Coating composition for forming an optical layer

Abstract

The present invention relates to a composition, preferably being a coating composition for forming an optical layer, comprising one or more of nanoparticles; and a silsesquioxane polymer. The composition of the present invention 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, Mixed Reality (MR) hardware, plasma (PDP) display and an electroluminescent (ELD) display.

Description

Foreignfiling text P24-230-SEC-W001 2025121 1- 1 -CompositionField of the inventionThe present invention relates to a composition, preferably being a coating5 composition for forming an optical layer, comprising one or more of nanoparticles; and a silsesquioxane polymer. Present invention further relates to use of the composition, method for preparing the composition, an optical layer, a use of the optical layer, method for preparing the optical layer, and a display device.Background ArtAugmented reality (AR) devices allow users to experience the world around them through transparent glasses while simultaneously displaying virtual images. These virtual images need to be directed to an area directly in front15 of the viewer's eye, known as the eye-box, which is accomplished using a waveguide. The waveguide efficiently propagates the image to the eye-box when the conditions for total internal reflection (TIR) are met.In the case of TIR, light within the waveguide strikes the boundary and is reflected back into the waveguide rather than exiting it. The greater the20 difference between the refractive index of the waveguide and the surrounding material, the stronger the TIR becomes, maximizing the field of view.For AR devices, the waveguide must be part of an optical stack. This optical stack includes focusing lenses on either side and adhesives to bond them, with refractive indices of approximately 1.6 and 1.5, respectively, which can weaken the TIR. The inventor of this invention realized that to maximize the difference in refractive index between the waveguide and the surrounding materials, a low refractive index coating on the waveguide is30 necessary.Summary of the inventionForeignfiling text P24-230-SEC-W001 2025121 1- 2 -The inventors newly have found that there are still one or more considerable problems for which improvement is desired, as listed below: improving stability of the low refractive index (Rl) value of an optical layer, namely under exposure to heat and / or humidity environments, realizing an5 increased mechanical stability of an optical layer, providing an optical layer having chemical stability, realizing lower Rl value of an optical layer below 1 .40, improving light transmission of an optical device such as a waveguide, reducing reflection at the interfaces of other layers with different refractive indices, improving light transmission of a display device such as AR device, enhancing image contrast, decreasing light scattering, improving visual comfort, reducing visual discomfort, increasing optical alignment between the waveguide and the lenses, aiding in the clarity of the image and enhancing overall optical performance, finding suitable, optimal materials and material combinations, composition realizing one or more of15 the above mentioned improvements.The inventors aimed to solve one or more of the above-mentioned problems.20 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.Namely, it is found a novel composition, preferably being a coating composition for forming an optical layer, more preferably for forming an optical coating layer of an optical waveguide, comprising, essentially consisting of, or consisting of; one or more of nanoparticles; and a silsesquioxane polymer.30 In another aspect, the present invention further relates to use of the composition of a present invention as a coating composition for forming anForeignfiling text P24-230-SEC-W001 2025121 1- 3 - optical layer, preferably for forming an optical coating layer of an optical waveguide.In another aspect, the present invention relates to a method for preparing5 the composition of the present invention, comprising at least following step (A):(A) Mixing one or more of nanoparticles; and silsesquioxane polymer; preferably said nanoparticle is optically transparent in visible wavelength 400 to 800nm and configured to show refractive index value (Rl) 1 .5 or less.In another aspect, the present invention also relates to an optical layer obtained by the method of the present invention, or an optical layer comprising one or more of nanoparticles; and silsesquioxane polymer,15 preferably said nanoparticles have one or more of acrylate ligands and said silsesquioxane polymer and said acrylate ligands are crosslinked or connected.In another aspect, the present invention also relates to an optical device20 comprising one or more of optical layers of the present invention.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.Technical effects of the inventionThe present invention may provide one or more of following effects; improving stability of the low refractive index (Rl) value of an optical layer,30 namely under exposure to heat and / or humidity environments, realizing an increased mechanical stability of an optical layer, providing an optical layer having chemical stability, realizing lower Rl value of an optical layer belowForeignfiling text P24-230-SEC-W001 2025121 1- 4 -1 .40, improving light transmission of an optical device such as a waveguide, reducing reflection at the interfaces of other layers with different refractive indices, improving light transmission of a display device such as AR device, enhancing image contrast, decreasing light scattering,5 improving visual comfort, reducing visual discomfort, increasing optical alignment between the waveguide and the lenses, aiding in the clarity of the image and enhancing overall optical performance, finding suitable, optimal materials and material combinations, composition realizing one or more of the above mentioned improvements.Brief description of the figuresFig.1 Schematic cross-sectional view of an optical layer (waveguide) with the low Rl layer of the present inventionFig.2 Schematic cross-sectional view of one embodiment of the display15 deviceFig.3 Schematic cross-sectional view of another embodiment of the display deviceList of reference signs20 Fig.1100. Optical device (e.g. optical waveguide)110. Surface relief gratings (optional) (e.g. Rl value around 1.8-2.2)120. Substrate (e.g. Rl value >1.8)130. Surface relief gratings (optional) (e.g. Rl value around 1.8-2.2)140. Optical layer (low Rl layer)150. Adhesive layer (e.g. Rl value around 1 .55)140. Optical lends (e.g. Rl value >1.6)Fig. 2 and Fig. 330 200. Display device210. Projector211. Image source such as OLED device, LCD device, micro-LED deviceForeignfiling text P24-230-SEC-W001 2025121 1- 5 -212. Projector optics (Optical lends)220. Waveguide230. Surface relief gratings (corresponding to 100a) as an input coupler 240. Substrate5 245. Optical layer (low Rl layer) of the present invention 250. Surface relief gratings as an output coupler 260. Optical lends (optional) 270. Direct extracted light 280. External light290. Eye291 . Eye-BoxDefinition of the termsAccording to the present invention, the term “refractive index” means15 absolute refractive index at 520nm light wavelength preferably measured by Elipsometry.According to the present invention, the term " transparent" is defined as having at least 70% light transmittance across the entire visible spectrum.20 Ideally, this transmittance should exceed 75%, and preferably surpass 80%, with the most desirable level being over 90%. Consequently, for "transparent nanoparticles," these nanoparticles are defined as having at least 70% light transmittance across the visible spectrum, preferably surpass 80%, with the most desirable level being over 90%. Similarly, for "transparent optical thin films," these films are also defined as having a minimum of 70% light transmittance in the visible range, preferably surpass 80%, with the most desirable level being over 90%. This definition is typically applied to optical thin films with thicknesses ranging from 1 .2 pm to 2.5 pm.30The term “optical device” as used herein, relates to a device containing one or more optical components for forming a light beam including, but notForeignfiling text P24-230-SEC-W001 2025121 1- 6 - limited to, gratings, lenses, prisms, mirrors, optical windows, filters, polarizing optics, UV and IR optics, waveguides, with or without an optical coatings. Preferred optical devices in the context of the present invention are waveguides for augmented reality (AR) device and / or for mixed reality5 (MR) device.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 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 an AR display or a MR display.15 Preferred embodiments of the present invention are described hereinafter and in the dependent claims.Detailed description of the inventionThe present invention relates to a composition, preferably being a coating20 composition for forming an optical layer, more preferably for forming an optical coating layer of an optical waveguide, comprising one or more of nanoparticles; and a silsesquioxane polymer. Said composition may optionally contain an additive such as surfactant, additional ligand material, polymerization initiator but preferably said composition does not contain any additives.NanoparticleIn a preferred embodiment of the present invention, said nanoparticle is optically transparent in visible wavelength 400 to 800nm and configured to30 show refractive index value (Rl) 1 .5 or less, more preferably the Rl is in the range from 1 .2 to 1 .5 at 520nm light wavelength. According to the present invention, said “refractive index value” is an absolute refractive index value.Foreignfiling text P24-230-SEC-W001 2025121 1- 7 -Said (absolute) Rl value may be measured, for examples, by Ellipsometer M2000 from J. A. Woolam.- Preparation of measurement samples5 1. Preparation of the Substrate: Clean a 2-inch silicon / quarts substrate and treat it with plasma using the following method:• Expose to an oxygen plasma chamber for 10 minutes at 200W.Optionally, before the oxygen plasma exposure, following cleaning process can be applied.• Immerse in 2-propanol for 10 minutes in an ultrasonic bath.• Rinse with de-ionized water.• Dry the sample completely on a hot plate at 100°C for 10 minutes.2. Spin Coating: Place the substrate in a spin coater and hold it using a15 vacuum chuck. Typical spin coating conditions use 0.5ml of the composition of the nanoparticles and the solvent of the present invention without silsesquioxane and at spin speed of 1 ,000rpm for 30 seconds and acceleration 1 ,500rpm / s to obtain 100nm layer thickness of a layer after soft baking.203. Soft Baking: After spin coating, soft bake the sample at 80°C on a hot plate for 3 minutes to evaporate the solvent.In more preferred embodiment of the present invention, preferably said nanoparticle is selected from one or more members of the group consisting of hollow metal oxide nanoparticles selected from hollow TiO2 nanoparticles, hollow ZnO nanoparticles; organic polymer nanoparticle selected from polymethyl methacrylate (PMMA) nanoparticles, hollow polymethyl methacrylate (PMMA) nanoparticles, hollow PS nanoparticles, hollow polycarbonate nanoparticles or any combination of polymethyl30 methacrylate (PMMA) nanoparticles, hollow polymethyl methacrylate (PMMA) nanoparticles, hollow polystyrene (PS) nanoparticles, hollowForeignfiling text P24-230-SEC-W001 2025121 1- 8 - polycarbonate nanoparticles; hollow silica nanoparticles; silica nanoparticles; organo-silica nanoparticles and hollow organo-silica nanoparticles. Preferably said organo-silica nanoparticle has an organic group selected from one or more members of the group consisting of5 methyl group, phenyl group, amino group, epoxy group, and an acrylic group.It is considered that by creating a hollow structure, it is possible to achieve lightweight properties and a low refractive index, while also enhancing transparency.Furthermore preferably, said nanoparticle is selected from a hollow silica nanoparticle; silica nanoparticle; organo-silica nanoparticle; hollow organo- silica nanoparticle or an any combination of hollow silica nanoparticle; silica15 nanoparticle, organo-silica nanoparticle and hollow organo-silica nanoparticle, from the viewpoint of higher thermal resistivity, better chemical compatibility with silsesquioxane, which can enhance the overall stability and performance, lower absolute Rl value, higher chemical resistivity including oxygen, moisture resistivities.20The most preferably said nanoparticle is hollow silica nanoparticle from the viewpoint of providing one or more of technical effects of the present invention.In a preferred embodiment, said nanoparticle without any ligand (without acrylate ligand mentioned below) has the average diameter in the range from 5nm to 100nm, preferably from 10 nm to 70nm, more preferably from 30nm to 50nm.30 It is believed that said average diameter may provide one or more of the following technical advantages: minimizing light scattering in the visible light spectrum, enhancing optical transparency; uniform dispersion within theForeignfiling text P24-230-SEC-W001 2025121 1- 9 - silsesquioxane polymer, ensuring consistent performance across the optical layer; enhanced low Rl properties, specifically hollow type may further incorporate air and further lowering the Rl and improving the functionality of the resulting optical layer; higher surface area, increasing interactions with5 the polymer, which can improve both mechanical and optical properties; increased durability of the resulting optical layer.Acrylate ligands of the nanoparticleAccording to the present invention, in a preferred embodiment, said nanoparticle has one or more of acrylate ligands, preferably said acrylate ligand is selected from one or more members of the group consisting of dipentaerythritol hexa-acrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexa-acrylate, tripentaerythritol triacrylate, diethylene glycol diacrylate, polyethylene glycol diacrylate, vinyl ester of acrylic acid,15 trimethylolpropane triacrylate, acrylic acid esters, methyl Acrylate, preferably said acrylate ligand is dipentaerythritol hexa-acrylate, dipentaerythritol pentaacrylate or a combination of dipentaerythritol hexaacrylate and dipentaerythritol pentaacrylate.20 It is believed that the said acrylate ligands of the nanoparticle may bond with the silsesquioxane polymer under UV irradiation, generating a network structure and / or a bonding state that incorporates nanoparticles within the silsesquioxane polymer.Moreover, from the perspective of the low Rl value after the reaction, ease of handling, and the technical effects of the invention, the aforementioned acrylate ligands, particularly dipentaerythritol hexa-acrylate, dipentaerythritol pentaacrylate, or a combination of dipentaerythritol hexaacrylate and dipentaerythritol pentaacrylate, are considered preferable.30Such acrylate ligands can be introduced to nanoparticles using publicly known materials and methods.Foreignfiling text P24-230-SEC-W001 2025121 1- 10 -Silsesquioxane polymerAccording to the present invention, the composition contains said silsesquioxane polymer. Any publicly known silsesquioxane polymer may5 be used.It is believed that silsesquioxane polymer may provide one or more of significant advantages over conventional siloxane polymer when used as a main component of the composition for forming a low Rl optical layer.These advantages include a lower refractive index, which enhances optical transparency and increases light transmission. Additionally, silsesquioxane polymer demonstrates excellent thermal stability and chemical resistance, making it highly durable under various conditions. Its superior mechanical properties contribute to greater resistance to physical stress. Furthermore,15 silsesquioxane polymer allows for adjustable surface properties, enabling customization for specific applications. When combined with nanoparticles, it can create nanocomposites that provide further functionality and performance enhancements. Lastly, silsesquioxane polymer exhibits improved processability, facilitating the formation of thin films and coatings20 in various manufacturing processes.In a preferred embodiment of the present invention, said silsesquioxane polymer is a silsesquioxane polymer containing at least one cyclic silsesquioxane network and / or one cylindrical silsesquioxane network.It is believed that this unique structure allows for the incorporation of air within the polymer matrix, resulting in a lower refractive index (Rl). The presence of air pockets within the silsesquioxane networks contributes to the overall reduction in Rl, enhancing the optical properties of the material30 and making it suitable for applications requiring low Rl optical layers.Foreignfiling text P24-230-SEC-W001 2025121 1- 11 -In more preferred embodiment, said silsesquioxane polymer contains at least one cage (POSS) structure, preferably at least one following structure A or structure B.Here, one or more CH3 groups or one or more H atoms of CH3 connected to the Si atom may be replaced with a direct bond that joins with other Silsesquioxane polymer portions, and / or they may be substituted with the substitutes described in paragraphs

[0129] -

[0157] and working examples 4- 14 of US2024 / 0318001 A1.According to the present invention, in a preferred embodiment, said silsesquioxane has Mw in the range from 1 ,000 to 1 ,000,000 g / mol.30Foreignfiling text P24-230-SEC-W001 2025121 1- 12 -Such silsesquioxane containing at least one cyclic silsesquioxane network and / or one cylindrical silsesquioxane network, can be obtained based on US2024 / 0318001 A1 (Optitune). As stated above, preferred silsesquioxane polymer contains at least one cage (POSS) structure. More preferably said5 cage structure is selected from the above mentioned structure A or structure B; such silsesquioxane polymer may be obtained based on US2024 / 0318001 A1 (Optitune). For examples, silsesquioxane of paragraphs

[0129] -

[0157] , working examples 4-14 of US2024 / 0318001 A1 may preferably be used.Alternatively, Silsesquioxane polymer with a cage (POSS) structure obtainable by reacting publicly known Silsesquioxane polymers with publicly known reactive ligands substituted POSS (such as (meth)acryl type ligand substituted POSS, epoxy type ligand substituted POSS, combination15 of (meth)acryl type ligand and epoxy type ligand substituted POSS etc.) using established methods, may also be used. However, from the perspective of achieving better technical effects of the invention, it is even more preferable for the Silsesquioxane polymer disclosed in US2024 / 0318001 A1 to be used.20In a preferred embodiment of the present invention, the mixing ratio of the silsesquioxane polymer to the nanoparticle is in the range from 0.01 to 0.9, preferably from 0.02 to 0.5, more preferably from 0.03 to 0.3 from the viewpoint of realizing one or more of the technical effects of the present invention more effectively.SolventIn a preferred embodiment of the present invention, the composition may further contains a solvent, preferably it is a miscible solvent in water, more30 preferably said solvent is selected from one or more member of the group consisting of ethylene glycol monoalkyl ethers, diethylene glycol dialkyl ethers, propylene glycol monoalkyl ethers, propylene glycol alkyl etherForeignfiling text P24-230-SEC-W001 2025121 1- 13 - acetates, alcohols and esters; preferably said ethylene glycol monoalkyl ether is ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, or any combination of these, diethylene glycol dialkyl ether is diethylene glycol5 dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dipropyl ether, diethylene glycol dibutyl ether, or any combination of these, propylene glycol monoalkyl ether is propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, or a combination of any of these, propylene glycol alkyl ether acetate is propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, or a combination of any of these, alcohol is ethanol, propanol, 1 ,3-dimethoxy-propanol, butanol, glycerin, propylene glycol or a combination of any of these, and ester is ethyl 3-15 ethoxypropionate, methyl 3-methoxypropionate or a combination of ethyl 3- ethoxypropionate and methyl 3-methoxypropionate.It is believed that using a hydrophilic solvent (excluding water) with silsesquioxane polymer and nanoparticles, preferably silica type20 nanoparticles offers several advantages as described below: Improved Dispersion: Hydrophilic solvents can enhance the dispersion of nanoparticles within the silsesquioxane polymer matrix, leading to a more uniform distribution and better performance of the composite material. Enhanced Compatibility: The use of a hydrophilic solvent can improve the compatibility between the silsesquioxane polymer and the nanoparticles, facilitating better interfacial interactions and enhancing the overall properties of the composite.Lower Viscosity: Hydrophilic solvents often lower the viscosity of the mixture, making it easier to process and apply, especially in coating or film¬30 forming applications.Facilitated Processing: The use of a hydrophilic solvent can simplify the processing conditions, allowing for easier handling and application of theForeignfiling text P24-230-SEC-W001 2025121 1- 14 - silsesquioxane polymer and nanoparticle mixture.Enhanced Functionalization: Hydrophilic solvents can promote the functionalization of nanoparticles, allowing for better surface modification that can enhance the properties of the composite material.5 Reduced Agglomeration: Using a hydrophilic solvent can help reduce the agglomeration of silica nanoparticles, maintaining their individual properties and preventing the formation of larger clusters that could negatively impact the material's performance.Improved Adhesion: The presence of a hydrophilic solvent can enhance the adhesion of the silsesquioxane polymer to various substrates, improving the overall durability and performance of the coatings or films produced.Especially, when using a hydrophilic solvent with nanoparticles, preferably silica type nanoparticles, that have the same hydrophilic acrylate-type15 ligands, it is believed that the benefits are further enhanced in the following ways:Enhanced Compatibility: The matching hydrophilic nature of the solvent and the acrylate-type ligands improves compatibility, leading to better interactions between the nanoparticles and the silsesquioxane polymer.20 Optimal Dispersion: The similar hydrophilic characteristics facilitate an even better dispersion of the nanoparticles, ensuring a more homogeneous mixture and improving the overall properties of the composite.Stronger Interfacial Bonding: The use of a hydrophilic solvent can enhance the interfacial bonding between the silsesquioxane polymer and the nanoparticles, leading to improved mechanical strength and stability of the composite material.Improved Surface Functionalization: The hydrophilic solvent can aid in better functionalization of the acrylate-type ligands on the nanoparticles, which can enhance their reactivity and compatibility with the polymer30 matrix.Reduced Agglomeration: The synergy between the hydrophilic solvent and the acrylate-type ligands helps to further minimize nanoparticleForeignfiling text P24-230-SEC-W001 2025121 1- 15 - agglomeration, maintaining their individual properties and ensuring consistent performance.Facilitated Polymerization: The presence of a hydrophilic solvent may assist in the polymerization process when the acrylate-type ligands are involved,5 improving the efficiency of the curing process and enhancing the final properties of the optical layer.Improved Adhesion and Coating Performance: The combination of a hydrophilic solvent and hydrophilic acrylate ligands can enhance the adhesion of the resulting composite to various substrates, leading to better coating performance and durability.Use of the compositionIn another aspect, the present invention may further relates to use of the composition of the present invention as a coating composition for forming15 an optical layer, preferably for forming an optical coating layer of an optical waveguide.Method for preparing the compositionIn another aspect, the present invention may further relates to a method for20 preparing the composition of the present invention, comprising at least, mainly consisting of or consisting of, following step (A):(A) Mixing one or more of nanoparticles; and silsesquioxane polymer; optionally with a solvent.Preferably said nanoparticle is optically transparent in visible wavelength 400 to 800nm and configured to show refractive index value (Rl) 1 .5 or less, preferably in the range from 1 .2 to 1 .5 at 520nm light wavelength.Preferably said nanoparticle is selected from one or more members of the30 group consisting of hollow metal oxide nanoparticles selected from hollow TiO2 nanoparticles, hollow ZnO nanoparticles; organic polymer nanoparticle selected from polymethyl methacrylate (PMMA) nanoparticles,Foreignfiling text P24-230-SEC-W001 2025121 1- 16 - hollow polymethyl methacrylate (PMMA) nanoparticles, hollow PS nanoparticles, hollow polycarbonate nanoparticles or any combination of polymethyl methacrylate (PMMA) nanoparticles, hollow polymethyl methacrylate (PMMA) nanoparticles, hollow polystyrene (PS) nanoparticles,5 hollow polycarbonate nanoparticles; hollow silica nanoparticles; silica nanoparticles; organo-silica nanoparticles and hollow organo-silica nanoparticles.In a preferred embodiment, said step (A) is carried out in the presence of the solvent.More details of said silsesquioxane polymer, said nanoparticles and the solvent are described in the above sections “Silsesquioxane polymer”, “Nanoparticle” (also “Acrylate ligands of the nanoparticle” when said15 nanoparticle has one or more of the ligands), and “Solvent”.Method for fabricating an optical layerIn another aspect, the present invention further relates to a method for fabricating an optical layer comprising nanoparticles; and silsesquioxane20 polymer, preferably for fabricating an optical coating layer of an optical waveguide; comprising the following steps (a) to (c), preferably the steps(a) to (c) are executed in this order or steps (a), (c), (b) are executed in this order:(a) providing the composition of the present invention onto a surface of a substrate or onto an optical waveguide, preferably by wet deposition process, more preferably by spin-coating or ink-jetting; and(b) irradiating the composition with UV light, preferably at wavelength around 365nm to form an optical layer; and(c) optionally applying a thermal treatment to remove any organic solvent30 in case the composition contains an organic solvent.Foreignfiling text P24-230-SEC-W001 2025121 1- 17 -In a preferred embodiment, step (c) is carried out and the steps (a) to (c) are executed in this order or steps (a), (c), (b) are executed in this order. More preferably step (c) is carried out and the steps (a),(c), (b) are executed in this order.5In a preferred embodiment, said UV irradiation step (b) is carried out for the time in the range from 5 second to 30min, preferably from 1 min to 10min, more preferably from 2 min to 8m in.In a preferred embodiment, in step (c), the thermal treatment is applied at the temperature in the range from 50 to 150 °C, preferably from 60 to 120°C, more preferably from 70 to 90°C.Optical layer15 In another aspect, the present invention also relates to an optical layer obtained by the method of the present invention, or an optical layer comprising one or more of nanoparticles; and silsesquioxane polymer. Preferably, said nanoparticles have one or more of acrylate ligands and said silsesquioxane polymer and said acrylate ligands are crosslinked or20 connected. Preferably said acrylate ligand is selected from one or more members of the group consisting of dipentaerythritol hexa-acrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexa-acrylate, tripentaerythritol triacrylate, diethylene glycol diacrylate, polyethylene glycol diacrylate, vinyl ester of acrylic acid, trimethylolpropane triacrylate, acrylic acid esters, methyl Acrylate, preferably said acrylate ligand is dipentaerythritol hexa-acrylate, dipentaerythritol pentaacrylate or a combination of dipentaerythritol hexa-acrylate and dipentaerythritol pentaacrylate.30 More details of said “silsesquioxane polymer”, said “nanoparticles”, and said “acrylate ligands” are defined in the above sections of “Silsesquioxane polymer”, “Nanoparticle” and “Acrylate ligands of the nanoparticle”.Foreignfiling text P24-230-SEC-W001 2025121 1- 18 -In a preferred embodiment, the optical layer of the present invention has the layer thickness of the optical layer is in the range from 0.5 urn to 10 urn, preferably from 0.8um to 5um, more preferably from 1 .Oum to 3um.5 Said layer thickness can be calculated by determining the average layer thickness based on ten measurements.In another preferred embodiment of the present invention, the optical layer has the absolute refractive index value 1 .4 or less. Preferably it is in the range from 1 .1 to 1 .4. more preferably in the range from 1 .20 to 1 .38 at 520nm light wavelength.Said relative refractive index value can be measured by the following Ellipsometry method.15- Preparation of measurement samples1. Preparation of the Substrate: Clean a 2-inch silicon / quarts substrate and treat it with plasma using the following method:• Expose to an oxygen plasma chamber for 10 minutes at 200W.20 Optionally, before the oxygen plasma exposure, following cleaning process can be applied.• Immerse in 2-propanol for 10 minutes in an ultrasonic bath.• Rinse with de-ionized water.• Dry the sample completely on a hot plate at 100°C for 10 minutes.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 the composition of the present invention and at spin speed of 1 ,000rpm for 30 seconds with acceleration of 1500 rpm / s to obtain 100nm layer thickness of the cured30 layer after the Soft Baking.Foreignfiling text P24-230-SEC-W001 2025121 1- 19 -3. Soft Baking: After spin coating, soft bake the sample at 80°C on a hot plate for 3 minutes.4. UV curing: UV curing the sample at 365nm for 5 min.5 Measurement:Measurement equipment: Ellipsometer M2000 from J. A. WoolamTurn 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).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 at 520nm light wavelength is taken.15 Use of the optical layerIn another aspect, present invention may further relates to use of the optical layer of the present invention in an optical device or for fabricating an optical device. More preferably as a low refractive index layer.Namely, it is preferable to use the optical layer of the present invention as a20 low refractive index layer (Rl value described above) placed in between the waveguide and an optical lends.Method of fabricating an optical deviceIn another aspect, the present invention further relates to a method for fabricating an optical device, comprising the step (A1 ) (A1 ) providing the optical layer onto an optical waveguide.Optical deviceIt is preferred that the optical device is a device containing one or more30 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 opticalForeignfiling text P24-230-SEC-W001 2025121 1- 20 - 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. More preferably it is waveguide for augmented reality (AR) device and / or for mixed reality (MR) device.5In a preferred embodiment, said optical device comprises one or more of optical layers of the present invention. Preferably said optical device is an optical waveguide as defined above. Furthermore preferably, an optical waveguide and said optical layer is placed onto the outermost surface of the waveguide.Thus, in more preferred embodiment, said optical device is an optical waveguide comprising an optical waveguide, one more or the optical layers of the present invention and an optical lends, and at least said one of the15 optical layer is placed between the outermost surface of the waveguide and the optical lends.In a preferred embodiment, said optical device, e.g. optical waveguide, may further contain one or more of surface relief gratings on the surface to20 efficiently capture and emit light or light images. Any publicly known surface relief gratings like described in Ding et al. eLight (2023) 3:24, https: / / doi.Org / 10.1186 / s43593-023-00057-z, WO 2023 / 141309 A1 can be used.Fig. 1 illustrates schematic cross-sectional view of waveguide with an optical layer (e.g. low Rl layer). The optical layer may be formed only in the areas where the adhesive layer or lenses are arranged, or it may be formed on the entire surface of the optical device's light extraction side. It may also be formed on both sides of the optical device or on the entire surface for30 processing purposes. From the perspective of material usage efficiency, manufacturing efficiency, and / or efficiently achieving the effects of the present invention, the optical layer can be formed only in the areas whereForeignfiling text P24-230-SEC-W001 2025121 1- 21 - the adhesive layer or lenses are arranged, or it can be formed on the entire surface of the optical device's light extraction side.Use of the optical device5 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.Method for fabricating a display deviceIn another aspect, present invention may further relates to method for fabricating a display device including step of providing the optical device into a display device.Display device15 Finally, in another aspect, the present invention may relate to a display device comprising at least one functional medium configured to direct and modulate a light or configured to emit light; and an optical device of the present invention.20 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), 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 device or MR hardware device.Thus, the term “functional medium” of the optical device of the present30 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).Foreignfiling text P24-230-SEC-W001 2025121 1- 22 -Preferably, said optical device is a waveguide, preferably as an input coupler or 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).5Preferably, said display device has a 1stoptical lends as an input coupler, a 2ndoptical lends 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, QLED, PDP, ELD layer)Figs. 2 and 3 illustrate schematic cross-sectional view of some embodiments of the display devices.In Figs. 2 and 3, an adhesive layer placed in between the optical layer of the present invention and said optical lends is present but not disclosed.15The 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 the20 invention as defined in the appended claims.Examples- Analytics and measurement methods Spectrophotometer Carry 7000 is used to determine absorption.The layer thickness (nm), (absolute) refractive index (n) (Rl) of the optical layer and / or the nanoparticle are measured 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 transparent30 behavior above a wavelength at 520nm and applying B-spline fitting for obtaining refractive indices (n) as well as absorption indices (k).Foreignfiling text P24-230-SEC-W001 2025121 1- 23 -Usually, quartz and / or silicon wafers, both 2 inch in diameter, are used throughout all coating experiments where flat and non-structured carriers for metal oxides are required (e. g. spectroscopic and ellipsometry measurements).5SEM images are recorded using either a Mira 3 LMU from Tescan or Sigma 300VP from Carl Zeiss or Supra 35 from Carl Zeiss.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 1 ,000 rpm where the acceleration to reach the final spin speed is set to 1500 rpm / s2. After spin coating, the coated substrates are subjected to thermal cure on a15 conventional lab hotplate. Usually, however not limited hereto, the coated layers are baked at 80 °C to 100 °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 examples20 unless other conditions are explicitly mentioned elsewhere.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.30All substrates, unless otherwise noted, were pre-treated in an oxygen plasma oven (200 watt, 10 minutes).Foreignfiling text P24-230-SEC-W001 2025121 1- 24 -Working example 1: Preparation of composition 1Composition 1 : Silsesquioxane polymer (from Optitune) in PGME and isopropanol, hollow silica nanoparticles (around 50nm average diameter)5 with dipentaerythritol pentaacrylate and dipentaerythritol hexa-acrylate ligands in PGME (Kriya) are mixed to archive the mix ratio of Silsesquioxane polymer (wt%) to hollow silica nanoparticles (wt%) of 0.04.Instead of or in addition to the silsesquioxane polymer used in working example 1 , other silsesquioxane polymer as defined in the section of “Silsesquioxane polymer” can be used preferably. Especially, one or more of the silsesquioxane polymers as described in US2024 / 0318001 A1 (Optitune) may be used. For examples, silsesquioxane of paragraphs

[0129] -

[0157] , working examples 4-14 of US2024 / 0318001 A1 may15 preferably be used. From the perspective of environmental friendliness, it is preferable to use Silsesquioxane polymers that do not incorporate fluorine, especially among those that do not contain fluorine.Working example 2 to 4: Preparation of compositions 2 to 420 Compositions 2 to 4 are prepared in the same manner as described in working example 1 above except for that the Silsesquioxane polymer (hereafter PSX) and the hollow silica nanoparticles (hereafter NP) are mixed with the mix ratio as described in table 1 .Table 1 :30Foreignfiling text P24-230-SEC-W001 2025121 1- 25 -Reference examples 1 to 2: Preparation of reference compositions 1 and 2Reference compositions 1 and 2 are prepared in the same manner as described in working example 1 above except for that the Silsesquioxane5 polymer (hereafter PSX) and the hollow silica nanoparticles (hereafter NP) are mixed with the mix ratio as described in table 1 .Namely, said reference composition 1 contains only NP and PGME solvent and reference composition 2 contains only PSX and PGME / isopropanol solvent.Working example 5: Forming an optical layer0.5 ml of composition 1 from working example 1 (W.E.1 ) is spin coated onto a plasma treated 2” silicon and quartz wafer at 1 ,000 rpm for 30 sec. Then it is soft baked for 3 min at 80C, followed by UV curing at 365nm for 5 min.15 Finally, Sample 1 is obtained.Working examples 6 to 8: Forming layersSamples 2 to 4 are made in the same manner as described in working example 5 above except for that the compositions 2 to 4 from working20 examples 2 to 4 are used instead of the composition 1 . Samples 2 to 4 are obtained.Reference examples 1 and 2: Forming layersReference Samples 1 and 2 are made in the same manner as described in working example 5 above except for that the reference compositions 1 and 2 from reference examples 1 and 2 are used instead of the composition 1.Reference Samples 1 and 2 are obtained.Working example 9: measurements and reliability testing (REL)30 The layer thickness and the initial (absolute) refractive index value of each samples are evaluated with using the Ellipsometry.Foreignfiling text P24-230-SEC-W001 2025121 1- 26 -Each sample films over quartz are measured by Carry 7000 to determine absorption.Then the obtained samples are subjected to reliability testing (REL) in5 which they are stored under conditions of 65 C, 90% humidity for extended periods.The results (Table 2) show that the samples 1 to 4 containing PSX and the NP resulted in films with Rl of <1 .37 on average, which are stable for 560 hours at 65C, 90% humidity. The reference sample 2, pure PSX film, on the other hand, does not have stable Rl over the REL test.Table 2:Further, addition of the PSX resin to the NP formulation (samples 1 to 4) resulted in transparent films with %Abs / 100nm of thickness <1.5%, and mostly under 1 %, stable for 560 hours at 65C, 90% humidity.Table 3 shows the measurement results of %Abs / 100nm thickness REL test.Table 3:30Foreignfiling text P24-230-SEC-W001 2025121 1- 27 -In the context of optical film reliability testing, "%Abs / 100nm thickness" refers to the percentage of light absorption per 100 nanometers of film thickness. This metric is used to quantify how much light is absorbed by the5 film relative to its thickness, allowing for the assessment of the film's optical properties.The average film thicknesses of samples 1 to 4 are ranged from around 1 .3 urn to around 1 ,8um, and are stable for 560 hours at 65C, 90% humidity. Table 4 show the results.Table 4:Finally, cross hatch testing is performed on comparative example 1 and samples 1 to 4 (examples 1 to 4) after the REL test using Cross-Cut Kit 6, 6-edges 1 mm. In this test, the fill is crossed with blades, and then adhesive tape is applied and stripped. It is seen that pure NP films (PSX:NP 0) delaminated from the substrate; after a sufficient quantity of PSX is included in blended formulations (PSX:NP 0.12 and up, samples 1 to 4), the films no longer delaminated during the cross hatch test and classified as ISO class 0 / ASTM Class 5B.This shows that the resin has significantly increased the mechanical stability of the film, enabling this formulation to be a low Rl waveguide30 coating.

Claims

Foreignfiling text P24-230-SEC-W001 2025121 1- 28 -Claims1. Composition, preferably being a coating composition for forming an optical layer, more preferably for forming an optical coating layer of an5 optical waveguide, comprising one or more nanoparticles; and a silsesquioxane polymer; preferably said nanoparticle is optically transparent in visible wavelength 400 to 800nm and configured to show refractive index value (Rl) 1 .5 or less, preferably in the range from 1 .2 to 1 .5 at 520nm light wavelength, preferably said nanoparticle is selected from one or more members of the group consisting of hollow metal oxide nanoparticles selected from hollow TiO2 nanoparticles, hollow ZnO nanoparticles; organic polymer nanoparticle selected from polymethyl methacrylate (PMMA) nanoparticles, hollow polymethyl methacrylate (PMMA) nanoparticles, hollow PS15 nanoparticles, hollow polycarbonate nanoparticles or any combination of polymethyl methacrylate (PMMA) nanoparticles, hollow polymethyl methacrylate (PMMA) nanoparticles, hollow polystyrene (PS) nanoparticles, hollow polycarbonate nanoparticles; hollow silica nanoparticles; silica nanoparticles; organo-silica nanoparticles and hollow organo-silica20 nanoparticles, preferably said organo-silica nanoparticle has an organic group selected from one or more members of the group consisting of methyl group, phenyl group, amino group, epoxy group, and an acrylic group.

2. The composition of claim 1 , wherein said silsesquioxane polymer is a silsesquioxane polymer containing at least one cyclic silsesquioxane network and / or one cylindrical silsesquioxane network.

3. The composition of claim 1 or 2, wherein said silsesquioxane polymer30 contains at least one cage (POSS) structure, preferably said cage structure is selected from following structure A or structure B.Foreignfiling text P24-230-SEC-W001 2025121 1wherein optionally, said silsesquioxane has Mw in the range from 1 ,000 to 1 ,000,000 g / mol.

4. The composition of any one of claims 1 to 3, wherein said nanoparticle is selected from a hollow silica nanoparticle; silica nanoparticle; organo-silica nanoparticle; hollow organo-silica nanoparticle or an any combination of hollow silica nanoparticle; silica nanoparticle, organo-silica nanoparticle and hollow organo-silica nanoparticle, preferably said nanoparticle is hollow silica nanoparticle.

5. The composition of any one of claims 1 to 4, wherein said nanoparticle30 has one or more of acrylate ligands, preferably said acrylate ligand is selected from one or more members of the group consisting ofForeignfiling text P24-230-SEC-W001 2025121 1- 30 - dipentaerythritol hexa-acrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexa-acrylate, tripentaerythritol triacrylate, diethylene glycol diacrylate, polyethylene glycol diacrylate, vinyl ester of acrylic acid, trimethylolpropane triacrylate, acrylic acid esters, methyl Acrylate,5 preferably said acrylate ligand is dipentaerythritol hexa-acrylate, dipentaerythritol pentaacrylate or a combination of dipentaerythritol hexaacrylate and dipentaerythritol pentaacrylate, wherein optionally, said nanoparticle without said ligand has the average diameter in the range from 5nm to 100nm, preferably from 10 nm to 70nm, more preferably from 30nm to 50nm.

6. The composition of any one of claims 1 to 5, further contains a solvent, preferably it is a miscible solvent in water, more preferably said solvent is selected from one or more member of the group consisting of ethylene15 glycol monoalkyl ethers, diethylene glycol dialkyl ethers, propylene glycol monoalkyl ethers, propylene glycol alkyl ether acetates, alcohols and esters; preferably said ethylene glycol monoalkyl ether is ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, or any combination of20 these, diethylene glycol dialkyl ether is diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dipropyl ether, diethylene glycol dibutyl ether, or any combination of these, propylene glycol monoalkyl ether is propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, or a combination of any of these, propylene glycol alkyl ether acetate is propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, or a combination of any of these, alcohol is ethanol, propanol, 1 ,3- dimethoxy-propanol, butanol, glycerin, propylene glycol or a combination of30 any of these, and ester is ethyl 3-ethoxypropionate, methyl 3- methoxypropionate or a combination of ethyl 3-ethoxypropionate and methyl 3-methoxypropionate.Foreignfiling text P24-230-SEC-W001 2025121 1- 31 -7. The composition of any one of claims 1 to 6, wherein the mixing ratio of the silsesquioxane polymer to the nanoparticle is in the range from 0.01 to 0.9, preferably from 0.02 to 0.5, more preferably from 0.03 to 0.3.

58. Method for preparing the composition of any one of claims 1 to 7, comprising at least following step (A):(A) Mixing one or more of nanoparticles; and silsesquioxane polymer; preferably said nanoparticle is optically transparent in visible wavelength 400 to 800nm and configured to show refractive index value (Rl) 1 .5 or less, preferably in the range from 1 .2 to 1 .5 at 520nm light wavelength, preferably said nanoparticle is selected from one or more members of the group consisting of hollow metal oxide nanoparticles selected from hollow TiO2 nanoparticles, hollow ZnO nanoparticles; organic polymer nanoparticle selected from polymethyl methacrylate (PMMA) nanoparticles,15 hollow polymethyl methacrylate (PMMA) nanoparticles, hollow PS nanoparticles, hollow polycarbonate nanoparticles or any combination of polymethyl methacrylate (PMMA) nanoparticles, hollow polymethyl methacrylate (PMMA) nanoparticles, hollow polystyrene (PS) nanoparticles, hollow polycarbonate nanoparticles; hollow silica nanoparticles; silica20 nanoparticles; organo-silica nanoparticles and hollow organo-silica nanoparticle, wherein optionally said step (A) is carried out in the presence of the solvent.

9. Method for fabricating an optical layer comprising nanoparticles; and silsesquioxane polymer, preferably for fabricating an optical coating layer of an optical waveguide; comprising the following steps (a) to (c), preferably the steps (a) to (c) are executed in this order or steps (a), (c), (b) are executed in this order:(a) providing the composition of any one of claims 1 to 7 onto a surface30 of a substrate or onto an optical waveguide, preferably by wet deposition process, more preferably by spin-coating or ink-jetting; andForeignfiling text P24-230-SEC-W001 2025121 1- 32 -(b) irradiating the composition with UV light, preferably at wavelength around 365nm to form an optical layer; and(c) optionally applying a thermal treatment to remove any organic solvent in case the composition contains an organic solvent,5 wherein optionally said UV irradiation step (b) is carried out for the time in the range from 5 second to 30min, preferably from 1 min to 10min, more preferably from 2 min to 8m in. wherein optionally, in step (c), the thermal treatment is applied at the temperature in the range from 50 to 150 °C, preferably from 60 to 120°C, more preferably from 70 to 90°C.

10. An optical layer obtained by the method of claim 9.11 . An optical layer comprising one or more of nanoparticles; and15 silsesquioxane polymer, preferably said nanoparticles have one or more of acrylate ligands and said silsesquioxane polymer and said acrylate ligands are crosslinked or connected, preferably said acrylate ligand is selected from one or more members of the group consisting of dipentaerythritol hexa-acrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexa¬20 acrylate, tripentaerythritol triacrylate, diethylene glycol diacrylate, polyethylene glycol diacrylate, vinyl ester of acrylic acid, trimethylolpropane triacrylate, acrylic acid esters, methyl Acrylate, preferably said acrylate ligand is dipentaerythritol hexa-acrylate, dipentaerythritol pentaacrylate or a combination of dipentaerythritol hexa-acrylate and dipentaerythritol pentaacrylate, wherein optionally, the layer thickness of the optical layer is in the range from 0.5 urn to 10 urn, preferably from 0.8um to 5um, more preferably from 1 .Oum to 3um.30 12. The optical layer of claim 10 or 11 , wherein the optical layer has the absolute refractive index value 1 .4 or less, preferably it is in the range fromForeignfiling text P24-230-SEC-W001 2025121 1- 33 -1 .1 to 1 .

4. more preferably in the range from 1 .20 to 1 .38 at 520nm light wavelength.

13. An optical device comprising one or more of optical layers of any one of5 claims 10 to 12, preferably said optical device is an optical waveguide, more preferably it is an optical waveguide and said optical layer is placed onto the outermost surface of the waveguide.

14. The optical device of claim 13 is an optical waveguide comprising an optical waveguide, the optical layer of any one of claims 10 to 12 and an optical lends, and at least said one of the optical layer is placed between the outermost surface of the waveguide and the optical lends.

15. A display device comprising at least one functional medium configured15 to direct and modulate a light or configured to emit light; and the optical device of claim 13 or 14.2030

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