Waveguide, display and method for manufacturing waveguide

Abstract

The present disclosure relates to a waveguide for an augmented reality or virtual reality display, a display, and a method of manufacturing a waveguide. In one embodiment, a waveguide for an augmented reality or virtual reality display comprises: an output diffractive element comprising a plurality of optical structures in a photonic crystal; a first main surface of the waveguide and a second main surface of the waveguide, the first main surface being separated from the second main surface in a direction perpendicular to the plane of the waveguide, where light propagates along the waveguide towards the output diffractive element by undergoing total internal reflection between the first main surface and the second main surface, a plurality of optical structures are arranged in a plane of the waveguide in an array configured to receive light from an input direction and diffract the light into a plurality of stages, some of which are diffracted in the plane of the waveguide at an angle to the input direction to provide a 2D extension across the plane of the waveguide, and the other stages are coupled out towards the viewer in a direction perpendicular to the plane of the waveguide.

Description

[0001] This application is a divisional application of the Chinese invention patent application with application number 202180026123.0, application date March 22, 2021, and invention name “Waveguide for Augmented Reality or Virtual Reality Display”. Technical Field

[0002] The present invention relates to waveguides for augmented reality or virtual reality displays. In particular, the present invention relates to a waveguide in which input light is expanded in two orthogonal directions in an output element and coupled out of the waveguide in a preferred direction towards a viewer. This may allow a physical extension of the eye range in an augmented reality display while ensuring an increased efficiency of the system. Background Art

[0003] Augmented reality displays allow users to view their surroundings along with projected images. In military or transportation applications, projected images can be overlaid on the user's perceived real world. Other applications for these displays include video games and wearable devices such as glasses.

[0004] In a normal augmented reality setup, a transparent display screen is placed in front of the user so that the user can continue to see the physical world. The display screen is typically a glass waveguide, and a projector is placed on one side. Light from the projector is coupled into the waveguide via a diffraction grating. The projected light is totally internally reflected within the waveguide. The light is then coupled out of the waveguide via another diffraction grating so that the user can see the light. The projector can provide information and / or images that enhance the user's view of the physical world.

[0005] An optical device for expanding input light in two dimensions in an augmented reality display is disclosed in WO 2016 / 020643. An input diffractive optical element is provided for coupling input light from a projector into a waveguide. The optical device also includes an output element having two diffractive optical elements overlapping each other in the waveguide, so that each of the two diffractive optical elements can receive light from the input diffractive optical element and couple it toward the other diffractive optical element in the pair, which can then be used as an output diffractive optical element, which couples light out of the waveguide toward a viewer. In one embodiment, two diffractive optical elements overlapping each other are provided in a photonic crystal. This is achieved by having an array of pillars arranged in the waveguide or on the surface of the waveguide, the array of pillars having a refractive index variation relative to the surrounding waveguide medium. The pillars in WO 2016 / 020643 are described as having a circular cross-sectional shape when viewed in the plane of the waveguide from the perspective of the viewer. It has been found that this arrangement is very effective in simultaneously expanding two-dimensional light and coupling light out of the waveguide. Advantageously, this may improve the use of space on the waveguide, which may reduce manufacturing costs.

[0006] An optical device having a column with a rhombus cross-sectional shape is disclosed in WO 2018 / 178626. Modified rhombus cross-sectional shapes are also shown, the modified rhombus having notches. Columns with these shapes, rather than circular cross-sections, have been shown to reduce the appearance of central stripes in the output element having a higher relative brightness than other parts, thereby reducing to some extent the undesirable "fringe" effect in the output image. Other shapes have also been proposed.

[0007] One disadvantage of these types of waveguides is that when light is incident on the output element, the diffraction orders that couple the light out of the waveguide may extend in opposite directions. This can include orders that are transmitted through the grating and out to the viewer, as well as orders that are reflected by the grating and out to the viewer. Generally, the waveguide system is designed so that the viewer only views a single one of these outcoupled orders. This results in a reduction in the efficiency of the waveguide because a portion of the light that could be used to form an image of the viewer is wasted in this undesired outcoupled direction. In addition, the undesired outcoupled orders also form an image that can cause privacy issues by allowing an external viewer to see what the wearer is viewing. Summary of the invention

[0008] According to one aspect of the present invention, there is provided a waveguide for an augmented reality or virtual reality display, the waveguide comprising: an output diffraction element comprising a plurality of optical structures in a photonic crystal; wherein the plurality of optical structures are arranged in an array in the plane of the waveguide, the array being configured to receive light from an input direction and diffract the light into a plurality of levels, some of the levels being diffracted in the plane of the waveguide at an angle to the input direction to provide a 2D extension across the plane of the waveguide, and other levels being coupled out toward a viewer; wherein at least one of the plurality of optical structures has a profile in a direction perpendicular to the plane of the waveguide, wherein the profile varies along one or more directions parallel to the plane of the waveguide so that the out-coupling level is preferentially provided from one major surface of the waveguide.

[0009] Preferably, the outcoupled stages are directed towards the viewer in a direction perpendicular to the waveguide plane.

[0010] Preferably, the waveguide comprises a first major surface of the waveguide and a second major surface of the waveguide, the first major surface being separated from the second major surface in a direction perpendicular to the waveguide plane, wherein light propagates along the waveguide to the output diffraction element by undergoing total internal reflection between the first major surface and the second major surface.

[0011] Preferably, the outcoupling stage is provided from the first main surface of the waveguide compared to the second main surface of the waveguide.This may be provided preferentially from the first main surface of the waveguide compared to the second main surface of the waveguide.

[0012] In this way, each of the optical structures can have a height that varies in the plane of the waveguide (i.e. across the waveguide plane). Thus, the optical structure can have a blazed structure. Advantageously, the blazed structure can preferentially diffract light from one major surface of the waveguide (i.e. the side) towards the viewer. In this way, the transmission level or the reflection level can be eliminated or significantly suppressed. Since light is only coupled out of the waveguide in a single direction (in the transmission level or the reflection level), the optical efficiency of the output diffractive optical element can be improved. This can advantageously improve battery savings in wearable devices, or can reduce the power requirements of a projector. The plane of the waveguide can be in the xy plane. In this notation, the height of the optical structure will be along the z-axis. The major surfaces can be opposite sides of the waveguide.

[0013] The 2D expansion in the waveguide plane produces a 2D pupil replication. Thus, the uncoupled orders are diffracted at an angle to the input direction to provide multiple diffraction orders. The angle to the input direction may be ±60°. Alternatively, it may be ±45°, alternatively, it may be any other angle different from the input direction.

[0014] In some arrangements, the profile of at least one of the plurality of optical structures may vary continuously along one or more directions parallel to the plane of the waveguide. In this way, the profile of the optical structure may have a gradient that varies continuously across the optical structure. The continuous slope may provide improved control over the efficiency and directivity of the diffraction orders.

[0015] Alternatively, at least one of the plurality of optical structures has a discontinuity in its profile. In other arrangements, at least one of the plurality of optical structures includes a plurality of discontinuities. In this way, a change in profile may be achieved by having one or more steps in the optical structure. Each step may have a substantially flat portion parallel to the waveguide plane, separated by a vertical portion perpendicular to the waveguide plane. This may facilitate manufacture of the optical structure while also providing the desired effect of increasing the efficiency of the reflective output stage relative to the transmissive output stage, and vice versa.

[0016] Preferably, the profile change of at least some of the multiple optical structures can be different from the profile change of other optical structures in the multiple optical structures. Not all optical structures have profiles that change in the same way. By having differences in the profile change between the optical structures, the optical structure can have a scattering property that changes. In some arrangements, the change in the profile of the optical structure changes on the output diffraction element. Therefore, the optical structures at different regions of the output diffraction element can have different profile changes (that is, different from each other). The change in the profile can be expressed as a measure of the change in the profile, which defines the degree to which the change in the profile can be measured.

[0017] In this way, the variation of the profile of the optical structure can vary across the output diffractive element to achieve the desired scattering in a specific region of the output diffractive element. For example, in a first region of the output diffractive element, the optical structures can all have similar profile variations, while in a different second region of the output diffractive element, the profile variations of the optical structures can be different from the profile variations in the first region. Alternatively, the different profile variations of the optical element can be randomly distributed across the output diffractive element.

[0018] The input direction may define a first axis in the plane of the waveguide, and one or more directions in which the optical structure varies in profile may be at an angle to the input direction. The angle may be ±60°. Typically, a portion of the input light may be diffracted by the optical structure at an angle of ±60°. This arrangement ensures that after the initial turn, when the light is incident on a subsequent optical structure, the slope of the height of the optical structure is substantially the same as the direction in which the light was incident on the optical structure. Alternatively, the angle may be ±45°, or any other angle. For example, using the notation given above, the input direction may be along the y-axis.

[0019] The direction in which the optical structure on the first side of the first axis changes in profile may be at a first angle to the input direction, and the direction in which the optical structure on the second side of the first axis changes in profile may be at a second angle to the input direction. The first side of the first axis and the second side of the first axis are separated in the plane of the waveguide by a line formed along the input direction, which extends from the point at which the light is incident on the output diffraction element. In this way, after the initial turn, when the light is incident on a subsequent optical structure, the slope of the profile of the optical structure is the same as the direction in which the light is incident on the optical structure. In one arrangement, the first angle may be +60° and the second angle may be -60°. In another arrangement, the first angle may be +45° and the second angle may be -45°. In other arrangements, the angles may be any other angles.

[0020] In some arrangements, the profile of the optical structure on the first axis varies in the input direction. Thus, the optical structure that provides the initial diffraction of light from the input grating may have a profile that varies along an axis defined by the input direction. This ensures that when the input light is initially diffracted by the output grating, the light is preferentially diffracted in a single intended direction (i.e., in either the transmission or reflection order).

[0021] In some arrangements, at least one of the multiple optical structures is arranged so that the profile of the at least one optical structure has a negative gradient in a direction away from the point where light is incident on the at least one optical structure. This causes reflected diffraction orders to be preferentially selected and transmitted diffraction orders to be preferentially suppressed. In some arrangements, all of the multiple optical structures can be arranged in this way. In other words, the profile on the light-incident side of the optical structure is higher or has a larger physical extent than the profile on the side of the optical structure farthest from the light-incident side. This means that the profile slopes downward from the light-incident side of the optical structure. The slope can be continuous or stepped. In this way, the portion of the optical structure at the light-incident side extends higher on the z-axis than the portion of the optical structure farthest from the light-incident side.

[0022] Alternatively or additionally, at least one of the plurality of optical structures is arranged such that the profile of the at least one optical structure has a positive gradient in a direction away from the point at which light is incident on the at least one optical structure. This causes the transmitted diffraction orders to be preferentially selected and the reflected diffraction orders to be preferentially suppressed. In some arrangements, all of the plurality of optical structures may be arranged in this manner. In other words, the profile on the light incident side of the optical structure is lower or has a smaller physical extent than the profile on the side of the optical structure farthest from the light incident side. This means that the profile slopes upward from the light incident side of the optical structure. The slope may be continuous or stepped. In this way, the optical structure extends higher along the z-axis at the farthest part of the optical structure where the light is incident than at the part of the optical structure where the light is incident.

[0023] Preferably, the waveguide may comprise an input diffractive optical element separate from the diffractive output optical element, the input diffractive optical element being configured to couple light into the waveguide and provide the light to the plurality of optical structures in the array in an input direction.

[0024] When viewed in the plane of the waveguide, the plurality of optical structures may respectively have a shape comprising a plurality of substantially straight sides having respective normal vectors at different angles. In other words, when viewed in the xy plane, the cross-section of the optical structure may be a shape having a plurality of substantially straight sides having respective normal vectors at different angles. For example, it may be a rhombus shape of a notch as described in WO 2018 / 178626. Alternatively, it may have a different cross-sectional shape, such as circular or rectangular.

[0025] An array of optical structures in a waveguide may be referred to as a photonic crystal.The waveguide may be arranged within an optical display.

[0026] The optical structure preferably exhibits a refractive index difference with the surrounding medium. In this way, optical structures can be embedded within a waveguide and their diffractive properties can be generated due to the difference in refractive index between the structure and the waveguide medium.

[0027] The optical structure may be provided as a surface relief feature on the waveguide surface. The mismatch between the refractive index of the surface relief features and the air surrounding them may provide the desired diffraction properties. In some embodiments, a coating may be provided on the optical structure to control the diffraction efficiency.

[0028] Preferably, the waveguide is a slab waveguide. When light is incident and reflected from a first major surface of the waveguide in the plane of the waveguide and a second major surface of the waveguide in the plane of the waveguide, the propagation of light through the waveguide is via total internal reflection. In this way, when light is reflected from each face, it propagates along the waveguide from the input diffractive element toward the output diffractive element.

[0029] According to another aspect, there is provided an augmented reality or virtual reality display comprising a waveguide of the above aspect.

[0030] According to another aspect, a method of manufacturing a waveguide for an augmented reality or virtual reality display is provided, comprising the steps of providing an output diffraction element comprising a plurality of optical structures in a photonic crystal; arranging the plurality of optical structures, wherein the plurality of optical structures are arranged in an array in the plane of the waveguide, the array being configured to receive light from an input direction and diffract the light into a plurality of orders, some of the orders being diffracted in the plane of the waveguide at an angle to the input direction to provide a 2D expansion across the plane of the waveguide, and other orders being coupled out toward a viewer, and wherein at least one of the plurality of optical structures has a profile in a direction perpendicular to the plane of the waveguide, wherein the profile varies along one or more directions parallel to the plane of the waveguide such that the outcoupled orders are preferentially provided from one major surface of the waveguide.

[0031] Preferably, the outcoupled stages are directed towards the viewer in a direction perpendicular to the waveguide plane.

[0032] Preferably, the waveguide comprises a first major surface of the waveguide and a second major surface of the waveguide, the first major surface being separated from the second major surface in a direction perpendicular to the waveguide plane, wherein light propagates along the waveguide to the output diffraction element by undergoing total internal reflection between the first major surface and the second major surface.

[0033] Preferably, the outcoupling stage is provided from the first main surface of the waveguide compared to the second main surface of the waveguide.This may be provided preferentially from the first main surface of the waveguide compared to the second main surface of the waveguide. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0035] Figure 1A and Figure 1B A top view and an edge view of a known waveguide are shown;

[0036] Figure 2A showing a waveguide wherein the output viewing position is from a major surface of the waveguide opposite to where the output grating is located;

[0037] Figure 2B showing the same major surface where the output viewing position is from the output grating of the waveguide;

[0038] FIG. 3A to FIG. 3F shows a number of different arrangements of optical structures for use in a diffractive output element according to the invention;

[0039] Figure 4 An example output grating according to the present invention is shown, the example output grating being configured to ensure that the reflected order is coupled out of the waveguide with a higher efficiency than the transmitted outcoupled order; and

[0040] Figure 5 It shows that according to the present invention Figure 4 An example output grating configured to ensure that the reflected order is coupled out of the waveguide with a higher efficiency than the transmitted out-coupled order, thereby illustrating the shape of the optical structure when viewed in the plane of the waveguide. DETAILED DESCRIPTION

[0041] Figure 1A 1 shows a top view of the waveguide 1 disclosed in WO 2016 / 020643, Figure 1B An edge view of the waveguide 1 disclosed in WO 2016 / 020643 is shown.

[0042] An input diffraction grating 2 is provided on the surface of the waveguide 1, which is used to couple light from a projector (not shown) into the waveguide 1. The light coupled into the waveguide travels by total internal reflection toward an output element 4 comprising a photonic crystal. In this example, the photonic crystal comprises a column. The column has a different refractive index relative to the refractive index of the surrounding waveguide medium, and the column is arranged in an array with hexagonal symmetry. The column may be referred to as a nanostructure, a diffractive optical structure or an optical structure.

[0043] from Figure 1A It can be seen that light from the input grating 2 is coupled along the input light path 8 toward the output grating 4. Figure 1B It can be seen that light propagates between the first major surface 5 and the second major surface 7 of the waveguide 1 by total internal reflection. Position 6a shows the point where the input light first interacts with the grating formed by the array of optical structures. The light is then diffracted into multiple diffraction orders at position 6a.

[0044] A portion of the light is diffracted at ±60° into turned orders as shown by paths 10a and 10b.

[0045] The rest of the light is diffracted out of the waveguide into so-called output stages. These can be Figure 1B is considered as reflection level 12b and transmission level 12a. Figure 1A The out-of-plane reflection level 12a is shown in FIG. Figure 1B There are two orders as shown. The reflection order 12b is where the light passes back through the waveguide 1 after diffraction with the output grating 4 and then exits the waveguide. The transmission order 12a is where the light passes from the output grating 4 on the same side of the waveguide 1 as the output grating 4 is located and passes out of the waveguide 1. Therefore, the reflection order 12b and the transmission order 12b extend from different respective major surfaces of the waveguide 1 in opposite directions to each other. The reflection order 12b passes out of the first major surface 5 of the waveguide 1. The transmission order 12a passes out of the second major surface 7 of the waveguide 1.

[0046] After diffraction at position 6a, light in each of the steering stages 10a, 10b is then diffracted at positions 6b, 6c by the array of optical structures at these positions, thereby producing additional steering stages and additional output stages. The additional output stages are Figure 1B Shown in FIG. 1 are a reflective stage 14b and a transmissive stage 14a.

[0047] It will be appreciated that both the reflective and transmissive stages are capable of forming an image. However, in conventional waveguide systems, typical designs dictate that only the reflective or transmissive stage is actually utilized by the viewer. This can be Figure 2A and Figure 2B Seen in.

[0048] Figure 2A The waveguide 1 is shown with a viewing position 16b of a viewer from the major surface 5 of the waveguide 1 opposite the major surface on which the output grating 4 is located, in which arrangement the reflection stage 12b provides an image to the viewing position 16b.

[0049] Figure 2B An alternative type of waveguide 1 is shown in which a viewing position 16a of a viewer is from the major surface 7 on which the output grating 4 of the waveguide 1 is located. In this arrangement, the transmission stage 12a provides an image to the viewing position 16a.

[0050] In conventional systems, such as those disclosed in the prior art cited above, even if only one of the transmissive or reflective stages is used to produce the image, the other stage still exists. This means that there is an image forming stage in a direction away from the eye. This means that light is lost, which reduces the efficiency of the system. This also leads to privacy issues, as a third party facing the user may be able to view the information that the user is viewing.

[0051] The present invention aims to prevent these problems of unwanted transmission or reflection levels so that only transmission or reflection levels are produced.

[0052] FIG. 3A to FIG. 3F A number of different arrangements of optical structures for use in the diffractive output element are shown. Figure 3A An optical structure 20 having a notched diamond shape as described in WO 2018 / 178626 is shown. It can be seen that the optical structure 20 has a flat uniform profile. An optical structure having such a profile results in the presence of both a transmission level and a reflection level, as shown in FIG. Figure 1B shown.

[0053] It has been found that by modifying the profile of the optical structure 20, such as Figure 3A As shown, one of the transmission output level or the reflection output level can be suppressed. In particular, this can be achieved by having a profile that changes in the optical structure.

[0054] Figure 3B An optical structure 22 is shown as an example of such a structure having a varying profile. In the plane of the waveguide, the optical structure 22 has the notched diamond shape of the optical structure 20. However, the profile of the optical structure 22 varies. This change in profile is in a direction across the plane of the waveguide. Thus, the optical structure 22 has a gradient or slope from one end of the optical structure 22 to the opposite end. It can be seen that the profile of the optical structure 22 varies continuously from one side of the optical structure 22 to the other side. When the profile of the optical structure 22 is changed from one side of the optical structure 22 to the other side, the profile of the optical structure 22 is changed from one side of the optical structure 22 to the other side. Figure 3B This is angled relative to the vertical when viewed at an angle of . The slope extends from the longest side 101 of the notch parallelogram at this angle to the vertical to the longest side 103, i.e., the diagonal across the optical element. This is along the y-axis and the x-axis when viewed in the plane of the waveguide.

[0055] Figure 3C An optical structure 24 is shown, which is another example of an optical structure that can selectively suppress transmission levels or reflection levels. It can be seen that the optical structure 24 has a varying profile. A discontinuity 28 separates two regions 30a, 30b of the profile of the optical structure 24. The first region 30a is higher than the second region 30b, thereby creating a profile variation. This creates a step at the discontinuity 28 between the two regions. The step, and therefore the discontinuity, extends across the entire extent of the optical structure from one side to the opposite side. The step (and discontinuity) extends across the optical structure at an angle to the vertical, such as Figure 3C. This angle is perpendicular to the angle at which the profile change occurs. The profile change is from side 101 to side 103 of the optical structure 24. In other words, the discontinuity is positioned at an angle parallel to side 103, side 101 of the notch parallelogram. The discontinuity 28 is positioned in the center of the optical structure 24 along the above angle. The physical extent of the optical structure perpendicular to the waveguide plane can be considered to be its height. The height of the step is half the height of the optical structure. It can also be seen that it can be considered that there is another step 29 between the edge 103 of the optical structure and the surrounding area of ​​the output grating 4.

[0056] Figure 3D An optical structure 26 is shown, which is another example of an optical structure that can selectively suppress a transmission level or a reflection level. It can be seen that the optical structure 26 has a changing profile. The optical structure 26 has four discontinuities 32a to 32d, each of which is located between five different flat areas 34a to 34e of the optical structure 26. Each of the discontinuities 32a to 32d is a vertical portion that separates two adjacent flat areas 30a to 30e of the profile of the optical structure 26. Each of the discontinuities is equidistantly spaced on the optical structure between the edge 101 and the edge 103. The height of the areas 30a to 30e decreases on the optical structure, thereby producing a change in profile. If the edge of the optical structure 33 and the surrounding area of ​​the output grating 4 act as another step, this produces five steps. Each of the discontinuities 32a to 32e (and the steps therefrom) is arranged as described above with respect to Figure 3C The angles are arranged such that each extends across the range of the optical structure. Figure 3D As shown, each of the steps has the same height. This is 20% of the height of the highest point of the optical structure 26. However, in other arrangements, the height of each step may vary relative to each other.

[0057] Advantageously, by having steps as in optical structure 24 and optical structure 26, the optical structures are easier to manufacture than optical structure 22 while still providing the effect of suppressing the transmission level or the reflection level.

[0058] Figure 3E An optical structure 25 is shown which is another example of such a structure having a varying profile. In the plane of the waveguide, the optical structure 25 has the notched diamond shape of the optical structure 20. However, the profile of the optical structure 25 varies. This change in profile is in a direction across the plane of the waveguide. Thus, the optical structure 25 has a gradient or slope from one end of the optical structure 25 to the opposite end. It can be seen that the profile of the optical structure 25 varies continuously from one side of the optical structure 25 to the other side. When the profile of the optical structure 25 is changed from one side of the optical structure 25 to the other side of the optical structure 25, the optical structure 25 can be changed. Figure 3E When viewed from an angle of , the gradient is between vertex 107 and vertex 105 of the optical structure. Vertex 105 and vertex 107 are the vertices between the two largest sides of the notch parallelogram cross section. Figure 3B The optical structure is different when Figure 3E When watching, Figure 3E The profile of the optical structure 25 shown in varies along a vertical axis, ie along the y-axis when viewed in the plane of the waveguide, rather than at an angle to said axis.

[0059] Figure 3F An optical structure 27 is shown which is another example of an optical structure that can selectively suppress either the transmission level or the reflection level. Figure 3F The optical structure 27 shown in FIG. 2 can be considered as Figure 4 The combination of the optical structure 42 and the optical structure 44 shown in FIG. Figure 3E The optical structure is the same as in Figure 3F The profile of the optical structure 27 shown in varies along a vertical axis, rather than at an angle to said axis. However, two discontinuities 38a and 38b separate two regions 39a and 39b of the profile of the optical structure 27. The first region 39a is higher than the second region 39b, thereby creating a profile variation. This creates a step at the discontinuities 38a, 38b between the two regions. Region 39b has a diamond cross-sectional shape with four sides, while region 39a has a cross-sectional shape with 10 sides. Discontinuities 38a, 38b are at right angles to each other in the cross-sectional plane and each extends from a different side of the optical structure 27 to intersect at a center point 41 of the optical structure 27. The physical extent of the optical structure 27 perpendicular to the plane of the waveguide can be considered to be its height. The height of the step 38 is half the height of the optical structure. The optical structure 27 can be considered to be Figure 3E A modified stepped version of the optical structure 25 shown in FIG.

[0060] FIG. 3B to FIG. 3F Each of the optical structures shown in can be used as Figure 1B , but provides preferential outcoupling in transmission or reflection so that it comes primarily from the first major surface 5 or the second major surface 7 of the waveguide.

[0061] Figure 4 An example output grating 4 is shown which is configured to ensure that the reflected order is preferentially coupled out of the waveguide (compared to the transmitted order). Light from the input grating 2 is incident on the output grating 4 along the input light path 8. The input light is initially diffracted from the grating formed by the array of optical structures at position 40a. This is as described with respect to FIG. 1. At this position 40a, the optical structure has Figure 3E as shown, or with a profile such as Figure 3F This produces turning stages 10a and 10b as described with respect to Figure 1. However, the outcoupled order produced when the input light interacts with the array of optical structures at position 40a is preferentially a reflected order, while the transmitted order is suppressed.

[0062] Light from the steering stage 10b is incident on the grating provided by the array of optical structures at position 40b. The profile of the optical structures 42 at position 40b is Figure 4 The optical structure 42 has a structure similar to Figure 3C . However, optical structure 42 has a profile that varies in the same direction as turning stage 10b. This is at an angle of -60° to the input direction. At position 40b, light from turning stage 10b is incident toward the side of optical structure 42 that extends the furthest in a plane perpendicular to the waveguide (i.e., the highest side or the side with the largest physical extent perpendicular to the waveguide plane) that extends the furthest in a plane perpendicular to the waveguide (i.e., when using Figure 4 Since the array of optical structures 42 at the position 40b has this profile, the outcoupling level from the optical structures 42 at the position 40b is preferentially the reflection level 52, while the transmission level is suppressed.

[0063] Light from the steering stage 10a is incident on the grating provided by the array of optical structures at position 40c. The profile of the optical structure 44 at this position is as follows: Figure 4 The optical structure 44 has the same Figure 3C 24. The optical structure 44 has a stepped profile similar to that of the optical structure 24 shown. However, the optical structure 44 has a profile that varies in the same direction as that of the steering stage 10a. This is at an angle of +60° to the input direction. At position 40c, the light from the steering stage 10a is incident toward the side of the optical structure 44 that extends the farthest in the plane perpendicular to the waveguide (i.e., the highest side or the side with the largest physical extent perpendicular to the waveguide plane). Since the array of optical structures 44 at position 40c has this profile, the outcoupling level from the optical structure 44 at position 40c is preferentially the reflection level 54, while the transmission level is suppressed.

[0064] The plane of the waveguide is defined by the xy plane, such that Figure 1A and Figure 4 As shown. Figure 4 When viewing the waveguide plane shown, all optical structures arranged to the left of the output grating relative to the input direction are the optical structures shown in inset (a). These are all optical structures in the -x direction relative to the input direction.

[0065] In addition, all optical structures arranged on the right side of the output grating relative to the input direction are optical structures as shown in inset (b). These are all optical structures in the +x direction relative to the input direction.

[0066] Any optical structure located in the input direction has Figure 3E or Figure 3FThe optical structure shown is described in profile.

[0067] although Figure 4 The shapes of the optical structures in inset (a) and inset (b) are shown, showing the change in profile, but in Figure 4 The actual shape of the optical structure in the waveguide plane is not shown on the output grating 4 in FIG. Figure 5 The shape of the optical structure in the waveguide plane is shown in FIG. Figure 5 It can be seen that each of the optical structures 42, 44, and 25 has a notched diamond shape when viewed from top to bottom in the xy plane. Figure 5 Only a single optical structure in each position 40a, 40b, 40c is actually shown in FIG, but in each position there will be an array of optical structures offset from each other, each having the same shape in that position of the waveguide. The discontinuities 28 indicating the positions of the steps can also be clearly seen on the optical structures 42 and 44, which are oriented as described above with respect to Figure 4 discussed.

[0068] In an alternative arrangement where only the transmission level is desired, the profile of each optical structure may be in accordance with Figure 4 For example, optical structure 40b and optical structure 40c can increase in height or physical extent in a direction perpendicular to the plane from the point at which light is incident toward the optical structure. This is also true for optical structures placed along the input direction.

[0069] It has been found that for an output grating with uniform profile for each optical structure, the average reflected brightness is 203 nits / L and the average transmitted brightness is 141 nits / L. This provides a reflected brightness to transmitted brightness ratio of 1.45. This has a Figure 3A The optical structure 20 is shown.

[0070] It has been found that for each optical structure profile such as Figure 4 The output grating of the variation shown has an average reflected brightness of 330 nits / L and an average transmitted brightness of 110 nits / L. This provides a reflected brightness to transmitted brightness ratio of 3.00.

[0071] These results show that using optical structures with varying profiles in the output grating can be used to preferentially diffract light in the direction towards the viewer, reducing unwanted diffraction in the opposite direction. It can be seen that using these structures (which can be referred to as pseudo-blaze structures) increases the brightness at the eye by 60%.

[0072] As discussed above, it will be appreciated that by directing the changes in profile in an opposite manner, a transmissive level may be preferentially selected over a transmissive level.

[0073] Having described aspects of the present disclosure in detail, it is apparent that modifications and variations are possible without departing from the scope of the present disclosure as defined in the appended claims. As various changes may be made to the above-described constructions, products, and methods without departing from the scope of the present disclosure, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not limiting.

[0074] The above optical structures can be 3D nanostructured elements or pillars, and the change in profile can be considered as a change in the height of the nanostructure or its physical extent perpendicular to the waveguide plane. Therefore, the height or physical extent of the nanostructure perpendicular to the waveguide plane can be varied. In other arrangements, the optical structure can be provided by a layer of operating surfaces in the waveguide having a refractive index. The profile of these surfaces (i.e., the position in a direction perpendicular to the plane of the waveguide) can be varied in the above manner.

[0075] In the embodiments shown above, the optical structures arranged along the input direction 8 are described as having a profile that varies in the same direction as the input direction. However, in other arrangements, the profile of such structures may be uniform (ie without glare), for example Figure 3A The optical structure 20 is shown. In other arrangements, only the first optical structure in the input direction may have this profile.

[0076] In other arrangements, the optical structure along the input direction may have Figure 4 The profile of the optical structure shown in inset (a) and / or inset (b). This is because the width of this very central line can be very small, for example about 0.5 μm wide. Therefore, the profile of the optical structure along this center line can have a minimal impact on the directionality of the overall image.

[0077] exist Figure 3C , Figure 3D and Figure 3F In the examples shown, the optical structure may have a stepped profile. The number of steps is not limited to the examples shown in these figures. For example, the number of steps may be 1, 2, 3, 4, 5 or more steps.

Claims

1. A waveguide for an augmented reality or virtual reality display, comprising: an output diffractive element comprising a plurality of optical structures in a photonic crystal; a first major surface of the waveguide and a second major surface of the waveguide, the first major surface being separated from the second major surface in a direction perpendicular to the plane of the waveguide, wherein light propagates along the waveguide to the output diffractive element and diffracts into a plurality of out-coupling orders when the light is incident on the output diffractive element; Wherein, at least one of the plurality of optical structures has a profile in the direction perpendicular to the plane of the waveguide, wherein the profile varies along one or more directions parallel to the plane of the waveguide such that the plurality of outcoupling levels are preferentially provided from the first major surface of the waveguide as compared to the second major surface of the waveguide.

2. The waveguide according to claim 1, wherein The profile of at least one optical structure of the plurality of optical structures varies continuously along the one or more directions parallel to the plane of the waveguide.

3. The waveguide according to claim 1, wherein The profile of at least one optical structure of the plurality of optical structures has at least one discontinuity.

4. The waveguide according to any one of claims 1 to 3, wherein: The profile variation of each optical structure in the plurality of optical structures varies on the output diffraction element, so that the optical structures at different regions of the output diffraction element have profile variations that are different from each other.

5. The waveguide according to claim 4, wherein: The plurality of optical structures are configured to receive light from an input direction, the input direction defining a first axis in the plane of the waveguide, and the one or more directions in which the optical structures vary in profile are angled with respect to the input direction.

6. The waveguide according to claim 5, wherein The direction in which the optical structure on the first side of the first axis varies in profile is at a first angle to the input direction, and the direction in which the optical structure on the second side of the first axis varies in profile is at a second angle to the input direction, wherein the first side of the first axis and the second side of the first axis are separated in the plane of the waveguide by a line formed along the input direction, the input direction extending from a point at which light is incident on the output diffraction element.

7. The waveguide according to any one of claims 1 to 3, wherein: At least one optical structure of the plurality of optical structures is arranged such that the profile of the at least one optical structure has a gradient in a direction away from a point at which light is incident on the at least one optical structure.

8. The waveguide according to any one of claims 1 to 3, comprising an input diffractive optical element separate from the output diffractive optical element, the input diffractive optical element being configured to provide light to the plurality of optical structures along an input direction.

9. An augmented reality or virtual reality display comprising a waveguide according to any one of claims 1 to 3.

10. A method of manufacturing a waveguide for an augmented reality or virtual reality display, the method comprising: providing an output diffractive element comprising a plurality of optical structures in a photonic crystal; as well as Arranging the plurality of optical structures, wherein the waveguide comprises: a first major surface of the waveguide and a second major surface of the waveguide, the first major surface being separated from the second major surface in a direction perpendicular to the plane of the waveguide, wherein light propagates along the waveguide to the output diffraction element and diffracts into a plurality of out-coupling orders when the light is incident on the output diffraction element; and Wherein, at least one of the plurality of optical structures has a profile in the direction perpendicular to the plane of the waveguide, wherein the profile varies along one or more directions parallel to the plane of the waveguide such that the outcoupling level is preferentially provided from the first major surface of the waveguide as compared to the second major surface of the waveguide.

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