GB2567037A - Device for augmented reality or virtual reality display - Google Patents

Device for augmented reality or virtual reality display Download PDF

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Publication number
GB2567037A
GB2567037A GB1812023.8A GB201812023A GB2567037A GB 2567037 A GB2567037 A GB 2567037A GB 201812023 A GB201812023 A GB 201812023A GB 2567037 A GB2567037 A GB 2567037A
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United Kingdom
Prior art keywords
waveguide
filter
optical structure
primary colours
light
Prior art date
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Withdrawn
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GB1812023.8A
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GB201812023D0 (en
Inventor
James Grey David
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Wave Optics Ltd
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Wave Optics Ltd
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Filing date
Publication date
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Priority to GB1812023.8A priority Critical patent/GB2567037A/en
Publication of GB201812023D0 publication Critical patent/GB201812023D0/en
Publication of GB2567037A publication Critical patent/GB2567037A/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
    • G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
    • G02B6/0075—Arrangements of multiple light guides
    • G02B6/0076—Stacked arrangements of multiple light guides of the same or different cross-sectional area
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29304—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating
    • G02B6/29316—Light guides comprising a diffractive element, e.g. grating in or on the light guide such that diffracted light is confined in the light guide
    • G02B6/29325—Light guides comprising a diffractive element, e.g. grating in or on the light guide such that diffracted light is confined in the light guide of the slab or planar or plate like form, i.e. confinement in a single transverse dimension only
    • G02B6/29328—Diffractive elements operating in reflection
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/01—Head-up displays
    • G02B27/017—Head mounted
    • G02B27/0172—Head mounted characterised by optical features
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29346—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by wave or beam interference
    • G02B6/29361—Interference filters, e.g. multilayer coatings, thin film filters, dichroic splitters or mirrors based on multilayers, WDM filters
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/01—Head-up displays
    • G02B27/0101—Head-up displays characterised by optical features
    • G02B2027/0112—Head-up displays characterised by optical features comprising device for genereting colour display
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/01—Head-up displays
    • G02B27/017—Head mounted
    • G02B27/0172—Head mounted characterised by optical features
    • G02B2027/0174—Head mounted characterised by optical features holographic
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29304—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating
    • G02B6/29316—Light guides comprising a diffractive element, e.g. grating in or on the light guide such that diffracted light is confined in the light guide
    • G02B6/29325—Light guides comprising a diffractive element, e.g. grating in or on the light guide such that diffracted light is confined in the light guide of the slab or planar or plate like form, i.e. confinement in a single transverse dimension only
    • G02B6/29329—Diffractive elements operating in transmission

Abstract

An optical structure suitable for use in an augmented reality or virtual reality display comprising: first 10 and second 20 waveguides with a (blue light) filter 14 therebetween. A first diffractive input 2 receives coloured light (RBG) from a projector 12 and diffracts a first portion of the coloured light into the first waveguide. The first input diffraction grating also transmits a second portion of the coloured (RGB) light through the (blue light) filter 14 to a second diffractive input 6 in the second waveguide. The second portion (RG) light is then diffracted into the second waveguide. First 4 and second 8 output diffractive elements diffract the first and second portions of light out of the first and second waveguides towards a viewer. The arrangement improves chromatic uniformity of the output image. The filter may be a dielectric coating on the first or (preferably) second waveguide. The filter may: have a thickness of less than 5mm, preferably less than 0.5mm; transmit blue colours with <1% efficiency; and be fixed to the first or second waveguide with an air space therebetween. A shim 18 may maintain separation between the first and second waveguides. The second optical structure may have a protective cover 30.

Description

The present invention relates to a device for use in an augmented reality or virtual reality display such as a headset or a head-up display. In particular, the invention relates to an arrangement that can improve chromatic uniformity in a full-colour display.
An augmented reality display allows a user to view their surroundings as well as projected images. In military or transportation applications the projected images can be overlaid on the real world perceived by the user. Other applications for these displays include video games and wearable devices, such as glasses. By contrast, in a virtual reality display a user can only perceive projected images and light from their real world surroundings is obscured.
In a normal augmented reality set-up a transparent display screen is provided in front of a user so that they can continue to see the physical world. The display screen is typically a glass waveguide, and a projector is provided to one side. Light from the projector is coupled into the waveguide by a diffraction grating (an input grating). The projected light is totally internally reflected within the waveguide. The light is then coupled out of the waveguide by another diffraction grating (an output grating) so that it can be viewed by a user. The projector can provide information and/or images that augment a user's view of the physical world.
A challenge in the field of augmented reality is to provide full colour augmented reality images. One approach is to use a stack of three waveguides and to couple first, second and third primary colours into respective waveguides. An example of such an arrangement is described in US 8,965,152 B2. Another example is described in US 7,206,107 B2.
In order to reduce the weight and thickness of the optical structure, another technique uses only two waveguides, and first, second and third primary colours are split between the two waveguides. An example of such an arrangement is described in US 9,946,068 B2. In this arrangement first, second and third primary colour component images are provided and an optical structure is configured to diffract a respective first portion of the field of view for each of the first, second and third primary colours into a first waveguide. A respective second portion of the field of view for each of the first, second and third primary colours is diffracted by an input diffraction grating into a second waveguide. Light can then be diffracted out of the first and second waveguides towards a viewer.
It has been found that issues regarding colour uniformity can be created in known techniques that use a stack of two waveguides. An object of the present invention is to address and overcome some of these issues.
According to an aspect of the present invention there is provided an optical structure for use in an augmented reality or virtual reality display, comprising: first and second waveguides, wherein the first waveguide comprises: a first input diffractive optical structure configured to receive light comprising first, second and third primary colours from a projector and to diffract at least a first portion of the first, second and third primary colours so that they are coupled into the first waveguide for total internal reflection within the first waveguide, and wherein the first input diffractive optical structure is configured to transmit at least a second portion of the first, second and third primary colours out of the first waveguide; and a first output diffractive optical structure configured to diffract the first portion of the first, second and third primary colours so that they are coupled out of the first waveguide and towards a viewer; wherein the optical structure further comprises a filter configured to receive the second portion of the first, second and third primary colours that are transmitted out of the first waveguide and to filter out the first primary colour so that only the second and third primary colours are transmitted; wherein the second waveguide comprises: a second input diffractive optical structure configured to receive light transmitted by the filter comprising the second portion of the second and third primary colours and to diffract at least a third portion of the second and third primary colours so that they are coupled into the second waveguide for total internal reflection within the second waveguide; and a second output diffractive optical structure configured to diffract the third portion of the second and third primary colours so that they are coupled out of the second waveguide and towards a viewer.
Surprisingly, it has been found that the filter can significantly improve the uniformity of the combined optical output from the first and second output diffractive optical structures. In particular, experimental results indicate that the filter can advantageously improve the uniformity of output of the first primary colour.
Preferably the first, second and third primary colours are blue, green and red respectively. Thus, the filter may be configured to filter out blue light. In some embodiments the filter may be a blue cut-off filter.
The filter may comprise a dielectric coating on or in the first or second waveguide. More preferably the dielectric coating may be provided on a surface of the second waveguide so that it can be provided on a flat waveguide surface that does not have any grating on it. This means that the function of the filter can be performed independently of the first and second input diffractive optical structures.
The filter may be fixed to the first or second waveguide with an air space provided between the filter and the first or second waveguide. In one embodiment the filter may be provided as a plastic film which may be fixed to the first or second waveguide using a thin glue gasket. The air gap can allow light to propagate freely towards and away from the filter. This can ensure that the filter properties can be tightly defined without risk of corruption from elements such as optical glue or cement. Precise alignment of the filter with the first and second waveguides is not considered strictly necessary because light is transmitted through both parallel faces of the filter which means that transmitted light continues in the same direction as before, even if there is a slight misalignment. This improves the ease of manufacture and allows the filter to be glued to the first or second waveguide using glue spots that may vary slightly in width.
The filter may have a thickness of less than 5mm, preferably less than 1mm, and more preferably less than 0.5mm. It has been determined that it is important to provide a thin filter. This means that the first and second waveguides can be provided very close to one another, and the filter does not unnecessarily space them apart or add significant width to the overall stack. A shim may be provided having the same thickness as the filter, so that the shim and the filter are together configured to maintain a substantially equal separation between the first and second waveguides. This is important in maintaining the first and second waveguides in a parallel arrangement as otherwise tilts between the first and second waveguides can introduce negative colour effects at a pixel level.
Preferably the optical structure comprises a protective cover adjacent the second waveguide to protect the second input diffractive optical structure and the second output diffractive optical structure from damage. The protective cover may be tinted to enhance the contrast of augmented reality images.
Preferably the filter is a high-pass filter, such as a blue cut-off filter, that transmits blue colours with <1% efficiency, preferably <0.1% efficiency. In this context blue wavelengths may mean wavelengths of less than around 465nm.
According to another aspect of the present invention there is provided an augmented reality or virtual reality device comprising: a projector configured to provide augmented reality or virtual reality images in first, second and third primary colours; and the optical structure as previously defined.
Embodiments of the invention are now described, by way of example, with reference to the drawings, in which:
Figure 1 is an exploded schematic side view of a stack of waveguides in an embodiment of the invention;
Figure 2A is a diagram showing uniformity of blue wavelengths of light in an output from the stack of waveguides in the absence of a blue cut-off filter;
Figure 2B is a diagram showing uniformity of blue wavelengths of light in an output from the stack of waveguides in the presence of a blue cut-off filter; and
Figure 3 is a graph showing the properties of a blue cut-off filter for use in an embodiment of the present invention.
Figure 1 is an exploded schematic view of a stack of waveguides in an embodiment of the invention. A projector 12 provides a full colour image using first, second and third primary colours which are red, green and blue. Light from the projector 12 is received at an optical structure which includes a first waveguide 10 and a second waveguide 12. The first waveguide 10 is sometimes referred to as the “blue waveguide” 10, since it is predominantly for carrying blue light. The second waveguide 12 is sometimes to as the “red waveguide” 12, since it is predominantly for carrying red light.
The first and second waveguides 10, 20 each comprise two major, flat, parallel faces and are made of a transparent medium, such as glass having a refractive index, n, of around 1.7. Light from the projector 12 is transmitted through a front surface of the first waveguide 10 and is incident on a first input diffraction grating 2 on a rear surface. In some embodiments the first input diffraction grating 2 is a blazed reflection grating having a period of around
335nm.
A second input diffraction grating 6 is provided on a rear surface of the second waveguide 20. The second input diffraction grating 6 in this embodiment is a blazed reflection grating having a period of around 440nm. In different embodiments it is envisaged that different types of grating may be used for the first and second input diffraction gratings 2, 6 such as binary gratings or gratings with a sinusoidal profile.
The first input diffraction grating 2 is configured to diffract incident light from the projector 12. In particular, because of its period, the first input diffraction grating 2 diffracts a large proportion of the blue wavelengths, some of the green wavelengths, and a small proportion of the red wavelengths. The diffracted light travels within the first waveguide 10 by total internal reflection towards an expansion grating 4 or output element. The expansion grating 4 diffracts the light that is totally internally reflected within the first waveguide 10 so that it is coupled out of the first waveguide 10 and towards a viewer. The expansion grating 4 also provides a one or two-dimensional expansion of the light so that it can provide a large eye box for a viewer.
Light that is not diffracted by the first input diffraction grating 2 is transmitted and continues to propagate in the same direction as it was output from the projector 12. The transmitted light from the first input diffraction grating 2 includes a large proportion of the red wavelengths, around half of the green wavelengths, and a small proportion of the blue wavelengths.
A filter 14 is positioned between the first and second waveguides 10, 20. In this example embodiment the filter 14 is a blue cut-off filter made of plastic which is designed substantially to block blue wavelengths of light and to allow red and green wavelengths to propagate towards the second waveguide 20. In this embodiment, glue spots 16 are provided between the edges of the filter 14 and the second waveguide 20. This is sometimes referred to as a glue gasket. The glue spots 16 have a width of around 50pm. In this way, the filter 14 is separated from the front surface of the second waveguide 20 by an air gap of approximately 50pm. The filter 14 has a thickness of around 0.5mm.
Light is transmitted directly through the filter 14. Therefore, precise alignment of the filter 14 with the first and second waveguides 10, 20 is not strictly necessary. Light will be transmitted out of the filter 14 in the same direction as it is received from the projector 12, even if there is a slight misalignment between the filter 14 and the first and second waveguides 10, 20. This reduces manufacturing tolerances and means that the optical arrangement can be produced more easily.
The filter 14 is positioned at one end of the second waveguide 20, adjacent the second input grating 6. A shim 18 is provided at the other end of the second waveguide 20, adjacent the second expansion grating 8. The shim 18 has a thickness of around 0.5mm, which is the same as the thickness of the filter 14. The shim 18 is fixed to the second waveguide 20 by glue spots 22 which have a thickness of around 50pm, respectively. In this way, the shim 18 can space the first and second waveguides 10, 20 apart by the same amount as the filter 14. This can ensure that the spacing of the first and second waveguides 10, 20 is even along their respective lengths. Glue 11 is provided between the edges of the first waveguide 10 and the filter 14 and shim 18 so that the first and second waveguides 10, 20 can be connected together.
In another embodiment the filter 14 and the shim 18 may be affixed to the rear surface of the first waveguide 10, rather than the front surface of the second waveguide 20. In a further alternative, the filter 14 may be provided as a dielectric film on the front surface of the second waveguide 20. In this embodiment the film may be provided directly on the surface of the second waveguide 20 so that there is no air gap. The shim 18 may be omitted where the filter is provided as a dielectric film.
Light that passes through the filter 14 is transmitted through a front surface of the second waveguide 20 and is then incident on the second input diffraction grating 6 on the rear surface. The second input diffraction grating 6 diffracts the filtered light and couples it into the second waveguide 20 to be totally internally reflected within the second waveguide 20. The diffracted light then travels within the second waveguide 20 under total internal reflection towards an expansion grating 8 which diffracts the light again and couples it out of the second waveguide 20 towards a viewer.
Light that is output by the first and second expansion gratings 4, 8 in the first and second waveguides 10, 20 respectively is combined so that a full colour augmented reality image can be formed and experienced by a viewer.
A tinted cover 30 is provided adjacent the second waveguide 20. Glue 32 is provided between the respective edges of the tinted cover 30 and the second waveguide 20. The tinted cover 30 provides protection for the second waveguide 20 since otherwise the second input diffraction grating 6 and the second expansion grating 8 would be exposed and accessible to damage. By providing a tint it is possible to reduce the brightness of light from the outside world and increase the contrast for augmented reality light. This can improve the efficiency by reducing the amount of power that needs to be supplied to the projector 12 to achieve a desired level of contrast. In other embodiments it is possible to provide a cover 30 that only provides protection and does not have any tint.
The first and second waveguides 10, 20 have respective thicknesses of around 1mm. The tinted cover 30 also has a thickness of around 1mm. In this example embodiment the shim 18 and the filter 14 have respective thicknesses of around 0.5mm and there are three layers of glue, each with a thickness of around 50pm. Therefore, the overall thickness of the stack may be around 3.65mm.
Figure 2A is a false colour image showing the uniformity of the output from the optical structure in blue wavelengths in an arrangement that does not include the filter 14 and is not within the scope of the present invention. Figure 2B is another false colour image showing the uniformity of the output from the optical structure in blue wavelengths in an arrangement that does include the filter 14 and is within the scope of the present invention. A uniformity metric UniCOeff is defined such that, for a given image I, the function UniCOeff(l) is the fraction of I which is brighter than avg(l)/2, where avg() is the average brightness. The higher the value of Unicoeff(l), the better the uniformity of the output. In the example of Figure 2A UniCOeff has a value of 0.812. In the example of Figure 2B Unicoeff has a value of 0.873. Thus, it has been established by experiment that the inclusion of the filter 14 can improve the uniformity of the blue light that is output from the first and second expansion gratings 4, 8 across a field of view of ±10° vertically and ±17° horizontally.
Figure 3 is a graph showing the properties of the filter 14 in an embodiment of the present invention, showing transmission percentage as a function of wavelength. A first plot 100 shows the transmission percentage as a function of wavelength when the projector 12 is normal to the major faces of the first and second waveguides 10, 20. A second plot 200 shows the transmission percentage when the projector 12 is arranged at 20° to the surface normal of the major faces of the first and second waveguides 10, 20. A third plot 300 is included for reference to show the emission brightness achieved using red, green and blue
LEDs in the projector 12. The filter 14 is designed so that <0.1% transmission is achieved at blue wavelengths (less than around 465nm).

Claims (10)

1. An optical structure for use in an augmented reality or virtual reality display, comprising:
first and second waveguides, wherein the first waveguide comprises:
a first input diffractive optical structure configured to receive light comprising first, second and third primary colours from a projector and to diffract at least a first portion of the first, second and third primary colours so that they are coupled into the first waveguide for total internal reflection within the first waveguide, and wherein the first input diffractive optical structure is configured to transmit at least a second portion of the first, second and third primary colours out of the first waveguide; and a first output diffractive optical structure configured to diffract the first portion of the first, second and third primary colours so that they are coupled out of the first waveguide and towards a viewer;
wherein the optical structure further comprises a filter configured to receive the second portion of the first, second and third primary colours that are transmitted out of the first waveguide and to filter out the first primary colour so that only the second and third primary colours are transmitted;
wherein the second waveguide comprises:
a second input diffractive optical structure configured to receive light transmitted by the filter comprising the second portion of the second and third primary colours and to diffract at least a third portion of the second and third primary colours so that they are coupled into the second waveguide for total internal reflection within the second waveguide; and a second output diffractive optical structure configured to diffract the third portion of the second and third primary colours so that they are coupled out of the second waveguide and towards a viewer.
2. The optical structure of claim 1, wherein the first, second and third primary colours are blue, green and red respectively.
3. The optical structure of claim 1 or claim 2, wherein the filter is a dielectric coating on the first or second waveguide.
4. The optical structure of claim 2, wherein the dielectric coating is provided on the second waveguide.
5. The optical structure of claim 1 or claim 2, wherein the filter is fixed to the first or second waveguide with an air space provided between the filter and the first or second waveguide.
6. The optical structure of any of the preceding claims, wherein the filter has a thickness of less than 5mm, preferably less than 1mm, and more preferably less than 0.5mm.
7. The optical structure of any of the preceding claims, further comprising a shim having the same thickness as the filter, so that the shim and the filter are together configured to maintain a substantially equal separation between the first and second waveguides.
8. The optical structure of any of the preceding claims, further comprising a protective cover adjacent the second waveguide to protect the second input diffractive optical structure and the second output diffractive optical structure from damage.
9. The optical structure of any of the preceding claims, wherein the filter is a high-pass filter that transmits blue colours with <1% efficiency.
10. An augmented reality or virtual reality device comprising:
a projector configured to provide augmented reality or virtual reality images in first, second and third primary colours; and the optical structure of any of the preceding claims.
GB1812023.8A 2018-07-24 2018-07-24 Device for augmented reality or virtual reality display Withdrawn GB2567037A (en)

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Application Number Priority Date Filing Date Title
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GB2567037A true GB2567037A (en) 2019-04-03

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2017120320A1 (en) * 2016-01-06 2017-07-13 Vuzix Corporation Two channel imaging light guide with dichroic reflectors
WO2017120341A1 (en) * 2016-01-06 2017-07-13 Vuzix Corporation Double-sided imaging light guide
US20180341111A1 (en) * 2017-05-24 2018-11-29 Microsoft Technology Licensing, Llc Diffractive filtering in waveguide display

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2017120320A1 (en) * 2016-01-06 2017-07-13 Vuzix Corporation Two channel imaging light guide with dichroic reflectors
WO2017120341A1 (en) * 2016-01-06 2017-07-13 Vuzix Corporation Double-sided imaging light guide
US20180341111A1 (en) * 2017-05-24 2018-11-29 Microsoft Technology Licensing, Llc Diffractive filtering in waveguide display

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