Light control film

Abstract

A method of manufacturing a light control film. The method includes providing a plurality of alternating layers of a transparent material and a light absorbing material, wherein the alternating layers of the transparent material and the light absorbing material are stacked in a stacking direction. The method also includes cutting the plurality of alternating layers of the transparent material and the light absorbing material in a first cutting plane and a second cutting plane with a triangular waveform blade, thereby producing the light control film including a serrated first surface and a serrated second surface, wherein each of the first and second cutting planes is oriented at an angle less than 90° to the stacking direction. The triangular waveform blade includes a cutting edge having a triangular waveform that is perpendicular to the first and / or second cutting plane.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a light-controlling film. Some embodiments relate to the use of the light-controlling film in holographic projectors, image generation units, or head-up displays. Background Technology

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

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

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

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

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

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

[0008] On one hand, a method for manufacturing a light-controlling film is provided. The method includes providing a plurality of alternating layers of transparent material and light-absorbing material. The alternating layers of transparent material and light-absorbing material are stacked along a stacking direction. The method includes cutting the plurality of alternating layers of transparent material and light-absorbing material in a first and second cutting plane using a triangular wave-shaped blade, thereby producing a light-controlling film including a serrated first surface and a serrated second surface. Each of the first and second cutting planes is oriented at an angle of less than 90° to the stacking direction. The triangular wave-shaped blade includes a cutting edge having a triangular wave shape perpendicular to the first and / or second cutting plane. Advantageously, the serrated / corrugated surface of the light-controlling film prevents direct sunlight reflection onto the eyepiece. Furthermore, the light-controlling film with the serrated surface can eliminate sunlight glare on transparent optical surfaces.

[0009] The method may also include placing the photocontrol film on a rigid, optically transparent, serrated substrate to support it. Advantageously, the serrated substrate tends to reduce / avoid deformation. This is because silicone rubber tends to soften after curing, so if the photocontrol film is located on a flat substrate, its serrated shape will deform.

[0010] Providing the stack may include: providing a first layer of uncured transparent silicone rubber, providing a first layer of uncured black silicone rubber on the first layer of uncured transparent silicone rubber, providing a second layer of uncured transparent silicone rubber on the first layer of uncured black silicone rubber, such that the first layer of uncured black silicone rubber is located between the first and second layers of uncured transparent silicone rubber, and providing a second layer of uncured black silicone rubber on the second layer of uncured transparent silicone rubber, such that the second layer of uncured transparent silicone rubber is located between the first and second layers of uncured black silicone rubber. Advantageously, the properties of silicone rubber ensure that the interface between the transparent region and the light-absorbing region is rough and diffuse, such that any light reaching the interface will be absorbed (mostly) or diffusely reflected (a minority).

[0011] Providing a stack may further include partially curing an uncured silicone rubber layer to set the layer thickness. Providing a stack may further include fully curing an uncured silicone rubber layer.

[0012] Cutting on multiple alternating layers may include aligning the ridge of a triangular wave-shaped cutting edge with the edge of the light-absorbing material layer. The triangular wave-shaped cutting edge may include a front facet and a rear facet defining the triangular wave. The ridge may be defined by the intersection of the front and rear facets. Cutting on multiple alternating layers may include orienting the triangular wave-shaped cutting edge such that the angle between the rear facet and the first and / or second cutting plane may be substantially the same as the angle between the light-absorbing material layer and the first and / or second cutting plane.

[0013] The serrated first surface may include a first front facet at an angle greater than 35° to the first cutting surface. The serrated second surface may include a second front facet at an angle greater than 35° to the second cutting surface.

[0014] Each layer of the transparent material may include opposing rough surfaces configured to scatter light. Each light-absorbing material layer may have a thickness of 10 μm to 100 μm. Each transparent material layer may have a thickness of 0.1 mm to 10 mm. The method may further include applying an anti-reflective coating to the serrated first and / or second surfaces. Each layer of the transparent material may be wedge-shaped. The layers in a plurality of alternating layers may be parallel to each other.

[0015] On the other hand, a method for manufacturing a vehicle head-up display is provided. The method includes: providing an optical component with a reflective surface arranged in a configuration that facilitates sunlight glare during operation of the head-up display; and disposing a light-controlling film manufactured using the method of any of the foregoing aspects on the reflective surface of the optical component.

[0016] In another aspect, a head-up display for a vehicle is provided. The head-up display includes: an optical component having a reflective surface arranged in a configuration that facilitates sunlight glare during operation of the head-up display; and a light-controlling layer manufactured using any of the foregoing aspects, disposed on the reflective surface of the optical component.

[0017] In this disclosure, the term "replica" is used only to reflect that spatially modulated light is segmented such that a composite light field is guided along multiple different optical paths. The term "replica" is used to refer to each occurrence or instance of the composite light field after a copying event—such as partial reflection-transmission of a pupil dilator. Each replica propagates along a different optical path. Some embodiments of this disclosure relate to the propagation of light encoded with a hologram rather than an image—that is, light spatially modulated with a hologram of an image rather than the image itself. Thus, it can be said that multiple replicas of a hologram are formed. Those skilled in the art of holography will understand that the composite light field associated with the propagation of hologram-encoded light will vary with the propagation distance. The term "replica" as used herein is independent of propagation distance, so two optical branches or paths associated with a copying event are still referred to as "replicas" of each other, even if the branches have different lengths, causing the composite light field to evolve differently along each path. That is, according to this disclosure, even if two composite light fields are associated with different propagation distances, they are still considered "replicas"—assuming they originate from the same copying event or a series of copying events.

[0018] According to this disclosure, a "diffracted light field" is a light field formed by diffraction. A diffracted light field can be formed by illuminating a corresponding diffraction pattern. According to this disclosure, an example of a diffraction pattern is a hologram, and an example of a diffracted light field is a holographic light field or a holographically reconstructed light field that forms an image. The holographic light field forms a (holographic) reconstruction of an image on the playback plane. The holographic light field propagating from the hologram to the playback plane can be said to include light encoded by the hologram or light in the holographic domain. The diffracted light field is characterized by a diffraction angle determined by the minimum feature size of the diffraction structure and the wavelength of the light (of the diffracted light field). According to this disclosure, a "diffracted light field" can also be said to be a reconstructed light field formed on a plane spatially separated from the corresponding diffraction structure. This document discloses an optical system for propagating a diffracted light field from a diffraction structure to an observer. The diffracted light field can form an image.

[0019] The term "hologram" is used to refer to a record containing amplitude or phase information about an object, or some combination thereof. The term "holographic reconstruction" is used to refer to the optical reconstruction of an object formed by illuminating a hologram. The system disclosed herein is described as a "holographic projector" because the holographic reconstruction is a real image and spatially separate from the hologram. The term "reproduced field" is used to refer to the 2D region within which the holographic reconstruction is formed and fully focused. If the hologram is displayed on a spatial light modulator including pixels, the reproduced field will be repeated in the form of multiple diffraction orders, where each diffraction order is a copy of the zero-order reproduced field. The zero-order reproduced field typically corresponds to the preferred or master reproduced field because it is the brightest reproduced field. Unless otherwise explicitly stated, the term "reproduced field" should be considered to refer to the zero-order reproduced field. The term "reproduced plane" is used to refer to a plane in space containing all reproduced fields. The terms "image," "reproduced image," and "image region" refer to the region of the reproduced field illuminated by the light reconstructed by the hologram. In some embodiments, an “image” may include discrete points, which may be referred to as “image points” or simply as “image pixels” for convenience.

[0020] 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.

[0021] 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 pure phase holograms. While the embodiments relate to pure phase holograms, this disclosure is equally applicable to pure amplitude holography.

[0022] 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.

[0023] 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 pure 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.

[0024] 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.

[0025] 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

[0026] Referring to the following figures, specific embodiments are described by way of example only:

[0027] Figure 1This is a schematic diagram illustrating a reflective SLM that generates holographic reconstruction on a screen;

[0028] Figure 2 The image used for projection is shown, including eight image regions / components V1 to V8, and cross-sections of the corresponding holographic channels H1-H8;

[0029] Figure 3 A hologram is shown on an LCOS that directs light to multiple discrete regions;

[0030] Figure 4 The diagram shows, including, as shown Figure 2 and 3 The system of the display device for the calculated hologram;

[0031] Figure 5 shows a perspective view of a first example two-dimensional pupil expander including two replicators;

[0032] Figure 5A A perspective view (not to scale) of a system including two replicators arranged to extend the beam in two dimensions is shown.

[0033] Figure 5B A perspective view (not to scale) of another system is shown, which includes two replicators arranged to replicate the beam in two dimensions;

[0034] Figure 6A This is a schematic side view (not to scale) showing the light path of image light from the head-up display in the vehicle to the eye box with a replicator having a light-controlled film. Figure 6B This is a schematic top view showing the light path of the image light from the light-controlled film to the eye box;

[0035] Figure 7 This is a cross-sectional view (not to scale) of an example light-controlled film including a louvered array;

[0036] Figure 8 This is a cross-sectional view of the light-controlled film including the louvered array (not to scale);

[0037] Figure 9A This is a schematic diagram of uncured transparent materials and uncured light-absorbing materials (not to scale);

[0038] Figure 9B It is a cross-sectional view of multiple alternating layers of transparent and light-absorbing materials (not to scale);

[0039] Figure 9C This is a cross-sectional view of a light-control film cut from multiple alternating layers (not to scale);

[0040] Figure 9DThis is a cross-sectional view (not to scale) of the photocontrol film deposited on the substrate; and

[0041] Figure 9E This is a cross-sectional view (not to scale) of the photocontrol film deposited on the substrate.

[0042] In all the accompanying drawings, the same or similar reference numerals will be used to refer to the same or similar parts. Detailed Implementation

[0043] 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.

[0044] Unless otherwise stated, singular terms may include plural forms.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] In this disclosure, the term "basic" when applied to a structural unit of an apparatus can be interpreted as the technical feature of the structural unit produced within the technical tolerances of the method used to manufacture it.

[0050] Traditional optical configuration of holographic projection

[0051] Figure 1An embodiment is shown 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 reproduction field, such as a light-receiving surface like a screen or diffuser.

[0052] A light source 110, such as a laser or laser diode, is configured to illuminate the SLM 140 via a collimating lens 111. The collimating lens causes the approximately plane wavefront of the light to be incident on the SLM. Figure 1 In this embodiment, the wavefront is oriented off-normal (e.g., two or three degrees away from a plane that is truly orthogonal to the transparent layer). However, in other embodiments, a generally planar wavefront is provided with normal incidence, and beam splitters are arranged to separate the input and output optical paths. Figure 1 In the illustrated embodiment, the arrangement is such that light from the light source is reflected from the mirrored rear surface of the SLM and interacts with the light modulation layer to form an outgoing wavefront 112. The outgoing wavefront 112 is applied to an optics device including a Fourier transform lens 120, the focal point of which is located at screen 125. More specifically, the Fourier transform lens 120 receives the modulated beam from the SLM 140 and performs a frequency-space transformation to produce a holographic reconstruction at screen 125.

[0053] 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.

[0054] In these embodiments, the spatial position of the holographic reconstruction is determined by the diopter (focusing) of the Fourier transform lens. Figure 1 In the illustrated embodiments, the Fourier transform lens is a physical lens. That is, the Fourier transform lens is an optical Fourier transform lens and performs a Fourier transform optically. Any lens can act as a Fourier transform lens, but the performance of the lens will limit the accuracy of the Fourier transform it performs. Those skilled in the art understand how lenses can be used to perform optical Fourier transforms. In some embodiments of this disclosure, the lens of an observer's eye performs a hologram-to-image conversion.

[0055] Holographic computation

[0056] In some embodiments, the computer-generated hologram is a Fourier transform hologram, or simply a Fourier hologram or a Fourier-based hologram, wherein the image is reconstructed in the far field by utilizing the Fourier transform properties of a positive lens. The Fourier hologram is computed by Fourier transforming the desired light field in the reproduction plane back to the lens plane. The Fourier transform can be used to compute computer-generated Fourier holograms. By way of example only, the embodiments relate to Fourier holography and Gerchberg-Saxton type algorithms. This disclosure is equally applicable to Fresnel holography and Fresnel holograms that can be computed using similar methods. In some embodiments, the hologram is a phase or pure phase hologram. However, this disclosure is also applicable to holograms computed using other techniques, such as point cloud-based methods.

[0057] In some embodiments, the hologram engine is arranged to exclude the contribution of light blocked by the limiting aperture of the display system from the hologram calculation. UK Patent Application GB2101666.2, filed February 5, 2021 and incorporated herein by reference, discloses a first hologram calculation method in which eye tracking and ray tracing are used to identify sub-regions of the display device for calculating a point cloud hologram of a ghost-free image. The sub-regions of the display device correspond to the aperture of this disclosure and are used to exclude light paths from the hologram calculation. UK Patent Application GB2112213.0, filed August 26, 2021 and incorporated herein by reference, discloses a second method based on an improved Gerchberg-Saxton type algorithm, which includes a step of clipping the light field according to the pupil of the optical system during hologram calculation. The clipping of the light field corresponds to the determination of the limiting aperture of this disclosure. UK patent application GB2118911.3, filed on December 23, 2021, and also incorporated herein by reference, discloses a third method for calculating holograms, which includes the step of determining a region of a so-called extended modulator formed by a hologram replicator. According to this disclosure, the region of the extended modulator is also the aperture.

[0058] 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.

[0059] Large eye box using small display devices

[0060] In summary, this disclosure relates to image projection. It relates to methods of image projection and image projectors including display devices. This disclosure also relates to projection systems including an image projector and an observation system, wherein the image projector projects or relays light from the display device to the observation system. This disclosure is equally applicable to monocular and binocular observation systems. An observation system may include one or more eyes of an observer. An observation system includes optical elements with optical power (e.g., the lens of the human eye) and an observation plane (e.g., the retina of the human eye). The projector may be referred to as a “light engine.” The display device and the image formed (or perceived) using the display device are spatially separated from each other. The observer forms or perceives the image on the display plane. In some embodiments, the image is a virtual image, and the display plane may be referred to as a virtual image plane. In other examples, the image is a real image formed by holographic reconstruction, and this image is projected or relayed to the observation plane. In these other examples, spatially modulated light from an intermediate holographic reconstruction formed in free space or on a screen or other light-receiving surface between the display device and the observer is propagated to the observer. In both cases, an image is formed by illuminating a diffraction pattern (such as a hologram or phase hologram) displayed on a display device.

[0061] Display devices consist of pixels. The pixels of a display can show diffraction patterns or structures of diffracted light. Diffracted light can form an image on a plane spatially separate from the display device. According to well-known optical principles, the magnitude of the maximum diffraction angle is determined by the pixel size and other factors such as the wavelength of light.

[0062] 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.

[0063] In some embodiments, the hologram itself (light) propagates to the eye. For example, the spatially modulated light of the hologram (not yet fully converted into a holographic reconstruction, i.e., an image)—which can be informally referred to as being “encoded” by / with the hologram—propagates directly to the observer's eye. The observer can perceive a real or virtual image. In these embodiments, no intermediate holographic reconstruction / image is formed between the display device and the observer. Sometimes it is said that in these embodiments, the lens of the eye performs the holographic-to-image conversion or transformation. The projection system or light engine can be configured to allow the observer to effectively look directly at the display device.

[0064] The "light field" mentioned here refers to a "composite light field." The term "light field" simply means a light pattern of finite size in at least two orthogonal spatial directions, such as x and y. The term "complex" as used here simply indicates that the light at each point in the light field can be defined by amplitude and phase values, and therefore can be represented by a complex number or a pair of values. For holographic computation purposes, a composite light field can be a complex two-dimensional array, where complex numbers define the light intensity and phase at multiple discrete locations within the light field.

[0065] According to well-known optical principles, the range of angles at which light propagating from a display device can be observed by an eye or other observing entity / system varies with the distance between the display device and the observing entity. For example, at an observation distance of 1 meter, only a small range of angles from the LCOS can propagate through the pupil of the eye to form an image on the retina at a given eye location. The range of angles at which light propagates from the display device determines the portion of the image that the observer can successfully propagate through the pupil of the eye to form an image on the retina at a given eye location. In other words, not all parts of the image are visible from any point on the observation plane (e.g., any eye position within the observation window of an eyebox).

[0066] In some embodiments, the image perceived by the observer is a virtual image appearing upstream of the display device; that is, the observer perceives the image as being farther away than the display device. Therefore, conceptually, it can be thought of as the observer viewing the virtual image through a "window the size of the display device," which can be very small, for example, 1 centimeter in diameter, at a relatively large distance, such as 1 meter. And the user will view the window the size of the display device through the pupil of their eye, which can also be very small. Therefore, at any given time, the field of view is small, and the range of specific angles that can be seen is heavily dependent on eye position.

[0067] A pupil expander addresses how to increase the angular range of light propagating from a display device so that the light can successfully pass through the pupil of the eye to form an image. Display devices are typically (relatively) small, with (relatively) large projection distances. In some embodiments, the projection distance is at least an order of magnitude larger than the diameter or width of the entrance pupil and / or aperture of the display device (i.e., the size of the pixel array), for example, at least two orders of magnitude larger.

[0068] The use of a pupil expander laterally increases the viewing area (i.e., the user's eyebox), allowing for some eye movement while still enabling the user to see the image. As those skilled in the art will understand, in an imaging system, the viewing area (the user's eyebox) is the region where the observer's eye can perceive the image. This disclosure includes non-infinite virtual image distances—i.e., near-field virtual images.

[0069] Traditionally, two-dimensional pupil expanders comprise one or more one-dimensional optical waveguides, each formed using a pair of opposing reflective surfaces, where output light from the surfaces forms an observation window or eyebox. Light received from a display device (e.g., spatially modulated light from LCOS) is replicated by this or each waveguide to increase the field of view (or observation area) in at least one dimension. In particular, the waveguides enlarge the observation window by generating additional light rays or "copies" through the division of the amplitude of the incident wavefront.

[0070] The display device can have an active or pixel display area, which has a first dimension of less than 10 cm, for example, less than 5 cm or less than 2 cm. The propagation distance between the display device and the observation system can be greater than 1 meter, for example, greater than 1.5 meters or greater than 2 meters. The optical propagation distance within the waveguide can be up to 2 meters, for example, up to 1.5 meters or up to 1 meter. This method is capable of receiving images and determining corresponding holograms of sufficient quality within a range of less than 20 meters, such as less than 15 meters or less than 10 meters.

[0071] In some embodiments described herein by way of examples of diffraction or holographic light fields only, the hologram is configured to route light into multiple channels, each corresponding to a different portion (i.e., sub-region) of the image. The channels formed by the diffraction structure are referred to herein as “holographic channels” simply to reflect that they are light channels encoded by a hologram containing image information. It can be said that the light in each channel is in the holographic domain, rather than in the image or spatial domain. In some embodiments, the hologram is a Fourier or Fourier transform hologram, and therefore the holographic domain is Fourier or the frequency domain. The hologram can also be a Fresnel or Fresnel transform hologram. The hologram can also be a point cloud hologram. The hologram is described herein as routing light into multiple holographic channels to reflect that the image reconstructable from the hologram has a finite size and can be arbitrarily divided into multiple image sub-regions, where each holographic channel will correspond to each image sub-region. Importantly, the hologram of this example is characterized by how it distributes the image content when illuminated. Specifically and uniquely, the hologram divides the image content by angle. In other words, each point on the image is associated with a unique ray angle in the spatially modulated light formed by the hologram during illumination—at least a unique pair of angles, since the hologram is two-dimensional. To avoid confusion, this holographic behavior is not conventional. When illuminated, the spatially modulated light formed by this particular type of hologram can be divided into multiple holographic channels, each defined by a range of ray angles (in two dimensions). As understood above, any holographic channel that can be considered in the spatially modulated light (i.e., a subrange of ray angles) will be associated with a corresponding part or subregion of the image. That is, all the information needed to reconstruct that part or subregion of the image is contained within the subrange of angles of the spatially modulated light formed by the hologram of the image. When the spatially modulated light is viewed as a whole, there is not necessarily any evidence of multiple discrete light channels.

[0072] Nevertheless, holograms can still be identified. For example, if only a continuous portion or sub-region of the spatially modulated light formed by the hologram is reconstructed, then only that sub-region of the image should be visible. If different continuous portions or sub-regions of the spatially modulated light are reconstructed, then different sub-regions of the image should be visible. Another identifying feature of this type of hologram is that the shape of the cross-section of any hologram channel substantially corresponds to (i.e., substantially the same as) the shape of the incident pupil, although the size may differ—at least in the correct plane in which the hologram is computed. Each light / hologram channel propagates from the hologram at a different angle or angular range. While these are example ways of characterizing or identifying this type of hologram, other methods may also be used. In summary, the holograms disclosed herein are characterized and identified by how the image content is distributed within the hologram-encoded light. Furthermore, to avoid any doubt, references herein to holograms configured to guide light or to divide an image at an angle into multiple hologram channels are by way of example only, and this disclosure is equally applicable to pupil expansion of any type of holographic light field or even any type of diffractive or diffracted light field.

[0073] The system can be offered in a compact and streamlined physical form. This makes it suitable for a wide range of practical applications, including those with limited space and high-value computing assets. For example, it can be implemented in a head-up display (HUD), such as a vehicle or automotive HUD.

[0074] According to this disclosure, a pupil expander is provided for diffracted light, which may include a diverging beam of light. The diffracted light field can be defined by a "light cone". Therefore, the magnitude of the diffracted light field (as defined in a two-dimensional plane) increases with the propagation distance from the corresponding diffractive structure (i.e., the display device). It can be said that the pupil expander replicates a hologram or forms at least one copy of a hologram to convey light transmitted to the observer that is spatially modulated according to the hologram.

[0075] In some embodiments, two one-dimensional waveguide pupil expanders are provided, each arranged to effectively increase the size of the system's exit pupil by forming multiple copies or replicas of the exit pupil (or the light from the exit pupil) of the spatial light modulator. The exit pupil can be understood as the physical region where the system outputs light. Alternatively, each waveguide pupil expander can be arranged to expand the size of the system's exit pupil. Also, each waveguide pupil expander can be arranged to expand / increase the size of the eyebox in which an observer's eye can reside, in order to see / receive the light output by the system.

[0076] Optical Channel

[0077] Holograms formed according to some embodiments angularly divide image content to provide multiple holographic channels, which may have a cross-sectional shape defined by the aperture of an optical system. The hologram is calculated to provide this guidance of the diffracted light field. In some embodiments, as described above, this is achieved during hologram calculation by taking into account the aperture (virtual or real) of the optical system.

[0078] Figure 2 and 3 An example of this type of hologram is shown, which can be used in conjunction with the pupil expander disclosed herein. However, this example should not be considered as a limitation of this disclosure.

[0079] Figure 2 An image 252 for projection is shown, comprising eight image regions / components V1 to V8. This is for illustrative purposes only. Figure 2 Eight image components are shown, and image 252 can be divided into any number of components. Figure 2 Also shown is an encoded light pattern 254 (i.e., a hologram) that can reconstruct image 252—for example, when transformed by a lens of a suitable observation system. The encoded light pattern 454 includes first to eighth sub-holograms or components H1 to H8, corresponding to first to eighth image components / regions V1 to V8. Figure 2 This further demonstrates how holograms decompose image content through angles. Therefore, a characteristic of holograms lies in their ability to guide light. This is in Figure 3 As shown in the example. Specifically, the hologram in this example guides light into multiple discrete regions. In the example shown, the discrete regions are disks, but other shapes can also be envisioned. After propagation through the waveguide, the optimal size and shape of the disk can be related to the size and shape of the aperture of the optical system (e.g., the entrance pupil of an observation system).

[0080] Figure 4 System 400 is shown, including displays such as Figure 2 and 3 The display device for the calculated hologram.

[0081] System 400 includes a display device comprising an LCOS 402 in this arrangement. The LCOS 402 is arranged to display a modulation pattern (or “diffraction pattern”) including a hologram and to project holographically encoded light onto an eye 405, which includes a pupil acting as an aperture 404, a lens 409, and a retina (not shown) acting as a viewing plane. A light source (not shown) is arranged to illuminate the LCOS 402. The lens 409 of the eye 405 performs the hologram-to-image conversion. The light source can be of any suitable type. For example, it can include a laser source.

[0082] The observation system 400 also includes a waveguide 408 located between the LCOS 402 and the eye 405. The presence of the waveguide 408 allows all angular content from the LCOS 402 to be received by the eye, even at the relatively large projection distance shown. This is because the waveguide 408 acts as a pupil expander in a well-known manner, and therefore will only be briefly described here.

[0083] in short, Figure 4 The waveguide 408 shown comprises a generally elongated structure. In this example, waveguide 408 comprises an optical plate of refractive material, but other types of waveguides are also well known and can be used. Waveguide 408 is positioned to intersect, for example, at an oblique angle, a light cone (i.e., a diffracted light field) projected from LCOS 402. In this example, the dimensions, position, and orientation of waveguide 408 are configured to ensure that light from each of the eight beams within the light cone enters waveguide 408. Light from the light cone enters waveguide 408 via a first planar surface (closest to LCOS 402) and is guided at least partially along the length of waveguide 408 before being emitted via a second planar surface (closest to the eye) substantially opposite the first surface. It is readily understood that the second planar surface is partially reflective and partially transmissive. In other words, as each ray of light propagates within waveguide 408 from the first planar surface and strikes the second planar surface, some light will be transmitted out of waveguide 408, and some light will be reflected back to the first planar surface by the second planar surface. A small amount of light is absorbed. The first planar surface is reflective, such that all light striking it from within waveguide 408 will be reflected back to the second planar surface. A small amount of light is absorbed. Therefore, some light can simply be refracted between the two planar surfaces of waveguide 408 before being transmitted, while other light can be reflected and thus undergo one or more reflections (or "bouncing") between the planar surfaces of waveguide 408 before being transmitted.

[0084] Figure 4 A total of nine "bounce" points B0 to B8 are shown along the length of waveguide 408. Although... Figure 2 As shown, light associated with all points in the image (V1-V8) is transmitted out of the waveguide at each "bounce" from the second planar surface of waveguide 408, but only light from one angular portion of the image (e.g., light from one of V1 to V8) has a trajectory that allows it to reach the eye 405 from each corresponding "bounce" point B0 to B8. Furthermore, light from different angular portions (V1 to V8) of the image reaches the eye 405 from each corresponding "bounce" point. Therefore, in Figure 4 In the example, each angular channel of the encoded light reaches the eye only once from waveguide 408.

[0085] Although virtual images have been discussed in general terms here, which require the eye to convert received modulated light to form a perceived image, the methods and apparatus described here can be applied to real images.

[0086] Two-dimensional pupil expansion

[0087] Although Figure 4 The arrangement shown includes a single waveguide providing pupil extension in one dimension, but pupil extension can be provided in more than one dimension, such as in two dimensions. Furthermore, although Figure 4 The examples in the document use holograms that have been calculated to create optical channels, each corresponding to a different part of the image, but this disclosure and the system described below are not limited to this type of hologram.

[0088] Figure 5A A perspective view of system 500 is shown, which includes two replicators 504 and 506 arranged to extend beam 502 in two dimensions.

[0089] exist Figure 5A In system 500, the first replicator 504 includes a first pair of surfaces stacked parallel to each other, arranged in a manner similar to Figure 4 The waveguide 408 provides replication or pupil expansion. The first pair of surfaces are similar in size and shape to each other (in some cases identical) and are substantially elongated in one direction. The collimated beam 502 is guided to the input on the first replicator 504. Due to the internal reflection process between the two surfaces, and from one of the surfaces (the upper surface, such as...) Figure 5A As shown, the light from each of the plurality of output points on the beam 502 is partially transmitted, which will be familiar to a skilled reader, and the light from beam 502 is replicated along the length of the first replicator 504 in a first direction. Thus, the first plurality of replica beams 508 are emitted from the first replicator 504 toward the second replicator 506.

[0090] The second replicator 506 includes a second pair of surfaces stacked parallel to each other, arranged to receive each collimated beam of the first plurality of beams 508, and further arranged to provide replication or pupil expansion by extending each of these beams in a second direction substantially orthogonal to the first direction. The first pair of surfaces are similar in size and shape to each other (in some cases identical) and are substantially rectangular. The second replicator is made rectangular so that it has a length along the first direction to receive the first plurality of beams 508, and a length along the second orthogonal direction to provide replication in that second direction. Due to the internal reflection process between the two surfaces, and from one of the surfaces (such as... Figure 5APartial transmission of light from each of the plurality of output points on the upper surface shown, and the light from each beam within the first plurality of beams 508 being replicated in the second direction. Therefore, a second plurality of beams 510 is emitted from the second replicator 506, wherein the second plurality of beams 510 comprises a copy of the input beam 502 along each of the first and second directions. Thus, the second plurality of beams 510 can be considered as a two-dimensional grid or array comprising the replicated beams.

[0091] Therefore, it can be said that Figure 5A The first and second replicators 504, 505 are combined to provide a two-dimensional replicator (or "two-dimensional pupil expander"). Thus, the replica beam 510 can be emitted along the optical path to the expanded eye box of a display system, such as a head-up display.

[0092] exist Figure 5A In this system, the first replicator 504 is a waveguide comprising a pair of elongated, straight, linear reflective surfaces stacked parallel to each other; similarly, the second replicator 504 is a waveguide comprising a pair of rectangular reflective surfaces stacked parallel to each other. In other systems, the first replicator may be a solid, elongated, straight waveguide, and the second replicator may be a solid planar rectangular waveguide, wherein each waveguide comprises an optically transparent solid material, such as glass. In this case, the pair of parallel reflective surfaces are formed by a pair of opposing main sidewalls, optionally including corresponding reflective and reflective-transmitting surface coatings, which will be familiar to the skilled reader.

[0093] Figure 5B A perspective view of system 500 is shown, which includes two replicators 520 and 540 arranged to replicate beam 522 in two-dimensional space, wherein the first replicator is a solid elongated waveguide 520 and the second replicator is a solid planar waveguide 540.

[0094] exist Figure 5B In the system, the first replicator / waveguide 520 is arranged such that its pair of elongated parallel reflective surfaces 524a, 524b are perpendicular to the plane of the second replicator / waveguide 540. Therefore, the system includes an optical coupler arranged to couple light from the output port of the first replicator 520 to the input port of the second replicator 540. In the illustrated arrangement, the optical coupler is a plane / folding mirror 530, which is arranged to fold or redirect the optical path of light to achieve the desired optical coupling from the first replicator to the second replicator. Figure 5BAs shown, mirror 530 is arranged to receive light from the output port / reflective-transmitting surface 524a of the first replicator / waveguide 520, comprising a one-dimensional array of replicas extending in the first dimension. Mirror 530 is tilted to redirect the received light at an angle onto the optical path of the input port in the (total) reflective surface of the second replicator 540, providing waveguide and replica formation along its length in the second dimension. It should be understood that mirror 530 is one example of an optical element capable of redirecting light in the manner shown, and one or more other elements may alternatively be used to perform this task.

[0095] In the arrangement shown, the (partial) reflective-transmitting surface 524a of the first replicator 520 is adjacent to the input port of the first replicator / waveguide 520, which receives the input beam 522 at an angle to provide a waveguide and copy formation along its length in the first dimension. Therefore, the input port of the first replicator / waveguide 520 is located at its input end, on the same surface as the reflective-transmitting surface 524a. The skilled reader will understand that the input port of the first replicator / waveguide 520 can be in any other suitable location.

[0096] therefore, Figure 5B The arrangement allows the first replicator 520 and mirror 530 to be provided as part of a first relatively thin layer in the first and third dimensional planes (shown as the xz plane). Specifically, the size or "height" of the first planar layer (in which the first replicator 520 is located) in the second dimension (shown as the y dimension) is reduced. Mirror 530 is configured to guide light from the first layer / plane (i.e., the "first planar layer") where the first replicator 520 is located and to the second layer / plane (i.e., the "second planar layer") where the second replicator 540 is located, which is located above and substantially parallel to the first layer / plane. Therefore, the overall size or "height" of the system—including in the first and third dimensions (shown as the xz plane) and in the second dimension (shown as the y dimension)—of the first and second replicators 520, 540 and mirror 530 in the stacked first and second planar layers, is compact. The skilled reader will understand that the components used to implement this disclosure... Figure 5B Many variations in the arrangement are possible and anticipated.

[0097] An image projector can be arranged to project a diverging or diffracted light field. In some embodiments, the light field is encoded with a hologram. In some embodiments, the diffracted light field comprises a diverging beam of light. In some embodiments, the image formed by the diffracted light field is a virtual image.

[0098] In some embodiments, the first pair of parallel / complementary surfaces are elongated or slender surfaces, relatively long along a first dimension and relatively short along a second dimension, for example, relatively short along each of two other dimensions, each dimension being substantially orthogonal to each of the corresponding other dimensions. The process of light reflection / transmission between / from the first pair of parallel surfaces is arranged such that light propagates within the first waveguide pupil expander, with the general direction of light propagation being the direction of the relatively longer portion of the first waveguide pupil expander (i.e., its "elongated" direction).

[0099] This paper discloses a system that uses diffracted light to form an image and provides eyebox sizes and fields of view suitable for real-world applications—such as head-up displays in the automotive industry. Diffracted light is light used to holographically reconstruct an image from a diffracted structure—such as a hologram like a Fourier or Fresnel hologram. The use of diffraction and diffracted structures requires high-density display devices with very small pixels (e.g., 1 micrometer)—which in practice means small display devices (e.g., 1 cm). The inventors have solved the problem of how to provide a diffracted light field for 2D pupil expansion, for example, by including diffracted light comprising divergent (non-collimated) beams.

[0100] In some embodiments, the display system includes display devices—such as pixelated display devices, such as spatial light modulators (SLMs) or liquid crystal on silicon (LCoS) SLMs—arranged to provide or form diffracted or diverging light. In these respects, the aperture of the spatial light modulator (SLM) is the limiting aperture of the system. That is, the aperture of the spatial light modulator—more specifically, the size of the region defining the light-modulating pixel array contained within the SLM—determines the size (e.g., spatial extent) of the light beam that can exit the system. According to this disclosure, it is stated that by using at least one pupil expander, the exit pupil of the system is expanded to reflect that the exit pupil of the system (which is limited by the small display device having pixel sizes for light diffraction) becomes larger in spatial extension.

[0101] A diffracted or diverging light field can be described as having a "light field size," which is defined in a direction substantially orthogonal to the direction of light field propagation. Because light is diffracted / divered, the light field size increases with the propagation distance.

[0102] In some embodiments, the diffracted light field is spatially modulated according to the hologram. In other words, in these aspects, the diffracted light field includes a “holographic light field.” The hologram can be displayed on a pixelated display device. The hologram can be a computer-generated hologram (CGH). It can be a Fourier hologram, a Fresnel hologram, a point cloud hologram, or any other suitable type of hologram. Optionally, the hologram can be computed to form channels of holographic light, each channel corresponding to a different portion of the image that an observer wants to observe (or perceive, if it is a virtual image). The pixelated display device can be configured to display multiple different holograms consecutively or sequentially. Each aspect and embodiment disclosed herein can be applied to the display of multiple holograms.

[0103] The output port of the first waveguide pupil expander can be coupled to the input port of the second waveguide pupil expander. The second waveguide pupil expander can be arranged to guide the diffracted light field (including some, preferably most, preferably all copies of the light field output by the first waveguide pupil expander) from its input port to the corresponding output port through internal reflection between the third pair of parallel surfaces of the second waveguide pupil expander.

[0104] A first waveguide pupil expander can be arranged to provide pupil expansion or replication in a first direction, while a second waveguide pupil expander can be arranged to provide pupil expansion or replication in a different second direction. The second direction can be substantially orthogonal to the first direction. The second waveguide pupil expander can be arranged to maintain the pupil expansion already provided by the first waveguide pupil expander in the first direction, and expand (or replicate) some, preferably most, preferably all, copies it receives from the first waveguide pupil expander in the different second directions. The second waveguide pupil expander can be arranged to receive the optical field directly or indirectly from the first waveguide pupil expander. One or more other elements can be provided along the propagation path of the optical field between the first and second waveguide pupil expanders.

[0105] The first waveguide pupil expander may be substantially elongated, and the second waveguide pupil expander may be substantially planar. The elongated shape of the first waveguide pupil expander may be defined by its length along a first dimension. The planar or rectangular shape of the second waveguide pupil expander may be defined by its length along the first dimension and its width or span along a second dimension substantially orthogonal to the first dimension. The dimension or length of the first waveguide pupil expander along its first dimension may correspond respectively to the length or width of the second waveguide pupil expander along its first or second dimension. The first surface of a pair of parallel surfaces of the second waveguide pupil expander, including its input port, may be shaped, sized, and / or positioned to correspond to the region defined by the output port on the first surface of the pair of parallel surfaces on the first waveguide pupil expander, such that the second waveguide pupil expander is arranged to receive each copy output by the first waveguide pupil expander.

[0106] The first and second waveguide pupil expanders can jointly provide pupil expansion in a first direction and a second direction perpendicular to the first direction. Optionally, the planes containing the first and second directions are substantially parallel to the plane of the second waveguide pupil expander. In other words, the first and second dimensions defining the length and width of the second waveguide pupil expander, respectively, can be parallel to the first and second directions (or parallel to the second and first directions, respectively), wherein the waveguide pupil expander provides pupil expansion. The combination of the first and second waveguide pupil expanders is generally referred to as a "pupil expander".

[0107] In essence, the expansion / replication provided by the first and second waveguide expanders has the effect of expanding the exit pupil of the display system in each of two directions. The area defined by the expanded exit pupil can further define the expanded eyebox region from which the observer can receive light from the input diffracted or diverging light field. The eyebox region can be said to lie on or define the observation plane.

[0108] The two directions of pupil expansion can be coplanar or parallel to the first and second directions of replication / expansion provided by the first and second waveguide pupil expanders. Alternatively, in arrangements that include other elements such as optical combiners, e.g., a vehicle's windshield, the pupil can be considered as the pupil of that other element, such as the windshield. In such an arrangement, the pupil can be non-coplanar and non-parallel to the first and second directions of replication / expansion provided by the first and second waveguide pupil expanders. For example, the pupil can be substantially perpendicular to the first and second directions of replication / expansion provided by the first and second waveguide pupil expanders.

[0109] The observation plane and / or eyebox region may not be coplanar or parallel to the first and second directions in which the first and second waveguide pupil expanders provide replication / expansion. For example, the observation plane may be substantially perpendicular to the first and second directions in which the first and second waveguide pupil expanders provide replication / expansion.

[0110] In order to provide suitable emission conditions to achieve internal reflection within the first and second waveguide pupil expanders, the elongated dimension of the first waveguide pupil expander may be tilted relative to the first and second dimensions of the second waveguide pupil expander.

[0111] Combiner shape compensation

[0112] The advantage of projecting a hologram onto an eyebox is that optical compensation can be encoded within the hologram (see, for example, European Patent Publication No. EP2936252, which is incorporated herein by reference). This disclosure is compatible with holograms that compensate for the complex curvature of an optical combiner used as part of a projection system. In some embodiments, the optical combiner is the windshield of a vehicle. Full details of this method are provided in EP2936252 and are not repeated here, as detailed features of these systems and methods are not essential to the novel teachings of this disclosure and are merely examples of configurations that benefit from the teachings of this disclosure.

[0113] Control device

[0114] This disclosure is also compatible with optical configurations that include control devices (e.g., optical shutter devices) to control the transmission of light from the optical channel hologram to the observer. The holographic projector may also include control devices arranged to control the transmission of the angular channel to the eyebox position. UK patent application GB2108456.1, filed June 14, 2021 and incorporated herein by reference, discloses at least one waveguide pupil expander and control device. The reader will understand from at least this prior disclosure that the optical configuration of the control device is substantially based on the user's eyebox position and is compatible with any hologram calculation method for implementing the optical channel described herein. The control device can be described as an optical shutter or aperture device. The optical shutter device may include a 1D array of apertures or windows, wherein each aperture or window can be independently switched between transparent and opaque states to control the transmission of the hologram optical channel and its replica to the eyebox. Each aperture or window may include multiple liquid crystal cells or pixels.

[0115] Figure 6A and 6B The use of this light-controlling film in a head-up display (HUD) operating in a vehicle is illustrated. In the illustrated arrangement, the HUD 608 has optical components (e.g., the second replicator 506 in FIG. 5) at the interface with air, as shown in the xy plane. For example, the optical components may be located in an opening on the upper surface of a vehicle dashboard. The transmissive surface of the optical components is covered by a light-controlling film 606 comprising an array of one-dimensional louvers. The louvers may be in a substantially vertical plane, illustrated in the xz plane. In the illustrated arrangement, the louvers are tilted relative to the vertical plane (i.e., tilted in an orthogonal direction relative to the plane of the light-controlling layer). In particular, the louvers have tilted sidewalls. The louvers may be light-absorbing or light-attenuating.

[0116] like Figure 6AAs shown, image light from head-up display 608 passes through the louvers of light-controlled film 606 and is transmitted to optical combiner 602 (e.g., windshield). Optical combiner 602 redirects the image light substantially horizontally, as shown in the y-direction, toward eyebox 612, where an observer (e.g., a vehicle driver) can perceive a virtual image (combined with the external scene observed through the windshield).

[0117] Figure 7 An exemplary light-controlled film including an array of louvers is shown in more detail.

[0118] The light-controlling film 712 includes a first (bottom / inner) and a second (top / outer) surface defining the thickness of the light-controlling film 712. In the illustrated arrangement, since the surface of the light-controlling film 712 may not be flat, an optically transparent coating (also referred to as a "cladding layer") is provided on each of the first and second surfaces for planarization. Thus, the light-controlling film 712 is sandwiched between a pair of optically transparent coatings or cladding layers or films having respective outer surfaces 720, 722. Those skilled in the art will understand that in an arrangement where the light-controlling film 712 is formed directly on a planar transmissive surface of an optical component (e.g., the second replicator 506), a coating / planarization layer is not required on the first (bottom / inner) surface. The light-controlling film 712 includes a core of optically transparent material in which a plurality of light-absorbing louvers are disposed. The louvers are periodically arranged in a one-dimensional array, illustrated as extending in the y-direction, with a uniform spacing or pitch 708 between adjacent louvers. The spacing between the louvers is small enough to optimize light absorption without causing diffraction or ghosting. In the example, the spacing between the louvers can be approximately 10-1000 micrometers, for example 50-250 micrometers. The louvers extend through the entire thickness of the light-control film 712 and are configured with orientations, spacing, and geometries arranged to limit the range of the transmission angle 706 from the second (top / outer) surface, as shown by dashed lines.

[0119] In the illustrated arrangement, each louver has a trapezoidal cross-section (i.e., with non-parallel inclined sidewalls) that tapers (narrows) to a thickness of 710 at the second (top / outer) surface of the light-control film 712. Therefore, the sidewalls of each louver are inclined relative to a plane perpendicular to the first and second surfaces of the light-control film 712 (shown as a vertical or xz plane), as indicated by an inclination angle 714. In the illustrated arrangement, the louver geometry is identical, and the opposite sidewalls of each louver are inclined at different angles. As those skilled in the art will understand, in other arrangements, the louvers may have a rectangular cross-section (i.e., with parallel, non-inclined sidewalls) and / or may be oriented in a plane perpendicular to the first and second surfaces of the light-control film 700, and at any desired inclination angle relative to it.

[0120] Therefore, image light 704 incident from the transmissive surface of the optical components of the head-up display passes through the associated coating / planarization layer between the light-control film 712 and the louvers. In an embodiment, the louvers are geometrically configured to allow image light 704 to pass through an optically transparent core between the louvers, with an angle range that is required for the image to be visible at all positions within the eye box. Thus, in an example of implementing a special hologram, as referenced herein... Figures 2 to 4 The range of transmission angles allows all angular channels of the hologram to reach the eyebox. For example, image light 704 can be transmitted at one or more defined optical path angles (e.g., as a beam of light from multiple transmission points of optical components, as described herein), said optical path angles being transmitted to the eyebox between the louvers, for example as... Figure 7 As shown by the solid arrows in the image. Due to the small spacing between the louvers, each copy formed at one of the multiple transmission points along the transmission surface of the optical component can be incident on the multiple louvers of the light control film 712.

[0121] However, as described above, sunlight may strike the second (top / outer) surface of the light-controlling film 712, as indicated by arrow 700. Therefore, the second (top / outer) surface of the light-controlling film 712 is described herein as a “light-receiving surface” of the light-controlling film 712. It should be understood that sunlight can strike the surface of the light-controlling film 712 at any angle; the angle of light shown by arrow 700 is merely an example. Sunlight coupled into the light-controlling film 712 at the planar top surface 720 (i.e., the external interface with air) can enter at an angle such that the light is directly absorbed by one of the louvers during the “first pass,” as indicated by arrow 700. Alternatively, sunlight coupled into the light-controlling film 712 at the planar top surface 720 can enter at an angle such that the light passes between the louvers and enters the optical component (not shown). In this case, the sunlight reflected from the optical component is absorbed by one of the louvers during the “second pass” and is therefore not transmitted through the light-controlling film 712. However, some sunlight may be reflected at the planar top surface 720 (i.e., the external interface with air). In this situation, there is a risk that sunlight may be reflected at an angle along the light path to the eye box. Figure 7An example ray 702 reflecting sunlight is shown in dashed lines at an angle parallel to the ray of image light 704 from the head-up display, which travels between the slats and exits from the light-control film 712. It should be understood that the illustrated image ray 704 is merely one example of multiple rays of a replica's diverging ray beam, which travel from the transmission point of the optical component at an angle passing between the slats. Furthermore, it is understood that rays from the same replica may pass between other pairs of adjacent slats at the same or different ray angles. Therefore, the reflected sunlight ray 702 will reach the eyebox along the same optical path as the illustrated image ray 704 and cause glare to the observer. This disclosure solves this problem as shown in the embodiments described below. In the description of the embodiments, similar reference numerals are used to indicate... Figure 7 Similar features to those in the example.

[0122] Figure 8 A light-controlling film 812 according to an embodiment of the present invention is shown. Except for omitting the coating on the second (top / outer) surface of the light-controlling film 812, the light-controlling film 812 is generally similar to the one described above. Figure 7 The example is the same. Therefore, the second (top / outer) surface of the light-controlling film 812 forms the sunlight-receiving surface 820. Therefore, as... Figure 7 As shown in the example, the light control film 812 includes a core of optically transparent material in which a one-dimensional array of uniformly spaced louvers is disposed. The louvers extend through the entire thickness of the light control film 812 and are configured in a trapezoidal configuration (i.e., having inclined or sloping sidewalls). As described above, the light control film 812 can be formed on a planar reflective surface of an optical component of a head-up display, such as the second replicator 506 of FIG. 5.

[0123] According to the present invention, the light-receiving surface 820 of the light-control film 812 is serrated. Specifically, the light-receiving surface 820 is serrated to cooperate with the louver array. For example, the arrangement of the serrations of the sunlight-receiving surface 820 is coordinated, synchronized, or aligned with the arrangement of the lower louver array. Therefore, the serrated configuration of the sunlight-receiving surface 820 is one-dimensional and extends in a first dimension. Figure 8 In some embodiments, the sawtooth configuration comprises a one-dimensional array of uniformly spaced sawtooths (also referred to as "bumps" or "teeth") separated by a surface angled relative to the plane of the light control film 812 / optical component (i.e., angled relative to a horizontal plane or xy plane). Therefore, in Figure 8 In one embodiment, the cross-section of the sunlight-receiving surface 820 has a generally serrated configuration. Furthermore, in... Figure 8 In this embodiment, the evenly spaced serrations are aligned with the louvers. Therefore, it can be said that the periodicity of the serrations on the sunlight receiving surface 820 is essentially equal to the periodicity of the louver array.

[0124] As per the above reference Figure 7 The light transmitted by the light-control film 812 is confined within an angular range 806 defined by the orientation, spacing, and geometry (e.g., sidewall angle) of the louvers. Therefore, the image light 804 from the optical components of the head-up display (not shown) is transmitted only at a limited angle falling within angle 806, so that it passes through the light-control film 712 between the louvers and reaches the eye box along the light path. Furthermore, as referenced above… Figure 7 The sunlight 800 coupled to the light control film 812 is either absorbed by one of the louvers and / or blocked from reaching the eye box due to the limited range of the transmission angle 806.

[0125] Furthermore, according to the invention, due to the sawtooth configuration, sunlight 800 reflected by the top surface 820 (i.e., the external interface with air) is reflected in a direction away from the eyepiece (e.g., in automotive applications, as described herein, in a direction away from the windshield that reflects the image light to the eyepiece), as shown by the dashed lines. Specifically, due to the angled second (top / outer) surface 820 of the light-control film 812 above the optically transparent core region between the louvers, the surface normal is similarly angled relative to the normal of the plane (i.e., the horizontal plane or the xy plane) of the light-control film 812 / optical component. Therefore, due to the law of reflection, with Figure 7 Compared to the reflection angle of the planar surface 720 of the light-controlling film 712, the angle of sunlight 800 changes (e.g., increases). In the example, the angled surface is angled or tilted relative to the plane (normal) of the light-controlling film 812 / optical component, with the angle in either direction ranging from 15 to 75 degrees, for example, 30 to 60 degrees. Importantly, the tilt or inclination of the tilted surface of the light-receiving surface 820 causes the angle of the reflected sunlight 802 to be outside the strictly permissible / required angle 806 of the image light 804 from the head-up display, thus the sunlight does not reach the eyepiece along the optical path and causes glare.

[0126] Methods for manufacturing light control films

[0127] In some holographic HUDs, glass waveguides are used to achieve 2D pupil expansion to accommodate the required eyebox size and field of view. Coated waveguides, along with optical steering components, form flat, highly reflective surfaces on a car's dashboard, any of which can be sources of sunlight glare (i.e., sunlight reflected into the observer's eyes). The reflected sunlight enters the eyebox at an angle along the light path emitted by the HUD. This means the driver may experience blindness and / or distraction. Specialized light-control films, also known as louvered films, can be used to reduce unwanted reflections of light emitted from displays (such as LCDs) on car windows. Typically made of plastic, these films have multiple transparent areas separated by light-absorbing louvers, which limit light transmission to a fixed angular range defined by the size and orientation of the louvers. However, these conventional light-control films cannot eliminate reflections from external light sources such as the sun.

[0128] The following reference Figures 9A to 9E A method for manufacturing a light-controlling film is described. The method includes providing a portion of a curable transparent material 902 in an uncured state and a portion of a curable light-absorbing material 904 in an uncured state. The curable transparent material 902 may be transparent silicone rubber. The curable light-absorbing material 904 may be black silicone rubber or a gel. Figure 9A A schematic diagram (not to scale) depicts some uncured transparent material 902 and some uncured light-absorbing material 904.

[0129] The method further includes alternately layering uncured transparent material 902 and uncured light-absorbing material 904. Specifically, a first layer of uncured transparent material 902 is provided. Then, a first layer of uncured light-absorbing material 904 is provided on top of the first layer of uncured transparent material 902. A second layer of uncured transparent material 902 is provided on top of the first layer of uncured light-absorbing material 904, such that the first layer of uncured light-absorbing material 904 is sandwiched between the first and second layers of uncured transparent material 902. A second layer of uncured light-absorbing material 904 is provided on top of the second layer of uncured transparent material 902, such that the second layer of uncured transparent material 902 is sandwiched between the first and second layers of uncured light-absorbing material 904. The transparent material 902 and light-absorbing material 904 are alternately layered until the desired total thickness is obtained. Multiple alternating layers 906 of transparent material 902 and light-absorbing material 904 can be considered as multiple layers of transparent material and light-absorbing material alternately stacked in the stacking direction. Figure 9B This is a cross-sectional view (not to scale) of multiple alternating layers 906 of transparent material 902 and light-absorbing material 904. There can be hundreds to thousands of layers in the multiple alternating layers 906.

[0130] Then, multiple alternating layers 906 undergo a first-stage curing process, allowing the layer to maintain a desired thickness, approximately 1 mm for the transparent layer and approximately 10-100 micrometers for the light-absorbing layer.

[0131] After the first stage of curing, the multiple alternating layers 906 then undergo a longer period of further curing, allowing the multiple alternating layers to achieve the desired physical and optical properties.

[0132] The method also includes providing a cutting tool. The cutting tool has a corrugated or repeating prism structure. The cutting tool defines a (cutting) plane extending from the repeating prism structure. The repeating prism structure includes a front facet and a rear facet. The front facet and the rear facet at least partially define the prism. The cutting tool also includes a ridge defined by the portion where the front facet and the rear facet intersect. There is an angle θ between the front facet and the plane. f There is an angle θ between the back facet and the plane. b The corrugated or repeating prism-like edge is a triangular wave-shaped blade used for cutting. The cutting tool cuts a serrated shape into the surface of the material it is cutting. The serrated shape can be triangular wave-shaped.

[0133] The method also includes a directional cutting tool relative to a plurality of alternating layers 906, such that ridges cover the edges of light-absorbing material layers 904 and front facets cover transparent material layers 902, and the plane is at an angle θ to the stacking direction (vertical / upright direction in FIG9). c . Figure 9C A cross-sectional view (not to scale) of a light-controlled film cut from multiple alternating layers is shown.

[0134] The method further includes cutting through multiple alternating layers at a first cutting plane 908 and a second cutting plane 910 with the triangular wave-shaped blade of the cutting tool while maintaining the orientation of the cutting tool. This results in the light-control film 912 having first and second serrated surfaces opposite to each other. The first and second cutting planes 908 and 910 are parallel to each other. Each of the first and second cutting planes 908 and 910 is oriented at an angle of less than 90° to the stacking direction.

[0135] To avoid any questions, Figure 9C The first dashed line P C Represents the cutting line, the second dashed line P f Representing a serrated surface or front facet, the third dashed line P b Represents the rear facet. In the embodiment, θ b >θ f Angle θ c It is also the angle of the louvers during use (measured from the surface normal). In some embodiments, the inventors have discovered that θ fThe angle must be greater than 30 degrees, for example, greater than 35 degrees, to achieve effective glare suppression (i.e., sunlight reflection suppression). Therefore, in these embodiments, the louver angle must be less than 60 degrees, for example, less than 55 degrees.

[0136] The method also includes depositing a light control film 912 onto an optically transparent serrated substrate 914 to support the structure of the light control film 912. Silicone rubber tends to soften after curing, so if the light control film 912 is located on a flat substrate, its serrated surface will deform. Figure 9D A cross-sectional view (not to scale) of a light-control film 912 deposited on an optically transparent sawtooth substrate 914 is shown, the substrate having serrations corresponding to the serrations of a first or second sawtooth surface. The optically transparent sawtooth substrate 914 has a serrated surface consistent with the serrated first and / or second surfaces of the light-control film 912. Furthermore, the ridges of the serrated first and / or second surfaces are aligned with the ridges of the optically transparent sawtooth substrate 914. Figure 9E A cross-sectional view (not to scale) of the photocontrol film deposited on the substrate is shown.

[0137] Example

[0138] The manufacturing process may include the following steps:

[0139] 1. Preparation of uncured transparent silicone rubber and black silicone rubber gel.

[0140] 2. Alternately lay transparent and black silicone rubber layers to form a block consisting of hundreds to thousands of layers. The material undergoes a first-stage curing process to maintain the required thickness of each layer, with the transparent layer approximately 1 mm thick and the black layer 10-100 μm thick.

[0141] 3. Further curing the block for an extended period of time allows the material to achieve the desired physical and optical properties.

[0142] 4. Cut the block at an angle using a knife with a serrated edge. The serrated edge must be aligned with the spacing of the alternating transparent and black silicone rubber (i.e., the side facets of the serrated edge are parallel to the light from the indicator lamp during operation and remain within the black silicone rubber). The other facet reflects sunlight off the eyepiece.

[0143] 5. After cutting, the film can optionally be placed on a rigid, optically transparent serrated substrate to support the structure. (Silicone rubber is flexible after curing. If it is placed on a flat substrate, the serrated shape may deform).

[0144] Additional features

[0145] 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.

[0146] 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).

[0147] 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 of making a light control film, the method comprising: providing a plurality of alternating layers of transparent material and light absorbing material, wherein the alternating layers of transparent material and light absorbing material are stacked in a stacking direction; and cutting the plurality of alternating layers of transparent material and light absorbing material in first and second cutting planes with a triangular waveform blade, thereby producing a light control film comprising a jagged first surface and a jagged second surface, wherein each of the first and second cutting planes is oriented at an angle of less than 90° to the stacking direction; wherein the triangular waveform blade comprises a cutting edge having a triangular waveform that is perpendicular to the first and / or second cutting planes.

2. The method of claim 1, further comprising placing the light control film on a rigid, optically transparent, jagged substrate to support the light control film.

3. The method of claim 1, wherein, providing the stack comprises: providing a first layer of uncured transparent silicone rubber; providing a first layer of uncured black silicone rubber on the first layer of uncured transparent silicone rubber; providing a second layer of uncured transparent silicone rubber on the first layer of uncured black silicone rubber, such that the first layer of uncured black silicone rubber is between the first and second layers of uncured transparent silicone rubber; and providing a second layer of uncured black silicone rubber on the second layer of uncured transparent silicone rubber, such that the second layer of uncured transparent silicone rubber is between the first and second layers of uncured black silicone rubber.

4. The method of claim 3, wherein, providing the stack further comprises partially curing the layers of uncured silicone rubber to set the thickness of the layers.

5. The method of claim 3, wherein, providing the stack further comprises fully curing the layers of uncured silicone rubber.

6. The method according to any one of the preceding claims, wherein, cutting the plurality of alternating layers comprises aligning a ridge of the triangular waveform blade with an edge of the layer of light absorbing material.

7. The method of claim 6, wherein, the triangular waveform blade comprises a leading facet and a trailing facet that define the triangular waveform, wherein the ridge is defined by the intersection of the leading facet and the trailing facet.

8. The method of claim 7, wherein, cutting the plurality of alternating layers comprises orienting the triangular waveform blade such that the angle between the trailing facet and the first and / or second cutting planes is substantially the same as the angle between the layer of light absorbing material and the first and / or second cutting planes.

9. The method of claim 1, wherein, the jagged first surface comprises a first leading facet that is at an angle of greater than 35° to the first cutting plane.

10. The method of claim 1, wherein, the jagged second surface comprises a second leading facet that is at an angle of greater than 35° to the second cutting plane.

11. The method of claim 1, wherein, each layer of transparent material comprises opposing rough surfaces configured to scatter light.

12. The method of claim 1, wherein, each layer of light absorbing material has a thickness of 10 μιη to 100 μιη.

13. The method of claim 1, wherein, each layer of transparent material has a thickness of 0.1 mm to 10 mm.

14. The method of claim 1, further comprising applying an anti-reflective coating on the jagged first and / or second surface.

15. The method of claim 1, wherein, each layer of transparent material is wedge-shaped.

16. The method of claim 1, wherein, each layer of the plurality of alternating layers is parallel to each other.

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