving the image quality. By ray-tracing the paths of each replica 602 from the viewer to the LCOS (through various optical components such as the curved optical component 608, the optical control devices 706, 706', the replication device / waveguide, etc.), the inventors have discovered that only a relatively small number of pixels on the LCOS control the appearance of each point of the image visible to the viewer.

[0150] FIG. 8A schematically shows the area of the LCOS 800a within an optical combiner in a flat (i.e., a flat optical component rather than the curved optical component 608) display system. In this ideal system (a system without distortion caused by the curvature of the curved optical component 608), the area of the pixels 802a determines the appearance of the conceptual points of the intended image from the viewer's perspective. As can be seen from the figure, the number of pixels is relatively large (since the area of the pixels 802a is large and symmetric), and the conceptual relevant points of the image can be rendered in detail.

[0151] FIG. 8B schematically shows a similar area of the LCOS 800b, but in the case of the system 600 shown in FIG. 6 (i.e., a system with a curved optical component 608 but without 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 conceptual points of the intended image is reduced and distorted. That is, the area 802b has lower symmetry and an increased aspect ratio (the length of the area 802b from the upper left to the lower right in the figure is shorter than the length of the area 802b from the lower left to the upper right). Therefore, the number of pixels available for rendering the conceptual points of the image is reduced, and as a result, the detail (quality) of that point is rendered lower than in the ideal system of FIG. 8A.

[0152] By using the optical correction of system 700 against the distortion caused by the curvature of the curved optical component 608, the region of the LCOS 800c in FIG. 8C is realized. As can be seen from the figure, the region of the pixel 802c is larger and more symmetric than the region of the uncorrected system 600 in FIG. 8B. That is, the region 802c is more symmetric than the region 802b, and the aspect ratio is close to that of the region 802a. Therefore, since there are more pixels in the region 802c, the conceptual points of the image can be rendered in more detail to the viewer.

[0153] Additional functions The methods and processes described herein can be implemented on a computer-readable medium. The term "computer-readable medium" includes media configured to temporarily or persistently store data, such as random access memory (RAM), read-only memory (ROM), buffer memory, flash memory, cache memory, etc. Also, the term "computer-readable medium" is to be interpreted as including any medium, or combination of multiple media, capable of storing instructions for execution by a machine, which when executed by one or more processors cause the machine to perform all or part of one or more of the methods described herein.

[0154] The term "computer-readable medium" also includes cloud-based storage systems. The term "computer-readable medium" includes, but is not limited to, one or more tangible and non-transitory data repositories (such as data volumes) in the form of solid-state memory chips, optical disks, magnetic disks, or suitable combinations thereof. In some embodiments, the executable instructions may be transmitted by a carrier medium. Examples of such carrier media include transient media (such as a propagation signal that transmits instructions).

[0155] 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. This disclosure covers all modifications and variations within the scope of the appended claims and their equivalents.

Claims

1. a replication device configured to receive spatially modulated light and replicate the spatially modulated light to form a plurality of replicas of the spatially modulated light by guiding the light between a reflective surface and a transflective surface, the transflective surface forming an output surface for the plurality of replicas of the spatially modulated light; a light control device disposed in an optical path of the plurality of replicas of the spatially modulated light downstream from the output surface of the replica device and configured to provide a first correction for a curvature of a curved optical component downstream from the light control device, the first correction being a function of position on the output surface and configured to only partially counteract the curvature of the optical component; A display system comprising:

2. 10. The display system of claim 1, wherein the spatially modulated light is a holographic wavefront and the replica device is configured to form multiple replicas of the holographic wavefront.

3. 3. The display system of claim 1 or 2, wherein the light control device comprises a lens, optionally a Fresnel lens, and further optionally the lens is a film, optionally less than 5 mm thick, such as less than 2 mm, less than 1 mm, or less than 0.5 mm.

4. 4. The display system of claim 1, wherein the first correction has an inverse lens effect to that of the curved optic.

5. 5. The display system of claim 1, wherein the first correction is a negative refractive power and / or the curved optic has a positive refractive power.

6. a processor configured to determine a hologram of an image and a lens function that provides a second correction for the curvature of the curved optical component downstream from the light control device, the second correction being set to only partially counteract the curvature of the optical component; a display device configured to spatially modulate light according to a diffraction pattern displayed thereon, said diffraction pattern including said hologram and said lens features; The display system of claim 1 , further comprising:

7. The display system of claim 6 , wherein the lens function is a pixelated lens function.

8. 8. The display system of claim 6 or 7, wherein the second correction is a negative refractive power.

9. 9. A display system according to claim 6, wherein the diffraction pattern comprises a superposition or summation of the hologram and the lens function.

10. 10. A display system as described in any one of claims 6 to 9, further comprising a viewer tracking system configured to determine a position within an eyebox and correlate said position to a sub-region of the curved optical component and a position on the output surface of the reproduction device, wherein the first and second corrections correct the curvature of the sub-region of the curved optical component.

11. 11. The display system of claim 6, wherein the first correction and the second correction collectively provide a complete correction for the curvature of the curved optical component.

12. 12. The display system of claim 6, wherein the first correction is between 2 and 10 times the second correction.

13. 12. A display system according to claim 6, wherein the first correction provides a virtual image offset correction in the range of 75% to 99%, and the second correction provides a virtual image offset correction in the range of 1% to 25%.

14. 14. A display system as claimed in any one of claims 6 to 13, wherein the magnitude of the first and / or second corrections is such that the spacing between each of the multiple replicas in a viewing surface of the display system is at least half the size of a human pupil.

15. 15. The display system of claim 14, wherein the spacing is controlled, at least in part, by respective corrections to the curvatures of the curved optics.

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

18. 18. A display system according to claim 6, wherein the correction for the curvature of the curved optics is such that the viewing pupil footprint on the display device is substantially symmetrical.

19. 19. A display system as claimed in any one of claims 6 to 18, wherein the correction for the curvature of the curved optics is such that the viewing pupil footprint on the display device has an area with an aspect ratio in the range of 1:1 to 1:1.

25.

20. 1. A method for processing spatially modulated light, comprising: receiving the spatially modulated light at a replication device, the replication device 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 replicas of the spatially modulated light by guiding the spatially modulated light between the reflective surface and the transflective surface, the plurality of replicas of the spatially modulated light being output from the replicator at the output surface; receiving the plurality of copies in a light control device; providing, via the light control device, a first correction for the curvature of a curved optical component downstream from the light control device, the first correction being a function of position on the output surface and configured to only partially counteract the curvature of the optical component; The method includes:

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