Method for determining a hologram of an image for a system

Abstract

A method of determining a hologram for an image for a system, the system comprising a display device and an observation system that observes the hologram through a pupil expander, the pupil expander providing a plurality of light propagation paths, the method comprising: determining a first complex light field at an entrance pupil of the observation system; determining a second complex light field at a sensor plane of the observation system, the second complex light field resulting from propagation of light of the first complex light field from the entrance pupil through a lens of the observation system and modification of an amplitude component according to the image; determining a third complex light field at the entrance pupil, the third complex light field resulting from back propagation of light of the second complex light field from the sensor plane through the lens and cropping according to the entrance pupil; determining a fourth complex light field at a display plane, the fourth complex light field resulting from back propagation of light of the third complex light field along the pupil expander and cropping according to the display device; and extracting the hologram from a data set corresponding to the fourth complex light field.

Description

Technical Field

[0001] This disclosure relates to image projection. More specifically, this disclosure relates to diffraction structures, such as holograms or phase holograms, and methods for determining, for example, calculating or retrieving them. Some embodiments relate to real-time hologram computation based on eye-tracking information. Some embodiments relate to virtual image projection. Some embodiments relate to the projection of real images. Embodiments relate to viewing projected images via waveguides. Some embodiments relate to optical engines such as image generation units. Some embodiments relate to head-up displays. Background Technology

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

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

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

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

[0006] The system described herein can be used to provide holographic projectors. For example, such projectors have been used in head-up displays (HUDs) and light detection and ranging (LiDAR). Summary of the Invention

[0007] For ease of explanation and illustration, this disclosure and the accompanying drawings generally depict a one-dimensional case. However, those skilled in the art of optics will understand that the concepts described and illustrated can be extended to two dimensions to provide a two-dimensional image from a two-dimensional hologram. For example, although only one-dimensional pupil dilation is described and illustrated, the reader should understand that this disclosure extends to two-dimensional pupil dilation—for example, using two one-dimensional pupil dilations in series.

[0008] In summary, this disclosure relates to image projection. It relates to methods of image projection and image projectors including display devices. This disclosure also relates to projection systems including image projectors and observation systems. This disclosure is equally applicable to monocular and binocular observation systems. An observation system may include one or more eyes of an observer. An observation system includes optical elements with optical power (e.g., the lens of the human eye) and an observation plane (e.g., the retina of the human eye). The projector may be referred to as a "light engine." The display device and the image formed (or perceived) using the display device are spatially separated from each other. An observer forms or perceives the image on the display plane. In some embodiments, the image is a virtual image, and the display plane may be referred to as a virtual image plane. The image is formed by illuminating a diffraction pattern (e.g., a hologram) displayed on the display device. This disclosure also relates to providing (e.g., calculating or determining) a diffraction pattern for image projection, and relates to the diffraction pattern.

[0009] Display devices consist of pixels. The pixels of a display device diffract light. According to well-known optical principles, the maximum diffraction angle depends on the pixel size (and other factors, such as the wavelength of light).

[0010] In this embodiment, the display device is a spatial light modulator, such as a liquid crystal on silicon (“LCOS”) spatial light modulator (SLM). Light travels from the LCOS to the observing entity / system, such as a camera or eye, within a diffraction angle range (e.g., from zero to the maximum diffraction angle). In some embodiments, amplification techniques may be used to increase the range of available diffraction angles beyond the conventional maximum diffraction angle of the LCOS.

[0011] In this embodiment, the image is a real image. In other embodiments, the image is a virtual image perceived by the human eye (or multiple eyes). The projection system or light engine can therefore be configured so that the observer looks directly at the display device. In such an embodiment, holographically encoded light propagates directly to the eye. This light may be referred to as “spatially modulated light” or “holographic light.” In such an embodiment, no intermediate holographic reconstruction is formed in the free space between the display device and the observer, or on the screen or other light-receiving surface. In such an embodiment, the pupil of the eye can be considered as the entrance aperture of the observation system, and the retina of the eye can be considered as the observation plane of the observation system. It is sometimes said that in this configuration, the lens of the eye performs the holographic-to-image conversion or transformation.

[0012] According to well-known optical principles, the range of angles at which light propagating from a display device or viewing window can be observed by the eye or other observation entity / system varies with the distance between the display device and the observation entity. For example, at an observation distance of 1 meter, only a small range of angles from the LCOS can propagate through the pupil of the eye to form an image on the retina at a given eye location. The range of angles at which light propagates from the display device determines the portion of the image that the observer can successfully propagate through the pupil of the eye to form an image on the retina at a given eye location. In other words, not all parts of the image are visible from any point on the observation plane (e.g., any eye position within the viewing window of an eye-tracking box).

[0013] In some embodiments, the image perceived by the observer is a virtual image appearing upstream of the display device; that is, the image is perceived by the observer as being farther away than the display device. Therefore, conceptually, the observer can be thought of viewing the virtual image through a "window the size of the display device," which can be very small, for example, 1 cm in diameter, at a relatively large distance, such as 1 meter. And the user will view the window the size of the display device through the pupil of their eye, which can also be very small. Therefore, at any given time, the field of view is small, and the range of specific angles that can be seen is highly dependent on eye position.

[0014] Optical systems are generally desirable for their small physical size—for example, in locations with limited space and / or high real estate value. However, physical constraints are often associated with functional limitations. For example, in conventional optical systems, the use of small display devices is often associated with a limited field of view (FOV), thus limiting image visibility. Pupil dilatators address the problem of how to increase the field of view—that is, how to increase the angular range of light propagating from the display device, and how this light can successfully propagate through the pupil of the eye to form an image. The display device is (relatively) small, and the projection distance is (relatively) large. In some embodiments, the projection distance is at least one (e.g., at least two) orders of magnitude larger than the diameter or width of the entrance pupil and / or aperture of the display device (i.e., the size of the pixel array). This disclosure relates to so-called direct-view holography, in which a hologram of an image, rather than the image itself, is propagated to the human eye. In other words, the light received by the observer is “holographic light” that has been spatially modulated according to a hologram of the image.

[0015] In an embodiment, the pupil dilator is a waveguide pupil dilator. This disclosure generally (but not exclusively) relates to non-infinite virtual image distances, i.e., near-field virtual images.

[0016] A pupil expander increases the field of view, thus increasing the maximum propagation distance usable across the full diffraction angle of the display device. The use of a pupil expander also laterally enlarges the user's eyebox, allowing for some eye movement while still enabling the user to see the image. In this embodiment, the pupil expander is a waveguide pupil expander. This disclosure generally relates to non-infinite virtual image distances, i.e., near-field virtual images.

[0017] Various aspects of this disclosure are defined in the appended independent claims.

[0018] This document discloses a method for determining the diffraction structure of an image for a system including a display device and an observation system. The image for which the diffraction structure is determined may be referred to as a “target” or “target image.” The diffraction structure may be a hologram; the term “hologram” is used hereafter only as an example of a diffraction structure according to this disclosure. The diffraction structure may be a phase hologram, a pure phase hologram, or a phase-to-phase hologram. The display device is arranged to display the hologram. The observation system is arranged to observe the hologram through a pupil dilator. The observation system includes at least one entrance pupil and a sensor, and may have a lens between the entrance pupil and the sensor. The pupil dilator provides multiple light propagation paths from the display device to the observation system.

[0019] The method includes five stages. The first stage includes determining a first composite light field at the entrance pupil of the observation system. The first composite light field is generated by the propagation of light from the display plane of the display device (meaning it is referred to instead as the "holographic plane" because it is a plane capable of displaying a hologram) along at least one light propagation path of the pupil dilator. The at least one light propagation path may include a single ("first") light propagation path or multiple light propagation paths among a plurality of light propagation paths through the pupil dilator. The first stage also includes trimming the composite light field according to the entrance pupil of the observation system. For example, it may be trimmed according to at least one of the size, shape, or position of the entrance pupil. The second stage includes determining a second composite light field at the sensor plane of the sensor of the observation system. The second composite light field is generated by the propagation of light from the first composite light field from the entrance pupil through a lens of the observation system to the sensor. The second stage also includes modifying the amplitude component of the composite light field according to an image, wherein the second composite light field is the result of said modification. The third stage includes determining a third composite light field at the entrance pupil. The third composite light field is generated by the backpropagation of light from the second composite light field from the sensor plane through a lens. The third stage also includes trimming the composite light field according to at least one of the size, shape, or position of the entrance pupil. The fourth stage includes determining the fourth composite light field at the display plane (i.e., at the holographic plane). The fourth composite light field is generated by the back propagation of light from the third composite light field along at least one light propagation path of the pupil dilator. The fourth stage also includes trimming the composite light field according to the display device. The hologram is extracted from a dataset corresponding to / representing the fourth composite light field. This dataset may be referred to as the "fourth dataset". Steps one through four can be repeated iteratively. With each iteration, the hologram converges, may improve, but tends to plateau. For example, the method may stop when the hologram that can be extracted from the fourth stage is considered to have acceptable quality, or when the rate of change in each iteration is below a threshold, or when the allocated time has expired. To avoid ambiguity, the extracted hologram is the hologram intended for display on the display device.

[0020] In an embodiment, "at least one light propagation path" includes a single ("first") light propagation path among a plurality of light propagation paths along which light can pass through the pupil dilator. For different second light propagation paths among the plurality of light propagation paths, the first through fourth stages can be repeated. Path-specific holograms can be extracted for each light propagation path, and multiple holograms corresponding to multiple corresponding light propagation paths can be combined to form a hologram for display on a display device.

[0021] The hologram can be configured to output holographic light through multiple channels, each channel corresponding to a different portion of the image to be seen / perceived by the observation system. A pupil dilator can be configured relative to the entrance pupil of the display device and the observation system such that each different corresponding channel of the holographic light received by the entrance pupil is output from a different corresponding transmission point on the output surface (or “output port”) of the pupil dilator. Therefore, each channel received by the observation system will experience a different number of reflections within the pupil dilator and will have a different respective optical propagation path. The method may include performing the first through fourth steps detailed above and outputting a separate channel-specific hologram for each channel. The method may also include combining those individual channel-specific holograms into a combined / final hologram, which will include a hologram of the entire image (i.e., the entire field of view) to be seen / perceived by the observation system.

[0022] More broadly, this document discloses a method for computing a hologram of an image, comprising at least one step of cropping according to the entrance pupil of an observation system to form a hologram, which, when illuminated, forms spatially modulated light, wherein consecutive optical channels of the spatially modulated light correspond to consecutive regions of the image. The consecutive optical channels may be defined by a consecutive range of ray angles of the spatially modulated light. All consecutive optical channels of the spatially modulated light correspond to consecutive regions of the image such that these channels, when combined, provide holographic light for the entire image. A pupil dilator may be provided between the display device and the observation system, arranged to guide each channel to the entrance aperture of the observation system. Each channel may be considered to have a unique, respective central axis that defines the primary (or “core”) direction of travel of the channel relative to the display device, for example, relative to the center point of the emitting surface of the display device or another reference point. The spatially modulated light may be divided into any number of consecutive optical channels. In some embodiments, the optical channels do not overlap. In other embodiments, such as those further including a light combiner with optical power (e.g., a vehicle windshield) between the waveguide and the observer, some optical channels may at least partially overlap. The method disclosed herein determines a diffraction structure arranged to spatially modulate light into an image that can be converted by an observation system, wherein the diffraction structure is configured to route light into multiple holographic channels, each holographic channel corresponding to a different portion of the image.

[0023] The size and / or shape of the cross-sectional area of ​​one or more channels may correspond to the size and / or shape of the incident aperture of the observation system. For example, if the incident aperture is the human eye, the cross-section of the channel may be substantially elliptical or oval. In embodiments that include hologram calculations, the calculation process may include limiting or cropping the hologram according to the size and / or shape of the incident aperture and / or according to the size and / or shape of the display device.

[0024] To avoid confusion, the image formed or perceived by the observer is a holographic reconstruction of the target image. Holographic reconstruction is formed from a hologram based on the target image. In some embodiments, a hologram is determined (e.g., calculated) from the target image.

[0025] The term "backward propagation" is used only to reflect that the direction of light propagation in the third and fourth stages is different from or substantially opposite to that in the first and second stages. In this respect, the light propagation in the first and second stages can be referred to as "forward propagation." In some embodiments, "forward propagation" and "backward propagation" are mathematical inverses of each other.

[0026] As used herein, the term "clipping" refers to the process of selectively discarding information (e.g., light field information) outside the region or extent of interest (e.g., outside the aperture). In some embodiments, "clipping" is a data processing step that includes discarding data points outside the aperture, zeroing out data points, or simply ignoring data points.

[0027] The term "composite light field" is mentioned here. The term "light field" simply refers to a light pattern of finite size in at least two orthogonal spatial directions (x and y). The term "complex" as used here simply means that the light at each point in the light field can be defined by amplitude and phase values, and therefore can be represented by a complex number or a pair of values. For holographic computation purposes, the composite light field can be a complex two-dimensional array, where the complex numbers define the light intensity and phase at multiple discrete locations within the light field. According to the method disclosed herein, the composite light field propagates forward and backward along the +z and -z directions between the holographic plane and the image plane. Light propagation can be simulated or modeled using any of a variety of different methods or mathematical transformations familiar to those skilled in the art of wave optics.

[0028] The inventors have devised a method for determining holograms for relatively small display devices and relatively long projection distances, wherein the holograms are directly projected onto an observation system, and this method can be implemented in real time. The relatively small size of the display device and the relatively long projection distance necessitate a pupil dilator. The inventors' method also addresses the optical complexity introduced by using a pupil dilator. The method also allows image content to appear at different and / or multiple distances from the observation system, optionally simultaneously, for example, using a single hologram. Furthermore, the method allows image content to appear downstream and upstream of the display device, optionally simultaneously, for example, using a single hologram.

[0029] Importantly, the hologram is propagated to the observation system, not a holographic reconstruction (i.e., an image) formed from the hologram. It can be said that the spatially modulated light received by the observation system is in the holographic domain, not in the spatial or image domain. It can also be said that the observation system performs the holographic-to-image conversion. More specifically, optical elements such as lenses of each observation system perform the conversion. In this embodiment, no holographic reconstruction or image is formed between the display device and the observation system. In some embodiments, optionally, an interleaving scheme is used to compute different holograms and propagate them to each eye of the observer.

[0030] The display device has an active / pixel display area, which has a first dimension of less than 10 cm, for example, less than 5 cm or less than 2 cm. The propagation distance between the display device and the observation system can be greater than 1 m, for example, greater than 1.5 m or greater than 2 m. The optical propagation distance within the waveguide can be up to 2 m, for example, up to 1.5 m or up to 1 m. This method is capable of receiving images and determining corresponding holograms of sufficient quality in less than 20 ms, such as less than 15 ms or less than 10 ms.

[0031] The method disclosed herein forms a hologram configured to route light into multiple channels, each corresponding to a different portion (i.e., a sub-region) of an image. The hologram can be displayed, for example, on a display device such as a spatial light modulator. When displayed on a suitable display device, the hologram can spatially modulate the light that can be converted into an image by an observation system. The channels formed by the diffraction structure are referred to herein as “hologram channels” simply to reflect that they are light channels encoded by a hologram containing image information. It can be said that the light in each channel is in the holographic domain, rather than in the image or spatial domain. In some embodiments, the hologram is a Fourier or Fourier transform hologram, and therefore the hologram domain is Fourier or the frequency domain. The hologram can also be a Fresnel or Fresnel transform hologram. The hologram is described herein as routing light into multiple hologram channels simply to reflect that the image reconstructed from the hologram has a finite size and can be arbitrarily divided into multiple image sub-regions, where each hologram channel corresponds to each image sub-region. Importantly, the hologram of this disclosure is characterized by how it distributes image content when illuminated. Specifically, holograms divide image content by angles. That is, for a continuous portion or segment of the image, a unique angle or a unique continuous angular range of light propagation (which can be simulated or virtual) between the image and the display device (or viewing window), when the hologram on the display device is illuminated, a corresponding continuous holographic channel of spatially modulated light is output. To avoid confusion, this holographic behavior is not conventional. When illuminated, the spatially modulated light formed by this particular type of hologram can be arbitrarily divided into multiple holographic channels. As understood above, any holographic channel that can be considered in the spatially modulated light will be associated with a corresponding portion or sub-region of the image. That is, all the information required to reconstruct that portion or sub-region of the image is contained within the angular sub-range of the spatially modulated light formed by the hologram of the image. When the spatially modulated light is viewed as a whole, there is not necessarily any evidence of multiple discrete light channels. However, in some embodiments, multiple spatially separated holographic channels are formed by intentionally leaving the region of the target image for hologram calculation blank or empty (i.e., without image content).

[0032] However, holograms can still be identified. For example, if only a continuous portion or sub-region of the spatially modulated light formed by the hologram is reconstructed, then only that sub-region of the image should be visible. If different continuous portions or sub-regions of the spatially modulated light are reconstructed, then different sub-regions of the image should be visible. Another identifying feature of this type of hologram is that the shape of the cross-sectional region of any hologram channel substantially corresponds to the shape of the incident pupil (i.e., substantially the same), although the dimensions may differ—at least in the correct plane in which the hologram is computed. Each light hologram channel propagates from the hologram at a different angle or angular range. While these are example ways of characterizing or identifying this type of hologram, other methods may also be used. In summary, the holograms disclosed herein are characterized and identified by how the image content is distributed within the hologram-encoded light, and the appended claims are stated accordingly.

[0033] A diffraction structure or hologram can be displayed at a display device, such as a spatial light modulator, including, but not limited to, a liquid crystal on silicon (LCOS) spatial light modulator (SLM). When the display device displaying the diffraction structure is properly illuminated, the diffraction structure is configured to spatially modulate light, resulting in the light emitted by the display device being routed to multiple hologram channels. A single (i.e., common) light source can be used to illuminate the entire diffraction structure. The diffraction structure may include multiple pixels, with each pixel contributing light to each hologram channel.

[0034] Holographic channels can be called "holographic channels" because they include light channels that have been spatially modulated by the diffraction structure.

[0035] A diffraction structure can be arranged such that holographic channels propagate from the diffraction structure at different angles. Each such angle can be defined between the main or core direction of travel of the corresponding channel and a point on the display device (e.g., the center point of the display device where the diffraction structure is displayed). Each pixel of the hologram or diffraction structure can output light from each channel. Individual pixels of the hologram can output light from each channel at their own different angles.

[0036] The diffraction structure can be a phase lattice or a hologram. It can include computer-generated holograms. A holographic engine or other controller or processor can be provided to output signals to control a display device to display the diffraction structure.

[0037] The method disclosed herein offers several technological advancements. First, it avoids creating ghosted images that might be produced by other methods, such as point cloud methods. This is because the method inherently ensures that the correct image content arrives at the correct position by fully considering all possible light propagation paths in the waveguide. Second, the method can render image content in any depth plane, unlike other methods, such as point cloud methods, which can be poor when the distance between image points is very small. This is a significant problem in optical systems that utilize optical combiners with optical power (e.g., car windshields) to form virtual images. Third, the method inherently considers the effect of wavelength, eliminating the need for image size correction by wavelength, as disclosed in U.S. Patent 10,514,658, in color projectors that include multiple monochrome holographic channels.

[0038] Different propagation paths can pass through the entrance aperture of the observation system at different angles. The pupil dilator can be arranged such that all holographic channels are routed through the entrance aperture of the observation system at any observation position on the observation plane. For each permitted observation position, the pupil dilator routes each holographic channel to the observation system via only one propagation path. At least two of the multiple holographic channels can partially overlap at the entrance aperture of the observation system.

[0039] The first through fourth stages can be ordered. The disclosed method operates by projecting back and forth between a sensor plane and a holographic plane, and the method can begin from either the sensor plane or the holographic plane. For clarity, the "sensor plane" is the plane to which the light from the hologram arrives so that an observer can form / see the image. For example, it can be the retinal plane of the observer's eye. The amplitude component of the light field is modified or constrained after each propagation to the sensor plane or the holographic plane, but the phase component is preserved. In some embodiments, the method begins with a first stage, which is equivalent to starting from the holographic plane. However, in other embodiments, the method begins with a third stage, which is equivalent to starting from the sensor plane. In these other embodiments, the third stage is followed by the fourth stage. The fourth stage is followed by the first stage, and the first stage is followed by the second stage. Each stage can be performed once before hologram extraction, or at least some stages can be performed multiple times before hologram extraction.

[0040] At least one light propagation path may include multiple light propagation paths provided by the pupil dilator. The pupil dilator is structured to facilitate or allow multiple different possible light paths to pass through. The different possible light paths may partially overlap. In some embodiments, the pupil dilator creates a series of different light paths, wherein each light path in the series is longer than the previous one. Each light path in the series exits the pupil dilator at a different point on its exit surface to create a corresponding series of light exit points or sub-regions. This series of light exit points or sub-regions may be substantially uniformly spaced along the exit surface of the pupil dilator.

[0041] A pupil dilator can be a waveguide pupil dilator. Each ray entering the pupil dilator can be replicated multiple times. The pupil dilator can be arranged to propagate light through a series of internal reflections and output light at multiple points along its principal surface. Each light propagation path can be defined by the number of internal reflections within the waveguide associated with that light propagation path. For example, a first light propagation path may include zero internal reflections, thus corresponding to light passing directly through the waveguide. A second light propagation path may include two internal reflections before leaving the waveguide, namely a first reflection at a first principal / reflecting surface of the waveguide and a second reflection at a second principal / reflecting surface of the waveguide, wherein the second principal / reflecting surface is opposite to or complementary to the first principal / reflecting surface. To avoid ambiguity, the light propagation paths therefore have some overlap. In other examples, the first light propagation path includes one reflection, and the second light propagation path includes three reflections. The first light propagation path can be the shortest light propagation path, and the nth light propagation path can be the longest light propagation path. Different propagation paths can pass through the entrance aperture of the observation system at different angles.

[0042] At least one light propagation path may be just one of multiple light propagation paths provided by the pupil dilator. First through fourth stages can be performed for each of the multiple light propagation paths to extract a hologram for each path. First through fourth stages can be performed independently for each light propagation path. Multiple holograms corresponding to the multiple light propagation paths can be combined to form a hologram for display on a display device.

[0043] It is worth noting that this method considers multiple optical propagation paths through the waveguide by performing steps one through four (regardless of the starting point) for each optical propagation path. Steps one through four can be performed sequentially for each propagation path. Alternatively, step one can be performed for each propagation path, followed by step two, then step three, and so on. It should be understood that, due to the partial overlap of different propagation paths, the steps performed for the nth propagation path can reuse the calculations for the (n-1)th propagation path, where the nth propagation path is the next longest propagation path after the (n-1)th propagation path. Multiple holograms determined for multiple different optical propagation paths can be combined by addition, especially if the hologram is a phase or pure phase hologram.

[0044] The light propagating from the display plane in the first stage may include a zeroth composite light field with random phase components, a quadratic function, or a sampled quadratic function.

[0045] The amplitude component of the zeroth composite optical field can be equal to the amplitude component of the illuminating beam. In some embodiments, the amplitude of the zeroth composite optical field is 1. If the method starts from the first stage, the phase component of the zeroth composite optical field may be random. The random phase distribution is sometimes referred to as a random phase seed, and when the method starts at the holographic plane (i.e., the first stage), it can be used only as the starting point of the method.

[0046] The first through fourth stages can be repeated iteratively before the step of extracting the hologram from the final iteration. For the second and subsequent iterations, the light propagating from the display device may include the phase distribution of the fourth composite light field from the previous iteration.

[0047] If further iterations of the first stage are performed before the method stops (i.e., holograms are acceptable), the phase components from the fourth step are saved, retained, or carried over. That is, the phase component of the composite light field propagating to the display plane according to the first stage is equal to the phase component of the fourth composite light field.

[0048] The hologram can be the phase component of the fourth dataset. The hologram can also be the phase component of the fourth dataset in the final iteration or stage of the method. In some embodiments, the hologram is a phase hologram, a phase hologram, or a pure phase hologram. The amplitude component of the fourth composite optical field can be discarded.

[0049] A hologram can be a hologram of multiple images. Each image can have a different image distance. The second stage of this method can be performed independently for each image. Importantly, the method disclosed herein forms a hologram that can simultaneously form image content on multiple planes. This is achieved by performing the second stage on each different plane and combining the results, for example, by adding composite light fields together. Each image can be a real image or a virtual image. The image content may be visible in front of the display device (i.e., downstream of the display device) and / or behind the display device (i.e., upstream of the display device).

[0050] Each composite optical field is determined by wave propagation optics, such as Fresnel propagation, shifted Fresnel propagation, fractional Fresnel propagation, fractional Fourier transform, or scaled fast Fourier transform.

[0051] The modification of the amplitude components in the second stage may include replacing the amplitude components of the second composite light field with the amplitude components of the image, or weighting the amplitude components of the second composite light field based on the amplitude components of the image.

[0052] Each step of the trimming process may include trimming the composite light field based on at least one of the size, shape, and position of the corresponding pupil. At least one of the size, shape, and position of the incident pupil may be determined by tracking or monitoring an observation system or by receiving information about the observation system. In embodiments where the observation system is an eye, the method may include eye tracking or head tracking. If at least one attribute of the incident pupil (e.g., position or size) changes, the first through fourth stages disclosed herein may be repeated.

[0053] The image(s) may be virtual images. The image(s) may appear to the observation system to be behind or outside the display device. That is, the image distance from the observation system to the perceived image may be greater than the distance from the observation system to the display device. However, in other embodiments, the image content may additionally or alternatively be formed downstream of the display device—i.e., between the display device and the observation system.

[0054] The observation system can be the observer's eye. The method may also include tracking the observer's eye or head to determine at least one of the size and position of the observation system's entrance pupil. In some embodiments, the size and / or position of the observation system's entrance pupil are used as part of the method for determining the hologram. In some embodiments, if observer movement or, for example, a change in ambient light conditions affects the size of the observer's entrance pupil, the method is performed in real time, e.g., at video rate, and the hologram is re-determined, e.g., recalculated.

[0055] Propagation along each light propagation path provided by the pupil dilator can include a separate composite light field combining the individual light propagation paths. These separate composite light fields can be combined by addition. Each of the multiple different light propagation paths provided by the pupil dilator is considered individually. The composite light field formed by each light propagation path is determined individually.

[0056] A pupil dilator can be a waveguide pupil dilator. Each light propagation path corresponds to a different number of internal reflections within the waveguide. In some embodiments, the pupil dilator is a waveguide pupil dilator having a substantially one-dimensional (i.e., elongated) or two-dimensional shape (e.g., substantially planar, such as a plate). In embodiments, the exit pupil is dilated along the longitudinal direction or dimension of the component. The pupil dilator may include a pair of opposing or complementary reflective surfaces. One of these surfaces may be only partially reflective to allow light to escape at a series of light exit points or sub-regions.

[0057] Combining individual composite light fields can include determining the lateral position of each individual composite light field on the plane containing the incident pupil. The number of internal reflections within the waveguide determines the lateral position.

[0058] Combining individual composite light fields can also include determining the total phase shift associated with internal reflections for each light propagation path. This can include summing multiple phase shifts associated with each light propagation path, where each phase shift is generated by reflections within the pupil dilator.

[0059] A holographic engine is also disclosed herein, arranged to determine a hologram of an image for observation using a head-up display. The head-up display includes a display device and a pupil dilator. The head-up display is configured to operate in conjunction with at least one observation system. Each observation system includes an entrance pupil on an entrance pupil plane, a lens on a lens plane, and a sensor on a sensor plane. The head-up display may be configured to operate in conjunction with a pair of observation systems, such as a pair of eyes. The display device (e.g., a spatial light modulator) is arranged to display a hologram on a hologram plane. The pupil dilator is arranged to receive light spatially modulated according to the hologram. For example, the displayed hologram may be illuminated with at least partially coherent light from a light source. The display device spatially modulates the received light according to the displayed hologram. The holographic engine is arranged to determine a first composite light field at the entrance pupil of the observation system. The first composite light field is generated by the propagation of light from the holographic plane (or “display plane”) of the display device along each light propagation path of the pupil dilator. The first composite light field is also generated by cropping the composite light field according to the entrance pupil of the observation system. The holographic engine is also arranged to determine a second composite light field at the sensor plane of the sensor in the observation system. The second composite light field is generated by light from the first composite light field propagating from the entrance pupil through the lens of the observation system to the sensor plane of the sensor in the observation system. The second composite light field is also generated by modifying the amplitude components according to the image. The holographic engine is also arranged to determine a third composite light field at the entrance pupil. The third composite light field is generated by light from the second composite light field propagating backward from the sensor plane through the lens. The third composite light field is also generated according to cropping of the entrance pupil. The holographic engine is also arranged to determine a fourth composite light field on the display plane. The fourth composite light field is generated by the backward propagation of light from the third composite light field along each light propagation of the pupil dilator. The fourth composite light field is also generated according to cropping of the display device. The holographic engine is arranged to extract a hologram from a dataset corresponding to the fourth composite light field. The holographic engine can be embodied in a display driver, such as a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC). The display driver can be part of an image generation unit (PGU) for a head-up display (HUD).

[0060] The term "hologram" is used to refer to a record containing amplitude or phase information about an object, or some combination thereof. The term "holographic reconstruction" is used to refer to the optical reconstruction of an object formed by illuminating a hologram. The system disclosed herein is described as a "holographic projector" because the holographic reconstruction is a real image and spatially separate from the hologram. The term "reproduced field" is used to refer to the 2D region within which the holographic reconstruction is formed and fully focused. If the hologram is displayed on a spatial light modulator including pixels, the reproduced field will be repeated in the form of multiple diffraction orders, where each diffraction order is a copy of the zero-order reproduced field. The zero-order reproduced field generally corresponds to the preferred or master reproduced field because it is the brightest reproduced field. Unless otherwise explicitly stated, the term "reproduced field" should be considered to refer to the zero-order reproduced field. The term "reproduced plane" is used to refer to a plane in space containing all reproduced fields. The terms "image," "reproduced image," and "image region" refer to the region of the reproduced field illuminated by the light reconstructed by the hologram. In some embodiments, an “image” may include discrete points, which may be referred to as “image points” or simply as “image pixels” for convenience.

[0061] The terms “encoding,” “writing,” and “addressing” are used to describe the process of providing multiple corresponding control values ​​to multiple pixels of an SLM, each determining the modulation level of the pixel. In other words, the pixels of an SLM are configured to “display” an optical modulation distribution in response to receiving multiple control values. Therefore, it can be said that an SLM “displays” a hologram, and a hologram can be considered an array of optical modulation values ​​or levels.

[0062] It has been found that acceptable-quality holographic reconstructions can be formed from "holograms" containing only phase information related to the Fourier transform of the original object. Such holographic records can be referred to as phase-only holograms. While the embodiments relate to phase-only holograms, this disclosure is equally applicable to amplitude-only holography.

[0063] This disclosure is equally applicable to forming holographic reconstructions using amplitude and phase information associated with the Fourier transform of the original object. In some embodiments, this is achieved by using complex modulation of a so-called fully complex hologram containing amplitude and phase information associated with the original object. Because the value (gray level) assigned to each pixel of the hologram has amplitude and phase components, such a hologram may be called a fully complex hologram. The value (gray level) assigned to each pixel can be represented as a complex number with amplitude and phase components. In some embodiments, a fully complex computer-generated hologram is computed.

[0064] The term "phase delay" can be a shorthand for the phase value, phase component, phase information, or simply phase of a pixel in a computer-generated hologram or spatial light modulator. That is, any phase value described is actually a number representing the amount of phase delay provided by that pixel (e.g., in the range of 0 to 2π). For example, a spatial light modulator is described as a pixel having a π / 2 phase value causing a π / 2 radian phase delay in the received light. In some embodiments, each pixel of a spatial light modulator can operate on one of a plurality of possible modulation values ​​(e.g., phase delay values). The term "gray level" can be used to refer to a plurality of available modulation levels. For example, the term "gray level" can be used for convenience to refer to a plurality of available phase levels in a phase modulator, even if different phase levels do not provide different shades of gray. For convenience, the term "gray level" can also be used to refer to a plurality of available complex modulation levels in a complex modulator.

[0065] Therefore, a hologram comprises an array of gray levels, i.e., an array of optical modulation values, such as phase delay values ​​or complex modulation values. A hologram is also considered a diffraction pattern because it is a pattern that causes diffraction when displayed on a spatial light modulator and illuminated with light whose wavelength is relative to (typically less than) the pixel spacing of the spatial light modulator. Reference is made herein to combining holograms with other diffraction patterns, such as those used as lenses or gratings. For example, a diffraction pattern used as a grating can be combined with a hologram to translate the playback field on the playback plane, or a diffraction pattern used as a lens can be combined with a hologram to focus the holographic reconstruction onto the playback plane in the near field.

[0066] Although different embodiments and groups of embodiments may be disclosed separately in the detailed description below, any feature of any embodiment or group of embodiments may be combined with any other feature or combination of features of any embodiment or group of embodiments. That is, all possible combinations and substitutions of the features disclosed in this disclosure are contemplated. Attached Figure Description

[0067] Specific embodiments are described by way of example only with reference to the following figures:

[0068] Figure 1 This is a schematic diagram illustrating a reflective SLM that generates holographic reconstruction on a screen;

[0069] Figure 2A The first iteration of the example Gerchberg-Saxton type algorithm is shown;

[0070] Figure 2B The second and subsequent iterations of the example Gerchberg-Saxton type algorithm are shown;

[0071] Figure 2CAlternative second and subsequent iterations of the example Gerchberg-Saxton type algorithm are shown;

[0072] Figure 3 This is a schematic diagram of a reflective LCOS SLM;

[0073] Figure 4 This shows the angular content of the virtual image effectively propagating from the display device to the aperture;

[0074] Figure 5A An observation system with a relatively short propagation distance is shown;

[0075] Figure 5B An observation system with a relatively large propagation distance is shown;

[0076] Figure 6A An observation system with a relatively large propagation distance is shown, which includes waveguides for forming virtual images at infinity;

[0077] Figure 6B It shows Figure 6A A magnified view of the optical path;

[0078] Figure 7 An optical system according to an embodiment is shown;

[0079] Figure 8 This is a flowchart illustrating the steps of a method according to an embodiment;

[0080] Figure 9A An image comprising multiple image regions (bottom) and a corresponding hologram comprising multiple holographic components (top) are shown;

[0081] Figure 9B The illustration shows a hologram according to the present disclosure, characterized in that holographically encoded light is routed or directed into a plurality of discrete hologram channels; and

[0082] Figure 10 An optimized system is shown, which is arranged to transmit the light content of each hologram channel to the eye through different optical paths.

[0083] In all the accompanying drawings, the same reference numerals will be used to refer to the same or similar parts. Detailed Implementation

[0084] This invention is not limited to the embodiments described below, but extends to the full scope of the appended claims. That is, the invention may be implemented in different forms and should not be construed as limited to the described embodiments, which are illustrated for illustrative purposes.

[0085] Unless otherwise stated, singular terms may include plural forms.

[0086] A structure described as being formed above or below another structure should be interpreted as including situations where the structures are in contact with each other, and also including situations where a third structure is placed between them.

[0087] When describing temporal relationships, such as when the chronological order of events is described as “after,” “following,” “next,” “before,” etc., this disclosure should be considered to include both consecutive and discontinuous events, unless otherwise stated. For example, unless terms such as “exactly,” “immediately,” or “directly” are used, the description should be considered to include discontinuous cases.

[0088] Although the terms “first,” “second,” etc., may be used herein to describe various elements, these elements are not limited by these terms. These terms are used only to distinguish individual elements. For example, without departing from the scope of the appended claims, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element.

[0089] Features of different embodiments may be coupled or combined with each other in part or in whole, and may interoperate differently with each other. Some embodiments may be implemented independently of each other, or may be implemented together in a mutually dependent relationship.

[0090] Optical configuration

[0091] Figure 1 An embodiment is illustrated in which a computer-generated hologram is encoded on a single spatial light modulator. The computer-generated hologram is a Fourier transform of the object used for reconstruction. Therefore, a hologram can be described as a Fourier domain, frequency domain, or spectral domain representation of the object. In this embodiment, the spatial light modulator is a reflective liquid crystal on silicon (LCOS) device. The hologram is encoded on the spatial light modulator, and a holographic reconstruction is formed at the playback field, such as a light-receiving surface like a screen or diffuser.

[0092] A light source 110, such as a laser or laser diode, is configured to illuminate the SLM 140 via a collimating lens 111. The collimating lens causes the approximately plane wavefront of the light to be incident on the SLM. Figure 1 In this embodiment, the wavefront is oriented off-normal (e.g., two or three degrees away from a plane that is truly orthogonal to the transparent layer). However, in other embodiments, a generally planar wavefront is provided with normal incidence, and beam splitters are arranged to separate the input and output optical paths. Figure 1In the illustrated embodiment, the arrangement is such that light from the light source is reflected from the mirrored rear surface of the SLM and interacts with the light modulation layer to form an outgoing wavefront 112. The outgoing wavefront 112 is applied to an optics device including a Fourier transform lens 120, the focal point of which is located at screen 125. More specifically, the Fourier transform lens 120 receives the modulated beam from the SLM 140 and performs a frequency-space transformation to produce a holographic reconstruction at screen 125.

[0093] It is worth noting that in this type of hologram, each pixel of the hologram contributes to the overall reconstruction. There is no one-to-one correlation between a specific point (or image pixel) on the playback field and a specific optical modulation element (or hologram pixel). In other words, the modulated light leaving the optical modulation layer is distributed across the entire playback field.

[0094] In these embodiments, the spatial position of the holographic reconstruction is determined by the diopter (focusing) of the Fourier transform lens. Figure 1 In the illustrated embodiment, the Fourier transform lens is a physical lens. That is, the Fourier transform lens is an optical Fourier transform lens and performs a Fourier transform optically. Any lens can act as a Fourier transform lens, but the lens's performance will limit the accuracy of the Fourier transform it performs. Those skilled in the art will understand how to use lenses to perform optical Fourier transforms.

[0095] Hologram Calculation Example

[0096] In some embodiments, the computer-generated hologram is a Fourier transform hologram, or simply a Fourier hologram or a Fourier-based hologram, wherein the image is reconstructed in the far field by utilizing the Fourier transform properties of a positive lens. The Fourier hologram is computed by Fourier transforming the desired light field in the reproduction plane back to the lens plane. The Fourier transform can be used to compute computer-generated Fourier holograms.

[0097] Algorithms such as the Gerchberg-Saxton algorithm can be used to compute Fourier transform holograms. Furthermore, the Gerchberg-Saxton algorithm can be used to compute holograms in the Fourier domain (i.e., Fourier transform holograms) based solely on amplitude-only information in the spatial domain (e.g., a photograph). This effectively "retrieves" phase information related to the object from the amplitude-only information in the spatial domain. In some embodiments, the Gerchberg-Saxton algorithm or its variants are used to compute computer-generated holograms from amplitude-only information.

[0098] The Gerchberg-Saxton algorithm takes into account the fact that the intensity cross section I of the beams in planes A and B is known. A (x,y) and I B(x,y) and I A (x,y) and I B The case where (x,y) is correlated via a single Fourier transform. For a given intensity cross section, the approximate phase distribution Ψ in planes A and B is obtained. A (x,y) and Ψ B (x,y). The Gerchberg-Saxton algorithm finds a solution to the problem by following an iterative process. More specifically, the Gerchberg-Saxton algorithm iteratively applies spatial and spectral constraints while repeatedly transferring the representation I between the spatial and Fourier (spectral or frequency) domains. A (x,y) and I B A dataset (x, y) containing amplitude and phase. A corresponding computer-generated hologram in the spectral domain is obtained through at least one iteration of the algorithm. The algorithm is convergent and arranged to produce a hologram representing the input image. The hologram can be an amplitude-only hologram, a phase-only hologram, or a fully complex hologram.

[0099] In some embodiments, the phase-only hologram is computed using an algorithm based on the Gerchberg-Saxton algorithm, such as the algorithm described in British Patents 2498170 or 2501112, the entire contents of which are incorporated herein by reference. However, the embodiments disclosed herein are described by way of example only when calculating the phase-only hologram. In these embodiments, the Gerchberg-Saxton algorithm retrieves the phase information Ψ[u,v] of the Fourier transform of a dataset, which produces known amplitude information T[x,y], where the amplitude information T[x,y] represents the target image (e.g., a photograph). Since amplitude and phase are inherently combined in the Fourier transform, the transformed amplitude and phase contain useful information about the accuracy of the computed dataset. Therefore, the algorithm can be used iteratively with feedback of amplitude and phase information. However, in these embodiments, the phase-only information Ψ[u,v] is used as a hologram to form a holographic representation of the target image at the image plane. The hologram is a dataset of phase values ​​(e.g., a 2D array).

[0100] In other embodiments, an algorithm based on the Gerchberg-Saxton algorithm is used to compute a fully complex hologram. A fully complex hologram is a hologram having amplitude and phase components. A hologram is a dataset (e.g., a 2D array) comprising an array of complex data values, where each complex data value includes an amplitude component and a phase component.

[0101] In some embodiments, the algorithm processes complex data, and the Fourier transform is a complex Fourier transform. Complex data can be viewed as comprising (i) real and imaginary components, or (ii) amplitude and phase components. In some embodiments, the two components of the complex data are processed differently at different stages of the algorithm.

[0102] Figure 2A A first iteration of an algorithm for computing a phase-only hologram, according to some embodiments, is shown. The input to the algorithm is an input image 210 comprising a 2D array of pixel or data values, where each pixel or data value is an amplitude or oscillation value. That is, each pixel or data value of the input image 210 does not have a phase component. Therefore, the input image 210 can be considered as an amplitude-only, oscillation-only, or intensity-only distribution. An example of such an input image 210 is a photograph or a frame of a video comprising a time-series of frames. The first iteration of the algorithm begins with a data formation step 202A, which includes assigning random phase values ​​to each pixel of the input image using a random phase distribution (or random phase seed) 230 to form an initial complex dataset, where each data element of the dataset includes both amplitude and phase. In other words, the initial complex dataset represents the input image in the spatial domain.

[0103] First processing block 250 receives an initial complex dataset and performs a complex Fourier transform to form a complex dataset of Fourier transforms. Second processing block 253 receives the complex dataset of Fourier transforms and outputs a hologram 280A. In some embodiments, hologram 280A is a phase-only hologram. In these embodiments, second processing block 253 quantizes each phase value and sets each amplitude value to 1 to form hologram 280A. Each phase value is quantized according to the phase level that can be represented on the pixel of the spatial light modulator that will be used to "display" the phase-only hologram. For example, if each pixel of the spatial light modulator provides 256 different phase levels, each phase value of the hologram is quantized to one of the 256 possible phase levels. Hologram 280A is a phase-only Fourier hologram representing an input image. In other embodiments, hologram 280A is a fully complex hologram comprising an array of complex data values ​​(each including an amplitude component and a phase component) derived from the received complex dataset of Fourier transforms. In some embodiments, the second processing block 253 constrains each complex data value to one of a plurality of permissible complex modulation levels to form a hologram 280A. The constraint step may include setting each complex data value to the closest permissible complex modulation level in the complex plane. The hologram 280A can be said to represent an input image in the spectral, Fourier, or frequency domain. In some embodiments, the algorithm stops at this point.

[0104] However, in other embodiments, the algorithm continues, such as Figure 2AAs shown by the dashed arrow in the image. In other words, follow... Figure 2A The steps indicated by the dashed arrows are optional (i.e., not essential for all embodiments).

[0105] The third processing block 256 receives the modified complex dataset from the second processing block 253 and performs an inverse Fourier transform to form a complex dataset with an inverse Fourier transform. The complex dataset with the inverse Fourier transform can be said to represent the input image in the spatial domain.

[0106] The fourth processing block 259 receives the complex dataset of the inverse Fourier transform and extracts the distribution of amplitude values ​​211A and the distribution of phase values ​​213A. Optionally, the fourth processing block 259 evaluates the distribution of amplitude values ​​211A. Specifically, the fourth processing block 259 can compare the distribution of amplitude values ​​211A of the complex dataset of the inverse Fourier transform with the input image 510, which itself is, of course, the distribution of amplitude values. If the difference between the distribution of amplitude values ​​211A and the input image 210 is sufficiently small, the fourth processing block 259 can determine that the hologram 280A is acceptable. That is, if the difference between the distribution of amplitude values ​​211A and the input image 210 is sufficiently small, the fourth processing block 259 can determine that the hologram 280A is a sufficiently accurate representation of the input image 210. In some embodiments, for comparison purposes, the distribution of phase values ​​213A of the complex dataset of the inverse Fourier transform is ignored. It will be understood that any number of different methods can be used to compare the distribution of amplitude values ​​211A with the input image 210, and this disclosure is not limited to any particular method. In some embodiments, the mean squared error is calculated, and if the mean squared error is less than a threshold, the hologram 280A is considered acceptable. If the fourth processing block 259 determines that the hologram 280A is unacceptable, further iterations of the algorithm can be performed. However, this comparison step is not required, and in other embodiments, the number of iterations of the algorithm performed is predetermined, preset, or user-defined.

[0107] Figure 2B This represents the second iteration of the algorithm and any further iterations of the algorithm. The distribution of the phase values ​​213A from previous iterations is fed back through the algorithm's processing block. Distributions of amplitude values ​​211A are rejected, favoring the distribution of amplitude values ​​of the input image 210. In the first iteration, data formation step 202A forms a first complex dataset by combining the distribution of amplitude values ​​of the input image 210 with the random phase distribution 230. However, in the second and subsequent iterations, data formation step 202B includes forming a complex dataset by combining (i) the distribution of phase values ​​213A from previous iterations of the algorithm with (ii) the distribution of amplitude values ​​of the input image 210.

[0108] Then, with reference Figure 2AThe same method described is handled by Figure 2B The complex dataset formed in step 202B is used to form the second iterative hologram 280B. Therefore, the description of this process will not be repeated here. The algorithm can stop when the second iterative hologram 280B has been computed. However, any number of further iterations of the algorithm can be performed. It will be understood that the third processing block 256 is only needed if a fourth processing block 259 is required or further iterations are needed. The output hologram 280B generally improves with each iteration. However, in practice, a point is often reached where measurable improvement is no longer observable, or the positive benefits of performing further iterations are offset by the negative impact of the additional processing time. Therefore, the algorithm is described as iterative and convergent.

[0109] Figure 2C This represents an alternative embodiment for the second and subsequent iterations. The distribution of the phase value 213A from the previous iteration is fed back through the algorithm's processing block. The distribution of the amplitude value 211A is rejected, favoring an alternative distribution of the amplitude value. In this alternative embodiment, the alternative distribution of the amplitude value is derived from the distribution of the amplitude value 211 from the previous iteration. Specifically, processing block 258 subtracts the distribution of the amplitude value of the input image 210 from the distribution of the amplitude value 211 from the previous iteration, scales the difference by a gain factor α, and subtracts the scaled difference from the input image 210. This is mathematically expressed by the following equation, where the subscript text and numbers represent the iteration number:

[0110] R n+1 [x,y]=F'{exp(iψ n [u,v])}

[0111] ψ n [u,v]=∠F{η·exp(i∠R n [x,y])}

[0112] η=T[x,y]-α(|R n [x,y]|-T[x,y])

[0113] in:

[0114] F' is the inverse Fourier transform;

[0115] F is the forward Fourier transform;

[0116] R[x,y] is the complex number dataset output by the third processing block 256;

[0117] T[x,y] is the input or target image;

[0118] ∠ is the phase component;

[0119] Ψ is a phase-only hologram 280B;

[0120] η is a new distribution of amplitude value 211B; and

[0121] α is the gain factor.

[0122] The gain factor α can be fixed or variable. In some embodiments, the gain factor α is determined based on the size and rate of the input target image data. In some embodiments, the gain factor α depends on the number of iterations. In some embodiments, the gain factor α is only a function of the number of iterations.

[0123] In all other respects, Figure 2C Implementation examples and Figure 2A and Figure 2B The implementation is the same. It can be said that only the phase hologram Ψ(u,v) includes the phase distribution in the frequency or Fourier domain.

[0124] In some embodiments, a spatial light modulator is used to perform a Fourier transform. Specifically, holographic data is combined with second data that provides optical power. That is, the data written into the spatial light modulator includes holographic data representing an object and lens data representing a lens. When displayed on the spatial light modulator and illuminated with light, the lens data simulates a physical lens—that is, it focuses light in the same way as a corresponding physical optical element. Therefore, the lens data provides optical power or focusing power. In these embodiments, [the following can be omitted] Figure 1A physical Fourier transform lens 120 is used. Data representing the lens is known. This data can be referred to as a software lens. For example, a phase-only lens can be formed by calculating the phase delay caused by the optical path length at each point of the lens due to its refractive index and spatial variation. For example, the optical path length at the center of a convex lens is greater than the optical path length at the edge of the lens. An amplitude-only lens can be formed from Fresnel zone plates. In the field of computer-generated holography, it is also known how to combine data representing the lens with a hologram to perform a Fourier transform of the hologram without requiring a physical Fourier lens. In some embodiments, the lensed data is combined with the hologram by simple addition, such as simple vector addition. In some embodiments, a physical lens is used in combination with a software lens to perform the Fourier transform. Alternatively, in other embodiments, the Fourier transform lens is omitted entirely, allowing holographic reconstruction to occur in the far field. In further embodiments, the hologram can be combined with grating data—i.e., data arranged to perform grating functions such as image steering—in the same manner. Again, how to calculate such data is known in the art. For example, a phase-only grating can be formed by modeling the phase delay caused by each point on the surface of the blazed grating. An amplitude-only grating can be simply superimposed on an amplitude-only hologram to provide angular steering for holographic reconstruction. The second data providing lensing and / or steering may be referred to as an optical processing function or optical processing pattern to distinguish it from the holographic data, which may be referred to as an image forming function or image forming pattern.

[0125] In some embodiments, the Fourier transform is performed jointly by a physical Fourier transform lens and a software lens. That is, the software lens provides some of the optical power that contributes to the Fourier transform, while one or more physical optics provide the remaining optical power that contributes to the Fourier transform.

[0126] In some embodiments, a real-time engine is provided, arranged to receive image data using an algorithm and compute holograms in real time. In some embodiments, the image data is video comprising a sequence of image frames. In other embodiments, the holograms are pre-computed, stored in computer memory, and retrieved as needed for display on an SLM. That is, in some embodiments, a library of predetermined holograms is provided.

[0127] The embodiments described herein are by way of example only and involve Fourier holography and Gerchberg-Saxton type algorithms. This disclosure is equally applicable to Fresnel holography and Fresnel holograms that can be computed using similar methods. This disclosure is also applicable to holograms computed using other techniques, such as point cloud-based methods.

[0128] Optical modulation

[0129] Spatial light modulators can be used to display diffraction patterns, including computer-generated holograms. If the hologram is a phase-only hologram, a spatial light modulator is needed to modulate the phase. If the hologram is a fully complex hologram, a spatial light modulator that modulates both the phase and amplitude can be used, or a first spatial light modulator that modulates the phase and a second spatial light modulator that modulates the amplitude can be used.

[0130] In some embodiments, the light modulation element (i.e., pixel) of the spatial light modulator is a cell comprising liquid crystal. That is, in some embodiments, the spatial light modulator is a liquid crystal device in which the optically active component is liquid crystal. Each liquid crystal cell is configured to selectively provide multiple light modulation levels. That is, each liquid crystal cell is configured at any time to operate at one light modulation level selected from multiple possible light modulation levels. Each liquid crystal cell can be dynamically reconfigured to a light modulation level different from the multiple light modulation levels. In some embodiments, the spatial light modulator is a reflective liquid crystal on silicon (LCOS) spatial light modulator, but this disclosure is not limited to this type of spatial light modulator.

[0131] LCOS devices provide a dense array of light-modulating elements or pixels within a small aperture (e.g., a few centimeters wide). Pixels are typically about 10 micrometers or smaller, resulting in a diffraction angle of a few degrees, meaning the optical system can be compact. The small aperture of an LCOS SLM is much easier to fully illuminate than the larger apertures of other liquid crystal devices. LCOS devices are typically reflective, meaning the circuitry driving the LCOS SLM pixels can be buried beneath the reflective surface. This results in a higher aperture ratio. In other words, the pixels are densely packed, meaning there are virtually no dead zones between pixels. This is advantageous because it reduces optical noise in the playback field. LCOS SLMs use a silicon substrate, which has the advantage of optically flat pixels. This is particularly important for phase modulation devices.

[0132] The following are just examples for reference. Figure 3 To describe a suitable LCOS SLM, an LCOS device is formed using a single-crystal silicon substrate 302. It has a 2D array of square planar aluminum electrodes 301, spaced apart by gaps 301a, arranged on the upper surface of the substrate. Each electrode 301 can be addressed by circuitry 302a buried in the substrate 302. Each electrode forms its own planar mirror. An alignment layer 303 is disposed on the electrode array, and a liquid crystal layer 304 is disposed on the alignment layer 303. A second alignment layer 305 is disposed on a planar transparent layer 306, for example, made of glass. A single transparent electrode 307, for example made of ITO, is disposed between the transparent layer 306 and the second alignment layer 305.

[0133] Each square electrode 301, together with the area covered by the transparent electrode 307 and the intermediate liquid crystal material, defines a controllable phase modulation element 308, commonly referred to as a pixel. Taking into account the space between pixels 301a, the effective pixel area, or fill factor, is the percentage of the total number of optically active pixels. By controlling the voltage applied to each electrode 301 relative to the transparent electrode 307, the properties of the liquid crystal material of the individual phase modulation elements can be altered, thereby providing a variable delay for light incident upon them. The effect is to provide phase-only modulation to the wavefront, i.e., without amplitude effects.

[0134] The described LCOS SLM outputs spatially modulated light in a reflective manner. The advantage of a reflective LCOS SLM is that the signal lines, grating lines, and transistors are located below the mirror, resulting in a high fill factor (typically greater than 90%) and high resolution. Another advantage of using a reflective LCOS spatial light modulator is that the thickness of the liquid crystal layer can be half that required when using a transmissive device. This significantly improves the switching speed of the liquid crystal (a key advantage for projecting moving video images). However, the teachings of this disclosure can also be implemented using a transmissive LCOS SLM.

[0135] Image projection using small display devices and long viewing distances

[0136] This disclosure relates to image projection, wherein the distance between the display device and the observer is much larger than the size of the display device. The viewing distance (i.e., the distance between the observer and the display device) can be at least one order of magnitude larger than the size of the display device. The viewing distance can be at least two orders of magnitude larger than the size of the display device. For example, the pixel area of ​​the display device can be 10 mm × 10 mm, and the viewing distance can be 1 m. The image projected by the system is formed on a display plane spatially separated from the display device. Compared to the viewing distance, the entrance aperture for the observer to view the image may also be relatively small.

[0137] According to this disclosure, the image is formed by holographic projection. The hologram is displayed on a display device. The hologram is illuminated by a light source (not shown), and the image is perceived on a display plane spatially separated from the hologram. The image can be real or virtual. For the purposes of the following explanation, it is helpful to consider a virtual image formed upstream of the display device—that is, appearing behind the display device. However, it is not important whether the image is virtual or not, and this disclosure applies equally to real images formed between the display device and the viewing system.

[0138] This disclosure enables the presentation of images (real or virtual) using very small display devices, even at relatively large viewing distances. This is achieved by providing a hologram simulating the presence of the image at the desired location and by intelligently guiding light that has been spatially modulated by the hologram, taking into account the location of the viewing system and the size and / or shape of the entrance aperture through which the light enters the viewing system.

[0139] Display devices consist of pixels that display holograms. The pixel structure of a display device is diffracted. Therefore, the size of the hologram is determined by diffraction rules. See below for reference. Figure 4 This is a result of explaining the very small size of display devices using broad optical terminology.

[0140] Figure 4 An aperture 402 is shown, which forms a small viewing window between the real object or image 401 and the viewing system 405. Figure 4 The effect of aperture 402 on light from a real object or real image 401 located at a finite distance upstream of aperture 402 is shown. Aperture 402 is very small relative to the distance between it and the observation system 405. In this illustrative arrangement, image 401, display device 402, and observation system 405 are arranged on the optical axis Ax.

[0141] Figure 4 Only those rays (or beams) from image 401 are shown, which will pass through the very small viewing window defined by aperture 402 and propagate toward viewing plane 406, which is defined perpendicular to the optical axis Ax. A skilled reader will understand that other rays will propagate from image 401 but will not coincide with aperture 402, so that they cannot (in this example) reach viewing plane 406. Furthermore, five rays (or beams) are shown propagating from image 401—each of five different portions of image 401—but it will also be appreciated by a skilled reader that this is merely illustrative and that this disclosure is not limited to five rays or beams.

[0142] The observation system 405 has an entrance aperture 404 located in front of the observation plane 406. The observation system 406 can be the human eye. Therefore, the entrance aperture 404 can be the pupil of the eye, and the observation plane 406 can be the retina of the eye. Therefore, the observation plane 406 can sometimes be referred to as the "sensor plane".

[0143] exist Figure 4 In the example, the light propagating between aperture 402 and observation system 405 is real, unmodulated light. Figure 4 This demonstrates how the very small size of the aperture 402 can effectively divide image content by angle. Figure 4Five example light beams are shown, each characterized by a corresponding angle relative to the optical axis Ax, and each propagating from a different corresponding portion of image 401. The beam propagating along the optical axis Ax carries the central portion of the image; that is, it is the light from the center of the image. The other beams carry other portions of the image. The very small viewing window defined by aperture 402 and the very small entrance aperture of pupil 404, compared to the large viewing distance, result in not all image content being able to pass through the entrance pupil 404 at any given viewing position. In other words, not all image content is received by the eye. Figure 4 In the example shown, only one of the five beams passes through the pupil 404 at any observation position.

[0144] In this example, at the pupil position 404 shown, the central portion of the image is visible to the eye. The rest of the image information is blocked. The reader will understand that if the observer moves up or down, the eye may receive different beams of light; for example, the central portion of the image may be blocked. Therefore, the observer can only see a portion of the entire image. The rest of the image information is blocked. In other words, the observer's field of view is severely limited because they are actually viewing the image through a small aperture in the display device itself.

[0145] In summary, light propagates from aperture 402 to the small observation window within a certain angular range. At an observation distance of 1 meter, for a given eye position, only a small range of angles from the small observation window can propagate through the pupil of the eye to form an image on the retina. Only the visible portion of the image falls on the retina. Figure 4 The portion shown is within a small angular range, passing through the entrance aperture 404. Therefore, the field of view is very small, and the specific angular range depends heavily on the eye position.

[0146] Reference Figure 4 The problems explaining the small field of view and sensitivity to eye position are a consequence of the large viewing distance and small aperture of the observation window, as well as the small incident aperture of the observation system. (See reference...) Figures 5A to 7 This further explains the importance of observation distance.

[0147] It is well known that holograms, displayed and illuminated on suitable display devices, form images (real or virtual) at desired locations. However, traditional holographic techniques are insufficient for forming images clearly and accurately using small display devices, especially for relatively large viewing distances or relatively small viewing apertures. This is particularly true if the image needs to be presented at a non-infinite distance from the observer, such as a virtual image. However, formation relying on temporary holographic reconstruction often requires additional optical elements, such as diffusers or screens, which can be impractical or undesirable, especially in applications requiring compactness and high property value.

[0148] Figure 5A A display device 502 is shown, which is arranged to display a hologram and propagate light that has been spatially modulated according to the hologram to an observation system including an incident aperture 504 and an observation plane 506. Figure 5A The display device 502 in the middle has the same Figure 4 It has a similar small physical size to the 402 observation aperture in the image. Figure 5A The light trails from the virtual image (not shown) represented by the hologram are also shown upstream of the display device 502. The virtual image 501 is at infinity, so the light rays traced between the virtual image and the display device 502 are collimated. The collimated light from the virtual image is depicted as comprising five rays or beams; however, it should be understood that this is merely illustrative and should not be considered a limitation of this disclosure.

[0149] Figure 5A The lower part shows an enlarged view of the observation system. This view is schematic and therefore does not show the physiological details of the eye. In reality, of course, there is a light source arranged to illuminate the display device 502. Figure 5A (Not shown in the image).

[0150] exist Figure 5A In this configuration, the distance between the display device and the viewing plane is small enough that the full diffraction angle of the light rays from the display device 502 can form an image on the retina. In other words, the light propagation paths of all five beams (shown as coming from the virtual image) pass through the incident aperture. Therefore, all points on the virtual image are mapped onto the retina, and all image content is transmitted to the viewing plane. Interestingly, the different image points on the retina are formed by light propagating from different areas on the display device 502, such as those closest to the retina. Figure 5A The image dot at the top is formed solely by light propagating from the bottom of the display device. Light propagating from other areas of the display device does not contribute to that image dot.

[0151] Figure 5B This shows what happens as the observation distance increases.

[0152] In more detail, Figure 5B A display device 502' is shown, which is arranged to display a hologram and propagate light modulated according to the hologram to an observation system including an incident aperture 504' and an observation plane 506'. The virtual image 501' is at infinity, so the light between the virtual image and the display device is collimated. Figure 5B The lower part shows an enlarged view of the observation system. This view is schematic and therefore does not show the physiological details of the eye. In reality, it certainly has a light source arranged to illuminate the display device 502'. Figure 5B (Not shown in the image).

[0153] Figure 5BOnly light rays that can propagate through aperture 504' are shown; any other light rays that cannot pass through aperture 504' are omitted. However, it will be understood that those other light rays will also propagate from display device 502'. Figure 5B At larger viewing distances, the light cone spreads out on the viewing plane to such an extent that some beams are blocked by the incident aperture 504' (i.e., they do not physically coincide). Specifically, in this example, the beams associated with the edge portions of the virtual image are blocked by the incident pupil 504'. However, if the incident aperture 504' moves to a position parallel to the viewing plane 506', different corresponding beams may coincide with the aperture 504', resulting in different portions of the virtual image being seen. Therefore, for any given aperture position, the entire virtual image is invisible, and the visible portion of the virtual image is heavily dependent on the aperture (e.g., eye) position. Consequently, large distances between the display device and the viewing system are problematic due to the small size of the display device, especially when combined with a relatively small incident aperture.

[0154] Figure 6A An improved system including a display device 602 is shown, which propagates light encoded with a hologram displayed on the display device 602 into an observation system including an entrance aperture 604 and an observation plane 606. In fact, a light source (not shown) is, of course, arranged to illuminate the display device 602. The improved system also includes a waveguide 608 located between the display device 602 and the entrance aperture 604. Figure 6A The lower part shows an enlarged view of the entrance pupil 604 and the viewing plane 606. This figure is schematic and therefore does not show the physiological details of the eye.

[0155] Figures 6A-6B observation distance and Figure 5B The same. However, in Figure 5B The blocked beam of light is effectively recovered by waveguide 608, allowing the observation system to receive complete image information—despite the longer observation distance.

[0156] The presence of waveguide 608 allows content from all angles of the display device 602 to be received by the eye, even at this relatively large projection distance. This is because waveguide 608 acts as a pupil dilator in a well-known manner, and will therefore be described only briefly here.

[0157] In short, waveguide 608 comprises a generally elongated structure. In this example, it comprises an optical plate of refractive material, but other types of waveguides are also well known and can be used. Waveguide 608 is positioned to intersect, for example, at an oblique angle, a light cone projected from display device 602. The size, position, and orientation of waveguide 608 are configured to ensure that light from each of the five beams within the light cone enters waveguide 608. Light from the light cone enters waveguide 608 via a first planar surface 610 (located closest to display device 602) and is guided at least partially along the length of waveguide 608 before being emitted via a second planar surface 612 substantially opposite the first surface 610 (located closest to the eye). It is readily understood that the second planar surface 612 is partially reflective and partially transmissive. In other words, as each ray of light propagates within waveguide 608 from its first planar surface 610 to its second planar surface 612, some light is transmitted through waveguide 608, and some is reflected back to its first planar surface 610 by the second planar surface 612. The first planar surface 610 is reflective, such that all light striking it from within waveguide 608 is reflected back to its second planar surface 612. Therefore, some light can be simply refracted between the two planar surfaces 610, 612 of waveguide 608 before transmission, while other light can be reflected and thus undergo one or more reflections (or "bouncing") between the planar surfaces 610, 612 of waveguide 608 before transmission. Thus, the net effect of waveguide 608 is that the transmission of light is effectively extended to multiple locations on the second planar surface 612 of waveguide 608. Therefore, compared to the case without waveguide 608, all angular content output by display device 602 can appear at a greater number of locations on the display plane (and at a greater number of locations on the aperture plane). This means that light from each beam can enter the entrance aperture 604 and contribute to the image formed by the viewing plane 606, despite the relatively large projection distance. In other words, the eye can receive content from all angles of the display device 602. Therefore, the full diffraction angle of the display device 602 is utilized, and the viewing window is maximized for the user. In turn, this means that all light contributes to the perceived virtual image 601.

[0158] Figure 6B The diagram shows the individual optical path of each of the five ray beams contributing to five corresponding image points within the virtual image 601. Figure 6AThe light from each of R1 and R2 is simply refracted and then transmitted through waveguide 608. On the other hand, the light from R4 experiences a single bounce before transmission. The light from R3 comprises some light from the corresponding first portion of display device 602, which is simply refracted by waveguide 608 before transmission, and some light from a different second corresponding portion of display device 602, which experiences a single bounce before transmission. Similarly, the light from R5 comprises some light from the corresponding first portion of display device 602 that experiences a single bounce before transmission, and some light from a different second corresponding portion of display device 602 that experiences two bounces before transmission. For each of R3 and R5, the two different portions of LCOS propagate light corresponding to the virtual image portion.

[0159] In at least some applications, the virtual image distance (i.e., the distance from the observer to the virtual image) is preferably finite, contrary to the notion of forming a virtual image at infinity. In some applications, there will be a preferred virtual image distance at which the appearance of the virtual image content is desired or necessary. This could be, for example, in a head-up display, such as in a car setting, if the virtual image content is to be superimposed on real content seen by the observer through the vehicle's windshield. For example, a desired virtual image distance could include virtual image content formed a few meters in front of the observer's vehicle or windshield, such as 3 meters or 5 meters.

[0160] Holographic computation for small display devices, long viewing distances, and pupil dilators

[0161] The inventor designed a computing Figure 7 A method for creating a hologram using the illustrated optical system. Importantly, the display device is relatively small, and the projection distance is relatively long. The hologram is projected directly onto the observation system, and the method can be implemented in real time. The relatively small size of the display device and the relatively long projection distance necessitate a pupil dilator. The method handles different paths via the pupil dilator. This method allows image content to appear at different and / or multiple distances from the observation system, optionally simultaneously, for example, using a single hologram. This method also allows image content to appear downstream and upstream of the display device, optionally simultaneously, for example, using a single hologram.

[0162] Figure 7 A spatial light modulator 701 for displaying an image hologram is shown. In this embodiment, the spatial light modulator 701 is a liquid crystal on silicon device arranged to modularize the phase of received light. The spatial light modulator 701 is illuminated by at least partially coherent light from a light source (not shown). The light source may be a laser diode. The spatial light modulator 701 outputs light spatially modulated according to the displayed hologram. Figure 7A ray 702 of spatially modulated light is shown. A pupil dilator 703 receives the spatially modulated light. The pupil dilator 703 is tilted relative to the plane of the display device 701. The pupil dilator 703 therefore receives light that is not perpendicularly incident. The angle of incidence (the angle formed by the optical axis and the pupil dilator) can be less than 25 degrees, for example, 10 to 20 degrees. The pupil dilator includes an input surface 703a and an output surface 703b for receiving the spatially modulated light. The input surface 703a and the output surface 703b are substantially parallel and extend in the direction of pupil dilation. The input surface 703a includes at least a portion that is substantially totally internally reflected (e.g., R = 1). The output surface 703b includes at least a portion that is highly reflective but partially transmissive (e.g., R = 0.9 and T = 0.1). The reflective surfaces are arranged such that the spatially modulated light is reflected back and forth between them, and the light is emitted at multiple points along the output surface 703b, as referenced above. Figures 6A-6B As described in waveguide 608. In this embodiment, the pupil dilator is substantially elongated. The pupil dilator provides pupil dilation in one direction—that is, the elongation direction—but this disclosure can be extended to include the presence of a second pupil dilator arranged to dilate the pupil in an orthogonal direction.

[0163] Figure 7 The diagram illustrates how ray 702 is effectively replicated twice to form three propagation paths 705, each associated with a different corresponding distance Z0, Z1, and Z2. The shortest propagation path corresponds to Z0, and in this example, the light has passed through the waveguide without any internal reflections. The mid-range propagation path of the three shown corresponds to Z1 and two internal reflections in the pupil dilator (one on each surface). The longest propagation path shown corresponds to Z2 and four internal reflections in the pupil dilator (two on each surface). Planes x0, x1, and x2 respectively show the spatial extent of the light field associated with each of the three propagation paths Z0, Z1, and Z2. More specifically, Figure 7 It shows how the three planes x0, x1, and x2 are offset from each other in the x-direction due to the different number of reflections the light undergoes in the pupil dilator 703, which in turn determines the position on the output surface 703b from which each copy is output.

[0164] Figure 7 An observation system 713 is also shown, which includes an entrance pupil 707, a lens 709, and a light sensor 711. In an embodiment, the observation system 713 is a human eye, and the light sensor 711 is the retina of the eye. Figure 7 It shows that only some of the light fields associated with each propagation path pass through inlet 707. Specifically, Figure 7 It is shown that each light field is significantly clipped by the aperture (e.g., pupil) 707, and for the three different example light paths shown, different corresponding portions of the (composite holographic) light field are clipped. Figure 7The diagram shows the light rays associated with the center of the mid-range propagation path passing through the center of the entrance pupil 707. However, for example, the light rays associated with the center of the light field of the shortest propagation path are blocked by the top of the aperture 707. However, other light rays associated with the light field of the shortest propagation path can pass through the aperture 707. The light rays associated with the center of the light field of the longest propagation path are blocked by the bottom of the aperture 707. However, other light rays associated with the light field of the longest propagation path can also pass through the aperture 707.

[0165] Light passing through aperture 707 is focused onto light sensor 711 by lens 709. The plane of light sensor 711 is substantially parallel to the display / holographic plane of display device 701, and is therefore also tilted relative to the elongated dimension of pupil dilator 703.

[0166] exist Figure 7 In this arrangement, an observer can see the entire image from all positions within the eyepiece. However, because the light field of each propagation path is clipped differently relative to each corresponding other light field through aperture 707, different parts of the image can correspond to different numbers of reflections. In other words, different parts of the image seen by the observer may originate from their respective different light propagation paths.

[0167] Figure 7 Three possible light propagation paths are illustrated by way of example only. This disclosure is not limited to the number of propagation paths. That is, those skilled in the art will understand from the following description that the method can be extended to consider any number of light propagation paths. Similarly, the pupil dilator is not necessarily tilted relative to the display plane and the sensor plane.

[0168] The inventor has designed a method, which will be described below in conjunction with... Figure 8 The method is described as follows: for a range of different pupil dilator settings and any possible number of light reflections within the pupil dilator, and therefore for any number of light propagation paths, this method can be used to calculate a suitable hologram to ensure that spatially modulated light correctly reaches the observer's eye. Importantly, it takes into account the size and shape of the entrance aperture of the observation system so that all the necessary light for the image reaches the observer.

[0169] In summary, the inventors have determined how to use a fast Gerchberg-Saxton type algorithm to compute channel holograms of an optical setup including a pixelated display device and a pupil dimmer (e.g., a head-up display (HUD)). The inventors have recognized the need to consider all reflections of light within the pupil dimmer and all possible light paths, and have done so by propagating a composite light field from each and summing them together. They have also recognized the need to crop each light field (on each corresponding light propagation path) according to the aperture between the pupil dimmer and the image plane (e.g., the observer's pupil). They have also recognized that at the aperture, between each different corresponding light propagation path, there is a lateral shift of the light field, and a phase shift within the pupil dimmer during light reflection. They have modified the algorithm accordingly to provide holograms suitable for the corresponding optical setup quickly and accurately, allowing the observer to accurately see / perceive the entire image from different ranges within the eye, even at relatively large viewing distances, and even when the display device (e.g., an SLM) and / or the aperture is relatively small.

[0170] Figure 8 This is a flowchart illustrating the steps of the method. The method is similar to a Gerchberg-Saxton type algorithm, which uses mathematical transformations back and forth between the image / sensor plane and the hologram / display plane to converge on a phase hologram corresponding to the image, which can be a virtual image and can be formed at a finite distance upstream of the spatial light modulator. After each propagation to the image plane or holographic plane, the amplitude components of the light field are modified or constrained, but the phase components are preserved.

[0171] The initial phase of the method includes steps 802 and 804. The initial phase includes forming a zeroth composite light field. Step 802 provides a random phase seed to form the phase component of the zeroth composite light field. Step 804 provides the amplitude component of the zeroth composite light field. The amplitude component can be a unit or amplitude distribution representing the light source light used to reconstruct the image from the hologram.

[0172] In step 806, the zeroth composite light field propagates Fresnelly from the spatial light modulator 701 (i.e., from the holographic plane) to the entrance pupil 707 of the observation system 713 (more specifically, to the plane containing the entrance pupil 707 of the observation system 713). Furthermore, this embodiment refers to Fresnel propagation as one example of a variety of different mathematical transformations that can be used without departing from the spirit or scope of this disclosure. Step 806 is performed for each number of bounces or internal reflections provided by the pupil dilator 703 to form a composite light field with respect to each light propagation path, such as... Figure 7x0, x1, and x2 are shown in the figure (for example only). Step 806 includes considering the lateral position of the composite light field in the x-direction at the plane of the entrance pupil 707, and the phase shift experienced by the light during each reflection within the pupil dilator 703. Different composite light fields can be combined, for example, by addition. The first stage also includes step 808, tailoring the combined composite light field according to the size and shape of the entrance pupil 707 to form a first composite light field at the entrance pupil 707.

[0173] The second phase of the method includes steps 810 and 812. In step 810, a second composite light field is determined by propagating a first composite light field from the entrance pupil through lens 709 to the plane of the light sensor 711. Step 812 includes modifying the amplitude component of the composite light field reaching the light sensor 711. More specifically, step 812 includes replacing the amplitude component of the composite light field with the amplitude component of the target image or an amplitude component based on the amplitude component of the target image (e.g., a weighted version of the amplitude component of the target image). The position of lens 709 used in the propagation determines the image distance, that is, the position of lens 709 determines where the image content will appear in space. In some embodiments, the image is a virtual image, and this distance may be referred to as the virtual image distance "VID".

[0174] Advantageously, the method disclosed herein allows the formation of image content at multiple different image distances (e.g., multiple VIDs) using the same hologram. The inventors recognize that this can be achieved by repeating the second stage for each image distance, taking into account the different positions of the lens 709 in the z-direction. For example, the composite light fields determined according to this method for each different image distance can be combined by addition.

[0175] The third stage of the method includes step 814, in which the second composite light field propagates back to the entrance pupil 707 via lens 709. This can be referred to as backpropagation, simply to reflect the travel of light in the opposite z-direction. In some embodiments, backpropagation is the mathematical inverse of the corresponding "forward" propagation. The third stage also includes tailoring the propagated light field according to the size and shape of the entrance pupil 707 to form a third composite light field. The plane of the entrance pupil 707 can be referred to as the "complex holographic plane," such as... Figure 8 As shown.

[0176] The fourth stage comprises steps 816 and 818. In step 816, light propagates from the plane of the incident pupil 707 back to the plane of the spatial light modulator 702 via each of the multiple light propagation paths of the pupil dilator, in the manner described above with respect to the first stage—but of course, in the opposite light direction (i.e., “reverse” propagation). Step 818 includes cropping the propagated light field according to the size and position of the effective / pixel area of ​​the display device to output a fourth composite light field. The number of complex values ​​for each composite light field may be equal to or less than the number of pixels in the display device.

[0177] Step 820 includes extracting a hologram (or "phase hologram") from a dataset corresponding to the fourth composite light field (which may be referred to as the "fourth dataset"). The hologram may include the phase values ​​of the fourth composite light field, in which case it may be referred to as a phase hologram. As explained earlier in this disclosure, the method can also begin from the image plane (i.e., the third stage). According to this disclosure, each stage requires at least one iteration. Figures 9 and 10 illustrate holograms formed using this method.

[0178] Optical Channel

[0179] The holograms (or "phase holograms" or "diffraction structures") calculated according to the present invention have unique properties that are not observable or can not be achieved using conventional hologram calculation methods.

[0180] In summary, the hologram calculated according to this disclosure enables a display device (e.g., but not limited to LCOS) to output channels of spatially modulated light, where each channel corresponds to a different corresponding portion of a corresponding image, on which the hologram is displayed and illuminated. This unique channel configuration allows the display device to work with suitable pupil dilators, such as waveguides, to allow an observer to accurately see the entire image through the relatively small aperture of their eye, even at relatively large viewing distances and when the display device is relatively small, without requiring eye movement. For example, a virtual image located at a finite distance upstream of the display device can be observed (correctly and completely) at a relatively large distance, even if both the observer's eye aperture and the display device displaying the hologram are relatively small. This was previously impossible, whether using conventional holography or non-holography.

[0181] According to one aspect of this disclosure, the inventors have discovered that when calculating holograms using Fresnel propagation, for example via the above... Figure 8The method shown corresponds to spatially modulated (i.e., “holographic”) light following different corresponding optical paths for different parts of the image. Therefore, the inventors recognized that a hologram could be used to simultaneously direct each of these optical paths to the observer's eye, enabling the observer to receive all the holographic light needed for their eye / brain to reconstruct the entire image without moving their eye or making any other physical changes. As illustrated in the detailed examples above, to achieve this, waveguides or other pupil dilators can be used in conjunction with a display device that displays the calculated hologram.

[0182] exist Figure 9A and 9B In the illustrated embodiment, the inventors configured an optical system to display a virtual image comprising multiple discrete virtual image components or regions to aid in understanding the unique properties of the holograms disclosed herein. However, this disclosure is equally applicable to calculating and displaying holograms corresponding to images having continuous (i.e., non-discrete) image content, and / or applicable to holograms of images having any number / size / division of discrete image portions. Figure 9A and 9B In simple terms, (i) the virtual image comprises multiple discrete virtual image components or regions, and (ii) the light of each virtual image component is associated with a different number of bounces / reflections within the waveguide. However, in some other embodiments, the light of two or more discrete virtual image components may undergo the same number of reflections within the waveguide.

[0183] Figure 9A An image 1552 for projection is shown, comprising eight discrete image regions / components V1 to V8. Figure 9A Eight image components are shown as an example only, and image 1552 can be divided into any number of components. Figure 9A Also shown is an encoded light pattern (i.e., a holographic light pattern) 1554 formed when a hologram (calculated as disclosed herein) is properly displayed and illuminated. The encoded light pattern 1554 can reconstruct an image 1552—for example, when transformed by a lens of a suitable observation system (e.g., an observer's eye). The encoded light pattern 1554 includes first to eighth components or channels H1 to H8 corresponding to the first to eighth image components / regions V1 to V8. Therefore, a hologram can be characterized by the channels of the holographic light it performs. The appearance of such light channels is solely due to the specific methods disclosed herein for determining holograms, such as... Figure 9BAs shown. Specifically, according to the hologram of this disclosure, holographic light is guided into multiple discrete channels, which can be formed as discrete corresponding regions on a plane. In the example shown, the discrete regions are disks, but other shapes are also conceivable. As mentioned above, the hologram is calculated (e.g., cropped) specifically using the size / shape of the light field at the display device and / or the size / shape of the light field at the viewing aperture. Therefore, the optimal disk size and shape may be related to the size and shape of the entrance pupil of the viewing system.

[0184] The channels of holographic light output from the hologram effectively decompose the image content (of the image to be holographically reconstructed by the observer) according to angles. This can be achieved through the above... Figure 4 To further understand this, we need to compare the optical arrangements. Figure 4 In the optical arrangement, light beams from multiple discrete positions on the real image 401 propagate to the aperture (or viewing window) 402 at multiple discrete corresponding angles, but at any given eye position, only one beam of light from these beams can pass through the observer's eye. A hologram calculated as described herein and displayed by a suitable display device can form a holographically reconstructed virtual image to simulate the presence of image 401 (or, in fact, any desired image / object) at a desired image distance. However, with... Figure 4 Compared to traditional holographic systems, a significant advantage of this optical system is that the hologram calculated herein can still be seen or perceived by the observer even when the display device is relatively small, the entrance aperture of the observation system (e.g., the observer's eye) is relatively small, and the observation distance is relatively large. In other words, as a non-limiting example, the hologram will enable... Figure 4 All five beams shown arrive at the observer simultaneously, thus forming the desired virtual image completely.

[0185] Importantly, when properly displayed and illuminated, this hologram causes the display device to output holographic light channels, where each holographic light channel corresponds to the angle (or in some cases, a beam angle) at which light from a corresponding portion of the desired image / object arrives at the display device. Thus, it can be said that the channels of holographic light correspond to different angular portions of the image content. This is not the case with conventional holograms. Furthermore, unlike unmodulated light from a real image / object or spatially modulated light formed by conventional holograms, the holographic light channels disclosed herein are specifically configured such that they can be guided by a suitable waveguide or other pupil dilator located between the display device and the observer to ensure that the observer can simultaneously receive holographic light from each channel and therefore corresponding to each (i.e., every) portion of the image. Moreover, in at least some embodiments, each channel may be received only once.

[0186] Figure 10 It shows according to Figure 9A and9B The improved observation system 1500 shown is an example of this. Figure 8 The method can be applied to calculation Figures 9A to 10 The hologram in the illustrated scheme. It is worth noting that... Figure 8 The method can be performed for each holographic optical channel that the hologram is configured to be output, wherein each channel corresponds to a different corresponding portion of the image seen / perceived by the observer, and wherein each optical channel will propagate to the observer via a different corresponding transmission point on the output surface of the pupil dilator. The method of claim 8 can be performed to output a hologram for each channel, and the channel-specific holograms can be combined to form a final complete hologram that, when properly displayed and illuminated by an optical system for which it has been calculated, will result in the holographic reconstruction of the target image.

[0187] The observation system 1500 includes a display device comprising an LCOS 1502 in this arrangement. The LCOS 1502 is arranged to display a modulation pattern (or “diffraction pattern”) including a hologram and to project holographically encoded light onto an eye 1505, which includes a pupil acting as an aperture 1504, a lens 1509, and a retina (not shown) acting as an observation plane. A light source (not shown) is arranged to illuminate the LCOS 1502. The light source may include, for example, a laser diode. The hologram is configured such that the entire hologram can be illuminated by a single light source (or a single beam of light). For it to function as described herein, multiple light sources or, for example, multiple light sources each with a different wavelength are not required to illuminate the hologram.

[0188] The lens 1509 of the eye 1505 performs the holographic-to-image conversion. Therefore, there is no holographic reconstruction of the image between the LCOS and the eye 1505.

[0189] The observation system 1500 also includes a waveguide 1508 located between the LCOS 1502 and the eye 1505. Figure 10 The projection distance may be relatively large. However, as described with respect to the preceding figures, the presence of waveguide 1508 allows all angular content from LCOS 1502 to be received by eye 1505, even at this relatively large projection distance. This is because waveguide 1508 acts as a pupil dilator in the manner already described above.

[0190] Furthermore, in this arrangement, when the LCOS1502 has been encoded according to the method described herein, the waveguide 1508 can be oriented at an angle relative to the LCOS1502 to establish a unique relationship between the light from the LCOS1502 and the virtual image perceived by the observer. The size, position, and orientation of the waveguide 1508 are configured to ensure that light from each holographic channel and light from each part of the virtual image enters the waveguide 1508 and is guided along its long axis, bouncing between the substantially flat surfaces of the waveguide 1508. Whenever light reaches the second planar surface (closest to the eye 1505), some light is transmitted and some is reflected.

[0191] Figure 10 A total of nine “bounce” points B0 to B8 are shown along the length of waveguide 1502. The reader will notice that the center of image 1552 remains blank. Figure 10 The 0th to 9th light "bounce" or reflection points B0 to B8 within the waveguide are shown. Although the light associated with all points of the image (V1-V8) (i.e., the light from each of the eight holographic light channels H1 to H8) is transmitted out of the waveguide at each "bounce" from the second planar surface of the waveguide 1508, only the light from a specific angular portion of the image (e.g., the light from one of V1 to V8) has a trajectory that allows it to reach the eye 1505 from each corresponding "bounce" point B0 to B8. Furthermore, in this embodiment, light from different channels, and therefore from different corresponding angular portions (V1 to V8) of the image, reaches the eye 1505 from each corresponding "bounce" point. Figure 10The light from all the different holographic light channels emitted at each "bounce" point is shown (represented by multiple short arrows at each transmission point), but only the light path to the eye 1505 for each channel is shown, which corresponds to the unique individual image portion (i.e., the unique individual angular image content) that will actually reach the eye 1505 from that bounce point. For each bounce point, its light path is shown as the channel that will contribute to the corresponding portion of the virtual image from the corresponding portion of the waveguide. For example, for the zeroth bounce B0, the light transmitted by waveguide 1508 is simply refracted and does not undergo any reflection therein. The light from the eighth sub-holographic sub-channel H8 reaches the eye from the zeroth bounce B0. For the next bounce B1, the light transmitted by waveguide 1502 undergoes one bounce therein before transmission. The light from the seventh hologram H7 reaches the eye from the next bounce B1. This continues sequentially until the light transmitted by waveguide 1508 at the last bounce B8 has undergone eight reflections before being transmitted and reaching the eye 1505, and includes light encoded according to the first hologram H1. In this arrangement, light from each channel will arrive at the observer substantially simultaneously within the eye's integral time—from multiple different bounce points on the waveguide, respectively. Therefore, the observer will simultaneously receive the holographic light corresponding to the entire virtual image without moving their eyes or making any other changes, even if their eyes and display device are relatively small and the viewing distance is relatively large.

[0192] exist Figure 10 In the example shown, light from only one image region reaches the eye from each bounce point. Therefore, when determining the hologram as described herein, a spatial correlation is established between the regions of the virtual image and their corresponding bounce points on the waveguide. In some other examples, there may be relatively small overlap, such that a region of the image originates from two adjacent transmission points and is thus contained within two adjacent optical discs propagating from the waveguide to the observation plane.

[0193] Therefore, the inventors recognize that the methods and apparatus described herein can generate diffraction patterns (or light modulation patterns) including holograms, which, when displayed on an LCOS or other suitable display device, enable the efficient emission of spatially modulated light or holographic light from multiple “disks” or holographic light channels, each “disk” or holographic light channel corresponding to (more specifically, encoding) a different corresponding portion of a corresponding virtual image.

[0194] Therefore, this paper describes improved methods and apparatuses that enable holograms to be computed and displayed on a suitable display device in such a way that an observer can see a clear image when the display device is illuminated by a suitable light source. For example, they enable an observer to see an image, such as a virtual image, at a finite distance (rather than infinite distance) from the display device, even if the viewing aperture (i.e., the eye) of the display device and the viewing distance is relatively small.

[0195] The improved methods and apparatus described herein can be executed in real time and can be repeated, for example, very rapidly, to adapt to changes in the position / orientation of the observation aperture. They can be implemented for more than one observation aperture, such as two eyes. They can be repeated, for example, very rapidly, to enable the display of multiple different holograms, thereby allowing the continuous and / or sequential, serial, patterned, or cyclical observation of multiple different corresponding images.

[0196] The improved methods and apparatus described herein can be implemented in a variety of different applications and viewing systems. For example, they can be implemented in head-up displays (HUDs). In many improvements to conventional HUDs, where the virtual image is formed at infinity, the improved methods and apparatus described herein can be implemented to create a virtual image at a finite image distance, which can be selected and adjusted by a suitable controller, while still eliminating ghosting.

[0197] Although virtual images have been discussed in general terms here, which require the eye to convert received modulated light to form a perceived image, the improved methods and apparatus described here can be applied to real images.

[0198] Additional features

[0199] The embodiments relate to electrically activated LCOS spatial light modulators by way of example only. The teachings of this disclosure can be equivalently implemented on any spatial light modulator capable of displaying computer-generated holograms according to this disclosure, such as any electrically activated SLM, optically activated SLM, digital micromirror device, or microelectromechanical device.

[0200] In some embodiments, the light source is a laser, such as a laser diode. The holographic projection system disclosed herein can be used to provide an improved head-up display. In some embodiments, a vehicle is provided that includes a holographic projection system mounted in the vehicle to provide a HUD. The vehicle can be a motor vehicle, such as a car, truck, van, lorry, motorcycle, train, airplane, boat, or ship.

[0201] The quality of holographic reconstruction can be affected by the so-called zero-order problem, which is a result of the diffraction characteristics of using a pixelated spatial light modulator. This zero-order light can be considered as "noise" and includes, for example, specular reflections and other unwanted light from the SLM.

[0202] In this embodiment, only the primary playback field is utilized, and the system includes physical blocks, such as baffles, arranged to restrict the propagation of higher-level playback fields through the system.

[0203] In some embodiments, the holographic reconstruction is in color. In some embodiments, a method known as Spatial Separated Color (SSC) is used to provide color holographic reconstruction. In other embodiments, a method known as Frame Sequential Color (FSC) is used.

[0204] The SSC method uses three spatially separated arrays of light-modulated pixels for three monochrome holograms. An advantage of the SSC method is that the images can be very bright because all three holographic reconstructions can be formed simultaneously. However, if three spatially separated arrays of light-modulated pixels are provided on a common SLM due to spatial constraints, the quality of each monochrome image is suboptimal because only a subset of the available light-modulated pixels is used for each color. Therefore, relatively low-resolution color images are provided.

[0205] The FSC method can use all pixels of a common spatial light modulator to sequentially display three monochrome holograms. Cyclic monochrome reconstruction (e.g., red, green, blue, red, green, blue, etc.) is fast enough that a human observer can perceive a multicolor image from the synthesis of the three monochrome images. The advantage of FSC is that the entire SLM is used for each color. This means the quality of the resulting three color images is optimal because all pixels of the SLM are used for each color image. However, the disadvantage of the FSC method is that the brightness of the synthesized color image is approximately three times lower than that of the SSC method because each monochrome illumination event can only occur within one-third of the frame time. This disadvantage can be addressed by over-exciting the laser or by using a higher-power laser, but this requires greater power, leading to higher cost and increased system size.

[0206] The example describes illuminating an SLM with visible light, but those skilled in the art will understand that, for example, the light source and the SLM can also be used to guide infrared or ultraviolet light, as disclosed herein. For example, to provide information to a user, those skilled in the art will know the techniques used to convert infrared and ultraviolet light into visible light. For example, this disclosure extends to the use of phosphors and / or quantum dot techniques for this purpose.

[0207] Some embodiments describe 2D holographic reconstruction by way of example only. In other embodiments, the holographic reconstruction is 3D holographic reconstruction. That is, in some embodiments, each computer-generated hologram forms a 3D holographic reconstruction.

[0208] The methods and processes described herein can be embodied on a computer-readable medium. The term "computer-readable medium" includes media arranged for temporary or permanent storage of data, such as random access memory (RAM), read-only memory (ROM), buffer memory, flash memory, and cache memory. The term "computer-readable medium" should also be considered to include any medium or combination of media capable of storing instructions for machine execution, such that when the instructions are executed by one or more processors, the machine performs, wholly or partially, any or all of the methods described herein.

[0209] The term "computer-readable medium" also covers cloud-based storage systems. The term "computer-readable medium" includes, but is not limited to, one or more tangible and non-transitory data repositories (e.g., data volumes) in the example forms of solid-state storage chips, optical discs, disks, or any suitable combinations thereof. In some example embodiments, instructions for execution may be transmitted by a carrier medium. Examples of such carrier media include transient media (e.g., propagation signals for transmitting instructions).

[0210] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the scope of the appended claims. This disclosure covers all modifications and variations within the scope of the appended claims and their equivalents.

Claims

1. A method for determining a hologram of a target image for a system, the system comprising a display device arranged to display the hologram on a hologram plane and an observation system, the observation system including an entrance pupil, a lens, and a sensor, wherein the observation system is arranged to observe the hologram through a pupil dilator that provides multiple light propagation paths from the display device to the observation system, the method comprising the steps of: In the first stage, for the first light propagation path, it includes determining a first composite light field at the entrance pupil of the observation system, wherein the first composite light field is generated by light from the hologram plane of the display device propagating along the first light propagation path to the entrance pupil, and by trimming the light field of the first light propagation path according to at least one of the size, shape or position of the entrance pupil to form the first composite light field. The second stage includes determining a second composite light field at the sensor plane of the sensor of the observation system, wherein the second composite light field is generated by the light of the first composite light field propagating from the entrance pupil through the lens of the observation system to the sensor and by replacing the amplitude component of the composite light field reaching the sensor plane with an amplitude component based on the amplitude component of the target image. The third stage includes determining the third composite light field at the entrance pupil, wherein the third composite light field is generated by the light of the second composite light field propagating backward from the sensor plane through the lens and according to the clipping of the entrance pupil; The fourth stage includes determining a fourth composite light field at the display plane, wherein the fourth composite light field is generated by the light of the third composite light field propagating in the reverse direction along the first light propagation path and by clipping the propagating light at the holographic plane according to at least one of the size or position of the pixel area of ​​the display device. as well as The fifth stage involves extracting holograms from the dataset corresponding to the fourth composite light field.

2. The method of claim 1, comprising repeatedly performing the first through fourth phases for each of the remaining light propagation paths of the plurality of light propagation paths provided by the pupil dilator.

3. The method as described in claim 1, wherein, The first to fourth stages are performed for each of the multiple light propagation paths to extract a hologram for each light propagation path, wherein multiple holograms corresponding to the multiple light propagation paths are combined to form a hologram for display on a display device.

4. The method according to any one of claims 1-3, wherein, In the first stage, the light propagating from the holographic plane includes a zeroth composite light field, which includes a random phase distribution.

5. The method according to any one of claims 1-3, wherein, Before the fifth stage of extracting the hologram from the last iteration, the first to fourth stages are repeated iteratively, and wherein for the second and subsequent iterations, the light propagating from the hologram plane of the display device includes the phase distribution of the fourth composite light field of the previous iteration.

6. The method according to any one of claims 1-3, wherein, The hologram is extracted from the phase components of the dataset corresponding to the fourth composite light field.

7. The method according to any one of claims 1-3, wherein, The hologram is a hologram of multiple images, each with a different image distance, and the second phase of the method is performed independently for each image.

8. The method according to any one of claims 1-3, wherein, Each of the composite optical fields, the second composite optical field, the third composite optical field, and the fourth composite optical field, is determined by wave propagation optics.

9. The method according to any one of claims 1-3, wherein, Replacing the amplitude component of the composite light field reaching the sensor plane with the amplitude component based on the target image includes replacing the amplitude component of the second composite light field with the amplitude component of the target image, or weighting the amplitude component of the second composite light field based on the amplitude component of the target image.

10. The method according to any one of claims 1-3, wherein, Each cutting step includes cutting according to at least one of size and position.

11. The method according to any one of claims 1-3, wherein, The target image is a virtual image.

12. The method according to any one of claims 1-3, wherein, The observation system is the observer's eye, and the method further includes tracking the observer's eye or head to determine at least one of the size and position of the observation system's entrance pupil.

13. The method according to any one of claims 1-3, wherein, The propagation along the first light propagation path of the pupil dilator includes propagation along a plurality of light propagation paths among the plurality of light propagation paths of the pupil dilator, and combining the respective individual composite light fields generated by the plurality of different light propagation paths of the pupil dilator.

14. The method of claim 13, wherein, The pupil expander is a waveguide pupil expander, and each light propagation path corresponds to a different number of internal reflections within the waveguide.

15. The method of claim 14, wherein, Combining individual composite light fields involves determining the lateral position of each individual composite light field on the plane of the incident pupil.

16. The method of claim 14 or 15, wherein, Combining individual composite light fields also includes determining the total phase shift associated with internal reflections for each light propagation path.

17. The method of claim 8, wherein, The wave propagation optical device is a Fresnel propagation optical device.

18. The method of claim 13, wherein, Individual composite light fields are combined by addition.

19. A holographic engine arranged to determine a hologram for viewing an image using a head-up display, wherein the head-up display is configured to operate in conjunction with an observation system, the head-up display comprising: Display devices are arranged to display holograms on a hologram plane; And a pupil dilator, arranged to receive light spatially modulated according to the hologram, wherein the holographic engine is arranged as follows: A first composite light field is determined at the entrance pupil of the observation system, wherein multiple light propagation paths of a pupil dilator are defined between the holographic plane of the display device and the entrance pupil, wherein the first composite light field is generated by light propagating along the first light propagation path and the light field of the first light propagation path being clipped according to at least one of the size, shape or position of the entrance pupil to form the first composite light field. A second composite light field is determined at the sensor plane of the sensor of the observation system, wherein the second composite light field is formed by the light of the first composite light field propagating from the incident aperture through the lens of the observation system, and replacing the amplitude component of the composite light field reaching the sensor plane with the amplitude component based on the target image. The third composite light field at the entrance pupil is determined, wherein the third composite light field is generated by the light of the second composite light field propagating backward from the sensor plane through the lens and according to the clipping of the entrance pupil; A fourth composite light field is determined at the hologram plane, wherein the fourth composite light field is generated by the light of the third composite light field propagating in the reverse along the first light propagation path and by clipping the propagating light according to at least one of the size or position of the pixel area of ​​the display device. as well as Holograms are extracted from the dataset corresponding to the fourth composite light field.

Images