Method of manufacturing continuously variable optical filter by inkjet printing

Abstract

The invention relates to a method for producing a continuously variable optical filter by inkjet printing, to an optical element obtainable by such a method and to the use of such an optical element.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for manufacturing a continuously variable optical filter by inkjet printing, comprising the steps of providing a substrate and applying and curing a first dielectric layer with a variable thickness and at least one second dielectric layer. Furthermore, the present invention relates to an optical element manufactured by the method and the use of the optical element as a color filter, a dielectric filter / mirror, or in a sensor or in a thin film coating. BACKGROUND

[0002] Optical filters are essential components in almost all optical and optoelectronic systems, such as cameras, lasers, spectroscopic systems and optical metrology. Any optical device that requires wavelength selectivity typically employs an optical filter. To make the system compact in terms of size and functionality, a continuously variable optical filter is employed.

[0003] Existing optical filters are manufactured, for example, by electron beam evaporation (EBE), ion beam sputtering (IBS), or atomic layer deposition (ALD). In the above-mentioned methods, a high-vacuum deposition environment and mask technology are required to continuously vary the thickness of the deposited layer. This makes the process costly and complex. Further, in the above-mentioned methods, it is technically complex to deposit a plurality of different materials in precisely controlled mixing ratios, thus resulting in high costs, i.e. the conventional price of a single continuously variable filter ranges from several hundred euros.

[0004] Further, controlling the spectral response in high-quality optical filters typically requires precise control of the layer thickness to within 10 nm. In manufacturing optical filters, precise control of the single- or multi-dimensional layer thickness variation is not achievable with commonly used solution processing methods such as spin coating, blade coating and screen printing.

[0005] Recently, inkjet printing has been applied to form optical structures on a substrate. However, the known methods obtain a coating with a constant thickness by applying a printing ink containing a dielectric component, see, for example, WO 2011 / 003987 A1; A. V. Yakovlev et al. Sci. Rep. 2016, 6, 37090; and Q. Jin et al. Adv. Mater. Technol. 2022, 7, 2101026. The inability to control the variable layer thickness in at least one lateral dimension results in limited applications or poor optical performance.

[0006] Other disadvantages of the above-mentioned methods include that the use of masks limits the method to specific sizes, positions, thicknesses and shapes; masks result in additional costs; layering of different materials is extremely difficult or time-consuming; and the above-mentioned methods require a long processing time in order to manufacture, for example, optical filters of larger size. SUMMARY

[0007] Thus, as described above, the known optical filter manufacturing method has various defects. Therefore, in view of the prior art, the fundamental object of the present application is to provide a method of manufacturing a continuously variable optical filter by inkjet printing, which is easy to implement and low in cost, and which is capable of manufacturing a continuously variable optical filter having an excellent spectral response when used in an optical system. Furthermore, the object of the present application is also to provide an optical element manufactured by the above-mentioned method and the use of the optical element.

[0008] The solution to the above technical problem is provided by the embodiments described in the claims.

[0009] Thus, in a first aspect, the present application relates to a method of manufacturing a continuously variable optical filter, the method comprising the steps of: a) providing a substrate; b) applying a first layer of a first liquid material onto a surface of the substrate by inkjet printing, the first layer having a uniform or continuously variable thickness in at least one lateral dimension; c) solidifying the first liquid material of the first layer to obtain a first dielectric layer; d) applying a second layer of a second liquid material onto the first dielectric layer by inkjet printing, the second layer having a uniform or continuously variable thickness in at least one lateral dimension; and e) solidifying the second liquid material of the second layer to obtain a second dielectric layer; wherein the first liquid material and the second liquid material comprise at least one dielectric component, and at least one of the first layer and the second layer has a continuously variable thickness in at least one lateral dimension.

[0010] The inventors, through extensive research, have provided a solution to the above problem and have found that the manufacturing of a continuously variable optical filter can be extremely effectively achieved by using inkjet printing in steps. Thus, a continuously variable optical filter can be manufactured at low cost under normal temperature conditions, which exhibits an excellent spectral response due to the high-precision adjustment of the thickness of each layer. DETAILED DESCRIPTION

[0011] In general, the method of manufacturing a continuously variable optical filter comprises at least 5 steps: a) providing a substrate; b) applying a first layer of a first liquid material onto a surface of the substrate by inkjet printing, the first layer having a uniform or continuously variable thickness in at least one lateral dimension; c) solidifying the first liquid material of the first layer to obtain a first dielectric layer; d) applying a second layer of a second liquid material onto the first dielectric layer by inkjet printing, the second layer having a uniform or continuously variable thickness in at least one lateral dimension; and e) curing the second liquid material of the second layer to obtain a second dielectric layer; wherein at least one of the first and second layers has a continuously variable thickness in at least one lateral dimension.

[0012] The method described in this application enables the fabrication of optical filters by direct layer deposition by inkjet printing at ambient conditions. The process does not require high vacuum chambers and expensive masks. The mixing of materials in the printing ink is easily achieved and is cost-effective.

[0013] In the method of fabricating a continuously variable optical filter, the steps will be described in detail below. Figure 1 An exemplary inkjet printing process for fabricating a continuously variable optical filter is shown. However, it is noted that certain features in this exemplary process relate to the specific embodiments discussed below. It can be seen that, Figure 1 A coordinate system is disclosed, which will be followed in the subsequent applications. In this application, the terms "z-direction" and "thickness direction" will be used interchangeably.

[0014] In this application, the term "continuously variable optical filter" is not specifically limited, as long as it refers to an optical filter whose optical performance varies continuously along one or more dimensions of the filter.

[0015] In step (a) of the method disclosed above, a substrate is provided. The substrate can be, for example, a flexible foil, a rigid plate or the top surface of a device, such as a photodiode array, a CMOS / CCD sensor or a solar cell. That is, the substrate can comprise or consist of various materials, such as glass, polymers or metals. Furthermore, the substrate can be pre-treated to ensure that the layers printed on top of it have sufficient adhesion or to provide suitable flow characteristics for the at least first liquid material applied. For example, the surface of the substrate can be cleaned, etched, hydrophobized or hydrophilized. The surface of the substrate can also be treated and / or coated with selected chemicals, such as silanes or hexamethyldisilazane. The treatment of the surface of the substrate can also be performed by means of plasma, flame or thermal annealing.

[0016] In step (b) of the method disclosed above, a first layer of a first liquid material is applied to the surface of the substrate, wherein the first layer has a uniform or continuously variable thickness in at least one lateral dimension. That is, the thickness of the first layer can be uniform, continuously variable in a single lateral dimension or continuously variable in multiple lateral dimensions, for example, along the x-direction and the radial direction or along multiple dimensions, such as the x- and y-directions.

[0017] In the present application, the term "liquid material" refers to any material that is flowable at the temperature of the inkjet printing and at room temperature (25°C). The use of such liquid materials allows for excellent handling and storage properties of the material and enables an efficient printing process by inkjet printing. The viscosity of such materials can be adjusted as desired, for example by using suitable solvents, dispersants and / or matrix materials as described below.

[0018] The term "surface of a substrate" is not specifically limited and includes the entire surface of a substrate, one or more surfaces of a substrate (i.e. a major surface or a side surface of a plate, for example), or even only a portion of a surface. Thus, the expression "surface of a substrate" is not limited to the full coverage of a substrate.

[0019] In the inkjet printing process, the liquid material is printed by applying minute droplets of the liquid material through a print head of an inkjet printer. The droplets are ejected from the print head through nozzles. In the present application, the term "inkjet printing" is not specifically limited and includes all known inkjet printing processes, such as drop-on-demand printing, continuous inkjet printing, or thermal inkjet printing. Figure 1 In the illustrated example, the print head comprises a plurality of nozzles. In general, a print head as developed for conventional inkjet printing or modified for printing the liquid material layers described herein can be used. By digitally controlled manipulation of the printer, droplets are successively deposited on the surface of the substrate to form the liquid layer on the surface step by step. Overall, the manufacturing of the optical filter by inkjet printing combines ease of implementation and cost-effectiveness while maintaining the high precision and reliability required for optical elements.

[0020] The volume of the droplets deposited on the surface of the substrate can be less than 100 nL, preferably less than 10 nL, less than 1 nL, less than 200 pL, less than 50 pL, less than 10 pL, or even less than 10 fL. This volume range applies equally to the other inkjet printed layers as will be explained below.

[0021] In step (c) of the above disclosed method, the first liquid material of the first layer is solidified to obtain the first dielectric layer. Since the first layer has been solidified before the application of the other liquid material, mixing of the liquid materials is prevented.

[0022] After solidification of the first liquid material of the first layer, at least a second liquid material of a second layer is applied, wherein the second layer has a uniform or continuously variable thickness in at least one lateral dimension (see step (d) of the above disclosed method). As mentioned above, the second layer can have a continuously variable thickness in a plurality of lateral dimensions, which can be the same or different from the lateral dimensions of the first layer.

[0023] In general, to achieve the effects described in the present application, at least one of the first and second layers has a continuously variable thickness in at least one lateral dimension.

[0024] In step (e) of the above disclosed method, the second liquid material of the at least second layer is solidified to obtain the at least second dielectric layer.

[0025] According to a first aspect of the present application, the first and second liquid materials each comprise at least one dielectric component. The dielectric component is necessary to achieve the interaction between the resulting optical filter and the light rays incident on the filter, and is required for the optical filter to function. The dielectric component comprises, for example, an inorganic substance such as an acrylic polymer, a vinyl polymer, or an oxide. The dielectric component is preferably selected from the following group in view of solubility and / or dispersibility: polymethyl methacrylate (PMMA), polystyrene (PS), polyvinyl alcohol (PVA), liquid crystals, inorganic particles such as silicon dioxide (Si02), zinc dioxide (Zn02), titanium dioxide (Ti02), aluminum oxide (AI2O3), zirconium oxide (Zr02), vanadium oxide (VO x

[0026] The liquid material preferably comprises the dielectric component in an amount of less than 50%, more preferably less than 20%, or even less than 10%, and the dielectric component is present in an amount of at least 0.01%, preferably at least 0.1%. In the present application, all percentages given are volume percentages (vol-%). For example, the dielectric component can be present in an amount ranging from 1% to 5% or from 2% to 4%. Preferably, the liquid material has a low content of, or is free of, light-absorbing components. For example, the light-absorbing component is preferably present in the liquid material in an amount of less than 10%, more preferably less than 5%, less than 2%, or less than 1%. In other words, the liquid material is preferably optically transparent, preferably having a transparency of more than 90%, more than 95%, more than 98%, or more than 99%.

[0027] ​According to a specific embodiment, the method as described above is characterized in that the first liquid material and the second liquid material further comprise a solvent and / or a fluid matrix material. In the present application, exemplary solvents include 1,3-dimethoxybenzene, cyclopentanone, cyclohexanone, isopropyl alcohol, cyclohexane, o-xylene, hexylbenzene, triethylene glycol monomethyl ether, 2-propoxyethanol, chlorobenzene, dichlorobenzene, ethyl acetate, dimethyl sulfoxide, toluene, water, N-methyl-2-pyrrolidone, butanone, ethylene glycol, propylene glycol methyl ether, dimethylacetamide, or a combination of the above solvents. Preferably, the solvent is 1,3-dimethoxybenzene.

[0028] Depending on the type of dielectric component contained in the liquid material, it can be necessary to add further components to ensure the ink used for inkjet printing has fluidity. For example, an additional humectant such as glycerol, 1,3-propanediol, 1,2-propanediol, diethylene glycol, propylene glycol or triethylene glycol can be added to the ink. Further, an additional surfactant such as Triton X series, BYK-346 or BYK-333 can be added to the ink. In this case, it is preferred that the dielectric component contained in the first liquid material is soluble or dispersible in the solvent contained in the first liquid material, but not soluble in the solvent contained in the second liquid material. With such a composition and solubility behavior, it can be ensured that the application of each subsequent liquid material does not dissolve the dielectric component in the already solidified lower dielectric layer. Thus, a clear and well-defined interface between the dielectric layers can be formed, thereby enhancing the sharpness of the optical performance change between the layers.

[0029] Another specific embodiment relates to the method as disclosed above, wherein the first liquid material and the second liquid material comprise a dielectric component having different refractive indices and / or having different concentrations of the dielectric component. By using dielectric components having different refractive indices and / or different concentrations, the optical properties of the dielectric layers can be adjusted, thereby allowing a targeted adjustment of the optical processes occurring at the interfaces between the layers. Thus, the spectral response of the manufactured optical element is influenced by both the type of dielectric component and the sequence of the dielectric layer stack.

[0030] Thus, in one embodiment, the dielectric component in the first liquid material and the second liquid material (and / or the third liquid material) is different. Alternatively, the dielectric component can remain the same, but the film layers are formed with different porosities by printing, thereby resulting in a difference in refractive index. For example, the dielectric component in the various liquid materials can be chosen such that the refractive index of the first dielectric component differs from the refractive index of the second dielectric component by at least 0.1, preferably by at least 0.4 or by at least 1.0. By providing such different refractive indices in the dielectric layers, the optical properties of the optical filter can be adjusted, for example to achieve a high reflectivity or a high transmissivity for a specific wavelength of light.

[0031] In another embodiment, the dielectric components in the liquid materials are the same, but have different concentrations. In yet another embodiment, the dielectric components can even be the same and have the same concentration, so that by repeatedly depositing and solidifying, a higher thickness of a particular material can be achieved. In this case, the shape of the optical filter can achieve a larger thickness variation in the thickness direction, which is not possible by providing a thinner dielectric layer.

[0032] According to the specific embodiment, after steps (d) and (e), the above disclosed method further comprises corresponding additional steps (f) and (g), wherein a third liquid material of a third layer is inkjet printed onto the second dielectric layer (step (f)). The optional step (f) is followed by a solidification step (g) to obtain a third dielectric layer. Like the first and second layers, the optional third layer also has a uniform or continuously variable thickness in at least one lateral dimension, and can have a continuously variable thickness in multiple lateral dimensions. The provision of the third dielectric layer enables fine tuning of the optical properties of the manufactured optical element, thereby achieving superior spectral response performance in the optical system.

[0033] As described above and below, the properties of the first and second liquid materials and the first and second layers / dielectric layers also apply to the corresponding third liquid material / layer / dielectric layer. That is, the third liquid material comprises at least one dielectric component as described above.

[0034] A specific embodiment relates to the above disclosed method, wherein the continuously variable thickness of the first and / or second layer can be adjusted by one or more of the following: changing the pitch of the applied droplets during the inkjet printing process (Process 1), changing the volume of the applied droplets during the inkjet printing process (Process 2), and changing the number of applied droplets at the same location during the inkjet printing process (Process 3). Each of the above processes can accurately and reliably regulate the thickness of the printed layer, so that the optical element manufactured by the above processes has excellent and stable optical properties. The above processes will be described in more detail below.

[0035] Process 1: Dot Per Inch Method Process 1 discloses a method of controlling the thickness of the deposited layer of the continuously variable optical filter by printing with different dot per inch (dpi) on a unit area. That is, the dot per inch determines the number of ink droplets applied in a predetermined area. The process schematic is shown in Figure 2The ink drops fuse to form a thin film after being printed on the substrate. The increase of dots per inch (dpi) in printing results in the increase of the solid film thickness. Ad is the increase step of the thickness, which is caused by the increase step of Ab (i.e. dpi). By printing with different dpi in the lateral direction, the thickness of the deposited layer of the continuously variable optical filter can be controlled. The resolution of the thickness control is in nanometer scale, and Ad ranges from sub-nanometer to micrometer.

[0036] Process 2: Halftone method Process 2 discloses a method to control the thickness of the deposited layer of the continuously variable optical filter by printing with different halftone patterns. The schematic diagram of this process is shown in FIG. Figure 3 a. As shown in FIG. Figure 3 b (1), halftone is a kind of copying technology to reconstruct a continuous tone image by dots. Figure 3 b (2) and (3) are typical examples of halftone patterns, in which the dots usually have different sizes. The shape of the dots can be circular, triangular, square, star-shaped or irregular. Figure 3 a shows the halftone method in inkjet printing process. By printing dots with different sizes on the surface of the substrate, the film thickness can be controlled with a resolution of Ad.

[0037] Process 3: Gray scale method Process 3 discloses a method to control the thickness of the deposited layer of the continuously variable optical filter by printing with different gray scales (GS). The process is shown in FIG. Figure 4 a. The gray scale in printing defines the number of droplets printed at the same position on the substrate. The gray scale can be a value x divided by another value n. In this application, x represents the current setting value of the gray scale, and n represents the total number of possible levels. For example, the gray scale can be 64 / 255, i.e. the current gray scale value is 64, and the total available gray scale value is 255. In inkjet printing, the maximum number of droplets that can be printed at the same position is usually 256, considering the formation quality of the final film. For example, when printing with a gray scale of 55, the thickness of the formed film is greater than that when printing with a gray scale of 195. The change of the gray scale results in the change of the film thickness, in which the resolution is defined by Ad.

[0038] In addition, it is found that the precise volume of single droplet is difficult to control. Therefore, to improve the controllability, multiple droplets can be deposited at the same position according to the gray scale method described above. In this way, the statistical effect of the droplet volume can make the printed liquid layer have a more uniform thickness.

[0039] To control the thickness of the deposited film, the dots per inch method, the gray scale method and the halftone method can be used alone or in combination. By using the combination of the above processes, more precise control can be exerted on the optical performance of the obtained optical element.

[0040] The detailed description of the invention relates to the above method, wherein the thickness of each of the first, second and optional third dielectric layer is preferably less than 10 pm, less than 1 pm, less than 500 nm, less than 200 nm, even less than 100 nm, respectively. This thickness has an influence on the reflection and refraction of incident light in optical applications of the resulting optical element. Therefore, thicknesses in the above ranges are well suited for use in combination with light of various wavelengths occurring in various optical applications, in particular in combination with visible light, ultraviolet light or infrared light.

[0041] Preferably, the thickness accuracy of each layer of inkjet printing is less than 20 nm, more preferably less than 10 nm, less than 5 nm, even more preferably less than 1 nm. In the present application, thickness accuracy is defined as the amount of variation in thickness within an area having the same predetermined thickness. The thickness accuracy directly depends on the optimization of the ink formulation and printing parameters, such as the accuracy of the droplet volume or the accuracy of the droplet deposition position. Ensuring the above-mentioned thickness accuracy, the optical element can be improved in its suitability for high-end optical devices by stable optical properties and performance.

[0042] Further, preferably, the thickness adjustment does not require the use of masking processes as commonly used in conventional methods. Further, the above method is preferably performed under ambient conditions, i.e. without the need to apply reduced pressure or even a vacuum environment. Both advantages make the method of the present invention easy to perform and cost-effective.

[0043] Another embodiment relates to the above disclosed method, wherein steps (b) to (e) are repeated at least once to obtain a stack of alternating dielectric layers. That is, the above steps can be repeated, for example, once, twice, five times, ten times, even more than one hundred times. By repeating the above steps several times, a stack of dielectric layers can be generated, wherein the thickness of each layer is continuously varied. The stack comprises a sequence of alternating layers of dielectric layers, which comprises dielectric components of the first, second and optional third liquid material. For example, by stacking the above layers by repeating steps (b) to (e), the suitability of the manufactured optical element for a specific optical device can be enhanced.

[0044] Further, in another embodiment, the optional steps (f) and (g) of the deposition of the third layer can also be repeated as required. However, according to the present invention, the respective application and curing steps (b) and (c), (d) and (e) and optionally (f) and (g) of each layer can be repeated independently from each other.

[0045] Examples of such stack configurations include the following arrangements: (S / A / B / A / B...), (S / A / B / C / A / B / C...), (S / A / B / A / B / C / A / B / A / B / C...), (S / A / A / B / B / A / A / B / B...), (S / A / B / C / C / A / B / C / C...), (S / A / B / B / A / B / B...) and the like, where S denotes a substrate, A denotes a first layer, B denotes a second layer, and C denotes an optional third layer. The total number of layers is not particularly limited and can be adjusted according to the desired application. In the present application, the above exemplary stack configurations involve materials A, B and C, wherein the respective thickness of each layer can be adjusted independently of the other layers, i.e. different layers of A can have different thicknesses, and the same applies to B and C.

[0046] In another particular embodiment, the method of the present application can comprise a step (h) of providing a protective layer on the top surface of the continuously variable optical filter. The protective layer is not particularly limited as long as it performs a protective function and has sufficient light transmittance for the incident light used in the target application. Thus, the protective layer can have abrasion resistance and be resistant to environmental conditions such as moisture and high-intensity light irradiation.

[0047] Furthermore, one particular embodiment relates to the method as described above, wherein the cross-sectional shape of the optical filter varies linearly, curvilinearly or randomly in the thickness direction, and / or the cross-sectional shape of any of the first and second (or third) layers varies linearly, curvilinearly or randomly in the thickness direction. That is, the cross-sectional shape of the optical filter refers to the profile of the filter in the thickness direction thereof. Figure 5 Exemplary shapes of the optical filter are shown in FIG. 2. The lateral layer thickness variation can be of any shape, such as linear, exponential or random. Combinations of the above shapes can be employed in different application scenarios. Furthermore, different shapes can be combined in the lateral direction, i.e. blocks of different shapes are arranged side by side, or even in the thickness direction, i.e. layers of different thickness variations are stacked on top of each other. In the present application, by adjusting the cross-sectional shape of the optical filter in the thickness direction, the optical filter can be adapted to a variety of different application scenarios in optical devices.

[0048] In a preferred embodiment of the above method, the thickness of the optical filter and / or the thickness of any of the first and second (and optionally, third) layers increases continuously in at least one lateral dimension, wherein the respective lateral dimension of each layer is the same. This configuration can form a wedge-shaped optical filter, an exemplary structure of which is shown in FIG. 3. Figure 1The variable optical filter can be used, for example, in spectrometers and sensors, including for spectral-based imaging, multispectral and hyperspectral applications, microscopes, including fluorescence-based applications, and the like. That is, the variable optical filter has advantages in these applications in that it can enable more compact systems without the need to combine multiple different optical filters.

[0049] In another specific embodiment according to the first aspect of the application, the method is as described above, wherein the curing steps (c) and (e) (and optionally the curing step (g)) each comprises one or more of drying, curing, heating, irradiation, or a combination thereof. This technique can be used to achieve efficient drying of the liquid materials that make up the layers, thereby allowing the majority of the volatile components to evaporate. If desired, the above measures can be further carried out under reduced pressure. In addition or in the alternative, any polymer or polymer precursor contained in the liquid materials can be cured by irradiation with visible or ultraviolet (UV) light, thereby allowing the polymer / precursor to crosslink and cure. The curing method is not limited to the above, but can also include, for example, annealing or sintering of solid particles, and the like. Thus, the type of curing process depends on the combination of dielectric components and optional solvent / fluid matrix materials in each of the liquid materials. That is, for example, if the dielectric component is a polymerizable monomer, then curing can be achieved by irradiation to allow crosslinking; if the dielectric component is an inorganic particle dispersed in a solvent, then the solvent can be evaporated by drying and / or heating to allow curing; or even if the dielectric component is an inorganic particle dispersed in a polymerizable fluid matrix material, then the matrix can be cured by irradiation to allow crosslinking of the matrix.

[0050] In the present application, the term "irradiation" refers to exposure to light, including, for example, visible light (i.e., wavelengths of 400 nm to 800 nm), ultraviolet light (i.e., wavelengths of 150 nm to 400 nm), infrared light (i.e., wavelengths of 800 nm to 3000 nm), or other wavelengths suitable to cause at least partial curing of the liquid materials. In addition, the term "heating" refers to exposure of the liquid materials to elevated temperatures, for example, at least 40 °C, at least 100 °C, or at least 200 °C. Other techniques can be used for surface curing, including plasma treatment, vacuum treatment, ultrasonic treatment, and / or imprinting treatment.

[0051] A second aspect of the application relates to an optical element manufactured by the method disclosed above.

[0052] Such optical elements can include, for example, a bandpass filter, a dichroic filter, a longpass filter, a shortpass filter, a notch filter, a response flattening filter, a neutral density filter, a beamsplitter, a polarizer, an anti-reflective coating, or a waveplate. The optical element can also include a substrate coated with an anti-reflective function.

[0053] The use of the above disclosed method for manufacturing an optical element ensures that the optical element has excellent spectral response performance when used in an optical system.

[0054] A third aspect of the present application relates to the use of the above optical element as a color filter, a dielectric filter / mirror, or in a sensor or in a thin film coating.

[0055] The accompanying drawings show: Figure 1 An exemplary inkjet printing process schematic for manufacturing a continuously variable optical filter is shown. Multiple layers (3) and (4) are alternately stacked on a substrate (1). These layers are formed from droplets (2) applied through nozzles (6) from a print head (5).

[0056] Figure 2 A basic process for controlling the thickness of a deposited layer by varying the spacing of the applied droplets (Dots Per Inch method) during the inkjet printing process is shown.

[0057] Figure 3 A basic process for controlling the thickness of a deposited layer by varying the volume of the applied droplets (Halftone method) during the inkjet printing process is shown.

[0058] Figure 3 An exemplary halftone pattern is depicted.

[0059] Figure 4 A basic process for controlling the thickness of a deposited layer by varying the number of applied droplets at the same location (Gray Scale method) during the inkjet printing process is shown.

[0060] Figure 5 An exemplary profile of a continuously variable optical filter printed in the z-direction is shown.

[0061] In particular, the optical element can be used as a color filter, for example for camera chips; as a dielectric filter / mirror applied to various optical systems, especially to devices requiring large area optical properties; as an integrated spectrometer for optical sensing; as a photovoltaic module with an aesthetic appearance (for example with an identification pattern); and as a light management film for displays. Such optical elements are typically applied in the field of optical systems, optoelectronics, sensors, photovoltaics or thin film coating related fields.

Claims

1. A method for manufacturing a continuously variable optical filter, comprising the following steps: a) Provide a substrate; b) Applying a first liquid material of the first layer to the surface of the substrate by inkjet printing, wherein the first layer has a uniform or continuously variable thickness in at least one lateral dimension; c) Solidify the first liquid material of the first layer to obtain the first dielectric layer; d) Applying a second liquid material of the second layer onto the first dielectric layer by inkjet printing, the second layer having a uniform or continuously variable thickness in at least one lateral dimension; and e) Curing the second liquid material of the second layer to obtain the second dielectric layer; Wherein, the first liquid material and the second liquid material include at least one dielectric component. Furthermore, at least one of the first layer and the second layer has a continuously variable thickness in at least one lateral dimension.

2. The method according to claim 1, wherein, The continuously variable thickness of the first layer and / or the second layer is adjusted by changing one or more of the following: changing the distance between droplets applied during the inkjet printing process, changing the volume of droplets applied during the inkjet printing process, and / or changing the number of droplets applied at the same location during the inkjet printing process.

3. The method according to claim 1 or 2, wherein, Steps b) through e) are repeated at least once to obtain an alternating stack of dielectric layers.

4. The method according to any one of claims 1 to 3, wherein, The cross-sectional shape of the optical filter varies linearly, curvilinearly, or randomly in the thickness direction, and / or the cross-sectional shape of either the first layer or the second layer varies linearly, curvilinearly, or randomly in the thickness direction.

5. The method according to any one of claims 1 to 4, wherein, The thickness of the optical filter and / or either the first layer or the second layer increases continuously in at least one lateral dimension.

6. The method according to any one of claims 1 to 5, wherein, The first liquid material and the second liquid material further include solvent and / or fluid matrix material.

7. The method according to any one of claims 1 to 6, wherein, The first liquid material and the second liquid material include dielectric components with different refractive indices and / or dielectric components with different concentrations.

8. The method according to any one of claims 1 to 7, wherein, Curing steps c) and e) respectively include drying, curing, heating, irradiating, or a combination thereof on the first layer and the second layer.

9. An optical element manufactured by the method according to any one of claims 1 to 8.

10. The optical element of claim 9 is used as a color filter, a dielectric filter / mirror, or in a sensor or in a thin film coating.

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