Waveguide comprising a volume bragg grating

Abstract

The present application relates to waveguides comprising volume Bragg gratings. A waveguide is provided for conveying image light. The waveguide includes an input port for receiving a first light beam of image light carrying an image in a wavelength segment. A first diffraction grating of the waveguide includes a plurality of volume Bragg gratings (VBGs) configured to expand the first light beam along a first axis and redirect the first light beam to a second diffraction grating of the waveguide. The second diffraction grating includes a plurality of VBGs configured to receive the first light beam from the first diffraction grating and out-couple different portions of the first wavelength segment of the first light beam along a second axis, thereby expanding the first light beam along the second axis for a user to observe the image.

Description

[0001] This application is a divisional application of the application filed on October 16, 2018, with application number 201880098739.7 and invention title "Waveguide Including Volume Bragg Grating". Technical Field

[0002] This disclosure relates to optical components and modules, and more particularly to optical waveguide-based components and modules that can be used in display systems. background

[0003] Head-mounted displays (HMDs), near-eye displays, and other types of wearable display systems can be used to provide users with virtual scenes or to enhance real-world scenes with additional information or virtual objects. Virtual or enhanced scenes can be three-dimensional (3D) to enhance the experience and match virtual objects to the real 3D scene observed by the user. In some display systems, the user's head and / or eye positioning and orientation are tracked in real time, and the displayed scene is dynamically adjusted based on the user's head orientation and gaze direction to provide an immersive experience in a simulated or enhanced 3D environment.

[0004] Lightweight and compact near-eye displays reduce strain on the user's head and neck and are generally more comfortable to wear. Optics are perhaps the heaviest module in a display. Compact planar optical components (such as waveguides, gratings, Fresnel lenses, etc.) can be used to reduce the size and weight of the optical block. However, compact planar optics may have limitations in areas such as image resolution, image quality, the ability to see the real world through the display, and the field of view of the generated image. Summary of the Invention

[0005] This application provides the following:

[0006] 1) A waveguide for transmitting image light, the waveguide comprising:

[0007] A first input port is used to receive a first beam of image light carrying an image in a first wavelength band;

[0008] Optical first and second external optical surfaces, used to propagate the first light beam between the first and second external optical surfaces; and

[0009] A first diffraction grating and a second diffraction grating are disposed in the waveguide between the first optical surface and the second optical surface and are laterally offset relative to each other;

[0010] The first diffraction grating includes a plurality of volume Bragg gratings (VBGs) configured to extend the first beam along a first axis and redirect the first beam to the second diffraction grating; and

[0011] The second diffraction grating includes a plurality of VBGs configured to receive the first beam from the first diffraction grating and to couple different portions of the first wavelength segment of the first beam outward along the second axis, thereby extending the first beam along the second axis for the user to observe the image.

[0012] 2) According to the waveguide described in 1), the projections of the first diffraction grating and the second diffraction grating onto the first optical surface do not overlap.

[0013] 3) The waveguide according to 1) or 2), wherein the first diffraction grating comprises between 300 and 1000 VBGs, and wherein the second diffraction grating comprises between 10 and 200 VBGs.

[0014] 4) The waveguide according to any one of 1) to 3), wherein the first wavelength segment corresponds to the color channel of the image.

[0015] 5) The waveguide according to any one of 1) to 4) further comprises:

[0016] The second input port is used to receive a second beam of image light carrying the image in a second wavelength band;

[0017] A third diffraction grating is disposed in the waveguide between the first optical surface and the second optical surface and is laterally offset relative to the first diffraction grating and the second diffraction grating;

[0018] The third diffraction grating includes a plurality of VBGs configured to extend the second beam along the first axis and redirect the second beam toward the second diffraction grating; and

[0019] The second diffraction grating's VBG is configured to receive the second beam from the third diffraction grating and to couple different portions of the second wavelength band of the second beam outward along the second axis, thereby extending the second beam along the second axis for the user to observe the image.

[0020] 6) The waveguide described in 5) further includes:

[0021] The third input port is used to receive a third beam of image light carrying the image in a third wavelength band;

[0022] A fourth diffraction grating is disposed in the waveguide between the first optical surface and the second optical surface, and is laterally offset relative to the first diffraction grating to the third diffraction grating;

[0023] The fourth diffraction grating includes a plurality of VBGs configured to extend the third beam along the first axis and redirect the third beam toward the second diffraction grating; and

[0024] The second diffraction grating's VBG is configured to receive the third beam from the fourth diffraction grating and to couple different portions of the third wavelength band of the third beam outward along the second axis, thereby extending the third beam along the second axis for the user to observe the image.

[0025] 7) The waveguide according to 6), wherein the first input port, the second input port and the third input port are offset relative to each other along the second axis.

[0026] 8) According to the waveguide described in 6), wherein the first wavelength segment, the second wavelength segment and the third wavelength segment correspond to the first color channel, the second color channel and the third color channel of the image, respectively.

[0027] 9) The waveguide according to any one of 1) to 8), wherein the VBG of the first diffraction grating and the VBG of the second diffraction grating are disposed in the same layer spaced apart from the first optical surface and the second optical surface.

[0028] 10) The waveguide according to any one of 1) to 9), wherein the VBG of the first diffraction grating has a grating period that varies spatially along the first axis.

[0029] 11) The waveguide according to 10), wherein the grating period of the VBG of the first diffraction grating varies in the range of 100 nm to 500 nm.

[0030] 12) The waveguide according to any one of 1) to 11), wherein the VBG of the second diffraction grating has a grating period that varies spatially along the second axis.

[0031] 13) According to the waveguide described in 12), wherein the grating period of the VBG of the second diffraction grating varies in the range of 100 nm to 300 nm.

[0032] 14) The waveguide according to any one of 1) to 13), wherein the VBG of the first diffraction grating is configured to redirect the first beam and the second beam of the image light by reflective diffraction.

[0033] 15) The waveguide according to 14), wherein the VBG of the first diffraction grating includes a plurality of stripes forming an angle between 34 degrees and 54 degrees with the first optical surface.

[0034] 16) The waveguide according to 15), wherein the VBG of the second diffraction grating includes a plurality of stripes forming an angle between 20 degrees and 38 degrees with the first optical surface.

[0035] 17) The waveguide according to any one of 1) to 13), wherein the VBG of the first diffraction grating is configured to redirect the first beam and the second beam of the image light by transmission diffraction.

[0036] 18) The waveguide according to 17), wherein the VBG of the first diffraction grating includes a plurality of stripes forming an angle greater than 80 degrees with the first optical surface.

[0037] 19) The waveguide according to 18), wherein the VBG of the second diffraction grating includes a plurality of stripes forming an angle between 50 and 70 degrees with the first optical surface.

[0038] 20) A waveguide according to any one of 1) to 4), wherein the image has a field of view (FOV), wherein a first beam of image light carries a first portion of the FOV of the image, and the waveguide further includes a second input port for receiving a second beam of image light carrying a second portion of the FOV of the image in the first wavelength band;

[0039] Wherein, the VBG of the first diffraction grating is configured to extend the second beam along the first axis and redirect the second beam to the second diffraction grating; and

[0040] The second diffraction grating's VBG is configured to receive the second beam from the first diffraction grating and to couple different portions of the first wavelength segment of the second beam outward along the second axis, thereby extending the second beam along the second axis for the user to observe the image. Brief description of the attached diagram

[0041] Exemplary embodiments will now be described in conjunction with the accompanying drawings, in which:

[0042] Figure 1A It is a planar (XY plane) view of a near-eye display (NED) including the waveguide of this disclosure;

[0043] Figure 1B yes Figure 1A Side view cross-section of the NED;

[0044] Figure 2A yes Figure 1A and Figure 1B A planar ray-trace view of one embodiment of the waveguide, including a reflective volume Bragg grating (VBG) in the top grating;

[0045] Figure 2B and Figure 2C They are Figure 2A Side view cross-section of the waveguide along lines BB and CC;

[0046] Figure 3 This is an example diffraction efficiency spectrum of a single-volume Bragg grating (VBG) that can be used in the waveguides of this disclosure;

[0047] Figure 4A It is a side view cross-section of the waveguide including the VBG layer;

[0048] Figure 4B It is a graph of FOV (vs.) wavelength for different VBG periods;

[0049] Figure 5 This is a side cross-sectional view of an NED including the waveguide of this disclosure, illustrating the principle of pupil expansion through wavelength division;

[0050] Figure 6 yes Figure 1A and Figure 1B A planar ray tracing diagram of an embodiment of a waveguide, including a transmission diffraction VBG in the top grating;

[0051] Figure 7A and Figure 7B yes Figure 6 The maximum and minimum VBG period maps of the waveguide diffraction grating;

[0052] Figure 8 It is a planar ray tracing diagram of a waveguide configured to carry three color channels injected at different locations on the waveguide, with a top grating including a reflective diffraction VBG;

[0053] Figure 9 This is a planar ray tracing diagram of a waveguide configured to carry three color channels injected at different locations on the waveguide, with a top grating comprising a transmission diffraction VBG;

[0054] Figure 10 It is a graph of waveguide size versus diagonal field of view (FOV);

[0055] Figure 11AThis is a plan view of a near-eye display (NED) including a waveguide with two input ports for the two FOV halves;

[0056] Figure 11B yes Figure 11A Side view cross-section of the NED;

[0057] Figure 12 yes Figure 11A and Figure 11B A planar ray tracing diagram of an embodiment of the waveguide, wherein the top grating includes a reflective diffraction VBG that transmits light from the left projector to the right FOV half and vice versa;

[0058] Figure 13A It is a planar ray tracing diagram of a waveguide configured to carry three color channels injected at different locations on the waveguide. The top grating includes a reflective diffraction VBG configured to send light from the left projector to the right FOV half and vice versa.

[0059] Figure 13B It is a planar ray tracing diagram of a waveguide configured to carry three color channels injected at different locations on the waveguide. The top grating includes a transmissive diffraction VBG configured to send light from the left projector to the right FOV half and vice versa.

[0060] Figure 13C This is a planar ray tracing diagram of another embodiment of the waveguide, which is configured to carry three color channels injected at different locations on the waveguide. The top grating includes a transmissive diffraction VBG, which is configured to send light from the left projector to the right FOV half and vice versa.

[0061] Figure 13D This is a planar ray tracing diagram of an embodiment of a waveguide configured to carry three color channels injected at different locations on the waveguide. The top grating includes a transmissive diffraction VBG that sends light from the left projector to the left FOV half and from the right projector to the right FOV half.

[0062] Figure 13E yes Figure 13D A planar ray tracing diagram of another embodiment of the waveguide;

[0063] Figure 13F This is a planar ray tracing diagram of an embodiment of a waveguide configured to carry three color channels injected at different locations on the waveguide. The top grating includes a transmissive diffraction VBG that sends light from the left projector to the left FOV half and from the right projector to the right FOV half.

[0064] Figure 13G yes Figure 13F A planar ray tracing diagram of another embodiment of the waveguide;

[0065] Figures 14A to 14C This is a side-view cross-sectional diagram showing different types of rainbow artifacts;

[0066] Figure 15A This is an isometric view of a near-eye AR / VR display incorporating the optical waveguide of this disclosure;

[0067] Figure 15B yes Figure 15A A side cross-sectional view of the display; and

[0068] Figure 16 This is an isometric view of a head-mounted display (HMD) incorporating the optical waveguide of this disclosure. Detailed description

[0069] While this teaching has been described in conjunction with various embodiments and examples, it is not intended to limit this teaching to these embodiments. Rather, as those skilled in the art will understand, this teaching includes various alternatives and equivalents. All statements herein recounting the principles, aspects, and embodiments of this disclosure, as well as specific examples thereof, are intended to include their structural and functional equivalents. Furthermore, it is intended that such equivalents include both currently known equivalents and those developed in the future (i.e., any elements developed that perform the same function), regardless of their structure.

[0070] Unless explicitly stated otherwise, as used herein, the terms "first," "second," etc., are not intended to imply sequential order, but rather to distinguish one element from another. Similarly, unless explicitly stated otherwise, the sequential order of method steps does not imply the sequential order of their execution. Figure 1A , Figure 1B , Figures 2A-2C , Figure 5 , Figure 6 , Figure 8 , Figure 9 , Figure 11A , Figure 11B , Figure 12 and Figures 13A-13G In this context, similar elements are represented by similar reference numerals.

[0071] The scope of this disclosure is not limited to the specific embodiments described herein. In fact, various other embodiments and modifications will be apparent to those skilled in the art, in addition to those described herein, based on the foregoing description and drawings. Therefore, such other embodiments and modifications are intended to fall within the scope of this disclosure. Furthermore, although this disclosure has been described herein in the context of a particular purpose, a particular environment, and a particular implementation, those skilled in the art will recognize that its usefulness is not limited thereto, and that this disclosure can be advantageously implemented in any number of environments for any number of purposes. Accordingly, the set forth claims should be interpreted in accordance with the full breadth and spirit of the disclosure described herein.

[0072] According to one aspect of this disclosure, the waveguide may include a diffraction grating configured to expand the pupil along one axis, coupled to another diffraction grating configured to expand the pupil along another axis (e.g., the vertical axis) and to couple light outward for observation by a user. The user can observe the external world through the second grating. To reduce haze caused by the multiple volume Bragg gratings (VBGs) of the second grating, the second grating may be configured to output different wavelengths of the same color channel of the image to be displayed at different locations along a second direction, thereby reducing the required VBG density and associated haze. In other words, the pupil is expanded in the second direction by wavelength segmentation.

[0073] According to one aspect of this disclosure, a waveguide for carrying image light may include multiple input ports for receiving beams, each beam carrying a portion of the field of view (FOV) of the displayed image. The waveguide's grating structure can be configured to expand the waveguide's output pupil while simultaneously coupling a portion of the FOV outwards for user observation in a manner that allows the user to perceive a single large FOV. The FOV can be increased by using multiple input ports.

[0074] According to this disclosure, a waveguide is provided for transmitting image light carrying an image having a field of view (FOV). The waveguide includes a first input port and a second input port for receiving a first beam and a second beam of image light carrying a first portion and a second portion of the FOV, respectively; opposing first and second external optical surfaces for propagating the first and second beams between them; and a first diffraction grating configured to extend the first and second beams along a first axis, wherein the first and second beams are coupled externally from the waveguide for viewing the first and second portions of the FOV of the image by a user. The first and second portions of the FOV may be adjacent or partially overlapping. The first and second input ports may be coupled to the first optical surface on opposite sides of the waveguide. The first and second beams of image light may carry color channels of the image.

[0075] In some embodiments, a second diffraction grating may be provided in the waveguide. The first and second diffraction gratings may be disposed in the waveguide between a first optical surface and a second optical surface, and laterally offset relative to each other. The first diffraction grating may include a plurality of volume Bragg gratings (VBGs) configured to extend a first beam and a second beam along a first axis and redirect the first and second beams to the second diffraction grating. The second diffraction grating may include a plurality of VBGs configured to receive the first and second beams from the first diffraction grating, extend the first and second beams along a second axis, and couple the first and second beams outward from the waveguide for a first and a second portion of the field of view (FOV) of the image observed by a user.

[0076] In some embodiments, the projections of the first diffraction grating and the second diffraction grating onto the first optical surface do not overlap. The first input port and the second input port may be coupled to the first optical surface on opposite sides of the waveguide, and at least one of the first diffraction grating and the second diffraction grating may be symmetrical about an axis equidistant from the first input port and the second input port.

[0077] The first and second beams of image light can carry at least one color channel of the image. In embodiments with more than one color channel, the waveguide may further include a third input port and a fourth input port for receiving the third and fourth beams of image light carrying the first and second portions of the FOV of the image, respectively, which carry the second color channel of the image. A third diffraction grating may be disposed in the waveguide between the first and second optical surfaces and laterally offset relative to the first and second diffraction gratings. The third diffraction grating may include a plurality of VBGs configured to extend the third and fourth beams along a first axis and redirect the third and fourth beams to the second diffraction grating. The VBGs of the second diffraction grating may be configured to receive the third and fourth beams from the third diffraction grating, extend the third and fourth beams along a second axis, and couple the third and fourth beams outward from the waveguide for user viewing of the image.

[0078] In embodiments with at least three color channels, the waveguide may further include a fifth input port and a sixth input port for receiving a fifth and a sixth beam of image light carrying a first portion and a second portion of the FOV of the image, respectively, which carry a third color channel of the image. A fourth diffraction grating may be disposed in the waveguide between a first optical surface and a second optical surface, and laterally offset relative to the first diffraction grating to the third diffraction grating. The fourth diffraction grating may include a plurality of VBGs configured to extend the fifth and sixth beams along a first axis and redirect the fifth and sixth beams to a second diffraction grating. The VBGs of the second diffraction grating may be configured to receive the fifth and sixth beams from the fourth diffraction grating, extend the fifth and sixth beams along a second axis, and couple the fifth and sixth beams out of the waveguide for user observation of the image.

[0079] According to this disclosure, a waveguide for transmitting image light is provided. The waveguide includes: a first input port for receiving a first beam of image light carrying an image in a first wavelength band; opposing first and second external optical surfaces for propagating the first beam therebetween; and a first and second diffraction grating disposed in the waveguide between the first and second optical surfaces and laterally offset relative to each other. The first diffraction grating may include a plurality of VBGs configured to extend the first beam along a first axis and redirect the first beam to the second diffraction grating. The second diffraction grating may include a plurality of VBGs configured to receive the first beam from the first diffraction grating and to outwardly couple different portions of a first wavelength band of the first beam along a second axis, thereby extending the first beam along the second axis for image viewing by a user.

[0080] In some embodiments, the projections of the first diffraction grating and the second diffraction grating onto the first optical surface do not overlap. The first diffraction grating may include, for example, between 300 and 1000 VBGs, and the second diffraction grating may include, for example, between 10 and 200 VBGs. The first wavelength band may correspond to the color channels of the image.

[0081] In some embodiments, a second input port may be provided in the waveguide for receiving a second beam of image light carrying an image in a second wavelength band. A third diffraction grating may be disposed in the waveguide between a first optical surface and a second optical surface, and laterally offset relative to the first and second diffraction gratings. The third diffraction grating may include a plurality of VBGs configured to extend the second beam along a first axis and redirect the second beam to the second diffraction grating. The VBGs of the second diffraction grating may be configured to receive the second beam from the third diffraction grating and to couple different portions of the second wavelength band of the second beam outward along a second axis, thereby extending the second beam along the second axis for the user to observe the image.

[0082] A third input port may also be provided in the waveguide for receiving a third beam of image light carrying the image in a third wavelength band. A fourth diffraction grating may be disposed in the waveguide between the first and second optical surfaces and laterally offset relative to the first and third diffraction gratings. The fourth diffraction grating may include a plurality of VBGs configured to extend the third beam along a first axis and redirect the third beam to the second diffraction grating. The VBGs of the second diffraction grating may be configured to receive the third beam from the fourth diffraction grating and to couple different portions of the third wavelength band of the third beam outward along a second axis, thereby extending the third beam along the second axis for the user to observe the image. The first, second, and third input ports may be offset relative to each other along the second axis, and the first, second, and third wavelength bands may correspond to the first, second, and third color channels of the image, respectively. The VBGs of the first and second diffraction gratings may be disposed in the same layer spaced apart from the first and second optical surfaces.

[0083] In at least some of the above embodiments, the VBG of the first diffraction grating may have a grating period that varies spatially along a first axis, for example, in the range of 100 nm to 500 nm. The VBG of the second diffraction grating may also have a grating period that varies spatially along a second axis, for example, in the range of 100 nm to 300 nm. In embodiments where the VBG of the first diffraction grating is configured to redirect a first beam and a second beam of image light by reflective diffraction, the VBG of the first diffraction grating may include a plurality of fringe that form an angle with the first optical surface, for example, between 34 degrees and 54 degrees. In embodiments where the VBG of the first diffraction grating is configured to redirect a first beam and a second beam of image light by transmission diffraction, for example, the VBG of the first diffraction grating may include a plurality of fringe that form an angle with the first optical surface greater than 80 degrees. In any of the above embodiments, the VBG of the second diffraction grating may include a plurality of fringe that form an angle with the first optical surface, for example, between 20 degrees and 38 degrees or between 50 degrees and 70 degrees. In an embodiment where the first beam and the second beam carry an image in a first wavelength segment corresponding to a color channel, the VBG of the second diffraction grating can be configured to receive the first beam and the second beam from the first diffraction grating and to couple different portions of the first wavelength segment of the first beam and the second beam outward along a second axis, thereby extending the first beam and the second beam along the second axis.

[0084] Now for reference Figure 1A and Figure 1BThe near-eye display (NED) 100 includes a waveguide 102 optically coupled to a projector 104. The waveguide 102 is configured to transmit a beam 111 of image light emitted by the projector 104. The waveguide 102 may be based on a flat slab or plate having opposing first and second external optical surfaces 131 and 132 for propagating the beam 111 between the optical surfaces 131 and 132, for example, by total internal reflection (TIR) ​​in a zigzag pattern. An input port 121 may be provided for receiving the beam 111. An input coupler, such as a prism 177, may be placed at the input port 121 for coupling the beam 111 into the waveguide 102 for subsequent propagation within it. The optical surfaces 131 and 132 may include, for example, the outer parallel surface of a flat slab, the outer surface of a volume Bragg grating (VBG), or a surface relief grating (SRG). In some embodiments, the first optical surface 131 and the second optical surface 132 may belong to different parallel substrates separated by an air gap in which the light beam 111 propagates.

[0085] The first diffraction grating 141 of waveguide 102 may include an SRG, a VBG, or both. The first diffraction grating 141 is configured to extend the beam 111 along a first axis 151. In this document, the term "extend the beam along the axis" means that the projection of the beam 111 onto the first axis 151 is extended. It should be noted that the beam does not need to extend precisely parallel to the axis 151 for the extended projection, but the direction of extension of the beam 111 can form an angle (e.g., less than 45 degrees) with the axis 151 such that the projection of the beam 111 onto the axis 151 is extended. For example, in… Figure 1A In this process, different beam portions 111A, 111B, and 111C can extend along a direction forming an acute angle with the first axis 151. Note that the first axis 151 simply refers to orientation, i.e. Figure 1A The horizontal orientation within waveguide 102. This orientation can also be relative to the edge of waveguide 102 or another axis (e.g., a second axis 152, which is located in...). Figure 1A The center is vertically set and perpendicular to the first axis 151) for reference.

[0086] The extended beam portions 111A, 111B, and 111C are ultimately guided by the first diffraction grating 141 to the second diffraction grating 142, where the second diffraction grating 142... Figure 1A The first and second diffraction gratings 141 are offset downwards relative to the first diffraction grating 141, that is, offset downwards along the second axis 152. The first and second diffraction gratings 141 and 142 can be completely offset such that their projections on the first optical surface 131 do not overlap (i.e., as shown). Figure 1A(as shown), or they may be offset and only partially overlap. The first diffraction grating 141 and the second diffraction grating 142 may be disposed in the waveguide 102 between the first external optical surface 131 and the second external optical surface 132, for example, as shown. Figure 1B As shown, the offset is adjacent to the corresponding first optical surface 131 and second optical surface 132, centered on waveguide 102, or disposed at any depth within waveguide 102. The second diffraction grating 142 may include an SRG, a VBG, or both types of gratings. The second diffraction grating 142 is configured to receive a beam 111 from the first diffraction grating 141, extend the beam 111 along a second axis 152, and couple the beam 111 outward from waveguide 102 for viewing a first and second portion of the FOV of the image by a user's eye 106 located at the eyebox 108. Throughout this disclosure, the term "eyebox" refers to a geometrically three-dimensional (3D) region of the displayed image of acceptable quality.

[0087] refer to Figure 2A Waveguide 202 is Figure 1A and Figure 1B An embodiment of waveguide 102. Figure 2A Waveguide 202 includes an input port 221, a first diffraction grating 241, and a second diffraction grating 242. Beam 111 is coupled into waveguide 202 at input port 221. The first diffraction grating 241 includes a first plurality of VBGs having fringes 261 indicated by dashed lines. The fringes 261 of the VBGs of the first diffraction grating 241 are configured to extend beam 111 along the X-axis and guide beam 111 to the second diffraction grating 242, as schematically shown with ray 211. Note that the term "extend beam 111 along the X-axis" includes the case where a portion of beam 111 propagates at an angle to the X-axis, similar to the reference above. Figure 1A The explanation is as follows. The term "beam extending along an axis" throughout this disclosure generally includes a beam extending at an angle to the axis. For example, Figure 2A The light ray 211 in the first diffraction grating 241 propagates at an angle different from the X-axis. It should also be noted that the light ray 211 of the beam 111 propagates in a zigzag pattern between the first optical surface 131 and the second optical surface 132 via TIR from the first optical surface 131 and the second optical surface 132. The zigzag pattern in... Figure 2A They are considered straight lines because they are in Figure 2A The view in the middle is from the top. Figure 2AIn the illustrated embodiment, the period of fringe 261, measured along the corresponding k-vector of the grating, varies from approximately 158 nm to 411 nm. This variation in fringe period is required such that the light ray 211 has a sharper diffraction angle at the right end (shorter period) of the first diffraction grating 241 than at the left end (longer period). The grating period is chosen such that the light ray 211 at different locations and all display wavelengths satisfies the Bragg condition. Typically, the grating period of the VBG of the first diffraction grating 241 can vary in the range of 100 nm to 500 nm.

[0088] The second diffraction grating 242 includes a second plurality of VBGs having fringes 262 indicated by dashed lines. The VBGs of the second diffraction grating 242 are configured to receive a beam 111 from the first diffraction grating 241, extend the beam 111 along the Y-axis, and couple the beam 111 outwardly from the waveguide 202 for viewing an image carried by the beam 111 by a user. The size of the viewing window 208 is typically smaller than that of the second diffraction grating 242. The solid line 207 on the first diffraction grating 241 represents the boundary of the light ray 211 reaching the user's eye located at the center of the viewing window at coordinates (0, 0, Z), where Z is the eye relief distance, typically 15 mm–20 mm. The period of the fringes 262 of the second diffraction grating 242 varies from approximately 152 nm to 291 nm. This variation in the fringe period is required to extend the output pupil along the Y-axis using wavelength-segmented pupil expansion, which will be further described below. Typically, the grating period of the VBG of the second diffraction grating 242 can vary in the range of 100 nm to 300 nm.

[0089] The fringe 261 of the VBG of the first diffraction grating 241 is oriented at approximately 24 degrees relative to the Y-axis, and as... Figure 2B As shown, the first optical surface 231 and the second optical surface 232 of the waveguide are tilted at approximately 44 degrees. The tilt angle can be between 34 degrees and 54 degrees. Within this tilt angle range, the VBG primarily redirects the beam 111 of the image light through reflective diffraction.

[0090] The second set of multiple VBG fringes 262 are oriented at approximately 104 degrees relative to the Y-axis, and as... Figure 2CAs shown, the first optical surface 231 and the second optical surface 232 of the waveguide are tilted at approximately 28 degrees. In a typical embodiment, the angle can be between 20 degrees and 38 degrees. When the thickness of the waveguide 202 is 1.5 mm, the first diffraction grating 241 and the second diffraction grating 242 can have a thickness of approximately 0.5 mm or greater, that is, approximately one-third or greater of the thickness of the waveguide 202. The first diffraction grating 241 and the second diffraction grating 242 can be disposed in the same layer spaced apart from the first optical surface 231 and the second optical surface 232. A reflective first diffraction grating 241 and second diffraction grating 242 are provided. Figure 2A The overall dimensions of waveguide 202 are 70 mm x 70 mm.

[0091] Go to Figure 3 The diffraction efficiency spectrum of a typical VBG (Vibration Variation Group) of the first diffraction grating 241 or the second diffraction grating 242 includes a sharp peak 300 of high efficiency with a spectral width of approximately 0.2 nm. The peak is separated by a region 302 of low diffraction efficiency, approximately 3.5 nm wide. At a given wavelength, the diffraction efficiency also depends on the incident angle. To provide high efficiency within a field of view (FOV) of several tens of degrees along the X and Y directions over a typical color channel wavelength range, such as 20 nm, it may be necessary to form a large number of VBGs. As a non-limiting example, the first diffraction grating 241 may include between 300 and 1000 VBGs. For augmented reality (AR) applications, it may be desirable to limit or reduce the number of VBGs in the second diffraction grating 242, since the second diffraction grating 242 is positioned close to the user's eye, and the user views the external world through the second diffraction grating 242. Numerous VBGs in the field of vision can make the view of external objects appear hazy or color-fringed, and they can also reduce the contrast of the displayed virtual world image. For at least these reasons, it may be preferable to limit the number of VBGs in the second diffraction grating 242, for example, between 10 and 200 VBGs.

[0092] According to this disclosure, by allowing light of different wavelengths to couple outward from waveguide 202 at different locations in window 208, the number of VBGs in the second diffraction grating 242 required for good image quality in window 208 can be reduced. (See reference...) Figure 4A An example of such a sparse diffraction grating 400 is shown in cross-section. The diffraction grating 400 has a thickness t, extends along the Y-axis, and has a VBG period that varies along the Y-axis. Image light 411 destined for viewport 408 is outwardly coupled at position 402 of the diffraction grating 400 with an outward coupling angle θ, which depends on the wavelength and VBG period at position 402. This correlation is shown in... Figure 4BThe diagram shows that the outward coupling angle θ is plotted as a function of wavelength for different VBG periods. To obtain the range of the grating period at position 402, the range of the outward coupling angle θ is first determined based on the desired size of window 408 and the eye relief, which is approximately equal to the distance between diffraction grating 400 and window 408. Figure 4A In the example shown, the outward coupling angle θ ranges from θ1 = 5 degrees to θ2 = 23 degrees. Once the values ​​of θ1 and θ2 at position 402 are determined, refer to... Figure 4B To obtain the corresponding VBG cycle range. Figure 4B In the diagram, different slashes 407 represent different VBG periods varying along the Y-axis from 310 nm to 620 nm. In this example, the VBG period at position 402 needs to cover the range from 360 nm to 590 nm so that image light 411 in the wavelength range of 450 nm to 630 nm is diffracted outwards to window 408. A VBG with a grating period of 360 nm can diffract 460 nm blue image light to window 408 at θ = 5 degrees, and a VBG with a grating period of 380 nm can diffract 460 nm light at θ = 10 degrees to window 408; the same grating can diffract 480 nm light at θ = 5 degrees, and so on. There is a small VBG period variation from position 402 to adjacent positions. For a fixed FOV angle θ, a small VBG period variation can cause a small outward coupling wavelength shift at different positions in window 408. While this may result in a slight color shift across the entire 408-inch viewport, such a shift can be acceptable when the wavelength band is sufficiently narrow and belongs to a single color channel of the image to be displayed. As a non-limiting example, for the red channel, a wavelength band between 620 nm and 660 nm can be chosen—light at either of these wavelengths is generally perceived as red. The wavelength-segmented pupil expansion described herein has the advantage of reducing the number of VBGs required to cover the FOV of interest. For example, only 10 to 200 VBGs per color channel may be needed for a single color channel.

[0093] Figure 5 The principle of pupil expansion through wavelength segmentation is further illustrated. The NED 500 includes a waveguide 502 coupled to an image projector 504. The waveguide 502 includes a first diffraction grating 541 and a second diffraction grating 542. The first diffraction grating 541 is perpendicular to... Figure 5 The image beam 511 is scattered in the direction of the plane, and the second diffraction grating 542 is in Figure 5The image beam 511 is vertically distributed. For the red (R) channel, light 581 at the first red wavelength λR1 is coupled outward at the first position 571; light 582 at the second red wavelength λR2 is coupled outward at the second position 572; light 583 at the third red wavelength λR3 is coupled outward at the third position 573; and light 584 at the fourth red wavelength λR4 is coupled outward at the fourth position 574. It should be understood that wavelengths λR1, λR2, λR3, and λR4 are the center wavelengths of a fairly wide wavelength range. That is, at the first position 571, light 581 occupies, for example, a wavelength range of 600 nm to 640 nm; at the second position 572, light 582 occupies, for example, a wavelength range of 601 nm to 641 nm; at the third position 573, light 583 occupies, for example, a wavelength range of 602 nm to 642 nm, and so on. This allows the color shift to be quite small compared to the wavelength bandwidth, which further reduces the perceived color shift across the entire viewport 408. The outward coupling of the green (G) channel and the blue (B) channel can be similarly configured to overlap with the outward coupling of the R channel.

[0094] refer to Figure 6 Waveguide 602 is Figure 1A and Figure 1B Waveguide 102 and Figure 2A An embodiment of waveguide 202. Figure 6 The waveguide 602 includes a first diffraction grating 641 and a second diffraction grating 642, each of which is aligned with the waveguide. Figure 2A The first diffraction grating 241 and the second diffraction grating 242 include multiple VBGs in a similar manner; for simplicity, Figure 6 The fringes of the VBG are not shown. The VBG of the first diffraction grating 641 is configured to extend the image beam 611 along the X-axis and guide the image beam 611 to the second diffraction grating 642, as schematically shown as the individual rays 621 of the image beam 611. The VBG of the second diffraction grating 642 is configured to receive the beam 611 from the first diffraction grating 641, extend the beam 611 along the Y-axis, and couple the beam 611 outward from the waveguide 602 for viewing the image carried by the beam 611 by the user. The solid line 607 on the first diffraction grating 641 represents the boundary of the ray 621 reaching the user's eye located at the center of the viewing window 608.

[0095] The VBG fringes of the first diffraction grating 641 form an angle of 34 degrees with the Y-axis and are oriented at approximately 90 degrees relative to the optical surface of the waveguide 602. At angles greater than approximately 80 degrees, the VBG fringes of the first diffraction grating 641 primarily redirect the first and second beams of image light through transmission diffraction (transmission grating configuration). The VBG fringes of the second diffraction grating 642 form an angle of 94 degrees with the Y-axis and are oriented at approximately 59 degrees relative to the optical surface of the waveguide 602. More generally, the VBG fringes of the second diffraction grating 642 may form an angle between 50 and 70 degrees with the optical surface of the waveguide 602. Figure 6 The waveguide 602 has an overall size of 45mm x 60mm, and in terms of area, it is only... Figure 2A 55% of the waveguide 202.

[0096] The period of the fringes of the first diffraction grating 641 and the second diffraction grating 642 varies spatially. Figure 7A and Figure 7B The spatial variation of the grating period is shown, and they illustrate the density maps of the fringes of diffraction gratings 641 and 642. Figure 7A The maximum fringe period pattern 741A of the first diffraction grating 641 and the maximum fringe period pattern 742A of the second diffraction grating 642 are shown, both measured along the grating vector Kg. Figure 7B The minimum fringe period pattern 741B of the first diffraction grating 641 and the minimum fringe period pattern 742B of the second diffraction grating 642 are shown, both measured along the grating vector Kg.

[0097] Go to Figure 8 Waveguide 802 is similar to Figure 2A Waveguide 202 has a reflective VBG in the first diffraction grating 241. Figure 8The waveguide 802 includes a first input port 821, a second input port 822, and a third input port 823 for receiving a first beam 811, a second beam 812, and a third beam 813 carrying image light in a first wavelength band, a second wavelength band, and a third wavelength band, respectively, and a pair of external optical surfaces for propagating the image light between the surfaces. As shown, the first input port 821, the second input port 822, and the third input port 823 can be offset in the Y-axis direction. The first diffraction grating 841 includes a plurality of VBGs configured to extend the first beam 811 along the X-axis and redirect the first beam 811 to the second diffraction grating 842. The third diffraction grating 843 includes a plurality of VBGs configured to extend the second beam 812 along the X-axis and redirect the second beam 812 to the second diffraction grating 842. The fourth diffraction grating 844 includes a plurality of VBGs configured to extend the third beam 813 along the X-axis and redirect the third beam 813 to the second diffraction grating 842. The first, second, and third wavelength bands can correspond to the red (R), green (G), and blue (B) channels of an image.

[0098] The second diffraction grating 842 includes a plurality of VBGs, which are configured to receive a first beam 811, a second beam 812, and a third beam 813 respectively from the first diffraction grating 841, the third diffraction grating 843, and the fourth diffraction grating 844, and to couple different portions of the corresponding first, second, and third wavelength segments outward along the Y-axis, thereby extending the first beam 811, the second beam 812, and the third beam 813 along the Y-axis for the user to view an image at the viewing window 808, as described above. Figure 5 As described above, at least two top gratings can be provided, such as a first diffraction grating 841 coupled to the first input port 821 and the second input port 822, respectively. Figure 8 The first diffraction grating 841, the third diffraction grating 843, and the fourth diffraction grating 844 have different reversal angles on the left and right sides, respectively. The VBG of these gratings can have a grating period that varies spatially from left to right (i.e. along the X-axis).

[0099] The waveguide beam gratings (VBGs) of the first, third, and fourth diffraction gratings 841, 843, and 844 include grooves at an angle of approximately 21 degrees relative to the Y-axis and tilted at approximately 47 degrees relative to the surface of waveguide 802. The VBG of the second diffraction grating 842 includes grooves at an angle of approximately 111 degrees relative to the Y-axis and tilted at approximately 29 degrees relative to the surface of waveguide 802. At these tilt angles, the VBGs primarily redirect beams 811, 812, and 813 of the image light through reflective diffraction; providing a diagonal field of view (FOV) of 60 degrees within a grating region size of only 75 mm x 62 mm in waveguide 802.

[0100] refer to Figure 9 Waveguide 902 includes a "transmission diffraction" top grating and is otherwise similar to Figure 8 Waveguide 802. Figure 9 The waveguide 902 includes a first input port 921, a second input port 922, and a third input port 923 for receiving image light carrying images in a first wavelength band, a second wavelength band, and a third wavelength band, respectively, and a pair of external optical surfaces for propagating the image light between the surfaces. As shown, the first input port 921, the second input port 922, and the third input port 923 can be offset in the Y-axis direction. The first diffraction grating 941 includes a plurality of VBGs configured to extend the first beam 911 generally along the X-axis and redirect the first beam 911 to the second diffraction grating 942. The third diffraction grating 943 includes a plurality of VBGs configured to extend the second beam 912 generally along the X-axis and redirect the second beam 912 to the second diffraction grating 942. The fourth diffraction grating 944 includes a plurality of VBGs configured to extend the third beam 913 approximately along the X-axis and redirect the third beam 913 to the second diffraction grating 942.

[0101] The second diffraction grating 942 includes a plurality of VBGs configured to receive a first beam 911, a second beam 912, and a third beam 913 from the first diffraction grating 941, the third diffraction grating 943, and the fourth diffraction grating 944, respectively, and to couple different portions of the corresponding first wavelength segment, second wavelength segment, and third wavelength segment outward along the Y-axis, thereby extending the first beam 911, the second beam 912, and the third beam 913 along the Y-axis for the user to observe the image at the viewing window 908.

[0102] The waveguide beam gratings (VBGs) of the first diffraction grating 941, the third diffraction grating 943, and the fourth diffraction grating 944 include grooves at an angle of approximately 30 degrees relative to the Y-axis and tilted at approximately 90 degrees relative to the surface of waveguide 902. At these tilt angles, the VBGs redirect beams 911, 912, and 913 of the image light primarily through transmission diffraction. The VBG of the second diffraction grating 942 includes grooves at an angle of approximately 102 degrees relative to the Y-axis and tilted at approximately 60 degrees relative to the surface of waveguide 902; providing a diagonal field of view (FOV) of 60 degrees within the 60mm x 70mm dimension of waveguide 902.

[0103] Go to Figure 10The required horizontal 1001 and vertical 1002 waveguide dimensions are plotted in degrees relative to the diagonal FOV at a 12mm x 10mm viewport and a 4:3 aspect ratio. The refractive index of the waveguide is taken as 1.5. It can be seen that, given the viewport size, the required diagonal FOV is the main factor driving the overall waveguide size.

[0104] According to one aspect of this disclosure, the overall waveguide size can be reduced by segmenting the image field of view (FOV) and providing different optical input ports to input optical signals carrying different FOV segments. As a non-limiting illustrative example, Figure 11A and Figure 11B The NED 1100 includes not one but two projectors, a first projector 1104 and a second projector 1105. Figure 11B The first beam 1111 and the second beam 1112 of the image light emitted by the first projector 1104 and the second projector 1105 respectively carry a first portion and a second portion of the field of view (FOV) of the image, such as adjacent portions or partially overlapping portions of the FOV. Waveguide 1102 is optically coupled to the first projector 1104 and the second projector 1105 at a first input port 1121 and a second input port 1122, respectively. The first input port 1121 and the second input port 1122 are on opposite sides of waveguide 1102 (i.e.,...). Figure 11A and Figure 11B The waveguide 1102 (left and right sides) is positioned at the first optical surface 1131. The waveguide 1102 may be based on a transparent plate or board having opposing first and second external optical surfaces 1131 and 1132 for propagating a first beam 1111 and a second beam 1112 therebetween. The first diffraction grating 1141 includes a first portion 1191 (solid outline) configured to extend the first beam 1111 along a first axis 1151, and a second portion 1192 (dashed outline) configured to extend the second beam 1112 along the first axis 1151. The first portion 1191 and the second portion 1192 may overlap as shown. The first beam 1111 and the second beam 1112 are then coupled outward from the waveguide 1102 for the first and second portions of the field of view (FOV) of the image observed by the user's eye 1106 at the viewing window 1108. The beams 1111 and 1112 may be coupled outward from the second diffraction grating 1142.

[0105] exist Figure 11A and Figure 11BIn the illustrated embodiment, a first diffraction grating 1141 and a second diffraction grating 1142 are disposed in the waveguide 1102 between a first optical surface 1131 and a second optical surface 1132, and are laterally offset relative to each other as shown. The first diffraction grating 1141 and the second diffraction grating 1142 do not overlap, that is, their projections on the first surface 1131 or the second surface 1132 do not overlap, although in other embodiments they may overlap. Figure 11A The first diffraction grating 1141 includes a plurality of beam vector groups (VBGs) configured to extend a first beam 1111 and a second beam 1112 along a first axis 1151 and redirect the first beam 1111 and the second beam 1112 to the second diffraction grating 1142. The second diffraction grating 1142 includes components configured to receive the first beam 1111 and the second beam 1112 from the first diffraction grating 1141, extend the first beam 1111 and the second beam 1112 along a second axis 1152, and couple the first beam 1111 and the second beam 1112 outward from the waveguide 1102 for the user's eye 1106 to observe a first and second portion of the field of view (FOV) of the image at a viewing window 1108. At least one or both of the diffraction gratings 1141 and 1142 may be symmetrical with respect to an axis 1153 equidistant from the first input port 1121 and the second input port 1122, although strict symmetry is not required.

[0106] refer to Figure 12 Waveguide 1202 is Figure 11A and Figure 11B An embodiment of waveguide 1102. Figure 12 Waveguide 1202 includes a first input port 1221, a second input port 1222, a first diffraction grating 1241, and a second diffraction grating 1242. A first beam 1111 is coupled into waveguide 1202 at the first input port 1221, and a second beam 1112 is coupled into waveguide 1202 at the second input port 1222. The first diffraction grating 1241 includes a first portion 1291 and a second portion 1292. The first portion 1291 has a plurality of VBGs with dashed fringes 1261, and the second portion 1292 has a plurality of VBGs with solid fringes 1262. The fringes 1261 of the first portion are configured to extend the first beam 1111 along the X-axis and guide the first beam 1111 to the second diffraction grating 1242. Similarly, the stripes 1262 of the second portion 1292 are configured to extend the second beam 1112 along the X-axis and guide the second beam 1112 to the second diffraction grating 1242.

[0107] exist Figure 12In the illustrated embodiment, a first input port 1221 is located on the left side of waveguide 1202 for inward coupling of image light pointing towards the right half of the field of view (FOV), and a second input port 1222 is located on the right side of waveguide 1202 for inward coupling of image light pointing towards the left half of the FOV. As measured along the corresponding k-vector of the first diffraction grating 1241, the fringe period of the VBG of the first portion 1291 and the second portion 1292 of the first diffraction grating 1241 varies from 163 nm to 337 nm. This fringe period variation is required so that the beams 1111, 1112 have sharper diffraction angles at the ends (shorter periods) opposite to the corresponding input ports 1221, 1222 than at the ends (longer periods) closer to the input ports 1221, 1222. The fringes 1261, 1262 of the VBG are oriented at approximately 50 degrees relative to the Y-axis and tilted at approximately 48 degrees relative to the optical surface of waveguide 1202. At these tilt angles, VBG primarily redirects the first beam 1111 and the second beam 1112 of the image light through reflective diffraction.

[0108] The second diffraction grating 1242 may also have two parts 1281 and 1282, each with fringes 1271 (dashed lines) and 1272 (solid lines), for extending the first beam 1111 and the second beam 1112 along the Y-axis, respectively, and for outputting the first beam 1111 and the second beam 1112 at the viewing window 1208 for user observation. The fringe periods of the second diffraction grating 1271 and 1272 vary from 153 nm to 294 nm to provide pupil expansion through wavelength division, as referenced above. Figure 4A , Figure 4B and Figure 5 As described. Stripes 1271, 1272 ( Figure 12 The orientation is approximately 74 degrees relative to the Y-axis and tilted approximately 30 degrees relative to the optical surface of waveguide 1202. The total dimensions of the grating region of waveguide 1202 are 48 mm x 60 mm.

[0109] In some embodiments, similar to Figure 8 Waveguide 802, with input ports 1221 and 1222, is inwardly coupled to two parts of the FOV with the same single color channel, and provides different input ports for different color channels. Figure 13AAn embodiment is shown. Waveguide 1302A has a first input port 1321 and a second input port 1322 for receiving a first beam 1311 and a second beam 1312 of image light carrying a first portion and a second portion of the FOV of the blue (B) channel of an image, respectively; a third input port 1323 and a fourth input port 1324 for receiving a third beam 1313 and a fourth beam 1314 of image light carrying a first portion and a second portion of the FOV of the green (G) channel, respectively; and a fifth input port 1325 and a sixth input port 1326 for receiving a fifth beam 1315 and a sixth beam 1316 of image light carrying a first portion and a second portion of the FOV of the red (R) channel of an image to be displayed, respectively. A first diffraction grating 1341 is disposed between the optical surfaces of waveguide 1302A and includes portions 1391 and 1392 having beam-varying gaussing (VBGs) configured to extend a first beam 1311 and a second beam 1312 along the X-axis, respectively, and to guide the first beam 1311 and the second beam 1312 to the second diffraction grating 1342A. A third diffraction grating 1343 is disposed between the optical surfaces of waveguide 1302A and laterally offset relative to the first diffraction grating 1341 and the second diffraction grating 1342A. The third diffraction grating includes portions 1393 and 1394 having VBGs configured to extend a third beam 1313 and a fourth beam 1314 along the X-axis, respectively, and to redirect the third beam 1313 and the fourth beam 1314 to the second diffraction grating 1342A. Similarly, a fourth diffraction grating 1344 may be disposed between the optical surfaces of waveguide 1302A and laterally offset relative to the first diffraction grating 1341, the second diffraction grating 1342A, and the third diffraction grating 1343. The fourth diffraction grating 1344 includes portions 1395 and 1396 having VBGs configured to extend a fifth beam 1315 and a sixth beam 1316 along the X-axis, respectively, and redirect the fifth beam 1315 and the sixth beam 1316 to the second diffraction grating 1342A.

[0110] The VBG of the second diffraction grating 1342A is configured to receive a first beam 1311 and a second beam 1312 from the first diffraction grating 1341, a third beam 1313 and a fourth beam 1314 from the third diffraction grating 1343, and a fifth beam 1315 and a sixth beam 1316 from the fourth diffraction grating 1344; extend beams 1311-1316 along the Y-axis; and couple beams 1311-1316 outward from waveguide 1302A at viewing window 1308 for user image viewing. Figure 13AIn the FOV, light from the first input port 1321, the third input port 1323 and the fifth input port 1325 on the left is sent to the right half of the FOV located at the window 1308, and light from the second input port 1322, the fourth input port 1324 and the sixth input port 1326 on the right is sent to the left half of the FOV located at the window 1308.

[0111] The VBG fringes of the first diffraction grating 1341, the third diffraction grating 1343, and the fourth diffraction grating 1344 are oriented at approximately 45 degrees relative to the Y-axis and tilted at approximately 51 degrees relative to the optical surface of waveguide 1302A. At these tilt angles, the VBG primarily redirects the image light beams 1311-1316 through reflective diffraction. The VBG fringes of the second diffraction grating 1342A are oriented at approximately 75 degrees relative to the Y-axis and tilted at approximately 60 degrees relative to the optical surface of waveguide 1302A. The total size of the grating region of waveguide 1302A is approximately 50 mm x 50 mm. Due to the compact placement of the waveguide, the size of waveguide 1302A can be reduced.

[0112] Go to Figure 13B Waveguide 1302B is similar to Figure 13A The waveguide is 1302A, but with a different VBG groove orientation and slightly different shape. Corresponding to... Figure 13A The top diffraction grating 1340B of the first diffraction grating 1341, the third diffraction grating 1343, and the fourth diffraction grating 1344 has VBG fringes that are 41 degrees relative to the Y-axis and 90 degrees tilted relative to the optical surface of the waveguide 1302B; this corresponds to a transmission diffraction grating configuration. Figure 13A The bottom diffraction grating 1342B of the second diffraction grating 1342A has VBG fringes that are 77 degrees relative to the Y-axis and 60 degrees tilted relative to the optical surface of waveguide 1302B. Image light is output at viewport 1308. Figure 13B The total dimensions of the grating region of waveguide 1302B are approximately 50 mm x 45 mm. The size of waveguide 1302B can be reduced due to the more compact placement of the waveguide.

[0113] Now go to Figure 13C Waveguide 1302C is similar to Figure 13A The waveguide is 1302A, but with a different VBG groove orientation and a slightly different shape. Corresponding to... Figure 13A The top diffraction grating 1340C of the first diffraction grating 1341, the third diffraction grating 1343, and the fourth diffraction grating 1344 has VBG fringes that are 42 degrees relative to the Y-axis and 90 degrees tilted relative to the optical surface of the waveguide 1302C; this corresponds to a transmission diffraction grating configuration. Figure 13AThe bottom diffraction grating 1342C of the second diffraction grating 1342A has VBG fringes that are 78 degrees relative to the Y-axis and 32 degrees tilted relative to the optical surface of waveguide 1302C. Image light is output at viewport 1308. Figure 13C The total dimensions of the grating region of the waveguide 1302C are approximately 50 mm x 45 mm. Due to the compact placement of the waveguide, the size of the waveguide 1302C can be reduced.

[0114] refer to Figure 13D The waveguide 1302D is similar to Figure 13A The waveguide 1302A has a different VBG fringe orientation, such that light from the left input port is directed to the left half of the FOV at window 1308, and light from the right input port is directed to the right half of the FOV. The VBG fringes of the top diffraction grating 1340D are tilted at approximately 35 degrees relative to the Y-axis and form an angle of approximately 51 degrees with the top or bottom plane of the waveguide 1302D (transmission grating configuration); and the VBG fringes of the bottom diffraction grating 1342D are tilted at approximately 106 degrees relative to the Y-axis and form an angle of approximately 60 degrees with the top or bottom plane of the waveguide 1302D (transmission grating configuration). The diagonal full FOV is approximately 60 degrees. The waveguide size depends on the required diagonal FOV; the required horizontal and vertical waveguide sizes can vary from 30mm-35mm to approximately 65mm to obtain a diagonal FOV ranging from 35 degrees to 75 degrees.

[0115] Reference Figure 13E Waveguide 1302E is similar to Figure 13D The waveguide is 1302D. The VBG fringes of the top diffraction grating 1340E are tilted at approximately 47 degrees relative to the Y-axis and form an angle of approximately 54 degrees with the top or bottom plane of the waveguide 1302E (transmission grating configuration); and the VBG fringes of the bottom diffraction grating 1342E are tilted at approximately 100 degrees relative to the Y-axis and form an angle of approximately 63 degrees with the top or bottom plane of the waveguide 1302E (transmission grating configuration). The diagonal full FOV is approximately 70 degrees. The waveguide size depends on the required diagonal FOV; the required horizontal and vertical waveguide sizes can vary from 30mm-35mm to approximately 55mm to obtain a diagonal FOV ranging from 35 degrees to 70 degrees.

[0116] Reference Figure 13F Waveguide 1302F is similar to Figure 13DThe waveguide is 1302D. The VBG fringes of the top diffraction grating 1340F are tilted at approximately 36 degrees relative to the Y-axis and form an angle of approximately 90 degrees with the top or bottom plane of the waveguide 1302F (transmission grating configuration); and the VBG fringes of the bottom diffraction grating 1342F are tilted at approximately 105 degrees relative to the Y-axis and form an angle of approximately 32 degrees with the top or bottom plane of the waveguide 1302F (reflection grating configuration). The diagonal full FOV is approximately 70 degrees. The waveguide size depends on the required diagonal FOV; the required horizontal and vertical waveguide sizes can vary from 30mm-35mm to 60mm-68mm to obtain a diagonal FOV ranging from 35 degrees to 90 degrees.

[0117] Reference Figure 13G Waveguide 1302G is similar to Figure 13F The waveguide is 1302F. The VBG fringes of the top diffraction grating 1340G are tilted approximately 38 degrees relative to the Y-axis and form an angle of approximately 90 degrees with the top or bottom plane of the waveguide 1302G (transmission grating configuration); and the VBG fringes of the bottom diffraction grating 1342G are tilted approximately 102 degrees relative to the Y-axis and form an angle of approximately 35 degrees with the top or bottom plane of the waveguide 1302G (reflection grating configuration). The diagonal full FOV is approximately 70 degrees. The waveguide size depends on the required diagonal FOV; the required horizontal and vertical waveguide sizes can vary from 30mm-35mm to 60mm-68mm to obtain a diagonal FOV ranging from 35 degrees to 90 degrees. Figures 13A to 13G In this model, the aspect ratio of the field of view (FOV) is 16:9.

[0118] Figure 14A , Figure 14B and Figure 14C The diagram illustrates a possible path for external light to reflect from the VBG fringes of an outwardly coupled diffraction grating, resulting in an artifact due to the so-called "rainbow" effect. The size of the rainbow artifact depends on the density and orientation of the VBG fringes. Fringe 1499A, 1499B, and 1499C of the VBG in waveguide 1400 can produce rainbow paths 1401 and 1402. Figure 14A ); 1403, 1404 Figure 14B ); and 1405, 1406 ( Figure 14C ), used for light to reach the user's eyes 1408. In the presented configuration, Figure 13A The waveguide 1302A does not exhibit any rainbow effect; Figure 13B Waveguide 1302B may have a rainbow path 1401 in the top diffraction grating 1340B; and Figure 13C Waveguide 1302C (the smallest of the three) may have rainbow paths 1403 and 1404 in the bottom diffraction grating 1342C. Similarly, Figure 13D Waveguide 1302D and Figure 13E The waveguide 1302E does not exhibit any rainbow effect; while Figure 13F waveguide 1302F and Figure 13G Waveguide 1302G may have rainbow paths 1403 and 1404 in the bottom diffraction gratings 1342F and 1342G, respectively, while providing a larger diagonal FOV. Therefore, there may be a trade-off between the overall size of the waveguide at the desired FOV and the presence of the rainbow effect; it is important to remember that in practice only the rainbow path that can reach the user's eye 1408 needs to be considered.

[0119] refer to Figure 15A and Figure 15B The near-eye artificial reality / virtual reality (AR / VR) display 1500 may include the waveguide disclosed herein, for example... Figure 1A and Figure 1B Waveguide 102, Figure 2A Waveguide 202, Figure 5 Waveguide 502, Figure 6 Waveguide 602, Figure 8 Waveguide 802, Figure 9 Waveguide 902, Figures 11A-11B Waveguide 1102, Figure 12 waveguide 1202, and / or Figure 13A , Figure 13B and Figure 13C The corresponding waveguides 1302A, 1302B, or 1302C are used to guide image light to the viewing window 1510 of the near-eye AR / VR display 1500. As shown in this example, the body or frame 1502 of the near-eye AR / VR display 1500 may have a shape factor similar to glasses. The display unit 1504 includes a display component 1506 ( Figure 15B The display component 1506 provides image light 1508 to the viewing window 1510 (i.e., the geometric area that can present a high-quality image to the user's eyes 1512). The display component 1506 may include a separate AR / VR display module for each eye, or a single AR / VR display module for both eyes. In the latter case, an optical switching device may be coupled to a single electronic display to sequentially guide images to the user's left and right eyes, one frame for the left eye and one frame for the right eye. The images can be presented quickly enough, i.e., at a sufficiently fast frame rate, that a single eye will not perceive flicker and will perceive a smooth, stable image of the surrounding virtual or augmented scene.

[0120] The electronic display of display component 1506 may include, for example, but not limited to, liquid crystal displays (LCDs), organic light-emitting displays (OLEDs), inorganic light-emitting displays (ILEDs), active-matrix organic light-emitting diode displays (AMOLEDs), transparent organic light-emitting diode displays (TOLEDs), projectors, or combinations thereof. The near-eye AR / VR display 1500 may also include an eye-tracking system 1514 for determining the gaze direction and / or vergence angle of the user's eyes 1512 in real time. Depending on the viewing angle and eye position, the determined gaze direction and vergence angle can also be used for real-time compensation of visual artifacts. Furthermore, the determined vergence angle and gaze angle can be used for user interaction, highlighting objects, bringing objects to the foreground, dynamically creating additional objects or pointers, etc. Additionally, the near-eye AR / VR display 1500 may include an audio system, such as a small speaker or headphones.

[0121] Now go to Figure 16 The HMD 1600 is an example of an AR / VR wearable display system that surrounds the user's face for greater immersion in the AR / VR environment. The HMD 1600 may include any waveguides disclosed herein to direct image light to a viewing window. The HMD 1600 can present content to the user as part of an AR / VR system that may also include a user position and orientation tracking system, an external camera, a gesture recognition system, control devices for providing user input and control to the system, and a central console for storing software programs and other data for interaction with the user and thus with the AR / VR environment. The HMD 1600 functions to enhance the view of the physical, real-world environment with computer-generated images and / or generate fully virtual 3D images. The HMD 1600 may include a front body 1602 and a strap 1604. The front body 1602 is configured to be placed reliably and comfortably in front of the user's eyes, and the strap 1604 can be stretched to secure the front body 1602 to the user's head. The display system 1680, including the waveguide disclosed herein, can be disposed in the front body 1602 for presenting AR / VR images to a user. The side portion 1606 of the front body 1602 can be opaque or transparent.

[0122] In some embodiments, the front body 1602 includes a locator 1608, an inertial measurement unit (IMU) 1610 for tracking the acceleration of the HMD 1600, and a position sensor 1612 for tracking the position of the HMD 1600. The locator 1608 is tracked by an external imaging device of the AR / VR system, enabling the AR / VR system to track the position and orientation of the entire HMD 1600. Information generated by the IMU and position sensor 1612 can be compared with the position and orientation obtained by tracking the locator 1608 to improve the tracking of the position and orientation of the HMD 1600. Accurate position and orientation are important for presenting the appropriate virtual scene to the user as they move and rotate in 3D space.

[0123] HMD 1600 may also include an eye-tracking system 1614 that determines the orientation and position of the user's eyes in real time. The obtained eye position and orientation allow HMD 1600 to determine the user's gaze direction and adjust the image generated by display system 1680 accordingly. In one embodiment, convergence is determined, i.e., the convergence angle of the user's gaze. Depending on the viewing angle and eye position, the determined gaze direction and convergence angle can also be used for real-time compensation of visual artifacts. Furthermore, the determined convergence and gaze angles can be used for user interaction, highlighting objects, bringing objects to the foreground, creating additional objects or pointers, etc. An audio system may also be provided, including, for example, a set of small speakers built into the front body 1602.

Claims

1. A waveguide for transmitting image light, the waveguide comprising: A first input port is used to receive a first beam of image light carrying a first color channel of an image in a first wavelength band; Optical first and second optical surfaces, used to propagate the first light beam between the first and second optical surfaces; and A first diffraction grating and a second diffraction grating are disposed in the waveguide between the first optical surface and the second optical surface and are laterally offset relative to each other; The first diffraction grating includes a plurality of volume Bragg gratings (VBGs), which are configured to extend the first beam along a first axis and redirect the first beam to the second diffraction grating; and The second diffraction grating includes a plurality of VBGs configured to receive the first beam from the first diffraction grating and to outwardly couple different portions of the first wavelength band of the first beam at different positions along the second axis, thereby extending the first beam along the second axis for the user to observe the image.

2. The waveguide according to claim 1, wherein, The first diffraction grating comprises between 300 and 1000 VBGs, and the second diffraction grating comprises between 10 and 200 VBGs.

3. The waveguide according to claim 1, further comprising: The second input port is used to receive a second beam of image light carrying the second color channel of the image in the second wavelength band; A third diffraction grating is disposed in the waveguide between the first optical surface and the second optical surface and is laterally offset relative to the first diffraction grating and the second diffraction grating; The third diffraction grating includes a plurality of VBGs configured to extend the second beam along the first axis and redirect the second beam toward the second diffraction grating; and The second diffraction grating's VBG is configured to receive the second beam from the third diffraction grating and to couple different portions of the second wavelength band of the second beam outward at different positions along the second axis, thereby extending the second beam along the second axis for the user to observe the image.

4. The waveguide according to claim 3, further comprising: The third input port is used to receive a third beam of image light carrying the third color channel of the image in the third wavelength band; A fourth diffraction grating is disposed in the waveguide between the first optical surface and the second optical surface, and is laterally offset relative to the first diffraction grating to the third diffraction grating; The fourth diffraction grating includes a plurality of VBGs configured to extend the third beam along the first axis and redirect the third beam toward the second diffraction grating; and The second diffraction grating's VBG is configured to receive the third beam from the fourth diffraction grating and to couple different portions of the third wavelength band of the third beam outward at different positions along the second axis, thereby extending the third beam along the second axis for the user to observe the image.

5. The waveguide according to claim 4, wherein, The first input port, the second input port, and the third input port are offset relative to each other along the second axis.

6. The waveguide according to claim 1, wherein, The VBG of the first diffraction grating and the VBG of the second diffraction grating are disposed in the same layer spaced apart from the first optical surface and the second optical surface.

7. The waveguide according to claim 1, wherein, The first diffraction grating has a grating period that varies spatially along the first axis.

8. The waveguide according to claim 7, wherein, The grating period of the VBG of the first diffraction grating varies in the range of 100 nm to 500 nm.

9. The waveguide according to claim 1, wherein, The second diffraction grating has a grating period that varies spatially along the second axis.

10. The waveguide according to claim 9, wherein, The grating period of the VBG of the second diffraction grating varies in the range of 100 nm to 300 nm.

11. The waveguide according to claim 1, wherein, The first diffraction grating's VBG is configured to redirect the first and second beams of the image light through reflective diffraction.

12. The waveguide according to claim 11, wherein, The first diffraction grating's VBG includes multiple stripes forming an angle between 34 and 54 degrees with the first optical surface.

13. The waveguide according to claim 12, wherein, The second diffraction grating's VBG includes multiple stripes forming an angle between 20 and 38 degrees with the first optical surface.

14. The waveguide according to claim 1, wherein, The first diffraction grating's VBG is configured to redirect the first and second beams of the image light through transmission diffraction.

15. The waveguide according to claim 14, wherein, The first diffraction grating's VBG includes multiple fringes forming an angle greater than 80 degrees with the first optical surface.

16. The waveguide according to claim 15, wherein, The second diffraction grating's VBG includes multiple stripes forming an angle between 50 and 70 degrees with the first optical surface.

17. The waveguide according to claim 1, wherein, The image has a field of view (FOV), wherein a first beam of image light carries a first portion of the FOV of the image, and the waveguide further includes a second input port for receiving a second beam of image light carrying a second portion of the FOV of the image in the first wavelength band; Wherein, the VBG of the first diffraction grating is configured to extend the second beam along the first axis and redirect the second beam to the second diffraction grating; and The second diffraction grating's VBG is configured to receive the second beam from the first diffraction grating and to couple different portions of the first wavelength band of the second beam outward at different positions along the second axis, thereby extending the second beam along the second axis for the user to observe the image.

Images