Diffraction grating

Abstract

According to an embodiment, a diffraction grating comprises: a plurality of grating lines; a first metal layer arranged at least partially between the plurality of grating lines; a first dielectric layer arranged onto the plurality of grating lines and the first metal layer; and a second metal layer arranged onto the first dielectric layer.

Description

DIFFRACTION GRATINGTECHNICAL FIELD

[0001] The present disclosure relates to the field of diffractive optics, and more particularly to a diffraction grating, 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 to achieve sufficient image uniformity and / or brightness.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 subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0004] It is an object to provide a diffraction grating, a display structure, and a display device. Theforegoing and other obj ects are 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, diffraction grating comprises : a plurality of grating lines ; a first metal layer arranged at least partially between the plurality of grating lines ; a first dielectric layer arranged onto the plurality of grating lines and the first metal layer ; and a second metal layer arranged onto the first dielectric layer .

[0006] In an implementation form of the first aspect , the plurality of grating lines comprise titanium dioxide .

[0007] In another implementation form of the first aspect , the first metal layer compri ses si lver or aluminium and / or the second metal layer comprises silver or aluminium .

[0008] In another implementation form of the first aspect , the first dielectric layer comprises aluminium oxide , silicon dioxide , and / or magnesium fluoride .

[0009] In another implementation form of the first aspect , the diffraction grating further comprises a second dielectric layer arranged below the plurality of grating lines .

[0010] In another implementation form of the first aspect , the diffraction grating further comprises a titanium dioxide layer arranged below the second dielectric layer .

[0011] In another implementation form of the first aspect , the second dielectric layer comprises aluminium oxide , silicon dioxide , and / or magnesium fluoride .

[0012] In another implementation form of the first aspect , a height of the plurality of grating lines is 10 - 50 nanometres , a height of the first dielectric layer is 10 - 50 nanometres , and / or a height of the first metal layer is 10 - 100 nanometres .

[0013] According to second aspect , a display structure comprises a planar waveguide and the diffraction grating according to the first aspect on the planar waveguide .

[0014] In an implementation form of the second aspect , the diffraction grating is arranged as an in-coupling grating for coupling light into the planar waveguide .

[0015] In another implementation form of the second aspect , the diffraction grating is arranged as a reflective diffraction grating onto the planar waveguide .

[0016] According to a third aspect , a display device comprises the display structure according to the second aspect .

[0017] In an implementation form of the third aspect , the display device is implemented as a see-through display device .

[0018] In another implementation form of the third aspect , the display device is implemented as a headmounted display device .

[0019] Many of the attendant features wil l be more readily appreciated as they become better understood byreference to the following detailed description considered in connection with the accompanying drawings .DESCRIPTION OF THE DRAWINGS

[0020] In the following, embodiments are described in more detail with reference to the attached figures and drawings , in which :

[0021] Fig . 1 illustrates a schematic representation of a diffraction grating according to an embodiment ;

[0022] Fig . 2 illustrates a schematic representation of a diffraction grating according to another embodiment ;

[0023] Fig . 3 illustrates a schematic representation of a diffraction grating according to another embodiment ;

[0024] Fig . 4 illustrates a schematic representation of a display structure according to an embodiment ;

[0025] Fig . 5 illustrates a schematic representation of a display structure according to another embodiment ; and

[0026] Fig . 6 illustrates a schematic representation of a display device according to an embodiment ;

[0027] Fig . 7 illustrates a plot representation of simulation results according to a comparative example ;

[0028] Fig . 8 illustrates a plot representation of simulation results according to an embodiment ;

[0029] Fig . 9 illustrates a plot representation of simulation results according to another embodiment ; and

[0030] Fig . 10 illustrates a plot representation of simulation results according to another embodiment .

[0031] In the following, identical reference signs refer to similar or at least functionally equivalent features .DETAILED DESCRIPTION

[0032] 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 .

[0033] 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 expl icitly described or il lustrated in the f igures . 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 .

[0034] Fig . 1 illustrates a schematic representation of a diffraction grating according to an embodiment .

[0035] According to an embodiment , a diffraction grating 100 comprises a plurality of grating lines 101 .

[0036] Herein, grating lines may also be referred to as grating features , diffractive grating lines , diffractive grating features , or similar .

[0037] Herein, grating lines may refer to grating features that have a spatial periodicity of the same order of magnitude or greater than the smallest wavelength of light incident onto the diffraction grating .

[0038] 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 either reflected or transmitted light , to emerge .

[0039] The diffraction grating 100 may further comprise a first metal layer 102 arranged at least partially between the plurality of grating lines 101 .

[0040] The first metal layer 102 may comprise features arranged between the plurality of grating lines 101 . Thus , the first metal layer 102 may not have a monolithicstructure . Thus , the features arranged between the plurality of grating lines 101 may not be in physical contact with each other .

[0041] In some embodiments , the first metal layer 102 may comprise features that are taller than the plurality of grating lines 101 , such as in the embodiment of Fig . 1 . In other embodiments , the first metal layer 102 may comprise features that are lower than the plurality of grating lines 101 .

[0042] In some embodiments , the first metal layer 102 may fill the space between the plurality of grating lines 101 . Thus , the first metal layer 102 and the plurality of grating l ines 101 may totally cover any area that is below the first metal layer 102 and the plurality of grating lines 101 . For example , in the embodiment of Fig . 1 , the first metal layer 102 and the plurality of grating lines 101 totally cover any area that i s below the first metal layer 102 and the plurality of grating lines 101 . In such embodiments , the thickness of the first metal layer 102 may be different from the thickness of the plurality of grating lines 101 .

[0043] Further, the first metal layer 102 and the plurality of grating lines 101 may form a substantially flat plane below the first metal layer 102 and the plurality of grating lines 101 . Further, the first metal layer 102 may be in contact with each grating line in the plurality of grating lines 101 .

[0044] The diffraction grating 100 may further comprise a first dielectric layer 103 arranged onto theplurality of grating lines 101 and the first metal layer 102 .

[0045] The first dielectric layer 103 may have a non- uniform thickness . For example , if the first metal layer 102 comprises features that are taller than the plurality of grating lines 101 , the first dielectric layer 103 may have a reduced thickness at the locations of the features of the first metal layer 102 compared to the locations of the plurality of grating lines 101 . I f the first metal layer 102 comprises features that are lower than the plurality of grating lines 101 , the first di electric layer 103 may have an increased thickness at the locations of the features of the first metal layer 102 compared to the locations of the plurality of grating lines 101 .

[0046] The f irst dielectric layer 103 may be in contact with the plurality of grating lines 101 and the first metal layer 102 .

[0047] The f irst dielectric layer 103 may be a monolithic layer . The first dielectric layer 103 may cover the plural ity of grating lines 101 and the f irst metal layer 102 . For example , the f irst dielectric layer 103 may comprise a monolithic layer of a dielectric material . The dielectric material may cover the plurality of grating lines 101 and the first metal layer 102 .

[0048] The diffraction grating 100 may further comprise a second metal layer 104 arranged onto the first dielectric layer 103 .

[0049] The second metal layer 104 may be on a different side of the first dielectric layer 103 from the plurality of grating lines 101 and the first metal layer 102 .

[0050] The second metal layer 104 may be a monolithic layer . The second metal layer 104 may cover a top surface of the first dielectric layer 103 . For example , the second metal layer 104 may compri se a monol ithic layer of a metal . The metal may cover a top surface of the first dielectric layer 103 . The top surface of the first dielectric layer 103 may be on a different side of the first dielectric layer 103 from the plurality of grating lines 101 and the first metal layer 102 .

[0051] According to an embodiment , the plurality of grating lines 101 comprise titanium dioxide ( TiCy ) .

[0052] For example , the plurality of grating lines may be made of titanium dioxide .

[0053] According to an embodiment , the first metal layer 102 comprises silver (Ag) or aluminium (Al ) and / or the second metal layer 104 compri ses silver or aluminium .

[0054] According to an embodiment , the first metal layer 102 comprises silver and the second metal layer 104 comprises silver .

[0055] According to an embodiment , the first metal layer 102 comprises aluminium and the second metal layer 104 comprises silver .

[0056] According to an embodiment , the first metal layer 102 comprises silver and the second metal layer 104 comprises aluminium .

[0057] According to an embodiment , the first metal layer 102 comprises aluminium and the second metal layer 104 comprises aluminium .

[0058] According to an embodiment , the first dielectric layer 103 comprises aluminium oxide (AI2O3 ) , si licon dioxide ( SiCy ) , and / or magnesium fluoride (MgF2 ) .

[0059] For example , the first dielectric layer 103 may be made of aluminium oxide , silicon dioxide , and / or magnesium fluoride .

[0060] The diffraction grating can, for example , improves the brightness and / or the image uniformity for at least some colour channels , such as white , red, green, and blue .

[0061] The dielectric-metal combination formed by the first dielectric layer 103 and the second metal layer 104 in the diffraction grating 100 can enhance the coupling efficiency and spread the light more uniformly over the visible wavelength band .

[0062] According to an embodiment , a height of the plurality of grating lines 101 is 10 - 50 nanometres (nm) , a height of the f irst dielectric layer 103 is 10 - 50 nanometres , and / or a height of the first metal layer 102 is 10 - 100 nanometres .

[0063] According to an embodiment , a height of the plurality of grating lines 101 is 10 - 50 nm, 10 - 40 nm, 20 - 40 nm, 10 - 30 nm, or 20 - 30 nm .

[0064] According to an embodiment , a height of the first dielectric layer 103 is 10 - 50 nm, 10 - 40 nm, 20 - 40 nm, 10 - 30 nm, or 20 - 30 nm . The height of the first dielectric layer 103 may refer to a minimum height / thickness of the first dielectric layer 103 . For example , if the first metal layer 102 comprises features that are taller than the plurality of grating lines 101 , the height / thickness of the first dielectric layer 103 may be measured at the locations of the features of the first metal layer 102 and if the first metal layer 102 comprises features that are lower than the plurality of grating lines 101 , the height / thickness of the first dielectric layer 103 may be measured at the locations of the plurality of grating lines 101 . Alternatively, the height of the first dielectric layer 103 may refer the height / thickness of the first dielectric layer 103 measured at the locations of the features of the first metal layer 102 . Alternatively, the height of the first dielectric layer 103 may refer to a maximum height / thickness of the first dielectric layer 103 .

[0065] According to an embodiment , a height of the first metal layer 102 is 10 - 100 nm, 20 - 100 nm, 30 - 100 nm, 10 - 90 nm, 10 - 80 nm, 20 - 90 nm, 20 - 80 nm, 30 - 90 nm, 30 - 80 nm, or 30 - 75 nm .

[0066] Fig . 2 illustrates a schematic representation of a diffraction grating according to another embodiment .

[0067] According to an embodiment, the diffraction grating further comprises a second dielectric layer 105 arranged below the plurality of grating lines.

[0068] The second dielectric layer 105 may be in contact with the plurality of grating lines 101 and the first metal layer 102.

[0069] The second dielectric layer 105 may be on a different side of the plurality of grating lines 101 and the first metal layer 102 from the first dielectric layer 103.

[0070] The second dielectric layer 105 may comprise a monolithic layer. For example, the second dielectric layer 105 may comprise a monolithic layer of a dielectric material.

[0071] In some embodiments, the first metal layer 102 may fill space between the plurality of grating lines 101. Thus, the first metal layer 102 and the plurality of grating lines 101 may totally cover any area of the second dielectric layer 105 that is below the first metal layer 102 and the plurality of grating lines 101. For example, in the embodiment of Fig. 2, the first metal layer 102 and the plurality of grating lines 101 totally cover the second dielectric layer 105.

[0072] The second dielectric layer 105 can function as an etch stop layer that can be used in manufacturing to stop etching into a titanium dioxide layer 106.

[0073] A thickness of the second dielectric layer 105 may be, for example, 5 - 50 nm, 5 - 40 nm, 5 - 30 nm, 5 - 20 nm, or 5 - 15 nm.

[0074] According to an embodiment, the second dielectric layer 105 comprises aluminium oxide , silicon dioxide , and / or magnesium fluoride .

[0075] For example , the second dielectric layer 105 may be made of aluminium oxide, silicon dioxide , and / or magnesium fluoride .

[0076] Fig . 3 illustrates a schematic representation of a diffraction grating according to another embodiment .

[0077] According to an embodiment , the diffraction grating further comprises a titanium dioxide layer 106 arranged below the second dielectric layer 105 .

[0078] The titanium dioxide layer 106 may also be referred to as a bottom layer .

[0079] The titanium dioxide layer 106 may be in contact with the second dielectric layer 105 .

[0080] The titanium dioxide layer 106 may be on a di fferent s ide of the second dielectric layer 105 from the plurality of grating l ines 101 and the first metal layer 102 .

[0081] A thickness of the titanium dioxide layer 106 may be , for example , 10 - 50 nm, 10 - 40 nm, 20 - 40 nm, 10 - 30 nm, 10 - 20 nm, 5 - 50 nm, 5 - 20 nm, or 20 - 30 nm .

[0082] Fig . 4 illustrates a schematic representation of a display structure according to an embodiment .

[0083] According to an embodiment , a display structure 400 comprises a planar waveguide 401 and the diffraction grating 100 on the planar waveguide 401 .

[0084] The planar waveguide 401 may comprise substantially planar sections . Alternatively or additionally, the planar waveguide 401 may al so compri se curved sections . For example , planar waveguide 401 may correspond to a lens or a layer of a lens of augmented reality (AR) glasses .

[0085] According to an embodiment , the diffraction grating 100 is arranged as an in-coupling grating for coupling light 402 into the planar waveguide 401 .

[0086] The light 402 may also be referred to as incident light .

[0087] According to an embodiment , the diffraction grating 100 is configured to coupling incident light 402 into the planar waveguide 401 .

[0088] According to an embodiment , the diffraction grating 100 is arranged as a reflective diffraction grating onto the planar waveguide 401 .

[0089] For example , in the embodiment of Fig . 4 , the diffraction grating 100 is arranged as a reflective diffraction grating onto the planar waveguide 401 . The diffraction grating 100 is on a first side 411 of the planar waveguide 401 . The diffraction grating 100 can in-couple light 402 incident onto a second side 412 of the planar waveguide 401 via diffraction .

[0090] According to an embodiment , the diffraction grating 100 is configured to in-couple light into the planar waveguide 401 via at least first order dif fraction .

[0091] It should be appreciated that the in-coupling of the l ight 402 is illustrated in a simpl ified manner in the embodiment of Fig . 4 . For example , the in-coupling illustrated in the embodiment of Fig . 4 may be due to first order di ffraction . Some of the incident light 402 may be in-coupled via other mechanisms . For example , some of the incident light 402 may propagate through the grating lines 101 and be reflected from the second metal layer 104 . Some of the reflected light may be guided inside the first dielectric layer 103 and at least partially in-coupled to the planar waveguide 401 each time the reflected light interacts with the grating lines 101 .

[0092] Fig . 5 illustrates a schematic representation of a display structure according to another embodiment .

[0093] In the embodiment of Fig . 5 , a di splay structure 400 comprises a planar waveguide 401 and the dif fraction grating 100 on the planar waveguide 400 . The diffraction grating 100 is arranged as an in-coupling grating for coupling light 402 into the planar waveguide 401 as a set of in-coupled beams 501 . The set of incoupled beams 501 may also be referred to as in-coupled light or similar . The in-coupling grating 100 may also be referred to as an in-coupling ( IC) structure or similar .

[0094] The display structure 400 may further comprise an exit pupil expansion (EPE ) structure 502 configuredto receive the set of in-coupled beams 501 and to di ffract the set of in-coupled beams 501 in a plurality of directions , producing a set of diffracted beams 503 .

[0095] It should be appreciated that the set of di ffracted beams 503 illustrated in the embodiment of Fig .5 are only illustrative . In practical embodiments , the EPE structure 502 can diffract the set of in-coupled beams 501 in a plurality of directions in a more complex manner and the set of diffracted beams 503 can interact with the EPE structure 502 a plurality of times .

[0096] The display structure 400 may further comprise an out-coupling (OC) structure 505 configured to receive , from the EPE structure 502 , at least the set of diffracted beams 503 and to out-couple at least the set of diffracted beams 503 from the planar waveguide 401 as a set of output beams 504 .

[0097] The set of output beams 504 may represent , for example, an expanded version of the image formed by the light 402 .

[0098] The set of in-coupled beams 501 and the set of diffracted beams 503 can be guided inside the planar waveguide 401 via total internal reflection ( TIR) .

[0099] The IC structure 100 , the EPE structure 502 and / or the OC structure 505 may comprise , for example , a dif fractive grating on a surface of the planar waveguide 401 . The IC structure 100 may couple the light 402 into the planar waveguide 401 via diffraction . The EPE structure 502 may expand the image corresponding to the set of in-coupled beams 501 via diffraction . The OCstructure 505 may out-couple the set of diffracted beams 503 from the planar waveguide 401 via diffraction.

[0100] The light 402 may be generated by, for example, a scanner-based optical engine. The light 402 may represent an image generated by, for example, such an optical engine. Thus, the light 402 may also be referred to as, for example, image-bearing light rays / beams, image-carrying light rays / beams, or similar.

[0101] It should be understood that the geometry of the display structure 400 illustrated in the embodiment of Fig. 5 is only exemplary and the display structure 400 may be implemented in various other ways.

[0102] Fig. 6 illustrates a schematic representation of a display device according to an embodiment.

[0103] According to an embodiment, a display device 600 comprises the display structure 400.

[0104] According to an embodiment, the display device 600 further comprises an optical engine 601 for directing the light 402 to the diffraction grating 100.

[0105] According to an embodiment, the display device 600 is implemented as a see-through display device.

[0106] According to an embodiment, the display device 600 is implemented as a head-mounted display device.

[0107] For example, in the embodiment of Fig. 6, the display device 600 is implemented as smart glasses. The planar waveguide 401 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) and / or virtual reality (VR) functionality.

[0108] In the embodiment of Fig . 6, the light 402 may be generated by, for example , an optical engine 601 , such as a scanner-based optical engine . The light 402 may represent an image generated by, for example , such an optical engine . The display structure 400 of the display device 600 can direct the light 402 representing the image generated by the optical engine 601 into the eye of a user .

[0109] 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 .

[0110] Fig . 7 illustrates a plot representation of simulation results according to a comparative example .[01 1 1 ] In the comparative example of Fig . 7 , the first order diffraction efficiency of a diffraction grating without the first dielectric layer 103 or the second metal layer 104 is plotted as a function of the wavelength of incident light . Height of the grating lines 101 is 30 nm and the grating lines 101 comprise TiCy . Curve 701 corresponds to the first order diffraction efficiency of transverse electric ( TE ) polari zation, curve 702 corresponds to the first order diffraction efficiency of transverse magnetic ( TM) polari zation, and curve 703 corresponds to the average of the first order diffraction efficiency . The average of the first order dif fraction ef ficiency refers to the average of the TE and TM polari zations .

[0112] Herein, TE polarization may refer to a polarization the electric field of which is substantially parallel with the grating lines 101 of the diffraction grating 100. Similarly, TM polarization may refer to a polarization the magnetic field of which is substantially parallel with the grating lines 101 of the diffraction grating 100.

[0113] The simulations of Figs. 7 - 10 were performed using the Fourier Modal Method.

[0114] Fig. 8 illustrates a plot representation of simulation results according to an embodiment.

[0115] In the embodiment of Fig. 8, the first order diffraction efficiency of a diffraction grating is plotted as a function of the wavelength of incident light. Curves 811 - 813 correspond to the first order diffraction efficiency of TE polarization, curves 821 - 823 correspond to the first order diffraction efficiency of TM polarization, and curves 831 - 833 correspond to the average of the first order diffraction efficiency.

[0116] Curves 811, 821, and 831 correspond to TiO2 grating lines 101 of height 20 nm. Curves 812, 822, and 832 correspond to TiO2 grating lines 101 of height 25 nm. Curves 813, 823, and 833 correspond to TiO2 grating lines 101 of height 30 nm.

[0117] Fig. 9 illustrates a plot representation of simulation results according to another embodiment.

[0118] In the embodiment of Fig. 9, the first order diffraction efficiency of a diffraction grating is plotted as a function of the wavelength of incident light.Curves 911 - 913 correspond to the first order diffraction efficiency of TE polarization, curves 921 - 923 correspond to the first order diffraction efficiency of TM polarization, and curves 931 - 933 correspond to the average of the first order diffraction efficiency.

[0119] Curves 911, 921, and 931 correspond to SiO2 first dielectric layer 103 of height 20 nm. Curves 912, 922, and 932 correspond to SiO2 first dielectric layer 103 of height 25 nm. Curves 913, 923, and 933 correspond to SiO2 first dielectric layer 103 of height 30 nm. Height of the first dielectric layer 103 is measured between the first metal layer 102 and the second metal layer 104. The grating lines 101 comprise TiO2 grating lines of heigh 30 nm.

[0120] Fig. 10 illustrates a plot representation of simulation results according to another embodiment.

[0121] In the embodiment of Fig. 10, the first order diffraction efficiency of a diffraction grating is plotted as a function of the wavelength of incident light. Curves 1011 - 1013 correspond to the first order diffraction efficiency of TE polarization, curves 1021 - 1023 correspond to the first order diffraction efficiency of TM polarization, and curves 1031 - 1033 correspond to the average of the first order diffraction efficiency .

[0122] Curves 1011, 1021, and 1031 correspond to Ag first metal layer 102 of height 30 nm. Curves 1012, 1022, and 1032 correspond to Ag first metal layer 102 of height 50 nm. Curves 1013, 1023, and 1033 correspondto Ag first metal layer 102 of height 75 nm . The grating lines 101 comprise TiCy grating lines of heigh 30 nm .

[0123] Although the subj ect matter has been described in language specific to structural features and / or acts , it i s to be understood that the subj ect matter def ined 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 .

[0124] 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 wil l further be understood that reference to ' an ' item may refer to one or more of those items .

[0125] 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 .

[0126] 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 exclusive list and a method or apparatus may contain additional blocks or elements .

[0127] It will be understood that the above description is given by way of example only and that various modif ications may be made by those ski lled 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 numer- ous alterations to the disclosed embodiments without departing from the spirit or scope of this specification .

Claims

CLAIMS :

1. A diffraction grating (100) comprising: a plurality of grating lines (101) ; a first metal layer (102) arranged at least partially between the plurality of grating lines (101) ; a first dielectric layer (103) arranged onto the plurality of grating lines (101) and the first metal layer (102) ; and a second metal layer (104) arranged onto the first dielectric layer (103) ; wherein the first dielectric layer (103) is in contact with the plurality of grating lines (101) and the first metal layer (102) .

2. The diffraction grating (100) according to claim 1, wherein the plurality of grating lines comprise titanium dioxide.

3. The diffraction grating (100) according to claim 1 or claim 2, wherein the first metal layer (102) comprises silver or aluminium and / or the second metal layer (104) comprises silver or aluminium.

4. The diffraction grating (100) according to any preceding claim, wherein the first dielectric layer (103) comprises aluminium oxide, silicon dioxide, and / or magnesium fluoride.

5. The diffraction grating (100) according to any preceding claim, further comprising a second dielectric layer (105) arranged below the plurality of grating lines (101) .

6. The diffraction grating (100) according to claim 5, further comprising a titanium dioxide layer (106) arranged below the second dielectric layer (105) .

7. The diffraction grating (100) according to claim 5 or claim 6, wherein the second dielectric layer comprises aluminium oxide, silicon dioxide, and / or magnesium fluoride.

8. The diffraction grating (100) according to any preceding claim, wherein a height of the plurality of grating lines (101) is 10 - 50 nanometres, a height of the first dielectric layer (103) is 10 - 50 nanometres, and / or a height of the first metal layer (102) is 10 - 100 nanometres.

9. A display structure (400) comprising a planar waveguide (401) and the diffraction grating (100) according to any preceding claim on the planar waveguide (401) .

10. The display structure (400) according to claim 9, wherein the diffraction grating (100) is arranged as an in-coupling grating for coupling light (402) into the planar waveguide (401) .

11. The display structure (400) according to claim 9 or claim 10, wherein the diffraction grating (100) is arranged as a reflective diffraction grating onto the planar waveguide (401) .

12. A display device (600) comprising the display structure (400) according to any of claims 9 - 11.

13. The display device (600) according to claim 12 implemented as a see-through display device.

14. The display device (600) according to claim 12 or claim 13 implemented as a head-mounted display de- vrce .

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