Stacked Waveguides with Different Gratings for Combined Field of View

Abstract

To provide stacked waveguides having different diffraction gratings for a combined field of view.SOLUTION: In one aspect, an optical device comprises a plurality of waveguides formed over one another and having formed thereon respective diffraction gratings, where the respective diffraction gratings are configured to diffract visible light incident thereon into the respective waveguides so that visible light diffracted into the respective waveguides propagates therein. The respective diffraction gratings are configured to diffract the visible light into the respective waveguides in respective fields of views (FOVs) with respect to layer-normal directions of the respective waveguides. The respective FOVs are such that the waveguides are configured to diffract the visible light in a combined FOV that is continuous and greater than each of the respective FOVs.SELECTED DRAWING: Figure 12A

Description

[Technical field]

[0001] (Incorporated by reference) This application claims the benefit of priority to U.S. Provisional Patent Application No. 62 / 474,529, filed March 21, 2017, entitled "STACKED WAVEGUIDES HAVING DIFFERENT DIFFRACTION GRATINGS FOR COMBINED FIELD OF VIEW," which is incorporated herein by reference in its entirety.

[0002] (Field) The present disclosure relates to display systems, and more particularly to augmented reality display systems comprising diffractive devices based on cholesteric liquid crystals. [Background technology]

[0003] 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 being 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, MR scenarios may include AR image content that appears to be blocked by or is perceived to otherwise interact with objects in the real world.

[0004] Referring to FIG. 1, an augmented reality scene 1 is depicted. A user of the AR technology sees a real-world park-like setting 20 featuring people, trees, buildings in the background, and a concrete platform 30. The user perceives that they are also "seeing" "virtual content," such as a robotic figure 40 standing on the real-world platform 1120, and a flying cartoon-like avatar character 50 that appears to be an anthropomorphic bumblebee. These elements 50, 40 are "virtual" in that they do not exist in the real world. Because of the complexity of the human visual perception system, it is difficult to produce AR technology that facilitates a comfortable, 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] In a first aspect, an optical device comprises a plurality of waveguides formed on one another and having respective diffraction gratings formed thereon, each diffraction grating configured to diffract visible light incident thereon into a respective waveguide such that the visible light diffracted into the respective waveguide propagates therein. Each diffraction grating is configured to diffract visible light incident on the respective waveguide within a respective field of view (FOV) relative to a layer normal direction of the respective waveguide, into the respective waveguide. The respective FOVs are such that the plurality of waveguides are contiguous and configured to diffract visible light within a combined FOV that is greater than each of the respective FOVs.

[0007] In a second aspect, an optical system includes a first waveguide having a first diffraction grating formed thereon. The first diffraction grating has a first period and is configured to diffract light having a first color incident on the first waveguide within a first FOV. The optical system additionally includes a second waveguide having a second diffraction grating formed thereon. The second diffraction grating has a second period and is configured to diffract light having a first color incident on the second waveguide within a second FOV. The first and second diffraction gratings are configured to diffract light having the first color within a respective field of view (FOV) relative to a layer normal direction of the respective waveguide into the respective waveguide. The respective FOVs are such that the first and second waveguides are contiguous and configured to diffract visible light having the first color within a combined FOV that is greater than each of the first and second FOVs.

[0008] In a third aspect, a display device includes a first waveguide having a first diffraction grating formed thereon comprising liquid crystal, the first diffraction grating configured to diffract a portion of light having a first color incident thereon into the first waveguide. The first diffraction grating is additionally configured to pass a portion of light having the first color incident thereon. The first diffraction grating is further configured to pass light having a second color. The display device additionally includes a second waveguide having a second diffraction grating formed thereon comprising liquid crystal, the second diffraction grating configured to diffract light having the second color into the second waveguide. The second diffraction grating is further configured to diffract a portion of light having the first color that passed through the first diffraction grating into the second waveguide.

[0009] In a fourth aspect, 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 comprises a frame configured to be supported on the user's head. The head mounted display device additionally comprises a display disposed on the frame. At least a portion of the display comprises a plurality of waveguides. The waveguides are transparent and positioned at a location in front of the user's eye when the user wears the head mounted display device 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. The display further comprises one or more light sources and a plurality of diffraction gratings in the display configured to couple light from the light sources into the waveguides in the display. The waveguides and diffraction gratings in the display comprise the waveguides and diffraction gratings of any one of the first to third aspects. The present invention provides, for example, the following: (Item 1) 1. An optical device comprising: the optical device comprises a plurality of waveguides formed on one another, the plurality of waveguides having respective diffraction gratings formed thereon, the respective diffraction gratings configured to diffract visible light incident thereon into the respective waveguides, the visible light diffracted into the respective waveguides propagating within the respective waveguides; the respective diffraction gratings are configured to diffract visible light incident on the respective waveguides within a respective field of view (FOV) relative to a layer normal direction of the respective waveguides into the respective waveguides, the respective FOVs being such that the multiple waveguides are configured to diffract the visible light within a combined FOV, the combined FOV being contiguous and larger than each of the respective FOVs; Optical devices. (Item 2) 2. The optical device of claim 1, wherein the plurality of waveguides are formed from a material whose refractive index is less than the effective refractive index of the respective diffraction grating, such that the visible light diffracted into the respective waveguide propagates within the respective waveguide under total internal reflection. (Item 3) Item 1, wherein the plurality of waveguides are in a stacked arrangement and configured to propagate the visible light in a substantially parallel direction under total internal reflection. (Item 4) 2. The optical device of claim 1, wherein different ones of the respective diffraction gratings are arranged to overlap each other in a lateral direction perpendicular to the layer normal direction. (Item 5) 2. The optical device of claim 1, wherein the different ones of the respective FOVs do not overlap by more than 20% based on the sum of the different ones of the respective FOVs. (Item 6) 6. The optical device of claim 1, wherein the plurality of waveguides includes a first waveguide having a first diffraction grating formed thereon, the first diffraction grating configured to partially diffract and partially transmit visible light incident thereon, and the plurality of waveguides includes a second waveguide having a second diffraction grating formed thereon, the second diffraction grating configured to at least partially diffract the transmitted visible light from the first diffraction grating incident thereon. (Item 7) 7. The optical device of claim 6, wherein the first and second diffraction gratings have different periods, and the first and second diffraction gratings are configured to diffract visible light having different wavelengths but the same color. (Item 8) 7. The optical device of claim 6, wherein the first and second diffraction gratings have substantially the same period and are configured to diffract visible light having substantially the same wavelength. (Item 9) 7. The optical device of claim 6, wherein the first and second diffraction gratings have different periods and are configured to diffract visible light having different wavelengths and different colors. (Item 10) 10. The optical device of claim 9, wherein the first diffraction grating has a first period and is configured to diffract visible light having a first color, and the second grating has a second period and is configured to diffract visible light having the first color and visible light having a second color. (Item 11) Item 11. The optical device of item 10, wherein the first color corresponds to a shorter wavelength compared to the second color. (Item 12) Item 11. The optical device of item 10, wherein the first diffraction grating is configured to partially diffract visible light having the first color incident thereon in a first FOV and partially transmit the visible light having the first color incident thereon in a second FOV, and the second diffraction grating is configured to at least partially diffract the visible light having the first color that is partially transmitted through the first diffraction grating. (Item 13) Item 13. The optical device of item 12, wherein the first diffraction grating is configured to substantially transmit the visible light having the second color, and the second diffraction grating is configured to at least partially diffract the visible light having the second color incident within the first FOV. (Item 14) Item 14. The optical device of item 13, further comprising a third waveguide having a third diffraction grating formed thereon, the third diffraction grating having a third period and configured to diffract visible light having a third color, the second color corresponding to a shorter wavelength compared to the third color. (Item 15) Item 15. The optical device of item 14, wherein the second diffraction grating is configured to at least partially transmit the visible light having the second color, and the third diffraction grating is configured to receive and at least partially diffract the partially transmitted visible light having the second color from the second diffraction grating within the second FOV. (Item 16) Item 16. The optical device of item 15, wherein the first and second diffraction gratings are configured to substantially transmit the visible light having the third color, and the third diffraction grating is configured to at least partially diffract the visible light having the third color that is transmitted through the first and second diffraction gratings within the first FOV. (Item 17) 1. An optical system, comprising: a first waveguide having a first diffraction grating formed thereon, the first diffraction grating having a first period and configured to diffract light having a first color incident on the first waveguide within a first FOV; a second waveguide having a second diffraction grating formed thereon, the second diffraction grating having a second period and configured to diffract light having the first color incident on the second waveguide within a second FOV; and Equipped with an optical system, wherein the first and second diffraction gratings are configured to diffract the light having the first color within a respective field of view (FOV) relative to a layer normal direction of the respective waveguide into the respective waveguide, the respective FOVs being such that the first and second waveguides are configured to diffract the visible light having the first color within a combined FOV, the combined FOV being contiguous and larger than each of the first and second FOVs. (Item 18) Item 18. The optical system of item 17, wherein the first waveguide and the second waveguide are in a stacked configuration, the first waveguide is configured to receive the light having the first color prior to the second waveguide, and the first period is shorter than the second period. (Item 19) Item 19. The optical system of item 18, wherein the second diffraction grating is configured to diffract the light having the first color within the second FOV after being substantially transmitted through the first diffraction grating substantially without diffraction. (Item 20) 20. The optical system of claim 19, wherein the first diffraction grating is configured to substantially transmit the light having the second color through the first diffraction grating without substantially diffracting the light, the light having the second color having a longer wavelength compared to the light having the first color. (Item 21) 21. The optical system of claim 20, wherein the second diffraction grating is configured to diffract the light having the second color within the second FOV to be guided into the waveguide. (Item 22) Item 18. The optical system of item 17, wherein each of the first and second diffraction gratings comprises a cholesteric liquid crystal (CLC) layer. (Item 23) The CLC layer comprises: a plurality of chiral structures, each chiral structure comprising a plurality of liquid crystal molecules, the plurality of liquid crystal molecules extending in a layer depth direction by at least a helical pitch and being continuously rotated in a first rotation direction; the helical pitch is a length in the layer depth direction corresponding to a net rotation angle of the liquid crystal molecules of the chiral structure through one rotation in the first rotation direction; 21. The optical system of item 20, wherein the alignment of the liquid crystal molecules in the chiral structure varies periodically in a lateral direction perpendicular to the layer depth direction. (Item 24) 21. The optical system of item 20, wherein each chiral structure comprises at least three calamitic liquid crystal molecules stretched along different stretching directions. (Item 25) A display device, comprising: A first waveguide having a first diffraction grating formed thereon, the first diffraction grating comprising a liquid crystal, the first diffraction grating comprising: diffracting a portion of light having a first color incident on the first diffraction grating into the first waveguide; passing a portion of the light having the first color incident on the first diffraction grating; passing light having a second color; A first diffraction grating configured to A second waveguide; Equipped with The second waveguide has a second diffraction grating formed thereon, the second diffraction grating comprising a liquid crystal, the second diffraction grating comprising: diffracting the light having the second color into the second waveguide; diffracting a portion of the light having the first color that passes through the first diffraction grating into the second waveguide; A display device configured to: (Item 26) 26. The display device of claim 25, wherein the first diffraction grating is configured to diffract light having the first color within a first range of angles of incidence relative to a layer normal, and the first diffraction grating is configured to pass light having the first color within a second range of angles of incidence relative to the layer normal. (Item 27) 27. The display device of claim 26, wherein the second diffraction grating is configured to diffract the light having the second color incident on the second diffraction grating within the first angle range, and the second diffraction grating is configured to diffract the light having the first color incident on the second diffraction grating within the second incident angle range. (Item 28) 28. The display device of claim 27, wherein the first angle range and the second angle range do not overlap by more than 20% based on the sum of the first angle range and the second angle range. (Item 29) Item 26. The display device of item 25, wherein the first color corresponds to a shorter wavelength compared to the second color. (Item 30) 26. The display device of claim 25, wherein the first diffraction grating comprises periodically varying liquid crystals arranged to have a first period in a lateral direction, and the second diffraction grating comprises periodically varying liquid crystals arranged to have a second period in the lateral direction that is greater than the first period. (Item 31) Item 31. The display device of item 30, wherein one or both of the first diffraction grating and the second diffraction grating are configured to diffract light having a wavelength and have a period in a lateral direction such that a wavelength / period ratio λ / Λ is between about 0.3 and 2.3. (Item 32) Item 31. The display device of item 30, wherein one or both of the first diffraction grating and the second diffraction grating are configured to diffract light having a wavelength and have a period such that the period is between 1 nm and 250 nm smaller than the wavelength. (Item 33) Item 26. The display device of item 25, wherein the liquid crystal comprises a cholesteric liquid crystal. (Item 34) Item 34. The display device of item 33, wherein the liquid crystal of the first diffraction grating has a helical pitch smaller than the helical pitch of the liquid crystal of the second diffraction grating. (Item 35) 35. The display device of any one of items 25-34, wherein one or both of the first diffraction grating and the second diffraction grating are configured to transparently diffract light into the respective waveguide. (Item 36) 35. The display device of any one of items 25-34, wherein one or both of the first diffraction grating and the second diffraction grating are configured to reflectively diffract light into the respective waveguide. (Item 37) 35. The display device of any one of items 25-34, wherein the first color is green and the second color is red. (Item 38) Item 35. The display device of any one of items 25-34, wherein the first color is blue and the second color is green. (Item 39) 1. A head mounted display device configured to project light to an eye of a user and display augmented reality image content, the head mounted display device comprising: a frame configured to be supported on a head of the user; a display disposed on the frame; Equipped with At least a portion of the display comprises a plurality of waveguides, the waveguides being transparent and positioned at a location in front of an eye of the user when the user wears 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 comprising one or more light sources and a plurality of diffraction gratings in the display, the plurality of diffraction gratings configured to couple light from the light sources into the waveguides in the display. 35. A device, wherein the display is according to any one of items 25-34. (Item 40) 40. The device of claim 39, wherein the one or more light sources comprise a fiber scanning projector. (Item 41) 41. The device of claim 39 or 40, wherein the display is configured to project light into a user's eye and present image content at multiple depth planes to the user. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 illustrates a user's view of an augmented reality (AR) device.

[0011] [Diagram 2] FIG. 2 illustrates an example of a wearable display system.

[0012] [Diagram 3] FIG. 3 illustrates a conventional display system for simulating a three-dimensional image for a user.

[0013] [Figure 4] FIG. 4 illustrates aspects of an approach for simulating a three-dimensional image using multiple depth planes.

[0014] [Diagram 5] 5A-5C illustrate the relationship between the radius of curvature and the radius of focus.

[0015] [Figure 6] FIG. 6 illustrates an example of a waveguide stack for outputting image information to a user.

[0016] [Figure 7] FIG. 7 illustrates an example of an output beam output by a waveguide.

[0017] [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.

[0018] [Figure 9A] FIG. 9A illustrates a cross-sectional side view of an example set of stacked waveguides, each containing an internal coupling optical element.

[0019] [Figure 9B] FIG. 9B illustrates a perspective view of the example of multiple stacked waveguides of FIG. 9A.

[0020] [Figure 9C] FIG. 9C illustrates a top-down plan view of the multiple stacked waveguide example of FIGS. 9A and 9B.

[0021] [Figure 10] 10 illustrates a cross-sectional view of a waveguide having a diffraction grating disposed thereon showing the acceptance angle Δα of the waveguide, which may be referred to herein as the field of view (FOV).

[0022] [Figure 11] FIG. 11 illustrates a cross-sectional view of a display device comprising stacked waveguides having respective diffraction gratings disposed thereon, in accordance with some embodiments, where the stack has a total acceptance angle or field of view (FOV) Δαtot that is greater than the acceptance angles or fields of view (FOV) Δα1 and Δα2 of the respective component waveguides.

[0023] [Figure 12A] 12A and 12B illustrate cross-sectional views of a display device including stacked waveguides having respective gratings formed thereon with different periodicities, according to some embodiments, where the stack has a total acceptance angle or combined effective field of view (FOV) that is greater than the FOV of the component waveguides. In addition, the second waveguide serves two wavelengths (e.g., two colors), providing a more compact design by potentially reducing the number of waveguides required in some cases. [Figure 12B]12A and 12B illustrate cross-sectional views of a display device including stacked waveguides having respective gratings formed thereon with different periodicities, according to some embodiments, where the stack has a total acceptance angle or combined effective field of view (FOV) that is greater than the FOV of the component waveguides. In addition, the second waveguide serves two wavelengths (e.g., two colors), providing a more compact design by potentially reducing the number of waveguides required in some cases.

[0024] [Figure 13A] FIG. 13A illustrates a schematic diagram of one of the component waveguides of the display device illustrated in FIGS. 12A and 12B, in which one of the component waveguides has a first period, and a resulting image corresponding to a first field of view.

[0025] [Figure 13B] FIG. 13B illustrates a schematic diagram of one of the component waveguides of the display device illustrated in FIGS. 12A and 12B in which one of the component waveguides has a second period, and a resulting image corresponding to a second field of view.

[0026] [Figure 13C] FIG. 13C illustrates a schematic diagram of the stacked waveguides of the display device illustrated in FIGS. 12A and 12B and the resulting image corresponding to a combined or total field of view that is greater than the first and second fields of view individually.

[0027] [Figure 14A]14A and 14B illustrate cross-sectional views of a display device comprising stacked waveguides having respective gratings formed thereon with different periodicities, according to some embodiments, where the pair of gratings provide a combined or total field of view (FOV) that is greater than that of the component waveguides. In addition, some of the waveguides serve multiple colors, providing increased compactness by potentially reducing the number of waveguides. [Figure 14B] 14A and 14B illustrate cross-sectional views of a display device comprising stacked waveguides having respective gratings formed thereon with different periodicities, according to some embodiments, where the pair of gratings provide a combined or total field of view (FOV) that is greater than that of the component waveguides. In addition, some of the waveguides serve multiple colors, providing increased compactness by potentially reducing the number of waveguides.

[0028] [Figure 15] FIG. 15 illustrates a cross-sectional view of a cholesteric liquid crystal (CLC) layer configured as a diffraction grating for Bragg reflection at off-axis angles of incidence.

[0029] [Figure 16A] FIG. 16A illustrates a cross-sectional view of a CLC layer having a first helical pitch and configured as a diffraction grating for Bragg reflection at a first off-axis angle of incidence.

[0030] [Figure 16B] FIG. 16B illustrates a cross-sectional view of a CLC layer having a second helical pitch and configured as a diffraction grating for Bragg reflection at a second off-axis angle of incidence.

[0031] [Figure 17] FIG. 17 illustrates a waveguide having a CLC grating formed thereon and configured to propagate light by total internal reflection (TIR).

[0032] [Figure 18A] FIG. 18A illustrates a waveguide having a CLC grating formed thereon and configured to selectively propagate light having certain wavelengths by total internal reflection (TIR).

[0033] [Figure 18B] FIG. 18B illustrates two waveguides in the same optical path, each having a CLC grating formed thereon and configured to selectively propagate light having certain wavelengths by total internal reflection (TIR).

[0034] [Figure 18C] FIG. 18C illustrates three waveguides in the same optical path, each coupled to a CLCG and configured to selectively propagate light having certain wavelengths by total internal reflection (TIR). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Throughout the drawings, reference numbers may be reused to indicate correspondence of referenced elements. The drawings are provided to illustrate example embodiments described herein and are not intended to limit the scope of the present disclosure.

[0036] An AR system may display virtual content to a user or viewer while still allowing the user to see the world around them. Preferably, this content is displayed on a wearable head-mounted display, for example as part of eyewear that projects image information to the user's eyes. In addition, the display may transmit light from the surrounding environment to the user's eyes, allowing 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.

[0037] FIG. 2 illustrates an example of a wearable display system 60. The display system 60 includes a display 70 and various mechanical and electronic modules and systems to support the functionality of the display 70. The display 70 may be coupled to a frame 80, which is wearable by a display system user or viewer 90 and configured to position the display 70 in front of the eye of the user 90. The display 70 may be considered eyewear in some embodiments. In some embodiments, a speaker 100 is coupled to the frame 80 and configured to be positioned adjacent to the ear canal of the user 90 (in some embodiments, another speaker, not shown, may optionally be positioned adjacent the user's other ear canal to provide stereo / shapeable sound control). The display system may also include one or more microphones 110 or other devices to detect sound. In some embodiments, the microphone 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 60 and / or to allow audio communication with other persons (e.g., other users of a similar display system). The microphone may be further configured as an ambient sensor to collect audio data (e.g., sounds from the user and / or the environment). In some embodiments, the display system may also include an ambient sensor 120a, which may be separate from the frame 80 and attached to the body of the user 90 (e.g., on the head, torso, limbs, etc. of the user 90). The ambient sensor 120a, in some embodiments, may be configured to obtain data characterizing a physiological state of the user 90. For example, the sensor 120a may be an electrode.

[0038] 2, the display 70 is operably coupled to the local data processing module 140 by a communication link 130, such as wired or wireless connectivity, which may be mounted in a variety of configurations, such as fixedly attached to the frame 80, fixedly attached to a helmet or hat worn by the user, built into headphones, or otherwise removably attached to the user 90 (e.g., in a backpack configuration, in a belt-connected configuration). Similarly, the sensor 120a may be operably coupled to the local data processing module 140 by a communication link 120b, such as wired or wireless connectivity. The local processing and data module 140 may include 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 80 or otherwise attached to the user 90), 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 150 and / or a remote data repository 160 (including data related to the virtual content), possibly for passing to the display 70 after processing or retrieval. The local processing and data module 140 may be operatively coupled to the remote processing module 150 and the remote data repository 160 by communication links 170, 180, such as via wired or wireless communication links, such that these remote modules 150, 160 are operatively coupled to each other and available as resources to the local processing and data module 140. In some embodiments, the local processing and data module 140 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 to the frame 80 or may be free-standing structures that communicate with the local processing and data module 140 by wired or wireless communication paths.

[0039] 2, in some embodiments, remote processing module 150 may comprise one or more processors configured to analyze and process data and / or image information. In some embodiments, remote data repository 160 may comprise digital data storage facilities that may be available through the Internet or other networking configurations in a "cloud" resource configuration. In some embodiments, remote data repository 160 may include one or more remote servers that provide information, e.g., information for generating augmented reality content, to local processing and data module 140 and / or remote processing module 150. In some embodiments, all data is stored and all computations are performed within the local processing and data module, allowing for fully autonomous use from the remote modules.

[0040] Referring now to FIG. 3, the perception of an image as "three-dimensional" or "3-D" may be achieved by providing a slightly different presentation of the image to each eye of a viewer. FIG. 3 illustrates a conventional display system for simulating a three-dimensional image for a user. Two different images 190, 200, one for each eye 210, 220, are output to the user. The images 190, 200 are spaced from the eyes 210, 220 by a distance 230 along an optical or z-axis parallel to the viewer's line of sight. The images 190, 200 are flat, and the eyes 210, 220 may focus on the images by assuming a single accommodated state. Such a 3-D display system relies on the human visual system to combine the images 190, 200 and provide the perception of depth and / or scale of the combined image.

[0041] However, it should be understood 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 viewers of an object may perceive the object as "three-dimensional" due to a combination of vergence and accommodation. Vergence of the two eyes relative to each other (i.e., eye rotation in which the pupils move toward or away from each other to converge the line of sight of the eyes and fixate on an object) is closely linked to the focusing (or "accommodation") of the eye's lens and pupil. Under normal conditions, changing the focus of the eye's lens or accommodating the eye to change focus from one object to another at different distances will automatically produce 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 using a slightly different presentation (and therefore a slightly different image) to each eye so that a three-dimensional perspective is perceived by the human visual system. However, such systems are uncomfortable for many viewers, especially since they simply provide a different presentation of the scene but work against the "accommodation-vergence reflex" when the eyes view all image information in a single accommodated state. Display systems that provide better matching between accommodation and vergence may produce a more realistic and comfortable simulation of a three-dimensional image.

[0042] 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 210, 220 on the z-axis are accommodated by the eyes 210, 220 such that the objects are in focus. The eyes 210, 220 assume a particular accommodated state and focus on 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 240 having an associated focal length such that an object or part of an object at a particular depth plane is in focus when the eye is in an accommodated state relative to that depth plane. In some embodiments, a three-dimensional image may be simulated by providing a different presentation of an image for each of the eyes 210, 220, and may also be simulated 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 210, 220 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 by the eye in a particular accommodated state.

[0043] The distance between an object and the eye 210 or 220 may also change the amount of divergence of light from that 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 210 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 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. The curvature increases with decreasing distance between the object and the eye 210. As a result, at different depth planes, the divergence of the light rays is also different, and the divergence increases with decreasing distance between the depth plane and the viewer's eye 210. Although only a monocular 210 is illustrated in FIGS. 5A-5C and various other figures herein for clarity of illustration, it should be understood that the discussion regarding eye 210 may apply to both eyes 210 and 220 of a viewer.

[0044] 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 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.

[0045] FIG. 6 illustrates an example of a waveguide stack for outputting image information to a user. The display system 250 includes a stack of waveguides or a stacked waveguide assembly 260 that can be utilized to provide a three-dimensional perception to the eye / brain using multiple waveguides 270, 280, 290, 300, 310. In some embodiments, the display system 250 is the system 60 of FIG. 2, and FIG. 6 illustrates several portions of the system 60 in greater detail. For example, the waveguide assembly 260 can be part of the display 70 of FIG. 2. It should be understood that the display system 250 can be considered a bright field display in some embodiments.

[0046] Continuing with reference to FIG. 6, the waveguide assembly 260 may include a number of features 320, 330, 340, 350 between the waveguides. In some embodiments, the features 320, 330, 340, 350 may be one or more lenses. The waveguides 270, 280, 290, 300, 310 and / or the number of lenses 320, 330, 340, 350 may be configured to transmit image information to the eye with various levels of wavefront curvature or light beam 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. Image input devices 360, 370, 380, 390, 400 may act as light sources for the waveguides, and the image input devices may be utilized to input image information into the waveguides 270, 280, 290, 300, 310, each of which may be configured as described herein to distribute incident light across each respective waveguide for output toward the eye 210. Light exits output surfaces 410, 420, 430, 440, 450 of the image input devices 360, 370, 380, 390, 400 and is input into corresponding input surfaces 460, 470, 480, 490, 500 of the waveguides 270, 280, 290, 300, 310. In some embodiments, each of the input surfaces 460, 470, 480, 490, 500 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 510 or the viewer's eye 210). 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 toward the eye 210 at a particular angle (and divergence) corresponding to the depth plane associated with the particular waveguide. In some embodiments, a single one of the image launch devices 360, 370, 380, 390, 400 may be associated with and launch light into multiple (e.g., three) waveguides 270, 280, 290, 300, 310.

[0047] In some embodiments, each of the image input devices 360, 370, 380, 390, 400 is a separate display that generates image information for input into the corresponding waveguide 270, 280, 290, 300, 310. In some other embodiments, the image input devices 360, 370, 380, 390, 400 are the output of a single multiplexed display that may, for example, send image information via one or more optical conduits (such as fiber optic cables) to each of the image input devices 360, 370, 380, 390, 400. It should be understood that the image information provided by the image input devices 360, 370, 380, 390, 400 may include light of different wavelengths or colors (e.g., different primary colors as discussed herein).

[0048] In some embodiments, the light injected into the waveguides 270, 280, 290, 300, 310 is provided by a light projector system 520, which includes a light modulator 530, which may include a light emitter such as a light emitting diode (LED). Light from the light modulator 530 may be directed through a beam splitter 550 to and modified by a light modulator 540, e.g., a spatial light modulator. The light modulator 540 may be configured to change the perceived intensity of the light injected into the waveguides 270, 280, 290, 300, 310. Examples of spatial light modulators include liquid crystal displays (LCDs), including liquid crystal on silicon (LCOS) displays.

[0049] In some embodiments, the display system 250 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 pattern, etc.) into one or more waveguides 270, 280, 290, 300, 310 and ultimately to the viewer's eye 210. In some embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may diagrammatically represent a single scanning fiber or a bundle of scanning fibers configured to inject light into one or more waveguides 270, 280, 290, 300, 310. In some other embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may diagrammatically represent multiple scanning fibers or multiple bundles of scanning fibers, each of which is configured to inject light into an associated one of the waveguides 270, 280, 290, 300, 310. It is understood that one or more optical fibers may be configured to transmit light from the light modulator 530 to one or more of the waveguides 270, 280, 290, 300, 310. It is understood that one or more intervening optical structures may be provided between the scanning fiber or fibers and one or more of the waveguides 270, 280, 290, 300, 310, for example, to redirect light exiting the scanning fiber into one or more of the waveguides 270, 280, 290, 300, 310.

[0050] The controller 560 controls the operation of one or more of the stacked waveguide assemblies 260, including the operation of the image input devices 360, 370, 380, 390, 400, the light source 530, and the light modulator 540. In some embodiments, the controller 560 is part of the local data processing module 140. The controller 560 includes programming (e.g., instructions in a non-transient medium) that coordinates the timing and provision of image information to the waveguides 270, 280, 290, 300, 310, 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 560 may be part of the processing module 140 or 150 (FIG. 2) in some embodiments.

[0051] Continuing with reference to FIG. 6, the waveguides 270, 280, 290, 300, 310 may be configured to propagate light within each respective waveguide by total internal reflection (TIR). Each of the waveguides 270, 280, 290, 300, 310 may be planar with major top and bottom surfaces and edges extending between their major top and bottom surfaces, or may have another shape (e.g., curved). In the illustrated configuration, each of the waveguides 270, 280, 290, 300, 310 may include an outcoupling optical element 570, 580, 590, 600, 610 configured to extract light from the waveguide by redirecting light propagating within each respective waveguide out of the waveguide and outputting image information to the eye 210. The extracted light may also be referred to as outcoupling light, and the outcoupling optical element light may also be referred to as light extraction optical element. The extracted beam of light may be output by the waveguide at a location where the light propagating within the waveguide strikes the light extraction optical element. The outcoupling optical element 570, 580, 590, 600, 610 may be, for example, a grating including diffractive optical features as further discussed herein. Although shown disposed on the bottom major surface of the waveguide 270, 280, 290, 300, 310 for ease of explanation and clarity of the drawings, in some embodiments the outcoupling optical element 570, 580, 590, 600, 610 may be disposed on the top and / or bottom major surfaces and / or directly within the volume of the waveguide 270, 280, 290, 300, 310 as further discussed herein. In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 may be attached to a transparent substrate and formed within a layer of material that forms the waveguide 270, 280, 290, 300, 310. In some other embodiments, the waveguide 270, 280, 290, 300, 310 may be a monolithic piece of material and the outcoupling optical elements 570, 580, 590, 600, 610 may be formed on a surface of and / or within that piece of material.

[0052] With continued reference to FIG. 6, as discussed herein, each waveguide 270, 280, 290, 300, 310 is configured to output light and form an image corresponding to a particular depth plane. For example, the waveguide 270 closest to the eye may be configured to deliver collimated light (injected into such waveguide 270) to the eye 210. The collimated light may represent an optical infinity focal plane. The next upper waveguide 280 may be configured to send collimated light that passes through a first lens 350 (e.g., a negative lens) before it can reach the eye 210. Such a first lens 350 may be configured to generate a slight convex wavefront curvature such that the eye / brain interprets the light originating from the next upper waveguide 280 as originating from a first focal plane closer inward from optical infinity toward the eye 210. Similarly, the third upper waveguide 290 passes its output light through both the first 350 and second 340 lenses before reaching the eye 210. The combined refractive power of the first 350 and second 340 lenses may be configured to produce another incremental amount of wavefront curvature such that the eye / brain interprets the light emerging from the third waveguide 290 as emerging from a second focal plane closer inward toward the person from optical infinity, which was the light from the next upper waveguide 280.

[0053] The other waveguide layers 300, 310 and lenses 330, 320 are similarly configured, with the highest waveguide 310 in the stack sending its output through all of the lenses between it and the eye for an aggregate focal power that represents the focal plane closest to the person. To compensate the stack of lenses 320, 330, 340, 350 when viewing / interpreting light originating from the world 510 on the other side of the stacked waveguide assembly 260, a compensating lens layer 620 may be placed on top of the stack to compensate for the aggregate power of the lens stacks 320, 330, 340, 350 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.

[0054] In some embodiments, two or more of the waveguides 270, 280, 290, 300, 310 may have the same associated depth plane. For example, multiple waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same depth plane, or multiple subsets of the waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same depth planes, one set for each depth plane. This may provide the advantage of forming tiled images to provide an extended field of view at those depth planes.

[0055] Continuing with reference to FIG. 6, the outcoupling optical elements 570, 580, 590, 600, 610 can be configured to both redirect light out of their respective waveguides and output this 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 can have different configurations of outcoupling optical elements 570, 580, 590, 600, 610 that output light with different amounts of divergence depending on the associated depth plane. In some embodiments, the light extraction optical elements 570, 580, 590, 600, 610 can be volume or surface features that can be configured to output light at a particular angle. For example, the light extraction optical elements 570, 580, 590, 600, 610 can be volume holograms, surface holograms, and / or diffraction gratings. In some embodiments, features 320, 330, 340, 350 may not be lenses. Rather, they may simply be spacers (e.g., cladding layers and / or structures for forming air gaps).

[0056] In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 are diffractive features or "diffractive optical elements" (also referred to herein as "DOEs") that form a diffraction pattern. Preferably, the DOEs have a low enough diffraction efficiency so that only a portion of the light in the beam is deflected towards the eye 210 with each intersection of the DOE, while the remainder continues to travel through the waveguide via TIR. The light carrying the image information is thus split into several related exit beams that exit the waveguide at various locations, and the result is a very uniform pattern of exit emission towards the eye 210 for this particular collimated beam bouncing within the waveguide.

[0057] 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 diffract significantly. 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).

[0058] In some embodiments, a camera assembly 630 (e.g., a digital camera including visible and infrared light cameras) may be provided to capture images of the eye 210 and / or tissue surrounding the eye 210, for example, to detect user input and / or to monitor a physiological condition of the user. As used herein, a camera may be any image capture device. In some embodiments, the camera assembly 630 may include an image capture device and a light source that projects light (e.g., infrared light) onto the eye that may then be reflected by the eye and detected by the image capture device. In some embodiments, the camera assembly 630 may be mounted on the frame 80 (FIG. 2) and may be in electrical communication with the processing modules 140 and / or 150 that may process image information from the camera assembly 630. In some embodiments, one camera assembly 630 may be utilized for each eye to monitor each eye separately.

[0059] 7, an example of an exit beam output by a waveguide is shown. Although one waveguide is illustrated, it should be understood that other waveguides in the waveguide assembly 260 (FIG. 6) may function similarly and that the waveguide assembly 260 includes multiple waveguides. Light 640 is launched into the waveguide 270 at the input surface 460 of the waveguide 270 and propagates within the waveguide 270 by TIR. At the point where the light 640 impinges on the DOE 570, a portion of the light exits the waveguide as an exit beam 650. The exit beams 650 are illustrated as substantially parallel, but as discussed herein, they may be redirected to propagate to the eye 210 at an angle (e.g., forming a diverging exit beam) depending on the depth plane associated with the waveguide 270. It should be understood that a substantially 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 210. Other sets of waveguides or other outcoupling optics may output a more divergent exit beam pattern, which would require the eye 210 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 210 than optical infinity.

[0060] 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 240a-240f, but more or less depths are also envisioned. 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 diopters (1 / m), i.e., the inverse of the 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.

[0061] 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.

[0062] 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 in place of one or more of the red, green, or blue colors.

[0063] It should be understood that references to a given color of light throughout this disclosure are understood to encompass one or more wavelengths of light within the range of wavelengths of light perceived by a viewer as that given color. For example, red light may include one or more wavelengths of light that are within the range of about 620-780 nm, green light may include one or more wavelengths of light that are within the range of about 492-577 nm, and blue light may include one or more wavelengths of light that are within the range of about 435-493 nm.

[0064] In some embodiments, the light source 530 (FIG. 6) may be configured to emit light at one or more wavelengths outside the range of a viewer's visual perception, e.g., infrared and / or ultraviolet wavelengths. Additionally, the waveguide in-coupling, out-coupling, and other light redirecting structures of the display 250 may be configured to direct and emit this light out of the display toward the user's eye 210, e.g., for imaging and / or user stimulation applications.

[0065] 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 660 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 660 may correspond to the stack 260 (FIG. 6), and the illustrated waveguides of the stack 660 may correspond to a portion of the plurality of waveguides 270, 280, 290, 300, 310, although it should be understood that light from one or more of the image input devices 360, 370, 380, 390, 400 is launched into the waveguide from a position that requires the light to be redirected for in-coupling.

[0066] The illustrated set 660 of stacked waveguides includes waveguides 670, 680, and 690. Each waveguide includes an associated incoupling optical element (which may also be referred to as the light input area on the waveguide), for example, incoupling optical element 700 is disposed on a major surface (e.g., the top major surface) of waveguide 670, incoupling optical element 710 is disposed on a major surface (e.g., the top major surface) of waveguide 680, and incoupling optical element 720 is disposed on a major surface (e.g., the top major surface) of waveguide 690. In some embodiments, one or more of the incoupling optical elements 700, 710, 720 may be disposed on a bottom major surface of the respective waveguide 670, 680, 690 (particularly, one or more of the incoupling optical elements are reflective polarizing optical elements). As shown, the incoupling optical elements 700, 710, 720 may be disposed on the upper major surfaces of their respective waveguides 670, 680, 690 (or on top of the next lower waveguide), and in particular, the incoupling optical elements are transmissive deflecting optical elements. In some embodiments, the incoupling optical elements 700, 710, 720 may be disposed within the body of the respective waveguides 670, 680, 690. In some embodiments, as discussed herein, the incoupling optical elements 700, 710, 720 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 their respective waveguides 670, 680, 690, it should be understood that the incoupling optical elements 700, 710, 720 may be disposed within other areas of their respective waveguides 670, 680, 690 in some embodiments.

[0067] As shown, the in-coupling optical elements 700, 710, 720 may be laterally offset from one another. In some embodiments, each in-coupling optical element may be offset such that it receives light without that light passing through another in-coupling optical element. For example, each in-coupling optical element 700, 710, 720 may be configured to receive light from a different image input device 360, 370, 380, 390, and 400, as shown in FIG. 6, and may be separated (e.g., laterally spaced) from the other in-coupling optical elements 700, 710, 720 such that it does not receive substantially any light from others of the in-coupling optical elements 700, 710, 720.

[0068] Each waveguide also includes an associated light distribution element, for example, light distribution element 730 is disposed on a major surface (e.g., a top major surface) of waveguide 670, light distribution element 740 is disposed on a major surface (e.g., a top major surface) of waveguide 680, and light distribution element 750 is disposed on a major surface (e.g., a top major surface) of waveguide 690. In some other embodiments, light distribution elements 730, 740, 750 may be disposed on the bottom major surfaces of the associated waveguides 670, 680, 690, respectively. In some other embodiments, the light distribution elements 730, 740, 750 may be disposed on both the top and bottom major surfaces of the associated waveguides 670, 680, 690, respectively, or the light distribution elements 730, 740, 750 may be disposed on different ones of the top and bottom major surfaces in different associated waveguides 670, 680, 690, respectively.

[0069] The waveguides 670, 680, 690 may be spaced apart and separated, for example, by gas, liquid and / or solid layers of material. For example, as shown, layer 760a may separate waveguides 670 and 680, and layer 760b may separate waveguides 680 and 690. In some embodiments, layers 760a and 760b are formed from a low index material (i.e., a material having a lower index of refraction than the material forming the immediately adjacent ones of the waveguides 670, 680, 690). Preferably, the index of refraction of the material forming layers 760a, 760b is 0.05 or greater, or 0.10 or less, than the index of refraction of the material forming the waveguides 670, 680, 690. Advantageously, the lower refractive index layers 760a, 760b may act as cladding layers to promote total internal reflection (TIR) ​​of light through the waveguides 670, 680, 690 (e.g., TIR between the top and bottom major surfaces of each waveguide). In some embodiments, the layers 760a, 760b are formed from air. Although not shown, it should be understood that the top and bottom of the illustrated set of waveguides 660 may include immediate cladding layers.

[0070] Preferably, for ease of manufacturing and other considerations, the materials forming the waveguides 670, 680, 690 are similar or identical, and the materials forming the layers 760a, 760b are similar or identical. In some embodiments, the materials forming the waveguides 670, 680, 690 may vary between one or more of the waveguides, and / or the materials forming the layers 760a, 760b may differ while still maintaining the various refractive index relationships discussed above.

[0071] 9A, light rays 770, 780, 790 are incident on the set of waveguides 660. It should be understood that light rays 770, 780, 790 may be injected into the waveguides 670, 680, 690 by one or more image injection devices 360, 370, 380, 390, 400 (FIG. 6).

[0072] In some embodiments, the light beams 770, 780, 790 have different properties, e.g., different wavelengths or different wavelength ranges, that may correspond to different colors. Each of the incoupling optical elements 700, 710, 720 deflects incident light such that the light propagates through a respective one of the waveguides 670, 680, 690 by TIR. In some embodiments, each of the incoupling optical elements 700, 710, 720 selectively deflects one or more particular wavelengths of light while transmitting other wavelengths to the underlying waveguide and associated incoupling optical element.

[0073] For example, the incoupling optical element 700 may be configured to selectively deflect light beam 770 having a first wavelength or wavelength range while transmitting light beams 1242 and 1244 having different second and third wavelengths or wavelength ranges. The transmitted light beam 780 impinges on and is deflected by the incoupling optical element 710 configured to selectively deflect light of the second wavelength or wavelength range. Light beam 790 is deflected by the incoupling optical element 720 configured to selectively deflect light of the third wavelength or wavelength range.

[0074] 9A, the deflected light rays 770, 780, 790 are deflected to propagate through the corresponding waveguides 670, 680, 690. That is, the incoupling optical element 700, 710, 720 of each waveguide deflects the light into its corresponding waveguide 670, 680, 690 and incouplings the light into its corresponding waveguide. The light rays 770, 780, 790 are deflected at an angle that causes the light to propagate through the respective waveguides 670, 680, 690 by TIR. The light rays 770, 780, 790 propagate through the respective waveguides 670, 680, 690 by TIR until they impinge on the corresponding light distribution element 730, 740, 750 of the waveguide.

[0075]

[0046] Referring now to Figure 9B, a perspective view of the example of multiple stacked waveguides of Figure 9A is illustrated. As previously described, the in-coupled light rays 770, 780, 790 are deflected by the in-coupling optical elements 700, 710, 720, respectively, and then propagate by TIR within the waveguides 670, 680, 690, respectively. The light rays 770, 780, 790 then impinge on the light distribution elements 730, 740, 750, respectively. The light distribution elements 730, 740, 750 deflect the light rays 770, 780, 790 to propagate towards the out-coupling optical elements 800, 810, 820, respectively.

[0076] In some embodiments, the light distribution elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some embodiments, the OPEs deflect or disperse the light to the out-coupling optical elements 800, 810, 820, and in some embodiments, the OPEs may increase the beam or spot size of the light as it propagates to the out-coupling optical elements. In some embodiments, the light distribution elements 730, 740, 750 may be omitted and the in-coupling optical elements 700, 710, 720 may be configured to deflect the light directly to the out-coupling optical elements 800, 810, 820. For example, referring to FIG. 9A, the light distribution elements 730, 740, 750 may be replaced with the out-coupling optical elements 800, 810, 820, respectively. In some embodiments, the outcoupling optical element 800, 810, 820 is an exit pupil (EP) or exit pupil expander (EPE) that directs light to the viewer's eye 210 (FIG. 7). It should be understood that an OPE may be configured to increase the size of the eyebox in at least one axis, and an EPE may increase the eyebox in an axis that intersects, e.g., perpendicular to, the axis of the OPE. For example, each OPE may be configured to redirect a portion of the light striking the OPE to an EPE of the same waveguide, while allowing the remaining portion of the light to continue propagating down the waveguide. Upon striking the OPE, again, another portion of the remaining light is redirected to the EPE, which continues to propagate further down the waveguide, etc. Similarly, striking the EPE, a portion of the striking light is directed out of the waveguide towards the user, and the remaining portion of that light continues to propagate through the waveguide until it again strikes an EP, at which point another portion of the striking light is directed out of the waveguide, etc. As a result, a single beam of internally coupled light may be "replicated" each time a portion of that light is redirected by an OPE or EPE, thereby forming a cloned beam field of light, as shown in Figure 6. In some embodiments, the OPE and / or EPE may be configured to modify the size of the beam of light.

[0077] Thus, referring to Figures 9A and 9B, in some embodiments, a waveguide set 660 includes, for each primary color, a waveguide 670, 680, 690, an in-coupling optical element 700, 710, 720, a light distribution element (e.g., OPE) 730, 740, 750, and an out-coupling optical element (e.g., EP) 800, 810, 820. The waveguides 670, 680, 690 may be stacked with an air gap / cladding layer between each one. The in-coupling optical element 700, 710, 720 redirects or deflects the incoming light into its waveguide (with different in-coupling optical elements receiving different wavelengths of light). The light then propagates at an angle that will result in TIR within the respective waveguide 670, 680, 690. In the example shown, light ray 770 (e.g., blue light) is deflected by the first in-coupling optical element 700 in the manner described above, then continues bouncing back down the waveguide, interacting with the light distribution element (e.g., OPE) 730 and then the out-coupling optical element (e.g., EP) 800. Light rays 780 and 790 (e.g., green and red light, respectively) pass through the waveguide 670, where light ray 780 strikes the in-coupling optical element 710 and is deflected thereby. Light ray 780 will then bounce back down the waveguide 680, via TIR, to its light distribution element (e.g., OPE) 740 and then the out-coupling optical element (e.g., EP) 810. Finally, light ray 790 (e.g., red light) passes through the waveguide 690 and strikes the light in-coupling optical element 720 of the waveguide 690. The light in-coupling optical element 720 deflects the light beam 790 so that it propagates by TIR to the light distribution element (e.g., OPE) 750 and then by TIR to the out-coupling optical element (e.g., EP) 820. The out-coupling optical element 820 then finally out-couples the light beam 790 to a viewer, who also receives the out-coupled light from the other waveguides 670, 680.

[0078] FIG. 9C illustrates a top-down plan view of the example of multiple stacked waveguides of FIGS. 9A and 9B. As shown, the waveguides 670, 680, 690 may be vertically aligned with each waveguide's associated light distribution element 730, 740, 750 and associated out-coupling optical elements 800, 810, 820. However, as discussed herein, the in-coupling optical elements 700, 710, 720 are not vertically aligned. Rather, the in-coupling optical elements preferably do not overlap (e.g., are 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 particular light source to be uniquely coupled to a particular waveguide. In some embodiments, an array including non-overlapping, spatially separated in-coupling optical elements may be referred to as a shifted pupil system, and the in-coupling optical elements in these arrays may correspond to sub-pupils.

[0079] (Stacked Waveguides with Combined Field of View) Providing an immersive experience to a user of a waveguide-based display system, such as the various translucent or transparent display systems configured for virtual / augmented / composite display applications described above, depends, among other things, on various characteristics of the light that couples into the waveguides of the display system. For example, a virtual / augmented / composite display with an increased field of view can potentially enhance the viewing experience. The field of view of the display depends on the angle of light output by the multiple waveguides in a waveguide stack contained within an eyepiece, through which the viewer sees an image projected into his or her eye. The angle of light output from the multiple waveguides, in turn, depends at least in part on the acceptance angle of the light that is coupled into the waveguide. As discussed above, an internal coupling optical element, such as an internal coupling grating, can be employed to couple light into the grating. However, in some cases, only light with a limited angular range can be coupled into a given waveguide using a given grating. This limited range of acceptance angles of light by the waveguide also limits the angular range output by the waveguide into the wearer's eye, and thus potentially reduces the field of view for the wearer. This particular limitation and designs for increasing the acceptance angle, and therefore the field of view, of the display are discussed below.

[0080] For example, as described above with reference to Figures 6 and 7, a display system according to various embodiments described herein may include optical elements, such as an in-coupling optical element, an out-coupling optical element, and a light distribution element, which may include a diffraction grating. For example, as described above with reference to Figure 7, light 640 launched into the waveguide 270 at the input surface 460 of the waveguide 270 propagates within the waveguide 270 by total internal reflection (TIR). At the point where the light 640 impinges on the out-coupling optical element 570, a portion of the light exits the waveguide as a beamlet 650. In some implementations, any of the optical elements 570, 580, 590, 600, 610 may be configured as a diffraction grating.

[0081] To achieve desired properties of incoupling of light into (or outcoupling of light from) the waveguides 270, 280, 290, 300, 310, the optical elements 570, 580, 590, 600, 610 configured as diffraction gratings can be formed from materials having structures configured to control various optical properties, including diffractive properties. Desirable diffractive properties include spectral selectivity, angular selectivity, polarization selectivity, high spectral bandwidth and diffraction efficiency, and wide field of view (FOV), among other properties.

[0082] To achieve one or more of these and other advantages, various examples described herein include a plurality of waveguides formed on one another and having respective diffraction gratings formed thereon. The diffraction gratings are configured to diffract visible light incident thereon into the respective waveguides, and the visible light diffracted into the waveguides propagates within each of the waveguides, e.g., by total internal reflection. The diffraction gratings are configured to diffract visible light into the respective waveguides when visible light is incident thereon within a respective angular range or field of view (FOV) (e.g., relative to a layer normal direction of the respective waveguide). The respective FOVs provided by the individual diffraction gratings and waveguides are such that the waveguides, when stacked together, are contiguous and have a total acceptance angle or FOV that is greater than the individual FOVs provided by the diffraction gratings and waveguides separately.

[0083] As described herein, visible light may include light having one or more wavelengths in various color ranges, including the red, green, or blue ranges. As described herein, red light may include one or more wavelengths of light in the range of about 620-780 nm, green light may include one or more wavelengths of light in the range of about 492-577 nm, and blue light may include one or more wavelengths of light in the range of about 435-493 nm. Thus, visible may include one or more wavelengths of light in the range of about 435 nm to 780 nm.

[0084] As described herein, a structure configured to diffract light, such as a diffraction grating, may diffract light in a transmission mode and / or a reflection mode. As described herein, a structure configured to diffract light in a transmission mode refers to a structure in which the intensity of the diffracted light on the side opposite the light incident side of the structure is, for example, at least, more than 10%, more than 20%, or more than 30% compared to the intensity of the diffracted light on the same side as the light incident side of the structure. Conversely, as described herein, a structure configured to diffract light in a reflection mode refers to a structure in which the intensity of the diffracted light on the same side as the light incident side of the structure is, for example, at least, more than 10%, more than 20%, or more than 30% compared to the intensity of the diffracted light on the same side as the light incident side of the structure.

[0085] FIG. 10 illustrates a cross-sectional view of a portion of a display device 1000 including a waveguide 1004 having a grating 1008 formed thereon, according to some embodiments. The coupled grating 1008 is configured to diffract light having wavelengths within the visible spectrum as the light is guided into the waveguide 1004. The waveguide 1004 may correspond, for example, to one of the waveguides 670, 680, 690 described above with respect to FIGS. 9A-9C. The grating 1008 may correspond, for example, to an in-coupling optical element (700, 710, 720, FIGS. 9A-9C). The display device 1000 additionally includes an optical element 1012, which may correspond, for example, to a light distribution element (730, 740, 750, FIGS. 9A-9C) or, for example, to one of the out-coupling optical elements (800, 810, 820, FIGS. 9A-9C).

[0086] In operation, when an incident light beam 1016, e.g., visible light, is incident on the diffraction grating 1008 at an incidence angle α measured with respect to a surface normal 1012 that is normal or orthogonal to the surface 1008S extending in the yz plane, the diffraction grating 1008 at least partially diffracts the incident light beam 1016 as a diffracted light beam 1024 with a diffraction angle θ measured with respect to the surface normal 1012, and at least partially transmits the incident light as a transmitted light beam 1020. As described herein, a light beam incident at an angle in a clockwise direction with respect to the surface normal 1012 (i.e., to the right of the surface normal 1012) as illustrated in the embodiment is said to have a negative α (α<0), while a light beam incident at an angle in a counterclockwise direction with respect to the surface normal 1012 (i.e., to the left of the surface normal) is said to have a positive α (α>0). The diffracted light beam 1024 is incident on the waveguide 1004 at a critical angle θ for the occurrence of total internal reflection. TIR Upon being diffracted at a diffraction angle θ greater than θ, the diffracted light beam 1024 propagates along the x-axis under total internal reflection (TIR) ​​until the diffracted light beam 1024 reaches an optical element 1012, which may correspond, for example, to one of the light distribution elements (730, 740, 750, FIGS. 9A-9C) or, for example, to one of the out-coupling optical elements (800, 810, 820, FIGS. 9A-9C).

[0087] As described further elsewhere herein, a suitable combination of materials and structures for the diffraction grating 1016 may be selected to obtain a particular range of incidence angles α (Δα), referred to herein as the range of acceptance angles or field of view (FOV). According to various embodiments, the diffraction grating 1008 and the waveguide 1004 are arranged such that Δα is greater than 20 degrees (e.g., + / -10 degrees), 30 degrees (e.g., + / -15 degrees), 40 degrees (e.g., + / -20 degrees), or 50 degrees (e.g., + / -25 degrees), or within an angular range defined by any of these values, including symmetric and asymmetric ranges about the surface normal 1012 (e.g., at 0 degrees). As described herein, the desired range Δα may be described by an angular range spanning negative and / or positive values ​​of α, outside of which the diffraction efficiency drops off by more than 10%, 25%, 50%, or 75% relative to the diffraction efficiency at α=0. It may be desirable to have Δα within a range in which the diffraction efficiency is relatively high and constant, for example if a uniform intensity of the diffracted light is desired within Δα. Thus, Δα is the ratio of the incident light beam 1016 within Δα to the diffraction efficiency of θ TIR is related to the angular bandwidth of the diffraction grating 1016 such that light is efficiently diffracted by the diffraction grating 1016 at a diffraction angle θ relative to the surface normal 1012 (e.g., the yz plane) greater than θ and the diffracted light propagates within the waveguide 1004 under total internal reflection (TIR).

[0088] In various embodiments, the diffraction grating 1008 (and the optical element 1012) is formed from a material whose refractive index (n1) or effective refractive index is higher than the refractive index n2 of the waveguide 1004, i.e., n1>n2. In some embodiments, the waveguide 1004 may correspond to, for example, the waveguides 310, 300, 290, 280, 270 (FIG. 6), and / or, for example, the waveguides 670, 680, and 690 (FIGS. 9A-9C). In some implementations, the material of the waveguide 1004, according to the embodiment, has a refractive index that is higher than that of air but less than n1, for example, 1.5, 1.6, 1.7, 1.8, 1.9, or within a range defined by any of these values, which may provide an advantage for increasing the Δα of a display that forms an image by outputting light from the waveguide 1004. Examples of materials for forming the waveguide 1004 include silica glass (e.g., doped silica glass), silicon oxynitride, transition metal oxides (e.g., hafnium oxide, tantalum oxide, zirconium oxide, niobium oxide, lithium niobate, aluminum oxide (e.g., sapphire)), plastics, polymers, or other substantially optically transparent materials to visible light having a suitable refractive index, for example, as described herein.

[0089] According to one embodiment, the diffraction grating 1008 has a period Λ a The periodic structure may have a periodic structure having a period Λ a repeats or substantially repeats at least twice at regular intervals laterally (e.g., in the x and y directions) across the waveguide 1004. In other words, the period Λ a can be the distance between identical points of immediately adjacent repeating structures. According to various embodiments, the period Λ a may correspond to that formed by alignment of liquid crystals, as described elsewhere herein. In various embodiments, Λ a can be less than the wavelength that the grating 1008 is configured to diffract, and can be less than a wavelength or any wavelength in the range of about 435 nm to 780 nm. In some embodiments configured to diffract at least red light, Λ acan be less than a wavelength (or any wavelength) in the range of about 620-780 nm. In some other embodiments configured to diffract at least green light, Λ a can be less than a wavelength (or any wavelength) in the range of about 492 to 577 nm. In some other embodiments configured to diffract at least blue light, Λ a can be less than a wavelength (or any wavelength) in the range of about 435-493 nm. Alternatively, according to various embodiments, Λ a can be in the range of 10 nm to 1 μm, including 10 nm to 500 nm or 300 nm to 500 nm. It should be understood that the diffraction gratings disclosed herein can be utilized to diffract light and can be part of a display system 250 (FIG. 6), which can be configured to direct light to a grating having a narrow band of wavelengths. In some embodiments, Λ for a given diffraction grating a is less than the minimum wavelength of the band of wavelengths that the light source of the display system is configured to direct at the diffraction grating.

[0090] Without being bound by any theory, in some embodiments, Λ a may have a value less than the ratio mλ / (sinα+n2sinθ), where m is an integer (e.g., 1, 2, 3...), and α, n2, and θ each have a value as described throughout this specification. For example, α may be in the range Δα of over 40 degrees, n2 may be in the range of 1 to 2, and θ may be in the range of 40-80 degrees.

[0091] In some embodiments, Λ a may be substantially constant across the surface 1008S of the grating 1008. However, embodiments are not so limited, and in some other embodiments, Λ a may vary across the surface 1008S.

[0092] As explained above, the field of view (FOV) or Δα corresponds to the angular range of incident light that can be coupled into the waveguide and cause TIR. As discussed above, this angular range also corresponds to the angular range of light that affects the waveguide and is output by the eyepiece, and therefore may also affect the field of view experienced by a viewer when viewing an image through a display. To couple the incident light into the waveguide and propagate therein under TIR, the light incident on the waveguide 1004 may be guided within a range of acceptance angles or FOV, Δα, that depends, among other things, on the refractive index n2 of the material of the waveguide 1004 and the refractive index n1 of the material of the diffraction grating 1008. For example, the FOV (Δα) of the waveguide 1004 comprising a glass substrate with a refractive index of 1.5 may be about 30 degrees. When the grating is designed to produce a symmetric FOV, the range of FOV or acceptance angles for the glass substrate may be within ±15 degrees in one dimension. Below, various embodiments are described in which the combined range of acceptance angles or effective FOV for a stack of waveguides is extended for individual component waveguides, which may have different and / or smaller FOVs relative to the effective FOV of the stack of waveguides.

[0093] As described herein, the combined, total, or effective FOV of multiple waveguides, e.g., a stack of waveguides, refers to the range of contiguous FOV resulting from the combination of the FOVs of the individual waveguides for a given color. If the FOVs overlap, the range of contiguous FOV may include non-overlapping portions of the FOVs of the individual waveguides, e.g., their sum. For example, if a first waveguide having a first diffraction grating formed thereon has an α1 of -5 to 20 degrees (i.e., Δα1=25 degrees) for light with a given color, and a second waveguide having a second diffraction grating formed thereon has an α2 of -20 to 5 degrees (i.e., Δα2=25 degrees) for a given color, then the complementary FOV for the given color from the stack is 40 degrees.

[0094] A display device according to various embodiments includes a plurality of waveguides formed on one another and having respective diffraction gratings formed thereon, the diffraction gratings configured to diffract visible light incident thereon into respective waveguides such that visible light diffracted into the respective waveguide propagates through each of the respective waveguides such that the visible light diffracted into the respective waveguide is guided therein by total internal reflection, the diffraction gratings configured to diffract visible light within different FOVs relative to a layer normal direction of the waveguides into the respective waveguides, the respective FOVs being such that the waveguides are contiguous and have a combined FOV that is greater than each of the individual respective FOVs.

[0095] 11 illustrates a cross-sectional view of a portion of a display device 1100 comprising stacked waveguides configured for an increased combined effective field of view (FOV) for light having a color in the visible wavelength range, according to an embodiment. The display device 100 comprises stacked waveguides 1004, 1104 having respective diffraction gratings 1008, 1108 formed thereon, the stack having a combined effective field of view (FOV) greater than the respective FOVs Δα1, Δα2 of the component waveguides 1004, 1104. The display device 1100 includes a first waveguide 1004 and a second waveguide 1104 formed on one another. The first waveguide 1004 has a first diffraction grating 1008 formed thereon, and the second waveguide 1104 has a second diffraction grating 1108 formed thereon. The first and second diffraction gratings 1008, 1108 are configured to diffract visible light 1116, 1124 incident thereon into the respective waveguides 1004, 1104, respectively, such that the visible light diffracted into the respective waveguides 1004, 1104 propagates within each of the respective waveguides. The first and second diffraction gratings 1008, 1108 are configured to diffract visible light incident thereon within different respective fields of view Δα1, Δα2 (relative to the layer normal 1012, e.g., the yz plane or z-direction) into the respective waveguides 1004, 1104. The display device 1100 additionally includes optical elements 1012 and 1112 formed on the waveguides 1004 and 1104, respectively.

[0096] In the illustrated embodiment, the first and second waveguides 1004, 1104 are in a stacked arrangement with a separator 1106 interposed therebetween and have substantially parallel propagation directions (eg, x-direction) under total internal reflection.

[0097] The first and second waveguides 1004 and 1104 are similar to each other, and the corresponding first and second gratings 1008 and 1012 are similar to each other, but the first and second gratings 1004 and 1108 have different periods Λ. 1、Λ and are configured to diffract light having the same general color (i.e., red, green, or blue) but different wavelengths. However, the embodiments are not so limited and the first and second diffraction gratings 1004, 1108 can have substantially the same period and be configured to diffract light having the same wavelength.

[0098] In addition, the first waveguide 1004 coupled to the first diffraction grating 1008 is configured to diffract light having a first, e.g., positive α (having a counterclockwise angle with respect to the surface normal 1012), while the second waveguide 1104 coupled to the second diffraction grating 1108 is configured to diffract light having a different, e.g., negative α (having a clockwise angle with respect to the surface normal 1012). However, the embodiments are not so limited. For example, both the first and second waveguides 1004 and 1104 can be configured to diffract positive or negative, but different, angles of incidence. Other variations are also possible. For example, either the first and second waveguides 1004 and 1104 can be configured to diffract positive or negative angles, or both, and the angular ranges Δα1 and Δα2 can be the same or different in magnitude.

[0099] The first diffraction grating 1008 is configured to partially diffract and partially transmit visible light 1116, 1124 incident thereon, respectively. In the illustrated embodiment, the first diffraction grating 1008 is configured to partially diffract visible light 1116 incident thereon within a first FOV (Δα1) and partially transmit visible light 1124 incident thereon within a second FOV (Δα2). The second diffraction grating 1108 is configured to receive light 1128 partially transmitted through the first diffraction grating 1008 as incident light and at least partially diffract the light 1128 into partially diffracted light 1132.

[0100] In the illustrated embodiment, the first and second diffraction gratings 1008 and 1108 are configured to diffract light having the same color. That is, each of the first and second diffraction gratings 1008 and 1108 is configured to diffract light having one or more wavelengths in the same color range (red, green, or blue range) within a wavelength range of about 435 nm to 780 nm. In various embodiments, the first and second diffraction gratings 1008 and 1108 can be configured to diffract light having the same or different wavelengths in a range of about 620 to 780 nm for red, diffract light having the same or different wavelengths in a range of about 492 to 577 nm for green, or diffract light having the same or different wavelengths in a range of about 435 to 493 nm for blue.

[0101] In some embodiments, the first and second diffraction gratings 1008 and 1108 have respective periods Λ 1、 By configuring Λ, it can be configured to diffract specific wavelengths. Without being bound by any theory, under some circumstances the period Λ can be generally related to α, n, θ, and λ by the following equation: Λ a (sinα+n2sinθ)=mλ [1] where m is an integer (e.g., 1, 2, 3...), and α, n2, θ, and λ are the angle of incidence, the refractive index of the waveguide, the angle of the diffracted light, and the wavelength of the light, respectively, and may have values ​​as described anywhere herein. Other types of diffractive optical elements and possibly holographic optical elements can also be used. Still referring to FIG. 11, in the illustrated embodiment, to configure each of the first and second diffraction gratings 1008 and 1108 to diffract light having one or more wavelengths within the same color range (red, green, or blue range), each of Λ1 and Λ2 can be selected to be smaller than the wavelength that the gratings 1008 and 1108 are configured to diffract. Thus, if each of the first and second diffraction gratings 1008 and 1108 is configured to diffract at least red light, each of Λ1 and Λ2 may be selected to be less than a wavelength (or any wavelength) in the range of about 620-780 nm; if each of the first and second diffraction gratings 1008 and 1108 is configured to diffract at least green light, each of Λ1 and Λ2 may be selected to be less than a wavelength (or any wavelength) in the range of about 492-577 nm; and if each of the first and second diffraction gratings 1008 and 1108 is configured to diffract at least blue light, each of Λ1 and Λ2 may be selected to be less than a wavelength (or any wavelength) in the range of about 435-493 nm. In various embodiments, Λ1 and Λ2 can be about 40% to about 99%, about 50% to about 90%, or about 60% to about 80%, e.g., about 71% of any of the wavelengths that the respective gratings are configured to diffract. For example, if the waveguide is configured to diffract light having a wavelength of 530 nm (green), the grating can have a period of 380 nm, and if the waveguide is configured to diffract light having a wavelength of 650 nm (red), the grating can have a period of 465 nm.

[0102] 11, the combination of the first grating 1008 and the first waveguide 1004 is configured to diffract light within a first FOV (Δα1) that is different from a second FOV (Δα2) that the combination of the second grating 1108 and the second waveguide 1104 is configured to diffract. In some embodiments, the different FOVs Δα1 and Δα2 can be obtained by configuring the refractive index n2 of each of the first and second waveguides 1004 and 1104 to have a value that is 1.5, 1.6, 1.7, 1.8, 1.9, or within a range defined by any of these values, or a different value that is higher but less than n1.

[0103] 11 , in operation, when incident light 1116, e.g., visible light, is incident on the first diffraction grating 1008 having a first period Λ at an incident angle α, the first diffraction grating 1008 at least partially diffracts the incident light 1116 at a first diffraction angle θ as diffracted light 1120. The first waveguide 1004 diffracts the incident light 1116 at a critical angle θ due to the occurrence of total internal reflection within the waveguide 1004. TIR-1 The first waveguide refractive index n 2-1 The resulting diffracted light 1120 propagates along the x-axis under total internal reflection (TIR) ​​until the light reaches and exits through optical element 1012.

[0104] The first diffraction grating 1108 at least partially transmits the incident light 1124 as transmitted light 1128, which then becomes light incident at an incidence angle α2 on a second diffraction grating 1108 having a second period Λ2. The second diffraction grating 1108 then at least partially diffracts the light 1128 at a second diffraction angle θ2 as diffracted light 1132. The second waveguide 1104 is configured such that when the light 1128 is incident on the surface 1108S within Δα2, the second waveguide 1104 diffracts the light 1128 at a critical angle θ2 due to the occurrence of total internal reflection within the waveguide 1104. TIR-2The second waveguide refractive index n 2-2 The resulting diffracted light 1132 propagates along the x-axis under total internal reflection (TIR) ​​until the light reaches optical element 1112.

[0105] Thus, a first waveguide 1004 having a first diffraction grating 1008 formed thereon and a second waveguide 1104 having a first diffraction grating 1108 formed thereon each have, individually, Δα1 and Δα2, but when stacked as shown in a portion of a display device 1100, the resulting stacked waveguides 1004, 1104 are contiguous and overlap each other over the respective FOVs of the component waveguides 1004, 1104. Δα1, Δα2 have a larger combined FOV.

[0106] In the illustrated embodiment, the diffraction gratings 1008 and 1108 have a suitable length in the x-direction and partially or completely overlap each other in the x-direction such that the overlap is sufficient for incident light 1124 within Δα2 to traverse both the first and second diffraction gratings 1008 and 1108.

[0107] It should be appreciated that in the illustrated embodiment, to have a combined FOV with high diffraction efficiency, the first diffraction grating 1008 is configured to diffract the incident light 1116 in Δα1 with high diffraction efficiency while being configured to at least partially transmit the incident light 1124, and the second diffraction grating 1108 is configured to diffract its incident light 1128 in Δα2 with high diffraction efficiency. According to an embodiment, the first and second diffraction gratings 1008 and 1108 are configured to diffract the incident light 1116 and 1124 in Δα1 and Δα2, respectively, with a diffraction efficiency having a percentage greater than about 20%, 40%, 60%, or 80%, or within any range defined by any of these values, according to an embodiment. According to an embodiment, the first diffraction grating 1008 is configured to transmit incident light 1124 within Δα2 with a transmission efficiency having a percentage greater than approximately 20%, 40%, 60%, or 80%, or within any range defined by any of these values, according to an embodiment.

[0108] In some embodiments, Δα1 and Δα2 may partially overlap. According to embodiments, Δα1 and Δα2 may be less than 20%, 40%, 60%, or 80% based on Δα1 or Δα2, or a percentage within any range defined by any of these values, or according to embodiments, less than 5%. ° , 10 ° , 15 ° , or 20 ° Less than or overlapping by values ​​within any range defined by any of these values.

[0109] In one example, the first waveguide 1004 is configured to couple light having an α1 between 0 and 30 degrees (i.e., Δα1=30 degrees) and a green wavelength (e.g., 530 nm) into the first waveguide 1004, while the second waveguide 1104 is configured to couple light having the same green wavelength and an α2 between -30 and 0 degrees (i.e., Δα2=30 degrees). The resulting combined FOV can be as high as 60 degrees.

[0110] Still referring to FIG. 11, although only two waveguides are stacked in the illustrated embodiment, the embodiment is not so limited. In other embodiments, additional waveguides may be further stacked to provide an even larger combined FOV. For example, a third waveguide and third diffraction grating combination may be formed below the second waveguide 1104 and configured such that visible light having the same color and the same or different wavelength as the incident light 1116, 1124 incident on the first diffraction grating 1008 within the third FOV Δα3 may be partially transmitted through the first and second diffraction gratings 1008, 1108 to be diffracted through the third diffraction grating.

[0111] 12A and 12B illustrate cross-sectional views of a portion of a display device 1200 including stacked waveguides configured for an increased combined effective field of view (FOV) for light having multiple colors in the visible wavelength range, according to an embodiment. Figures 12A and 12B illustrate cross-sectional views of a portion of a display device 1200 including stacked waveguides 1004, 1204 having respective diffraction gratings 1008, 1208 formed thereon, according to some embodiments, where the stack has a combined field of view (FOV) that is greater than the respective field of view (FOV) of the component waveguides 1004, 1204. Similar to the display device 1100 illustrated with respect to FIG. 11 above, the display device 1200 includes a first waveguide 1004 and a second waveguide 1204 formed on top of each other. The first waveguide 1004 has a first diffraction grating 1008 formed thereon, and the second waveguide 1204 has a second diffraction grating 1208 formed thereon. The display device 1200 additionally includes optical elements 1012 and 1212 formed on the waveguides 1004 and 1204, respectively. Other arrangements of the display device 1200 that are the same as or similar to the display device 1100 illustrated with respect to FIG. 11 above are omitted herein.

[0112] However, unlike the display device 1100 illustrated with respect to FIG. 11 above, the first and second diffraction gratings 1008, 1208 have different periods Λ1, Λ2, respectively, and are configured to diffract light having different colors (i.e., red, green, or blue).

[0113] 12A, the first and second diffraction gratings 1008, 1208 are configured to diffract visible light 1116, 1124 having a first color and a first wavelength λ1 incident thereon into the respective waveguides 1004, 1204, such that the visible light having the first color and λ1 is diffracted into and propagates within the respective waveguides 1004, 1204. The first and second diffraction gratings 1008, 1208 are configured to diffract visible light having a first color incident thereon into the respective waveguides 1004, 1204 in different fields of view Δα1, Δα2 relative to the surface normal 1012, e.g., the z-direction.

[0114] 12B, the first diffraction grating 1008 is configured to substantially transmit visible light 1216, 1214 having a second color and a second wavelength λ2. Here, the transmitted visible light 1226 having the second color and wavelength λ2 incident on the second diffraction grating 1208 is at least partially diffracted into the second waveguide 1204 and propagated in the x-direction. The second diffraction grating 1208 is configured to diffract the visible light 1216, 1214 having the second color and incident on the first diffraction grating 1008 within one or both of the fields of view Δα1, Δα2 into the second waveguide 1204. In the illustrated embodiment, the visible light 1216 is diffracted so as to be diffracted into the second waveguide 1204.

[0115] In summary, referring to FIG. 12A, the first waveguide 1004 and the first diffraction grating 1008 are configured to diffract visible light having a first color and λ1 and having positive α1 (within Δα1), while the second waveguide 1204 and the second diffraction grating 1208 are configured to diffract visible light having a first color and λ1 and having negative α2 (within Δα2).

[0116] 12B, the first waveguide 1004 and the first diffraction grating 1008 are configured to substantially transmit visible light 1216, 1214 having a second color and λ2 and having positive α1 (within Δα1) and negative α2 (within Δα2), respectively, while the second waveguide 1204 and the second diffraction grating 1208 are configured to at least partially diffract visible light having a second color and λ2 and having at least one of positive α1 (within Δα1) and negative α2 (within Δα2). In some embodiments, the different FOVs Δα1 and Δα2 are determined by the respective refractive indices n of the first and second waveguides 1004 and 1204. 2-1 and n 2-1 can be obtained by configuring the diffraction gratings 1004, 1208 to have different values, which may be 1.5, 1.6, 1.7, 1.8, 1.9 or more, or a value within a range defined by any of these values, but less than n1.

[0117] Unlike the embodiment illustrated with respect to FIG. 11, in the illustrated embodiment of FIGS. 12A and 12B, the first and second diffraction gratings 1008 and 1208 are configured to diffract light having one or more wavelengths corresponding to different colors (red, green, or blue ranges) within a wavelength range of about 435 nm to 780 nm. For example, the first and second diffraction gratings 1008 and 1208 are configured to diffract light having different wavelengths within different ranges of about 620 to 780 nm for red, about 492 to 577 nm for green, or about 435 to 493 nm for blue. In particular, in the illustrated embodiment, the first diffraction grating 1008 is configured to diffract green light and the second diffraction grating 1208 is configured to diffract green and red light.

[0118] In the illustrated embodiment, to configure each of the first and second diffraction gratings 1008 and 1208 to diffract light having one or more wavelengths corresponding to different colors (red, green, or blue), the respective Λ1 and Λ2 may be selected to be different from and smaller than the wavelengths that the gratings 1008 and 1208 are configured to diffract. Thus, if the first and second diffraction gratings 1008 and 1208 are configured to diffract green and red light, respectively, Λ1 and Λ2 may be selected to be less than a wavelength (or any wavelength) within different ranges, from about 492 to 577 nm for green and about 620 to 780 nm for red, respectively. Additionally, when the first and second diffraction gratings 1008 and 1208 are configured to diffract blue and green light, respectively, Λ1 and Λ2 may be selected to be less than a wavelength (or any wavelength) within different ranges, between about 435 and 493 nm for blue and about 492 and 577 nm for green, respectively.

[0119] 12A , in operation, when incident light 1116, e.g., visible light having a first color and λ1, is incident on the first diffraction grating 1008 having a first period Λ1 at an incident angle α1, the first diffraction grating 1008 at least partially diffracts the incident light 1116 at a first diffraction angle θ1 as a diffracted light beam 1120. The first waveguide 1004 is configured such that when the incident light 1116 is incident on the surface 1008S within Δα1, the first diffraction grating 1008 diffracts the incident light 1116 at a critical angle θ1 due to the occurrence of total internal reflection (TIR) ​​within the waveguide 1004. TIR-1 The first waveguide refractive index n 2-1 The resulting diffracted light 1120 propagates along the x-axis under TIR until it reaches and exits through optical element 1012.

[0120] The first diffraction grating 1016 at least partially transmits incident light 1124 thereon at an incidence angle α2 having a first color and λ1 as transmitted light 1128, which then becomes light 1128 incident on the second diffraction grating 1208 having a second period Λ2. The second diffraction grating 1208 at least partially diffracts the light 1128 incident within Δα2 as diffracted light 1232 at a second diffraction angle θ2. The second waveguide 1204 is configured such that when the light 1128 is incident within Δα2, the second waveguide 1204 diffracts the light 1128 at a critical angle θ2 due to the occurrence of total internal reflection within the waveguide 1204. TIR-2 The second waveguide refractive index n 2-2 The resulting diffracted light 1232 propagates along the x-axis under total internal reflection (TIR) ​​until the light reaches and exits through optical element 1212.

[0121] 12B, when incident light 1216 and 1214, e.g., visible light having a second color and λ2, is incident on the first diffraction grating 1008 at α1 within Δα1 and α2 within Δα2, respectively, the first diffraction grating 1008 substantially transmits the incident light 1216 and 1214 into corresponding substantially transmitted lights 1226 and 1224, respectively. The transmitted lights 1226 and 1224 are then incident on the second diffraction grating 1208 at α1 within Δα1 and α2 within Δα2, respectively. The second waveguide 1204 is configured such that when light 1216 is incident on the surface 1208S within Δα1, the diffraction grating 1208 is oriented at a critical angle θ due to the occurrence of total internal reflection within the second waveguide 1204. TIR-2 diffracts the light 1226 at a diffraction angle greater than 1236, and the second waveguide refractive index n 2-2 has.

[0122] Thus, by stacking a first waveguide 1004 having a first grating 1008 formed thereon with a first period Λ1 and a second waveguide 1204 having a second period Λ2, the first grating 1008 is configured to diffract light having a first color and λ1 in Δα1, the second grating 1208 is configured to diffract light having a first color and λ1 in Δα2, and the second grating 1208 is further configured to diffract light having a second color and λ2 in at least Δα1. The resulting stack has a combined field of view (FOV) greater than the respective FOVs Δα1, Δα2 of the component waveguides 1004, 1204. Additionally, the second waveguide may propagate more than one color, potentially reducing the number of waveguides in the stack.

[0123] In the illustrated embodiment, referring to Fig. 12A, in order to have a combined FOV with high diffraction efficiency, it should be understood that the first diffraction grating 1008 is configured to diffract the incident light 1116 having a first color in Δα1 with high diffraction efficiency, while at least partially transmitting the incident light 1124 having a first color in Δα2. In addition, referring to Fig. 12B, the first diffraction grating 1008 is configured to substantially transmit the incident lights 1216, 1214 having second colors in Δα1 and Δα2, respectively. In addition, the second diffraction grating 1208 is configured to diffract its incident light 1128 having a first color in Δα2 and 1226 having at least a second color in Δα2 with high diffraction efficiency. According to an embodiment, when configured to diffract light with high efficiency, the first and / or second diffraction gratings 1008 and / or 1208 are configured to diffract incident light within Δα1 or Δα2 with a diffraction efficiency having a percentage greater than about 20%, 40%, 60%, or 80%, or within any range defined by any of these values, according to an embodiment. According to an embodiment, when configured to substantially transmit light, the first diffraction grating 1008 is configured to transmit incident light within Δα1 or Δα2 with a transmission efficiency having a percentage greater than about 20%, 40%, 60%, or 80%, or within any range defined by any of these values, according to an embodiment.

[0124] Still referring to Figures 12A and 12B, in some embodiments, the second color corresponds to a color having a longer wavelength compared to the first color. For example, when the second color is red, the first color can be green (or blue), and when the second color is green, the first color can be blue. Such an arrangement allows for the transmittance of the first diffraction grating 1008 discussed above. However, the embodiments are not so limited, and in some other embodiments, the second color may correspond to a color having a shorter wavelength compared to the first color.

[0125] In some embodiments, Δα1 and Δα2 may partially overlap. According to embodiments, Δα1 and Δα2 may be less than 20%, 40%, 60%, or 80% based on Δα1 or Δα2, or a percentage within any range defined by any of these values, or according to embodiments, 5 ° , 10 ° , 15 ° , or 20 ° Overlaps only values ​​that are less than or within a range defined by one of these values.

[0126] In one example, the first waveguide 1004 can be configured to couple green light (e.g., 530 nm) having α1 between −5 and 20 degrees (i.e., Δα1 = 25 degrees) into the first waveguide 1004 using a first diffraction grating 1008 having Λ1 = 380 nm. The second waveguide 1204 can be configured to couple green light (e.g., 530 nm) having α2 between −20 and 5 degrees (i.e., Δα2 = 25 degrees) into the second waveguide 1204 using a second diffraction grating 1208 having Λ2 = 465 nm. The resulting combined FOV is 40 degrees, which is a significant improvement over either Δα1 = 25 degrees or Δα2 = 25 degrees. In addition, a second waveguide 1204 configured with a second diffraction grating 1208 having Λ2=465 nm can couple red light (e.g., 650 nm) with α1 between -5 and 20 degrees (i.e., Δα1=25 degrees) into the second waveguide 1204. Thus, the stack can be used to project a green color image (e.g., 530 nm) with a combined FOV of 40 degrees and a red color image (e.g., 650 nm) with an FOV of 25 degrees.

[0127] 13A-13C diagrammatically illustrate the visual effect to a user of combining or stacking waveguides in a configuration similar to that illustrated above with respect to FIGs. 12A and 12B, in operation, according to an embodiment. FIG 13A illustrates a schematic perspective view of a display device 1200A including a waveguide configured similarly to the first waveguide (1012 in FIGs. 12A, 12B), FIG 13B illustrates a schematic perspective view of a display device 1200B including a waveguide configured similarly to the second waveguide (1112 in FIGs. 12A and 1212 in FIGs. 12B), and FIG 13C illustrates a schematic perspective view of a display device 1200 including stacked waveguides (1100 in FIGs. 11, 1200 in FIGs. 12) configured for an increased combined effective field of view (FOV), according to an embodiment. In operation, the first (1012, FIG. 13A) and second (1212, FIG. 13B) waveguides of the component are configured to receive incident image information for a given color contained within the incident light 1116 (FIG. 13A), 1124 (FIG. 13B) that is incident on the display device within the respective FOVs Δα1 and Δα2, as described above. With reference to FIG. 13C, when the first and second waveguides 1012, 1212 are stacked, the incident light 1116, 1124 having a first color (e.g., green) and λ1 is internally coupled into the waveguides 1004, 1204 by being diffracted by the respective diffraction gratings 1008, 1208 to be propagated within the respective waveguides 1004, 1204 under TIR. The diffracted light 1120, 1232 subsequently impinges on the respective light distribution elements 1010, 1210. The light distribution elements 1010, 1210 deflect the light, which propagates towards the outcoupling optical elements 1012, 1212 and is outcoupled as outcoupled light 1140, 1148, respectively. The visual effect of stacking waveguides to a user is described below.

[0128] 13A illustrates, for illustrative purposes only, a schematic diagram of a display device 1200A including only the first waveguide 1004 (waveguide 1004 having a first diffraction grating 1008 formed thereon having a first period Λ1) of the display device 1200 illustrated in FIGS. 12A and 12B, and the resulting image 1144. Although the waveguide 1004 is configured to incouple the incident light 1116 in Δα1, the incident image information is additionally contained in the incident light 1124 in Δα2, so that the resulting image 1144 contains only a portion of the incident information of a first color (e.g., green).

[0129] 13B illustrates, for illustrative purposes only, a schematic diagram of a display device 1200B including only the second waveguide 1204 of the display device 1200 illustrated in FIGS. 12A and 12B (the waveguide 1204 has a second diffraction grating 1208 formed thereon having a second period Λ2), and the resulting image 1152. The waveguide 1204 is configured to incouple the incident light 1124 in Δα2, but the incident image information is additionally contained in the incident light 1116 in Δα1, so that the resulting image 1144 includes only a portion of the incident information of a first color (e.g., green).

[0130] 13C illustrates a schematic diagram of a display device 1200 comprising stacked first and second waveguides 1004 and 1204 similar to those illustrated in FIGS. 12A and 12B, where the waveguide 1004 has a first grating 1008 formed thereon with a first period Λ1 and the waveguide 1204 has a second grating 1208 formed thereon with a second period Λ2. The combination of the first and second waveguides 1004, 1204 is configured to in-couple both the incident light 1116 having a first color within Δα1 and the incident light 1124 having a first color within Δα2, such that the resulting image 1160 includes the sum of the information of the first color (e.g., green) from the first waveguide 1004 and the second waveguide 1204.

[0131] 14A and 14B respectively illustrate cross-sectional views of display devices 1400A and 1400B according to embodiments, each comprising a plurality of stacked waveguides 1004, 1204, 1304, 1404 having respective diffraction gratings 1008, 1208, 1308, 1408 formed thereon, the stacked waveguides configured for an increased combined effective field of view (FOV) for light having multiple colors within the visible wavelength range. The stacked waveguides are configured according to some embodiments to have a combined field of view (FOV) or total field of view that is greater than the respective FOVs of the component waveguides 1004, 1204, 1304, 1404. Display devices 1400A and 1400B are similar to each other, except that display device 1400A has gratings 1008, 1208, 1308, 1408 facing the incident light, while display device 1400B has gratings 1008, 1208, 1308, 1408 facing away from the incident light. The operating principles of the display devices are similar between 1400A and 1400B and will be described together herein.

[0132] Similar to the display device 1200 illustrated with respect to Figures 12A and 12B above, the display devices 1400A and 1400B include a first waveguide 1004 having a first diffraction grating 1008 disposed thereon, a second waveguide 1204 having a second diffraction grating 1208 disposed thereon, a third waveguide 1304 having a third diffraction grating 1308 disposed thereon, and a fourth waveguide 1404 having a fourth diffraction grating 1408 disposed thereon. The first to fourth diffraction gratings 1008, 1208, 1308, 1408 have first to fourth periods Λ1, Λ2, Λ3, Λ4. Additional optical elements similar to the previous embodiment (e.g., 1012, Figures 12A, 12B) are omitted herein for clarity. Other similar arrangements of display devices 1400A and 1400B that are the same as or similar to the display device 1200 illustrated with respect to FIGS. 12A and 12B above are omitted herein.

[0133] In operation, with reference to the coupling of light having λ1, when incident light 1116, e.g., visible light, each having a first color and λ1, is incident on the first diffraction grating 1008 at an incident angle α1, the first diffraction grating 1008 at least partially diffracts the incident light 1116. In particular, the first waveguide 1004 is configured such that when the incident light 1116 is incident on its surface within Δα1, the first waveguide 1004 diffracts the incident light 1116 at a critical angle θ due to the occurrence of total internal reflection within the waveguide 1004. TIR-1 diffracts the incident light 1116 at a diffraction angle greater than 1114 and the diffracted light 1120 propagates along the x-axis under total internal reflection (TIR). 2-1 has.

[0134] The first diffraction grating 1008 at least partially transmits incident light 1124 of a first color and λ1, which then is incident on a second diffraction grating 1208 having a second period Λ2 at an incident angle α2. The second diffraction grating 1208 at least partially diffracts the light 1224 of the first color and wavelength within Δα2 as diffracted light 1232. In particular, the second waveguide 1204 is configured such that when light 1128 of the first color and wavelength is incident on the surface 1208S within Δα2, the second waveguide 1204 diffracts the light 1224 at a critical angle θ due to the occurrence of total internal reflection within the waveguide 1204. TIR-2 diffracts the light 1124 at a diffraction angle greater than θ and the diffracted light 1232 propagates along the x-axis under total internal reflection (TIR) ​​with a second waveguide refractive index n 2-2 has.

[0135] Referring to the coupling of light having λ2, when incident light 1226 and 1224, e.g., visible light having a second color and λ2, is incident on the first diffraction grating 1008, the first diffraction grating 1008 substantially transmits the incident light 1226 and 1224, which are then incident on the second diffraction grating 1208 at α1 within Δα1 and α2 within Δα2, respectively. The second waveguide 1204 is configured such that when light 1226 of a second color and wavelength is incident on its surface within Δα1, the second waveguide 1204 is incident at a critical angle θ due to the occurrence of total internal reflection within the second waveguide 1204. TIR-2and a second waveguide refractive index n such that the diffracted light 1236 of the second color and wavelength propagates along the x-axis under total internal reflection (TIR). 2-2 On the other hand, the second diffraction grating 1208 substantially transmits light 1224 of the second color and wavelength, which then becomes incident on the third diffraction grating 1308 at α2 within Δα2. The third waveguide 1304 has a critical angle θ due to the occurrence of total internal reflection within the third waveguide 1304 when the light 1224 of the second color and wavelength is incident on its surface within Δα2. TIR-3 and a third waveguide refractive index n such that the diffracted light 1324 of the second color and wavelength propagates along the x-axis under total internal reflection (TIR). 2-3 has.

[0136] Referring to the coupling of light having λ3, when incident light 1316 and 1324, e.g., visible light having a third color and λ3, is incident on the first and second diffraction gratings 1008, 1208, the first and second diffraction gratings 1008, 1208 substantially transmit the incident light 1316 and 1324, which are then incident on the third diffraction grating 1308 at α1 within Δα1 and α2 within Δα2, respectively. The third waveguide 1304 is configured such that when light 1316 is incident on its surface within Δα1, the third waveguide 1304 is incident at a critical angle θ due to the occurrence of total internal reflection within the third waveguide 1304. TIR-3 diffracts light 1316 at a diffraction angle greater than 1328 such that the diffracted light 1328 propagates along the x-axis under total internal reflection (TIR). 2-3 On the other hand, the third diffraction grating 1308 substantially transmits the light 1324, which then becomes incident on the fourth diffraction grating 1408 at α2 within Δα2. The fourth waveguide 1404 has a critical angle θ due to the occurrence of total internal reflection within the fourth waveguide 1404 when the light 1324 is incident on its surface within Δα2. TIR-4diffracting light 1324 at a diffraction angle greater than 1324 and causing the diffracted light 1332 to propagate along the x-axis under total internal reflection (TIR); 2-4 has.

[0137] Still referring to Figures 14A and 14B, in some embodiments, λ3 corresponds to a color having a longer wavelength compared to λ2, which corresponds to a color having a longer wavelength compared to λ1. For example, λ3 corresponds to red, λ2 corresponds to green, and λ1 corresponds to blue. The first to fourth periods Λ1, Λ2, Λ3, Λ4 may have values ​​that decrease in the light propagation direction in some cases. For example, Λ1 may have a suitable value corresponding to a grating configured to diffract blue light, as described above, Λ2 may have a suitable value corresponding to a grating configured to diffract, for example, green (and blue), as described above, and each of Λ3 and Λ4 may have a suitable value corresponding to a grating configured to diffract red (and green) light, as described above. However, the embodiments are not so limited, and in some other embodiments, Λ1, Λ2, Λ3, Λ4 may have values ​​that increase or have a random order in the light propagation direction.

[0138] Thus, by stacking the first to fourth waveguides 1004, 1204, 1304, 1404 having respective diffraction gratings 1008, 1208, 1308, 1408 formed thereon with respective periods Λ1, Λ2, Λ3, Λ4, the first waveguide 1004 has a first color and λ1 and is configured to diffract light in Δα1 and the second waveguide 1204 is configured to diffract light in Δα2 such that a combined FOV greater than the respective fields of view FOV Δα1, Δα2 of the component first and second waveguides 1004, 1204 is achieved for light having a first color (e.g., blue) at λ1. Similarly, the second waveguide 1204 is configured to have a second color and λ2 and diffract light within Δα1, and the third waveguide 1304 is configured to have a second color and λ2 and diffract light within Δα2, such that a combined FOV greater than the respective FOVs Δα1, Δα2 of the component second and third waveguides 1204, 1304 is achieved for light having a second color (e.g., green) at λ2. Similarly, the third waveguide 1304 is configured to have a third color and λ2 and diffract light within Δα1, and the fourth waveguide 1404 is configured to have a third color and λ3 and diffract light within Δα2, such that a combined FOV greater than the respective FOVs Δα1, Δα2 of the component third and fourth waveguides 1304, 1404 is achieved for light having a third color (e.g., red) at λ3.

[0139] It is worth noting that some waveguides serve multiple colors and corresponding wavelengths, and therefore fewer waveguides are potentially used in some cases, and the stack may therefore be simpler and potentially smaller, lighter, cheaper, or at least less complex.

[0140] (Stacked Waveguides with Combined Field of View Based on Liquid Crystal-Based Diffraction Gratings) As described above, various embodiments include a plurality of waveguides formed on top of each other, for example in a stacked configuration, with each grating configured to diffract visible light incident thereon into a respective waveguide, such that the visible light diffracted into the respective waveguide propagates within each of the respective waveguides. Each grating is configured to diffract visible light within a respective field of view (FOV) relative to a layer normal direction of the respective waveguide into the respective waveguide, the respective FOVs being contiguous and such that the waveguides have a combined FOV that is greater than each of the respective FOVs. In the following, embodiments of a liquid crystal-based grating and a waveguide with a liquid crystal grating are described. The waveguides and gratings are configured to achieve the specific arrangements described above, including the wavelength selectivity of diffraction and transmission, and their FOVs, to form a stacked waveguide with a combined FOV.

[0141] In general, 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 liquid crystals exhibits some structural order. Different types of liquid crystals include thermotropic, lyotropic, and polymeric liquid crystals. The thermotropic liquid crystals disclosed herein can be implemented in a variety of physical states, including, for example, nematic states / phases, smectic states / phases, chiral nematic states / phases, or chiral smectic states / phases.

[0142] 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 being substantially 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 a nematic phase can be uniaxial, i.e., 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, i.e., in addition to aligning its long axis, the liquid crystal can also align along a secondary axis.

[0143] 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 generally perpendicular to the plane of the liquid crystal layer, while in other implementations, the long axes of the molecules can be tilted relative to the direction perpendicular to the plane of the layer.

[0144] Here, and throughout this disclosure, nematic liquid crystals consist of rod-shaped molecules in which the long axes of neighboring molecules are approximately aligned with each other. To describe this anisotropic structure, a dimensionless unit vector, called the director,

number

[0145] Here, and throughout this disclosure, the 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 between the alignment direction and the major surface or in a direction parallel to the major surface, e.g., the x-direction.

[0146] Here, and throughout this disclosure, the azimuthal angle or rotation angle φ is used to describe the rotation angle about an axis perpendicular to the layer normal direction or major surfaces of the liquid crystal layer, measured in a plane parallel to the major surfaces of the liquid crystal layer or substrate, e.g., the xy plane, and measured between the alignment direction, e.g., the stretch direction or director direction, and a direction parallel to the major surfaces, e.g., the y-direction.

[0147] Here, and throughout this disclosure, when angles such as rotation angle φ or pre-tilt angle Φ are referred to as being substantially identical between different regions, it should be understood that 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.

[0148] Here and throughout this specification, 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 in which the alignment of the liquid crystal does not vary between different zones.

[0149] As described herein, liquid crystals in the nematic or smectic state can also exhibit chirality. Such liquid crystals are said to be in the chiral or cholesteric phase. In the chiral or cholesteric phase, the liquid crystals 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 results in a longer-range chiral order.

[0150] As described herein, liquid crystals in a chiral smectic state or phase can be configured such that the liquid crystal 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 of the liquid crystal molecules from one liquid crystal molecule in the layer normal direction to the next, relative to a direction perpendicular to the layer normal, thereby producing a helical twist of the molecular axes along the layer normal.

[0151] As described herein, and throughout this disclosure, a chiral structure refers to a plurality of liquid crystal molecules in a cholesteric phase that extend in a direction perpendicular to the director, e.g., the layer depth direction, and are continuously rotated or twisted in a rotational direction, e.g., clockwise or counterclockwise. In one aspect, the director of the liquid crystal molecules in the chiral structure can be characterized as a spiral having a helical pitch.

[0152] As described herein, liquid crystals in the cholesteric phase that exhibit chirality can be described as having a chiral pitch or helical pitch (p) that corresponds to the length in the layer depth direction that corresponds to the net rotation angle of the liquid crystal molecules of the chiral structure by one turn in the first rotation direction. In other words, the helical pitch refers to the distance over which the liquid crystal molecules undergo a full 360° twist. The helical pitch (p) can change, for example, when the temperature is altered or when other molecules are added to the liquid crystal host (an achiral liquid host material can form a chiral phase when doped with a chiral material), allowing the helical pitch (p) of a given material to be tailored accordingly. In some liquid crystal systems, the helical pitch is of the same order as the wavelength of visible light. As described herein, liquid crystals that exhibit chirality can also be described as having a twist angle or rotation angle (φ), which may refer, for example, to the relative azimuthal rotation between successive liquid crystal molecules in the layer normal direction, and a net twist angle or net rotation angle, which may refer, for example, to the relative azimuthal rotation between the top and bottom liquid crystal molecules across a defined length, e.g., the length of the chiral structure or the thickness of a liquid crystal layer.

[0153] 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 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 exhibiting spatially varying diffractive properties, e.g., gradient diffraction efficiency, can be fabricated.

[0154] As described herein, "polymerizable liquid crystal" may refer to a liquid crystal material that can be polymerized, e.g., photopolymerized in situ, and may be described herein as a reactive mesogen (RM).

[0155] It should be understood that the liquid crystal molecules may be polymerizable in some embodiments, and when polymerized, may form large-scale networks with other liquid crystal molecules. For example, the liquid crystal molecules may be linked by chemical bonds or by linking chemical species with other liquid crystal molecules. When 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.

[0156] According to certain embodiments described herein, photopolymerizable liquid crystal materials can be configured to form Bragg reflective structures, e.g., diffraction gratings, and their material properties, including birefringence, chirality, and ease for multiple coatings, can be exploited to create diffraction gratings with different material properties, e.g., birefringence, chirality, and thickness, which can result in different optical properties, e.g., diffraction efficiency, wavelength selectivity, and off-axis diffraction angle selectivity, to name a few.

[0157] 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). If 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 over the grating area, the grating can exhibit graded diffraction efficiency. Such an approach is described below with reference to the figures.

[0158] In the following, various embodiments of cholesteric liquid crystal gratings (CLCGs) optimized for various optical properties are described. Generally, a 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. In order to optimize certain optical properties, such as diffraction efficiency, for certain applications, such as internal coupling optical elements (1008, 1208 in Figs. 12A and 12B) or external coupling optical elements (1012, 1212 in Figs. 12A and 12B), various material properties of the CLC can be optimized, as described below.

[0159] As described above, the liquid crystal molecules of a cholesteric liquid crystal (CLC) layer in the chiral (nematic) or cholesteric phase are characterized by a plurality of liquid crystal molecules arranged to have a continuous azimuthal twist of the director as a function of position within the film in the normal or depth direction of the liquid crystal layer. Liquid crystal molecules arranged to have a continuous azimuthal twist as described herein are collectively referred to herein as a chiral structure. As described herein, the angle of azimuthal twist or rotation (φ) is described as the angle between the directors of the liquid crystal molecules relative to a direction parallel to the layer normal, as described above. The spatially varying directors of the liquid crystal molecules of the chiral structure can be described as forming a helical pattern, and the helical pitch (p) is defined as the distance the director rotates 360° (e.g., in the layer normal direction of the liquid crystal layer), as described above. As described herein, a CLC layer configured as a diffraction grating has a lateral dimension whereby the molecular structure of the liquid crystal repeats periodically in a lateral direction normal to the depth direction. This periodicity in the lateral direction is called the grating period (Λ).

[0160] According to various embodiments described herein, a diffraction grating comprises a cholesteric liquid crystal (CLC) layer comprising a plurality of chiral structures, each chiral structure extending in a layer depth direction by at least a helical pitch and comprising a plurality of liquid crystal molecules rotated successively in a first rotation direction. The helical pitch is a length in the layer depth direction corresponding to a net rotation angle of the liquid crystal molecules of the chiral structures through one turn in the first rotation direction. The alignment of the liquid crystal molecules of the chiral structures varies periodically in a lateral direction perpendicular to the layer depth direction.

[0161] Without being bound by any theory, under the Bragg reflection condition, the wavelength of incident light (λ) can be proportional to the average or representative refractive index (n) and helical pitch (p) of the CLC layer, and under some circumstances can be expressed as satisfying the following condition:

number

[0162] In addition, the bandwidth of the Bragg reflection wavelengths (Δλ) may be proportional to the birefringence Δn (e.g., the difference in refractive index between different polarizations of light) and the helical pitch (p) of the CLC layer, and under some circumstances may be expressed as satisfying the following condition: Δλ=Δn p [3]

[0163] In various embodiments described herein, the bandwidth Δλ is about 60 nm, about 80 nm, or about 100 nm.

[0164] According to various embodiments, the peak reflectance intensity within the visible wavelength range, for example, from about 390 nm to about 700 nm, or within the near infrared wavelength range, for example, from about 700 nm to about 2500 nm, can be greater than about 60%, about 70%, about 80%, or about 90%. Additionally, according to various embodiments, the full width at half maximum (FWHM) can be less than about 100 nm, less than about 70 nm, less than about 50 nm, or less than about 20 nm.

[0165] 15 illustrates a cross-sectional side view of a CLC layer 1158 configured for high bandwidth of reflection at off-axis angles of incidence for light incident on a display device similar to that illustrated with respect to FIGS. 12A and 12B above, for example, α1 within off-axis angles Δα1 or α2 within Δα2, according to an embodiment. As described herein, an off-axis angle of incidence is an angle of incidence θ of an incident beam 1216 with respect to the direction of the layer normal (e.g., the z-direction in FIG. 12) that has a non-zero value and results in a Bragg-reflected beam 1220 at a reflection angle θ. inc In some circumstances, the reflection angle can be varied to a limited extent by varying λ / Λ. Without being limited by any theory, in some circumstances, the off-axis reflection can be explained based on the following relationship: n sin(θ) = λ / Λ + sin(θ) inc ) [4] In the formula, θ incwhere θ is the angle of incidence relative to the direction of the layer normal, θ is the angle of reflection relative to the direction of the layer normal, and n is the reflectivity of the medium through which the reflected beam propagates. When the CLC layer 1158 is illuminated at an off-axis angle with the incident beam 1216, the reflection spectrum can be shifted towards shorter wavelengths. According to various embodiments disclosed herein, the ratio λ / Λ can have a value of 0.5-0.8, 0.6-0.9, 0.7-1.0, 0.8-1.1, 0.9-1.2, 1.0-1.6, 1.1-1.5, or 1.2-1.4.

[0166] Without being bound by any theory, the off-axis angles at which the CLC layer 1158 is configured to Bragg reflect with high efficiency may also depend on the helical pitch p of the chiral structure.

[0167] 16A and 16B illustrate cross-sectional side views of a CLC layer configured for reflection at an off-axis incidence angle, e.g., α1 within off-axis angles Δα1 or α2 within Δα2, for light incident on a display device similar to that illustrated with respect to FIGS. 12A and 12B above, according to an embodiment. Referring to FIG. 16A, a first cholesteric liquid crystal (CLC) layer 1358A comprises a first plurality of chiral structures having a first helical pitch (p1). The first CLC layer 1358A is configured such that a first incident light beam 1316A is incident at a first off-axis angle θ inc,1 , the first helical pitch p1 is such that the Bragg reflection is maximized when the first helical pitch p1 is directed to the incident surface of the CLC layer 1358A, and the first off-axis angle θ inc,1 results in a first reflected light beam 1320A at a first reflection angle θ1. As shown, the CLC layer 1358A is further configured to have a first range 1324A of off-axis incidence angles, which may correspond to Δα1 or Δα2 for light incident on the display device 1200 illustrated with respect to FIGS. 12A and 12B above, where a relatively high diffraction efficiency may be obtained. The first range 1324A may correspond to a range of off-axis incidence angles outside of which the intensity of the first reflected light beam 1320A drops off, for example, by more than 1 / e. For example, the first range 1324A may correspond to a range of off-axis incidence angles outside of which the intensity of the first reflected light beam 1320A drops off, for example, by more than 1 / e. inc,1±3°, θ inc,1 ±5°, θ inc,1 ±7°, θ inc,1 ±10°, or θ inc,1 It can have a value of ±20°.

[0168] Referring to FIG. 16B, the second cholesteric liquid crystal (CLC) layer 1358B is different from the first CLC layer 1358A and has a second plurality of chiral structures having a second helical pitch (p2) different from the first helical pitch p1 of the first CLC layer 1358A in FIG. 16A.

[0169] As shown, the second CLC layer 1358B is configured to reflect the second incident light beam 1316B at a first off-axis angle θ inc1 A second off-axis angle θ inc,2 16A , such that when directed at the incident surface of the CLC layer 1358B, a second reflected light beam 1320B is generated having a second reflection angle θ2 that is different from the first reflection angle θ1. As shown, the CLC layer 1358B is further configured to have a second range of off-axis angles 1324B similar to the first range 1324A described above with respect to FIG.

[0170] As described above, for various applications including incoupling and outcoupling of light, the waveguide device can be configured to propagate light by total internal reflection (TIR). FIG. 17 illustrates an example of an optical waveguide device 1600 comprising a waveguide 1604 coupled to a CLCG 1150. The waveguide device 1600 may correspond to the display device 1000 described above with respect to FIG. 10, for example, where the waveguide 1604 corresponds to the waveguide 1004 and the CLCG 1150 corresponds to the diffraction grating 1008. The CLCG 1150 comprises liquid crystal molecules arranged in a plurality of chiral structures, as described above. The waveguide 1604 is disposed above the CLCG 1150 and is optically coupled to the CLCG 1150. When the elliptically / circularly polarized incident light 1016-R / L has a polarization handedness that matches the rotation direction of the chiral structured liquid crystal molecules, the incident light 1016-R / L is Bragg reflected by the CLCG 1150 and coupled into the waveguide 1604 by total internal reflection (TIR) ​​at an angle such that the coupled light travels in a lateral direction (e.g., x-direction). Without being bound by any theory, the TIR condition is: C In some circumstances, the TIR condition may be expressed as: sin(θ C )=1 / n t [5] In the formula, n t is the refractive index of the waveguide 1604. According to various embodiments, n t can be from about 1 to about 2, from about 1.4 to about 1.8, or from about 1.5 to about 1.7. For example, the waveguide can comprise a polymer, such as polycarbonate, or glass.

[0171] FIG. 18A shows a first CLCG 1750A coupled to a first CLCG 1750B, where θ>θ c317 illustrates a first optical guiding device 1700A comprising a first waveguide 1704A configured to propagate light having a third wavelength λ3 by total internal reflection (TIR) ​​when λ3=λ3 / ... According to some other embodiments, the first waveguiding device 1700A may be configured to propagate light in the infrared spectrum (e.g., the near infrared portion of the spectrum with wavelengths between about 700 nm and 1400 nm) by TIR. As explained above, Bragg reflection occurs at wavelengths expressed by equation [2] above and within a bandwidth of wavelength Δλ expressed by equation [3] above. For example, the first CLCG 1750A may be designed to couple, by TIR, a third incident light 1736 having one of blue (e.g., about 450 nm), green (e.g., about 550 nm), red (e.g., about 650 nm), or a third wavelength λ3 in the infrared. As shown, the first and second lights 1716 and 1726 having first and second wavelengths λ1, λ2 are substantially transmitted when Δλ is about 60 nm, about 80 nm, or about 100 nm, as explained above. Because equation [2] is not satisfied for these colors, they will not be coupled into the first waveguide 1704 because equation [5] is not satisfied.

[0172] 18B illustrates a second optical guiding device 1700B in combination with the first optical guiding device 1700A illustrated with respect to FIG. 18A above. The optical guiding device 1700B is disposed in an optical path following the optical guiding device 1700A and is coupled to a second CLCG 1750B, and has a wavelength of θ>θ c2and a second waveguide 1704B configured to propagate a second light 1726 having a second wavelength λ2 by total internal reflection (TIR) ​​when λ1, λ2 ... Of the first and second lights 1716 and 1726 transmitted, the second CLCG 1750B has a wavelength of θ>θ c2 When Δλ is about 60 nm, about 80 nm, or about 100 nm, as described above, the first light 1716 having the first wavelength λ1 is substantially transmitted further through the second waveguide device 1700B.

[0173] 18C illustrates a third optical guiding device 1700C in combination with the first and second optical guiding devices 1700A and 1700B illustrated with respect to FIG. 18B above. The third optical guiding device 1700C is disposed in an optical path following the first and second optical guiding devices 1700A and 1700B and is coupled to a third CLCG 1750C and is coupled by total internal reflection (TIR) ​​to a third CLCG 1750C such that θ>θ c1and a third waveguide 1704C configured to propagate a first light 1716 having a first wavelength λ2 when λ1 = λ1 / λ2 / λ2 / λ1 ...2 / λ1 / λ2 / λ1 / λ2 / λ1 / λ2 / λ1 / λ2 / λ1 / λ2 / λ2 / λ1 / λ2 / λ1 / λ2 / λ1 / λ2 / λ2 / λ1 / λ2 / λ1 / λ2 / λ2 / λ1 / λ2 / λ1 / λ2 / λ1 / λ2 / λ2 / λ1 / λ2 / λ1 / λ2 / λ2 / λ1 / λ2 / λ1 / λ2 / λ2 / λ1 / λ2 / λ1 / λ2 / λ2 / λ1 / λ2 / λ1 / λ2 / λ2 / λ1 / λ2 / λ2 / λ1 / λ2 / λ2 / λ1 / λ2 / λ2 / λ1 / λ2 / λ1 / λ2 / λ2 / λ1 / λ2 / λ2 / λ1 / λ The third CLCG1750C is θ>θ c1 , the third waveguide 1704C may be designed to couple a first incident light 1716 having a first wavelength λ1 within a transmitted one of blue (e.g., about 450 nm), green (e.g., about 550 nm), red (e.g., about 650 nm), or infrared, by the TIR. Thus, as shown, when Δλ is about 60 nm, about 80 nm, or about 100 nm, as described above, the first light 1716 having the first wavelength λ1 is substantially coupled into the third waveguide 1704C because equation [5] is satisfied.

[0174] Thus, as described above with respect to Figures 18A-18C, by placing one or more of the first, second, and third optical wave-guiding devices 1700A, 1700B, and 1700C within the same optical path, one or more of the first, second, and third lights 1716, 1726, and 1736 having different wavelengths λ1, λ2, and λ3 can be coupled by TIR to propagate within one of the first, second, and third waveguides 1704A, 1704B, and 1704C, respectively. In each of Figures 18A-18C, each of the first to third optical wave-guiding devices 1704A, 1704B, and 1704C has a dedicated first to third waveguide 1704A, 1704B, and 1704C, respectively, and a dedicated first to third CLCG 1750A, 1750B, and 1750C, respectively, but the embodiments are not so limited. For example, a single waveguide can combine light Bragg reflected from a stack of multiple CLCGs by TIR. In addition, any suitable number of optical wave-guiding devices greater than three (or less than two) can be combined for further selective combination by Bragg reflection.

[0175] As described above with respect to Figures 18A-18C, the first to third CLCGs 1750A, 1750B, 1750C have first to third periods Λ1, Λ2, and Λ3, respectively, and first to third helical pitches p1, p2, and p3, respectively. In various embodiments, each of the CLCGs can be configured such that the wavelength / period ratio λ / Λ is about 0.3 to 2.3, about 0.8 to 1.8, or about 1.1 to about 1.5, e.g., about 1.3. Alternatively, the period (Λ) can be configured to be about 1 nm to 250 nm less, about 50 nm to 200 nm less, or about 80 nm to 170 nm less than the respective wavelengths (λ) at which the CLCGs are configured for Bragg reflection. For example, when λ1, λ2, and λ3 are within the visible range, e.g., about 620 nm to about 780 nm, e.g., about 650 nm (red), about 492 nm to about 577 nm, e.g., about 550 nm (green), and about 435 nm to about 493 nm, e.g., about 450 nm (blue), the corresponding periods Λ1, Λ2, and Λ3 can be about 450 nm to about 550 nm, e.g., about 500 nm, about 373 nm to about 473 nm, e.g., about 423 nm, and about 296 nm to about 396 nm, e.g., about 346 nm, respectively. Alternatively, when λ1, λ2, and λ3 are within the infrared range, e.g., the near infrared range, about 750 nm to about 1400 nm, e.g., about 850 nm, the corresponding periods Λ1, Λ2, and Λ3 can be about 975 nm to about 1820 nm, e.g., about 1105 nm. In various additional embodiments, each of the CLCGs can be configured such that the wavelength / helical pitch ratio λ / p is about 0.6 to 2.6, about 1.1 to 2.1, or about 1.4 to about 1.8, e.g., about 1.6. Alternatively, the helical pitch (p) can be configured to be about 50 nm to 350 nm smaller, about 100 nm to 300 nm smaller, or about 140 nm to 280 nm smaller than the respective wavelengths (λ) at which the CLCGs are configured for Bragg reflection.For example, when λ1, λ2, and λ3 are about 620 nm to about 780 nm, for example, about 650 nm (red), about 492 nm to about 577 nm, for example, 550 nm (green), and about 435 nm to about 493 nm, for example, about 450 nm (blue), the corresponding helical pitches p1, p2, and p3 can be about 350 nm to about 450 nm, for example, about 400 nm, about 290 nm to about 390 nm, for example, about 340 nm, and about 230 nm to about 330 nm, for example, about 280 nm, respectively. Alternatively, when λ1, λ2, and λ3 are in the infrared range, e.g., the near infrared range from about 750 nm to about 1400 nm, e.g., about 850 nm, the corresponding periods Λ1, Λ2, and Λ3 can be from about 1200 nm to about 2240 nm, e.g., about 1360 nm. (Additional Aspects)

[0176] In a first example, the optical device comprises a plurality of waveguides formed on one another and having respective diffraction gratings formed thereon, each diffraction grating configured to diffract visible light incident thereon into a respective waveguide such that the visible light diffracted into the respective waveguide propagates therein. Each diffraction grating is configured to diffract visible light within a respective field of view (FOV) relative to a layer normal direction of the respective waveguide into the respective waveguide. The respective FOVs are such that the plurality of waveguides are contiguous and configured to diffract visible light within a combined FOV that is greater than each of the respective FOVs.

[0177] In a second example, in the optical device of the first example, the plurality of waveguides are arranged such that the refractive index of each waveguide is such that visible light diffracted into the waveguide propagates therein under total internal reflection. Each is formed from a material less than the effective refractive index of the diffraction grating.

[0178] In a third example, in the optical device of the first or second example, the multiple waveguides are in a stacked arrangement and configured to propagate visible light in substantially parallel directions under total internal reflection.

[0179] In a fourth example, in the optical devices of the first to third examples, different ones of the respective diffraction gratings are arranged to overlap each other in a lateral direction perpendicular to the layer normal direction.

[0180] In a fifth example, in any one of the optical devices in the first to fourth examples, the different ones of the respective FOVs do not overlap by more than 20% based on the sum of the different ones of the respective FOVs.

[0181] In a sixth example, in the optical device of any one of the first to fifth examples, the plurality of waveguides includes a first waveguide having a first diffraction grating formed thereon configured to partially diffract and partially transmit visible light incident thereon, and a second waveguide having a second diffraction grating formed thereon configured to at least partially diffract transmitted visible light from the first diffraction grating incident thereon.

[0182] In a seventh example, in the optical device of the sixth example, the first and second diffraction gratings have different periods and are configured to diffract visible light having different wavelengths but the same color.

[0183] In an eighth example, in the optical device of the sixth example, the first and second diffraction gratings have substantially the same period and are configured to diffract visible light having substantially the same wavelength.

[0184] In a ninth example, in the optical device of the sixth example, the first and second diffraction gratings have different periods and are configured to diffract visible light having different wavelengths and different colors.

[0185] In a tenth example, in the optical device of the ninth example, the first diffraction grating has a first period and is configured to diffract visible light having a first color, and the second grating has a second period and is configured to diffract visible light having the first color and visible light having a second color.

[0186] In an eleventh example, in the optical device of the tenth example, the first color corresponds to a shorter wavelength compared to the second color.

[0187] In a twelfth example, in the optical device of the tenth or eleventh examples, the first diffraction grating is configured to partially diffract visible light having a first color incident thereon in the first FOV and partially transmit visible light having the first color incident thereon in the second FOV, and the second diffraction grating is configured to at least partially diffract the visible light having the first color that is partially transmitted through the first diffraction grating.

[0188] In a thirteenth example, in the optical device of the twelfth example, the first diffraction grating is configured to substantially transmit visible light having a second color, and the second diffraction grating is configured to at least partially diffract incident visible light having the second color within the first FOV.

[0189] In a fourteenth example, in the optical device of the thirteenth example, the optical device further comprises a third waveguide having a third diffraction grating formed thereon having a third period and configured to diffract visible light having a third color, the second color corresponding to a shorter wavelength compared to the third color.

[0190] In a fifteenth example, in the optical device of the fourteenth example, the second diffraction grating is configured to at least partially transmit visible light having a second color, and the third diffraction grating is configured to receive and at least partially diffract the partially transmitted visible light having the second color from the second diffraction grating within the second FOV.

[0191] In a sixteenth example, in the optical device of the fifteenth example, the first and second diffraction gratings are configured to substantially transmit visible light having a third color, and the third diffraction grating is configured to at least partially diffract the visible light having the third color that is transmitted through the first and second diffraction gratings within the first FOV.

[0192] In a seventeenth example, the optical system includes a first waveguide having a first diffraction grating formed thereon. The first diffraction grating has a first period and is configured to diffract light having a first color within a first FOV that is incident on the first waveguide. The optical system additionally includes a second waveguide having a second diffraction grating formed thereon. The second diffraction grating has a second period and is configured to diffract light having a first color within a second FOV that is incident on the second waveguide. The first and second diffraction gratings are configured to diffract light having the first color within a respective field of view (FOV) relative to a layer normal direction of the respective waveguide into the respective waveguide. The respective FOVs are such that the first and second waveguides are contiguous and configured to diffract visible light having the first color within a combined FOV that is greater than each of the first and second FOVs.

[0193] In an eighteenth example, in the optical system of the seventeenth example, the first waveguide and the second waveguide are in a stacked configuration, the first waveguide is configured to receive light having a first color prior to the second waveguide, and the first period is shorter than the second period.

[0194] In a 19th example, in the optical system of the 18th example, the second diffraction grating is configured to diffract light having the first color within the second FOV after it is substantially transmitted through the first diffraction grating without substantially diffraction.

[0195] In a twentieth example, in the optical system of the nineteenth example, the first diffraction grating is configured to substantially transmit light having a second color therethrough without substantially diffracting the light having the second color, the light having a longer wavelength compared to the light having the first color.

[0196] In a twenty-first example, in the optical system of the twentieth example, the second diffraction grating is configured to diffract light having a second color within a second FOV to be guided into the waveguide.

[0197] In a twenty-second example, in the optical system of the seventeenth example, each of the first and second diffraction gratings includes a cholesteric liquid crystal (CLC) layer.

[0198] In a twenty-third example, in the optical system of the twentieth example, the CLC layer comprises a plurality of chiral structures, each chiral structure extending in a layer depth direction by at least a helical pitch and comprising a plurality of liquid crystal molecules rotated successively in a first rotation direction. The helical pitch is a length in the layer depth direction that corresponds to a net rotation angle of the liquid crystal molecules of the chiral structure by one rotation in the first rotation direction. The alignment of the liquid crystal molecules of the chiral structure varies periodically in a lateral direction perpendicular to the layer depth direction.

[0199] In a twenty-fourth example, in the optical system of the twentieth example, each chiral structure comprises at least three calamitic liquid crystal molecules elongated along different elongation directions.

[0200] In a twenty-fifth example, the display device comprises a first waveguide having a first diffraction grating formed thereon comprising liquid crystal, the first diffraction grating configured to diffract a portion of light having a first color incident thereon into the first waveguide. The first diffraction grating is additionally configured to pass a portion of light having the first color incident thereon. The first diffraction grating is further configured to pass light having a second color. The display device additionally comprises a second waveguide having a second diffraction grating formed thereon comprising liquid crystal, the second diffraction grating configured to diffract light having the second color into the second waveguide. The second diffraction grating is further configured to diffract a portion of the light having the first color that passed through the first diffraction grating.

[0201] In a 26th example, in the display device of the 25th example, the first diffraction grating is configured to diffract light having a first color within a first range of incidence angles relative to the layer normal, and the first diffraction grating is configured to pass light having the first color within a second range of incidence angles relative to the layer normal.

[0202] In a 27th example, in the display device of the 26th example, the second diffraction grating is configured to diffract light having a second color incident thereon within a first angle range, and the second diffraction grating is configured to diffract light having a first color incident thereon within a second incident angle range.

[0203] In a twenty-eighth example, in the display device of the twenty-seventh example, the first angle range and the second angle range do not overlap by more than 20% based on the sum of the first angle range and the second angle range.

[0204] In a twenty-ninth example, in the display device of any one of the twenty-fifth to twenty-eighth examples, the first color corresponds to a shorter wavelength as compared to the second color.

[0205] In a 30th example, in a display device of any one of the 25th to 29th examples, the first diffraction grating comprises periodically varying liquid crystals arranged to have a first period in the lateral direction, and the second diffraction grating comprises periodically varying liquid crystals arranged to have a second period in the lateral direction that is greater than the first period.

[0206] In a thirty-first example, in the display device of the thirty-first example, one or both of the first diffraction grating and the second diffraction grating are configured to diffract light having a wavelength; It has a period in the lateral direction such that the wavelength / period ratio (λ / Λ) is about 0.3 to 2.3.

[0207] In a thirty-second example, in the display device of the thirty-first example, one or both of the first diffraction grating and the second diffraction grating are configured to diffract light having a wavelength and have a period that is between 1 nm and 250 nm smaller than the wavelength.

[0208] In a thirty-third example, in the display device of any one of the twenty-fifth to thirty-second examples, the liquid crystal comprises a cholesteric liquid crystal.

[0209] In a thirty-fourth example, in the display device of the thirty-third example, the liquid crystal of the first diffraction grating has a smaller helical pitch than that of the liquid crystal of the second diffraction grating.

[0210] In a thirty-fifth example, in the display device of any one of the twenty-fifth to thirty-fourth examples, one or both of the first diffraction grating and the second diffraction grating are configured to transparently diffract light into their respective waveguides.

[0211] In a 36th example, in the display device of any one of the 25th to 34th examples, one or both of the first diffraction grating and the second diffraction grating are configured to reflectively diffract light into their respective waveguides.

[0212] In a thirty-seventh example, in any one display device of the twenty-fifth to thirty-sixth examples, the first color is green and the second color is red.

[0213] In a thirty-eighth example, in the display device of any one of the twenty-fifth to thirty-sixth examples, the first color is blue and the second color is green.

[0214] In a thirty-ninth example, the head mounted display device is configured to project light to the 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 additionally includes a display disposed on the frame. At least a portion of the display includes a plurality of waveguides. The waveguides are transparent and positioned at a location in front of the user's eye when the user wears the head mounted display device 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. The display further includes one or more light sources and a plurality of diffraction gratings in the display configured to couple light from the light sources into the waveguides in the display. The waveguides and diffraction gratings in the display include the waveguides and diffraction gratings of any one of the first to thirty-eighth examples.

[0215] In a fortieth example, in the device of the thirty ninth example, the one or more light sources include a fiber scanning projector.

[0216] In a forty-first example, in the thirty-ninth or fortieth example, 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. (Additional Considerations)

[0217] 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 will 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.

[0218] Unless the context clearly requires otherwise, throughout the description and claims, the words "comprising," "comprising," "including," "including," and the like, should be construed 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 connected 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 connected 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, the word encompasses 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 one or more of the items in the list. Additionally, the articles "a," "an," and "the," as used in this application and the appended claims, shall be interpreted to mean "one or more" or "at least one," unless otherwise specified.

[0219] As used herein, a phrase referring to a list of items "at least one of" refers to any combination of those items, including single elements. As an example, "at least one of A, B, or C" is intended to cover A, B, C, A and B, A and C, B and C, and A, B, and C. Transitive phrases such as "at least one of X, Y, and Z" are generally understood differently in the context in which they are used to convey that an item, term, etc. may be at least one of X, Y, or Z, unless specifically stated otherwise. Thus, such transitive phrases are generally not intended to suggest that an embodiment requires that each of at least one of X, at least one of Y, and at least one of Z be present.

[0220] 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.

[0221] 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 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 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, sub-divided, 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 one another or may be combined in various ways. No element or combination of elements is necessary or essential for all embodiments. All suitable combinations and sub-combinations of features of the present disclosure are intended to be within the scope of the present disclosure.

Claims

1. 1. A display device, comprising: the display device comprises a first waveguide and a second waveguide; the first waveguide having a first diffraction grating formed thereon, the first diffraction grating comprising a liquid crystal; The first diffraction grating comprises: diffracting a portion of light having a first color incident on the first diffraction grating into the first waveguide; passing a portion of the light having the first color incident on the first diffraction grating; passing light having a second color; The device is configured to: the second waveguide having a second diffraction grating formed thereon, the second diffraction grating comprising a liquid crystal; The second diffraction grating comprises: diffracting the light having the second color into the second waveguide; diffracting a portion of the light having the first color that passes through the first diffraction grating into the second waveguide; The device is configured to: the first diffraction grating is configured to diffract the light having the first color within a first range of angles of incidence relative to a layer normal, and the first diffraction grating is configured to pass the light having the first color within a second range of angles of incidence relative to the layer normal; The second diffraction grating is configured to diffract the light having the first color that is incident on the second diffraction grating within the second range of angles of incidence.

2. 10. The display device of claim 1 , wherein the second diffraction grating is configured to diffract the light having the second color that is incident on the second diffraction grating within the first range of angles of incidence.

3. 2. The display device of claim 1, wherein the portion of the first incidence angle range and the portion of the second incidence angle range that overlap with each other is less than 20% of the sum of the first incidence angle range and the second incidence angle range.

4. The display device of claim 1 , wherein the first color corresponds to a shorter wavelength compared to the second color.

5. 2. The display device of claim 1, wherein the first diffraction grating comprises periodically varying liquid crystals arranged in a lateral direction with a first period Λ1, and the second diffraction grating comprises periodically varying liquid crystals arranged in the lateral direction with a second period Λ2 that is greater than the first period Λ1.

6. 6. The display device of claim 5, wherein one or both of the first and second diffraction gratings are configured to diffract light having a wavelength λ and have a lateral period (Λ1, Λ2) such that the wavelength / period ratio (λ / Λ1, λ / Λ2) is between 0.3 and 2.

3.

7. 6. The display device of claim 5, wherein one or both of the first and second diffraction gratings are configured to diffract light having a wavelength λ and have a period (Λ 1 , Λ 2 ) such that the period is less than the diffracted wavelength λ by 1 nm to 250 nm.

8. 10. The display device of claim 1, wherein the liquid crystal comprises a cholesteric liquid crystal.

9. 9. The display device of claim 8, wherein the liquid crystal of the first diffraction grating has a helical pitch that is smaller than the helical pitch of the liquid crystal of the second diffraction grating.

10. 10. The display device of claim 1, wherein one or both of the first and second diffraction gratings are configured to transparently diffract light into a respective waveguide.

11. 10. The display device of claim 1, wherein one or both of the first and second diffraction gratings are configured to reflectively diffract light into a respective waveguide.

12. 10. The display device of claim 1, wherein the first color is green and the second color is red.

13. 10. The display device of claim 1, wherein the first color is blue and the second color is green.

14. 1. A head mounted display device configured to display augmented reality image content by projecting light to a user's eye, the head mounted display device comprising: a frame configured to be supported on a head of the user; and a display disposed on the frame; Equipped with at least a portion of the display comprises a plurality of waveguides, the plurality of waveguides being transparent, the plurality of waveguides being positioned at a location in front of an eye of the user when the user wears the head mounted display device, the plurality of waveguides providing a view of the portion of the environment in front of the user by transmitting light from the portion of the environment in front of the user to the user's eye, the display further comprising one or more light sources and a plurality of diffraction gratings in the display, the plurality of diffraction gratings being configured to couple light from the light sources into the plurality of waveguides in the display; A head mounted display device, wherein the display comprises the display device of claim 1 .

15. The head mounted display device of claim 14 , wherein the one or more light sources comprise a fiber scanning projector.

16. 15. The head mounted display device of claim 14, wherein the display is configured to present image content to the user at multiple depth planes by projecting light into the user's eyes.

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