Optical system

Abstract

An optical system with an observation window is provided. The optical system includes a display device arranged to spatially modulate light according to a hologram displayed thereon to form a holographic wavefront. The holographic wavefront forms a holographic reconstruction of an image downstream of the display device. The optical system also includes a waveguide arranged to receive the holographic wavefront and guide it between a pair of reflective surfaces. One of the reflective surfaces is partially transmissive, allowing multiple copies of the holographic wavefront to be emitted therefrom. The optical system also includes an optical component between the holographic reconstruction and the waveguide, wherein the optical component is arranged to (a) form a holographically reconstructed virtual image upstream of the display device and (b) form an image of the displayed hologram at infinity or downstream of the waveguide.

Description

Technical Field

[0001] This disclosure relates to optical systems and methods of imaging using optical systems. More specifically, this disclosure relates to optical systems arranged to form a holographically reconstructed virtual image, which is distant from the image of a hologram. The invention also relates to methods for moving the image plane of a hologram and methods for increasing the distance between the holographically reconstructed image and the corresponding holographic image. Some embodiments relate to holographic projectors, image generation units, or head-up displays. Background Technology

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

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

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

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

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

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

[0008] A holographic projector is disclosed herein, including an optical system comprising a display device. The holographic projector may include an optical repeater. The optical repeater may include a first lens and a second lens. The first and second lenses may be arranged in a so-called 4f configuration. The holographic projector may further include one or more waveguide pupil expanders. The display device is arranged to spatially modulate light according to a hologram of an image displayed thereon. The display device may be located at the front focal plane of the first lens. The optical system may be arranged such that the display device is illuminated by coherent light, which is spatially modulated according to the hologram, and then received by the first lens of the optical repeater, such that a holographic reconstruction of the image is formed at the rear focal plane of the first lens. The light may then continue to propagate and be received by the second lens of the optical repeater, such that a relayed image of the display device (i.e., a relayed image of the hologram) can be formed at the rear focal plane of the second lens. A first waveguide is located near the rear focal plane of the second lens and may be arranged to receive and replicate the spatially modulated light to expand the exit pupil of the optical system in a first direction. A second waveguide may also be provided, arranged to receive light output from the first waveguide, to extend the exit pupil of the optical system in a second direction. Conceptually, this results in the creation of a replica array of the display device. The replica array can be said to exist on a “virtual surface” that can be staggered, as described in UK patent application GB2118911.3 filed December 23, 2021. Specifically, each replica can be at a different vertical distance from the display device due to the different path lengths in the waveguides associated with each replica. Therefore, the portion of the virtual surface associated with each replica (e.g., in the x, y dimensions) is offset from the display device in the vertical direction (e.g., in the z dimension). The holographically reconstructed virtual image is visible when the viewing system (e.g., the user's eye) is located at the viewing window downstream of the waveguide. The virtual image can be formed at a virtual image distance upstream of the display device. Typically, the virtual image distance can be between approximately 1 meter and approximately 10 or 20 meters.

[0009] As used herein, the terms "upstream" and "downstream" can be used to describe features, elements, or components of an optical system, or the relative position of a (real or virtual) image or holographic reconstruction formed by the optical system relative to the direction of light propagation through the optical system. For example, in an optical system where light propagates to a first component and then to a second component, the first component can be described as upstream of the second component, and the second component can be described as downstream of the first component. A virtual image formed by an optical component can be described as being formed upstream of the respective optical component. A real image formed by an optical component can be described as being formed downstream of the respective optical component.

[0010] One advantage of the aforementioned optical system is that it adds a one-dimensional or two-dimensional viewing window (i.e., the user's eyebox), allowing the eye (or other viewing system) to make some movements while still enabling the viewing system to see the holographic reconstruction even in the case of very small display devices / holograms. However, the inventors have discovered that although the holographically reconstructed virtual image itself (when focused at the virtual image distance) may have good quality, artifacts may form / be seen. These artifacts may appear in front of (i.e., downstream of) the holographically reconstructed virtual image. These artifacts can form or be seen on a virtual surface—that is, in the area corresponding to the replica array of the display device. When the waveguide forms the replica array, each artifact formed in a single replica will be repeated a certain number of times, forming a repeating pattern of artifacts on the replica array of the display device. The viewing system / user at the viewing window may actually have to look through or across the pattern of artifacts to see the holographically reconstructed virtual image.

[0011] The inventors have discovered that the eye is generally very capable of observing image content at different depths, or at least being aware of the presence of features at different depths. Therefore, the holographically reconstructed virtual image and the non-uniform intensity array on the replica plane can be simultaneously perceived by a human observer, at least partially. The inventors have also discovered that the user's eye is drawn to artifacts (repeating patterns) that distract the user's attention from the holographically reconstructed virtual image they wish to observe—even when the observer is focused on the image (i.e., the holographic reconstruction) rather than on the corresponding hologram (or its image) at a different distance. Through their research, the inventors have recognized (even if some observers do not initially notice) that once the observer becomes aware of the artifact (repeating pattern), it is (or can become) a significant distraction. The inventors propose a similar analogy: observing a distant scene through a transparent glass window. In this case, markings or features on the glass (such as dirt or grime) can constitute artifacts, requiring the observer to look through or over them to see the scene behind. If the observer is aware of the markings on the glass (again, they may not be), their presence can at least partially disrupt the view of the scene, even if the observer's attention is focused on the scene rather than the glass. In summary, the inventors have discovered that the virtual surface formed by the waveguide replicator of this disclosure can affect the quality of the viewing experience.

[0012] Many different artifacts may form on the virtual surface (i.e., the replica area of ​​the display device). These artifacts may be caused by light scattering from the optical system, such as scattering from a holographic wavefront formed by the display device. Physical features of the display device (such as the boundaries of the display device) may also contribute to the formation of artifacts. Similarly, these artifacts may appear at the location of the replica array rather than at the location of the virtual image, thus potentially attracting the user's attention and distracting from the virtual image.

[0013] There are several reasons why virtual surfaces can be distracting. By way of example, the inventors have recognized that one source of distraction on virtual surfaces may be the result of uneven illumination of the display device. This uneven illumination can occur if the contours of the light source are non-uniform (e.g., with a Gaussian intensity contour). The inventors have found that minute reductions in intensity at the edges of the light spot illuminating the hologram result in the formation of extended contrast bands or contours (adjacent to the replica) visible from the eyebox. Notably, these bands or contours are substantially straight (and substantially aligned / parallel to the two orthogonal directions of the hologram replication). While these bands are extremely subtle (in terms of intensity), the human eye is very sensitive to edge and line features (i.e., straight-line contrast), thus the negative impact on the quality of the visual experience is surprisingly high. That is, extended straight bands or contours—produced by the regular pattern of the hologram replication and the “normal” non-uniformity of the light source, which is perfectly acceptable for other types of holographic displays—are strikingly prominent to some human observers. Dark bands can form at the replica plane, so the viewing system may have to effectively observe the holographically reconstructed virtual image through or across these dark bands.

[0014] The optical system disclosed herein provides a means for significantly reducing or minimizing the visual impact of a virtual surface on a replica.

[0015] In summary, an optical system with an observation window is provided. The optical system includes a display device arranged to spatially modulate light according to a hologram displayed thereon. The spatially modulated light forms a holographic wavefront, which forms a holographic reconstruction of an image downstream of the display device. The optical system also includes optical components (e.g., lenses). The optical components are arranged downstream of the holographic reconstruction (such that the spatially modulated light forms the holographic reconstruction, for example, on a playback plane, and is then received at the optical components). The optical components are arranged to form: a) a holographically reconstructed virtual image; and b) an image of the displayed hologram / display device. The optical components are arranged such that the distance between the holographically reconstructed virtual image and the displayed hologram / display device image is greater than the virtual image distance of the holographically reconstructed virtual image. Thus, the displayed hologram / display device image is further away from the holographically reconstructed virtual image. In some embodiments, the separation magnitude between the holographically reconstructed virtual image and the displayed hologram / display device image can be at least twice the magnitude of the virtual image distance of the holographically reconstructed virtual image, for example, at least three times or at least five times the virtual image distance. In some embodiments, the separation magnitude between the holographically reconstructed virtual image and the displayed image of the hologram / display device can be at least an order of magnitude larger than the magnitude of the virtual image distance of the holographically reconstructed virtual image. For example, in some embodiments, the virtual image of the display device is formed at infinity, such that the effective distance between the virtual image of the display device and the holographically reconstructed virtual image is infinite. In other embodiments, the real image of the display device is formed downstream of the optical components, also far from the holographically reconstructed virtual image (which will be upstream of the optical components). For example, the real image of the display device can be formed downstream of the waveguide of the optical system, optionally downstream of the viewing window / eyebox of the optical system. In either case, the optical components are arranged such that the holographically reconstructed virtual image is far from the displayed image of the hologram / display device. The inventors have found that arranging the optical components in this way advantageously and significantly reduces the obstruction / interference effect of artifacts of the virtual surface on the observer at the viewing window. In particular, the inventors have recognized that the optical components can be arranged to form the image of the hologram / display device at infinity (far beyond the holographically reconstructed virtual image) or downstream of the optical components (typically behind the viewing system). In any embodiment, when the optical components are arranged in this manner, the observer does not need to look through or pass through the image of the hologram / display device to observe the holographically reconstructed virtual image. The inventors have found this to significantly improve the viewing experience. Specifically, artifacts in the image of the hologram / display device (e.g., uneven intensity patterns of dark bands) are less distracting. When at the image distance, the viewing system / eye / brain is able to more effectively ignore artifacts.

[0016] In some embodiments, optical components are arranged to perform Fourier transforms. For example, in these embodiments, the optical components may be described as Fourier transform components, such as Fourier transform lenses, or simply Fourier lenses. Optical components (particularly when used as Fourier lenses) may include a front focal plane and a rear focal plane. The front focal plane may be referred to as the object plane, and the rear focal plane may be referred to as the Fourier transform plane. The optical components may be arranged to form a Fourier transform of the object at the front (object) plane at the rear (Fourier) plane. According to the invention, an optical component is provided that performs a Fourier transform of a holographic wavefront before being replicated by a waveguide. In some embodiments, the transform of the holographic wavefront may be described as being input to a waveguide and / or the waveguide is arranged to replicate the transform of a relay hologram / holographic wavefront.

[0017] In a first aspect, an optical system with an observation window is provided. The optical system includes a display device. The display device is arranged to spatially modulate light according to a hologram or diffraction structure displayed thereon to form a holographic wavefront, which forms a holographic reconstruction of an image downstream of the display device. The optical system also includes optical components. The optical components may be referred to as imaging components. Examples of optical components include lenses, such as converging lenses. The optical components are arranged to: (a) form a holographically reconstructed virtual image upstream of the display device, and (b) form an image of the displayed hologram at infinity or downstream of the optical components. The image of the hologram displayed at infinity may be at infinity upstream of the display device (i.e., behind the display device).

[0018] In one embodiment, the optical system further includes a waveguide. The waveguide is arranged to receive a holographic wavefront. The waveguide can receive a holographic wavefront from optical components. The waveguide can be arranged to receive the holographic wavefront directly or indirectly. The waveguide can be arranged to guide the holographic wavefront between a pair of reflective surfaces. One of the reflective surfaces can be partially transmissive, such that multiple copies of the holographic wavefront are emitted from that surface. In another embodiment, the optical components can be arranged to form an image displaying a hologram at infinity, at the waveguide, or downstream of it.

[0019] In an embodiment, the holographically reconstructed image is formed by optical elements or components at locations different from the image of the displayed hologram. As used herein, an optical element may be referred to as an optical component. In an embodiment, the image distance of the holographically reconstructed image differs from the image distance of the displayed hologram. In an embodiment, the image distance of the holographically reconstructed image is less than infinity, for example, less than 30 meters.

[0020] In some embodiments, the hologram on the display device is arranged such that spatially modulated light forms a holographic reconstruction of the holographic image downstream of the display device without passing through optical elements or components such as (physical) (imaging) lenses. In one embodiment, the optical components may be arranged to form a virtual image of the holographic reconstruction (directly formed by the hologram on the display device). In other embodiments, the holographic reconstruction may be relayed downstream of the holographic reconstruction directly formed by the hologram on the display device. In such an embodiment, the optical components may be arranged to form a virtual image of the relayed holographic reconstruction. In other words, instead of directly forming a virtual image of the holographic reconstruction formed by the hologram on the display device, the optical components may be arranged to (directly) form a virtual image of the relayed holographic reconstruction.

[0021] In some embodiments, the optical components are arranged to perform a Fourier transform. For example, the optical components may be Fourier lenses. The optical components (Fourier lenses) may include a front focal plane and a rear focal plane. The front focal plane may be referred to as the object plane, and the rear focal plane may be referred to as the Fourier transform plane. The optical components may be arranged to form a Fourier transform of the light / object / image at the front (object) plane at the rear (Fourier) plane.

[0022] The back (Fourier) plane of an optical component can be coupled to a waveguide (when present in an optical system). As used herein, a back (Fourier) plane coupled to a waveguide can mean that the back focal plane of the optical component coincides (i.e., substantially coincides) with the input of the waveguide. In some embodiments, the back (Fourier) plane is adjacent to / overlaps with the input coupling port of the waveguide. In some embodiments, the back (Fourier) plane is within the waveguide. For example, the back (Fourier) plane can be between a pair of reflective surfaces of the waveguide. In this way, the optical component can be arranged such that the Fourier transform of light / object / image at the front (object) plane of the optical component is coupled into the waveguide.

[0023] In some embodiments, optical components may be arranged to perform a space-frequency transformation such that the transformed display hologram is coupled into a waveguide. As used herein, a transformed display hologram means a hologram that is primarily or entirely in the frequency domain. The space-frequency transformation may be a Fourier transform. In other words, optical components may be arranged such that the Fourier transform of the hologram is coupled into a waveguide. In some embodiments, optical components may be arranged such that the Fourier transform of the hologram displayed on a display device is coupled into a waveguide. This may be the case, for example, when optical components are arranged to form an image of the displayed hologram at infinity.

[0024] Optical components can be arranged such that the wavefront coupled into the waveguide is the (Fourier transform) of the holographic wavefront of the encoded image.

[0025] In some embodiments, the object (e.g., a display device / displayed hologram or a relay display device / relay displayed hologram) may be substantially / precisely located at the front focal plane of the optical component. A waveguide (e.g., an input coupling port) may be coupled to the rear focal plane of the optical component. For example, the rear focal plane of the optical component may be located at the input port of the waveguide or within the waveguide. The optical component may be arranged such that the Fourier transform of the displayed hologram is coupled to the waveguide.

[0026] In some embodiments, the optical system is arranged to perform an odd number of (frequency-time) transformations / Fourier transforms (e.g., first or third transformations / first or third Fourier transforms between the frequency and time domains) on light propagating between the display device and the waveguide. Thus, when the wavefront is coupled into the waveguide, it can be said to be in the frequency domain (even though it has undergone multiple (odd) transformations between the spatial and frequency domains as it propagates from the display device to the waveguide). For example, the optical system may include multiple components (e.g., multiple Fourier transform lenses) arranged to perform Fourier transforms. The aforementioned optical components may be a first Fourier transform lens. As described below, the optical system may further include an optical repeater comprising a pair of Fourier lenses. The optical system may be arranged such that each of the pair of Fourier lenses in the optical repeater and each of the optical components sequentially performs a frequency-time transformation / Fourier transform.

[0027] In some embodiments, the optical system further includes an optical repeater. The optical repeater may be located downstream of the display device. The optical repeater may be located between the display device and a waveguide (if present). The optical repeater may include two lenses. These two lenses may be arranged in a coordinated manner to form a relay hologram and a relay hologram reconstruction. The relay hologram may be an image of a hologram displayed on the display device. The relay hologram reconstruction may be an image of a hologram reconstructed from the hologram displayed on the display device. Therefore, in embodiments including an optical repeater, the (virtual) image of the hologram reconstructed by optical components (e.g., lenses) is the (virtual) image of the relay hologram reconstruction. The (real) image of the displayed hologram formed by optical components (e.g., lenses) is the (real) image of the relay hologram.

[0028] An optical repeater may include a first lens and a second lens. The first lens of the optical repeater may be closer to the display device than the second lens. The distance between the first and second lenses of the optical repeater may be substantially equal to the sum of the focal lengths of the first and second lenses. In some embodiments, the focal length of the first lens is equal to the focal length of the second lens. In other embodiments, the focal length of the first lens is different from the focal length of the second lens. In such embodiments, the optical repeater may have a magnification (or reduction) effect on relayed holographic reconstruction and / or relayed holograms. An optical repeater may be referred to as a telescope (e.g., a magnifying or reducing telescope). When the distance between the first and second lenses of the optical repeater is substantially equal to the sum of the focal lengths of the first and second lenses, the optical repeater may be referred to as a "4f" system. This may be because the distance between the front focal plane of the first lens and the rear focal plane of the second lens is equal to four focal lengths. When the focal lengths of the first and second lenses are the same, the distance between the front focal plane of the first lens and the rear focal plane of the second lens can be equal to four times the focal length of either the first or second lens. In some embodiments, the first lens includes a front focal plane and a rear focal plane, and the second lens includes a front focal plane and a rear focal plane. In some embodiments, the display device can be substantially located at the front focal plane of the first lens of the optical repeater. In some embodiments, the rear focal plane of the first lens of the optical repeater can substantially coincide with the front focal plane of the second lens of the optical repeater. The rear focal plane of the first lens of the optical repeater can be substantially parallel to the front focal plane of the second lens of the optical repeater. The rear focal plane of the first lens of the optical repeater can be substantially coplanar with the front focal plane of the second lens of the optical repeater.

[0029] The relay hologram and the relay holographic reconstruction (relayed by an optical repeater) can be relayed to a corresponding location downstream of the optical repeater, such as downstream of the second lens of the optical repeater. In some embodiments, the relay holographic reconstruction is located downstream of the relay hologram. In other words, the distance between the optical repeater (second lens) and the relay holographic reconstruction can be greater than the distance between the optical repeater (second lens) and the relay hologram.

[0030] In some embodiments, the relay hologram may form / relay to the rear focal plane of the second lens of the optical repeater. This may mean that the image of the hologram displayed on a display device is substantially focused on the rear focal plane of the second lens of the optical repeater. In some embodiments, the relay holographic reconstruction may form / relay to the focal plane of the relay holographic reconstruction. This may mean that the image of the holographic reconstruction is substantially focused on the focal plane of the relay holographic reconstruction. The focal plane of the relay holographic reconstruction may be substantially parallel to the rear focal plane of the second lens of the optical repeater. The focal plane of the relay holographic reconstruction may be downstream of the rear focal plane of the second lens of the optical repeater.

[0031] In some embodiments, optical components (e.g., lenses) are downstream of the relay hologram reconstruction. Optical components may also be downstream of the relay hologram. Optical components may be closer to the relay hologram reconstruction than the relay hologram itself.

[0032] In embodiments that include a waveguide, the optical components may be located between the relay holographic reconstruction and the waveguide.

[0033] In some embodiments, the optical component may be arranged between the relay holographic reconstruction and the waveguide such that (a) the distance between the relay holographic reconstruction and the optical component is less than the focal length of the optical component. Therefore, the virtual image of the holographic reconstruction formed by the optical component can be the virtual image of the relay holographic reconstruction. The optical component may also be arranged between the relay holographic reconstruction and the waveguide such that (b) the distance between the relay hologram and the optical component is (substantially) equal to the focal length of the optical component. Therefore, the image of the hologram formed by the optical component can be a virtual image formed (substantially) at infinity. The virtual image of the hologram can be formed upstream of the relay hologram / upstream of the optical component / upstream of the display device. The virtual image of the holographic reconstruction formed by the optical component can also be upstream of the optical component, but at a finite image distance. Thus, the effective distance or interval between the virtual image of the hologram (at infinity) and the virtual image of the hologram (not at infinity) is practically infinite.

[0034] In other embodiments (including optical repeaters as defined above), optical components may be arranged between the relay holographic reconstruction and the waveguide such that (a) the distance between the relay holographic reconstruction and the optical components is less than the focal length of the optical components. Therefore, the virtual image of the holographic reconstruction formed by the optical components can be the virtual image of the relay holographic reconstruction. Optical components may also be arranged between the relay hologram and the optical components such that (b) the distance between the relay hologram and the optical components is greater than the focal length of the optical components. Therefore, the image of the hologram formed by the optical components can be a real image. The real image of the hologram can be formed downstream of the optical components. The real image of the hologram can be substantially formed at or downstream of the waveguide. The virtual image of the holographic reconstruction formed by the optical components can be upstream of the optical components (at a finite image distance). Therefore, there may be a relatively large distance or gap between the virtual image of the holographic reconstruction (upstream of the optical components) and the real image of the hologram (downstream of the optical components).

[0035] In some embodiments, the optical system does not include an optical repeater. In such embodiments, the optical components (e.g., lenses) of the optical system may be arranged to form a (virtual) image of a virtual hologram reconstruction and a (real) image of a displayed hologram based on a holographic reconstruction formed downstream of a display device and a hologram displayed on the display device, respectively.

[0036] In some embodiments, the distance between the holographic reconstruction (rather than the relay holographic reconstruction in the above embodiments) and the optical components is less than the focal length of the optical components. Therefore, the holographically reconstructed image can be a virtual image. The holographically reconstructed virtual image can be formed upstream of the display device. The distance between the display device or hologram (rather than the relay hologram in the above embodiments) and the optical components can be substantially equal to the focal length of the optical components. Therefore, the virtual image of the hologram can be formed at infinity. The virtual image of the hologram can be formed upstream of the hologram displayed on the display device / upstream of the optical components. The holographically reconstructed virtual image formed by the optical components can also be upstream of the optical components, but at a finite image distance. Thus, the effective distance or interval between the virtual image of the hologram (at infinity) and the virtual image of the hologram (not at infinity) can actually be infinite.

[0037] In some embodiments, the distance between the holographic reconstruction (not relay holographic reconstruction) and the optical components is less than the focal length of the optical components. Therefore, the holographically reconstructed image can be a virtual image. The virtual image of the holographic reconstruction can be formed upstream of the optical components and / or the display device. The distance between the display device / the hologram displayed on the display device (not a relay hologram) and the waveguide can be greater than the focal length of the optical components. Therefore, the image of the hologram (displayed on the display device) can be formed downstream of the optical components. The real image of the hologram can be substantially formed at or downstream of the waveguide. Therefore, there may be a relatively large distance or gap between the holographically reconstructed virtual image (upstream of the optical components and / or the display device) and the real image of the hologram (downstream of the optical components and / or at or downstream of the waveguide). The image of the hologram can be a real image.

[0038] In some embodiments, the image of the hologram formed by the optical components is a real image of the hologram formed downstream of the viewing window (e.g., eyebox) of the optical system.

[0039] In some embodiments, the distance between the holographically reconstructed virtual image and the (real or virtual) image of the displayed hologram formed by optical components is greater than 1 meter, for example, greater than 2 meters or greater than 5 meters. In some embodiments, the interval between the holographically reconstructed (virtual) image and the virtual image of the display device can actually be infinite. More generally, the interval between the holographically reconstructed (virtual) image and the (virtual or real) image of the display device can be greater than the virtual image distance of the holographically reconstructed virtual image.

[0040] In some embodiments, the optical components are arranged such that the distance from the optical components to the holographically reconstructed virtual image is in the range of 0.5 to 10 meters. For example, the optical components may be positioned (relative to holographic reconstruction or relay holographic reconstruction) and / or have appropriate optical power to form the holographically reconstructed virtual image within the said distance range.

[0041] In some embodiments, the focal length of the optical component may be 150 mm or less, such as 120 mm or less, or 100 mm or less. The optical component may be a lens. The optical component may be a converging lens. The optical component may include a front focal plane at its focal length. The optical component may include a rear focal plane at its focal length.

[0042] The distance from the holographic reconstruction or relay holographic reconstruction (if an optical relay exists) to the optical component can be less than the distance from the front focal plane to the optical component. In other words, the holographic reconstruction or relay holographic reconstruction may be closer to the optical component than its front focal plane.

[0043] In embodiments where the optical components are arranged such that the image of the hologram formed by the optical components is a virtual image formed at infinity, the front focal plane of the optical components may substantially coincide with the rear focal plane of the second lens of a) the display device or b) the optical repeater (if the optical repeater is present). The front focal plane of the optical components may be substantially parallel to the plane of the display device or the rear focal plane of the second lens of the optical repeater. The front focal plane of the optical components may be substantially coplanar with the plane of the display device or the rear focal plane of the second lens of the optical repeater.

[0044] In some embodiments, the holographic wavefront received by the waveguide includes non-collimated light, such as divergent light.

[0045] In some embodiments, the display device is a pixelated display device. For example, a spatial light modulator may include a regular array of pixels. The pixel array may cover a basic quadrilateral display area of ​​the display device. In some embodiments, the display device is a spatial light modulator. In some embodiments, the display device is a liquid crystal on silicon spatial light modulator.

[0046] In some embodiments, the hologram includes multiple superimposed diffraction patterns, each diffraction pattern representing a lens (e.g., a Fresnel lens) that forms an image point.

[0047] In some embodiments, each diffraction pattern represents a lens / brings light to a focal point.

[0048] In a second aspect, an image generation unit is provided. The image generation unit may include the optical system of the first aspect. The image generation unit may also include a light source arranged to illuminate a display device of the optical system. The light source may be a coherent light source, such as a laser.

[0049] In a third aspect, a head-up display for a vehicle is provided, including the aforementioned optical system and / or image generation unit.

[0050] In a fourth aspect, an optical system with an observation window is provided. The optical system includes a display device arranged to spatially modulate light according to a hologram or diffraction structure displayed thereon to form a holographic wavefront. The holographic wavefront forms a holographic reconstruction of an image downstream of the display device. The optical system also includes a waveguide arranged to receive the holographic wavefront. The waveguide may receive the holographic wavefront directly or indirectly. The waveguide may be arranged to guide the holographic wavefront between a pair of reflective surfaces. One of the reflective surfaces is partially transmissive, such that multiple copies of the holographic wavefront are emitted from that surface. The optical system also includes optical components, such as imaging components, such as a lens (e.g., a converging lens) between the holographic reconstruction and the waveguide. The optical components are arranged to (a) form a holographically reconstructed virtual image upstream of the display device, and (b) form an image displaying the hologram at infinity or downstream of the optical components, such as at or downstream of the waveguide. The optical components may be arranged such that the wavefront coupled into the waveguide is a (Fourier) transform of the holographic wavefront encoding the image.

[0051] In a fifth aspect, a method for forming a holographic image is provided. The method includes the step of spatially modulating light according to a hologram. The hologram may be a hologram of an image and is displayed on a display device to form a holographic wavefront. The method further includes the step of forming a holographic reconstruction of the image downstream of the display device. The method further includes the step of forming a holographically reconstructed virtual image upstream of the display device using optical components. The optical components may be lenses, such as converging lenses and / or Fourier lenses (as described in the foregoing aspects). The method may further include the step of forming an image of the displayed hologram at infinity or downstream of a waveguide using the optical components. In an embodiment, the method further includes receiving the holographic wavefront at the waveguide. The method may further include a waveguide holographic wavefront between a pair of reflective surfaces, wherein one of the reflective surfaces is partially transmissive, such that multiple replicas of the holographic wavefront are emitted therefrom. The optical components may be downstream of the holographic reconstruction. In an embodiment, the optical components may be between the holographic reconstruction and the waveguide.

[0052] In some embodiments, the method includes transforming a relay hologram into an image of a hologram displayed on a display device. The step of forming the relay hologram may include using an optical repeater between the display device and the waveguide. The optical repeater includes two lenses arranged in a mating configuration.

[0053] In some embodiments, the method includes reconstructing a relay hologram into a holographically reconstructed image formed by a hologram displayed on a display device. The relay holographic reconstruction step may include using an optical relay.

[0054] In some embodiments, the step of forming the holographic reconstruction virtual image includes forming the relay holographic reconstruction virtual image. The distance between the relay holographic reconstruction and the optical component may be less than the focal length of the optical component.

[0055] In some embodiments, the step of forming an image displaying a hologram includes forming a virtual image of the hologram at infinity, and wherein the distance between the relay hologram and the optical component is (substantially) equal to the focal length of the optical component.

[0056] In some embodiments, the step of forming an image displaying a hologram includes forming a real image of the hologram downstream of an optical component / waveguide, and wherein the distance between the relay hologram and the optical component is greater than the focal length of the optical component.

[0057] In some embodiments, the step of forming a holographically reconstructed virtual image includes forming the holographically reconstructed virtual image upstream of the display device, wherein the distance between the holographic reconstruction and the optical component is less than the focal length of the optical component.

[0058] In some embodiments, the step of forming an image of a hologram includes forming a (virtual) image of the hologram at infinity (upstream of the hologram), and wherein the distance between the display device and the waveguide is equal to the focal length of the optical components.

[0059] In some embodiments, the step of forming an image of a hologram includes forming a (real) image of a hologram downstream of an optical component (waveguide), wherein the distance between the display device and the waveguide is equal to the focal length of the optical component.

[0060] In some embodiments, the step of forming a holographic image includes forming a real image of the hologram downstream of the viewing window (e.g., eyebox) of the optical system.

[0061] Features and advantages disclosed in one aspect can be applied to other aspects. In particular, features and advantages described with respect to an optical system can be applied to holographic imaging methods, and vice versa.

[0062] In this disclosure, the term "replica" is used only to reflect that spatially modulated light is segmented such that a composite light field is guided along multiple different optical paths. The term "replica" is used to refer to each occurrence or instance of the composite light field after a copying event—such as partial reflection-transmission of a pupil dilator. Each replica propagates along a different optical path. Some embodiments of this disclosure relate to the propagation of light encoded with a hologram rather than an image—that is, light spatially modulated with a hologram of an image rather than the image itself. Thus, it can be said that multiple replicas of a hologram are formed. Those skilled in the art of holography will understand that the composite light field associated with the propagation of hologram-encoded light will vary with the propagation distance. The term "replica" as used herein is independent of propagation distance, so two optical branches or paths associated with a copying event are still referred to as "replicas" of each other, even if the branches have different lengths, causing the composite light field to evolve differently along each path. That is, according to this disclosure, even if two composite light fields are associated with different propagation distances, they are still considered "replicas"—assuming they originate from the same copying event or a series of copying events.

[0063] According to this disclosure, a "diffracted light field" is a light field formed by diffraction. A diffracted light field can be formed by illuminating a corresponding diffraction pattern. According to this disclosure, an example of a diffraction pattern is a hologram, and an example of a diffracted light field is a holographic light field or a holographically reconstructed light field that forms an image. The holographic light field forms a (holographic) reconstruction of an image on the playback plane. The holographic light field propagating from the hologram to the playback plane can be said to include light encoded by the hologram or light in the holographic domain. The diffracted light field is characterized by a diffraction angle determined by the minimum feature size of the diffraction structure and the wavelength of the light (of the diffracted light field). According to this disclosure, a "diffracted light field" can also be said to be a reconstructed light field formed on a plane spatially separated from the corresponding diffraction structure. This document discloses an optical system for propagating a diffracted light field from a diffraction structure to an observer. The diffracted light field can form an image.

[0064] The term "hologram" is used to refer to a record containing amplitude or phase information about an object, or some combination thereof. The term "holographic reconstruction" is used to refer to the optical reconstruction of an object formed by illuminating a hologram. The system disclosed herein is described as a "holographic projector" because the holographic reconstruction is a real image and spatially separate from the hologram. The term "reproduced field" is used to refer to the 2D region within which the holographic reconstruction is formed and fully focused. If the hologram is displayed on a spatial light modulator including pixels, the reproduced field will be repeated in the form of multiple diffraction orders, where each diffraction order is a copy of the zero-order reproduced field. The zero-order reproduced field typically corresponds to the preferred or master reproduced field because it is the brightest reproduced field. Unless otherwise explicitly stated, the term "reproduced field" should be considered to refer to the zero-order reproduced field. The term "reproduced plane" is used to refer to a plane in space containing all reproduced fields. The terms "image," "reproduced image," and "image region" refer to the region of the reproduced field illuminated by the light reconstructed by the hologram. In some embodiments, an “image” may include discrete points, which may be referred to as “image points” or simply as “image pixels” for convenience.

[0065] The terms “encoding,” “writing,” and “addressing” are used to describe the process of providing multiple corresponding control values ​​to multiple pixels of an SLM, each determining the modulation level of the pixel. In other words, the pixels of an SLM are configured to “display” an optical modulation distribution in response to receiving multiple control values. Therefore, it can be said that an SLM “displays” a hologram, and a hologram can be considered an array of optical modulation values ​​or levels.

[0066] It has been found that acceptable-quality holographic reconstructions can be formed from "holograms" containing only phase information related to the Fourier transform of the original object. Such holographic records can be referred to as phase-only holograms. While the embodiments relate to phase-only holograms, this disclosure is equally applicable to amplitude-only holography.

[0067] This disclosure is equally applicable to forming holographic reconstructions using amplitude and phase information associated with the Fourier transform of the original object. In some embodiments, this is achieved by using complex modulation of a so-called fully complex hologram containing amplitude and phase information associated with the original object. Because the value (gray level) assigned to each pixel of the hologram has amplitude and phase components, such a hologram may be called a fully complex hologram. The value (gray level) assigned to each pixel can be represented as a complex number with amplitude and phase components. In some embodiments, a fully complex computer-generated hologram is computed.

[0068] The term "phase delay" can be a shorthand for the phase value, phase component, phase information, or simply phase of a pixel in a computer-generated hologram or spatial light modulator. That is, any phase value described is actually a number representing the amount of phase delay provided by that pixel (e.g., in the range of 0 to 2π). For example, a spatial light modulator is described as a pixel having a π / 2 phase value causing a π / 2 radian phase delay in the received light. In some embodiments, each pixel of a spatial light modulator can operate on one of a plurality of possible modulation values ​​(e.g., phase delay values). The term "gray level" can be used to refer to a plurality of available modulation levels. For example, the term "gray level" can be used for convenience to refer to a plurality of available phase levels in a phase modulator, even if different phase levels do not provide different shades of gray. For convenience, the term "gray level" can also be used to refer to a plurality of available complex modulation levels in a complex modulator.

[0069] Therefore, a hologram comprises an array of gray levels, i.e., an array of optical modulation values, such as phase delay values ​​or complex modulation values. A hologram is also considered a diffraction pattern because it is a pattern that causes diffraction when displayed on a spatial light modulator and illuminated with light whose wavelength is relative to (typically less than) the pixel spacing of the spatial light modulator. Reference is made herein to combining holograms with other diffraction patterns, such as those used as lenses or gratings. For example, a diffraction pattern used as a grating can be combined with a hologram to translate the playback field on the playback plane, or a diffraction pattern used as a lens can be combined with a hologram to focus the holographic reconstruction onto the playback plane in the near field.

[0070] Although different embodiments and groups of embodiments may be disclosed separately in the detailed description below, any feature of any embodiment or group of embodiments may be combined with any other feature or combination of features of any embodiment or group of embodiments. That is, all possible combinations and substitutions of the features disclosed in this disclosure are contemplated. Attached Figure Description

[0071] Referring to the following figures, specific embodiments are described by way of example only:

[0072] Figure 1 This is a schematic diagram illustrating a reflective SLM that generates holographic reconstruction on a screen;

[0073] Figure 2 The image used for projection is shown, including eight image regions / components V1 to V8, and cross-sections of the corresponding holographic channels H1-H8;

[0074] Figure 3 A hologram is shown on an LCOS that directs light to multiple discrete regions;

[0075] Figure 4 The diagram shows, including, as shown Figure 2 and 3 The system of the display device for the calculated hologram;

[0076] Figure 5A A perspective view of a first example two-dimensional pupil expander including two replicators, each replicator comprising a pair of stacked surfaces;

[0077] Figure 5B A perspective view of a first example two-dimensional pupil expander including two replicators, each in the form of a solid waveguide, is shown.

[0078] Figure 6 This is a cross-sectional schematic diagram of an optical component of an optical system not based on this disclosure;

[0079] Figure 7 This is a cross-sectional schematic diagram of the optical components of a first optical system according to the present invention, the first optical system including an optical repeater and arranged to form a virtual image of a relay hologram at infinity;

[0080] Figure 8 The display shows Figure 7 A schematic cross-sectional ray diagram of the characteristics of the first optical system;

[0081] Figure 9 This is a cross-sectional schematic diagram of the optical components of a second optical system according to the present invention, the second optical system including an optical repeater and arranged to form a real image of a repeater hologram;

[0082] Figure 10 The display shows Figure 9 A schematic cross-sectional ray diagram of the characteristics of the first optical system;

[0083] Figure 11 A cross-sectional schematic diagram of the optical components of a third optical system according to the present invention is shown. This third optical system does not include an optical repeater and is arranged to form a virtual image of a hologram at infinity; and

[0084] Figure 12 A cross-sectional schematic diagram of the optical components of a fourth optical system according to the present invention is shown. This fourth optical system does not include an optical repeater and is arranged to form a real image of a hologram.

[0085] In all the accompanying drawings, the same reference numerals will be used to refer to the same or similar parts. Detailed Implementation

[0086] This invention is not limited to the embodiments described below, but extends to the full scope of the appended claims. That is, the invention may be implemented in different forms and should not be construed as limited to the described embodiments, which are illustrated for illustrative purposes.

[0087] Unless otherwise stated, singular terms may include plural forms.

[0088] A structure described as being formed above or below another structure should be interpreted as including situations where the structures are in contact with each other, and also including situations where a third structure is placed between them.

[0089] When describing temporal relationships, such as when the chronological order of events is described as “after,” “following,” “next,” “before,” etc., this disclosure should be considered to include both consecutive and discontinuous events, unless otherwise stated. For example, unless terms such as “exactly,” “immediately,” or “directly” are used, the description should be considered to include discontinuous cases.

[0090] Although the terms “first,” “second,” etc., may be used herein to describe various elements, these elements are not limited by these terms. These terms are used only to distinguish individual elements. For example, without departing from the scope of the appended claims, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element.

[0091] Features of different embodiments may be coupled or combined with each other in part or in whole, and may interoperate differently with each other. Some embodiments may be implemented independently of each other, or may be implemented together in a mutually dependent relationship.

[0092] In this disclosure, the term "basic" when applied to a structural unit of an apparatus can be interpreted as the technical feature of the structural unit produced within the technical tolerances of the method used to manufacture it.

[0093] Traditional optical configuration of holographic projection

[0094] Figure 1 An embodiment is illustrated in which a computer-generated hologram is encoded on a single spatial light modulator. The computer-generated hologram is a Fourier transform of the object used for reconstruction. Therefore, a hologram can be described as a Fourier domain, frequency domain, or spectral domain representation of the object. In this embodiment, the spatial light modulator is a reflective liquid crystal on silicon (LCOS) device. The hologram is encoded on the spatial light modulator, and a holographic reconstruction is formed at the playback field, such as a light-receiving surface like a screen or diffuser.

[0095] A light source 110, such as a laser or laser diode, is configured to illuminate the SLM 140 via a collimating lens 111. The collimating lens causes the approximately plane wavefront of the light to be incident on the SLM. Figure 1 In this embodiment, the wavefront is oriented off-normal (e.g., two or three degrees away from a plane that is truly orthogonal to the transparent layer). However, in other embodiments, a generally planar wavefront is provided with normal incidence, and beam splitters are arranged to separate the input and output optical paths. Figure 1 In the illustrated embodiment, the arrangement is such that light from the light source is reflected from the mirrored rear surface of the SLM and interacts with the light modulation layer to form an outgoing wavefront 112. The outgoing wavefront 112 is applied to an optics device including a Fourier transform lens 120, the focal point of which is located at screen 125. More specifically, the Fourier transform lens 120 receives the modulated beam from the SLM 140 and performs a frequency-space transformation to produce a holographic reconstruction at screen 125.

[0096] It is worth noting that in this type of hologram, each pixel of the hologram contributes to the overall reconstruction. There is no one-to-one correlation between a specific point (or image pixel) on the playback field and a specific optical modulation element (or hologram pixel). In other words, the modulated light leaving the optical modulation layer is distributed across the entire playback field.

[0097] In these embodiments, the spatial position of the holographic reconstruction is determined by the diopter (focusing) of the Fourier transform lens. Figure 1 In the illustrated embodiments, the Fourier transform lens is a physical lens. That is, the Fourier transform lens is an optical Fourier transform lens and performs a Fourier transform optically. Any lens can act as a Fourier transform lens, but the performance of the lens will limit the accuracy of the Fourier transform it performs. Those skilled in the art understand how lenses can be used to perform optical Fourier transforms. In some embodiments of this disclosure, the lens of an observer's eye performs a hologram-to-image conversion.

[0098] Holographic computation

[0099] In some embodiments, the computer-generated hologram is a Fourier transform hologram, or simply a Fourier hologram or a Fourier-based hologram, wherein the image is reconstructed in the far field by utilizing the Fourier transform properties of a positive lens. The Fourier hologram is computed by Fourier transforming the desired light field in the reproduction plane back to the lens plane. The Fourier transform can be used to compute computer-generated Fourier holograms. By way of example only, the embodiments relate to Fourier holography and Gerchberg-Saxton type algorithms. This disclosure is equally applicable to Fresnel holography and Fresnel holograms that can be computed using similar methods. In some embodiments, the hologram is a phase or pure phase hologram. However, this disclosure is also applicable to holograms computed using other techniques, such as point cloud-based methods.

[0100] In some embodiments, the hologram engine is arranged to exclude the contribution of light blocked by the limiting aperture of the display system from the hologram calculation. UK Patent Application 2101666.2, filed February 5, 2021 and incorporated herein by reference, discloses a first hologram calculation method in which eye tracking and ray tracing are used to identify sub-regions of the display device for calculating a point cloud hologram of a ghost-free image. The sub-regions of the display device correspond to the aperture of this disclosure and are used to exclude light paths from the hologram calculation. UK Patent Application 2112213.0, filed August 26, 2021 and incorporated herein by reference, discloses a second method based on an improved Gerchberg-Saxton type algorithm, which includes a step of clipping the light field according to the pupil of the optical system during hologram calculation. The clipping of the light field corresponds to the determination of the limiting aperture of this disclosure. UK Patent Application 2118911.3, filed on December 23, 2021, and also incorporated herein by reference, discloses a third method for calculating holograms, which includes the step of determining a region of a so-called extended modulator formed by a hologram replicator. According to this disclosure, the region of the extended modulator is also the aperture.

[0101] In some embodiments, a real-time engine is provided, arranged to receive image data using an algorithm and compute holograms in real time. In some embodiments, the image data is video comprising a sequence of image frames. In other embodiments, the holograms are pre-computed, stored in computer memory, and retrieved as needed for display on an SLM. That is, in some embodiments, a library of predetermined holograms is provided.

[0102] Large field of view using small display devices

[0103] In summary, this disclosure relates to image projection. It relates to methods of image projection and image projectors including display devices. This disclosure also relates to projection systems including an image projector and an observation system, wherein the image projector projects or relays light from the display device to the observation system. This disclosure is equally applicable to monocular and binocular observation systems. An observation system may include one or more eyes of an observer. An observation system includes optical elements with optical power (e.g., the lens of the human eye) and an observation plane (e.g., the retina of the human eye). The projector may be referred to as a “light engine.” The display device and the image formed (or perceived) using the display device are spatially separated from each other. The observer forms or perceives the image on the display plane. In some embodiments, the image is a virtual image, and the display plane may be referred to as a virtual image plane. In other examples, the image is a real image formed by holographic reconstruction, and this image is projected or relayed to the observation plane. In these other examples, spatially modulated light from an intermediate holographic reconstruction formed in free space or on a screen or other light-receiving surface between the display device and the observer is propagated to the observer. In both cases, an image is formed by illuminating a diffraction pattern (such as a hologram or phase hologram) displayed on a display device.

[0104] Display devices consist of pixels. The pixels of a display can show diffraction patterns or structures of diffracted light. Diffracted light can form an image on a plane spatially separate from the display device. According to well-known optical principles, the magnitude of the maximum diffraction angle is determined by the pixel size and other factors such as the wavelength of light.

[0105] In this embodiment, the display device is a spatial light modulator, such as a liquid crystal on silicon (“LCOS”) spatial light modulator (SLM). Light travels from the LCOS to the observing entity / system, such as a camera or eye, within a diffraction angle range (e.g., from zero to the maximum diffraction angle). In some embodiments, amplification techniques may be used to increase the range of available diffraction angles beyond the conventional maximum diffraction angle of the LCOS.

[0106] In some embodiments, the hologram itself (light) propagates to the eye. For example, the spatially modulated light of the hologram (not yet fully converted into a holographic reconstruction, i.e., an image)—which can be informally referred to as being “encoded” by / with the hologram—propagates directly to the observer's eye. The observer can perceive a real or virtual image. In these embodiments, no intermediate holographic reconstruction / image is formed between the display device and the observer. Sometimes it is said that in these embodiments, the lens of the eye performs the holographic-to-image conversion or transformation. The projection system or optical system can be configured such that the observer can effectively look directly at the display device.

[0107] The "light field" mentioned here refers to a "composite light field." The term "light field" simply means a light pattern of finite size in at least two orthogonal spatial directions, such as x and y. The term "complex" as used here simply indicates that the light at each point in the light field can be defined by amplitude and phase values, and therefore can be represented by a complex number or a pair of values. For holographic computation purposes, a composite light field can be a complex two-dimensional array, where complex numbers define the light intensity and phase at multiple discrete locations within the light field.

[0108] According to well-known optical principles, the range of angles at which light propagating from a display device can be observed by an eye or other observing entity / system varies with the distance between the display device and the observing entity. For example, at an observation distance of 1 meter, only a small range of angles from the LCOS can propagate through the pupil of the eye to form an image on the retina at a given eye location. The range of angles at which light propagates from the display device determines the portion of the image that the observer can successfully propagate through the pupil of the eye to form an image on the retina at a given eye location. In other words, not all parts of the image are visible from any point on the observation plane (e.g., any eye position within the observation window of an eyebox).

[0109] In some embodiments, the image perceived by the observer is a virtual image appearing upstream of the display device; that is, the observer perceives the image as being farther away than the display device. Therefore, conceptually, it can be thought of as the observer viewing the virtual image through a "window the size of the display device," which can be very small, for example, 1 centimeter in diameter, at a relatively large distance, such as 1 meter. And the user will view the window the size of the display device through the pupil of their eye, which can also be very small. Therefore, at any given time, the field of view is small, and the range of specific angles that can be seen is heavily dependent on eye position.

[0110] A pupil expander addresses how to increase the angular range of light propagating from a display device so that the light can successfully pass through the pupil of the eye to form an image. Display devices are typically (relatively) small, with (relatively) large projection distances. In some embodiments, the projection distance is at least an order of magnitude larger than the diameter or width of the entrance pupil and / or aperture of the display device (i.e., the size of the pixel array), for example, at least two orders of magnitude larger.

[0111] The use of a pupil expander laterally increases the viewing area (i.e., the user's eyebox), allowing for some eye movement while still enabling the user to see the image. As those skilled in the art will understand, in an imaging system, the viewing area (the user's eyebox) is the region where the observer's eye can perceive the image. This disclosure includes non-infinite virtual image distances—i.e., near-field virtual images.

[0112] Traditionally, two-dimensional pupil expanders comprise one or more one-dimensional optical waveguides, each formed using a pair of opposing reflective surfaces, where output light from the surfaces forms an observation window or eyebox. Light received from a display device (e.g., spatially modulated light from LCOS) is replicated by this or each waveguide to increase the field of view (or observation area) in at least one dimension. In particular, the waveguides enlarge the observation window by generating additional light rays or "copies" through the division of the amplitude of the incident wavefront.

[0113] The display device can have an active or pixel display area, which has a first dimension of less than 10 cm, for example, less than 5 cm or less than 2 cm. The propagation distance between the display device and the observation system can be greater than 1 m, for example, greater than 1.5 m or greater than 2 m. The optical propagation distance within the waveguide can be up to 2 m, for example, up to 1.5 m or up to 1 m. This method is capable of receiving images and determining corresponding holograms of sufficient quality in less than 20 ms, such as less than 15 ms or less than 10 ms.

[0114] In some embodiments described herein by way of examples of diffraction or holographic light fields only, the hologram is configured to route light into multiple channels, each corresponding to a different portion (i.e., sub-region) of the image. The channels formed by the diffraction structure are referred to herein as “holographic channels” simply to reflect that they are light channels encoded by a hologram containing image information. It can be said that the light in each channel is in the holographic domain, rather than in the image or spatial domain. In some embodiments, the hologram is a Fourier or Fourier transform hologram, and therefore the holographic domain is Fourier or the frequency domain. The hologram can also be a Fresnel or Fresnel transform hologram. The hologram can also be a point cloud hologram. The hologram is described herein as routing light into multiple holographic channels to reflect that the image reconstructable from the hologram has a finite size and can be arbitrarily divided into multiple image sub-regions, where each holographic channel will correspond to each image sub-region. Importantly, the hologram of this example is characterized by how it distributes the image content when illuminated. Specifically and uniquely, the hologram divides the image content by angle. In other words, each point on the image is associated with a unique ray angle in the spatially modulated light formed by the hologram during illumination—at least a unique pair of angles, since the hologram is two-dimensional. To avoid confusion, this holographic behavior is not conventional. When illuminated, the spatially modulated light formed by this particular type of hologram can be divided into multiple holographic channels, each defined by a range of ray angles (in two dimensions). As understood above, any holographic channel that can be considered in the spatially modulated light (i.e., a subrange of ray angles) will be associated with a corresponding part or subregion of the image. That is, all the information needed to reconstruct that part or subregion of the image is contained within the subrange of angles of the spatially modulated light formed by the hologram of the image. When the spatially modulated light is viewed as a whole, there is not necessarily any evidence of multiple discrete light channels.

[0115] Nevertheless, holograms can still be identified. For example, if only a continuous portion or sub-region of the spatially modulated light formed by the hologram is reconstructed, then only that sub-region of the image should be visible. If different continuous portions or sub-regions of the spatially modulated light are reconstructed, then different sub-regions of the image should be visible. Another identifying feature of this type of hologram is that the shape of the cross-section of any hologram channel substantially corresponds to (i.e., substantially the same as) the shape of the incident pupil, although the size may differ—at least in the correct plane in which the hologram is computed. Each light / hologram channel propagates from the hologram at a different angle or angular range. While these are example ways of characterizing or identifying this type of hologram, other methods may also be used. In summary, the holograms disclosed herein are characterized and identified by how the image content is distributed within the hologram-encoded light. Furthermore, to avoid any doubt, references herein to holograms configured to guide light or to divide an image at an angle into multiple hologram channels are by way of example only, and this disclosure is equally applicable to pupil expansion of any type of holographic light field or even any type of diffractive or diffracted light field.

[0116] The system can be offered in a compact and streamlined physical form. This makes it suitable for a wide range of practical applications, including those with limited space and high asset value. For example, it can be implemented in a head-up display (HUD), such as a vehicle or automotive HUD.

[0117] According to this disclosure, a pupil expander is provided for diffracted light, which may include a diverging beam of light. The diffracted light field can be defined by a "light cone". Therefore, the magnitude of the diffracted light field (as defined in a two-dimensional plane) increases with the propagation distance from the corresponding diffractive structure (i.e., the display device). It can be said that the pupil expander replicates a hologram or forms at least one copy of a hologram to convey light transmitted to the observer that is spatially modulated according to the hologram.

[0118] In some embodiments, two one-dimensional waveguide pupil expanders are provided, each arranged to effectively increase the size of the system's exit pupil by forming multiple copies or replicas of the exit pupil (or the light from the exit pupil) of the spatial light modulator. The exit pupil can be understood as the physical region where the system outputs light. Alternatively, each waveguide pupil expander can be arranged to expand the size of the system's exit pupil. Also, each waveguide pupil expander can be arranged to expand / increase the size of the eyebox in which an observer's eye can reside, in order to see / receive the light output by the system.

[0119] Optical Channel

[0120] Holograms formed according to some embodiments angularly divide image content to provide multiple holographic channels, which may have a cross-sectional shape defined by the aperture of an optical system. The hologram is calculated to provide this guidance of the diffracted light field. In some embodiments, as described above, this is achieved during hologram calculation by taking into account the aperture (virtual or real) of the optical system.

[0121] Figure 2 and 3 An example of this type of hologram is shown, which can be used in conjunction with the pupil expander disclosed herein. However, this example should not be considered as a limitation of this disclosure.

[0122] Figure 2 An image 252 for projection is shown, comprising eight image regions / components V1 to V8. This is for illustrative purposes only. Figure 2 Eight image components are shown, and image 252 can be divided into any number of components. Figure 2 Also shown is an encoded light pattern 254 (i.e., a hologram) that can reconstruct image 252—for example, when transformed by a lens of a suitable observation system. The encoded light pattern 454 includes first to eighth sub-holograms or components H1 to H8, corresponding to first to eighth image components / regions V1 to V8. Figure 2 This further demonstrates how holograms decompose image content through angles. Therefore, a characteristic of holograms lies in their ability to guide light. This is in Figure 3 As shown in the example. Specifically, the hologram in this example guides light into multiple discrete regions. In the example shown, the discrete regions are disks, but other shapes can also be envisioned. After propagation through the waveguide, the optimal size and shape of the disk can be related to the size and shape of the aperture of the optical system (e.g., the entrance pupil of an observation system).

[0123] Figure 4 System 400 is shown, including displays such as Figure 2 and 3 The display device for the calculated hologram.

[0124] System 400 includes a display device comprising an LCOS 402 in this arrangement. The LCOS 402 is arranged to display a modulation pattern (or “diffraction pattern”) including a hologram and to project holographically encoded light onto an eye 405, which includes a pupil acting as an aperture 404, a lens 409, and a retina (not shown) acting as a viewing plane. A light source (not shown) is arranged to illuminate the LCOS 402. The lens 409 of the eye 405 performs a hologram-to-image conversion. The light source can be of any suitable type. For example, it can include a laser source.

[0125] The observation system 400 also includes a waveguide 408 located between the LCOS 402 and the eye 405. The presence of the waveguide 408 allows all angular content from the LCOS 402 to be received by the eye, even at the relatively large projection distance shown. This is because the waveguide 408 acts as a pupil expander in a well-known manner, and therefore will only be briefly described here.

[0126] in short, Figure 4 The waveguide 408 shown comprises a generally elongated structure. In this example, waveguide 408 comprises an optical plate of refractive material, but other types of waveguides are also well known and can be used. Waveguide 408 is positioned to intersect, for example, at an oblique angle, a light cone (i.e., a diffracted light field) projected from LCOS 402. In this example, the dimensions, position, and orientation of waveguide 408 are configured to ensure that light from each of the eight beams within the light cone enters waveguide 408. Light from the light cone enters waveguide 408 via a first planar surface (closest to LCOS 402) and is guided at least partially along the length of waveguide 408 before being emitted via a second planar surface (closest to the eye) substantially opposite the first surface. It is readily understood that the second planar surface is partially reflective and partially transmissive. In other words, as each ray of light propagates within waveguide 408 from the first planar surface and strikes the second planar surface, some light will be transmitted out of waveguide 408, and some light will be reflected back to the first planar surface by the second planar surface. The first planar surface is reflective, such that all light striking it from within waveguide 408 will be reflected back to the second planar surface. Thus, some light can be simply refracted between the two planar surfaces of waveguide 408 before being transmitted, while other light can be reflected and thus undergo one or more reflections (or "bouncing") between the planar surfaces of waveguide 408 before being transmitted.

[0127] Figure 4 A total of nine "bounce" points B0 to B8 are shown along the length of waveguide 408. Although... Figure 2 As shown, light associated with all points in the image (V1-V8) is transmitted out of the waveguide at each "bounce" from the second planar surface of waveguide 408, but only light from one angular portion of the image (e.g., light from one of V1 to V8) has a trajectory that allows it to reach the eye 405 from each corresponding "bounce" point B0 to B8. Furthermore, light from different angular portions (V1 to V8) of the image reaches the eye 405 from each corresponding "bounce" point. Therefore, in Figure 4 In the example, each angular channel of the encoded light reaches the eye only once from waveguide 408.

[0128] Waveguide 408 forms multiple replicas of the hologram at corresponding "bounce" points B1 to B8 along its length, corresponding to the direction of pupil expansion. As shown in Figure 5, the multiple replicas can be linearly pushed back to their respective replicas or virtual display devices 402'. This process corresponds to the step of "unfolding" the optical path within the waveguide, such that the light from the replicas is pushed back to the "virtual surface" without internal reflection within the waveguide. Therefore, the light from the expanded exit pupil can be considered to originate from the virtual surface (also referred to here as the "expanded modulator") comprising display device 402 and the replicated display device 402'.

[0129] Although virtual images have been discussed in general terms here, which require the eye to convert received modulated light to form a perceived image, the methods and apparatus described here can be applied to real images.

[0130] Two-dimensional pupil expansion

[0131] Although Figure 4 The arrangement shown includes a single waveguide providing pupil extension in one dimension, but pupil extension can be provided in more than one dimension, such as in two dimensions. Furthermore, although Figure 4 The examples in the document use holograms that have been calculated to create optical channels, each corresponding to a different part of the image, but this disclosure and the system described below are not limited to this type of hologram.

[0132] Figure 5A A perspective view of system 500 is shown, which includes two replicators 504 and 506 arranged to extend beam 502 in two dimensions.

[0133] exist Figure 5A In system 500, the first replicator 504 includes a first pair of surfaces stacked parallel to each other, arranged in a manner similar to Figure 4 The waveguide 408 provides replication or pupil expansion. The first pair of surfaces are similar in size and shape to each other (in some cases identical) and are substantially elongated in one direction. The collimated beam 502 is guided to the input on the first replicator 504. Due to the internal reflection process between the two surfaces, and from one of the surfaces (the upper surface, such as...) Figure 5A As shown, the light from each of the plurality of output points on the beam 502 is partially transmitted, which will be familiar to a skilled reader, and the light from beam 502 is replicated along the length of the first replicator 504 in a first direction. Thus, the first plurality of replica beams 508 are emitted from the first replicator 504 toward the second replicator 506.

[0134] The second replicator 506 includes a second pair of surfaces stacked parallel to each other, arranged to receive each collimated beam of the first plurality of beams 508, and further arranged to provide replication or pupil expansion by extending each of these beams in a second direction substantially orthogonal to the first direction. The first pair of surfaces are similar in size and shape to each other (in some cases identical) and are substantially rectangular. The second replicator is made rectangular so that it has a length along the first direction to receive the first plurality of beams 508, and a length along the second orthogonal direction to provide replication in that second direction. Due to the internal reflection process between the two surfaces, and from one of the surfaces (such as... Figure 5A Partial transmission of light from each of the plurality of output points on the upper surface shown, and the light from each beam within the first plurality of beams 508 being replicated in the second direction. Therefore, a second plurality of beams 510 is emitted from the second replicator 506, wherein the second plurality of beams 510 comprises a copy of the input beam 502 along each of the first and second directions. Thus, the second plurality of beams 510 can be considered as a two-dimensional grid or array comprising the replicated beams.

[0135] Therefore, it can be said that Figure 5A The first and second replicators 504, 505 are combined to provide a two-dimensional replicator (or "two-dimensional pupil expander"). Thus, the replicated beam 510 can be emitted along the optical path to the expanded eye box of a display system, such as a head-up display.

[0136] exist Figure 5A In this system, the first replicator 504 is a waveguide comprising a pair of elongated, straight, reflective surfaces stacked parallel to each other; similarly, the second replicator 504 is a waveguide comprising a pair of rectangular, stacked, parallel to each other. In other systems, the first replicator may be a solid, elongated, straight waveguide, and the second replicator may be a solid planar rectangular waveguide, wherein each waveguide comprises an optically transparent solid material, such as glass. In this case, the pair of parallel reflective surfaces are formed by a pair of opposing main sidewalls, optionally including respective reflective and reflect-transmittance surface coatings, which will be familiar to the skilled reader.

[0137] Figure 5B A perspective view of system 500 is shown, which includes two replicators 520 and 540 arranged to replicate beam 522 in two-dimensional space, wherein the first replicator is a solid elongated waveguide 520 and the second replicator is a solid planar waveguide 540.

[0138] exist Figure 5BIn the system, the first replicator / waveguide 520 is arranged such that its pair of elongated parallel reflective surfaces 524a, 524b are perpendicular to the plane of the second replicator / waveguide 540. Therefore, the system includes an optical coupler arranged to couple light from the output port of the first replicator 520 to the input port of the second replicator 540. In the illustrated arrangement, the optical coupler is a plane / folding mirror 530, which is arranged to fold or redirect the optical path of light to achieve the desired optical coupling from the first replicator to the second replicator. Figure 5B As shown, mirror 530 is arranged to receive light from the output port / reflective-transmitting surface 524a of the first replicator / waveguide 520, comprising a one-dimensional array of replicas extending in the first dimension. Mirror 530 is tilted to redirect the received light at an angle onto the optical path of the input port in the (total) reflective surface of the second replicator 540, providing waveguide and replica formation along its length in the second dimension. It should be understood that mirror 530 is one example of an optical element capable of redirecting light in the manner shown, and one or more other elements may alternatively be used to perform this task.

[0139] In the arrangement shown, the (partial) reflective-transmitting surface 524a of the first replicator 520 is adjacent to the input port of the first replicator / waveguide 520, which receives the input beam 522 at an angle to provide a waveguide and copy formation along its length in the first dimension. Therefore, the input port of the first replicator / waveguide 520 is located at its input end, on the same surface as the reflective-transmitting surface 524a. The skilled reader will understand that the input port of the first replicator / waveguide 520 can be in any other suitable location.

[0140] therefore, Figure 5B The arrangement allows the first replicator 520 and mirror 530 to be provided as part of a first relatively thin layer in the first and third dimensional planes (shown as the xz plane). Specifically, the size or "height" of the first planar layer (in which the first replicator 520 is located) in the second dimension (shown as the y dimension) is reduced. Mirror 530 is configured to guide light from the first layer / plane (i.e., the "first planar layer") where the first replicator 520 is located and to the second layer / plane (i.e., the "second planar layer") where the second replicator 540 is located, which is located above and substantially parallel to the first layer / plane. Therefore, the overall size or "height" of the system—including in the first and third dimensions (shown as the xz plane) and in the second dimension (shown as the y dimension)—of the first and second replicators 520, 540 and mirror 530 in the stacked first and second planar layers, is compact. The skilled reader will understand that the components used to implement this disclosure... Figure 5B Many variations in the arrangement are possible and anticipated.

[0141] An image projector can be arranged to project a diverging or diffracted light field. In some embodiments, the light field is encoded with a hologram. In some embodiments, the diffracted light field comprises a diverging beam of light. In some embodiments, the image formed by the diffracted light field is a virtual image.

[0142] In some embodiments, the first pair of parallel / complementary surfaces are elongated or slender surfaces, relatively long along a first dimension and relatively short along a second dimension, for example, relatively short along each of two other dimensions, each dimension being substantially orthogonal to each of the corresponding other dimensions. The process of light reflection / transmission between / from the first pair of parallel surfaces is arranged such that light propagates within the first waveguide pupil expander, with the general direction of light propagation being the direction of the relatively longer portion of the first waveguide pupil expander (i.e., its "elongated" direction).

[0143] This paper discloses a system that uses diffracted light to form an image and provides eyebox sizes and fields of view suitable for real-world applications—such as head-up displays in the automotive industry. Diffracted light is light used to holographically reconstruct an image from a diffracted structure—such as a hologram like a Fourier or Fresnel hologram. The use of diffraction and diffracted structures requires high-density display devices with very small pixels (e.g., 1 micrometer)—which in practice means small display devices (e.g., 1 cm). The inventors have solved the problem of how to provide a diffracted light field for 2D pupil expansion, for example, by including diffracted light comprising divergent (non-collimated) beams.

[0144] In some embodiments, the display system includes display devices—such as pixelated display devices, such as spatial light modulators (SLMs) or liquid crystal on silicon (LCoS) SLMs—arranged to provide or form diffracted or diverging light. In these respects, the aperture of the spatial light modulator (SLM) is the limiting aperture of the system. That is, the aperture of the spatial light modulator—more specifically, the size of the region defining the light-modulating pixel array contained within the SLM—determines the size (e.g., spatial extent) of the light beam that can exit the system. According to this disclosure, it is stated that by using at least one pupil expander, the exit pupil of the system is expanded to reflect that the exit pupil of the system (which is limited by the small display device having pixel sizes for light diffraction) becomes larger in spatial extension.

[0145] A diffracted or diverging light field can be described as having a "light field size," which is defined in a direction substantially orthogonal to the direction of light field propagation. Because light is diffracted / divered, the light field size increases with the propagation distance.

[0146] In some embodiments, the diffracted light field is spatially modulated according to the hologram. In other words, in these aspects, the diffracted light field includes a “holographic light field.” The hologram can be displayed on a pixelated display device. The hologram can be a computer-generated hologram (CGH). It can be a Fourier hologram, a Fresnel hologram, a point cloud hologram, or any other suitable type of hologram. Optionally, the hologram can be computed to form channels of holographic light, each channel corresponding to a different portion of the image that an observer wants to observe (or perceive, if it is a virtual image). The pixelated display device can be configured to display multiple different holograms consecutively or sequentially. Each aspect and embodiment disclosed herein can be applied to the display of multiple holograms.

[0147] The output port of the first waveguide pupil expander can be coupled to the input port of the second waveguide pupil expander. The second waveguide pupil expander can be arranged to guide the diffracted light field (including some, preferably most, preferably all copies of the light field output by the first waveguide pupil expander) from its input port to the corresponding output port through internal reflection between the third pair of parallel surfaces of the second waveguide pupil expander.

[0148] A first waveguide pupil expander can be arranged to provide pupil expansion or replication in a first direction, while a second waveguide pupil expander can be arranged to provide pupil expansion or replication in a different second direction. The second direction can be substantially orthogonal to the first direction. The second waveguide pupil expander can be arranged to maintain the pupil expansion already provided by the first waveguide pupil expander in the first direction, and expand (or replicate) some, preferably most, preferably all, copies it receives from the first waveguide pupil expander in the different second directions. The second waveguide pupil expander can be arranged to receive the optical field directly or indirectly from the first waveguide pupil expander. One or more other elements can be provided along the propagation path of the optical field between the first and second waveguide pupil expanders.

[0149] The first waveguide pupil expander may be substantially elongated, and the second waveguide pupil expander may be substantially planar. The elongated shape of the first waveguide pupil expander may be defined by its length along a first dimension. The planar or rectangular shape of the second waveguide pupil expander may be defined by its length along the first dimension and its width or span along a second dimension substantially orthogonal to the first dimension. The dimension or length of the first waveguide pupil expander along its first dimension may correspond respectively to the length or width of the second waveguide pupil expander along its first or second dimension. The first surface of a pair of parallel surfaces of the second waveguide pupil expander, including its input port, may be shaped, sized, and / or positioned to correspond to the region defined by the output port on the first surface of the pair of parallel surfaces on the first waveguide pupil expander, such that the second waveguide pupil expander is arranged to receive each copy output by the first waveguide pupil expander.

[0150] The first and second waveguide pupil expanders can jointly provide pupil expansion in a first direction and a second direction perpendicular to the first direction. Optionally, the planes containing the first and second directions are substantially parallel to the plane of the second waveguide pupil expander. In other words, the first and second dimensions defining the length and width of the second waveguide pupil expander, respectively, can be parallel to the first and second directions (or parallel to the second and first directions, respectively), wherein the waveguide pupil expander provides pupil expansion. The combination of the first and second waveguide pupil expanders is generally referred to as a "pupil expander".

[0151] In essence, the expansion / replication provided by the first and second waveguide expanders has the effect of expanding the exit pupil of the display system in each of two directions. The area defined by the expanded exit pupil can further define the expanded eyebox region from which the observer can receive light from the input diffracted or diverging light field. The eyebox region can be said to lie on or define the observation plane.

[0152] The two directions of pupil expansion can be coplanar or parallel to the first and second directions of replication / expansion provided by the first and second waveguide pupil expanders. Alternatively, in arrangements that include other elements such as optical combiners, e.g., a vehicle's windshield, the pupil can be considered as the pupil of that other element, such as the windshield. In such an arrangement, the pupil can be non-coplanar and non-parallel to the first and second directions of replication / expansion provided by the first and second waveguide pupil expanders. For example, the pupil can be substantially perpendicular to the first and second directions of replication / expansion provided by the first and second waveguide pupil expanders.

[0153] The observation plane and / or eyebox region may not be coplanar or parallel to the first and second directions in which the first and second waveguide pupil expanders provide replication / expansion. For example, the observation plane may be substantially perpendicular to the first and second directions in which the first and second waveguide pupil expanders provide replication / expansion.

[0154] In order to provide suitable emission conditions to achieve internal reflection within the first and second waveguide pupil expanders, the elongated dimension of the first waveguide pupil expander may be tilted relative to the first and second dimensions of the second waveguide pupil expander.

[0155] Combiner shape compensation

[0156] The advantage of projecting a hologram onto an eyebox is that optical compensation can be encoded in the hologram (see, for example, European Patent 2936252, incorporated herein by reference). This disclosure is compatible with holograms that compensate for the complex curvature of an optical combiner used as part of a projection system. In some embodiments, the optical combiner is the windshield of a vehicle. The full details of this method are provided in European Patent 2936252 and are not repeated here, as the detailed features of these systems and methods are not essential to the novel teachings of this disclosure and are merely examples of configurations that benefit from the teachings of this disclosure.

[0157] Control device

[0158] This disclosure is also compatible with optical configurations that include control devices (e.g., optical shutter devices) to control the transmission of light from the optical channel hologram to the observer. The holographic projector may also include control devices arranged to control the transmission of the angular channel to the eyebox position. UK Patent Application 2108456.1, filed June 14, 2021 and incorporated herein by reference, discloses at least one waveguide pupil expander and control device. The reader will understand from at least this prior disclosure that the optical configuration of the control device is substantially based on the user's eyebox position and is compatible with any hologram calculation method for implementing the optical channel described herein. The control device can be described as an optical shutter or aperture device. The optical shutter device may include a 1D array of apertures or windows, wherein each aperture or window can be independently switched between transparent and opaque states to control the transmission of the hologram optical channel and its replica to the eyebox. Each aperture or window may include multiple liquid crystal cells or pixels.

[0159] Image Formation

[0160] Figure 6 This is a cross-sectional schematic diagram of the optical components of the optical system 600, which is not based on this disclosure. The optical axis of the optical system 600 is formed by... Figure 6 The dashed line 602 is shown in the diagram. The optical system 600 includes a display device 604, which in this example is a liquid crystal on silicon spatial light modulator. The display device 604 is arranged to display a hologram of an image. Downstream of the display device 604 is an optical repeater 606. The optical repeater 606 includes a first lens 608 and a second lens 610. The optical system 600 also includes a waveguide 611 downstream of the second lens 610 of the optical repeater 606. The waveguide 611 includes a pair of opposing surfaces 622, 624, which, according to the previously described example, are arranged to provide a waveguide for light therebetween.

[0161] The first lens 608 of the optical repeater 606 includes a front focal plane 612 and a rear focal plane 614. The front focal plane 612 is upstream of the first lens 608, and the rear focal plane 614 is downstream of the first lens 608. The second lens 608 of the optical repeater 606 includes a front focal plane 616 and a rear focal plane 618. The front focal plane 616 is upstream of the second lens 610, and the rear focal plane 618 is downstream of the second lens 610. The normals of the front and rear focal planes of each of the first and second lenses 608 and 610 are parallel to the optical axis 602, and the distance from each of the front and rear focal planes to the corresponding first or second lens is equal to the focal length f of the corresponding lens. In this example, the display device 604 is substantially located at the front focal plane 612 of the first lens 608. In this example, the front focal plane 616 of the second lens 610 is substantially coplanar with the rear focal plane 614 of the first lens 608. In this example, waveguide 611 is arranged such that the back focal plane 618 of the second lens 610 is located between the first and second surfaces of waveguides 622 and 624. Figure 6 In the example shown, the focal length f of the first and second lenses 608 and 610 is the same. Thus, the optical repeater forms a 4f system (i.e., the length of the optical repeater is four times the focal length of the first and second lenses 608 and 610). However, in other embodiments, the focal length of the first lens 608 may be different from the focal length of the second lens 610. In this case, the optical repeater can form a magnifying (or reducing) telescope.

[0162] The optical system 600 also includes a coherent light source, such as a laser. The coherent light source is not included in... Figure 6 As shown in the figure. In the operation of the optical system 600, coherent light is arranged to illuminate the display device 604. Therefore, the light can be spatially modulated according to a hologram of an image displayed on the display device. The spatially modulated light can be received by a first lens 608 and relayed to a second lens 610. Between the first and second lenses 608, 610, a holographic reconstruction 626 of the image is formed on the back focal plane 612 of the first lens 608. The second lens 610 relays the spatially modulated light to a waveguide 611. As described with respect to the previous figures, the waveguide 611 replicates the light received from the display device to form multiple copies or replicas of the display device 604, such that each copy includes light spatially modulated according to a hologram on the display device. In an embodiment, the optical system also includes a second waveguide (not shown) to provide waveguide and replication in a second direction, such that a two-dimensional array of copies is output from the second waveguide. The spatially modulated light is relayed from the output of the second waveguide to the eyebox / viewing plane (extended due to the replication achieved by the waveguide). When an observation system (e.g., a user's eye) is placed at an eye box / observation plane, the observation system receives spatially modulated light that forms a virtual image of a hologram image displayed on a display device at a virtual image distance, which is encoded in the hologram.

[0163] The inventors have discovered that the optical system 600 can provide a good virtual image of the hologram when the observation system is located in the observation plane / eyebox. However, the inventors have also discovered that artifacts may form / appear at the observation plane (i.e., the plane comprising multiple copies). Artifacts may include dark bands caused by the display device being illuminated by light of non-uniform intensity, and / or may be caused by physical characteristics of the display device (e.g., scattering of features of the display device). In any case, artifacts can be replicated by a waveguide to form a repeating pattern of artifacts at the observation plane. For example, this might appear as a grid of dark bands. Therefore, while the virtual image reconstructed from the image / hologram may itself be of high quality, the view of the image virtual image at the observation plane may appear obstructed by the repeating pattern of artifacts. The observation system may have to effectively “see through” the repeating pattern of artifacts to observe the virtual image.

[0164] Separation of holographic image and holographic reconstructed image

[0165] Figure 7 This is a cross-sectional schematic diagram of the optical components of the first optical system 700 according to the present disclosure, which is arranged such that the image of the hologram / display device is far from the virtual image of the holographic reconstruction of the hologram, thereby reducing or eliminating the occurrence of the aforementioned artifacts.

[0166] Optical system 700 includes: Figure 7 The dashed line 702 in the diagram represents the optical axis 702. The optical system 700 includes a display device 704, which in this example is a liquid crystal on silicon spatial light modulator. The display device 704 is arranged to display a hologram of an image. Downstream of the display device 704 is an optical repeater 706. The optical repeater 706 includes a first lens 708 and a second lens 710.

[0167] The display device 704 and optical repeater 706 of optical system 700 are very similar to the display device 604 and optical repeater 706 of optical system 600. For example, the first lens 708 of optical repeater 706 includes a front focal plane 712 and a rear focal plane 714. The front focal plane 712 is upstream of the first lens 708, and the rear focal plane 714 is downstream of the first lens 708. The second lens 708 of optical repeater 706 includes a front focal plane 716 and a rear focal plane 718. The front focal plane 716 is upstream of the second lens 710, and the rear focal plane 718 is downstream of the second lens 710. The normals of the front and rear focal planes of each of the first and second lenses 708, 710 are parallel to the optical axis 702, and the distance from each of the front and rear focal planes to the corresponding first or second lens is equal to the focal length f of the corresponding lens. In this example, the display device 704 is substantially located at the front focal plane 712 of the first lens 708. In this example, the front focal plane 716 of the second lens 710 is substantially coplanar with the rear focal plane 714 of the first lens 708. Figure 7 In the example shown, the focal length f of the first and second lenses 708 and 710 is the same. Thus, the optical repeater forms a 4f system (i.e., the length of the optical repeater is four times the focal length f of the first and second lenses 708 and 710). However, in other embodiments, the focal length of the first lens 708 may be different from the focal length of the second lens 710. In this case, the optical repeater may be a magnifying (or reducing) telescope.

[0168] Unlike optical system 600, optical system 700 also includes an optical component 750 located between the second lens 710 and the waveguide 711. In this example, the optical component 750 is a (third) lens. In this example, the third lens 750 is a Fourier lens. The front focal plane 754 of the third lens 750 is upstream of the third lens 750 and is substantially coplanar with the rear focal plane 718 of the second lens 710. The rear focal plane 756 of the third lens 750 is located between the first and second surfaces 722, 724 of the waveguide 711.

[0169] In this example, the focal length f of the third lens 750 is the same as the focal length f of the first and second lenses 708, 710. Thus, the optical repeater 706 and the third lens 750 together define a 6f system (where the interval between the front focal plane 712 of the first lens 708 and the rear focal plane 756 of the third lens 750 is equal to six times the focal length of the first / second or third lens 708, 710, 752). However, in other examples, the focal length of the third lens 750 may differ from the focal length of the first lens 708 and / or the second lens 710.

[0170] Therefore, the key difference between the optical system 600 and the optical system 700 according to this disclosure is that the optical system 700 according to this disclosure includes an additional lens 750 between the display device 704 and the waveguide 711.

[0171] Another important difference between optical system 600 and optical system 700 is that, in optical system 700, the hologram displayed on display device 704 is arranged such that when display device 704 is illuminated by coherent light from a coherent light source such as a laser, a holographic reconstruction 756 of the hologram image is formed downstream of the display device. This holographic reconstruction 756 is formed without using a physical lens between display device 704 and holographic reconstruction 756. Instead, the hologram is calculated to form holographic reconstruction 756 at that location. Specifically, the hologram is calculated / arranged such that holographic reconstruction 756 is formed such that the distance between holographic reconstruction 756 and first lens 708 is less than the focal length f of first lens 708, while the distance between display device 704 and first lens 708 is equal to the focal length f of first lens 708.

[0172] An optical repeater 706 is arranged to relay a hologram on a display device to form a relay hologram 760 downstream of the second lens 710, and a relay hologram reconstruction 758 downstream of the relay hologram 760. The relay hologram 760 corresponds to a display device (including a display hologram of an image). The relay hologram reconstruction 758 corresponds to the hologram reconstruction 756.

[0173] In this example, the relay holographic reconstruction 758 is configured such that the distance between the relay holographic reconstruction 758 and the third lens 750 is less than the focal length of the third lens 750, while the distance between the relay hologram 760 and the third lens 750 is equal to the focal length of the third lens 750. By positioning the relay hologram 760 and the relay holographic reconstruction 758 relative to the third lens 750 in this way, the third lens 750 can form images of the relay hologram and the relay holographic reconstruction that are far apart from each other. This will refer to... Figure 8 To provide a more detailed explanation.

[0174] Figure 8 It shows Figure 7 A cross-sectional schematic diagram of the third lens 750 and waveguide 711 (as well as relay hologram 760 and relay holographic reconstruction 758). These components are shown separately from other optical components of the optical system 700 (such as display device 704 and optical repeater 706). Figure 8 This is a schematic ray diagram showing the rays from relay hologram 760 and relay holographic reconstruction 758.

[0175] Those skilled in the art will understand that when the object to be imaged is located at the focal length of the lens, the (convex) lens (e.g., the third lens 750) will form a virtual image of the object at infinity. As described above, a relay hologram 760 is formed at the focal length f of the third lens 750 (specifically, at the front focal plane 752 of the third lens 750) (via the optical repeater 706). Therefore, the third lens 750 is arranged to form a virtual image of the relay hologram 760 at infinity. The virtual image at infinity is upstream of the display device 704 / third lens 750. The formation of this virtual image is represented by rays extending parallel from the relay hologram 760 to the third lens 750. Figure 8 In the image, the light rays are represented by dashed lines comprising alternating dotted and dashed lines.

[0176] Those skilled in the art will also understand that when an object to be imaged is positioned such that the distance between the object and the lens is less than the focal length of the lens, the (convex) lens (e.g., the third lens 750) will form a virtual image of the object at a finite image distance upstream of the lens. As described above, a relay holographic reconstruction 758 is formed (via the optical repeater 706) such that the distance between the relay holographic reconstruction 758 and the third lens 750 is less than the focal length of the third lens 750. In other words, the relay holographic reconstruction 758 is located between the front focal plane 752 of the third lens 750 and the third lens 750 itself. By forming the relay holographic reconstruction 758 here, the third lens 750 is arranged upstream of the third lens 750 and forms a virtual image 800 of the relay holographic reconstruction 758 at a finite image distance. The formation of this virtual image 800 is represented by rays from the relay holographic reconstruction 758 to the third lens 750 and then converging upstream of the third lens 750. Figure 8 The area is shown only by the dashed line containing the point.

[0177] Both the virtual image 760 of the relay hologram and the virtual image 800 of the relay holographic reconstruction 758 are upstream of the third lens 750. However, the virtual image distance of the virtual image of the relay hologram 760 is at infinity, while the virtual image distance of the virtual image 800 of the relay holographic reconstruction 758 is finite. Therefore, the two virtual images are far apart from each other (in fact, the interval between the two virtual images is practically infinite). Artifacts (as described above) can be a feature in the virtual image of the relay hologram 760. The appearance of artifacts may be absent or inconspicuous in the virtual image 800 of the relay holographic reconstruction 758. The inventors have found that by separating the two virtual images as described above, the salience of artifacts in the field of view of the observation system can be significantly reduced or even eliminated. Not wishing to be bound by theory, it is believed that this is because the virtual image of the relay hologram 760 (including artifacts) is far from the virtual image of the relay holographic reconstruction 758, and in this case, is projected exactly at infinity, beyond the virtual image of the relay holographic reconstruction 758. Therefore, the observation system does not need to "see through" the virtual image of the relay hologram 760 to observe the virtual image of the relay holographic reconstruction 758.

[0178] Figure 9 This is a cross-sectional schematic diagram of the optical components of the second optical system 900 according to the present disclosure, which is arranged such that the image of the hologram / display device is far from the virtual image of the holographic reconstruction, thereby reducing or eliminating the aforementioned artifacts. The second optical system 900 is similar to the first optical system 700 in that the second optical system 900 is arranged such that the relay hologram and the relay holographic reconstruction are formed at positions relative to the third lens, such that their images are far apart from each other. However, in the second optical system 900, the image of the relay hologram is a real image formed downstream of the waveguide (e.g., behind the observation system), rather than at infinity and upstream of the third lens. This will be described in more detail below.

[0179] Optical system 900 includes: Figure 9 The dashed line 902 in the diagram represents the optical axis. The optical system 900 includes a display device 904, which in this example is a liquid crystal on silicon spatial light modulator. The display device 904 is arranged to display a hologram of an image. Downstream of the display device 904 is an optical repeater 906. The optical repeater 906 includes a first lens 908 and a second lens 910. The optical system 900 also includes a third lens 950.

[0180] The display device 904, optical repeater 906, and third lens 950 of optical system 900 are very similar to those of the display device 704, optical repeater 706, and third lens of first optical system 700. For example, the first lens 908 of optical repeater 906 includes a front focal plane 912 and a rear focal plane 914. The front focal plane 912 is upstream of the first lens 908, and the rear focal plane 914 is downstream of the first lens 908. The second lens 910 of optical repeater 906 includes a front focal plane 916 and a rear focal plane 918. The front focal plane 916 is upstream of the second lens 910, and the rear focal plane 918 is downstream of the second lens 910. The normals of the front and rear focal planes of each of the first and second lenses 908 and 910 are parallel to the optical axis 902, and the distance from each of the front and rear focal planes to the corresponding first or second lens is equal to the focal length f of the corresponding lens. In this example, the front focal plane 916 of the second lens 910 is substantially coplanar with the rear focal plane 914 of the first lens 908. Figure 9 In the example shown, the focal length f of the first and second lenses 908 and 910 is the same. Thus, the optical repeater forms a 4f system (i.e., the length of the optical repeater is four times the focal length f of the first and second lenses 908 and 910). However, in other embodiments, the focal length of the first lens 908 may be different from the focal length of the second lens 910. In this case, the optical repeater can form a magnifying (or reducing) telescope. As in the first optical system 700, the third lens 950 is a Fourier lens. The front focal plane 954 of the third lens 950 is upstream of the third lens and is substantially coplanar with the rear focal plane 918 of the second lens 910. The rear focal plane 956 of the third lens 950 is located between the first and second surfaces of the waveguide 911. In this example, the focal length f of the third lens 950 is the same as the focal length of the first and second lenses 908 and 910. Thus, the optical repeater 906 and the third lens 950 together define a 6f system (where the distance between the front focal plane 912 of the first lens 908 and the rear focal plane 956 of the third lens 950 is equal to six times the focal length of the first / second or third lenses 908, 910, 952). However, in other examples, the focal length of the third lens 950 may differ from the focal length of the first lens 908 and / or the second lens 910.

[0181] The key difference between the first optical system 700 and the second optical system 900 is that, in the second optical system 900, the display device 904 is not substantially located at the front focal plane 912 of the first lens 908 (as in the first optical system 700). Instead, the distance between the display device 904 and the first lens 908 is greater than the focal length f of the first lens 908. However, similar to the first optical system 700, in the second optical system 900, the hologram displayed on the display device 904 is arranged such that a holographic reconstruction 956 of the hologram image is formed downstream of the display device, such that the distance between the holographic reconstruction 956 and the first lens 908 is less than the focal length f of the first lens 908. Thus, the distance between the display device 904 and the holographic reconstruction 956 in the second optical system 900 is greater than the distance between the display device 704 and the holographic reconstruction 956 in the second optical system 700.

[0182] An optical repeater 906 is arranged to relay a hologram on a display device to form a relay hologram 960 downstream of the second lens 910, and a relay hologram reconstruction 958 downstream of the relay hologram 960. The relay hologram 960 corresponds to a display device (including a display hologram of an image). The relay hologram reconstruction 958 corresponds to hologram reconstruction 956.

[0183] In this example, the relay holographic reconstruction 958 is configured such that the distance between the relay holographic reconstruction 958 and the third lens 950 is less than the focal length of the third lens 950, while the distance between the relay hologram 960 and the third lens 950 is greater than the focal length of the third lens 950. By positioning the relay hologram 960 and the relay holographic reconstruction 986 relative to the third lens 950 in this way, the third lens 950 can form images of the relay hologram and the relay holographic reconstruction that are far apart from each other. This will refer to... Figure 10 To provide a more detailed explanation.

[0184] Figure 10 It shows Figure 9 A cross-sectional schematic diagram of the third lens 950 and waveguide 911 (as well as relay hologram 960 and relay holographic reconstruction 958). These components are shown separately from other optical components of the optical system 900 (such as display device 904 and optical repeater 906). Figure 10 This is a schematic ray diagram showing the rays from relay hologram 960 and relay holographic reconstruction 958.

[0185] Those skilled in the art will understand that when the object to be imaged is located outside the focal length of the lens, the (convex) lens (e.g., the third lens 958) will form a real image of the object. This real image will be formed at a finite image distance downstream of the lens. As described above, the relay hologram 960 is formed outside the focal length f of the third lens 950 (via the optical repeater 906). Specifically, the distance between the relay hologram 960 and the third lens 950 is greater than the focal length f of the third lens. Therefore, the third lens 950 is arranged to form a real image 1002 of the relay hologram 960 downstream of the third lens 950. The formation of this real image 1002 is represented by rays that travel from the relay hologram 960 to the third lens 950 and then converge at a point downstream of the third lens 950 (and waveguide 911). Figure 10 In the image, the light rays are represented by dashed lines comprising alternating dotted and dashed lines.

[0186] In the first and second optical systems 700 and 900, a relay holographic reconstruction is formed (via an optical relay) such that the distance between the relay holographic reconstruction and the third lens is less than the focal plane of the third lens. Therefore, as in the first optical system 700, in the second optical system 900, the third lens 950 is arranged upstream of the third lens 950 and forms a virtual image 1000 of the relay holographic reconstruction 958 at a finite image distance. The formation of this virtual image 1000 is represented by rays from the relay holographic reconstruction 958 to the third lens 950 and then converging at a point upstream of the third lens 950. These rays... Figure 10 The area is shown only by the dashed line containing the point.

[0187] Therefore, the third lens 950 (and the more general optical system 900) is arranged to form a virtual image of the relay holographic reconstruction 958 upstream of the third lens and a real image of the relay hologram 960 downstream of the waveguide 911. In this way, the two images (virtual and real) are far apart from each other.

[0188] In the example, the real image of relay hologram 960 is downstream of the observation window / eyebox (not shown in the figure, but will be located between waveguide 911 and the real image of relay hologram 960). Therefore, as described above, since the artifact is believed to be visible / obvious in the image of relay hologram 960, but not in relay holographic reconstruction 958, the salience of the artifact in the field of view of the observation system can be significantly reduced or even eliminated. In particular, the image of relay holographic reconstruction 958 is in front of the observation system, and relay hologram 960 is behind the observation system, so that the observation system does not need to "see through" the image of the relay hologram (including the artifact) when observing the virtual image of holographic reconstruction 958.

[0189] Each of the first and second optical systems 700, 900 described above (according to this disclosure) includes an optical repeater 702, 902. In each example, the optical repeater forms a relay hologram 760, 960 and a relay holographic reconstruction 758, 958 of the holographic image. A third lens 750, 950 in each example then forms the images of the relay hologram and the relay holographic reconstruction. Some examples according to this disclosure do not include an optical repeater. These examples include a (single) lens that forms an image of the hologram / display device itself and the holographic reconstruction itself, rather than a relay version of the hologram and the holographic reconstruction. However, the principle is essentially the same as described above, because the hologram / display device and the holographic reconstruction are positioned relative to the (single) lens, such that the image of the hologram / display device is far removed from the image of the holographic reconstruction, thereby reducing / eliminating the occurrence / effect of the aforementioned artifacts. Such examples (without an optical repeater) are combined here. Figure 11 and 12 Describe it.

[0190] Figure 11 A cross-sectional schematic diagram of a third example of optical system 1100 is shown. Optical system 1100 does not include an optical repeater.

[0191] Optical system 1100 includes: Figure 11 The dashed line 1102 in the diagram represents the optical axis. The optical system 1100 includes a display device 1104, which in this example is a liquid crystal on silicon spatial light modulator. The display device 1104 is arranged to display a hologram of an image. The optical system 1100 also includes a (single) lens 1150 downstream of the display device 1104, which in this example is a converging Fourier lens. The front focal plane 1154 of the third lens 1150 is upstream of the lens. The rear focal plane 1156 of the lens 1150 is located between the first and second surfaces of the waveguide 1111. The display device 1104 is substantially located at the front focal plane 1152 of the lens 1150, such that the distance between the display device 1104 and the lens 1150 is equal to the focal length f of the third lens 1150. The holograms displayed on display device 1104 are arranged such that a holographic reconstruction 1156 of the hologram image is formed downstream of the display device, such that the distance between the holographic reconstruction 1156 and lens 1150 is less than the focal length f of lens 950. By positioning hologram 1160 and relay holographic reconstruction 1186 relative to lens 1150 in this way, lens 1150 can form holograms and holographic reconstruction images that are far apart from each other. In particular, lens 1158 will form a virtual image of hologram 1160 upstream of display device 1104 at infinity, and a virtual image of holographic reconstruction 1158 upstream of display device 1104 at a finite image distance. Therefore, the two virtual images are far apart from each other (in fact, the interval between the two virtual images is practically infinite).

[0192] Figure 12 A cross-sectional schematic diagram of a fourth example of the optical system 1200 is shown. Similarly, the optical system 1200 does not include an optical repeater.

[0193] Optical system 1200 includes: Figure 12 The dashed line 1202 in the diagram represents the optical axis. The optical system 1200 includes a display device 1204, which in this example is a liquid crystal on silicon spatial light modulator. The display device 1204 is arranged to display a hologram of an image. The optical system 1200 also includes a (single) lens 1250 downstream of the display device 1204, which in this example is a converging Fourier lens. The front focal plane 1254 of the lens 1250 is upstream of the lens. The rear focal plane 1256 of the lens 1250 is located between the first and second surfaces of the waveguide 1211. The display device 1204 is located outside the front focal plane 1254 of the lens 1250, such that the distance between the display device 1204 and the lens 1250 is greater than the focal length f of the lens 1250. The holograms displayed on the display device 1204 are arranged such that a holographic reconstruction 1256 of the hologram image is formed downstream of the display device, such that the distance between the holographic reconstruction 1256 and the lens 1250 is less than the focal length f of the lens 1250. By positioning the hologram 1260 and the relay holographic reconstruction 1256 relative to the lens 1250 in this way, the lens 1250 can form holograms and holographic reconstruction images that are far apart from each other. Specifically, the lens 1250 will form a real image of the hologram 1160 downstream of the waveguide 1211 and a virtual image of the holographic reconstruction 1258 upstream of the display device 1204 at a finite image distance. Therefore, the two virtual images are far apart from each other (in fact, the interval between the two virtual images is practically infinite).

[0194] Additional features

[0195] The methods and processes described herein can be embodied on a computer-readable medium. The term "computer-readable medium" includes media arranged for temporary or permanent storage of data, such as random access memory (RAM), read-only memory (ROM), buffer memory, flash memory, and cache memory. The term "computer-readable medium" should also be considered to include any medium or combination of media capable of storing instructions for machine execution, such that when the instructions are executed by one or more processors, the machine performs, wholly or partially, any or all of the methods described herein.

[0196] The term "computer-readable medium" also covers cloud-based storage systems. The term "computer-readable medium" includes, but is not limited to, one or more tangible and non-transitory data repositories (e.g., data volumes) in the example forms of solid-state storage chips, optical discs, disks, or any suitable combinations thereof. In some example embodiments, instructions for execution may be transmitted by a carrier medium. Examples of such carrier media include transient media (e.g., propagation signals for transmitting instructions).

[0197] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the scope of the appended claims. This disclosure covers all modifications and variations within the scope of the appended claims and their equivalents.

Claims

1. An optical system having an observation window, wherein, The optical system includes: A display device is arranged to spatially modulate light according to a hologram displayed thereon to form a holographic wavefront, wherein the holographic wavefront forms a holographic reconstruction of an image downstream of the display device; A waveguide, arranged to receive a holographic wavefront and between a pair of reflecting surfaces, wherein one of the reflecting surfaces is partially transmissive, such that multiple copies of the holographic wavefront are emitted therefrom; and An optical component between the holographic reconstruction and the waveguide, wherein the optical component is arranged to form a holographically reconstructed virtual image upstream of the display device, and to form an image of the displayed hologram at infinity or downstream of the waveguide. The optical system also includes: An optical repeater between the display device and the waveguide includes two lenses arranged in a cooperative manner to form a relay hologram and a relay holographic reconstruction. The relay hologram is an image of a hologram displayed on the display device, and the relay holographic reconstruction is a holographically reconstructed image formed from the hologram displayed on the display device. The optical component is located between the relay holographic reconstruction and the waveguide, and the distance between the relay holographic reconstruction and the optical component is less than the focal length of the optical component, such that the virtual image of the holographic reconstruction formed by the optical component is the virtual image of the relay holographic reconstruction; and The distance between the relay hologram and the optical components is equal to the focal length of the optical components, such that the image of the hologram formed by the optical components is a virtual image formed at infinity, or The distance between the relay hologram and the optical components is greater than the focal length of the optical components, so that the image of the hologram formed by the optical components is a real image formed downstream of the waveguide.

2. The optical system of claim 1, wherein, The optical components are arranged such that the wavefront coupled into the waveguide is a transformation of the holographic wavefront of the encoded image.

3. The optical system of claim 1, wherein, The optical components are arranged such that the wavefront coupled to the waveguide is a Fourier transform of the holographic wavefront of the encoded image.

4. The optical system of any one of claims 1-3, wherein, (i) the distance between the holographic reconstruction and the optical component is less than the focal length of the optical component, such that the holographically reconstructed image is a virtual image formed upstream of the display device, and (ii) the distance between the display device and the waveguide is equal to the focal length of the optical component, such that the image of the hologram is formed at infinity upstream of the hologram.

5. The optical system of any one of claims 1-3, wherein, (i) the distance between the holographic reconstruction and the optical component is less than the focal length of the optical component, such that the holographically reconstructed image is a virtual image formed upstream of the display device, and (ii) the distance between the display device and the waveguide is greater than the focal length of the optical component, such that the image of the hologram is formed downstream of the waveguide.

6. The optical system of claim 1, wherein, The image of the hologram or relay hologram formed by the optical components is a real image formed downstream of the observation window of the optical system.

7. The optical system of any one of claims 1-3, wherein, The distance between the holographically reconstructed virtual image and the image of the displayed hologram formed by the optical components is greater than 1 meter.

8. The optical system of any one of claims 1-3, wherein, The distance between the holographically reconstructed virtual image and the image of the displayed hologram formed by the optical components is greater than 2 meters.

9. The optical system of any one of claims 1-3, wherein, The distance between the holographically reconstructed virtual image and the image of the displayed hologram formed by the optical components is greater than 5 meters.

10. The optical system of any one of claims 1-3, wherein, The optical components are arranged such that the distance from the optical components to the holographically reconstructed virtual image is in the range of 0.5 to 10 meters.

11. The optical system of any one of claims 1-3, wherein, The focal length of the optical component is less than 150mm.

12. The optical system of any one of claims 1-3, wherein, The focal length of the optical component is less than 120mm.

13. The optical system of any one of claims 1-3, wherein, The focal length of the optical component is less than 100mm.

14. The optical system of any one of claims 1-3, wherein, The holographic wavefront received by the waveguide includes non-collimated light.

15. The optical system of claim 14, wherein, The non-collimated light is divergent light.

16. The optical system of any one of claims 1-3, wherein, The hologram includes multiple superimposed diffraction patterns, each diffraction pattern representing a lens that forms an image point, and each diffraction pattern representing a lens that brings light to the focal point.

17. A method for forming a holographic image, the method comprising: Spatially modulate light based on a hologram displayed on a display device to form a holographic wavefront; A holographic reconstruction of the image is formed downstream of the display device; A holographically reconstructed virtual image is formed upstream of the display device using optical components; The image of the displayed hologram is formed at infinity or downstream of the waveguide using optical components; as well as A holographic wavefront is received at a waveguide and a waveguide holographic wavefront is placed between a pair of reflective surfaces, one of which is partially transmissive, such that multiple copies of the holographic wavefront are emitted from it. The optical components are located between the holographic reconstruction and the waveguide. An optical repeater is arranged between the display device and the waveguide. The optical repeater includes two lenses, which are arranged in combination to form a relay hologram and a relay holographic reconstruction. The relay hologram is an image of the hologram displayed on the display device, and the relay holographic reconstruction is a holographic reconstruction image formed by the hologram displayed on the display device. The optical component is located between the relay holographic reconstruction and the waveguide, and the distance between the relay holographic reconstruction and the optical component is less than the focal length of the optical component, such that the virtual image of the holographic reconstruction formed by the optical component is the virtual image of the relay holographic reconstruction; and The distance between the relay hologram and the optical components is equal to the focal length of the optical components, such that the image of the hologram formed by the optical components is a virtual image formed at infinity, or The distance between the relay hologram and the optical components is greater than the focal length of the optical components, so that the image of the hologram formed by the optical components is a real image formed downstream of the waveguide.

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