Holographic system and pupil expander for the same

Abstract

A holographic system includes a spatial light modulator and a pupil expander. The spatial light modulator is configured to display a hologram of an image and output spatially modulated light encoded in the hologram. In embodiments, the pupil expander includes a plurality of optical fibers, each of which has an input end and an output end. The pupil expander is configured such that the spatially modulated light output by the spatial light modulator is coupled into the input end of each optical fiber and output from the output end of the optical fiber to a viewing area. Each of the plurality of optical fibers is configured to propagate the spatially modulated light received at the input end to expand the output pupil of the system to a first dimension typically corresponding to the dimension of the viewing area.

Description

Technology Field

[0001] The present disclosure relates to a holographic system. More specifically, the present disclosure relates to a holographic imaging system and a holographic imaging method. Some embodiments relate to a picture generating unit and a head-up display. Some embodiments relate to a pupil extension method and a pupil extension device for a viewing area of ​​a holographic system. Background Technology

[0002] Light scattered from an object contains both amplitude and phase information. This amplitude and phase information can be captured on a photosensitive plate by, for example, holographic recording containing interference fringes, or by known interference techniques to form a "hologram." The hologram may also be reconstructed by illumination using light suitable to form a two-dimensional or three-dimensional holographic reconstruction or replay image representing the original object.

[0003] Computer-generated holography can also numerically simulate interference processes. Computer-generated holograms (CGHs) may be computed by techniques based on mathematical transformations such as the Fresnel transform or the Fourier transform. These types of holograms may be referred to as Fresnel / Fourier transform holograms or simply Fresnel / Fourier holograms. A Fourier hologram may be considered as a Fourier domain / planar representation of an object or a frequency domain / planar representation of an object. Computer-generated holograms may also be computed by techniques such as coherent ray tracing or point cloud.

[0004] Computer-generated holograms may also be encoded on a spatial light modulator (SLM) configured to modulate the amplitude and / or phase of incident light. Light modulation may be achieved, for example, using electrically addressable liquid crystals (LCs), optically addressable liquid crystals, or micromirrors.

[0005] A spatial light modulator comprises a plurality of individually addressable pixels, which may also be referred to as cells or elements. The light modulation scheme may be binary, multi-level, or continuous. Alternatively, the device may be continuous (i.e., not composed of pixels), and thus the light modulation may be continuous across the device. A spatial light modulator may be reflective, meaning that the modulated light is output upon reflection. A spatial light modulator may also be transmissive, meaning that the modulated light is output upon transmission.

[0006] A holographic projector may be provided using the system described herein. Such projectors are applied to head-up displays, "HUDs".

[0007] The embodiments of the present disclosure are defined in the appended independent claims.

[0008] Generally, the present disclosure relates to image projection. The present invention relates to an image projector comprising an image projection method and a display device. The present disclosure also relates to a projection system comprising an image projector and a viewing system, wherein the image projector projects or relays light from the display device to the viewing system. The present disclosure is equally applicable to monocular viewing systems and binocular viewing systems. The viewing system may include the viewer's eye or eyes. The viewing system includes an optical element having optical power (e.g., a lens / lenses of a human eye) and a viewing plane (e.g., the retina of a human eye / eyes). 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 a display plane or perceived by the viewer. In some embodiments, the image may be 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 the image is projected or relayed onto a viewing plane. The image is formed by irradiating a diffraction pattern (e.g., a hologram) displayed on a display device.

[0009] A display device contains pixels. The pixels of a display device diffract light. According to well-understood optics, the magnitude of the maximum diffraction angle is determined by the size of the pixels (and other factors such as the wavelength of light).

[0010] In embodiments, the display device is a spatial light modulator, such as an "LCOS" (liquid crystal on silicon) spatial light modulator (SLM). Light is propagated from the LCOS toward a viewing entity / system, such as a camera or eye, over a range of diffraction angles (e.g., from zero to the maximum diffraction angle). In some embodiments, magnification techniques may be used to increase the range of available diffraction angles beyond the conventional maximum diffraction angle of the LCOS.

[0011] In some examples, an image (formed from a displayed hologram) is propagated to the eyes. For example, spatially modulated light of an intermediate holographic reconstruction / image formed in free space or on a screen or other light-receiving surface between the display device and the viewer may be propagated to the viewer.

[0012] In other examples, the hologram itself is propagated to the eyes. That is, the spatially modulated light of the hologram is propagated to the eyes. A real image or a virtual image may be perceived by the viewer. It may also be said that the light encoded in the hologram is propagated directly to the eye(s). In these embodiments, there is no intermediate holographic reconstruction / image formed between the display device and the viewer. Sometimes, in these embodiments, the lens of the eye is said to perform a hologram-to-image conversion or transformation. The projection system, or light engine, may be configured so that the viewer effectively looks directly at the display device.

[0013] According to well-understood principles of optical systems, the range of angles of light propagating from a display device that can be viewed by the eye or other viewing entity / system varies depending on the distance between the display device and the viewing entity. At a viewing distance of 1 m, for example, only a small range of angles from the LCOS can propagate through the pupil of the eye to form an image on the retina for a predetermined (given) eye position. The range of angles of light rays propagating from the display device that can successfully propagate through the pupil of the eye to form an image on the retina for a predetermined eye position determines the portion of the image that is 'visible' to the viewer. That is, not all portions of the image are visible from any point on the viewing plane (for example, any eye position within the viewing window, such as the eye-motion box).

[0014] In some embodiments, the image perceived by the viewer is a virtual image appearing upstream of the display device—that is, the viewer perceives the image as being further away from the viewer than the display device. Thus, conceptually, the viewer may be considered to be looking at the virtual image through a 'display device-size window' that is very small, for example, with a diameter of 1 cm, at a relatively large distance, for example, 1 m. And the user will also be viewing the display device-size window through the pupil(s) of the eye(s), which may be very small. Consequently, the field of view is reduced, and the specific angle range visible depends significantly on the eye position at any predetermined time.

[0015] A pupil expander solves the problem of a method to increase the field of view—that is, a method to increase the range of angles of light rays propagated from a display device that can be successfully propagated through the pupil of the eye to form an image. The display device is small (relatively), and the projection distance is large (relatively). In some embodiments, the projection distance is at least 10 times—e.g., at least 100 times—larger than the diameter or width (i.e., the size of the array of pixels) of the entrance pupil and / or aperture of the display device. The embodiments of the present disclosure described herein relate to a configuration in which a hologram of an image is propagated to the human eye rather than to the image itself. That is, light received by a viewer is modulated according to the hologram of the image. However, other embodiments of the present disclosure may relate to configurations in which an image is transmitted to the human eye instead of a hologram—for example, light from a holographic reconstruction or "replay image" formed on a screen (or even in free space) is transmitted to the human eye by a so-called indirect view.

[0016] A pupil expander is used to increase the field of view and thus increase the maximum propagation distance over which the full diffraction angle of the display device may be utilized. The use of a pupil expander can also increase the viewing area (i.e., the user's eye-box) laterally, thereby causing some movement of the eyes while allowing the user to view the image. As will be recognized by those skilled in the art, in an imaging system, the viewing area (the user's eye-box) is the area where the viewer's eyes can perceive an image. This disclosure generally relates to virtual image distances that are not infinite—i.e., near-field virtual images. However, the pupil expander of this disclosure may be applied to forms of imaging that may benefit from pupil expansion in the path relaying light between the display device and the viewing area.

[0017] Conventionally, a pupil expander comprises one or more one-dimensional optical waveguides, each formed using a bulk optical system such as a block of glass or planar mirrors, in which output light from a surface forms a viewing window—e.g., an eye-box or eye motion box viewed by a viewer. Light received from a display device (e.g., light spatially modulated from an LCOS) is replicated by the waveguide or each waveguide to increase the field of view (or viewing area) in at least one dimension. In particular, the waveguide expands the viewing window due to the generation of additional rays or "replicas" by splitting the amplitude of the incident wavefront. However, to achieve this, the display device must be very close to (e.g., adjacent to) the waveguide pupil expander(s). This places limitations on the overall configuration, size, and volume of the display device and prevents the design of more compact devices. Furthermore, the exit pupil of the pupil expander must be positioned so that the output light is relayed to the viewing area where the viewing system, such as the viewer's eye, is positioned. This requirement, along with the size of the display device, in situ ( in situ ) restricts placement. For example, when implemented as a head-up display for a vehicle driver, the display device must be placed within the vehicle dashboard at a location where output light can be relayed to a viewing area where the driver's eyes are positioned.

[0018] The present disclosure proposes an alternative approach to pupil expansion. Instead of using one or more bulk optical pupil expanders in a relay path between a display device and a viewing area, pupil expansion is achieved using a device comprising a plurality of optical fibers forming an "optical fiber pupil expander." In particular, according to the present disclosure, output light from a display device is received by the input ends of a plurality of optical fibers. The output ends of the plurality of optical fibers are positioned to form an expanded output window having an increased large field (i.e., an increased range of angles of light rays propagated from the display device to the viewer), and consequently, an increased viewing area for the viewing system. Accordingly, each optical fiber may be considered to replicate at least a portion of the input light field so that the plurality of optical fibers form a plurality of replicas to achieve pupil expansion in one or two dimensions, or may be considered to form a replica. The term "replica" may generally be understood to refer to light rays output across an output pupil expanded by a pupil expander as a result of the propagation (and amplitude splitting) of input light, and the term "replicate" has the corresponding meaning. More detailed definitions of these terms are provided below.

[0019] As described above, the need for pupil extension arises in display systems comprising a relatively small display device and a relatively large projection / propagation distance. Typically, the projection distance is at least 10 times larger than the aperture of the display device. In embodiments, the display system comprises a relatively small display device (e.g., a so-called "micro-display" with a diameter of about 0.8 to 3 cm) and a viewing area with a relatively large propagation distance from it (e.g., 30 cm to 1.5 meters), so that without pupil extension, the field of view is limited to a predetermined eye position. Accordingly, the fiber pupil extender of the present disclosure is applicable to display systems, particularly those comprising a micro-display (e.g., LCOS) having a viewing area separated by a relatively large distance from the viewing area, and the viewing area must allow a range of eye positions. Examples of such display systems include head-up displays for automobiles and other applications, as described herein.

[0020] Although the present disclosure describes a plurality of optical fibers to achieve pupil expansion, the principles of the present disclosure may be implemented by replacing the optical fibers with any type of light guide or optical pipe to propagate light from the input end to the output end by internal reflection (e.g., total reflection). Accordingly, references to "optical fiber pupil expanders" in the present description are for convenience only and are not intended to limit the scope of the present disclosure.

[0021] A holographic system is provided comprising a display device configured to display a diffraction pattern of an image, such as a hologram. The display device is further configured to output light encoded (or modulated) with a diffraction pattern. The holographic system further comprises a pupil expander. The pupil expander comprises a plurality of light guide plates, each of which has an input end and an output end. The pupil expander is configured such that output light from the display device is coupled into the input end of each light guide plate and output from its output end to a viewing area (where a viewer can perceive an image). Each of the plurality of light guide plates is configured to propagate light received at the input end to expand the output pupil of the system to a first dimension. The first dimension may correspond to the dimension of the viewing area.

[0022] In embodiments, the aperture of the spatial light modulator is the limiting aperture of the holographic system. That is, the aperture of the spatial light modulator—more specifically, the size of the delimiting region that partitions the array of light-modulated pixels—determines the size (e.g., spatial size) of the beam of light that can exit the system. Accordingly, according to this disclosure, it is stated that the output pupil of the holographic system is expanded by an array of optical fibers to reflect that the pupil expander makes the output pupil of the system larger / bigger. It may also be said that each of the plurality of light guide plates is configured to form a "replica" of the spatially modulated light received at the input end to expand the output pupil of the holographic system. In some embodiments, the holographic light content output by the spatial light modulator is divided into light channels, each light guide plate receives light from one respective light channel, and the plurality of light guide plates collectively deliver all the holographic light content to the viewer (e.g., at all possible viewing positions). These embodiments synergistic with the special type of channeling hologram described herein. In other embodiments, each of the plurality of light guide plates increases the size of the output pupil by forming multiple replicas or copies of the output pupil (or the light of the output pupil) of the spatial light modulator. The plurality of light guide plates may also expand / increase the size of the received pupil. To reflect that the spatial light modulator displays a hologram and thus the light transmitted to the viewer is spatially modulated according to the hologram of the image rather than the image itself, the pupil expander may replicate the hologram or form at least one replica of the hologram.

[0023] In embodiments, the output ends of a plurality of light guide plates are arranged in a one-dimensional array of a first dimension. In other embodiments, the output ends of a plurality of light guide plates are arranged in a two-dimensional array of a first dimension and a second dimension orthogonal to the first dimension.

[0024] In the embodiments, light output from the output ends of the light guide plates is collimated (e.g., by a collimating lens) before being relayed to a viewing system. The light may also be coupled into the input ends of the light guide plates by each lens.

[0025] In some embodiments, the display device is a holographic display device, such as a spatial light modulator (e.g., LCOS SLM) that spatially modulates light according to a hologram. In the embodiments described herein, light encoded using a hologram is output by the holographic display device to a fiber pupil expander (i.e., without forming an intermediate holographic reconstruction). Thus, the hologram of the image is propagated by the output light rather than by the image itself.

[0026] In some examples, (modulated) light is simultaneously coupled to the input ends of each of a plurality of light guide plates using a light guide plate splitter, such as a fiber optic splitter. In other embodiments, the modulated light is coupled into the input ends of each of the plurality of light guide plates in a time-multiplexed manner. That is, the (modulated) light is coupled to each of the plurality of light guide plates one at a time in a defined sequence. In the examples, the total duration of the sequence (i.e., for the input of light to each of the plurality of light guide plates) is shorter than the human eye's exposure time (integration time).

[0027] In other embodiments, modulated light may be provided by a display device at multiple angles by encoding a so-called "channeling hologram" on the display device as described herein. In some embodiments, the angles may be selected so that the light for each angle is coupled (or launched) into the input end of each of the multiple light guide plates. That is, the input light field for each of the light guide plates is identical and contains the (image) content of all angle channels. Thus, each light guide plate replicates all angles / channels of the channeling hologram to provide pupil expansion. In other embodiments, the angles may be selected so that the light for each angle is coupled into the input end of each of the multiple light guide plates. Thus, the input light field for each of the multiple light guide plates contains the (image) content of each of the angle channels.

[0028] The same input light field may be coupled (or launched) into the input ends of at least two of the plurality of light guide plates so that at least two light guide plates replicate the same angle / channel of the channeling hologram to provide pupil expansion.

[0029] In some embodiments, light guide plates carrying the same angle / channel have adjacent output ends in an array of their output ends, and thus replicas of their input light fields are continuous. In other embodiments, angles may be selected so that light from a subset of angle channels is coupled into the input end of each of the plurality of light guide plates. Thus, the input light field of each of the plurality of light guide plates includes the (image) content of a subset of adjacent angle channels, and thus overlapping regions of the (image) content of a subset of adjacent angle channels. The input light field of each angle channel (or subset) is coupled to the input ends of at least two light guide plates so that at least two of the plurality of light guide plates replicate the same angle / channel (or subset) of the channeling hologram to provide pupil extension. In these embodiments, light guide plates carrying the same or adjacent angle channels have adjacent output ends in an array of output ends so that replicas of the light fields of each angle channel are continuous. In at least some of these embodiments, the modulated light may be simultaneously coupled to the input ends of each of the plurality of optical fibers. Accordingly, each light guide plate replicates one or more respective angles / channels of the channeling hologram.

[0030] The disclosed novel technique for providing pupil expansion using multiple light guide plates has many advantages over conventional techniques using one or more bulk optical waveguides. In particular, the display device or optical engine no longer needs to be adjacent to an emission window (e.g., on a vehicle dashboard) that provides light to a viewing system, such as the driver's eye. Consequently, the size, volume, and weight of the components of the projection system within the dashboard can be reduced. Furthermore, the light field received from the display device can be relayed and / or replicated along different groups of light guide plates to provide respective emission windows to different viewing areas of the vehicle. Consequently, additional viewers, such as passengers, can view images of the same holographic system without requiring an additional complete holographic imaging system.

[0031] A method for expanding the output pupil of a holographic system is further provided. The method includes the step of displaying a diffraction pattern of an image (e.g., a hologram) by a display device. The method further includes the step of outputting light encoded (i.e., modulated) by the display device as a diffraction pattern. In embodiments, the display device is a spatial light modulator, and the method includes the step of illuminating the spatial light modulator that displays the hologram to output spatially modulated light encoded as a hologram. The method further includes the step of coupling the light output (modulated) by the display device to the input end of each of the plurality of light guide plates by a pupil expander comprising a plurality of light guide plates. The method further includes the step of propagating the light received at the input end for output at the output end by each of the plurality of light guide plates of the pupil expander to expand the output pupil of the pupil expander by a first dimension. The first dimension may correspond to the dimension of a viewing area (where a viewer can perceive an image).

[0032] The term "hologram" is used to refer to a recording containing amplitude information or phase information regarding an object, or a combination thereof. A recording of a hologram may be stored in a data storage device (i.e., memory) or may be implemented as light (e.g., as an optical signal) forming a carrier wave for the amplitude and / or phase information. That is, the light may be described as being "encoded as a hologram" or "modulated according to a hologram" to propagate a hologram rather than an image.

[0033] The term “holographic reconstruction” is used to refer to the optical reconstruction of an object formed by irradiating a hologram. Holographic reconstruction may also be referred to as a “replay image” or a “holographic image.” Embodiments of the holographic system disclosed herein may be described as a “holographic projector” because the holographic reconstruction is a real image and is spatially separated from the hologram. The term “replay field” is used to refer to the 2D region where the holographic reconstruction is formed and fully focused. If the hologram is displayed on a spatial light modulator (SLM) containing pixels, the replay field will be repeated in the form of multiple diffracted orders, each diffracted order being a replica of the zero-order replay field. The zero-order replay field is generally preferred or corresponds to the primary replay field because it is the brightest replay field. Unless otherwise explicitly stated, the term “replay field” should be considered to refer to the zero-order replay field. The term "replay plane" is used to refer to a plane of space containing all replay fields. The terms "image," "replay image," and "image region" refer to regions of the replay field illuminated by light of holographic reconstruction. In some embodiments, the "image" may include discrete spots, which may be referred to as "image spots" or, for convenience only, "image pixels."

[0034] The terms "encoding," "writing," or "addressing" are used to describe the process of providing multiple control values ​​to multiple pixels of an SLM, each determining a modulation level of each pixel. The pixels of the SLM may be said to be configured to "display" an optical modulation distribution in response to receiving multiple control values. Thus, the SLM may be said to "display" a hologram, and the hologram may be regarded as an array of optical modulation values ​​or levels.

[0035] It has been found that a holographic reconstruction of acceptable quality can be formed from a "hologram" containing only phase information related to the Fourier transform of the original object. Such a holographic recording may also be referred to as a phase-only hologram. Although the embodiments relate to phase-only holograms, the present disclosure is equally applicable to amplitude-only holography.

[0036] The present disclosure is also equally applicable to forming a holographic reconstruction using amplitude and phase information associated with the Fourier transform of the original object. In some embodiments, this is achieved by complex modulation using a so-called fully complex hologram that includes both amplitude and phase information associated with the original object. Such a hologram may be referred to as a fully complex 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 may be expressed as a complex number having both an amplitude component and a phase component. In some embodiments, a fully complex computer-generated hologram (CGH) is computed.

[0037] References to the phase of pixels of a computer-generated hologram or spatial light modulator may be made as a phase value, phase component, phase information, or simply as an abbreviation of "phase-delay." That is, any described phase value is actually a number (e.g., in the range of 0 to 2π) representing the amount of phase delay provided by the corresponding pixel. For example, a pixel of a spatial light modulator described as having a phase value of π / 2 will delay the phase of the received light by π / 2 radians. In some embodiments, each pixel of a spatial light modulator can operate as one of a plurality of possible modulation values ​​(e.g., phase delay values). The term "gray level" may be used to refer to a plurality of available modulation levels. For example, the term "gray level" may be used for convenience to refer to a plurality of available phase levels in a phase-only modulator, even if different phase levels do not provide different shades of gray. The term "gray level" may also be used for convenience to refer to a plurality of available complex modulation levels in a complex modulator.

[0038] Therefore, a hologram comprises an array of gray levels, that is, an array of optical modulation values ​​such as an array of phase-delay values ​​or an array of complex modulation values. A hologram is also considered a diffraction pattern because it is a pattern that causes diffraction when displayed on a spatial light modulator and is generally illuminated with light having a wavelength less than the pixel pitch of the spatial light modulator. Reference is made herein to combining a hologram with other diffraction patterns, such as diffraction patterns that function as lenses or gratings. For example, a diffraction pattern functioning as a grating may be combined with the hologram to transform the replay field on the replay plane, or a diffraction pattern functioning as a lens may be combined with the hologram to focus a holographic reconstruction on the replay plane near the field.

[0039] References to "complex light field" are made herein. The term "light field" refers to a pattern of light having a finite size in only at least two orthogonal spatial directions, x and y. The word "complex" is used herein simply to indicate that at each point in the light field, the light may be defined by an amplitude value and a phase value, and thus may be represented by a complex number or a pair of values. For the purposes of holographic computation, the complex light field may be a two-dimensional array of complex numbers, where the complex numbers define the light intensity and phase at multiple discrete locations within the light field. The complex light field may propagate forward and backward in the +z and -z directions between the holographic plane and the image plane. Light propagation may be simulated or modeled using any one of a number of different approaches or mathematical transformations familiar to those skilled in the art of wave optics.

[0040] In this disclosure, the term “replica” is used herein merely to reflect that spatially modulated light is split so that a complex light field is directed along a plurality of different optical paths. The word “replica” is used to refer to each occurrence or instance of a complex light field following a replication event, such as partial reflection-transmission by a pupil expander. Each replica travels along a different optical path. Some embodiments of this disclosure relate to the propagation of light encoded as a hologram rather than an image—that is, light spatially modulated as a hologram of an image rather than the image itself. Those skilled in the art of holography will recognize that the complex light field associated with the propagation of light encoded using a hologram will vary with the propagation distance. The use of the term “replica” herein is independent of the propagation distance, and thus two optical paths or branches associated with a replication event are still referred to as “replicas” of each other even if the branches are of different lengths, and the complex light field evolves differently along each path. That is, two complex optical fields are still considered “replicas” according to the present disclosure, even if they are associated with different propagation distances, if they arise from the same replication event or a series of replication events.

[0041] Different embodiments and groups of embodiments may be disclosed individually in the following detailed description, but any feature of any embodiment or group of embodiments may be combined with any other feature or combination of features of any embodiment or group of embodiments. That is, all possible combinations and substitutions of the features disclosed in this disclosure are conceived. Brief explanation of the drawing

[0042] Specific embodiments are described merely as examples with reference to the following drawings. Figure 1 is a schematic diagram illustrating a reflective SLM that generates a holographic reconstruction on a screen. Figure 2a illustrates the first iteration of an exemplary Gerchberg-Saxton type algorithm. FIG. 2b illustrates the second and subsequent iterations of an exemplary Gerchberg-Saxton type algorithm. FIG. 2c illustrates alternative second and subsequent iterations of an exemplary Gerchberg-Saxton type algorithm. Figure 3 is a schematic diagram of a reflective LCOS SLM. Figure 4 illustrates angular content of a virtual image that effectively propagates from a display device toward an aperture. FIG. 5a illustrates a viewing system having a relatively small propagation distance. FIG. 5b illustrates a viewing system having a relatively large propagation distance. FIG. 6a illustrates a viewing system having a relatively large propagation distance, including a waveguide, for forming a virtual image infinitely. Figure 6b shows an enlarged view of the optical paths of Figure 6a. FIG. 7 illustrates an optical system according to embodiments. FIG. 8 illustrates an image including a plurality of image regions (bottom) and a corresponding hologram (top) including a plurality of holographic components. FIG. 9 illustrates a hologram according to the present disclosure, characterized by routing or channeling light encoded as a hologram into a plurality of individual hologram channels. FIG. 10 illustrates an optimized system configured to route the optical content of each holographic channel to the eye through different optical paths. FIG. 11 is a schematic diagram of an optical fiber pupil expander according to embodiments. FIG. 12 is a schematic diagram of a head-up display including the pupil expander of FIG. 11 positioned in a vehicle according to one example. Identical reference numbers will be used throughout the drawings to refer to identical or similar parts. Specific details for implementing the invention

[0043] The present invention is not limited to the embodiments described below but extends to the full scope of the appended claims. That is, the present invention may be embodied in different forms and should not be interpreted as being limited to the described embodiments presented for illustrative purposes.

[0044] Singular terms may include plural forms unless otherwise specified.

[0045] A structure described as being formed above / below another structure or in the upper / lower part of another structure should be interpreted to include cases where the structures come into contact with each other and also cases where a third structure is disposed between them.

[0046] When describing temporal relationships—for example, when the temporal order of events is described as “after,” “subsequent,” “next,” “before,” etc.—the present disclosure is taken to include continuous and non-continuous events unless otherwise specified. For example, the description is taken to include non-continuous cases unless expressions such as “just,” “immediate,” or “direct” are used.

[0047] Although terms “first,” “second,” etc. may be used in this specification 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, the first element may be referred to as the second element, and similarly, the second element may be referred to as the first element.

[0048] Features of different embodiments may be coupled or combined with one another, either partially or wholly, and may interact with one another in various ways. Some embodiments may be performed independently of one another, or they may be performed together in a codependent relationship.

[0049] Optical configuration

[0050] FIG. 1 illustrates an embodiment in which a computer-generated hologram is encoded on a single spatial light modulator. The computer-generated hologram is the Fourier transform of an object for reconstruction. Thus, the hologram may be described as a Fourier domain, frequency domain, or spectral domain representation of an object. In this embodiment, the spatial light modulator is a reflective silicon liquid crystal, "LCOS", device. The hologram is encoded on the spatial light modulator, and the holographic reconstruction is formed on a replay field, such as a light receiving surface, such as a screen or a diffuser.

[0051] A light source (110), for example, a laser or laser diode, is positioned to illuminate the SLM (140) through a collimating lens (111). The collimating lens typically causes a planar wavefront of light to be incident on the SLM. In FIG. 1, the direction of the wavefront is deviated from the vertical (e.g., 2° or 3° from being exactly orthogonal to the plane of the transparent layer). However, in other embodiments, a planar wavefront is typically provided at a vertical incidence, and a beam splitter configuration is used to separate the input optical path and the output optical path. In the embodiment illustrated in FIG. 1, this configuration interacts with the optical-modulating layer so that light from the light source is reflected from the mirrored back surface of the SLM and forms an exit wavefront (112). The output wavefront (112) is applied to an optical system (optics) including a Fourier transform lens (120) that has focus on a screen (125). More specifically, the Fourier transform lens (120) receives a beam of light modulated from an SLM (140) and performs a frequency-space transformation to produce a holographic reconstruction on the screen (125).

[0052] In particular, in this type of holography, each pixel of the hologram contributes to the overall reconstruction. There is no one-to-one correlation between specific points (or image pixels) on the replay field and specific optical-modulating elements (or hologram pixels). That is, the modulated light exiting the optical-modulating layer is distributed across the replay field.

[0053] In these embodiments, the position of the holographic reconstruction in space is determined by the refractive (dioptric) (focusing) magnification of the Fourier transform lens. In the embodiment illustrated in FIG. 1, the Fourier transform lens is a physical lens. That is, the Fourier transform lens is an optical Fourier transform lens, and the Fourier transform is performed optically. Any lens can function as a Fourier transform lens, but the performance of the lens will limit the accuracy of the Fourier transform performed. Those skilled in the art understand how to use a lens to perform an optical Fourier transform.

[0054] The embodiment of FIG. 1 may be used as part of a holographic system in which a holographic reconstruction or replay image is relayed to a viewing area. As will be recognized by those skilled in the art, in other embodiments, the holographic system may be used in a holographic system in which the emitted wavefront (112) is relayed to a viewing area without forming an intermediate holographic reconstruction.

[0055] Hologram calculation

[0056] In some embodiments, the computer-generated hologram is a Fourier transform hologram, or simply a Fourier hologram or a Fourier-based hologram, wherein the image is reconstructed from the far field by utilizing the Fourier transform properties of the positive lens. The Fourier hologram is computed by Fourier transforming the targeted light field in the replay plane back to the lens plane. Computer-generated Fourier holograms may also be computed using Fourier transforms.

[0057] Fourier transform holograms may also be computed using algorithms such as the Gerchberg-Saxton algorithm. Furthermore, the Gerchberg-Saxton algorithm may be used to compute a hologram in the Fourier domain (i.e., a Fourier transform hologram) from amplitude-only information in the spatial domain (such as photographs). Phase information associated with an object is effectively "retrieved" from the amplitude-only information in the spatial domain. In some embodiments, computer-generated holograms are computed from amplitude-only information using the Gerchberg-Saxton algorithm or a variation thereof.

[0058] The Gerchberg-Saxton algorithm uses light beams I in planes A and B, respectively. A (x, y) and I B (x, y) is announced and I A (x, y) and I B (x, y) is related by a single Fourier transform. Using predetermined (given) intensity sections, plane A and plane B, Ψ A (x, y) and Ψ B Approximations for the phase distribution are found at each (x, y). The Gerchberg-Saxton algorithm finds solutions to this problem by following an iterative process. More specifically, the Gerchberg-Saxton algorithm [finds] I between the spatial domain and the Fourier (spectral or frequency) domain A (x, y) and I BSpatial and spectral constraints are applied iteratively while repeatedly transmitting a data set (amplitude and phase) representing (x, y). A corresponding computer-generated hologram in the spectral domain is obtained through at least one iteration of the algorithm. The algorithm is configured to converge and generate a hologram representing the input image. The hologram may be an amplitude-only hologram, a phase-only hologram, or a fully complex hologram.

[0059] In some embodiments, the phase-only hologram is computed using an algorithm based on the Gerchberg-Saxton algorithm as described in British Patent No. 2,498,170 or No. 2,501,112, which is incorporated herein by reference in its entirety. However, the embodiments disclosed herein describe the computement of the phase-only hologram merely as an example. In these embodiments, the Gerchberg-Saxton algorithm retrieves the phase information Ψ[u, v] of the Fourier transform of a data set that generates known amplitude information T[x, y], where the amplitude information T[x, y] represents a target image (e.g., a photograph). Because amplitude and phase are essentially combined in the Fourier transform, the transformed amplitude and phase contain useful information regarding the accuracy of the computed data set. Thus, the algorithm may be used iteratively with feedback on both the amplitude and phase information. However, in these embodiments, only phase information Ψ[u, v] is used as a hologram to form a holographic representing a target image in an image plane. The hologram is a data set of phase values ​​(e.g., a 2D array).

[0060] In other embodiments, an algorithm based on the Gerchberg-Saxton algorithm is used to compute a full complex hologram. A full complex hologram is a hologram having a magnitude component and a phase component. The hologram is a data set (e.g., a 2D array) containing an array of complex data values, and each complex data value includes a magnitude component and a phase component.

[0061] In some embodiments, the algorithm processes complex data and the Fourier transforms are complex Fourier transforms. The complex data is (i) mistake Components and imaginary number component or (ii) size Components and phase It may be considered to include components. In some embodiments, the two components of the complex data are processed differently at various stages of the algorithm.

[0062] FIG. 2a illustrates a first iteration of an algorithm according to some embodiments for calculating a phase-only hologram. The input to the algorithm is an input image (210) comprising a 2D array of pixels or data values, where each pixel or data value is a magnitude, or amplitude, value. That is, each pixel or data value of the input image (210) does not have a phase component. Thus, the input image (210) may be considered as a magnitude-only, amplitude-only, or intensity-only distribution. An example of such an input image (210) is a single frame of a photograph or video comprising a temporal sequence of frames. The first iteration of the algorithm begins with a data formation step (202A) comprising the step of assigning a random phase value to each pixel of the input image using a random phase distribution (or random phase seed) (230) to form a starting complex data set, wherein each data element of the set includes a magnitude and a phase. It can be said that the starting complex dataset represents the input image in the spatial domain.

[0063] The first processing block (250) receives a starting complex data set and performs a complex Fourier transform to form a Fourier transformed complex data set. The second processing block (253) receives the Fourier transformed complex data set and outputs a hologram (280A). In some embodiments, the hologram (280A) is a phase-only hologram. In these embodiments, the second processing block (253) quantizes each phase value and sets each amplitude value to 1 to form the hologram (280A). Each phase value is quantized according to phase levels that may be represented on the pixels of a spatial optical modulator used to "display" the phase-only hologram. For example, if each pixel of the spatial optical modulator provides 256 different phase levels, each phase value of the hologram is quantized to one of the 256 possible phase levels. The hologram (280A) is a phase-only Fourier hologram representing an input image. In other embodiments, the hologram (280A) is a full complex hologram comprising an array of complex data values ​​(each including an amplitude component and a phase component) derived from a received Fourier-transformed complex data set. In some embodiments, the second processing block (253) restricts each complex data value to one of a plurality of acceptable complex modulation levels to form the hologram (280A). The restricting step may include setting each complex data value to the acceptable complex modulation level closest to the complex plane. The hologram (280A) may be said to represent an input image in the spectral, Fourier, or frequency domain. In some embodiments, the algorithm stops at this point.

[0064] However, in other embodiments, the algorithm continues as indicated by the dashed arrow in FIG. 2a. That is, the steps following the dashed arrow in FIG. 2a are optional (i.e., not essential in all embodiments).

[0065] The third processing block (256) receives the modified complex data set from the second processing block (253) and performs an inverse Fourier transform to form an inverse Fourier transformed complex data set. The inverse Fourier transformed complex data set may be said to represent an input image in the spatial domain.

[0066] The fourth processing block (259) receives an inverse Fourier transformed complex data set and extracts a distribution of magnitude values ​​(211A) and a distribution of phase values ​​(213A). Optionally, the fourth processing block (259) evaluates the distribution of magnitude values ​​(211A). Specifically, the fourth processing block (259) may compare the distribution of magnitude values ​​(211A) of the inverse Fourier transformed complex data set with an input image (510), which is a distribution of magnitude values. If the difference between the distribution of magnitude values ​​(211A) and the input image (210) is sufficiently small, the fourth processing block (259) may determine that the hologram (280A) is acceptable. That is, if the difference between the distribution of magnitude values ​​(211A) and the input image (210) is sufficiently small, the fourth processing block (259) may determine that the hologram (280A) represents the input image (210) sufficiently accurately. In some embodiments, the distribution of phase values ​​(213A) of the inverse Fourier transformed complex data set is ignored for comparison purposes. Any number of different methods may be employed to compare the distribution of magnitude values ​​(211A) and the input image (210), and it will be recognized that the present disclosure is not limited to any particular method. In some embodiments, the mean square difference is calculated, and if the mean square difference is smaller than a threshold value, the hologram (280A) is considered acceptable. If the fourth processing block (259) determines that the hologram (280A) is not acceptable, further iterations of the algorithm may be performed. However, this comparison step is not essential, and in other embodiments, the number of iterations of the algorithm performed is predetermined, pre-set, or user-defined.

[0067] FIG. 2b illustrates a second iteration of the algorithm and any additional iterations of the algorithm. The distribution of phase values ​​(213A) of the preceding iteration is fed back through the processing blocks of the algorithm. The distribution of magnitude values ​​(211A) is rejected for the distribution of magnitude values ​​of the input image (210). In the first iteration, the data forming step (202A) forms a first complex data set by combining the distribution of magnitude values ​​of the input image (210) with a random phase distribution (230). However, in the second and subsequent iterations, the data forming step (202B) includes forming a complex data set by combining (i) the distribution of phase values ​​(213A) from the previous iteration of the algorithm with (ii) the distribution of magnitude values ​​of the input image (210).

[0068] Subsequently, the complex data set formed by the data formation step (202B) of FIG. 2b is processed in the same manner as described with reference to FIG. 2a to form a second iteration hologram (280B). Thus, the description of the process is not repeated here. The algorithm may be paused when the second iteration hologram (280B) is calculated. However, any number of additional iterations of the algorithm may be performed. It will be understood that a third processing block (256) is required only when a fourth processing block (259) is required or additional iterations are required. The output hologram (280B) generally gets better with each iteration. However, in practice, usually no measurable improvement is observed, or a point is reached where the positive benefits of performing additional iterations are out-weighted by the negative effects of additional processing time. Therefore, the algorithm is described as iterative and convergent.

[0069] FIG. 2c illustrates an alternative embodiment of the second and subsequent iterations. The distribution of phase values ​​(213A) of the preceding iteration is fed back through the processing blocks of the algorithm. The distribution of magnitude values ​​(211A) is rejected for an alternative distribution of magnitude values. In this alternative embodiment, the alternative distribution of magnitude values ​​is derived from the distribution of magnitude values ​​(211) of the previous iteration. Specifically, the processing block (258) subtracts the distribution of magnitude values ​​of the input image (210) from the distribution of magnitude values ​​(211) of the previous iteration, scales this difference by a gain factor α, and subtracts the scaled difference from the input image (210). This is mathematically expressed by the following equations, where the subscript text and numbers represent the number of iterations:

[0070]

[0071] Here,

[0072] F' is the inverse Fourier transform;

[0073] F is the forward Fourier transform;

[0074] R[x, y] is a complex data set output by the third processing block (256);

[0075] T[x, y] is an input image or a target image;

[0076] ∠ is a topological component and;

[0077] Ψ is a phase-only hologram (280B) and;

[0078] η is the new distribution of magnitude values ​​(211B); and

[0079] α is the gain coefficient.

[0080] The gain factor α may be fixed or variable. In some embodiments, the gain factor α is determined based on the size and rate of the incoming target image data. In some embodiments, the gain factor α depends on the number of iterations. In some embodiments, the gain factor α is a sole function of the number of iterations.

[0081] The embodiment of FIG. 2c is identical to the embodiments of FIG. 2a and FIG. 2b in all other respects. The phase-only hologram Ψ(u, v) may be said to include a phase distribution in the frequency or Fourier domain.

[0082] In some embodiments, the Fourier transform is performed using a spatial light modulator. Specifically, holographic data is combined with second data that provides optical power. That is, data written to the spatial light modulator includes holographic data representing an object and lens data representing a lens. When displayed on the spatial light modulator and illuminated with light, the lens data emulates a physical lens—that is, focuses light in the same way as the corresponding physical optics. Thus, the lens data provides optical power or focusing power. In these embodiments, the physical Fourier transform lens (120) of FIG. 1 may be omitted. Methods for calculating data representing a lens are known. Data representing a lens may be referred to as a software lens. For example, a phase-only lens may be formed by calculating the phase delay caused by each point of the lens due to the refractive index and spatially variable optical path length. For example, the optical path length at the center of a convex lens is greater than the optical path length at the edges of the lens. Amplitude-only lenses may also be formed by Fresnel zone plates. Methods of combining lens-representing data with a hologram are also known in the field of computer-generated holography technology so that the Fourier transform of a hologram can be performed without requiring a physical Fourier lens. In some embodiments, lensing data is combined with the hologram by simple addition, such as simple vector addition. In some embodiments, a physical lens is used in conjunction with a software lens to perform the Fourier transform. Alternatively, in other embodiments, the Fourier transform lens is omitted entirely so that holographic reconstruction occurs in the far-field.In other embodiments, the hologram may be combined in the same way with grating data—that is, data configured to perform the function of a grating, such as image steering. Again, methods for computing such data are known in the art. For example, a phase-only grating may be formed by modeling the phase delay induced by each point on the surface of a blazed grating. An amplitude-only grating may simply superimpose the amplitude-only hologram to provide angular steering of the holographic reconstruction. The second data providing lensing and / or steering may be referred to as an optical processing function or an optical processing pattern to distinguish it from the hologram data, which may be referred to as an image forming function or an image forming pattern.

[0083] In some embodiments, the Fourier transform is performed jointly by a physical Fourier transform lens and a software lens. That is, some optical magnification contributing to the Fourier transform is provided by the software lens, and the remaining optical magnification contributing to the Fourier transform is provided by the physical optics or optical system.

[0084] In some embodiments, a real-time engine configured to receive image data and use an algorithm to compute holograms in real time is provided. In some embodiments, the image data is a video containing a sequence of image frames. In other embodiments, the holograms are pre-computed, stored in computer memory, and recalled as needed for display on an SLM. That is, in some embodiments, a storage of predetermined holograms is provided.

[0085] The embodiments relate merely to Fourier holography and Gerchberg-Saxton type algorithms. The present disclosure is equally applicable to Fresnel holography and Fresnel holograms that may be computed by similar methods. The present disclosure is also applicable to holograms computed by other techniques, such as those based on point cloud methods.

[0086] Optical modulation

[0087] A spatial light modulator may also be used to display a diffraction pattern containing a computer-generated hologram. If the hologram is a phase-only hologram, a spatial light modulator that modulates the phase is required. If the hologram is a full-complex hologram, a spatial light modulator that modulates both the phase and the amplitude may be used, or a first spatial light modulator that modulates the phase and a second spatial light modulator that modulates the amplitude may be used.

[0088] In some embodiments, the optical modulation elements (i.e., pixels) of the spatial optical modulator are cells containing liquid crystal. That is, in some embodiments, the spatial optical modulator is a liquid crystal device in which the optically active component is a liquid crystal. Each liquid crystal cell is configured to selectively provide a plurality of optical modulation levels. That is, each liquid crystal cell is configured at any time to operate at one optical modulation level selected from a plurality of possible optical modulation levels. Each liquid crystal cell is dynamically reconfigurable to a different optical modulation level from the plurality of optical modulation levels. In some embodiments, the spatial optical modulator is a reflective LCOS (liquid crystal on silicon) spatial optical modulator, but the present disclosure is not limited to this type of spatial optical modulator.

[0089] LCOS devices provide a dense array of optical modulation elements, or pixels, within a small aperture (e.g., a few centimeters wide). Pixels are typically approximately 10 µm or less, which generates diffraction angles of a few degrees, meaning the optical system can be compact. It is easier to properly illuminate the small aperture of an LCOS SLM than the larger aperture of other liquid crystal devices. LCOS devices are typically reflective, which means the circuitry driving the pixels of an LCOS SLM can be embedded beneath the reflective surface. The result is a higher aperture ratio; that is, the pixels are tightly packed, meaning there is very little dead space between them. This is advantageous because it reduces optical noise in the replay field. LCOS SLMs utilize a silicon backplane, which has the advantage of the pixels being optically flat. This is particularly important for phase modulation devices.

[0090] A suitable LCOS SLM is described below with reference to FIG. 3 merely as an example. The LCOS device is formed using a single-crystal silicon substrate (302). It has a 2D array of square planar aluminum electrodes (301) spaced apart by a gap (301a) and disposed on the upper surface of the substrate. Each of the electrodes (301) can be addressed through a circuit (302a) embedded within the substrate (302). Each of the electrodes forms a planar mirror. An alignment layer (303) is disposed on the array of electrodes, and a liquid crystal layer (304) is disposed on the alignment layer (303). A second alignment layer (305) is disposed on a planar transparent layer (306), for example, of glass. For example, a single transparent electrode (307) of ITO is disposed between the transparent layer (306) and the second alignment layer (305).

[0091] Each of the square electrodes (301) defines a controllable phase-modulation element (308), often referred to as a pixel, together with a transparent electrode (307) and an overlying region of the interposed liquid crystal material. The effective pixel area, or filling factor, is the percentage of the total optically active pixels, taking into account the space between the pixels (301a). By controlling the voltage applied to each electrode (301) with respect to the transparent electrode (307), the characteristics of the liquid crystal material of each phase-modulation element may be varied, thereby providing a variable delay to the incident light. This effect provides phase-only modulation to the wavefront, i.e., no amplitude effect occurs.

[0092] The described LCOS SLM outputs spatially modulated light by reflecting it. Reflective LCOS SLMs have the advantage that signal lines, gate lines, and transistors are located beneath a mirrored surface, which results in high fill factors (typically exceeding 90%) and high resolutions. Another advantage of using a reflective LCOS spatial light modulator is that if a transmissive device is used, the liquid crystal layer can be half the required thickness. This significantly improves the switching speed of the liquid crystal (a major advantage for projecting moving video images). However, the teachings of the present disclosure may be equally implemented using a transmissive LCOS SLM.

[0093] Image projection using a small display device and a long viewing distance

[0094] The present disclosure relates to image projection in which the separation between a display device and a viewer is much larger than the size of the display device. The viewing distance (i.e., the distance between the viewer and the display device) may be at least 10 times larger than the size of the display device. The viewing distance may be at least 100 times larger than the size of the display device. For example, the pixel area of ​​the display device may be 10 mm x 10 mm and the viewing distance may be 1 m. An image projected by the system is formed on a display plane spatially separated from the display device.

[0095] According to the present disclosure, an image is formed by holographic projection. A hologram is displayed on a display device. The hologram is illuminated by a light source (not shown), and the image is perceived on a display plane spatially separated from the hologram. The image may be real or virtual. For the purposes of the following description, it is helpful to consider a virtual image formed upstream of the display device, that is, appearing behind the display device. However, it is not necessary that the image be a virtual image, and the present disclosure is equally applicable to a real image formed between the display device and the viewing system.

[0096] The display device includes pixels that display a hologram. The pixel structure of the display device is diffractive. Therefore, the size of the holographic image is determined by diffraction rules. The results of the diffraction characteristics of the display device are described below with reference to FIG. 4.

[0097] FIG. 4 illustrates a pixelated display device (402) configured to display a hologram forming a virtual image (401) upstream of a display device (402). The diffraction angle, q, of the display device determines the size of the virtual image (401). The virtual image (401), the display device (402), and the viewing system (405) are positioned on an optical axis, Ax.

[0098] The viewing system (405) has an incident aperture (404) and a viewing plane (406). The viewing system (405) may be a human eye. Thus, the incident aperture (404) may be the pupil of the eye and the viewing plane (406) may be the retina of the eye.

[0099] Light traveling between the display device (402) and the viewing system (405) is modulated into a hologram of the image (rather than the image itself). However, FIG. 4 illustrates a method by which the hologram divides the virtual image content by angle. Each of the illustrated beams of light is associated with a different part of the virtual image (401). More specifically, the light of each beam of light is encoded by the hologram along with information about a part of the virtual image. FIG. 4 illustrates five exemplary beams of light, each characterized by an angle with respect to the optical axis, Ax, and each representing a different part of the virtual image. In this example, one of the beams of light passes through the pupil (404), and the other four beams of light are blocked by the pupil (404). Again, the five different beams of light correspond to five different parts of the virtual image (401). The entire image content of the virtual image is effectively divided by angle. A beam of light traveling along the optical axis, Ax, carries information about the center of the image information, that is, the center of the image. Other beams of light carry other parts of the image information. Two beams of light shown at the extremes of the light cone carry edge parts of the image information. The result of this division of image information by angle is that not all image content can pass through the incident aperture (404) of the viewing system at a predetermined viewing position. That is, not all image content is received by the eye. In the example of FIG. 4, only one of the five beams of light shown passes through the pupil (404) at any viewing position. The reader will understand that the five beams of light are shown merely as an example and that the described process is not limited to dividing the image information of a virtual image into only five beams of light.

[0100] In this example, the central part of the image information is received by the eye. The edge parts of the image information are blocked by the pupil of the eye. The reader will understand that if the viewer moves up or down, different beams of light may be received by the eye, and, for example, the central part of the image information may be blocked. Therefore, the viewer sees only a part of the entire image. The remaining image information is blocked by the incident pupil. The viewer's field of view is significantly limited because it effectively views the image through the small aperture of the display device itself.

[0101] In summary, light propagates from the display device over a range of diffraction angles. At a viewing distance of 1 m, only a small range of angles from the display device can propagate through the pupil of the eye to form an image on the retina for a predetermined eye position. The only parts of the visible virtual image are within the small angle range shown in Fig. 4 that pass through the incident aperture. Therefore, the field of view is very small, and the specific angle range is highly dependent on the eye position.

[0102] The problem of sensitivity to a small field of view and eye position, as described with reference to FIG. 4, is a result of the large viewing distance and small aperture of the display device. The importance of the viewing distance is further explained with reference to FIGS. 5 through 7.

[0103] FIG. 5a illustrates a display device (502) configured to display a hologram and propagate light modulated according to the hologram to a viewing system comprising an incident aperture (504) and a viewing plane (506). The virtual image (501) is at infinity, and thus the rays traced between the virtual image and the display device are collimated. The lower part of FIG. 5a illustrates an enlarged view of the viewing system. This drawing is schematic, and therefore physiological details of the eye are not illustrated. In fact, of course, there is a light source (not shown in FIG. 5a) configured to illuminate the display device (502).

[0104] FIG. 5a illustrates only the rays that can propagate through the aperture (504), and any other rays that cannot pass through the aperture (504) are omitted. However, it will be understood that these other rays will also actually propagate from the display device (502). In FIG. 5a, the distance between the display device and the viewing plane is sufficiently small so that the full diffraction angle from the display device can form an image on the retina. All light propagation paths illustrated from the virtual image pass through the incident aperture. Thus, all points on the virtual image are mapped onto the retina, and all image content is transmitted to the viewing plane. Therefore, the field of view of the perceived image is maximum. At the optimal position, the field of view is equal to the diffraction angle of the display device. Interestingly, different image points on the retina are formed from light propagating from different regions on the display device (502)—for example, the image point closest to the top of FIG. 5a is formed from light propagating only from the lower part of the display device. Light propagating from other regions of the display device does not contribute to this image point.

[0105] Figure 5b illustrates the situation that occurs as the viewing distance increases.

[0106] More specifically, FIG. 5b illustrates a display device (502') configured to display a hologram and propagate light modulated according to the hologram to a viewing system comprising an incident aperture (504') and a viewing plane (506'). The virtual image (501') is at infinity, and thus the traced rays between the virtual image and the display device are collimated. The lower part of FIG. 5b illustrates an enlarged view of the viewing system. This drawing is schematic, and therefore physiological details of the eye are not illustrated. In fact, of course, there is a light source (not shown in FIG. 5b) configured to illuminate the display device (502').

[0107] FIG. 5b illustrates only the rays that can propagate through the aperture (504'). At a larger viewing distance in FIG. 5b, some of the ray bundles are blocked by the incident aperture (504'). Specifically, ray bundles associated with the edge portions of the virtual image are blocked by the incident aperture (504'). Consequently, the entire virtual image is not visible, and the visible portion of the virtual image is highly dependent on the eye position. Therefore, a large distance between the display device and the viewing system becomes a problem due to the small size of the display device.

[0108] FIG. 6a illustrates an improved system comprising a display device (602) and propagates light encoded as a hologram displayed on the display device (602) toward a viewing system comprising an incident aperture (604) and a viewing plane (606). In fact, of course, there is a light source (not shown) configured to irradiate the display device (602). The improved system further comprises a bulk optical waveguide (608) positioned between the display device (602) and the incident aperture (604). The lower part of FIG. 6a illustrates an enlarged view of the incident aperture (604) and the viewing plane (606). This drawing is schematic and therefore physiological details of the eye are not illustrated.

[0109] The viewing distances of FIGS. 6a and 6b are the same as the viewing distance of FIGS. 5b. However, the beams of light blocked in FIGS. 5b—despite the longer viewing distance—are effectively recovered by the waveguide (608) so that the entire image information is received by the viewing system.

[0110] The presence of the waveguide (608) allows all angular content from the display device (602) to be received by the eye even at this relatively large projection distance. This is because the waveguide (608) acts as a pupil expander in a known manner and is therefore briefly described in this specification.

[0111] Simply put, the bulk optical waveguide (608) comprises a substantially elongated formation having a first planar (major) surface and second planar (major) surfaces (610, 612). In this example, it comprises an optical slab of refractive material, but other types of waveguides comprising a pair of parallel planar reflective surfaces are also well known and may be used. The waveguide (608) is positioned to intersect, for example, at an oblique angle with a light cone projected from a display device (602). The size and position of the waveguide (608) are configured to ensure that light from each of the five beams within the light cone is incident on the waveguide (608). Light from a light cone is incident on a waveguide (608) through a first planar surface (610) (located closest to the display device (602)) and is at least partially guided along the length of the waveguide (608) before being emitted through a second planar surface (612) substantially opposite the first surface (610) (located closest to the eye). As will be well understood, the second planar surface (612) is partially reflective and partially transmissive. That is, when each beam of light travels from the first planar surface (610) to the second planar surface (612) of the waveguide (608) within the waveguide (608), some of the light will be transmitted from the waveguide (608) as a "replica" of the received light, and some will be reflected by the second planar surface (612) back toward the first planar surface (610). The first planar surface (610) is reflective such that all light hitting it from within the waveguide (608) is reflected back toward the second planar surface (612).Accordingly, while some of the light may simply be refracted between the two planar (primary) surfaces (610, 612) of the waveguide (608) before being transmitted, other light may be reflected and thus undergo one or more reflections (or 'bounces') between the planar surfaces (610, 612) of the waveguide (608) before being transmitted. Thus, the net effect of the waveguide (608) is that the transmission of light is effectively extended by transmitting a series of copies along the length across multiple positions on the second planar surface (612) of the waveguide (608). Thus, all angular content output by the display device (602) may exist in a greater number of positions on the display plane (and a greater number of positions on the aperture plane) than in the absence of the waveguide (608). This means that light from each beam of light can enter the incident aperture (604) and contribute to the image formed by the viewing plane (606) despite the relatively large projection distance. In other words, all angular content from the display device (602) can be received by the eye. Thus, the entire diffraction angle of the display device (602) is utilized, and the viewing window is maximized for the user. Ultimately, this means that all light rays contribute to the perceived virtual image (601).

[0112] FIG. 6b illustrates individual optical paths for each of the five beams of light contributing to each of the five respective image points within the virtual image (601) formed in FIG. 6a—labeled R1 to R5 from top to bottom, respectively. As can be seen here, the light of R1 and R2 is simply refracted and then transmitted by the waveguide (608). Meanwhile, the light of R4 faces a single bounce before being transmitted. The light of R3 includes some light from a corresponding first part of the display device (602) that is simply refracted by the waveguide (608) before being transmitted, and some light from a second, different corresponding part of the display device (602) that faces a single bounce before being transmitted. Similarly, the light of R5 includes some light from a corresponding first part of the display device (602) facing a single bounce before being transmitted, and some light from a second, different corresponding part of the display device (602) facing two bounces before being transmitted. For each of R3 and R5, the two different parts of the LCOS propagate light corresponding to parts of the virtual image.

[0113] The inventors have recognized that, in at least some applications, it is desirable for the virtual image distance—i.e., the distance from the viewer to the virtual image—to be finite, as opposed to the virtual image being formed infinitely. In certain applications, there may be a desirable virtual image distance at which the virtual image content is desirable or essential to appear. For example, in a head-up display, for example in a car setting, for example, the virtual image content may be superimposed on actual content visible to the viewer through the vehicle windscreen. For example, the desired virtual image distance may include virtual image content formed at a distance of several meters, for example, 3 meters or 5 meters, in front of the viewer's vehicle or windscreen.

[0114] Holographic computation for small display devices, long viewing distances, and pupil expanders

[0115] The inventors have devised a method for calculating a hologram for the optical system illustrated in FIG. 7 using a point cloud method or an iterative algorithm, as disclosed in British patent applications Nos. GB2101666.2, GB2101667.0, and GB2112213.0, which are previously cited by reference in this specification. This type of hologram is informally referred to in this specification as an "optical channeling hologram" or simply a "channeling hologram." Importantly, the display device is relatively small and the projection distance is relatively long. The hologram is projected directly onto a viewing system, and the method can be implemented in real time. The relatively small size of the display device and the relatively long projection distance require a pupil expander. This method handles different paths through the pupil expander. The method causes image content to appear simultaneously at different distances and / or multiple distances from the viewing system, selectably—for example, using a single hologram. This method allows image content to be simultaneously displayed downstream and upstream of a display device, selectably—for example, by using a single hologram.

[0116] FIG. 7 illustrates a spatial light modulator (701) operable to display a hologram of an image. In this embodiment, the spatial light modulator (701) is a liquid crystal on a silicon device configured to modularize the phase of the received light. The spatial light modulator (701) is irradiated at least partially by coherent light from a light source not illustrated. The light source may be a laser diode. The spatial light modulator (701) outputs spatially modulated light according to the display hologram. FIG. 7 illustrates one beam (702) of spatially modulated light. The spatially modulated light is received by a pupil expander (703). The pupil expander (703) is tilted with respect to the plane of the display device (701). Thus, the pupil expander (703) receives light with non-orthogonal incidence. The angle of incidence (the angle the optical axis makes with the pupil expander) may be less than 25°, such as 10 to 20°. The pupil expander includes an input surface (703a) and an output surface (703b) that receive spatially modulated light. The input surface (703a) and the output surface (703b) are substantially parallel and elongated in the direction of pupil expansion. The input surface (703a) includes at least a portion that is substantially completely reflective (e.g., R = 1). The output surface (703b) includes at least a portion that is highly reflective but partially transmissive (e.g., R = 0.9 and T = 0.1). As described above with reference to the waveguide (608) of FIG. 6, the reflective surfaces are positioned so that the spatially modulated light bounces back and forth between them, and the light is emitted at a plurality of points along the output surface (703b). In this embodiment, the pupil expander is substantially elongated. The pupil expander provides pupil expansion in one direction—that is, in the longitudinal direction—but the present disclosure may be extended to include the presence of a second pupil expander configured to expand the pupil in an orthogonal direction.

[0117] FIG. 7 illustrates how a light ray (702) is effectively duplicated twice to form three propagation paths (705) associated with different distances, Z0, Z1, and Z2, respectively. The shortest propagation path corresponds to Z0, and in this example, corresponds to light passing through the waveguide without any internal reflections. The three intermediate-distance propagation paths illustrated correspond to Z1 and the two internal reflections of the pupil expander (one by each surface). The longest propagation path illustrated corresponds to Z2 and the four internal reflections of the pupil expander (two by each surface). Planes x 0, x 1 and x 2 represents the spatial size of the optical field associated with each of the three propagation paths, Z0, Z1, and Z2. More specifically, FIG. 7 shows three planes x 0, x 1 and x Illustrates how 2 is offset from each other in the x-direction.

[0118] FIG. 7 further illustrates a viewing system (713) comprising an incident pupil (707), a lens (709), and a light sensor (711). In embodiments, the viewing system (713) is a human eye and the light sensor (711) is the retina of the eye. FIG. 7 illustrates how only a portion of the light field associated with each propagation path passes through the entrance (707). FIG. 7 illustrates a ray associated with the center of an intermediate-distance propagation path passing through the center of the incident pupil (707). However, for example, a ray associated with the center of the light field of the shortest-distance propagation path is blocked by the upper part of the aperture (707). However, other rays associated with the light field of the shortest-distance propagation path may pass through the aperture (707). A ray associated with the center of the light field of the longest-distance propagation path is blocked by the lower part of the aperture (707). However, other rays associated with the light field of the longest propagation path can also pass through the aperture (707).

[0119] Light passing through the aperture (707) is focused onto the light sensor (711) by the lens (709). The plane of the light sensor (711) is substantially parallel to the plane of the display device (701) and is therefore inclined with respect to the long dimension of the pupil expander (703).

[0120] FIG. 7 illustrates three possible optical propagation paths merely as an example. The present disclosure is not limited by the number of propagation paths. That is, as will be recognized by those skilled in the art from the following description, the method may be extended to be factored in by any number of optical propagation paths. Similarly, it is not essential that the pupil expander be tilted with respect to the display plane and the sensor plane.

[0121] FIGS. 8 and 9 illustrate examples of channeling holograms formed by a point cloud method or a method using an iterative algorithm as disclosed in the aforementioned UK patent applications GB2101666.2, GB2101667.0 and GB2112213.0.

[0122] Light channeling

[0123] FIG. 8 illustrates a projected image (1552) comprising eight image regions / components, V1 through V8. FIG. 8 illustrates eight image components merely as an example, and the image (1552) may be divided into any number of components. FIG. 8 also illustrates an encoded light pattern (1554) (i.e., a hologram) capable of reconstructing the image (1552)—for example, when transformed by a lens of a suitable viewing system. The encoded light pattern (1554) comprises a first sub-hologram or component through an eighth sub-hologram or component, H1 through H8, corresponding to the first image component / region through the eighth image component / region, V1 through V8. FIG. 8 further illustrates a method by which this type of hologram effectively decomposes image content by angle. Therefore, the hologram may be characterized by performing light channeling, and thus is referred to as an "optical channeling hologram" or simply a "channeling hologram." This is exemplified in FIG. 9. Specifically, the hologram directs light into a plurality of discrete regions. The discrete regions are disks in the illustrated example, but other shapes are conceived. This optical channeling occurs only due to a specific method of determining the hologram.

[0124] FIG. 10 illustrates an improved viewing system (1500) according to the recognitions exemplified in FIG. 8 and FIG. 9.

[0125] The viewing system (1500) includes a display device comprising an LCOS (1502) in this arrangement. The LCOS (1502) is configured to display a modulation pattern (or 'diffraction pattern') containing a hologram and to project holographically encoded light toward an eye (1505) comprising a pupil acting as an aperture (1504), a lens (1509), and a retina (not shown) acting as a viewing plane. There is a light source (not shown) configured to irradiate the LCOS (1502). The lens (1509) of the eye (1505) performs hologram-to-image conversion.

[0126] The viewing system (1500) further includes a bulk optical waveguide (1508) positioned between the LCOS (1502) and the eye (1505). The projection distance of FIG. 10 may be relatively large. However, as described in relation to the previous drawings, the presence of the waveguide (1508) allows all angular content from the LCOS (1502) to be received by the eye (1505) even at this relatively large projection distance. This is because, in the manner described above, the waveguide (1508) acts as a pupil expander.

[0127] Additionally, in this configuration, when the LCOS (1502) is encoded as a channeling hologram, the waveguide (1508) may be oriented obliquely with respect to the LCOS (1502) to establish a unique relationship between the light from the LCOS (1502) and the virtual image perceived by the viewer. The size and position of the waveguide (1508) are configured to ensure that light from each part of the virtual image is incident on the waveguide (1508) and guided along a long axis that bounces between substantially planar surfaces of the waveguide (1508). Whenever the light reaches a second planar surface (closest to the eye (1505)), some of the light is transmitted and some of the light is reflected.

[0128] FIG. 10 illustrates a total of nine "bounce" points, B0 through B8, along the length of the waveguide (1508). The reader will notice that the center of the image (1552) remains blank. FIG. 10 illustrates the zeroth through ninth light "bounce" or reflection points, B0 through B8, within the waveguide. Light associated with all points (V1 through V8) of the image is transmitted from the waveguide at each "bounce" from the second planar surface of the waveguide (1508), but only light from one of the angled portions of the image (e.g., light from one of V1 through V8) has a trajectory that allows it to reach the eye (1505) from each of the respective "bounce" points, B0 through B8. Furthermore, light from different angled portions of the image, V1 through V8, reaches the eye (1505) from each of the respective "bounce" points. FIG. 10 illustrates light from all different angle contents emitted at each "bounce" point (indicated by multiple short arrows at each transmission point), but only the optical path from each part of the waveguide to the eye (1505) of each angle content that actually reaches the eye (1505)—thus contributing to each part of the virtual image perceived by the viewer. For example, for the 0th bounce, B0, the light transmitted by the waveguide (1508) is simply refracted and undergoes no internal reflection. The light from the 8th sub-hologram, H8, reaches the eye from the 0th bounce, B0. For the next bounce B1, the light transmitted by the waveguide (1502) undergoes one bounce internally before transmission. The light from the 7th hologram H7 reaches the eye from the next bounce B1. This continues sequentially until the light, B8, transmitted by the waveguide (1508) in the final bounce, passes through 8 bounces before reaching the eye (1505), and includes the light encoded according to the first hologram, H1.

[0129] In the example illustrated in FIG. 10, only light from one image region reaches the eye from each bounce point. Thus—when the hologram is determined as described herein—a spatial correlation is established between regions of the virtual image and their associated bounce points on the waveguide. In some other examples, there may be relatively small overlaps such that one region of the image emerges from two adjacent transmission points and is therefore contained within two adjacent optical discs propagating from the waveguide toward the viewing plane.

[0130] Accordingly, the recognitions made by the inventors, and the methods and configurations described above, can generate a diffraction pattern (or optical modulation pattern) comprising a hologram, which, when displayed on an LCOS or other suitable display device, can cause light to be effectively emitted from a plurality of 'disks' or beams of light corresponding to (more specifically, encoding) different parts of a corresponding virtual image. As previously known, in this disclosure, this type of hologram is referred to as an "optical channeling hologram" or simply a "channeling hologram."

[0131] Fiber Optic Pupil Expansion

[0132] FIG. 11 is a schematic example of a novel technique for pupil expansion according to embodiments of the present disclosure. Instead of using bulk optics as pupil expander(s), this technique uses a plurality of optical fibers (also referred to as “optical fibers”). In other embodiments, the optical fibers may be replaced with other types of light guides or optical pipes to propagate light from the input end to the output end.

[0133] A pupil expander (1100) is formed by a plurality of optical fibers (1120). Each optical fiber (1120) includes an input end (1122) and an output end (1124). In the configuration shown in FIG. 11, the input ends (1122) of the optical fibers (1120) are arranged in a two-dimensional array on the input plane (1130) of the pupil expander (1100), and the output ends (1124) of the optical fibers (1120) are arranged in a corresponding two-dimensional array on the output plane (1140) of the pupil expander (1100). As illustrated by the arrow in FIG. 11, the pupil expander (1100) is configured to receive light from a hologram (1150) displayed on a display device to an input plane (1130) and to output light from an output plane (1140) toward a viewing area of ​​a viewing system or viewer (not shown).

[0134] Accordingly, light (modulated) output by a display device encoded with a hologram (1150) is coupled into a pupil expander (1100) by a coupler (1160). In particular, the coupler (1160) couples light into the input ends (1122) of a plurality of optical fibers (1120) in the input plane (1130). In some examples, a coupling lens or an array of coupling lenses may be placed upstream of each input end (1122) of the plurality of optical fibers (1120). Various techniques for coupling light into the pupil expander (1100) are possible as described below. In addition, in some configurations, the light coupled into each input end (1122) of each of the plurality of optical fibers may be the same (e.g., corresponding to the entire hologram (1150)). Accordingly, all optical fibers (1120) output light of the entire hologram at the output ends (1124) of the array of output planes (1140), forming an array of “replicas” (1150’’), thus forming an extension of the pupil. In other configurations, the light coupled into each input end (1122) of each of the plurality of optical fibers (1120) may be different (e.g., corresponding to a part of the hologram (1150)). In one example, light corresponding to only each part of a single hologram may be coupled to each of the optical fibers (1120) according to a position within the array (e.g., based on angular content such as a single channel or a subset of channels of a channeling hologram). In this example, pupil expansion may be achieved by coupling light from each part of the hologram into two or more optical fibers (1120) having adjacent output ends (1124) of the array at the output plane (1140) to form successive "replicas." In another example, multiple optical fibers (1120) may receive light from different holograms. In this example, each hologram may correspond to a different part of the image.Pupil expansion may be achieved by coupling the light of each hologram into two or more optical fibers (1120) having adjacent output ends (1124) of the array at the output plane (1140) to form successive “replicas” thereof. The array may be dynamically reconfigurable so that pairs of holograms and optical fibers may change over time based on eye-tracking information (i.e., information about the position of the viewer’s eye(s) within the viewing window). Thus, as illustrated in FIG. 11, the coupler (1160) couples separate channels of input light encoded with each hologram (1150’) (which may be all or part of the hologram (1150)) into each input end (1122) of the optical fiber (1120).

[0135] Each optical fiber (1120) is configured to propagate the (modulated) light of each optical channel received at the input end (1122) to the output end (1124), thereby effectively forming a “replica” (1150’’) of the encoded light using a hologram (1150’) (the same hologram or a different hologram as described above). In particular, as will be recognized by those skilled in the art, each optical fiber (1120) may propagate a complex input light field corresponding to the hologram (1150’) along its length by total internal reflection within the core of the optical fiber. Thus, by controlling the hologram (1150), it is possible to control the complex output light field provided to the viewing area by the pupil expander (1110) from the output end (1124) of each optical fiber (1120). In some examples, the output ends (1124) of each of the multiple optical fibers (1120) may be coupled to a lens. Thus, the light field output by the output plane (1140) of the pupil expander (1100) may be optically processed, such as collimation, before being relayed to a viewing area according to application requirements.

[0136] In the configuration illustrated in FIG. 11, the pupil expander (1100) comprises 15 optical fibers (1110a to 1110o) each having inputs (1122a to 1122o) and outputs (1124a to 1124o) arranged in a 3 x 5 array. In other configurations, any number of optical fibers (1110) may be used with input and output ends arranged in any target 1-dimensional array (for 1-dimensional pupil expansion) or 2-dimensional array (for 2-dimensional pupil expansion) depending on the application requirements.

[0137] In some embodiments, the plurality of optical fibers (1120) of the pupil expander (1100) is a bundle of optical fibers (1120) having an input end of the bundle comprising input ends (1122) of optical fibers arranged in an array in an input plane (1130), and an output end (1124) of the bundle comprising output ends (1124) of optical fibers arranged in an array in an output plane (1140). In other embodiments, the plurality of optical fibers (1120) of the pupil expander are a plurality of individual multi-mode fibers having respective input ends (1122) and output ends (1124) arranged in an array as described above. In other embodiments, the plurality of optical fibers (1120) of the pupil expander (1100) is a bundle of multi-mode optical fibers having input ends (1122) of optical fibers arranged in an array in an input plane (1130), and output ends (1124) of optical fibers arranged in an array in an output plane (1140). In other embodiments, each optical fiber is a single-mode optical fiber.

[0138] A method for expanding the exit pupil of a holographic system using a pupil expander comprising a plurality of light guide plates, such as optical fibers, is provided. The method includes the step of displaying a diffraction pattern of an image (e.g., a hologram). For example, the diffraction pattern may be displayed by a spatial light modulator that is encoded or addressed to the hologram. The method may further include the step of irradiating the diffraction pattern by a light source. The method further includes the step of outputting light encoded using the hologram by the diffraction pattern. For example, the spatial light modulator may be irradiated with light and may output light that is spatially modulated according to the hologram. The method further includes the step of coupling the light encoded by the hologram into the pupil expander comprising a plurality of light guide plates to the input end of each of the plurality of light guide plates. For example, the light output (modulated) by the spatial light modulator may be coupled by a coupler to the input end of each of the plurality of light guide plates of the pupil expander. The method further includes the step of propagating light received at an input end for output at an output end by each of a plurality of light guide plates of a pupil expander to expand the output pupil to a first dimension. The first dimension may correspond to the dimension of a viewing area (where a viewer can perceive an image). In one example, the output ends of the plurality of light guide plates may be arranged in a one-dimensional array to expand the output pupil along the dimension of the array. In another example, the output ends of the plurality of light guide plates may be arranged in a two-dimensional array to expand the output pupil along two dimensions of the array.

[0139] As will be recognized by those skilled in the art, the optical fiber pupil expander of the present disclosure may be used with one or more conventional optical components, including optical / bulk optical waveguides, in the path of an optical system for relaying light from a display device to a viewing area for viewing by a viewing system, as described herein. For example, the optical fiber pupil expander may be used to extend the outgoing pupil to the first dimension for input to a waveguide pupil expander that extends the outgoing pupil at a second dimension orthogonal to the first dimension.

[0140] Accordingly, it can be seen that a plurality of light guide plates, such as optical fibers, which may be bundled together in an array configuration as described in this specification, may perform pupil expansion in one or two dimensions by forming "replicas" in the same manner as conventional bulk optical systems. However, unlike bulk optical systems which can generally only expand the output pupil in one dimension, an optical fiber pupil expander can simultaneously expand the output pupil into two dimensions by arranging the output ends of a two-dimensional array. Furthermore, a pupil expander comprising a plurality of light guide plates, for example, allows the lengths and routing of the light guide plates in situ ( in situ By modifying it, it may be positioned more flexibly with respect to the viewing area of ​​the display device and / or (holographic) imaging system.

[0141] For example, as illustrated in FIG. 12, in a head-up display for a vehicle (1200), the display device (1250) may be positioned at the rear of the vehicle (e.g., at the boot / trunk), having an input plane (1130) of the pupil expander (1100) of the embodiment of FIG. 11 adjacent thereto, and a plurality of optical fibers (1120) of the pupil expander (1100) may extend along the sides of the vehicle (1200) to an output plane (1140) of the pupil expander (1100) on the vehicle dashboard. In this way, the head-up display consumes a reduced amount of valuable space within the vehicle dashboard. In addition, it may be possible to provide an optical channel feed from the display device (1250) (or another) through multiple optical fibers (1120) to another location within the vehicle (1200), such as the vehicle dashboard on the passenger side for the passenger to view.

[0142] Coupling techniques

[0143] As previously noted with reference to FIG. 11, various techniques may be used by a coupler (1160) to couple light encoded in a hologram from a display device into a pupil expander (1100) comprising a plurality of optical fibers (1120).

[0144] In the first coupling technique, the same (modulated) light is coupled into each of the input ends (1122) of a plurality of optical fibers (1120) using, for example, an optical fiber splitter (also referred to as an "optical fiber splitter"). Accordingly, the coupler (1160) may include an optical fiber splitter having a plurality of output ports corresponding to the number of input ports and optical fibers (1120) of the fiber expander (1100). The optical fiber splitter receives light encoded as a hologram (1150) from a display device (not shown) at the input port and "splits" the received light into a plurality of identical channels (1150') for output from the output ports. The output ports of the optical fiber splitter may be configured at a plurality of angles to couple each output light channel into each of the input ends (1122) of an array of input ends (1122) of the plurality of optical fibers (1120). Therefore, all optical fibers (1120) receive the same (modulated) light simultaneously. It can also be said that the same hologram is launched simultaneously into each of the optical fibers at different angles. Thus, multiple optical fibers (1120) form identical copies (i.e., copies of the same information / image content) at all positions of the output pupil extended from the output plane (1140) for relay toward the viewing area.

[0145] In the second coupling technique, the same (modulated) light is coupled into the input ends (1122) of each of the multiple optical fibers (1120) in a time-multiplexed manner. That is, the light is coupled into each of the multiple optical fibers (1120) one at a time in a defined sequence. Thus, the coupler (1160) may include an input port, at least one output port, and a multiplexer. The multiplexer sequentially couples light from each output port (e.g., at different angles) to each of the multiple optical fibers (1120) of the pupil expander (1100). This may be achieved by using any suitable technique, such as using scanning mirrors or beam manipulation to output light from one output port at different angles, or by sequentially outputting light to multiple output ports arranged at different angles. Thus, all optical fibers (1120) receive the same encoded light, but at different times in the time sequence. It may be said that the same hologram is launched sequentially or in a time-multiplexed manner into each of the optical fibers at different angles. Thus, multiple optical fibers (1120) form identical copies (i.e., duplicate the same information / image content) at all positions of the output pupil extended in the output plane (1140) for relay toward the viewing area, but at different times. In the examples, the total duration of the sequence (i.e., the time for the input of light into all optical fibers forming the pupil extender) is shorter than the human eye's exposure time (integration time).

[0146] In some examples, the hologram (1150) itself distributes the necessary information down each optical fiber. That is, the hologram may be configured to route holographically encoded light down each of the multiple optical fibers. The encoded light coupled to each optical fiber may contain holographic-domain information for the entire image or holographic-domain information for each part of the image (e.g., channels).

[0147] In the third coupling technique, different (modulated) light is coupled into the input ends (1122) of different optical fibers (1120) according to, for example, each position within the array. For example, a type of hologram described below and informally referred to as a "channeling hologram" in British Patent Application No. 2101666.2, GB2101667.0 and GB2112213.0 may be calculated and displayed by a display device (not shown). By encoding the channeling hologram on the display device (not shown), the modulated light forms optical channels that are output at multiple angles. The angles of the channeling hologram may be selected so that the light at each angle is coupled or launched into the respective input ends (1122) of the multiple optical fibers (1120) of the pupil expander (1100). Accordingly, different modulated light is simultaneously coupled into the input ends (1122) of different optical fibers of a plurality of optical fibers (1120). Two or more optical fibers (1120) having adjacent input / output ends may receive light of the same optical channel or light at the same angle for pupil expansion as described herein. Light of a single optical channel / angle or a subset of (adjacent) optical channels / angles may be coupled to each of the optical fibers (1120). Thus, different holograms (e.g., different information) are coupled to each of the plurality of optical fibers (1120) according to the position of the input end (1122) in the array. Consequently, each optical fiber (1120) propagates a different part of the image (although it is in the hologram domain). It may be said that multiple optical fibers (1120) form different copies or parts of an image (i.e., copied or corresponding to different information / image content) at different positions of the output pupil extended from the output plane (1140) for relay to a viewing area.

[0148] Application of fiber optic pupil expanders to channeling holograms

[0149] As described in this specification, the optical fiber pupil expansion according to the present disclosure may be implemented as a so-called channeling hologram, as described above and in the aforementioned UK patent applications Nos. GB2112216.3, GB2101667.0 and GB2112213. As described above, a channeling hologram may be calculated that distributes light angularly (in a hologram domain) according to the position within the image and the propagation of the light through a pupil expander providing a plurality of light propagation paths or “channels,” wherein each light propagation path corresponds to a respective consecutive region of the image. Methods for calculating the channeling hologram effectively calculate a plurality of sub-holograms of each image and combine these sub-holograms to form a hologram for display. In embodiments, the image may be said to include a first image component and a second image component, and each image component is a different sub-area or sub-region of the image. That is, image components are the spatial components of an image that collectively constitute the entire image—for example, contiguous and / or continuous blocks of image pixels. However, according to this disclosure, the image may be decomposed differently. That is, "image components" may be different modes or component elements of the image.

[0150] Accordingly, depending on the position of the input / output end within the array of input / output end of multiple optical fibers, a channeling hologram that distributes light angularly (in the hologram domain) such that each optical channel (angle content) or a subset thereof is coupled to each optical channel among the multiple optical fibers may be calculated.

[0151] In some embodiments, the eye tracking system may be used to track the position of the viewer's eyes within a viewing area (e.g., an eye motion box). In this case, the system may be configured to dynamically control the coupling of optical channels into multiple optical fibers. Thus, as the viewer's eyes move within the eye motion box, the system may be configured to reconfigure the allocation of angle content (i.e., image content) between the optical fibers based on eye-tracking data received as feedback, so that the eyes receive all angle content (i.e., all parts of the image).

[0152] Additional features

[0153] The embodiments refer merely to an electrically activated LCOS spatial light modulator. The teachings of the present disclosure may be implemented identically on any spatial light modulator capable of displaying a computer-generated hologram according to the present disclosure, such as, for example, any electrically activated SLMs, an optically activated SLM, a digital micromirror device, or a microelectromechanical device.

[0154] In some embodiments, the light source is a laser, such as a laser diode. The holographic projection system of the present disclosure may also be used to provide an improved head-up display (HUD) or a head-mounted display. In some embodiments, a vehicle is provided that includes a holographic projection system installed in the vehicle to provide a HUD. The vehicle may be an automotive vehicle, such as a car, truck, van, lorry, motorcycle, train, airplane, boat, or ship.

[0155] In the embodiments, the holographic reconstruction is in color. In some embodiments, spatially-separated colors, an approach known as "SSC" is used to provide a color holographic reconstruction. In other embodiments, frame sequential colors, an approach known as "FSC" is used.

[0156] The SSC method uses an array of three spatially separated optically modulated pixels for three single-color holograms. The advantage of the SSC method is that the image can be very bright because all three holographic reconstructions can be formed simultaneously. However, due to spatial constraints, if the arrays of three spatially separated optically modulated pixels are provided on a common SLM, the quality of each single-color image is suboptimal because only a subset of available optically modulated pixels is used for each color. Consequently, relatively low-resolution color images are provided.

[0157] The FSC method can utilize all pixels of a common spatial light modulator to sequentially display three single-color holograms. The single-color reconstructions cycle through quickly enough for a human viewer to perceive a polychromatic image from the integration of the three single-color images (e.g., red, green, blue, red, green, blue, etc.). The advantage of FSC is that the entire SLM is used for each color. This means that the quality of the three generated color images is optimal because all pixels of the SLM are used for each color image. However, the disadvantage of the FSC method is that the brightness of the composite color image is lower—about three times—than when using the SSC method, because each single-color illumination event can only occur for one-third of the frame time. This disadvantage can potentially be resolved by overdriving the lasers or using more powerful lasers, but this requires more power, resulting in higher costs and an increase in the size of the system.

[0158] While the examples describe irradiating an SLM with visible light, those skilled in the art will understand that light sources and the SLM may be used in the same way to direct infrared or ultraviolet light, for example, as disclosed herein. For example, those skilled in the art will recognize techniques for converting infrared and ultraviolet light into visible light for the purpose of providing information to a user. For example, the present disclosure extends to the use of phosphors and / or quantum dot technologies for this purpose.

[0159] Some embodiments describe 2D holographic reconstructions merely as examples. In other embodiments, the holographic reconstruction is a 3D holographic reconstruction. That is, in some embodiments, each computer-generated hologram forms a 3D holographic reconstruction.

[0160] The methods and processes described herein may be implemented on a computer-readable medium. The term "computer-readable medium" includes media configured to store data temporarily or permanently, such as RAM (random-access memory), ROM (read-only memory), buffer memory, flash memory, and cache memory. The term "computer-readable medium" is also considered to include any medium, or a combination of multiple media, capable of storing instructions for execution by a machine such that, when executed by one or more processors, the instructions cause the machine to perform any one or more of the methodologies described herein, wholly or in part.

[0161] The term "computer-readable medium" also encompasses cloud-based storage systems. The term "computer-readable medium" includes, but is not limited to, one or more types of (tangible) non-transient data storage devices (e.g., data volumes) in exemplary forms of solid-state memory chips, optical discs, magnetic discs, or any suitable combination thereof. In some exemplary embodiments, instructions for execution may be transmitted by a carrier medium. Examples of such carrier media include a transient medium (e.g., a propagation signal transmitting instructions).

[0162] It will be obvious to those skilled in the art that various modifications and variations may 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

Claim 1 A spatial light modulator configured to display a hologram of an image and output spatially modulated light encoded in said hologram; a fiber pupil expander comprising a plurality of optical fibers, wherein each optical fiber comprises an input end and an output end, said fiber pupil expander comprising a spatially modulated light output by said spatial light modulator coupled into said input end of each optical fiber and output from said output end to a viewing area, said pupil expander comprising a plurality of optical fibers, said pupil expander comprising a plurality of optical fibers each configured to propagate said spatially modulated light received at an input end to expand an exit pupil of a holographic system to a first dimension and a second dimension, said first dimension and said second dimension corresponding to the dimensions of said viewing area, and said second dimension orthogonal to said first dimension. Claim 2 A holographic system according to claim 1, wherein each of the plurality of optical fibers is configured to form a replica of the spatially modulated light received at an input end to expand the output pupil to the first dimension. Claim 3 A holographic system according to claim 1 or 2, wherein the output ends of the plurality of optical fibers are arranged in a one-dimensional array of the first dimension. Claim 4 A holographic system according to claim 1 or 2, further comprising a fiber splitter configured to simultaneously couple the spatially modulated light output by the spatial light modulator into the input ends of each of the plurality of optical fibers. Claim 5 A holographic system according to claim 1 or 2, further comprising a multiplexer configured to couple the spatially modulated light output by the spatial light modulator to each of the plurality of optical fibers one at a time in a sequence defined thereto, optionally wherein the duration of the sequence is shorter than the human eye's exposure time (integration time). Claim 6 A holographic system according to claim 1 or 2, wherein the spatial light modulator is configured to output spatially modulated light encoded in the hologram at a plurality of angles such that the light output at each angle forms a respective light channel coupled into each of the plurality of optical fibers or one or more of the input ends of each of the plurality of optical fibers, and optionally, each angle light channel comprises a portion of image information divided by angle. Claim 7 A holographic system according to claim 6, wherein each optical channel is coupled into the input ends of at least two optical fibers, each of the at least two optical fibers replicates each optical channel to extend the output pupil to the first dimension, and optionally, each of the at least two optical fibers has adjacent output ends of the first dimension. Claim 8 In claim 6, the holographic system is configured to dynamically control the allocation of the optical channels to the plurality of optical fibers in response to feedback from the eye tracking system. Claim 9 delete Claim 10 A holographic system according to claim 1, wherein the output ends of the plurality of optical fibers are arranged in a two-dimensional array of the first dimension and the second dimension. Claim 11 A holographic system according to claim 1 or 2, further comprising a collimating lens configured to collimate light output from the output ends of the optical fibers to relay to the viewing area. Claim 12 A holographic system according to claim 1 or 2, further comprising a light source configured to irradiate the spatial light modulator to spatially modulate the light according to the hologram. Claim 13 A holographic system according to claim 1 or 2, wherein the spatial light modulator comprises an LCOS (liquid crystal on silicon) spatial light modulator encoded with the hologram. Claim 14 A holographic system according to claim 1 or 2, further comprising a magnifying optical system configured to increase the range of diffraction angles available for the viewing area beyond the diffraction angle of the spatial light modulator. Claim 15 A holographic system according to claim 1 or 2, wherein the holographic system is arranged in a direct view configuration and the viewing area is an area for viewing the image by a human eye. Claim 16 A holographic system according to claim 1 or 2, wherein the viewing area is spatially separated from the spatial light modulator by a propagation distance at least 10 times greater than the width of the aperture of the spatial light modulator, and optionally the projection distance is within the range of 30 cm to 150 cm. Claim 17 A head-up display comprising a holographic system as described in claim 1 or 2, wherein the viewing area is optionally an eye-motion box. Claim 18 A method for expanding an output pupil of a holographic system, comprising: displaying a hologram of an image by means of a spatial light modulator; outputting spatially modulated light encoded in the hologram by means of the spatial light modulator; coupling the spatially modulated light output by the spatial light modulator into the input end of each of the plurality of optical fibers by means of an optical fiber pupil expander comprising a plurality of optical fibers; and propagating the spatially modulated light received at the input end of the optical fiber for output to the output end of the optical fiber by means of each of the plurality of optical fibers of the optical fiber pupil expander in order to expand the output pupil of the holographic system to a first dimension and a second dimension, wherein the first dimension and the second dimension correspond to the dimensions of a viewing area and the second dimension is orthogonal to the first dimension. Claim 19 A holographic system comprising: a spatial light modulator configured to display a hologram of an image and output spatially modulated light encoded in said hologram; a plurality of optical fibers each having an input end and an output end, wherein the plurality of optical fibers are configured such that spatially modulated light output by said spatial light modulator is coupled into the input end of each optical fiber and output from the output end to a viewing area, wherein each of said plurality of optical fibers is configured to form a replica of said spatially modulated light received at the input end of said optical fiber so as to expand the output pupil of said plurality of optical fibers to a first dimension and a second dimension, wherein said first dimension and second dimension correspond to the dimensions of said viewing area and said second dimension is orthogonal to said first dimension. Claim 20 A spatial light modulator configured to display a hologram of an image and output spatially modulated light encoded in the hologram, which includes a plurality of light channels; a plurality of optical fibers each having an input end and an output end, wherein the plurality of optical fibers are configured such that spatially modulated light, which includes one or more of the light channels output by the spatial light modulator, is coupled into the input end of each of the respective optical fibers and output from the output end to a viewing area, and wherein each of the plurality of optical fibers is configured to propagate the respective light channel received at the input end of the optical fiber so that the plurality of optical fibers expand the output pupil to a first dimension and a second dimension, wherein the first dimension and the second dimension correspond to the dimensions of the viewing area and the second dimension is orthogonal to the first dimension.

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