Holographic projector

Abstract

There is provided a holographic projector comprising a display device arranged to form a holographic wavefront by spatially modulating light in accordance with a hologram displayed thereon; and a waveguide having an input arranged to receive the holographic wavefront, and a first surface and a second surface arranged to guide the holographic wavefront therebetween, wherein the first surface is partially reflective-transmissive such that multiple copies of the holographic wavefront are emitted therefrom. The hologram has a size that is smaller than a size of an entrance pupil of an observation system for receiving the holographic wavefront from the first surface of the waveguide, and the hologram comprises a first sub-hologram of a first region of an image adjacent to a second sub-hologram of a second region of the image.

Description

Technical Field

[0001] This disclosure relates to image projection systems and methods. More specifically, this disclosure relates to holographic projectors and methods for reducing ghosting images. More specifically, this disclosure relates to display control of a holographic display device for a holographic projector, wherein the display control is arranged to divide the pixels of the display device to reduce or prevent duplicate holographic content from reaching one or each observation position of the observation area or observation volume. Some embodiments relate to holographic generation units, image generation units, or head-up displays. 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 a holographic projector. This type of projector is already being used in head-up displays (HUDs). Summary of the Invention

[0007] The aspects of this disclosure are defined in the appended independent claims.

[0008] In summary, holographic projection systems and methods are provided that avoid or at least reduce the occurrence of ghosting images when an image (i.e., holographic reconstruction) is formed by the holographic projection system. The holographic projection system includes a display device and a waveguide. The display device is arranged to spatially modulate light according to a hologram displayed thereon. The waveguide is arranged to receive a holographic wavefront modulated according to the hologram and output multiple copies of the holographic wavefront. This system and method are particularly suitable for holographic reconstructions formed at non-infinite image distances, and / or when the aperture size of the observation system used to observe the image is similar to the size of the display device displaying the hologram.

[0009] The background of this disclosure is described in British Patent GB2603517, which is incorporated herein by reference in its entirety. In general, the aperture / pupil of a display device limits the size of the viewing window (e.g., the eyebox). Waveguides can be used to form an extended (increased in size) viewing window by creating and emitting multiple replicas of the pupil. Each waveguide generates multiple replicas of the holographic wavefront formed by illuminating a hologram displayed on the display device. In short, each waveguide generates multiple replicas of the hologram. The problem of ghosting images is solved in British Patent GB2603517. This solution is based on the understanding that different replicas provide both the main image content and the ghosting image content (within the holographic domain).

[0010] This disclosure describes an alternative solution to the problem of ghosting images formed by waveguides. The methods disclosed herein provide benefits regarding holographic algorithms. By way of example only, the methods disclosed herein are particularly effective for holograms where the characteristics of the hologram (e.g., the number of pixels or the size / shape of the pixel array) are substantially the same as those of the corresponding image it reconstructs. An example of such a hologram is a hologram formed by an iterative phase retrieval algorithm, such as the algorithm described in UK patent application GB2112213.0, which is incorporated herein by reference in its entirety. However, this disclosure is not limited to such holograms, and other holograms may benefit from the concepts disclosed herein.

[0011] The inventors first discovered that increasing the spacing between hologram replicas reduces the likelihood of light from the ghosted image passing through the aperture of the observation system. They recognized this was achievable if the hologram was displayed only on a sub-region of the display device (with a pupil replicated by a waveguide). However, in simulations and experiments, they found that while this method was indeed effective in reducing the prominence of ghosted images, it introduced a new problem: dark bands (loss of image content) in the field of view. Therefore, the problem the inventors addressed was how to reduce the likelihood of ghosting without degrading image quality. More specifically, how to reduce the likelihood of ghosting by separating the hologram replicas without introducing dark bands in the field of view. These issues will be further elaborated in the following paragraphs.

[0012] Because different possible light propagation paths exist through the waveguide, so-called "ghost images" can form at non-infinite image distances. Specifically, the light propagation paths associated with different replicas of the holographic wavefront can have different lengths. These different light propagation paths can also originate from different regions of the spatial light modulator. At any given location, the observation system can receive the same image content from multiple replicas of the holographic wavefront. This can result in the primary image being associated with a first region of the first replica, and the second ghost image being associated with a second region of the second replica. In one example, at a first observation location, a first portion of the display device can contribute the primary image. Light from the first portion can be received at the observation system via the first replica. A second portion of the display device can contribute the ghost image. Light from the second portion can be received at the observation system via the second replica. At non-infinite image distances, the primary (first) image and the ghost (secondary) image may partially overlap. This partial overlap significantly degrades the quality of the perceived virtual image. The ghost image may make the primary (first) image appear blurry.

[0013] The disclosed system and method avoid or at least reduce the occurrence of ghosting images by (i) dividing the field of view (target image) into spatial regions (hereinafter referred to as "parts"), (ii) computing a smaller hologram (with fewer pixels than the target image) for each part (hereinafter referred to as a "sub-hologram"), and (iii) displaying each sub-hologram on different sub-regions of a display device. In practice, this method involves reducing the area of ​​the display device encoded with a specific (sub)hologram. Reducing the area of ​​the display device encoded with a specific (first)hologram substantially reduces the likelihood that light encoded with the same (sub)hologram (or the same part of a hologram) will be received from multiple replicas of the spatial light modulator at the aperture of an observation system that may include the human eye. Therefore, this reduces the likelihood that light containing the same image content will be received by the aperture more than once at a given observation location. This is achieved by displaying hologram pixels corresponding to the image content only on some of the available display pixels—for example, on half, one-third, or one-quarter of the available display pixels. Specifically, a (first) sub-hologram corresponding to a specific image content can be displayed on a continuous group of pixels that includes some (but not all) of the available display pixels. In other words, the (first) sub-hologram may not fill the display area of ​​the display device, and may fill less than half, less than one-third, or less than one-quarter of the available display area. The inventors have discovered that filling the display device with each sub-hologram significantly increases the chance that the observation system receives the sub-hologram content from only a single replica in the first position, because the replicas of the sub-holograms are farther apart and therefore less likely to fall within the angular observation range of the observation system.

[0014] The replicas formed by waveguides include replicas of the light from the display device, wherein the waveguides effectively form an array of such replicas (in one or more dimensions). Configuring the (first sub)hologram to occupy only a portion of the display device may result in some separation between adjacent examples of the light from the first sub-hologram in the replica array formed by the waveguides.

[0015] The inventors have discovered that while insufficient filling of a display device with, for example, a (first sub) hologram can reduce the risk of the observation system receiving unwanted light (ghosting light), gaps or dark bands appear in the perceived image. The inventors have discovered that this reduction in "desired" light can be recovered without introducing the risk of ghosting content again. According to this disclosure, a target image can be divided into two or more image sub-parts (or sub-regions). Separate corresponding sub-holograms can be calculated for each image sub-region, wherein the dimensions of each sub-hologram are arranged such that both / all of them can be displayed substantially simultaneously on the display device. Each sub-hologram can be displayed on a corresponding (contiguous) group of pixels on the display device. Because each sub-hologram occupies only a portion of the display device, it is ensured that for each individual sub-hologram, a light replica (formed by waveguides) of that sub-hologram is physically separated from each other to prevent light from more than one such replica from reaching the observer at any given time or observation location. Conversely, the light from each sub-hologram is sufficiently close to at least one example of the light from the corresponding (each) other sub-hologram to enable the observation system to receive light from each sub-hologram, thereby allowing the entire image to be observed from a predetermined observation position at any given time. The inventors found the embodiments effective because the size of the display device is smaller than the size of the entrance pupil of the observation system (e.g., the length or size of the main dimensions, such as width or diameter). Adjacent groups of sub-holograms representing different portions of the field of view can be collectively referred to as “holograms” displayed on the display device. Therefore, it can be said that, in the embodiments, the size of the holograms is smaller than the size of the entrance pupil of the observation system.

[0016] Subholograms can be computed using any suitable method, and can be computed for predetermined observation system configurations and observer / aperture positions. Subhologram computation can consider observation systems with more than one aperture, such as an observer with two eyes. Although each individual subhologram has fewer holographic pixels than a single hologram displayed across the entire display device, the inventors have found that the loss of image resolution is not significant, and the potential disadvantage of this resolution reduction is offset by the benefits of reducing and even eliminating ghosting images. This is particularly realistic if each individual subhologram comprises at least a quarter of the pixels, such as at least a third or at least half of the pixels.

[0017] According to one aspect, a holographic projector is provided, comprising: a display device arranged to form a holographic wavefront by spatially modulating light according to a hologram displayed thereon; and a waveguide having an input arranged to receive the holographic wavefront, and a first surface and a second surface arranged therebetween to guide the holographic wavefront, wherein the first surface is partially reflective-transmissive, such that a plurality of replicas of the holographic wavefront are emitted therefrom. The size of the hologram (or display device) is smaller than the size of the entrance pupil of an observation system for receiving the holographic wavefront from the first surface of the waveguide. The hologram includes a first sub-hologram of a first region of an image (e.g., a first angular sub-range of the field of view). The first sub-hologram may underfill the display device (i.e., use only a subset of the pixels of the display device). The hologram may include a second sub-hologram of a second region of the image (i.e., a second angular sub-range of the field of view). The first sub-hologram may be adjacent to (or adjacent to or directly adjacent to) the second sub-hologram. For clarity, the first region of the image is different from the second region of the image. Therefore, the first sub-hologram is different from the second sub-hologram. Each of the first and second sub-holograms may underfill the display device. Therefore, the ghosting in the second region of the image can be substantially reduced / eliminated at the viewing window for the same reason as the ghosting in the first region of the image was substantially reduced / eliminated, as described above regarding the first region.

[0018] A display device may include a display area. The display area may be pixelated. The display area may include an array of display pixels. The size of the display area formed by the array of display pixels may be smaller than or substantially equal to the size of the entrance pupil of the observation system.

[0019] A hologram (as a whole) can be configured to occupy some or preferably all of the display pixels of the array. However, as mentioned above, the first sub-hologram of the hologram may not be sufficient to fill the display area. In other words, the first sub-hologram may occupy less than all the display pixels of the array. Specifically, less than half, optionally less than one-third, optionally less than one-quarter of the array's display pixels. The array's display pixels occupied by the first sub-hologram can form one or more first consecutive groups. A second sub-hologram may also occupy less than half, optionally less than one-third, optionally less than one-quarter of the array's display pixels. The array's display pixels occupied by the second sub-hologram can form one or more second consecutive groups. The first and second sub-holograms may each occupy the same number of display pixels, or they may each occupy different numbers of display pixels in the display device.

[0020] An observation system may include a human observer. An entrance pupil (or "aperture") may include the pupil of the observer's eye. An observation system may have more than one entrance pupil. Sub-holograms can be computed to illustrate multiple apertures.

[0021] A holographic projector can be configured to display multiple different holograms corresponding to multiple different corresponding images at different corresponding times (each hologram includes two or more sub-holograms).

[0022] Holograms (including two or more sub-holograms) can be calculated based on predetermined (i.e. known) properties of the holographic projector and / or observation system, such as, but not limited to: the type, size, and / or shape of the display device; the size, shape, and / or configuration of the waveguide, including the distance between the waveguide and the display device and / or the orientation of the waveguide relative to the display area of ​​the display device; the position and / or size and / or shape of the entrance pupil; the position where the image is to be formed; whether the image to be observed is a real or virtual image; and whether the system is configured for direct or indirect holography. Holograms (including two or more sub-holograms) can be recalculated when the position of the entrance pupil moves away from its initial position or moves at least a predetermined distance.

[0023] A holographic projector may include a holographic engine for computing holograms. The holographic engine may be configured to compute a first sub-hologram based on a first region of the (target) image. The holographic engine may be configured to compute a second sub-hologram based on a second region of the (target) image. The holographic engine may be configured to compute holograms (e.g., the first and / or second sub-holograms) using a Gerchberg-Saxton type algorithm. Advantageously, this can be an efficient and fast means of computing holograms (and may be, for example, faster and more efficient than point cloud-type hologram computing methods).

[0024] The hologram may also include a third sub-hologram of a third region of the image, which may be adjacent to at least one of the first or second sub-holograms, and optionally may also include a fourth sub-hologram of a fourth region of the image, which may be adjacent to at least one of the first, second, or third sub-holograms. Each sub-hologram may be configured to occupy fewer than all display pixels of the display device (i.e., underfill the display device).

[0025] The first and second regions of the image may be adjacent to each other to form a substantially continuous image on the image plane. Optional third and / or fourth regions of the image (if present) may be adjacent to each other and / or adjacent to at least one of the first or second regions of the image. Alternatively, gaps may exist between at least one region of the image and at least one corresponding other region of the image.

[0026] A hologram can be configured such that when a display device displaying the hologram is properly illuminated, light modulated by each (i.e., all) sub-hologram spaces will enter the entrance pupil of the observation system substantially simultaneously. The hologram can also be configured such that, for a given location of the entrance pupil, at a given time, only one instance of light modulated by a particular sub-hologram space will enter the entrance pupil of the observation system (i.e., the observation system will receive the "master" image and not a second or ghosted version of that image).

[0027] The holographic projector may also include an illumination system arranged to illuminate a hologram displayed on a display device to form a holographic wavefront. The illumination system may include a collimating light source. The illumination system may also include one or more lenses. The illumination system may include a laser source, such as a laser diode.

[0028] The size (i.e., diameter) of the entrance pupil may not exceed 15 mm, for example, not exceeding 12 mm or 10 mm. For instance, the diameter of the entrance pupil may be between approximately 8 mm and approximately 20 mm. The entrance pupil may include the pupil of the human eye or the aperture of a camera or other mechanical observation system. The cross-section of the entrance pupil may be circular, or it may be another shape, such as, but not limited to, an oval, elliptical, square, or rectangular cross-section. The size and / or shape of the entrance pupil may vary dynamically. There may be more than one entrance pupil.

[0029] A holographic wavefront formed by a display device may include a first holographic wavefront formed by a first sub-hologram and a different second holographic wavefront formed by a second sub-hologram. A waveguide may be configured to form an extended modulator (which may be referred to as a “virtual surface” or “replica surface”) comprising multiple replicas of the holographic wavefront formed by the display device, arranged in an array, wherein the array includes at least one replica of the first holographic wavefront alternating with at least one replica of the second holographic wavefront. In other words, within the extended modulator, each example (or sub-replica) of the light from the first holographic wavefront may be separated from each of the corresponding other examples in one or more dimensions. Each example (or sub-replica) of the light from the second holographic wavefront may occupy the space between the corresponding examples / sub-replicas of the first holographic wavefront to form the extended modulator.

[0030] The image can be formed at a non-infinite image distance from the display device. In other words, it may be a "near-field" image. The non-infinite image distance can be 5 meters or less, optionally 3 meters or less. It may be a real image or a virtual image. It can be formed by direct-view holography, in which light encoded by the hologram propagates to the observer's eye. Alternatively, the image can be formed by indirect-view holography, in which light encoded by the hologram is converted into a holographic reconstruction upstream of the observer, for example in free space or on a surface such as a screen or diffuser, and the holographically reconstructed light propagates to the observer's eye.

[0031] According to one aspect, a method for calculating a hologram of a holographic projection system is provided. The holographic projection system includes: a display device configured to display a hologram and output a holographic wavefront when illuminated; and a waveguide arranged to receive the holographic wavefront and emit multiple copies of the holographic wavefront. The method includes: obtaining a target image for which a hologram is to be generated; obtaining the position of the entrance pupil of an observation system for observing the holographic reconstruction of the target image; dividing the target image into a first image region and a second image region; and generating a first sub-hologram corresponding to the first image region and a second sub-hologram corresponding to the second image region.

[0032] A hologram can be formed by substantially simultaneously displaying first and second sub-holograms on a common display device. The first sub-hologram can be displayed on a first portion of the display device, such as a first portion of the display area of ​​the display device. The display device can be pixelated. The display area can include an array of display pixels. The first sub-hologram can be displayed on a first subset of the display pixels. The second sub-hologram can be displayed on a second portion of the display device. The second portion of the display device can be different from the first portion of the display device. The first sub-hologram can be displayed on a second subset of the display pixels. When displayed on the display device, the first and second portions of the display device can be adjacent to the second sub-hologram.

[0033] According to one aspect, a holographic engine is provided, configured to perform a method for calculating a hologram according to the above aspect. The holographic engine can be included in or incorporated into any suitable controller, computer, or processor. According to the above aspect, it can be integrated into a holographic projector or be separate from but in communication with the holographic projector.

[0034] According to one aspect, a holographic projection method is provided, comprising displaying a hologram on a display device, illuminating the displayed hologram to form a holographic wavefront, and guiding the holographic wavefront through a waveguide. The waveguide includes first and second surfaces arranged to receive an input to the holographic wavefront and arranged therebetween to guide the holographic wavefront, wherein the first surface is partially reflective-transmissive, such that a plurality of replicas of the holographic wavefront are emitted therefrom. The size of the hologram is smaller than the size of the entrance pupil of an observation system for receiving the holographic wavefront from the first surface of the waveguide. The hologram includes a first sub-hologram of a first region of the image adjacent to a second sub-hologram of a second region of the image.

[0035] The method may include calculating a hologram for observing an image through an observation system as an initial step.

[0036] The methods described in any aspect of this article can be implemented at least partially by a computer. They can be automatic or semi-automatic.

[0037] Features and advantages disclosed in one aspect may be applicable to other aspects. In particular, features and advantages disclosed in a holographic projector may be applicable to methods for calculating holograms, and vice versa.

[0038] In this disclosure, the term "replica" is used only to reflect that spatially modulated light is segmented such that a composite light field is guided along multiple different optical paths. The term "replica" is used to refer to each occurrence or instance of the composite light field after a copying event—such as partial reflection-transmission of a pupil dilator. Each replica propagates along a different optical path. Some embodiments of this disclosure relate to the propagation of light encoded with a hologram rather than an image—that is, light spatially modulated with a hologram of an image rather than the image itself. Thus, it can be said that multiple replicas of a hologram are formed. Those skilled in the art of holography will understand that the composite light field associated with the propagation of hologram-encoded light will vary with the propagation distance. The term "replica" as used herein is independent of propagation distance, so two optical branches or paths associated with a copying event are still referred to as "replicas" of each other, even if the branches have different lengths, causing the composite light field to evolve differently along each path. That is, according to this disclosure, even if two composite light fields are associated with different propagation distances, they are still considered "replicas"—assuming they originate from the same copying event or a series of copying events.

[0039] According to this disclosure, a "diffracted light field" is a light field formed by diffraction. A diffracted light field can be formed by illuminating a corresponding diffraction pattern. According to this disclosure, an example of a diffraction pattern is a hologram, and an example of a diffracted light field is a holographic light field or a holographically reconstructed light field that forms an image. The holographic light field forms a (holographic) reconstruction of an image on the playback plane. The holographic light field propagating from the hologram to the playback plane can be said to include light encoded by the hologram or light in the holographic domain. The diffracted light field is characterized by a diffraction angle determined by the minimum feature size of the diffraction structure and the wavelength of the light (of the diffracted light field). According to this disclosure, a "diffracted light field" can also be said to be a reconstructed light field formed on a plane spatially separated from the corresponding diffraction structure. This document discloses an optical system for propagating a diffracted light field from a diffraction structure to an observer. The diffracted light field can form an image.

[0040] 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 is a real image and spatially separate from the hologram. The term "reproduced field" is used to refer to the 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 typically 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.

[0041] 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.

[0042] It has been found that acceptable-quality holographic reconstructions can be formed from "holograms" containing only phase information related to the Fourier transform of the original object. Such holographic records can be referred to as phase-only holograms. While the embodiments relate to phase-only holograms, this disclosure is equally applicable to amplitude-only holography.

[0043] This disclosure is equally applicable to forming holographic reconstructions using amplitude and phase information associated with the Fourier transform of the original object. In some embodiments, this is achieved by using complex modulation of a so-called fully complex hologram containing 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.

[0044] The phase value, phase component, phase information, or simply phase of a pixel in a computer-generated hologram or spatial light modulator can be used as a reference, often shortened to "phase delay." That is, any phase value described is actually a number representing the amount of phase delay provided by that pixel (e.g., between 0 and 2). (within the range). For example, a spatial light modulator is described as having The phase value of the pixel will cause a phase delay in the received light. Radius. In some embodiments, each pixel of the 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 only, 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.

[0045] 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.

[0046] 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

[0047] Referring to the following figures, specific embodiments are described by way of example only:

[0048] Figure 1 This is a schematic diagram illustrating a reflective SLM that generates holographic reconstruction on a screen;

[0049] Figure 2 The image used for projection is shown, including eight image regions / components V1 to V8, and cross-sections of the corresponding holographic channels H1-H8;

[0050] Figure 3 A hologram is shown on an LCOS that directs light to multiple discrete regions;

[0051] Figure 4 The diagram shows, including, as shown Figure 2 and 3 The system of the display device for the calculated hologram;

[0052] Figure 5A A perspective view of a first example two-dimensional pupil expander including two replicators, each replicator comprising a pair of stacked surfaces;

[0053] Figure 5B A perspective view of a first example two-dimensional pupil expander including two replicators, each in the form of a solid waveguide, is shown.

[0054] Figure 6A An extended modulator formed by a waveguide is shown, which guides light from a display device;

[0055] Figure 6B An extended modulator formed by a waveguide is shown, which guides light from a display device that displays first and second interleaved sub-holograms;

[0056] Figure 6C An extended modulator formed by a waveguide is shown, which guides light from a display device that displays first, second, third, and fourth interlaced sub-holograms;

[0057] Figure 7 It shows Figure 6B A replica of the waveguide and the display device formed therefrom; and

[0058] Figure 8 It shows the result of Figure 6B An example image formed by replicas of two sub-holograms.

[0059] In all the accompanying drawings, the same reference numerals will be used to refer to the same or similar parts. Detailed Implementation

[0060] 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.

[0061] Unless otherwise stated, singular terms may include plural forms.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] In this disclosure, the term "basic" when applied to a structural unit of an apparatus can be interpreted as the technical feature of the structural unit produced within the technical tolerances of the method used to manufacture it.

[0067] Traditional optical configuration of holographic projection

[0068] 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.

[0069] 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.

[0070] 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.

[0071] In these embodiments, the spatial position of the holographic reconstruction is determined by the diopter (focusing) of the Fourier transform lens. Figure 1 In the illustrated embodiments, the Fourier transform lens is a physical lens. That is, the Fourier transform lens is an optical Fourier transform lens and performs a Fourier transform optically. Any lens can act as a Fourier transform lens, but the performance of the lens will limit the accuracy of the Fourier transform it performs. Those skilled in the art understand how lenses can be used to perform optical Fourier transforms. In some embodiments of this disclosure, the lens of an observer's eye performs a hologram-to-image conversion.

[0072] Holographic computation

[0073] 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. By way of example only, the embodiments relate to 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. In some embodiments, the hologram is a phase or pure phase hologram. However, this disclosure is also applicable to holograms computed using other techniques, such as point cloud-based methods.

[0074] 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.

[0075] Large field of view using small display devices

[0076] 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 an image projector and an observation system, wherein the image projector projects or relays light from the display device to the observation system. 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. The 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. In other examples, the image is a real image formed by holographic reconstruction, and this image is projected or relayed to the observation plane. In these other examples, spatially modulated light from an intermediate holographic reconstruction formed in free space or on a screen or other light-receiving surface between the display device and the observer is propagated to the observer. In both cases, an image is formed by illuminating a diffraction pattern (such as a hologram or phase hologram) displayed on a display device.

[0077] Display devices consist of pixels. The pixels of a display can show diffraction patterns or structures of diffracted light. Diffracted light can form an image on a plane spatially separate from the display device. According to well-known optical principles, the magnitude of the maximum diffraction angle is determined by the pixel size and other factors such as the wavelength of light.

[0078] 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.

[0079] In some embodiments, the hologram itself (light) propagates to the eye. For example, the spatially modulated light of the hologram (not yet fully converted into a holographic reconstruction, i.e., an image)—which can be informally referred to as being “encoded” by / with the hologram—propagates directly to the observer's eye. The observer can perceive a real or virtual image. In these embodiments, no intermediate holographic reconstruction / image is formed between the display device and the observer. Sometimes it is said that in these embodiments, the lens of the eye performs the holographic-to-image conversion or transformation. The projection system or light engine can be configured to allow the observer to effectively look directly at the display device.

[0080] The "light field" mentioned here refers to a "composite light field." The term "light field" simply means a light pattern of finite size along at least two orthogonal spatial directions (x and y). The term "complex" as used here simply indicates that the light at each point in the light field can be defined by amplitude and phase values, and therefore can be represented by a complex number or a pair of values. For holographic computation purposes, a composite light field can be a complex two-dimensional array, where the complex number defines the light intensity and phase at multiple discrete locations within the light field.

[0081] 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 observing entity / system varies with the distance between the display device and the observing entity. For example, at an observation distance of 1 meter, only a small 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 eyebox).

[0082] In some embodiments, the image perceived by the observer is a virtual image appearing upstream of the display device; that is, the observer perceives the image as being farther away than the display device. Therefore, conceptually, it can be thought of as the observer viewing the virtual image through a "window the size of the display device," which can be very small, for example, 1 centimeter 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 pupil of their eye, which can also be very small. Therefore, at any given time, the field of view is small, and the range of specific angles that can be seen is heavily dependent on eye position.

[0083] A pupil expander addresses how to increase 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. Display devices are typically (relatively) small, with (relatively) large projection distances. In some embodiments, the projection distance is at least an order of magnitude larger than the diameter or width of the entrance pupil and / or aperture of the display device (i.e., the size of the pixel array), for example, at least two orders of magnitude larger.

[0084] The use of a pupil expander laterally increases the viewing area (i.e., the user's eyebox), allowing for some eye movement while still enabling the user to see the image. As those skilled in the art will understand, in an imaging system, the viewing area (the user's eyebox) is the region where the observer's eye can perceive the image. This disclosure includes non-infinite virtual image distances—i.e., near-field virtual images.

[0085] Traditionally, two-dimensional pupil expanders comprise one or more one-dimensional optical waveguides, each formed using a pair of opposing reflective surfaces, where output light from the surfaces forms an observation window or eyebox. Light received from a display device (e.g., spatially modulated light from LCOS) is replicated by this or each waveguide to increase the field of view (or observation area) in at least one dimension. In particular, the waveguides enlarge the observation window by generating additional light rays or "copies" through the division of the amplitude of the incident wavefront.

[0086] The display device can have an active or pixel display area, which has a first dimension of less than 10 cm, for example, less than 5 cm or less than 2 cm. The propagation distance between the display device and the 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 in less than 20 ms, such as less than 15 ms or less than 10 ms.

[0087] In some embodiments described herein by way of examples of diffraction or holographic light fields only, the hologram is configured to route light into multiple channels, each corresponding to a different portion (i.e., sub-region) of the image. The channels formed by the diffraction structure are referred to herein as “holographic channels” simply to reflect that they are light channels encoded by a hologram containing 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 holographic domain is Fourier or the frequency domain. The hologram can also be a Fresnel or Fresnel transform hologram. The hologram can also be a point cloud hologram. The hologram is described herein as routing light into multiple holographic channels to reflect that the image reconstructable from the hologram has a finite size and can be arbitrarily divided into multiple image sub-regions, where each holographic channel will correspond to each image sub-region. Importantly, the hologram of this example is characterized by how it distributes the image content when illuminated. Specifically and uniquely, the hologram divides the image content by angle. In other words, each point on the image is associated with a unique ray angle in the spatially modulated light formed by the hologram during illumination—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 divided into multiple holographic channels, each defined by a range of ray angles (in two dimensions). As understood above, any holographic channel that can be considered in the spatially modulated light (i.e., a subrange of ray angles) will be associated with a corresponding part or subregion of the image. That is, all the information needed to reconstruct that part or subregion of the image is contained within the subrange of angles 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 light channels.

[0088] Nevertheless, holograms can still be identified. For example, if only a continuous portion or sub-region of the 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 the 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-section of any hologram channel substantially corresponds to (i.e., substantially the same as) the shape of the incident pupil, although the size may differ—at least in the correct plane in which the hologram is computed. 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. Furthermore, to avoid any doubt, references herein to holograms configured to guide light or to divide an image at an angle into multiple hologram channels are by way of example only, and this disclosure is equally applicable to pupil expansion of any type of holographic light field or even any type of diffractive or diffracted light field.

[0089] The system can be offered in a compact and streamlined physical form. This makes it suitable for a wide range of practical applications, including those with limited space and high asset value. For example, it can be implemented in a head-up display (HUD), such as a vehicle or automotive HUD.

[0090] According to this disclosure, a pupil expander is provided for diffracted light, which may include a diverging beam of light. The diffracted light field can be defined by a "light cone". Therefore, the magnitude of the diffracted light field (as defined in a two-dimensional plane) increases with the propagation distance from the corresponding diffractive structure (i.e., the display device). It can be said that the pupil expander replicates a hologram or forms at least one copy of a hologram to convey light transmitted to the observer that is spatially modulated according to the hologram.

[0091] In some embodiments, two one-dimensional waveguide pupil expanders are provided, each arranged to effectively increase the size of the system's exit pupil by forming multiple copies or replicas of the exit pupil (or the light from the exit pupil) of the spatial light modulator. The exit pupil can be understood as the physical region where the system outputs light. Alternatively, each waveguide pupil expander can be arranged to expand the size of the system's exit pupil. Also, each waveguide pupil expander can be arranged to expand / increase the size of the eyebox in which an observer's eye can reside, in order to see / receive the light output by the system.

[0092] Optical Channel

[0093] Holograms formed according to some embodiments angularly divide image content to provide multiple holographic channels, which may have a cross-sectional shape defined by the aperture of an optical system. The hologram is calculated to provide this guidance of the diffracted light field. In some embodiments, as described above, this is achieved during hologram calculation by taking into account the aperture (virtual or real) of the optical system.

[0094] Figure 2 and 3 An example of this type of hologram is shown, which can be used in conjunction with the pupil expander disclosed herein. However, this example should not be considered as a limitation of this disclosure.

[0095] Figure 2 An image 252 for projection is shown, comprising eight image regions / components V1 to V8. This is for illustrative purposes only. Figure 2 Eight image components are shown, and image 252 can be divided into any number of components. Figure 2 Also shown is an encoded light pattern 254 (i.e., a hologram) that can reconstruct image 252—for example, when transformed by a lens of a suitable observation system. The encoded light pattern 454 includes first to eighth sub-holograms or components H1 to H8, corresponding to first to eighth image components / regions V1 to V8. Figure 2 This further demonstrates how holograms decompose image content through angles. Therefore, a characteristic of holograms lies in their ability to guide light. This is in Figure 3 As shown in the example. Specifically, the hologram in this example guides light into multiple discrete regions. In the example shown, the discrete regions are disks, but other shapes can also be envisioned. After propagation through the waveguide, the optimal size and shape of the disk can be related to the size and shape of the aperture of the optical system (e.g., the entrance pupil of an observation system).

[0096] Figure 4 System 400 is shown, including displays such as Figure 2 and 3 The display device for the calculated hologram.

[0097] System 400 includes a display device comprising an LCOS 402 in this arrangement. The LCOS 402 is arranged to display a modulation pattern (or “diffraction pattern”) including a hologram and to project holographically encoded light onto an eye 405, which includes a pupil acting as an aperture 404, a lens 409, and a retina (not shown) acting as a viewing plane. A light source (not shown) is arranged to illuminate the LCOS 402. The lens 409 of the eye 405 performs the hologram-to-image conversion. The light source can be of any suitable type. For example, it can include a laser source.

[0098] The observation system 400 also includes a waveguide 408 located between the LCOS 402 and the eye 405. The presence of the waveguide 408 allows all angular content from the LCOS 402 to be received by the eye, even at the relatively large projection distance shown. This is because the waveguide 408 acts as a pupil expander in a well-known manner, and therefore will only be briefly described here.

[0099] in short, Figure 4 The waveguide 408 shown comprises a generally elongated structure. In this example, waveguide 408 comprises an optical plate of refractive material, but other types of waveguides are also well known and can be used. Waveguide 408 is positioned to intersect, for example, at an oblique angle, a light cone (i.e., a diffracted light field) projected from LCOS 402. In this example, the dimensions, position, and orientation of waveguide 408 are configured to ensure that light from each of the eight beams within the light cone enters waveguide 408. Light from the light cone enters waveguide 408 via a first planar surface (closest to LCOS 402) and is guided at least partially along the length of waveguide 408 before being emitted via a second planar surface (closest to the eye) substantially opposite the first surface. It is readily understood that the second planar surface is partially reflective and partially transmissive. In other words, as each ray of light propagates within waveguide 408 from the first planar surface and strikes the second planar surface, some light will be transmitted out of waveguide 408, and some light will be reflected back to the first planar surface by the second planar surface. The first planar surface is reflective, such that all light striking it from within waveguide 408 will be reflected back to the second planar surface. Thus, some light can be simply refracted between the two planar surfaces of waveguide 408 before being transmitted, while other light can be reflected and thus undergo one or more reflections (or "bouncing") between the planar surfaces of waveguide 408 before being transmitted.

[0100] Figure 4 A total of nine "bounce" points B0 to B8 are shown along the length of waveguide 408. Although... Figure 2 As shown, 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 408, but only light from one angular portion of the image (e.g., light from one of V1 to V8) has a trajectory that allows it to reach the eye 405 from each corresponding "bounce" point B0 to B8. Furthermore, light from different angular portions (V1 to V8) of the image reaches the eye 405 from each corresponding "bounce" point. Therefore, in Figure 4 In the example, each angular channel of the encoded light reaches the eye only once from waveguide 408.

[0101] Waveguide 408 forms multiple replicas of the hologram at corresponding "bounce" points B1 to B8 along its length, corresponding to the direction of pupil expansion. As shown in Figure 5, the multiple replicas can be linearly pushed back to their respective replicas or virtual display devices 402'. This process corresponds to the step of "unfolding" the optical path within the waveguide, such that the light from the replicas is pushed back to the "virtual surface" without internal reflection within the waveguide. Therefore, the light from the expanded exit pupil can be considered to originate from the virtual surface (also referred to here as the "expanded modulator") comprising display device 402 and the replicated display device 402'.

[0102] Although virtual images have been discussed in general terms here, which require the eye to convert received modulated light to form a perceived image, the methods and apparatus described here can be applied to real images.

[0103] Two-dimensional pupil expansion

[0104] Although Figure 4 The arrangement shown includes a single waveguide providing pupil extension in one dimension, but pupil extension can be provided in more than one dimension, such as in two dimensions. Furthermore, although Figure 4 The examples in the document use holograms that have been calculated to create optical channels, each corresponding to a different part of the image, but this disclosure and the system described below are not limited to this type of hologram.

[0105] Figure 5A A perspective view of system 500 is shown, which includes two replicators 504 and 506 arranged to extend beam 502 in two dimensions.

[0106] exist Figure 5A In system 500, the first replicator 504 includes a first pair of surfaces stacked parallel to each other, arranged in a manner similar to Figure 4 The waveguide 408 provides replication or pupil expansion. The first pair of surfaces are similar in size and shape to each other (in some cases identical) and are substantially elongated in one direction. The collimated beam 502 is guided to the input on the first replicator 504. Due to the internal reflection process between the two surfaces, and from one of the surfaces (the upper surface, such as...) Figure 5A As shown, the light from each of the plurality of output points on the beam 502 is partially transmitted, which will be familiar to a skilled reader, and the light from beam 502 is replicated along the length of the first replicator 504 in a first direction. Thus, the first plurality of replica beams 508 are emitted from the first replicator 504 toward the second replicator 506.

[0107] The second replicator 506 includes a second pair of surfaces stacked parallel to each other, arranged to receive each collimated beam of the first plurality of beams 508, and further arranged to provide replication or pupil expansion by extending each of these beams in a second direction substantially orthogonal to the first direction. The first pair of surfaces are similar in size and shape to each other (in some cases identical) and are substantially rectangular. The second replicator is made rectangular so that it has a length along the first direction to receive the first plurality of beams 508, and a length along the second orthogonal direction to provide replication in that second direction. Due to the internal reflection process between the two surfaces, and from one of the surfaces (such as... Figure 5A Partial transmission of light from each of the plurality of output points on the upper surface shown, and the light from each beam within the first plurality of beams 508 being replicated in the second direction. Therefore, a second plurality of beams 510 is emitted from the second replicator 506, wherein the second plurality of beams 510 comprises a copy of the input beam 502 along each of the first and second directions. Thus, the second plurality of beams 510 can be considered as a two-dimensional grid or array comprising the replicated beams.

[0108] Therefore, it can be said that Figure 5A The first and second replicators 504, 505 are combined to provide a two-dimensional replicator (or "two-dimensional pupil expander"). Thus, the replicated beam 510 can be emitted along the optical path to the expanded eye box of a display system, such as a head-up display.

[0109] exist Figure 5A In this system, the first replicator 504 is a waveguide comprising a pair of elongated, straight, reflective surfaces stacked parallel to each other; similarly, the second replicator 504 is a waveguide comprising a pair of rectangular, stacked, parallel to each other. In other systems, the first replicator may be a solid, elongated, straight waveguide, and the second replicator may be a solid planar rectangular waveguide, wherein each waveguide comprises an optically transparent solid material, such as glass. In this case, the pair of parallel reflective surfaces are formed by a pair of opposing main sidewalls, optionally including respective reflective and reflect-transmittance surface coatings, which will be familiar to the skilled reader.

[0110] Figure 5B A perspective view of system 500 is shown, which includes two replicators 520 and 540 arranged to replicate beam 522 in two-dimensional space, wherein the first replicator is a solid elongated waveguide 520 and the second replicator is a solid planar waveguide 540.

[0111] exist Figure 5BIn the system, the first replicator / waveguide 520 is arranged such that its pair of elongated parallel reflective surfaces 524a, 524b are perpendicular to the plane of the second replicator / waveguide 540. Therefore, the system includes an optical coupler arranged to couple light from the output port of the first replicator 520 to the input port of the second replicator 540. In the illustrated arrangement, the optical coupler is a plane / folding mirror 530, which is arranged to fold or redirect the optical path of light to achieve the desired optical coupling from the first replicator to the second replicator. Figure 5B As shown, mirror 530 is arranged to receive light from the output port / reflective-transmitting surface 524a of the first replicator / waveguide 520, comprising a one-dimensional array of replicas extending in the first dimension. Mirror 530 is tilted to redirect the received light at an angle onto the optical path of the input port in the (total)reflective surface of the second replicator 540, providing waveguide and replica formation along its length in the second dimension. It should be understood that mirror 530 is one example of an optical element capable of redirecting light in the manner shown, and one or more other elements may alternatively be used to perform this task.

[0112] In the arrangement shown, the (partial) reflective-transmitting surface 524a of the first replicator 520 is adjacent to the input port of the first replicator / waveguide 520, which receives the input beam 522 at an angle to provide a waveguide and copy formation along its length in the first dimension. Therefore, the input port of the first replicator / waveguide 520 is located at its input end, on the same surface as the reflective-transmitting surface 524a. The skilled reader will understand that the input port of the first replicator / waveguide 520 can be in any other suitable location.

[0113] therefore, Figure 5B The arrangement allows the first replicator 520 and mirror 530 to be provided as part of a first relatively thin layer in the first and third dimensional planes (shown as the xz plane). Specifically, the size or "height" of the first planar layer (in which the first replicator 520 is located) in the second dimension (shown as the y dimension) is reduced. Mirror 530 is configured to guide light from the first layer / plane (i.e., the "first planar layer") where the first replicator 520 is located and to the second layer / plane (i.e., the "second planar layer") where the second replicator 540 is located, which is located above and substantially parallel to the first layer / plane. Therefore, the overall size or "height" of the system—including in the first and third dimensions (shown as the xz plane) and in the second dimension (shown as the y dimension)—of the first and second replicators 520, 540 and mirror 530 in the stacked first and second planar layers, is compact. The skilled reader will understand that the components used to implement this disclosure... Figure 5B Many variations in the arrangement are possible and anticipated.

[0114] An image projector can be arranged to project a diverging or diffracted light field. In some embodiments, the light field is encoded with a hologram. In some embodiments, the diffracted light field comprises a diverging beam of light. In some embodiments, the image formed by the diffracted light field is a virtual image.

[0115] In some embodiments, the first pair of parallel / complementary surfaces are elongated or slender surfaces, relatively long along a first dimension and relatively short along a second dimension, for example, relatively short along each of two other dimensions, each dimension being substantially orthogonal to each of the corresponding other dimensions. The process of light reflection / transmission between / from the first pair of parallel surfaces is arranged such that light propagates within the first waveguide pupil expander, with the general direction of light propagation being the direction of the relatively longer portion of the first waveguide pupil expander (i.e., its "elongated" direction).

[0116] This paper discloses a system that uses diffracted light to form an image and provides eyebox sizes and fields of view suitable for real-world applications—such as head-up displays in the automotive industry. Diffracted light is light used to holographically reconstruct an image from a diffracted structure—such as a hologram like a Fourier or Fresnel hologram. The use of diffraction and diffracted structures requires high-density display devices with very small pixels (e.g., 1 micrometer)—which in practice means small display devices (e.g., 1 cm). The inventors have solved the problem of how to provide a diffracted light field for 2D pupil expansion, for example, by including diffracted light comprising divergent (non-collimated) beams.

[0117] In some embodiments, the display system includes display devices—such as pixelated display devices, such as spatial light modulators (SLMs) or liquid crystal on silicon (LCoS) SLMs—arranged to provide or form diffracted or diverging light. In these respects, the aperture of the spatial light modulator (SLM) is the limiting aperture of the system. That is, the aperture of the spatial light modulator—more specifically, the size of the region defining the light-modulating pixel array contained within the SLM—determines the size (e.g., spatial extent) of the light beam that can exit the system. According to this disclosure, it is stated that by using at least one pupil expander, the exit pupil of the system is expanded to reflect that the exit pupil of the system (which is limited by the small display device having pixel sizes for light diffraction) becomes larger in spatial extension.

[0118] A diffracted or diverging light field can be described as having a "light field size," which is defined in a direction substantially orthogonal to the direction of light field propagation. Because light is diffracted / divered, the light field size increases with the propagation distance.

[0119] In some embodiments, the diffracted light field is spatially modulated according to the hologram. In other words, in these aspects, the diffracted light field includes a “holographic light field.” The hologram can be displayed on a pixelated display device. The hologram can be a computer-generated hologram (CGH). It can be a Fourier hologram, a Fresnel hologram, a point cloud hologram, or any other suitable type of hologram. Optionally, the hologram can be computed to form channels of holographic light, each channel corresponding to a different portion of the image that an observer wants to observe (or perceive, if it is a virtual image). The pixelated display device can be configured to display multiple different holograms consecutively or sequentially. Each aspect and embodiment disclosed herein can be applied to the display of multiple holograms.

[0120] The output port of the first waveguide pupil expander can be coupled to the input port of the second waveguide pupil expander. The second waveguide pupil expander can be arranged to guide the diffracted light field (including some, preferably most, preferably all copies of the light field output by the first waveguide pupil expander) from its input port to the corresponding output port through internal reflection between the third pair of parallel surfaces of the second waveguide pupil expander.

[0121] A first waveguide pupil expander can be arranged to provide pupil expansion or replication in a first direction, while a second waveguide pupil expander can be arranged to provide pupil expansion or replication in a different second direction. The second direction can be substantially orthogonal to the first direction. The second waveguide pupil expander can be arranged to maintain the pupil expansion already provided by the first waveguide pupil expander in the first direction, and expand (or replicate) some, preferably most, preferably all, copies it receives from the first waveguide pupil expander in the different second directions. The second waveguide pupil expander can be arranged to receive the optical field directly or indirectly from the first waveguide pupil expander. One or more other elements can be provided along the propagation path of the optical field between the first and second waveguide pupil expanders.

[0122] The first waveguide pupil expander may be substantially elongated, and the second waveguide pupil expander may be substantially planar. The elongated shape of the first waveguide pupil expander may be defined by its length along a first dimension. The planar or rectangular shape of the second waveguide pupil expander may be defined by its length along the first dimension and its width or span along a second dimension substantially orthogonal to the first dimension. The dimension or length of the first waveguide pupil expander along its first dimension may correspond respectively to the length or width of the second waveguide pupil expander along its first or second dimension. The first surface of a pair of parallel surfaces of the second waveguide pupil expander, including its input port, may be shaped, sized, and / or positioned to correspond to the region defined by the output port on the first surface of the pair of parallel surfaces on the first waveguide pupil expander, such that the second waveguide pupil expander is arranged to receive each copy output by the first waveguide pupil expander.

[0123] The first and second waveguide pupil expanders can jointly provide pupil expansion in a first direction and a second direction perpendicular to the first direction. Optionally, the planes containing the first and second directions are substantially parallel to the plane of the second waveguide pupil expander. In other words, the first and second dimensions defining the length and width of the second waveguide pupil expander, respectively, can be parallel to the first and second directions (or parallel to the second and first directions, respectively), wherein the waveguide pupil expander provides pupil expansion. The combination of the first and second waveguide pupil expanders is generally referred to as a "pupil expander".

[0124] In essence, the expansion / replication provided by the first and second waveguide expanders has the effect of expanding the exit pupil of the display system in each of two directions. The area defined by the expanded exit pupil can further define the expanded eyebox region from which the observer can receive light from the input diffracted or diverging light field. The eyebox region can be said to lie on or define the observation plane.

[0125] The two directions of pupil expansion can be coplanar or parallel to the first and second directions of replication / expansion provided by the first and second waveguide pupil expanders. Alternatively, in arrangements that include other elements such as optical combiners, e.g., a vehicle's windshield, the pupil can be considered as the pupil of that other element, such as the windshield. In such an arrangement, the pupil can be non-coplanar and non-parallel to the first and second directions of replication / expansion provided by the first and second waveguide pupil expanders. For example, the pupil can be substantially perpendicular to the first and second directions of replication / expansion provided by the first and second waveguide pupil expanders.

[0126] The observation plane and / or eyebox region may not be coplanar or parallel to the first and second directions in which the first and second waveguide pupil expanders provide replication / expansion. For example, the observation plane may be substantially perpendicular to the first and second directions in which the first and second waveguide pupil expanders provide replication / expansion.

[0127] In order to provide suitable emission conditions to achieve internal reflection within the first and second waveguide pupil expanders, the elongated dimension of the first waveguide pupil expander may be tilted relative to the first and second dimensions of the second waveguide pupil expander.

[0128] Combiner shape compensation

[0129] The advantage of projecting a hologram onto an eyebox is that optical compensation can be encoded in the hologram (see, for example, European Patent 2936252, incorporated herein by reference). This disclosure is compatible with holograms that compensate for the complex curvature of an optical combiner used as part of a projection system. In some embodiments, the optical combiner is the windshield of a vehicle. The full details of this method are provided in European Patent 2936252 and are not repeated here, as the detailed features of these systems and methods are not essential to the novel teachings of this disclosure and are merely examples of configurations that benefit from the teachings of this disclosure.

[0130] Control device

[0131] This disclosure is also compatible with optical configurations that include control devices (e.g., optical shutter devices) to control the transmission of light from the optical channel hologram to the observer. The holographic projector may also include control devices arranged to control the transmission of the angular channel to the eyebox position. UK Patent Application 2108456.1, filed June 14, 2021 and incorporated herein by reference, discloses at least one waveguide pupil expander and control device. The reader will understand from at least this prior disclosure that the optical configuration of the control device is substantially based on the user's eyebox position and is compatible with any hologram calculation method for implementing the optical channel described herein. The control device can be described as an optical shutter or aperture device. The optical shutter device may include a 1D array of apertures or windows, wherein each aperture or window can be independently switched between transparent and opaque states to control the transmission of the hologram optical channel and its replica to the eyebox. Each aperture or window may include multiple liquid crystal cells or pixels.

[0132] Ghosting images

[0133] While waveguides can be used in image projection systems to allow all angular content from the display device to be received by the eye, even at relatively large projection distances, and to allow the eye to make some lateral movements within the eye box, the inventors have observed that for non-infinite virtual image distances—i.e., near-field virtual images—so-called "ghost images" can occur due to the different possible light propagation paths through the waveguide and because different replicas of the holographic wavefront have different lengths. A ghost image is a low-brightness replica of the main image. The primary, highest-intensity image may be referred to as the primary image. Each ghost image may be referred to as a secondary image. The presence of ghost images significantly reduces the quality of the perceived virtual image. Ghost images may make the primary image appear blurry. In arrangements that convey safety-critical information via images, ghost images can even be a security issue. This disclosure relates at least in part to addressing the problem caused by ghost images through improved techniques for computing holograms for display on a display device replicated by waveguides, to reduce and preferably avoid ghost images in the resulting image.

[0134] Traditionally, when a hologram is computed from a (target) image and displayed on a display device, each hologram pixel contributes to the entire image (i.e., each part of the holographic reconstruction). For purposes such as hologram robustness and image resolution, it is traditionally desirable to display the hologram on as many display pixels as possible on the display device. In arrangements where the number of display pixels in the display device exceeds the number of hologram pixels to be displayed, tiling can be employed, where at least one hologram pixel of the hologram is displayed more than once on the display pixels of the display device at a given time.

[0135] As noted earlier in this disclosure, a method for resolving ghosting images is described in UK Patent Application 2101666.2, filed February 5, 2021, which is incorporated herein by reference. This patent application discloses a first hologram calculation method in which eye tracking and ray tracing are used to identify sub-regions of a display device for calculating point cloud holograms contributing to the ghosting image. Hologram values ​​are then excluded from this sub-region (or sub-regions) of the display device to reduce or eliminate ghosting. However, this method may not be compatible with all image projection systems because it reduces the number of display device pixels available for hologram display—and thus potentially reduces the number of hologram pixels that can be included in the hologram of the target image—and may therefore result in a reduction in image resolution. It may also be computationally intensive and time-consuming, which may make it less suitable for complex target images.

[0136] The inventors have proposed a new solution for ghosting images, which can be understood from the following description of the accompanying drawings, such as 6A.

[0137] Figure 6A An example extended modulator 600 is shown formed when a waveguide (not shown) receives and replicates light from a display device, which may be, for example, a spatial light modulator (SLM), such as a liquid crystal on silicon (LCoS) SLM. The extended modulator 600 includes a replica array of LCoS light. The extended modulator 600 in… Figure 6AWhile it is presented in two dimensions, it can also have depth in a third orthogonal dimension (i.e., in the "z" direction). In this example, there are 16 replicas in the extended modulator 600, but this is merely illustrative and should not be considered a limitation of this disclosure. The LCoS replicated by the waveguide to form the extended modulator 600 can display any suitable pattern. For example, it can display diffraction structures, such as holograms, which can be properly illuminated to form an image (i.e., holographic reconstruction). As can be understood from the above description, conventionally, a hologram of an image will preferably be displayed across the entire display device (i.e., using every display pixel, or as many display pixels as possible), and each displayed hologram pixel will contribute to the overall resulting image when the hologram is displayed and properly illuminated.

[0138] However, the inventors have recognized that when waveguides or other replicators are used in conjunction with display devices such as LCoS in an image projection system, the creation of one or more replicas of the light illuminating the hologram output displayed on the display device (i.e., such as...) Figure 6A The creation of the extended modulator 600 shown causes light of the same image content to reach the observer's eye more than once via different corresponding copies (and from different regions of the LCOS). This, in turn, causes the observer to see one or more "ghost images" in addition to the main (primary) image, which is generally undesirable.

[0139] The inventors also recognized that the ghosting problem in near-field images is exacerbated when the size of the display device and the size of the aperture through which the observer receives light content are similar. For example, the situation may worsen when the display device (e.g., LCoS) has a size similar to that of the human eye. The ghosting problem also becomes more severe as the virtual image distance (VID)—the distance between the observer and the image—decreases. It should be understood that, in practice, it is generally undesirable—and even impossible—to change the relative sizes of the display device and the aperture (e.g., the eye), nor to significantly change the VID. For example, in many devices, such as, but not limited to, head-up displays at least partially housed under a vehicle dashboard, the available space volume for accommodating the image projection system and / or the degrees of freedom in choosing its location and / or the location where the image should be formed are limited, thus necessitating an alternative method for addressing ghosting images.

[0140] As proposed by the inventors, one solution to ghosting images is to reduce the number of display pixels of the hologram—for example, displaying the hologram only on half, one-third, or one-quarter of the display pixels of the display device. In other words, the hologram is insufficient to fill the display device. Doing so allows the light replicas of the hologram—generated by waveguides in the image projection system—to be separated from each other. This introduces separation between the replicas of the (sub)hologram. This reduces (or eliminates) the possibility of more than one replica of light reaching the observer's eye from any given viewing position, thus reducing the likelihood of ghosting images.

[0141] The inventors have discovered that while insufficient filling of a display device with, for example, a (first sub) hologram can reduce the risk of the observation system receiving unwanted light (ghosting light), gaps or dark bands appear in the perceived image where unused pixels of the display device no longer transmit image / hologram content to the eye. The inventors have discovered that this reduction in "desired" light can be restored without introducing the risk of ghosting content again. According to this disclosure, a target image can be divided into two or more image sub-parts (or sub-regions). Separate corresponding sub-holograms can be calculated for each image sub-region, wherein the dimensions of each sub-hologram are arranged such that both / all of them can be displayed substantially simultaneously on the display device. Each sub-hologram can be displayed on a corresponding (contiguous) group of pixels of the display device. Because each sub-hologram occupies only a portion of the display device, it is ensured that for each individual sub-hologram, a light replica (formed by waveguides) of that sub-hologram is physically separated from each other to prevent light from reaching the observer at any given time exceeding that of one such replica. Conversely, the light from each sub-hologram is sufficiently close to at least one example of the light from each of the corresponding other sub-holograms, enabling the observation system to receive light from each sub-hologram, thereby allowing the entire image to be observed from a predetermined observation position at any given time. The inventors found the embodiments effective because the size of the display device is smaller than the size of the entrance pupil of the observation system (e.g., the length or size of the main dimensions, such as width or diameter). Adjacent groups of sub-holograms in different portions of the field of view can be collectively referred to as “holograms” displayed on the display device. Therefore, it can be said that, in the embodiments, the size of the holograms is smaller than the size of the entrance pupil of the observation system.

[0142] Figure 6B An improved solution proposed by the inventors for resolving ghosting images in near-field images is shown. Figure 6B An exemplary extended modulator 602 is shown, formed when a waveguide (not shown) receives and replicates light from a display device, which may be, for example, a spatial light modulator (SLM), such as a liquid crystal on silicon (LCoS) SLM. Figure 6A As shown, the extended modulator 602 in Figure 6BIt is represented in two dimensions, but it can also have depth in a third orthogonal dimension (i.e., in the "z" direction). In this example, there are 16 copies in the extended modulator 602, but this is merely illustrative and should not be considered a limitation of this disclosure. Figure 6B In the image, the copies are shown separated from each other by thicker grid lines.

[0143] The extended modulator includes a copy of the light from a display device configured to display two holograms substantially simultaneously—namely, a first (sub)hologram 604 (composed of...). Figure 6B The white portion of each replica is shown in the middle) and the second (sub) hologram 606 (by... Figure 6B (The shaded portions of each replica are shown in the diagram), and are displayed side-by-side on the same (i.e., common) LCoS, substantially simultaneously with each other. The first and second (sub)holograms 604 and 606 may also be referred to as the first and second sub-holograms, respectively. Each (sub)hologram 604 and 606 includes a corresponding group of holographic pixels displayed on a corresponding consecutive group of display pixels in the LCoS. Furthermore, according to the solution proposed by the inventors, the first (sub)hologram 604 and the second (sub)hologram 606 respectively correspond to the first and second portions of the same target image (i.e., corresponding to the first and second corresponding portions of the common holographic reconstruction that will be seen / formed by the observer's eye at a given time). Each of the first (sub)hologram 604 and the second (sub)hologram 606 has fewer holographic pixels than the number of display pixels of the display device. In this example, the first hologram 604 and the second hologram 606 each occupy half of the LCoS, but this is merely illustrative and should not be considered a limitation of this disclosure.

[0144] Each of the first hologram 604 and the second hologram 606 can be considered a "sub-hologram" because each corresponds to a specific sub-part of the target image to be holographically reconstructed. It should be noted that this differs from the above discussion regarding... Figure 3 The arrangement shown and described. In Figure 3 In the arrangement, a single hologram is configured such that, when properly displayed and illuminated on a display device, it causes light from different corresponding portions of the image to be output in their respective corresponding channels (H1 to H8). However, from Figure 3 As can be seen, each hologram pixel in this arrangement (and each display pixel of the display device) contributes light to each (i.e., all) channel, and thus to each part of the resulting image. On the other hand, in Figure 6B In the solution shown, the hologram pixels of the first (sub)hologram 604 occupy only half of the LCoS pixels and also contribute light to the corresponding first (sub) portion of the image, while the hologram pixels of the second (sub)hologram 606 occupy the corresponding other half of the LCoS pixels and contribute light to the corresponding second (sub) portion of the image.

[0145] therefore, Figure 6B Each replica in the LCoS comprises the light of the first sub-hologram 604, side-by-side with the light of the second sub-hologram 606. As a result, in the extended modulator 602, which replicates the light of the entire LCoS in each of both dimensions, each example of the light of the first sub-hologram 604 is separated by the corresponding next example of the light of the first sub-hologram 604, and an example of the light of the second sub-hologram 606. In other words, in each of its two dimensions, the extended modulator 602 effectively includes multiple replicas of the light of the first sub-hologram 604, alternating with multiple replicas of the light of the second sub-hologram 606. This means that two examples / replicas of the light of the same (sub)hologram will never be directly adjacent to each other. The inventors have recognized that this separation / alternation helps to solve the problem of ghosting images because the chance of the observation system receiving light from different replicas associated with the same (sub)hologram is significantly reduced.

[0146] It should be noted that for each (sub)hologram, all pixels of that (sub)hologram contribute to all image pixels of the corresponding sub-part of the image. Furthermore, in the angular space of the waveguide 700 output side, the holographic light output from the first (sub)hologram will be output side-by-side with the holographic light output from the second (sub)hologram. This will be explained below. Figure 7 and 8 Further understanding can be gained from the description. Furthermore, Figure 6B Examples include an extended modulator 602, which replicates an LCoS displaying two sub-holograms; however, the method described herein can be extended to any suitable display device displaying two or more holograms. This will be combined below. Figure 6C Further discussion.

[0147] Go to Figure 7 The waveguide 700 is shown, including a first reflective surface 702 and a second transmission-reflection surface 704. Although Figure 7 Not shown, but it should be understood that when holographic light within waveguide 700 strikes each "bounce point" of the second surface 704, some light will be transmitted through waveguide 700 toward the observer (not shown), and the remaining light will be reflected toward the first surface 702, such as... Figure 7 As shown by the arrow in the image.

[0148] Please refer to this briefly again. Figure 4 Recall that the waveguide in the image projection system can be configured to produce (from the observer's perspective) a display device (in) at different locations upstream of waveguide 700. Figure 4 The example shown is multiple copies of the LCoS. This has the effect of increasing the eyebox volume, allowing an observer to be positioned within the eyebox and still see an image corresponding to the illumination hologram displayed on the LcoS. However, as described herein, the presence of such copies often causes the observer to form a ghosted image.

[0149] Figure 7 Waveguide 700 is shown, which is arranged to guide the display device ( Figure 7 The light emitted (not shown) is displayed side-by-side on a display device with two distinct sub-holograms, each corresponding to a specific sub-part of the target image to be holographically reproduced. The portion of the display device displaying the corresponding sub-holograms may be referred to as the first and second corresponding sub-display devices. Because the two (sub)holograms are displayed simultaneously on the display device, the waveguide 700 has the effect of creating two types of sub-replicas 706, 708 within each replica of the display device (from the observer's perspective). Each example of the first sub-replica type 706 is a replica of the light from the first sub-hologram 604 (or the first sub-display device) and is shown by the white portion of each replica. Each example of the second sub-replica type 708 is a replica of the second sub-hologram 606 and is shown by the solid / dark portions of each replica. The light of each sub-replica type 706, 708 is guided separately within the waveguide 700, following the same pattern for each sub-replica type, but the wavefronts of the two corresponding types are spatially offset from each other. As a result, on the second surface 704 of waveguide 700, the bounce point of the light of the first sub-replica type 706, and the position from which the light of the first (sub)hologram will be emitted from waveguide 700, are offset from and alternate with the bounce point of the light of the second sub-replica type 708. Therefore, the two types of sub-replicas 706, 708 create corresponding light cones that spatially alternate with each other downstream of waveguide 700. An example of the first sub-replica type 706 is spatially separated from other examples of the first sub-replica type at least by an example of the second sub-replica type 708 (e.g., ...). Figure 6B (As shown). This reduces the likelihood of two light cones of the same (sub) type overlapping each other, while still allowing two light cones of different (sub) types to overlap each other at the aperture of the observation system located downstream of the waveguide, especially at relatively short observation distances. Therefore, the observer may receive light from both sub-holograms and thus receive enough light to form / see the entire target image, but is less likely to receive more than one instance of light from a single sub-hologram, thus reducing the risk of forming ghosting images.

[0150] It should be noted that, in Figure 7 In this embodiment, the wavefront enters the waveguide 700 through the first surface 702, but this is only illustrative. In other embodiments, the wavefront may instead enter the waveguide 700 through the second transmission-reflection surface 704.

[0151] Therefore, the inventors have recognized that if two (sub)holograms displayed substantially simultaneously on a display device correspond to two different corresponding portions of a common (i.e., identical) target image, and if they are displayed on corresponding consecutive groups of display pixels of the display device, and illuminated such that the light from the first (sub)hologram alternates and overlaps with the light from a different second (sub)hologram in angular space, the occurrence of ghosting images in the image seen by the observer can be reduced, or even eliminated in at least some arrangements, without forming dark bands, when the waveguide is located between the display device and the observer. This is especially true when the physical size of the display device displaying the holograms is similar to or smaller than the aperture through which the image is seen (e.g., similar in size to the human eye) and / or when the image is a near-field image. As the inventors have recognized, this is because, for any given position of the aperture within the eyebox (e.g., the observer's eye), it is impossible (or at least unlikely) for two light samples of the same hologram to enter the aperture simultaneously. In other words, the first sample of light from the first (sub)hologram is too far from the next nearest sample of light from that first hologram, such that two samples of that first light cannot enter the aperture simultaneously.

[0152] Note that the two sub-holograms are relative to each other. Figure 6B and 7 Describing them as "side by side" indicates that they are directly adjacent to each other. This is not mandatory. In some cases, there may be separation or gaps between holograms when displayed on a display device. Furthermore, they may not each have the same number of holographic pixels. They may not each occupy the same number of display pixels on the display device. Two sub-holograms may not correspond to equal-sized sub-parts of the target image. On the image plane, two sub-parts of the image can be directly adjacent / adjacent to each other, or there may be gaps between them. As mentioned above, corresponding to more than two corresponding image sub-parts, two or more holograms can be displayed substantially simultaneously.

[0153] Figure 8 An example of a simple image—comprising a "circle" and a "star"—is shown to the observer without ghosting, using the above example. Figure 6B and 7 The holographic projection system shown and described herein is for illustrative purposes only. Figure 8 A simple image with only two distinct components was chosen. In fact, the method described herein can be used for more complex images, including (but not limited to) images in which two image sub-parts corresponding to the first and second sub-holograms, respectively, are directly adjacent to and adjacent to each other on the image plane to form a continuous image. Furthermore, as will be further described below, according to the method described herein, at a given time, more than two image sub-parts can be displayed on a display device, and therefore more than two corresponding sub-holograms can be displayed.

[0154] Figure 8 An image 800 as seen by an observer's eye 804 is shown, the eye including a pupil 806 (i.e., aperture 806), a lens 808, and a retina 810 (i.e., image plane). In this example, the image seen is a virtual image—that is, it is perceived by the observer as being upstream of the display device, but this disclosure applies to both real and virtual images. Figure 8 The system is configured for direct-view holography, wherein holographically encoded light is directed to eye 804 so that an image is formed by the observer. However, this disclosure is also applicable to indirect-view holography, wherein holographically encoded light is converted to form an image upstream of the observer in free space or on a surface such as a screen or diffuser, and the light of that image is transmitted to the observer.

[0155] exist Figure 8 In the middle, two sub-holograms are displayed on a display device such as LCoS, which is not in Figure 8 It is shown in the image, but configured to display two sub-holograms, such as when combined. Figure 6B and 7 The first sub-hologram corresponds to the "circle" image content, and the second sub-hologram corresponds to the "star" image content. Although not shown, the display device is located... Figure 8 The system includes multiple copies (801a, 802a, 801b) in the vicinity. A waveguide (not shown) is also present in the system, located between the display device and the observer, and arranged to generate multiple copies, as described herein.

[0156] Figure 8 The three copies shown are formed by a display device via a waveguide and corresponding image content 812a, 814a, 812b. If an observer receives light from each of the three corresponding copies 801a, 802a, 801b, the observer will see these image contents. Figure 8 Only three copy examples are shown, but there are usually more in reality.

[0157] The first replica 801a is a light replica of the first sub-hologram on a display device (not shown). Therefore, if an observer receives light from the first replica 801a, the light from the first replica 801a will cause the observer to see image content 812a including a circle. The third replica 801b is also a replica of the first sub-hologram on the display device, so if an observer receives light from the third replica 801b, the observer will see image content 812b including a circle. Conversely, the second replica 802a is a replica of the second sub-hologram on the display device (not shown). Therefore, if an observer receives light from the second replica 802a, the light from the second replica 802a will cause the observer to see image content 814a including a star.

[0158] Figure 8 The arrangement is configured such that, in the plane where aperture 806 is located, the light cone of the second replica 802a overlaps in angular space with the corresponding light cones of each of the first replica 801a and the third replica 801b. However, the light cones of the first replica 801a and the third replica 801b do not overlap with each other. As a result, the observer will not receive more than one example of any part of the image content simultaneously. Instead, if the eye is located within the eyebox, for example, at the position of eye 804 shown, the observer receives one light example corresponding to the circular image content and one light example corresponding to the star image content. Therefore, the observer will see the entire image they want to observe—i.e., a circle and a star side by side—without any duplication of the image content, and thus no ghosting of any part of the image content. Furthermore, the eye can be moved laterally to multiple different positions within the eyebox, at least along the plane where aperture 806 is located, and still receive two sets of image content without any overlap, as from Figure 8 This is understandable.

[0159] Note that, for the sake of simplicity, Figure 8 A single eye is shown. However, the concepts described herein, including the calculation of sub-holograms as further described below, can be extended to cases with multiple apertures, most commonly, but not limited to, cases where light is received by both of the observer's eyes.

[0160] Although the examples described so far in this disclosure include two sub-holograms that are substantially simultaneously displayed on a display device, the concepts described herein can be extended to more than two sub-holograms, such as (but not limited to) three, four, or more sub-holograms that are substantially simultaneously displayed on a display device. Regardless of the number of sub-holograms used, they can be configured such that the corresponding holographic reconstructions (i.e., sub-images) combine to form a single target image, which is observed by an observer without (or with fewer) conventionally seen ghost images.

[0161] exist Figure 6C In the example shown, four sub-holograms—the first sub-hologram 616 represented by a white rectangle, the second sub-hologram 610 by dots, the third sub-hologram 612 by thin downward-sloping lines from left to right, and the fourth sub-hologram 614 by thick upward-sloping lines from left to right—are displayed substantially simultaneously on the display device. The display device has been replicated by a waveguide to form an extended modulator 624, the type of which is... Figure 6A and 6BSimilar to that shown. Again, it has 16 copies, this is merely for illustration, and this disclosure is not limited to this numerical example. Four sub-holograms 616, 610, 612, and 614 each occupy one-quarter of the display device and are arranged in a grid, each sub-hologram occupying a corresponding corner of the display device and adjacent to a corresponding other sub-hologram in each of the two dimensions, with all four sub-holograms meeting at the midpoint of the display device. Each sub-hologram corresponds to a corresponding quarter of the target image. That is; the first sub-hologram 616 corresponds to the first quarter of the target image, the second sub-hologram 610 corresponds to the second quarter of the target image, and so on.

[0162] The extended modulator 604 includes replicas of the light from the entire display device in each of the two dimensions. Therefore, for each sub-hologram 616, 610, 612, 614, in each of the two dimensions of the display device 6161, the corresponding examples of light from that sub-hologram within the extended modulator 624 are not adjacent to each other, but are separated from each other by examples of light from the corresponding other sub-hologram. The sub-holograms 616, 610, 612, 614 are configured for a specific holographic projection system including waveguides or other replicas, and for a predetermined observer / aperture position, such that the light cone of each of the four different sub-holograms 616, 610, 612, 614 will enter the observer's eye to provide all the light for the desired image content. However, for this predetermined observer / aperture position, two or more replicas of the light from the same sub-hologram should not enter the observer's eye simultaneously. Therefore, the observer will be able to see the entire image without ghosting. Note that the light cones of two or more replicas of the same sub-hologram may overlap at another point in space outside the eyebox (i.e., away from the intended observer's eye position). From the observer's perspective, this overlap does not produce a ghosting image because the observer's eye does not receive more than one example of each light cone from each of the corresponding sub-holograms.

[0163] The display device, which is replicated to form an extended modulator as described herein, can be configured to display a single hologram or any number of holograms or subholograms at a given corresponding time. The number of holograms or subholograms it displays can vary dynamically, for example, between directly consecutive image frames. In at least some arrangements, the display of multiple subholograms can be combined with tiling of at least one of these subholograms. Furthermore, one or more subholograms can be displayed together with another diffraction structure, such as a grating or a soft lens.

[0164] For a given image projection system, a (sub)hologram can be computed for the target image, where variables such as (but not limited to) waveguide configuration, display device type, size, and shape, and observer / aperture position are known. This can be accomplished using any suitable hologram computation method, employing any suitable controller or processor (which may be referred to as a "hologram engine"). For example, a Gerchberg-Saxton type method, a point cloud type method, or any other suitable hologram computation technique can be used to compute the sub-hologram. Such methods can be executed quickly and efficiently, allowing them to be rapidly and continuously repeated for different target images and / or for different corresponding observer positions and eyebox sizes / positions. For example, the Gerchberg-Saxton Fidoc method can be used, which is fast and efficient while still maintaining good image quality.

[0165] As described above, each sub-hologram can be configured to produce a unique corresponding sub-image (or sub-target), which is a sub-part of the entire target image. The corresponding sub-images can be directly adjacent to each other to form continuous image content, or the sub-images can be spaced apart from at least some of the corresponding other sub-images on the image plane. The position (or center point) of each sub-image on the image plane will (typically) differ from the position / center point of each of the corresponding other sub-images. The method may include calibration of the angular content of each sub-image, where such calibration should be repeated for different corresponding eyebox locations. However, calibration can be implemented at a high level, which will account for various possible systematic errors, such as waveguide misalignment, such that only one calibration is needed for each imaging system and for each corresponding eyebox location.

[0166] It should be understood that each sub-hologram displayed only on some display pixels of a display device has fewer hologram pixels than a single “complete” hologram that can be displayed on all display pixels. Therefore, theoretically, sub-holograms can be expected to produce lower-resolution sub-images compared to the resolution of an image formed from a single complete hologram. However, the inventors have discovered that, in practice, as described herein, dividing a hologram into multiple sub-holograms, such as, but not limited to, 2, 3, or 4 sub-holograms, does not significantly sacrifice image quality. Therefore, this approach is entirely advantageous because it successfully reduces and often eliminates the presence of ghosting images while still producing high-quality images. Consequently, the observer can see the image more clearly, thus making it safer than using conventional methods. This is achieved in a compact and computationally inexpensive manner, which can be implemented in both new and existing image projection systems. The method described herein can be executed quickly, allowing the target image to be changed and those different corresponding target images to be displayed sequentially without causing the observer to experience lag or delay.

[0167] Additional features

[0168] 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.

[0169] 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).

[0170] 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 holographic projector, comprising: Display devices arranged to form holographic wavefronts by spatially modulating light according to holograms displayed thereon; A waveguide having: an input arranged to receive a holographic wavefront; and a first surface and a second surface arranged therebetween to guide the holographic wavefront, wherein the first surface is partially reflective-transmissive, such that multiple copies of the holographic wavefront are emitted therefrom. The hologram is smaller than the size of the entrance pupil of the observation system used to receive the holographic wavefront from the first surface of the waveguide, and the hologram includes a first sub-hologram of the first region of the image adjacent to a second sub-hologram of the second region of the image. The holographic wavefront formed by the display device includes a first holographic wavefront formed by the first sub-hologram, and different second holographic wavefronts formed by the second sub-hologram. The waveguide is configured to form an extended modulator, the extended modulator including a plurality of replicas of a holographic wavefront formed by the display device, the plurality of replicas being arranged in an array, wherein the array includes at least one replica of the first holographic wavefront alternating with at least one replica of the second holographic wavefront.

2. The holographic projector as described in claim 1, wherein, The hologram also includes a third sub-hologram of a third region of the image, adjacent to at least one of the first or second sub-holograms.

3. The holographic projector of claim 2, wherein the hologram further includes a fourth sub-hologram of a fourth region of the image, adjacent to at least one of the first, second, or third sub-holograms.

4. The holographic projector as described in any one of claims 1-3, wherein, The first and second regions of the image are adjacent to each other to form a substantially continuous image on the image plane.

5. The holographic projector as described in any one of claims 1-3, wherein, The hologram is configured such that when the display device displaying the hologram is illuminated, light spatially modulated by each sub-hologram will enter the entrance pupil of the observation system substantially simultaneously.

6. The holographic projector as described in any one of claims 1-3, further comprising: An illumination system, arranged to illuminate a hologram displayed on the display device, to form a holographic wavefront.

7. The holographic projector as described in any one of claims 1-3, wherein, The size of the entrance pupil does not exceed 15mm.

8. The holographic projector as described in any one of claims 1-3, wherein, The size of the entrance pupil does not exceed 12mm.

9. The holographic projector as described in any one of claims 1-3, wherein, The size of the entrance pupil does not exceed 10mm.

10. The holographic projector as described in any one of claims 1-3, wherein, An image is formed at a non-infinite image distance from the display device.

11. A method for calculating a hologram of a holographic projection system, the holographic projection system comprising a display device configured to display a hologram and output a holographic wavefront when illuminated, and a waveguide arranged to receive and transmit a plurality of replicas of the holographic wavefront, the method comprising: Obtain the target image from which a hologram will be generated; The target image is segmented into a first image region and a second image region; as well as Generate a first sub-hologram corresponding to the first image region and a second sub-hologram corresponding to the second image region. The holographic wavefront output by the display device includes a first holographic wavefront formed by the first sub-hologram, and different second holographic wavefronts formed by the second sub-hologram. The waveguide is configured to form an extended modulator, the extended modulator including a plurality of replicas of a holographic wavefront output by the display device, the plurality of replicas being arranged in an array, wherein the array includes at least one replica of the first holographic wavefront alternating with at least one replica of the second holographic wavefront.

12. A holographic projection method, comprising: Displaying a hologram on a display device, the hologram including a first sub-hologram of a first region of an image adjacent to a second sub-hologram of a second region of an image; Illuminate the displayed hologram to form a holographic wavefront; Guiding the holographic wavefront through the waveguide; The waveguide includes an arrangement to receive an input to a holographic wavefront; and first and second surfaces arranged therebetween to guide the holographic wavefront, wherein the first surface is partially reflective-transmissive, such that multiple copies of the holographic wavefront are emitted therefrom. The size of the hologram is smaller than the size of the entrance pupil of the observation system used to receive the holographic wavefront from the first surface of the waveguide. The holographic wavefront formed by the display device includes a first holographic wavefront formed by the first sub-hologram, and different second holographic wavefronts formed by the second sub-hologram. The waveguide is configured to form an extended modulator, the extended modulator including a plurality of replicas of a holographic wavefront formed by the display device, the plurality of replicas being arranged in an array, wherein the array includes at least one replica of the first holographic wavefront alternating with at least one replica of the second holographic wavefront.

13. The method of claim 12, comprising calculating a sub-hologram for observing an image through the observation system as an initial step.

14. The method of claim 12 or 13, wherein, The method is implemented in at least part of a computer.

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