Compact heads-up display and waveguide therefor

Abstract

A display system includes a waveguide forming a pupil expander. The waveguide includes a pair of opposing surfaces arranged to guide a diffracted light field between them by internal reflections. An input port of the waveguide is arranged to receive light from the display system. An output port of the waveguide is formed by a first transmissive-reflective element of a first surface of the pair of opposing surfaces. The first transmissive-reflective element causes the diffracted light field to be split at each internal reflection, and multiple replicas of the diffracted light field are transmitted out of the waveguide through the output port. The input port includes a second transmissive-reflective element arranged to receive at least a portion of the light from the display system.

Description

Technical Field

[0001] This disclosure relates to pupil expansion or replication, particularly for diffracted light fields comprising diverging light beams. More specifically, this disclosure relates to a display system including a waveguide pupil expander and a method for pupil expansion using waveguides. Some embodiments relate to two-dimensional pupil expansion using first and second waveguide pupil expanders. Some embodiments relate to an image generation unit and a head-up display, such as an automotive head-up display (HUD). Background Technology

[0002] Light scattered from an object contains amplitude and phase information. This amplitude and phase information can be obtained through a public...

[0003] Known interferometry techniques capture images on, for example, a photosensitive plate to form a holographic record, or "hologram," which includes interference fringes. The hologram can be reconstructed by illuminating it with appropriate light to form a two-dimensional representation of the original object.

[0004] Or, three-dimensional holographic reconstruction or replay of images.

[0005] 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 holography...

[0006] The image can be called a Fresnel / Fourier transform hologram or simply a Fresnel / Fourier hologram. A Fourier 20 hologram can be considered a Fourier domain / plane representation of an object or a frequency domain / plane representation of an object. Example

[0007] For example, computer-generated holograms can also be calculated using coherent ray tracing or point cloud techniques.

[0008] 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.

[0009] 25 Spatial light modulators typically include multiple individually addressable pixels, which can also be referred to as single...

[0010] A spatial light modulator can be a binary, multi-level, or continuous device or element. Alternatively, the device can be continuous (i.e., excluding pixels), thus allowing continuous light modulation across the device. A spatial light modulator can be reflective, meaning the modulated light is output via reflection. A spatial light modulator can also be transmissive, meaning the modulated light is output via transmission.

[0011] 30. The system described herein can be used to provide a holographic projector. Such a projector is already used in head-up displays (HUDs). Summary of the Invention

[0012] Various aspects of this disclosure are defined in the appended independent claims.

[0013] 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 image is formed on the display plane or perceived by the observer 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 embodiments, the image is a real image formed by holographic reconstruction, and this image is projected or relayed to the observation plane. The image is formed by illuminating a diffraction pattern (e.g., a hologram) displayed on the display device.

[0014] Display devices consist of pixels. Pixels of a display device can display diffraction patterns or structures that diffract light. The diffracted light can form an image on a plane spatially separate from the display device. According to well-known optical principles, the maximum diffraction angle is determined by the pixel size and other factors such as the wavelength of light.

[0015] In this embodiment, the display device is a spatial light modulator, such as a liquid crystal on silicon (“LCoS”) spatial light modulator (SLM). Light propagates from the LCoS to the observed entity / system (such as a camera or eye) within a certain 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.

[0016] In some examples, the image (formed by the displayed diffraction pattern / hologram) propagates to the eye. For example, spatially modulated light from an intermediate holographic reconstruction / image formed in the free space between the display device and the observer, or on a screen or other light-receiving surface, can propagate to the observer.

[0017] In other examples, the light from the diffraction pattern / hologram itself is propagated to the eye. For instance, the spatially modulated light of the hologram (not yet fully converted into a holographic reconstruction, i.e., an image) (which can be informally described as being "encoded" with / through 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, 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.

[0018] The "light field" mentioned here is a "composite light field." The term "light field" simply refers to a light pattern of finite size in at least two orthogonal spatial directions, such as x and y. The term "composite" 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 complex numbers or a pair of values. For the purposes of holographic calculations, 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.

[0019] According to well-known optical principles, the range of angles at which light propagating from a display device can be observed by the 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 position. 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 position. 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, such as the eye-tracking range).

[0020] 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 farther away than the display device. Conceptually, it can therefore 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 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 pupils of their eyes, which can also be very small. Therefore, at any given time, the field of view shrinks, and the range of specific angles that can be seen is heavily dependent on eye position.

[0021] A pupil expander addresses the problem of increasing the angular range of light propagating from a display device so that it can successfully pass through the pupil of the eye to form an image. Display devices are typically (relatively) small, while projection distances are (relatively) large. In some embodiments, the projection distance is at least an order of magnitude, for example, at least two orders of magnitude, larger than the diameter or width (i.e., the size of the pixel array) of the entrance pupil and / or aperture of the display device. Embodiments of this disclosure relate to a configuration 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 modulated (or encoded with / through a hologram of the image). However, other embodiments of this disclosure may relate to a configuration in which an image, rather than a hologram, is propagated to the human eye, for example, through so-called indirect observation, where light from a holographic reconstruction or "replay" of an image formed on a screen (or even in free space) is propagated to the human eye.

[0022] The use of a pupil expander laterally increases the viewing area (i.e., the user's eyebox), thereby allowing the eye to move to some extent 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 area where the observer's eye can perceive the image. This disclosure relates to non-infinite virtual image distances, i.e., near-field virtual images.

[0023] 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, such as an eyebox or eye-tracking range for the observer to view. Light received from a display device (e.g., spatially modulated light from LCOS) is replicated by this waveguide or each waveguide to increase the field of view (or observation area) in at least one dimension. In particular, the waveguide expands the observation window by generating additional light or "replicas" through the division of the amplitude of the incident wavefront.

[0024] In some embodiments, the first pair of opposing surfaces of the waveguide are elongated or slender surfaces, relatively long along a first dimension and relatively short along a second dimension (e.g., relatively short along each of the 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 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., in its "elongated" direction).

[0025] This paper discloses a system that uses diffracted light to form an image and provides an eyebox size and field 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 diffractive structure (e.g., a hologram such as a Fourier or Fresnel hologram or a point cloud hologram). The use of diffraction and diffractive 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 (e.g., diffracted light comprising divergent (non-collimated) beams) for 2D pupil expansion.

[0026] In some aspects, the display system includes display devices, such as pixelated display devices, such as spatial light modulators (SLMs) or liquid crystal on silicon (LCoS) SLMs, which are arranged to provide or form diffracted (e.g., diverging) light. In these aspects, 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 array of light-modulating pixels contained in 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 the exit pupil of the system is expanded to reflect that the exit pupil of the system (which is limited by a small display device having pixel sizes for light diffraction) becomes larger in the space extended by using at least one pupil expander.

[0027] A diffracted (e.g., 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 / diverged, the light field size increases with the propagation distance.

[0028] 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 corresponding 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.

[0029] 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.

[0030] A first waveguide pupil expander can be arranged to provide pupil expansion or replication in a first direction, and 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, of the replicas it receives from the first waveguide pupil expander in the different second directions. The second waveguide pupil expander can be arranged to receive the light field directly or indirectly from the first waveguide pupil expander. One or more other elements can be provided along the propagation path of the light field between the first and second waveguide pupil expanders.

[0031] The first waveguide pupil expander may be substantially elongated (e.g., rod-shaped), while the second waveguide pupil expander may be substantially planar (e.g., rectangular). 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 width along a second dimension substantially orthogonal to the first dimension. The dimension or length of the first waveguide pupil expander along its first dimension corresponds 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 area defined by the output port on the first surface of the pair of parallel surfaces of 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.

[0032] The first and second waveguide pupil expanders can jointly provide pupil expansion in a first direction and a second direction orthogonal 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 can generally be referred to as a "pupil expander".

[0033] 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 an expanded eyebox region from which the observer can receive light from the input diffracted or diverging light field. It can be said that the eyebox region lies on or defines the observation plane.

[0034] The two directions of the exit pupil expansion can be coplanar or parallel to the first and second directions in which the first and second waveguide pupil expanders provide replication / expansion. Alternatively, in arrangements that include other elements such as optical combiners, e.g., a vehicle's windshield (or windshield), the exit pupil can be considered as an exit pupil from that other element, such as an exit pupil from the windshield. In such an arrangement, the exit pupil can be non-coplanar and non-parallel to the first and second directions in which the first and second waveguide pupil expanders provide replication / expansion. For example, the exit pupil can be substantially orthogonal to the first and second directions in which the first and second waveguide pupil expanders provide replication / expansion.

[0035] 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.

[0036] 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.

[0037] The display device can have an effective or display area with a first dimension 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 within less than 20 ms, for example, less than 15 ms or less than 10 ms.

[0038] In some embodiments, described only by way of examples of diffractive or holographic light fields according to this disclosure, a hologram is configured to route optical paths into multiple channels, each corresponding to a different portion (i.e., sub-region) of an image. The hologram can be displayed on a display device such as a spatial light modulator. When displayed on a suitable display device, the hologram can spatially modulate light that can be converted into an image by an observation system. The channels formed by the diffractive structures (including the hologram) 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 hologram 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 can also be a point cloud hologram. Holograms are described in this paper as having optical paths routed through multiple holographic 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 holographic channel corresponds to each image sub-region. Importantly, the hologram in this example is characterized by how it distributes its image content when illuminated. Specifically, the hologram divides its image content by angles. That is, 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 arbitrarily divided into multiple holographic channels, where each holographic channel is defined by a range of ray angles (two-dimensional). As understood above, any holographic channel that can be considered in the spatially modulated light (i.e., a sub-range of ray angles) will be associated with a corresponding part or sub-region of the image. That is, all the information needed to reconstruct that part 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 spatially modulated light is observed as a whole, there is not necessarily any evidence of multiple discrete optical channels. However, in some arrangements, multiple spatially separated holographic channels are formed by intentionally leaving blank or empty areas of the target image from which the hologram is calculated (i.e., no image content).

[0039] 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 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 (special type of) holograms disclosed herein are characterized and identified by the distribution of image content within the hologram-encoded light. Again, to avoid any doubt, references in this document 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 diffraction or diffracted light field.

[0040] In summary, this paper discloses a system for providing pupil expansion for an input light field, wherein the input light field is a diffracted or holographic light field comprising a diverging beam of light. As described above, by creating one or more replicas of the input light rays (or beams of light), pupil expansion (also referred to as "image replication," "copying," or "pupil replication") increases the size of the area in which an observer can see the image (or receive the light of the hologram, and the observer's eye forms the image). Pupil expansion can be provided in one or more dimensions. For example, two-dimensional pupil expansion can be provided, where each dimension is substantially orthogonal to its respective other dimension.

[0041] The system can be provided in a compact and streamlined physical form. This makes it suitable for a wide range of real-world applications, including those with limited space and high property value. For example, it can be implemented in a head-up display (HUD), such as a vehicle or automotive HUD.

[0042] According to this disclosure, a pupil expansion is provided for diffracted light or diffracted beams, which may include a diverging beam of light. The diffracted light or diffracted beams may be output by a display device, such as a pixelated display device, or a spatial light modulator (SLM) arranged to display a diffractive structure (e.g., a hologram). The diffracted light field may be defined by a "light cone". Therefore, for a diverging light field, the size 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).

[0043] Spatial light modulators can be arranged to display a hologram (or a diffraction pattern including a hologram). The diffracted or diverging light can include light encoded with / through a hologram, rather than the light from the image or holographic reconstruction. Therefore, in such embodiments, it can be said that the pupil expander replicates a hologram or forms at least one copy of a hologram to convey that the light transmitted to the observer is spatially modulated according to a hologram of the image rather than the image itself. That is, a diffracted light field is propagated to the observer.

[0044] In some embodiments, two one-dimensional waveguide pupil expanders are provided, each arranged to effectively increase the size of the system's output pupil by forming multiple replicas or copies of the output pupil (or the light from the output pupil) of the spatial light modulator. The output pupil can be understood as the physical area of ​​the system's output light. Alternatively, each waveguide pupil expander is arranged to expand the size of the system's output pupil. Also, each waveguide pupil expander is arranged to expand / increase the size of the eyebox in which an observer's eye can be placed in order to see / receive the light output by the system.

[0045] In this disclosure, the term "replica" is used only to reflect that spatially modulated light is segmented such that the 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 replication event, such as partial reflection-transmission by a pupil dilator. Each replica travels along a different optical path. Some embodiments of this disclosure relate to the propagation of light encoded with holograms rather than images, i.e., light spatially modulated with a hologram of an image rather than the image itself. Those skilled in the art of holography will understand that the composite light field associated with the propagation of holographically encoded light will vary with the propagation distance. The term "replica" as used herein is independent of propagation distance, so two branches or paths of light associated with a replication 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 replication event or a series of replication events.

[0046] According to this disclosure, a "diffracted light field" or "diffractive 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 a playback plane. The holographic light field propagating from the hologram to the playback plane can be said to include light encoded by / through 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 diffracting 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 diffracting structure. An optical system is disclosed herein for propagating a diffracted light field from a diffracting structure to an observer (e.g., from a display device to an observation system). The diffracted light field can form an image.

[0047] The optical system includes a waveguide, such as the waveguide pupil expander described herein. The waveguide includes an input port, an output port, and a pair of opposing surfaces. The pair of opposing surfaces is arranged to guide a diffracted light field therebetween via internal reflection. The input port is arranged to receive light from a display system. The output port is formed by a first transmission-reflection element on a first surface of the pair of opposing surfaces. The first transmission-reflection element causes the diffracted light field to be segmented upon each internal reflection, and multiple copies of the diffracted light field are transmitted out of the waveguide through the output port. The input port includes a second transmission-reflection element arranged to receive, partially transmit, and partially reflect at least a portion of the light from the display system.

[0048] In conventional waveguides arranged to guide a diffracted light field via internal reflection, the input port typically includes an optically transparent incident window or opening, and the waveguide is oriented such that the propagation axis of the diffracted light field is incident on the input port at a desired angle. This arrangement avoids the need for an input coupler at the input port to couple light into the waveguide at the desired angle. For example, a conventional input coupler may include a grating structure specifically configured to diffract incident collimated light of a particular wavelength into the waveguide at a desired angle to provide phase matching and effective in-coupling. However, such an input coupler is typically undesirable for the input of a diffracted light field, in which the light beam diverges. Furthermore, those skilled in the art will recognize that additional diffraction of the diffracted light field received by the grating coupler from the display system can undesirably alter the diffracted light field, thereby adversely affecting image quality.

[0049] Therefore, compared to conventional waveguides, the input port of the waveguide disclosed herein is at least partially formed by a transmission-reflection element. That is, at least a portion of the surface of the waveguide forming the input port is partially transmissive and partially reflective of light. Thus, the transmission-reflection element of the input port is arranged to receive, partially transmit, and partially reflect at least a portion of the light from the display system. This is counterintuitive, as it reduces the optical efficiency of coupling the received light into the waveguide by partially reflecting a certain proportion of the light incident on the transmission-reflection element and thus preventing its internal coupling. However, as described herein, this allows all the light rays of the diverging beam incident on the input port to be internally coupled and trapped (referred to herein as “proper” or “complete” coupling), although at the cost of lower optical efficiency due to reduced coupling efficiency of the received light, and the potential loss of some light returning through the input port after one reflection from the opposing surfaces of the waveguide. Therefore, in embodiments including multiple angular channels of a diffracted light field, this allows light representing all different angular components to be coupled into the waveguide and then trapped inside the waveguide, at the cost of lower optical efficiency. Furthermore, there are no restrictions on the size of the light beams that can be coupled into the waveguide (e.g., the maximum diffraction angle corresponding to the cone angle). Instead, all light beam angles of the diffracted field can be preserved.

[0050] In one embodiment, the second transmission-reflection element is arranged to internally reflect at least some of the diffracted light field within the waveguide. In some examples, the second transmission-reflection element is configured such that at least some of the diffracted light field is incident on it only once. In one example, the second transmission-reflection element is configured such that all rays of the diffracted light field are incident on it only once.

[0051] An input port may be formed on a second surface of the pair of opposing surfaces. The waveguide may also include a reflective element arranged to reflect the diffracted light field internally within the waveguide. The reflective element may be arranged on the second surface immediately adjacent to the input port. In some examples, the transmittance of the second surface is continuous, for example, continuously decreasing, from the starting point of the second transmission-reflection element to the ending point of the reflective element.

[0052] The second transmission-reflection element may include a surface coating or layer that partially reflects and partially transmits light. The surface coating may cover at least a portion of the input port region (i.e., a "portion" of the input port). For example, the surface coating may extend beyond a portion of the length of the input port in the waveguide direction. The term "coating" is used only to indicate that the element covers a segment or region of the input port, and not to indicate the manner in which the element is formed or manufactured. Thus, in some examples of surface coatings, the second transmission-reflection element may be a partially reflective-partially transmittance component or facet that is superimposed to cover a portion of the input port region. In other examples of surface coatings, the second transmission-reflection element may be one or more layers of partially reflective and partially transmittance material formed on a portion of the input port region on the waveguide surface, thereby covering that portion of the region. The second transmission-reflection element (e.g., the surface coating) may be substantially planar.

[0053] In the examples described herein, the region or segment comprising the input port of the second transmissive-reflective element is continuous along its length (i.e., in the waveguide direction). The second transmissive-reflective element can be described as uniform because it uniformly covers the continuous portion of the input port. However, in some examples, the reflectivity-transmittance of the element may be gradient, and therefore variable over the continuous portion, for example, gradient along the length of the input port. In some examples, the gradient is achieved using a series of stacked thin film layers. As a result, the thickness of the second transmissive element is substantially uniform, but may vary slightly due to the different number of thin film layers at different locations along the gradient direction.

[0054] In some embodiments, the second transmissive-reflective element is arranged to receive all light from the display system. In other embodiments, the input port also includes a transmissive element or region arranged to receive a portion of the light from the display system. The transmissive element may be adjacent to the second transmissive-reflective element, and / or the second transmissive-reflective element may be adjacent to a reflective element.

[0055] In waveguide implementations, the display system includes a spatial light modulator arranged to display a hologram and / or spatially modulate the diffracted light field according to the hologram. In some examples, the display system includes a display device having a pixel region that defines an exit pupil of the display system extended by the waveguide.

[0056] A system including a waveguide, such as a display system or a projection system, is also provided. The waveguide is the second one-dimensional pupil expander in a pair of waveguide pupil expanders, which are arranged to expand the pupil of the system in a first direction and a second orthogonal direction, respectively.

[0057] In some embodiments, the diffracted light field comprises a diverging beam of light. Reference is made herein to a diffracted light field comprising light rays having multiple different ray angles. While embodiments describe diverging beams of light, those skilled in the art will understand that the same basic principles can be applied to the propagation of converging beams of light. Therefore, more generally, this disclosure relates to a waveguide arranged to guide a “non-collimated” or “uncollimated” light field or beam of light. However, in the described embodiments, the size or range of the diverging beam of light may be characterized by the maximum and minimum ray angles relative to the optical axis / projection axis or, for example, relative to the normal to the light-receiving surface of the waveguide or display device. In some embodiments, the diffracted light field is formed by a display device comprising pixels. In some embodiments, the diffracted light field is encoded or spatially modulated according to a hologram displayed on the display device. In some embodiments, the diffracted light field propagates from an image of the display device formed inside or outside the waveguide. In some embodiments, but not all, the light received at the input port is a diffracted light field. In some embodiments, the image formed by the diffracted light field is a virtual image.

[0058] This invention relates to various "elements" of waveguides, and to their optical transmittance and / or reflectance. In some embodiments, each element is a segment of a surface of a waveguide extending in the waveguide direction. Thus, the term "segment" refers to a continuous (i.e., uninterrupted) region forming a portion of a corresponding surface of the waveguide. Typically, the surface of the waveguide is substantially planar, and therefore segments of the surface are also substantially planar. The direction of the waveguide is the direction in which the light field is generally guided by the waveguide, although the light actually reflects back and forth between the two surfaces. In embodiments, the direction of the waveguide is also the direction of the pupil expansion of the display system and / or the direction in which a replica of the diffracted light field is output through the output port. Each element is configured to receive light and transmit and / or reflect light as described. Some elements in some embodiments receive light multiple times, for example, at multiple different points along their length in the waveguide direction. In some embodiments, different elements (in the waveguide direction) are adjacent, and the optical properties (e.g., reflectance) of adjacent elements can be "continuous." The term "continuous" is used to indicate that there is no abrupt change or discontinuity in the optical properties at the boundary between adjacent elements. In some embodiments, the continuity of optical properties at the boundary between adjacent elements makes the elements indistinguishable by those optical properties. However, these elements can still be distinguished by other functions they perform. In embodiments, the term "transmission" means substantially complete transmission of light received for a waveguide, e.g., T > 0.9. In embodiments, the term "reflection" means substantially complete reflection of light, e.g., R > 0.9. In embodiments, the terms "transmission-reflection," "semi-transmission-reflection," or "partial transmission-reflection" refer to materials or materials or materials with both a transmittance such as T > 0.1 and a reflectance such as R > 0.1.

[0059] 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 "reproduction field" is used to refer to a 2D region in which the holographic reconstruction is formed and fully focused. If the hologram is displayed on a spatial light modulator including pixels, the reproduction field will be repeated in the form of multiple diffraction orders, where each diffraction order is a copy of the zero-order reproduction field. The zero-order reproduction field typically corresponds to the preferred or dominant reproduction field because it is the brightest reproduction field. Unless explicitly stated otherwise, the term "reproduction field" should be considered to refer to the zero-order reproduction field. The term "reproduction plane" is used to refer to a plane in space containing all the reproduction fields. The terms "image," "reproduced image," and "image region" refer to the region of the reproduction field illuminated by the holographically reconstructed light. In some embodiments, an “image” may include discrete points, which may be referred to as “image points” or, for convenience, “image pixels”.

[0060] The terms "encoding," "writing," or "addressing" are used to describe the process of providing multiple control values ​​to multiple pixels of an SLM, each of which determines the modulation level of the pixel. It can be said that 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 this hologram can be considered an array of optical modulation values ​​or levels.

[0061] 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. The embodiments relate to phase-only holograms, but this disclosure is equally applicable to amplitude-only holography.

[0062] This disclosure is also applicable to forming holographic reconstructions using amplitude and phase information associated with the Fourier transform of the original object. In some embodiments, this is achieved by using composite modulation of a so-called fully composite hologram, which contains amplitude and phase information associated with the original object. Such a hologram can be called a fully composite hologram because the value (gray level) assigned to each pixel of the hologram has amplitude and phase components. 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 composite computer-generated hologram is computed.

[0063] The phase value, phase component, phase information, or simply phase of a pixel in a computer-generated hologram or spatial light modulator can be used as a shorthand for "phase delay." 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 pixel in a spatial light modulator described as having a π / 2 phase value would delay the phase of received light by π / 2 radians. 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 gray levels. For convenience, the term "gray level" can also be used to refer to a plurality of available composite modulation levels in a composite modulator.

[0064] Therefore, a hologram contains an array of gray levels, i.e., an array of optical modulation values, such as phase delay values ​​or composite 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 comparable to, and typically smaller than, the pixel spacing of the spatial light modulator. Reference is made here to combining a hologram with other diffraction patterns, such as diffraction patterns used as lenses or gratings. For example, a diffraction pattern used as a grating can be combined with a hologram to translate the reproduction field on the reproduction plane, or a diffraction pattern used as a lens can be combined with a hologram to focus the holographic reconstruction onto the reproduction plane in the near field.

[0065] Although different embodiments and groups of embodiments may be disclosed individually 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 permutations of the features disclosed in this disclosure are contemplated. Attached Figure Description

[0066] Referring to the following figures, specific embodiments are described by way of example only:

[0067] Figure 1 This is a schematic diagram of a reflective SLM that generates holographic reconstruction on a screen;

[0068] Figure 2 An image comprising multiple image regions (bottom) and a corresponding hologram comprising multiple holographic components (top) are shown;

[0069] Figure 3 The diagram shows a hologram characterized by transmitting or channelizing holographically encoded optical paths into multiple discrete hologram channels.

[0070] Figure 4 A system is shown that is arranged to transmit through different optical paths Figure 3 The light content of each hologram channel is transmitted to the eye;

[0071] Figure 5 A perspective view of a pair of stacked image replicators arranged to extend a beam in two dimensions is shown.

[0072] Figure 6 This demonstrates the optimal or ideal coupling of a collimated beam into a waveguide through an input port including an optically transparent window;

[0073] Figure 7 The image shows an uncollimated beam of light coupled into a waveguide through an input port including an optically transparent window;

[0074] Figure 8 The first embodiment of the present invention illustrates the coupling of a diffracted light field into a waveguide including an input port;

[0075] Figure 9 The image shows a light beam from a diffracted light field coupled into a waveguide including an input port, according to a second embodiment of the present invention.

[0076] Figure 10 It is a graph showing the ideal surface transmission of a waveguide with an input port including a transparent window and the distances to the incident and exit surfaces;

[0077] Figure 11 This is a graph showing the surface transmittance of a waveguide having an input port including a uniformly portioned transmission-reflection element according to an embodiment, versus the distance between the incident and exit surfaces.

[0078] Figure 12 It is a graph showing the surface transmittance of a waveguide with an input port according to other embodiments as a function of the distance between the incident and exit surfaces, the input port including a gradient partial transmission-reflection element.

[0079] In all the accompanying drawings, the same reference numerals will be used to refer to the same or similar parts. Detailed Implementation

[0080] This invention is not limited to the embodiments described below, but extends to the full scope of the appended claims. That is, the invention can be embodied in different forms and should not be construed as limited to the described embodiments, which are set forth for illustrative purposes.

[0081] Unless otherwise stated, a singular term may include a plural term.

[0082] A structure described as being formed above or below another structure should be interpreted to include cases where these structures are in contact with each other, and also cases where a third structure is arranged between them.

[0083] When describing temporal relationships, such as when the chronological order of events is described as "after," "following," "next," "before," etc., this disclosure should be understood to include both consecutive and discontinuous events unless otherwise stated. For example, unless terms such as "just," "immediately," or "directly" are used, the description should include discontinuous cases.

[0084] 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 one element from another. 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.

[0085] Features of different embodiments may be partially or wholly coupled or combined with each other, and may interoperate differently with each other. Some embodiments may be implemented independently of each other, or may be implemented together in an interdependent relationship.

[0086] Optical configuration

[0087] Figure 1 One 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, the 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 the holographic reconstruction is formed in a playback field, such as a light-receiving surface like a screen or diffuser.

[0088] A light source 110, such as a laser or laser diode, is configured to illuminate the SLM 140 through a collimating lens 111. The collimating lens causes the wavefront of the light, approximately in a plane, to be incident on the SLM. Figure 1 In this embodiment, the wavefront is oriented away from the normal (e.g., 2 or 3 degrees away from being truly perpendicular to the plane of the transparent layer). However, in other embodiments, the generally planar wavefront is provided with normal incidence, and beam splitter devices are used to separate the input and output optical paths. Figure 1In the illustrated embodiment, this arrangement causes light from the light source to be reflected by the mirrored back surface of the SLM and interact 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, which is focused on a 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 on the screen 125.

[0089] It is worth noting that in this type of holography, each pixel of the hologram contributes to the overall reconstruction. There is no one-to-one relationship between a specific point (or image pixel) in 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 playback field.

[0090] In these embodiments, the spatial position of the holographic reconstruction is determined by the refractive (focusing) capability 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 the Fourier transform is performed optically. Any lens can act as a Fourier transform lens, but the lens's performance limits the accuracy with which it performs the Fourier transform. Those skilled in the art know how to use lenses to perform optical Fourier transforms.

[0091] Holographic computation

[0092] 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 calculated by Fourier transforming the desired light field in the reproduction plane back to the lens plane. Computer-generated Fourier holograms can be calculated using Fourier transform. Algorithms for generating Fourier holograms of images (using image data representing the image), such as Gerchberg-Saxton type algorithms, are well known in the art and will not be described in detail here. 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 calculated using similar methods. In some embodiments, the hologram is a phase or pure phase hologram. However, this disclosure is also applicable to holograms calculated using other techniques, such as point cloud-based methods. UK patent application GB 2112213.0, filed on August 26, 2021, discloses an example hologram calculation method that can be combined with this disclosure, which is incorporated herein by reference. In particular, this earlier patent application describes a method for calculating one type of hologram, which will be referenced below. Figure 2 and Figure 3 The hologram is described as providing angular segmentation / channelization guidance for the image content.

[0093] In some embodiments, a real-time engine is provided, which is configured to receive image data and compute holograms in real time using algorithms. 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 when needed for display on an SLM. That is, in some embodiments, a library of predetermined holograms is provided.

[0094] Optical modulation

[0095] The display system includes a display device defining an exit pupil of the display system. In embodiments, the display device is a spatial light modulator. For example, the spatial light modulator may be a phase modulator. In some embodiments, the display device is a silicon-based liquid crystal “LCOS” or a spatial light modulator “SLM”, both well-known in the art. The LCOS SLM includes a plurality of pixels, such as an array of quadrilateral LC pixels. Pixels can be addressed or encoded using a diffraction pattern including a hologram. The LCOS SLM can be said to be arranged to “display” a hologram. The LCOS SLM is arranged to be illuminated and output spatially modulated light according to the hologram. The spatially modulated light output by the LCOS SLM includes a diffraction or holographic light field as described herein.

[0096] Optical channelization guidance

[0097] The optical systems disclosed herein are applicable to pupil expansion with any diffractive light field. In some embodiments, the diffractive light field is a holographic light field, i.e., a composite light field that has been spatially modulated according to a hologram of the image rather than the image itself. In some embodiments, the hologram is a special type of hologram that angularly divides / channels the guiding image content. This type of hologram is further described herein merely as an example of a diffractive light field compatible with this disclosure. Other types of holograms can be used in conjunction with the display systems and light engines disclosed herein.

[0098] A display system and method comprising a waveguide pupil expander is described below. As is familiar to the reader in the art, a waveguide can be configured as a “pupil expander” because it can be used to increase the area in which light emitted by a relatively small light emitter (e.g., a relatively small SLM or other pixelated display device used in the arrangement described herein) can be observed by a human observer or other observation system located at a distance (e.g., a relatively large distance) from the light emitter. The waveguide achieves this by increasing the number of transmission points that output light to the observer. As a result, light can be seen from multiple different observer positions; for example, the observer can move their head, thereby moving their line of sight, while still being able to see the light from the light emitter. Thus, it can be said that by using a waveguide pupil expander, the observer’s “eyebox” or “eye movement range” is magnified. This has many useful applications, such as, but not limited to, head-up displays, such as, but not limited to, automotive head-up displays.

[0099] The display system described herein can be configured to guide light (such as a diffracted light field) through a waveguide pupil expander to provide pupil expansion in at least one dimension (e.g., in two dimensions). The diffracted light field can include light output from a spatial light modulator (SLM) such as an LCOS SLM. For example, the diffracted light field can include light encoded by a hologram displayed by the SLM. For example, the diffracted light field can include light from a holographically reconstructed image corresponding to a hologram displayed by the SLM. The hologram can include a computer-generated hologram (CGH), such as, but not limited to, a point cloud hologram, a Fresnel hologram, or a Fourier hologram. The hologram can be referred to as a “diffracted structure” or a “modulation pattern.” The SLM or other display device can be arranged to display the diffracted pattern (or modulation pattern) in a manner familiar to those skilled in the art, the diffracted pattern comprising the hologram and one or more other elements, such as a software lens or a diffraction grating.

[0100] Holograms can be computed to provide channelized guidance for the diffracted light field. This is described in detail in GB2101666.2, GB2101667.0, and GB2112213.0, all of which are incorporated herein by reference. Generally, a hologram can be computed to correspond to an image to be holographically reconstructed. The image corresponding to the hologram may be referred to as the “input image” or the “target image.” A hologram can be computed such that, when displayed on an SLM and properly illuminated, it forms a light field comprising a light cone (output by the SLM) comprising spatially modulated light. In some embodiments, the light cone comprises a plurality of consecutive optical channels of spatially modulated light corresponding to corresponding consecutive regions of the image. However, this disclosure is not limited to this type of hologram.

[0101] Although we refer to it herein as a "hologram" or "computer-generated hologram (CGH)," it should be understood that the SLM can be configured to display multiple different holograms continuously or dynamically according to a sequence. The systems and methods described herein are suitable for the dynamic display of multiple different holograms.

[0102] Figure 2 and 3 An example of one type of hologram that can be displayed on a display device such as an SLM 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.

[0103] Figure 2 An image 252 for projection is shown, comprising eight image regions / components, V1 to V8. Figure 2 Eight image components are shown by way of example only, 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 254 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 angle. Therefore, a characteristic of a hologram lies in the channelization and guidance of light it performs. This is as follows... Figure 3 As shown. 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 imagined. After propagation through the waveguide, the optimal size and shape of the disk can be related to the size and shape of the entrance pupil of the observation system.

[0104] Figure 4 The system 400 is shown, including a display that has been shown as Figure 2 and 3 The display device for the calculated hologram.

[0105] System 400 includes a display device that, in this arrangement, includes an LCOS SLM 402 (which may be simply referred to as LCOS 402). 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 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 light source.

[0106] 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.

[0107] 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 known and can be used. Waveguide 408 is positioned to intersect, for example, a light cone (i.e., a diffracted light field) projected from LCOS 402 at an angle. In this example, the dimensions, orientation, and position of waveguide 408 are configured to ensure that light from each of the eight light beams within the light cone enters waveguide 408. Light from the light cone enters waveguide 408 via a second planar surface (closest to LCOS 402) and is guided at least partially along the length of waveguide 408 before being emitted via a first planar surface of waveguide 408 substantially opposite the second surface (closest to the eye). It is readily understood that the first planar surface is partially reflective and partially transmissive. In other words, as each ray propagates from the second planar surface within waveguide 408 and strikes the first planar surface, some light will be transmitted out of waveguide 408, and some light will be reflected back from the first planar surface to the second planar surface. The second planar surface is (highly) reflective, such that all light striking it from within waveguide 408 will be reflected back to the first planar surface. Thus, some light can be simply refracted between the two planar surfaces of waveguide 408 before being transmitted, while other light can be reflected and thus undergo one or more reflections (or "bouncing") between the planar surfaces of waveguide 408 before being transmitted.

[0108] Figure 4 A total of nine "bounce" points B0 to B8 are shown along the length of waveguide 408. Despite... Figure 2 The light associated with all points in the image (V1-V8) is transmitted out of the waveguide at each "bounce" from the first planar surface of waveguide 408, but only the light from a corner portion of the image (e.g., the 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 corner portions of the image (V1 to V8) reaches the eye 405 from each corresponding "bounce" point. Therefore, in Figure 4 In the example, each corner channel of the encoded light reaches the eye only once from waveguide 408.

[0109] Waveguide 408 forms multiple replicas of the hologram at corresponding "bounce" points B1 to B8 along its length, corresponding to the direction of pupil expansion. For example... Figure 4 As shown, multiple replicas can be pushed back in a straight line to their corresponding multiple replicas or virtual display devices 402'. This process corresponds to the step of "unfolding" the optical path within the waveguide, such that the light from the replicas is pushed back to the "virtual surface" without internal reflection within the waveguide. Therefore, the light from the extended exit pupil can be considered to originate from the virtual surface (also referred to here as the "extended modulator") comprising display device 402 and the replica display device 402'.

[0110] The methods and arrangements described above can be implemented in a variety of different applications and observation systems. For example, they can be implemented in head-up displays (HUDs) or in head-mounted or helmet-mounted devices (HMDs) such as augmented reality (AR) HMDs.

[0111] In some embodiments, the image perceived by an observer or observation system (e.g., a camera) is a virtual image. That is, an image that appears / forms upstream (i.e., behind) the display device. However, this disclosure is equally applicable to forming a real image or simultaneously forming a virtual and a real image using the same hologram.

[0112] Similarly, some embodiments describe waveguides and replication of holograms, but this disclosure is equally applicable to waveguides and replication of images (optionally, images formed from holograms).

[0113] Two-dimensional pupil expansion

[0114] 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 angular content and / or a different portion of the image, but this disclosure and the system described below are not limited to this type of hologram.

[0115] Figure 5 A perspective view of system 500 is shown, which includes two replicators 504 and 506 arranged to extend beam 502 in two dimensions.

[0116] exist Figure 5 In system 500, the first replicator 504 includes a first pair of surfaces stacked parallel to each other and arranged in a manner similar to Figure 4The 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 end of 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 the upper surface, etc.), the beam is reflected. Figure 5 As shown, light from each of the plurality of output points on the first replicator 504 is partially transmitted (as is familiar to the reader in the art), and the light from beam 502 is replicated along the length of the first replicator 504 in a first direction. Therefore, the first plurality of replicated beams 508 are emitted from the first replicator 504 toward the second replicator 506.

[0117] 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 5 Partial transmission of light from each of the plurality of output points on the upper surface shown, and the replication of light from each of the first plurality of beams 508 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 replicas 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.

[0118] Therefore, it can be said that Figure 5 The first and second replicators 504 and 505, combined together, provide a two-dimensional replicator (or “two-dimensional pupil expander”). Each of the first and second replicators 504 and 505 takes the form of a waveguide pupil expander, comprising a pair of opposing surfaces arranged therebetween to guide light through internal reflection, as described herein. Figure 5The waveguides shown each include a pair of first and second opposing surfaces, which are arranged substantially parallel to each other and spatially separated (e.g., through air). In other arrangements, the waveguides may include so-called “plate waveguides,” where the first and second opposing surfaces are opposing (primary) parallel surfaces of a plate of optically transparent solid material. In this case, the first replicator 504 may include an elongated rod-shaped plate for providing an ID pupil expansion in a first direction along the length of the rod, and the second replicator may include a planar rectangular plate for providing pupil expansion in a second direction orthogonal to the first direction.

[0119] Couple the diffraction light field into the waveguide

[0120] Figure 6 This is a schematic ray diagram illustrating optimal or ideal coupling of a collimated beam into a conventional waveguide via an input port including a transparent window.

[0121] Specifically, the waveguide shown includes a pair of opposing surfaces 610, 620 arranged to guide light therebetween in a direction along the length of the waveguide, as illustrated by two example rays representing a beam of light including more rays. In particular, the two example rays are located at the extreme points of the beam (i.e., at opposing “edges” of the beam, described herein as “front edge” and “back edge”). Specifically, the light undergoes a series of internal reflections or “bouncing” between the pair of opposing surfaces 610, 620. The first surface 610 of the pair of opposing surfaces includes a first transmission-reflection element (e.g., a surface including a partially reflective-partially transmission coating) that forms the output port of the waveguide. Thus, as... Figure 6 As shown, due to the segmentation of light by the first transmission-reflection element at each internal reflection or "bounce" at the first surface 610, a series of replicas of the two example light rays are formed. These replicas are transmitted through the output port of the waveguide, as indicated by the arrow. The second surface 620 of the pair of opposing surfaces includes a reflective element (e.g., a surface including a (highly) reflective coating) having a transparent window 630 forming an input port therein. In the arrangement shown, the transparent window 630 is adjacent to the first end 680 of the waveguide, such that light is guided from the input port in a direction toward the second end 690 of the waveguide.

[0122] For a beam with a width of W (including such as Figure 6The optimal or ideal coupling of the beams (a beam of light parallel to each other) is achieved by aligning the ray at the leading edge of the beam (i.e., furthest from the first end 680 of the waveguide or furthest to the right in the figure) with the corresponding edge of the transparent window 630 (i.e., the right-hand edge in the figure). The incident angle of the beam causes the ray at the trailing edge of the beam (i.e., closest to the first end 680 of the waveguide or furthest to the left in the figure) to couple into the waveguide through a first "bounce" at the first surface 610 and be captured inside the waveguide. Therefore, all the rays of the (collimated) beam are incident on the second surface 620 at the same angle of inclination, pass through the transparent window 630, and are fully coupled into the waveguide. As a result, all the rays of the beam are incident on the first transmission-reflection element of the first surface 610 at the same angle of inclination. It is worth noting that this results in a series of internal reflections or "bouncings" of the light, and a corresponding series of replicas output, which are parallel to each other, as shown. Figure 6 As shown. Therefore, there is no loss of light from the input (collimated) beam, and everything of the input beam exists in all the copies of the extended exit pupil at the output port.

[0123] However, in some applications, the beam may not be collimated, so that all the rays are not perfectly parallel to each other. For example, the beam may be divergent, causing the ray beam to take the form of a light cone, where the size of the diffracted light field (as defined in a two-dimensional plane) increases with the propagation distance. In particular, in some applications, the beam must diverge in order to image at a finite virtual image distance, rather than in the far field, i.e., at infinity. Therefore, it is important that the rays propagate in different directions. As those skilled in the art will understand, in other applications, the beam may be convergent, and the teachings of this disclosure apply equally to divergent and convergent beams.

[0124] Figure 7 It is similar to Figure 6 A schematic ray diagram illustrates coupling a diverging beam through an input port including a transparent window into a conventional waveguide. The beam is coupled with... Figure 6 The collimated beam is aligned with the input port in the same way.

[0125] Similar to Figure 6 waveguide, Figure 7 The waveguide includes a pair of opposing surfaces 710, 720 arranged to guide light between them along their length, as shown by example rays, which represent beams of light including more rays with different ray angles. Specifically, the light undergoes a series of internal reflections or "bouncing" between the pair of opposing surfaces 710, 720. The first surface 710 of the pair of opposing surfaces includes a first transmission-reflection element forming the output port of the waveguide. As indicated by the arrows, a series of replicas are formed and transmitted through the output port, as referenced above. Figure 6 The second surface 720 of the pair of opposing surfaces includes a reflective element having a transparent window that forms an input port adjacent to the first end 780 of the waveguide, as described above. Figure 6 As stated above.

[0126] Figure 7 Two pairs of example rays are shown. Specifically, the first pair of example rays includes a first example ray 703 (represented by a dashed line) at a first angle and a second example ray (represented by a solid line) at a second angle. The second pair of example rays includes a third example ray 704 (represented by a dashed line) at a third angle and a fourth example ray (represented by a solid line) at a fourth angle.

[0127] Some rays in the beam are parallel to each other, as shown by the second and fourth rays of the first and second pair of example rays. These example / representative rays are orthogonal to the display device (not shown), i.e., the second and fourth angles are 0° (or parallel) to the surface normal of the display device, and therefore can be considered parallel to the propagation direction (or propagation axis) of the beam. These rays are incident on the second surface 720 at the same angle of inclination, pass through the transparent window, and remain in the waveguide, as shown in the example. Figure 6 As shown. Therefore, the "parallel" rays of the beam (corresponding to the second and fourth example rays shown by solid lines) are incident on the first transmission-reflection element of the first surface 710 at the same angle of inclination. The fourth example ray of the second pair of example rays of the beam (i.e., the one furthest from the first end 780 of the waveguide or furthest to the right in the figure) is aligned with the corresponding edge of the transparent window 630, as shown. Figure 6 That's how it is. Therefore, as Figure 7 As shown by the solid lines in the diagram, the second and fourth example rays are fully coupled into the waveguide and guided between the pair of opposing surfaces 710 and 720, which are parallel to each other.

[0128] However, some rays in the beam have different angles (i.e., have a propagation direction or propagation axis that is not parallel to the beam). Such rays are illustrated by the first and third example rays of the first and second pairs of example rays, although it will be understood that many other rays at multiple other ray angles will exist in the beam of the diverging beam. Specifically, the first example ray 703, indicated by the dashed line, is at a first angle, and the third example ray 704 is at a third angle, wherein the first and third angles are different from each other and different from the second / fourth angle.

[0129] like Figure 7As shown, a first example ray 703 (indicated by dashed lines) is incident on the second surface 720 near the first end 780 of the waveguide (i.e., furthest to the left in the figure). Therefore, the first example ray 703 passes through the transparent window into the waveguide and is incident on the first transmission-reflection element of the first surface 710. However, the first example ray 703, indicated by dashed lines, is incident on the second surface 720 at a different angle than the second (and fourth) example rays, indicated by solid lines. Specifically, the first angle of the first example ray 703 is at its maximum angle (the maximum angle relative to the surface normal of the display device / propagation direction or axis) at the trailing edge of the diverging beam. Therefore, since the first angle of the first example ray 703 forms a non-zero angle with the surface normal of the display device / propagation axis of the beam, it has a smaller angle of incidence on the second surface 720 and a larger angle of incidence on the first surface 710 compared to the second example ray indicated by solid lines. Therefore, the first internal reflection or "bounce" of the first example ray 703 at the first transmission-reflection element of the first surface 710 is "steeper" than the equivalent internal reflection or "bounce" of the second and fourth example rays. As a result, the first example ray 703 is reflected back to the position at the transparent window of the second surface 720 and is transmitted through the transparent window out of the waveguide, as indicated by the arrow. Therefore, the first example ray 703 is not properly coupled into the waveguide and is instead lost.

[0130] The third example ray 704 is incident on the leading edge of the transparent window on the second surface 720 (farthest from the first end 780 of the waveguide, or as far as the right side of the figure). The third angle of the third example ray 704 is at its maximum angle (the maximum angle relative to the propagation direction / axis) at the leading edge of the diverging beam, preventing it from passing through the transparent window into the waveguide. Therefore, the third example ray 704 is also not properly coupled into the waveguide and is instead lost.

[0131] As described above, the first and third example rays 703 and 704 have ray angles at opposite, extreme positions corresponding to the ray beam of the diverging beam, including many other rays at different ray angles. Therefore, the first and third example rays 703 and 704 are merely two examples of rays of the diverging beam that may be lost.

[0132] therefore, Figure 7 Coupled image beams to a conventional waveguide via an input port including a transparent window result in poor image quality because some rays in the input beam (e.g., rays at the edges) are lost. Therefore, the content carried by the lost rays may not be coupled into and propagate through the waveguide to form a copy. Consequently, the lost content may not be visible at the corresponding location in the eyepiece. Due to this problem, a significant degrade in image quality is observed because not all image content is transmitted to all eyepiece locations.

[0133] For example, in holographic projection systems, the aforementioned light loss problem is particularly problematic for coupling diffracted light fields (i.e., the "light of the hologram" or "light signal carrying the hologram" as described herein) into waveguides. In particular, in some applications as described above, the diffracted light field can be divergent (or convergent). Therefore, some rays, especially at the edges of divergent beams, may be lost, resulting in the loss of associated image content of the beam coupled into the waveguide.

[0134] Furthermore, in embodiments including holograms that guide the angular division / channelization of image content as described above, these rays can form (at least a portion) individual holographic channels, each containing angular content corresponding to a specific portion of the image to be observed. Therefore, the light output from the waveguide output port (i.e., the replica) may not contain all holographic channels corresponding to the portion of the image content, thus enabling the observation system to holographically reconstruct the complete target image. Specifically, as those skilled in the art will understand, each "replica" formed by the waveguide must contain rays from all ray angles (corresponding to angular components / holographic channels) so that the observation system faithfully reconstructs the image at the corresponding eyebox location. The loss of some rays means that at least some replicas do not contain rays from one or more desired ray angles. In summary, the loss of rays can result in the complete loss of a portion of the image content, leaving gaps in the image perceived by the observer. These gaps in the image content can be described as "dark bands" at certain locations within the eyebox.

[0135] Recognizing this problem, the inventors proposed replacing the optically transparent window forming the input port of the waveguide with an entrance aperture that is at least partially reflective and partially transmissive in a portion of its area. As described below, this ensures that all rays of the beam incident on the entrance aperture are fully or properly coupled into the waveguide. Therefore, when the beam includes a diffracted light field or a hologram, this ensures that all image content encoded by the hologram is properly coupled into the waveguide through the input port and thus output from the extended exit pupil for observation. Thus, the ray coupling efficiency of the waveguide is optimized. It should be understood that the optimization of "ray coupling efficiency" comes at the cost of reduced "optical efficiency" of the waveguide due to light intensity loss caused by reflection at the entrance aperture. Therefore, some embodiments include mitigation measures for the intensity loss of light coupled into the waveguide by increasing the optical power of the beam emitted by the light source, or, in the case of a pulsed beam, additionally or alternatively increasing the duration of the light pulse.

[0136] Partial reflection incident aperture

[0137] Figure 8This is a schematic ray diagram illustrating the coupling of a diverging light beam into a waveguide having an input port (or "incident aperture"), the waveguide including a transmission-reflection element according to a first embodiment. In this arrangement, the light beam... Figure 6 and 7 A beam of light is incident on the input port in a similar configuration. However, the input port is extended (or conversely, the reflective element is displaced) so that the light rays at the leading edge of the diverging beam (i.e., furthest from the first end 880 of the waveguide or furthest to the right in the figure) are incident on it.

[0138] Similar to Figure 6 and 7 waveguide, Figure 8 The waveguide includes a pair of opposing surfaces 810, 820 arranged to guide light therebetween in a direction along the waveguide length from a first end 880 to a second end 890, as illustrated by the example ray. Specifically, the light undergoes a series of internal reflections or "bouncing" between the pair of opposing surfaces 810, 820. The first surface 810 of the pair of opposing surfaces includes a first transmission-reflection element forming the waveguide output port. As indicated by the arrows, a series of replicas are formed and transmitted through the output port, as shown in the reference above. Figure 6 The second surface 820 of the pair of opposing surfaces includes a reflective element 870 that extends along its length to a second end 890 of the waveguide. The second surface 820 also includes a second transmission-reflection element 860 adjacent to the first end 880 of the waveguide, forming an input port or incident aperture.

[0139] Figure 8 Two pairs of example rays are shown. Specifically, the first pair of example rays includes a first example ray 803 (represented by a dashed line) at a first angle and a second example ray (represented by a solid line) at a second angle. The second pair of example rays includes a third example ray 804 (represented by a dashed line) at a third angle and a fourth example ray (represented by a solid line) at a fourth angle.

[0140] according to Figure 8 In some embodiments, the second transmissive-reflective element 860 includes a surface that partially transmits and partially reflects light. In some examples, the second transmissive-reflective element 860 includes a surface with uniform transmittance / reflectance. See below for further details. Figure 11 The description includes an example of a uniform second transmission-reflection element 860. In other examples, the second transmission-reflection element 860 includes a surface with a gradient transmittance in a direction from a first end 880 to a second end 890 of the waveguide. For example, a gradient facet (e.g., a coating with a gradient surface transmittance / reflectance) may be formed across at least a portion of the incident aperture. See below. Figure 12 The description includes an example of a gradient second transmissive-reflective element 860.

[0141] Therefore, the light incident on the entrance aperture is partially transmitted and partially reflected by the second transmission-reflection element 860. Thus, a certain proportion of the light incident on the entrance aperture is transmitted by the second transmission-reflection element 860 and coupled into the waveguide as indicated by the arrow. Simultaneously, the remaining proportion of the light incident on the entrance aperture is reflected by the second transmission-reflection element 860 and is therefore not coupled into the waveguide. For ease of explanation, Figure 8 These reflected rays are omitted from the text.

[0142] Therefore, some rays in the beam's beam, such as the second pair of example rays including the third example ray 804 (indicated by the dashed line) at the leading edge of the beam (i.e., furthest from the first end 880 of the waveguide or furthest to the right in the figure), are used in conjunction with... Figure 7 The second and third example rays are coupled into the waveguide in the same manner, as indicated by the arrows. Specifically, these rays are incident on the second transmission element 860 only once. However, some rays may be incident twice at the entrance aperture. For example, the first pair of example rays, including the first example ray 803 (indicated by the dashed line) at the trailing edge of the beam (i.e., closest to the first end 880 of the waveguide or furthest to the left in the figure), may be incident on the entrance aperture and reflected or “bounced” back to the location of the entrance aperture on the second surface 820. This is equivalent to… Figure 7 The first example ray 703 (indicated by dashed lines) is lost. However, according to this embodiment, these rays are partially internally reflected within the waveguide by the second transmission-reflection element 860 and partially transmitted out of the waveguide (not shown for illustration purposes). Furthermore, due to the expansion of the second end 890 of the radial waveguide of the entrance aperture, some rays at the leading edge of the beam (e.g., the second pair of example rays including the third example ray 804 (indicated by dashed lines)) are incident on the entrance aperture. This is related to the lost... Figure 7 The third example ray 704 (indicated by the dashed line) forms a contrast. Therefore, a portion of the intensity of all these rays is fully coupled into the waveguide by the second transmission-reflection element, as shown by the arrow.

[0143] Advantageously, because a certain proportion of the light is coupled into the waveguide, there is no loss of image content related to the angle of these rays. Therefore, the coupling of the light rays is improved.

[0144] The ratio of light coupled into / out of the waveguide at the entrance aperture depends on the relative transmittance / reflectance of the second transmission-reflection element 860. Furthermore, the size of the beam forming the input beam affects the waveguide's energy efficiency. For example, if the second transmission-reflection element uniformly transmits / reflects partially, the optical efficiency of some rays will decrease. For instance, if the second transmission-reflection element 860 uniformly transmits 50% and reflects 50% (i.e., 50%R, 50%T) along the length of the entrance aperture, the energy loss could be 75% (e.g., the first example ray 803 indicated by the dashed line). Therefore, the relative transmittance / reflectance of the second transmission-reflection element 860 along the length of the entrance aperture can be optimized according to application requirements, including beam size. This can be achieved by selecting one or more coatings formed on the second surface 820 of the waveguide.

[0145] Figure 9 This is a schematic ray diagram illustrating the coupling of a diverging beam into a waveguide having an input port (or "incident aperture"), the waveguide including a transmission-reflection element according to a second embodiment. In this arrangement, the beam... Figure 8 The beam of the embodiment is similarly configured to be incident on the input port, and the input port is configured to be... Figure 8 The same approach is extended from the embodiments.

[0146] As in Figure 8 As in the previous embodiment, Figure 9 The waveguide includes a pair of opposing surfaces 910, 920, arranged to guide light therebetween in a direction along the waveguide length from a first end 980 to a second end 990, as shown by the light rays. Specifically, the light rays undergo a series of internal reflections or "bouncing" between the pair of opposing surfaces 910, 920. The first surface 910 of the pair of opposing surfaces includes a first transmission-reflection element forming the output port of the waveguide. As indicated by the arrows, a series of replicas are formed and transmitted through the output port, as referenced above. Figure 6 The second surface 920 of the pair of opposing surfaces includes a reflective element 970 that extends along its length to a second end 990 of the waveguide. The second surface 920 also includes a second transmission-reflection element 960 adjacent to the first end 980 of the waveguide, forming an input port or incident aperture.

[0147] Figure 9 Two pairs of example rays are shown. Specifically, the first pair of example rays includes a first example ray 903 at a first angle (represented by a dashed line) and a second example ray at a second angle (represented by a solid line). The second pair of example rays includes a third example ray 904 at a third angle (represented by a dashed line) and a fourth example ray at a fourth angle (represented by a solid line).

[0148] In one example, the incident aperture includes a partial transmission / reflection element (e.g., uniformly 50%R, 50%T) 960 that extends only a portion of the length of the incident aperture of the reflective element 970 adjacent to the second surface 920 of the waveguide. The incident aperture also includes a (high) transmission element 950 that extends over the remainder of the incident aperture adjacent to the first end 980 of the waveguide. Some rays of the beam incident on the transmission element 950 of the incident aperture are transmitted through the incident aperture, as indicated by the arrows (e.g., a first pair of example rays including the first example ray 903 (indicated by the dashed line)). These rays are incident on the incident aperture twice because they are internally reflected in a "bounce" through the first surface 910 of the waveguide and incident on the partial transmission / reflection element 960 of the incident aperture at the second surface 920. The second transmission / reflection element 960 of the entrance aperture transmits a certain proportion (e.g., 50%) of the intensity of these rays out of the waveguide (not shown for illustration), while reflecting the remaining proportion (e.g., 50%) of the intensity of these rays back into the waveguide, as indicated by the arrows. Conversely, only a certain proportion (e.g., 50%) of the intensity of some other rays of the beam incident on a portion of the transmission / reflection region 960 of the entrance aperture is transmitted into the waveguide, while the remaining proportion (e.g., 50%) is reflected and does not enter the waveguide (not shown for illustration). These rays are incident on the entrance aperture only once and are internally reflected in a "bounce" through the first surface 910, and incident on the reflective element 970 of the second surface 920, and thus fully coupled into the waveguide.

[0149] In this embodiment, the length of the partial transmission / reflection element 960 of the incident aperture is configured such that all incident rays pass through this region only once. Therefore, all incident rays are fully coupled into and guided within the waveguide with substantially the same optical efficiency, in this example, 50%. This results in a consistent pupil expansion for all rays and all image content. Those skilled in optics will understand that this is a simple geometric problem.

[0150] exist Figure 8 and 9 In the illustrated embodiment, each of the first and second pairs of example rays is shown with corresponding ray angles originating from a common location, which may correspond to a pixel of a display device outside the waveguide. However, due to the arrangement of the incident aperture according to the invention, the advantage of improved ray coupling can be achieved regardless of the ray divergence point. For example, if the divergence of the input beam occurs downstream of the incident aperture, then rays incident twice on the incident aperture at ray angles can be appropriately coupled into the waveguide; otherwise, these rays would be lost through the transparent incident aperture.

[0151] Figure 10This shows the light transmission rate. Figure 6 A graph showing the variation in the distance between the opposing first and second surfaces of a (conventional) waveguide. Specifically, the x-axis represents the distance from the first end 680 to the second end 690 of the waveguide. The first y-axis 1010 (on the left-hand side) and the associated line graph (shown as a solid line) represent the light transmission at the second opposing surface 620, which forms the incident surface (i.e., the input port), and the second y-axis 1020 (on the right-hand side) and the associated line graph (shown as a dashed line) represent the light transmission value at the first opposing surface 610, which forms the exit surface (i.e., including the output port). Figure 10 As shown, the light transmittance of the first opposing surface 610 increases with distance from the first end 680 to the second end 690 of the waveguide. At the output port formed by the first surface 610, the transmittance increases with distance from the first end 680, which compensates for the segmentation of light at each "bounce" along the waveguide length (some is reflected / some is transmitted), so that the replica is formed with substantially the same light intensity and is therefore perceived as having the same brightness within the eye box. As is known to those skilled in the art, the desired variation of transmittance with distance from the second surface 610 can be achieved by selecting a suitable gradient surface coating. The light transmittance of the second opposing surface 620 at the first end 680 of the waveguide is 1 (i.e., 100%) and extends a distance of 1030. The distance 1030 corresponds to the width of the transmission window forming the input port of the waveguide. Here, the "width" of the transmission window / incident aperture / input port is measured along the "length" of the waveguide (e.g., from...). Figure 6 (From the first end 680 to the second end 690 of the waveguide). Furthermore, extending from a distance of 1030 to the second end 690 of the waveguide, the second opposing surface 620 has a light transmission value that is substantially 0 (preferably <0.05), which corresponds to the length of the reflective element 640.

[0152] Figure 11 It is similar to Figure 10 of Figure 8 An example of the first embodiment is a graph showing the light transmission as a function of distance, wherein the second transmission-reflection element 860 includes a surface with uniform transmittance / reflectance. Therefore, the x-axis represents the distance from the first end 880 of the waveguide to the second end 890 of the waveguide. The first y-axis 1110 (on the left-hand side) and the associated line graph (shown as a solid line) represent the light transmission at the second opposing surface 820 forming the incident surface (i.e., including the input port), and the second y-axis 1120 (on the right-hand side) and the associated line graph (shown as a dashed line) represent the light transmission at the first opposing surface 810 forming the exit surface (i.e., including the output port). Figure 8 In the embodiments, the first opposing surface 810 including the first transmission-reflection element has a surface with... Figure 6The light transmission varies with distance in the same way as in conventional waveguides. Therefore, the second y-axis 1120 and the associated lines (shown as dashed lines) are similar. Figure 10 The same as in. However, as Figure 11 As shown, the second opposing surface 820 has a light transmittance of 0.3 (i.e., 30%, other examples may have any transmittance in the range of about 0.1 to about 0.5, for example 0.2 to 0.4) at the first end 880 of the waveguide and extends a distance 1130. Distance 1130 corresponds to... Figure 8 The incident aperture / width of the second transmission-reflection element 860, which extends to a point greater than the width of the second transmission-reflection element 860. Figure 6 The width of the transmission window 1030 is slightly longer. Furthermore, extending from distance 1130 to the second end 890 of the waveguide, the second opposing surface 820 has a light transmittance value that is substantially 0 (preferably <0.05), corresponding to the length of the reflective element 640. As those skilled in the art will understand, in this embodiment, the transmittance of the (high)reflective element is less than 0.1, for example less than 0.07 or less than 0.05.

[0153] Figure 12 It is similar to Figure 10 and 11 of Figure 8 Another example of the embodiment is a graph showing the light transmission as a function of distance. In this example, the second (partial) transmission-reflection element 860 of the incident aperture has a gradually changing reflectivity along a portion of its width. Therefore, the x-axis represents the distance from the first end 880 of the waveguide to the second end 890 of the waveguide. The first y-axis 1210 (on the left-hand side) and the associated line graph (shown as a solid line) represent the light transmission at the second opposing surface 820 forming the incident surface (i.e., including the input port), and the second y-axis 1220 (on the right-hand side) and the associated line graph (shown as a dashed line) represent the light transmission at the first opposing surface 810 forming the exit surface (i.e., including the output port). In this embodiment, the first opposing surface 810 including the first transmission-reflection element has a reflectivity that is consistent with... Figure 6 and 8 The waveguide's light transmission varies with distance. Therefore, the second y-axis 1220 and the associated line graph (shown as a dashed line) are similar. Figure 10 and 11 The same as in. However, as Figure 12As shown, the second opposing surface 820 has a light transmittance of 0.14 at the first end 880 of the waveguide (i.e., 14%; other examples may have any transmittance in the range of about 0.1 to about 0.3) and extends to a distance 1230. The distance 1230 corresponds to the width of the first region of the second transmission-reflection element 860 of the incident aperture (the entire width of the incident aperture extends to a distance 1240). The second transmission-reflection element 860 has a uniform partial transmittance / reflectance (i.e., 86%R; 14%T). Furthermore, the light transmittance of the second opposing surface 820 varies with distance from the distance 1230 toward the second end 890 of the waveguide, decreasing continuously. The variable transmittance / reflectance (shown as a solid line) shown in the line graph associated with the first y-axis 1210 corresponds to a gradually changing second region of the second transmission-reflection element 860, extending from the first uniform transmission / reflection region at a distance 1230 to a point at the boundary between the incident aperture and the reflective element 870 of the second opposing surface 820 at a distance 1240. Furthermore, the variable transmittance / reflectance (shown as a solid line) shown in the line graph associated with the first y-axis 1210 also corresponds to the region of the reflective element 870. Specifically, in contrast to embodiments where the reflective element on the second opposing surface is uniformly (highly) reflective, the second region of the reflective element 870 and the partially transmissive / reflective element 860 gradually and continuously changes along the length of the second opposing surface 220 until the light transmittance value is substantially 0 (preferably <0.05) at a distance of 1250. From point 1250 to the second end 890 of the waveguide, the light transmittance value of the reflective element 870 is substantially 0. Therefore, the second opposing surface 820 includes a (continuously) gradually changing partially transmissive / reflective layer that forms a portion of the incident aperture / second transmissive / reflective element 860 and a portion of the reflective element 870. This advantageously avoids any abrupt discontinuities in the intensity of the internally coupled light, which can improve image quality.

[0154] exist Figure 12 In the example of the first embodiment shown, the second transmissive-reflective element 860 has a gradient transmittance / reflectance only along a portion of its width. As those skilled in the art will understand, in other examples, the entire width of the second transmissive-reflective element 860 may be gradient, such that the entire second surface 820 (e.g., from the first end 880 to...) is gradient. Figure 12 The distance (1250) in the middle can be continuously and gradually changed.

[0155] Therefore, the waveguide embodiments disclosed herein have optimized light coupling efficiency, such that all rays in the beam of the input beam (e.g., a diverging beam) are completely coupled into the waveguide and thus guided from the input port to the output port. This prevents any gaps in the image perceived by the observer at all positions within the eyebox, gaps that might manifest as dark bands. Furthermore, the tolerance of the waveguide angle is improved during alignment of the waveguide input port with the optical axis / projection axis of the display / projection system. The advantage of the holographic display device is that it does not require modification of the coded diffraction field / hologram within the beam, and therefore does not require changing the method of generating the diffraction field.

[0156] Additional features

[0157] 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.

[0158] The example describes illuminating an SLM with visible light; however, those skilled in the art will understand that the light source and the SLM can also be used to guide infrared or ultraviolet light, for example, as disclosed herein. For example, to provide information to a user, those skilled in the art will know 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.

[0159] Some arrangements are described as 2D holographic reconstructions only by way of example. In other arrangements, the holographic reconstruction is a 3D holographic reconstruction. That is, in some arrangements, each computer-generated hologram forms a 3D holographic reconstruction.

[0160] The methods and processes described herein can be implemented on a computer-readable medium. The term "computer-readable medium" includes media used 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 understood to include any medium or combination of media capable of storing machine-executable instructions such that, when executed by one or more processors, the machine performs, wholly or partially, any or all of the methods described herein.

[0161] The term "computer-readable medium" also includes cloud-based storage systems. The term "computer-readable medium" includes, but is not limited to, one or more tangible and non-transitory data repositories (e.g., data volumes) in example forms such as solid-state memory chips, optical discs, disks, or any suitable combinations thereof. In some example embodiments, instructions for execution may be transmitted via a carrier medium. Examples of such carrier media include transient media (e.g., propagation signals for transmitting instructions).

[0162] 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 waveguide, comprising: A pair of opposing surfaces are arranged to guide a diffracted light field between them via internal reflection; The input port is configured to receive light from the display system; An output port is formed by a first transmission-reflection element on the first surface of the pair of opposing surfaces, wherein the first transmission-reflection element causes the diffracted light field to be segmented upon each internal reflection, and multiple copies of the diffracted light field are transmitted out of the waveguide through the output port. The input port includes a second transmissive-reflective element extending through at least a portion of the input port, the second transmissive-reflective element being arranged to receive and partially transmit and partially reflect at least a portion of the light from the display system. The input port further includes a transmissive element arranged to receive a portion of light from the display system, wherein the transmissive element is adjacent to the second transmissive-reflective element, and wherein the waveguide further includes a reflective element, wherein the second transmissive-reflective element is adjacent to the reflective element. The second transmission-reflection element includes a surface coating that partially transmits and partially reflects light.

2. The waveguide of claim 1, wherein the second transmission-reflection element is arranged to reflect at least some diffraction light field inside the waveguide.

3. The waveguide of claim 1 or 2, wherein the second transmission-reflection element is configured such that at least some of the diffracted light fields are incident on it only once.

4. The waveguide of claim 1 or 2, wherein the input port is formed on the second surface of the pair of opposing surfaces.

5. The waveguide of claim 1 or 2, wherein the transmittance of the second transmission-reflection element is 0.1 to 0.

5.

6. The waveguide of claim 1 or 2, wherein the reflecting element is arranged to reflect the diffracted light field inside the waveguide.

7. The waveguide of claim 4, wherein the reflecting element is disposed on the second surface, adjacent to the input port.

8. The waveguide as claimed in claim 4, wherein: From the starting point of the second transmissive-reflective element to the ending point of the reflective element, the transmittance of the second surface is continuous, and / or The transmittance of the reflective element is less than 0.

1.

9. The waveguide of claim 1 or 2, wherein the second transmission-reflection element is arranged to receive all light from the display system.

10. The waveguide as claimed in claim 1 or 2, wherein The input port has a length in the direction of the waveguide, and the second transmission-reflection element extends over at least a portion of the length of the input port.

11. The waveguide of claim 1 or 2, wherein the display system includes a spatial light modulator arranged to display a hologram, and / or spatially modulates the diffracted light field according to the hologram.

12. The waveguide of claim 1 or 2, wherein the display system includes a display device having a pixel region defining an exit pupil of the display system extended by the waveguide.

13. A system comprising a waveguide as claimed in claim 1 or 2, wherein the waveguide is a second one-dimensional pupil expander in a pair of waveguide pupil expanders arranged to expand the pupil of the display system in a first direction and a second orthogonal direction, respectively.

14. A system comprising the waveguide as described in claim 1 or 2, comprising: A display system, arranged to form a diffracted light field for observation by an observation system, and A waveguide is used to receive the diffracted light field at its input port. The magnitude of the diffraction field increases with the propagation distance from the display system, enabling the observation system to perceive the virtual image at a finite virtual image distance.

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