Eyebox targeting using image duplication combiner

Abstract

A method for displaying a light field of an object using an image duplication combiner is described. The method includes determining a light field of the object to be displayed at a viewing position, determining a transfer function describing the propagation of light through the image duplication combiner between the viewing position and an input position proximate an input surface of the image duplication combiner, determining an input light field by applying the determined transfer function to the light field of the object, and displaying the input light field at the input position. A display system for displaying the light field of the object is also described.

Description

[Technical Field]

[0001] The present invention uses an image duplication combiner Target Light Field The present invention relates to a method and system for generating and displaying computer-generated holography (CGH). [Background technology]

[0002] Display systems capable of showing images with a continuous depth range are collectively referred to as Right Field Such displays are known as CGH technology or so-called 4D Right Field Either technique may be widely used. Both techniques typically result in a display with a rather small eyebox. As used herein, "eyebox" defines the location of the pupil through which an image can be seen, i.e., the volume within which a viewer's pupil can be positioned to view an image from an image source. To view an image, the viewer's pupil must be located within the eyebox, which may not be much larger than the pupil itself. This presents a challenge in aligning the eyebox with the viewer's pupil.

[0003] Some display systems involve mechanical adjustments to physically move the eyebox and align it with the viewer's pupils, such as adjusting the interpupillary distance (IPD) on a head-mounted display or mechanically adjusting the position of a head-up display so the viewer can see it. Other displays are custom-made for specific users, such as the Focals 1.0 marketed by North®, which is designed to align the display system's eyebox with the viewer's pupils through a custom fitting procedure. Such hardware methods are typically not scalable or require significant effort on the part of the viewer to accurately align the eyebox with the pupil. Using a display system with multiple users also requires time-consuming readjustments or is simply not possible.

[0004] Another approach is to enlarge the eyebox using an image duplication combiner, also known as a waveguide combiner. This enlarges the eyebox provided by the image source by creating multiple spatially separated copies of the image. This allows the viewer's pupils to be positioned over a larger area and still be able to see the complete image. However, image duplication combiners suffer from image quality degradation due to issues such as focal spread.

[0005] It would be desirable to provide an improved method for aligning the eyebox of a display with the pupil of a viewer. Summary of the Invention

[0006] According to a first aspect of the present invention, a display is displayed at a viewing position. Target Light Field determining a transfer function describing the propagation of light through the image duplication combiner between a viewing position and an input position proximate an input surface of the image duplication combiner; and Target Light Field By applying Right Field and input to the input position. Right Field and displaying the image using an image duplication combiner. Target Light Field A method for displaying is provided.

[0007] The transfer function may be determined in any suitable manner. In some examples, the transfer function may be calculated or otherwise determined using analytical and / or numerical methods based on knowledge of the image duplication combiner characteristics, the viewing position, and the input position. In other examples, the transfer function may be determined by looking up or using a previously determined transfer function for a given combination of input position, viewing position, and image duplication combiner characteristics.

[0008] Unlike conventional image duplication combiners, Right Field Rather than generating multiple copies without knowledge of the viewing position, Target Light Field The characteristics of the image duplication combiner are determined as follows: Target Light Field However, the inputs that have taken different paths through the image duplication combiner Right Field This allows the input Right Field By changing Target Light Field The position of the image can be adjusted in place. Other copies are still formed by the image replication waveguide, but are not seen, so these other copies Target Light Field It doesn't matter whether it accurately reflects

[0009] The method requires no hardware adjustments or custom fittings. Target Light Field to allow adjustment in place (although these may still be present as part of the viewing system, for example to provide a comfortable fit rather than align the eyebox, or to provide a wide range of adjustment in a way that provides fine adjustment).

[0010] The propagation of light through an optical system may be determined by a transfer function. The transfer function may be an optical transfer function that defines the propagation of a coherent wavefront through the optical system. Alternatively, the transfer function may be a function of the inputs 4d entering and leaving the optical system, respectively. Right Field and output 4d Right Field The mapping between rays may have the form

[0011] Through an optical system Right Field The result of propagating the Right Field Thus, the term "propagating" may be used synonymously with determining a transfer function and applying a transfer function.

[0012] Propagation may be between an input location and a viewing location, sometimes referred to as "forward propagation," or may be in a direction toward the viewing location. Propagation may also be between a viewing location and an input location, sometimes referred to as "reverse propagation" or "back-propagating," or may be in a direction away from the viewing location. This is because the direction of propagation of light rays is reversible. Propagation may be performed in any suitable manner, such as by Fourier transform or ray tracing techniques.

[0013] The method comprises: combining multiple copies of a ray of light incident on an input face of the image duplication combiner; Target Light Field and input Right Field This can improve image quality, as the additional copies are perceived by the viewer as noise or image artifacts.

[0014] Not all rays with multiple copies may be filtered out. For example, the method may filter out multiple copies of a ray incident on the input face of the image duplication combiner such that: Target Light Field and determining that at least two copies of the light beam are substantially equivalent, and inputting at least two copies of the light beam. Right Field If the light rays are substantially identical, the light rays can be kept without adversely affecting image quality. Examples of substantially identical light rays include light rays that have traveled by different paths but have substantially the same path length.

[0015] In some instances, Target Light Field Rays for which multiple copies exist may be selectively retained or discarded. For example, copies of rays that are determined to be substantially equivalent may be retained and others discarded.

[0016] The method is: Target Light Field The rays propagated back from the input Right Field determining that the value does not exist in Target Light FieldThis may include excluding light rays from the image, which may improve image quality.

[0017] The rays Target Light Field or enter Right Field When a ray is excluded from the image, the method may include increasing the power of another ray to compensate for the excluded ray. This may improve the perceived image quality compared to simply excluding the ray. For example, this may help to maintain a more accurate brightness.

[0018] Target Light Field may be at least as large as the viewer's pupil at the viewing position, in which case the possibility of receiving stray light from other copies is reduced, improving image quality.

[0019] Target Light Field If the area of ​​is less than the area of ​​the viewer's pupil, the method then uses elements of zero amplitude to Target Light Field Expanding the result Target Light Field may include having an area at least the size of the pupil. The zero amplitude element acts to reduce erratic light rays from reaching the viewer's pupil, improving image quality.

[0020] Target Light Field Determining the Target Light Field into a set of plane waves and padding with zero amplitude elements Target Light Field and applying the method to the boundary of the Target Light Field Padding the boundaries of reduces potentially spurious spillover from tiled copies during propagation.

[0021] The method may include determining a position of a viewer's pupil, and the viewing position is the determined position of the viewer's pupil. Determining the position may occur dynamically during viewing, such as by using an eye-tracking system, may be part of an initial calibration process, or may be performed at the viewer's request.

[0022] Target Light Field is a set of multiple separate audiovisual systems, each with its own viewing position. Right Field and the method may comprise: Target Light Field Determine multiple separate Right Field Each input of Right Field and multiple separate Right Field Each input of Right Field For example, combining separate Right Field which in turn allows for binocular viewing from a single display. Right Field Combining may be done in any suitable manner, such as by addition.

[0023] The input location may be a surface that is not parallel to the input face of the image duplication combiner. This may improve the uniformity of the image as seen by the eye by minimizing the gap between the exit pupil images. Furthermore, this may improve the resolution of the image as seen by the eye by minimizing the optical path length between adjacent exit pupil images, so that coherence may be maintained across the entire exit pupil image even if the illumination source of the image generation unit has a low coherence length. The surface of the input location may be a surface that is not parallel to the desired Target Light Field It may be planar or curved, depending on the input surface. There are several ways in which the surface at the input location can be made non-parallel to the input face of the image duplication combiner. This includes one or more of tilting, pitching, and / or skewing the input location relative to the input face, and rotating the surface at the input location about an axis parallel to an axis in the plane of the input face.

[0024] When the input location is on a surface that is not parallel to the input surface, the method Right Field or as part of the transfer function to compensate for distortion introduced by the non-parallel relationship. For example, the pre-distortion may be such that the center output replica appears substantially distortion-free when viewed at the listening position.

[0025] In the above method, the input Right Field is a holographic field or fourth dimension Right Field It may be.

[0026] input Right Field is holographic Right Field and when the listening position is substantially constant, the input Right Field Determining Λ may use a predetermined constant transfer function based on the propagation between the viewing position and the input position. Target Light Field Input from Right Field It has been found that the part of the transformation to is constant, reducing the computational load and processing resources.

[0027] Determining the transfer function is done by input Right Field The rays received from at least two different copies of Target Light Field For example, Target Light Field Some part of the image may be formed from rays from one copy, Target Light Field Another part of may be formed from rays from another copy. Target Light Field allows for regions that span more than one copy, resulting in Target Light Field can be in any position. In some examples, light rays from at least two different replicas coincide at a single point on the virtual object. In some examples, light rays from at least two different replicas coincide at a single virtual object point.

[0028] According to a second aspect, there is provided an image duplication combiner, an image generation unit arranged to provide an input to the image duplication combiner, and a method according to the first aspect described above, with or without any of the optional features similarly described, for providing an input to the image generation unit. Right Field and a processing system configured to cause the display of the

[0029] According to a third aspect, an image duplication combiner having an input surface and an output surface, and an input device near the input surface. Right Field A display system is provided that includes a display unit for providing a desired image for viewing and a processing system. Right Field and determining a desired position for the viewing position. Right Field and the input position close to the input surface by propagating through an image duplication combiner. Right Field and input to the display unit. Right Field Any of the method features of the first aspect may be applied to this third aspect.

[0030] Either the second or third embodiment may include an eye-tracking system arranged to provide data indicative of viewing position to the processing system.

[0031] In either the second or third embodiment, the image duplication combiner is adjusted so that all copies have substantially the same output power for the same input power. This is because the light rays pass through the image duplication combiner Target Light Field This means that the perceived brightness of the light beam is substantially the same regardless of the path it takes to the output, improving image quality. In other words, the output power is substantially the same regardless of how many times the light beam bounces within the image duplication combiner.

[0032] In either the second or third aspect, the input location may be on a surface that is not parallel to the input surface of the image duplication combiner. This may improve uniformity and resolution of the image as viewed by the eye. In either the second or third aspect, the display system may include an optical system disposed in an optical path between the image generation unit and the input surface of the image duplication combiner. The optical system receives an input from the image generation unit and Right Field is not parallel to the input surface. Right Field to the input surface. The optical system may include one or more of a diffraction grating and a prism.

[0033] In some examples, the image replication combiner may include an input coupling grating, a redirection grating, and an output coupling grating, the coupling efficiencies of the redirection grating and the output coupling grating being configured such that for a given ray combined by the input coupling grating, each ray extracted at the output coupling grating is of substantially equal intensity.

[0034] The image duplication combiner is Right Field The image may be arranged to generate multiple replicated images of the same size, with the gap between adjacent replicated images being no larger than the diameter of the viewer's pupil. A "gap" refers to the space between the replicates where there is substantially no light. For example, the replicates may be spaced apart so that there is an area between them where there is substantially no light. Having these gaps allows for a greater range (since the input light is preserved across all replicates), and ensuring that the gaps are no larger than the size of the viewer's pupil ensures that light is visible for all positions of the viewer's pupil. In some examples, the diameter of the viewer's pupil is assumed to be 4 mm, 4.5 mm, 5 mm, 5.5 mm, or 6 mm, and therefore the space between directly adjacent replicates may be 4 mm, 4.5 mm, 5 mm, 5.5 mm, or 6 mm or less.

[0035] The image duplication combiner is Right Field The phase volumes of the replicate images may be arranged to overlap only a small portion of the phase volume of the object.

[0036] The replication pitch of the image replication combiner may be greater than half the diameter of the viewer's pupil. As mentioned above, the diameter of the viewer's pupil may be assumed to be 4 mm, 4.5 mm, 5 mm, 5.5 mm, or 6 mm, and therefore the replication pitch may be greater than 2 mm, 2.25 mm, 2.5 mm, 2.75 mm, or 3 mm. Alternatively or additionally, the replication pitch of the image replication combiner may be approximately equal to the width of the input pupil.

[0037] The display system may form part of any display where an image needs to be aligned with the viewer's pupils. Examples include head-mounted displays such as augmented or virtual reality headsets, or head-up displays such as automotive head-up displays. [Brief explanation of the drawings]

[0038] [Figure 1] Schematic representation of the topological volume of a 2D light field. [Figure 2A] A further schematic representation of the topological volume of a 2D light field. [Figure 2B] 10 is a schematic representation of yet another topological volume of a 2D light field. [Figure 3] 1 is a schematic diagram of the operation of a conventional image duplication combiner; [Figure 4] 1 is an alternative schematic diagram of the operation of a conventional image duplication combiner. [Figure 5] 1 shows an exemplary scene for display. [Figure 6] 1 shows an exemplary scene displayed through a conventional display system including an image duplication combiner. [Figure 7A] FIG. 2 is a schematic diagram of a first replica produced by an exemplary image replica combiner according to the present disclosure. [Figure 7B] FIG. 10 is a schematic diagram of a second replica produced by an exemplary image replica combiner according to the present disclosure. [Figure 7C] FIG. 10 is a schematic diagram of a third replica produced by an exemplary image replica combiner according to the present disclosure. [Figure 7D] 7A-7C are schematic diagrams of an image produced by an exemplary image replica combiner according to the present disclosure, including the three replicas shown in FIGS. 7A-7C. [Figure 8] 1 is a schematic diagram of an image produced by an exemplary image duplication combiner according to the present disclosure; [Figure 9]3 is a schematic diagram of a holographic image generated by another example of an exemplary image duplication combiner according to the present disclosure. [Figure 10A] 1 illustrates a method for computing an input light field according to one embodiment. [Figure 10B] 1 illustrates another method for computing an input light field according to one embodiment. [Figure 11] 1 shows a schematic diagram of an exemplary image duplication combiner that transforms an input light field into a target light field. [Figure 12] FIG. 1 is a schematic diagram of the propagation of light rays through an image duplication combiner. [Figure 13A] 10C illustrates a first ray that does not meet the first condition for high quality image display using the method of FIG. 10A or FIG. 10B. [Figure 13B] 10C illustrates a second ray that does not meet the second condition for high quality image display using the method of FIG. 10A or FIG. 10B. [Figure 13C] 10B , which illustrates a third ray that does not meet the third condition required for high quality image display using the method of FIG. 10A or FIG. 10B . [Figure 14A] 1 shows a schematic diagram of an exemplary display system illustrating the geometry of the replicas produced by an image replica combiner. [Figure 14B] 10 shows a further schematic diagram of an exemplary display system illustrating the geometry of the replicas produced by the image replica combiner. [Figure 14C] 10 shows yet a further schematic diagram of an exemplary display system illustrating the geometry of the replicas produced by the image replica combiner. [Figure 14D] 10 shows yet a further schematic diagram of an exemplary display system illustrating the geometry of the replicas produced by the image replica combiner. [Figure 15] 10 shows a representation of exemplary paths that rays can traverse within an image duplication combiner, with the property that the same pairing of input and output rays can be achieved via multiple paths through the combiner. [Figure 16] FIG. 1 is a schematic diagram of two object light fields generated by an exemplary image duplication combiner. [Figure 17] 1 illustrates an exemplary image duplication combiner that transforms an input light field into two target light fields. [Figure 18] 18 shows an example of a copy produced by the image copy combiner of FIG. 17. [Figure 19] 1 is a schematic diagram of a display system according to one embodiment. [Figure 20] 1 shows an exemplary schematic diagram of an imaging system in which the image generation unit is tilted relative to the image duplication combiner. [Figure 21] 1 shows an example image displayed without using the techniques described herein. [Figure 22] 1 shows an exemplary image displayed using the techniques described herein. DETAILED DESCRIPTION OF THE INVENTION

[0039] An image duplication combiner increases the size of the visible area of ​​an image for a viewer. The image duplication combiner includes an input surface, also known as an input coupler or entrance pupil, for receiving light rays corresponding to the input image. The entrance pupil concept corresponds to a limiting aperture at the input of the image duplication combiner. The input surface is a coupling mechanism that couples light waves propagating from the outside into the interior of the image duplication combiner. The coupling mechanism may be, for example, an array of mirrors, an array of prisms, a diffracted photon, or a hologram. Additional possible coupling mechanisms include embedded mirrors, microprisms, surface-relief tilted gratings, surface-relief blazed gratings, surface-relief binary gratings, multi-level surface-relief gratings, thin volume holograms, thin photopolymer holograms, dispersed holographic polymer liquid crystal (H-PDLC) volume holographic couplers, thick photopolymer holograms, resonant waveguide gratings, metasurface couplers, and embedded half-tone mirrors. The image duplication combiner further includes an output surface, also known as an output coupler, for outputting light corresponding to the input image. The output face is an additional combining mechanism that may use the same technology as the input face. The image replication combiner may be fabricated from a material with a high refractive index that supports total internal reflection over a wide range of internal angles of incidence. For example, lanthanum high density flint glass, such as N-LASF46 from Schott™, has a refractive index of θ 1 at a wavelength λ = 530 nm. c = 31°. The image duplication combiner propagates waves by total internal reflection at all internal angles above the critical angle.

[0040] In one example, the image duplication combiner takes the form of a substantially planar sheet. The planar sheet may be constructed from a transparent material such as glass. In this case, one arrangement of the input and output surfaces is to position the input and output surfaces on the same side of the planar sheet so that light enters and exits the same side of the planar sheet. In another arrangement, the input and output surfaces may be positioned on opposite sides of the planar sheet. The particular arrangement may be selected based on the function of the image duplication combiner. In another example, the combiner takes the form of a non-planar sheet. Such a combiner may be used, for example, as a pair of lenses in eyeglasses. In a non-planar combiner, as described above, the input and output surfaces of the combiner may be on the same or opposite sides of the sheet depending on the function of the combiner.

[0041] A feature of the image replication combiner is that the internal rays are repeatedly split into reflected and transmitted rays. Thus, the etendue of the output ray ensemble is larger than the etendue of the input ensemble. In terms of phase space, the phase volume of possible output ray positions and angles is larger than the phase volume of possible input ray positions and momentum. The inventors have found that the desired Right Field The topological volume of the input Right Field If it is not greater than Right Field It was discovered that it was possible to generate

[0042] In one example, this is the output after propagation through a typical planar image replication combiner: Right Field The maximum effective eyebox and field of view (or more specifically, the phase volume) of Right Field The term "effective eyebox" here refers to an eyebox that is substantially free of noise and / or artifacts. This means that the effective eyebox is no larger than the field of view (or specifically the phase volume) of a 2D Right Field The different phase volumes are shown in FIG. 1, which is a schematic representation 100 of the phase volumes. FIG. 1 shows a 2D Right Field However, the concept is a 4D model with two spatial dimensions and two angular dimensions. Right FieldNote that it is easy to see how this can be extended to further dimensions such as Right Field can be considered as a 2D cross section of

[0043] A topological space is usually four-dimensional, containing two spatial and two angular dimensions. A topological space representation labels each ray passing through a given plane with a spatial coordinate (representing the point where the ray intersects the plane) and an angular coordinate (representing the direction in which the ray is traveling relative to the plane). Right Field describes the intensity of each point in this phase space. Right Field spans some volume 102 in topological space (the "topological volume"), and the output Right Field spreads into a phase volume 104 that is larger than the input due to the replication process. Due to the "replication phenomenon", the second volume 104 appears elongated along the ray position (space) axis compared to the first volume 102. The inventors have determined that the second volume 104, whose volume in phase space 106 is not larger than the first volume 102, can be targeted anywhere within the second volume 104. Target Light Field It was discovered that it is possible to generate

[0044] FIG. 2A shows the image that is incident on the input face of the image duplication combiner. Right Field 202 topological space, and the resulting output plane (i.e., output eyebox) Right Field 2 provides a schematic diagram of the topological space of 204. As in FIG. 1, for clarity, the topological volume is shown in 2D space (x, θ).

[0045] The operation of the image duplication combiner shown in Figure 2A is to combine inputs that are spatially separated in the x-dimension. Right Field Furthermore, the input Right Field The replicas are offset in the z direction from the plane of the output eyebox. Additionally, the different replicas are offset in the z direction relative to each other. This description of a basic image replica combiner is illustrated in FIG.

[0046] In the phase space representation, the displacement in z corresponds to a shear in the (x, θ) plane, and is therefore replicated in the output of Figure 2A. Right Fieldis thus sheared. The replicas are also displaced from each other in the z direction, so the degree of shearing will be shown to vary slightly for each replica. The size of the topological volume of each output replica is Right Field The image duplication combiner may have a duplication pitch chosen to minimize overlaps and gaps between the duplicated images.

[0047] Figure 2B shows the pre-distorted input signal incident on the replica combiner input face. Right Field 206. Right Field 206 may be calculated according to the methods of this disclosure. In particular, the predistortion may be chosen so that the central output replica is accurately displayed in a subset of the phase volume of the output eyebox 208. Right Field is at a chosen position within the output eyebox Target Light Field may be generated by applying a transfer function to

[0048] input Right Field 206 is calculated to produce a good quality image in one position and a poor quality image in another position. The image duplication combiner's eyebox can be aligned with the viewer's pupil to provide a high quality image without the need for custom fitting procedures or mechanical adjustments.

[0049] The above description with reference to Figures 1, 2A, and 2B describes the transformation of a 1D replicated waveguide into a 2D phase volume for simplicity. However, it should be understood that the concept can be directly transferred to a 2D replicated waveguide and a 4D phase volume. Furthermore, the concept of a 4D phase volume can be easily transferred to a hologram image and a 4D phase volume by replacing the concepts of ray direction and ray position with the concept of a range of spatial frequencies within a localized region (e.g., by replacing each ray with a Gaussian beam having the same pointing direction and position as the ray, and expanding the hologram in a basis defined by this set of Gaussian beams). Right Field can be applied to.

[0050] 3 is a schematic diagram of a conventional display system 300 with an image duplication combiner 304 to aid in understanding conventional operation and limitations. Right Field The image generation unit 302 is configured to generate an image 310, and an image duplication combiner 304 includes an input surface 306 and an output surface 308. Right Field Multiple copies of 310 are generated at output face 308. The image generation units are preferably positioned so that the exit pupil of image generation unit 302 coincides with input face 306. In Figure 3, three copies 312, 314, 316 are shown, each corresponding to light that has undergone a different number of internal reflections within image replica combiner 304.

[0051] As can be observed from Figure 3, the input Right Field Light corresponding to 310 is (by definition) focused at the exit pupil of the image generation unit 302. Right Field 3, each of the replicas 312, 314, and 316 forms part of a corresponding one of the input replicas 312, 314, and 316. As the light travels beyond the exit pupil and through the input face of the image replica combiner, it diverges. As a result, each of the replicas 312, 314, and 316 diverges upon extraction at the output face 308 of the image replica combiner 304. Thus, the pupil of the viewer's eye 324 aligned with replica 314 also receives light rays from the adjacent replicas 312 and 316. As can be further observed from FIG. 3, each of the replicas 312, 314, and 316 is located at a different horizontal position along the image replica combiner 304, and as a result, the viewer will see the light rays from the input replicas 312, 314, and 316 diverging from the pupil of the viewer's eye 324 aligned with replica 314. Right Field 310. Each of the replicates 312, 314, 316 contains the same input Right Fieldis represented by a horizontal translation relative to the figure. When the image displayed by the image generation unit 302 includes a virtual object at finite depth, a noticeable effect can be observed in the resulting replicas due to parallax; the viewer will perceive three copies (in this example) of the virtual object at different perceptible positions. This contrasts with far-field images, in which all light rays entering the image replica combiner 304 appear to emanate from a common point at infinity. Thus, the horizontal distance between successive replicas has little effect on the perceptible position of the object in the image. Due to parallax, the difference in the position of the virtual object at finite depth in each replica becomes more noticeable as the object moves closer to each pupil. That is, the perceptible effect is a function of the virtual object's distance from the pupil.

[0052] Furthermore, because each replica 312, 314, 316 results from light undergoing a different number of internal reflections before extraction, and therefore a different optical path length, each replica is perceived as having a different depth of focus. In other words, the replicas 312, 314, 316 appear at different depths and therefore have different apparent sizes. Thus, the viewer Right Field Seeing three copies of the virtual object in 310 at slightly different depths / sizes results in an unsatisfying viewing experience, known as "focal diffusion."

[0053] For example, to include depth information in an image, such as a CGH image, regions of the image (corresponding to virtual objects in the image) may need to be displayed close to the viewer. In some instances, regions of the image may need to be displayed as close as 100 mm from the viewer. As noted above, display system 300 is not sufficient to produce satisfactory images. It should be understood that unsatisfactory image quality (e.g., from duplicate images of different apparent sizes and perceived positions) applies at all depths except infinity, but has a greater impact the closer the apparent distance of the image region from the viewer. Thus, image quality at display depths in the 50 mm to 300 mm range, and even at 1 m or 2 m, may be adversely affected by unsatisfactory image quality.

[0054] Figure 4 shows the input Right Field This figure shows how a naive attempt to display an image at finite depth through an image duplication combiner results in unwanted double images, due to the focusing of light rays from a single point on a virtual object in the image. Display system 400 is the same as display system 300 shown in FIG. 3, and the reference numerals of corresponding parts begin with "4" instead of "3". Image generation unit 402 is preferably positioned so that the exit pupil of image generation unit 402 coincides with input plane 406. Right Field A cone of rays (indicated by the diagonally shaded area) from virtual object point 430 in 410 is shown filling the exit pupil of image generation unit 402. This is consistent with how conventional display systems operate.

[0055] The image replica combiner generates replicas 412, 414, and 416. Each replica is a replica at the exit pupil of the image generation unit 402. Right Field A display system 400 is shown that performs one-dimensional pupil dilation. An image duplication combiner that performs two-dimensional pupil dilation corresponds to the duplication of the input pupil and Right Field Generate a 2D grid of

[0056] Duplicated, as indicated by the horizontally shaded area Right Field Only a subset of the light rays from the replicas 416 and 414 reach the eye pupil 424 through the eyebox 426. The light rays reaching the eye pupil 424 appear to originate from different replicas 416 and 414 and diverge from two separate replica points 436 and 434 corresponding to the virtual object point 430. Thus, two separate images (i.e., "ghosts") are perceived instead of one single image. The number of ghost images can be more than two, as there is no inherent limit to the number of replicas that can be simultaneously seen by the eye pupil. Right Field Note that the diagonally shaded region of is shown cut off by the replicated pupil. While those rays do propagate from the combiner output face 408, they do not reach the eye pupil 424. For example, rays propagating from replicated point 432, which corresponds to virtual object point 430, do not reach the eye pupil 424.

[0057] In two-dimensionally replicated systems, four or more ghost images may be observed. Many image replication combiners produce a single replicated image when viewed through the pupil of the eye. Right Field The pupils overlap significantly. In this situation, more ghost images may be observed.

[0058] Figure 4 shows the situation for light rays emanating from a single point on a virtual object. Other object points generate different cones of rays that behave differently. Specifically, different subsets of the replicated rays reach the pupil of the eye.

[0059] Figure 5 shows an example scene 500 containing objects at different depths, and Figure 6 shows how this scene would appear when viewed through an image duplication combiner with the conventional display system shown in Figures 3 and 4.

[0060] Planet 502 in scene 500 is an object at infinite depth. Light rays emanating from any point on this object are collimated. Therefore, the object is expected to appear accurately when viewed through an image duplication combiner. Astronaut 504 in scene 500 is an object with finite depth. Light rays emanating from any point on this object are not collimated.

[0061] A holographic image generation unit is an example of a system that can display such a scene with objects at different depths. The displayed scene is accurate when viewed directly by the human eye, and the eye must adapt differently to see different objects.

[0062] However, scene 500, which appears accurate when viewed directly, appears inaccurate when viewed through an image duplication combiner. This is shown in FIG. 6. In scene 600, planet 602 appears accurate because it is placed at infinite depth. Astronaut 604 appears as multiple ghost images because it is placed at finite depth. This is the problem of focal spread that the example techniques described herein address.

[0063] The image duplication combiner would seem to be a poor choice for expanding the eyebox of a CGH image. However, the inventors have Right Field By controlling Right Field have discovered that positioning the lens at the viewer's pupil can address one or more of the above problems.

[0064] 7A to 7D show inputs from the image generation unit 702. Right Field 7 shows an example display system 700 illustrating how a single point in an image can be configured to display a single point in an image at a finite depth without ghost images or focus diffusion through an image duplication combiner 704.

[0065] 7A to 7C are generated by the image generation unit 702. Right FieldThe image generation unit 702 generates a cone of rays that, in this example, appear to diverge from two points 730. Right Field Neither cone of rays fills the exit pupil of the image generation unit 702, which may preferably be positioned to coincide with the input face 706 of the image duplication combiner 704. The image generation unit 702 must have the ability to control not only the positions of the virtual object point sources, but also the direction of the rays emanating from those point sources. Holographic Displays and 4D Right Field The display provides this type of control.

[0066] Figure 7A shows the input Right Field 7 shows a first replica 716 of virtual object point 710. Only the cone of rays branching from virtual object point 736, represented by the diagonally shaded area, reaches the effective eyebox 726 and eye pupil 724. Dotted lines from a second cone of rays branching from a second point, virtual object point 737, represented by the horizontally shaded area, are shown to show how the rays miss the effective eyebox 726 and eye pupil 724.

[0067] Figure 7B shows the input Right Field 7 shows a second replica 714 of virtual object point 735. In this case, only the cone of rays branching from virtual object point 735 and represented by the horizontally shaded area reaches the effective eyebox 726 and eye pupil 724. Dotted lines from the second cone of rays branching from virtual object point 734 and represented by the diagonally shaded area are shown to show how the rays miss the effective eyebox 726 and eye pupil 724.

[0068] Figure 7C shows the input Right Field 7 shows a third replica 712 of the virtual object point 733. In this case, no rays from either cone diverging from the virtual object point 733, 732 reach the effective eyebox 726 and eye pupil 724.

[0069] Figure 7D shows the combined effect of all three replicas shown in Figures 7A-7C. It can be seen that virtual object point 736 in Figure 7A and 735 in Figure 7B coincide due to the positions of the two points 730. Therefore, all light rays reaching the effective eyebox 726 and eye pupil 724 appear to diverge from a single point on the virtual object. This shows how a single point in a virtual image can be displayed without ghost images or focal diffusion. The light rays that appear to diverge from a single virtual object point include light rays from multiple replicas (in this example, the two replicas shown in Figures 7A and 7B).

[0070] Every virtual object point requires a different set of cones for that point to be displayed accurately. Right Field A process for determining is described herein.

[0071] Note that the image duplication combiner 704 shown appropriately positions the duplications to enable reconstruction of the intended image. That is, (i) the pupils of the replicated images do not overlap significantly, but (ii) do not have large gaps between their full extents. A large overlap or gap would be comparable to the diameter of the pupils of the eye. For example, the pupils of the replicated images may overlap or may be separated by gaps of less than 4 mm, less than 3 mm, less than 2 mm, less than 1 mm, or less than 0.5 mm. In general, the image duplication combiner does not have the first property because (i) the first property is not required to display a virtual object at infinity.

[0072] 8 is a schematic diagram of an exemplary arrangement 800 that addresses the ghosting or focus diffusion problem discussed above. Such an arrangement 800 allows for replicating the system 700 shown in FIG. 7D. The arrangement 800 is Right Field in the effective eyebox 806 of the combiner 802 Target Light FieldThe effective eyebox can be positioned anywhere within the volume of the addressable eyebox 808, allowing for increased freedom in pupil positioning.

[0073] input Right Field is a holographic technique in which depth information in an associated image is represented by modulation of the phase and / or amplitude of a coherent light source. Right Field Alternatively, the input Right Field is a 4D representation of the intensity of a ray in x, y, θ, φ space. Right Field It may be.

[0074] In this example, the effective eyebox 806 of the combiner 802 is located within a predetermined volume 808 that does not include any portion of the combiner 802 . Target Light Field is centered at the input at the entrance pupil 804 of the combiner 802 Right Field is located at a distance |s| from the center of the Target Light Field can be achieved without increasing the phase volume, so that Target Light Field The etendue of the input Right Field This is the same as the etendue of

[0075] Generated Input Right Field Based on Target Light Field By determining in advance where the combiner 802 will be placed, characteristics such as interpupillary distance (IPD) and vertex distance can be set in software without requiring any mechanical adjustments in the headset that includes the combiner 802. These characteristics can be set, for example, by a calibration routine using user feedback and / or can be set automatically via an eye-tracking sensor.

[0076] input Right Field is holographic Right Field When this is the case, the image generation unit (not shown) receives an input including depth information. Right FieldThe image generating unit includes an at least partially coherent light source, in this case a laser diode, configured to illuminate a light modulation element in the form of a spatial light modulator. The laser diode is, for example, a Sumitomo Electric™ SLM-RGB-T20-F-2 laser diode, although other laser diodes may be used. The RGB diode can rapidly switch between emitting different colored laser light, sequentially emitting red, green, and blue light. By modulating the laser light at different times when different colors are emitted, the appearance of a color holographic image can be created to the viewer through persistence of vision. Other examples may be black and white or may use red, green, and blue light sources simultaneously, and it should be understood that the present disclosure is not limited to any particular light source.

[0077] An exemplary spatial light modulator is the Compound Photonics (RTM) DP1080p26 microdisplay, which is configured to adjust the phase of light. By controlling the phase of light, holographic images can be produced using interference. Right Field This disclosure is not limited to any particular spatial light modulator technology or component. The holographic reconstructed image is output from the image generation unit at the final optical element.

[0078] Figure 9 shows the effective eyebox 904 Target Light Field 9 shows a portion of an exemplary optical system 900 including an image duplication combiner 902 arranged to generate a three-dimensional scene for display. Right Field H in is generated at the entrance pupil 906 of the combiner 902. As mentioned above, H in 9 can be generated by an appropriate image generation unit. From FIG. 9, it can be seen that rays corresponding to a first virtual object 908 at a first depth and a second virtual object 910 at a second depth are generated by the input Right Field H in through the image duplication combiner 902 Target Light Fieldis known to be generated at the object by determining the form it must take by backpropagating rays from Right Field H in appears on the surface as a combination of rays that do not appear to correspond to the image produced in the effective eyebox 904. However, forward propagation of rays through the image replication combiner 902 shows that the rays extracted from the combiner 902 do in fact represent the first and second virtual objects 908, 910 at the required depth. It can be seen that the rays corresponding to the first and second virtual objects 908, 910 are extracted from the combiner 902 and undergo different numbers of internal reflections within the combiner 902 before reaching the effective eyebox 904. Furthermore, Target Light Field By ensuring that the rays forming (i.e., θ) satisfy several conditions, which are explained in detail below, the eyebox visible to the aligned pupil perceives the image substantially free of spurious noise and / or artifacts (hence the eyebox is "effective").

[0079] The present disclosure provides a method for providing a desired Target Light Field (In this case, holographic Right Field H, but it should be understood that this disclosure is not limited to generating a holographic field of interest. in An exemplary process for generating an effective eyebox within an arbitrary volume in three-dimensional space is now described in more detail with respect to FIGS.

[0080] FIG. 10A shows the input as shown in FIGS. Right Field within a given volume Target Light Field 10 shows an exemplary method 1000 for converting H in teeth, Target Light Field From H through combiner 902 to H in This is the result of considering the reverse path to the position of Right Field can be determined by calculating

[0081] At block 1002, the method 1000 Target Light Field This involves determining the required position of H (i.e., the effective eyebox). This corresponds to determining the displacement vector s in FIGS. 8 and 9, which may be set according to the known positions of the viewer's pupils. For example, one or more eye-tracking sensors may be used to determine the current three-dimensional position of the center of the viewer's pupils. In this case, the eye-tracking sensors generate data indicative of the current position of the center of the viewer's pupils and relay that data to a computing device. The computing device may be configured to determine the position of H to coincide with the determined position of the center of the viewer's pupils.

[0082] In another example, the required positions may be predetermined. For example, the viewer may undergo a calibration routine, which involves the image generation unit being scanned for a series of images in various three-dimensional positions. Target Light Field The method may include configuring the device to pass through a series of Target Light Field Of Target Light Field Each time H is displayed, the computing device may ask the viewer whether the image is of acceptable quality. At the end of the calibration procedure, the computing device may determine that the position that produces the best image quality as perceived by the viewer is the position where H should be generated.

[0083] In some instances, Target Light Field teeth, Target Light Field Determining the required location of Right Field determining the required position of each of the plurality of Right Field (H1, H2, ...). This can be useful in binocular displays where only a single image generation unit and image duplication combiner are needed to generate images of an object in both of the viewer's pupils. An example of this is described in more detail with respect to Figures 16-18.

[0084] In some examples, block 1002 may be omitted and a predetermined position input may be used (eg, from the calibration process described above).

[0085] At block 1004, the method 1000 transmits a combined light beam through the combiner to an input face near the entrance pupil of the combiner at a required location. Right Field Block 1004 will now be described in detail by reference to FIG. 11, which shows an exemplary image duplication combiner 1100. The specifications of the image duplication combiner 1100 are determined by the physical requirements of the display system. For example, the image duplication combiner 1100 needs to be able to support total internal reflection over a wide range of internal incidence angles. For example, lanthanum high density flint glass, such as N-LASF46 manufactured by Schott™, has a wavelength λ=530 nm and a θ c = 31°. The image replication combiner propagates waves by total internal reflection at all internal angles of incidence above the critical angle.

[0086] The image duplication combiner 1100 receives an input corresponding to a holographic image. Right Field The combiner 1100 includes an input coupling grating 1102, also known as an input surface or input coupler, to receive the free-space wave. The input coupling grating 1102 represents a surface-relief grating such that the free-space wave is coupled into the combiner 1100 at the input coupling grating 1102 by diffraction. A surface-relief grating with a groove frequency of 2580 lines / mm can function as an input or output coupler between free space and total internal reflection in the N-LASF46. More complex surface-relief gratings can be fabricated that exhibit optical power in addition to simple diffraction from parallel, equally spaced linear grooves.

[0087] The image duplication combiner 1100 receives the input Right Field The image replication combiner 1100 further includes an output coupling grating 1106, also known as an output facet or output coupler, positioned to redirect light that undergoes internal reflection from the input coupling grating 1102 towards the output coupling grating 1106.

[0088] The image replication combiner 1100 in this example has an input coupling grating 1102, a redirection grating 1104, and an output coupling grating 1106, all on the same face. This means that all internal rays, as evidenced by the rays incident at 1110, traverse the combiner an even number of times before redirection by the redirection grating (if present) and before exiting the combiner. Other embodiments may have either or both the input coupling grating and the redirection grating on the opposite face from the output coupling grating. In these cases, internal rays may traverse the combiner an odd number of times before redirection by the redirection grating and / or before exiting the combiner.

[0089] The example in Figure 11 shows an image replication combiner operating with the incident rays to input coupler 1102 and the output rays from output coupler 1106 all on the same side of the combiner (i.e., the positive z direction). In some configurations, the incident rays can enter the combiner from the negative z direction, i.e., the side opposite where the incident rays exit the output coupler grating. The optimal choice of configuration is often determined by constraints in the overall layout of the optical system.

[0090] 11, the image duplication combiner 1100 includes a diffraction grating as the combining mechanism, but it should be understood that other types of couplers are contemplated. For example, the input coupler to the image duplication combiner may include a mirror, a prism, or a hologram. It should also be understood that other examples may use image duplication combiners of other forms, including curved or non-planar designs.

[0091] A typical image replication combiner, including a coupler in the form of a diffraction grating, such as the grating of FIG. gratingThe image replication combiner 1100 is characterized by a set of grating k vectors parameterized by (k) = (k, t), the thickness of the combiner t, and the refractive index n of the material comprising the combiner. The grating k vectors describe how the input coupling grating, redirection grating, and output coupling grating affect the light waves incident on each grating. For the exemplary image replication combiner 1100 shown in FIG. 11, the grating k vectors for each grating are: For input coupling gratings, k in =(0,-k grating ,0), In a redirection grating, k redirection =(k grating ,k grating ,0), For output coupling gratings, k out =(-k grating ,0,0).

[0092] Simply put, the input coupling grating redirects the light rays downward (towards the redirection grating in Figure 11). The redirection grating then redirects the light rays horizontally to the right, undoing the vertical redirection. Finally, the output coupling grating undoes the horizontal redirection upon extraction from the combiner.

[0093] The coupling efficiencies of the redirection and output coupling gratings 1104, 1106 can be adjusted so that for a given ray coupled in by the input coupling grating 1102, each ray extracted by the output coupling grating 1106 is of approximately equal intensity.

[0094] Furthermore, the described properties of the image duplication combiner 1100 are such that for k vectors (k x , k y For a ray incident on the input coupling grating 1102 with θ=(0,0), the ray in the combiner 1100 is given by sinθ=k grating λ / 2πn, resulting in a replication pitch (spacing between nearest inter-input pupil replications) of 2t tan θ.

[0095] In the example shown in FIG. 11, the origin of the coordinate system 1108 is the coordinate system determined in block 1002. Target Light Field By this definition, the entrance pupil of the image duplication combiner 1100 is positioned at position s relative to the determined position of H. pupil =(x pupil , y pupil , z pupil ) is located at H in can be calculated by backpropagating H (determined in block 1004) from the determined position (determined in block 1002) through combiner 1100 to the entrance pupil. Right Field H is the complex electric field strength

number

number

[0096] So, at position (x, y, z) Target Light Field H can be evaluated according to Equation 1. equation 1

number

[0097] In this case, the constraint on the integral is k min Less than or k max This ensures that H is defined so that coefficients larger than k are zero. This corresponds to restricting the field of view of the hologram. In effect, this decomposition is performed as a discrete Fourier transform, with integrals replaced by sums over discrete values ​​of k. Since this results in a tiled representation of H, zeros can be padded into H before the Fourier decomposition to avoid spurious spillover from the tiled copies during propagation.

[0098] From the origin of the coordinate system 1108, k z0 The path value k to the output coupling grating 1106 is denoted by z is, as mentioned above, the relation

number

[0099] In the output coupling grating 1106, the k vector k out A grating effect represented by Right Field The x and y components of wave vector k are k+k out and then replace it with the components of

number

[0100] Propagating a distance along the z-axis through the image replication combiner 1100 Right Field does not undergo any internal reflections. This situation can be understood by considering an equivalent situation where we have an image duplication combiner 1200 with thickness t and k in This discussion will be given with reference to FIG. 12, which shows an example of a ray propagating through a coupling grating with a grating k vector parameterized by: Ray 1210, which has a component in the z direction, is incident on the coupling grating in a direction perpendicular to the grating. Ray 1210 is coupled into combiner 1200 by the coupling grating. Upon entering combiner 1200, ray 1210 is deflected at an angle θ with respect to the lower surface normal of combiner 1200, and is given by sinθ=k in λ / 2πn, where θ is the angle between the ray and the normal to the lower surface of combiner 1200. The ray travels a distance t in the z direction and a distance t tan θ in the negative x direction, at which point it undergoes a first internal reflection off the interior surface of combiner 1200 according to the law of reflection. In reality, the ray returns toward the surface from which it entered combiner 1200, but mathematically this is equivalent to the ray continuing along the positive z direction into a virtual volume 1202 that is stacked on top of combiner 1200 and has the same geometric properties as combiner 1200. As shown in FIG. 12 , the virtual ray continuing in the positive z direction is shown as a dotted arrow passing through successive virtual volumes 1202, 1204, and 1206. Each time a virtual ray crosses a horizontal internal boundary of a virtual volume 1202-1206, the virtual ray is equivalent to a real ray that undergoes internal reflection within combiner 1200. In other words, a virtual ray that crosses 2n horizontal boundaries is equivalent to a real ray that traverses the combiner 2n times. Thus, after 2n traversals of the combiner, the ray has traveled a distance of 2t in the z direction.

[0101] Applying this logic to the example shown in Figure 11, if a ray travels a distance of -2n along the z axis, x After traveling t, it is confirmed that the beam reaches the redirection grating 1104. At the redirection grating 1104, the effect of the grating is expressed as k vectors k redirection Represented by Right Field This is evaluated here at the redirection grating and is denoted k1. Right Field The x and y components of the wave vector are k'+k redirection Substitute with components from k z1 As noted above with respect to the relationship

number

[0102] Right Field Then, the distance along the z axis is -2n y t propagates, where n y is the number of internal traversals of the combiner 1100 between the input coupling grating 1102 and the redirection grating 1104, using the same logic as shown in Figure 12. For the input coupling grating 1102, the effect of the grating is expressed as k vector k in Represented by Right Field This is evaluated here at the input coupling grating and is denoted k2 Right Field The x and y components of the wave vector are k''+k in Substitute with components from k z1 As noted above with respect to the relationship

number

[0103] The above process is Target Light Field H propagates only in the z direction to the entrance pupil of the combiner 1100. Right Field To complete the propagation of Right Field is the distance (x pupil , y pupil , 0) is propagated.

[0104] As explained so far, the propagation of a set of plane waves from the viewer's pupil has been considered. The set of plane waves is propagated along a defined path (set by the number of internal reflections between each diffraction grating) through combiner 1100 to the entrance pupil of combiner 1100. For a complete solution, n x , n y It is necessary to sum all possible routes through the combiner 1100, which is limited to the value of H in have energies above some threshold within the entrance pupil of combiner 1100.

[0105] The total number of possible routes is the coherence length of the illumination, and the number of different n x , n y The light may be coherent or incoherent, depending on factors such as the difference in optical path length between the two paths.

[0106] If the coherence length is much larger than the difference in path lengths, the contributions sum coherently: the complex amplitudes of the different paths add together and the interference effects are different n x , n y It is possible between contributions.

[0107] If the coherence length is much smaller than the difference in path lengths, the contributions sum incoherently. The complex amplitudes of the different paths are effectively multiplied by a time-varying random phase factor before summing. The phase factor can change quickly compared to the perception time of the human eye, so the contributions of different n x , n y No interference effects between the contributions are observed.

[0108] H in the coherent case in The complete solution is given by Equation 2. equation 2

number

[0109] The prime coordinates x', y', z' are the coordinates of the prime coordinate system 1110 whose origin is the displacement vector s pupil is defined relative to the entrance pupil so as to be related to the origin of the non-prime coordinate system 1108 by:

[0110] As mentioned above, Equation 2 is given by Target Light Field To generate H, the required Right Field The calculation can be performed in software, in which case the integral becomes the sum. The calculation is typically performed when new information is added, such as a new video frame or new information on a static display. Target Light Field This could be done every time an H needs to be displayed.

[0111] The transfer function determined by the above calculation is Right Field The rays received from at least two different copies of Target Light Field In other words, Target Light Field A portion of the H may be formed from one replica, and another portion of the H may be formed from another replica. This can be seen in Figure 7D, where the light reaching the viewer's pupil 724 includes light from different replicas of the virtual object 730.

[0112] In the above example, the input coupler 1102 and the output coupler 1106 share the same face of the combiner 1100. If the input coupler and the output coupler are located on opposite faces of the combiner, then: (i) Target Light Field and (ii) the point on the output coupler combiner that faces closest to the center of the entrance pupil, s pupil It is necessary to define

[0113] In systems where the input coupler, redirection coupler, and output coupler do not share the same combiner facet, the optical path length between couplers may be defined by an odd number of traversals of the combiner. In this situation, the exponent (n x +1 / 2) to n x , and / or (n y +1 / 2) to n y You may need to replace it with .

[0114] Referring back to FIG. 10A, at block 1006, the method 1000 proceeds to step 1006. Target Light Field This involves calculating H, i.e. Target Light Field The characteristics of H are determined to generate the desired image at the determined location. In the example shown in Figure 9, determining H is used to generate first and second images 908, 910 at their respective depths. Right Field Those skilled in the art will recognize techniques for determining this image.

[0115] It should be understood that blocks 1002 and 1006 may occur in any particular order. Target Light Field Determining the location of Target Light Field However, first Target Light Field After calculating Target Light Field It is also possible to determine the position where the

[0116] At block 1008, the method 1000 calculates the optical transfer function by Target Light Field By applying H to the input Right Field H in That is, using Equation 2, H in Calculate.

[0117] At block 1010, the method 1000 receives input using a suitable display. Right Field H in This includes displaying the Target Light Field is holographic Right FieldIf so, then H in is holographic Right Field In the example shown in FIG. 11, H is a holographic Right Field Therefore, H in is generated at the entrance pupil of the combiner 1100. in corresponds to Right Field H includes using an image generation unit to generate a 4D Right Field If so, then H in is a proper 4D Right Field One such suitable 4D generator can be generated using Right Field The generator is described in Lanman et al., "Near-eye light field displays," available at https: / / research.nvidia.com / sites / default / files / pubs / 2013-11_Near-Eye-Light-Field / NVIDIA-NELD.pdf, published November 1, 2013, and first archived by web.archive.org on November 14, 2020. Lanman 4D Right Field The generator consists of an OLED microdisplay and an intermediate microlens array between the microdisplay and the viewer's eye.

[0118] Referring back to Equation 2, this can be rewritten as Equation 3: equation 3

number

number

[0119] That is, the order of summation and integration can be reversed, and the additional propagation term can be absorbed into a newly defined set of Fourier coefficients. In particular, the summation part of Equation 4 is the optical transfer function, H in Since it can be evaluated independently of the Fourier coefficients of , pupil needs to be recalculated only if changes. This is done (at block 1002) Target Light Field This is particularly useful when the determined position of changes infrequently or is completely fixed as a function of time. In these cases, the number of calculations is reduced and processing efficiency is improved.

[0120] input Right Field and Target Light Field The planes of the input couplers and the output couplers of the combiner may be parallel to each other, but not to each other. Right Field and Target Light Field is rotated about the x-axis by an angle α and about the y-axis by an angle β, the rotated wave vector k′ in the combiner's local coordinate system is defined as follows:

number

[0121] In this case, Equation 4 is modified by replacing the wave vector k in the sum term with the rotated wave vector k', as shown in Equation 5. equation 5

number

[0122] 11, the image duplication combiner 1100 takes the form of a rectangular planar sheet. However, the present disclosure is not limited to image duplication combiners having any particular shape. In particular, the method 1000 is applicable when the combiner is non-planar. In this case, the image duplication combiner 1100 is configured to transmit light through the combiner. Target Light Field By backpropagating the input Right FieldCalculating H for the example described with respect to FIG. in is calculated in a similar manner, but with consideration given to the particular geometry of the combiner.

[0123] Additionally, input Right Field Calculating Right Field Although the present disclosure is described with respect to calculating 4D images of a desired object at a determined location, the present disclosure is not tied to holography. Right Field Input 4D to generate Right Field It is possible to calculate 4D Right Field specifies the light intensity as a function of x, y, θ, and φ, where x, y are the spatial coordinates at the location of the center of the viewer's pupil, and θ, φ are the angular coordinates of the light at that location. Propagation through a combiner (such as combiner 1100) entails a remapping of the 4D phase space, and each ray with values ​​of x, y, θ, and φ in H is represented by H in has a unique corresponding ray with values ​​x', y', θ', φ' at θ. This mapping can be determined using standard ray tracing techniques. However, typical Right Field The display is coarsely sampled in x, y and finely sampled in θ, φ, as these set the apparent resolution of the display. H in This sparse sampling of x, y at can appear as image artifacts at H, hence the holographic Right Field may have higher image quality.

[0124] The method 1000 Target Light Field Input required to generate Right FieldIn some examples, the desired position may change as a function of time. For example, one or more eye-tracking sensors may be used to determine the required position of H in block 1002 based on the real-time position of the viewer's pupils. The eye-tracking sensors may generate live data about the current position of the viewer's pupils and relay this to a computing device. The computing device may then Target Light Field may be determined such that s(t) needs to be generated at the current position of the center of the viewer's pupil. In practice, the viewer may move their eyes based on several factors, such as changes in the position of the object of interest within the currently displayed image, changes in brightness of the displayed image, and the user's own movement as they view the image. In this case, the required position of H is a function of time, s(t), and the determined required position of H changes correspondingly as a function of time.

[0125] In other examples, Target Light Field The determined position may be based on an initial calibration. Target Light Field The advantage of displaying is that the expression in Equation 4 only needs to be calculated once, since it depends only on terms evaluated at a determined fixed position. This makes the process more efficient, allowing for faster frame rates and / or higher resolutions with the same processing resources or power-saving operation. The disadvantage of this is that the displayed Target Light Field Since the position of the image is fixed, the movement of the viewer's pupils Target Light Field may not overlap with the current area occupied by the viewer's pupil.

[0126] FIG. 10B shows the input as shown in FIGS. Right Field within a given volume Target Light Field 10 shows another exemplary method 1020 for converting an input Right Field H inAfter displaying Target Light Field This includes determining whether the position of Target Light Field It may be determined that should be displayed at a different position. This is because, for example, the viewer's pupils may move, resulting in Target Light Field It will be based on the determination that the eye should be repositioned to the new pupil position.

[0127] In block 1012, Right Field If it is determined that the position of should be changed, method 1020 Target Light Field Returning to block 1002, an updated position of is determined, followed by determining a transfer function for that updated position in block 1004.

[0128] In block 1012, Right Field If it is determined that the position of should not be changed, then the method 1020 Target Light Field The process returns to block 1006 where the is (re)calculated to be displayed in the required position.

[0129] Thus, in the method of Figure 10B, the decision at block 1012 determines whether the transfer function should be updated due to a change in viewing position. Target Light Field may also vary with successive loops of method 1020. For example, Target Light Field If the position of changes, the input Right Field may be recalculated in block 1008, where the new transfer function is determined in block 1004, Target Light Field Alternatively, or in addition, if there is a change in data for display, Right Field For example, the display system may be configured to display video content such that each loop of method 1020 (either 1002-1012 or 1006-1012) may correspond to the display of a single frame of video content. Each time method 1020 proceeds to block 1006, a corresponding new Target Light Field At block 1008, there may be a new frame with input Right Field is the transfer function Target Light Field The transfer function is calculated by applying Target Light Field The method 1020 may be recalculated based on changes in the position of Target Light Field But it's not just changed frame by frame, Target Light Field This can be used in a video update loop where the position of may change as the viewing position changes.

[0130] In another example, the display system includes: Target Light Field However, a static image may be displayed so that it cannot change between these loops, in which case some examples would be H and H in blocks 1006 and 1008. in However, the calculation of Right Field teeth, Target Light Field may still be recalculated based on changes in the position of

[0131] input Right Field It should be understood that does not have to coincide with the physical input face of the image duplication combiner. For example, an input Right Field If you set it as your target, you will get a satisfactory Target Light Field In this context, "close" means that the input Right Field The specific distances may include being coincident with the input surface or being a specific distance of the input field from the input surface. In examples, the specific distances may be 5 mm, 10 mm, 20 mm, 30 mm, and 40 mm. Target Light Field For example, one consideration in a display system is Target Light Field The goal is to ensure that the physical area of ​​the lens closely matches the area of ​​the human pupil. Target Light Field It may depend on the area of ​​the input Right Field The closer to the input surface, the more the image generation unit will be affected by the diffusion of the light rays as they cross the combiner. Target Light Field The area of ​​is large. Right Field The closer to the input surface, the more on the other side of the image generation unit, Target Light Field The area of ​​becomes smaller.

[0132] Corresponding Input Right Field through combiner 1100 to calculate Target Light Field The backpropagation of such an input Right Field This disclosure is not limited to any particular method for performing such a calculation. Method 1000 involves passing the light through the combiner to the entrance pupil of the combiner. Target Light Field By backpropagating the input Right Field It explains how to calculate the input Right Field is also from the entrance pupil Target Light Field To the position Right Field For example, forward propagation is calculated from a given input field as Target Light Field This can be used in conjunction with an inverse problem solver to determine the input Right Field is the desired Target Light Field may undergo some form of iteration to generate , since for a given number of internal reflections, the propagation is strictly reversible and therefore the direction of propagation is arbitrary.

[0133] input Right Field Regardless of how is determined, Target Light Field To improve the resulting image quality, one or more of three conditions may be applied, which will now be described with respect to Figures 13A, 13B, and 13C.

[0134] The first condition is H in For each ray propagating forward from the combiner, we require that there be only one ray contributing to H. As a result of the properties of the combiner, multiple copies are extracted at the combiner's output coupler. It is possible for two or more copies of a ray entering the combiner's entrance pupil to form part of H. The result of additional unintended rays forming H appears as image noise or artifacts. An example of a ray that does not satisfy this condition is shown in FIG. 13A. In this configuration, it can be seen that a single incident ray 1302 to the combiner 1300 causes two rays 1304, 1306 to be extracted from the combiner 1300 and form part of H.

[0135] In some instances, the first condition does not apply to copies of rays that are substantially equivalent. Substantially equivalent rays include rays that have substantially the same path length but follow different routes through the combiner. This is not the situation shown in FIG. 13A, where each ray 1304, 1306 has a different path length. This is further explained below with respect to FIG. 15.

[0136] The second condition requires that H be defined over an area large enough to completely cover the viewer's pupil. If the area of ​​H is smaller than the viewer's pupil, then replicated rays that do not form H may be received by the viewer's pupil, resulting in undefined rays seen by the viewer appearing as image noise or artifacts. To overcome this, H may be defined to span at least the area of ​​the viewer's pupil, for example, at least 4 mm or at least 6 mm in diameter (corresponding to the typical size of a light-adapted pupil), or at least 8 mm or at least 10 mm in diameter (corresponding to the typical size of a dark-adapted, i.e., scotopic, pupil). Alternatively, H may be defined to span at least the area of ​​the viewer's pupil, for example, at least 4 mm or at least 6 mm in diameter (corresponding to the typical size of a light-adapted, i.e., scotopic, pupil). Right Field If H is smaller than the area of ​​the viewer's pupil, H may be defined to be zero for some boundary area of ​​this region to reduce the required etendue. An example of a ray 1308 that does not satisfy the second condition is shown in FIG. 13B. In this example, H is defined to occupy an area smaller than the area of ​​the viewer's pupil. Consequently, the incident ray 1308 does not form part of H, but has a copy 1310 that intersects with the viewer's pupil.

[0137] The third condition is that for each ray backpropagated from H, in If this is not the case, then H in Since there is no possibility of generating a ray with a ray starting from H, there is a ray missing from H. An example of a counterpropagated ray 1312 that does not satisfy the third condition is shown in FIG. 13C. In this example, a counterpropagating ray 1312 entering the output coupler of combiner 1300 causes H inA reflected ray of light that does not form a

[0138] For any process implementing method 1000 shown in FIG. 10A , the above three conditions must be substantially met to achieve satisfactory results. While it is not important that all conditions be met for every ray, rays that do not meet these conditions will be displayed as errors in the image, so the total percentage of non-compliant rays (rays that do not meet all three conditions) should be small, such as less than 10%, less than 5%, less than 1%, less than 0.5%, or less than 0.1%. In some cases, if the inclusion of a particular ray would violate one (or more) of the conditions, that ray may be selected to be excluded from H. If this is the case, other rays in H may optionally be selected to have increased intensity to compensate for the exclusion of the non-compliant ray.

[0139] Enter according to Method 1000 or an alternative method Right Field By calculating the above three conditions, we can obtain the image duplication combiner in any volume. Target Light Field Not only can you place Target Light Field The image is displayed with reduced spurious noise and artifacts. In particular, problems typically associated with displaying near-field images using image duplication combiners, such as focal spread, are reduced to reduce the desired image quality displayed to the viewer. Right Field To generate the input Right Field Clearly calculate the desired Right Field This is avoided by ensuring that the input Right Field is first calculated and displayed at the combiner entrance pupil Target Light Field This is in contrast to the usual method of generating

[0140] Now, going back to Figure 2B, with the above understanding in mind, within a given region of the phase space at the output, Target Light Field So that the following is achieved: Right Fieldcan be chosen at the input. For this to be achieved with the greatest success, the phase volumes of each separate replica should overlap as little as possible (this corresponds indirectly to the requirement shown in FIG. 13A that for a given ray at the input, there should be only one ray at the output). Furthermore, the combined phase volumes of the separate replicas should cover as large a fraction of the specified output phase volume 208 as possible (this corresponds to the requirement shown in FIG. 13C that every ray at the output must have a corresponding ray at the input).

[0141] As explained, these conditions do not have to be met exactly, and slight deviations from these conditions can be compensated for by excluding certain rays and replacing them with conforming rays originating from the same object point.

[0142] The geometry of how the separate replicas appear in phase space is a property of the image replication combiner. To generally comply with the above conditions, it is clear that the image replication combiner must be designed to provide optimal tiling of the replicated output in phase space. Specifically, the image replication combiner must be designed such that 1) a high percentage of the volume in phase space required for the output phase volume of interest is spanned by the combined phase volume of the separate replicas, and 2) a low percentage of the volume in phase space required for the output phase volume of interest is covered by multiple overlapping separate replicas. In some instances, the combiner must be designed such that the combined phase volume of the separate replicas spans as much as 75%, 80%, 90%, 95%, and 99% of the volume in phase space required for the output phase volume of interest, provided that a sufficiently high percentage is Right Field and the characteristics of the user's pupil size. In certain cases, the acceptable percentage may be as low as 5% (e.g., in a sparsely sampled Right Fieldand for highly dilated pupils). The volume in phase space covered by the multiple overlapping separate replicas may be between 50% and 10% of the subject's output phase volume in some examples, such as 50%, 40%, 30%, 20%, or 10%. The volume in phase space covered by the multiple overlapping separate replicas may be lower in other examples, such as 5% or 1% of the subject's output phase volume.

[0143] We will now use Figures 14A, 14B, 14C, and 14D to explain how the geometry of an image duplication combiner can be considered for compliance with the above conditions. While Figures 14A, 14B, 14C, and 14D show duplication along one axis, it is easy to see how this concept can be extended to duplication in two directions.

[0144] An ideal situation is described above, where most of the phase volume of interest spans with minimal overlap, and little or no correction for missing or overlapping rays needs to be applied. However, it may not be possible or efficient to create an image generation unit with a sufficiently large phase volume, nor to create an image replica combiner with no gaps between replicas, and therefore the preferred design may need to take practical limitations into account.

[0145] Referring to FIG. 14A, an input consisting only of rays traveling in the direction of normal incidence Right Field 1410 is shown. This input Right Field is replicated multiple times as 1412, 1414, 1416. Multiple replicas of a single ray are extracted from the image replication combiner 1404 at the output plane 1408 at a specific spacing 1418, called the replication pitch. If the width of the limiting aperture 1406 is smaller than the replication pitch 1418, there will be gaps 1420 between the replicas and no ray will be present at this angle of incidence. Note that the limiting aperture of the system 1400 can be the exit pupil of the image generation unit 1402 or the input pupil 1406 of the image replication combiner 1404, regardless of which is smaller (although typically both will be designed to be approximately the same size).

[0146] The replica pitch 1418, and therefore the gap between replicas 1420, is also a function of the angle at which light is incident on the image replica combiner 1404. Referring to FIG. 14B, an input consisting only of light rays at an incident angle shown at 1428 Right Field In the case of 1426 , the replica pitch 1430 is maximized, resulting in the largest gap between replicas shown as 1432 .

[0147] Not only is the position of the viewer's eye 1424 shown, but also the size of the viewer's pupil, shown at 1422. If the viewer's pupil width is larger than the maximum gap between replicas, then at least one ray from every angle will enter the eye, and any ray that cannot be represented due to the gap between replicas can be compensated for by increasing the intensity of other rays.

[0148] Referring to FIG. 14C, a different input consisting only of rays at an incident angle shown at 1436 Right Field In the case of 1434, the replica pitch 1438 is minimized, resulting in a minimum gap between replicas shown as 1440. In certain embodiments, such as the embodiment shown in Figure 14D, the minimum replica pitch 1442 may be smaller than the limiting aperture 1406. This causes the minimum gap 1444 between replicas to be negative, meaning that there is an overlap, rather than a gap, between adjacent replicas.

[0149] In either case, if the minimum replication pitch is greater than the width of the viewer's pupil, the viewer will see only one replication of any given ray. If the viewer's pupil size is greater than the minimum replication pitch, then rays with multiple replications entering the pupil will be filtered out and may be compensated for by increased intensity of other rays. This allows the maximum pupil size to be approximately twice the minimum replication pitch.

[0150] Because the width of a viewer's pupil depends on lighting conditions and varies from person to person, a range of possible pupil sizes must be considered. The specific design of the image generation unit and image duplication combiner depends on the specified range of viewer pupil sizes with which the system is designed to work.

[0151] A typical application might be designed for nominal viewer pupil widths ranging from 2 to 8 mm. Meeting these conditions would require the maximum gap between replicas to be less than the minimum viewer pupil size of 2 mm, and the minimum replica pitch to be 4 mm or greater (i.e., greater than half the maximum viewer pupil size). The output of such an image replica combiner, while providing acceptable performance across a range of pupil sizes, may only span a relatively small percentage of the subject's phase volume.

[0152] A specific non-limiting example of a waveguide may have the following parameters (with reference to elements of Figures 14A-14D): The limiting aperture 1406 is 5.5 mm and the field of view is 18 degrees.

[0153] The waveguide has a glass substrate with a thickness of 4.0 mm and a refractive index of 2.0. The input coupling grating has a replica pitch 1418 that matches the limiting aperture width 1406 of 5.5 mm when the angles of incidence 1428, 1436 are zero.

[0154] At an angle of incidence of +9° 1428 (FIG. 14B), the replica pitch is 6.7 mm, resulting in a maximum gap between replicas 1432 of 1.2 mm, which is less than the typical minimum diameter of the pupil of the human eye.

[0155] At an incidence angle 1436 of -9° (Figure 14D), the minimum replication pitch 1442 is 4.5 mm. This distance is suitable for an ambient luminance of 1 Cd / m 2 , which is larger than the diameter of the pupil of a typical human eye.

[0156] These parameters consider one-dimensional replication along the same axis as the perimetry, but they do not change significantly for two-dimensional replication combiners, which one skilled in the art can derive for themselves.

[0157] Other designs of 2D image replication combiners may be designed such that the replicated phase volumes are tessellated on a non-rectilinear grid.

[0158] For image replication combiner designs in which the same pairing of input and output rays can be achieved via multiple separate paths through the combiner (e.g., as in a WaveOptics® waveguide), the condition of non-overlapping phase volumes may be ignored for overlapping phase volumes that are nearly identical to one another. An example of how this type of combiner design works is shown in FIG. 15. In particular, FIG. 15 shows a representation of separate paths through such a combiner and how rays travel along different paths but arrive at the same point 1508 on the output face of the combiner. For example, rays traveling along two separate paths through the combiner, labeled 1502 and 1504, arrive at the same point on or within the combiner. A ray extracted at point 1508 will have traveled along both paths 1502 and 1504 (as well as other possible paths through the combiner).

[0159] In some cases, such as with the image duplication combiner of Figure 15, the input Right Field The rays received from at least two different copies of Target Light Field The rays coincide at a single point in H. This is acceptable because they generally followed the same path length through the combiner and are therefore substantially equivalent. In some instances, the ray received at the single point in H at a first angle may be from a first replica, and the ray received at the single point in H at a second angle may be from a second replica.

[0160] The light rays that follow different paths but are substantially equivalent are not limited to the combiner configuration shown in FIG.

[0161] Binocular Imaging The above description is based on the desired Right Field Input for generating H Right Field where H corresponds to a single continuous pupil. In practice, a binocular image can be formed by providing two displays, one for each pupil. Such a solution would be well suited to conventional glasses in the form of a head-mounted display, for example.

[0162] The above principle can be extended to allow multiple images to be displayed at any position relative to the image duplication combiner when they appear at the entrance pupil of the combiner. Target Light Field Inputs that form Right Field In particular, the process described above for the backpropagated pupil is still applicable, and H is now calculated using multiple backpropagated Right Field This is the sum of the two Target Light Field This may be useful in head-mounted and head-up displays, where only one image generation unit and one image duplication combiner are needed to generate an image, displayed at a position corresponding to the position of the viewer's pupils. Such a head-mounted display may, for example, include a single visor that covers both eyes, while a head-up display may include a single screen, such as a windscreen, that is viewed by both eyes.

[0163] FIG. 16 shows the combined beam at the entrance pupil 1602 of the combiner 1600. Right Field However, the combiner 1600 has two effective eyeboxes 1604 and 1606. Target Light Field, H1, and H2. A first effective eyebox 1604 is located a distance |s1| from the center of the entrance pupil 1602 of the combiner 1600. A second effective eyebox 1606 is located a distance |s2| from the center of the entrance pupil 1602 of the combiner 1600, where s1 and s2 are displacement vectors from the centers of the effective eyeboxes 1604, 1606 to the center of the entrance pupil 1602. Choosing s1 and s2 to align with the pupils of a viewer allows this arrangement to form part of a binocular display, allowing for a single input Right Field H in is a desired volume positioned relative to the combiner 1600. Right Field may be calculated to produce H1 and H2 and displayed at the entrance pupil 1602 of the combiner 1600.

[0164] Multiple Target Light Field If the combined etendue of (H1, H2, ...) is less than the etendue available at H, then a solution may still exist. However, a more complex geometry means that the combiner that simultaneously satisfies the three conditions described above with reference to Figures 13A, 13B, and 13C for all pupils is more complex.

[0165] Figure 17 shows a single input Right Field from Target Light FieldFIG. 17 shows an exemplary image duplication combiner 1700, including a grating geometry that can be used to generate H1 and H2. Combiner 1700 includes an input coupling grating 1702, a redirection grating 1704, and an output coupling grating 1706 with coupling mechanisms similar to the corresponding gratings 1102, 1104, and 1106 of combiner 1100. However, the area of ​​the entrance pupil of combiner 1700 is twice the area of ​​the target pupil with the same field of view (the area of ​​H1 and H2, respectively) to achieve the required étendue. In this case, this is achieved with a 2:1 portrait aspect ratio, assuming the viewer's eyes are horizontal relative to combiner 1700. In FIG. 17, for example, both the line combining H1 and H2 and combiner 1700 are aligned along the x-direction.

[0166] Method 1000 Target Light Field Input for display at the entrance pupil of the combiner to generate H1 and H2 Right Field can be applied to this arrangement to calculate: Target Light Field A required position for each of H1 and H2 can be determined relative to the combiner, and the required position may be the determined position of the viewer's pupil so that H1 and H2 are positioned to align with the pupil.

[0167] Displayed where needed Target Light Field H1 and H2 are calculated. As mentioned above, calculating H1 and H2 can occur before determining their required positions. Right Field is then transmitted through the combiner to the combiner entrance pupil. Target Light Field H1 and H2 are computed by backpropagating H1 and H2. This can be accomplished as described above with reference to FIG. 11, taking into account more complex geometries of combiners (such as combiner 1700). Right Field can then be displayed at the combiner's entrance pupil using an appropriate display method.

[0168] To improve the viewing experience for binocular viewing, the three conditions described above with reference to FIGS. 13A, 13B, and 13C should be at least approximately met. This can be achieved by the design of the combiner. For example, the diffraction grating of the combiner can be rotated around a line perpendicular to the surface of the combiner and positioned at the center of the combiner. In the example of FIG. 17, the diffraction gratings 1702, 1704, and 1706 of the combiner 1700 are rotated with respect to the diffraction gratings 1102, 1104, and 1106. As a result, the replicas form a grid that is rotated with respect to the combiner 1700 compared to the replicas generated by the combiner 1100. In particular, the orientation of the diffraction gratings is rotated by an angle set during the design of the combiner 1700 to be the arctangent (pupil diameter / IPD) for a given IPD. Typical values ​​for IPD for most human adults range from 50 to 75 mm, with research finding the average IPD for adults to be approximately 63 mm. When the viewer's eye line is horizontal with respect to the combiner 1700, this maximizes the number of rays that meet the three required conditions above. That is, considering all copies of a ray that passes through H1, a minimum number of unintended rays also pass through H2, and vice versa.

[0169] This example is now further explained by reference to FIG. 18 , which shows an array of replicas 1800 produced by combiner 1700. A bundle of rays from a given field passing through H1 is replicated at a set pitch (shown in long-dashed outline), and similarly for H2 (shown in short-dashed outline). Depending on the angle and aspect ratio of the replication pitch, replicated rays from H1 generally do not intersect with H2, and vice versa. Because the replication pitch is generally a function of ray angle, it is generally not possible to satisfy the required conditions for all rays. However, as noted above, rays that do not satisfy the three conditions can be filtered out and replaced with other rays that originate from the same image point but that satisfy the conditions, if possible.

[0170] The above arrangement is for viewing by both pupils of the viewer. Target Light FieldThe present disclosure may be implemented in any system requiring the display of a combined image. Examples include a head-mounted display, a head-up display, a display panel, or other display types. In the case of an automotive HUD, a combiner according to the present disclosure may form part of a curved windshield that reflects light from the combiner back to the viewer. This windshield effect is reflected in block 1004 of method 1000 (through the combiner). Target Light Field can be modeled and taken into account during the propagation of the

[0171] Exemplary Display System 19 shows a schematic diagram of an exemplary display system 1900 that may be implemented in any of the systems described above to generate and display images to a viewer. The display system 1900 includes a processing system 1910, an image generation unit 1920, an image duplication combiner 1930, and an eye-tracking system 1940. The processing system 1910 may include one or more processors, memory, and software components. The one or more processors are configured to process data, and the memory may include a computer-readable medium (e.g., a tangible, non-transitory computer-readable medium, a data storage device loaded with one or more of the software components) configured to store instructions for performing various operations and / or functions. The processor is configured to execute the instructions stored in the memory to perform one or more of the operations.

[0172] The processing system 1910 executes the processing according to the instructions received from the processing system 1910. Right Field The image generation unit 1920 is coupled to an image generation unit 1920 configured to generate an image duplication combiner 1930 for display to a viewer. Target Light Field near the entrance pupil of the image duplication combiner 1930 to generate Right Field are positioned to display

[0173] The eye tracking system 1940 is coupled to the processing system 1910 and configured to monitor the position of the viewer's pupils. The eye tracking system 1940 provides data indicative of the position of the viewer's pupils to the processing system 1910. The eye tracking system 1940 may provide updated data indicative of the position of the viewer's pupils periodically, aperiodically, or continuously as a function of time. The processing system 1910 uses the provided data to: Target Light Field The processing system 1910 also determines a location for displaying the image at the determined location (e.g., at block 1002 of the method 1000). Target Light Field (e.g., block 1006 of method 1000). Additionally, processing system 1910 may also calculate Target Light Field and an input location close to the input face of the image duplication combiner by first determining a transfer function that defines the propagation of light through the image duplication combiner. Right Field Calculate and enter Right Field To get Target Light Field Apply the transfer function to the input at the input position Right Field The processing system 1910 is configured to provide the image generation unit 1920 with the calculated input Right Field (eg, block 1010 of method 1000).

[0174] In some examples, the eye tracking system 1940 is configured to generate data indicative of the position of the viewer's pupils as part of an initial calibration procedure, after which the eye tracking system 1940 may not further monitor the position of the viewer's pupils, so that the position remains the same until another calibration is performed.

[0175] Gradient Image Generation Unit In FIG. 11, an image generating unit (not shown) is configured to receive an input coupler 1102 of combiner 1100 such that the exit pupil of the image generating unit is approximately coincident with and generally parallel to the input coupler 1102 of combiner 1100 (similar to the arrangement shown in FIGS. 7a-7d). Right Field, however, this need not be the case. FIG. 20 shows an example optical system 2000 having an image generation unit 2002, an image duplication combiner 2004, and a diffraction grating 2006 at the exit pupil of the image generation unit 2002, such that the exit pupil of the image generation unit 2002 is tilted with respect to the input plane of the image duplication combiner. The duplicated images of the exit pupil lie on a single plane when viewed from the combiner output eyebox. Thus, gaps between the exit pupil images can be minimized, which may improve the uniformity of the image as viewed by the eye. Furthermore, the optical path length between adjacent exit pupil images can be minimized, so that coherence can be maintained across the exit pupil images even if the illumination source of the image generation unit has a low coherence length. This may improve the resolution of the image as viewed by the eye.

[0176] In this example, a diffraction grating 2006 at the exit pupil of image generation unit 2002 allows the field of view to be centered on an axis perpendicular to the output face of image duplication combiner 2004. Another means of tilting the bundle of rays emitted by image generation unit 2002 is a prism. Such a diffraction grating or prism would be an integral part of image duplication combiner 2004.

[0177] Experimental results FIG. 21 shows an image 2100 generated by a conventional display system, such as the display system 300 shown in FIG. 3. In this example, the image generation unit has an exit pupil diameter of 14 mm and a field of view (diagonal) of approximately 10 degrees. The image 2100 was captured using a camera with an input pupil size of 5 mm. The image 2100 is similar to the example described with respect to FIGS. 5 and 6, except that the astronauts 504, 604 have been replaced with a spaceship 2104. Again, the planet 2102 is an object at infinite depth, such that light rays emanating from any point on the planet 2102 are collimated. Thus, as expected, the planet 2102 is displayed without artifacts. On the other hand, the spaceship 2104 is an object with a finite depth, such that light rays emanating from any point on the spaceship 2104 object are not collimated. Ghosting artifacts resulting from the finite depth of the spaceship 2104 are clearly visible, resulting in an unsatisfactory holographic viewing experience.

[0178] FIG. 22 illustrates an image 2200 generated by a display system according to examples described herein, where a transfer function is determined and displayed prior to display. Target Light Field21 ) (such as any of display systems 700, 800, 900, 1600, or 1900). The image generation unit used was the same as that used in the conventional display system used to generate image 2100 shown in FIG. 21 . The same camera used to capture image 2100 shown in FIG. 21 was also used to capture image 2200 shown in FIG. 2200. It can be observed that the effect of applying either method 1000 or 1020 is to produce a holographic image in which the ghosting of objects at finite depth is significantly reduced. As in FIG. 21 , planet 2202 is displayed without ghosting because it is displayed at infinite depth using collimated light rays. However, here too, spaceship 2204 is shown as a single object without significant ghosting. It can thus be seen that the techniques described herein can be used to generate holographic images and provide an improved viewing experience compared to holographic images generated using conventional display systems.

[0179] Note that parts of this disclosure refer to the concept of rays. If H describes a hologram, then the concept of "filtering out rays" can be interpreted to mean "removing spatial frequencies from some localized region of H."

[0180] The above embodiments should be understood as illustrative examples of the present invention. For example, the image duplication combiner may include any type of image duplication combiner, examples of which include waveguide combiners and freeform combiners, and the image duplication combiner is not limited to the specific example of a 2D image duplication waveguide with planar input and output faces used in some embodiments.

[0181] For a detailed explanation, Target Light Field Input from Right Field The method focuses on backpropagation back to the input Right Field from Target Light Field It is equally applicable to forward propagation to

[0182] Further embodiments of the present invention are contemplated using alternative design methods, such as methods using similar design constraints and assumptions. It should be understood that any feature described in connection with any one embodiment may be used alone or in combination with other features described, and may also be used in combination with one or more features of any other embodiment, or in any combination of any other embodiment. Moreover, equivalents and modifications not described above may also be employed without departing from the scope of the present invention, as defined in the appended claims.

Claims

1. 1. A method for displaying an object light field using an image duplication combiner, comprising: determining a target light field to be displayed at a viewing position; determining a transfer function describing propagation of light through the image duplication combiner between the viewing position and an input position proximate an input face of the image duplication combiner; determining an input light field by applying the determined transfer function to the target light field; displaying the input light field at the input position; A method comprising:

2. determining that multiple copies of a light ray incident on the input face of the image duplication combiner are present in the object light field; removing said rays from said input light field; The method of claim 1 , comprising:

3. determining that multiple copies of a light ray incident on the input face of the image duplication combiner are present in the object light field; determining that at least two copies of the light ray are substantially equivalent and retaining the at least two copies of the light ray in the input light field; The method of claim 1 further comprising:

4. determining that a ray backpropagated from the object light field to an entrance pupil of the image duplication combiner is not present in the input light field; excluding the ray from the object light field; The method of claim 1 , comprising:

5. 3. The method of claim 2, further comprising increasing the power of another beam to compensate for the excluded beam.

6. The method of claim 1 , wherein the object light field is at least as large as a pupil of a viewer at the viewing position.

7. The area of ​​the object light field is less than the area of ​​a viewer's pupil, and the method comprises: Expanding the object light field with zero amplitude elements so that the expanded object light field has an area at least the size of the pupil. The method of claim 1 , comprising:

8. determining the target light field decomposing the object light field into a set of plane waves using a discrete Fourier transform; applying padding including elements of zero amplitude to the boundary of the target light field; The method of claim 1 , comprising:

9. Determining the position of the viewer's pupils Including, the viewing position is the determined position of the viewer's pupil; The method of claim 1.

10. The object light field includes a plurality of separate light fields, each having a respective viewing position, and the method further comprises: determining a target light field and an input light field for each of the plurality of distinct light fields; combining the input light fields of each of the plurality of separate light fields for display; The method of claim 1 , comprising:

11. The method of claim 1 , wherein the target light field and the input light field are holographic fields or four-dimensional light fields.

12. the object light field is a holographic light field, the listening position is substantially constant; determining the input light field uses a predetermined constant based on the propagation between the viewing position and the input position. The method of claim 1.

13. The method of claim 1 , wherein the input location is on a surface that is not parallel to the input surface of the image duplication combiner.

14. The method of claim 1 , wherein determining the transfer function comprises determining that light rays received from at least two different copies of the input light field form the target light field.

15. The method of claim 14 , wherein the rays received from the at least two different replicas coincide at a single point on the virtual object.

16. 1. A display system comprising: an image duplication combiner; an image generation unit arranged to provide an input to said image duplication combiner; a processing system configured to perform the method of any one of claims 1 to 15 and to cause the image generation unit to display the input light field; The display system comprises:

17. 17. The display system of claim 16, comprising an eye-tracking system arranged to provide data indicative of the viewing position to the processing system.

18. 17. The display system of claim 16, wherein the image replica combiner is configured so that all replicas have substantially the same output power for the same input power.

19. 17. The display system of claim 16, wherein the input to the image duplication combiner is not parallel to the input face of the image duplication combiner.

20. 17. The display system of claim 16, wherein the image replication combiner is arranged to generate a plurality of replicated images of the input light field, the gap between adjacent replicated images being no larger than the diameter of a viewer's pupil.

21. 17. The display system of claim 16, wherein the image duplication combiner is arranged to generate multiple duplicate images of the input light field, the combined phase volume of the multiple duplicate images covering a majority of a phase volume of an object.

22. 22. The display system of claim 21, wherein the phase volume of the replica image overlaps a small portion of the phase volume of the object.

23. 17. The display system of claim 16, wherein a replication pitch of the image replication combiner is approximately equal to a width of the input pupil.

24. 17. The display system of claim 16, wherein the replication pitch of the image replication combiner is greater than half the diameter of the viewer's pupil.

25. A head-mounted or head-up display comprising a display system according to claim 16.

Images