Projection Component

Abstract

A projection assembly (600) is described. The projection assembly (600) includes a first holographic projection channel (602) configured to output a first holographic light field (603). The projection assembly (600) also includes a second holographic projection channel (604) configured to output a second holographic light field (605). The first holographic projection channel (602) and the second holographic projection channel (604) are arranged such that the first holographic light field (603) and the second holographic light field (605) are adjacent to each other to form a continuous field of view.

Description

Technical Field

[0001] The present disclosure relates to a light engine, such as a holographic light engine. The present disclosure also relates to a holographic projector and projection assembly for outputting a holographic light field. More specifically, the present disclosure relates to a compact holographic projector with a large field of view. Some embodiments relate to an image generation unit or hologram generation unit for a head-up display. Other embodiments relate to a head-up display for a vehicle. Background Art

[0002] Light scattered from an object contains both amplitude and phase information. This amplitude and phase information can be captured, for example, on a photographic plate using well-known interference techniques to form a holographic recording or "hologram" consisting of interference fringes. The hologram can be reconstructed by illuminating it with appropriate light to form a two- 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 computed using techniques based on mathematical transformations such as the Fresnel or Fourier transforms. These types of holograms are referred to as Fresnel / Fourier transform holograms or simply Fresnel / Fourier holograms. Fourier holograms can be considered either Fourier domain / planar representations of an object or frequency domain / planar representations of an object. Computer-generated holograms can also be computed, for example, using coherent ray tracing or point cloud techniques.

[0004] The computer generated hologram may be encoded on a spatial light modulator (SLM) arranged to modulate the amplitude and / or phase of the incident light. For example, light modulation may be achieved using electrically addressable liquid crystals, optically addressable liquid crystals, or micromirrors.

[0005] A spatial light modulator typically comprises a plurality of individually addressable pixels, which may also be referred to as cells or elements. The light modulation scheme may be binary, multi-level, or continuous. Alternatively, the device may be continuous (i.e., comprise no pixels), so that the light modulation may be continuous across the device. A spatial light modulator may be reflective, meaning that the light is modulated to reflect the output. A spatial light modulator may also be transmissive, meaning that the light is modulated to transmit the output.

[0006] The system described here can be used to provide a holographic projector, which is already used in head-up displays (HUDs). Summary of the Invention

[0007] Various aspects of the disclosure are defined in the accompanying independent claims.

[0008] In a first aspect, a projection assembly is provided. The projection assembly includes a first holographic projection channel configured to form a first holographic light field from a first hologram of a first image, and a second holographic projection channel configured to form a second holographic light field from a second hologram of a second image. Each hologram is configured to form a holographic light field, for example, when illuminated by a respective light source, in which the content (e.g., spatial content) of the corresponding image in a first dimension is encoded by angle (in the hologram domain), such that each angular channel of holographic light corresponds to a respective slice of the corresponding image in the first dimension. The projection assembly is further arranged to combine a first plurality of angular channels of the first holographic projection channel with a second plurality of angular channels of the second holographic projection channel in the first dimension. This combination allows an observer to receive the first and second holographic light fields, thereby forming an extended image that includes the first image adjacent to the second image. The first and second holographic light fields can be said to be co-receivable (by an observer). The term "co-receivable" as used herein means, for example, received together substantially simultaneously. The extended image can include the first image positioned adjacent to and contiguous with the second image. When an observer positioned at the eyebox receives the first and second holographic light fields, the observer sees an extended image formed by the first and second holographic light fields. It can be said that the first and second holographic light fields can be converted into an extended image to reflect the observer or the observation system (more specifically, its lens) converting the holographic light field or wavefront from the holographic domain into a meaningful image in the spatial domain. The extended image includes the first image adjacent to and contiguous with the second image. It can also be said that the first and second images are merged. Advantageously, the projection assembly has an increased angular range / field of view.

[0009] A first holographic projection channel may include a first display device configured to display a first hologram corresponding to a first image. When the first display device is illuminated by first light, the first light is spatially modulated according to the displayed first hologram, so that the first holographic projection channel outputs a first holographic light field. The first holographic light field may encode the first image. A second holographic projection channel may include a second display device configured to display a second hologram corresponding to a second image. When the second display device is illuminated by second light, the second light is spatially modulated according to the displayed second hologram, so that the second holographic projection channel outputs a second holographic light field. The second holographic light field may encode the second image. The first and second display devices may be tilted relative to each other such that a first propagation direction of the first holographic light field deviates from a second propagation direction of the second holographic light field. The first and second display devices may be tilted relative to each other at an angle substantially equal to the sum of the diffraction angles of the adjacent first and second holographic light fields. The tilt may be a rotation about a second dimension (e.g., a y-axis) perpendicular to the first dimension (e.g., an x-axis) such that the first and second holographic light fields are adjacent in the first dimension. For example, the first display device and the second display device are tilted relative to each other in a plane defined by the x-axis and the z-axis such that the first and second holographic light fields abut along the x-axis.

[0010] The angular field of view of the projection system in a first principal dimension may be equal to the sum of the angular field of view of the first holographic light field in the first principal dimension and the angular field of view of the second holographic light field in the first principal dimension. The angular field of view of the projection assembly in the second dimension may be substantially equal to the angular field of view of the first holographic light field in the second dimension and / or the angular field of view of the second holographic light field in the second dimension. The second dimension may be perpendicular to the first dimension. The angular field of view of the first holographic light field and the angular field of view of the second holographic light field may be the same or different. The angular field of view of the projection system may be considered to be the angular field of view of the adjacent first and second holographic light fields. The first holographic light field may have a first field of view. The second holographic light field may have a second field of view. The adjacent first and second holographic light fields may have a third field of view. The third angular field of view in the first dimension may be substantially equal to the sum of the first and second angular fields of view in the first dimension. The third field of view in the second dimension may be substantially equal to the first field of view in the second dimension and / or the second field of view in the second dimension. The second dimension may be perpendicular to the first dimension.

[0011] The first holographic projection channel can include a first light source for forming a first holographic light field by illuminating a first hologram. The second holographic projection channel can include a second light source for forming a second holographic light field by illuminating a second hologram. The first light source can be different from the second light source. Advantageously, if two different light sources are used, there is little or no coherent interference between the two holographic light fields, even if they have similar specifications.

[0012] The projection assembly can be arranged to form two or more multiplexed channels. Each multiplexed channel can include a portion of the first holographic light field adjacent to a portion of the second holographic light field. Advantageously, each multiplexed channel can serve as an input to a corresponding waveguide or pupil expander. The multiplexed channels can be substantially parallel to each other. The multiplexed channels can be spatially offset from each other in two perpendicular directions. The two perpendicular directions can be first and second dimensions. The projection assembly can also include a plurality of waveguides. Each waveguide can be arranged to receive a corresponding one of the multiplexed channels. A first waveguide in the plurality of waveguides can be configured to replicate the light field in a first direction. The first direction can be a first dimension. A second waveguide in the plurality of waveguides can be configured to replicate the light field in a second direction opposite the first direction. The second direction can be in the first dimension.

[0013] The projection assembly may further include a beam combiner configured to receive the first holographic light field and the second holographic light field and output two multiplexed channels. The beam combiner may include a beam splitter arranged to receive the first holographic light field on a first side thereof and the second holographic light field on a second side thereof. The beam splitter may include a transmissive-reflective element arranged to transmit a first portion of light incident thereon and reflect a second portion of light incident thereon. The beam splitter may be configured to: split the first holographic light field into a first transmitted light field and a first reflected light field; split the second holographic light field into a second transmitted light field and a second reflected light field; merge or combine the first transmitted light field with the second reflected light field to form a first multiplexed channel of the two or more multiplexed channels; and merge or combine the first reflected light field with the second transmitted light field to form a second multiplexed channel of the two or more multiplexed channels. The first and second multiplexed channels may be identical to each other. The path propagated by the first transmitted light field can be the same as the path propagated by the second reflected light field, thereby forming one of the multiplexed channels, and / or the path propagated by the first reflected light field can be the same as the path propagated by the second transmitted light field. Advantageously, the use of a beam splitter helps to reduce or eliminate light losses in the projection system. This is because both multiplexed channels are used as inputs to the corresponding waveguides. Another advantage is that seamless merging of the first and second holographic light fields is often achievable. This is due to the use of continuous components (i.e., the reflective and transmissive elements in the beam splitter), which helps to avoid the formation of discontinuities in the image that may occur if sharp-edged mirrors are used to combine the light fields. For dual-rod pupil expanders, the beam splitter tends to achieve seamless merging of the light fields from the two display devices (for angular range expansion) with high efficiency.

[0014] The first and second holographic projection channels can each include a corresponding optical repeater configured to form an intermediate image of the corresponding holographic light field. Each optical repeater can change the diffraction angle of the corresponding holographic light field. Using the optical repeater to reduce the holographic light field before the adjacent holographic light field means that a high field of view (FOV) is preferably achieved without any ghost images. Each intermediate image of the corresponding holographic light field can have a size greater than 5 mm, for example, greater than 7 mm or 10 mm.

[0015] In another aspect, a projection assembly is provided, comprising a first holographic projection channel configured to output a first holographic light field and a second holographic projection channel configured to output a second holographic light field. The first holographic projection channel and the second holographic projection channel are arranged such that the first holographic light field and the second holographic light field are adjacent to each other to form a continuous field of view. The combination of the adjacent first and second holographic light fields can be considered a third holographic light field.

[0016] In this disclosure, the term "replica" is used with respect to waveguides, such as waveguide pupil expanders, to reflect that spatially modulated light is split, such that the composite light field is directed along multiple distinct optical paths. The term "replica" is used to refer to each occurrence or instance of the composite light field following a replication event—such as the partial reflection-transmission of a pupil expander. Each replica propagates along a different optical path. Some embodiments of the present disclosure relate to the propagation of light encoded with 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 the hologram are formed. Those skilled in the art of holography will understand that the composite light field associated with the propagation of light encoded with a hologram will vary with propagation distance. The term "replica" as used herein is independent of propagation distance, so two light branches or paths associated with a replication 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 replication event or series of replication events.

[0017] According to the present disclosure, a "diffraction light field" is a light field formed by diffraction. The diffraction light field can be formed by illuminating a corresponding diffraction pattern. According to the present disclosure, an example of a diffraction pattern is a hologram, and an example of a diffraction light field is a holographic light field or a light field of a holographic reconstruction that forms an image. The holographic light field forms a (holographic) reconstruction of an image on a playback plane. The holographic light field that propagates from the hologram to the reproduction plane can be said to include light encoded with the hologram or light in the holographic domain. The diffraction light field is characterized by a diffraction angle determined by the minimum characteristic size of the diffraction structure and the wavelength of the light (of the diffraction light field). According to the present disclosure, it can also be said that the "diffraction light field" is a reconstructed light field formed on a plane that is spatially separated from the corresponding diffraction structure. Disclosed herein is an optical system for propagating a diffraction light field from a diffraction structure to an observer. The diffraction light field can form an image.

[0018] The term "hologram" is used to refer to a record that contains amplitude information or phase information, or some combination thereof, about an object. 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 is spatially separated from the hologram. The term "replay field" is used to refer to the 2D region within which the holographic reconstruction is formed and is perfectly focused. If the hologram is displayed on a spatial light modulator comprising pixels, the replay field will be repeated in the form of multiple diffraction orders, where each diffraction order is a replica of the zeroth order replay field. The zeroth order replay field typically corresponds to the preferred or primary replay field because it is the brightest replay field. Unless otherwise explicitly stated, the term "replay field" should be taken to refer to the zeroth order replay field. The term "replay plane" is used to refer to the plane in space that contains all replay fields. The terms "image," "replay image," and "image area" refer to the area of ​​the replay field that is illuminated by the light of the holographic reconstruction. In some embodiments, an "image" may comprise discrete points, which may be referred to as "image points," or, for convenience only, as "image pixels."

[0019] The terms "encoding," "writing," and "addressing" are used to describe the process of providing a plurality of control values, each of which determines the modulation level of each pixel, to a plurality of pixels of the SLM. It can be said that the pixels of the SLM are configured to "display" a light modulation profile in response to receiving the plurality of control values. Thus, the SLM can be said to "display" a hologram, and a hologram can be considered an array of light modulation values ​​or levels.

[0020] It has been found that holographic reconstructions of acceptable quality can be formed from "holograms" that contain only phase information related to the Fourier transform of the original object. Such holographic recordings can be referred to as pure phase holograms. The embodiments relate to pure phase holograms, but the present disclosure is equally applicable to pure amplitude holography.

[0021] The term "eye box" or "eye box" is a well-known term in the art and is generally defined as the region or volume of space (remote from a display device) within which a visible image formed by a display system is visible or viewable to a viewing system or observer. The visible image may be a virtual image.

[0022] The "field of view" of a display system can be considered to be the size or extent of the image formed by the display system as seen by a viewing system or observer located within the eyebox of the display system. The size of the image is typically defined in angular space by the angular extent of the image as seen by an observer from the eyebox. The angular extent can be defined relative to a central axis, such as the projection axis. The field of view can be defined in two perpendicular directions. For example, the horizontal angular field of view can be -10 degrees to +10 degrees, and the vertical angular field of view can be -5 degrees to +5 degrees. In some embodiments, the field of view is defined from the center of the eyebox. In some embodiments, the field of view is substantially the same from all positions within the eyebox.

[0023] The present disclosure is also applicable to forming a holographic reconstruction 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 full complex hologram that contains amplitude and phase information related to the original object. Because the value (gray level) assigned to each pixel of the hologram has both amplitude and phase components, such a hologram can be referred to as a full complex hologram. The value (gray level) assigned to each pixel can be represented as a complex number having both amplitude and phase components. In some embodiments, a full complex computer-generated hologram is calculated.

[0024] Reference may be made to the phase value, phase component, phase information, or simply phase of a pixel of a computer-generated hologram or spatial light modulator as shorthand for "phase delay". That is, any phase value described is actually a number (e.g., in the range of 0 to 2π) that represents the amount of phase delay provided by that pixel. For example, a pixel of a spatial light modulator described as having a phase value of π / 2 will delay the phase of received light by π / 2 radians. In some embodiments, each pixel of the spatial light modulator can operate at one of a plurality of possible modulation values ​​(e.g., phase delay values). The term "grayscale" may be used to refer to a plurality of available modulation levels. For example, the term "grayscale" may be used for convenience to refer to a plurality of available phase levels in a pure phase modulator, even though the different phase levels do not provide different shades of gray. The term "grayscale" may also be used for convenience to refer to a plurality of available complex modulation levels in a complex modulator.

[0025] Thus, a hologram comprises an array of gray levels, i.e. an array of light modulation values, such as phase delay values ​​or an array of complex modulation values. A hologram is also considered a diffraction pattern, since it is a pattern that causes diffraction when displayed on a spatial light modulator and illuminated with light of a wavelength relative to (usually less than) the pixel pitch of the spatial light modulator. Reference is made herein to combining a hologram with other diffraction patterns, such as diffraction patterns used as lenses or gratings. For example, a diffraction pattern used as a grating can be combined with a hologram to shift the replay field on the replay plane, or a diffraction pattern used as a lens can be combined with a hologram to focus the holographic reconstruction on the replay plane in the near field.

[0026] 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 permutations of the features disclosed in this disclosure are contemplated. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Specific embodiments are described by way of example only with reference to the following drawings:

[0028] Figure 1 is a schematic diagram showing a reflective SLM producing a holographic reconstruction on a screen;

[0029] Figure 2 An image for projection is shown, comprising eight image regions / components V1 to V8, and corresponding cross sections of hologram channels H1-H8;

[0030] Figure 3 shows a hologram displayed on an LCOS that directs light to multiple discrete areas;

[0031] Figure 4 Shown includes display such as Figure 2 and 3 A system for displaying a computer generated hologram;

[0032] Figure 5 shows a perspective view of a first example two-dimensional pupil expander comprising two replicators;

[0033] Figure 6 shows a schematic diagram of the projection assembly (not to scale);

[0034] Figure 7A A schematic diagram (not to scale) showing a first light beam from a first display device forming an image on the first display device;

[0035] Figure 7B a schematic diagram (not to scale) showing a second light beam from a second display device forming an image of the second display device;

[0036] Figure 7C a schematic diagram (not to scale) showing the superposition of images of a first and a second display device;

[0037] Figure 8A a schematic diagram (not to scale) showing a first side view of the first and second outputs;

[0038] Figure 8B a schematic diagram (not to scale) showing a second side view opposite the first side view of the first and second outputs;

[0039] Figure 9A shows a schematic diagram of a beam combiner (not to scale);

[0040] Figure 9B shows a schematic diagram (not to scale) of a beam combiner with a first holographic light field propagating therethrough; and

[0041] Figure 9C A schematic diagram (not to scale) of a beam combiner is shown having a second holographic light field propagating therethrough.

[0042] The same reference numbers will be used throughout the drawings to refer to the same or like parts. DETAILED DESCRIPTION

[0043] The present invention is not limited to the embodiments described below, but extends to the full scope of the appended claims. That is, the present invention can be embodied in different forms and should not be construed as limited to the described embodiments, which are set forth for illustrative purposes.

[0044] Unless otherwise stated, terms in the singular may include plural forms.

[0045] A structure described as being formed on / under or above / below another structure should be construed to include a case where the structures are in contact with each other and, further, a case where a third structure is provided therebetween.

[0046] When describing a temporal relationship, for example, when the temporal order of events is described as "after," "followed," "next," "before," etc., the present disclosure should be considered to include both consecutive and non-consecutive events unless otherwise specified. For example, unless terms such as "just," "immediately," or "directly" are used, the description should be considered to include non-consecutive situations.

[0047] 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 only used to distinguish between the various elements. For example, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element without departing from the scope of the appended claims.

[0048] The features of different embodiments may be coupled or combined with each other in part or in whole, and may interoperate with each other in different ways. Some embodiments may be performed independently of each other, or may be performed together in a mutually dependent relationship.

[0049] In the present disclosure, the term “substantially” when applied to a structural unit of a device may be interpreted as technical features of the structural unit being produced within the technical tolerances of the method for manufacturing it.

[0050] Traditional optical configuration for holographic projection

[0051] Figure 1 An embodiment is shown in which a computer-generated hologram is encoded on a single spatial light modulator. The computer-generated hologram is a Fourier transform of the object being reconstructed. Thus, the hologram can be said to be a Fourier, frequency, 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 a replay field, such as a light-receiving surface like a screen or diffuser.

[0052] A light source 110, such as a laser or laser diode, is arranged to illuminate the SLM 140 via a collimating lens 111. The collimating lens causes a substantially planar wavefront of light to be incident on the SLM. Figure 1 In embodiments, the direction of the wavefront is off-normal (e.g., two or three degrees from a plane that is truly normal to the transparent layer). However, in other embodiments, a substantially planar wavefront is provided at normal incidence, and a beam splitter arrangement is used to separate the input and output optical paths. Figure 1 In the embodiment shown, the arrangement is such that light from the light source reflects from the mirrored back surface of the SLM and interacts with the light modulating layer to form an exit wavefront 112. The exit wavefront 112 is applied to an optical device including a Fourier transform lens 120, the focus of which is located at a screen 125. More specifically, the Fourier transform lens 120 receives the modulated light beam from the SLM 140 and performs a frequency-to-space transform to produce a holographic reconstruction at the screen 125.

[0053] It's important to note that in this type of hologram, every pixel of the hologram contributes to the entire reconstruction. There is no one-to-one correlation between a specific point on the replay field (or image pixel) and a specific light modulation element (or hologram pixel). In other words, the modulated light leaving the light modulation layer is distributed across the entire replay field.

[0054] In these embodiments, the position of the holographic reconstruction in space is determined by the power (focus) 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 optically performs the Fourier transform. Any lens can function 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 to use lenses to perform an optical Fourier transform. In some embodiments of the present disclosure, the lens of the observer's eye performs the conversion of the hologram into an image.

[0055] Hologram computing

[0056] In some embodiments, the computer-generated hologram is a Fourier transform hologram, or simply a Fourier hologram or a Fourier-based hologram, where the image is reconstructed in the far field by exploiting the Fourier transform properties of a positive lens. The Fourier hologram is computed by Fourier transforming the desired light field in the replay plane back to the lens plane. The computer-generated Fourier hologram can be computed using the Fourier transform. By way of example only, embodiments relate to Fourier holography and Gerchberg-Saxton type algorithms. The present disclosure is equally applicable to Fresnel holography and Fresnel holograms that can be computed by similar methods. In some embodiments, the hologram is a phase or pure phase hologram. However, the present disclosure is also applicable to holograms computed by other techniques, such as techniques based on point cloud methods.

[0057] In some embodiments, the hologram engine is arranged to exclude from the hologram calculation the contribution of light blocked by the limiting aperture of the display system. UK patent application 2101666.2, filed on February 5, 2021, and incorporated herein by reference, discloses a first hologram calculation method in which eye tracking and ray tracing are used to identify sub-areas of a display device for calculating a point cloud hologram that eliminates ghost images. The sub-areas of the display device correspond to the aperture of the present disclosure and are used to exclude optical paths from the hologram calculation. UK patent application 2112213.0, filed on August 26, 2021, and incorporated herein by reference, discloses a second method based on a modified Gerchberg-Saxton type algorithm, which includes a step of performing light field clipping according to the pupil of the optical system during the hologram calculation. The clipping of the light field corresponds to the determination of the limiting aperture of the present disclosure. UK patent application GB2118911.3, filed on December 23, 2021 and also incorporated herein by reference, discloses a third method for computing a hologram, which includes the step of determining the area of ​​a so-called extended modulator formed by a hologram replicator. According to the present disclosure, the area of ​​the extended modulator is also the aperture.

[0058] In some embodiments, a real-time engine is provided that uses an algorithm to receive image data and calculate holograms in real time. In some embodiments, the image data is a video comprising a sequence of image frames. In other embodiments, the holograms are pre-calculated, stored in computer memory, and recalled as needed for display on the SLM. That is, in some embodiments, a repository of pre-determined holograms is provided.

[0059] Big eye box using small display device

[0060] In general, the present disclosure relates to image projection. It relates to methods of image projection and image projectors including a display device. The present 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. The present disclosure is equally applicable to monocular and binocular observation systems. The observation system may include one or more eyes of an observer. The observation system includes an optical element having optical power (e.g., the lens of a human eye) and an observation plane (e.g., the retina of a human eye). The projector may be referred to as a "light engine." The display device and the image formed (or perceived) using the display device are spatially separated from each other. The observer forms or perceives the image on 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 the image is projected or relayed to the observation plane. In these other examples, spatially modulated light of an intermediate holographic reconstruction formed in free space or on a screen or other light-receiving surface between the display device and the observer is transmitted to the observer. In both cases, the image is formed by illuminating a diffraction pattern (eg a hologram or kinoform) displayed on a display device.

[0061] A display device includes pixels. The pixels of the display can display a diffraction pattern or structure of diffracted light. The diffracted light can form an image on a plane spatially separated from the display device. According to well-known optical principles, the magnitude of the maximum diffraction angle is determined by the size of the pixel and other factors, such as the wavelength of the light.

[0062] In an embodiment, the display device is a spatial light modulator, such as a liquid crystal on silicon ("LCOS") spatial light modulator (SLM). Light is transmitted from the LCOS to a viewing entity / system, such as a camera or an eye, over a range of diffraction angles (e.g., from zero to a maximum diffraction angle). In some embodiments, amplification techniques can be used to increase the range of available diffraction angles beyond the conventional maximum diffraction angle of the LCOS.

[0063] In some embodiments, the hologram itself (the light thereof) is transmitted 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 with / by the hologram"—is transmitted 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. It is sometimes said that in these embodiments, the lens of the eye performs the conversion or transformation of the hologram into the image. The projection system or light engine can be configured so that the observer effectively looks directly into the display device.

[0064] The "light field" mentioned here is a "composite light field". The term "light field" simply means a light pattern with a finite size in at least two orthogonal spatial directions, such as x and y. The term "light field" simply means a light pattern with a finite size in at least two orthogonal spatial directions (x and y). The word "complex" used here simply means that the light at each point in the light field can be defined by an amplitude value and a phase value, and can therefore be represented by a complex number or a pair of values. For the purpose of hologram calculation, the composite light field can be a two-dimensional array of complex numbers, where the complex numbers define the intensity and phase of light at multiple discrete locations within the light field. Therefore, a "holographic light field" can be thought of as the light field used to form the final image seen by an observer.

[0065] According to well-known optical principles, the angular range of light propagating from a display device that 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 a viewing distance of 1 meter, only a small range of angles of light from an LCOS can propagate through the pupil of the eye to form an image on the retina at a given eye position. The angular range of light propagating from the display device that can successfully propagate through the pupil of the eye to form an image on the retina at a given eye position determines the portion of the image that is "visible" to the observer. In other words, not all portions of the image are visible from any one point on the viewing plane (e.g., any one eye position within a viewing window such as an eyebox).

[0066] In some embodiments, the image perceived by the observer is a virtual image that appears upstream from the display device—that is, the observer perceives the image as being farther away from them than the display device. Thus, conceptually, the observer can be thought of as viewing the virtual image through a "display-sized window," which can be very small, such as 1 cm in diameter, and at a relatively large distance, such as 1 meter. Furthermore, the user will be viewing the display-sized window through their eye's pupil, which can also be very small. Consequently, the field of view is reduced at any given time, and the specific angular range that can be seen is heavily dependent on eye position.

[0067] Pupil expanders address how to increase the angular range of light rays propagating from a display device so that they can successfully propagate through the pupil of the eye to form an image. Display devices are typically (relatively) small and have a (relatively) large projection distance. In some embodiments, the projection distance is at least an order of magnitude, for example, at least two orders of magnitude, greater than the diameter or width of the display device's entrance pupil and / or aperture (i.e., the size of the pixel array).

[0068] The use of a pupil expander laterally increases the viewing area (i.e., the user's eyebox), thereby allowing for some eye movement while still allowing the user to see the image. As will be appreciated by those skilled in the art, in an imaging system, the viewing area (i.e., the user's eyebox) is the area within which the viewer's eye can perceive the image. The present disclosure encompasses non-infinite virtual image distances—i.e., near-field virtual images.

[0069] Traditionally, a two-dimensional pupil expander comprises one or more one-dimensional optical waveguides, each formed using a pair of opposing reflective surfaces, where the output light from the surfaces forms an observation window or eyebox. Light received from a display device (e.g., spatially modulated light from an LCOS) is replicated by the or each waveguide to increase the field of view (or observation area) in at least one dimension. In particular, the waveguide enlarges the observation window by generating additional light rays or "replicas" by dividing the amplitude of the incident wavefront.

[0070] The display device can have an active or pixel display area having a first dimension of less than 10 centimeters, such as less than 5 centimeters or less than 2 centimeters. The propagation distance between the display device and the viewing system can be greater than 1 meter, such as greater than 1.5 meters or greater than 2 meters. The optical propagation distance within the waveguide can be up to 2 meters, such as up to 1.5 meters or up to 1 meter. The method can receive an image and determine a corresponding hologram of sufficient quality in less than 20 milliseconds, such as less than 15 milliseconds or less than 10 milliseconds.

[0071] In some embodiments described herein solely through examples of diffraction or holographic light fields, the hologram is configured to route light into multiple channels, each corresponding to a different portion (i.e., subregion) of the image. The channels formed by the diffraction structure are referred to herein as "hologram channels" simply to reflect that they are channels of light encoded by the hologram with image information. It can be said that the light of each channel is in the holographic domain, rather than in the image or spatial domain. In some embodiments, the hologram is a Fourier or Fourier transform hologram, so the hologram domain is the Fourier or 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 hologram channels to reflect that the image reconstructable from the hologram has a finite size and can be arbitrarily divided into multiple image subregions, where each hologram channel corresponds to each image subregion. Importantly, the hologram of this example is characterized by how it distributes the image content when illuminated. Specifically and uniquely, the hologram divides the image content by angle. That is, every point on the image is associated with a unique ray angle in the spatially modulated light formed by the hologram when illuminated - at least a unique pair of angles, because the hologram is two-dimensional. For the avoidance of doubt, this holographic behavior is not conventional. When illuminated, the spatially modulated light formed by this particular type of hologram can be separated into a plurality of hologram channels, where each hologram channel is defined by a range of ray angles (in two dimensions). It will be appreciated from the above that any hologram channel (i.e., a sub-range of ray angles) that can be considered in the spatially modulated light will be associated with a corresponding portion or sub-region of the image. That is, all of the information required to reconstruct that portion or sub-region of the image is contained within the sub-range of angles in 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.

[0072] Despite this, the hologram can still be recognized. For example, if only a continuous portion or subregion of the spatially modulated light formed by the hologram is reconstructed, only a subregion of the image should be visible. If a different continuous portion or subregion of the spatially modulated light is reconstructed, a different subregion of the image should be visible. Another identifying feature of this type of hologram is that the shape of the cross-section of any hologram channel substantially corresponds to (i.e., is substantially identical to) the shape of the entrance pupil, although the size may differ—at least at the correct plane from which the hologram was calculated. Each light / hologram channel propagates from the hologram at a different angle or range of angles. While these are example ways to characterize or identify this type of hologram, other approaches may also be used. In summary, the holograms disclosed herein are characterized and identified by how the image content is distributed within the light encoded by the hologram. Furthermore, for the avoidance of doubt, references herein to holograms configured to direct light or angularly divide an image into multiple hologram channels are by way of example only, and the present disclosure is equally applicable to any type of holographic light field or even any type of diffraction or pupil expansion of a diffracted light field.

[0073] The system can be provided in a compact and streamlined physical form. This makes the system suitable for a wide range of practical applications, including those where space is limited and asset value is high. For example, it can be implemented in a head-up display (HUD), such as a vehicle or automotive HUD.

[0074] According to the present disclosure, pupil expansion is provided for diffracted light, which can include a diverging bundle of light rays. The diffracted light field can be defined by a "light cone." Thus, the size of the diffracted light field (as defined in a two-dimensional plane) increases with propagation distance from the corresponding diffractive structure (i.e., the display device). The pupil expander can be said to replicate the hologram, or form at least one replica of the hologram, to convey that the light transmitted to the observer is spatially modulated according to the hologram.

[0075] In some embodiments, two one-dimensional waveguide pupil expanders are provided, each of which is arranged to effectively increase the size of the system's exit pupil by forming multiple copies or replicas of the spatial light modulator's exit pupil (or the light of the exit pupil). The exit pupil can be understood as the physical area from which the system outputs light. Alternatively, each waveguide pupil expander can be said to expand the size of the system's exit pupil. Alternatively, each waveguide pupil expander can be said to expand / increase the size of the eyebox within which an observer's eye can be positioned in order to see / receive the light output by the system.

[0076] Optical Channel

[0077] Holograms formed according to some embodiments angularly divide the image content to provide multiple hologram channels, which can have a cross-sectional shape defined by the aperture of the optical system. The hologram is calculated to provide this guidance of the diffracted light field. In some embodiments, this is achieved by taking into account the aperture (virtual or real) of the optical system during the hologram calculation, as described above.

[0078] Figure 2 and 3 An example of this type of hologram is shown, which may be used in conjunction with the pupil expander disclosed herein. However, this example should not be considered a limitation of the present disclosure.

[0079] Figure 2 An image 252 is shown for projection, comprising eight image regions / components V1 to V8. By way of example only, Figure 2 Eight image components are shown, and image 252 may be separated into any number of components. Figure 2 Also shown is a coded light pattern 254 (i.e., a hologram) that can reconstruct image 252—for example, when transformed by a lens of a suitable viewing system. The coded light pattern 454 includes first through eighth sub-holograms or components H1 through H8, corresponding to first through eighth image components / regions V1 through V8. Figure 2 It further shows how a hologram decomposes the image content by angle. Therefore, a hologram is characterized by its guidance of light. Figure 3 Specifically, the hologram in this example directs light into multiple discrete regions. In the example shown, the discrete regions are disks, but other shapes are also contemplated. After propagation through the waveguide, the optimal disk size and shape can be related to the size and shape of the optical system's aperture (e.g., the entrance pupil of the observation system).

[0080] Figure 4 A system 400 is shown, including a display such as Figure 2 and 3 A display device for a computed hologram is shown.

[0081] System 400 includes a display device that, in this arrangement, includes an LCOS 402. LCOS 402 is arranged to display a modulation pattern (or "diffraction pattern") comprising a hologram and projects holographically encoded light into an eye 405, which includes a pupil serving as an aperture 404, a lens 409, and a retina (not shown) serving as an observation plane. There is a light source (not shown) arranged to illuminate LCOS 402. The lens 409 of eye 405 performs the conversion of the hologram into an image. The light source can be of any suitable type. For example, it can include a laser source.

[0082] The viewing system 400 also includes a waveguide 408 located between the LCOS 402 and the eye 405. The presence of the waveguide 408 enables all angular content from the LCOS 402 to be received by the eye, even at the relatively large projection distance shown. This is because the waveguide 408 acts as a pupil expander in a well-known manner and will therefore only be briefly described here.

[0083] in short, Figure 4 The illustrated waveguide 408 comprises a generally elongated structure. In this example, waveguide 408 comprises an optical plate of refractive material, but other types of waveguides are well known and may be used. Waveguide 408 is positioned to intersect the light cone (i.e., the diffracted light field) projected from LCOS 402, for example, at an oblique angle. In this example, the size, position, and orientation of waveguide 408 are configured to ensure that light from each of the eight light beams within the light cone enters waveguide 408. Light from the light cone enters waveguide 408 via a first planar surface of waveguide 408 (located closest to LCOS 402) and is guided at least partially along the length of waveguide 408 before being emitted via a second planar surface of waveguide 408, substantially opposite the first surface (located closest to the eye). As will be readily appreciated, the second planar surface is partially reflective and partially transmissive. In other words, as each light ray propagates within waveguide 408 from the first planar surface and strikes the second planar surface, some light will be transmitted through waveguide 408, and some light will be reflected by the second planar surface back toward the first planar surface. The first planar surface is reflective so that all light striking it from within the waveguide 408 will be reflected back toward the second planar surface. Thus, some light may simply be refracted between the two planar surfaces of the waveguide 408 before being transmitted, while other light may be reflected and, therefore, may experience one or more reflections (or "bounces") between the planar surfaces of the waveguide 408 before being transmitted.

[0084] Figure 4 A total of nine "bounce" points B0 to B8 are shown along the length of waveguide 408. Each "bounce" point B1 to B8 corresponds to a respective LCOS 402'. Figure 2 As shown, light associated with all points of the image (V1-V8) is transmitted out of the waveguide at each "bounce" from the second planar surface of the waveguide 408, but only light from one angular portion of the image (e.g., light from one of V1 to V8) has a trajectory that enables it to reach the eye 405 from each corresponding "bounce" point B0 to B8. In addition, light from a different angular portion of the image (V1 to V8) reaches the eye 405 from each corresponding "bounce" point. Therefore, Figure 4 In the example shown, each angular channel of coded light reaches the eye only once from waveguide 408.

[0085] Although virtual images have been discussed generally herein, which require the eye to convert received modulated light to form a perceived image, the methods and apparatus described herein can be applied to real images.

[0086] 2D Pupil Expansion—Example 1

[0087] Although Figure 4 The arrangement shown includes a single waveguide that provides pupil expansion in one dimension, but pupil expansion can be provided in more than one dimension, for example in two dimensions. Figure 4 The examples in use a hologram that has been calculated to create channels of light, each corresponding to a different portion of an image, but the present disclosure and the systems described below are not limited to this type of hologram.

[0088] Figure 5 A perspective view of a system 500 is shown, comprising two replicators 504, 506 arranged to expand a light beam 502 in two dimensions.

[0089] exist Figure 5 In the 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 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 light beam 502 is directed to the input of the first replicator 504. Due to internal reflection processes between the two surfaces, as well as from one of the surfaces (the upper surface, such as Figure 5 As will be familiar to the skilled reader, light from beam 502 is replicated in a first direction along the length of first replicator 504 by partial transmission of light from each of a plurality of output points on a first replicator 504. Thus, a first plurality of replica light beams 508 are emitted from first replicator 504 toward second replicator 506.

[0090] The second replicator 506 includes a second pair of surfaces stacked parallel to one another, arranged to receive each collimated beam of the first plurality of light beams 508, and further arranged to provide replication or pupil expansion by expanding each of these beams in a second direction that is substantially orthogonal to the first direction. The first pair of surfaces are similar in size and shape to one another (in some cases identical), and are substantially rectangular. The rectangular shape is implemented for the second replicator so that it has a length along the first direction so as to receive the first plurality of light beams 508, and a length along the second orthogonal direction so as to provide replication in the second direction. Due to internal reflection processes between the two surfaces, as well as from one of the surfaces (such as Figure 5The light of each beam in the first plurality of light beams 508 is replicated in the second direction by partial transmission of light from each of the plurality of output points on the upper surface (as shown in FIG. 1 ). Thus, a second plurality of light beams 510 is emitted from the second replicator 506, wherein the second plurality of light beams 510 includes a replica of the input light beam 502 along each of the first and second directions. Thus, the second plurality of light beams 510 can be viewed as a two-dimensional grid or array including replicated light beams.

[0091] Therefore, it can be said that Figure 5 The first and second replicators 504, 505 are combined to provide a two-dimensional replicator (or "two-dimensional pupil expander").

[0092] 2D Pupil Expansion—Example 2

[0093] UK patent application GB2113454.9, filed on September 21, 2021 and incorporated herein by reference, discloses an image projector comprising a more advanced two-dimensional pupil expander arranged in accordance with the present disclosure.

[0094] The image projector can be arranged to project a diverging or diffracted light field. In some embodiments, the light field is encoded with a hologram. In some embodiments, the diffracted light field comprises a diverging bundle of light rays. In some embodiments, the image formed by the diffracted light field is a virtual image.

[0095] In some embodiments, the first pair of parallel / complementary surfaces are elongated or slender surfaces that are relatively long along a first dimension and relatively short along a second dimension, e.g., relatively short along each of two other dimensions, each dimension being substantially orthogonal to each of the respective other dimensions. The process of light reflecting / transmitting between / from the first pair of parallel surfaces is arranged such that light propagates within the first waveguide pupil expander in a general direction that is the relatively long direction of the first waveguide pupil expander (i.e., in its "elongated" direction).

[0096] A system is disclosed herein that uses diffracted light to form images and provides an eyebox size and field of view suitable for real-world applications - for example, in the automotive industry via heads-up displays. Diffracted light is light that forms a holographic reconstruction of an image from a diffractive structure - for example, a hologram such as a Fourier or Fresnel hologram. The use of diffraction and diffractive structures requires a high density of display devices with very small pixels (e.g., 1 micron) - 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, diffracted light comprising a diverging (non-collimated) bundle of light rays.

[0097] In some embodiments, a display system includes a display device—such as a pixelated display device, e.g., a spatial light modulator (SLM) or a liquid crystal on silicon (LCoS) SLM—that is arranged to provide or form diffracted or divergent light. In these aspects, the aperture of the spatial light modulator (SLM) is the limiting aperture of the system. That is, the aperture of the spatial light modulator—more specifically, the size of the area defining the array of light modulating pixels contained within the SLM—determines the size (e.g., spatial extent) of the bundle of light rays that can exit the system. In accordance with the present 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 a pixel size for light diffraction) becomes larger in spatial extension.

[0098] A diffracted or diverging light field may be referred to as having a "light field size," which is defined in a direction substantially orthogonal to the direction of propagation of the light field. Because light is diffracted / diverged, the light field size increases with propagation distance.

[0099] In some embodiments, the diffracted light field is spatially modulated according to a hologram. In other words, in these aspects, the diffracted light field comprises a "holographic light field". The hologram can be displayed on a pixelated display device. The hologram can be a computer-generated hologram (CGH). It can be a Fourier hologram or a Fresnel hologram or a point cloud hologram or any other suitable type of hologram. Optionally, the hologram can be calculated so as to form channels of holographic light, each channel corresponding to a different part of the image that the observer wants to observe (or perceive, if it is a virtual image). The pixelated display device can be configured to display multiple different holograms continuously or sequentially. Each of the aspects and embodiments disclosed herein can be applied to the display of multiple holograms.

[0100] The output port of the first waveguide pupil expander may be coupled to the input port of the second waveguide pupil expander. The second waveguide pupil expander may be arranged to guide the diffracted light field (including some, preferably most, preferably all replicas of the light field output by the first waveguide pupil expander) from its input port to the corresponding output port by internal reflection between a third pair of parallel surfaces of the second waveguide pupil expander.

[0101] The first waveguide pupil expander can be arranged to provide pupil expansion or replication in a first direction, while the second waveguide pupil expander can be arranged to provide pupil expansion or replication in a second, different direction. The second direction can be substantially orthogonal to the first direction. The second waveguide pupil expander can be arranged to maintain the pupil expansion already provided by the first waveguide pupil expander in the first direction and expand (or replicate) some, preferably most, or preferably all of the copies it receives from the first waveguide pupil expander in the second, different direction. The second waveguide pupil expander can be arranged to receive the light field directly or indirectly from the first waveguide pupil expander. One or more other elements can be provided along the propagation path of the light field between the first and second waveguide pupil expanders.

[0102] The first waveguide pupil expander can be substantially elongated and the second waveguide pupil expander can be substantially planar. The elongated shape of the first waveguide pupil expander can be defined by a length along a first dimension. The planar or rectangular shape of the second waveguide pupil expander can be defined by a length along the first dimension and a width or breadth along a second dimension substantially orthogonal to the first dimension. The size or length of the first waveguide pupil expander along its first dimension can correspond to the length or width of the second waveguide pupil expander along its first or second dimension, respectively. A first surface of a pair of parallel surfaces of the second waveguide pupil expander, including its input port, can be shaped, sized, and / or positioned to correspond to an area defined by an 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 replica output by the first waveguide pupil expander.

[0103] The first and second waveguide pupil expanders can collectively provide pupil expansion in a first direction and in a second direction perpendicular to the first direction, optionally wherein a plane containing the first and second directions is substantially parallel to a plane of the second waveguide pupil expander. In other words, the first and second dimensions defining the length and width, respectively, of the second waveguide pupil expander can be parallel to the first and second directions, respectively (or to the second and first directions, respectively), wherein the waveguide pupil expander provides pupil expansion. The combination of the first waveguide pupil expander and the second waveguide pupil expander can generally be referred to as a "pupil expander."

[0104] It can be said that the expansion / replication provided by the first and second waveguide expanders has the effect of expanding the exit pupil of the display system in each of two directions. The area defined by the expanded exit pupil can, in turn, define an expanded eyebox region from which an observer can receive light of the input diffracted or diverging light field. The eyebox region can be said to be located in or define the viewing plane.

[0105] The two directions of exit 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 an arrangement that includes other elements such as an optical combiner, for example, a vehicle windshield, the exit pupil can be considered to be the exit pupil from the other element, such as the windshield. In such an arrangement, the exit 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 exit pupil can be substantially perpendicular to the first and second directions of replication / expansion provided by the first and second waveguide pupil expanders.

[0106] The viewing plane and / or the eyebox region may be non-coplanar or non-parallel to the first and second directions in which the first and second waveguide pupil expanders provide replication / expansion. For example, the viewing plane may be substantially perpendicular to the first and second directions in which the first and second waveguide pupil expanders provide replication / expansion.

[0107] In order to provide suitable launch conditions to achieve internal reflections 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.

[0108] Combiner shape compensation

[0109] An advantage of projecting a hologram into the eyebox is that optical compensation can be encoded in the hologram (e.g., see European Patent 2936252, incorporated herein by reference). The present disclosure is compatible with holograms that compensate for the complex curvature of an optical combiner used as part of a projection system. In some embodiments, the optical combiner is a vehicle windshield. Full details of this approach 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.

[0110] Control device

[0111] The present disclosure is also compatible with an optical configuration including a control device (e.g., an optical shutter device) to control the transmission of light from the optical channel hologram to the observer. The holographic projector may also include a control device arranged to control the transmission of the angular channel to the eye box position. British patent application GB2108456.1, filed on June 14, 2021 and incorporated herein by reference, discloses at least one waveguide pupil expander and a control device. The reader will understand from at least this prior disclosure that the optical configuration of the control device is substantially based on the user's eye box position and is compatible with any hologram calculation method for implementing the optical channel described herein. The control device can be said to be an optical shutter or aperture device. The optical shutter device may include a 1D array of apertures or windows, each of which can be independently switched between a light-transmitting and a light-opaque state to control the transmission of the hologram optical channel and its replica to the eye box. Each aperture or window may include multiple liquid crystal cells or pixels.

[0112] Projection components for increasing field of view

[0113] Conventional holographic displays form an image seen by an observer at the eyebox of the holographic display. The maximum size of the image that a conventional holographic display can form (i.e., the field of view) seen by the observer is limited by diffraction. This is because the angular spread of light from a diffractive structure such as a hologram is determined by (and therefore limited by) the pixel pitch of the display device of the holographic display. Therefore, it is challenging to use conventional holographic devices to provide the angular field of view and eyebox size required by industry (such as the head-up display industry). It may be beneficial to find methods and / or devices to increase the FOV of a holographic display device to increase the size of the projected holographic image seen by the observer. In the following, the FOV and the eyebox are in substantially parallel planes and define the first (x) and second (y) principal dimensions of the projection system, where the third dimension (z) is the propagation axis of the system. The first, second, and third dimensions are all perpendicular to each other.

[0114] Figure 6 A schematic diagram (not to scale) of a projection assembly 600 is depicted. The projection assembly 600 includes a first holographic projection channel 602 and a second holographic projection channel 604. The first holographic projection channel 602 is configured to output a first holographic light field 603. The second holographic projection channel 604 is configured to output a second holographic light field 605. The holographic light field of a holographic projection channel can be considered to include all light rays output by the holographic projection channel in 3D space at a particular time.

[0115] The first holographic projection channel 602 includes a first display device 606 configured to display a first hologram corresponding to a first image. The first image can be the image seen by a viewer at the eye box of the projection assembly 600. The first display device 606 can be an SLM, such as an LCOS. When the first display device 606 displaying the first hologram is illuminated by light from a first light source (not shown), the light from the first light source is spatially modulated according to the displayed first hologram to form a holographic light field encoding the first image.

[0116] The first holographic projection channel 602 further includes a first optical repeater 610. The first optical repeater 610 is configured to reduce the holographic light field encoding the first image. The first optical repeater 610 outputs a reduced holographic light field encoding the first image. The reduced holographic light field is the first holographic light field 603 output by the first holographic projection channel 602. The first optical repeater 610 may be a reduced 4f system. In other embodiments without the first optical repeater 610, the holographic light field encoding the first image is the first holographic light field 603.

[0117] The second holographic projection channel 604 includes a second display device 608 configured to display a second hologram corresponding to a second image. The second image can be the image seen by an observer at a different eyebox of the projection assembly. The second image can be the same as the first image. The second display device 608 can also be an SLM, such as an LCOS. When the second display device 608 displaying the second hologram is illuminated by light from a second light source (not shown), the light from the second light source is spatially modulated according to the displayed second hologram to form a holographic light field that encodes the second image.

[0118] The second holographic projection channel 604 further includes a second optical relay 612. The second optical relay 612 is configured to reduce the holographic light field encoding the second image. The second optical relay 612 outputs a reduced holographic light field encoding the second image, which is the second holographic light field 605 output by the second holographic projection channel 604. The second optical relay 612 can be a reduced 4f system. In other embodiments without the second optical relay 612, the holographic light field encoding the second image is the second holographic light field 605.

[0119] The angular content available from the holograms displayed on the first and second display devices 606, 608 is limited by the pixel size (e.g., LCOS may have available content over an angular range of approximately -4° to +4°). The angular range can be increased by optically reducing the diffractive structure / hologram encoding the first and second images (e.g., using one or more optical relays, such as first and / or second optical relays 610, 612). This reduction effectively reduces the size of the pixels forming the holographic light field, thereby increasing the diffraction angle. For example, if the diffractive structure (e.g., displayed on LCOS) has a size of 12 mm and the angular range of approximately -4° to +4° is reduced by 2, the corresponding reduced diffractive structure has a size of 6 mm and an angular range of approximately -8° to +8°. Importantly, to avoid the perception of ghosting in the image by the observer, the inventors have recognized that it is highly beneficial for the reduced size to be no smaller than the diameter of the human pupil. Typically, the maximum diameter of the human pupil is 7 mm. If the diffractive structure / hologram in the first dimension (x) is smaller than 7 mm, then after replication in the waveguide / pupil expander according to the present disclosure, the inventors have found that the same area of ​​the image can be effectively received by more than one replica, and this can result in ghost images, which significantly degrades the viewing experience. Therefore, if the diffractive structure / hologram is reduced to increase the angle / diffraction range, the amount of reduction used should be carefully limited according to the inventors' findings. In practice, the inclusion of a windshield in the holographic image projection means that this direct relationship between the pupil diameter of the eye and the minimum size is not exact; for example, the minimum size can actually be 5 mm.

[0120] The projection assembly 600 also includes a beam combiner 614 configured to concatenate / combine the first and second holographic light fields 603, 605. The beam combiner 614 includes a beam splitter 902. The use of the beam combiner 614 produces a first output 616 and a second output 618. The second output 618 can be identical to the first output 616. Each of the first and second outputs 616, 618 is a multiplexed channel comprising the first holographic light field 603 concatenated / combined with the second holographic light field 605. Each of the first and second outputs 616, 618 has a larger continuous FOV than the first or second holographic light field 603, 605 alone. That is, as seen by an observer at the eyebox, the image corresponding to the first or second output 616, 618 extends continuously over a larger angular range than the image corresponding to the first or second holographic light field. The first and second outputs 616, 618 can each have a FOV that is substantially equal to the sum of the FOVs of the first and second holographic light fields 603, 605. In the context of the present application, adjoining light fields means that the light fields are positioned / oriented to propagate adjacent to each other and share boundaries with each other. Adjoining light fields may be considered to be continuous. In other words, the volumes propagated by the adjoining propagating light fields are positioned adjacent to each other and adjoin each other. When the first holographic light field 603 has the same angular range / FOV as the second holographic light field 605, the first holographic projection channel 602 may be considered to deliver the first half of the angular range of the FOV of the first and / or second output 616, 618 in the first dimension (x). Similarly, when the first holographic light field 603 has the same angular range / FOV as the second holographic light field 605, the second holographic projection channel 604 may be considered to deliver the second half of the angular range of the FOV of the first and / or second output 616, 618 in the first dimension (x). Reference Figure 8A and 8B The first and second outputs 616, 618 are described in more detail. Figures 9A to 9C The beam combiner 614 is explained in more detail.

[0121] In an example, each of the first and second holographic projection channels 602, 604 has a natural emission of + / - 4° in the first and second dimensions (x, y). In this case, the first holographic projection channel 602 is arranged to deliver the first holographic light field 603 within an angular range of -8° to 0° in the first dimension (x) and an angular range of -4° to +4° in the second dimension (y). The second holographic projection channel 604 is arranged to deliver the second holographic light field 605 within an angular range of 0° to +8° in the first dimension (x) and an angular range of -4° to +4° in the second dimension (y). In this way, the third holographic light field (i.e., the contiguous / merged first and second holographic light fields) has a FOV of -8 to +8° in the first dimension (x) and a FOV of -4 to +4° in the second dimension (y). Thus, an increase in FOV is achieved.

[0122] The projection assembly 600 may further include a first mirror 620 arranged to direct the first holographic light field 603 to the beam combiner 614. The projection assembly 600 may further include a second mirror 622 arranged to direct the second holographic light field 605 to the beam combiner 614. The projection assembly 600 may further include one or more output mirrors or other optical devices for directing the first output 616 and the second output 618 to respective eyeboxes.

[0123] Waveguides or pupil expanders can additionally be used to increase the angular content delivered to the observer. Horizontal waveguides / pupil expanders are often referred to as rods. Vertical waveguides / pupil expanders are often referred to as plates.

[0124] The first and second outputs 616, 618 are particularly useful when used as inputs to multiple waveguides. For example, pupil expansion in the first dimension can be provided by a pair of elongated waveguides (e.g., rods). Each waveguide needs to receive the first and second holographic light fields, otherwise the entire / combined FOV will not be visible from all eyebox positions. Such a pupil expansion system is described in GB2206791.2 filed on May 10, 2022.

[0125] The light sources used to illuminate the first and second display devices 606, 608 may be different from each other. This tends to reduce or eliminate the occurrence of coherent interference between the propagating first and second holographic light fields 603, 605.

[0126] Figure 7A A schematic diagram (not to scale) depicts a first bundle of light rays from a first display device 606 forming an image on a first display device 606 ′. Figure 7B A schematic diagram (not to scale) depicts a second light beam from a second display device 608 forming an image on a second display device 608 ′.

[0127] The first display device 606 is tilted relative to the second display device 608. In this arrangement, the respective axes of the holographic light fields encoding the first and second images are divergent (at least at locations between the display devices and their respective optical relays). In other words, the holographic light fields from the first and second display devices 606, 608 initially propagate away from each other. The first and second display devices 606, 608 are tilted / rotated relative to each other about the second dimension (y). The first and second holographic light fields encoding the first and second images can abut or merge with each other in the first dimension (x).

[0128] The first display 606 is also tilted in a first direction relative to the propagation direction of the projection assembly 600, i.e., the third dimension (z). Each field point on the first display 606 forms a respective first light beam, which forms a corresponding image point on the image of the first display device 606'. Each first light beam converges to a corresponding point on the image of the first display device 606'. The image of the first display device 606' can be a first hologram or a reduced first hologram (if the optical relay has optical power). Each first light beam propagates within a respective first volume 702, as shown in FIG. Figure 7A Each first volume 702 has a corresponding first boundary 704 that is substantially parallel to the third dimension (z).

[0129] The second display device 608 is also tilted in a second direction relative to the propagation direction of the projection assembly 600, i.e., the third dimension (z). The second direction is opposite to the first direction. Each field point on the second display device 608 forms a respective second light beam, which forms a corresponding image point on the image of the second display device 608'. Each second light beam converges to a corresponding point on the image of the second display device 608'. The image of the second display device 608' can be a second hologram or a reduced second hologram (if the optical repeater has optical power). Each second light beam propagates within a respective second volume 706, as shown in FIG. Figure 7B Each second volume 706 has a respective second boundary 708 that is substantially parallel to the third dimension (z).

[0130] Figure 7CA schematic diagram (not to scale) depicts the superposition of images from first and second display devices 606', 608', along with examples of the bundles of light rays that form each image. The image from the first display device 606' can be considered a first LCOS image. The image from the second display device 608' can be considered a second LCOS image. The first and second optical channels are arranged (e.g., using a beam combiner 614 discussed below with respect to FIG. 9 ) such that the images from the first and second display devices 606', 608' overlap one another. This overlap of the images from the first and second display devices 606', 608' means that the first and second holographic light fields propagating away from the LCOS images are combined. More specifically, because the first and second display devices 606, 608 (and therefore the images from the first and second display devices 606', 608') are tilted relative to one another in the manner described above, the combining of the holographic light fields includes merging, abutting, or stitching together. This combined holographic light field is formed by combining bundles of light rays, each of which includes a corresponding first bundle of light rays on one side that is adjacent to / abuts a corresponding second bundle of light rays on the opposite side. The first and / or second outputs 616, 618 can each include a holographic light field that is combined in this manner. The combined holographic light field has different propagation directions because there is an angle θ between the image on the first display device 606' and the image on the second display device 608'. In addition, the first and second volumes 702, 706 share a boundary that is substantially parallel to the third dimension (z), i.e., the first boundary 704 of the first volume 702, which is substantially parallel to the third dimension (z), overlaps the second boundary 708 of the second volume 706, which is substantially parallel to the third dimension (z). The tilt angle θ, i.e., the angle between the images of the first and second display devices (e.g., the first and second LCOS images) 606', 608', is defined by the angular extent of the image formed by the holographic light fields 603, 605. The tilt angle θ is the same as the angular extent of the first and second images encoded in the holographic light field. For the avoidance of doubt, the combined / merged holographic light field or wavefront (not shown in FIG. 7 ) propagating away (in the positive z-direction) from each pair of superimposed LCOS images 606′, 608′ is contiguous in the same manner as the bundles of rays forming the LCOS images 606′, 608′ (shown in FIG. 7 ). That is, the combined holographic light field or wavefront arriving at the observer comprises a first holographic light field (containing angular information for the first half of the field of view) adjacent to a second holographic light field (containing angular information for the second half of the field of view). Again, this is possible due to the unusual way in which holograms divide image content by angle in the holographic domain, and the method by which image information is conveyed to the observer in holographic form (i.e., in the holographic domain). By adding more angles to the holographic domain, an increase in image size (i.e., field of view) can effectively be achieved. This is achieved via the second display device 608. The first and second display devices 606, 608 are tilted so that the two angular ranges are perfectly stitched together.For further avoidance of doubt, each output 616 , 618 comprises a combined holographic light field as described herein.

[0131] Figure 8A Depicted by Figure 6 A schematic diagram (not to scale) of a first side view of first and second outputs 616, 618 of the projection assembly 600 is shown (from the left side of the projection assembly 600). Figure 8B Depicts the Figure 6 Schematic diagram (not to scale) of a first side view versus a second side view of the first and second outputs 616, 618 output by the projection assembly 600 (as viewed from the right side of the projection assembly 600). When the first and second outputs 616, 618 emerge from the beam combiner 614, they each comprise first and second holographic light fields 603, 605 that merge with one another in a first dimension (x). This means that, as Figure 8A As shown, from a first direction in a first dimension (x), the outer portion of the first holographic light field 603 of the first and second outputs 616, 618 can be seen (e.g., Figure 8A As shown in the dot in Figure 8B As shown, from a second direction (opposite to the first direction) in the first dimension (x), the outer portion of the second holographic light field 605 of the first and second outputs 616, 618 can be seen (as Figure 8B ). The first and second outputs 616, 618 are offset from each other in both the third dimension (z) and the second dimension (y). The first and second outputs 616, 618 are oriented identically to each other in the first dimension (x). The first and second outputs 616, 618 are particularly useful when each of the first and second outputs 616, 618 is used as an input to a respective waveguide in a dual 1D waveguide configuration (e.g., as described in UK patent application GB2206791.2 filed on May 10, 2022, which is incorporated herein by reference in its entirety). In this way, light that would normally be lost or wasted using a beam splitter is recovered or put to use.

[0132] Figure 9AA schematic diagram (not drawn to scale) of a beam combiner 614 is depicted that adjoins / combines the first and second holographic light fields 603, 605. The beam combiner 614 includes a beam splitter 902. The beam splitter 902 includes a partially transmissive and partially reflective element 904. The partially transmissive and partially reflective element 904 can transmit 50% of the incident light and reflect 50% of the incident light. The beam combiner 614 also includes an output mirror 906 positioned to direct / orient the first output 616 such that the first output 616 is offset from the second output 618 in the second and third dimensions (y, z) and is oriented in the same direction as the second output 618 in the first dimension (x). The beam combiner 614 can also include one or more first input mirrors 912 positioned to receive the first holographic light field 603 and redirect the first holographic light field 603 toward a first side 908 of the beam splitter 902. The beam combiner 614 may also include one or more second input mirrors 914 positioned to receive the second holographic light field 605 and redirect the second holographic light field 605 toward a second side 910 of the beam splitter 902. The first side 908 is distinct from the second side 910. The first side 908 is perpendicular to the second side 910. The element 904 is at a 45° angle to the first side 908. The element 904 is also at a 45° angle to the second side 910.

[0133] Figure 9B A schematic diagram (not drawn to scale) of a beam combiner 614 is depicted, through which the first holographic light field 603 propagates. The first holographic light field 603 enters the beam splitter 902 at a first side 908 of the beam splitter 902. A portion (e.g., 50%) of the first holographic light field 603 is transmitted through the element 904. The transmitted portion then forms part of the first output 616. The remaining portion (e.g., 50%) of the first holographic light field 603 is reflected by the element 904. The reflected portion then forms part of the second output 618.

[0134] Figure 9C A schematic diagram (not drawn to scale) of beam combiner 614 is depicted, through which second holographic light field 605 propagates. Second holographic light field 605 enters beam splitter 902 at second side 910 of beam splitter 902. A portion, for example, 50%, of second holographic light field 605 is transmitted through element 904. The transmitted portion then forms part of second output 618. The remaining portion, for example, 50%, of second holographic light field 605 is reflected by element 904. The reflected portion then forms part of first output 616.

[0135] The transmitted portion of the first holographic light field 603 is combined with the reflected portion of the second holographic light field 605 to form a first output 616. The reflected portion of the first holographic light field 603 is combined with the transmitted portion of the second holographic light field 605 to form a second output 618.

[0136] The first and second holographic projection channels 602, 604 are arranged so that the first and second holographic light fields 603, 605 are incident on the element 904 at the same position on the element 904. In other words, the footprints of the first and second holographic light fields 603, 605 on the element 904 largely overlap. The first and second holographic light fields 603, 605 exiting the beam splitter are considered to be the first holographic light field 603 combined with the second holographic light field 605.

[0137] An example method for outputting a first holographic light field 603 that is combined with a second holographic light field 605 is provided below. The example method may include positioning the first and second holographic projection channels 602, 604 such that the first and second display devices 606, 608 are tilted relative to each other at a predetermined angle θ therebetween. Subsequently, a beam splitter 902 may be positioned / arranged to receive the first holographic light field 603 on a first side 908 of the beam splitter 902 and to receive the second holographic light field 605 on a second side 910 of the beam splitter 902. The first and second holographic light fields 603, 605 are incident on the same location on the partially transmissive and partially reflective element 904 of the beam splitter 902. In this way, the transmitted portion of the first holographic light field 603 is combined with the reflected portion of the second holographic light field 605. Similarly, the reflected portion of the first holographic light field 603 is combined with the transmitted portion of the second holographic light field 605. This will result in the first and second outputs 616, 618 each comprising a portion of the first holographic light field 603 that is contiguous with / merged with the second holographic light field 605, as described above.

[0138] Additional Features

[0139] The methods and processes described herein may be embodied on a computer-readable medium. The term "computer-readable medium" includes media arranged to store data temporarily or permanently, such as random access memory (RAM), read-only memory (ROM), buffer memory, flash memory, and cache memory. The term "computer-readable medium" should also be taken to include any medium or combination of media that can store instructions for execution by a machine, such that when the instructions are executed by one or more processors, the machine performs, in whole or in part, any one or more of the methods described herein.

[0140] The term "computer-readable medium" also encompasses cloud-based storage systems. The term "computer-readable medium" includes, but is not limited to, one or more tangible and non-transitory data storage repositories (e.g., data volumes) in the example form of solid-state memory chips, optical disks, magnetic disks, or any suitable combination thereof. In some example embodiments, instructions for execution may be conveyed by a carrier medium. Examples of such carrier media include transient media (e.g., a propagated signal conveying the instructions).

[0141] 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 projection assembly, comprising: a first holographic projection channel configured to form a first holographic light field from a first hologram of a first image, the first holographic projection channel comprising a first display device configured to display the first hologram, wherein when the first display device is illuminated by first light, the first light is spatially modulated according to the displayed first hologram such that the first holographic projection channel forms the first holographic light field; and a second holographic projection channel configured to form a second holographic light field from a second hologram of a second image, the second holographic projection channel comprising a second display device configured to display the second hologram, wherein when the second display device is illuminated by second light, the second light is spatially modulated according to the displayed second hologram, such that the second holographic projection channel forms the second holographic light field, wherein each hologram is configured to form a holographic light field in which the content of the corresponding image in the first dimension is encoded by angle, such that angular channels of the holographic light each correspond to a respective slice of the corresponding image in the first dimension, wherein the projection assembly is arranged to combine a first plurality of angular channels of a first holographic projection channel and a second plurality of angular channels of a second holographic projection channel in a first dimension so that the first holographic light field and the second holographic light field are co-receivable and convertible into an extended image comprising the first image contiguous with the second image; and The first display device and the second display device are tilted relative to each other at an angle equal to the sum of the encoded angles of the adjacent first and second holographic light fields, so that the first propagation direction of the first holographic light field deviates from the second propagation direction of the second holographic light field.

2. The projection assembly according to claim 1, wherein: The tilt is a rotation about a second dimension, which is perpendicular to the first dimension, such that the first and second holographic light fields are adjacent in the first dimension.

3. The projection assembly according to any one of claims 1 or 2, wherein: The angular field of view of the projection assembly in the first dimension is equal to the sum of the angular field of view of the first holographic light field in the first dimension and the angular field of view of the second holographic light field in the first dimension.

4. The projection assembly according to claim 3, wherein: The angular field of view of the projection assembly in the second dimension is equal to the angular field of view of the first holographic light field in the second dimension and / or the angular field of view of the second holographic light field in the second dimension, and the second dimension is perpendicular to the first dimension.

5. The projection assembly according to claim 1, wherein: The first holographic projection channel includes a first light source for forming the first holographic light field by illuminating the first hologram; The second holographic projection channel comprises a second light source for forming the second holographic light field by illuminating the second hologram; and The first light source is different from the second light source.

6. The projection assembly according to claim 4, wherein: The projection assembly is arranged to form two multiplexed channels, each multiplexed channel comprising a portion of the first holographic light field adjacent to a portion of the second holographic light field.

7. The projection assembly according to claim 6, wherein: The multiplexing channels are parallel and spatially offset in two perpendicular directions; and The two perpendicular directions are the second and third dimensions.

8. The projection assembly of claim 6, further comprising a plurality of waveguides, each waveguide being arranged to receive a respective one of the multiplexed channels.

9. The projection assembly according to claim 8, wherein: A first waveguide of the plurality of waveguides is configured to replicate a light field along a first direction, and a second waveguide of the plurality of waveguides is configured to replicate a light field along a second direction opposite the first direction.

10. The projection assembly of claim 6, further comprising a beam combiner configured to receive the first and second holographic light fields and output the two multiplexed channels.

11. The projection assembly according to claim 10, wherein: The beam combiner comprises a beam splitter arranged to receive the first holographic light field on a first side thereof and the second holographic light field on a second side thereof.

12. The projection assembly according to claim 11, wherein: The beam splitter configuration is: dividing the first holographic light field into a first transmitted light field and a first reflected light field; dividing the second holographic light field into a second transmitted light field and a second reflected light field; Combining the first transmitted light field with the second reflected light field to form a first multiplexing channel of the two multiplexing channels; as well as combining the first reflected light field and the second transmitted light field to form a second multiplexing channel of the two multiplexing channels; and The first and second multiplexing channels are identical to each other.

13. The projection assembly according to claim 1, wherein: The first holographic projection channel and the second holographic projection channel each include a corresponding optical repeater configured to form an intermediate reconstructed image of the corresponding holographic light field, wherein each optical repeater changes the diffraction angle of the corresponding holographic light field.

14. The projection assembly according to claim 13, wherein: The size of each intermediate reconstructed image of the corresponding holographic light field is larger than 5 mm.

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