Compact Head-Up Display

Abstract

To provide a head-up display for a vehicle comprising a first pupil replicator and a second pupil replicator.SOLUTION: The first pupil replicator extends in a first direction. The first pupil replicator is arranged to receive a holographic light field from a spatial light modulator having a pixel array defining a limiting aperture of the head-up display. The holographic light field is a complex light field spatially modulated in accordance with a hologram displayed on the spatial light modulator. The second pupil replicator extends in the first direction and in a second direction perpendicular to the first direction. The second pupil replicator comprises a first major surface forming an output, and a second major surface parallel to the first major surface. The first pupil replicator is arranged within a planar layer substantially parallel and adjacent to the second major surface of the second pupil replicator.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present disclosure relates to pupil dilation or replication, particularly for diffracted light fields containing diverging ray bundles. More particularly, the present disclosure relates to display systems including waveguide pupil dilators and methods of pupil dilation using waveguides. Some embodiments relate to two-dimensional pupil dilation using first and second waveguide pupil dilators. Some embodiments relate to image generation units and head-up displays, such as automotive head-up displays (HUDs). [Background technology]

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

[0003] Computer-generated holography can numerically simulate interference processes. Computer-generated holograms can be calculated by techniques based on mathematical transforms, such as the Fresnel transform or the Fourier transform. These types of holograms may be called Fresnel / Fourier transform holograms or simply Fresnel / Fourier holograms. Fourier holograms may be thought of as a Fourier domain / planar representation of an object or a frequency domain / planar representation of an object. Computer-generated holograms may be calculated, for example, by coherent ray tracing or point cloud techniques.

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

[0005] A spatial light modulator typically contains a plurality of individually addressable pixels, which may also be called cells or elements. The light modulation scheme may be binary, multi-level, or continuous. Alternatively, the device may be continuous (i.e., not pixelated), and thus the light modulation may be continuous throughout the device. A spatial light modulator may be reflective, meaning that modulated light is output in reflection. A spatial light modulator may also be transmissive, meaning that modulated light is output in transmission.

[0006] Holographic projectors may be implemented using the systems described herein, and such projectors find application in heads-up displays (HUDs). Summary of the Invention

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

[0008] Generally, the present disclosure relates to image projection. The present disclosure relates to a method of image projection and an image projector comprising a display device. The present disclosure also relates to a projection system comprising an image projector and a viewing system, where the image projector projects or relays light from a display device to the viewing system. The present disclosure is equally applicable to monocular and binocular viewing systems. The viewing system may include one or more eyes of an observer. The viewing system comprises an optical element having optical power (e.g., one or more lenses in a human eye) and a viewing surface (e.g., the retina of a human eye). The projector may also 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 image is formed on a display surface or perceived by the observer. In some embodiments, the image is a virtual image, and the display surface may be referred to as a virtual image surface. In other embodiments, the image is a real image formed by holographic reconstruction, and the image is projected or relayed to the viewing surface. The image is formed by illuminating a diffraction pattern (e.g., a hologram) displayed on the display device.

[0009] The display comprises pixels. The pixels of the display may display a diffraction pattern or structure that diffracts light. The diffracted light may be imaged onto a plane spatially separated from the display. In accordance with well-understood optical systems, 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.

[0010] In embodiments, the display device is a spatial light modulator, such as a liquid crystal on silicon ("LCOS") spatial light modulator (SLM). Light propagates from the LCOS toward an observing entity / system, such as a camera or an eye, over a range of diffraction angles (e.g., from 0 to a maximum diffraction angle). In some embodiments, magnification techniques can be used to increase the range of available diffraction angles beyond the conventional maximum diffraction angle of the LCOS.

[0011] In some instances, an image (formed from the displayed hologram) is propagated to the eye. For example, spatially modulated light of an intermediate holographic reconstruction / image formed in free space or on a screen or other light-receiving surface between the display device and the observer can be propagated to the observer.

[0012] In some other examples, the (light from) the hologram itself is propagated to the eye. For example, the spatially modulated light of the hologram (not yet fully converted into a holographic reconstruction, i.e., image), which can informally be said to be "encoded" in / by the hologram, is propagated directly to the observer's eye. A real or virtual image may be perceived by the observer. In these embodiments, there is no intermediate holographic reconstruction / image formed between the display device and the observer. In these embodiments, the lens of the eye is sometimes said to perform the conversion or transformation from hologram to image. A projection system or light engine may be configured so that the observer effectively views the display device directly.

[0013] Herein, we refer to a "light field" that is a "complex light field." The term "light field" simply refers to a pattern of light that has a finite size in at least two orthogonal spatial directions, e.g., x and y. The term "complex" is used herein simply to indicate that the light at each point in the light field can be defined by an amplitude and phase value and can therefore be represented by a complex number or pair of values. For hologram calculations, the complex light field may be a two-dimensional array of complex numbers, where the complex numbers define the light intensity and phase at multiple discrete locations within the light field. According to the methods disclosed herein, the complex light field is propagated forward and backward, e.g., in the +z and -z directions, between the hologram plane and the image plane. Light propagation can be simulated or modeled using any one of several different techniques or mathematical transformations familiar to those skilled in the art of wave optics.

[0014] According to well-understood principles of optics, the range of angles of light propagating from a display device that can be seen by the 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 one meter, only a narrow range of angles from the LCOS can propagate through the pupil and form an image on the retina for a given eye position. The range of angles of light rays propagating from the display device that can successfully propagate through the eye's pupil to form an image on the retina for a given eye position determines the portion of the image that is "seen" by the observer. In other words, not all portions of the image are visible from any single point on the viewing surface (e.g., any single eye position within a viewing window such as an eye-motion box).

[0015] In some embodiments, the image perceived by the observer is a virtual image that appears upstream of the display device. That is, the observer perceives the image as being further away from them than the display device. Conceptually, therefore, the observer may be thought of as viewing the virtual image through a "display-sized window," which may be very small, e.g., 1 cm in diameter, at a relatively long distance, e.g., 1 meter. The user also views the display-sized window through the pupil(s) of the eye, which may also be very small. The field of view is therefore small, and the particular angular range that can be seen at any given time is highly dependent on the position of the eye.

[0016] Pupil dilators address the problem of how to increase the angular range of light rays propagated from a display device that can successfully propagate through the eye's pupil to form an image. Display devices are typically (relatively) small and have (relatively) long projection distances. In some embodiments, the projection distance is at least one order of magnitude, e.g., at least two orders of magnitude, larger than the diameter or width of the entrance pupil and / or aperture of the display device (i.e., the size of the array of pixels). Embodiments of the present disclosure relate to configurations in which a hologram of an image, rather than the image itself, is propagated to the human eye. In other words, light received by the observer is modulated according to the hologram of the image. However, other embodiments of the present disclosure may relate to configurations in which an image, rather than a hologram, is propagated to the human eye, for example, by so-called indirect viewing, in which light from a holographic reconstruction or "reconstructed image" formed on a screen (or even in free space) is propagated to the human eye.

[0017] The use of a pupil dilator increases the viewing area (i.e., the user's eye-box) laterally, thus allowing some movement of one or more eyes while still allowing the user to see the image. As will be understood by those skilled in the art, in an imaging system, the viewing area (user's eye-box) is the area in which the observer's eyes can perceive an image. The present disclosure relates to non-infinite virtual image distances, i.e., near-distance virtual images.

[0018] Conventionally, a two-dimensional pupil dilator comprises one or more one-dimensional optical waveguides, each formed using a pair of opposing reflective surfaces, with output light from the surfaces forming an observation window, e.g., an eyebox or eye motion box, through which an observer views. 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 viewing area) in at least one dimension. Specifically, the waveguides enlarge the observation window by dividing the amplitude of the incident wavefront to create extra rays or "replicas."

[0019] The display device may have an active or display area with one dimension that may be less than 10 cm, such as less than 5 cm or less than 2 cm. The propagation distance between the display device and the observation system may be greater than 1 meter, such as greater than 1.5 m or greater than 2 m. The light propagation distance in the waveguide may be up to 2 m, such as up to 1.5 m or up to 1 m. The method may be capable of receiving an image and determining a corresponding hologram of sufficient quality in less than 20 ms, such as less than 15 ms or less than 10 ms.

[0020] In some embodiments, described solely as examples of diffractive or holographic light fields according to the present disclosure, a hologram is configured to route light into multiple channels, each channel corresponding to a different portion (i.e., sub-region) of an image. The hologram can be displayed on a display device, such as a spatial light modulator, or otherwise represented. When displayed on an appropriate display device, the hologram can spatially modulate light that can be converted into an image by a viewing system. The channels formed by the diffractive structure are referred to herein as "hologram channels" simply to reflect that they are channels of light encoded by a hologram with image information. The light in each channel is said to be in the hologram domain rather than the image or spatial domain. In some embodiments, the hologram is a Fourier or Fourier transform hologram, and therefore the hologram domain is the Fourier or frequency domain. The hologram may also be a Fresnel or Fresnel transform hologram. Holograms are described herein as routing light into multiple hologram channels, each corresponding to a respective image sub-region, simply to reflect that an image that can be reconstructed from a hologram has a finite size and can be arbitrarily divided into multiple image sub-regions. Importantly, the hologram in this example is characterized by how it distributes image content when illuminated. Specifically, the hologram divides the image content by angle. That is, each point on the image, when illuminated, is associated with a unique ray angle of the spatially modulated light formed by the hologram—at least a unique pair of angles because the hologram is two-dimensional. For the avoidance of doubt, this hologram behavior is unconventional. When illuminated, the spatially modulated light formed by this special type of hologram may be arbitrarily divided into multiple hologram channels, each defined by a range of (two-dimensional) ray angles. From the above, it will be appreciated that any hologram channel (i.e., subrange of ray angles) that can be considered in the spatially modulated light is associated with a respective portion or subregion of the image.That is, all of the information needed to reconstruct that portion or subregion of the image is contained within a subrange of angles of the spatially modulated light formed from the hologram of the image. When the spatially modulated light is viewed as a whole, there is not necessarily evidence of multiple discrete light channels. However, in some arrangements, multiple spatially separated hologram channels are formed by intentionally blanking or emptying (i.e., having no image content) the region of the target image from which the hologram is computed.

[0021] Nevertheless, the hologram can still be identified. For example, if only a successive portion or subregion of the spatially modulated light formed by the hologram is reconstructed, only a subregion of the image will be visible. If a different successive portion or subregion of the spatially modulated light is reconstructed, a different subregion of the image will be visible. A further distinguishing feature of this type of hologram is that the shape of the cross-sectional area of ​​any hologram channel substantially corresponds to (i.e., is substantially the same as) the shape of the entrance pupil, although they may vary in size, at least in the correct plane in which the hologram was calculated. Each light / hologram channel propagates from the hologram at a different angle or range of angles. These are exemplary methods for characterizing or identifying this type of hologram, although other methods may be used. In summary, the holograms disclosed herein are characterized and identifiable by how the image content is distributed within the light encoded by the hologram. Again, for the avoidance of doubt, references herein to holograms configured to direct light or angularly split an image into multiple holographic channels are made by way of example only, and the present disclosure is equally applicable to pupil dilation of any type of holographic light field, or even any type of diffractive or diffractive light field.

[0022] Generally, disclosed herein is a system for providing pupil dilation relative to an input light field, the input light field being a diffractive or holographic light field comprising diverging ray bundles. As discussed above, pupil dilation (also referred to as "image duplication" or "replication" or "pupil duplication") allows an observer to increase the size of the area in which the image can be seen (or in which the observer's eye can receive the light of a hologram forming the image) by creating one or more replicas of the input light beam (or ray bundle). Pupil dilation can be provided in one or more dimensions. For example, two-dimensional pupil dilation can be provided, with each dimension being substantially orthogonal to each other.

[0023] The system may be provided in a compact and streamlined physical form, which allows it to be suitable for a wide range of real-world applications, including those where space is limited and real estate is at a premium, for example, it may be implemented in a heads-up display (HUD), such as a vehicle or automotive HUD.

[0024] According to the present disclosure, pupil dilation is provided for diffracted or diffractive light, which may include diverging ray bundles. The diffractive or diffracted light may be output by a display device, such as a pixelated display device, such as a spatial light modulator (SLM), arranged to display a diffractive structure, such as a hologram. The diffractive light field may be defined by a "cone of light." Thus, the size of the diffractive light field (defined on a two-dimensional plane) increases with propagation distance from the corresponding diffractive structure (i.e., the display device).

[0025] The spatial light modulator may be arranged to display a hologram. The diffracted or divergent light may include light encoded in / by the hologram, rather than light of the image or holographic reconstruction. Thus, in such an embodiment, the pupil dilator may be said to replicate the hologram or form at least one replica of the hologram, to convey that the light delivered to the observer is spatially modulated according to the hologram of the image, rather than the image itself. That is, a diffracted light field is propagated to the observer.

[0026] In some embodiments, two one-dimensional waveguide pupil dilators are provided, each positioned to effectively increase the size of the system's exit pupil by forming multiple replicas or copies of the spatial light modulator's exit pupil (or the light at the exit pupil). An exit pupil may be understood to be the physical region from which light is output by the system. Each waveguide pupil dilator may also be said to be positioned to expand the size of the system's exit pupil. Each waveguide pupil dilator may also be said to be positioned to enlarge / increase the size of the eyebox within which an observer's eye may be positioned to view / receive the light output by the system.

[0027] In this disclosure, the term "replica" is used merely to reflect the division of spatially modulated light so that the complex light field is directed along multiple different optical paths. The term "replica" is used to refer to each occurrence or instance of the complex light field after a replication event, such as partial reflection transmission through a pupil dilator. Each replica travels 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, i.e., light that is spatially modulated with a hologram of an image rather than the image itself. Those skilled in the art of holography will understand that the complex light field associated with the propagation of holographically encoded light changes with propagation distance. Because the use of the term "replica" herein is independent of propagation distance, two branches or paths of light associated with a replication event are still referred to as "replicas" of each other, even if the branches are of different lengths, resulting in complex light fields that evolve differently along each path. That is, two complex light fields, even if associated with different propagation distances, are still considered "replicas" according to the present disclosure, provided they result from the same replication event or series of replication events.

[0028] According to a first aspect, a display system is provided that includes a first waveguide pupil dilator. The first waveguide pupil dilator includes an input port, an output port, a first pair of parallel surfaces, and a second pair of parallel surfaces. The first pair of parallel surfaces is orthogonal to the second pair of parallel surfaces. The first pair of parallel surfaces is arranged to guide a diffracted or divergent (e.g., holographic) light field from the input port to the output port by internal reflection therebetween. The first surface of the first pair of parallel surfaces is partially transflective so that the light field is split with each internal reflection, and multiple replicas of the light field are transmitted through an area of ​​the first surface that forms the output port. The second pair of parallel surfaces is also arranged to guide the light field from the input port to the output port by at least one internal reflection. The input port may be formed on / by the first surface or on / by the second surface of the first pair of parallel surfaces.

[0029] According to the present disclosure, a "diffracted light field" or "diffractive light field" is a light field formed by diffraction. The diffracted 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 diffracted light field is a holographic light field or a light field forming a holographic reconstruction of an image. The holographic light field forms a (holographic) reconstruction of an image on a reconstruction surface. The holographic light field propagating from a hologram to a reconstruction surface can be said to contain light encoded in the hologram or light from the hologram region. The diffracted light field is characterized by a diffraction angle determined by the minimum feature size of the diffracting structure and the wavelength of the light (in the diffracted light field). According to the present disclosure, a "diffracted light field" can also be said to be a light field forming a reconstruction on a plane spatially separated from a corresponding diffracting structure. Optical systems for propagating a diffracted light field from a diffracting structure to an observer are disclosed herein. The diffracted light field can form an image. In some embodiments, the diffracted light field includes diverging ray bundles. In some embodiments, the image formed by the diffracted light field is a virtual image.

[0030] In some embodiments, the first pair of parallel / complementary surfaces are elongated or elongated 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 other dimensions. The process of light reflection / transmission between / from the first pair of parallel surfaces is arranged to cause light to propagate within the first waveguide pupil dilator, and the general direction of light propagation is the direction in which the first waveguide pupil dilator is relatively long (i.e., its "elongated" direction).

[0031] In some embodiments, the second pair of parallel surfaces are elongated 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 other dimensions.

[0032] The first waveguide pupil expander ensures that light in the diffracted light field is not lost through the second pair of parallel surfaces during propagation of the light within the first waveguide pupil expander, as a result of the second pair of parallel surfaces also being arranged to guide the light field from the input port to the output port by at least one internal reflection. This can be particularly advantageous when the first waveguide pupil expander is relatively thin, and in particular when the size of the first waveguide pupil expander along one or both of its relatively short dimensions is substantially equal to or smaller than the size of the light field defined by the diffracted or divergent light as it propagates through the first waveguide pupil expander.

[0033] Disclosed herein is a system that uses diffracted light to form an image, providing an eyebox size and field of view suitable for real-world applications in the automotive industry, for example, via a head-up display. Diffracted light is light that forms a holographic reconstruction of an image from a diffractive structure, e.g., a hologram, such as a Fourier or Fresnel hologram. The use of diffraction and diffractive structures requires a display device with a high density of very small pixels (e.g., 1 micrometer), which in practice means a small display device (e.g., 1 cm). The inventors have addressed the problem of how to provide a diffracted light field, e.g., diffracted light comprising a diverging (uncollimated) bundle of rays, to a 2D pupil dilation.

[0034] In an embodiment, the display system comprises a display device, such as a pixelated display device, e.g., a spatial light modulator (SLM) or a liquid crystal on silicon (LCoS) SLM, arranged to provide or shape diffracted or diverging light. In such an embodiment, the aperture of the spatial light modulator (SLM) is the limiting aperture of the system. That is, the aperture of the spatial light modulator, and 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. According to the present disclosure, it is stated that the exit pupil of the system (limited by the small display device with pixel size for light diffraction) is expanded to reflect the larger, larger, or expanded spatial extent through the use of at least one pupil expander.

[0035] A diffracted or diverging light field can be said to have a "light field size" defined in a direction substantially perpendicular to the propagation direction of the light field. Because light diffracts / diverges, the light field size increases with propagation distance. In some embodiments, the size of the light field within the first waveguide pupil dilator exceeds the size of the first waveguide pupil dilator, i.e., the size of the light field is larger than the size of the first waveguide pupil dilator in at least one dimension. In other words, the light field size may be substantially equal to or larger than at least one of a "first spacing size" defined between the first and second surfaces of the first pair of parallel surfaces and a "second spacing size" defined between the first and second surfaces of the second pair of parallel surfaces during internal reflection of the light field within the first waveguide pupil dilator. In other words, the size of the light field may be equal to or larger than the thickness of the first waveguide pupil dilator in at least one dimension. According to the present disclosure, the second pair of parallel surfaces is configured to provide reflection of the light field to retain it within the first waveguide pupil dilator as a result of internal reflection between the surfaces of the first pair of parallel surfaces, ensuring that it only exits the first waveguide pupil dilator via the output port.

[0036] In some embodiments, the diffracted light field is spatially modulated according to a hologram. In other words, in such aspects, the diffracted light field comprises a "holographic light field." The hologram may be displayed on a pixelated display device. The hologram may be a computer-generated hologram (CGH). It may be a Fourier hologram, a Fresnel hologram, a point cloud hologram, or any other suitable type of hologram. The hologram may optionally be calculated to form channels of holographic light, each channel corresponding to a different respective portion of the image intended to be seen (or perceived, if virtual) by the observer. The pixelated display device may be configured to display multiple different holograms sequentially or sequentially. Each of the aspects and embodiments disclosed herein may be applied to the display of multiple holograms.

[0037] 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 positioned to guide a diffracted light field containing some, preferably most, or preferably all, of the replicas of the light field output by the first waveguide pupil expander from its input port to a respective output port by internal reflection between a third pair of parallel surfaces of the second waveguide pupil expander. A first surface of the third pair of parallel surfaces may be partially transflective such that the light field is split with each internal reflection and multiple replicas of the light field are transmitted through an area of ​​the first surface on the second waveguide pupil expander that forms the output ports.

[0038] The first waveguide pupil dilator may be positioned to provide pupil dilation or replication in a first direction, and the second waveguide pupil dilator may be positioned to provide pupil dilation or replication in a second, different direction. The second direction may be substantially orthogonal to the first direction. The second waveguide pupil dilator may be positioned to preserve the pupil dilation provided by the first waveguide pupil dilator in the first direction and dilate (or replicate) a portion, preferably a majority, or preferably all, of the replica received from the first waveguide pupil dilator in a second, different direction. The second waveguide pupil dilator may be positioned to receive the light field directly or indirectly from the first waveguide pupil dilator. One or more other elements may be included along the propagation path of the light field between the first and second waveguide pupil dilators.

[0039] The first waveguide pupil dilator may be substantially elongated and the second waveguide pupil dilator may be substantially planar. The elongated shape of the first waveguide pupil dilator may be defined by a length along a first dimension. The planar or rectangular shape of the second waveguide pupil dilator may be defined by a length along the first dimension and a width or lateral width along a second dimension substantially orthogonal to the first dimension. The size or length of the first waveguide pupil dilator along its first dimension corresponds to the length or width of the second waveguide pupil dilator along its first or second dimension, respectively. The first face of the third pair of parallel surfaces of the second waveguide pupil expander, including its input port, may be shaped, sized, and / or positioned to correspond to an area defined by the output ports on the first face of the first pair of parallel surfaces on the first waveguide pupil expander, such that the second waveguide pupil expander is positioned to receive each of the replicas output by the first waveguide pupil expander.

[0040] The first and second waveguide pupil dilators may collectively provide pupil dilation in a first direction and a second direction perpendicular to the first direction, and optionally a plane containing the first and second directions is substantially parallel to the plane of the second waveguide pupil dilator. In other words, the first and second dimensions defining the length and width, respectively, of the second waveguide pupil dilator may be parallel to the first and second directions (or the second and first directions, respectively) in which the waveguide pupil dilator provides pupil dilation. The combination of the first waveguide pupil dilator and the second waveguide pupil dilator may be generally referred to as a "pupil dilator."

[0041] The expansion / duplication provided by the first and second waveguide expanders can be said to have 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 define an expanded eyebox region where an observer can receive light from the input diffracted or divergent light field. The eyebox region may be said to be located on or define a viewing plane.

[0042] The two directions in which the exit pupil is dilated may be coplanar with or parallel to the first and second directions in which the first and second waveguide pupil dilators provide duplication / dilation. Alternatively, in an arrangement that includes another element, such as an optical combiner, e.g., a vehicle windscreen (or windshield), the exit pupil may be considered to be the exit pupil from the other element, such as the windshield. In such an arrangement, the exit pupil may not be coplanar with or parallel to the first and second directions in which the first and second waveguide pupil dilators provide duplication / dilation. For example, the exit pupil may be substantially perpendicular to the first and second directions in which the first and second waveguide pupil dilators provide duplication / dilation.

[0043] The viewing plane and / or eyebox region may not be coplanar or parallel to the first and second directions in which the first and second waveguide pupil dilators provide replication / dilation. For example, the viewing plane may be substantially perpendicular to the first and second directions in which the first and second waveguide pupil dilators provide replication / dilation.

[0044] In some embodiments, a waveguide coupler may be provided between the first waveguide pupil dilator and the second waveguide pupil dilator. The waveguide coupler may be configured to directly or indirectly receive some or all of the replicas of the light field output by the first waveguide pupil dilator. The waveguide coupler may be further configured to output some or all of the replicas and transmit them directly or indirectly toward the second waveguide pupil dilator.

[0045] The waveguide coupler may have a light-receiving surface with an input port configured to receive some, preferably most, or preferably all of the multiple replicas of the light field output by the first waveguide pupil dilator. The light-receiving surface of the waveguide coupler may be positioned parallel to the first pair of parallel faces of the first waveguide pupil dilator, although this is not required. One or more other elements may be provided to ensure a proper angle of incidence of the light field replicas onto the waveguide coupler. The waveguide coupler may further include a transmission surface with an output port configured to transmit some, preferably most, or preferably all of the multiple replicas of the light field toward the second waveguide pupil dilator.

[0046] The waveguide coupler may further include a fourth pair of parallel reflective surfaces arranged to guide the light field from the receiving surface toward the transmitting surface of the waveguide coupler by at least one internal reflection. The fourth pair of parallel surfaces may substantially correspond to the second pair of parallel surfaces of the first waveguide pupil expander. For example, a first surface in the fourth pair of parallel surfaces may be coplanar with a first surface in the second pair of parallel surfaces, and / or a second surface in the fourth pair of parallel surfaces may be coplanar with a second surface in the second pair of parallel surfaces.

[0047] The second spacing size, which includes the size of the separation between two of the second pair of parallel surfaces, may be substantially equal to the size of the separation between two of the fourth pair of parallel surfaces. Thus, the correspondence between the fourth pair of parallel surfaces and the second pair of parallel surfaces can determine that the first waveguide pupil expander and the waveguide coupler occupy a common plane or layer.

[0048] The first waveguide pupil expander and, optionally, the waveguide coupler may be arranged to occupy a first plane or layer. The second waveguide pupil expander may be arranged to occupy a second, different plane or layer. The second layer may be substantially parallel to the first layer. The shape and size of the second waveguide pupil expander may be said to define an area or "footprint" on / within the second layer. Because the first and second layers are substantially parallel, the "footprint" of the second pupil expander may also be described as being defined on the first layer. The first waveguide pupil expander and, optionally, the waveguide coupler may be arranged within an area of ​​the first layer that is equal to or smaller than the footprint of the second waveguide pupil expander on the second layer. One or more additional elements, such as a mirror, may also be arranged within that area of ​​the first layer.

[0049] The first and second layers may be arranged relative to one another such that the area occupied by the second waveguide pupil expander on the second layer overlaps the area of ​​the first layer in which the first waveguide pupil expander and, optionally, the waveguide combiner are also arranged. In other words, in such an arrangement, by adopting a "plan" or "bird's-eye" view of the second waveguide pupil expander on the second layer, an observer cannot see the area of ​​the first layer occupied by the first waveguide pupil expander, and optionally also occupied by the waveguide combiner and / or one or more additional elements.

[0050] The waveguide coupler may have a shape that substantially fills the space or gap between the first and second waveguide pupil dilators. For example, the waveguide coupler may be generally triangular in shape.

[0051] To provide suitable launch conditions for achieving internal reflection within the first and second waveguide pupil expanders, the elongated dimension of the first waveguide pupil expander may be tilted relative to the first and second dimensions of the second waveguide pupil expander. Such tilting may create an essentially triangular shaped gap that the waveguide combiner may be positioned to at least partially occupy.

[0052] The display system may further include an element arranged to fold the optical path of the replica of the light field between the first waveguide pupil dilator and the second waveguide pupil dilator, for example, between the waveguide combiner and the second waveguide pupil dilator. The element may include a folding mirror. The folding mirror may be arranged to occupy a first layer that also occupies the first waveguide pupil dilator and, optionally, the waveguide combiner. The folding mirror may be arranged to direct light from the first layer to the second layer. The folding mirror may be arranged to provide suitable launch conditions to achieve internal reflection within the second waveguide pupil dilator. The use of a folding mirror may allow the second layer to overlap the first layer, thereby enabling a compact, low-volume system.

[0053] In embodiments in which the coverage area of ​​the second waveguide pupil dilator on the second layer overlaps the area of ​​the first layer in which the first waveguide pupil dilator and, optionally, the waveguide coupler are also disposed, the second waveguide pupil dilator can be said to define respective first and second dimensions, or axes, of the coverage area. Light output by the first waveguide pupil dilator can be arranged to be parallel to one of the first and second dimensions of the coverage area. The elongated dimension of the first waveguide pupil dilator can be arranged to be oblique with respect to the respective other of the first and second dimensions of the coverage area.

[0054] According to some embodiments, the controller may be located within the display system. For example, the controller may be located downstream of the first waveguide pupil dilator, such as between the first and second waveguide pupil dilators, and comprise an array of apertures, each aperture selectively operable between a transmissive state and a non-transmissive state.

[0055] Thus, the controller can be configured to dynamically and selectively control which light is transmitted and which light is not transmitted between the first and second waveguide pupil dilators. In some embodiments, the controller can be controlled to allow some replicas of the output diffracted light field from the first waveguide pupil dilator to be transmitted to the second waveguide pupil dilator while preventing certain others from doing so. The controller can be controlled to allow all replicas of a given diffracted light field to be transmitted to the second waveguide pupil dilator, but not all at exactly the same time. For example, the transmission of the replicas may be staggered, sequenced, or otherwise time-controlled. For example, this allows the controller, and thus the display system, to adapt to movement of the observer's head and, therefore, eyebox. Alternatively or additionally, it may be useful to accommodate the fact that an observer will almost certainly have multiple viewing apertures, i.e., two eyes; therefore, because the eyes are physically displaced from one another and have different, respective fields of view, the human brain will inherently expect at least a slightly different field of view for each eye, ensuring that the two eyes do not receive holographic light corresponding to the exact same image content at the exact same time.

[0056] The series of apertures in the control device can extend along the elongated direction of the first waveguide pupil dilator. The apertures can be physically separate apertures or can be software-controlled portions of the control device. Thus, the size, number, and location of the apertures within the control device can be dynamically variable. The control device can include multiple liquid crystal cells or regions that can be independently switched between transmissive and non-transmissive states.

[0057] The control device may be located between the first waveguide pupil expander and the waveguide coupler, or between the waveguide coupler and the second waveguide pupil expander, or between the folding mirror and the second waveguide pupil expander.

[0058] In some embodiments, the first waveguide pupil expander and the waveguide combiner may be bonded together. In some embodiments, the first waveguide pupil expander, the waveguide combiner, and the controller may be bonded together. In any such aspect, the bonding may include any suitable type of attachment between the respective components. Bonding the components of the display system together may increase the overall mechanical and thermal stability of the display system. It may also enhance and ensure optical alignment between the components, thereby ensuring accurate propagation of light through the system to the viewer.

[0059] Each "waveguide pupil dilator" replicates the light in the pupil to perform pupil dilation.

[0060] According to a second aspect, the light engine is arranged in a stacked or layered configuration including a first layer and a second layer. The first layer comprises a first pupil duplicator and a waveguide coupler. The first pupil duplicator is arranged to receive a diffracted light field from a diffractive structure having a pupil. The first pupil duplicator is substantially elongated. The second layer includes a second pupil duplicator. The second pupil duplicator is substantially elongated. The second pupil duplicator has a first major surface arranged to form an input and a second major surface arranged to form an output of the light engine. The waveguide coupler is arranged to couple the output of the first pupil duplicator to the input of the second pupil duplicator. The first layer and second layer are substantially parallel and adjacent to each other.

[0061] The first pupil replicator may be positioned to replicate the pupil of the diffractive structure in a first direction, and the second pupil replicator may be positioned to replicate the pupil of the diffractive structure in a second direction, which may be substantially perpendicular to the second direction.

[0062] The first pupil replicator and the waveguide coupler may be disposed within a coverage area of ​​the second pupil replicator, the coverage area including the area occupied by each layer when viewed in a direction substantially perpendicular to that layer.

[0063] The first pupil replicator may include a primary pair of opposing surfaces arranged to provide light guidance and pupil replication therebetween.

[0064] The waveguide coupler may include a primary pair of opposing faces each comprising an input face and an output face, the input and output faces being at an angle to each other.

[0065] The first pupil replicator and the waveguide coupler may be substantially coplanar.

[0066] The first pupil replicator and waveguide coupler of the first layer may be arranged to guide the diffracted light field in a plane substantially parallel to the second layer, where "waveguide" means to propagate light by internal reflection.

[0067] The second layer may be defined by first and second axes, and an elongated dimension of the first pupil duplicator may be angled relative to at least one of the first and second axes of the second layer. The angle of the elongated dimension of the first pupil duplicator relative to the first axis or the second axis of the second layer may be substantially equal to the angle of incidence of the diffracted light received by the first pupil duplicator.

[0068] The second pupil replicator may have a substantially quadrilateral cross-sectional shape.

[0069] The input of the second pupil replicator may be elongated and may correspond to the first axis of the second layer.

[0070] The first and second major surfaces of the second pupil replicator may form a primary pair of opposing surfaces arranged to provide light guidance and pupil replication therebetween.

[0071] A second pupil replicator in the second layer may be positioned to direct the diffracted light field in a plane substantially parallel to the first layer.

[0072] The first pupil replicator and the waveguide coupler may be affixed to a first major surface of the second pupil replicator.

[0073] The first pupil replicator and the waveguide coupler may each comprise a secondary pair of opposing surfaces arranged to confine the diffracted light field within its plane, where "confine" means to prevent the diffracted light from exiting therethrough. At least one surface of each secondary pair of opposing surfaces may comprise a reflective component (e.g., a mirror coating), and at least one surface of each secondary pair of opposing surfaces may be fixed to a common substrate via the reflective component. The common substrate may be a component of the vehicle housing the second pupil replicator or the light engine.

[0074] The first pupil replicator and the waveguide coupler may be joined together.

[0075] The light engine may further include a controller. The controller may include a plurality of independently controlled apertures arranged to determine which pupil duplicators are relayed from the first pupil duplicator to the second pupil duplicator. The first pupil duplicator, the waveguide coupler, and / or the controller may be coupled to one another.

[0076] According to a third aspect, a head-up display for a vehicle includes a first pupil replicator, a second pupil replicator, and a waveguide coupler. The first pupil replicator extends in a first direction. The first pupil replicator is positioned to receive a holographic light field from a spatial light modulator having a pixel array defining a limiting aperture of the head-up display. The holographic light field is a complex light field spatially modulated in accordance with a hologram displayed on the spatial light modulator. The second pupil replicator extends in the first direction and a second direction perpendicular to the first direction. The second pupil replicator includes a first major surface forming an output portion and a second major surface parallel to the first major surface. The waveguide coupler is positioned to optically couple the output of the first pupil replicator to the input of the second pupil replicator. The first pupil replicator and the waveguide coupler are disposed in a planar layer substantially parallel to and adjacent to the second major surface of the second pupil replicator. Optionally, the first pupil replicator and the waveguide coupler may be attached to the second major surface of the second pupil replicator or to a structural framework of the vehicle housing the head-up display.

[0077] Also provided is a light engine comprising a first layer comprising a first pupil replicator, the first pupil replicator being substantially planar and comprising a first major surface arranged to form an input and a second major surface arranged to form an output. The light engine further comprises a second layer including a second pupil replicator and a waveguide coupler arranged to couple the output of the second pupil replicator to the input of the first pupil replicator, the second pupil replicator being substantially elongated and the waveguide coupler being substantially planar, the first layer being defined by first and second axes, the elongated dimension of the second pupil replicator being angled with respect to at least one of the first and second axes such that the light coverage area of ​​the second layer is contained within the light coverage area of ​​the first layer.

[0078] The surface area of ​​the first layer may be substantially equal to or greater than, for example slightly greater than, the surface area of ​​each of the major surfaces of the first pupil duplicator. In other words, the first layer may comprise only the first pupil duplicator, or in addition to comprising the first pupil duplicator, may include other materials and / or one or more other components.

[0079] The first pupil replicator may be quadrilateral in shape, and the length and width of the quadrilateral may be substantially parallel to first and second axes, respectively, that define the first layer of the light engine.

[0080] The first and second layers may be substantially parallel and adjacent, so that the first and second layers may be provided in a compact, space-saving configuration.

[0081] A first pupil replicator may be positioned to replicate in a first direction and a second pupil replicator may be positioned to replicate in a second direction, the second pupil replicator being angled in the second layer.

[0082] The optical footprint of each layer can be defined as the footprint or area that each layer occupies when viewed in a direction perpendicular to the first and second layers.

[0083] The second pupil replicator may be angled relative to the second layer such that the light coverage area of ​​the second layer is contained within the light coverage area of ​​the first layer, and thus the two layers may be provided together in a configuration having a cross-sectional area no greater than the cross-sectional area of ​​the first layer.

[0084] Also provided is a light engine comprising a first pupil replicator extending in a first direction and a second direction perpendicular to the first direction, the first pupil replicator having a first major surface forming an output and a second major surface parallel to the first major surface. The light engine further comprises a second pupil replicator extending in the first direction and positioned to receive the diffracted light field from the spatial light modulator, and a waveguide coupler between the first pupil replicator and the second pupil replicator, the second pupil replicator and the waveguide coupler being positioned in a plane substantially parallel to and adjacent to the second major surface of the first pupil replicator.

[0085] The second pupil replicator (which may alternatively be called a "pupil dilator") may comprise a primary pair of opposing surfaces arranged to provide light guidance therebetween and pupil replication in a first direction. The waveguide coupler may comprise a primary pair of opposing surfaces forming an input and an output, respectively, the input and output surfaces being at an angle to each other. The input and output surfaces may intersect or meet each other at a vertex or corner.

[0086] The second pupil replicator and the waveguide coupler may each comprise a secondary pair of opposing surfaces arranged to confine the diffracted light field within its plane, thus preventing light leakage from its secondary pair of opposing surfaces when diffracted or divergent light is input to the second pupil replicator or waveguide. For each of the second pupil replicator and the waveguide coupler, each secondary pair of opposing surfaces may be arranged substantially perpendicular to the corresponding primary pair of opposing surfaces.

[0087] The first pupil dilator may comprise a primary pair of opposing surfaces arranged to provide light guidance therebetween and pupil replication in a second direction.

[0088] The second pupil replicator and the waveguide coupler may be affixed to a second major surface of the first pupil replicator.

[0089] At least one surface of each secondary pair of opposing surfaces (of the second pupil replicator and the waveguide coupler) may be fixed to a common substrate, which may be the second pupil replicator.

[0090] The light engine may form part of a head-up display (HUD), such as a vehicle HUD. At least one surface of each secondary pair of opposing surfaces may be bonded to another component or portion of the vehicle in which the HUD is provided. The common substrate may therefore be a component of the vehicle that houses the light engine, such as the chassis of the automobile.

[0091] Bonding the second pupil replicator and the waveguide coupler to a common substrate helps to reduce manufacturing costs and ensure robustness of the light engine, for example by ensuring that they are provided in a compact form, e.g., a relatively flat and streamlined form.

[0092] The second pupil replicator and the waveguide coupler may be disposed within the area occupied by the first pupil replicator. The light engine may be arranged in a stacked / layered configuration comprising a first layer and a second layer, where the first layer comprises the first pupil replicator and the waveguide coupler and the second layer comprises the second pupil replicator, or vice versa.

[0093] The first layer and the second layer may be substantially parallel and adjacent.

[0094] The second pupil replicator and the waveguide coupler may be arranged to propagate light in a plane substantially parallel to the plane of the first pupil replicator.

[0095] The second pupil replicator may be positioned to replicate the diffracted light field in a first direction, and the first pupil replicator may be positioned to replicate the diffracted light field in a second direction.

[0096] The second pupil replicator may comprise a first pair of opposing surfaces arranged to guide in a plane parallel to the plane of the first pupil dilator.

[0097] The second pupil dilator may include a second pair of opposing surfaces positioned to prevent the diffracted light field from exiting the first pupil dilator through the second pair of opposing surfaces.

[0098] The second pair of opposing surfaces may be perpendicular to the first pair of opposing surfaces, and at least one of the second pair of opposing surfaces may include a reflective coating arranged to provide internal reflection within the second pupil replicator.

[0099] There is also provided a light engine comprising a first pupil replicator extending in a first direction and arranged to receive a diffracted light field from a spatial light modulator (SLM), and a second pupil replicator extending in the first direction and a second direction perpendicular to the first direction, the second pupil replicator having a first main surface forming an output portion and a second main surface parallel to the first main surface, and a waveguide coupler arranged to optically couple the output portion of the first pupil replicator to the input portion of the second pupil replicator, the first pupil replicator and the waveguide coupler being fixed to the second main surface of the second pupil replicator.

[0100] By providing the first pupil replicator and the waveguide coupler fixed to the second major surface of the second pupil replicator, the light engine may be provided in a compact, streamlined, and robust form. For example, by fixing the components together, the light engine may be protected from potential damage that may otherwise occur when the light engine is provided in an unstable environment, such as a moving or vibrating environment in a vehicle.

[0101] The first pupil replicator and the waveguide coupler may be provided in a common plane or layer, the SLM, and optionally the light source, may also be provided in that common layer, and the second pupil replicator may be provided in a second, different layer.

[0102] Also provided is a head-up display (HUD) system comprising the display device of any of the above aspects. The HUD system may be implemented in a vehicle, including, but not limited to, an automobile vehicle. The HUD system may further comprise an optical combiner, such as a windscreen or windshield. In some aspects, the display system may be positioned to direct output light to the optical combiner, which may be positioned to direct (or redirect) the output light to an eyebox of an intended observer. The eyebox may be substantially orthogonal to a plane defined by the second waveguide pupil dilator.

[0103] Also provided is a method for providing pupil dilation for a diffracted light field, comprising directing the diffracted light field into a first waveguide pupil dilator, the first waveguide pupil dilator having an input port, an output port, a first pair of parallel surfaces, and a second pair of parallel surfaces, the first pair of parallel surfaces being orthogonal to the second pair of parallel surfaces, the method further comprising guiding the diffracted light field from the input port to the output port by internal reflection between the first pair of parallel surfaces, a first surface of the first pair of parallel surfaces being partially transflective such that the light field splits at each internal reflection and multiple replicas of the light field transmit through an area of ​​the first surface that forms the output port, and the second pair of parallel surfaces are also positioned to guide the light field from the input port to the output port by at least one internal reflection.

[0104] The term "hologram" refers to a recording containing amplitude or phase information about an object, or some combination thereof. The term "holographic reconstruction" refers to an optical reconstruction of an object formed by illuminating a hologram. Because the holographic reconstruction is a real image and spatially separated from the hologram, the system disclosed herein is described as a "holographic projector." The term "reconstruction field" refers to the 2D region in which the holographic reconstruction is formed and perfectly focused. When a hologram is displayed on a spatial light modulator containing pixels, the reconstructed field is repeated in the form of multiple diffraction orders, each of which is a replica of the zeroth-order reconstructed field. The zeroth-order reconstructed field is the brightest reconstructed field and therefore generally corresponds to the preferred or first-order reconstructed field. Unless otherwise specified, the term "reconstruction field" should be interpreted as referring to the zeroth-order reconstructed field. The term "reconstruction plane" refers to a plane in space that contains all the reconstructed fields. The terms "image," "reconstructed image," and "image region" refer to the region of the reconstructed field illuminated by the light of the holographic reconstruction. In some embodiments, an "image" may include discrete spots that may be referred to as "image spots" or, for convenience only, "image pixels."

[0105] The terms "encoding," "writing," or "addressing" are used to describe the process of providing a plurality of pixels of an SLM with respective control values ​​that respectively determine the modulation level of each pixel. The pixels of the SLM can be said to be configured to "display" a light modulation distribution in response to receiving the control values. The SLM can therefore be said to "display" a hologram, and a hologram can be thought of as an array of light modulation values ​​or levels.

[0106] 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 may be referred to as phase-only holograms. While the embodiments relate to phase-only holograms, the present disclosure is equally applicable to amplitude-only holography.

[0107] The present disclosure is also equally 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 complex modulation using a so-called full complex hologram, which contains both amplitude and phase information about the original object. Such a hologram may be referred to as a full complex hologram because the value (grayscale) assigned to each pixel of the hologram has an amplitude and a phase component. The value (grayscale) assigned to each pixel may be represented as a complex number having both an amplitude and a phase component. In some embodiments, a full complex computer-generated hologram is calculated.

[0108] As shorthand for "phase delay," one can refer to a phase value, phase component, phase information, or simply the phase of a computer-generated hologram or a pixel of a spatial light modulator. That is, any phase value described is actually a number (e.g., ranging from 0 to 2π) representing the amount of phase delay provided by that pixel. For example, a spatial light modulator pixel described as having a phase value of π / 2 delays the phase of received light by π / 2 radians. In some embodiments, each pixel of a spatial light modulator is operable at one of multiple possible modulation values ​​(e.g., phase delay values). The term "grayscale" may be used to refer to multiple available modulation levels. For example, the term "grayscale" may be conveniently used to refer to multiple available phase levels in a phase-only modulator, even if the different phase levels do not provide different shades of gray. The term "grayscale" may also be conveniently used to refer to multiple available complex modulation levels in a complex modulator.

[0109] Thus, a hologram comprises an array of gray levels, i.e., an array of optical modulation values, such as an array of phase delay values ​​or complex modulation values. A hologram is also considered a diffraction pattern because it is a pattern displayed on a spatial light modulator and causes diffraction when illuminated with light having a wavelength comparable to, but generally less than, the pixel pitch of the spatial light modulator. Reference is made herein to combining holograms with other diffraction patterns, such as diffraction patterns that function as lenses or gratings. For example, a diffraction pattern that functions as a grating may be combined with a hologram to translate the reconstruction field on the reconstruction plane, or a diffraction pattern that functions as a lens may be combined with a hologram to focus the holographic reconstruction on the reconstruction plane in the near field.

[0110] In the following detailed description, different embodiments and groups of embodiments may be disclosed separately, but any feature of any embodiment or group of embodiments may be combined with any other feature or combination of features of any embodiment or group of embodiments, i.e., all possible combinations and permutations of features disclosed in this disclosure are contemplated.

[0111] Particular embodiments will now be described, by way of example only, with reference to the following figures: [Brief explanation of the drawings]

[0112] [Figure 1] FIG. 1 is a schematic diagram showing a reflective SLM generating a holographic reconstruction on a screen. [Figure 2A] 1 illustrates the first iteration of an exemplary Gerchberg-Saxton type algorithm. [Figure 2B] 1 illustrates the second and subsequent iterations of an exemplary Gerchberg-Saxton type algorithm. [Figure 2C] 1 illustrates alternative second and subsequent iterations of an exemplary Gerchberg-Saxton type algorithm. [Figure 3] FIG. 1 is a schematic diagram of a reflective LCOS SLM. [Figure 4A] Shown is an image (bottom) containing multiple image areas and a corresponding hologram (top) containing multiple hologram elements. [Figure 4B] 1 illustrates a hologram characterized by routing or channeling holographically encoded light into multiple discrete holographic channels. [Figure 5] 4B through different optical paths to the eye. FIG. [Figure 6] FIG. 1 shows a perspective view of a pair of stacked image replicators arranged to expand a beam in two dimensions. [Figure 7] 1 shows an improved display system with a two-dimensional pupil dilator. [Figure 8] 3 shows the diffracted light cones output by the diffractive structure. [Figure 9] A two-layer pupil dilator is shown. [Figure 10] 10 shows an enlarged view of the two-layer pupil dilator of FIG. 9. [Figure 11] 11 shows a plan view of the two-layer pupil dilator of FIG. 10, further including a spatial light modulator (SLM). [Figure 12] 1 illustrates a head-up display system including a pupil dilator. DETAILED DESCRIPTION OF THE INVENTION

[0113] The same reference numbers are used throughout the drawings to refer to the same or similar parts.

[0114] The present invention is not limited to the embodiments described below, but extends to the full scope of the appended claims, i.e., the present invention may be embodied in different forms and should not be construed as being limited to the embodiments set forth above for illustrative purposes.

[0115] Singular terms may include plurals unless specifically stated otherwise.

[0116] A structure described as being formed on top / bottom of another structure or above / below other structures should be interpreted to include cases where the structures contact each other and also where a third structure is disposed between them.

[0117] In describing temporal relationships, for example, when the temporal order of events is described as "after," "succeeding," "next," "before," etc., the present disclosure should be construed to include consecutive and non-sequential events unless otherwise specified. For example, unless expressions such as "just," "immediately," or "directly" are used, the description should be construed to include non-sequential cases.

[0118] In this specification, terms such as "first" and "second" may be used to describe various elements, but these elements are not limited by these terms. These terms are used only to distinguish one element from another. For example, a first element could be referred to as a second element, and similarly, a second element could be referred to as a first element, without departing from the scope of the appended claims.

[0119] Features of different embodiments may be partially or wholly combined or combined with each other and may interoperate with each other in various ways. Some embodiments may be implemented independently of each other or may be implemented together in a co-dependent manner.

[0120] optical configuration FIG. 1 shows an embodiment in which a computer-generated hologram is encoded on a single spatial light modulator. The computer-generated hologram is the Fourier transform of the object for reconstruction. Thus, the hologram can be said to be a Fourier domain, frequency domain, or spectral domain representation of the object. In this embodiment, the spatial light modulator is a reflective liquid crystal on silicon (LCOS) device. The hologram is encoded on the spatial light modulator, and the holographic reconstruction is formed at a receiving surface, such as a screen or diffuser, in the replay field.

[0121] A light source 110, e.g., a laser or laser diode, is positioned to illuminate the SLM 140 through a collimating lens 111. The collimating lens causes a substantially planar wavefront of light to be incident on the SLM. In FIG. 1, the wavefront direction is off-normal (e.g., 2-3 degrees away from being truly perpendicular to the plane of 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. In the embodiment shown in FIG. 1, the arrangement is such that light from the light source is reflected from the mirrored rear surface of the SLM and interacts with the light modulating layer to form an exit wavefront 112. The exit wavefront 112 is applied to an optical system including a Fourier transform lens 120 having its focus at a screen 125. More specifically, the Fourier transform lens 120 receives the beam of modulated light from the SLM 140 and performs a frequency-space transformation to generate a holographic reconstruction on the screen 125.

[0122] In particular, in this type of holography, each pixel of the hologram contributes to the overall reconstruction: there is no one-to-one correlation between a particular point on the reconstructed field (or image pixel) and a particular light-modulating element (or hologram pixel). In other words, the modulated light leaving the light-modulating layer is dispersed across the reconstructed field.

[0123] In these embodiments, the position of the holographic reconstruction in space is determined by the refractive power (focusing power) of the Fourier transform lens. In the embodiment shown in FIG. 1, the Fourier transform lens is a physical lens. That is, the Fourier transform lens is an optical Fourier transform lens, and the Fourier transform is performed optically. Any lens can act as a Fourier transform lens, but the performance of the lens limits the accuracy of the Fourier transform it performs. Those skilled in the art understand how to use lenses to perform an optical Fourier transform.

[0124] Hologram Calculation In some embodiments, the computer-generated hologram is a Fourier transform hologram, or simply a Fourier hologram or Fourier-based hologram, in which an image is reconstructed in the far field by exploiting the Fourier transform properties of a positive lens. A Fourier hologram is calculated by Fourier transforming the desired light field in the reconstruction plane back to the lens plane. A computer-generated Fourier hologram can be calculated using the Fourier transform.

[0125] Fourier transform holograms can be calculated using algorithms such as the Gerchberg-Saxton algorithm. Furthermore, the Gerchberg-Saxton algorithm can be used to calculate Fourier domain holograms (i.e., Fourier transform holograms) from amplitude-only information in the spatial domain (such as a photograph). Phase information about an object is effectively "retrieved" from amplitude-only information in the spatial domain. In some embodiments, computer-generated holograms are calculated from amplitude-only information using the Gerchberg-Saxton algorithm or a variant thereof.

[0126] The Gerchberg-Saxton algorithm calculates the intensity cross section I of the light beam in plane A and plane B. A (x, y) and I B (x, y) is known and I A (x, y) and I B Consider the situation when (x, y) are related by a single Fourier transform: with a given intensity cross section, the phase distribution Ψ in plane A and plane B A (x, y) and Ψ B An approximation to (x, y) is found for each. The Gerchberg-Saxton algorithm finds a solution to this problem by following an iterative process. More specifically, the Gerchberg-Saxton algorithm finds the solution to I A (x, y) and I BA data set (amplitude and phase) representing (x, y) is repeatedly transferred between the spatial and Fourier (spectral or frequency) domains while iteratively applying spatial and spectral constraints. A corresponding computer-generated hologram in the spectral domain is obtained by at least one iteration of the algorithm. The algorithm is arranged to converge and produce a hologram representing the input image. The hologram may be an amplitude-only hologram, a phase-only hologram, or a fully complex hologram.

[0127] In some embodiments, phase-only holograms are calculated using an algorithm based on the Gerchberg-Saxton algorithm, such as those described in British Patent Nos. 2,498,170 or 2,501,112, the entire contents of which are incorporated herein by reference. However, the embodiments disclosed herein describe calculating phase-only holograms merely by way of example. In these embodiments, the Gerchberg-Saxton algorithm retrieves phase information Ψ[u,v] of the Fourier transform of a data set that yields known amplitude information T[x,y], which represents a target image (e.g., a photograph). Because magnitude and phase are inherently combined in the Fourier transform, the transformed magnitude and phase contain useful information about the accuracy of the calculated data set. Therefore, the algorithm can be used iteratively with feedback on both the amplitude and phase information. However, in these embodiments, only the phase information Ψ[u,v] is used as the hologram to form a holographic representation of the target image at the image plane. The hologram is a data set (e.g., a 2D array) of phase values.

[0128] In another embodiment, an algorithm based on the Gerchberg-Saxton algorithm is used to calculate a full complex hologram. A full complex hologram is a hologram that has a magnitude component and a phase component. A hologram is a data set (e.g., a 2D array) that includes an array of complex data values, each of which includes a magnitude component and a phase component.

[0129] In some embodiments, the algorithm processes complex data and the Fourier transform is a complex Fourier transform. The complex data may be considered to include (i) a real component and an imaginary component, or (ii) a magnitude component and a phase component. In some embodiments, the two components of the complex data are treated differently at various stages of the algorithm.

[0130] FIG. 2A illustrates a first iteration of an algorithm according to some embodiments for computing phase-only holograms. The input to the algorithm is an input image 210, which includes a two-dimensional array of pixels or data values, each of which is a magnitude or amplitude value. That is, each pixel or data value of the input image 210 does not have a phase component. Thus, the input image 210 can be considered a magnitude-only, amplitude-only, or intensity-only distribution. An example of such an input image 210 is a photograph or a frame of a video, which includes a time series of frames. The first iteration of the algorithm begins with a data formation step 202A, which involves assigning a random phase value to each pixel of the input image using a random phase distribution (or random phase seed) 230 to form a starting complex data set, where each data element of the set includes a magnitude and a phase. The starting complex data set can be said to represent the input image in the spatial domain.

[0131] First processing block 250 receives a starting complex data set and performs a complex Fourier transform to form a Fourier transform complex data set. Second processing block 253 receives the Fourier transformed complex data set and outputs hologram 280A. In some embodiments, hologram 280A is a phase-only hologram. In these embodiments, second processing block 253 quantizes each phase value and sets each amplitude value to 1 to form hologram 280A. Each phase value is quantized according to a phase level that can be represented on a pixel of a spatial light modulator used to "display" the phase-only hologram. For example, if each pixel of the spatial light modulator provides 256 different phase levels, each phase value of the hologram is quantized to one of the 256 possible phase levels. Hologram 280A is a phase-only Fourier hologram representing an input image. In other embodiments, hologram 280A is a full complex hologram including an array of complex data values ​​(each including an amplitude component and a phase component) derived from the received Fourier transform complex data set. In some embodiments, second processing block 253 constrains each complex data value to one of a plurality of allowable complex modulation levels to form hologram 280A. The constraining step may include setting each complex data value to the closest allowable complex modulation level in the complex plane. Hologram 280A may be said to represent the input image in the spectral domain, the Fourier domain, or the frequency domain. In some embodiments, the algorithm stops at this point.

[0132] However, in other embodiments, the algorithm continues as represented by the dotted arrow in Figure 2A. In other words, the steps following the dotted arrow in Figure 2A are optional (i.e., not required for all embodiments).

[0133] A third processing block 256 receives the modified complex data set from the second processing block 253 and performs an inverse Fourier transform to form an inverse Fourier transformed complex data set, which can be said to represent the input image in the spatial domain.

[0134] The fourth processing block 259 receives the inverse Fourier transformed complex data set and extracts a magnitude value distribution 211A and a phase value distribution 213A. Optionally, the fourth processing block 259 evaluates the magnitude value distribution 211A. Specifically, the fourth processing block 259 can compare the magnitude value distribution 211A of the inverse Fourier transformed complex data set with the input image 210, which is itself, of course, a magnitude value distribution. If the difference between the magnitude value distribution 211A and the input image 210 is sufficiently small, the fourth processing block 259 can determine that the hologram 280A is acceptable. That is, if the difference between the magnitude value distribution 211A and the input image 210 is sufficiently small, the fourth processing block 259 can determine that the hologram 280A represents the input image 210 sufficiently accurately. In some embodiments, the phase value distribution 213A of the inverse Fourier transformed complex data set is ignored for purposes of comparison. It will be understood that any number of different methods for comparing magnitude value distribution 211A to input image 210 may be utilized, and the present disclosure is not limited to any particular method. In some embodiments, a mean squared difference is calculated, and if the mean squared difference is less than a threshold, hologram 280A is deemed acceptable. If fourth processing block 259 determines that hologram 280A is unacceptable, further iterations of the algorithm may be performed. However, this comparison step is not required, and in other embodiments, the number of iterations of the algorithm performed is predetermined, pre-set, or user-defined.

[0135] 2B illustrates the second iteration of the algorithm and any further iterations of the algorithm. The phase value distribution 213A of the previous iteration is fed back through the processing blocks of the algorithm. The magnitude value distribution 211A is rejected in favor of the magnitude value distribution of the input image 210. In the first iteration, the data formation step 202A formed the first complex data set by combining the magnitude value distribution of the input image 210 with the random phase distribution 230. However, in the second and subsequent iterations, the data formation step 202B includes forming a complex data set by combining (i) the phase value distribution 213A from the previous iteration of the algorithm and (ii) the magnitude value distribution of the input image 210.

[0136] The complex data set formed by data formation step 202B of FIG. 2B is then processed in the same manner as described with reference to FIG. 2A to form second iteration hologram 280B. Therefore, the description of the process will not be repeated here. The algorithm can stop when second iteration hologram 280B has been calculated. However, any number of further iterations of the algorithm may be performed. It will be understood that third processing block 256 is only required if fourth processing block 259 or further iterations are required. The output hologram 280B generally improves with each iteration. However, in practice, a point is usually reached where no significant improvement is observed, or the positive benefits of performing further iterations outweigh the negative effects of additional processing time. Therefore, the algorithm is described as iterative and convergent.

[0137] 2C depicts an alternative embodiment of the second and subsequent iterations. The distribution of phase values ​​213A of the previous iteration is fed back through the processing blocks of the algorithm. The distribution of magnitude values ​​211A is rejected in favor of an alternative distribution of magnitude values. In this alternative embodiment, the alternative distribution of magnitude values ​​is derived from the distribution of magnitude values ​​211 of the previous iteration. Specifically, processing block 258 subtracts the distribution of magnitude values ​​of the input image 210 from the distribution of magnitude values ​​211 of the previous iteration, scales the difference by a gain factor α, and subtracts the scaled difference from the input image 210. This is mathematically represented by the following equation, where the subscripts and numbers indicate the iteration number:

number

[0138] The gain factor α may be fixed or variable. In some embodiments, the gain factor α is determined based on the size and rate of the incoming target image data. In some embodiments, the gain factor α depends on the number of iterations. In some embodiments, the gain factor α is simply a function of the number of iterations.

[0139] The embodiment of Figure 2C is in all other respects identical to the embodiment of Figures 2A and 2B. A phase-only hologram Ψ(u,v) can be said to contain a phase distribution in the frequency domain or the Fourier domain.

[0140] In some embodiments, the Fourier transform is performed using a spatial light modulator. Specifically, the hologram data is combined with second data that provides optical power. That is, the data written to the spatial light modulator includes hologram data representing the object and lens data representing the lens. When displayed on the spatial light modulator and illuminated with light, the lens data emulates a physical lens, i.e., brings light to a focal point in the same manner as a corresponding physical optical system. Thus, the lens data provides optical or focusing power. In these embodiments, the physical Fourier transform lens 120 in FIG. 1 may be omitted. Methods for calculating the data representing a lens are known. The data representing a lens is sometimes referred to as a software lens. For example, a phase-only lens may be formed by calculating the phase delay caused at each point in the lens due to its refractive index and spatially varying optical path length. For example, the optical path length at the center of a convex lens is greater than the optical path length at the edge of the lens. An amplitude-only lens may be formed by a Fresnel zone plate. In the field of computer-generated holography, methods are also known for combining data representing lenses with holograms so that the Fourier transform of the hologram can be performed without the need for a physical Fourier lens. In some embodiments, lens data is combined with the hologram by simple addition, such as simple vector addition. In some embodiments, physical lenses are used in conjunction with software lenses to perform the Fourier transform. Alternatively, in other embodiments, the Fourier transform lens is omitted entirely, so that the holographic reconstruction occurs in the far field. In further embodiments, the hologram can be combined in the same way with grating data, i.e., data arranged to perform the function of a grating, such as image steering. Again, methods for calculating such data are known in the art. For example, a phase-only grating can be formed by modeling the phase delay caused by each point on the surface of a blazed grating. An amplitude-only grating can simply be superimposed with an amplitude-only hologram to provide angular steering of the holographic reconstruction.The second data providing lens and / or steering may be referred to as a light processing function or a light processing pattern to distinguish it from the holographic data, which may be referred to as an image forming function or an image forming pattern.

[0141] In some embodiments, the Fourier transform is performed jointly by a physical Fourier transform lens and a software lens, i.e., some of the optical power contributing to the Fourier transform is provided by a software lens, and the remaining optical power contributing to the Fourier transform is provided by one or more physical optics systems.

[0142] In some embodiments, a real-time engine is provided that is arranged to receive image data and use an algorithm to calculate a hologram in real time. In some embodiments, the image data is a video comprising a sequence of image frames. In other embodiments, the hologram is pre-calculated, stored in computer memory, and recalled as needed for display on the SLM. That is, in some embodiments, a repository of pre-defined holograms is provided.

[0143] The embodiments relate, by way of example only, to Fourier holography and Gerchberg-Saxton type algorithms. The present disclosure is equally applicable to Fresnel holography and Fresnel holograms, which can be calculated by similar methods. The present disclosure is also applicable to holograms calculated by other techniques, such as those based on point cloud methods.

[0144] Light Modulation Spatial light modulators can be used to display diffraction patterns, including computer-generated holograms. If the hologram is a phase-only hologram, a spatial light modulator that modulates phase is required. If the hologram is a fully complex hologram, a spatial light modulator that modulates phase and amplitude may be used, or a first spatial light modulator that modulates phase and a second spatial light modulator that modulates amplitude may be used.

[0145] In some embodiments, the light modulation elements (i.e., pixels) of the spatial light modulator are cells containing liquid crystals. That is, in some embodiments, the spatial light modulator is a liquid crystal device in which the optically active component is a liquid crystal. Each liquid crystal cell is configured to selectively provide a plurality of light modulation levels. That is, each liquid crystal cell is configured to operate at one light modulation level selected from a plurality of possible light modulation levels at any given time. Each liquid crystal cell is dynamically reconfigurable to a light modulation level different from the plurality of light modulation levels. In some embodiments, the spatial light modulator is a reflective liquid crystal on silicon (LCOS) spatial light modulator, although the disclosure is not limited to this type of spatial light modulator.

[0146] LCOS devices offer a dense array of light-modulating elements, or pixels, within a small aperture (e.g., a few centimeters wide). The pixels are typically less than 10 microns, resulting in a diffraction angle of a few degrees, meaning the optical system can be compact. Properly illuminating the small aperture of an LCOS SLM is easier than the larger apertures of other liquid crystal devices. LCOS devices are typically reflective, meaning the circuitry that drives the LCOS SLM's pixels can be embedded beneath the reflective surface, resulting in a high aperture ratio. In other words, the pixels are densely packed, meaning there is little dead space between them. This is advantageous because it reduces optical noise in the playback field. LCOS SLMs use silicon backplanes, which have the advantage that the pixels are optically flat. This is particularly important for phase-modulating devices.

[0147] A suitable LCOS SLM is described below, by way of example only, with reference to FIG. 3. The LCOS device is formed using a single-crystal silicon substrate 302. It has a two-dimensional array of square planar aluminum electrodes 301, spaced apart by gaps 301a, disposed on the upper surface of the substrate. Each of the electrodes 301 can be addressed via circuitry 302a embedded in the substrate 302. Each electrode forms a respective planar mirror. An alignment layer 303 is disposed on the electrode array, and a liquid crystal layer 304 is disposed on the alignment layer 303. A second alignment layer 305 is disposed on a planar transparent layer 306, for example of glass. A single transparent electrode 307, for example of ITO, is disposed between the transparent layer 306 and the second alignment layer 305.

[0148] Each square electrode 301, together with the area overlying the transparent electrode 307 and the intervening liquid crystal material, defines a controllable phase-modulating element 308, often referred to as a pixel. The effective pixel area, or fill factor, is the percentage of the total pixel that is optically active, taking into account the space 301a between pixels. By controlling the voltage applied to each electrode 301 relative to the transparent electrode 307, the properties of the liquid crystal material in the respective phase-modulating element can be changed, thereby imparting variable retardation to light incident thereon. The effect is to impart phase-only modulation to the wavefront; i.e., no amplitude effects occur.

[0149] The described LCOS SLMs output spatially modulated light in a reflective manner. Reflective LCOS SLMs have the advantage that the signal lines, gate lines, and transistors are located below the mirror surface, resulting in a high fill factor (typically greater than 90%) and high resolution. Another advantage of using a reflective LCOS spatial light modulator is that the liquid crystal layer can be half the thickness that would be required using a transmissive device. This significantly improves the switching speed of the liquid crystal (an important advantage for projecting moving images). However, the teachings of this disclosure can be implemented using a transmissive LCOS SLM as well.

[0150] Light Channeling The optical system of the present disclosure is applicable to pupil dilation with any diffractive light field. In some embodiments, the diffractive light field is a holographic light field, i.e., a complex light field that is spatially modulated according to a hologram of an image rather than the image itself. In some embodiments, the hologram is a special type of hologram that angularly splits / channels image content. This type of hologram is further described herein only as one example of a diffractive light field compatible with the present disclosure. Other types of holograms may also be used in conjunction with the display systems and light engines disclosed herein.

[0151] As will be further understood from the discussion beginning with FIG. 7 , display systems and methods including a waveguide pupil dilator are described below. As is well known to those skilled in the art, a waveguide may be considered a “pupil dilator” because it can be used to increase the area upon which light emitted by (or into) a relatively small light emitter, such as a relatively small SLM or other pixelated display device used in the arrangements described herein, can be viewed by a human observer or other viewing system positioned at a distance, such as a relatively long distance, from the light emitter. The waveguide achieves this by increasing the number of transmission points through which light is output toward the observer. As a result, the light can be seen from multiple different observer positions; for example, the observer can move their head, and therefore their gaze, while still being able to see the light from the light emitter. Thus, the observer’s “eyebox” or “eye motion box” is said to be enlarged using a waveguide pupil dilator. This has many useful applications, such as, but not limited to, head-up displays, including, but not limited to, automotive head-up displays.

[0152] The display systems described herein may be configured to guide light, such as a diffracted light field, through a waveguide pupil dilator to provide pupil dilation in at least one dimension, e.g., two dimensions. The diffracted light field may include light output by a spatial light modulator (SLM), such as an LCOS SLM. For example, the diffracted light field may include light encoded by a hologram displayed by the SLM. For example, the diffracted light field may include light of a holographically reconstructed image corresponding to the hologram displayed by the SLM. The hologram may include a computer-generated hologram (CGH), such as, but not limited to, a point cloud hologram, a Fresnel hologram, or a Fourier hologram. The hologram may be referred to as a "diffractive structure" or a "modulation pattern." The SLM or other display device may be configured to display a diffractive pattern (or modulation pattern) including a hologram and one or more other elements, such as a software lens or a diffraction grating, in a manner well known to those skilled in the art.

[0153] Holograms can be calculated to provide channeling of diffracted light fields. This is described in detail in GB Patent No. 2101666.2, GB Patent Application No. 2101667.0, and GB Patent No. 2112213.0, all of which are incorporated herein by reference. Generally speaking, holograms can be calculated to correspond to an image to be holographically reconstructed. The image to which the hologram corresponds is sometimes referred to as the "input image" or "target image." When displayed on an SLM and appropriately illuminated, the hologram can be calculated to form a light field (output by the SLM) that includes a cone of spatially modulated light. In some embodiments, the cone includes multiple successive optical channels of spatially modulated light corresponding to respective successive regions of the image. However, this disclosure is not limited to this type of hologram.

[0154] Although reference is made herein to a "hologram" or a "computer-generated hologram (CGH)," it will be understood that the SLM may be configured to dynamically display multiple different holograms, either sequentially or as a result. The systems and methods described herein are applicable to the dynamic display of multiple different holograms.

[0155] 4A-5 show examples of the types of holograms that can be displayed on a display device such as an SLM that can be used with the pupil dilators disclosed herein, however, this example should not be considered limiting with respect to the present disclosure.

[0156] FIG. 4A shows an image 452 for projection, including eight image regions / components V1 through V8. FIG. 4A shows eight image components by way of example only; image 452 can be divided into any number of components. FIG. 4A also shows an encoded light pattern 454 (i.e., a hologram) that can reconstruct image 452 when transformed, for example, by the lenses of an appropriate observation system. Encoded light pattern 454 includes first through eighth sub-holograms or components H1 through H8, corresponding to the first through eighth image components / regions V1 through V8. FIG. 4A further illustrates how a hologram decomposes image content by angle. Thus, a hologram can be characterized by the light channeling it performs. This is illustrated in FIG. 4B. Specifically, the hologram in this example directs light to multiple discrete regions. In the illustrated example, the discrete regions are disks, but other shapes are also contemplated. The optimal disk size and shape, after propagation through a waveguide, may be related to the size and shape of the observation system's entrance pupil.

[0157] FIG. 5 shows a viewing system 500 including a display device that displays the hologram calculated as shown in FIGS. 4A and 4B.

[0158] The observation system 500 comprises a display device, which in this arrangement comprises an LCOS 502. The LCOS 502 is arranged to display a modulation pattern (or "diffraction pattern") comprising a hologram and to project the holographically encoded light towards an eye 505, which comprises a pupil acting as an aperture 504, a lens 509, and a retina (not shown) acting as a viewing surface. There is a light source (not shown) arranged to illuminate the LCOS 502. The lens 509 of the eye 505 performs the conversion from hologram to image. The light source may be of any suitable type and may comprise, for example, a laser light source.

[0159] Observation system 500 further comprises a waveguide 508 positioned between LCOS 502 and eye 505. The presence of waveguide 508 allows all angular content from LCOS 502 to be received by the eye, even at the relatively large projection distances shown, because waveguide 508 acts as a pupil dilator in a manner that is well known and therefore only briefly described herein.

[0160] In summary, the waveguide 508 shown in FIG. 5 comprises a substantially elongated formation. In this example, the waveguide 508 comprises an optical slab of refractive material, although other types of waveguides are well known and may be used. The waveguide 508 is positioned to intersect with a light cone (i.e., a diffracted light field) projected from the LCOS 502, e.g., at an oblique angle. In this example, the size, location, and position of the waveguide 508 are configured to ensure that light from each of the eight ray bundles within the light cone enters the waveguide 508. Light from the light cone enters the waveguide 508 through its first plane (located closest to the LCOS 502) and is guided at least partially along the length of the waveguide 508 before being emitted through its second plane substantially opposite the first surface (located closest to the eye). As will be appreciated, the second plane is partially reflective and partially transmissive. In other words, as each ray of light travels from a first plane within the waveguide 508 and hits a second plane, some of the light is transmitted out of the waveguide 508 and some is reflected by the second plane back to the first plane. The first plane is reflective, so that all of the light that hits the first plane from within the waveguide 508 is reflected back towards the second plane. Thus, some of the light may simply be refracted between the two planes of the waveguide 508 before being transmitted, while other light may be reflected and therefore undergo one or more reflections (or "bounces") between the planes of the waveguide 508 before being transmitted.

[0161] FIG. 5 shows a total of nine "bounce" points B0-B8 along the length of waveguide 508. Light for all points (V1-V8) of the image as shown in FIG. 4A is transmitted from the waveguide at each "bounce" from the second plane of waveguide 508, but has a trajectory that allows light from only one angular portion of the image (e.g., one light from V1-V8) to reach eye 505 from each "bounce" point B0-B8. Furthermore, light from different angular portions of the image V1-V8 reaches eye 505 from each "bounce" point. Thus, in the example of FIG. 5, each angular channel of encoded light reaches the eye only once from waveguide 508.

[0162] The methods and arrangements described above can be implemented in a variety of different applications and viewing systems, for example they may be implemented in a head- or helmet-mounted device (HMD) such as a head-up display (HUD) or an augmented reality (AR) HMD.

[0163] Although virtual images, which require the eye to transform received modulated light to form a perceived image, are generally discussed herein, the methods and arrangements described herein can be applied to real images.

[0164] Two-dimensional pupil dilation While the arrangement shown in Figure 5 includes a single waveguide that provides pupil dilation in one dimension, pupil dilation can be provided in multiple dimensions, such as two. Additionally, while the example of Figure 5 uses calculated holograms to create channels of light, each corresponding to a different portion of the image, this disclosure and the systems described below are not limited to such types of holograms.

[0165] FIG. 6 shows a perspective view of a system 600 that includes two replicators 604, 606 arranged to expand a light beam 602 in two dimensions.

[0166] In the system 600 of FIG. 6, the first replicator 604 includes a first pair of surfaces stacked parallel to one another and arranged to provide replication or pupil dilation similar to the waveguide 508 of FIG. 5. The first pair of surfaces are similarly sized and shaped (possibly identically) to one another and are substantially elongated in one direction. A collimated light beam 602 is directed to an input on the first replicator 604. Through processes well known to those skilled in the art, such as internal reflection between the two surfaces and partial transmission of light from each of multiple output points on one surface (the top surface, as shown in FIG. 6), the light of the light beam 602 is replicated in a first direction along the length of the first replicator 604. Thus, a first plurality of replica light beams 608 are emitted from the first replicator 604 toward the second replicator 606.

[0167] The second duplicator 606 includes a second pair of surfaces stacked parallel to one another and positioned to receive each of the collimated light beams of the first plurality of light beams 608 and to provide replication, i.e., pupil dilation, by expanding each of those light beams in a second direction substantially orthogonal to the first direction. The first pair of surfaces are similarly sized and shaped (possibly identically) to one another and are substantially rectangular. The rectangular shape is implemented on the second duplicator to have a length along the first direction to receive the first plurality of light beams 608 and a length along a second, orthogonal direction to provide replication in that second direction. Through a process of internal reflection between the two surfaces and partial transmission of light from each of a plurality of output points on one surface (the top surface as shown in FIG. 6 ), the light of each light beam in the first plurality of light beams 608 is replicated in the second direction. Thus, a second plurality of light beams 610 is emitted from the second duplicator 606, the second plurality of light beams 610 comprising replicas of the input light beam 602 along each of the first direction and the second direction, and the second plurality of light beams 610 may therefore be considered to comprise a two-dimensional grid or array of replica light beams.

[0168] Thus, the first and second replicators 604, 605 of Figure 6 can be said to combine to provide a two-dimensional replicator (or "two-dimensional pupil dilator"). Improved two-dimensional pupil dilator The inventors have identified limitations to the usefulness and efficiency of pupil dilators in practical applications. For example, those skilled in the art will recognize that many practical applications requiring the use of pupil dilation have physical space constraints. For example, in an automotive head-up display, it may be desirable for the pupil dilator to be located in a limited space, such as under the vehicle's dashboard. Furthermore, such spaces are often unstable environments that move or vibrate, which presents challenges for many conventional pupil dilators. Furthermore, pupil dilators are typically provided as part of a larger display or viewing system that includes other optical elements, all of which may need to be physically constrained within a limited space. However, known pupil dilators generally require a non-optimal compromise between the degree (or range) of pupil dilation provided and the physical volume in space and compatibility with the surrounding environment that the two-dimensional pupil dilator occupies.

[0169] Furthermore, the inventors have identified technical problems associated with using a waveguide to replicate / dilate the pupil when the light field is a diffracted light field, such as a holographic light field from a miniature display device. Unlike conventional imaging, holography involves diffraction, and when an image is formed by holographic reconstruction in the eye, it is advantageous to propagate diffracted / diverging light within the waveguide rather than collimated light. A key issue is that the small pixel size required for diffraction requires a very small display device, which necessitates a (relatively) large projection distance, and therefore a large light field size (cross-sectional dimension). In particular, the inventors have found that by using simple internal reflections from two complementary surfaces of an elongated waveguide—i.e., two other elongated surfaces that do not contribute to replicating / dilating the pupil—it is possible to effectively "fold" the holographic light field in this dimension, preserving all image content (albeit in the hologram region). Furthermore, the inventors have devised a compact stacked configuration that utilizes a waveguide coupler to further fold the holographic light field, thereby facilitating optimal (i.e., low-volume) packaging.

[0170] The inventors have recognized that it is possible to provide a two-dimensional pupil dilator for holography that enhances the balance between efficiency, robustness, and compactness. The two-dimensional pupil dilator disclosed herein allows a user to have a wide field of view by allowing the user to receive all (or at least a necessary portion) of the light output by the light emitter (such as an SLM or another pixelated device) with which the two-dimensional pupil dilator is used, and also provides the user with a larger eyebox than previously achievable, thus allowing the user to move their head and still see the light they need. All of this is provided in a compact, robust, and space-efficient manner. This can be further understood from FIG. 7 onward.

[0171] FIG. 7 shows an improved system 700 comprising a first waveguide pupil dilator 702, a waveguide coupler 704 (which is optional in some embodiments), and a second waveguide pupil dilator 706.

[0172] First waveguide pupil dilator 702 comprises a three-dimensional element. First waveguide pupil dilator 702 is generally rectangular shaped with three pairs of mutually orthogonal faces, and first waveguide pupil dilator 702 is relatively long along one dimension and relatively short along each of the other two dimensions. However, the present disclosure is not limited to the particular size or shape of first waveguide pupil dilator 702 shown in FIG. 7 .

[0173] First waveguide pupil expander 702 includes a first pair of parallel elongated surfaces 708a, 708b, which are shown as top and bottom surfaces, respectively, in the particular orientation shown in FIG. 7. First waveguide pupil expander 702 includes a second pair of parallel elongated surfaces 710a, 710b, which are shown as side surfaces in the particular orientation shown in FIG. 7. First waveguide pupil expander 702 further includes a pair of relatively small end surfaces 712a, 712b that are also parallel to one another. The relative terms “top,” “bottom,” “side,” and “end” are used herein in the description of FIG. 7 for ease of understanding and convenience, although it will be understood that the present disclosure is not limited to these relative terms and that system 700 can be moved, rotated, or translated in any suitable manner while still functioning as described herein.

[0174] The input port of the upper elongated surface 708a is positioned to receive input light 714. The upper elongated surface 708a also includes an output port (not specifically shown in FIG. 7) at an end of the upper elongated surface 708a substantially opposite the input port, the output port being the last transmission point of a plurality of transmission points defined along the upper elongated surface 708a.

[0175] 7, the input light 714 is shown as a single line, but the inventors recognize the need / desire for the input light 714 to be uncollimated and / or to include a diverging bundle of rays. Thus, in embodiments, the input light 714 includes diffracted or diverging light. The input light 714 may be received directly or indirectly from an SLM; for example, there may be one or more other optical elements between the SLM and the first waveguide pupil expander 702.

[0176] The first pair of parallel elongated surfaces 708a, 708b are arranged to function as a waveguide pupil expander (or replicator) in a manner similar to that described above in connection with Figures 5 and 6. The inner surface of the bottom surface 708b is reflective, and the top surface 708a is partially transflective. Thus, the first pair of parallel elongated surfaces 708a, 708b are arranged to internally reflect or "bounce" light between the first pair of parallel elongated surfaces 708a, 708b along the elongated direction of the first waveguide pupil expander 702, transmitting some light from each of a plurality of transmission points on the top surface 708a between the input and output ports. Thus, the light of the hologram is replicated or expanded in a first direction. In short, the hologram can be said to be replicated.

[0177] However, the inventors have recognized that if input light 714 is diffracted or diverging light (i.e., light comprising diverging ray bundles), it comprises an expanding cone of light (as opposed to one or more parallel beams contained within collimated light) such that the size of the light cone, i.e., the size "L" of the diffracted light field defined by the end or mouth of the cone, as shown in FIG. 8 herein, increases as the light propagates along its optical path. This is a well-established principle of diffracted / diverging light and can be understood, for example, from light cone 802 shown as emanating from SLM 804 in FIG. 8. As shown therein, light cone 802 is emitted at a diffraction angle θ, which is the angle defined between optical axis "A" (extending substantially perpendicular to a center point on the face of SLM 804 from which the light is emitted) and the outermost or limit of light cone 802 in a positive or negative direction relative to that axis "A" (i.e., above or below optical axis "A" in the example shown in FIG. 8). The size "L" of the diffracted light field can be seen, based on well-established principles of trigonometry, to depend on both the diffraction angle θ and the distance "d" from SLM 804 at which the size "L" is measured.

[0178] Accordingly, the inventors have further recognized that if diffracted / divergent light is input to the elongated face of the first image replicator in a conventional configuration, there is a risk that the size of the light cone, i.e., the size "L" of the diffracted light field defined by the end or mouth of the cone, will exceed the size of the pupil replicator along one of its shorter dimensions. In other words, if the first waveguide pupil dilator 702 shown in FIG. 7 is in a conventional configuration, there is a risk that the size "L" of the diffracted light field will exceed the lateral thickness of the first waveguide pupil dilator 702 at some point along its propagation path between the upper and lower portions 708a and 708b. If that were to happen, in a conventional pupil dilator, at least some of the light from the input light cone 714 would leak out through one or both of the sides and therefore not properly reach the intended observer.

[0179] Thus, the inventors have provided an improved first waveguide pupil expander 702 in which a second pair of parallel surfaces (in the example of FIG. 7 , a pair of elongated side surfaces 710 a, 710 b) are also positioned to guide the light field from the input port toward the output port by at least one internal reflection. Such internal reflections allow the spatially modulated light cone of light to remain confined within the first waveguide pupil expander, even if the size of the diffracted light field would otherwise expand in one or more dimensions to a size exceeding the size of the first waveguide pupil expander 702, and the light is transmitted only through multiple transmission points defined on the elongated surface specifically intended for pupil expansion, i.e., the upper elongated surface 708 a in the example shown in FIG. 7 . Thus, light containing desired information, such as image-related information (e.g., encoded light of a hologram corresponding to an image), is not lost through the secondary surfaces of the first waveguide pupil expander 702. In essence, the inventors have discovered that it is possible to effectively "fold" the diffractive / holographic light field in this direction (using additional reflections from other opposing surfaces) in order to retain all of the diffractive / holographic light content necessary for the eye's reconstruction of a good quality image.

[0180] The inventors have recognized that, in at least some embodiments, the light launch conditions should be actively controlled so that light within the first waveguide pupil expander 702 is internally reflected by a second pair of opposing surfaces in addition to being reflected / transmitted by a first pair of opposing surfaces. For example, from the example of FIG. 7, it can be seen that input light 714 should enter the first waveguide pupil expander 702 at an angle of incidence (AOI) defined relative to a normal to surface 708a through which input light 714 enters. Such an angle is necessary for propagation between at least the first pair of opposing surfaces to be established.

[0181] The inventors have found that the combination of the relatively thin thickness and angle of incidence (AOI) of the first waveguide pupil dilator 702 enables the first waveguide pupil dilator 702 to provide high quality pupil dilation in a first direction (e.g., no vertical dark / white bands).

[0182] The first waveguide coupler 704 may be formed of any suitable material to function as a waveguide as described herein. In embodiments, the inherent difference between the refractive index "n" of the first waveguide coupler 704 and air allows the second pair of parallel surfaces to provide internal reflection (e.g., total internal reflection), thus keeping the diffracted light within the first waveguide coupler 704 except when the diffracted light is transmitted in a controlled manner from an output port on the reflective / transmissive surface of the first pair of parallel surfaces. In other embodiments, at least one surface of the second pair of parallel surfaces may be coated or otherwise augmented with another material to achieve the desired internal reflection and light trapping. This is further described below in connection with subsequent figures.

[0183] The light output from the first waveguide pupil dilator 702 includes multiple replica light beams output from corresponding multiple transmission points (not specifically shown in FIG. 7 ) on the upper elongated surface 708 a. The output light is emitted from the transmission points at an angle (not specifically shown in FIG. 7 ), with each of the output light beams being substantially parallel to each of the other respective beams. This can be seen from the light path shown in FIG. 10 , which illustrates one embodiment of an improved system disclosed herein and described further below. Returning to FIG. 7 , in some embodiments, pupil dilation is provided in only one direction, such that the waveguide coupler 704 and second waveguide pupil dilator 706 shown in FIG. 7 are not needed.

[0184] Thus, there is provided a display system comprising a first waveguide pupil dilator comprising an input port, an output port, a first pair of parallel surfaces, and a second pair of parallel surfaces, the first pair of parallel surfaces being orthogonal to the second pair of parallel surfaces, the first pair of parallel surfaces being arranged to direct a diffracted light field from the input port to the output port by internal reflection therebetween, a first surface of the first pair of parallel surfaces being partially transflective such that the light field is split at each internal reflection and multiple replicas of the light field are transmitted through an area of ​​the first surface forming the output port, and the second pair of parallel surfaces being also arranged to direct the light field from the input port to the output port by at least one internal reflection. The second pair of parallel surfaces are not arranged to provide pupil replication by allowing partial transmission, and optionally both surfaces thereof may be arranged for complete light directing to the output port, i.e., 100% (or close to 100%) reflection.

[0185] The improved first waveguide pupil dilator 702 disclosed herein allows a diffracted light field to propagate therethrough and thereby be expanded in one dimension. Thus, for example, holographic light, i.e., light that has been spatially modulated by a hologram displayed on an SLM or other display device but has not been transformed to form a holographic reconstructed image, can be propagated and expanded by the improved first waveguide pupil dilator 702. Each "replica," i.e., output light beam, formed by the first waveguide pupil dilator is effectively a replica of the hologram because the light is spatially modulated according to the hologram. Informally, one can say that the light is "encoded" with the hologram.

[0186] In embodiments in which the first waveguide pupil dilator is provided in a compact form (such as the relatively thin, elongated form shown in Figures 7 to 11 herein), the first waveguide pupil dilator advantageously reduces the overall size and weight of the display system in which it is included.

[0187] In embodiments where pupil dilation is required in two dimensions, the first waveguide pupil dilator 702 is oriented such that the multiple output light beams are directed (directly or indirectly, e.g., via one or more other components, as further described below) toward a light receiving surface 716b of a second waveguide pupil dilator 706 that is positioned to provide pupil dilation in a second direction substantially perpendicular to the first direction.

[0188] 7, second waveguide pupil dilator 706 comprises a three-dimensional element. Second waveguide pupil dilator 706 is substantially planar and has three pairs of mutually orthogonal faces, with second waveguide pupil dilator 706 being relatively long along two dimensions and relatively short along its third dimension. However, the present disclosure is not limited to the particular size or shape of second waveguide pupil dilator 706 shown in FIG. 7.

[0189] The second waveguide pupil expander 706 comprises a first pair of parallel rectangular (or quadrilateral, or planar) faces 716a, 716b, which are shown as the top and bottom faces, respectively, in the particular arrangement shown in FIG. 7. These may be referred to as the "major faces" or "main surfaces" of the second waveguide pupil expander. Each of the parallel rectangular faces 716a, 716b has a relatively large surface area, with the length and width of the rectangle defined along first and second elongated dimensions of the second waveguide pupil expander 706. The second waveguide pupil expander 706 further comprises a pair of parallel elongated side faces 718 and a pair of parallel elongated end faces 720, all of which have relatively small surface areas.

[0190] The first waveguide pupil expander 702 and the second waveguide pupil expander 706 are oriented relative to one another such that multiple output light beams from the first waveguide pupil expander 702 are directed toward a light-receiving surface 716b, which in this non-limiting example is the lower surface 716b of the second waveguide pupil expander 706. Preferably, they are directed toward one edge of the lower surface 716b such that multiple input ports are defined along or near that edge, which input ports receive the multiple output light beams from the first waveguide pupil expander 702. The system 700 is configured such that the light beams enter the second waveguide pupil expander 706 through the input ports at an oblique angle relative to the surface normal of the lower surface 716b. Additionally, the second waveguide pupil dilator 706 is preferably sized and oriented to receive each of the output light beams from the first waveguide pupil dilator, to maintain the pupil dilation provided in one direction by the first waveguide pupil dilator 702, and to expand each of those light beams in a second substantially orthogonal direction defined by a second elongated dimension of the second waveguide pupil dilator 706.

[0191] The inner surface of the bottom surface 716b is reflective, and the top (transmissive) surface 716a is partially transflective. Thus, through a process of internal reflection between the two surfaces and partial transmission of light from each of the multiple output points on the top surface 716a, the light of each light beam received through the input port of the second waveguide pupil expander 706 is expanded (or replicated) in a second direction. Thus, a second plurality of light beams is emitted from the waveguide pupil expander 706, the second plurality of light beams comprising multiple replicas of the input light beam 714 along each of the first and second directions. Thus, the second plurality of light beams can be considered to comprise a two-dimensional grid or array of replica light beams. In embodiments where the input diffracted / divergent light is holographic light, i.e., light that has been spatially modulated according to a hologram and not yet transformed to form a holographic reconstruction, each replica is actually a replica of the hologram.

[0192] Those skilled in the art will understand, for example, how the thickness and angle of incidence AOI of the second waveguide pupil dilator can be determined for optimal two-dimensional pupil dilation, where the replicas are perfectly stitched together, i.e., bonded.

[0193] In a further technological advancement, a waveguide coupler 704 is provided between the first waveguide pupil dilator 702 and the second waveguide pupil dilator 706. The waveguide coupler 704 is positioned to couple or guide light between the first waveguide pupil dilator 702 and the second waveguide pupil dilator 706. While the shape of the waveguide coupler 704 may vary depending on the physical configuration and / or constraints of any given display system, in the exemplary arrangement of FIGS. 7-11 , the waveguide coupler 704 is substantially triangular in cross section. The waveguide coupler 704 has a relatively large surface area and includes two triangular-shaped parallel faces 722, which can be said to form the “major faces” of the waveguide coupler 704. In this example, they are right-angled triangular in shape, although this should not be considered limiting. It also has three substantially rectangular faces 724 of relatively small surface area that form connecting walls or sides between the two triangular faces 722, so that they can be said to form the "facets" of the waveguide coupler 704.

[0194] The waveguide coupler 704 is arranged to receive the multiple replica light beams output from the first waveguide pupil dilator 702 and output them toward the second waveguide pupil dilator 706. As seen in FIG. 7 , in this exemplary arrangement, the multiple replica light beams are received by a first facet 724 and output by a second, different facet 724, which directs the multiple replica light beams toward the lower surface 716 b of the second waveguide pupil dilator 706. The waveguide coupler 704 can have any suitable shape, depending on the desired or required relative positioning of the first and second waveguide pupil dilators 702, 706. In the particular arrangement shown in FIG. 7 , factors such as the angular requirements for inputting light into each of the waveguide pupil dilators 702, 706 to achieve the desired internal reflections and pupil dilation essentially result in a triangular-shaped gap existing between the two waveguide pupil dilators 702, 706. The waveguide coupler 704 occupies the gap and is configured to couple or guide light between the two waveguide pupil dilators 702, 706 so that no light is lost during propagation between the two waveguide pupil dilators 702, 706.

[0195] In embodiments in which input light 714 includes diffracted or divergent light, each of the replicas output by first waveguide pupil dilator 702 also includes diffracted or divergent light. Thus, each replica includes a cone of uncollimated light, and the light field defined by the mouth of the cone increases in size as the light travels further. As a result, if light travels uncontrolled between first waveguide pupil dilator 702 and second waveguide pupil dilator 706, there is a risk that some of that light will diverge and be lost from the area defined by the input port on second waveguide pupil dilator 706, or at least not properly reach the end observer. For example, in head-up display (HUD) systems, particularly vehicular head-up display (HUD) systems, physical compactness is often required, making increasing the surface area of ​​second waveguide pupil dilator 706 undesirable in many applications.

[0196] Accordingly, the inventors have recognized that providing a waveguide coupler 704 between two waveguide pupil dilators 702, 706 is an efficient and advantageous solution because the waveguide coupler 704 can be appropriately formed, shaped, and sized to fit into any gap required between the two waveguide pupil dilators and provide very useful and important light control functions within that gap. The inventors have further recognized that while including an additional component within a pupil dilator system may seem counterintuitive, the presence of the waveguide coupler and the advantages it provides as described herein may outweigh the potential drawbacks of introducing an additional component, particularly when the system is intended to be incorporated into an environment where compactness and / or light weight are advantageous. Furthermore, the inventors have recognized that, in at least some embodiments, the waveguide coupler can be formed to fit into the gap that must inherently exist between the first and second waveguide pupil dilators, such that the waveguide coupler does not significantly increase the overall size of the system.

[0197] For example, a facet of the waveguide coupler 704 may be sized and shaped to correspond to the output facet of the first waveguide pupil expander, or at least to correspond to the multiple output rays from the first waveguide pupil expander 702, to receive some or all of those replicas. This is most clearly seen in the arrangements of FIGS. 10 and 11 herein. In these arrangements, as in FIG. 7, the cross-sectional shape of the waveguide coupler 704 is substantially a right triangle. A first facet 724 of the waveguide coupler 704 (in trigonometric terms, the facet on the "hypotenuse" side in this example) is positioned to receive light from the first waveguide pupil expander 702. The light travels through the waveguide coupler 704 and is output from the second facet 724 toward the second waveguide pupil expander 706. 10 and 11, light output from waveguide coupler 704 is indirectly directed via mirror 1002 towards second waveguide pupil expander 706, as described further below. However, the present disclosure also contemplates direct movement of light from waveguide coupler 704 to second waveguide pupil expander 706, as well as indirect movement of light therebetween via any other suitable element or elements.

[0198] The waveguide coupler 704 is formed of any suitable material or materials that allow it to retain light therein and direct it toward the second waveguide pupil dilator 706. In embodiments in which the input light 714, and therefore the multiple replicas output by the first waveguide pupil dilator 702, include diffracted or divergent light, one or more faces of the waveguide coupler 704 may be arranged to provide internal reflection to prevent the divergent light from escaping the waveguide coupler 704 except through designated areas, such as an output port intended to direct the light toward the second waveguide coupler 706. Thus, in the example arrangements of Figures 10 and 11, one or more of the triangular major faces 722 and / or facets 724 that do not include an output port may be configured to provide internal reflection so that light cannot escape except through other facets (which may be referred to as "output faces") through which the light is intended to travel toward the second waveguide pupil dilator 706. The output surface through which light is intended to travel towards the second waveguide pupil expander 706 may comprise a transmissive surface.

[0199] The output face of waveguide coupler 704 may be positioned, sized, and / or shaped to correspond to an input port on second waveguide coupler 706. One or more other elements may also be used between waveguide coupler 704 and second waveguide pupil dilator 706 to appropriately direct multiple replica light beams to second waveguide pupil dilator 706 for pupil dilation in a second direction. Again, this can be seen most clearly in FIGS. 10 and 11 , where light beams output from waveguide coupler 704 are directed onto mirror 1002, which reflects the light beams toward a region located proximate one end of the receiving side (in these examples, the lower side) of second waveguide pupil dilator 706, from where they undergo the reflections and transmissions described above to achieve two-dimensional pupil dilation. Similar to ensuring that the replica light beams reach the second waveguide pupil dilator 706, the waveguide coupler 704 also ensures that the replica light beams reach it at the desired angle. This can ensure that internal reflections are achievable in the second waveguide pupil dilator 706 and that the output of the second waveguide pupil dilator 706 is correspondingly accurately oriented. This helps ensure the overall corrective function of the display system, for example, helping to ensure accurate positioning of the desired observer eyebox. The inventors have found that the waveguide coupler significantly helps minimize horizontal dark / white bands in 2D pupil dilation.

[0200] As discussed above, in many practical applications, it is desirable, and sometimes necessary, to provide pupil dilation in a compact, space-efficient arrangement for implementing the pupil dilation system in a larger system, such as a vehicle. Compactness can also be beneficial when the environment in which the pupil dilation system is to be provided is a moving, vibrating, or otherwise unstable environment, such as a vehicle. The inventors have recognized that one or more of the waveguide pupil dilators, and optionally also the waveguide coupler, described above, can be arranged in a very compact and efficient manner. For example, they recognize that a first waveguide pupil dilator and a waveguide combiner, optionally together with another suitable optical element such as a turning mirror (or "folding mirror"), can be placed within a physical area defined by the "footprint" of a second waveguide pupil dilator (which is necessarily larger than the first waveguide pupil dilator because it is positioned to preserve pupil dilation in a first direction and add pupil dilation in a second, substantially orthogonal direction), and can provide the efficiency and effectiveness of the two-dimensional pupil dilation described herein even for diffracted / diverging input light rays.

[0201] Thus, in at least some instances, in accordance with the realizations made by the inventors, a display system (or light engine) can be provided in which the first waveguide pupil dilator, the waveguide coupler, and optionally one or more other elements can be provided in a first layer, e.g., a lower layer, and the second waveguide pupil dilator can be provided in a second layer, e.g., an upper layer, of a compact two-dimensional pupil dilation system. The compact two-dimensional pupil dilation system can have a cross-sectional area equal to or substantially equal to the cross-sectional area of ​​a major surface of the second waveguide pupil dilator. In some cases, the compact two-dimensional pupil dilation system can have a cross-sectional area slightly larger, e.g., larger than within a predetermined threshold or tolerance level, than the cross-sectional area of ​​the major surface of the second waveguide pupil dilator.

[0202] The compact two-dimensional pupil dilation system can form part of a viewing system, a light engine, or a display system, e.g., a head-up display (HUD) system that includes an SLM or other pixelated display device capable of displaying images or holograms. In at least some cases, the SLM or other display device may also be positioned to be within the footprint of a second waveguide pupil dilator. For example, the SLM or other display device may be provided in a lower layer together with a first waveguide pupil dilator and a waveguide coupler, and optionally one or more other optical elements, with the second waveguide pupil dilator forming (at least a portion of) a second, upper layer. The optical path of light traveling from the display device to the second waveguide pupil dilator via the first waveguide pupil dilator, the waveguide coupler, and any other optical elements provided may also be positioned to be within the physical footprint defined by the cross-sectional area of ​​the second waveguide dilator or within the physical footprint defined by the layer in which at least the second waveguide pupil dilator is included. A first layer including the first waveguide pupil dilator and the waveguide coupler may be contiguous with a second layer including the second waveguide pupil dilator. For example, the first and second layers may abut one another. For example, the first and second layers may be attached to one another. For example, the first and second layers may be bonded to one another. The bond may be provided via any suitable material that allows light propagation in the two-dimensional pupil dilation system to occur as disclosed herein to provide compact and efficient two-dimensional pupil dilation. This can be further understood in FIGS. 9-12.

[0203] Figure 10 shows an exemplary arrangement including a first waveguide pupil expander 702, a waveguide combiner 704, and a second waveguide pupil expander 706 that function in a manner similar to that described in detail above with respect to the similar arrangement shown in Figure 7. The arrangement of Figure 10 therefore embodies the realizations made by the inventors as described above. In Figure 10 (and Figure 7), the major surface 722 of the waveguide combiner 704 is coplanar with a second pair of elongated parallel surfaces 710a, 710b in the first waveguide pupil expander 702, which (as described above) are arranged to provide internal reflections to confine light within the first waveguide pupil expander 702, thereby ensuring that it escapes only through an output port defined on one of the other first pair of parallel elongated surfaces 708a, 708b of the first waveguide pupil expander 702. Next, a first pair of parallel elongated faces 708a, 708b of the first waveguide pupil expander 702, through which light enters and exits, are positioned substantially parallel to a minor “input” face 724 of the waveguide coupler 704, which is configured to receive the plurality of replica lights from the first waveguide pupil expander 702. In trigonometric terms, this facet 724 is the “hypotenuse” of a substantially right-angled triangle defined, in this example, by the major faces of the waveguide coupler. This allows the first waveguide pupil expander 702 and the waveguide coupler 704 to be provided as part of a first relatively thin layer. Also provided within the first relatively thin layer of FIG. 10 is a mirror 1002, sometimes referred to as a “turn mirror.” The mirror 1002 is positioned to redirect the light output from the waveguide coupler 704. Mirror 1002 is one example of an optical element that can redirect light in the manner shown, and it will be understood that one or more other elements can be used instead to perform this task.

[0204] In the arrangement shown in Figure 10, mirror 1002 is configured to direct light away from the layer / plane in which first waveguide pupil expander 702 and waveguide coupler 704 are located and instead direct light toward a second layer substantially parallel to the first layer, with second waveguide pupil expander 706 located within that second layer. While mirror 1002 is suitably positioned within the first layer and tilted to direct light toward the second layer, which in the illustrated example is located above the first layer, this relative positioning should not be considered a limitation of the present disclosure. As can be seen even more clearly from the plan view shown in Figure 11, the first waveguide pupil expander 702, waveguide coupler 704, and mirror 1002, which are contained within the first layer, are all within the physical footprint of the second layer defined by the cross-sectional area of ​​the major surface of second waveguide pupil expander 706 in this exemplary arrangement. Figure 11 also shows SLM 1102 located in the first layer, within the same footprint, where light output by SLM 1102 is directed to the input port of first waveguide pupil expander 702 by one or more suitable optical elements not shown, but preferably within the same footprint.

[0205] 10 and 11, alternative arrangements are contemplated in which a mirror or other optical element is not required to direct the light replica from a first layer, in which the first waveguide pupil expander 702 and waveguide combiner 704 are located, to a second, preferably parallel, layer, in which the second waveguide pupil expander 706 is located. For example, one or more surfaces of the waveguide combiner 704 may be shaped or coated or otherwise arranged to direct light directly output by the waveguide combiner 704 in a direction that is not coplanar with the first layer and direct the light to an appropriate input port region of the second waveguide pupil expander 706.

[0206] 11 also shows that to ensure the correct input and output angles of the waveguide pupil expanders 702, 706, e.g., to achieve internal reflections thereof, the elongated dimension of the first waveguide pupil expander 702 is tilted relative to each of the dimensions defining the major surface of the second waveguide pupil expander 706. The inventors have recognized that when the first waveguide pupil expander 702 is tilted in this plane, it can be positioned within the physical footprint of the major surface of the second waveguide pupil expander 706. In contrast, if the first waveguide pupil expander 702 were not tilted in this plane, it would be necessary to tilt the second waveguide pupil expander 706 in that plane instead, or optical performance would be compromised. Thus, the tilt of the first waveguide pupil expander 702 on the lower layer provides a technological advancement that optimizes packaging, i.e., minimizes volume by allowing the bottom layer of the component to fit within the footprint of the top layer of the component. Such tilt naturally creates a roughly triangular gap between the perimeter of the footprint of the first and second waveguide pupil expanders. This unique triangular gap shape is therefore suitable for the roughly triangular waveguide combiner 704, as shown in FIG. 11 and described in detail herein above.

[0207] 9 herein, a first layer including the first waveguide pupil expander 702 and waveguide combiner 704, and optional mirror 1002, may be provided immediately adjacent to or adjacent to a second layer including the second waveguide pupil expander 706. Optionally, a reflective coating may be provided on any surface(s) in the first layer that abuts the second layer. In some embodiments, the second pair of parallel surfaces 710 a, 710 b of the first waveguide pupil expander 702 and the triangular major surface 722 of the waveguide combiner 704 provide light guiding by total internal reflection based on refractive index difference and an appropriate angle of incidence (as is well known to those skilled in the art). However, in other embodiments, a suitable mirror coating can be applied to the second pair of parallel surfaces 710a, 710b of the first waveguide pupil expander 702 and / or the triangular major surface 722 of the waveguide combiner 704 to achieve internal reflections within the first waveguide pupil expander 702 and the waveguide combiner 704, respectively, that complement the diffraction angle of the diffracted light.

[0208] As shown in FIG. 12 herein, the inventors' realization allows a system including or comprising the two-dimensional pupil dilation system described herein to be provided in a very compact and stable form. For example, FIG. 12 illustrates a head-up display (HUD) system provided as a HUD package 1202 comprising a plurality of abutting, generally quadrilateral layers, which may be joined together in any suitable manner, for example. The HUD package 1202 comprises the elements shown in and described above in connection with FIG. 11 in first and second layers. The HUD package may also comprise additional elements within these layers and / or within a third (or subsequent) substantially parallel, relatively thin (flat) layer that abuts one or more respective other layer(s) within the HUD package 1202. As a result, the HUD package 1202 is formed in a compact, regular shape that can be incorporated into a variety of different environments. For example, while the example in FIG. 12 is shown positioned beneath an automobile dashboard 1203, this should not be construed as limiting the present disclosure. Because of the regular shape and layered configuration of the HUD package 1202, it is relatively simple for a user, e.g., a manufacturer, to assemble it into their surroundings in a desired orientation and location. For example, in FIG. 12 , the HUD package 1202 is oriented so that the major surfaces of its layers are substantially horizontal, so that light is directed toward the vehicle's windscreen 1204 at an appropriate angle to ensure that light is reflected or otherwise redirected from the windscreen 1204 toward the observer's eyebox 1206, which is defined in a substantially vertical plane. However, in other examples, the HUD package 1202 is tilted relative to the horizontal to provide optimal packaging, e.g., minimal volume.

[0209] Providing a two-dimensional pupil dilation (or pupil duplication) system such as those described herein in a compact form, e.g., a compact form with a regular shape, in which its components are located as close to each other as possible while still ensuring the correct light propagation angles, is further beneficial in simplifying and reducing the financial costs of manufacturing. In other words, it is easier and more cost-effective to manufacture the first and second waveguide pupil dilators, and, if applicable, the waveguide coupler, together, e.g., as a single layered component, rather than manufacturing them separately and then arranging them together. Furthermore, reducing the physical size of the waveguide pupil dilators, such as by fabricating the first waveguide pupil dilator in a thin, elongated shape, is beneficial both from a manufacturing efficiency perspective and a financial cost perspective. This, in turn, may allow for the use of higher quality optical surfaces or optical materials than would be possible with conventional, less compact, and / or more irregular system configurations. Furthermore, the regular and compact shape of the two-dimensional pupil dilation systems described herein allows them to be more physically stable and robust than is typically achievable with conventional two-dimensional pupil dilation systems when located in challenging environments, such as within a vehicle.

[0210] The improved systems disclosed herein allow diffracted or diverging light to be replicated in at least one dimension via one or more waveguide pupil dilators, something not achievable with conventional viewing systems. As a result, light output by a diffractive structure, including but not limited to light encoded by a hologram, can be replicated or expanded in one or more dimensions before being transmitted to an observer. Such expansion allows the observer to have a larger eyebox within which their eye(s) can be positioned while still capturing the necessary light, thereby enabling the observer to view or perceive an image (such as an image corresponding to a hologram) from a greater number of different eye positions.

[0211] waveguide aperture The arrangements and methods described herein are applicable to viewing systems with a single viewing aperture, or entrance pupil, as well as to viewing systems with multiple entrance pupils, including, but not limited to, the most common, two-eyed human observer.

[0212] The inventors have recognized that, at least in some cases, consideration should be given to the effects that can occur when a viewing system has multiple entrance pupils. In other words, the inventors have recognized that it may be appropriate to provide control over how and when multiple replicas of a common diffracted light field reach an observer or other viewing system. For example, at least in some cases, it may be appropriate to prevent two replicas of the same diffracted light field from reaching both the left and right eyes of an observer simultaneously. This is because the human brain does not expect both eyes to receive identical content at the same time, given that the eyes are physically displaced from one another. The inventors have recognized that controls can be implemented to account for the different respective positions of an observer's eyes (and, correspondingly, the different respective positions of two or more entrance pupils in any multi-entrance pupil viewing system) to prevent an image or portion of an image (or holographic light associated with the same image or portion of an image) from being received identically by both eyes at substantially the same time. This is described in more detail with particular reference to the types of holograms described with respect to Figures 4A-5 herein (see co-pending UK Patent Application No. 2108456.1), which is incorporated herein by reference in its entirety. However, the present disclosure is applicable to pupil dilation for any type of diffractive or diverging light field, including but not limited to, a diffractive light field modulated by any type of hologram, including but not limited to, a Fourier hologram, a point cloud hologram, or a Fresnel hologram, including the use of a waveguide aperture as described further below.

[0213] Thus, in some embodiments, a controller is provided within the display system and is arranged to control the transmission of at least some of the diffracted light replicas within the system. The controller may be configured to allow selective blocking and transmission of apertures or specific light paths through which one or more components of the system are configured to output, and thus may be referred to as an "aperture" or "waveguide aperture." It is configured to do so by selectively having one or more "open zones" that transmit light and one or more "closed zones" that block light (i.e., are non-transparent). While the "zones" may be referred to as "apertures," it should be understood that they need not be physically distinct or discrete configurations but may be software-controlled and therefore dynamically variable in position and configuration. For example, the ratio of open to closed zones may be dynamically variable, as may the size and position of any given zone. The period during which a particular configuration of open and closed zones of the controller is adopted may be referred to as a "phase." The controller may be controlled to cycle or change between respective phases dynamically, often very rapidly.

[0214] In some embodiments, the control device is provided downstream, e.g., immediately downstream, of the first waveguide pupil dilator. For example, the control device may be provided between the first waveguide pupil dilator and the waveguide coupler (if present), or more generally, between the first waveguide pupil dilator and the second waveguide pupil dilator. In some embodiments, the control device may be provided downstream of the second waveguide pupil dilator instead of, or in addition to, providing a control device between the first and second waveguide pupil dilator.

[0215] 10 and 11 herein, the control device may be provided in substantially the same layer as the first waveguide pupil expander 702 and (if present) the waveguide coupler 704. For example, the control device may be fixed, e.g., bonded, to the first waveguide pupil expander 702 and / or the waveguide coupler 704.

[0216] For example, the control device may comprise an elongated structure that may be located between the first waveguide pupil expander 702 and the waveguide combiner 704. The control device may be positioned substantially parallel to the first waveguide pupil expander 702 and / or have an elongated size that allows it to block some, preferably most, and preferably all, of the replicas of the diffracted light field that the first waveguide pupil expander 702 is configured to output. The control device may be controlled to selectively transmit or block the forward transmission of at least some of these replicas to control the hologram content that reaches the observer, e.g., to dynamically control which hologram content reaches each of the observer's eyes. The control device may be switchable between transmitting none, all, or a selected number of the replicas.

[0217] In some embodiments, the control device comprises a substantially flat liquid crystal display panel arranged to provide customized shuttering of light to selectively pass particular replicas based on the position of the observer's eye. The eye position may be known to a controller of the control device via any suitable sensor and / or feedback means. The control device may be substantially coplanar with the waveguide pupil dilator it is configured to operate.

[0218] In embodiments, the controller may also be configured to selectively control which portions of the diffracted light fields within each replica of the input diffracted light field reach the observer at any given time, for example, to dynamically control which ranges of one or more diffraction angles within the light cone defined by the diffracted light are transmitted and which ranges are blocked.

[0219] Although the control device is referred to above as a "waveguide aperture," any suitable control device can be used to provide the functionality described herein. A control device, such as a waveguide aperture, can be formed of any suitable material. For example, it can comprise one or more liquid crystal devices, such as an array of liquid crystal devices, each of which can be switched between being opaque and transmissive. For example, the control device can comprise "smart glass" or "switchable glass" that can change its light transmission properties when voltage, light, or heat is applied. The control device can be controlled by any suitable processor or controller. Its configuration can be rapidly changed, for example, to transmit holographic light corresponding to different respective target images and / or to accommodate movement of an observer or viewing system, to coordinate or synchronize with the dynamic display of multiple different holograms on a display device.

[0220] The controller disclosed herein can take any number of different forms. In some embodiments, the controller comprises a plurality of individually controllable light receiving / processing elements, such as pixels, e.g., a 2D array. In some embodiments, the controller comprises a pixelated liquid crystal device or display. In some embodiments, the elements or pixels are operable in contiguous groups, forming transmissive and non-transmissive "shutter zones." Each group of pixels may be switchable between a first mode, e.g., a transmissive mode, and a second mode, e.g., a reflective mode. Those skilled in the art are familiar with how pixelated display devices can be controlled to change the size and position of groups or zones of pixels (each zone having a different response to light) in real time or other operational modes. In embodiments, each zone is larger than the pixel size of the controller. Thus, each zone can include multiple pixels. Those skilled in the art are equally familiar with how optical components, such as polarizers and waveplates, can be implemented in combination with pixelated liquid crystal devices to achieve reconfigurable light shutters. By way of example only, the controller may utilize polarization selection, although other schemes based on other properties of light are equally applicable. In some embodiments, the control device comprises a pixelated liquid crystal display and, optionally, other optical elements collectively configured to transmit light having a first polarization and absorb or reflect light having a second polarization, optionally the first polarization and the second polarization being opposite or complementary. For the avoidance of doubt, any number of different optical systems may be used to form the control device, depending on the characteristics, such as polarization and wavelength, of the light forming the image, and thus the present disclosure is not limited by the structure of the control device. It will therefore be understood that the control device disclosed herein is defined by its function, not its structure.

[0221] The control device is dynamically reconfigurable. The reader should understand that the total area of ​​the control device that is blocking / non-transmitting or non-blocking / transmitting is generally not constant during its operation. In some embodiments, the control device is pixelated. That is, the control device comprises an array of individually controllable pixels. Each pixel may include, for example, a liquid crystal that is configurable between a transmissive and a non-transmissive state. Imperfections in the alignment between the edges of the pixel and the edges of the ideal aperture zone can be addressed by passing too much or too little light.

[0222] The above examples should not be considered limiting. For example, the observation system can have three or more observation apertures, or entrance pupils. For example, the operation of the controller can be controlled according to any suitable "phase sequence" or timing scheme. For example, the controller can be selectively paused.

[0223] In embodiments, two or more holograms or other diffraction patterns may be intertwined with one another, that is, two holograms may be displayed alternating in rapid succession such that a viewer perceives two corresponding images as being formed substantially simultaneously.

[0224] Some phases of the control device can deliver more light content than some other respective phases. Similarly, when multiple phases of the control device are interdigitated with each other, both eyes need not receive the same amount of light content in each phase or in total. For example, one eye may be able to see more light content than the respective other eye, depending on their relative positions and / or other factors.

[0225] Display systems including controllers such as the waveguide apertures described herein can be configured to display multiple different diffraction patterns and output multiple corresponding different diffracted or divergent light fields one after the other and / or at different respective times. Thus, the display devices in such systems can be configured to display different respective holograms, sometimes in rapid succession. The controllers can be configured to be dynamically adaptable to accommodate changes in the diffracted light fields and / or changing viewing requirements.

[0226] The system may be configured to display a diffraction pattern corresponding to a sequence of images, such as a video-rate sequence of images. Each image may correspond to a frame of the frame sequence having a frame rate, such as 50 or 60 Hz. Each frame may comprise multiple subframes. The subframe rate may be, for example, four or eight times the frame rate. The displayed hologram may change for each successive subframe. Each subframe may be considered an individual display event. Each subframe may correspond to an image or at least a portion of an image. While embodiments show light being delivered to both eyes for each display event, the disclosure is not limited in this respect. For example, the light engine may be configured to deliver light to only one eye / entrance pupil for each display event. The configuration of the waveguide aperture (i.e., the size and / or distribution of the open / closed aperture / opening) may be changed for every display event or for n display events, where n is an integer. In some embodiments, only one angular range of light is delivered to one eye for each display event / aperture configuration. In some embodiments, the control system is configured to deliver light to each eye / entrance pupil in sequence.

[0227] In some embodiments, a hologram of a target image may be calculated for a particular size and position of the viewing aperture, for example, for a particular size and position of the entrance pupil of an observer's eye. If constraints such as entrance pupil diameter or position change, the hologram may be recalculated even though the currently reconstructed target image (and therefore the image content seen or perceived by the observer) remains the same. Each hologram need not have the same number or size of zones, even if two holograms represent the same target image.

[0228] Additional Features The embodiments refer, by way of example only, to an electrically activated LCOS spatial light modulator, and the teachings of the present disclosure may equally be implemented in any spatial light modulator capable of displaying computer-generated holograms according to the present disclosure, such as, for example, any electrically actuated SLM, optically actuated SLM, digital micromirror device, or microelectromechanical device.

[0229] In some embodiments, the light source is a laser, such as a laser diode. In some embodiments, the detector is a photodetector, such as a photodiode. In some embodiments, the light receiving surface is a diffuser surface, such as a diffuser, or a screen. The holographic projection system of the present disclosure can be used to provide an improved head-up display (HUD). In some embodiments, a vehicle is provided that includes a display system installed in the vehicle to provide the HUD. The vehicle may be a motor vehicle, such as a car, truck, van, freight car, motorcycle, train, airplane, boat, or ship.

[0230] The quality of the holographic reconstruction can be affected by the so-called zero-order problem, which is a result of the diffraction properties of pixelated spatial light modulators. Such zero-order light can be considered "noise" and includes, for example, specularly reflected light and other unwanted light from the SLM.

[0231] In the example of Fourier holography, this "noise" is focused at the focal point of the Fourier lens, resulting in a bright spot at the center of the holographic reconstruction. The zeroth order light may simply be blocked, which replaces the bright spot with a dark spot. Some embodiments include an angle-selective filter to remove only the collimated zeroth order light. Embodiments also include the method of managing the zeroth order described in European Patent No. 2,030,072, the entire contents of which are incorporated herein by reference.

[0232] In some embodiments, the size of the hologram (number of pixels in each direction) is equal to the size of the spatial light modulator, so that the hologram fills the spatial light modulator. That is, the hologram uses all of the pixels of the spatial light modulator. In other embodiments, the hologram is smaller than the spatial light modulator. More specifically, the number of hologram pixels is less than the number of light-modulating pixels available in the spatial light modulator. In some of these other embodiments, a portion of the hologram (i.e., a contiguous subset of the hologram's pixels) is repeated in the unused pixels. This technique is sometimes referred to as "tiling," in which the surface area of ​​the spatial light modulator is divided into several "tiles," each of which represents at least a subset of the hologram. Each tile is therefore smaller in size than the spatial light modulator. In some embodiments, "tiling" techniques are implemented to improve image quality. Specifically, some embodiments implement tiling techniques to minimize the size of the image pixels while maximizing the amount of signal content that enters the holographic reconstruction. In some embodiments, the holographic pattern written to the spatial light modulator includes at least one entire tile (i.e., the complete hologram) and at least one portion of a tile (i.e., a contiguous subset of the pixels of the hologram).

[0233] In an embodiment, only primary regenerative fields are utilized and the system includes physical blocks, such as baffles, positioned to limit the propagation of higher order regenerative fields through the system.

[0234] In embodiments, the holographic reconstruction is color. In some embodiments, a technique known as spatially separated color "SSC" is used to provide the color holographic reconstruction. In other embodiments, a technique known as frame sequential color "FSC" is used.

[0235] The SSC method uses three spatially separated arrays of light-modulating pixels for three monochromatic holograms. The advantage of the SSC method is that all three holographic reconstructions can be formed simultaneously, resulting in very bright images. However, due to space limitations, when three spatially separated arrays of light-modulating pixels are provided on a common SLM, the quality of each monochromatic image is not optimal because only a subset of the available light-modulating pixels is used for each color. Therefore, a relatively low-resolution color image is provided.

[0236] The FSC method can sequentially display three monochromatic holograms using all pixels of a common spatial light modulator. The monochromatic reconstructions are cycled quickly enough that a human observer perceives a multicolor image from the integration of the three monochromatic images (e.g., red, green, blue, red, green, blue, etc.). An advantage of FSC is that the entire SLM is used for each color. This means that the quality of the three color images produced is optimal, since every pixel of the SLM is used for each color image. However, a disadvantage of the FSC method is that each monochromatic illumination event can only occur for one-third of the frame time, resulting in a composite color image that is approximately three times lower in brightness than the SSC method. This drawback can potentially be addressed by overdriving the laser or using a more powerful laser, but this requires more power, resulting in higher cost and larger system size.

[0237] Although the examples describe illuminating the SLM with visible light, those skilled in the art will understand that the light source and SLM could equally be used to direct infrared or ultraviolet light, e.g., as disclosed herein. For example, those skilled in the art will recognize techniques for converting infrared and ultraviolet light to visible light for the purpose of providing information to a user. For example, the present disclosure extends to using phosphor and / or quantum dot technology for this purpose.

[0238] Some arrangements describe 2D holographic reconstructions as examples only. In other arrangements, the holographic reconstructions are 3D holographic reconstructions. That is, in some arrangements, each computer-generated hologram forms a 3D holographic reconstruction.

[0239] The methods and processes described herein may be embodied on a computer-readable medium. The term "computer-readable medium" includes a medium arranged to store data temporarily or permanently, such as a random access memory (RAM), a read-only memory (ROM), a buffer memory, a flash memory, and a cache memory. The term "computer-readable medium" should also be taken to include any medium, or combination of media, capable of storing instructions for execution by a machine, such that the instructions, when executed by one or more processors, cause the machine to perform, in whole or in part, any one or more of the methodologies described herein.

[0240] 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, non-transitory data repositories (e.g., data volumes) in the exemplary form of a solid-state memory chip, an optical disk, a magnetic disk, or any suitable combination thereof. In some exemplary embodiments, instructions for execution may be carried by a carrier medium. Such carrier media include, for example, transient media (e.g., a propagated signal carrying the instructions).

[0241] 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 includes all modifications and variations that come within the scope of the appended claims and their equivalents.

[0242] The following numbered items are also disclosed:

[0243] Item 1. A first layer including a first pupil replicator positioned to receive a diffracted light field from a diffractive structure defining a pupil, and a waveguide coupler, wherein the first pupil replicator is substantially elongated; a second layer comprising a second pupil replicator, the second pupil replicator being substantially planar and having a first major surface arranged to form an input and a second major surface arranged to form an output of the light engine, the waveguide coupler being arranged to couple the output of the first pupil replicator to the input of the second pupil replicator; Equipped with the first layer and the second layer are substantially parallel and adjacent to one another; Light engine.

[0244] Item 2. The light engine of item 1, wherein the first pupil replicator and the waveguide coupler are disposed within a region occupied by the second pupil replicator.

[0245] Item 3. A light engine described in any one of items 1 or 2, wherein the first pupil replicator comprises a primary pair of opposing surfaces arranged to provide light guidance and pupil replication therebetween.

[0246] Item 4. A light engine described in any one of items 1 to 3, wherein the waveguide coupler comprises a primary pair of opposing surfaces each comprising an input surface and an output surface, the input surface and the output surface being at an angle to each other.

[0247] Item 5. The light engine of any one of items 1 to 4, wherein the first pupil replicator and the waveguide coupler are substantially coplanar.

[0248] Item 6. A light engine described in any one of items 1 to 5, wherein the first pupil replicator and waveguide coupler of the first layer are arranged to guide the diffracted light field in a plane substantially parallel to the second layer.

[0249] Item 7. A light engine described in any one of items 1 to 6, wherein the second layer is defined by a first and a second axis, and the elongated dimension of the first pupil replicator is tilted with respect to at least one of the first and second axes of the second layer.

[0250] Item 8. The light engine described in Item 7, wherein the angle of the elongated dimension of the first pupil replicator relative to the first axis or the second axis of the second layer is substantially equal to the angle of incidence of the diffracted light received by the first pupil replicator.

[0251] Item 9. The light engine of any one of items 1 to 8, wherein the second pupil replicator has a substantially quadrilateral cross-sectional shape.

[0252] Item 10. The light engine of any one of items 1 to 9, wherein the input of the second pupil replicator is elongated and corresponds to the first axis of the second layer.

[0253] Item 11. A light engine described in any one of items 1 to 10, wherein the first and second major surfaces of the second pupil replicator form a primary pair of opposing surfaces arranged to provide light guiding and pupil replication therebetween.

[0254] Item 12. A light engine described in any one of items 1 to 11, wherein the second pupil replicator of the second layer is positioned to guide the diffracted light field in a plane substantially parallel to the first layer.

[0255] Item 13. A light engine described in any one of items 1 to 12, wherein the first pupil replicator and the waveguide coupler are fixed to a second major surface of the second pupil replicator.

[0256] Item 14. A light engine described in any one of items 1 to 13, wherein the first pupil replicator and the waveguide coupler each comprise a respective secondary pair of opposing surfaces arranged to confine the diffracted light field within that plane.

[0257] Item 15. A light engine as described in Item 14, wherein at least one surface of each secondary pair of opposing surfaces comprises a reflective component, and at least one surface of each secondary pair of opposing surfaces is fixed to a common substrate via the reflective component.

[0258] Item 16. The light engine of item 15, wherein the common substrate is a component of the vehicle housing the second pupil replicator or light engine.

[0259] Item 17. The light engine of any one of items 1 to 16, wherein the first pupil replicator and the waveguide coupler are joined together.

[0260] Item 18. The light engine of any one of items 1 to 17, wherein the light engine further comprises a control device, the control device comprising a plurality of independently controlled apertures arranged to determine which pupil replica is relayed from the first pupil replicator to the second pupil replicator, and optionally, the first pupil replicator, the waveguide coupler, and the control device are joined together.

[0261] Item 19. A head-up display for a vehicle, a first pupil replicator positioned to receive a holographic light field from a spatial light modulator having a pixel array extending in a first direction and defining a limiting aperture of the head-up display, the holographic light field being a complex light field spatially modulated in accordance with a hologram displayed on the spatial light modulator; and a second pupil duplicator extending in a first direction and a second direction perpendicular to the first direction, the second pupil duplicator having a first major surface forming an output portion and a second major surface parallel to the first major surface; a waveguide coupler positioned to optically couple the output of the first pupil replicator to the input of the second pupil replicator; Equipped with A head-up display, wherein the first pupil replicator and the waveguide coupler are disposed in a planar layer substantially parallel to and adjacent to the second major surface of the second pupil replicator.

[0262] Item 20. The head-up display of item 19, wherein the first pupil replicator and waveguide coupler are mounted to a second major surface of the second pupil replicator or to the structural framework of the vehicle housing the head-up display.

Claims

1. 1. A light engine, comprising: a first layer including a first pupil replicator positioned to receive a diffracted light field from a diffractive structure defining a pupil, the first pupil replicator adapted to dilate the pupil in a first direction, the first layer being substantially elongated in the first direction; a second layer comprising a second pupil replicator adapted to dilate a pupil in a second direction, the second direction being perpendicular to the first direction, the second pupil replicator comprising a first major surface that is planar and includes the first and second directions and that is arranged to form an input and a second major surface that is arranged to form an output of the light engine; the first layer and the second layer are substantially parallel and adjacent to one another; the second pupil duplicator defines a coverage area on the first layer extending in the first direction and the second direction, the first pupil duplicator being positioned such that light output by the first pupil duplicator is parallel to the second direction of the coverage area; the second layer is defined by a first axis and a second axis, the first axis being an axis in the first direction and the second axis being an axis in the second direction, an elongated dimension of the first pupil replicator being tilted with respect to at least one of the first and second axes of the second layer; light output by the first pupil replicator is coupled to the input of the second pupil replicator; Light engine.

2. The first pupil replicator is positioned within the occupied area of ​​the second pupil replicator. The light engine of claim 1 .

3. the first layer further comprising a waveguide coupler positioned to couple an output of the first pupil replicator to the input of the second pupil replicator. The light engine of claim 1 .

4. the waveguide coupler comprises a primary pair of opposing surfaces each comprising an input surface and an output surface, the input surface and the output surface being at an angle to each other; 4. The light engine of claim 3.

5. the first pupil replicator and the waveguide coupler are substantially coplanar; 4. The light engine of claim 3.

6. The first pupil replicator and waveguide coupler of the first layer are positioned to guide the diffracted light field in a plane substantially parallel to the second layer.

4. The light engine of claim 3.

7. The second pupil replicator of the second layer is positioned to guide the diffracted light field in a plane substantially parallel to the first layer.

4. The light engine of claim 3.

8. The first pupil replicator and the waveguide coupler are fixed to the first major surface of the second pupil replicator.

4. The light engine of claim 3.

9. the first pupil replicator and the waveguide coupler each comprise a respective secondary pair of opposing surfaces arranged to confine the diffracted light field within the plane of the respective secondary pair of opposing surfaces; 4. The light engine of claim 3.

10. At least one surface of each secondary pair of opposing surfaces includes a reflective component, and the at least one surface of each secondary pair of opposing surfaces is fixed to a common substrate via the reflective component.

10. The light engine of claim 9.

11. the common substrate is a component of the vehicle housing the second pupil replicator or the light engine; The light engine of claim 10.

12. the first pupil replicator and the waveguide coupler are joined together 4. The light engine of claim 3.

13. the light engine further comprising a controller, the controller comprising a plurality of independently controlled apertures arranged to determine which pupil replicas are relayed from the first pupil replicator to the second pupil replicator; 4. The light engine of claim 3.

14. the elongated dimension of the first pupil replicator is positioned to be oblique with respect to the other of the first and second directions of the occupied area. The light engine of claim 1 .

15. the angle of the elongated dimension of the first pupil replicator relative to the first axis or the second axis of the second layer is substantially equal to the angle of incidence of diffracted light received by the first pupil replicator; The light engine of claim 1 .

16. the second pupil replicator having a substantially quadrilateral cross-sectional shape; The light engine of claim 1 .

17. The input portion of the second pupil replicator is elongated and corresponds to an axis of the second layer in the first direction. The light engine of claim 1 .

18. the first and second major surfaces of the second pupil replicator form a primary pair of opposing surfaces arranged to provide light guidance and pupil replication therebetween. The light engine of claim 1 .

19. the first pupil replicator comprising a primary pair of opposing surfaces arranged to provide light guidance and pupil replication therebetween; The light engine of claim 1 .

20. A head-up display for a vehicle, a first pupil replicator positioned to receive a holographic light field from a spatial light modulator having an array of pixels extending in a first direction and defining a limiting aperture of the head-up display, the first pupil replicator adapted to dilate a pupil in the first direction, the holographic light field being a complex light field spatially modulated in accordance with a hologram displayed on the spatial light modulator; a second pupil duplicator adapted to dilate the pupil in a second direction, the second pupil duplicator being provided on a second layer and being in a plane containing the first direction and the second direction, the second pupil duplicator having a first major surface forming an output portion and a second major surface forming an input portion parallel to the first major surface; the first pupil replicator is disposed in a planar layer substantially parallel to and adjacent to the second major surface of the second pupil replicator; the first pupil replicator is positioned such that light output by the first pupil replicator is parallel to the second direction; the second layer is defined by a first axis and a second axis, the first axis being an axis in the first direction and the second axis being an axis in the second direction, an elongated dimension of the first pupil replicator being tilted with respect to at least one of the first and second axes of the second layer; light output by the first pupil replicator is coupled to the input of the second pupil replicator; Head-up display.

21. the first pupil replicator is attached to the second major surface of the second pupil replicator or to a structural framework of the vehicle housing the head-up display; 21. The head-up display of claim 20.

22. 22. A head-up display according to claim 20 or 21, The head-up display further comprises a waveguide coupler arranged to optically couple the output of the first pupil replicator to the input of the second pupil replicator, the waveguide coupler being arranged within the planar layer of the first pupil replicator.

Images