Input / output coupling grating and display including the same

Abstract

A head-mounted display system includes a waveguide configured to guide light coupled to the waveguide from a light projection system; and a grating structure optically coupled to the waveguide, the grating structure configured to couple light from the light projection system into the waveguide. The grating structure includes a grating layer having a grating having a plurality of ridges having a blaze profile in at least one cross-section, the blaze profile having an anti-blaze angle of 85 DEG or less; and one or more additional layers on the grating layer, the additional layers including a first layer of a material having a refractive index of 1.5 or less at an operating wavelength of the head mounted display, the first layer being an outermost layer of the grating structure.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority to U.S. Application No. 63 / 342,004, filed on May 13, 2022, and U.S. Application No. 63 / 348,694, filed on June 3, 2022, the contents of which are hereby incorporated by reference. Technical Field

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

[0004] Modern computing and display technologies have facilitated the development of systems for so-called "virtual reality" or "augmented reality" experiences, in which digitally reproduced images, or portions thereof, are presented to a user in a manner that appears to be real or can be perceived as real. Virtual reality or "VR" scenes generally involve the presentation of digital or virtual image information without being transparent to other actual real-world visual input; augmented reality or "AR" scenes generally involve the presentation of digital or virtual image information as an enhancement to the visualization of the actual world around the user. Mixed reality or "MR" scenes are a type of AR scene, and generally involve virtual objects that are integrated into and responsive to the natural world. For example, in an MR scene, AR image content can be occluded by objects in the real world or perceived to interact with objects in the real world.

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

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

[0007] Disclosed are grating structures suitable for: an input coupling grating (ICG) for coupling light into a waveguide; an orthogonal pupil expander (OPE) for expanding an eye box by spacing the coupled light into multiple parallel beams; an exit pupil expander (EPE) for redirecting and coupling light out of the waveguide; and a combined pupil expander (CPE) for performing aspects of the OPE and the EPE, the grating structures being substantially polarization insensitive, having low back reflections, and allowing operation over a wide range of input angles. Such grating structures can be used in an inline alignment configuration, in which the ICGs for multiple stacked waveguides are aligned along a common optical path. Such ICGs are particularly useful for head-mounted displays using microLED (μLED) light projection systems that emit unpolarized light over a wide range of angles.

[0008] Examples of grating structures include asymmetric blazed (or "blazed") gratings formed from and / or coated with high refractive index materials (such as titanium dioxide, gallium phosphide, silicon carbide, and others). Such high refractive index layers can provide grating structures with relatively low optical losses. Due to the high refractive index film, reflected light can be very significant (e.g., >10% for some incident angles), which can lead to undesirable results, such as unwanted back-reflection coupling and ghosting in virtual images, reduced contrast, etc. Reducing such back-reflections causes more light to be diffracted and coupled in the waveguide in the correct order as TIR, so the benefit of reduced reflections outweighs the benefit of possible light recycling from the reflections.

[0009] The grating structures described herein have low reflection and high diffraction efficiency in both transverse electric (TE) and transverse magnetic (TM) polarization modes. This optical performance can enable overall eyepiece efficiency per watt of energy used by a projector (e.g., a μLED projection system), for example, where the projector uses unpolarized light and operates ideally with reduced back reflections from the grating structure into the lens of the projection system. This grating structure can also work well for single active layer architectures, in which all colors (e.g., R, G, B) are waveguided in a single high refractive index active layer, but the use of high diffraction efficiency in orthogonal polarization states is tethered using a grating structure operating in transmission mode, for example, enabling the use of a μLED projection system.

[0010] The grating structures described herein can have high directivity, which can cause light to propagate in a controlled direction within an eyepiece that includes the grating structure. For example, a blazed grating can focus diffracted light more in a specific direction determined by the geometry of the blazed grating than a non-blazed grating.

[0011] Various aspects of the disclosed subject matter are summarized below.

[0012] In general, in a first aspect, the present disclosure features a head-mounted display system, the 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 coupled into the waveguide from the light projection system; a grating structure optically coupled to the waveguide, the grating structure configured to couple the light from the light projection system into the waveguide. The grating structure comprises a grating layer having a plurality of (e.g., parallel) ridges having a blazed profile in at least one cross-section, the blazed profile having an anti-blazed angle of 85° or less; and one or more additional layers on the grating layer, the one or more layers comprising a first layer of a material having a refractive index of 1.5 or less at an operating wavelength of the head-mounted display, the first layer being the outermost layer of the grating structure.

[0013] Examples of head mounted display systems may include one or more of the following features. For example, the blaze profile may have a blaze angle of 95° or greater. The ridge may have a profile shape selected from the following: a trapezoid, a parallelogram, a triangle, and a step. The anti-blaze angle may be in a range from 1° to 89° (e.g., 5° to 85°, 20° to 60°, 45° to 75°, 50° to 60°, 60° to 70°, 70° to 80°). The ridge may have a height in a range from 10nm to 1000nm (e.g., 50nm to 500nm, 100nm to 400nm, 200nm to 400nm, 250nm to 350nm). The grating may have a pitch in the range of 100 nm to 5000 nm (e.g., 100 nm to 2500 nm, 100 nm to 1000 nm, 200 nm to 750 nm, 250 nm to 500 nm, 300 nm to 400 nm). The grating may have a duty cycle in the range of 5% to 95% (e.g., 10% to 75%, 20% to 50%, 30% to 0%). The first layer may 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).

[0014] In some embodiments, the one or more additional layers include a second layer located between the first layer and the grating layer, the second layer including a second material having a refractive index greater than 1.5 (e.g., 1.6 or higher, 1.7 or higher, 1.8 or higher, 1.9 or higher) at the operating wavelength. The second layer can have a thickness in a range from 5 nm to 500 nm (e.g., 10 nm to 400 nm, 20 nm to 300 nm, 50 nm to 250 nm, 100 nm to 200 nm, 130 nm to 170 nm).

[0015] The grating layer may include a grating material having a refractive index of 1.5 or higher (e.g., 1.6 or higher, 1.7 or higher, 1.8 or higher, 1.9 or higher) at the operating wavelength. The grating material may include a cross-linked polymer (e.g., a thermally cross-linked or UV cross-linked polymer). The grating material may include nanoparticles (e.g., TiO2 or ZrO2 nanoparticles).

[0016] The grating structure may be at least partially transmissive (eg, highly transmissive or partially reflective) at the operating wavelength.

[0017] The grating structure may be configured to couple light at an operating wavelength corresponding to a plurality of different color pixels of the light projection system into the waveguide during operation.

[0018] The grating layer and the waveguide may comprise the same material. The material may comprise a polymer. The material may have a refractive index of 1.7 or higher (e.g., 1.8 or higher, 1.9 or higher, 2.0 or higher, 2.1 or higher). The material may be a composite material. The composite material may comprise nanoparticles.

[0019] The light from the light projection system may be unpolarized light.

[0020] The light projection system may include a microLED display, an LCoS display, or a laser beam scanner display.

[0021] The head mounted display may include one or more additional waveguides and one or more additional grating structures, each additional grating structure being associated with a respective one of the additional waveguides. The grating structures of each waveguide may be arranged in a serial configuration. At least one of the grating structures may be a reflective grating. The reflective grating may be the grating structure of the waveguide that is farthest from the light projection system (e.g., for recycling light).

[0022] At least some of the ridges may have a single-order geometry.At least some of the ridges may have a multi-order geometry.

[0023] In general, in another aspect, the disclosure features an article that includes: a waveguide layer including a waveguide material having a refractive index of 1.7 or higher at an operating wavelength; a grating structure located at a surface of the waveguide layer. The grating structure may include: a grating layer having a grating including a plurality of (e.g., parallel) ridges, the plurality of ridges having a blaze profile in at least one cross section, the blaze profile having a reverse blaze angle of 89° or less, a height in a range from 10 nm to 1,000 nm, and a duty cycle in a range from 5% to 95%; and one or more additional layers disposed on the grating layer, the one or more layers including a first layer of a material having a thickness in a range from 5 nm to 500 nm and a refractive index of 1.5 or lower at an operating wavelength, the first layer being the outermost layer of the grating structure.

[0024] Embodiments of the article may include one or more features of the previous aspects of the present disclosure.

[0025] In general, in a further aspect, the present disclosure features a head-mounted display system, the 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 coupled into the waveguide from the light projection system; a grating structure optically coupled to the waveguide, the grating structure configured to couple the light guided by the waveguide out of the waveguide. The grating structure comprises a grating layer having a grating having a plurality of (e.g., parallel) ridges and having a blazed profile in at least one cross section, the blazed profile having an anti-blazed angle of 89° or less; and one or more additional layers on the grating layer, the one or more layers comprising a first layer of a material having a refractive index of 1.5 or less at an operating wavelength of the head-mounted display, the first layer being the outermost layer of the grating structure.

[0026] Embodiments of the head mounted display system may include one or more of the following features and / or features of other aspects. For example, the grating structure may be part of an exit pupil expander (EPE) or a combined pupil expander (CPE). The grating structure may be part of an orthogonal pupil expander.

[0027] In general, in another aspect, the disclosure features a device that includes: a waveguide for guiding light at an operating wavelength; a grating layer supported by the waveguide, the grating layer including a plurality of spaced-apart ridges of a grating material forming the grating, the plurality of spaced-apart ridges having a blazed profile in at least one cross-section, each ridge having a blazed side and an anti-blazed side opposite the blazed side, the anti-blazed side having a concave cross-sectional shape; and one or more additional layers supported by the grating layer, the one or more additional layers including a first layer including a first material different from the grating material, the first material being located on and between the ridges.

[0028] In general, in another aspect, the disclosure features a device that includes: a waveguide for guiding light at an operating wavelength; a grating layer extending in a plane, the grating layer being supported by the waveguide and including a plurality of spaced-apart ridges of a grating material forming the grating, the plurality of spaced-apart ridges having a blazed profile in at least one cross section, each ridge having a blazed side and an anti-blazed side opposite the blazed side, wherein the anti-blazed side has a nonlinear shape in the cross section, and a vertex of the anti-blazed side is aligned with a base point of the anti-blazed side in a direction normal to the plane of the grating layer in the cross section; and one or more additional layers supported by the grating layer, the one or more additional layers including a first layer including a first material different from the grating material, the first material being located on and between the ridges.

[0029] In general, in another aspect, the disclosure features a device that includes: a waveguide for guiding light at an operating wavelength; a grating layer supported by the waveguide, the grating layer including a plurality of spaced-apart ridges of a grating material forming the grating, the plurality of spaced-apart ridges having a blazed profile in at least one cross-section, each ridge having a blazed side and an anti-blazed side opposite the blazed side; and one or more additional layers supported by the grating layer, the one or more additional layers including a first layer including a first material different from the grating material, the first material being located on and between the ridges, wherein for at least some of the ridges, the ridges and the one or more additional layers form an air gap on the anti-blazed side of the ridges.

[0030] Embodiments of the three devices in these aspects may include one or more of the following features and / or features of other aspects. For example, the concave cross-sectional shape of the anti-glare side includes a curved portion. The anti-glare side may include a curved portion.

[0031] The radius of curvature of the curved portion may be in the range from 20 nm to 500 nm.

[0032] In some examples, the concave cross-sectional shape of the anti-flare side includes one or more line segments. The anti-flare side may include one or more line segments. The first line segment may have a positive slope and the second line segment has a negative slope, and the first line segment may be higher than the second line segment in a vertical direction. In some examples, at least two of the one or more line segments intersect at an obtuse angle. The length of at least one of the line segments may be in the range of 5 nm to 500 nm.

[0033] In some examples, an edge and an anti-blaze side of at least one of the one or more additional layers define an air gap.

[0034] The first layer of the one or more additional layers has a refractive index of at least 1.5 at the operating wavelength.

[0035] The one or more additional layers may include a second layer having a refractive index of at least 1.5 at the operating wavelength.

[0036] In some examples, one or more additional layers do not coat the anti-blaze side of each ridge.

[0037] Each ridge may have a blaze angle of 95° or greater. Each ridge may have a back blaze angle in the range of 1° to 89°. The ridges may have a height in the range of 10 nm to 1,000 nm. The grating may have a pitch in the range of 100 nm to 5000 nm. The grating may have a duty cycle in the range of 5% to 95%.

[0038] The first layer may have a thickness in the range from 5 nm to 500 nm. The second layer may have a thickness in the range from 5 nm to 500 nm.

[0039] The grating material may comprise a cross-linked polymer.The grating material may comprise nanoparticles.

[0040] The grating structure may be at least partially transmissive at the operating wavelength.

[0041] The grating layer and the waveguide may comprise the same material.

[0042] In some examples, the material includes a polymer. The material may have a refractive index of 1.7 or higher. The material may be a composite material (eg, including nanoparticles).

[0043] The apparatus may comprise one or more additional waveguides and one or more additional grating structures, each additional grating structure being associated with a respective one of the additional waveguides.

[0044] The grating structures of each waveguide may be arranged in a tandem configuration.At least one of the grating structures may be a reflective grating.

[0045] At least some of the ridges may include a blaze side having a single-step geometry.At least some of the ridges may include a blaze side having a multi-step geometry.

[0046] In a further aspect, the present disclosure features a head-mounted display (HMD) configured to be worn on a user's head, the HMD comprising: a frame; a pair of optical elements supported by the frame so that each of the pair of optical elements can be positioned in front of the user's eyes; a device according to the previous aspects, wherein the device is positioned on at least one of the pair of optical elements; and a projection system configured to project light into a waveguide of the device for display to the user's eyes.

[0047] Each optical element may include a distal surface and a proximal surface, wherein the proximal surface is closer to the user's eye than the distal surface, and the grating of the device is disposed on the proximal surface.

[0048] Each optical element may include a distal surface and a proximal surface, wherein the proximal surface is closer to the user's eye than the distal surface, and the grating of the device is disposed on the distal surface.

[0049] The grating structure may be configured to couple light at an operating wavelength corresponding to a plurality of different color pixels into the waveguide during operation.

[0050] The light from the light projection system can be polarized or unpolarized.

[0051] The light projection system may include a microLED display, an LCoS display, or a laser beam scanner display.

[0052] The apparatus may comprise one or more additional grating structures, wherein the grating structure furthest from the light projection system is a reflective grating.

[0053] In general, on the other hand, the present disclosure features a method comprising: depositing an etch stop layer on a substrate; depositing a grating material on the etch stop layer; depositing a blazed grating template on the grating material; etching the grating material using the blazed grating template, thereby transferring the shape of the blazed grating template to the grating material and forming a blazed grating; coating the blazed grating with an etching mask at a first non-zero angle relative to a vertical direction so that an anti-blazed side of the grating remains uncoated; etching at a second non-zero angle relative to the vertical direction and having a sign opposite to the sign of the first non-zero angle, thereby removing an inner portion of the anti-blazed side; and stripping the etching mask from the blazed grating.

[0054] Implementations of the head mounted display system may include one or more of the following features and / or features of other aspects. For example, the substrate is a waveguide.

[0055] The shape of the blazed grating template may extend vertically beyond the shape of the blazed grating.

[0056] Etching of the grating material can be completed before the blazed grating template is fully used.

[0057] The method may include, prior to applying the etch mask to the blazed grating, stripping remaining portions of the blazed grating template from the grating material.

[0058] Etching the grating material may include at least one of dry plasma etching, chemical etching, and wet chemical etching.

[0059] The first non-zero angle may be determined by the reverse blaze angle of the blazed grating. The absolute value of the first non-zero angle may be at least equal to the difference between the reverse blaze angle and 90°.

[0060] The anti-blaze side may include a concave curvature.The anti-blaze side may include one or more linear segments.

[0061] The method may further include coating the blazed grating with one or more additional layers, wherein at least one of the one or more additional layers comprises a material having a refractive index of at least 1.5 at the operating wavelength. Coating the blazed grating with the one or more layers may result in an air gap being formed between an edge of at least one of the one or more additional layers and an anti-blazed side.

[0062] In general, in another aspect, the present disclosure features a head-mounted display (HMD) comprising: a waveguide for guiding light at an operating wavelength; and a grating structure comprising: a grating layer supported by the waveguide, the grating layer comprising a plurality of spaced-apart ridges of a grating material forming the grating, the plurality of spaced-apart ridges having a blazed profile in at least one cross-section, each ridge having a blazed side and an anti-blazed side opposite the blazed side, the anti-blazed side having a concave cross-sectional shape; and one or more additional layers supported by the grating layer, the one or more additional layers comprising a first layer comprising a first material different from the grating material, the first material being located on and between the ridges.

[0063] Embodiments of the head mounted display system may include one or more of the following features and / or features of other aspects. For example, for unpolarized light with a wavelength ranging from 400 nm to 700 nm incident at an incident angle ranging from -20° to +20°, the diffraction efficiency of the grating structure may be 10% or more (e.g., 20% or more, 30% or more).

[0064] The back reflectivity of the grating structure may be 30% or less for unpolarized light in the wavelength range from 400 nm to 700 nm within the incident angle range from -20° to +20°.

[0065] The HMD may include a projection system, and during operation, the grating structure receives unpolarized light or polarized light from the projection system.

[0066] The grating structure may be positioned to receive light from the projection system which passes through the waveguide before being coupled into the waveguide by the grating structure.

[0067] Other features and advantages will be apparent from the accompanying drawings, the following description, and the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1An augmented reality (AR) view seen by a user through an AR device is shown.

[0069] Figure 2 A conventional display system for simulating a three-dimensional image for a user is shown.

[0070] Figures 3A to 3C The relationship between the radius of curvature and the focal radius is shown.

[0071] Figure 4A Shown is a representation of the accommodation-vergence response of the human visual system.

[0072] Figure 4B Examples of different accommodation and convergence states of a pair of eyes of a user are shown.

[0073] Figure 4C An example of a top view representation of a user viewing content via a display system is shown.

[0074] Figure 4D Another example of a top view representation of a user viewing content via a display system is shown.

[0075] Figure 5 Aspects of a method for simulating three-dimensional images by modifying wavefront divergence are shown.

[0076] Figure 6 An example of a waveguide stack for outputting image information to a user is shown.

[0077] Figure 7 An example of an outgoing light beam output by a waveguide is shown.

[0078] Figure 8 An example of a stacked waveguide assembly is shown where each depth plane includes an image formed using multiple different component colors.

[0079] Fig. 9A A cross-sectional side view of an example of a set of stacked waveguides each including an in-coupling optical element is shown.

[0080] Fig. 9B Shows Fig. 9A A perspective view of an example of multiple stacked waveguides.

[0081] Fig. 9C Shows Fig. 9A and 9B A top plan view of an example of multiple stacked waveguides.

[0082] Fig.9D An example of a wearable display system is shown.

[0083] Fig. 10ASchematically shown is a cross-sectional view of a portion of a waveguide on which a diffraction grating is provided, for example for coupling light into the waveguide.

[0084] Fig. 10B A cross-sectional view of a waveguide having a blazed diffraction grating disposed thereon is shown, showing the field of view (FOV) of the waveguide for a range of angles of incidence Δα.

[0085] Fig.11A A cross-sectional view of a portion of a grating structure is shown, in which the grating pattern is transferred from the resist layer to the substrate layer by dry etching.

[0086] Fig. 11B So Fig.11A SEM micrograph of an example grating structure formed in the manner shown.

[0087] Fig.12 is a schematic cross-sectional view showing a single pitch length of a grating structure comprising a tilted grating having first and second coatings thereon.

[0088] Figures 13A-13D The comparison includes two coatings ( Figures 13A-13B ) and a coating ( Figures 13C-13D ) is a graph of the diffraction efficiency and reflectivity of an example grating structure.

[0089] Figures 14A-14D Compared with Fig. 14C and Fig.14D The simulated diffraction efficiency of the grating structure shown ( Fig.14A ) and measured diffraction efficiency ( Fig. 14B ) results.

[0090] Fig.15A is a graph of measured diffraction efficiency for an example grating structure with a single coating.

[0091] Fig. 15B yes Fig.15A Graph of measured diffraction efficiency of an example grating structure with a second coating layer shown in FIG.

[0092] Fig. 15C It is for Fig.15A and Fig. 15B A graph of the measured % reflectivity of the grating structure shown as a function of wavelength.

[0093] Figures 16A-16F are respectively compared with uncoated ( Fig.16A and 16B ), having a coating ( Fig. 16C and 16D ) and with two coatings ( Fig.16E and 16F) is a graph and SEM micrograph of the diffraction efficiency as a function of angle for an example of a tilted grating.

[0094] Fig.17A A cross-sectional view of an example blazed grating with a concave anti-blaze side is shown.

[0095] Fig. 17B A cross-sectional view of another example of a blazed grating with a concave anti-blaze side is shown.

[0096] Fig. 17C and 17D A cross-sectional view of an example grating with a faceted anti-blaze side is shown.

[0097] Fig.17E A cross-sectional view of an example blazed grating with a concave anti-blaze side and two layers deposited on the grating is shown.

[0098] Fig.18 are scanning electron microscope (SEM) images of reentrant blazed gratings with different slopes on the anti-blazed sidewalls.

[0099] Figures 19A-19I is a cross-sectional diagram describing the fabrication process for a re-entrant grating with a multi-faceted anti-blaze side.

[0100] Fig. 20 is a flow chart of a process for forming a blazed grating having a concave anti-blaze side.

[0101] Throughout the drawings, reference numerals may be repeated to indicate corresponding relationships between referenced elements. The drawings are provided to illustrate example embodiments described herein and are not intended to limit the scope of the present disclosure. DETAILED DESCRIPTION

[0102] AR systems can display virtual content to a user or viewer while still allowing the user to see the world around them. Preferably, the content is displayed on a head-mounted display, such as part of glasses, which projects image information into the user's eyes. In addition, the display can also transmit light from the surrounding environment to the user's eyes to allow viewing of the surrounding environment. As used herein, it should be understood that a "head-mounted" or "head-mountable" display is a display that can be worn on the head of a viewer or user.

[0103] In some AR systems, virtual / augmented / hybrid displays with relatively high fields of view (FOV) can improve the viewing experience. The FOV of the display depends on the angle of light output by the waveguide of the eyepiece, through which the viewer sees the image projected into his or her eyes. A waveguide with a relatively high refractive index (e.g., 1.7 or higher) can provide a relatively high FOV. However, in order to effectively couple light into the high refractive index waveguide, the diffractive optical coupling element should also have a corresponding high refractive index. To achieve this goal, among other advantages, according to the embodiments described herein, some displays for AR systems include a waveguide comprising a material with a relatively high refractive index (e.g., 1.8 or higher, such as 2.0 or higher), on which a corresponding diffraction grating with a corresponding high refractive index is formed, such as a titanium-based, tantalum-based, or lithium-based oxide. For example, by patterning a surface portion of a waveguide formed of a titanium-based, tantalum-based, or lithium-based oxide, a diffraction grating can be formed directly on a titanium-based, tantalum-based, or lithium-based oxide waveguide.

[0104] Some high refractive index diffractive optical coupling elements (such as coupling-in or coupling-out optical elements) have strong polarization dependence. For example, an in-coupling grating (ICG) for coupling light into a waveguide, in which the diffractive optical coupling element includes a high refractive index material, can accept light of a specific polarization significantly more than light of another polarization. For example, such an element can couple light with TM polarization into the waveguide at a ratio of approximately 3 times that of light with TE polarization. Diffractive optical coupling elements with such polarization dependence may have reduced efficiency (due to low efficiency and general rejection of one polarization), and may also produce coherence artifacts and reduce the uniformity of the far-field image formed by the light coupled out of the birefringent waveguide. In order to obtain a diffractive optical coupling element that is polarization-insensitive or at least has reduced polarization sensitivity (e.g., it couples light with efficiency that is relatively independent of polarization), according to various embodiments described herein, some displays for AR systems include a waveguide having a diffraction grating formed with a blazed geometry. Diffraction gratings may also be formed directly in a waveguide, which may include a high refractive index material (e.g., having a refractive index of at least 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, or up to 2.7, or any range between any of the above values). For example, a diffraction grating may be formed in a high refractive index material, such as a titanium-based, tantalum-based, or lithium-based oxide, such as lithium niobate (LiNbO3) or lithium tantalate (LiTaO3), or a material such as zirconium oxide (ZrO2), titanium dioxide (TiO2), or silicon carbide (SiC), by patterning the high refractive index material with a blazed geometry.

[0105] Reference will now be made to the drawings, in which like reference numerals represent like parts throughout the drawings. Unless otherwise indicated, the drawings are schematic and are not necessarily drawn to scale.

[0106] Figure 2 A conventional display system for simulating a three-dimensional image for a user is shown. The user's eyes are spaced apart, and when viewing a real object in space, each eye will have a slightly different view of the object, and an image of the object may be formed at a different location on the retina of each eye. This may be referred to as binocular parallax, and may be used by the human visual system to provide a sense of depth. Conventional display systems simulate binocular parallax by presenting two different images 190, 200 (one for each eye 210, 220) with slightly different views of the same virtual object, corresponding to views of the virtual object that will be seen by each eye as a real object at the desired depth. These images provide binocular cues that the user's visual system may interpret to obtain a sense of depth.

[0107] Continue to refer Figure 2 , the images 190, 200 are spaced a distance 230 from the eyes 210, 220 on the z-axis. The z-axis is parallel to the optical axis of the viewer with the eyes looking at an object at optical infinity directly in front of the viewer. The images 190, 200 are flat and at a fixed distance from the eyes 210, 220. Based on the slightly different views of the virtual objects in the images presented to the eyes 210, 220, respectively, the eyes can naturally rotate so that the image of the object falls on the corresponding point on the retina of each eye to maintain a single binocular vision. The rotation can cause the line of sight of each eye 210, 220 to converge to the point in space where the virtual object is perceived to exist. Therefore, providing a three-dimensional image generally involves providing binocular cues that can manipulate the convergence of the user's eyes 210, 220 and be interpreted by the human visual system to provide a sense of depth.

[0108] However, producing a realistic and comfortable sense of depth is challenging. It should be understood that light from objects at different distances from the eye has wavefronts with different amounts of divergence. Figures 3A to 3C The relationship between distance and light divergence is shown in FIG. 2 . The distance between the object and the eye 210 is represented in the order of decreasing distance R1, R2, and R3. Figures 3A to 3C As shown, as the distance to the object decreases, the light becomes more divergent. Conversely, as the distance increases, the light becomes more collimated. In other words, it can be said that the light field generated by a point (object or part of an object) has 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. Although for clarity in the description of Figures 3A to 3C Only a single eye 210 is shown in and other figures herein, but the discussion regarding eye 210 is applicable to both eyes 210 and 220 of a viewer.

[0109] Continue to refer Figures 3A to 3C , light from an object being looked at by a viewer's eye can have different degrees of wavefront divergence. Due to different amounts of wavefront divergence, light can be focused differently by the lens of the eye, which in turn may require the lens to assume different shapes to form a focused image on the retina of the eye. In the absence of a focused image formed on the retina, the resulting retinal blur acts as an accommodation cue that causes a change in the shape of the eye lens until a focused image is formed on the retina. For example, an accommodation cue can trigger the ciliary muscles surrounding the eye lens to relax or contract, thereby adjusting the force applied to the suspensory ligaments that hold the lens, thereby changing the shape of the eye lens until the retinal blur of the looked object is eliminated or minimized, thereby forming a focused image of the looked object on the retina of the eye (e.g., the fovea). The process by which the eye lens changes shape may be referred to as accommodation, and the shape of the eye lens required to form a focused image of the looked object on the retina of the eye (e.g., the fovea) may be referred to as an accommodation state.

[0110] Reference now Figure 4A , shows a representation of the accommodation-convergence response of the human visual system. Movement of the eyes to fixate on an object causes the eyes to receive light from the object, where the light forms an image on each retina of the eye. The presence of retinal blur in the image formed on the retina can provide accommodation cues, and the relative positions of the images on the retina can provide vergence cues. Accommodation cues cause accommodation to occur, so that the eye lenses respectively assume a specific accommodation state that forms a focused image of the object on the retinas of the eyes (e.g., the fovea). On the other hand, vergence cues cause vergence movements (eye rotations) to occur so that the images formed on each retina of each eye are at corresponding retinal points that maintain a single binocular vision. In these positions, it can be said that the eyes have assumed a specific vergence state. Continue with reference to Figure 4A , accommodation can be understood as the process by which the eye achieves a specific accommodation state, and vergence can be understood as the process by which the eye achieves a specific vergence state. Figure 4A As shown, if the user looks at another object, the accommodation and convergence states of the eyes may change. For example, if the user looks at a new object at a different depth on the z-axis, the accommodation state may change.

[0111] Without being limited by theory, it is believed that a viewer of an object may perceive the object as "three-dimensional" due to a combination of vergence and accommodation. As described above, the vergence movement of the two eyes relative to each other (e.g., the eyes rotate so that the pupils move toward or away from each other so that the eyes' line of sight converges to fixate on an object) is closely related to the accommodation of the eye lenses. Under normal circumstances, changing the shape of the eye lenses to change the focus from one object to another at a different distance will automatically cause a matching change in vergence to the same distance, under the relationship known as the "accommodation-convergence reflex." Likewise, under normal circumstances, a change in vergence will trigger a matching change in lens shape.

[0112] Reference now Figure 4B , examples of different accommodation states and convergence states of eyes are shown. A pair of eyes 222a is fixated on an object at optical infinity, while a pair of eyes 222b is fixated on a point 221 that is less than optical infinity. It is noteworthy that the convergence state of each pair of eyes is different, with one pair of eyes 222a looking straight ahead and one pair of eyes 222 converging on point 221. The accommodation state of the eyes forming each pair of eyes 222a and 222b is also different, as represented by the different shapes of the lenses 210a, 220a.

[0113] Unexpectedly, many users of conventional "3D" display systems find that such conventional systems are uncomfortable or may not perceive a sense of depth at all due to the mismatch between the accommodation and convergence states in these displays. As described above, many stereoscopic or "3D" display systems display a scene by providing slightly different images to each eye. Such systems are uncomfortable for many viewers because, among other things, such systems only provide different presentations of the scene and cause changes in the convergence state of the eyes, but there is no corresponding change in the accommodation state of these eyes. Instead, the image is displayed by a display at a fixed distance from the eyes so that the eyes view all image information in a single accommodation state. This arrangement violates the "accommodation-convergence reflex" by causing a change in the convergence state without a matching change in the accommodation state. This mismatch is believed to cause discomfort to the viewer. A display system that provides a better match between accommodation and convergence can form a more realistic and comfortable three-dimensional image simulation.

[0114] Without being limited by theory, it is believed that the human eye can generally interpret a limited number of depth planes to provide a sense of depth. Therefore, a highly credible 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 can provide both vergence cues and matching accommodation cues, thereby providing a physiologically correct accommodation-vergence match.

[0115] Continue to refer Figure 4B, two depth planes 240 are shown, corresponding to different distances in space from the eyes 210, 220. For a given depth plane 240, convergence cues may be provided by displaying images of appropriately different perspectives for each eye 210, 220. In addition, 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 a point at the distance of that depth plane 240.

[0116] In the illustrated embodiment, the distance along the z-axis of the depth plane 240 containing point 221 is 1 meter. As used herein, the distance or depth along the z-axis can be measured by locating the zero point at the exit pupil of the user's eye. Therefore, the depth plane 240 located at a depth of 1 meter corresponds to a distance of 1 meter from the exit pupil of the user's eye on the optical axis of the user's eye when the eye is pointed to optical infinity. As an approximation, the depth or distance along the z-axis can 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. This value can be called the eye relief and corresponds to the distance between the exit pupil of the user's eye and the display worn by the user in front of the eye. In practice, the value of the eye relief can be a standardized value common to all viewers. For example, it can be assumed that the eye relief is 20 mm, and the depth plane at a depth of 1 meter can be at a distance of 980 mm in front of the display.

[0117] Reference now Figure 4C and 4D , respectively show examples of matched accommodation-convergence distances and mismatched accommodation-convergence distances. Figure 4C As shown, the display system can provide an image of a virtual object to each eye 210, 220. These images can cause the eyes 210, 220 to present a state of convergence, in which the eyes converge at a point 15 on the depth plane 240. In addition, the image can be formed by light having a wavefront curvature corresponding to a real object at the depth plane 240. As a result, the eyes 210, 220 present an accommodation state, in which the image is focused on the retinas of these eyes. Therefore, the user can perceive the virtual object as being located at a point 15 on the depth plane 240.

[0118] It should be understood that each of the accommodation and convergence states of the eyes 210, 220 is associated with a specific distance on the z-axis. For example, an object at a specific distance from the eyes 210, 220 causes these eyes to present a specific accommodation state based on the distance of the object. The distance associated with a specific accommodation state can be referred to as the accommodation distance Ad. Similarly, there is a specific convergence distance Vd associated with the eyes in a specific convergence state or relative to each other. When the accommodation distance and the convergence distance match, it can be said that the relationship between accommodation and convergence is physiologically correct. This is considered to be the most comfortable scenario for the viewer.

[0119] However, in stereoscopic displays, the accommodation distance and the convergence distance may not always match. Figure 4D As shown, the image displayed to the eyes 210, 220 can be displayed with a wavefront divergence corresponding to the depth plane 240, and the eyes 210, 220 can present a specific accommodation state in which the points 15a, 15b on the depth plane are in focus. However, the image displayed to the eyes 210, 220 can provide a convergence cue that causes the eyes 210, 220 to converge at 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 pupil of the eyes 210, 220 to the depth plane 240, while the convergence distance corresponds to a greater distance from the exit pupil of the eyes 210, 220 to the point 15. The accommodation distance is different from the convergence distance. Therefore, there is an accommodation-convergence mismatch. This mismatch is considered to be undesirable and may cause discomfort to the user. It should be understood that the mismatch corresponds to a distance (e.g., Vd-Ad) and can be characterized using diopters.

[0120] In some embodiments, it should be appreciated that a reference point other than the exit pupil of the eye 210, 220 may be used to determine the distance used to determine the accommodation-vergence mismatch, as long as the same reference point is used for both the accommodation distance and the 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 eyepiece (e.g., a waveguide of a display device) to the depth plane, and so forth.

[0121] Without being limited by theory, it is believed that users may still perceive accommodation-convergence mismatches of up to about 0.25 diopters, up to about 0.33 diopters, and up to about 0.5 diopters as physiologically correct without causing noticeable discomfort by the accommodation-convergence mismatch itself. In some embodiments, the display systems disclosed herein (e.g., Figure 6The display system 250 in the embodiment of the present invention presents an image with an accommodation-convergence mismatch of about 0.5 diopters or less to a viewer. In some other embodiments, the accommodation-convergence mismatch of the image provided by the display system is about 0.33 diopters or less. In some other embodiments, the accommodation-convergence mismatch of the image provided by the display system is about 0.25 diopters or less, including about 0.1 diopters or less.

[0122] Figure 5 Aspects of a method for simulating a three-dimensional image by modifying wavefront divergence are shown. The display system includes a waveguide 270 configured to receive light 770 encoded with image information and output the light to the user's eye 210. The waveguide 270 can output an outgoing light beam 650 having a defined amount of wavefront divergence that corresponds to the wavefront divergence of the light field produced by a point on the desired depth plane 240. In some embodiments, the same amount of wavefront divergence is provided for all objects presented on the depth plane. In addition, it will be described that image information from a similar waveguide can be provided to the user's other eye.

[0123] In some cases, a single waveguide may be configured to output light having a set amount of wavefront divergence corresponding to a single depth plane or a finite number of depth planes, and / or the waveguide may be configured to output light of a finite wavelength range. Thus, in some embodiments, multiple waveguides or waveguide stacks may be utilized to provide different amounts of wavefront divergence for different depth planes and / or output light of different wavelength ranges. As used herein, it should be understood that a depth plane may be planar or may follow a curved profile.

[0124] Figure 6 An example of a waveguide stack for outputting image information to a user is shown. The display system 250 includes a waveguide stack or stacked waveguide assembly 260, which can be used to provide a three-dimensional perception to the eye / brain using multiple waveguides 270, 280, 290, 300, 310. It should be understood that in some embodiments, the display system 250 can be considered a light field display. In addition, the waveguide assembly 260 can also be referred to as an eyepiece.

[0125] In some embodiments, the display system 250 is configured to provide a substantially continuous vergence cue and a plurality of discrete accommodation cues. The vergence cue can be provided by displaying a different image to each eye of the user, and the accommodation cue can be provided by outputting image-forming light having a selectable discrete amount of wavefront divergence. In other words, the display system 250 can be configured to output light having variable wavefront divergence levels. In some embodiments, each discrete level of wavefront divergence corresponds to a particular depth plane and can be provided by a particular one of the waveguides 270, 280, 290, 300, 310.

[0126] Continue to refer Figure 6 , the waveguide assembly 260 may also include a plurality of features 320, 330, 340, 350 between the waveguides. In some embodiments, the features 320, 330, 340, 350 may be one or more lenses. The waveguides 270, 280, 290, 300, 310 and / or the plurality of lenses 320, 330, 340, 350 may be configured to send image information to the eye at various levels of wavefront curvature or light divergence. Each waveguide level may be associated with a particular depth plane and may be configured to output image information corresponding to the depth plane. The image injection device 360, 370, 380, 390, 400 may be used as a light source for the waveguide and may be used to inject image information into the waveguides 270, 280, 290, 300, 310, each waveguide may be configured to distribute incident light across each respective waveguide for output toward the eye 210, as described herein. Light exits the output surfaces 410, 420, 430, 440, 450 of the image injection devices 360, 370, 380, 390, 400 and is injected into the corresponding input surfaces 460, 470, 480, 490, 500 of the waveguides 270, 280, 290, 300, 310. In some embodiments, each of the input surfaces 460, 470, 480, 490, 500 may be an edge of the corresponding waveguide, or may be part 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 beam (e.g., a collimated beam) may be injected into each waveguide to output an entire field of cloned collimated beams directed toward the eye 210 at a particular angle (and divergence) corresponding to a depth plane associated with a particular waveguide. In some embodiments, a single one of image injection devices 360, 370, 380, 390, 400 may be associated with and inject light into multiple (e.g., three) of waveguides 270, 280, 290, 300, 310.

[0127] In some embodiments, the image injection devices 360, 370, 380, 390, 400 are discrete displays that each generate image information for injection into a corresponding waveguide 270, 280, 290, 300, 310. In some other embodiments, the image injection devices 360, 370, 380, 390, 400 are outputs of a single multiplexed display, which may pipe the image information to each of the image injection devices 360, 370, 380, 390, 400 via one or more optical conduits (such as fiber optic cables), for example. It should be understood that the image information provided by the image injection devices 360, 370, 380, 390, 400 may include light of different wavelengths or colors (e.g., different component colors as discussed herein).

[0128] In some embodiments, the light injected into the waveguides 270, 280, 290, 300, 310 is provided by a light projector system 520, which includes a light module 530, which may include a light emitter, such as a light emitting diode (LED). The light from the light module 530 can be directed to a light modulator 540 (e.g., a spatial light modulator) via a beam splitter 550 and modified by the light modulator 540. The light modulator 540 can be configured to change the perceived intensity of the light injected into the waveguides 270, 280, 290, 300, 310 to encode the light with image information. Examples of spatial light modulators include liquid crystal displays (LCDs), including liquid crystal on silicon (LCOS) displays. It should be understood that the image injection devices 360, 370, 380, 390, 400 are shown schematically, and in some embodiments, these image injection devices can represent different optical paths and positions in a common projection system that is configured to output light into associated waveguides in the waveguides 270, 280, 290, 300, 310. In some embodiments, the waveguides in the waveguide assembly 260 can act as ideal lenses while relaying the light injected into the waveguides to the user's eyes. In this concept, the object can be the spatial light modulator 540, and the image can be an image on a depth plane.

[0129] In some examples, a μLED display can be used in the light projector system 520. The μLED display can not polarize light within a large range of angles. Therefore, the μLED display can advantageously provide images efficiently within a wide field of view.

[0130] In some embodiments, the display system 250 may be a scanning fiber display that includes one or more scanning fibers configured to project light into one or more waveguides 270, 280, 290, 300, 310 in various patterns (e.g., raster scan, spiral scan, Lissajous pattern, etc.), and ultimately into the viewer's eye 210. In some embodiments, the image injection devices 360, 370, 380, 390, 400 shown may schematically represent a single scanning fiber or a scanning fiber bundle configured to inject light into one or more of the waveguides 270, 280, 290, 300, 310. In some other embodiments, the image injection devices 360, 370, 380, 390, 400 shown may schematically represent a plurality of scanning optical fibers or a plurality of scanning optical fiber bundles, each of which is configured to inject light into an associated waveguide of the waveguides 270, 280, 290, 300, 310. It should be understood that one or more optical fibers may be configured to transmit light from the optical module 530 to the one or more waveguides 270, 280, 290, 300, 310. It should be understood that one or more intermediate optical structures may be provided between the one or more scanning optical fibers and the one or more waveguides 270, 280, 290, 300, 310 to, for example, redirect light emitted from the scanning optical fibers into the one or more waveguides 270, 280, 290, 300, 310.

[0131] The controller 560 controls the operation of one or more components in the stacked waveguide assembly 260, including the operation of the image injection devices 360, 370, 380, 390, 400, the light module 530, and the light modulator 540. In some embodiments, the controller 560 is part of the local processing and data module 140. The controller 560 includes programming (e.g., instructions in a non-transitory medium) that regulates the timing and provision of image information to the waveguides 270, 280, 290, 300, 310 according to, for example, any of the various schemes disclosed herein. In some embodiments, the controller can be a single integral device, or a distributed system connected by wired or wireless communication channels. In some embodiments, the controller 560 can be a local processing and data module 140 or a remote processing module 150 ( Fig.9D ) part.

[0132] Continue to refer Figure 6, the waveguides 270, 280, 290, 300, 310 can be configured to propagate light within each respective waveguide by total internal reflection (TIR). The waveguides 270, 280, 290, 300, 310 can each be planar or have another shape (e.g., curved) with a top major surface and a bottom major surface and an edge extending between these top major surfaces and bottom major surfaces. In the illustrated configuration, the waveguides 270, 280, 290, 300, 310 can each include an outcoupling optical element 570, 580, 590, 600, 610, which is configured to extract light from the waveguide by redirecting light propagating within the respective corresponding waveguide out of the waveguide to output image information to the eye 210. The extracted light can also be referred to as outcoupled light, and the outcoupling optical element light can also be referred to as a light extraction optical element. The extracted light beam can be output by the waveguide at the location where the light propagating in the waveguide is incident on the light extraction optical element. As further discussed herein, the coupling-out optical element 570, 580, 590, 600, 610 can be, for example, a grating of diffractive optical features. Although shown as being disposed at the bottom major surface of the waveguide 270, 280, 290, 300, 310, for ease of description and clarity of drawing, in some embodiments, as further discussed herein, the coupling-out optical element 570, 580, 590, 600, 610 can be disposed at the top and / or bottom major surface, and / or can be disposed directly within the volume of the waveguide 270, 280, 290, 300, 310. In some embodiments, the coupling-out optical element 570, 580, 590, 600, 610 can be formed in a material layer attached to a transparent substrate to form the waveguide 270, 280, 290, 300, 310. In some other embodiments, the waveguides 270, 280, 290, 300, 310 may be a single piece of material and the outcoupling optical elements 570, 580, 590, 600, 610 may be formed on a surface and / or within the interior of the piece of material.

[0133] Continue to refer Figure 6As 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 can be configured to deliver collimated light (which is injected into such a waveguide 270) to the eye 210. The collimated light can represent an optical infinity focal plane. The next upstream waveguide 280 can be configured to emit collimated light that passes through a first lens 350 (e.g., a negative lens) before it can reach the eye 210; such a first lens 350 can be configured to produce a slightly convex wavefront curvature so that the eye / brain interprets the light from the next upstream waveguide 280 as coming from a first focal plane that is closer to the eye 210 from optical infinity inward. Similarly, the third upstream waveguide 290 causes its output light to pass through both the first lens 350 and the second lens 340 before reaching the eye 210; the combined optical power of the first lens 350 and the second lens 340 can be configured to produce another increment of wavefront curvature so that the eye / brain interprets light from the third waveguide 290 as coming from a second focal plane that is further inward from optical infinity and closer to the person than light from the next upstream waveguide 280.

[0134] The other layers of 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 to obtain a total focal power that represents the focal plane closest to the person. In order to compensate for the stack of lenses 320, 330, 340, 350 when observing / interpreting light from the world 510 on the other side of the stacked waveguide assembly 260, a compensating lens layer 620 can be provided on top of the stack to compensate for the total focal power of the stack of lenses 320, 330, 340, 350 below. This configuration provides as many perceived focal planes as there are available waveguide / lens pairs. Both the outcoupling optics of the waveguide and the focusing aspects of the lenses can be static (i.e., not dynamic or electro-active). In some alternative embodiments, one or both of them can be dynamic by using electro-active features.

[0135] 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 image sets to the same depth plane, or multiple subsets of the waveguides 270, 280, 290, 300, 310 may be configured to output image sets to the same multiple depth planes, one image set per depth plane. This may provide advantages for forming a stitched image to provide an extended field of view at those depth planes.

[0136] Continue to refer Figure 6, the out-coupling optical elements 570, 580, 590, 600, 610 can be configured to both redirect light out of their respective waveguides and output the light with an appropriate amount of divergence or collimation for a particular depth plane associated with the waveguide. As a result, waveguides with different associated depth planes can have differently configured out-coupling optical elements 570, 580, 590, 600, 610, and the differently configured out-coupling optical elements 570, 580, 590, 600, 610 output light with different amounts of divergence depending on the associated depth plane. In some embodiments, the out-coupling optical elements 570, 580, 590, 600, 610 can be volume features or surface features that can be configured to output light at a particular angle. For example, the out-coupling optical elements 570, 580, 590, 600, 610 can be volume holograms, surface holograms, and / or diffraction gratings. In some embodiments, features 320, 330, 340, 350 may not be lenses; rather, they may simply be spacers (eg, cladding and / or structures used to form air gaps).

[0137] In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 are diffractive features that form a diffraction pattern, or "diffractive optical elements" (also referred to herein as "DOEs"). Preferably, the DOE has a sufficiently low diffraction efficiency that only a portion of the beam is deflected away toward the eye 210 by each intersection with the DOE, while the remainder continues through the waveguide via TIR. Thus, the light carrying the image information is split into multiple related exit beams that exit the waveguide at multiple locations, and the result is a fairly uniform pattern of exit toward the eye 210 for this particular collimated beam bouncing within the waveguide.

[0138] In some embodiments, one or more DOEs can be switched between an "on" state in which they actively diffract and an "off" state in which they do not significantly diffract. For example, a switchable DOE can include a polymer dispersed liquid crystal layer in which a droplet includes a diffraction pattern in a host medium, and the refractive index of the droplet can be switched to substantially match the refractive index of the host material (in which case the pattern does not significantly diffract incident light) or the droplet can be switched to a refractive index that mismatches the refractive index of the host medium (in which case the pattern actively diffracts incident light).

[0139] In some embodiments, a camera assembly 630 (e.g., a digital camera, including a visible light camera and an infrared light camera) can 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 a physiological state of the user. As used herein, a camera can be any image capture device. In some embodiments, the camera assembly 630 can include an image capture device and a light source to project light (e.g., infrared light) to the eye, which can then be reflected by the eye and detected by the image capture device. In some embodiments, the camera assembly 630 can be attached to the frame 80 ( Fig.9D ) and can be in electrical communication with the local processing and data module 140 and / or the remote processing module 150, which can process image information from the camera assembly 630. In some embodiments, one camera assembly 630 can be used for each eye to monitor each eye separately.

[0140] Reference now Figure 7 , showing an example of an outgoing light beam output by a waveguide. One waveguide is shown, but it should be understood that in the case where the waveguide assembly 260 includes a plurality of waveguides, the waveguide assembly 260 ( Figure 6 ) may function similarly. Light 640 is injected into the waveguide 270 at the input surface 460 of the waveguide 270 and propagates within the waveguide 270 by TIR. At the point where the light 640 is incident on the outcoupling optical element 570 (e.g., a DOE), a portion of the light emerges from the waveguide as an exit beam 650. The exit beams 650 are shown as being substantially parallel, but as discussed herein, they may also be redirected to propagate to the eye 210 at an angle (e.g., to form diverging exit beams) that depends on the depth plane associated with the waveguide 270. It should be understood that substantially parallel exit beams may be indicative of a waveguide having an outcoupling optical element that outcouples light to form an image that appears to be disposed at a depth plane that is a long distance away from the eye 210 (e.g., optical infinity). Other waveguides or other sets of outcoupling optical elements can output a more divergent exit beam pattern that will require the eye 210 to adjust to a closer distance in order to focus the more divergent exit beam pattern on the retina and will be interpreted by the brain as light coming from a distance closer to the eye 210 than optical infinity.

[0141] In some embodiments, a full-color image can be formed at each depth plane by superimposing images in each of the component colors (eg, three or more component colors). Figure 8An example of a stacked waveguide assembly is shown, wherein each depth plane includes an image formed using a plurality of different component colors. The illustrated embodiment shows depth planes 240a-240f, but more or fewer depths are also contemplated. Each depth plane may have three or more component color images associated therewith, including: a first image of a first color G; a second image of a second color R; and a third image of a third color B. Different depth planes are represented in the figure by different numbers for the diopters (dpt) following the letters G, R, and B. By way of example only, the numbers following each of these letters represent the diopters (1 / m), or the inverse of the distance of the depth plane from the viewer, and each box in the figure represents a separate component color image. In some embodiments, the precise placement of depth planes of different component colors may vary in order to account for differences in the eye's focus on light of different wavelengths. For example, different component color images of a given depth plane may be placed on depth planes corresponding to different distances from the user. Such an arrangement may increase visual acuity and user comfort, and / or may reduce chromatic aberration.

[0142] In some embodiments, light of each component color can be output by a single dedicated waveguide, and therefore, each depth plane can have multiple waveguides associated with it. In such embodiments, each box in the figure including the letters G, R, or B can be understood to represent a separate waveguide, and each depth plane can provide three waveguides, wherein each depth plane provides three component color images. Although for ease of description, the waveguides associated with each depth plane in this figure are shown as being adjacent to each other, it should be understood that in a physical device, the waveguides can all be arranged in a stacked form with one waveguide per layer. In some other embodiments, multiple component colors can be output by the same waveguide, so that, for example, each depth plane can provide only a single waveguide.

[0143] Continue to refer Figure 8 In some embodiments, G is green, R is red, and B is blue. In some other embodiments, other colors associated with other wavelengths of light (including magenta and cyan) may be used in addition to red, green, or blue, or these other colors may replace one or more of red, green, or blue.

[0144] It should be understood that references throughout this disclosure to light of a given color will be understood to include light of one or more wavelengths within a range of wavelengths perceived by a viewer as light of the given color. For example, red light may include light of one or more wavelengths within a range of about 620-780 nm, green light may include light of one or more wavelengths within a range of about 492-577 nm, and blue light may include light of one or more wavelengths within a range of about 435-493 nm.

[0145] In some embodiments, the optical module 530 ( Figure 6 ) can be configured to emit one or more wavelengths of light outside the visual perception range of a viewer, such as infrared and / or ultraviolet wavelengths of light. In addition, the incoupling, outcoupling, and other light redirection structures of the waveguides of the display system 250 can be configured to guide this light and direct it out of the display toward the user's eye 210, for example, for imaging and / or user stimulation applications.

[0146] Reference now Fig. 9A In some embodiments, it may be necessary to redirect light incident on a waveguide to couple the light into the waveguide. An incoupling optical element may be used to redirect and couple the light into its corresponding waveguide. Fig. 9A A cross-sectional side view of an example of a plurality of stacked waveguides or stacked waveguide sets 660 is shown, each waveguide including an incoupling optical element. The waveguides can each be configured to output one or more different wavelengths of light, or one or more different wavelength ranges of light. It should be understood that the stacked waveguide set 660 can correspond to the waveguide assembly 260 ( Figure 6 ), and the waveguides shown in the stacked waveguide set 660 may correspond to a portion of the plurality of waveguides 270, 280, 290, 300, 310, in addition to light from one or more image injection devices 360, 370, 380, 390, 400 being injected into the waveguide from a location where the light needs to be redirected for coupling.

[0147] The illustrated stacked waveguide set 660 includes waveguides 670, 680, and 690. Each waveguide includes an associated coupling optical element (which may also be referred to as a light input region on the waveguide), wherein, for example, coupling optical element 700 is disposed on a major surface (e.g., top major surface) of waveguide 670, coupling optical element 710 is disposed on a major surface (e.g., top major surface) of waveguide 680, and coupling optical element 720 is disposed on a major surface (e.g., top major surface) of waveguide 690. In some embodiments, one or more of the coupling optical elements 700, 710, 720 may be disposed on the bottom major surface of the corresponding waveguide 670, 680, 690 (particularly in the case where one or more coupling optical elements are reflective deflection optical elements). As shown, coupling optical elements 700, 710, 720 may be disposed on the top major surface (or the top of the next downstream waveguide) of their corresponding waveguides 670, 680, 690, particularly in the case where those coupling optical elements are transmissive deflection optical elements. In some embodiments, the coupling-in optical elements 700, 710, 720 can be disposed in the body of the respective waveguides 670, 680, 690. In some embodiments, as discussed herein, the coupling-in optical elements 700, 710, 720 are wavelength selective such that they selectively redirect light of one or more wavelengths while transmitting light of other wavelengths. Although shown on one side or corner of their respective waveguides 670, 680, 690, it should be understood that in some embodiments, the coupling-in optical elements 700, 710, 720 can be disposed in other areas of their respective waveguides 670, 680, 690.

[0148] As shown, the coupling optical elements 700, 710, 720 can be laterally offset from each other. In some embodiments, each coupling optical element can be offset so that the coupling optical element receives light without the light passing through another coupling optical element. For example, each coupling optical element 700, 710, 720 can be configured to be offset from the Figure 6 The different image injection devices 360, 370, 380, 390 and 400 shown receive light and can be separated from other coupling optical elements 700, 710, 720 (e.g., laterally spaced apart) so that the coupling optical element does not substantially receive light from other coupling optical elements in the coupling optical elements 700, 710, 720.

[0149] Each waveguide further includes an associated light distribution element, wherein, for example, the light distribution element 730 is disposed on a major surface (e.g., top major surface) of the waveguide 670, the light distribution element 740 is disposed on a major surface (e.g., top major surface) of the waveguide 680, and the light distribution element 750 is disposed on a major surface (e.g., top major surface) of the waveguide 690. In some other embodiments, the light distribution elements 730, 740, 750 may be disposed on the bottom major surface of the associated waveguides 670, 680, 690, respectively. In some other embodiments, the light distribution elements 730, 740, 750 may be disposed on the top major surface and the bottom major surface of the associated waveguides 670, 680, 690, respectively; or the light distribution elements 730, 740, 750 may be disposed on different major surfaces of the top major surface and the bottom major surface in different associated waveguides 670, 680, 690, respectively.

[0150] The waveguides 670, 680, 690 can be separated and separated by layers of, for example, gas, liquid, and / or solid material. For example, as illustrated, layer 760a can separate waveguide 670 from waveguide 680; and layer 760b can separate waveguide 680 from waveguide 690. In some embodiments, layers 760a and 760b are formed of a low refractive index material (i.e., a material having a lower refractive index than the material forming the immediately adjacent waveguide in waveguides 670, 680, 690). Preferably, the refractive index of the material forming layers 760a, 760b is 0.05 or more, or 0.10 less than the refractive index of the material forming waveguides 670, 680, 690. Advantageously, the lower refractive index layers 760a, 760b can act as cladding that facilitates total internal reflection (TIR) ​​of light passing 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 of air. Although not shown, it should be understood that the top and bottom of the illustrated waveguide assembly 660 can include a cladding in close proximity.

[0151] 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 can be different between one or more waveguides, and / or the materials forming layers 760a, 760b can be different, while still maintaining the various refractive index relationships described above.

[0152] Continue to refer Fig. 9A, light rays 770, 780, 790 are incident on the waveguide set 660. It should be understood that light rays 770, 780, 790 may be injected through one or more image injection devices 360, 370, 380, 390, 400 ( Figure 6 ) are injected into waveguides 670, 680, and 690.

[0153] In some embodiments, the light rays 770, 780, 790 have different characteristics, such as different wavelengths corresponding to different colors or different wavelength ranges. The incoupling optical elements 700, 710, 720 each deflect the incident light so that the light propagates through a corresponding one of the waveguides 670, 680, 690 as TIR. In some embodiments, the incoupling optical elements 700, 710, 720 each selectively deflect one or more specific wavelengths of light while transmitting other wavelengths to the underlying waveguide and associated incoupling optical element.

[0154] For example, the coupling-in optical element 700 can be configured to deflect light 770 having a first wavelength or a first wavelength range, while transmitting light 780 having a different second wavelength or a second wavelength range and light 790 having a third wavelength or a third wavelength range, respectively. The transmitted light 780 is incident on and deflected by the coupling-in optical element 710, which is configured to deflect light of the second wavelength or the second wavelength range. The light 790 is deflected by the coupling-in optical element 720, which is configured to selectively deflect light of the third wavelength or the third wavelength range.

[0155] Continue to refer Fig. 9A , the deflected light rays 770, 780, 790 are deflected so that the light rays 770, 780, 790 propagate through the corresponding waveguides 670, 680, 690; that is, the coupling optical element 700, 710, 720 of each waveguide deflects the light into the corresponding waveguide 670, 680, 690 to couple the light into the corresponding waveguide. The light rays 770, 780, 790 are deflected at an angle that causes the light to propagate through the corresponding waveguides 670, 680, 690 with TIR. The light rays 770, 780, 790 propagate through the corresponding waveguides 670, 680, 690 with TIR until they are incident on the corresponding light distribution elements 730, 740, 750 of the waveguides.

[0156] Reference now Fig. 9B , showing Fig. 9A6. As described above, the incoupled light rays 770, 780, 790 are deflected by the incoupling optical elements 700, 710, 720, respectively, and then propagate by TIR in the waveguides 670, 680, 690, respectively. Then, the light rays 770, 780, 790 are incident on the light distribution elements 730, 740, 750, respectively. The light distribution elements 730, 740, 750 deflect the light rays 770, 780, 790 so that the light rays 770, 780, 790 propagate toward the outcoupling optical elements 800, 810, 820, respectively.

[0157] 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 optical elements 800, 810, 820, and in some embodiments, may also increase the beam size or spot size of the light as it propagates to the outcoupling optical elements. In some embodiments, the light distribution elements 730, 740, 750 may be omitted, and the incoupling optical elements 700, 710, 720 may be configured to deflect light directly to the outcoupling optical elements 800, 810, 820. For example. Reference Fig. 9A , the light distribution elements 730, 740, 750 can be replaced by outcoupling optical elements 800, 810, 820, respectively. In some embodiments, the outcoupling optical elements 800, 810, 820 are exit pupils (EP) or exit pupil expanders (EPE) that direct light into the viewer's eye 210 ( Figure 7 ). It should be understood that the OPE can be configured to increase the size of the eye box in at least one axis, and the EPE can increase the eye box in an axis that intersects (e.g., is orthogonal) to the axis of the OPE. For example, each OPE can be configured to redirect a portion of the light that strikes the OPE to the EPE of the same waveguide, while allowing the remainder of the light to continue to propagate along the waveguide. Upon again impinging on the OPE, another portion of the remaining light is redirected to the EPE, and the remainder of that portion continues to propagate further along the waveguide, and so on. Similarly, upon striking the EPE, a portion of the incident light is directed out of the waveguide toward the user, and the remainder of the light continues to propagate through the waveguide until it strikes the EPE again, at which time another portion of the incident light is directed out of the waveguide, and so on. Therefore, whenever a portion of a single beam of coupled-in light is redirected by an OPE or EPE, that light can be "copied," thereby forming a field of cloned beams, such as Figure 6 In some embodiments, the OPE and / or EPE can be configured to modify the size of the light beam.

[0158] Therefore, reference Fig. 9A and Fig. 9B, in some embodiments, the waveguide set 660 includes: waveguides 670, 680, 690 for each component color; coupling optical elements 700, 710, 720; light distribution elements (e.g., OPE) 730, 740, 750; and outcoupling optical elements (e.g., EP) 800, 810, 820. The waveguides 670, 680, 690 can be stacked with air gaps / cladding between each waveguide. The coupling optical elements 700, 710, 720 redirect or deflect the incident light (light of different wavelengths received by different coupling optical elements) into its waveguide. The light then propagates at an angle that will cause TIR within the corresponding waveguide 670, 680, 690. In the example shown, light ray 770 (e.g., blue light) is deflected by the first coupling-in optical element 700 in the manner previously described, and then continues to bounce along the waveguide, interacting with the light distribution element (e.g., OPE) 730 and the coupling-out optical element (e.g., EP) 800. Light rays 780 and 790 (e.g., green light and red light, respectively) are transmitted through the waveguide 670, where light ray 780 is incident on and deflected by the coupling-in optical element 710. Light ray 780 then bounces along the waveguide 680 via TIR, proceeds to its light distribution element (e.g., OPE) 740, and then to the coupling-out optical element (e.g., EP) 810. Finally, light ray 790 (e.g., red light) is transmitted through the waveguide 690 and is incident on the coupling-in optical element 720 of the waveguide 690. The light incoupling optical element 720 deflects the light 790 so that it propagates through TIR to the light distribution element (e.g., OPE) 750, and then propagates through TIR to the outcoupling optical element (e.g., EP) 820. The outcoupling optical element 820 then finally couples the light 790 out to the viewer, who also receives the outcoupled light from the other waveguides 670, 680.

[0159] Fig. 9C Shows Fig. 9A and Fig. 9B A top plan view of an example of multiple stacked waveguides. As illustrated, the waveguides 670, 680, 690 and the associated light distribution elements 730, 740, 750 and associated outcoupling optical elements 800, 810, 820 of each waveguide can be vertically aligned. However, as discussed herein, the coupling-in optical elements 700, 710, 720 are not vertically aligned; rather, the coupling-in optical elements do not overlap (e.g., are laterally spaced apart when viewed in a top view). As further discussed herein, this non-overlapping spatial arrangement facilitates one-to-one injection of light from different resources into different waveguides, thereby allowing a particular light source to be uniquely coupled to a particular waveguide. In some embodiments, arrangements including non-overlapping spatially separated coupling-in optical elements can be referred to as shifted pupil systems, and the coupling-in optical elements within these arrangements can correspond to sub-pupils.

[0160] Alternatively, in some embodiments, two or more coupling optical elements can be arranged in series, in which they are vertically aligned. In this arrangement, light for a waveguide farther from the projection system is transmitted through the coupling optical element for a waveguide closer to the projection system, preferably with minimal scattering or diffraction.

[0161] The in-line configuration can advantageously reduce the size of the projector and simplify the projector. In addition, it also increases the field of view of the eyepiece, for example, by coupling light of the same color to multiple waveguides using crosstalk. For example, green light can be coupled into the blue and red active layers. Since the pitch of each ICG can be different to provide improved (e.g., optimal) performance for a specific color, the allowed field of view can be increased.

[0162] In an in-line configuration, except for the last layer in the optical path, the ICG should at most partially reflect or otherwise transmit light at the operating wavelength of the subsequent layers in the waveguide stack. In each case, unless the grating is etched in a high refractive index layer (e.g., 1.8 or higher for polymer-based layers), or a high refractive index coating is deposited or grown on the grating, the efficiency will be very low. However, this approach will increase back reflections into the projector lens, which may therefore produce image artifacts, such as image ghosting.

[0163] Fig.9D An example of a wearable display system 60 is shown into which the various waveguides and related systems disclosed herein may be integrated. In some embodiments, the display system 60 is Figure 6 The display system 250, wherein Figure 6 Some components of the display system 60 are schematically shown in more detail. For example, Figure 6 The waveguide assembly 260 can be part of the display 70.

[0164] Continue to refer Fig.9D, the display system 60 includes a display 70, and various mechanical and electronic modules and systems that support the functions of the display 70. The display 70 can be coupled to a frame 80 that can be worn by a display system user or a user 90, and the frame 80 is configured to position the display 70 in front of the eyes of the user 90. In some embodiments, the display 70 can be regarded as glasses. In some embodiments, a speaker 100 is coupled to the frame 80 and is configured to be positioned adjacent to the ear canal of the user 90 (in some embodiments, another speaker (not shown) can be optionally positioned adjacent to the other ear canal of the user to provide stereo / shaped sound control). The display system 60 may also include one or more microphones 110 or other devices to detect sound. In some embodiments, the microphone is configured to allow a user to provide input or commands to the display system 60 (e.g., selection of a voice menu command, a natural language question, etc.), and / or may allow audio communication with other people (e.g., with other users of a similar display system). The microphone may be further configured as a peripheral sensor to collect audio data (e.g., sound from the user and / or the environment). In some embodiments, the display system may further include a peripheral sensor 120a, which may be separated from the frame 80 and attached to the body of the user 90 (e.g., on the head, torso, limbs, etc. of the user 90). In some embodiments, the peripheral sensor 120a may be configured to acquire data representing a physiological state of the user 90. For example, the sensor 120a may be an electrode.

[0165] Continue to refer Fig.9D, the display 70 is operably coupled to a local processing and data module 140 via a communication link 130 (such as, via a wired lead or a wireless connection), and the local processing and data module 140 can 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 removably attached to the user 90 in other ways (e.g., in a backpack configuration, in a belt-coupled configuration). Similarly, the sensor 120a can be operably coupled to the local processing and data module 140 via a communication link 120b (e.g., a wired lead or a wireless connection). The local processing and data module 140 can include a hardware processor and digital memory, such as non-volatile memory (e.g., flash memory or a hard drive), both of which can be used to assist in the processing, caching and storage of data. Optionally, the local processing and data module 140 can include one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, and the like. The data may include a) data captured from sensors (which may, for example, be operably coupled to the frame 80 or otherwise attached to the user 90), such as image capture devices (such as cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, radios, gyroscopes, and / or other sensors disclosed herein; and / or b) data acquired and / or processed using the remote processing module 150 and / or remote data repository 160 (including data related to virtual content), possibly for transmission to the display 70 after such processing or retrieval. The local processing and data module 140 may be operably coupled to the remote processing module 150 and the remote data repository 160 via communication links 170, 180 (such as via a wired or wireless communication link) so that these remote processing module 150 and remote data repository 160 are operably coupled to each other and can be used as resources for the local processing and data module 140. In some embodiments, the local processing and data module 140 may include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a radio, and / or a gyroscope. In some other embodiments, one or more of these sensors may be attached to the frame 80, or may be an independent structure that communicates with the local processing and data module 140 via a wired or wireless communication path.

[0166] Continue to refer Fig.9DIn some embodiments, the remote processing module 150 may include one or more processors configured to analyze and process data and / or image information, for example, including one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, etc. In some embodiments, the remote data repository 160 may include a digital data storage facility that may be obtained via the Internet or other network configurations in a "cloud" resource configuration. In some embodiments, the remote data repository 160 may include one or more remote servers that provide information to the local processing and data module 140 and / or the remote processing module 150, for example, information for generating augmented reality content. In some embodiments, all data is stored in the local processing and data module, and all calculations are performed, allowing for full autonomous use from the remote module. Optionally, an external system (e.g., a system of one or more processors, one or more computers) including a CPU, GPU, etc. may perform at least a portion of the processing (e.g., generating image information, processing data), and provide information to the local processing and data module 140, the remote processing module 150, and the remote data repository 160, for example, via a wireless or wired connection, and receive information from these modules.

[0167] Diffraction grating with reduced polarization sensitivity

[0168] Providing a high-quality immersive experience to a user of a waveguide-based display system (such as, for example, the various display systems configured for the virtual / augmented / hybrid display applications described above) depends, among other things, on various characteristics of light coupled into and / or coupled out of a waveguide in an eyepiece of the display system. For example, a virtual / augmented / hybrid display with high light coupling-in and coupling-out efficiency can enhance the viewing experience by increasing the brightness of the light directed to the user's eyes. As discussed above, an in-coupling optical element (such as an in-coupling diffraction grating) can be used to couple light into a waveguide to be guided therein by total internal reflection. Similarly, an out-coupling optical element (such as an out-coupling diffraction grating) can also be used to couple light guided within a waveguide by total internal reflection out of the waveguide.

[0169] As mentioned above, for example, reference Figure 6 and Figure 7 , a display system according to various embodiments described herein may include optical elements, such as in-coupling optical elements, which may include diffraction gratings, out-coupling optical elements, light distribution elements, and / or combined pupil expander-extractors (CPEs). As disclosed herein, the CPE may function both as a light distribution element to disperse or distribute light within a waveguide, thereby potentially increasing the beam size and / or eyebox, and as an out-coupling optical element to couple light out of the waveguide.

[0170] For example, as mentioned above Figure 7As described, light 640 injected into the waveguide 270 at the input surface 460 of the waveguide 270 propagates and is guided within the waveguide 270 by total internal reflection (TIR). In various embodiments, at the point where the light 640 is incident on the outcoupling optical element 570, a portion of the light guided within the waveguide may exit the waveguide as an exit light beam 650 (e.g., a beamlet). In some embodiments, any optical element 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.

[0171] In order to achieve the desired characteristics of coupling light into (or out of) the waveguides 270, 280, 290, 300, 310, the optical elements 570, 580, 590, 600, 610 configured as diffraction gratings may be formed of suitable materials and have suitable structures for controlling various optical properties, including diffraction properties, such as diffraction efficiency that varies according to polarization. Possible desired diffraction properties may include any one or more of the following, among other properties: spectral selectivity, angular selectivity, polarization selectivity (or non-selectivity), high spectral bandwidth, high diffraction efficiency, or a wide field of view (FOV).

[0172] Some diffraction gratings have strong polarization dependence and therefore may have a relatively reduced overall efficiency (due to rejecting one polarization). Such diffraction gratings may also produce coherence artifacts and reduce the uniformity of the far-field image. In order to provide a diffraction grating with reduced polarization sensitivity (e.g., a diffraction grating that couples light with an efficiency that is relatively independent of polarization), some displays for AR systems according to embodiments described herein include a waveguide having a blazed diffraction grating formed therein. For example, the blazed grating may include diffraction features having a "sawtooth" shape. In some embodiments, the blazed grating can achieve improved grating diffraction efficiency for specific diffraction orders while reducing or minimizing the diffraction efficiency for other orders. Thus, in some embodiments, more light can be directed to a particular given diffraction order relative to any other diffraction order.

[0173] Fig. 10AA cross-sectional view of a portion of a display device 1000 (such as an eyepiece) according to some designs described herein is shown, the display device including a waveguide 1004 and a blazed diffraction grating 1008 formed on a substrate that serves as the waveguide 1004. In the illustrated embodiment, the blazed diffraction grating 1008 is formed in the substrate / waveguide 1004 (in this example, the substrate / waveguide 1004 is planar). The surface of the substrate or waveguide 1004 has a surface topography including diffraction features that together form the diffraction grating 1008. The blazed diffraction grating 1008 is configured to diffract light having a wavelength within the visible spectrum so that light incident thereon is guided within the waveguide 1004 by TIR. The waveguide 1004 can be transparent and can form part of an eyepiece through which a user's eye can view. Such a waveguide 1004 and eyepiece can be included in a head-mounted display, such as an augmented reality display. For example, the waveguide 1004 can correspond to the above description of Figures 9A-9C For example, the blazed diffraction grating 1008 may correspond to the waveguides 670, 680, 690 described above. Figures 9A-9C The blazed diffraction grating 1008 configured to couple light into the waveguide 1004 may be referred to herein as an in-coupling grating (ICG). The display device 1000 may further include an optical element 1012, which may correspond to a light distribution element (e.g., Figures 9A-9C ) or an outcoupling optical element (e.g., one of the light distribution elements 730, 740, 750 shown in Figures 9A-9C One of the outcoupling optical elements 800, 810, 820 shown in FIG. 8 ).

[0174] In operation, when an incident light beam 1016 (e.g., visible light, such as from a light projection system providing image content) is incident on a surface 1004S of the waveguide 1004 (e.g., a major surface of the waveguide on which the grating is formed (e.g., a major surface of the waveguide on which the grating is formed)) with respect to a plane perpendicular to or normal to the blazed diffraction grating or the substrate / waveguide, Fig. 10A As shown, when the incident angle α of the plane normal 1002 of the major surface () extending parallel to the Y axis is incident on the blazed diffraction grating 1008, the blazed diffraction grating at least partially diffracts the incident light beam 1016 into a diffracted light beam 1024 at a diffraction angle θ measured relative to the plane normal 1002. When the diffracted light beam 1024 exceeds the critical angle θ for total internal reflection to occur in the waveguide 1004, the diffraction light beam 1024 is diffracted into the waveguide 1008 at least partially. TIRWhen diffracted at a diffraction angle θ of θ, the diffracted light beam 1024 propagates and is guided within the waveguide 1004 in a direction generally parallel to the x-axis and along the length of the waveguide via total internal reflection (TIR). For example, a portion of the light guided within the waveguide 1004 may reach one of the light distribution elements 730, 740, 750 or the outcoupling optical elements (800, 810, 820, Figures 9A-9C ) and diffracts again.

[0175] As described herein, as in the illustrated embodiment, a light beam incident at an angle clockwise relative to the plane normal 1002 (i.e., to the right of the plane normal 1002) is referred to as having a negative angle of incidence α (α<0), while a light beam incident at an angle counterclockwise relative to the plane normal 1002 (i.e., to the left of the plane normal) is referred to as having a positive angle of incidence α (α>0).

[0176] As further described elsewhere in this specification, appropriate combinations of high refractive index materials and / or structures of the diffraction grating 1008 can produce a particular range of incident angles α (Δα), referred to herein as a range of acceptance angles or field of view (FOV). A range Δα can be described by an angular range spanning negative and / or positive values ​​of α, outside of which the diffraction efficiency drops by more than 10%, 25%, more than 50%, or more than 75%, 80%, 90%, 95%, 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 embodiments, it may be desirable to have a range Δα where the diffraction efficiency is relatively high and constant, for example, a uniform diffracted light intensity is desired within the range Δα. Thus, in some embodiments, the range Δα is associated with the angular bandwidth of the diffraction grating 1008 such that an incident light beam 1016 within the range Δα is effectively diffracted by the diffraction grating 1008 at a diffraction angle θ relative to the plane normal 1002 (e.g., a direction parallel to the yz plane), where θ exceeds θ TIR , so that the diffracted light is guided within the waveguide 1004 under total internal reflection (TIR). In some embodiments, this range Δα may affect the field of view seen by the user. It should be understood that in various embodiments, light can be guided to the incoupling grating (ICG) from either side. For example, light can be guided through the substrate or waveguide 1004 and incident on a Fig. 10A 1008. Light may experience the same effects, for example, being coupled into the substrate or waveguide 1004 by the diffraction grating 1008 so 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 acceptance angle range or field of view (FOV), may be affected by the refractive index of the substrate or waveguide material. For example, Fig. 10AIn FIG. 5 , the reduced angular range (Δα′) shows the effect of the high refractive index material on the refraction of light incident on the incoupling grating (ICG). However, the angular range (Δα) or FOV is much larger.

[0177] Fig. 10B A cross-sectional view of an example blazed transmission diffraction grating 1008 is shown. The diffraction grating 1008 includes grating features having peaks 1003 and grooves 1005. The blazed transmission diffraction grating 1008 includes a surface corresponding to a surface 1004S of a substrate or waveguide, which surface 1004S has a "sawtooth" shaped pattern when viewed in the cross section shown. The "sawtooth" pattern is formed by a first inclined portion 1007 of the surface 1004S. Fig. 10B In the example shown, the diffraction grating 1008 also includes a second (steeper) inclined portion 1009. In the example shown, the first inclined portion 1007 has a shallower inclination than the second inclined portion 1009, which has a steeper inclination. In this example, the first inclined portion 1007 is also wider than the second inclined portion 1009.

[0178] Peak 1003 has a height H, which corresponds to the vertical distance from the bottom of groove 1005 to the top of peak 1003. Therefore, this value may be referred to herein as peak height and / or groove depth, and may also be referred to as grating height or grating depth, or as the height of the diffraction features of the diffraction grating. In some embodiments, the height H of adjacent ridges may be different, for example, may be gradient. Fig. 10B In the example shown, the bottom of the groove 1005 is formed by the intersection of the first inclined portion 1007 and the second inclined portion 1009 of two adjacent peaks 1003. The first inclined portion 1007 is located on one of the adjacent peaks 1003, while the second inclined portion 1009 is located on the other adjacent peak. Similarly, the top of the peak 1003 is formed by the intersection of the first inclined portion 1007 and the second inclined portion 1009 at the top of the peak 1003. However, other configurations are also possible. For example, the first and second inclined portions do not necessarily intersect, such as, as will be discussed below, where the bottom of the groove 1005 has a flat bottom, or where the top of the peak 1003 includes a flat plateau. The blazed diffraction grating 1008 has a line spacing or pitch d, which in some embodiments can be constant. For example, the line spacing or pitch can be in a state having a spacing with respect to Fig. 10B The line spacing or pitch d is a measure of the spacing between the vertices of the peaks 1003 in a similarly shaped diffraction grating 1008. Similarly, the line spacing or pitch d can be a measure of the spacing between the deepest locations of adjacent grooves 1005. The line spacing or pitch d can be measured from other locations on the grating features.

[0179] The bevel may be arranged relative to a surface parallel to the diffraction grating 1008 or the waveguide surface (e.g., the surface 1004S of the waveguide, which may extend beyond the grating or waveguide and Fig. 10A The grating of the first (shallower) inclined portion 1007 is inclined at an angle δ relative to the plane of the surface 1004S'). This angle δ of the first (shallower) inclined portion 1007 may be referred to herein as the blaze angle.

[0180] like Fig. 10B As shown, the blazed diffraction grating 1008 may include lines or features having asymmetrical shapes, for example, including asymmetrically shaped peaks 1003 and / or grooves 1005. For example, in Fig. 10B In the diffraction grating shown, the diffractive features include peaks 1003 and / or grooves 1005 having an asymmetric triangular cross-sectional shape. As described above, this asymmetric shape results in different inclinations and / or widths of the first inclined portion 1007 and the second inclined portion 1009. However, other shapes may also be used.

[0181] In a design where the diffractive feature is asymmetric, for example, the first inclined portion has a shallower inclination and the second inclined portion has a steeper inclination, the diffractive feature can be formed by repeated slopes and steps. This structure may be referred to herein as an inclined step structure. In some embodiments, the second portion may be steep to non-inclined; for example, the second portion may be parallel to the plane normal 1002.

[0182] However, in other embodiments of the "sawtooth" pattern, the peaks 1003 and / or the grooves 1005 may be symmetrical. For example, the first and second inclined portions 1007, 1009 may have the same inclination and the same width.

[0183] Fig. 10B The cross-sectional pattern shown may be referred to herein as a single-order geometry, although multi-order structures are also possible.

[0184] Regardless of whether the diffraction feature is asymmetric or symmetric, in some embodiments, as will be discussed below, a plateau or flat portion may be located on top of peak 1003. Fig. 11B The diffraction grating 1008 is shown to include diffractive features having a plateau or flat portion on top of the peak 1003.

[0185] Fig. 10B An incident light beam 1016 is shown incident on the diffraction grating 1008 at an angle α relative to the plane normal 1002. (As discussed above with respect to Fig. 10AAs discussed above, in other examples, light may pass through the substrate or waveguide 1004 and be incident on the diffraction grating 1008 from the other side). As discussed above, the plane normal 1002 is perpendicular or orthogonal to the extended surface of the blazed diffraction grating 1008 or the plane of the grating or waveguide and / or the surface 1004S of the waveguide 1004, e.g., the major surface of the waveguide on which the grating is formed or an opposing planar surface 1004S'. Fig. 10B , an incident light beam 1016 incident on the diffraction grating 1008 is shown as being diffracted at an angle β relative to the plane normal 1002.

[0186] When configured as an in-coupling optical element or an in-coupling diffraction grating, the diffraction grating 1008 can diffractively couple light incident to the substrate 1004, which can be a waveguide as described above. If desired, the diffraction grating 1008 can be configured as an out-coupling optical element, and in such an embodiment, can diffractively couple light from the substrate 1004, which can also be a waveguide as described above.

[0187] refer to Fig. 10A and 10BIn some embodiments, the substrate 1004 includes a high refractive index material having a refractive index of at least 1.9. For example, the refractive index may be at least 2.0, at least 2.1, at least 2.2, or at least 2.3, and may be no more than 2.4, 2.5, 2.6, 2.7, 2.8, or may be within any range formed by any of these values, or may be outside these ranges. For example, in some embodiments, the substrate includes a titanium-based, tantalum-based, or lithium-based oxide. In various examples disclosed herein, the diffraction features of the diffraction grating 1008 may be formed on a surface of the substrate 1004. The diffraction features may be formed in the substrate 1004 (e.g., a waveguide), or in a separate layer formed on the substrate 1004 (e.g., a waveguide), and are configured to be in optical communication with the substrate 1004, such as coupling light into or out of the substrate 1004. In the illustrated example, the diffraction features (such as lines) of the diffraction grating 1008 are formed in the substrate 1004, such as on the surface of the substrate. For example, the diffraction features can be etched into the substrate 1004, which includes a high refractive index material, such as a titanium-based, tantalum-based or lithium-based oxide. For example, the substrate may include lithium niobate, and the diffraction grating may be formed in the lithium niobate substrate by etching or patterning the substrate surface. Other materials with a high refractive index may also be used. Other lithium-containing materials (such as lithium oxides, for example, lithium tantalate (LiTaO3)) may also be used as substrates. Silicon carbide (SiC) is another option for substrate materials. Examples are not limited. In other examples, the diffraction features of the diffraction grating 1008 may be formed in a separate layer disposed on the substrate 1004 (e.g., in physical contact with the substrate 1004). For example, a thin film coating of zinc oxide (ZnO), silicon nitride (Si3N4), zirconium dioxide (ZrO2), titanium dioxide (TiO2), silicon carbide (SiC), etc. with a thickness of less than 200nm may be provided on an existing high refractive index substrate. The thin film coating may be patterned to form the diffraction features. However, in some embodiments, the diffractive features (such as lines) of the diffraction grating 1008 can be formed of a material different from the substrate. For example, the substrate can include a high refractive index material, such as a titanium-based, tantalum-based, or lithium-based oxide (e.g., lithium niobate LiNbO3 or lithium tantalate LiTaO3), however, the diffractive features can be formed of a different material, such as a coating of zinc oxide (ZnO), zirconium dioxide (ZrO2), titanium dioxide (TiO2), silicon carbide (SiC), or other materials described herein. In some embodiments, such other materials formed on the substrate can have a lower refractive index.In some cases, substrate 1004 may include materials (including amorphous high refractive index glass substrates) such as silicon-based glass (e.g., doped silicon glass), silicon oxynitride, transition metal oxides (e.g., hafnium oxide, tantalum oxide, zirconium oxide, niobium oxide, aluminum oxide (e.g., sapphire)), plastics, polymers, or other materials that are optically transmissive to visible light, such as having an appropriate refractive index as described above, which is different from materials characterized by titanium-based, tantalum-based, or lithium-based oxides.

[0188] However, as described above, in various embodiments described herein, the diffraction grating 1008 and the substrate 1004 or waveguide both include the same material, such as a titanium-based, tantalum-based, or lithium-based oxide. In some embodiments, the diffraction grating 1008 is patterned directly into the substrate 1004 so that the diffraction grating 1008 and the substrate 1004 form a monolithic or monolithic structure. For example, the substrate 1004 includes a waveguide and the diffraction grating 1008 is formed directly on the surface of the waveguide or substrate. In these embodiments, the bulk titanium-based, tantalum-based, or lithium-based oxide material may be patterned at the surface 1004S to form the diffraction grating 1008, and the titanium-based, tantalum-based, or lithium-based oxide material below the diffraction grating 1008 may form the waveguide. In yet other embodiments, the bulk or substrate 1004 and the surface 1004S that are patterned to form the diffraction grating 1008 include different titanium-based, tantalum-based, or lithium-based oxides. For example, the main titanium-based, tantalum-based, or lithium-based oxide material patterned in the surface region to form the diffraction grating 1008 may be formed of a first titanium-based, tantalum-based, or lithium-based oxide material, and the titanium-based, tantalum-based, or lithium-based oxide material forming the substrate 1004 or the substrate region below the diffraction grating 1008 may be formed of a second titanium-based, tantalum-based, or lithium-based oxide material different from the first titanium-based, tantalum-based, or lithium-based oxide material. As described above, in some other embodiments, the diffraction grating 1008 includes a different high refractive index material, such as zirconium dioxide (ZrO2), titanium dioxide (TiO2), silicon carbide (SiC), etc., and the material forming the substrate 1004 or the substrate region below the diffraction grating 1008 may be formed of a second material, such as LiTaO3, LiNbO3, etc., and different from the first material coated as a thin film.

[0189] exist Fig. 10A and Fig. 10BIn the example shown in , the diffraction grating 1008 may include a plurality of blazed diffraction grating lines that are elongated in a first horizontal direction or y-direction and periodically repeated in a second horizontal direction or x-direction. For example, the diffraction grating lines may be straight and continuous lines extending in the y-direction. However, the embodiments are not limited thereto. In some embodiments, the diffraction grating lines may be discontinuous lines, for example in the y-direction. In some other embodiments, the discontinuous lines may form a plurality of columns protruding from the surface of the grating substrate. In some embodiments, at least some of the diffraction grating lines may have different widths in the x-direction.

[0190] In the illustrated example, the diffraction grating lines of the diffraction grating 1008 have a profile, such as a sawtooth profile, having asymmetric opposite side surfaces forming different angles relative to the substrate plane. However, the embodiment is not limited thereto, and in other embodiments, the diffraction grating lines may have symmetric opposite side surfaces forming similar angles relative to the substrate plane.

[0191] refer to Fig. 10A and 10B , according to various embodiments, the diffraction grating 1008 can have various sizes. For example, according to an embodiment, the diffraction features of the diffraction grating 1008 can have a height (H) of 10nm or 40nm to 150nm or 200nm, 50nm to 110nm, 60nm to 100nm, 70nm to 90nm, or about 80nm, or a height within a range defined by any of these values. The height can correspond to the height of the peaks 1003 and / or the depth of the grooves 1005. Such a height and a blazed geometry in a high refractive index material can provide a diffraction grating with reduced polarization sensitivity. However, other heights are also possible.

[0192] According to various embodiments, the diffraction grating 1008 can have a pitch of 250 nm to 350 nm, 300 nm to 400 nm, 250 nm to 450 nm, or a pitch within any range defined by any of the above values. Other pitches are also possible.

[0193] In some embodiments, the blaze angle (shallow side) of the diffraction grating 1008 can be about 10 to 70 degrees and the reverse blaze angle (steep side) can be 140 to 70 degrees or any value within the range defined by these values. As discussed below, values ​​outside of these ranges are also possible.

[0194] In general, blazed diffraction gratings of either single-order or multi-order geometries are possible, and a variety of techniques can be used to form the gratings. Figures 11A-11B In the example shown, the grating can be formed by depositing a blaze and then etching and patterning the photoresist.

[0195] Example methods of forming blazed gratings and examples of various blazed grating geometries are described in US20210072437A1, entitled “Display device with diffraction grating having reduced polarization sensitivity”, the entire contents of which are incorporated herein by reference. The methods disclosed in this publication can be applied to the curved and multi-faceted anti-blazed structures disclosed herein.

[0196] Fig.11A The formation of a single-order blazed grating 1106 in a substrate 1104 is shown, and the substrate 1104 may be a waveguide 1004 ( Fig. 10A ). A patternable material (such as photoresist 1102) is deposited onto a substrate 1104, which may be or include a waveguide. The patternable material / photoresist 1102 is patterned to have the shape of a blazed grating. In some embodiments, forming a blazed geometry in the photoresist 1102 involves imprinting a pattern, such as a single-step "sawtooth" pattern, in the photoresist 1102 (e.g., depositing the photoresist on the substrate 1104 and then imprinting the blazed geometry). The photoresist 1102 may include a mask, such as a hard mask. The patterned photoresist 1102 and substrate 1104 may then be etched to form a blazed pattern in the substrate 1104. For example, etching the photoresist 1102 and substrate 1104 may involve dry plasma or chemical etching and / or wet chemical etching. In some embodiments, Fig.11A The etching shown can etch away material at a relatively constant rate such that the portions where the patterned photoresist is thickest result in relatively small amounts of material being removed from the substrate, such as negligible or no removal, while the portions where the patterned photoresist is thinnest (or non-existent) result in relatively large amounts of material being removed from the substrate or the deepest etching into the substrate.

[0197] Fig. 11B is a scanning electron micrograph of a blazed diffraction grating 1112, wherein the blazed grating pattern is formed in a photoresist substrate 1104, such as by imprinting the photoresist with a patterned master. The diffraction grating 1112 shown has a single-order blazed geometry.

[0198] In some embodiments, the blazed grating used for ICG has a sharp anti-blaze angle. Fig.12, shows a cross-sectional profile of one pitch length of such a grating, wherein the grating structure 1200 includes a grating layer including a ridge 1220 on a substrate 1210. A Cartesian coordinate system is provided for reference. The grating extends in the y-direction, and the ridge 1220 extends from the base portion in the z-direction, having a relative slope at an angle relative to the top surface of the ridge 1220 and the substrate surface. Due to the tilt of the ridge, for most of the anti-blaze side, there is a non-zero horizontal distance between the anti-blaze side and a vertical line 1235 that intersects the vertex 1237 of the ridge 1220, for example, the vertex 1237 and the vertical line have the same value along the x-axis. The horizontal distance refers to the distance along the x-axis between two points that have the same value along the z-axis.

[0199] Two additional coatings 1230 and 1240 are formed on the surface of the grating layer. Coatings 1230 and 1240 are formed on the top surface of ridge 1220 and in the valleys between consecutive ridges, but only one slope of ridge 1220 (the left side in this case) is coated, while the other slope is substantially free of these coatings. Coatings 1230 and 1240 can be formed using a directional deposition method (e.g., evaporation, flash angle deposition). The asymmetric coating of the two ridge slopes may be caused by directional deposition and the resulting self-shadowing. Depending on the deposition method, erosion of coatings 1230 and 1240 under the overhanging portion may occur.

[0200] Fig.12 The grating design shown can be characterized by, among others, six geometrical parameters and three materials. Depending on the illumination wavelength and the desired response, these parameters can vary within the following ranges:

[0201] parameter scope Anti-blaze angle 5°-85° high 10nm–1000nm Pitch 100nm–5,000nm Duty cycle (width / pitch) 5％-95％ First coating thickness 5nm–500nm Second coating thickness 5nm–500nm

[0202] Table 1. Parameter ranges of grating structure 1200

[0203] like Fig.12 As shown, the anti-blaze angle refers to the acute angle between the right slope of the ridge 1220 and the substrate surface. The anti-blaze angle can be in the range of from 5° to 85° (e.g., 10° to 80°, 30° to 80°, 40° to 75°, 50° to 70°, 60° to 70°).

[0204] The blaze angle refers to the obtuse angle between the left slope of the ridge 1220 and the substrate surface. Fig.12The parallelogram geometry shown, the angle is the complement of the anti-blaze angle (i.e., 180° minus the blaze angle). The angle can be in the range of from 95° to 160° (e.g., 100° or greater, 110° or greater, 120° or greater, 150° or less, 140° or less). However, other geometries are possible. For example, the blaze profile can be a trapezoid, where both the blaze side and the anti-blaze side have positive slopes, but different absolute values. In other words, at least a portion of the anti-blaze side can have a tangent line with the same sign as the slope of the blaze side.

[0205] The height of the grating layer refers to the ridge dimension along the Z direction. The ridges 1220 may have a height in a range from 10 nm to 1,000 nm (eg, 50 nm to 500 nm, 100 nm to 400 nm, 200 nm to 400 nm, 250 nm to 350 nm).

[0206] The pitch of the grating layer is the dimension between adjacent ridges or adjacent valleys along the X direction. In general, the pitch, like 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. In general, the pitch is in the range of 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).

[0207] The ridges have a width, which refers to the dimension along the X direction. For the grating structure 1200, the ridges 1220 are parallel across the opposite slopes of the illustrated cross section, so the ridge thickness is constant throughout the entire height of the ridge. However, in some embodiments, the width may vary (e.g., narrow) from the bottom to the top of the ridge. In embodiments where the width varies, the width may be determined at the midpoint of the ridge height.

[0208] Duty cycle refers to the ratio of width to pitch, expressed as a percentage. In embodiments, the grating structure may have a duty cycle in a range from 5% to 95% (eg, 10% to 75%, 20% to 50%, 30% to 40%).

[0209] The ridge has a height corresponding to the dimension of the ridge in the Z direction measured from its base to its top surface. The ridge may have a height in a range from 10 nm to 1,000 nm (e.g., 50 nm to 500 nm, 100 nm to 400 nm, 200 nm to 400 nm, 250 nm to 350 nm).

[0210] The thickness of a layer, such as the thickness of coatings 1230 and 1240, refers to the dimension of the layer in the Z direction measured at a point on the surface of the support layer perpendicular to the Z direction. The first coating 1230 and / or the second layer may have a thickness in the range of from 5 nm to 500 nm (e.g., 10 nm to 400 nm, 20 nm to 300 nm, 50 nm to 250 nm, 100 nm to 200 nm, 130 nm to 170 nm). Generally, the thickness of the first layer and the second layer may be the same or different.

[0211] The base material of the grating structure (i.e., substrate 1210 and ridges 1220) can be a UV or thermally cross-linked polymer. The refractive index of the base material can be in the range of from 1.5 to 2.2 (e.g., 1.6 or higher, 1.7 or higher, 1.8 or higher, 1.9 or higher, 2.1 or higher, such as up to 2.2). A high refractive index (e.g., 1.8 or higher) can be achieved using a polymer composite material, for example, a polymer composite material including nanoparticles (e.g., high refractive index nanoparticles, such as TiO2 nanoparticles and / or ZrO2 nanoparticles).

[0212] Without wishing to be bound by theory, it is believed that the high refractive index of the base patterning material can help make the diffraction efficiency relatively uniform over a larger angle. For example, the variation in average TE and TM diffraction efficiency can be + / -15% or less (e.g., + / -10% or less, + / -8% or less, + / -5% or less) of the absolute average diffraction efficiency.

[0213] In some embodiments, the first coating 1240 includes a material having a high refractive index (eg, 1.8 or higher). The first coating 1240 may be formed of a dielectric material including, but not limited to, titanium dioxide, gallium phosphide, and silicon carbide.

[0214] In some embodiments, the second coating 1230 includes a material having a low refractive index dielectric (e.g., 1.6 or less, 1.5 or less, 1.45 or less). For example, the second coating can be formed of a dielectric material such as (but not limited to) silicon dioxide, magnesium fluoride, and calcium fluoride.

[0215] In general, the grating layer of the grating structure 1200 and similar grating structures can be formed using the techniques described herein and in US20210033867A1 and US20210072437, the entire contents of which are incorporated herein by reference.

[0216] The first coating 1230 can be formed using various physical vapor deposition techniques, including but not limited to sputtering and electron beam deposition. The second coating 1240 can be formed by various physical vapor deposition techniques, including but not limited to sputtering and electron beam deposition. In general, the technique used to form the coating 1230 can be the same as or different from the technique used to form the coating 1240.

[0217] As above Fig.12 The optical performance of the example grating structure described in is simulated using rigorous coupled wave analysis (RWCA) as follows. The parameter values ​​of the grating structure are:

[0218] parameter Numeric Anti-blaze angle 70° high 260nm Pitch 382nm Duty cycle (width / pitch) 40％ <![CDATA[First coating thickness (TiO2)]]> 120nm <![CDATA[Second coating thickness (MgF2)]]> 70nm

[0219] Table 2. Parameters and values ​​for an example ICG operating at green wavelength

[0220] For simulation purposes, the operating wavelength used was 525 nm and the refractive index of the matrix material was 2.0.

[0221] Fig.13A -D includes graphs of diffraction efficiency and reflectance, i.e., what percentage of light incident on the diffraction grating is diffracted or reflected as the emission angle changes. Fig.13A The diffraction efficiency of the simulated grating in the emission direction over a 55° field of view is shown as a function of the illumination angle. The three curves correspond to TM polarized light, TE polarized light, and unpolarized light, respectively. The integral average of the diffraction efficiency is calculated to be about 52%. In general, it is believed that within a range of incident angles of + / -20°, such a grating can provide an average diffraction efficiency of 50% or more for TE and TM polarized light. Fig. 13B The reflection efficiency of the simulated grating for TM polarized light, TE polarized light and non-polarized light as a function of the illumination angle is shown. The integrated average value of the reflection efficiency is calculated to be 0.93%. Fig. 13C and 13D Corresponding to Fig.13A and 13B The same graph shown in , which is simulated for the same structure except without the second layer. The diffraction efficiency is still high, e.g., an integrated average of 40.62%, but the back reflection increases significantly, e.g., an integrated average of 4.13%.

[0222] Additional experiments were performed to compare the results of the simulated grating structures with the measured results of similarly fabricated samples. The results of these experiments are shown in Figures 14A-14D shown. Specifically, Fig.14A and 14B A graph showing the variation of diffraction efficiency with incident angle for TM, TE and unpolarized light within a certain range of incident angles. Fig.14A shows simulated data, and Fig. 14BMeasurement results for fabricated samples of a subset of the simulation range for p-polarized light (TM) and s-polarized light (TE) are shown. Fig. 14C and 14D A schematic diagram of the cross-sectional profile of the grating structure is shown ( Fig. 14C ) and SEM images of the cross-section of the fabricated samples ( Fig.14D ).

[0223] Figures 15A-15C The effect of including a low refractive index layer as the topmost layer of the grating structure is shown. Fig.15A is a graph of the diffraction efficiency as a function of the incident angle for orthogonal polarization states (eg, s-polarization and p-polarization) for a SiO2 grating structure having a TiO2 coating thereon. A SEM of the cross-sectional profile of the grating structure is shown in the inset. Fig. 15B is a graph of the diffraction efficiency as a function of the angle of incidence for the same grating structure, but with a further SiO2 layer formed on the TiO2 layer. The average diffraction efficiency and the diffraction efficiencies for s-polarization and p-polarization are shown. Fig. 15C A graph showing the reflectivity of normally incident light (e.g., 0° emission angle) as a function of wavelength in the visible light spectrum is shown for grating structures with and without SiO2 coating (e.g., solid and dashed lines). For the grating with additional SiO2 coating, the reflectivity is lower across almost the entire visible spectrum.

[0224] Figures 16A-16F Measurement results from a further example are shown in . Fig.16A , 16C The three lines in 16E correspond to p-polarized light, s-polarized light, and the average of the other two lines. Fig.16A It is for Fig. 16B A graph of the diffraction efficiency of a grating structure shown in the SEM in FIG. 1 as a function of the incident angle, the grating structure comprising a high refractive index (n=2.0) composite material on a glass substrate (n=1.78). The blaze angle (e.g., "Aa1") is about 53°, the pitch "V3" is about 383nm, the height "H1" of the planar portion between the ridges is about 39nm, the height "H2" of the ridge relative to the planar portion is about 181nm, the width "V2" of the top of the ridge is about 119nm, and the width of the bottom of the ridge is about 186nm. The height "H1" can have a thinner resist layer thickness (RLT), for example, less than 50nm or less than 20nm. Fig. 16C It is for Fig.16D A graph showing the diffraction efficiency of the grating structure as a function of the incident angle shown in the SEM. Fig.16DThe grating structure comprises a high refractive index (n=2.0 for light at 530 nm) composite material on a substrate (n=2.0 for light at 530 nm), wherein the grating layer is coated with TiO2 (n=2.2 for light at 530 nm). The maximum height "H2" of the ridges relative to the substrate is about 196 nm. The coating has a stepped shape, wherein the first level is at a height "H3" of 37.65 nm relative to the substrate, and the second level is at a height "H1" of about 173 nm above the maximum height of the ridges. Fig.16E It is for Fig.16F Graph of the diffraction efficiency of a grating structure shown in the SEM in FIG. 1 as a function of the incident angle, the grating structure comprising a high refractive index (n=2.0 for light at 530 nm) composite material on a glass (e.g. SiO2) substrate (n=1.45 for light at 530 nm) with a TiO2 (n=2.15 for light at 530 nm) coating, wherein a further SiO2 (n=1.45 at 530 nm) coating is applied on the TiO2 layer. The coating has a stepped shape, with the maximum width "H1" of the first TiO2 coating being approximately 181 nm, and the maximum width "H2" of the second SiO2 coating being approximately 64 nm. Clearly, the overall diffraction efficiency is increased compared to a single coating, especially at higher incident angles.

[0225] Although the foregoing examples are of grating structures having parallelogram-shaped ridges, more generally, other cross-sectional shapes are possible. For example, trapezoids, triangles, and steps are possible. Furthermore, although the shapes described correspond to parallelograms to mathematical precision, deviations from these shapes are inevitable due to manufacturing limitations, etc. In general, as used herein, such ridges and other features are considered to have a particular shape, i.e., their design dictates that the shape and / or structure have such a shape within the capabilities of the process used to manufacture such structures on a large scale.

[0226] For example, the shape of the ridges of the grating structure can facilitate material deposition between the ridges without coating the anti-blaze side of the ridges. Applying a high refractive index coating on the anti-blaze side and not coating the flat portion of the grating between the ridges can reduce diffraction efficiency. Fig.17A A cross-sectional view of an example of a blazed grating 1700 with a concave anti-blaze side is shown, where the concave side can be curved or polygonal, e.g., non-linear. The blaze side 1704 of the ridge 1702 is linear, while the anti-blaze side 1706 of the ridge 702 is concave. Thus, during deposition, only the portion of the grating that does not have a portion of the ridge that obstructs a path in a vertical direction will be coated. Fig.17A, a vertical line 1710a, e.g., a vertical line 1710a along a direction perpendicular to the flat portion of the grating between the ridges, connects a vertex 1712 (e.g., the uppermost vertex of the anti-blaze side) and a base point 1714 of the anti-blaze side 1706, e.g., the base point 1714 is located directly below the vertex 1712. For most of the anti-blaze side, there is a non-zero parallel distance between the anti-blaze side and the vertical line 1710a along the anti-blaze side. In other words, a portion of the anti-blaze side 1706 can overhang a lower portion of the anti-blaze side. The curved concave anti-blaze side can be characterized by an angle formed by a tangent line 1701 near the bottom of the ridge. The tangent line 1701 can form an angle of 89° or less with the flat portion of the grating.

[0227] Accordingly, because the anti-blaze side 1706 curves outward near the bottom of the ridges, the flat portion 1716 of the grating between the ridges can be more completely covered during the vertical deposition process without coating the anti-blaze side 1706, compared to the case where the anti-blaze side is only a slanted line. Increasing the coverage of the portion of the grating between the ridges with a high refractive index coating (coating in the grooves) can increase the diffraction efficiency of the grating (e.g., by 20% or more, 30% or more, 50% or more, up to 60%). Because the anti-blaze side 1706 is concave, uniform coverage of the flat portion of the grating between the ridges can be achieved without significantly coating the anti-blaze side 1706, which may reduce the diffraction efficiency of the blazed grating 1700.

[0228] Fig. 17B A cross-sectional view of another example of a blazed grating 1720 having a concave anti-blaze side is shown. In some embodiments, the apex 712 and base 714 do not necessarily have the same value along the horizontal direction (e.g., the x-axis), but some of the benefits discussed above can still be achieved. For example, the first ridge 1702a has a concave anti-blaze side, where the apex 1712a and base 1714a have different values ​​along the horizontal direction, for example, the apex 1712a is further to the right than the base 1714a (using the vertical line 1710b that is perpendicular to the flat portion of the grating between the ridges as a reference). Therefore, during the deposition process, a portion 1722a of the anti-blaze side will be coated. However, this portion 1722a is smaller than the portion that would be coated if the anti-blaze side was simply a tangent 1718a that follows the initial curvature of the anti-blaze side near the apex 1712a. Therefore, even if the apex 1712a and base 1714a of the anti-blaze side are not perfectly aligned, the concave shape can reduce the amount of coating on the anti-blaze side. In some cases, the amount of lower shadow (1722a) or upper shadow (1722b) may be about 30% of the groove width.

[0229] As another example, the second ridge 1702b has a concave anti-blaze side, where the apex 1712b and the base 1714b have different values ​​in the horizontal direction, for example, the apex 1712b is further to the left than the base 1714b (using a vertical line 1710c that is perpendicular to the normal of the flat portion of the grating between the ridges as a reference). Therefore, during the deposition process, a portion 1722b of the substrate will not be coated. However, this portion 1722b is less than the portion that is not coated during the deposition process if the anti-blaze side is simply a tangent 1718b that follows the initial curvature of the anti-blaze side near the apex 1712b. Therefore, even if the apex 1712a and the base 1714a of the anti-blaze side are not perfectly aligned, the concave shape helps to increase the amount of the substrate that is coated during the deposition process.

[0230] Note that both tangent lines 1718a and 1718b have negative slopes, similar to the blaze side. In other words, at least a portion of the anti-blaze side has a tangent line with the same sign as the blaze side slope.

[0231] In some embodiments, the anti-blaze side has a constant radius of curvature. In some embodiments, the radius of curvature varies along the anti-blaze side. The radius of curvature can be 20 nm or more (e.g., 50 nm or more, 100 nm or more, 200 nm or more, 300 nm or more, up to 1,000 nm, such as 750 nm or less, 500 nm or less, 400 nm or less).

[0232] Although Fig.17A and 17B A concave shape of the anti-flare side is described, but other shapes can also provide the above benefits. For example, Fig. 17C and 17D Cross-sectional views of other examples of gratings with faceted anti-blaze sides are shown. Fig. 17C The anti-blaze side in has a profile of two lines 1711 and 1713 connected at a certain angle, such as an obtuse angle θ1. In other words, the anti-blaze side includes a series of line segments. Relative to the reference horizontal line 1715a, line 1711 can extend at a negative angle θ2, such as having a negative slope, and line 1713 can extend at a positive angle relative to the reference horizontal line 1715b, such as having a positive slope. The length of each line segment is generally equal to or less than the height of the grating divided by the sine of the blaze angle.

[0233] In some embodiments, the anti-flare side may have a profile of three or more lines, e.g. Fig.17D The lines 1717, 1719, 1721 connected at different angles (e.g., θ4 and θ5) in FIG. 1717, 1719, 1721 are connected at different angles (e.g., θ4 and θ5). Similar to the example where the ridge has an inclined or concave anti-flare side, Fig. 17C and 17DThe multi-faceted example in also exhibits the following behavior: for at least a portion of the anti-blaze side, along the anti-blaze side, there is a non-zero horizontal distance between the anti-blaze side and, for example, a vertical line 1710d along a direction perpendicular to the normal of the flat portion of the grating between the ridges.

[0234] Although Fig. 17C and 17D An example of an obtuse angle is given in , but other angles are possible, wherein the anti-flare side has no portion protruding beyond a vertical line 1710d determined by the vertex, base point, or both of the anti-flare side, for example, the anti-flare side has no portion extending beyond the vertical line in the -x direction. Fig. 17C and 17D Examples are described in which the anti-blaze side has a facet having a slope with the same sign as the slope of the blaze side, and another facet having a slope with an opposite sign to the slope of the blaze side. This geometric arrangement can achieve at least some of the benefits described above with respect to reducing the amount of the anti-blaze side that is coated during deposition, and coating the flat portions between the ridges of the grating.

[0235] In some embodiments, there is a gap between where one ridge begins and where another ridge ends, e.g. Fig. 17C In some embodiments, the gap "g" described in the figure is located between the location where the blazed side intersects the flat portion of the grating and the location where the adjacent anti-blazed side rises from the flat portion of the grating. Fig.17D As shown, there is no gap between where one ridge begins and where another ridge ends. For example, the location where adjacent blaze and anti-blaze sides meet can be at or above the height (along the Z axis) of the flat portion of the grating.

[0236] Fig.17E A cross-sectional view of an example of a blazed grating 1730 with a concave anti-blaze side covered by two layers of coating is shown. Each ridge 1722 is coated with a first layer 1724 and a second layer 1726. Fig.16F The description of the two-layer coating in may apply to the first layer 1724 and the second layer 1726. Due to the shape of the ridge, for example, having a horizontal top and an inclined blaze side, and the width of the first and second layers 1724 and 1726, the first layer 1724 of the second ridge 1702d and the second layer 1726 of the first ridge, the edges and anti-blaze sides of the first and second layers 1724 and 1726 on the first ridge 1702c define an air gap 1732. The presence of the air gap 1732 means that at least a portion of the anti-blaze side is not coated. The air gap 1732 extends in the y-direction. In some embodiments, it is beneficial to reduce the volume of the air gap because the refractive index of the air gap is generally lower than the refractive index of the ridge and the coating, for example n≈1. Reducing the size of the region within the coated grating having a lower refractive index can improve the diffraction efficiency of the grating.

[0237] In some embodiments, when there is only one coating layer on the diffraction grating, air gaps are formed if the coating surface is not parallel to the blazed side, e.g., has a less negative slope. In some embodiments, such as when the coating surfaces are approximately parallel to the ridges and parallel to each other, air gaps are formed when there are at least two coating layers.

[0238] The bottom of the second layer 1726 coating the first ridge 1702c is adjacent to the base point 1714c of the second ridge 1702d, which means that no part of the grating is exposed. However, other embodiments are possible.

[0239] Fig.18 is a scanning electron microscope (SEM) image of a reentrant blazed grating with different slopes on the anti-blaze sidewall. The reentrant grating is typically located on the side of the waveguide opposite the light source and couples the light into the waveguide after it has passed through the waveguide. The reentrant blazed grating is characterized by a curved portion on the anti-blaze side where the radius of curvature is larger at the top than at the bottom. The slope of the blazed side (right side of the ridge) decreases from the left to the right side of the grating. In practice, the geometry of the blazed grating can be determined using SEM analysis, which can include measuring the distances between line segments representing areas of high contrast.

[0240] In some embodiments, such as when the blazed grating is used as an OPE, EPE or CPE, the blazed grating is located, for example, Fig. 9C On the grating surfaces shown (e.g., ICG 700, 710 and 720, OPE 730, 740 and 750, and EPE 800, 810 and 820).

[0241] Figures 19A-19I is a cross-sectional diagram illustrating the fabrication process for a re-entrant grating with a multi-faceted anti-blaze side. Fig.19A Starting with a substrate 1901 (e.g., silicon or silicon dioxide) as described in Fig.19B As shown, an etch stop layer 1903 is coated on the substrate 1901. The etch stop layer 1903 may be, for example, chromium (Cr) or aluminum oxide (Al2O3), and may protect the substrate in subsequent steps including dry etching. Fig.19C In the embodiment of the present invention, a layer that will become a grating, such as a grating layer 1905, is imprinted on the etch stop layer 1903. The grating layer 1905 can be made of materials discussed previously in this disclosure, such as silicon dioxide.

[0242] Fig.19DA blazed grating template 1907, which can be wet etched silicon, is depicted on top of a grating layer 1905. In some embodiments, the template has a narrower flat top than the flat top of the final blazed grating. A template with a narrow flat top can provide additional protection during the dry etching step because the narrower top provides an additional portion on top that can be removed by stripping rather than etching.

[0243] Fig.19E A dry etching step (indicated by the downward arrow) is depicted, which transfers the shape of the grating from the template to the grating layer 1905. During the dry etching process, the top corners of the blazed grating shape are etched faster than the rest of the shape. After the dry etching, some of the blazed grating template 1907 remains. Fig.19F As shown, after dry etching, the remaining portion of the blazed grating can be stripped away. Stripping away the remaining portion of the blazed grating template 1907 instead of etching it can ensure feature fidelity, for example, the shape of the grating layer 1905 will be similar to the shape of the blazed grating template 1907 except for the portion remaining after dry etching.

[0244] exist Figure 19G In FIG. 1 , the etching mask 1909 is directionally coated at an angle (indicated by the tilted arrow). Coating at an angle can advantageously prevent coating of the anti-flare side because the flat top and the flare side would block the path to the anti-flare side. The coating angle can be determined by the anti-flare angle θ AB It is determined, for example, that the angle between the coating direction and the vertical line can be equal to 90°-θ AB or smaller. Since θ AB Greater than 90°, the coating angle can be negative, e.g. Figure 19G In other words, the absolute value of the angle between the coating direction and the vertical line can be at least 90°-θ AB The difference between .

[0245] Fig.19H Described is dry etching the anti-blaze side with plasma from a Faraday cage at an angle indicated by the tilted arrow. Due to the shielding effect, the Faraday cage can deflect ions in the plasma in a direction perpendicular to the furnace of the Faraday cage. Therefore, the use of the Faraday cage can deflect ions from the plasma in the direction of etching the anti-blaze side of the grating layer 1905. The etching mask 1909 can protect the top surface and the blaze side of the grating layer 1905 during the etching process. As a result of dry etching using the Faraday cage, the inner portion of the anti-blaze side, such as Fig.19H The area to the left of the dashed vertical line.

[0246] Fig.19IThe final grating structure is depicted after the etching mask 1909 is stripped off. Accordingly, the grating layer 1905 after dry etching has a different shape compared to the blazed grating template 1907 before etching, for example, the top layer is removed and the multi-faceted anti-blazed side.

[0247] In some embodiments, dry etching using a Faraday cage is repeated multiple times at different angles to obtain the desired profile of the anti-flare side. Fig.19A -I shows how dry etching at one angle using a Faraday cage produces an anti-blaze side with two facets. However, dry etching more times at different angles can produce an anti-blaze side with three or more facets. Depending on the duration of dry etching using the Faraday cage, a smooth, curved anti-blaze side can be obtained.

[0248] Fig. 20 is a flow chart of a process 2000 for forming a blazed grating having a concave anti-blaze side (eg, the cross-section of the anti-blaze side is concave). At least some steps may be performed using a system such as that described in US20210072437A1 (incorporated by reference above).

[0249] Process 2000 includes providing a substrate (2002), such as substrate 1901. The substrate can be a waveguide. In some embodiments, for example, substrate 1004 can include a material such as discussed with reference to substrate 1004, such as an amorphous high refractive index glass.

[0250] Process 2000 includes depositing an etch stop layer on the substrate (2004), such as etch stop layer 1903. The etch stop layer may be, for example, chromium (Cr) or aluminum oxide (Al2O3), and may protect the substrate during subsequent steps including dry etching.

[0251] The process 2000 includes depositing a grating material on the etch stop layer (2006), such as the grating layer 1905. The grating material may be a patternable material, such as a photoresist.

[0252] Process 2000 includes depositing a blazed grating template (2008), such as blazed grating template 1907, on a grating material. In some embodiments, the blazed grating template is wet-etched silicon.

[0253] In some embodiments, the blazed grating template extends vertically beyond the final shape of the grating. Fig.19D and 19E , the blazed grating template 1907 can have a narrower upper portion due to the triangular shape of the base portion of the template. The shape of the top narrow portion is not intended to be transferred to the grating layer 1905, but rather to provide a buffer for the top of the grating during the etching process.

[0254] The process 2000 includes etching the grating material, thereby transferring the shape of the blazed grating template to the grating material and forming the blazed grating (2010). The etching may include dry plasma etching, chemical etching, wet chemical etching, or a combination thereof.

[0255] In some embodiments, Fig.19E As shown, step 2010 ends before the entire grating template is etched. When there are remaining portions of the blazed grating template, process 2000 may include stripping the remaining portions of the blazed grating template before proceeding to step 2012.

[0256] Process 2000 includes coating a blazed grating with an etch mask (e.g., etch mask 1909) at a first non-zero angle relative to vertical such that an anti-blazed side of the grating remains uncoated (2012). For example, the non-zero angle may be Figure 19G The angle between the arrow and the vertical line.

[0257] Process 2000 includes etching at a second non-zero angle relative to the vertical direction and having a sign opposite to the sign of the first non-zero angle, thereby removing an inner portion of the anti-flare side (2014). In some embodiments, etching includes dry etching the anti-flare side with plasma from a Faraday cage. By removing the inner portion of the anti-flare side, the anti-flare side becomes concave. In some implant processes, the profile of the anti-flare side is curved, includes a line segment, or both.

[0258] Process 2000 includes stripping the etch mask from the blazed grating (2016). Fig.19I Blazed grating on the concave anti-blaze side shown.

[0259] In some embodiments, process 2000 may include additional steps, or some steps may be divided into multiple steps. For example, process 2000 may continue by coating the blazed grating with one or more additional layers of a high refractive index material. Depending on the geometry, coating the blazed grating with one or more additional layers of a high refractive index material results in an air gap being formed between the edge of one of the additional layers and the anti-blaze side. In some embodiments, to avoid coating the anti-blaze side, it is not necessary to use a non-zero angle relative to the vertical direction when coating the blazed grating with the high refractive index coating. In addition, in the case where the overhang of the anti-blaze side does not block the flat portion of the diffraction grating between the ridges, the vertical deposition can substantially cover the flat portion of the grating between the ridges.

[0260] Other manufacturing variations are also possible. For example, while the examples discussed above feature one or two layers coating the grating layer, additional layers are also possible. For example, additional layers may be included between the grating layer and the outermost low refractive index layer.

[0261] Although the grating structures of the aforementioned examples are one-dimensional gratings, other embodiments are possible. For example, in some embodiments, the array of structures can also be arranged in two directions to form a two-dimensional (2D) array of diffraction features. The 2D array of diffraction features can include undulations in two directions. In some cases, the undulations can be periodic, while in other cases, the pitch of the undulations can vary in at least one direction. According to various examples described herein, the diffraction features have relative sidewalls that are asymmetrically angled or inclined. According to various examples described herein, the diffraction features can be conical.

[0262] In some embodiments, the diffraction feature may have relative sidewalls that are substantially angled or tilted. In some embodiments, the relative sidewalls may be tilted in the same direction, while in other embodiments, the relative sidewalls may be tilted in opposite directions. In some other embodiments, one of the relative sidewalls of the diffraction feature may be substantially tilted, while the other sidewall of the sidewall is substantially perpendicular or orthogonal to the horizontal axis or at least less tilted than the other sidewall. In various examples of 2D diffraction features described herein, the 2D diffraction feature may be formed in or on an underlying substrate, which may be a waveguide, as described above for various examples of one-dimensional diffraction features. For example, the 2D diffraction feature may be etched into the underlying substrate, or formed by patterning a separate layer formed thereon. Therefore, the 2D diffraction feature may be formed by a material that is the same as or different from the substrate material in a manner similar to the various 2D diffraction features described above. Other variations and configurations are also possible.

[0263] Thus, any structure or device described herein, such as a grating structure, may include a one-dimensional grating. Similarly, any structure or device described herein, such as a grating structure, may also include a 2D grating. Such a 2D grating may scatter light. These gratings may also include a blazed grating. Such a blazed grating may preferably direct light into certain directions. In some embodiments, a 2D grating (e.g., having one tilted facet on a diffraction feature) preferably directs light into one direction, while in other embodiments, a 2D grating (e.g., having two tilted facets on a diffraction feature that are different) preferably directs light into multiple directions. Similarly, any method or process described herein may be used for a 1D grating. Similarly, any method or process described herein may be used for a 2D grating. These 1D or 2D gratings may be included in or on a substrate and / or waveguide, and may be included in an eyepiece, and may also be integrated into a head-mounted display disclosed herein. These gratings can be used as input gratings (e.g. ICG), output gratings (EPE), light distribution gratings (OPE), or combined light distribution grating / output gratings (e.g. CPE). For example, an output coupling grating is Fig. 9Cand 10A Alternatively, or in addition, such a grating may be used in an orthogonal pupil expander (e.g. Fig. 9C 730, 740, 750 in FIG. 1 ). Such geometries can be similarly optimized for polarization insensitive output couplers and improve transparency of the display in the area in front of the user's eyes, thereby reducing back reflections that can be a problem when the diffractive face relief grating is used as a wearable waveguide.

[0264] Other embodiments are described in the following claims.

Claims

1. A head mounted display system comprising: 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 light coupled into the waveguide from the light projection system; a grating structure optically coupled to the waveguide, the grating structure being configured to couple light from the light projection system into the waveguide, the grating structure comprising: a grating layer, the grating layer comprising a grating, the grating comprising a plurality of ridges having a blaze profile in at least one cross section, the blaze profile comprising a reverse blaze angle of 89° or less; as well as One or more additional layers are disposed on the grating layer, the one or more layers including a first layer of a material having a refractive index of 1.5 or less at an operating wavelength of the head mounted display, the first layer being an outermost layer of the grating structure.

2. The head mounted display system according to claim 1, wherein: The blaze profile has a blaze angle of 95° or greater.

3. The head mounted display system according to claim 1 or 2, wherein: The ridge has a profile shape selected from the group consisting of a trapezoid, a parallelogram, a triangle, and a step shape.

4. A head mounted display system according to any one of the preceding claims, wherein: The anti-blaze angle is in the range from 1° to 89°.

5. A head mounted display system according to any one of the preceding claims, wherein: The ridges have a height in the range from 10 nm to 1000 nm.

6. A head mounted display according to any one of the preceding claims, wherein: The grating has a pitch in the range from 100 nm to 5000 nm.

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

8. A head mounted display according to any one of the preceding claims, wherein: The first layer has a thickness in the range from 5 nm to 500 nm.

9. A head mounted display according to any one of the preceding claims, wherein: The one or more additional layers include a second layer located between the first layer and the grating layer, the second layer including a second material having a refractive index greater than 1.5 at an operating wavelength.

10. The head mounted display according to claim 9, wherein: The second layer has a thickness in the range from 5 nm to 500 nm.

11. A head mounted display according to any one of the preceding claims, wherein: The grating layer includes a grating material having a refractive index of 1.5 or higher at an operating wavelength.

12. A head mounted display according to any one of the preceding claims, wherein: The grating material includes a cross-linked polymer.

13. The head mounted display according to claim 12, wherein: The grating material includes nanoparticles.

14. A head mounted display according to any one of the preceding claims, wherein: The grating structure is at least partially transmissive at an operating wavelength.

15. A head mounted display according to any one of the preceding claims, wherein: The grating structure is configured to couple light into the waveguide at an operating wavelength corresponding to a plurality of different color pixels of the light projection system during operation.

16. A head mounted display according to any one of the preceding claims, wherein: The grating layer and the waveguide include the same material.

17. The head mounted display according to claim 16, wherein: The material comprises a polymer.

18. The head mounted display according to claim 16, wherein: The material has a refractive index of 1.7 or higher.

19. The head mounted display according to claim 16, wherein: The material is a composite material.

20. The head mounted display according to claim 19, wherein: The composite material includes nanoparticles.

21. A head mounted display according to any one of the preceding claims, wherein: The light from the light projection system is unpolarized light or polarized light.

22. A head mounted display according to any preceding claim, wherein: The light projection system includes a microLED display, an LCoS display, or a laser beam scanner display.

23. The head-mounted display system of claim 1 , further comprising a second grating structure, the second grating structure being located on a side of the waveguide opposite to the first grating structure, the second grating structure being optically coupled to the waveguide and comprising a second grating layer, the second grating layer comprising a second grating, the second grating comprising a plurality of ridges having a blaze profile in at least one cross section, the blaze profile comprising an anti-blaze angle of 89° or less.

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

25. The head mounted display according to claim 24, wherein: The grating structure of each of the waveguides is arranged in a tandem configuration.

26. The head mounted display according to claim 25, wherein: At least one of the grating structures is a reflective grating.

27. The head mounted display according to claim 26, wherein: The reflection grating is the grating structure of the waveguide that is farthest from the light projection system.

28. A head mounted display according to any preceding claim, wherein: At least some of the ridges have a single-order geometry.

29. A head mounted display according to any preceding claim, wherein: At least some of the ridges have a multi-step geometry.

30. An article comprising: a waveguide layer comprising a waveguide material having a refractive index of 1.7 or greater at an operating wavelength; A grating structure is provided at a surface of the waveguide layer, the grating structure comprising: a grating layer, the grating layer comprising a grating, the grating comprising a plurality of ridges having a blaze profile in at least one cross section, the blaze profile comprising a reverse blaze angle of 85° or less, a height in a range from 10 nm to 1,000 nm, and a duty cycle in a range from 5% to 95%; as well as One or more additional layers are disposed on the grating layer, the one or more layers comprising a first layer of a material having a thickness in the range from 5 nm to 500 nm and a refractive index of 1.5 or less at an operating wavelength, the first layer being the outermost layer of the grating structure.

31. A head mounted display system, comprising: 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 light coupled into the waveguide from the light projection system; a grating structure optically coupled to the waveguide, the grating structure being configured to couple light guided by the waveguide out of the waveguide, the grating structure comprising: a grating layer, the grating layer comprising a grating, the grating comprising a plurality of ridges having a blaze profile in at least one cross section, the blaze profile comprising a reverse blaze angle of 89° or less; as well as one or more additional layers disposed on said grating layer, The one or more layers include a first layer of a material having a refractive index of 1.5 or less at an operating wavelength of the head mounted display, The first layer is the outermost layer of the grating structure.

32. An apparatus comprising: a waveguide for guiding light at an operating wavelength; a grating layer supported by the waveguide, the grating layer comprising a plurality of spaced-apart ridges of grating material forming a grating, the plurality of spaced-apart ridges having a blazed profile in at least one cross-section, each ridge having a blazed side and an anti-blazed side opposite the blazed side, the anti-blazed side having a concave cross-sectional shape; as well as One or more additional layers supported by the grating layer, the one or more additional layers comprising a first layer comprising a first material different from the grating material, the first material being located on and between the ridges.

33. An apparatus comprising: a waveguide for guiding light at an operating wavelength; a grating layer extending in a plane, the grating layer being supported by the waveguide and comprising a plurality of spaced-apart ridges of grating material forming a grating, the plurality of spaced-apart ridges having a blaze profile in at least one cross section, each ridge having a blaze side and an anti-blaze side opposite the blaze side, wherein the anti-blaze side has a nonlinear shape in the cross section, and a vertex of the anti-blaze side is aligned with a base point of the anti-blaze side in a direction normal to the plane of the grating layer in the cross section; as well as One or more additional layers supported by the grating layer, the one or more additional layers comprising a first layer comprising a first material different from the grating material, the first material being located on and between the ridges.

34. An apparatus comprising: a waveguide for guiding light at an operating wavelength; a grating layer supported by the waveguide, the grating layer comprising a plurality of spaced-apart ridges of grating material forming a grating, the plurality of spaced-apart ridges having a blazed profile in at least one cross-section, each ridge having a blazed side and an anti-blazed side opposite the blazed side; as well as one or more additional layers supported by the grating layer, the one or more additional layers comprising a first layer, the first layer comprising a first material different from the grating material, the first material being located on and between the ridges, Wherein, for at least some of the ridges, the ridge and the one or more additional layers form an air gap on an anti-blaze side of the ridge.

35. The device according to claim 32, wherein: The concave cross-sectional shape of the anti-blaze side includes a curved portion.

36. The device according to claim 33 or 34, wherein: The anti-glare side includes a curved portion.

37. The device according to claim 34 or 35, wherein: The curvature radius of the curved portion is in the range from 20 nm to 500 nm.

38. The device according to any one of claims 32 or 35, wherein The concave cross-sectional shape of the anti-blaze side includes one or more line segments.

39. The device according to any one of claims 33, 34 and 36, wherein: The anti-flare side includes one or more line segments.

40. The device according to claim 38 or 39, wherein: The first line segment has a positive slope, the second line segment has a negative slope, and the first line segment is vertically higher than the second line segment.

41. The device according to any one of claims 37 to 39, wherein: At least two of the one or more line segments intersect at an obtuse angle.

42. The device according to any one of claims 37 to 40, wherein: A length of at least one of the line segments is in the range of 5 nm to 500 nm.

43. The device according to any one of claims 32 and 33, wherein: An edge of at least one of the one or more additional layers and the anti-glare side define an air gap.

44. The device according to any one of claims 32 to 42, wherein: The first of the one or more additional layers has a refractive index of at least 1.5 at the operating wavelength.

45. The device according to any one of claims 32 to 43, wherein: The one or more additional layers include a second layer, and the second layer has a refractive index of at least 1.5 at the operating wavelength.

46. ​​The device according to any one of claims 32 to 44, wherein: The one or more additional layers do not coat the anti-blaze side of each ridge.

47. The device according to any one of claims 32 to 45, wherein: Each ridge has a blaze angle of 95° or more.

48. The device according to any one of claims 32 to 46, wherein: Each ridge has a back blaze angle ranging from 1° to 89°.

49. The device according to any one of claims 32 to 47, wherein: The ridges have a height in the range from 10 nm to 1000 nm.

50. The device according to any one of claims 32 to 48, wherein: The grating has a pitch in the range from 100 nm to 5000 nm.

51. The device according to any one of claims 32 to 49, wherein: The grating has a duty cycle in the range from 5% to 95%.

52. The device according to any one of claims 32 to 50, wherein: The first layer has a thickness in the range from 5 nm to 500 nm.

53. The apparatus of claim 44, wherein: The second layer has a thickness in the range from 5 nm to 500 nm.

54. The device according to any one of claims 32 to 52, wherein: The grating material includes a cross-linked polymer.

55. The apparatus of claim 53, wherein: The grating material includes nanoparticles.

56. The device according to any one of claims 32 to 54, wherein: The grating structure is at least partially transmissive at the operating wavelength.

57. The device according to any one of claims 32 to 55, wherein: The grating layer and the waveguide comprise the same material.

58. The apparatus of claim 56, wherein: The material comprises a polymer.

59. The apparatus of claim 56, wherein: The material has a refractive index of 1.7 or higher.

60. The apparatus of claim 56, wherein: The material is a composite material.

61. The apparatus of claim 59, wherein: The composite material includes nanoparticles.

62. The apparatus of any one of claims 32-60, further comprising one or more additional waveguides and one or more additional grating structures, each additional grating structure being associated with a respective one of the additional waveguides.

63. The apparatus of claim 61, wherein: The grating structure of each of the waveguides is arranged in a tandem configuration.

64. The apparatus of claim 62, wherein: The at least one grating structure is a reflection grating.

65. The device according to any one of claims 32 to 62, wherein: At least some of the ridges include a blazed side having a single-step geometry.

66. The device according to any one of claims 32 to 63, wherein: At least some of the ridges include a blazed side having a multi-step geometry.

67. A head mounted display (HMD) configured to be worn on a user's head, the HMD comprising: frame; a pair of optical elements supported by the frame so that each of the pair of optical elements can be positioned in front of an eye of the user; The device according to any one of claims 32 to 65, wherein the device is disposed on at least one optical element of the pair of optical elements; and A projection system is configured to project light into the waveguide of the device for display to the user's eyes.

68. The HMD of claim 66, wherein: Each optical element comprises a distal surface and a proximal surface, wherein the proximal surface is closer to the user's eye than the distal surface, and the grating of the device is arranged on the proximal surface.

69. The HMD of claim 66, wherein: Each optical element comprises a distal surface and a proximal surface, wherein the proximal surface is closer to the user's eye than the distal surface, and the grating of the device is disposed on the distal surface.

70. The HMD according to any one of claims 66-68, wherein: The grating structure is configured to couple light at an operating wavelength corresponding to a plurality of different color pixels into the waveguide during operation of the HMD.

71. The HMD of any one of claims 66-69, wherein: The light from the light projection system is unpolarized light.

72. The HMD of any one of claims 66-70, wherein: The light projection system includes a microLED display, an LCoS display, or a laser beam scanner display.

73. The HMD of any one of claims 66-71, wherein: The device comprises one or more additional grating structures, wherein the grating structure farthest from the light projection system is a reflective grating.

74. A method comprising: depositing an etch stop layer on the substrate; depositing a grating material on the etch stop layer; depositing a blazed grating template on the grating material; Using the blazed grating template, etching the grating material, thereby transferring the shape of the blazed grating template to the grating material and forming a blazed grating; coating the blazed grating with an etch mask at a first non-zero angle relative to vertical such that an anti-blazed side of the grating remains uncoated; etching at a second non-zero angle relative to perpendicular and having a sign opposite to the sign of the first non-zero angle to remove an inner portion of the anti-flare side; as well as The etching mask is stripped from the blazed grating.

75. The method of claim 73, wherein: The substrate is a waveguide.

76. The method of claim 73 or 74, wherein: The shape of the blazed grating template extends vertically beyond the shape of the blazed grating.

77. The method of any one of claims 73-75, wherein: The etching of the grating material is completed before the blazed grating template is fully used.

78. The method of claim 75, further comprising: Prior to coating the blazed grating with the etch mask, the remaining portion of the blazed grating template is stripped from the grating material.

79. The method of any one of claims 73-77, wherein: Etching the grating material includes at least one of dry plasma etching, chemical etching, and wet chemical etching.

80. The method of any one of claims 73-78, wherein: The first non-zero angle is determined by the anti-blaze angle of the blazed grating.

81. The method of claim 79, wherein: The absolute value of the first non-zero angle is at least equal to the difference between the anti-blaze angle and 90°.

82. The method of any one of claims 73-80, wherein: The anti-blaze side includes a concave curvature.

83. The method of any one of claims 73-81, wherein: The blazed side includes one or more line segments.

84. The method of any one of claims 73-82, further comprising: The blazed grating is coated with one or more additional layers, wherein at least one of the one or more additional layers comprises a material having a refractive index of at least 1.5 at an operating wavelength.

85. The method of claim 83, wherein: Coating the blazed grating with the one or more additional layers results in the formation of an air gap between an edge of at least one of the one or additional layers and the anti-blaze side.

86. A head mounted display (HMD) comprising: a waveguide for guiding light at an operating wavelength; as well as A grating structure comprising: a grating layer supported by the waveguide, the grating layer comprising a plurality of spaced-apart ridges of grating material forming a grating, the plurality of spaced-apart ridges having a blazed profile in at least one cross-section, each ridge having a blazed side and an anti-blazed side opposite the blazed side, the anti-blazed side having a concave cross-sectional shape; as well as One or more additional layers supported by the grating layer, the one or more additional layers comprising a first layer comprising a first material different from the grating material, the first material being located on and between the ridges.

87. The HMD of claim 85, wherein: The diffraction efficiency of the grating structure is 10% or more for non-polarized light with a wavelength ranging from 400 nm to 700 nm incident within an incident angle range from -20° to +20°.

88. The HMD of claim 85 or 86, wherein: The back reflectivity of the grating structure is 30% or less for unpolarized light with a wavelength ranging from 400 nm to 700 nm incident within an incident angle range from -20° to +20°.

89. The HMD of any one of claims 85-87, further comprising a projection system, and during operation, the grating structure receives unpolarized light or polarized light from the projection system.

90. The HMD of any one of claims 88, wherein: The grating structure is positioned to receive light from the projection system, the light passing through the waveguide before being coupled into the waveguide by the grating structure.

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