DISPLAY FOR AUGMENTED REALITY OR VIRTUAL REALITY

Abstract

An AR or VR display device. First and third input gratings receive light of a first color from first and second projectors, respectively, coupling the light into a first waveguide.Second and fourth input gratings receive light of a second color from the first and second projectors, respectively, coupling the light into a second waveguide.An output diffractive optical element couples light out of the waveguides towards a viewing position.The first and second projectors provide light to the input diffractive optical elements in directions that are at a first and second angle, respectively, to a waveguide normal vector.The output diffractive optical element couples light out of the waveguides in a first range of angles for light from the first projector and in a second range of angles for light from the second projector, the first range of angles and the second range of angles differing but partially overlapping.

Claims

1. A display device, comprising: a waveguide assembly comprising at least one waveguide defining a plane; an output diffractive optical element positioned in or on the waveguide assembly parallel to the waveguide plane; first and second input diffractive optical elements positioned in or on the waveguide assembly parallel to the waveguide plane, the first input diffractive optical element being positioned in a first region on a first side of the output diffractive optical element, the second input diffractive optical element being positioned in a second region on a second side of the output diffractive optical element opposite the first side, the first input diffractive optical element configured to couple light into the at least one waveguide in a first propagation direction toward the output diffractive optical element, and the second input diffractive optical element configured to couple light into the at least one waveguide in a second propagation direction toward the output diffractive optical element opposite to the first propagation direction; a first light source positioned in the first region to project first light toward the first input diffractive optical element; a second light source positioned in the first region; and a periscope to receive second light in the first region from the second light source and direct the received second light toward the second input diffractive optical element in the second region.

2. The display device of claim 1, wherein: the first input diffractive optical element receives the first light from a first direction that is at a first angle to a waveguide normal vector; the second input diffractive optical element receives the second light from a second direction that is at a second angle to the waveguide normal vector; and the first and second angles are angled respectively away from the output diffractive optical element.

3. The display device of claim 1, wherein: the output diffractive optical element is configured to couple the first light and second light out of the at least one waveguide toward a notional viewing position.

4. The display device of claim 1, wherein: the output diffractive optical element is configured to couple the first light out of the at least one waveguide in a first range of angles and to couple the second light out of the at least one waveguide in a second range of angles, wherein the first range of angles and the second range of angles are different.

5. The display device of claim 4, wherein: the first range of angles and the second range of angles are partially overlapping.

6. The display device of claim 5, further comprising a third input diffractive optical element positioned in or on the waveguide assembly to receive third light from a third direction and to couple the light into the at least one waveguide; wherein: the output diffractive optical element couples the third light out of the at least one waveguide in a third range of angles; and the third range of angles partially overlaps with one or both of the first range of angles or the second range of angles.

7. The display device of claim 1, wherein: the at least one waveguide comprises a first waveguide and a second waveguide; the first input diffractive optical element couples the first light into the first waveguide; and the second input diffractive optical element couples the second light into the second waveguide.

8. The display device of claim 1, wherein: the at least one waveguide comprises a first stack of waveguides; there is a plurality of first input diffractive optical elements respectively positioned in or on each waveguide in the first stack of waveguides; and the first light comprises a plurality of wavelengths of light which are coupled by the plurality of first input diffractive optical elements into the first stack of waveguides.

9. The display device of claim 8, wherein: the at least one waveguide further comprises a second stack of waveguides; there is a plurality of second input diffractive optical elements respectively positioned in or on each waveguide in the second stack of waveguides; and the second light comprises a plurality of wavelengths of light which are coupled by the plurality of second input diffractive optical elements into the second stack of waveguides.

10. The display device of claim 1, wherein the first and second input diffractive optical elements are positioned above and below the output diffractive optical element from a perspective of a user.

11. The display device of claim 1, wherein the first and second input diffractive optical elements are positioned to left and right sides of the output diffractive optical element from a perspective of a user.

12. The display device of claim 11, further comprising a third input diffractive optical element and a fourth input diffractive optical element, wherein the third and fourth input diffractive optical elements are positioned above and below the output diffractive optical element from the perspective of the user.

13. The display device of claim 1, further comprising a prism to reduce a spread of angles of light rays of the first light where they encounter the waveguide assembly.

14. The display device of claim 1, further comprising a prism to reduce a spread of angles of light rays of the second light where they encounter the waveguide assembly.

15. A method for projecting light via an augmented reality or virtual reality display device, comprising: receiving first light from a first light source in a first region at a first input diffractive optical element positioned in or on a waveguide assembly in the first region; receiving second light from a second light source in the first region at a periscope; directing the received second light, via the periscope, toward a second input diffractive optical element in a second region, the first and second regions being on opposite sides of an output diffractive optical element positioned in or on the waveguide assembly, the first input diffractive optical element, second input diffractive optical element, and output diffractive optical element being parallel to a waveguide plane of at least one waveguide of the waveguide assembly; coupling the first light into the at least one waveguide in a first propagation direction toward the output diffractive optical element; and coupling the second light into the at least one waveguide in a second propagation direction toward the output diffractive optical element opposite to the first propagation direction.

16. The method of claim 15, wherein: the first input diffractive optical element receives the first light from a first direction that is at a first angle to a waveguide normal vector; the second input diffractive optical element receives the second light from a second direction that is at a second angle to the waveguide normal vector; and the first and second angles are angled respectively away from the output diffractive optical element.

17. The method of claim 15, wherein: the output diffractive optical element is configured to couple the first light and second light out of the at least one waveguide toward a notional viewing position.

18. The method of claim 15, wherein: the output diffractive optical element is configured to couple the first light out of the at least one waveguide in a first range of angles and to couple the second light out of the at least one waveguide in a second range of angles, wherein the first range of angles and the second range of angles are different.

19. The method of claim 18, wherein: the first range of angles and the second range of angles are partially overlapping.

20. A waveguide assembly, comprising: at least one waveguide defining a plane; an output diffractive optical element positioned parallel to the waveguide plane; first and second input diffractive optical elements positioned parallel to the waveguide plane, the first input diffractive optical element being positioned in a first region on a first side of the output diffractive optical element, the second input diffractive optical element being positioned in a second region on a second side of the output diffractive optical element opposite the first side, the first input diffractive optical element configured to couple light into the at least one waveguide in a first propagation direction toward the output diffractive optical element, and the second input diffractive optical element configured to couple light into the at least one waveguide in a second propagation direction toward the output diffractive optical element opposite to the first propagation direction; and a periscope to receive light from a light source in the first region and direct the received light toward the second input diffractive optical element in the second region.

Description

[0025] Embodiments of the invention are now described, by way of example, with reference to the drawings, in which:

[0026] FIG. 1 is a schematic side view of an optical set up in an augmented reality display in an embodiment of the invention;

[0027] FIG. 2A is a diagram showing the angular field of view for light emanating from the first projector shown in FIG. 1;

[0028] FIG. 2B is a diagram showing the angular field of view for light emanating from the second projector shown in FIG. 1;

[0029] FIG. 2C is a diagram showing the angular field of view for light emanating from the third projector shown in FIG. 1;

[0030] FIG. 3 is a schematic side view of an optical set up in an augmented reality display in another embodiment of the invention;

[0031] FIG. 4A is a diagram showing the angular field of view for light emanating from the first projector shown in FIG. 3;

[0032] FIG. 4B is a diagram showing the angular field of view for light emanating from the second projector shown in FIG. 3;

[0033] FIG. 4C is a diagram showing the angular field of view for light emanating from the third projector shown in FIG. 3;

[0034] FIG. 5 is a schematic side view of an optical set up in an augmented reality display in another embodiment of the invention;

[0035] FIG. 6 is a schematic side view of an optical set up in an augmented reality display in another embodiment of the invention;

[0036] FIG. 7A is a diagram showing the angular field of view for light emanating from the first projector shown in FIG. 6;

[0037] FIG. 7B is a diagram showing the angular field of view for light emanating from the second projector shown in FIG. 6;

[0038] FIG. 8 is a schematic side view of an optical set up in an augmented reality display in another embodiment of the invention;

[0039] FIG. 9A is a diagram showing the angular field of view for light emanating from the first projector shown in FIG. 8;

[0040] FIG. 9B is a diagram showing the angular field of view for light emanating from the second projector shown in FIG. 8;

[0041] FIG. 10 is a schematic diagram showing where the first and second projectors depicted in FIG. 8 can be positioned with respect to a users head;

[0042] FIG. 11 is a schematic side view of an optical set up in an augmented reality display in another embodiment of the invention;

[0043] FIG. 12 is a diagram showing the angular fields of view for light emanating from the first, second, third and fourth projectors shown in FIG. 11;

[0044] FIG. 13 is a schematic diagram showing where the first, second, third and fourth projectors depicted in FIG. 11 can be positioned with respect to a users head;

[0045] FIG. 14A is a side view of a waveguide in one arrangement; and

[0046] FIG. 14B is a side view of a waveguide in another configuration in an embodiment of the invention.

[0047] FIG. 1 is a schematic side view of an optical set up in an augmented reality display. The display comprises a first input projector 2 and a first waveguide stack 4. The display also includes a second input projector 12, a second waveguide stack 14, a third input projector 22 and a third waveguide stack 24.

[0048] The first waveguide stack 4 includes an input grating 6 and an output structure 8, which may be a photonic crystal or crossed gratings, as described in WO2016/020643. As such, the output structure 8 can receive light that is totally internally reflected within the waveguide and can provide two-dimensional expansion while simultaneously outcoupling light from the waveguide so that it can be viewed by a user.

[0049] The second waveguide stack 14 also includes an input grating 16 and an output structure 18, and the third waveguide stack 24 includes an input grating 26 and an output structure 28. The first, second and third waveguide stacks 4, 14, 24 have surface normal vectors, n.sub.1, n.sub.2, n.sub.3 which are parallel to one another, but which are offset from one another at the location of the respective input gratings 6, 16, 26.

[0050] The first projector 2 is configured so that its projected beam of light subtends an angle a.sub.1 to the waveguide normal vector, n.sub.1. The angle a.sub.1 is within the range of 5-25 degrees, measured in a counter-clockwise direction from the waveguide normal vector, n.sub.1. Using different terminology, the angle a.sub.1 may be expressed as a negative angle in the range from -25 degrees to -5 degrees. The input grating 6 receives and diffracts light from the first projector 2. The diffracted light travels within the first waveguide stack 4 by total internal reflection towards the output structure 8. Light is coupled out of the first waveguide stack 4 by the output structure 8 in order to provide augmented reality or virtual reality images. The output structure 8 provides augmented reality images within a first range of angles.

[0051] FIG. 2A is a diagram showing the first range of angles 7 which are provided from the output structure 8 in the first waveguide stack 4. The users complete field of view is shown as a rectangle 9 with a vertical range of 48 degrees and a horizontal range of 75 degrees. From a practical perspective, this represents the effective range of a humans visible field of view, without turning their head. The first range of angles 7 is provided towards the left of the visible field of view, with a vertical angular range of 24 degrees and a horizontal angular range between around -37 degrees and -5 degrees. In this way, the first projector 2 can position augmented reality images within the first range of angles 7, which are provided towards the left hand side of the users field of view 9.

[0052] The second projector 12 is configured to direct its projected beam of light in a direction that is substantially parallel to the waveguide normal vector, n.sub.2. In other words, the angle between the beam and the waveguide normal vector, n.sub.2, is approximately 0 degrees. The input grating 16 receives and diffracts light from the second projector 12. The diffracted light travels within the second waveguide stack 14 by total internal reflection towards the output structure 18. Light is coupled out of the second waveguide stack 14 by the output structure 18 in order to provide augmented reality or virtual reality images.

[0053] FIG. 2B is a diagram showing the second range of angles 17 which are provided from the output structure 18 in the second waveguide stack 14. The second range of angles 17 is provided centrally within the users field of view, with a vertical angular range of 24 degrees and a horizontal angular range between around 16 degrees.

[0054] The second range of angles 17 is therefore partially overlapping with the first range of angles 7 between -5 degrees and -16 degrees.

[0055] The third projector 22 is configured to direct light so that the beam of light from the third projector subtends an angle a.sub.3 to the waveguide normal vector, n.sub.3. The angle a.sub.3 is within the range of 5-25 degrees, measured in a clockwise direction from the waveguide normal vector. The input grating 26 receives and diffracts light from the third projector 22. The diffracted light travels within the third waveguide stack 24 by total internal reflection towards the output structure 28. Light is coupled out of the third waveguide stack 24 by the output structure 28 in order to provide augmented reality or virtual reality images.

[0056] FIG. 2C is a diagram showing the third range of angles 27 which are provided from the output structure 28 in the third waveguide stack 24. The third range of angles 27 is provided to the right of the users field of view. The third range of angles 27 has a reduced horizontal and vertical range in comparison to the first and second ranges of angles 7, 17 due to the fact that the third projector 22 is angled to project light toward the third output structure 28, rather than away from it (as is the case with the first projector 2). The third range of angles 27 is partially overlapping with the second range of angles 17. It should be noted, however, that the third range of angles 27 and the first range of angles 7 are non-overlapping.

[0057] Each of the first, second and third waveguide stacks 4, 14, 24 respectively comprise three separate waveguides for respective primary colours. Taking the first waveguide stack 4 as an example, a full colour display can be provided by using three distinct waveguides in a stack, each waveguide made of high index (n~1.7) glass. Each waveguide in the stack is similar in structure, and each waveguide includes an input grating 6 and an output structure 8. However, the properties of the respective input gratings 6 and output structures 8 are different in the different waveguide layers. In a first waveguide layer (not shown) the input grating 6 and the output structures 8 are provided with a pitch of between 240nm and 300nm. In a second waveguide layer (not shown) the input grating 6 and the output structures 8 are provided with a pitch of between 280nm to 360nm. In a third waveguide layer (not shown) the input grating 6 and the output structures 8 are provided with a pitch of between 330nm and 420nm. The pitch of a grating corresponds to the separation of diffractive features. This corresponds to the separation of grooves in the input grating.

[0058] The first projector 2 directs polychromatic light towards the first waveguide stack 4. The first layer in the first waveguide stack 4 preferentially diffracts red wavelengths of light and couples these red wavelengths into the first layer. Green and blue wavelengths are generally transmitted by the first layer in the waveguide stack 4. The input grating in the second layer in the first waveguide stack preferentially diffracts green light so that these wavelengths can be coupled into the second layer. Blue wavelengths are transmitted and are preferentially coupled into the third layer of the waveguide stack 4 by an input grating that is optimised for blue light. Each waveguide layer has an output element 8 with a grating pitch that is optimised to couple the relevant wavelength out of the waveguide layer and towards a user. In this way, each waveguide layer can be optimised for blue, green and red respectively so that, collectively, a full colour output can be provided.

[0059] FIG. 3 is a schematic side view of an optical set up in another configuration for use in an augmented reality display. In this arrangement there are only two waveguide stacks: a first waveguide stack 104 and a second waveguide stack 114. The first and second projectors 102, 112 are positioned in a substantially similar manner to the arrangement depicted in FIG. 1. However, in this configuration the third projector 122 is directed towards an input grating 126 that is positioned in or on the first waveguide stack 104. The input grating 126 is positioned on the opposite side of the output structure 108 to the input grating 106 that receives light from the first projector 102.

[0060] The third projector 122 is configured to direct light so that the beam of light subtends an angle a.sub.3 to the waveguide normal vector, n.sub.3. The angle a.sub.3 is within the range of 5- 25 degrees, measured in a clockwise direction from the waveguide normal vector. However, unlike the embodiment shown in FIG. 1, the third projector 122 is angled away from the output structure 108 (whereas it is angled towards the output structure 28 in the arrangement of FIG. 1). The input grating 126 receives and diffracts light from the third projector 122. The diffracted light travels within the first waveguide stack 104 towards the output structure 108. Light is coupled out of the first waveguide stack 104 by the output structure 108 in order to provide augmented reality or virtual reality images. Thus, the output structure 108 couples light towards a user from the first projector 102 and the third projector 122. The configuration is chosen so that light from the first and third projectors 102, 122 does not interact with the input grating 106, 126 for the other projector as this would create undesirable image features.

[0061] FIG. 4A is a diagram showing the first range of angles 7 which are provided from the output structure 108 in the first waveguide stack 104, and which are formed of light emitted by the first projector 102. Like FIG. 2A, the first range of angles 7 is provided towards the left of the visible field of view, with a vertical angular range of 24 degrees and a horizontal angular range between around -37 degrees and -5 degrees.

[0062] FIG. 4B is a diagram showing the second range of angles 17 which are provided from the output structure 118 in the second waveguide stack 104. The second range of angles 17 is provided centrally within the users field of view 109, with a vertical angular range of 24 degrees and a horizontal angular range between around 16 degrees. The second range of angles 17 is therefore partially overlapping with the first range of angles 7 between -5 degrees and -16 degrees.

[0063] FIG. 4C is a diagram showing the third range of angles 27 which are provided from the output structure 108 in the first waveguide stack 104, and which are formed of light emitted by the third projector 122. The third range of angles 27 is provided to the right of the users field of view. The vertical angular range of 24 degrees and the horizontal angular range is between around +5 to +37 degrees. The third range of angles 27 is therefore partially overlapping with the second range of angles 17 between +5 degrees and +16 degrees.

[0064] The third range of angles 27 in FIG. 4C is larger, both in horizontal and vertical extent, than the third range of angles 27 in FIG. 2C. This effect is created because the third projector 122 is angled away from the output structure 108 in FIG. 3, whereas the third projector 22 is angled towards the output structure 28 in FIG. 1.

[0065] A potential difficulty arises with the arrangement depicted in FIG. 3 when it is implemented in an augmented reality headset. This issue arises because the output structures 108, 118 must be positioned in front of a users eyes, which means that the first and second projectors 102, 112 can be positioned to the side of a users head, whereas the third projector 122 must be positioned towards the bridge of a users nose. This may create challenges in some circumstances because it means that electrical components need to be positioned in more than one location which can increase obscuration of a users face and potentially increase the number of positions in which electrical components can interfere with a users peripheral vision. FIG. 5 is a schematic side view of an optical set up in another configuration for use in an augmented reality display, and which is designed to mitigate some of these issues.

[0066] In the arrangement in FIG. 5 there are two waveguide stacks: a first waveguide stack 204 and a second waveguide stack 214. The first and second projectors 202, 212 are positioned in a substantially similar manner to the arrangements depicted in FIGS. 1 and 3. The third projector 222 is directed towards a periscope 230 having reflective surfaces oriented so that light is coupled out of the periscope 230 in the same direction as it is coupled in. The third projector 222 is oriented to project light in a direction that is orthogonal to an angled input surface 232 of the periscope 230. Light from the third projector 222 is then totally internally reflected within the periscope 230 until it encounters an angled reflective surface 234 that couples the light out of the periscope and towards an input grating 226 in or on the first waveguide stack 204. Light is coupled from the periscope 230 towards the input grating 226 so that the beam of light subtends an angle a.sub.3 to the waveguide normal vector, n.sub.3. The angle a.sub.3 is within the range of 5-25 degrees, measured in a clockwise direction from the waveguide normal vector. Like the embodiment shown in FIG. 3, the light directed towards the input grating 226 (from the reflective surface 234 in the periscope 230) is angled away from the output structure 208.

[0067] FIGS. 4A-C show the first, second and third range of angles 107, 117, 127 which are provided from the output structures 208, 218, and which are formed respectively of light emitted by the first, second and third projectors 202, 212, 222. In this way, the range of angles output from the optical arrangement in FIG. 5 is the same as the range of angles output from the optical arrangement in FIG. 3. However, in the FIG. 5 configuration all of the projectors 202, 212, 222 can be grouped in a similar position, to one side of the output structures 208, 218. In an augmented reality device this is important because it can allow all of the light engines to be provided to one side of the headset, to the side of a users head adjacent their temple where space for these components is available.

[0068] FIG. 6 is a schematic side view of an optical set up in another configuration for use in an augmented reality display. In this arrangement there is only one waveguide stack, referred to as a first waveguide stack 304.

[0069] A first projector 302 is configured to direct light so that the beam of light from the first projector subtends an angle a.sub.1 to the waveguide normal vector, n.sub.1. The angle a.sub.1 is within the range of 5-25 degrees, measured in a counter-clockwise direction from the waveguide normal vector, n.sub.1. Using different terminology, the angle a.sub.1 may be expressed as a negative angle in the range from -25 degrees to -5 degrees. The input grating 306 receives and diffracts light from the first projector 302. The diffracted light travels within the first waveguide stack 304 by total internal reflection towards the output structure 308. Light is coupled out of the first waveguide stack 304 by the output structure 308 in order to provide augmented reality or virtual reality images.

[0070] The output structure 308 provides augmented reality images within a first range of angles for light that has originated with the first projector 302.

[0071] FIG. 7A is a diagram showing the first range of angles 307 which are provided from the output structure 308 in the first waveguide stack 304 for light emanating from the first projector 302. The first range of angles 307 is provided towards the left of the visible field of view, with a vertical angular range of 24 degrees and a horizontal angular range between around -38 degrees to +1 degrees. In this way, the first projector 302 can position augmented reality images within the first range of angles 307, which are provided towards the left hand side of the users field of view 309.

[0072] The second projector 312 is directed towards a periscope 330 having reflective surfaces oriented so that light is coupled out of the periscope 330 in the same direction as it is coupled in. Light is coupled from the periscope 330 towards the input grating 316 so that the beam of light subtends an angle a.sub.2 to the waveguide normal vector, n.sub.2. The angle a.sub.2 is within the range of 5-25 degrees, measured in a clockwise direction from the waveguide normal vector. Like the embodiment shown in FIGS. 3 and 5, the light directed towards the input grating 316 (from the reflective surface 234 in the periscope 230) is angled away from the output structure 308.

[0073] FIG. 7B is a diagram showing the second range of angles 317 which are provided from the output structure 308 in the first waveguide stack 304 for light emanating from the second projector 312. The second range of angles 317 is provided towards the right of the visible field of view, with a vertical angular range of 24 degrees and a horizontal angular range between around -1 degrees to +38 degrees. In this way, the second projector 312 can position augmented reality images within the first range of angles 317, which are provided towards the right hand side of the users field of view 309. The first range of angles 307 and the second range of angles are partially overlapping, and an overlap region is provided between 1 degrees. In this way, it is possible to stitch together the first and second ranges of angles to provide augmented reality images within 38 degrees horizontally and 24 degrees vertically, which represents a large extent of a users field of view. In the arrangement of FIG. 6 this can be achieved using a single waveguide stack, which offers advantages in terms of thickness of display and weight.

[0074] FIG. 8 is a schematic side view of an optical set up in another configuration for use in an augmented reality display. This arrangement demonstrates how augmented reality images can be stitched together to enhance the effective vertical field of view. A first projector 402 is oriented away from an output structure 408 to project light towards an input grating 406. The light beam from the first projector 402 subtends an angle a.sub.1 to the waveguide normal vector, n.sub.1. The angle a.sub.1 is within the range of 5-25 degrees, measured in a counter-clockwise direction from the waveguide normal vector, n.sub.1.

[0075] The output structure 408 provides augmented reality images within a first range of angles 407 for light that has originated with the first projector 402. FIG. 9A is a diagram showing the first range of angles 407 which are provided from the output structure 408 in the first waveguide stack 404 for light emanating from the first projector 402. The first range of angles 407 is provided towards the lower portion of the visible field of view, with a horizontal range of 24 degrees and a vertical angular range from +1 degrees to -26 degrees. In this way, the first projector 402 can position augmented reality images within the first range of angles 407, which are provided in the lower portion of the users field of view 409.

[0076] A second projector 412 is also oriented away from the output structure 408 to project light towards an input grating 416. The input grating 416 is located on the opposite side of the output structure 408 to the input grating 406 for the first projector 402. The light beam from the second projector 412 subtends an angle a.sub.2 to the waveguide normal vector, n.sub.2. The angle a.sub.1 is within the range of 5-25 degrees.

[0077] The output structure 408 provides augmented reality images within a second range of angles 417 for light that has originated with the second projector 412. FIG. 9B is a diagram showing the second range of angles 417 which are provided from the output structure 408 in the first waveguide stack 404 for light emanating from the second projector 412. The second range of angles 417 is provided towards the upper portion of the visible field of view, with a horizontal range of 24 degrees and a vertical angular range from -1 degrees to +26 degrees. In this way, the first projector 402 can position augmented reality images within the second range of angles 417, which are provided in the upper portion of the users field of view 409. The first and second ranges of angles 407, 417 are partially overlapping in the region between 1 degrees vertically. This can allow the two angular ranges to be stitched together, providing an increased field of view for a user.

[0078] FIG. 10 is a schematic diagram showing where the first and second projectors 402, 412 can be positioned with respect to a users head. The first projector 402 can be positioned above a users eye, adjacent their brow. The second projector 412 can be positioned below the users eye, adjacent their cheek.

[0079] FIG. 11 is a schematic side view of an optical set up in another configuration for use in an augmented reality display. This arrangement demonstrates how augmented reality images can be stitched together to enhance the effective vertical and horizontal fields of view. In this arrangement first and second projectors 502, 512 are configured with respect to a first waveguide stack 504 in the manner described above, with reference to FIG. 8. With reference to FIG. 12, this provides a first range of angles 507 positioned in the lower portion of a users field of view, and a second range of angles 517, partially overlapping with the first range of angles 507, positioned in the upper portion of the users field of view.

[0080] In addition, the arrangement in FIG. 11 includes a third projector 522 and a fourth projector 550. The third projector 522 is directed towards an input grating 526 in a second waveguide stack 514. Light from the third projector 522 is diffracted by the input grating 526 and totally internally reflected within the second waveguide stack 514 to an output structure 518 which couples light out of the second waveguide stack 514 in a third range of angles 527. The third projector is angled in order to provide the third range of angles 527 towards the left of the users field of view, and partially overlapping with the first and second ranges of angles 507, 517. This can be achieved in a number of ways, as described above. For example, it may be accomplished using a third projector 522 configured similarly to the first projector 302 in FIG. 6.

[0081] The fourth projector 550 is directed towards an input grating 536 in a third waveguide stack 524. Light from the fourth projector 550 is diffracted by the input grating 536 and totally internally reflected within the third waveguide stack 524 to an output structure 528 which couples light out of the third waveguide stack 524 in a fourth range of angles 557. The fourth projector 550 is angled in order to provide the fourth range of angles 557 towards the right of the users field of view, and partially overlapping with the first and second ranges of angles 507, 517. This can be achieved in a number of ways, as described above. For example, it may be accomplished using a fourth projector 550 configured similarly to the second projector 312 in FIG. 6.

[0082] As can be appreciated from FIG. 12, the first, second, third and fourth ranges of angles 507, 517, 527, 557 can therefore be stitched together in order to create an effective field of view for augmented reality images between 24 degrees vertically and 49 degrees horizontally.

[0083] FIG. 13 is a schematic diagram showing where the first, second, third and fourth projectors 502, 512, 522, 550 can be positioned with respect to a users head. The first projector 502 can be positioned above a users eye, adjacent their brow. The second projector 512 can be positioned below the users eye, adjacent their cheek. The third and fourth projectors 522, 550 can be positioned to the side of a users head.

[0084] FIG. 14A is a side view of a waveguide 600 where light is injected into the waveguide at an angle to the surface normal vector. Light is provided to the waveguide 600 so that it can be coupled into the waveguide by an input diffraction grating 602 provided on a rear surface. As shown in FIG. 14A, a spread of angles is provided within a solid angle in the input beam. These light rays are refracted on interaction with the waveguide 600. The spread of refracted angles means that a minimum size is provided for the input diffraction grating 602 so that all of the refracted rays are effectively diffracted. In some configurations the physical size of the input diffraction grating 602 can introduce issues because some of the diffracted rays will re-interact with the input grating, following initial diffraction. This can cause undesirable viewing features.

[0085] FIG. 14B is a side view of the waveguide 600 where a prism 604 is provided between a projector and the waveguide 600. The prism 604 provides an initial refraction of light from the projector, before it encounters the waveguide 600 in order to reduce the spread of angles in the input beam. This can advantageously allow use of an input diffraction grating 606 that has a reduced physical size. This is advantageous because the input diffraction grating 606 can diffract received light so that it does not re-interact with the input diffraction grating 606, but is totally internally reflected within the waveguide 600 for further interaction with another diffractive feature such as an output structure (not shown). A prism like this can be used in any of the embodiments described above in order to reduce the physical size of an input grating and improve quality in an augmented reality image.