Multi-path optical device

Abstract

An optical device for use in an augmented reality display or a virtual reality display, comprising: a waveguide; an input diffractive optical element DOE configured to receive light from the projector and couple the received light into the waveguide along a plurality of optical paths; an output DOE offset relative to the input DOE in a first direction and configured to couple the received light out of the waveguide toward the viewer; a first steering DOE offset with respect to the input DOE in a second direction different from the first direction; wherein the input DOE is configured to couple a first portion of the received light toward the first turning DOE in a second direction, and the first turning DOE is configured to diffract the first portion of the received light toward the output DOE, and the input DOE is configured to couple a second portion of the received light toward the output DOE in the first direction.

Description

Technical Field

[0001] The present disclosure relates to optical devices suitable for use in displays such as augmented reality displays or virtual reality displays. Such optical devices typically include a waveguide and a diffractive optical element for coupling light into and out of the waveguide. Virtual reality displays and augmented reality displays include wearable devices such as glasses, displays for video games, and screens for military or transportation applications. Background Art

[0002] In conventional augmented reality displays, a transparent display screen is placed in front of the user, allowing the user to continue to see the physical world. The display screen can be a glass waveguide, with the projector attached to one surface of the waveguide. For example, the display screen can be placed in a pair of glasses or a vehicle window. Light from the projector is coupled into the waveguide via an input 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, allowing the user to view the light. The projector can provide information and / or images that enhance the user's view of the physical world.

[0003] WO 2016 / 020643 discloses an optical device for expanding input light in two dimensions in an augmented reality display. 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 stacked one above the other in the waveguide, such that each of the two diffractive optical elements can receive light from the input diffractive optical element and couple the light toward the other diffractive optical element of the pair. The other diffractive optical element can then serve as an output diffractive optical element for coupling the light out of the waveguide toward a viewer. In one embodiment, the two stacked diffractive optical elements are arranged in a photonic crystal. This is achieved by having an array of pillars arranged within or on the surface of the waveguide, the array of pillars having an increased refractive index relative to the surrounding waveguide medium. This arrangement has been found to be very effective in simultaneously expanding the light in two dimensions and coupling the light out of the waveguide. Advantageously, this can improve the use of space on the waveguide, which can reduce manufacturing costs.

[0004] WO 2018 / 178626 describes a problem that may arise in an output element having two diffractive optical elements superimposed on each other, wherein a central band in the output image is observed to have a higher relative brightness than the rest of the image, because the waveguide is oriented so that light enters the output element along its centre line and a large portion of the light is diffracted out of the waveguide in a central band around the centre line before being able to spread across the full width of the output element perpendicular to the centre line. Figure 2 Such a central strip 6 is shown in FIG, which will be discussed further below.

[0005] However, the inventors also found that if Figure 3 As shown, in some cases the central band may have a lower brightness. Figure 3 The distribution of the brightness of light refracted out of the waveguide by the output element of the planar waveguide in different angular directions is shown. Figure 3 The example distribution of is produced when light is introduced to the output element from the right. The horizontal axis indicates the horizontal gaze direction θ in degrees. X , and the vertical axis indicates the vertical gaze direction θ in degrees Y The grayscale shading shows brightness from maximum brightness (100, white) to minimum brightness (0, black) - the range of brightness is not particularly limited for the purpose of illustrating the central band. The lower brightness central band may appear because light is less likely to couple out of the waveguide before interacting with both of the superimposed diffractive optical elements that make up the output element, and therefore only a small portion of the light is coupled out of the waveguide near the path it takes to enter the output element.

[0006] When a user views the light output from the waveguide, the higher brightness bands and the lower brightness bands described above may each be visible to the user and may affect the uniformity of an image displayed using the waveguide, thereby reducing the wearer experience.

[0007] Therefore, in addition to or as an alternative to the solution provided in WO 2018 / 178626, it would be desirable to provide a way of mitigating the lower brightness band in the light coupled out of the waveguide towards the viewer.

[0008] This specification corresponds to European patent application EP 22195747.5. The search report of this European patent application identifies US2018 / 0052276 A1 as an earlier publication. US2018 / 0052276 A1 shares a common priority claim with granted European patent EP 3571535 B1. Summary of the Invention

[0009] According to a first aspect, the present invention provides an optical device for use in an augmented reality display or a virtual reality display, the optical device comprising: a waveguide; an input diffractive optical element (DOE) configured to receive light from a projector and couple the received light into the waveguide along multiple optical paths; an output DOE offset relative to the input DOE in a first direction and configured to couple the received light out of the waveguide toward a viewer; a first steering DOE offset relative to the input DOE in a second direction different from the first direction; wherein the input DOE is configured to couple a first portion of the received light toward the output DOE in the first direction, and the input DOE is configured to couple a second portion of the received light toward the first steering DOE in the second direction, and the first steering DOE is configured to diffract the second portion of the received light toward the output DOE.

[0010] The first and second portions of the received light follow different optical paths to the output DOE and produce overlapping patterns of light that are coupled out of the waveguide toward the user's eye. These overlapping patterns can help smooth out any central bands of higher or lower brightness associated with the separate optical paths.

[0011] Preferably, the output DOE is wider in the second direction than the input DOE, and the first steering DOE is configured to diffract a second portion of the received light in the first direction towards the output DOE.

[0012] Preferably, the input DOE comprises a first grating configured to diffract a first portion of the received light in a first direction; and a second grating configured to diffract a second portion of the received light in a second direction.

[0013] Preferably, the first grating or the second grating comprises a blazed grating.For example, the first grating may have a blazed grating configured to efficiently couple light towards the output DOE.

[0014] Preferably, the repeating unit of the input DOE comprises a grid of rectangular elements, each rectangular element having a respective height perpendicular to the plane of the waveguide, wherein at least three of the rectangular elements have different heights. This provides a simple and easily reconfigurable technique for constructing the input DOE.

[0015] More preferably, the grid of rectangular elements includes a first region having a stepped series of rectangular elements, wherein the height of the stepped series of rectangular elements gradually changes (i.e., increases or decreases) in one of a first direction and a second direction. In a preferred embodiment, the first region extends across the length of the repeating unit in one direction, and the height of the stepped series of rectangular elements changes at regular intervals in one direction, such that the input DOE approximates a blazed grating for coupling light in the first direction.

[0016] As an additional preferred option, the grid of rectangular elements includes a second region offset relative to the first region in the other of the first and second directions, wherein the average height of the rectangular elements in the second region is different from the average height of the rectangular elements in the first region. This provides a simple technique for producing a cross grating having two grating vectors.

[0017] Preferably, the input DOE is further configured to couple a third portion of the received light in a third direction different from the first and second directions, the optical device includes a second steering DOE offset relative to the input DOE in the third direction, and the second steering DOE is configured to diffract the third portion of the received light toward the output DOE. Preferably, the third direction is opposite to the second direction. This achieves a symmetrical configuration in which the input DOE and the output DOE share a common central axis.

[0018] The first grating and the second grating may be arranged on the same surface of the waveguide, or on opposite surfaces of the waveguide. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

[0020] Figure 1 is a top view of a known waveguide;

[0021] Figure 2 is another top view of the known waveguide;

[0022] Figure 3 is the brightness graph of the light coupled out of the known waveguide;

[0023] Figure 4 is a top view of a waveguide according to an embodiment;

[0024] Figure 5 is a top view of another waveguide according to an embodiment;

[0025] Figure 6 is a perspective view of two surfaces of a waveguide according to an embodiment;

[0026] Figure 7A and Figure 7B is a diagram of an input diffraction grating for a waveguide according to an embodiment;

[0027] Figure 7C is a diagram of an input diffraction grating for a waveguide according to an embodiment;

[0028] Figures 8A to 8D is a diagram of an input diffraction grating for a waveguide according to an embodiment;

[0029] Figure 8E is an illustration of an input diffraction grating for a waveguide, according to an embodiment. DETAILED DESCRIPTION

[0030] Figure 1 and Figure 2 FIG2 is a top view of a known waveguide 1, serving as an example of a modified waveguide to which the claimed invention may be applied. In the known waveguide, an input diffractive optical element (DOE) 2 (e.g., a diffraction grating) is disposed in or on the surface of waveguide 1 for coupling light from a projector (not shown) into waveguide 1. Waveguide 1 is formed from a material with a defined refractive index, such as glass or plastic. The light coupled into the waveguide travels by total internal reflection toward an output DOE 3, which may comprise, for example, a photonic crystal 4.

[0031] In a typical application, a projector directs at least one beam of image light into an input diffraction grating 2, wherein the image light defines an image pupil that represents a complete image (i.e., contains all angular information defining the image) that can be perceived by an individual if their eyes are properly aligned with the image pupil. A photonic crystal 4 expands the input light in two dimensions within a waveguide and couples the light out of the waveguide, for example as previously described in WO 2016 / 020643 or WO 2018 / 178626.

[0032] The invention can also be applied to other waveguides comprising a diffractive optical element for coupling light out of the waveguide. For example, the invention can be applied to a diffractive optical element comprising a plurality of parallel grating lines, each grating line having a cross section in a plane perpendicular to the lines.

[0033] Reference Figure 2 The output DOE 3 deflects at least a portion of the light coupled into the waveguide from the input DOE 2 so that the light is diffused over a two-dimensional area corresponding to the photonic crystal 4 . Figure 2 Reference numeral 5 in indicates an area not reached by the light coupled within the waveguide, since the light is not diverted that far by the photonic crystal 4 and there is only one path for the light from the input DOE 1 to the output DOE 2 .

[0034] At the same time, it has been discovered that, in some cases, the image diffracted from the output DOE 3 can have a central band 6 that has a lower relative brightness than the rest of the image. This effect arises due to the diffraction efficiency of the diffractive optical structure formed by the array in the photonic crystal 4. Specifically, when the light received from the input DOE 2 encounters the photonic crystal 4, only a relatively small proportion of the light is diffracted directly toward the glasses, rather than first being diffracted and rotated through ±60° in the plane of the waveguide 1. (±60° is only an example configuration, and light can be diffracted and rotated through other angles by other photonic crystals.)

[0035] Figure 3 An example of such a central band with lower brightness is shown. More specifically, Figure 3 is the output from DOE 3 at different angles (θ along the horizontal axis X and θ along the vertical axis Y ) shows the brightness variation of the light output by the waveguide. This corresponds to different positions within the "eye box" of the image visible to the user of the waveguide. The light coupled into the waveguide enters the output DOE 3 at a single entry point on one side from the entry direction indicated by the arrow. Figure 3 As shown, the dark central band 6 extends in a direction parallel to the DOE 3 and away from the entry point of the DOE 3.

[0036] To mitigate the effects of such a dark central band, a waveguide has been proposed in which light enters the output DOE via multiple entry points but from the same direction. This is achieved by guiding the light from the input DOE to the output DOE along multiple paths within the waveguide.

[0037] Figure 4 is a top view of a planar waveguide 100 according to an embodiment.

[0038] like Figure 4 As shown, the waveguide 100 includes a first DOE 101 , a second DOE 102 , and a third DOE 103 .

[0039] For example, each of the first DOE 101, the second DOE 102, and the third DOE 103 may include a diffraction grating and / or a photonic crystal.The first DOE 101, the second DOE 102, and the third DOE 103 may be arranged as surface elements on a waveguide or structures embedded in a waveguide, or a combination of both.

[0040] The first DOE 101 is configured as an input DOE, which is structured and arranged to receive light incident on the waveguide (from Figure 4 The projector (not shown) and couples the received light into the waveguide in at least two directions toward the second DOE 102 and the third DOE 103, respectively.

[0041] The second DOE 102 is configured as a first turning and expanding DOE that is structured and arranged to receive light traveling within the waveguide from the input DOE 101 and diffract the received light within the waveguide toward the output DOE 103 .

[0042] The third DOE 103 is configured as an output DOE that is structured and arranged to couple light out of the waveguide. For example, the third DOE 103 may be similar to Figure 1 and Figure 2 Output of DOE 3.

[0043] The waveguide 100 also includes a bulk substrate adapted to guide light between the first DOE, the second DOE, and the third DOE using total internal reflection. The bulk substrate can be a planar waveguide having a first surface and a second surface. The bulk substrate can be substantially flat. In some embodiments, the bulk substrate can include curved portions between the DOEs. For example, the bulk substrate can be configured to conform to the shape of a surface of eyeglasses. The bulk substrate can also have a substantially uniform thickness. More generally, the shape of the bulk substrate can be reconfigured as long as the bulk substrate guides light between the DOEs as described.

[0044] More specifically, the output DOE 103 is offset in a first direction relative to the input DOE 101. The input DOE 101 is configured to couple a first portion P1 of received light towards the output DOE 103 in the first direction.

[0045] Furthermore, first steering DOE 102 is offset relative to input DOE 101 along a second direction. The second direction is different from the first direction and, for example, may be perpendicular to the first direction within the plane of waveguide 100. Input DOE 101 is configured to couple a second portion P2 of the received light toward first steering DOE 102 in the second direction. First steering DOE 102 is configured to diffract the second portion P2 of the received light toward output DOE 3. Simultaneously, first steering DOE 102 diffractively expands the second portion P2 of the received light along the second direction. In other words, each time the second portion P2 of the received light interacts with first steering DOE 102, a portion of the light is diffracted toward output DOE 103, and the remainder of the light continues in the second direction through total internal reflection until it interacts with first steering DOE 102 again. These multiple interactions with first steering DOE 102 generate multiple portions of light that travel along parallel paths P21, P22, P23, and so on toward output DOE 103, with these paths diverging along the second direction.

[0046] The output DOE 103 receives a first portion P1 of the received light at one entry point and multiple portions diffracted by the first steering DOE 102 at multiple other entry points along a common edge of the DOE 103. Each entry point results in a light beam that is the same as Figure 3 Similar luminance patterns are formed so that each luminance pattern will overlap across the "eyebox" area of ​​the DOE 103, thereby contributing to the image seen by the user. The effect of the overlapping patterns is to reduce or eliminate the visible appearance of the dark central band present for each entry point as described above for each individual luminance pattern, which thereby serves to reduce or mitigate dark band artifacts that might otherwise be perceived when light output from the waveguide is viewed by a user.

[0047] Figure 5 FIG. 1 is a top view of a planar waveguide according to another embodiment. Figure 4 The difference is that the waveguide 100 additionally comprises a further second DOE 104 which is configured as a second steering DOE 102 .

[0048] The second steering DOE 104 is offset relative to the input DOE 101 in a third direction that is different from the first and second directions. The function of the second steering DOE 104 is similar to that of the first steering DOE 102, in that the second steering DOE 104 is configured to receive a third portion P3 of the light from the input DOE 101 and diffract the received light toward the output DOE 103. This can increase the number of entry points for the light guided to the output DOE 103 and thereby further reduce or eliminate the dark center band effect of the combined light output from the waveguide.

[0049] Preferably, the third direction is opposite to the second direction. This configuration has the advantage that the input DOE 101 can use a single linear grating structure or one-dimensional photonic crystal structure to couple light into the waveguide in both the second and third directions toward the first and second steering DOEs. However, in other examples, the input DOE can couple light in a third direction that is independent of the first or second directions, and can even couple light in more than three directions within the waveguide.

[0050] Figure 6 are perspective views of two surfaces of a waveguide according to an embodiment.

[0051] More specifically, in Figure 6 In an embodiment, the waveguide includes a first grating 111 arranged on a first surface 110 and a second grating 121 arranged on a second surface 120. The first grating 111 and the second grating 121 together provide a Figure 4 or Figure 51 and 2. The functionality of the input DOE 101 is described. Preferably, the first grating 111 is a transmission grating configured to diffract light when light is received into the waveguide (e.g., from a projector), and the second grating 121 is a reflection grating configured to reflect light within the waveguide and couple the light into the waveguide.

[0052] In one instance, the first grating 111 is configured to couple a first portion P1 of the received light in a first direction toward an output DOE 123, and the second grating 121 is configured to couple a second portion P2 of the received light in a second direction toward a first steering DOE 122 (and optionally a third portion P3 in a third direction toward a second steering DOE 124).

[0053] Alternatively, the roles of the first and second gratings may be reversed such that the first grating 111 is configured to couple the second portion P2 of the received light in the second direction toward the first steering DOE 122, and the second grating 121 is configured to couple the first portion P1 of the received light in the first direction toward the output DOE 123.

[0054] exist Figure 6 In the example of FIG, the first grating 111 is configured to selectively direct input light in the direction of the output DOE 123 and avoid directing light in directions equal to and opposite to the output DOE 123. For example, the first grating 111 may be a blazed grating. On the other hand, the second grating 121 is configured to direct input light equally in the direction of the first steering DOE 122 and the direction of the second steering DOE 124.

[0055] Alternatively, each of the first grating 111 and the second grating 121 can be configured to direct the input light in any proportional combination of the direction of the output DOE 123, the direction of the first steering DOE 122, and the direction of the second steering DOE 124. For example, each of the first grating 111 and the second grating 121 can be individually similar to Figure 4 or Figure 5 Input DOE101.

[0056] exist Figure 6 In an embodiment, the steering DOEs 122, 124 and the output DOE 123 can each be disposed on the first surface 110 or the second surface 120, or embedded in a waveguide between the surfaces 110, 120. In addition, each of the steering DOEs 122, 124 and the output DOE 123 can be replicated independently on the first surface 110 and the second surface 120.

[0057] Figure 7A and Figure 7Bis a diagram of the input DOE for a waveguide. For example, Figure 7A and Figure 7B The input DOE is applied to Figure 4 or Figure 5 implementation method.

[0058] exist 7A to 7B In an embodiment of the present invention, the input DOE 200 includes a blazed grating configured to direct input light in a first direction (labeled X direction). The blazed grating includes repeating rows 211 extending perpendicular to the first direction (ie, in the Y direction).

[0059] However, each row 211 further comprises regular notches 210 extending perpendicularly to the second direction (denoted Y direction).The regular notches 210 are configured to direct input light in the second direction (and optionally also in a third direction opposite to the second direction).

[0060] In this example, the regular notch 210 is a flat portion where the surface of the bulk waveguide is not modified. However, the regular notch 210 can also be elevated above the bulk waveguide or embedded in the bulk waveguide. In addition, similar to the row 211, the regular notch 210 itself can include a blazed portion configured to guide the input light in a first direction (e.g., as Figure 7C However, the average height of the regular notches 210 is either higher or lower than the average height of the rows 211.

[0061] Figure 7A is a top view of the input DOE 200 in which grayscale is used to indicate the varying heights of the blazed grating rows 211. Figure 7B is a stereogram of the input DOE 200.

[0062] Figures 8A to 8D is an illustration of another input DOE for a waveguide. For example, Figures 8A to 8D The input DOE is applied to Figure 4 or Figure 5 implementation method.

[0063] exist Figures 8A to 8D In an embodiment, DOE 300 ( Figure 8C and Figure 8D ) is a repeating unit comprising 310( Figure 8A Each repeating unit 310 consists of a grid of rectangular elements, each rectangular element having a respective height perpendicular to the plane of the waveguide (the plane defined by the X and Y directions shown). Figure 8A and Figure 8C is a top view of the input DOE 300 , where grayscale is used to indicate the corresponding height. Figure 8B and Figure 8D 3 are perspective views showing the height dimension of the repeating unit 310 and the overall input DOE 300, respectively.

[0064] Reference Figure 8A and Figure 8B In this example, the grid of rectangular elements includes a first region 311, 312, 313 having a stepped series of rectangular elements, wherein the height of the stepped series of rectangular elements decreases from element 313 at one end to element 311 at the other end. The stepped series of rectangular elements approximates a smooth slope. When such a pseudo slope is repeated across multiple repeating units 310 in the positive X direction (e.g., Figure 8C The overall effect is to approximate the repeating ramps of a blazed grating configured to couple light in the positive X direction. This may also be referred to as a pseudo-blazed grating.

[0065] Furthermore, in the repeating unit 310, the grid of rectangular elements includes a second region 314 that is offset relative to the first regions 311, 312, 313 in the Y direction, which is a direction perpendicular to the stepping of the rectangular elements of the first region. The second region 314 has an average height that is different from the average height of the first regions 311, 312, 313. When the unit 310 is repeated in the Y direction to generate the input DOE 300 ( Figure 8C and Figure 8D ), the alternating average heights between the first and second regions provide a linear grating configured to couple light equally in the positive and negative Y directions.

[0066] In this example, the second region 314 is a flat portion where the surface of the bulk waveguide is not modified. However, the second region 314 can also be elevated above the bulk waveguide or embedded in the bulk waveguide. In addition, similar to the first regions 311, 312, 313, the second region 314 itself can include a blazed portion or a pseudo-blazed portion configured to guide the input light in the first direction (e.g., as Figure 8E However, the average height of the second region 314 is higher or lower than the average height of the first regions 311, 312, 313.

[0067] Reference Figures 8A to 8D As an example, a combination of a blazed grating or a pseudo-blazed grating having a grating vector parallel to the X direction and a linear grating having a grating vector parallel to the Y direction provides an input DOE that can couple a first portion of the received light in the positive X direction, a second portion of the light in the positive Y direction, and a third portion of the received light in the negative Y direction. Figure 4 or Figure 5Example of a single grating structure of the input DOE 101 function.

[0068] Furthermore, since the grating having the grating vector parallel to the X direction is blazed or pseudo-blazed, a portion of the light diffracted in the negative X direction is reduced, and therefore, the input DOE can be Figure 5 Couple light more efficiently in three directions.

[0069] The pseudo blaze can be extended to both the X and Y directions by providing an additional step of repeating units in the Y direction. With this configuration, a portion of the light diffracted in the negative Y direction can also be reduced, and the input DOE can be Figure 4 , which couples light more efficiently in both directions. Similarly, blaze can be applied in both directions as a linear combination of one-dimensional blaze in each of the directions. Furthermore, blaze and pseudo-blaze can be combined in both directions using linear combinations.

Claims

1. An optical device for use in an augmented reality display or a virtual reality display, comprising: waveguide; an input diffractive optical element (DOE) configured to receive light from a projector and couple the received light into the waveguide along a plurality of optical paths; an output DOE offset in a first direction relative to the input DOE and configured to couple the received light out of the waveguide toward a viewer; a first steering DOE that is offset relative to the input DOE in a second direction different from the first direction; wherein the input DOE is configured to couple a first portion of the received light in the first direction towards the output DOE, and The input DOE is configured to couple a second portion of the received light in the second direction toward the first steering DOE, and the first steering DOE is configured to diffract a second portion of the received light toward the output DOE.

2. The optical device according to claim 1, wherein The output DOE is wider than the input DOE in the second direction, and the first steering DOE is configured to diffract a second portion of the received light in the first direction toward the output DOE.

3. An optical device according to any one of the preceding claims, wherein: The input DOE includes a first grating configured to diffract a first portion of the received light in the first direction and a second grating configured to diffract a second portion of the received light in the second direction.

4. The optical device according to claim 3, wherein: The first grating or the second grating includes a blazed grating.

5. An optical device according to claim 3 or 4, wherein: The repeating unit of the input DOE comprises a grid of rectangular elements, each rectangular element having a respective height perpendicular to the plane of the waveguide, wherein at least three of the rectangular elements have different heights.

6. The optical device according to claim 5, wherein: The grid of rectangular elements includes a first region having a stepped series of rectangular elements, wherein the height of the stepped series of rectangular elements gradually changes in one of the first direction and the second direction.

7. The optical device according to claim 6, wherein: The first region extends across the length of the repeating unit in the one direction, and the height of the stepped series of rectangular elements varies at regular intervals in the one direction, so that the input DOE approximates a blazed grating for coupling light in the one direction.

8. An optical device according to claim 6 or 7, wherein: The grid of rectangular elements includes a second region offset relative to the first region in the other of the first direction and the second direction, wherein an average height of the rectangular elements in the second region is different from an average height of the rectangular elements in the first region.

9. An optical device according to any one of the preceding claims, wherein: The input DOE is also configured to couple a third portion of the received light in a third direction different from the first direction and the second direction, the optical device includes a second steering DOE offset relative to the input DOE along the third direction, and the second steering DOE is configured to diffract the third portion of the received light toward the output DOE.

10. The optical device according to claim 9, wherein: The third direction is opposite to the second direction.

11. The optical device according to any one of claims 1 to 10, wherein: The first grating and the second grating are arranged on a same surface of the waveguide.

12. An optical device according to any one of claims 1 to 10, wherein: The first grating and the second grating are arranged on opposite surfaces of the waveguide.

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