Polarization-based processing of unpolarized image light

Abstract

A display system comprising: a source of unpolarized image light; and a stack of polarization selective optical elements operable to switchably convert the unpolarized image light into two orthogonal polarized beams, each of which is switchable in at least one beam characteristic. An output polarizer selects one of the two orthogonal polarized beams to be provided to a user. A depolarizer may be disposed between an electronic display emitting polarized light and the stack. The depolarizer may be in the form of an LC bilayer having a random in-plane optical axis.

Description

Technical Field

[0001] The present disclosure relates to display devices, and more particularly to near-eye displays and components thereof. Background Art

[0002] Head-mounted displays (HMDs), helmet-mounted displays, near-eye displays (NEDs), and the like are increasingly being used to display virtual reality (VR) content, augmented reality (AR) content, mixed reality (MR) content, and to name just a few examples, with applications in a variety of fields including entertainment, education, training, and biomedical sciences. VR / AR / MR content can be three-dimensional (3D) to enhance the experience and match virtual objects with real objects observed by the user. The user's eye position and gaze direction and / or orientation can be tracked in real time, and the displayed image can be dynamically adjusted based on the user's head orientation and gaze direction to provide a better immersion experience into a simulated or augmented environment. One or more varifocal lenses can be used to dynamically adjust the focus image position of each eye, for example, to reduce the difference between eye vergence and visual accommodation, known as vergence accommodation conflict.

[0003] For head mounted displays, compact display devices are desired. Because the display of an HMD or NED is typically worn on the user's head, a large, bulky, unbalanced, and / or heavy display device would be cumbersome and may be uncomfortable for the user to wear. To reduce the size and / or weight of an HMD or NED, polarization-based optics using thin liquid crystal (LC) layers and stacks may be used to implement lenses and other light processing devices. Summary of the invention

[0004] According to a first aspect of the present invention, there is provided a display system comprising: a source of non-polarized image light; a stack of polarization-selective optical elements, the polarization-selective optical elements being arranged to receive the non-polarized image light and being operable to switchably convert the non-polarized image light into two orthogonal polarized light beams; and an output polarizer being arranged to receive the two orthogonal polarized light beams and being configured to select one of the two orthogonal polarized light beams to form an image.

[0005] The display system may be configured to be mounted on a user's head for near-eye display of images. The stack may be devoid of an input polarizer.

[0006] The stack may include one or more Pancharatnam-Berry Phase (PBP) optical elements. At least one of the one or more PBP optical elements may be configured to receive unpolarized image light.

[0007] The stack may include one or more switchable half-wave plates (HWPs).

[0008] The one or more PBP optical elements may include a plurality of PBP lenses of different nominal optical powers. The stack may be configured to function as a zoom lens.

[0009] The plurality of PBP lenses may include a switchable liquid crystal (LC) PBP lens.

[0010] The plurality of PBP lenses may include one or more passive PBP lenses. Each of the one or more passive PBP lenses may be followed by a switchable HWP.

[0011] One or more of the PBP optical elements may include a polarization grating.

[0012] The polarization grating may be directly followed by a switchable HWP.

[0013] The polarisation grating may comprise an LC PBP grating switchable to a non-diffractive state.

[0014] The source of unpolarized image light may include an electronic display configured to emit unpolarized light.

[0015] The source of unpolarized image light may include an electronic display configured to emit polarized image light, and a depolarizer disposed in an optical path between the electronic display and the stack.

[0016] The polarized image light may be linearly polarized.The depolarizer may include a half wave plate (HWP) having a spatially random in-plane optical axis.

[0017] The depolarizer may be positioned proximate to the electronic display.

[0018] The stack may include a series of LC PBP optical elements. Each LC PBP optical element may be paired with a switchable LCHWP.

[0019] At least one polarization selective element of the stack may comprise a switchable LC PBP optical element.

[0020] According to a second aspect of the present invention, there is provided a method for polarization-based processing of image light in a display system, the method comprising: passing non-polarized image light through a series of polarization-selective optical elements to obtain two orthogonally polarized light beams, each of the orthogonally polarized light beams being switchable in at least one beam characteristic; and using an optical polarizer disposed downstream of the series of polarization-selective optical elements to select one of the two orthogonally polarized light beams as an output light beam to form an image.

[0021] The method may further include passing the polarized image light through a depolarizer to obtain unpolarized image light for providing to a series of polarization selective optical elements.

[0022] The passing may include passing the unpolarized image light through a series of PBP lenses having different nominal optical powers.

[0023] The passing may include passing the unpolarized image light through a series of polarization gratings. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Exemplary embodiments will now be described with reference to the accompanying drawings, in which like elements are designated by like reference numerals, the drawings are not drawn to scale, and in which:

[0025] Figure 1 is a schematic perspective view of a liquid crystal (LC) polarization device;

[0026] Figure 2 is a schematic cross-sectional view of an electrically controlled active LC device;

[0027] Figure 3A is a schematic diagram showing an example liquid crystal orientation in the plane of the LC layer of a LC PBP lens;

[0028] Figure 3B is a schematic diagram showing an example liquid crystal orientation in the plane of the LC layer of the LC PBP grating;

[0029] Figure 4A is a schematic diagram illustrating the operation of an example PBP lens for RHCP light;

[0030] Figure 4B is a schematic diagram illustrating the operation of an example PBP lens for LHCP light;

[0031] Figure 5 is a schematic diagram showing the operation of the PBP grating for RHCP and LHCP light;

[0032] Figure 6 is a schematic side cross-sectional view of a virtual reality (VR) HMD having an optical block that focuses image light for a user;

[0033] Figure 7 is a schematic diagram showing the operation of a PBP lens in cooperation with a switchable HWP;

[0034] Figure 8 is a schematic diagram showing the operation of a zoom lens formed as a switchable PBP stack having a first PBP element that receives polarized light;

[0035] Fig. 9 It is shown Figure 8Schematic diagram of an integrated implementation of a switchable PBP stack;

[0036] Fig.10 It shows the use of Figure 8 Schematic diagram of possible ring artifacts in a display that operates on polarized image light using a switchable PBP stack;

[0037] Fig.11 is a schematic cross-sectional view of a switchable PBP stack for operation with unpolarized incident light;

[0038] Fig. 12A is a schematic diagram of a switchable PBP stack with active PBP elements of the same chirality separated by a passive HWP;

[0039] Fig. 12B is a schematic diagram of a switchable PBP stack having active PBP elements of opposite chirality stacked in direct order;

[0040] Fig.13 is coupled to an electronic display that emits unpolarized image light. Fig.11 Schematic side cross-sectional view of an HMD with a switchable PBP lens stack;

[0041] Fig.14 is a schematic side cross-sectional view of an HMD having a depolarizer disposed between a switchable PBP lens stack and an electronic display emitting polarized image light;

[0042] Fig.15 is a schematic side cross-sectional view of an HMD having a depolarizer disposed downstream of a pancake lens and upstream of a switchable PBP lens stack;

[0043] Fig.16 is a schematic cross-sectional view of a switchable PBP lens stack including an input depolarizer;

[0044] Fig.17 is a schematic diagram showing a wave plate with spatially varying in-plane optical axis orientation used as a depolarizer;

[0045] Fig.18 is a schematic diagram showing an LC alignment layer with spatially varying alignment directions for an LC depolarizer;

[0046] Fig.19 is a schematic cross-sectional view of a depolarizer formed with an LC bilayer having an antisymmetric twist and spatially randomized optical axis in the plane of the wave plate;

[0047] Fig. 20A is a schematic plan view of one depolarizer segment showing the twist of the LC director in the lower layer of the LC bilayer; the LC director at the top of the layer is shown with a solid arrow;

[0048] Fig. 20B yes Fig. 20A Schematic plan view of a depolarizer fragment of , showing LC director twist in the second layer of the LC bilayer; the dashed arrow shows the LC director at the bottom of the layer at the boundary with the lower layer;

[0049] Fig.21A is an isometric view of a head mounted display of the present disclosure; and

[0050] Fig. 21B Yes Fig.21A Block diagram of a virtual reality system with a head mounted device. DETAILED DESCRIPTION

[0051] Although the present invention has been described in conjunction with various embodiments and examples, it is not intended that the teachings herein be limited to these embodiments. On the contrary, the teachings herein include various alternatives and equivalents, as understood by those skilled in the art. All statements of the principles, aspects and embodiments of the present disclosure and their specific examples are described herein to encompass their structural and functional equivalents. In addition, these equivalents are intended to include currently known equivalents and equivalents developed in the future, i.e., any element that performs the same function developed, regardless of structure.

[0052] As used herein, the terms "first", "second", etc. are not intended to imply a sequential order, but are intended to distinguish one element from another, unless explicitly stated. Similarly, the sequential ordering of method steps does not imply a sequential order of their execution, unless explicitly stated. The terms "NED" and "HMD" are used interchangeably herein to refer to a head-mounted display device capable of providing VR / AR / MR content to a user.

[0053] One aspect of the present invention relates to an optical depolarizer and its use in a display system. In some embodiments, the display system can be configured to be mounted on a user's head for near-eye display of images.

[0054] One aspect of the present disclosure relates to a display system including a stack of polarization selective optical elements, the stack including one or more switchable polarization selective elements, the stack configured to operate on unpolarized image light without an input polarizer to output two orthogonally polarized light beams with switchable beam characteristics. The stack may be followed by a clean-up polarizer for selecting one of the two orthogonally polarized light beams with desired beam characteristics for forming an image.

[0055] In some embodiments, the stack comprises a series of liquid crystal (LC) Pancharatnam-Berry (or PB) phase (PBP) optical elements, each paired with a switchable LC HWP. In some embodiments, at least one polarization-selective element of the stack comprises a passive or switchable LC PBP optical element. In some embodiments, the stack comprises a plurality of layers having polarization-selective optical properties, wherein orthogonal polarizations are treated differently and are both passed to the next layer. In some embodiments, the stack comprises a plurality of LC layers. In some embodiments, the stack comprises a series of LC PBP lenses having different nominal optical powers. In some embodiments, the stack comprises one or more LC PBP lenses and one or more active LC wave plates, wherein at least one LC PBP lens is configured to receive unpolarized light. In some embodiments, the stack comprises one or more LC PBP gratings and one or more active LC wave plates, wherein at least one LC PBP grating is configured to receive unpolarized light. In some embodiments, the stack comprises a clean-up polarizer, or is followed by a clean-up polarizer.

[0056] One aspect of the present disclosure relates to a display system comprising: a non-polarized image light source; a stack of polarization-selective optical elements, the polarization-selective optical elements being configured to receive the non-polarized image light and being operable to switchably convert the non-polarized image light into two orthogonal polarized light beams; and an output polarizer, which is configured to receive the two orthogonal polarized light beams and is configured to select one of the two orthogonal polarized light beams to form an image. Each of the two orthogonal polarized light beams can be switchable in at least one beam characteristic. In some embodiments, at least one beam characteristic can include a beam converging characteristic. In some embodiments, at least one beam characteristic can include a beam deflection angle. The display system can be configured to be mounted on a user's head for near-eye display of an image.

[0057] In some embodiments, the stack may include one or more PB phase (PBP) optical elements, wherein at least one of the one or more PBP optical elements is arranged to receive the unpolarized image beam. In some embodiments, one or more PB phase (PBP) optical elements may be switchable. In some embodiments, each of the one or more PBP elements may be directly followed by a switchable HWP. In some embodiments, one or more PBP optical elements may include a plurality of PBP lenses having different nominal optical powers, and the stack may be configured to operate as a variable focal length lens. In some embodiments, a plurality of PBP lenses may include a liquid crystal (LC) PBP lens that may be switched to a neutral state without optical power. In some embodiments, the stack may include a plurality of switchable half-wave plates (HWPs). In some embodiments, the PBP lenses may be paired sequentially with the switchable HWPs; in some embodiments, each switchable HWP may be directly followed by one of the PBP lenses. In some embodiments, one or more PBP optical elements may include a polarization grating. In some embodiments, the polarization grating may be directly followed by a switchable HWP. In some embodiments, the polarization grating may include an LC PBP grating that may be switched to a non-diffractive state.

[0058] In some embodiments, the non-polarized image light source includes an electronic display configured to emit non-polarized light. In some embodiments, the non-polarized image light source includes an electronic display configured to emit polarized image light, and a depolarizer disposed between the electronic display and the stack. In some embodiments, the polarized image light is linearly polarized, and the depolarizer includes a half-wave plate (HWP) having a random in-plane optical axis. In some embodiments, the depolarizer may be disposed adjacent to the electronic display.

[0059] In some embodiments of the display system, the depolarizer includes a birefringent layer having an in-plane optical axis, the orientation of which varies randomly or pseudo-randomly from one position to another in the plane of the birefringent layer - a property that can be referred to as a random in-plane optical axis. In some embodiments, the birefringent layer has a delay that is substantially constant across the wave plate. In some embodiments, the birefringent layer has a half-wave optical delay. In some embodiments, the orientation of the in-plane optical axis varies randomly or pseudo-randomly along the birefringent layer. In some embodiments, the birefringent layer includes an LC material. In some embodiments, the birefringent layer includes a twisted nematic LC material. In some embodiments, the birefringent layer includes a plurality of uniform domain segments, each domain segment having an optical axis, wherein the orientation of the optical axis varies randomly or pseudo-randomly between adjacent domain segments. In some embodiments, the depolarizer includes a double layer of a twisted LC material, the double layer including two layers of opposite chirality. In some embodiments, each of the two layers of the double layer has a half-wave delay.

[0060] One aspect of the present disclosure provides a method for polarization-based processing of image light in a display system, the method comprising: sequentially passing non-polarized image light through a plurality of polarization-selective optical elements to obtain two orthogonal polarized light beams, each of which is switchable in at least one beam characteristic; and selecting one of the orthogonal polarized light beams as an output light beam using an optical polarizer disposed downstream of the plurality of polarization-selective optical elements. In some embodiments, the method may include passing polarized image light from an electronic display through a depolarizer to obtain non-polarized image light for providing to sequential polarization-selective optical elements. In some embodiments, sequentially passing non-polarized image light may include passing the non-polarized image light through a series of PBP lenses having different nominal optical powers. In some embodiments, sequentially passing non-polarized image light may include passing the non-polarized image light through a series of LC polarization gratings.

[0061] One aspect of the present disclosure relates to a method for manufacturing a depolarizer, the method comprising exposing an alignment layer comprising a photosensitive material to polarized UV light such that adjacent regions of the alignment layer are exposed to polarized UV light of different polarization directions. In some embodiments, the method may include exposing multiple region segments of the alignment layer to polarized UV light such that the polarization of the UV light changes randomly or pseudo-randomly when adjacent region segments are exposed. LC material may then be deposited onto the exposed alignment layer to a target thickness to obtain an LC layer having a random LC director orientation. In some embodiments, the target thickness corresponds to a half-wave delay. The method may include polymerizing the LC material after deposition to obtain an LC layer having a fixed random LC director orientation.

[0062] One aspect of the present disclosure relates to a depolarizer comprising a birefringent layer having a spatially varying orientation of an in-plane optical axis. In some embodiments, the orientation of the in-plane optical axis varies randomly or pseudo-randomly along the birefringent layer. In some embodiments, the birefringent layer has a substantially constant delay across a wave plate. In some embodiments, the birefringent layer has a half-wave optical delay. In some embodiments, the birefringent layer comprises an LC material. In some embodiments, the birefringent layer comprises a twisted nematic LC material. In some embodiments, the birefringent layer comprises a plurality of uniform domain segments, wherein the orientation of the optical axis varies randomly or pseudo-randomly between adjacent domain segments. In some embodiments, the birefringent layer of the depolarizer is a bilayer consisting of two layers of twisted LC material having opposite chirality.

[0063] One aspect of the present disclosure provides a depolarizer comprising: a substrate; a double layer of twisted LC material disposed on the substrate, the double layer comprising: a first layer of twisted LC material disposed on the substrate, the first layer having an LC director having a first sense of twist in a thickness direction, wherein the thickness direction is perpendicular to the substrate; and a second layer of twisted LC material disposed on the first layer, the second layer having an LC having a second sense of twist in the thickness direction, wherein the second sense of twist is opposite to the first sense of twist. The LC director of the first layer has a direction that varies randomly or pseudo-randomly in the plane of the substrate at an interface with the second layer. The double layer can have a half-wave delay that is generally constant in the plane of the substrate. In some embodiments, the first layer and the second layer of the double layer can have LC twist parameters optimized for broadband operation.

[0064] refer to Figure 1 -4, the embodiments described herein may utilize liquid crystal (LC) based devices that operate in a polarization sensitive manner without substantially discriminating between orthogonal polarizations based on the power of the transmitted light. Such devices include, but are not limited to, LC PBP lenses, LC PBP gratings, and LC polarization switches. First, refer to Figure 1 , the LC device described herein may be in the form of or include an LC layer 31, which may be supported by a transparent or reflective substrate 30. The substrate 30 may be flat or curved. The polarization properties of such a device may depend on the material properties of the LC layer 31, the orientation of the LC molecules 35 within the layer, the chirality of the LC molecules 35, the thickness of the LC layer 31 and the wavelength λ of the incident light. The predominant orientation of the LC molecules at any position (x, y, z) in the LC layer may conveniently be represented by a unit vector n(x, y, z) called the LC director, with n(x, y, z) = -n(x, y, z). For convenience, a Cartesian coordinate system (x, y, z) is used herein, wherein the (x, y) plane is parallel to the plane of the LC layer 31. Within the LC layer 31, the orientation of the LC director may be defined at least in part by one or more orientation layers 37 which may be disposed proximate to the LC layer 31. LC devices in which the orientation of the LC molecules is generally uniform across the LC layer may be used as wave plate retarders. For incident light of a particular polarization, LC devices in which the orientation of the LC director varies in the plane of the layer may, but not exclusively, function as a lens, grating, or depolarizer as described below, depending on the LC director orientation pattern.

[0065] LC devices can be active, where the LC material orientation is electrically controlled, or passive, where the LC material orientation is fixed in place by material properties, e.g. by orientation layers and / or by polymers mixed into the LC fluid and solidified with a specific orientation within the LC layer.

[0066] refer to Figure 2 , an active LC device may consist of an LC layer 31 sandwiched between two electrodes 39, at least one of which is transparent in the wavelength range of intended operation. In an embodiment operating in transmission, both electrodes 39 may be optically transparent. The transparent electrode 39 may be in the form of, or include, an ITO (indium tin oxide) layer, for example. In the absence of a voltage between the electrodes, the LC molecules 35 may be oriented in a default pattern that imposes a desired birefringence property on the device, such as a desired uniform or non-uniform retardation. Applying a sufficient voltage V between the electrodes 39 may reversibly reorient the LC molecules 35 in a manner that changes the birefringence property of the LC layer. For example, in some LC materials, applying a sufficient voltage V to the electrodes 39 may orient the LC molecules along the electric field, as shown in 35a in the figure, so that the LC layer 31 will lose its birefringence for light incident at or near normal incidence. An example of an active LC device is an active wave plate, the retardation of which may be turned off and turned back on by applying a voltage V and by turning off the voltage, respectively. For example, an active LC device can be constructed to provide the retardation of a half-wave plate (HWP) in the absence of an applied voltage, and to provide substantially zero retardation when a sufficient voltage V is applied. One or more embodiments described herein can utilize such a switchable HWP, hereinafter referred to as an s-HWP, as a polarization switch for polarized light. For example, a properly oriented s-HWP can reverse the chirality of circularly polarized (CP) light incident thereon in the absence of a voltage (OFF state), and can maintain the incident polarization state unchanged in the presence of a voltage (ON state). In other embodiments, the relationship between the applied voltage and the polarization effect of the LC waveplate can be reversed.

[0067] refer to Figure 3A , a PB phase (PBP) lens 40 with desired polarization handling and focusing properties can be fabricated, wherein the orientation of the LC molecules 45 varies radially in the plane of the LC layer, and possibly also in a direction perpendicular thereto, i.e., relative to the optical axis ( Figure 1 -4) radially. The LC azimuth angle θ, i.e., the rotation angle of the projection of the LC director on the plane (x, y) of the LC layer, can vary radially from the center 41 to the edge 44 of the lens 40 with a varying spacing 43Λ. The spacing Λ represents the distance spanned by a 180° rotation of the azimuth angle θ of the LC director, and can be a function of the radial distance r from the center 41 of the PBP lens. A polarized light beam passing through such a lens experiences a radius-dependent delay that adds a varying phase shift to the wavefront of the entire beam, resulting in a lensing action for a properly selected LC orientation profile. In some embodiments, the azimuth angle θ of the LC orientation in the PBP LC lens 40 can be varied according to the following equation:

[0068]

[0069] Where f0 corresponds to the focal length of the PBP lens 40, and λ0 corresponds to the wavelength of the incident light on the lens. In other embodiments, the tilt angle φ of the LC molecules of the PBP lens, which describes the tilt angle of the molecules relative to the optical axis of the lens, can be radially varied to provide a desired phase distribution. Such a lens can be active, where the LC material orientation is electrically controlled, or can be passive, where the LC material orientation is fixed in place by material properties and / or orientation layers. An active LC PBP lens can be as described above with reference to Figure 2 The active LC PBP lens is constructed as described. For example, the optical power and polarization switching properties of the active LC PBP lens can be turned on by applying an appropriate voltage across the LC layer to switchably orient the LC molecules along the optical axis (z-axis) of the lens. The following state of the active LC PBP lens can be referred to as a neutral state, in which it has an optical power of substantially zero, or an optical power less than a threshold value. The state of the active LC PBP lens having a desired non-zero nominal optical power can be referred to as a neutral state.

[0070] Reference Figure 3B , the LC device 60 can be used as a polarization grating in which the orientation of the LC director varies periodically or nearly periodically in one dimension (1D) along a particular direction in the plane of the LC layer. The polarization grating can direct incident light at an angle that depends on the pitch of the grating and the polarization state of the incident light. An example of an LC polarization grating is a PBP grating, in which the "grooves" of the grating are formed by spatially varying the birefringence in the plane of the grating. The LC directors (represented in the figure by "LC molecules" 65) in the grating change their orientation in the plane of the LC layer (which is represented in the figure as the (x, y) plane), thereby defining the device birefringence distribution in the plane of the LC layer. The azimuth angle θ of the LC directors 65 in the grating plane varies continuously from one edge to another, which typically has a fixed pitch 63. The LC PBP grating can be active, in which the LC material orientation is electrically controlled, or can be passive, in which the LC material orientation is fixed in place by material properties and / or alignment layers, or can be passive. Active LC PBP grating can be as referenced above Figure 2 It is designed as described so that its diffraction capability can be switched off.

[0071] Figure 4A and Figure 4B An example PBP lens 50 with a focal length f is shown for left-handed circularly polarized (LHCP) light ( Figure 4A ) and right-handed circularly polarized (RHCP) light ( Figure 4B) operation. In this example, the PBP lens 50 has a positive optical power for LHCP light while switching its polarization to RHCP, and has a negative optical power for RHCP light while switching its polarization to LHCP. Therefore, the collimated LHCP beam 51 leaves the lens as a converging RHCP beam that converges to a focus at a distance f from the lens, while the collimated LHCP beam 53 leaves the lens as a diverging LHCP beam that appears to diverge from a virtual focus at a distance -f from the lens. The focal length f of the PBP lens defines its nominal optical power 1 / f.

[0072] refer to Figure 5 , the PBP grating 70 can be configured to deflect the RHCP light by a diffraction angle θd in one direction, and to deflect the LHCP light by generally the same diffraction angle θd in the opposite direction. In both cases, the PBP grating 70 switches the circular polarization to its orthogonal polarization. The pitch of the LC PBP grating can be configured to provide a desired size of the diffraction angle θd. Such a grating can be active, where the LC material orientation is electrically controlled, or can be passive, where the LC material orientation is fixed in place by material properties and / or orientation layers. The active LC PBP grating can be described above with reference to Figure 2 The active LC PBP grating can be constructed as described. For example, the active LC PBP grating can deflect the incident CP light by a diffraction angle of +\-θd according to the chirality of the incident light, while reversing its chirality in the absence of voltage (OFF state), and can keep the propagation direction and polarization state of the incident light unchanged in the presence of voltage (ON state). The PBP grating is an example of a polarization grating. Another example of a polarization grating is a volume holographic LC grating, in which the orientation of the LC layer material can change both in the plane of the LC layer and in a direction perpendicular to the LC layer (which can be called the thickness direction). Such a grating can be constructed to selectively deflect only one of two orthogonal linear polarizations without substantially changing the propagation direction of the other of the two orthogonal polarizations. The volume holographic LC grating can be operated, for example, as an active element in which the LC material is electrically controlled, and / or as a passive element, together with a linear polarizer and an active polarization rotator operable to switch the polarization state of the incident light. The embodiments described below with reference to the LC PBP grating can be modified to use such a volume holographic LC grating instead.

[0073] Reference now Figure 6, schematically illustrates an example HMD 100 in partial cross-section, in which a stack of active and / or passive LC devices as described above may be used. The HMD 100 includes an electronic display 153 disposed at a front face 152 of a rigid body 151, facing an eye box 157. When the user wears the HMD 100, the eye box 157 defines the location of the user's eye 160. An optical block 155 disposed in the optical path between the electronic display 153 and the eye box 157 transmits image light from the electronic display 153 to the eye box 157. In one or more embodiments, the optical block 155 may form a magnified virtual image of a pixelated light emitting surface 154 of the electronic display 153, which is typically further away from the eye box 157 than the electronic display 153. The virtual image of the light emitting surface 154 of the display is then projected by the lens 161 of the eye 160 onto the retina 163 to form an image thereon. Although only a single optical block 155 is shown, the HMD 100 may include two instances of the block, one for each eye of the user, and may also include two instances of the electronic display 153. The electronic display 153 may be a pixelated display, such as a microdisplay whose total pixel count may be less than, for example, a conventional direct-view LED TV display. The HMD 100 may also include various other elements, such as one or more position sensors, one or more positioners, an inertial measurement unit (IMU), etc., which may be coupled to the rigid body 151 and may be at least partially positioned at its front face 152 in some cases. In one or more embodiments, the HMD 100 may include one or more cameras 159, which may be configured for eye tracking and / or display calibration and may be disposed downstream of the optical block 155. The camera 159 may also be disposed upstream of the optical block, or integrated into the optical block 155. The electronic display 153 may be, for example, an LCD display, an OLED display, an AMOLED display, or any other suitable display. In some embodiments, the electronic display 153 may be configured to emit polarized light. In other embodiments, the electronic display 153 may be configured to emit unpolarized light. The electronic display 153 is operably coupled to the display processor 170. In operation, the electronic display 153 receives image or video data from the processor 170, for example, in the form of a sequence of input image frames, and presents corresponding images to a user. The optical block 155 may include one or more optical elements, such as, but not limited to, a convex lens, a concave lens, a Fresnel lens, an LC lens, a liquid lens, a pancake lens, an aperture, a grating, a filter, a polarizer and / or a polarization converter, or any suitable optical element. The optical block 155 may be configured to form a magnified image of the light emitting surface 154 of the electronic display 153 or a region thereof, and may also correct optical aberrations and other optical errors in the image light received from the electronic display 153.

[0074] In some embodiments, the display 100 may use a varifocal lens that can dynamically adjust the optical power to enhance the user experience. In some embodiments, the varifocal lens may cooperate with the eye tracking system of the HMD 100 to dynamically change the focus characteristics of the HMD optical device to improve the user's experience. In some embodiments, the varifocal lens can be constructed by stacking several PBP lenses of different optical powers, and in some embodiments, these PBP lenses may be interspersed with s-HWP. By appropriately selecting the optical power of the PBP lenses, such a multi-element or multi-layer LC PBP lens stack can be controlled to provide an optical power range with a step size defined by the minimum optical power lens.

[0075] Figure 7 An example PBP lens system with an optical power switchable between +D1 and -D1 diopters (D) is schematically shown. In the illustrated embodiment, it includes a circular polarizer (CPr) 220, followed by an s-HWP 230, followed by a PBP lens 210 of nominal optical power D1. The CPr 220 may be, for example, an RHC polarizer configured to convert input polarized or unpolarized light 201 into RHCP light 203. When the s-HWP 230 is in the ON state, it transmits the RHCP light 203 without polarization change, so that the PBP lens 210 acts on the RHCP light 205 as a focusing lens with an optical power of +D1, thereby outputting a converging LHCP beam 207. When the S-HWP 230 is in the OFF state, it changes the beam polarization to an orthogonal polarization, sending the LHCP light to the PBP lens 210. The PBP lens 210 acts as a defocusing lens with optical power (-D1) on the LHCP light, outputting a divergent RHCP beam. Therefore, the sequential assembly of the PBP lens and the s-HWP operates on the CP light as a switchable ±D1 lens. In some embodiments, the PBP lens 210 can be active and can be electrically switched to a state with zero or near zero optical power, thereby increasing the number of switchable optical power states. Stacking such a dual element assembly with different D1 values ​​(e.g., D1, D1 / 2, D1 / 4, etc.) provides a multi-state zoom lens.

[0076] As an example, Figure 8Such a switchable LC stack is shown, which includes three PBP lenses 211, 212 and 213 with nominal optical powers of 1D, 0.5D and 0.25D. The first PBP lens 211 is preceded by a RHC polarizer 221 and a first s-HWP 231. The second s-HWP 232 is arranged between the first PBP lens 211 and the second PBP lens 212, and the third s-HWP 233 is arranged between the second PBP lens 212 and the third PBP lens 213, which may be followed by a fourth s-HWP 234 and a clean-up RHC polarizer 222. The arrangement can be switched between 8 focal lengths corresponding to -1.75D, -1.25D, -0.75D, -0.25D, 0.25D, 0.75D, 1.25D and 1.75D. In embodiments with active PBP lenses that can turn off optical power, the optical power of the stack can be stepped from -1.75D to +1.75D in steps of 0.25D. Other arrangements with different numbers (e.g., more) of PBP lenses can also be used. Increasing the number of PBP lenses can expand the adjustable focal length range and / or reduce the step size in which the focal length can be adjusted. In some embodiments, such as where some PBP lenses are active, the number of PBP lenses can exceed the number of s-HWPs in the stack.

[0077] exist Figure 8 The zoom lens stack 200 shown in the enlarged view in FIG. 1 includes three LC PBP lenses as an example. Typically, Figure 8 A zoom lens stack of the type shown may include any number N ≥ 1 of PBP lenses, at least some of which are used for switching before or after the s-HWP. The elements of the stack may be sequentially laminated on a common surface or carrier, with the sequential elements optionally sharing a substrate, to provide an integrated LC stack, such as Fig. 9 The PBP lens before or after the s-HWP can be referred to as a switchable lens pair or a switchable lens unit.

[0078] Fig. 9 An exemplary embodiment is shown in which N≥2 switchable lens pairs 320 of a switchable LC stack 310 are sequentially stacked to form a variable focus LC block 350, which can be sandwiched between two CP polarizers 321 and 322. In some embodiments, the input CP polarizer 321 can be co-laminated as part of the variable focus LC block 350, or can be a separate element, such as laminated on a light reflective surface of an electronic display.

[0079] refer to Fig.10 , we noticed that when using in HMD Figure 8When a switchable LC stack of the type shown in FIG. 9 is used to provide dynamically adjustable focus, such as within the optical block 155 of the HMD 100, a ring artifact can sometimes be observed in the pupil plane or eye box 157 of the HMD. Fig.10 These ring artifacts 337, schematically represented as concentric rings in FIG, can be in the form of multi-color ring modulations superimposed on or added to the image formed by the HMD. These ring artifacts may be due to the limited polarization selection efficiency of the PBP lens and / or the s-HWP, resulting in polarization leakage, whereby the undesired polarization state leaks into subsequent elements of the stack. The leakage of the undesired polarization state to subsequent polarization selective elements and / or through the clean-up or output polarizers may produce a non-uniform transmission pattern. We have also found that the ring artifacts 337 can be substantially eliminated or at least reduced when using a switchable LC stack with a first PBP lens receiving unpolarized light.

[0080] Fig.11 An example stack 510 of polarization selective elements that receives non-polarized image light 401 is shown. In the context of this specification, "non-polarized light" may refer to a beam having a degree of polarization (DOP) of at most 30%, or preferably at most 10%. The stack 410 may be formed by a series of switchable lens pairs 320. In operation, each PBP lens of the stack and each of its switchable lens pairs 320 outputs LHCP and RHCP beams, thereby adding a power Di to one of the output beams and subtracting the power Di from the other; where Di is the nominal power of the i-th PBP lens of the stack under consideration. If the non-polarized image light 401 is collimated, one of the CP output beams diverges and the other converges. Typically, the stack 410 switchably converts the non-polarized image light 401 into two orthogonal polarized beams 403, 402 with different converging characteristics. The conversion performed by the stack can switch between two states, namely, a state in which the stack adds optical power to the output RHCP beam and subtracts optical power from the output LHCP beam, and a state in which the stack adds optical power to the output RHCP beam and subtracts optical power from the output RHCP beam. In an embodiment in which the unpolarized image light 401 is collimated, the stack outputs a converging beam and a diverging beam, such as Fig.11 Each beam can be switched between two orthogonal polarization states, as shown at 402 and 403, respectively. Thus, stack 410 can switchably convert the unpolarized light it receives into two orthogonal polarized beams 402 and 403. Each of the two orthogonal polarized beams can be switched between two or more converging states, such as described above with reference to Figure 8 The stack of PBP lenses with three different optical powers is described as follows. The final CP selection can be performed by the last s-HWP in the stack in cooperation with the output polarizer 322. Stacked consecutive polarization-selective elements, such as PBP lenses and s-HWPs, can be as Fig.11 In some embodiments, the output polarizer 322 may be in direct contact with the stack, or they may be spaced apart from each other. In some embodiments, the output polarizer 322 may be part of the stack, for example, the last element thereof in the direction of beam propagation. In some embodiments, the output polarizer 322 may be outside the stack.

[0081] In some embodiments, the number of PBP lenses in the stack 410 may be different from the number of s-HWPs. Some embodiments of the stack 410 may combine one or more active (i.e., switchable) PBP lenses with a switchable HWP. An active LC PBP lens may be switched to a neutral state, in which it does not affect the optical power of the system and does not change the polarization of light passing through the lens. In its active state, the active LC PBP lens adds optical power to the system for CP light with one chirality and subtracts optical power from the system for CP light with the opposite chirality. A PBP lens that adds optical power when receiving LHCP light may be referred to as an LHPBP lens, and a PBP lens that adds optical power when receiving RHCP light may be referred to as an RH PBP lens.

[0082] Fig. 12A and Fig. 12B An exemplary switchable stack is shown, which includes two active PBP lenses 311 and 312, followed by s-HWP 333 and CPr 322. The first active PBP lens 311 may have a nominal optical power D1, such as 1D, and the second active PBP lens 312 may have a nominal optical power D2, such as 0.5D. Fig. 12A In the embodiment, the first and second PBP lenses 311, 312 have the same chirality, for example both are LH PBP lenses, and the stack includes a passive HWP disposed between the two PBP lenses for converting the circular polarization passing through the first PBP lens 311 back to its input chirality before entering the second PBP lens 312. However, if the consecutive PBP lenses have opposite chirality, i.e., a RH PBP lens immediately follows or precedes a LH PBP lens, then there may be no need to have a passive HWP between the two active PBP lenses. Fig. 12B In the embodiment, the second active PBP lens 312 has an opposite chirality to the first PBP lens 311, for example, if the first PBP lens 311 is a LH PBP lens, it can be a RH PBP lens; therefore, in Fig. 12B The passive HWP 331 between the two PBP lenses 311, 312 is omitted.

[0083] When both active PBP lenses 311, 312 are in a neutral state, Fig. 12A and 12BEach stack shown in 333 essentially acts as a CP polarizer for an input unpolarized light 301 with zero total optical power. When both active PBP lenses 311, 312 are in their active state, the output s-HWP 333 receives two CP beams 302, 303 with opposite chirality and different converging / diverging beam characteristics, one with increased positive optical power, i.e. (D1+D2), e.g. 1.5D, and the other with increased negative optical power, i.e. -(D1+D2), e.g. -1.5D. By switching the output s-HWP 333 on and off, the total optical power of the stack is switched between +(D1+D2) and -(D1+D2). When one of the active PBP lenses 311 and 312 is in its active state and the other is in its passive state, the total optical power of the stack can be switched by the output s-HWP 333 between +\-D2 (if the first active PBP lens 311 is in its neutral state, e.g., +\-0.5D), or between +\-D1 (if the second active PBP lens 312 is in its neutral state, e.g., +\-1D). Therefore, when D1≠D2, Fig. 12A and 12B Each stack shown in FIG. 1 can be operated as a zoom lens whose optical power can be switched between 7 different states - (-D1+D2), -D1, -D2, 0, +D2, +D1 and +(D1+D2). The number of states with different optical powers that the stack can switch between can be increased by adding a PBP lens to the stack, and if the PBP lens has the same chirality, an additional HWP can be placed after or before it.

[0084] Reference Fig.13 , shows an exemplary wearable display system or HMD 400 utilizing a switchable LC stack 510. The switchable LC stack 510 may be, for example, as described above with reference to Figures 11 to 12B The embodiment described above can be operated as a variable focus lens and can be implemented without an input polarizer to receive unpolarized light. Figures 6 to 12B Elements that function the same or similarly are described are denoted by the same reference numerals. HMD 400 may be viewed as an embodiment or modification of HMD 100, wherein electronic display 453 emits unpolarized light and the optical block comprises a pancake lens 455 disposed downstream of switchable LC stack 510. HMD 400 may comprise other optical elements instead of or in addition to pancake lens 455 as described above with reference to optical block 155. It is observed that removing the input polarizer upstream of the first PBP lens of stack 510, such that switchable LC stack 510, or at least the first PBP element thereof, receives unpolarized image light from display 453, substantially eliminates the appearance of ring artifacts at the eye box.

[0085] Reference Fig.14, a wearable display system or HMD 500 is shown having an electronic display 553 that emits linearly polarized image light. One example is an LC-based electronic display in which light is substantially modulated by controlling its polarization, and thus polarized light is typically output. In such an embodiment, a depolarizer 530 may be provided upstream of the switchable LC stack 510 to depolarize polarized light from the display. In some embodiments, in which the polarization of the image light emitted by the display is linear, the depolarizer 530 may be specifically configured to depolarize linearly polarized light. In embodiments in which the polarization of the image light emitted by the display is circular, the depolarizer 530 may be specifically configured to depolarize CP light. It was observed that adding the depolarizer 530 in the optical path between the electronic display 553 and the first PBP lens of the switchable LC stack 510, such that the switchable LC stack 510 receives unpolarized image light, substantially eliminates or at least mitigates the ring artifact. In Fig.14 , similar in functionality to the above reference Figure 6 to Figure 1 2 are denoted by the same reference numerals. It should be understood that Fig.13 The HMD architecture shown in allows for various modifications. For example, in some embodiments, in addition to Fig.14 In addition to the optical elements shown in , the optical block of the HMD may include other optical elements. In some embodiments, the optical elements or devices shown may be arranged in a different order. Fig.15 An exemplary embodiment 600 of the HMD 500 is shown in which the depolarizer 530 and the switchable LC stack 510 are disposed downstream of the pancake lens 455 .

[0086] In some embodiments, the depolarizer 530 may be included in a switchable LC stack, such as the stack 510 or 410 described above, and may be formed therewith as Fig.16 Manifold 610 is shown. In some embodiments, the depolarizer can be a separate component. In some embodiments, the depolarizer can be laminated on another component of the HMD, such as on a pixelated surface of the electronic display 553 that emits polarized image light.

[0087] In embodiments where the depolarizer 530 operates as a diffuser that spatially perturbs the optical phase of light passing through it in a random or quasi-random manner, it may be preferred to position the depolarizer near the electronic display 553. In some embodiments, the depolarizer may be positioned at a distance d from the display, where each position receives image light emitted by at most only a few (e.g., four) adjacent pixels (e.g., pixels that are immediately adjacent to each other). In some embodiments, the depolarizer-display distance d≤p·cot(β), where p is the pixel pitch and β is half the emission angle of the pixel. In some embodiments, the depolarizer may be placed in direct contact with the pixelated face of the electronic display 553, such as a liquid crystal display panel or an LED array panel. In some embodiments, the depolarizer may be laminated to the electronic display 553. In some embodiments, the layers of the switchable LC stack 510 may be laminated on the depolarizer on the electronic display 553.

[0088] Fig.17 An example depolarizer 700 that can be used as a depolarizer 530 in some embodiments of the present disclosure is schematically shown. The depolarizer 700 can be in the form of a wave plate with a birefringent layer of some retardation Q, or include such a wave plate, wherein the in-plane orientation of the optical axis 701 of the wave plate (e.g., described by its azimuth in the plane of the layer) varies spatially across the wave plate. In some embodiments, the azimuth of the optical axis 701 varies up to + / -90° or more across a region of the wave plate, randomly, pseudo-randomly, or according to some suitable function or rule, and the region of the wave plate is several times smaller than the total working area of ​​the wave plate. In some embodiments, the length l over which the optical axis 701 can be rotated at least 90 degrees can be at least 2 times smaller than the dimension a of the working area of ​​the wave plate in at least one direction across the wave plate (e.g., in the x-axis or y-axis directions shown in the figure), and preferably 5-10 times smaller. In some embodiments, the length l, which can be referred to as the correlation length, can be at least 2 times smaller than the dimension of the working area of ​​the wave plate in any direction across the wave plate, and preferably 5-10 times smaller. Here, the working area of ​​the wave plate is the area illuminated by the light beam that the wave plate operates on. In some embodiments, for example when the depolarizer 700 is placed adjacent to or close to an electronic display (e.g., the electronic display 553 of the display system 500), the correlation length l of the optical axis of the depolarizer 700 can be smaller than the pixel size b of the display, for example, 2-5 times smaller, so that the light from each pixel of the display exhibits a certain range of polarization states and is depolarized.

[0089] The depolarizer 700 can be formed by a layer of birefringent material having uniform in-plane birefringence and the same retardation Q across the layer. In some embodiments, the depolarizer 700 can be configured to depolarize linearly polarized light. In some embodiments, the retardation Q corresponds to a half-wave retardation, so that the depolarizer 700 is a HWP with a spatially varying in-plane optical axis orientation. In some embodiments, the in-plane spatial variation of the optical axis orientation can be random or pseudo-random, where the in-plane correlation length l is at least 5 times smaller than the characteristic dimension a of the working area of ​​the depolarizer (i.e., its dimensions in each x and y in-plane dimension or the expected diameter of the incident light beam). In some embodiments, the in-plane correlation length l can be at least 2 times smaller than the pixel size b of the electronic display coupled to the depolarizer. In some embodiments, the in-plane correlation length l can be at least 5 times smaller than the pixel size b of the electronic display coupled to the depolarizer. It is also conceivable that the orientation of the optical axis 701 varies in a slightly regular manner across the wave plate, although in some cases this may result in the appearance of visual artifacts.

[0090] In some embodiments, the depolarizer 700 may be in the form of an LC wave plate, such as an LC HWP, whose in-plane orientation of the optical axis 701, as may be defined by the orientation of the LC director, varies spatially in the plane of the LC layer. In some embodiments, the variation may be random or pseudo-random in the in-plane direction of the LC layer, wherein the dimension c of the region segment 703 plays the role of the optical axis correlation length l. In some embodiments, the LC wave plate may include a plurality of regions 703 having substantially the same delay, such as the delay of the HWP, but different in-plane orientations of the optical axis 701 or the LC director. In some embodiments, the in-plane orientation of the optical axis varies randomly or pseudo-randomly from one region segment 703 to the next. In the context of this specification, the term "pseudo-random" refers to a statistical process that can be simulated using a computer-implemented pseudo-random number generator. In some embodiments, the LC layer comprises a nematic LC material. In some embodiments, the nematic LC material may be a twisted nematic LC for wide spectrum operation. In some embodiments, the LC layer may be stabilized by a polymer network.

[0091] In some embodiments, the following “phase randomization” conditions may be satisfied:

[0092]

[0093] where N is the number of segments across the active area of ​​the wave plate in the in-plane dimension (i.e., along the x-axis or y-axis, or along any diameter of a circular wave plate), and is an in-plane vector of unit length whose direction corresponds to the characteristic in-plane direction of the optical axis 701 of the i-th region segment. In some embodiments, the dimension c of the region segment 703 can be smaller than the pixel pitch p of the electronic display to which the depolarizer is coupled when placed adjacent to the electronic display. In some embodiments, the dimension c of the region segment 703 can be at least 2 times smaller than the pixel pitch p. In some embodiments, the dimension c of the region segment 703 can be at least 5 times smaller than the pixel pitch p.

[0094] refer to Fig.18 , the LC depolarizer 700 can be manufactured as follows: on a substrate (eg, Figure 1 An orientation layer 800 of a photo-orientable material is selectively deposited on a substrate 30 (shown in FIG. 1 ), and the orientation layer 800 is exposed to UV light having a spatially varying polarization so as to orient the molecules of the orientation layer in a spatially varying direction as described above. In some embodiments, the polarized UV beam can be focused on a region segment 803 of the orientation layer 800 so as to orient the material of the orientation layer in an orientation direction 801 defined by the polarization of the UV beam. The UV beam can then be stepped across the orientation layer segment by segment, changing its polarization at each step in a random or pseudo-random manner so as to form an array of region segments 803 of the orientation layer 800 with random or pseudo-random orientation of the orientation direction 801. In some embodiments, the mask can be step-by-step and used to pseudo-randomly change the linear polarization of the UV beam and / or the exposed area, while changing the beam polarization, or more generally changing the aggregated beam of the aggregated wavelength. Next, a layer of LC material can be deposited (e.g., spin-coated) on the orientation layer 800, wherein the LC director is oriented in each region segment 803 along the orientation direction 801 in that segment. In some embodiments, the LC material can then be polymerized under UV light, for example in the presence of nitrogen, to fix the LC orientation in a random or pseudo-random pattern. In some embodiments, a second substrate can optionally be attached to the first substrate to cover the LC layer. In some embodiments, the LC material comprises a nematic LC. In some embodiments, the LC material comprises a chiral or twisted nematic LC. In some embodiments, the pitch of the chiral LC material of the LC layer - that is, the distance it takes for the LC director to rotate one full turn in a spiral in a direction perpendicular to the LC layer - can be selected to provide HWP retardation for visible light. In some embodiments, a chiral dopant or chiral material can be added to the LC material.

[0095] Reference Fig.19 , Fig. 20A and Fig. 20BIn some embodiments, the delay compensation method can be used to provide HWP operation over a wide wavelength range (e.g., across the RGB spectrum). According to an embodiment of the method, the broadband depolarizer 900 may include a depolarizing bilayer 920 disposed on an optional substrate 910. The depolarizing bilayer 920 may be flat or curved and may be formed by two depolarizing layers of chiral liquid crystal stacked on each other, namely a first layer 921 and a second layer 922. The LC director of each layer is Fig. 20A and Fig. 20B The projection on the plane of the layer is indicated by 903. The first layer 921 has an LC director 903 ( Fig. 20A , Fig. 20B ), wherein the thickness direction is perpendicular to the substrate 910 ( Fig.19 The second layer 922 of twisted LC material is disposed on the first layer 921, and the LC director 903 has a second twist sense in the thickness direction, wherein the second twist sense in the second layer is opposite to the first twist sense in the first layer. The first layer 921 as the lower layer can be disposed on the orientation layer 915 and the optically transparent optional substrate 910. The LC director 903 of the first layer is at a specific distance from the substrate 910, for example, at the interface with the second layer 922, such as Fig. 20A The solid arrows in FIG. 1 schematically show directions that vary randomly or pseudo-randomly in the plane (x, y) of the substrate. The alignment layer 915 can be randomly photo-oriented, for example, as described above with reference to Fig.18 The LC director 903 is located at the nth segment ( Fig.19 , the orientation in the vertical (x, z) section of the LC director (not shown) can be described by the azimuthal angle φ(n,x,z), which can vary according to equation (2):

[0096]

[0097] Here d is the thickness of each depolarization layer, i.e., the first layer 921 and the second layer 922, Φn is the azimuth angle of the LC director in the first layer 921 at the boundary with the alignment layer 915 in the n-th region segment of the depolarizer 900, and may be referred to as the base angle of the LC director of the n-th segment. The base angle values ​​{Φn} may form a random or pseudo-random set having a uniform probability distribution over a range of 180 degrees.

[0098] Fig. 20A and Fig. 20B The orientation of the LC director 903 in the nth segment at different distances from the alignment layer 915 is schematically shown in plan view. Fig. 20A, the orientation of the LC director 903 is schematically shown as a dotted arrow at the boundary with the orientation layer 915, a dashed arrow in the middle of the first layer 921, and a solid arrow at the boundary with the second layer 922. Fig. 20B , the orientation of the LC director 903 is schematically shown as a dotted arrow at the boundary with the first layer 921, a dashed arrow in the middle of the second layer 922, and a solid arrow at the top surface of the second layer 922. Therefore, in this example, the LC directors 903 in the first layer 921 and the second layer 922 have opposite twist senses, and the absolute value of the twist angle Φ in each layer is equal, where the total twist angle across the two layers is zero. The first layer 921 and the second layer 922 can each have a thickness of a half-wave plate within the operating wavelength range, thereby providing a total retardation of HWP for the double layer 920.

[0099] By adding chiral dopants of opposite chirality to a curable polymer liquid crystal mixture (CPLCM), an opposite sense of twist along the thickness of the layer can be obtained. A chiral dopant with right-handed (RH) chirality can be used to form one layer, and a chiral dopant with left-handed (LH) chirality can be used to form another layer. The method may include depositing a linear photopolymerizable polymer (LPP) onto a suitable substrate to form an alignment layer, recording a desired random or pseudo-random orientation pattern into the alignment layer, coating the alignment layer with a first CPLCM layer doped with a suitable chiral molecule of a first chirality (e.g., RH) to form a first layer 921, and depositing a second CPLCM layer doped with a suitable chiral molecule of a second chirality (e.g., LH) on the first CPLCM layer to form a second layer 922. In other embodiments, an LH chiral dopant can be used for the first layer, and an RH chiral dopant can be used for the second layer. Examples of suitable chiral dopants include chiral dopants R811 (right-handed) and S811 (left-handed) available from Merck & CO., Inc. The degree of twist or twist angle Φ in each layer is determined by the layer thickness d and the pitch of the chiral LC solution (i.e. the distance it takes the LC director to make one full rotation in the helix in a direction perpendicular to the LC layers). The chiral pitch (p) is related to the concentration of the chiral dopant (c) and the helical twisting power (HTP) (p = 1 / (HTP*c).

[0100] It should be understood that other types of depolarizers can be used in conjunction with the switchable LC stack in NED and other compact display systems, including but not limited to LC-based depolarizers, non-LC depolarizers, and depolarizers capable of depolarizing CP light. In addition, many variations and modifications of the above-described exemplary embodiments will be apparent to those of ordinary skill in the art in light of the foregoing description and accompanying drawings. For example, in some embodiments, in addition to or in place of the above-described PBP lens, the switchable multilayer LC stack operating with unpolarized incident light may include other PBP optical elements, such as PBP gratings (see, e.g., Figure 3B ). For example, in some embodiments, each PBP lens in the switchable stack 410 or 510 can be replaced with a polarization grating such as a PBP grating to provide a switchable image light shifter or deflector. Similarly, in some embodiments, Fig. 12A , Fig. 12B Each active PBP lens in the exemplary switchable stack shown can be replaced with an active polarization grating (e.g., an active LC PBP grating). In some embodiments, using such a switchable beam deflector with unpolarized light can reduce circular or linear visual artifacts that may appear due to polarization leakage. In some embodiments, a depolarizer can be used as part of the HDM before a non-switchable LC stack, which can include a polarizer or polarization selector.

[0101] Embodiments of the present disclosure may include an artificial reality system or be implemented in conjunction with an artificial reality system. The artificial reality system adjusts sensory information about the external world obtained through senses such as visual information, audio, touch (somatosensory) information, acceleration, balance, etc. in some way before presenting it to the user. As a non-limiting example, artificial reality may include virtual reality (VR), augmented reality (AR), mixed reality (MR), mixed reality, or some combination and / or derivative thereof. Artificial reality content may include fully generated content or generated content combined with captured (e.g., real world) content. Artificial reality content may include video, audio, somatic or tactile feedback, or some combination thereof. Any of the content may be presented in a single channel or multiple channels, such as in a stereoscopic video that produces a three-dimensional effect on the viewer. In addition, in some embodiments, artificial reality may also be associated with an application, product, accessory, service, or some combination thereof, which is used, for example, to create content in artificial reality and / or otherwise used in artificial reality (e.g., performing activities in artificial reality). Artificial reality systems that provide artificial reality content may be implemented on a variety of platforms, including wearable displays such as HMDs connected to a host system, standalone HMDs, near-eye displays with eyeglass form factors, mobile devices or computing systems, or any other hardware platform capable of providing artificial reality content to one or more viewers.

[0102] Reference Fig.21A , HMD 1100 is an example of an AR / VR wearable display system that surrounds the user's face for greater immersion in an AR / VR environment. HMD 1100 may be, for example Fig.13 Wearable display system 400 or Fig.14 An embodiment of a wearable display system 500 of the present invention. The function of the HMD 1100 is to enhance the view of the physical, real environment with computer-generated images, and / or to generate a completely virtual 3D image. The HMD 1100 may include a front body 1102 and a band 1104. The front body 1102 is configured to be placed in front of the user's eyes in a secure and comfortable manner, and the band 1104 can be stretched to secure the front body 1102 on the user's head. The display system 1180 can be set in the front body 1102 for presenting AR / VR images to the user. The side 1106 of the front body 1102 can be opaque or transparent.

[0103] In some embodiments, the front body 1102 includes a positioner 1108 and an inertial measurement unit (IMU) 1110 for tracking the acceleration of the HMD 1100, and a position sensor 1112 for tracking the position of the HMD 1100. The IMU 1110 is an electronic device that generates data indicating the position of the HMD 1100 based on measurement signals received from one or more position sensors 1112, which generate one or more measurement signals in response to the movement of the HMD 1100. Examples of the position sensor 1112 include: one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects movement, a type of sensor used for error correction of the IMU 1110, or some combination thereof. The position sensor 1112 may be located outside the IMU 1110, inside the IMU 1110, or some combination thereof.

[0104] The localizer 1108 is tracked by an external imaging device of the virtual reality system so that the virtual reality system can track the position and orientation of the entire HMD 1100. The information generated by the IMU 1110 and the position sensor 1112 can be compared with the position and orientation obtained by tracking the localizer 1108 to improve the tracking accuracy of the position and orientation of the HMD 1100. As the user moves and turns in 3D space, the accurate position and orientation can help present the user with an appropriate virtual scene.

[0105] The HMD 1100 may also include a depth camera assembly (DCA) 1111 that captures data describing depth information of a local area surrounding part or all of the HMD 1100. To this end, the DCA 1111 may include a laser radar (LIDAR) or similar device. The depth information may be compared with information from the IMU 1110 to better accurately determine the position and orientation of the HMD 1100 in 3D space.

[0106] The HMD 1100 may also include an eye tracking system 1114 for determining the orientation and position of the user's eyes in real time. The position and orientation of the eyes obtained may allow the HMD 1100 to determine the gaze direction of the user and adjust the image generated by the display system 1180 accordingly. In one embodiment, the convergence, i.e., the convergence angle of the gaze of the user's eyes, is determined. The determined gaze direction and convergence angle may also be used to compensate for visual artifacts that depend on the viewing angle and eye position in real time. In addition, the determined convergence and gaze angles may be used to interact with the user, highlight objects, bring objects to the foreground, create additional objects or pointers, etc. An audio system may also be provided, comprising, for example, a set of small speakers built into the front body 1102.

[0107] Reference Fig. 21B, the AR / VR system 1150 may be Fig.13 Wearable display system 400, Fig.14 Wearable display system 500 or Fig.15 An example implementation of the wearable display system 600 of FIG. 1150 includes: Fig.21A The HMD 1100 includes an external console 1190 that stores various AR / VR applications, setup and calibration procedures, 3D videos, etc.; and an input / output (I / O) interface 1115 for operating the console 1190 and / or interacting with the AR / VR environment. The HMD 1100 can be "tethered" to the console 1190 via a physical cable, or via a wireless communication link (e.g., Wi-Fi, etc.) to the console 1190. There may be multiple HMDs 1100, each with an associated I / O interface 1115, wherein each HMD 1100 and I / O interface 1115 communicate with the console 1190. In alternative configurations, different and / or additional components may be included in the AR / VR system 1150. In addition, in some embodiments, the combination Fig.21A and Fig. 21B The functionality described in one or more of the components shown may be combined with Fig.21A and Fig. 21B The described methods are distributed among the components in different ways. For example, some or all of the functions of the console 1190 may be provided by the HMD 1100, or vice versa. The HMD 1100 may be equipped with a processing module capable of implementing such functions.

[0108] As above reference Fig.21A As described above, the HMD 1100 may include an eye tracking system 1114 (eg, a system for tracking eye position and orientation, determining gaze angle and convergence angle, etc.) Fig. 21B ); an IMU 1110 for determining the position and orientation of the HMD 1100 in 3D space; a DCA 1111 for capturing the external environment; a position sensor 1112 for independently determining the position of the HMD 1100; and a display system 1180 for displaying AR / VR content to the user. The display system 1180 includes ( Fig. 21B) electronic display 1125, such as but not limited to: a liquid crystal display (LCD), an organic light emitting display (OLED), an inorganic light emitting display (ILED), an active matrix organic light emitting diode (AMOLED) display, a transparent organic light emitting diode (TOLED) display, a projector or a combination thereof. The display system 1180 also includes an optical block 1130, whose function is to transmit the image generated by the electronic display 1125 to the user's eyes. The optical block may include various lenses, such as refractive lenses, Fresnel lenses, diffractive lenses, active or passive PB phase (PBP) lenses, liquid lenses, liquid crystal lenses, etc., pupil replica waveguides, grating structures, coatings, etc. The display system 1180 may also include a zoom module 1135, which may be part of the optical block 1130. The function of the zoom module 1135 is to adjust the focus of the optical block 1130, such as compensating for visual convergence and accommodation conflicts, correcting visual defects of a specific user, offsetting aberrations of the optical block 1130, etc. The zoom module 1135 may, for example, be used with a lens such as Fig.11 , Fig. 12A , Fig. 12B , Fig.15 The switchable PBP lens groups shown, their variations and combinations are implemented, and in some embodiments may include a depolarizer.

[0109] The I / O interface 1115 is a device that allows a user to send an action request and receive a response from the console 1190. An action request is a request to perform a specific action. For example, an action request may be an instruction to start or end the capture of image or video data or an instruction to perform a specific action within an application. The I / O interface 1115 may include one or more input devices, such as a keyboard, a mouse, a game controller, or any other suitable device for receiving an action request and transmitting the action request to the console 1190. The action request received by the I / O interface 1115 is transmitted to the console 1190, and the console 1190 performs an action corresponding to the action request. In some embodiments, the I / O interface 1115 includes an IMU that captures calibration data indicating an estimated position of the I / O interface 1115 relative to the initial position of the I / O interface 1115. In some embodiments, the I / O interface 1115 may provide tactile feedback to the user according to the instructions received from the console 1190. For example, tactile feedback may be provided when an action request is received, or the console 1190 transmits instructions to the I / O interface 1115 so that the I / O interface 1115 generates tactile feedback when the console 1190 performs an action.

[0110] The console 1190 may provide content to the HMD 1100 for processing based on information received from one or more of the following: the IMU 1110, the DCA 1111, the eye tracking system 1114, and the I / O interface 1115. Fig. 21BIn the example shown, the console 1190 includes an application memory 1155, a tracking module 1160, and a processing module 1165. Some embodiments of the console 1190 may have a Fig. 21B Similarly, the functions described further below may be combined with Fig.21A and Fig. 21B The described methods are distributed among the components of console 1190 in different ways.

[0111] The application memory 1155 may store one or more applications executed by the console 1190. An application is a set of instructions that, when executed by a processor, generates content for presentation to a user. The content generated by the application may be responsive to input received from the user via movement of the HMD 1100 or the I / O interface 1115. Examples of applications include: gaming applications, presentation and conferencing applications, video playback applications, or other suitable applications.

[0112] The tracking module 1160 may calibrate the AR / VR system 1150 using one or more calibration parameters, and may adjust the one or more calibration parameters to reduce errors in the position determination of the HMD 1100 or the I / O interface 1115. The calibration performed by the tracking module 1160 also takes into account information received from the IMU 1110 in the HMD 1100 and / or the IMU (if any) included in the I / O interface 1115. In addition, if tracking of the HMD 1100 is lost, the tracking module 1160 may recalibrate some or all of the AR / VR system 1150.

[0113] The tracking module 1160 may track the movement of the HMD 1100 or the I / O interface 1115, the IMU 1110, or some combination thereof. For example, the tracking module 1160 may determine the location of a reference point of the HMD 1100 in a map of the local area based on information from the HMD 1100. The tracking module 1160 may also determine the location of the reference point of the HMD 1100 or the reference point of the I / O interface 1115 using data from the IMU 1110 indicating the location of the HMD 1100 or using data from an IMU included in the I / O interface 1115 indicating the location of the I / O interface 1115, respectively. Furthermore, in some embodiments, the tracking module 1160 may use partial data from the IMU 1110 indicating the location of the HMD 1100 and a representation of the local area from the DCA 1111 to predict the future location of the HMD 1100. The tracking module 1160 provides the estimated or predicted future position of the HMD 1100 or the I / O interface 1115 to the processing module 1165 .

[0114] The processing module 1165 may generate a 3D map of an area surrounding part or all of the HMD 1100 (a "local area") based on information received from the HMD 1100. In some embodiments, the processing module 1165 determines depth information for the 3D map of the local area based on information related to a technique for calculating depth received from the DCA 1111. In various embodiments, the processing module 1165 may use the depth information to update a model of the local area and generate content based in part on the updated model.

[0115] The processing module 1165 executes an application within the AR / VR system 1150 and receives position information, acceleration information, velocity information, predicted future position, or some combination thereof of the HMD 1100 from the tracking module 1160. Based on the received information, the processing module 1165 determines the content to be provided to the HMD 1100 for presentation to the user. For example, if the received information indicates that the user has looked to the left, the processing module 1165 generates content for the HMD 1100 that reflects the user's movement in a virtual environment or in an environment that enhances a local area with additional content. In addition, the processing module 1165 performs an action within an application executed on the console 1190 in response to an action request received from the I / O interface 1115, and provides feedback to the user of the execution of the action. The feedback provided may be visual or auditory feedback via the HMD 1100 or tactile feedback via the I / O interface 1115.

[0116] In some embodiments, based on the eye tracking information (e.g., the orientation of the user's eyes) received from the eye tracking system 1114, the processing module 1165 determines the resolution of the content provided to the HMD 1100 for presentation to the user on the electronic display 1125. The processing module 1165 may provide the HMD 1100 with content having the maximum pixel resolution in the foveal region of the electronic display 1125 where the user is gazing. The processing module 1165 may provide lower pixel resolution in other areas of the electronic display 1125, thereby reducing the power consumption of the AR / VR system 1150 and saving computing resources of the console 1190 without compromising the user's visual experience. In some embodiments, the processing module 1165 may further use the eye tracking information to adjust the position of objects displayed on the electronic display 1125 to prevent visual convergence-accommodation conflicts and / or to counteract optical distortions and aberrations.

[0117] Hardware for implementing the various illustrative logics, logic blocks, modules, and circuits described in conjunction with the aspects disclosed herein may be implemented or executed using a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in an alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. The processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, a combination of multiple microprocessors, a combination of one or more microprocessors and a DSP core, or any other such configuration. Alternatively, some steps or methods may be performed by circuits specific to a given function.

[0118] The present disclosure is not limited to the scope of the specific embodiments described herein, and various other embodiments and modifications will become apparent to those skilled in the art of the present disclosure. Therefore, these other embodiments and modifications are intended to fall within the scope of the present disclosure. In addition, although the present disclosure has been described herein in the context of a specific implementation in a specific environment for a specific purpose, a person skilled in the art will recognize that its usefulness is not limited thereto, and the present disclosure may be advantageously implemented in any number of environments for any number of purposes. For example, the embodiments described herein with reference to a wearable display system such as an HMD may also be implemented in other display systems, such as, but not limited to, a heads-up display (heads-up display, or HUD) and a heads-down display (heads-down display). Therefore, the claims set forth herein should be interpreted according to the full scope of the present disclosure as described herein.

Claims

1. A head mounted device, comprising a display system, characterized in that: The display system comprises: a source of unpolarized image light; a stack of polarization selective optical elements arranged to receive the unpolarized image light and operable to switchably convert the unpolarized image light into two orthogonally polarized light beams; and an output polarizer arranged to receive the two orthogonally polarized light beams and configured to select one of the two orthogonally polarized light beams to form an image; The stack comprises one or more PBP optical elements, the one or more PBP optical elements comprising a plurality of PBP lenses having different nominal optical powers, at least one of the one or more PBP optical elements being configured to receive the unpolarized image light, and the stack comprising one or more switchable half-wave plates HWP.

2. The head mounted device according to claim 1, wherein: The display system is configured to be mounted on a user's head for displaying images near the eye, wherein the stack is devoid of an input polarizer.

3. The head mounted device according to claim 1, wherein: The stack is configured to operate as a variable focus lens.

4. The head mounted device according to claim 1, wherein: The plurality of PBP lenses include a switchable LCPBP lens.

5. The head mounted device according to claim 1, wherein: The plurality of PBP lenses include one or more passive PBP lenses, each passive PBP lens being followed by a switchable HWP.

6. The head mounted device according to any one of claims 1 to 5, characterized in that: The one or more PBP optical elements include a polarization grating, wherein the polarization grating is directly followed by a switchable HWP, and further wherein the polarization grating includes a LC PBP grating switchable to a non-diffractive state.

7. A head mounted device according to any one of claims 1 to 5, characterized in that: The source of unpolarized image light includes an electronic display configured to emit unpolarized light.

8. A head mounted device according to any one of claims 1 to 5, characterized in that: The source of unpolarized image light includes an electronic display configured to emit polarized image light and a depolarizer disposed in an optical path between the electronic display and the stack.

9. The head mounted device according to claim 8, wherein: The polarized image light is linearly polarized, and wherein the depolarizer comprises a half-wave plate (HWP) having a spatially randomized in-plane optical axis, wherein the depolarizer is disposed adjacent to the electronic display.

10. The head mounted device according to claim 8, wherein: The stack includes a series of LC PBP optical elements, each LC PBP optical element is paired with a switchable LC HWP.

11. The head mounted device according to claim 10, wherein: At least one of the polarization-selective optical elements of the stack comprises a switchable LC PBP optical element.

12. A method for processing image light based on polarization in a display system of a head mounted device, characterized in that: The method comprises: passing the unpolarized image light through a series of polarization selective optical elements to obtain two light beams of orthogonal polarizations, each light beam being switchable in at least one beam characteristic; and using an optical polarizer disposed downstream of the series of polarization selective optical elements to select one of the two orthogonally polarized light beams as an output light beam for forming an image, The polarization-selective optical element comprises one or more PBP optical elements and one or more switchable half-wave plates HWP, so that the unpolarized image light passes through the one or more PBP optical elements to obtain the two orthogonally polarized light beams, and the one or more PBP optical elements comprise a plurality of PBP lenses with different nominal optical powers.

13. The method according to claim 12, characterized in that include: Passing the polarized image light through a depolarizer to obtain the unpolarized image light for providing to the series of polarization selective optical elements, wherein the passing comprises passing the unpolarized image light through a series of PBP lenses having different nominal optical powers.

14. The method according to claim 12 or claim 13, characterized in that The passing includes passing the unpolarized image light through a series of polarization gratings.

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