CN116057452A - Waveguide assembly - Google Patents

Abstract

A waveguide assembly is disclosed. The waveguide assembly includes a first waveguide plate and a second waveguide plate. The first waveguide plate is arranged to receive the image bearing light and to magnify a pupil size of the image bearing light parallel to the first axis. The first waveguide plate comprises a first in-coupling device arranged to couple image-bearing light into the first waveguide plate under Total Internal Reflection (TIR) and a first out-coupling region arranged to decouple image-bearing light from the first waveguide plate by means of reflection. The second waveguide plate is arranged to couple at least a portion of the coupled-out 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 incoupling region and a transmissive diffractive outcoupling region through which a user can view the real world image and the outcoupled image-bearing light simultaneously.

Description

Waveguide assembly

Background

For augmented reality applications, it is desirable that the field of view of the display be large. It is also desirable for the display to include a large exit pupil due to variations in the physical characteristics of the user to allow for universal assembly of the display and movement of the user's eyes relative to the display surface. In order to reduce the overall size of the optics used to display the image while providing a large FOV and exit pupil, pupil expansion techniques are used.

Drawings

Fig. 1 shows a waveguide configured to expand an image bearing pupil in a single dimension.

Fig. 2a is an expanded view of a waveguide assembly for expanding an image bearing pupil in two dimensions.

Fig. 2b is a diagram of a waveguide assembly for expanding an image bearing pupil in two dimensions.

Figure 3a shows a single waveguide with a fixed pitch grating coupling red light into the waveguide.

Fig. 3b shows the same single waveguide as fig. 3a with the same fixed pitch grating coupling blue light into the waveguide.

Fig. 4 shows a pupil expander using reflective coupling elements instead of diffractive elements.

Fig. 5a shows a side view of a reflective waveguide plate.

Fig. 5b shows a top view of the reflective waveguide plate.

Fig. 5c shows a top view of the transmissive waveguide plate.

Fig. 5d shows a side view of the transmissive waveguide plate.

Fig. 6 shows a coplanar waveguide device including 3 waveguide plates.

Fig. 7a shows a single ray in a waveguide under TIR.

Figure 7b shows a single ray coupled out of the waveguide.

Fig. 8a shows a single ray confined in a waveguide comprising two waveguide plates bonded together.

Fig. 8b shows a single ray output from a waveguide comprising two waveguide plates bonded together.

Fig. 9 shows a binocular device.

Fig. 10 shows an alternative binocular device.

Detailed Description

As shown in fig. 1, pupil expansion may be achieved using a waveguide 100 that includes a diffraction grating. Waveguide 100 includes an input grating 110 and an output grating 120. The output grating is configured to output light from the waveguide and spread the light in a single dimension. Gratings are periodic structures that can separate and diffract light into different directions. This periodic structure is commonly referred to as a line and will be referred to as such throughout the specification.

As shown in fig. 2, expansion in two dimensions can be achieved using two orthogonal waveguides. The grating lines on each waveguide are substantially orthogonal to each other. An input pupil is coupled into the first waveguide 100a using an input grating 110 a. The input pupil expands within the waveguide 100a and is coupled out of the waveguide 100a through the output grating 120 a.

The second waveguide 100b is arranged such that the grating lines of the second extended grating 120b are substantially orthogonal to the grating lines of the first extended grating 120a, and such that light output from the first waveguide through the output grating 120a is coupled into the second waveguide 100b through the input grating 110 b. The 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.

The arrangement shown in fig. 2a and 2b is inefficient due to the use of an inefficient grating for performing cross-coupling between the first waveguide and the second waveguide. Since the arrangement in fig. 2a and 2b uses a diffraction grating, the arrangement also has an inherent field of view (FOV) and wavelength bandwidth limitations.

For a single diffractive waveguide with a fixed pitch input grating, it is difficult to couple a large wavelength range over a large FOV because the diffraction angles for certain wavelengths fall outside the TIR condition of the glass substrate.

Thus, for a wide FOV image comprising multiple wavelengths (i.e. full color), both the horizontal and vertical expanders in this setting typically require multiple stacked waveguides. A single waveguide with a fixed pitch input grating is shown in fig. 3 a. As shown in fig. 3a, when red light is input, the full red FOV is coupled under TIR. However, as shown in fig. 3b, when blue light is input, the blue FOV is mostly emitted, because the FOV cannot be constrained by TIR and cannot be coupled.

An alternative is to use a pupil expander that uses reflective coupling elements instead of diffractive elements. This is shown in fig. 4.

Waveguides that include reflective or transmissive input coupling devices such as prisms do not have the same chromaticity constraints as diffraction gratings and multiple wavelengths can be coupled over a larger FOV. Thus, in contrast to the arrangement of fig. 3a and 3b, a single waveguide may be used to constrain a full-bandwidth FOV image under TIR. The reflective output structure attached to the waveguide plate may also output waveguide light in a more efficient manner than a typical diffraction grating.

Reflective output couplers for pupil expansion only (i.e. in the case of horizontal expanders) do not have transmission/perspective requirements and can therefore be coated for high reflection (high efficiency mirror coating) where uniform output is produced with graded efficiency.

Because multiple reflective surfaces are used within the line of sight, it may be difficult to optimize the reflective out-coupling structure to maintain a clear perspective path with minimal artifacts within the field of view. In contrast, typical diffractive outcoupling structures can be optimized to have a high degree of perspective with minimal artifacts, especially when embedded within a glass substrate, since the nano-sized diffractive structures used are not perceivable by the human eye.

Thus, combining a reflective pupil expander with a diffractive pupil expander can produce a combined two-dimensional pupil expander of optimal quality that includes both techniques.

A waveguide assembly 500 according to some examples is described with reference to fig. 5 a-5 d. The waveguide assembly 500 includes a first waveguide plate 500a and a second waveguide plate 500b.

The first waveguide plate 500a is arranged to receive the image bearing light and to magnify a pupil of the image bearing light parallel to the first axis. The first waveguide plate 500a comprises a first in-coupling device 510a arranged to couple light into the first waveguide plate under Total Internal Reflection (TIR). The first waveguide plate 500a further comprises a first outcoupling 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 couple out image-bearing light from the first waveguide plate 500 a.

The first waveguide plate 500a is shown in a side view in fig. 5a and in a top view in fig. 5 b.

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

The second waveguide plate 500b comprises a diffractive incoupling region 510b and a transmissive diffractive incoupling region 520b through which the user is able to view the real world image and the coupled-out image bearing light simultaneously.

The second waveguide plate 500b is shown in top view in fig. 5c and in side view in fig. 5 d.

The first waveguide plate 500a including the first out-coupling region 520a using reflection technology may carry a large FOV and spectral range within a single plate arrangement. The first waveguide plate 500a including the first outcoupling region 520a may be optimized to be efficient and graded in uniformity without requiring perspective.

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

In some examples, the height or depth of the grating (e.g., 10's μm to 100's μm) may be varied, preferably in the range of 10's μm to 100's μm.

In some examples, the spacing between adjacent features may be varied, preferably in the range of 10's μm to 1000's μm (e.g., 10's μm to 1000's μm).

In some examples, the angle of the light emitting face (blaze face) may be varied, preferably in the range of 20 degrees to 35 degrees.

The gradient of the features may be optimized to produce the best output uniformity for a particular setting, e.g., according to the desired FOV and output area.

The second waveguide plate 500b using diffraction techniques can be optimized for high perspective with minimal perspective artifacts while expanding the vertical pupil over a large area.

In some examples, the first input coupling device 510a is attached to the exterior of the first waveguide plate 500 a. This may enable the first input coupling device 510a to be manufactured separately and bonded or glued to the outside of the first waveguide plate 500 a.

In some examples, the first input coupling device 510a may include a prismatic device, such as a prism or prisms. The prismatic input device may be optimized to couple a wide range of wavelengths and a large FOV in-coupling.

In some examples, the image bearing light may be uniformly decoupled over the first outcoupling region 520a.

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

Since the user does not need to observe through the first waveguide plate 500a, the first waveguide plate 500a or the first outcoupling region 520a may be substantially reflective and/or non-transmissive.

To meet a wider FOV having multiple wavelengths, multiple waveguide plates similar to the second waveguide plate 500b may be used in the coplanar waveguide assembly 600. This is shown in fig. 6. The plurality of wavelength waveguide assemblies includes 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 fig. 6) arranged to expand the pupil in a direction parallel to the first axis by means of reflection. The out-coupling region is further arranged to couple image bearing light out of the horizontal waveguide plate 610 towards the first 620 and second 630 vertical waveguide plates.

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

The gap may comprise an air gap or may be filled with a material such as an optical glue.

In the coplanar waveguide assembly 600, the FOV is effectively split upon exiting from the horizontal waveguide plate 610 due to the optical path taken within the horizontal waveguide plate 610. The two vertical waveguide plates may be arranged to receive only a portion of the FOV and couple it into the respective waveguides. The grating pitch of the two incoupling gratings on the vertical waveguide plate may be different, as different grating pitches may be used to optimize the coupling efficiency of different parts of the FOV.

Coplanar waveguide assembly 600 may also include more than two vertical waveguide plates.

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 may be curved and/or non-planar.

In some examples, at least one of the first waveguide plate 500a and the second waveguide plate 500b may be formed from one or more substrates bonded together. An optical coating may be included between these bonded substrates.

In some examples, the optical coating may include a beam-splitting coating. The beam-splitting coating separates the light into a transmissive portion and a reflective portion. The beam-splitting coating is typically formed of a low refractive index dielectric material and a high refractive index dielectric material (e.g., mgF2, siO2, tiO 2) or a metallic material (e.g., al, ag).

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

In fig. 7a, a single ray propagates along the waveguide plate under TIR. As shown in fig. 7b, when the rays are output from the waveguide plate, there is a gap between the output rays.

In fig. 8a, two waveguide plates of different thickness are bonded together using a beam splitting coating. The individual rays interact with the beam-splitting coating and the individual rays are separated into a transmitted beam and a reflected beam. Subsequent reflected and transmitted beams also interact with the beam splitting coating. This process is repeated a number of times.

As shown in fig. 8b, when light is emitted from the waveguide plate, the gap between the pupils is reduced compared to the example of fig. 7 b.

Fig. 6 shows light passing through the first vertical waveguide plate 620 before being input into the second vertical waveguide plate 630. However, in some examples, light input to the second vertical waveguide plate 630 may be input into the second waveguide plate 630 in a direct optical path from the horizontal waveguide plate 610. The direct optical path refers to the fact that light does not interact with other elements before being input into the second vertical waveguide plate 630. The light may then interact with the first vertical waveguide 620, for example, in case the first waveguide plate 620 and the second waveguide plate are joined together as described in relation to fig. 8a and 8 b.

A plurality of individual waveguide assemblies may be used to provide a binocular assembly as shown in fig. 9 and 10. In the device shown in fig. 9, the reflective waveguide plate is arranged above the eyes of the user. In an alternative arrangement shown in fig. 10, reflective waveguide plates are arranged on both sides of the user's eye.

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

Claims (17)

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 device arranged to couple the image-bearing light into the first waveguide plate under Total Internal Reflection (TIR) and a first out-coupling region arranged to decouple the image-bearing light from the first waveguide plate by means of reflection;

a second waveguide plate arranged to couple at least a portion of the coupled-out 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; wherein, the liquid crystal display device comprises a liquid crystal display device,

the second waveguide plate comprises a diffractive incoupling region and a transmissive diffractive outcoupling region through which a user can view a real world image and coupled-out image bearing light simultaneously.

2. The waveguide assembly of claim 1, wherein the first outcoupling 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 decoupled over the outcoupling region.

4. A waveguide assembly according to any preceding claim, wherein the first input coupling device comprises a prismatic device.

5. A waveguide assembly according to any preceding claim, wherein the first outcoupling region is substantially fully reflective and/or non-transmissive.

6. The waveguide assembly of any preceding claim, further comprising a third waveguide plate arranged to couple image-bearing light from the first waveguide plate into the third waveguide plate under TIR that is not coupled into the second waveguide plate, and wherein the third waveguide plate comprises a transmissive diffractive outcoupling region through which a user can view both a real world image and the coupled-out image-bearing light.

7. The waveguide assembly of claim 6, wherein light coupled into the third waveguide plate does not interact with the second waveguide plate before being input into the second waveguide.

8. The waveguide assembly of claim 6 or 7, wherein the coupling-in region of the second waveguide plate and the coupling-in region of the third waveguide plate have different grating pitch dimensions.

9. The waveguide assembly of any of claims 6-8, wherein the third waveguide plate is coplanar with the second waveguide plate on the first and second axes and offset on a third axis that is orthogonal to the first and second axes.

10. The waveguide assembly of any of claims 6-9, wherein the second waveguide plate and the third waveguide plate are joined together.

11. The waveguide assembly of claim 10, wherein the second waveguide plate and the third waveguide plate have different thicknesses.

12. A waveguide assembly according to any preceding claim, wherein the second waveguide is curved and/or non-planar.

13. A waveguide assembly according to any preceding claim, wherein the first waveguide plate is arranged to receive collimated image bearing light.

14. The waveguide assembly of any preceding claim, further comprising a collimating device for outputting a collimated exit pupil received by the first waveguide.

15. A binocular device comprising: the first waveguide assembly of any of claims 1 to 14, for providing a first image to an eye of a user; and a second waveguide assembly according to any one of claims 1 to 14 for providing a second image to the eye of a user.

16. An augmented reality glasses comprising the binocular assembly of claim 15.

17. A head-mounted display or head-up display comprising the waveguide assembly of any one of claims 1 to 14.

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