Spatially variable liquid crystal diffraction grating

Abstract

To provide spatially variable liquid crystal diffraction gratings.SOLUTION: The present disclosure relates to display systems, and more specifically to augmented reality display systems. A diffraction grating includes a plurality of different diffracting zones having a periodically repeating lateral dimension corresponding to a grating period adapted for light diffraction. The diffraction grating additionally includes a plurality of different liquid crystal layers corresponding to the different diffracting zones. The different liquid crystal layers have liquid crystal molecules that are aligned differently, such that the different diffracting zones have different optical properties associated with light diffraction.SELECTED DRAWING: None

Description

[Technical field]

[0001] (Citation of Related Application) This application claims the benefit of priority to U.S. Provisional Patent Application No. 62 / 424,310, filed Nov. 18, 2016, entitled "SPATIALLY VARIABLE LIQUID CRYSTAL DIFFRACTION GRATINGS," the contents of which are incorporated herein by reference in their entirety.

[0002] (Field) The present disclosure relates to display systems, and more particularly to augmented reality display systems. [Background technology]

[0003] Description of Related Art Modern computing and display technologies have facilitated the development of systems for so-called "virtual reality" or "augmented reality" experiences, in which digitally reproduced images or portions thereof are presented to a user in a manner that appears or may be perceived as real. Virtual reality, or "VR", scenarios typically involve the presentation of digital or virtual image information without transparency to other actual real-world visual inputs, while augmented reality or "AR" scenarios typically involve the presentation of digital or virtual image information as an augmentation to the visualization of the real world around the user. Mixed reality or "MR" scenarios are a type of AR scenario, typically involving virtual objects that are integrated into and responsive to the natural world. For example, in MR scenarios, AR image content may be perceived to appear blocked by or otherwise interact with objects in the real world.

[0004] 1, an augmented reality scene 1 is depicted in which a user of the 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 the AR technology also perceives that they are "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 appears to be an anthropomorphic bumblebee, even though these elements 1130, 1110 do not exist in the real world. The human visual perception system is complex, making it difficult to produce AR technology that facilitates a pleasing, natural-feeling, and rich presentation of virtual image elements among other virtual or real-world image elements.

[0005] The systems and methods disclosed herein address various challenges associated with AR or VR technology. Summary of the Invention [Means for solving the problem]

[0006] (summary) Thus, numerous devices, systems, structures, and methods are disclosed herein. For example, an exemplary diffraction grating is disclosed that includes a plurality of different diffractive zones having periodically repeating lateral dimensions corresponding to a grating period adapted for light diffraction. The diffraction grating additionally includes a plurality of different liquid crystal layers corresponding to the different diffractive zones. The different liquid crystal layers have liquid crystal molecules aligned differently such that the different diffractive zones have different optical properties associated with light diffraction.

[0007] An exemplary method of fabricating a diffraction grating is disclosed that includes providing a substrate and providing a plurality of distinct diffractive zones on the substrate having periodically repeating lateral dimensions corresponding to a grating period adapted for light diffraction. The method further includes forming a plurality of distinct liquid crystal layers comprising liquid crystal molecules over the substrate, the distinct liquid crystal layers corresponding to the distinct diffractive zones, and forming the distinct liquid crystal layers includes aligning the liquid crystal molecules differently to thereby provide the distinct diffractive zones with different optical properties associated with light diffraction.

[0008] Another exemplary diffraction grating is disclosed that includes multiple successive liquid crystal layers that extend in a lateral direction and are arranged to have periodically repeating lateral dimensions, thicknesses, and refractive indices such that the liquid crystal layers are configured to diffract light, the liquid crystal molecules of the liquid crystal layers being arranged differently in different liquid crystal layers along the lateral direction such that the successive liquid crystal layers are configured to diffract light with a gradient in diffraction efficiency.

[0009] An exemplary head-mounted display device is also disclosed, which is configured to project light to a user's eye and display augmented reality image content. The head-mounted display device includes a frame configured to be supported on the user's head. The head-mounted display device further includes a display disposed on the frame, at least a portion of which includes one or more waveguides, the one or more waveguides being transparent, the transparent portion being disposed in a location in front of the user's eye when the user wears the head-mounted display device so as to transmit light from a portion of the environment in front of the user to the user's eye and provide a view of the portion of the environment in front of the user, the display further includes one or more light sources and at least one diffraction grating configured to couple light from the light sources into the one or more waveguides or couple light out of the one or more waveguides. The diffraction grating includes a plurality of different diffractive zones having periodically repeating lateral dimensions corresponding to a grating period adapted for light diffraction. The diffraction grating additionally includes a number of different liquid crystal layers corresponding to the different diffractive zones, the different liquid crystal layers having liquid crystal molecules aligned differently such that the different diffractive zones have different optical properties associated with light diffraction. For example, the present application provides the following: (Item 1) A diffraction grating, the diffraction grating comprising: a plurality of distinct diffractive zones having periodically repeating lateral dimensions corresponding to grating periods adapted for light diffraction; a plurality of different liquid crystal layers corresponding to the different diffractive zones; Equipped with A diffraction grating, wherein the different liquid crystal layers have differently aligned liquid crystal molecules, whereby the different diffractive zones have different optical properties associated with light diffraction. (Item 2) Item 2. The diffraction grating of item 1, wherein the optical properties include one or more of a refractive index, an absorption coefficient, a diffraction efficiency, and a birefringence. (Item 3) Item 2. The diffraction grating of item 1, wherein each of the different liquid crystal layers has a plurality of differently aligned regions, the differently aligned regions having liquid crystal molecules differently aligned relative to one another. (Item 4) 2. The diffraction grating of claim 1, wherein each of the different diffraction zones further comprises an alignment layer interposed between a substrate and the corresponding liquid crystal layer, the different alignment layers between the different diffraction zones and the substrate being formed from the same material composition, and the different alignment layers causing the liquid crystal molecules to be aligned differently within the different diffraction zones. (Item 5) Item 2. The diffraction grating of item 1, wherein the liquid crystal molecules are stretched and comprise calamitic liquid crystal molecules aligned along the stretch direction. (Item 6) 2. The diffraction grating of item 1, wherein each of the different liquid crystal layers includes a first region and a second region, the liquid crystal molecules in the first region being aligned along a first alignment direction, the first alignment direction forming a first alignment angle with a reference direction, and the liquid crystal molecules in the second region being aligned along a second alignment direction, the second alignment direction forming a second alignment angle with the reference direction, the second alignment angle being different from the first alignment angle. (Item 7) 7. The diffraction grating of item 6, wherein the liquid crystal molecules in the first regions of the first liquid crystal layer and the liquid crystal molecules in the corresponding first regions of the second liquid crystal layer have substantially the same alignment angle. (Item 8) 8. The diffraction grating of claim 7, wherein the liquid crystal molecules in the second regions of the first liquid crystal layer and the liquid crystal molecules in the corresponding second regions of the second liquid crystal layer have different alignment angles. (Item 9) 7. The diffraction grating of item 6, wherein the liquid crystal molecules in a first region of a first liquid crystal layer and the liquid crystal molecules in a corresponding first region of a second liquid crystal layer have substantially different alignment angles, and the liquid crystal molecules in a second region of the first liquid crystal layer and the liquid crystal molecules in a corresponding second region of the second liquid crystal layer have different alignment angles. (Item 10) 7. The diffraction grating of claim 6, wherein the ratio of lateral widths between the first and second regions is substantially the same between different diffractive zones. (Item 11) 7. The diffraction grating of claim 6, wherein the liquid crystal molecules in the second regions of the first liquid crystal layer and the liquid crystal molecules in the second regions of the second liquid crystal layer have substantially identical alignment angles, and a lateral width ratio between the first regions and the second regions is substantially different between different diffraction zones. (Item 12) 7. The diffraction grating of claim 6, wherein the liquid crystal molecules in the second regions of the first liquid crystal layer and the liquid crystal molecules in the second regions of the second liquid crystal layer have different alignment angles, and a ratio of lateral widths between the first regions and the second regions is substantially different between different diffractive zones. (Item 13) 7. The diffraction grating of claim 6, wherein the first and second alignment angles are pre-tilt angles, the pre-tilt angles being measured between the respective alignment directions and the major surface of a substrate in a plane perpendicular to the major surface. (Item 14) 7. The diffraction grating of claim 6, wherein the first and second alignment angles are azimuth angles, the azimuth angles being measured in a plane parallel to a major surface of a substrate between the respective alignment directions and a reference direction parallel to the major surface. (Item 15) 4. The diffraction grating of item 3, wherein the different liquid crystal layers include first regions and second regions, the liquid crystal molecules in the first regions are aligned along a plurality of first alignment directions, the plurality of first alignment directions forming a plurality of first alignment angles with a reference direction, and the liquid crystal molecules in the second regions are aligned along a plurality of second alignment directions, the plurality of second alignment directions forming a plurality of second alignment angles with the reference direction. (Item 16) Item 2. The diffraction grating of item 1, wherein the diffraction grating is a transmission diffraction grating having a transparent substrate. (Item 17) a diffraction grating comprising a plurality of laterally extending contiguous liquid crystal layers arranged to have periodically repeating lateral dimensions, thicknesses and refractive indices, whereby the liquid crystal layers are configured to diffract light; A diffraction grating, wherein the liquid crystal molecules of the liquid crystal layers are arranged differently in different liquid crystal layers along the lateral direction, whereby the successive liquid crystal layers are configured to diffract light with a gradient in diffraction efficiency. (Item 18) Item 18. The diffraction grating of item 17, wherein the liquid crystal layer has first regions and second regions, and the continuous liquid crystal layer is arranged such that a plurality of first regions and a plurality of second regions alternate in the lateral direction. (Item 19) Item 19. The diffraction grating of item 18, wherein the liquid crystal molecules in the first regions have substantially the same aligned orientation, while the liquid crystal molecules in the second regions have substantially a different aligned orientation. (Item 20) 1. A head mounted display device configured to display augmented reality image content by projecting light to an eye of a user, the head mounted display device comprising: a frame configured to be supported on a user's head; a display disposed on the frame; Equipped with at least a portion of the display comprises one or more waveguides, the one or more waveguides being transparent, the one or more waveguides being positioned at a location in front of an eye of the user when the user is wearing the head mounted display device, whereby the transparent portion transmits light from a portion of an environment in front of the user to the user's eye to provide a view of the portion of the environment in front of the user, the display further comprises one or more light sources and at least one diffraction grating, the at least one diffraction grating configured to couple light from the light sources into or out of the one or more waveguides, the diffraction grating being a plurality of distinct diffractive zones having periodically repeating lateral dimensions corresponding to grating periods adapted for light diffraction; a plurality of different liquid crystal layers corresponding to the different diffractive zones; Equipped with A head mounted display device, wherein the different liquid crystal layers have differently aligned liquid crystal molecules, whereby the different diffractive zones have different optical properties associated with light diffraction. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 illustrates a user's view of an augmented reality (AR) device. [Diagram 2] FIG. 2 illustrates an example of a wearable display system. [Diagram 3] FIG. 3 illustrates a conventional display system for simulating a three-dimensional image for a user. [Figure 4] FIG. 4 illustrates aspects of an approach for simulating a three-dimensional image using multiple depth planes. [Diagram 5] 5A-5C illustrate the relationship between the radius of curvature and the radius of focus. [Figure 6] FIG. 6 illustrates an embodiment of a waveguide stack for outputting image information to a user. [Figure 7] FIG. 7 illustrates an example of an output beam output by a waveguide. [Figure 8] FIG. 8 illustrates an example of a stacked waveguide assembly where each depth plane contains an image formed using multiple different primary colors. [Figure 9A] FIG. 9A illustrates a cross-sectional side view of an embodiment of a set of stacked waveguides, each of which includes an incoupling optical element. [Figure 9B] FIG. 9B illustrates a perspective view of the multiple stacked waveguide embodiment of FIG. 9A. [Figure 9C] FIG. 9C illustrates a top-down plan view of the multiple stacked waveguide embodiment of FIGS. 9A and 9B. [Figure 10] 10A-10C illustrate cross-sectional side views of a diffraction grating having zones in which the liquid crystal molecules have different pretilt angles, according to an embodiment. [Figure 11] 11A-11B are cross-sectional side views of intermediate structures and gratings illustrating a method of fabricating the gratings shown in FIGS. 10A-10C, according to an embodiment. [Figure 12] 12A-12C are cross-sectional side views of intermediate structures and gratings illustrating a method of fabricating the gratings shown in FIGS. 10A-10C, according to an embodiment. [Figure 13] 13A-13B illustrate cross-sectional side views of a diffraction grating having zones in which the liquid crystal molecules have different pretilt angles, according to an embodiment. [Figure 14] 14A-14B are cross-sectional side views of intermediate structures and gratings illustrating a method of fabricating the gratings shown in FIGS. 13A-13B, according to an embodiment. [Figure 15] 15A-15C illustrate top-down views of a diffraction grating having zones in which liquid crystal molecules have different azimuthal angles, according to an embodiment. [Figure 16A] FIG. 16A illustrates a top-down plan view of a diffraction grating having zones in which liquid crystal molecules have different azimuthal angles, according to an embodiment. [Figure 16B] FIG. 16B is a schematic graph illustrating the variation in azimuthal angle in the lateral direction across different zones of the diffraction grating illustrated in FIG. 16A. [Figure 17A] 17A-17D illustrate cross-sectional side views of intermediate structures and gratings illustrating a method of fabricating the gratings illustrated in FIGS. 15A-15C, according to an embodiment. [Figure 17B] 17A-17D illustrate cross-sectional side views of intermediate structures and gratings illustrating a method of fabricating the gratings illustrated in FIGS. 15A-15C, according to an embodiment. [Figure 17C] 17A-17D illustrate cross-sectional side views of intermediate structures and gratings illustrating a method of fabricating the gratings illustrated in FIGS. 15A-15C, according to an embodiment. [Figure 17D] 17A-17D illustrate cross-sectional side views of intermediate structures and gratings illustrating a method of fabricating the gratings illustrated in FIGS. 15A-15C, according to an embodiment. [Figure 17E] FIG. 17E illustrates a top-down plan view of the grating illustrated in FIG. 17D, according to an embodiment. [Figure 18A] 18A-18C illustrate cross-sectional side views of intermediate structures and a grating illustrating a method of fabricating the grating illustrated in FIG. 16A, according to an embodiment. [Figure 18B] 18A-18C illustrate cross-sectional side views of intermediate structures and a grating illustrating a method of fabricating the grating illustrated in FIG. 16A, according to an embodiment. [Figure 18C] 18A-18C illustrate cross-sectional side views of intermediate structures and a grating illustrating a method of fabricating the grating illustrated in FIG. 16A, according to an embodiment. [Figure 18D] FIG. 18D illustrates a top-down plan view of the grating illustrated in FIG. 18C, according to an embodiment. [Figure 19] 19A-19B illustrate top down and cross-sectional side views of a diffraction grating having zones in which liquid crystal molecules have different chirality, according to an embodiment. [Figure 20] FIG. 20 is a cross-sectional side view of a diffraction grating having zones in which liquid crystal molecules have different chirality, according to an embodiment. [Figure 21] FIG. 21 is a cross-sectional side view of a diffraction grating having zones in which the liquid crystal molecules are formed from different liquid crystal materials, according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] (Detailed Description) The AR system may display virtual content to the user or viewer while still allowing the user to see the world around them. Preferably, this content is displayed on a head-mounted display that projects image information to 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 the surrounding environment. As used herein, it should be understood that a "head-mounted" display is a display that may be mounted on the viewer's head.

[0012] Reference is now made to the drawings, in which like reference numbers refer to like parts throughout.

[0013] FIG. 2 illustrates an example 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 functionality of the display 62. The display 62 may be coupled to a frame 64, which is wearable by a display system user or viewer 60 and configured to position the display 62 in front of the user's 60 eyes. The display 62 may be considered eyewear in some embodiments. In some embodiments, a speaker 66 is coupled to the frame 64 and positioned adjacent to the ear canal of the user 60 (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., voice menu command selections, natural language questions, etc.) to the system 80 and / or enable audio communication with other persons (e.g., other users of similar display systems). The microphone may further be configured as an ambient sensor to continuously collect audio data (e.g., to passively collect from the user and / or the environment). Such audio data may include user sounds, such as heavy breathing, or environmental sounds, such as commotion, indicative of a nearby event. The display system may also include an ambient sensor 30a, which may be separate from the frame 64 and attached to the body of the user 60 (e.g., on the head, torso, limbs, etc. of the user 60). The ambient sensor 30a may be configured to obtain data characterizing a physiological state of the user 60, in some embodiments, as further described herein. For example, the sensor 30a may be an electrode.

[0014] 2, the display 62 is operably coupled by a communication link 68, such as wired or wireless connectivity, to a local data processing module 70, which may be mounted in a variety of configurations, such as fixedly attached to the frame 64, fixedly attached to a helmet or hat worn by the user, built into headphones, or otherwise removably attached to the user 60 (e.g., in a backpack or belt-type configuration). Similarly, the sensor 30a may be operably coupled to the local processor and data module 70 by a communication link 30b, such as wired or wireless connectivity. The local processing and data module 70 may comprise a hardware processor and digital memory, such as non-volatile memory (e.g., flash memory or hard disk drive), both of which may be utilized to aid in processing, caching, and storing data. The data includes a) captured from sensors (e.g., which may be operatively coupled to the frame 64 or otherwise attached to the user 60), such as image capture devices (such as cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, wireless devices, gyroscopes, and / or other sensors disclosed herein, and / or b) data obtained and / or processed using a remote processing module 72 and / or a remote data repository 74 (including data related to the virtual content), possibly after processing or reading, for passage through the display 62. The local processing and data module 70 may be operatively coupled to the remote processing module 72 and the remote data repository 74 by communications links 76, 78, such as via wired or wireless communication links, such that these remote modules 72, 74 are operatively coupled to each other and available as resources to the local processing and data module 70. In some embodiments, local processing and data module 70 may include one or more of an image capture 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 may be stand-alone structures that communicate with the local processing and data module 70 by wired or wireless communication paths.

[0015] 2, in some embodiments, the remote processing module 72 may comprise one or more processors configured to analyze and process the 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 include one or more remote servers, which provide information, e.g., 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, allowing for fully autonomous use from the remote modules.

[0016] The perception of an image as being "three-dimensional" or "3-D" may be achieved by providing a slightly different presentation of the image to each eye of the viewer. FIG. 3 illustrates a conventional display system for simulating a three-dimensional image for a user. Two distinct images 5, 7, one for each eye 4, 6, are output to the user. The images 5, 7 are spaced apart from the eyes 4, 6 by a distance 10 along an optical or z-axis parallel to the viewer's line of sight. The images 5, 7 are flat and the eyes 4, 6 may focus on the images by assuming a single accommodation state. Such a system relies on the human visual system to combine the images 5, 7 and provide the perception of depth ~ or scale for the combined image.

[0017] However, it should be appreciated that the human visual system is more complex and providing a realistic perception of depth is more difficult. For example, many viewers of conventional "3-D" display systems may find such systems uncomfortable or may not perceive any sense of depth at all. Without being limited by theory, it is believed that a viewer of an object may perceive the object as "three-dimensional" due to a combination of vergence and accommodation. Vergence movement of the two eyes relative to each other (i.e., rotation of the eyes such that the pupils move toward or away from each other, converging the gaze of the eyes to fixate on the object) is closely linked to the focusing (or "accommodation") of the eye's lenses and pupils. Under normal conditions, a change in focus of the eye's lenses or accommodation of the eye to change focus from one object to another at a different distance will automatically cause a matching change in vergence to the same distance, under a relationship known as the "accommodation-vergence reflex" and pupil dilation or constriction. Similarly, changes in vergence will induce matching changes in accommodation of lens shape and pupil size under normal conditions. As described herein, many stereoscopic, or "3-D," display systems display a scene to each eye using a slightly different presentation (and therefore a slightly different image) so that a three-dimensional perspective is perceived by the human visual system. However, such systems are uncomfortable for many viewers because, among other things, they simply provide a different presentation of the scene but oppose the "accommodation-vergence reflex" in which the eye views all image information in a single accommodation state. Display systems that provide better matching between accommodation and vergence may form a more realistic and comfortable simulation of a three-dimensional image and contribute to increased duration of wear and thus compliance with diagnostic and therapy protocols.

[0018] FIG. 4 illustrates aspects of an approach for simulating a three-dimensional image using multiple depth planes. With reference to FIG. 4, objects at various distances from the eyes 4, 6 on the z-axis are accommodated by the eyes 4, 6 such that the objects are in focus. The eyes (4 and 6) assume a particular accommodated state and focus objects at different distances along the z-axis. As a result, a particular accommodated state may be said to be associated with a particular one of the depth planes 14 having an associated focal length such that an object or part of an object at the particular depth plane is in focus when the eye is in the accommodated state for that depth plane. In some embodiments, a three-dimensional image may be simulated by providing a different presentation of an image for each eye 4, 6, and by providing a different presentation of an image corresponding to each of the depth planes. Although shown as separate for clarity of illustration, it should be understood that the fields of view of the eyes 4, 6 may overlap, for example, as the distance along the z-axis increases. Additionally, while shown to be flat for ease of illustration, it should be understood that the contour of the depth plane may be curved in physical space such that all features within the depth plane are in focus with the eye in a particular accommodated state.

[0019] The distance between an object and the eye 4 or 6 may also change the amount of light emitted from the object as viewed by that eye. Figures 5A-5C illustrate the relationship between distance and divergence of light rays. The distance between the object and the eye 4 is represented in the order of decreasing distances R1, R2, and R3. As shown in Figures 5A-5C, the light rays become more divergent as the distance to the object decreases. As the distance increases, the light rays become more collimated. In other words, the light field generated by a point (an object or a part of an object) may be said to have a spherical wavefront curvature that is a function of the distance the point is away from the user's eye. As the curvature increases, the distance between the object and the eye 4 decreases. As a result, at different depth planes, the degree of divergence of the light rays is also different, and the degree of divergence increases with decreasing distance between the depth plane and the viewer's eye 4. Only a single eye 4 is shown in Figures 5A-5C and other figures herein for clarity of illustration, but it should be understood that the discussion regarding eye 4 may apply to both eyes 4 and 6 of a viewer.

[0020] Without being limited by theory, it is believed that the human eye is typically capable of interpreting a finite number of depth planes to provide depth perception. As a result, a highly realistic simulation of perceived depth may be achieved by providing the eye with different presentations of images corresponding to each of these limited number of depth planes. The different presentations may be focused separately by the viewer's eye, thereby serving to provide depth cues to the user based on the ocular accommodation required to focus on different image features for a scene located on different depth planes and / or based on the observation of different image features on different depth planes that are out of focus.

[0021] FIG. 6 illustrates an example of a waveguide stack for outputting image information to a user. The display system 1000 includes a stack of waveguides or a stacked waveguide assembly 1178 that can be utilized to provide a three-dimensional perception to the eye / brain using multiple waveguides 1182, 1184, 1186, 1188, 1190. In some embodiments, the display system 1000 is the system 80 of FIG. 2, and FIG. 6 illustrates several portions of the system 80 in greater detail. For example, the waveguide assembly 1178 can be part of the display 62 of FIG. It should be understood that the display system 1000 can be considered a bright field display in some embodiments.

[0022] 6, the waveguide assembly 1178 may also include a number of features 1198, 1196, 1194, 1192 between the waveguides. In some embodiments, the features 1198, 1196, 1194, 1192 may be one or more lenses. The waveguides 1182, 1184, 1186, 1188, 1190 and / or the number of lenses 1198, 1196, 1194, 1192 may be configured to transmit image information to the eye with various levels of wavefront curvature or ray divergence. Each waveguide level may be associated with a particular depth plane and may be configured to output image information corresponding to that depth plane. The image input devices 1200, 1202, 1204, 1206, 1208 may act as light sources for the waveguides and may be utilized to input image information into the waveguides 1182, 1184, 1186, 1188, 1190, each of which may be configured to disperse incident light across each respective waveguide for output towards the eye 4, as described herein. The light exits output surfaces 1300, 1302, 1304, 1306, 1308 of the image input devices 1200, 1202, 1204, 1206, 1208 and is input into corresponding input surfaces 1382, 1384, 1386, 1388, 1390 of the waveguides 1182, 1184, 1186, 1188, 1190. In some embodiments, each of the input surfaces 1382, 1384, 1386, 1388, 1390 may be an edge of the corresponding waveguide or may be a portion of the major 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 launched into each waveguide and output a total field of cloned collimated beams that are directed towards the eye 4 at a particular angle (and amount of divergence) corresponding to the depth plane associated with the particular waveguide. In some embodiments, a single one of the image launch devices 1200, 1202, 1204, 1206, 1208 may be associated with and launch light into multiple (e.g., three) waveguides 1182, 1184, 1186, 1188, 1190.

[0023] In some embodiments, each of the image input devices 1200, 1202, 1204, 1206, 1208 is a discrete display that produces image information for input into the corresponding waveguides 1182, 1184, 1186, 1188, 1190, respectively. In some other embodiments, the image input devices 1200, 1202, 1204, 1206, 1208 are the output of a single multiplexed display that may, for example, send image information to each of the image input devices 1200, 1202, 1204, 1206, 1208 via one or more optical conduits (such as fiber optic cables). It should be understood that the image information provided by the image input devices 1200, 1202, 1204, 1206, 1208 may include light of different wavelengths or colors (e.g., different primary colors as discussed herein).

[0024] In some embodiments, the light injected into the waveguides 1182, 1184, 1186, 1188, 1190 is provided by a light projector system 2000, which includes a light module 2040, which may include light emitters such as light emitting diodes (LEDs). Light from the light module 2040 may be directed and modified by a light modulator 2030, e.g., a spatial light modulator, via a beam splitter 2050. The light modulator 2030 may be configured to vary the perceived intensity of the light injected into the waveguides 1182, 1184, 1186, 1188, 1190. The light modulator 2030 may be configured to vary the perceived intensity of the light injected into the waveguides 1182, 1184, 1186, 1188, 1190. Examples of spatial light modulators include liquid crystal displays (LCDs), including liquid crystal on silicon (LCOS) displays.

[0025] 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 scan, spiral scan, Lissajous patterns, etc.) into one or more waveguides 1182, 1184, 1186, 1188, 1190 and ultimately to a viewer's eye 4. In some embodiments, the illustrated image injection devices 1200, 1202, 1204, 1206, 1208 may diagrammatically represent a single scanning fiber or a bundle of scanning fibers configured to inject light into one or more waveguides 1182, 1184, 1186, 1188, 1190. In some other embodiments, the illustrated image injection devices 1200, 1202, 1204, 1206, 1208 may diagrammatically represent multiple scanning fibers or multiple bundles of scanning fibers, each configured to inject light into an associated one of the waveguides 1182, 1184, 1186, 1188, 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 of the waveguides 1182, 1184, 1186, 1188, 1190. It should be understood that one or more intervening optical structures may be provided between the scanning fiber or fibers and one or more of the waveguides 1182, 1184, 1186, 1188, 1190, for example, to redirect light exiting the scanning fiber into one or more of the waveguides 1182, 1184, 1186, 1188, 1190.

[0026] 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 light 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-transitory medium) that coordinates the timing and provision 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. The controller 1210 may be part of the processing module 70 or 72 (FIG. 1) in some embodiments.

[0027] Continuing with reference to FIG. 6, the waveguides 1182, 1184, 1186, 1188, 1190 may be configured to propagate light within each respective waveguide by total internal reflection (TIR). Each of the waveguides 1182, 1184, 1186, 1188, 1190 may be planar or have another shape (e.g., curved) with major top and bottom surfaces and edges extending between their major top and bottom surfaces. In the illustrated configuration, each of the waveguides 1182, 1184, 1186, 1188, 1190 may include external coupling optical elements 1282, 1284, 1286, 1288, 1290 configured to extract light from the waveguide by redirecting the light and propagating it within each respective waveguide and outputting image information from the waveguide to the eye 4. The extracted light may also be referred to as out-coupled light, and the out-coupling optical element may also be referred to as a light extraction optical element. The extracted light beam is output by the waveguide at the location where the light propagating in the waveguide strikes the light extraction optical element. The out-coupling optical element 1282, 1284, 1286, 1288, 1290 may be, for example, a grating, including diffractive optical features as further discussed herein. Although shown disposed on the bottom major surface of the waveguides 1182, 1184, 1186, 1188, 1190 for ease of explanation and clarity of drawing, in some embodiments, the out-coupling optical element 1282, 1284, 1286, 1288, 1290 may be disposed on the top and / or bottom major surfaces and / or directly within the volume of the waveguides 1182, 1184, 1186, 1188, 1190, as further discussed herein. In some embodiments, the outcoupling optical elements 1282, 1284, 1286, 1288, 1290 may be formed in a layer of material that is attached to a transparent substrate and forms the waveguides 1182, 1184, 1186, 1188, 1190. In some other embodiments, the waveguides 1182, 1184, 1186, 1188, 1190 may be monolithic pieces of material and the outcoupling optical elements 1282, 1284, 1286, 1288, 1290 may be formed on and / or within that piece of material.

[0028] With continued reference to FIG. 6, as discussed herein, each waveguide 1182, 1184, 1186, 1188, 1190 is configured to output 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 an optical infinity focal plane. The next upper waveguide 1184 may be configured to send collimated light that passes through a first lens 1192 (e.g., a negative lens) before it can reach the eye 4. Such a first lens 1192 may be configured to generate a slight convex wavefront curvature such 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 second 1194 lenses before reaching the eye 4. The combined refractive power of the first 1192 and second 1194 lenses may be configured to produce another incremental amount of wavefront curvature such that the eye / brain interprets the light originating from the third waveguide 1186 as originating from a second focal plane that is closer inward toward the person from optical infinity where the light from the next upper waveguide 1184 was.

[0029] The other waveguide layers 1188, 1190 and lenses 1196, 1198 are similarly configured, with the highest waveguide 1190 in the stack sending its output through all of the lenses between it and the eye for an aggregate focal force that represents the focal plane closest to the person. To compensate for the stack of lenses 1198, 1196, 1194, 1192 when viewing / interpreting light originating from the world 1144 on the other side of the stacked waveguide assembly 1178, a compensating lens layer 1180 may be placed on top of the stack to compensate for the aggregate force of the lens stacks 1198, 1196, 1194, 1192 below. Such a configuration provides as many perceived focal planes as there are waveguide / lens pairs available. Both the outcoupling 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.

[0030] In some embodiments, two or more of the waveguides 1182, 1184, 1186, 1188, 1190 may have the same associated depth plane. For example, multiple waveguides 1182, 1184, 1186, 1188, 1190 may be configured to output images set at the same depth plane, or multiple subsets of the waveguides 1182, 1184, 1186, 1188, 1190 may be configured to output images set at the same depth planes, with one set per depth plane. This may provide the advantage of forming tiled images to provide an extended field of view at those depth planes.

[0031] Continuing with reference to FIG. 6, the out-coupling optical elements 1282, 1284, 1286, 1288, 1290 may be configured to redirect light from its respective waveguide and output the light with an appropriate amount of divergence or collimation for a particular depth plane associated with the waveguide. As a result, waveguides with different associated depth planes may have different configurations of out-coupling optical elements 1282, 1284, 1286, 1288, 1290 that 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, 1290 may be volume or surface features that may be configured to output light at specific angles. For example, the light extraction optical elements 1282, 1284, 1286, 1288, 1290 may be volume holograms, surface holograms, and / or diffraction gratings. In some embodiments, features 1198, 1196, 1194, 1192 may not be lenses. Rather, they may simply be spacers (e.g., cladding layers and / or structures for forming air gaps).

[0032] In some embodiments, the outcoupling optical elements 1282, 1284, 1286, 1288, 1290 are diffractive features that form a diffraction pattern or "diffractive optical elements" (also referred to herein as "DOEs"). Preferably, the DOEs have a sufficiently low diffraction efficiency such that only a portion of the light in the beam is deflected toward the eye 4 with each intersection point of the DOE, while the remainder continues traveling through the waveguide via total internal reflection. The light carrying the image information is thus split into several related exit beams that exit the waveguide at various locations, resulting in a very uniform pattern of exit emission toward the eye 4 for this particular collimated beam bouncing within the waveguide.

[0033] 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 comprise a diffractive pattern in a 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).

[0034] In some embodiments, a camera assembly 500 (e.g., a digital camera, including visible and infrared light cameras) is provided to capture images of the eye 4 and / or tissue surrounding the eye 4, for example, to detect user input and / or monitor the physiological state of the user. As used herein, a camera may be any image capture device. In some embodiments, the camera assembly 500 may include an image capture device and a light source that projects light (e.g., infrared light) onto the eye, which may then be reflected by the eye and detected by the image capture device. In some embodiments, the camera assembly 500 may be mounted on a frame 64 (FIG. 2) and may be in electrical communication with processing modules 70 and / or 72, which may process image information from the camera assembly 500 and make various determinations regarding the physiological state of the user, for example, as discussed herein. It should be understood that information regarding the physiological state of the user may be used to determine the behavior or emotional state of the user. Examples 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 relationships 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 utilized per eye to monitor each eye separately.

[0035] 7, an example of an output beam output by a waveguide is shown. Although one waveguide is shown, it should be understood that other waveguides in the waveguide assembly 1178 (FIG. 6) may function similarly and that the waveguide assembly 1178 includes multiple waveguides. Light 400 is launched into the waveguide 1182 at the input surface 1382 of the waveguide 1182 and propagates within the waveguide 1182 by TIR. At the point where the light 400 impinges on the DOE 1282, a portion of the light exits the waveguide as an output beam 402. The output beam 402 is shown as approximately parallel, but may be redirected to propagate to the eye 4 at an angle (e.g., divergent output beam formation) as discussed herein and depending on the depth plane associated with the waveguide 1182. It should be understood that a nearly collimated exit beam may refer to a waveguide with outcoupling optics that outcouples light to form an image that appears to be set at a depth plane at a large distance (e.g., optical infinity) from the eye 4. Other sets of waveguides or other outcoupling optics may output a more divergent exit beam pattern, which would require the eye 4 to accommodate to a closer distance and focus on the retina, and would be interpreted by the brain as light from a distance closer to the eye 4 than optical infinity.

[0036] In some embodiments, a full color image may be formed at each depth plane by overlaying an image on each of the primary colors, for example, three or more primary colors. FIG. 8 illustrates an example of a stacked waveguide assembly, where each depth plane includes an image formed using multiple different primary colors. The illustrated embodiment shows depth planes 14a-14f, but more or less depths are also contemplated. Each depth plane may have three or more primary color images associated with it, including 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. The different depth planes are indicated in the diagram by different numbers for diopters (dpt) following the letters G, R, and B. By way of example only, the numbers following each of these letters indicate the diopters (1 / m), i.e., the inverse distance of the depth plane from the viewer, and each box in the diagram represents an individual primary color image. In some embodiments, the exact location of the depth planes for the different primary colors may vary to account for differences in the eye's focusing of different wavelengths of light. For example, different primary color images for 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.

[0037] In some embodiments, the light of each primary color may be output by a single dedicated waveguide, such that each depth plane may have multiple waveguides associated with it. In such embodiments, each box in the figure containing the letter G, R, or B may be understood to represent an individual waveguide, and three waveguides may be provided per depth plane, with three primary color images provided per depth plane. The waveguides associated with each depth plane are shown adjacent to each other in this drawing for ease of illustration, but it should be understood that in a physical device, the waveguides may all be arranged in a stack with one waveguide per level. In some other embodiments, multiple primary colors may be output by the same waveguide, such that, for example, only a single waveguide may be provided per depth plane.

[0038] 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 the red, green, or blue colors. 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 eye.

[0039] It should be appreciated that references throughout this disclosure to a given color of light will be understood to encompass one or more wavelengths of light within the range of wavelengths of light that are perceived by a viewer to be of that given color. For example, red light may include one or more wavelengths of light within the range of about 620-780 nm, green light may include one or more wavelengths of light within the range of about 492-577 nm, and blue light may include one or more wavelengths of light within the range of about 435-493 nm.

[0040] In some embodiments, the light source 2040 (FIG. 6) may be configured to emit light at one or more wavelengths outside the range of visual perception of a viewer, e.g., infrared and / or ultraviolet wavelengths. Additionally, the waveguide in-coupling, out-coupling, and other light redirecting structures of the display 1000 may be configured to direct and emit this light from the display toward the user's eye 4, e.g., for imaging and / or user stimulation applications.

[0041] 9A, in some embodiments, light impinging on a waveguide may need to be redirected to in-couple the light into the waveguide. An in-coupling optical element may be used to redirect and in-couple the light into its corresponding waveguide. FIG. 9A illustrates a cross-sectional side view of an example of a plurality or set 1200 of stacked waveguides, each including an in-coupling optical element. Each of the waveguides may be configured to output light of one or more different wavelengths or one or more different wavelength ranges. The stack 1200 may correspond to the stack 1178 (FIG. 6), and the illustrated waveguides of the stack 1200 may correspond to a portion of the plurality of waveguides 1182, 1184, 1186, 1188, 1190, although 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 that requires the light to be redirected for in-coupling.

[0042] The illustrated set 1200 of stacked waveguides includes waveguides 1210, 1220, and 1230. Each waveguide includes an associated incoupling optical element (which may also be referred to as the light input area on the waveguide), e.g., incoupling optical element 1212 is disposed on a major surface (e.g., the top major surface) of waveguide 1210, incoupling optical element 1224 is disposed on a major surface (e.g., the top major surface) of waveguide 1220, and incoupling optical element 1232 is disposed on a major surface (e.g., the top major surface) of waveguide 1230. In some embodiments, one or more of the incoupling optical elements 1212, 1222, 1232 may be disposed on a bottom major surface of the respective waveguide 1210, 1220, 1230 (particularly, one or more of the incoupling optical elements are reflective polarizing optical elements). As shown, the incoupling optical elements 1212, 1222, 1232 may be disposed on the upper major surface of their respective waveguides 1210, 1220, 1230 (or on top of the next lower waveguide), and in particular, the incoupling optical elements are transmissive turning optical elements. In some embodiments, the incoupling optical elements 1212, 1222, 1232 may be disposed within the body of the respective waveguides 1210, 1220, 1230. In some embodiments, as discussed herein, the incoupling optical elements 1212, 1222, 1232 are wavelength selective such that they selectively redirect one or more wavelengths of light while transmitting other wavelengths of light. Although illustrated on one side or corner of its respective waveguide 1210, 1220, 1232, it should be understood that the internal coupling optical elements 1212, 1222, 1232 may be located within other areas of its respective waveguide 1210, 1220, 1230 in some embodiments.

[0043] As shown, the in-coupling optical elements 1212, 1222, 1232 may be laterally offset from one another. In some embodiments, each in-coupling optical element may be offset to receive light without that light passing through another in-coupling optical element. For example, each in-coupling optical element 1212, 1222, 1232 may be configured to receive light from different image input devices 1200, 1202, 1204, 1206, and 1208 as shown in FIG. 6, and may be separated (e.g., laterally spaced) from the other in-coupling optical elements 1212, 1222, 1232 so as to not substantially receive light from others of the in-coupling optical elements 1212, 1222, 1232.

[0044] Each waveguide also includes an associated optically dispersive element, for example, optically dispersive element 1214 is disposed on a major surface (e.g., the top major surface) of waveguide 1210, optically dispersive element 1214 is disposed on a major surface (e.g., the top major surface) of waveguide 1220, and optically dispersive element 1234 is disposed on a major surface (e.g., the top major surface) of waveguide 1230. In some other embodiments, optically dispersive elements 1214, 1224, 1234 may be disposed on the bottom major surfaces of the associated waveguides 1210, 1220, 1230, respectively. In some other embodiments, the optically dispersive elements 1214, 1224, 1234 may be disposed on both the top and bottom major surfaces of the associated waveguides 1210, 1220, 1230, respectively, or the optically dispersive elements 1214, 1224, 1234 may be disposed on different ones of the top and bottom major surfaces in different associated waveguides 1210, 1220, 1230, respectively.

[0045] The waveguides 1210, 1220, 1230 may be spaced apart and separated by, for example, gas, 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 index material (i.e., a material having a lower index of refraction than the material forming the immediate neighbors of waveguides 1210, 1220, 1230). Preferably, the index of refraction of the material forming layers 1218a, 1218b is 0.05 or more, or 0.10 or less, than the index of refraction of the material forming waveguides 1210, 1220, 1230. Advantageously, the lower refractive index layers 1218a, 1218b may act as cladding layers to promote total internal reflection (TIR) ​​of light through the waveguides 1210, 1220, 1230 (e.g., TIR between the top and bottom major surfaces of each waveguide). In some embodiments, the layers 1218a, 1218b are formed from air. Although not shown, it should be understood that the top and bottom of the illustrated set of waveguides 1200 may include immediate cladding layers.

[0046] Preferably, for ease of manufacturing and other considerations, the materials forming the waveguides 1210, 1220, 1230 are similar or the same, and the materials forming the layers 1218a, 1218b are similar or the same. In some embodiments, the materials forming the waveguides 1210, 1220, 1230 may vary between one or more of the waveguides, and / or the materials forming the layers 1218a, 1218b may differ while still maintaining the various refractive index relationships discussed above.

[0047] 9A, light rays 1240, 1242, 1244 are incident on the set of waveguides 1200. It should be understood that light rays 1240, 1242, 1244 may be injected into the waveguides 1210, 1220, 1230 by one or more image injection devices 1200, 1202, 1204, 1206, 1208 (FIG. 6).

[0048] In some embodiments, the light beams 1240, 1242, 1244 have different properties, e.g., different wavelengths or different wavelength ranges, that may correspond to different colors. Each of the internal coupling optical elements 1212, 122, 1232 deflects the incident light such that the light propagates through a respective one of the waveguides 1210, 1220, 1230 by TIR.

[0049] For example, the incoupling optical element 1212 may be configured to deflect light ray 1240 having a first wavelength or range of wavelengths. Similarly, the transmitted light ray 1242 impinges on and is deflected by the incoupling optical element 1222, which is configured to deflect light of a second wavelength or range of wavelengths. Similarly, the light ray 1244 is deflected by the incoupling optical element 1232, which is configured to selectively deflect light of a third wavelength or range of wavelengths.

[0050] 9A, the deflected light rays 1240, 1242, 1244 are deflected to propagate through the corresponding waveguides 1210, 1220, 1230. That is, the incoupling optical element 1212, 1222, 1232 of each waveguide deflects the light into its corresponding waveguide 1210, 1220, 1230 and incouplings the light into the corresponding waveguide. The light rays 1240, 1242, 1244 are deflected at an angle that causes the light to propagate through the respective waveguides 1210, 1220, 1230 by TIR. The light rays 1240, 1242, 1244 propagate through the respective waveguides 1210, 1220, 1230 by TIR until they impinge on the corresponding optical dispersive element 1214, 1224, 1234 of the waveguide.

[0051] 9B, a perspective view of the multiple stacked waveguide embodiment of FIG. 9A is illustrated. As previously described, the in-coupled light rays 1240, 1242, 1244 are deflected by the in-coupling optical elements 1212, 1222, 1232, respectively, and then propagate by TIR within the waveguides 1210, 1220, 1230, respectively. The light rays 1240, 1242, 1244 then impinge on the optically dispersive elements 1214, 1224, 1234, respectively. The optically dispersive elements 1214, 1224, 1234 deflect the light rays 1240, 1242, 1244 to propagate towards the out-coupling optical elements 1250, 1252, 1254, respectively.

[0052] In some embodiments, the optically dispersive elements 1214, 1224, 1234 are orthogonal pupil expanders (OPEs). In some embodiments, the OPEs both deflect or disperse the light into the out-coupling optical elements 1250, 1252, 1254 and also increase the beam or spot size of this light as it propagates into the out-coupling optical elements. In some embodiments, for example, if the beam size is already the desired size, the optically dispersive elements 1214, 1224, 1234 may be omitted and the in-coupling optical elements 1212, 1222, 1232 may be configured to deflect the light directly into the out-coupling optical elements 1250, 1252, 1254. For example, referring to FIG. 9A, the optically dispersive elements 1214, 1224, 1234 may be replaced with the out-coupling optical elements 1250, 1252, 1254, respectively. In some embodiments, the outcoupling optical elements 1250, 1252, 1254 are exit pupils (EP) or exit pupil expanders (EPE) that direct light into the viewer's eye 4 (FIG. 7).

[0053] Thus, referring to Figures 9A and 9B, in some embodiments, a set of waveguides 1200 includes, for each primary color, a waveguide 1210, 1220, 1230, an in-coupling optical element 1212, 1222, 1232, an optically dispersive element (e.g., OPE) 1214, 1224, 1234, and an out-coupling optical element (e.g., EP) 1250, 1252, 1254. The waveguides 1210, 1220, 1230 may be stacked with an air gap / cladding layer between each one. The in-coupling optical element 1212, 1222, 1232 redirects or deflects the incoming light into that waveguide (different in-coupling optical elements receive different wavelengths of light). The light then propagates at an angle that will result in TIR within the respective waveguide 1210, 1220, 1230. In the example shown, light ray 1240 (e.g., blue light) is deflected by the first in-coupling optical element 1212 in the manner previously described, then continues bouncing back down the waveguide, interacting with the optically dispersive element (e.g., OPE) 1214 and then the out-coupling optical element (e.g., EP) 1250. Light rays 1242 and 1244 (e.g., green and red light, respectively) pass through the waveguide 1210, with light ray 1242 hitting and being deflected by the in-coupling optical element 1222. Light ray 1242 then travels via TIR back down the waveguide 1220, bouncing back to its optically dispersive element (e.g., OPE) 1224 and then to the out-coupling optical element (e.g., EP) 1252. Finally, light ray 1244 (e.g., red light) passes through waveguide 1220 and impinges on light in-coupling optical element 1232 of waveguide 1230. Light in-coupling optical element 1232 deflects light ray 1244 such that it propagates by TIR to light dispersive element (e.g., OPE) 1234 and then by TIR to out-coupling optical element (e.g., EP) 1254. Out-coupling optical element 1254 then finally out-couples light ray 1244 to a viewer, who also receives light out-coupled from the other waveguides 1210, 1220.

[0054] 9C illustrates a top-down plan view of the multiple stacked waveguide embodiment of FIGS. 9A and 9B. As shown, the waveguides 1210, 1220, 1230 may be vertically aligned with each waveguide's associated optical dispersion elements 1214, 1224, 1234 and associated external coupling optical elements 1250, 1252, 1254. However, as discussed herein, the internal coupling optical elements 1212, 1222, 1232 are not vertically aligned. Rather, the internal coupling optical elements are preferably non-overlapping (e.g., spaced apart laterally as seen in the top-down view). As discussed further herein, this non-overlapping spatial arrangement facilitates the injection of light from different sources into different waveguides on a one-to-one basis, thereby allowing a specific light source to be uniquely coupled to a specific waveguide. In some embodiments, arrays that include non-overlapping, spatially separated internal coupling optical elements may be referred to as shifted pupil systems, and the internal coupling optical elements in these arrays may correspond to sub-pupils. (Space variable liquid crystal diffraction grating)

[0055] As described above with reference to FIGS. 6 and 7, a display system according to various embodiments described herein may include an outcoupling optical element (e.g., optical elements 1282, 1284, 1286, 1288, 1290 in FIG. 6), which may include a diffraction grating. As described above with reference to FIG. 7, light 400 launched into the waveguide 1182 at the input surface 1382 of the waveguide 1182 propagates within the waveguide 1182 by total internal reflection (TIR). Referring back to FIG. 7, at the point where the light 400 impinges on the outcoupling optical element 1282, a portion of the light exits the waveguide as an exit beam 402. In some implementations, it may be desirable to have the optical element 1282 configured as a diffraction grating, with spatially variable optical properties including diffractive properties. Such a configuration may be desirable, for example, when the intensity of the light substantially attenuates as it propagates within the waveguide 1182. Under such circumstances, it may be desirable to have certain diffractive properties of the grating 1282, such as the diffraction efficiency (ratio of diffracted beam intensity to incident beam intensity) or refractive index, vary along the light propagation direction, such that the uniformity of the intensity of the output beam 402 is improved. Such a configuration may also be desirable, for example, to intentionally distort the light intensity across the grating 1282 to match the spatial and / or angular variations in sensing efficiency associated with the human eye and maximize the user experience. Thus, the outcoupling optical element, such as a diffraction grating, needs to have spatially variable optical properties.

[0056] For some applications, graded diffractive properties can be achieved by structurally varying the periodic structure of the grating, for example, by using semiconductor processing techniques. For example, semiconductor etching techniques can be used to holographically pattern the grating into a rigid substrate material such as fused silica. By spatially varying etching profiles, for example, correspondingly spatially varying duty cycles or grating depths can be produced. However, such approaches often involve relatively complex and expensive processes, for example, multiple etching processes. Therefore, diffraction gratings with spatially varying optical properties that can be fabricated using relatively simple processing techniques can be beneficial. To this end, according to various embodiments disclosed herein, a liquid crystal material is used to spatially vary the diffractive properties across the area of ​​the diffraction grating, for example, by the spatially varying matching properties of the liquid crystal molecules or other material properties. In various embodiments, a photopolymerizable liquid crystal material or reactive mesogens is used to spatially vary the diffractive properties of the diffraction grating. For example, by coating different areas of the grating with a liquid crystal material and spatially varying its properties, for example, the matching properties, a spatially varying diffractive property can be generated.

[0057] In the following, various embodiments of liquid crystal (LC) gratings have variable optical properties, such as variable diffraction properties including diffraction efficiency, e.g., gradient optical properties. Generally, a diffraction grating has a periodic structure that splits and diffracts light into several beams traveling in different directions. The direction of these beams depends, among other things, on the period of the periodic structure and the wavelength of the light. For certain applications, such as an outcoupling optical element 282 with a uniform intensity of the outgoing light beam 402, to achieve certain optical properties that vary spatially across the area of ​​the grating, e.g., spatially variable diffraction efficiency, the material properties of the liquid crystal can be spatially varied.

[0058] Generally, liquid crystals possess physical properties that may be intermediate between traditional fluids and solids. Liquid crystals are fluid-like in some aspects, but unlike most fluids, the arrangement of molecules within them 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 into a variety of physical states, e.g., phases, including nematic states / phases, smectic states / phases, chiral nematic states / phases, or chiral smectic states / phases.

[0059] As described herein, liquid crystals in a nematic state or phase can have calamitic (rod-shaped) or discotic (disk-shaped) organic molecules that have relatively little positional order, but long-range directional order with their long axes approximately parallel. Thus, the organic molecules can flow freely with their center of mass positions randomly distributed as in a liquid, while still maintaining their long-range directional order. In some implementations, liquid crystals in the nematic phase can be uniaxial; that is, the liquid crystal has one axis that is longer and preferred, and the other two are approximately equal. In other implementations, the liquid crystal can be biaxial; that is, in addition to the orientation of its long axis, the liquid crystal can also be oriented along a secondary axis.

[0060] As described herein, liquid crystals in a smectic state or phase can have organic molecules that form relatively well-defined layers that can slide over one another. 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 can 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 can be tilted relative to a direction approximately normal to the plane of the layer.

[0061] As described herein, nematic liquid crystals consist of rod-like molecules with the long axes of neighboring molecules approximately aligned with one another. To describe this anisotropic structure, a dimensionless unit vector n, called the director, can be used to describe the direction of preferred orientation of the liquid crystal molecules.

[0062] As described herein, liquid crystals in the nematic or smectic state can also exhibit chirality. In the chiral phase, the liquid crystal can exhibit a twist of the molecules perpendicular to the director, with the molecular axes parallel to the director. The finite twist angle between adjacent molecules results from their asymmetric packing, which leads to a longer-range chiral order.

[0063] As described herein, liquid crystals in a chiral smectic state or phase can be configured such that the molecules have positional order in a layered structure, with the molecules tilted by a finite angle relative to the layer normal. In addition, the chirality can induce a continuous azimuthal twist from one layer to the next, producing a helical twist of the molecular axes along the layer normal.

[0064] As described herein, liquid crystals that exhibit chirality may be described as having a chiral pitch p, which may refer to the distance over which the liquid crystal molecules undergo a full 360° twist. The pitch p may change 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), allowing the pitch of a given material to be tailored accordingly. In some liquid crystal systems, the pitch is in the same order as the wavelength of visible light. As described herein, liquid crystals that exhibit chirality may also be described as having a twist angle, which may refer to, for example, the relative azimuthal rotation between the top and bottom liquid crystal molecules across the thickness of the liquid crystal material.

[0065] According to various embodiments described herein, liquid crystals having various states or phases as described above can be configured to provide various desirable material properties for diffraction gratings, including, for example, birefringence, optical anisotropy, and manufacturability using thin film processes. For example, by varying the surface conditions of the liquid crystal layer and / or mixing different liquid crystal materials, grating structures can be fabricated that exhibit spatially variable diffractive properties, e.g., gradient diffraction efficiency.

[0066] As described herein, "polymerizable liquid crystal" may refer to a liquid crystal material that can be polymerized, e.g., photopolymerized in situ, and may also be described herein as a reactive mesogen (RM).

[0067] It should be understood that the liquid crystal molecules may be polymerizable in some embodiments and, once polymerized, may form extensive networks with other liquid crystal molecules. For example, the liquid crystal molecules may be linked by chemical bonds or by linking chemical species to other liquid crystal molecules. Once joined together, the liquid crystal molecules may form liquid crystal domains that have substantially the same orientation and location as before they were linked together. For ease of explanation, the term "liquid crystal molecules" is used herein to refer to both the liquid crystal molecules before polymerization and the liquid crystal domains formed by these molecules after polymerization.

[0068] According to certain embodiments described herein, photopolymerizable liquid crystal materials can be configured to form diffraction gratings, and their material properties, including birefringence, chirality, and ease of multiple coatings, can be exploited to create gratings with graded diffraction efficiency, as variations in these material properties (e.g., birefringence, chirality, and thickness) result in variations in diffraction efficiency as appropriate.

[0069] As described herein, it should be understood that a "transmitting" or "transparent" structure, e.g., a transparent substrate, may allow at least a portion, e.g., at least 20, 30, or 50%, of the incident light to pass therethrough. Thus, the transparent substrate may be a glass, sapphire, or polymer substrate in some embodiments. In contrast, a "reflective" structure, e.g., a reflective substrate, may reflect and have reflected therefrom at least a portion, e.g., at least 20, 30, 50, 70, 90%, or more, of the incident light.

[0070] The optical properties of the grating are determined by the physical structure of the grating (e.g., periodicity, depth, and duty cycle) and the material properties of the grating (e.g., refractive index, absorptivity, and birefringence). When liquid crystals are used, the optical properties of the grating 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 grating area, the grating can exhibit graded diffraction efficiency. Such an approach is described below with reference to the figures.

[0071] In various embodiments, the diffraction grating comprises a substrate and a plurality of different diffractive zones having periodically repeating lateral dimensions corresponding to a grating period adapted for diffracting light, the diffraction grating further comprises a plurality of different liquid crystal layers corresponding to the different diffractive zones, the different liquid crystal layers having liquid crystal molecules aligned differently such that the different diffractive zones have different optical properties associated with the diffraction of light. (Photo-aligned spatially variable liquid crystal grating)

[0072] 10A-10C, cross-sectional side views (viewed along the xz plane) of diffraction gratings 100A-100C are shown according to some embodiments. Each of the diffraction gratings 100A-100C includes a substrate 104 and a plurality of diffraction zones, i.e., diffraction zones 108A-1, 108A-2, ..., and 108A-n as shown in FIG. 10A, diffraction zones 108B-1, 108B-2, ..., and 108B-n as shown in FIG. 10B, and diffraction zones 108C-1, 108C-2, ..., and 108C-n as shown in FIG. 10C.

[0073] Each diffractive zone of the diffraction gratings 100A-100C has a periodically repeating lateral dimension or grating period ∧ and includes a corresponding liquid crystal layer formed from liquid crystal molecules 112. In the illustrated embodiments and throughout this disclosure, the liquid crystal molecules 112 may be in a nematic or smectic state or a mixture thereof, among other possible states of the liquid crystal molecules. In the illustrated embodiments and throughout this disclosure, various embodiments may have a grating period ∧ of about 100 nm to about 10,000 nm, about 200 nm to about 2000 nm, or about 300 nm to about 1000 nm, such that the multiple diffractive zones are configured to diffract visible light.

[0074] The diffraction zones 108A-1, 108A-2, ... 108A-n of diffraction grating 100A have corresponding liquid crystal layers 116A-1, 116A-2, ... 116A-n, respectively; the diffraction zones 108B-1, 108B-2, ... 108B-n of diffraction grating 100B have corresponding liquid crystal layers 116B-1, 116B-2, ... 116B-n, respectively; and the diffraction zones 108C-1, 108C-2, ... 108C-n of diffraction grating 100C have corresponding liquid crystal layers 116C-1, 116C-2, and 116C-n, respectively.

[0075] It should be understood that throughout this specification, "n" may be any suitable integer to represent the number of different zones. For example, diffractive zones 108B-1, 108B-2, ... 108B-n indicate that there may be n number of diffractive zones, where n is an integer. The number of diffractive zones (n) omitted from the figures may be, for example, 1 to about 500, about 1 to about 200, or about 1 to about 100. In some implementations, the optical properties of the diffraction grating may vary continuously across the surface. In one implementation, for example, there may be one grating period ∧ per diffractive zone for at least some of the diffractive zones. When each diffractive zone has one grating period ∧, the number of diffractive zones (n) may represent the number of grating periods ∧.

[0076] It should be understood that throughout this specification, "...", when shown in the figures, may represent the presence of additional diffractive zones between the illustrated zones that are continuously connected and may be similar or identical to any other adjacent illustrated zone. In addition, "..." may also represent an arrangement of diffractive zones that repeats periodically any suitable number of times.

[0077] Each of the liquid crystal layers 116A-1, 116A-2, and 116A-n of the diffraction grating 100A has, in turn, first and second diffraction regions 116A-1L and 116A-1R, 116A-2L and 116A-2R, ..., and 116A-nL and 116A-nR, respectively, that are arranged differently. Similarly, each of the liquid crystal layers 116B-1, 116B-2, and 116B-n of the diffraction grating 100B has, in turn, first and second diffraction regions 116B-1L and 116B-1R, 116B-2L and 116B-2R, ..., and 116B-nL and 116B-nR, respectively, that are arranged differently. Similarly, each of the liquid crystal layers 116C-1, 116C-2, and 116C-n of the diffraction grating 100C in turn has differently arranged first and second diffraction regions 116C-1L and 116C-1R, 116C-2L and 116C-2R, ... and 116C-nL and 116C-nR, respectively, the regions sometimes being referred to as domains of the liquid crystal molecules.

[0078] 10A-10C, each of the different diffractive zones further comprises an alignment layer 120 interposed between the substrate 104 and the corresponding liquid crystal layer, the alignment layer being configured to induce alignment of the liquid crystal molecules in the different regions of each zone. Interposed between the substrate 104 of FIG. 10A and the first / second diffractive zones 116A-1L / 116A-1R, 116A-2L / 116A-2R, ... and 116A-nL / 116A-nR of the diffraction grating 100A are first and second alignment layers 120A-1L / 120A-1R, 120A-2L / 120A-2R, ... and 120A-nL / 120A-nR, respectively. Similarly, interposed between the substrate 104 of FIG. 10B and the first / second diffraction regions 116B-1L / 116B-1R, 116B-2R / 116B-2R, ... and 116B-nL / 116B-nR of the diffraction grating 100C are first / second matching layers 120B-1L / 120B-1R, 120B-2L / 120B-2R, ... and 120B-nL / 120B-nR, respectively. Similarly, interposed between the substrate 104 of FIG. 10C and the differently arranged first / second diffraction regions 116C-1L / 116C-1R, 116C-2L / 116C-2R, ... and 116C-nL / 116C-nR of the diffraction grating 100C are first / second matching layers 120C-1L / 120C-1R, 120C-2L / 120C-2R, ... and 120C-nL / 120C-nR, respectively.

[0079] Herein, throughout this disclosure, the alignment direction of the elongated liquid crystal molecules may refer to the elongation direction of the liquid crystal molecules or the direction of the director vector n.

[0080] As used herein, throughout this disclosure, tilt angle or pre-tilt angle Φ may refer to the angle measured in a plane perpendicular to the major surface (xy plane) of the liquid crystal layer or substrate, e.g., the xz plane, and measured between the alignment direction and a direction parallel to the major surface or to the major surface, e.g., the x-direction.

[0081] As used herein and throughout this disclosure, the azimuthal angle or rotation angle φ is used to describe the angle of rotation about an axis normal to a major surface (xy-plane), which is measured in a plane parallel to the major surfaces of the liquid crystal layer or substrate, e.g., the xy-plane, and is measured between the alignment direction and a direction parallel to the major surfaces, e.g., the y-direction.

[0082] It should be understood that, herein, and throughout this disclosure, when alignment angles, such as pre-tilt angle Φ or rotation angle φ, are referred to as being substantially identical between different regions, the average alignment angles may be, for example, within about 1%, about 5%, or about 10% of each other, although the average alignment may be greater in some cases.

[0083] As used herein and throughout the specification, a duty cycle may refer, for example, to the ratio between a first lateral dimension of a first region having liquid crystal molecules aligned in a first alignment direction and the grating period of a zone having the first region. Where applicable, the first region corresponds to a region where the alignment of the liquid crystal does not vary between different zones.

[0084] 10A-10C, each zone of gratings 100A, 100B, and 100C includes first and second regions that alternate in the x-direction. Each of first regions 116A-1L, 116A-2L, ..., and 116A-nL of grating 100A, each of first regions 116B-1L, 116B-2L, ..., and 116B-nL of grating 100B, and each of first regions 116C-1L, 116C-2L, ..., and 116A-nL of grating 100C have liquid crystal molecules 112 substantially aligned along the same first alignment direction and have substantially the same first pre-tilt angles Φ. Each of the second regions 116A-1R, 116A-2R, ... and 116A-nR of diffraction grating 100A, each of the second regions 116B-1R, 116B-2R, ... and 116B-nL of diffraction grating 100B, and each of the second regions 116C-1R, 116C-2R, ... and 116C-nR of diffraction grating 100C has liquid crystal molecules 112 substantially aligned along a second alignment direction different from the first alignment direction and has a second pre-tilt angle Φ different from, e.g., greater than, the first pre-tilt angle Φ of the respective first region.

[0085] In each of the diffraction gratings 100A-100C of Figures 10A-10C, according to an embodiment, at least some of the diffractive zones each have a liquid crystal layer formed from liquid crystal molecules that are arranged in a spatially different manner such that the diffractive zones have different optical properties, e.g., different refractive indices and different diffraction efficiencies, e.g., have different pre-tilt angles from each other (Figures 10A and 10C), or have laterally variable duty cycles (Figures 10B and 10C).

[0086] In particular, with reference to diffraction grating 100A of FIG. 10A, in addition to having an alignment direction and pre-tilt angle Φ that differs from the first pre-tilt angle Φ of first regions 116A-1L, 116A-2L, ..., and 116A-nL, the liquid crystal molecules of different second regions 116A-1R, 116A-2R, ..., and 116A-nR are aligned along a second alignment direction that is different from one another. For example, in the illustrated embodiment, the zones 108A-1, 108A-2, and 108A-n are arranged such that the first and second regions alternate in the x-direction, and the first regions 116A-1L, 116A-2L, ..., and 116A-nL each have substantially the same pre-tilt angle Φ, while the second regions 116A-1R, 116A-2R, ..., and 116A-nR have different pre-tilt angles Φ from one another. As an example, the first regions 116A-1L, 116A-2L, ..., and 116A-nL have pre-tilt angles Φ of about ±15 degrees or about ±10 degrees or about ±5, e.g., 0 degrees. The second regions 116A-1R, 116A-2R, ..., and 116A-nR are different from each other and can each have a pre-tilt angle Φ of about 60 degrees to about 90 degrees or about 65 degrees to about 85 degrees, for example, about 75 degrees, about 35 degrees to about 65 degrees, or about 40 degrees to about 60 degrees, for example, about 50 degrees, about 10 degrees to about 40 degrees, or about 15 degrees to about 35 degrees, for example, about 25 degrees.

[0087] 10A , in some embodiments, as shown, the second regions 116A-1R, 116A-2R, ..., and 116A-nR can have a tilt angle Φ that varies, e.g., increases or decreases, in one direction in a lateral direction such that a gradient of diffractive properties is created. In other embodiments, the second regions 116A-1R, 116A-2R, ..., and 116A-nR can have a tilt angle Φ that does not vary in one direction in a lateral direction.

[0088] Still referring to FIG. 10A, the duty cycle, as defined above, can be about 10% to about 30%, about 30% to about 50%, about 40% to 60% (e.g., about 50%), about 50% to about 70%, or about 70% to about 90%.

[0089] 10B, a diffraction grating 100B shares some common features with the diffraction grating 100A of FIG 10A. However, unlike the diffraction grating 100B of FIG 10A, the liquid crystal molecules of the different second regions 116B-1R, 116B-2R, ..., and 116B-nR have a pre-tilt angle Φ that is different from the first pre-tilt angle Φ of the first regions 116B-1L, 116B-2L, ..., and 116B-nL, but they are not aligned differently from each other. For example, in the illustrated embodiment, zones 108B-1, 108B-2, and 108B-n are arranged such that the first and second regions alternate in the x-direction, and each of the first regions 116B-1L, 116B-2L, ..., and 116B-nL have a substantially identical first pre-tilt angle Φ, and each of the second regions 116B-1R, 116B-2R, ..., and 116B-nR have a substantially identical second pre-tilt angle Φ. The first and second pre-tilt angles of the first and second regions can have any of the values ​​discussed above with respect to the diffraction grating 100A of FIG.

[0090] Still referring to FIG. 10B, unlike grating 100A of FIG. 10A, zones 116B-1, 116B-2, and 116B-3 have substantially identical pre-tilt angles, e.g., about 0 to 90 degrees, but have duty cycles of about 40% to about 60%, e.g., about 50%, about 30% to about 50%, e.g., about 40% to about 20% to about 40%, e.g., about 30%, respectively, such that diffraction grating 100B has spatially variable optical properties.

[0091] Still referring to Figure 10B, in some embodiments, as shown, the zones can have a duty cycle that varies, e.g., increases or decreases, in one lateral direction such that a gradient of optical properties is created. In other embodiments, the duty cycle does not vary in one lateral direction.

[0092] 10C, the illustrated grating 100C combines features similar to those described above with respect to the gratings 100A and 100B of FIGS. 10A and 10B. In particular, the liquid crystal molecules of the different second regions 116C-1R, 116C-2R, ..., and 116C-nR can have pretilt angles Φ that are different from the first pretilt angles Φ of the first regions 116C-1L, 116C-2L, ..., and 116C-nL and are aligned differently from each other. In addition, the duty cycle varies between adjacent zones across a lateral direction, e.g., the x-direction. The first and second pretilt angles of the first and second regions can have any of the values ​​discussed above with respect to the grating 100A of FIG. 10A. In addition, the duty cycle variation between adjacent zones in a lateral direction, eg, across the x-direction, can also have values ​​as discussed above with respect to the grating 100B of FIG. 10B.

[0093] In the diffraction gratings 100A-100C illustrated in Figures 10A-10C, it should be understood that throughout this disclosure, in addition to the grating period and duty cycle discussed above, the diffractive properties may be further defined by, among other things, the thickness and refractive index of the liquid crystal layer 116. According to various embodiments disclosed herein, the thickness of the liquid crystal layer disclosed herein may have a thickness of about 1 μm to about 100 μm, about 0.5 μm to about 20 μm, or about 0.1 μm to about 10 μm. The average refractive index of the liquid crystal layer disclosed herein may be about 1.8 to about 2.0, about 1.6 to about 1.8, or about 1.4 to about 1.2. The resulting average diffraction efficiency of the various diffraction gratings disclosed herein may be about 1% to about 80%, about 1% to about 50%, or about 5% to about 30%.

[0094] As a result of implementing various embodiments disclosed herein, throughout this disclosure, different zones can have refractive indices that vary from about -30% to about +30%, from about -20% to about +20%, or from about -10% to about +10% across the surface area of ​​the grating, relative to the average refractive index. As a further result, different zones can have diffraction efficiencies that vary from about 1% to about 80%, from about 1% to about 50%, or from about 1% to about 30%, relative to the average diffraction efficiency, across the surface area of ​​the grating.

[0095] 11A and 11B illustrate a method for fabricating a grating having liquid crystal molecules with a non-uniform pre-tilt angle across its surface, such as the gratings 100A-100C of FIGS. 10A-10C described above, using a photoalignment technique according to an embodiment.

[0096] 11A, intermediate structure 100a is provided, upon which is formed optical alignment layer 120. Substrate 104 can be an optically transparent substrate that is transparent in the visible spectrum, such as, for example, silica-based glass, quartz, sapphire, indium tin oxide (ITO), or a polymer substrate, to name a few examples.

[0097] As described herein, a photo-alignment layer may refer to a layer onto which liquid crystal molecules are deposited, such as due to anchoring energy imparted to the liquid crystal molecules by the photo-alignment layer. Examples of photo-alignment layers include polyimides, linearly polarized photopolymerizable polymers (LPPs), azo-containing polymers, coumarin-containing polymers, and cinnamic acid-containing polymers, to name a few.

[0098] The optical alignment layer 120 can be formed by dissolving a precursor, e.g., a monomer, in a suitable solvent and coating the solution, i.e., spin coating, on the surface of the substrate 104. The solvent can then be removed from the coated solution.

[0099] After coating and drying optical matching layer 120, a photomask 130 can be used to expose different regions of underlying optical matching layer 120 to different doses of light and / or different polarizations of light. For example, the regions of optical matching layer 120 that are to be differently exposed can correspond to the first (e.g., left) and second (e.g., right) regions of zones 108A-1 and 108A-2, respectively, described above with respect to diffraction grating 100A of FIG.

[0100] In some embodiments, the optical alignment layer 120 can be configured such that the resulting liquid crystal molecules are oriented approximately parallel to the polarization direction of the exposing light (e.g., the azimuthal angle φ and the linear polarization angle of the exposing light are substantially identical). In other embodiments, the optical alignment layer 120 can be configured such that the liquid crystal molecules are oriented substantially orthogonal to the polarization direction of the exposing light (e.g., the azimuthal angle φ and the linear polarization angle of the exposing light are substantially offset by about + / - 90 degrees).

[0101] In one example, the photomask 130 can be a grayscale mask having a plurality of mask regions 130a-130d that are at least partially transparent and possibly have one or more opaque regions. Different ones of the plurality of mask regions 130a-130d can be configured to transmit different amounts of the incident light 140 such that the transmitted light 140a-140d transmitted through different ones of the plurality of mask regions 130a-130d has a variable intensity proportional to the relative transparency of the different mask regions 130a-130d to the incident light 140. However, the embodiments are not so limited and other mask types can also be used. For example, the photomask 130 can be a binary mask having a plurality of mask regions 130a-130d that are completely or nearly completely transparent or completely or nearly completely opaque, respectively, such that the transmitted light 140a-140d transmitted through the plurality of mask regions 130a-130d has a binary intensity.

[0102] The photomask 130 can be formed of a suitable material that, at least in part, absorbs UV light. In some embodiments, variable intensities of light transmitted across the different mask regions 130a-130d can be achieved by using different materials (e.g., having different absorption coefficients) in the different regions, materials possibly doped in different amounts in the different regions, or by using different thicknesses in the different regions. Other types of masks can also be used. In some embodiments, the photomask 130 can contact the underlying optical matching layer 120, while in other embodiments, the photomask 130 does not contact the underlying optical matching layer 120.

[0103] The incident light can be UV light, for example from a high pressure Hg-lamp, for its spectral lines at 436 nm ("g-line"), 405 nm ("h-line"), and 365 nm ("i-line"). However, the embodiment is not so limited and the incident light can be any suitable light to which the optical matching layer 120 is responsive, including visible light. If polarized, the incident UV-light can be polarized using a suitable polarizer. Thus, in various cases, the mask is transparent to UV-light. In addition to utilizing a photomask, other patterning methods can also be employed.

[0104] In some embodiments, the incident light 140 can be generated for a duration by using a single uniform incident light source. However, embodiments are not so limited and in other embodiments, the incident light 140 can vary in intensity across the different mask regions 130a-130d. Furthermore, in still other embodiments, the incident light 140 can be selectively generated for different durations across the different mask regions 130a-130d.

[0105] Additionally, in the illustrated embodiment, the incident light 140 can be polarized, e.g., linearly polarized, as depicted diagrammatically by the polarization vectors 134a-134d. However, according to other embodiments, the incident light 140 can be circularly or elliptically polarized. In some embodiments, the polarization vectors 134a-134d can represent different polarization angles, while in some other embodiments, the incident light 140 can have a single polarization angle.

[0106] Without being bound by any theory, the combination of different doses and polarizations of the photo-alignment material and the transmitted light 140a-140d causes various regions of the resulting photo-alignment layer 120 to impart different amounts of anchoring energy onto the overlying liquid crystal molecules, thereby resulting in different orientations of the liquid crystal molecules, as described herein. Other methods, which may or may not employ masks, may be used as well.

[0107] Referring to FIG. 11B, after exposing the optical alignment layer 120 to varying doses of transmitted light 140a-140d using the various techniques described above, a liquid crystal layer 116 can be formed on the optical alignment layer 120.

[0108] The liquid crystal layer 116 can be formed by dissolving a liquid crystal precursor, e.g., a monomer, in a suitable solvent and coating, e.g., spin coating, the surface of the matching layer 120 with the solution having the liquid crystal precursor dissolved therein. The solvent can then be removed from the coated solution.

[0109] In various embodiments, the reactive mesogenic material used to form the liquid crystal layer 116 includes, for example, a liquid crystalline mono- or diacrylate.

[0110] As described above, due to different doses and / or polarization angles of light received by different regions of the optical alignment layer 120, for example, the as-deposited liquid crystal layer forms liquid crystal layers 116A-1 and 116A-2 in zones 108A-1 and 108A-2, respectively. The liquid crystal layers 116A-1 and 116A-2, in turn, have first and second diffraction regions 116A-1L and 116A-1R and 116A-2L and 116A-2R, respectively. As described above with respect to FIG. 10A, the first and second regions alternate in the x-direction, and each of the first regions 116A-1L and 116A-2L has a substantially identical first pre-tilt angle Φ, while the second regions 116A-1R and 116A-2R have a pre-tilt angle Φ different from each other and from the first region's first pre-tilt angle. Without being bound by any theory, it is believed that for some types of photo-alignment materials, exposure of the lower photo-alignment layer 120 to light increases the anchoring energy that causes in-plane alignment of the liquid crystal molecules. As a result, for these photo-alignment materials, increased exposure leads to a corresponding decrease in the pre-tilt angle Φ of the liquid crystal layer formed thereon, according to embodiments. However, for other types of photo-alignment materials, exposure of the lower photo-alignment layer 120 to light decreases the anchoring energy that causes in-plane alignment of the liquid crystal molecules. As a result, for these photo-alignment materials, increased exposure leads to a corresponding increase in the pre-tilt angle Φ of the liquid crystal layer formed thereon, according to embodiments.

[0111] Thus, according to an embodiment, the degree of tilt, as measured by pretilt angle Φ, is inversely proportional to the dose of transmitted light received by the underlying optical matching layer 120. For example, in the illustrated embodiment, optical matching layers 120A-1L and 120A-2L receive the highest amount of incident light, followed by matching layer 120A-1R, then matching layer 120-2R. As a result, the resulting pretilt angle is highest for the second region 116A-2R of zone 108A-2, followed by the second region 116A-1R of zone 108A-1, then the first regions 116A-1L and 116A-2L of zones 108A-1 and 108A-2, respectively.

[0112] 12A-12C illustrate another method for fabricating a grating having a non-uniform pre-tilt angle, such as the gratings 100A-100C of FIGs. 10A-10C described above, using a photoalignment technique, according to an embodiment. In particular, in the illustrated embodiment, the method uses multiple exposures of an alignment layer prior to formation of the liquid crystal.

[0113] In the method illustrated in Figures 12A-12C, similar to the method illustrated with respect to Figures 11A-11B, a substrate 104 is provided and an optical matching layer 120 is formed thereon. However, unlike the method illustrated with respect to Figures 11A-11B, the optical matching layer 120 is exposed to a primary (e.g., blanket) pattern of light using a first incident light 140A prior to exposing different regions of the underlying optical matching layer 120 to different doses of light and / or different polarizations of light using a photomask 130. The primary pattern of light may be produced, for example, using a blanket exposure, for example, using a blanket semi-transparent grayscale mask (not shown). In the illustrated embodiment, the mask may be omitted for the blanket exposure to the primary pattern of light.

[0114] The first incident light 140A can be polarized, e.g., linearly polarized with a first polarization angle, as depicted diagrammatically by the polarization vectors 134a-134d. The linearly polarized first incident light 140A can create uniform alignment of the liquid crystal molecules. Following exposure to the primary (e.g., blanket) pattern of light, the alignment layer 120 can be further exposed to a secondary pattern of light using a second incident light 140B and a photomask 130 configured to expose different regions of the underlying optical alignment layer 120 to different doses of light and / or different polarizations of light, in a manner substantially similar to that described above with respect to FIGS. 11A-11B. For example, as described above with respect to the diffraction grating 100A, different regions of the optical alignment layer 120 corresponding to the first (e.g., left) and second (e.g., right) regions of the zones 108A-1 and 108A-2, respectively, can be exposed to different doses and / or different polarizations of light. Unlike the first incident light 140A, the second incident light 140B can be unpolarized or circularly polarized. The unpolarized or circularly polarized second incident light 140B can redisperse the alignment direction of the liquid crystal molecules. The resulting diffraction grating 100A is similar to that described above with respect to FIG. 11B, in which the first and second regions alternate in the x-direction, and each of the first regions 116A-1L and 116A-2L has a substantially identical first pre-tilt angle Φ, while the second regions 116A-1R and 116A-2R have a pre-tilt angle Φ different from each other and from the first region's first pre-tilt angle.

[0115] The second incident light 140B can be polarized, e.g., linearly polarized, with a second polarization angle different from, e.g., orthogonal to, the second polarization angle of the first incident light 140A, as depicted diagrammatically by polarization vectors 134e-134h. In some other embodiments, the first and second polarization angles are the same. In yet some other embodiments, the first and second polarization angles are different, but not orthogonal. Furthermore, the second incident light 140B according to other embodiments can be circularly or elliptically polarized, with a similar or different polarization orientation relative to the first incident light 140A.

[0116] In the embodiment described above with reference to Figures 11A-11B and Figures 12A-12C, a method of controlling the pretilt angle of liquid crystals using photo-alignment techniques has been described. However, it should be understood that other embodiments are also possible, including a process called micro-abrasion, in which the alignment layer is abraded under load with a metal object, e.g., a metal sphere. For example, a metal sphere in direct contact with the alignment layer can be moved across the alignment layer to create micrometer-sized abrasive lines, which induce a pretilt of the subsequently deposited liquid crystal. In yet other embodiments, alignment materials that are pre-configured to induce different pretilt angles can be deposited to induce a pretilt of the liquid crystal molecules, instead of post-treating them.

[0117] 13A and 13B, cross-sectional (xz-plane) views of diffraction gratings 103A and 103B according to some other embodiments are illustrated. The diffraction gratings 103A and 103B can be polarization gratings (PG) that are configured to locally modify the polarization state of transmitted light, which can be achieved by spatially variable birefringence and / or dichroism. Although not shown for clarity, each of the diffraction gratings 103A and 103B comprises a substrate, a matching layer formed thereon, and a plurality of differently arranged diffraction zones 154A-1 and 154A-2 in FIG. 13A and 154B-1 and 154B-2 in FIG. 13B. Diffraction zones 154A-1 and 154A-2 of diffraction grating 103A have corresponding liquid crystal layers 144A-1 and 144A-2, respectively, and diffraction zones 154A-1 and 154A-2 of diffraction grating 103B have corresponding liquid crystal layers 154B-1 and 154B-2, respectively.

[0118] Each of the liquid crystal layers 144A-1 and 144A-2 of the diffraction grating 103A, in turn, has a plurality of differently arranged diffraction regions 144A-1a-144A-1g and 144A-2a-144A-2g, respectively. Similarly, each of the liquid crystal layers 144B-1 and 144B-2 of the diffraction grating 103B, in turn, has a plurality of differently arranged diffraction regions 144B-1a-144B-1g and 144B-2a-144A-2g, respectively.

[0119] Referring to the diffraction grating 103A of FIG. 13A, each of the multiple regions 144A-1a-144A-1g of the zone 154A-1 and each of the multiple regions 144A-2a-144A-2g of the zone 154A-2 have liquid crystal molecules 112 substantially aligned along the same alignment direction within the same region. The liquid crystal molecules 112 in all the regions of the zone 154A-1 have substantially the same first pretilt angle Φ. In contrast, the liquid crystal molecules 112 in different regions of the zone 154A-2 have different pretilt angles Φ. In the illustrated embodiment, the pretilt angle Φ of the central region (144A-2d) of the zone 154A-2 has a pretilt angle Φ that is minimum with increasing pretilt angle Φ for increasingly outer regions of the zone 154A-2, but the embodiment is not so limited. In addition, the central region (144A-2d) has a pre-tilt angle Φ similar to the first pre-tilt angle Φ of zone 154A-1 in the illustrated embodiment, although the embodiment is not so limited. The pre-tilt angles of the different regions of the diffraction grating 103A can have any of the magnitudes described above with respect to FIGS. 10A-10C.

[0120] Still referring to Figure 13A, in the illustrated embodiment, the liquid crystal molecules 112 in different regions of zone 154A-1 have different azimuthal angles φ. However, the embodiment is not so limited and in other embodiments, the liquid crystal molecules 112 in different regions of zone 154A-1 can have the same azimuthal angle φ. The azimuthal angles of the different regions of the diffraction grating 103A can have any of the magnitudes described below with respect to Figures 15A-15C.

[0121] Referring to the diffraction grating 103B of FIG. 13B, similar to the diffraction grating 103A of FIG. 13A, each of the multiple regions 144B-1a-144B-1g of the zone 154B-1 has liquid crystal molecules 112 substantially aligned along the same alignment direction in the same region. Similar to the zone 154A-2 of the diffraction grating 103A of FIG. 13A, the liquid crystal molecules 112 in different regions of the zone 154B-1 have substantially different pretilt angles Φ and substantially different azimuthal angles φ. In contrast, each of the multiple regions 144B-2a-144B-2g of the zone 154B-2 has liquid crystal molecules 112 substantially aligned differently in the same region. That is, the individual liquid crystal molecules 112 in each region of the zone 154B-2 have substantially different pretilt angles Φ and substantially different azimuthal angles φ. For example, the liquid crystal molecules 112 in each region of zone 154B-2 may have chirality, as will be explained in more detail with respect to Figures 19A and 19B below.

[0122] 13A and 13B, specific combinations of zones and regions within different zones are presented as examples, but it should be understood that zones and regions within zones can be mixed and matched, for example, combining zone 154A-1 of FIG. 13A with zone 154B-2 of FIG. 13B in a diffraction grating is a possibility.

[0123] 14A-14B each illustrate another method for fabricating a grating having a non-uniform pre-tilt angle, such as gratings 103A and 103B of FIGs. 13A and 13B, using a photoalignment technique, according to an embodiment. In particular, in the illustrated embodiment, the method includes polarization interference holographic exposure using a grayscale mask, according to an embodiment.

[0124] Polarization interference holographic exposure is a technique that uses multiple beams of coherent light to create an interference pattern. While most conventional holography uses intensity modulation, polarization holography involves modulation of the polarization state to create the interference pattern.

[0125] 14A, in the illustrated method, the process leads to exposing the optical matching layer 120 to UV light, similar to the method described above with respect to FIGS. 11A-11B. In particular, the optical matching layer 120 is formed on the substrate 104, and the grayscale mask 130 is partially disposed over the optical matching layer 120. Then, a plurality of coherent light beams 142a, 142b having different polarizations are directed to a plurality of differently arranged diffraction zones 154A-1 and 154A-2. In the illustrated embodiment, the light beams 142a and 142b include orthogonal circularly polarized beams. However, the light beams 142a and 142b can also include, for example, non-orthogonal circularly polarized beams. In the illustrated embodiment, the zone 154A-1 is exposed, while the zone 154A-2 is masked with the grayscale mask 130. The multiple light beams 142a and 142b are positioned and polarized such that the resulting interference effect results in the liquid crystal layers 144A-1 and 144A-2 of the diffraction grating 103A having multiple differently arranged diffraction regions 144A-1a-144A-1g and 144A-2a-144A-2g, respectively, as described above with respect to Figure 13A. Similarly, using a similar concept with reference back to Figure 13B, the liquid crystal layers 144B-1 and 144B-2 of the diffraction grating 103B can be fabricated having multiple differently arranged diffraction regions 144B-1a-144B-1g and 144B-2a-144B-2g, respectively.

[0126] 15A-15C, a top-down view (seen along the xy plane) of a diffraction grating 150A-150C according to various embodiments is shown. Because Figs. 15A-15C are top-down views, only the liquid crystal layer (as opposed to the matching layer or substrate) is shown, while the underlying features are not shown. However, it should be understood that the liquid crystal layer of each of the diffraction gratings 150A-150C is formed across the substrate and includes a plurality of diffraction zones, i.e., in Fig. 15A, diffraction zones 148A-1, 148A-2, ... and 148A-n; in Fig. 15B, diffraction zones 148B-1, 148B-2, ... and 148B-n; and in Fig. 15C, diffraction zones 148C-1, 148C-2, ... and 148C-n.

[0127] Each diffractive zone of the diffraction gratings 150A-150C has a periodically repeating lateral dimension or grating period ∧ and includes a corresponding liquid crystal layer formed from liquid crystal molecules 112. The lateral dimension or grating ∧ can be similar to that described above with respect to Figures 10A-10C.

[0128] 10A-10C, the diffraction zones 148A-1, 148A-2, ... 148A-n of the diffraction grating 150A have corresponding liquid crystal layers 156A-1, 156A-2, ... 156A-n, respectively, the diffraction zones 148B-1, 148B-2, ... 148B-n of the diffraction grating 150B have corresponding liquid crystal layers 156B-1, 156B-2, ... 156B-n, respectively, and the diffraction zones 148C-1, 148C-2, ... 148C-n of the diffraction grating 150C have corresponding liquid crystal layers 156C-1, 156C-2, and 156C-n, respectively. The number of diffraction zones of each type can be similar to those described above with respect to FIGS. 10A-10C. In addition, the diffraction zones as arranged can be periodically repeated any suitable number of times.

[0129] Each of the liquid crystal layers 156A-1, 156A-2, and 156A-n of the diffraction grating 150A, in turn, has first and second diffraction regions 156A-1L and 156A-1R, 156A-2L and 156A-2R, ..., and 156A-nL and 156A-nR, respectively, that are arranged differently. Similarly, each of the liquid crystal layers 156B-1, 156B-2, and 156B-n of the diffraction grating 150B, in turn, has first and second diffraction regions 156B-1L and 156B-1R, 156B-2L and 156B-2R, ..., and 156B-nL and 156B-nR, respectively, that are arranged differently. Similarly, each of the liquid crystal layers 156C-1, 156C-2, and 156C-n of the diffraction grating 150C in turn has first and second diffraction regions 156C-1L and 156C-1R, 156C-2L and 156C-2R, ..., and 156C-nL and 156C-nR, respectively, that are arranged differently.

[0130] Similar to the gratings 100A-100C described above with respect to Figures 10A-10C, each of the different diffractive zones further comprises a matching layer (not shown) interposed between the substrate and the corresponding liquid crystal layer. That is, although not shown for clarity, interposed between the substrate 104 of Figure 15A and the differently arranged first / second diffractive regions 156A-1L / 156A-1R, 156A-2L / 156A-2R, ... and 156A-nL / 156A-nR of the grating 150A are first and second matching layers 160A-1L / 160A-1R, 160A-2L / 160A-2R, ... and 160A-nL / 160A-nR, respectively. Similarly, interposed between the substrate 104 of FIG. 15B and the differently arranged first / second diffraction regions 156B-1L / 156B-1R, 156B-2L / 156B-2R, ... and 156B-nL / 156B-nR of the diffraction grating 150C are first / second matching layers 160B-1L / 160B-1R, 160B-2L / 160B-2R, ... and 160B-nL / 160B-nR, respectively. Similarly, interposed between the substrate 104 of FIG. 15C and the differently arranged first / second diffraction regions 156C-1L / 156C-1R, 156C-2L / 156C-2R, ... and 156C-nL / 156C-nR of the diffraction grating 150C are first / second matching layers 160C-1L / 160C-1R, 160C-2L / 160C-2R, ... and 160C-nL and 160C-nR, respectively.

[0131] 15A-15C, each zone of gratings 150A, 150B, and 150C includes first and second regions that alternate in the x-direction. Each of first regions 156A-1L, 156A-2L, ..., and 156A-nL of grating 150A, each of first regions 156B-1L, 156B-2L, ..., and 156B-nL of grating 150B, and each of first regions 156C-1L, 156C-2L, ..., and 156C-nL of grating 150C have liquid crystal molecules 112 substantially aligned along the same first alignment direction and have substantially the same azimuthal angles φ. In contrast, each of the second regions 156A-1R, 156A-2R, ... and 156A-nR of diffraction grating 150A, each of the second regions 156B-1R, 156B-2R, ... and 156B-nL of diffraction grating 150B, and each of the second regions 156C-1R, 156C-2R, ... and 156A-nR of diffraction grating 150C have liquid crystal molecules 112 substantially aligned along a second alignment direction that is different from the first alignment direction and have a second azimuthal angle φ that is different, e.g., smaller, than the first azimuthal angle φ of the respective first regions.

[0132] In each of the diffraction gratings 150A-150C of Figures 15A-15C, at least some of the diffractive zones, according to an embodiment, have liquid crystal layers formed from liquid crystal molecules that are arranged in a spatially different manner, e.g., have different azimuthal angles from one another (Figures 15A and 15C), and have different duty cycles from one another (Figures 15B and 15C), such that the diffractive zones have different optical properties, e.g., different refractive indices and / or different diffraction efficiencies.

[0133] In particular, with reference to diffraction grating 150A of FIG. 15A, in addition to having an alignment direction and azimuth angle φ that differs from the first azimuth angle φ of first regions 156A-1L, 156A-2L, ..., and 156A-nL, the liquid crystal molecules of second regions 156A-1R, 156A-2R, ..., and 156A-nR are aligned along a second alignment direction that is different from one another. For example, in the illustrated embodiment, zones 148A-1, 148A-2, and 148A-n are arranged such that the first and second regions alternate in the x-direction, and each of first regions 156A-1L, 156A-2L, ..., and 156A-nL have substantially the same azimuth angle φ, while second regions 156A-1R, 156A-2R, ..., and 156A-nR have different azimuth angles φ from one another. As an example, first regions 156A-1L, 156A-2L, ..., and 156A-nL have azimuth angles φ of about 0 to about 15 degrees or about 0 to 10 degrees, e.g., 0 degrees. The second regions 156A-1R, 156A-2R, ... and 156A-nR can have different azimuth angles φ from each other, and can be about 75 degrees to about 90 degrees, for example, about 90 degrees, about 60 degrees to about 90 degrees, or about 65 degrees to about 85 degrees, for example, about 75 degrees, about 30 degrees to about 60 degrees, or about 35 degrees to about 55 degrees, for example, about 45 degrees, about 10 degrees to about 40 degrees, or about 15 degrees to about 35 degrees, for example, about 25 degrees.

[0134] 15A, in some embodiments, as shown, the second regions 156A-1R, 156A-2R,..., and 156A-nR can have an azimuthal angle φ that varies, e.g., increases or decreases, in one direction in a lateral direction such that a gradient of diffractive properties is created. In other embodiments, the second regions 156A-1R, 156A-2R,..., and 156A-nR can have an azimuthal angle φ that does not vary in one direction in a lateral direction.

[0135] Still referring to FIG. 15A, the duty cycle can be from about 10% to about 30%, from about 30% to about 50%, from about 50% to about 70%, or from about 70% to about 90%, which in the illustrated embodiment is substantially constant in the x-direction.

[0136] 15B, as discussed above, diffraction grating 150B shares some common features with diffraction grating 150A of FIG 15A. However, unlike diffraction grating 150B of FIG 15A, the liquid crystal molecules of different second regions 156B-1R, 156B-2R, ..., and 156B-nR have a different azimuthal angle φ than the first azimuthal angle φ of first regions 156B-1L, 156B-2L, ..., and 156B-nL, but they are not aligned differently from one another. For example, in the illustrated embodiment, zones 148B-1, 148B-2, and 148B-n are arranged such that the first and second regions alternate in the x-direction, and each of first regions 156B-1L, 156B-2L, ..., and 156B-nL has a substantially identical first azimuthal angle φ, and each of second regions 156B-1R, 156B-2R, ..., and 156B-nR has a substantially identical second azimuthal angle φ. The first and second azimuthal angles of the first and second regions can have any of the values ​​discussed above with respect to diffraction grating 150A of FIG. 15A.

[0137] However, unlike grating 150A of FIG. 15A, zones 148B-1, 148B-2, and 148B-3 have substantially the same unidirectional angle, e.g., about 0 to 50 degrees, while having substantially different duty cycles, e.g., about 40% to about 60%, e.g., about 50%, about 30% to about 50%, e.g., about 40%, and about 20% to about 40%, e.g., about 30%, such that diffraction grating 150B has spatially variable optical properties.

[0138] Still referring to Figure 15B, in some embodiments, as shown, the zones can have a duty cycle that varies, e.g., increases or decreases, in one lateral direction such that a gradient of optical properties is created. In other embodiments, the duty cycle does not vary in one lateral direction.

[0139] Referring now to FIG. 15C, the illustrated grating 150C combines features similar to those described above with respect to the gratings 150A and 150B of FIGS. 15A and 15B. In particular, the liquid crystal molecules of the different second regions 156C-1R, 156C-2R, ..., and 156C-nR can have an azimuthal angle φ that is different from the first azimuthal angle φ of the first regions 116C-1L, 116C-2L, ..., and 116C-nL and different from each other. In addition, the duty cycle varies between adjacent zones across a lateral direction, e.g., the x-direction. The first and second azimuthal angles of the first and second regions can have any of the values ​​discussed above with respect to the grating 150A of FIG. 15A. In addition, the duty cycle variation between adjacent zones across a lateral direction, e.g., the x-direction, can also have the values ​​discussed above with respect to the grating 150B of FIG. 15B.

[0140] 16A, a top-down view (xy plane) of a diffraction grating 160 according to some other embodiments is illustrated in which the azimuthal angle of the liquid crystal molecules rotates across the lateral length of the zone. A diffraction grating with such an arrangement is sometimes referred to as a polarization grating. Although not shown for clarity, the diffraction grating 160 comprises a substrate, a matching layer formed thereon, and a plurality of differently arranged diffraction zones 164-1 and 164-2. The diffraction zones 164-1 and 164-2 have corresponding liquid crystal layers 168-1 and 168-2, respectively. Each of the liquid crystal layers 168-1 and 168-2 of the diffraction grating 160, in turn, has a plurality of differently arranged diffraction regions 168-1a-168-1i and 168-2a-168-2i, respectively. Each of the plurality of regions 168-1a-168-1i in zone 164-1 and each of the plurality of regions 168-2a-168-2i in zone 164-2 have liquid crystal molecules 112 substantially aligned along the same alignment direction within the same region, and thus it should be understood that each of the zones includes a stack of liquid crystal molecules stacked in the z-direction.

[0141] The liquid crystal molecules 112 in each of the diffraction regions 168-1a-168-1i of the zone 164-1 and the regions 168-2a-168-2i of the zone 164-2 have substantially the same azimuthal angle φ within the same region. However, the liquid crystal molecules 112 in different diffraction regions have substantially different azimuthal angles. In addition, the liquid crystal molecules 112 in different diffraction regions can have substantially the same or different pretilt angles Φ, similar to those described above with respect to Figures 13A and 13B.

[0142] In the illustrated embodiment, the liquid crystal molecules 112 of the diffraction regions 168-1a-168-1i of the zone 164-1 and the corresponding regions 168-2a-168-2i of the zone 164-2 have substantially the same azimuthal angle φ within the same region. However, the distance between adjacent regions is substantially different between the zones 164-1 and 164-2 such that a spatially variable diffractive property is generated, as illustrated with reference to FIG. 16B. With reference to FIG. 16B, a graph 162 is illustrated which diagrammatically illustrates the azimuthal angle φ as a function of the lateral position x for the diffraction grating 160 in FIG. 16A. The x-axis represents the lateral distance in the x-direction, and the y-axis represents the azimuthal angle φ. The curves 162-1 and 162-2 represent the azimuthal angle φ as a function of the lateral position x for the zones 164-1 and 164-2, respectively.

[0143] Referring back to FIG. 16A, the liquid crystal molecules 112 of the diffractive region 164-1 are arranged such that the rate of change of the azimuthal angle φ per unit of lateral length, i.e., Δφ / Δx in the x-direction, is relatively constant, as illustrated by curve 162-1 in FIG. 16B. In contrast, the liquid crystal molecules 112 of the diffractive region 164-2 are arranged such that Δφ / Δx in the x-direction varies substantially across x, as illustrated by curve 162-2 in FIG. 16B. As a result, curve 162-2 is characterized by a central region of the zone 164-2 where Δφ / Δx varies relatively slowly, and edge regions of the zone 164-2 where Δφ / Δx varies relatively quickly. As a result, the diffractive properties (including efficiency and refractive index) differ from those of a grating with a uniform variation of its azimuthal angle of the liquid crystal.

[0144] 17A-17E illustrate a method for fabricating a grating having a non-uniform azimuth angle using an optical alignment technique, such as the gratings 150A-150C of FIGS. 15A-15C described above, according to an embodiment. In particular, in the illustrated embodiment, the method uses multiple exposures of an alignment layer prior to deposition of the liquid crystal. In the method illustrated in FIGS. 17A-17E, a substrate 104 is provided and an optical alignment layer 120 is formed thereon, similar to the method illustrated with respect to FIGS. 11A-11B.

[0145] 17A, after optical matching layer 120 is formed on substrate 104, a first photomask 174A is used to expose different regions of underlying optical matching layer 120 to different doses of light and / or different polarizations of light. For example, the different regions of optical matching layer 120 correspond to first (e.g., left) and second (e.g., right) regions of zones 148A-1 and 148A-2, respectively, as described above with respect to diffraction grating 150A in FIG.

[0146] In some embodiments, the first photomask 174A can be a grayscale mask having a plurality of mask regions 174A-1-174A-4 that are at least partially transparent and possibly have one or more opaque regions. Different ones of the plurality of mask regions 174A-1-174A-4 can be configured to transmit different doses of the first incident light 172A such that the transmitted light 172A transmitted through different ones of the plurality of mask regions has a variable intensity proportional to the relative transparency of the different mask regions. In other embodiments, the photomask 174A can be a binary mask having a plurality of mask regions 174A-1-174A-4 that are each completely or nearly completely transparent or completely or nearly completely opaque, such that the transmitted light 172A has a binary intensity. In the illustrated embodiment, the first incident light 172A is polarized, e.g., linearly polarized at a first angle, e.g., 0 degrees, as depicted diagrammatically by polarization vector 178A, and can be substantially transmitted through mask regions 174A-1 and 174A-3 corresponding to first (e.g., left) regions of zones 148A-1 and 148A-2, respectively, of diffraction grating 150A, while being substantially blocked in other regions, as shown in FIG. 15A.

[0147] Referring to intermediate structure 150B illustrated in FIG. 17B, after exposing different regions of optical alignment layer 120 to the first incident light 172A, a second photomask 174B is used to expose different regions of the underlying optical alignment layer 120 to different doses of light and / or different polarizations of light using a second incident light 172B.

[0148] In some embodiments, the second photomask 174B can be a grayscale mask having a plurality of mask regions 174B-1-174B-4 that are at least partially transparent, and possibly have one or more opaque regions, unlike the first photomask 174A. Different ones of the plurality of mask regions 174B-1-174B-4 can be configured to transmit different doses of the second incident light 172B. In other embodiments, the photomask 174B can be a binary mask having a plurality of mask regions 174B-1-174B-4 that are fully or nearly fully transparent or fully or nearly fully opaque, respectively, such that the transmitted light 172B has a binary intensity. The second incident light 172B can be polarized, e.g., linearly polarized, at a second angle that is different from, e.g., orthogonal to, the first polarization angle of the first incident light 178A. For example, the second incident light 172B may be linearly polarized orthogonal to the first incident light 172A, e.g., at 90 degrees, as depicted diagrammatically by polarization vector 178B, and may be substantially transmitted through mask region 174B-2 corresponding to the second (e.g., right) region of zone 148A-1 of diffraction grating 150A shown in FIG. 15A, while being substantially blocked in other regions.

[0149] Referring to the intermediate structure in FIG. 17C, after exposing different regions of the optical alignment layer 120 to the second incident light 172B, a third photomask 174C is used to expose different regions of the underlying optical alignment layer 120 to different doses of light and / or different polarizations of light using the third incident light 172C.

[0150] In some embodiments, the third photomask 174C can be a grayscale mask having a plurality of mask regions 174C-1-174C-4 that are at least partially transparent and possibly have one or more opaque regions, unlike the first and second photomasks 174A, 174B. Different ones of the plurality of mask regions 174C-1-174C-4 can be configured to transmit different doses of the third incident light 172C. In other embodiments, the photomask 174C can be a binary mask having a plurality of mask regions 174C-1-174C-4 that are fully or nearly fully transparent or fully or nearly fully opaque, respectively, such that the transmitted light 172C has a binary intensity. The third incident light 178C can be polarized, for example, linearly polarized, at a third angle that is different from the first and second polarization angles of the first and second incident lights 178A and 178B. In the illustrated embodiment, the third incident light 172C is linearly polarized at 45 degrees, as depicted diagrammatically by polarization vector 178C, and is substantially transmitted through mask region 174A-4 corresponding to the second (e.g., right) region of zone 148A-2 of diffraction grating 150A shown in FIG. 15A, while being substantially blocked in other regions.

[0151] 17D (cross-sectional view) and 17E (top-down view), after exposing different regions of optical alignment layer 120 through the multi-exposure process described above with respect to FIGS. 17A-17C, a liquid crystal layer can be deposited on optical alignment layer 120. As a result of different doses and / or polarizations of light received by different regions of optical alignment layer 120, differently configured liquid crystal layers 156A-1 and 156A-2 are formed in respective zones 148A-1 and 148A-2, respectively. Liquid crystal layers 156A-1 and 156A-2 have first and second diffractive regions 156A-1L and 156A-1R and 156A-2L and 156A-2R, respectively. 15A, the first and second regions alternate in the x-direction, with first regions 156A-1L and 156A-2L each having a substantially identical first azimuthal angle φ, while second regions 156A-1R and 156A-2R have an azimuthal angle φ that differs from each other and from the first azimuthal angles of the first regions. Without being bound by any theory, in some cases, exposure of lower optical alignment layer 120 to light having different polarization angles leads to different azimuthal angles of the liquid crystal molecules.

[0152] Still referring to Figures 17D and 17E, the azimuthal angle φ of the liquid crystal molecules can be determined by the linear polarization angle of the exposure light and the type of optical alignment layer 120. In the illustrated embodiment, the optical alignment layer 120 is configured such that the degree of rotation of the liquid crystal molecules as measured by the absolute value of the azimuthal angle φ up to + / - 90 degrees is determined by the linear polarization orientation angle of the transmitted light received by the underlying alignment layer up to + / - 90 degrees. In some embodiments, such as the illustrated embodiment, the optical alignment layer 120 can be configured such that the liquid crystal molecules are oriented approximately parallel to the polarization direction of the exposure light (e.g., the azimuthal angle φ and the linear polarization angle of the exposure light are substantially identical). However, the embodiments are not so limited, and in other embodiments, the optical alignment layer 120 can be configured such that the liquid crystal molecules are oriented substantially orthogonal to the polarization direction of the exposure light (e.g., the azimuthal angle φ and the linear polarization angle of the exposure light are substantially offset by about + / - 90 degrees). For example, in the illustrated embodiment, optical matching layers 160A-1L and 160A-2L receive light with the same linear polarization orientation, and optical matching layer 160A-1R receives light with a larger difference in linear polarization orientation angle relative to the linear polarization orientation of optical matching layers 160A-1L and 160A-2L, followed by optical matching layer 160A-2R, so that the resulting azimuthal angles are the same for first regions 156A-1L and 156A-2L, and the difference in the resulting azimuthal angles for first regions 156A-1L and 156A-2L is larger for second region 156A-1R than for second region 156A-2R.

[0153] In various embodiments described herein, the photomask can include a linear polarizer, such as a wire grid polarizer, having a regular array of parallel metal wires arranged in a plane perpendicular to the propagation direction of the incident light. In some embodiments described herein, the photomask can be configured to provide illumination with a uniform polarization angle across the optical matching layer. When including a wire grid polarizer, these embodiments can be achieved by configuring the array of metal wires to be uniform across the photomask, e.g., the thickness and / or density of the metal wires is uniform. In other embodiments, the photomask can be configured to provide illumination with non-uniform or multiple polarization angles across different regions of the optical matching layer. When including a wire grid polarizer, these embodiments can be achieved by configuring the array of metal wires to be non-uniform and variable across the photomask, e.g., the thickness and / or density of the metal wires is non-uniform and variable. Thus, by varying the thickness and density of the metal wires, both the polarization angle and the transmittance of the light can be controlled according to various embodiments.

[0154] 18A-18D illustrate another method for fabricating a diffraction grating 160 according to some other embodiments, where the azimuthal angle of the liquid crystal molecules is rotated across the lateral length of the zone, e.g., polarization grating. In particular, in the illustrated embodiment, the method uses polarization interference holographic exposure using a grayscale mask according to an embodiment.

[0155] Referring to FIG. 18A showing intermediate structure 160A, in the illustrated method, the process leading to forming optical matching layer 120 for UV light is similar to the method described above with respect to FIGS. 17A-17E. Then, a plurality of coherent light beams 182A, 182B having different polarizations are directed to a plurality of differently arranged diffractive zones 164A-1 and 164A-2. In the illustrated embodiment, light beams 182A and 182B include orthogonal circularly polarized beams. However, light beams 182A and 182B can also include, for example, elliptically polarized beams. In the illustrated embodiment, both zones 164-1 and 164-2 are not masked.

[0156] Then, referring to FIG. 18B, which shows intermediate structure 160B, a photomask 184 is used to expose different zones of underlying optical alignment layer 120 to different doses of light and / or different polarizations using linearly polarized incident light 188 having any of the polarization angles discussed above with respect to FIGS. 17A-17E. For example, different zones of optical alignment layer 120 may correspond to zones 164-1 and 164-2, as described above with respect to grating 160 in FIG. 16B. As a result of a secondary exposure to linearly polarized light 188, a proportion of optical alignment layer 120 may be realigned. Without being bound by any theory, when optical alignment layer 120 is exposed a second time with different linear polarization orientations, the orientation of the liquid crystal molecules may be determined by the relative linear polarization orientations and exposure doses of the two exposures.

[0157] 18C and 18D, cross-sectional (xz-plane) and top-down (xy-plane) views of the diffraction grating 160 are shown, corresponding to those in FIG. 16B. As a result of the first and second exposures, at least in part as described above with respect to FIGS. 18A and 18B, liquid crystal layers 168-1 and 168-2, respectively, are produced, each having a plurality of differently arranged diffraction regions 168-1a-168-1i and 168-2a-168-2i. Each of the plurality of regions 168-1a-168-1i of the zone 164-1 and each of the plurality of regions 168-2a-168-2i of the zone 164-2 have liquid crystal molecules 112 substantially aligned along the same alignment direction within the same region. It should therefore be understood that each of the zones includes a stack of liquid crystal molecules stacked in the z-direction. (Space-variable liquid crystal diffraction gratings based on space-variable liquid crystal materials)

[0158] In the various embodiments discussed above, the liquid crystal molecules are processed using photoalignment techniques, however, other embodiments are possible, which can be processed with or without photoalignment.

[0159] 19A and 19B, there are illustrated top-down (viewed along the xy plane) and side-on (viewed along the xz plane) views of a diffraction grating 190, which may be fabricated with or without photo-alignment, according to some embodiments. The diffraction grating 190 comprises a plurality of diffractive zones, i.e., diffractive zones 198-1, 198-2, ..., and 198-n, having a periodically repeating lateral dimension or grating period ∧ and including corresponding liquid crystal layers formed from liquid crystal molecules 112. The lateral dimension or grating period ∧ may be similar to those described above with respect to Figures 10A-10C.

[0160] The diffraction zones 198-1, 198-2, ... 198-n of the diffraction grating 190 have corresponding liquid crystal layers 186-1, 186-2, ... 186-n, respectively. The number of diffraction zones of each type can be similar to that described above with respect to Figures 10A-10C. In addition, the diffraction zones as arranged can be repeated periodically any suitable number of times. Each of the liquid crystal layers 186-1, 186-2, and 186-n of the diffraction grating 190, in turn, has first and second diffraction regions 186-1L and 186-1R, 186-2L and 186-2R, ... and 186-nL and 186-nR, respectively, which are arranged differently.

[0161] The different liquid crystal layers 186-1, 186-2, and 186-n have liquid crystal molecules 112 arranged to have different degrees of chirality. As explained above, chirality can be described by chiral pitch p, which may refer to the distance over which the liquid crystal molecules undergo a full 360° twist. Chirality can also be characterized by a twist deformation angle, which is the angle of twist of the liquid crystal molecules undergo within the thickness of the liquid crystal layer. For example, in the illustrated embodiment, the first liquid crystal layer 186-1 has first and second diffractive regions 186-1L and 186-1R with liquid crystal molecules 112 having different azimuthal angles with little or no chirality (very large or infinite chiral pitch p). The second and third liquid crystal layers 186-2 and 186-n each have a respective first / second diffraction region 186-2L / 186-2R and 186-nL / 186-nR having liquid crystal molecules 112 with a substantial and substantially different degree of chirality. Similarly, in various embodiments, the azimuthal angle or difference in azimuthal angle between the top liquid crystal molecules in the first and second diffraction regions 186-2L / 186-2R and 186-nL / 186-nR of the second and nth liquid crystal layers 186-2 and 186-n, respectively, can be any value described above with respect to the diffraction gratings 150A-150C in FIGS. 15A-15C.

[0162] In some embodiments, each pair of first / second diffractive regions in a zone, e.g., pair of regions 186-2L / 186-2R in zone 198-2 (see FIG. 19A ) and pair of regions 186-nL / 186-nR in zone 198-n, have uppermost liquid crystal molecules with different azimuthal angles φ but the same chiral pitch p. In some other embodiments, pair of regions in a zone have uppermost liquid crystal molecules with the same azimuthal angles φ but different chiral pitch p. In various embodiments, the chiral twist (e.g., twist angle or twist deformation angle) of the liquid crystal molecules in a given region of pair of regions 186-2L / 186-2R in zone 198-2 and pair of regions 186-nL / 186-nR in zone 198-n is, for example, about + / - 45°. o , about + / -90 o , about + / -135 o , or about + / - 180 o The corresponding chiral periodicity p can be 8D, 4D, or 3D, where 2D is the thickness of the liquid crystal layer.

[0163] For example, in the illustrated embodiment, the topmost liquid crystal molecules in the first and second regions 186-2L and 186-2R, respectively, are, for example, 135 o and 45 o 1 and 2, while having a first chiral pitch of, for example, about 8D, where D is the thickness of the liquid crystal layer. As a result, in each of the first and second regions 186-2L and 186-2R, the top and bottom liquid crystal molecules are twisted about -45 degrees with respect to each other. In addition, in the illustrated embodiment, the top liquid crystal molecules in the first and second regions 186-nL, 186-nR, respectively, are twisted about 90 degrees with respect to each other. o and 0 oand a second chiral pitch of about 4D, where D is the thickness of the liquid crystal layer. As a result, in the first and second regions 186-nL and 186-nR, respectively, the top and bottom liquid crystal molecules are twisted about -90 degrees relative to each other. However, the azimuthal angles φ of the top liquid crystal molecules of the first / second diffraction regions 186-2L / 186-2R and 186-nL / 186-nR can have any value as described above with respect to Figures 15A-15C.

[0164] Still referring to Figures 19A and 19B, in some embodiments, the liquid crystal molecules 112 in each region have the same pre-tilt angle Φ, which can be zero or higher.

[0165] Still referring to Figures 19A and 19B, the duty cycles of the different liquid crystal layers 186-1, 186-2, and 186-n may be different and may be from about 10% to about 30%, from about 30% to about 50%, from about 50% to about 70%, or from about 70% to about 90%, respectively.

[0166] 20, a cross-sectional side (xz plane) view of a diffraction grating 200 is illustrated, according to some other embodiments. Although not shown for clarity, the diffraction grating 200 comprises a substrate and a plurality of differently arranged diffractive zones 208-1 and 208-2 with corresponding liquid crystal layers 196-1 and 196-2, respectively. Each of the liquid crystal layers 196-1 and 196-2 of the diffraction grating 200, in turn, has a plurality of differently arranged diffractive regions 196-1a-196-1g and 196-2a-196-2g, respectively.

[0167] Similar to the liquid crystal molecules 112 of the liquid crystal layer 186-1 of Figures 19A / 19B, the liquid crystal molecules 112 of the diffractive regions 196-1a-196-1g of the liquid crystal layer 196-1 illustrated in Figure 20 have different azimuthal angles from layer to layer, but little or no chirality (very large or infinite chiral pitch p). The azimuthal angles and other arrangements of adjacent diffractive regions 196-1a-196-1g are similar to those described for the first and second diffractive regions 186-1L and 186-1R with respect to Figures 19A / 19B.

[0168] Similar to the liquid crystal molecules 112 of the liquid crystal layers 186-2 and 186-n of Figures 19A / 19B, the liquid crystal molecules 112 of the diffractive regions 196-2a-196-2g of the liquid crystal layer 196-2 illustrated in Figure 20 have uppermost liquid molecules with substantial and substantially different degrees of chirality and different azimuth angles along the length of the zone (along the x-direction). The azimuth angles, chirality, and other arrangements of adjacent diffractive regions 196-2a-196-2g are similar to those described with respect to the first and second diffractive regions 186-2L / 186-2R and 186-nL / 186-nR of the second and nth liquid crystal layers 186-2 and 186-n.

[0169] It should be appreciated that when twists are induced on liquid crystal molecules, as illustrated above with respect to Figures 19A / 19B and 20, the resulting diffraction grating exhibits spatially variable diffractive properties, including refractive index and diffraction efficiency. Some liquid crystal molecules can be made chiral by asymmetrically substituting one or more of the carbon atoms with four different ligands. Other liquid crystal molecules can be made chiral by adding mesogenic or non-mesogenic chiral dopants at varying concentrations to one of the liquid crystal phases described above. According to embodiments, chirality-related effects can be increased with the concentration of the dopant, for example, by adding small concentrations, including but not limited to, below 5%-10% by weight. Some examples of chiral liquid crystal molecules include cholesteryl benzoate, ferroelectric liquid crystal N(pn-decycloxybenzylidene)p-amino 2-methylbutylcinnamate (DOBAMBC), and achiral MBBA (4-butyl-N-[4-methoxy-benzylidene]-aniline), which is a room temperature nematic doped with chiral R1011. Other chiral liquid crystal molecules may also be used.

[0170] Referring to FIG. 21, a side view (viewed along the xz plane) of a diffraction grating 210 is illustrated, which may be fabricated with or without photo-alignment according to some embodiments. The diffraction grating 210 comprises a plurality of diffraction zones, i.e., diffraction zones 218-1, 218-2, ..., and 218-n, having a lateral dimension or grating period ∧ that repeats periodically in a manner similar to that described above with respect to FIGS. 10A-10C. The diffraction zones 218-1, 218-2, ..., and 218-n of the diffraction grating 210 have corresponding liquid crystal layers 206-1, 206-2, ..., and 206-n, respectively. The number of diffraction zones of each type may be similar to that described above with respect to FIGS. 10A-10C. In addition, the diffraction zones as arranged may repeat periodically any suitable number of times.

[0171] In the diffraction grating 210, the different liquid crystal layers 206-1, 206-2, and 206-n are made of different liquid crystal materials. In particular, the first and second diffraction regions 206-1L and 206-1R, 206-2L and 206-2R, ..., and 206-nL and 206-nR have liquid crystal molecules 212-1L and 212-1R, 212-2L and 212-2R, ..., and 212-nL and 212-nR, respectively, which may be the same or different liquid crystal molecules. For example, in some implementations, the region in the first zone can have a first liquid crystal material, the region in the second zone can have a first liquid crystal material, and the region in the third zone can have a third liquid crystal material. In other implementations, any given zone can have a first region having a first liquid crystal material and a second region having a second liquid crystal material. Thus, the optical properties can be changed along the length of the diffraction grating without having to change the orientation of the liquid crystal molecules by changing the composition of the material, for example by using the same host material with different levels of the same dopant (or different dopants with the same or different levels).

[0172] In some embodiments, the different zones have different liquid crystal molecules while other aspects of the liquid crystal alignment, such as tilt angle, azimuth angle, and chirality as described above, are similar or identical between the different zones. In some other embodiments, the different zones have different liquid crystal molecules while other aspects of the liquid crystal alignment, such as tilt angle, azimuth angle, and chirality, are similarly different as discussed above in the context of various embodiments.

[0173] During deposition, by depositing different liquid crystal materials, or by modifying the liquid crystal material after deposition, the local birefringence can be controlled to be different across different zones. In various embodiments, the birefringence of the individual zones can be from about 0.05 to about 0.15, e.g., about 0.10, from about 0.15 to about 0.25, e.g., about 0.2, and from about 0.25 to about 0.35, e.g., about 0.3. Additional Examples

[0174] In a first embodiment, the diffraction grating includes a plurality of different diffractive zones having periodically repeating lateral dimensions corresponding to a grating period adapted for light diffraction. The diffraction grating additionally includes a plurality of different liquid crystal layers corresponding to the different diffractive zones. The different liquid crystal layers have liquid crystal molecules aligned differently such that the different diffractive zones have different optical properties associated with light diffraction.

[0175] In a second embodiment, in the diffraction grating of the first embodiment, the optical property includes one or more of a refractive index, an absorption coefficient, a diffraction efficiency, and a birefringence.

[0176] In a third embodiment, in the diffraction grating of any of the first or second embodiments, each of the different liquid crystal layers has a plurality of differently aligned regions, and the differently aligned regions have liquid crystal molecules that are differently aligned relative to each other.

[0177] In a fourth embodiment, in the diffraction grating of any of the first to third embodiments, each of the different diffraction zones further comprises an alignment layer interposed between the substrate and the corresponding liquid crystal layer, and the different alignment layers between the different diffraction zones and the substrate are formed from the same material composition, and the different alignment layers align the liquid crystal molecules differently in the different diffraction zones.

[0178] In a fifth embodiment, in the diffraction grating of any one of the first to fourth embodiments, the liquid crystal molecules are stretched and include calamitic liquid crystal molecules aligned along the stretching direction.

[0179] In a sixth embodiment, in the diffraction grating of any of the first to fifth embodiments, the different liquid crystal layer includes a first region and a second region, the liquid crystal molecules in the first region are aligned along a first alignment direction, which forms a first alignment angle with respect to a reference direction, and the liquid crystal molecules in the second region are aligned along a second alignment direction, which forms a second alignment angle with respect to the reference direction, which is different from the first alignment angle.

[0180] In a seventh embodiment, in the diffraction grating of the sixth embodiment, the liquid crystal molecules in the first region of the first liquid crystal layer and the liquid crystal molecules in the corresponding first region of the second liquid crystal layer have substantially the same alignment angle.

[0181] In an eighth embodiment, in the diffraction grating of the seventh embodiment, the liquid crystal molecules in the second region of the first liquid crystal layer and the liquid crystal molecules in the corresponding second region of the second liquid crystal layer have different alignment angles.

[0182] In a ninth embodiment, in the diffraction grating of the sixth embodiment, the liquid crystal molecules in a first region of the first liquid crystal layer and the liquid crystal molecules in the corresponding first region of the second liquid crystal layer have substantially different alignment angles, and the liquid crystal molecules in a second region of the first liquid crystal layer and the liquid crystal molecules in the corresponding second region of the second liquid crystal layer have different alignment angles.

[0183] In a tenth embodiment, in the grating of the sixth embodiment, the ratio of the lateral width between the first and second regions is substantially the same between different zones.

[0184] In an eleventh embodiment, in the diffraction grating of the sixth embodiment, the liquid crystal molecules in the second region of the first liquid crystal layer and the liquid crystal molecules in the second region of the second liquid crystal layer have substantially identical alignment angles, and the ratio of lateral widths between the first region and the second region is substantially different between different diffraction zones.

[0185] In a twelfth embodiment, in the diffraction grating of the sixth embodiment, the liquid crystal molecules in the second region of the first liquid crystal layer and the liquid crystal molecules in the second region of the second liquid crystal layer have different alignment angles, and the ratio of lateral widths between the first region and the second region is substantially different between different diffraction zones.

[0186] In a thirteenth embodiment, in the diffraction grating of the sixth embodiment, the first and second alignment angles are pre-tilt angles measured between the respective alignment directions and the major surface in a plane perpendicular to the major surface of the substrate.

[0187] In a fourteenth embodiment, in the diffraction grating of the sixth embodiment, the first and second alignment angles are azimuth angles measured in a plane parallel to the major surface of the substrate and between the respective alignment directions and a reference direction parallel to the major surface.

[0188] In a fifteenth embodiment, in the diffraction grating of the third embodiment, the different liquid crystal layer includes a first region and a second region, the liquid crystal molecules in the first region are aligned along a plurality of first alignment directions and form a plurality of first alignment angles with respect to a reference direction, and the liquid crystal molecules in the second region are aligned along a plurality of second alignment directions and form a plurality of second alignment angles with respect to the reference direction.

[0189] In a sixteenth embodiment, in the diffraction grating of any one of the first to fifteenth embodiments, the diffraction grating is a transmission diffraction grating having a transparent substrate.

[0190] In a seventeenth embodiment, in the diffraction grating of any of the first to sixteenth embodiments, different diffraction zones have different material compositions such that the different diffraction zones have different optical properties associated with light diffraction.

[0191] In an eighteenth embodiment, a method of fabricating a diffraction grating includes providing a substrate. The method additionally includes providing a plurality of different diffractive zones having periodically repeating lateral dimensions corresponding to a grating period adapted for light diffraction. The method further includes forming a plurality of different liquid crystal layers comprising liquid crystal molecules over the substrate, the different liquid crystal layers corresponding to the different diffractive zones, and forming the different liquid crystal layers includes aligning the liquid crystal molecules differently to thereby provide the different diffractive zones with different optical properties associated with light diffraction.

[0192] In a 19th embodiment, in the method of the 18th embodiment, the method further includes forming an optical alignment layer on the substrate prior to forming the liquid crystal layer, and illuminating the optical alignment layer, thereby causing the liquid crystal molecules formed on the alignment layer to be aligned differently in different diffraction zones.

[0193] In a twentieth embodiment, in the method of the nineteenth embodiment, forming the optical alignment layer includes depositing a material selected from the group consisting of polyimide, linearly polarized photopolymerizable polymer, azo-containing polymer, coumarin-containing polymer, cinnamic acid-containing polymer, and combinations thereof.

[0194] In a 21st embodiment, in the method of either of the 19th and 20th embodiments, the method further includes exposing different diffractive zones to different doses of light using a grayscale mask after forming the optical alignment layer and prior to forming the liquid crystal layer.

[0195] In a 22nd embodiment, in the method of any of the 19th to 21st embodiments, forming the different liquid crystal layers includes forming a plurality of differently aligned regions in the different liquid crystal layers, the differently aligned regions having liquid crystal molecules that are differently aligned relative to one another.

[0196] In a 23rd embodiment, in the method of the 22nd embodiment, forming the different liquid crystal layers includes forming a first region and a second region, where forming the first region includes aligning the liquid crystal molecules in the first region along a first alignment direction to form a first alignment angle with respect to a reference direction, and forming the second region includes aligning the liquid crystal molecules in the second region along a second alignment direction to form a second alignment angle with respect to the reference direction, where the second alignment angle is different from the first alignment angle.

[0197] In a twenty-fourth embodiment, in the method of the twenty-third embodiment, aligning the liquid molecules in the first and second regions includes forming respective first and second alignment angles that are inversely proportional to the different doses of light.

[0198] In a 25th embodiment, in any of the methods of the 18th to 24th embodiments, forming the multiple distinct liquid crystal layers includes inducing chirality in at least some of the liquid crystal molecules by adding a chiral dopant to the liquid crystal layer.

[0199] In a 26th embodiment, in the method of the 18th embodiment, forming the distinct liquid crystal layers includes forming first regions and second regions in the liquid crystal layer, where the liquid crystal molecules in the first regions are aligned along a plurality of first alignment directions and form a plurality of first alignment angles with respect to a reference direction, and the liquid crystal molecules in the second regions are aligned along a plurality of second alignment directions and form a plurality of second alignment angles with respect to the reference direction.

[0200] In a twenty-seventh embodiment, the diffraction grating includes a plurality of successive liquid crystal layers extending in a lateral direction and arranged to have periodically repeating lateral dimensions, thicknesses, and refractive indices such that the liquid crystal layers are configured to diffract light, the liquid crystal molecules of the liquid crystal layers being arranged differently in different liquid crystal layers along the lateral direction such that the successive liquid crystal layers are configured to diffract light with a gradient in diffraction efficiency.

[0201] In a 28th embodiment, in the diffraction grating of the 27th embodiment, the liquid crystal layer has a first region and a second region, and the continuous liquid crystal layer is arranged such that the multiple first regions and the multiple second regions alternate in the lateral direction.

[0202] In a 29th embodiment, in the diffraction grating of the 28th embodiment, the liquid crystal molecules in the first region have substantially the same alignment orientation, while the liquid crystal molecules in the second region have substantially a different alignment orientation.

[0203] In a thirtieth embodiment, a head-mounted display device is configured to project light to a user's eye and display augmented reality image content. The head-mounted display device includes a frame configured to be supported on the user's head. The head-mounted display device further includes a display disposed on the frame, at least a portion of the display comprising one or more waveguides, the one or more waveguides being transparent such that the transparent portion transmits light from a portion of the environment in front of the user to the user's eye to provide a view of the portion of the environment in front of the user, and disposed at a location in front of the user's eye when the user wears the head-mounted display device, the display further comprising one or more light sources and at least one diffraction grating configured to couple light from the light sources into the one or more waveguides or couple light out of the one or more waveguides. The diffraction grating includes a plurality of different diffractive zones having periodically repeating lateral dimensions corresponding to a grating period adapted for light diffraction. The diffraction grating additionally includes a number of different liquid crystal layers corresponding to the different diffractive zones, the different liquid crystal layers having liquid crystal molecules aligned differently such that the different diffractive zones have different optical properties associated with light diffraction.

[0204] In a thirty-first embodiment, in the device of the thirtieth embodiment, the one or more light sources include a fiber scanning projector.

[0205] In a thirty-second embodiment, in a device of any of the thirty-first to thirty-first embodiments, the display is configured to project light into the user's eye so as to present image content to the user at multiple depth planes.

[0206] In a thirty-third embodiment, in the diffraction grating of any of the thirty-first to thirty-second embodiments, the optical properties include one or more of a refractive index, an absorption coefficient, a diffraction efficiency, and a birefringence.

[0207] In the above described embodiments, the augmented reality display system, more specifically the space-variable diffraction grating, is described in relation to a specific embodiment. However, it should be understood that the principles and advantages of the embodiments can be used for any other system, device, or method involving the need for a space-variable diffraction grating. In the foregoing, it should be understood that any feature of any one of the embodiments can be combined with and / or substituted for any other feature of any other one of the embodiments.

[0208] Unless otherwise clearly required by context, throughout the description and claims, the words "comprises," "comprising," "including," "including," and the like, should be interpreted in an inclusive sense, i.e., "including but not limited to," as opposed to an exclusive or inclusive sense. The word "coupled," as generally used herein, refers to two or more elements that may be either directly connected or continued via one or more intermediate elements. Similarly, the word "connected," as generally used herein, refers to two or more elements that may be either directly connected or continued via one or more intermediate elements. In addition, the words "herein," "above," "below," "hereinafter," "above," and words of similar import, when used in this application, shall refer to this application as a whole and not to any particular portions of this application. Where permitted by context, words in the above detailed description using the singular or plural form may also include the plural or singular form, respectively. When the word "or" refers to a list of two or more items, this word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list.

[0209] Furthermore, it should be understood that conditional statements used herein, such as, among others, "can," "could," "might," "may," "eg," "for example," "such as," and the like, are generally intended to convey that certain embodiments include certain features, elements, and / or conditions while other embodiments do not, unless specifically stated otherwise or understood otherwise within the context as used. Thus, such conditional statements are generally not intended to suggest that features, elements, and / or conditions are in any way required for one or more embodiments or whether these features, elements, and / or conditions should be included or implemented in any particular embodiment.

[0210] Although certain embodiments have been described, these embodiments are presented by way of example only and are not intended to limit the scope of the present disclosure. Indeed, the novel apparatus, methods, and systems described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions, and changes in the form of the methods and systems described herein may be made without departing from the spirit of the present disclosure. For example, although blocks are presented in a given arrangement, 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 a variety of different ways. Any suitable combination of elements and acts of the various embodiments described above may be combined to provide further embodiments. The various features and processes described above may be implemented independently of each other or may be combined in various ways. All suitable combinations and subcombinations of features of the present disclosure are intended to be within the scope of the present disclosure.

Claims

1. 1. A method for fabricating a diffraction grating, the method comprising: providing a plurality of zones on a substrate defined by the diffraction grating, the plurality of zones being laterally arranged in a lateral direction parallel to a major surface of the substrate, the plurality of zones having a periodically repeating grating period adapted for light diffraction; forming the diffraction grating by forming a plurality of different liquid crystal layers, the plurality of different liquid crystal layers comprising a plurality of liquid crystal molecules across the substrate, the plurality of different liquid crystal layers being arranged differently within the plurality of zones so as to diffract light through the plurality of zones; Including, the plurality of different liquid crystal layers include a plurality of liquid crystal molecules oriented at a plurality of different orientation angles; the different liquid crystal layers of the different zones are formed laterally as continuous layers contacting a common surface across the substrate; The method of claim 1, wherein the different liquid crystal layers comprise corresponding regions in which the liquid crystal molecules have different orientation angles with respect to a reference direction, and the zones have different optical properties associated with optical diffraction between different zones.

2. The method comprises: forming an optical alignment layer on the substrate prior to forming the plurality of liquid crystal layers; illuminating the optical alignment layer to cause the liquid crystal molecules formed on the optical alignment layer to be oriented at a plurality of different orientation angles within the plurality of zones; The method of claim 1 further comprising:

3. 3. The method of claim 2, wherein forming the optical alignment layer comprises depositing a material selected from the group consisting of polyimide, linearly polarized photopolymerizable polymer, azo-containing polymer, coumarin-containing polymer, cinnamic acid-containing polymer, or any combination thereof.

4. 3. The method of claim 2, wherein the method further comprises exposing the plurality of zones to different doses of light using a grayscale mask after forming the optical alignment layer and prior to forming the plurality of liquid crystal layers.

5. 2. The method of claim 1 , wherein forming the plurality of distinct liquid crystal layers comprises forming the plurality of regions within the plurality of distinct liquid crystal layers, at least some of the plurality of regions within the plurality of distinct liquid crystal layers comprising a plurality of liquid crystal molecules oriented at a plurality of different orientation angles relative to one another.

6. 6. The method of claim 5, wherein forming the plurality of distinct liquid crystal layers comprises forming a first region and a second region, wherein forming the first region comprises aligning a plurality of liquid crystal molecules of the first region along a first orientation direction that forms a first orientation angle with respect to a reference direction, and forming the second region comprises aligning a plurality of liquid crystal molecules of the second region along a second orientation direction that forms a second orientation angle with respect to the reference direction, the second orientation angle being different from the first orientation angle.

7. 7. The method of claim 6, wherein aligning the plurality of liquid crystal molecules in the first region and the plurality of liquid crystal molecules in the second region comprises forming respective first and second orientation angles that are inversely proportional to different doses of light.

8. The method of claim 6 , wherein the liquid crystal molecules in the first region of the first liquid crystal layer and the liquid crystal molecules in the corresponding first region of the second liquid crystal layer have the same orientation angle.

9. The method of claim 8 , wherein a plurality of liquid crystal molecules in a second region of the first liquid crystal layer and a plurality of liquid crystal molecules in a corresponding second region of the second liquid crystal layer have different orientation angles.

10. 7. The method of claim 6, wherein a plurality of liquid crystal molecules in a first region of a first liquid crystal layer and a plurality of liquid crystal molecules in a corresponding first region of a second liquid crystal layer have different orientation angles, and a plurality of liquid crystal molecules in a second region of the first liquid crystal layer and a plurality of liquid crystal molecules in a corresponding second region of the second liquid crystal layer have different orientation angles.

11. The method of claim 6 , wherein the ratio of lateral widths between the first region and the second region is the same among a plurality of zones.

12. 7. The method of claim 6, wherein the liquid crystal molecules in the second region of the first liquid crystal layer and the liquid crystal molecules in the second region of the second liquid crystal layer have the same orientation angle, and a ratio of lateral widths between the first region and the second region is different among the multiple zones.

13. 7. The method of claim 6, wherein a plurality of liquid crystal molecules in a second region of the first liquid crystal layer and a plurality of liquid crystal molecules in a second region of the second liquid crystal layer have different orientation angles, and a ratio of lateral widths between the first region and the second region differs among the plurality of zones.

14. 7. The method of claim 6, wherein the first and second orientation angles are pretilt angles, the pretilt angles being measured in a plane perpendicular to a major surface of a substrate between the respective alignment directions and the major surface.

15. 7. The method of claim 6, wherein the first orientation angle and the second orientation angle are azimuthal angles, the azimuthal angles being measured in a plane parallel to a major surface of a substrate between the respective orientation direction and a reference direction parallel to the major surface.

16. 10. The method of claim 1, wherein forming the plurality of distinct liquid crystal layers comprises inducing chirality in at least some of the plurality of liquid crystal molecules by adding a chiral dopant to the plurality of liquid crystal layers.

17. The method of claim 1 , wherein the plurality of optical properties comprises one or more of a refractive index, an absorption coefficient, a diffraction efficiency, and a birefringence.

18. 2. The method of claim 1 , wherein each of the plurality of different liquid crystal layers has a plurality of differently aligned regions, the plurality of differently aligned regions comprising a plurality of liquid crystal molecules oriented at different orientation angles relative to one another.

19. 2. The method of claim 1, wherein the plurality of liquid crystal molecules comprises a plurality of calamitic liquid crystal molecules, the plurality of calamitic liquid crystal molecules being elongated and aligned along an elongation direction.

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