FI20235940A1 - Screen structure - Google Patents

Abstract

According to one embodiment, the display structure comprises: a first waveguide; a first coupling structure; a first waveplate configured to perform a first polarization modification for the first polarization; a first reflector configured to reflect a first wavelength range incident on the first reflector back towards the first waveplate as a first reflected light beam; a second waveguide; and a second coupling structure configured to couple at least a portion of the second wavelength range to the second waveguide; wherein the first waveplate is further configured to perform a second polarization modification for the first reflected light beam, wherein the first polarization modification and the second polarization modification convert the polarization of the first reflected light beam to a second polarization and the first coupling structure is configured to couple the second polarization of the first reflected light beam to the first waveguide.

Description

DISPLAY STRUCTURE

TECHNICAL 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] In various optical applications, such as aug- mented reality (AR) applications, it is typically de- sirable to improve the optical properties of the used components. However, since optical properties of many components and/materials depend on the wavelength of the light used, it can be challenging to design optical components for broad wavelength ranges, such as for dif- ferent colours, while maintaining good optical proper- ties. Thus, it may be desirable to be able to separate different wavelength ranges.

SUMMARY

O

O [0003] This summary is provided to introduce a selec- 3 tion of concepts in a simplified form that are further

TN described below in the detailed description. This sum-

E mary is not intended to identify key features or essen- o 25 tial features of the claimed subject matter, nor is it > intended to be used to limit the scope of the claimed

S subject matter.

[0004] It is an object to provide a display structure and a display device. The foregoing and other objects are achieved by the features of the independent claims.

Further implementation forms are apparent from the de- pendent claims, the description and the figures.

[0005] According to a first aspect, a display struc- ture comprises: display structure, comprising: a first waveguide configured to receive a first input light beam in a first polarization comprising at least a first wavelength range and a second wavelength range; a first in-coupling structure in/on the first waveguide config- ured to let at least part of the first polarization pass through the first in-coupling structure; a first wave- plate configured to perform a first polarization manip- ulation on the first polarization passed through the first in-coupling structure; a first reflector config- ured to reflect at least part of the first wavelength range arriving to the first reflector through the first waveplate back towards the first waveplate as a first reflected light beam and let at least part of the second n wavelength range pass through the first reflector; a

S second waveguide; and a second in-coupling structure

Od in/on the second waveguide configured to couple at least + part of the second wavelength range passed through the : 25 first reflector into the second waveguide; wherein the > first waveplate is further configured to perform a sec- 3 ond polarization manipulation on the first reflected 2 light beam and let the first reflected light beam pass

N to the first in-coupling structure, wherein the first polarization manipulation and the second polarization manipulation are configured to convert a polarization of the first reflected light beam at least partially into a second polarization and the first in-coupling structure is further configured to couple at least part of the second polarization of the first reflected light beam into the first waveguide.

[0006] According to second aspect, a display device comprises a display structure according to the first aspect.

[0007] Many of the attendant features will be more readily appreciated as they become better understood by reference to the following detailed description consid- ered in connection with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

[0008] In the following, embodiments are described in more detail with reference to the attached figures and drawings, in which:

[0009] Fig. 1 illustrates a schematic representation = of a display structure according to an embodiment;

N [0010] Fig. 2 illustrates a schematic representation

S of a display structure according to another embodiment;

NN [0011] Fig. 3 illustrates a schematic representation

E 25 of a display structure according to another embodiment; 3 [0012] Fig. 4 illustrates a schematic representation 2 of a display structure according to another embodiment;

O

N

[0013] Fig. 5 illustrates a schematic representation of a unit cell of an in-coupling structure according to an embodiment;

[0014] Fig. 6 illustrates a schematic representation of an in-coupling structure according to an embodiment;

[0015] Fig. 7 illustrates a schematic representation of an in-coupling structure according to another embod- iment;

[0016] Fig. 8 illustrates a schematic representation of an in-coupling structure according to another embod- iment;

[0017] Fig. 9 illustrates a schematic representation of a waveguide according to an embodiment; and

[0018] Fig. 10 illustrates a schematic representation of a display device according to an embodiment.

[0019] In the following, identical reference signs refer to similar or at least functionally equivalent features.

DETAILED DESCRIPTION

& [0020] In the following description, reference is made 3 to the accompanying drawings, which form part of the + disclosure, and in which are shown, by way of illustra-

N tion, specific aspects in which the present disclosure

E 25 may be placed. It is understood that other aspects may 3 be utilised, and structural or logical changes may be 2 made without departing from the scope of the present

N disclosure. The following detailed description, there- fore, is not to be taken in a limiting sense, as the scope of the present disclosure is defined by the ap- pended claims.

[0021] For instance, it is understood that a disclo- sure in connection with a described method may also hold 5 true for a corresponding device or system configured to perform the method and vice versa. For example, 1f a specific method step is described, a corresponding de- vice 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 ex- ample, if a specific apparatus is described based on functional units, a corresponding method may include a step performing the described functionality, even if such 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 oth- erwise.

[0022] Fig. 1 illustrates a schematic representation of a display structure according to an embodiment. e [0023] According to an embodiment, a display structure

S 100 comprises a first waveguide 101 configured to re-

Od ceive a first input light beam 161 in a first polariza- x tion 151 comprising at least a first wavelength range z 25 and a second wavelength range. > [0024] The first input light beam 161 may also be > referred to as a first input light, a first plurality & of input beams, a first plurality of input light beams,

N a first plurality of input rays, a first plurality of input light rays, or similar.

[0025] Although various light paths, such as the first input light beam 161, are illustrated using single light rays in Fig. 1 and other embodiments disclosed herein, this is only for illustrative purposes. Any light dis- closed herein may comprise, for example, a plurality of light beams that may propagate in various directions.

For example, the first input light beam 161 may comprise a cone of light arriving to the first waveguide 101 from a plurality of directions.

[0026] The first input light beam 161 may be generated by, for example, a scanner-based optical engine or a liquid crystal on silicon (LCOS) based optical engine.

The first input light beam 161 may represent an image generated by, for example, such an optical engine. Thus, the first input light beam 161 may also be referred to as, for example, image-bearing light, image-carrying light, image-bearing light rays/beams, image-carrying light rays/beams, or similar. Alternatively or addi- n tionally, the first input light beam 161 may be provided

S by some other optical components such as those disclosed

Od in the embodiments herein. x [0027] The first waveguide 101 may comprise, for ex-

I 25 ample, a substantially planar waveguide. Alternatively - or additionally, the first waveguide 101 may also com- > prise curved sections. For example, the first waveguide & 101 may correspond to a lens of augmented reality (AR)

N glasses. For example, the first waveguide 101 may cor- respond to a layer of a lens of such AR glasses.

[0028] The first wavelength range may be different from the second wavelength range. The first wavelength range and the second wavelength range may be non-over- lapping.

[0029] The display structure 100 may further comprise a first in-coupling structure 111 in/on the first wave- guide 101. The first in-coupling structure 111 may be configured to let at least part of the first polariza- tion 151 pass through the first in-coupling structure 111.

[0030] For example, in an ideal situation, the first in-coupling structure 111 may let all of the first po- larization 151 pass through the first in-coupling struc- ture 111. In practical implementations, the first in- coupling structure 111 may let most of the first polar- ization 151 pass through the first in-coupling structure 111.

[0031] The display structure 100 may further comprise en a first waveplate 121 configured to perform a first

S polarization manipulation on the first polarization 151

Od passed through the first in-coupling structure 111. a [0032] The first waveplate 121 may comprise, for ex-

E 25 ample, a first quarter-wave plate. o [0033] Herein, a quarter-wave plate may also be re-

D ferred to as a 4/4 waveplate or similar.

O [0034] The display structure 100 may further comprise a first reflector 131 configured to reflect at least part of the first wavelength range arriving to the first reflector 131 through the first waveplate 121 back to- wards the first waveplate 121 as a first reflected light beam 171 and let at least part of the second wavelength range pass through the first reflector 131.

[0035] For example, in an ideal situation, the first reflector 131 may reflect all of the first wavelength range back towards the first waveplate 121. Similarly, in an ideal situation, the first reflector 131 may let all of the second wavelength range pass through the first reflector 131. In practical implementations the first reflector 131 may reflect most the first wave- length range back towards the first waveplate 121 and let most of the second wavelength range pass through the first reflector 131.

[0036] The display structure 100 may further comprise a second waveguide 102 and a second in-coupling struc- ture 112 in/on the second waveguide 102. The second in- coupling structure 112 may be configured to couple at least part of the second wavelength range passed through n the first reflector 131 into the second waveguide 102.

S [0037] The second waveguide 102 may comprise, for ex-

Od ample, a substantially planar waveguide. Alternatively x or additionally, the second waveguide 102 may also com-

I 25 prise curved sections. For example, the second waveguide > 102 may correspond to a lens of augmented reality (AR) > glasses. For example, the second waveguide 102 may cor- & respond to a layer of a lens of such AR glasses.

N

[0038] For example, in an ideal situation, the second in-coupling structure 112 may couple all of the second wavelength range passed through the first reflector 131 into the second waveguide 102. In practical implementa- tions, the second in-coupling structure 112 may couple most of the second wavelength range passed through the first reflector 131 into the second waveguide 102.

[0039] In some embodiments, the second in-coupling structure 112 may in practice couple also some of the first wavelength range passed through the first reflec- tor 131 into the second waveguide 102.

[0040] The first waveplate 121 may be further config- ured to perform a second polarization manipulation on the first reflected light beam 171 and let the first reflected light beam 171 pass to the first in-coupling structure 111. The first polarization manipulation and the second polarization manipulation may be configured to convert a polarization of the first reflected light beam 171 at least partially into a second polarization 152. The first in-coupling structure 111 may be further n configured to couple at least part of the second polar-

S ization 152 of the first reflected light beam 171 into

Od the first waveguide 101. x [0041] The first polarization 151 may also be referred =E 25 oto as a first linear polarization. The second polariza- - tion 152 may also be referred to as a second linear > polarization. & [0042] When the first polarization manipulation and = the second polarization manipulation are configured to convert the polarization of the first reflected light beam 171 at least partially into the second polarization 152, the combined effect of the first polarization ma- nipulation and the second polarization may convert the polarization of the first reflected light beam 171 at least partially into the second polarization 152.

[0043] For example, if the first waveplate 121 com- prises a quarter-wave plate, the first polarization ma- nipulation can convert the first polarization 151 into a circular polarization, a substantially circular po- larization, or an elliptical polarization. Then, the second polarization manipulation can convert the circu- lar, substantially circular, or elliptical polarization into the second polarization 152.

[0044] For example, in an ideal situation, as is il- lustrated in the embodiment of Fig. 1, the first polar- ization manipulation and the second polarization manip- ulation may convert the polarization of the first re- flected light beam 171 into the second polarization 152.

In practical implementations, the first polarization n manipulation and the second polarization manipulation

S may convert the polarization of the first reflected

Od light beam 171 substantially into the second polariza- x tion 152 and/or mostly into the second polarization 152.

I 25 [0045] In an ideal situation, the first in-coupling > structure 111 may couple all of the second polarization > 152 of the first reflected light beam 171 into the first & waveguide 101. In practical implementations, the first

N in-coupling structure 111 may couple most of the second polarization 152 of the first reflected light beam 171 into the first waveguide 101.

[0046] Since the first in-coupling structure 111 may be configured to let at least part of the first polar- ization 151 pass through the first in-coupling structure 111 and to couple at least part of the second polariza- tion 152 of the first reflected light beam 171 into the first waveguide 101, the first in-coupling structure 111 may be considered a polarization-sensitive in-coupling structure. For example, the first in-coupling structure 111 may in-couple the first polarization 151 with a first in-coupling efficiency mm and in-couple the second polarization 152 with a second in-coupling efficiency n, . In some embodiments, 1N2>19, 12>2X19, 12>5*X0%9,, and/or mm > 10 Xm.

[0047] The second polarization 152 may be non-parallel with the first polarization 151.

[0048] According to an embodiment, the first polari- zation 151 and the second polarization 152 are substan- tially orthogonal.

Q [0049] In some embodiments, the first polarization 151

N and the second polarization 152 may be orthogonal.

S [0050] For example, in the embodiment of Fig. 1, the

N first polarization 151 is perpendicular to the plane of s 25 Fig. 1 and the second polarization 152 is parallel with

S the plane of Fig. 1. 3 [0051] The positioning of the first in-coupling struc-

S ture 111 illustrated in the embodiment of Fig. 1 is only exemplary and the first in-coupling structure 111 may be positioned in various other ways. In some embodi- ments, the first in-coupling structure 111 may be posi- tioned on any surface of the first waveguide 101. In other embodiments, the first in-coupling structure 111 be positioned inside the first waveguide 101.

[0052] The light coupled into the first waveguide 101 can be guided inside the first waveguide 101 via total internal reflection (TIR). Similarly, the light coupled into the second waveguide 102 can be guided inside the second waveguide 10? via TIR.

[0053] According to an embodiment, the first in-cou- pling structure 111 is configured to couple at least part of the second polarization 152 of the first re- flected light beam 171 into the first waveguide 101 via zeroth order and first order diffractions.

[0054] In any embodiment disclosed herein, the first in-coupling structure 111 and/or the second in-coupling structure 112 may comprise a reflective or a transmis- sive diffractive grating.

[0055] It should be understood that the geometry of e the display structure 100 illustrated in the embodiment

S of Fig. 1 is only exemplary and the display structure

Od 100 may be implemented in various other ways. For exam- x ple, the dimensions of the first waveguide 101 and the = 25 dimensions of the first in-coupling structure 111 have - been chosen for illustrative purposes. > [0056] Fig. 2 illustrates a schematic representation

S of a display structure according to another embodiment.

[0057] According to an embodiment, the display struc- ture 100 further comprises a second waveplate 122 con- figured to receive the second wavelength range passed through the first reflector 131, perform a third polar- ization manipulation on the second wavelength range passed through the first reflector 131, wherein the first polarization manipulation and the third polariza- tion manipulation are configured to convert the first polarization 151 of the second wavelength range at least partially into the second polarization 152, and pass the second wavelength range to the second waveguide 102 and wherein the second in-coupling structure 112 is further configured to couple at least part of the second polar- ization 152 of the second wavelength range into the second waveguide 102.

[0058] In the embodiment of Fig. 2, the second in- coupling structure 112 can be polarization selective similarly to the first in-coupling structure 111. The second in-coupling structure 112 may be configured to let at least part and/or most of the first polarization n 151 pass through the second in-coupling structure 112.

S [0059] The second in-coupling structure 112 may be

Od configured to let at least part of the first polariza- x tion 151 pass through the second in-coupling structure z 25 112 and to couple at least part of the second polariza- > tion 152 into the second waveguide 102, the second in- > coupling structure 112 may be considered a polarization- & sensitive in-coupling structure. For example, the second

N in-coupling structure 112 may in-couple the first po- larization 151 with a third in-coupling efficiency 13 and in-couple the second polarization 152 with a fourth in-coupling efficiency 4. In some embodiments, na >13, 14>2X7193, 14 >5X13, and/or Nn, > 10 Xn3.

[0060] Fig. 3 illustrates a schematic representation of a display structure according to another embodiment.

[0061] The display structure 100 may further comprise a third waveguide 103 configured receive a second input light beam 162 in the second polarization 152 comprising at least the first wavelength range, the second wave- length range, and a third wavelength range.

[0062] The second input light beam 162 may also be referred to as a second input light, a second plurality of input beams, a second plurality of input light beams, a second plurality of input rays, a second plurality of input light rays, or similar.

[0063] The second input light beam 162 may be gener- ated by, for example, a scanner-based optical engine or an LCOS-based optical engine. The second input light

D beam 162 may represent an image generated by, for exam-

N ple, such an optical engine. Thus, the second input 3 light beam 162 may also be referred to as, for example,

N image-bearing light, image-carrying light, image-bear-

E 25 ing light rays/beams, image-carrying light rays/beams,

S or similar.

O [0064] The third waveguide 103 may comprise, for ex-

O ample, a substantially planar waveguide. Alternatively or additionally, the third waveguide 103 may also com- prise curved sections. For example, the third waveguide 103 may correspond to a lens of augmented reality (AR) glasses. For example, the third waveguide 103 may cor- respond to a layer of a lens of such AR glasses.

[0065] In some embodiments, the first 101, second 102, and third waveguide 103 may be implemented, for example, as layers in a lens of AR glasses.

[0066] The first wavelength range may be different from the second wavelength range and from the third wavelength range. The first wavelength range, the second wavelength range, and the third wavelength range may be non-overlapping.

[0067] The display structure 100 may further comprise a third in-coupling structure 113 in/on the third wave- guide 103. The third in-coupling structure 113 may be configured to let at least part of the second polariza- tion 152 pass through the third in-coupling structure 113.

[0068] For example, in an ideal situation, the third en in-coupling structure 113 may let all of the second

S polarization 152 pass through the third in-coupling

Od structure 113. In practical implementations, the third x in-coupling structure 113 may let most of the second

E 25 polarization 152 pass through the third in-coupling o structure 113.

D [0069] The display structure 100 may further comprise

O a third waveplate 123 configured to perform a fourth polarization manipulation on the second polarization 152 passed through the third in-coupling structure 113.

[0070] The third waveplate 123 may comprise, for ex- ample, a third quarter-wave plate.

[0071] The display structure 100 may further comprise a second reflector 132 configured to reflect at least part of the third wavelength range arriving to the sec- ond reflector 132 through the third waveplate 123 back towards the third waveplate 123 as a second reflected light beam 172 and let at least part of the first and second wavelength range pass through the second reflec- tor 132.

[0072] For example, in an ideal situation, the second reflector 132 may reflect all of the third wavelength range back towards the third waveplate 123 as a second reflected light beam 172 and let all of the first and second wavelength range pass through the second reflec- tor 132. In practical implementations, the second re- flector 132 may reflect most of the third wavelength range back towards the third waveplate 123 as a second n reflected light beam 172 and let most of the first and

S second wavelength range pass through the second reflec-

Od tor 132. x [0073] The display structure 100 may further comprise =E 25 a fourth waveplate 124 configured to receive the first > and second wavelength range passed through the second > reflector 132, perform a fifth polarization manipulation & on the first and second wavelength range passed through

N the second reflector 132, wherein the fourth polariza- tion manipulation and the fifth polarization manipula- tion are configured to convert the second polarization 152 of the first and second wavelength range at least partially into the first polarization 151, and pass the first wavelength range and the second wavelength range to the first waveguide 101 as the first input light beam 161.

[0074] For example, in an ideal situation, as is il- lustrated in the embodiment of Fig. 3, the fourth po- larization manipulation and the fifth polarization ma- nipulation may be configured to convert the second po- larization 152 of the first and second wavelength range into the first polarization 151. In practical implemen- tations, the fourth polarization manipulation and the fifth polarization manipulation may be configured to convert the second polarization 152 of the first and second wavelength range substantially into the first polarization 151 and/or mostly into the first polariza- tion 151.

N [0075] The fourth waveplate 124 may comprise, for ex-

S ample, a fourth guarter-wave plate.

Od [0076] The third waveplate 123 may be further config- x ured to perform a sixth polarization manipulation on the z 25 second reflected light beam 172 and let the second re- > flected light beam 172 pass to the third in-coupling > structure 113, wherein the fourth polarization manipu- & lation and the sixth polarization manipulation are con-

N figured to convert a polarization of the second re- flected light beam 172 at least partially into the first polarization 151. The third in-coupling structure 113 may be further configured to couple at least part of the first polarization 151 of the second reflected light beam 172 into the third waveguide 103.

[0077] For example, in an ideal situation, as is il- lustrated in the embodiment of Fig. 3, the fourth po- larization manipulation and the sixth polarization ma- nipulation may convert the polarization of the second reflected light beam 172 into the first polarization 151. In practical implementations, the fourth polariza- tion manipulation and the sixth polarization manipula- tion may convert the polarization of the second re- flected light beam 172 substantially into the first po- larization 151 and/or mostly into the first polarization 151.

[0078] Since the third in-coupling structure 113 may be configured to let at least part of the second polar- ization 152 pass through the third in-coupling structure n 113 and to couple at least part of the first polarization

S 151 of the second reflected light beam 172 into the

Od third waveguide 103, the third in-coupling structure 113 + may be considered a polarization-sensitive in-coupling : 25 structure. For example, the third in-coupling structure > 113 may in-couple the first polarization 151 with a 3 fifth in-coupling efficiency 15 and in-couple the second & polarization 152 with a sixth in-coupling efficiency Nc.

N

In some embodiments, Ns >1ng, Ns >2XNg, Ns >5Xns, and/or ns > 10 X ne.

[0079] According to an embodiment, the second wave- length range comprises wavelengths longer than the first wavelength range, and/or the second wavelength range comprises wavelengths longer than the third wavelength range.

[0080] The first wavelength range may comprise wave- lengths longer than the third wavelength range.

[0081] For example, the first wavelength range may correspond to the colour green, the second wavelength range may correspond to the colour red, and/or the third wavelength range may correspond to the colour blue.

[0082] According to an embodiment, the first reflector 131 comprises a first dichroic mirror and/or the second reflector 132 comprises a second dichroic mirror.

[0083] The first dichroic mirror may be configured similarly to the first reflector 131. Any disclosure herein in relation to the first reflector 131 may apply to the first dichroic mirror. = [0084] The second dichroic mirror may be configured

N similarly to the second reflector 132. Any disclosure

S herein in relation to the second reflector 132 may apply

N to the second dichroic mirror.

E 25 [0085] The display structure 100 can enable coupling

S each wavelength range into a corresponding waveguide. 3 Thus, each waveguide and corresponding optical compo-

S nents can be designed for the corresponding wavelength range. This can improve the optical properties of the display structure 100.

[0086] Fig. 4 illustrates a schematic representation of a display structure according to another embodiment.

[0087] According to an embodiment, the display struc- ture 100 further comprises a third waveguide 103 con- figured receive a second input light beam 162 in the first polarization 151 comprising at least the first wavelength range, the second wavelength range, and a third wavelength range.

[0088] The display structure 100 may further comprise a third in-coupling structure 113 in/on the third wave- guide 103 configured to let at least part of the first polarization 151 pass through the third in-coupling structure 113.

[0089] The display structure 100 may further comprise a third waveplate 123 configured to perform a fourth polarization manipulation on the first polarization 151 passed through the third in-coupling structure 113.

[0090] The display structure 100 may further comprise 0 a second reflector 132 configured to reflect at least

S part of the third wavelength range arriving to the sec- 3 ond reflector 132 through the third waveplate 123 back

TN towards the third waveplate 123 as a second reflected

E 25 light beam 172 and let at least part of the first and

Oo second wavelength range pass through the second reflec- : tor 132.

S [0091] The display structure 100 may further comprise a fourth waveplate 124 configured to receive the first and second wavelength range passed through the second reflector 132, perform a fifth polarization manipulation on the first and second wavelength range passed through the second reflector 132, wherein the fourth polariza- tion manipulation and the fifth polarization manipula- tion are configured to maintain the first polarization 151 of the first and second wavelength range, and pass the first wavelength range and the second wavelength range to the first waveguide 101 as the first input light beam 161.

[0092] The third waveplate 123 may be further config- ured to perform a sixth polarization manipulation on the second reflected light beam 172 and let the second re- flected light beam 172 pass to the third in-coupling structure 113, wherein the fourth polarization manipu- lation and the sixth polarization manipulation are con- figured to convert a polarization of the second re- flected light beam 172 at least partially into the sec- ond polarization 152, and the third in-coupling struc- ture 113 is further configured to couple at least part of the second polarization 152 of the second reflected & light beam 172 into the third waveguide 103. 3 [0093] The fourth waveplate 124 of the embodiment of x Fig. 4 may comprise, for example, a 34/4 waveplate. Such

I 25 a waveplate may be implemented using, for example, three - A/4 waveplates or using a single appropriately config- > ured waveplate.

N

&

[0094] Since the third in-coupling structure 113 may be configured to let at least part of the first polar- ization 151 pass through the third in-coupling structure 113 and to couple at least part of the second polariza- tion 152 of the second reflected light beam 172 into the third waveguide 103, the third in-coupling structure 113 may be considered a polarization-sensitive in-coupling structure. For example, the third in-coupling structure 113 may in-couple the first polarization 151 with a fifth in-coupling efficiency 15 and in-couple the second polarization 152 with a sixth in-coupling efficiency Nc.

In some embodiments, Ng >Ns5, Ng >2XMNs, Ng >5Xns, and/or

Ne > 10 X ns.

[0095] The embodiment of Fig. 3 or the embodiment of

Fig. 4 may be combined with the embodiment of Fig. 2 to form another embodiment.

[0096] Fig. 5 illustrates a schematic representation of a unit cell of an in-coupling structure according to an embodiment.

[0097] The unit cell of the in-coupling structure il- = lustrated in the embodiment of Fig. 5 may correspond to

N the first in-coupling structure 111, the second in-cou-

S pling structure 112, and/or to the third in-coupling

N structure 113.

E 25 [0098] According to an embodiment, the first in-cou-

S pling structure 111 comprises first diffractive grating

D features and first sub-wavelength grating features,

O wherein the first diffractive grating features are con-

figured to couple at least part of the second polariza- tion 152 into the first waveguide 101 and the first sub- wavelength grating features are configured to make the first diffractive grating features at least partially transparent to the first polarization 151.

[0099] Since the first diffractive grating features are configured to couple at least part of the second polarization 152 into the first waveguide 101, some part of the second polarization 152 can also pass through the first in-coupling structure 111 and/or the first wave- guide 101.

[0100] Since the first sub-wavelength grating fea- tures can make the first diffractive grating features at least partially transparent to the first polarization 151, at least a part of the first polarization 151 can pass through the first waveguide 101.

[0101] According to an embodiment, the second in-cou- pling structure 112 comprises second diffractive grating features and second sub-wavelength grating features, wherein the second diffractive grating features are con- n figured to couple at least part of the second polariza-

S tion 152 into the second waveguide 102 and the second

Od sub-wavelength grating features are configured to make x the second diffractive grating features at least par- z 25 tially transparent to the first polarization 151. > [0102] According to an embodiment, the third in-cou- > pling structure 113 comprises third diffractive grating & features and third sub-wavelength grating features,

N wherein the third diffractive grating features are con- figured to couple at least part of the first/second polarization 151, 152 into the third waveguide 103 and the third sub-wavelength grating features are configured to make the third diffractive grating features at least partially transparent to the second/first polarization 152, 151. For example, in the embodiment of Fig. 3, the third diffractive grating features may be configured to couple at least part of the first polarization 151 into the third waveguide 103 and the third sub-wavelength grating features may be configured to make the third diffractive grating features at least partially trans- parent to the second polarization 152. In the embodiment of Fig. 4, the third diffractive grating features may be configured to couple at least part of the second polarization 152 into the third waveguide 103 and the third sub-wavelength grating features may be configured to make the third diffractive grating features at least partially transparent to the first polarization 151.

[0103] 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

N wavelength of the first/second input light beam 161, = 162. Alternatively or additionally, sub-wavelength

N 25 grating features may refer to grating features that have

E a spatial periodicity of the same order of magnitude or 3 less than the smallest wavelength of visible light, such 2 as less than 380 nanometres (nm).

O

N

[0104] Alternatively or additionally, diffractive grating features may refer to grating features that have a spatial periodicity, which, in the used incidence mounting, allows propagating diffraction orders, in ei- ther reflected or transmitted light, to emerge.

[0105] Alternatively or additionally, sub-wavelength grating features may refer to grating features that have a spatial periodicity, which, in the used incidence mounting, does not allow diffraction orders to emerge.

[0106] The sub-wavelength grating features may also be referred to as zeroth order grating features.

[0107] For example, the embodiment of Fig. 5 illus- trates a unit cell of an in-coupling structure compris- ing diffractive grating features along the x direction and sub-wavelength grating features along the y direc- tion. A grating period of the diffractive grating fea- tures, denoted by dy, may be 300 - 500 nanometres (nm) and a grating period of the sub-wavelength grating fea- tures, denoted by dy, may be 200 nm. The diffractive grating features and the sub-wavelength grating features 0 may be made of a dielectric material 301, such as tita-

N nium dioxide (Ti0,). The refractive index of TiO, is 3 approximately 2.4. The diffractive grating features and

N the sub-wavelength grating features may be separated by

E 25 air 302. 3 [0108] The grating period of the diffractive grating

D features is denoted by d, in the embodiments of Figs.

O 5 - 8.

[0109] The grating period of the sub-wavelength grat- ing features is denoted by dy in the embodiments of

Figs. 5 - 8

[0110] Alternatively or additionally, the grating pe- riod of the diffractive grating features is greater than 260 nm, 270 nm, 280 nm, 290 nm, or 300 nm.

[0111] Alternatively or additionally, the grating pe- riod of the sub-wavelength grating features is less than 240 nm, 230 nm, or 220 nm.

[0112] According to an embodiment, a grating period of the diffractive grating features is 300 - 500 nm.

[0113] Any disclosure herein in relation to diffrac- tive grating features may apply to the first diffractive grating features, the second diffractive grating fea- tures, and/or to the third diffractive grating features.

[0114] Any disclosure herein in relation to sub-wave- length grating features may apply to the first sub- wavelength grating features, the second sub-wavelength grating features, and/or to the third sub-wavelength grating features. = [0115] Fig. 6 illustrates a schematic representation dS of an in-coupling structure according to an embodiment. = [0116] The first 111, second 112, and/or third in-

N coupling structure 113 may comprise an in-coupling fz 25 structure similar to that illustrated in the embodiment 3 of Fig. 6. Any disclosure herein in relation to the 2 embodiment of Fig. 6 may apply to any of the first 111,

N second 112, and/or third in-coupling structure 113. The polarization sensitivity of each in-coupling structure can be adjusted by rotating the in-coupling structure appropriately. For example, the first in-coupling struc- ture 111 may be configured to in-couple the second po- larization 152 and the third in-coupling structure 113 may be configured to in-couple the first polarization 151. These in-coupling structure can be implemented us- ing the same or at least similar gratings, such as what is illustrated in the embodiment of Fig. 6, and the gratings of the first in-coupling structure 111 can be rotated by 90 degrees compared to the gratings of the third in-coupling structure 113 in order to achieve the aforementioned polarization sensitivity.

[0117] According to an embodiment, the first diffrac- tive grating features comprise a first plurality of dif- fractive grating lines 201 and the first sub-wavelength grating features comprise a first plurality of sub-wave- length grating lines 202.

[0118] According to an embodiment, the third diffrac- tive grating features comprise a third plurality of dif- fractive grating lines 201 and the third sub-wavelength n grating features comprise a third plurality of sub-wave-

S length grating lines 202.

Od [0119] According to an embodiment, grating lines in x the first plurality of diffractive grating lines are

I 25 substantially parallel with the second polarization 152. > [0120] According to an embodiment, grating lines in > the third plurality of diffractive grating lines are & substantially parallel with the first polarization 151.

N

[0121] According to an embodiment, each grating line in the first plurality of diffractive grating lines com- prises an air gap 203.

[0122] According to an embodiment, each grating line in the third plurality of diffractive grating lines com- prises an air gap 203.

[0123] According to an embodiment, a grating period of the first diffractive grating features is greater than 250 nanometres, a grating period of the first sub- wavelength grating features is less than 250 nanometres.

[0124] According to an embodiment, a width of each air gap 203 in the first/third plurality of diffractive grating lines 201 is 30 — 100 nm.

[0125] According to an embodiment, a grating period of the third diffractive grating features is greater than 250 nanometres, a grating period of the third sub- wavelength grating features is less than 250 nanometres.

[0126] The width of the air gap 203 is denoted by a, in the embodiment of Fig. 6.

[0127] For example, in the embodiments of Figs. 6 - = 8, the plurality of diffractive grating lines 201 and

N the plurality of sub-wavelength grating lines 202 are 3 non-parallel. For example, the plurality of diffractive

J grating lines 201 and the plurality of sub-wavelength

E 25 grating lines 20? may be substantially orthogonal such 3 as in the embodiments of Figs. 6 - 8. Alternatively, the

D plurality of diffractive grating lines 201 and the plu-

O rality of sub-wavelength grating lines 202 can be in any other non-parallel orientation.

[0128] According to an embodiment, a distance between grating lines in each consecutive grating line pair in the plurality of sub-wavelength grating lines 202 is 60 - 150 nm.

[0129] In the embodiments of Fig. 6 and Fig. 7, the distance between grating lines in each consecutive grat- ing line pair in the plurality of sub-wavelength arating lines 202 is denoted by ay.

[0130] According to an embodiment, a width of each grating line in the first/third plurality of sub-wave- length grating lines is 50 - 160 nm.

[0131] According to an embodiment, grating lines in the first/third plurality of diffractive grating lines are substantially parallel with the first polarization.

[0132] In the embodiment of Fig. 6, cross-sections of the in-coupling structure 111, 113 along the dashed line 210 and along the dotted line 211 are also illustrated.

In the first in-coupling structure 111, the second po- larization 152 can be along the dotted line 211 and the first polarization 151 can be along the dashed line 210.

Q In the third in-coupling structure 113, the first po-

N larization 151 can be along the dotted line 211 and the 3 second polarization 152 can be along the dashed line

N 210.

E 25 [0133] Light experiences the sub-wavelength grating 3 features as a birefringent medium. Thus, the effective

D refractive indices for polarizations along the dashed

O line 210 and along the dotted line 211 are different.

By tuning the dimensions of the subwavelength features,

refractive indices can be tuned such that the diffrac- tive grating becomes at least partially transparent to the polarization along the dashed line 210.

[0134] Herein transverse electric (TE) polarization may refer to a polarization the electric field of which is substantially parallel with the diffractive grating lines of the diffractive grating features of the in- coupling structure. Thus, the polarization long the dot- ted line 211 may be referred to as TE polarization.

Similarly, transverse magnetic (TM) polarization may refer to a polarization the magnetic field of which is substantially parallel with the diffractive grating lines of the diffractive grating features of the in- coupling structure. Thus, the polarization long the dashed line 210 may be referred to as TM polarization.

[0135] In the embodiment of Fig. 6, for example, the diffractive grating features can be made at least par- tially transparent to the firs/second polarization 151, 152 by tuning a,, dx, Ay, dy, the refractive index of the material of the diffractive grating feature, and/or n the refractive index of the material of the sub-wave-

S length grating feature. Appropriate values for at least

Od some of these parameters can be found using, for exam- x ple, optical simulations. In some cases, some of these

E 25 parameters can have predetermined values and the values - of the rest of these parameters can be found using op- > tical simulations. For example, the refractive index of & the material of the diffractive grating feature, and/or

N the refractive index of the material of the sub-wave- length grating feature 202 may be pre-determined by the used material(s) and ay, dx, a, and/or dy can be found using optical simulations.

[0136] According to an embodiment, the sub-wavelength grating features are configured to make the diffractive grating features at least partially transparent to the first/second polarization 151, 152 via a spatial re- fractive index average along a direction of the first/second polarization 151, 152 being substantially constant.

[0137] According to an embodiment, a refractive index of a material of the diffractive grating features is in the range 1.9 — 2.4 and a refractive index of a material of the sub-wavelength arating features is in the range 1.9 — 2.4.

[0138] According to an embodiment dy is in the range 200 — 220 nm, dy is in the range 300 — 500 nm, Ay is in the range 60 - 150 nm, a, is in the range 30 - 100, a refractive index of a material of the diffractive grat-

Q ing features is substantially 2.4, and a refractive in-

N dex of a material of the sub-wavelength grating features 3 is substantially 2.4.

N [0139] Fig. 7 illustrates a schematic representation = 25 of an in-coupling structure according to another embod- 3 iment.

O [0140] The first 111, second 112, and/or third in-

O coupling structure 113 may comprise an in-coupling structure similar to that illustrated in the embodiment of Fig. 7. Any disclosure herein in relation to the embodiment of Fig. 7 may apply to any of the first 111, second 112, and/or third in-coupling structure 113. The polarization sensitivity of each in-coupling structure can be adjusted by rotating the in-coupling structure.

[0141] According to an embodiment, the first plurality of diffractive grating lines is made of a material with a first refractive index, and the first plurality of sub-wavelength grating lines is made of a material with a second refractive index different from the first re- fractive index.

[0142] According to an embodiment, the third plurality of diffractive grating lines is made of a material with a first refractive index, and the third plurality of sub-wavelength grating lines is made of a material with a second refractive index different from the first re- fractive index.

[0143] The first refractive index may be denoted by nj, and the second refractive index may be denoted by nm.

[0144] A refractive index of a material may refer to

O a refractive index that light experiences when the light

O interacts with a substantially homogeneous piece of the 3 material. The refractive index of a material may be

S wavelength dependent. It should be appreciated that an

E 25 effective refractive index caused by, for example, the o sub-wavelength grating features can differ from the re- > fractive index of the material of which the sub-wave- & length grating features are made of due to the sub- = wavelength grating features having a sub-wavelength size. Since the sub-wavelength grating features have a sub-wavelength size, the light experiences a spatially averaged effective refractive index that depends on the relative orientation of the sub-wavelength grating fea- tures and the polarization of the light. Thus, the ef- fective refractive index of the sub-wavelength grating features is anisotropic and polarization dependent.

[0145] In the embodiment of Fig. 7, cross-sections of the in-coupling structure 111, 113 along the dashed line 310 and along the dotted line 311 are also illustrated.

In the first in-coupling structure 111, the second po- larization 152 can be along the dotted line 311 and the first polarization 151 can be along the dashed line 310.

In the third in-coupling structure 113, the first po- larization 151 can be along the dotted line 311 and the second polarization 152 can be along the dashed line 310.

[0146] Light experiences the sub-wavelength grating features as a birefringent medium. Thus, the effective refractive indices for polarizations along the dashed n line 310 and along the dotted line 311 are different.

S By tuning the dimensions of the subwavelength features,

Od refractive indices can be tuned such that the diffrac- x tive grating structure become at least partially trans-

I 25 parent to the polarization along the dashed line 310. - [0147] In the embodiment of Fig. 7, for example, the > diffractive grating features can be made at least par- & tially transparent to the first/second polarization 151,

N 152 by tuning dx, Ay, dy, the refractive index of the material of the diffractive grating features, and/or the refractive index of the material of the sub-wavelength grating feature 202. Appropriate values for at least some of these parameters can be found using, for exam- ple, optical simulations. In some cases, some of these parameters can have predetermined values and the values of the rest of these parameters can be found using op- tical simulations. For example, the refractive index of the material of the diffractive grating feature 201, and/or the refractive index of the material of the sub- wavelength grating feature 20? may be pre-determined by the used material(s) and dy, a, and/or dy can be found using optical simulations.

[0148] According to an embodiment, each grating line in the plurality of diffractive grating lines comprises an air gap 203, the plurality of diffractive grating lines is made of a material with a first refractive index, and the plurality of sub-wavelength grating lines 202 is made of a material with a second refractive index different from the first refractive index. Thus, the n embodiments of Fig. 6 and Fig. 7 may be combined into

S another embodiment.

Od [0149] According to an embodiment, the first plurality x of sub-wavelength grating lines are positioned between z 25 the first plurality of diffractive grating lines and the > first plurality of diffractive grating lines and the > first plurality of sub-wavelength grating lines are non-

N parallel. &

[0150] According to an embodiment, the third plurality of sub-wavelength grating lines are positioned between the third plurality of diffractive grating lines and the third plurality of diffractive grating lines and the third plurality of sub-wavelength grating lines are non- parallel.

[0151] Fig. 8 illustrates a schematic representation of an in-coupling structure according to another embod- iment.

[0152] The first 111, second 112, and/or third in- coupling structure 113 may comprise an in-coupling structure similar to that illustrated in the embodiment of Fig. 8. Any disclosure herein in relation to the embodiment of Fig. 8 may apply to any of the first 111, second 112, and/or third in-coupling structure 113. The polarization sensitivity of each in-coupling structure can be adjusted by rotating the in-coupling structure.

[0153] The in-coupling structure illustrated in the embodiment of Fig. 8 can be obtained by, for example, repeating the unit cell illustrated in the embodiment en of Fig. 5.

S [0154] In the embodiment of Fig. 8, the plurality of 3 diffractive grating lines 201 and the plurality of sub- a wavelength grating lines 202 are made of the same mate-

E 25 rial. For example, the plurality of diffractive grating

S lines 201 and the plurality of sub-wavelength grating 2 lines 202 can be made of titanium dioxide (Ti0.). The

N refractive index of TiO. is approximately 2.4. The space = between the plurality of diffractive grating lines 201 and the plurality of sub-wavelength grating lines 202 can be, for example, air.

[0155] According to an embodiment, a width of each grating line in the plurality of diffractive grating lines 201 is 80 nm and a width of each grating lines in the plurality of sub-wavelength grating lines 202 is 80 nm.

[0156] According to an embodiment, a grating period d, is in the range 300 — 400 nm.

[0157] According to an embodiment, a grating period dy is in the range 150 — 200 nm.

[0158] Fig. 9 illustrates a schematic representation of a waveguide according to an embodiment.

[0159] The waveguide illustrated in the embodiment of

Fig. 9 may correspond to any of the first 101, second 102, and/or third waveguide 103. For example, in some embodiments, the first 101, second 102, and/or third waveguide 103 may be implemented as layers of the dis- play structure 100. Each such layer may be implemented in a fashion similar to what is illustrated in the em- = bodiment of Fig. 9.

N [0160] The in-coupling structure 111, 112, 113 can

S couple light into the waveguide 101, 102, 103, as dis-

N closed herein, as in-coupled light 701. The in-coupled

E 25 light 701 can be guided in the waveguide 101, 102, 103 3 via TIR. 2 [0161] The display structure 100 may further comprise

N an exit pupil expansion (EPE) structure 703 configured to receive the in-coupled light 701 guided inside the waveguide 101, 102, 103, and to diffract the in-coupled light 701 in a plurality of directions, producing a set of diffracted beams 712.

[0162] It should be appreciated that the set of dif- fracted beams 712 illustrated in the embodiment of Fig. 9 are only illustrative. In practical embodiments, the

EPE structure 703 can diffract the in-coupled light 701 in a plurality of directions in a much more complex manner and the set of diffracted beams 712 can interact with the EPE structure 703 a plurality of times.

[0163] The display structure 100 may further comprise an out-coupling structure 704 in/on the waveguide 101, 102, 103 configured to receive, from the EPE structure 703, at least the set of diffracted beams 712 and to out-couple at least the set of diffracted beams 712 from the planar waveguide 101, 102, 103 as a set of output beams 713.

[0164] The set of output beams 713 may represent, for example, an expanded version of the image formed by the input light beam 161, 162. e [0165] The in-coupling structure 111, 112, 113, the

S EPE structure 703 and/or the out-coupling structure 704

Od may comprise, for example, a diffractive grating on a x surface of the waveguide 101, 102, 103. The in-coupling = 25 structure 111, 112, 113 may couple light into the wave- - guide 101, 102, 103 via diffraction. The EPE structure > 703 may expand the image corresponding to the in-coupled & light 701 via diffraction. The out-coupling structure

N

704 may out-couple the set of diffracted beams 712 from the waveguide 101, 102, 103 via diffraction.

[0166] Fig. 10 illustrates a schematic representation of a display device according to an embodiment.

[0167] According to an embodiment, a display device 800 comprises the display structure 100.

[0168] According to an embodiment, display device 800 further comprises an optical engine 801 for directing the first input light beam 161 to the first waveguide 101 and/or for directing the second input light beam 162 to the third waveguide 103.

[0169] For example, if the display structure 100 is implemented without the third waveguide 103, such as in the embodiment of Fig. 1, the optical engine 801 may be configured to direct the first input light beam 161 to the first waveguide 101. If the display structure 100 is implemented with the third waveguide 103, such as in the embodiment of Fig. 2, the optical engine 801 may be configured to direct the second input light beam 162 to the third waveguide 103. ™ [0170] According to an embodiment, the optical engine

S 801 is configured to generate the first input light beam 3 161 in a manner that the first wavelength range and the

S second wavelength range are in the first polarization

E 25 and/or the optical engine 801 is configured to generate

Oo the second input light beam 162 in a manner that the > first wavelength range, the second wavelength range, and & the third wavelength range are in the second polariza- = tion.

[0171] According to an embodiment, the display device 800 is implemented as a see-through display device.

[0172] According to an embodiment, the display device 800 is implemented as a head-mounted display device.

[0173] For example, in the embodiment of Fig. 10, the display device 800 is implemented as smart glasses. The waveguides 101, 102, 103 can correspond to layers 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) func- tionality.

[0174] In the embodiment of Fig. 10, the input light beam 161, 162 may be generated by, for example, an op- tical engine 801, such as a scanner-based optical engine or an LCOS-based optical engine. The input light beam 161, 162 may represent an image generated by, for exam- ple, such an optical engine. The display structure 100 of the display device 800 can direct the set of output beams 713 representing the image generated by the opti- cal engine 801 into the eye of a user. ™ [0175] Any range or device value given herein may be

S extended or altered without losing the effect sought. 3 Also any embodiment may be combined with another embod-

S iment unless explicitly disallowed.

E 25 [0176] Although the subject matter has been described 2 in language specific to structural features and/or acts,

D it is to be understood that the subject matter defined

O 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 equiv- alent features and acts are intended to be within the scope of the claims.

[0177] 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 un- derstood that reference to 'an' item may refer to one or more of those items.

[0178] Aspects of any of the embodiments described above may be combined with aspects of any of the other embodiments described to form further embodiments with- out losing the effect sought.

[0179] The term 'comprising' is used herein to mean including the method, blocks or elements identified, but that such blocks or elements do not comprise an exclu- sive list and a method or apparatus may contain addi- n tional blocks or elements.

S [0180] It will be understood that the above descrip-

Od tion is given by way of example only and that various x modifications may be made by those skilled in the art. =E 25 The above specification, examples and data provide a - complete description of the structure and use of exem- > plary embodiments. Although various embodiments have & been described above with a certain degree of particu-

N larity, or with reference to one or more individual embodiments, those skilled in the art could make numer- ous alterations to the disclosed embodiments without departing from the spirit or scope of this specifica- tion. 0

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Claims (17)

CLAIMS:

1. A display structure (100), comprising: - a first waveguide (101) configured to receive a first input light beam (161) in a first polarization (151) comprising at least a first wavelength range and a second wavelength range; - a first in-coupling structure (111) in/on the first waveguide (101) configured to let at least part of the first polarization (151) pass through the first in-coupling structure (111); - a first waveplate (121) configured to perform a first polarization manipulation on the first polari- zation (151) passed through the first in-coupling struc- ture (111); - a first reflector (131) configured to reflect at least part of the first wavelength range arriving to the first reflector (131) through the first waveplate (121) back towards the first waveplate (121) as a first reflected light beam (171) and let at least part of the second wavelength range pass through the first reflector e (131); < - a second waveguide (102); and Od - a second in-coupling structure (112) in/on the a second waveguide (102) configured to couple at least I 25 part of the second wavelength range passed through the - first reflector (131) into the second waveguide (102); > wherein the first waveplate (121) is further con- & figured to perform a second polarization manipulation N on the first reflected light beam (171) and let the first reflected light beam (171) pass to the first in- coupling structure (111), wherein the first polarization manipulation and the second polarization manipulation are configured to convert a polarization of the first reflected light beam (171) at least partially into a second polarization (152) and the first in-coupling structure (111) is further configured to couple at least part of the second polarization (152) of the first re- flected light beam (171) into the first waveguide (101).

2. The display structure according to claim 1, fur- ther comprising a second waveplate (122) configured to receive the second wavelength range passed through the first reflector (131), perform a third polarization ma- nipulation on the second wavelength range passed through the first reflector (131), wherein the first polariza- tion manipulation and the third polarization manipula- tion are configured to convert the first polarization (151) of the second wavelength range at least partially into the second polarization (152), and pass the second wavelength range to the second waveguide (102) and & wherein the second in-coupling structure (112) is fur- N ther configured to couple at least part of the second ? polarization (152) of the second wavelength range into 3 25 the second waveguide (102). =

3 3. The display structure (100) according to claim D 1 or claim 2 further comprising: O - a third waveguide (103) configured receive a second input light beam (162) in the second polarization

(152) comprising at least the first wavelength range, the second wavelength range, and a third wavelength range;

- a third in-coupling structure (113) in/on the third waveguide (103) configured to let at least part of the second polarization (152) pass through the third in-coupling structure (113);

- a third waveplate (123) configured to perform a fourth polarization manipulation on the second polar- ization (152) passed through the third in-coupling structure (113);

- a second reflector (132) configured to reflect at least part of the third wavelength range arriving to the second reflector (132) through the third waveplate

(123) back towards the third waveplate (123) as a second reflected light beam (172) and let at least part of the first and second wavelength range pass through the sec- ond reflector (132);

- a fourth waveplate (124) configured to receive the first and second wavelength range passed through the second reflector (132), perform a fifth polarization

& manipulation on the first and second wavelength range N passed through the second reflector (132), wherein the = fourth polarization manipulation and the fifth polari- N 25 zation manipulation are configured to convert the second s polarization (152) of the first and second wavelength 3 range at least partially into the first polarization 2 (151), and pass the first wavelength range and the sec- & ond wavelength range to the first waveguide (101) as the first input light beam (161);

wherein the third waveplate (123) is further con- figured to perform a sixth polarization manipulation on the second reflected light beam (172) and let the second reflected light beam (172) pass to the third in-coupling structure (113), wherein the fourth polarization manip- ulation and the sixth polarization manipulation are con- figured to convert a polarization of the second re- flected light beam (172) at least partially into the first polarization (151), and the third in-coupling structure (113) is further configured to couple at least part of the first polarization (151) of the second re- flected light beam (172) into the third waveguide (103).

4. The display structure (100) according to claim 1 or claim 2 further comprising: - a third waveguide (103) configured receive a second input light beam (162) in the first polarization (151) comprising at least the first wavelength range, the second wavelength range, and a third wavelength range; - a third in-coupling structure (113) in/on the & third waveguide (103) configured to let at least part N of the first polarization (151) pass through the third = in-coupling structure (113); N 25 - a third waveplate (123) configured to perform E a fourth polarization manipulation on the first polar- 3 ization (151) passed through the third in-coupling 2 structure (113); & - a second reflector (132) configured to reflect at least part of the third wavelength range arriving to the second reflector (132) through the third waveplate (123) back towards the third waveplate (123) as a second reflected light beam (172) and let at least part of the first and second wavelength range pass through the sec- ond reflector (132);

- a fourth waveplate (124) configured to receive the first and second wavelength range passed through the second reflector (132), perform a fifth polarization manipulation on the first and second wavelength range passed through the second reflector (132), wherein the fourth polarization manipulation and the fifth polari- zation manipulation are configured to maintain the first polarization (151) of the first and second wavelength range, and pass the first wavelength range and the sec-

ond wavelength range to the first waveguide (101) as the first input light beam (161);

wherein the third waveplate (123) is further con- figured to perform a sixth polarization manipulation on the second reflected light beam (172) and let the second reflected light beam (172) pass to the third in-coupling structure (113), wherein the fourth polarization manip-

& ulation and the sixth polarization manipulation are con- N figured to convert a polarization of the second re- = flected light beam (172) at least partially into the N 25 second polarization (152), and the third in-coupling x structure (113) is further configured to couple at least 3 part of the second polarization (152) of the second 2 reflected light beam (172) into the third waveguide & (103).

5. The display structure (100) according to any preceding claim, wherein the first reflector (131) com- prises a first dichroic mirror and/or the second re- flector (132) comprises a second dichroic mirror.

6. The display structure (100) according to any preceding claim, wherein the second wavelength range comprises wavelengths longer than the first wavelength range and/or the second wavelength range comprises wave- lengths longer than the third wavelength range.

7. The display structure (100) according to any preceding claim, wherein: the first in-coupling structure (111) com- prises first diffractive grating features and first sub- wavelength grating features, wherein the first diffrac- tive grating features are configured to couple at least part of the second polarization (152) into the first waveguide (101) and the first sub-wavelength grating features are configured to make the first diffractive Q grating features at least partially transparent to the N first polarization (151). & S 25

8. The display structure (100) according to E claim 7, wherein the first diffractive grating features o comprise a first plurality of diffractive grating lines D and the first sub-wavelength grating features comprise O a first plurality of sub-wavelength grating lines.

9. The display structure (100) according to claim 8, wherein grating lines in the first plurality of diffractive grating lines are substantially parallel with the second polarization (152).

10. The display structure (100) according to any claim 8 or claim 9, wherein each grating line in the first plurality of diffractive grating lines comprises an air gap.

11. The display structure (100) according to any of claims 8 —- 10, wherein the first plurality of diffractive grating lines is made of a material with a first refractive index, and the first plurality of sub- wavelength grating lines is made of a material with a second refractive index different from the first re- fractive index.

12. The display structure (100) according to any of claims 8 —- 11, wherein the first plurality of sub-wavelength grating lines are positioned between the = first plurality of diffractive grating lines and the N first plurality of diffractive grating lines and the 3 first plurality of sub-wavelength grating lines are non- J 25 parallel. 7 S

13. The display structure (100) according to D any of claims 7 — 12, wherein a grating period of the O first diffractive grating features is greater than 250 nanometres, a grating period of the first sub-wavelength grating features is less than 250 nanometres.

14. The display structure (100) according to any preceding claim, wherein the first polarization and the second polarization are substantially orthogonal.

15. A display device (800) comprising the dis- play structure (100) according to any preceding claims.

16. The display device (800) according to claim 15, further comprising an optical engine (801) for directing the first input light beam (161) to the first waveguide (101) and/or for directing the second input light beam (162) to the third waveguide (103).

17. The display device (800) according to claim 16, wherein the optical engine (801) is configured to generate the first input light beam (161) in a manner that the first wavelength range and the second wave- length range are in the first polarization (151) and/or © the optical engine (801) is configured to generate the < second input light beam (162) in a manner that the first x wavelength range, the second wavelength range, and the S 25 third wavelength range are in the second polarization = (152). a O <t (e LO O N O N