Optical arrangement for a display

Abstract

A folded-optical arrangement to use in a display, the display to transmit an image from an image plane to a user's eye, the folded-optical arrangement providing a folded-optical- transmission path and comprising: a collimating element having at least a first optical element comprising a first plurality of optically-powered surfaces, the collimating element configured to receive light forming the image from the image plane and to collimate and output the light, the collimating element being arranged such that, in use, the user's eye can view the image plane and does not look through the collimating element to view an exterior environment. 20 25 20 23 24 01 A pr 2 02 5 A B S T R A C T 2 0 2 5 2 0 2 3 2 4 0 1 A p r 2 0 2 5

Description

[0097] In the embodiment of Figure 5 or 8, the prism element 612, gap 624, and wedge element 614 provide a number of degrees of freedom that are used to manipulate the light in order to result in collimated, well-corrected exit pupil. The collimated light exits the collimating element 608 at the wedge element 614. In some embodiments, further components may be incorporated to increase the number of degrees of freedom of the arrangement and collimated light may enter or exit the collimating element 608 via a different component. For example, a third optical element, a field lens, may be incorporated into the collimating element 608 to further reduce residual aberrations such as distortion and / or field curvature. In some embodiments, a further corrective element may be incorporated in the collimating element 608 to chromatically correct the light.

[0098] Moreover, in the embodiment of Figure 5 or 8, any of the three surfaces 618, 620, 622 of the prism element 612 and either of the two surfaces 626, 628 of the wedge 614 may have varied optical power and surface forms. In some embodiments, the optical properties of the surface 620 of the prism element 612 and the input surface 626 of the wedge element 614 may be matched or designed to be complementary for specific applications.

[0099] The materials of the prism element 612 and wedge element 614 may be the same or may be different to take advantage of the optical characteristics such as refractive indices that different materials have. Similarly, the surrounding material and / or spacing material of the gap 624 are variable to optimise the optical characteristics of the collimating element 608. Materials for the optical elements can be of any appropriate nature. For example, the materials may comprise one or more of optical glasses, polymers and plastics of varying refractive index and abbe number may be used, such as: N-BK7 (low index glass), N-SF6 (high index glass), 7980_0F (low index fused silica), PMMA (low index polymer) and E48R (low index polymer). It may be advantageous to have both optical elements made from different materials so as to combine materials with different indices and different dispersion characteristics. For example, the optical wedge may be manufactured from a material with low dispersion to mitigate chromatic splitting of light during the interaction with the optically powered surface.

[0100] Returning to Figure 5, collimated light from the collimating element 608 enters the pupil expanding element 610. The pupil expanding element 610 comprises a waveguide 640, an incoupling region 642, and an outcoupling region 644. The pupil expanding element 610 is arranged so that the collimated light is incident on the waveguide 640. A first end 646 of the waveguide 640 is aligned with the wedge element 614 so that the collimated light is incident upon a first surface 648 of the waveguide 640, in use.

[0101] The waveguide 640 is a planar slab waveguide. The waveguide 640 comprises an optically transmissive substrate. The waveguide 640 is arranged adjacent to the collimating 2025202324   01 Apr 2025 element 608. The light exiting the collimating element 608 passes into the waveguide 640 via the first surface 648. In some embodiments, the waveguide may also be curved in one or two dimensions.

[0102] The in coupling region 642 in Figure 5 may comprise a mirror, a diffraction grating, a hologram or other suitable optical coupling device. The incoupling region 642 abuts the second surface 650 of the waveguide 640 at the first end 646 of the waveguide 640. The incoupling region 642 couples the light into the waveguide 640 under TIR, the light is then able to travel along the waveguide 640 from the first end 646 to a second end 652 of the waveguide 640.

[0103] The incoupling region 642 is dimensioned to couple light that is incident on the waveguide 640 into the waveguide 640 over a coupling area or aperture. The dimensions, typically the height and width, of the incoupling region 642 dictate the size of the coupling area. Light from the collimating element 608 incident on both the waveguide 640 and the incoupling region 642 is coupled into the waveguide 640. Light from the collimating element 608 incident on the waveguide 640 but not on the incoupling region 642 is not coupled to the waveguide 640 and passes through the waveguide 640.

[0104] The dimensions of the incoupling region 642 are chosen to correspond to a portion of the exit pupil output from the collimating element 608 where the light is well corrected. Therefore, if a well corrected image is output from the collimating element 608, the incoupling region 642 can be matched dimensionally to the dimensions of the well corrected exit pupil and remove any surrounding area of exit pupil that is not well corrected by permitting them to pass directly through the waveguide 640 and remain uncoupled to the waveguide 640.

[0105] Light is coupled to the waveguide 640 by the incoupling region 642 by causing it to reflect or diffract towards the second end 652 of the waveguide 640. The angle at which the light is reflected or diffracted within the waveguide 640 by the incoupling region 642 is greater than critical angle for the interface of the waveguide 640 with the external environment 606, i.e. the surrounding air. Therefore, the coupled light undergoes total internal reflection at each interface along the waveguide 640 until it reaches the outcoupling region 644.

[0106] The outcoupling region 644 of Figure 5 may comprise a mirror array, a diffraction grating, a hologram or other suitable optical decoupling device. In Figure 5, the outcoupling region 644 abuts the first surface 648 of the waveguide 640 and the user’s eye is spaced from the second surface 650 of the waveguide 640. In other embodiments, the outcoupling region 644 may abut the second surface, and the user may view the waveguide’s first surface. The outcoupling region 644 is positioned at the second end of the waveguide. 2025202324   01 Apr 2025

[0107] The outcoupling region 644 effectively performs the opposite function to the incoupling region 642 and decouples the light travelling along the waveguide 640 from the waveguide 640. The decoupling is achieved by reflection or diffraction, dependent upon the type of decoupling element used. The light is therefore transmitted out of the waveguide 640 at the outcoupling region 644.

[0108] The outcoupling region 644 is dimensioned to decouple light from the waveguide 640 over a decoupling area or aperture. In other words, the exit pupil of the light exiting the waveguide 640 has a particular area or aperture because the outcoupling region 644 decouples light over that area of the waveguide. The dimensions of the exit pupil generated out of the waveguide are dictated by the dimensions of the outcoupling region 644. To achieve an expanded exit pupil, the dimensions of the outcoupling region are greater than those of the incoupling region. Accordingly, the input and output regions of Figure 5 are dimensioned so that the input region is smaller than the output region.

[0109] Once the light has been decoupled from the waveguide 640 and exits the waveguide 640, it is directed to the user’s eye. The decoupled light remains collimated and exits over a larger area than the area of the exit pupil of the collimated light exiting the collimating element 608 and of the collimated light entering the waveguide 640 that is coupled to the waveguide 640.

[0110] In use, the user’s eye is positioned to view the second surface 650 of the waveguide 640. The user’s eye is also aligned with the outcoupling region 644. The outcoupling region 644 and waveguide 640 permit light from the external environment to pass through them towards the user’s eye so that the user can view the external environment. The outcoupling region 644 and waveguide are transparent or translucent to permit the user to view the external environment.

[0111] By viewing the outside world through the waveguide 640 the user does not have to look through a thick and powered optical element. This can help to mitigate issues encountered with the external view from the outside world being distorted after the light from the outside world has been transmitted through a thick, powered optical element, which can induce refractive errors

[0112] In some embodiments, the incoupling region and / or outcoupling region may be fully or partially optically coated, optionally using a dielectric, to vary the optical qualities of each. If the outcoupling region is fully coated so as not to transmit light from an external environment, the user will be able to see the image alone when viewing the waveguide.

[0113] The folded optical arrangement 600 described above is particularly beneficial for use in head-mounted displays. The use of a thin waveguide optic removes the requirement for a user to view the generated image and outside world through a thick or powered optical element. For the user to view the external environment, light from the external environment needs to only travel 2025202324   01 Apr 2025 through the outcoupling region and the waveguide to reach the user’s eye. In addition, the collimating element 608 can be specifically designed to improve the quality of the image displayed to the user because the user does not have to view the external environment through the collimating element 608. Furthermore, the expansion of the exit pupil performed by the pupil expanding element 610 permits a smaller, more compact collimating element 608 with improved exit pupil performance, thereby reducing the volume occupied by the arrangement and the mass of the arrangement. It is envisaged that a significant volume reduction can be achieved as compared to a conventional eyepiece optic. Furthermore, the use of a waveguide permits the folding of the optical system to move the bulk of the optical elements away from the user’s eye.

[0114] Figures 10A and |10B show respectively a 2D and a 3D representation of the prism and the wedge combination. Figure 10A shows a 2D representation side on with an exemplary ray path shown and 10B shows a 3D view of the combination of the prism and wedge with optically powered surfaces shown.

[0115] Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term ‘comprising’ does not exclude the presence of other elements or steps.

[0116] Furthermore, the order of features in the claims does not imply any specific order in which the features must be performed and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. In addition, singular references do not exclude a plurality. Thus, references to ‘a’, ‘an’, ‘first’, ‘second’, etc. do not preclude a plurality. In the claims, the term ‘comprising’ or “including” does not exclude the presence of other elements. 2025202324   01 Apr 2025

[0117] Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0118] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Claims

2025202324   09 Sep 20261. A folded-optical arrangement to use in a display, the display to transmit an image from an image plane to a user’s eye, the folded-optical arrangement providing a folded-optical-transmission path and comprising:a collimating element having at least a first optical element comprising a first plurality of optically-powered surfaces and a second optical element comprising a second plurality of optically-powered surfaces, the collimating element configured to receive light forming the image from the image plane and to collimate and output the collimated light, wherein the first optical element is to receive the light forming the image from the image plane at a first optically-powered surface of the first plurality of optically-powered surfaces, and the first optical element and the second optical element to cooperatively collimate the light and output the collimated light from the second optical element at a first optically-powered surface of the second plurality of optically-powered surfaces, anda pupil-expanding element having a waveguide, the waveguide to receive the collimated light output by the second optical element and decouple the collimated light from the waveguide to the user’s eye,wherein a second optically-powered surface from the first plurality of optically-powered surfaces and a second optically-powered surface from the second plurality of optically-powered surfaces are adjacent to one another and have different shapes, and an angle at an end of the second optical element that is formed between the first optically-powered surface from the second plurality of optically-powered surfaces and the second optically-powered surface from the second plurality of optically-powered surfaces of the second optical element is less than an angle at an end of the first optical element that opposes the end of the second optical element, and is formed between the second optically-powered surface from the first plurality of optically-powered surfaces and a third optically-powered surface from the first plurality of optically-powered surfaces; andwherein the collimating element is non-overlapping with the user’s eye such that, in use, the user’s eye views an exterior environment through the waveguide but not through the collimating element.

2. The folded-optical arrangement of claim 1, wherein the first optical element comprising the first plurality of optically-powered surfaces is arranged to receive the light forming the image, and the second optical element comprising second plurality of optically-powered surface is reflective and arranged to receive light from the first plurality of optically-powered surfaces, the first plurality of optically-powered surfaces and the second plurality of optically-powered surface being arranged to define a plurality of interfaces along the folded-optical-transmission path.2025202324   09 Sep 20263. The folded-optical arrangement of claim 1, wherein a refractive index change at each interface is predetermined to control a direction of light passing through each interface.

4. The folded-optical arrangement of claim 1, wherein the angle at the end of the second optical element is less than 30 degrees.

5. The folded-optical arrangement of claim 1, further comprising:a coupling element configured to couple the light output from the collimating element into the waveguide; anda decoupling element configured to decouple the light from the waveguide to the user’s eye.

6. The folded-optical arrangement of claim 5, wherein the decoupled light has a larger exit pupil than the coupled light.

7. The folded-optical arrangement of claim 1, further comprising a third optical element comprising at least one optically-powered surface located between the image plane and the first optical element.

8. The folded-optical arrangement of claim 1, wherein an incoupling region comprises a diffraction grating and an outcoupling region comprises a diffraction grating.

9. A folded-optical arrangement to use in a display, the display to transmit an image from an image plane to a user’s eye, the folded-optical arrangement providing a folded-optical-transmission path and comprising:a collimating element having a first optical element and a second optical element, the first optical element comprising a first plurality of surfaces including two or more optically-powered surfaces, the second optical element comprising a second plurality of surfaces including at least one optically-powered surface, the collimating element configured to receive light forming the image from an image source in the image plane at a first surface of the first plurality of surfaces, and to collimate and output the collimated light, wherein the first optical element is to receive the light forming the image from the image plane, and the first optical element and the second optical element to cooperatively collimate the light and output the collimated light from the second optical element at a first surface of the second plurality of surfaces; anda pupil-expanding element having a waveguide, the waveguide to receive the collimated light output by the second optical element and decouple the collimated light from the waveguide to the user’s eye,wherein a second surface from the first plurality of surfaces and a second surface from the second plurality of surfaces are adjacent to one another and have different shapes, and an angle2025202324   09 Sep 2026at an end of the second optical element that is formed between the first surface from the second plurality of surfaces and the second surface from the second plurality of surfaces of the second optical element is less than an angle at an end of the first optical element that opposes the end of the second optical element, and is formed between the second surface from the first plurality of surfaces and a third surface from the first plurality of surfaces,wherein the collimating element is non-overlapping with the user’s eye such that, in use, the user’s eye views an exterior environment through the waveguide but not through the collimating element.

10. The folded-optical arrangement of claim 9, wherein the first optical element comprising the first optically-powered surface is arranged to receive the light forming the image, and the second optically-powered surface is reflective and arranged to receive light from the first optically-powered surfaces.

11. The folded-optical arrangement of claim 9, further comprising:a coupling element configured to couple the light output from the collimating element into the waveguide; anda decoupling element configured to decouple the light from the waveguide for output to the user’s eye, the decoupled light having a larger exit pupil than the coupled light.

12. The folded-optical arrangement of claim 9, wherein a refractive index change at each interface is predetermined to control a direction of light passing through each interface.

13. A folded-optical arrangement to use in a display, the display to transmit an image from an image plane to a user’s eye, the folded-optical arrangement providing a folded optical-transmission path and comprising:a collimating element having a first optical element, a second optical element, and a third optical element located such that the first optical element is between the second optical element and the third optical element, the first optical element comprising a first plurality of surfaces, the second optical element comprising a second plurality of surfaces, and the third optical element comprising at least one optically-powered surface, and the collimating element configured to receive light forming the image from an image source, and to collimate and output the light, wherein the third optical element is to receive the light forming the image from the image plane, and the first optical element, the second optical element, and the third optical element to cooperatively collimate the light and output the collimated light from the second optical element at a first surface of the second plurality of surfaces;2025202324   09 Sep 2026a pupil-expanding element having a waveguide, the waveguide to receive the collimated light output by the second optical element and decouple the collimated light from the waveguide to the user’s eye,wherein a second surface from the first plurality of surfaces and a second surface from the second plurality of surfaces are adjacent to one another and have different shapes, and an angle at an end of the second optical element that is formed between the first surface from the second plurality of surfaces and the second surface from the second plurality of surfaces of the second optical element is less than an angle at an end of the first optical element that opposes the end of the second optical element, and is formed between the second surface from the first plurality of surfaces and a third surface from the first plurality of surfaces,wherein the collimating element is non-overlapping with the user’s eye such that, in use, the user’s eye views an exterior environment through the waveguide but not through the collimating element.

14. The folded-optical arrangement of claim 13, wherein the first plurality of surfaces includes three or more optically-powered surfaces and the second plurality of surfaces including at least two optically-powered surfaces.

15. The folded-optical arrangement of claim 14, wherein:the first optical element comprising one of the first optically-powered surfaces is arranged to receive the light forming the image;the second optically-powered surface is reflective and is arranged to receive light from the first optically-powered surface; andthe third optically-powered surface is configured to receive light reflected by the second optically-powered surface and reflect it back towards the second optically-powered surface.

16. The folded-optical arrangement of claim 14, wherein:the optically-powered surfaces of at least the first optical element and the second optical element are arranged to define a plurality of interfaces along the folded optical-transmission path and a refractive index change at each interface is predetermined to control a direction of light passing through a respective one of the interfaces.

17. The folded-optical arrangement of claim 13, further comprising:a coupling element configured to couple the light output from the collimating element into the waveguide; anda decoupling element configured to decouple the light from the waveguide for output to the user’s eye.

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