Spatially multiplexed volume Bragg grating with variable refractive index modulation for waveguide displays

Abstract

The present application relates to a spatially multiplexed volume Bragg grating with variable refractive index modulation for a waveguide display, and a waveguide display comprising a waveguide transparent to visible light, a first volume Bragg grating (VBG) on the waveguide, the first volume Bragg grating (VBG) characterized by a first refractive index modulation, and a second reflective VBG on the waveguide, the second volume Bragg grating (VBG) characterized by a second refractive index modulation. The second reflective VBG includes a plurality of regions characterized by different respective refractive index modulation. The first reflective VBG is configured to diffract display light in a first wavelength range and a first field of view (FOV) range such that the display light in the first wavelength range and the first FOV range propagates in the waveguide by total internal reflection to a plurality of regions of the second reflective VBG. The plurality of regions of the second reflective VBG are configured to diffract display light within different respective ones of the first wavelength ranges and the first FOV range.

Description

[0001] This application is a divisional application of an application with an application date of August 24, 2020, application number 202080059760.3, and invention name “Spatially multiplexed volume Bragg grating with variable refractive index modulation for waveguide displays”. Technical Field

[0002] The present invention generally relates to volume Bragg grating based waveguide displays for near-eye displays. Background Art

[0003] Artificial reality systems such as head-mounted display (HMD) or head-up display (HUD) systems typically include a near-eye display (e.g., in the form of a headset or a pair of glasses) that is configured to present content to a user via, for example, an electronic display or an optical display within approximately 10 mm-20 mm in front of the user's eyes. As in virtual reality (VR), augmented reality (AR), or mixed reality (MR) applications, the near-eye display can display virtual objects or combine images of real objects with virtual objects. For example, in an AR system, a user can view both an image of a virtual object (e.g., a computer-generated image (CGI)) and the surrounding environment by, for example, looking through transparent display glasses or lenses (commonly referred to as optical see-through).

[0004] An example 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 implementations, a diffractive optical element (e.g., a grating) may be used to couple light for a projected image into or out of the waveguide. Light from the surrounding environment may pass through the see-through region of the waveguide and also reach the user's eyes. Summary of the invention

[0005] The present invention generally relates to volume Bragg grating-based waveguide displays for near-eye displays. More specifically, techniques are disclosed herein for using volume Bragg grating (VBG) couplers to expand the eyebox, reduce display haze, reduce physical size, improve optical efficiency, reduce optical artifacts, and increase the field of view of optical see-through near-eye display systems. Various invention embodiments are described herein, including devices, systems, methods, and the like.

[0006] In one aspect, the present invention provides a waveguide display, which may include a substrate, a first reflective VBG (reflection VBG) on the substrate, and a second reflective VBG on the substrate, the first reflective VBG being characterized by a first refractive index modulation, and the second reflective VBG including a first region and a second region. The first reflective VBG may be configured to diffract display light within a first wavelength range, so that the display light within the first wavelength range propagates in the substrate to the first region and the second region of the second reflective VBG by total internal reflection. The first region of the second reflective VBG may be characterized by a second refractive index modulation lower than the first refractive index modulation, and may be configured to diffract display light within a second wavelength range within the first wavelength range. The second region of the second reflective VBG may be characterized by a third refractive index modulation greater than the second refractive index modulation, and may be configured to diffract display light within a third wavelength range including and greater than the second wavelength range. The first region and the second region of the second reflective VBG may be arranged so that the display light within the first wavelength range reaches the first region before reaching the second region.

[0007] In some embodiments, the first reflective VBG and the second reflective VBG may have the same grating vector in a plane perpendicular to the surface normal direction of the substrate. The third refractive index modulation may be equal to or less than the first refractive index modulation, and the first wavelength range may be the same as or include the third wavelength range. In some embodiments, the second reflective VBG may further include a third region between the first region and the second region, wherein the third region may be characterized by a fourth refractive index modulation greater than the second refractive index modulation but lower than the third refractive index modulation, and may be configured to diffract display light within a fourth wavelength range that includes the second wavelength range and is within the third wavelength range.

[0008] In some embodiments, the waveguide display may further include a third reflective VBG multiplexed with the first reflective VBG and characterized by a fourth refractive index modulation, and a fourth reflective VBG multiplexed with the second reflective VBG in the first region and the second region. The third reflective VBG may be configured to diffract display light within a fourth wavelength range, such that the display light within the fourth wavelength range propagates in the substrate to the first region and the second region of the fourth reflective VBG by total internal reflection. The first region of the fourth reflective VBG may be characterized by a fifth refractive index modulation lower than the fourth refractive index modulation, and may be configured to diffract display light within a fifth wavelength range within the fourth wavelength range. The second region of the fourth reflective VBG may be characterized by a sixth refractive index modulation greater than the fifth refractive index modulation, and may be configured to diffract display light within a sixth wavelength range including and greater than the fifth wavelength range.

[0009] In some embodiments, the first reflective VBG may be configured to diffract display light within a first wavelength range and a first field of view (FOV), and to diffract display light within a fourth wavelength range and a second FOV range different from the first FOV range. In some embodiments, the substrate may be transparent to visible light, and the second reflective VBG may be transparent to visible light from the surrounding environment. In some embodiments, the first reflective VBG may be configured to couple display light within the first wavelength range into the substrate, and the second reflective VBG may be configured to couple display light within the first wavelength range out of the substrate. In some embodiments, the waveguide display may further include a third grating and a fourth grating, wherein the third grating may be configured to diffract display light within the first wavelength range from the first reflective VBG to the fourth grating, and the fourth grating may be configured to diffract display light within the first wavelength range to the second reflective VBG at two or more regions of the fourth grating. The third grating and the fourth grating may have the same grating vector in a plane perpendicular to the surface normal direction of the substrate.

[0010] In some embodiments, a waveguide display may include an input coupler configured to couple display light in a first wavelength range into a substrate, and an output coupler configured to couple display light diffracted by a second reflective VBG out of the substrate. The input coupler and the output coupler may include a multiplexed VBG. In some embodiments, a waveguide display may include a light source configured to generate display light, and a projector optical device configured to collimate the display light and direct the display light to the first reflective VBG.

[0011] In another aspect, the present invention provides a waveguide display, which may include a waveguide transparent to visible light, a first VBG on the waveguide, and a second reflective VBG on the waveguide, wherein the first VBG is characterized by a first refractive index modulation, and the second reflective VBG includes a plurality of regions characterized by different corresponding refractive index modulations. The first reflective VBG may be configured to diffract display light within a first wavelength range and a first FOV range, so that the display light within the first wavelength range and the first FOV range may propagate in the waveguide to the plurality of regions of the second reflective VBG by total internal reflection. The plurality of regions of the second reflective VBG may be configured to diffract display light within different corresponding wavelength ranges within the first wavelength range and within the first FOV range. The first reflective VBG and the second reflective VBG may have the same grating vector in a plane perpendicular to the surface normal direction of the waveguide.

[0012] In some embodiments of the waveguide display, at least one of the first refractive index modulation and the different corresponding refractive index modulations of the plurality of regions of the second reflective VBG can be greater than a minimum refractive index modulation at which the diffraction efficiency is saturated. In some embodiments, the plurality of regions of the second reflective VBG can be configured such that display light within the first wavelength range and the first FOV range can reach a first region of the plurality of regions, the first region having a second refractive index modulation, before reaching a second region of the plurality of regions, the second region having a third refractive index modulation greater than the second refractive index modulation.

[0013] In some embodiments, the first reflective VBG may be configured to couple display light within a first wavelength range and a first FOV range into the waveguide, and the second reflective VBG may be configured to couple display light within the first wavelength range and the first FOV range out of the waveguide and may be transparent to visible light from the surrounding environment. In some embodiments, the waveguide display may further include a third grating and a fourth grating. The third grating may be configured to diffract display light within the first wavelength range and the first FOV range from the first reflective grating to the fourth grating. The fourth grating may be configured to diffract display light within the first wavelength range and the first FOV range to the second reflective VBG at two or more regions of the fourth grating. The third grating and the fourth grating may have the same grating vector in a plane perpendicular to the surface normal direction of the waveguide.

[0014] The invention is defined in the appended claims. 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 present disclosure, any or all of the drawings, and each claim. The foregoing and other features and examples are described in more detail below in the following description, claims, and drawings. It should be understood that any feature discussed as suitable for inclusion in any aspect described herein is also suitable for inclusion in any other aspect in any combination.

[0015] This application provides the following:

[0016] 1) A waveguide display comprising:

[0017] substrate;

[0018] a first reflective volume Bragg grating (VBG) on the substrate characterized by a first refractive index modulation; and

[0019] a second reflective VBG on the substrate, comprising a first region and a second region,

[0020] wherein the first reflective VBG is configured to diffract display light within a first wavelength range so that the display light within the first wavelength range propagates in the substrate to the first region and the second region of the second reflective VBG by total internal reflection;

[0021] wherein the first region of the second reflective VBG is characterized by a second refractive index modulation lower than the first refractive index modulation and is configured to diffract display light within a second wavelength range within the first wavelength range; and

[0022] Wherein, the second region of the second reflective VBG is characterized by a third refractive index modulation greater than the second refractive index modulation, and is configured to diffract display light within a third wavelength range that includes and is greater than the second wavelength range.

[0023] 2) The waveguide display according to 1), wherein the first region and the second region of the second reflective VBG are arranged so that display light in the first wavelength range reaches the first region before reaching the second region.

[0024] 3) A waveguide display according to 1) or 2), wherein:

[0025] The third refractive index modulation is equal to or less than the first refractive index modulation; and

[0026] The first wavelength range is the same as or includes the third wavelength range.

[0027] 4) A waveguide display according to any preceding claim, wherein the first reflective VBG and the second reflective VBG have the same grating vector in a plane perpendicular to the surface normal direction of the substrate.

[0028] 5) A waveguide display according to any of the preceding claims, wherein the second reflective VBG further comprises a third region between the first region and the second region, the third region being characterized by a fourth refractive index modulation greater than the second refractive index modulation but lower than the third refractive index modulation, and being configured to diffract display light within a fourth wavelength range that includes the second wavelength range and is within the third wavelength range.

[0029] 6) A waveguide display according to any preceding claim, further comprising:

[0030] a third reflective VBG multiplexed with the first reflective VBG and characterized by a fourth refractive index modulation; and

[0031] a fourth reflective VBG, which is multiplexed with the second reflective VBG in the first area and the second area,

[0032] wherein the third reflective VBG is configured to diffract display light within a fourth wavelength range, so that the display light within the fourth wavelength range propagates in the substrate to the first region and the second region of the fourth reflective VBG by total internal reflection;

[0033] wherein the first region of the fourth reflective VBG is characterized by a fifth refractive index modulation lower than the fourth refractive index modulation and is configured to diffract display light within a fifth wavelength range within the fourth wavelength range; and

[0034] Wherein, the second region of the fourth reflective VBG is characterized by a sixth refractive index modulation that is larger than the fifth refractive index modulation, and is configured to diffract display light within a sixth wavelength range that includes and is larger than the fifth wavelength range.

[0035] 7) A waveguide display according to any preceding claim, and one or more of the following holds:

[0036] Wherein, the first reflective VBG is configured as:

[0037] diffracting display light within said first wavelength range and within a first field of view (FOV); and

[0038] diffracting display light within a fourth wavelength range and a second FOV range different from the first FOV range;

[0039] in:

[0040] The substrate is transparent to visible light; and

[0041] The second reflective VBG is transparent to visible light from the surrounding environment.

[0042] 8) A waveguide display according to any preceding claim, wherein:

[0043] The first reflective VBG is configured to couple display light in the first wavelength range into the substrate; and

[0044] The second reflective VBG is configured to couple display light in the first wavelength range out of the substrate.

[0045] 9) The waveguide display according to 8), further comprising a third grating and a fourth grating, wherein:

[0046] The third grating is configured to diffract display light within the first wavelength range from the first reflective VBG to the fourth grating; and

[0047] The fourth grating is configured to diffract display light within the first wavelength range to the second reflective VBG at two or more regions of the fourth grating;

[0048] Optionally, the third grating and the fourth grating have the same grating vector in a plane perpendicular to the surface normal direction of the substrate.

[0049] 10) A waveguide display according to any preceding claim, further comprising:

[0050] an input coupler configured to couple display light within the first wavelength range into the substrate; and

[0051] an output coupler configured to couple the display light diffracted by the second reflective VBG out of the substrate;

[0052] Optionally, the input coupler and the output coupler comprise a multiplexed VBG.

[0053] 11) A waveguide display according to any preceding claim, further comprising:

[0054] a light source configured to generate the display light; and

[0055] Projector optics configured to collimate the display light and direct the display light toward the first reflective VBG.

[0056] 12) A waveguide display comprising:

[0057] waveguides transparent to visible light;

[0058] a first reflective volume Bragg grating (VBG) on the waveguide characterized by a first refractive index modulation; and

[0059] a second reflective VBG on the waveguide comprising a plurality of regions characterized by different respective refractive index modulations,

[0060] wherein the first reflective VBG is configured to diffract display light within a first wavelength range and a first field of view (FOV), so that the display light within the first wavelength range and the first FOV propagates in the waveguide to a plurality of regions of the second reflective VBG by total internal reflection; and

[0061] Wherein, the plurality of regions of the second reflective VBG are configured to diffract display light within different corresponding wavelength ranges within the first wavelength range and within the first FOV range.

[0062] 13) A waveguide display according to 12), wherein the first reflective VBG and the second reflective VBG have the same grating vector in a plane perpendicular to the surface normal direction of the waveguide.

[0063] 14) The waveguide display according to 12) or 13), and one or more of the following is true:

[0064] wherein at least one of the first refractive index modulation and the different corresponding refractive index modulations of the plurality of regions of the second reflective VBG is greater than a minimum refractive index modulation at which the diffraction efficiency is saturated;

[0065] Wherein, the multiple regions of the second reflective VBG are configured so that the display light within the first wavelength range and the first FOV range reaches the first region among the multiple regions before reaching the second region among the multiple regions, the first region has a second refractive index modulation, and the second region has a third refractive index modulation greater than the second refractive index modulation.

[0066] 15) A waveguide display according to any one of 12) to 14), and one or more of the following is true:

[0067] in:

[0068] The first reflective VBG is configured to couple display light within the first wavelength range and the first FOV range into the waveguide; and

[0069] The second reflective VBG is configured to couple display light within the first wavelength range and within the first FOV range out of the waveguide and is transparent to visible light from a surrounding environment;

[0070] in:

[0071] The third grating is configured to diffract the display light within the first wavelength range and the first FOV range from the first reflection grating to a fourth grating;

[0072] the fourth grating being configured to diffract display light within the first wavelength range and the first FOV range to the second reflective VBG at two or more regions of the fourth grating; and

[0073] The third grating and the fourth grating have the same grating vector in a plane perpendicular to the surface normal direction of the waveguide. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Illustrative embodiments are described in detail below with reference to the following drawings.

[0075] Figure 1is a simplified block diagram of an example of an artificial reality system environment including a near-eye display system in accordance with certain embodiments.

[0076] 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 of the examples disclosed herein.

[0077] 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.

[0078] Figure 4 is a simplified diagram showing an example of an optical system in a near-eye display system.

[0079] Figure 5 An example of an optical see-through augmented reality system including a waveguide display for exit pupil expansion is shown in accordance with some embodiments.

[0080] Figure 6 An example of an optical see-through augmented reality system including a waveguide display for exit pupil expansion is shown in accordance with certain embodiments.

[0081] Fig. 7A The spectral bandwidth of an example of a reflective volume Bragg grating (VBG) and the spectral bandwidth of an example of a transmissive surface relief grating (SRG) are shown. Figure 7B An example angular bandwidth of a reflective VBG and an example angular bandwidth of a transmissive SRG are shown.

[0082] Fig. 8A An example of an optical see-through augmented reality system is shown, in accordance with certain embodiments, that includes a waveguide display and a surface relief grating for exit pupil expansion. Figure 8B An example of an eye box including a two-dimensionally replicated exit pupil is shown in accordance with some embodiments.

[0083] Fig.9A Wave vectors of light diffracted by an example of a surface relief grating for exit pupil expansion and multiple color exit pupils in a waveguide display are shown. Fig. 9B Field of view clipping is shown by the example of a surface relief grating for exit pupil expansion in a waveguide display.

[0084] Fig. 10A An example of a volume Bragg grating based waveguide display in accordance with some embodiments is shown. Fig. 10B Shows Fig. 10AA top view of an example of a volume Bragg grating based waveguide display is shown. Fig. 10C Shows Fig. 10A A side view of an example of a volume Bragg grating based waveguide display is shown.

[0085] Fig.11 Light dispersion in an example of a volume Bragg grating based waveguide display according to some embodiments is shown.

[0086] Fig. 12A An example of a volume Bragg grating (VBG) is shown. Fig. 12B Shows Fig. 12A The Bragg condition of a volume Bragg grating is shown.

[0087] Fig.13A A front view of an example of a volume Bragg grating-based waveguide display with exit pupil expansion and dispersion reduction in accordance with certain embodiments is shown. Fig. 13B Shows Fig.13A A side view of an example of a volume Bragg grating based waveguide display is shown.

[0088] Fig.14A The propagation of light from different fields of view in a reflective volume Bragg grating based waveguide display is shown in accordance with some embodiments. Fig. 14B The propagation of light from different fields of view in a transmissive volume Bragg grating based waveguide display is shown in accordance with some embodiments.

[0089] Fig.15 An example of a reflective volume Bragg grating based waveguide display with exit pupil expansion and dispersion reduction in accordance with certain embodiments is shown.

[0090] Fig.16 An example of a transmissive volume Bragg grating based waveguide display with exit pupil expansion and form factor reduction in accordance with certain embodiments is shown.

[0091] Fig.17A An example of a transmissive volume Bragg grating in a waveguide display according to some embodiments is shown. Fig. 17B An example of a transmission VBG in a waveguide display is shown, where light diffracted by the reflective VBG is not totally reflected and guided in the waveguide. Fig. 17C An example of a reflective volume Bragg grating in a waveguide display according to some embodiments is shown. Fig.17D An example of a reflective VBG in a waveguide display is shown, where light diffracted by the transmissive VBG is not totally reflected and guided in the waveguide.

[0092] Fig.18A Light dispersion of an example of a reflective volume Bragg grating in a waveguide display according to some embodiments is shown. Fig.18B Light dispersion of an example of a transmissive volume Bragg grating in a waveguide display according to some embodiments is shown.

[0093] Fig.19A is a front view of an example of a volume Bragg grating-based waveguide display with exit pupil expansion and dispersion reduction in accordance with certain embodiments. Fig.19B is a side view of an example of a volume Bragg grating based waveguide display including an image projector and multiple polymer layers according to some embodiments.

[0094] Fig. 20A Another example of a volume Bragg grating based waveguide display with exit pupil expansion, reduced dispersion, reduced form factor, and improved power efficiency in accordance with certain embodiments is shown. Fig. 20B Shown in Fig. 20A Example of a replicated exit pupil at the viewport of a volume Bragg grating based waveguide display shown in .

[0095] Fig.21A An example of a volume Bragg grating based waveguide display with exit pupil expansion, dispersion reduction, and form factor reduction in accordance with certain embodiments is shown. Fig. 21B An example of a volume Bragg grating based waveguide display with exit pupil expansion, reduced dispersion, reduced form factor, and improved efficiency in accordance with certain embodiments is shown.

[0096] Fig.22A is a front view of an example of a volume Bragg grating-based waveguide display including two image projectors in accordance with certain embodiments. Fig. 22B is a side view of an example of a volume Bragg grating-based waveguide display including two image projectors in accordance with certain embodiments.

[0097] Fig.23A is a front view of an example of a volume Bragg grating-based waveguide display including a single image projector and gratings for field of view stitching in accordance with certain embodiments. Fig. 23B is a side view of an example of a volume Bragg grating-based waveguide display with a single image projector and gratings for field of view stitching in accordance with certain embodiments.

[0098] Fig.24 An example of a volume Bragg grating based waveguide display including multiple grating layers for different fields of view and / or wavelengths of light is shown in accordance with some embodiments.

[0099] Fig.25Shown is the field of view of multiple gratings in an example of a volume Bragg grating based waveguide display in accordance with some embodiments.

[0100] Fig.26A An example of a volume Bragg grating is shown diffracting light of different colors from different corresponding fields of view. Fig.26B The relationship between the grating period of a volume Bragg grating and the corresponding field of view for incident light of different colors is shown.

[0101] Fig.27A The diffraction efficiency of an example of a transmissive volume Bragg grating with the same thickness but different refractive index modulation is shown. Fig.27B The diffraction efficiency of an example of a reflective volume Bragg grating having the same thickness but different refractive index modulation is shown.

[0102] Fig.28A The diffraction efficiency of an example of a transmissive volume Bragg grating with a first refractive index modulation is shown as a function of the deviation of the incident angle from the Bragg condition. Fig.28B The diffraction efficiency of an example of a transmissive volume Bragg grating with a second refractive index modulation is shown as a function of the deviation of the incident angle from the Bragg condition. Fig.28C The diffraction efficiency of an example of a transmissive volume Bragg grating with a third refractive index modulation is shown as a function of the deviation of the incident angle from the Bragg condition. Fig.28D The diffraction efficiency of an example of a transmissive volume Bragg grating with a fourth refractive index modulation is shown as a function of the deviation of the incident angle from the Bragg condition.

[0103] Fig.29A The diffraction efficiency of an example of a reflective volume Bragg grating with a first refractive index modulation is shown as a function of the deviation of the incident angle from the Bragg condition. Fig.29B The diffraction efficiency of an example of a reflective volume Bragg grating with a second refractive index modulation is shown as a function of the deviation of the incident angle from the Bragg condition. Fig.29C The diffraction efficiency of an example of a reflective volume Bragg grating with a third refractive index modulation is shown as a function of the deviation of the incident angle from the Bragg condition. Fig.29D The diffraction efficiency of an example of a reflective volume Bragg grating with a fourth refractive index modulation is shown as a function of the deviation of the incident angle from the Bragg condition.

[0104] Fig. 30A The diffraction efficiency of an example of a transmissive VBG with a first refractive index modulation is shown for blue light from different fields of view. Fig. 30B The diffraction efficiency of an example of a transmissive VBG with a first refractive index modulation is shown for green light from different fields of view. Fig. 30CThe diffraction efficiency of an example of a transmissive VBG with a first refractive index modulation is shown for red light from different fields of view. Fig.30D The diffraction efficiency of an example of a transmissive VBG with a second refractive index modulation is shown for blue light from different fields of view. Fig.30E The diffraction efficiency of an example of a transmissive VBG with a second refractive index modulation is shown for green light from different fields of view. Fig.30F The diffraction efficiency of an example of a transmissive VBG with a second refractive index modulation is shown for red light from different fields of view. Figure 30G The diffraction efficiency of an example of a transmissive VBG with a third refractive index modulation is shown for blue light from different fields of view. Fig. 30H The diffraction efficiency of an example of a transmissive VBG with a third refractive index modulation is shown for green light from different fields of view. Fig. 30I The diffraction efficiency of an example of a transmissive VBG with a third refractive index modulation is shown for red light from different fields of view.

[0105] Fig.31A The minimum refractive index modulation of transmissive volume Bragg gratings with different grating periods in order to achieve diffraction saturation of different color lights is shown. Fig.31B The maximum refractive index modulation of transmissive gratings with different grating periods is shown in order to avoid refractive index modulation saturation for blue, green and red light. Fig. 31C An example of a grating layer including multiplexed VBGs with different pitches and refractive index modulations for optimizing diffraction efficiency and uniformity is shown in accordance with certain embodiments.

[0106] Fig.32A Shown is the FOV crosstalk caused by an example of a multiplexed volume Bragg grating. Fig.32B The relationship between the grating period of a volume Bragg grating and the corresponding field of view for incident light of different colors is shown.

[0107] Fig.33A The line widths of the Bragg peaks of transmissive and reflective volume Bragg gratings for different fields of view are shown. Fig.33B Examples of Bragg peaks of a transmissive volume Bragg grating for different fields of view are shown. Fig.33C Examples of Bragg peaks of a reflective volume Bragg grating for different fields of view are shown.

[0108] Fig.34A The trade-off between crosstalk and efficiency in the example of a multiplexed volume Bragg grating is shown. Fig.34B The trade-off between crosstalk and efficiency in the example of a multiplexed volume Bragg grating is shown.

[0109] Fig.35AThe relationship between the minimum diffraction efficiency and the total refractive index modulation and the corresponding crosstalk in a multiplexed transmissive volume Bragg grating is shown. Fig.35B The relationship between the minimum diffraction efficiency and the total refractive index modulation and the corresponding crosstalk in a multiplexed reflective volume Bragg grating is shown.

[0110] Fig.36 An example of a waveguide display including spatially multiplexed reflective volume Bragg gratings with different refractive index modulations is shown in accordance with some embodiments.

[0111] Fig.37 An example of a waveguide display including two multiplexed volume Bragg gratings and a polarization converter between the two multiplexed volume Bragg gratings is shown in accordance with some embodiments.

[0112] Fig.38 An example of a waveguide display including an anti-reflection layer and an angle-selective transmission layer according to some embodiments is shown.

[0113] Fig.39 is a simplified block diagram of an example of an electronic system in an example of a near-eye display in accordance with some embodiments.

[0114] The accompanying drawings depict embodiments of the present invention for purposes of illustration only. Those skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods shown may be employed without departing from the principles or intended benefits of the present invention.

[0115] 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. DETAILED DESCRIPTION

[0116] The present invention generally relates to a volume Bragg grating (VBG) based waveguide display for a near-eye display system. In a near-eye display system, it is generally desirable to expand the viewport, reduce display haze, improve image quality (e.g., resolution and contrast), reduce physical size, increase power efficiency, and increase field of view. In a waveguide-based near-eye display system, light for a projected image can be coupled into a waveguide (e.g., a transparent substrate), propagated within the waveguide, and coupled out of the waveguide at different locations to replicate the exit pupil and expand the viewport. Two or more gratings can be used to expand the exit pupil in two dimensions. In a waveguide-based near-eye display system for augmented reality applications, light from the surrounding environment can pass through at least a see-through region of the waveguide display (e.g., a transparent substrate) and reach the user's eyes. In some embodiments, a diffractive optical element (e.g., a grating) can be used to couple light for a projected image into or out of a waveguide.

[0117] Due to the angular dependence of grating efficiency, an optical coupler implemented using a diffractive optical element may have a limited field of view. Therefore, light incident on the coupler from multiple incident angles (e.g., from different fields of view) may not be diffracted with equal or similar efficiency. In addition, a coupler implemented using a diffractive optical element may cause dispersion between light of different colors and may have different diffraction angles for light of different colors. Therefore, different color components in a color image may not overlap with each other. Therefore, the quality of the displayed image (e.g., color reproduction neutrality) may be reduced. In addition, due to light dispersion and the limited range of wave vectors of light that a waveguide display can guide, the field of view of light of different colors may be reduced or partially truncated. To reduce dispersion and improve the field of view (FOV) range and diffraction efficiency, thick transmissive and / or reflective VBG gratings may be used, including many multiplexed gratings to cover different FOVs for different color components, which may be impractical in many cases and / or may result in significant display and see-through haze due to the thickness of the gratings and the large number of exposures to record the multiplexed VBG gratings. For example, in some cases, a transmissive VBG grating with a thickness greater than 1 mm may be required to reduce dispersion and obtain the desired FOV range and diffraction efficiency. Reflective VBG gratings with relatively low thickness may be used to achieve the desired performance. However, with reflective gratings, the gratings used for two-dimensional pupil expansion may not overlap, so the physical size of the waveguide display may be large and the display haze may still be large.

[0118] According to certain embodiments, two VBG gratings (or two parts of the same grating) with matching grating vectors (e.g., having the same grating vector in a plane perpendicular to the surface normal direction of the transparent substrate) can be used to diffract the display light and expand the exit pupil in one dimension. Due to the opposite Bragg conditions at the two VBG gratings (e.g., +1 and -1 order diffraction), the two VBG gratings can compensate for the dispersion of the display light caused by each other to reduce the total dispersion. Therefore, thin VBG gratings can be used and the desired resolution can still be obtained. Due to the dispersion compensation, thin transmissive VBG gratings can be used to achieve the desired resolution, and the gratings used for two-dimensional pupil expansion can be at least partially overlapped to reduce the physical size of the waveguide display.

[0119] In some embodiments, in order to achieve the desired FOV, coupling efficiency, and coupling efficiency uniformity over the full FOV and color spectrum, multiple VBG layers including multiplexed VBGs may be formed on one or more waveguide plates. Each VBG layer may be used to couple light within a specific FOV and / or color range with relatively high efficiency, and the combination of multiple VBG layers may provide full coverage of the desired FOV and color range with relatively high and uniform coupling efficiency.

[0120] In some embodiments, a first pair of VBG gratings (or two portions of gratings) can be used to expand the exit pupil in one dimension and compensate for the dispersion caused by each other, and a second pair of VBG gratings (or two portions of gratings) can be used to expand the exit pupil in another dimension and compensate for the dispersion caused by each other. Thus, the exit pupil can be replicated in two dimensions, and the resolution of the displayed image can be high in both dimensions.

[0121] According to some embodiments, the first pair and / or the second pair of gratings may each include a multiplexed reflective volume Bragg grating. The multiplexed reflective VBG may include a reflective VBG that may have high diffraction efficiency and low crosstalk between the reflective VBGs in the multiplexed reflective VBG. In some embodiments, the refractive index modulation of the reflective VBG may be greater than the minimum refractive index modulation at which the diffraction efficiency is saturated, and thus may have high diffraction efficiency and a wider full-width-half-magnitude (FWHM) wavelength range and / or FWHM angle range. In this way, fewer reflective VBGs may be used to cover the wavelength range and full FOV of the light source to improve the efficiency and performance of the waveguide display.

[0122] In some embodiments, each of the first pair of gratings and / or the second pair of gratings may include a first reflective VBG characterized by a first refractive index modulation, and a second reflective VBG including a plurality of regions characterized by different corresponding refractive index modulations. The first reflective VBG may be configured to diffract display light within a first wavelength range (and / or a first FOV range), such that the display light within the first wavelength range (and / or the first FOV range) may propagate in the waveguide to the plurality of regions of the second reflective VBG by total internal reflection. The plurality of regions of the second reflective VBG may be configured to diffract display light within different corresponding wavelength (and / or FOV) ranges within the first wavelength range (and / or the first FOV range) due to different corresponding refractive index modulations. The first reflective VBG and the second reflective VBG may have the same grating vector in a plane perpendicular to the surface normal direction of the waveguide to reduce dispersion. At least one of the first refractive index modulation and the different corresponding refractive index modulations of the plurality of regions of the second reflective VBG may be greater than the minimum refractive index modulation at which the diffraction efficiency is saturated. The multiple regions of the second reflective VBG can be arranged so that display light within the first wavelength range (and / or the first FOV range) reaches the first region having a lower refractive index modulation in the multiple regions before reaching the second region having a higher refractive index modulation in the multiple regions. In this way, display light in a narrower portion of the first wavelength range (and / or the first FOV) can be diffracted by the first region, and display light in the first wavelength range (and / or the first FOV) but outside the narrower portion can be diffracted by the second region.

[0123] In the following description, various embodiments of the invention are described, including devices, systems, methods, etc. For the purpose of explanation, specific details are set forth in order to provide a thorough understanding of the examples of the present invention. However, it will be apparent that various examples can be implemented without these specific details. For example, devices, systems, structures, components, 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 devices, processes, systems, structures, and techniques can be shown without the necessary details to avoid blurring the examples. The drawings and descriptions are not intended to be restrictive. The terms and expressions used in this 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 mean "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.

[0124] Figure 1 is a simplified block diagram of an example of an artificial reality system environment 100 including a near-eye display 120 in accordance with some embodiments. Figure 1 The illustrated artificial reality system environment 100 may include a near-eye display 120, an optional external 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 of an artificial reality system environment 100 including one near-eye display 120, one external imaging device 150, and one input / output interface 140 is shown, 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 displays 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 external 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.

[0125] The near-eye display 120 may be a head-mounted display that presents content to a user. Examples of content presented by the near-eye display 120 include one or more of the following: images, video, audio, or any combination thereof. In some embodiments, the audio may be presented via an external device (e.g., a speaker and / or headphones) that receives audio information from the near-eye display 120, the console 110, or both the near-eye display 120 and the console 110 and presents audio data based on the audio information. The near-eye display 120 may include one or more rigid bodies that may be rigidly or non-rigidly coupled to each other. Rigid couplings between rigid bodies may cause the coupled rigid bodies to act as a single rigid entity. Non-rigid couplings between rigid bodies may allow the rigid bodies to move relative to each other. In various embodiments, the near-eye display 120 may be implemented in any suitable form factor, including a pair of glasses. Referring below to Figure 2 and Figure 3 Some embodiments of the near-eye display 120 are further described. 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 120 with artificial reality content (e.g., computer-generated images). Thus, the near-eye display 120 may augment an image of a physical, real-world environment external to the near-eye display 120 with generated content (e.g., images, videos, sounds, etc.) to present an augmented reality to the user.

[0126] In various embodiments, the near eye display 120 may include one or more of display electronics 122, display optics 124, and an eye tracking unit 130. In some embodiments, the near eye display 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 120 may omit any of the following: eye tracking unit 130, positioners 126, position sensors 128, and IMU 132, or include additional elements. Additionally, in some embodiments, the near eye display 120 may include a combination of the eye tracking unit 130, the positioners 126, the position sensors 128, and the IMU 132. Figure 1 The functions of the various components are described in detail.

[0127] 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 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 produced 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 (eg, a perception of depth in an image by a user viewing the image).

[0128] In some embodiments, the display optics 124 can optically display image content (e.g., using optical waveguides and couplers), or 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 120. In various embodiments, the display optics 124 can include one or more optical elements, such as 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 can affect the image light emitted from the display electronics 122. The display optics 124 can include a combination of different optical elements and mechanical couplings to maintain the relative spacing and orientation of the optical elements in the combination. One or more of the optical elements in the display optics 124 can have an optical coating, such as an anti-reflective coating, a reflective coating, a filter coating, or a combination of different optical coatings.

[0129] 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 120.

[0130] 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 any 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.

[0131] The locators 126 may be objects located at specific locations on the near eye display 120 relative to each other and relative to reference points on the near eye display 120. In some embodiments, the console 110 may identify the locators 126 in an image captured by the external imaging device 150 to determine the position, orientation, or both of the artificial reality head mounted device. The locators 126 may be LEDs, corner cube reflectors, reflective markers, a light source that contrasts with the environment in which the near eye display 120 operates, or any 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.

[0132] The external imaging device 150 may include one or more cameras, one or more video cameras, any other device capable of capturing an image including one or more locators 126, or any combination thereof. Additionally, the external imaging device 150 may include one or more filters (e.g., to improve the signal-to-noise ratio). The external imaging device 150 may be configured to detect light emitted or reflected from the locators 126 in the field of view of the external imaging device 150. In embodiments where the locators 126 include passive elements (e.g., retroreflectors), the external imaging device 150 may include a light source that illuminates some or all of the locators 126, which may reflect light back into the external imaging device 150. Slow calibration data may be transmitted from the external imaging device 150 to the console 110, and the external imaging device 150 may receive one or more calibration parameters from the console 110 for adjusting one or more imaging parameters (e.g., focal length, focus, frame rate, sensor temperature, shutter speed, aperture, etc.).

[0133] The position sensor 128 may generate one or more measurement signals in response to the movement of the near-eye display 120. Examples of the position sensor 128 may include an accelerometer, a gyroscope, a magnetometer, other motion detection or error correction sensors, or any 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.

[0134] 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 any 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 120 relative to an initial position of the near eye display 120. For example, the IMU 132 may integrate the measurement signals received from the 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 120. Alternatively, the IMU 132 may provide the sampled measurement signals to the console 110, which may determine the fast calibration data. Although the 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 120 (e.g., the center of the IMU 132).

[0135] The eye tracking unit 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 120, including the orientation and position of the eye. The eye tracking system may include an imaging system that images one or more eyes, and may optionally include a light emitter that may generate light directed toward the eye so that light reflected by the eye can be captured by the imaging system. For example, the eye tracking unit 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 unit 130 may capture reflected radio waves emitted by a miniature radar unit. The eye tracking unit 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 unit 130 may be arranged to increase the contrast in the eye image captured by the eye tracking unit 130 while reducing the total power consumed by the eye tracking unit 130 (e.g., reducing the power consumed by the light emitter and imaging system included in the eye tracking unit 130). For example, in some implementations, eye tracking unit 130 may consume less than 100 milliwatts of power.

[0136] For example, the near-eye display 120 can use the orientation of the eyes to perform the following operations: determine the user's interpupillary distance (IPD), determine the 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 user's eye, or any combination thereof. Because the orientation of the user's eyes can be determined, the eye tracking unit 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.

[0137] 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 external 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 action. In some embodiments, the near-eye display 120 may include one or more imaging devices 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 motion.

[0138] The console 110 may provide content to the near-eye display 120 for presentation to the user based on information received from one or more of the external imaging device 150, the near-eye display 120, and the input / output interface 140. Figure 1In 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.

[0139] 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 non-transitory 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 1 The 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.

[0140] 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.

[0141] The head mounted device tracking module 114 may use the slow calibration information from the external imaging device 150 to track the movement of the near eye display 120. For example, the head mounted device tracking module 114 may use the observed localizers from the slow calibration information and the model of the near eye display 120 to determine the position of the reference point of the near eye display 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 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 any combination thereof to predict the future position of the near eye display 120. The head mounted device tracking module 114 may provide the estimated or predicted future position of the near eye display 120 to the artificial reality engine 116.

[0142] 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 120, acceleration information of the near-eye display 120, velocity information of the near-eye display 120, predicted future position of the near-eye display 120, or any 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 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 120 that reflects (mirror) 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 can be visual or auditory feedback via the near-eye display 120, or tactile feedback via the input / output interface 140.

[0143] The eye tracking module 118 may receive eye tracking data from the eye tracking unit 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 120 or any element thereof. Because the rotational axis of the eye changes depending on the position of the eye in the socket, determining the position of the eye in the socket may allow the eye tracking module 118 to more accurately determine the orientation of the eyes.

[0144] Figure 2 2 is a perspective view of an example of a near-eye display in the form of an HMD device 200 for implementing some of the examples disclosed herein. The HMD device 200 may be, for example, part of a VR system, an AR system, an MR system, or any combination thereof. The HMD device 200 may include a body 220 and a headband 230. Figure 2 The bottom side 223, front side 225, and left side 227 of the body 220 are shown in perspective. 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, for example, the following Figure 3 Eyeglass temples and temple tips are shown, rather than headband 230 .

[0145] 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 any 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 In various embodiments, one or more display components may include a single electronic display panel or multiple electronic display panels (e.g., one display panel for each eye of the user). For example, examples of electronic display panels may include LCDs, OLED displays, ILED displays, μLED displays, AMOLEDs, TOLEDs, some other displays, or any combination thereof. HMD device 200 may include two window areas.

[0146] 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) that may execute applications within the HMD device 200 and receive depth information, position information, acceleration information, velocity information, predicted future positions, or any 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) that 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 may be detected by an external imaging device.

[0147] Figure 3 is a perspective view of an example of a near-eye display 300 in the form of a pair of glasses for implementing some examples disclosed herein. The near-eye display 300 may be Figure 1 Specific embodiments of near-eye display 120 can be configured for use as a virtual reality display, an augmented reality display, and / or a mixed reality display. Near-eye display 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 1As described above with respect to the near-eye display 120 , the display 310 may include an LCD display panel, an LED display panel, or an optical display panel (eg, a waveguide display component).

[0148] The near-eye display 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 300, and / or provide an interactive VR / AR / MR experience to the user of the near-eye display 300. In some embodiments, the sensors 350a-350e may also be used for stereoscopic imaging.

[0149] In some embodiments, the near-eye display 300 may further 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 in the dark environment. In some embodiments, the illuminator 330 may be used to project a specific light pattern onto an object in 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.

[0150] In some embodiments, the near-eye display 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 1 The captured image may be processed by an artificial reality engine 116) to add virtual objects to the captured image or modify physical objects in the captured image, and the processed image may be displayed to the user by a display 310 for AR or MR applications.

[0151] Figure 4 4 is a simplified diagram showing an example of an optical system 400 in a near-eye display system. The optical system 400 may include an image source 410 and a projector optical device 420. Figure 4In the example shown, image source 410 is in front of projector optics 420. In various embodiments, image source 410 may be located outside the field of view of user eye 490. For example, one or more reflectors or directional couplers may be used to deflect light from the image source outside the field of view of user eye 490 so that the image source appears to be located outside the field of view of user eye 490. Figure 4 The position of the image source 410 is shown. Light from areas (e.g., pixels or light emitters) on the image source 410 can be collimated by the projector optics 420 and directed to the exit pupil 430. As a result, objects at different spatial locations on the image source 410 may appear to be objects farther away from the user's eye 490 in different fields of view (FOV). The collimated light from the different fields of view can then be focused by the lens of the user's eye 490 to different locations on the retina 492 of the user's eye 490. For example, at least some portions of the light can be focused on the fovea 494 on the retina 492. Collimated light rays from areas on the image source 410 and incident on the user's eye 490 from the same direction can be focused to the same location on the retina 492. In this way, a single image of the image source 410 can be formed on the retina 492.

[0152] The user experience of using an artificial reality system may depend on several characteristics of the optical system, including the field of view (FOV), image quality (e.g., angular resolution), the size of the viewport (to accommodate eye and head movements), and the brightness (or contrast) of the light within the viewport. The field of view describes the angular range of the image that the user sees, and is usually measured in degrees observed by one eye (for a monocular HMD) or two eyes (for a binocular or binocular HMD). The human visual system can have a total binocular FOV of approximately 200° (horizontal) by 130° (vertical). To create a fully immersive visual environment, a large FOV is required because a large FOV (e.g., greater than about 60°) can provide a sense of "being in" the image rather than just looking at it. A smaller field of view may also exclude some important visual information. For example, an HMD system with a small FOV can use a gesture interface, but the user may not be able to see their hands in the small FOV to ensure that they are using the correct movements. On the other hand, a wider field of view may require a larger display or optical system, which may affect the size, weight, cost, and comfort of using the HMD.

[0153] Resolution may refer to the angular size of a displayed pixel or image element seen by a user, or the ability of a user to see and correctly interpret objects imaged by a pixel and / or other pixels. For a given FOV value, the resolution of an HMD may be specified as the number of pixels on the image source, whereby the angular resolution may be determined by dividing the FOV in one direction by the number of pixels in the same direction on the image source. For example, for a 40° horizontal FOV and 1080 pixels in the horizontal direction on the image source, the corresponding angular resolution may be approximately 2.2 arc minutes, compared to the 1 arc minute resolution associated with Snellen 20 / 20 human visual acuity.

[0154] In some cases, the viewing window may be a two-dimensional box in front of the user's eyes from which a displayed image from an image source may be viewed. If the user's pupil moves outside the viewing window, the user may not see the displayed image. For example, in a non-pupil forming configuration, there is a viewing window within which there will be an unvignetted viewing of the HMD image source, and when the pupil of the user's eye is outside the viewing window, the displayed image may be vignette or may be clipped, but still visible. In a pupil forming configuration, the image may not be visible outside the exit pupil.

[0155] The fovea of ​​the human eye, where the highest resolution can be obtained on the retina, may correspond to a FOV of about 2° to about 3°. This may require the eye to rotate in order to view off-axis objects at the highest resolution. Since the eye rotates around a point approximately 10 mm behind the pupil, rotating the eye to view off-axis objects introduces a translation of the pupil. In addition, the user may not always be able to precisely position the pupil of the user's eye (e.g., a radius of approximately 2.5 mm) at an ideal location in the field of view. In addition, the environment in which the HMD is used may require a larger field of view to allow the user's eyes and / or head to move relative to the HMD, for example, when the HMD is used in a moving vehicle or is designed to be used while the user is walking. The amount of movement in these cases may depend on the degree of coupling of the HMD to the user's head.

[0156] Therefore, in order to accommodate the movement of the user's pupil relative to the HMD, the optical system of the HMD may need to provide a sufficiently large exit pupil or viewing window for viewing the full FOV at full resolution. For example, in a pupil forming configuration, a minimum size of 12mm to 15mm may be desired for the exit pupil. If the window is too small, a slight misalignment between the eye and the HMD may cause the image to be at least partially lost, and the user experience may be severely impaired. In general, the lateral extent of the window is more important than the vertical extent of the window. This may be due in part to the significant differences in eye separation distances between users, and the fact that misalignment of eyewear tends to occur more frequently in the lateral dimension, and users tend to adjust their gaze more frequently left and right, and to a greater extent than up and down. Therefore, technologies that can increase the lateral size of the window can significantly improve the user's experience of using the HMD. On the other hand, the larger the window, the larger the optical device, and the heavier and more cumbersome the near-eye display device may be.

[0157] In order to view the displayed image against a bright background, the image source of the AR HMD may need to be bright enough, and the optical system may need to effectively provide a bright image to the user's eyes so that the displayed image can be visible against a background that includes strong ambient light (e.g., sunlight). The optical system of the HMD can be designed to focus light in the viewport. When the viewport is large, a high-power image source can be used to provide a bright image visible within the large viewport. Therefore, there may be a trade-off between the size of the viewport, cost, brightness, optical complexity, image quality, and the size and weight of the optical system.

[0158] Figure 5An example of an optical see-through augmented reality system 500 including a waveguide display for exit pupil expansion according to certain embodiments is shown. The augmented reality system 500 may include a projector 510 and a combiner 515. The projector 510 may include a light source or image source 512 and a projector optical device 514. In some embodiments, the light source or image source 512 may include one or more micro-LED devices. In some embodiments, the image source 512 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 512 may include a light source that generates coherent light or partially coherent light. For example, the image source 512 may include a laser diode, a vertical cavity surface emitting laser, an LED, a super radiant LED (sLED), and / or the micro-LEDs described above. In some embodiments, the image source 512 may include a plurality of light sources (e.g., the micro-LED arrays described above), 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 512 may include three two-dimensional arrays of micro-LEDs, each of which may include micro-LEDs configured to emit primary color (e.g., red, green, or blue) light. In some embodiments, the image source 512 may include an optical pattern generator, such as a spatial light modulator. The projector optics 514 may include one or more optical components that may adjust the light from the image source 512, such as expanding, collimating, scanning the light from the image source 512, or projecting the light from the image source 512 to the combiner 515. The one or more optical components may include, for example, one or more lenses, liquid lenses, mirrors, free-form optical devices, apertures, and / or gratings. For example, in some embodiments, the image source 512 may include one or more one-dimensional arrays or elongated two-dimensional arrays of micro-LEDs, and the projector optics 514 may include one or more one-dimensional scanners (e.g., micro-mirrors or prisms) configured to scan the one-dimensional array or elongated two-dimensional array of micro-LEDs to generate an image frame. In some embodiments, projector optics 514 may include a liquid lens (e.g., a liquid crystal lens) having multiple electrodes that allow light from image source 512 to be scanned.

[0159] The combiner 515 may include an input coupler 530 for coupling light from the projector 510 into a substrate 520 of the combiner 515. The input coupler 530 may include a volume holographic grating or another diffractive optical element (DOE) such as a surface relief grating (SRG), an angled reflective surface of the substrate 520, or a refractive coupler such as a wedge or a prism. For example, the input coupler 530 may include a reflective volume Bragg grating or a transmissive volume Bragg grating. The input coupler 530 may have a coupling efficiency greater than 30%, 50%, 75%, 90%, or more for visible light. The light coupled into the substrate 520 may propagate within the substrate 520 by, for example, total internal reflection (TIR). The substrate 520 may be in the form of a lens of a pair of glasses. The substrate 520 may have a flat or curved surface and may include one or more types of dielectric materials such as glass, quartz, plastic, polymer, polymethyl methacrylate (PMMA), crystal, ceramic, etc. The thickness of the substrate may range, for example, from less than about 1 mm to about 10 mm or more. The substrate 520 may be transparent to visible light.

[0160] The substrate 520 may include or may be coupled to a plurality of output couplers 540, each of which is configured to extract at least a portion of the light guided by and propagating within the substrate 520 from the substrate 520, and to guide the extracted light 560 to a viewing window 595, where an eye 590 of a user of the augmented reality system 500 may be located when the augmented reality system 500 is used. The plurality of output couplers 540 may replicate an exit pupil to increase the size of the viewing window 595 so that the displayed image may be visible in a larger area. As with the input coupler 530, the output coupler 540 may include a grating coupler (e.g., a volume holographic grating or a surface relief grating), other diffractive optical elements (DOEs), prisms, and the like. For example, the output coupler 540 may include a reflective volume Bragg grating or a transmissive volume Bragg grating. The output coupler 540 may have different coupling (e.g., diffraction) efficiencies at different locations. The substrate 520 may also allow light 550 from the environment in front of the combiner 515 to pass through with little or no loss. The output coupler 540 may also allow light 550 to pass through with little loss. For example, in some embodiments, the output coupler 540 may have a very low diffraction efficiency for light 550, so that the light 550 may be refracted or otherwise pass through the output coupler 540 with little loss, and thus may have a higher intensity than the extracted light 560. In some embodiments, the output coupler 540 may have a high diffraction efficiency for the light 550, and may diffract the light 550 in 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 the combiner 515 and the image of the virtual object projected by the projector 510. In some embodiments, the output coupler 540 may have a high diffraction efficiency for the light 550, and may diffract the light 550 to certain desired directions (e.g., diffraction angles) with little loss.

[0161] In some embodiments, the projector 510, the input coupler 530, and the output coupler 540 can be on either side of the substrate 520. The input coupler 530 and the output coupler 540 can be reflective gratings (also called reflection gratings) or transmissive gratings (also called transmission gratings) to couple the display light into or out of the substrate 520.

[0162] Figure 6An example of an optical see-through augmented reality system 600 including a waveguide display for exit pupil expansion is shown in accordance with some embodiments. Augmented reality system 600 can be similar to augmented reality system 500 and can include a waveguide display and a projector, which can include a light source or image source 612 and projector optics 614. The waveguide display can include a substrate 630, an input coupler 640, and a plurality of output couplers 650, as described above with respect to augmented reality system 500. Although Figure 5 Only the propagation of light from a single field of view is shown, but Figure 6 The propagation of light from multiple fields of view is shown.

[0163] Figure 6 The exit pupil is shown to be replicated by output coupler 650 to form a focused exit pupil or window, where different fields of view (e.g., different pixels on image source 612) can be associated with different corresponding propagation directions toward the window, and light from the same field of view (e.g., the same pixel on image source 612) can have the same propagation direction for different individual exit pupils. Thus, a single image of image source 612 can be formed by a user's eye located anywhere in the window, where light from different individual exit pupils and propagating in the same direction can come from the same pixel on image source 612 and can be focused to the same location on the retina of the user's eye. Figure 6 It is shown that the image of the image source can be seen by the user's eyes even if the user's eyes move to different positions in the viewing window.

[0164] In many waveguide-based near-eye display systems, in order to expand the viewport of the waveguide-based near-eye display in two dimensions, two or more output gratings may be used to expand the display light in two dimensions or along two axes (this may be referred to as dual-axis pupil expansion). The two gratings may have different grating parameters, such that one grating may be used to replicate the exit pupil in one direction, while the other grating may be used to replicate the exit pupil in another direction.

[0165] As mentioned above, the above-mentioned input and output grating couplers can be volume holographic gratings or surface relief gratings, which can have very different Klein-Cook parameters Q:

[0166]

[0167] Where d is the thickness of the grating, λ is the wavelength of the incident light in free space, Λ is the grating period, and n is the refractive index of the recording medium. The Klein-Cook parameter Q can divide the light diffraction of the grating into three regimes. When the grating is characterized by Q<<1, the light diffraction of the grating can be called Raman-Nath diffraction, where multiple diffraction orders can appear for normal and / or oblique incident light. When the grating is characterized by Q>>1 (for example, Q≥10), the light diffraction of the grating can be called Bragg diffraction, where for light incident on the grating at an angle that satisfies the Bragg condition, typically only the zeroth and ±1st order diffraction appear. When the grating is characterized by Q≈1, the diffraction of the grating can be between Raman-Nath diffraction and Bragg diffraction. In order to meet the Bragg condition, the thickness d of the grating can be higher than certain values ​​to occupy the volume (rather than the surface) of the medium, and thus can be called a volume Bragg grating. VBGs can typically have relatively small refractive index modulation (e.g., Δn≤0.05) and high spectral and angular selectivity, while surface relief gratings can typically have large refractive index modulation (e.g., Δn≥0.5) and wide spectral and angular bandwidth.

[0168] Fig. 7A The spectral bandwidth of an example of a volume Bragg grating (e.g., a reflective VBG) and the spectral bandwidth of an example of a surface relief grating (e.g., a transmissive SRG) are shown. The horizontal axis represents the wavelength of incident visible light, and the vertical axis corresponds to the diffraction efficiency. As shown by curve 710, the diffraction efficiency of the reflective VBG is high in a narrow wavelength range such as green light. In contrast, as shown by curve 720, the diffraction efficiency of the transmissive SRG can be high in a very wide wavelength range such as from blue light to red light.

[0169] Figure 7B An example angular bandwidth of a volume Bragg grating (e.g., a reflective VBG) and an example angular bandwidth of a surface relief grating (e.g., a transmissive SRG) are shown. The horizontal axis represents the incident angle of visible light incident on the grating, and the vertical axis corresponds to the diffraction efficiency. As shown by curve 715, the diffraction efficiency of the reflective VBG is high for light incident on the grating from a narrow range of angles (e.g., about ±2.5° from a perfect Bragg condition). In contrast, the diffraction efficiency of the transmissive SRG is high over a very wide range of angles (e.g., greater than about ±10° or wider), as shown by curve 725.

[0170] Due to the high spectral selectivity under Bragg conditions, VBG (e.g., reflective VBG) can allow a single waveguide design without crosstalk between primary colors and can exhibit excellent see-through quality. However, the spectral and angular selectivity may result in lower efficiency because only a portion of the display light in the full FOV may be diffracted and reach the user's eyes.

[0171] Fig. 8A An example of an optical see-through augmented reality system according to some embodiments is shown, which includes a waveguide display 800 and a surface relief grating for exit pupil expansion. The waveguide display 800 may include a substrate 810 (e.g., a waveguide), which may be similar to the substrate 520. The substrate 810 may be transparent to visible light and may include, for example, a glass, quartz, plastic, polymer, PMMA, ceramic, or crystal substrate. The substrate 810 may be a flat substrate or a curved substrate. The substrate 810 may include a first surface 812 and a second surface 814. The display light may be coupled into the substrate 810 by an input coupler 820 and may be reflected by the first surface 812 and the second surface 814 by total internal reflection, so that the display light may propagate within the substrate 810. As described above, the input coupler 820 may include a grating, a refractive coupler (e.g., an optical wedge or a prism), or a reflective coupler (e.g., a reflective surface having an oblique angle relative to the substrate 810). For example, in one embodiment, the input coupler 820 may include a prism that can couple different colors of display light into the substrate 810 at the same refraction angle. In another example, the input coupler 820 may include a grating coupler that can diffract different colors of light into the substrate 810 in different directions. For visible light, the input coupler 820 may have a coupling efficiency greater than 10%, 20%, 30%, 50%, 75%, 90%, or more.

[0172] The waveguide display 800 may also include a first grating 830 and a second grating 840 located on one or both surfaces (e.g., the first surface 812 and the second surface 814) of the substrate 810 for expanding an incident display light beam in two dimensions so as to fill a viewing window (or an output or exit pupil) with the display light. The first grating 830 may be configured to expand at least a portion of the display light beam along one direction, for example, approximately in the x-direction. The display light coupled into the substrate 810 may propagate along the direction indicated by line 832. When the display light propagates within the substrate 810 along the direction indicated by line 832, each time the display light propagating within the substrate 810 reaches the first grating 830, a portion of the display light may be diffracted by a portion of the first grating 830 toward the second grating 840, as indicated by line 834. Then, the second grating 840 may expand the display light from the first grating 830 in a different direction (e.g., approximately in the y-direction) by diffracting a portion of the display light to the viewing window each time the display light propagating within the substrate 810 reaches the second grating 840. On the second grating 840, an exit region 850 represents the region in which the full FOV of display light at a pupil position in the viewing window (e.g., at the center of the viewing window) can be coupled out of the waveguide display 800.

[0173] Figure 8B An example of a viewing window comprising a two-dimensionally replicated exit pupil is shown. Figure 8B It is shown that a single input pupil 805 can be replicated by a first grating 830 and a second grating 840 to form a concentrated exit pupil 860 including a two-dimensional array of a single exit pupil 852. For example, the exit pupil can be replicated in approximately the x-direction by the first grating 830 and in approximately the y-direction by the second grating 840. As described above, the output light from the single exit pupil 852 and propagating in the same direction can be focused to the same location in the retina of the user's eye. Therefore, the user's eye can form a single image from the output light in the two-dimensional array of the single exit pupil 852.

[0174] Fig.9A Wave vectors of light diffracted by an example of a surface relief grating for exit pupil expansion and multiple colors of exit pupils in a waveguide display are shown. Circle 910 may represent the wave vector of light that may be guided by a waveguide. For light with a wave vector outside of circle 910, the light may become evanescent. Circle 920 may represent the wave vector of light that may leak out of the waveguide due to not satisfying the total internal reflection condition. Therefore, the ring between circle 910 and circle 920 may represent the wave vector of light that may be guided by the waveguide and may propagate within the waveguide by TIR. Wave vector 932 shows the light dispersion caused by the input grating, where light of different colors may have different wave vectors and different diffraction angles. Wave vector 942 shows the light dispersion caused by the front grating (e.g., the first grating 830), where light of different colors may have different diffraction angles. Wave vector 952 shows the light dispersion caused by the rear grating (e.g., the second grating 840), where light of different colors may have different diffraction angles. The wave vectors of each color may form their own closed triangle, and triangles of different colors may share a common origin vertex 922. Therefore, the total dispersion of the three gratings may be close to zero.

[0175] Even though the total dispersion of the three gratings may be zero, the dispersion of each grating may result in a reduced or truncated field of view for the waveguide display due to the conditions under which the waveguide may guide light as shown by the ring between circle 910 and circle 920. For example, for FOV 924, the footprint of the FOV after diffraction by the input grating may be different for different colors due to the dispersion of the input grating. Fig.9A In the example shown, the footprint 936 of the FOV for the first color of light may be located within the ring, while a portion of the footprint 934 of the FOV for the second color of light and a portion of the footprint 938 of the FOV for the third color of light may fall outside the ring and therefore not be guided by the waveguide. Furthermore, the footprint of the FOV may be further truncated or reduced after being diffracted by the front grating. Fig.9AIn the example shown, a small portion of the footprint 946 of the FOV for the first color of light, a large portion of the footprint 944 of the FOV for the second color of light, and a large portion of the footprint 948 of the FOV for the third color of light may fall outside the annulus and therefore will not be guided by the waveguide and will not be diffracted by the rear grating to reach the exit pupil.

[0176] Fig. 9B Field of view truncation is illustrated by the example of a surface relief grating for exit pupil expansion in a waveguide display. For example, the FOV of the first color light after diffraction by the rear grating can be illustrated by the coverage area 956, which can be close to the full FOV. For the second color light, the top of the FOV may be truncated after diffraction by the first grating, and the right part of the FOV may be truncated after diffraction by the front grating. Therefore, the FOV of the second color light after diffraction by the rear grating can be illustrated by the coverage area 954, which can be much smaller than the full FOV. Similarly, for the third color light, the bottom of the FOV may be truncated after diffraction by the first grating, and the left part of the FOV may be truncated after diffraction by the front grating. Therefore, the FOV of the third color light after diffraction by the rear grating can be illustrated by the coverage area 958, which can be much smaller than the full FOV. Therefore, for some fields of view, some color components of the image may be lost. Thus, to achieve full FOV for different colors, two or more waveguides and corresponding gratings may be used. In addition, as mentioned above, the wide bandwidth of the SRG may cause crosstalk between different primary colors and / or light from different FOVs, so multiple waveguides may also be used to avoid crosstalk.

[0177] Due to the high spectral selectivity under Bragg conditions, VBGs (e.g., reflective VBGs) can allow single waveguide designs without crosstalk between primary colors in volume Bragg gratings, and can achieve excellent see-through quality. Therefore, the input coupler 530 or 640 and the output coupler 540 or 650 may include a volume Bragg grating, which may be a volume hologram recorded in a holographic recording material by exposing the holographic recording material to a light pattern generated by interference between two or more coherent light beams. In a volume Bragg grating, the incident angle and wavelength of the incident light may need to satisfy the Bragg phase matching condition so that the incident light is diffracted by the Bragg grating. When a single Bragg grating is used in a waveguide-based near-eye display, the spectral and angular selectivity of the volume Bragg grating may result in lower efficiency because only a portion of the display light can be diffracted and reach the user's eyes, and the field of view and operating wavelength range of the waveguide-based near-eye display may be limited. In some embodiments, multiplexed VBGs may be used to improve efficiency and increase FOV.

[0178] Fig. 10AA front view of an example of a volume Bragg grating based waveguide display 1000 according to some embodiments is shown. The waveguide display 1000 may include a substrate 1010, which may be similar to the substrate 520. The substrate 1010 may be transparent to visible light and may include, for example, glass, quartz, plastic, polymer, PMMA, ceramic, or a crystalline substrate. The substrate 1010 may be a flat substrate or a curved substrate. The substrate 1010 may include a first surface 1012 and a second surface 1014. Display light may be coupled into the substrate 1010 by an input coupler 1020 and may be reflected by the first surface 1012 and the second surface 1014 by total internal reflection, so that the display light may propagate within the substrate 1010. As described above, the input coupler 1020 may include a diffractive coupler (e.g., a volume holographic grating or a surface relief grating), a refractive coupler (e.g., an optical wedge or a prism), or a reflective coupler (e.g., a reflective surface having an inclined angle relative to the substrate 1010). For example, in one embodiment, the input coupler 1020 may include a prism that can couple display lights of different colors at the same refraction angle into the substrate 1010. In another example, the input coupler may include a grating coupler that can diffract light of different colors into the substrate 1010 in different directions.

[0179] The waveguide display 1000 may further include a first grating 1030 and a second grating 1040 located on one or both surfaces (e.g., the first surface 1012 and the second surface 1014) of the substrate 1010 for expanding an incident display light beam in two dimensions so as to fill the viewing window with the display light. The first grating 1030 may include one or more multiplexed volume Bragg gratings, each of which is configured to expand at least a portion of the display light beam (e.g., light corresponding to a specific field of view and / or wavelength range) along one direction, as indicated by lines 1032, 1034, and 1036. For example, when the display light propagates within the substrate 1010 along the direction indicated by lines 1032, 1034, or 1036, each time the display light propagating within the substrate 1010 reaches the first grating 1030, a portion of the display light may be diffracted by the first grating 1030 to the second grating 1040. Then, the second grating 1040 can expand the display light from the first grating 1030 in different directions by diffracting a portion of the display light to the viewing window each time the display light propagating in the substrate 1010 reaches the second grating 1040. On the second grating 1040, the exit area 1050 represents such an area in which the display light of the full FOV at a pupil position in the viewing window (for example, at the center of the viewing window) can be coupled out from the waveguide display 1000.

[0180] As described above, the first grating 1030 and the second grating 1040 may each include a multiplexed VBG including a plurality of VBGs, each VBG being designed for a specific FOV range and / or wavelength range. For example, the first grating 1030 may include hundreds or more VBGs (e.g., about 300 to about 1000 VBGs) recorded by hundreds or more exposures, wherein each VBG may be recorded under different conditions. The second grating 1040 may also include tens or hundreds of VBGs (e.g., 50 or more VBGs) recorded by tens or hundreds of exposures. The first grating 1030 and the second grating 1040 may each be a transmission grating or a reflection grating.

[0181] Fig. 10B and Fig. 10C A top view and a side view of a volume Bragg grating based waveguide display 1000 are shown, respectively. The input coupler 1020 may include a projector optical device (not shown, such as a lens) and a prism. The display light may be collimated by the projector optical device and projected onto the prism, and may be coupled into the substrate 1010 by the prism. The prism may have a refractive index that matches the refractive index of the substrate 1010, and may include an optical wedge having a certain angle so that the light coupled into the substrate 1010 may be incident on a surface 1012 or 1014 of the substrate 1010 at an incident angle greater than the critical angle of the substrate 1010. In this way, the display light coupled into the substrate 1010 may be guided by the substrate 1010 through total internal reflection, and may be diffracted by multiple regions of the first grating 1030 to the second grating 1040, as described above. The second grating 1040 may then diffract the display light out of the substrate 1010 at multiple regions to replicate the exit pupil.

[0182] Fig.11Light dispersion in an example of a volume Bragg grating based waveguide display (e.g., waveguide display 1000) according to some embodiments is shown. As shown in the example, sphere 1110 can represent the wave vector of light that can be guided by the waveguide. For light with a wave vector outside of sphere 1110, the light can become evanescent. Cone 1120 can represent the wave vector of light that can leak out of the waveguide due to not meeting the total internal reflection condition. Therefore, the area of ​​sphere 1110 outside of cone 1120 can represent the wave vector of light that can be guided by the waveguide and can propagate within the waveguide by TIR. Point 1130 can represent the wave vector of display light coupled into the waveguide by, for example, a prism. Wave vector 1140 shows the light dispersion caused by the first grating 1030, where light of different colors can have different diffraction angles. Wave vector 1150 shows the light dispersion caused by the second grating 1040, where light of different colors can have different diffraction angles. Therefore, the light coupled out from the substrate may have some dispersion, so that images of different colors may not perfectly overlap each other to form one image. Therefore, the displayed image may be blurred and the resolution of the displayed image may be reduced.

[0183] Fig. 12A An example of a volume Bragg grating 1200 is shown. Fig. 12A The volume Bragg grating 1200 shown may include a transmission holographic grating having a thickness D. The refractive index n of the volume Bragg grating 1200 may be modulated with an amplitude Δn, and the grating period of the volume Bragg grating 1200 may be Λ. Incident light 1210 having a wavelength λ may be incident on the volume Bragg grating 1200 at an incident angle θ and may be refracted into the volume Bragg grating 1200 as incident light 1220, where the incident light 1220 is refracted at an angle θ in the volume Bragg grating 1200. n The incident light 1220 may be diffracted by the volume Bragg grating 1200 into diffracted light 1230. The diffracted light 1230 may be diffracted in the volume Bragg grating 1200 at a diffraction angle θ d propagates and can be refracted out of the volume Bragg grating 1200 as diffracted light 1240.

[0184] Fig. 12B Shows Fig. 12A The Bragg condition of the volume Bragg grating 1200 is shown. The volume Bragg grating 1200 may be a transmission grating. Vector 1205 may represent the grating vector in The vector 1225 can represent the incident wave vector The vector 1235 can represent 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 a wavelength λ that completely satisfies the Bragg condition. In this way, diffraction can occur in a small wavelength range and a small incident angle range around the perfect Bragg condition. The diffraction efficiency, wavelength selectivity, and angle selectivity of the volume Bragg grating 1200 can be functions of the thickness D of the volume Bragg grating 1200. For example, the full width at half maximum (FWHM) wavelength range and the FWHM angle range of the volume Bragg grating 1200 around the Bragg condition can be inversely proportional to the thickness D of the volume Bragg grating 1200, and the maximum diffraction efficiency under the Bragg condition can be a function of sin 2 (a×Δn×D), where a is a coefficient. For a reflective volume Bragg grating, the maximum diffraction efficiency under Bragg conditions can be expressed as the function tanh 2 (a×Δn×D).

[0185] As described above, in some designs, to obtain a large FOV (e.g., greater than ±30°) and diffract light of different colors, multiple polymer layers can be stacked, each polymer layer including a Bragg grating for a different color (e.g., R, G, or B) and / or a different FOV for coupling the display light to the user's eyes. In some designs, a multiplexed Bragg grating can be used, where each portion of the multiplexed Bragg grating can be used to diffract light in a different FOV range and / or a different wavelength range. Therefore, in some designs, to obtain the desired diffraction efficiency and large FOV for the entire visible spectrum (e.g., from about 400nm to about 700nm, or from about 450nm to about 650nm), one or more thick volume Bragg gratings can be used, each thick volume Bragg grating including a large number of gratings (or holograms) recorded by a large number of exposures (e.g., holographic recordings) (such as hundreds of times or more than 1000 times).

[0186] The VBG or other holographic optical elements described above may be recorded in a layer of holographic material (e.g., photopolymer). In some embodiments, the VBG 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 VBG may be recorded in the layer of holographic material.

[0187] Typically, to record a holographic optical element in a photosensitive material layer, two coherent light beams may interfere with each other at an angle to produce a unique interference pattern in the photosensitive material layer, which in turn may produce 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, silver halide emulsions, dichromated gelatin, photopolymers comprising photopolymerizable monomers suspended in a polymer matrix, photorefractive crystals, and the like. An example of a photosensitive material layer for holographic recording is a two-stage photopolymer that may include matrix precursors that may be pre-cured to form a polymer binder prior to holographic recording and a write monomer for holographic recording.

[0188] In one example, the photosensitive material layer may include a polymer binder, a monomer (e.g., an acrylic monomer) and an initiating agent, such as an initiator, a chain transfer agent or a photosensitive dye. The polymer binder may serve as a support matrix. The monomer may be dispersed in the support matrix and may be used as a refractive index modifier. The photosensitive dye may absorb light and interact with the initiator to polymerize the monomer. Therefore, in each exposure (recording), the interference pattern may cause monomer polymerization and diffusion to bright stripes, thereby generating a concentration and density gradient that may cause refractive index modulation. For example, areas with higher monomer and polymerization concentrations may have a higher refractive index. As exposure and polymerization proceed, fewer monomers are available for polymerization, and diffusion may be suppressed. After all or substantially all monomers have been polymerized, no new gratings are recorded in the photosensitive material layer. In a thick VBG including a large number of gratings recorded with a large number of exposures, the display haze may be large.

[0189] As described above, in some waveguide-based near-eye display systems, in order to expand the viewing window of the waveguide-based near-eye display, two output gratings (or two grating layers or two parts of a multiplexed grating) can generally be used to expand the display light in two dimensions or along the two axes of the dual-axis pupil expansion. Spatially separating the two output gratings and reducing the total number of exposures of each output grating can help reduce the display haze because the perspective area (e.g., the middle) of the waveguide-based near-eye display can include only one output grating. For example, in some embodiments, the first output grating can be recorded with more exposures (e.g., >500 times or >1000 times) and can be located outside the perspective area of ​​the waveguide-based near-eye display. The second output grating can be recorded with fewer exposures (e.g., <100 times or <50 times) and can be located in the perspective area of ​​the waveguide-based near-eye display. Therefore, the display haze in the perspective area can be significantly reduced. However, due to the spatial separation of the two output gratings, the overall size of the waveguide-based near-eye display may be very large.

[0190] The grating coupler described above may include a transmissive VBG or a reflective VBG, which may have some similar and some different characteristics. For example, as described above, the FWHM wavelength range and FWHM angle range of a transmissive or reflective volume Bragg grating near the Bragg condition may be inversely proportional to the thickness D of the transmissive or reflective volume Bragg grating. The maximum diffraction efficiency of the transmissive VBG under the Bragg condition may be a function of sin 2 (a×Δn×D), where a is the coefficient, Δn is the refractive index modulation, and the maximum diffraction efficiency of the reflective VBG under Bragg conditions can be the function tanh 2 (a×Δn×D). In addition, the parameters of the transmissive and reflective volume Bragg gratings (e.g., grating tilt angles) can be different so as to couple the display light into the waveguide at a specific angle so that the coupled display light can be guided by the waveguide through TIR. Due to the different grating parameters, the dispersion characteristics of the transmission grating and the reflection grating may be different.

[0191] Fig.13A A front view of an example of a volume Bragg grating based waveguide display 1300 with exit pupil expansion and dispersion reduction in accordance with some embodiments is shown. Fig. 13BA side view of an example of a volume Bragg grating-based waveguide display 1300 with exit pupil expansion and dispersion reduction in accordance with some embodiments is shown. The waveguide display 1300 can be similar to the waveguide display 1000 and can include an input coupler 1320 at a different location than the input coupler 1020. The waveguide display 1300 can include a substrate 1310, and a first grating 1330 and a second grating 1340 formed on or in the substrate 1310. As with the input coupler 1020, the input coupler 1320 can include a projector optics 1322 (e.g., a lens) and a prism 1324. Display light can be coupled into the substrate 1310 through the input coupler 1320 and can be guided by the substrate 1310. The display light may reach the first portion 1332 of the first grating 1330, and may be diffracted by the first portion 1332 of the first grating 1330 to change the propagation direction, and reach other portions of the first grating 1330, each of which may diffract the display light toward the second grating 1340. The second grating 1340 may diffract the display light out of the substrate 1310 at different positions to form a plurality of exit pupils as described above.

[0192] The first portion 1332 and each other portion of the first grating 1330 may have matching grating vectors (e.g., having the same grating vector in the xy plane and the same grating vector, opposite grating vectors in the z direction, or having the same and opposite grating vectors in the z direction, but recorded with different exposure durations to achieve different diffraction efficiencies). Therefore, due to the opposite Bragg conditions of diffraction at the first portion 1332 and each other portion of the first grating 1330 (e.g., +1 and -1 order diffraction), they may compensate for the dispersion of the display light to reduce the total dispersion. Therefore, the total dispersion of the display light by the waveguide display 1300 may be reduced in at least one direction.

[0193] Fig.14A The propagation of light from different fields of view in a reflective volume Bragg grating based waveguide display 1400 is shown in accordance with certain embodiments. The waveguide display 1400 may include a reflective VBG 1410. Due to the grating tilt angle and the grating vector of the reflective VBG 1410, light from the positive field of view (shown by line 1422) may have a smaller incident angle on the stripes of the reflective VBG 1410 and also have a smaller incident angle on the top surface 1402 of the waveguide display 1400. On the other hand, light from the negative field of view (shown by line 1424) may have a larger incident angle on the stripes of the reflective VBG 1410 and also have a larger incident angle on the top surface 1402 of the waveguide display 1400.

[0194] Fig. 14BThe propagation of light from different fields of view in a transmissive volume Bragg grating based waveguide display 1450 is shown in accordance with certain embodiments. The waveguide display 1450 may include a transmissive VBG 1460. Due to the difference in grating tilt angles, the transmissive VBG 1460 may diffract light from different fields of view differently compared to the reflective VBG 1410. For example, as shown, light from the positive field of view (shown by line 1472) may have a smaller incident angle on the fringes of the transmissive VBG 1460, but a larger incident angle on the bottom surface 1452 of the waveguide display 1450. On the other hand, light from the negative field of view (shown by line 1474) may have a larger incident angle on the fringes of the transmissive VBG 1460, but a smaller incident angle on the bottom surface 1452 of the waveguide display 1450. The manner in which the reflective or transmissive grating diffracts light from different fields of view may affect the form factor and performance of the waveguide display.

[0195] Fig.15 An example of a reflective volume Bragg grating based waveguide display 1500 with exit pupil expansion and dispersion reduction according to some embodiments is shown. The waveguide display 1500 may include a top grating 1505 and a bottom grating 1515. In the illustrated example, the top grating 1505 may be a reflective VBG, and the bottom grating 1515 may also be a reflective grating. On the bottom grating 1515, the exit region 1550 represents the region in which the full FOV of display light at a pupil position in the viewing window (e.g., at the center of the viewing window) can be coupled out of the bottom grating. Fig.15 As shown, the top FOV at the exit region 1550 represented by the line between the upper right corner 1522 and the upper left corner 1524 can be mapped to the curve 1530 on the top grating 1505, wherein the upper right corner 1522 and the upper left corner 1524 of the exit region 1550 can be mapped to the position 1532 and the position 1534 on the top grating 1505, respectively. The bottom FOV at the exit region 1550 represented by the line between the lower right corner 1542 and the lower left corner 1544 can be mapped to the curve 1510 on the top grating 1505, wherein the lower right corner 1542 and the lower left corner 1544 of the exit region 1550 can be mapped to the position 1512 and the position 1514 on the top grating 1505, respectively. Therefore, if the curve 1530 is below the line between the upper right corner 1522 and the upper left corner 1524 of the exit region 1550, there may be some FOV truncation. Thus, to maintain full FOV, the curve 1530 may be above a line between the upper right corner 1522 and the upper left corner 1524 of the exit area 1550. Thus, the size of the waveguide display 1500 may be large.

[0196] Fig.16An example of a transmissive volume Bragg grating based waveguide display 1600 with exit pupil expansion and form factor reduction in accordance with certain embodiments is shown. The waveguide display 1600 may include a top grating 1605 and a bottom grating 1615. In the illustrated example, the top grating 1605 may be a reflective VBG and the bottom grating 1615 may be a transmissive VBG. On the bottom grating 1615, an exit region 1650 represents the region in which the full FOV of display light at one pupil location in the viewing window (e.g., at the center of the viewing window) may be coupled out of the bottom grating. Fig.16 As shown, the top FOV at the exit region 1650 represented by the line between the upper right corner 1622 and the upper left corner 1624 can be mapped to the curve 1610 on the top grating 1605, wherein the upper right corner 1622 and the upper left corner 1624 of the exit region 1650 can be mapped to the position 1612 and the position 1614 on the top grating 1605, respectively. The bottom FOV at the exit region 1650 represented by the line between the lower right corner 1642 and the lower left corner 1644 can be mapped to the curve 1630 on the top grating 1605, wherein the lower right corner 1642 and the lower left corner 1644 of the exit region 1650 can be mapped to the position 1632 and the position 1634 on the top grating 1605, respectively. Therefore, there can be some overlap between the top grating 1605 and the bottom grating 1615 to reduce the overall size of the waveguide display 1600. For example, position 1632 may be below upper right corner 1622 and still be mapped to lower right corner 1642 .

[0197] Fig.17A An example of a transmissive volume Bragg grating 1700 in a waveguide display according to some embodiments is shown. The grating tilt angle α of the transmissive VBG 1700 may need to be within a certain range to transmissively diffract the display light. For example, if the grating tilt angle α of the transmissive VBG 1700 is below a certain value, the transmissive VBG 1700 may become a reflective VBG, the distance between two consecutive positions where the display light may reach the grating may be too large (so the exit pupil may be sparsely replicated in the viewport), or the display light may become evanescent. Therefore, the grating tilt angle α of the transmissive VBG 1700 needs to be greater than a certain value to transmissively diffract the display light.

[0198] Fig. 17BAn example of a transmissive VBG 1710 in a waveguide display is shown, where light diffracted by the transmissive VBG may not be totally reflected and guided in the waveguide. The grating tilt angle α of the transmissive VBG 1710 may be greater than a certain value, for example, greater than about 60°. In this way, light coupled into the waveguide may be incident on the surface of the waveguide at an incident angle less than the critical angle, and thus may not be totally reflected and guided in the waveguide. Therefore, the grating tilt angle α of the transmissive VBG may also need to be lower than a certain value (e.g., about 60°) to transmissively diffract the display light into the waveguide so that the diffracted light can be guided by the waveguide through total internal reflection. In this way, the grating tilt angle α of the transmissive VBG may need to be within a certain range.

[0199] Fig. 17C An example of a reflective volume Bragg grating 1750 in a waveguide display according to certain embodiments is shown. The grating tilt angle α of the reflective VBG 1750 may also need to be within a certain range to reflectively diffract the display light. If the grating tilt angle α of the reflective VBG 1750 is greater than a certain value, the reflective VBG 1750 may become a transmissive VBG, the distance between two consecutive positions where the display light may reach the grating may be too large (so the exit pupil may be sparsely replicated in the viewport), or the display light may become evanescent. Therefore, the grating tilt angle α of the reflective VBG may also need to be below a certain value to reflectively diffract the display light. In one example, the grating tilt angle α of the reflective VBG 1750 may be about 30°.

[0200] Fig.17D An example of a reflective VBG 1760 in a waveguide display is shown, where light diffracted by the reflective VBG is not totally reflected and guided in the waveguide. Fig.17D The grating tilt angle α of the reflective VBG 1760 shown in FIG. 17 may be less than a specific value. In this way, the light coupled into the waveguide may be incident on the surface of the waveguide at an incident angle less than the critical angle, and thus may not be totally reflected and guided in the waveguide. The grating tilt angle α of the reflective VBG 1760 may be less than about 30°. Therefore, the grating tilt angle α of the reflective VBG may also need to be greater than a specific value. In this way, the grating tilt angle α of the reflective VBG may also need to be within a certain range to reflectively diffract the display light into the waveguide so that the diffracted light can be guided by the waveguide through total internal reflection. Figures 17A-17D It is shown that the grating tilt angle α of the reflection grating may be smaller than the grating tilt angle α of the transmission grating.

[0201] Fig.18A FIG. 1 shows the optical dispersion of an example of a reflective volume Bragg grating 1800 in a waveguide display according to some embodiments. The reflective VBG 1800 may be formed with a grating vector k g, thickness d and average refractive index n. The surface normal direction of the reflective VBG 1800 is N. The light dispersion of the reflective VBG 1800 can be determined by the following formula:

[0202]

[0203] Where λ0 is the wavelength of light that fully satisfies the Bragg condition, k out is the wave vector of the light diffracted by the reflective VBG 1800. When the grating tilt angle α of the reflective VBG 1800 is about 30°, the light dispersion amount of the reflective VBG 1800 may be approximately:

[0204]

[0205] Therefore, to obtain an angular resolution of approximately 2 arc minutes, the thickness d of the reflective VBG 1800 may be at least approximately 0.5 mm.

[0206] Fig.18B FIG. 1 shows the light dispersion of an example of a transmissive volume Bragg grating 1850 in a waveguide display according to some embodiments. The transmissive VBG 1850 can be similarly configured with a grating vector k g , thickness d and average refractive index n. The surface normal direction of the transmissive VBG 1850 is N. The light dispersion of the transmissive VBG 1850 can be determined by the following formula:

[0207]

[0208] Where λ0 is the wavelength of light that fully satisfies the Bragg condition, k out is the wave vector of the light diffracted by the transmissive VBG 1850. When the grating tilt angle α of the transmissive VBG 1850 is about 60°, the light dispersion amount of the transmissive VBG 1850 may be approximately:

[0209]

[0210] Therefore, to obtain an angular resolution of approximately 2 arc minutes, the thickness d of the transmissive VBG 1850 may be at least approximately 1.5 mm, which is approximately three times the thickness of a reflective VBG with the same angular resolution and may be difficult to achieve or may result in significant display haze.

[0211] In order to reduce the physical size of a VBG-based waveguide display, reduce the thickness of the VBG and the display haze, and obtain a desired resolution, dispersion compensation may be required in a VBG-based waveguide display. According to certain embodiments, one or more pairs of gratings (e.g., transmission gratings) having matching grating vectors and operating under opposite diffraction conditions (e.g., +1 order diffraction versus -1 order diffraction) may be used to compensate for the dispersion caused by each other.

[0212] Fig.19A is a front view of an example of a volume Bragg grating based waveguide display 1900 with exit pupil expansion and dispersion reduction in accordance with some embodiments. Fig.19B is a side view of an example of a volume Bragg grating-based waveguide display 1900 with exit pupil expansion and dispersion reduction in accordance with certain embodiments. The waveguide display 1900 can be similar to the waveguide display 1300, but can include an input coupler that is different from the input coupler 1320. The waveguide display 1900 can include a substrate 1910, and a first grating 1930 and a second grating 1940 formed on or in the substrate 1910. The input coupler can include projector optics 1920 (e.g., a lens) and an input grating 1922, rather than a prism. The display light can be collimated by the projector optics 1920 and projected onto the input grating 1922, which can couple the display light into the substrate 1910 by diffraction, as described above with reference to, for example Figure 5 and Figure 6 The display light may reach the first portion 1932 of the first grating 1930, and may be diffracted by the first portion 1932 of the first grating 1930 to change the propagation direction, and reach other portions of the first grating 1930, each of which may diffract the display light toward the second grating 1940. The second grating 1940 may diffract the display light out of the substrate 1910 at different positions to form a plurality of exit pupils as described above.

[0213] The first portion 1932 and each other portion of the first grating 1930 can have matching grating vectors (e.g., having the same grating vector in the xy plane and having the same grating vector and / or opposite grating vectors in the z direction, but recorded with different exposure durations to achieve different diffraction efficiencies). Therefore, due to the opposite Bragg conditions of diffraction at the first portion 1932 and each other portion of the first grating 1930 (e.g., +1 order and -1 order diffraction), they can compensate for the dispersion of the display light caused by each other to reduce the total dispersion in one direction. In addition, the input grating 1922 and the second grating 1940 can have matching grating vectors (e.g., having the same grating vector in the xy plane and having the same grating vector and / or opposite grating vectors in the z direction, but recorded with different exposure durations to achieve different diffraction efficiencies), where the input grating 1922 can couple the display light into the substrate 1910, and the second grating 1940 can couple the display light out of the waveguide. Therefore, due to the opposite diffraction directions and opposite Bragg conditions (e.g., +1 and -1 order diffraction) of the diffraction at the input grating 1922 and the second grating 1940, the input grating 1922 and the second grating 1940 can compensate for the dispersion of the display light caused by each other to reduce the total dispersion in at least one direction. In this way, the total dispersion of the first portion 1932 and each other portion of the first grating 1930 can be reduced or offset, and the total dispersion of the input grating 1922 and the second grating 1940 can also be reduced or offset. Therefore, the total dispersion of the display light by the waveguide display 1900 can be minimized in any direction. In this way, a higher resolution of the displayed image can be achieved. Therefore, a thin reflective or transmissive VBG can be used as an input and output coupler, and the desired resolution can still be obtained. The transmissive VBG can also allow the first grating and the second grating to overlap at least partially to reduce the physical size of the waveguide display, as described above.

[0214] The waveguide display 1900 can include multiple polymer layers on one or more waveguide plates, where the input grating 1922, the first grating 1930, and the second grating 1940 can each be divided into multiple gratings recorded in multiple polymer layers. The gratings on each polymer layer can cover different corresponding FOVs and spectra, and the combination of multiple polymer layers can provide full FOV and spectrum coverage. In this way, each polymer layer can be very thin (e.g., about 20 μm to about 100 μm) and can be exposed fewer times (e.g., less than about 100 times) to record fewer gratings to reduce haze, and the overall efficiency of the multiple polymer layers can still be high for the full FOV and spectrum. Fig.19A and Fig.19BIn the example shown, the waveguide display 1900 may include a first polymer layer 1912 and a second polymer layer 1914 on one or more plates or substrates. Each polymer layer 1912 or 1914 may include a portion of an input grating 1922, a first grating 1930, and / or a second grating 1940.

[0215] Fig. 20A Another example of a volume Bragg grating-based waveguide display 2000 with exit pupil expansion, reduced dispersion, reduced form factor, and improved efficiency according to some embodiments is shown. As with waveguide display 2000, waveguide display 2000 may include a substrate 2010, which may be similar to substrate 1910. Substrate 2010 may include a first surface 2012 and a second surface 2014. Display light from a light source (e.g., an LED) may be coupled into substrate 2010 by input coupler 2020, and may be reflected by first surface 2012 and second surface 2014 by total internal reflection, so that the display light may propagate within substrate 2010 (e.g., in the -y direction). As described above, input coupler 2020 may include a diffractive coupler, such as a multiplexed VBG, which may couple display light of different colors into substrate 2010 at different diffraction angles.

[0216] The waveguide display 2000 may include a first grating 2030 and a second grating 2040 formed on the first surface 2012 and / or the second surface 2014. The waveguide display 2000 may also include a third grating 2060 and a fourth grating 2070 formed on the first surface 2012 and / or the second surface 2014. The third grating 2060 and the fourth grating 2070 may each be a multiplexed VBG including a plurality of VBGs. In some embodiments, the third grating 2060, the fourth grating 2070, and the first grating 2030 may be on the same surface or different surfaces of the substrate 2010. In some embodiments, the third grating 2060, the fourth grating 2070, and the first grating 2030 may be in different regions of the same grating or the same grating material layer.

[0217] In some embodiments, the first grating 2030, the third grating 2060, and the fourth grating 2070 may each include a plurality of VBGs. The third grating 2060 and the first grating 2030 may be recorded in multiple exposures and under similar recording conditions (but may be recorded for different exposure durations to achieve different diffraction efficiencies), such that each VBG in the third grating 2060 may match a corresponding VBG in the first grating 2030 (e.g., having the same grating vector in the xy plane and the same and / or opposite grating vectors in the z direction). For example, in some embodiments, the VBG in the third grating 2060 and the corresponding VBG in the first grating 2030 may have the same grating period and the same grating tilt angle (thus having the same grating vector) and the same thickness. The fourth grating 2070 and the first grating 2030 may also be recorded in multiple exposures and under similar recording conditions (but for different exposure durations), such that each VBG in the fourth grating 2070 may match a corresponding VBG in the first grating 2030 (e.g., having the same grating vector in the xy plane and the same and / or opposite grating vectors in the z direction). In some embodiments, the recording conditions for recording the third grating 2060 may be different from the recording conditions for recording the fourth grating 2070, such that the third grating 2060 and the fourth grating 2070 may have different Bragg conditions (and different grating vectors), and thus may diffract light from different FOV ranges and / or wavelength ranges to improve the overall diffraction efficiency of visible light in a large FOV range. In some embodiments, the third grating 2060 and the fourth grating 2070 may have similar grating vectors, and thus may diffract light from the same FOV range and / or wavelength range with similar or different diffraction efficiencies to improve the overall diffraction efficiency of light in certain FOV ranges and / or wavelength ranges.

[0218] In some embodiments, the VBG in the first grating 2030 that matches the VBG in the third grating 2060 may be recorded in one region (e.g., an upper region) of the first grating 2030, and the other VBG in the first grating 2030 that matches the VBG in the fourth grating 2070 may be recorded in a different region (e.g., a lower region) of the first grating 2030. In one example, the third grating 2060 and the fourth grating 2070 may each have a thickness of about 20 μm, and may each include about 20 VBGs recorded by about 20 exposures. In this example, the first grating 2030 may have a thickness of about 20 μm or more, and may include about 40 VBGs recorded in different regions by about 40 exposures. The second grating 2040 may have a thickness of about 20 μm or more, and may include about 50 VBGs recorded by about 50 exposures.

[0219] The input coupler 2020 may couple the display light from the light source into the substrate 2010. The display light may directly reach the third grating 2060, or may be reflected by the first surface 2012 and / or the second surface 2014 to the third grating 2060, wherein the size of the display light beam may be slightly larger than the size at the input coupler 2020. Each VBG in the third grating 2060 may diffract a portion of the display light within the FOV range and the wavelength range that approximately satisfies the Bragg condition of the VBG to the upper region of the first grating 2030. As described above, the upper region of the first grating 2030 may include a VBG that matches the VBG in the third grating 2060. Therefore, when the display light diffracted by the VBG in the third grating 2060 propagates within the substrate 2010 (for example, along the direction shown by line 2032) by total internal reflection, each time the display light propagating within the substrate 2010 reaches the first grating 2030, a portion of the display light can be diffracted by the corresponding VBG in the first grating 2030 to the second grating 2040.

[0220] The display light that is not diffracted by the third grating 2060 (for example, due to a diffraction efficiency of less than 100% or due to a small FOV range and / or a wavelength range near the Bragg condition) may continue to propagate within the substrate 2010 and may reach the fourth grating 2070. Each VBG in the fourth grating 2070 may diffract a portion of the display light within the FOV range and the wavelength range that approximately satisfies the Bragg condition of the VBG to the lower region of the first grating 2030. As described above, the lower region of the first grating 2030 may include a VBG that matches the VBG in the fourth grating 2070. Therefore, when the display light diffracted by the VBG in the fourth grating 2070 propagates within the substrate 2010 (for example, along the direction shown by the line 2034) by total internal reflection, each time the display light propagating within the substrate 2010 reaches the first grating 2030, a portion of the display light may be diffracted by the corresponding VBG in the first grating 2030 to the second grating 2040. The second grating 2040 can expand the display light from the first grating 2030 in a different direction (e.g., approximately in the y direction) by diffracting a portion of the display light to the viewing window 2050 (e.g., a distance of about 18 mm from the second grating 2040 in the +z or -z direction) each time the display light propagating within the substrate 2010 reaches the second grating 2040. In this way, the display light can be expanded in two dimensions to fill the viewing window 2050.

[0221] Fig. 20BAn example of replicated exit pupils at a window 2080 (e.g., window 2050) of a volume Bragg grating-based waveguide display 2000 is shown. The exit pupils may include a first set of exit pupils 2082 replicated by gratings 2060, 2030, and 2040, and a second set of exit pupils 2084 replicated by gratings 2070, 2030, and 2040. In embodiments where gratings 2060 and 2070 have different grating vectors, the first set of exit pupils 2082 and the second set of exit pupils 2084 may correspond to different FOV ranges and / or different wavelength ranges. In embodiments where gratings 2060 and 2070 have similar grating vectors, the first set of exit pupils 2082 and the second set of exit pupils 2084 may correspond to the same FOV range and / or wavelength range. The first set of exit pupils 2082 and the second set of exit pupils 2084 may overlap or partially overlap. In this way, due to the diffraction of the display light by the two sets of spatially multiplexed VBGs, the pupil replication density can be increased and the light in the window can be more uniform.

[0222] In addition, due to the double diffraction in each dimension of a pair of matched gratings operating under opposite Bragg conditions as described above, dispersion can be reduced in two dimensions. In addition, due to the fewer exposure times (and therefore the higher refractive index modulation Δn of each VBG), a wider bandwidth of display light can be diffracted to the window by the gratings with higher diffraction efficiency. Therefore, the power efficiency of the waveguide display can be improved. In some embodiments, the first grating 2030 and the second grating 2040 can at least partially overlap to reduce the form factor of the waveguide display 2000, as described above.

[0223] Fig.21A Another example of a volume Bragg grating-based waveguide display 2100 with exit pupil expansion, dispersion reduction, and form factor reduction in accordance with certain embodiments is shown. As with the waveguide display 2100, the waveguide display 2100 may include a substrate 2110, which may be similar to the substrate 2110. The substrate 2110 may include a first surface 2112 and a second surface 2114. Display light from a light source (e.g., an LED) may be coupled into the substrate 2110 via an input coupler 2120, and may be reflected by the first surface 2112 and the second surface 2114 via total internal reflection, such that the display light may propagate within the substrate 2110. As described above, the input coupler 2120 may include a diffraction coupler, such as a VBG. The waveguide display 2100 may also include a first grating 2130 and a second grating 2140 formed on the first surface 2112 and / or the second surface 2114. In Fig.21AIn the example shown, the first grating 2130 and the second grating 2140 may be at different positions in the x-direction and may overlap in at least a portion of the see-through area of ​​the waveguide display 2100. The first grating 2130 and the second grating 2140 may be used for biaxial pupil expansion to expand an incident display beam in two dimensions to fill the viewing window 2150 with display light (e.g., at a distance of approximately 18 mm from the second grating 2140 in the +z or -z direction). For example, the first grating 2130 may expand the display beam in approximately the y-direction, while the second grating 2140 may expand the display beam in approximately the x-direction.

[0224] In addition, the waveguide display 2100 may include a third grating 2160 formed on the first surface 2112 and / or the second surface 2114. In some embodiments, the third grating 2160 and the first grating 2130 may be arranged at different positions in the y direction on the same surface of the substrate 2110. In some embodiments, the third grating 2160 and the first grating 2130 may be in different regions of the same grating or the same grating material layer. In some embodiments, the third grating 2160 may be spatially separated from the first grating 2130. In some embodiments, the third grating 2160 and the first grating 2130 may be recorded at the same number of exposures and under similar recording conditions (but may be recorded for different exposure durations to achieve different diffraction efficiencies), so that each VBG in the third grating 2160 may match a corresponding VBG in the first grating 2130 (e.g., having the same grating vector in the xy plane and having the same and / or opposite grating vectors in the z direction).

[0225] The input coupler 2120 may couple the display light from the light source into the substrate 2110. The display light may propagate approximately along the x-direction within the substrate 2110, and may directly reach the third grating 2160, or may be reflected by the first surface 2112 and / or the second surface 2114 to the third grating 2160. Each VBG in the third grating 2160 may diffract a portion of the display light within the FOV range and the wavelength range approximately satisfying the Bragg condition of the VBG downward to the first grating 2130. When the display light diffracted by the VBG in the third grating 2160 propagates in one direction (e.g., approximately in the y-direction shown by the line 2132) within the substrate 2110 by total internal reflection, each time the display light propagating within the substrate 2110 reaches the first grating 2130, a portion of the display light may be diffracted by the corresponding VBG in the first grating 2130 to the second grating 2140. The second grating 2140 can then expand the display light from the first grating 2130 in a different direction (e.g., approximately in the x-direction) by diffracting a portion of the display light propagating within the substrate 2110 to the viewing window 2150 each time the display light propagating within the substrate 2110 reaches the second grating 2140. The input coupler 2120 and the second grating 2140 can include matched VBGs (e.g., the VBGs have the same grating vector in the xy plane and the same or opposite grating vectors in the z direction) to reduce the total dispersion caused by the input coupler 2120 and the second grating 2140. Similarly, the gratings 2130 and 2160 can include matched VBGs (e.g., the VBGs have the same grating vector in the xy plane and the same and / or opposite grating vectors in the z direction) to reduce the total dispersion caused by the gratings 2130 and 2160. Therefore, the total dispersion of the gratings in the waveguide display 2100 can be reduced or minimized.

[0226] Each of the first grating 2130 and the second grating 2140 may have a thickness of less than, for example, 100 μm (e.g., 20 μm), and may include, for example, less than 50 VBGs. Thus, any area in the optical see-through region of the waveguide display 2100 may include less than 100 VBGs. Thus, display haze may not be noticeable. Furthermore, the first grating 2130 and the second grating 2140 may at least partially overlap to reduce the form factor of the waveguide display 2100, so that the physical size of the waveguide display 2100 may be similar to the physical size of the lenses in an ordinary pair of glasses.

[0227] Fig. 21BAn example of a volume Bragg grating-based waveguide display 2105 with exit pupil expansion, reduced dispersion, reduced form factor, and improved efficiency according to some embodiments is shown. As with the waveguide display 2100, the waveguide display 2105 may include a first grating 2135, a second grating 2145, a third grating 2165, and a fourth grating 2175 formed on a first surface 2116 and / or a second surface 2118 of a substrate 2115. The first grating 2135, the second grating 2145, the third grating 2165, and the fourth grating 2175 may each include a multiplexed VBG including a plurality of VBGs. In some embodiments, the third grating 2165, the fourth grating 2175, and the first grating 2135 may be on the same surface of the substrate 2115. In some embodiments, the third grating 2165, the fourth grating 2175, and the first grating 2135 may be in different regions of the same grating or the same grating material layer.

[0228] Each VBG in the third grating 2165 may have a grating vector that matches the grating vector of the corresponding VBG in the first grating 2135 (e.g., having the same grating vector in the xy plane and having the same and / or opposite grating vectors in the z direction). Each VBG in the fourth grating 2175 may have a grating vector that matches the grating vector of the corresponding VBG in the first grating 2135 (e.g., having the same grating vector in the xy plane and having the same and / or opposite grating vectors in the z direction). In some embodiments, the third grating 2165 and the fourth grating 2175 may have different grating vectors and thus may diffract light from different FOV ranges and / or wavelength ranges to improve the overall diffraction efficiency of visible light in a large FOV range. In some embodiments, the third grating 2165 and the fourth grating 2175 may have similar grating vectors and thus may diffract light from the same FOV range and / or wavelength range with similar or different diffraction efficiencies to improve the overall diffraction efficiency of light in certain FOV ranges and / or wavelength ranges.

[0229] The input coupler 2125 may couple the display light from the light source into the substrate 2115. The display light may directly reach the third grating 2165, or may be reflected by the first surface 2116 and / or the second surface 2118 to the third grating 2165. Each VBG in the third grating 2165 may diffract a portion of the display light within the FOV range and the wavelength range that approximately satisfies the Bragg condition of the VBG to the left region of the first grating 2135. When the display light diffracted by the VBG in the third grating 2165 propagates within the substrate 2115 (e.g., along the direction indicated by the line 2136) by total internal reflection, each time the display light propagating within the substrate 2115 reaches the first grating 2135, a portion of the display light may be diffracted by the corresponding VBG in the first grating 2135 to the second grating 2145.

[0230] The display light that is not diffracted by the third grating 2165 (e.g., due to a diffraction efficiency of less than 100% or due to a small FOV range and / or a wavelength range near the Bragg condition) may continue to propagate within the substrate 2115, and may reach the fourth grating 2175. Each VBG in the fourth grating 2175 may diffract a portion of the display light within the FOV range and the wavelength range that approximately satisfies the Bragg condition of the VBG to the right region of the first grating 2135. When the display light diffracted by the VBG in the fourth grating 2175 propagates within the substrate 2115 (e.g., along the direction indicated by the line 2138) by total internal reflection, each time the display light propagating within the substrate 2115 reaches the first grating 2135, a portion of the display light may be diffracted by the corresponding VBG in the first grating 2135 to the second grating 2145.

[0231] The second grating 2145 can expand the display light from the first grating 2135 in different directions (e.g., approximately in the x direction) by diffracting a portion of the display light to a viewing window 2155 (e.g., about 18 mm from the second grating 2145 in the +z or -z direction) each time the display light propagating within the substrate 2115 reaches the second grating 2145. In this way, the display light can be expanded in two dimensions to fill the viewing window 2155. The final exit pupil may include a first group of exit pupils replicated by the gratings 2165, 2135, and 2145, and a second group of exit pupils replicated by the gratings 2175, 2135, and 2145. In embodiments where the gratings 2165 and 2175 have different grating vectors, the first group of exit pupils and the second group of exit pupils may correspond to different FOV ranges and / or different wavelength ranges. In embodiments where gratings 2165 and 2175 have similar grating vectors, the first set of exit pupils and the second set of exit pupils may correspond to the same FOV range and / or wavelength range. The first set of exit pupils and the second set of exit pupils may overlap or partially overlap. In this way, due to the diffraction of the display light by the two sets of spatially multiplexed VBGs, the pupil replication density may be increased, and the light in the viewport may be more uniform.

[0232] In some embodiments, the full FOV range of the displayed image can be divided into two or more FOV ranges covered by two or more sets of gratings. Two or more FOV ranges can be spliced ​​together to provide a full field of view. For each FOV range, a set of gratings can be used to expand the exit pupil in two dimensions to fill the viewing window.

[0233] Fig.22A is a front view of an example of a volume Bragg grating based waveguide display 2200 including two image projectors 2220 and 2250 in accordance with certain embodiments. Fig. 22B 2 is a side view of an example of a volume Bragg grating-based waveguide display 2200 including two image projectors 2220 and 2250 in accordance with certain embodiments. The image projector 2220, the first input grating 2222, the first top grating 2230, and the bottom grating 2240 may be used to provide a first portion (e.g., the left half) of the full FOV of the waveguide display 2200. Display light for the first portion of the full FOV may be collimated and projected onto the first input grating 2222, which may couple the display light into the waveguide 2210 by diffraction, as described above with reference to, for example Figure 5-Figure 6As described. The display light may reach the first portion 2232 of the first top grating 2230, and may be diffracted by the first portion 2232 of the first top grating 2230 to change the propagation direction and reach other portions of the first top grating 2230, each of which may diffract the display light toward the bottom grating 2240. The bottom grating 2240 may diffract the display light out of the waveguide 2210 at different positions to form a plurality of exit pupils as described above. The first portion 2232 of the first top grating 2230 and each of the other portions of the first top grating 2230 may have similar grating parameters (but may be recorded at different exposure durations to achieve different diffraction efficiencies). Therefore, due to the opposite Bragg conditions of diffraction at the first portion 2232 of the first top grating 2230 and each of the other portions of the first top grating 2230 (e.g., +1 order and -1 order diffraction), they may compensate for the dispersion of the display light caused by each other to reduce the total dispersion.

[0234] In addition, the first input grating 2222 and the bottom grating 2240 may have similar grating parameters or similar grating vectors at least in the xy plane (but may be recorded with different exposure durations to achieve different diffraction efficiencies), wherein the first input grating 2222 may couple the display light into the waveguide 2210, and the bottom grating 2240 may couple the display light out of the waveguide 2210. Therefore, the first input grating 2222 and the bottom grating 2240 may compensate for the dispersion of the display light caused by each other to reduce the total dispersion, which is due to the opposite diffraction directions and opposite Bragg conditions (e.g., +1-order and -1-order diffraction) of the respective diffractions. In this way, the dispersion of the first portion 2232 of the first top grating 2230 and each other portion of the first top grating 2230 may be canceled, and the dispersion of the first input grating 2222 and the bottom grating 2240 may also be canceled.

[0235] Similarly, the image projector 2250, the second input grating 2252, the second top grating 2260, and the bottom grating 2240 (or a different bottom grating) can be used to provide another portion (e.g., the right half) of the full FOV of the waveguide display 2200. As described above, the bottom grating 2240 can be used for both portions of the field of view, or can include two gratings, each for a portion of the field of view. The dispersion of the first portion 2262 and each other portion of the second top grating 2260 can be canceled, and the dispersion of the second input grating 2252 and the bottom grating 2240 can also be canceled. Therefore, the total dispersion of the display light by the waveguide display 2200 can be minimized in any direction. In this way, even if the polymer layer is thin and the transmissive VBG is recorded in the thin polymer layer, a higher resolution of the displayed image can be achieved.

[0236] The waveguide display 2200 may include multiple polymer layers on one or more waveguide plates, such as the first waveguide plate 2212 and the second waveguide plate 2214. The input gratings 2222 and 2252, the top gratings 2230 and 2260, and the bottom grating 2240 may each be divided into multiple gratings recorded in multiple polymer layers. The gratings on each polymer layer may cover different respective FOVs and spectra. The combination of multiple polymer layers may provide full FOV and spectral coverage. In this way, each polymer layer may be thin (e.g., about 20 μm to about 100 μm) and may be exposed fewer times (e.g., less than about 100 times) to record fewer gratings, thereby reducing the haze of the perspective image. The overall efficiency of the multiple polymer layers may still be high for the full FOV and visible light spectrum.

[0237] Fig.23A is a front view of an example of a volume Bragg grating based waveguide display 2300 including a single image projector 2320 and gratings for field of view stitching in accordance with some embodiments. Fig. 23B 2 is a side view of an example of a volume Bragg grating based waveguide display 2300 having an image projector 2320 and gratings for field of view stitching according to some embodiments. The waveguide display 2300 can include multiple polymer layers on one or more waveguide plates 2310. The image projector 2320, the input grating 2330, the top grating 2340, and the bottom grating 2350 can be used to provide a first portion (e.g., the left half) of the full FOV of the waveguide display 2300. As described above, display light for the first portion of the FOV can be collimated and projected onto the input grating 2330, which can couple the display light into the waveguide plate 2310 by diffraction as described above. The display light can reach a first portion of the top grating 2340 and can be diffracted by the first portion of the top grating 2340 to other portions of the top grating 2340, each of which can diffract the display light toward the bottom grating 2350. The bottom grating 2350 can diffract the display light out of the waveguide plate 2310 at different locations to replicate the exit pupil as described above. The first portion and each other portion of the top grating 2340 can compensate for the dispersion caused by each other, and as described above, the input grating 2330 and the bottom grating 2350 can also compensate for the dispersion caused by each other.

[0238] The image projector 2320, the input grating 2332, the top grating 2342, and the bottom grating 2352 can be used to provide a portion (e.g., the right half) of the full FOV of the waveguide display 2300. The display light can be collimated and coupled into the waveguide plate 2310 by the input grating 2332. The display light can reach a first portion of the top grating 2342 and can be diffracted by the first portion of the top grating 2342 to other portions of the top grating 2342, each of which can diffract the display light toward the bottom grating 2352. The bottom grating 2352 can diffract the display light out of the waveguide plate 2310 at different locations to replicate the exit pupil as described above. The first portion and each other portion of the top grating 2342 can compensate for the dispersion caused by each other, and as described above, the input grating 2332 and the bottom grating 2352 can also compensate for the dispersion caused by each other.

[0239] The waveguide display 2300 can include multiple polymer layers on one or more waveguide plates 2310, wherein the input gratings 2330 and 2332, the top gratings 2340 and 2342, and the bottom gratings 2350 and 2352 can each be divided into multiple gratings recorded in multiple polymer layers, wherein the gratings on each polymer layer can cover different corresponding FOVs and spectra. The combination of multiple polymer layers can provide full FOV and spectrum coverage. In this way, each polymer layer can be very thin (e.g., about 20 μm to about 100 μm) and can be exposed fewer times (e.g., less than about 100 times) to record fewer gratings to reduce haze, and the overall efficiency of the multiple polymer layers can still be high for the full FOV and visible light spectrum.

[0240] exist Fig. 23B In the example shown, each of the input grating 2330, the top grating 2340, and the bottom grating 2350 can be divided into two multiplexed gratings, each multiplexed grating is recorded in a corresponding polymer layer and each multiplexed grating covers a corresponding FOV, wherein multiple VBGs can be recorded in each corresponding polymer layer to form the multiplexed grating. Similarly, each of the input grating 2332, the top grating 2342, and the bottom grating 2352 can be divided into two multiplexed gratings, each multiplexed grating is recorded in a corresponding polymer layer and each multiplexed grating covers a corresponding FOV, wherein multiple VBGs can be recorded in each corresponding polymer layer to form the multiplexed grating. Fig. 23B As shown, input gratings 2332 and 2330 can be in different polymer layers. Similarly, top gratings 2340 and 2342 can be in different polymer layers, and bottom gratings 2350 and 2352 can be in different polymer layers. Therefore, crosstalk between them can be reduced.

[0241] Fig.24 An example of a volume Bragg grating-based waveguide display 2400 is shown, which includes multiple grating layers for different fields of view and / or wavelengths of light, in accordance with certain embodiments. The VBG-based waveguide display 2400 may be an example of the VBG-based waveguide display 2300 described above. In the waveguide display 2400, the gratings may be spatially multiplexed along the z-direction. For example, the waveguide display 2400 may include multiple substrates, such as substrates 2410, 2412, 2414, etc. The substrates may include the same material or materials with similar refractive indices. One or more VBGs (e.g., VBGs 2420, 2422, 2424, etc.) may be fabricated on each substrate, such as recorded in a layer of holographic material formed on the substrate. The VBG may be a reflection grating or a transmission grating. Substrates with VBGs may be arranged in a substrate stack along the z-direction for spatial multiplexing. Each VBG may be a multiplexed VBG including multiple gratings designed for different Bragg conditions to couple display light of different wavelength ranges and / or different FOVs into or out of the waveguide.

[0242] exist Fig.24 In the example shown, VBG 2420 can couple light 2434 from the positive field of view into the waveguide, as shown by light 2444 within the waveguide. VBG 2422 can couple light 2430 from approximately a 0° field of view into the waveguide, as shown by light 2440 within the waveguide. VBG 2424 can couple light 2432 from the negative field of view into the waveguide, as shown by light 2442 within the waveguide. As described above, each of VBGs 2420, 2422, and 2424 can be a multiplexed VBG with multiple exposures, and thus can couple light from different FOV ranges into or out of the waveguide.

[0243] Fig.25 25 shows the field of view of multiple gratings in an example of a volume Bragg grating based waveguide display according to some embodiments. In some embodiments, each grating can be in a respective grating layer or on a respective waveguide plate. Each grating can be a multiplexed grating including many exposures and can be used to couple display light from multiple FOV ranges into or out of the waveguide with high efficiency. For example, curve 2510 can show that a first VBG (e.g., Fig.24 Curve 2520 may show the diffraction efficiency of a second VBG (e.g., Fig.24 Curve 2530 may show the diffraction efficiency of a third VBG (e.g., Fig.24The diffraction efficiency of the VBG 2424) for light from different fields of view. When the first VBG, the second VBG, and the third VBG are arranged in a stack, light can be diffracted more uniformly with higher efficiency in the full field of view (e.g., from about -20° to about 20°). In some embodiments, the first VBG, the second VBG, and the third VBG can be used to couple display light of the same color. Different groups of VBGs can be used to cover the full field of view of display light of different colors.

[0244] A VBG designed to diffract light of one wavelength and from one range of angles can also diffract light of another wavelength and from another range of angles. For example, a VBG characterized by a specific period and tilt angle can diffract light of different wavelengths and from different angles of incidence.

[0245] Fig.26A An example of a volume Bragg grating 2610 diffracting light of different colors from a corresponding field of view is shown. As shown in the example, the VBG 2610 can diffract blue light 2602 from a first incident angle into the waveguide at a first diffraction angle. The VBG 2610 can also diffract green light 2604 from a second incident angle into the waveguide at a second diffraction angle. The VBG 2610 can further diffract red light 2606 from a third incident angle into the waveguide at a third diffraction angle.

[0246] Fig.26B The relationship between the grating period of the volume Bragg grating and the corresponding fields of view for incident light of different colors is shown. Curve 2620 shows that red light from different fields of view can be diffracted by VBGs with different grating periods. Similarly, curve 2630 shows that green light from different fields of view can be diffracted by VBGs with different grating periods, and curve 2630 shows that blue light from different fields of view can be diffracted by VBGs with different grating periods. Fig.26B It is also shown that a VBG with a specific grating period and tilt angle can diffract light of different wavelengths and from different angles of incidence (e.g., from different fields of view). Fig.26B Region 2605 in shows a grating that can diffract light of two or more colors from two or more corresponding FOVs. For example, Fig.26B The dashed line 2650 in may correspond to a VBG having a grating period of approximately 450 nm, where the VBG may diffract red light from approximately a -7° field of view, green light from approximately a 2° field of view, and blue light from approximately a 6° field of view.

[0247] As described above, the VBG may be a reflective VBG or a transmissive VBG. The reflective VBG and the transmissive VBG may have different diffraction characteristics. Fig.18A and Fig.18BAs described above, the reflection grating can have a relatively lower dispersion than a transmission grating of similar thickness. The use of a transmission grating as an output grating can allow grating overlap for two-dimensional exit pupil replication to reduce the physical size of the waveguide display, as described above with reference to Fig.16 As mentioned above, the reflection grating cannot do this. Fig.15 described.

[0248] Fig.27A 27 shows the diffraction efficiency of an example of a transmissive volume Bragg grating having the same thickness but different refractive index modulations. The diffraction efficiency may be polarization dependent. Curve 2710 shows the diffraction efficiency of an example of a transmissive VBG for s-polarized light, while curve 2720 shows the diffraction efficiency of an example of a transmissive VBG for p-polarized light. Curve 2730 shows the average diffraction efficiency of an example of a transmissive VBG for s-polarized light and p-polarized light (e.g., unpolarized light). Fig.27A As shown, curve 2710 and curve 2720 may correspond to a function proportional to the square of a sine function (eg, ∝sin 2 (a×n1×D)). The diffraction efficiency of a transmission grating increases or decreases with the increase of the refractive index modulation. Therefore, increasing the refractive index modulation of a transmission VBG does not necessarily increase the diffraction efficiency of the transmission VBG.

[0249] Fig.27B 27 shows the diffraction efficiency of an example of a reflective volume Bragg grating having the same thickness but different refractive index modulation. The diffraction efficiency of a reflective VBG is also polarization dependent. Curve 2760 shows the diffraction efficiency of an example of a reflective VBG for s-polarized light, while curve 2720 shows the diffraction efficiency of an example of a reflective VBG for p-polarized light. Curve 2730 shows the average diffraction efficiency of an example of a reflective VBG for s-polarized light and p-polarized light (e.g., unpolarized light). Fig.27B As shown, the diffraction efficiency of a reflective VBG can be increased with increasing refractive index modulation (e.g., ∝sin 2 (a×n1×D)), and can be saturated when the refractive index modulation reaches a certain value.

[0250] Figure 28A-Figure 28D The diffraction efficiency of examples of transmissive volume Bragg gratings with different refractive index modulations is shown as a function of the deviation of the incident angle from the Bragg condition. Fig.28A Curve 2810 in shows the diffraction efficiency of an example of a transmissive VBG with a refractive index modulation of approximately 0.002, where the peak diffraction efficiency of the main lobe is close to 100%. Fig.28B Curve 2820 in FIG. 2 shows the diffraction efficiency of an example of a transmissive VBG with a refractive index modulation of about 0.004, where Fig.28ACompared to the transmissive VBG, the peak diffraction efficiency drops to about 0 at about 0°, the diffraction efficiency curve 2820 has two peaks, and the side lobes increase. Fig.28C Curve 2830 in FIG. 2 shows the diffraction efficiency of an example of a transmissive VBG with a refractive index modulation of about 0.0054, where Fig.28B Compared with the transmissive VBG, the peak diffraction efficiency, the FWHM angular range of the main lobe and the side lobes can be increased. Fig.28D Curve 2840 in FIG. 2 shows the diffraction efficiency of an example of a transmissive VBG with a refractive index modulation of about 0.0078, where Fig.28C Compared with the transmissive VBG, the peak diffraction efficiency is reduced, the diffraction efficiency curve 2840 has two peaks, and the side lobes are increased.

[0251] Figure 29A-Figure 29D The diffraction efficiency of examples of reflective volume Bragg gratings with different refractive index modulations is shown as a function of the deviation of the incident angle from the Bragg condition. Fig.29A Curve 2910 in shows the diffraction efficiency of an example of a reflective VBG with a refractive index modulation of approximately 0.002, where the peak diffraction efficiency of the main lobe is greater than 80%. Fig.29B Curve 2920 in FIG. 2 shows the diffraction efficiency of an example of a reflective VBG with a refractive index modulation of about 0.004, where Fig.29A Compared with the reflective VBG, the peak diffraction efficiency increases to 100%, the FWHM angle range of the main lobe increases, and the side lobes increase. Fig.29C Curve 2930 in FIG. 2 shows the diffraction efficiency of an example of a reflective VBG with a refractive index modulation of about 0.0054, where the peak diffraction efficiency is about 100%, which is similar to Fig.29B Compared with the reflective VBG, the FWHM angle range of the main lobe is further increased, and the side lobe is also further increased. Fig.29D Curve 2940 in FIG. 2 shows the diffraction efficiency of an example of a reflective VBG with a refractive index modulation of about 0.0078, where the peak diffraction efficiency is about 100%, which is similar to Fig.29C Compared with the reflective VBG, the FWHM angle range of the main lobe is further increased, and the side lobe is also further increased.

[0252] For a transmissive VBG, the diffraction efficiency of polarized light can be a function of the refractive index modulation (e.g., ∝sin 2 (a×n1×D)), such as Fig.27A In addition, the diffraction efficiency may be color-dependent. For example, for one color (e.g., blue), a transmissive VBG may require a lower refractive index modulation than for another color (e.g., green or red) to achieve Fig.27A The first diffraction peak shown. Fig.27AA particular refractive index modulated grating with the refractive index modulation of the first diffraction peak shown may have a higher diffraction efficiency for blue light than for green or red light.

[0253] Figure 30A-Figure 30C 1 shows the diffraction efficiency of an example of a transmissive VBG with a first refractive index modulation (e.g., about 0.01). The transmissive VBG can diffract light of different colors from different corresponding fields of view with different corresponding diffraction efficiencies, as described above with reference to FIG. Fig.26A and Fig.26B For example, Fig. 30A Curve 3010 in FIG. 3 may illustrate the diffraction efficiency of a transmissive VBG for blue light from a field of view of approximately 14°, where the peak diffraction efficiency may be close to 100%. Fig. 30B Curve 3020 in may show the diffraction efficiency of the same transmissive VBG for green light from approximately a 10° field of view, where the peak diffraction efficiency has not yet reached 100% (eg, approximately 90%). Fig. 30C Curve 3030 in may show the diffraction efficiency of the same transmissive VBG for red light from approximately a 3° field of view, where the peak diffraction efficiency may be approximately 80%.

[0254] Figure 30D-Figure 30F FIG. 1 shows the diffraction efficiency of an example of a transmissive VBG with a second refractive index modulation (e.g., 0.012). The transmissive VBG may differ from the transmissive VBG only in its refractive index modulation. Figure 30A-Figure 30C The transmissive VBG can diffract light of different colors from different corresponding fields of view with different corresponding diffraction efficiencies. For example, Fig.30D Curve 3012 in FIG. 3 may show the diffraction efficiency of a transmissive VBG for blue light from a field of view of approximately 14°, where the peak diffraction efficiency may have been Fig. 30A The approximately 100% peak drop shown in Fig. 30A The refractive index modulation associated with the first diffraction efficiency peak shown in FIG. Fig.30E Curve 3022 in may show the diffraction efficiency of the same transmissive VBG for green light from approximately a 10° field of view, where the peak diffraction efficiency may have been increased (e.g., greater than 90%). Fig.30F Curve 3032 in may show the diffraction efficiency of the same transmissive VBG for red light from approximately a 3° field of view, where the peak diffraction efficiency may have increased to greater than 80%.

[0255] Figure 30G-Figure 30I FIG. 4 shows the diffraction efficiency of an example of a transmissive VBG with a third refractive index modulation (e.g., 0.015). The transmissive VBG may differ from the first transmissive VBG only in terms of the refractive index modulation. Figure 30A-Figure 30FThe transmissive VBG can diffract light of different colors from different corresponding fields of view with different corresponding diffraction efficiencies. For example, Figure 30G Curve 3014 in FIG. 3 may show the diffraction efficiency of a transmissive VBG for blue light from a field of view of approximately 14°, where the peak diffraction efficiency may have been Fig.30D The values ​​shown are further reduced because the refractive index modulation is larger than that of Fig. 30A The first diffraction efficiency peak shown is associated with the refractive index modulation. Fig. 30H Curve 3024 in may show the diffraction efficiency of the same transmissive VBG for green light from approximately a 10° field of view, where the peak diffraction efficiency may also have dropped from its maximum value. Fig. 30I Curve 3034 in may show the diffraction efficiency of the same transmissive VBG for red light from approximately a 3° field of view, where the peak diffraction efficiency may have been further increased.

[0256] On the contrary, for the reflective VBG, Fig.27B and Figure 29A-Figure 29D As shown, the diffraction efficiency may not decrease with increasing refractive index modulation. The FWHM angular range of the main lobe and side lobes of the diffraction efficiency curve may increase with increasing refractive index modulation.

[0257] Fig.31A The minimum refractive index modulation of a transmissive volume Bragg grating with different grating periods in order to achieve diffraction saturation for different colors is shown. Curve 3110 shows the minimum refractive index modulation of the transmissive VBG to achieve maximum diffraction efficiency for red light, curve 3120 shows the minimum refractive index modulation of the transmissive VBG to achieve maximum diffraction efficiency for green light, and curve 3130 shows the minimum refractive index modulation of the transmissive VBG to achieve maximum diffraction efficiency for blue light. As shown, for a grating with a given grating period and thickness, the minimum refractive index modulation to achieve maximum diffraction efficiency may vary for different colors. For example, the minimum refractive index modulation for maximum diffraction efficiency for blue light may be lower than that for green or red light. Therefore, similarly Figure 30A-Figure 30I As shown, for a grating capable of diffracting multiple colors of light, when the refractive index modulation is at a value that enables the highest diffraction efficiency for blue light, the diffraction efficiency of the same grating for green and red light may be lower; when the refractive index modulation is at a value that enables the highest diffraction efficiency for red light, the diffraction efficiency of the same grating for blue and green light may be reduced from their peaks. Therefore, some trade-offs may need to be made between the diffraction efficiencies of different colors.

[0258] Fig.31BA curve 3140 is shown, which shows the refractive index modulation of a transmission grating with different grating periods in order to avoid saturation of the refractive index modulation of any color. For example, for a grating that can diffract blue light, the refractive index modulation can be determined based on the refractive index modulation saturation of blue light. For a grating that can only diffract green and red light, the refractive index modulation can be determined based on the refractive index modulation saturation of green light. For a grating that can only diffract red light, the refractive index modulation can be determined based on the refractive index modulation saturation of red light.

[0259] As described above, to cover the full field of view of red, green, and blue light, the VBG can be a multiplexed grating that is exposed multiple times to different recorded light patterns, where each exposure can record a grating that can diffract red, green, and blue light from different corresponding fields of view. The gratings in the multiplexed VBG can have different grating periods. The multiplexed VBG can be used to diffract light of all colors from the full field of view. In addition, the gratings in the multiplexed VBG can have different refractive index modulations in order to optimize the diffraction efficiency of different colors.

[0260] Fig. 31C 3150 is a diagram showing an example of a grating layer including multiplexed VBGs with different pitches and different refractive index modulations for optimizing diffraction efficiency and diffraction efficiency uniformity in accordance with certain embodiments. Each data point 3152 in the diagram 3150 shows the period of the grating and the corresponding refractive index modulation. In the illustrated example, the grating layer may include more than 40 gratings. The grating layer may have a maximum refractive index modulation of about 0.08. Each grating may have a refractive index modulation of about 0.002 or less. In combination, the multiplexed gratings may provide a full FOV for visible light.

[0261] It may be desirable to multiplex more gratings in a multiplexed VBG to increase the diffraction efficiency of light over a large field of view. However, when many gratings are multiplexed in a multiplexed VBG, crosstalk may occur between the gratings.

[0262] Fig.32ACrosstalk caused by an example of a multiplexed volume Bragg grating in a waveguide display 3200 is shown. The waveguide display 3200 may include a multiplexed input grating including an input grating 3212. The waveguide display 3200 may also include a multiplexed output grating 3210 including two or more output gratings, such as a first output grating 3214 and a second output grating 3216, which may be recorded in the same grating layer or multiple grating layers. Display light of a first color and a first field of view may be coupled into the waveguide through the input grating 3212 and may be coupled out of the waveguide through the first output grating 3214 at a desired angle, such as an output angle equal to the input angle (e.g., approximately 90° in the example shown). The input grating 3212 and the first output grating 3214 may have matching grating vectors (e.g., at least in the xy plane) and may therefore compensate for dispersion caused by each other and keep the output angle equal to the input angle.

[0263] Due to the non-zero width of the diffraction efficiency curve of each grating (e.g. Figures 28A-30I 3214), and the FOV associated with the second output grating 3216 may at least partially overlap with the first FOV associated with the first output grating 3214. Therefore, display light from the first field of view and coupled into the waveguide through the input grating 3212 may be at least partially coupled out of the waveguide at an undesirable angle through the second output grating 3216. Due to the grating vector mismatch between the input grating 3212 and the second output grating 3216, the input angle (e.g., about 90° in this example) and the output angle of the display light in the first FOV and coupled out of the waveguide through the second output grating 3216 may be different, as shown. Fig.32A As a result, an undesirable ghost image may be produced.

[0264] Fig.32BThe relationship between the grating period of the volume Bragg grating and the corresponding fields of view for incident light of different colors is shown. As shown, the same VBG (e.g., the VBG represented by line 3230) can diffract red light of a first wavelength from a negative field of view (as shown by the intersection of line 3230 and curve 3240). The same VBG can also diffract red light of a different (e.g., second) wavelength from a different negative field of view (as shown by the intersection of line 3230 and curve 3242). The red light of the first wavelength and the second wavelength can be emitted by the same light source (e.g., a red LED) that emits light in a narrow spectral range. Similarly, the same VBG can diffract green light of a third wavelength from a positive field of view (as shown by the intersection of line 3230 and curve 3250) and green light of a different (e.g., fourth) wavelength from a different positive field of view (as shown by the intersection of line 3230 and curve 3252). The green light of the third wavelength and the fourth wavelength can be emitted by the same light source (e.g., a green LED) that emits light in a narrow spectral range. The same VBG may further diffract blue light at a fifth wavelength from a normal field of view (as shown by the intersection of line 3230 and curve 3260) and blue light at a different (e.g., sixth) wavelength from a different normal field of view (as shown by the intersection of line 3230 and curve 3262). The fifth and sixth wavelengths of blue light may be emitted by the same light source (e.g., a blue LED) that emits light within a narrow spectral range.

[0265] In some cases, a ghosting effect may be caused by undesired diffraction of display light of a first field of view by a grating for a different field of view. For example, if display light of the left half of the FOV is diffracted by a top grating of the right half of the FOV, or if display light of the right half of the FOV is diffracted by a top grating of the left half of the FOV, a ghost image may exist. In some embodiments, to reduce ghosting effects, two or more top gratings may be offset from each other and may not overlap. In some embodiments, the two or more top gratings may be designed so that undesired diffraction of display light by the gratings does not reach the viewing window and therefore is not observed by the user.

[0266] As described above, the transmission grating and the reflection grating can have different performance characteristics, such as diffraction efficiency, diffraction efficiency saturation, dispersion, FWHM angular range, etc. For example, the transmission grating can have a wider Bragg peak linewidth than the reflection grating. In addition, the Bragg peak linewidth of the transmission VBG or the reflection VBG can vary with the corresponding field of view.

[0267] Fig.33AThe line widths of the Bragg peaks of a transmissive volume Bragg grating and a reflective volume Bragg grating for different fields of view are shown. Curve 3310 shows the line width of the Bragg peak of a transmissive VBG for different fields of view. Curve 3310 shows that the line width of the Bragg peak of a transmissive VBG can increase significantly as the corresponding field of view increases. Curve 3320 shows the line width of the Bragg peak of a reflective VBG for different fields of view. Curve 3320 shows that the line width of the Bragg peak of a reflective VBG can increase only slightly as the corresponding field of view increases.

[0268] Fig.33B Examples of Bragg peaks 3330 of transmissive volume Bragg gratings for different fields of view are shown. As shown, the line width of a transmissive VBG for a larger field of view can be much wider than the line width of a transmissive VBG for a smaller field of view, and thus a larger FOV range can be covered.

[0269] Fig.33C Examples of Bragg peaks 3340 of reflective volume Bragg gratings for different fields of view are shown. As shown, the line width of a reflective VBG for a larger field of view can be approximately the same as the line width of a reflective VBG for a smaller field of view.

[0270] Fig.34A The trade-off between crosstalk and efficiency is shown in the example of a multiplexed volume Bragg grating comprising multiple VBGs. Fig.34A In the example shown, the VBGs can be loosely multiplexed to avoid overlap of Bragg peaks and thus avoid crosstalk between the VBGs for blue light from a large positive field of view, as shown by curve 3410. As described above, the VBGs can also diffract light of other colors from other fields of view. Thus, a grating used to diffract blue light from the positive field of view can also diffract red light from the negative field of view. However, because the gratings are loosely multiplexed, and the linewidth of the Bragg peak of the transmission grating is narrower at the negative field of view, as shown in the above reference Figure 33A-Figure 33B As described, red light from some negative fields of view may not be diffracted by the grating, as shown by the gaps between the peaks in curve 3420, thereby reducing the efficiency of red light at certain negative fields of view.

[0271] Fig.34B The trade-off between crosstalk and efficiency in an example of a multiplexed volume Bragg grating including multiple VBGs is shown. In the illustrated example, the VBGs can be densely multiplexed to increase coverage of the negative field for red light, as shown by curve 3440. The densely multiplexed VBGs can also diffract blue light from the positive field. Because the VBGs are densely multiplexed and the line width of the Bragg peak of the transmission grating is wider at the positive field, the Bragg peak of the blue light at the positive field may overlap and cause crosstalk between the VBGs for blue light from the large positive field, as shown by curve 3430.

[0272] Therefore, in transmissive gratings, it is difficult to simultaneously minimize crosstalk and maximize efficiency. In many cases, the maximum achievable efficiency of a waveguide display based on a transmissive VBG may be limited by the maximum allowed crosstalk.

[0273] Fig.35A The relationship between the minimum diffraction efficiency and the total refractive index modulation and the corresponding crosstalk in a multiplexed transmissive volume Bragg grating is shown. Fig.35A The horizontal axis of corresponds to the desired minimum efficiency. Data point 3520 shows the minimum refractive index modulation to achieve the corresponding desired minimum diffraction efficiency. Data point 3510 shows the maximum crosstalk value associated with the corresponding minimum refractive index modulation to achieve the corresponding desired minimum efficiency.

[0274] exist Fig.35A In the example shown, as shown by dashed line 3530, the desired crosstalk can be less than, for example, 0.06 (so that the checker board contrast can be approximately 30). Each waveguide plate can have two polymer layers attached thereto. The maximum refractive index modulation in each polymer layer can be, for example, approximately 0.05, so that the total refractive index modulation can be approximately 0.1, as shown by dashed line 3540. As shown by data point 3542, when the total refractive index modulation of the two polymer layers is 0.1 to achieve the desired efficiency, the crosstalk can be much higher than the maximum allowable crosstalk shown by dashed line 3530. As shown by data point 3532, in order to achieve a crosstalk of less than 0.06, the maximum refractive index modulation of the polymer layers may not be fully utilized and the minimum efficiency may be relatively low. Fig.35A In the example shown at data point 3532 in , only about 20% of the total refractive index modulation of the two polymer layers may be utilized to achieve crosstalk performance. Therefore, the efficiency of a transmissive VBG-based waveguide display may be limited by the maximum allowed crosstalk.

[0275] Fig.35B The relationship between the minimum diffraction efficiency and the total refractive index modulation and the corresponding crosstalk in a multiplexed reflective volume Bragg grating is shown. The horizontal axis corresponds to the desired minimum efficiency. Data point 3570 shows the refractive index modulation to achieve the corresponding desired minimum efficiency. Data point 3560 shows the maximum crosstalk value associated with the corresponding refractive index modulation to achieve the corresponding desired minimum efficiency.

[0276] exist Fig.35B In the example shown, each waveguide plate can have two polymer layers attached thereto. The maximum refractive index modulation in each polymer layer can be, for example, about 0.05, so that the total refractive index modulation can be, for example, about 0.1, as shown by dashed line 3580. Fig.35BAs shown at point 3582 in FIG. 35, when the maximum refractive index modulation of the polymer layer (e.g., 0.1) is fully utilized, the crosstalk of the grating is still much lower than the maximum allowed crosstalk indicated by line 3590 (e.g., about 0.06), and the efficiency may be relatively high. Therefore, in a reflective VBG-based waveguide display, the diffraction efficiency may be limited by the maximum refractive index modulation of the polymer layer. In various embodiments, the transmission grating and the reflection grating may be selected based on design considerations such as form factor, efficiency, image quality, etc.

[0277] Based on the characteristics of transmissive VBG and reflective VBG, and the desired characteristics of the waveguide display (e.g., efficiency, field of view, resolution, contrast, crosstalk, ghost images, rainbow effect, physical size, etc.), a transmissive VBG or a reflective VBG may be selected to implement a waveguide display. Fig.27B and Figure 29A-Figure 29D As mentioned above, for a reflective grating, when the refractive index modulation is above a threshold, the diffraction efficiency may be saturated. As the refractive index modulation continues to increase, the FWHM angle range or the FWHM wavelength range may become wider. This characteristic of a reflective VBG can be used in some waveguide systems.

[0278] For example, in the example of a waveguide display, a light source in a projector may emit light with a wavelength bandwidth of about 10 nm to about 30 nm. For an unsaturated reflective VBG with a thickness of about 50 μm, the FWHM wavelength range is about 1 nm. Therefore, in order to diffract the emitted light within the wavelength bandwidth of the light source, multiple VBGs may be required. A saturated reflective VBG with a thickness of about 50 μm may have a FWHM wavelength range much wider than 1 nm, so fewer reflective VBGs may be required to diffract the emitted light within the wavelength bandwidth of the light source.

[0279] Fig.36 An example of a waveguide display 3600 including spatially multiplexed reflective volume Bragg gratings with different refractive index modulations is shown in accordance with certain embodiments. Fig.36 The reflective VBG shown can be used for one-dimensional pupil expansion and dispersion compensation. Note that Fig.36 The reflective VBGs shown in FIG. 3 are for illustration purposes only. In some embodiments, additional reflective or transmissive VBG gratings 3615 may be used to expand the pupil in another dimension to achieve two-dimensional pupil expansion as described above. For example, the VBG gratings 3615 may include another set of reflective VBGs that may be used for pupil expansion and dispersion compensation in a second dimension substantially perpendicular to the first dimension as described above.

[0280] exist Fig.36In the example shown, the waveguide display 3600 may include a first reflective grating 3610 and a second reflective grating 3620. The first reflective grating 3610 and the second reflective grating 3620 may have matching grating vectors, such as having the same grating vector in the xy plane and having the same and / or opposite grating vectors in the z direction. For example, the first reflective grating 3610 and the second reflective grating 3620 may have some of the same grating parameters, such as grating period, tilt angle, thickness, etc. As described above, the first reflective grating 3610 and the second reflective grating 3620 may compensate for the dispersion caused by each other.

[0281] In some embodiments, the first reflection grating 3610 may be an example of the above-mentioned input grating, such as the input gratings 1922, 2222, 2252, 2330, 2332, etc. The second reflection grating 3620 may be an example of the above-mentioned output grating or bottom grating, such as the second grating 1940, the bottom grating 2240, the bottom gratings 2350 and 2352, etc. The first reflection grating 3610 and the second reflection grating 3620 may be used to couple the display light into and out of the waveguide, respectively.

[0282] In some embodiments, the first reflection grating 3610 may be an example of the first portion 1932 of the first grating 1930, the first portion 2232 of the first top grating 2230, the first portion 2262 of the second top grating 2260, the first portion of the top grating 2340, the first portion of the top grating 2342, etc. The second reflection grating 3620 may be an example of other portions of the first grating 1930, the first top grating 2230, the second top grating 2260, the top grating 2340, the top grating 2342, etc.

[0283] In the waveguide display 3600, the first reflection grating 3610 and the second reflection grating 3620 may have different refractive index modulations. For example, the first reflection grating 3610 may be severely saturated, so the diffraction efficiency of the first reflection grating 3610 may be approximately as shown by the graph 3612, where the FWHM wavelength range (and / or FWHM angle range) may be wide to cover a large wavelength range (and / or a large FOV range). Therefore, the first reflection grating 3610 can diffract display light within a large wavelength range (and / or a large FOV range).

[0284] The second reflective grating 3620 may include a plurality of sections 3622, 3624, 3626, etc. The display light diffracted by the first reflective grating 3610 (e.g., coupled into a waveguide or deflected to a different direction) may propagate within the waveguide by total internal reflection, and may reach each of the plurality of sections of the second reflective grating 3620 directly or indirectly (e.g., through the grating 3615). The plurality of sections of the second reflective grating 3620 may each couple a portion of the display light, for example, out of the waveguide or toward the output (or bottom) grating. Each of the plurality of sections 3622, 3624, 3626, etc. may have a different corresponding refractive index modulation, and thus may be saturated at a different corresponding level, and may have a different corresponding FWHM wavelength range (and / or FWHM angular range). For example, the first section 3622 may have a refractive index modulation below, equal to, or slightly above the saturation level, and thus may have a diffraction efficiency curve as shown by the graph 3632. The second portion 3624 may have a higher refractive index modulation and thus may have a wider FWHM wavelength range (and / or FWHM angular range), as shown in graph 3634. The third portion 3626 may have an even higher refractive index modulation and thus may have an even wider FWHM wavelength range (and / or FWHM angular range), as shown in graph 3636. In some embodiments, the second reflective grating 3620 may include multiple (e.g., more than three) portions, which may have different refractive index modulations and different FWHM wavelength ranges (and / or FWHM angular ranges).

[0285] In some embodiments, the first portion 3622 of the second reflective grating 3620 can couple display light within a first wavelength (and / or FOV) range out of the waveguide with high efficiency (e.g., close to 100% as shown in graph 3632) to replicate a pupil of light within the first wavelength (and / or FOV) range. The second portion 3624 of the second reflective grating 3620 can couple display light within a second wavelength (and / or FOV) range out of the waveguide with high efficiency, as shown in graph 3634. The second wavelength (and / or FOV) range can include the first wavelength (and / or FOV) range and can be wider than the first wavelength (and / or FOV) range. Because most or all of the light in the first wavelength (and / or FOV range) may have been diffracted by the first portion 3622, the second portion 3624 can only diffract light within the second wavelength (and / or FOV) range and not diffracted by the first portion 3622, as shown in area 3644 in graph 3634, to replicate another pupil. Similarly, the third portion 3626 of the second reflective grating 3620 can efficiently couple display light within a third wavelength (and / or FOV) range out of the waveguide, as shown in graph 3636. The third wavelength (and / or FOV) range may include the second wavelength (and / or FOV) range and may be wider than the second wavelength (and / or FOV) range. Because most or all of the light within the second wavelength (and / or FOV) range may have been diffracted by the first portion 3622 and the second portion 3624, the third portion 3626 may only diffract light within the third wavelength (and / or FOV) range that has not been diffracted by the first portion 3622 and the second portion 3624, as shown in graph 3636, to replicate a third pupil.

[0286] In some embodiments, the first reflective grating 3610 and the second reflective grating 3620 can each be a grating in a corresponding multiplexed grating including a plurality of saturated reflective VBGs. Each saturated reflective VBG in the multiplexed grating can diffract red light, green light, and / or blue light from different corresponding wavelengths and / or FOV ranges, as described above with reference to, for example Fig.26A , Fig.26B and Fig.32B The multiple saturated reflective VBG can thus provide full FOV for red, green, and blue light emitted by light sources (e.g., red LEDs, green LEDs, and blue LEDs) for displaying an image, as described above with reference to, for example Fig.19B , Fig. 22B , Fig. 23B , Fig.25 and Fig.33C described.

[0287] In some embodiments, because the diffraction efficiency of the transmission grating may be polarization sensitive and the incident display light may be unpolarized, some components of the display light may not be diffracted by the grating, and thus the efficiency of the waveguide display may be reduced. To improve the efficiency of unpolarized light or light of a specific polarization state, a polarization converter and two spatial multiplexing gratings may be used to couple the display light into or out of the waveguide.

[0288] Fig.37 An example of a waveguide display 3700 is shown that includes two multiplexed volume Bragg gratings 3710 and 3740 and a polarization converter 3730 between the two multiplexed volume Bragg gratings 3710 and 3740 in accordance with some embodiments. In some embodiments, because the diffraction efficiency of the transmission grating may be polarization sensitive and the incident display light may be unpolarized, some components of the display light may not be diffracted by the grating, and thus the efficiency of the waveguide display may be reduced. To improve the efficiency of unpolarized light or light of a specific polarization state, a polarization converter and two spatial multiplexing gratings may be used to couple the display light into or out of the waveguide. The first VBG 3710 may be formed on a substrate 3720 or on a surface of the polarization converter 3730. The second VBG 3740 may be formed on a substrate 3750 or on another surface of the polarization converter 3730.

[0289] The non-polarized light 3702 may include s-polarized light and p-polarized light. The first VBG 3710 may diffract most of the s-polarized light and a portion of the p-polarized light, as shown by diffracted light 3704. The diffracted light 3704 may be partially converted by the polarization converter 3730 and pass through the second VBG 3740 without being diffracted by the second VBG 3740, as shown by transmitted light 3706, because the Bragg condition is not satisfied. A portion 3708 of the p-polarized light that is not diffracted by the first VBG 3710 may pass through the polarization converter 3730 and may be converted into s-polarized light and may be diffracted by the second VBG 3740, wherein the diffracted light 3712 may have the same propagation direction as the transmitted light 3706. In this way, the non-polarized light 3702 may be more effectively diffracted by the waveguide display 3700.

[0290] External light (e.g., from an external light source, such as a lamp or the sun) can reflect from the surface of the grating coupler and return to the grating coupler, where the light reflected at the grating coupler can be diffracted by the grating coupler to generate a rainbow image. In some waveguide displays, ambient light with a large incident angle outside the see-through field of view of the waveguide display can also be diffracted by the grating coupler to produce a rainbow image. According to some embodiments, additional structures can be used in the waveguide display, such as a reflective coating (e.g., for light from a large see-through FOV) and / or an anti-reflective coating (e.g., for light from a small see-through FOV) to reduce optical artifacts, such as the rainbow effect. For example, an angle-selective transmission layer can be placed in front of (or behind) the waveguide and grating coupler of the waveguide display to reduce artifacts caused by external light sources. The angle-selective transmission layer can be configured to reflect, diffract, or absorb ambient light with an incident angle greater than half of the see-through field of view of the waveguide display, while allowing ambient light within the see-through field of view of the near-eye display to pass through and reach the user's eyes with little or no loss. The angle selective transmission layer may include, for example, a coating which may include one or more dielectric layers, diffractive elements such as gratings (e.g., meta-gratings), nanostructures (e.g., nanowires, nanopillars, nanoprisms, nano-pyramids), and the like.

[0291] Fig.38 An example of a waveguide display 3800 including an anti-reflection layer 3850 and an angle selective transmission layer 3840 according to some embodiments is shown. The waveguide display 3800 may include a waveguide 3810 and a grating coupler 3820 located on the bottom surface of the waveguide 3810. The grating coupler 3820 may be similar to the grating coupler described above. External light 3830 incident on the waveguide 3810 may be refracted into the waveguide 3810 as external light 3832, and may then be diffracted by the grating coupler 3820. The diffracted light may include a 0-order diffraction 3834 (e.g., a refractive diffraction) and a -1-order diffraction (not shown). The height, period, and / or tilt angle of the grating coupler 3820 may be configured such that -1-order diffraction may be reduced or minimized for external light.

[0292] The waveguide display 3800 may include an anti-reflective layer 3850 on the bottom surface 3822 of the grating coupler 3820. The anti-reflective layer 3850 may include, for example, one or more dielectric thin film layers or other anti-reflective layers coated on the bottom surface 3822, and may be used to reduce reflection of external light at the bottom surface 3822. Thus, little or no external light may be reflected back to the grating coupler 3820 at the bottom surface 3822 of the grating coupler 3820, and thus rainbow artifacts that may otherwise be formed due to diffraction of external light reflected by the grating coupler 3820 at the bottom surface 3822 may be reduced or minimized. Some portion of the display light may be diffracted by the grating coupler 3820 and may be coupled out of the waveguide 3810 toward the user's eye (e.g., due to -1 order diffraction). The anti-reflective layer 3850 may also help reduce reflection of the portion of the display light that is coupled out of the waveguide 3810 by the grating coupler 3820.

[0293] The angle selective transmission layer 3840 may be coated on the top surface of the waveguide 3810 or on the grating coupler 3820. The angle selective transmission layer 3840 may have high reflectivity, high diffraction efficiency, or high absorption for incident light having an incident angle greater than a certain threshold, and may have low loss for incident light having an incident angle below the threshold. The threshold may be determined based on the see-through field of view of the waveguide display 3800. For example, incident light 3860 having an incident angle greater than the see-through field of view may be mostly reflected, diffracted, or absorbed by the angle selective transmission layer 3840, and may not reach the waveguide 3810. External light 3830 having an incident angle within the see-through field of view may mostly pass through the angle selective transmission layer and the waveguide 3810, and may be refracted or diffracted by the grating coupler 3820.

[0294] The above-mentioned angle selective transmission layer 3840 can be implemented in various ways. In some embodiments, the angle selective transmission layer may include one or more dielectric layers (or air gaps). Each dielectric layer may have its own refractive index, and adjacent dielectric layers may have different refractive indices. In some embodiments, the angle selective transmission layer may include, for example, micro-mirrors or prisms, gratings, meta-gratings, nanowires, nano-pillars, or other microstructures or nanostructures. In some examples, the angle selective transmission layer may include a grating (e.g., a surface relief grating or a holographic grating) with a small grating period formed on a substrate. The grating may only diffract light with a large incident angle (e.g., about 75° to about 90°), and the diffracted light may propagate in a direction that prevents the diffracted light from reaching the window. The grating period may be, for example, less than 280 nm (e.g., about 200 nm) so that the angle selective transmission layer does not affect the light within the perspective field of view. In some examples, the angle selective transmission layer may include a micrometer-scale or nanometer-scale anisotropic structure that can reflect, diffract, or absorb incident light with a large incident angle. Anisotropic structures can include, for example, high-aspect ratio nanoparticles aligned and immersed in a transparent medium, nanowire arrays, certain liquid crystal materials, and the like.

[0295] Embodiments of the present invention may be used to implement components of an artificial reality system or may be implemented in conjunction with an artificial reality system. Artificial reality is a form of reality that has been adjusted in some way before being presented to a user, which may include, for example, virtual reality (VR), augmented reality (VR), 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 multiple channels (e.g., stereoscopic video that produces a three-dimensional effect to 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.

[0296] Fig.393900 is a simplified block diagram of an example electronic system 3900 for implementing an example near-eye display (e.g., HMD device) of some examples disclosed herein. The electronic system 3900 can be used as an electronic system for the HMD device or other near-eye display described above. In this example, the electronic system 3900 may include one or more processors 3910 and a memory 3920. The processor 3910 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 3910 may be communicatively coupled to multiple components within the electronic system 3900. To achieve this communicatively coupling, the processor 3910 may communicate with other illustrated components across a bus 3940. The bus 3940 may be any subsystem suitable for transmitting data within the electronic system 3900. The bus 3940 may include multiple computer buses and additional circuits to transmit data.

[0297] Memory 3920 may be coupled to processor 3910. In some embodiments, memory 3920 may provide both short-term storage and long-term storage, and may be divided into several units. Memory 3920 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 3920 may include removable storage devices such as secure digital (SD) cards. Memory 3920 may provide storage of computer-readable instructions, data structures, program modules, and other data for electronic system 3900. In some embodiments, memory 3920 may be distributed in different hardware modules. A set of instructions and / or codes may be stored in memory 3920. The instructions may be in the form of executable code that can be executed by the electronic system 3900, and / or may be in the form of source code and / or installable code that, when compiled and / or installed on the electronic system 3900 (e.g., using any of a variety of commonly available compilers, installers, compression / decompression utilities, etc.), may be in the form of executable code.

[0298] In some embodiments, the memory 3920 may store a plurality of application modules 3922 to 3924, 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 3922-3924 may include specific instructions to be executed by the processor 3910. In some embodiments, some applications or portions of the application modules 3922-3924 may be executed by other hardware modules 3980. In some embodiments, the memory 3920 may additionally include a secure memory, which may include additional security controls to prevent copying or other unauthorized access to secure information.

[0299] In some embodiments, the memory 3920 may include an operating system 3925 loaded therein. The operating system 3925 may be operable to initiate execution of instructions provided by the application modules 3922-3924 and / or manage other hardware modules 3980 and interfaces with the wireless communication subsystem 3930, which may include one or more wireless transceivers. The operating system 3925 may be adapted to perform other operations across components of the electronic system 3900, including threading, resource management, data storage control, and other similar functions.

[0300] The wireless communication subsystem 3930 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 3900 may include one or more antennas 3934 for wireless communication as part of the wireless communication subsystem 3930 or as a separate component coupled to any part of the system. Depending on the desired functionality, the wireless communication subsystem 3930 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, IEEE 802.15x, 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 3930 may allow data to be exchanged with a network, other computer systems, and / or any other device described herein. The wireless communication subsystem 3930 may include means for sending or receiving data (e.g., an identifier of the HMD device, location data, geographic maps, heat maps, photos, or videos) using an antenna 3934 and a wireless link 3932. The wireless communication subsystem 3930, the processor 3910, and the memory 3920 may together comprise at least a portion of one or more of the means for performing some of the functions disclosed herein.

[0301] Embodiments of the electronic system 3900 may also include one or more sensors 3990. The sensor 3990 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 3990 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.

[0302] The electronic system 3900 may include a display module 3960. The display module 3960 may be a near-eye display and may graphically present information from the electronic system 3900, such as images, videos, and various instructions, to a user. Such information may be derived from one or more application modules 3922-3924, a virtual reality engine 3926, one or more other hardware modules 3980, a combination thereof, or any other suitable means for parsing graphical content for a user (e.g., via an operating system 3925). The display module 3960 may use liquid crystal display (LCD) technology, light emitting diode (LED) technology (including, for example, OLED, ILED, μLED, AMOLED, TOLED, etc.), light emitting polymer display (LPD) technology, or some other display technology.

[0303] The electronic system 3900 may include a user input / output module 3970. The user input / output module 3970 may allow a user to send an action request to the electronic system 3900. 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 3970 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 3900. In some embodiments, the user input / output module 3970 may provide tactile feedback to the user according to instructions received from the electronic system 3900. For example, tactile feedback may be provided when an action request is received or an action request has been executed.

[0304] The electronic system 3900 may include a camera 3950, which may be used to take photos or videos of the user, for example, to track the user's eye position. The camera 3950 may also be used to take photos or videos of the environment, for example, for VR applications, AR applications, or MR applications. The camera 3950 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 3950 may include two or more cameras, which may be used to capture 3D images.

[0305] In some embodiments, the electronic system 3900 may include a plurality of other hardware modules 3980. Each of the other hardware modules 3980 may be a physical module within the electronic system 3900. Although each of the other hardware modules 3980 may be permanently configured as a structure, some of the other hardware modules 3980 may be temporarily configured to perform a specific function or be temporarily activated. Examples of other hardware modules 3980 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 3980 may be implemented in software.

[0306] In some embodiments, the memory 3920 of the electronic system 3900 may also store a virtual reality engine 3926. The virtual reality engine 3926 may execute an application within the electronic system 3900 and receive position information, acceleration information, velocity information, predicted future position, or some combination thereof of the HMD device from a variety of sensors. In some embodiments, the information received by the virtual reality engine 3926 may be used to generate a signal (e.g., a display instruction) for the display module 3960. For example, if the received information indicates that the user has looked to the left, the virtual reality engine 3926 may generate content for the HMD device that reflects the user's movement in the virtual environment. Additionally, the virtual reality engine 3926 may perform an action within the application in response to an action request received from the user input / output module 3970 and provide feedback to the user. The feedback provided may be visual feedback, auditory feedback, or tactile feedback. In some embodiments, the processor 3910 may include one or more GPUs that may execute the virtual reality engine 3926.

[0307] 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 (e.g., GPU, virtual reality engine 3926, 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.

[0308] In alternative configurations, different and / or additional components may be included in the electronic system 3900. 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 3900 may be modified to include other system environments, such as an AR system environment and / or an MR environment.

[0309] The methods, systems and devices discussed above are examples. Various embodiments may omit, replace or add various processes or components as appropriate. For example, in an optional configuration, the described method may be performed in a different order than described, and / or various 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 invention to those specific examples.

[0310] 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 only provides exemplary 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 those skilled in the art with enabling descriptions for implementing various embodiments. Various changes may be made in the functions and arrangements of the elements without departing from the scope of the present invention as defined in the appended claims.

[0311] 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 embodiments of the method can be implemented by hardware, software, firmware, middleware, microcode, hardware description language or any combination thereof. When implemented with 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 tasks.

[0312] It will be apparent to those skilled in the art that substantial variations may be made depending on specific requirements. For example, customized hardware 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.

[0313] 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.

[0314] 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.

[0315] 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.

[0316] In addition, although certain embodiments have been described using a specific 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 codes 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.

[0317] 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 techniques (including, but not limited to, conventional techniques for inter-process communication), and different pairs of processes may use different techniques, or the same pair of processes may use different techniques at different times.

[0318] The present invention is defined in the appended claims. 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 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 waveguide display, comprising: waveguides transparent to visible light; a first reflective volume Bragg grating VBG on the waveguide characterized by a first refractive index modulation; and a second reflective VBG on the waveguide comprising a plurality of regions characterized by different respective refractive index modulations, wherein the first reflective VBG is configured to diffract display light within a first wavelength range and a first field of view FOV, so that the display light within the first wavelength range and the first FOV propagates in the waveguide to a plurality of regions of the second reflective VBG by total internal reflection; and Wherein, the plurality of regions of the second reflective VBG are configured to diffract display light within different corresponding wavelength ranges within the first wavelength range and within the first FOV range.

2. The waveguide display according to claim 1, wherein: The first reflective VBG and the second reflective VBG have the same grating vector in a plane perpendicular to a surface normal direction of the waveguide.

3. A waveguide display according to claim 1 or claim 2, and one or more of the following is true: in, at least one of the first refractive index modulation and the different corresponding refractive index modulations of the plurality of regions of the second reflective VBG is greater than a minimum refractive index modulation at which diffraction efficiency is saturated; Wherein, the multiple regions of the second reflective VBG are configured so that the display light within the first wavelength range and the first FOV range reaches the first region among the multiple regions before reaching the second region among the multiple regions, the first region has a second refractive index modulation, and the second region has a third refractive index modulation greater than the second refractive index modulation.

4. A waveguide display according to any preceding claim, and one or more of the following holds: in: The first reflective VBG is configured to couple display light within the first wavelength range and the first FOV range into the waveguide; and The second reflective VBG is configured to couple display light within the first wavelength range and within the first FOV range out of the waveguide and is transparent to visible light from a surrounding environment; in: The third grating is configured to diffract the display light within the first wavelength range and the first FOV range from the first reflection grating to a fourth grating; The fourth grating is configured to diffract display light within the first wavelength range and the first FOV range to the second reflective VBG at two or more regions of the fourth grating; and The third grating and the fourth grating have the same grating vector in a plane perpendicular to the surface normal direction of the waveguide.

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