Polarization-based dual imaging optics

Abstract

Aspects of this disclosure provide an optical system. The optical system includes a polarization controller that controls the polarization state of light beams such that each light beam passing through the polarization controller has one of a first polarization state and a second polarization state. The optical system includes a beam splitter, a reflective polarizer, and one or more lenses between the beam splitter and the reflective polarizer. If the polarization state of a first light beam among the light beams passing through the polarization controller is the first polarization state, the first light beam passes through the one or more lenses only once. If the polarization state of a second light beam among the light beams passing through the polarization controller is the second polarization state, the second light beam passes through the one or more lenses multiple times.

Description

Technical Field

[0001] Incorporation by Reference This application claims the benefit of priority to U.S. Patent Application No. 18 / 142,440, filed May 2, 2023, "POLARIZATION BASED DUAL IMAGING OPTICAL SYSTEM", which is hereby incorporated by reference in its entirety.

[0002] This disclosure relates to near-eye display technology.

Background Art

[0003] The description of the background art provided herein is for the purpose of generally presenting the context of the present disclosure. The inventors' research, insofar as that research is described in this background art section, and aspects of the description that may not otherwise be recognized as prior art at the time of filing, are not recognized as prior art to the present disclosure, either explicitly or implicitly.

[0004] Near-eye display (NED) devices have been developed to provide improved user experiences in fields such as augmented reality (AR) and virtual reality (VR). NED devices can include various wearable devices such as head-mounted display (HMD) devices, smart glasses, and the like. In one example, an HMD device includes a relatively small display device and optics capable of creating a virtual image within the field of view of one or both eyes. To the eye, the virtual image appears at a distance and appears much larger than the relatively small display device.

Summary of the Invention

Means for Solving the Problems

[0005] Aspects of this disclosure provide an optical system. The optical system includes a polarization controller configured to control the polarization state of light beams incident on the polarization controller such that each light beam passing through the polarization controller has a polarization state of one of a first polarization state and a second polarization state. The optical system includes a beam splitter configured to partially transmit and partially reflect light beams incident on the beam splitter. The optical system includes a reflective polarizer configured to transmit light beams having a third polarization state and reflect light beams having a fourth polarization state orthogonal to the third polarization state, and one or more lenses between the beam splitter and the reflective polarizer. If the polarization state of a first light beam among the light beams passing through the polarization controller is the first polarization state, the first light beam passes through one or more lenses only once. If the polarization state of a second light beam among the light beams passing through the polarization controller is the second polarization state, the second light beam passes through one or more lenses multiple times.

[0006] In one embodiment, the polarization state of a first light beam passing through a polarization controller is a first polarization state, the first light beam passes through one or more lenses only once, and the first focal length of one or more lenses for the first light beam in the first polarization state is different from the second focal length of one or more lenses for the second light beam in the second polarization state.

[0007] In one embodiment, the polarization state of a second light beam passing through a polarization controller is a second polarization state, and the second light beam passes through one or more lenses multiple times.

[0008] In one embodiment, an optical cavity containing one or more lenses is formed between a beam splitter and a reflective polarizer, and the second light beam passes through the optical cavity three times before reaching the viewpoint.

[0009] In one embodiment, the optical system includes a quarter-wave plate (QWP) positioned between a beam splitter and a reflective polarizer.

[0010] In one example, the optical system further includes a first lens, and one or more lenses include a second lens, the second lens being positioned between the first lens and the display device, and the first lens being positioned between the second lens and the viewpoint. The first and second lenses may be separated by a gap.

[0011] One of the first lens and the second lens includes a Fresnel structure.

[0012] In one example, the beam splitter is positioned between the second lens and the display device, the reflective polarizer is positioned between the first lens and the second lens, and the QWP is positioned between the beam splitter and the reflective polarizer.

[0013] In one example, a first light beam passes through the polarization controller at a first time point, and the optical system has a first focal length at that time point. A second light beam passes through the polarization controller at a second time point, different from the first time point, and the optical system has a second focal length at that second time point, different from the first focal length.

[0014] In one embodiment, the optical system forms a first virtual image of a first object located at a certain distance from the optical system at a first time point, the first virtual image is perceived at a first distance from the viewpoint, and the first magnification is the ratio of the size of the first virtual image to the size of the first object; the optical system forms a second virtual image of a second object located at the aforementioned distance from the optical system at a second time point, the second virtual image is perceived at a second distance from the viewpoint, the second distance is different from the first distance, the second magnification is the ratio of the size of the second virtual image to the size of the second object, and the second magnification is different from the first magnification.

[0015] In one example, the first distance is a multiple of the second distance.

[0016] In one example, a first light beam passes through a first region of the polarization controller, and the optical system has a first focal length for the first light beam passing through the first region of the polarization controller; a second light beam passes through a second region of the polarization controller, which is different from the first region, and the optical system has a second focal length, different from the first focal length, for the second light beam passing through the second region of the polarization controller.

[0017] In one example, the optical system forms a first virtual image of a first object located at a certain distance from the optical system, a first light beam from the first object passes through a first region of the polarization controller, and the first virtual image is perceived at a first distance from the viewpoint. The optical system then forms a second virtual image of a second object located at the same distance from the optical system, a second light beam from the second object passes through a second region of the polarization controller, and the second virtual image is perceived at a second distance from the viewpoint, the second distance being different from the first distance.

[0018] In one embodiment, the first magnification is the ratio of the size of the first virtual image to the size of the first object, and the second magnification is the ratio of the size of the second virtual image to the size of the second object, and the second magnification is different from the first magnification.

[0019] An image can be formed based on the first virtual image and the second virtual image.

[0020] Further features, properties, and various advantages of the disclosed subject matter will become clearer from the following detailed description and accompanying drawings. [Brief explanation of the drawing]

[0021] [Figure 1] Figure 1 is a side view showing a display system according to several embodiments of the present disclosure. [Figure 2] Figure 2 is a side view showing a display system according to several embodiments of the present disclosure. [Figure 3] Figure 3 shows the modulation transfer function (MTF) of an optical system according to one embodiment of the present disclosure. [Figure 4] FIG. 4 is a diagram showing exemplary virtual image points corresponding to pixels on a display device according to an embodiment of the present disclosure. [Figure 5] FIG. 5 is a diagram showing the MTF of an optical system according to an embodiment of the present disclosure. [Figure 6] FIG. 6 is a diagram showing exemplary virtual image points corresponding to pixels on a display device according to an embodiment of the present disclosure. [Figure 7] A is a diagram showing an exemplary liquid crystal spatial light modulator according to an embodiment of the present disclosure, and B is a diagram showing an exemplary liquid crystal spatial light modulator according to an embodiment of the present disclosure. [Figure 8] FIG. 8 is a diagram showing a lens and a corresponding Fresnel lens according to an embodiment of the present disclosure. [Figure 9] FIG. 9 is a schematic diagram of a computer system according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0022] The display system can include an optical system that directs a light beam from a display device or a real object toward a viewpoint. A light receiver can be disposed at the viewpoint to receive the light beam. In one example, the optical system and the display device can be configured to be disposed within a distance threshold (e.g., 35 mm) of the user's eye, and the display system can be referred to as a near-eye display (NED) system. For example, the display system is a head-mounted display (HMD) system worn by a user.

[0023] The optical system can include one or more lenses. The refractive power of the optical system can indicate the degree to which the optical system converges or diverges light, and can be indicated by the focal length f of the optical system. In one example, the refractive power of the optical system is equal to the reciprocal of the focal length f of the optical system. A higher refractive power indicates (i) a stronger focusing ability for a converging optical system, or (ii) a stronger diverging ability for a diverging optical system. In one example, the refractive power and the focal length of the optical system vary depending on the number of times the light beam passes through a lens within one or more lenses.

[0024] According to one embodiment of the present disclosure, when a first light beam incident on a lens in one or more lenses has a first polarization state, the first light beam passes through the lens in one or more lenses N1 times. When a second light beam incident on a lens in one or more lenses has a second polarization state, the second light beam passes through the lens in one or more lenses N2 times. N1 and N2 are different positive integers. In one example, N1 is 1 (for example, shown in Figure 1) and N2 is 3 (for example, shown in Figure 2). In one example, the first focal length of the optical system for the first light beam in the first polarization state is different from the second focal length of the optical system for the second light beam in the second polarization state. The optical system can be configured to form an image using the first light beam in the first polarization state in a first imaging mode, and to form an image using the second light beam in the second polarization state in a second imaging mode. The optical system may be referred to as a dual imaging optical system.

[0025] In one example, 3D glasses function by forming two different images for each eye, allowing the observer's left and right eyes to see left and right viewpoint images. These different viewpoint images can be reconstructed into a 3D image by the brain. For example, the screen image may include overlapping images projected from two separate projectors, one projector projecting an image with a polarization base (or polarization state) (e.g., vertical linear polarization or left-hand circular polarization), and the other projector projecting an image with a different polarization base (e.g., horizontal linear polarization or right-hand circular polarization). 3D glasses may include a pair of glass windows with different polarizing filters to allow light with only one suitable polarization base to pass through and reach each eye.

[0026] A dual imaging optical system (e.g., the display system (100) shown in Figures 1-2) is described herein by multiplexing sources having different polarization bases. The display system, such as an optical imaging system for NEDs, may include any suitable optical elements such as Fresnel / diffractive lens elements, lenses (e.g., polarization base-dependent lenses), a polarization controller (e.g., a switchable polarization rotor), and / or a display device. The polarization controller (e.g., a switchable polarization rotor) can control the polarization base used in the display system so that the polarization base can be one of two polarization states. A first image associated with a first state (or first polarization state) of the polarization base can be imaged through an optical system (e.g., including a lens system) at a first focal length or first magnification, and a second image associated with a second state of the polarization base can be imaged through an optical system at a second focal length or second magnification. The first and second images can be multiplexed in the time domain or the space domain. In one embodiment, multiplexing (for example, in the time domain or spatial domain) can enable an observer to view a high-resolution image at a lower magnification with a low-resolution image at a higher magnification superimposed on it, thereby rendering a high-resolution foveal view. In another embodiment, multiplexing can enable an observer to view a multi-focus scene or a 3D scene. In yet another embodiment, multiplexing can enable an observer and a content provider to switch between focus scenes.

[0027] In one embodiment, a special glass (including, for example, a display system (100)) is described in this disclosure. The focal length of the special glass may depend on the polarization base of the light beam used to form the image. When an image associated with one polarization base is formed by the special glass, the observer can see the image at one imaging plane (sometimes referred to as the focal plane). When an image associated with another polarization base is formed by the glass, the observer can see the image at a different imaging plane. In one example, the observer can perceive an object about 0.25 m away from the observer by looking through the special glass with one polarization base, and can perceive the same object about 2 m away from the observer by looking through the special glass with the other polarization base. The special glass can be applied to virtual reality (VR) NED. In a VR environment, the user can interact with objects at arm's length (e.g., 0.25 m) or observe objects at a comfortable viewing distance (e.g., 2 m). By switching between two polarization bases, the special glass can help the user interact with objects in a more natural field of view.

[0028] In one embodiment, the magnification of a special glass may depend on the polarization base associated with the image. When an image associated with one polarization base is formed by the glass, the observer can view this image at a first magnification, and when an image associated with another polarization base is formed by the glass, the observer can view this image at a second magnification. In one example, the observer can see through the special glass and perceive an object in detail (or high resolution) over a first field of view (FOV) area (e.g., 10°FOV) with a certain polarization base, and the observer can see through the special glass and perceive the same object over a second FOV area (e.g., 100°FOV) associated with another polarization base. The FOV can indicate the range of the observable world that can be seen or detected by a photodetector (also called a light sensor), such as the eye. In one example, the FOV is indicated by the solid angle over which the photodetector can detect or receive light.

[0029] The human eye can detect objects with resolutions exceeding 30 cycles / degree (CPD) or 60 pixels / degree (PPD) for narrow FOVs (e.g., a first FOV of less than 10°), so for large FOVs (e.g., a second FOV of 100°), it is not necessary to generate high-resolution images (e.g., 60 PPD images). Therefore, a high-resolution image covering a first FOV (e.g., a 10° FOV) can be generated under one polarization basis, and a low-resolution image covering a second FOV (e.g., a 100° FOV) can be generated under another polarization basis using the same display system (e.g., special glass). Based on the high-resolution and low-resolution images, a foveal image can be generated. In one example, the overlap of the high-resolution and low-resolution images can generate a foveal image. By switching between the two polarization basis, the special glass can generate a foveal image using temporal or spatial multiplexing.

[0030] NED optics can utilize a variety of optical elements. Refractive optical elements can provide refractive power using the refraction and geometric structure of the lens material. Fresnel lens surfaces can provide a compact form of Fresnel lens with the same or identical focal length as a non-Fresnel lens by replacing the curved surface of a refractive optical element (e.g., a lens) with a series of concentric grooves. In one example, the extrusion profile of a Fresnel lens is similar to the surface profile of a refractive optical element. Diffractive optical elements (DOEs) may include phase lenses with microstructures for diffracting light into a pattern to provide lens refractive power. Reflective / Catoptric optics can use curved mirrors to reflect light and form an image. Refractive and diffractive optical elements may be wavelength sensitive, for example, due to material dispersion. Reflective optical elements may have weak wavelength dependence. In one example, reflective optical elements are less wavelength-dependent than refractive and diffractive optical elements. Reflective and refractive optics can improve imaging capabilities by using both reflective and refractive optical elements.

[0031] An optical system is described that includes a reflecting / refracting optical subsystem and optionally includes other optical subsystems, such as the optical system (110) in Figures 1 and 2. The reflecting / refracting optical subsystem may depend on the polarization basis of the incident light beam into the optical system. When the incident light beam has one polarization basis, the incident light beam is not folded by the reflecting optical cavity, and the optical system can provide refractive power. When the incident light beam has another polarization basis, the incident light beam is folded by the reflecting optical cavity, and a different refractive power can be provided.

[0032] Figures 1 and 2 show side views of display systems (e.g., near-eye display systems) (100) according to several embodiments of the present disclosure. The display system (100) includes an optical system (110), a shift block (170), and a controller (180). In one example, the display system (100) includes a display device (120) and a polarization controller (e.g., a polarization rotor or a switchable polarization rotor) (155).

[0033] The optical system (110) may include any suitable optical elements such as diffracting elements (e.g., gratings), refractive elements (e.g., lenses), guide elements (e.g., plane waveguides and / or fibers), and polarizing elements (e.g., polarizers, half-wave plates, quarter-wave plates, polarizing rotors, Pancharatnam-Berry (PB) phase lenses, etc.). The optical system (110) may also include a lens system (130), a beam splitter (141), and a reflective polarizer (139). In one example, the optical system (110) may include a waveplate such as a quarter-wave plate (QWP) (142). The display device (120) may include a pixel array configured to emit a light beam to display an image. The polarization controller (155) can be configured to control the polarization state of light beams incident on the polarization controller (155) such that the polarization state of each light beam passing through the polarization controller is one of a first polarization state (e.g., a first circular polarization state or first CP) and a second polarization state (e.g., a second circular polarization state or second CP). In one example, the polarization controller (155) is integrated with a display device (120) and is a component of the display device (120). In one example, such as those shown in Figures 1 and 2, the polarization controller (155) is located outside the display device (120), and the optical system (110) may include the polarization controller (155).

[0034] The optical system (110) can be positioned between the display device (120) and the viewpoint. The optical system (110) can direct an emitted light beam from the display device (120) or a light beam from a real object towards a viewpoint, such as an area (151) of the viewpoint. In one example, the area (151) is located in the XY plane and is referred to as the exit pupil of the optical system (110). The XY plane includes the X axis and the Y axis perpendicular to the X axis. A photodetector or light receiver, such as the user's eye (60), may be located in the area (151).

[0035] The lens system (130) may include one or more lenses, such as a first lens (131) and a second lens (132). The first lens (131) may include an optically transparent member (145) having two opposing surfaces (135) to (136). The second lens (132) may include an optically transparent member (146) having two opposing surfaces (137) to (138). The second lens (132) may be disposed between the first lens (131) and a polarizing controller (155). In one example, the first lens (131) may be referred to as an eye lens according to its proximity to an area (151) (e.g., an eye (60)), and the second lens (132) may be referred to as a display lens according to its proximity to a display device (120).

[0036] The surfaces of one or more lenses in the lens system (130), such as surfaces (135) to (138), can have any suitable shape or surface curvature, such as a planar shape parallel to the XY plane, a spherical shape with any suitable radius of curvature, an aspherical shape, or other shapes. One or more of surfaces (135) to (138) may be smooth. One or more of surfaces (135) to (138) may be grooved and include microstructures such as a Fresnel structure. In one example, surface (136) is grooved to include a Fresnel structure. The shapes of surfaces (135) to (138) can be determined based on design parameters such as focal length, aberration requirements, lens thickness, and lens flatness.

[0037] In one example, the first lens (131) is a converging lens with a positive focal length, and the second lens (132) is a diverging lens with a negative focal length. The optical axis (160) of the lens system (130) can be parallel to the Z axis, which is perpendicular to the XY plane. The first lens (131) and the second lens (132) can be circularly symmetric about the optical axis (160). The first lens (131) and the second lens (132) can be separated by a gap (133). In one example, the gap (133) is greater than 0. In another example, a portion of the first lens (131) is in contact with a portion of the second lens (132), for example, the minimum distance between the first lens (131) and the second lens (132) is zero.

[0038] Optically transparent components (145) to (146) may include any suitable material, including but not limited to glass (e.g., borosilicate glass, high-density flint glass), polymers, poly(methyl methacrylate) (PMMA), polyimide, acrylic, styrene, cyclic olefin polymers, cyclic olefin copolymers, polycarbonate, and other plastic materials. Glass lenses can be manufactured by grinding and polishing, glass molding, etc. Polymer or plastic lenses can be manufactured by diamond turning, polishing, injection molding, casting, etc.

[0039] The beam splitter (141) and reflective polarizer (139) can be positioned between the area (151) and the polarization controller (155). The quarter-wave plate (142) can be positioned between the beam splitter (141) and the reflective polarizer (139). An anti-reflective (AR) coating can be applied to any suitable surface of the optical system (110) to reduce undesirable reflections of the light beam, for example, to reduce or eliminate ghosting due to multiple reflections at various interfaces. The beam splitter (141), reflective polarizer (139), and / or quarter-wave plate (142) can be thin-film optical components, for example, comprising one or more layers of an optical film. The thickness (e.g., maximum or average thickness) of the thin-film optical components (e.g., beam splitter (141), reflective polarizer (139), or quarter-wave plate (142)) can be less than a thickness threshold such as 500 microns, 200 microns, or 100 microns. A thin-film optical component (e.g., a BS (141), a reflective polarizer (139), or a quarter-wave plate (142)) can be disposed on the surface of the first lens (131) or the second lens (132). The shape of the thin-film optical component (e.g., a BS (141), a reflective polarizer (139), or a quarter-wave plate (142)) may substantially or completely match the shape of the surface of the first lens (131) or the second lens (132).

[0040] Referring to Figures 1 and 2, the beam splitter (141) is positioned between the second lens (132) and the display device (120), the reflective polarizer (139) is positioned between the first lens (131) and the second lens (132), and the QWP (142) is positioned between the beam splitter (141) and the reflective polarizer (139).

[0041] A reflective polarizer (139) can be configured to allow a light beam having a first linearly polarized state (first LP) to pass through and to reflect a light beam having a second linearly polarized state (second LP). The reflective polarizer (139) may also be called a reflective polarizer mirror. The second linearly polarized state is orthogonal to the first linearly polarized state. In one example, the reflective polarizer (139) can be formed on the surface (138) of a lens system (130). The shape of the reflective polarizer (139) may substantially or completely match the shape of the surface (138) of the second lens (132). In the example shown in Figures 1 and 2, the surface (138) of the second lens (132) is planar, so the shape of the reflective polarizer (139) is planar.

[0042] The reflective polarizer mirror (139) in a pancake lens (e.g., lens system (130)) can be fabricated using polymers, birefringent, multilayer reflective polarizers to achieve high quality, such as high reflectivity in the blocking direction (in the blocking state) (e.g., high average reflectivity), high transmittance in the passing direction (in the passing state) (e.g., high average transmittance), low haze, a smooth surface finish (or relatively low surface roughness), and low scattering with low orange peel or undulation.

[0043] The beam splitter (141) can be configured to partially transmit and partially reflect a light beam incident on it. The beam splitter (141) may have an average light transmittance T and an average light reflectance R. In one example, the sum of T and R is 1 (i.e., 100%) over a wavelength range (e.g., 380 to 780 nanometers (nm)). The average light transmittance T and average light reflectance R of the beam splitter (141) may be referred to as T / R. T or R may be within a range (e.g., 40% to 60%). In one example, the beam splitter (141) may have a T / R of 40 / 60, 50 / 50, or 60 / 40. For example, if T and R are 50%, the beam splitter (141) transmits 50% of the light beam incident on it and reflects 50%. The beam splitter (141) partially transmits and partially reflects the light beam from the display device (120). In one example, the BS (141) is disposed on the surface (137) of a second lens (132). The surface (137) of the second lens (132) can have any suitable shape, such as aspherical or spherical. The shape of the BS (141) may substantially or completely match the shape of the surface (137) of the second lens (132) (e.g., spherical or aspherical shape).

[0044] The polarization state of a light beam can be changed when the light beam passes through a specific optical element. In one embodiment, the polarization state of a light beam can be changed by a waveplate or phase difference plate as the light beam travels through the waveplate. A quarter wave plate (142) can change the polarization state of a light beam traveling through the quarter wave plate (142) by, for example, 90° or π / 2. In one example, the quarter wave plate (142) converts linearly polarized light to circularly polarized light, or circularly polarized light to linearly polarized light. The quarter wave plate (142) can be formed on the surface (138) of a lens system (130). In one example, the quarter wave plate (142) is formed on the surface (138), and a reflective polarizer (139) is formed on the quarter wave plate (142).

[0045] A light beam can be randomly polarized if it contains a rapidly fluctuating set of different polarization states. A light beam can be polarized in various ways, such as linearly polarized (e.g., in a linearly polarized state), circularly polarized (e.g., in a circularly polarized state), or elliptically polarized (e.g., in an elliptically polarized state). For linearly polarized light, the electric field vector of the light beam follows a specific line. For circularly polarized light, the electric field vector of the light beam rotates, for example, clockwise or counterclockwise, relative to the observer from which the light beam is propagating.

[0046] Degree of polarization (DOP) is a quantity that indicates a portion of a polarized electromagnetic wave (e.g., a light beam). A fully polarized wave can have a DOP of 100%, while an unpolarized wave can have a DOP of 0%. A partially polarized wave can be represented by the superposition of its polarized and unpolarized components, and therefore can have a DOP between 0% and 100%. DOP can be calculated as part of the total power carried by the polarized component of the wave (e.g., a light beam).

[0047] A light beam (for example, a light beam generated from each pixel in a display device (120)) can have any suitable polarization state or DOP. In one example, the light beam is circularly polarized and has a DOP of 100%. In another example, the light beam is mainly circularly polarized and has a relatively large DOP exceeding a threshold (e.g., 80% or more), such as a superposition of (i) a circularly polarized component and (ii) an unpolarized component and / or another polarization component. A circularly polarized light beam having a DOP of 100% or a mainly circularly polarized light beam having a relatively large DOP may be referred to as a circularly polarized light beam in this disclosure. In another example, the light beam is linearly polarized and has a DOP of 100%, or is mainly linearly polarized and has a relatively large DOP exceeding a threshold. A linearly polarized light beam having a DOP of 100% or a mainly linearly polarized light beam having a relatively large DOP may be referred to as a linearly polarized light beam in this disclosure.

[0048] The display device (120) may include a pixel array. In some examples, the pixel array includes a plurality of pixels arranged to form a two-dimensional surface. The two-dimensional surface of the display device (120) may be substantially flat or planar, curved, or include a combination of flat and planar panels. The display device (120) may be a display panel. The display device (120) may include any suitable type of display panel, such as a liquid crystal display (LCD) panel or an organic light-emitting diode (OLED) panel. The resolution of the display device (120) may be defined according to the pixels in either the two-dimensional or one of the two-dimensional aspects of the two-dimensional surface.

[0049] Each pixel in the pixel array of the display device (120) can generate a light beam. The light beam from each pixel in the display device (120) can contain a beam of light in any appropriate direction. Referring to Figure 1, for example, pixel A on the display device (120) emits a light beam (one of the first light beams) containing a beam of light in an appropriate direction. A subset of rays (124) in the light beam can be directed towards area (151) by the optical system (110). The angular span of the subset of light beam (124) can be determined based on the allowable angle ω of the optical system (110). Three rays (121) to (123) of the subset of light beam (124) are shown in Figure 1. The three rays (121) to (123) can include boundary rays (121) and (123) as well as a central ray (122).

[0050] The light beam generated by the pixels in the display device (120) may have any suitable polarization state, such as circularly polarized or linearly polarized. A polarization controller (155) may be employed to manipulate the polarization state of the light beam generated by the pixels in the display device (120). In one embodiment, the polarization controller (155) is integrated with the display device (120) and is a component of the display device (120). In one embodiment, the polarization controller (155) is located next to the display device (120).

[0051] An optical cavity can be formed between the beam splitter (141) and the reflective polarizer (139). In the example shown in Figures 1 and 2, the optical cavity may include a second lens (132) and a QWP (142). According to one embodiment of the present disclosure, the optical system (110) can direct a light beam from, for example, a display device (120) to a viewpoint such as an area (151) using a plurality of imaging modes based on the respective polarization states of the light beam incident on the optical cavity. In one embodiment, the plurality of imaging modes include two imaging modes, such as a first imaging mode shown in Figure 1 and a second imaging mode shown in Figure 2.

[0052] Various configurations of optical cavities (e.g., reflective optical cavities) are possible. In one example, the optical cavity includes a single lens. In another example, a bonded double design may include two lenses bonded together. A gap design may include two or more lenses. A gap design can introduce more surfaces within the optical cavity formed by two mirrors. Additional surfaces inside the optical cavity can act as additional mirrors to form ghost images whose intensity can be reduced with an AR coating. A gap design can allow for more optical surfaces for a more flexible optical design, with a trade-off of more ghost images. Referring to Figures 1 and 2, the optical cavity includes a second lens (132), and the description can be appropriately adapted if the optical cavity includes one or more lenses such as the first lens (131).

[0053] Figure 1 shows an example of a first imaging mode. In one embodiment, one of the first light beams from the display device (120) (e.g., the first light beam including rays (121) to (123) from pixel A) has a first polarization state after passing through a polarization controller (155), and the first light beam in the first polarization state is incident on a beam splitter (141). After passing through the beam splitter (141), the first light beam in the first polarization state is incident on an optical cavity. The first light beam can pass through the optical cavity (including, for example, a second lens (132) and QWP (142)) only once, as indicated by the widened path (125). Next, the first light beam passes once through the reflective polarizer (139) and the first lens (131) and enters area (151) as indicated by the rays (121') to (123') corresponding to rays (121) to (123), respectively.

[0054] Figure 2 shows an example of a second imaging mode. In one embodiment, one of the second light beams from the display device (120) (e.g., a second light beam including rays (221)-(223) from pixel B) has a second polarization state after passing through the polarization controller (155), and the second light beam in the second polarization state is incident on the beam splitter (141). Rays (221)-(223) may include boundary rays (221) and (223) and central ray (222) within a subset (224) of the second light beam. The description of the first light beam including rays (121)-(123) from pixel A in Figure 1 can be appropriately adapted to describe the second light beam including rays (221)-(223) from pixel B. In one example, the first light beam from pixel A and the second light beam from pixel B have different polarization states from the polarization controller (155). After passing through the beam splitter (141), the second light beam, in a second polarization state, is incident on the optical cavity. The second light beam can pass through the optical cavity (including, for example, the second lens (132) and QWP (142)) multiple times (e.g., three times) as indicated by the folded path (225). Subsequently, the first light beam passes through the first lens (131) once and is incident on area (151) as indicated by rays (221') to (223') corresponding to rays (221) to (223), respectively.

[0055] The second polarization state may differ from the first polarization state. In one example, the second polarization state is orthogonal to the first polarization state.

[0056] Comparing the first imaging mode with the second imaging mode, the first optical path (or first optical route) of the first light beam from the display device (120) to area (151) in Figure 1 may differ from the second optical path of the second light beam from the display device (120) to area (151) in Figure 2. The second optical path can pass through optical cavities (including, for example, the second lens (132)) more times than the first optical path. As the second optical path passes through the lens (e.g., the second lens (132)) more times and thus undergoes further refraction at the surface of the lens, the first focal length of the optical system (110) associated with the first polarization state of the first light beam from the polarization controller (155) may differ from the second focal length of the optical system (110) associated with the second polarization state of the second light beam from the polarization controller (155).

[0057] In the example shown in Figure 1, the optical system (110) can convert rays (121) to (123) in the first light beam into rays (121') to (123'), respectively. The extensions of rays (121') to (123') may intersect at point A' on the imaging plane (199). The optical system (110) can form an image (e.g., point A') from an object (e.g., pixel A on a display device (120)). Image A' is the intersection of the extensions of rays (121') to (123'), and since rays (121') to (123') do not intersect at point A', for example, image A' can be a virtual image formed by the optical system (110). In one example, the lens (63) in the eye (60) forms an image Ai on the retina (65) of the eye (60) based on light rays (121')~(123'), and thus the eye (60) perceives an object (e.g., pixel A) on the display device (120) as a point A' located on the image plane (199).

[0058] Similarly, a light beam from another pixel (e.g., pixel C) on the display device (120) has a first polarization state and can pass through the optical cavity only once. Pixel C can be imaged by the optical system (110) as an image (e.g., a point) C' on the imaging plane (199). In the example shown in Figure 1, the optical system (110) can form an image (e.g., a virtual image) C'A' on the imaging plane (199) from an object CA on the display device (120). The lens (63) in the eye (60) can form an image CiAi on the retina (65) based on the virtual image C'A', and thus the eye (60) perceives the object OA displayed on the display device (120) as a virtual image C'A' located on the imaging plane (199).

[0059] The virtual image C'A' appears larger than the object CA on the display device (120) when viewed from an area (151) located at the viewpoint at a distance (e.g., a first image distance) D2. The distance D2 is greater than, and in some cases much greater than, the distance D1 between area (151) and the display device (120). The magnification of the optical system can be expressed by the ratio of the image size to the object size. Referring to Figure 1, the first magnification of the optical system (110) associated with a light beam having a first polarization state can be expressed as the ratio of the image size (e.g., height) H2 of the virtual image C'A' to the object size (e.g., height) H1 of the object CA.

[0060] The polarization state of a light beam can change after passing through a specific optical element (e.g., (155) or (142)) that can alter the polarization state of the light beam. In the example shown in Figure 1, the first polarization state of the first light beam used in the first imaging mode may refer to the polarization state of the first light beam before it comes from the polarization controller (155) and is incident on the reflective polarizer (139), and this may also be the polarization state of the first light beam as it is incident on the optical cavity or beam splitter (141). In the example shown in Figure 2, the second polarization state of the second light beam used in the second imaging mode may refer to the polarization state of the second light beam before it comes from the polarization controller (155) and is first incident on the reflective polarizer (139), and this may also be the polarization state of the second light beam as it is first incident on the beam splitter (141) or the optical cavity.

[0061] The above description can be adapted to a second polarization state. Referring to Figure 2, the optical system (110) can convert rays (221) to (223) in the second light beam into rays (221') to (223'), respectively. The extensions of rays (221') to (223') may intersect at point B' on the imaging plane (299). The optical system (110) can form an image (e.g., point B') from an object (e.g., pixel B on a display device (120)). Since image B' is the intersection of the extensions of rays (221') to (223'), image B' can be a virtual image formed by the optical system (110). In one example, the lens (63) forms an image Bi on the retina (65) based on light rays (221')~(223'), and therefore the eye (60) perceives an object (e.g., pixel B) on the display device (120) as an image B' located on the imaging plane (299).

[0062] Similarly, another of the second light beams from another pixel (e.g., pixel D) on the display device (120) has a second polarization state and can pass through the optical cavity multiple times (e.g., three times). Pixel D can be imaged by the optical system (110) as an image (e.g., a point) D' on the imaging plane (299). In the example shown in Figure 2, the optical system (110) can form an image (e.g., a virtual image) D'B' on the imaging plane (299) from an object DB on the display device (120). The lens (63) can form an image DiBi on the retina (65) based on the virtual image D'B', and thus the eye (60) perceives the object DB displayed on the display device (120) as a virtual image D'B' located on the imaging plane (299).

[0063] The virtual image D'B' appears at a distance (e.g., a second image distance) D2' from the area (151) located at the viewpoint, and appears larger than the object DB on the display device (120). The distance D2' is greater than, and in some cases much greater than, the distance D1 between the area (151) and the display device (120). Referring to Figure 2, the second magnification of the optical system (110) associated with the light beam having a second polarization state can be expressed as the ratio of the image size (e.g., height) H2' of the virtual image D'B' to the object size (e.g., height) H1' of the object DB.

[0064] According to one embodiment of the present disclosure, the first magnification may differ from the second magnification. In one example, the second magnification is greater than the first magnification. According to one embodiment of the present disclosure, the first image distance D2 may differ from the second image distance D2'. In one example, the second image distance D2' (e.g., 2 meters (m)) is greater than the first image distance D2 (e.g., 0.25 m).

[0065] As explained with reference to Figures 1 and 2, the focal length of the optical system (e.g., (110)) may depend on the polarization state of the light beam, such as the first or second light beam incident on the beam splitter (141) or optical cavity. The magnification of the optical system (e.g., (110)) may depend on the polarization state of the light beam, such as the first or second light beam incident on the beam splitter (141) or optical cavity.

[0066] Examples of the first optical path of the first light beam (Figure 1) and the second optical path of the second light beam (Figure 2) will be described with reference to Figures 1 and 2, respectively. Referring to Figure 1, the first light beam from pixel A in the display device (120) can pass through the polarization controller (155), and the first light beam may have a first polarization state coming from the polarization controller (155). In one example, the first polarization state is the first CP. The first light beam may be partially transmitted by the beam splitter (141). The first light beam then passes once through an optical cavity. For example, the first light beam passes once through the second lens (132) and is incident on the QWP (142). The QWP (142) can manipulate the first polarization state of the first light beam (e.g., the first CP) to a certain polarization state, thereby allowing the reflective polarizer (139) to transmit the first light beam in that polarization state with relatively high transmittance. For example, QWP(142) manipulates the first CP to a first linearly polarized state (first LP). The first light beam, which is the first LP, can be incident on a reflective polarizer (139). In one example, the first linearly polarized state is parallel to the transmission direction of the reflective polarizer (139). Thus, the reflective polarizer (139) transmits the first light beam having the first LP so that the rays (121)~(123) are directed towards area (151) with a relatively high transmittance of a value (e.g., 90%) or more over the wavelength range (e.g., 380~780 nm). Thus, pixels from a display device (120) emitting the first light beam may have the first polarization state from the polarization controller (155) and can pass through the optical cavity only once. The pixels can be imaged on the imaging plane (199) in a first imaging mode. The image displayed by the display device (120) (for example, formed based on pixels) can be imaged onto the imaging plane (199) by the display system (100), and the eye (60) can perceive a virtual image on the imaging plane (199) that is larger than the image displayed by the display device (120) and farther from the eye (60).

[0067] The resolution of an optical system can indicate its ability to distinguish the details of an object. For example, resolution is expressed in units of lines per millimeter (lp / mm), where a line pair is a sequence of one black line and one white line. Image contrast or modulation is expressed as contrast (%) = (I max -I min ) / (I max +I min It can be defined as, in formula I max and I min These represent the maximum and minimum intensity of the image, respectively.

[0068] One parameter that indicates the performance of an optical system is its modulation transfer function (MTF). The MTF of an optical system can indicate its ability to transfer contrast from an object to an image of that object at a specific resolution. In one example, the MTF combines resolution and contrast into a single parameter. As the line spacing decreases (for example, as the resolution increases), it becomes increasingly difficult for the optical system to efficiently transfer the decrease in contrast. Therefore, the MTF decreases.

[0069] The sagittal line used to determine the MTF can refer to the line radiating from the center to the periphery of the effective image circle. The tangent (or meridian) line is perpendicular to the sagittal line. Because optical systems may not equally focus lines in both directions on the same plane, sagittal and tangential measurements of the same optical system may differ. The MTF may be a sagittal MTF if the sagittal line is used to determine the MTF, or a tangential MTF if the tangential line is used to determine the MTF.

[0070] Figure 3 shows the MTF of the optical system (110) in the first imaging mode shown in Figure 1. In one example, the eye (60) is positioned in area (151) and fixating straight ahead without rotation (e.g., field of view or eye rotation is 0°). Figure 3 shows the tangential MTF (301) and sagittal MTF (302) with respect to the field of view (e.g., Y field of view from 0° to 50°) at a resolution of 10 lp / mm (or 10 cycles / mm). Figure 3 shows that the FOV of the first imaging mode is 100°.

[0071] In one example, the distance D2 from the area (151) and the imaging plane (199) (e.g., the first virtual image distance) is 0.25 m. Figure 4 shows exemplary virtual image points (601') to (606') formed in a first imaging mode by an optical system (110) corresponding to object points or pixels (601) to (606) on a display device (120) according to one embodiment of the present disclosure. Light beams from pixels (601) to (606) may have a first polarization state when the light beam exits the polarization controller (155), and the light beam can be directed by the optical system (110) in the same manner as described above with reference to the first light beam from pixel A. Extensions of light rays incident on area (151) from pixels (601) to (606) may each form virtual image points (601') to (606') on the imaging plane (199). In one example, point (602) is pixel C on the display device (120), and virtual image point (602') is virtual image point C' shown in Figure 1. Point (603) is pixel A on the display device (120), and virtual image point (603') is virtual image point A' shown in Figure 1. In one example, the field of view corresponding to virtual image point (601') is 0°. The field of view corresponding to virtual image point (606') can be 50°, which corresponds to a 100° FOV in the first imaging mode.

[0072] Referring to Figure 2, a second light beam from pixel B in the display device (120) can pass through a polarization controller (155), and the second light beam may have a second polarization state coming from the polarization controller (155). The second polarization state may be orthogonal to the first polarization state. In one example, the second polarization state is a second CP. The first and second CPs may include left-hand circular polarization states and right-hand circular polarization states. The second light beam may be partially transmitted by a beam splitter (141). According to one embodiment of the present disclosure, the second polarization state of the second light beam coming from the polarization controller (155) is such that the second light beam is reflected by a reflective polarizer (139) after passing through the optical cavity for the first time, and the second light beam is in a different polarization state and transmitted by the reflective polarizer (139) after passing through the optical cavity for the third time.

[0073] The optical system (110) in Figure 2 may be referred to as a folded optical system. When the light beam is reflected in the optical cavity between the beam splitter (141) and the reflective polarizer (139) and travels multiple times (e.g., three times) within the optical cavity, the second optical path between the display device (120) and the area (151) includes a folded path (225) between the beam splitter (141) and the reflective polarizer (139). By folding the second optical path, it may be possible to reduce the distance D1, and the display system (100) including the optical system (110) can be used as a NED system. In one example, the lens system (130) is designed to have a relatively thin thickness D5 and may be referred to as a pancake lens system.

[0074] Referring to Figure 2, the second light beam (including rays (221) to (223)) emitted from pixel B of the display device (120) is partially transmitted by the beam splitter (141). Subsequently, the second light beam passes through the optical cavity for the first time, where it sequentially passes through the second lens (132) and QWP (142). The second light beam can then be incident on the reflective polarizer (139) for the first time. The second light beam is then reflected back into the optical cavity by the reflective polarizer (139). Subsequently, the second light beam passes through the optical cavity a second time, where it sequentially passes through the QWP (142) and the second lens (132).

[0075] After the second light beam passes through the optical cavity for the second time, it is partially reflected back into the optical cavity by the beam splitter (141). Subsequently, the second light beam passes through the optical cavity for the third time, where it sequentially passes through the second lens (132) and QWP (142). The second light beam is then transmitted by the reflective polarizer (139) and proceeds to area (151). In one example, the second light beam (including, for example, rays (221') to (223')) is focused onto the retina (65) by the lens (63) of the eye (60), and the eye (60) perceives the second light beam as if it were originating from a virtual point B' on the image plane (299).

[0076] Referring to Figure 2, in one example, the second light beam has a second polarization state, such as a second CP, coming from the polarization controller (155). The second light beam may be partially transmitted by the beam splitter (141). The second light beam then passes through the optical cavity for the first time as described above. During the first pass, the second CP of the second light beam is converted to a second linear polarization state (second LP) by the QWP (142). The second LP may be orthogonal to the first LP. The second linear polarization state is along the blocking direction of the reflective polarizer (139). The blocking direction of the reflective polarizer (139) refers to the direction in which the light beam is blocked by the reflective polarizer (139) and not transmitted through the reflective polarizer (139) if the electric field vector of the light beam is along the blocking direction. The reflective polarizer (139) reflects the second light beam having a second linear polarization state with a relatively high average reflectivity, for example, a value (e.g., 90%) or more over a wavelength range (e.g., 380-780 nm). The second light beam then passes through the optical cavity a second time as described above, and the second light beam is partially reflected by the beam splitter (141). Subsequently, the second light beam passes through the optical cavity a third time as described above. During both the second and third passes, the QWP (142) changes the polarization state of the second light beam. This converts the second linear polarization state of the second light beam to a first linear polarization state parallel to the transmission direction of the reflective polarizer (139). Therefore, the reflective polarizer (139) transmits the second light beam having the first linear polarization state so that the second light beam is directed to area (151) with a relatively high transmittance of a value (e.g., 90%) or more over the wavelength range (e.g., 380–780 nm). Referring to Figure 2, the second optical path includes a folded path (225) between the reflective polarizer (139) and the beam splitter (141) due to the polarization change.

[0077] Figure 5 shows the MTF of the optical system (110) in the second imaging mode shown in Figure 2. In one example, the eye (60) is positioned in area (151) and fixating straight ahead without rotation (e.g., field of view or eye rotation is 0°). Figure 5 shows the tangential MTF (501) and sagittal MTF (502) with respect to the field of view (e.g., Y field of view from 0° to 50°) at a resolution of 10 lp / mm (or 10 cycles / mm). Figure 5 shows that the FOV in the second imaging mode is 100°.

[0078] Referring to Figures 2 and 6, in one example, the distance D2' from area (151) and the imaging plane (299) (e.g., the second virtual image distance) is 2m. Figure 6 shows exemplary virtual image points (801') to (806') formed in a second imaging mode by an optical system (110) corresponding to object points or pixels (801) to (806) on a display device (120) according to one embodiment of the present disclosure. The light beams from pixels (801) to (806) may have a second polarization state when the light beam exits the polarization controller (155), and the light beams may be directed by the optical system (110) in the same manner as described above with reference to the second light beam from pixel B or similarly. The extensions of the light rays incident on area (151) from pixels (801) to (806) may each form virtual image points (801') to (806') on the imaging plane (299). In one example, point (802) is pixel D on the display device (120), and virtual image point (802') is virtual image point D' shown in Figure 2. Point (803) is pixel B on the display device (120), and virtual image point (803') is virtual image point B' shown in Figure 2. In one example, the field of view corresponding to virtual image point (801') is 0°. The field of view corresponding to virtual image point (806') can be 50°, which corresponds to a 100° FOV in the second imaging mode.

[0079] Comparing the two imaging modes shown in Figures 1 and 2, the virtual images C'A' and D'B' can have different image resolution densities. In one example, the display size in Figure 1 has a radius of 14.9 mm and an FOV of 100°. The display size can be indicated by the effective image circle of the display, which is imaged onto the area (151) by the optical system (110) (for example, on the display device (120)). Thus, a display diameter of 29.8 mm over a 100° FOV corresponds to a 0.3 mm / degree FOV. If the display device (120) has a resolution of 40 lp / mm (or 80 pixels / mm), the first image resolution density corresponding to the first imaging mode in Figure 1 is 0.3 × 80 pixels / degree or 24 pixels / degree. The display size in Figure 2 has a radius of 21.6 mm and an FOV of 100°. Thus, a display diameter of 43.2 mm over a 100° FOV corresponds to a 0.43 mm / degree FOV. For the same 40 lp / mm (or 80 pixels / mm) resolution of the display device (120), the second image resolution density corresponding to the second imaging mode in Figure 2 is 0.34 × 80 pixels / degree or 34 pixels / degree.

[0080] Figures 1 and 2 show two imaging modes of the display system (100). The polarization state of the light beam can be changed by a specific optical element (e.g., (155) or (142)), and the two imaging modes can correspond to two sets of polarization states of the light beam traveling within the display system (100), such as a first set of polarization states of the first light beam at various positions in the first optical path in the first imaging mode, and a second set of polarization states of the second light beam at various positions in the second optical path in the second imaging mode. Referring to Figures 1 and 2, the polarization controllers (155) and QWP (142) can control or change the polarization state. In the example shown in Figure 1, the first set of polarization states of the first light beam includes (i) a first initial polarization state when the first light beam is between the display device (120) and the polarization controller (155), (ii) a first CP when the first light beam is between the polarization controller (155) and the QWP (142), and (iii) a first LP when the first light beam is between the QWP (142) and the area (151). The polarization controller (155) can be configured to change the first initial polarization state to the first CP, and the QWP (142) can be configured to change the first CP to the first LP.

[0081] Referring to Figure 2, in one example, the second set of polarization states includes (i) a second initial polarization state of the second light beam between the display device (120) and the polarization controller (155), (ii) a second CP of the second light beam between the polarization controller (155) and the QWP (142) before and during the first pass, (iii) a second LP after the second light beam has come from the QWP (142) during the first pass and before the second light beam is incident on the QWP (142) during the second pass, (iv) an intermediate polarization state after the second light beam has come from the QWP (142) during the second pass and before the second light beam is incident on the QWP (142) during the third pass, and (v) a first LP of the second light beam between the QWP (142) and the area (151) during and after the third pass. The polarization controller (155) can be configured to change the second initial polarization state to a second CP, the QWP (142) can be configured to change the second CP to a second LP during the first pass, and the QWP (142) can be configured to change the second LP back to the first LP after the second light beam has passed through the QWP (142) twice during the second and third passes.

[0082] The first initial polarization state may be the same as or different from the second initial polarization state.

[0083] In one example, the first imaging mode corresponds to a first polarization state (e.g., first CP) coming from the polarization controller (155), and the second imaging mode corresponds to a second polarization state (e.g., second CP) coming from the polarization controller (155).

[0084] According to one embodiment of the present disclosure, the two imaging modes can be multiplexed, for example, in the time domain (e.g., time-domain multiplexing) or in the spatial domain (e.g., spatial-domain multiplexing). The images formed by the two imaging modes can be multiplexed or combined into a single image, for example, an image formed based on two images each formed by the two imaging modes. Time-domain multiplexing and spatial-domain multiplexing can be applied separately or in combination to the display system (100).

[0085] In time-domain multiplexing, the first imaging mode shown in Figure 1 can be performed in a first time period (e.g., at a first time point in time), and the second imaging mode shown in Figure 2 can be performed in a second time period (e.g., at a second time point in time). The first time period may differ from the second time period. In one example, the first time period does not overlap with the second time period. The second time point in time may differ from the first time point in time.

[0086] For example, referring to Figure 1, a first light beam passes through a polarization controller (155) and is in a first polarization state (e.g., first CP) at a first time point. The optical system (110) may have a first focal length and a first magnification at a first time period (e.g., at a first time point). The optical system (110) may form a first virtual image (e.g., C'A') of a first object (e.g., CA) located at a distance D4 from the optical system (110) at a first time period (e.g., at a first time point). For example, the first object (e.g., CA) is located on a display device (120), and the location of the first object can be indicated by the distance D1 between the display device (120) and the viewpoint (e.g., area (151)). The first virtual image located on the imaging plane (199) may be perceived at a first image distance D2 between the viewpoint (e.g., area (151)) and the imaging plane (199).

[0087] For example, referring to Figure 2, the second light beam passes through the polarization controller (155) and is in a second polarization state (e.g., second CP) at a second time point. The optical system (110) may have a second focal length and a second magnification at a second time period (e.g., at a second time point). The optical system (110) may form a second virtual image (e.g., D'B') of a second object (e.g., DB) located at a distance D4 from the optical system (110) at a second time period (e.g., at a second time point). For example, the second object (e.g., DB) is located on a display device (120), and the position of the second object can be represented by a distance D1. The second virtual image located on the imaging plane (299) may be perceived at a second image distance D2' between the viewpoint (e.g., area (151)) and the imaging plane (299). In the examples shown in Figures 1 and 2, the second focal length is different from the first focal length, the first image distance D2 is different from the second image distance D2', and the first magnification is different from the second magnification. For example, the first image distance D2 is 0.25m and the second image distance D2' is 2m.

[0088] In an example of time-domain multiplexing, during a first time period (e.g., at a first time point), a first light beam from a pixel of the display device (120) can pass through a polarization controller (155), which can control the polarization state of the light beam so that the first light beam has a first polarization state (e.g., a first CP) coming from the polarization controller (155). Each of the first light beams can pass through the optical cavity only once, and the pixels of the display device (120) can be imaged onto the imaging plane (199) using a first imaging mode. During a second time period (e.g., at a second time point), a second light beam from a pixel of the display device (120) can pass through the polarization controller (155), which can control the polarization state of the second light beam so that the second light beam has a second polarization state (e.g., a second CP) coming from the polarization controller (155). Each of the second light beams can pass through the optical cavity multiple times (e.g., three times), and pixels of the display device (120) can be imaged onto the imaging plane (299) using the second imaging mode. The pixels of the display device (120) may include all pixels of the display device (120) or a portion of the display device (120).

[0089] In time-domain multiplexing, two imaging modes can be switched at any appropriate frequency. For example, if the two imaging modes are switched at a frequency greater than a threshold (e.g., frame rate), such as 30 Hz and 60 Hz, the eye may perceive two images formed by the two imaging modes at two different time periods (e.g., at two different points) as a single image.

[0090] In time-domain multiplexing, the first imaging mode and the second imaging mode can be applied to the same object (e.g., the same region within the display device (120)) or different objects (e.g., different regions within the display device (120)). In one example of time-domain multiplexing, the polarization controller (155) is configured to uniformly control the polarization state of the light beam incident on different regions of the polarization controller (155).

[0091] In spatial domain multiplexing, the first imaging mode and the second imaging mode can be applied over the same time period (e.g., at the same time or simultaneously). In an example of spatial domain multiplexing, the first imaging mode shown in Figure 1 can be performed on a first region of the display device (120), and the second imaging mode shown in Figure 2 can be performed on a second region of the display device (120). The first region of the display device (120) (e.g., the central region) can correspond to the first region of the polarization controller (155) (e.g., the central region), and the second region of the display device (120) (e.g., the peripheral region) can correspond to the second region of the polarization controller (155) (e.g., the peripheral region).

[0092] In one embodiment, the polarization controller (155) includes wire grid cells (e.g., liquid crystal pixels). In one example, a liquid crystal pixel having a first type of wire grid (e.g., a 0° wire grid) can manipulate the polarization state of a light beam to a first polarization state, and a liquid crystal pixel having a second type of wire grid (e.g., a 90° wire grid) can manipulate the polarization state of a light beam to a second polarization state. In one example, pixels A and B are located at different positions on the display device (120). A first light beam from pixel A is manipulated by a liquid crystal pixel located at a first position in the polarization controller (155), and a second light beam from pixel B is manipulated by a liquid crystal pixel located at a second position in the polarization controller (155). The liquid crystal pixel located at the first position is associated with a first type of wire grid, and the liquid crystal pixel located at the second position is associated with a second type of wire grid.

[0093] For example, referring to Figure 1, a first light beam from a first region (or first object) (e.g., including CA) of a display device (120) passes through a first region of a polarization controller (155) and has a first polarization state (e.g., a first CP). The optical system (110) may have a first focal length and a first magnification with respect to the first light beam passing through the first region of the polarization controller (155). The optical system (110) may form a first virtual image (e.g., including C'A') of a first object located at a distance D4 from the optical system (110). For example, the first object is located on the display device (120), and the position of the first object may be indicated by the distance D1 between the display device (120) and the viewpoint (e.g., area (151)). The first virtual image located on the imaging plane (199) can be perceived at a first image distance D2 between the viewpoint (e.g., area (151)) and the imaging plane (199).

[0094] Referring to Figure 2, a second light beam from a second region (or second object) (e.g., including DB) of the display device (120) passes through a second region of the polarization controller (155) and has a second polarization state (e.g., second CP). The optical system (110) may have a second focal length and a second magnification with respect to the second light beam passing through the second region of the polarization controller (155). The optical system (110) may form a second virtual image (e.g., including D'B') of a second object located at a distance D4 from the optical system (110). For example, the second object is located on the display device (120), and the position of the second object may be represented by a distance D1. The second virtual image located on the imaging plane (299) may be perceived at a second image distance D2' between the viewpoint (e.g., area (151)) and the imaging plane (299).

[0095] In the examples shown in Figures 1 and 2, the second focal length is different from the first focal length, the first image distance D2 (e.g., 0.25m) is different from the second image distance D2' (e.g., 2m), and the first magnification is different from the second magnification.

[0096] Multiplexing can enable an observer to view multifocal or 3D scenes. For example, an eye (e.g., eye (60)) can perceive virtual images (or scenes) (e.g., C'A' and D'B') located at different distances from the eye (e.g., D2 and D2'). By controlling a polarization controller (155) using time-domain or spatial-domain multiplexing, the scenes (e.g., C'A' or D'B') can be selected or switched.

[0097] Two imaging modes can be multiplexed (for example, in the time domain or in the spatial domain) to generate a foveal image. In one embodiment, the first imaging mode shown in Figure 1 is used to form a first virtual image having a first spatial resolution and a first magnification, where the first virtual image extends to a first field of view (FOV). The second imaging mode shown in Figure 2 is used to form a second virtual image having a second spatial resolution and a second magnification, where the second virtual image extends to a second FOV. In one example, the first FOV is smaller than the second FOV, and the first spatial resolution is higher than the second spatial resolution. In one example, the first magnification is smaller than the second magnification. For example, the first FOV is 10°, and the field of view of the foveal image extends from -5° to 5°. The field of view of the foveal image associated with the second FOV may extend from (i) -50° to -5° and from 5° to 50°, or (ii) from -50° to 50°. For example, the surfaces of the lens system (130) (e.g., one or more of (135) to (138)), the gap (133), etc., can be determined such that the first focal length of the optical system (110) in the first imaging mode is the same as or identical to the second focal length of the optical system (110) in the second imaging mode. An image (e.g., a foveal image) can be formed based on the first virtual image and the second virtual image.

[0098] The display system (100) can be used for one eye, where two imaging modes can be multiplexed in any suitable manner (e.g., in the time domain, in the spatial domain, or in a combination of time-domain and spatial domain multiplexing). The two imaging modes can be applied to different eyes in any suitable manner.

[0099] Multiplexing can enable an observer to view a multifocal or 3D scene. In one example, a first imaging mode with a first focal length is applied to a display device for the first eye, and a second imaging mode with a second focal length is applied to a display device for the second eye. In another example, two first imaging modes with two focal lengths are applied to a display device for the first eye, and two second imaging modes with two focal lengths are applied to a display device for the second eye. The two first imaging modes may be the same as or different from the two second imaging modes.

[0100] The optical system (110) includes a reflector-refractor optical system. For example, the reflector-refractor optical system (110) includes (i) a refractive optical component (e.g., a lens system (130)) and (ii) a reflective optical component (e.g., a beam splitter (141) acting as a reflector for reflecting light and a reflective polarizer (139) acting as a reflector for reflecting light).

[0101] The reflecting-refracting optical system (110) shown in Figure 2 may include a polarizing reflecting-refracting optical system. For example, when a light beam passes through the QWP (142), the polarization state of the light beam is manipulated by the QWP (142). Thus, after the first pass, the light beam is in one polarization state (e.g., a second LP) and is reflected by the reflective polarizer (139), and after the third pass through the optical cavity, the light beam is in another polarization state (e.g., a first LP) and is transmitted by the reflective polarizer (139).

[0102] The polarization controller (155) can be configured to manipulate the polarization state of a light beam passing through it. For example, the light beam coming from the polarization controller (155) can have a first polarization state (e.g., first CP) or a second polarization state (e.g., second CP), as described above with reference to Figures 1 and 2. The polarization controller (155) can be a switchable polarization rotor configured to rotate the polarization state of the light beam. For example, the polarization controller (155) is a switchable half-wave plate (1 / 2 wave plate) for rotating the polarization state of a light beam by 90°, such as from 0° to 90°. A switchable half-wave plate can be used, for example, in a liquid crystal display (LCD) to turn pixels on or off.

[0103] In one example, a light beam emitted from a display device (120) has a first polarization state, such as a first CP. The polarization controller (155) can be a liquid crystal device controlled by an input voltage. When the input voltage is a first voltage, the polarization controller (155) does not affect the polarization state of the light beam emitted from the display device (120), and the light beam coming from the polarization controller (155) can have a first CP, as shown in Figure 1. When the input voltage is a second voltage, the polarization controller (155) can rotate the polarization state of the light beam emitted from the display device (120), and the light beam coming from the polarization controller (155) can have a second CP, as shown in Figure 2.

[0104] Figures 7A to 7B show an example of an LC spatial light modulator (SLM) (743). In one example, a polarization controller (155) includes the SLM (743) when a light beam from a display device (120) is linearly polarized. In one example, the LC SLM (743) is made from a torsion nematic (TN)LC material (704) arranged in a 90° twisted configuration and is referred to as a TN SLM. The TN LC material can be disposed between two electrodes (e.g., ITO) (701) and (702). Each electrode can be disposed on its respective transparent substrate (e.g., a glass substrate). In one example, an orientation material (e.g., polyimide) is disposed between the TN LC material (704) and the electrodes (e.g., (701)) to align the TN LC material (704).

[0105] Since LC SLM(743) can modulate the polarization state of light, LC SLM(743) can be used as a TN LC polarization modulator. TN LC SLM(743) can be used to rotate the plane of polarization of light or to manipulate the polarization state of light. Advantages of using LC SLM(743) include the ability to easily control and switch it on and off using an electric field. Therefore, the plane of polarization can be rapidly changed or switched in displays or optical switches, etc. LC SLM(743) can be a high-speed switchable TN SLM.

[0106] Figure 7A shows a schematic diagram of a 90° TN SLM with the voltage "off" (e.g., 0V). Figure 7B shows a schematic diagram of a 90° TN SLM with the voltage "on" (e.g., 6V). A linearly polarized light beam (703), polarized, for example along the Y-axis, is incident on the LC SLM (743). Referring to Figure 7A, when the voltage is "off", the TN LC material can rotate 90° along the optical path (e.g., along the Z-axis) when no voltage is applied. The LC SLM (743) rotates the polarization of the light beam (703) by 90° (e.g., from the Y-axis to the X-axis), so the output light beam (713) is linearly polarized along the X-axis. Referring to Figure 7B, when the voltage is "on", the TN LC material is oriented, for example along the Z-axis, by the electric field, and the LC SLM (743) does not change the polarization of the light beam (703). Therefore, the output light beam (723) is linearly polarized along the Y-axis. The output light beam (713) or (723) can then pass through the QWP to become circularly polarized light such as the RCP light beam (714) or LCP light beam (715), respectively.

[0107] One or more lenses within the lens system (130) may include a microstructure such as a Fresnel structure containing multiple grooves, such as a set of concentric grooves or concentric annular sections, and may be referred to as a Fresnel lens. Figure 8 shows a lens (190) and a corresponding Fresnel lens (191) according to one embodiment of the present disclosure. The lens (190) includes an optically transparent member between its surfaces (193) to (194). The lens (190) has a maximum thickness T1, for example, at the center of the lens (190). The Fresnel lens (191) may include an optically transparent member between its surfaces (195) to (196). The surface curvature of the smooth surface (193) of the lens (190) can be maintained by the grooved surface (195) of the Fresnel lens (191), and thus the Fresnel lens (191) can have the same or substantially the same focal length as that of the lens (190). For example, the smooth surface (193) of lens (190) is divided into smaller concentric portions (181) to (185), and these portions (181) to (185) are shifted along the optical axis of lens (190) (for example, parallel to the Z-axis in Figure 8) to form a Fresnel lens (191). In one example, the shapes of portions (181) to (185) within lens (190) are identical or substantially identical to the shapes of portions (181) to (185) within Fresnel lens (191).

[0108] The portions (181) to (185) of the Fresnel lens (191) correspond to the portions (181) to (185) of the lens (190), for example, the portions (181) to (185) of the Fresnel lens (191) have the same shape and material as those of the portions (181) to (185) of the lens (190). To explain the relationship between the lens (190) and the Fresnel lens (191), we can consider that portions (161) to (164) of the lens (190) have been removed, and the remaining portions (181) to (185) of the lens (190) have been realigned or shifted to the surface (196) (for example, parallel to the XY plane). The lens (190) can be considered folded within the Fresnel lens (191) while retaining the surface curvature of the surface (193) and therefore retaining the refractive power of the lens (190). A smooth surface (193) can become a grooved surface (195) having discontinuities between adjacent portions (181) to (185). For example, the maximum thickness T2 at the center of the Fresnel lens (191) is smaller than the thickness T1 at the center of the lens (190). Various methods can be applied to manufacture the Fresnel lens (191).

[0109] In some embodiments, the surface of a portion of the Fresnel lens (191) (e.g., the central portion) (181) is continuous or smooth and does not include a Fresnel structure. The surface of the peripheral portion of the Fresnel lens (191) surrounding the central portion (181) (e.g., including portions (182) to (185)) can be grooved and may include a Fresnel structure. The size of the central portion (181) without a Fresnel structure and the size of the peripheral portion with a Fresnel structure can be selected, for example, based on design requirements.

[0110] Referring to Figure 8, the Fresnel structure may include multiple grooves (e.g., concentric grooves) such as sections (182) to (185). The pitch P can represent the distance between adjacent prisms. The pitch P may be non-uniform or uniform (e.g., as shown in Figure 8). The inclination angle θ can represent the angle between surface (196) and each section of surface (195) (e.g., (195(1))). Parameters of the Fresnel lens (191), including but not limited to the size of the pitch P, the distribution of pitch P across the Fresnel structure, and the inclination angle θ, can be determined, for example, based on design requirements.

[0111] In some examples, the size of each central portion of a Fresnel lens, such as the size of the central portion (181), is below a threshold, for example, the size of the central portion (181) is equal to or the same as the pitch of another groove (e.g., (182)), and multiple grooves may contain the central portion (e.g., (181)), and the Fresnel structure may contain the entire Fresnel lens.

[0112] In one example, as shown in Figures 1 and 2, the first lens (131) is a Fresnel lens. The Fresnel lens (131) may include a Fresnel structure (175). The surface (135) and / or surface (136) may include a grooved surface. Referring to Figures 1 and 2, the surface (136) may include a Fresnel structure (175). As shown in Figure 8, the grooved surface of the Fresnel lens (131) may be flatter than the surface of a lens having the same or similar focal length. The Fresnel lens (131) may be thinner or flatter than a corresponding lens having the same or similar focal length. In one example, the Fresnel structure (175) surrounds the smooth central portion of the surface (136).

[0113] The descriptions of the two imaging modes and multiplexing methods can be applied to optical systems that do not include Fresnel lenses, those with one Fresnel lens (for example, the Fresnel lens shown in Figures 1-2 (131), or the Fresnel lens shown (132)), or those with multiple Fresnel lenses.

[0114] Referring to Figures 1 and 2, in one example, the lens system (130) includes two lens subsystems: a Fresnel lens (131) and a pancake lens. The pancake lens may include a lens (132), a beam splitter (141) (e.g., a 50 / 50 beam splitter), a reflective polarizer mirror (e.g., a reflective polarizer (139)), and a waveplate (e.g., QWP (142)) to control polarization within an optical cavity (e.g., a folded mirror cavity in Figure 2). The display system (100) may include a display device (120), a lens module (e.g., the lens system (130)), and a switchable polarization rotor (e.g., (155)). In one example, the display system (100) includes a photodetector or light receiver such as an eye (60). A switchable polarization rotor (e.g., (155)) can control the polarization basis of the light beam in the display system (100), where the polarization basis can be one of two polarization bases.

[0115] The display system (100) may be a component of an artificial reality system. The artificial reality system can somehow adapt reality to an artificial reality and then present the artificial reality to the user. The artificial reality may include, for example, virtual reality (VR), augmented reality (AR), mixed reality (MR), hybrid reality, or any combination thereof and / or derivatives. The artificial reality content may include entirely generated content or generated content combined with captured (e.g., real-world) content. The artificial reality content may include video, audio, haptic feedback, or any combination thereof, any of which may be presented in a single channel or in multiple channels (such as stereo video that produces a three-dimensional effect for the user). In some examples, the display system (100) may be applied to the playback of live or pre-recorded video.

[0116] In one embodiment, a “near-eye” display system may include an optical system (e.g., including one or more optical elements) and a display device that are placed within a distance threshold of the user’s eye when the NED system (100) (e.g., an HMD or smart glasses) is used. Referring to Figures 1 and 2, the distance D1 between the display device (120) and the area (151) may be less than or equal to the distance threshold. In one example, the distance D1 is between the display device (120) and the eye (60).

[0117] The display system (100) can be an NED system implemented in various forms, such as an HMD system, smart glasses, or a smartphone. In some examples, the artificial reality system is implemented as a standalone NED system. In some examples, the artificial reality system is implemented as an NED system connected to a host computer system, such as a server device or console device.

[0118] Polarization leakage can be reduced by controlling the polarization state of the light beam traveling within the display system (100). Waveplates (e.g., (142) and / or (155)) that can control the polarization rotation over a designed wavelength range (e.g., a wide wavelength range over which the waveplate is achromatic) and over a designed angular range (e.g., a large angular range) within the display system (100) can reduce ghosting within the display system (100). In one example, the birefringence characteristics of injection-molded lenses in a pancake optical system (e.g., display system (100)) should be considered to maintain polarization control in the pancake optical system (e.g., display system (100)). Haze, including scattering, surface scattering, and bulk scattering, can result in lower image clarity and more out-of-focus light. For reflection-based optical systems, mirror quality and surface finish can be important for reflected wavefront quality. Therefore, in optical modeling, surface finish of the manufacturing process can be considered to better simulate the design performance.

[0119] Polarized reflector-refracting optical systems are a new solution for virtual reality HMDs. A good VR optical system can accommodate multiple interpupillary distances and include a large pupillary volume (also called an eyebox) to allow eye rotation as the user scans across the field of view (FOV). In one example, the eyebox represents the volume from which the eye receives an acceptable view of the image. The size and position of the eyebox may be related to several constraints, such as FOV and image quality. In one example, the eyebox represents the range of eye positions from which the image produced by the optical system (110) can be seen, at the eye relief distance. The eyebox can include eye movements such as eye rotation and / or lateral movement.

[0120] In polarized reflector-refracting optical systems such as display systems (100), folded optical paths (e.g., folded path (225) between a beam splitter (141) and a reflective polarizer (139)) can be used to achieve relatively high refractive power in a compact form factor. In the example shown in Figure 2, the beam splitter (141) is a curved mirror that partially reflects and partially transmits light, and the reflective polarizer (139) can either reflect or transmit light as a plane mirror depending on the polarization state of the light. The design freedom available in folded optical systems (e.g., optical system (110)) can benefit HMD systems. Advantages may include high resolution achieved by reflective imaging, a wide FOV (e.g., by using low-aberration lenses), compact size, reduced weight, the ability to adjust focus, and the formation of a larger eyebox. The optical system (110) shown in Figures 1 and 2 can be manufactured, for example, by controlling the curved shape and surface finish of the first lens (131) and the second lens (132). A pancake optical system (e.g., a display system (100)) can provide a comfortable and immersive user experience.

[0121] The display system (100) can accommodate multiple interpupillary distances and may have a large pupillary volume to allow eye rotation when the user scans across the field of view. Interpupillary distance (IPD) is the distance between the centers of the pupils of the user's eyes. IPD can vary with respect to age, sex, etc. The display system (100) can be designed by taking IPD variance into account so that the optical system (110) can accommodate various users with different IPDs. In one example, IPD varies from approximately 50 to 80 mm.

[0122] In one example, to enable a user to enjoy VR without prescription glasses or using dynamic focus, the display system (100) can adjust the diopter of the lenses of the lens system (130) to match the prescription. In one example, the diopter indicates the virtual object distance. Increasing the diopter makes the object appear closer. Focus adjustment can be achieved by changing the refractive power of the optical system. The refractive power of a folded mirror cavity (e.g., the optical cavity between a beam splitter (141) and a reflective polarizer (139)) can be changed by varying the cavity length (or gap) relative to a reference cavity length corresponding to a reference refractive power.

[0123] Referring back to Figures 1 and 2, the shift block (170) can be coupled to the optical system (110) and optionally to the display device (120) to apply appropriate spatial pixel shift adjustments to the virtual image. The controller (180) can be coupled to the optical system (110) and the shift block (170) to control the operation of the optical system (110) and the shift block (170).

[0124] The shift block (170) can apply spatial pixel shift adjustment mechanically or optically. The shift block (170) may include a mechanical shifter for applying spatial pixel shift adjustment. In some examples, the mechanical shifter can shift the display device (120) to apply spatial pixel shift adjustment. In some examples, the mechanical shifter can shift at least one optical element (e.g., a first lens (131) or a second lens (132)) to apply spatial pixel shift adjustment. The folded path (225) in the optical cavity in Figure 2 can amplify relatively small adjustments to the gap (133) by, for example, three times.

[0125] The display system (100) may include other suitable mechanical, electrical, and optical components. For example, the display system (100) may include a frame (101) that can protect other components of the display system (100). In another example, the display system (100) may include a strap (not shown) for fitting the display system (100) to the user's head. In yet another example, the display system (100) may include communication components (not shown, e.g., communication software and hardware) for wirelessly communicating with a network, a host device, and / or other devices. In some examples, the display system (100) may include an optical combiner that can combine virtual content with a see-through reality environment.

[0126] In some examples, the parameters of the display system (100) include FOV, eye relief, lens track length, display size, and area (151) size. Eye relief can refer to the distance between the viewpoint of the receiver (e.g., area (151)) and the lens system (130). Lens track length can refer to the distance between the display device (120) and the lens system (130). Display size is indicated by the effective image circle of the display image imaged onto area (151) by the optical system (110). The display systems (100) in Figures 1 and 2 may have the same eye relief, the same lens track length, and the same size of area (151) (e.g., pupil size) (e.g., 5 mm). The optical system (110) can form a virtual image on the imaging plane (199) or (299) using two imaging modes for a suitable range of multicolor wavelengths, such as visible wavelengths (e.g., 380-780 nm with 400 nm) and multicolor wavelengths close to green (e.g., 500-540 nm with a bandwidth of 40 nm).

[0127] The embodiments of this disclosure may be used separately or combined in any order.

[0128] A computer or computer-readable medium can control various aspects of an HMD system incorporating a display system (100) including an optical system (110). Various aspects of the display system (100), including control of the movement and positioning of optical components (e.g., a first lens (131), a second lens (132), a display device (120)) and the operation of a polarization controller (155), can be implemented as computer software using computer-readable instructions and can be physically stored on one or more computer-readable media. For example, Figure 9 shows a computer system (900) suitable for implementing a particular embodiment of the subject matter disclosed.

[0129] Computer software can be coded using any suitable machine code or computer language that can be assembled, compiled, linked, or similarly configured to create code that includes instructions that can be executed directly or via interpretation, microcode execution, etc., by one or more computer central processing units (CPUs), graphics processing units (GPUs), etc.

[0130] Instructions can be executed on various types of computers or their components, including, for example, personal computers, tablet computers, servers, smartphones, gaming devices, and Internet of Things devices.

[0131] The components of the computer system (900) shown in Figure 9 are essentially illustrative and are not intended to imply any limitation on the scope of use or functionality of computer software implementing embodiments of the present disclosure. The configuration of the components should not be construed as having any dependencies or requirements on any or any combination of components shown in the exemplary embodiments of the computer system (900).

[0132] The computer system (900) may include certain human interface input devices. Such human interface input devices can respond to input from one or more human users via, for example, haptic input (keystrokes, swipes, data glove movements, etc.), audio input (voices, applause, etc.), visual input (gestures, etc.), and olfactory input (not shown). The human interface devices may also be used to capture certain media that are not necessarily directly related to conscious human input, such as audio (voices, music, ambient sounds, etc.), images (e.g., scanned images, photographic images taken from a still image camera, etc.), and video (2D video, 3D video including stereoscopic video, etc.).

[0133] The input human interface device may include one or more of the following (each of which is shown): a keyboard (901), a mouse (902), a trackpad (903), a touchscreen (910), a data glove (not shown), a joystick (905), a microphone (906), a scanner (907), and a camera (908).

[0134] The computer system (900) may also include certain human interface output devices. Such human interface output devices can stimulate the senses of one or more human users, for example, by tactile output, sound, light, and smell / taste. Such human interface output devices may include tactile output devices (e.g., tactile feedback via a touchscreen (910), data glove (not shown), or joystick (905), although there may also be tactile feedback devices that do not function as input devices), audio output devices (e.g., speakers (909), headphones (not shown)), visual output devices (touchscreen (910), including CRT screens, LCD screens, plasma screens, OLED screens, each having or not having touchscreen input capability, each having or not having tactile feedback capability, and some of which may be capable of outputting two-dimensional visual output or three-dimensional hyper-output via means such as stereoscopic output; virtual reality glasses (not shown), holographic displays, and smoke tanks (not shown)), and printers (not shown).

[0135] The computer system (900) may also include, for example, optical media including CD / DVD ROM / RW (920) having CD / DVD or similar media (921), thumb drives (922), removable hard drives or solid-state drives (923), legacy magnetic media such as tapes and floppy disks (not shown), and human-accessible storage devices and their associated media, such as dedicated ROM / ASIC / PLD-based devices such as security dongles (not shown).

[0136] Those skilled in the art should also understand that the term “computer-readable medium” as used in connection with the subject matter of this disclosure does not include transmission media, carrier waves, or other transient signals.

[0137] The computer system (900) may also include interfaces (954) to one or more communication networks (955). These networks may be, for example, wireless, wired, or optical. Networks may further be local, wide-area, metropolitan, vehicle and industrial, real-time, or latency-tolerant. Examples of networks include local area networks such as Ethernet and Wi-Fi; cellular networks including GSM, 3G, 4G, 5G, and LTE; wired or wireless wide-area digital television networks including cable TV, satellite TV, and terrestrial broadcast TV; and vehicle and industrial networks including CANBus. Certain networks generally require external network interface adapters attached to specific general-purpose data ports or peripheral buses (949) (e.g., USB ports on the computer system (900)), while others are generally integrated into the core of the computer system (900) by attachment to system buses as described later (e.g., Ethernet interfaces to PC computer systems or cellular network interfaces to smartphone computer systems). Using any of these networks, the computer system (900) may communicate with other entities. Such communications may be unidirectional, receive-only (e.g., broadcast TV), transmit-only (e.g., CANbus to a specific CANbus device), or bidirectional to other computer systems using local or wide-area digital networks. Specific protocols and protocol stacks can be used on each of those networks and network interfaces, as described above.

[0138] The aforementioned human interface device, human-accessible storage device, and network interface can be attached to the core (940) of the computer system (900).

[0139] The core (940) may include one or more central processing units (CPUs) (941), graphics processing units (GPUs) (942), dedicated programmable processing units in the form of field-programmable gate areas (FPGAs) (943), hardware accelerators (944) for specific tasks, graphics adapters (950), and the like. These devices may be connected via a system bus (948) along with read-only memory (ROM) (945), random access memory (946), internal mass storage such as internal non-user-accessible hard drives (947), SSDs, and the like. In some computer systems, the system bus (948) may be accessible in the form of one or more physical plugs to allow expansion with additional CPUs, GPUs, etc. Peripheral devices may be connected directly to the core's system bus (948) or via a peripheral bus (949). For example, a touchscreen (910) can be connected to a graphics adapter (950). Peripheral bus architectures include PCI, USB, and the like.

[0140] The CPU (941), GPU (942), FPGA (943), and accelerator (944) can execute specific instructions that can be combined to form the computer code described above. This computer code can be stored in ROM (945) or RAM (946). Transition data can also be stored in RAM (946), while persistent data can be stored, for example, in internal mass storage (947). Fast storage and retrieval to any of the memory devices can be enabled by the use of cache memory, which can be closely associated with one or more CPUs (941), GPUs (942), mass storage (947), ROMs (945), RAM (946), etc.

[0141] A computer-readable medium may contain computer code for performing various computer implementation operations. The medium and computer code may be specifically designed and constructed for the purposes of this disclosure, or they may be of a type well known and available to those skilled in the computer software technology.

[0142] For example, but not limited to, a computer system having an architecture (900), in particular a core (940), can provide functionality as a result of a processor (including a CPU, GPU, FPGA, accelerator, etc.) that runs software embodied in one or more tangible computer-readable media. Such computer-readable media can be non-transient, such as internal mass storage (947) or ROM (945), user-accessible mass storage as introduced above, and media associated with specific storage of the core (940). Software implementing various embodiments of the present disclosure can be stored in such devices and executed by the core (940). The computer-readable media can include one or more memory devices or chips, depending on the specific needs. The software can cause the core (940), and specifically the processor (including a CPU, GPU, FPGA, etc.) within it, to execute specific processes or specific parts of specific processes as described herein, including defining data structures stored in RAM (946) and modifying such data structures according to processes defined by the software. In addition, or alternatively, a computer system may provide functionality as a result of logic embodied in hardwired or otherwise in circuitry (e.g., accelerators (944)), which may, in place of or in conjunction with software, perform certain processes or specific parts of certain processes described herein. References to software may, where appropriate, encompass logic, and vice versa. References to computer-readable media may, where appropriate, encompass circuitry that stores software for execution (such as integrated circuits (ICs)), circuitry that embodies logic for execution, or both. This disclosure encompasses any appropriate combination of hardware and software.

[0143] While this disclosure has described several exemplary embodiments, there are many variations, substitutions, and alternative equivalents that fall within the scope of this disclosure. Those skilled in the art will therefore understand that it is possible to devise numerous systems and methods that embody the principles of this disclosure and thus fall within its spirit and scope, although these are not expressly shown or described herein.

Claims

1. A polarization controller configured to control the polarization state of a light beam incident on the polarization controller such that the polarization state of each light beam passing through the polarization controller is one of a first polarization state and a second polarization state, A beam splitter configured to partially transmit and partially reflect the light beam incident on the beam splitter, A reflective polarizer configured to allow a light beam having a third polarization state to pass through and to reflect a light beam having a fourth polarization state orthogonal to the third polarization state, One or more lenses between the beam splitter and the reflective polarizer Equipped with, Depending on whether the polarization state of the first light beam among the light beams passing through the polarization controller is the first polarization state, the first light beam passes through the one or more lenses only once. An optical system in which, depending on the polarization state of the second light beam among the light beams passing through the polarization controller, the second light beam passes through the one or more lenses multiple times.

2. The polarization state of the first light beam passing through the polarization controller has the first polarization state, The first light beam passes through the one or more lenses only once. The optical system according to claim 1, wherein the first focal length of the one or more lenses with respect to the first light beam in the first polarization state is different from the second focal length of the one or more lenses with respect to the second light beam in the second polarization state.

3. The polarization state of the second light beam passing through the polarization controller has the second polarization state, The optical system according to claim 1, wherein the second light beam passes through the one or more lenses multiple times.

4. The optical cavity containing one or more lenses is formed between the beam splitter and the reflective polarizer. The optical system according to claim 3, wherein the second light beam passes through the optical cavity three times before reaching the viewpoint.

5. A quarter-wave plate (QWP) is placed between the beam splitter and the reflective polarizer. The optical system according to claim 1, further comprising:

6. The optical system further includes a first lens, The one or more lenses include a second lens, The second lens is positioned between the first lens and the display device. The optical system according to claim 5, wherein the first lens is positioned between the second lens and the viewpoint.

7. The optical system according to claim 6, wherein the first lens and the second lens are separated by a gap.

8. The optical system according to claim 6, wherein one of the first lens and the second lens includes a Fresnel structure.

9. The beam splitter is positioned between the second lens and the display device. The reflective polarizer is placed between the first lens and the second lens. The optical system according to claim 6, wherein the QWP is disposed between the beam splitter and the reflective polarizer.

10. The first light beam passes through the polarization controller at a first time point, The optical system has a first focal length at the first time point, The second light beam passes through the polarization controller at a second time point different from the first time point, The optical system according to claim 1, wherein the optical system has a second focal length different from the first focal length at the second time point.

11. The optical system forms a first virtual image of a first object located at a certain distance from the optical system at the first time point, and the first virtual image is perceived at a first distance from the viewpoint at a first magnification that is the ratio of the size of the first virtual image to the size of the first object. The optical system forms a second virtual image of a second object located at the distance from the optical system at the second time point, the second virtual image is perceived at a second distance from the viewpoint at a second magnification which is the ratio of the size of the second virtual image to the size of the second object, and the second distance is different from the first distance. The optical system according to claim 10, wherein the second magnification is different from the first magnification.

12. The optical system according to claim 11, wherein the first distance is a multiple of the second distance.

13. The optical system according to claim 11, wherein an image is formed based on the first virtual image and the second virtual image.

14. The first light beam passes through the first region of the polarization controller, The optical system has a first focal length with respect to the first light beam passing through the first region of the polarization controller, The second light beam passes through a second region of the polarization controller that is different from the first region, The optical system according to claim 1, wherein the optical system has a second focal length with respect to the second light beam passing through the second region of the polarization controller, and the second focal length is different from the first focal length.

15. The optical system forms a first virtual image of a first object located at a certain distance from the optical system, the first light beam from the first object passes through the first region of the polarization controller, and the first virtual image is perceived at a first distance from the viewpoint. The optical system according to claim 14, wherein the optical system forms a second virtual image of a second object located at the distance from the optical system, a second light beam from the second object passes through the second region of the polarization controller, the second virtual image is perceived at a second distance from the viewpoint, and the second distance is different from the first distance.

16. The first magnification is the ratio of the size of the first virtual image to the size of the first object. The second magnification is the ratio of the size of the second virtual image to the size of the second object. The optical system according to claim 15, wherein the second magnification is different from the first magnification.

17. The optical system according to claim 15, wherein an image is formed based on the first virtual image and the second virtual image.

Images