Refractive Index Modification in Holographic Gratings

Abstract

The technology disclosed herein relates to modifying the refractive index modulation in a holographic optical element, such as a holographic grating. According to certain embodiments, the holographic optical element or apodization grating includes a polymer layer including a first region characterized by a first refractive index and a second region characterized by a second refractive index. The holographic optical element or apodization grating includes a plurality of nanoparticles dispersed in the polymer layer. The nanoparticles have a higher concentration in the first region or the second region. In some embodiments, the nanoparticles can be configured to increase the refractive index modulation. In some embodiments, the nanoparticles can be configured to apodize the grating by reducing the refractive index modulation near the sides of the grating. The refractive index can be modulated by applying a monomer storage buffer layer to the polymer layer before or after the hologram is manufactured.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Application No. 16 / 550,046, filed on August 23, 2019, the contents of which are incorporated herein by reference in their entirety for all purposes.

[0003] background

[0004] Artificial reality systems such as head-mounted displays (HMDs) or heads-up display (HUD) systems typically include a near-eye display system in the form of a head-mounted device (headset) or a pair of glasses and are configured to present content to a user via an electronic or optical display, for example, within about 10-20 mm in front of the user's eyes. As in virtual reality (VR) applications, augmented reality (AR) applications, or mixed reality (MR) applications, the near-eye display system can display virtual objects or combine images of real objects with virtual objects. For example, in an AR system, a user can view both images of virtual objects (e.g., computer-generated images (CGI)) and the surrounding environment by, for example, looking through transparent display glasses or lenses (commonly referred to as optical see-through).

[0005] One example of an optical see-through AR system may use a waveguide-based optical display, where light for a projected image may be coupled into a waveguide (e.g., a transparent substrate), propagated within the waveguide, and coupled out of the waveguide at different locations. In some embodiments, a diffractive optical element (such as a holographic grating) may be used to couple light for a projected image into or out of the waveguide. In some embodiments, an artificial reality system may employ an eye tracking subsystem that may track the user's eyes (e.g., gaze direction) to modify or generate content based on the direction the user is looking, thereby providing the user with a more immersive experience. The eye tracking subsystem may be implemented using various optical components such as holographic optical elements.

[0006] Overview

[0007] The present disclosure generally relates to holographic optical elements. According to some embodiments, the holographic grating may include a polymer layer. The polymer layer includes a first region characterized by a first refractive index, a second region characterized by a second refractive index, the second refractive index being higher than the first refractive index, and a plurality of nanoparticles dispersed in the polymer layer, the nanoparticles having a higher concentration in the first region or the second region.

[0008] According to some embodiments, in the holographic grating, the nanoparticles are monomers. In some embodiments, the nanoparticles have a higher concentration in the second region and the nanoparticles have a third refractive index higher than the second refractive index. In some embodiments, the nanoparticles have a higher concentration in the first region and the nanoparticles have a third refractive index lower than the first refractive index. In some embodiments, the nanoparticles in the first region or the second region have a substantially constant concentration relative to the thickness of the polymer layer. In some embodiments, the polymer layer comprises a multiplexed volume Bragg grating.

[0009] According to some embodiments, the grating includes a polymer layer. The polymer layer includes a first region characterized by a first refractive index, a second region characterized by a second refractive index, the second refractive index being higher than the first refractive index, and a plurality of nanoparticles dispersed in the polymer layer, the nanoparticles having a higher concentration near a surface of the polymer layer in one or more of the first region or the second region, such that the refractive index modulation of the grating is apodized.

[0010] According to certain embodiments, in the grating, the nanoparticles are monomers. In some embodiments, the nanoparticles have a higher concentration in the first region and the nanoparticles have a third refractive index higher than the first refractive index. In some embodiments, the nanoparticles have a higher concentration in the second region and the nanoparticles have a third refractive index lower than the second refractive index. In some embodiments, the polymer layer includes a multiplexed volume Bragg grating.

[0011] According to some embodiments, the holographic grating may include a polymer matrix. The polymer matrix includes a first region characterized by a first refractive index and a second region characterized by a second refractive index, the second refractive index being higher than the first refractive index. The holographic grating also includes a resin layer disposed on the polymer matrix, the resin layer including a support layer and a first plurality of nanoparticles dispersed in the support layer of the resin layer.

[0012] According to certain embodiments, in the holographic grating, the nanoparticles are monomers. In some embodiments, the polymer matrix further comprises a second plurality of nanoparticles, the concentration of the second plurality of nanoparticles in the second region is higher than the concentration in the first region, and the second plurality of nanoparticles have a third refractive index higher than the second refractive index. In some embodiments, the polymer matrix further comprises a second plurality of nanoparticles, the concentration of the second plurality of nanoparticles in the first region is higher than the concentration in the second region, and the second plurality of nanoparticles have a third refractive index lower than the first refractive index. In some embodiments, the nanoparticles in a given region have a substantially constant concentration relative to the thickness of the polymer matrix. In some embodiments, the polymer matrix comprises a multiplexed volume Bragg grating.

[0013] According to some embodiments, the holographic grating may be manufactured by the following process. A holographic recording material layer is obtained. The holographic recording material layer is exposed to a recording light pattern, and the recording light pattern generates a first region having a first refractive index and a second region having a second refractive index in the holographic recording material layer, the second refractive index being higher than the first refractive index. After the holographic recording material layer is exposed to the recording light pattern, a first resin layer containing a first plurality of nanoparticles is applied to the holographic recording material layer, so that at least a portion of the first plurality of nanoparticles diffuses into the holographic recording material layer.

[0014] According to certain embodiments, in the manufactured holographic grating, the first plurality of nanoparticles has a third refractive index higher than the second refractive index, and the first plurality of nanoparticles diffuse preferentially into the second region. In some embodiments, the first plurality of nanoparticles has a third refractive index lower than the second refractive index, and the first plurality of nanoparticles diffuse preferentially, thereby being more highly concentrated near one or more of the top side or bottom side of the second region. In some embodiments, the first plurality of nanoparticles has a third refractive index lower than the first refractive index, and the first plurality of nanoparticles diffuse preferentially into the first region. In some embodiments, the first plurality of nanoparticles has a third refractive index higher than the first refractive index; and the first plurality of nanoparticles diffuse further, thereby being more highly concentrated near one or more of the top side or bottom side of the first region. In some embodiments, the steps further include removing the first resin layer and disposing the substrate on the holographic recording material layer. In some embodiments, the steps further include applying a second resin layer containing a second plurality of nanoparticles to the holographic recording material layer, thereby causing at least a portion of the second plurality of nanoparticles to diffuse into the holographic recording material layer. In some embodiments, the nanoparticles in a given region have a substantially constant concentration relative to the thickness of the holographic recording material layer.

[0015] According to some embodiments, the holographic grating can be manufactured by the following process. A holographic recording material layer is obtained. A first resin layer containing a first plurality of nanoparticles is applied to the holographic recording material layer. After applying the first resin layer, the holographic recording material layer is exposed to a recording light pattern, which generates a first region having a first refractive index and a second region having a second refractive index in the holographic recording material layer, the second refractive index being higher than the first refractive index, wherein at least a portion of the first plurality of nanoparticles diffuses from the first resin layer into the holographic recording material layer.

[0016] According to certain embodiments, in the manufactured holographic grating, the first plurality of nanoparticles has a third refractive index higher than the second refractive index, and the first plurality of nanoparticles diffuse preferentially into the second region. In some embodiments, the first plurality of nanoparticles has a third refractive index lower than the second refractive index, and the first plurality of nanoparticles diffuse so as to be more highly concentrated near the top side or bottom side of the second region. In some embodiments, the first plurality of nanoparticles has a third refractive index lower than the first refractive index, and the first plurality of nanoparticles diffuse preferentially into the first region. In some embodiments, the first plurality of nanoparticles has a third refractive index higher than the first refractive index, and the first plurality of nanoparticles diffuse so as to be more highly concentrated near the top side or bottom side of the first region. In some embodiments, the steps further include applying a second resin layer containing the second plurality of nanoparticles to the holographic recording material layer, thereby causing at least a portion of the second plurality of nanoparticles to diffuse into the holographic recording material layer. In some embodiments, the nanoparticles in a given region have a substantially constant concentration relative to the thickness of the holographic recording material layer.

[0017] This summary is neither intended to identify key or essential features of the claimed subject matter nor to be used in isolation to determine the scope of the claimed subject matter. The subject matter should be understood with reference to appropriate portions of the entire specification of the disclosure, any or all of the drawings, and each claim. The foregoing and other features and examples will be described in more detail below in the following description, claims, and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Illustrative embodiments are described in detail below with reference to the following drawings.

[0020] Figure 1 is a simplified block diagram of an example of an artificial reality system environment including a near-eye display system in accordance with certain embodiments.

[0021] Figure 2 is a perspective view of an example of a near-eye display system in the form of a head-mounted display (HMD) device for implementing some examples disclosed herein.

[0022] Figure 3 is a perspective view of an example of a near-eye display system in the form of a pair of glasses for implementing some of the examples disclosed herein.

[0023] Figure 4 An example of an optical see-through augmented reality system using a waveguide display including an optical combiner is shown in accordance with certain embodiments.

[0024] Figure 5A An example of a volume Bragg grating (VBG) is shown. Figure 5B Shows Figure 5AThe Bragg condition of a volume Bragg grating is shown.

[0025] Figure 6 An example of a holographic recording material including a two-stage photopolymer is shown.

[0026] Fig. 7A A recording beam used to record a volume Bragg grating and a beam reconstructed from the volume Bragg grating are shown.

[0027] Figure 7B is an example of a holographic momentum diagram showing the wave vectors of the recording and reconstruction beams and the grating vector of the recorded volume Bragg grating.

[0028] Figure 8 An example of a holographic recording system for recording a holographic optical element is shown.

[0029] Fig. 9 An example of a grating comprising multiple regions of different refractive indices is shown.

[0030] Figure 10A-10B An example of modifying the refractive index modulation in a holographic grating is shown.

[0031] Figures 11A-11C Example techniques for modifying the refractive index modulation in a holographic grating are shown.

[0032] Figures 12A-12D An example of a refractive index modulation modification according to some embodiments is shown.

[0033] Figure 13A-13B Variations of refractive index modulation modifications in a grating are shown according to some embodiments.

[0034] Fig.14 A grating with tapered refractive index modification is shown.

[0035] Figure 15A-15B An example of a refractive index modulation profile in an apodized grating is shown.

[0036] Figure 16A-16B Sidelobe reduction using apodization gratings according to some embodiments is shown.

[0037] Fig.17 is a simplified flow chart illustrating an example of a method of manufacturing a holographic optical element according to some embodiments.

[0038] Fig.18 is a schematic diagram illustrating another method for manufacturing a holographic optical element according to some embodiments.

[0039] Fig.19is a simplified block diagram of an example of an electronic system for implementing some of the example near-eye display systems (e.g., HMD devices) disclosed herein, in accordance with certain embodiments.

[0040] The accompanying drawings depict embodiments of the present disclosure for purposes of illustration only. Those skilled in the art will readily recognize from the following description that alternative embodiments of the illustrated structures and methods may be employed without departing from the principles or benefits of the present disclosure.

[0041] In the drawings, similar components and / or features may have the same reference number. In addition, various components of the same type may be distinguished by following the reference number with a dash and a second reference that distinguishes between the similar components. If only the first reference number is used in the specification, the description applies to any one of the similar components having the same first reference number, regardless of the second reference number.

[0042] Detailed Description

[0043] The technology disclosed herein generally relates to holographic optical elements. More specifically, but not limited thereto, the present disclosure relates to modifying the refractive index of a recorded holographic optical element (HOE) to enhance the refractive index modulation or to apodize the recorded holographic optical element so as to improve the diffraction efficiency and / or the contrast of a displayed image by, for example, increasing the number of gratings in a multiplexed grating and reducing the side lobes of the gratings (and thus reducing the crosstalk between gratings in the multiplexed gratings). Various inventive embodiments are described herein, including materials, systems, modules, devices, components, methods, compositions, etc.

[0044] In various optical systems, such as artificial reality systems including virtual reality, augmented reality (AR), and mixed reality (MR) systems, in order to improve the performance of the optical system, such as improving the brightness of the displayed image, expanding the eyebox, reducing artifacts, increasing the field of view, and improving the user's interaction with the presented content, various holographic optical elements can be used for beam coupling and shaping, such as coupling light into or out of a waveguide display, or tracking the movement of the user's eyes. These holographic optical elements may need to have high refractive index modulation, small pitch or feature size, high definition, high diffraction efficiency, etc.

[0045] The diffraction efficiency of a holographic optical element is related to the difference in refractive index in different areas of the grating. Given the relatively small range of refractive index modulation available in materials suitable for recording holographic gratings, there are limits to the diffraction efficiency that can be achieved using traditional methods. Another limitation of these gratings is the sidelobes in the diffraction pattern, which can affect image quality. In the case of multiplexed gratings, the sidelobes of one grating may overlap with the mainlobes of other gratings, resulting in crosstalk. To reduce crosstalk, one option is to reduce the number of multiplexed gratings, which is undesirable in many applications. The techniques described in this article can be used to increase the refractive index modulation in the HOE to increase the diffraction efficiency, and / or to apodize the gratings to eliminate or reduce sidelobes / crosstalk, without limiting the number of gratings that can be multiplexed in a layer of holographic material.

[0046] According to some embodiments, before or after holographic recording in the photopolymer layer, a resin material layer may be formed on the photopolymer layer, the resin material layer including a support matrix and monomers (or other nanoparticles) dispersed in the support matrix, such as a monomer storage buffer layer. Depending on, for example, the size of the monomers in the recorded holographic optical element and the affinity between the monomers and the polymer, the monomers in the resin material layer may diffuse more preferentially to the high refractive index region of the HOE rather than the low refractive index region of the HOE, or diffuse more preferentially to the low refractive index region rather than the high refractive index region. In this way, the refractive index in the high refractive index region (or low refractive index region) may change more than the low refractive index region (or high refractive index region). These changes may include increasing the refractive index in the diffusion region if the refractive index of the monomers in the resin material layer is higher than the refractive index in the diffusion region, or decreasing the refractive index in the diffusion region if the refractive index of the monomers in the resin material layer is lower than the refractive index in the diffusion region. Therefore, the refractive index may be selectively increased or decreased in different regions to increase or decrease the refractive index modulation.

[0047] In some embodiments, the refractive index in the low refractive index region of the HOE can be reduced by preferentially diffusing lower refractive index monomers into the low refractive index region. In some embodiments, the refractive index in the high refractive index region of the HOE can be increased by preferentially diffusing higher refractive index monomers into the high refractive index region. In some embodiments, the refractive index in both the high and low refractive index regions of the HOE can be increased, but the refractive index in the high refractive index region of the HOE can be increased more due to the preferential diffusion of higher refractive index monomers. In some embodiments, the refractive index in both the high and low refractive index regions of the HOE can be reduced, but the refractive index in the low refractive index region of the HOE can be reduced more due to the preferential diffusion of lower refractive index monomers. Therefore, the refractive index modulation of the HOE can be increased to improve the diffraction efficiency and / or multiplex more gratings in the photopolymer material layer.

[0048] In some embodiments, the resin material layer may include a lower concentration of monomers, or the diffusion may be controlled to occur in a limited time, and thus the monomers may not diffuse through the entire depth of the HOE. As a result, the HOE may have different refractive index modulations at different depths. For example, the monomers in the resin material layer may have a lower refractive index and may diffuse more preferentially through a specific thickness of the HOE into a high refractive index region, so that the refractive index modulation may taper in the thickness direction from the center of the HOE. In some embodiments, a resin material layer including a supporting matrix and a monomer may be formed on opposite sides of the photopolymer layer, so that the refractive index modulation may taper in the thickness direction from the center of the HOE to the opposite side, forming a bell-shaped refractive index modulation distribution. Therefore, the HOE can be apodized to reduce the side lobes in the diffraction efficiency curve, and thereby reduce the crosstalk between gratings in the multiplexed grating.

[0049] In some embodiments, a resin material layer including a supporting matrix and monomers (or other nanoparticles) dispersed in the supporting matrix can be formed after the HOE is recorded and the cover layer is removed, and may or may not remain in the final device after the monomers in the resin material layer diffuse. In some embodiments, a resin material layer (e.g., a monomer storage buffer layer) can be formed on the photopolymer layer before holographic recording, and may or may not remain in the final device. For example, the supporting matrix of the monomer storage buffer layer can be similar to a substrate, and may remain in the final device after the monomers diffuse into the HOE.

[0050] As used herein, visible light can refer to light with a wavelength between about 380nm and about 750nm, about 400nm and about 700nm, or about 440nm and about 650nm. Near infrared (NIR) light can refer to light with a wavelength between about 750nm and about 2500nm. Desired infrared (IR) wavelength range can refer to the wavelength range of IR light that can be detected by a suitable IR sensor (e.g., complementary metal oxide semiconductor (CMOS), charge coupled device (CCD) sensor, or InGaAs sensor), such as between 830nm and 860nm, between 930nm and 980nm, or between about 750nm and about 1000nm.

[0051] Also as used herein, a substrate may refer to a medium in which light can propagate. The substrate may include one or more types of dielectric materials, such as glass, quartz, plastic, polymer, polymethyl methacrylate (PMMA), crystal, or ceramic. At least one type of substrate material may be transparent to visible light and NIR light. The thickness of the substrate may range, for example, from less than about 1 mm to about 10 mm or more. As used herein, a material may be "transparent" to a light beam if the light beam can pass through the material with a high transmittance (such as greater than 60%, 75%, 80%, 90%, 95%, 98%, 99% or more), wherein a small portion of the light beam (e.g., less than 40%, 25%, 20%, 10%, 5%, 2%, 1% or less) may be scattered, reflected, or absorbed by the material. The transmittance (i.e., transmissivity) may be represented by a photopic weighted average transmittance or an unweighted average transmittance within a wavelength range, or by the minimum transmittance within a wavelength range (such as a visible wavelength range).

[0052] Also as used herein, the term "support matrix" refers to a material, medium, substrate, etc. in which the polymerizable component is dissolved, dispersed, embedded, encapsulated, etc. In some embodiments, the support matrix is ​​typically a low T g Polymer. The polymer may be organic, inorganic or a mixture of the two. In the absence of particular limitations, the polymer may be thermosetting or thermoplastic.

[0053] Also as used herein, the term "polymerizable component" refers to one or more photoactive polymerizable materials, and possibly one or more additional polymerizable materials, such as monomers and / or oligomers, that are capable of forming a polymer.

[0054] Also as used herein, the term "photoactive polymerizable material" refers to monomers, oligomers, and combinations thereof that polymerize in the presence of a photoinitiator that has been activated by exposure to a photoinitiating light source (e.g., recording light). With respect to functional groups that undergo curing, the photoactive polymerizable material comprises at least one such functional group. It is also understood that there are photoactive polymerizable materials that are also photoinitiators, such as N-methylmaleimide, derivatized acetophenone, and the like, and in such cases, it is understood that the photoactive monomers and / or oligomers of the present disclosure may also be photoinitiators.

[0055] Also as used herein, the term "photopolymer" refers to a polymer formed from one or more photoactive polymerizable materials and possibly one or more additional monomers and / or oligomers.

[0056] In the following description, for the purpose of explanation, specific details are set forth in order to provide a thorough understanding of the examples of the present disclosure. However, it will be apparent that various examples can be implemented without these specific details. For example, equipment, systems, structures, assemblies, methods and other components can be shown as components in block diagram form to avoid blurring the examples in unnecessary details. In other cases, well-known equipment, processes, systems, structures and techniques can be shown without necessary details to avoid blurring the examples. The accompanying drawings and descriptions are not intended to be restrictive. The terms and expressions used in the present disclosure are used as descriptive terms rather than restrictive terms, and when using such terms and expressions, it is not intended to exclude any equivalents of the features shown and described or parts thereof. The word "example" is used herein to represent "used as an example, instance or illustration". Any embodiment or design described herein as an "example" is not necessarily interpreted as being more preferred or more advantageous than other embodiments or designs.

[0057] Figure 1 is a simplified block diagram of an example of an artificial reality system environment 100 including a near-eye display system 120 in accordance with some embodiments. Figure 1 The artificial reality system environment 100 shown in FIG. 1 may include a near-eye display system 120, an optional imaging device 150, and an optional input / output interface 140, each of which may be coupled to an optional console 110. Figure 1 An example artificial reality system environment 100 is shown that includes a near-eye display system 120, an imaging device 150, and an input / output interface 140, but any number of these components may be included in the artificial reality system environment 100, or any of these components may be omitted. For example, there may be multiple near-eye display systems 120 that are monitored by one or more external imaging devices 150 that communicate with the console 110. In some configurations, the artificial reality system environment 100 may not include the imaging device 150, the optional input / output interface 140, and the optional console 110. In alternative configurations, different or additional components may be included in the artificial reality system environment 100. In some configurations, the near-eye display system 120 may include an imaging device 150 that can be used to track one or more input / output devices (e.g., the input / output interface 140), such as a handheld controller.

[0058] The near-eye display system 120 may be a head-mounted display that presents content to a user. Examples of content presented by the near-eye display system 120 include one or more of images, videos, audio, or some combination thereof. In some embodiments, the audio may be presented via an external device (e.g., a speaker and / or a headset) that receives audio information from the near-eye display system 120, the console 110, or both, and presents audio data based on the audio information. The near-eye display system 120 may include one or more rigid bodies that may be rigidly or non-rigidly coupled to each other. The rigid coupling between the rigid bodies may enable the coupled rigid bodies to act as a single rigid entity. The non-rigid coupling between the rigid bodies may allow the rigid bodies to move relative to each other. In various embodiments, the near-eye display system 120 may be implemented in any suitable form factor, including a pair of glasses. Some embodiments of the near-eye display system 120 are further described below. Additionally, in various embodiments, the functionality described herein may be used in a head-mounted device that combines an image of an environment external to the near-eye display system 120 and artificial reality content (e.g., a computer-generated image). Thus, the near-eye display system 120 may augment images of a physical, real-world environment external to the near-eye display system 120 with generated content (e.g., images, video, sound, etc.) to present an augmented reality to the user.

[0059] In various embodiments, the near eye display system 120 may include one or more of display electronics 122, display optics 124, and an eye tracking system 130. In some embodiments, the near eye display system 120 may also include one or more positioners 126, one or more position sensors 128, and an inertial measurement unit (IMU) 132. In various embodiments, the near eye display system 120 may omit any of these elements, or may include additional elements. Additionally, in some embodiments, the near eye display system 120 may include a combination of Figure 1 The functions of the various components are described in detail.

[0060] The display electronics 122 may display an image to a user or facilitate the display of an image based on data received from, for example, the console 110. In various embodiments, the display electronics 122 may include one or more display panels, such as a liquid crystal display (LCD), an organic light emitting diode (OLED) display, an inorganic light emitting diode (ILED) display, a micro light emitting diode (μLED) display, an active matrix OLED display (AMOLED), a transparent OLED display (TOLED), or some other display. For example, in one embodiment of the near-eye display system 120, the display electronics 122 may include a front TOLED panel, a rear display panel, and optical components (e.g., an attenuator, a polarizer, or a diffractive or spectral film) between the front display panel and the rear display panel. The display electronics 122 may include pixels that emit light of a predominant color such as red, green, blue, white, or yellow. In some embodiments, the display electronics 122 may display a three-dimensional (3D) image through a stereoscopic effect generated by a two-dimensional panel to create a subjective perception of image depth. For example, the display electronics 122 may include a left display and a right display located in front of the left eye and the right eye of the user, respectively. The left and right displays may present copies of an image that are horizontally offset relative to each other to create a stereoscopic effect (ie, the perception of depth in the image by a user viewing the image).

[0061] In certain embodiments, the display optics 124 may display image content optically (e.g., using optical waveguides and couplers), amplify image light received from the display electronics 122, correct optical errors associated with the image light, and present the corrected image light to a user of the near-eye display system 120. In various embodiments, the display optics 124 may include one or more optical elements, such as, for example, a substrate, an optical waveguide, an aperture, a Fresnel lens, a convex lens, a concave lens, an optical filter, an input / output coupler, or any other suitable optical element that may affect the image light emitted from the display electronics 122. The display optics 124 may include a combination of different optical elements and mechanical couplings for maintaining the relative spacing and orientation of the optical elements in the combination. One or more of the optical elements in the display optics 124 may have an optical coating, such as an anti-reflective coating, a reflective coating, a filter coating, or a combination of different optical coatings.

[0062] The amplification of the image light by the display optics 124 can allow the display electronics 122 to be physically smaller, lighter, and consume less power than a larger display. Additionally, the amplification can increase the field of view of the displayed content. The amplification of the image light by the display optics 124 can be changed by adjusting optical elements, adding optical elements, or removing optical elements from the display optics 124. In some embodiments, the display optics 124 can project the displayed image to one or more image planes that can be farther away from the user's eyes than the near eye display system 120.

[0063] The display optics 124 may also be designed to correct one or more types of optical errors, such as two-dimensional optical errors, three-dimensional optical errors, or a combination thereof. Two-dimensional errors may include optical aberrations that occur in two dimensions. Example types of two-dimensional errors may include barrel distortion, pincushion distortion, longitudinal chromatic aberration, and lateral chromatic aberration. Three-dimensional errors may include optical errors that occur in three dimensions. Example types of three-dimensional errors may include spherical aberration, comatic aberration, field curvature, and astigmatism.

[0064] The locators 126 may be objects located at specific locations on the near-eye display system 120 relative to each other and relative to reference points on the near-eye display system 120. In some embodiments, the console 110 may identify the locators 126 in the images captured by the imaging device 150 to determine the position, orientation, or both of the artificial reality head mounted device. The locators 126 may be light emitting diodes (LEDs), corner cube reflectors, reflective markers, a type of light source that contrasts with the environment in which the near-eye display system 120 operates, or some combination thereof. In embodiments where the locators 126 are active components (e.g., LEDs or other types of light emitting devices), the locators 126 may emit light in the visible light band (e.g., about 380 nm to 750 nm), light in the infrared (IR) band (e.g., about 750 nm to 1 mm), light in the ultraviolet band (e.g., about 10 nm to about 380 nm), light in another portion of the electromagnetic spectrum, or light in any combination of portions of the electromagnetic spectrum.

[0065] The imaging device 150 may be part of the near eye display system 120 or may be external to the near eye display system 120. The imaging device 150 may generate slow calibration data based on calibration parameters received from the console 110. The slow calibration data may include one or more images showing the viewing position of the locators 126, which are detectable by the imaging device 150. The imaging device 150 may include one or more cameras, one or more video cameras, any other device capable of capturing images including one or more locators 126, or some combination thereof. Additionally, the imaging device 150 may include one or more filters (e.g., for improving the signal-to-noise ratio). The imaging device 150 may be configured to detect light emitted or reflected from the locators 126 in the field of view of the imaging device 150. In embodiments where the locators 126 include passive elements (e.g., retroreflectors), the imaging device 150 may include a light source that illuminates some or all of the locators 126, which may reflect light back into the imaging device 150. Slow calibration data may be transmitted from imaging device 150 to console 110, and imaging device 150 may receive one or more calibration parameters from console 110 for adjusting one or more imaging parameters (e.g., focal length, focus, frame rate, sensor temperature, shutter speed, aperture, etc.).

[0066] The position sensor 128 may generate one or more measurement signals in response to the movement of the near-eye display system 120. Examples of the position sensor 128 may include an accelerometer, a gyroscope, a magnetometer, other motion detection or error correction sensors, or some combination thereof. For example, in some embodiments, the position sensor 128 may include multiple accelerometers that measure translational motion (e.g., forward / backward, up / down, or left / right) and multiple gyroscopes that measure rotational motion (e.g., pitch, yaw, or roll). In some embodiments, the individual position sensors may be oriented orthogonally to each other.

[0067] The IMU 132 may be an electronic device that generates fast calibration data based on measurement signals received from one or more position sensors 128. The position sensors 128 may be located external to the IMU 132, internal to the IMU 132, or some combination thereof. Based on one or more measurement signals from the one or more position sensors 128, the IMU 132 may generate fast calibration data that indicates an estimated position of the near-eye display system 120 relative to an initial position of the near-eye display system 120. For example, the IMU 132 may integrate measurement signals received from an accelerometer over time to estimate a velocity vector, and integrate the velocity vector over time to determine an estimated position of a reference point on the near-eye display system 120. Alternatively, the IMU 132 may provide sampled measurement signals to the console 110, which may determine the fast calibration data. Although a reference point may generally be defined as a point in space, in various embodiments, the reference point may also be defined as a point within the near-eye display system 120 (e.g., the center of the IMU 132).

[0068] The eye tracking system 130 may include one or more eye tracking systems. Eye tracking may refer to determining the position of an eye relative to the near-eye display system 120, including the orientation and positioning of the eye. The eye tracking system may include an imaging system that images one or more eyes, and may generally include a light emitter that may generate light directed toward the eye so that light reflected by the eye may be captured by the imaging system. For example, the eye tracking system 130 may include an incoherent light source or a coherent light source (e.g., a laser diode) that emits light in the visible spectrum or infrared spectrum, and a camera that captures light reflected by the user's eye. As another example, the eye tracking system 130 may capture reflected radio waves emitted by a miniature radar unit. The eye tracking system 130 may use a low-power light emitter that emits light at a frequency and intensity that does not harm the eye or cause physical discomfort. The eye tracking system 130 may be arranged to increase the contrast in the eye image captured by the eye tracking system 130 while reducing the total power consumed by the eye tracking system 130 (e.g., reducing the power consumed by the light emitter and imaging system included in the eye tracking system 130). For example, in some implementations, eye tracking system 130 may consume less than 100 milliwatts of power.

[0069] The eye tracking system 130 may be configured to estimate the orientation of the user's eyes. The orientation of the eyes may correspond to the gaze direction of the user within the near-eye display system 120. The orientation of the user's eyes may be defined as the direction of the foveal axis, which is the axis between the fovea (the area on the retina of the eye where the photoreceptors are most concentrated) and the center of the pupil of the eye. Typically, when the user's eyes are fixed on a point, the foveal axis of the user's eyes intersects the point. The pupil axis of the eye may be defined as an axis passing through the center of the pupil and perpendicular to the corneal surface. Typically, even if the pupil axis and the foveal axis intersect at the center of the pupil, the pupil axis may not be directly aligned with the foveal axis. For example, the orientation of the foveal axis may deviate from the pupil axis laterally by about -1° to 8°, and vertically by about ±4° (this may be referred to as the kappa angle, which may vary from person to person). Because the foveal axis is defined based on the fovea located at the back of the eye, in some eye tracking embodiments, the foveal axis may be difficult or impossible to measure directly. Accordingly, in some embodiments, the orientation of the pupil axis can be detected and the foveal axis can be estimated based on the detected pupil axis.

[0070] Typically, the movement of the eye corresponds not only to the angular rotation of the eye, but also to the translation of the eye, the change in the torsion of the eye, and / or the change in the shape of the eye. The eye tracking system 130 may also be configured to detect the translation of the eye, which may be a change in the position of the eye relative to the eye socket. In some embodiments, the translation of the eye may not be detected directly, but may be approximated based on a mapping from the detected angular orientation. The eye translation corresponding to the change in the position of the eye relative to the eye tracking system may also be detected, which is due to, for example, a change in the position of the near-eye display system 120 on the user's head. The eye tracking system 130 may also detect the torsion of the eye and the rotation of the eye around the pupil axis. The eye tracking system 130 may use the detected torsion of the eye to estimate the orientation of the foveal axis relative to the pupil axis. In some embodiments, the eye tracking system 130 may also track changes in the shape of the eye, which may be approximated as a skew or scale linear transformation or a distorted distortion (e.g., due to torsion deformation). In some embodiments, the eye tracking system 130 may estimate the foveal axis based on some combination of the angular orientation of the pupil axis, the translation of the eye, the torsion of the eye, and the current shape of the eye.

[0071] In some embodiments, the eye tracking system 130 may include multiple transmitters or at least one transmitter that can project a structured light pattern on all or a portion of the eye. When viewed from an offset angle, the structured light pattern may be distorted due to the shape of the eye. The eye tracking system 130 may also include at least one camera that can detect the distortion (if any) of the structured light pattern projected onto the eye. The camera may be oriented on an axis to the eye that is different from the transmitter. By detecting the deformation of the structured light pattern on the surface of the eye, the eye tracking system 130 can determine the shape of the portion of the eye illuminated by the structured light pattern. Therefore, the captured distorted light pattern can indicate the 3D shape of the illuminated portion of the eye. Therefore, the orientation of the eye can be derived from the 3D shape of the illuminated portion of the eye. The eye tracking system 130 can also estimate the pupil axis, the translation of the eye, the torsion of the eye, and the current shape of the eye based on the image of the distorted structured light pattern captured by the camera.

[0072] The near-eye display system 120 can use the orientation of the eyes to, for example, determine the user's inter-pupillary distance (IPD), determine gaze direction, introduce depth cues (e.g., blur images outside the user's primary line of sight), collect heuristics about user interactions in VR media (e.g., based on the time spent on any particular subject, object, or frame based on the stimulus experienced), some other function based at least in part on the orientation of at least one of the user's eyes, or some combination thereof. Because the orientation of the user's eyes can be determined, the eye tracking system 130 can determine where the user is looking. For example, determining the direction of the user's gaze can include determining a point of convergence based on the determined orientation of the user's left and right eyes. The convergence point can be the point where the two foveal axes of the user's eyes intersect. The direction of the user's gaze can be the direction of a line passing through the convergence point and the midpoint between the pupils of the user's eyes.

[0073] The input / output interface 140 may be a device that allows a user to send an action request to the console 110. The action request may be a request to perform a specific action. For example, the action request may be to start or end an application, or to perform a specific action within an application. The input / output interface 140 may include one or more input devices. Example input devices may include a keyboard, a mouse, a game controller, a glove, a button, a touch screen, or any other suitable device for receiving an action request and transmitting the received action request to the console 110. The action request received by the input / output interface 140 may be transmitted to the console 110, and the console 110 may perform an action corresponding to the requested action. In some embodiments, the input / output interface 140 may provide tactile feedback to the user according to the instruction received from the console 110. For example, when an action request is received, or when the console 110 has performed the requested action and transmitted the instruction to the input / output interface 140, the input / output interface 140 may provide tactile feedback. In some embodiments, the imaging device 150 may be used to track the input / output interface 140, such as tracking the position or location of a controller (which may include, for example, an IR light source) or a user's hand to determine the user's movement. In some embodiments, the near-eye display system 120 may include one or more imaging devices (eg, imaging device 150 ) to track the input / output interface 140 , such as tracking the position or location of a controller or a user's hand to determine the user's movements.

[0074] The console 110 may provide content to the near-eye display system 120 for presentation to the user based on information received from one or more of the imaging device 150, the near-eye display system 120, and the input / output interface 140. Figure 1 In the example shown, the console 110 may include an application store 112, a head mounted device tracking module 114, an artificial reality engine 116, and an eye tracking module 118. Some embodiments of the console 110 may include a combination of Figure 1 Different or additional modules than those described. The functionality described further below may be allocated among the components of console 110 in a manner different from that described here.

[0075] In some embodiments, console 110 may include a processor and a non-transitory computer-readable storage medium storing instructions executable by the processor. The processor may include multiple processing units that execute instructions in parallel. The computer-readable storage medium may be any memory, such as a hard drive, removable memory, or a solid-state drive (e.g., flash memory or dynamic random access memory (DRAM)). In various embodiments, in combination with Figure 1The described modules of the console 110 may be encoded as instructions in a non-transitory computer-readable storage medium that, when executed by a processor, cause the processor to perform the functions described further below.

[0076] The application storage 112 may store one or more applications for execution by the console 110. An application may include a set of instructions that, when executed by a processor, generates content for presentation to a user. The content generated by the application may respond to input received from the user via movement of the user's eyes or from input / output interface 140. Examples of applications may include: gaming applications, conferencing applications, video playback applications, or other suitable applications.

[0077] The head mounted device tracking module 114 may use the slow calibration information from the imaging device 150 to track the movement of the near eye display system 120. For example, the head mounted device tracking module 114 may use the localizers observed from the slow calibration information and the model of the near eye display system 120 to determine the position of the reference point of the near eye display system 120. The head mounted device tracking module 114 may also use the position information from the fast calibration information to determine the position of the reference point of the near eye display system 120. Additionally, in some embodiments, the head mounted device tracking module 114 may use the fast calibration information, portions of the slow calibration information, or some combination thereof to predict the future position of the near eye display system 120. The head mounted device tracking module 114 may provide the estimated or predicted future position of the near eye display system 120 to the artificial reality engine 116.

[0078] The head mounted device tracking module 114 may use one or more calibration parameters to calibrate the artificial reality system environment 100, and may adjust one or more calibration parameters to reduce errors in determining the position of the near eye display system 120. For example, the head mounted device tracking module 114 may adjust the focus of the imaging device 150 to obtain a more accurate position of the localizers observed on the near eye display system 120. Moreover, the calibration performed by the head mounted device tracking module 114 may also take into account information received from the IMU 132. Additionally, if tracking of the near eye display system 120 is lost (e.g., the imaging device 150 loses sight of at least a threshold number of localizers 126), the head mounted device tracking module 114 may recalibrate some or all of the calibration parameters.

[0079] The artificial reality engine 116 can execute an application within the artificial reality system environment 100 and receive position information of the near-eye display system 120, acceleration information of the near-eye display system 120, velocity information of the near-eye display system 120, predicted future position of the near-eye display system 120, or some combination thereof from the head mounted device tracking module 114. The artificial reality engine 116 can also receive estimated eye position and orientation information from the eye tracking module 118. Based on the received information, the artificial reality engine 116 can determine the content to be provided to the near-eye display system 120 for presentation to the user. For example, if the received information indicates that the user has looked to the left, the artificial reality engine 116 can generate content for the near-eye display system 120 that mirrors the movement of the user's eyes in the virtual environment. Additionally, the artificial reality engine 116 can perform an action within an application executed on the console 110 in response to an action request received from the input / output interface 140, and provide feedback to the user indicating that the action has been performed. The feedback may be visual or auditory feedback via the near-eye display system 120 , or tactile feedback via the input / output interface 140 .

[0080] The eye tracking module 118 may receive eye tracking data from the eye tracking system 130 and determine the position of the user's eyes based on the eye tracking data. The position of the eyes may include the orientation, position, or both of the eyes relative to the near-eye display system 120 or any element thereof. Because the rotational axis of the eye changes depending on the position of the eye in the eye socket, determining the position of the eye in the eye socket may allow the eye tracking module 118 to more accurately determine the orientation of the eyes.

[0081] In some embodiments, the eye tracking module 118 may store a mapping between images captured by the eye tracking system 130 and eye positions to determine a reference eye position from the images captured by the eye tracking system 130. Alternatively or additionally, the eye tracking module 118 may determine an updated eye position relative to the reference eye position by comparing the image from which the reference eye position was determined and the image from which the updated eye position was determined. The eye tracking module 118 may use measurements from different imaging devices or other sensors to determine the eye position. For example, the eye tracking module 118 may use measurements from a slow eye tracking system to determine a reference eye position and then determine an updated position relative to the reference eye position from a fast eye tracking system until the next reference eye position is determined based on measurements from the slow eye tracking system.

[0082] The eye tracking module 118 may also determine eye calibration parameters to improve the precision and accuracy of eye tracking. The eye calibration parameters may include parameters that change whenever the user wears or adjusts the near-eye display system 120. Example eye calibration parameters may include an estimated distance between a component of the eye tracking system 130 and one or more parts of the eye (such as the center of the eye, the pupil, the corneal boundary, or a point on the surface of the eye). Other example eye calibration parameters may be specific to a particular user and may include an estimated average eye radius, an average corneal radius, an average scleral radius, a feature map on the surface of the eye, and an estimated eye surface profile. In embodiments where light from outside the near-eye display system 120 can reach the eye (such as in some augmented reality applications), the calibration parameters may include correction factors for intensity and color balance due to changes in light from outside the near-eye display system 120. The eye tracking module 118 may use the eye calibration parameters to determine whether the measurements captured by the eye tracking system 130 allow the eye tracking module 118 to determine accurate eye positions (also referred to herein as "valid measurements"). Invalid measurements from which eye tracking module 118 may be unable to determine accurate eye position may be caused by the user blinking, adjusting the head mounted device, or removing the head mounted device, and / or may be caused by near-eye display system 120 experiencing a greater than threshold illumination change due to external light. In some embodiments, at least some of the functions of eye tracking module 118 may be performed by eye tracking system 130.

[0083] Figure 2 2 is a perspective view of an example of a near-eye display system in the form of a head mounted display (HMD) device 200 for implementing some examples disclosed herein. The HMD device 200 may be, for example, part of a virtual reality (VR) system, an augmented reality (AR) system, a mixed reality (MR) system, or some combination thereof. The HMD device 200 may include a body 220 and a headband 230. Figure 2 The top side 223, front side 225, and right side 227 of the body 220 are shown in perspective view. The headband 230 can have an adjustable or extendable length. There can be enough space between the body 220 of the HMD device 200 and the headband 230 to allow the user to mount the HMD device 200 on the user's head. In various embodiments, the HMD device 200 can include additional, fewer, or different components. For example, in some embodiments, the HMD device 200 can include eyeglass temples and temple tips (e.g., as shown in FIG. 1 ). Figure 2 as shown) instead of headband 230.

[0084] The HMD device 200 can present media including virtual and / or augmented views of a physical, real-world environment with computer-generated elements to a user. Examples of media presented by the HMD device 200 can include images (e.g., two-dimensional (2D) or three-dimensional (3D) images), video (e.g., 2D or 3D video), audio, or some combination thereof. The images and videos can be displayed via one or more display components (e.g., a display unit 220) enclosed in the body 220 of the HMD device 200. Figure 2 The HMD device 200 may include two viewing areas.

[0085] In some embodiments, the HMD device 200 may include various sensors (not shown), such as depth sensors, motion sensors, position sensors, and eye tracking sensors. Some of these sensors may sense using structured light patterns. In some embodiments, the HMD device 200 may include an input / output interface for communicating with a console. In some embodiments, the HMD device 200 may include a virtual reality engine (not shown), which may execute applications within the HMD device 200 and receive depth information, position information, acceleration information, velocity information, predicted future positions, or some combination thereof of the HMD device 200 from various sensors. In some embodiments, the information received by the virtual reality engine may be used to generate signals (e.g., display instructions) to one or more display components. In some embodiments, the HMD device 200 may include a locator (not shown, such as the locator 126), which is located at a fixed position on the body 220 relative to each other and relative to a reference point. Each locator may emit light that can be detected by an external imaging device.

[0086] Figure 3 is a perspective view of an example of a near-eye display system 300 in the form of a pair of glasses for implementing some examples disclosed herein. The near-eye display system 300 may be Figure 1Specific embodiments of near-eye display system 120 can be configured to operate as a virtual reality display, an augmented reality display, and / or a mixed reality display. Near-eye display system 300 can include frame 305 and display 310. Display 310 can be configured to present content to a user. In some embodiments, display 310 can include display electronics and / or display optics. For example, as described above with reference to Figure 1 As described above with respect to the near-eye display system 120 , the display 310 may include an LCD display panel, an LED display panel, or an optical display panel (eg, a waveguide display component).

[0087] The near-eye display system 300 may also include various sensors 350a, 350b, 350c, 350d, and 350e on or within the frame 305. In some embodiments, the sensors 350a-350e may include one or more depth sensors, motion sensors, position sensors, inertial sensors, or ambient light sensors. In some embodiments, the sensors 350a-350e may include one or more image sensors configured to generate image data representing different fields of view in different directions. In some embodiments, the sensors 350a-350e may be used as input devices to control or affect the display content of the near-eye display system 300, and / or provide an interactive VR / AR / MR experience to the user of the near-eye display system 300. In some embodiments, the sensors 350a-350e may also be used for stereoscopic imaging.

[0088] In some embodiments, the near-eye display system 300 may also include one or more illuminators 330 to project light into the physical environment. The projected light may be associated with different frequency bands (e.g., visible light, infrared light, ultraviolet light, etc.) and may serve various purposes. For example, the illuminator 330 may project light in a dark environment (or in an environment with low-intensity infrared light, ultraviolet light, etc.) to help the sensors 350a-350e capture images of different objects within the dark environment. In some embodiments, the illuminator 330 may be used to project a specific light pattern onto an object within the environment. In some embodiments, the illuminator 330 may be used as a locator, such as described above with reference to Figure 1 The locator 126 is described.

[0089] In some embodiments, the near-eye display system 300 may also include a high-resolution camera 340. The camera 340 may capture images of the physical environment in the field of view. The captured images may be generated, for example, by a virtual reality engine (e.g., Figure 1The artificial reality engine 116) is processed to add virtual objects to the captured images or modify physical objects in the captured images, and the processed images can be displayed to the user by the display 310 for AR or MR applications.

[0090] Figure 4 An example of an optical see-through augmented reality system 400 using a waveguide display according to certain embodiments is shown. The augmented reality system 400 may include a projector 410 and a combiner 415. The projector 410 may include a light source or image source 412 and a projector optical device 414. In some embodiments, the image source 412 may include a plurality of pixels displaying a virtual object, such as an LCD display panel or an LED display panel. In some embodiments, the image source 412 may include a light source that generates coherent light or partially coherent light. For example, the image source 412 may include a laser diode, a vertical cavity surface emitting laser, and / or a light emitting diode. In some embodiments, the image source 412 may include a plurality of light sources, each of which emits a monochromatic image light corresponding to a primary color (e.g., red, green, or blue). In some embodiments, the image source 412 may include an optical pattern generator, such as a spatial light modulator. Projector optics 414 may include one or more optical components that may condition the light from image source 412, such as expanding, collimating, scanning, or projecting the light from image source 412 to combiner 415. For example, one or more optical components may include one or more lenses, liquid lenses, mirrors, apertures, and / or gratings. In some embodiments, projector optics 414 may include a liquid lens (e.g., a liquid crystal lens) having multiple electrodes that allows the light from image source 412 to be scanned.

[0091] The combiner 415 may include an input coupler 430 for coupling light from the projector 410 into a substrate 420 of the combiner 415. The combiner 415 may transmit at least 50% of the light in a first wavelength range and reflect at least 25% of the light in a second wavelength range. For example, the first wavelength range may be visible light from about 400 nm to about 650 nm, and the second wavelength range may be in the infrared band, for example, from about 800 nm to about 1000 nm. The input coupler 430 may include a volume holographic grating, a diffractive optical element (DOE) (e.g., a surface relief grating), an inclined surface of the substrate 420, or a refractive coupler (e.g., a wedge or a prism). The input coupler 430 may have a coupling efficiency greater than 30%, 50%, 75%, 90% or more for visible light. The light coupled into the substrate 420 may propagate within the substrate 420 by, for example, total internal reflection (TIR). The substrate 420 may be in the form of a lens of a pair of glasses. Substrate 420 can have a flat surface or a curved surface and can include one or more types of dielectric materials, such as glass, quartz, plastic, polymer, poly (methyl methacrylate) (PMMA), crystal or ceramic. The thickness of the substrate can range from less than about 1 mm to about 10 mm or more, for example. Substrate 420 can be transparent to visible light.

[0092] The substrate 420 may include or may be coupled to a plurality of output couplers 440 configured to extract at least a portion of the light directed by and propagating within the substrate 420 from the substrate 420 and direct the extracted light 460 to the eye 490 of the user of the augmented reality system 400. Like the input coupler 430, the output coupler 440 may include a grating coupler (e.g., a volume holographic grating or a surface relief grating), other DOEs, prisms, etc. The output coupler 440 may have different coupling (e.g., diffraction) efficiencies at different locations. The substrate 420 may also allow light 450 from the environment in front of the combiner 415 to pass through with little or no loss. The output coupler 440 may also allow light 450 to pass through with little loss. For example, in some embodiments, output coupler 440 can have a low diffraction efficiency for light 450, so that light 450 can be refracted or otherwise pass through output coupler 440 with little loss, and thus can have a higher intensity than extracted light 460. In some embodiments, output coupler 440 can have a high diffraction efficiency for light 450, and can diffract light 450 to certain desired directions (i.e., diffraction angles) with little loss. As a result, the user can view a combined image of the environment in front of combiner 415 and the virtual object projected by projector 410.

[0093] In addition, as described above, in an artificial reality system, in order to improve the user's interaction with the presented content, the artificial reality system can track the user's eyes and modify or generate content based on the position or direction the user is looking at. Tracking the eyes can include tracking the position and / or shape of the pupil and / or cornea of ​​the eye, and determining the rotational position or gaze direction of the eye. A technique (known as the pupil center corneal reflection or PCCR method) involves using a NIR LED to generate a bright spot (glint) on the surface of the cornea of ​​the eye, and then capturing an image / video of the eye area. The gaze direction can be estimated from the relative movement between the center of the pupil and the bright spot. Various holographic optical elements can be used in an eye tracking system to illuminate the user's eyes or collect light reflected by the user's eyes.

[0094] An example of a holographic optical element for eye tracking or image display in an artificial reality system may be a holographic volume Bragg grating, which may be recorded on a layer of holographic material by exposing the layer of holographic material to a light pattern generated by interference between two or more coherent light beams.

[0095] Figure 5A An example of a volume Bragg grating (VBG) 500 is shown. Figure 5A The volume Bragg grating 500 shown may include a transmission holographic grating having a thickness D. The refractive index n of the volume Bragg grating 500 may be modulated with an amplitude n1, and the grating period of the volume Bragg grating 500 may be Λ. Incident light 510 having a wavelength λ may be incident on the volume Bragg grating 500 at an incident angle θ and may be refracted into the volume Bragg grating 500 as incident light 520, which is refracted at an angle θ in the volume Bragg grating 500. n The incident light 520 may be diffracted by the volume Bragg grating 500 into diffracted light 530. The diffracted light 530 may be diffracted in the volume Bragg grating 500 at a diffraction angle θ d propagates and can be refracted out of the volume Bragg grating 500 as diffracted light 540.

[0096] Figure 5B Shows Figure 5A The Bragg condition of the volume Bragg grating 500 is shown. Vector 505 represents the grating vector in Vector 525 represents the incident wave vector and vector 535 represents the diffraction wave vector in Under the Bragg phase matching condition, Therefore, for a given wavelength λ, there may be only one pair of incident angles θ (or θ n ) and the diffraction angle θ d. Similarly, for a given incident angle θ, there may be only one wavelength λ that fully satisfies the Bragg condition. Therefore, diffraction may only occur within a small wavelength range and a small incident angle range. The diffraction efficiency, wavelength selectivity, and angle selectivity of the volume Bragg grating 500 may be functions of the thickness D of the volume Bragg grating 500. For example, the full-width-half-magnitude (FWHM) wavelength range and FWHM angle range of the volume Bragg grating 500 under Bragg conditions may be inversely proportional to the thickness D of the volume Bragg grating 500, while the maximum diffraction efficiency under Bragg conditions may be a function of sin 2 (a×n1×D), where a is a coefficient. For a reflective Bragg grating, the maximum diffraction efficiency under Bragg conditions can be the function tanh 2 (a×n1×D).

[0097] In some embodiments, a multiplexed Bragg grating can be used to achieve desired optical properties, such as high diffraction efficiency and a large field of view (FOV) for the entire visible spectrum (e.g., from about 400 nm to about 700 nm or from about 440 nm to about 650 nm). Each portion of the multiplexed Bragg grating can be used to diffract light from a corresponding FOV range and / or within a corresponding wavelength range. Therefore, in some designs, multiple volume Bragg gratings can be used, each volume Bragg grating being recorded under corresponding recording conditions.

[0098] The holographic optical element described above may be recorded in a layer of holographic material (e.g., photopolymer). In some embodiments, the HOE may be recorded first and then laminated on a substrate in a near-eye display system. In some embodiments, a layer of holographic material may be coated or laminated on a substrate and then the HOE may be recorded in the layer of holographic material.

[0099] Typically, to record a holographic optical element in a photosensitive material layer, two coherent light beams may interfere with each other at a certain angle to generate a unique interference pattern in the photosensitive material layer, which in turn may generate a unique refractive index modulation pattern in the photosensitive material layer, wherein the refractive index modulation pattern may correspond to the light intensity pattern of the interference pattern. The photosensitive material layer may include, for example, a silver halide emulsion, a dichromated gelatin, a photopolymer comprising a photopolymerizable monomer suspended in a polymer matrix, a photorefractive crystal, etc. An example of a photosensitive material layer for holographic recording is a two-stage photopolymer.

[0100] Figure 6An example of a holographic recording material including a two-stage photopolymer is shown. The raw material 610 of the two-stage photopolymer can be a resin including a matrix precursor 612 and an imaging component 614. The matrix precursor 612 in the raw material 610 can include a monomer, which can be thermally cured or otherwise cured in the first stage to polymerize and form a photopolymer film 620 including a cross-linked matrix formed by a polymer binder 622. The imaging component 614 can include a writing monomer and a polymerization initiating agent, such as a photosensitive dye, an initiator, and / or a chain transfer agent. Therefore, the photopolymer film 620 can include a polymer binder 622, a writing monomer (e.g., an acrylate monomer) and an initiating agent, such as a photosensitive dye, an initiator, and / or a chain transfer agent. The polymer binder 622 can serve as a skeleton or supporting matrix for the writing monomer and the initiating agent. For example, in some embodiments, the polymer binder 622 may include a low refractive index (e.g., <1.5) rubbery polymer (e.g., polyurethane) that can provide mechanical support during holographic exposure and ensure that the refractive index modulation caused by the light pattern is permanently maintained.

[0101] An imaging component 614 including a writing monomer and a polymerization initiation medium can be dispersed in a supporting matrix. The writing monomer can be used as a refractive index modulator. For example, the writing monomer can include a high refractive index acrylate monomer that can react with an initiator and polymerize. The photosensitive dye can be used to absorb light and interact with the initiator to produce an active substance, such as a free radical, a cation (e.g., an acid), or an anion (e.g., a base). The active substance (e.g., a free radical) can initiate polymerization by attacking the monomer. For example, in some monomers, an electron pair can be firmly held between two carbons in a σ bond, while another electron pair can be more loosely held in a π bond, and the free radical can use an electron from the π bond to form a more stable bond with the first carbon atom of the two carbon atoms. Another electron from the π bond may return to the second carbon atom of the two carbon atoms and turn the entire molecule into another free radical. Therefore, a monomer chain (e.g., a polymer) can be formed by adding additional monomers to the end of the monomer chain and transferring free radicals to the end of the monomer chain to attack the monomer and add more monomers to the chain.

[0102] During the recording process (e.g., the second stage), the interference pattern generated by the interference between the two coherent light beams can cause the photosensitive dye and the initiator in the bright stripes to generate active substances from the initiator, such as free radicals, cations (e.g., acids) or anions (e.g., bases), wherein the active substances (e.g., free radicals) can be transferred from the initiator to the monomers and cause the monomers in the bright stripes to polymerize as described above. When hydrogen atoms on the polymer matrix are extracted, the initiator or free radicals can be bound to the polymer matrix. The free radicals can be transferred to the ends of the monomer chains to add more monomers to the chains. When the monomers in the bright stripes are attached to the monomer chains, the monomers in the unexposed dark areas can diffuse to the bright stripes to enhance polymerization. As a result, a polymerization concentration and density gradient can be formed in the photopolymer film 620, resulting in a refractive index modulation in the photopolymer film 620 due to the higher refractive index of the writing monomer. For example, a region with a higher concentration of monomers and polymerization can have a higher refractive index. Therefore, a hologram or holographic optical element 630 can be formed in the photopolymer film 620.

[0103] During the exposure process, a free radical at the end of a monomer chain can combine with a free radical at the end of another monomer chain to form a longer chain and terminate polymerization. In addition to termination due to free radical combination, polymerization can also be terminated by a disproportionation reaction of the polymer, in which hydrogen atoms from one chain can be extracted to another chain to generate a polymer with a terminal unsaturated group and a polymer with a terminal saturated group. Polymerization may also terminate due to interaction with impurities or inhibitors (such as oxygen). In addition, as exposure and polymerization proceed, fewer monomers are available for diffusion and polymerization, and therefore diffusion and polymerization can be inhibited. Polymerization can stop until there are no more monomers or until the monomer chain used for exposure terminates. After all or substantially all of the monomers have been polymerized, no new holographic optical element 630 (such as a grating) can be recorded in the photopolymer film 620.

[0104] In some embodiments, the holographic optical element recorded in the photosensitive material layer can be UV cured or thermally cured or enhanced, for example, for dye bleaching, to complete polymerization, to permanently fix the recorded pattern, and to enhance refractive index modulation. At the end of the process, a holographic optical element, such as a holographic grating, can be formed. The holographic grating can be a volume Bragg grating with a thickness of, for example, a few micrometers, tens of micrometers, or hundreds of micrometers.

[0105] In order to generate the desired light interference pattern for recording the HOE, two or more coherent light beams can usually be used, one of which can be a reference beam and the other can be an object beam with a desired wavefront profile. When the HOE being recorded is illuminated by the reference beam, the object beam with the desired wavefront profile can be reconstructed.

[0106] In some embodiments, the holographic optical element can be used to diffract light outside the visible light band. For example, IR light or NIR light (e.g., 940nm or 850nm) can be used for eye tracking. Therefore, the holographic optical element may need to diffract IR or NIR light instead of visible light. However, there may be very few holographic recording materials that are sensitive to infrared light. Therefore, in order to record a holographic grating that can diffract infrared light, a recording light of a shorter wavelength (e.g., in the visible light band or UV band, such as at about 660nm, about 532nm, about 514nm, or about 457nm) can be used, and the recording conditions (e.g., the angle of the two interfering coherent light beams) can be different from the reconstruction conditions.

[0107] Fig. 7A A recording beam for recording a volume Bragg grating 700 and a beam reconstructed from the volume Bragg grating 700 are shown. In the illustrated example, the volume Bragg grating 700 may include a transmission volume hologram recorded using a reference beam 720 of a first wavelength (such as 660 nm) and an object beam 710. When a beam 730 of a second wavelength (e.g., 940 nm) is incident on the volume Bragg grating 700 at an incident angle of 0°, the incident beam 730 may be diffracted by the volume Bragg grating 700 at a diffraction angle as shown by a diffracted beam 740.

[0108] Figure 7B is an example of a holographic momentum diagram 705 showing the wave vectors of the recording and reconstruction beams and the grating vector of the recorded volume Bragg grating. Figure 7B The Bragg matching condition during holographic grating recording and reconstruction is shown. The lengths of the wave vectors 750 and 760 of the recording beams (eg, object beam 710 and reference beam 710) can be calculated according to 2πn / λ c Based on the recording light wavelength λ c (e.g., 660 nm), where n is the average refractive index of the holographic material layer. The directions of the wave vectors 750 and 760 of the recording beam can be determined based on the desired grating vector K(770), so that the wave vectors 750 and 760 and the grating vector K(770) can form a Figure 7B The grating vector K may have an amplitude of 2π / Λ, where Λ is the grating period. The grating vector K may in turn be determined based on the desired reconstruction conditions. For example, based on the desired reconstruction wavelength λ r(e.g., 940 nm) and the directions of the incident beam (e.g., beam 730 at 0°) and the desired diffracted beam (e.g., diffracted beam 740), the grating vector K (770) of the volume Bragg grating 700 can be determined based on the Bragg condition, where the wave vector 780 of the incident beam (e.g., beam 730) and the wave vector 790 of the diffracted beam (e.g., diffracted beam 740) can have an amplitude of 2πn / λ r , and can be compared with Figure 7B The raster vectors K (770) are shown to form an isosceles triangle.

[0109] As described above, for a given wavelength, there may be only one pair of incident angle and diffraction angle that fully satisfies the Bragg condition. Similarly, for a given incident angle, there may be only one wavelength that fully satisfies the Bragg condition. When the incident angle of the reconstruction beam is different from the incident angle that satisfies the Bragg condition of the volume Bragg grating, or when the wavelength of the reconstruction beam is different from the wavelength that satisfies the Bragg condition of the volume Bragg grating, the diffraction efficiency may decrease as a function of the Bragg mismatch factor caused by the angle or wavelength being detuned from the Bragg condition. Therefore, diffraction may only occur in a small wavelength range and a small incident angle range.

[0110] Figure 8 An example of a holographic recording system 800 for recording a holographic optical element is shown. The holographic recording system 800 includes a beam splitter 810 (e.g., a beam splitter cube) that can split an incident collimated laser beam 802 into two beams 812 and 814 that are coherent and can have similar intensities. The beam 812 can be reflected by a first mirror 820 toward a plate 830, as shown by a reflected beam 822. On another path, the beam 814 can be reflected by a second mirror 840. The reflected beam 842 can be directed to the plate 830 and can interfere with the beam 822 at the plate 830 to generate an interference pattern including light fringes and dark fringes. In some embodiments, the plate 830 can also be a mirror. A holographic recording material layer 850 can be formed on the plate 830 or on a substrate mounted on the plate 830. The interference pattern can cause the holographic optical element to be recorded in the holographic recording material layer 850, as described above.

[0111] In some embodiments, the mask 860 can be used to record different HOEs in different areas of the holographic recording material layer 850. For example, the mask 860 can include holes 862 for holographic recording, and can be moved to place the holes 862 in different areas on the holographic recording material layer 850, thereby recording different HOEs in different areas under different recording conditions (e.g., with recording beams at different angles).

[0112] A holographic recording material may be selected for a particular application based on certain parameters of the holographic recording material, such as its spatial frequency response, dynamic range, photosensitivity, physical dimensions, mechanical properties, wavelength sensitivity, and development or bleaching methods.

[0113] The dynamic range indicates the refractive index variation that can be achieved in the holographic recording material. The dynamic range can affect, for example, the thickness of the device that can achieve high efficiency and the number of holograms that can be multiplexed in a layer of holographic material. The dynamic range can be expressed in terms of the refractive index modulation (RIM), which can be half of the total variation in refractive index. Typically, a large refractive index modulation in a holographic optical element is desired in order to improve the diffraction efficiency and to record multiple holographic optical elements in the same holographic material layer. However, for holographic photopolymer materials, the maximum achievable refractive index modulation or dynamic range may be limited due to solubility limitations of the monomers in the holographic photopolymer material.

[0114] The spatial frequency response is a measure of the feature size that can be recorded by the holographic material and can indicate the type of Bragg conditions that can be achieved. The spatial frequency response can be characterized by a modulation transfer function, which can be a curve that depicts a sine wave of varying frequency. Typically, a single spatial frequency value can be used to represent the frequency response, which can indicate the spatial frequency value at which the refractive index modulation begins to drop or the spatial frequency value at which the refractive index modulation decreases by 3dB. The spatial frequency response can also be expressed in lines / mm, line pairs / mm, or the period of the sine curve.

[0115] The photosensitivity of the holographic recording material can dictate the light dosage used to achieve a specific efficiency such as 100% (or 1% for photorefractive crystals). The physical dimensions that can be achieved in a particular holographic material can affect the hole size and the spectral selectivity of the HOE device. The physical parameters of the holographic recording material can include, for example, damage threshold and environmental stability. Wavelength sensitivity can be used to select the light source for the recording setup and can also affect the minimum achievable period. Some materials may be sensitive to light over a wide range of wavelengths. Many holographic materials may require post-exposure development or bleaching. Development considerations can include how the holographic material is developed or otherwise processed after recording.

[0116] In order to record holographic optical elements for artificial reality systems, it may be desirable for the photosensitive polymer material to be sensitive to visible light, to be able to produce a large refractive index modulation Δn (e.g., a high dynamic range), and to have temporally and spatially controllable reaction and / or diffusion of monomers and / or polymers such that chain transfer and termination reactions can be suppressed.

[0117] Fig. 9An example of a grating 900 is shown. The grating 900 includes two substrate layers 910, 915 and a polymer layer 920. The grating 900 may correspond to a volume Bragg grating and / or a multiplexed volume Bragg grating.

[0118] In some embodiments, the first substrate 910 is disposed on a first side of the polymer layer 920. The first substrate 910 may be composed of, for example, glass, quartz, plastic, polymer, or any other suitable material that is transparent to visible light and NIR light. The thickness of the first substrate 910 may be in the range of about 0.1 mm to about 10 mm. In some embodiments, the first substrate 910 may not be included and / or may be replaced by another component.

[0119] In some embodiments, the second substrate 915 is disposed on the second side of the polymer layer 920. The second substrate 915 may be composed of, for example, glass, quartz, plastic, polymer, or any other suitable material that is transparent to visible light and NIR light. The thickness of the second substrate 915 may be in the range of about 0.1 mm to about 10 mm. In some embodiments, the second substrate 915 may not be included and / or may be replaced by another component.

[0120] The polymer layer 920 includes a first region 922 having a first refractive index (n1) and a second region 924 having a second refractive index (n2). The refractive index of the second region can be higher than that of the first region (or vice versa). The refractive index difference between the regions (e.g., |n1-n2|) can be between approximately 0 and about 0.2.

[0121] In addition to the refractive index of regions 922, 924, grating 900 is characterized by the fringe tilt angle θ(940) and pitch 950. The fringe tilt angle θ(940) may be between approximately 0 degrees and about 90 degrees. The pitch 950 may be between approximately 0.1 and about 1.5 μm.

[0122] The parameters θ (940) and pitch 950 can affect the behavior of incident light 960 approaching the grating 900. Based on these parameters and other parameters (such as the relative refractive index in the grating), the diffracted light 970 can have a specific power and can be in a specific direction. The diffraction efficiency of the grating 900 is the ratio between the power of the diffracted light and the power of the incident light.

[0123] Figure 10A-10BAn example of a grating with a modified refractive index modulation according to some embodiments is shown. When the refractive index difference between regions in the grating increases within a certain range, the diffraction efficiency can be improved. Similarly, when the refractive index difference between regions in the grating decreases within a certain range, the diffraction efficiency can decrease. In some cases, it may be desirable to increase the refractive index difference between regions. This can be achieved by modifying the refractive index in the regions, such as Fig. 10A and Fig. 10B shown.

[0124] Fig. 10A A grating 1000 having a specific initial refractive index modulation and diffraction efficiency is shown. The grating 1000 includes two substrate layers 1010 and 1020 and a polymer layer 1030 including regions 1032 and 1034. Each region 1032 is a region of relatively high refractive index (compared to each region 1034). Each region 1034 is a region of relatively low refractive index (compared to each region 1032). When incident light 1040 passes through the grating 1000, a certain percentage of the incident light 1040 is diffracted as diffracted light 1045 according to the diffraction efficiency of the grating 1000.

[0125] Fig. 10B A grating 1050 with modified refractive index modulation and improved diffraction efficiency is shown. The grating 1050 includes two substrate layers 1060, 1070 and a polymer layer 1080 including regions 1082 and 1084. Each region 1082 is a region of relatively high refractive index (compared to each region 1084). Each region 1084 is a region of relatively low refractive index (compared to the first region 1082).

[0126] There are ways to modify the refractive index modulation of the grating 1050 by modifying the refractive index of the polymer layer 1080 in whole or in part. For example, the refractive index modulation of the grating 1050 can be increased by reducing the refractive index in region 1084 while keeping the refractive index of region 1082 substantially constant. The refractive index modulation of the grating 1050 can alternatively be increased by increasing the refractive index in region 1082 while keeping the refractive index of region 1084 substantially constant. The refractive index modulation of the grating 1050 can also be increased by reducing the refractive index of both regions, but decreasing the refractive index more in region 1084. The refractive index modulation of the grating 1050 can be increased by increasing the refractive index in both regions, but increasing the refractive index more in region 1082.

[0127] When incident light 1090 passes through grating 1050, a certain percentage of incident light 1090 is diffracted into diffracted light 1095 according to the diffraction efficiency of grating 1050. Fig. 10A Compared with the diffraction efficiency of the grating 1000, Fig. 10BThe diffraction efficiency of the grating 1050 is improved, and a larger portion of the incident light is diffracted into diffracted light 1095 compared to the diffracted light 1045.

[0128] Figures 11A-11C Example techniques for modifying the refractive index modulation in a holographic grating are shown. Fig.11A shows the grating after recording, Fig. 11B A grating is shown in which the substrate is replaced by a resin layer including nanoparticles (eg, monomers), and Fig. 11C The grating is shown after the nanoparticles have diffused from the resin layer into the grating.

[0129] Fig.11A A recorded holographic grating 1100 is shown. The grating 1100 comprises a first substrate 1102 disposed on the bottom side of a polymer layer. The polymer layer comprises regions of relatively high refractive index 1104 and regions of relatively low refractive index 1106. The polymer layer may, for example, have been exposed to a holographic recording light pattern to record a refractive index modulation pattern in the polymer layer. The grating 1100 further comprises a second substrate 1103 disposed on the top side of the polymer layer.

[0130] Fig. 11B A grating 1120 is shown including a resin layer 1123 containing nanoparticles. Fig.11A The grating 1100 includes a first substrate 1122 disposed on the bottom side of the polymer layer and regions 1124 and 1126 of different refractive indices. The second substrate (e.g., Fig.11A The second substrate 1103 shown has been removed and replaced by a resin layer 1123. The resin layer 1123 includes a support layer or matrix filled with high refractive index nanoparticles (e.g., having a higher refractive index than the high refractive index region of the polymer layer). The resin layer filled with nanoparticles is also referred to as a "monomer storage buffer layer" in this article. Alternatively, nanoparticles of low or medium refractive index can be used, depending on the desired modification. In some embodiments, the nanoparticles can be monomers. In some embodiments, the nanoparticles can be in the form of a liquid. The resin layer 1123 is disposed on the top side of the polymer layer so that the resin layer 1123 and the polymer layer are in contact with each other. The sponge layer can be a polymer film, typically an elastomer. Typical elastomers include crosslinked films of polyester, polyether, polyurethane or polysiloxane.

[0131] When the resin layer 1123 and the polymer layer are placed in contact, the nanoparticles can diffuse from the resin layer 1123 into the polymer layer. As shown by the gradient in regions 1124, 1126, the introduction of the nanoparticles in the polymer layer modifies the refractive index of regions 1124, 1126.

[0132] Fig. 11C A grating 1140 with a modified refractive index modulation is shown. The grating 1140 comprises a substrate 1142, a resin layer 1143 filled with nanoparticles and a polymer layer comprising regions 1144, 1146 of different refractive index. The nanoparticles further diffuse into the polymer layer, producing a change in the refractive index in the regions 1144, 1146.

[0133] Figures 12A-12D An example of a modification of the refractive index modulation in a holographic grating according to some embodiments is shown. Depending on the properties of the nanoparticles in the resin layer, the diffusion of the nanoparticles and the resulting modification of the refractive index modulation may vary. The diffusion properties may be controlled based on the properties of the nanoparticles in the resin layer, such as the refractive index and the solubility in different regions of the polymer layer. The solubility of the nanoparticles in a given region may be controlled, for example, based on the size of the nanoparticles and / or the affinity between the nanoparticles and the material in the region of interest.

[0134] Fig. 12A A first example of a grating 1200 modified for refractive index modulation using a monomer (or other nanoparticle) storage buffer layer 1202 is shown. The grating 1200 includes a polymer layer including a relatively low refractive index region 1204 (with an initial refractive index n1) and a relatively high refractive index region 1206 (with an initial refractive index n2). A substrate layer 1201 is disposed on the bottom side of the polymer layer. A monomer storage buffer layer 1202 is disposed on the top side of the polymer layer.

[0135] exist Fig. 12A 1209A ). In the embodiment of the present invention, the monomer storage buffer layer 1202 includes a monomer having a relatively large refractive index n3 (>n2). In addition, the monomer is more soluble in the low refractive index stripes (e.g., in region 1204) than in the high refractive index stripes (e.g., in region 1206). Therefore, as shown in the refractive index modulation curve graph 1208, the effect on the refractive index modulation is most significant in the dips in the initial refractive index modulation distribution. The curve graph 1208 shows the refractive index of the grating 1200 as a function of position, which spans the polymer layer from left to right. Initially, before the monomer storage buffer layer 1202 is added, the refractive index of the grating 1200 varies between n1 and n2 (as shown in curve 1209A). With the refractive index change introduced by the monomer storage buffer layer, the refractive index modulation distribution changes as shown in curve 1209B due to the increase in the refractive index of the low refractive index region 1204 (corresponding to the dip in the refractive index modulation distribution).

[0136] Fig. 12BShows a second example of a grating 1210 with refractive index modulation modification using a monomer storage buffer layer 1212. The grating 1210 includes a polymer layer that includes regions 1214 of relatively low refractive index (having refractive index n1) and regions 1216 of relatively high refractive index (having refractive index n2). A substrate layer 1211 is disposed on the bottom side of the polymer layer. A monomer storage buffer layer 1212 is disposed on the top side of the polymer layer.

[0137] In Fig. 12B it, the monomer storage buffer layer 1212 includes a monomer having a relatively large refractive index n3 (>n2). Additionally, the monomer is more soluble in the high refractive index stripes (e.g., in region 1216) than in the low refractive index stripes (e.g., in region 1214). Thus, as shown in the refractive index modulation graph 1218 (showing an initial refractive index modulation 1219A and a modified refractive index modulation 1219B), the effect on the refractive index is most significant in terms of the peaks in the refractive index modulation profile. In particular, by introducing a material of a larger refractive index into the relatively high refractive index region 1216 via the monomer storage buffer layer 1212, the refractive index in the relatively high refractive index region 1216 is increased. This increase in the refractive index causes the peak in the refractive index graph 1219B to increase to a level higher than the initial level n2.

[0138] Fig. 12C Shows a third example of a grating 1220 with refractive index modulation modification using a monomer storage buffer layer 1222. The grating 1220 includes a polymer layer that includes regions 1224 of relatively low refractive index (having refractive index n1) and regions 1226 of relatively high refractive index (having refractive index n2). A substrate layer 1221 is disposed on the bottom side of the polymer layer. A monomer storage buffer layer 1222 is disposed on the top side of the polymer layer.

[0139] In Fig. 12C it, the monomer storage buffer layer 1222 includes a monomer having a relatively small refractive index n4 (<n1). Additionally, the monomer is more soluble in the low refractive index stripes (e.g., in region 1224) than in the high refractive index stripes (e.g., in region 1226). Thus, as shown in the refractive index modulation graph 1228 (showing an initial refractive index modulation 1229A and a modified refractive index modulation 1229B), the effect on the refractive index modulation is most significant in terms of the dips in the refractive index modulation profile. By introducing a lower refractive index material into the lower refractive index region 1224 via the monomer storage buffer layer 1222, the refractive index in the relatively low refractive index region 1224 is decreased, causing the refractive index at the low point in graph 1229B to drop below n1.

[0140] Fig.12DShows a fourth example of a grating 1230 with refractive index modulation modification using a monomer storage buffer layer 1232. The grating 1230 includes a polymer layer that includes a relatively low refractive index region 1234 (having a refractive index n1) and a relatively high refractive index region 1236 (having a refractive index n2). A substrate layer 1231 is disposed on the bottom side of the polymer layer. A monomer storage buffer layer 1232 is disposed on the top side of the polymer layer.

[0141] In Fig.12D , the monomer storage buffer layer 1232 includes a monomer having a relatively small refractive index n4 (<n1). Additionally, the monomer is more soluble in the high refractive index stripes (e.g., in region 1236) than in the low refractive index stripes (e.g., in region 1234). Thus, as shown in the refractive index modulation graph 1238 (the peak is reduced in the modified 1239B compared to the initial refractive index modulation 1239A), the effect on the refractive index is most significant in terms of the peak in the refractive index modulation profile. By introducing a lower refractive index material into the higher refractive index region 1236 via the monomer storage buffer layer 1232, the refractive index in the higher refractive index region 1236 is reduced, causing the refractive index at the high point in graph 1239B to drop below n2.

[0142] Figure 13A-13B Shows the variation of refractive index modulation modification in a grating according to some embodiments. In Fig.13A , the refractive index modulation modification is substantially constant over the thickness of the polymer layer region, while in Fig. 13B , the refractive index modification varies over the thickness of the polymer layer region. "Thickness" represents the z - direction of the polymer layer from bottom to top.

[0143] Fig.13A Shows a grating 1300 that includes a first region 1302 having an initial refractive index n1 and a second region 1304 having an initial refractive index n2. In the grating 1300, the refractive index modification occurs over the entire thickness of the polymer layer. The refractive index modulation graphs 1306, 1308 show the refractive index modulation across the polymer layer. The refractive index modulation graph 1306 shows the refractive index modulation as a function of the position through a cross - section 1305 towards the upper side of the polymer layer. The refractive index modulation graph 1308 shows the refractive index modulation as a function of the position through a cross - section 1307 towards the lower side of the polymer layer. In the grating 1300, the refractive index modulation modification distributions at the cross - sections 1305, 1307 are substantially the same. This corresponds to the concentration of nanoparticles (e.g., monomers) being at a substantially constant concentration across the thickness of the polymer layer in a given region. The substantially constant concentration can correspond to some small variations, such as 0.1%, 0.5%, 1%, or 5%.

[0144] Fig. 13BA grating 1350 is shown, which includes a first region 1352 with an initial refractive index n1 and a second region 1354 with an initial refractive index n2. In the grating 1350, the refractive index modulation modification occurs in a portion of the polymer layer. The refractive index modulation graphs 1356, 1358 show the refractive index modulation across the polymer layer. The refractive index modulation graph 1356 shows the refractive index modulation as a function of the position through the section 1355 toward the upper side of the polymer layer. The refractive index modulation graph 1358 shows the refractive index modulation as a function of the position through the section 1357 toward the lower side of the polymer layer. In the grating 1350, the refractive index modulation at the section 1355 has been modified. Monomers with a refractive index of n3 (n3 is greater than n1) preferentially diffuse into the region 1352 near the top surface of the polymer layer, which causes the refractive index in the region 1352 to shift upward from n1 in the curve graph 1356. In contrast, at cross section 1357 , the monomer has not diffused into that portion of the polymer layer, and therefore the refractive index modulation is not modified as shown in graph 1358 . Fig. 13B The refractive index modulation modification shown corresponds to a higher concentration of monomers or other nanoparticles near the upper edge of the polymer layer (e.g. Fig. 13B The top surface of the polymer layer is shown).

[0145] Thus, based on the location and content of the (one or more) monomer storage buffer layers, the refractive index modulation modification can be tailored to be tapered according to the thickness within the polymer layer. The refractive index modulation modification can occur only at a specific diffusion depth. The refractive index modulation can be tapered to smooth the refractive index modulation from the upper and / or lower edge of the polymer layer toward the center of the polymer layer. Such tapered refractive index modulation can be used to reduce the side lobes of the diffraction orders and improve the performance of the waveguide display.

[0146] Fig.14 A grating 1400 is shown having a refractive index modulation profile that is tapered at both the top and bottom edges of the grating. Region 1402 has an initial refractive index of n1, and region 1402 has an initial refractive index of n2. The refractive index across the grating has been modulated (e.g., by attaching a monomer storage buffer layer to the upper and lower edges of the polymer layer). The modulation has the greatest effect on the grating at the top and bottom, where the monomer is more concentrated near the upper and lower edges of the polymer layer. Graph 1430 shows the refractive index modulation across the grating at a section 1432 at the center of the grating 1400 in terms of thickness. The refractive index modulation modification from the monomer storage buffer layer does not reach the center. Therefore, at section 1432, the refractive index modulation remains at the initial level.

[0147] Graph 1410 shows the refractive index modulation across the grating at section 1412 near the bottom of the grating 1400. The refractive index modulation modification from the monomer storage buffer layer at the bottom of the grating has reached the depth level indicated by section 1412. Thus, at section 1412, the refractive index modulation has been modified such that the refractive index in region 1402 is increased, as shown in graph 1410. In graph 1410, the lowest point of the refractive index is shifted upward from n1 compared to graph 1430.

[0148] Graph 1420 shows the refractive index modulation across the grating at section 1422 near the top of the grating 1400. The refractive index modulation modification from the monomer storage buffer layer at the top of the grating has reached the depth level indicated by section 1422. Thus, at section 1422, the refractive index modulation has been modified such that the refractive index in region 1402 is increased, as shown in graph 1420. In graph 1420, the minimum point of the refractive index is shifted upward from n1 compared to graph 1430.

[0149] Figure 15A-15B An example of refractive index modulation in an apodization grating according to some embodiments is shown. Fig.15A The refractive index modulation (with and without refractive index modification) is shown as a function of the grating depth z ( Fig. 15B .

[0150] exist Fig.15A In Figure 1, the refractive index modulation distribution in the apodized grating is shown. Fig. 15B As shown, such apodized gratings can be used for 1-D or 2-D pupil expanders in waveguide-based near-eye display systems. The refractive index modulation 1502 without refractive index profile modulation has a constant profile with respect to the normalized grating depth z. The refractive index modulation 1504 with refractive index profile modulation can be used to reduce or eliminate side lobes, such as Figure 16A-16B shown.

[0151] Figure 16A-16B FIG. 4 illustrates sidelobe reduction using an apodized grating according to some embodiments. Fig.16A , the normalized diffraction efficiency of a single grating is shown as a function of wavelength. Graph 1602 may correspond to a grating without apodization. Sidelobes 1606 are visible. These sidelobes are undesirable, especially in multiplexed gratings. In multiplexed gratings, the sidelobes of the diffraction pattern can cause crosstalk, reducing image contrast. To avoid this crosstalk, the number of multiplexed gratings may be limited, which limits the achievable efficiency.

[0152] On the other hand, graph 1604 corresponds to a grating with a variable refractive index across the grating thickness, reducing the side lobes. To reduce the side lobes, the refractive index of the grating should be modified so that the refractive index modulation is higher at the center of the grating and lower at one or more sides of the grating, such as Fig. 13B and Fig.14 In some embodiments, Figure 15A-15B As shown, a bell-shaped refractive index modulation profile across the z-direction in the grating can be produced. Therefore, varying the refractive index across the thickness of the grating can reduce side lobes and crosstalk in multiplexed gratings. This improves image contrast and enables the multiplexing of a greater number of gratings, thereby increasing overall efficiency.

[0153] exist Fig. 16B , graphs 1602 and 1604 of normalized diffraction efficiency versus wavelength are shown on a logarithmic scale, further highlighting the side lobes 1606 and their reduction.

[0154] Fig.17 1700 is a simplified flowchart 1700 illustrating an example of a method of manufacturing a holographic optical element according to some embodiments. The operations described in flowchart 1700 are for illustration purposes only and are not intended to be limiting. In various implementations, flowchart 1700 may be modified to add additional operations, omit some operations, merge some operations, separate some operations, or reorder some operations.

[0155] At block 1710, a holographic recording material layer may be obtained. The holographic recording material layer may include a mixture of matrix monomers and writing monomers. The matrix monomers may be configured to polymerize (e.g., by thermal treatment) to form a polymer matrix. The writing monomers may be dispersed in the matrix monomers and may be configured to polymerize when the holographic recording material is exposed to recording light. The matrix monomers may have a refractive index (one or more) different from that of the writing monomers. For example, the writing monomers may have a higher refractive index than the matrix monomers.

[0156] In some embodiments, the holographic recording material layer can be cured, for example, thermally cured or photocured, to polymerize the matrix monomers and form a polymer matrix. The writing monomers may not polymerize under the curing conditions and may be dispersed in the formed polymer matrix. The polymer matrix can be used as a supporting matrix or skeleton for the holographic recording material layer.

[0157] At block 1720, the layer of holographic recording material may be exposed to a recording light pattern to polymerize writing monomers in selected areas (such as bright stripes of the recording light pattern), as described above with reference to, for example Figure 7A-Figure 8The recording light pattern may correspond to a grating, a lens, a diffuser, etc. The recording light pattern may cause polymerization and diffusion of the writing monomer to form a holographic optical element corresponding to the recording light pattern. Exposure to the recording light pattern generates a first region having a first refractive index and a second region having a second refractive index.

[0158] In box 1730, a resin layer containing nanoparticles can be applied to the holographic recording material layer. For example, the holographic recording material layer can be deposited or laminated on the first resin layer. In some embodiments, the holographic recording material layer can be laminated on a substrate, which can be removed before applying the resin layer. In some embodiments, the holographic recording material layer can be sandwiched between two resin layers. Alternatively, the holographic recording material layer can be laminated on a substrate (e.g., glass or plastic) layer on one side, and the resin layer is applied to the holographic recording material layer on the other side. The application of the resin layer causes the nanoparticles to diffuse from the resin layer into the holographic recording material layer. The particles will also diffuse from the holographic recording material layer into the resin layer. If the unreacted monomers from the initial holographic film are not present in the resin layer, the monomers will diffuse from the holographic film to the resin layer, simply because there is a natural concentration gradient between the two films. Therefore, the refractive index in the holographic recording material layer is modified due to the diffusion of the particles. The concentration of the nanoparticles in the resin layer can be controlled so that after a period of time, no nanoparticles can diffuse into the holographic recording material layer. Alternatively or additionally, the removal of the resin layer may be timed to tailor the nanoparticle concentration in the holographic recording material layer.The concentration of the nanoparticles may be tailored to achieve any configuration for improving diffraction efficiency or apodizing the gratings described above.

[0159] Optionally, at block 1740, the resin layer(s) may be removed from the holographic recording material layer. The holographic recording material layer may then be laminated on one or more substrates. For example, the resin layer may include a flexible polyester film or a plastic sheet. Such a flexible resin layer may be peeled off from the holographic recording material layer. The holographic recording material layer on a substrate may then be laminated on a substrate such as an optical component (e.g., quartz, glass, a crystal plate, or a lens).

[0160] Removing the resin layer and / or substrate without damaging the holographic recording material layer can be achieved in a variety of ways. Using a pliable material such as a flexible plastic can help achieve low-impact layer removal. Alternatively or additionally, the resin layer or substrate can be treated with an anti-adhesive composition to make the layer easy to remove.

[0161] Fig.18 is a schematic diagram illustrating another HOE manufacturing method 1800 according to some embodiments. The HOE manufacturing method 1800 is similar to the method described above with reference to FIG7, but the resin layer(s) are applied prior to the holographic exposure.

[0162] At 1802, a resin layer 1810 is applied to a first substrate 1820, the resin layer 1810 being filled with nanoparticles, such as a monomer having a predetermined refractive index. The resin layer 1810 may be bonded to or deposited on the first substrate 1820. A holographic recording material layer 1830 is applied to a second substrate 1840. Similarly, the holographic recording material layer 1830 may be bonded to or deposited on the second substrate 1840. In some embodiments, the resin layer and the holographic recording material layer have similar properties. For example, both the resin layer and the holographic recording material layer may include a polymer matrix. However, the holographic recording material layer may differ in the addition of a photoinitiator for holographic recording.

[0163] At 1804, a resin layer 1810 and a first substrate 1820 are disposed on a holographic recording material layer 1830 and a second substrate 1840. The resin layer 1810 is placed in contact with the holographic recording material layer 1830. The resin layer 1810 is laminated or bonded to the holographic recording material layer 1830. Nanoparticles may diffuse from the resin layer 1810 into the holographic recording material layer 1830. Substances may also diffuse from the holographic recording material layer 1830 into the resin layer 1810. The dispersion of the nanoparticles may be tailored to achieve any configuration for improving diffraction efficiency or apodizing the above-described gratings.

[0164] At 1806, the hologram is recorded in the holographic recording material layer 1830. As described above with reference to Fig.17 As described above, the recording light pattern is applied at least to the recording material layer.

[0165] At 1808, the hologram has been recorded in the holographic recording material layer 1830. The resin layer 1810 can remain attached to the holographic recording material layer 1830. After the hologram is recorded, diffusion may continue for a period of time. As the nanoparticles diffuse from the resin layer 1810 into the holographic recording material layer 1830, or vice versa, the refractive index modulation can continue to change. The amount of diffusion and the corresponding refractive index change can be controlled by controlling the amount of nanoparticles in the resin layer 1810 (for example, so that only the desired amount of nanoparticles is available). The speed of the diffusion process (and the solubility of the monomer in the grating) can be controlled by raising / lowering the temperature. In addition, the diffusion process can be stopped by flood exposing the two films to polymerize the diffused monomers. In addition, the support layer of the resin layer can be selected so that the support layer is transparent to visible light (for example, similar to the substrate layer) to avoid affecting the performance of the holographic optical element.

[0166] Embodiments may be used to manufacture components of artificial reality systems, or may be implemented in conjunction with artificial reality systems. Artificial reality is a form of reality that is adjusted in some way before being presented to a user, which may include, for example, virtual reality (VR), augmented reality (AR), mixed reality (MR), mixed reality, or some combination and / or derivative thereof. Artificial reality content may include fully generated content or generated content combined with captured (e.g., real-world) content. Artificial reality content may include video, audio, tactile feedback, or some combination thereof, and any of them may be presented in a single channel or in multiple channels (such as, stereoscopic video that produces a three-dimensional effect on the viewer). Additionally, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof for, for example, creating content in artificial reality and / or otherwise using it in artificial reality (e.g., performing activities in artificial reality). Artificial reality systems that provide artificial reality content may be implemented on various platforms, including head-mounted displays (HMDs) connected to a host computer system, independent HMDs, mobile devices or computing systems, or any other hardware platform capable of providing artificial reality content to one or more viewers.

[0167] Fig.19 1 is a simplified block diagram of an example of an electronic system 1900 for implementing some of the example near-eye display systems (e.g., HMD devices) disclosed herein. The electronic system 1900 can be used as an electronic system for the HMD device or other near-eye displays described above. In this example, the electronic system 1900 may include one or more processors 1910 and a memory 1920. The processor 1910 may be configured to execute instructions for performing operations at multiple components, and may be, for example, a general-purpose processor or a microprocessor suitable for implementation in a portable electronic device. The processor 1910 may be communicatively coupled to multiple components within the electronic system 1900. To achieve this communicatively coupling, the processor 1910 may communicate with other illustrated components across a bus 1940. The bus 1940 may be any subsystem suitable for transmitting data within the electronic system 1900. The bus 1940 may include multiple computer buses and additional circuits to transmit data.

[0168] Memory 1920 may be coupled to processor 1910. In some embodiments, memory 1920 may provide both short-term storage and long-term storage, and may be divided into several units. Memory 1920 may be volatile (such as static random access memory (SRAM) and / or dynamic random access memory (DRAM)) and / or non-volatile (such as read-only memory (ROM), flash memory, etc.). In addition, memory 1920 may include a removable storage device such as a secure digital (SD) card. Memory 1920 may provide storage of computer-readable instructions, data structures, program modules, and other data for electronic system 1900. In some embodiments, memory 1920 may be distributed in different hardware modules. A set of instructions and / or codes may be stored in memory 1920. The instructions may be in the form of executable code that can be executed by the electronic system 1900, and / or may be in the form of source code and / or installable code that, when compiled and / or installed on the electronic system 1900 (e.g., using any of a variety of commonly available compilers, installers, compression / decompression utilities, etc.), may be in the form of executable code.

[0169] In some embodiments, the memory 1920 may store a plurality of application modules 1922 to 1924, which may include any number of applications. Examples of applications may include gaming applications, conference applications, video playback applications, or other suitable applications. These applications may include depth sensing functions or eye tracking functions. The application modules 1922-1924 may include specific instructions to be executed by the processor 1910. In some embodiments, specific applications or portions of the application modules 1922-1924 may be executed by other hardware modules 1980. In some embodiments, the memory 1920 may additionally include a secure memory, which may include additional security controls to prevent copying or other unauthorized access to secure information.

[0170] In some embodiments, the memory 1920 may include an operating system 1925 loaded therein. The operating system 1925 may be operable to initiate the execution of instructions provided by the application modules 1922-1924 and / or manage other hardware modules 1980 and interfaces with the wireless communication subsystem 1930, which may include one or more wireless transceivers. The operating system 1925 may be adapted to perform other operations across components of the electronic system 1900, including threading, resource management, data storage control, and other similar functions.

[0171] The wireless communication subsystem 1930 may include, for example, an infrared communication device, a wireless communication device and / or a chipset (such as, Device, IEEE 802.11 device, Wi-Fi device, WiMax device, cellular communication facility, etc.) and / or similar communication interfaces. The electronic system 1900 may include one or more antennas 1934 for wireless communication as part of the wireless communication subsystem 1930 or as a separate component coupled to any part of the system. Depending on the desired functionality, the wireless communication subsystem 1930 may include a separate transceiver to communicate with base transceiver stations and other wireless devices and access points, which may include communicating with different data networks and / or network types (such as, wireless wide area network (WWAN), wireless local area network (WLAN) or wireless personal area network (WPAN)). The WWAN may be, for example, a WiMax (IEEE 802.16) network. The WLAN may be, for example, an IEEE 802.11x network. The WPAN may be, for example, a Bluetooth network, IEEE802.15x or some other type of network. The techniques described herein may also be used for any combination of WWAN, WLAN and / or WPAN. The wireless communication subsystem 1930 may allow data to be exchanged with a network, other computer systems and / or any other device described herein. The wireless communication subsystem 1930 may include means for sending or receiving data (such as an identifier of the HMD device, location data, geographic maps, heat maps, photos, or videos) using an antenna 1934 and a wireless link 1932. The wireless communication subsystem 1930, the processor 1910, and the memory 1920 may together include at least a portion of one or more of the means for performing some of the functions disclosed herein.

[0172] Embodiments of the electronic system 1900 may also include one or more sensors 1990. The sensor 1990 may include, for example, an image sensor, an accelerometer, a pressure sensor, a temperature sensor, a proximity sensor, a magnetometer, a gyroscope, an inertial sensor (e.g., a module combining an accelerometer and a gyroscope), an ambient light sensor, or any other similar module operable to provide a sensing output and / or receive a sensing input, such as a depth sensor or a position sensor. For example, in some embodiments, the sensor 1990 may include one or more inertial measurement units (IMUs) and / or one or more position sensors. The IMU may generate calibration data based on measurement signals received from one or more position sensors, the calibration data indicating an estimated position of the HMD device relative to an initial position of the HMD device. The position sensor may generate one or more measurement signals in response to a movement of the HMD device. Examples of position sensors may include, but are not limited to, one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects movement, a type of sensor used for error correction of the IMU, or some combination thereof. The position sensors may be located external to the IMU, internal to the IMU, or some combination thereof.At least some of the sensors may use structured light patterns for sensing.

[0173] The electronic system 1900 may include a display module 1960. The display module 1960 may be a near-eye display and may graphically present information from the electronic system 1900, such as images, videos, and various instructions, to a user. Such information may be derived from one or more application modules 1922-1924, a virtual reality engine 1926, one or more other hardware modules 1980, a combination thereof, or any other suitable means for parsing graphical content for a user (e.g., via an operating system 1925). The display module 1960 may use liquid crystal display (LCD) technology, light emitting diode (LED) technology (including, for example, OLED, ILED, mLED, AMOLED, TOLED, etc.), light emitting polymer display (LPD) technology, or some other display technology.

[0174] The electronic system 1900 may include a user input / output module 1970. The user input / output module 1970 may allow a user to send an action request to the electronic system 1900. The action request may be a request to perform a specific action. For example, the action request may be to start or end an application, or to perform a specific action within an application. The user input / output module 1970 may include one or more input devices. Example input devices may include a touch screen, a touch pad, a microphone, a button, a dial, a switch, a keyboard, a mouse, a game controller, or any other suitable device for receiving an action request and transmitting the received action request to the electronic system 1900. In some embodiments, the user input / output module 1970 may provide tactile feedback to the user according to instructions received from the electronic system 1900. For example, tactile feedback may be provided when an action request is received or an action request has been performed.

[0175] The electronic system 1900 may include a camera 1950, which may be used to take photos or videos of the user, for example, to track the user's eye position. The camera 1950 may also be used to take photos or videos of the environment, for example, for VR applications, AR applications, or MR applications. The camera 1950 may include, for example, a complementary metal oxide semiconductor (CMOS) image sensor having millions or tens of millions of pixels. In some embodiments, the camera 1950 may include two or more cameras, which may be used to capture 3D images.

[0176] In some embodiments, the electronic system 1900 may include a plurality of other hardware modules 1980. Each of the other hardware modules 1980 may be a physical module within the electronic system 1900. Although each of the other hardware modules 1980 may be permanently configured as a structure, some of the other hardware modules 1980 may be temporarily configured to perform a specific function or be temporarily activated. Examples of other hardware modules 1980 may include, for example, an audio output and / or input module (e.g., a microphone or a speaker), a near field communication (NFC) module, a rechargeable battery, a battery management system, a wired / wireless battery charging system, and the like. In some embodiments, one or more functions of the other hardware modules 1980 may be implemented in software.

[0177] In some embodiments, the memory 1920 of the electronic system 1900 may also store a virtual reality engine 1926. The virtual reality engine 1926 may execute an application within the electronic system 1900 and receive position information, acceleration information, velocity information, predicted future position, or some combination thereof of the HMD device from various sensors. In some embodiments, the information received by the virtual reality engine 1926 may be used to generate a signal (e.g., a display instruction) for the display module 1960. For example, if the received information indicates that the user has looked to the left, the virtual reality engine 1926 may generate content for the HMD device that reflects the user's movement in the virtual environment. Additionally, the virtual reality engine 1926 may perform an action within the application in response to an action request received from the user input / output module 1970 and provide feedback to the user. The feedback provided may be visual feedback, auditory feedback, or tactile feedback. In some embodiments, the processor 1910 may include one or more GPUs that may execute the virtual reality engine 1926.

[0178] In various embodiments, the hardware and modules described above can be implemented on a single device, or on multiple devices that can communicate with each other using wired or wireless connections. For example, in some embodiments, some components or modules (such as a GPU, virtual reality engine 1926, and applications (e.g., tracking applications)) can be implemented on a console separate from the head-mounted display device. In some embodiments, a console can be connected to more than one HMD or can support more than one HMD.

[0179] In alternative configurations, different and / or additional components may be included in the electronic system 1900. Similarly, the functionality of one or more components may be distributed among the components in a manner different from that described above. For example, in some embodiments, the electronic system 1900 may be modified to include other system environments, such as an AR system environment and / or an MR environment.

[0180] The methods, systems, and devices discussed above are examples. Various embodiments may omit, replace, or add individual processes or components as appropriate. For example, in alternative configurations, the described methods may be performed in an order different from that described, and / or individual stages may be added, omitted, and / or combined. In addition, the features described with respect to certain embodiments may be combined in various other embodiments. Different aspects and elements of the embodiments may be combined in a similar manner. In addition, technology is constantly evolving, and therefore many elements are examples, which do not limit the scope of the present disclosure to those specific examples.

[0181] Specific details are given in the description to provide a thorough understanding of the embodiments. However, embodiments may be implemented without these specific details. For example, in order to avoid obscuring the embodiments, well-known circuits, processes, systems, structures, and techniques have been shown without unnecessary details. This description provides only example embodiments and is not intended to limit the scope, applicability, or configuration of the present invention. Rather, the foregoing description of the embodiments will provide enabling descriptions (enabling descriptions) for implementing various embodiments to those skilled in the art. Various changes may be made in the functions and arrangements of elements without departing from the spirit and scope of the present disclosure.

[0182] In addition, some embodiments are described as processes, and the processes are depicted as flow charts or block diagrams. Although each can describe the operation as a sequential process, many operations can be performed in parallel or concurrently. In addition, the order of the operations can be rearranged. The process can have additional steps not included in the figure. In addition, the embodiment of the method can be implemented by hardware, software, firmware, middleware, microcode, hardware description language or any combination thereof. When implemented in software, firmware, middleware or microcode, the program code or code segment performing the associated task can be stored in a computer-readable medium such as a storage medium. The processor can perform the associated task.

[0183] It will be apparent to those skilled in the art that substantial variations may be made depending on specific requirements. For example, customized or dedicated hardware may also be used, and / or specific elements may be implemented in hardware, software (including portable software, such as applets, etc.), or both. In addition, connections to other computing devices (such as network input / output devices) may be employed.

[0184] With reference to the accompanying drawings, the components that may include memory may include non-temporary machine-readable media. The terms "machine-readable medium" and "computer-readable medium" may refer to any storage medium that participates in providing data that enables a machine to operate in a particular manner. In the embodiments provided above, various machine-readable media may involve providing instructions / codes to a processing unit and / or other devices for execution. Additionally or alternatively, a machine-readable medium may be used to store and / or carry such instructions / codes. In many embodiments, a computer-readable medium is a physical storage medium and / or a tangible storage medium. Such a medium may take a variety of forms, including but not limited to non-volatile media, volatile media, and transmission media. Common forms of computer-readable media include, for example, magnetic media and / or optical media (such as compact disks (CDs) or digital versatile disks (DVDs)), punch cards, paper tapes, any other physical media with hole patterns, RAM, programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), flash-EPROM, any other memory chip or box, a carrier wave as described below, or any other medium from which a computer can read instructions and / or codes. A computer program product may include code and / or machine executable instructions, which may represent a procedure, function, subprogram, program, routine, application (App), subroutine, module, software package, class, or any combination of instructions, data structures, or program statements.

[0185] Those skilled in the art will appreciate that the information and signals used to transmit the messages described herein may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0186] The terms "and" and "or" as used herein may include multiple meanings, which are also expected to depend at least in part on the context in which such terms are used. Generally, "or", if used in an associative list, such as A, B, or C, is intended to mean A, B, and C (used herein in an inclusive sense) as well as A, B, or C (used herein in an exclusive sense). In addition, the term "one or more" as used herein may be used to describe any feature, structure, or characteristic in a singular form, or may be used to describe a certain combination of features, structures, or characteristics. However, it should be noted that this is merely an illustrative example, and the subject matter claimed is not limited to this example. In addition, the term "at least one of...", if used in an associative list, such as A, B, or C, may be interpreted to mean any combination of A, B, and / or C, such as A, AB, AC, BC, AA, ABC, AAB, AABBCCC, etc.

[0187] In addition, although certain embodiments have been described using a particular combination of hardware and software, it should be appreciated that other combinations of hardware and software are possible. Certain embodiments may be implemented in hardware only, or in software only, or using a combination thereof. In one example, the software may be implemented using a computer program product comprising computer program code or instructions that may be executed by one or more processors for performing any or all of the steps, operations, or processes described in this disclosure, wherein the computer program may be stored on a non-transitory computer-readable medium. The various processes described herein may be implemented on the same processor or on different processors in any combination.

[0188] Where a device, system, component or module is described as being configured to perform certain operations or functions, such configuration may be accomplished, for example, by designing electronic circuits that perform the operations, by programming programmable electronic circuits (such as microprocessors) to perform the operations (such as by executing computer instructions or code), or by a processor or core programmed to execute code or instructions stored on a non-transitory memory medium, or any combination thereof. Processes may communicate using a variety of technologies (including, but not limited to, conventional technologies for inter-process communication), and different pairs of processes may use different technologies, or the same pair of processes may use different technologies at different times.

[0189] Therefore, the description and drawings should be regarded as illustrative rather than restrictive. However, it will be apparent that additions, subtractions, deletions and other modifications and changes may be made thereto without departing from the broader spirit and scope as set forth in the claims. Therefore, although specific embodiments have been described, these embodiments are not intended to be limiting. Various modifications and equivalents are within the scope of the appended claims.

Claims

1. A holographic grating, comprising: A polymer layer comprising: a first region characterized by a first refractive index; a second region characterized by a second refractive index that is higher than the first refractive index; and A plurality of nanoparticles are dispersed in the polymer layer, wherein the nanoparticles have a higher concentration in the first region or the second region; wherein the plurality of nanoparticles are monomers.

2. The holographic grating according to claim 1, wherein: The nanoparticles have a higher concentration in the second region; and The nanoparticles have a third refractive index higher than the second refractive index.

3. The holographic grating according to claim 1, wherein: The nanoparticles have a higher concentration in the first region; and The nanoparticles have a third refractive index lower than the first refractive index.

4. The holographic grating according to claim 1, wherein: The nanoparticles in the first region or the second region have a substantially constant concentration relative to the thickness of the polymer layer.

5. The holographic grating according to claim 1, wherein: The polymer layer includes a multiplexed volume Bragg grating.

6. A method for manufacturing a holographic grating according to any one of claims 1 to 5, comprising the following steps: obtaining a holographic recording material layer; exposing the holographic recording material layer to a recording light pattern that produces in the holographic recording material layer a first region having a first refractive index and a second region having a second refractive index that is higher than the first refractive index; and A first resin layer containing a first plurality of nanoparticles is applied to the holographic recording material layer such that at least a portion of the first plurality of nanoparticles diffuses into the holographic recording material layer.

7. The method according to claim 6, wherein: The first resin layer is applied before exposing the holographic recording material layer to the recording light pattern.

8. A method according to claim 6 or claim 7, wherein: The first plurality of nanoparticles have a third refractive index higher than the second refractive index; and The first plurality of nanoparticles preferentially diffuse into the second region.

9. The method according to claim 6 or claim 7, wherein: The first plurality of nanoparticles have a third refractive index lower than the second refractive index; and The first plurality of nanoparticles preferentially diffuse so as to be more highly concentrated near one or more of a top side or a bottom side of the second region.

10. The method according to claim 6 or claim 7, wherein: The first plurality of nanoparticles have a third refractive index lower than the first refractive index; and The first plurality of nanoparticles preferentially diffuse into the first region.

11. The method according to claim 6 or claim 7, wherein: The first plurality of nanoparticles have a third refractive index higher than the first refractive index; and The first plurality of nanoparticles further diffuse to be more highly concentrated near one or more of the top side or the bottom side of the first region.

12. The method according to claim 6 or claim 7, wherein: The steps also include: removing the first resin layer; and A substrate is provided on the holographic recording material layer.

13. The method according to claim 6 or claim 7, further comprising: A second resin layer containing a second plurality of nanoparticles is applied to the holographic recording material layer such that at least a portion of the second plurality of nanoparticles diffuses into the holographic recording material layer.

14. The method according to claim 6 or claim 7, wherein: The nanoparticles in a given area have a substantially constant concentration relative to the thickness of the layer of holographic recording material.

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