Waveguide assembly

Abstract

A waveguide assembly is disclosed. The waveguide assembly comprises a first waveguide plate and a second waveguide plate. The first waveguide plate is arranged to receive image-bearing light and to magnify a pupil size of the image-bearing light parallel to a first axis. The first waveguide plate comprises a first in-coupling means arranged to in-couple the image-bearing light into the first waveguide plate under total internal reflection (TIR) and a first out-coupling region arranged to out-couple the image-bearing light from the first waveguide plate by means of reflection. The second waveguide plate is arranged to in-couple at least a portion of the out-coupled image-bearing light from the first waveguide plate into the second waveguide plate and to magnify the pupil size parallel to a second axis, which is substantially orthogonal to the first axis. The second waveguide plate comprises a diffractive in-coupling region and a transmissive diffractive out-coupling region through which a user is able to simultaneously view a real-world image and the out-coupled image-bearing light.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of optical technology, and in particular to a waveguide assembly. BACKGROUND

[0002] For augmented reality applications, it is desirable for the field of view of the display to be large. Due to variations in the physical characteristics of users, it is also desirable for the display to include a large exit pupil to allow for universal fitting of the display and to allow for movement of the user's eye relative to the surface of the display. To reduce the overall size of the optics used to display an image while providing a large FOV and exit pupil, pupil expansion techniques are used. SUMMARY

[0003] In one aspect, the present invention proposes a waveguide assembly. The waveguide assembly comprises: a first waveguide plate arranged to receive image-bearing light and to magnify a pupil size of the image-bearing light parallel to a first axis, the first waveguide plate comprising a first in-coupling means arranged to in-couple image-bearing light into the first waveguide plate under total internal reflection, TIR, and a first out-coupling region arranged to out-couple image-bearing light from the first waveguide plate by means of reflection; a second waveguide plate arranged to in-couple at least a portion of the out-coupled image-bearing light from the first waveguide plate into the second waveguide plate and to magnify the pupil size parallel to a second axis, the second axis being substantially orthogonal to the first axis, the second waveguide plate comprising a diffractive in-coupling region and a transmissive diffractive out-coupling region, through which a user is able to simultaneously view a real-world image and the out-coupled image-bearing light; and a third waveguide plate arranged to in-couple image-bearing light from the first waveguide plate that is not in-coupled into the second waveguide plate into the third waveguide plate under TIR, the third waveguide plate comprising a transmissive diffractive out-coupling region, through which a user is able to simultaneously view a real-world image and the out-coupled image-bearing light, the second waveguide plate being between the first waveguide plate and the third waveguide plate, wherein light in-coupled into the third waveguide plate is input into the third waveguide plate from the first waveguide plate in a direct optical path that does not pass through the second waveguide plate, such that the light does not interact with the second waveguide plate before being input into the third waveguide plate.

[0004] In another aspect, the present invention proposes a binocular device. The binocular device comprises: a first waveguide assembly for providing a first image to an eye of a user; and a second waveguide assembly for providing a second image to an eye of a user, wherein each of the first waveguide assembly and the second waveguide assembly is the waveguide assembly according to the preceding aspect.

[0005] In yet another aspect, the application proposes an augmented reality eyeglass. The augmented reality eyeglass comprises a binocular device according to the previous aspect as a binocular assembly.

[0006] In yet another aspect, the application proposes a head-mounted display or head-up display. The head-mounted display or head-up display comprises a waveguide assembly according to the above aspect. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 A waveguide is shown configured to expand an image-bearing pupil in a single dimension.

[0008] Figure 2a is an expansion of a waveguide assembly for expanding an image-bearing pupil in two dimensions.

[0009] Figure 2b is a diagram of a waveguide assembly for expanding an image-bearing pupil in two dimensions.

[0010] Figure 3a A single waveguide is shown with a fixed pitch grating, coupling red light into the waveguide.

[0011] Figure 3b A single waveguide is shown with the same fixed pitch grating, coupling blue light into the waveguide. Figure 3a

[0012] Figure 4 A pupil expander is shown using a reflective coupling element instead of a diffractive element.

[0013] Figure 5a A side view of a reflective waveguide plate is shown.

[0014] Figure 5b A top view of a reflective waveguide plate is shown.

[0015] Figure 5c A top view of a transmissive waveguide plate is shown.

[0016] Figure 5d A side view of a transmissive waveguide plate is shown.

[0017] Figure 6 A coplanar waveguide device is shown comprising 3 waveguide plates.

[0018] Figure 7a A single ray in a waveguide under TIR is shown.

[0019] Figure 7b A single ray is shown being coupled out of a waveguide.

[0020] Figure 8a ​A single ray confined in a waveguide comprising two waveguide plates joined together is shown.

[0021] Figure 8b A single ray output from a waveguide comprising two waveguide plates joined together is shown.

[0022] Figure 9 A binocular device is shown.

[0023] Figure 10 An alternative binocular device is shown. DETAILED DESCRIPTION

[0024] As shown in Figure 1 , pupil expansion can be implemented using a waveguide 100 comprising a diffraction grating. The waveguide 100 comprises an input grating 110 and an output grating 120. The output grating is configured to output light from the waveguide and expand the light in a single dimension. A grating is a periodic structure that can separate and diffract light to different directions. This periodic structure is often referred to as a line and will be referred to as such throughout the specification.

[0025] As shown in Figure 2, expansion in two dimensions can be implemented using two orthogonal waveguides. The grating lines on each waveguide are substantially orthogonal to each other. An input grating 110a is used to couple an input pupil into a first waveguide 100a. The input pupil is expanded within the waveguide 100a and coupled out of the waveguide 100a by an output grating 120a.

[0026] A second waveguide 100b is arranged such that the grating lines of a second expansion grating 120b are substantially orthogonal to the grating lines of a first expansion grating 120a, and such that light output from the first waveguide is coupled into the second waveguide 100b by an input grating 110b through the output grating 120a. An output grating 120b of the second waveguide 100b is used to expand the pupil in a second direction orthogonal to the first direction and output light from the second waveguide.

[0027] The arrangement as shown in Figure 2a and Figure 2b is inefficient due to the use of low efficiency gratings for performing cross-coupling between the first and second waveguides. Figure 2a and Figure 2b The arrangement also has inherent field of view (FOV) and wavelength bandwidth limitations due to the use of diffraction gratings in the arrangement.

[0028] For a single diffraction waveguide with a fixed pitch input grating, it is difficult to couple a large wavelength range over a large FOV due to the fact that the diffraction angle for certain wavelengths falls outside the TIR condition of the glass substrate.

[0029] Thus, for a wide FOV image comprising multiple wavelengths (i.e. full color), both the horizontal and vertical expander in this setup would typically require multiple stacked waveguides. Figure 3a A single waveguide with a fixed pitch input grating is shown in Figure 3a As shown, when red light is input, the full red FOV is coupled under TIR. However, as Figure 3b shown, when blue light is input, the blue FOV is mostly out-coupled, as this FOV cannot be confined by TIR and cannot be coupled.

[0030] An alternative is to utilize a pupil expander that uses reflective coupling elements instead of diffractive elements. This is shown in Figure 4 .

[0031] Waveguides that include reflective or transmissive input coupling devices, such as prisms, do not have the same chromaticity constraints as diffractive gratings, and multiple wavelengths can be coupled over a larger FOV. Thus, a single waveguide can be used to confine a full color wide FOV image under TIR, as compared to the arrangements of Figure 3a and Figure 3b .

[0032] Reflective output couplers used only for pupil expansion (i.e. in the case of a horizontal expander) do not have the requirement of being transmissive / see-through, and thus can be coated for high reflectivity (high efficiency mirror coating), where a uniform output is produced with graded efficiency.

[0033] Due to the use of multiple reflective surfaces within the line of sight, it can be difficult to optimize a reflective out-coupling structure to maintain a clear see-through path with minimized artifacts within the field of view. In contrast, a typical diffractive out-coupling structure can be optimized to be highly see-through with minimal artifacts, especially when embedded within a glass substrate, as the nanometer-sized diffractive structures used are not perceivable by the human eye.

[0034] Thus, combining a reflective pupil expander with a diffractive pupil expander can result in a combined two-dimensional pupil expander that includes the best qualities of both technologies.

[0035] Referring to Figure 5a to Figure 5d A waveguide assembly 500 according to some examples is described. The waveguide assembly 500 includes a first waveguide plate 500a and a second waveguide plate 500b.

[0036] The first waveguide plate 500a is arranged to receive image-bearing light and to magnify a pupil of the image-bearing light parallel to a first axis. The first waveguide plate 500a comprises a first in-coupling means 510a arranged to in-couple light into the first waveguide plate under total internal reflection (TIR). The first waveguide plate 500a further comprises a first out-coupling region 520a arranged to expand the pupil in a direction parallel to the first axis by means of reflection. The first out-coupling region 520a is further arranged to out-couple image-bearing light from the first waveguide plate 500a.

[0037] The first waveguide plate 500a is illustrated in a side view in Figure 5a and in a top view in Figure 5b .

[0038] The second waveguide plate 500b is arranged to in-couple at least a portion of the out-coupled light from the first waveguide plate 500a into the second waveguide plate 500b and to expand the image-bearing light in a direction substantially parallel to a second axis. The second axis is substantially orthogonal to the first axis.

[0039] The second waveguide plate 500b comprises a diffractive in-coupling region 510b and a transmissive diffractive out-coupling region 520b through which a user can simultaneously view a real-world image and the out-coupled image-bearing light.

[0040] The second waveguide plate 500b is illustrated in a top view in Figure 5c and in a side view in Figure 5d .

[0041] The first waveguide plate 500a comprising the first out-coupling region 520a using reflection technology can carry a large FOV and spectral range within a single plate arrangement. The first waveguide plate 500a comprising the first out-coupling region 520a can be optimized to be highly efficient and graded in uniformity without requiring to be see-through.

[0042] In some examples, the grading can be performed by changing the size, shape and spacing of the structures, preferably non-linearly.

[0043] In some examples, the height or depth of the gratings (e.g. 10’s pm to 100’s pm) can be changed, preferably in the range of 10’s pm to 100’s pm.

[0044] In some examples, the spacing between adjacent features can be changed, preferably in the range of 10’s pm to 1000’s pm (e.g. 10’s pm to 1000’s pm).

[0045] In some examples, the angle of the blaze face can be varied, preferably in the range of 20 to 35 degrees.

[0046] The gradient of the features can be optimized to produce the best output uniformity for a particular setup, e.g. according to the required FOV and output area.

[0047] The second waveguide plate 500b using a diffraction technique can be optimized to be highly see-through with minimal see-through artifacts, while expanding the vertical pupil over a large area.

[0048] In some examples, the first input coupling means 510a is attached to the exterior of the first waveguide plate 500a. This can enable the first input coupling means 510a to be manufactured separately and bonded or glued to the exterior of the first waveguide plate 500a.

[0049] In some examples, the first input coupling means 510a can comprise a prismatic means, e.g. one prism or a plurality of prisms. The prismatic input means can be optimized to couple in a wide range of wavelengths and a large FOV.

[0050] In some examples, the image-bearing light can be uniformly decoupled over the first out-coupling region 520a.

[0051] In some examples, at least one of the first waveguide plate 500a and the second waveguide plate 500b can be curved and / or non-planar.

[0052] Since the user does not need to view through the first waveguide plate 500a, the first waveguide plate 500a or the first out-coupling region 520a can be substantially reflective and / or non-transmissive.

[0053] To accommodate a wider FOV with multiple wavelengths, a plurality of waveguide plates similar to the second waveguide plate 500b can be used in the co-planar waveguide assembly 600. This is shown in Figure 6 The multiple wavelength waveguide assembly comprises a horizontal waveguide plate 610, a first vertical waveguide plate 620 and a second vertical waveguide plate 630. The horizontal waveguide plate 610 is substantially similar to the first waveguide plate 510 and comprises an out-coupling region (not shown in Figure 6 The out-coupling region is further arranged to couple image-bearing light out of the horizontal waveguide plate 610 towards the first vertical waveguide plate 620 and the second waveguide plate 630.

[0054] The horizontal waveguide plate 610 is arranged to expand the pupil parallel to a first axis. The first vertical waveguide plate 620 and the second vertical waveguide plate 630 are arranged to be coplanar with the horizontal waveguide plate 610 and are arranged to expand the pupil parallel to a second axis, where the second axis is substantially orthogonal to the first axis. The first vertical waveguide plate 620 and the second vertical waveguide plate 630 are offset along a third axis by a minimum gap. The first and second vertical waveguide plates are substantially similar to the second waveguide plate 500b.

[0055] The gap can comprise an air gap, or can be filled with a material such as optical cement.

[0056] In the coplanar waveguide assembly 600, the FOV is effectively split as it exits the horizontal waveguide plate 610 due to the optical path taken within the horizontal waveguide plate 610. The two vertical waveguide plates can be arranged to receive only a portion of the FOV and couple it into the respective waveguide. The grating pitch of the two in-coupling gratings on the vertical waveguide plates can be different, as different grating pitches can be used to optimize the coupling efficiency for different portions of the FOV.

[0057] The coplanar waveguide assembly 600 can also include more than two vertical waveguide plates.

[0058] In some examples, at least one of the horizontal waveguide plate 610, the first vertical waveguide plate 620, and the second vertical waveguide plate 630 can be curved and / or non-planar.

[0059] In some examples, at least one of the first waveguide plate 500a and the second waveguide plate 500b can be formed from one or more substrates that are bonded together. An optical coating can be included between the bonded substrates.

[0060] In some examples, the optical coating can comprise a beamsplitting coating. The beamsplitting coating splits light into a transmitted portion and a reflected portion. The beamsplitting coating is typically formed from a low refractive index dielectric material and a high refractive index dielectric material (e.g., MgF2, SiO2, TiO2) or a metallic material (e.g., Al, Ag).

[0061] If the beamsplitting coating is placed between substrates or plates of unequal thickness (e.g., substrate 1 is 1 mm thick and substrate 2 is 2 mm thick), then the rays begin to be split multiple times, resulting in many generations of rays from a single source ray. This is illustrated in Figure 7a to Figure 7b and Figure 8a to Figure 8b

[0062] In Figure 7a a single ray propagates under TIR along the waveguide plate. As shown in Figure 7b there is a gap between the output rays when the rays exit the waveguide plate. ​

[0063] In Figure 8a some examples, two waveguide panels of different thicknesses are joined together using a beamsplitting coating. Individual rays interact with the beamsplitting coating and the individual rays are split into a transmitted beam and a reflected beam. Subsequent reflected and transmitted beams also interact with the beamsplitting coating. This process is repeated multiple times.

[0064] As Figure 8b shown, when light is emitted from the waveguide panel, the gap between the pupils is reduced compared to the example of Figure 7b .

[0065] Figure 6 Light is shown passing through the first vertical waveguide panel 620 before being input into the second vertical waveguide panel 630. However, in some examples, light input into the second vertical waveguide panel 630 can be input into the second waveguide panel 630 from the horizontal waveguide panel 610 in a direct optical path. A direct optical path refers to the fact that the light does not interact with other elements before being input into the second vertical waveguide panel 630. The light can then interact with the first vertical waveguide 620, for example, in the case where the first waveguide panel 620 and the second waveguide panel are joined together as described with respect to Figure 8a and Figure 8b .

[0066] Multiple individual waveguide assemblies can be used to provide a binocular assembly, as shown in Figure 9 and Figure 10 . In the apparatus shown in Figure 9 , a reflective waveguide panel is arranged above the user’s eye. In the alternative apparatus shown in Figure 10 , a reflective waveguide panel is arranged to the side of the user’s eye.

[0067] In some examples, the apparatus shown in Figure 9 and Figure 10 may be used as augmented reality glasses. In some examples, the apparatus shown in Figure 9 and Figure 10 may be used in a head-mounted display or a heads-up display.

Claims

1. A waveguide assembly comprising: a first waveguide plate arranged to receive image-bearing light and to magnify a pupil size of the image-bearing light parallel to a first axis, the first waveguide plate comprising a first in-coupling means arranged to in-couple image-bearing light into the first waveguide plate under total internal reflection, TIR, and a first out-coupling region arranged to out-couple image-bearing light from the first waveguide plate by means of reflection; a second waveguide plate arranged to in-couple at least a portion of the out-coupled image-bearing light from the first waveguide plate into the second waveguide plate and to magnify the pupil size parallel to a second axis, the second axis being substantially orthogonal to the first axis, the second waveguide plate comprising a diffractive in-coupling region and a transmissive diffractive out-coupling region through which a user can simultaneously view a real-world image and the out-coupled image-bearing light; and a third waveguide plate arranged to in-couple image-bearing light from the first waveguide plate that is not in-coupled into the second waveguide plate under TIR into the third waveguide plate, the third waveguide plate comprising a transmissive diffractive out-coupling region through which a user can simultaneously view a real-world image and the out-coupled image-bearing light, the second waveguide plate being between the first waveguide plate and the third waveguide plate, wherein light in-coupled into the third waveguide plate is input into the third waveguide plate from the first waveguide plate in a direct optical path that does not pass through the second waveguide plate, such that the light does not interact with the second waveguide plate before being input into the third waveguide plate.

2. The waveguide assembly of claim 1, wherein, The first out-coupling region is attached to an outer surface of the first waveguide plate.

3. The waveguide assembly of any of claims 1 or 2, wherein, The image-bearing light is uniformly out-coupled over the respective out-coupling region.

4. The waveguide assembly of claim 1 or 2, wherein, The first in-coupling means comprises a prism means.

5. The waveguide assembly of claim 1 or 2, wherein, The first out-coupling region is substantially fully reflective and / or non-transmissive.

6. The waveguide assembly of claim 1, wherein, The in-coupling region of the second waveguide plate and the in-coupling region of the third waveguide plate have different grating pitch sizes.

7. The waveguide assembly of claim 6, wherein, The third waveguide plate is co-planar with the second waveguide plate in the first and second axes and offset in a third axis, the third axis being orthogonal to the first and second axes.

8. The waveguide assembly of any of claims 6-7, wherein, The second waveguide plate and the third waveguide plate are joined together.

9. The waveguide assembly of claim 8, wherein, The second waveguide plate and the third waveguide plate have different thicknesses.

10. The waveguide assembly of claim 1 or 2, wherein, The second waveguide plate is curved and / or non-planar.

11. The waveguide assembly of claim 1 or 2, wherein, The first waveguide plate is arranged to receive collimated image-bearing light.

12. The waveguide assembly of claim 1 or 2, further comprising collimating means for outputting a collimated exit pupil received by the first waveguide plate.

13. A binocular device, comprising: a first waveguide assembly for providing a first image to an eye of a user; and a second waveguide assembly for providing a second image to the eye of the user, wherein each of the first and second waveguide assemblies is the waveguide assembly of any one of claims 1 to 12.

14. An augmented reality eyewear comprising the binocular device of claim 13 as a binocular assembly.

15. A head-mounted display or head-up display comprising the waveguide assembly of any of claims 1-12.

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