Display structure
The display structure addresses brightness and color variations in augmented reality displays by using a waveguide with selective diffraction and polarization rotation, improving image quality.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- DISPELIX OY
- Filing Date
- 2025-10-24
- Publication Date
- 2026-06-04
AI Technical Summary
Existing diffraction gratings in augmented reality applications face challenges in minimizing brightness- and/or color variations in generated images due to polarization-dependent diffraction effects.
A display structure comprising a waveguide with an in-coupling structure, an exit pupil expansion structure featuring diffractive and sub-wavelength grating features, and an out-coupling structure, which selectively diffracts and rotates polarizations to minimize diffraction variations.
The solution effectively reduces brightness and color variations in augmented reality displays by optimizing polarization-dependent diffraction, enhancing image quality.
Smart Images
Figure FI2025060045_04062026_PF_FP_ABST
Abstract
Description
DISPLAY STRUCTURETECHNICAL FIELD
[0001] The present disclosure relates to the field of diffractive optics, and more particularly to a display structure and a display device.BACKGROUND
[0002] Diffraction gratings can be utilized in various optical applications, such as in augmented reality (AR) applications. For example, diffraction gratings can be used to couple light into a waveguide, manipulate light coupled into a waveguide, and couple light out of a waveguide. When designing diffraction gratings for AR applications, for example, various challenges may arise, such as how minimize brightness- and / or color variations in the generated image.SUMMARY
[0003] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subj ect matter, nor is it intended to be used to limit the scope of the claimed subj ect matter.
[0004] It is an object to provide a display structure and a display device. The foregoing and other obj ectsare achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.
[0005] According to a first aspect, a display structure comprises: a waveguide; an in-coupling structure configured to receive a set of input beams and couple the set of input beams into the waveguide as a set of in-coupled beams, wherein the set of in-coupled beams comprises a first polarization and a second polarization; an exit pupil expansion structure configured to receive the set of in-coupled beams, wherein the exit pupil expansion structure comprises diffractive grating features configured to diffract at least the first polarization in the set of in-coupled beams to form a set of diffracted beams and to rotate at least a part of the first polarization in the set of in-coupled beams into the second polarization in the set of diffracted beams and the diffractive grating features are at least partially transparent to the second polarization; and an out-coupling structure configured to receive the set of diffracted beams and to outcouple the set of diffracted beams from the waveguide as a set of out-coupled beams.
[0006] In an implementation form of the first aspect, the exit pupil expansion structure further comprises sub-wavelength grating features configured to make the diffractive grating features at least partially transparent to the second polarization.
[0007] In another implementation form of the first aspect, the sub-wavelength grating features are configured to make the diffractive grating features at least partially transparent to the second polarization via a spatial refractive index average along a direction of the second polarization being substantially constant.
[0008] In another implementation form of the first aspect, the diffractive grating features comprise a plurality of diffractive grating lines and the sub-wave-length grating features comprise a plurality of subwavelength grating lines.
[0009] In another implementation form of the first aspect, each grating line in the plurality of diffractive grating lines comprises an air gap.
[0010] In another implementation form of the first aspect, the plurality of diffractive grating lines are made of a material with a first refractive index and the plurality of sub-wavelength grating lines are made of a material with a second refractive index different from the first refractive index.
[0011] In another implementation form of the first aspect, the plurality of sub-wavelength grating lines are positioned between the plurality of diffractive grating lines and the plurality of diffractive grating lines and the plurality of sub-wavelength grating lines are non-parallel.
[0012] In another implementation form of the first aspect, a grating period of the diffractive gratinglines is greater than 250 nanometres and a grating period of the sub-wavelength grating lines is less than 250 nanometres.
[0013] In another implementation form of the first aspect, the exit pupil expansion structure further comprises birefringent material configured to make the diffractive grating features at least partially transparent to the second polarization.
[0014] In another implementation form of the first aspect, the diffractive grating features comprise a plurality of diffractive grating lines and the birefringent material is positioned between the plurality of diffractive grating lines.
[0015] In another implementation form of the first aspect, the plurality of diffractive grating lines are made of a material with a first refractive index and a refractive index of the birefringent material along a direction of the second polarization is substantially equal to the first refractive index.
[0016] In another implementation form of the first aspect, a refractive index of the birefringent material along a direction of the first polarization is greater than the first refractive index.
[0017] In another implementation form of the first aspect, the first polarization and the second polarization are substantially orthogonal.
[0018] According to a second aspect, a display device comprises the display structure according to the first aspect.
[0019] In an implementation form of the second aspect, the display device comprises an optical engine for directing the set of input beams to the in-coupling structure.
[0020] Many of the attendant features will be more readily appreciated as they become better understood by reference to the following detailed description considered in connection with the accompanying drawings.DESCRIPTION OF THE DRAWINGS
[0021] In the following, embodiments are described in more detail with reference to the attached figures and drawings, in which:
[0022] Fig. 1 illustrates a schematic representation of a display structure according to an embodiment;
[0023] Fig. 2 illustrates a schematic representation of an exit pupil expansion structure according to another embodiment;
[0024] Fig. 3 illustrates a schematic representation of polarization directions according to an embodiment;
[0025] Fig. 4 illustrates a schematic representation of an exit pupil expansion structure according to another embodiment;
[0026] Fig. 5 illustrates a schematic representation of an exit pupil expansion structure according to another embodiment;
[0027] Fig. 6 illustrates a k-space representation of diffraction according to an embodiment; and
[0028] Fig. 7 illustrates a schematic representation of a display device according to an embodiment.
[0029] In the following, identical reference signs refer to similar or at least functionally equivalent features.DETAILED DESCRIPTION
[0030] In the following description, reference is made to the accompanying drawings, which form part of the disclosure, and in which are shown, by way of illustration, specific aspects in which the present disclosure may be placed. It is understood that other aspects may be utilised, and structural or logical changes may be made without departing from the scope of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense, as the scope of the present disclosure is defined by the appended claims.
[0031] For instance, it is understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if a specific method step is described, a corresponding device may include a unit to perform the described method step, even if such unit is not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on functional units, a corresponding method may include a step performing the described functionality, even ifsuch step is not explicitly described or illustrated in the figures. Further, it is understood that the features of the various example aspects described herein may be combined with each other, unless specifically noted otherwise.
[0032] Fig. 1 illustrates a schematic representation of a display structure according to an embodiment.
[0033] According to an embodiment, a display structure 100 comprises a waveguide 101.
[0034] The waveguide 101 may comprise, for example, a planar waveguide. The waveguide 101 may comprise substantially planar sections. Alternatively or additionally, the waveguide 101 may also comprise curved sections. For example, the waveguide 101 may correspond to a lens or a layer of a lens of augmented reality (AR) glasses.
[0035] The display structure 100 may further comprise an in-coupling ( IC) structure 102 configured to receive a set of input beams 103 and couple the set of input beams 103 into the waveguide 101 as a set of in-coupled beams 104, wherein the set of in-coupled beams 104 comprises a first polarization and a second polarization.
[0036] The in-coupling ( IC) structure 102 may comprise, for example, an in-coupling diffraction grating. The IC structure 102 may be configured to couple the set of input beams 103 into the waveguide 101 as the set of in-coupled beams 104 via diffraction.
[0037] The set of input beams 103 may be generated by, for example, a scanner-based optical engine. The set ofinput beams 103 may represent an image generated by, for example, such an optical engine. Thus, the set of input beams 103 may also be referred to as, for example, imagebearing light rays / beams, image-carrying light rays / beams, or similar.
[0038] The first polarization may also be referred to as a first linear polarization. The second polarization may also be referred to as a second linear polarization.
[0039] Herein, a polarization may refer to the direction of the electric field of the light in question.
[0040] The display structure 100 may further comprise an exit pupil expansion (EPE) structure 105 configured to receive the set of in-coupled beams 104, wherein the exit pupil expansion structure 105 comprises diffractive grating features configured to diffract at least the first polarization in the set of in-coupled beams 104 to form a set of diffracted beams 106 and to rotate at least a part of the first polarization in the set of incoupled beams 104 into the second polarization in the set of diffracted beams 106 and the diffractive grating features are at least partially transparent to the second polarization.
[0041] The display structure 100 may further comprise an out-coupling (OC) structure 107 configured to receive the set of diffracted beams 106 and to outcouple the set of diffracted beams 106 from the waveguide 101 as a set of out-coupled beams 108.
[0042] Since the diffractive grating features are at least partially transparent to the second polarization,the EPE structure 105 may be considered polarization selective. Since the first polarization can interact with the EPE structure 105 more strongly than the second polarization, the first polarization and the second polarization may be referred to as a hot polarization and a cold polarization, respectively. For light polarized in the cold polarization direction, there may be no diffraction or less diffraction than for the light polarized in the hot polarization direction. Since arbitrary polarizations can be divided into components along the cold polarization direction and the hot polarization direction, light with any polarization direction other than the cold polarization direction can experience diffraction from the EPE structure 105.
[0043] The set of in-coupled beams 104 can have a sufficiently large polarization component in the direction of the first polarization, and thus the set of incoupled beams 104 can be diffraction from the EPE structure 105 at each interaction with the EPE structure 105. The set of diffracted beams 106 can have zero or sufficiently small polarization component in the direction of the first polarization and thus the set of diffracted beams 106 may not diffract when interacting with EPE structure 105.
[0044] For example, the EPE structure 105 may diffract the first polarization with a first diffraction efficiency η1and diffract the second polarization with a second diffraction efficiency 7]2. In some embodiments, Ih > il2r 771 > 2 X 7]2,?7I > 5 X 7]2, and / or 7]! > 10 X 7]2.
[0045] The effects disclosed herein may be achieved by appropriately configuring, for example, the mutual geometry of the direction of the set of in-coupled beams 104, the direction of the set of diffracted beams 106, and / or the direction of the cold polarization.
[0046] The polarization selectivity of the EPE structure 105 can be achieved by, for example, placing subwavelength grating features or birefringent material between the diffractive grating features and by making the effective refractive index of sub-wavelength grating features or of the birefringent material and the refractive index of the diffractive grating features be substantially equal for the cold polarization and unequal for the hot polarization.
[0047] It should be understood that the geometry of the display structure 100 illustrated in the embodiment of Fig. 1 is only exemplary and the display structure 100 may be implemented in various other ways.
[0048] Fig. 2 illustrates a schematic representation of an exit pupil expansion structure according to another embodiment.
[0049] In the embodiment of Fig. 2, the EPE structure 105 receives the set of in-coupled beams 104. The EPE structure 105 comprises diffractive grating features 201 configured to diffract at least the first polarization in the set of in-coupled beams 104 to form the set of diffracted beams 106 and to rotate at least a part of the first polarization in the set of in-coupled beams into the second polarization in the set of diffractedbeams. The diffractive grating features 201 are at least partially transparent to the second polarization.
[0050] In the embodiment of Fig. 2, the set of incoupled beams 104 comprises an elliptical polarization. The elliptical polarization can comprise the first polarization and the second polarization, such as any linear combination of the first polarization and the second polarization.
[0051] According to an embodiment, the exit pupil expansion structure 105 further comprises sub-wavelength grating features 202 configured to make the diffractive grating features 201 at least partially transparent to the second polarization.
[0052] For example, in the embodiment of Fig. 2, the EPE structure 105 comprises sub-wavelength grating features 202 configured to make the diffractive grating features 201 at least partially transparent to the second polarization.
[0053] The sub-wavelength grating features 202 may also be referred to as a zero-order grating, zero-order gating features, or similar.
[0054] The sub-wavelength grating features 202 can comprise spatially periodic variation between air and a high refractive index dielectric material. The period can be smaller than a threshold value below which the structure becomes a zeroth-order grating. This periodicity may not create propagating diffraction orders. The threshold value may be, for example, the wavelengthof the light interacting with the grating or some smaller value.
[0055] Herein, diffractive grating features may refer to grating features that have a spatial periodicity of the same order of magnitude or greater than the smallest wavelength of the set of in-coupled beams 104. Alternatively or additionally, sub-wavelength grating features may refer to grating features that have a spatial periodicity of the same order of magnitude or less than the smallest wavelength of visible light, such as less than 380 nanometres (nm). Alternatively, sub-wavelength grating features may refer to grating features that have a spatial periodicity smaller than the smallest wavelength of the set of in-coupled beams 104.
[0056] According to an embodiment, the diffractive grating features 201 comprise a plurality of diffractive grating lines and the sub-wavelength grating features 202 comprise a plurality of sub-wavelength grating lines.
[0057] For example, in the embodiment of Fig. 2, the diffractive grating features 201 comprise a plurality of diffractive grating lines and the sub-wavelength grating features 202 comprise a plurality of sub-wave-length grating lines.
[0058] According to an embodiment, the sub-wavelength grating features are configured to make the diffractive grating features at least partially transparent to thesecond polarization via a spatial refractive index average along a direction of the second polarization being substantially constant.
[0059] For example, in the embodiment of Fig. 2, the sub-wavelength grating features 202 can make the diffractive grating features 201 at least partially transparent to the second polarization via a spatial refractive index average along a direction of the second polarization being substantially constant. For example, the pitch, angle, and / or material of the sub-wavelength grating features 202 can be adjusted so that the spatial refractive index average along the direction of the second polarization is substantially constant.
[0060] According to an embodiment, the plurality of diffractive grating lines are made of a material with a first refractive index and the plurality of sub-wave-length grating lines are made of a material with a second refractive index different from the first refractive index.
[0061] In any embodiment, the plurality of diffractive grating lines may be made of, for example, silicon dioxide or titanium dioxide.
[0062] A refractive index of a material may refer to a refractive index that light experiences when the light interacts with a substantially homogeneous piece of the material. The refractive index of a material may be wavelength dependent. It should be appreciated that an effective refractive index caused by, for example, the sub-wavelength grating features 202 can differ from therefractive index of the material of which the sub-wave-length grating features 202 are made of due to the subwavelength grating features 202 having a sub-wavelength size. Since the sub-wavelength grating features 202 have a sub-wavelength size, light experiences a spatially averaged effective refractive index that depends on the relative orientation of the sub-wavelength grating features 202 and the polarization of the light. Thus, the effective refractive index of the sub-wavelength grating features 202 can be anisotropic and polarization dependent.
[0063] The set of in-coupled beams 104 can be guided inside the waveguide 101 via total internal reflection (TIR). As the set of in-coupled beams 104 propagate in the area of the EPE structure 105, the corresponding light can interact with the EPE structure 105 each time the light hits the side of the waveguide 101 on which the EPE structure 105 is located. In the interaction, a part of the light can diffract from the EPE structure 105 as the set of diffracted beams 106 and a part can continue to propagate in the original direction. For example, in the embodiment of Fig. 2, this is illustrated in locations 211. Thus, the EPE structure 105 can perform exit pupil expansion.
[0064] As the set of diffracted beams 106 propagate in the area of the EPE structure 105, the corresponding light can interact with the EPE structure 105 each time the light hits the side of the waveguide 101 on which the EPE structure 105 is located. In the interaction, apart of the light can diffract from the EPE structure 105. For example, in the embodiment of Fig. 2, this is illustrated in locations 212. This diffracted light 213 can propagate in the same direction with the set of incoupled beams 104. However, since the EPE structure 105 can rotate at least a part of the first polarization in the set of in-coupled beams 104 into the second polarization in the set of diffracted beams 106 and the diffractive grating features of the EPE structure 105 are at least partially transparent to the second polarization, this diffraction can be minimized. Thus, light 213 is marked with dashed arrows in the embodiment of Fig.2.
[0065] Without the rotation of at least a part of the first polarization in the set of in-coupled beams 104 into the second polarization in the set of diffracted beams 106 and the diffractive grating features of the EPE structure 105 being at least partially transparent to the second polarization, the light 213 could again diffract from the EPE structure resulting in light propagating in the same direction with the set of diffracted beams 106. This light can again diffract from the EPE structure resulting in light propagating in the same direction with the set of in-coupled beams 104 and so on. Thus, these diffractions can create multiple paths for the light to propagate to the OC structure 107 in a grid-like pattern. Light arriving via different paths can then interfere at the OC structure 107 and / or in the set of out-coupled beams 108. This cause local brightness- and / or color variations in the image generated bythe set of out-coupled beams 108. These interference issues can be presented with both coherent and noncoherent light sources. The display structure 100 can mitigate these effects.
[0066] Fig. 3 illustrates a schematic representation of polarization directions according to an embodiment.
[0067] Fig. 3 illustrates an example of the first polarization 301 and of the second polarization 302 and their orientation with respect to the EPE structure 105.
[0068] In any embodiment herein, the orientation of the first polarization 301 and of the second polarization 302 may be defined in relation to the grating of the EPE structure 105. Thus, even though the set of incoupled beams 104 and the set of diffracted beams 106 may propagate in different directions, the first polarization 301 in the set of in-coupled beams 104 and the first polarization 301 in the set of diffracted beams 106 may be parallel. Similarly, the second polarization 302 in the set of in-coupled beams 104 and the second polarization 302 in the set of diffracted beams 106 may be parallel.
[0069] For example, the EPE structure 105 may only diffract the first polarization 301 or diffract the first polarization 301 more strongly than the second polarization 302. Due to the diffraction, the propagation direction of the set of diffracted beams 106 may be different from the propagation direction of the set of in-coupled beams 104. Since the orientation of the first polarization 301 and the orientation of the secondpolarization 302 may be defined in relation to the grating of the EPE structure 105, the rotation of at least a part of the first polarization 301 in the set of incoupled beams 104 into the second polarization 302 in the set of diffracted beams 106 can be caused at least partially by the polarization selectivity of the EPE structure 105 and by the change in the propagation direction of the light. The orientation of the first polarization 301 with respect to the propagation direction of the light may remain the same before the diffraction and after the diffraction, but because the propagation direction of the light changes in the diffraction and the plane of incidence of the light with the EPE structure 105 changes, the first polarization 301 effectively rotates with respect to the EPE structure 105.
[0070] According to an embodiment, the first polarization 301 and the second polarization 302 are substantially orthogonal.
[0071] Herein, substantially orthogonal may mean that the angle between the first polarization 301 and the second polarization 302 is substantially 90 degrees, such as 85 - 95 degrees, 89 - 91 degrees, 89.5 - 90.5 degrees, or 89.9 - 90.1 degrees.
[0072] The embodiment of Fig. 3 also illustrate an example of the orientation between first polarization 301 and the EPE structure 105 and an example of the orientation between second polarization 302 and the EPE structure 105.
[0073] According to an embodiment, the second polarization 302 is substantially parallel with the sub-wave-length grating lines. Thus, the second polarization 302 may be substantially orthogonal with the grating vector of the sub-wavelength grating lines.
[0074] Herein, substantially parallel may mean that the angle between the second polarization 302 and the sub-wavelength grating lines is substantially 0 degrees, such as less than 5 degrees, less than 1 degrees, or less than 0.1 degrees.
[0075] The directions of the first polarization 301 and of the second polarization 302 illustrated in the embodiment of Fig. 3 are only exemplary. In other embodiments, the first polarization 301 and / or of the second polarization 302 may have any other orientation.
[0076] Fig. 4 illustrates a schematic representation of an exit pupil expansion structure according to another embodiment.
[0077] According to an embodiment, each grating line in the plurality of diffractive grating lines comprises an air gap.
[0078] The embodiment of Fig. 4 illustrates an example of the diffractive grating lines comprising an air gap 401. The air gap 401 in each diffractive grating line may run along the length direction of the diffractive grating line, as is illustrated in the embodiment of Fig. 4.
[0079] The air gap 401 in the diffractive grating lines may be used to match the effective refractiveindex of the plurality of sub-wavelength grating lines with the effective refractive index of the plurality of diffractive grating lines along the direction of the second polarization in order to make the plurality of diffractive grating lines at least partially transparent to the second polarization.
[0080] A width of the air gap 401 in each grating line in the plurality of diffractive grating lines may be sub-wavelength. Thus, the width of the air gap 401 in each grating line in the plurality of diffractive grating lines may smaller than the wavelength of the set of in-coupled beams 104.
[0081] According to an embodiment, a width of each air gap 401 in the plurality of diffractive grating lines is 30 - 100 nm.
[0082] When each grating line in the plurality of diffractive grating lines comprises an air gap, such as in the embodiment of Fig. 4, the plurality of diffractive grating lines may be made of a material with a first refractive index and the plurality of sub-wavelength grating lines are made of a material with a second refractive index different from the first refractive index or the plurality of diffractive grating lines and the plurality of sub-wavelength grating lines may be made of a material with a first refractive index.
[0083] According to an embodiment, the plurality of sub-wavelength grating lines are positioned between the plurality of diffractive grating lines and the pluralityof diffractive grating lines and the plurality of subwavelength grating lines are non-parallel.
[0084] In any embodiment disclosed herein, the plurality of diffractive grating lines and the plurality of sub-wavelength grating lines may be non-parallel and / or non-perpendicular. For example, in the embodiments of Figs. 2, 4, and 5 the plurality of diffractive grating lines and the plurality of sub-wavelength grating lines may be non-parallel and non-perpendicular.
[0085] According to an embodiment, a grating period of the diffractive grating lines is greater than 250 nanometres and a grating period of the sub-wavelength grating lines is less than 250 nanometres.
[0086] Fig. 5 illustrates a schematic representation of an exit pupil expansion structure according to another embodiment.
[0087] According to an embodiment, the exit pupil expansion structure 105 further comprises birefringent material configured to make the diffractive grating features at least partially transparent to the second polarization.
[0088] The birefringent material may comprise, for example, a uniaxially anisotropic dielectric material. A uniaxially anisotropic dielectric material can exhibit strong birefringence. The directions of the hot and cold polarizations can be determined by the orientation of the crystal lattice of the birefringent material. The crystal lattice can in principle be oriented freely with respect to the coordinate system of the diffractivegrating. The directions of the hot and cold polarizations can be, for example, any two orthogonal directions in the three-dimensional system.
[0089] According to an embodiment, the diffractive grating features 201 comprise a plurality of diffractive grating lines and the birefringent material 501 is positioned between the plurality of diffractive grating lines.
[0090] For example, in the embodiment of Fig. 5, the diffractive grating features 201 comprise a plurality of diffractive grating lines and the birefringent material 501 is positioned between the plurality of diffractive grating lines.
[0091] According to an embodiment, the plurality of diffractive grating lines are made of a material with a first refractive index and a refractive index of the birefringent material along a direction of the second polarization is substantially equal to the first refractive index.
[0092] By having the refractive index of the birefringent material along the direction of the second polarization be substantially equal to the first refractive index, the diffractive grating features 201 can be made at least partially transparent to the second polarization.
[0093] For example, a ratio between the first refractive index and the refractive index of the birefringent material along the direction of the second polarizationcan be 0.9 - 1.1, 0.95 - 1.05, 0.975 - 1.025, or 0.99 -1.01.
[0094] According to an embodiment, a refractive index of the birefringent material along a direction of the first polarization is greater than the first refractive index.
[0095] Fig. 6 illustrates a k-space representation of diffraction according to an embodiment.
[0096] Each k-vector in k-space can represent a propagation direction of a beam inside the waveguide 101. The magnitude of each k-vector corresponds to a wavenumber k. A k-vector can be expressed as k = nv, where n is the refractive index of the medium of the waveguide 101 and v is a unit vector pointing towards the propagation direction of the k-vector. k may also be referred to as a normalized k-vector.
[0097] An annular guided propagation domain 610 may refer to a part of the k-space in which beams are guided inside the waveguide 101. An example of an annular guided propagation domain 610 is illustrated in the embodiment of Fig. 6.
[0098] The waveguide 101 can guide beams having certain k-vectors via TIR. A coupling domain 620 corresponds to k-vectors that do not have sufficient x and / or y components to be guided inside the waveguide 101 via TIR. Here, the x and y axes are in the plane of the waveguide 101 while the z axis is along a thickness direction of the waveguide 101. For such beams, the angle between the beam and the surface (s) of the waveguide 101is not sufficient to cause TIR as governed by Snell ' s law. K-vectors inside the annular guided propagation domain 610 have sufficient x and / or y components to be guided inside the waveguide 101 via TIR. K-vectors at the outer circumference of the annular guided propagation domain 610 correspond to beams propagating along the plane of the waveguide 101, i. e. such beams do not have any z component. Radius of the coupling domain 620 may be 1 and radius of the annular guided propagation domain 610 may be n.
[0099] A transition in k-space may correspond to an interaction of light with a diffraction grating. Such an interaction can cause the light to propagate into a different direction or directions than before the interaction. The change in propagation direction can be observed as a translation in k-space along a transition.
[0100] The set of input beams 103 can be associated with corresponding k-vectors 621 in the coupling domain 620. The IC structure 102 can couple the set of input beams 103 into the waveguide 101 as the set of incoupled beams 104. This corresponds to shifting the k-vectors into the annular guided propagation domain 610 along transition 601.
[0101] The set of in-coupled beams 104 can be associated with a set of in-coupled k-vectors 622 in the annular guided propagation domain 610 associated with the waveguide 101.
[0102] The EPE structure 105 can receive the set of in-coupled beams 104 and diffract at least the firstpolarization in the set of in-coupled beams 104 to form a set of diffracted beams 106 and to rotate at least a part of the first polarization in the set of in-coupled beams 104 into the second polarization in the set of diffracted beams 106. The diffraction caused by the EPE structure 105 can be illustrated in k-space using transition 602.
[0103] The set of diffracted beams 106 can be associated with a set of diffracted k-vectors 623 in the annular guided propagation domain 610 associated with the waveguide 101.
[0104] The OC structure 107 can receive the set of diffracted beams 106 and outcouple the set of diffracted beams 106 from the waveguide as a set of out-coupled beams 108. The out-coupling caused by the OC structure 107 can be illustrated in k-space using transition 603.
[0105] The different k-vectors in the k-vectors 621, the set of in-coupled k-vectors 622, and the set of diffracted k-vectors 623 illustrated by the rectangles in the embodiment of Fig. 6, may correspond to, for example, different parts of an image represented by the set of input beams 103.
[0106] As the set of in-coupled beams 104 propagate in the area of the EPE structure 105, the corresponding light can interact with the EPE structure 105 each time the light hits the side of the waveguide 101 on which the EPE structure 105 is located. In the interaction, a part of the light can diffract from the EPE structure 105 as the set of diffracted beams 106 according totransition 602 and a part can continue to propagate in the original direction. Thus, the EPE structure 105 can perform exit pupil expansion.
[0107] As the set of diffracted beams 106 propagate in the area of the EPE structure 105, the corresponding light can interact with the EPE structure 105 each time the light hits the side of the waveguide 101 on which the EPE structure 105 is located. In the interaction, a part of the light can diffract from the EPE structure 105 according to transition 604. This diffracted light can propagate in the same direction with the set of incoupled beams 104. However, since the EPE structure 105 can rotate at least a part of the first polarization in the set of in-coupled beams 104 into the second polarization in the set of diffracted beams 106 and the diffractive grating features of the EPE structure 105 are at least partially transparent to the second polarization, this diffraction can be minimized. Thus, transition 604 is marked with a dashed arrow in the embodiment of Fig. 6.
[0108] Fig. 7 illustrates a schematic representation of a display device according to an embodiment.
[0109] According to an embodiment, a display device 700 comprises the display structure 100.
[0110] According to an embodiment, the display device 700 further comprises an optical engine 701 for directing the set of input beams 103 to the in-coupling structure 102.
[0111] According to an embodiment, the display device 700 comprises a scanner-based optical engine and / or a laser-scanning optical engine 701, for directing the set of input beams 103 to the in-coupling structure 102.
[0112] A laser-scanning optical engine may comprise, for example, a laser beam scanning (LBS) optical engine.
[0113] In some embodiments, the optical engine may comprise a liquid crystal on silicon (LCOS) based optical engine, a digital light processing (DLP) based optical engine, and / or a microLED based optical engine.
[0114] According to an embodiment, the display device 700 is implemented as a see-through display device.
[0115] According to an embodiment, the display device 700 is implemented as a head-mounted display device.
[0116] For example, in the embodiment of Fig. 7, the display device 700 is implemented as smart glasses. The waveguide 101 can correspond to a lens or a layer of a lens of such smart glasses. Such smart glasses may be used to, for example, implement augmented reality (AR), virtual reality (VR), and / or extended reality (XR) functionality.
[0117] In the embodiment of Fig. 7, a set of input beams 103 may be generated by, for example, an optical engine 701, such as a scanner-based optical engine. The set of input beams 103 may represent an image generated by, for example, the optical engine 701. The display structure 100 of the display device 700 can direct the set of out-coupled beams, representing the image generated by the optical engine 701, into the eye of a user.
[0118] Any range or device value given herein may be extended or altered without losing the effect sought. Also any embodiment may be combined with another embodiment unless explicitly disallowed.
[0119] Although the subj ect matter has been described in language specific to structural features and / or acts, it is to be understood that the subj ect matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as examples of implementing the claims and other equivalent features and acts are intended to be within the scope of the claims.
[0120] It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages. It will further be understood that reference to ' an' item may refer to one or more of those items.
[0121] Aspects of any of the embodiments described above may be combined with aspects of any of the other embodiments described to form further embodiments without losing the effect sought.
[0122] The term ' comprising' is used herein to mean including the method, blocks or elements identified, butthat such blocks or elements do not comprise an exclusive list and a method or apparatus may contain additional blocks or elements.
[0123] It will be understood that the above descrip-tion is given by way of example only and that various modifications may be made by those skilled in the art. The above specification, examples and data provide a complete description of the structure and use of exemplary embodiments. Although various embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this specifica-tion.
Claims
CLAIMS:
1. A display structure ( 100 ), comprising:a waveguide ( 101 );an in-coupling structure ( 102 ) configured to receive a set of input beams ( 103 ) and couple the set of input beams ( 103 ) into the waveguide ( 101 ) as a set of in-coupled beams ( 104 ), wherein the set of in-coupled beams ( 104 ) comprises a first polari zation ( 301 ) and a second polari zation ( 302 );an exit pupil expansion structure ( 105 ) configured to receive the set of in-coupled beams ( 104 ), wherein the exit pupil expansion structure ( 105 ) comprises di f fractive grating features configured to di ffract at least the first polari zation ( 301 ) in the set of in-coupled beams to form a set of di f fracted beams ( 106 ) and to rotate at least a part of the first polari zation ( 301 ) in the set of in-coupled beams ( 104 ) into the second polari zation ( 302 ) in the set of di f fracted beams ( 106 ) and the dif fractive grating features are at least partially transparent to the second polari zation ( 302 ); andan out-coupling structure ( 107 ) configured to receive the set of di f fracted beams ( 106 ) and to out-couple the set of di f fracted beams ( 106 ) from the waveguide ( 101 ) as a set of out-coupled beams ( 108 ).
2. The display structure ( 100 ) according to claim 1, wherein the exit pupil expansion structure ( 105 ) further comprises sub-wavelength grating features ( 202 )configured to make the diffractive grating features (201 ) at least partially transparent to the second polarization (302 ).
3. The display structure ( 100) according to claim 2, wherein the sub-wavelength grating features (202 ) are configured to make the diffractive grating features (201 ) at least partially transparent to the second polarization (302 ) via a spatial refractive index average along a direction of the second polarization (302 ) being substantially constant.
4. The display structure ( 100) according to claim 2 or claim 3, wherein the diffractive grating features (201 ) comprise a plurality of diffractive grating lines and the sub-wavelength grating features (202 ) comprise a plurality of sub-wavelength grating lines.
5. The display structure ( 100) according to any claim 4, wherein each grating line in the plurality of diffractive grating lines comprises an air gap (401 ).
6. The display structure ( 100) according to claim 4 or claim 5, wherein the plurality of diffractive grating lines are made of a material with a first refractive index and the plurality of sub-wavelength grating lines are made of a material with a second refractive index different from the first refractive index.
7. The display structure ( 100) according to any of claims 4 – 6, wherein the plurality of sub-wavelength grating lines are positioned between the plurality of diffractive grating lines and the plurality of diffractive grating lines and the plurality of sub-wavelength grating lines are non-parallel.
8. The display structure ( 100) according to any of claims 4 – 7, wherein a grating period of the diffractive grating lines is greater than 250 nanometres and a grating period of the sub-wavelength grating lines is less than 250 nanometres.
9. The display structure ( 100) according to claim 1, wherein the exit pupil expansion structure ( 105) further comprises birefringent material (501 ) configured to make the diffractive grating features (201 ) at least partially transparent to the second polarization (302 ).
10. The display structure ( 100) according to claim 9, wherein the diffractive grating features (201 ) comprise a plurality of diffractive grating lines and the birefringent material (501 ) is positioned between the plurality of diffractive grating lines.
11. The display structure ( 100) according to claim 9 or claim 10, wherein the plurality of diffractive grating lines are made of a material with a first refractive index and a refractive index of the birefringent material (501 ) along a direction of the secondpolarization (302 ) is substantially equal to the first refractive index.
12. The display structure ( 100) according claim 11, wherein a refractive index of the birefringent material (501 ) along a direction of the first polarization (301 ) is greater than the first refractive index.
13. The display structure ( 100) according to any preceding claim, wherein the first polarization (301 ) and the second polarization (302 ) are substantially orthogonal.
14. A display device (700) comprising the display structure ( 100) according to any preceding claims.
15. The display device (700) according to claim 14, further comprising an optical engine (701 ) for directing the set of input beams ( 103) to the in-coupling structure ( 102).