Polarization-insensitive diffraction grating and display including same

Abstract

Polarization-insensitive gratings and displays including same are disclosed. In general, in a first aspect, the disclosure features a head-mounted display system including a head-mountable frame, an optical projection system configured to output light to provide image content, a waveguide supported by the frame, the waveguide configured to guide at least a portion of the light from the optical projection system coupled into the waveguide, and a grating structure optically coupled to the waveguide, the grating structure configured to couple the light from the optical projection system into the waveguide.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of priority to Provisional Application No. 63 / 423,286, filed November 7, 2022, entitled "POLARIZATION INSENSITIVE DIFFRACTION GRATING AND DISPLAY INCLUDING THE SAME," the contents of which are incorporated herein by reference.

[0002] (background) (Field) The present disclosure relates to display systems, and more particularly to augmented and virtual reality display systems and input coupling grids (ICGs) or output coupling grids for use therewith. [Background technology]

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

[0004] Referring to FIG. 1 , an augmented reality scene 10 is shown in which a user of the AR technology sees a real-world, park-like setting 20 featuring people, trees, buildings, and a concrete platform 30 in the background. In addition to these items, the user of the AR technology also perceives "seeing" "virtual content," such as a robotic figure 40 standing on the real-world platform 30 and a flying, cartoon-like avatar character 50 resembling an anthropomorphic bumblebee, although these elements 40, 50 do not even exist in the real world. Due to the complexity of the human visual perception system, it is difficult to create AR technology that facilitates the comfortable, natural-feeling, and rich presentation of virtual image elements among other virtual or real-world image elements.

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

[0006] overview Grating structures suitable for input coupling gratings (ICGs) for coupling light into waveguides are described and disclosed, which are substantially insensitive to polarization, have low back reflection, and enable operation over a wide range of input angles. Such grating structures can be used in an in-line alignment configuration, where ICGs of multiple stacked waveguides are aligned along a common optical path. Such ICGs can be particularly useful for head-mounted displays that use micro LED (μLED) light projection systems that can emit unpolarized light over a wide range of angles.

[0007] Examples of grating structures include asymmetric blazed gratings formed from and / or coated with high-refractive-index materials (e.g., titanium dioxide, gallium phosphide, silicon carbide, etc.). Such high-refractive-index layers can provide grating structures with relatively low optical loss. However, high-refractive-index films can significantly reflect light (e.g., >10% at some angles of incidence), resulting in undesirable back-reflected coupling and ghosting in virtual images, reduced contrast, and other undesirable results. Reducing this back-reflection allows more light to be diffracted and coupled in the correct order during TIR within the waveguide; therefore, the benefits of reduced reflection may outweigh the benefits of light recycling that can result from reflection.

[0008] The grating structures described herein can have low reflectance with high diffraction efficiency in both TE and TM polarization modes. Such optical performance can enable overall eyepiece efficiency per watt of energy used by projectors, such as μLED projection systems, that use unpolarized light and ideally operate with reduced back-reflection from the grating structure to the projection system's lenses. Such grating structures can also work well for single active layer architectures, where all colors (e.g., R, G, B) are guided in a single high-index active layer, but use grating structures operating in transmission mode to take advantage of the high diffraction efficiency in orthogonal polarization states, enabling the use of μLED projection systems, for example.

[0009] Various aspects of the disclosed subject matter are summarized as follows.

[0010] In general, in a first aspect, the disclosure features a head-mounted display system that includes a head-mountable frame; an optical projection system configured to output light to provide image content; a waveguide supported by the frame, the waveguide configured to guide at least a portion of the light from the optical projection system that is coupled into the waveguide; and a grating structure optically coupled to the waveguide, the grating structure configured to couple the light from the optical projection system into the waveguide. The grating structure includes a grating layer having a plurality of ridges with a blazed profile in at least one cross section, and one or more dielectric layers disposed on the grating layer, such that for unpolarized incident light at at least one operating wavelength of the output light, the grating structure has a polarization of 40% or more (e.g., greater than 10° or 0°, greater than 15° or 15°, greater than 20° or 20°, greater than 22° or 22°, greater than 25° or 25°, e.g., up to less than 45° or 45°, less than 40° or 40°, less than 35° or 35°, less than 30° or 30°, less than 25° or 25°, less than 22° or 22°) in at least one direction. For example, having an average launch efficiency of at or above 45%, at or above 50%, at or above 55%, at or above 60%, at or above 65%, e.g., less than 75%, at or below 70%, at or below 65%, at or below 60%, at or below 55% and an average back reflection of at or below 15% (e.g., less than 12%, at or below 10%, at or below 9%, less than 8%, less than 7%, less than 6%, less than 6%, less than 5%, less than 4%, less than 3%, e.g., greater than 1%, greater than 2%, greater than 3%).

[0011] Implementations of head-mounted displays can include one or more of the following features and / or features of other embodiments: For example, for unpolarized incident light at at least two operating wavelengths of output light that are at least 100 nm apart, the grating structure can provide a polarized light distribution of at least 40% or more (e.g., at or above 45%, at or above 50%, at or above 50%, at or above 50%) across a field of view of at least 10° or more (e.g., at or above 15°, at or above 20°, at or above 22°, at or above 25°, e.g., up to or below 45°, at or below 40°, at or below 35°, at or below 30°, at or below 25°, at or below 22°) in at least one direction. It can have an average launch efficiency of greater than 5% or 55%, greater than 60%, greater than 65%, e.g., less than 75%, less than 70%, less than 65%, less than 60%, less than 55%, and an average back reflection of 15% or less (e.g., less than 12%, less than 10%, less than 9%, less than 8%, less than 7%, less than 6%, less than 6%, less than 5%, less than 4%, less than 3%, e.g., greater than 1%, greater than 2%, greater than 3%).For unpolarized incident light at three operating wavelengths of output light spanning 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., 400 nm to 800 nm, e.g., 430 nm to 650 nm), the grating structure has an inclination angle of 10° or greater (e.g., 15° or greater, 20° or greater, 22° or greater, 25° or greater, e.g., at most 45° or less, 40° or less, 35° or less, 30° or less) in at least one direction. , at or less than 25°, to at or less than 22°), it may have an average launch efficiency of at or above 40% (e.g., greater than or equal to 45%, greater than or equal to 50%, greater than or equal to 55%, greater than or equal to 60%, greater than or equal to 65%, e.g., less than or equal to 75%, less than or equal to 70%, less than or equal to 65%, less than or equal to 60%, less than or equal to 55%) and an average back-reflection of at or below 15% (e.g., less than or equal to 12%, less than or equal to 10%, less than or equal to 9%, less than or equal to 8%, less than or equal to 7%, less than or equal to 6%, less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, e.g., greater than or equal to 1%, greater than or equal to 2% or less, greater than or equal to 3%). The three wavelengths can be a blue wavelength, a green wavelength, and a red wavelength, hi some examples, the three wavelengths are 465 nm, 545 nm, and 625 nm.

[0012] The field of view can be 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 orthogonal directions. In a particular example, the field of view is 22° by 22° in orthogonal directions.

[0013] The grating structure may be a reflective grating structure or a transmissive grating structure. The plurality of ridges may be inclined ridges.

[0014] The grating structure may include a metal layer disposed on one or more dielectric layers.

[0015] The one or more dielectric layers may include at least one continuous layer.

[0016] In some examples, the one or more dielectric layers include at least one discontinuous layer.

[0017] The 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 first dielectric layer having a refractive index at the operating wavelength that is greater than the refractive index of the grating layer and the refractive index of the second dielectric layer.

[0018] The one or more dielectric layers can include a layer having a thickness in the range of 50 nm to 150 nm (eg, 75 nm to 125 nm, 80 nm to 100 nm, 85 nm to 95 nm).

[0019] The 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).

[0020] The multiple ridges can have a pitch in the range of 200 nm to 500 nm (eg, 250 nm to 450 nm, 300 nm to 400 nm, 325 nm to 375 nm, 350 nm to 370 nm).

[0021] The multiple protrusions can have a top width in the range of 50 nm to 150 nm (eg, 60 nm to 140 nm, 70 nm to 130 nm, 80 nm to 100 nm).

[0022] The multiple protrusions can have a bottom width in the range of 10 nm to 150 nm (eg, 20 nm to 120 nm, 50 nm to 100 nm).

[0023] The multiple ridges can have a blaze angle in the range of 20° to 50° (e.g., 25° to 45°, 30° to 40°). The multiple 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°).

[0024] The launch efficiency of the grating structure can correspond to the first order diffraction efficiency of the grating structure.

[0025] The grating structure can be a first grating structure, and the system can further include a second grating structure on a side of the waveguide opposite 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 with a plurality of ridges and at least one dielectric layer supported by the grating layer.

[0026] The ridges may have a profile shape selected from the group including trapezoidal, parallelogram, triangular, and stepped.

[0027] The grating can have a duty cycle ranging from 5% to 95% (e.g., 10% to 75%, 20% to 50%, 30% to 40%).

[0028] The grating material can include a cross-linked polymer (e.g., thermally or UV-cross-linked 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.

[0029] The waveguide can support a film of material, and the ridges can be etched into the film. The material can be inorganic. 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 material can have a refractive index higher than that of the waveguide. The material can have a refractive index lower than that of the waveguide.

[0030] The grating structure may be configured, during operation, to couple light into the waveguide at operating wavelengths corresponding to a plurality of different color pixels of the optical projection system.

[0031] The grating layer and the waveguide can be made of the same material, which can include a polymer. The polymer can have a refractive index of 1.75 or less. The material can have a refractive index of 1.8 or greater (e.g., 1.9 or greater, 2.0 or greater, 2.1 or greater, e.g., 2.8 or less, 2.7 or less, 2.6 or less, 2.5 or less). The material can be a composite material (e.g., a composite material including nanoparticles).

[0032] The light from the optical projection system may be unpolarized light.

[0033] The light projection system can include a micro LED display, an LCoS display, or a laser beam scanner display.

[0034] The head-mounted display may include one or more additional waveguides and one or more additional grating structures, each associated with a corresponding one of the additional waveguides. The grating structures of each waveguide may be arranged in an in-line configuration. At least one of the grating structures may be a reflective grating. The reflective grating may be the grating structure of the waveguide farthest from the optical projection system.

[0035] The waveguide and optical projection system can be arranged relative to one another such that light from the projection system is incident on the grating structure non-normal to the surface of the waveguide. The light from the projection system can be incident on the grating structure at an angle ranging from 1° to 20° (e.g., 3° ​​to 15°, 5° to 12°, 5° to 10°) relative to the surface normal of the waveguide.

[0036] In general, in another aspect, the disclosure features an article that includes a waveguide layer and a grating structure optically coupled to the waveguide, the grating structure configured to couple light from an optical 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. For unpolarized incident light at at least one operating wavelength of the output light, the grating structure has a polarization of at least 40% or more (e.g., at or above 45%, at or above 50%, at or above 50%, at or above 55% or more) over a field of view of at least 10° or more (e.g., at or above 15°, at or above 20°, at or above 22°, at or above 25°, e.g., up to or below 45° or less, 40° or less, 35° or less, 30° or less, 25° or less, 22° or less) in at least one direction. having an average launch efficiency of greater than 55%, greater than or equal to 60%, greater than or equal to 65%, e.g., less than or equal to 75%, less than or equal to 70%, less than or equal to 65%, less than or equal to 60%, less than or equal to 55%; and an average back reflection of less than or equal to 15% (e.g., less than or equal to 12%, less than or equal to 10%, less than or equal to 9%, less than or equal to 8%, less than or equal to 7%, less than or equal to 6%, less than or equal to 6%, less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, e.g., greater than or equal to 1%, greater than or equal to 2%, greater than or equal to 3%).

[0037] Implementations of the article can include one or more of the features of the aforementioned aspects.

[0038] Other features and advantages will become apparent from the drawings, the following description, and the claims. [Brief explanation of the drawings]

[0039] [Figure 1] FIG. 1 shows a user's view of an augmented reality (AR) device.

[0040] [Figure 2] FIG. 2 shows a conventional display system for simulating a three-dimensional image for a user.

[0041] [Figure 3] 3A-3C show the relationship between the radius of curvature and the radius of focus.

[0042] [Figure 4A] Figure 4A shows a display of the accommodation-vergence-divergence motor response of the human visual system.

[0043] [Figure 4B] FIG. 4B shows examples of different accommodation and vergence / divergence states of a user's eye pair.

[0044] [Figure 4C] FIG. 4C shows an example of a display of an overhead view of a user viewing content through a display system.

[0045] [Figure 4D] FIG. 4D shows another example of a display of an overhead view of a user viewing content through a display system.

[0046] [Figure 5] FIG. 5 illustrates an embodiment of a technique for simulating a three-dimensional image by correcting for wavefront divergence.

[0047] [Figure 6] FIG. 6 shows an example of a waveguide stack for outputting image information to a user.

[0048] [Figure 7] FIG. 7 shows an example of an emitted beam output by a waveguide.

[0049] [Figure 8]FIG. 8 shows an example of a stacked waveguide assembly where each depth plane contains an image formed using multiple different component colors.

[0050] [Figure 9A] FIG. 9A shows a cross-sectional side view of an example set of stacked waveguides, each containing an incoupling optical element.

[0051] [Figure 9B] FIG. 9B shows a perspective view of an example of multiple stacked waveguides of FIG. 9A.

[0052] [Figure 9C] FIG. 9C shows a top view of an example of multiple stacked waveguides of FIGS. 9A and 9B.

[0053] [Figure 9D] FIG. 9D shows an example of a wearable display system.

[0054] [Figure 10A] FIG. 10A, for example, shows a schematic cross-sectional view of a portion of a waveguide having a diffraction grating disposed thereon for incoupling light into the waveguide.

[0055] [Figure 10B] FIG. 10B shows a cross-sectional view of a waveguide with a blazed grating placed on it, showing the field of view (FOV) Δα of the waveguide.

[0056] [Figure 11A] FIG. 11A shows a cross-sectional view of a portion of a grating structure in which the grating pattern is transferred from a resist layer to a substrate layer by dry etching.

[0057] [Figure 11B] FIG. 11B is an SEM micrograph of an example of a grating structure formed as shown in FIG. 11A.

[0058] [Figure 12]FIG. 12 is a schematic cross-sectional view showing a single pitch length of a grating structure comprised of a tilted grating with first and second coatings thereon.

[0059] [Figure 13] Figures 13A-13D are plots comparing the diffraction efficiency and reflectance of an example grating structure composed of two coatings (Figures 13A-13B) and an example grating structure on a coating (Figures 13C-13D), respectively.

[0060] [Figure 14] 14A-14D compare simulated diffraction efficiency results (FIG. 14A) with measured diffraction efficiency results (FIG. 14B) for the grating structures shown in FIGS. 14C and 14D, respectively.

[0061] [Figure 15A] FIG. 15A is a plot of the measured diffraction efficiency of an example grating structure with a single coating.

[0062] [Figure 15B] FIG. 15B is a plot of the measured diffraction efficiency for the example grating structure shown in FIG. 15A with a second coating.

[0063] [Figure 15C] FIG. 15C is a plot of the measured % reflectance as a function of wavelength for the grating structures shown in FIGS. 15A and 15B, respectively.

[0064] [Figure 16]Figures 16A-16F are plots and SEM micrographs comparing the diffraction efficiency as a function of angle for an example of a tilted grating with no coating (Figures 16A and 16B), a plot and SEM micrograph comparing the diffraction efficiency as a function of angle for an example of a tilted grating with one coating (Figures 16C and 16D), and a plot and SEM micrograph comparing the diffraction efficiency as a function of angle for an example of a tilted grating with two coatings (Figures 16E and 16F).

[0065] [Figure 17A] FIG. 17A is a plot showing the emission efficiency (as %) for red, green, and blue wavelengths as a function of polarization state in a first example of transmission ICG.

[0066] [Figure 17B] FIG. 17B is a plot showing back reflection (as %) for red, green, and blue wavelengths as a function of polarization state for a first example of transmitted ICG.

[0067] [Figure 18-1] 18A-18C are plots showing the reflection efficiency at zero-order reflection for TM polarization as a function of angle of incidence for a first example of a transmission ICG, the transmission efficiency at zero-order transmission for TM polarization as a function of angle of incidence for a first example of a transmission ICG, and the transmission efficiency at first-order diffraction for TM polarization as a function of angle of incidence for a first example of a transmission ICG. Each plot shows performance at red (625 nm), green (545 nm), and blue (465 nm) wavelengths, respectively.

[0068] [Figure 18-2]18D-18F are plots showing the reflection efficiency at zero-order reflection for TE-polarized light as a function of angle of incidence for a first example of transmission ICG, the transmission efficiency at zero-order transmission for TE-polarized light as a function of angle of incidence for a first example of transmission ICG, and the transmission efficiency at first-order diffraction for TE-polarized light as a function of angle of incidence for a first example of transmission ICG. Each plot shows performance at red (625 nm), green (545 nm), and blue (465 nm) wavelengths, respectively.

[0069] [Figure 18-3] 18G-18I are plots showing the reflection efficiency in the zeroth order reflection as a function of incidence angle, averaged for TM and TE polarizations, for the first example of transmission ICG; the transmission efficiency in the zeroth order transmission as a function of incidence angle, averaged for TM and TE polarizations, for the first example of transmission ICG; and the transmission efficiency in the first diffraction order as a function of incidence angle, averaged for TM and TE polarizations, for the first example of transmission ICG. Each plot shows performance at red (625 nm), green (545 nm), and blue (465 nm) wavelengths, respectively.

[0070] [Figure 19A] FIG. 19A is a plot showing the emission efficiency (as %) for red, green, and blue wavelengths as a function of polarization state in a second example of transmission ICG.

[0071] [Figure 19B] FIG. 19B is a plot showing back reflection (as %) for red, green, and blue wavelengths as a function of polarization state for a second example of transmission ICG.

[0072] [Figure 19C] FIG. 19C is a schematic cross-sectional view of a portion of a second example of transmission ICG.

[0073] [Figure 20-1] 20A-20C are plots showing the reflection efficiency at zero-order reflection for TM polarization as a function of angle of incidence for a second example of a transmission ICG, the transmission efficiency at zero-order transmission for TM polarization as a function of angle of incidence for a second example of a transmission ICG, and the transmission efficiency at first-order diffraction for TM polarization as a function of angle of incidence for a second example of a transmission ICG. Each plot shows performance at red (625 nm), green (545 nm), and blue (465 nm) wavelengths, respectively.

[0074] [Figure 20-2] 20D-20F are plots showing the reflection efficiency at zero-order reflection for TE-polarized light as a function of angle of incidence for the second example of transmission ICG, the transmission efficiency at zero-order transmission for TE-polarized light as a function of angle of incidence for the second example of transmission ICG, and the transmission efficiency at first-order diffraction for TE-polarized light as a function of angle of incidence for the second example of transmission ICG. Each plot shows performance at red (625 nm), green (545 nm), and blue (465 nm) wavelengths, respectively.

[0075] [Figure 20-3] 20G-20I are plots showing the reflection efficiency in the zeroth order reflection as a function of incidence angle, averaged for TM and TE polarizations, for a second example of transmission ICG; the transmission efficiency in the zeroth order transmission as a function of incidence angle, averaged for TM and TE polarizations, for a second example of transmission ICG; and the transmission efficiency in the first order diffraction as a function of incidence angle, averaged for TM and TE polarizations, for a second example of transmission ICG. Each plot shows performance at red (625 nm), green (545 nm), and blue (465 nm) wavelengths, respectively.

[0076] [Figure 21]21A and 21B are plots showing sensitivity analysis of the launch efficiency and back-reflection performance of dual-coated graded (first example) and blazed (second example) ICG to random design perturbations (+ / -10 nm) in the lattice parameters.

[0077] [Figure 22] FIG. 22 is a schematic diagram showing the operation of reflected ICG in a waveguide.

[0078] [Figure 23] FIG. 23 is a schematic diagram showing the structural features of an example of a reflectance ICG.

[0079] [Figure 24A] FIG. 24A is a plot showing the emission efficiency (as a %) for red, green, and blue wavelengths as a function of polarization state in a first example of a reflective ICG.

[0080] [Figure 24B] FIG. 24B is a plot showing back reflection (as %) for red, green, and blue wavelengths as a function of polarization state in a first example of a reflectance ICG.

[0081] [Figure 25-1] 25A-25C are plots showing the reflection efficiency at the −1st diffraction order for TM polarization as a function of incident angle for a first example of a reflective ICG, the reflection efficiency at the 0th diffraction order for TM polarization as a function of incident angle for a first example of a reflective ICG, and the transmission efficiency at the +1st diffraction order for TM polarization as a function of incident angle for a first example of a reflective ICG. Each plot shows performance at red (625 nm), green (545 nm), and blue (465 nm) wavelengths, respectively.

[0082] [Figure 25-2]25D-25F are plots showing the reflection efficiency at the −1st diffraction order for TE-polarized light as a function of incident angle for the first example of the reflective ICG, the reflection efficiency at the 0th diffraction order for TE-polarized light as a function of incident angle for the first example of the reflective ICG, and the transmission efficiency at the +1st diffraction order for TE-polarized light as a function of incident angle for the first example of the reflective ICG. Each plot shows performance at red (625 nm), green (545 nm), and blue (465 nm) wavelengths, respectively.

[0083] [Figure 25-3] 25G-25I are plots showing the reflection efficiency in the −1st diffraction order as a function of incident angle, averaged for TM and TE polarizations, for the first example of a reflective ICG; the reflection efficiency in the 0th diffraction order as a function of incident angle, averaged for TM and TE polarizations, for the first example of a reflective ICG; and the transmission efficiency in the +1st diffraction order as a function of incident angle, averaged for TM and TE polarizations, for the first example of a reflective ICG. Each plot shows performance at red (625 nm), green (545 nm), and blue (465 nm) wavelengths, respectively.

[0084] [Figure 26] FIG. 26 is a schematic cross-sectional view of a portion of a second example of reflected ICG.

[0085] [Figure 27A] FIG. 27A is a plot showing the emission efficiency (as a %) for red, green, and blue wavelengths as a function of polarization state in a first example of a reflective ICG.

[0086] [Figure 27B] FIG. 27B is a plot showing back reflection (as %) for red, green, and blue wavelengths as a function of polarization state in a first example of a reflectance ICG.

[0087] [Figure 28-1] 28A-28C are plots showing the reflection efficiency at the −1st diffraction order for TM polarization as a function of incident angle for a first example of a reflective ICG, the reflection efficiency at the 0th diffraction order for TM polarization as a function of incident angle for a first example of a reflective ICG, and the transmission efficiency at the +1st diffraction order for TM polarization as a function of incident angle for a first example of a reflective ICG. Each plot shows performance at red (625 nm), green (545 nm), and blue (465 nm) wavelengths, respectively.

[0088] [Figure 28-2] 28D-28F are plots showing the reflection efficiency at the −1st diffraction order for TE-polarized light as a function of incident angle for the first example of the reflected ICG, the reflection efficiency at the 0th diffraction order for TE-polarized light as a function of incident angle for the first example of the reflected ICG, and the transmission efficiency at the +1st diffraction order for TE-polarized light as a function of incident angle for the first example of the reflected ICG. Each plot shows performance at red (625 nm), green (545 nm), and blue (465 nm) wavelengths, respectively.

[0089] [Figure 28-3] 28G-28I are plots showing the reflection efficiency in the −1st diffraction order as a function of incident angle, averaged for TM and TE polarizations, for the first example of a reflective ICG; the reflection efficiency in the 0th diffraction order as a function of incident angle, averaged for TM and TE polarizations, for the first example of a reflective ICG; and the transmission efficiency in the +1st diffraction order as a function of incident angle, averaged for TM and TE polarizations, for the first example of a reflective ICG. Each plot shows performance at red (625 nm), green (545 nm), and blue (465 nm) wavelengths, respectively.

[0090] [Figure 29] FIG. 29 is a schematic cross-sectional view of a portion of a third example of reflected ICG.

[0091] [Figure 30] FIG. 30 is a schematic cross-sectional view of a portion of a fourth example of a reflected ICG.

[0092] [Figure 31A] FIG. 31A is a plot showing the emission efficiency (as %) for red, green, and blue wavelengths as a function of polarization state in a first example of a reflective ICG.

[0093] [Figure 31B] FIG. 31B is a plot showing back reflection (as %) for red, green, and blue wavelengths as a function of polarization state in a first example of a reflectance ICG.

[0094] [Figure 32-1] 32A-32C are plots showing the reflection efficiency at the −1st diffraction order for TM polarization as a function of incident angle for a first example of a reflective ICG, the reflection efficiency at the 0th diffraction order for TM polarization as a function of incident angle for a first example of a reflective ICG, and the transmission efficiency at the +1st diffraction order for TM polarization as a function of incident angle for a first example of a reflective ICG. Each plot shows performance at red (625 nm), green (545 nm), and blue (465 nm) wavelengths, respectively.

[0095] [Figure 32-2]32D-32F are plots showing the reflection efficiency at the −1st diffraction order for TE-polarized light as a function of incident angle for the first example of the reflected ICG, the reflection efficiency at the 0th diffraction order for TE-polarized light as a function of incident angle for the first example of the reflected ICG, and the transmission efficiency at the +1st diffraction order for TE-polarized light as a function of incident angle for the first example of the reflected ICG. Each plot shows performance at red (625 nm), green (545 nm), and blue (465 nm) wavelengths, respectively.

[0096] [Figure 32-3] 32G-32I are plots showing the reflection efficiency in the −1st diffraction order as a function of incident angle, averaged for TM and TE polarizations, for the first example of a reflective ICG; the reflection efficiency in the 0th diffraction order as a function of incident angle, averaged for TM and TE polarizations, for the first example of a reflective ICG; and the transmission efficiency in the +1st diffraction order as a function of incident angle, averaged for TM and TE polarizations, for the first example of a reflective ICG. Each plot shows performance at red (625 nm), green (545 nm), and blue (465 nm) wavelengths, respectively.

[0097] [Figure 33A] FIG. 33A is a schematic cross-sectional view of a portion of a fifth example of a reflected ICG.

[0098] [Figure 33B] FIG. 33B is a schematic cross-sectional view of a portion of another example of transmission ICG.

[0099] [Figure 34A] FIG. 34A is a plot showing emission efficiency (as %) for red, green, and blue wavelengths as a function of polarization state in a fifth example of a reflective ICG.

[0100] [Figure 34B]FIG. 34B is a plot showing back reflection (as %) for red, green, and blue wavelengths as a function of polarization state in a fifth example of a reflectance ICG.

[0101] [Figure 35-1] 35A-35C are plots showing the reflection efficiency at the −1st diffraction order for TM polarization as a function of incident angle for the fifth example of the reflection ICG, the reflection efficiency at the 0th diffraction order for TM polarization as a function of incident angle for the fifth example of the reflection ICG, and the transmission efficiency at the +1st diffraction order for TM polarization as a function of incident angle for the fifth example of the reflection ICG. Each plot shows performance at red (625 nm), green (545 nm), and blue (465 nm) wavelengths, respectively.

[0102] [Figure 35-2] 35D-35F are plots showing the reflection efficiency at the −1st diffraction order for TE-polarized light as a function of incident angle for the fifth example of the reflective ICG, the reflection efficiency at the 0th diffraction order for TE-polarized light as a function of incident angle for the fifth example of the reflective ICG, and the transmission efficiency at the +1st diffraction order for TE-polarized light as a function of incident angle for the fifth example of the reflective ICG. Each plot shows performance at red (625 nm), green (545 nm), and blue (465 nm) wavelengths, respectively.

[0103] [Figure 35-3]35G-35I are plots showing the reflection efficiency in the −1st diffraction order as a function of incident angle, averaged for TM and TE polarizations, for a fifth example of a reflection ICG; the reflection efficiency in the 0th diffraction order as a function of incident angle, averaged for TM and TE polarizations, for a fifth example of a reflection ICG; and the transmission efficiency in the +1st diffraction order as a function of incident angle, averaged for TM and TE polarizations, for a fifth example of a reflection ICG. Each plot shows performance at red (625 nm), green (545 nm), and blue (465 nm) wavelengths, respectively.

[0104] [Figure 36A] Figures 36A-36C are plots of the magnitude of the total electric field within the unit cell of each grating structure in the first, second, fourth, and fifth examples of reflective ICG. The plot shown in Figure 36A is for a red wavelength (625 nm). The plot shown in Figure 36B is for a green wavelength (545 nm). The plot shown in Figure 36C is for a blue wavelength (465 nm). [Figure 36B] Figures 36A-36C are plots of the magnitude of the total electric field within the unit cell of each grating structure in the first, second, fourth, and fifth examples of reflective ICG. The plot shown in Figure 36A is for a red wavelength (625 nm). The plot shown in Figure 36B is for a green wavelength (545 nm). The plot shown in Figure 36C is for a blue wavelength (465 nm). [Figure 36C] Figures 36A-36C are plots of the magnitude of the total electric field within the unit cell of each grating structure in the first, second, fourth, and fifth examples of reflective ICG. The plot shown in Figure 36A is for a red wavelength (625 nm). The plot shown in Figure 36B is for a green wavelength (545 nm). The plot shown in Figure 36C is for a blue wavelength (465 nm).

[0105] [Figure 37]FIG. 37 is a plot of the average polarized launch efficiency and back reflection (as %) for the first and second transmission ICG examples and the first, second, fourth and fifth reflection ICG examples.

[0106] [Figure 38] FIG. 38 is a schematic cross-sectional view of a portion of a sixth example of a reflected ICG.

[0107] [Figure 39] FIG. 39 is a schematic cross-sectional view of an example of a waveguide with transmitted and reflected ICG.

[0108] [Figure 40] FIG. 40 is a schematic cross-sectional view of another example of a waveguide with transmitted and reflected ICG.

[0109] Throughout the drawings, reference numbers may be reused to indicate correspondence between referenced elements. The figures are provided to illustrate exemplary embodiments described herein and are not intended to limit the scope of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0110] (Detailed explanation) The AR system may display virtual content to a user or viewer while allowing the user to see the surrounding world. Preferably, this content is displayed on a head-mounted display, e.g., part of eyewear, that projects image information to the user's eyes. In addition, the display may also transmit light from the surrounding environment to the user's eyes to enable a view of the surrounding environment. As used herein, a "head-mounted" or "head-mountable" display is understood to be a display that can be worn on the viewer's or user's head.

[0111] In some AR systems, virtual / augmented / composite displays with a relatively high field of view (FOV) can enhance the viewing experience. The FOV of a display depends on the angle of light output by the waveguide in the eyepiece through which the viewer views the image projected onto their eye. A waveguide with a relatively high refractive index, e.g., 2.0 or greater, can provide a relatively high FOV. However, to efficiently couple light into a high-index waveguide, the diffractive optical coupling element must also have a correspondingly high refractive index. To achieve this goal, among other advantages, some displays for AR systems according to embodiments described herein include waveguides comprising a material with a relatively high refractive index (e.g., greater than or equal to 2.0), such as Li-based oxide, on which respective diffraction gratings with correspondingly high refractive indexes are formed. For example, diffraction gratings may be formed directly on Li-based oxide waveguides by patterning a surface portion of the waveguide formed from the Li-based oxide.

[0112] Some high-index diffractive optical coupling elements, such as incoupling or outcoupling optical elements, have strong polarization dependence. For example, an incoupling grating (ICG) for incoupling light into a waveguide, where the diffractive optical coupling element comprises a high-index material, may admit significantly more light of a given polarization than light of another polarization. Such an element may, for example, incouple light with TM polarization into the waveguide about three times faster than light with TE polarization. Diffractive optical coupling elements with this type of polarization dependence may have reduced efficiency (due to low efficiency and total rejection of one polarization) and may also create coherence artifacts, reducing 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 polarization insensitive or at least has reduced polarization sensitivity (e.g., couples light with efficiency that is relatively polarization-independent), some displays for AR systems according to various implementations described herein include a waveguide with a diffraction grating formed with a blazed geometry. Diffraction gratings may also be formed directly within a waveguide, which may comprise 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 range of values ​​between any of these values). Diffraction gratings may be formed within a high refractive index material, such as, for example, a Li-based oxide such as lithium niobate (LiNbO) or lithium tantalate (LiTaO), or zirconium oxide (ZrO), titanium dioxide (TiO), or silicon carbide (SiC), by patterning the high refractive index material, for example, in a blazed geometry.

[0113] Reference will now be made to the drawings, in which like reference numerals refer to like parts throughout. Unless otherwise indicated, the drawings are schematic representations which are not necessarily drawn to scale.

[0114] FIG. 2 illustrates a conventional display system for simulating a three-dimensional image for a user. When a user's eyes are spaced apart and view a real object in space, each eye may have a slightly different view of the object, forming an image of the object at a different location on each eye's retina. This may be called binocular disparity and may be exploited by the human visual system to provide the perception of depth. Conventional display systems simulate binocular disparity by presenting two separate images 190, 200, one to each eye, with slightly different views of the same virtual object, corresponding to the views of the virtual object that would be seen by each eye 210, 220 if the virtual object were a real object at a desired depth. These images provide binocular cues that the user's visual system can interpret to derive the perception of depth.

[0115] Continuing with reference to FIG. 2 , images 190 and 200 are spaced a distance 230 along the z-axis from eyes 210 and 220. The z-axis is parallel to the viewer's optical axis, with the viewer's eyes fixating on an object at optical infinity directly in front of the viewer. Images 190 and 200 are flat and are at a fixed distance from eyes 210 and 220. Based on slightly different views of a virtual object in the images presented to each eye 210 and 220, the eyes naturally rotate, causing the image of the object to fall on corresponding points on each eye's retina to maintain single binocular vision. This rotation can cause the gaze of each eye 210 and 220 to converge on a point in space where the virtual object is perceived to reside. As a result, providing a three-dimensional image traditionally involves manipulating the convergence and divergence of the user's eyes 210 and 220 and providing binocular cues that the human visual system interprets to provide the perception of depth.

[0116] However, creating a realistic and comfortable depth perception is challenging. It is understood that light from objects at different distances from the eye has wavefronts with different amounts of divergence. Figures 3A-3C illustrate the relationship between distance and divergence of light rays. The distances between the object and the eye 210 are represented by R1, R2, and R3, in order of decreasing distance. As shown in Figures 3A-3C, light rays become more divergent as the distance to the object decreases. Conversely, as the distance increases, light rays become more collimated. In other words, the light field produced by a point (an object or portion of an object) may be said to have a spherical wavefront curvature that is a function of how far the point is from the user's eye. The curvature increases as the distance between the object and the eye 210 decreases. While only a single eye 210 is shown in Figures 3A-3C and other figures herein for clarity, discussions regarding the eye 210 may also apply to both eyes 210 and 220 of a viewer.

[0117] Continuing with reference to FIGS. 3A-3C , light from an object at which a viewer's eye is fixating may have different degrees of wavefront divergence. Due to the different amounts of wavefront divergence, the light may be focused differently by the eye's lens, which may then need to assume different shapes to form a focused image on the eye's retina. If a focused image is not formed on the retina, the resulting retinal blur acts as an accommodative cue, causing the shape of the eye's lens to change until a focused image is formed on the retina. For example, the accommodative cue may trigger the ciliary muscles surrounding the eye's lens to relax or contract, thereby adjusting the force applied to the suspensory ligaments that hold the lens in place, thus changing the shape of the eye's lens until retinal blur of the fixated object is eliminated or minimized, thereby forming a focused image of the fixated object on the eye's retina (e.g., the fovea). The process by which the eye's lens changes shape may be called accommodation, and the shape of the eye's lens required to form a focused image of a gazed object on the eye's retina (e.g., the fovea) may be called the state of accommodation.

[0118] Referring now to Figure 4A, a display of the accommodation-vergence response of the human visual system is shown. Eye movements to fixate an object cause the eye to receive light from the object, which forms an image on each of the eye's retinas. The presence of retinal blur in the image formed on the retina may provide a cue for accommodation, and the relative location of the image on the retina may provide a cue for vergence. Accommodative cues cause accommodation, resulting in each eye's lens adopting a specific accommodation state that forms a focused image of the object on the eye's retina (e.g., the fovea). Conversely, vergence cues cause vergence movements (eye rotations) so that the images formed on each retina of each eye are at corresponding retinal points, maintaining single binocular vision. In these positions, the eyes may be said to adopt a specific vergence state. Continuing with reference to FIG. 4A , accommodation may be understood as the process by which the eyes achieve a particular accommodation state, and convergence may be understood as the process by which the eyes achieve a particular convergence state. As shown in FIG. 4A , the accommodation state and convergence state of the eyes may change when the user gazes at a different object. For example, the accommodation state may change when the user gazes at a new object at a different depth on the z-axis.

[0119] Without being limited by theory, it is believed that a viewer of an object may perceive the object as "three-dimensional" through a combination of convergence-divergence and accommodation. As noted above, the vergence-divergence movement of the two eyes relative to one another (e.g., the rotation of the eyes so that the pupils move toward or away from one another to converge the eyes' gaze to fixate on an object) is closely coupled to the accommodation of the eye's lenses. Under normal conditions, changing the shape of the eye's lenses to change focus from one object to another at a different distance automatically produces a corresponding change in vergence-divergence for the same distance, under a relationship known as the "accommodation-vergence-divergence reflex." Similarly, changes in vergence-divergence cause a corresponding change in lens shape under normal conditions.

[0120] 4B, examples of different accommodation and convergence states of the eyes are shown. Eye pair 222a is fixating on an object at optical infinity, while eye pair 222b is fixating on object 221 at less than optical infinity. Notably, the convergence states of each eye pair are different, with eye pair 222a looking straight ahead and eye pair 222 converging on object 221. The accommodation states of the eyes forming each eye pair 222a and 222b are also different, as represented by the different shapes of lenses 210a, 220a.

[0121] Unfortunately, many users of conventional "3D" display systems find them uncomfortable or experience no depth perception at all due to the mismatch between accommodation and convergence states in these displays. As noted 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, they only provide different presentations of the scene, causing changes in the eyes' convergence states without a corresponding change in the eyes' accommodation states. Rather, images are presented by displays at a fixed distance from the eyes, causing the eyes to view all image information in a single accommodation state. This arrangement adversely affects the "accommodation-vergence-divergence reflex" by causing changes in convergence states without a corresponding change in accommodation states. This mismatch is thought to cause discomfort to viewers. Display systems that provide better matching between accommodation and convergence may produce more realistic and comfortable simulations of three-dimensional images.

[0122] Without being limited by theory, it is believed that the human eye can typically interpret a finite number of depth planes to provide depth perception. As a result, a highly realistic simulation of perceived depth can be achieved by providing the eye with different presentations of images corresponding to each of these limited number of depth planes. In some embodiments, the different presentations may provide both convergence cues and accommodation matching cues, thereby providing physiologically correct accommodation-vergence divergence matching.

[0123] 4B, two depth planes 240 are shown corresponding to different distances in space from the eyes 210, 220. For a given depth plane 240, vergence-divergence cues may be provided by displaying appropriately different viewpoint images for each eye 210, 220. Additionally, for a given depth plane 240, the light forming the image provided to each eye 210, 220 may have a wavefront divergence corresponding to the light field produced by points at that depth plane 240.

[0124] In the illustrated embodiment, the distance along the z-axis of depth plane 240 containing point 221 is 1 meter. As used herein, distance or depth along the z-axis may be measured at a zero point located at the exit pupil of a user's eye. Thus, depth plane 240 located at a depth of 1 meter corresponds to a distance of 1 meter away from the exit pupil of a user's eye on the optical axis of those eyes when the eyes are pointed at optical infinity. As an approximation, depth or distance along the z-axis may be measured from the display in front of the user's eye (e.g., from the surface of the waveguide) plus the value of the distance between the device and the exit pupil of the user's eye. That value may be referred to as 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 eye. In practice, the eye relief value may be a normalized value commonly used for all viewers. For example, the eye relief may be assumed to be 20 mm, and a depth plane at a depth of 1 meter may be at a distance of 980 mm in front of the display.

[0125] 4C and 4D, examples of matched and mismatched accommodation-vergence-divergence distances are shown, respectively. As shown in FIG. 4C, the display system may provide an image of a virtual object to each eye 210, 220. The image may cause the eyes 210, 220 to assume a convergence-divergence state in which the eyes converge at point 15 on the depth plane 240. In addition, the image may be formed by light having a wavefront curvature corresponding to the real object at that depth plane 240. As a result, both eyes 210, 220 assume an accommodation state in which the image is focused on the retinas of the eyes. Therefore, the user may perceive the virtual object as being at point 15 on the depth plane 240.

[0126] It will be appreciated that each of the accommodation states and convergence states of the eyes 210, 220 is associated with a particular distance on the z-axis. For example, an object at a particular distance from the eyes 210, 220 will cause the eyes to assume a particular accommodation state based on the object's distance. The distance associated with a particular accommodation state may be referred to as the accommodation distance Ad. Similarly, there is a particular convergence distance Vd, or position relative to one another, associated with the eyes in a particular convergence state. When the accommodation distance and the convergence distance match, the relationship between accommodation and convergence may be said to be physiologically correct. This is believed to be the most comfortable scenario for the viewer.

[0127] However, in a stereoscopic display, the accommodation distance and the vergence distance may not necessarily match. For example, as shown in FIG. 4D , images displayed to the eyes 210, 220 may be displayed with a wavefront divergence corresponding to a depth plane 240, and the eyes 210, 220 may be in a particular accommodation state focused on points 15a, 15b on that depth plane. However, the images displayed to the eyes 210, 220 may provide a convergence cue that causes the eyes 210, 220 to converge on a point 15 that is not located on the depth plane 240. As a result, in some embodiments, the accommodation distance corresponds to the distance from the exit pupils of the eyes 210, 220 to the depth plane 240, while the vergence distance corresponds to the greater distance from the exit pupils of the eyes 210, 220 to point 15. The accommodation distance is different from the vergence distance. As a result, an accommodation-vergence mismatch exists. Such a mismatch may be considered undesirable and may cause discomfort to the user. It will be appreciated that the mismatch corresponds to a distance (e.g., Vd-Ad) and may be characterized using diopters.

[0128] It will be appreciated that in some embodiments, a reference point other than the exit pupil of the eye 210, 220 may be used to determine the distance for determining accommodation-vergence discrepancy, so long as that reference point is used for accommodation distance and vergence distance. For example, the distance may be measured from the cornea to the depth plane, from the retina to the depth plane, from the ocular lens (e.g., a waveguide in a display device) to the depth plane, etc.

[0129] Without being limited by theory, it is believed that a user may still perceive an accommodation-vergence-divergence mismatch of up to about 0.25 diopters, up to about 0.33 diopters, and up to about 0.5 diopters as physiologically correct, and the mismatch itself does not cause significant discomfort. In some embodiments, a display system disclosed herein (e.g., display system 250 of FIG. 6 ) presents a viewer with an accommodation-vergence-divergence mismatch of about 0.5 diopters or less. In some other embodiments, the accommodation-vergence-divergence mismatch of images provided by the display system is about 0.33 diopters or less. In still other embodiments, the accommodation-vergence-divergence mismatch of images provided by the display system is about 0.25 diopters or less, including about 0.1 diopters or less.

[0130] 5 illustrates aspects of an approach for simulating a three-dimensional image by modifying wavefront divergence. 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 prescribed amount of wavefront divergence corresponding to the wavefront divergence of the light field produced by a point on a desired depth plane 240. In some embodiments, the same amount of wavefront divergence is provided for all objects presented on that depth plane. Additionally, it is shown that image information can be provided to the user's other eye from a similar waveguide.

[0131] In some embodiments, a single waveguide may be configured to output light with a set amount of wavefront divergence corresponding to a single or limited number of depth planes, and / or the waveguide may be configured to output light in a limited wavelength range. As a result, in some embodiments, multiple waveguides or stacks of waveguides may be utilized to provide different amounts of wavefront divergence for different depth planes and / or to output light in different wavelength ranges. As used herein, it will be understood that a depth plane may be planar or may follow the contours of a curved surface.

[0132] 6 shows an example of a waveguide stack for outputting image information to a user. Display system 250 includes a stack of waveguides or stacked waveguide assembly 260 that can be utilized to provide three-dimensional perception to the eye / brain using multiple waveguides 270, 280, 290, 300, 310. It will be appreciated that in some embodiments, display system 250 may be considered a light field display. Additionally, waveguide assembly 260 may also be referred to as an eyepiece.

[0133] In some embodiments, display system 250 is configured to provide a substantially continuous convergence cue and multiple distinct accommodation cues. Convergence cues can be provided by displaying different images to each of the user's eyes, and accommodation cues can be provided by outputting light forming images with selectable distinct amounts of wavefront divergence. Stated another way, display system 250 can be configured to output light having variable levels of wavefront divergence. In some embodiments, each distinct level of wavefront divergence corresponds to a particular depth plane and may be provided by a particular one of waveguides 270, 280, 290, 300, 310.

[0134] Continuing with reference to FIG. 6 , the waveguide assembly 260 may also include multiple features 320, 330, 340, 350 between the waveguides. In some embodiments, the features 320, 330, 340, 350 may be one or more lenses. The waveguides 270, 280, 290, 300, 310 and / or multiple lenses 320, 330, 340, 350 may be configured to deliver image information to the eye at various levels of wavefront curvature or ray divergence. Each waveguide level may be associated with a particular depth plane and can be configured to output image information corresponding to that depth plane. The image injection devices 360, 370, 380, 390, 400 may act as light sources for the waveguides and may be utilized to inject image information into the waveguides 270, 280, 290, 300, 310, each of which may be configured to distribute incident light across each respective waveguide for output toward the eye 210, as described herein. Light exits output faces 410, 420, 430, 440, 450 of the image injection devices 360, 370, 380, 390, 400 and is injected into corresponding input faces 460, 470, 480, 490, 500 of the waveguides 270, 280, 290, 300, 310. In some embodiments, each of the input faces 460, 470, 480, 490, 500 may be an edge of the corresponding waveguide or may be a portion of a major surface of the corresponding waveguide (i.e., one of the waveguide surfaces that directly faces the world 510 or the viewer's eye 210). In some embodiments, a single light beam (e.g., a collimated beam) may be injected into each waveguide to output a full field of cloned collimated beams, which are directed toward the 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 one of the image injection devices 360, 370, 380, 390, 400 may be associated with and inject light into multiple (e.g., three) waveguides 270, 280, 290, 300, 310.

[0135] In some embodiments, image injection devices 360, 370, 380, 390, 400 are individual displays that each produce image information for injection into corresponding waveguides 270, 280, 290, 300, 310. In some other embodiments, image injection devices 360, 370, 380, 390, 400 are outputs of a single multiplexed display that may, for example, send image information via one or more optical conduits (such as fiber optic cables) to each of image injection devices 360, 370, 380, 390, 400. It will be understood that the image information provided by image injection devices 360, 370, 380, 390, 400 may include light of different wavelengths or colors (e.g., different component colors as discussed herein).

[0136] In some embodiments, light injected into the waveguides 270, 280, 290, 300, 310 is provided by a light projector system 520 comprising a light module 530, which may include light emitters such as light emitting diodes (LEDs). Light from the light module 530 may be directed through a beam splitter 550 to and modified by a light modulator 540, such as a spatial light modulator. The light modulator 540 may be configured to change the perceived intensity of the light injected into the waveguides 270, 280, 290, 300, 310 to encode the light with image information. Examples of spatial light modulators include liquid crystal displays (LCDs), including liquid crystal on silicon (LCOS) displays. It will be understood that image injection devices 360, 370, 380, 390, 400 are shown schematically, and in some embodiments, these image injection devices may represent different light paths and locations within a common projection system configured to output light to associated ones of waveguides 270, 280, 290, 300, 310. In some embodiments, the waveguides of waveguide assembly 260 may act as ideal lenses, relaying light injected into the waveguides to the user's eye. In this concept, the object may be a spatial light modulator 540, and the image may be an image on a depth plane.

[0137] In some examples, μLED displays can be used in light projector system 520. μLED displays can emit unpolarized light over a wide range of angles, and thus can beneficially provide images over a wide field of view with high efficiency.

[0138] In some embodiments, the display system 250 may be a scanning fiber display comprising one or more scanning fibers configured to project light in various patterns (e.g., raster scan, spiral scan, Lissajous pattern, etc.) into one or more waveguides 270, 280, 290, 300, 310 and ultimately to the viewer's eye 210. In some embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may generally represent a single scanning fiber or a bundle of scanning fibers configured to inject light into one or more of the waveguides 270, 280, 290, 300, 310. In some embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may generally represent multiple scanning fibers or multiple bundles of scanning fibers each configured to inject light into an associated one of the waveguides 270, 280, 290, 300, 310. It will be appreciated that the one or more optical fibers may be configured to transmit light from the optical module 530 to one or more of the waveguides 270, 280, 290, 300, 310. It will be appreciated that one or more intervening optical structures may be provided between the scanning fiber or fibers and the one or more waveguides 270, 280, 290, 300, 310, for example, to redirect light exiting the scanning fiber into the one or more waveguides 270, 280, 290, 300, 310.

[0139] Controller 560 controls the operation of one or more of stacked waveguide assembly 260, including the operation of image injection devices 360, 370, 380, 390, 400, light source 530, and light modulator 540. In some embodiments, controller 560 is part of local data processing module 140. Controller 560 includes programming (e.g., instructions in a non-transitory medium) that coordinates the timing and provision of image information to waveguides 270, 280, 290, 300, 310, for example, by any of the various manners disclosed herein. In some embodiments, the controller may be a single integrated device or a distributed system connected by wired or wireless communication channels. Controller 560 may, in some embodiments, be part of processing module 140 or 150 (FIG. 9D).

[0140] Continuing with reference to FIG. 6 , the waveguides 270, 280, 290, 300, and 310 can be configured to propagate light within each respective waveguide by total internal reflection (TIR). The waveguides 270, 280, 290, 300, and 310 can each be planar or have another shape (e.g., curved) and have upper and lower major end faces and edges extending between the upper and lower major end faces. In the illustrated configuration, the waveguides 270, 280, 290, 300, and 310 can each include outcoupling optics 570, 580, 590, 600, and 610 configured to extract light from the waveguide by redirecting light propagating within the respective waveguide out of the waveguide to output image information to the eye 210. The extracted light may be referred to as outcoupled light, and the outcoupling optic may be referred to as a light extraction optic. The extracted light beam may be output by the waveguide where light propagating within the waveguide impinges on the light extraction optic. The outcoupling optic 570, 580, 590, 600, 610 may be, for example, a grating including diffractive optical features, as described further herein. While shown mounted on the bottom major surface of the waveguides 270, 280, 290, 300, 310 for ease of explanation and clarity of illustration, the outcoupling optic 570, 580, 590, 600, 610 may, in some embodiments, be mounted on the top and / or bottom major surfaces and / or directly within the volume of the waveguides 270, 280, 290, 300, 310, as discussed further herein. In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 may be formed in a layer of material attached to a transparent substrate to form the waveguides 270, 280, 290, 300, 310. In some other embodiments, the waveguides 270, 280, 290, 300, 310 may be a monolithic piece of material, and the outcoupling optical elements 570, 580, 590, 600, 610 may be formed on and / or within that piece of material.

[0141] Continuing with reference to FIG. 6 , as discussed herein, each waveguide 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 may be configured to deliver collimated light (injected into such waveguide 270) to the eye 210. The collimated light may represent an optical infinity focal plane. The next-up waveguide 280 may be configured to send collimated light that passes through a first lens 350 (e.g., a negative lens) before reaching the eye 210. Such a first lens 350 may be configured to create a slightly convex wavefront curvature so that the eye / brain interprets light coming from the neighboring waveguide 280 as coming from a first focal plane closer inward from optical infinity toward the eye 210. Similarly, the third upper waveguide 290 passes its output light through both the first lens 350 and the second lens 340 before reaching the eye 210. The combined refractive power of the first lens 350 and the second lens 340 may be configured to create another incremental amount of wavefront curvature, causing the eye / brain to interpret the light coming from the third waveguide 290 as coming from a second focal plane that is further inward from optical infinity towards the person than the light from the next upper waveguide 280.

[0142] The other waveguide layers 300, 310 and lenses 330, 320 are similarly configured, with the highest waveguide 310 in the stack sending its output through all lenses between it and the eye for a collective focal power representing the focal plane closest to the person. To compensate the stack of lenses 320, 330, 340, 350 on the other side of the stacked waveguide assembly 260 when viewing / interpreting light coming from the world 510, a compensatory lens layer 620 may be placed at the top of the stack to compensate for the collective power of the lens stacks 320, 330, 340, 350 below. Such a configuration provides as many perceived focal planes as there are available waveguide / lens pairings. Both the waveguide outcoupling optics and the lens focal aspects may be static (i.e., not dynamic or electrically active). In some alternative embodiments, either or both may be dynamic using electro-active features.

[0143] In some embodiments, two or more of the waveguides 270, 280, 290, 300, 310 may have the same associated depth plane. For example, multiple waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same depth plane, or multiple subsets of waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same depth planes, one set for each depth plane. This may provide advantages for forming tiled images to provide an extended field of view at those depth planes.

[0144] Continuing with reference to FIG. 6 , outcoupling optics 570, 580, 590, 600, 610 may be configured to redirect light out of their respective waveguides and output this light with the appropriate amount of divergence or collimation for the particular depth plane associated with the waveguide. As a result, waveguides with different associated depth planes may have different configurations of outcoupling optics 570, 580, 590, 600, 610 that output light with different amounts of divergence depending on the associated depth plane. In some embodiments, light extraction optics 570, 580, 590, 600, 610 may be volume or surface features that may be configured to output light at a specific angle. For example, light extraction optics 570, 580, 590, 600, 610 may be volume holograms, surface holograms, and / or diffraction gratings. In some embodiments, features 320, 330, 340, 350 may not be lenses. Rather, they may simply be spacers (eg, cladding layers and / or structures to form an air gap).

[0145] In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 are diffractive features, or "diffractive optical elements" (also referred to herein as "DOEs"), that form a diffraction pattern. Preferably, the DOEs have a sufficiently low diffraction efficiency so that only a portion of the light in the beam is deflected toward the eye 210 at each intersection of the DOE, while the remainder continues traveling through the waveguide via TIR. Thus, the light carrying the image information is split into several related exit beams that exit the waveguide at multiple locations, resulting in a fairly uniform pattern of exit radiation toward the eye 210 for this particular collimated beam bouncing within the waveguide.

[0146] In some embodiments, one or more DOEs may be switchable between an actively diffracting "on" state and a significantly non-diffracting "off" state. For example, a switchable DOE may include a layer of polymer-dispersed liquid crystal in which microdroplets contain a diffractive pattern in a host medium, and the refractive index of the microdroplets may be switched to substantially match the refractive index of the host material (in which case the pattern does not appreciably diffract incident light), or the microdroplets may be switched to a refractive index that does not match the refractive index of the host medium (in which case the pattern actively diffracts incident light).

[0147] In some embodiments, a camera assembly 630 (e.g., a digital camera including a visible light and infrared light camera) may be provided to capture images of the eye 210 and / or tissue surrounding the eye 210, for example, to detect user input and / or monitor the physiological condition of the user. As used herein, a camera may be any image capture device. In some embodiments, the camera assembly 630 may include an image capture device and a light source for projecting light (e.g., infrared light) onto the eye, which may then be reflected by the eye and detected by the image capture device. In some embodiments, the camera assembly 630 may be mounted on the frame 80 (FIG. 9D) and may be in electrical communication with processing modules 140 and / or 150, which may process image information from the camera assembly 630. In some embodiments, one camera assembly 630 may be utilized for each eye to monitor each eye separately.

[0148] 7, an example of an exit beam output by a waveguide is shown. While one waveguide is shown, it will be understood that if the waveguide assembly 260 includes multiple waveguides, other waveguides within the waveguide assembly 260 (FIG. 6) may function similarly. Light 640 is injected into the waveguide 270 at the input face 460 of the waveguide 270 and propagates within the waveguide 270 by TIR. At the point where the light 640 impinges on the DOE 570, a portion of the light exits the waveguide as exit beam 650. Although exit beam 650 is shown as substantially parallel, it may be redirected to propagate to the eye 210 at an angle (e.g., forming a diverging exit beam) depending on the depth plane associated with the waveguide 270, as discussed herein. It will be understood that a substantially parallel exit beam may refer to a waveguide having outcoupling optics that outcouples light to form an image that appears to be set on a depth plane at a large distance (e.g., optical infinity) from the eye 210. Other waveguides or other sets of outcoupling optics may output an exit beam pattern that is more divergent, which requires the eye 210 to accommodate to a closer distance to focus on the retina, and is interpreted by the brain as light from a distance closer to the eye 210 than optical infinity.

[0149] In some embodiments, a full-color image may be formed in each depth plane by overlapping images of each of the component colors, for example, three or more component colors. FIG. 8 shows an example of a stacked waveguide assembly in which each depth plane includes an image formed using multiple different component colors. The illustrated embodiment shows depth planes 240a-240f, but more or fewer depths are contemplated. Each depth plane may have three or more component color images associated with it, including a first image of a first color, G, a second image of a second color, R, and a third image of a third color, B. Different depth planes are indicated in the diagram by different numbers of diopters (dpt) following the letters G, R, and B. By way of example, the number following each of these letters indicates the diopter (1 / m) or inverse distance of the depth plane from the viewer, and each box in the diagram represents an individual component color image. In some embodiments, the exact placement of the different component color depth planes may vary to account for differences in the eye's focusing of different wavelengths of light. For example, different component color images for a given depth plane may be arranged on the depth plane corresponding to different distances from the user. Such an arrangement may improve visual acuity and user comfort and / or reduce chromatic aberration.

[0150] In some embodiments, light for each component color may be output by a single dedicated waveguide, such that each depth plane may have multiple waveguides associated with it. In such embodiments, each box in the diagram containing the letter G, R, or B may be understood to represent an individual waveguide, and three waveguides may be provided per depth plane, in which case three component color images are provided per depth plane. While the waveguides associated with each depth plane are shown adjacent to each other in this diagram for ease of illustration, it will be understood that in a physical device, the waveguides may all be arranged in a stack with one waveguide per level. In some other embodiments, multiple component colors may be output by the same waveguide, such that, for example, only a single waveguide may be provided per depth plane.

[0151] 8, in some embodiments, G is green, R is red, and B is blue. In some other embodiments, other colors associated with other wavelengths of light, including magenta and cyan, may be used in addition to or may replace one or more of red, green, or blue.

[0152] It will be understood that references throughout this disclosure to a given color of light are understood to encompass light of one or more wavelengths within the wavelength range of light perceived by a viewer as being of that given color. For example, red light may include one or more wavelengths of light in the range of about 620-780 nm, green light may include one or more wavelengths of light in the range of about 492-577 nm, and blue light may include one or more wavelengths of light in the range of about 435-493 nm.

[0153] In some embodiments, the light source 530 (FIG. 6) may be configured to emit light at one or more wavelengths outside the viewer's visual range, for example, infrared and / or ultraviolet wavelengths. Additionally, the waveguide incoupling, outcoupling, and other light redirecting structures of the display 250 may be configured to direct and emit this light from the display toward the user's eye 210, for example, for imaging and / or user stimulation applications.

[0154] Referring now to FIG. 9A , in some embodiments, light impinging on a waveguide may need to be redirected to incouple the light into the waveguide. An incoupling optical element may be used to redirect and incouple the light into its corresponding waveguide. FIG. 9A shows a cross-sectional side view of an example of a plurality or set 660 of stacked waveguides, each including an incoupling optical element. The waveguides may each be configured to output light of one or more different wavelengths or one or more different wavelength ranges. It will be understood that stack 660 may correspond to stack 260 ( FIG. 6 ), and the illustrated waveguides of stack 660 may correspond to portions of the plurality of waveguides 270, 280, 290, 300, 310, except that light from one or more of image injection devices 360, 370, 380, 390, 400 is injected into the waveguide from a location requiring the light to be redirected for incoupling.

[0155] The illustrated stacked waveguide set 660 includes waveguides 670, 680, and 690. Each waveguide includes an associated incoupling optical element (which may also be referred to as a light input region on the waveguide), having, for example, an incoupling optical element 700 located on a major surface (e.g., the top major surface) of waveguide 670, an incoupling optical element 710 located on a major surface (e.g., the top major surface) of waveguide 680, and an incoupling optical element 720 located on a major surface (e.g., the top major surface) of waveguide 690. In some embodiments, one or more of incoupling optical elements 700, 710, 720 may be located on the bottom major surface of the respective waveguide 670, 680, 690 (particularly when one or more incoupling optical elements are reflective deflecting optical elements). As shown, the incoupling optical elements 700, 710, 720 may be located on the upper major surfaces of their respective waveguides 670, 680, 690 (or on the upper ends of the next lower waveguide), particularly if the incoupling optical elements are transmissive deflecting optical elements. In some embodiments, the incoupling optical elements 700, 710, 720 may be located within the body of the respective waveguides 670, 680, 690. In some embodiments, as discussed herein, the incoupling optical elements 700, 710, 720 are wavelength selective, such that they selectively redirect one or more wavelengths of light while transmitting other wavelengths of light. Although shown on one side or corner of their respective waveguides 670, 680, 690, it will be understood that in some embodiments, the incoupling optical elements 700, 710, 720 may be located within other regions of their respective waveguides 670, 680, 690.

[0156] As shown, the incoupling optical elements 700, 710, 720 may be laterally offset from one another. In some embodiments, each incoupling optical element may be offset to receive light without the light passing through another incoupling optical element. For example, each incoupling optical element 700, 710, 720 may be configured to receive light from a different image injection device 360, 370, 380, 390, and 400, as shown in FIG. 6 , and may be separated (e.g., laterally spaced) from the other incoupling optical elements 700, 710, 720 so as to substantially not receive light from another one of the other incoupling optical elements 700, 710, 720.

[0157] Each waveguide also includes an associated light distribution element, having, for example, a light distribution element 730 disposed on a major surface (e.g., the top major surface) of waveguide 670, a light distribution element 740 disposed on a major surface (e.g., the top major surface) of waveguide 680, and a light distribution element 750 disposed on a major surface (e.g., the top major surface) of waveguide 690. In some other embodiments, light distribution elements 730, 740, 750 may be disposed on the bottom major surfaces of the associated waveguides 670, 680, 690, respectively. In some other embodiments, the light distribution elements 730, 740, 750 may be disposed on both the top and bottom major surfaces of the associated waveguides 670, 680, 690, respectively, or the light distribution elements 730, 740, 750 may be disposed on different ones of the top and bottom major surfaces of different associated waveguides 670, 680, 690, respectively.

[0158] The waveguides 670, 680, 690 may be spaced apart and separated by, for example, gas, liquid, and / or solid material layers. For example, as shown, layer 760a may separate waveguides 670 and 680, and layer 760b may separate waveguides 680 and 690. In some embodiments, layers 760a and 760b are formed from a low refractive index material (i.e., a material having a lower refractive index than the material forming the immediately adjacent ones of the waveguides 670, 680, 690). Preferably, the refractive index of the material forming layers 760a, 760b is 0.05 or greater, or 0.10 or less than the refractive index of the material forming waveguides 670, 680, 690. Advantageously, the low refractive index layers 760a, 760b may function as cladding layers to facilitate total internal reflection (TIR) ​​of light through the waveguides 670, 680, 690 (e.g., TIR between the top and bottom major surfaces of each waveguide). In some embodiments, the layers 760a, 760b are formed from air. Although not shown, it will be understood that the top and bottom ends of the illustrated set of waveguides 660 may include immediately adjacent cladding layers.

[0159] Preferably, for ease of manufacturing and other considerations, the materials forming waveguides 670, 680, 690 are similar or the same, and the materials forming layers 760a, 760b are similar or the same. In some embodiments, the materials forming waveguides 670, 680, 690 may differ between one or more waveguides, and / or the materials forming layers 760a, 760b may differ while still maintaining the various refractive index relationships noted above.

[0160] 9A, light rays 770, 780, 790 are incident on the set of waveguides 660. It will be appreciated that light rays 770, 780, 790 may be injected into the waveguides 670, 680, 690 by one or more image injection devices 360, 370, 380, 390, 400 (FIG. 6).

[0161] In some embodiments, the light rays 770, 780, 790 have different properties, for example, different wavelengths or different wavelength ranges that may correspond to different colors. Each of the incoupling optics 700, 710, 720 deflects incident light such that the light propagates through a respective one of the waveguides 670, 680, 690 by TIR. In some embodiments, each of the incoupling optics 700, 710, 720 selectively deflects one or more particular wavelengths of light while transmitting other wavelengths to the underlying waveguide and associated incoupling optic.

[0162] For example, incoupling optical element 700 may be configured to deflect light beam 770 having a first wavelength or wavelength range while transmitting light beams 780 and 790 having different second and third wavelengths or wavelength ranges, respectively. Transmitted light beam 780 impinges on and is deflected by incoupling optical element 710 configured to deflect light of the second wavelength or wavelength range. Light beam 790 is deflected by incoupling optical element 720 configured to selectively deflect light of the third wavelength or wavelength range.

[0163] 9A , the deflected light rays 770, 780, 790 are deflected such that they propagate through their corresponding waveguides 670, 680, 690. That is, the incoupling optical element 700, 710, 720 of each waveguide deflects the light into its corresponding waveguide 670, 680, 690, incoupling the light into its corresponding waveguide. The light rays 770, 780, 790 are deflected at an angle that causes the light to propagate through their respective waveguides 670, 680, 690 by TIR. The light rays 770, 780, 790 propagate through their respective waveguides 670, 680, 690 by TIR until they impinge on the waveguide's corresponding light distribution element 730, 740, 750.

[0164] Figure 9B shows a perspective view of one example of the multiple stacked waveguides of Figure 9A. As noted above, incoupled light rays 770, 780, and 790 are deflected by incoupling optical elements 700, 710, and 720, respectively, and then propagate by TIR within waveguides 670, 680, and 690, respectively. Light rays 770, 780, and 790 then impinge on light distribution elements 730, 740, and 750, respectively. Light distribution elements 730, 740, and 750 deflect light rays 770, 780, and 790 to propagate toward outcoupling optical elements 800, 810, and 820, respectively.

[0165] In some embodiments, the light distribution elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some embodiments, the OPEs deflect or distribute light to the outcoupling optics 800, 810, 820, and in some embodiments, may increase the beam or spot size of the light as it propagates to the outcoupling optics. In some embodiments, the light distribution elements 730, 740, 750 may be omitted, and the incoupling optics 700, 710, 720 may be configured to deflect light directly to the outcoupling optics 800, 810, 820. For example, referring to FIG. 9A , the light distribution elements 730, 740, 750 may be replaced with the outcoupling optics 800, 810, 820, respectively. In some embodiments, the outcoupling optical elements 800, 810, 820 are exit pupils (EPs) or exit pupil expanders (EPEs) that direct light to the viewer's eye 210 ( FIG. 7 ). It will be appreciated that an OPE may be configured to increase the size of the eyebox in at least one axis, and that an EPE may increase the eyebox in an axis that intersects the axis of the OPE, e.g., orthogonal to the axis of the OPE. For example, each OPE may be configured to redirect a portion of the light striking the OPE to the EPE of the same waveguide while allowing the remaining portion of the light to continue propagating through the waveguide. Upon striking the OPE again, another portion of the remaining light is redirected to the EPE, which continues to propagate further through the waveguide, and so on. Similarly, upon striking the EPE, a portion of the striking light is guided out of the waveguide to the user, and the remaining portion of that light continues to propagate through the waveguide until it again strikes the EP, at which point another portion of the striking light is guided out of the waveguide, and so on. As a result, a single incoupled light beam may be "replicated" each time a portion of that light is redirected by an OPE or EPE, thereby forming a field of cloned light beams, as shown in Figure 6. In some embodiments, the OPE and / or EPE may be configured to modify the size of the light beam.

[0166] 9A and 9B, in some embodiments, a waveguide set 660 includes waveguides 670, 680, 690, incoupling optical elements 700, 710, 720, light distribution elements (e.g., OPEs) 730, 740, 750, and outcoupling optical elements (e.g., EPs) 800, 810, 820 for each component color. The waveguides 670, 680, 690 may be stacked with an air gap / cladding layer between each one. The incoupling optical elements 700, 710, 720 redirect or deflect incident light into their respective waveguides (with different incoupling optical elements receiving light of different wavelengths). The light then propagates at an angle that results in TIR within each waveguide 670, 680, 690. In the illustrated example, light ray 770 (e.g., blue light) is deflected by the first incoupling optical element 700 and then continues bouncing down the waveguide, interacting with the light distribution element (e.g., OPE) 730 and then the outcoupling optical element (e.g., EP) 800 in the manner previously described. Light rays 780 and 790 (e.g., green and red light, respectively) pass through the waveguide 670, whereupon light ray 780 strikes and is deflected by the incoupling optical element 710. Light ray 780 then bounces down the waveguide 680 via TIR to its light distribution element (e.g., OPE) 740 and then to the outcoupling optical element (e.g., EP) 810. Finally, light ray 790 (e.g., red light) passes through the waveguide 690 and strikes the incoupling optical element 720 of the waveguide 690. The incoupling optic 720 deflects the light ray 790 so that it propagates by TIR to the light distribution element (e.g., OPE) 750 and then by TIR to the outcoupling optic (e.g., EP) 820. The outcoupling optic 820 then finally outcouples the light ray 790 to the viewer, who also receives outcoupled light from the other waveguides 670, 680.

[0167] FIG. 9C shows a top-down view of an example of the multiple stacked waveguides of FIGS. 9A and 9B. As shown, the waveguides 670, 680, 690, along with each waveguide's associated light distribution element 730, 740, 750 and associated outcoupling optical elements 800, 810, 820, may be vertically aligned. However, as discussed herein, the incoupling optical elements 700, 710, 720 are not vertically aligned. Rather, the incoupling optical elements do not overlap (e.g., are laterally spaced apart as seen in the top-down view). As discussed further herein, this non-overlapping spatial arrangement facilitates one-to-one injection of light from different sources into different waveguides, thereby enabling unique coupling of specific light sources to specific waveguides. In some embodiments, arrangements including non-overlapping, spatially separated incoupling optical elements may be referred to as shifted pupil systems, and the incoupling optical elements in these arrangements may correspond to sub-pupils.

[0168] Alternatively, in certain embodiments, two or more of the incoupling optics may be in a vertically aligned in-line arrangement, in which light for a waveguide further from the projection system is transmitted, preferably with minimal scattering or diffraction, through the incoupling optics for a waveguide closer to the projection system.

[0169] An in-line configuration can advantageously reduce and simplify the size of the projector. Furthermore, it can increase the field of view of the eyepiece by, for example, coupling the same color into several waveguides by exploiting crosstalk. For example, green light can be coupled into blue and red active layers. The pitch of each ICG can be different to provide improved (e.g., optimal) performance for a specific color, thereby increasing the permissible field of view.

[0170] In an in-line configuration, except for the last layer in the optical path, the ICG must be at most partially reflective or otherwise transparent to light at the operating wavelength of subsequent layers in the waveguide stack. In either case, the efficiency can be undesirably low unless the grating is etched with a high-index layer (e.g., 1.8 or above for polymer-based layers) or unless a high-index coating is deposited or grown on the grating. However, this approach can increase back reflections into the projector lens, potentially creating image artifacts such as image ghosting.

[0171] 9D shows an example of a wearable display system 60 into which the various waveguides and associated systems disclosed herein may be incorporated. In some embodiments, the display system 60 is the system 250 of FIG. 6, which schematically illustrates some portions of the system 60 in more detail. For example, the waveguide assembly 260 of FIG. 6 may be part of the display 70.

[0172] 9D , display system 60 includes display 70 and various mechanical and electronic modules and systems to support the functionality of display 70. Display 70 is coupled to a frame 80 that is wearable by a user or viewer 90 of the display system and configured to position display 70 in front of the user's 90 eyes. Display 70 may be considered eyewear in some embodiments. In some embodiments, speakers 100 are coupled to frame 80 and configured to be positioned adjacent to the user's 90 ear canals (in some embodiments, an additional speaker, not shown, may be positioned adjacent the user's other ear canal, if desired, to provide stereo / shapeable sound control). Display system 60 may also include one or more microphones 110 or other devices for detecting sound. In some embodiments, the microphones are configured to allow a user to provide input or commands to system 60 (e.g., selecting voice menu commands, natural language questions, etc.) and / or enable voice communication with others (e.g., with other users of similar display systems). The microphone may further be configured as an ambient sensor for collecting audio data (e.g., sounds from the user and / or the environment). In some embodiments, the display system may also include ambient sensors 120a that are separate from the frame 80 and may be attached to the body of the user 90 (e.g., on the head, torso, limbs, etc. of the user 90). The ambient sensors 120a, in some embodiments, may be configured to obtain data characterizing a physiological state of the user 90. For example, the sensors 120a may be electrodes.

[0173] 9D , the display 70 is operably coupled to a local data processing module 140 by a communication link 130, such as a wired lead or a wireless connection, which may be mounted in a variety of configurations, such as fixedly attached to the frame 80, fixedly attached to a helmet or hat worn by the user, embedded in headphones, or otherwise removably attached to the user 90 (e.g., a backpack-type configuration, a belt-type configuration). Similarly, the sensor 120 a may be operably coupled to the local processor and data module 140 by a communication link 120 b, such as a wired lead or a wireless connection. The local processing and data module 140 may comprise a hardware processor and digital memory, such as non-volatile memory (e.g., flash memory or a hard disk drive), both of which may be utilized to assist in processing, caching, and storing data. If desired, the local processor and data module 140 may include one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, etc. The data may include a) data captured from sensors (e.g., which may be operatively coupled to frame 80 or otherwise attached to user 90), such as image capture devices (e.g., cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, wireless devices, gyros, and / or other sensors disclosed herein, and / or b) data obtained and / or processed using remote processing module 150 and / or remote data repository 160 (including data related to virtual content) for passing to display 70 after such processing or retrieval, if possible.The local processing and data module 140 may be operably coupled by communication links 170, 180 to a remote processing module 150 and a remote data repository 160, e.g., via wired or wireless communication links, such that the remote modules 150, 160 are operably coupled to each other and available as resources to the local processing and data module 140. In some embodiments, the local processing and data module 140 may include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyro. In some other embodiments, one or more of these sensors may be mounted on the frame 80 or may be a standalone structure that communicates with the local processing and data module 140 by a wired or wireless communication path.

[0174] 9D , in some embodiments, remote processing module 150 may comprise one or more processors configured to analyze and process data and / or image information, including, for example, one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, etc. In some embodiments, remote data repository 160 may be a digital data storage facility that may be available via the Internet or other networking configuration in a “cloud” resource configuration. In some embodiments, remote data repository 160 may include one or more remote servers that provide information to local processing and data module 140 and / or remote processing module 150, e.g., information for generating augmented reality content. In some embodiments, all data is stored and all computations are performed within the local processing and data module, enabling fully autonomous use from the remote module. Optionally, an external system (e.g., one or more processors, one or more computer systems) including a CPU, GPU, etc. may perform at least a portion of the processing (e.g., generating image information, processing data) and provide and receive information to and from modules 140, 150, 160, e.g., via a wireless or wired connection.

[0175] Polarization-desensitized diffraction grating Providing a high-quality immersive experience to users of waveguide-based display systems, such as the various display systems configured for virtual / augmented / composite display applications described above, relies, among other things, on various characteristics of light coupling into and / or out of a waveguide within the eyepiece of the display system. For example, a virtual / augmented / composite display with high light incoupling and outcoupling efficiency can enhance the viewing experience by increasing the brightness of light guided to the user's eye. As discussed above, incoupling optical elements, such as incoupling gratings, may be used to couple light into a waveguide and guide it within the waveguide by total internal reflection. Similarly, outcoupling optical elements, such as outcoupling gratings, may be used to couple light guided into a waveguide out of the waveguide by total internal reflection.

[0176] 6 and 7, display systems according to various implementations described herein may include optical elements, such as incoupling optics, which may include a diffraction grating, outcoupling optics, light distribution elements, and / or compound pupil expander extractors (CPEs). As disclosed herein, CPEs can operate both as light distribution elements that spread or distribute light within the waveguide, potentially increasing the beam size and / or eyebox, and as outcoupling optics that couple light out of the waveguide.

[0177] 7, light 640 injected into the waveguide 270 at the input face 460 of the waveguide 270 propagates and is guided within the waveguide 270 by total internal reflection (TIR). In various implementations, at the point where the light 640 impinges on the outcoupling optical element 570, a portion of the light guided within the waveguide may exit the waveguide as beamlet 650. In some implementations, any of the optical elements 570, 580, 590, 600, 610, which 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.

[0178] To achieve desired characteristics of incoupling of light into (or outcoupling of light from) the waveguides 270, 280, 290, 300, 310, the optical elements 570, 580, 590, 600, 610 configured as diffraction gratings can be formed of suitable materials and have appropriate structures to control various optical properties, including diffractive properties such as diffraction efficiency as a function of polarization. Possible desired diffractive properties may include any one or more of spectral selectivity, angular selectivity, polarization selectivity (or non-selectivity), high spectral bandwidth, high diffraction efficiency, or wide field of view (FOV), among other properties.

[0179] Some diffraction gratings have strong polarization dependence and therefore may have relatively reduced overall efficiency (due to the rejection of one polarization). Such diffraction gratings may also create coherence artifacts and reduce the uniformity of far-field images. To provide a diffraction grating with reduced polarization sensitivity (e.g., coupling light with efficiency that is relatively polarization-independent), some displays for AR systems according to implementations described herein include a waveguide on which a blazed diffraction grating is formed. The blazed grating may have diffractive features with, for example, a “sawtooth” shape. In some implementations, the blazed grating may achieve improved grating diffraction efficiency in a given diffraction order, while the diffraction efficiency in other orders is reduced or minimized. As a result, in some implementations, more light may be directed to a particular given diffraction order as opposed to any of the other orders.

[0180] Transparent ICG In certain examples, the diffraction gratings described herein can be transmission ICGs for coupling incident light into a waveguide. Such diffraction gratings can be transmission diffraction gratings, e.g., transmission diffraction orders, e.g., T 10A transmission ICG launches light into the waveguide via a blazed diffraction grating 1008. For example, FIG. 10A shows a cross-sectional view of a portion of a display device 1000, such as an eyepiece, comprising a waveguide 1004 and a blazed diffraction grating 1008 formed on a substrate that is the waveguide 1004, according to some designs described herein. In the illustrated implementation, the blazed diffraction grating 1008 is formed in the substrate / waveguide 1004 (which is planar in this example). The surface of the substrate or waveguide 1004 has a surface topography with diffractive features that together form the diffraction grating 1008. The blazed diffraction grating 1008 is configured to diffract light having wavelengths in the visible spectrum such that light incident thereon is guided within the waveguide 1004 by TIR. The waveguide 1004 may be transparent and may form part of the eyepiece through which a user's eye can see. Such a waveguide 1004 and eyepiece may be included in a head-mounted display, such as an augmented reality display. The waveguide 1004 may correspond, for example, to one of the waveguides 670, 680, 690 described above with respect to Figures 9A-9C. The blazed grating 1008 may correspond, for example, to one of the incoupling optical elements 700, 710, 720 described above with respect to Figures 9A-9C. The blazed grating 1008 configured to incouple light into the waveguide 1004 may be referred to herein as an incoupling grating (ICG). The display device 1000 may further include an optical element 1012, which may correspond, for example, to a light distribution element (e.g., one of the light distribution elements 730, 740, 750 shown in Figures 9A-9C) or an outcoupling optical element (e.g., one of the outcoupling optical elements 800, 810, 820 shown in Figures 9A-9C).

[0181] In operation, when an incident light beam 1016, e.g., visible light, such as from an optical projection system providing image content, is incident on the blazed grating 1008 at an angle of incidence α measured with respect to a plane normal 1002 that is perpendicular or orthogonal to the blazed grating or the extension or plane of the substrate / waveguide and / or the surface 1004S of the waveguide 1004, e.g., the major surface of the waveguide on which the grating is formed (shown in FIG. 10A as extending parallel to the yx plane), the blazed grating at least partially diffracts the incident light beam 1016 as a diffracted light beam 1024 at a diffraction angle θ measured with respect to the plane normal 1002. The diffracted light beam 1024 falls within the critical angle θ for the occurrence of total internal reflection within the waveguide 1004. TIR Upon diffracting at a diffraction angle θ greater than θ, the diffracted light beam 1024 propagates and is guided within the waveguide 1004 via total internal reflection (TIR) ​​along a direction parallel to the x-axis and approximately along the length of the waveguide. A portion of this light guided within the waveguide 1004 may reach, for example, one of the light distribution elements 730, 740, 750 or one of the outcoupling optical elements (800, 810, 820; FIGS. 9A-9C ) and be diffracted again.

[0182] As described herein, in the illustrated implementation, a light beam incident at an angle in a clockwise direction relative to the plane normal 1002 (i.e., to the right of the plane normal 1002) is said to have a negative α (α<0), while a light beam incident at an angle in a counterclockwise direction relative to the plane normal 1002 (i.e., to the left of the plane normal) is said to have a positive α (α>0).

[0183] As further described elsewhere herein, an appropriate combination of high-index materials and / or the structure of the diffraction grating 1008 can result in a particular range of incident angles α (Δα), referred to herein as the angular acceptance range or field of view (FOV). One range Δα may be described by a range of angles spanning negative and / or positive values ​​of α, outside of which the diffraction efficiency drops by 10%, greater than 25%, greater than 50%, or greater than 75%, 80%, 90%, 95%, or any value within a range defined by any of these values, relative to the diffraction efficiency at α=0 or some other direction. In some implementations, it may be desirable to have Δα within a range in which the diffraction efficiency is relatively high and constant; for example, a uniform intensity of the diffracted light is desired within Δα. Thus, in some implementations, Δα is related to the angular bandwidth of the diffraction grating 1008, such that an incident light beam 1016 within Δα is efficiently diffracted by the diffraction grating 1008 at a diffraction angle θ relative to the surface normal 1002 (e.g., in a direction parallel to the yz plane), where θ is θ ≈ ... TIR exceeding . In some implementations, this angle Δα range can affect the field of view seen by a user. It will be appreciated that in various implementations, light can be guided into the incoupling grating (ICG) from either side. For example, light can be guided through a substrate or waveguide 1004 and incident on a reflective incoupling grating (ICG) 1008, such as that shown in FIG. 10A. The light may experience the same effect, for example, be coupled into the substrate or waveguide 1004 by the incoupling grating 1008, such that the light is guided within the substrate or waveguide by total internal reflection. The range of incident angles α (Δα), referred to herein as the accepted angular range or field of view (FOV), can be affected by the refractive index of the substrate or waveguide material. In FIG. 10A, for example, the reduced angular range (Δα') indicates the effect of refraction of the high refractive index material on the light incident on the incoupling grating (ICG). However, the range of angles (Δα) or FOV is larger.

[0184] FIG. 10B shows a cross-sectional view of an example of a blazed transmission grating 1008. The grating 1008 includes grating features having peaks 1003 and grooves 1005. The blazed transmission grating 1008 includes a surface that corresponds to the surface of a substrate or waveguide 1004S, which has a "sawtooth" shaped pattern when viewed from the cross-section shown. The patterned "sawtooth" is formed by first slope portions 1007 of the surface 1004S. In the example shown in FIG. 10B, the grating 1008 also includes second (steeper) slope portions 1009. In the example shown, the first slope portions 1007 have a shallower slope than the second slope portions 1009, which have a steeper slope. The first slope portions 1007 are wider than the second slope portions 1009 in this example.

[0185] The peaks 1003 have a height H corresponding to the distance from the bottom of the grooves 1005 to the top of the peaks 1003. Accordingly, this value may be referred to herein as the peak height and / or groove depth, the grating height or grating depth, or the height of the diffractive features of the diffraction grating. In the example shown in FIG. 10B , the bottom of the grooves 1005 is formed by the intersection of the first and second slope portions 1007, 1009 of two adjacent peaks 1003. The first slope portion 1007 is on one of the adjacent peaks 1003, and the second slope portion 1009 is on the other adjacent peak. Similarly, the top of the peaks 1003 is formed by the intersection of the first and second slope portions 1007, 1009 at the top of the peaks 1003. However, other configurations are also possible. For example, as described below, the first and second slope portions do not necessarily intersect if the bottom of the groove 1005 has a flat base or if the top of the peak 1003 includes a flat plateau. The blazed diffraction grating 1008 has a line spacing or pitch d, which may be constant in some implementations. The line spacing or pitch d may be a measure of the separation of the peaks of the peaks 1003 in a grating 1008 having a shape similar to that shown in FIG. 10B, for example. Similarly, the line spacing or pitch d may be a measure of the separation of the deepest points of adjacent grooves 1005. The line spacing or pitch d may also be measured from other locations on the grating feature.

[0186] The slope may be oblique at an angle δ with respect to a plane parallel to the grating 1008 or the surface of the waveguide (e.g., the surface 1004S of the waveguide that may extend beyond the grating or surface 1004S' of the waveguide opposite the grating in FIG. 10A). This angle δ of the first (shallower) slope portion 1007 is sometimes referred to herein as the blaze angle.

[0187] As shown in FIG. 10B, the blazed diffraction grating 1008 can include grating lines or features with asymmetric shapes, such as asymmetrically shaped peaks 1003 and / or grooves 1005. For example, in the diffraction grating shown in FIG. 10B, the diffractive features include peaks 1003 and / or grooves 1005 with asymmetric triangular cross-sectional shapes. As previously mentioned, this asymmetric shape results in different slopes and / or widths of the first and second sloped portions 1007, 1009. However, other shapes are also contemplated.

[0188] In designs in which the diffractive features are asymmetric, e.g., where the first sloped portion has a shallower slope and the second sloped portion has a steeper slope, the diffractive features can be considered to be formed from repeated slopes and steps. Such structures are sometimes referred to herein as diagonal step structures. In some implementations, the second portion can be steep so as not to slope, e.g., the second portion can be parallel to the normal 1002.

[0189] However, in other implementations of the "sawtooth" pattern, the peaks 1003 and / or grooves 1005 may be symmetrical. For example, the first and second sloped portions 1007, 1009 may have the same slope and be the same width.

[0190] The cross-sectional pattern shown in FIG. 10B may be referred to herein as a single-step configuration, as compared to a multi-step structure, which is also contemplated.

[0191] Regardless of whether the diffractive features are asymmetric or symmetric, in some implementations, as described below, plateaus or flat portions may be located on top of the peaks 1003. A diffraction grating 1008 with diffractive features having plateaus or flat portions on top of the peaks 1003 is shown, for example, in FIG.

[0192] Figure 10B shows an incident light beam 1016 incident on the grating 1008 at an angle α relative to the normal direction 1002. (As discussed above with respect to Figure 10A, the light can pass through the substrate or waveguide 1004 and, in other instances, enter the diffraction grating 1008 from the opposite side.) As discussed above, the normal 1002 is perpendicular or orthogonal to the plane of extension of the blazed diffraction grating 1008, or the plane of the grating or waveguide, and / or to a surface 1004S of the waveguide 1004, e.g., a major surface of the waveguide on which the grating is formed, or an opposite plane 1004S'. In Figure 10B, the light 1016 incident on the diffraction grating 1008 is shown to be diffracted at an angle β relative to the normal direction 1002.

[0193] When configured as an incoupling optical element or incoupling grating, the grating 1008 can diffractively couple light incident on the substrate 1004, which can be a waveguide as described above. The grating 1008 can also be configured as an outcoupling optical element, if desired, and in such embodiments can diffractively couple light out of the substrate 1004, which can also be a waveguide as described above.

[0194] 10A and 10B , in some implementations, the substrate 1004 includes a high-refractive index material having a refractive index of at least 1.9. The refractive index can be, for example, at least 2.0, at least 2.1, at least 2.2, or at least 2.3, and can be equal to or less than 2.4, 2.5, 2.6, 2.7, 2.8, or within any range formed by any of these values, or outside these ranges (e.g., 3.0 or greater, such as up to 4.0). In some implementations, for example, the substrate includes a Li-based oxide. In various examples disclosed herein, diffractive features of the diffraction grating 1008 may be formed on the surface of the substrate 1004. The diffractive features may be formed within the substrate 1004, e.g., a waveguide, or may be formed within a separate layer formed above the substrate 1004, e.g., a waveguide, and may be in optical communication with the substrate 1004, configured to couple light into or out of the substrate 1004, for example. In the illustrated example, the diffraction features of the diffraction grating 1008, such as lines, are formed in a substrate 1004, such as the surface of the substrate. The diffraction features may be etched into the substrate 1004, which may include a high refractive index material, such as a Li-based oxide. The substrate may include, for example, lithium niobate, and the diffraction grating may be formed in the lithium niobate substrate by etching or patterning the surface of the substrate. Other materials with high refractive indexes may also be used. For example, other lithium-containing materials, such as lithium oxides, may be employed as the substrate, for example, lithium tantalate (LiTaO). Silicon carbide (SiC) is another option for the substrate material. Examples are not so limited. In other examples, the diffraction features of the diffraction grating 1008 may be formed in a separate layer disposed above, for example, in physical contact with, the substrate 1004. For example, a thin film coating less than 200 nm thick, such as zinc oxide (ZnO), silicon nitride (Si3N4), zirconium dioxide (ZrO2), titanium dioxide (TiO2), or silicon carbide (SiC), may be deposited on an existing high-index substrate. The thin film coating may be patterned to form diffractive features. However, in some implementations, the diffractive features, such as the lines of the diffraction grating 1008, may be formed from a different material than that of the substrate.The substrate may include a high refractive index material such as, for example, a Li-based oxide (e.g., lithium niobate, LiNbO, or lithium tantalate, LiTaO), while the diffractive features may be formed from a different material, such as a coating of zinc oxide (ZnO), zirconium dioxide (ZrO), titanium dioxide (TiO), silicon carbide (SiC), or another material described herein. In some implementations, this other material formed on the substrate may have a lower refractive index. In some cases, the substrate 1004 may include a material (including an amorphous high refractive index glass substrate), such as, for example, silica glass (e.g., doped silica glass), silicon oxynitride, transition metal oxide (e.g., hafnium oxide, tantalum oxide, zirconium oxide, niobium oxide, aluminum oxide (e.g., sapphire)), plastic, polymer-based material, or a material that is materially optically transparent to visible light with an appropriate refractive index, e.g., as described above, different from the material of the Li-based oxide features 1008.

[0195] However, as previously mentioned, in various implementations described herein, the grating 1008 and the substrate 1004 or waveguide both comprise the same material, e.g., a Li-based oxide. In some implementations, the grating 1008 is patterned directly into the substrate 1004 such that the grating 1008 and the substrate 1004 form a single component or monolithic structure. For example, the substrate 1004 comprises a waveguide with the grating 1008 formed directly in the surface of the substrate. In these implementations, a bulk Li-based oxide material may be patterned at the surface 1004S to form the grating 1008, and the Li-based oxide material below the grating 1008 may form the waveguide. In yet some other implementations, the bulk or substrate 1004 and the surface 1004S patterned to form the grating 1008 comprise different Li-based oxides. For example, the bulk Li-based oxide material patterned on the surface region to form the grating 1008 may be formed from a first Li-based oxide material, and the Li-based oxide material below the substrate 1004 or the substrate region forming the grating 1008 may be formed from a second Li-based oxide material that is different from the first Li-based oxide material. As mentioned above, in some other implementations, the grating 1008 is composed of a different high refractive index material, such as zirconium dioxide (ZrO), titanium dioxide (TiO), silicon carbide (SiC), etc., and the material below the substrate 1004 or the substrate region forming the grating 1008 may be formed from a second material, such as LiTaO, LiNbO, etc., different from the first material coated as a thin film.

[0196] In the example shown in FIGS. 10A and 10B , the diffraction grating 1008 may include a plurality of blazed grating lines that are elongated in a first horizontal direction, or y-direction, and periodically repeat in a second horizontal direction, or x-direction. The grating lines may be, for example, straight and continuous lines extending in the y-direction. However, embodiments are not so limited. In some implementations, the grating lines may be discontinuous lines, for example, in the y-direction. In some other implementations, the discontinuous lines may form a plurality of pillars that protrude from the surface of the grating substrate. In some implementations, at least some of the grating lines may have different widths in the x-direction.

[0197] In the illustrated example, the grating lines of the grating 1008 have a profile with asymmetric opposing sides that form different angles with respect to the plane of the substrate, e.g., a sawtooth profile. However, the embodiment is not so limited, and in other implementations, the grating lines can have symmetric opposing sides that form similar angles with respect to the plane of the substrate.

[0198] 10A and 10B, according to various embodiments, the diffraction grating 1008 may have a variety of dimensions. For example, the diffractive 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 approximately 80 nm, according to embodiments, or within a range defined by any of these values. This height may correspond to the height of the peaks 1003 and / or the depth of the grooves 1005. Such heights, along with blazed shapes in high refractive index materials, may provide a diffraction grating with low polarization sensitivity. However, other heights may also be possible.

[0199] 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 any range defined by any of these values, according to various embodiments. Other pitches are also contemplated.

[0200] In some embodiments, the diffraction grating 1008 may have a blaze angle of approximately 20 to 89 degrees and an anti-blaze angle of 70 to 150 degrees, or any value within a range defined by these values. Values ​​outside these ranges are also possible, as described below.

[0201] In general, blazed diffraction gratings can be single-stage or multi-stage geometries, and various techniques can be used to form the gratings. In the example shown in Figures 11A-11B, the gratings can be formed by depositing blazed photoresist followed by etching and patterning the photoresist.

[0202] Exemplary methods for forming blazed gratings and examples of various blazed grating geometries are described in U.S. Patent Application Publication No. 20210072437, entitled "Display device with diffraction grating having reduced polarization sensitivity," the entire contents of which are incorporated herein by reference.

[0203] FIG. 11A shows the formation of a single-stage blazed grating 1106 in a substrate 1104 that may be a waveguide 1004 (see FIG. 10A). A patternable material such as photoresist 1102 is deposited on the substrate 1104 that is or includes the waveguide 1104. The patternable material / photoresist 1102 is patterned to have the shape of a blazed grating. Forming a blazed shape within the photoresist 1102 may, in some implementations, involve imprinting a pattern such as a single-stage "sawtooth" pattern within the photoresist 1102 (e.g., depositing the photoresist on the substrate 1104 and then imprinting the blazed geometry). The photoresist 1102 may comprise a mask such as a hard mask. Then, the patterned photoresist 1102 and substrate 1104 may be etched to form a blazed pattern within the substrate 1106. The etching of the photoresist 1102 and substrate 1104 may include, for example, dry plasma or chemical etching and / or wet chemical etching. In some implementations, the etching shown in FIG. 11A may etch the material at a relatively constant rate such that the portion of the patterned photoresist that is thickest results in a relatively small amount of removal of material from the substrate, e.g., negligible removal or non-removal, while the portion of the patterned photoresist that is thinnest (or non-existent) results in a relatively large amount of removal of material from the substrate or the deepest etching into the substrate.

[0204] FIG. 11B is a scanning electron micrograph of a blazed photoresist grating 1112, where the blazed grating pattern is formed within the photoresist 1104, for example, by imprinting a patterned master into the photoresist. The illustrated diffraction grating 1112 has a single-stage blazed shape.

[0205] In some examples, a blazed grating has parallel sidewalls. Such gratings may also be referred to as "tilted gratings." For example, referring to FIG. 12, a cross-sectional profile for one pitch length of such a grating is shown, in which a grating structure 1200 includes a grating layer composed of ridges 1220 on a substrate 1210. A Cartesian coordinate system is provided for reference. The grating extends in the x-direction, the ridges 1220 extend from the base in the z-direction, and the opposing slopes are angled relative to both the top surfaces of the ridges 1220 and the substrate surface. Two additional layers 1230, 1240 are formed on the surface of the grating layer. The layers 1230 and 1240 are formed on the top surfaces of the ridges 1220 and in the valleys between successive ridges, with only one slope of the ridges 1220 (in this case, the left-hand side) coated, while the other slope remains substantially free of these layers. Layers 1230 and 1240 can be formed using directional deposition techniques (e.g., evaporation, oblique angle deposition). Asymmetric coating of the two ridge slopes can result from the resulting directional deposition and self-shadowing.

[0206] The grating design shown in Figure 12 can be characterized by, among other things, six geometric parameters and three materials. Depending on the illumination wavelength and desired response, these parameters can vary in the following ranges: [Table 1]

[0207] 12, the anti-blaze angle refers to the acute angle between the right slope of ridge 1220 and the base surface. The anti-blaze angle can be in the range of 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°).

[0208] The blaze angle refers to the angle between the left slope of the ridge 1220 and the base surface. For the geometry shown in FIG. 12, a tilted grating, this angle is the complement of the anti-blaze angle (i.e., 180° minus the blaze angle). This angle can 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°).

[0209] The height of the grating layer refers to the ridge dimension along the z-direction. The ridges 1220 can have a height in the range of 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).

[0210] The pitch of the grating layer is the dimension along the x-direction between adjacent ridges or adjacent valleys. Generally, the pitch, as well as 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 ranges 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).

[0211] The ridges have a width, which refers to the dimension along the x-direction. For the lattice structure 1200, the opposing slopes of the ridges 1220 through the cross section shown are parallel, so the thickness of the ridges is constant for the ridges through their height. However, in certain implementations, the width can vary (e.g., narrow) from the base to the top of the ridge. In embodiments where the width varies, the width can be determined at the midpoint of the ridge's height.

[0212] The top width of the protrusion refers to the width of the protrusion at the top of the grating layer, as shown in Figure 12. In one example, the top width can be within a range of 50 nm to 150 nm (e.g., 60 nm to 140 nm, 70 nm to 130 nm, 80 nm to 100 nm).

[0213] Duty cycle refers to the ratio of width to pitch, expressed as a percentage. In embodiments, the grating structure can have a duty cycle in the range of 5% to 95% (e.g., 10% to 75%, 20% to 50%, 30% to 40%).

[0214] The ridges have a height corresponding to the dimension of the ridge in the z-direction, measured from its "base" to its "top surface." The ridges can have a height in the range of 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 thickness of layers 1230, 1240 refers to the z-direction dimension of the layer measured at a point where the surface supporting the layer is perpendicular to the z-direction. The first layer 1230 and / or the second layer can have a thickness in the range of 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). In general, the thicknesses of the first and second layers can be the same or different.

[0216] The substrate of the grating structure (i.e., substrate 1210 and ridges 1220) can be a UV or thermally crosslinked polymer. The refractive index of the substrate can range from 1.5 to 2.2 (e.g., 1.6 or greater, 1.7 or greater, 1.8 or greater, 1.9 or greater, 2.1 or greater, e.g., up to 2.2). A high refractive index (e.g., 1.8 or greater) can be achieved, for example, using a polymer composite containing nanoparticles (e.g., high refractive index nanoparticles, such as TiO2 nanoparticles and / or ZrO2 nanoparticles).

[0217] Without wishing to be bound by theory, it is believed that a higher refractive index of the base patterning material may help to make the diffraction efficiency similar over larger angles.

[0218] In some embodiments, the first coating 1240 is composed of a material having a high refractive index (e.g., 1.8 or greater). The first coating 1240 can be formed from a dielectric material, including, but not limited to, titanium dioxide, gallium phosphide, and silicon carbide.

[0219] In certain embodiments, the second coating 1230 is composed of a material having a low refractive index dielectric (e.g., 1.6 or less, 1.5 or less, 1.45 or less). The second coating can be formed from a dielectric material such as, but not limited to, silicon dioxide, magnesium fluoride, and calcium fluoride.

[0220] In general, lattice structure 1200 and lattice layers of similar lattice structures can be formed using the techniques described herein and in U.S. Patent Application Publication Nos. 20210033867 and 20210072437, the entire contents of both U.S. Patent Application Publications being incorporated herein by reference.

[0221] First coating 1230 can be formed using a variety of physical vapor deposition techniques, including, but not limited to, sputtering and electron beam evaporation. Second coating 1240 can be formed by a variety of physical vapor deposition techniques, including, but not limited to, sputtering and electron beam evaporation. In general, the technique used to form coating 1230 can be the same as or different from the technique used to form coating 1240.

[0222] The optical performance of the example grating structure described in Figure 12 above was simulated using rigorous coupled wave analysis (RWCA) as follows: The parameter values ​​in the grating structure were as follows: [Table 2-1] [Table 2-2]

[0223] For simulation purposes, an operating wavelength of 525 nm was used and the refractive index of the substrate was 2.0.

[0224] Figure 13A shows the diffraction efficiency in the launch direction as a function of illumination angle for a simulated grating over a 55° field of view. The three curves correspond to TM-polarized, TE-polarized, and unpolarized light. A diffraction efficiency of 52.46% was calculated. Figure 13B shows the reflection efficiency as a function of illumination angle for the simulated grating for TM-polarized, TE-polarized, and unpolarized light. A reflection efficiency of 0.93% was calculated. Figures 13C and 13D correspond to the same plots shown in Figures 13A and 13B, respectively, simulated for the same structure except without the second layer. The diffraction efficiency is still high, but back reflection is significantly increased.

[0225] Further experiments were performed to compare the results of the simulated grating structure with measurements of similarly fabricated samples. The results of these experiments are shown in Figures 14A-14D. Specifically, Figures 14A and 14B show plots of diffraction efficiency as a function of incident angle over a range of incident angles for TM, TE, and unpolarized light. Figure 14A shows the simulated data, while Figure 14B shows measurements of a fabricated sample for a subset of the simulated range. Figures 14C and 14D show a schematic of the cross-sectional profile of this grating structure (Figure 14C) and an SEM of the cross-section of a fabricated sample (Figure 14D).

[0226] Figures 15A-15C show the effect of including a low-index layer as the top layer in a grating structure. Figure 15A is a plot of diffraction efficiency as a function of incidence angle for orthogonal polarization states for a grating structure with a TiO coating thereon. An SEM of the cross-sectional profile of the grating structure is shown in the inset. Figure 15B is a plot of diffraction efficiency as a function of incidence angle for the same grating structure, except with an additional layer of SiO formed on top of the TiO layer. The average diffraction efficiency is shown, along with the diffraction efficiencies for both s-pol and p-pol. Figure 15C shows a plot of reflectance for normally incident light as a function of wavelength for the visible light spectrum for grating structures with and without a SiO coating. Reflectance is lower across nearly the entire visible spectral range.

[0227] Measurements from further examples are shown in Figures 16A-16F. Specifically, Figure 16A is a plot of diffraction efficiency as a function of incident angle for the grating structure shown in the SEM of Figure 16B, which is composed of a high-index (n=2.0) composite on a glass substrate (n=1.78). Figure 16C is a plot of diffraction efficiency as a function of incident angle for the grating structure shown in the SEM of Figure 16D, in which the grating layer is composed of a high-index (n=2.0) composite on a glass substrate (n=1.78) coated with TiO (n=2.15). Figure 16E is a plot of diffraction efficiency as a function of incident angle for the grating structure shown in the SEM of Figure 16F, which is composed of a high-index (n=2.0) composite on a glass substrate (n=1.78) with a TiO (n=2.15) coating, and an additional coating of SiO (n=1.45) coated on the TiO layer. It is clear that the overall diffraction efficiency is increased compared to a single coating, especially at higher angles of incidence.

[0228] While the foregoing example is a tilted lattice structure with ridges that are parallelogram-shaped, more generally, other cross-sectional shapes are contemplated. For example, trapezoidal, triangular, and stepped shapes are also contemplated. Also, while the shapes are depicted with mathematical precision corresponding to parallelogram shapes, deviations from these shapes are unavoidable due to manufacturing constraints, etc. Generally, as used herein, such ridges and other features are considered to have specific shapes where their design dictates such shapes and / or the structures have such shapes within the capabilities of the processes used to manufacture such structures on a large scale.

[0229] Furthermore, in some examples, ICGs can be designed to efficiently couple light (e.g., unpolarized light) of more than one wavelength (e.g., wavelengths spanning the visible spectrum, such as red, green, and blue wavelengths) into the waveguide. In some instances, the ICG is 120 nm or greater (e.g., 150 nm or greater) over 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 less than 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 vertical and horizontal). The polarized light may have an average emission efficiency of 40% or greater (e.g., greater than 45%, greater than 50%, greater than 55%, greater than 60%, greater than 65%, e.g., less than 75%, less than 70%, less than 65%, less than 60%, less than 60%, less than 55%) for unpolarized incident light of multiple wavelengths spanning a spectral range of greater than 200 nm, greater than 250 nm, e.g., less than 500 nm, less than 400 nm, less than 300 nm, less than 250 nm, e.g., 400 nm to 800 nm, e.g., 430 nm to 650 nm).

[0230] In some instances, ICG can be designed to have relatively low back reflection of incident light (e.g., unpolarized light) at more than one wavelength (e.g., wavelengths spanning the visible spectrum, such as red, green, and blue wavelengths). For example, the ICG may be 120 nm or greater (e.g., 150 nm or greater) across 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 less than 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 vertical and horizontal). For unpolarized incident light of multiple wavelengths spanning a spectral range of greater than or equal to 200 nm, greater than or equal to 250 nm, e.g., less than or equal to 500 nm, less than or equal to 400 nm, less than or equal to 300 nm, less than or equal to 250 nm, e.g., 400 nm to 800 nm, e.g., 430 nm to 650 nm), the average back reflection may be at or less than 15% (e.g., less than or equal to 12%, less than or equal to 10%, less than or equal to 9%, less than or equal to 8%, less than or equal to 7%, less than or equal to 6%, less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, e.g., greater than or equal to 1%, greater than or equal to 2%, greater than or equal to 3%).

[0231] In certain examples, an ICG can be designed to efficiently couple light (e.g., unpolarized light) and have relatively low back-reflection of incident light (e.g., unpolarized light) at more than one wavelength. For example, the ICG can be designed to have an angle of 10° or more (e.g., 15° or more, 20° or more, 22° or more, 25° or more, 30° or more, 40° or more, 50° or more, 60° or more, 70° or more, e.g., up to 70° or less) in at least one direction (e.g., two orthogonal directions, such as vertical and horizontal). , 60° or less, 50° or less, 40° or less, 35° or less, 30° or less, 25° or less, 22° or less), 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 For unpolarized incident light of multiple wavelengths spanning a spectral range of 40% or more (e.g., 45% or more, 50% or more, 55% or more, 60% or more, 65% or more, e.g., 75% or less, 70% or less, 60% or less, 65% or less, e.g., 75% or less, 70% or less, 65 ... 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 more, 2% or more, 3% or more).

[0232] Without wishing to be bound by theory, it is believed that the inclusion of one or more dielectric layers above the grating layer of a blazed ICG can facilitate both efficient coupling of light into the waveguide and low back reflection. This performance is evident based on the following exemplary ICG structure modeled by computer simulation. However, the described structure is an example, and other structures are possible. In general, the structural parameters of a blazed grating can be optimized for a particular application experimentally and / or using computational optimization methods.

[0233] An example of a tilted transmission grating with two dielectric layers has the following structure: [Table 3]

[0234] The grating ridges are formed from K21 resist and are covered first with a layer of TiO2 and second with a layer of MgF2.

[0235] The performance in this example was evaluated by calculating the 0th, +1st, and -1st order diffraction efficiencies for transmitted light at three different wavelengths (625 nm, 545 nm, and 465 nm) at angles of incidence ranging from -45° to +45° for incident light with TM and TE polarizations in the unit cell of the grating structure. For brevity, this analysis is hereafter referred to as Metric I.

[0236] Performance is also evaluated by calculating the launch efficiency into and back reflection from 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. Calculations are performed as a function of the polarization state relative to the launch, with an angle of 0 corresponding to TM light and an angle of 90 corresponding to TE light. Calculations are also performed at three different wavelengths (625 nm, 545 nm, and 465 nm). For simplicity, this analysis is hereafter referred to as Metric II.

[0237] Metric II is shown for the example of Table 3 in Figures 17A and 17B. In particular, Figure 17A shows the emission efficiency (as a percentage) for incident light with polarization between 0° and 90°. Figure 17B shows the back reflection (as a percentage) for incident light with polarization between 0° and 90°.

[0238] In this example, based on calculations in Metric II, the average emission efficiencies of red, green, and blue light are 50.20%, 49.63%, and 36.26%, respectively. The average reflections of red, green, and blue light are 7.23%, 9.18%, and 13.95%, respectively.

[0239] Metric I is shown for the example of Table 3 in Figures 18A-18I. Figures 18A-18C show the normalized zeroth-order reflectance, normalized zeroth-order transmittance, and first-order transmittance, respectively, as a function of incidence angle for incident TM light. The first-order transmittance corresponds to the light launched into the waveguide. Figures 18D-18F show the normalized zeroth-order reflectance, normalized zeroth-order transmittance, and first-order transmittance, respectively, as a function of incidence angle for incident TE light. Figures 18G-18I show the normalized zeroth-order reflectance, normalized zeroth-order transmittance, and first-order transmittance, respectively, as a function of incidence angle for incident light averaged over TM and TE polarizations.

[0240] Another example of a blazed transmission grating with two dielectric layers has the following structure: [Table 4]

[0241] Metric II is shown for the example of Table 4 in Figures 19A and 19B. In particular, Figure 19A shows the emission efficiency (as a percentage) for incident light with polarization between 0° and 90°. Figure 19B shows the back reflection (as a percentage) for incident light with polarization between 0° and 90°. A cross-section of a double-coated blazed transmission ICG is shown in Figure 19C.

[0242] In this example, based on Metric II calculations, the average emission efficiencies for red, green, and blue light are 42.19%, 28.01%, and 12.64%, respectively. The average reflections for red, green, and blue light are 9.23%, 13.92%, and 16.08%, respectively.

[0243] Metric I is shown for the example of Table 4 in Figures 20A-20I. Figures 20A-20C show the normalized zeroth-order reflectance, normalized zeroth-order transmittance, and first-order transmittance, respectively, as a function of incidence angle for incident TM light. The first-order transmittance corresponds to the light launched into the waveguide. Figures 20D-20F show the normalized zeroth-order reflectance, normalized zeroth-order transmittance, and first-order transmittance, respectively, as a function of incidence angle for incident TE light. Figures 20G-20I show the normalized zeroth-order reflectance, normalized zeroth-order transmittance, and first-order transmittance, respectively, as a function of incidence angle for incident light averaged over TM and TE polarizations.

[0244] 21A and 21B, sensitivity analysis of launch efficiency and back-reflection performance for double-coated graded (Table 3) and blazed (Table 4) ICG to random design perturbations (+ / - 10 nm) in the lattice parameters was evaluated by further calculations. In these plots, Lr, Lg, and Lb represent launch efficiency values ​​for red, green, and blue wavelengths, respectively, and Rr, Rg, and Rb represent back-reflection values ​​for red, green, and blue wavelengths, respectively, averaged over all angles within the illumination field of view (approximately 30 degrees diagonal for these calculations).

[0245] Based on these calculations, it is believed that tilted gratings (e.g., Table 3) may have greater sensitivity to perturbations in grating dimensions than blazed gratings (e.g., Table 4). In other words, from the perspective of large-scale manufacturability, this means that fabrication of double-coated blazed ICG gratings may not require the greater precision in layer dimensions and thicknesses that is required for fabricating tilted gratings.

[0246] (Reflection ICG) Furthermore, although the above examples include ICGs that are transmission gratings for launching light into the waveguide, reflective gratings are also contemplated. As referred to herein, reflective ICGs are used to measure the reflection diffraction orders, e.g., R 10 22, an example of a reflective ICG 2200 for a single-layer RGB waveguide 2210 includes a blazed grating 2202 covered by a reflective material 2204, such as a reflective metal (e.g., Al, Au, Ag, or alloys thereof).

[0247] The structure of an exemplary blazed reflection grating 2300 is shown in Figure 23, where parameters such as blaze angle 2302, anti-blaze angle 2304, pitch 2306, top width 2308, and bottom width 2310 are the same as those previously described for the tilted grating shown in Figure 12, and "rlt" refers to the thickness (in the z-direction) of a continuous layer 2320 of material (e.g., a polymer such as a polymer resist) that forms the grating ridge 2301 between the ridge and the top of the waveguide 2330.

[0248] A layer of metal 2312 is formed over the ridges, conforming to the shape of the ridges and filling the spaces between them.

[0249] A first example of a reflection grating is parameterized as follows: [Table 5]

[0250] Metric II for the exemplary metalized blazed grating in Table 5 is shown in Figures 24A and 24B. As shown, the launch efficiency and back reflection values ​​are optimized for TM polarization while increasing or decreasing for TE polarization, respectively. The average polarization average reflection across the FoV (22° x 22°) using an elliptical beam (2mm x 3.5mm) for RGB wavelengths is 27.43%, 32.62%, and 22.14%, respectively. The launch light of average polarization into the waveguide is 44.94%, 42.59%, and 32.32%, respectively.

[0251] Metric I for the exemplary metallized blazed grating of Table 5 is shown in FIGS. 25A-25I, where FIGS. 25A-25C show the normalized reflection efficiency as a function of incident angle for TM-polarized light reflected into the -1, 0, and +1 diffraction orders, respectively. The 0th order reflection corresponds to back reflection, and the +1st order corresponds to light launched into the waveguide. FIGS. 25D-25F show the normalized reflection efficiency as a function of incident angle for TE-polarized light reflected into the -1, 0, and +1 diffraction orders, respectively. FIGS. 25G-25I show the normalized reflection efficiency as a function of incident angle averaged for TE and TM-polarized light reflected into the -1, 0, and +1 diffraction orders, respectively. As can be seen from the Metric I results, the unit cell 0th-order reflection values ​​for TM-polarized light are less than 5% for all colors, while the values ​​for TE-polarized light are close to approximately 60%, 40%, and 20% for RGB, respectively.

[0252] A second example of a blazed reflection grating is summarized below. [Table 6]

[0253] The profile shape for this example is shown in FIG.

[0254] Metric II for the exemplary metallized blazed grating of Table 6 is shown in Figures 27A and 27B. As can be seen from Figures 27A and 27B, the average polarized back reflection for all three colors (RGB), as well as the average polarized back reflection for green and red, is significantly reduced, and for blue, there is not a reasonable reduction in the average polarized back reflection, but the first-order diffraction efficiency is low. For the blue wavelength, the first-order diffraction efficiency is low, but the value is also reduced in the -1 order, which is believed to be due to the phenomenon previously described as multiple bouncing, which may result in reduced back reflection.

[0255] The average polarization average reflection over the FoV (22° × 22°) using an elliptical beam (2mm × 3.5mm) for RGB wavelengths is 16.74%, 7.73%, and 7.53%, respectively, and the average polarization launch light into the waveguide is 49.74%, 45.65%, and 27.82%, respectively.

[0256] The metric I for the exemplary metallized blazed gratings of Table 6 is shown in Figures 28A-28I.

[0257] A further example of a blazed reflection grating is parameterized as follows: [Table 7]

[0258] A cross-sectional profile 2900 of this example is shown in Figure 29. A grating ridge 2910 is supported on a waveguide 2940. A TiO2 coating 2920 is conformal to the underlying ridge 2910 and is continuous across the grating layer. A reflective metal layer 2930 is coated on top of the coating 2920.

[0259] Yet another example of a blazed reflection grating is parameterized as follows: [Table 8]

[0260] A cross-sectional profile 3000 of this example is shown in Figure 30. Grating ridges 3010 are supported on waveguides 3040. TiO coating 3020 is deposited in a directional process (e.g., a GLAD process) such that the ridge walls 3011 on the anti-blaze side of each ridge are shadowed by the coating. As a result, the TiO layer 3020 is discontinuous across the grating layer.

[0261] Metric II for the exemplary metallized blazed grating of Table 8 is shown in Figures 31A and 31B. As can be seen in Figures 31A and 31B, the average polarized back reflection for all three colors (RGB), as well as the average polarized back reflection for green and red, is significantly reduced, and for blue, there is a low first-order diffraction efficiency, although there is not a reasonable reduction in the average polarized back reflection. For the blue wavelength, the first-order diffraction efficiency is low, but the value is also reduced in the -1 order, which is believed to be due to the phenomenon previously described as multiple bouncing, which may result in reduced back reflection.

[0262] The average polarization average reflection over the FoV (22° × 22°) using an elliptical beam (2mm × 3.5mm) for RGB wavelengths is 10.57%, 14.76%, and 17.63%, respectively, and the average polarization launch light into the waveguide is 52.63%, 49.40%, and 35.23%, respectively.

[0263] As is evident from Metric II, the launch efficiency into the waveguide for all colors increases compared to the examples parameterized in Tables 5 and 6. Back reflection is reduced for red, and for large anti-blazed angles (e.g., Table 6), the TE-polarized back reflection for red is still high, in the range of 30%.

[0264] The metric I for the exemplary metallized blazed gratings of Table 8 is shown in Figures 32A-32I.

[0265] The parameters of an exemplary two-layer coated blazed grating are as follows: [Table 9]

[0266] A cross-sectional profile 3300 of this example is shown in Figure 33A. The grating includes ridges 3310 supported on waveguides 3340. The first layer coating 3310 is a TiO2 coating, and the second layer coating 3312 is a SiO2 coating. Both coatings 3312 and 3314 can be deposited by a directional process (e.g., glancing angle deposition (GLAD)), such that the ridge wall 3311 on the anti-blaze side of each ridge is in the shadow of the coating. As a result, the two dielectric layers are discontinuous across the grating layer, specifically at the anti-blaze side sidewall 3311. The reflective layer 3320, e.g., a metal layer, can be deposited using either directional or isotropic deposition techniques (e.g., evaporation). In some examples, the dielectric layer can be deposited using isotropic deposition and then patterned to provide a discontinuous layer or layers (e.g., patterned by lithography).

[0267] Although FIG. 33A shows an example of a reflective ICG, a similar structure can be used for a transmissive ICG as shown in FIG. 33B, which shows a similar structure 3300' but without the reflective layer.

[0268] Metric II for the exemplary metallized blazed grating of Table 8 is shown in Figures 34A and 34B. As can be seen in Figures 34A and 34B, the launch efficiency is nearly polarization insensitive for red and green wavelengths. For blue wavelengths, the launch efficiency varies by about 5% between TM and TE light. Back reflection varies by about 5% or less between TM and TE light for all three wavelengths.

[0269] The average polarization average reflection over the FoV (22° × 22°) using an elliptical beam (2mm × 3.5mm) for RGB wavelengths is 5.84%, 9.45%, and 21.76%, respectively, and the average polarization launch light into the waveguide is 60.33%, 67.81%, and 48.62%, respectively.

[0270] The metric I for the exemplary metallized blazed gratings of Table 8 is shown in Figures 35A-35I.

[0271] Referring to Figures 36A-36C, the magnitude of the electric field is plotted within the unit cell of each lattice structure specified in Tables 5, 6, 8, and 9. In particular, column A corresponds to the plot for the structure in Table 5, column B corresponds to the plot for the structure in Table 6, column C corresponds to the plot for the structure in Table 8, and column D corresponds to the plot for the structure in Table 9. The plot shown in Figure 36A is generated for red wavelength (625 nm) light. The plot shown in Figure 36B is generated for green wavelength (545 nm) light. The plot shown in Figure 36C is generated for blue wavelength (465 nm) light. In each of these figures, 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). Units along both axes are in microns. In particular, for the structure in Table 9 (column D), the confinement of the electric field to the TiO2 layer is evident, especially for TE red light.

[0272] Therefore, a two-layer dielectric coating, in which the refractive index of the first dielectric layer is higher than that of the ridges and the second dielectric layer, may be advantageous due to the waveguide-like confinement that can occur within this layer. This confinement can modify the wavefront in the direction of the first diffraction order for both TE and TM polarizations.

[0273] Referring to Figure 37, the launch efficiency and back reflection at each wavelength are summarized in a plot for each of the structures summarized in Tables 3-6 and 8-9. The y-axis shows the average diffraction efficiency (both launch and back reflection) as a percentage. The x-axis contains six points. The first three points are the launch efficiencies of R, G, and B, respectively. The last three points are the back reflection efficiencies of R, G, and B, respectively.

[0274] Generally, various materials including the above materials can be used for the dielectric layer. The refractive index of these materials can vary from 1.5 to 4.0. Exemplary materials include MgF2, SiN2, SiO2, Al2O3, TiO2, and SiN.

[0275] (Further embodiments) Other variations are also possible. For example, the foregoing examples feature either 0, 1, or 2 dielectric layers covering the grating layer, but additional layers are also possible. For example, an additional layer can be included between the grating layer and the outermost low refractive index layer. An exemplary structure 3800 is shown in FIG. 38, which shows a grating structure having a ridge 3810 that 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.

[0276] The performance of the foregoing exemplary grating structures is determined at a single red wavelength, a single green wavelength, and a single blue wavelength, but performance can also be determined at other wavelengths (e.g., C, M, Y wavelengths). Generally, performance can be determined and optimized for any combination of operating wavelengths.

[0277] Furthermore, the foregoing exemplary grating structures are one-dimensional gratings, but other implementations are also possible. For example, in some embodiments, an array of structures can 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 examples, the undulations can be periodic, but in other examples, the pitch of the undulations can vary in at least one direction. According to various examples described herein, the diffraction features have opposing sidewalls that are angled asymmetrically or obliquely. According to various examples described herein, the diffraction features can be tapered.

[0278] In some implementations, the diffractive feature can have opposing sidewalls that are substantially angled or beveled. In some implementations, the opposing sidewalls can be beveled in the same direction, while in other implementations, the opposing sidewalls can be beveled in opposite directions. In some other implementations, the diffractive feature can have one of the opposing sidewalls that is substantially beveled, while the other sidewall is substantially perpendicular or orthogonal to the horizontal axis, or at least less beveled than the other sidewall. In various examples of 2D diffractive features described herein, the 2D diffractive feature can be formed in or on an underlying substrate, which can be a waveguide, as described above for various examples of 1D diffractive features. For example, the 2D diffractive feature can be etched into the underlying substrate or can be formed by patterning a separate layer formed thereon. Thus, the 2D diffractive feature can be formed from a material that is the same as or different from the material of the substrate, in a manner similar to that described above for the various 2D diffractive features. Other variations and configurations are also contemplated.

[0279] Thus, any of the structures or devices described herein, such as grating structures, may include 1D gratings. Similarly, any of the structures or devices described herein, such as grating structures, may include 2D gratings. Such 2D gratings may diffuse light. These gratings may also include blazed gratings. Such blazed gratings may preferentially direct light in a particular direction. In some implementations, a 2D grating (e.g., having one angled facet on the diffractive features) preferentially directs light in one direction, while in other implementations, a 2D grating (e.g., having two differently angled facets on the diffractive features) preferentially directs light in multiple directions. Similarly, any of the methods or processes described herein can be used with 1D gratings. Similarly, any of the methods or processes described herein can be used with 2D gratings. These 1D or 2D gratings may be included in or on a substrate and / or waveguide, included in an eyepiece, or, in some cases, incorporated into a head-mounted display as disclosed herein. These gratings may be employed as input gratings (e.g., ICG), output gratings (EPE), light distribution gratings (OPE), or combined light distribution / output gratings (e.g., CPE). Examples of output coupling gratings are shown, for example, in Figures 9C and 10A. Alternatively or additionally, such gratings can be used in orthogonal pupil expanders (e.g., 730, 740, 750 in Figure 9C). Such geometries can be similarly optimized for polarization-insensitive output couplers to improve display transparency in the region in front of the user's eyes, thereby reducing back reflections that can be problematic for diffractive surface relief gratings when used as wearable waveguides.

[0280] In some examples, a waveguide can include two ICGs on either side of the waveguide. For example, referring to FIG. 39, a waveguide 3910 includes a transmissive ICG 3920 on the side of the waveguide facing the projector 3940 and a reflective ICG 3930 on the opposite side. The structures of the two ICGs can be optimized together to achieve low back reflection and high launch efficiency, using the structures described in the examples above. Both the transmissive ICG 3920 and the reflective ICG 3930 launch light from the projector 3940 into the waveguide 3910.

[0281] As shown in Figure 39, the projector 3940 is aligned with respect to the waveguide 3910 so that light from the projector 3940 enters the transmission mode ICG 3920 at an angle of incidence that is substantially normal to the surface of the waveguide 3910. However, in other examples, the projector can be aligned so that its light enters the waveguide non-normally. Such an arrangement is shown in Figure 40, where the projector 4040 is aligned so that the light is incident at an angle θ that is not normal to the top surface of the waveguide 4010. in In such an arrangement, the incident angle θ in can be in the range of about 1° to 20° (measured from the normal to the waveguide surface) (e.g., in the range of about 3° to 15°, about 5° to 12°, about 5° to 10°).

[0282] Accordingly, other embodiments are within the scope of the following claims.

Claims

1. 1. A head-mounted display system, comprising: a head-mountable frame; a light projection system configured to output light to provide image content; a waveguide supported by the frame, the waveguide configured to guide at least a portion of the light from the optical projection system coupled into the waveguide; a grating structure optically coupled to the waveguide, the grating structure configured to couple light from the optical projection system into the waveguide, the grating structure comprising: a grating layer comprising a plurality of ridges having a blazed profile in at least one cross section; one or more dielectric layers disposed on the grating layer; a lattice structure comprising: Equipped with A head-mounted display system, wherein for unpolarized incident light at at least one operating wavelength of the output light, the grating structure has an average emission efficiency of 40% or greater than 40% and an average back reflection of 15% or less over a field of view of 10° or greater in at least one direction.

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

3. 3. The head-mounted display system of claim 2, wherein for unpolarized incident light at three operating wavelengths of the output light spanning a spectral range of 120 nm or greater, the grating structure has an average emission efficiency of 40% or greater than 40% and an average back reflection of 15% or less over a field of view of 10° or greater in at least one direction.

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

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

6. The head-mounted display system of claim 1 , wherein the field of view is 10° or more than 10° orthogonal.

7. The head mounted display system of claim 6 , wherein the field of view is 22°×22° in orthogonal directions.

8. The head mounted display system of claim 1 , wherein the grating structure is a reflective grating structure.

9. The head-mounted display system of claim 1 , wherein the grating structure is a transmission grating structure.

10. The head mounted display of claim 9 , wherein the plurality of ridges are sloping ridges.

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

12. The head mounted display system of claim 1 , wherein the one or more dielectric layers comprise at least one continuous layer.

13. The head-mounted display system of claim 1 , wherein the one or more dielectric layers comprise at least one discontinuous layer.

14. 2. The head-mounted display system of claim 1, wherein the one or more dielectric layers comprise a first dielectric layer disposed directly on the grating layer and a second dielectric layer disposed directly on the first dielectric layer, the first dielectric layer having a refractive index at the operating wavelength that is greater than the refractive index of the grating layer and the refractive index of the second dielectric layer.

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

16. 10. The head-mounted display system of claim 1, wherein the one or more dielectric layers comprise 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 of 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 of 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 of 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 of claim 1 , wherein the plurality of ridges have a blaze angle in the range of 15° to 50°.

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

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

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

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

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

26. The head mounted display system of claim 1 or 2, wherein the protrusion has a profile shape selected from the group consisting of a trapezoid, a parallelogram, a triangle, and a staircase.

27. 10. A head mounted display system according to any preceding claim, wherein the grating has a duty cycle in the range of 5% to 95%.

28. 10. A head mounted display system according to any preceding claim, wherein the grating material comprises a cross-linked polymer.

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

8.

30. 30. The head mounted display system of claim 28, wherein the grating material comprises nanoparticles.

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

25.

32. 10. A head mounted display system according to any preceding claim, wherein the waveguide supports a film of material and the ridges are etched into the film.

33. 33. The head mounted display system of claim 32, wherein the material is an inorganic material.

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

8.

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

45.

36. 33. The head mounted display system of claim 32, wherein the material has a refractive index higher than the refractive index of the waveguide.

37. 33. The head mounted display system of claim 32, wherein the material has a refractive index lower than the refractive index of the waveguide.

38. 10. A head mounted display according to any preceding claim, wherein in operation the grating structure is configured to couple light into the waveguide at operating wavelengths corresponding to a plurality of different coloured pixels of the optical projection system.

39. 10. A head mounted display according to any preceding claim, wherein the grating layer and the waveguide are constructed from the same material.

40. 40. The head mounted display of claim 39, wherein the material comprises a polymer.

41. 41. The head mounted display of claim 40, wherein the polymer has a refractive index of 1.75 or less.

42. 40. A head mounted display as described in claim 39, wherein the material has a refractive index of 1.8 or greater.

43. 40. The head mounted display of claim 39, wherein the material is a composite material.

44. 44. The head mounted display of claim 43, wherein the composite material comprises nanoparticles.

45. 10. A head mounted display according to any preceding claim, wherein the light from the optical projection system is unpolarized light.

46. 10. A head-mounted display according to any preceding claim, wherein the light projection system comprises a micro LED display, an LCoS display, or a laser beam scanner display.

47. 10. A head mounted display according to any preceding claim, further comprising one or more further waveguides and one or more further grating structures, each associated with a corresponding one of the further waveguides.

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

49. 49. The head mounted display of claim 48, wherein at least one of the grating structures is a reflective grating.

50. 50. The head mounted display of claim 49, wherein the reflective grating is the grating structure of the waveguide furthest from the optical projection system.

51. A head-mounted display as described in any preceding claim, wherein the waveguide and the optical projection system are arranged relative to each other such that the light from the projection system enters the grating structure from a direction non-normal to the surface of the waveguide.

52. 52. A head mounted display as described in claim 51, wherein the light from the projection system is incident on the grating structure at an angle in the range of 0° to 25° relative to the surface normal of the waveguide.

53. An article, the article comprising: a waveguide layer; a grating structure optically coupled to the waveguide, the grating structure configured to couple light from an optical projection system into the waveguide, the grating structure comprising: a grating layer comprising a plurality of ridges having a blazed profile in at least one cross section; one or more dielectric layers disposed on the grating layer; a lattice structure comprising: Equipped with and wherein for unpolarized incident light at at least one operating wavelength of the output light, the grating structure has an average emission efficiency of 40% or greater than 40% and an average back reflection of 15% or less over a field of view of 10° or greater in at least one direction.

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