Optical device

Abstract

The present invention relates to an optical device (100) for a display device comprising: i) a substrate (110); ii) one or more of gratings (120) placed onto the substrate; and iii) one or more of recessed grooves (130) at least partly filled by a material (140). The optical device may be made by using an advanced material or by using a high-performance material. The optical device may be used to make display device application, for example, a Liquid crystal display (LCD), Light emitting diode display (LED display), organic light emitting display (OLED), micro-LED display, quantum dot display (QLED), Augmented Reality (AR) hardware, Virtual Reality (VR) hardware, Mixed Reality (MR) hardware, plasma (PDP) display and an electroluminescent (ELD) display.

Description

[0001] Foreignfiling text P24-193

[0002] - 1 -

[0003] Optical device

[0004] Field of the invention

[0005] The present invention relates to an optical device for a display device,

[0006] 5 process for fabricating an optical device, use of an optical device and a display device.

[0007] Background Art

[0008] The design and manufacture of surface relief gratings (SRG) is key to the performance of future Augmented (AR) headsets. The design layout and choice of materials within a SRG is carefully optimized by companies to try to find a balance between parameters such as field of view, efficiency (power usage), brightness and cost. Due to limitations on material properties, especially refractive index, the majority of SRG tend to follow a

[0009] 15 similar layout (shown below).

[0010] Such a design would be built on top of one of the state-of-the-art glass substrates, such as Corning 2.0 or Schott 2.0 refractive index. However, there is a clear drawback to such an approach, and this is because the

[0011] 20 overall waveguide efficiency (as a result of grating acceptance range) is directly proportional to the average index of the entire waveguide. And since in this case one of the layers is ‘low’ refractive index - there is often an air gap after the NIL grating - then this contributes to overall lower performance.

[0012] An alternative design could incorporate a high index gap fill material. But then attention needs to be paid to the relative refractive index of the NIL layer. The field of view (related to the grating diffraction angle) is proportional to the difference of the refractive index of the NIL layer

[0013] 30 compared to the layer above it (either air or gap fill). Therefore, a new way of thinking is needed to find a new optimum in terms of overall performance. Since just adding a high index gap fill material on top of the Foreignfiling text P24-193

[0014] - 2 -

[0015] NIL layer would not necessarily result in improved performance unless the other layers were optimized to perform in a new configuration.

[0016] “Design and manufacture AR head-mounted displays: A review and outlook”, Cheng et al. Light: Advanced Manufacturing (2021 )2:24,

[0017] 5 https: / / doi.Org / 10.37188 / lam.2O21 .024.

[0018] Summary of the invention

[0019] The inventors newly have found that there are still one or more considerable problems for which improvement is desired, as listed below: expanding the parameter space that allows adjusting the optical parameters / optical properties of an obtained optical layer / composite through the combination of at least two metal precursors, providing a new inventive concept to improve the overall light utilization efficiency of the optical device, preferably improving overall light utilization

[0020] 15 efficiency of a waveguide. Preferably, improving diffraction efficiency and angular aperture, and the combined effect of diffraction efficiency and angular aperture as the overall light utilization efficiency of an optical device at the same time.

[0021] 20 The inventors aimed to solve one or more of the above-mentioned problems.

[0022] Then, the present inventors have surprisingly found that one or more of the above-described technical problems can be solved by the features as defined in the claims.

[0023] Namely, it is found a novel optical device (100) for a display device comprising, essentially consisting of or consists of: i) a substrate (110);

[0024] 30 ii) one or more of gratings (120) placed onto the substrate; and iii) one or more of recessed grooves (130), wherein Foreignfiling text P24-193

[0025] - 3 - said one or more of recessed grooves (130) is at least partly filled by a material (140); and wherein the relative refractive index value of said one or more of gratings (HNIL) is < 1 .8 and the relative refractive index value of the material (ng) is >

[0026] 5 2.0 at 589.3nm light wavelength.

[0027] In another aspect, the present invention also relates to a process for fabricating the device of the present invention, comprising the following steps A) and B)):

[0028] A) Fabricating one or more of gratings (120) having the refractive index value < 1 .8 with using a metal oxide precursor after curing by solution deposition method, preferably by sol-gel method;

[0029] B) Fabricating one or more of recessed grooves (130) filled by said material (140) having the refractive index value > 2.0 with using a metal oxide

[0030] 15 precursor by solution deposition method, preferably by sol-gel method.

[0031] In another aspect, the present invention further relates to use of an optical device of a present invention in a display device or for fabricating a display device

[0032] 20

[0033] In another aspect, the present invention further relates to a display device comprising at least one functional medium configured to direct and modulate a light or configured to emit light; and the device of the present invention.

[0034] Technical effects of the invention

[0035] The present invention may provide one or more of following effects; expanding the parameter space that allows adjusting the optical parameters / optical properties of an obtained optical layer / composite

[0036] 30 through the combination of at least two metal precursors, providing a new inventive concept to improve the overall light utilization efficiency of the optical device, preferably improving overall light utilization Foreignfiling text P24-193

[0037] - 4 - efficiency of a waveguide. Preferably, improving diffraction efficiency and angular aperture, and the combined effect of diffraction efficiency and angular aperture as the overall light utilization efficiency of an optical device at the same time.

[0038] 5

[0039] Brief description of the figures

[0040] Fig. 1 : Schematic cross-sectional view of one embodiment of the optical device (100) of the present invention (Binary gratings)

[0041] Fig. 2: Schematic cross-sectional view of another embodiment of the optical device (100) of the present invention (Slanted gratings)

[0042] Fig. 3: Schematic cross-sectional view of the model domain of working example

[0043] Fig. 4: Schematic cross-sectional view of one embodiment of surface relief gratings (100a) of the optical device (100) of the present invention

[0044] 15 Fig. 5: Schematic cross-sectional view of one embodiment of the display device (200) of the present invention (an example of an optical see-through augmented reality device system)

[0045] Fig. 6: Schematic cross-sectional view of one embodiment of surface relief gratings (Blazed gratings)

[0046] 20 Fig. 7: Schematic cross-sectional view of one embodiment of surface relief gratings (Analog surface relief gratings)

[0047] Fig. 8: Schematic cross-sectional view of one embodiment of surface relief gratings (Multilevel structured gratings)

[0048] Fig. 9: Schematic cross-sectional view of one embodiment of surface relief gratings (The combination of slanted gratings and a blazed gratings)

[0049] List of reference signs

[0050] Fig.1 , Fig.2 and Fig.4

[0051] 100. Optical device

[0052] 30 100a. Surface relief gratings

[0053] 110. Substrate

[0054] 120. Gratings Foreignfiling text P24-193

[0055] - 5 -

[0056] 120a. Grating period

[0057] 120G. Grating gap width (Gw)

[0058] 120d. Grating depth (d)

[0059] 130. Recessed grooves

[0060] 5 140. Material (filling material)

[0061] [3. Slant angle

[0062] Fig. 3

[0063] 110. Substrate

[0064] 120. Gratings

[0065] 140. Material (filling material)

[0066] A. Grating period (nm) d. SRG thickness (nm) g. Gap width (nm)

[0067] 15 h . Overburden layer thickness (nm) ho Zero residual layer thickness (nm)

[0068] Fig. 5

[0069] 200. Display device

[0070] 20 210. Projector

[0071] 211. Image source such as OLED device, LCD device, micro-LED device

[0072] 212. Projector optics (Optical lends)

[0073] 220. Waveguide

[0074] 230. Surface relief gratings (corresponding to 100a) as an input coupler

[0075] 240. Substrate

[0076] 250. Surface relief gratings as an output coupler

[0077] 260. Optical lends (optional)

[0078] 270. Direct extracted light

[0079] 280. External light

[0080] 30 290. Eye

[0081] Fig. 6, Fig. 7, Fig. 8 Foreignfiling text P24-193

[0082] - 6 -

[0083] 110. Substrate

[0084] |3bl. Blaze angle

[0085] 120bl. Blazed gratings 120an. Analog gratings

[0086] 5 120mu. Multilevel structured gratings

[0087] Fig. 9

[0088] 110. Substrate

[0089] 120co. Combination slanted gratings and a blazed gratings (or trapezoid gratings)

[0090] Gp. Grating period (corresponding to 120a)

[0091] Gw. Grating gap width (corresponding to 120G) d. Grating depth (corresponding to 120d)

[0092] Ptop. Top slant angle

[0093] 15 bottom. Bottom slant angle front. Front slant angle Pback. Back slant angle

[0094] Definition of the terms

[0095] 20 According to the present invention, the term “refractive index” means relative refractive index at 589.3nm light wavelength (Sodium D line).

[0096] The term “optical device” as used herein, relates to a device containing one or more optical components for forming a light beam including, but not limited to, gratings, lenses, prisms, mirrors, optical windows, filters, polarizing optics, UV and IR optics, waveguides and optical coatings. Preferred optical devices in the context of the present invention are waveguides for augmented reality (AR) device, for virtual reality (VR) device and / or for mixed reality (MR) device, or preferred optical devices are

[0097] 30 augmented reality (AR) glasses, virtual reality (VR) glasses and / or mixed reality (MR) glasses. Foreignfiling text P24-193

[0098] - 7 -

[0099] The term “display device” as used herein, is a kind of an optical device configured to output / present information in visual or tactile form. Examples are Liquid crystal display (LCD), Light emitting diode display (LED display), organic light emitting display (OLED), micro-LED display, quantum dot

[0100] 5 display (QLED), AR display, VR display, MR display, plasma (PDP) display, electroluminescent (ELD) display. Preferred optical devices in the context of the present invention is AR display, VR display or MR display.

[0101] Preferred embodiments of the present invention are described hereinafter and in the dependent claims.

[0102] Detailed description of the invention

[0103] The present invention relates to an optical device (100) for a display device comprises, essentially consists of or consists of:

[0104] 15 i) a substrate (110); ii) one or more of gratings (120) placed onto the substrate; and iii) one or more of recessed grooves (130), wherein said one or more of recessed grooves (130) is at least partly filled by a material (140); and

[0105] 20 wherein the relative refractive index value of said one or more of gratings (HNIL) is < 1 .8 and the relative refractive index value of the material (ng) is > 2.0 at 589.3nm light wavelength.

[0106] It is believed that the above mentioned device configuration setting the relative refractive index value of the gratings and the relative refractive index value of the material is a new inventive concept introduced by the inventors of the present invention and it may improve the overall light utilization efficiency of the optical device of the present invention, preferably overall light utilization efficiency of a waveguide. Preferably, diffraction

[0107] 30 efficiency and angular aperture, and the combined effect of diffraction efficiency and angular aperture as the overall light utilization efficiency may be improved. Foreignfiling text P24-193

[0108] - 8 -

[0109] In a preferable embodiment of the present invention, the refractive index value of said gratings (HNIL) is in the range 1 .5 < nNiL< 1 .7.

[0110] 5 In a preferable embodiment of the present invention, the refractive index value of said material (ng) is more than 2.0, preferably more than 2.1 , more preferably more than 2.15 and it is 2.8 or less, preferably it is in the range 2.0 < ng< 2.8, more preferably 2.1 < ng< 2.5, even more preferably 2.15 < ng< 2.35.

[0111] Furthermore preferably, the refractive index value of said gratings (HNIL) is 1 .5 < nNn< 1 .7 and the refractive index value of said material (ng) is more than 2.0, preferably more than 2.1 , more preferably more than 2.15 and it is 2.8 or less, preferably it is in the range 2.0 < ng< 2.8, more preferably 2.1 <

[0112] 15 ng< 2.5, even more preferably 2.15 < ng< 2.35.

[0113] It is believed that above mentioned preferable embodiments may further improve / optimize said overall light utilization efficiency.

[0114] 20 Said relative refractive index value (HNIL), (ng) can be measured by the following Ellipsometry method.

[0115] Preparation of measurement samples where formulation medium to be used for the fabricating gratings (120) or for the filing material is / are available.

[0116] 1 . Preparation of the Substrate: Clean a 2-inch quartz or silicon substrate and treat it with plasma using the following method:

[0117] • Immerse in 2-propanol for 10 minutes in an ultrasonic bath.

[0118] • Rinse with de-ionized water.

[0119] 30

[0120] • Dry the sample completely on a hot plate at 100°C for 10 minutes.

[0121] • Expose to an oxygen plasma chamber for 5 minutes. Foreignfiling text P24-193

[0122] - 9 -

[0123] 2. Spin Coating: Place the substrate in a spin coater and hold it using a vacuum chuck. Typical spin coating conditions use 0.5ml of formulation and a spin speed of 2500rpm to obtain 100nm layer thickness of the cured layer after the Hard Baking.

[0124] 5 3. Hard Baking: After spin coating, hard-bake the sample at 150°C on a hot plate for 5 minutes.

[0125] Preparation of measurement samples where an optical device having gratings (120) placed on to the substrate and recessed grooves (130) is available / obtained.

[0126] 1. Cut out a 2-inch size including the substrate, gratings placed onto the substrate, and recessed grooves.

[0127] 2. Optionally clean the 2-inch size sample by well-known method, e.g., by air blowing, rinse with de-ionized water and dry the sample or a

[0128] 15 combination of air blowing, rinse and dry.

[0129] Measurement:

[0130] Measurement equipment: Elipsometry (manufacturer Wollam, model M- 2000)

[0131] 20 Turn on the ellipsometer for at least 20 minutes to stabilize it. Place the sample directly in the ellipsometer. The standard routine performs an angle scan from 65° to 75° in 5° steps and records data across the full wavelength range (192-1000nm).

[0132] Said measurement is performed for 5 different locations of the sample including the center and the periphery of the sample and the average of the measurement results is taken.

[0133] - Substrate (110)

[0134] According to the present invention, said substrate (110) can be flexible,

[0135] 30 semi-rigid or rigid. The material for a substrate is not particularly limited but preferably transparent in visible light wavelength. Foreignfiling text P24-193

[0136] - 10 -

[0137] Preferably, as a transparent substrate, a transparent polymer substrate, glass substrate (optical glass substrate), thin glass substrate stacked on a transparent polymer film, transparent metal oxides (for example, silicone dioxides (SiC>2), preferably quarts, aluminum dioxides (AI2O3), Zinc oxide

[0138] 5 (ZnO), Indium Tin Oxide (ITO), Titanium dioxides (TiO2)) substrate, can be used.

[0139] A transparent polymer substrate can be polymethyl methacrylate (PMMA), transparent polystyrene (PS), polyvinyl alcohol(PVA), polyvinyl butyral (PVB), polycarbonate (PC), acrylic resin (PMMA), transparent Epoxy Resin, Polytetrafluoroethylene (PTFE) or a combination of any of these.

[0140] In more preferable embodiment of the present invention from the viewpoint of having high heat resistance, chemical resistance, physical resistance,

[0141] 15 environmental durability and / or having high refractive index value, said substrate (110) is an optical glass substrate, silicone dioxides (SiCh) substrate, preferably quarts substrate, aluminum dioxides (AI2O3) substrate, Zinc oxide (ZnO) substrate, Indium Tin Oxide (ITO) substrate, Titanium dioxides (TiO2) substrate. Furthermore preferably it is an aluminum dioxides

[0142] 20 (AI2O3) substrate, Zinc oxide (ZnO) substrate or an Indium Tin Oxide (ITO) substrate from the viewpoint of having higher refractive index value (around in the range from 1 .8 to 2.2).

[0143] The term “transparent” means at least around 60 % of visible light wavelength of incident light used in the optical device. Preferably, it is over 70 %, more preferably, over 75%, the most preferably, it is over 80 %.

[0144] In a preferred embodiment of the present invention, said substrate (110) has the refractive index value (nSUb) in the range from 1.8 to 2.2. Preferably

[0145] 30 it is from 1.9 to 2.1. Foreignfiling text P24-193

[0146] - 11 -

[0147] Said relative refractive index value (nSUb) of the substrate, can be measured by the above mentioned Ellipsometry method without steps 2 and 3.

[0148] It is believed that the above mentioned substrate is especially suitable for

[0149] 5 the optical device of the present invention where the relative refractive index value of said one or more of gratings (HNIL) is < 1 .8 and the relative refractive index value of the material (ng) is > 2.0 at 589.3nm light wavelength and said preferred embodiment may further optimize / im prove said overall light utilization efficiency.

[0150] - Gratings (120) and Recessed grooves (130)

[0151] In a preferred embodiment of the present invention, said optical device contains one or more of surface relief gratings (100a) and said ii) one or more of gratings (120) and iii) one or more of recessed grooves (130) forms

[0152] 15 said surface relief gratings (100a).

[0153] Thus, in a preferred embodiment of the present invention, said one or more of gratings is a plurality of gratings and said one or more of recessed grooves is a plurality of recessed grooves. More preferably it is a plurality of

[0154] 20 nanosized gratings and a plurality of nanosized recessed grooves.

[0155] In a preferable embodiment of the present invention, said optical device (100) is an optical waveguide, more preferably said optical device (100) is an optical waveguide for a display device, even more preferably it is an optical waveguide for AR device or for MR device.

[0156] Preferably, the gratings (120) has a grating period (120a) in the range from 400nm to 700nm.

[0157] 30 In a preferred embodiment of the present invention, the gratings (120) of the optical device has the grating gap width Gw (120G) in the range from Foreignfiling text P24-193

[0158] - 12 -

[0159] 10nm to 500nm. Preferably from 20 to 250nm, more preferably from 30 to 150nm.

[0160] It is believed having the grating gap like above mentioned ranges is suitable

[0161] 5 for waveguide for an optical device namely for VR or MR devices in view of increasing the overall light utilization efficiency of the optical device. It is also believed that the above mentioned range is suitable to have bigger contribution from gap filing material to average refractive index and to grating diffraction efficiency.

[0162] In a preferred embodiment of the present invention, the grating depth d (120d) of the optical device is in the range from 50nm to 1 pm, preferably from 100nm to 600nm, more preferably from 200nm to 400nm.

[0163] 15 It is believed that above mentioned parameter ranges may further optimize and / or improve the overall said overall light utilization efficiency of the optical device of the present invention.

[0164] Preferably, said one or more of gratings (120) is a slanted gratings, blazed

[0165] 20 gratings, binary gratings, analog surface relief gratings, multilevel structured gratings or a combination of a slanted gratings and a blazed gratings.

[0166] Like described in Ding et al. eLight (2023) 3:24, https: / / doi.Org / 10.1186 / s43593-023-00057-z.

[0167] In a preferred embodiment of the present invention, at least one of said gratings (120) is a binary grating having the slant angle 0°, a slanted grating having the slant angle in the range from +0.1 ° to +45°, a blazed grating having the blaze angle +1 to +60°, Preferably the slant angle of said slanted grating is in the range from +1 ° to +35°, more preferably from +1 to +30°,

[0168] 30 preferably said blaze angle of the blazed grating is in the range from +5 to +45°, more preferably from +10 to +40° Foreignfiling text P24-193

[0169] - 13 -

[0170] Figs. 1 to 9 describe cross sectional views of a schematic of the optical device of the present invention.

[0171] It is believed that above mentioned parameter ranges may further optimize

[0172] 5 and / or improve the overall said overall light utilization efficiency of the optical device of the present invention.

[0173] In a preferred embodiment of the present invention, said one or more of gratings (120) is a metal oxide, preferably said metal oxide is selected from, preferably said metal oxide is an optically transparent in visible wavelength, more preferably it is selected from TiCh, Nb20s, SnO, SnCh, V2O5, Ta2Os, ZrO2 or ZnO, even more preferably selected from SnO, SnO2, V2O5, Ta2Os, ZrO2 or ZnO.

[0174] 15 As for such materials, any publicly know one (e.g., CP5-UV from HighRI Optics (Rl = 1 .80 at 590nm)) can be used.

[0175] According to the present invention, said one or more of gratins may be fabricated by any publicly known methods. Such as fabricating by

[0176] 20 nanoimprint lithography, preferably by UV nanoimprint lithography (UV- NIL), or thermal nanoimprint lithography (TNIL) or by a combination of UV- NIL and TNIL.

[0177] [Material (140) for filling recessed grooves(130)]

[0178] According to the present invention, one or more of recessed grooves (130) is at least partly filled by a material (140). Preferably all the recessed grooves are filled by said material (140).

[0179] In a preferred embodiment of the present invention, said material (140) is a

[0180] 30 metal oxide, preferably said metal oxide is an optically transparent in visible wavelength, more preferably it is selected from TiCh, Nb20s, SnO, SnO2, Foreignfiling text P24-193

[0181] - 14 -

[0182] V2O5, Ta20s, ZrO2 or ZnO, even more preferably it is TiCh, Nb20s, SnO or SnO2.

[0183] Said material may be fabricated in one or more of the recessed grooves to

[0184] 5 fill it partly or fully by publicly known method.

[0185] [Optical device]

[0186] In a preferred embodiment of the present invention, said optical device (100) is an optical waveguide, more preferably said optical device (100) is an optical waveguide for a display device, even more preferably it is an optical waveguide for AR device or for MR device.

[0187] It is believed that waveguide as the optical device of the present invention is most preferable device for AR device or for MR device to improve overall

[0188] 15 optical performance of these devices.

[0189] [Process for fabricating the optical device]

[0190] According to the present invention, said optical device may be fabricated by the claimed process.

[0191] 20

[0192] Thus, in another aspect, the present invention further relates to a process for fabricating the device of the present invention, comprises, essentially consists of or consists of, the following steps A) and B)):

[0193] A) Fabricating one or more of gratings (120) having the refractive index value < 1 .8 with using a metal oxide precursor after curing by solution deposition method, preferably by sol-gel method;

[0194] B) Fabricating one or more of recessed grooves (130) filled by said material (140) having the refractive index value > 2.0 with using a metal oxide precursor by solution deposition method, preferably by sol-gel

[0195] 30 method. Foreignfiling text P24-193

[0196] - 15 -

[0197] According to the present invention, said one or more of gratins may be fabricated by any publicly known methods. Such as fabricating by nanoimprint lithography, preferably by UV nanoimprint lithography (UV- NIL), or thermal nanoimprint lithography (TNIL) or by a combination of UV-

[0198] 5 NIL and TNIL.

[0199] Thus, in a preferred embodiment of the present invention, said step A) comprises the following steps:

[0200] A1 ) preparing a substrate;

[0201] A2) providing a formulation containing the metal oxide precursor by wet deposition process onto a surface of the substrate, preferably by dip coating, spin-coating or ink-jetting;

[0202] A3) applying a thermal treatment to the formulation to convert at least a part of the metal oxide precursor of the formulation to a metal oxide to

[0203] 15 form an optical layer.

[0204] A4) forming gratings by pressing a patterned mold onto the optical layer, A5) optionally, heating the optical layer;

[0205] A6) optionally, irradiating the optical layer with the light, preferably said light is UV light.

[0206] 20

[0207] More details of the substate to be used on step A1 ) is disclosed in the section of “Substrate (110)” above.

[0208] In step A2) of the process, the formulation is applied onto a surface of a substrate or a surface of an underlayer, wherein said surface may be either a surface of a base material of the substrate or a surface of a layer of a material being different from the base material of the substrate, wherein such layer has been formed prior to applying said formulation.

[0209] 30 In a preferred embodiment of the process of the present invention, the surface of the substrate is pre-treated by a surface cleaning process. Preferred surface cleaning processes are silicon wafer cleaning processes Foreignfiling text P24-193

[0210] - 16 - such as described in W. Kern, The Evolution of Silicon Wafer Cleaning Technology, J. Electrochem. Soc., Vol. 137, 6, 1990, 1887-1892 and in New Process Technologies for Microelectronics, RCA Review 1970, 31 , 2, 185-454. Such silicon wafer cleaning processes include wet cleaning

[0211] 5 process involving cleaning solvents (e.g., isopropanol (IPA)); wet etching processes involving hydrogen peroxide solutions (e.g., piranha solution, SC1 , and SC2), choline solutions, or HF solutions; dry etching processes involving chemical vapor etching, UV / ozone treatments or glow discharge techniques (e.g., O2 plasma etching); and mechanical processes involving brush scrubbing, fluid jet or ultrasonic techniques (sonification). The surface of the substrate can also be pre-treated by salinization or an atomic layer deposition (ALD) process. The pre-treatment of the surface of the substrate serves to modify the hydrophobicity / hydrophi licity of the surface. This can improve the adhesion and filling characteristics of the optical metal oxide

[0212] 15 layer on the surface of the substrate.

[0213] In a more preferred embodiment, a wet cleaning process involving cleaning solvents (e.g., isopropanol (IPA)) is combined with one or more of a wet etching process involving hydrogen peroxide solutions (e.g., piranha

[0214] 20 solution, SC1 , and SC2), choline solutions, or HF solutions; dry etching process involving chemical vapor etching, UV / ozone treatments or glow discharge techniques (e.g., O2 plasma etching); and mechanical process involving brush scrubbing, fluid jet or ultrasonic techniques (sonification).

[0215] In a most preferred embodiment, a wet cleaning process involving cleaning solvents (e.g., isopropanol (IPA)) is combined with a mechanical process involving brush scrubbing, fluid jet or ultrasonic techniques (sonification) and with a wet etching process involving hydrogen peroxide solutions (e.g., piranha solution, SC1 , and SC2), choline solutions, or HF solutions.

[0216] 30 Foreignfiling text P24-193

[0217] - 17 -

[0218] And more details of the above mentioned and / or the other steps may be adjusted based on the disclosure of WO 2023 / 0114997 A1 , US 2022 / 260904A2 and US 2020 / 285145 A2 (Myrias Optics).

[0219] 5 And as for materials, any publicly known one like described in the above mentioned patent applications, or CP5-UV from HighRI Optics (Rl = 1.80 at 590nm) can be used preferably.

[0220] In a preferred embodiment, said step B) comprises the following steps: B1 ) preparing a substrate obtained in step A);

[0221] B2) providing a formulation containing the metal oxide precursor by wet deposition process onto a surface of the substrate, preferably by dip coating, spin-coating or ink-jetting;

[0222] B3) applying a thermal treatment to the formulation to convert at least a

[0223] 15 part of the metal oxide precursor of the formulation to a metal oxide.

[0224] According to the present invention, in a preferred embodiment, said metal oxide precursor used in step A) is a metal halide, metal alkoxide or a metal carboxylate containing a metal element selected from the group consisting

[0225] 20 of group 1 elements, group 4 elements, group 5 elements, group 6 elements, group 12 elements, group 14 elements and group 15 elements of the periodic table and the metal oxide precursor used in step B) is a metal halide, metal alkoxide or a metal carboxylate containing a metal element selected from the group consisting of group 1 elements, group 4 elements, group 5 elements, group 6 elements, group 12 elements, group 14 elements and group 15 elements of the periodic table.

[0226] The publicly known material like disclosed in EP 23206761.1 , EP 23212576.5 may be used preferably.

[0227] 30

[0228] -Solvent Foreignfiling text P24-193

[0229] - 18 -

[0230] According to the present invention, the formulation for step A2) and / or the formulation for step B2) of the present invention may contains a solvent.

[0231] In a preferred embodiment of the present invention, the solvent is an

[0232] 5 organic solvent. More preferably said organic solvent is selected from one or more members of the group consisting of ethylene glycol monoalkyl ethers, preferably it is ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether and / or ethylene glycol monobutyl ether; diethylene glycol dialkyl ethers, preferably it is diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dipropyl ether and / or diethylene glycol dibutyl ether; propylene glycol monoalkyl ethers, preferably it is propylene glycol monomethyl ether (PGME), propylene glycol monoethyl ether and / or propylene glycol monopropyl ether; 1 ,3-dimethoxy-2-propanol, ethylene glycol alkyl ether

[0233] 15 acetates, preferably it is methyl cellosolve acetate and / or ethyl cellosolve acetate; propylene glycol alkyl ether acetates, preferably it is propylene glycol monomethyl ether acetate (PGMEA), propylene glycol monoethyl ether acetate and / or propylene glycol monopropyl ether acetate; ketones, preferably it is methyl ethyl ketone, acetone, methyl amyl ketone, methyl

[0234] 20 isobutyl ketone and / or cyclohexanone; alcohols, preferably it is ethanol, propanol, butanol, hexanol, cyclo hexanol, ethylene glycol, propylene glycol, triethylene glycol and / or glycerin; esters, preferably it is ethyl 3- ethoxypropionate, methyl 3-methoxypropionate and / or ethyl lactate; and cyclic esters, preferably it is gamma-butyro-lactone; preferably said solvent is ethylene glycol monoalkyl ethers, diethylene glycol dialkyl ethers, propylene glycol, ethylene glycol, propylene glycol monoalkyl ethers, ethylene glycol alkyl ether acetates, propylene glycol alkyl ether acetate, more preferably said solvent is selected from propylene glycol alkyl ether acetates, ethylene glycol monoalkyl ethers, propylene glycol and propylene

[0235] 30 glycol monoalkyl ethers, 1 ,3-dimethoxy-2-propanol. Foreignfiling text P24-193

[0236] - 19 -

[0237] It is believed that the printing, especially ink jetting of structures is considered as a highly cost-efficient production step. Spin-coating is a convenient method and is preferable to form a uniform thin layer. Thus, suitable solvents of the formulation for spin-coating / inkjet printing the

[0238] 5 structures or filling up of cavities and structures, is described here.

[0239] After printing, deposition and fill up of structures, at least a part of the material as the metal halide precursor needs to become converted into the respective metal oxides by any known means know to the persons skilled in the art (thermally, photochemically, etc.).

[0240] - Water

[0241] According to the present invention, the formulation for step A2) and / or the formulation for step B2) of the present invention may preferably contains

[0242] 15 water, and the stoichiometric amount of water is in the range from 100 to 400 mol% based on the total amount of metal oxide precursor, preferably the stoichiometric amount of water based on the total amount of the metal oxide precursor is in the range from 150 to 300 mol%, even more preferably from 180 to 270 mol%.

[0243] 20

[0244] -Additives

[0245] In some embodiments of present invention, the formulation for step A2) and / or the formulation for step B2) may optionally comprise one or more additives selected from surfactants, wetting and dispersion agents, adhesion promoters, and polymer matrices.

[0246] Or, in some embodiments, the formulation of the present invention does not comprise any additives.

[0247] In a preferred embodiment of the present invention, the formulation is an

[0248] 30 ink formulation being suitable for inkjet printing. Typical requirements for ink formulations are surface tensions in the range from 20 mN / m to 30 mN / m and viscosities in the range from 5 mPa s to 30 mPa s. Foreignfiling text P24-193

[0249] - 20 -

[0250] Thus, in a preferable embodiment, in step A2) and / or in step B2), the formulation is applied to a surface of a substrate or to a surface of an underlayer by spin-coating or ink-jetting.

[0251] 5

[0252] In a preferable embodiment, the formulation is at least partly converted on the surface of the substrate. Namely, the formulation in step B3) may at least partly converted on the surface or inside of said grooves of the gratings (120) to a material composite, wherein said material contains a metal oxide, preferably selected from metal monoxide, metal dioxide and / or metal pentoxide; and a metal oxide precursor.

[0253] -Step B3)

[0254] It is believed that the formulation is at least partly converted in step B3) on

[0255] 15 the surface of the substrate or on the surface of the underlayer to a metal oxide to form a material composite by exposure to thermal treatment. Said composite is preferably a layered material composite. And said solvent is usually removed in step B3).

[0256] 20 Preferred thermal treatment includes exposure to elevated temperature from 50 to 600 °C, preferably it is from 80 to 500°C, more preferably from 100 to 300°C. It is believed that applying a higher temperature such as in the range from 100 to 600°C, preferably 125 to 450°C, more preferably from 150 to 250 °C can realize an improved gap fill.

[0257] It is preferred to use the formulation containing a lower amount of the metal oxide precursor based on the total amount of the formulation in step B2) to realize an improved gap filing, for examples, in the range from 0.1 to 30wt% based on the total amount of the formulation, more preferably in the range

[0258] 30 from 1 to 20wt%, even more preferably from 5 to 15wt% based on the total amount of the formulation; and applying a higher temperature in step B3) Foreignfiling text P24-193

[0259] - 21 - such as in the range from 100 to 600°C, preferably 125 to 450°C, more preferably from 150 to 250°C to realize an improved gap fill.

[0260] In some embodiments of the process, in Step B, a pre-baking step can be

[0261] 5 applied before step B3) after step B2) to remove a solvent of the formulation. The formulation can also be partly converted on the surface of the substrate to an optical metal oxide layer by pre-baking (soft baking) at a temperature from 40 to 150 °C, preferably from 50 to 120 °C, more preferably from 60 to 100 °C; then, baking of step (b) (hard baking, sintering or annealing) at a temperature from 100 to 600 °C, preferably from 125 to 450 °C, more preferably from 150 to 255 °C is applied.

[0262] Pre-baking (soft baking) serves the purpose to remove volatile and low boiling components such as, e.g., volatile and low boiling formulation media

[0263] 15 or additives from the drop casted, coated or printed films. Pre-baking is preferably carried out for a period of 1 to 60 minutes. After pre-baking, layers of substrate adhering films of metal oxide precursor or metal oxide precursor mixtures are obtained. The films may still comprise residual formulation media or additives.

[0264] 20

[0265] In an alternative preferred embodiment of the step B) of the present invention, pre-baking is omitted so that the formulation is converted in step B) to an optical metal oxide layer directly.

[0266] Baking (hard baking, sintering or annealing) serves the purpose to convert the metal oxide precursor or metal oxide precursor mixture layers on the substrate into a metal oxide layer. Moreover, the final properties of the metal oxide layer may be adjusted by the baking treatment. Baking is preferably carried out at the time in the range from 1 to 60min, preferably 2

[0267] 30 to 20 min, more preferably 3 to 10m in. Foreignfiling text P24-193

[0268] - 22 -

[0269] Said Pre-baking and baking (step B3)) may be carried out under ambient atmosphere or atmospheres with increased oxygen content to decompose unwanted organic components, which can lead to a lower activation energy when the material composite is formed and is believed to improve the

[0270] 5 physical-chemical properties of the resulting layered composite material.

[0271] In step B2) of the process, the formulation is applied onto a surface of a substrate obtained in step A) of the process.

[0272] Thus, in a preferable embodiment, in step B3), the formulation is at least partly converted on the surface of the substrate to a material composite, by baking it at a temperature from 50 to 400 °C, preferably it is from 80 to 350°C, more preferably from 100 to 300°C. According to the present invention, said surface of the substrate obtained in step A) may include the

[0273] 15 surface of one or more of gratings.

[0274] In a preferred embodiment of the present invention, said thermal treatment of step B3) is applied at the time in the range from 1 to 60min, preferably 2 to 20 min, more preferably 3 to 10m in.

[0275] 20

[0276] In some embodiments, the formulation is at least partly converted on the surface of the substrate to the material (140) during the thermal treatment process of step B3), wherein said material contains a metal oxide, preferably selected from metal monoxide, dioxide and / or pentoxide; and a metal alkoxide.

[0277] - Optical device

[0278] It is preferred that the optical device is a device containing one or more optical components for forming a light beam including, but not limited to,

[0279] 30 gratings, lenses, prisms, mirrors, optical windows, filters, polarizing optics, UV and IR optics, waveguides and optical coatings. Preferred optical devices in the context of the present invention are waveguides for Foreignfiling text P24-193

[0280] - 23 - augmented reality (AR) device, for virtual reality (VR) device and / or for mixed reality (MR) device, or preferred optical devices are augmented reality (AR) glasses, virtual reality (VR) glasses and / or mixed reality (MR) glasses.

[0281] 5

[0282] - Use of the optical device (100)

[0283] In another aspect, present invention may further relates to use of the optical device of the present invention in a display device or for fabricating a display device. The details of the optical device of the present invention is described in whole part of Detailed description of the invention.

[0284] - Display device (200)

[0285] Finally, the present invention relates to a display device (200) comprising at least one functional medium configured to modulate a light or configured to

[0286] 15 emit light; and the composite, or an optical device of the present invention.

[0287] Examples of said display device is selected from a Liquid crystal display (LCD), Light emitting diode display (LED display), organic light emitting display (OLED), micro-LED display, quantum dot display (QLED),

[0288] 20 Augmented Reality (AR) hardware, Virtual Reality (VR) hardware, Mixed Reality (MR) hardware, plasma (PDP) display and an electroluminescent (ELD) display. Said AR, VR and MR hardware are also called as AR, VR and MR display. Preferably said display device is AR hardware, VR hardware or MR hardware.

[0289] Thus, the term “functional medium” of the optical device of the present invention may be LCD, LED, OLED, micro-LED, PDP, ELD layer, array, or display included in said display device (e.g., Image source 211 of Fig. 5).

[0290] 30 Preferably, said optical device is a waveguide, preferably as an input coupler or as an output coupler, and said functional medium is an image Foreignfiling text P24-193

[0291] - 24 - source selected from one or more members of the group consisting of LCD, LED, OLED, micro-LED, PDP, ELD layer).

[0292] Preferably, said display device has a 1stoptical device (waveguide) as an

[0293] 5 input coupler, a 2ndoptical device (waveguide) as an output coupler and said functional medium is an image source selected from one or more members of the group consisting of LCD, LED, OLED, micro-LED, PDP, ELD layer)

[0294] The present invention is further illustrated by the examples following hereinafter which shall in no way be construed as limiting. The skilled person will acknowledge that various modifications, additions and alternations may be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims.

[0295] 15

[0296] Examples

[0297] - Analytics and measurement methods

[0298] Ellipsometry is used to determine layer thickness (nm), refractive index (n) (Rl) and absorption index (k) of a metal oxide layer. Measurements are

[0299] 20 performed using an ellipsometer M2000 from J. A. Woolam and three different angles of incidence (65°, 70 ° and 75°). The measurement data is analyzed with software CompleteEase from J. A. Woolam, assuming either full or almost nearly complete transparent behavior above a wavelength of 600 nm (at 560nm) and applying B-spline fitting for obtaining refractive indices (n) as well as absorption indices (k). The optical constants are averaged from three to four measured samples each of them providing a different layer thickness either after soft bake or after hard bake or after combined soft and subsequent hard bake.

[0300] Usually, quartz and / or silicon wafers, both 2 inch in diameter, are used

[0301] 30 throughout all coating experiments where flat and non-structured carriers for metal oxides are required (e. g. spectroscopic and ellipsometry measurements). Foreignfiling text P24-193

[0302] - 25 -

[0303] SEM images are recorded using either a Mira 3 LMU from Tescan or Sigma 300VP from Carl Zeiss or Supra 35 from Carl Zeiss.

[0304] 5 Substrate coating, usually wafers, is done using a spin coater (LabSpin 150i) from Suess. The spin coating process using planar substrates is as follows: deposition of 0.5 ml of the coating onto static quartz wafers followed by a spinning interval of 30 seconds at a given spin speed where the acceleration to reach the final spin speed is set to 500 rpm / s2. Different layers and coating thicknesses are achieved using either different spin speeds or different coating formulations having different concentrations of the metal oxide precursor or mixtures of different metal oxide precursors. After spin coating, the coated substrates are subjected to thermal cure on a conventional lab hotplate. Usually, however not limited hereto, the coated

[0305] 15 layers are baked at 100 °C to 200 °C for between 1 to 10 minutes. Layer baking is performed using high temperature hotplates from Harry Gestigkeit allowing for reaching temperatures of up to 600 °C. Afore-mentioned conditions and parameters apply to all following experimental examples unless other conditions are explicitly mentioned elsewhere.

[0306] 20

[0307] As an alternative film preparation technique, inkjet printing can be used. The formulations can be filled into single-use cartridges (Dimatix Materials Cartridge with a nominal drop weight of 10 pL) and may be printed using a laboratory scale inkjet printing equipment (Dimatix Materials Printer DMP- 2850 or a Pixdro LP50). The temperature of the printhead and the substrate holder can be set to 30°C. Squares of approximately two by two cm are printed with varying resolutions to obtain different film thicknesses. After printing, the substrates are thermally dried and hardbaked.

[0308] 30 All substrates, unless otherwise noted, were cleaned by immersion in 2- propanol and ultrasonication for ten minutes; successively immersion in deionized water and ultrasonication for ten minutes and drying on a hot Foreignfiling text P24-193

[0309] - 26 - plate at 100°C for 10 minutes. Afterwards the substrates were treated in an oxygen plasma oven (450 watt, 5 minutes).

[0310] All chemicals for synthesis described are purchased from Sigma Aldrich

[0311] 5 and used without further purification, unless differently mentioned elsewhere. 98 % anhydrous SnC is used for the experiments described successively.

[0312] As already discussed, the one or more of gratings (120) having the relative refractive index value (HNIL) is < 1 .8 may be realized by using publicly known material and process like discussed in WO 2023 / 0114997 A1 , US 2022 / 260904A2 and US 2020 / 285145 A2 (Myrias Optics), material like described in EP 24157386.4 can also be used for this invention. And the material having the relative refractive index value (ng) > 2.0 at 589.3nm

[0313] 15 light wavelength can be made by using a publicly known materials and / or publicly known methods, like described in EP 23206761.1 , EP 23212576.5.

[0314] As one example, following is performed based on the disclosed of EP 23206761.1 , EP 23212576.5.

[0315] 20 Working example 1 : Preparation of formulation 1

[0316] Formulation 1 : NbCIs (5.7wt%), SnC 2H2O (4.3wt%) nominal solid content dissolved in 90wt% PGME is made.

[0317] Working example 2: Forming a layer as the material (140) of the present invention

[0318] Formulation 1 from working example 1 (W.E.1 ) is spin coated with 2,000 rpm onto an O2 plasma pretreated SisN^Si substrate having 150nm width trenches (recessed grooves made by gratings (120)) on the surface. Then the coated layer is baked at 250°C for 5min. Finally, Sample 1 is obtained.

[0319] 30

[0320] Sample 2 (a layer made from Formulation 2, baking temperature 250°C / 5min) is made in the same manner as described in working example Foreignfiling text P24-193

[0321] - 27 -

[0322] 1 above except for that the baking temperature 250°C / 5min for forming sample 2 is used. The layer thickness and the refractive index value of each samples 1 and 2 are evaluated with using the Ellipsometry.

[0323] Below table 3 shows the results of Rl measurements.

[0324] 5 As mentioned in table 3, higher Rl value (around 2.0 or more) can be obtained by applying lower baking temperature (200°C / 5min, 250°C / 5min). These show good gap fill properties.

[0325] Table 3

[0326] Working example 3: Simulation of domains in an SRG

[0327] A finite element numerical model is used in Comsol Multiphysics to simulate the domain in a Surface Relief Gratings (SRG). The conditions investigated

[0328] 15 are shown below.

[0329] <Model description>

[0330] Model domain includes one period of the grating with periodic boundary conditions on side walls, replicating infinite grating.

[0331] 20

[0332] Modelling method: finite element method in Comsol Multiphysics

[0333] Model parameters (Fig.3)

[0334] • Air n = 1.0

[0335] • Substrate n = 2.0

[0336] • Grating period A= 400nm

[0337] • SRG thickness d = 250nm

[0338] • Gap width g = 200, 150, 100nm

[0339] • Overburden layer thickness h = 30nm

[0340] • Zero residual layer thickness ho = 30nm

[0341] 30 • Wavelength 1 = 532nm

[0342] • Material refractive indices for NIL (gratings) (n_nil): 1.6 - 2.15 Foreignfiling text P24-193

[0343] • Material refractive indices for gap fill (material) (n_gap): 1.6 - 2.25

[0344] • Slant angle: 0, 20, 30 degrees

[0345] For each set of conditions investigated there are multiple curves generated

[0346] 5 which highlight the impact on diffraction efficiency and field of view (FOV) as a function of NIL and gap fill refractive index. The calculation results done for three different gap widths, 200nm, 150nm, 100nm, and three different slant angles, 0°, 20°, 30°are mentioned in the below tables. n_nil = Material refractive indices for NIL (gratings) n_gap = Material refractive indices for gap fill (material)

[0347] Obtained value = multiplication result of the diffraction efficiency and the field of view (FOV)

[0348] Table 1A: Slant angle 0 degrees, Gap width g =100nm

[0349] 30 Foreignfiling text P24-193

[0350] Table 1 B: Slant angle 0 degrees, Gap width g =150nm

[0351] 5

[0352] Table 1 C: Slant angle 0 degrees, Gap width g =200nm

[0353] 30 Foreignfiling text P24-193

[0354] 5

[0355] Table 1 D: Slant angle 20 degrees, Gap width g =1 OOnm

[0356] Table 1 E: Slant angle 20 degrees, Gap width g =150nm Foreignfiling text P24-193

[0357] 5

[0358] Table 1 F: Slant angle 20 degrees, Gap width g =200nm

[0359] Foreignfiling text P24-193

[0360] - 32 -

[0361] 5

[0362] Table 1 G: Slant angle 30 degrees, Gap width g =1 OOnm

[0363] Table 1 H: Slant angle 30 degrees, Gap width g =150nm

[0364] 30 Foreignfiling text P24-193

[0365] 5

[0366] Table 11: Slant angle 30 degrees, Gap width g =200nm

[0367] 30 Foreignfiling text P24-193

[0368] 5

[0369] In the above mentioned tables 1 A to 11, the very left end column line (the vertical axis) of the tables shows the Material refractive indices for NIL (gratings): n_nil.

[0370] And the very top row line (the horizontal axis) of the tables indicates the Material refractive indices for gap fill (material): n_gap.

[0371] 15 And the obtained values of in the tables are multiplication result of the diffraction efficiency and the field of view (FOV).

[0372] As the results, the claimed ranges show the most efficient values. In some graphs the ‘classic’ region of high index NIL with lower index Gap Fill is also

[0373] 20 clear, but this usually requires a refractive index for the NIL material which is impossible in reality (>2.05).

[0374] Thus, it is clear from the results that the claimed ranges of the present invention may realize the improved overall light utilization efficiency (preferably based on improved diffraction efficiency and angular aperture) of an optical device, may be realized.

[0375] 30

Claims

Foreignfiling text P24-193- 35 -Claims1 . An optical device (100) for a display device comprising: i) a substrate (110);5 ii) one or more of gratings (120) placed onto the substrate; and iii) one or more of recessed grooves (130), wherein said one or more of recessed grooves (130) is at least partly filled by a material (140); and wherein the relative refractive index value of said one or more of gratings (HNIL) is < 1 .8 and the relative refractive index value of the material (ng) is > 2.0 at 589.3nm light wavelength, optionally said optical device (100) is an optical waveguide, preferably said optical device (100) is an optical waveguide for a display device, more preferably it is an optical waveguide for AR device or for MR device, optionally said one or more of gratings15 (120) is slanted gratings, blazed gratings, binary gratings, analog surface relief gratings, multilevel structured gratings or a combination of slanted gratings and blazed gratings.

2. The device of claim 1 , wherein the refractive index value of said gratings20 (HNIL) is 1.5 < nNiL< 1.7.

3. The device (100) of claim 1 or 2, wherein the refractive index value of said material (ng) is more than 2.1 at 589.3nm light wavelength, preferably more than 2.15 and it is 2.8 or less, preferably it is in the range 2.0 < ng< 2.8, more preferably 2.1 < ng< 2.5, even more preferably 2.15 < ng< 2.35.

4. The device (100) of any one of claims 1 to 3, contains surface relief gratings (100a) and said ii) one or more of gratings (120) and iii) one or more of recessed grooves (130) forms said surface relief gratings (100a).

305. The device (100) of any one of claims 1 to 4, wherein the gratings (120) has a grating period (120a) in the range from 400nm to 700nm.Foreignfiling text P24-193- 36 -6. The device (100) of any one of claims 1 to 5, wherein the gratings (120) has grating gap width Gw (120G) in the range from 10nm to 500nm. Preferably from 20 to 250nm, more preferably from 30 to 150nm.

57. The device (100) of any one of claims 1 to 6, wherein the grating depth d (120d) is in the range from 50nm to 1 pm, preferably from 100nm to 600nm, more preferably from 200nm to 400nm.

8. The device (100) of any one of claims 1 to 7, wherein at least one of said gratings (120) is a binary grating having the slant angle (120c) 0°, a slanted grating having the slant angle (120c) in the range from +0.1 ° to +45°, a blazed grating having the blaze angle +1 to +60°, preferably the slant angle of said slanted grating is in the range from +1 ° to +35°, more preferably from +1 to +30°, preferably said blaze angle of the blazed grating is in the15 range from +5 to +45°, more preferably from +10 to +40°.

9. The device (100) of any one of claims 1 to 8, wherein said substrate (110) has the refractive index value (nSUb) in the range from 1 .8 to 2.2, preferably it is from 1 .9 to 2.1 .2010. The device (100) of any one of claims 1 to 9, wherein said one or more of gratings (120) is a metal oxide, preferably said metal oxide is selected from, preferably said metal oxide is an optically transparent in visible wavelength, more preferably it is selected from TiO2, Nb2Os, SnO, SnO2, V2O5, Ta20s, ZrO2 or ZnO, even more preferably selected from SnO, SnO2, V2O5, Ta20s, ZrO2 or ZnO.11 . The device (100) of any one of claims 1 to 10, wherein said material (140) is a metal oxide, preferably said metal oxide is an optically transparent in visible wavelength, more preferably it is selected from TiO2,30 Nb2Os, SnO, SnO2, V2O5, Ta20s, ZrO2 or ZnO, even more preferably it is TiO2, Nb2Os, SnO or SnO2.Foreignfiling text P24-193- 37 -12. Process for fabricating the device of any one of claims 1 to 11 , comprising the following steps A) and B)):A) Fabricating one or more of gratings (120) having the refractive index value < 1 .8 with using a metal oxide precursor after curing by solution5 deposition method, preferably by sol-gel method;B) Fabricating one or more of recessed grooves (130) filled by said material (140) having the refractive index value > 2.0 with using a metal oxide precursor by solution deposition method, preferably by sol-gel method.

13. Process of claims 12, wherein said step A) comprises the following steps:A1 ) preparing a substrate;A2) providing a formulation containing the metal oxide precursor by wet deposition process onto a surface of the substrate, preferably by dip15 coating, spin-coating or ink-jetting;A3) applying a thermal treatment to the formulation to convert at least a part of the metal oxide precursor of the formulation to a metal oxide to form an optical layer;A4) forming gratings by pressing a patterned mold onto the optical layer;20 A5) optionally, heating the optical layer;A6) optionally, irradiating the optical layer with the light, preferably said light is UV light; optionally, said step B) comprises the following steps:B1 ) preparing a substrate obtained in step A);B2) providing a formulation containing the metal oxide precursor by wet deposition process onto a surface of the substrate, preferably by dip coating, spin-coating or ink-jetting;B3) applying a thermal treatment to the formulation to convert at least a part of the metal oxide precursor of the formulation to a metal oxide.3014. Process of any one of claims 12 or 13, wherein said metal oxide precursor used in step A) is a metal halide, metal alkoxide or a metalForeignfiling text P24-193- 38 - carboxylate containing a metal element selected from the group consisting of group 1 elements, group 4 elements, group 5 elements, group 6 elements, group 12 elements, group 14 elements and group 15 elements of the periodic table and the metal oxide precursor used in step B) is a metal5 halide, metal alkoxide or a metal carboxylate containing a metal element selected from the group consisting of group 1 elements, group 4 elements, group 5 elements, group 6 elements, group 12 elements, group 14 elements and group 15 elements of the periodic table.

15. A display device (200) comprising at least one functional medium (210) configured to direct and modulate a light or configured to emit light, and the device (100) of any one of claims 1 to 11 .1520

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