Holographic projection system

Abstract

Figure 8 A holographic projection system is provided that includes a hologram engine. The hologram engine is configured to divide a target image into at least a first and a second part. The hologram engine is further configured to compute a first subhologram of the first part of the target image and a second subhologram of the second part of the target image. The hologram engine is further configured to spatially interlace the first and second subholograms to form a hologram. The system further includes a wavefront redirector positioned on or substantially adjacent to the hologram or a relay copy of the hologram. The wavefront redirector comprises a plurality of first redirect regions optically coupled to the first subhologram and a plurality of second redirect regions optically coupled to the second subhologram. Each of the first redirect regions is positioned to deflect the received light at a first deflection angle with respect to the propagation axis of the system, and each of the second redirect regions is positioned to deflect the received light at a second deflection angle with respect to the propagation axis, and the wavefront redirector is positioned to expand the field of view of the system.

Description

Technical Field

[0001] The present disclosure relates to holographic projection systems. More specifically, it relates to holographic projection systems having a relatively wide field of view, and methods for expanding the field of view of holographic projection systems. Even more specifically, it relates to holographic projection systems comprising a wavefront redirector arranged to receive first and second spatially interleaved sub-holograms. The holographic projection system and the wavefront redirector are arranged to expand the field of view of an optical system. Some embodiments relate to holographic projectors, image generation units, or head-up displays.

Background Art

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

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

[0004] The computer-generated hologram may be encoded into a spatial light modulator positioned to modulate the amplitude and / or phase of the incident light. Light modulation can be achieved, for example, using electrically addressable liquid crystals, optically addressable liquid crystals, or micromirrors.

[0005] A spatial light modulator typically consists of multiple individually addressable pixels, also called cells or elements. The optical modulation scheme can be binary, multilevel, or continuous. Alternatively, the device may be continuous (i.e., not composed of pixels), and therefore the optical modulation may be continuous throughout the device. A spatial light modulator may be reflective, meaning that the modulated light is reflected and output. Similarly, a spatial light modulator may be transmissive, meaning that the modulated light is transmitted and output.

[0006] A holographic projector can be provided using the system described herein. Such projectors are used in head-up displays (HUDs). [Overview of the Initiative]

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

[0008] In the field of holographic projection systems, a relatively wide field of view is required for the user / viewing system within the observation window of the holographic projection system. The field of view refers to the angular range of the holographic reconstruction (i.e., image) that can be viewed from the observation window. Therefore, the field of view is generally determined by the angular range (e.g., horizontal and vertical angles) from which the user / viewing system can view the entire image. In holographic projection systems equipped with a display device, the field of view is usually limited by the diffraction angle of the display device. However, the inventors have provided a holographic projection system according to this disclosure that breaks this rule. The holographic projection system according to this disclosure is configured to provide a field of view wider than the basic limit defined by the diffraction angle (of the display device of the holographic projector), for example, a field of view of twice or three times the diffraction angle.

[0009] The holographic projection system proposed by the inventors offers an unconventional approach to expanding the system's field of view, freeing up the need to primarily consider achieving the desired field of view in the design / selection of the display device. Generally, a holographic projection system is provided. This holographic projection system includes a holographic wavefront redirector positioned to deflect (or redirect, or bend) light spatially modulated according to a hologram composed of multiple sub-holograms. Thus, light associated with different sub-holograms is deflected by different amounts by the holographic wavefront redirector. In this way, the holographic projection system (particularly the holographic wavefront redirector and holograms) is configured to increase the system's field of view (arbitrarily by at least two or at least three times). Angularly, the field of view is expanded beyond the diffraction angle of the display device. The angular field of view can be two or three times the diffraction angle. In particular, the inventors recognized that by applying different rotation or deflection angles to the light of different sub-holograms, the entire angular range of light propagating downstream of the holographic wavefront redirector can be expanded. In some embodiments, the holographic projection system includes a display device, which is a pixelated display device such as a spatial light modulator (e.g., a liquid crystal spatial light modulator on silicon). In some embodiments, the holographic projection system is configured to expand the field of view of the system to exceed the maximum diffraction angle of the display device. Importantly, this field of view expansion can be achieved without changing the physical properties of the display device (e.g., pixel size or display device size (display area of ​​the display device)) and without relying on adjustment of the holographic wavefront by scaling. This allows for the selection / design of the display device based on other design considerations (such as cost, practicality, manufacturability, and / or suitability for forming a good holographic reconstruction) without being constrained by the need to provide a wide field of view. Importantly, holographic wavefront redirectors are compatible with relatively small display devices.Furthermore, the holographic projection system proposed by the inventors has the advantage of being able to achieve different fields of view (or the same field of view under different conditions) using the same display device simply by changing or modifying the holographic wavefront redirector. This makes it possible to easily adapt the holographic projection system to various usage scenarios. For example, in the context of a vehicle head-up display, the holographic projection system can be easily modified for use in different vehicle models. As will be discussed later, the vehicle's windshield acts as an optical combiner and may have a magnification / contraction effect that reduces or expands the field of view. Different vehicle models may have different windshields. The holographic projection system can be simply modified to have a holographic wavefront redirector suitable for achieving the desired field of view regardless of the specific vehicle model (without changing the display device).

[0010] An obvious way to enlarge the field of view of a system is to reduce the pixel pitch in the display device (a device for displaying holograms) within the system. However, as described herein, the inventors have found this to be an efficient way to achieve a field of view large enough to be suitable, for example, for a vehicle head-up display. More specifically, a holographic projector may include a pixelated display device (such as a spatial light modulator). This pixelated display device is associated with a (maximum) diffraction angle. This (maximum) diffraction angle is determined by the pixel pitch of the display device (equal to the distance between the centers of adjacent pixels). The smaller the pitch, the larger the (maximum) diffraction angle. The (maximum) diffraction angle of the display device is a crucial factor in determining the field of view of the system. In the absence of other magnification / reduction optics, the field of view of the system (in the eyebox / observation window) is identical to the diffraction angle of the display device. However, the inventors recognize that there is a practical limit to how much the pixel size of the display device in a holographic projection system can be reduced. The smaller the pixel size, the higher the cost of the display device. Furthermore, there is a limit to the minimum pixel size of the display device that manufacturers can currently provide. The inventors discovered that a display device with appropriately miniaturized pixels to achieve the desired field of view solely through the selection of pixel size is currently unavailable (at least one that is cost-effective and reliable). Furthermore, in vehicle head-up displays, light from the holographic projection system may be relayed to the observation window / eyebox via the vehicle's windshield (or windshield). The windshield typically has a magnifying effect, which reduces the system's field of view in the observation window / eyebox relative to the (maximum) diffraction angle. Therefore, when attempting to achieve the desired field of view by reducing the pixel pitch, the presence of the windshield may further reduce the required pixel size (beyond practical limits).

[0011] Reducing the pixel size / pitch presents another problem: it increases the total number of pixels (assuming the display device size remains constant). The inventors found that this results in a total number of pixels far exceeding the number required for good quality holographic reconstruction. Therefore, from the standpoint of holographic reconstruction quality, the "extra" pixels resulting from selecting a display device with (smaller but more) pixels to expand the field of view are unnecessary. However, these extra pixels not only increase the overall cost of the display device / holographic projector but also significantly increase the computational cost of calculating large / high-resolution holograms for high-resolution displays. In short, the inventors concluded that simply selecting a display device with a smaller pixel pitch to expand the field of view is inefficient and impractical. Of course, reducing the display size can reduce the total number of pixels, but it has also been found that other design constraints exist that prevent the display device size from being easily reduced (and without compromising the viewing experience).

[0012] Therefore, the inventors found that the obvious approach to expanding the field of view of a system has drawbacks and compromises, such as limiting the choice of display devices for the holographic projector to achieve the desired field of view, at the expense of cost (both real and computational costs), complexity, and efficiency. The unconventional holographic projection system of this disclosure provides a means to expand the field of view of a system without such compromises and, in particular, without being limited by the choice of display devices used in the holographic projection system.

[0013] A holographic projection system is provided according to a first aspect of the present disclosure. The holographic projection system includes a hologram engine. The hologram engine may be configured to divide a target image. The hologram engine may be configured to divide the target into a first part and a second part. In some embodiments, the hologram engine may further divide the target, for example, into a third part. In some embodiments, each part may correspond to a different field of view of the target image. For example, the first part may correspond to the left part (or field of view) of the target image. The second part may correspond to the right part (or field of view) of the target image. If present, the third part may correspond to the central part (or field of view) of the target image, which may be located between the first and second parts. The hologram engine may further be configured to calculate a first subhologram corresponding to the first part of the target image. The hologram engine may further be configured to calculate a second subhologram of the second part of the target image. In other words, the hologram engine may individually calculate different subholograms for different parts of the target image (which may correspond to different fields of view of the target image). A hologram engine may be configured to simply receive a first subhologram and a second subhologram. The hologram engine may be configured to interlace the first and second subholograms to form a hologram, for example, spatially or temporally. The hologram engine may be configured to form a hologram by joining or adding sequentially corresponding portions of the first and second subholograms in a substantially alternating configuration. If other subholograms (e.g., a third subhologram) exist, the hologram engine may include those other subholograms in the spatial interlacing.

[0014] The holographic projection system further comprises a wavefront redirector, also referred to herein as a holographic wavefront redirector. The holographic wavefront redirector is positioned on or substantially adjacent to the hologram or a relay copy of the hologram. The hologram may be displayed on a display device (which is a feature of the holographic projection system in some embodiments). A holographic wavefront redirector positioned substantially adjacent to the hologram may mean that it is positioned on or adjacent to the display device. In some embodiments, the holographic projection system includes an optical relay (e.g., a magnifying telescope). The optical relay may be positioned to form a relay hologram, as will be discussed later. In such embodiments, the holographic wavefront redirector may be positioned adjacent to the relay hologram. The holographic wavefront redirector includes a plurality of first redirection regions optically coupled to a first subhologram. The holographic wavefront redirector includes a plurality of second redirection regions optically coupled to a second subhologram. Here, the optical coupling of the first and second redirect regions to the first and second subholograms means that each first redirect region is substantially aligned with or corresponds to a portion of the first subhologram within the hologram or relay hologram, and each second redirect region is substantially aligned with or corresponds to a portion of the second subhologram within the hologram or relay hologram. Thus, light spatially modulated according to the first subhologram (or its corresponding portion) is received in each first redirect region, and light spatially modulated according to the second subhologram (or its corresponding portion) is received in each second redirect region. The holographic wavefront redirector is configured to expand the system's field of view. For example, the holographic wavefront redirector is configured to receive and process the holographic wavefront formed by the hologram at a position adjacent to the hologram (or relay hologram) to expand the system's field of view.

[0015] In some embodiments, each first redirection region is positioned to deflect incident light at a first deflection angle with respect to the propagation axis of the system. In some embodiments, each second redirection region is positioned to deflect incident light at a second deflection angle (different from the first deflection angle) with respect to the propagation axis, thereby configuring the holographic wavefront redirector to expand the field of view of the system. Hereinafter, the (first or second) deflection angle refers to the amount by which light is deflected / diverted / refracted / redirected upon incidence into each redirection region. This angle is measured with respect to the propagation axis of the holographic projection system. The deflection angle may be substantially zero. In other words, either the first or second redirection region may be positioned to apply substantially zero (or substantially near zero) deflection to the incident light. However, because the first and second deflection angles are different, the other of the first and second deflection angles must be non-zero to achieve the expanded field of view of the system. In some embodiments, both the first and second deflection angles are non-zero. Advantageously, the first and second deflection angles may be in opposite directions and equal in magnitude. The holographic wavefront redirector may be configured to provide the system with a field of view larger than the maximum diffraction angle of the display device of the holographic projection system. In some embodiments, the magnitude of the first deflection angle is substantially equal to half the (maximum) diffraction angle of the display device, and optionally, the magnitude of the second deflection angle is substantially equal to half the (maximum) diffraction angle of the display device.

[0016] More specifically, at the point of reception by a holographic wavefront redirector (e.g., near a display device or a relay hologram), the holographic wavefront formed by the hologram may diverge over a continuous angular range. The divergence angle of the holographic wavefront may be equal to the (maximum) diffraction angle of the display device showing the hologram. Within this (continuous) angular range, the holographic wavefront contains light spatially modulated according to both the first and second subholograms (which are spatially interlaced). Thus, the hologram can be positioned such that, if a holographic reconstruction of the hologram were formed in the absence of a holographic wavefront redirector, the reconstructions of the first and second parts of the (target) image would appear to overlap at least partially. Because a holographic wavefront redirector expands the field of view, it deflects the light of different subholograms at different angles. Therefore, downstream of the holographic wavefront redirector, the holographic wavefront may diverge over an expanded continuous angular range. In other words, downstream of the holographic wavefront redirector, the holographic wavefront may diverge over an angular range exceeding the (maximum) diffraction angle of the display device. The first portion of the (extended) continuous angular range of the holographic wavefront may contain only the light of the first subhologram. In other words, downstream of the holographic wavefront redirector, the holographic wavefront may diverge over an angular range greater than the (maximum) diffraction angle of the display device. The first portion of the (extended) continuous angular range of the holographic wavefront may contain only the light of the first subhologram as a result of the deflection by the holographic wavefront redirector, and the second portion of the (extended) angular range of the holographic wavefront may contain only the light of the second subhologram. This results in a holographic reconstruction with reduced overlap between, for example, the holographic reconstructions of the first and second parts of the image. That is, the hologram is positioned so that different parts of the target image correspond to different fields of view. Without the holographic wavefront redirector, the holographic reconstruction could result in those different fields of view overlapping each other.However, by applying deflection / rotation, different fields of view of the image can appear adjacent to each other during playback.

[0017] The target image can be divided into any number of parts. The holographic projector has sub-holograms corresponding to each part, and the holographic wavefront redirector has subsets of redirection regions corresponding to each part of the target image, each subset positioned to deflect light at a different angle. It should be noted that the maximum increase in the system's field of view achieved by the holographic wavefront redirector can be a multiple equal to the number of parts into which the target image is divided. For example, if the target image is divided into two, the field of view doubles, with each part occupying half of the field of view. Similarly, if the target image is divided into three, the holographic wavefront redirector triples the system's field of view.

[0018] The holographic projection system described herein was counterintuitive. In particular, it was counterintuitive to develop this holographic projection system further comprising waveguides arranged to duplicate a hologram to form an extended modulator consisting of multiple holographic duplicates. This is because the hologram is composed of sub-holograms that encode different parts of the target image. If these sub-holograms are placed adjacent to each other (for example, a relatively small (first) sub-hologram corresponding to the left portion of the target image adjacent to a relatively large (second) sub-hologram corresponding to the right portion of the target image), there is a risk that the user / observation system in the observation window will perceive a dark band. For this reason, there was concern about simultaneously displaying different holograms (different images or parts of images) on a display device. However, the inventors surprisingly discovered that the risk of dark bands could be greatly reduced or eliminated by (spatially) interlacing the first and second sub-holograms (as described above). The inventors found that it is particularly advantageous when the discrete regions of the modulator radiate different angular components if these discrete regions are small enough that they are not distinguishable to the naked eye. The inventors recognize that in such cases, the dark band is substantially negligible / non-existent. Therefore, it is desirable that the discrete regions have an angular range or spread in the first direction of preferably 1 / 20 degree or less, optionally 1 / 40 degree or less, and optionally 1 / 60 degree or less. For example, the expansion modulator may be about 1 meter away from the eyebox. If the width of each discrete region on the expansion modulator in the first direction is about 1 millimeter or less, optionally 0.8 millimeters or less, and optionally 0.5 millimeters or less, the angular range or spread of the width in the first direction of adjacent discrete regions will appear so small that the user in the eyebox may not be able to distinguish between different discrete regions with the naked eye.

[0019] In some embodiments, each first and second redirection region may be positioned such that, when viewed from the eyebox of the holographic projection system, the angular range in the first direction is 1 / 20 degree or less, optionally 1 / 40 degree or less, and optionally 1 / 60 degree or less. In some embodiments, each first and second redirection region has a width in the first direction of 1 millimeter or less, optionally 0.8 millimeters or less, and optionally 0.5 millimeters or less.

[0020] Similarly, each portion of the first and second subholograms of a hologram (which may be displayed on a display device) or relay hologram may have an angular range in the first direction of 1 / 20 degree or less, optionally 1 / 40 degree or less, and optionally 1 / 60 degree or less when viewed from the eyebox of a holographic projection system. In some embodiments, each portion of the first and second subholograms of the hologram may have a corresponding width in the first direction (in other words, each portion of the first and second subholograms may have a width of 1 millimeter or less, optionally 0.8 millimeters or less, and optionally 0.5 millimeters or less). For example, each subhologram may be divided or separated into strips with a width of 1 millimeter or less, optionally 0.8 millimeters or less, and optionally 0.5 millimeters or less. The first and second redirect regions / first and second holograms of the hologram may have a larger range in the second direction (e.g., a direction perpendicular to the first direction) than in the first direction.

[0021] In some embodiments, the holographic wavefront redirector is configured to expand the system's field of view by at least 1.5 times, optionally by at least 2 times, and optionally by at least 3 times.

[0022] In some embodiments, the hologram engine is configured to receive the target image. The hologram engine can receive the target image before it is divided.

[0023] In some embodiments, the hologram engine is further configured to provide a first subhologram as a plurality of first parts or strips. In some embodiments, the hologram engine is further configured to separate / divide the first subhologram into a plurality of first subregions or strips. The hologram engine may be further configured to provide a second subhologram as a plurality of second parts or strips. This includes separating / dividing the second subhologram into a plurality of second parts or strips.

[0024] The hologram engine is further configured to spatially interlace the first and second subholograms by spatially interlacing multiple first subregions or strips and multiple second subregions or strips. The strips can be elongated in the second direction described above. Each first and second strip may have a width of 1 millimeter or less in the first direction, optionally 0.8 millimeters or less, and optionally 0.5 millimeters or less.

[0025] In some embodiments, each first redirect region (of the holographic wavefront redirector) is optically coupled to a corresponding first strip of a first subhologram, and each second redirect region is optically coupled to a corresponding second strip of a second subhologram. In embodiments in which the subholograms are divided into elongated strips, the redirect regions of the holographic wavefront redirector may also have the form of elongated strips (elongated in the second direction).

[0026] In some embodiments, the holographic projection system includes a display device. In such embodiments, the hologram engine may be configured to output a hologram to the display device. The hologram engine may be configured to drive the display device to display the hologram.

[0027] In some embodiments, the holographic projector is configured to spatially modulate light according to a hologram to form a holographic wavefront that forms a holographic reconstruction of an image visible from the eyebox. A holographic wavefront redirector may be configured to receive the holographic wavefront. The holographic wavefront includes a plurality of first portions spatially modulated according to a first subhologram and a plurality of second portions spatially modulated according to a second subhologram. The holographic wavefront redirector is also arranged such that each first redirection region receives the first portion of the holographic wavefront and each second redirection region receives the second portion of the holographic wavefront. The holographic wavefront redirector may be arranged such that the light spatially modulated according to the first subhologram forms a first continuous range of the field of view of the holographic reconstruction visible from the eyebox, and the light spatially modulated according to the second subhologram forms a second continuous range of the field of view of the holographic reconstruction visible from the eyebox. The first continuous angular range of the field of view may correspond to the left portion of the field of view. The second continuous angular range of the field of view may correspond to the right-hand portion of the field of view.

[0028] In some embodiments, the holographic wavefront redirector includes an array of prisms. The array of prisms may include a first prism subset and a second prism subset. Each prism may form a corresponding (first or second) redirection region of the holographic wavefront redirector. The prisms of the first prism subset may be spatially interlaced with the prisms of the second prism subset in the array of prisms. The holographic wavefront redirector may be arranged such that each first redirection region is formed by the prisms of the first prism subset, and each second redirection region is formed by the prisms of the second prism subset. Each prism of the first prism subset is arranged to deflect incident light at a first deflection angle with respect to the propagation axis of the holographic projection system. Each prism of the second prism subset is arranged to deflect incident light at a second deflection angle different from the first deflection angle.

[0029] Each prism may have an input surface. The input surface may extend elongately in the second direction and may have a width in the first direction as described above (for example, 1 millimeter or less, optionally 0.8 millimeter or less, optionally 0.5 millimeter or less). Each input surface may be arranged to receive a portion of the holographic wavefront. Each prism may further have an output surface. Each output surface may be arranged substantially opposite to the corresponding input surface. Each output surface may be arranged to output the corresponding portion of the holographic wavefront. In some embodiments, the holographic wavefront redirector is arranged such that the first angle between the input surface and the output surface in the first subset of prisms is different from the second angle between the input surface and the output surface in the second subset of prisms. The first angle and the second angle between the input surface and the output surface can define the deflection angle such that different subsets of prisms are arranged to deflect the received light by different amounts.

[0030] In some embodiments, each prism of the holographic wavefront material may be formed of a substantially transparent material. The substantially transparent material may have a refractive index greater than 1. Thus, the prism may be arranged to deflect light as a result of refraction of light at the air / input surface and output surface / air boundaries of the prism. Due to the angular difference between the input surface and the output surface in the first and second subsets of the prism, the amount of deflection due to refraction is different.

[0031] In some (other) embodiments, the holographic wavefront redirector is a diffractive optical element. In some embodiments, the diffractive optical element is positioned such that the redirection region of the holographic wavefront redirector is defined within the diffraction pattern of the diffractive optical element. In some embodiments, the diffractive optical element is positioned such that light incident in a first subset of the redirection region is primarily redirected to a non-zero diffraction dimension defined by a first diffraction angle. In some embodiments, the diffractive optical element is further positioned such that light incident in a second subset of the redirection region is primarily redirected to a non-zero diffraction dimension defined by a second diffraction angle, which is different from the first diffraction angle. In some embodiments, the first diffraction angle is equal to the second diffraction angle and in opposite directions. In such embodiments, the first diffraction angle may correspond to a first deflection angle, and the second diffraction angle may correspond to a second deflection angle.

[0032] In some embodiments, the holographic wavefront redirector may include an array of diffraction gratings (e.g., brazing gratings). As is well known to those skilled in the art, each diffraction grating in the array may be positioned to redirect or deflect incident light. A first redirection region of the holographic wavefront redirector may be formed or defined by a first subset of the diffraction grating array. Each diffraction grating in the first subset of the diffraction grating array may be positioned to redirect or steer incident light at a first deflection angle. A second redirection region of the holographic wavefront redirector may be formed or defined by a second subset of the diffraction grating array. Each diffraction grating in the second subset of the diffraction grating array may be positioned to redirect or steer incident light at a second deflection angle. Thus, the pitch or spacing (between the slits of each grating) may have a first value for each diffraction grating in the first subset and a second (different) value for each diffraction grating in the second subset.

[0033] In some embodiments, the holographic projector further includes an optical relay. The optical relay may be positioned between the hologram (e.g., a display device on which the hologram is displayed) and a holographic wavefront redirector. The optical relay may comprise two lenses (a first lens and a second lens). The first and second lenses are arranged to cooperate in receiving the holographic wavefront and forming a relay hologram. The relay hologram is the image of the hologram displayed on the display device. The relay hologram is formed in a first plane.

[0034] In some embodiments, the holographic wavefront redirector is positioned in the first plane.

[0035] In some embodiments, the holographic wavefront redirector may instead be positioned on or near the hologram (i.e., on the display device). For example, the holographic wavefront redirector may be in contact with, mounted to, or otherwise fixed to the display device. In embodiments in which the holographic wavefront redirector consists of an array of diffraction gratings (such as a brazing grating), the pitch or spacing (between the slits of each grating) may be smaller than the pixel pitch of the display device. In other words, the slit density of each diffraction grating (at least in a first direction) may be greater than the pixel density in a first direction. Thus, the holographic wavefront redirector is advantageously suited to providing a deflection or rotation angle beyond the available diffraction angle range of the display device (determined by the pixel pitch as described above). Therefore, the holographic wavefront redirector can extend the field of view of the system beyond the diffraction angle of the display device.

[0036] Holographic wavefronts, formed by spatial modulation according to a hologram, can be formed by the diffraction of light in a display device that displays the hologram. As those skilled in the art will recognize, such holographic wavefronts may encompass multiple non-zero diffraction orders. One of these (non-zero) diffraction orders is sometimes called the principal diffraction order. This may be the (non-zero) diffraction order with the highest intensity in the holographic wavefront. The holographic reconstruction formed by the principal (non-zero) diffraction order may be the holographic reconstruction of interest, i.e., intended to be viewed by the user in the eyebox / observation window of a holographic projection system. In some embodiments, the optical relay includes a filter positioned in the midplane between a first lens and a second lens. In some embodiments, the filter may be positioned to capture and filter non-principal (e.g., first-order or higher) diffraction orders of the holographic wavefront. In other words, the filter may be positioned to prevent non-principal diffraction orders from propagating along the propagation axis of the projector. This may improve the viewing experience. When filtering of non-principal diffraction orders is desired, the inventors have found it advantageous to do so before the holographic wavefront reaches the holographic wavefront redirector. This is because, after the holographic wavefront redirector has processed the holographic wavefront, it may become difficult to filter the non-principal diffraction orders because they may have been deflected by the redirector and are mixed with the principal diffraction orders. Therefore, in embodiments including an optical repeater and a filter, it is advantageous to position the holographic wavefront redirector at the location where the repeater hologram is received (i.e., in the first plane of the optical relay). In some embodiments, the filter may be positioned to remove so-called DC spot light.

[0037] In some embodiments, the holographic project system may further include a waveguide. The waveguide may be configured to receive the holographic wavefront. The waveguide may be configured to guide the received holographic wavefront between its pair of reflective surfaces, where one of the pair of reflective surfaces is partially transparent, thereby emitting multiple copies of the holographic wavefront.

[0038] A holographic projection system equipped with a hologram engine is provided. The hologram engine is configured to divide a target image into at least a first and a second part. The hologram engine is further configured to calculate a first subhologram from the first part of the target image and a second subhologram from the second part of the target image.

[0039] In some embodiments, the hologram engine is further configured to drive the display device to display the first and second subholograms. The hologram engine may be configured to drive the display device so that the first subhologram is displayed in a plurality of first sub-regions or first zones of the display device. The hologram engine may be configured to drive the display device so that the second subhologram is displayed in a plurality of second sub-regions or second zones of the display device. In some embodiments, each first sub-region or zone of the display device may contain a plurality of pixels. In some embodiments, each second sub-region or zone of the display device may contain a plurality of pixels. The (first and second) sub-regions / zones of the display device do not have to overlap each other. In other words, the pixels forming each sub-region or zone may be different. In some embodiments, the first and second sub-regions / zones may be arranged alternately. In other words, the first and second sub-regions / zones may be interlaced. Therefore, when the (first and second) subholograms are displayed in their respective (first and second) sub-regions / zones of the display device, the first and second subholograms may be interlaced. In some embodiments, the first and second subholograms may be spatially interlaced. In some embodiments, the first and second subholograms may be temporally interlaced. In some embodiments, each sub-region / zone may have the shape of an (elongated) strip. The width of each strip (in the first direction, as described above) may be less than 1 millimeter, and optionally less than 0.5 millimeters.

[0040] The system further comprises a holographic wavefront redirector positioned on or substantially adjacent to the hologram or relay hologram. The holographic wavefront redirector comprises a plurality of first redirect regions. Each first redirect region can be optically coupled to a first sub-region / zone of the display device. Thus, when the first sub-hologram is displayed on the display device, each first redirect region can be optically coupled to the first sub-hologram. The holographic wavefront redirector further comprises a plurality of second redirect regions. Each second redirect region can be optically coupled to a second sub-region / zone of the display device. Thus, when the second sub-hologram is displayed on the display device, each second redirect region can be optically coupled to the second sub-hologram.

[0041] In some embodiments, each of the first redirection regions is positioned to deflect the incident light at a first deflection angle with respect to the propagation axis of the system. In some embodiments, each of the second redirection regions is positioned to deflect the incident light at a second deflection angle with respect to the propagation axis.

[0042] In a second embodiment, a hologram engine is provided for a holographic projection system (e.g., the holographic projection system of the first embodiment) configured to spatially modulate light according to a hologram of a target image. The hologram engine is configured to divide the target image into at least a first and a second part. The hologram engine is further configured to compute a first subhologram of the first part of the target image. The hologram engine is further configured to compute a second subhologram of the second part of the target image. The hologram engine is further configured to spatially interlace the first and second subholograms to form a hologram. The hologram engine may be configured to output the hologram to a display device of the holographic projection system and / or to drive the display device to display the (output) hologram.

[0043] In some embodiments, the hologram engine may be further configured to provide a first subhologram as a plurality of first parts or strips. This may include dividing the first subhologram into a plurality of first parts or strips. The hologram engine may be further configured to provide a second subhologram as a plurality of second parts or strips. This may include dividing the first subhologram into a plurality of parts or strips. The hologram engine may be configured to spatially interlace the first subhologram and the second subhologram by spatially interlacing the plurality of first parts or strips and the plurality of second parts or strips.

[0044] In some embodiments, the widths of the first and second portions or strips (of each first or second subhologram) are 1 millimeter or less, optionally 0.8 millimeters or less, and optionally 0.5 millimeters or less.

[0045] In a third embodiment, a holographic wavefront redirector is provided for a holographic projection system that spatially modulates light according to a hologram to form a holographic wavefront. The hologram includes a first subhologram of a first portion of an image of interest and a second subhologram of a second portion of the image of interest, the first and second subholograms being spatially interlaced (wherein the holographic projection system may follow the first embodiment and may further include a hologram engine according to the second embodiment). The holographic wavefront redirector comprises a plurality of first redirect regions for optical coupling to the first subhologram (of the holographic projection system). The holographic wavefront redirector further comprises a plurality of second redirect regions for optical coupling to the second subhologram. Each first redirect region is positioned to deflect incident light at a first deflection angle with respect to the propagation axis of the system. Each second redirection region is positioned to deflect the incident light at a second deflection angle with respect to the propagation axis, and the holographic wavefront redirector is positioned to expand the field of view of the holographic wavefront formed by the hologram.

[0046] In some embodiments, the width of each of the first and second redirect regions is 1 millimeter or less, optionally 0.8 millimeters or less, and optionally 0.5 millimeters or less.

[0047] A fourth aspect provides a method for expanding the field of view of a holographic projection system. This method includes the step of dividing a target image into at least a first and a second part. This method further includes the step of calculating a first subhologram of the first part of the target image. This method further includes the step of calculating a second subhologram of the second part of the target image. This method further includes the step of forming a hologram by spatially interlacing the first subhologram and the second subhologram. This method further includes the step of receiving light in a plurality of first redirect regions of a holographic wavefront redirector. The first redirect regions are optically coupled to the first subhologram. The holographic wavefront redirector is positioned on or substantially adjacent to the hologram or relay hologram. This method further includes the step of receiving light in a plurality of second redirect regions of the holographic wavefront redirector. Each of the second redirect regions is optically coupled to the second subhologram.

[0048] In some embodiments, each of the first redirection regions is positioned to deflect incident light at a first deflection angle with respect to the propagation axis of the system. In some embodiments, each of the second redirection regions is positioned to deflect incident light at a second deflection angle with respect to the propagation axis. In embodiments, the holographic wavefront redirector is positioned to expand the field of view of the system. In some embodiments, this method further includes separating the first subhologram into a plurality of first parts or strips. In some embodiments, this method further includes separating the second subhologram into a plurality of second parts or strips. In some embodiments, spatially interlacing the first and second subholograms includes spatially interlacing the plurality of first parts or strips with the plurality of second parts or strips.

[0049] In some embodiments, the width of each of the first and second strips is 1 millimeter or less, optionally 0.8 millimeters or less, and optionally 0.5 millimeters or less.

[0050] A fifth aspect provides a method for calculating a hologram. This method includes dividing a target image into at least a first part and a second part. Furthermore, this method includes calculating a first subhologram of the first part of the target image. Furthermore, this method includes calculating a second subhologram of the second part of the target image. Furthermore, this method includes forming a hologram by spatially interlacing the first subhologram and the second subhologram.

[0051] In some embodiments, the method further includes dividing a first subhologram into a plurality of first parts or strips. In some embodiments, the method further includes dividing a second subhologram into a plurality of second parts or strips. In some embodiments, spatially interlacing the first and second subholograms includes spatially interlacing the plurality of first parts or strips and the plurality of second parts or strips.

[0052] In some embodiments, the width of each of the first and second strips is 1 millimeter or less, optionally 0.8 millimeters or less, and optionally 0.5 millimeters or less.

[0053] A sixth aspect provides a method for processing a holographic wavefront formed by spatially modulating light according to a hologram. The hologram includes a first subhologram of a first portion of a target image and a second subhologram of a second portion of the target image, the first and second subholograms being spatially interlaced. The method includes receiving light in a plurality of first redirect regions of a holographic wavefront redirector, the first redirect regions being optically coupled to (or configured to be optically coupled to) the first subhologram. In some embodiments, the holographic wavefront redirector is positioned in or substantially adjacent to the hologram or relay hologram. The method further includes receiving light in a plurality of second redirect regions of the holographic wavefront redirector. The second redirect regions are optically coupled to (or configured to be optically coupled to) the second subhologram. Each first redirect region is positioned to deflect incident light at a first deflection angle with respect to the propagation axis of the system. Each second redirect region is positioned to deflect incident light at a second deflection angle with respect to the propagation axis to expand the field of view of the system.

[0054] In some embodiments, the width of each of the first and second redirect regions is 1 millimeter or less, optionally 0.8 millimeters or less, and optionally 0.5 millimeters or less.

[0055] In the embodiments, the term "holographic wavefront" is described only as an example. Therefore, the term "holographic wavefront" is used broadly to refer to the fact that at least one image or figure (or part thereof) is formed by reproduction from a hologram. The disclosure also applies to the reorientation of conventional or non-holographic wavefronts, such as image wavefronts (i.e., wavefronts that are spatially modulated in accordance with an image).

[0056] This disclosure relates, at least in part, to a method for displaying two holograms on the same display device. In some embodiments, the first hologram corresponds to a first image or photograph, and the second hologram corresponds to a second image or photograph. In other embodiments, the first hologram corresponds to a first sub-region, zone, or portion of the image or photograph, and the second hologram corresponds to a second sub-region, zone, or portion of the (identical) image or photograph. The first and second sub-regions do not have to overlap or be adjacent. The holograms according to this disclosure can be computed by any means, such as the point cloud method or the iterative phase retrieval method.

[0057] According to this disclosure, the first and second holograms are also referred to as the first and second sub-holograms, reflecting that they are components of a pattern or composite “hologram” displayed on a display device. The first and second (sub)holograms can be combined with or without discarding pixel values. As an example, the first and second holograms may each be half the size of the display device (e.g., using half the pixels of the display device). In alternative embodiments, the first and second (sub)holograms are each derived from a larger hologram. The first and second (sub)holograms may be different sizes (e.g., having different numbers of pixels and / or different aspect ratios). The first and second (sub)holograms may be computed independently before spatial interlacing (i.e., combination). Herein, the term “spatially interlace” is used to refer to any method for combining (i.e., displaying) two (sub)holograms simultaneously on the same display device (i.e., a “common” display device).

[0058] In summary, the wavefront redirectors of this disclosure can take any number of different forms. In some embodiments, the wavefront redirector is a hardware component, i.e., a physical optical component. In other embodiments, the wavefront redirector may be described as a software component to indicate that it is an amplitude and / or phase (optical modulation) pattern that can be displayed on a display device. The term “software component” is used to indicate that the component is reproducible (unlike hardware components such as optical components, it is temporally modifiable) and can be represented by data that can control or drive a display device. In other embodiments, the wavefront redirector is a hybrid component that includes both hardware and software components. That is, the optical function of the wavefront redirector is provided partly by the hardware component and partly by the software component.

[0059] The hardware component may be a prism structure comprising a plurality of first prism regions (or simply prisms) that guide light in a first direction (e.g., one dimension) and a plurality of second prism regions (or simply prisms) that guide light in a second direction (e.g., one dimension) opposite to the first direction. The hardware component may be a physical diffraction structure, such as a diffractive optical element (DOE), designed to provide the optical functions described herein. Those skilled in the art of optical design will be familiar with DOEs and how DOEs are designed to provide, for example, diffraction-based optical steering. This disclosure is not limited to any particular DOE design, as an infinite number of different designs may be used to provide the systems of this disclosure. Accordingly, aspects of this disclosure are described by the optical functions provided, reflecting the design flexibility related to the concepts of the present invention.

[0060] The software component, as described later, is a so-called grating function or phase ramp function, which can be used in the field of dynamic holography to steer a (single) wavefront encoding a (single) hologram. Optically speaking, the phase ramps described later are relatively coarse (in terms of feature size, e.g., pixel size) and are therefore limited in terms of the maximum optical reversal (angular displacement or distance) they can provide. However, in some embodiments, the concepts of this disclosure can be implemented with a “coarse” phase ramp. In some embodiments, the “coarse” phase ramp function is displayed on the same display device as the (image) hologram, or on a display device having at least the same feature size, e.g., pixel size as the hologram. In some embodiments, the pixel pitch is greater than 1 micrometer. That is, in this specification, the term “coarse” means a feature size or pixel pitch of up to 1 micrometer, and the term “fine” means less than 1 micrometer. In other embodiments, a smaller (fine) pixel pitch is used to display a diffraction structure that provides a larger displacement (i.e., reversal) of the wavefront encoded by the hologram. That is, the system may comprise a first display device having relatively large (coarse) pixels (e.g., a pixel pitch of at least 1 micrometer) for displaying a hologram of an image (or portion of an image), and a second display device having relatively small (fine) pixels (e.g., a pixel pitch of less than 1 micrometer) for displaying a diffraction pattern that provides the wavefront reversal disclosed herein. In some embodiments, the diffraction pattern is a "fine" grid with a relatively small pitch or periodicity to provide greater displacement / translation / reversal.

[0061] In some embodiments, the wavefront redirectors described herein are implemented comprehensively by using a combination of hardware and software components. These embodiments are particularly advantageous because the majority of the redirector (e.g., at least 75% of the angular displacement or linear distance) is implemented using hardware components, and the remaining redirection (e.g., up to 25% of the angular displacement or linear distance) is implemented "in software" using a display device, allowing for fine-tuning and reconfiguration to accommodate component tolerances.

[0062] In this disclosure, the term “replica” is used solely to indicate that spatially modulated light is split and the composite light field is directed along multiple different optical paths. The term “replica” is used to refer to each occurrence or instance of the composite light field after a replication event (e.g., partial reflection and transmission by a pupil dilator). Each replica travels along a different optical path. Some embodiments of this disclosure relate to the propagation of light encoded in a hologram rather than an image; that is, to the propagation of light spatially modulated in a hologram of an image, rather than the image itself. Thus, it can be said that multiple replicas of the hologram are formed. Those skilled in the art of holography will understand that the composite light field associated with the propagation of hologram-encoded light changes with respect to propagation distance. The use of the term “replica” in this specification is independent of propagation distance, and therefore, two light branches or paths associated with a replication event are called “replicas” of each other, even if the lengths of the branches are different. In other words, the composite light field evolves differently along each path. That is, two composite light fields are considered “replicas” according to this disclosure, even if their propagation distances are different. However, this is conditional on them originating from the same replication event or a series of replication events.

[0063] In this disclosure, “diffractive field” or “diffractive optical field” means an optical field formed by diffraction. A diffractive optical field can be formed by irradiating with a corresponding diffraction pattern. According to this disclosure, an example of a diffraction pattern is a hologram, and an example of a diffractive optical field is a holographic optical field, or an optical field that forms a holographic reconstruction of an image. A holographic optical field forms a (holographic) reconstruction of an image on a reconstruction plane. A holographic optical field propagating from a hologram to a reconstruction plane can be said to contain light encoded in the hologram, or light within the holographic region. A diffractive optical field is characterized by a diffraction angle determined by the minimum feature size of the diffractive structure and the wavelength of the light (of the diffractive optical field). According to this disclosure, a “diffractive optical field” can also be said to be an optical field that forms a reconstructed image on a plane spatially separated from the corresponding diffractive structure. This specification discloses an optical system for propagating a diffractive optical field from a diffractive structure to an observer. A diffractive optical field can form an image.

[0064] The term “hologram” is used to refer to a record containing amplitude information, phase information, or a combination thereof, about an object. The term “holographic reconstruction” is used to refer to the optically reconstructed image of an object formed by illuminating a hologram. The systems disclosed herein are described as “holographic projectors” because the holographic reconstruction is a real image and is spatially separated from the hologram. The term “reconstruction field” is used to refer to the two-dimensional region in which the holographic reconstruction is formed and fully focused. When a hologram is displayed on a spatial light modulator containing pixels, the reconstruction field is repeated in the form of multiple diffraction orders, each diffraction order being a copy of the zeroth reconstruction field. The zeroth reconstruction field is the brightest reconstruction field and therefore generally corresponds to the preferred or primary reconstruction field. Unless otherwise specified, the term “reconstruction field” is interpreted to refer to the zeroth reconstruction field. The term “reconstruction plane” is used to refer to a plane in space that contains all reconstruction fields. The terms “image,” “reconstruction image,” and “image region” refer to the region of the reconstruction field illuminated by the light of the holographic reconstruction. In some embodiments, the “image” may consist of discrete spots called “image spots” or, for convenience, “image pixels.”

[0065] The terms "encoding," "writing," or "addressing" are used to describe the process of providing multiple control values ​​to multiple pixels of an SLM, each determining the modulation level of that pixel. It can be said that the pixels of the SLM are configured to "display" an optical modulation distribution in response to the reception of these control values. Therefore, it can be said that the SLM "displays" a hologram, which can be thought of as an array of optical modulation values ​​or levels.

[0066] It has been discovered that a holographic reconstruction of acceptable quality can be formed from a “hologram” containing only phase information related to the Fourier transform of the original object. Such holographic recordings are sometimes called phase-only holograms. Although the embodiments relate to phase-only holograms, this disclosure also applies to amplitude-only holography.

[0067] This disclosure is also 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 complex modulation using a so-called fully complex hologram, which includes both amplitude and phase information associated with the original object. Such a hologram is sometimes called a fully complex hologram because the value (gray level) assigned to each pixel of the hologram has both amplitude and phase components. The value (gray level) assigned to each pixel can be represented as a complex number having both amplitude and phase components. In some embodiments, a fully complex computer-generated hologram is computed.

[0068] The terms phase value, phase component, phase information, or simply phase may be used as an abbreviation for “phase delay” when referring to the phase of a pixel in a computer-generated hologram or spatial light modulator. That is, the phase value is actually a numerical value (e.g., in the range of 0 to 2π) that represents the amount of phase delay provided by that pixel. For example, a pixel in a spatial light modulator described as having a phase value of π / 2 delays the phase of the received light by π / 2 radians. In some embodiments, each pixel in a spatial light modulator can operate at any of several possible modulation values ​​(e.g., phase delay values). The term “gray level” may be used to refer to multiple available modulation levels. For example, the term “gray level” may be used for convenience to refer to multiple available phase levels in a phase-only modulator, although different phase levels may not provide different shades of gray. The term “gray level” may also be used for convenience to refer to multiple available complex modulation levels in a complex modulator.

[0069] Therefore, a hologram consists of a grayscale array, i.e., an array of optical modulation values ​​such as phase delay values ​​or complex modulation values. A hologram can also be considered a diffraction pattern, as it is a pattern that is displayed on a spatial light modulator and causes diffraction when illuminated with light of a wavelength equivalent to (usually shorter than) the pixel pitch of the spatial light modulator. This specification refers to combining holograms with other diffraction patterns, such as diffraction patterns that function as lenses or gratings. For example, a diffraction pattern that functions as a grating can be combined with a hologram to translate the reconstructed field on the reconstructed surface, or a diffraction pattern that functions as a lens can be combined with a hologram to focus the holographic reconstruction on the reconstructed surface in the near field.

[0070] In the following detailed description, different embodiments and groups of embodiments may be disclosed separately, but any feature of any embodiment or group of embodiments can be combined with other features or combinations of features of any embodiment or group of embodiments. In other words, all possible combinations and permutations of the features disclosed herein are assumed. [Brief explanation of the drawing]

[0071] Specific embodiments are described only as examples, with reference to the following diagram.

[0072] [Figure 1] Figure 1 is a schematic diagram showing a reflective SLM that generates a holographic reconstruction on a screen. [Figure 2] Figure 2 shows a projection image containing eight image regions / components V1 to V8, and cross-sections of the corresponding hologram channels H1 to H8. [Figure 3] Figure 3 shows a hologram displayed on an LCOS that directs light to multiple separate regions. [Figure 4] Figure 4 shows a system including a display device that shows the calculated hologram as shown in Figures 2 and 3. [Figure 5A] Figure 5A shows a perspective view of a two-dimensional pupil dilator of the first embodiment, which comprises two replicators, each containing a pair of stacked surfaces. [Figure 5B] Figure 5B shows a perspective view of a two-dimensional pupil dilator of the first embodiment, which comprises two replicators, each having the shape of a solid waveguide. [Figure 6] Figure 6 shows a visualization of an example of an extended modulator formed by waveguides. [Figure 7] Figure 7 shows how light from the holographic projector inside the vehicle is relayed to the eye box. [Figure 8] Figure 8A shows a schematic diagram of an example of a pixelated display device for a holographic projection system. Figure 8B shows the maximum diffraction angle of the pixelated display device in Figure 8A. [Figure 9] Figure 9 shows a schematic cross-sectional view of one example of a holographic projection system according to this disclosure. [Figure 10] Figure 10 schematically illustrates the calculation of the hologram projected by the holographic projection system shown in Figure 9. [Figure 11] Figure 11 shows a cross-sectional view of the holographic wavefront redirector of the holographic projection system shown in Figure 9. [Figure 12] Figure 12 schematically shows how the angular range of light emitted from a holographic wavefront redirector is compared to the diffraction angle of a display device. [Figure 13] Figure 13 schematically shows the effect of a holographic wavefront redirector on the holographic reconstruction formed by a holographic projection system. [Figure 14] Figure 14 schematically illustrates the calculation of the second hologram projected by the holographic projection system in Figure 9. [Figure 15] Figure 15 shows a cross-sectional view of the second holographic wavefront redirector of the holographic projection system of Figure 9 when the second hologram is displayed / projected. [Figure 16] Figure 16 schematically shows the effect of a second holographic wavefront redirector on the holographic reconstruction of the second hologram formed by the holographic projection system.

[0073] Throughout the drawing, the same reference number is used to refer to the same or similar parts. [Modes for carrying out the invention]

[0074] The present invention is not limited to the embodiments described below, but extends to the entire scope of the appended claims. That is, the present invention can be carried out in different forms and should not be construed as being limited to the embodiments described for illustrative purposes.

[0075] Unless otherwise specified, singular terms may include their plural forms.

[0076] Structures described as being formed on or below other structures, or above or below other structures, are interpreted to include cases where structures are in contact with each other, and even cases where a third structure is positioned between them.

[0077] When describing relationships between events, for example, if the temporal order of events is described as "after," "successor," "next," or "before," unless otherwise specified, this disclosure should be interpreted as including both consecutive and discontinuous events. For example, unless words such as "just," "immediately," or "directly" are used, the description should be interpreted as including cases that are not consecutive.

[0078] In this specification, terms such as “first,” “second,” etc., may be used to describe various elements, but these elements are not limited by these terms. These terms are used solely to distinguish one element from another. For example, without departing from the scope of the appended claims, the first element may be called the second element, and similarly, the second element may be called the first element.

[0079] Features of different embodiments can be combined or combined with each other, either partially or entirely, and can interoperate with each other in various ways. Depending on the embodiment, they can be performed independently or together in an interdependent manner.

[0080] In this disclosure, the term “substantially” when applied to a structural unit of an apparatus may be interpreted as the technical features of the structural unit being generated within the technical tolerances of the methods used to manufacture it.

[0081] Conventional optical configurations of holographic projection Figure 1 shows an embodiment in which a computer-generated hologram is encoded into a single spatial light modulator. The computer-generated hologram is the Fourier transform of the object for reconstruction. Thus, the hologram can be said to be the Fourier domain, frequency domain, or spectral domain representation of the object. In this embodiment, the spatial light modulator is a reflective liquid crystal (LCOS) device on silicon. The hologram is encoded into the spatial light modulator, and a holographic reconstruction is formed at a regeneration field, such as an optical receiving surface like a screen or diffuser.

[0082] A light source 110, such as a laser or laser diode, is positioned to illuminate the SLM 140 via a collimating lens 111. The collimating lens causes a nearly planar wavefront of light to be incident on the SLM. In Figure 1, the direction of the wavefront is not perpendicular (for example, 2 or 3 degrees away from true orthogonality with respect to the plane of the transparent layer). However, in other embodiments, a nearly planar wavefront is provided with perpendicular incidence, and a beam splitter arrangement is used to separate the input and output optical paths. In the embodiment shown in Figure 1, light from the light source is reflected off the back of the mirror on the SLM and is positioned to interact with the optical modulation layer to form an output wavefront 112. The output wavefront 112 is applied to an optical system including a Fourier transform lens 120 focused on the screen 125. More specifically, the Fourier transform lens 120 receives the modulated beam of light from the SLM 140 and performs a frequency-space transformation to produce a holographic reconstruction on the screen 125.

[0083] In particular, in this type of holography, each pixel of the hologram contributes to the entire reconstructed image. There is no one-to-one correlation between a specific point (or image pixel) on the reconstruction field and a specific light modulation element (or hologram pixel). In other words, the modulated light emanating from the light modulation layer is distributed throughout the entire reconstruction field.

[0084] In these embodiments, the position of the holographic reconstruction in space is determined by the refractive power (focusing power) of the Fourier transform lens. In the embodiment shown in Figure 1, the Fourier transform lens is a physical lens; that is, the Fourier transform lens is an optical Fourier transform lens, and the Fourier transform is performed optically. Any lens can function as a Fourier transform lens, but the performance of the lens limits the accuracy of the Fourier transform performed. Those skilled in the art understand how to perform an optical Fourier transform using a lens. In some embodiments of this disclosure, the lens of the observer's eye performs the hologram-to-image transformation.

[0085] Hologram calculation In some embodiments, the computer-generated hologram is a Fourier transform hologram, or simply a Fourier hologram, or a Fourier-based hologram, in which the image is reconstructed in the far field using the Fourier transform properties of a positive lens. A Fourier hologram is computed by a Fourier transform that returns the desired light field of the reconstruction plane to the lens plane. Computer-generated Fourier holograms can be computed using the Fourier transform. Embodiments relate only, as examples, to Fourier holography and Gerchberg-Saxton type algorithms. This disclosure is equally applicable to Fresnel holography and Fresnel holograms, which can be computed in a similar manner. In some embodiments, the hologram is a phase or phase-only hologram. However, this disclosure is also applicable to holograms computed by other techniques, such as those based on the point cloud method.

[0086] In some embodiments, the hologram engine is configured 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 5 February 2021 and incorporated herein by reference, discloses a first hologram calculation method that uses eye-tracking and ray tracing to identify sub-areas of a display device for calculating a point cloud hologram that eliminates ghost images. The sub-areas of the display device correspond to the aperture in this disclosure and are used to exclude the light path from the hologram calculation. UK Patent Application 2112213.0, filed 26 August 2021 and incorporated herein by reference, discloses a second method based on a modified Gercberg-Saxton algorithm, which includes the step of cropping the light field according to the pupil of the optical system during the hologram calculation. The cropping of the light field corresponds to the determination of the limiting aperture in this disclosure. Filing on 23 December 2021 and incorporated herein by reference, UK Patent Application 2118911.3 discloses a third method for calculating a hologram, comprising the step of determining a region of a so-called expansion modulator formed by a hologram replicator. According to this disclosure, the region of the expansion modulator is also an opening.

[0087] In some embodiments, a real-time engine is provided that is configured to receive image data and compute holograms in real time using an algorithm. In some embodiments, the image data is a video containing a series of image frames. In other embodiments, the holograms are pre-computed, stored in computer memory, and called upon as needed to be displayed on the SLM. In other words, in some embodiments, a repository of predetermined holograms is provided.

[0088] Pupil dilation Broadly speaking, this disclosure relates to image projection. This disclosure relates to an image projector comprising an image projection method and a display device. This disclosure also relates to a projection system comprising an image projector and a display system. In this projection system, the image projector projects or relays light from a display device to a display system. This disclosure is equally applicable to monocular and binocular display systems. The display system may comprise one or more eyes of the viewer. The display system comprises optical elements having optical power (e.g., the lens of a human eye) and a display surface (e.g., the retina of a human eye). The projector is sometimes referred to as an “optical engine”. The display device and the image formed (or perceived) using the display device are spatially separated from each other. The image is formed on a display surface or perceived by the viewer. In some embodiments, the image is a virtual image, and the display surface may be referred to as a virtual image surface. In other examples, the image is a real image formed by holographic reconstruction, and the image is projected or relayed to the display surface. In these other examples, spatially modulated light of an intermediate holographic reconstruction formed in free space or on a screen or other light-receiving surface between the display device and the viewer is propagated to the viewer. In both cases, the image is formed by irradiating the display device with a diffraction pattern (such as a hologram or kinoform).

[0089] Display devices are composed of pixels. Pixels on a display can show diffraction patterns or structures that diffract light. The diffracted light forms an image on a plane spatially distant from the display device. According to well-known optics, the magnitude of the maximum diffraction angle is determined by other factors such as the size of the pixel and the wavelength of light.

[0090] In some embodiments, the display device is a spatial light modulator, such as a liquid crystal on silicon ("LCOS") spatial light modulator (SLM). Light propagates from the LCOS towards a display entity / system, such as a camera or eye, across a range of diffraction angles (e.g., from zero to the maximum diffraction angle). In some embodiments, magnification techniques can be used to extend the range of available diffraction angles beyond the conventional maximum diffraction angle of the LCOS.

[0091] In some embodiments, the hologram (or its light) itself is transmitted to the eye. For example, the spatially modulated light of the hologram (holographic reconstruction, i.e., not yet fully converted into an image), which could informally be said to be "encoded" by the hologram, is transmitted directly to the viewer's eye. The viewer can perceive a real or virtual image. In these embodiments, no intermediate holographic reconstruction / image is formed between the display device and the viewer. In these embodiments, it may be said that the lens of the eye performs the hologram-to-image conversion or transformation. The projection system or optical engine can be configured so that the viewer effectively looks directly at the display device.

[0092] The specification refers to a “light field,” but this is a “complex light field.” The term “light field” simply refers to a pattern of light with a finite size in at least two orthogonal spatial directions, e.g., x and y. The word “complex” is used herein solely to indicate that the light at each point in the light field may be defined by amplitude and phase values ​​and therefore representable by complex numbers or pairs of values. For the purposes of holographic calculations, a complex light field is a two-dimensional array of complex numbers, where the complex numbers define the intensity and phase of light at multiple discrete locations within the light field.

[0093] According to well-known optical principles, the range of angles of light propagating from a display device that can be observed by the eye or other object / system of observation depends on the distance between the display device and the object of observation. For example, at an observation distance of 1 meter, only a small portion of the angle from the LCOS (Low-Core Optical System) can pass through the pupil of the eye and form an image on the retina at a particular eye position. The range of angles of light rays propagating from the display device is the range that can pass through the pupil of the eye and form an image on the retina, and it determines the portion of the image that the observer "sees." In other words, not all parts of the image are visible from any single point on the observation plane (for example, any single eye position within an observation window such as an eyebox).

[0094] In some embodiments, the image perceived by the viewer is a virtual image displayed upstream of the display device. That is, the viewer perceives the image as being farther away than the display device. Conceptually, one can think of the viewer as seeing the virtual image through a very small "display device-sized window," such as a 1 cm diameter window at a relatively large distance, e.g., 1 m. Furthermore, the user is viewing the display device-sized window through a very small pupil of the eye. Consequently, the field of view is narrowed, and the specific angular range that can be seen depends heavily on the position of the eye at any given time.

[0095] Pupil dilators address the problem of how to extend the angular range of light rays propagated from a display device and pass through the pupil of the eye effectively to form an image. Display devices are generally (relatively) small, and the projection distance is (relatively) large. In some embodiments, the projection distance is at least one order of magnitude, for example, at least two orders of magnitude, larger than the diameter or width (i.e., the size of the pixel array) of the entrance pupil and / or opening of the display device.

[0096] Using a pupil dilator expands the field of view (i.e., the user's eye box) laterally, allowing eye movement while the user can still see the image. As those skilled in the art will understand, in an image system, the field of view (the user's eye box) is the area in which the observer's eye can perceive an image. This disclosure deals with non-infinite virtual image distances, i.e., near-field virtual images.

[0097] Conventionally, a two-dimensional pupil dilator consists of one or more one-dimensional optical waveguides, each formed using a pair of opposing reflective surfaces, where the output light from the surfaces forms an observation window or eyebox. Light received from a display device (e.g., spatially modulated light from an LCOS) is replicated by the waveguides or each waveguide so that the field of view (or display area) is expanded in at least one dimension. In particular, the waveguides expand the observation window by generating additional rays or "replicas" through the division of the amplitude of the incident wavefront.

[0098] The display device may have an active area or display area that is less than 10 cm, for example, less than 5 cm or less than 2 cm. The propagation distance between the display device and the display system may be more than 1 m, for example, more than 1.5 m or more than 2 m. The optical propagation distance in the waveguide may be up to 2 m, for example, up to 1.5 m or up to 1 m. This method can receive an image and determine a corresponding hologram of sufficient quality in less than 20 ms, for example, less than 15 ms or less than 10 ms.

[0099] In some embodiments, although described only as examples of diffracted or holographic light fields according to this disclosure, a hologram is configured to route light into multiple channels, each corresponding to a different part (i.e., sub-area) of the image. The channels formed by the diffracted structure are referred to here simply as “holographic channels” to reflect that they are channels of light encoded by the hologram with image information. The light in each channel can be said to be in the holographic region, not the image or spatial region. In some embodiments, the hologram is a Fourier or Fourier transform hologram, and therefore the holographic region is the Fourier or frequency domain. The hologram may also be a Fresnel or Fresnel transform hologram. The hologram may also be a point cloud hologram. Hereinafter, a hologram is described as routing light into multiple holographic channels to reflect that the image that can be reconstructed from the hologram has a finite size and can be arbitrarily divided into multiple image sub-regions, each holographic channel corresponding to each image sub-region. Importantly, the hologram in this example is characterized by how it distributes its image content when illuminated. Specifically, the hologram divides its image content by angle. In other words, each point on the image is associated with an intrinsic ray angle in the spatially modulated light formed by the hologram when illuminated. At the very least, since the hologram is two-dimensional, it is a pair of intrinsic angles. To avoid any doubt, the behavior of this hologram is different from conventional ones. The spatially modulated light formed by this special type of hologram, when illuminated, is divided into multiple holographic channels, each holographic channel defined by a range of ray angles (two-dimensional). From the above, it is understood that the holographic channels (i.e., subranges of ray angles) that may be considered in spatially modulated light are associated with each part or subregion of the image. That is, all the information necessary to reconstruct that part or subregion of the image is contained within the subrange of angles of the spatially modulated light formed from the hologram of the image.When spatially modulated light is observed as a whole, evidence of multiple individual optical channels is not necessarily present.

[0100] Nevertheless, holograms are identifiable. For example, if only a continuum or subregion of the spatially modulated light formed by the hologram is reconstructed, only a subregion of the image should be visible. If different continuums or subregions of the spatially modulated light are reconstructed, different subregions of the image should be visible. A further identifying feature of this type of hologram is that the shape of the cross-sectional area of ​​the hologram channel substantially corresponds to (i.e., is substantially the same as) the shape of the entrance pupil, although their size may differ, at least in the correct plane from which the hologram was calculated. Each light / hologram channel propagates from the hologram at different angles or angular ranges. These are exemplary ways of characterizing or identifying this type of hologram, but other methods may also be used. In summary, the holograms disclosed herein are characterized and identifiable by how the image content is dispersed within the light encoded by the hologram. Again, to avoid any doubt, references herein to holograms configured to guide light or to angularly divide an image into multiple holographic channels are made for illustrative purposes only, and this disclosure is equally applicable to any type of holographic light field, and even to any type of diffracted light field or pupil dilation of a diffracted light field.

[0101] This system can be delivered in a compact and streamlined physical form. This allows for the creation of systems suitable for a variety of real-world applications, such as those where space is limited and real estate value is high. For example, it can be implemented in head-up displays (HUDs) such as those in vehicles and automobiles.

[0102] According to this disclosure, pupil dilation is provided for diffracted light or diffracted light containing a divergent beam. The diffracted light field is defined by a “light cone”. Thus, the size of the diffracted light field (defined on a two-dimensional plane) increases with the propagation distance from the corresponding diffracting structure (i.e., the display device). It can be said that the pupil dilator replicates a hologram or forms a replica of at least one hologram, conveying that the light delivered to the viewer is spatially modulated according to the hologram.

[0103] In some embodiments, two one-dimensional waveguide pupil dilators are provided, each one-dimensional waveguide pupil dilator positioned to effectively expand the size of the system's exit pupil by forming multiple replicas or copies of the exit pupil (or light from the exit pupil) of the spatial light modulator. The exit pupil can be understood as the physical region from which light is emitted by the system. It can also be said that each waveguide pupil dilator is positioned to expand the size of the system's exit pupil. Furthermore, it can also be said that each waveguide pupil dilator is positioned to expand / increase the size of the eyebox in which the observer's eye can be positioned to see / receive the light emitted by the system.

[0104] Light Channeling Holograms formed according to some embodiments provide multiple hologram channels that can have cross-sectional shapes defined by the apertures of an optical system by angularly dividing the image content. The hologram is computed to provide this channeling of the diffracted light field. In some embodiments, this is achieved during hologram computation by considering the apertures (virtual or real) of the optical system, as described above.

[0105] Figures 2 and 3 show examples of this type of hologram that can be used in combination with the pupil dilation devices disclosed herein. However, these examples are not intended to limit the invention.

[0106] Figure 2 shows a projection image 252 containing eight image regions / components V1 to V8. While Figure 2 shows eight image components as an example, image 252 can be divided into any number of components. Figure 2 also shows an encoded optical pattern 254 (i.e., a hologram) that can reconstruct image 252, such as when transformed by the lens of a suitable display system. The encoded optical pattern 254 consists of first to eighth sub-holograms or components H1 to H8, corresponding to the first to eighth image components / regions V1 to V8. Figure 2 further illustrates how a hologram decomposes its image content by angle. Thus, a hologram is characterized by the channeling of light it performs, as shown in Figure 3. Specifically, the hologram in this example directs light into multiple distinct regions. These distinct regions are disks in the example shown, but other shapes are also conceivable. The optimal disk size and shape may depend on the size and shape of the aperture of the optical system, such as the entrance pupil of the observation system, after propagation through the waveguide.

[0107] Figure 4 shows a system 400 that includes a display device for displaying the calculated hologram as shown in Figures 2 and 3.

[0108] System 400 includes a display device, in this configuration, an LCOS 402. The LCOS 402 displays a modulation pattern (or "diffraction pattern") containing a hologram and is positioned to project the holographically encoded light toward an eye 405, which includes a pupil, a lens 409, and a retina (not shown), which serves as an aperture 404. There is a light source (not shown) positioned to illuminate the LCOS 402. The lens 409 of the eye 405 performs the conversion from hologram to image. The light source may be of any suitable type; for example, it may be a laser light source.

[0109] The visual system 400 further includes a waveguide 408 positioned between the LCOS 402 and the eye 405. The presence of waveguide 408 ensures that all angular content from the LCOS 402 is received by the eye, even at the relatively long projection distance shown in the figure. This is because waveguide 508 acts as a pupil dilator. This method is well known and will be described only briefly here.

[0110] Simply put, the waveguide 408 shown in Figure 4 consists of a substantially elongated structure. In this example, waveguide 408 is made of an optical slab of refractive material, but other types of waveguides are also known and may be used. Waveguide 408 is positioned, for example, at an oblique angle so as to intersect the light cone (i.e., the diffracted light field) projected from LCOS 402. In this example, the size, location, and position of waveguide 408 are configured so that light from each of the eight ray beams in the light cone enters waveguide 408. Light from the light cone enters waveguide 408 via a first planar surface of waveguide 408 (closest to LCOS 402), is at least partially guided along the length of waveguide 408, and then emitted via a second planar surface (closest to the eye) substantially opposite the first surface. As is well understood, the second plane is partially reflective and partially transmissive. In other words, as each ray travels from the first plane through the waveguide 408 and strikes the second plane, some of the light is transmitted through the waveguide 408, and some is reflected by the second plane and returns to the first plane. The first plane is reflective, and all light that strikes the first plane from within the waveguide 408 is reflected by the second plane. Therefore, some of the light is refracted between the two planes of the waveguide 408 and then transmitted, while other light is reflected and undergoes one or more reflections (or "bounces") between the planes of the waveguide 408 before being transmitted.

[0111] Figure 4 shows a total of nine “reflection” points B0 through B8 along the length of waveguide 408. As shown in Figure 2, the light associated with all points in the image (V1-V8) is transmitted from the waveguide at each “reflection” from the second plane of waveguide 408, but only the light from one angular portion of the image (for example, any light from V1 through V8) has a trajectory that allows it to reach eye 405 from each “reflection” point B0 through B8. Furthermore, the light from different angular portions of the image V1 through V8 also reaches eye 405 from each “reflection” point. Thus, in the example in Figure 4, each angular channel of encoded light reaches the eye only once from waveguide 408.

[0112] Waveguide 408 forms multiple replicas of the hologram along its length at respective “bounce” points B1 to B8 corresponding to the direction of pupil dilation. As shown in Figure 5, the multiple replicas are extrapolated linearly to the corresponding multiple replicas or virtual display devices 402'. This process corresponds to the step of “unfolding” the optical path within the waveguide so that the rays of the replicas are extrapolated to the “virtual surface” without internal reflection within the waveguide. Thus, the light from the dilated exit pupil can be considered to originate from the virtual surface (also referred to herein as the “expanded modulator”) that constitutes the display device 402 and the replica display device 402'.

[0113] While this specification has generally described virtual images, which require the eye to transform received modulated light to form a perceived image, the methods and configurations described herein can also be applied to real images.

[0114] 2D pupil dilation The configuration shown in Figure 4 includes a single waveguide that provides pupil dilation in one dimension, but pupil dilation can be provided in multiple dimensions, such as two dimensions. Furthermore, the example in Figure 4 uses a computed hologram to create light channels corresponding to different parts of the image, but the systems described in this disclosure and below are not limited to such hologram types.

[0115] Figure 5A shows a perspective view of system 500, which includes two replicators 504 and 506 arranged to extend the ray 502 into two dimensions.

[0116] In system 500 of Figure 5A, the first replicator 504 consists of a first pair of surfaces stacked parallel to each other and arranged to provide replication (or pupil dilation) similar to the waveguide 408 of Figure 4. The first pair of surfaces are similar (and possibly identical) in size and shape to each other and are substantially elongated in one direction. The collimated ray 502 is directed towards the input of the first replicator 504. As is well known to those skilled in the art, due to an internal reflection process between the two surfaces and partial transmission of light from each of several output points on one of the surfaces (the top surface as shown in Figure 5A), the light of the ray 502 is replicated in a first direction along the length of the first replicator 504. Thus, a first plurality of replica rays 508 are emitted from the first replicator 504 toward the second replicator 506.

[0117] The second replicator 506 comprises a second pair of surfaces stacked parallel to each other and is positioned to receive each of the collimated rays of the first plurality of rays 508, and further positioned to replicate, i.e., provide pupil dilation, by extending each of those rays in a second direction substantially orthogonal to the first direction. The first pair of surfaces are similar (and possibly identical) in size and shape to each other and are substantially rectangular. The second replicator is implemented in a rectangular shape so that it has a length along the first direction to receive the first plurality of rays 508, a length along the second orthogonal direction, and provides replication in the second direction. Due to the process of internal reflection between the two surfaces, and the partial transmission of light from each of the multiple output points on one of the surfaces (the top surface as shown in Figure 5A), the light of each ray in the first plurality of rays 508 is replicated in the second direction. Therefore, a second plurality of rays 510 are emitted from the second replication device 506, and the second plurality of rays 510 include replicas of the input rays 502 along the first and second directions, respectively. Thus, the second plurality of rays 510 can be considered to include a two-dimensional grid or array of replica rays.

[0118] Therefore, it can be said that the combination of the first and second replicators 504 and 505 in Figure 5A provides a two-dimensional replicator (or "two-dimensional pupil dilator"). Thus, the replica rays 510 may be emitted along the optical path to an extended eye box in a display system such as a head-up display.

[0119] In the system shown in Figure 5A, the first replicator 504 is a waveguide containing a pair of elongated straight reflectors stacked parallel to each other, and similarly, the second replicator 504 is a waveguide containing a pair of rectangular reflectors stacked parallel to each other. In other systems, the first replicator is a solid elongated straight waveguide, and the second replicator is a solid planar rectangular waveguide, with each waveguide containing an optically transparent solid material such as glass. In this case, the pair of parallel reflectors are formed by a pair of opposing main sidewalls, each optionally containing reflective and reflective-transmitting surface coatings, as is well known to those skilled in the art.

[0120] Figure 5B shows a perspective view of system 500, which includes two replicators 520 and 540 arranged to replicate a ray 522 in two dimensions, the first replicator being a solid elongated waveguide 520 and the second replicator being a solid planar waveguide 540.

[0121] In the system shown in Figure 5B, the first replicator / waveguide 520 is positioned such that its pair of elongated parallel reflecting surfaces 524a, 524b are perpendicular to the plane of the second replicator / waveguide 540. Thus, the system includes an optical coupler positioned to couple light from the output port of the first replicator 520 to the input port of the second replicator 540. In the illustrated configuration, the optical coupler is a planar / bending mirror 530 positioned to bend or rotate the optical path of light to achieve the required optical coupling from the first replicator to the second replicator. As shown in Figure 5B, the mirror 530 is positioned to receive light from the output port / reflecting surface 524a of the first replicator / waveguide 520, containing a one-dimensional array of replicas extending to the first dimension. Mirror 530 is tilted at an angle that provides guidance and replica formation along the length of the second dimension, redirecting the received light into the optical path to the input port of the (perfect) reflective surface of the second replicator 540. Mirror 530 is an example of an optical element that can redirect light in the manner illustrated, and it will be understood that one or more other elements could be used instead to perform this task.

[0122] In the illustrated configuration, the (partially) reflective and transmitted surface 524a of the first replicator 520 is adjacent to the input port of the first replicator / waveguide 520, receiving the input beam 522 at a certain angle to perform guiding and replica formation along the length of the first dimension. Thus, the input port of the first replicator / waveguide 520 is located at the input end of the same surface as the reflective and transmitted surface 524a. Those skilled in the art will understand that the input port of the first replicator / waveguide 520 may be located in other suitable locations.

[0123] Therefore, the arrangement in Figure 5B allows the first replicator 520 and the mirror 530 to be provided as part of a relatively thin first layer in the planes of the first and third dimensions (illustrated as the xz plane). In particular, the size or "height" of the first planar layer in which the first replicator 520 is located is reduced in the second dimension (illustrated as the y dimension). The mirror 530 is configured to direct light away from the first layer / plane in which the first replicator 520 is located (i.e., the "first planar layer") and to direct light towards the second layer / plane in which the second replicator 540 is located (i.e., the "second planar layer"), which is above the first layer / plane and substantially parallel to the first layer / plane. Therefore, the overall size or "height" of the system, including the first and second replicators 520, 540 and the mirrors 530 arranged in stacked first and second planar layers in the first and third dimensions (illustrated as the xz plane), is compact in the second dimension (illustrated as the y dimension). Those skilled in the art will understand that many variations of the arrangement in Figure 5B for implementing this disclosure are possible and have been considered.

[0124] The image projector may be positioned to project a divergent or diffracted light field. In some embodiments, the diffracted light field is encoded as a hologram. In some embodiments, the diffracted light field consists of a beam of divergent rays. In some embodiments, the image formed by the diffracted light field is a virtual image.

[0125] In some embodiments, the first pair of parallel / complementary surfaces are elongated or slender surfaces, relatively long along the first dimension and relatively short along the second dimension, for example, relatively short along each of the two other dimensions, with each dimension substantially orthogonal to the other. The process of reflection / transmission of light from between the first pair of parallel surfaces is arranged so that the light propagates within the first waveguide pupil dilator, and the general direction of light propagation is in the direction in which the first waveguide pupil dilator is relatively long (i.e., its “slender” direction).

[0126] This specification discloses a system that uses diffracted light to form an image and provide an eyebox size and field of view suitable for real-world applications, such as applications in the automotive industry using head-up displays. Diffracted light is light that forms a holographic reconstruction of an image from a diffracted structure, such as a Fourier hologram or a Fresnel hologram. The use of diffraction and diffracted structures requires a display device with a high density of very small pixels (e.g., 1 micrometer), which in practice means a small display device (e.g., 1 centimeter). The inventors have addressed the problem of a method for providing 2D pupil dilation with a diffracted light field, for example, diffracted light consisting of a diverging (uncollimated) beam of light rays.

[0127] In some embodiments, the display system comprises a display device, such as a spatial light modulator (SLM) or a pixelated display device, such as a Liquid Crystal on Silicon (LCoS) SLM, arranged to supply or form diffracted or divergent light. In such embodiments, the aperture of the spatial light modulator (SLM) is the limiting aperture of the system. That is, the size of the aperture of the spatial light modulator, more specifically, the size of the region that demarcates the array of light-modulated pixels configured within the SLM, determines the size (e.g., spatial spread) of the beam of light that can exit the system. In accordance with this disclosure, it is stated that the exit pupil of the system (limited by a small display device having a pixel size for light diffraction) is expanded to reflect the increased or increased spatial spread by using at least one pupil expander.

[0128] A diffracted or divergent light field can be said to have a "magnitude of the light field" defined in a direction substantially perpendicular to the direction of propagation of the light field. Because light diffracts / diverges, the magnitude of the light field increases with propagation distance.

[0129] In some embodiments, the diffracted light field is spatially modulated according to the hologram. In other words, in such embodiments, the diffracted light field constitutes a “holographic light field.” The hologram may be displayed on a pixelated display device. The hologram may be a computer-generated hologram (CGH). The hologram may be a Fourier hologram, a Fresnel hologram, a point cloud hologram, or any other suitable type of hologram. The hologram may optionally be computed to form channels of holographic light, each corresponding to a different part of the image that the viewer is intended to see (or perceive, if it is a virtual image). The pixelated display device may be configured to display multiple different holograms sequentially or in sequence. Each embodiment and example disclosed herein can be applied to the display of multiple holograms.

[0130] The output port of the first waveguide pupil dilator may be coupled to the input port of the second waveguide pupil dilator. The second waveguide pupil dilator may be positioned to guide the diffracted light field—including a portion, preferably a large portion, preferably all, of the replica of the light field output by the first waveguide pupil dilator—from its input port to its respective output port by internal reflection between a third pair of parallel planes of the second waveguide pupil dilator.

[0131] A first waveguide pupil dilator may be positioned to provide pupil dilation or replication in a first direction, and a second waveguide pupil dilator may be positioned to provide pupil dilation or replication in a second different direction. The second direction may be substantially orthogonal to the first direction. The second waveguide pupil dilator may be positioned to maintain the pupil dilation provided by the first waveguide pupil dilator in the first direction and to dilate (or replicate) a portion, preferably most, preferably all, of the replicas it receives from the first waveguide pupil dilator in the second different direction. The second waveguide pupil dilator may be positioned to receive the light field directly or indirectly from the first waveguide pupil dilator. One or more other elements may be provided along the light field propagation path between the first waveguide pupil dilator and the second waveguide pupil dilator.

[0132] The first waveguide pupil dilator may be substantially elongated, and the second waveguide pupil dilator may be substantially planar. The elongated shape of the first waveguide pupil dilator may be defined by a length along a first dimension. The planar, i.e., rectangular shape of the second waveguide pupil dilator may be defined by a length along a first dimension and a width along a second dimension substantially perpendicular to the first dimension. The length along the first dimension of the first waveguide pupil dilator corresponds to the length or width along the first or second dimension of the second waveguide pupil dilator, respectively. The first face of the pair of parallel faces of the second waveguide pupil dilator constituting its input port may be shaped, sized, and / or positioned to correspond to an area defined by the output ports on the first pair of parallel faces of the first waveguide pupil dilator, such that the second waveguide pupil dilator is positioned to receive each of the replicas output by the first waveguide pupil dilator.

[0133] The first and second waveguide pupil dilators may collectively provide pupil dilation in a first direction and a second direction perpendicular to the first direction, and optionally, the plane containing the first and second directions is substantially parallel to the plane of the second waveguide pupil dilator. In other words, the first and second dimensions defining the length and width of the second waveguide pupil dilator, respectively, may be parallel to the first and second directions (or parallel to the second and first directions, respectively) in which the waveguide pupil dilator provides pupil dilation. The combination of the first waveguide pupil dilator and the second waveguide pupil dilator is sometimes commonly referred to as a "pupil dilator".

[0134] The expansion / replication provided by the first and second waveguide expanders can be said to have the effect of expanding the exit pupil of the display system in each of the two directions. The area defined by the expanded exit pupil may define an expanded eyebox area from which the viewer can receive light from the input diffracted or divergent light field. The eyebox area can be said to be located on or define the field of view plane.

[0135] The two directions in which the exit pupil expands may be coplanar or parallel to the first and second directions in which the first and second waveguide pupil dilators provide replication / expansion. Alternatively, in arrangements that include other elements such as an optical combiner, e.g., a vehicle's windshield (or windshield), the exit pupil may be considered an exit pupil from the other element such as the windshield. In such arrangements, the exit pupil may be non-parallel to the first and second directions in which the first and second waveguide pupil dilators provide replication / expansion. For example, the exit pupil may be substantially perpendicular to the first and second directions in which the first and second waveguide pupil dilators provide replication / expansion.

[0136] The field of view plane and / or eyebox region may be non-planar or non-parallel to the first and second directions in which the first and second waveguide pupil dilators provide replication / dilation. For example, the field of view plane may be substantially perpendicular to the first and second directions in which the first and second waveguide pupil dilators provide replication / dilation.

[0137] To provide suitable emission conditions for achieving internal reflection within the first and second waveguide pupil dilators, the elongated dimensions of the first waveguide pupil dilator may be inclined relative to the first and second dimensions of the second waveguide pupil dilator.

[0138] Combiner Shape Correction The advantage of projecting a hologram onto an eyebox is that optical compensation can be encoded in the hologram (see, for example, European Patent No. 2936252, incorporated herein). 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 a vehicle windshield. Details of this approach are described in European Patent No. 2936252, and the detailed features of those systems and methods are not essential to the novel teachings of this disclosure and are merely illustrative of configurations that may benefit from the teachings of this disclosure, so they are not repeated here.

[0139] control device This disclosure is also compatible with optical configurations including a control device (e.g., an optical shutter device) for controlling the delivery of light from an optical channeling hologram to a viewer. A holographic projector may further include a control device arranged to control the delivery of an angular channel to an eyebox position. UK Patent Application 2108456.1, filed on 14 June 2021 and incorporated herein by reference, discloses at least one waveguide pupil dilator and control device. Readers will understand from at least this prior disclosure that the optical configuration of the control device is essentially based on the user's eyebox position and is compatible with any hologram calculation method that realizes optical channeling as described herein. The control device can be said to be an optical shutter or aperture device. An optical shutter device comprises a 1D array of apertures or windows, each aperture or window being able to be independently switched between a light-transmitting state and a light-blocking state to control the delivery of the holographic optical channel and its replica to the eyebox. Each aperture or window may comprise a plurality of liquid crystal cells or pixels.

[0140] A virtual replica of a waveguide or a display device formed by a waveguide. Figure 6 shows an example of visualization of an "extended modulator" or "virtual surface" with a 3D array containing a hologram formed on a display device and multiple replicas of the hologram formed by waveguides.

[0141] As described above with reference to Figure 4, the one-dimensional waveguide 408 can be positioned to enlarge the exit pupil of the display system. The display system includes a display device 402 that displays a hologram, which is output from the “reflection” point B0 of the waveguide 408. Furthermore, the waveguide forms multiple replicas of the hologram at their respective “reflection” points B1 to B8 along its longitudinal direction, corresponding to the direction of pupil dilation. As shown in Figure 4, the multiple replicas can be linearly extrapolated to the corresponding multiple replicas or virtual display devices 402'. This process corresponds to the step of “unfolding” the optical path within the waveguide, and the rays of the replicas are extrapolated to the “virtual surface” without internal reflection within the waveguide. Thus, the light of the enlarged exit pupil can be considered to originate from a virtual surface (also referred to herein as the “extension modulator”) containing the display device 402 and the replica display device 402'.

[0142] The method for calculating the hologram defines a so-called "extended modulator." In this method, a display device (e.g., an LCOS SLM) is "extended" by an array of virtual replicas formed by one or more waveguide pupil dilators to form an "extended modulator" or "virtual surface" (e.g., as shown in Figure 4). For example, the display device (e.g., an LCOS SLM) is positioned at the position (0,0) of the extended modulator shown in Figure 6, and the (virtual) replicas (i.e., replica display devices) formed by two one-dimensional pupil dilators are positioned to extend to (0,2) in the first direction of pupil dilation and to (4,0) in the second direction. The direction of the optical path is indicated by arrow 601, which is perpendicular to the first and second directions of pupil dilation.

[0143] Therefore, an expanded modulator is defined as including (i) a first offset between replicas generated by a first waveguide pupil dilator (e.g., an elongated waveguide) defined by an angle (in space) and the corresponding pupil dilation direction; (ii) a second offset between replicas generated by a second waveguide pupil dilator (e.g., a planar waveguide) defined by an angle (in space) and the corresponding pupil dilation direction; (iii) a skew between the direction of the first offset and the direction of the second offset (creating a general parallelogram in Figure 6); and (iv) the optical path length (difference) between the replica of the display device and the position of the eye in the direction 601 shown in Figure 6.

[0144] Field of view of a holographic projection system Figure 7 illustrates how light from a holographic projector (e.g., part of a vehicle head-up display) in a vehicle equipped with first and second replicators (e.g., first and second replicators 520, 540) is relayed to an eyebox. In particular, the (replicated) holographic wavefront 702 is relayed from the transmission / emission surface 742 of the second replicator 540. Figure 7 shows a single ray emitted from the emission surface 742. It is clear that multiple rays are emitted simultaneously from different parts of the emission surface 742. The (replicated) holographic wavefront 702 is relayed to an optical combiner 730 (in this example, the vehicle's windshield or windshield). At least a portion of the holographic wavefront 702 is reflected by the optical combiner 730 and transmitted to the eyebox. A viewing system 710 (in this example, the user's pupil) is positioned within the eyebox to receive the light from the holographic wavefront. Holographic reconstruction can be observed from the eye box.

[0145] As described above, the challenge of how to expand the angular range of light rays propagating from the display device to pass through the pupil of the eye and form an image can be addressed by using one or more waveguide pupil dilators. Specifically, different angular portions of the image are received by the viewing system 710 in the eyebox from different replicas of the expanding modulator (see Figures 4 and 6). In this way, the viewing system 710 (in the eyebox) receives the entire field of view (not partial) of the holographic reconstruction image projected by the holographic projection system. However, one or more waveguide pupil dilators themselves do not expand the maximum field of view of the holographic projection system. In other words, the above arrangement of pupil dilators allows the viewing system 710 to receive all angular content so that a complete holographic reconstruction of the image is formed, but the total amount of available angular content does not increase, nor does the total field of view of the holographic reconstruction increase. For example, the field of view of the holographic reconstruction depends on, or is determined by, the diffraction angle of the display device of the holographic projector. In particular, the (maximum) diffraction angle of the display device imposes an upper limit on the range of angular content received by the eyebox, and therefore also imposes a maximum limit on the field of view for holographic reconstruction. This is explained in more detail in Figures 8A and 8B.

[0146] Figure 8A shows a schematic diagram of an example of a display device 840 of a holographic projection system. In this example, the display device 840 is a pixelated liquid crystal on silicon (LCoS) spatial light modulator. The display device 840 has a display area 842 in which the pixels of the display device are arranged in a regular square array. Part 810 of the display device 840 has been enlarged to more clearly show how the individual pixels 812 of the display device 840 are arranged within the array. In this example, each pixel 812 is square. The pixel pitch 820 of the display device 840 is defined as the distance between the centers of adjacent pixels 812. In this example, since the pixels 812 are square, the pixel pitch 820 is equal in the first direction (x direction) and in the second direction (y direction) perpendicular to the x direction. The (maximum) diffraction angle of the display device 840 depends on this pixel pitch. This is expressed by the following equation:

number

[0147] Figure 8B shows the maximum range of diffraction angles of the display device. The central arrow 850 represents the projection axis of the holographic projection system. In all examples, the field of view of the holographic projection system is essentially limited by or dependent on the maximum diffraction angle. For example, the field of view of a holographic projection system may be substantially equal to 2θ. This is true when there is no net expansion or contraction of the holographic wavefront formed by the display device between the display device and the eyebox. Even if there is net contraction or expansion (which, as experienced readers will understand, may expand or contract the field of view, and expand or contract the field of view relative to the maximum diffraction angle), the field of view still essentially depends on the diffraction angle of the display device 840. This fundamental limitation can make it difficult to provide a holographic projection system that can achieve the desired field of view (where a wide field of view is generally required).

[0148] One option for expanding the field of view is to reduce the pixel pitch 820 of the display device. However, as mentioned above, reducing the pixel pitch sufficiently to achieve the desired field of view is often impossible or inefficient. For example, it may not be possible to reliably manufacture a display device with a sufficiently small pixel pitch, and even if it is possible, it may increase the manufacturing cost and complexity of the display device. Furthermore, it is desirable to maintain the replica pitch between replicas of the expansion modulator (without leaving empty space between adjacent replicas). Since the replicas of the expansion modulator are replicas of the hologram displayed on the display device 840, the size of the replica corresponds to the size of the display device. Therefore, to maintain the replica pitch, the size of the display device must be maintained while reducing the pixel pitch. Thus, even if a display device with the desired small pixel pitch could be selected, the total number of pixels would need to be significantly increased to cover the corresponding total area of ​​the display device 840 with pixels. Increasing the number of pixels is usually unnecessary for achieving high-quality holographic reconstruction, but it is necessary to obtain the desired diffraction angle / field of view. Therefore, this approach to expanding the field of view may lead to the use of unnecessarily high-resolution displays. Another option for expanding the field of view is to include net reduction of the holographic wavefront. However, this method requires increasing the size of the display device in order to maintain the replica pitch of the extended modulator. In this case as well, the total number of pixels must be increased (to cover the larger display device), leading to the same problems as the aforementioned drawbacks.

[0149] Expanding the field of view Figure 9 shows a schematic cross-sectional view of an example of a part of the holographic projection system 900 according to this disclosure. The holographic projection system 900 includes a holographic wavefront redirector 950. The inventors have found that by combining the holographic wavefront redirector 950 with a specific hologram calculation method, the field of view of the holographic projection system 900 can be expanded. In particular, this unconventional holographic projection system can expand the field of view beyond the usual fundamental limits determined by the maximum diffraction angle of the display device without requiring net reduction in the holographic projection system (however, in some examples, the holographic projection system may have net expansion or reduction as a result of expansion due to other reasons, e.g., the shape of the optical combiner 730).

[0150] More specifically, Figure 9 shows the display device 940. Downstream of the display device 940 is an optical relay 906. The optical relay 906 comprises a first lens 908 and a second lens 910 located downstream of the first lens 908. In this example, the optical output of the first lens 908 is equal to the optical output of the second lens 910. Furthermore, the focal lengths of the first lens 908 and the second lens 910 are the same (equal to f, as indicated by the arrow in Figure 9). The first lens 908 comprises a front focal plane 912 and a rear focal plane 914. The second lens 910 comprises a front focal plane 916 and a rear focal plane 918. The rear focal plane 914 of the first lens 908 and the front focal plane 916 of the second lens 910 are coplanar. Therefore, this optical relay is sometimes called a "4f" system. This is because the distance between the front focal plane 912 of the first lens 908 and the back focal plane 918 of the second lens 910 is equal to four times the focal length f of the first lens 908 and the second lens 910. The display device 940 is substantially coplanar with the front focal plane 912 of the first lens 908. The holographic wavefront redirector 950 is substantially coplanar with the back focal plane 918 of the second lens 910.

[0151] In this example, the display device 940 is an LCoS spatial light modulator. The display device 940 is configured to display a sequence of holograms for each sequence of the target image. The calculation of each hologram will be described later. The display device 940 is configured to be illuminated by coherent light from a light source (e.g., laser light). The display device 940 is configured to spatially modulate the incident light according to each hologram of each image. This forms a holographic wavefront. The holographic projection system 900 is configured so that the holographic wavefront is relayed / propagated to an optical relay 906 and received sequentially by a first lens 908 and a second lens 910. The first lens 908 of the optical relay is positioned to form a holographic reconstruction 926. This holographic reconstruction 926 is substantially formed at the back focal plane 912 of the first lens 908. The second lens 910 is positioned to form a hologram 922 relayed to the back focal plane 918. The relayed hologram 922 corresponds to the display device (including the hologram of the displayed image). In this example, the holographic wavefront redirector 950 (located at the back focal plane 918) is positioned to act on / process the holographic wavefront.

[0152] The holographic projection system 900 further comprises first and second waveguides downstream of the holographic wavefront redirector 950. These waveguides are not shown in the drawings. However, it should be understood that the processed holographic wavefront is relayed from the holographic wavefront redirector 950 to the first and second waveguides, where the holographic wavefront is duplicated to form the extended modulator as described above. After duplication, the holographic projection system 900 is positioned so that the duplicated holographic wavefront is relayed to an optical combiner (e.g., a windshield or windscreen). At least a portion of the intensity of the holographic wavefront is reflected / relayed by the optical combiner and sent to the eyebox.

[0153] Figure 10 schematically illustrates the calculation of a hologram for projection by the holographic projection system 900. In this example, although not specifically shown in the figure, this calculation step is performed by the hologram engine of the holographic projection system 900.

[0154] Figure 10 shows the target image 1000. This is an image intended to be displayed / holographically reproduced in the eyebox of the holographic projection system 900. The target image 1000 consists of a left field of view 1002 (represented by the letter "L" in Figure 10) and a right field of view 1004 (represented by the letter "R" in Figure 10).

[0155] The first step performed by the hologram engine is to receive the target image 1000. The second step performed by the hologram engine is to divide the target image into a first (left) portion containing the left field of view 1002 and a second (right) portion containing the right field of view 1004. The third step performed by the hologram engine is to compute the first subhologram 1020 of the left field of view 1002 of the (divided) target image and the second subhologram 1022 of the right field of view 1004 of the (divided) target image. In this example, the hologram engine is configured to divide the first subhologram into a plurality of first strips 1021 or to compute a plurality of first strips 1021. Each first strip 1021 contains diffraction content or holographic content. Between each first strip 1021 are empty strips 1025 of non-holographic or non-diffraction content. The hologram engine is further configured to divide the second subhologram into multiple second strips 1023 or to calculate to include multiple second strips 1023. Each second strip 1023 contains diffraction content or holographic content. Between each first strip 1023 are empty strips 1027 containing non-holographic content or non-diffraction content. A fourth step performed by the hologram engine is to spatially interlace the first subhologram 1020 and the second subhologram 1022 to form a hologram 1030. The hologram 1030 is constructed by alternating the first strip 1023 of the first subhologram 1020 and the second strip 1025 of the second subhologram 1022. In particular, the hologram engine is configured such that each empty strip 1025 (of the first subhologram 1020) is filled with the corresponding second strip 1025 of the second subhologram 1022, and each empty strip 1027 of the second subhologram 1022 is filled with the corresponding first strip 1023 of the first hologram 1020. In other words, in this example, spatial interlacing essentially involves superimposing the first subhologram 1020 and the second subhologram 1022.In this example, the width (x-direction) of the first strip 1023 and the second strip 1027 are each 0.5 mm. The hologram engine is further configured to output the hologram 1030 to the display device 940. The holographic projection system 900 is configured to drive the display device 940 to display the hologram 1030.

[0156] Figure 11 shows a cross-sectional view of the holographic wavefront redirector 950 in the xz plane. In this example, the holographic wavefront redirector 950 is composed of a prism array 1102. Each prism in the prism array 1102 is made of a transparent material with a refractive index greater than 1. The prism array 1102 consists of a first subset of prisms 1104 and a second subset of prisms 1106. In Figure 11, each prism in the first subset of prisms 1104 is shown with vertical shading. Each prism in the first subset of prisms 1104 can be said to form a first redirection region. In Figure 11, each prism in the second subset of prisms 1106 is shown with horizontal shading. Each prism in the second subset of prisms 1106 can be said to form a second redirection region. Each prism in the prism array 1102 has an input surface 1108 positioned to receive light and an output surface 1110 (substantially opposite the input surface 1108) positioned to output light that has been deflected relative to the light received at the input surface. Specifically, each prism / each first redirection region of the first prism subset 1104 is positioned to deflect light received at a first deflection angle with respect to the Z axis, as shown in Figure 9. Each prism / each second redirection region of the second prism subset 1106 is positioned to deflect light received at a second deflection angle with respect to the Z axis. In this example, the first and second deflection angles are equal in magnitude but opposite in direction. Each deflection angle exists only in the xz plane. The first deflection angle is counterclockwise (see Figure 9), and the second deflection angle is clockwise. In Figure 9, the light incident on and processed (bent) by the first prism subset 1104 is shaded vertically. The light that enters the second prism subset 1106 and is processed (blinded) is shaded horizontally.

[0157] As described above, the holographic wavefront redirector 950 is coplane with the back focal plane 918 of the second lens 910 of the optical relay 906. The holographic wavefront can be said to substantially form the relay hologram 922 at this position. The relay hologram 922 substantially corresponds to the hologram displayed on the display device 940. Therefore, when the hologram 1030 is displayed on the display device, the relay hologram 922 has a corresponding striped appearance, with the strips 1023 of the first subhologram and the strips 1027 of the second subhologram spatially interlaced. These stripes 1023 and 1027 are arranged alternately. The prism array 1102 of the holographic wavefront redirector 950 is arranged such that the input surface of each prism in the first prism subset 1104 is optically coupled to the (first) strip 1021 of the first subhologram (of the relayed hologram), and the input surface of each prism in the second prism subset 1106 is optically coupled to the (second) strip 1125 of the second subhologram (of the relayed hologram). In other words, light from a holographic wavefront spatially modulated according to the first subhologram is receivable by the first prism subset 1104, and light from a holographic wavefront spatially modulated according to the second subhologram is receivable by the second prism subset 1106. Due to the position of the holographic wavefront redirector 950 in the system, the light associated with different subholograms may be substantially spatially separated into the first and second strips, respectively, and these strips may not substantially overlap (at the back focal plane 918). Therefore, at this position, the holographic wavefront redirector 950 can process / deflect the light associated with different subholograms in different ways. Specifically, the light associated with the first subhologram is deflected at a first deflection angle, and the light associated with the second subhologram is deflected at a second deflection angle.

[0158] The effect of the holographic wavefront redirector 950 (in combination with the "stripe" hologram) is to expand the field of view of the holographic projection system 900. In some examples, the holographic wavefront redirector 950 can double the field of view of the holographic projection system 900 (compared to the corresponding holographic projection system without the redirector 950). Thus, the field of view can be expanded beyond the (maximum) diffraction angle of the display device 950 (for example, the field of view can be expanded to twice the maximum diffraction angle of the display device 950). This is illustrated in relation to Figure 12.

[0159] Figure 12 is a schematic cross-sectional view of the holographic wavefront redirector 950 in the xz plane. The solid line in Figure 12 represents the angular range 1202 over which light is emitted from the holographic wavefront redirector 950 after the first portion of the holographic wavefront has been deflected at the first deflection angle and the second portion of the holographic wavefront has been deflected at the second deflection angle (as described above). The first angular range 1204 consists mainly of light from the first subhologram. The second angular range 1206 consists mainly of light from the second subhologram. The dotted line in Figure 12 represents the (maximum) diffraction angle of the display device 950. Figure 12 shows how the angular range 1202 is substantially expanded with respect to the diffraction angle 2θ of the display device 950. Specifically, since both of the first angular subranges 1204 are substantially equal to the maximum diffraction angle of the display device 950, the holographic wavefront redirector 950 doubles the angular range over which light is emitted. This expands the field of view of the holographic projection system 900 (for example, by twice as much).

[0160] Figure 13 schematically illustrates the effect of the holographic wavefront redirector 950 on the holographic reconstruction formed by the holographic projection system 900 (and the field of view of system 900).

[0161] The left side of Figure 13 is a representation 1302 of the holographic reconstruction 926 formed on the back focal plane 914 by the first lens 908. At this point, the field of view of the holographic reconstruction 926 is entirely dependent on the display device 950 (specifically, the pixel pitch of the display device 950) and the wavelength of light incident upon it. For example, the field of view of the holographic reconstruction 926 can be 6 degrees. The hologram 1030 is calculated to compensate for the presence of the holographic wavefront redirector 950. Therefore, in the (intermediate) holographic reconstruction 926, the reconstructed image of the left field of view 1002 of the target image overlaps with the right field of view 1004 of the target image. Thus, in representation 1302 of Figure 13, "L" and "R" overlap. In other words, the 6-degree field of view of the holographic reconstruction 926 is filled with the overlapping reconstructed images of the left field of view 1002 and the right field of view 1004 of the target image.

[0162] The right side of Figure 13 shows the holographic reconstruction image 1304 of the target image visible from the eyebox of system 900 (i.e., after the holographic wavefront has been processed by the holographic wavefront redirector). At this point, the holographic wavefront redirector redirects the appropriate portion of the holographic wavefront so that the holographic reconstruction image in the left field of view 1002 is adjacent to the holographic reconstruction image in the right field of view 1004. Each reconstructed image occupies / fills a 6-degree field of view, and the entire field of view of the holographic reconstruction image visible in the eyebox has been expanded / increased / doubled to 12 degrees by the holographic wavefront redirector.

[0163] The inventors recognized that spatial interlacing of the first and second subholograms is a crucial element in achieving a wider field of view (beyond the diffraction angle of the display device 950). Different subsets of zones on the holographic wavefront redirector deflect light at different angles. Therefore, not all zones / regions on the holographic wavefront redirector emit light at all angles. This can result in dark bands in the holographic reconstructed image if the viewing system / user does not receive content at all angles at a particular eyebox position. The inventors recognized that spatial interlacing significantly reduces the risk of dark bands. The inventors found that spatially interlacing subhologram bands that are narrow enough (e.g., 1 meter) that the viewing system cannot distinguish individual bands is particularly effective in minimizing / eliminating dark bands and other related artifacts that may be visible to the naked eye. To the viewing system / eye, it may appear as if all angle content is radiated from all zones of the holographic wavefront redirector.

[0164] In the example above, the target image is divided into two parts 1002 and 1004. Two subholograms are calculated and spatially interlaced to form hologram 1030. The holographic wavefront redirector consists of subsets of two corresponding prism / redirection regions. However, it will be obvious to those skilled in the art that this is merely illustrative. In particular, the target image can also be divided into three or more parts (e.g., three parts). A corresponding number of subholograms are calculated and spatially interlaced (e.g., three subholograms). The holographic wavefront redirector is provided with a number of subsets of prism / redirection regions corresponding to the number of subholograms, with each subset arranged to deflect light at different discrete angles (e.g., three subsets and three different deflection angles). Those skilled in the art will see that in examples where the target image is divided into two or more parts, the field of view can be expanded even further than in the example above. For example, dividing the target image into three parts expands the field of view of the system threefold. This is shown in Figure 14.

[0165] Figure 14 shows the target image 1400. This is the image intended to be visible / holographically reconstructed in the eyebox of the holographic projection system 900. The target image 1400 consists of the left field of view 1402 (represented by the letter "L" in Figure 14), the right field of view 1404 (represented by the letter "R" in Figure 14), and the intermediate field of view 1406 between the left field of view 1402 and the right field of view 1404 (represented by the letter "M" in Figure 14).

[0166] The first step performed by the hologram engine is to receive the target image 1400. The second step performed by the hologram engine is to divide the target image into a first (left) portion including the left field of view 1402, a second (right) portion including the right field of view 1404, and an intermediate portion including the intermediate field of view 1406. The third step performed by the hologram engine is to compute the first subhologram 1420 of the left field of view 1402 of the (divided) target image, the second subhologram 1422 of the right field of view 1404 of the (divided) target image, and the third subhologram 1430 of the intermediate field of view 1406 of the (divided) target image. In this example, the hologram engine is configured to either divide the first subhologram into multiple first strips 1421 or compute to contain multiple first strips 1421. Each first strip 1421 contains diffraction content or hologram content. Between each first strip 1421, there is an empty strip 1425 containing non-holographic or non-diffraction content. The hologram engine is further configured to divide the second subhologram 1422 into multiple second strips 1423 or to calculate to include multiple second strips 1423. Each second strip 1423 contains diffraction or holographic content. Between each first strip 1423, there is an empty strip 1427 containing non-holographic or non-diffraction content. The hologram engine is further configured to divide the third subhologram 1430 into multiple third strips 1431 or to calculate to include multiple third strips 1431. Each third strip 1431 contains diffraction or holographic content. Between each third strip 1431, there is an empty strip 1435 that does not contain holograms or diffraction effects. Compared to the example in Figure 10, the widths of the empty strips 1425, 1427, and 1435 in Figure 14 are relatively wider (specifically, twice the width of the corresponding empty strips in Figure 10, and twice the width of the first, second, and third strips 1421, 1423, and 1431 that exhibit diffraction effects).This allows three subholograms to be spatially interlaced instead of two. The fourth step performed by the hologram engine is to spatially interlace the first, second, and third subholograms 1420, 1422, and 1430 to form hologram 1440. Hologram 1440 consists of, in an alternating configuration, a first strip 1421 (of the first subhologram 1420), a second strip 1423 (of the second subhologram 1422), and a third strip 1431 (of the third subhologram 1430). Specifically, the hologram engine is positioned so that each empty strip 1425 (of the first subhologram 1420) is filled with the second strip 1423 of the second subhologram 1422 and the third strip 1431 of the third subhologram 1430, respectively. The other empty strips 1435 and 1427 are similarly filled with the diffraction content / strips of the other subholograms. In other words, in this example, spatial interlacing essentially involves superimposing the first, second, and third subholograms 1420, 1422, and 1430. In this example, the width (x-direction) of the first, second, and third strips 1421, 1423, and 1431 is 0.5 mm each. The hologram engine is further configured to output the hologram 1440 to the display device 940. The holographic projection system 900 is configured to drive the display device 940 to display the hologram 1440.

[0167] Figure 15 shows a cross-sectional view of a second embodiment of the holographic wavefront redirector 1550 in the xz plane, used with the hologram 1440 of Figure 14. In this embodiment, the holographic wavefront redirector 1550 comprises a prism array 1502. Each prism in the prism array 1502 is formed of a transparent material with a refractive index greater than 1. The prism array 1502 comprises a first subset of prisms 1504, a second subset of prisms 1506, and a third subset of prisms 1528. Each prism in the first subset of prisms 1504 is represented by vertical shading in Figure 15. Each prism in the first subset of prisms 1504 can be said to form a first redirection region. In Figure 15, each prism in the second subset of prisms 1506 is represented by horizontal shading. Each prism in the second subset of prisms 1506 can be said to form a second redirection region. In Figure 15, each prism in the third prism subset 1528 is represented by a dark shade containing a white dot. Each prism in the third prism subset 1506 can be said to form a third redirection region. Each prism in the prism array 1502 has an input surface 1508 positioned to receive light and an output surface 1510 (approximately opposite the input surface 1508) positioned to output light that has been deflected relative to the light received at the input surface. Specifically, each prism / each first redirection region in the first prism subset 1504 is positioned to deflect the incident light at a first deflection angle with respect to the Z axis. Each prism / each second redirection region in the second prism subset 1506 is positioned to deflect the incident light at a second deflection angle with respect to the Z axis. Each prism / each third redirection region in the third prism subset 1528 is positioned to deflect the incident light at a third deflection angle with respect to the Z axis. In this example, the first and second deflection angles are equal in magnitude but opposite in direction. The third deflection angle is zero. Therefore, the three deflection angles are all distinct. Each deflection angle lies only in the xz plane. The first deflection angle is counterclockwise (see Figure 15), and the second deflection angle is clockwise. In Figure 15, the light incident on the first prism subset 1504 and processed (deflected) is shaded vertically.Light incident on the second prism subset 1506 and processed (blinded) is shaded laterally. Light incident on the third prism subset 1528 and processed (blinded) is shown as a dark shade consisting of white dots.

[0168] Similar to the holographic wavefront redirector 950, if the holographic wavefront redirector 1550 is part of a holographic projection system (such as the system shown in Figure 9), the holographic wavefront redirector 1550 is coplanar with the back focal plane 918 of the second lens 910 of the optical relay 906. The holographic wavefront can be said to substantially form the relayed hologram 922 at this position. The relayed hologram 922 substantially corresponds to the hologram displayed on the display device 940. Thus, when the hologram 1440 is displayed on the display device, the relayed hologram has a corresponding striped appearance, with the strip 1421 of the first subhologram spatially interlaced with the strip 1423 of the second subhologram and the strip 1431 of the third subhologram, and the strips 1421, 1423, and 1431 arranged alternately. The prism array 1502 of the holographic wavefront redirector 1550 is arranged such that the input surface of each prism in the first prism subset 1504 is optically coupled to the (first) strip 1421 of the first subhologram (of the relay hologram). The input surface of each prism in the second prism subset 1506 is optically coupled to the (second) strip 1423 of the second subhologram (of the relay hologram), and the input surface of each prism in the third prism subset 1528 is optically coupled to the (third) strip 1431 of the third subhologram (of the relay hologram). In other words, light from a holographic wavefront spatially modulated according to the first subhologram is received or receivable by the first prism subset 1504, and light spatially modulated according to the second subhologram is received or receivable by the second prism subset 1506. The light, spatially modulated according to the third subhologram, is then received or made receivable by the third prism subset 1528. Depending on the position of the holographic wavefront redirector 1550 in the system, the light associated with different subholograms may be spatially substantially separated into first and second strips, respectively, which may not substantially overlap (at the back focal plane 918).Therefore, at this position, the holographic wavefront redirector 1550 can process / bend the light associated with different subholograms in different ways. Specifically, the light associated with the first subhologram is deflected at a first deflection angle, the light associated with the second subhologram is deflected at a second deflection angle, and the light associated with the third subhologram is deflected at a third deflection angle (as shown in Figure 15).

[0169] The effect of the holographic wavefront redirector 1550 (in combination with the "stripe" hologram 1440) is to expand the field of view of the holographic projection system 900. In some examples, the holographic wavefront redirector 1550 can triple the field of view of the holographic projection system 900 (compared to the corresponding holographic projection system without the redirector 1550). Thus, the field of view can be expanded beyond the (maximum) diffraction angle of the display device 1550 (for example, the field of view can be expanded to three times the maximum diffraction angle of the display device 950).

[0170] Figure 16 schematically illustrates the effect of the holographic wavefront redirector 1550 on the holographic reconstruction formed by the holographic projection system 900 (and the field of view of the system 900).

[0171] The left side of Figure 16 shows the representation 1602 of the holographic reconstruction formed on the back focal plane 914 by the first lens 908 when the hologram 1440 is displayed on the system's display device 940. At this point, the field of view of the holographic reconstruction depends on the display device 950 (specifically, the pixel pitch of the display device 950) and the wavelength of light incident on it. For example, the field of view of the holographic reconstruction 926 is 6 degrees. The hologram 1440 is calculated to compensate for the presence of the holographic wavefront redirector 1550. Therefore, in the (intermediate) holographic reconstruction 926, the reconstruction of the left field of view 1402 of the target image overlaps with the right field of view 1404 and the central field of view 1406 of the target image. Thus, in representation 1602 of Figure 16, "L", "R", and "M" overlap. In other words, the 6-degree field of view of the holographic reconstruction 926 is filled with reconstructed images where the left, right, and center fields of view 1402, 1404, and 1406 of the target image overlap.

[0172] The right side of Figure 16 shows the holographic reconstruction image 1604 of the target image visible from the eyebox of system 900 (i.e., after the holographic wavefront has been processed by the holographic wavefront redirector 1550). At this point, the holographic wavefront redirector has redirected the appropriate portion of the holographic wavefront, so that the holographic reconstruction of the left field of view 1402 is adjacent to the holographic reconstruction image of the central field of view 1406, and the holographic reconstruction image of the central field of view 1406 is adjacent to the right field of view 1404. Each reconstructed image occupies a 6-degree field of view, and the entire field of view of the holographic reconstruction image visible in the eyebox has been expanded (increased) (3x) to 18 degrees by the holographic wavefront redirector.

[0173] In the example above, the holographic wavefront redirector comprises a prism array that deflects light based on refraction. Those skilled in the art will understand that this is merely one example and that there are other options for providing different zones on the optical component that deflect incident light at different angles. For example, deflection can be achieved by diffraction. For example, the holographic wavefront redirector may comprise a diffractive optical element (DOE). In some examples, the holographic wavefront redirector may comprise multiple diffraction gratings.

[0174] In the example above, the holographic wavefront redirector is positioned to process the relayed hologram. However, experienced readers will understand that this is merely one example, and the holographic wavefront redirector can be positioned on or adjacent to the display device, or even provided as a function of the display device.

[0175] Additional features The methods and processes described herein can be incorporated into a computer-readable medium. The term “computer-readable medium” includes media configured to store data temporarily or permanently, such as random access memory (RAM), read-only memory (ROM), buffer memory, flash memory, and cache memory. The term “computer-readable medium” is also interpreted to include any medium, or combination of media, on which instructions for execution by a machine can be stored. These instructions, when executed by one or more processors, cause the machine to execute one or more of the methods described herein, either in whole or in part.

[0176] The term “computer-readable medium” also includes cloud-based storage systems. The term “computer-readable medium” includes, but is not limited to, one or more tangible, non-temporary data repositories (such as data volumes), including solid-state memory chips, optical discs, magnetic discs, or any suitable combination thereof. In some embodiments, execution instructions may be transmitted via carrier media. Examples of such carrier media include temporary media (such as propagating signals that transmit instructions).

[0177] It will be apparent to those skilled in the art that various modifications and changes can be made without departing from the scope of the appended claims. This disclosure covers all modifications and changes within the scope of the appended claims and their equivalents.

Claims

1. The holographic projection system It is a hologram engine, Having received the first sub-hologram and the second sub-hologram, The system includes a hologram engine arranged to display the hologram on a display device by spatially interlacing the first and second sub-holograms to form a hologram, The system further comprises a wavefront redirector positioned on or substantially adjacent to the hologram or a relay copy of the hologram, wherein the wavefront redirector comprises a plurality of first redirect regions optically coupled to the first subhologram and a plurality of second redirect regions optically coupled to the second subhologram. A holographic projection system in which each of the first redirect regions is arranged to deflect the received light by a first deflection angle with respect to the propagation axis of the system, and each of the second redirect regions is arranged to deflect the received light by a second deflection angle with respect to the propagation axis.

2. The holographic projection system according to claim 1, wherein each first and second redirection region is arranged such that it has an angular amount of 1 / 20 degree or less in the first direction.

3. The holographic projection system according to claim 1 or 2, wherein each first and second redirection region has a width in the first direction of 1 millimeter or less, and optionally 0.5 millimeters or less.

4. The holographic projection system according to any one of claims 1 to 3, wherein the wavefront redirector is arranged to increase the field of view of the system by at least two times, and optionally at least three times.

5. The holographic projection system according to any one of claims 1 to 4, wherein the hologram engine is further arranged to spatially interlace the first and second subholograms by separating the first subhologram into a plurality of first strips and the second subhologram into a plurality of second strips, and spatially interlacing the plurality of first strips with the plurality of second strips.

6. The holographic projection system according to claim 5, wherein each of the first redirect regions is optically coupled to a corresponding first strip of the first subhologram, and each of the second redirect regions is optically coupled to a corresponding second strip of the second subhologram.

7. The holographic projection system according to any one of claims 1 to 6, wherein the holographic projector is arranged to spatially modulate light according to the hologram to form a holographic wavefront that forms a holographic reconstruction of an image visible from the eye box.

8. The holographic projection system according to claim 7, wherein the wavefront redirector is arranged such that the holographic reconstruction visible from the eyebox includes a holographic reconstruction of a first portion of the image substantially adjacent to the holographic reconstruction of a second portion of the image.

9. A holographic projection system according to any one of claims 1 to 8, wherein the wavefront redirector is arranged to receive the holographic wavefront, and the holographic wavefront includes a plurality of first portions spatially modulated according to the first subhologram and a plurality of second portions spatially modulated according to the second subhologram, and the wavefront redirector is arranged such that each first redirect region receives the first portion of the holographic wavefront and each second redirect region receives the second portion of the holographic wavefront.

10. A holographic projection system according to any one of claims 1 to 9, wherein a first portion of the target image is a first (e.g., left) field of view, and a second portion of the target image is a second (e.g., right) field of view.

11. The holographic projection system according to any one of claims 1 to 10, further comprising a display device arranged to display the hologram, wherein the wavefront redirector is arranged to expand the field of view of the system to be greater than the maximum diffraction angle of the display device.

12. The holographic projection system according to any one of claims 1 to 11, wherein the first deflection angle is equal to and opposite to the second deflection angle.

13. The holographic projection system according to any one of claims 1 to 12, wherein the wavefront redirector comprises an array of prisms, and each prism forms a redirection region of the wavefront redirector.

14. The holographic projection system according to claim 13, wherein each prism comprises an input surface configured to receive a portion of the holographic wavefront and an output surface configured to output a corresponding portion of the holographic wavefront, and the wavefront redirector is configured such that a first angle between the input surface and the output surface of a first subset of the prism is different from a second angle between the input surface and the output surface of a second subset of the prism.

15. The holographic projection system according to any one of claims 1 to 14, further comprising an optical repeater including two lenses arranged in cooperation to receive a holographic wavefront and form a repeat copy of the hologram, wherein the repeat copy of the hologram is an image of the hologram displayed on a display device and formed in a first plane.

16. The holographic projection system according to claim 15, wherein the wavefront redirector is positioned in the first plane.

17. The holographic projection system according to claim 15 or 16, wherein the optical repeater comprises a filter positioned in the intermediate plane between the two lenses, the filter being configured to receive and filter the holographic wavefront of a non-principal diffraction order.

18. A hologram engine for a holographic projection system equipped with a display device for displaying holograms, wherein the hologram engine is The target image is divided into at least a first part and a second part, The first subhologram of the first part of the target image and the second subhologram of the second part of the target image are calculated. The first and second sub-holograms are arranged to be spatially interlaced to form a hologram. Hologram engine.

19. A wavefront redirector for a holographic projection system that spatially modulates light according to a hologram to form a holographic wavefront, wherein the hologram includes a first subhologram of a first portion of a target image and a second subhologram of a second portion of the target image, the first and second subholograms are spatially interlaced, and the wavefront redirector, A plurality of first redirect regions for optically coupling to the first subhologram, It comprises a plurality of second redirect regions for optically coupling to the second subhologram, A wavefront redirector in which each of the first redirect regions is arranged to deflect the received light at a first deflection angle with respect to the propagation axis of the system, each of the second redirect regions is arranged to deflect the received light at a second deflection angle with respect to the propagation axis, and the wavefront redirector is arranged to expand the field of view of the holographic wavefront formed by the hologram.

20. A method for expanding the field of view of a holographic projection system, wherein the method is The steps include receiving a first sub-hologram of the first part of the target image and a second sub-hologram of the second part of the target image, The steps of forming a hologram by spatially interlacing the first and second sub-holograms, A step of receiving light in a plurality of first redirect regions of a wavefront redirector, wherein the first redirect regions are optically coupled to the first subhologram, and the wavefront redirector is positioned in relation to the hologram or a relay copy of the hologram, or substantially adjacent to it. The steps include receiving light in a plurality of second redirection regions of the wavefront redirector, wherein the second redirection regions are optically coupled to the second subhologram, A method wherein each of the first redirect regions is arranged to deflect the received light at a first deflection angle with respect to the propagation axis of the system, each of the second redirect regions is arranged to deflect the received light at a second deflection angle with respect to the propagation axis, and the wavefront redirector is arranged to expand the field of view of the system.

21. A method for calculating a hologram, wherein the method is A step of dividing the target image into at least a first part and a second part, A step of calculating a first subhologram of the first part of the target image and a second subhologram of the second part of the target image, A method comprising the step of forming a hologram by spatially interlacing the first and second subholograms.

22. A method for processing a holographic wavefront formed by spatially modulating light according to a hologram, wherein the hologram includes a first subhologram of a first portion of a target image and a second subhologram of a second portion of the target image, the first and second subholograms are spatially interlaced, and the method is A step of receiving light in a plurality of first redirection regions of a wavefront redirector, wherein the first redirection regions are optically coupled to the first subhologram, A step of receiving light in a plurality of second redirection regions of the wavefront redirector, wherein the second redirection regions are optically coupled to the second subhologram, A method wherein each of the first redirect regions is arranged to deflect the received light at a first deflection angle with respect to the propagation axis of the system, each of the second redirect regions is arranged to deflect the received light at a second deflection angle with respect to the propagation axis, and the wavefront redirector is arranged to expand the field of view of the system.

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