Polarization-based variable focus imaging device

Abstract

To provide a favorable variable-focus image devices based on polarization conversion.SOLUTION: Example display devices include a waveguide configured to propagate visible light under total internal reflection in a direction parallel to a major surface of the waveguide. The waveguide has formed thereon an outcoupling element configured to outcouple a portion of the visible light in a direction normal to the major surface of the waveguide. The example display devices additionally include a polarization-selective notch reflector disposed on a first side of the waveguide and configured to reflect the visible light having a first polarization while transmitting the portion of the visible light having a second polarization. The example display devices further include a polarization-independent notch reflector disposed on a second side of the waveguide and configured to reflect the visible light having the first polarization and the second polarization, where the polarization-independent notch reflector is configured to convert the polarization of the visible light reflecting therefrom.SELECTED DRAWING: Figure 25A

Description

[Technical Field]

[0001] (References provided) This application claims the benefits of U.S. Provisional Patent Application No. 62 / 462,850, filed on 23 February 2017 and titled “VARIABLE-FOCUS VIRTUAL IMAGE DEVICES,” which is incorporated herein by reference in its entirety. This Provisional Patent Application includes the following sections, both of which are incorporated by reference and form part of this Application. 1. Section I: Specification and drawings relating to the portion of the application titled “DISPLAY SYSTEM WITH VARIABLE POWER REFLECTOR” 2. Section II: Specification and drawings titled “VARIABLE-FOCUS VIRTUAL IMAGE DEVICES BASED ON POLARIZATION CONVERSION”

[0002] Both Section I and Section II discuss variable focus or variable refractive power devices and features associated with these devices, and both sections equally form part of the discussion of this application. Therefore, the various features, elements, structures, methods, etc. discussed in Section I may be used, combined with, incorporated into, or otherwise compatible with the features, elements, structures, methods, etc. discussed in Section II in any combination. Similarly, the various features, elements, structures, methods, etc. discussed in Section II may be used, combined with, incorporated into, or otherwise compatible with the features, elements, structures, methods, etc. discussed in Section I in any combination.

[0003] This application also incorporates by reference, in whole, each of the following patent applications: U.S. Application No. 14 / 555,585 (filed November 27, 2014); U.S. Application No. 14 / 690,401 (filed April 18, 2015); U.S. Application No. 14 / 212,961 (filed March 14, 2014); and U.S. Application No. 14 / 331,218 (filed July 14, 2014).

[0004] (Field) This disclosure relates to a display system, and more specifically, to an augmented reality display system comprising at least partially a polarization conversion-based diffraction device. [Background technology]

[0005] Modern computing and display technologies are driving the development of systems for so-called "virtual reality" or "augmented reality" experiences, where digitally reproduced images or parts thereof are presented to the user in a manner that appears, or can be perceived, as real. Virtual reality, or "VR," scenarios typically involve the presentation of digital or virtual imagery without transparency to other real-world visual inputs, while augmented reality, or "AR," scenarios typically involve the presentation of digital or virtual imagery as an extension of the user's visualization of the real world around them. Mixed reality, or "MR," scenarios are a type of AR scenario that typically involves virtual objects integrated into and responding to the natural world. For example, in an MR scenario, AR imagery may appear blocked by, or be perceived as interacting with, objects in the real world in a different way.

[0006] Referring to Figure 1, Augmented Reality Scene 1 is depicted, and the user of AR technology sees a real-world park-like setting 1100 featuring people, trees, buildings in the background, and a concrete platform 1120. In addition to these items, the user of AR technology also perceives "seeing" "virtual content" such as a robotic figure 1110 standing on the real-world platform 1120, and a flying cartoon-like avatar character 1130 that looks like an anthropomorphic bumblebee, even though these elements 1130, 1110 do not exist in the real world. The human visual perception system is complex, and producing AR technology that facilitates a comfortable, natural, and rich presentation of virtual image elements among other virtual or real-world image elements is difficult.

[0007] The systems and methods disclosed herein address various challenges related to AR or VR technologies. [Overview of the project] [Means for solving the problem]

[0008] This application includes a discussion of systems and methods that may be employed to provide variable refractive power. Variable focus or variable refractive power devices may find applications in certain head-mounted display devices that project images as if they originated from different depths. By changing the refractive power of optical elements within a head-mounted display device, images presented to the wearer of the head-mounted display device appear as if they were located at different distances from the wearer. Variable focus or variable refractive power optical devices can therefore be modulated to display different image content as if the image content were located at different locations relative to the user. Some variable refractive power elements include a reflector with a movable membrane. Other variable refractive power elements include a liquid crystal switchable device that can switch refractive power levels using a switchable liquid crystal element. Some variable focus devices described herein utilize the polarization properties of light to facilitate switching from one focus to another.

[0009] In one aspect, a display device includes a waveguide configured to propagate visible light under total internal reflection in a direction parallel to a major surface of the waveguide, and an external coupling element formed on the waveguide and configured to externally couple a portion of the visible light in a direction normal to the major surface of the waveguide. The display device further includes a polarization-selective notch reflector disposed on a first side of the waveguide and configured to reflect visible light having a first polarization while transmitting a portion of the visible light having a second polarization. The display device further includes a polarization-independent notch reflector disposed on a second side of the waveguide and configured to reflect visible light having the first polarization and visible light having the second polarization, and the polarization-independent notch reflector is configured to convert the polarization of the visible light reflected therefrom.

[0010] In another aspect, a display device includes a waveguide device interposed between a first switchable lens and a second switchable lens, the waveguide device including one or more cholesteric liquid crystal (CLC) layers each including a plurality of chiral structures, each chiral structure including a plurality of liquid crystal molecules extending in a layer depth direction and continuously rotated in a first rotation direction, and the arrangement of the liquid crystal molecules of the chiral structures varying periodically in a lateral direction perpendicular to the layer depth direction such that the one or more CLC layers are configured to Bragg reflect incident light. The waveguide device further includes one or more waveguides formed across the one or more CLC layers and configured to propagate visible light under total internal reflection (TIR) in a direction parallel to a major surface of the waveguide and to optically couple the visible light to and from the one or more CLC layers.

[0011] In another aspect, a display device configured to display an image to a user's eye includes an optical display. The optical display has a front side and a rear side, and the rear side is closer to the user's eye than the front side. The optical display is configured to output light having a wavelength range toward the rear side. A first notch reflector is disposed behind the optical display, and the first notch reflector is configured to reflect light having the wavelength range output from the optical display. A second notch reflector is disposed in front of the optical display, and the second notch reflector is configured to reflect light having the wavelength range. The first notch reflector is configured to substantially transmit light having a first polarization and substantially reflect light having a second polarization different from the first polarization. The second notch reflector is configured to convert light having the second polarization and incident on the rear surface into the first polarization and redirect the light rearward.

[0012] In another aspect, a dynamic focusing display system includes a display configured to output circularly polarized light in a first circular polarization state. The display is disposed along an optical axis and has a front side and a rear side, and the rear side is closer to the user's eye than the front side. The optical display is configured to output light having a wavelength range toward the rear side. A first switchable optical element is disposed along the optical axis, and the first switchable optical element is configured to change the circular polarization state of the light transmitted through the first switchable optical element from the first circular polarization state to a second different circular polarization state. A first cholesteric liquid crystal (CLC) lens is disposed in front of the first switchable optical element along the optical axis. A second switchable optical element is disposed in front of the first CLC lens along the optical axis, and the second switchable optical element is configured to change the circular polarization state of the light transmitted through the second switchable optical element from the first circular polarization state to a second different circular polarization state. A second CLC lens is disposed in front of the second switchable optical element along the optical axis. A controller is configured to electronically switch the states of the first and second switchable optical elements and dynamically select either the first CLC lens or the second CLC lens.

[0013] In another respect, a wearable augmented reality head-mounted display system is configured to allow light to pass from the world in front of the wearer into the wearer's eyes. A wearable augmented reality head-mounted display system comprises: an optical display configured to output light and form an image; one or more waveguides arranged to receive light from the display; a frame configured such that the one or more waveguides have a front side and a rear side, with the rear side being closer to the eye than the front side; a cholesteric liquid crystal (CLC) reflector positioned on the front side of the one or more waveguides, the CLC reflector being configured to have a refractive power or depth of focus adjustable in response to the application of an electrical signal; and one or more external coupling elements positioned relative to the one or more waveguides to extract light from the one or more waveguides and direct at least a portion of the light propagating within the waveguides to the CLC reflector, the light being directed back through the waveguides from the CLC reflector and into the wearer's eye to present an image from the display into the wearer's eye.

[0014] In another aspect, the display device comprises a waveguide configured to propagate visible light under total internal reflection parallel to the main surface of the waveguide and to externally couple the visible light in the direction normal to the main surface. A notch reflector is configured to reflect visible light having a first polarization, and the notch reflector comprises one or more cholesteric liquid crystal (CLC) layers, each CLC layer comprising a plurality of chiral structures, each chiral structure comprising a plurality of liquid crystal molecules extending in the layer depth direction and continuously rotating in a first rotational direction, wherein the arrangement of liquid crystal molecules in the chiral structures varies periodically in a lateral direction perpendicular to the layer depth direction, such that one or more CLC layers are configured to Bragg reflect incident light.

[0015] Details of one or more implementations of the subject matter described herein are provided in the accompanying drawings and the description below. Other features, aspects, and advantages will be evident from the description, drawings, and claims. Neither this summary nor the following detailed description claims to define or limit the scope of the subject matter of the invention. The present invention provides, for example, the following: (Item 1) A display device, A waveguide configured to propagate visible light under total internal reflection in a direction parallel to the main surface of the waveguide, An external coupling element, wherein the external coupling element is formed on the waveguide and configured to externally couple a portion of the visible light in the direction normal to the main surface of the waveguide, A polarization-selective notch reflector, wherein the polarization-selective notch reflector is positioned on the first side of the waveguide and is configured to transmit visible light having a second polarization while reflecting visible light having a first polarization, A polarization-independent notch reflector, wherein the polarization-independent notch reflector is positioned on the second side of the waveguide and is configured to reflect visible light having the first polarization and visible light having the second polarization, and the polarization-independent notch reflector is configured to convert the polarization of the visible light reflected therefrom. A display device equipped with the following features. (Item 2) The display device according to item 1, wherein the polarization-selective notch reflector and the polarization-independent notch reflector are each configured to transmit light having wavelengths outside the wavelength range while reflecting visible light having wavelengths within the wavelength range corresponding to one of red, green, or blue light. (Item 3) The display device according to item 1, wherein the polarization-selective notch reflector comprises one or more cholesteric liquid crystal (CLC) layers. (Item 4) Each of the one or more CLC layers comprises multiple chiral structures, Each of the chiral structures comprises a plurality of liquid crystal molecules, the plurality of liquid crystal molecules extending in the layer depth direction by at least a helical pitch and continuously rotating in a first rotational direction. The helical pitch is the length in the layer depth direction that corresponds to the net rotation angle of the chiral liquid crystal molecule due to one complete rotation in the first rotation direction. The arrangement of the chiral liquid crystal molecules fluctuates periodically in the lateral direction perpendicular to the layer depth direction. The display device described in item 3. (Item 5) The display device according to item 3, wherein the first polarization is a first circular polarization and the second polarization is a second circular polarization. (Item 6) The display device according to item 1, further comprising a first quarter-wave plate and a second quarter-wave plate, wherein the polarization-independent notch reflector is interposed between the first quarter-wave plate and the waveguide, and the polarization-selective notch reflector is interposed between the waveguide and the second quarter-wave plate. (Item 7) The display device according to item 6, further comprising a first linear polarizing lens and a second linear polarizing lens, wherein the first quarter-wave plate is interposed between the first linear polarizing lens and the polarization-independent notch reflector, and the second quarter-wave plate is interposed between the polarization-selective notch reflector and the second linear polarizing lens. (Item 8) The display device according to item 1, further comprising a first Pancharatnam Berry (PB) lens and a second Pancharatnam Berry (PB) lens, disposed outside the polarization-independent notch reflector and the polarization-selective notch reflector. (Item 9) The display device according to item 1, further comprising a first quarter-wave plate interposed between the polarization-independent notch reflector and the waveguide. (Item 10) The display device according to item 9, further comprising a second quarter-wave plate, wherein the polarization-independent notch reflector is interposed between the first quarter-wave plate and the second quarter-wave plate. (Item 11) The display device according to item 10, further comprising a first linear polarizing lens and a second linear polarizing lens, wherein the first quarter-wave plate is interposed between the first linear polarizing lens and the polarization-independent notch reflector, and the polarization-selective notch reflector is interposed between the waveguide and the second linear polarizing lens. (Item 12) The display device according to item 9, further comprising a first Pancharatnam Berry (PB) lens disposed outside the polarization-independent notch reflector and the polarization-selective notch reflector, a second Pancharatnam Berry (PB) lens, and a second quarter-wave plate interposed between the second PB lens and the polarization-selective notch reflector. (Item 13) A display device configured to display an image to the user's eyes, wherein the display device is An optical display comprising a front side and a rear side, wherein the rear side is closer to the user's eye than the front side, and the optical display is configured to output light having a wavelength range toward the rear side. A first notch reflector positioned behind the optical display, wherein the first notch reflector is configured to reflect light having the wavelength range output from the optical display, A second notch reflector positioned in front of the optical display, wherein the second notch reflector is configured to reflect light having the wavelength range, and Equipped with, The first notch reflector is configured to substantially transmit light having a first polarization and substantially reflect light having a second polarization different from the first polarization. The second notch reflector is configured to convert light incident on its rear surface having the second polarization to the first polarization and to redirect the light backward. Display device. (Item 14) The display device according to item 13, wherein the first notch reflector comprises a cholesteric liquid crystal (CLC) grid (CLCG). (Item 15) The display device according to item 23, wherein the first notch reflector comprises a multilayer, and the second notch reflector comprises a non-polarizing notch reflector and a quarter-wave plate. (Item 16) The display device according to item 13, further comprising a first variable focus lens positioned behind the first notch reflector and a second variable focus lens positioned in front of the second notch reflector, wherein the second optical properties of the second variable focus lens compensate for the first optical properties of the first variable focus lens. (Item 17) The display device according to item 16, wherein the first variable focus lens and the second variable focus lens each comprise a linear polarizing lens. (Item 18) The display device according to item 16, wherein the first variable focus lens and the second variable focus lens each comprise a Pancharatnam Berry (PB) phase lens. (Item 19) The display device according to item 18, further comprising a spatial offset compensator configured to compensate for the spatial offset introduced by the PB phase lens. (Item 20) A display device, A waveguide, wherein the waveguide is configured to propagate visible light under total internal reflection in a direction parallel to the main surface of the waveguide, and to externally couple the visible light in a direction normal to the main surface, A notch reflector configured to reflect visible light having a first polarization, wherein the notch reflector comprises one or more cholesteric liquid crystal (CLC) layers, each of the CLC layers comprises a plurality of chiral structures, each of the chiral structures comprises a plurality of liquid crystal molecules, the plurality of liquid crystal molecules extend in the layer depth direction and are continuously rotated in a first rotation direction, and the arrangement of the liquid crystal molecules of the chiral structures is periodically varied in a lateral direction perpendicular to the layer depth direction such that the one or more CLC layers are configured to Bragg reflect incident light, and A display device equipped with the following features. (Item 21) The display device according to item 20, wherein the waveguide is configured to selectively externally couple the visible light toward the notch reflector. (Item 22) The display device according to item 20, wherein the notched reflector comprises a deformable mirror, and the deformable mirror has one or more CLC layers formed thereon. (Item 23) The display device according to item 20, wherein one or more different CLC layers are configured to transmit light having wavelengths outside the wavelength range, while reflecting visible light having wavelengths within the wavelength range corresponding to different red, green, or blue light. (Item 24) The display device according to item 20, wherein each of the chiral structures of the CLC layers comprises a plurality of liquid crystal molecules extending in the layer depth direction by at least a helical pitch, and different of the one or more CLC layers have different helical pitches. (Item 25) The display device according to item 20, wherein one or more different CLC layers have substantially the same refractive power. (Item 26) The display device according to item 20, comprising a plurality of notch reflectors, each of which is configured to reflect visible light having a first polarization, each of which comprises one or more cholesteric liquid crystal (CLC) layers, each of which comprises a plurality of chiral structures, each of which comprises a plurality of liquid crystal molecules, the plurality of liquid crystal molecules extending in the layer depth direction and continuously rotating in a first rotation direction, and the arrangement of the liquid crystal molecules of the chiral structures periodically fluctuates in a lateral direction perpendicular to the layer depth direction such that one or more CLC layers are configured to Bragg reflect incident light. (Item 27) The display device according to item 26, wherein different of the multiple notched reflectors have different refractive powers. (Item 28) The display device according to item 26, further comprising a half-wave plate corresponding to each of the plurality of notched reflectors. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 illustrates the user's view of augmented reality (AR) through an AR device.

[0017] [Figure 2] Figure 2 illustrates an embodiment of a wearable display system.

[0018] [Figure 3] Figure 3 illustrates a conventional display system for simulating a three-dimensional image for the user.

[0019] [Figure 4] Figure 4 illustrates aspects of an approach to simulating a 3D image using multiple depth planes.

[0020] [Figure 5] Figures 5A-5C illustrate the relationship between the radius of curvature and the radius of focus.

[0021] [Figure 6] Figure 6 illustrates an example of a waveguide stack for outputting image information to the user.

[0022] [Figure 7] Figure 7 illustrates an example of an output beam produced by a waveguide.

[0023] [Figure 8] Figure 8 illustrates an embodiment of a stacked waveguide assembly, where each depth plane includes an image formed using multiple different primary colors.

[0024] [Figure 9A] Figure 9A shows a cross-sectional side view of an embodiment of a stacked waveguide set, each including an internally coupled optical element.

[0025] [Figure 9B] Figure 9B shows a perspective view of an embodiment of the multiple stacked waveguides shown in Figure 9A.

[0026] [Figure 9C] Figure 9C shows top and bottom plan views of the embodiment of the multiple stacked waveguides shown in Figures 9A and 9B.

[0027] [Figure 10] Figure 10 shows a cross-sectional side view of an example of a cholesteric liquid crystal diffraction grating (CLCG) having multiple uniform chiral structures.

[0028] [Figure 11] Figure 11 shows a cross-sectional side view of an embodiment of CLCG having chiral structures arranged differently in the lateral direction.

[0029] [Figure 12] Figure 12 shows a cross-sectional side view of an embodiment of a CLC layer configured to produce Bragg reflection at an off-axis incidence angle.

[0030] [Figure 13A] Figure 13A shows a cross-sectional side view of an embodiment of a CLC layer having a first helical pitch and configured to undergo Bragg reflection at a first off-axis incidence angle.

[0031] [Figure 13B] Figure 13B shows a cross-sectional side view of an embodiment of a CLC layer having a second helical pitch and configured to exhibit Bragg reflection at a second off-axis incidence angle.

[0032] [Figure 13C] Figure 13C shows a cross-sectional side view of an embodiment of CLCG, including the CLC layers of Figures 13A and 13B, which have different helical pitches in a stacked configuration to produce Bragg reflections at multiple off-axis incidence angles and high diffraction bandwidths.

[0033] [Figure 14] Figure 14 shows a cross-sectional side view of an embodiment of CLCG, which includes a CLC layer having vertical regions with different helical pitches along the depth direction to induce Bragg reflection at multiple off-axis incidence angles and high diffraction bandwidths.

[0034] [Figure 15] Figure 15 shows a cross-sectional side view of an embodiment of CLCG, which includes a CLC layer having lateral regions with different helical pitches along the lateral direction to spatially vary the Bragg reflection.

[0035] [Figure 16] Figure 16 illustrates an embodiment of an optical waveguide device comprising a waveguide coupled to a CLCG and configured to propagate light by total internal reflection (TIR).

[0036] [Figure 17A]Figure 17A illustrates an embodiment of an optical waveguide device comprising a waveguide coupled to a CLCG and configured to selectively propagate light of a certain wavelength by total internal reflection (TIR).

[0037] [Figure 17B] Figure 17B illustrates an embodiment of multiple optical waveguide devices within the same optical path, each comprising a waveguide coupled to a CLCG and configured to selectively propagate light of a certain wavelength by total internal reflection (TIR).

[0038] [Figure 17C] Figure 17C illustrates an embodiment of multiple optical waveguide devices within the same optical path, each comprising a waveguide coupled to a CLCG and configured to selectively propagate light of a certain wavelength by total internal reflection (TIR).

[0039] [Figure 18] Figure 18 illustrates an embodiment of an optical waveguide device comprising a common waveguide, which is coupled to multiple CLCGs and configured to selectively propagate light of multiple wavelengths by total internal reflection (TIR).

[0040] [Figure 19] Figure 19 illustrates an embodiment of an optical waveguide device comprising a waveguide coupled to a CLCG and configured to propagate light by total internal reflection (TIR).

[0041] [Figure 20] Figure 20 illustrates an embodiment of an optical waveguide device comprising a waveguide coupled to a CLCG and a polarization-converting reflector, wherein the CLCG is configured to receive incident light, and the waveguide is configured to propagate the light Bragg reflected from the CLCG by total internal reflection (TIR).

[0042] [Figure 21A]Figure 21A illustrates the optical waveguide device of Figure 20, where the CLCG is configured to receive incident light that is linearly polarized or unpolarized, and the waveguide is configured to propagate the light Bragg reflected from the CLCG and the light reflected by the reflector by total internal reflection (TIR).

[0043] [Figure 21B] Figure 21B illustrates the optical waveguide device of Figure 20, where the CLCG is configured to receive incident light that has been modified into an orthogonal elliptical or circularly polarized beam, and the waveguide is configured to propagate the light Bragg reflected from the CLCG and the light reflected by the reflector by total internal reflection (TIR).

[0044] [Figure 22A] Figure 22A illustrates an embodiment of an optical waveguide device comprising multiple CLC layers coupled to a common waveguide, each including a first CLC layer having a chiral structure with a first direction of rotation and a second CLC layer having a chiral structure with a second direction of rotation opposite to the first direction of rotation, under conditions where the incident light beam is linearly polarized or unpolarized.

[0045] [Figure 22B] Figure 22B illustrates the optical waveguide device shown in Figure 22A under the condition that the incident light is polarized into an orthogonal elliptical or circularly polarized beam.

[0046] [Figure 22C] Figure 22C illustrates an embodiment of an optical waveguide device comprising multiple CLC layers, coupled to a common waveguide interposed between two CLC layers, each CLC layer having a chiral structure with a first rotational direction and a second CLC layer having a chiral structure with a second rotational direction opposite to the first rotational direction, under conditions where the incident light beam is linearly polarized or unpolarized.

[0047] [Figure 23]Figure 23 illustrates an embodiment of an imaging system comprising a forward-facing camera configured to image the wearer's eye using a cholesteric liquid crystal (CLC) off-axis mirror.

[0048] [Figure 24A] Figures 24A-24F illustrate an embodiment of an imaging system comprising a forward-facing camera configured to image the wearer's eye using a CLC off-axis mirror. [Figure 24B] Figures 24A-24F illustrate an embodiment of an imaging system comprising a forward-facing camera configured to image the wearer's eye using a CLC off-axis mirror. [Figure 24C] Figures 24A-24F illustrate an embodiment of an imaging system comprising a forward-facing camera configured to image the wearer's eye using a CLC off-axis mirror. [Figure 24D] Figures 24A-24F illustrate an embodiment of an imaging system comprising a forward-facing camera configured to image the wearer's eye using a CLC off-axis mirror. [Figure 24E] Figures 24A-24F illustrate an embodiment of an imaging system comprising a forward-facing camera configured to image the wearer's eye using a CLC off-axis mirror. [Figure 24F] Figures 24A-24F illustrate an embodiment of an imaging system comprising a forward-facing camera configured to image the wearer's eye using a CLC off-axis mirror.

[0049] [Figure 24G] Figures 24G and 24H illustrate an embodiment of an imaging system comprising a forward-facing camera configured to image the wearer's eye using a diffractive optical element comprising multiple segments, each including one or more CLC off-axis mirrors, where each segment may have different optical properties. [Figure 24H]Figures 24G and 24H illustrate an embodiment of an imaging system comprising a forward-facing camera configured to image the wearer's eye using a diffractive optical element comprising multiple segments, each including one or more CLC off-axis mirrors, where each segment may have different optical properties.

[0050] [Figure 25A] Figure 25A illustrates an exemplary display device that includes a polarization converter and is configured to output an image to the user.

[0051] [Figure 25B] Figure 25B illustrates an exemplary display device that includes a polarization converter and is configured to output an image to the user.

[0052] [Figure 26A] Figure 26A illustrates an exemplary display device configured to output a virtual image to the user, comprising a polarization converter and a switchable lens.

[0053] [Figure 26B] Figure 26B illustrates an exemplary display device configured to output a real image to the user, comprising a polarization converter and a switchable lens.

[0054] [Figure 26C] Figure 26C illustrates an exemplary display device configured to output a virtual image to the user, comprising a polarization converter and a switchable lens.

[0055] [Figure 26D] Figure 26D illustrates an exemplary display device comprising a polarization converter and a switchable lens, configured to output a real image to the user.

[0056] [Figure 27A]Figure 27A illustrates an exemplary display device comprising a polarization converter and a Pancharatnam Berry (PB) lens, configured to output a virtual image to the user.

[0057] [Figure 27B] Figure 27B illustrates an exemplary display device comprising a polarization converter and a PB lens, configured to output a real image to the user.

[0058] [Figure 27C] Figure 27C illustrates an exemplary display device comprising a polarization converter and a PB lens, configured to output a virtual image to the user.

[0059] [Figure 27D] Figure 27D illustrates an exemplary display device comprising a polarization converter and a PB lens, configured to output a real image to the user.

[0060] [Figure 28A] Figure 28A illustrates the spatial offset created by two orthogonal polarization images formed by an exemplary display device comprising a polarization converter and a PB lens.

[0061] [Figure 28B] Figure 28B illustrates an exemplary offset compensator, which includes a pair of lenses for compensating for the spatial offset illustrated in Figure 28A.

[0062] [Figure 28C] Figure 28C illustrates the negative effect of the spatial offset shown in Figure 28A, using the embodiment of the offset compensator shown in Figure 28B.

[0063] [Figure 29]Figure 29 illustrates an exemplary display device configured to output an image to a user, comprising a waveguide assembly configured to project light asymmetrically and a PB lens.

[0064] [Figure 30] Figure 30 illustrates an exemplary display device comprising a waveguide assembly having a CLCG and a deformable mirror, and configured to output an image to the user.

[0065] [Figure 31] Figures 31A-31C illustrate exemplary reflective diffractive lenses that can be implemented as part of a display device, in which the reflective diffractive lens is formed from a patterned CLC material that acts as a reflective polarizing mirror.

[0066] [Figure 32A] Figure 32A illustrates an example of chromatic aberration observed in a diffractive lens.

[0067] [Figure 32B] Figure 32B illustrates an exemplary reflective diffracting lens comprising multiple reflective diffracting lenses in a stacked configuration.

[0068] [Figure 33A] Figures 33A–33D illustrate exemplary reflection-diffractive lens assemblies and their operation for dynamic switching between different focal lengths. [Figure 33B] Figures 33A–33D illustrate exemplary reflection-diffractive lens assemblies and their operation for dynamic switching between different focal lengths. [Figure 33C] Figures 33A–33D illustrate exemplary reflection-diffractive lens assemblies and their operation for dynamic switching between different focal lengths. [Figure 33D] Figures 33A–33D illustrate exemplary reflection-diffractive lens assemblies and their operation for dynamic switching between different focal lengths.

[0069] [Figure 34] Figure 34 illustrates an exemplary combination of waveguide assemblies, comprising an eyepiece configured to direct light towards the world and a CLC lens configured to redirect light towards the eye. [Modes for carrying out the invention]

[0070] Throughout the drawings, reference numbers may be reused to indicate correspondences between the referenced elements. The drawings are provided to illustrate exemplary embodiments described herein and are not intended to limit the scope of this disclosure.

[0071] AR systems can still display virtual content to a user or viewer while allowing the user to see the world around them. Preferably, this content is displayed on a head-mounted display that projects image information onto the user's eyes, for example, as part of eyewear. In addition, the display may also transmit light from the surrounding environment to the user's eyes, providing a view of that environment. It should be understood that, as used herein, a “head-mounted” display is a display that can be mounted on the viewer’s head.

[0072] Figure 2 illustrates an embodiment of a wearable display system 80. The display system 80 includes a display 62 and various mechanical and electronic modules and systems to support the functions of the display 62. The display 62 may be coupled to a frame 64, which is wearable by the display system user or viewer 60 and is configured to position the display 62 in front of the user 60's eyes. In some embodiments, the display 62 may be considered eyewear. In some embodiments, a speaker 66 is coupled to the frame 64 and positioned adjacent to the user 60's ear canal (in some embodiments, another speaker, not shown, is positioned adjacent to the user's other ear canal to provide stereo / adjustable sound control). In some embodiments, the display system may also include one or more microphones 67 or other devices to detect sound. In some embodiments, the microphones may be configured to allow the user to provide input or commands (e.g., selection of voice menu commands, natural language questions, etc.) to the system 80 and / or enable audio communication with other persons (e.g., other users of a similar display system). The microphone may also be configured as a peripheral sensor to continuously collect audio data (e.g., passively collected from the user and / or the environment). Such audio data may include user sounds such as heavy breathing or environmental sounds such as commotion indicating a nearby event. The display system may also include a peripheral sensor 30a, which is separate from the frame 64 and may be mounted on the user 60's body (e.g., on the user 60's head, torso, limbs, etc.). In some embodiments, the peripheral sensor 30a may be configured to obtain data characterizing the user 60's physiological state, as further described herein. For example, the sensor 30a may be an electrode.

[0073] Continuing to refer to Figure 2, the display 62 is operably coupled to the local data processing module 70 by a communication link 68, such as a wired connection or wireless connectivity, which may be mounted in various configurations, such as being fixedly attached to the frame 64, fixedly attached to a helmet or hat worn by the user, built into headphones, or otherwise detachably attached to the user 60 (e.g., in a backpack configuration, in a belt-mounted configuration). Similarly, the sensor 30a may be operably coupled to the local processor and data module 70 by a communication link 30b, such as a wired connection or wireless connectivity. The local processing and data module 70 may also include a hardware processor and digital memory such as non-volatile memory (e.g., flash memory or a hard disk drive), both of which may be used to assist in data processing, caching, and storage. The data includes a) data captured by sensors such as an image capture device (camera, etc.), microphone, inertial measurement unit, accelerometer, compass, GPS unit, wireless device, gyroscope, and / or other sensors disclosed herein (for example, operably coupled to frame 64 or otherwise attached to user 60), and / or b) optionally, data obtained and / or processed using the remote processing module 72 and / or remote data repository 74 (including data related to virtual content) for passage to display 62 after processing or reading. The local processing and data module 70 may be operably coupled to the remote processing module 72 and the remote data repository 74 by communication links 76, 78 via wired or wireless communication links, etc., so that these remote modules 72, 74 are operably coupled to each other and available as resources to the local processing and data module 70. In some embodiments, the local processing and data module 70 may include one or more of the following: an image acquisition device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyroscope.In some other embodiments, one or more of these sensors may be mounted on the frame 64, or they may be standalone structures that communicate with the local processing and data module 70 via a wired or wireless communication path.

[0074] Continuing with Figure 2, in some embodiments, the remote processing module 72 may comprise one or more processors configured to analyze and process data and / or image information. In some embodiments, the remote data repository 74 may comprise a digital data storage facility, which may be available through the internet or other networking configurations in a “cloud” resource configuration. In some embodiments, the remote data repository 74 may comprise one or more remote servers, which provide information, for example, information for generating augmented reality content, to the local processing and data module 70 and / or the remote processing module 72. In some embodiments, all data is stored, and all calculations are performed in the local processing and data module, enabling fully autonomous use from the remote module.

[0075] The perception of an image as "three-dimensional" or "3-D" may be achieved by providing each eye of the viewer with a slightly different presentation of the image. Figure 3 illustrates a conventional display system for simulating a three-dimensional image for a user. Two distinctly different images 5,7 are output to the user, one for each eye 4,6. Images 5,7 are spaced 10 units apart from eyes 4,6 along the optical or z-axis parallel to the viewer's line of sight. Images 5,7 are flat, and eyes 4,6 can focus on the image by taking a single accommodative state. Such a system relies on the human visual system to combine images 5,7 and provide a perception of depth and / or scale for the combined image.

[0076] However, it will be understood that the human visual system is more complex and that providing a realistic perception of depth is more difficult. For example, many viewers of conventional "3-D" display systems may find such systems unpleasant or may not perceive any sense of depth at all. While not limited by theory, it is thought that viewers of objects may perceive them as "three-dimensional" due to a combination of vergence and accommodation. The vergence and divergence movements of two eyes relative to each other (i.e., rotations of the eyes such that the pupils move toward or away from each other, converging the lines of sight and fixing on an object) are closely related to the focusing (or "accommodation") of the eye's lens and pupil. Under normal conditions, a change in the focus of the eye's lens or the eye's accommodation to change the focus from one object to another at a different distance will automatically produce a consistent change in vergence and divergence movements at the same distance, under the relationship known as the "accommodation-vergence-divergence reflex" and pupillary dilation or miosis. Similarly, changes in convergence and divergence movements will, under normal conditions, induce changes in the accommodation-to-focal

[0077] Figure 4 illustrates aspects of an approach to simulating a three-dimensional image using multiple depth planes. Referring to Figure 4, objects at various distances from eyes 4, 6 on the z-axis are accommodated by eyes 4, 6 so that those objects are in focus. Eyes (4 and 6) take on specific accommodated states to focus objects at different distances along the z-axis. As a result, a specific accommodated state can be associated with one of the specific depth planes 14, having an associated focal length such that an object or part of an object in a particular depth plane is in focus when the eye is accommodated to that depth plane. In some embodiments, the three-dimensional image may be simulated by providing a different presentation of the image for each eye 4, 6, and by providing a different presentation of the image corresponding to each depth plane. For the sake of clarity in the illustration, it should be understood that the fields of view of eyes 4, 6 may overlap, for example, as the distance along the z-axis increases. In addition, although shown as flat for the sake of illustration, it will be understood that the contour of the depth plane may be curved in physical space so that all features within the depth plane are in focus with the eye in a particular state of perspective adjustment.

[0078] The distance between the object and eye 4 or 6 can also change the amount of light emitted from the object so that it is visible to that eye. Figures 5A-5C illustrate the relationship between distance and ray divergence. The distance between the object and eye 4 is expressed in the order of decreasing distances R1, R2, and R3. As shown in Figures 5A-5C, the ray diverges more as the distance to the object decreases. As the distance increases, the ray becomes more collimated. In other words, the light field generated by a point (object or part of an object) can be said to have a spherical wavefront curvature, which is a function of the distance the point is from the user's eye. As the curvature increases, the distance between the object and eye 4 decreases. Consequently, the degree of ray divergence also differs in different depth planes, and the degree of divergence increases with decreasing distance between the depth plane and the viewer's eye 4. Although only monocular eye 4 is illustrated in Figures 5A–5C and other figures herein for illustrative purposes, it will be understood that the discussion relating to eye 4 may apply to both eyes 4 and 6 of the viewer.

[0079] While not limited by theory, the human eye is typically thought to be capable of interpreting a finite number of depth planes and providing depth perception. Consequently, a highly realistic simulation of perceived depth can be achieved by providing the eye with different presentations of images corresponding to each of these limited number of depth planes. These different presentations can be individually focused by the viewer's eye and thus help provide the user with depth cues based on the eye's accommodation required to focus on different image features for scenes located on different depth planes, and / or based on the observation of different image features on different depth planes that are out of focus.

[0080] Figure 6 illustrates an embodiment of a waveguide stack for outputting image information to a user. The display system 1000 includes a waveguide stack or a stacked waveguide assembly 1178, which may be used to provide three-dimensional perception to the eye / brain using a plurality of waveguides 1182, 1184, 1186, 1188, 1190. In some embodiments, the display system 1000 is system 80 in Figure 2, and Figure 6 schematically shows some parts of that system 80 in more detail. For example, the waveguide assembly 1178 may be part of the display 62 in Figure 2. It will be understood that in some embodiments, the display system 1000 may be considered a light field display.

[0081] Continuing with reference to Figure 6, the waveguide assembly 1178 may also include several features 1198, 1196, 1194, and 1192 between the waveguides. In some embodiments, features 1198, 1196, 1194, and 1192 may be one or more lenses. Waveguides 1182, 1184, 1186, 1188, and 1190 and / or several lenses 1198, 1196, 1194, and 1192 may be configured to transmit image information to the eye using various levels of wavefront curvature or ray divergence. Each waveguide level may be associated with a specific depth plane and may be configured to output image information corresponding to that depth plane. Image input devices 1200, 1202, 1204, 1206, and 1208 may function as light sources for the waveguides and may be used to input image information into the waveguides 1182, 1184, 1186, 1188, and 1190, each of which may be configured to disperse incident light across each individual waveguide for output toward eye 4, as described herein. The light exits from the output surfaces 1300, 1302, 1304, 1306, and 1308 of the image input devices 1200, 1202, 1204, 1206, and 1208 and is input into the corresponding input surfaces 1382, 1384, 1386, 1388, and 1390 of the waveguides 1182, 1184, 1186, 1188, and 1190. In some embodiments, the input surfaces 1382, 1384, 1386, 1388, and 1390 may each be the edge of the corresponding waveguide or a portion of the main surface of the corresponding waveguide (i.e., one of the waveguide surfaces that directly faces the world 1144 or the viewer's eye 4). In some embodiments, a single beam of light (e.g., a collimated beam) may be injected into each waveguide to output a whole field of cloned collimated beams, which are directed toward the eye 4 at a specific angle (and divergence) corresponding to the depth plane associated with the particular waveguide. In some embodiments, one of the image input devices 1200, 1202, 1204, 1206, and 1208 may be associated with a plurality (e.g., three) of waveguides 1182, 1184, 1186, 1188, and 1190 to injected light into them.

[0082] In some embodiments, the image input devices 1200, 1202, 1204, 1206, and 1208 are discrete displays that generate image information for input into the corresponding waveguides 1182, 1184, 1186, 1188, and 1190, respectively. In some other embodiments, the image input devices 1200, 1202, 1204, 1206, and 1208 are output terminals of a single multiplexed display that can send image information to each of the image input devices 1200, 1202, 1204, 1206, and 1208, for example, via one or more optical conduits (such as optical fiber cables). It should be understood that the image information provided by the image input devices 1200, 1202, 1204, 1206, and 1208 may include light of different wavelengths or colors (e.g., different primary colors, as discussed herein).

[0083] In some embodiments, the light introduced into waveguides 1182, 1184, 1186, 1188, and 1190 is provided by an optical projector system 2000, which comprises an optical module 2040, which may include an optical emitter such as a light-emitting diode (LED). The light from the optical module 2040 may be directed and modified via a beam splitter 2050 by an optical modulator 2030, for example, a spatial light modulator. The optical modulator 2030 may be configured to change the perceived intensity of the light introduced into waveguides 1182, 1184, 1186, 1188, and 1190. Embodiments of the spatial light modulator include liquid crystal displays (LCDs), including liquid crystal on silicon (LCOS) displays.

[0084] In some embodiments, the display system 1000 may be a scanning fiber display comprising one or more scanning fibers configured to project light in various patterns (e.g., raster scanning, helical scanning, Lissajous patterns, etc.) into one or more waveguides 1182, 1184, 1186, 1188, 1190, ultimately to the viewer's eye 4. In some embodiments, the illustrated image input devices 1200, 1202, 1204, 1206, 1208 may schematically represent a single scanning fiber or a bundle of scanning fibers configured to input light into one or more waveguides 1182, 1184, 1186, 1188, 1190. In some other embodiments, the illustrated image input devices 1200, 1202, 1204, 1206, and 1208 may schematically represent multiple scanning fibers or multiple bundles of scanning fibers, each configured to input light into one of the associated waveguides 1182, 1184, 1186, 1188, and 1190. It should be understood that one or more optical fibers may be configured to transmit light from the optical module 2040 into one or more waveguides 1182, 1184, 1186, 1188, and 1190. It should be understood that one or more intervening optical structures may be provided between the scanning fibers or multiple fibers and one or more waveguides 1182, 1184, 1186, 1188, and 1190, for example, to redirect light emanating from the scanning fibers into one or more waveguides 1182, 1184, 1186, 1188, and 1190.

[0085] The controller 1210 controls the operation of one or more of the stacked waveguide assemblies 1178, including the operation of the image input devices 1200, 1202, 1204, 1206, 1208, the light source 2040, and the optical modulator 2030. In some embodiments, the controller 1210 is part of the local data processing module 70. The controller 1210 includes programming (e.g., instructions in a non-transient medium) to coordinate the timing and delivery of image information to the waveguides 1182, 1184, 1186, 1188, 1190, for example, according to any of the various schemes disclosed herein. In some embodiments, the controller may be a single integrated device or a distributed system connected by wired or wireless communication channels. In some embodiments, the controller 1210 may be part of the processing module 70 or 72 (Figure 1).

[0086] Continuing with Figure 6, waveguides 1182, 1184, 1186, 1188, and 1190 may be configured to propagate light within each individual waveguide by total internal reflection (TIR). Waveguides 1182, 1184, 1186, 1188, and 1190 may each be planar or have another shape (e.g., curved), with major upper and lower surfaces and edges extending between their major upper and lower surfaces. In the illustrated configuration, waveguides 1182, 1184, 1186, 1188, and 1190 may each include externally coupled optical elements 1282, 1284, 1286, 1288, and 1290, which are configured to extract light from the waveguides by redirecting the light propagating within each individual waveguide and outputting image information to eye 4. The extracted light may also be referred to as externally coupled light, and the externally coupled optical element light may also be referred to as light extraction optical element. The beam of extracted light is output by the waveguide at the point where light propagating within the waveguide strikes the light extraction optical element. The externally coupled optical elements 1282, 1284, 1286, 1288, 1290 may be gratings, for example, including diffractive optical features as further discussed herein. For ease of explanation and clarity of the drawings, they are shown positioned on the bottom main surface of the waveguides 1182, 1184, 1186, 1188, 1190, but in some embodiments, the externally coupled optical elements 1282, 1284, 1286, 1288, 1290 may be positioned on the top and / or bottom main surface, and / or directly within the volume of the waveguides 1182, 1184, 1186, 1188, 1190, as further discussed herein. In some embodiments, the external coupling optical elements 1282, 1284, 1286, 1288, and 1290 may be mounted on a transparent substrate and formed within a layer of material that forms the waveguides 1182, 1184, 1186, 1188, and 1190. In some other embodiments, the waveguides 1182, 1184, 1186, 1188, and 1190 may be monolithic material components, and the external coupling optical elements 1282, 1284, 1286, 1288, and 1290 may be formed on and / or inside the surface of that material component.

[0087] Continuing with reference to Figure 6, as discussed herein, each waveguide 1182, 1184, 1186, 1188, 1190 is configured to emit light and form an image corresponding to a particular depth plane. For example, the waveguide 1182 closest to the eye may be configured to deliver collimated light (injected into such waveguide 1182) to the eye 4. The collimated light may represent the optical infinity focal plane. The next upper waveguide 1184 may be configured to emit collimated light that passes through a first lens 1192 (e.g., a negative lens) before reaching the eye 4. Such a first lens 1192 may generate some convex wavefront curvature so that the eye / brain interprets the light originating from the next upper waveguide 1184 as originating from a first focal plane closer inward from optical infinity toward the eye 4. Similarly, the third upper waveguide 1186 passes its output light through both the first 1192 and the second 1194 lenses before reaching the eye 4. The combined refractive power of the first 1192 and the second 1194 lenses may be configured to generate another gradually increasing wavefront curvature so that the eye / brain interprets the light originating from the third upper waveguide 1186 as originating from a second focal plane that is even closer inward toward the person from optical infinity than the light from the next waveguide 1184.

[0088] Other waveguide layers 1188, 1190 and lenses 1196, 1198 are configured similarly, with the highest waveguide 1190 in the stack emitting its output through all the lenses between it and the eye for a convergent focusing force representing the focal plane closest to the person. When viewing / interpreting light originating from the other side world 1144 of the stacked waveguide assembly 1178, a compensating lens layer 1180 may be positioned on top of the stack to compensate for the convergent force of the lower lens stacks 1198, 1196, 1194, 1192 to compensate for the stack of lenses 1198, 1196, 1194, 1192. Such a configuration provides the same number of perceived focal planes as there are available waveguide / lens pairs. Both the external coupling optical elements of the waveguides and the focusing sides of the lenses may be static (i.e., not dynamic or electroactive). In some alternative embodiments, one or both may be dynamic using electroactive features.

[0089] In some embodiments, two or more of the waveguides 1182, 1184, 1186, 1188, and 1190 may have the same associated depth plane. For example, a plurality of waveguides 1182, 1184, 1186, 1188, and 1190 may be configured to output images set in the same depth plane, or a plurality of subsets of waveguides 1182, 1184, 1186, 1188, and 1190 may be configured to output images set in the same plurality of depth planes, with one set for each depth plane. This may offer the advantage of forming tiled images to provide an extended field of view in those depth planes.

[0090] Continuing with Figure 6, the external coupling optical elements 1282, 1284, 1286, 1288, and 1290 may be configured to redirect light from their respective waveguides for a specific depth plane associated with the waveguide, and to output this light with an appropriate amount of divergence or collimation. As a result, waveguides with different associated depth planes may have different configurations of the external coupling optical elements 1282, 1284, 1286, 1288, and 1290, which will output light with different amounts of divergence depending on the associated depth plane. In some embodiments, the light extraction optical elements 1282, 1284, 1286, 1288, and 1290 may be volumetric or surface features, which may be configured to output light at a specific angle. For example, the light extraction optical elements 1282, 1284, 1286, 1288, and 1290 may be volumetric holograms, surface holograms, and / or diffraction gratings. In some embodiments, features 1198, 1196, 1194, and 1192 may not be lenses. Rather, they may simply be spacers (e.g., structures for forming cladding layers and / or voids).

[0091] In some embodiments, the external coupling optical elements 1282, 1284, 1286, 1288, and 1290 are diffractive features that form a diffraction pattern or “diffractive optical element” (also referred to herein as “DOE”). Preferably, the DOE has a sufficiently low diffraction efficiency (ratio of diffracted beam intensity to incident beam intensity) such that only a portion of the beam light is deflected toward the eye 4 through each intersection of the DOE, while the remainder continues to travel through the waveguide via total internal reflection. The light carrying the image information is therefore split into several associated outgoing beams that exit the waveguide at various locations, resulting in a very uniform pattern of outgoing emission toward the eye 4 with respect to this particular collimated beam bouncing within the waveguide.

[0092] In some embodiments, one or more DOEs may be switchable between an "on" state in which they actively diffract and an "off" state in which they do not significantly diffract. For example, a switchable DOE may comprise a layer of polymer-dispersed liquid crystal, in which microdroplets have a diffraction pattern in the host medium, and the refractive index of the microdroplets may be switched to substantially match the refractive index of the host material (in which case the pattern does not significantly diffract incident light), or the microdroplets may be switched to a refractive index that does not match that of the host medium (in which case the pattern actively diffracts incident light).

[0093] In some embodiments, a camera assembly 500 (e.g., a digital camera including visible light and infrared light cameras) is provided to capture images of the eye 4 and / or the tissue surrounding the eye 4, for example, to detect user input and / or monitor the user's physiological state. As used herein, the camera may be any image-capturing device. In some embodiments, the camera assembly 500 may include the image-capturing device and a light source that projects light (e.g., infrared light) onto the eye, which is then reflected by the eye and can be detected by the image-capturing device. In some embodiments, the camera assembly 500 may be mounted on a frame 64 (Figure 2) and may communicate with processing modules 70 and / or 72 that process image information from the camera assembly 500 and can make various decisions regarding the user's physiological state, for example, as discussed herein. It should be understood that information regarding the user's physiological state may be used to determine the user's behavior or emotional state. Embodiments of such information include the user's movements and / or the user's facial expressions. The user's behavior or emotional state may then be triangulated with the collected environmental and / or virtual content data to determine the relationship between the behavior or emotional state, the physiological state, and the environmental or virtual content data. In some embodiments, one camera assembly 500 may be used for each eye, monitoring each eye separately.

[0094] Referring here to Figure 7, an embodiment of an outgoing beam output by a waveguide is shown. Although one waveguide is illustrated, other waveguides in waveguide assembly 1178 (Figure 6) may function similarly, and it should be understood that waveguide assembly 1178 includes multiple waveguides. Light 400 is introduced into waveguide 1182 at the input surface 1382 of waveguide 1182 and propagates through waveguide 1182 by TIR. At the point where light 400 collides on DOE 1282, a portion of the light exits the waveguide as an outgoing beam 402. The outgoing beam 402 is illustrated as substantially parallel, but may be redirected to propagate to eye 4 at a certain angle (e.g., divergent outgoing beam formation) depending on the depth plane associated with waveguide 1182, as discussed herein. It should be understood that a nearly parallel emitted beam may represent a waveguide with an externally coupled optical element that externally couples the light to form an image that appears to be set in the depth plane at a distance from eye 4 (e.g., optical infinity). Other waveguides or other sets of externally coupled optical elements may output a more divergent emitted beam pattern, which would require eye 4 to adjust to a closer distance and focus on the retina, and would be interpreted by the brain as light from a distance closer to eye 4 than optical infinity.

[0095] In some embodiments, a full-color image may be formed in each depth plane by overlaying an image onto each of the primary colors, for example, three or more primary colors. Figure 8 illustrates an embodiment of a stacked waveguide assembly, where each depth plane includes an image formed using several different primary colors. The illustrated embodiment shows depth planes 14a–14f, but more or fewer depths may also be considered. Each depth plane may have three or more primary color images associated with a first image of a first color G, a second image of a second color R, and a third image of a third color B. Different depth planes are indicated in the figure by different numbers relating to diopters (dpt) following the letters G, R, and B. As merely an embodiment, the numbers following each of these letters indicate diopters (1 / m), i.e., the inverse distance of the depth plane from the viewer, and each box in the figure represents an individual primary color image. In some embodiments, the exact location of the depth planes relating to different primary colors may vary to account for differences in the focusing of light of different wavelengths on the eye. For example, different primary color images with respect to a given depth plane may be placed on depth planes corresponding to different distances from the user. Such an arrangement may increase visual acuity and user comfort and / or reduce chromatic aberration.

[0096] In some embodiments, each primary color light may be output by a single dedicated waveguide, and as a result, each depth plane may have multiple waveguides associated with it. In such embodiments, each box in the figure, including the letters G, R, or B, can be understood to represent an individual waveguide, and three waveguides may be provided for each depth plane, and three primary color images are provided for each depth plane. The waveguides associated with each depth plane are shown adjacent to each other in this drawing for ease of explanation, but it should be understood that in a physical device, all waveguides may be arranged in a stack with one waveguide per level. In some other embodiments, multiple primary colors may be output by the same waveguide, for example, so that only a single waveguide may be provided for each depth plane.

[0097] Continuing to refer to Figure 8, in some embodiments, G is green, R is red, and B is blue. In some other embodiments, other colors associated with other wavelengths of light, including magenta and cyan, may be used in addition to or replace one or more of red, green, or blue. In some embodiments, features 198, 196, 194, and 192 may be active or passive optical filters configured to selectively block light from the surrounding environment to the viewer's eyes.

[0098] It should be recognized that any reference to a given color of light throughout this disclosure will be understood to encompass light of one or more wavelengths within a range of wavelengths that is perceived by the viewer as that given color. For example, red light may include light of one or more wavelengths in the range of approximately 620–780 nm, green light may include light of one or more wavelengths in the range of approximately 492–577 nm, and blue light may include light of one or more wavelengths in the range of approximately 435–493 nm.

[0099] In some embodiments, the light source 2040 (Figure 6) may be configured to emit light of one or more wavelengths outside the viewer's visual perception range, such as infrared and / or ultraviolet wavelengths. In addition, internal coupling, external coupling, and other light redirection structures of the waveguide of the display 1000 may be configured to direct and emit this light from the display toward the user's eye 4, for example, for imaging and / or user stimulation applications.

[0100] Referring here to Figure 9A, in some embodiments, light impacting a waveguide may need to be redirected to internally couple that light into the waveguide. Internal coupling optical elements may be used to redirect and internally couple the light into its corresponding waveguide. Figure 9A illustrates cross-sectional side views of embodiments of multiple or set 1200 stacked waveguides, each including an internal coupling optical element. Each waveguide may be configured to output light of one or more different wavelengths or one or more different wavelength ranges. Stack 1200 may correspond to stack 1178 (Figure 6), and the illustrated waveguides of stack 1200 may correspond to some of the multiple waveguides 1182, 1184, 1186, 1188, 1190, but it should be understood that light from one or more of the image input devices 1200, 1202, 1204, 1206, 1208 is input into the waveguide from a position where the light is required to be redirected for internal coupling.

[0101] The illustrated set 1200 of stacked waveguides includes waveguides 1210, 1220, and 1230. Each waveguide includes associated internal coupling optical elements (which may also be referred to as optical input areas on the waveguide), for example, internal coupling optical element 1212 is located on the main surface (e.g., upper main surface) of waveguide 1210, internal coupling optical element 1224 is located on the main surface (e.g., upper main surface) of waveguide 1220, and internal coupling optical element 1232 is located on the main surface (e.g., upper main surface) of waveguide 1230. In some embodiments, one or more of the internal coupling optical elements 1212, 1222, and 1232 may be located on the bottom main surfaces of individual waveguides 1210, 1220, and 1230 (in particular, one or more internal coupling optical elements are reflective deflection optical elements). As shown in the figures, the internally coupled optical elements 1212, 1222, and 1232 may be located on the upper main surface of their respective waveguides 1210, 1220, and 1230 (or on the upper part of the following lower waveguide), and in particular, these internally coupled optical elements are transmissive deflection optical elements. In some embodiments, the internally coupled optical elements 1212, 1222, and 1232 may be located within the bodies of the respective waveguides 1210, 1220, and 1230. In some embodiments, as discussed herein, the internally coupled optical elements 1212, 1222, and 1232 are wavelength-selective, selectively redirecting one or more wavelengths of light while transmitting other wavelengths of light. Although the internal coupling optical elements 1212, 1222, and 1232 are shown on one side or corner of the individual waveguides 1210, 1220, and 1230, it should be understood that in some embodiments, they may be located within other areas of the individual waveguides 1210, 1220, and 1230.

[0102] As illustrated, the internally coupled optical elements 1212, 1222, and 1232 may be offset laterally from one another. In some embodiments, each internally coupled optical element may be offset so that its light does not pass through another internally coupled optical element before receiving light. For example, each internally coupled optical element 1212, 1222, and 1232 may be configured to receive light from different image input devices 1200, 1202, 1204, 1206, and 1208, as shown in Figure 6, and may be separated from the other internally coupled optical elements 1212, 1222, and 1232 (e.g., separated laterally) so that it does not substantially receive light from the other internally coupled optical elements 1212, 1222, and 1232.

[0103] Each waveguide also includes associated optical dispersion elements, for example, optical dispersion element 1214 is located on the main surface (e.g., upper main surface) of waveguide 1210, optical dispersion element 1224 is located on the main surface (e.g., upper main surface) of waveguide 1220, and optical dispersion element 1234 is located on the main surface (e.g., upper main surface) of waveguide 1230. In some other embodiments, optical dispersion elements 1214, 1224, and 1234 may be located on the bottom main surfaces of the associated waveguides 1210, 1220, and 1230, respectively. In some other embodiments, the light dispersion elements 1214, 1224, and 1234 may be located on both the upper and lower main surfaces of the associated waveguides 1210, 1220, and 1230, respectively, or the light dispersion elements 1214, 1224, and 1234 may be located on different upper and lower main surfaces within different associated waveguides 1210, 1220, and 1230, respectively.

[0104] Waveguides 1210, 1220, and 1230 may be separated and isolated by, for example, gaseous, liquid, and / or solid layers of material. For example, as shown, layer 1218a may separate waveguides 1210 and 1220, and layer 1218b may separate waveguides 1220 and 1230. In some embodiments, layers 1218a and 1218b are formed from a low refractive index material (i.e., a material having a lower refractive index than the material forming the nearest waveguides 1210, 1220, and 1230). Preferably, the refractive index of the material forming layers 1218a and 1218b is 0.05 or more, or 0.10 or more, less than the refractive index of the material forming waveguides 1210, 1220, and 1230. Advantageously, lower refractive index layers 1218a, 1218b may function as cladding layers that promote total internal reflection (TIR) ​​of light through waveguides 1210, 1220, 1230 (e.g., TIR between the upper and lower main surfaces of each waveguide). In some embodiments, layers 1218a, 1218b are formed from air. It should be understood that the upper and lower parts of the illustrated set of waveguides 1200 may also include an immediate cladding layer, although not shown.

[0105] Preferably, to facilitate manufacturing and other considerations, the materials forming waveguides 1210, 1220, and 1230 are similar or identical, and the materials forming layers 1218a and 1218b are similar or identical. In some embodiments, the materials forming waveguides 1210, 1220, and 1230 may differ between one or more waveguides, and / or the materials forming layers 1218a and 1218b may differ, while still maintaining the various refractive index relationships described above.

[0106] Continuing to refer to Figure 9A, rays 1240, 1242, and 1244 are incident on set of waveguides 1200. It should be understood that rays 1240, 1242, and 1244 may also be introduced into waveguides 1210, 1220, and 1230 by one or more image input devices 1200, 1202, 1204, 1206, and 1208 (Figure 6).

[0107] In some embodiments, the rays 1240, 1242, and 1244 may have different properties, such as different wavelengths or different wavelength ranges, which may correspond to different colors. The internally coupled optical elements 1212, 1222, and 1232 each deflect the incident light so that it propagates through one of the waveguides 1210, 122, and 1230 by TIR.

[0108] For example, the internally coupled optical element 1212 may be configured to deflect a ray 1240 having a first wavelength or wavelength range. Similarly, a transmitted ray 1242 collides with an internally coupled optical element 1222, configured to selectively deflect light of a second wavelength or wavelength range, and is deflected by it. Similarly, a ray 1244 is deflected by an internally coupled optical element 1232, configured to selectively deflect light of a third wavelength or wavelength range.

[0109] Continuing with Figure 9A, the deflected rays 1240, 1242, and 1244 are deflected so that they propagate through the corresponding waveguides 1210, 1220, and 1230. That is, the internal coupling optical elements 1212, 1222, and 1232 of each waveguide deflect the light into its corresponding waveguide 1210, 1220, and 1230, and internally couple the light into the corresponding waveguide. The rays 1240, 1242, and 1244 are deflected at an angle that causes the light to propagate through the individual waveguides 1210, 1220, and 1230 by TIR. The rays 1240, 1242, and 1244 propagate through the individual waveguides 1210, 1220, and 1230 by TIR until they collide with the corresponding optical dispersion elements 1214, 1224, and 1234 of the waveguide.

[0110] Referring now to Figure 9B, a perspective view of an embodiment of the multiple stacked waveguides shown in Figure 9A is illustrated. As previously mentioned, the internally coupled rays 1240, 1242, and 1244 are deflected by the internally coupled optical elements 1212, 1222, and 1232, respectively, and then propagate by TIR within waveguides 1210, 1220, and 1230, respectively. The rays 1240, 1242, and 1244 then collide with the optical dispersion elements 1214, 1224, and 1234, respectively. The optical dispersion elements 1214, 1224, and 1234 deflect the rays 1240, 1242, and 1244 so that they propagate toward the externally coupled optical elements 1250, 1252, and 1254, respectively.

[0111] In some embodiments, the light dispersion elements 1214, 1224, and 1234 are orthogonal pupil expanders (OPEs). In some embodiments, the OPEs both deflect or disperse light to the external coupling optical elements 1250, 1252, and 1254, and increase the beam or spot size of the light as it propagates to the external coupling optical elements. In some embodiments, for example, if the beam size is already of a desired size, the light dispersion elements 1214, 1224, and 1234 may be omitted, and the internal coupling optical elements 1212, 1222, and 1232 may be configured to deflect light directly to the external coupling optical elements 1250, 1252, and 1254. Referring to Figure 9A, for example, the light dispersion elements 1214, 1224, and 1234 may be replaced by the external coupling optical elements 1250, 1252, and 1254, respectively. In some embodiments, the external coupling optical elements 1250, 1252, and 1254 are exit pupils (EPs) or exit pupil expanders (EPEs) that direct light into the viewer's eye 4 (Figure 7).

[0112] Therefore, referring to Figures 9A and 9B, in some embodiments, the set of waveguides 1200 includes, for each primary color, waveguides 1210, 1220, 1230, internally coupled optical elements 1212, 1222, 1232, optical dispersion elements (e.g., OPE) 1214, 1224, 1234, and externally coupled optical elements (e.g., EP) 1250, 1252, 1254. Waveguides 1210, 1220, 1230 may be stacked with air gaps / cladding layers between each one. The internally coupled optical elements 1212, 1222, 1232 redirect or deflect incident light into their waveguides (different internally coupled optical elements receive light of different wavelengths). The light then propagates at an angle, which will result in TIR within the individual waveguides 1210, 1220, 1230. In the embodiment shown, a ray 1240 (e.g., blue light) is deflected by the first internally coupled optical element 1212 in the manner previously described, and then continues to bounce along the waveguide, interacting with the optical dispersion element (e.g., OPE) 1214 and then the externally coupled optical element (e.g., EP) 1250. Rays 1242 and 1244 (e.g., green and red light, respectively) pass through the waveguide 1210, and ray 1242 will collide with the internally coupled optical element 1222, thereby being deflected. Ray 1242 then bounces along the waveguide 1220 via TIR, proceeding to its optical dispersion element (e.g., OPE) 1224 and then the externally coupled optical element (e.g., EP) 1252. Finally, the ray 1244 (e.g., red light) passes through waveguide 1220 and collides with the internal optical coupling element 1232 of waveguide 1230. The internal optical coupling element 1232 deflects the ray 1244 so that it propagates by TIR to the optical dispersion element (e.g., OPE) 1234, and then by TIR to the external coupling element (e.g., EP) 1254. The external coupling element 1254 then, finally, externally couples the ray 1244 to the viewer, who also receives externally coupled light from the other waveguides 1210 and 1220.

[0113] Figure 9C illustrates upper and lower plan views of the embodiment of the multiple stacked waveguides shown in Figures 9A and 9B. As shown, waveguides 1210, 1220, and 1230 may be vertically aligned with their associated optical dispersion elements 1214, 1224, and 1234 and associated external coupling optical elements 1250, 1252, and 1254. However, as discussed herein, the internal coupling optical elements 1212, 1222, and 1232 are not vertically aligned. Rather, the internal coupling optical elements are preferably non-overlapping (e.g., laterally spaced as seen in the upper and lower figures). As further discussed herein, this non-overlapping spatial arrangement facilitates the input of light from different resources into different waveguides on a one-to-one basis, thereby enabling specific light sources to be uniquely coupled to specific waveguides. In some embodiments, an array containing non-overlapping, spatially separated internally coupled optical elements may be referred to as a pupil-shifting system, where the internally coupled optical elements within these arrays may correspond to subpupils. (Bragg reflective structure based on liquid crystal)

[0114] Generally, liquid crystals possess physical properties that can be intermediate between conventional fluids and solids. While liquid crystals are fluid in some respects, unlike most fluids, the arrangement of molecules within a liquid crystal exhibits some structural order. Different types of liquid crystals include thermotropic, lyotropic, and polymeric liquid crystals. The thermotropic liquid crystals disclosed herein can be implemented in various physical states, e.g., phases, including nematic states / phases, smectic states / phases, chiral nematic states / phases, or chiral smectic states / phases.

[0115] As described herein, liquid crystals in a nematic state or phase may have calamistic (rod-shaped) or discotic (disc-shaped) organic molecules that have relatively little positional order but possess long-range directional order with their long axes substantially parallel. Thus, the organic molecules can still flow freely with their centers of mass randomly dispersed, as they are in a liquid, while maintaining their long-range directional order. In some implementations, liquid crystals in a nematic phase may be uniaxial; that is, the liquid crystal has one longer and preferred axis, with the other two being substantially equivalent. In other implementations, the liquid crystal may be biaxial; that is, in addition to its orientation along its long axis, the liquid crystal may also be oriented along a secondary axis.

[0116] As described herein, liquid crystals in a smectic state or phase may have organic molecules forming relatively clearly defined layers that can slide across each other. In some implementations, liquid crystals in a smectic phase can be positionally ordered along one direction. In some implementations, the long axes of the molecules may be oriented along a direction approximately normal to the plane of the liquid crystal layer, while in other implementations, the long axes of the molecules may be tilted with respect to a direction approximately normal to the plane of the layer.

[0117] Throughout this disclosure, nematic liquid crystals consist of rod-shaped molecules, and the long axes of neighboring molecules are approximately aligned with one another. To describe this anisotropic structure, a dimensionless unit vector n, called an orientor, may be used to describe the preferred orientation of the liquid crystal molecules.

[0118] Throughout this disclosure, the tilt angle or pre-tilt angle Φ may refer to an angle measured in a plane perpendicular to the main surface (xy plane) of the liquid crystal layer or substrate, for example, the xz plane, and between the alignment direction and the main surface or a direction parallel to the main surface, for example, the x-direction.

[0119] Throughout this disclosure, the azimuthal angle or rotation angle φ is used to describe the angle of rotation about the axis normal to the layer normal direction or the main surface of the liquid crystal layer, which is measured in a plane parallel to the main surface of the liquid crystal layer or substrate, for example, the xy plane, and between the alignment direction, for example, the height direction or orientation direction, and the direction parallel to the main surface, for example, the y-direction.

[0120] Throughout this disclosure, when matching angles such as rotation angle φ or pre-tilt angle Φ are referred to as substantially identical across different regions, the average matching angles may be, for example, within approximately 1%, 5%, or 10% of each other, but the average matching may be larger in some cases.

[0121] Throughout this specification, the duty cycle may refer, for example, to the ratio between the first lateral dimension of a first region having liquid crystal molecules aligned in a first alignment direction and the lattice period of the zone having the first region. Where applicable, the first region corresponds to a region in which the alignment of liquid crystals does not vary between different zones.

[0122] As described herein, liquid crystals in the nematic or smectic state can also exhibit chirality. Such liquid crystals are referred to as being in the chiral or cholesteric phase. In the chiral or cholesteric phase, the liquid crystal can exhibit molecular torsion perpendicular to the oriented molecule, with the molecular axis parallel to the oriented molecule. The finite torsion angles between adjacent molecules result in their asymmetric filling, which leads to longer-range chiral order.

[0123] As described herein, liquid crystals in a chiral smectic state or phase can be configured such that the liquid crystal molecules have positional order within a layered structure, and the molecules are tilted at a finite angle with respect to the layer normal. In addition, chirality induces a continuous azimuthal torsion of the liquid crystal molecules from one liquid crystal layer to the next in the direction perpendicular to the layer normal, thereby producing a helical torsion of the molecular axis along the layer normal.

[0124] As described herein, throughout this disclosure, a chiral structure refers to a plurality of liquid crystal molecules in a cholesteric phase that extend perpendicular to an orienting element in a certain direction, such as the layer depth direction, and are continuously rotated or twisted in a certain rotational direction, such as clockwise or counterclockwise. In one aspect, the orienting element of the liquid crystal molecules in a chiral structure can be characterized as a helix having a certain helical pitch.

[0125] As described herein, a liquid crystal in a cholesteric phase exhibiting chirality may be described as having a chiral pitch or helical pitch (p), which corresponds to the length in the layer depth direction, corresponding to the net rotation angle of the liquid crystal molecule in the chiral structure due to a complete rotation in a first rotational direction. In other words, the helical pitch refers to the distance over which the liquid crystal molecule undergoes a complete 360° twist. The helical pitch (p) changes, for example, when the temperature is altered or when other molecules are added to the liquid crystal host (an achiral liquid host material may form a chiral phase when doped with a chiral material), and may allow the helical pitch (p) of a given material to be adjusted as appropriate. In some liquid crystal systems, the helical pitch is identical in order to the wavelength of visible light. As described herein, a chiral liquid crystal may also be described as having a torsion angle or rotation angle (φ), which may refer, for example, to the relative azimuthal rotation between continuous liquid crystal molecules in the layer normal direction, and may also be described as having a net torsion angle or net rotation angle, which may refer, for example, to the relative azimuthal rotation between the uppermost and lowermost liquid crystal molecules across a defined length, e.g., the length of the chiral structure or the thickness of the liquid crystal layer.

[0126] According to various embodiments described herein, liquid crystals having various states or phases as described above can be configured to yield various desirable material properties, including, for example, birefringence, optical anisotropy, and manufacturability using thin-film processes. For example, by changing the surface conditions of the liquid crystal layer and / or mixing different liquid crystal materials, a lattice structure exhibiting spatially variable diffraction properties, such as gradient diffraction efficiency, can be fabricated.

[0127] As described herein, “polymerizable liquid crystal” may refer to a liquid crystal material that can be polymerized, for example, by photopolymerization in situ, and which may be described herein as a reactive mesogen (RM).

[0128] It should be understood that, in some embodiments, liquid crystal molecules may be polymerizable, and once polymerized, they can form large networks with other liquid crystal molecules. For example, liquid crystal molecules may be linked by chemical bonds or chemical species. Once joined together, the liquid crystal molecules can form liquid crystal domains that have substantially the same orientation and location as before they were joined together. For ease of explanation, the term “liquid crystal molecule” is used herein to refer to both the liquid crystal molecules before polymerization and the liquid crystal domains formed by these molecules after polymerization.

[0129] According to certain embodiments described herein, photopolymerizable liquid crystal materials can be configured to form Bragg reflective structures, such as diffraction gratings, and their material properties, including birefringence, chirality, and ease of multiple coatings, can be utilized to create diffraction gratings with different material properties, such as birefringence, chirality, and thickness, which can result in different optical properties, such as diffraction efficiency, wavelength selectivity, and off-axis diffraction angle selectivity.

[0130] It should be understood that, as described herein, a “transmissive” or “transparent” structure, such as a transparent substrate, may allow at least a portion of incident light, for example, at least 20, 30, or 50%, to pass through it. Therefore, the transparent substrate may, in some embodiments, be glass, sapphire, or a polymer substrate. In contrast, a “reflective” structure, such as a reflective substrate, may reflect at least a portion of incident light, for example, at least 20, 30, 50, 70, 90%, or more.

[0131] The optical properties of a lattice are determined by its physical structure (e.g., periodicity, depth, and duty cycle) and its material properties (e.g., refractive index, absorptivity, and birefringence). When liquid crystals are used, the optical properties of the lattice can be controlled, for example, by controlling the molecular orientation or distribution of the liquid crystal material. For example, by varying the molecular orientation or distribution of the liquid crystal material across the lattice area, the lattice can exhibit stepped diffraction efficiencies. Such approaches are described below with reference to the figures. (Cholesteric liquid crystal diffraction grating (CLCG))

[0132] As described above with reference to Figures 6 and 7, the display systems according to various embodiments described herein may include optical elements, such as internally coupled optical elements, externally coupled optical elements, and optical dispersion elements, which may include diffraction gratings. For example, as described above with reference to Figure 7, light 400, which is introduced into the waveguide 1182 at the input surface 1382 of the waveguide 1182, propagates within the waveguide 1182 by total internal reflection (TIR). At the point where the light 400 collides with the externally coupled optical element 1282, a portion of the light exits the waveguide as an exit beam 402. In some implementations, any of the optical elements 1182, 1282, or 1382 can be configured as a diffraction grating.

[0133] Efficiently internally coupling (or externally coupling) light into (or out of) the waveguide 1182 can be a challenge, for example, when designing waveguide-based see-through displays for virtual / augmented / mixed reality display applications. For these and other applications, it is desirable to have a diffraction grating formed from a material whose structure can be configured to optimize various optical properties, including diffraction properties. Desired diffraction properties include, among others, polarization selectivity, spectral selectivity, angular selectivity, high spectral bandwidth, and high diffraction efficiency. To address these and other needs, in various embodiments disclosed herein, the optical element 1282 is configured as a cholesteric liquid crystal diffraction grating (CLCG). As described below, CLCGs in various embodiments can be configured to optimize, among other things, polarization selectivity, bandwidth, phase profile, spatial variation of diffraction properties, spectral selectivity, and high diffraction efficiency.

[0134] The following describes various embodiments of CLCGs, which are configured as reflective liquid crystal diffraction gratings, comprising cholesteric liquid crystals (CLCs) optimized for various optical properties. Generally, diffraction gratings have a periodic structure, which splits and diffracts light into several beams traveling in different directions. The directions of these beams depend, in particular, on the period of the periodic structure and the wavelength of the light. For certain applications, such as external coupling optical elements 1282 (Figures 6 and 7), various material properties of the CLC can be optimized to optimize certain optical properties, such as diffraction efficiency, as will be described below.

[0135] As described above, the liquid crystal molecules in a cholesteric liquid crystal (CLC) layer in a chiral (nematic) or cholesteric phase are characterized by a plurality of liquid crystal molecules arranged such that they have a continuous azimuthal twist of the oriented elements as a function of the film's position in the normal or depth direction of the liquid crystal layer. As described herein, liquid crystal molecules arranged such that they have a continuous azimuthal twist are collectively referred herein to as a chiral structure. As described herein, the angle of azimuthal twist or rotation (φ) is described as the angle between the oriented elements of the liquid crystal molecules with respect to the direction parallel to the layer normal, as described above. The spatially variable oriented elements of the liquid crystal molecules in a chiral structure may be described as forming a helical pattern, and the helical pitch (p) is as described above, when the oriented elements are 360° o It is defined as the distance rotated (for example, in the layer normal direction of the liquid crystal layer). As described herein, a CLC layer configured as a diffraction grating has a lateral dimension in which the molecular structure of the liquid crystal periodically repeats in a direction lateral to the normal to the depth direction. This periodicity in the lateral direction is called the grating period (∧).

[0136] According to various embodiments described herein, the diffraction grating comprises a cholesteric liquid crystal (CLC) layer having a plurality of chiral structures, each chiral structure comprising a plurality of liquid crystal molecules extending in the layer depth direction by at least a helical pitch and continuously rotated in a first rotational direction. The helical pitch is the length in the layer depth direction corresponding to the net rotation angle of the liquid crystal molecules of the chiral structure by a complete rotation in the first rotational direction. The arrangement of the liquid crystal molecules of the chiral structure fluctuates periodically in a lateral direction perpendicular to the layer depth direction.

[0137] Figure 10 shows a cross-sectional side view of a cholesteric liquid crystal (CLC) layer 1004 comprising multiple uniform chiral structures. CLC 1004 comprises a CLC layer 1008 comprising liquid crystal molecules arranged as multiple chiral structures 1012-1, 1012-2, ... 1012-i, where each chiral structure comprises multiple liquid crystal molecules, i being any preferred integer greater than 2. For example, chiral structure 1012-1 comprises multiple liquid crystal molecules 1012-1-1, 1012-1-2, ... 1012-1-j, arranged to extend in the layer normal direction, for example, in the z-direction in the illustrated embodiment, where j is any preferred integer greater than 2. The liquid crystal molecules of each chiral structure are continuously rotated in a first rotational direction. In the illustrated embodiment, the liquid crystal molecules are continuously rotated clockwise when viewed in the positive z-axis direction (i.e., the direction of the axial arrow) or in the propagation direction of the incident light beams 1016-L, 1016-R. For example, in the illustrated embodiment, the liquid crystal molecules 1012-1-1, 1012-1-2, ... 1012-1-j of the chiral structure 1012-1 are continuously rotated by, for example, rotation angles φ1, φ2, ... φj with respect to the positive x-direction. In the illustrated embodiment, for illustrative purposes, each of the multiple liquid crystal molecules of the chiral structure 1012-1, 1012-2, ... 1012-i between opposing ends in the z-direction has a net rotation angle of approximately 360°. o Thus, it is rotated by a full rotation or a full 360-degree turn. As a result, the chiral structures 1012-1, 1012-2, ... 1012-i have a length L in the z-direction that is the same as the helical pitch p. However, embodiments are not limited thereto, and the chiral structures 1012-1, 1012-2, ... 1012-i may be rotated by any number of full rotations greater than or less than one, 360-degree turns. o It can have any preferred net rotation angle that is lower or higher, and / or any preferred length L in the z-direction that is shorter or longer than the helical pitch p. For example, in the various embodiments described herein, the number of complete rotations of the chiral structure can be 1-3, 2-4, 3-5, 4-6, 5-7, 6-8, 7-9, or 8-10, among other numbers.

[0138] Referring still to Figure 10, the continuous rotation angles φ1, φ2, ... φj between adjacent liquid crystal molecules in the z-direction are identical according to some embodiments, or different according to some other embodiments. For example, in the illustrated embodiments, the length of the chiral structures 1012-1, 1012-2, ... 1012-i is about p, and the net rotation angle between adjacent liquid crystal molecules in the z-direction is about 360. o / (m-1) rotates 360 o Here, m is the number of liquid crystal molecules in the chiral structure. For example, for illustrative purposes, the chiral structures 10¹²-1, 10¹²-2, ... 10¹²-i each have approximately 30 adjacent liquid crystal molecules relative to each other in the z-direction. o It has 13 liquid crystal molecules so as to be rotated. Naturally, the chiral structure in various embodiments can have any preferred number of liquid crystal molecules.

[0139] Therefore, still referring to Figure 10, the chiral structures adjacent to each other in the lateral direction, for example, in the x-direction, have similarly arranged liquid crystal molecules. In the illustrated embodiment, the chiral structures 1012-1, 1012-2, ... 1012-i are similarly configured such that the liquid crystal molecules of different chiral structures at approximately the same depth, for example, the liquid crystal molecules closest to the light incident surface 1004S, have the same rotation angle at approximately the same depth, and the continuous rotation angle of the continuous liquid crystal molecules, and the net rotation angle of the liquid crystal molecules of each chiral structure.

[0140] In the following, the CLC layer 1004 illustrated in Figure 10 will be described in operation. As described, the CLC layer 1004 comprises chiral structures 1012-1, 1012-2, ..., 1012-i having a uniform arrangement in the lateral direction, e.g., in the x-direction. In operation, when incident light having a combination of a light beam with left-handed circular polarization and a light beam with right-handed circular polarization is incident on the surface 1004S of the CLC layer 1008 by Bragg reflection, the light with one of the circular polarization pendulums is reflected by the CLC layer 1004, while the light with the opposite circular polarization pendulum is transmitted through the CLC layer 1008 with virtually no interference. Throughout this disclosure, as described herein, pendulum is defined as being observed in the direction of propagation. According to the embodiment, incident light is reflected when the polarization direction or polarization palmarity of the light beams 1016-L, 1016-R are matched so that they have the same rotational direction as the liquid crystal molecules of the chiral structures 1012-1, 1012-2, ... 1012-i. As shown in the figure, incident on the surface 1004S are a light beam 1016-L having left-handed circular polarization and a light beam 1016-R having right-handed circular polarization. In the illustrated embodiment, the liquid crystal molecules of the chiral structures 1012-1, 1012-2, ... 1012-i are continuously rotated clockwise in the positive x-direction, which is the same rotational direction as the light beam 1016-R having right-handed circular polarization, i.e., in the direction of propagation of the incident light beams 1016-L, 1016-R. As a result, the light beam 1016-R, which has right-handed circular polarization, is substantially reflected, while the light beam 1016-L, which has left-handed circular polarization, is substantially transmitted through the CLC layer 1004.

[0141] Although not constrained by any particular theory, under Bragg reflection conditions, the wavelength (λ) of the incident light can be proportional to the characteristic or mean refractive index (n) and helical pitch (p) of the CLC layer, and under some circumstances can be expressed such that the following conditions are met: [ka]

[0142] In addition, the bandwidth (Δλ) of the Bragg reflection wavelength can be proportional to the birefringence Δn (e.g., the difference in refractive index between different polarizations of light) and the helical pitch (p) of the CLC layer 1004, and under some circumstances can be expressed such that the following conditions are met. Δλ = Δn·p [2]

[0143] In the various embodiments described herein, the bandwidth Δλ is about 60 nm, about 80 nm, or about 100 nm.

[0144] According to various embodiments, for example, the peak reflectance in the visible wavelength range of about 390 nm to about 700 nm, or in the near-infrared wavelength range of about 700 nm to about 2500 nm, can exceed about 60%, about 70%, about 80%, or about 90%. In addition, according to various embodiments, the full width at half maximum (FWHM) can be less than about 100 nm, less than about 70 nm, less than about 50 nm, or less than about 20 nm.

[0145] Figure 11 shows a cross-sectional side view of a CLC grating (CLCG) 1150 having chiral structures arranged differently in the lateral direction, for example, with a laterally varying torsion angle. Similar to the CLC layer 1004 in Figure 10, the diffraction grating 1150 comprises a cholesteric liquid crystal (CLC) layer 1158 comprising liquid crystal molecules arranged as a plurality of chiral structures 1162-1, 1162-2, ..., 1162-i, each chiral structure comprising a plurality of liquid crystal molecules. For example, the chiral structure 1162-1 comprises a plurality of liquid crystal molecules 1162-1-1, 1162-1-2, ..., 1162-1-j, arranged to extend in the layer normal direction, which in the illustrated embodiment is represented as the z-direction. The liquid crystal molecules of each chiral structure are continuously rotated in a first rotational direction in a manner analogous to that described with respect to Figure 10. In addition, various other parameters of the chiral structure, including length L, the number of complete rotations performed by the liquid crystal molecules, and the number of liquid crystal molecules per chiral structure, are similar to those of the chiral structure described above with respect to Figure 10.

[0146] However, in contrast to the embodiment illustrated in FIG. 10, in the embodiment illustrated in FIG. 11, the chiral structures adjacent in the lateral direction, e.g., the x-direction, have liquid crystal molecules arranged differently. The chiral structures 1162-1, 1162-2,... 1162-i are configured differently in the x-direction such that the liquid crystal molecules of different chiral structures at approximately the same depth have different angles of rotation. For example, in the illustrated embodiment, the liquid crystal molecules 1162-1-1, 1162-2-1,... 1162-i-1 closest to the incident surface 1158S of the chiral structures 1162-1, 1162-2,... 1162-i are each rotated continuously by angles φ1, φ2,... φi in the positive x-axis direction, e.g., with respect to the positive x-direction. In the illustrated embodiment, the net angle of rotation of the liquid crystal molecules 1162-1-1, 1162-2-1,... 1162-i-1 closest to the incident surface 1158S, across the lateral length ∧ corresponding to the period of the diffraction grating 1150, is about 180 o degrees of rotation. Additionally, the liquid crystal molecules of different chiral structures arranged at approximately the same depth level are rotated by approximately the same angle of rotation with respect to the liquid crystal molecules closest to the individual surfaces.

[0147] Still referring to FIG. 11A, the continuous angles of rotation φ1, φ2,... φi of the liquid crystal molecules at the same depth level in the x-direction across the period ∧ can be the same according to some embodiments, or different according to some other embodiments. In the illustrated embodiment, for the period ∧, when the net angle of rotation is 360 o as in the illustrated embodiment, the liquid crystal molecules adjacent in the x-direction are rotated by about 360 o / (m - 1), where m is the number of liquid crystal molecules extending in the x-direction by the period ∧. For example, for illustrative purposes, there are 7 liquid crystal molecules extending across the period ∧ such that adjacent liquid crystal molecules at the same vertical level in the x-direction are rotated by about 30 o degrees relative to each other. Of course, the chiral structures in various embodiments can have any suitable number of liquid crystal molecules.

[0148] For illustrative purposes, it should be understood that the CLC layer 1158 is illustrated to have only one period ∧. Of course, embodiments are not limited in this way, and the CLC layer 1158 may have any preferred number of periods, determined by the lateral dimensions of the CLC in the x-direction.

[0149] As illustrated by CLCG1150, when chiral structures in the lateral direction, for example in the x-direction, are arranged differently, for example, continuously rotated, the continuously rotated chiral structures induce a shift in the relative phase of the light reflected along the x-direction. This is illustrated with respect to graph 1170, which plots the phase shift φ resulting from chiral structures continuously rotated by rotation angles φ1, φ2, ..., φi in the x-axis direction over one period ∧. Although not constrained by any theory, the relative phase difference (ΔΦ) of the reflected light 1018 can be expressed as ΔΦ(x) = (2πx / Λ), where x is the position along the lateral direction and ∧ is the period. The bandwidth can be expressed as Δλ ≈ Δn·p.

[0150] Referring back to Figure 10-11 and equations [1] and [2], according to various embodiments, the Bragg reflected wavelength can be varied by varying the helical pitch p of the chiral structure. In various embodiments, although not constrained by any theory, the helical pitch p can be varied by increasing or decreasing the helical twisting force (HTP), which refers to the ability of the chiral composite to induce a rotation or twist angle as described above. The HTP can, in turn, be varied by changing the amount of chiral composite relative to the amount of non-chiral composite. In various embodiments, the Bragg reflected wavelength, and therefore the color, can be varied based on the inverse relationship between the relative proportion of chiral composite and the helical pitch by chemically and / or mechanically mixing chiral and non-chiral composites, e.g., nematic composites. In various embodiments disclosed herein, the ratio of the amount of chiral composite to the amount of non-chiral composite can be about 20:1, 10:1, 5:1, 4:1, 3:1, 2:1, 1:1, 1:2, 1:3, 1:4, 1:5, 1:10, or about 1:20 by weight.

[0151] In the above description with respect to Figures 10 and 11, the incident light beams 1016-L and 1016-R are illustrated to propagate parallel to the layer normal, for example, in the z-direction. However, for various applications, for example, as described above with respect to Figures 6 and 7, light propagating within the waveguide 1182, for example, propagating by total internal reflection (TIR), collides with the externally coupled optical elements 1282, 1284, 1286, 1288, 1290, for example, diffraction gratings, at a certain off-axis angle. Diffraction gratings as described herein can be configured to maximize bandwidth and diffraction efficiency for such configurations, as described below.

[0152] In the above description with respect to Figures 10 and 11, the liquid crystal molecules are depicted as not being pre-tilted. However, embodiments are not limited in this way, and according to some embodiments, the liquid crystal molecules may have a pre-tilt angle Φ with respect to the direction parallel to the main surface of the CLCG, for example with respect to the xy plane, such as about + / -60 to about + / -90 or about + / -65 to about + / -85, for example, about + / -75, about + / -35 to about + / -65 or about + / -40 to about + / -60, for example, about + / -50, about + / -10 to about + / -40 or about + / -15 to about + / -35, for example, about + / -25. According to some other embodiments, the pre-tilt angle Φ may be about ±15 or about ±10 or about ±5, for example, 0 degrees. (CLCG configured for high-bandwidth reflection at off-axis incidence angles)

[0153] Figure 12 illustrates a cross-sectional side view of the CLC layer 1158 configured for a high reflection bandwidth at off-axis incidence angles. As described herein, the off-axis incidence angle has a non-zero value and results in a Bragg-reflected beam 1220 at the angle of incidence θ of the incident beam 1216 with respect to the direction of the layer normal (e.g., the z-direction in Figure 12). inc This refers to... Under certain circumstances, the reflection angle can be varied to a limited extent by varying λ / Λ. Although not limited by any theory, under certain circumstances, off-axis reflection can be explained based on the following relationship. n·sin(θ)=λ / Λ+sin(θ inc ) [3] In the formula, θ incn is the angle of incidence with respect to the direction of the layer normal θ, where θ is the angle of reflection with respect to the direction of the layer normal, and n is the reflectance of the medium through which the reflected beam propagates. When the CLC layer 1158 is illuminated with the incident beam 1216 at an off-axis angle, the reflection spectrum can be shifted toward shorter wavelengths. According to various embodiments disclosed herein, the ratio λ / Λ can have values ​​of 0.5-0.8, 0.6-0.9, 0.7-1.0, 0.8-1.1, 0.9-1.2, 1.0-1.6, 1.1-1.5, or 1.2-1.4.

[0154] Although not constrained by any particular theory, the off-axis angle, which configures the CLC layer 1158 to perform Bragg reflections with high efficiency, may also depend on the helical pitch p of the chiral structure.

[0155] Figures 13A and 13B illustrate cross-sectional side views of CLC layers configured for reflection at off-axis incidence angles. Referring to Figure 13A, the first cholesteric liquid crystal (CLC) layer 1358A comprises a first plurality of chiral structures having a first helical pitch (p1). The first CLC layer 1358A is configured such that the first incident light beam 1316A is directed at the incident surface of the CLC layer 1358A at a first off-axis angle θ inc,1 The beam is directed to have a first helical pitch p1 such that the Bragg reflection is maximized when this results in a first reflected light beam 1320A at a first reflection angle θ1. As shown in the figure, the CLC layer 1358A is further configured to have an off-axis incidence angle of a first range 1324A, where relatively high diffraction efficiency can be obtained. The first range 1324A may correspond to a range of off-axis incidence angles, outside of which the intensity of the first reflected light beam 1320A decreases, for example, to more than 1 / e. For example, the first range 1324A is θ inc,1 ±3°, θ inc,1 ±5°, θ inc,1 ±7°, θ inc,1 ±10°, or θ inc,1 It can have a value of ±20°.

[0156] Referring to Figure 13B, the second cholesteric liquid crystal (CLC) layer 1358B differs from the first CLC layer 1358A in that it has a second helical pitch (p2) that is different from the first helical pitch p1 of the first CLC layer 1358A in Figure 13A, and comprises a second set of chiral structures.

[0157] As shown in the figure, the second CLC layer 1358B is such that the second incident light beam 1316B is directed to the incident surface of the CLC layer 1358B at a first off-axis angle θ inc,1 A second off-axis angle θ that is different from the first. inc,2 When directed, a second reflected light beam 1320B is generated having a second reflection angle θ2 that is different from the first reflection angle θ1. As shown in the figure, the CLC layer 1358B is further configured to have a second off-axis angle range 1324B, similar to the first range 1324A described above with respect to Figure 13A.

[0158] Figure 13C illustrates a cross-sectional side view of CLCG1358, which includes multiple CLC layers having different helical pitches in a stacked configuration to achieve Bragg reflection at multiple off-axis incidence angles and high diffraction bandwidths. CLCG1358 includes CLC layers 1358A and 1358B, respectively, formed across each other, for example, in a stacked configuration and / or in contact with each other, as described above with respect to Figures 13A and 13B. Various parameters of the multiple CLC layers 1358A and 1358B, including different helical pitches, can be modified or optimized so that CLCG1358 is configured for efficient reflection at multiple off-axis incidence angles and high diffraction efficiency over a wider range of off-axis angles than can be achieved using only one CLC. For example, in the illustrated embodiment, p1 and p2 can be selected such that the resulting first and second ranges 1324A and 1324B overlap at least partially and provide high diffraction efficiency over a continuous wavelength range including the first and second ranges 1324A and 1324B. However, in other embodiments, p1 and p2 can be selected such that the first and second ranges 1324A and 1324B do not overlap.

[0159] During operation, the first and second CLC layers 1358A and 1358B are positioned at the first and second off-axis angles θ. inc,1 , θ inc,2 In this configuration, when the first and second incident light beams 1316A and 1316B are directed to the incident surface of the first CLC layer 1358A, the first incident light beam 1316A is substantially reflected by the first CLC layer 1358A at a first reflection angle θ1, while the second incident light beam 1358B is substantially transmitted through the first CLC layer 1358A toward the incident surface of the second CLC layer 1358B and substantially reflected by the second CLC layer 1358B at a second reflection angle θ2, thus forming across each other. For clarity, it should be understood that the concepts described above can be extended to any preferred number of CLC layers.

[0160] As described herein, throughout this specification, a light beam that “substantially transmits” through a layer may mean light that, as it exits the layer, has at least 20%, 30%, 50%, 70%, or 90% of the remaining incident light intensity. Similarly, a light beam that “substantially reflects” through a layer may mean light that, as reflected, has at least 20%, 30%, 50%, 70%, or 90% of the remaining incident light intensity.

[0161] Referring still to Figure 13C, in various embodiments, the liquid crystal molecules of the first and second CLC layers 1358A and 1358B may contain different amounts of the same chiral composite, such that the CLC layers 1358A and 1358B have different helical twisting forces (HTPs), as described above. For example, the second CLC layer 1358B may have a higher relative amount of the same chiral composite compared to the first CLC layer 1358A. In some embodiments, the pitch p may be inversely proportional to the ratio of chiral composites to the total liquid crystal composite, including chiral and non-chiral composites. However, embodiments are not limited in this way, and the first and second CLC layers 1358A and 1358B may have different chiral composites.

[0162] In addition, in various embodiments, the liquid crystal molecules of the first and second CLC layers 1358A and 1358B have different ratios λ / Λ1 and λ / Λ2, respectively, and the CLC layers 1358A and 1358B have different incident angles θ according to, for example, equation [3] inc,1 , θ inc,2 The same or different chiral composites may be included so that they can be configured for high diffraction efficiency.

[0163] Still referring to Figure 13C, the first and second CLC layers 1358A and 1358B can be fabricated directly on each other according to some embodiments. For example, the first CLC layer 1358A can be deposited on a matching layer that provides matching conditions for the first CLC layer 1358A, and then the second CLC layer 1358B can be deposited on the first CLC layer 1358B. Under these fabrication conditions, the surface of the first CLC layer 1358A can provide matching conditions for the second CLC layer 1358B. In some other embodiments, the CLC layers 1358A and 1358B can each be fabricated using separate matching layers. For example, the first CLC layer 1358A can be formed on the first matching layer, the second matching layer can be formed on the first CLC layer 1358A, and the second CLC layer 1358B can be formed on the second matching layer. According to some embodiments, an isolation layer, such as a thin oxide layer, may be formed on the first CLC layer 1358A prior to the formation of the second matching layer and / or the second CLC layer 1358B. In yet another embodiment, the two CLC layers 1358A and 1358B can be individually fabricated on different substrates and then stacked. In various embodiments, an intermediate layer can be formed between the two CLC layers 1358A and 1358B to improve adhesion, for example.

[0164] The concept described above with respect to CLCG having multiple CLC layers optimized for optimal diffraction efficiency at different off-axis angles can be extended to other alternative embodiments. In particular, in some embodiments, instead of forming multiple layers, a single CLC layer can be configured to have different regions optimized for optimal diffraction efficiency at different off-axis angles.

[0165] Figure 14 illustrates a cross-sectional side view of a CLCG 1400, which includes a single CLC layer 1404 having vertical regions with different helical pitches along the depth direction to produce Bragg reflections in different vertical regions with high diffraction bandwidths at multiple off-axis incidence angles. The CLC layer 1404 has multiple vertical regions with different parameters, e.g., different helical pitches, optimized so that high diffraction efficiency can be obtained over a wider range of off-axis angles than can be obtained using a single CLC layer with a uniform pitch in the depth direction. In the illustrated embodiment, the single CLC layer 1404 includes multiple vertical regions 1404A, 1404B, 1404C, and 1404D, which may each have different helical pitches p1, p2, p3, and p4. With respect to Figure 13C, as described above, the helical pitches p1, p2, p3, and p4 are such that multiple vertical regions 1404A, 1404B, 1404C, and 1404D have an incidence angle θ, respectively. incA , θ incB , θ incC , and θ incD It is configured for optimal diffraction efficiency in the following conditions, where the corresponding reflection angles are θA, θB, and θ, respectively. C, and can be selected to result in light beams reflected at different vertical depths at θD. Furthermore, as described above with respect to Figure 13C, the CLC layer 1404 can be further configured to have off-axis angles in separate ranges, from which relatively high diffraction efficiency can be obtained. Naturally, four vertical regions are illustrated for clarity, but any number of preferred regions can be included within the CLC layer 1404. In addition, different variations having multiple CLC layers, as described above with respect to CLCG 1358 in Figure 13C, may also be applicable to CLCG 1400.

[0166] In the embodiment illustrated in Figure 14, the values ​​of the helical pitches p1, p2, p3, and p4 decrease with increasing depth from the incident surface 1404S, such that a decrease in the helical pitch gradient is created in the depth direction (negative z-direction). When the rate of decrease of the helical pitch as a function of the layer depth in the z-direction is uniform across the thickness of the CLC layer 1404, a graph 1408 representing a linear relationship between depth and helical pitch can be obtained. However, embodiments are not limited thereto. For the embodiment, the helical pitches p1, p2, p3, and p4 can be increased or decreased at any depth according to some other embodiments and can vary at different rates as a function of the layer depth.

[0167] A CLC layer 1404 having a gradient of helical pitch can be processed by varying, for example, increasing or decreasing, the helical twisting force (HTP) of liquid crystal molecules at different depths of the CLC layer. The HTP can be spatially varied by changing the relative amount of chiral composites. In various embodiments, by chemically and / or mechanically mixing chiral and non-chiral composites, such as nematic composites, at different vertical depths, the helical pitches of vertical regions 1404A, 1404B, 1404C, and 1404D are each set to different incident angles θ, based on the inverse relationship between the relative proportion of chiral composites and the helical pitch. incA , θ incB , θ incC , and θ incDIt can be configured for optimal diffraction efficiency. For example, a mixture of different chemical components (e.g., chiral diacrylate monomers and nematic / non-chiral monoacrylate monomers) that undergo a polymerization process at different reaction rates under UV irradiation can be used. In addition, or alternatively, HTP can be spatially varied by changing irradiation conditions, including the exposure intensity and / or exposure time of UV irradiation at different depths of the CLC layer. HTP can also be spatially varied by varying pre / post-treatment of the UV polymerization process, including heat treatment before, after, and / or during UV irradiation. For example, when a UV-absorbing dye is added to the mixture, an intensity gradient of UV light at different depths of the CLC layer can be created. For example, due to the UV intensity gradient, polymerization near the surface may proceed faster compared to the bottom region of the CLC layer. For example, when the cholesteric component is a diacrylate, the probability of it being incorporated into the resulting polymer is much higher, for example, twice as high, than the probability of a nematic monoacrylate being incorporated into the polymer. Under certain circumstances, the overall polymerization rate is controlled so that the depletion of chiral diacrylate near the surface region of the CLC layer generates a diacrylate concentration gradient in the depth direction of the CLC layer. This, in turn, initiates the diffusion of diacrylate toward the surface region of the CLC layer. After complete photopolymerization, the surface region of the CLC layer may contain more chiral material and therefore a shorter helical pitch compared to the bottom region of the CLC layer, which contains a relatively larger amount of non-chiral composites. Under certain other circumstances, heat treatment before / after or during UV irradiation can be added to the polymerization process to control the helical pitch gradient. Thus, with or without heat treatment, a helical pitch gradient can be achieved along the depth direction of the CLC layer by controlling the ratio between two different liquid crystal monomers and / or the dose of UV irradiation at different depths.

[0168] For some applications, it may be desirable for a diffraction grating to have certain optical properties, among other parameters, such as off-angle diffraction efficiency, refractive index, wavelength selectivity, polarization selectivity, and phase selectivity, in order to vary along a lateral direction perpendicular to the layer normal. Lateral variation is desired when the grating is stacked with a waveguide, for example, as illustrated in relation to Figures 6 and 7 above, so that light propagates laterally. However, in such a configuration, the intensity of the light may attenuate as it propagates within the waveguide (e.g., 1182 in Figure 7). Such a configuration may also be desirable to intentionally distort the light intensity across the grating (e.g., 1282 in Figure 7) to match the spatial and / or angular variations in sensing efficiency associated with the human eye, thereby maximizing the user experience. Thus, there is a need for an optical element, such as a diffraction grating, that has spatially tunable optical properties.

[0169] Figure 15 illustrates a cross-sectional side view of a CLCG including a CLC layer having lateral regions with different helical pitches along the lateral direction to spatially vary Bragg reflection. The CLC layer 1424 has multiple lateral regions having different liquid crystal material parameters, e.g., helical pitches, so that laterally variable properties, e.g., laterally variable off-axis incidence angles for Bragg reflection, can be obtained. In the illustrated embodiment, the CLC layer 1424 includes multiple lateral regions 1424A, 1424B, and 1424C, each having a period ∧ and individual helical pitches p1, p2, and p3. The helical pitches p1, p2, and p3 correspond to multiple vertical regions 1424A, 1424B, and 1424C, each having different off-axis incidence angles θ. incA , θ incB , and θ incC It is configured for optimal diffraction efficiency in which the corresponding reflection angle θ is A , θ B , and θ CIt can be selected to yield a reflected light beam at [location]. Furthermore, as described above with respect to Figure 13C, different lateral regions of the CLC layer 1424 can be further configured to have similar distinct ranges of off-axis angles, which can yield relatively high diffraction efficiencies. Naturally, three vertical regions are illustrated for clarity, but any number of preferred regions can be included within the CLC layer 1424.

[0170] In the embodiment illustrated in Figure 15, the magnitudes of the helical pitches p1, p2, and p3 can be monotonically varied laterally so as to create a gradient of helical pitch. When the rate of change of the helical pitch in the x-direction is uniform across the width or length of the CLC layer 1424, a linear relationship between length or width and helical pitch can be obtained as shown in Graph 1428. However, embodiments are not limited thereto. For the embodiment, the helical pitches p1, p2, and p3 can be increased or decreased at any lateral position and can be varied at different rates in the x-direction along length or width according to various other embodiments.

[0171] According to various embodiments, the CLC layer can be processed to have laterally variable diffraction properties by, for example, spatially varying the matching properties of the liquid crystal molecules or other material properties. For example, in the similar configuration described above with respect to Figure 14, a lateral helical pitch gradient can be achieved along the lateral dimension by, for example, controlling the ratio between two different liquid crystal monomers and / or the dose of UV irradiation in different lateral regions. (Waveguide coupled with CLCG for wavelength-selective photocoupling)

[0172] As described above, for various applications, including internal and external coupling of light, waveguide devices can be configured to propagate light by total internal reflection (TIR). Figure 16 illustrates an embodiment of an optical waveguide device 1600, comprising a waveguide 1604 coupled to CLCG 1150. CLCG 1150 comprises liquid crystal molecules arranged as a plurality of chiral structures, similar in style to the chiral structures 1162-1, 1162-2, ..., 1162-i described above with respect to Figure 11. Waveguide 1604 is positioned across CLCG 1150 and optically coupled to CLCG 1150. When the elliptic / circularly polarized incident light 1016-R / L has polarization variability that matches the rotation direction of the chiral liquid crystal molecule, the incident light 1016-R / L is Bragg reflected by CLCG1150 at an angle such that the coupled light propagates laterally (e.g., in the x-direction) by total internal reflection (TIR), and coupled into waveguide 1604. Although not constrained by any theory, the TIR condition is that the diffraction angle θ is equal to the critical angle θ of the waveguide. C It can be satisfied when it exceeds [a certain value]. Under some circumstances, the TIR condition can be expressed as follows: sin(θ C ) = 1 / n t [4] In the formula, n t n is the refractive index of waveguide 1604. According to various embodiments, t This can be approximately 1 to 2, approximately 1.4 to 1.8, or approximately 1.5 to 1.7. For example, the waveguide may be made of a polymer such as polycarbonate or glass.

[0173] Figure 17A shows the first CLCG1750A coupled with θ>θ c3When this is the case, a first optical waveguide device 1700A is illustrated, comprising a first waveguide 1704A configured to propagate light having a third wavelength λ3 by total internal reflection (TIR). The first CLCG 1750A has a first period ∧1 and a first helical pitch p1. According to some embodiments, the first waveguide device 1700A may be configured by TIR to propagate light in the visible spectrum (e.g., with wavelengths approximately 400 nm to 700 nm). According to some other embodiments, the first waveguide device 1700A may be configured by TIR to propagate light in the infrared spectrum (e.g., in the near-infrared portion of the spectrum with wavelengths approximately 700 nm to 1400 nm). As described above with respect to Figures 10 and 11, Bragg reflection occurs at the wavelengths represented by the aforementioned equation [1] within a bandwidth of wavelength Δλ represented by the aforementioned equation [2]. For example, the first CLCG1750A may be designed by TIR to couple a third incident light 1736 having a third wavelength λ3 in one of the following colors: blue (e.g., about 450 nm), green (e.g., about 550 nm), red (e.g., about 650 nm), or infrared. As shown in the figure, when Δλ is about 60 nm, about 80 nm, or about 100 nm, as described above, the first and second lights 1716 and 1726 having first and second wavelengths λ1, λ2 are substantially transmitted, since equation [1] is not satisfied with respect to these colors, and this is not coupled into the first waveguide 1704, since equation [4] is not satisfied.

[0174] Figure 17B illustrates a second optical waveguide device 1700B, which is combined with the first optical waveguide device 1700A illustrated above with respect to Figure 17A. The optical waveguide device 1700B comprises a second waveguide 1704B, which is positioned in the optical path following the optical waveguide device 1700A and coupled to a second CLCG 1750B, and is configured to propagate a second light 1726 having a second wavelength λ2 by total internal reflection (TIR) ​​when θ > θc2. The second CLCG 1750B has a second period ∧2 and a second helical pitch p2. As described above with respect to Figure 17A, the first and second light 1716 and 1726, having first and second wavelengths λ1 and λ2, are substantially transmitted through the first optical waveguide device 1700A. Of the transmitted first and second optics 1716 and 1726, the second CLCG 1750B may be designed to couple a second incident optics 1726 having a second wavelength λ2 among the transmitted optics, which are blue (e.g., about 450 nm), green (e.g., about 550 nm), red (e.g., about 650 nm), or infrared, by TIR when θ > θc2. Thus, as shown in the figure, when Δλ is about 60 nm, about 80 nm, or about 100 nm, as described above, the first optics 1716 having a first wavelength λ1 is substantially transmitted further through the second waveguide device 1700B.

[0175] Figure 17C illustrates a third optical waveguide device 1700C, which is combined with the first and second optical waveguide devices 1700A and 1700B illustrated above with respect to Figure 17B. The third optical waveguide device 1700C comprises a third waveguide 1704C, which is positioned in the optical path following the first and second optical waveguide devices 1700A and 1700B, coupled to a third CLCG 1750C, and configured to propagate a first light 1716 having a first wavelength λ2 by total internal reflection (TIR) ​​when θ > θc1. The third CLCG 1750C has a third period ∧3 and a third helical pitch p3. As described above with respect to Figure 17B, the first light 1716 having a first wavelength λ1 is substantially transmitted through the first and second waveguide devices 1700A and 1700B. A third CLCG1750C may be designed to couple a first incident light 1716 having a first wavelength λ1 in the transmitted light of blue (e.g., about 450 nm), green (e.g., about 550 nm), red (e.g., about 650 nm), or infrared, by TIR when θ > θc1. Thus, as shown in the figure, when Δλ is about 60 nm, about 80 nm, or about 100 nm, as described above, the first light 1716 having the first wavelength λ1 is substantially coupled into the third waveguide 1704C because equation [4] is satisfied.

[0176] Therefore, as described above with respect to Figures 17A-17C, by placing one or more of the first, second, and third optical waveguide devices 1700A, 1700B, and 1700C in the same optical path, one or more of the first, second, and third optics 1716, 1726, and 1736 having different wavelengths λ1, λ2, and λ3 can be coupled to propagate by TIR in one of the first, second, and third waveguides 1704A, 1704B, and 1704C, respectively. In Figures 17A–17C, the first to third optical waveguide devices 1704A, 1704B, and 1704C each have dedicated first to third waveguides 1704A, 1704B, and 1704C and dedicated first to third CLCGs 1750A, 1750B, and 1750C, respectively, but the embodiments are not limited thereto. For example, a single waveguide can couple Bragg-reflected light from a stack of multiple CLCGs by TIR, as illustrated later with respect to Figure 18. In addition, any number of optical waveguide devices greater than (or less than) three can also be combined for further selective coupling by Bragg reflection.

[0177] Figure 18 illustrates an optical waveguide device 1800 comprising a common waveguide 1704 coupled to a plurality of CLCGs 1750. The plurality of CLCGs 1750 are configured as a stack comprising first to third CLCGs 1750A-1750C, each configured to propagate third, second, and first optics 1736, 1726, and 1716 having third, second, and first wavelengths λ3, λ2, and λ1, respectively, by total internal reflection (TIR). TIR occurs when one or more of the third, second, and first optics 1736, 1726, and 1716 satisfy the conditions θ>θc3, θ>θc2, and θ>θc1, respectively, in a similar manner to that described above with respect to Figures 17A-17C. In a similar manner, the first, second, and third CLCGs 1750A, 1750B, and 1750C are configured to selectively Bragg reflect the third, second, and first optics 1736, 1726, and 1716 when θ > θc3, θ > θc2, and θ > θc1, respectively. Naturally, any number of CLCGs (more than three, or less than three) can be stacked for further selective coupling by Bragg reflection. Thus, a more compact waveguide device 1800 can be obtained by employing a common waveguide 1704 compared to the embodiments described above with respect to Figures 17B and 17C. Also, instead of three distinctly different CLCG layers (as shown in Figure 18), the stack of CLCG layers can be arranged as a single (or more) layer with a helical pitch gradient including the range p1 to p3.

[0178] As described above with respect to Figures 17A-18, the first to third CLCGs 1750, 1750B, and 1750C each have first to third periods ∧1, ∧2, and ∧3, respectively, and first to third helical pitches p1, p2, and p3, respectively. In various embodiments, each CLCG can be configured such that the wavelength / period ratio λ / ∧ is about 0.3 to 2.3, about 0.8 to 1.8, or about 1.1 to about 1.5, for example, about 1.3. Alternatively, the period (∧) can be configured to be about 1 nm to 250 nm smaller, about 50 nm to 200 nm smaller, or about 80 nm to 170 nm smaller than the individual wavelengths (λ) for which the CLCG is configured for Bragg reflection. For example, when λ1, λ2, and λ3 are within the visible range, e.g., approximately 620 nm to 780 nm, e.g., approximately 650 nm (red), approximately 492 nm to 577 nm, e.g., 550 nm (green), and approximately 435 nm to 493 nm, e.g., approximately 450 nm (blue), respectively, the corresponding periods Λ1, Λ2, and Λ3 can be approximately 450 nm to 550 nm, e.g., approximately 500 nm, approximately 373 nm to 473 nm, e.g., approximately 423 nm, and approximately 296 nm to 396 nm, e.g., approximately 346 nm, respectively. Alternatively, when λ1, λ2, and λ3 are in the infrared range, for example, within the near-infrared range of about 750 nm to about 1400 nm, for example, about 850 nm, the corresponding periods Λ1, Λ2, and Λ3 can be in the range of about 975 nm to about 1820 nm, for example, about 1105 nm. In addition, in various embodiments, each CLCG can be configured such that the wavelength / helical pitch ratio λ / p is about 0.6 to 2.6, about 1.1 to 2.1, or about 1.4 to about 1.8, for example, about 1.6. Alternatively, the helical pitch (p) can be configured to be about 50 nm to 350 nm smaller, about 100 nm to 300 nm smaller, or about 140 nm to 280 nm smaller than the individual wavelengths (λ) in which the CLCG is configured for Bragg reflection.For example, when λ1, λ2, and λ3 are approximately 620nm to 780nm, e.g., 650nm (red), 492nm to 577nm, e.g., 550nm (green), and 435nm to 493nm, e.g., 450nm (blue), respectively, the corresponding helical pitches p1, p2, and p3 can be approximately 350nm to 450nm, e.g., 400nm, 290nm to 390nm, e.g., 340nm, and 230nm to 330nm, e.g., 280nm, respectively. Alternatively, when λ1, λ2, and λ3 are in the infrared range, for example, within the near-infrared range of approximately 750 nm to approximately 1400 nm, for example, approximately 850 nm, the corresponding periods Λ1, Λ2, and Λ3 can be approximately 1200 nm to approximately 2240 nm, for example, approximately 1360 nm. (Waveguide coupled with CLCG and mirrors for wavelength-selective photocoupling)

[0179] Figure 19 illustrates an optical waveguide device 1900, which includes a waveguide 1604 coupled to the CLCG1150, similar to the optical waveguide device described above with respect to Figure 16. As described above with respect to Figures 10 and 11, when operating, the CLCG1150 substantially reflects incident light when the polarization palmarity of the elliptic / circularly polarized incident light has the same rotational direction as the chiral liquid crystal molecules of the CLCG1150. As shown, incident on the surface 1050S are a light beam 1016-L with left-handed circular polarization and a light beam 1016-R with right-handed circular polarization. In the illustrated embodiment, the chiral liquid crystal molecules are continuously rotated clockwise when viewed in the direction in which the incident light beams 1016-L and 1016-R travel, i.e., in the negative z-direction, such that the rotational direction of the liquid crystal molecules matches the palmarity of the light beam 1016-R with right-handed circular polarization. As a result, the light beam 1016-R, which has right-handed circular polarization, is substantially reflected by CLCG1150, while the light beam 1016-L, which has left-handed circular polarization, is substantially transmitted through CLCG1150.

[0180] For some applications, it may be desirable to reverse the polarization palm of elliptic or circularly polarized light prior to coupling into a waveguide device similar to that described above with respect to Figure 19. This may be the case, for example, when the polarization palm of the incident elliptic or circularly polarized light does not match the direction of rotation of the chiral structure in the CLCG, so that the CLCG is not configured to Bragg reflect the light for coupling into the waveguide, as discussed above. For some other applications, it may be desirable to recycle the light transmitted through the CLCG due to the lack of matching between the polarization palm of the incident elliptic or circularly polarized light and the direction of rotation of the chiral structure in the CLCG. To address these and other needs, various embodiments of waveguide devices that employ polarization-converting reflectors to address these needs are disclosed below.

[0181] Figure 20 illustrates an optical waveguide device 2000 comprising a waveguide 1150 coupled to a CLCG 1604 and a polarization-shifting reflector 2004, wherein the CLCG 1604 is configured to receive incident light, and the waveguide 1150 is configured to propagate the light Bragg-reflected from the CLCG by total internal reflection (TIR). The polarization-shifting reflector 2004 is configured such that, depending on the reflection from there, the polarization angle of the incident elliptical or circularly polarized light is reversed to the opposite polarization angle (e.g., left-handed to right-handed or right-handed to left-handed). Waveguide device 2000 is similar to waveguide device 1900 described above with respect to Figure 19, but instead of being initially configured to receive the incident light beam through the waveguide 1150, waveguide device 2000 is initially configured to receive, for example, an incident light beam 2016-L having left-handed circular polarization through the CLCG 1604. The incident light beam 2016-L has polarization variability such that, when viewed in the propagation direction of the incident light beam 2016-L (negative z-direction), it does not match the rotation direction of the chiral structure within CLCG1604, so that it is not Bragg reflected by CLCG1604. As a result, the incident light beam 2016-L is substantially transmitted through CLCG1604 and subsequently reflected by the polarization-converting reflector 2004. For example, the reflected light beam 2016-R, which has right-handed circular polarization, thereby becomes the incident light beam onto the surface 1150S of waveguide 1150. Due to the inverted polarization variability, the reflected light beam 2016-R, here incident on the surface 1150S of waveguide 1150, has polarization variability such that, when viewed in the propagation direction of the reflected light beam 2016-R (positive z-direction), it matches the rotation direction of the chiral structure within CLCG1604, so that it is Bragg reflected by CLCG1604. Furthermore, as the reflected beam 2018 is reflected at an angle θ>θc with respect to the layer normal direction (z-axis), the reflected beam 2016-R is coupled to the waveguide 1150 and propagates through it laterally (e.g., in the x-direction).

[0182] Figure 21A illustrates the optical waveguide device 2000, as described above with respect to Figure 20, under conditions of linear polarization or depolarization, such that the incident light beam 2116 can be processed to include both left-handed and right-handed circularly polarized components, respectively. Under such conditions, the incident light beam 2116 can be coupled into the waveguide by TIR in both lateral directions. For example, as described above with respect to Figure 20, a component of the incident light beam 2116 having a polarization palmarity, e.g., left-handed, that does not match the rotation direction of the chiral structure in CLCG 1604 is substantially transmitted through CLCG 1604, subsequently reflected by the polarization conversion reflector 2004, its polarization palmarity is reversed, e.g., to right-handed, and it is coupled into the waveguide 1150, through which it propagates in a first lateral direction (e.g., the positive x-direction). On the other hand, as described above with respect to Figure 19, a component of the incident light beam 2116 having polarization palpability, e.g., right-palpability, that matches the rotational direction of the chiral structure in CLCG 1604 is substantially reflected directly by CLCG 1604 and subsequently coupled into waveguide 1150, through which it propagates in a second lateral direction opposite to the first lateral direction (e.g., the negative x-direction).

[0183] Figure 21B illustrates the optical waveguide device 2000 described above with respect to Figure 21A, under the condition that the incident light is polarized into two orthogonal elliptical or circularly polarized beams, e.g., a left-handed circularly polarized light beam 1016-L and a right-handed circularly polarized light beam 1016-R. Under such conditions, the incident light beams 1016-L and 1016-R can be coupled into the waveguide so as to propagate bilaterally by TIR in a manner similar to that described above with respect to Figure 21A. For example, a light beam 1016-L having a polarization palmarity, e.g., left-handed, that does not match the rotation direction of the chiral structure in CLCG 1604 is substantially transmitted through CLCG 1604, subsequently reflected by the polarization conversion reflector 2004, its polarization palmarity is reversed, e.g., to right-handed, and it is coupled into the waveguide 1150, through which it propagates in a first lateral direction (e.g., the positive x-direction). On the other hand, an incident light beam 1016-R having polarization palpability, e.g., right-handed palpability, that matches the rotational direction of the chiral structure within CLCG1604, is substantially reflected directly by CLCG1604 and subsequently coupled into waveguide 1150, through which it propagates in a second lateral direction opposite to the first lateral direction (e.g., the negative x-direction).

[0184] Figure 22A illustrates an optical waveguide device 2200 comprising a common waveguide 2204 coupled to a plurality of CLCGs arranged as a stack, including, for example, a first CLCG 2204 having a chiral structure with a first rotational direction and a second CLCG 2208 having a chiral structure with a second rotational direction opposite to the first rotational direction. As described above with respect to various embodiments, during operation, the incident light is reflected when the direction of the polarization of the incident light beam matches the direction of rotation of the liquid crystal molecules in the chiral structure of the CLCG. The illustrated optical waveguide device 2200 is under conditions in which the incident light beam 2116 is linearly polarized or unpolarized. Under such conditions, the incident light beam 2116 can be coupled into the waveguide by TIR in both bidirectional directions (positive and negative x-directions). In the illustrated embodiment, when viewed in the direction of the incident light 2116, i.e., the negative z-direction, the chiral liquid crystal molecules of the first CLCG2204 are continuously rotated clockwise, while the chiral liquid crystal molecules of the second CLCG2204 are continuously rotated in the opposite counterclockwise direction.

[0185] Still referring to Figure 22A, the components of the elliptic or circular incident light beam 2116 having a first polarization variability, e.g., a right-handed polarization component, which matches the rotational direction of the chiral structure of the first CLCG 2204, e.g., clockwise, are substantially reflected by the first CLCG 2204, thereby resulting in the first reflected beam 2118A at an angle θ>θc1 with respect to the layer normal direction (z-axis), which couples to the common waveguide 2204 and propagates through it in a first lateral direction (e.g., positive x-direction).

[0186] Still referring to Figure 22A, on the other hand, a component of the elliptic or circular incident light beam 2116 having a second polarization palmarity, e.g., a left-handed polarization component, which does not match the rotational direction of the chiral structure of the first CLCG 2204, is substantially transmitted through the first CLCG 2204. After being transmitted through the first CLCG 2204, the elliptic or circular incident light beam 2116 having a second polarization palmarity 2116 that matches the rotational direction of the chiral structure of the second CLCG 2208, e.g., a counterclockwise direction, is substantially reflected by the second CLCG 2208, thereby resulting in a second reflected beam 2118B at an angle θ>θc2 with respect to the layer normal direction (z-axis), which couples to the common waveguide 2204 and propagates through it in a second lateral direction (e.g., the negative x-direction).

[0187] Figure 22B illustrates the optical waveguide device 2000 described above with respect to Figure 22A, under different conditions in which the incident light is polarized into two orthogonal elliptical or circularly polarized beams, e.g., a left-handed elliptical / circularly polarized beam, e.g., a light beam 1016-L, and e.g., a right-handed elliptical / circularly polarized light beam, e.g., a light beam 1016-R. Under such conditions, the incident light beams 1016-L and 1016-R, having first and second polarization palpations, e.g., left-handed and right-handed, can be coupled into a common waveguide 2204 by TIR in both bidirectional directions, in a manner similar to that described above with respect to Figure 22A.

[0188] The embodiments described above with respect to Figures 21B and 22B may be particularly advantageous in certain applications where different optical signals (i.e., images) are encoded in orthogonal circular polarization. In such circumstances, the light can be coupled in opposite directions (e.g., positive and negative x-directions) depending on the polarization palmarity.

[0189] Figure 22C illustrates an optical waveguide device 2220 comprising a common waveguide 2250 coupled to a plurality of CLCGs arranged as a stack, including, for example, a first CLCG 2204 having a chiral structure with a first rotational direction and a second CLCG 2208 having a chiral structure with a second rotational direction opposite to the first rotational direction. Unlike the embodiments described with respect to Figures 22A and 22B, in the waveguide device 2220, the common waveguide 2250 is interposed between the first and second CLCG layers 2204, 2208. For illustrative purposes, the illustrated optical waveguide device 2220 is under conditions in which the incident light beam 2116 is linearly polarized or unpolarized. Under such conditions, the incident light beam 2116 can be coupled into the waveguide in both lateral directions by TIR. In the illustrated embodiment, when viewed in the direction of the incident light 2116, i.e., the negative z-direction, the chiral liquid crystal molecules of the first CLCG2204 are continuously rotated clockwise, while the chiral liquid crystal molecules of the second CLCG2204 are continuously rotated in the opposite counterclockwise direction. Naturally, the opposite arrangement is also possible.

[0190] Still referring to Figure 22C, a component of an elliptical or circular incident light beam 2116 having a first polarization variability, e.g., a right-handed polarization component, which matches the rotational direction of the chiral structure of the first CLCG 2204, e.g., clockwise, is substantially reflected by the first CLCG 2204, thereby yielding a first reflected beam 2118A at an angle θ>θc1 with respect to the layer normal direction (z-axis), which is subsequently reflected from the outer surface of the first CLCG 2204 before being coupled by TIR into the common waveguide 2250 and propagating through it in a first lateral direction (e.g., negative x-direction).

[0191] Still referring to Figure 22C, on the other hand, a component of the elliptic or circular incident light beam 2116 having a second polarization palmarity, e.g., a left-handed polarization component, which does not match the rotational direction of the chiral structure of the first CLCG 2204, e.g., clockwise, is substantially transmitted through the first CLCG 2204 and further through the common waveguide 2204, and then substantially reflected by the second CLCG 2208, thereby yielding a second reflected beam 2218B at an angle θ>θc2 with respect to the layer normal direction (z-axis), which is coupled by TIR to the common waveguide 2250 and propagates through it in a second lateral direction (e.g., positive x-direction). (Cholesteric liquid crystal off-axis mirror)

[0192] As described above with respect to various embodiments, a CLC layer can be configured as a Bragg reflector by matching the polarization palmarity of incident elliptical or circularly polarized light with the rotational direction of the liquid crystal molecules in the chiral structure of the CLC layer. Furthermore, one or more CLC layers having different helical pitches can be configured as a wavelength-selective Bragg reflector with high bandwidth. Based on the concepts described herein with respect to various embodiments, a CLC layer can be configured as an off-axis mirror configured to selectively reflect a first range of wavelengths, such as infrared wavelengths (e.g., near-infrared), while transmitting another range of wavelengths, such as visible wavelengths. The following discloses the applications of various embodiments of CLC off-axis mirrors implemented in eye-tracking systems.

[0193] Figure 23 illustrates embodiments of an eye-tracking system 2300 employing a cholesteric liquid crystal reflector (CLCR), such as a wavelength-selective CLCR 1150, configured to image the viewer's eye 302, according to various embodiments. Eye tracking can be an important feature in bidirectional vision or control systems, particularly in wearable displays for virtual / augmented / mixed reality display applications, such as the wearable display system 200 in Figure 2 or the system 700 described in Figures 24A-24H, among other applications. To achieve good eye tracking, it may be desirable to acquire an image of the eye 302 at a low viewpoint angle, and therefore, it may be desirable to position the eye-tracking camera 702b near the center of the viewer's eye. However, such a position of the camera 702b may interfere with the user's view. Alternatively, the eye-tracking camera 702b may be positioned lower or to the side. However, such camera placement can increase the difficulty of achieving robust and accurate eye tracking because eye images are captured at a steeper angle. By configuring the CLCR1150 to selectively reflect infrared (IR) light 2308 (e.g., having a wavelength of 850 nm) from the eye 302 while transmitting visible light 2304 from the world, as shown in Figure 4, the camera 702b can be positioned away from the user's view while capturing eye images at a normal or low viewpoint angle. Such a configuration does not interfere with the user's view because visible light is not reflected. The same CLCR1150 can also be configured as an IR illuminator 2320, as shown. The low viewpoint angle of the IR illuminator results in little occlusion, for example, from the eyelashes, and its configuration allows for more robust detection of specular reflections, which can be an important feature in modern eye tracking systems.

[0194] Referring still to Figure 23, according to various embodiments, the CLCR1150 comprises one or more cholesteric liquid crystal (CLC) layers, each comprising a plurality of chiral structures, and each chiral structure comprises a plurality of liquid crystal molecules extending in the layer depth direction (e.g., the z-direction) and continuously rotated in a first rotational direction, as described above. The arrangement of the liquid crystal molecules in the chiral structures varies periodically in a lateral direction perpendicular to the layer depth direction, such that one or more CLC layers are configured to substantially Bragg reflect a first incident light having a first wavelength (λ1) while substantially transmitting a second incident light having a second wavelength (λ2). As described in any of the foregoing, one or more CLC layers are configured to substantially Bragg reflect first and second elliptical or circularly polarized incident light having polarization palmarity that matches a first rotational direction when viewed in the layer depth direction, while substantially transmitting first and second elliptical or circularly polarized incident light having polarization palmarity opposite to the first rotational direction when viewed in the layer depth direction. According to the embodiment, the arrangement of liquid crystal molecules that periodically vary laterally is arranged to have a period laterally such that the ratio of the first wavelength to the period is about 0.5 to about 2.0. According to the embodiment, the first wavelength is in the near-infrared range of about 600 nm to about 1.4 μm, for example, about 850 nm, as described in any of the foregoing, and the second wavelength is in the visible range having one or more colors. According to the embodiment, the chiral liquid crystal molecules are pre-tilted with respect to the direction normal to the layer depth direction. As configured, one or more CLC layers are such that the first incident light is directed at a certain angle (θR) with respect to the depth of the layer (z-direction), for example, based on the equation described above [3], approximately 50° with respect to the depth of the layer o , about 60 o , about 70 o , or about 80 o It is designed to reflect light beyond a certain degree.

[0195] Referring back to Figure 2, the eyes of a wearer of a head-mounted display (HMD) (e.g., the wearable display system 200 in Figure 2) can be imaged using a reflective off-axis diffractive optical element (DOE), which may be a holographic optical element (HOE). The resulting image can be used to track one or both eyes, image the retina, reconstruct the eye shape in three dimensions, extract biometric information from the eye (e.g., iris recognition), etc.

[0196] There are several reasons why a head-mounted display (HMD) may use information about the wearer's eye condition. For example, this information can be used to estimate the wearer's gaze direction or for biometric identification. However, this problem is difficult due to the short distance between the HMD and the wearer's eyes. This is further complicated by the fact that gaze tracking requires a larger field of view, while biometric identification requires a relatively high number of pixels on a target on the iris. With respect to imaging systems that would attempt to accomplish both of these objectives, the requirements of the two tasks primarily conflict. Finally, both problems are further complicated by occlusion by the eyelids and eyelashes. Embodiments of imaging systems described herein address some or all of these problems. Various embodiments of the imaging system 700 described herein with reference to Figures 24A–24F can be used in conjunction with an HMD, including a display device described herein (e.g., the wearable display system 200 shown in Figure 2 and / or the display system 1000 shown in Figure 6).

[0197] Figure 24A schematically illustrates an embodiment of the imaging system 700, which includes an imaging unit 702b used to visualize eye 304 and mounted close to the wearer's temple (e.g., on the frame 64 of the wearable display system 200, Figure 2, e.g., on the ear hook). In other embodiments, a second imaging unit is used for the wearer's other eye 302 so that each eye is imaged separately. The imaging unit 702b may include an infrared digital camera sensitive to infrared radiation. The imaging unit 702b is mounted facing forward (in the direction of the wearer's vision) rather than facing backward and directed towards eye 304 (similar to the camera 500 shown in Figure 6). By positioning the imaging unit 702b closer to the wearer's ear, the weight of the imaging unit 702b is also closer to the ear, and the HMD may be easier to wear compared to an HMD in which the imaging unit faces backward and is positioned closer to the front of the HMD (for example, close to the display 62 in Figure 2). In addition, by positioning the forward-facing imaging unit 702b near the wearer's temple, the distance from the wearer's eye 304 to the imaging unit is approximately twice that of a rear-facing imaging unit positioned near the front of the HMD (for example, compared to the camera 500 shown in Figure 4). Since the depth of field of the image is approximately proportional to this distance, the depth of field for the forward-facing imaging unit 702b is approximately twice that of a rear-facing imaging unit. The greater depth of field for the imaging unit 702b may be advantageous for imaging the eye area of ​​a wearer who has a large or protruding nose, brow ridge, etc.

[0198] The imaging unit 702b is positioned to view the inner surface 704 of an otherwise transparent optical element 706. The optical element 706 may be part of the HMD's display 708 (or lenses in a pair of glasses). The optical element 706 may be transparent to at least 10%, 20%, 30%, 40%, 50%, or more of the visible light incident on the optical element. In other embodiments, the optical element 706 does not need to be transparent (e.g., in a virtual reality display). The optical element 706 may comprise a CLC off-axis mirror 708. The CLC off-axis mirror 708 may be a surface that reflects a first range of wavelengths while being substantially transparent to a second range of wavelengths (different from the first range of wavelengths). The first range of wavelengths may be in the infrared spectrum, and the second range of wavelengths may be in the visible spectrum. For example, the CLC off-axis mirror 708 may comprise a hot mirror, which reflects infrared light while transmitting visible light. In such embodiments, infrared light 710a, 712a, 714a from the wearer propagates to the optical element 706, is reflected from there, and yields reflected infrared light 710b, 712b, 714b, which can be imaged by the imager 702b. In some embodiments, the imager 702b may be sensitive to, or capable of capturing, at least a subset (non-empty subset and / or subset less than all) of a first range of wavelengths reflected by the CLC off-axis mirror 708. For example, the CLC off-axis mirror 708 may reflect infrared light in the range of 700 nm to 1.5 μm, and the imager 702b may be sensitive to, or capable of capturing, near-infrared light in the wavelength range of 700 nm to 900 nm. In another embodiment, the CLC off-axis mirror 708 may reflect infrared light in the range of 700 nm to 1.5 μm, and the imaging unit 702b may include a filter that filters out infrared light in the range of 900 nm to 1.5 μm so that the imaging unit 702b can capture near-infrared light in the wavelength range of 700 nm to 900 nm.

[0199] Visible light from the outside world (1144, Figure 6) is transmitted through the optical element 706 and can be perceived by the wearer. In effect, the imaging system 700 shown in Figure 24A acts as if there were a virtual imager 702c directed in the opposite direction toward the wearer's eye 304. The virtual imager 702c can image virtual infrared light 710c, 712c, 714c (shown as dotted lines) propagating from the wearer's eye 704 through the optical element 706. A hot mirror (or other DOE as described herein) may be placed on the inner surface 704 of the optical element 706, but this is not limiting. In other embodiments, the hot mirror or DOE may be placed on the outer surface of the optical element 706 or within the optical element 706 (e.g., a volume HOE).

[0200] Figure 24B schematically illustrates another embodiment of the imaging system 700. In this embodiment, viewpoint distortion can be reduced or eliminated by the use of a viewpoint control lens assembly 716b (e.g., a deflection lens assembly, a tilt lens assembly, or a tilt-deflection lens assembly) with the visual imaging unit 702b. In some embodiments, the viewpoint control lens assembly 716b may be part of the lens of the imaging unit 702b. The viewpoint control lens 716b can be configured such that its normal to the imaging unit 702b is substantially parallel to the normal to a region of the surface 704, including the DOE (or HOE) or hot mirror. In effect, the imaging system 700 shown in Figure 24B acts as if it were a virtual imaging unit 702c with a virtual viewpoint control lens assembly 716c that is pointed backward toward the wearer's eye 304.

[0201] In addition, or alternatively, as schematically shown in Figure 24C, the CLC off-axis mirror 708 of the optical element 706 may have an off-axis holographic mirror (OAHM) on its surface 704, which is used to facilitate viewing by the eye 304 by the camera imaging unit 702b by reflecting light 710a, 712a, 714a and capturing the reflected light 710b, 712b, 714b. The OAHM 708 may also have refractive power, in which case it can be an off-axis stereodiffractive optical element (OAVDOE), as schematically shown in Figure 24D. In the embodiment shown in Figure 24D, the effective location of the virtual camera 702c is at infinity (and is not shown in Figure 24D).

[0202] In some embodiments, the HOE (e.g., OAHM or OAVDOE) can be divided into multiple segments. Each of these segments may have different optical properties or characteristics, including, for example, the angle of reflection or refractive power at which the segment reflects incident (infrared) light. The segments can be configured such that light is reflected from each segment toward the imaging unit 702b. As a result, the image obtained by the imaging unit 702b is also divided into a corresponding number of segments, each effectively viewing the eye from a different angle. Figure 24E schematically illustrates an embodiment of a display system 700 having an OAHM with three segments 718a1, 718a2, and 718a3, respectively, acting as separate virtual cameras 702c1, 702c2, and 702c3 that image the eye 304 at different angular locations.

[0203] Figure 24F schematically illustrates another embodiment of the display system 700, which has an OAHM with three segments 718a1, 718a2, and 718a3, each having refractive power (e.g., segmented OAHDOE) that generates a virtual camera at infinity, each segment forming an image of the eye 304 at different angular locations. Three segments are schematically illustrated in Figures 24E and 24F, but this is for illustrative purposes only and is not limiting. In other embodiments, two, four, five, six, seven, eight, nine, or more segments can be used. None of these segments of the HOE have refractive power, or some or all of them may have refractive power.

[0204] In Figures 24E and 24F, the three segments 718a1, 718a2, and 718a3 are shown to be spaced horizontally across the optical element 706. In other embodiments, the segments can be spaced vertically on the optical element 706. For example, Figure 24G schematically shows a DOE 718 having two vertically spaced segments 718a1 and 718a2, wherein segment 718a1 includes a CLC off-axis mirror configured to reflect light toward the imager 702b (which may be in the same substantially horizontal plane as segment 718a1), and segment 718a2 is configured to reflect light upward toward the imager 702b. Similar to a bifocal lens, the arrangement shown in Figure 24G may be advantageous in allowing the imaging system 700 to use a reflected image obtained by the imaging unit 702b from the upper segment 718a1 when the wearer is looking forward through the upper portion of the HMD (indicated graphically via the solid arrow), and to use a reflected image from the lower segment 718a2 when the wearer is looking downward through the lower portion of the HMD (indicated graphically via the dashed arrow).

[0205] In other embodiments, a mixture of horizontally and vertically separated segments can be used. For example, FIG. 24H shows another embodiment of HOE718 with an array of 3×3 segments each with an off-axis CLC mirror. Imaging machine 702b can obtain reflection data from each of these nine segments representing light rays originating from different areas of the eye region and angular directions therefrom. Two exemplary light rays propagating from the eye region to HOE718 and reflected to imaging machine 702b are shown as solid and dashed lines. Imaging system 700 (or processing module 224 or 228) can analyze the reflection data from the plurality of segments and computationally determine the three-dimensional shape of the eye or the line-of-sight direction of the eye (e.g., eye pose) in a multi-viewpoint manner.

[0206] Embodiments of optical system 700 utilizing segments can have multiple advantages. For example, the segments can be used individually by selecting the particular segment best suited for a particular task, or they can be used collectively to computationally estimate the three-dimensional shape or pose of the eye in a multi-viewpoint manner. In the former case, this selectivity can be used, for example, to select an image of the wearer's iris having at least occlusion by eyelids or eyelashes. In the latter case, three-dimensional reconstruction of the eye can be used to estimate orientation (e.g., by estimating the location of the corneal paracellular flow) or accommodation state (e.g., by estimating lens-induced distortion on the apparent location of the pupil). (Polarization Converter Based on Notch Reflector)

[0207] To implement a light field display, the focus of the virtual image should be adjusted to resolve the convergence-divergence-depth of focus conflict. A variable focus lens can be placed to vary the focus of the virtual image between the display and the user's eye. However, most variable / switchable focus lenses are polarization sensitive, while the projected virtual image may not be sufficiently polarized. Such a display may require a polarization insensitive lens (often a pair of lens sets) or a polarizer (brightness is reduced by >50% due to light loss in non-transmissive polarization). Efficient conversion of virtual image polarization is desired to create a compact / light efficient variable focus light field display.

[0208] To generate a virtual image in an augmented reality display, several narrowband sources (e.g., red, green, blue (RGB) LEDs or lasers) are often used. A waveguide-based display system can be constructed with diffractive optical elements to project an image into the user's eye. The projected image often does not preserve polarization purity, even when a well-defined polarization of the image is introduced into the waveguide.

[0209] As described herein, a notch reflector generally refers to an optical reflector that transmits most wavelengths of light substantially unaltered but reflects light within a specific wavelength range with relatively high efficiency. The specific wavelength range from which light is reflected is called the "notch." Notch reflectors are sometimes also called narrowband reflectors. The wavelength range within the notch may be a different range, including, for example, <10 nm, <50 nm, <100 nm, <250 nm, or any two of these values. Notch reflectors can be formed from multiple dielectric layers (multilayers), liquid crystals, metamaterials, metastructures, etc. Notch reflectors may include diffractive optical elements, surface or volume holograms, etc. Notch reflectors can be laminated on a substrate material (e.g., polymer or glass). In many of the implementations described herein, to reflect RGB light, the reflector comprises multiple notched reflectors, with each notch within the reflector tuned to one of the specific RGB colors (e.g., a reflector comprising an R-notched reflector, a G-notched reflector, and a B-notched reflector). Thus, the wavelength range of each notch can match the wavelength range of light input into the display (e.g., the R-notch matches the wavelength range of red light input by a red LED or laser, and so on for the G and B notches).

[0210] Various embodiments described herein include notch reflectors comprising a transparent substrate, for example, a polished glass or polymer substrate having one or more active layers formed thereon. As described herein, the active layers comprise a layer or coating configured to provide one or more of the notch reflectance properties described herein. One or more active layers are configured to notch reflect light having a wavelength range Δλ in the range of about 50 nm, about 70 nm, about 100 nm, about 150 nm, or less than any of these values, or in the range defined by any two of these values, the range being centered on red light, including light of one or more wavelengths in the range of about 620 to 780 nm, green light, including light of one or more wavelengths in the range of about 492 to 577 nm, or blue light, including light of one or more wavelengths in the range of about 435 to 493 nm. In some embodiments, the wavelength range Δλ may substantially cover the red light range of about 620–780 nm, the green light range of about 492–577 nm, or the blue light range of about 435–493 nm.

[0211] Various embodiments described herein include a notch reflector configured as a polarization notch reflector. Within the notch reflection range, the polarization notch reflector substantially reflects light having the opposite polarity while allowing light having one polarity to pass through substantially. For example, when light having both left-handed polarization (LHCP) and right-handed circular polarization (RHCP) within the notch reflection range is incident on the polarization notch reflector, the notch reflector substantially reflects the light having one of the RHCP and LHCP while substantially allowing the light having the opposite of the RHCP and LHCP to pass through. Similarly, when light having both linear vertical polarization (LVP) and linear horizontal polarization (LHP) is incident on the polarization notch reflector, the notch reflector substantially reflects the light having one of the LVP and LHP while substantially allowing the light having the opposite of the LVP and LHP to pass through.

[0212] Various embodiments described herein include a notch reflector configured as a non-polarizing notch reflector. Within the notch reflection range, the non-polarizing notch reflector substantially reflects light incident on it, regardless of its polarization. For example, when light having both LHCP and RHCP within the notch reflection range is incident on the non-polarizing notch reflector, the notch reflector can substantially reflect the light having both RHCP and LHCP. Similarly, when light having both LVP and LHP is incident on a polarizing notch filter, the notch filter can substantially reflect the light having both LVP and LHP.

[0213] In the various embodiments described herein, a notch reflector configured as a polarizing or non-polarizing notch reflector may also be configured independently as a polarization-converting notch reflector. Depending on the reflection of polarized light within the notch reflection range, the polarization-converting notch reflector converts the polarization of the reflected light to the opposite polarity. For example, when light having one of LHCP and RHCP within the notch reflection range is incident on a polarization-converting notch reflector, the notch reflector converts one of RHCP and LHCP to the opposite of RHCP and LHCP. Similarly, when light having one of LVP and LHP is incident on a polarization-converting notch reflector, the notch reflector converts one of LVP and LHP to the opposite of LVP and LHP.

[0214] As described herein, a notch reflector configured to reflect light having one or more polarizations within a notch reflection range (Δλ) can be configured to reflect substantially all of the light having one or more polarizations incident on it. For example, when a notch reflector is configured to reflect light having one or both of RHCP and LHCP, the notch reflector may reflect, for example, more than 80%, more than 90%, more than 95%, more than 99%, more than 99%, more than 99.99%, more than 99.999%, or more than 99.9999% of the light having one or both of RHCP and LHCP incident on it. On the other hand, when a notch reflector is configured to reflect light that has one of RHCP and LHCP but not the other, the notch reflector may reflect, for example, more than 80%, more than 90%, more than 95%, more than 99%, more than 99%, more than 99.99%, more than 99.999%, or more than 99.9999% of the light incident on it that has one of RHCP and LHCP but not the other. Conversely, the notch reflector is configured so that light that is not reflected, for example, wavelengths outside the notch reflection range (Δλ), or light having polarizations that the notch reflector is not configured to reflect, can be transmitted substantially completely, for example, more than 80%, more than 90%, more than 95%, more than 99%, more than 99%, more than 99.99%, more than 99.999%, or more than 99.9999% of the light incident on it.

[0215] In a display device described herein, it may be desirable to recycle some of the light externally coupled from the waveguide. For example, while the waveguide may externally couple light having more than one polarization, optical elements such as lenses, e.g., transmissive or reflective lenses, which are configured to exert an optical function, e.g., refractive power, on the externally coupled light, may be polarization-selective before being viewed by the user. Under certain circumstances, light having a polarization not configured for which the optical elements exert an optical function may be transmitted without being viewed by the user. For example, a lens coupled to a waveguide may be configured to exert refractive power on light having one of the polarizations, e.g., RHCP or LHCP, while transmitting light having another polarization, e.g., the other of RHCP or LHCP, through it due to a lack of match between the polarization palmarity of the incident elliptic or circularly polarized light and the rotational direction of the chiral structure in the CLCG. In these circumstances, it may be desirable to recycle the light having the other of RHCP or LHCP to deliver a viewing experience to the user with higher brightness. To address these and other needs, various embodiments of waveguide devices that employ one or more polarization-converting reflectors to address these needs are disclosed below. (Exemplary circular polarization conversion display device)

[0216] Figure 25A illustrates a display device 2500A configured to output image information to the user. The display device 2500A includes a waveguide assembly 2504, also referred to as an eyepiece, interposed between a non-polarizing notch reflector 2508 and a polarizing notch reflector 2512. In various embodiments, the waveguide assembly 2504 can be configured in a manner similar to the waveguide assembly 1178 described above with respect to Figure 6. Similar to the configuration described above with respect to Figure 6, during operation, the display device 2500A will be positioned between the world 1114 and the eye 4 so that the eye 4 receives light from both the display device 2500A and the world 1114.

[0217] In particular, in various embodiments described herein, the waveguide assembly 2504 of the display device 2500A comprises one or more waveguides (e.g., 1182, 1184, 1186, 1188, 1190 in Figure 6), each configured to propagate light in each individual waveguide by total internal reflection (TIR) ​​in the x-direction. The light propagating substantially in the x-direction may be output using external coupling optical elements or light extraction optical elements (e.g., 1282, 1284, 1286, 1288, 1290 in Figure 6), which are configured to extract the light from the waveguides by, for example, redirecting the light propagating in each individual waveguide out of the waveguide and outputting image information to the eye 4 in the z-direction. In various embodiments, although not shown for clarity, the waveguide assembly 2504 may include any of CLCGs formed from one or more CLC layers configured as external coupling optical elements, as described above. Various other details of the waveguide assembly 2504 described above are omitted herein.

[0218] Still referring to Figure 25A, the unpolarized notch reflector 2508 according to various embodiments described herein is configured such that, within the notch reflection range, the unpolarized notch reflector 2508 substantially reflects light incident on it regardless of its polarization. Furthermore, in the illustrated embodiments, the unpolarized reflector is configured as a polarization-converting notch reflector such that, within the notch reflection range, the polarization-converting notch reflector converts the polarization of the reflected light to the opposite polarity in response to the reflection of polarized light. The unpolarized notch reflector 2508 includes a transparent substrate, for example, a polished glass or polymer substrate having one or more active layers formed thereon. In some embodiments of the notch reflectors described herein, the one or more active layers formed on the substrate may include one or more dielectric coatings, the combination of which produces the various notch reflection properties described above.

[0219] Referring still to Figure 25A, the polarizing notch reflector 2512 according to the various embodiments described herein is configured such that, within the notch reflection range, the polarizing notch reflector 2512 substantially reflects light incident thereon in a polarization-selective manner. Furthermore, in the illustrated embodiments, unlike the non-polarizing notch reflector 2508, the polarizing notch reflector 2512 is not configured as a polarization-converting notch reflector, and is therefore configured such that, in response to reflecting polarized light, the polarizing notch reflector 2512 does not convert the polarization of the reflected light to the opposite polarity. The polarizing notch reflector 2512 includes a transparent substrate, for example, a polished glass or polymer substrate having one or more active layers formed thereon. In some embodiments of the notch reflector described herein, the one or more active layers formed on the substrate may include one or more cholesteric liquid crystal (CLC) layers. The one or more active layers formed on the substrate may include one or more cholesteric liquid crystal (CLC) layers, as described according to the various embodiments described above.

[0220] Referring still to Figure 25A, the operation of the display device 2500A will be described below. As described above, a portion of the light propagating in the x-direction within one or more waveguides in the waveguide assembly 2504 may be redirected or externally coupled in the z-direction. In the illustrated embodiment, the light externally coupled from the waveguide assembly 2504 includes a circularly polarized beam 2516-L having an LHCP and 2516-R having an RHCP. The light beams 2516-L with the LHCP and 2516-R with the RHCP propagate, for example, in the positive z-direction until the beams collide with the surface of the polarization notch reflector 2512.

[0221] The polarization notch reflector 2512 comprises a CLC layer 1004 having a chiral structure similar to that described above, for example, the chiral structures 1012-1, 1012-2, ..., 1012-i described above with respect to Figure 10. When incident light, having a combination of a left-handed circularly polarized beam and a right-handed circularly polarized beam, is incident on the surface of the polarization notch reflector 2512 by Bragg reflection, light with one of the circular polarization pendulums is reflected by the CLC layer 1004, while light with the opposite polar polarization pendulum is transmitted through the CLC layer 1008 with virtually no interference. Throughout this disclosure, as described herein, pendulum is defined as being observed in the direction of propagation. According to the embodiment, incident light is reflected when the polarization direction or polarization palmarity of the light beams 2516-L, 2516-R are matched to have the same rotation direction as the liquid crystal molecules of the chiral structures 1012-1, 1012-2, ..., 1012-i. As shown in the figure, the light beams incident on the surface of the CLC layer 1004 are left-handed circularly polarized light beam 2516-L and right-handed circularly polarized light beam 2516-R. In the illustrated embodiment, the liquid crystal molecules of the chiral structures 1012-1, 1012-2, ..., 1012-i are continuously rotated clockwise in the direction in which the incident light beams 2516-L, 2516-R travel in the positive x-direction, which is, for example, the same rotation direction as the light beam 1016-L having left-handed circular polarization. As a result, the light beam 2516-L, which has right-handed circular polarization, is substantially reflected from the polarization notch reflector 2512, while the light beam 2516-R, which has right-handed circular polarization, is substantially transmitted through the polarization notch reflector 2512.

[0222] The optical beam 2516-L, externally coupled from the CLC layer 1004 and having LHCP, is reflected by the polarization notch reflector 2512 as optical beam 2520-L, which retains the same polarization as optical beam 2516-L. The resulting optical beam 2520-L propagates toward the unpolarized notch reflector 2508 until the optical beam 2520-L with LHCP is substantially reflected by the unpolarized notch reflector 2508 into optical beam 2520-R having the opposite polarization, for example, RHCP, due to the polarization conversion properties of the unpolarized notch reflector 2508. The resulting optical beam 2520-R with RHCP is substantially transmitted through the CLC layer 1004 and then through the polarization notch reflector 2512 so that it enters the eye 4. Still referring to Figure 25A, to summarize, by placing a polarization notch reflector 2512 (e.g., a cholesteric liquid crystal (CLC) notch reflector) between the waveguide assembly 2504 and the user's eye 4, a light beam 2516-R with one polarization (e.g., right-handed circular polarization (RHCP)) is transmitted through the polarization notch reflector 2512, while light 2516-L with orthogonal polarization (e.g., left-handed circular polarization (LHCP)) is reflected back to the world 1114 as a light beam 2520-L. Another notch reflector, namely a non-polarizing notch reflector 2508 (e.g., a multilayer notch reflector), is placed between the world 1114 and the waveguide assembly 2504 and is configured to reflect the light beam 2520-L back to the user's eye as a light beam 2520-R. Since a polarizing notch reflector 2512, such as a CLC notch reflector, does not change the polarization of the light reflected from it, while a non-polarizing notch reflector, such as a multilayer reflector, does change the polarization of the light reflected from it, the light beam 2516-R can also be transmitted through the polarizing notch reflector 2512 as shown. It should be understood that both notch reflectors 2512, 2508 (e.g., CLC and multilayer) can be designed to reflect only the light source for the virtual image and minimize the impact of the image on the world 1114. (Example linear polarization conversion display device)

[0223] Figure 25B illustrates a display device 2500B configured to output image information to a user. Similar to the display device 2500A illustrated above with respect to Figure 25A, the display device 2500B comprises a waveguide assembly 2504 interposed between a non-polarizing notch reflector 2508 and a polarizing notch reflector 2514, for example, a linearly polarizing notch reflector. The waveguide assembly 2504 and the non-polarizing notch reflector 2508 are configured in a similar manner to those described above with respect to Figure 25A and are therefore not described in detail herein.

[0224] Referring still to Figure 25B, the polarizing notch reflector 2514, similar to the polarizing notch reflector 2512 described above with respect to Figure 25A, is configured in the illustrated embodiment such that, within the notch reflection range, the notch reflector 2514 substantially reflects light incident on it in a polarization-selective manner. Furthermore, in the illustrated embodiment, the polarizing reflector 2514 is configured such that, unlike the non-polarizing notch reflector 2508, the polarizing reflector 2514 does not convert the polarization of the reflected light to the opposite polarity.

[0225] However, unlike the polarizing notch reflector 2512 described above with respect to Figure 25A, the polarizing notch reflector 2514 is configured such that, in the illustrated embodiment, the polarizing notch reflector 2514 does not include a CLC layer. Instead, the polarizing notch reflector 2514 includes a transparent substrate, for example, a polished glass or polymer substrate having one or more active layers formed thereon. In some embodiments of the notch reflectors described herein, the one or more active layers formed on the substrate may include one or more dielectric coatings, the combination of which produces the various notch reflection properties described above.

[0226] Referring still to Figure 25B, the display device 2500B further comprises a quarter-wave plate 2510 interposed between the non-polarizing notch reflector 2508 and the waveguide assembly 2504.

[0227] Still referring to FIG. 25B, the display device 2500B will now be further described in terms of its operation. As described above, a portion of the light propagating in the x-direction within one or more waveguides in the waveguide assembly 2504 may be redirected or externally coupled in the z-direction. In the illustrated embodiment, the light externally coupled from the waveguide assembly 2504 includes a linearly polarized beam 2516-V with LVP and 2516-H with LHP. The light beam 2516-V with LVP and 2516-H with LHP travel, for example, in the positive z-direction until the beams impinge on the surface of the polarization notch reflector 2514. Then, while the light beam 2516-V with LVP is substantially reflected from the polarization notch reflector 2514, the light beam 2516-H with LHP is substantially transmitted through the polarization notch reflector 2514.

[0228] The light beam 2516-V, which is externally coupled from the waveguide assembly 2504 and has LVP, is reflected by the polarization notch reflector 2514 as a light beam 2520-V that retains the same polarization as the light beam 2516-V. The resulting light beam 2520-V with LVP propagates towards the quarter-wave plate 2510, is transmitted through it, is reflected from the non-polarization notch reflector 2508, and further, due to the polarization conversion characteristics of the non-polarization notch reflector 2508, is transmitted through the quarter-wave plate 2510 as a light beam 2520-H with the opposite polarization handedness, for example, LHP. The resulting light beam 2520-H with LHP is substantially transmitted through the polarization notch reflector 2514.

[0229] Still referring to Figure 25B, to summarize, instead of the CLC-containing polarizing notch reflector 2512 (Figure 25A), a polarizing notch reflector 2514 is placed that reflects one linear polarization (e.g., linear vertical polarization (LVP)) for a specific wavelength, and further, by placing a quarter-wave plate 2510 interposed between the unpolarizing notch reflector 2508 and the waveguide assembly 2504, the polarization of the light reflected from the unpolarizing notch reflector 2508 becomes orthogonal (e.g., linear horizontal polarization (LHP)) as shown. Similar to the CLC-containing notch reflector described above with respect to Figure 25A, the polarization of the projected virtual image is converted to one linear polarization in an efficient manner (e.g., close to 100% efficiency). (A variable-focus virtual image system based on a polarization converter) (Example linear polarization variable focus lens)

[0230] Figures 26A and 26B illustrate display devices 2600A and 2600B, configured to output image information to the user. Display devices 2600A and 2600B are structurally identical. Display device 2600A is used herein to illustrate outputting a virtual image to the user, while display device 2600B is used herein to illustrate outputting a real-world image to the user.

[0231] The display device 2600A / 2600B comprises various components of the display device 2500A as described above with respect to Figure 25A, and further includes additional optical components for focusing and converting the light output therefrom. Similar to the display device 2500A illustrated above with respect to Figure 25A, the display device 2600A / 2600B comprises a waveguide assembly 2504 interposed between a non-polarizing notch reflector 2508 and a polarizing notch reflector 2512. The waveguide assembly 2504, the non-polarizing notch reflector 2508, and the polarizing notch reflector 2512 are configured in a similar manner as described above with respect to Figure 25A, and are therefore not described in further detail herein.

[0232] The display device 2600A / 2600B also includes a non-polarizing notch reflector 2508, e.g., a multilayer notch reflector, and a polarizing notch reflector 2512, e.g., a first quarter-wave plate (QWP1) 2604 and a second quarter-wave plate (QWP2) 2608 formed outside the CLC notch reflector, and further includes a first linear polarizing lens (L1) 2612 and a second linear polarizing lens (L2) 2616 formed outside the QWP1 2504 and QWP2 2608. In various embodiments, one or both of L1 and L2 may be switchable lenses that can be switched, for example, by the application of an electric field, voltage, or current. Furthermore, one or both of L1 and L2 may have a variable focal intensity or depth of focus, which can be controlled, for example, by the application of an electric field, voltage, or current.

[0233] Referring to Figure 26A, the display device 2600A is used herein to illustrate outputting a virtual image to the user. As described above with respect to Figure 25A, a portion of the light propagating in the x-direction within one or more waveguides in the waveguide assembly 2504 may be redirected or externally coupled in the z-direction. In the illustrated embodiment, the light externally coupled from the waveguide assembly 2504 includes a circularly polarized beam 2516-L having LHCP and 2516-R having RHCP. The light beams 2516-L with LHCP and 2516-R with RHCP propagate, for example, in the positive z-direction until the beams collide with the surface of the polarization notch reflector 2512. Due to the CLC layer 1004 contained within the polarization notch reflector 2512, the light beam 2516-L having right-handed circular polarization is substantially reflected from the polarization notch reflector 2512, while the light beam 2516-R having right-handed circular polarization is substantially transmitted through the polarization notch reflector 2512.

[0234] The optical beam 2516-L, externally coupled from the CLC layer 1004 and having LHCP, is reflected by the polarization notch reflector 2512 as optical beam 2520-L, which retains the same polarization as optical beam 2516-L. The resulting optical beam 2520-L propagates toward the unpolarized notch reflector 2508 until the optical beam 2520-L with LHCP is substantially reflected by the unpolarized notch reflector 2508 into optical beam 2520-R having the opposite polarization, for example, RHCP, due to the polarization conversion properties of the unpolarized notch reflector 2508. The resulting optical beam 2520-R with RHCP is substantially transmitted through the polarization notch reflector 2512 having the CLC layer 1004.

[0235] As they exit the polarization notch reflector 2512, the RHCP-containing light beams 2516-R and 2520-R are further transmitted through QWP2 2608, which converts the circularly polarized beams 2516-R and 2520-R into linearly polarized beams 2520-H and 2516-H, respectively. Subsequently, as they exit QWP2 2608, the light beams 2520-H and 2516-H are further transmitted through L2 2616. When activated, L2 2616 focuses or defocuses the light beams 2520-H and 2516-H onto the focused output light beam 2620 prior to being visible to eye 4.

[0236] In summary, the embodiment illustrated in Figure 26A illustrates an embodiment of a waveguide-based projection display having a variable focus / switchable lens configured to act on light having linear polarization (e.g., LHP in the illustrated embodiment). Thus, the polarization of the light of the virtual image is transformed to have one of the circular polarizations (e.g., RHCP in Figure 26A) as the light passes through the polarization notch reflector 2512, e.g., the CLC notch reflector, and further transformed to have one of the linear polarizations (e.g., LHP in Figure 26A) by the QWP2 2608. The focus of the virtual image is controlled by the L2 2616, as shown in Figure 26A.

[0237] Referring to Figure 26B, the display device 2600B is used herein to illustrate that it outputs a world image to the user. As shown, incident light beams 2632-H and 2624-V, having LHP and LVP respectively, enter and are transmitted through L1 2612. As they exit L1 2612, the light beams 2632-H and 2624-V pass through QWP1 2604, which converts the individual light beams into light beams 2632-R and 2624-L, having RHCP and LHCP respectively. The optical beams 2632-R and 2624-L are then transmitted through the non-polarizing notch reflector 2508, waveguide assembly 2504, polarizing notch reflector 2512, and QWP2 2608, thereby reconverting the individual optical beams into optical beams 2636-H and 2628-V, which have LHP and LVP respectively. The optical beams 2636-H and 2628-V are then transmitted through L2 2616, thereby outputting the individual optical beams 2636 and 2628, respectively.

[0238] To output a real-world image, lenses L1 2612 and L2 2616 are configured to act on light having one of linear polarizations but not the other. As a result, in the illustrated embodiment, one of the incident light beams 2632-H and 2624-V, for example, the light beam 2632-H having LHP, is not affected by lenses L1 2612 and L2 2616.

[0239] L1 2612 and L2 2616 can be configured to exert an opposing lens effect or refractive force on the light passing through them. For example, if L1 2612 is configured to have a focusing lens effect, L2 2616 can be configured to have a focusing effect such that the opposing lens effects cancel each other out. Thus, one of the incident light beams 2632-H and 2624-V, for example, the light beam 2632-V with LVP, undergoes a lens effect, e.g., focusing or defocusing, by L1 2612 as it passes through it. However, after being converted to the light beam 2624-L with LHCP and then converted back to the light beam 2628-V with LVP, the lens effect of L1 2612 is neutralized by L2 2616, which has an opposing lens effect. Therefore, since there are two quarter-wave plates QWP1 2604 and QWP2 2608 whose light delay effects cancel each other out, and two lenses L1 2612 and L2 2616 whose lens effects cancel each other out, the image of the world 1114 as seen by eye 4 is substantially unaffected, while the virtual image is affected by L2 2616, as described above with respect to Figure 26B.

[0240] As described above, polarization conversion similar to that performed using display device 2500A (Figure 25A), which has a polarization notch reflector 2512 containing a CLC layer 1004, can also be performed using display device 2500B (Figure 25B), which has a polarization notch reflector 2514 that does not contain a CLC layer. Thus, Figures 26C and 26D illustrate display devices 2600C and 2600D configured to output image information to a user, and display devices 2600C and 2600D have a polarization notch reflector 2514 that does not contain a CLC layer. Display devices 2600C and 2600D are structurally identical. Display device 2600C is used herein to illustrate outputting a virtual image to a user, while display device 2600D is used herein to illustrate outputting a real-world image to a user.

[0241] Similar to the display device 2500B illustrated above with respect to Figure 25B, the display device 2600C / 2600D comprises a waveguide assembly 2504 interposed between a non-polarizing notch reflector 2508 and a polarizing notch reflector 2514. The waveguide assembly 2504 and the non-polarizing notch reflector 2508 are configured in a similar manner to those described above with respect to Figure 25A and are therefore not described in further detail herein.

[0242] Referring still to Figure 26C, in a manner similar to that described above with respect to Figure 25B, the polarizing notch reflector 2514 is configured such that, in the illustrated embodiment, the notch reflector 2514 substantially reflects light incident on it in a polarization-selective manner within the notch reflection range. Furthermore, in the illustrated embodiment, the polarizing reflector 2514 is configured such that, unlike the non-polarizing notch reflector 2508, the polarizing reflector 2514 does not convert the polarization of the reflected light to the opposite polarity.

[0243] Still, as described above with respect to Figure 25B, the polarization notch reflector 2514 of the display device 2600C / 2600D is configured such that the polarization notch reflector 2514 does not include a CLC layer in the illustrated embodiment. In addition, the display device 2600C / 2600D further comprises a second quarter-wave plate QWP1 2510 interposed between the non-polarizing notch reflector 2508 and the waveguide assembly 2504.

[0244] The display device 2600C / 2600D also includes a non-polarizing notch reflector 2508, for example, a first quarter-wave plate (QWP1) 2604 formed on the left side (world side) of the multilayer notch reflector, and further includes a first linear polarizing lens (L1) 2612 and a second linear polarizing lens (L2) 2616 formed outside the QWP1 2504 and the polarizing notch reflector 2514, respectively. In various embodiments, one or both of L1 and L2 may be switchable lenses that can be switched by, for example, the application of an electric field, voltage, or current. Furthermore, one or both of L1 and L2 may have a variable focal intensity or depth of focus, which can be controlled by, for example, the application of an electric field, voltage, or current.

[0245] Referring to Figure 26C, the display device 2600C is used herein to illustrate outputting a virtual image to the user. As described above with respect to Figure 25B, a portion of the light propagating in the x-direction within one or more waveguides in the waveguide assembly 2504 may be redirected or externally coupled in the z-direction. In the illustrated embodiment, the light externally coupled from the waveguide assembly 2504 includes a linearly polarized beam 2516-V having an LVP and a beam 2516-H having a LHP. The light beams 2516-V with the LVP and 2516-H with the LHP propagate, for example, in the positive z-direction until the beams collide with the surface of the polarization notch reflector 2514. Thereafter, the light beam 2516-V with the LVP is substantially reflected from the polarization notch reflector 2514, while the light beam 2516-H with the LHP is substantially transmitted through the polarization notch reflector 2514.

[0246] Externally coupled from waveguide assembly 2504, the optical beam 2516-V, having LVP, is reflected by polarization notch reflector 2514 as optical beam 2520-V, which retains the same polarization as optical beam 2516-V. The resulting optical beam 2520-V, having LVP, propagates toward QWP2 2510, is transmitted through it, is reflected by unpolarized notch reflector 2508, and is further transmitted through QWP2 2510 as optical beam 2520-H, having opposite polarization characteristics, e.g., LHP, due to the polarization conversion properties of unpolarized notch reflector 2508. The resulting optical beam 2520-H, having LHP, is substantially transmitted through polarization notch reflector 2514.

[0247] As they exit the polarizing notch reflector 2514, the light beams 2516-V and 2516-H having LHPs are further transmitted through L2 2616. When activated, L2 focuses or defocuses the light beams 2520-H and 2516-H on the focused output light beam 2620 prior to being visible to eye 4.

[0248] Referring to Figure 26D, the display device 2600D is used herein to illustrate that it outputs a world image to the user. As illustrated, incident light beams 2632-H and 2624-V, having LHP and LVP respectively, enter and are transmitted through L1 2612. As they exit L1 2612, the light beams 2632-H and 2624-V pass through QWP1 2604, which converts the individual light beams into light beams having RHCP and LHCP, respectively. The light beams 2632-R and 2624-L are then transmitted through a non-polarized notch reflector 2508, followed by QWP2 2510, which backconverts the light beams having RHCP and LHCP into light beams 2636-H and 2628-V, having LHP and LVP, respectively. Subsequently, the light beams 2636-H and 2628-V are transmitted through the waveguide assembly 2504, followed by the polarization notch reflector 2514, and then L2 2616, which outputs the individual light beams 2636 and 2628, respectively.

[0249] With respect to Figures 26A / 26B, similar to the display devices described above, lenses L1 2612 and L2 2616 are configured to act on light having one of linear polarizations but not the other. As a result, in the illustrated embodiment, one of the incident light beams 2632-H and 2624-V, for example, light beam 2632-H having LHP, is not affected by lenses L1 2612 and L2 2616.

[0250] Furthermore, with respect to Figures 26A / 26B, similar to the display device described above, there are two quarter-wave plates QWP1 2604 and QWP2 2608 whose light delay effects cancel each other out, and two lenses L1 2612 and L2 2616 whose lens effects cancel each other out, so that the image of the world as seen by eye 4 is substantially unaffected, while the virtual image is affected by L2 2616, as described above with respect to Figure 26C.

[0251] In summary, polarization conversion similar to that achieved using display devices 2600A / 2600B, which have a polarization notch reflector having a CLC layer in the embodiments illustrated in Figures 26C and 26D, can be achieved using a polarization notch reflector 2514, e.g., a linear polarization notch reflector, instead of the polarization notch reflector 2514 having a CLC layer in it (Figures 26A / 26B), as shown in Figures 26C and 26D. To convert the polarization of the virtual image, QWP2 2510 is placed between the unpolarized notch reflector 2508 and the waveguide assembly 2504. Another quarter-wave plate QWP1 2604 is placed between L1 2612 and the unpolarized notch reflector 2508 to compensate for the polarization notch reflector 2514, e.g., a linear polarization notch reflector, which converts the virtual image polarization to linear polarization (e.g., LHP). (Example of a circularly polarized variable focus lens)

[0252] While not constrained by any particular theory, when a light beam is traced along a closed cycle in space of light polarization states, dynamic phase can be obtained from the cumulative path length and from the geometric phase. The dynamic phase obtained from the geometric phase is due to local changes in polarization. In contrast, some optical elements that rely on the geometric phase to form a desired phase plane may be called Pancharatnambury phase optical elements (PBOEs). PBOEs may be constructed from waveplate elements in which the orientation of the high-speed axis depends on the spatial position of the waveplate element. Applications of PBOEs include, among many other applications, diffraction gratings, such as blazed gratings, focusing lenses, and axicons.

[0253] In the following, with reference to Figures 27A-27D, display devices employing switchable lens elements or switchable lens assemblies, including, for example, Pancharatnam Berry phase (PB) lens elements, which can be dynamically switched by direct modulation of the PB lens or by modulation of an LC waveplate coupled to a static PB lens. When multiple PB lens elements with different focal lengths are stacked, the overall focus of the lens stack can be switched between them by modulating the PB lenses or LC waveplates placed between them. Advantageously, the PB lenses can be configured to focus or defocus circularly polarized light. As a result, quarter-waveplates included as part of the display devices, e.g., display devices 2600A and 2600B, can be omitted because the virtual image polarization is converted to circular polarization (e.g., RHCP) through the CLC reflector.

[0254] Figures 27A and 27B illustrate display devices 2700A and 2700B, configured to output image information to the user. Display devices 2700A and 2700B are structurally identical. Display device 2700A is used herein to illustrate outputting a virtual image to the user, while display device 2700B is used herein to illustrate outputting a real-world image to the user.

[0255] The display device 2700A / 2700B comprises various components of the display device 2600A / 2600B as described above with respect to Figures 26A and 26B, and further includes additional optical components for focusing and converting the light output therefrom. Similar to the display device 2600A / 2600B illustrated above with respect to Figures 26A and 26B, the display device 2700A / 2700B comprises a waveguide assembly 2504 interposed between a non-polarizing notch reflector 2508 and a polarizing notch reflector 2512. The waveguide assembly 2504, the non-polarizing notch reflector 2508, and the polarizing notch reflector 2512 are configured in a similar manner as described above with respect to Figures 26A and 26B, and are therefore not described in further detail herein.

[0256] However, unlike the display devices 2600A / 2600B, the display devices 2700A / 2700B omit the non-polarizing notch reflector 2508, e.g., a multilayer notch reflector, and the polarizing notch reflector 2512, e.g., a quarter-wave plate formed outside the CLC notch reflector. Furthermore, unlike the display devices 2600A / 2600B, instead of a linear polarizing lens, the display devices 2700A / 2700B include a first PB lens (PB L1) 2712 and a second PB lens (PB L2) 2716, respectively, formed outside the non-polarizing notch reflector 2508 and the polarizing notch reflector 2512. In various embodiments, one or both of PB L1 2712 and PB L2 2716 may be switchable lenses that can be switched, for example, by the application of an electric field, voltage, or current. Furthermore, one or both of PB L1 2712 and PB L2 2716 may have variable focal intensity, refractive power, or depth of focus, which can be controlled, for example, by applying an electric field, voltage, or current.

[0257] Referring to Figure 27A, the display device 2700A is used herein to illustrate outputting a virtual image to the user. During operation, as described above with respect to Figure 25A, a portion of the light propagating in the x-direction within one or more waveguides in the waveguide assembly 2504 may be redirected or externally coupled in the z-direction. The path of the light beams externally coupled from the waveguide assembly 2504, including the circularly polarized beam 2516-L with LHCP and 2516-R with RHCP, is the same as described above with respect to Figure 26A until the light beams 2516-R and 2520-R with RHCP are transmitted through the polarization notch reflector 2512 having a CLC layer 1004. Upon exiting the polarization notch reflector 2512, the light beams 2516-R and 2520-R with RHCP are further transmitted through PB L2 2716. When activated, PB L2 causes the light beams 2520-H and 2516-H to focus on or defocus on the focused output light beam 2620 prior to being visible to eye 4.

[0258] Referring to Figure 27B, display device 2700B is used herein to illustrate outputting a world image to the user. As illustrated, incident light beams 2632-R and 2624-L, having RHCP and LHCP respectively, are subsequently transmitted through PB L1 2712 as light beams 2636-R and 2628-L, respectively, through a non-polarizing notch reflector 2508, waveguide assembly 2504, polarizing notch reflector 2512, and PB L2 2716. Unlike display device 2600B illustrated above with respect to Figure 26B, there is no quarter-wave plate in display device 2700, so the light beams remain as circularly polarized beams throughout the phase transformation and focusing. The light beams 2636-R and 2628-L are then transmitted through PB L2 2716, thereby outputting separate light beams 2632 and 2628, respectively.

[0259] To output a real-world image, lenses PB L1 2712 and PB L2 2716 are configured to act on light that has one of the circular polarizations but not the other. As a result, in the illustrated embodiment, one of the incident light beams 2632-R and 2624-L, for example, the light beam 2624-L having LHCP, is not affected by lenses PB L1 2712 and PB L2 2716.

[0260] PB L1 2712 and PB L2 2716 can be configured to exert an anti-lens effect on the light passing through them. For example, if PB L1 2712 is configured to have a focusing lens effect, PB L2 2716 can be configured to have a defocusing effect such that the anti-lens effects cancel each other out. As a result, the image of the world 1114 as seen by eye 4 remains substantially unaffected, while the virtual image is affected by PB L2 2716, as described above with respect to Figure 27A.

[0261] As described above, polarization conversion similar to that performed using display device 2500A (Figure 25A), which has a polarization notch reflector 2512 containing a CLC layer 1004, can also be performed using display device 2500B (Figure 25B), which has a polarization notch reflector 2514 that does not contain a CLC layer. Thus, Figures 27C and 27D illustrate display devices 2700C and 2700D configured to output image information to the user, and display devices 2700C and 2700D have a polarization notch reflector 2514 that does not contain a CLC layer. Display devices 2600C and 2600D are structurally identical. Display device 2700C is used herein to illustrate outputting a virtual image to the user, while display device 2700D is used herein to illustrate outputting a real-world image to the user.

[0262] Similar to the display device 2500B illustrated above with respect to Figure 25B, the display device 2700C / 2700D comprises a waveguide assembly 2504 interposed between a non-polarizing notch reflector 2508 and a polarizing notch reflector 2514. The waveguide assembly 2504 and the non-polarizing notch reflector 2508 are configured in a similar manner to those described above with respect to Figure 25A and are therefore not described in further detail herein.

[0263] The display device 2700C / 2700D also includes, in addition, a non-polarizing notch reflector 2508, for example, a first quarter-wave plate (QWP1) 2604 formed between the multilayer notch reflector and the waveguide assembly 2504, and a second quarter-wave plate (QWP2) 2510 formed between the polarizing notch reflector 2514 and the second PB lens (PB L2) 2616. The display device 2700C / 2700D further includes a first PB lens (PB L1) 2612 outside the non-polarizing notch reflector 2508. Thus, the display device 2700C / 2700D is similar to the display device 2600C / 2600D described with respect to Figures 26C and 27D, except for the relative positions of QWP1 2604 and QWP2510 and the type of lens.

[0264] In various embodiments, one or both of PB L1 2612 and PB L2 2616 may be switchable lenses that can be switched by, for example, the application of an electric field, voltage, or current. Furthermore, one or both of PB L1 2612 and PB L2 2616 may have variable focal intensity or depth of focus, which can be controlled by, for example, the application of an electric field, voltage, or current.

[0265] Referring to Figure 27C, the display device 2700C is used herein to illustrate outputting a virtual image to the user. As described above with respect to Figure 25B, a portion of the light propagating in the x-direction within one or more waveguides in the waveguide assembly 2504 may be redirected or externally coupled in the z-direction. The path of the light beams externally coupled from the waveguide assembly 2504, including the linearly polarized beam 2516-V with LVP and 2516-H with LHP, is the same as described above with respect to Figure 26C until the light beams 2516-V and 2520-V with LVP are transmitted through the polarization notch reflector 2514, e.g., a linearly polarized notch reflector. Upon exiting the polarization notch reflector 2514, the light beams 2516-V and 2520-V are transmitted through the QWP2 2510, thereby being converted into light beams 2516-R and 2520-R with RHCP. Subsequently, the RHCP-containing light beams 2516-R and 2520-R are further transmitted through PB L2 2716. When activated, PB L2 focuses or defocuses the light beams 2520-R and 2516-R onto the focused output light beam 2620 prior to being visible to eye 4.

[0266] Referring to Figure 27D, the display device 2700D is used herein to illustrate the output of a world image to the user. As illustrated, incident light beams 2632-R and 2624-L, having RHCP and LHCP respectively, are transmitted through PB L1 2712, through a non-polarizing notch reflector 2508, and through QWP1 2604, and accordingly the light beams are converted to linearly polarized beams. The circularly polarized beams are further transmitted through waveguide assembly 2504, a polarization notch reflector 2514, for example, a linearly polarizing notch reflector, and through QWP2 2510, and accordingly the light beams are backconverted to circularly polarized beams 2636-R and 2628-L, having RHCP and LHCP respectively. Subsequently, the light beams 2636-R and 2628-L are transmitted through PB L2 2716, thereby outputting separate light beams 2636 and 2628, respectively.

[0267] To output a real-world image, lenses PB L1 2712 and PB L2 2716 are configured to act on light that has one of the circular polarizations but not the other. As a result, in the illustrated embodiment, one of the incident light beams 2632-R and 2624-L, for example, the light beam 2624-L having LHCP, is not affected by lenses PB L1 2712 and PB L2 2716.

[0268] PB L1 2712 and PB L2 2716 can be configured to exert an anti-lens effect on the light passing through them. For example, if PB L1 2712 is configured to have a focusing lens effect, PB L2 2716 can be configured to have a defocusing effect such that the anti-lens effects cancel each other out. As a result, the image of the world 1114 as seen by eye 4 remains substantially unaffected, while the virtual image is affected by PB L2 2716, as described above with respect to Figure 27C. (Exemplary spatial offset compensator for polarization-sensitive variable focus lenses)

[0269] When polarization-sensitive lenses such as PB lenses are used, two orthogonal polarization images undergo different optical passages through the lens. For example, a PB lens can split a world image into two polarization images with different magnifications (which may lead to a double image with a spatial offset between them). This effect is illustrated in Figure 28A, which illustrates a display device 2800A configured similarly to the display devices 2700A / 2700B in Figures 27A and 27B. As described above, the two PB lenses can be configured to cancel out each other's lensing effects, however, a size offset 2804 between the two polarization images formed by the light beam 2632 with LHCP and the light beam 2628 with RHCP may remain, as illustrated in Figure 28A. For example, in Figure 28A, PB L1 exerts a negative refractive power on the light beam 2624-L with LHCP, while exerting a positive refractive power on the light beam 2632-R with RHCP. Various sequences configured to compensate for offset 2804 are disclosed below.

[0270] Figure 28B illustrates an offset compensator 2800B comprising a pair of lenses 2804, 2808, for example, a pair of PB lenses. L4 2808 is configured such that when an incident light beam having RHCP and LHCP is incident on PB L3, PB L3 exerts a positive refractive force on the light beam having LHCP while exerting a negative refractive force on the light beam having RHCP. Therefore, the refractive forces of PB L3 2804 and PL4 2808 are opposite to those of PB L1 2612 and PB L2 2716, respectively, such that the spatial offset 2812 exists between the output light beams 2632 and 2628 output from the display device 2800A (Figure 28A), which are in opposite directions and substantially the same magnitude as the output light beams 2632 and 2628 output from the offset compensator 2800B. Thus, the spatial offset 2804 illustrated in Figure 28A can be compensated by installing a pair of lenses that generate an offset 2812 of the same magnitude but in the opposite direction to that illustrated in Figure 28B.

[0271] Figure 28C illustrates a combination of a display device 2800A (Figure 28A) stacked with an offset compensator 2800B (Figure 28B). A variable focus lens of the same type as that used in the optical system of Figure 28A can be used to construct the offset compensator. A static lens can be used when partial compensation is acceptable. As illustrated, the offset can be avoided by placing a polarizer (e.g., a linear polarizer for linear LC lenses or a circular polarizer for PB lenses) before the notch filter, while sacrificing the brightness of the world image. The virtual image remains unaffected. The offset compensator 2800B can be positioned towards the world side of the eyepiece (e.g., as shown in Figure 28C) or towards the eye side of the eyepiece (e.g., to the right where the user's eye is located). Multiple offset compensators can be used.

[0272] As described above with respect to various display devices, in one or more waveguides (e.g., 1182, 1184, 1186, 1188, 1190 in Figure 6) within the waveguide assembly 2504, light generally propagating in the propagation direction, e.g., in the x-direction, may be output from the waveguide using, for example, an external coupling optical element or a light extraction optical element (e.g., 1282, 1284, 1286, 1288, 1290 in Figure 6) to output image information in the orthogonal direction, e.g., in the z-direction. As described above, various embodiments of the external coupling optical element may include a cholesteric liquid crystal grating (CLCG). When light propagates within one or more waveguides (e.g., 1182, 1184, 1186, 1188, 1190 in Figure 6), the CLCG (e.g., 1282, 1284, 1286, 1288, 1290 in Figure 6) couples the light outward from one or more waveguides. Under certain configurations of the CLC layer of the CLCG, the externally coupled light can have a substantially uniform polarization state in a single direction, e.g., the z-direction. For example, the CLC layer of a CLCG having a chiral structure (e.g., 1012-1, 1012-2, ..., 1012-i in Figure 10) in which the liquid crystal molecules are rotated in the same direction, e.g., clockwise or counterclockwise, may externally couple light having a substantially uniform polarization, e.g., LHCP or RHCP. In these embodiments, since the waveguide assembly 2504 externally couples light having substantially uniform polarization, the display device incorporating the waveguide assembly 2504 with CLCG may omit some of the optical elements described above for converting the polarization of the output light. (Exemplary polarizing eyepiece with variable focus lens)

[0273] In the following, the eyepiece 1004 may preferentially project light in a particular direction (e.g., to the right in Figure 29, towards the eye) compared to other directions (e.g., to the left in Figure 29, towards the world). Referring to Figure 29, the display device 2900 comprises a waveguide assembly 2904 interposed between first and second PB lenses 2612 and 2616, respectively. Advantageously, in this embodiment, since the image light beam 2636-R output from the waveguide assembly 2904 is already polarized (e.g., right-handed circular polarization or RHCP), an additional polarizer or polarization converter may be omitted because the light projected from the eyepiece 1004 is already preferentially polarized by lens 2616 (RHCP in this embodiment). Therefore, within the waveguide assembly 2904, a portion of the light propagating under TIR may be externally coupled by a DOE formed therein, for example, as a circularly polarized beam 2636-R (or a linearly polarized beam in other implementations). The optical beam 2636-R with RHCP propagates, for example, in the positive z-direction, until the beam collides with PB L2 2616 without passing through a polarization notch reflector before being seen by eye 4. The eyepiece 1004 may include a DOE, metamaterial, or hologram, designed to project light asymmetrically in a desired direction and (optionally) with a desired polarization state (for example, to the right with RHCP in Figure 29). (Example of a variable-focus mirror display)

[0274] In some embodiments, a deformable mirror can be used to produce a variable focus effect on a virtual image when reflected from the mirror. Figure 30 illustrates a display device 3000 configured to output image information to a user using a waveguide assembly 2904 and a deformable mirror 3004. The display device 3000 comprises a waveguide assembly 2904 interposed between a curved or deformable mirror 3004 (to have refractive power) and an optional clean polarizer 3008. As described with reference to Figure 29, the eyepiece 2904 may, in this embodiment, be configured to project light asymmetrically to the left (towards the world) rather than to the right (towards the eye). The eyepiece 2904 may comprise a DOE, metamaterial, or hologram that can preferentially project light in a desired asymmetric direction and / or a desired polarization state (e.g., linear or circular). For example, as shown in Figure 34, the eyepiece 2904 may comprise a CLC layer or CLCG.

[0275] During operation, as described above with respect to Figure 29, a portion of the light propagating in the x-direction within one or more waveguides in the waveguide assembly 2904 may be redirected or externally coupled in the z-direction as a light beam 3012 having uniform circular polarization (e.g., RHCP). The waveguide assembly 2904 projects the light beam 3012 of the virtual image toward a bendable or deformable mirror 3004 (opposite the user's eye 4). In some embodiments, the deformable mirror 3004 is coated with a polarization-reflective layer (e.g., a multilayer linear polarization reflector or a broadband cholesteric liquid crystal circular polarization reflector) to reflect light having a specified polarization, e.g., light having the same polarization as the external coupling polarization of CLCG, and to allow light from the real world 1114 to be transmitted toward the eye 4. In some other embodiments, instead of a polarizing reflective layer, the deformable mirror 3004 is coated with a notch reflective layer or a CLC reflective layer designed to reflect light within a narrow bandwidth Δλ that matches the virtual image bandwidth of the externally coupled light from the waveguide assembly 2904. In some embodiments, a cleanup polarizer 3008 may be optionally installed as shown in Figure 30 to eliminate any afterimages without passing through the deformable mirror. (Cholesteric liquid crystal lens)

[0276] As described elsewhere in this specification (see, for example, Figures 30 and 34), some display devices include an eyepiece configured to project light asymmetrically toward the world (for example, toward the world 1114 away from the user's eye 4), and an optical structure (e.g., a deformable mirror 3004 in Figure 30 or a CLC lens in Figure 34) that reverses the direction of the light (e.g., by reflection or diffraction) toward the user's eye 4.

[0277] Figures 31A and 31B illustrate a reflective diffraction lens 3100A that can be implemented as part of a display device, wherein the reflective diffraction lens 3100A is formed from a patterned CLC material and acts as a reflective polarizing mirror in a manner similar to that of a transmissive PB LC lens. Figure 31A illustrates the local orientation of liquid crystal aligners (arrows) on a binary Fresnel lens pattern. Thus, the CLC lens 3100A can be configured to have refractive power (which may be adjustable by an applied electric field, etc.). Embodiments of the CLC lens 3100A can be used as a substitute for the deformable mirror 3004 in the display of Figure 30, or can be used to provide additional reflectivity or refractive power in the display of Figure 30 (for example, by coating or laminating the CLC lens on the surface of the mirror 3004, or by combining the CLC lens 3100A and the mirror 3004).

[0278] Referring to Figure 31B, when lens 3100A is illuminated with circularly polarized incident light 3012 having circular polarization corresponding to (e.g., having the same palmarity as) the palmarity of CLC chirality (e.g., RHCP), the reflected light 3016 exhibits a lensing effect similar to that of a transmissive PB lens. On the other hand, light with orthogonal polarization (e.g., LHCP) is transmitted without interference. Lens 3100A can be configured to have a bandwidth in the range of less than about 10 nm, less than about 25 nm, less than about 50 nm, less than about 100 nm, or some other range.

[0279] Figure 31C illustrates a reflective diffraction lens 3100C comprising a plurality of reflective diffraction lenses 3100-R, 3100-G, and 3100-B. In the illustrated embodiment, the reflective diffraction lenses 3100-R, 3100-G, and 3100-B are in a stacked configuration and are configured to reflect light within the wavelength range Δλ in the red, green, and blue spectra, respectively. When lens 3100C is illuminated with circularly polarized incident light 3012 having circular polarization (e.g., RHCP) corresponding to the palpability of CLC chirality and wavelengths within the wavelength range Δλ in the red, green, and blue spectra, the reflected light 3016 exhibits a lensing effect similar to that of a transmissive PB lens. On the other hand, light with orthogonal polarization (e.g., LHCP) is transmitted without interference.

[0280] Diffractive lenses (e.g., Fresnel lenses) often suffer from severe chromatic aberration as the focal length 3204 varies with respect to the wavelength of light. This is illustrated in Figure 32A with respect to the diffractive lens 3200A, showing incident red, green, and blue light focused at different distances from the lens 3200A.

[0281] Taking advantage of the moderate bandwidth of the CLC material, the lens stack can be implemented to have substantially identical focal lengths with respect to different colors. Figure 32B illustrates a reflective diffracting lens 3200B comprising multiple reflective diffracting lenses 3200-R, 3200-G, and 3200-B in a stacked configuration similar to the reflective diffracting lens 3100C illustrated with respect to Figure 31C. As shown in Figure 32B, the three individual lenses 3200-R, 3200-G, and 3200-B are designed to have substantially identical focal lengths or refractive powers with respect to red, green, and blue wavelengths, respectively. Because the bandwidth of the CLC material is approximately 50 nm to 100 nm in many implementations, crosstalk between the three wavelengths can be reduced or minimized. Although three CLC layers are shown, fewer or more layers can be used corresponding to the colors of light incident on lens 3200B. (Exemplary dynamic switching between CLC lenses)

[0282] Figure 33A illustrates a reflection-diffractive lens assembly 3300 configured for dynamic switching between different focal lengths. Dynamic switching is achieved by stacking multiple reflection-diffractive lens subassemblies 3300-1, 3300-2, and 3300-3, each comprising first, second, and third multilayer diffractive lenses CLC L1, CLC L2, and CLC L3, respectively, with each multilayer diffractive lens CLC L1, CLC L2, and CLC L3 comprising multiple lenses 3100-R, 3100-G, and 3100-B. When configured, the reflection-diffractive lens subassemblies 3300-1, 3300-2, and 3300-3 are configured to have different focal lengths. Multiple reflection-diffractive lens subassemblies 3300-1, 3300-2, and 3300-3 include first, second, and third switchable half-wave plates HWP1, HWP2, and HWP3 (e.g., switchable LC half-wave plates). In the illustrated embodiment, the reflection-diffractive lens subassemblies 3300-1, 3300-2, and 3300-3 are stacked in such a configuration that the multilayer diffraction lenses CLC L1, CLC L2, and CLC L3 of subassemblies 3300-1, 3300-2, and 3300-3 alternate with the switchable half-wave plates (HWPs) of subassemblies 3300-1, 3300-2, and 3300-3.

[0283] Figures 33B and 33C illustrate exemplary switching operations between two different reflection-diffractive lens subassemblies 3300-1 and 3300-2 by modulating the HWPs located within them, respectively. When the first HWP (HWP1) is in the off state (e.g., no delay), light is reflected by the first CLC lens (CLC L1), and the image focus is determined by the first CLC L1. When both HWP1 and HWP2 are in the on state (e.g., half-wave delay), light is not reflected from CLC L1 because its polarization is orthogonal to the operating polarization (e.g., RHCP) (e.g., LHCP). The polarization state is restored by HWP2, and light is reflected from CLC L2. The image focus is now determined by CLC L2.

[0284] Similarly, three different focal lengths can be implemented by adding an additional pair of CLC lenses and HWPs, as shown in Figure 33D. The light polarization is converted by HWP1 to orthogonal polarization (e.g., LCHP) relative to the working polarization (e.g., RHCP). Since HWP2 is off, the polarization is unaffected, and the light propagates through CLC L2 without interference. After HWP3, the polarization is reversed again to the working polarization (e.g., RHCP), and the light is reflected by CLC L3. The image focus is now determined by CLC L3, as shown in Figure 33D.

[0285] In some embodiments, the variable focus of the virtual image can be implemented by combining a waveguide assembly 3404 (and a CLC lens 3408 as well) as shown in Figure 34. The CLC lens 3408 may include any of the embodiments of the CLC lenses 3100A, 3100C, 3200A, 3200B, and 3300 described herein. The image focus can be controlled by the CLC lens as described above, since the image projected from the waveguide assembly 3404 propagates preferentially toward the CLC lens (e.g., toward the world, away from the user's eye) with uniform circular polarization. The CLC lens 3408 may include multiple depth planes (e.g., DoF1-DoF3 shown in Figure 33A) and may be dynamically switchable as described with reference to Figures 33B-33D. When a color sequential display is used to generate a virtual image, the waveplates in the CLC lens need to be modulated in sync with the working color projected by the eyepiece 3404. As described above, the CLC lens 3408 can be used alone or in combination with a deformable mirror (e.g., mirror 3004) to provide a variable focus display device for virtual images. (Additional aspects)

[0286] In the first aspect, the display device comprises a waveguide configured to propagate visible light under total internal reflection in a direction parallel to the main surface of the waveguide. An external coupling element is formed on the waveguide and configured to externally couple a portion of the visible light in a direction normal to the main surface of the waveguide. A polarization-selective notch reflector is positioned on the first side of the waveguide and configured to reflect visible light having the first polarization while transmitting a portion of visible light having the second polarization. A polarization-independent notch reflector is positioned on the second side of the waveguide and configured to reflect visible light having the first polarization and visible light having the second polarization, and the polarization-independent notch reflector is configured to convert the polarization of the visible light reflected therefrom.

[0287] In the second aspect, in the display device of the first aspect, the polarization-selective notch reflector and the polarization-independent notch reflector are configured to transmit light having wavelengths outside the wavelength range while reflecting visible light having wavelengths within the wavelength range corresponding to one of red, green, or blue light.

[0288] In the third aspect, in any of the display devices from the first to the second aspect, the polarization-selective notch reflector comprises one or more cholesteric liquid crystal (CLC) layers.

[0289] In the fourth aspect, in any of the display devices from the first to third aspects, one or more CLC layers each comprise multiple chiral structures, each chiral structure comprising multiple liquid crystal molecules that extend in the layer depth direction and are continuously rotated in a first rotational direction by at least a helical pitch. The helical pitch is the length in the layer depth direction corresponding to the net rotation angle of the liquid crystal molecules of the chiral structure due to one complete rotation in the first rotational direction. The arrangement of the liquid crystal molecules of the chiral structure fluctuates periodically in the lateral direction perpendicular to the layer depth direction.

[0290] In the fifth aspect, in any of the display devices from the first to fourth aspects, the first polarization is a first circular polarization, and the second polarization is a second circular polarization.

[0291] In the sixth aspect, in any of the first to fifth aspects of the display device, the display device further comprises a first quarter plate and a second quarter plate, wherein a polarization-independent notch reflector is interposed between the first quarter plate and a waveguide, and a polarization-selective notch reflector is interposed between the waveguide and the second quarter plate.

[0292] In the seventh aspect, in the display device of the sixth aspect, the display device further comprises a first linear polarizing lens and a second linear polarizing lens, wherein a first quarter-wave plate is interposed between the first linear polarizing lens and a polarization-independent notch reflector, and a second quarter-wave plate is interposed between a polarization-selective notch reflector and a second linear polarizing lens.

[0293] In the eighth aspect, in any of the display devices of the first to fourth aspects, the display device further comprises a first Pancharatnam Berry (PB) lens and a second Pancharatnam Berry (PB) lens, which are positioned outside the polarization-independent notch reflector and the polarization-selective notch reflector.

[0294] In the ninth aspect, in a display device in either the first or second aspect, the display device further comprises a first quarter-wave plate interposed between a polarization-independent notch reflector and a waveguide.

[0295] In the tenth aspect, in the display device of the ninth aspect, the display device further comprises a second quarter-wave plate, and a polarization-independent notch reflector is interposed between the first quarter-wave plate and the second quarter-wave plate.

[0296] In the eleventh aspect, in the display device of the tenth aspect, the display device further comprises a first linear polarizing lens and a second linear polarizing lens, wherein a first quarter-wave plate is interposed between the first linear polarizing lens and a polarization-independent notch reflector, and a polarization-selective notch reflector is interposed between a waveguide and the second linear polarizing lens.

[0297] In the twelfth aspect, in the display device of the ninth aspect, the display device further comprises a first Pancharatnam Berry (PB) lens, a second Pancharatnam Berry (PB) lens, and a second quarter-wave plate interposed between the second PB lens and the polarization-selective notch reflector, all positioned outside the polarization-independent notch reflector and the polarization-selective notch reflector.

[0298] In the thirteenth aspect, the display device comprises a waveguide device interposed between a first switchable lens and a second switchable lens. Each waveguide device comprises one or more cholesteric liquid crystal (CLC) layers, each having multiple chiral structures, each comprising multiple liquid crystal molecules extending in the layer depth direction and continuously rotating in a first rotational direction, the arrangement of liquid crystal molecules in the chiral structures being periodically varied in a lateral direction perpendicular to the layer depth direction such that one or more CLC layers are configured to Bragg reflect incident light. One or more waveguides are formed across one or more CLC layers and are configured to propagate visible light under total internal reflection (TIR) ​​in a direction parallel to the main surface of the waveguide, and to optically couple the visible light to or from one or more CLC layers.

[0299] In the fourteenth aspect, in the display device of the thirteenth aspect, one or more waveguides are interposed between a polarization-selective notch reflector and a polarization-independent notch reflector, wherein the polarization-selective notch reflector is configured to transmit visible light having a second polarization while reflecting visible light having a first polarization, and the polarization-independent notch reflector is configured to reflect visible light having a first polarization and visible light having a second polarization.

[0300] In the 15th aspect, in the display device of the 13th aspect, one or more CLC layers act as polarization-selective notch reflectors.

[0301] In the sixteenth aspect, in the display device of the thirteenth aspect, the polarization-selective notch reflector comprises one or more cholesteric liquid crystal (CLC) layers.

[0302] In the 17th aspect, in the display device of the 16th aspect, one or more CLC layers each comprise multiple chiral structures, each chiral structure comprising multiple liquid crystal molecules that extend in the layer depth direction and are continuously rotated in a first rotational direction by at least a helical pitch. The helical pitch is the length in the layer depth direction corresponding to the net rotation angle of the liquid crystal molecules of the chiral structure due to one complete rotation in the first rotational direction. The arrangement of the liquid crystal molecules of the chiral structure fluctuates periodically in the lateral direction perpendicular to the layer depth direction.

[0303] In the 18th aspect, in any one of the display devices from the 13th to the 17th aspects, a polarization-selective notch reflector is configured to store the polarization of the visible light reflected therefrom, and a polarization-independent notch reflector is configured to convert the polarization of the visible light reflected therefrom.

[0304] In the 19th aspect, in any one of the display devices from the 13th to the 18th aspects, the first switchable lens and the second switchable lens have refractive forces with opposite signs when activated.

[0305] In the 20th aspect, in any one of the display devices from the 13th to the 19th aspects, the first switchable lens comprises a Pancharatnam Berry (PB) lens, and the second switchable lens comprises a second Pancharatnam Berry (PB) lens.

[0306] In the 21st aspect, in any one of the 13th to 20th aspects of the display device, the display device further comprises a first quarter-wave plate interposed between a polarization-independent notch reflector and a waveguide.

[0307] In the 22nd aspect, in any one of the 13th to 21st aspects of the display device, the display device further comprises a second quarter-wave plate interposed between a second switchable lens and a polarization-selective notch reflector.

[0308] In the 23rd aspect, a display device configured to display an image to a user's eye is an optical display comprising a front side and a rear side, wherein the rear side is closer to the user's eye than the front side and is configured to output light having a wavelength range toward the rear. A first notch reflector is positioned behind the optical display and is configured to reflect light having a wavelength range output from the optical display. A second notch reflector is positioned in front of the optical display and is configured to reflect light having a wavelength range. The first notch reflector is configured to substantially transmit light having a first polarization and substantially reflect light having a second polarization different from the first polarization. The second notch reflector is configured to convert light having a second polarization incident on the rear surface to a first polarization and to redirect the light toward the rear.

[0309] In the 24th aspect, in the display device of the 23rd aspect, the first notch reflector comprises a cholesteric liquid crystal (CLC) grid (CLCG).

[0310] In the 25th aspect, in the display device of the 23rd aspect, the first notch reflector comprises a multilayer, and the second notch reflector comprises a non-polarizing notch reflector and a quarter-wave plate.

[0311] In the 26th aspect, in any one of the 23rd to 25th aspects of the display device, the display device further comprises a first variable focus lens positioned behind a first notch reflector and a second variable focus lens positioned in front of a second notch reflector, wherein the second optical properties of the second variable focus lens compensate for the first optical properties of the first variable focus lens.

[0312] In the 27th aspect, in the display device of the 26th aspect, the first variable focus lens and the second variable focus lens each include a linear polarizing lens.

[0313] In the 28th aspect, in the display device of the 26th aspect, the first variable focus lens and the second variable focus lens each include a Pancharatnamberry (PB) phase lens.

[0314] In the 29th aspect, in the display device of the 28th aspect, the display device further comprises a spatial offset compensator configured to compensate for the spatial offset introduced by the PB phase lens.

[0315] In the 30th aspect, the dynamic focusing display system includes a display configured to output circularly polarized light in a first circularly polarized state. The display is positioned along the optical axis and has a front side and a rear side, the rear side being closer to the user's eye than the front side, and the optical display is configured to output light having a wavelength range toward the rear side. A first switchable optical element is positioned in front of a first CLC lens along the optical axis and is configured to change the circularly polarized state of light transmitted through the first switchable optical element from a first circularly polarized state to a second different circularly polarized state. A first cholesteric liquid crystal (CLC) lens is positioned in front of the first switchable optical element along the optical axis. A second switchable optical element is positioned in front of the first CLC lens along the optical axis and is configured to change the circularly polarized state of light transmitted through the second switchable optical element from a first circularly polarized state to a second different circularly polarized state. The second CLC lens is positioned in front of the second switchable optical element along the optical axis. The controller is configured to electronically switch the states of the first and second switchable optical elements and dynamically select either the first CLC lens or the second CLC lens.

[0316] In the 31st aspect, in the dynamic focusing display system of the 30th aspect, in response to the selection of a first CLC lens, a first switchable optical element may be switched to allow transmission of light having a first polarization state. In response to the selection of a second CLC lens, the first switchable optical element may be switched to change the polarization of the light from a first circularly polarized state to a second circularly polarized state, and the second switchable optical element may be switched to change the polarization of the light from a second circularly polarized state to a first circularly polarized state.

[0317] In the 32nd aspect, in the dynamic focusing display device of the 30th or 31st aspect, the first and second switchable optical elements include half-wave plates.

[0318] In aspect 33, the wearable augmented reality display system comprises a dynamic focusing display system from any one of aspects 30 to 32.

[0319] In the 34th aspect, the wearable augmented reality head-mounted display system is configured to allow light to pass from the world in front of the wearer into the wearer's eyes. A wearable augmented reality head-mounted display system comprises: an optical display configured to output light and form an image; one or more waveguides arranged to receive light from the display; a frame configured such that the one or more waveguides have a front side and a rear side, with the rear side being closer to the eye than the front side, and the waveguides are positioned in front of the eye; a cholesteric liquid crystal (CLC) reflector positioned on the front side of the one or more waveguides, configured to have a refractive power or depth of focus that is adjustable in response to the application of an electrical signal; and one or more external coupling elements positioned relative to the one or more waveguides to extract light from the one or more waveguides and direct at least a portion of the light propagating within the waveguides to the CLC reflector, the light being directed back through the waveguides from the CLC reflector and into the eye to present an image from the display into the wearer's eye.

[0320] In the 35th aspect, the display device comprises a waveguide configured to propagate visible light under total internal reflection in a direction parallel to the main surface of the waveguide and to externally couple the visible light in a direction normal to the main surface. A notch reflector is configured to reflect visible light having a first polarization, and the notch reflector comprises one or more cholesteric liquid crystal (CLC) layers, each CLC layer comprising a plurality of chiral structures, each chiral structure comprising a plurality of liquid crystal molecules extending in the layer depth direction and continuously rotating in a first rotational direction, wherein the arrangement of liquid crystal molecules in the chiral structures varies periodically in a lateral direction perpendicular to the layer depth direction, such that one or more CLC layers are configured to Bragg reflect incident light.

[0321] In the 36th aspect, in the display device of the 35th aspect, the waveguide is configured to selectively externally couple visible light toward a notch reflector.

[0322] In the 37th aspect, in the display device of the 35th or 36th aspect, the notch reflector comprises a deformable mirror having one or more CLC layers formed thereon (or disposed thereon).

[0323] In the 38th aspect, in any one of the display devices from the 35th to the 37th aspects, one or more different CLC layers are configured to transmit light having wavelengths outside the wavelength range, while reflecting visible light having wavelengths within the wavelength range corresponding to different red, green, or blue light.

[0324] In the 39th aspect, in any one of the display devices from the 35th to the 38th aspects, each chiral structure of the CLC layer comprises multiple liquid crystal molecules extending in the layer depth direction by at least a helical pitch, and one or more different CLC layers have different helical pitches.

[0325] In the 40th aspect, in the display device of the 38th or 39th aspect, one or more different CLC layers have substantially the same refractive power.

[0326] In the 41st aspect, in any one of the 35th to 40th aspects, the display device comprises a plurality of notch reflectors, each notch reflector configured to reflect visible light having a first polarization, each notch reflector comprises one or more cholesteric liquid crystal (CLC) layers, each CLC layer comprises a plurality of chiral structures, each chiral structure comprises a plurality of liquid crystal molecules extending in the layer depth direction and continuously rotated in a first rotation direction, and the arrangement of the liquid crystal molecules in the chiral structures varies periodically in a lateral direction perpendicular to the layer depth direction such that one or more CLC layers are configured to Bragg reflect incident light.

[0327] In the 42nd aspect, in any one of the display devices from the 35th to the 41st aspects, different notch reflectors have different refractive powers.

[0328] In the 43rd aspect, in the display device of the 41st or 42nd aspect, the display device further comprises a half-wave plate corresponding to each of the notch reflectors. (Additional considerations)

[0329] In the embodiments described above, the augmented reality display system, more specifically the spatially variable diffraction grating, is described in relation to a particular embodiment. However, it will be understood that the principles and advantages of the embodiments can be used for any other system, apparatus, or method that involves the need for a spatially variable diffraction grating. It will be understood that any feature of any one embodiment can be combined with and / or substituted with any other feature of any other embodiment.

[0330] Unless otherwise explicitly required by context, throughout the description and claims, the words “equipped with,” “featuring,” “containing,” “including,” and their equivalents should be interpreted in an inclusive sense, i.e., “not limited to, but containing,” as opposed to an exclusive or comprehensive sense. The word “combined” refers to two or more elements that may be directly connected or continued through one or more intermediate elements, as is generally used herein. Similarly, the word “connected” refers to two or more elements that may be directly connected or continued through one or more intermediate elements, as is generally used herein. In addition, the words “in this specification,” “above,” “below,” “subsequently mentioned,” “previously mentioned,” and words with similar meanings, when used in this Application, refer to the Application as a whole and not to any particular part of the Application. Where permitted by context, words in the above detailed description that use singular or plural forms may also include plural or singular forms, respectively. When the word "or" refers to a list of two or more items, it encompasses all of the following interpretations: any of the items in the list, all of the items in the list, and any combination of one or more items in the list. In addition, the articles "a," "an," and "the," as used in this application and the attached claims, should be interpreted as meaning "one or more" or "at least one," unless otherwise specified.

[0331] As used herein, the phrase referring to a list of items “at least one of ~” refers to any combination of those items that includes a single element. In one embodiment, “at least one of A, B, or C” is intended to encompass A, B, C, A and B, A and C, B and C, and A, B, and C. Connecting phrases such as “at least one of X, Y, and Z” are generally understood differently in contexts such as those used to convey that an item, term, etc., may be at least one of X, Y, or Z, unless otherwise specifically stated. Thus, such connecting phrases are generally not intended to suggest that one embodiment requires the presence of at least one of X, at least one of Y, and at least one of Z, respectively.

[0332] Furthermore, it should be understood that, in particular, conditional statements used herein, such as “can,” “could,” “might,” “may,” “eg,” “for example,” “such as,” and equivalents, are generally intended to convey that one embodiment includes certain features, elements, and / or conditions, while other embodiments do not, unless otherwise specifically stated or understood in the context in which they are used. Therefore, such conditional statements are generally not intended to suggest that features, elements, and / or conditions are required in any way for one or more embodiments, or that these features, elements, and / or conditions are included or should be implemented in any particular embodiment.

[0333] While certain embodiments have been described, these embodiments are presented only as examples and are not intended to limit the scope of the disclosure. In fact, the novel devices, methods, and systems described herein may be embodied in various other forms. Furthermore, various omissions, substitutions, and modifications in the forms of methods and systems described herein may be made without departing from the spirit of the disclosure. For example, blocks are presented in a given arrangement, but alternative embodiments may implement similar functionality using different components and / or circuit topologies, and some blocks may be deleted, moved, added, subdivided, combined, and / or modified. Each of these blocks may be implemented in various different ways. Any preferred combination of elements and operations of the various embodiments described above can be combined to provide further embodiments. The various features and processes described above may be implemented independently of each other or in various combinations. No element or combination of elements is required or essential for all embodiments. All preferred and secondary combinations of the features of the disclosure are intended to be within the scope of the disclosure.

Claims

1. A dynamic focusing display system, wherein the dynamic focusing display system is A display configured to output circularly polarized light in a first circularly polarized state, wherein the display is arranged along an optical axis and has a front side and a rear side, the rear side being closer to the user's eye than the front side, and the display is configured to output light having a wavelength range that will be reflected back toward the user's eye, away from the user's eye. A first switchable optical element along the optical axis, wherein the first switchable optical element is configured, when activated, to change the circular polarization state of light transmitted through the first switchable optical element from a first circular polarization state to a second circular polarization state different from the first circular polarization state, A first cholesteric liquid crystal (CLC) lens is positioned in front of the first switchable optical element along the optical axis, A second switchable optical element positioned in front of the first CLC lens along the optical axis, wherein the second switchable optical element is configured, when activated, to change the circular polarization state of light transmitted through the second switchable optical element from a second circular polarization state to a first circular polarization state. A second CLC lens positioned in front of the second switchable optical element along the optical axis, A controller configured to dynamically select either the first CLC lens or the second CLC lens by electronically switching between the activated and deactivated states of the first and second switchable optical elements, A dynamic focusing display system equipped with the following features.

2. In response to the selection of the first CLC lens, the first switchable optical element is switched to the deactivated state to allow transmission of light having the first circularly polarized state. The dynamic focusing display system according to claim 1, wherein, in response to the selection of the second CLC lens, the first switchable optical element is switched to the activated state so as to change the circular polarization state of the light from a first circular polarization state to a second circular polarization state, and the second switchable optical element is switched to the activated state so as to change the circular polarization state of the light from a second circular polarization state to a first circular polarization state.

3. The dynamic focusing display system according to claim 1, wherein the first and second switchable optical elements each comprise a half-wave plate.

4. A wearable augmented reality display system comprising the dynamic focusing display system described in claim 1.

5. A third switchable optical element positioned in front of the second CLC lens along the optical axis, wherein the third switchable optical element is configured, when activated, to change the circular polarization state of light transmitted through the third switchable optical element from a second circular polarization state to a first circular polarization state. A third CLC lens positioned in front of the third switchable optical element along the optical axis, Furthermore, The dynamic focusing display system according to claim 1, wherein the controller is configured to dynamically select any of the first CLC lens, the second CLC lens, or the third CLC lens by electronically switching the first, second, and third switchable optical elements between activated and deactivated states.

6. The dynamic focusing display system according to claim 5, wherein the first, second, and third switchable optical elements and the first, second, and third CLC lenses are stacked in such a configuration that the first, second, and third CLC lenses alternate with the first, second, and third switchable optical elements.

7. The dynamic focusing display system according to claim 1, wherein the controller is configured to provide dynamic switching between different focal lengths by electronically switching the activated and deactivated states of the first and second switchable optical elements to dynamically select either the first CLC lens or the second CLC lens.

8. The dynamic focusing display system according to claim 1, wherein each of the first, second, and third CLC lenses is a multilayer diffraction lens, and each of the multilayer diffraction lenses has a plurality of lenses.

9. The dynamic focusing display system according to claim 1, wherein when the first switchable optical element is deactivated, light is reflected in operation by the first CLC lens and the image focus is determined by the first CLC lens.

10. The dynamic focusing display system according to claim 1, wherein when both the first and second switchable optical elements are activated, light is reflected by the second CLC lens instead of being reflected by the first CLC lens during operation, and the image focus is determined by the second CLC lens.

11. The display is A waveguide, wherein the waveguide is configured to propagate visible light under total internal reflection in a direction parallel to the main surface of the waveguide, An external coupling element, wherein the external coupling element is formed on the waveguide and configured to externally couple a portion of the visible light in the direction normal to the main surface of the waveguide. Equipped with, The dynamic focusing display system according to claim 1, wherein during operation, light from the waveguide is projected away from the user toward the first and second CLC lenses.

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