Polarization insensitive diffraction grating and display including same

Abstract

A polarization insensitive grating and a display including the same are disclosed.

Description

[0001] Cross - reference to related applications

[0002] This application claims the benefit of priority of Provisional Application No. 63 / 423,286, filed on November 7, 2022, entitled "Polarization - Insensitive Diffraction Gratings and Displays Incorporating the Same", the content of which is hereby incorporated by reference. Technical Field

[0003] The present disclosure relates to display systems, and more particularly, to augmented and virtual reality display systems and input - coupling gratings (ICGs) or output - coupling gratings for use therewith. Background Art

[0004] 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 way that appears to be real or can be perceived as real. Virtual reality or "VR" scenarios typically involve the presentation of digital or virtual image information in a manner that is opaque to other actual real - world visual inputs; augmented reality or "AR" scenarios typically involve the presentation of digital or virtual image information as an augmentation of the visualization of the user's surrounding real world. Mixed reality or "MR" scenarios are a type of AR scenario and typically involve virtual objects integrated into the natural world and responsive to the natural world. For example, in an MR scenario, AR image content can be occluded by objects in the real world or perceived as interacting with objects in the real world.

[0005] Reference Figure 1 , shows an augmented reality scenario 10, in which a user of AR technology sees a real - world park - like setting 20, which features people, trees, buildings in the background, and a concrete platform 30. In addition to these items, the user of AR technology also perceives that he "sees" "virtual content", such as a robotic statue 40 standing on the real - world platform 30, and a flying cartoon - like avatar character 50, which appears to be an avatar of a bumblebee, even though these elements 40, 50 do not exist in the real world. Since the human visual perception system is complex, it is extremely challenging to develop AR technologies that facilitate the comfortable, natural, and rich presentation of virtual image elements among other virtual or real - world image elements.

[0006] The systems and methods disclosed herein address various challenges associated with AR and VR technologies. Summary of the Invention

[0007] Describes grating structures suitable for use as input coupling gratings (ICGs) for coupling light into waveguides. These grating structures are substantially polarization-insensitive, have low back-reflection, and allow operation over a wide input angle range. Such grating structures can be used in inline alignment configurations, in which the ICGs for multiple stacked waveguides are aligned along a common optical path. Such ICGs are particularly useful for head-mounted displays using micro-LED (μLED) light projection systems, which can emit unpolarized light over a wide angular range.

[0008] Examples of grating structures include asymmetric blazed gratings formed of and / or coated with a high refractive index material such as titanium dioxide, gallium phosphide, silicon carbide, and others. Such a high refractive index layer can provide a grating structure with relatively low optical losses. However, due to the high refractive index film, the reflected light can be quite significant (e.g., >10% for some incident angles), and undesired back-reflection coupling and ghosting in the virtual image, reduced contrast, etc. can be undesirable outcomes. Reducing such back-reflection causes more light to diffract and couple in the waveguide in the correct order by TIR, so the benefit of reduced reflection outweighs the possible benefit of light recycling from the reflection.

[0009] The grating structures described herein have low reflection and high diffraction efficiency in both TE and TM polarization modes. Such optical performance can enable an overall eyepiece efficiency per watt of energy used by a projector (e.g., a μLED projection system), e.g., the projector uses unpolarized light and ideally operates with reduced back-reflection from the grating structure into the lens of the projection system. Such grating structures can also be well-suited for single active layer architectures, in which all colors (e.g., R, G, B) are waveguided in a single high refractive index active layer, but use a grating structure operating in transmission mode to harness the use of high diffraction efficiency in orthogonally polarized states, e.g., enabling the use of a μLED projection system.

[0010] Aspects of the disclosed subject matter are outlined below.

[0011] Generally, in a first aspect, the present disclosure features a head-mounted display system that includes: a head-wearable frame; a light projection system configured to output light to provide image content; a waveguide supported by the frame, the waveguide being configured to direct at least a portion of the light coupled into the waveguide from the light projection system; and a grating structure optically coupled to the waveguide, the grating structure being configured to couple light from the light projection system into the waveguide. The grating structure includes: a grating layer including a plurality of ridges having a blazed profile in at least one cross-section; and one or more dielectric layers disposed on the grating layer, wherein, for unpolarized incident light at at least one operating wavelength of the output light, within a field of view of 10° or greater (e.g., 15° or greater, 20° or greater, 22° or greater, 25° or greater, e.g., up to 45° or less, 40° or less, 35° or less, 30° or less, 25° or less, 22° or less) in at least one direction, the grating structure has an average emission efficiency of 40% or higher (e.g., 45% or higher, 50% or higher, 55% or higher, 60% or higher, 65% or higher, e.g., 75% or lower, 70% or lower, 65% or lower, 60% or lower, 55% or lower), and an average back reflection of 15% or lower (e.g., 12% or lower, 10% or lower, 9% or lower, 8% or lower, 7% or lower, 6% or lower, 5% or lower, 4% or lower, 3% or lower, e.g., 1% or higher, 2% or higher, 3% or higher).

[0012] Embodiments of the head-mounted display may include the following features and / or features of other aspects. For example, for unpolarized incident light at at least two operating wavelengths that are at least 100 nm apart in the output light, in a field of view of 10° or greater (e.g., 15° or greater, 20° or greater, 22° or greater, 25° or greater, e.g., up to 45° or less, 40° or less, 35° or less, 30° or less, 25° or less, 22° or less) in at least one direction, the grating structure may have an average emission efficiency of 40% or higher (e.g., 45% or higher, 50% or higher, 55% or higher, 60% or higher, 65% or higher, e.g., 75% or lower, 70% or lower, 65% or lower, 60% or lower, 55% or lower), and an average back reflection of 15% or lower (e.g., 12% or lower, 10% or lower, 9% or lower, 8% or lower, 7% or lower, 6% or lower, 5% or lower, 4% or lower, 3% or lower, e.g., 1% or higher, 2% or higher, 3% or higher). For unpolarized incident light at three operating wavelengths across a spectral range of 120 nm or wider (e.g., 150 nm or wider, 200 nm or wider, 250 nm or wider, e.g., 500 nm or narrower, 400 nm or narrower, 300 nm or narrower, 250 nm or narrower, e.g., from 400 nm to 800 nm, e.g., from 430 nm to 650 nm) in the output light, in a field of view of 10° or greater (e.g., 15° or greater, 20° or greater, 22° or greater, 25° or greater, e.g., up to 45° or less, 40° or less, 35° or less, 30° or less, 25° or less, 22° or less) in at least one direction, the grating structure may have an average emission efficiency of 40% or higher (e.g., 45% or higher, 50% or higher, 55% or higher, 60% or higher, 65% or higher, e.g., 75% or lower, 70% or lower, 65% or lower, 60% or lower, 55% or lower), and an average back reflection of 15% or lower (e.g., 12% or lower, 10% or lower, 9% or lower, 8% or lower, 7% or lower, 6% or lower, 5% or lower, 4% or lower, 3% or lower, e.g., 1% or higher, 2% or higher, 3% or higher). These three wavelengths may be a blue wavelength, a green wavelength, and a red wavelength. In some examples, these three wavelengths are 465 nm, 545 nm, and 625 nm respectively.

[0013] The field of view may be in orthogonal directions of 10° or greater (e.g., 15° or greater, 20° or greater, 22° or greater, 25° or greater, e.g., up to 45° or less, 40° or less, 35° or less, 30° or less, 25° or less, 22° or less). In certain examples, the field of view is 22° x 22° in orthogonal directions.

[0014] The grating structure can be a reflective grating structure or a transmissive grating structure. The plurality of ridges can be tilted ridges.

[0015] The grating structure can include a metal layer disposed on one or more dielectric layers.

[0016] One or more dielectric layers can include at least one continuous layer.

[0017] In some examples, one or more dielectric layers include at least one discontinuous layer.

[0018] One or more dielectric layers can include a first dielectric layer disposed directly on the grating layer and a second dielectric layer disposed directly on the first dielectric layer, the refractive index of the first dielectric layer at the operating wavelength being greater than the refractive index of the grating layer and the refractive index of the second dielectric layer.

[0019] One or more dielectric layers can include a layer having a thickness in the range of 50 nm to 150 nm (e.g., 75 nm to 125 nm, 80 nm to 100 nm, 85 nm to 95 nm).

[0020] One or more dielectric layers can include a first layer having a thickness in the range of 30 nm to 100 nm (e.g., 40 nm to 80 nm, 50 nm to 70 nm) and a second layer having a thickness in the range of 30 nm to 100 nm (e.g., 40 nm to 80 nm, 50 nm to 70 nm).

[0021] The plurality of ridges can have a pitch in the range of 200 nm to 500 nm (e.g., 250 nm to 450 nm, 300 nm to 400 nm, 325 nm to 375 nm, 350 nm to 370 nm).

[0022] The plurality of ridges can have a top width in the range of 50 nm to 150 nm (e.g., 60 nm to 140 nm, 70 nm to 130 nm, 80 nm to 100 nm).

[0023] The plurality of ridges can have a bottom width in the range of 10 nm to 150 nm (e.g., 20 nm to 120 nm, 50 nm to 100 nm).

[0024] The plurality of ridges have a blaze angle in the range of 20° to 50° (e.g., 25° to 45°, 30° to 40°). The plurality of ridges can have an anti-blaze angle in the range of 75° to 150° (e.g., 80° to 140°, 85° to 130°, 90° to 120°, 90° to 100°).

[0025] The emission efficiency of the grating structure can correspond to the first-order diffraction efficiency of the grating structure.

[0026] The grating structure can be a first grating structure, and the system can further include a second grating structure located on a side of the waveguide opposite to the first grating structure. The first grating structure can be a reflective grating structure, and the second grating structure can be a transmissive grating structure. The second grating structure can include a grating layer having a plurality of ridges and at least one dielectric layer supported by the grating layer.

[0027] The ridges can have a profile shape selected from trapezoidal, parallelogram, triangular, and stepped.

[0028] The grating can have a duty cycle in the range of 5% to 95% (e.g., 10% to 75%, 20% to 50%, 30% to 40%).

[0029] The grating material can include a crosslinked polymer (e.g., a thermally crosslinked or UV crosslinked polymer). The grating material can have a refractive index in the range of 1.5 to 1.8. The grating material can include nanoparticles (e.g., TiO2 nanoparticles or ZrO2 nanoparticles). The grating material can have a refractive index in the range of 1.5 to 2.1.

[0030] The waveguide can support a material film, and the ridges are etched into the film. The material can be an inorganic material. The material can have a refractive index in the range of 1.8 to 2.8. The material can have a refractive index in the range of 1.38 to 1.45. The refractive index of the material can be higher than the refractive index of the waveguide. The refractive index of the material can be lower than the refractive index of the waveguide.

[0031] The grating structure can be configured to couple light at a working wavelength corresponding to a plurality of different color pixels of the light projection system into the waveguide during operation.

[0032] The grating layer and the waveguide can be made of the same material, which can include a polymer. The refractive index of the polymer can be 1.75 or lower. The material can have a refractive index of 1.8 or higher (e.g., 1.9 or higher, 2.0 or higher, 2.1 or higher, e.g., 2.8 or lower, 2.7 or lower, 2.6 or lower, 2.5 or lower). The material can be a composite material (e.g., a composite material including nanoparticles).

[0033] The light from the light projection system can be unpolarized light.

[0034] The light projection system can include a micro-LED display, an LCoS display, or a laser beam scanner display.

[0035] The head mounted display may include one or more additional waveguides and one or more additional grating structures, each additional grating structure being associated with a respective one of the additional waveguides. The grating structures of each waveguide may be arranged in a serial configuration. At least one of the grating structures may be a reflective grating. The reflective grating may be the grating structure of the waveguide that is farthest from the light projection system.

[0036] The waveguide and the light projection system can be arranged relative to each other so that light from the projection system is incident on the grating structure from a non-normal direction relative to the waveguide surface. The light from the projection system can be incident on the grating structure at an angle of 1° to 20° (e.g., 3° ​​to 15°, 5° to 12°, 5° to 10°) relative to the surface normal of the waveguide.

[0037] In general, in another aspect, the disclosure features an article comprising: a waveguide layer; and a grating structure optically coupled to the waveguide, the grating structure configured to couple light from a light projection system into the waveguide. The grating structure comprises: a grating layer comprising a plurality of ridges having a blazed profile in at least one cross-section; and one or more dielectric layers disposed on the grating layer. The grating structure has a 40% or greater (e.g., 45% or greater, 50% or greater, 55% or greater) polarization performance over a field of view of 10° or greater (e.g., 15° or greater, 20° or greater, 22° or greater, 25° or greater, e.g., up to 45° or less, 40° or less, 35° or less, 30° or less, 25° or less, 22° or less) in at least one direction. , 60% or more, 65% or more, for example, 75% or less, 70% or less, 65% or less, 60% or less, 55% or less) an average transmission efficiency and an average back reflection of 15% or less (for example, 12% or less, 10% or less, 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, 3% or less, for example, 1% or more, 2% or more, 3% or more).

[0038] Implementations of the article may include one or more features of the aforementioned aspects.

[0039] Other features and advantages will be apparent from the accompanying drawings, the following description, and the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 An augmented reality (AR) view seen by a user through an AR device is shown.

[0041] Figure 2 A conventional display system for simulating a three-dimensional image for a user is shown.

[0042] Figures 3A to 3C Shows the relationship between the radius of curvature and the focal radius.

[0043] Figure 4A Shows a representation of the accommodation-vergence response of the human visual system.

[0044] Figure 4B Shows examples of different accommodation states and vergence states of a user's pair of eyes.

[0045] Figure 4C Shows an example of a top-view representation of a user viewing content via a display system.

[0046] Figure 4D Shows another example of a top-view representation of a user viewing content via a display system.

[0047] Figure 5 Shows aspects of a method for simulating a three-dimensional image by modifying wavefront divergence.

[0048] Figure 6 Shows an example of a waveguide stack for outputting image information to a user.

[0049] Figure 7 Shows an example of an outgoing light beam output from a waveguide.

[0050] Figure 8 Shows an example of a stacked waveguide assembly, where each depth plane includes an image formed using multiple different component colors.

[0051] Figure 9A Shows a cross-sectional side view of an example of a group of stacked waveguides each including a coupled-in optical element.

[0052] Figure 9B Shows Figure 9A a perspective view of an example of multiple stacked waveguides.

[0053] Figure 9C Shows Figure 9A and 9B a top-plan view of an example of multiple stacked waveguides.

[0054] Figure 9D Shows an example of a wearable display system.

[0055] Figure 10A Schematically shows a cross-sectional view of a portion of a waveguide on which a diffraction grating is provided, for example, for coupling light into the waveguide.

[0056] Figure 10BA cross-sectional view of a waveguide provided with a blazed diffraction grating thereon is shown, which shows the field of view (FOV) Δα of the waveguide.

[0057] Figure 11A A cross-sectional view of a partial grating structure is shown, in which the grating pattern is transferred from the resist layer to the substrate layer by dry etching.

[0058] Figure 11B is Figure 11A SEM micrograph of an exemplary grating structure formed in the manner shown.

[0059] Figure 12 Is a schematic cross-sectional view showing a single pitch length of a grating structure including a tilted grating having first and second coatings thereon.

[0060] Figures 13A - 13D Is a graph comparing the diffraction efficiency and reflectivity of exemplary grating structures including two coatings ( Figures 13A - 13B ) and one coating ( Figures 13C - 13D ), respectively.

[0061] Figures 14A - 14D Compares the results of the simulated diffraction efficiency ( Figure 14C ) and the measured diffraction efficiency ( Figure 14D ) for the grating structures shown for Figure 14A and Figure 14B , respectively.

[0062] Figure 15A Is a graph of the measured diffraction efficiency for an exemplary grating structure with a single coating.

[0063] Figure 15B Is Figure 15A A graph of the measured diffraction efficiency of the exemplary grating structure with a second coating shown in

[0064] Figure 15C Is for Figure 15A and Figure 15B A graph showing the variation of the measured reflectivity % with wavelength for the grating structures shown.

[0065] Figures 16A - 16F Is a graph and SEM micrograph comparing the diffraction efficiency as a function of angle for examples of tilted gratings without a coating ( Figures 16A - 16B ), with one coating ( Figures 16C - 16D ), and with two coatings ( Figures 16E - 16F ), respectively.

[0066] Figure 17A Is a graph showing the variation of the emission efficiency (percentage) with the polarization state for red, green, and blue wavelengths for a first example of transmitting ICG.

[0067] Figure 17BA graph showing the change of back reflection (percentage) with respect to the polarization state for red, green, and blue wavelengths, which shows the first example of transmitting ICG.

[0068] Figures 18A - 18C A graph showing the change of the reflection efficiency of the zero - order reflection, the transmission efficiency of the zero - order transmission, and the transmission efficiency of the first - order diffraction with respect to the incident angle for TM polarization, which shows the first example of transmitting ICG. Each graph shows the corresponding performance for red (625 nm), green (545 nm), and blue (465 nm) wavelengths.

[0069] Figures 18D - 18F A graph showing the change of the reflection efficiency of the zero - order reflection, the transmission efficiency of the zero - order transmission, and the transmission efficiency of the first - order diffraction with respect to the incident angle for TE polarization, which shows the first example of transmitting ICG. Each graph shows the corresponding performance for red (625 nm), green (545 nm), and blue (465 nm) wavelengths.

[0070] Figures 18G - 18I A graph showing the change of the reflection efficiency of the average zero - order reflection, the transmission efficiency of the zero - order transmission, and the transmission efficiency of the first - order diffraction with respect to the incident angle for TM and TE polarizations, which shows the first example of transmitting ICG. Each graph shows the corresponding performance for red (625 nm), green (545 nm), and blue (465 nm) wavelengths.

[0071] Figure 19A A graph showing the change of the emission efficiency (percentage) with respect to the polarization state for red, green, and blue wavelengths, which shows the second example of transmitting ICG.

[0072] Figure 19B A graph showing the change of the back reflection (percentage) with respect to the polarization state for red, green, and blue wavelengths, which shows the second example of transmitting ICG.

[0073] Figure 19C A schematic cross - sectional view of a part of the second example of transmitting ICG.

[0074] Figures 20A - 20C A graph showing the change of the reflection efficiency of the zero - order reflection, the transmission efficiency of the zero - order transmission, and the transmission efficiency of the first - order diffraction with respect to the incident angle for TM polarization, which shows the second example of transmitting ICG. Each graph shows the corresponding performance for red (625 nm), green (545 nm), and blue (465 nm) wavelengths.

[0075] Figures 20D - 20FA graph showing the reflectance efficiency of the zero - order reflection for TE polarization, the transmittance efficiency of the zero - order transmission, and the transmittance efficiency of the first - order diffraction of the second example of transmitting ICG as a function of the incident angle. Each graph shows the corresponding performance at wavelengths of red (625 nm), green (545 nm), and blue (465 nm).

[0076] Figures 20G - 20I A graph showing the reflectance efficiency of the average zero - order reflection, the transmittance efficiency of the zero - order transmission, and the transmittance efficiency of the first - order diffraction of the second example of transmitting ICG for TM and TE polarizations as a function of the incident angle. Each graph shows the corresponding performance at wavelengths of red (625 nm), green (545 nm), and blue (465 nm).

[0077] Figure 21A and 21B A graph showing the sensitivity analysis of the emission efficiency and the back - reflection performance of the dual - coated tilted ICG (first example) and the blazed ICG (second example) with respect to random design perturbations (+ / - 10 nm) of the grating parameters.

[0078] Figure 22 A schematic diagram showing the operation of the reflective ICG for a waveguide.

[0079] Figure 23 A schematic diagram showing the structural features of an example reflective ICG.

[0080] Figure 24A A graph showing the emission efficiency (percentage) of the first example of reflective ICG as a function of the polarization state for red, green, and blue wavelengths.

[0081] Figure 24B A graph showing the back - reflection (percentage) of the first example of reflective ICG as a function of the polarization state for red, green, and blue wavelengths.

[0082] Figures 25A - 25C A graph showing the reflectance efficiency of the - 1 diffraction order, the reflectance efficiency of the 0 diffraction order, and the transmittance efficiency of the +1 diffraction order of the first example of reflective ICG for TM polarization as a function of the incident angle. Each graph shows the corresponding performance at wavelengths of red (625 nm), green (545 nm), and blue (465 nm).

[0083] Figures 25D - 25F A graph showing the reflectance efficiency of the - 1 diffraction order, the reflectance efficiency of the 0 diffraction order, and the transmittance efficiency of the +1 diffraction order of the first example of reflective ICG for TE polarization as a function of the incident angle. Each graph shows the corresponding performance at wavelengths of red (625 nm), green (545 nm), and blue (465 nm).

[0084] Figures 25G - 25IIt is a graph showing the reflection efficiency of the -1 diffraction order, the reflection efficiency of the 0 diffraction order, and the transmission efficiency of the +1 diffraction order for TM and TE polarizations of the first example of reflective ICG as a function of the incident angle. Each graph shows the corresponding performance at wavelengths of red (625 nm), green (545 nm), and blue (465 nm).

[0085] Figure 26 It is a schematic cross-sectional view of a part of the second example of reflective ICG.

[0086] Figure 27A It is a graph showing the emission efficiency (percentage) of the first example of reflective ICG at red, green, and blue wavelengths as a function of the polarization state.

[0087] Figure 27B It is a graph showing the back reflection (percentage) of the first example of reflective ICG at red, green, and blue wavelengths as a function of the polarization state.

[0088] Figures 28A - 28C It is a graph showing the reflection efficiency of the -1 diffraction order, the reflection efficiency of the 0 diffraction order, and the transmission efficiency of the +1 diffraction order for TM polarization of the first example of reflective ICG as a function of the incident angle. Each graph shows the corresponding performance at wavelengths of red (625 nm), green (545 nm), and blue (465 nm).

[0089] Figures 28D - 28F It is a graph showing the reflection efficiency of the -1 diffraction order, the reflection efficiency of the 0 diffraction order, and the transmission efficiency of the +1 diffraction order for TE polarization of the first example of reflective ICG as a function of the incident angle. Each graph shows the corresponding performance at wavelengths of red (625 nm), green (545 nm), and blue (465 nm).

[0090] Figures 28G - 28I It is a graph showing the reflection efficiency of the -1 diffraction order, the reflection efficiency of the 0 diffraction order, and the transmission efficiency of the +1 diffraction order for TM and TE polarizations of the first example of reflective ICG as a function of the incident angle. Each graph shows the corresponding performance at wavelengths of red (625 nm), green (545 nm), and blue (465 nm).

[0091] Figure 29 It is a schematic cross-sectional view of a part of the third example of reflective ICG.

[0092] Figure 30 It is a schematic cross-sectional view of a part of the fourth example of reflective ICG.

[0093] Figure 31A It is a graph showing the emission efficiency (percentage) of the first example of reflective ICG at red, green, and blue wavelengths as a function of the polarization state.

[0094] Figure 31B It is a graph showing the change of the back reflection (percentage) of the first example of reflecting ICG with respect to the red wavelength, green wavelength, and blue wavelength as the polarization state changes.

[0095] Figures 32A - 32C It is a graph showing the change of the reflection efficiency of the -1 diffraction order, the reflection efficiency of the 0 diffraction order, and the transmission efficiency of the +1 diffraction order of the first example of reflecting ICG with respect to the incident angle for TM polarization. Each graph shows the corresponding performance at the red (625 nm), green (545 nm), and blue (465 nm) wavelengths.

[0096] Figures 32D - 32F It is a graph showing the change of the reflection efficiency of the -1 diffraction order, the reflection efficiency of the 0 diffraction order, and the transmission efficiency of the +1 diffraction order of the first example of reflecting ICG with respect to the incident angle for TE polarization. Each graph shows the corresponding performance at the red (625 nm), green (545 nm), and blue (465 nm) wavelengths.

[0097] Figures 32G - 32I It is a graph showing the change of the average reflection efficiency of the -1 diffraction order, the reflection efficiency of the 0 diffraction order, and the transmission efficiency of the +1 diffraction order of the first example of reflecting ICG with respect to the incident angle for TM and TE polarizations. Each graph shows the corresponding performance at the red (625 nm), green (545 nm), and blue (465 nm) wavelengths.

[0098] Figure 33A It is a schematic cross-sectional view of a part of the fifth example of reflecting ICG.

[0099] Figure 33B It is a schematic cross-sectional view of a part of another example of transmitting ICG.

[0100] Figure 34A It is a graph showing the change of the emission efficiency (percentage) of the fifth example of reflecting ICG with respect to the red wavelength, green wavelength, and blue wavelength as the polarization state changes.

[0101] Figure 34B It is a graph showing the change of the back reflection (percentage) of the fifth example of reflecting ICG with respect to the red wavelength, green wavelength, and blue wavelength as the polarization state changes.

[0102] Figure 35A -35C is a graph showing the change of the reflection efficiency of the -1 diffraction order, the reflection efficiency of the 0 diffraction order, and the transmission efficiency of the +1 diffraction order of the fifth example of reflecting ICG with respect to the incident angle for TM polarization. Each graph shows the corresponding performance at the red (625 nm), green (545 nm), and blue (465 nm) wavelengths.

[0103] Figure 35D -35F is a graph showing the reflection efficiency of the -1 diffraction order, the reflection efficiency of the 0 diffraction order, and the transmission efficiency of the +1 diffraction order for TE polarization as a function of the incident angle for the fifth example of reflecting ICG. Each graph shows the corresponding performance at wavelengths of red (625 nm), green (545 nm), and blue (465 nm).

[0104] Figure 35G -35I is a graph showing the average reflection efficiency of the -1 diffraction order, the reflection efficiency of the 0 diffraction order, and the transmission efficiency of the +1 diffraction order for TM and TE polarization as a function of the incident angle for the fifth example of reflecting ICG. Each graph shows the corresponding performance at wavelengths of red (625 nm), green (545 nm), and blue (465 nm).

[0105] Figures 36A - 36C is a graph of the total electric field amplitude within the unit cell of each grating structure for the first, second, fourth, and fifth examples of reflecting ICG. Figure 36A Shown therein is the graph for the red wavelength (625 nm). Figure 36B Shown therein is the graph for the green wavelength (545 nm). Figure 36C Shown therein is the graph for the blue wavelength (465 nm).

[0106] Figure 37 is a graph of the average polarization emission efficiency and back reflection (percentage) for the first and second examples of transmitting ICG and the first, second, fourth, and fifth examples of reflecting ICG.

[0107] Figure 38 is a cross-sectional schematic view of a part of the sixth example of reflecting ICG.

[0108] Figure 39 is a cross-sectional schematic view of an example waveguide having transmitting ICG and reflecting ICG.

[0109] Figure 40 is a cross-sectional schematic view of another example waveguide having transmitting ICG and reflecting ICG.

[0110] Throughout the drawings, reference numerals may be reused to indicate corresponding relationships between the elements mentioned. The drawings are provided to illustrate the example embodiments described herein and are not intended to limit the scope of the present disclosure. Detailed Description

[0111] An AR system can display virtual content to a user or viewer while still allowing the user to see the world around them. Preferably, the content is displayed on a head-mounted display, such as part of glasses, which projects image information onto the user's eyes. In addition, the display can also transmit light from the surrounding environment to the user's eyes to allow the surrounding environment to be viewed. As used herein, it should be understood that a "head-mounted" or "head-wearable" display is a display that can be worn on the head of a viewer or user.

[0112] In some AR systems, a virtual / augmented / mixed display with a relatively large field of view (FOV) can enhance the viewing experience. The FOV of the display depends on the angle of the light output from the waveguide of the eyepiece through which the viewer sees the image projected into his or her eyes. A waveguide with a relatively high refractive index (e.g., 2.0 or above) can provide a relatively high FOV. However, in order to effectively couple light into a high refractive index waveguide, the diffractive optical coupling element should also have a corresponding high refractive index. To achieve this goal, among other advantages, according to the embodiments described herein, some displays for AR systems include a waveguide that comprises a material with a relatively high refractive index (e.g., greater than or equal to 2.0) on which a corresponding diffractive grating with a high refractive index, such as lithium-based oxide, is formed. For example, by patterning a surface portion of the waveguide formed of lithium-based oxide, the diffractive grating can be directly formed on the lithium-based oxide waveguide.

[0113] Some high refractive index diffractive optical coupling elements, such as input or output optical elements, have strong polarization dependence. For example, an input coupling grating (ICG) for coupling light into a waveguide, where the diffractive optical coupling element includes a high refractive index material, can admit significantly more light of a particular polarization than of the other polarization. For example, such an element can couple light with TM polarization into the waveguide at a rate approximately three times that of light with TE polarization. Diffractive optical coupling elements with such polarization dependence may have reduced efficiency (due to low efficiency and general rejection of one polarization), and may also produce coherent artifacts and reduce the uniformity of the far-field image formed by the light coupled out of the waveguide. To obtain a diffractive optical coupling element that is insensitive to polarization or at least has reduced polarization sensitivity (e.g., that couples light with relatively polarization-independent efficiency), according to various embodiments described herein, some displays for AR systems include waveguides having diffractive gratings formed with a blazed geometry. The diffractive grating can also be formed directly in the waveguide, which can include a high refractive index material (e.g., having a refractive index of at least 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, or up to 2.7, or any value within any range between any of the foregoing values). For example, by patterning the high refractive index material with a blazed geometry, the diffractive grating can be formed in the high refractive index material, such as a lithium-based oxide like lithium niobate (LiNbO3) or lithium tantalate (LiTaO3), or such as zirconia (ZrO2), titanium dioxide (TiO2), or silicon carbide (SiC).

[0114] Reference will now be made to the accompanying drawings, in which like reference numerals refer to like components throughout. Unless otherwise indicated, the drawings are schematic and not necessarily drawn to scale.

[0115] Figure 2 A conventional display system for simulating three-dimensional images for a user is shown. The user's eyes are spaced apart, and when viewing a real object in space, each eye will have a slightly different view of the object, and an image of the object can be formed at different positions on the retina of each eye. This can be referred to as binocular parallax and can be used by the human visual system to provide a sense of depth. The conventional display system simulates binocular parallax by presenting two different images 190, 200 (one image for each eye 210, 220) with slightly different views of the same virtual object, which correspond to the views of the virtual object that would be seen by each eye as a real object at the desired depth. These images provide binocular cues that the user's visual system can interpret to obtain a sense of depth.

[0116] Continue to refer to Figure 2, images 190, 200 are spaced apart from eyes 210, 220 by a distance 230 along the z-axis. The z-axis is parallel to the optical axis of a viewer whose eyes are gazing at an object at optical infinity directly in front of the viewer. Images 190, 200 are flat and are at a fixed distance from eyes 210, 220. Based on slightly different views of a virtual object in the images presented to eyes 210, 220 respectively, the eyes can rotate naturally so that the images of the object fall on corresponding points on the retina of each eye to maintain single binocular vision. This rotation can cause the lines of sight of each eye 210, 220 to converge on the spatial point where the virtual object is perceived to exist. Thus, providing three-dimensional images generally involves providing binocular cues that can manipulate the vergence of the user's eyes 210, 220 and are interpreted by the human visual system to provide a sense of depth.

[0117] However, creating a realistic and comfortable sense of depth is challenging. It should be understood that light from objects at different distances from the eyes has wavefronts with different amounts of divergence. Figures 3A to 3C The relationship between distance and light divergence is shown. The distances between the object and eye 210 are represented in decreasing order of distance as R1, R2, and R3. As Figures 3A to 3C shown, as the distance to the object decreases, the light becomes more divergent. Conversely, as the distance increases, the light becomes more collimated. In other words, it can be said that the light field generated by a point (an object or a part of an object) has a spherical wavefront curvature that is a function of how far that point is from the user's eye. The curvature increases as the distance between the object and eye 210 decreases. Although only a single eye 210 is shown in Figures 3A to 3C and other figures in this document for clarity, the discussion regarding eye 210 applies to both eyes 210 and 220 of the viewer.

[0118] Continuing to refer to Figures 3A to 3C, light from an object that a viewer's eyes are fixated on can have different degrees of wavefront divergence. Due to the different amounts of wavefront divergence, the light can be focused differently by the eye's lens, which in turn may require the lens to assume different shapes to form a focused image on the retina of the eye. In the case where a focused image is not formed on the retina, the resulting retinal blur serves as an accommodation cue that causes a change in the shape of the eye's lens until a focused image is formed on the retina. For example, the accommodation cue can trigger the relaxation or contraction of the ciliary muscle surrounding the eye's lens, thereby regulating the force applied to the zonular ligaments that hold the lens, so that the shape of the eye's lens changes until the retinal blur of the fixated object is eliminated or minimized, thereby forming a focused image of the fixated object on the retina (e.g., fovea) of the eye. The process by which the eye's lens changes shape can be referred to as accommodation, and the shape of the eye's lens required to form a focused image of a fixated object on the retina (e.g., fovea) of the eye can be referred to as the accommodative state.

[0119] Now referring to Figure 4A , a representation of the accommodation-vergence response of the human visual system is shown. Eye movement to fixate on an object causes the eyes to receive light from the object, where the light forms an image on each retina of the eyes. The presence of retinal blur in the image formed on the retina can provide an accommodation cue, and the relative position of the image on the retina can provide a vergence cue. The accommodation cue causes accommodation to occur, such that the eye's lens assumes a specific accommodative state that forms a focused image of the object on the retina (e.g., fovea) of the eye, respectively. On the other hand, the vergence cue causes vergence movement (eye rotation) to occur so that the images formed on each retina of each eye are at corresponding retinal points that maintain single binocular vision. In these positions, it can be said that the eyes have assumed a specific vergence state. Continuing to refer to Figure 4A , accommodation can be understood as the process by which the eyes achieve a specific accommodative state, and vergence can be understood as the process by which the eyes achieve a specific vergence state. As Figure 4A shown, if the user fixates on another object, the accommodation and vergence states of the eyes can change. For example, if the user fixates on a new object at a different depth along the z-axis, the accommodative state may change.

[0120] Without being limited by theory, it can be considered that a viewer of an object may perceive the object as "three-dimensional" due to the combination of convergence and accommodation. As described above, the convergence movement of the two eyes relative to each other (e.g., the eyes rotate so that the pupils move towards or away from each other to converge the lines of sight of the eyes to fixate on an object) is closely related to the accommodation of the eye lenses. Under normal circumstances, under the known "accommodation-convergence reflex" relationship, changing the shape of the eye lens to change the focus from one object to another object at a different distance will automatically cause a matching convergence change to the same distance. Similarly, under normal circumstances, a change in convergence will trigger a matching change in the shape of the lens.

[0121] Now referring to Figure 4B , an example of different accommodation states and convergence states of the eyes is shown. A pair of eyes 222a is fixated on an object at optical infinity, while a pair of eyes 222b is fixated on an object 221 that is less than optical infinity. It is noted that the convergence states of each pair of eyes are different, where a pair of eyes 222a looks straight ahead, while a pair of eyes 222 converges on the object 221. The accommodation states of the eyes forming each pair of eyes 222a and 222b are also different, as represented by the different shapes of the lenses 210a, 220a.

[0122] Unfortunately, many users of traditional "3D" display systems find that such traditional systems are uncomfortable or may not be able to perceive a sense of depth at all due to the mismatch between the accommodation and convergence states in these displays. As described above, many stereoscopic or "3D" display systems display a scene by providing slightly different images to each eye. Such systems are uncomfortable for many viewers because, among other things, such systems only provide different presentations of the scene and cause a change in the convergence state of the eyes, but there is no corresponding change in the accommodation state of these eyes. Instead, the images are displayed by a display at a fixed distance from the eyes so that the eyes view all the image information in a single accommodation state. This arrangement violates the "accommodation-convergence reflex" by causing a change in the convergence state without a matching change in the accommodation state. This mismatch is believed to cause discomfort to the viewer. A display system that provides a better match between accommodation and convergence can form a more realistic and comfortable three-dimensional image simulation.

[0123] Without being limited by theory, it can be considered that the human eye can generally interpret a limited number of depth planes to provide a sense of depth. Therefore, a highly believable perceived depth simulation can be achieved by providing different presentations of images corresponding to each of these limited number of depth planes to the eyes. In some embodiments, the different presentations can simultaneously provide convergence cues and matching accommodation cues, thereby providing a physiologically correct accommodation-convergence match.

[0124] Continuing to refer toFigure 4B shows two depth planes 240 corresponding to different distances from the eyes 210, 220 in space. For a given depth plane 240, vergence cues can be provided by displaying appropriately different perspectives of an image for each eye 210, 220. Additionally, for a given depth plane 240, the light forming the images provided to each eye 210, 220 can have a wavefront divergence corresponding to the light field generated by points at the distance of that depth plane 240.

[0125] In the illustrated embodiment, the depth plane 240 containing the point 221 is at a distance of 1 meter along the z - axis. As used herein, the distance or depth along the z - axis can be measured with the zero point at the exit pupil of the user's eye. Thus, the depth plane 240 at a depth of 1 meter corresponds to a distance of 1 meter from the exit pupil of the user's eye on the optical axis of the user's eye when the eyes are directed to optical infinity. As an approximation, the depth or distance along the z - axis can be measured from a display in front of the user's eyes (e.g., from the surface of a waveguide), plus the value of the distance between the device and the exit pupil of the user's eye. This value can be referred to as the eye relief and corresponds to the distance between the exit pupil of the user's eye and the display worn by the user in front of the eyes. In practice, the value of the eye relief can be a standardized value common to all viewers. For example, it can be assumed that the eye relief is 20 mm, and the depth plane at a depth of 1 meter can be at a distance of 980 mm in front of the display.

[0126] Now referring to Figure 4C and 4D , examples of a matched accommodation - vergence distance and a mismatched accommodation - vergence distance are shown respectively. As Figure 4C shown, the display system can provide images of a virtual object to each eye 210, 220. These images can cause the eyes 210, 220 to assume a vergence state in which the eyes converge at a point 15 on the depth plane 240. Additionally, the images can be formed by light having a wavefront curvature corresponding to a real object at that depth plane 240. As a result, the eyes 210, 220 assume an accommodation state in which the images are focused on the retinas of these eyes. Thus, the user can perceive the virtual object as being located at the point 15 on the depth plane 240.

[0127] It should be understood that each of the accommodation and convergence states of eyes 210, 220 is associated with a specific distance on the z-axis. For example, an object at a specific distance from eyes 210, 220 causes these eyes to assume a specific accommodation state based on the distance of the object. The distance associated with a specific accommodation state may be referred to as the accommodation distance Ad. Similarly, there is a specific convergence distance Vd associated with the eyes in a specific convergence state or their positions relative to each other. When the accommodation distance and the convergence distance match, it can be said that the relationship between accommodation and convergence is physiologically correct. This is considered to be the most comfortable scenario for the viewer.

[0128] However, in a stereoscopic display, the accommodation distance and the convergence distance may not always match. For example, as Figure 4D shown, the images presented to eyes 210, 220 may be presented with a wavefront divergence corresponding to depth plane 240, and eyes 210, 220 may assume a specific accommodation state in which points 15a, 15b on that depth plane are in focus. However, the images presented to eyes 210, 220 may provide a convergence cue that causes eyes 210, 220 to converge at point 15, which is not located on depth plane 240. As a result, in some embodiments, the accommodation distance corresponds to the distance from the exit pupils of eyes 210, 220 to depth plane 240, while the convergence distance corresponds to a greater distance from the exit pupils of eyes 210, 220 to point 15. The accommodation distance is different from the convergence distance. Thus, there is an accommodation-convergence mismatch. This mismatch is considered undesirable and may cause discomfort to the user. It should be understood that the mismatch corresponds to a distance (e.g., Vd - Ad) and can be characterized using diopters.

[0129] In some embodiments, it should be understood that reference points other than the exit pupils of eyes 210, 220 can be used to determine the distances for determining the accommodation-convergence mismatch, as long as the same reference point is used for both the accommodation distance and the convergence distance. For example, the distance from the cornea to the depth plane, from the retina to the depth plane, from the eyepiece (e.g., the waveguide of the display device) to the depth plane, etc., can be measured.

[0130] Without being bound by theory, it can be considered that in cases where the accommodation-convergence mismatch itself does not cause significant discomfort, the user may still perceive accommodation-convergence mismatches of up to approximately 0.25 diopters, up to approximately 0.33 diopters, and up to approximately 0.5 diopters as being physiologically correct. In some embodiments, the display systems disclosed herein (e.g., Figure 6The display system 250) presents an image to a viewer with an accommodation-convergence mismatch of about 0.5 diopters or less. In some other embodiments, the accommodation-convergence mismatch of the image provided by the display system is about 0.33 diopters or less. In still other embodiments, the accommodation-convergence mismatch of the image provided by the display system is about 0.25 diopters or less, including about 0.1 diopters or less.

[0131] Figure 5 Aspects of a method for simulating a three-dimensional image by modifying wavefront divergence are shown. The display system includes a waveguide 270 configured to receive light 770 encoded with image information and output the light to a user's eye 210. The waveguide 270 may output light 650 with a limited amount of wavefront divergence corresponding to the wavefront divergence of the light field generated by points on a desired depth plane 240. In some embodiments, the same amount of wavefront divergence is provided for all objects presented on the depth plane. Additionally, it will be described that image information from a similar waveguide may be provided to the user's other eye.

[0132] In some embodiments, a single waveguide may be configured to output light with a set amount of wavefront divergence corresponding to a single depth plane or a limited number of depth planes, and / or the waveguide may be configured to output light within a limited wavelength range. Thus, in some embodiments, multiple waveguides or a stack of waveguides may be utilized to provide different amounts of wavefront divergence for different depth planes and / or output different wavelength ranges of light. As used herein, it should be understood that a depth plane may be planar or may follow a curved surface profile.

[0133] Figure 6 An example of a waveguide stack for outputting image information to a user is shown. The display system 250 includes a waveguide stack or a stacked waveguide assembly 260 that may be used to provide a three-dimensional perception to the eye / brain using multiple waveguides 270, 280, 290, 300, 310. It should be understood that in some embodiments, the display system 250 may be considered a light field display. Additionally, the waveguide assembly 260 may also be referred to as an eyepiece.

[0134] In some embodiments, the display system 250 is configured to provide substantially continuous convergence cues and multiple discrete accommodation cues. The convergence cues may be provided by displaying different images to each eye of the user, and the accommodation cues may be provided by outputting image-forming light with a selectable discrete amount of wavefront divergence. In other words, the display system 250 may be configured to output light with a variable wavefront divergence level. In some embodiments, each discrete level of wavefront divergence corresponds to a specific depth plane and may be provided by a specific one of the waveguides 270, 280, 290, 300, 310.

[0135] Continuing reference Figure 6 to, waveguide assembly 260 may also include a plurality of features 320, 330, 340, 350 between waveguides. In some embodiments, features 320, 330, 340, 350 may be one or more lenses. Waveguides 270, 280, 290, 300, 310 and / or the plurality of lenses 320, 330, 340, 350 may be configured to send image information to the eye with various levels of wavefront curvature or ray divergence. Each waveguide level may be associated with a particular depth plane and may be configured to output image information corresponding to that depth plane. Image injection devices 360, 370, 380, 390, 400 may serve as light sources for the waveguides and may be used to inject image information into waveguides 270, 280, 290, 300, 310, and as described herein, each waveguide may be configured to distribute incident light across each respective waveguide for output toward eye 210. Light exits from output surfaces 410, 420, 430, 440, 450 of image injection devices 360, 370, 380, 390, 400 and is injected into corresponding input surfaces 460, 470, 480, 490, 500 of waveguides 270, 280, 290, 300, 310. In some embodiments, each of input surfaces 460, 470, 480, 490, 500 may be an edge of the corresponding waveguide or may be a portion of the main surface of the corresponding waveguide (i.e., one of the waveguide surfaces directly facing the world 510 or the viewer's eye 210). In some embodiments, a single light beam (e.g., a collimated beam) may be injected into each waveguide to output an entire field of cloned collimated beams that are directed toward eye 210 at a particular angle (and amount of divergence) corresponding to the depth plane associated with the particular waveguide. In some embodiments, a single image injection device among image injection devices 360, 370, 380, 390, 400 may be associated with and inject light into a plurality (e.g., three) of waveguides among waveguides 270, 280, 290, 300, 310.

[0136] In some embodiments, the image injection devices 360, 370, 380, 390, 400 are discrete displays, each discrete display separately generating image information for injection into a corresponding waveguide 270, 280, 290, 300, 310. In some other embodiments, the image injection devices 360, 370, 380, 390, 400 are output terminals of a single multiplexed display. For example, the output terminals of the multiplexed display can pipe image information to each of the image injection devices 360, 370, 380, 390, 400 via one or more optical conduits such as fiber optic cables. It should be understood that the image information provided by the image injection devices 360, 370, 380, 390, 400 can include light of different wavelengths or colors (e.g., different component colors as discussed herein).

[0137] 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 module 530 that can include a light emitter such as a light emitting diode (LED). Light from the light module 530 can be directed via a beam splitter 550 to a light modulator 540 (e.g., a spatial light modulator) and modified by the light modulator 540. The light modulator 540 can be configured to change the perceived intensity of the light injected into the waveguides 270, 280, 290, 300, 310 to encode the light with image information. Examples of spatial light modulators include liquid crystal displays (LCDs), which include liquid crystal on silicon (LCOS) displays. It should be understood that the image injection devices 360, 370, 380, 390, 400 are schematically shown, and in some embodiments, these image injection devices can represent different optical paths and positions in a common projection system configured to output light into an associated waveguide among the waveguides 270, 280, 290, 300, 310. In some embodiments, the waveguides in the waveguide assembly 260 can act as ideal lenses while relaying the light injected into the waveguides out to the user's eyes. In this concept, the object can be the spatial light modulator 540, and the image can be an image on a depth plane.

[0138] In some examples, a μLED display can be used in the light projector system 520. The μLED display can unpolarize light over a large angular range. Thus, the μLED display can advantageously provide images efficiently over a wide field of view.

[0139] In some embodiments, the display system 250 can be a scanned fiber optic display that includes one or more scanned optical fibers configured to project light into one or more waveguides 270, 280, 290, 300, 310 in various patterns (e.g., raster scan, helical scan, Lissajous pattern, etc.) and ultimately to the viewer's eye 210. In some embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 can schematically represent a single scanned optical fiber or a bundle of scanned optical fibers configured to inject light into one or more of the waveguides 270, 280, 290, 300, 310. In some other embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 can schematically represent multiple scanned optical fibers or multiple bundles of scanned optical fibers, each of which is configured to inject light into an associated one of the waveguides 270, 280, 290, 300, 310. It should be understood that one or more optical fibers can be configured to transmit light from the optical module 530 to one or more of the waveguides 270, 280, 290, 300, 310. It should be understood that one or more intermediate optical structures can be disposed between the one or more scanned optical fibers and the one or more waveguides 270, 280, 290, 300, 310 to redirect, for example, light exiting the scanned optical fibers into the one or more waveguides 270, 280, 290, 300, 310.

[0140] The controller 560 controls the operation of one or more components in the stacked waveguide assembly 260, including the operation of the image injection 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-transitory medium) that regulates the timing and provision of image information to the waveguides 270, 280, 290, 300, 310 according to any of the various schemes disclosed herein, for example. In some embodiments, the controller can be a single monolithic device or a distributed system connected via wired or wireless communication channels. In some embodiments, the controller 560 can be part of the processing module 140 or 150 ( Figure 9D ).

[0141] Continuing to refer Figure 6, waveguides 270, 280, 290, 300, 310 can be configured to propagate light within each respective waveguide by total internal reflection (TIR). Waveguides 270, 280, 290, 300, 310 can each be planar or have another shape (e.g., curved), having a top major surface and a bottom major surface and an edge extending between these top and bottom major surfaces. In the illustrated configuration, waveguides 270, 280, 290, 300, 310 can each include light extraction optical elements 570, 580, 590, 600, 610, which are configured to extract light from the waveguides by redirecting the light propagating inside the respective corresponding waveguides out of the waveguides to output image information to the eye 210. The extracted light can also be referred to as the coupled-out light, and the light extraction optical elements can also be referred to as light extraction optical elements. The extracted light beam can be output from the waveguide at the position where the light propagating in the waveguide is incident on the light extraction optical element. As further discussed herein, the light extraction optical elements 570, 580, 590, 600, 610 can be, for example, gratings of diffractive optical features. Although shown as being disposed at the bottom major surface of waveguides 270, 280, 290, 300, 310, for ease of description and clarity of drawing, in some embodiments, as further discussed herein, the light extraction optical elements 570, 580, 590, 600, 610 can be disposed at the top and / or bottom major surfaces, and / or can be disposed directly within the volume of waveguides 270, 280, 290, 300, 310. In some embodiments, the light extraction optical elements 570, 580, 590, 600, 610 can be formed in a material layer attached to a transparent substrate to form waveguides 270, 280, 290, 300, 310. In some other embodiments, waveguides 270, 280, 290, 300, 310 can be a single-piece material, and the light extraction optical elements 570, 580, 590, 600, 610 can be formed on and / or within the surface of the piece of material.

[0142] Continue to refer to Figure 6, as discussed herein, each of the waveguides 270, 280, 290, 300, 310 is configured to output light to form an image corresponding to a particular depth plane. For example, the waveguide 270 closest to the eye can be configured to deliver collimated light (which is injected into such waveguide 270) to the eye 210. This collimated light can represent an optically infinite focal plane. The next upstream waveguide 280 can be configured to emit collimated light that passes through a first lens 350 (e.g., a negative lens) before it can reach the eye 210; such first lens 350 can be configured to produce a slightly convex wavefront curvature such that the eye / brain interprets the light from this next upstream waveguide 280 as coming from a first focal plane that is closer to the eye 210 inward from the optically infinite. Similarly, the third upstream waveguide 290 has its output light pass through both the first lens 350 and the second lens 340 before reaching the eye 210; the combined optical power of the first lens 350 and the second lens 340 can be configured to produce another increment of wavefront curvature such that the eye / brain interprets the light from the third waveguide 290 as coming from a second focal plane that is closer to the person further inward from the optically infinite than the light from the next upstream waveguide 280.

[0143] The other waveguide layers 300, 310 and lenses 330, 320 are configured similarly, where the highest waveguide 310 in the stack sends its output through all of the lenses between it and the eye to obtain the total optical power representative of the focal plane closest to the person. To compensate for the lens stack 320, 330, 340, 350 when observing / interpreting light from the world 510 on the other side of the stacked waveguide assembly 260, a compensating lens layer 620 can be provided at the top of the stack to compensate for the total optical power of the lens stack 320, 330, 340, 350 below. This configuration provides as many perceived focal planes as there are available waveguide / lens pairs. Both the outcoupling optical elements of the waveguides and the focusing aspects of the lenses can be static (i.e., not dynamic or electroactive). In some alternative embodiments, one or both of them can be dynamic by using electroactive features.

[0144] In some embodiments, two or more of the waveguides 270, 280, 290, 300, 310 can have the same associated depth plane. For example, multiple waveguides 270, 280, 290, 300, 310 can be configured to output a set of images to the same depth plane, or multiple subsets of the waveguides 270, 280, 290, 300, 310 can be configured to output a set of images to the same multiple depth planes, one set of images per depth plane. This can provide an advantage for forming a stitched image to provide an extended field of view at those depth planes.

[0145] Continuing to refer to Figure 6, the output optical elements 570, 580, 590, 600, 610 can be configured to both redirect light out of their respective waveguides and output the light with an appropriate amount of divergence or collimation for a particular depth plane associated with the waveguide. As a result, waveguides with different associated depth planes can have differently configured output optical elements 570, 580, 590, 600, 610, and the differently configured output optical elements 570, 580, 590, 600, 610 output light with different amounts of divergence according to the associated depth plane. In some embodiments, the light extraction optical elements 570, 580, 590, 600, 610 can be volume features 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, the features 320, 330, 340, 350 can not be lenses; rather, they can simply be spacers (e.g., cladding and / or structures for forming an air gap).

[0146] In some embodiments, the output optical elements 570, 580, 590, 600, 610 are diffraction features that form a diffraction pattern, or “diffractive optical elements” (also referred to herein as “DOEs”). Preferably, the DOE has a low enough diffraction efficiency such that only a portion of the light beam is deflected towards the eye 210 with each intersection with the DOE, while the remainder continues to propagate through the waveguide via TIR. Thus, the light carrying the image information is split into multiple related output beams that exit the waveguide at multiple locations, and as a result, a relatively uniform pattern exits towards the eye 210 for this particular collimated beam bouncing within the waveguide.

[0147] In some embodiments, one or more DOEs can switch between an “on” state in which they actively diffract and an “off” state in which they do not significantly diffract. For example, a switchable DOE can include a polymer dispersed liquid crystal layer, where microdroplets include a diffraction pattern in a host medium, and the refractive index of the microdroplets can be switched to substantially match the refractive index of the host material (in which case the pattern does not significantly diffract the incident light) or the microdroplets can be switched to a refractive index that is mismatched with the refractive index of the host medium (in which case the pattern actively diffracts the incident light).

[0148] In some embodiments, a camera component 630 (e.g., a digital camera, including a visible light camera and an infrared light camera) may be provided to capture images of the eye 210 and / or the tissue around the eye 210 to, for example, detect user input and / or monitor the user's physiological state. As used herein, a camera may be any image capture device. In some embodiments, the camera component 630 may include an image capture device and a light source to project light (e.g., infrared light) onto the eye, and then the light may be reflected by the eye and detected by the image capture device. In some embodiments, the camera component 630 may be attached to the frame 80( Figure 9D ) and may be in electrical communication with the processing module 140 and / or 150, and the local processing and data module 140 and / or the remote processing module 150 may process the image information from the camera component 630. In some embodiments, one camera component 630 may be used for each eye to monitor each eye separately.

[0149] Now referring to Figure 7 , an example of an outgoing light beam output from a waveguide is shown. One waveguide is shown, but it should be understood that in the case where the waveguide assembly 260 includes multiple waveguides, the other waveguides in the waveguide assembly 260( Figure 6 ) may function similarly. Light 640 is injected 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 is incident on the DOE 570, a portion of the light exits the waveguide as an outgoing light beam 650. The outgoing light beams 650 are shown as being substantially parallel, but as discussed herein, they may also be redirected to propagate at an angle (e.g., to form a diverging outgoing light beam) to the eye 210, and the angle depends on the depth plane associated with the waveguide 270. It should be understood that the substantially parallel outgoing light beams may indicate a waveguide having an outcoupling optical element that outcouples light to form an image on a depth plane that appears to be set at a long distance from the eye 210 (e.g., optical infinity). Other waveguides or other sets of outcoupling optical elements may output a more diverging pattern of outgoing light beams, and this pattern of outgoing light beams will require the eye 210 to accommodate to a closer distance in order to focus the more diverging pattern of outgoing light beams on the retina and will be interpreted by the brain as light from a distance closer to the eye 210 than optical infinity.

[0150] In some embodiments, a full-color image may be formed at each depth plane by superimposing images in each of the component colors (e.g., three or more component colors). Figure 8An example of a stacked waveguide assembly is shown, where each depth plane includes an image formed using a plurality of different component colors. The illustrated embodiment shows depth planes 240a - 240f, but more or fewer depths may also be contemplated. Each depth plane may have three or more component color images associated therewith, 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. For the diopters (dpt) after the letters G, R, and B, different depth planes are represented by different numbers in the figure. By way of example only, the numbers following each of these letters represent the diopter (1 / m), or the reciprocal of the distance of that depth plane from the viewer, and each box in the figure represents an individual component color image. In some embodiments, to account for differences in the focusing of the eye for different wavelengths of light, the exact placement of the depth planes of different component colors may vary. For example, the different component color images of 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 may reduce chromatic aberration.

[0151] In some embodiments, the light of each component color may be output by a single dedicated waveguide, and thus, each depth plane may have a plurality of waveguides associated therewith. In such embodiments, each box in the figure that includes the letter G, R, or B may be understood to represent an individual waveguide, and each depth plane may provide three waveguides, where each depth plane provides three component color images. Although, for ease of description, the waveguides associated with each depth plane are shown adjacent to each other in this figure, it should be understood that in a physical device, the waveguides may all be arranged in a stack with one waveguide per layer. In some other embodiments, a plurality of component colors may be output by the same waveguide, such that, for example, each depth plane may provide only a single waveguide.

[0152] Continuing to refer to Figure 8 , in some embodiments, G is green, R is red, and B is blue. In some other embodiments, in addition to red, green, or blue, other colors associated with light of other wavelengths (including magenta and cyan) may be used, or these other colors may replace one or more of red, green, or blue.

[0153] It should be understood that references throughout this disclosure to light of a given color will be understood to include light of one or more wavelengths within the wavelength range of light that is perceived by a viewer as having that given color. For example, red light may include light of one or more wavelengths in the range of approximately 620 - 780 nm, green light may include light of one or more wavelengths in the range of approximately 492 - 577 nm, and blue light may include light of one or more wavelengths in the range of approximately 435 - 493 nm.

[0154] In some embodiments, the light source 530( Figure 6 ) may be configured to emit light at one or more wavelengths outside the viewer's visual perception range, such as infrared and / or ultraviolet wavelengths. Additionally, the light coupling, decoupling, and other light redirecting structures of the waveguide of the display 250 may be configured to direct this light and cause this light to exit the display towards the user's eye 210, for example, for imaging and / or user stimulation applications.

[0155] Now referring to Figure 9A , in some embodiments, it may be desirable to redirect light incident on a waveguide to couple the light into the waveguide. An optical coupling element may be used to redirect and couple the light into its corresponding waveguide. Figure 9A A cross-sectional side view of an example of a plurality of stacked waveguides or a set of stacked waveguides 660 is shown, each waveguide including an optical coupling element. The waveguides may each be configured to output light at one or more different wavelengths, or one or more different wavelength ranges. It should be understood that the stack 660 may correspond to the stack 260( Figure 6 ), and the waveguides shown in the stack 660 may correspond to a portion of the plurality of waveguides 270, 280, 290, 300, 310, except that light from one or more image injection devices 360, 370, 380, 390, 400 is injected into the waveguide at a location where the light needs to be redirected for coupling.

[0156] The illustrated stacked waveguide assembly 660 includes waveguides 670, 680, and 690. Each waveguide includes an associated optical coupling element (which may also be referred to as an optical input region on the waveguide), where for example, the optical coupling element 700 is disposed on the main surface (e.g., the top main surface) of the waveguide 670, the optical coupling element 710 is disposed on the main surface (e.g., the top main surface) of the waveguide 680, and the optical coupling element 720 is disposed on the main surface (e.g., the top main surface) of the waveguide 690. In some embodiments, one or more of the optical coupling elements 700, 710, 720 may be disposed on the bottom main surface of the respective waveguides 670, 680, 690 (particularly in the case where one or more of the optical coupling elements are reflective deflecting optical elements). As shown, the optical coupling elements 700, 710, 720 may be disposed on the top main surface (or the top of the next lower waveguide) of their respective waveguides 670, 680, 690, particularly in the case where the optical coupling elements are transmissive deflecting optical elements. In some embodiments, the optical coupling elements 700, 710, 720 may be disposed within the body of the respective waveguides 670, 680, 690. In some embodiments, as discussed herein, the optical coupling elements 700, 710, 720 are wavelength selective such that they selectively redirect light of one or more wavelengths while transmitting light of other wavelengths. Although shown on one side or corner of their respective waveguides 670, 680, 690, it should be understood that in some embodiments, the optical coupling elements 700, 710, 720 may be disposed in other regions of their respective waveguides 670, 680, 690.

[0157] As illustrated, the optical coupling elements 700, 710, 720 may be laterally offset from each other. In some embodiments, each optical coupling element may be offset such that the optical coupling element receives light without the light passing through another optical coupling element. For example, each of the optical coupling elements 700, 710, 720 may be configured to receive light from different image injection devices 360, 370, 380, 390, and 400 as Figure 6 shown, and may be separated (e.g., laterally spaced apart) from the other optical coupling elements 700, 710, 720 such that the optical coupling element substantially does not receive light from the other optical coupling elements among the optical coupling elements 700, 710, 720.

[0158] Each waveguide further includes an associated optical distribution element. For example, the optical distribution element 730 is disposed on the main surface (e.g., the top main surface) of the waveguide 670, the optical distribution element 740 is disposed on the main surface (e.g., the top main surface) of the waveguide 680, and the optical distribution element 750 is disposed on the main surface (e.g., the top main surface) of the waveguide 690. In some other embodiments, the optical distribution elements 730, 740, 750 may be respectively disposed on the bottom main surfaces of the associated waveguides 670, 680, 690. In some other embodiments, the optical distribution elements 730, 740, 750 may be respectively disposed on both the top main surface and the bottom main surface of the associated waveguides 670, 680, 690; or the optical distribution elements 730, 740, 750 may be respectively disposed on different main surfaces among the top main surface and the bottom main surface of different associated waveguides 670, 680, 690.

[0159] The waveguides 670, 680, 690 may be separated and spaced apart by, for example, gas, liquid, and / or solid material layers. For example, as illustrated, the layer 760a may separate the waveguide 670 and the waveguide 680; and the layer 760b may separate the waveguide 680 and the waveguide 690. In some embodiments, the layers 760a and 760b are formed of a low refractive index material (i.e., a material having a refractive index lower than that of the material adjacent to the waveguides forming the waveguides 670, 680, 690). Preferably, the refractive index of the material forming the layers 760a, 760b is less than that of the material forming the waveguides 670, 680, 690 by 0.05 or more, or 0.10. Advantageously, the lower refractive index layers 760a, 760b can act as claddings, which facilitate total internal reflection (TIR) of light passing through the waveguides 670, 680, 690 (e.g., TIR between the top main surface and the bottom main surface of each waveguide). In some embodiments, the layers 760a, 760b are formed of air. Although not shown, it should be understood that the top and bottom of the illustrated waveguide set 660 may include adjacent claddings.

[0160] Preferably, for ease of manufacturing and other considerations, the materials forming the waveguides 670, 680, 690 are similar or the same, and the materials forming the layers 760a, 760b are similar or the same. In some embodiments, the materials forming the waveguides 670, 680, 690 may be different between one or more waveguides, and / or the materials forming the layers 760a, 760b may be different, while still maintaining the various refractive index relationships described above.

[0161] Continuing to refer to Figure 9A, light rays 770, 780, 790 are incident on waveguide set 660. It should be understood that light rays 770, 780, 790 can be injected into waveguides 670, 680, 690 through one or more image injection devices 360, 370, 380, 390, 400( Figure 6 ).

[0162] In some embodiments, light rays 770, 780, 790 have different characteristics, e.g., different wavelengths or different wavelength ranges corresponding to different colors. Coupling optical elements 700, 710, 720 each deflect the incident light such that the light propagates through a corresponding one of waveguides 670, 680, 690 by TIR. In some embodiments, coupling optical elements 700, 710, 720 each selectively deflect light of one or more specific wavelengths while transmitting other wavelengths to the underlying waveguides and associated coupling optical elements.

[0163] For example, coupling optical element 700 can be configured to deflect light ray 770 having a first wavelength or first wavelength range while transmitting light rays 780 having a different second wavelength or second wavelength range and light ray 790 having a third wavelength or third wavelength range, respectively. The transmitted light ray 780 is incident on coupling optical element 710 and is deflected by coupling optical element 710, which is configured to deflect light of the second wavelength or second wavelength range. Light ray 790 is deflected by coupling optical element 720, which is configured to selectively deflect light of the third wavelength or third wavelength range.

[0164] Continuing to refer to Figure 9A , the deflected light rays 770, 780, 790 are deflected such that light rays 770, 780, 790 propagate through corresponding waveguides 670, 680, 690; that is, the coupling optical elements 700, 710, 720 of each waveguide deflect light into the corresponding waveguide 670, 680, 690 to couple the light into the corresponding waveguide. Light rays 770, 780, 790 are deflected at an angle that causes the light to propagate through the corresponding waveguides 670, 680, 690 by TIR. Light rays 770, 780, 790 propagate through the corresponding waveguides 670, 680, 690 by TIR until incident on corresponding light distribution elements 730, 740, 750 of the waveguides.

[0165] Now referring to Figure 9B , shows Figure 9APerspective view of an example of multiple stacked waveguides. As described above, the coupled-in light rays 770, 780, 790 are deflected by the optical elements 700, 710, 720 respectively, and then propagate through TIR in the waveguides 670, 680, 690 respectively. Then, the light rays 770, 780, 790 are incident on the light distribution elements 730, 740, 750 respectively. The light distribution elements 730, 740, 750 deflect the light rays 770, 780, 790 so that the light rays 770, 780, 790 propagate towards the out-coupling optical elements 800, 810, 820 respectively.

[0166] In some embodiments, the light distribution elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some embodiments, the OPE deflects or distributes light to the out-coupling optical elements 800, 810, 820, and in some embodiments, the beam size or spot size of this light can also be increased as the light propagates to the out-coupling optical elements. In some embodiments, the light distribution elements 730, 740, 750 can be omitted, and the in-coupling optical elements 700, 710, 720 can be configured to deflect light directly to the out-coupling optical elements 800, 810, 820. For example. Refer Figure 9A , the light distribution elements 730, 740, 750 can be replaced by the out-coupling optical elements 800, 810, 820 respectively. In some embodiments, the out-coupling optical elements 800, 810, 820 are the exit pupil (EP) or exit pupil expander (EPE) that guides light into the viewer's eye 210 ( Figure 7 ). It should be understood that the OPE can be configured to increase the size of the eye box in at least one axis, and the EPE can increase the eye box in an axis that intersects (e.g., is orthogonal to) the axis of the OPE. For example, each OPE can be configured to redirect a portion of the light impinging on the OPE to the EPE of the same waveguide while allowing the remaining portion of the light to continue propagating along the waveguide. When the remaining light is incident on the OPE again, another portion of the remaining light is redirected to the EPE, and the remaining portion of this portion continues to propagate further along the waveguide, and so on. Similarly, when impinging on the EPE, a portion of the incident light is directed out of the waveguide towards the user, and the remaining portion of this light continues to propagate through the waveguide until it impinges on the EPE again, at which time another portion of the incident light is directed out of the waveguide, and so on. Therefore, whenever a portion of a single beam of coupled-in light is redirected by the OPE or EPE, this light can be "duplicated", thus forming a field of cloned light beams, as Figure 6 shown. In some embodiments, the OPE and / or EPE can be configured to modify the size of the light beam.

[0167] Therefore, referring to Figure 9A and Figure 9B, in some embodiments, waveguide group 660 includes, for each component color: waveguides 670, 680, 690; input coupling optical elements 700, 710, 720; light distribution elements (e.g., OPE) 730, 740, 750; and output coupling optical elements (e.g., EP) 800, 810, 820. Waveguides 670, 680, 690 may be stacked via an air gap / cladding between each waveguide. Input coupling optical elements 700, 710, 720 redirect or deflect incident light (receiving light of different wavelengths through different input coupling optical elements) into their waveguides. The light then propagates at an angle that will result in TIR within the respective waveguides 670, 680, 690. In the example shown, light ray 770 (e.g., blue light) is deflected by the first input coupling optical element 700 in the manner previously described and then continues to bounce along the waveguide, interacting with light distribution element (e.g., OPE) 730 and output coupling optical element (e.g., EP) 800. Light rays 780 and 790 (e.g., green and red light, respectively) will transmit through waveguide 670, where light ray 780 impinges on input coupling optical element 710 and is deflected by it. Then, light ray 780 bounces along waveguide 680 via TIR, proceeds to its light distribution element (e.g., OPE) 740, and then proceeds to output coupling optical element (e.g., EP) 810. Finally, light ray 790 (e.g., red light) transmits through waveguide 690 and impinges on the light input coupling optical element 720 of waveguide 690. Light input coupling optical element 720 deflects light ray 790 such that the light ray propagates to light distribution element (e.g., OPE) 750 via TIR and then to output coupling optical element (e.g., EP) 820 via TIR. Then, output coupling optical element 820 finally couples out light ray 790 to the viewer, who also receives the output-coupled light from the other waveguides 670, 680.

[0168] Figure 9C A top plan view showing an example of Figure 9A and Figure 9B a plurality of stacked waveguides. As illustrated, waveguides 670, 680, 690 and the associated light distribution elements 730, 740, 750 of each waveguide and the associated output coupling optical elements 800, 810, 820 may be vertically aligned. However, as discussed herein, input coupling optical elements 700, 710, 720 are not vertically aligned; rather, the input coupling optical elements do not overlap (e.g., are laterally spaced apart when viewed in a top view). As further discussed herein, this non-overlapping spatial arrangement helps to inject light from different sources into different waveguides one-to-one, thereby allowing a particular light source to be uniquely coupled to a particular waveguide. In some embodiments, an arrangement including non-overlapping spatially separated input coupling optical elements may be referred to as a shifted pupil system, and the input coupling optical elements within these arrangements may correspond to sub-pupils.

[0169] Alternatively, in some embodiments, two or more coupled-in optical elements may be in a tandem arrangement, in which they are vertically aligned. In such an arrangement, light for a waveguide further from the projection system is transmitted through the coupled-in optical element for a waveguide closer to the projection system, preferably with minimal scattering or diffraction.

[0170] The tandem configuration can advantageously reduce the size of the projector and simplify the projector. In addition, it also increases the field of view of the eyepiece, for example, by using crosstalk to couple light of the same color onto multiple waveguides. For example, green light can be coupled into the active layers of blue and red. Since the pitch of each ICG can be different to provide improved (e.g., optimal) performance for a particular color, the allowable field of view can be increased.

[0171] In the tandem configuration, except for the last layer in the optical path, the ICG should at most partially reflect or otherwise transmit light at the operating wavelength of the subsequent layer in the stack of waveguides. In each case, unless a grating is etched in a high refractive index layer (e.g., 1.8 or above for a polymer-based layer), or a high refractive index coating is deposited or grown on the grating, the efficiency will be very low. However, this method increases the back reflection into the projector lens, which may thus produce image artifacts such as image ghosts.

[0172] Figure 9D An example of a wearable display system 60 is shown into which various waveguides and related systems disclosed herein may be integrated. In some embodiments, the display system 60 is Figure 6 system 250, where Figure 6 Some components of the system 60 are shown schematically in more detail. For example, Figure 6 the waveguide assembly 260 can be part of the display 70.

[0173] Continuing to refer to Figure 9D, the display system 60 includes a display 70, as well as various mechanical and electronic modules and systems that support the functions of the display 70. The display 70 can be coupled to a frame 80 that can be worn by a user or viewer 90 of the display system, and the frame 80 is configured to position the display 70 in front of the eyes of the user 90. In some embodiments, the display 70 can be considered to be glasses. In some embodiments, a speaker 100 is coupled to the frame 80 and is configured to be positioned adjacent to the ear canal of the user 90 (in some embodiments, another speaker (not shown) can optionally be positioned adjacent to the other ear canal of the user to provide stereo / plastic sound control). The display system 60 can also include one or more microphones 110 or other devices to detect sound. In some embodiments, the microphone is configured to allow the user to provide input or commands to the system 60 (e.g., selection of voice menu commands, natural language questions, etc.), and / or can allow audio communication with other people (e.g., other users of a similar display system). The microphone can further be configured as a peripheral sensor to collect audio data (e.g., sounds from the user and / or the environment). In some embodiments, the display system can also include a peripheral sensor 120a that can be separated 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). In some embodiments, the peripheral sensor 120a can be configured to acquire data characterizing the physiological state of the user 90. For example, the sensor 120a can be an electrode.

[0174] Continuing to refer to Figure 9D, the display 70 is operably coupled to the local processing and data module 140 via a communication link 130 (such as, via a wired lead or a wireless connection). The local data processing module 140 can be installed in various configurations, such as fixedly attached to the frame 80, fixedly attached to a helmet or hat worn by the user, embedded in the earphone, or removably attached to the user 90 in other ways (e.g., in a backpack configuration, in a belt-coupled configuration). Similarly, the sensor 120a can be operably coupled to the local processing and data module 140 via a communication link 120b (e.g., a wired lead or a wireless connection). The local processor and data module 140 can include a hardware processor and a digital memory, such as a non-volatile memory (e.g., flash memory or a hard disk drive), both of which can be used to assist in the processing, caching, and storage of data. Optionally, the local processor and data module 140 can include one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, and so on. The data can include a) data captured from sensors (which can be operably coupled to the frame 80 or attached to the user 90 in other ways), such as image capture devices (such as cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, radio devices, gyroscopes, and / or other sensors disclosed herein; and / or b) data obtained and / or processed using the remote processing module 150 and / or the remote data repository 160 (including data related to virtual content), which may be used to transmit to the display 70 after such processing or retrieval. The local processing and data module 140 can be operably coupled to the remote processing module 150 and the remote data repository 160 via communication links 170, 180 (such as via wired or wireless communication links), such that these remote modules 150, 160 are operably coupled to each other and can be used as resources for the local processing and data module 140. In some embodiments, the local processing and data module 140 can include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a radio device, and / or a gyroscope. In some other embodiments, one or more of these sensors can be attached to the frame 80, or can be an independent structure communicating with the local processing and data module 140 via a wired or wireless communication path.

[0175] Continue to refer to Figure 9D, in some embodiments, the remote processing module 150 may include one or more processors configured to analyze and process data and / or image information. For example, it may include one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, and so on. In some embodiments, the remote data repository 160 may include a digital data storage facility, which may be obtained through the Internet or other network configurations in a "cloud" resource configuration. In some embodiments, the remote data repository 160 may include one or more remote servers that provide information to the local processing and data module 140 and / or the remote processing module 150, such as information for generating augmented reality content. In some embodiments, all data is stored in the local processing and data module, and all calculations are performed, thereby allowing for complete autonomous use from the remote module. Optionally, an external system including a CPU, GPU, etc. (e.g., a system of one or more processors, one or more computers) may perform at least a portion of the processing (e.g., generating image information, processing data), and provide information to and receive information from modules 140, 150, 160, for example, via a wireless or wired connection.

[0176] Diffraction grating with reduced polarization sensitivity

[0177] Providing a high-quality immersive experience to the user of a waveguide-based display system (such as various display systems configured for the above virtual / augmented / mixed display applications) depends, among other things, on various characteristics of the light coupled into and / or out of the waveguide in the display system eyepiece. For example, a virtual / augmented / mixed display with high light coupling-in and coupling-out efficiency can enhance the viewing experience by increasing the brightness of the light guided to the user's eyes. As discussed above, an input coupling optical element (such as an input coupling diffraction grating) can be employed to couple light into the waveguide for guiding therein by total internal reflection. Similarly, an output coupling optical element (such as an output coupling diffraction grating) can also be employed to couple the light guided within the waveguide by total internal reflection out of the waveguide.

[0178] As described above, for example, with reference to Figure 6 and Figure 7 , a display system according to various embodiments described herein may include optical elements, such as an input coupling optical element that may include a diffraction grating, an output coupling optical element, a light distribution element, and / or a combined pupil expander-extractor (CPE). As disclosed herein, the CPE can both disperse or distribute light within the waveguide as a light distribution element, thereby possibly increasing the beam size and / or the eye box, and also act as an out-coupling optical element to couple light out of the waveguide.

[0179] For example, as previously referenced Figure 7As described above, the light 640 injected into the waveguide 270 at the input surface 460 of the waveguide 270 propagates and is guided within the waveguide 270 by total internal reflection (TIR). In various embodiments, at the point where the light 640 is incident on the outcoupling optical element 570, a portion of the light guided within the waveguide may leave the waveguide as, for example, a small beam 650. In some embodiments, any of the optical elements 570, 580, 590, 600, 610 that may include one or more of an incoupling optical element, an outcoupling optical element, a light distribution element, or a CPE may be configured as a diffraction grating.

[0180] To achieve the desired characteristics for the incoupling (or outcoupling) of light into the waveguides 270, 280, 290, 300, 310, the optical elements 570, 580, 590, 600, 610 configured as diffraction gratings may be formed of a suitable material and have a suitable structure for controlling various optical characteristics, including diffraction characteristics, such as diffraction efficiency according to polarization variations. Among other characteristics, possible desired diffraction characteristics may include any one or more of the following characteristics: spectral selectivity, angular selectivity, polarization selectivity (or non - selectivity), high spectral bandwidth, high diffraction efficiency, or wide field of view (FOV).

[0181] Some diffraction gratings have a strong polarization dependence and may thus have a relatively reduced overall efficiency (due to rejecting one polarization). Such diffraction gratings may also produce coherent artifacts and reduce the uniformity of the far - field image. To provide a diffraction grating with reduced polarization sensitivity (e.g., a diffraction grating that couples light with an efficiency relatively independent of polarization), some displays for AR systems according to embodiments described herein include waveguides having a blazed diffraction grating formed therein. For example, the blazed grating may include diffraction features having a "sawtooth" shape. In some embodiments, the blazed grating may achieve improved grating diffraction efficiency for a particular diffraction order while reducing or minimizing the diffraction efficiency for other orders. Thus, in some embodiments, more light may be directed to a particular given diffraction order relative to any other diffraction order.

[0182] Transmissive ICG

[0183] In some examples, the diffraction gratings described herein may be transmissive ICGs for coupling input light into a waveguide. Such a diffraction grating is referred to as a transmissive diffraction grating, e.g., a transmissive ICG that emits light into the waveguide via a transmissive diffraction order (e.g., T 10 ) Figure 10AFIG. 0 shows a cross-sectional view of a portion of a display device 1000 (such as an eyepiece) according to some designs described herein, the display device including a waveguide 1004 and a blazed diffraction grating 1008 formed on a substrate that is the waveguide 1004. In the illustrated embodiment, the blazed diffraction grating 1008 is formed in the substrate / waveguide 1004 (in this example, the substrate / waveguide 1004 is planar). The surface of the substrate or waveguide 1004 has a surface topography including diffraction features that together form the diffraction grating 1008. The blazed diffraction grating 1008 is configured to diffract light having wavelengths within the visible spectrum such that light incident thereon is guided within the waveguide 1004 by TIR. The waveguide 1004 can be transparent and can form part of an eyepiece through which a user's eye can view. Such a waveguide 1004 and eyepiece can be included in a head-mounted display, such as an augmented reality display. For example, the waveguide 1004 can correspond to one of the waveguides 670, 680, 690 described above with respect to Figures 9A - 9C For example, the blazed diffraction grating 1008 can correspond to one of the light coupling optical elements 700, 710, 720 described above with respect to Figures 9A - 9C The blazed diffraction grating 1008 configured to couple light into the waveguide 1004 can herein be referred to as an input coupling grating (ICG). The display device 1000 can also include an optical element 1012. For example, the optical element 1012 can correspond to a light distribution element (e.g., Figures 9A - 9C One of the light distribution elements 730, 740, 750 shown in ) or an output coupling optical element (e.g., Figures 9A - 9C One of the output coupling optical elements 800, 810, 820 shown in ).

[0184] In operation, when an incident light beam 1016 (e.g., visible light, such as visible light from a light projection system providing image content) is incident on the blazed diffraction grating 1008 at an incident angle α with respect to a plane normal 1002 of a plane that is orthogonal or normal perpendicular to an extended surface or plane of the blazed diffraction grating or the substrate / waveguide or the surface 1004S of the waveguide 1004 (e.g., the major surface of the waveguide on which the grating is formed (as Figure 10A Shown, the major surface extending parallel to the Y-axis)), the blazed diffraction grating diffracts the incident light beam 1016 at least partially into a diffracted light beam 1024 at a diffraction angle θ measured with respect to the plane normal 1002. When the diffracted light beam 1024 exceeds the critical angle θ for total internal reflection to occur in the waveguide 1004 TIRWhen diffracted at a diffraction angle θ, the diffracted light beam 1024 propagates in the waveguide 1004 generally in a direction parallel to the x-axis and along the length of the waveguide via total internal reflection (TIR) and is guided. For example, a portion of the light guided in the waveguide 1004 may reach one of the light distribution elements 730, 740, 750 or one of the outcoupling optical elements (800, 810, 820, Figures 9A - 9C ) and is diffracted again.

[0185] As described herein, in the illustrated embodiments, a light beam incident at an angle in the clockwise direction with respect to the plane normal 1002 (i.e., on the right side of the plane normal 1002) is referred to as having a negative α (α < 0), while a light beam incident at an angle in the counterclockwise direction with respect to the plane normal 1002 (i.e., on the left side of the plane normal) is referred to as having a positive α (α > 0).

[0186] As further described in other parts of this specification, an appropriate combination of a high refractive index material and / or the structure of the diffraction grating 1008 can produce a specific range (Δα) of the incident angle α, herein referred to as the acceptance angle range or the field of view (FOV). A range Δα can be described by an angular range spanning negative and / or positive values of α, outside of which the diffraction efficiency drops by more than 10%, 25%, more than 50%, or more than 75%, 80%, 90%, 95% relative to the diffraction efficiency at α = 0 or some other direction, or any value within a range defined by any of these values. In some embodiments, it may be desirable to have a Δα within a range where the diffraction efficiency is relatively high and constant. For example, a uniform diffracted light intensity within Δα is desired. Thus, in some embodiments, Δα is associated with the angular bandwidth of the diffraction grating 1008 such that the incident light beam 1016 within Δα is effectively diffracted by the diffraction grating 1008 at a diffraction angle θ with respect to the surface normal 1002 (e.g., in a direction parallel to the y-z plane), where θ exceeds θ TIR , such that the diffracted light is guided in the waveguide 1004 under total internal reflection (TIR). In some embodiments, this angular Δα range may affect the field of view seen by the user. It should be understood that in various embodiments, light can be guided to the input coupling grating (ICG) from either side. For example, light can be guided through the substrate or the waveguide 1004 and incident on the Figure 10A illustrated reflective input coupling grating (ICG) 1008. The light can experience the same effects, e.g., be coupled into the substrate or the waveguide 1004 by the input coupling grating 1008 such that the light is guided in the substrate or the waveguide by total internal reflection. The range (Δα) of the incident angle α, herein referred to as the acceptance angle range or the field of view (FOV), may be affected by the refractive index of the substrate or waveguide material. For example, in Figure 10AAmong them, the reduced angular range (Δα’) shows the influence of the high refractive index material on the refraction of light incident on the input coupling grating (ICG). However, the angular range (Δα) or the FOV is larger.

[0187] Figure 10B A cross-sectional view of an exemplary blazed transmission diffraction grating 1008 is shown. The grating 1008 includes grating features having peaks 1003 and grooves 1005. The blazed transmission grating 1008 includes a surface corresponding to the surface 1004S of the substrate or waveguide, which, as observed from the cross-section shown, has a pattern in the shape of a "sawtooth". The "sawtooth" pattern is formed by a first inclined portion 1007 of the surface 1004S. In Figure 10B In the example shown, the grating 1008 further includes a second (steeper) inclined portion 1009. In the example shown, the first inclined portion 1007 has a shallower inclination than the second inclined portion 1009, and the second inclined portion 1009 has a steeper inclination. In this example, the first inclined portion 1007 is also wider than the second inclined portion 1009.

[0188] The peak 1003 has a height H, which corresponds to the distance from the bottom of the groove 1005 to the top of the peak 1003. Thus, this value can be referred to herein as the peak height and / or the groove depth, and can also be referred to as the grating height or the grating depth, or as the height of the diffraction feature of the diffraction grating. In Figure 10B In the example shown, the bottom of the groove 1005 is formed by the intersection of the first inclined portion 1007 and the second inclined portion 1009 of two adjacent peaks 1003. The first inclined portion 1007 is located on one of the adjacent peaks 1003, while the second inclined portion 1009 is located on the other adjacent peak. Similarly, the top of the peak 1003 is formed by the intersection of the first inclined portion 1007 and the second inclined portion 1009 at the top of the peak 1003. However, other configurations are also possible. For example, the first and second inclined portions do not necessarily intersect. For example, as will be discussed below, in the case where the bottom of the groove 1005 has a flat bottom, or in the case where the top of the peak 1003 includes a flat plateau. The blazed diffraction grating 1008 has a line spacing or pitch d, which can be constant in some embodiments. For example, the line spacing or pitch can be a measure of the spacing between the vertices of the peaks 1003 in the grating 1008 having a shape similar to the Figure 10B shape shown. Similarly, the line spacing or pitch d can be a measure of the spacing between the deepest positions of adjacent grooves 1005. The line spacing or pitch d can be measured from other positions on the grating features.

[0189] The inclined plane can be relative to being parallel to the grating 1008 or the waveguide surface (e.g., the surface 1004S of the waveguide, which can extend beyond the grating or the waveguide and Figure 10Ais inclined at an angle δ with respect to the plane of the surface 1004S' opposite to the grating. This angle δ of the first (shallower) inclined portion 1007 may be referred to as the blaze angle herein.

[0190] As Figure 10B shown, the blazed diffraction grating 1008 may include grating lines or features having an asymmetric shape, e.g., including asymmetrically shaped peaks 1003 and / or grooves 1005. For example, in Figure 10B the diffraction grating shown, the diffraction features include peaks 1003 and / or grooves 1005 having an asymmetric triangular cross-sectional shape. As described above, such an asymmetric shape results in the first inclined portion 1007 and the second inclined portion 1009 having different inclinations and / or widths. However, other shapes may also be employed.

[0191] In a design where the diffraction features are asymmetric, e.g., the inclination of the first inclined portion is shallower while the slope of the second inclined portion is steeper, the diffraction features may be considered to be formed by repeating inclined planes and steps. Such a structure may be referred to as an inclined step structure herein. In some embodiments, the second portion may be so steep as to be non-inclined; for example, the second portion may be parallel to the normal 1002.

[0192] However, in other embodiments of the "sawtooth" pattern, the peaks 1003 and / or grooves 1005 may be symmetric. For example, the first and second inclined portions 1007, 1009 may have the same inclination and the same width.

[0193] Figure 10B The cross-sectional pattern shown may be referred to as a single-step geometry herein, and a multi-step structure is also possible.

[0194] Regardless of whether the diffraction features are asymmetric or symmetric, in some embodiments, as will be discussed below, a plateau or flat portion may be located at the top of the peak 1003. For example, in Figure 11B it is shown that the diffraction grating 1008 includes diffraction features having a plateau or flat portion at the top of the peak 1003.

[0195] Figure 10B An incident beam 1016 is shown incident on the grating 1008 at an angle α with respect to the normal direction 1002. (As discussed above with respect to Figure 10A In other examples, light may pass through the substrate or waveguide 1004 and be incident on the diffraction grating 1008 from the other side). As discussed above, the normal 1002 is normal perpendicular or orthogonal to the extended surface of the blazed diffraction grating 1008 or the plane of the grating or waveguide and / or the surface 1004S of the waveguide 1004, e.g., the main surface of the waveguide on which the grating is formed or the opposite planar surface 1004S'. In Figure 10BIn this case, the light 1016 incident on the diffraction grating 1008 is shown to be diffracted at an angle β with respect to the normal direction 1002.

[0196] When configured to couple into an optical element or into a diffraction grating, the diffraction grating 1008 can diffractively couple light incident on the substrate 1004, which can be a waveguide as described above. If desired, the diffraction grating 1008 can be configured to couple out of an optical element, and in such an embodiment, can diffractively couple light from the substrate 1004, which can also be a waveguide as described above.

[0197] Reference Figure 10A and 10B, in some embodiments, the substrate 1004 comprises a high refractive index material having a refractive index of at least 1.9. For example, the refractive index can be at least 2.0, at least 2.1, at least 2.2, or at least 2.3, and can be no more than 2.4, 2.5, 2.6, 2.7, 2.8, or can be within any range formed by any of these values, or can be outside of these ranges (e.g., 3.0 or higher, such as up to 4.0). For example, in some embodiments, the substrate comprises a lithium-based oxide. In the various examples disclosed herein, the diffractive features of the diffraction grating 1008 can be formed on the surface of the substrate 1004. The diffractive features can be formed in the substrate 1004 (e.g., waveguide), or in a separate layer formed on the substrate 1004 (e.g., waveguide), and are configured to optically communicate with the substrate 1004, such as coupling light into or out of the substrate 1004. In the illustrated example, the diffractive features (such as lines) of the diffraction grating 1008 are formed in the substrate 1004, such as the surface of the substrate. For example, the diffractive features can be etched into the substrate 1004, which comprises a high refractive index material, such as a lithium-based oxide. For example, the substrate can comprise lithium niobate, and the diffraction grating can be formed in the lithium niobate substrate by etching or patterning the substrate surface. Other materials having a high refractive index can also be used. Other lithium-containing materials (such as lithium oxides, e.g., lithium tantalate (LiTaO3)) can also be used as the substrate. Silicon carbide (SiC) is another option for the substrate material. The examples are not limited. In other examples, the diffractive features of the diffraction grating 1008 can be formed in a separate layer disposed on the substrate 1004 (e.g., in physical contact with the substrate 1004). For example, thin film coatings such as zinc oxide (ZnO), silicon nitride (Si3N4), zirconium dioxide (ZrO2), titanium dioxide (TiO2), silicon carbide (SiC), etc., with a thickness less than 200 nm can be disposed on an existing high refractive index substrate. The thin film coating can be patterned to form the diffractive features. However, in some embodiments, the diffractive features (such as lines) of the diffraction grating 1008 can be formed of a material different from the substrate. For example, the substrate can comprise a high refractive index material, such as a lithium-based oxide (e.g., lithium niobate LiNbO3 or lithium tantalate LiTaO3), however, the diffractive features can be formed of a different material, such as a coating of zinc oxide (ZnO), zirconium dioxide (ZrO2), titanium dioxide (TiO2), silicon carbide (SiC), or other materials described herein. In some embodiments, such other materials formed on the substrate can have a lower refractive index.In some cases, the substrate 1004 may include the following materials (including amorphous high refractive index glass substrates): such as silicon-based glass (e.g., doped silicon glass), silicon oxynitride, transition metal oxides (e.g., hafnium oxide, tantalum oxide, zirconium oxide, niobium oxide, aluminum oxide (e.g., sapphire)), plastics, polymers, or other materials that are optically transmissive to visible light, which materials, for example, have an appropriate refractive index as described above and are different from the materials of the lithium-based oxide feature 1008.

[0198] However, as described above, in various embodiments described herein, the diffraction grating 1008 and the substrate 1004 or the waveguide both include the same material, such as a lithium-based oxide. In some embodiments, the diffraction grating 1008 is directly patterned into the substrate 1004 such that the diffraction grating 1008 and the substrate 1004 form a monolithic or single-piece structure. For example, the substrate 1004 includes a waveguide, and the diffraction grating 1008 is directly formed on the surface of the waveguide or the substrate. In these embodiments, the main lithium-based oxide material may be patterned at the surface 1004S to form the diffraction grating 1008, while the lithium-based oxide material below the diffraction grating 1008 may form the waveguide. In still some other embodiments, the main body or substrate 1004 and the surface 1004S that are patterned to form the diffraction grating 1008 include different lithium-based oxides. For example, the main lithium-based oxide material patterned in the surface region to form the diffraction grating 1008 may be formed of a first lithium-based oxide material, while the lithium-based oxide material forming the substrate 1004 or the substrate region below the diffraction grating 1008 may be formed of a second lithium-based oxide material different from the first lithium-based oxide material. As described above, in some other embodiments, the diffraction grating 1008 includes different high refractive index materials, such as zirconium dioxide (ZrO2), titanium dioxide (TiO2), silicon carbide (SiC), etc., and the material forming the substrate 1004 or the substrate region below the diffraction grating 1008 may be formed of a second material, such as LiTaO3, LiNbO3, etc., and is different from the first material as a thin film coating.

[0199] In Figure 10A and Figure 10B In the example shown in, the diffraction grating 1008 may include a plurality of blazed diffraction grating lines that are elongated in a first horizontal direction or the y direction and periodically repeated in a second horizontal direction or the x direction. For example, the diffraction grating lines may be straight and continuous lines extending in the y direction. However, the embodiments are not limited thereto. In some embodiments, the diffraction grating lines may be discontinuous lines, for example, in the y direction. In some other embodiments, the discontinuous lines may form a plurality of columnar objects protruding from the surface of the grating substrate. In some embodiments, at least some of the diffraction grating lines may have different widths in the x direction.

[0200] In the illustrated example, the diffraction grating lines of the diffraction grating 1008 have a profile, such as a sawtooth profile, that has asymmetric opposing side surfaces forming different angles relative to the substrate plane. However, the embodiments are not limited thereto, and in other embodiments, the diffraction grating lines may have symmetric opposing side surfaces forming similar angles relative to the substrate plane.

[0201] Reference Figure 10A and 10B , according to various embodiments, the diffraction grating 1008 may have various dimensions. For example, according to an embodiment, the diffraction features of the diffraction grating 1008 may have a height (H) of 10 nm or 40 nm to 150 nm or 200 nm, 50 nm to 110 nm, 60 nm to 100 nm, 70 nm to 90 nm, or about 80 nm, or a height within a range defined by any of these values. This height may correspond to the height of the peak 1003 and / or the depth of the trench 1005. Such a height and the blaze geometry in a high refractive index material can provide a diffraction grating with reduced polarization sensitivity. However, other heights are also possible.

[0202] According to various embodiments, the diffraction grating 1008 may have a pitch of 250 nm to 350 nm, 300 nm to 400 nm, 250 nm to 450 nm, or a pitch within any range defined by any of the above values. Other pitches are also possible.

[0203] In some embodiments, the blaze angle of the diffraction grating 1008 may be about 20 to 89 degrees and the anti-blaze angle may be 70 to 150 degrees or any value within the range defined by these values. As discussed below, values outside of these ranges are also possible.

[0204] Generally, single-order or multi-order geometry blaze diffraction gratings are possible, and various techniques can be used to form the grating. In Figures 11A - 11B the illustrated example, the grating can be formed by depositing a blaze and then etching and patterning a photoresist.

[0205] Example methods of forming a blaze grating and examples of various blaze grating geometries are described in US20210072437A1, titled "Display device with diffraction grating having reduced polarization sensitivity", the entire content of which is incorporated herein by reference.

[0206] Figure 11Ashows the formation of a first-order blazed grating 1106 in a substrate 1104, which may be a waveguide 1004( Figure 10A ). A patternable material, such as photoresist 1102, is deposited onto a substrate 1104, which is or includes a waveguide 1104. The patternable material / photoresist 1102 is patterned to have the shape of a blazed grating. In some embodiments, forming a blazed geometry in the photoresist 1102 involves imprinting a pattern in the photoresist 1102, such as a first-order "sawtooth" pattern (e.g., depositing photoresist on the substrate 1104 and then imprinting the blazed geometry). The photoresist 1102 may include a mask, such as a hard mask. The patterned photoresist 1102 and the substrate 1104 may then be etched to form a blazed pattern in the substrate 1106. For example, etching the photoresist 1102 and the substrate 1104 may involve dry plasma or chemical etching and / or wet chemical etching. In some embodiments, Figure 11A the etching shown may etch away the material at a relatively constant rate such that the thickest part of the patterned photoresist results in a relatively small amount of material removed from the substrate, e.g., negligible or no removal, while the thinnest (or absent) part of the patterned photoresist results in a relatively large amount of material removed from the substrate or the deepest etch into the substrate.

[0207] Figure 11B is a scanning electron micrograph of a blazed photoresist grating 1112, where the blazed grating pattern is formed in the photoresist substrate 1104, e.g., by imprinting the photoresist with a patterned master. The diffraction grating 1112 shown has a first-order blazed geometry.

[0208] In some embodiments, the blazed grating has parallel sidewalls. Such a grating may also be referred to as an "angled grating". For example, referring to Figure 12 , a cross-sectional profile of one pitch length of such a grating is shown, where the grating structure 1200 includes a grating layer that includes ridges 1220 on a substrate 1210. A Cartesian coordinate system is provided for reference. The grating extends in the x direction, and the ridges 1220 extend in the z direction from a substrate portion, having angled relative slopes with respect to the top surface of the ridges 1220 and the substrate surface. Two additional layers 1230 and 1240 are formed on the surface of the grating layer. Layers 1230 and 1240 are formed on the top surface of the ridges 1220 and in the valleys between contiguous ridges, but only one slope of the ridges 1220 (the left side in this example) is coated, while the other slope is substantially free of these coatings. Layers 1230 and 1240 may be formed using a directional deposition method (e.g., evaporation, angled deposition). The asymmetric coating of the two ridge slopes may be due to directional deposition and the resulting self-shadowing.

[0209] Figure 12The grating design shown can be characterized by six geometric parameters and three materials among others. Depending on the illumination wavelength and the desired response, these parameters can vary within the following ranges:

[0210] Parameter Range Anti - blaze angle 95°-165° Height 10 nm – 1000 nm Pitch 100 nm – 5,000 nm Duty cycle (width / pitch) 5％-95％ First coating thickness 5 nm – 500 nm Second coating thickness 5 nm – 500 nm

[0211] Table 1. Parameter ranges of grating 1200

[0212] As Figure 12 shown, the anti-blaze angle is the acute angle between the right inclined plane of the ridge 1220 and the substrate surface. The anti-blaze angle can be in the range from 75° to 165° (e.g., 75° to 150°, 80° to 140°, 85° to 130°, 90° to 120°, 90° to 100°, 100° to 160°, 120° to 160°, 130° to 150°, 135° to 140°).

[0213] The blaze angle is the angle between the left inclined plane of the ridge 1220 and the substrate surface. For the geometry of the tilted grating shown in Figure 12 this angle is the complementary angle of the anti-blaze angle (i.e., 180° minus the blaze angle). This angle can be in the range from 20° to 85° (e.g., 20° to 80°, 20° to 70°, 20° to 60°, 20° to 50°, 25° to 50°, 25° to 45°, 30° to 40°).

[0214] The height of the grating layer refers to the ridge dimension along the Z direction. The ridge 1220 can have a height in the range from 10 nm to 1,000 nm (e.g., 50 nm to 500 nm, 100 nm to 400 nm, 200 nm to 400 nm, 250 nm to 350 nm).

[0215] The pitch of the grating layer is the dimension along the X direction between adjacent ridges or adjacent valleys. Generally, the pitch, like the other parameters of the grating structure 1200, can be determined empirically and / or by simulation. The pitch can be adjusted according to the operating wavelength of the grating. Generally, the pitch is in the range from 100 nm to 5,000 nm (e.g., 100 nm to 2,500 nm, 100 nm to 1,000 nm, 200 nm to 750 nm, 250 nm to 500 nm, 300 nm to 400 nm, 200 nm to 500 nm, 250 nm to 450 nm, 300 nm to 400 nm, 325 nm to 375 nm, 350 nm to 370 nm).

[0216] The ridge has a width, which refers to the dimension along the X direction. For the grating structure 1200, the opposing inclined surfaces of the ridge 1220 passing through the illustrated cross-section are parallel, so the ridge thickness is constant throughout the entire height of the ridge. However, in some embodiments, the width may vary (e.g., narrow) from the bottom to the top of the ridge. In embodiments where the width varies, the width can be determined at the midpoint of the ridge height.

[0217] The top width of the ridge refers to the width of the ridge at the top of the grating layer, as Figure 12 shown. In the example, the top width can be in the range of 50 nm to 150 nm (e.g., 60 nm to 140 nm, 70 nm to 130 nm, 80 nm to 100 nm).

[0218] The duty cycle refers to the ratio of the width to the pitch, expressed as a percentage. In an embodiment, the grating structure can have a duty cycle in the range from 5% to 95% (e.g., 10% to 75%, 20% to 50%, 30% to 40%).

[0219] The ridge has a height corresponding to the dimension of the ridge in the Z direction measured from its bottom to its top surface. The ridge can have a height in the range from 10 nm to 1,000 nm (e.g., 50 nm to 500 nm, 100 nm to 400 nm, 200 nm to 400 nm, 250 nm to 350 nm).

[0220] The thicknesses of layers 1230 and 1240 refer to the dimensions of the layers in the Z direction measured at points on the surface of the support layer perpendicular to the Z direction. The first layer 1230 and / or the second layer can have a thickness in the range from 5 nm to 500 nm (e.g., 10 nm to 400 nm, 20 nm to 300 nm, 50 nm to 250 nm, 100 nm to 200 nm, 130 nm to 170 nm). Generally, the thicknesses of the first layer and the second layer can be the same or different.

[0221] The matrix material of the grating structure (i.e., the substrate 1210 and the ridge 1220) can be an ultraviolet or thermally crosslinkable polymer. The refractive index of the matrix material can be in the range from 1.5 to 2.2 (e.g., 1.6 or above, 1.7 or above, 1.8 or above, 1.9 or above, 2.1 or above, such as up to 2.2). A high refractive index (e.g., 1.8 or above) can be achieved using a polymer composite, for example, a polymer composite including nanoparticles (e.g., high refractive index nanoparticles, such as TiO2 nanoparticles and / or ZrO2 nanoparticles).

[0222] Without wishing to be bound by theory, it is believed that the high refractive index of the matrix patterning material can help make the diffraction efficiency similar at larger angles.

[0223] In some embodiments, the first coating 1240 comprises a material having a high refractive index (e.g., 1.8 or above). The first coating 1240 may be formed of a dielectric material including, but not limited to, titanium dioxide, gallium phosphide, and silicon carbide.

[0224] In certain embodiments, the second coating 1230 comprises a material having a low refractive index dielectric (e.g., 1.6 or lower, 1.5 or lower, 1.45 or lower). For example, the second coating may be formed of a dielectric material such as (but not limited to) silicon dioxide, magnesium fluoride, and calcium fluoride.

[0225] Generally, the grating layer of the grating structure 1200 and similar grating structures can be formed using the techniques described herein and in US20210033867A1 and US20210072437, the entire contents of both of which are incorporated herein by reference.

[0226] The first coating 1230 can be formed using various physical vapor deposition techniques including, but not limited to, sputtering and electron beam deposition. The second coating 1240 can be formed by various physical vapor deposition techniques including, but not limited to, sputtering and electron beam deposition. Generally, the techniques used to form the coating 1230 can be the same as or different from those used to form the coating 1240.

[0227] As described above in Figure 12 The optical properties of the exemplary grating structure are simulated using Rigorous Coupled Wave Analysis (RWCA) as follows. The parameter values of the grating structure are:

[0228]

[0229]

[0230] Table 2. Parameters and values for an exemplary ICG operating at the green wavelength

[0231] For simulation purposes, the operating wavelength used is 525 nm, and the refractive index of the substrate material is 2.0.

[0232] Figure 13A Shows the variation of the diffraction efficiency of the simulated grating in the emission direction within a 55° field of view with the illumination angle. The three curves correspond to TM polarized light, TE polarized light, and unpolarized light respectively. The calculated diffraction efficiency is 52.46%. Figure 13B Shows the variation of the reflection efficiency of the simulated grating for TM polarized light, TE polarized light, and unpolarized light with the illumination angle. The calculated reflection efficiency is 0.93%. Figure 13C and 13D correspond to Figure 13A and 13BThe same figure as shown, which is simulated for the same structure except without the second layer. The diffraction efficiency is still high, but the back reflection increases significantly.

[0233] Additional experiments were conducted to compare the results of the simulated grating structure with the measurements of similar fabricated samples. The results of these experiments are as Figures 14A - 14D shown. Specifically, Figure 14A and 14B show plots of the diffraction efficiency as a function of the angle of incidence for TM, TE, and unpolarized light over a certain range of angles of incidence. Figure 14A shows the simulated data, while Figure 14B shows the measurements of the fabricated samples for a subset of the simulated range. Figure 14C and 14D show a schematic cross-sectional profile of the grating structure ( Figure 14C ) and the SEM of the cross-section of the fabricated sample ( Figure 14D ).

[0234] Figures 15A - 15C shows the effect of including a low refractive index layer as the topmost layer of the grating structure. Figure 15A is a plot of the diffraction efficiency as a function of the angle of incidence for orthogonal polarization states for a grating structure with a TiO2 coating on it. The SEM of the cross-sectional profile of the grating structure is shown in the inset. Figure 15B is a plot of the diffraction efficiency as a function of the angle of incidence for the same grating structure, but with a further SiO2 layer formed on the TiO2 layer. The average diffraction efficiency as well as the diffraction efficiency for s-polarization and p-polarization are shown. Figure 15C shows a plot of the reflectance of normal incident light as a function of the wavelength of the visible light spectrum for grating structures with and without an SiO2 coating. The reflectance is low over almost the entire visible spectrum.

[0235] Figures 16A - 16F The measurements from a further example are shown. Specifically, Figure 16A is a plot of the diffraction efficiency as a function of the angle of incidence for the grating structure shown in the SEM in Figure 16B , which consists of a high refractive index (n = 2.0) composite material on a glass substrate (n = 1.78). Figure 16C is Figure 16D a plot of the diffraction efficiency as a function of the angle of incidence for the grating structure shown in the SEM in Figure 16E is Figure 16FGraph showing the variation of the diffraction efficiency of the grating structure shown in the SEM therein with the incident angle. The grating structure includes a high refractive index (n = 2.0) composite material with a TiO2 (n = 2.15) coating on a glass substrate (n = 1.78), and a SiO2 (n = 1.45) coating is also applied on the TiO2 layer. Apparently, compared with a single coating, the overall diffraction efficiency increases, especially at higher incident angles.

[0236] Although the foregoing examples are of tilted grating structures with parallelogram-shaped ridges, more generally, other cross-sectional shapes are possible. For example, trapezoidal, triangular, and stepped shapes are also possible. In addition, although the described shapes correspond to parallelograms with mathematical precision, deviations from these shapes are inevitable due to manufacturing limitations and the like. Generally speaking, as used herein, such ridges and other features are considered to have a specific shape, that is, their design stipulates that this shape and / or structure has this shape within the process capabilities for large-scale manufacturing of such structures.

[0237] In addition, in some examples, the ICG can be designed to effectively couple light (e.g., unpolarized light) of more than one wavelength (e.g., wavelengths across the visible spectrum, such as red, green, and blue wavelengths) into the waveguide. In some examples, within a field of view of 10° or greater (e.g., 15° or greater, 20° or greater, 22° or greater, 25° or greater, 30° or greater, 40° or greater, 50° or greater, 60° or greater, 70° or greater, e.g., up to 70° or less, 60° or less, 50° or less, 40° or less, 35° or less, 30° or less, 25° or less, 22° or less) in at least one direction (e.g., two orthogonal directions, such as the vertical and horizontal directions), the ICG has an average emission efficiency of 40% or higher (e.g., 45% or higher, 50% or higher, 55% or higher, 60% or higher, 65% or higher, e.g., 75% or less, 70% or less, 65% or less, 60% or less, 55% or less) for unpolarized incident light at multiple wavelengths over a spectral range of 120 nm or greater (e.g., 150 nm or greater, 200 nm or greater, 250 nm or greater, e.g., 500 nm or less, 400 nm or less, 300 nm or less, 250 nm or less, e.g., from 400 nm to 800 nm, e.g., from 430 nm to 650 nm).

[0238] In some examples, the ICG can be designed to have a relatively low back reflectance for incident light (e.g., unpolarized light) at more than one wavelength (e.g., wavelengths across the visible spectrum such as red, green, and blue wavelengths). For example, in a field of view of 10° or greater (e.g., 15° or greater, 20° or greater, 22° or greater, 25° or greater, 30° or greater, 40° or greater, 50° or greater, 60° or greater, 70° or greater, e.g., up to 70° or less, 60° or less, 50° or less, 40° or less, 35° or less, 30° or less, 25° or less, 22° or less) in at least one direction (e.g., two orthogonal directions such as the vertical and horizontal directions), the ICG can have an average back reflectance of 15% or less (e.g., 12% or less, 10% or less, 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, 3% or less, e.g., 1% or greater, 2% or greater, 3% or greater) for unpolarized incident light at multiple wavelengths in a spectral range of 120 nm or greater (e.g., 150 nm or greater, 200 nm or greater, 250 nm or greater, e.g., 500 nm or less, 400 nm or less, 300 nm or less, 250 nm or less, e.g., from 400 nm to 800 nm, e.g., from 430 nm to 650 nm).

[0239] In some examples, the ICG can be designed to both effectively couple light (e.g., unpolarized light) and have a relatively low back reflectivity for incident light (e.g., unpolarized light) at more than one wavelength. For example, within a field of view of 10° or greater (e.g., 15° or greater, 20° or greater, 22° or greater, 25° or greater, 30° or greater, 40° or greater, 50° or greater, 60° or greater, 70° or greater, e.g., up to 70° or less, 60° or less, 50° or less, 40° or less, 35° or less, 30° or less, 25° or less, 22° or less) in at least one direction (e.g., two orthogonal directions such as the vertical direction and the horizontal direction), the ICG can have an average emission efficiency of 40% or higher (e.g., 45% or higher, 50% or higher, 55% or higher, 60% or higher, 65% or higher, e.g., 75% or lower, 70% or lower, 65% or lower, 60% or lower, 55% or lower) for unpolarized incident light at multiple wavelengths across a spectral range of 120 nm or greater (e.g., 150 nm or greater, 200 nm or greater, 250 nm or greater, e.g., 500 nm or lower, 400 nm or lower, 300 nm or lower, 250 nm or lower, e.g., from 400 nm to 800 nm, e.g., from 430 nm to 650 nm), and have an average back reflectivity of 15% or lower (e.g., 12% or lower, 10% or lower, 9% or lower, 8% or lower, 7% or lower, 6% or lower, 5% or lower, 4% or lower, 3% or lower, e.g., 1% or higher, 2% or higher, 3% or higher).

[0240] Without being bound by theory, it is believed that adding one or more dielectric layers to the grating layer of the blazed ICG can facilitate effective coupling of light into the waveguide and achieve a low back reflectivity. This performance is evident based on the following example ICG structures modeled by computer simulation. However, the structures are merely examples and other structures are possible. In general, the structural parameters of the blazed grating can be optimized for a particular application based on experience and / or using computational optimization methods.

[0241] An example tilted transmission grating with two dielectric layers has the following structure:

[0242] Parameter Value Pitch 370 nm Height 339 nm Blaze angle 68° Anti - blaze angle 112° Duty cycle 45％ First coating thickness – TiO2 121 nm Second coating thickness – MgF2 38 nm

[0243] Table 3: Parameters of an example double-coated tilted transmission grating

[0244] The grating ridges are formed of K21 resist and are first covered by a TiO2 layer and then by an MgF2 layer.

[0245] The performance of this example was evaluated by calculating the diffraction efficiencies of the 0th, +1st, and -1st orders of the transmitted light of incident light (with TM and TE polarizations) at three different wavelengths (625 nm, 545 nm, and 465 nm) and with incident angles in the range of -45° to +45° for the unit primitive of the grating structure. For the sake of brevity, this analysis will be referred to as Metric I hereinafter.

[0246] The performance was also evaluated by calculating the emission efficiency into a waveguide with a refractive index of 2.00, an aperture size of 2 mm x 3.5 mm, and a waveguide thickness of 600 microns and the back reflection from this waveguide. The calculation was performed according to the polarization state with respect to the emission, where 0 degrees corresponds to TM light and 90 degrees corresponds to TE light. The calculation was also performed at three different wavelengths (625 nm, 545 nm, and 465 nm). For the sake of brevity, this analysis will be referred to as Metric II hereinafter.

[0247] Figure 17A and 17B Metric II of the example in Table 3 is shown in. In particular, Figure 17A the emission efficiency (percentage) of the incident light with polarization from 0° to 90° is shown. Figure 17B the back reflectance (percentage) of the incident light with polarization from 0° to 90° is shown.

[0248] In this example, according to the calculation for Metric II, the average emission efficiencies of red, green, and blue light are 50.20%, 49.63%, and 36.26% respectively. The average reflectances of red, green, and blue light are 7.23%, 9.18%, and 13.95% respectively.

[0249] Figures 18A - 18I Metric I of the example in Table 3 is shown in. Figures 18A - 18C The variation of the normalized 0th-order reflectance, normalized 0th-order transmittance, and 1st-order transmittance of the incident TM light with the incident angle are shown respectively. The 1st-order transmittance corresponds to the light incident into the waveguide. Figures 18D - 18F The variation of the normalized 0th-order reflectance, normalized 0th-order transmittance, and 1st-order transmittance of the incident TE light with the incident angle are shown respectively. Figures 18G - 18I The variation of the normalized 0th-order reflectance, normalized 0th-order transmittance, and 1st-order transmittance of the average incident light for TM and TE polarizations with the incident angle are shown respectively.

[0250] Another example of a blazed transmission grating with two dielectric layers has the following structure:

[0251] Parameter Value Pitch 370 nm Top width 103 nm Bottom width 60 nm Blaze angle 85° Anti - blaze angle 50° First coating thickness – TiO₂ 165 nm Second coating thickness – MgF₂ 150 nm

[0252] Table 4: Parameters of the example double-coated blazed transmission grating

[0253] Figure 19A and 19B shows Index II of an example in Table 4. In particular, Figure 19A shows the emission efficiency (percentage) of incident light with polarization from 0° to 90°. Figure 19B shows the back reflectance (percentage) of incident light with polarization from 0° to 90°. Figure 19C shows a cross-sectional view of a double-coated blazed transmissive ICG.

[0254] In this example, according to the calculations for Index II, the average emission efficiencies of red, green, and blue light are 42.19%, 28.01%, and 12.64% respectively. The average reflectances of red, green, and blue light are 9.23%, 13.92%, and 16.08% respectively.

[0255] Figures 20A - 20I shows Index I of an example in Table 4. Figures 20A - 20C Shows the variation of the normalized zero-order reflectance, normalized zero-order transmittance, and first-order transmittance of incident TM light with the angle of incidence. The first-order transmittance corresponds to the light entering the waveguide. Figures 20D - 20F Shows the variation of the normalized zero-order reflectance, normalized zero-order transmittance, and first-order transmittance of incident TE light with the angle of incidence. Figures 20G - 20I Shows the variation of the normalized zero-order reflectance, normalized zero-order transmittance, and first-order transmittance of the average incident light with TM and TE polarizations with the angle of incidence.

[0256] Reference Figure 21A and 21B , through further calculations, a sensitivity analysis of the emission efficiency and back reflection performance of double-coated tilted (Table 3) and blazed (Table 4) ICGs with respect to random design perturbations (+ / - 10 nm) of grating parameters was evaluated. In these figures, Lr, Lg, and Lb represent the emission efficiency values of red, green, and blue wavelengths respectively, and Rr, Rg, and Rb represent the back reflection values of red, green, and blue wavelengths respectively, which are the averages of all angles within the illumination field of view (for these calculation purposes, approximately 30-degree diagonal field of view).

[0257] Based on these calculation results, it is considered that the sensitivity of the tilted grating (such as Table 3) to perturbations in grating size may be higher than that of the blazed grating (such as Table 4). In other words, from the perspective of large-scale manufacturing, this means that manufacturing double-coated blazed ICG gratings may not require as high a precision in size and layer thickness as that required for manufacturing tilted gratings.

[0258] Reflective ICG

[0259] In addition, although the ICG in the above examples is a transmissive grating for emitting light into the waveguide, a reflective grating is also feasible. The reflective ICG mentioned here is an ICG that injects light into the waveguide through the reflection diffraction order (e.g., R 10 ). Referring to Figure 22 , an example of the reflective ICG 2200 for the single-layer RGB waveguide 2210 includes a blazed grating 2202 covered with a reflective material 2204 (such as a reflective metal (e.g., Al, Au, Ag, or their alloys)).

[0260] Figure 23 shows the structure of an example blazed reflective grating 2300. Here, parameters such as the blaze angle 2302, the anti-blaze angle 2304, the pitch 2306, the top width 2308, and the bottom width 2310 are the same as those described above for the tilted grating shown in Figure 12 . "rlt" refers to the thickness (z direction) of the continuous layer 2320 of the material (e.g., a polymer, such as a polymer resist) forming the grating ridge between the grating ridge 2301 and the top of the waveguide 2330.

[0261] A metal layer 2312 is formed on the ridge. The space between the ridges is filled with metal, conforming to the shape of the ridges.

[0262] The parameters of the first example of the reflective grating are as follows:

[0263] Parameter Value Top width 100 nm Bottom width 60 nm Pitch 370 nm Blaze angle 28 Anti - blaze angle 85 rlt 20 nm

[0264] Table 5: Examples of metallized blazed gratings

[0265] Figure 24A and 24B show the metrics II of the example metallized blazed gratings in Table 5. As shown, the emission efficiency and the back reflection are optimized for TM polarization while increasing / decreasing for TE polarization, respectively. By using a (2mm x 3.5mm) elliptical beam, the average polarization-averaged reflectivities for the RGB wavelengths within the FoV (22 degrees x 22 degrees) are 27.43%, 32.62%, and 22.14%, respectively. In addition, the emitted light of the average polarization entering the waveguide is 44.94%, 42.59%, and 32.32%, respectively.

[0266] Figures 25A - 25I show the metrics I of the example metallized blazed gratings in Table 5. Here, Figures 25A - 25C show the variation of the normalized reflection efficiency with the incident angle for TM-polarized light reflected into the -1, 0, and +1 diffraction orders, respectively. The zero-order reflection corresponds to the back reflection, and the +1 order corresponds to the light entering the waveguide. Figures 25D - 25FThe variation of the normalized reflection efficiency with the incident angle for TE-polarized light reflected into the -1, 0, and +1 diffraction orders is shown respectively. Figures 25G - 25I The variation of the average normalized reflection efficiency with the incident angle for TE and TM polarized light reflected into the -1, 0, and +1 diffraction orders is shown respectively. From the results of Index I, it can be seen that for all colors, the 0th order reflection value of the unit element for TM polarization is less than 5%, while for RGB, the values for TE polarization are close to ~60%, ~40%, and ~20% respectively.

[0267] A second example of a blazed reflection grating is outlined as follows:

[0268] Parameter Value Top width 150 nm Bottom width 64 nm Pitch 370 nm Blaze angle 31° Anti - blaze angle 140° rlt 20 nm

[0269] Table 6: Second example of a metallized blazed grating

[0270] The profile shape of this example is as Figure 26 shown.

[0271] Figure 27A and 27B show Index II of the example metallized blazed grating in Table 6. From Figure 27A and 27B it can be seen that the average polarization back-reflectance for all three colors (RGB) has decreased, significantly for green and red. For blue, the average polarization back-reflectance has not decreased significantly, while the first-order diffraction efficiency is low. For the blue wavelength, although the first-order diffraction efficiency is low, the -1 order diffraction efficiency value has also decreased, which is considered to contribute to the multiple bounce phenomenon described previously, which may lead to a reduction in back-reflectance.

[0272] Using an elliptical beam of (2mm x 3.5mm), the average polarization average reflectance for RGB wavelengths in the FoV (22 degrees x 22 degrees) range is 16.74%, 7.73%, and 7.53% respectively. In addition, the emitted light of the average polarization entering the waveguide is 49.74%, 45.65%, and 27.82% respectively.

[0273] Figures 28A - 28I show Index I of the example metallized blazed grating in Table 6.

[0274] The parameters of another example of a blazed reflection grating are as follows:

[0275] Parameter Value Top width 81 nm Bottom width 20 nm Pitch 370 nm Blaze angle 25 Anti - blaze angle 90 Coating thickness – TiO₂ 87 nm rlt 20 nm

[0276] Table 7: Example of a conformal coated blazed reflection grating

[0277] The cross-sectional profile 2900 of this example is in Figure 29Shown in. The grating ridge 2910 is supported on the waveguide 2940. The TiO2 coating 2920 conforms to the underlying ridge 2910 and is continuous over the grating layer. The reflective metal layer 2930 is coated on the coating 2920.

[0278] The parameters of another example of a blazed reflective grating are as follows:

[0279] Parameter Value Top width 96 nm Bottom width 120 nm Pitch 370 nm Blaze angle 27 Anti - blaze angle 91 Coating thickness – TiO₂ 95 nm rlt 20 nm

[0280] Table 8: Examples of directionally coated blazed reflective gratings

[0281] The cross-sectional profile 3000 of this example is shown in Figure 30 Shown in. The grating ridge 3010 is supported on the waveguide 3040. The TiO2 coating 3020 is deposited in a directional process (such as the GLAD process) such that the ridge walls 3011 on the anti-blazed side of each ridge are in the shadow of the coating. Thus, the TiO2 layer 3020 is discontinuous over the grating layer.

[0282] Figure 31A and 31B and show the metrics II of the example metallized blazed gratings in Table 8. From Figure 31A and 31B it can be seen that the average polarization back reflectivity of all three colors (RGB) is reduced, significantly reduced for green and red, for blue, the average polarization back reflectivity is not significantly reduced, and the first-order diffraction efficiency is low. For the blue wavelength, although the first-order diffraction efficiency is low, the -1 order diffraction efficiency value is also reduced, which is considered to contribute to the multiple bounce phenomenon described previously, which may lead to a reduction in back reflectivity.

[0283] Using an elliptical beam of (2mm x 3.5mm), the average polarization average reflectivities of the RGB wavelengths in the FoV (22 degrees x 22 degrees) range are 10.57%, 14.76%, and 17.63% respectively. In addition, the emitted light of the average polarization entering the waveguide is 52.63%, 49.40%, and 35.23% respectively.

[0284] It is obvious from the metrics II that the emission efficiency of all colors entering the waveguide has increased compared to the examples parameterized in Tables 5 and 6. The back reflectivity for red is reduced, while in the case of a larger anti-blazed angle (e.g., Table 6), the TE polarization back reflectivity for red is still high, in the range of 30%.

[0285] Figures 32A - 32I Show the metrics I of the example metallized blazed gratings in Table 8.

[0286] The parameters of the example double-layer coated blazed grating are as follows:

[0287] Parameter Value Top width 72 nm Bottom width 78 nm Pitch 370 nm Blaze angle 27° Anti - blaze angle 92° First coating – TiO₂ 50 nm Second coating – SiO₂ 71 nm rlt 20 nm

[0288] Table 9: Examples of Directional Dual-Coated Blazed Reflective Gratings

[0289] The cross-sectional profile 3300 of this example is shown in Figure 33A . The grating includes a ridge 3310 supported on a waveguide 3340. The first layer coating 3310 is a TiO2 coating, and the second layer coating 3312 is an SiO2 coating. Both coatings 3312 and 3314 can be deposited by a directional process (such as glancing angle deposition (GLAD)) such that the ridge walls 3311 on the anti-blazed side of each ridge are in the shadow of the coating. Thus, the two dielectric layers are discontinuous on the grating layer, especially at the sidewalls 3311 on the anti-blazed side. The reflective layer 3320 (such as a metal layer) can be deposited using a directional or isotropic deposition technique (such as evaporation). In some examples, the dielectric layer can be deposited using isotropic deposition and then patterned to provide one or more discontinuous layers (such as lithographic patterning).

[0290] Although Figure 33A shows an example of a reflective ICG, a similar structure can also be used for a transmissive ICG, such as Figure 33B shown, Figure 33B which shows a similar structure 3300' but without a reflective layer.

[0291] Figure 34A and 34B show the metrics II of the example metallized blazed gratings of Table 8. As can be seen from Figure 34A and 34B , for red and green wavelengths, the emission efficiency is substantially polarization-insensitive. For the blue wavelength, the emission efficiency varies by about 5% between TM and TE light. For all three wavelengths, the back reflectance varies by about 5% or less between TM and TE light.

[0292] Using an elliptical beam of (2 mm x 3.5 mm), the average polarization-averaged reflectance of the RGB wavelengths in the FoV (22 degrees x 22 degrees) range is 5.84%, 9.45%, and 21.76% respectively. In addition, the emission light of the average polarization entering the waveguide is 60.33%, 67.81%, and 48.62% respectively.

[0293] Figure 35A -35I shows the metrics I of the example metallized blazed gratings of Table 8.

[0294] Referring to Figures 36A - 36C, the electric field amplitude is plotted within the unit primitive of each grating structure specified in Tables 5, 6, 8, and 9. In particular, column A corresponds to the plot of the structure in Table 5, column B corresponds to the plot of the structure in Table 6, column C corresponds to the plot of the structure in Table 8, and column D corresponds to the plot of the structure in Table 9. Figure 36A The plots shown are for light at the red wavelength (625 nm). Figure 36B The plots shown are for light at the green wavelength (545 nm). Figure 36C The plots shown are for light at the blue wavelength (465 nm). In each of these plots, the first row is the TE field and the second row is the TM field. In each plot, the X-axis is the lateral dimension (x), and the Y-axis is the longitudinal dimension (z). The units along both axes are micrometers. It is noted that for the structure in Table 9 (column D), the confinement of the electric field to the TiO2 layer is very evident, especially for TE red light.

[0295] Therefore, a double dielectric coating in which the refractive index of the first dielectric layer is higher than that of the ridge and the refractive index of the second dielectric layer is considered potentially advantageous because waveguide-like confinement is generated in this layer. It is believed that this confinement can alter the wavefront in the direction of the first diffraction order for TE and TM polarizations.

[0296] Referring to Figure 37 , the emission efficiency and back reflectivity of each structure summarized in Tables 3 - 6 and Tables 8 - 9 at each wavelength are summarized in the figure. The Y-axis shows the average diffraction efficiency (for emission and back reflectivity) expressed as a percentage. The x-axis includes 6 points. The first three points are the emission efficiencies for R, G, and B respectively. The last three points are the back reflection efficiencies for R, G, and B respectively.

[0297] Generally, the dielectric layer can be made of a variety of materials, including those listed above. The refractive indices of these materials can vary from 1.5 to 4.0. Example materials include MgF2, SiN2, SiO2, Al2O3, TiO2, and SiN.

[0298] Further examples

[0299] There can also be other variations. For example, while the examples discussed above feature zero, one, or two dielectric layers coating the grating layer, additional layers can also be present. For example, an additional layer can be included between the grating layer and the outermost low refractive index layer. Figure 38 Example structure 3800 is shown in which shows a grating structure having a ridge 3810, and the grating structure includes three dielectric layers 3812, 3814, and 3816 between the ridge 3810 of the grating and the metal layer 3820. In some examples, n1 < n2 and n3 < n2, where n1 is the refractive index of coating 1, n2 is the refractive index of coating 2, and n3 is the refractive index of coating 3.

[0300] While the performance of the above example grating structures is determined at a single red wavelength, a single green wavelength, and a single blue wavelength, the performance can also be determined at other wavelengths (e.g., C, M, Y wavelengths). In general, the performance can be determined and optimized at any combination of operating wavelengths.

[0301] In addition, while the grating structures of the foregoing examples are one-dimensional gratings, other embodiments are possible. For example, in some embodiments, the structure arrays can also be arranged in two directions to form a two-dimensional (2D) array of diffraction features. The 2D array of diffraction features can include undulations in two directions. In some cases, the undulations can be periodic, while in other cases, the pitch of the undulations can vary in at least one direction. According to various examples described herein, the diffraction features have asymmetric angled or tilted opposing sidewalls. According to various examples described herein, the diffraction features can be conical.

[0302] In some embodiments, the diffraction features can have substantially angled or tilted opposing sidewalls. In some embodiments, the opposing sidewalls can be tilted in the same direction, while in other embodiments, the opposing sidewalls can be tilted in opposite directions. In some other embodiments, one of the opposing sidewalls of the diffraction feature can be substantially tilted, while the other sidewall is substantially perpendicular or orthogonal to the horizontal axis or is at least less tilted than the other sidewall. In various examples of the 2D diffraction features described herein, the 2D diffraction features can be formed in or on a bottom substrate, which can be a waveguide, as described above for various examples of one-dimensional diffraction features. For example, the 2D diffraction features can be etched into the bottom substrate or formed by patterning a separate layer formed thereon. Thus, the 2D diffraction features can be formed of the same or different materials as the substrate material in a manner similar to the various 2D diffraction features described above. Other variations and configurations are possible.

[0303] Thus, any structure or device described herein, such as a grating structure, may include a one-dimensional grating. Similarly, any structure or device described herein, such as a grating structure, may also include a 2D grating. Such a 2D grating may disperse light. These gratings may also include blazed gratings. Such blazed gratings may preferably direct light into certain directions. In some embodiments, a 2D grating (e.g., having one tilted facet in the diffractive feature) preferably directs light into one direction, while in other embodiments, a 2D grating (e.g., having two tilted facets differently in the diffractive feature) preferably directs light into multiple directions. Similarly, any method or process described herein may be used for a 1D grating. Similarly, any method or process described herein may be used for a 2D grating. These 1D or 2D gratings may be included in or on a substrate and / or waveguide, and may be included in an eyepiece, and may also be integrated into the head-mounted display disclosed herein. These gratings may be used as input gratings (e.g., ICG), output gratings (EPE), optical distribution gratings (OPE), or combined optical distribution grating / output gratings (e.g., CPE). For example, examples of output coupling gratings are as shown in Figure 9C and 10A Alternatively, or additionally, such gratings may be used for an orthogonal pupil expander (e.g., Figure 9C 730, 740, 750 in). Such geometries may be similarly optimized for polarization-insensitive output couplers and improve the transparency of the display in the area in front of the user's eyes, thereby reducing back reflections, which may be a problem when diffractive surface relief gratings are used as wearable waveguides.

[0304] In some examples, a waveguide may include two ICGs located on opposite sides of the waveguide. For example, referring to Figure 39 , waveguide 3910 includes a transmissive ICG 3920 on the side of the waveguide facing projector 3940 and a reflective ICG 3930 on the opposite side. The structures of the two ICGs may be optimized together to achieve low back reflections and high emission efficiency using the structures described in the above examples. Both the transmissive ICG 3920 and the reflective ICG 3930 emit light from projector 3940 into waveguide 3910.

[0305] As shown in Figure 39 , projector 3940 is arranged relative to waveguide 3910 such that light from projector 3940 is incident on transmissive mode ICG 3920 at an incident angle substantially normal to the surface of waveguide 3910. However, in other examples, the projector may be arranged such that its light is incident on the waveguide non-normally. Figure 40 Such an arrangement is described in, where projector 4040 is arranged such that light is incident at an angle θ that is not perpendicular to the top surface of waveguide 4010 inIncident on the transmissive ICG 4020. In such an arrangement, the incident angle θ in can be in the range of about 1° to 20° (measured from the normal of the waveguide surface) (for example, in the range of about 3° to 15°, about 5° to 12°, about 5° to 10°).

[0306] Other embodiments are in the following claims.

Claims

1. A head-mounted display system, comprising: A head-wearable frame; A light projection system configured to output light to provide image content; A waveguide supported by the frame, the waveguide being configured to guide at least a portion of the light coupled into the waveguide from the light projection system; A grating structure optically coupled to the waveguide, the grating structure being configured to couple light from the light projection system into the waveguide, the grating structure comprising: A grating layer including a plurality of ridges having a blazed profile in at least one cross-section; and One or more dielectric layers disposed on the grating layer, Wherein, for unpolarized incident light at at least one operating wavelength of the output light, within a field of view of 10° or greater in at least one direction, the grating structure has an average emission efficiency of 40% or higher and an average back reflectivity of 15% or lower.

2. The head-mounted display system according to claim 1, wherein, For unpolarized incident light at at least two operating wavelengths of the output light that are at least 100 nm apart, within a field of view of 10° or greater in at least one direction, the grating structure has an average emission efficiency of 40% or higher and an average back reflectivity of 15% or lower.

3. The head-mounted display system according to claim 2, wherein, For unpolarized incident light at three operating wavelengths of the output light across a spectral range of 120 nm or wider, within a field of view of 10° or greater in at least one direction, the grating structure has an average emission efficiency of 40% or higher and an average back reflectivity of 15% or lower.

4. The head-mounted display system according to claim 3, wherein, The three wavelengths are a blue wavelength, a green wavelength, and a red wavelength, respectively.

5. The head-mounted display system according to claim 4, wherein, The three wavelengths are 465 nm, 545 nm, and 625 nm, respectively.

6. The head-mounted display system according to claim 1, wherein The field of view is an orthogonal direction of 10° or greater.

7. The head-mounted display system according to claim 6, wherein, The field of view is 22° x 22° in the orthogonal direction.

8. The head-mounted display system according to claim 1, wherein, The grating structure is a reflective grating structure.

9. The head-mounted display system according to claim 1, wherein, The grating structure is a transmissive grating structure.

10. The head-mounted display according to claim 9, wherein, The plurality of ridges are tilted ridges.

11. The head-mounted display system according to claim 1, wherein, The grating structure further includes a metal layer disposed on the one or more dielectric layers.

12. The head-mounted display system according to claim 1, wherein, The one or more dielectric layers include at least one continuous layer.

13. The head-mounted display system according to claim 1, wherein, The one or more dielectric layers include at least one discontinuous layer.

14. The head-mounted display system according to claim 1, wherein, The one or more dielectric layers include a first dielectric layer directly disposed on the grating layer and a second dielectric layer directly disposed on the first dielectric layer, the refractive index of the first dielectric layer at the operating wavelength being greater than the refractive index of the grating layer and the refractive index of the second dielectric layer.

15. The head-mounted display system according to claim 1, wherein, The one or more dielectric layers include layers having a thickness in the range of 1 nm to 150 nm.

16. The head-mounted display system according to claim 1, wherein, The one or more dielectric layers include a first layer having a thickness in the range of 1 nm to 150 nm and a second layer having a thickness in the range of 30 nm to 100 nm.

17. The head-mounted display system according to claim 1, wherein, The plurality of ridges have a pitch in the range of 200 nm to 500 nm.

18. The head-mounted display system according to claim 1, wherein, The plurality of ridges have a top width in the range of 10 nm to 150 nm.

19. The head-mounted display system according to claim 1, wherein, The plurality of ridges have a bottom width in the range of 10 nm to 150 nm.

20. The head-mounted display system according to claim 1, wherein, The plurality of ridges have a blazed angle in the range of 15° to 50°.

21. The head-mounted display system according to claim 20, wherein, The plurality of ridges have an anti-blazed angle in the range of 70° to 150°.

22. The head-mounted display system according to claim 1, wherein, The emission efficiency of the grating structure corresponds to the first-order diffraction efficiency of the grating structure.

23. The head-mounted display system according to claim 1, wherein, The grating structure is a first grating structure, and the system further includes a second grating structure located on a side of the waveguide opposite to the first grating structure.

24. The head-mounted display system according to claim 23, wherein, The first grating structure is a reflective grating structure, and the second grating structure is a transmissive grating structure.

25. The head-mounted display system according to claim 23, wherein, The second grating structure includes a grating layer having a plurality of ridges and at least one dielectric layer supported by the grating layer.

26. The head-mounted display system according to claim 1 or 2, wherein The ridges have a profile shape selected from trapezoidal, parallelogram, triangular, and stepped.

27. The head-mounted display system according to any one of the preceding claims, wherein, The grating has a duty cycle in the range of 5% to 95%.

28. The head-mounted display system according to any one of the preceding claims, wherein, The grating material includes a crosslinked polymer.

29. The head-mounted display system according to claim 28, wherein, The grating material has a refractive index in the range of 1.5 to 1.

8.

30. The head-mounted display system according to claim 28, wherein, The grating material includes nanoparticles.

31. The head-mounted display system according to claim 30, wherein, The grating material has a refractive index in the range of 1.5 to 2.

25.

32. The head-mounted display system according to any one of the preceding claims, wherein, The waveguide supports a material film, and the ridges are etched into the film.

33. The head-mounted display system according to claim 32, wherein, The material is an inorganic material.

34. The head-mounted display system according to claim 32, wherein, The material has a refractive index in the range of 1.8 to 2.

8.

35. The head-mounted display system according to claim 32, wherein, The material has a refractive index in the range of 1.38 to 1.

45.

36. The head-mounted display system according to claim 32, wherein, The refractive index of the material is higher than the refractive index of the waveguide.

37. The head-mounted display system according to claim 32, wherein, The refractive index of the material is lower than the refractive index of the waveguide.

38. The head-mounted display according to any one of the preceding claims, wherein, During operation, the grating structure is configured to couple light at a working wavelength corresponding to a plurality of different color pixels of the light projection system into the waveguide.

39. The head-mounted display according to any one of the preceding claims, wherein, The grating layer and the waveguide are made of the same material.

40. The head-mounted display according to claim 39, wherein, The material includes a polymer.

41. The head-mounted display according to claim 40, wherein, The polymer has a refractive index of 1.75 or lower.

42. The head-mounted display according to claim 39, wherein, The material has a refractive index of 1.8 or higher.

43. The head-mounted display according to claim 39, wherein, The material is a composite material.

44. The head-mounted display according to claim 43, wherein, The composite material includes nanoparticles.

45. The head-mounted display according to any one of the preceding claims, wherein, The light from the light projection system is unpolarized light.

46. The head-mounted display according to any one of the preceding claims, wherein, The light projection system includes a micro-LED display, an LCoS display, or a laser beam scanner display.

47. The head-mounted display according to any one of the preceding claims, further comprising one or more additional waveguides and one or more additional grating structures, each additional grating structure being associated with a corresponding one of the additional waveguides.

48. The head-mounted display according to claim 47, wherein, The grating structures of each waveguide are arranged in an in-line configuration.

49. The head-mounted display according to claim 48, wherein, At least one of the grating structures is a reflective grating.

50. The head-mounted display according to claim 49, wherein the reflective grating is the grating structure of the waveguide that is farthest from the light projection system.

51. The head-mounted display according to any one of the preceding claims, wherein, The waveguide and the light projection system are arranged opposite to each other such that light from the projection system is incident on the grating structure from a non-normal direction with respect to the surface of the waveguide.

52. The head-mounted display according to claim 51, wherein, Light from the projection system is incident on the grating structure at an angle in the range of 0° to 25° with respect to the surface normal of the waveguide.

53. An article, comprising: A waveguide layer; A grating structure optically coupled to the waveguide, the grating structure being configured to couple light from the light projection system into the waveguide, the grating structure including: A grating layer including a plurality of ridges having a blazed profile in at least one cross-section; and One or more dielectric layers disposed on the grating layer, Among them, for non-polarized incident light at at least one working wavelength of the output light, within a field of view of 10° or greater in at least one direction, the grating structure has an average emission efficiency of 40% or higher and an average back reflectivity of 15% or lower.

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