Head-up display

Abstract

A head-up display includes an eyebox. The eyebox has a first dimension and a second dimension. The head-up display is arranged to form a first image in a first image region at a first image region distance from the eyebox. The head-up display is further arranged to form a second image in a second image region at a second image region distance from the eyebox. The image region distance is a distance normal to a plane containing the first dimension and the second dimension. The first image region distance is less than the second image region distance. The first image region at least partially overlaps the second image region in the first dimension. The overlap can be an overlap in angular space from the center of the eyebox. The second image region extends further in angular space in at least one direction of the first dimension than the first image region.

Description

Technical Field

[0001] This disclosure relates to image projectors and image projection methods. Some embodiments relate to holographic projectors and holographic projection methods. More specifically, this disclosure relates to the projection of multiple images. This disclosure also relates to apparatus arranged to form virtual images using an optical combiner and methods for forming multiple images using an optical combiner. Embodiments relate to head-up displays and methods for head-up displays. Some embodiments relate to an image generation unit for a vehicle head-up display. Other embodiments relate to methods for optimizing the field of view of an image formed by an image projector, such as methods for cropping or expanding the field of view of one of multiple images formed substantially simultaneously on different image planes. Background Technology

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

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

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

[0005] Spatial light modulators typically comprise multiple individually addressable pixels, which may also be referred to as cells or elements. The light modulation scheme can be binary, multilevel, or sequential. Alternatively, the device can be sequential (i.e., excluding pixels), so the light modulation can be continuous on the device. Spatial light modulators can be reflective, meaning the modulated light is output as reflected light. Spatial light modulators can also be transmissive, meaning the modulated light is output as transmitted light.

[0006] The system described herein can be used to provide holographic projectors. For example, such projectors have been used in head-up displays (HUDs) and light detection and ranging systems (LIDARs). Summary of the Invention

[0007] For ease of explanation and illustration, this disclosure and the accompanying drawings generally depict a one-dimensional case. However, those skilled in the art of optics will understand that the concepts described and illustrated can be extended to two dimensions to provide a two-dimensional image from a two-dimensional hologram. For example, although only one-dimensional pupil dilation is described and illustrated, the reader should understand that this disclosure extends to two-dimensional pupil dilation—for example, using two one-dimensional pupil dilations in series.

[0008] In summary, this disclosure relates to image projection. It relates to methods of image projection and image projectors including display devices. This disclosure also relates to projection systems including image projectors and observation systems. This disclosure is equally applicable to monocular and binocular observation systems. An observation system may include one or more eyes of an observer. An observation system includes optical elements with optical power (e.g., the lens of the human eye) and an observation plane (e.g., the retina of the human eye). The projector may be referred to as a "light engine." The display device and the image formed (or perceived) using the display device are spatially separated from each other. An observer forms or perceives the image on the display plane. In some embodiments, the image is a virtual image, and the display plane may be referred to as a virtual image plane. The image is formed by illuminating a diffraction pattern (e.g., a hologram) displayed on the display device.

[0009] Display devices consist of pixels. The pixels of a display device diffract light. According to well-known optical principles, the magnitude of the maximum diffraction angle depends on the pixel size (and other factors, such as the wavelength of light).

[0010] In this embodiment, the display device is a spatial light modulator, such as a liquid crystal on silicon (“LCOS”) spatial light modulator (SLM). Light travels from the LCOS to the observing entity / system, such as a camera or eye, within a diffraction angle range (e.g., from zero to the maximum diffraction angle). In some embodiments, amplification techniques may be used to increase the range of available diffraction angles beyond the conventional maximum diffraction angle of the LCOS.

[0011] In this embodiment, the image is a real image. In other embodiments, the image is a virtual image perceived by the human eye (or multiple eyes). The projection system or light engine can therefore be configured so that the observer looks directly at the display device. In such an embodiment, holographically encoded light propagates directly to the eye, and no intermediate holographic reconstruction is formed in the free space between the display device and the observer, or on the screen or other light-receiving surface. In such an embodiment, the pupil of the eye can be considered as the entrance aperture (or "entrance pupil") of the observation system, and the retina of the eye can be considered as the observation plane of the observation system. It is sometimes said that in this configuration, the lens of the eye performs the holographic-to-image conversion.

[0012] According to well-known optical principles, the range of angles at which light propagating from a display device can be observed by an eye or other observation entity / system varies with the distance between the display device and the observation entity. For example, at an observation distance of 1 meter, only a small range of angles from the LCOS can propagate through the pupil of the eye to form an image on the retina at a given eye location. The range of angles at which light propagates from the display device determines the portion of the image that the observer can successfully propagate through the pupil of the eye to form an image on the retina at a given eye location. In other words, not all parts of the image are visible from any point on the observation plane (e.g., any eye position within the observation window of an eye-tracking box).

[0013] In some embodiments, the image perceived by the observer is a virtual image appearing upstream of the display device; that is, the image perceived by the observer is farther away than the display device. Conceptually, multiple different virtual image points can be considered. The distance from this virtual image point to the observer is referred to here as the virtual image distance. Of course, different virtual points can have different virtual image distances. Individual rays in the ray beam associated with each virtual point can reach the observer via different corresponding optical paths through the display device. However, only some portions of the display device, and therefore only some rays from one or more virtual points of the virtual image, may be within the user's field of view. In other words, only some rays from some virtual points on the virtual image will propagate through the display device to the user's eyes and thus be visible to the observer. Therefore, conceptually, it can be considered that the observer is viewing the virtual image through a "window the size of the display device," which can be very small, for example, 1 cm in diameter, at a relatively large distance, such as 1 meter. And the user will view the window the size of the display device through the pupils of their eyes, which can also be very small. Therefore, at any given time, the field of view shrinks, and the specific range of angles that can be seen heavily depends on the eye position.

[0014] Each image point in an image can have a different image distance, but according to the embodiment, each image is formed in an image region, so the "image region distance" can be associated with each image, where the image region distance is the length of the shortest straight line connecting the center of the eye box and the plane containing the image region.

[0015] A pupil dilator addresses the problem of increasing the field of view—that is, increasing the angular range of light propagating from a display device so that the light can successfully pass through the pupil of the eye to form an image. The display device is (relatively) small, and the projection distance is (relatively) large. In some embodiments, the projection distance is at least one (e.g., at least two) orders of magnitude larger than the diameter or width of the entrance pupil and / or aperture of the display device (i.e., the size of the pixel array). This disclosure relates to so-called direct-view holography, in which a hologram of an image, rather than the image itself, is propagated to the human eye. In other words, the light received by the observer is modulated according to the hologram of the image.

[0016] A pupil expander increases the field of view, thus increasing the maximum propagation distance usable across the full diffraction angle of the display device. The use of a pupil expander also laterally enlarges the user's eyebox, allowing for some eye movement while still enabling the user to see the image. In this embodiment, the pupil expander is a waveguide pupil expander. This disclosure generally relates to non-infinite virtual image distances, i.e., near-field virtual images.

[0017] The embodiments describe one-dimensional pupil expansion, but this disclosure extends to two-dimensional pupil expansion, using, for example, a first elongated waveguide extended in a first dimension and a second waveguide extended in a second vertical dimension.

[0018] Various aspects of this disclosure are defined in the appended independent claims.

[0019] A heads-up display including an eye box is provided. The eye box, or eye-tracking box, has a first dimension and a second dimension. The heads-up display is arranged to form a first image in a first image region at a distance from a first image region of the eye box. The heads-up display is also arranged to form a second image in a second image region at a distance from a second image region of the eye box. The image region distance is a distance perpendicular to a plane containing the first and second dimensions (in one direction). The first and second images can be formed substantially simultaneously, for example from the same display event or at the same display interval. Alternatively, the first and second images can be formed rapidly and sequentially, for example using time-staggered methods. The distance between the first and second image regions is less than the distance between the second and third image regions. The first image may be referred to as a near image or near-field image. The second image may be referred to as a far image or far-field image. The first image region at least partially overlaps with the second image region in the first dimension. This overlap may be an overlap in angular space from the center of the eye box. The overlap may be noticeable when viewed from the eye box (e.g., from the center of the eye box). The second image region extends less in angular space in at least one direction of the first dimension than the first image region. In some embodiments, the second image region is cropped on at least one side such that the second image region extends less than the first image region. In at least one direction of the first dimension, the field of view of the second image region is smaller than the field of view of the first image region.

[0020] The far-field / second image region is farther from the eyebox than the near-field / first image region. In other words, the image region distance associated with the second image region is greater than the image region distance of the first image region. As described herein, in a holographic head-up display, image content is displayed on a playback field of a playback plane, where the playback field is the region from which light can be received from the displayed hologram. Skilled readers will understand that the maximum size of the playback field is determined by the diffraction angle of the display device (e.g., LCOS). Therefore, it can be said that the first image region is the region of the first playback field at a distance from the first image region forming the first image / image content, and the second image region is the region of the second playback field at a distance from the second image region forming the second image / image content. When an image is displayed, the region of the playback field displaying the image / image content depends on the displayed hologram (from which light is received).

[0021] A key feature of a head-up display (HUD) is its field of view, which defines the size of the area where image content can be displayed. The inventors recognized that even if the field of view (i.e., the size in angular space) of a far-field image is the same as that of a near-field image, far-field images require a larger clearance space (or volume) within the system housing the HUD (e.g., a vehicle) than near-field images due to the size of the light beam required to form the far image at each viewing position within the eyebox. The inventors found that this larger requirement is often due to limiting eyebox locations (e.g., peripheral eyebox locations). Such a spatial volume is required so that there is a clear path for the light rays forming both near-field and far-field images for all eyebox locations. Therefore, this spatial volume can be identified from the light beams required to form multiple images for each corresponding eyebox location. Those skilled in the art of HUD design are familiar with how the size of the light beam (i.e., the spatial extent) at each eyebox location is crucial in determining how the HUD can be integrated into a vehicle (e.g., how the HUD can be “packaged” under the dashboard).

[0022] An eyebox can be a two-dimensional region, such as an observation window. Therefore, an eyebox has a first dimension (e.g., width) and a second dimension (e.g., height). The terms "width" and "height" can be used to refer to dimensions from the perspective of an observer of the head-up display (e.g., the driver of a vehicle including a head-up display). Width can be called the "horizontal dimension," and height can be called the "vertical dimension." For example, an eyebox can be contained in the xy-plane, where the z-direction is the optical axis or visual axis of the head-up display. The "direction" of each dimension mentioned here refers to the positive and negative directions of the dimension, such as the positive and negative x-directions of the horizontal dimension.

[0023] In this embodiment, the first and second dimensions of the eye box are aligned with the first and second dimensions of the first and second images, respectively. That is, the first dimension of the eye box is parallel to the first dimension of the first image and the first dimension of the second image. Similarly, the second dimension of the eye box is parallel to the second dimension of the first image and the second dimension of the second image. The eye box, the first image, and the second image may each be longer than the second dimension in the first dimension.

[0024] The term "angular space" is used here as a way to define the dimensions of an aspect or feature of a head-up display, such as an image region or a beam of light forming at least one image in at least one image region. Angular space is typically considered in different planes of an optical system, such as two orthogonal planes, for example, the xz plane and the yz plane. Therefore, angular space can be defined as a first angle on a first plane and a second angle on a second plane, wherein the second plane is orthogonal to the first plane. The angular space of a feature is defined by the angle from a point in the eyebox (e.g., the center of the eyebox) to an end or boundary of the feature. By way of example only, in some embodiments, the horizontal field of view of the first image region is + / - 10 degrees from each point in the eyebox, i.e., +10 degrees in one direction of the horizontal dimension and -10 degrees in the other direction, and the vertical field of view of the first image region is + / - 5 degrees from each point in the eyebox, i.e., +5 degrees in one direction of the vertical dimension and -5 degrees in the other direction. Unless otherwise specified, the field of view of the image region mentioned herein should be considered as the region defined in angular space at a distance from the eyebox by a first angle on a first plane containing the visual axis and a second angle on a second plane containing the visual axis, wherein the first plane is orthogonal to the second plane, and the field of view is obtained for each point in the eyebox. The first plane may contain a first dimension, and the second plane may contain a second dimension. In some embodiments, the eyebox, the first image region, and the second image region are planar. In some embodiments, the eyebox, the first image region, and the second image region are three substantially parallel planes on the visual axis of the head-up display. In some embodiments, the eyebox, the first image, and the second image are coaxial, and optionally, substantially orthogonal to the axis.

[0025] According to this disclosure, in at least one direction of the first dimension, the second image region extends less in angular space than the first image region. For example, at one side / vertical end, the vertical field of view of the second image region is smaller than that of the first image region. The resulting technological advancement is a significant reduction in the clearance volume required for the image light of the head-up display. Specifically, the inventors have recognized that cropping / reducing the size or extent of the second image region (compared to the first image region) on at least one side is sufficient to avoid a serious conflict between the light from the head-up display and the space volume typically allocated to the head-up display within the host vehicle or the host vehicle dashboard. Furthermore, the inventors have further recognized that in some practical situations, the size or extent of the first image region (e.g., the vertical field of view) can actually be increased according to the desired field of view of the second image region without consequences.

[0026] In some embodiments, the hologram is propagated to the observation system, rather than a holographic reconstruction (i.e., an image) formed from the hologram. It can be said that the spatially modulated light received by the observation system is in the holographic domain, rather than in the spatial or image domain. It can also be said that the observation system performs the holographic-to-image conversion. More specifically, optical elements such as lenses of each observation system perform the conversion. In embodiments, no holographic reconstruction or image is formed between the display device and the observation system. In some embodiments, optionally, an interleaving scheme is used to compute different holograms and propagate them to each eye of the observer.

[0027] The display device has an effective or display area with a first dimension less than 10 cm, for example, less than 5 cm or less than 2 cm. The propagation distance between the display device and the observation system can be greater than 1 m, for example, greater than 1.5 m or greater than 2 m. The optical propagation distance within the waveguide can be up to 2 m, for example, up to 1.5 m or up to 1 m. This method is capable of receiving images and determining corresponding holograms of sufficient quality within less than 20 ms, such as less than 15 ms or less than 10 ms.

[0028] In some embodiments, the hologram is configured to route light into multiple channels, each corresponding to a different portion (i.e., sub-region) of the image. In some embodiments, the light channels do not overlap. In other embodiments, such as those including an additional light combiner with optical power (e.g., a vehicle windshield) between the waveguide and the observer, some light channels may at least partially overlap. However, the use of this type of hologram is not necessary, and this disclosure is equally applicable to any method of forming a first and a second image as described in the appended claims. In some embodiments, the hologram is presented, for example, on a display device, which may be a spatial light modulator, such as a liquid crystal on silicon spatial light modulator. When displayed on a suitable display device, the hologram can spatially modulate the light that can be converted into an image by the observation system. The channels formed by the diffraction structure are referred to herein as “hologram channels” simply to reflect that they are light channels encoded by a hologram with image information. It can be said that the light in each channel is in the holographic domain, rather than in the image or spatial domain. In some embodiments, the hologram is a Fourier or Fourier transform hologram, and therefore the hologram domain is the Fourier or frequency domain. Holograms can also be Fresnel or Fresnel transform holograms. Holograms are described in this paper as routing light into multiple holographic channels simply to reflect that the image reconstructed from the hologram has a finite size and can be arbitrarily divided into multiple image sub-regions, where each holographic channel corresponds to each image sub-region. Importantly, this type of hologram is characterized by how it distributes the image content when illuminated. Specifically, the hologram divides the image content by angles. That is, each point on the image is associated with a unique ray angle in the spatially modulated light formed by the hologram when illuminated—at least a unique pair of angles, since the hologram is two-dimensional. To avoid confusion, this holographic behavior is not conventional. When illuminated, the spatially modulated light formed by this particular type of hologram can be arbitrarily divided into multiple holographic channels, where each holographic channel is defined by a series of ray angles (two-dimensional). As can be understood from the above, any holographic channel (i.e., a subrange of ray angles) that can be considered in the spatially modulated light will be associated with a corresponding portion or sub-region of the image. In other words, all the information needed to reconstruct that part or sub-region of the image is contained within the angular sub-range of the spatially modulated light formed by the hologram of the image. When the spatially modulated light is viewed as a whole, there is not necessarily any evidence of multiple discrete optical channels. However, in some embodiments, multiple spatially separated holographic channels are formed by intentionally leaving areas of the target image for hologram computation blank or empty (i.e., without image content).

[0029] However, this type of hologram can still be identified. For example, if only a continuous portion of a sub-region of spatially modulated light formed by the hologram is reconstructed, then only that sub-region of the image should be visible. If different continuous portions or sub-regions of spatially modulated light are reconstructed, then different sub-regions of the image should be visible. Another identifying feature of this type of hologram is that the shape of the cross-sectional region of any hologram channel substantially corresponds to the shape of the incident pupil (i.e., substantially the same), although the dimensions may differ. Each light hologram channel propagates from the hologram at a different angle or angular range. While these are example ways of characterizing or identifying this type of hologram, other methods may also be used. In summary, the holograms disclosed herein are characterized and identified by how the image content is distributed within the hologram-encoded light, and the appended claims are stated accordingly.

[0030] In this embodiment, the second image region extends less than the first image region in both directions of the first dimension (in the angular space from all positions within the eyebox). Therefore, the total size of the second image region in the angular space is not greater than, for example, smaller than, the size of the first image region.

[0031] According to these embodiments, far-field images do not require any additional clearance within the vehicle to accommodate the head-up display. This is because the light rays forming the far-field image can be completely contained within the volume required for the near-field image.

[0032] The first and second images can be formed (essentially) simultaneously by a common display pattern displayed on a display device such as a spatial light modulator. That is, the first and second images can be formed during the same display event or as part of the same display event. The display event may include displaying a pattern on the display device and illuminating the display pattern to spatially modulate light according to that pattern. In these cases, information facilitating the formation of the first and second images is contained within the same light pattern, for example, it is encoded. The technical advancement achieved by these embodiments is that an interleaving scheme is not required to form the two images.

[0033] The displayed pattern can be a diffraction pattern, such as a hologram.

[0034] The diffraction pattern can be a Fourier hologram, a Fresnel hologram, a point cloud hologram, or a combination thereof.

[0035] The first image can be a first virtual image. Alternatively, the second image can be a second virtual image. In an embodiment, the virtual image is formed using an optical combiner or window (e.g., a windshield) of the main vehicle. For example, the light forming the first and second images can be reflected towards the observer by the windshield.

[0036] The second image region can extend in angular space from all positions within the eyebox in at least one direction of the first dimension, not exceeding the first image region. Therefore, the light beams forming the first and second images (substantially) are defined according to the first image region. Thus, it can be said that the light rays forming the far-field image do not require additional volumetric space than those required for the near-field image. In this respect, it can be said that, apart from the near-field image, there are no costs associated with providing the far-field image (in terms of space / volume).

[0037] The first dimension can be vertical (from the perspective of an observer, such as the driver of the main vehicle). Alternatively, the first dimension can be horizontal (from the perspective of an observer, such as the driver of the main vehicle).

[0038] The center of the first image region in the second dimension can be substantially aligned with the center of the second image region in the second dimension. For example, the near-field image and the far-field image can be aligned in the second / horizontal direction.

[0039] When viewed from within the eyebox / in the angular space from the center of the eyebox, the first image region may at least partially overlap with the second image region in a first dimension. Viewed from all positions within the eyebox, the second image region extends in the angular space from all positions within the eyebox in at least one direction in the first dimension (when viewed) no more than the first image region.

[0040] The distance between the first image regions can be less than 5 meters, for example, less than 3 meters. The distance between the second image regions can be less than 20 meters, for example, less than 15 meters.

[0041] A head-up display (HUD) has a field of view ranging from 5 to 25 degrees in the second dimension. Its field of view in the first dimension can range from 3 to 10 degrees.

[0042] Heads-up displays also include user tracking systems, such as eye-tracking systems. The heads-up display can be arranged to determine the display pattern in real time, at least in part, based on the position of the eye box within the eye box as determined by the user tracking system.

[0043] A method for displaying multiple images using the head-up display is also disclosed herein. The method may include changing at least one of a first and second image region distance based on a change in the eye-box position determined by a user tracking system. In these embodiments, the image region distance associated with the far-field image may be maximized in real time based on eye-tracking information. The image region distance associated with the central region of the eye-box may be greater than the image region distance associated with the peripheral region of the eye-box. For example, if the user tracking system determines that the user has moved from the center of the eye-box to the periphery, the system may be configured to decrease the image region distance for presenting / perceiving the far-field image to ensure that the light from the far-field image does not interfere with the vehicle. Similarly, for example, if the user tracking system determines that the user has moved from the periphery of the eye-box to the center, the system may be configured to increase the image region distance for presenting / perceiving the far-field image.

[0044] By changing at least one lens function associated with the diffraction pattern, at least one of the distances between the first and second image regions can be changed.

[0045] A head-up display (HUD) may include an image generation unit, such as an image projector, like a holographic projector. The HUD or image generation unit may include a display device, such as a spatial light modulator, like a liquid crystal on silicon spatial light modulator. The HUD or image generation unit may also include a light source, such as a laser diode arranged to illuminate the display device. The HUD or image generation unit may also include a waveguide arranged to extend the exit pupil of the image generation unit. The waveguide may be positioned between the display device and the eyebox / observer. An image or picture can be formed by reconstructing a target image from / using a diffraction structure including a hologram. The diffraction structure or display pattern is displayed on the display device. The diffraction structure or hologram may be configured to distribute image content at an angle according to positions within the image. The hologram may be a Fourier hologram, a Fresnel hologram, a point cloud hologram, or any combination thereof. The hologram may be determined or calculated from the target image in real time. The HUD may be configured to operate in conjunction with an optical combiner, such as the windshield of a vehicle. The optical combiner forms at least one virtual image visible to the observer from the eyebox. The head-up display may include an eye-tracking system that provides information about the observation position within the eyebox that is needed / used during the determination / computation of the hologram. This system is characterized by the absence of bulky optics, such as mirrors, that provide magnification. In some embodiments, diffraction patterns compensate for any curvature of the optical combiner and / or provide any necessary magnification for real-world applications.

[0046] The term "hologram" is used to refer to a record containing amplitude or phase information about an object, or some combination thereof. The term "holographic reconstruction" is used to refer to the optical reconstruction of an object formed by illuminating a hologram. The system disclosed herein is described as a "holographic projector" because the holographic reconstruction can be a real image and is spatially separate from the hologram. The term "reproduced field" is used to refer to a 2D region within which the holographic reconstruction is formed and fully focused. If the hologram is displayed on a spatial light modulator including pixels, the reproduced field will be repeated in the form of multiple diffraction orders, where each diffraction order is a copy of the zero-order reproduced field. The zero-order reproduced field generally corresponds to the preferred or master reproduced field because it is the brightest reproduced field. Unless otherwise explicitly stated, the term "reproduced field" should be considered to refer to the zero-order reproduced field. The term "reproduced plane" is used to refer to a plane in space containing all reproduced fields. The terms "image," "reproduced image," and "image region" refer to the region of the reproduced field illuminated by the light reconstructed by the hologram. In some embodiments, an “image” may include discrete points, which may be referred to as “image points” or simply as “image pixels” for convenience.

[0047] The terms “encoding,” “writing,” and “addressing” are used to describe the process of providing multiple corresponding control values ​​to multiple pixels of an SLM, each determining the modulation level of the pixel. In other words, the pixels of an SLM are configured to “display” an optical modulation distribution in response to receiving multiple control values. Therefore, it can be said that an SLM “displays” a hologram, and a hologram can be considered an array of optical modulation values ​​or levels.

[0048] It has been found that acceptable-quality holographic reconstructions can be formed from "holograms" containing only phase information related to the original object (i.e., the target image used for reconstruction). Such holographic records can be referred to as phase-only holograms. Embodiments relate to phase-only holograms, but this disclosure is equally applicable to amplitude-only holography. This disclosure is not limited to any particular method of hologram computation. By way of example only, some embodiments relate to point cloud holograms, i.e., holograms constructed using point cloud methods. However, this disclosure is equally applicable to Fourier or Fresnel-type holograms and holograms computed according to other techniques such as coherent ray tracing.

[0049] This disclosure is equally applicable to forming holographic reconstructions using amplitude and phase information associated with the original object (i.e., the target image). In some embodiments, this is achieved by using complex modulation of a so-called fully complex hologram that incorporates amplitude and phase information associated with the original object. Because the value (gray level) assigned to each pixel of the hologram has amplitude and phase components, such a hologram may be called a fully complex hologram. The value (gray level) assigned to each pixel can be represented as a complex number with amplitude and phase components. In some embodiments, a fully complex computer-generated hologram is computed.

[0050] The term "phase delay" can be a shorthand for the phase value, phase component, phase information, or simply phase of a pixel in a computer-generated hologram or spatial light modulator. That is, any phase value described is actually a number representing the amount of phase delay provided by that pixel (e.g., in the range of 0 to 2π). For example, a spatial light modulator is described as a pixel having a π / 2 phase value causing a π / 2 radian phase delay in the received light. In some embodiments, each pixel of a spatial light modulator can operate on one of a plurality of possible modulation values ​​(e.g., phase delay values). The term "gray level" can be used to refer to a plurality of available modulation levels. For example, the term "gray level" can be used for convenience to refer to a plurality of available phase levels in a phase modulator, even if different phase levels do not provide different shades of gray. For convenience, the term "gray level" can also be used to refer to a plurality of available complex modulation levels in a complex modulator.

[0051] Therefore, a hologram comprises an array of gray levels, i.e., an array of optical modulation values, such as phase delay values ​​or complex modulation values. A hologram is also considered a diffraction pattern because it is a pattern that causes diffraction when displayed on a spatial light modulator and illuminated with light whose wavelength is relative to (typically less than) the pixel spacing of the spatial light modulator. Reference is made herein to combining holograms with other diffraction patterns, such as those used as lenses or gratings. For example, a diffraction pattern used as a grating can be combined with a hologram to translate the playback field on the playback plane, or a diffraction pattern used as a lens can be combined with a hologram to focus the holographic reconstruction onto the playback plane in the near field.

[0052] Although different embodiments and groups of embodiments may be disclosed separately in the detailed description below, any feature of any embodiment or group of embodiments may be combined with any other feature or combination of features of any embodiment or group of embodiments. That is, all possible combinations and substitutions of the features disclosed in this disclosure are contemplated. Attached Figure Description

[0053] Specific embodiments are described by way of example only with reference to the following figures:

[0054] Figure 1 This is a schematic diagram illustrating a reflective SLM that generates holographic reconstruction on a screen;

[0055] Figure 2A The first iteration of the example Gerchberg-Saxton type algorithm is shown;

[0056] Figure 2B The second and subsequent iterations of the example Gerchberg-Saxton type algorithm are shown;

[0057] Figure 2CAlternative second and subsequent iterations of the example Gerchberg-Saxton type algorithm are shown;

[0058] Figure 3 This is a schematic diagram of a reflective LCOS SLM;

[0059] Figure 4 This shows the angular content of the virtual image effectively propagating from the display device to the aperture;

[0060] Figure 5A An observation system with a relatively short propagation distance is shown;

[0061] Figure 5B An observation system with a relatively large propagation distance is shown;

[0062] Figure 6A An observation system with a relatively large propagation distance is shown, which includes waveguides for forming virtual images at infinity;

[0063] Figure 6B It shows Figure 6A A magnified view of the optical path;

[0064] Figure 7 An optical system according to an embodiment is shown;

[0065] Figure 8 This is a flowchart illustrating the steps of a method according to an embodiment;

[0066] Figure 9A and 9B A head-up display is shown, in which the angular field of view of the near-field image region is equal to the angular field of view of the far-field image region;

[0067] Figure 10 An improved head-up display according to some embodiments is shown, wherein the field of view of the far-field image region is cropped according to the near-field image region on one side in order to reduce the size of the light beams that form the near-field and far-field image content;

[0068] Figure 11A , 11B 11C illustrates how the far-field image determines the size of the HUD beam when an eyebox of finite size is provided; and

[0069] Figure 12A , 12B 12C illustrates how the size of near-field or far-field images can be optimized according to some embodiments.

[0070] In all the accompanying drawings, the same reference numerals will be used to refer to the same or similar parts. Detailed Implementation

[0071] This invention is not limited to the embodiments described below, but extends to the full scope of the appended claims. That is, the invention may be implemented in different forms and should not be construed as limited to the described embodiments, which are illustrated for illustrative purposes.

[0072] Unless otherwise stated, singular terms may include plural forms.

[0073] A structure described as being formed above or below another structure should be interpreted as including situations where the structures are in contact with each other, and also including situations where a third structure is placed between them.

[0074] When describing temporal relationships, such as when the chronological order of events is described as “after,” “following,” “next,” “before,” etc., this disclosure should be considered to include both consecutive and discontinuous events, unless otherwise stated. For example, unless terms such as “exactly,” “immediately,” or “directly” are used, the description should be considered to include discontinuous cases.

[0075] Although the terms “first,” “second,” etc., may be used herein to describe various elements, these elements are not limited by these terms. These terms are used only to distinguish individual elements. For example, without departing from the scope of the appended claims, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element.

[0076] Features of different embodiments may be coupled or combined with each other in part or in whole, and may interoperate differently with each other. Some embodiments may be implemented independently of each other, or may be implemented together in a mutually dependent relationship.

[0077] Optical configuration

[0078] Figure 1 An embodiment is illustrated in which a computer-generated hologram is encoded on a single spatial light modulator. The computer-generated hologram is a Fourier transform of the object used for reconstruction. Therefore, a hologram can be described as 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 on the spatial light modulator, and a holographic reconstruction is formed at the playback field, such as a light-receiving surface like a screen or diffuser.

[0079] A light source 110, such as a laser or laser diode, is configured to illuminate the SLM 140 via a collimating lens 111. The collimating lens causes the approximately plane wavefront of the light to be incident on the SLM. Figure 1In this embodiment, the wavefront is oriented off-normal (e.g., two or three degrees away from a plane that is truly orthogonal to the transparent layer). However, in other embodiments, a generally planar wavefront is provided with normal incidence, and beam splitters are arranged to separate the input and output optical paths. Figure 1 In the illustrated embodiment, the arrangement is such that light from the light source is reflected from the mirrored rear surface of the SLM and interacts with the light modulation layer to form an outgoing wavefront 112. The outgoing wavefront 112 is applied to an optics device including a Fourier transform lens 120, the focal point of which is located at screen 125. More specifically, the Fourier transform lens 120 receives the modulated beam from the SLM 140 and performs a frequency-space transformation to produce a holographic reconstruction at screen 125.

[0080] It is worth noting that in this type of hologram, each pixel of the hologram contributes to the overall reconstruction. There is no one-to-one correlation between a specific point (or image pixel) on the playback field and a specific optical modulation element (or hologram pixel). In other words, the modulated light leaving the optical modulation layer is distributed across the entire playback field.

[0081] In these embodiments, the spatial position of the holographic reconstruction is determined by the refractive power (focusing) of the Fourier transform lens. Figure 1 In the illustrated embodiment, the Fourier transform lens is a physical lens. That is, the Fourier transform lens is an optical Fourier transform lens and performs a Fourier transform optically. Any lens can act as a Fourier transform lens, but the lens's performance will limit the accuracy of the Fourier transform it performs. Those skilled in the art will understand how to use lenses to perform optical Fourier transforms.

[0082] Hologram Calculation Example

[0083] In some embodiments, the computer-generated hologram is a Fourier transform hologram, or simply a Fourier hologram or a Fourier-based hologram, wherein the image is reconstructed in the far field by utilizing the Fourier transform properties of a positive lens. The Fourier hologram is computed by Fourier transforming the desired light field in the reproduction plane back to the lens plane. The Fourier transform can be used to compute computer-generated Fourier holograms.

[0084] Algorithms such as the Gerchberg-Saxton algorithm can be used to compute Fourier transform holograms. Furthermore, the Gerchberg-Saxton algorithm can be used to compute holograms in the Fourier domain (i.e., Fourier transform holograms) based solely on amplitude-only information in the spatial domain (e.g., a photograph). This effectively "retrieves" phase information related to the object from the amplitude-only information in the spatial domain. In some embodiments, the Gerchberg-Saxton algorithm or its variants are used to compute computer-generated holograms from amplitude-only information.

[0085] The Gerchberg-Saxton algorithm takes into account the fact that the intensity cross section I of the beams in planes A and B is known. A (x,y) and I B (x,y) and I A (x,y) and I B The case where (x,y) is correlated via a single Fourier transform. For a given intensity cross section, the approximate phase distribution Ψ in planes A and B is obtained. A (x,y) and Ψ B (x,y). The Gerchberg-Saxton algorithm finds a solution to the problem by following an iterative process. More specifically, the Gerchberg-Saxton algorithm iteratively applies spatial and spectral constraints while repeatedly transferring the representation I between the spatial and Fourier (spectral or frequency) domains. A (x,y) and I B A dataset (x, y) containing amplitude and phase. A corresponding computer-generated hologram in the spectral domain is obtained through at least one iteration of the algorithm. The algorithm is convergent and arranged to produce a hologram representing the input image. The hologram can be an amplitude-only hologram, a phase-only hologram, or a fully complex hologram.

[0086] In some embodiments, the phase-only hologram is computed using an algorithm based on the Gerchberg-Saxton algorithm, such as the algorithm described in British Patents 2498170 or 2501112, the entire contents of which are incorporated herein by reference. However, the embodiments disclosed herein are described by way of example only when calculating the phase-only hologram. In these embodiments, the Gerchberg-Saxton algorithm retrieves the phase information Ψ[u,v] of the Fourier transform of a dataset, which produces known amplitude information T[x,y], where the amplitude information T[x,y] represents the target image (e.g., a photograph). Since amplitude and phase are inherently combined in the Fourier transform, the transformed amplitude and phase contain useful information about the accuracy of the computed dataset. Therefore, the algorithm can be used iteratively with feedback of amplitude and phase information. However, in these embodiments, the phase-only information Ψ[u,v] is used as a hologram to form a holographic representation of the target image at the image plane. The hologram is a dataset of phase values ​​(e.g., a 2D array).

[0087] In other embodiments, an algorithm based on the Gerchberg-Saxton algorithm is used to compute a fully complex hologram. A fully complex hologram is a hologram having amplitude and phase components. A hologram is a dataset (e.g., a 2D array) comprising an array of complex data values, where each complex data value includes an amplitude component and a phase component.

[0088] In some embodiments, the algorithm processes complex data, and the Fourier transform is a complex Fourier transform. Complex data can be viewed as comprising (i) real and imaginary components, or (ii) amplitude and phase components. In some embodiments, the two components of the complex data are processed differently at different stages of the algorithm.

[0089] Figure 2A A first iteration of an algorithm for computing a phase-only hologram, according to some embodiments, is shown. The input to the algorithm is an input image 210 comprising a 2D array of pixel or data values, where each pixel or data value is an amplitude or oscillation value. That is, each pixel or data value of the input image 210 does not have a phase component. Therefore, the input image 210 can be considered as an amplitude-only, oscillation-only, or intensity-only distribution. An example of such an input image 210 is a photograph or a frame of a video comprising a time-series of frames. The first iteration of the algorithm begins with a data formation step 202A, which includes assigning random phase values ​​to each pixel of the input image using a random phase distribution (or random phase seed) 230 to form an initial complex dataset, where each data element of the dataset includes both amplitude and phase. In other words, the initial complex dataset represents the input image in the spatial domain.

[0090] First processing block 250 receives an initial complex dataset and performs a complex Fourier transform to form a complex dataset of Fourier transforms. Second processing block 253 receives the complex dataset of Fourier transforms and outputs a hologram 280A. In some embodiments, hologram 280A is a phase-only hologram. In these embodiments, second processing block 253 quantizes each phase value and sets each amplitude value to 1 to form hologram 280A. Each phase value is quantized according to the phase level that can be represented on the pixel of the spatial light modulator that will be used to "display" the phase-only hologram. For example, if each pixel of the spatial light modulator provides 256 different phase levels, each phase value of the hologram is quantized to one of the 256 possible phase levels. Hologram 280A is a phase-only Fourier hologram representing an input image. In other embodiments, hologram 280A is a fully complex hologram comprising an array of complex data values ​​(each including an amplitude component and a phase component) derived from the received complex dataset of Fourier transforms. In some embodiments, the second processing block 253 constrains each complex data value to one of a plurality of permissible complex modulation levels to form a hologram 280A. The constraint step may include setting each complex data value to the closest permissible complex modulation level in the complex plane. The hologram 280A can be said to represent an input image in the spectral, Fourier, or frequency domain. In some embodiments, the algorithm stops at this point.

[0091] However, in other embodiments, the algorithm continues, such as Figure 2AAs shown by the dashed arrow in the image. In other words, follow... Figure 2A The steps indicated by the dashed arrows are optional (i.e., not essential for all embodiments).

[0092] The third processing block 256 receives the modified complex dataset from the second processing block 253 and performs an inverse Fourier transform to form a complex dataset with an inverse Fourier transform. The complex dataset with the inverse Fourier transform can be said to represent the input image in the spatial domain.

[0093] The fourth processing block 259 receives the complex dataset of the inverse Fourier transform and extracts the distribution of amplitude values ​​211A and the distribution of phase values ​​213A. Optionally, the fourth processing block 259 evaluates the distribution of amplitude values ​​211A. Specifically, the fourth processing block 259 can compare the distribution of amplitude values ​​211A of the complex dataset of the inverse Fourier transform with the input image 510, which itself is, of course, the distribution of amplitude values. If the difference between the distribution of amplitude values ​​211A and the input image 210 is sufficiently small, the fourth processing block 259 can determine that the hologram 280A is acceptable. That is, if the difference between the distribution of amplitude values ​​211A and the input image 210 is sufficiently small, the fourth processing block 259 can determine that the hologram 280A is a sufficiently accurate representation of the input image 210. In some embodiments, for comparison purposes, the distribution of phase values ​​213A of the complex dataset of the inverse Fourier transform is ignored. It will be understood that any number of different methods can be used to compare the distribution of amplitude values ​​211A with the input image 210, and this disclosure is not limited to any particular method. In some embodiments, the mean squared error is calculated, and if the mean squared error is less than a threshold, the hologram 280A is considered acceptable. If the fourth processing block 259 determines that the hologram 280A is unacceptable, further iterations of the algorithm can be performed. However, this comparison step is not required, and in other embodiments, the number of iterations of the algorithm performed is predetermined, preset, or user-defined.

[0094] Figure 2B This represents the second iteration of the algorithm and any further iterations of the algorithm. The distribution of the phase values ​​213A from previous iterations is fed back through the algorithm's processing block. Distributions of amplitude values ​​211A are rejected, favoring the distribution of amplitude values ​​of the input image 210. In the first iteration, data formation step 202A forms a first complex dataset by combining the distribution of amplitude values ​​of the input image 210 with the random phase distribution 230. However, in the second and subsequent iterations, data formation step 202B includes forming a complex dataset by combining (i) the distribution of phase values ​​213A from previous iterations of the algorithm with (ii) the distribution of amplitude values ​​of the input image 210.

[0095] Then, with reference Figure 2AThe same method described is handled by Figure 2B The complex dataset formed in step 202B is used to form the second iterative hologram 280B. Therefore, the description of this process will not be repeated here. The algorithm can stop when the second iterative hologram 280B has been computed. However, any number of further iterations of the algorithm can be performed. It will be understood that the third processing block 256 is only needed if a fourth processing block 259 is required or further iterations are needed. The output hologram 280B generally improves with each iteration. However, in practice, a point is often reached where measurable improvement is no longer observable, or the positive benefits of performing further iterations are offset by the negative impact of the additional processing time. Therefore, the algorithm is described as iterative and convergent.

[0096] Figure 2C This represents an alternative embodiment for the second and subsequent iterations. The distribution of the phase value 213A from the previous iteration is fed back through the algorithm's processing block. The distribution of the amplitude value 211A is rejected, favoring an alternative distribution of the amplitude value. In this alternative embodiment, the alternative distribution of the amplitude value is derived from the distribution of the amplitude value 211 from the previous iteration. Specifically, processing block 258 subtracts the distribution of the amplitude value of the input image 210 from the distribution of the amplitude value 211 from the previous iteration, scales the difference by a gain factor α, and subtracts the scaled difference from the input image 210. This is mathematically expressed by the following equation, where the subscript text and numbers represent the iteration number:

[0097] R n+1 [x,y]=F'{exp(iψ n [u,v])}

[0098] ψ n [u,v]=∠F{η·exp(i∠R n [x,y])}

[0099] η=T[x,y]-a(|R n [x,y]|-T[x,y])

[0100] in:

[0101] F' is the inverse Fourier transform;

[0102] F is the forward Fourier transform;

[0103] R[x,y] is the complex number dataset output by the third processing block 256;

[0104] T[x,y] is the input or target image;

[0105] ∠ is the phase component;

[0106] Ψ is a phase-only hologram 280B;

[0107] η is a new distribution of amplitude value 211B; and

[0108] α is the gain factor.

[0109] The gain factor α can be fixed or variable. In some embodiments, the gain factor α is determined based on the size and rate of the input target image data. In some embodiments, the gain factor α depends on the number of iterations. In some embodiments, the gain factor α is only a function of the number of iterations.

[0110] In all other respects, Figure 2C Implementation examples and Figure 2A and Figure 2B The implementation is the same. It can be said that only the phase hologram Ψ(u,v) includes the phase distribution in the frequency or Fourier domain.

[0111] In some embodiments, a spatial light modulator is used to perform a Fourier transform. Specifically, holographic data is combined with second data that provides optical power. That is, the data written into the spatial light modulator includes holographic data representing an object and lens data representing a lens. When displayed on the spatial light modulator and illuminated with light, the lens data simulates a physical lens—that is, it focuses light in the same way as a corresponding physical optical element. Therefore, the lens data provides optical power or focusing power. In these embodiments, [the following can be omitted] Figure 1A physical Fourier transform lens 120 is used. Data representing the lens is known. This data can be referred to as a software lens. For example, a phase-only lens can be formed by calculating the phase delay caused by the optical path length at each point of the lens due to its refractive index and spatial variation. For example, the optical path length at the center of a convex lens is greater than the optical path length at the edge of the lens. An amplitude-only lens can be formed from Fresnel zone plates. In the field of computer-generated holography, it is also known how to combine data representing the lens with a hologram to perform a Fourier transform of the hologram without requiring a physical Fourier lens. In some embodiments, the lensed data is combined with the hologram by simple addition, such as simple vector addition. In some embodiments, a physical lens is used in combination with a software lens to perform the Fourier transform. Alternatively, in other embodiments, the Fourier transform lens is omitted entirely, allowing holographic reconstruction to occur in the far field. In further embodiments, the hologram can be combined with grating data—i.e., data arranged to perform grating functions such as image steering—in the same manner. Again, how to calculate such data is known in the art. For example, a phase-only grating can be formed by modeling the phase delay caused by each point on the surface of the blazed grating. An amplitude-only grating can be simply superimposed on an amplitude-only hologram to provide angular steering for holographic reconstruction. The second data providing lensing and / or steering may be referred to as an optical processing function or optical processing pattern to distinguish it from the holographic data, which may be referred to as an image forming function or image forming pattern.

[0112] In some embodiments, the Fourier transform is performed jointly by a physical Fourier transform lens and a software lens. That is, the software lens provides some of the optical power that contributes to the Fourier transform, while one or more physical optics provide the remaining optical power that contributes to the Fourier transform.

[0113] In some embodiments, a real-time engine is provided, arranged to receive image data using an algorithm and compute holograms in real time. In some embodiments, the image data is video comprising a sequence of image frames. In other embodiments, the holograms are pre-computed, stored in computer memory, and retrieved as needed for display on an SLM. That is, in some embodiments, a library of predetermined holograms is provided.

[0114] The embodiments described herein are by way of example only and involve Fourier holography and Gerchberg-Saxton type algorithms. This disclosure is equally applicable to Fresnel holography and Fresnel holograms that can be computed using similar methods. This disclosure is also applicable to holograms computed using other techniques, such as point cloud-based methods.

[0115] Optical modulation

[0116] Spatial light modulators can be used to display diffraction patterns, including computer-generated holograms. If the hologram is a phase-only hologram, a spatial light modulator is needed to modulate the phase. If the hologram is a fully complex hologram, a spatial light modulator that modulates both the phase and amplitude can be used, or a first spatial light modulator that modulates the phase and a second spatial light modulator that modulates the amplitude can be used.

[0117] In some embodiments, the light modulation element (i.e., pixel) of the spatial light modulator is a cell comprising liquid crystal. That is, in some embodiments, the spatial light modulator is a liquid crystal device in which the optically active component is liquid crystal. Each liquid crystal cell is configured to selectively provide multiple light modulation levels. That is, each liquid crystal cell is configured at any time to operate at one light modulation level selected from multiple possible light modulation levels. Each liquid crystal cell can be dynamically reconfigured to a light modulation level different from the multiple light modulation levels. In some embodiments, the spatial light modulator is a reflective liquid crystal on silicon (LCOS) spatial light modulator, but this disclosure is not limited to this type of spatial light modulator.

[0118] LCOS devices provide a dense array of light-modulating elements or pixels within a small aperture (e.g., a few centimeters wide). Pixels are typically about 10 micrometers or smaller, resulting in a diffraction angle of a few degrees, meaning the optical system can be compact. The small aperture of an LCOS SLM is much easier to fully illuminate than the larger apertures of other liquid crystal devices. LCOS devices are typically reflective, meaning the circuitry driving the LCOS SLM pixels can be buried beneath the reflective surface. This results in a higher aperture ratio. In other words, the pixels are densely packed, meaning there are virtually no dead zones between pixels. This is advantageous because it reduces optical noise in the playback field. LCOS SLMs use a silicon substrate, which has the advantage of optically flat pixels. This is particularly important for phase modulation devices.

[0119] The following are just examples for reference. Figure 3 To describe a suitable LCOS SLM, an LCOS device is formed using a single-crystal silicon substrate 302. It has a 2D array of square planar aluminum electrodes 301, spaced apart by gaps 301a, arranged on the upper surface of the substrate. Each electrode 301 can be addressed by circuitry 302a buried in the substrate 302. Each electrode forms its own planar mirror. An alignment layer 303 is disposed on the electrode array, and a liquid crystal layer 304 is disposed on the alignment layer 303. A second alignment layer 305 is disposed on a planar transparent layer 306, for example, made of glass. A single transparent electrode 307, for example made of ITO, is disposed between the transparent layer 306 and the second alignment layer 305.

[0120] Each square electrode 301, together with the area covered by the transparent electrode 307 and the intermediate liquid crystal material, defines a controllable phase modulation element 308, commonly referred to as a pixel. Taking into account the space between pixels 301a, the effective pixel area, or fill factor, is the percentage of the total number of optically active pixels. By controlling the voltage applied to each electrode 301 relative to the transparent electrode 307, the properties of the liquid crystal material of the individual phase modulation elements can be altered, thereby providing a variable delay for light incident upon them. The effect is to provide phase-only modulation to the wavefront, i.e., without amplitude effects.

[0121] The described LCOS SLM outputs spatially modulated light in a reflective manner. The advantage of a reflective LCOS SLM is that the signal lines, grating lines, and transistors are located below the mirror, resulting in a high fill factor (typically greater than 90%) and high resolution. Another advantage of using a reflective LCOS spatial light modulator is that the thickness of the liquid crystal layer can be half that required when using a transmissive device. This significantly improves the switching speed of the liquid crystal (a key advantage for projecting moving video images). However, the teachings of this disclosure can also be implemented using a transmissive LCOS SLM.

[0122] This disclosure relates to a heads-up display of near-field and far-field images, optionally wherein there is at least partial overlap between the near-field and far-field images. For the avoidance of doubt, the teachings of this disclosure apply to any image forming method, and embodiments using holography are described by way of example only. Some embodiments describe a method for computing a hologram of an image, which is particularly suitable when the display device for the hologram is relatively small and the viewing distance is relatively long. These embodiments are provided merely as examples of how multiple images can be formed according to this disclosure. This disclosure is not limited to holography or image projection using small display devices and long viewing distances; however, these examples are particularly compatible with image region optimization as defined herein.

[0123] Image projection using small display devices and long viewing distances

[0124] In some embodiments, the distance between the display device and the observer is much larger than the size of the display device. The viewing distance (i.e., the distance between the observer and the display device) can be at least one order of magnitude larger than the size of the display device. The viewing distance can be at least two orders of magnitude larger than the size of the display device. For example, the pixel area of ​​the display device can be 10mm × 10mm, and the viewing distance can be 1m. The image projected by the system is formed on a display plane that is spatially separated from the display device.

[0125] According to some embodiments, the image is formed by holographic projection. The hologram is displayed on a display device. The hologram is illuminated by a light source (not shown), and the image is perceived on a display plane spatially separated from the hologram. The image can be real or virtual. For the purposes of the following explanation, it is helpful to consider a virtual image formed upstream of the display device—that is, appearing behind the display device. However, it is not important whether the image is virtual, and this disclosure applies equally to real images formed between the display device and the viewing system.

[0126] Display devices consist of pixels that display holograms. The pixel structure of a display device is diffracted. Therefore, the size of the hologram is determined by diffraction rules. See below for reference. Figure 4 The results of the interpretation of the diffraction characteristics of the display device are presented.

[0127] Figure 4 A pixelated display device 402 is shown, arranged to display a hologram forming a virtual image 401 upstream of the display device 402. The diffraction angle θ of the display device determines the size of the virtual image 401. The virtual image 401, the display device 402, and the observation system 405 are arranged on the optical axis Ax.

[0128] The observation system 405 has an entrance aperture 404 and an observation plane 406. The observation system 405 can be a human eye. Therefore, the entrance aperture 404 can be the pupil of the eye, and the observation plane 406 can be the retina of the eye.

[0129] The light propagating between the display device 402 and the observation system 405 is modulated by the hologram of the image (not the image itself). However, Figure 4 This illustrates how a hologram divides the content of a virtual image by angle. Each illustrated beam of light relates to a different portion of the virtual image 401. More specifically, the light in each beam is encoded by the hologram with information about a portion of the virtual image. Figure 4 Five example light beams are shown, each characterized by a corresponding angle relative to the optical axis Ax, and each beam represents a corresponding portion of the virtual image. In this example, one beam passes through the pupil 404, while the other four beams are blocked by the pupil 404. Similarly, the five different light beams correspond to five different portions of the virtual image 401. The complete image content of the virtual image is effectively divided by angle. The beams propagating along the optical axis Ax carry the central portion of the image information, i.e., information related to the image center. The other beams carry other portions of the image information. The two beams shown at the ends of the light cone carry the edge portions of the image information. The result of dividing the image information by angle is that not all image content can pass through the entrance aperture 404 of the observation system at a given viewing position. In other words, not all image content is received by the eye. Figure 4In the example shown, only one of the five beams passes through the pupil 404 at any viewing position. The reader will understand that the five beams are shown only by way of example, and the process described is not limited to dividing the image information of a virtual image into just five beams.

[0130] In this example, the central portion of the image information is received by the eye. The edges of the image information are blocked by the pupil. The reader will understand that if the observer moves up or down, the eye may receive different beams of light; for example, the central portion of the image information may be blocked. Therefore, the observer can only see a portion of the entire image. The remaining image information is blocked by the incident pupil. The observer's field of vision is severely limited because they are actually viewing the image through a small aperture in the display device itself.

[0131] In short, light travels from a display device within a diffraction angle range. At a viewing distance of 1 meter, for a given eye position, only a small range of angles from the display device can travel through the pupil of the eye to form an image on the retina. The visible portion of a virtual image is only what falls within the diffraction angle. Figure 4 The field of view is shown as a small angular range passing through the incident aperture. Therefore, the field of view is very small, and the specific angular range depends heavily on the eye position.

[0132] refer to Figure 4 The issues of a small field of view and sensitivity to eye position are a result of the large viewing distance and small aperture of the display device. The importance of viewing distance is further explained with reference to Figures 5 through 7.

[0133] Figure 5A A display device 502 is shown, arranged to display a hologram and propagate light modulated according to the hologram to an observation system including an incident aperture 504 and an observation plane 506. The virtual image 501 is at infinity, so the light rays tracked between the virtual image and the display device are collimated. Figure 5A The lower part shows an enlarged view of the observation system. This view is schematic and therefore does not show the physiological details of the eye. In reality, of course, there is a light source arranged to illuminate the display device 502. Figure 5A (Not shown in the image).

[0134] Figure 5A Only light rays that can propagate through aperture 504 are shown; any other light rays that cannot pass through aperture 504 are omitted. However, it will be understood that in practice, those other light rays will also propagate from display device 502. Figure 5AIn this configuration, the distance between the display device and the viewing plane is small enough that the full diffraction angle from the display device can form an image on the retina. All light propagation paths from the virtual image pass through the incident aperture. Therefore, all points on the virtual image are mapped onto the retina, and all image content is transmitted to the viewing plane. Consequently, the field of view for perceiving the image is maximized. At the optimal position, the field of view equals the diffraction angle of the display device. Interestingly, different image points on the retina are formed by light propagating from different areas of the display device 502, for example, the closest to the retina. Figure 5A The image dot at the top is formed solely by light propagating from the bottom of the display device. Light propagating from other areas of the display device does not contribute to that image dot.

[0135] Figure 5B This shows what happens as the observation distance increases.

[0136] More in detail, Figure 5B A display device 502' is shown, which is arranged to display a hologram and propagate light modulated according to the hologram to an observation system including an incident aperture 504' and an observation plane 506'. The virtual image 501' is at infinity, so the light between the virtual image and the display device is collimated. Figure 5B The lower part shows an enlarged view of the observation system. This view is schematic and therefore does not show the physiological details of the eye. In reality, it certainly has a light source arranged to illuminate the display device 502'. Figure 5B (Not shown in the image).

[0137] Figure 5B Only light rays that can propagate through an aperture of 504' are shown. Figure 5B At larger viewing distances, some light beams are blocked by the entrance aperture 504'. Specifically, light beams associated with the edges of the virtual image are blocked by the entrance pupil 504'. Therefore, the entire virtual image is invisible, and the visible portion of the virtual image heavily depends on eye position. Thus, large distances between the display device and the viewing system are problematic due to the small size of the display device.

[0138] Figure 6A An improved system including a display device 602 is shown, which propagates light encoded with a hologram displayed on the display device 602 into an observation system including an entrance aperture 604 and an observation plane 606. In fact, a light source (not shown) is, of course, arranged to illuminate the display device 602. The improved system also includes a waveguide 608 located between the display device 602 and the entrance aperture 604. Figure 6A The lower part shows an enlarged view of the entrance pupil 604 and the viewing plane 606. This figure is schematic and therefore does not show the physiological details of the eye.

[0139] The observation distance in Figure 6 is... Figure 5B The same. However, in Figure 5B The blocked beam of light is effectively recovered by waveguide 608, allowing the observation system to receive complete image information—despite the longer observation distance.

[0140] The presence of waveguide 608 allows content from all angles of the display device 602 to be received by the eye, even at this relatively large projection distance. This is because waveguide 608 acts as a pupil dilator in a well-known manner, and will therefore be described only briefly here.

[0141] In short, waveguide 608 comprises a generally elongated structure. In this example, it comprises an optical plate of refractive material, but other types of waveguides are also well known and can be used. Waveguide 608 is positioned to intersect, for example, at an oblique angle, a light cone projected from display device 602. The size, position, and orientation of waveguide 608 are configured to ensure that light from each of the five beams within the light cone enters waveguide 608. Light from the light cone enters waveguide 608 via a first planar surface 610 (located closest to display device 602) and is guided at least partially along the length of waveguide 608 before being emitted via a second planar surface 612 substantially opposite the first surface 610 (located closest to the eye). It is readily understood that the second planar surface 612 is partially reflective and partially transmissive. In other words, as each ray of light propagates within waveguide 608 from its first planar surface 610 to its second planar surface 612, some light is transmitted through waveguide 608, and some is reflected back to its first planar surface 610 by the second planar surface 612. The first planar surface 610 is reflective, such that all light striking it from within waveguide 608 is reflected back to its second planar surface 612. Therefore, some light can be simply refracted between the two planar surfaces 610, 612 of waveguide 608 before transmission, while other light can be reflected and thus undergo one or more reflections (or "bouncing") between the planar surfaces 610, 612 of waveguide 608 before transmission. Thus, the net effect of waveguide 608 is that the transmission of light is effectively extended to multiple locations on the second planar surface 612 of waveguide 608. Therefore, compared to the case without waveguide 608, all angular content output by display device 602 can appear at a greater number of locations on the display plane (and at a greater number of locations on the aperture plane). This means that light from each beam can enter the entrance aperture 604 and contribute to the image formed by the viewing plane 606, despite the relatively large projection distance. In other words, the eye can receive content from all angles of the display device 602. Therefore, the full diffraction angle of the display device 602 is utilized, and the viewing window is maximized for the user. In turn, this means that all light contributes to the perceived virtual image 601.

[0142] Figure 6B The diagram shows the individual optical path of each of the five ray beams contributing to five corresponding image points within the virtual image 601. Figure 6A The light from each of R1 and R2 is simply refracted and then transmitted through waveguide 608. On the other hand, the light from R4 experiences a single bounce before transmission. The light from R3 comprises some light from the corresponding first portion of display device 602, which is simply refracted by waveguide 608 before transmission, and some light from a different second corresponding portion of display device 602, which experiences a single bounce before transmission. Similarly, the light from R5 comprises some light from the corresponding first portion of display device 602 that experiences a single bounce before transmission, and some light from a different second corresponding portion of display device 602 that experiences two bounces before transmission. For each of R3 and R5, the two different portions of LCOS propagate light corresponding to the virtual image portion.

[0143] In some applications, the virtual image distance (i.e., the distance from the observer to the virtual image) is preferably finite, contrary to the notion of forming a virtual image at infinity. In some applications, there will be a preferred virtual image distance at which the appearance of the virtual image content is desired or necessary. This could be, for example, in a head-up display, such as in a car setting, if the virtual image content is to be superimposed on real content seen by the observer through the vehicle's windshield. For example, a desired virtual image distance could include virtual image content formed a few meters in front of the observer's vehicle or windshield, such as 3 meters or 5 meters.

[0144] Holographic calculations of first and second images formed on different planes

[0145] According to this disclosure, image content appears at different distances and / or multiple distances from the observation system, optionally simultaneously, for example using a display pattern. The method also allows image content to optionally appear simultaneously downstream and upstream of the display device, for example using a display pattern. In some embodiments—described only by way of examples of how first and second image content are formed on different planes—an iterative algorithm is used to compute a hologram that reconstructs the image content upon illumination.

[0146] Figure 7A spatial light modulator 701 for displaying an image hologram is shown. In this embodiment, the spatial light modulator 701 is a liquid crystal on silicon device arranged to modularize the phase of received light. The spatial light modulator 701 is illuminated by at least partially coherent light from a light source (not shown). The light source may be a laser diode. The spatial light modulator 701 outputs light spatially modulated according to the displayed hologram. Figure 7 A ray 702 of spatially modulated light is shown. A pupil dilator 703 receives the spatially modulated light. The pupil dilator 703 is tilted relative to the plane of the display device 701. The pupil dilator 703 therefore receives light that is not perpendicularly incident. The angle of incidence (the angle formed by the optical axis and the pupil dilator) can be less than 25 degrees, for example, 10 to 20 degrees. The pupil dilator includes an input surface 703a and an output surface 703b for receiving the spatially modulated light. The input surface 703a and the output surface 703b are substantially parallel and elongate in the direction of pupil dilation. The input surface 703a includes at least a portion that is substantially totally internally reflected (e.g., R = 1). The output surface 703b includes at least a portion that is highly reflective but partially transmissive (e.g., R = 0.9 and T = 0.1). The reflective surfaces are arranged such that the spatially modulated light is reflected back and forth between them, and the light is emitted at multiple points along the output surface 703b, as described above with reference to waveguide 608 in FIG. 6. In this embodiment, the pupil dilator is substantially elongated. A pupil dilator provides pupil dilation in one direction—that is, the elongation direction—but this disclosure can be extended to include the presence of a second pupil dilator arranged to dilate the pupil in an orthogonal direction.

[0147] Figure 7 The diagram illustrates how ray 702 is effectively replicated twice to form three propagation paths 705, each associated with a different distance Z0, Z1, and Z2. The shortest propagation path corresponds to Z0, and in this example, the light has passed through the waveguide without any internal reflections. The mid-range propagation path of the three shown corresponds to Z1 and two internal reflections in the pupil dilator (one on each surface). The longest propagation path shown corresponds to Z2 and four internal reflections in the pupil dilator (two on each surface). Planes x0, x1, and x2 respectively show the spatial extent of the light field associated with each of the three propagation paths Z0, Z1, and Z2. More specifically, Figure 7 This shows how the three planes x0, x1, and x2 are offset from each other in the x-direction.

[0148] Figure 7 An observation system 713 is also shown, which includes an entrance pupil 707, a lens 709, and a light sensor 711. In an embodiment, the observation system 713 is a human eye, and the light sensor 711 is the retina of the eye. Figure 7 This demonstrates how only a few light fields associated with each propagation path pass through inlet 707. Figure 7 The diagram shows the light rays associated with the center of the mid-range propagation path passing through the center of the entrance pupil 707. However, for example, the light rays associated with the center of the light field of the shortest propagation path are blocked by the top of the aperture 707. However, other light rays associated with the light field of the shortest propagation path can pass through the aperture 707. The light rays associated with the center of the light field of the longest propagation path are blocked by the bottom of the aperture 707. However, other light rays associated with the light field of the longest propagation path can also pass through the aperture 707.

[0149] Light passing through aperture 707 is focused onto light sensor 711 by lens 709. The plane of light sensor 711 is substantially parallel to the plane of display device 701, and therefore also tilted relative to the elongated dimension of pupil dilator 703.

[0150] Figure 7 Three possible light propagation paths are shown by way of example only. This example is not limited to the number of propagation paths. That is, those skilled in the art will understand from the following description that the method can be extended to consider any number of light propagation paths. Similarly, it is not necessary for the pupil dilator to be tilted relative to the display plane and the sensor plane.

[0151] Figure 8 This is a flowchart illustrating the steps of the method. The method is similar to a Gerchberg-Saxton type algorithm, which uses mathematical transformations back and forth between the image plane and the hologram to converge on a phase hologram corresponding to the image. After each propagation to the image plane or the holographic plane, the amplitude components of the light field are modified or constrained, but the phase components are preserved.

[0152] The zeroth stage of this method includes steps 802 and 804. The zeroth stage includes forming a zeroth composite light field. Step 802 provides a random phase seed to form the phase component of the zeroth composite light field. Step 804 provides the amplitude component of the zeroth composite light field. The amplitude component can be a unit value or amplitude distribution representing the light source light used to reconstruct the image from the hologram.

[0153] In step 806, the zeroth composite light field propagates Fresnelly from the spatial light modulator 701 (i.e., from the holographic plane) to the entrance pupil 707 of the observation system 713 (more specifically, to the plane containing the entrance pupil 707 of the observation system 713). Furthermore, this embodiment refers to Fresnel propagation as one example of a variety of different mathematical transformations that can be used without departing from the spirit or scope of this disclosure. Step 806 is performed for each number of bounces or internal reflections provided by the pupil dilator 703 to form a composite light field with respect to each light propagation path. Step 806 includes taking into account the lateral position of the composite light field in the x-direction at the plane of the entrance pupil 707, and the phase shift within the pupil dilator 703 for each reflection. Different composite light fields can be combined, for example, by addition. The first stage also includes step 808, tailoring the combined composite light field according to the size and shape of the entrance pupil 707 to form a first composite light field at the entrance pupil 707.

[0154] The second phase of the method includes steps 810 and 812. In step 810, a second composite light field is determined by propagating a first composite light field from the entrance pupil through lens 709 to the plane of the photosensor 711. Step 812 includes modifying the amplitude component of the composite light field reaching the photosensor 711. More specifically, step 812 includes replacing the amplitude component of the composite light field with the amplitude component of the target image or an amplitude component based on the amplitude component of the target image (e.g., a weighted version of the amplitude component of the target image). The position of lens 709 used in the propagation determines the image distance, i.e., the space in which the image content will appear. In some embodiments, the image is a virtual image, and this distance may be referred to as the virtual image distance "VID".

[0155] Advantageously, the method disclosed herein allows the formation of image content at multiple different image distances (e.g., multiple VIDs) using the same hologram. This can be achieved by repeating the second stage for each image distance, taking into account the different positions of the lens 709 in the z-direction. For example, the composite light fields determined according to this method for each different image distance can be combined by addition.

[0156] The third stage of the method includes step 814, in which the second composite light field propagates back to the entrance pupil 707 via lens 709. This can be referred to as backpropagation, simply to reflect the travel of light in the opposite z-direction. In some embodiments, backpropagation is the mathematical inverse of the corresponding "forward" propagation. The third stage also includes tailoring the propagated light field according to the size and shape of the entrance pupil 707 to form a third composite light field.

[0157] The fourth stage comprises steps 816 and 818. In step 816, light propagates back to the plane of the spatial light modulator 702 via multiple light propagation paths of the pupil dilator, in the manner described above with respect to the first stage—but of course, in the opposite light direction (i.e., “reverse” propagation). Step 818 includes trimming the propagated light field according to the size and position of the effective / pixel area of ​​the display device. The number of complex values ​​of each composite light field can be equal to or less than the number of pixels of the display device.

[0158] Step 820 includes extracting a hologram from the fourth composite optical field. The hologram may include the phase value of the fourth composite optical field; in this case, the hologram may be referred to as a phase hologram. As explained earlier in this disclosure, the method can also begin from the image plane (i.e., the third stage). According to this disclosure, each stage requires at least one iteration.

[0159] However, here refer to Figures 4 to 8 The disclosed method is provided by way of example only, and this disclosure is not limited to this method, as other ways of forming the first and second images on different planes in a head-up display (e.g., partial overlap) are equally applicable.

[0160] In another embodiment, point cloud holograms are used to form the first and second images. It is well known that, typically to compute a point cloud hologram of an image (e.g., a virtual image), the image is decomposed (i.e., represented by it) into multiple individual points—here referred to as “virtual points”, since we have described the formation of a virtual image. Spherical waves (or “wavelets”) are then propagated from the expected or desired location of each virtual point within the virtual image to the plane of the display device, such as the plane of the display device in the example above, by computation (i.e., using a model or other theoretical tool). The manner in which these wavelets interfere with each other is considered, and the final amplitude and / or phase of the wavelets received at each pixel of the display device are calculated. The display device can then be tuned in a well-known manner, and therefore will not be described here, to demonstrate the amplitude and / or phase modulation required at each pixel location to simulate the computed wavelets, thereby creating a hologram of one or more images. In yet another embodiment, Fresnel holograms are used to form the first and second images.

[0161] Figures 9A-9B And 10 describes the... Figure 8 Holograms formed using this method.

[0162] Optical Channel

[0163] Figure 9A An image 1552 for projection is shown, comprising eight image regions / components V1 to V8. Figure 9A Eight image components are shown as an example only, and image 1552 can be divided into any number of components. Figure 9AAlso shown is an encoded light pattern 1554 (i.e., a hologram) that can reconstruct image 1552—for example, when transformed by a lens of a suitable observation system. The encoded light pattern 1554 includes first to eighth sub-holograms or components H1 to H8, corresponding to first to eighth image components / regions V1 to V8. Figure 9A This further demonstrates how the calculated hologram effectively decomposes image content through angles. Therefore, a characteristic of a hologram lies in its guidance of light. This is in Figure 9B As shown in the diagram, the hologram guides light to multiple discrete regions. In the example shown, the discrete regions are disks, but other shapes are also conceivable. After propagation through the waveguide, the optimal disk size and shape can be correlated with the size and shape of the entrance pupil of the observation system. This optical path arises solely from the specific method for determining the hologram disclosed herein.

[0164] Figure 10 It shows according to Figure 9A and 9B The improved observation system 1500 shown is an example of this.

[0165] The observation system 1500 includes a display device comprising an LCOS 1502 in this arrangement. The LCOS 1502 is arranged to display a modulation pattern (or "diffraction pattern") including a hologram and to project holographically encoded light onto an eye 1505, which includes a pupil serving as an aperture 1504, a lens 1509, and a retina (not shown) serving as an observation plane. A light source (not shown) is arranged to illuminate the LCOS 1502. The lens 1509 of the eye 1505 performs a hologram-to-image conversion.

[0166] The observation system 1500 also includes a waveguide 1508 located between the LCOS 1502 and the eye 1505. Figure 10 The projection distance may be relatively large. However, as described with respect to the preceding figures, the presence of waveguide 1508 allows all angular content from LCOS 1502 to be received by eye 1505, even at this relatively large projection distance. This is because waveguide 1508 acts as a pupil dilator in the manner already described above.

[0167] Furthermore, in this arrangement, when the LCOS1502 has been encoded according to the method described herein, the waveguide 1508 can be oriented at an angle relative to the LCOS1502 to establish a unique relationship between the light from the LCOS1502 and the virtual image perceived by the observer. The size, position, and orientation of the waveguide 1508 are configured to ensure that light from each portion of the virtual image enters the waveguide 1508 and is guided along its elongated axis, bouncing between the substantially flat surfaces of the waveguide 1508. Whenever light reaches the second planar surface (closest to the eye 1505), some light is transmitted and some is reflected.

[0168] Figure 10 A total of nine “bounce” points B0 to B8 are shown along the length of waveguide 1502. The reader will notice that the center of image 1552 remains blank. Figure 10 The diagram shows the 0th to 9th light "bounce" or reflection points B0 to B8 within the waveguide. Although light associated with all points in the image (V1-V8) is transmitted out of the waveguide at each "bounce" from the second planar surface of waveguide 1508, only light from a corner portion of the image (e.g., light from one of V1 to V8) has a trajectory that allows it to reach eye 1505 from each corresponding "bounce" point B0 to B8. Furthermore, light from different angular portions of the image V1 to V8 reaches eye 1505 from each corresponding "bounce" point. Figure 10 The image shows light emitted from all the different angular contents at each “bounce” point (represented by multiple short arrows at each transmission point), but only the light path from each angular content to the eye 1505 is shown subsequently. This path will actually travel from the corresponding portion of the waveguide to the eye 1505—thus helping the observer perceive the corresponding portion of the virtual image. For example, for the zeroth bounce B0, the light transmitted by waveguide 1508 is simply refracted and undergoes no reflection within it. The light from the eighth sub-hologram H8 reaches the eye from the zeroth bounce B0. For the next bounce B1, the light transmitted by waveguide 1502 undergoes one bounce within it before transmission. The light from the seventh hologram H7 reaches the eye from the next bounce B1. This continues sequentially until the light transmitted by waveguide 1508 at the last bounce B8 has undergone eight reflections before being transmitted and reaching the eye 1505, and includes light encoded according to the first hologram H1.

[0169] exist Figure 10 In the example shown, light from only one image region reaches the eye from each bounce point. Therefore, when determining the hologram as described herein, a spatial correlation is established between the regions of the virtual image and their corresponding bounce points on the waveguide. In some other examples, there may be relatively small overlap, such that a region of the image originates from two adjacent transmission points and is thus contained within two adjacent optical discs propagating from the waveguide to the observation plane.

[0170] Therefore, a diffraction pattern (or light modulation pattern) including a hologram is produced, which, when displayed on an LCOS or other suitable display device, enables light to be effectively emitted from it in the form of multiple "disks" or beams, each disk or beam corresponding to (more specifically, encoding) a different corresponding portion of the corresponding virtual image.

[0171] Furthermore, although virtual images have been discussed in general here, which require the eye to convert received modulated light to form a perceived image, the improved methods and apparatus described herein can be applied to real images.

[0172] Field of view optimization of two image planes

[0173] Specific methods for forming first and second images in a head-up display (HUD) are described by way of example. The inventors have studied in depth the optical geometry that appears in a vehicle's HUD when near-field and far-field image content is presented to an observer. In particular, this disclosure relates to eye boxes of finite size. Some embodiments involve cases where there is at least partial overlap between near and far images. The terms "near" and "far" are used only to distinguish two spatially separated image planes (e.g., playback planes) and are not limiting. These terms merely reflect the relative distance between the image plane and the viewing plane. The inventors have identified optimization conditions that surprisingly significantly reduce the physical volume of the system. In some of the described embodiments, the optimization conditions identified by the inventors and disclosed herein are the distinction between being able to encapsulate a HUD assembly in a real-world vehicle and not being able to encapsulate a HUD assembly.

[0174] Figure 11A The yz plane of a system including a HUD assembly 1101 housed in a vehicle having a windshield 1105 is shown. The x-direction is horizontal, and the y-direction is vertical. Figure 11AThe diagram also shows an eye box 1107 for the head-up display (HUD) and a portion of a vehicle assembly 1103, which may be, for example, part of a vehicle plenum. The eye box is housed in the xy-plane. The eye box is separated from the image plane space in the z-direction. The "viewing axis" of the HUD may be parallel to the z-direction, or there may be a small angle between the viewing axis and the z-direction, such as a so-called "top-down view." The viewing axis extends from the center of the eye box, and in some examples, from the center of at least one image region. For example, the viewing axis may be a straight line connecting the center of the eye box and the center of the near-field virtual image region. The HUD assembly 1101 must be appropriately sized and positioned, for example, within a dashboard to avoid physical interference with vehicle structures, including, for example, a pressurization chamber. The viewing axis 1150 may extend / extend from the eye box 1107 to the HUD assembly via reflection from the windshield 1105. Because the HUD image is reflected from the windshield 1105 to the observer / eyebox 1107, the image is virtual—that is, for the observer's position in the eyebox 1107, it appears on the other side of the windshield 1105, i.e., outside the vehicle. The near-field virtual image area 1109 and the far-field virtual image area 1111 are typically located on or near the visual axis, but this is not required. The near-field and far-field virtual image areas can be substantially perpendicular to the visual axis. Near-field image content, such as fuel or speed information, can be displayed in the near-field virtual image area 1109. Far-field image content, such as navigation or warning information, can be displayed in the far-field virtual image area 1111. The near-field and far-field image content can change in real time. The head-up display can be an augmented reality head-up display.

[0175] Figure 11A The field of view of the observer from the center of the eyebox 1107 is also shown by a first line 1151 and a second line 1152, which extend from the center of the eyebox to the opposite ends of the two virtual image region planes 1109 and 1111 in the yz plane, respectively. More specifically, the first line 1151 is a straight line connecting the center of the eyebox 1107, the top of the near-field virtual image region 1109, and the top of the far-field virtual image region 1111. The second line 1152 is a straight line connecting the center of the eyebox 1107, the bottom of the near-field virtual image region 1109, and the bottom of the far-field virtual image region 1111. In terms of angle, the field of view in the vertical direction of the near-field virtual image region plane 1109 is substantially equal to the field of view in the vertical direction of the far-field virtual image region plane 1111 from the center of the eyebox.

[0176] Figure 11B and 11C The same system is shown, but in contrast, the corresponding lines from the top and bottom of the eye box are shown respectively. Figure 11BA pair of lines are shown extending from the top of eyebox 1107 to the top of near-field virtual image region 1109 and far-field image 1111, respectively. More specifically, a third line 1153 is a straight line connecting the top of eyebox 1107 and the top of far-field virtual image region 1111, and a fourth line 1154 is a straight line connecting the top of eyebox 1107 and the top of near-field virtual image region 1109. The angle between visual axis 1150 and third line 1153 is different from the angle between visual axis 1150 and fourth line 1154. More specifically, in this example, the angle between visual axis 1150 and third line 1153 is greater than the angle between visual axis 1150 and fourth line 1154. This is because the centers of the two virtual image regions are aligned on the visual axis and have the same field of view in angular space, but the eyebox position is offset in the positive y-direction relative to visual axis 1150.

[0177] The angular difference between the third line 1153 and the fourth line 1154 may result in different sizes of the light beams required for each individual image. Figure 11B The first region 1181 of the optical configuration is highlighted using a first circle, and the second region 1182 of the optical configuration is highlighted using a second circle. The lines shown in the first region 1181 highlight how much the light beam must be larger in the positive y-direction so that the top of the far-field image region receives light from the HUD component 1101. Similarly, the lines present in the second region 1182 show how the size of the light beam associated with the far-field image must be larger than the size of the near-field image, even though the two virtual images have the same size in angular space (i.e., the same field of view—at least in the plane shown). The lines within the second region 1182 effectively show how much additional clearance volume must be provided within the vehicle for the head-up display in order to form a far-field image with the same angular size as the near-field image.

[0178] Figure 11C The corresponding optical geometry from the lower position of eyebox 1107 is shown. Figure 11C A pair of lines are shown, extending from the bottom of eyebox 1107 to the bottom of near-field virtual image region 1109 and far-field virtual image region 1111, respectively. More specifically, the sixth line 1156 is a straight line connecting the bottom of eyebox 1107 and the bottom of far-field virtual image region 1111, and the fifth line 1155 is a straight line connecting the bottom of eyebox 1107 and the bottom of near-field virtual image region 1109. The angle between visual axis 1150 and the sixth line 1156 is different from the angle between visual axis 1150 and the fifth line 1155. More specifically, in this example, the angle between visual axis 1150 and the sixth line 1156 is greater than the angle between visual axis 1150 and the fifth line 1155. This is because the centers of the two virtual image regions are aligned on the visual axis and have the same field of view in angular space, but the eyebox position is offset in the negative y-direction relative to visual axis 1150.

[0179] The angular difference between line 1156 (sixth line) and line 1155 (fifth line) means that the size of the light beam required for each individual image may differ. Figure 11C The third region 1183 of the optical configuration is highlighted using a third circle, and the fourth region 1184 of the optical configuration is highlighted using a fourth circle. The lines shown in the third region 1183 highlight how much larger the light beam must be in the negative y-direction in order for the bottom of the far-field virtual image region to receive light from the HUD component 1101. Similarly, the lines present in the fourth region 1184 show how the size of the light beam associated with the far-field image must be larger than the size of the near-field image, even though the two virtual images have the same size in angular space (i.e., the same field of view—at least in the plane shown). The lines within the fourth region 1184 effectively show how much additional clearance volume within the vehicle must be provided for the head-up display in order to form a far-field image with the same angular size as the near-field image.

[0180] Figure 11A -C shows that the far-field virtual image region actually needs to reserve more volume within the vehicle for the light beam of the HUD components than the near-field virtual image region. This can be understood by considering the eyebox locations at the boundaries (i.e., the top and bottom in Figure 11). This finding was particularly unexpected, especially given that the field of view of the far-field virtual image region is no larger than that of the near-field virtual image region.

[0181] from Figure 11B and 11C It is understood that, in one embodiment, the field of view of the near-field virtual image region is increased to effectively fill the gaps between the third and fourth lines, and / or the fifth and sixth lines. As can be understood from the above, this embodiment is advantageous because the field of view of the near-field virtual image region can be increased without affecting the size of the light beam required to form the image. A larger field of view is typically required in head-up displays, therefore this embodiment can be implemented without adversely affecting volume. The inventors have found that this enhancement is achievable without consequences.

[0182] exist Figure 11AIn this modification of -C, it can be said that in at least one direction (e.g., the positive direction) of the first dimension (e.g., the y-direction), the field of view of the near-field / first image region is greater than that of the far-field / second image region. It can also be said that the light beams forming the first and second image contents are defined according to the second virtual image region. Furthermore, it can be said that in the first dimension (e.g., the y-axis) of the two orthogonal dimensions of the eyepiece (e.g., the x-axis and y-axis), the field of view angle of the near-field / first image region is defined in a plane (e.g., the yz plane) encompassing the first dimension and the visual axis by a straight line connecting one end of the eyepiece and the corresponding end of the far-field / second image region (in the same plane). The field of view of the near-field / first image region can also be defined in this plane by a second straight line connecting the opposite end of the eyepiece and the corresponding opposite end of the far-field / second image region. In other words, the near-field virtual image region 1109 can extend / extend in both directions. Because the near-field virtual image region 1109 is extended, it can be said that the far-field virtual image region 1111 is not as far in angular space as the near-field virtual image region 1109 (in at least one direction in one dimension of the eyebox).

[0183] Although Figure 11A -C shows a cross-section of the system, but the reader will understand that the same principle can be applied to orthogonal planes (e.g., the xz plane). For example, the field of view of the near-field virtual image plane can be expanded / increased in the x-direction / horizontal direction relative to the far-field virtual image region without increasing the size of the ray beam required to form two images.

[0184] A skilled reader will understand that, according to the above embodiments, the field of view of the near-field virtual image region is increased by increasing the size of the region receiving light from the hologram in the near-field reproduction field. This can be achieved, for example, by editing the target near-field image (e.g., expanding or increasing the size of the target image) before hologram computation. Typically, the target image has a content-free boundary region surrounding the image content, which is chosen according to application requirements. Therefore, by editing the target near-field image before hologram computation, the image content of the near-field virtual image can be extended into the boundary region in at least one direction to increase the size of the near-field / first image region. As a result, as described above, the far-field / second image region extends less in angular space than the near-field / first image region.

[0185] In reference Figure 12A -In another embodiment that can be understood by C, the size of the far-field virtual image region is reduced / cropped in order to reduce / cropped the spatial volume required for the light beam within the vehicle.

[0186] Figure 12A -C largely corresponds to Figure 11A -C. However, Figure 12A -C shows the clipping of the lower far-field virtual image region 1211, as shown in the figure (negative y-direction). Therefore, Figure 12A The field of view of the far-field virtual image region 1211 in -C is smaller than that of the near-field virtual image region 1209. More specifically, the far-field virtual image region 1209 extends less than the near-field virtual image region 1211 in one direction of the first dimension (e.g., the negative y-direction).

[0187] Figure 12A The yz plane of a system including a HUD component 1201 housed in a vehicle having a windshield 1205 is shown. Figure 12A The eye box 1207 of the head-up display (HUD) and a portion of a vehicle component 1203 are also shown, which may be, for example, part of a vehicle pressurization chamber. The HUD component 1201 must be appropriately sized and positioned, for example, within a dashboard to avoid physical interference with vehicle structures including, for example, the pressurization chamber. The system's line of sight 1250 is shown as a dashed line from the HUD component 1201 via reflection from the windshield 1205 to the eye box 1207. Because the HUD image is reflected from the windshield 1205 to the observer / eye box 1207, the image is virtual—that is, for the observer's position in the eye box 1207, it appears on the other side of the windshield 1205, i.e., outside the vehicle. The line of sight 1250 extends through the windshield 1205 to show the positions of the near-field virtual image region 1209 and the far-field virtual image region 1211. Near-field image content, such as fuel or speed information, can be displayed in the near-field virtual image region 1209. Far-field image content, such as navigation or warning information, can be displayed in the far-field virtual image region 1211.

[0188] Figure 12A The field of view of the observer from the center of eyebox 1207 is also shown by a first line 1251 and a second line 1252, which extend from the center of the eyebox to the opposite ends of the far-field virtual image region 1211 in the yz plane. More specifically, the first line 1251 is a straight line connecting the center of eyebox 1207, the top of the near-field virtual image region 1209, and the top of the far-field virtual image region 1211. The second line 1252 is a straight line connecting the center of eyebox 1107 and the bottom of the far-field virtual image region 1211. In terms of angle, the field of view in the vertical direction of the near-field virtual image region plane 1209 is substantially equal to the field of view in the vertical direction of the far-field virtual image region plane 1111 from the center of the eyebox in one direction of the first dimension (e.g., the positive y-direction), but not equal in another direction of the first dimension (e.g., the negative y-direction).

[0189] Figure 11A and 12A The difference is that the second line 1252 connecting the center of the eye box 1207 and the bottom of the far field virtual image region 1211 is not aligned with the bottom of the near field virtual image region 1209. Figure 12A The first region 1281 is highlighted by the first circle, which shows the relationship with... Figure 11A In contrast, how is the bottom of the far-field virtual image region 1211 cropped / removed / non-existent? The dashed line 1252X indicates if the bottom of the far-field virtual image region 1211 is not cropped (i.e., according to...). Figure 11A The second line 1252 will be located at the position.

[0190] Figure 12B and 12C It shows the relationship with Figure 12A The same system, but showing the corresponding lines from the top and bottom of the eye box respectively. Figure 12B A pair of lines are shown extending from the top of eyebox 1207 to the top of near-field virtual image region 1209 and far-field image 1211, respectively. More specifically, a third line 1253 is a straight line connecting the top of eyebox 1207 and the top of far-field virtual image region 1211, and a fourth line 1254 is a straight line connecting the top of eyebox 1207 and the top of near-field virtual image region 1209. The angle between visual axis 1250 and third line 1253 is different from the angle between visual axis 1250 and fourth line 1254. More specifically, in this example, the angle between visual axis 1250 and third line 1253 is greater than the angle between visual axis 1250 and fourth line 1254. This is because the centers of the two virtual image regions are aligned on the visual axis and have the same field of view in angular space on this side of the eyebox, but the eyebox position is offset in the positive y-direction relative to visual axis 150.

[0191] Figure 12B In all other respects, it corresponds to Figure 11B And again, it is shown how the size of the light beam in one direction (e.g., the positive z-direction) is determined by the size / range of the far-field virtual image region 1211. In this embodiment, from Figure 12C Understandably, the situation is not the same on the other side of the eye box / virtual image area.

[0192] Figure 12C The corresponding optical geometry from the lower position of eyebox 1207 is shown. On this side of the eyebox, the far-field virtual image area is reduced (compared to...). Figure 11C compared to). Figure 12CA line (e.g., the negative y-direction) defining the field boundaries of the two virtual image regions in this direction is shown. More specifically, the fifth line 1255 is a straight line connecting the bottom of the eyebox 1207, the bottom of the far-field virtual image region 1211, and the bottom of the near-field virtual image region 1209. In this direction of the first dimension (e.g., the negative y-direction), the far-field virtual image region 1211 extends less than the near-field virtual image region (in terms of angle / space). The second dashed line 1256X is a straight line connecting the bottom of the eyebox and the bottom of the far-field virtual image region 1211. The second dashed line effectively represents the light rays clipped / removed due to the clipping of the far-field virtual image region 1211. The angle between the visual axis 1250 and the fifth line 1255 is smaller than the angle between the visual axis 1250 and the second dashed line 1256X. If the far-field virtual image region 1211 were not clipped, the second dashed line 1256X would represent the light ray path (according to...). Figure 11C ).

[0193] exist Figure 12A In the embodiment of -C, it can also be said that in at least one direction (e.g., the negative direction) of the first dimension (e.g., the y-direction), the field of view of the near-field / first image region is greater than that of the far-field / second image region. It can also be said that the light beams forming the first image content and the second image content (substantially simultaneously) are defined according to the first virtual image region. Furthermore, it can be said that in the first dimension (e.g., the y-axis) of the two orthogonal dimensions (e.g., the x-axis and y-axis) of the eyepiece, the field of view angle of the far-field / second image region is defined in a plane (e.g., the yz plane) encompassing the first dimension and the visual axis by a straight line connecting one end of the eyepiece and the corresponding end of the near-field / first image region (in the same plane). The field of view of the far-field / second image region can also be defined in this plane by a second straight line connecting the opposite end of the eyepiece and the corresponding opposite end of the near-field / first image region. In other words, to reduce the size of the light beam, the far-field virtual image region can be cropped on both sides.

[0194] A skilled reader will understand, according to Figure 12A In the embodiment of -C, the field of view of the far-field virtual image region is reduced by decreasing the size of the region of the far-field replay field receiving light from the hologram. This can be achieved, for example, by editing the target far-field image (e.g., cropping or reducing the size of the target image) before hologram computation. As mentioned above, the target image typically has a content-free boundary region surrounding the image content. Therefore, by editing the target far-field image before hologram computation, the boundary of the image content surrounding the far-field virtual image can be increased in at least one direction to reduce the size of the far-field / second image region. As a result, as mentioned above, the far-field / second image region extends less in angular space than the near-field / first image region.

[0195] Therefore, in the context of Figure 11A The above embodiments with modifications to -C and Figure 12AThere are commonalities among the embodiments of -C. The commonality is that a head-up display is provided, comprising an eyebox having a first dimension and a second dimension, wherein the head-up display is arranged to (simultaneously) form first image content in a first image region at a first image distance from the eyebox (wherein the image distance is a distance perpendicular to a plane containing the first and second dimensions), and form second image content in a second image region at a second image distance from the eyebox, wherein the first image distance is less than the second image distance, and the first image region at least partially overlaps with the second image region in the first dimension (when viewed from the eyebox / in the angular space from the center of the eyebox), wherein the second image region extends less than the first image region in the angular space in at least one direction of the first dimension.

[0196] Additional features

[0197] The embodiments relate to electrically activated LCOS spatial light modulators by way of example only. The teachings of this disclosure can be equivalently implemented on any spatial light modulator capable of displaying computer-generated holograms according to this disclosure, such as any electrically activated SLM, optically activated SLM, digital micromirror device, or microelectromechanical device.

[0198] In some embodiments, a vehicle including the head-up display of this disclosure is provided. The vehicle may be a motor vehicle, such as a car, truck, van, lorry, motorcycle, train, airplane, boat, or ship. However, the image projector of this disclosure can be used in any device including an optical combiner to form a virtual image. For example, the image projector of this disclosure can also be used to form an improved near-eye device, such as eyeglasses or a head-mounted display.

[0199] The methods and processes described herein can be embodied on a computer-readable medium. The term "computer-readable medium" includes media arranged for temporary or permanent storage of data, such as random access memory (RAM), read-only memory (ROM), buffer memory, flash memory, and cache memory. The term "computer-readable medium" should also be considered to include any medium or combination of media capable of storing instructions for machine execution, such that when the instructions are executed by one or more processors, the machine performs, wholly or partially, any or all of the methods described herein.

[0200] The term "computer-readable medium" also covers cloud-based storage systems. The term "computer-readable medium" includes, but is not limited to, one or more tangible and non-transitory data repositories (e.g., data volumes) in the example forms of solid-state storage chips, optical discs, disks, or any suitable combinations thereof. In some example embodiments, instructions for execution may be transmitted by a carrier medium. Examples of such carrier media include transient media (e.g., propagation signals for transmitting instructions).

[0201] 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 head-up display (HUD) comprising an eye box having a first dimension and a second dimension, wherein the HUD is arranged to form first image content in a first image region at a distance from the eye box relative to a first image region, and to form second image content in a second image region at a distance from the eye box relative to a second image region. The head-up display further includes an image generation unit, which includes a display device arranged such that a display pattern displayed on the display device forms the first image content and the second image content. The head-up display further includes a waveguide arranged to extend the exit pupil of the image generation unit. Wherein the distance between the first image regions is less than the distance between the second image regions, and the first image region at least partially overlaps with the second image region in the first dimension. The second image region extends less than the first image region in at least one direction of the first dimension in angular space. The first image content and the second image content are formed substantially simultaneously by a common display pattern displayed on the display device, which is a spatial light modulator.

2. The head-up display as claimed in claim 1, wherein, The second image region extends less than the first image region in both directions of the first dimension, such that the size of the second image region in angular space is no greater than the size of the first image region.

3. The head-up display as claimed in claim 1, wherein, The displayed pattern is a diffraction pattern.

4. The head-up display as claimed in claim 3, wherein, The displayed pattern is a hologram.

5. The head-up display as claimed in claim 3, wherein, The diffraction pattern is a Fourier hologram, a Fresnel hologram, a point cloud hologram, or a combination thereof.

6. The head-up display as claimed in claim 1, wherein, The first image content and the second image content are simultaneously formed by a common display pattern displayed on the display device.

7. The head-up display as claimed in claim 6, wherein, The common display pattern is a diffraction pattern.

8. The head-up display as claimed in claim 1 or 2, wherein, The first image content is a first virtual image content, and / or the second image content is a second virtual image content.

9. The head-up display as claimed in claim 1 or 2, wherein, The second image region extends in angular space from all positions within the eye box in at least one direction of the first dimension without exceeding the first image region, such that the light beams forming the first image content and the second image content are delimited according to the first image region.

10. The head-up display as claimed in claim 1 or 2, wherein, The first dimension is the vertical direction.

11. The head-up display as claimed in claim 1 or 2, wherein, The center of the first image region in the second dimension is basically aligned with the center of the second image region in the second dimension.

12. The head-up display of claim 11, wherein, The second dimension is the horizontal direction.

13. The head-up display as claimed in claim 1 or 2, wherein, The first image region at least partially overlaps with the second image region in the first dimension, and the second image region extends in angular space from all positions within the eye box in at least one direction in the first dimension without exceeding the first image region.

14. The head-up display as claimed in claim 1 or 2, wherein, The distance between the first image and the second image is less than 5 meters, and / or the distance between the second image and the second image is less than 20 meters.

15. The head-up display of claim 14, wherein, The distance between the first image and the second image is less than 3 meters, and / or the distance between the second image and the second image is less than 15 meters.

16. The head-up display as claimed in claim 1 or 2, wherein, The head-up display has a viewing angle of 5 to 25 degrees in the second dimension, and / or the head-up display has a viewing angle of 3 to 10 degrees in the first dimension.

17. The head-up display of claim 1 or 2, further comprising a user tracking system, wherein, The head-up display is arranged to determine the display pattern in real time based at least in part on the position of the eye box within the eye box, as determined by the user tracking system.

18. The head-up display of claim 17, wherein the user tracking system is an eye-tracking system.

19. A method of displaying image content using a head-up display as claimed in claim 17, wherein the method includes changing at least one of a first and second image region distance based on a change in eyebox position determined by a user tracking system, wherein the head-up display further includes an image generation unit, the image generation unit including a display device arranged to form the first image content and the second image content from a display pattern displayed on the display device, wherein the head-up display further includes a waveguide arranged to extend an exit pupil of the image generation unit.

20. The method for displaying image content as described in claim 19, wherein, The display device is a spatial light modulator of the head-up display, wherein at least one of the first and second image region distances is changed by altering at least one lens function associated with the diffraction pattern.

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