Optical element with a stack of layer packages

Abstract

Optical element (100) comprising a substrate (20) and an interferometric reflection-reducing layer system (10) on at least one surface (22) of the substrate (20), wherein the layer system (10) comprises a stack (40) of at least four successive layer packages (42, 44, 46, 48), wherein each layer package (42, 44, 46, 48) comprises a first sublayer (60) with a first optical thickness (t1) and a second sublayer (62) with a second optical thickness (t2) different from the first optical thickness (t1), wherein a refractive index (n1) of the first sublayer (60) closer to the substrate is greater than a refractive index (n2) of the second sublayer (62) further away from the substrate of the stack (40), wherein the first sublayer (60) is made of Ta2O5 and the second sublayer (62) is made of SiO2, wherein the layer system (10) has a brightness (L*), a chroma (C*) and a hue angle (h) of a residual reflection color, characterized by the fact that the magnitude of a change (Δh) of the hue angle (h) of the residual reflection color in an interval of a viewing angle (AOI) with limit values ​​of 0° and 30° relative to a surface normal (70) to the layer system (10) is smaller than the magnitude of a change (ΔC*) of the chroma (C*) in the interval of the viewing angle (AOI), where for four layer packages (42, 44, 46, 48) with a blue residual reflection color, in the lowest, first layer package (42) the first sublayer (60) has a thickness of 7.5 nm and the second sublayer (62) has a thickness of 54.9 nm, in the following second layer package (44) the first sublayer (60) has a thickness of 20.1 nm and the second sublayer (62) has a thickness of 49.7 nm, in the following third layer package (46) the first sublayer (60) has a thickness of 27.4 nm and the second sublayer (62) has a thickness of 17.6 nm, and in the following fourth layer package (48) the first sublayer (60) has a thickness of 119.2 nm and the second sublayer (62) has a thickness of 81.7 nm, or with a green residual reflection color in the lowest, first layer package (42), the first sublayer (60) has a thickness of 5 nm and the second sublayer (62) has a thickness of 64.3 nm, in the following second layer package (44) the first sublayer (60) has a thickness of 12 nm and the second sublayer (62) has a thickness of 75.9 nm, in the following third layer package (46) the first sublayer (60) has a thickness of 24.6 nm and the second sublayer (62) has a thickness of 19.1 nm, and in the following fourth layer package (48) the first sublayer (60) has a thickness of 103 nm and the second sublayer (62) has a thickness of 70.7 nm, or with a yellow residual reflection color in the lowest, first layer package (42), the first sublayer (60) has a thickness of 20 nm and the second sublayer (62) has a thickness of 28.8 nm, in the following second layer package (44) the first sublayer (60) has a thickness of 62 nm and the second sublayer (62) has a thickness of 6.7 nm, in the following third layer package (46) the first sublayer (60) has a thickness of 72 nm and the second sublayer (62) has a thickness of 9 nm, and in the following fourth layer package (48) the first sublayer (60) has a thickness of 136 nm and the second sublayer (62) has a thickness of 62 nm, or with a red residual reflection color in the lowest, first layer package (42) the first sublayer (60) has a thickness of 5 nm and the second sublayer (62) has a thickness of 41 nm, in the following second layer package (44) the first sublayer (60) has a thickness of 29.4 nm and the second sublayer (62) has a thickness of 4 nm, in the following third layer package (46) the first sublayer (60) has a thickness of 3.5 nm and the second sublayer (62) has a thickness of 13.48 nm, and in the following fourth layer package (48) the first sublayer (60) has a thickness of 72 nm and the second sublayer (62) has a thickness of 71 nm.

Description

State of the art

[0001] The invention relates to an optical element with a stack of layer packages.

[0002] Known optical elements with interferometric antireflection coatings, such as those described in WO 2016 / 110339 A1, typically exhibit a light reflectance of approximately 1%, calculated according to the standard DIN EN ISO 13666:2013-10. The color of the remaining residual reflection shows a strong variation when the viewing angle is changed. This variation extends across virtually the entire visual color scale.

[0003] DE 102015100091 A1 and US 2016 / 0154254 A1 disclose optical elements with interferometrically reflection-reducing layer systems. Disclosure of the invention

[0004] The object of the invention is to provide an optical element with an interferometrically reflection-reducing layer system that exhibits only a slight viewing-angle-dependent variation in the color of the residual reflection.

[0005] The problem is solved by the features of the independent claim. Favorable embodiments and advantages of the invention become apparent from the further claims, the description, and the drawing.

[0006] Unless otherwise stated, the terms used in this disclosure shall be understood in accordance with the standards DIN EN ISO 13666:2013-10 (EN ISO 13666:2012 (D / E)) and DIN EN ISO 11664-4:2012-06 (EN ISO 11664-4:2011) of the German Institute for Standardization eV.

[0007] According to section 4.2 of the standard DIN EN ISO 13666:2013-10, the term visible light, visible radiation, or a visible wavelength range refers to optical radiation that is capable of directly producing a sensation of light in humans. Visible radiation generally refers to a wavelength range from 400 nm to 780 nm.

[0008] Within the scope of this disclosure, visible radiation can preferably refer to a wavelength range of 400 nm or 460 nm to 700 nm, corresponding to the sensitivity maximum of the human eye. This simultaneously increases the design flexibility for the filter properties and slope steepness.

[0009] The term spectral reflectance, reflectance, or reflectivity, according to section 15.1 of the standard DIN EN ISO 13666:2013-10, refers to the ratio of the spectral radiant power reflected by the respective material, surface, or coating to the incident radiant power for a specific wavelength (λ). In this case, reflectivity refers to the reflectivity of the entire coating with its multiple high- and low-refractive-index sublayers, and not to the reflectivity of a single sublayer.

[0010] The invention relates to an optical element comprising a substrate and an interferometrically reflection-reducing layer system on at least one surface of the substrate, wherein the layer system comprises a stack of at least four successive layer packages, each layer package comprising a first sublayer with a first optical thickness and a second sublayer with a second optical thickness different from the first optical thickness, wherein a refractive index of the first sublayer closer to the substrate is greater than a refractive index of the second sublayer further away from the substrate in the stack, wherein the first sublayer is formed from Ta2O5 and the second sublayer is formed from SiO2, wherein the layer system has a brightness, a chroma and a hue angle of a residual reflection color.

[0011] It is proposed that the magnitude of a change in the hue angle of the residual reflection color in an interval of a viewing angle with limit values ​​of 0° and 30° relative to a surface normal to the layer system is smaller than the magnitude of a change in hue in the interval of the viewing angle, where, for four layer packages With a blue residual reflection color, in the lowest, first layer package the first sublayer has a thickness of 7.5 nm and the second sublayer has a thickness of 54.9 nm, in the following second layer package the first sublayer has a thickness of 20.1 nm and the second sublayer has a thickness of 49.7 nm, in the following third layer package the first sublayer has a thickness of 27.4 nm and the second sublayer has a thickness of 17.6 nm, and in the following fourth layer package the first sublayer has a thickness of 119.2 nm and the second sublayer has a thickness of 81.7 nm, or With a green residual reflection color, in the lowest, first layer package the first sublayer has a thickness of 5 nm and the second sublayer (62) has a thickness of 64.3 nm, in the following second layer package the first sublayer has a thickness of 12 nm and the second sublayer has a thickness of 75.9 nm, in the following third layer package the first sublayer has a thickness of 24.6 nm and the second sublayer has a thickness of 19.1 nm, and in the following fourth layer package the first sublayer has a thickness of 103 nm and the second sublayer has a thickness of 70.7 nm, or With a yellow residual reflection color, in the lowest, first layer package the first sublayer has a thickness of 20 nm and the second sublayer has a thickness of 28.8 nm, in the following second layer package the first sublayer has a thickness of 62 nm and the second sublayer has a thickness of 6.7 nm, in the following third layer package the first sublayer has a thickness of 72 nm and the second sublayer has a thickness of 9 nm, and in the following fourth layer package the first sublayer has a thickness of 136 nm and the second sublayer has a thickness of 62 nm. or With a red residual reflection color, in the lowest, first layer package the first sublayer has a thickness of 5 nm and the second sublayer has a thickness of 41 nm, in the following second layer package the first sublayer has a thickness of 29.4 nm and the second sublayer has a thickness of 4 nm, in the following third layer package the first sublayer has a thickness of 3.5 nm and the second sublayer has a thickness of 13.48 nm, and in the following fourth layer package the first sublayer has a thickness of 72 nm and the second sublayer has a thickness of 71 nm.

[0012] Chromaticity can also be referred to as color saturation. Hue angle can also be referred to as color angle.

[0013] Advantageously, varying the thickness of the sublayers can provide a color-stable layer system whose residual reflection color does not change, or only changes slightly, even with significant changes in the viewing angle. A suitable combination of hue and hue angle can advantageously achieve a color-stable residual reflection color over a wide viewing angle range.

[0014] The first, substrate-closer sub-layers of the layer packages in the stack can be formed from the same first material.

[0015] The second, more distant sublayers can also be formed from the same material, but different from the material of the first sublayers. It can be provided that in the layer stack furthest from the substrate, a functional layer made of a third material is arranged between the first and second sublayers, exhibiting refractive properties comparable to the second sublayer. For computational purposes, the functional layer can optionally be assigned to the second sublayer. Alternatively, the materials of the first sublayers can vary within the stack. Likewise, it can be alternatively provided that the materials of the second sublayers vary within the stack.

[0016] The shift system can advantageously have four or five shift packages; more than five shift packages can also be provided.

[0017] With a favorable design of the optical element, the hue angle can change by a maximum of 15°, preferably by a maximum of 10°, within the interval of the viewing angle with the limit values ​​of 0° and 30°. The color impression of the residual reflection from the optical system remains completely or almost unchanged for an observer.

[0018] According to a favorable design of the optical element, the magnitude of the change in hue angle in a second interval of a viewing angle from 0° up to a limiting viewing angle with upper limits of 30° and 45° relative to the surface normal to the layer system can be smaller than the magnitude of a change in hue in the second interval of the viewing angle, and the magnitude of hue at the limiting viewing angle can be at least equal to 2.

[0019] In particular, the hue angle h in the second interval can change by a maximum of 20°, preferably by a maximum of 15°. Advantageously, a color-stable residual reflection color is obtained even with larger variations in the viewing angle.

[0020] According to a favorable design of the optical element, the photopic reflectance in the interval of the viewing angle with the limit values ​​0° and 30° can be at most 1.5%, preferably at most 1.2%.

[0021] According to a favorable design of the optical element, the scotopic reflectance in the interval of the viewing angle with the limit values ​​0° and 30° can be at most 1.5%, preferably at most 1.2%.

[0022] According to an unstressed favorable embodiment of the optical element, the first sublayers can be formed from a high-refractive-index material.

[0023] Advantageously, the first sublayers can consist of at least one or more of the compounds Ta2O5, TiO2, ZrO2, Al2O3, Nd2O5, Pr2O3, PrTiO3, La2O3, Nb2O5, Y2O3, HfO2, InSn oxide, Si3N4, MgO, CeO2, ZnS and / or their modifications, in particular their other oxidation states. If two or more compounds are contained in a first sublayer, they can, for example, be applied layer by layer or mixed in one layer, for example by simultaneous application.

[0024] These materials are known as materials with a high classical refractive index for use in optical elements, such as for coating spectacle lenses. However, the higher-refractive-index sublayers can also contain SiO2 or other lower-refractive-index materials, as long as the refractive index of the entire sublayer is greater than 1.6, preferably at least 1.7, particularly preferably at least 1.8, and most preferably at least 1.9.

[0025] According to an unconstrained favorable embodiment of the optical element, the second sublayers can be formed from a low-refractive-index material.

[0026] The lower refractive index sublayers can comprise at least one of the materials MgF₂, SiO₂, SiO₂, or SiO₂ with additions of Al, silanes, or siloxanes in pure form or with their fluorinated derivatives. However, the lower refractive index sublayers can also contain a mixture of SiO₂ and Al₂O₃. Preferably, the lower refractive index sublayers contain at least 80% by weight of SiO₂, and particularly preferably at least 90% by weight of SiO₂.

[0027] Preferably, the refractive index of the low-refractive-index sublayers is at most 1.55, more preferably at most 1.48, and most preferably at most 1.4. These refractive indices are based on standard conditions at a temperature of 25°C and a reference wavelength of 550 nm for the light intensity used.

[0028] Typical examples of coating materials with different refractive indices are silicon dioxide (SiO2) with a refractive index of 1.46, aluminum oxide (Al2O3) with a refractive index of 1.7, zirconium dioxide (ZrO2) with a refractive index of 2.05, praseodymium titanium oxide (PrTiO3) with a refractive index of 2.1, titanium oxide (TiO2) and zinc sulfide (ZnS), each with a refractive index of 2.3. These values ​​represent average values ​​that can vary by up to 10% depending on the coating process and layer thickness.

[0029] Typical optical glasses have refractive indices between 1.5 and 2.0. Layered materials with refractive indices less than 1.5, such as MgF2, SiO2, and Al2O3, are therefore referred to as low-refractive-index materials when combined with optical glasses, while layered materials with refractive indices greater than 2.0, such as ZrO2, PrTiO3, TiO2, and ZnS, are referred to as high-refractive-index materials when combined with optical glasses.

[0030] The difference in refractive indices between the high-refractive and low-refractive materials of the first and second sub-layers is preferably at least 0.2 to at least 0.5, depending on the coating process and layer thickness.

[0031] The materials used for this type of coating are the typical materials that are applied to a substrate in optics using, for example, PVD processes (PVD = Physical Vapor Deposition) or CVD processes (CVD = Chemical Vapor Deposition).

[0032] According to a favorable design of the optical element, at least the first sublayers can be formed from the same first material and the second sublayers can be formed at least predominantly from the same second material.

[0033] Optionally, the second sublayers can be formed from the same second material and only have a functional layer between the first and second sublayers in the layer package furthest from the substrate. This functional layer can be low-refractive-index and, if necessary, added to the second sublayer for calculation purposes.

[0034] In a favorable method for designing an optical element according to the invention, the optical element comprises a substrate and an interferometrically reflection-reducing layer system on at least one surface of the substrate, wherein the layer system comprises a stack of at least four successive layer packages, each layer package comprising a first sublayer with a first optical thickness and a second sublayer with a second optical thickness different from the first optical thickness, wherein a refractive index of the first sublayer closer to the substrate is greater than a refractive index of the second sublayer further away from the substrate in the stack, wherein the layer system has a brightness, a chroma, and a hue angle of a residual reflection color.The magnitude of a change in the hue angle of the residual reflection color in an interval of a viewing angle with the limiting values ​​0° and 30° relative to a surface normal to the layer system is smaller than the magnitude of a change in hue in the interval of the viewing angle.

[0035] The process involves the following steps: defining a layer design, comprising at least a first material for high-refractive-index sublayers and a second material for low-refractive-index sublayers, the number of desired layer packages with the sublayers, and initial values ​​for the thickness of the sublayers; defining target color values, comprising brightness, hue, and hue angle at least at limit values ​​for an interval of a viewing angle with limit values ​​of 0° and 30°; and performing an optimization procedure to vary the individual layer thicknesses until an optimization target is achieved.

[0036] The target color values ​​can be chosen to be the same or similar at the limits of the interval.

[0037] In particular, maximum deviations for the hue angles of different residual reflection colors can be specified.

[0038] For the residual reflection color blue, a favorable permissible change Δh of the hue angle in the interval of the viewing angle from 0° to 30° may preferably be at most Δh = 4°, and particularly preferably at most Δh = 3.5°. A favorable permissible change Δh of the hue angle in the interval of the viewing angle from 0° to 33° may preferably be at most Δh = 5°, and particularly preferably at most Δh = 4.5°.

[0039] For a residual reflection color green, a favorable permissible change Δh of the hue angle in the interval of the viewing angle from 0° to 30° may preferably be at most Δh=3°, more preferably at most Δh=2°. A favorable permissible change Δh of the hue angle in the interval of the viewing angle from 0° to 45° may preferably be at most Δh=5°, more preferably at most Δh=4.6°.

[0040] For a residual reflection color yellow, a favorable permissible change Δh of the hue angle in the interval of the viewing angle from 0° to 30° may preferably be at most Δh = 1.5°, and particularly preferably at most Δh = 0.9°. A favorable permissible change Δh of the hue angle in the interval of the viewing angle from 0° to 45° may preferably be at most Δh = 5°, and particularly preferably at most Δh = 4.6°.

[0041] For a residual reflection color red, a favorable permissible change Δh of the hue angle in the interval of the viewing angle from 0° to 30° may preferably be at most Δh = 6°, and particularly preferably at most Δh = 5.3°. A favorable permissible change Δh of the hue angle in the interval of the viewing angle from 0° to 45° may preferably be at most Δh = 20°, and particularly preferably at most Δh = 16.8°. drawing

[0042] Further advantages will become apparent from the following description of the drawings. The figures illustrate exemplary embodiments of the invention. The figures, the description, and the claims contain numerous features in combination. A person skilled in the art will expediently consider the features individually and combine them into meaningful further combinations.

[0043] They show, for example: Fig. 1 an embodiment of the invention in which a layer system comprises four layer packages on a substrate; Fig. 2 an embodiment of the invention in which a layer system comprises five layer packages on a substrate; Fig. 3 a reflectivity of a layer system according to the invention with a residual reflection color blue in the wavelength range between 280 nm and 1400 nm; Fig. 4 a detail of the representation in Fig. 3 in the wavelength range 380 nm to 780 nm; Fig. 5. Depending on the angle of incidence between 0° and 45°, a gradient of chroma C* with the residual reflection color blue according to Fig. 3; Fig. 6. Depending on the angle of incidence between 0° and 45°, the brightness L* of the residual reflection color blue varies according to Fig. 3; Fig. 7. Depending on the angle of incidence between 0° and 45°, a gradient of the hue angle h with the residual reflection color blue according to Fig. 3; Fig. 8 Depending on the angle of incidence between 0° and 45°, a course of the photopic reflectance Rv and the scotopic reflectance Rv' with the residual reflection color blue according to Fig. 3; Fig. 9 a reflectivity of a layer system according to the invention with a residual reflection color green in the wavelength range between 280 nm and 1400 nm; Fig. 10 a detail of the representation in Fig. 9 in the wavelength range 380 nm to 780 nm; Fig. 11 Depending on the angle of incidence between 0° and 45°, a gradient of chroma C* with the residual reflection color green according to Fig. 9; Fig. 12 Depending on the angle of incidence between 0° and 45°, a gradient of brightness L* of the residual reflection color green according to Fig. 9; Fig. 13 Depending on the angle of incidence between 0° and 45°, a progression of the hue angle h with the residual reflection color green according to Fig. 9; Fig. 14 Depending on the angle of incidence between 0° and 45°, a course of the photopic reflectance Rv and the scotopic reflectance Rv' with the residual reflection color green according to Fig. 9; Fig. 15 a reflectivity of a layer system according to the invention with a residual reflection color yellow in the wavelength range between 280 nm and 1400 nm; Fig. 16 a detail of the representation in Fig. 15 in the wavelength range 380 nm to 780 nm; Fig. 17 Depending on the angle of incidence between 0° and 45°, a gradient of chroma C* with the residual reflection color yellow according to Fig. 15; Fig. 18 Depending on the angle of incidence between 0° and 45°, a gradient of brightness L* of the residual reflection color yellow according to Fig. 15; Fig. 19 Depending on the angle of incidence between 0° and 45°, a progression of the hue angle h with the residual reflection color yellow according to Fig. 15; Fig. 20 Depending on the angle of incidence between 0° and 45°, a course of the photopic reflectance Rv and the scotopic reflectance Rv' with the residual reflection color yellow according to Fig. 15; Fig. 21 a reflectivity of a layer system according to the invention with a residual reflection color red in the wavelength range between 280 nm and 1400 nm, Fig. 22 a detail of the representation in Fig. 21 in the wavelength range 380 nm to 780 nm; Fig. 23 depending on the angle of incidence between 0° and 45° a gradient of chroma C* with the residual reflection color red according to Fig. 21; Fig. 24 Depending on the angle of incidence between 0° and 45°, a gradient of brightness L* of the residual reflection color red according to Fig. 21; Fig. 25 depending on the angle of incidence between 0° and 45° a course of the hue angle h with the residual reflection color red according to Fig. 21; Fig. 26 Depending on the angle of incidence between 0° and 45°, a course of the photopic reflectance Rv and the scotopic reflectance Rv' with the residual reflection color red according to Fig. 21; Fig. 27 a polar diagram with measured values ​​on layer systems according to the invention with different residual reflection colors and a layer system according to the prior art in a first interval of a viewing angle from 0° to 30°; Fig. 28 the polar diagram according to Fig. 27 in a further interval of viewing angle from 0° to 45°; Fig. 29 a favorable method for designing a layer system according to the invention. Embodiments of the invention

[0044] In the figures, similar or equivalent components are numbered with the same reference symbols. The figures merely show examples and are not to be understood as limiting.

[0045] The directional terminology used below, including terms like "left," "right," "above," "below," "in front," "behind," "after," and the like, serves only to improve the understanding of the figures and is in no way intended to limit their generality. The components and elements depicted, their interpretation, and their use may vary according to the considerations of a person skilled in the art and be adapted to the specific applications.

[0046] The Fig. 1 and Fig. Figure 2 shows an exemplary optical element 100, for example a spectacle lens, according to an embodiment of the invention.

[0047] The optical element 100 comprises in Fig. 1 a layer system 10 with a stack 40 of four layer packages 42, 44, 46, 48 on a surface 22 of a substrate 20.

[0048] In Fig. 2 the optical element 100 comprises a layer system 10 with a stack 40 of five layer packages 42, 44, 46, 48, 50 on a surface 22 of a substrate 20.

[0049] Except for the different number of shift packages 42, 44, 46, 48, 50 (four in Fig. 1 and five in Fig. 2) the further statements of a general and specific nature apply to Fig. 1 also for the design in Fig. 2, unless otherwise stated.

[0050] The layer system is viewed by an observer at a viewing angle AOI of 0° up to a limiting angle, for example 30°, measured from the surface normal 70.

[0051] Substrate 20, for example, is a plastic, in particular a transparent plastic for a spectacle lens.

[0052] Within the scope of this disclosure, the term spectacle lens refers in particular to a coated spectacle lens in accordance with section 8.1.13 of the standard DIN EN ISO 13666:2013-10, i.e. a spectacle lens onto which one or more surface coatings have been applied, in particular to change one or more of its properties.

[0053] Such lenses can be particularly advantageously used as eyeglasses (with and without correction), sunglasses, ski goggles, occupational eyeglasses and eyeglasses in conjunction with head-mounted display devices.

[0054] Within the scope of this disclosure, the term spectacle lens may also include spectacle lens semi-finished products, in particular a spectacle lens blank or spectacle lens semi-finished product as defined in section 8.4.2 of the standard DIN EN ISO 13666:2013-10, i.e. a lens blank or blank with only one optical, finished surface.

[0055] Regarding the details in the Fig. 1 and Fig. 2 The opposite surface 24 of the substrate 20 may optionally have another, similar or identical layer system 10, no coating or merely a protective coating.

[0056] As the bottom layer on the substrate 20, the layer system 10 typically includes a single-layer or multi-layer intermediate layer 32, for example to improve the adhesion of the stack 40 and / or as scratch protection for the substrate 20. This intermediate layer 32 can consist, for example, of substoichiometric refractory metal oxides, chromium, silanes, or siloxanes. The intermediate layer 32 is not relevant for further considerations.

[0057] On intermediate layer 32 are in Fig. 1 the four layer packages 42, 44, 46, 48 of the stack 40 are arranged successively, each of the layer packages 42, 44, 46, 48 consisting of a sublayer 60 closer to the substrate followed by a sublayer 62 further away from the substrate.

[0058] Preferably, each of the sublayers 60 closest to the substrate is formed from an identical first material. Preferably, the first material is a higher refractive index material with a first refractive index n1.

[0059] Preferably, each of the sublayers 62 furthest from the substrate is formed from an identical second material. Preferably, the second material is a low-refractive-index material with a second refractive index n2. The refractive index n1 is greater than the refractive index n2; preferably, the difference between the refractive indices n1 and n2 is at least 0.2, preferably up to at least 0.5.

[0060] The order of the sublayers 60, 62 remains the same in the stack 40, so that in each layer package 42, 44, 46, 48 the respective sublayer 60 closer to the substrate is always the higher refractive index and the respective sublayer 62 further away from the substrate is always the lower refractive index of the sublayers 60, 62.

[0061] In particular, the higher refractive index sublayers 60 may be layers made of high refractive index materials and the lower refractive index sublayers 62 may be layers made of low refractive index materials.

[0062] The layer packages 42, 44, 46, 48 in the stack 40 differ only in their respective thickness and / or in the thicknesses of the individual sub-layers 60, 62 in the respective layer package 42, 44, 46, 48.

[0063] The stack 40 is finished in a manner known per se with a top layer 34, which, for example, serves to maintain the layer system 10. The top layer 34 is applied to the last optically relevant sublayer 62 of the uppermost layer package 48 of the stack 40 and may contain fluorine-containing molecules. The top layer 34 typically imparts improved maintenance properties to the stack 40, with characteristics such as water repellency and oil repellency at a surface energy of typically less than 15 mN / m.

[0064] The top layer 34 is not relevant for further considerations.

[0065] The uppermost layer package furthest from the substrate 48 (or layer package 50 in Fig. 2) Optionally, a functional layer 64 is located between the sublayer 60 closer to the substrate and the sublayer 62 further away from the substrate. This functional layer 64 can, for example, increase electrical conductivity, equalize mechanical stresses, or act as a diffusion barrier. It can be made of a low-refractive-index material or alloyed with other metal oxides, such as aluminum. For calculation and simulation purposes of the optical properties, the functional layer 64 can be located in the lower-refractive-index sublayer 62 of the uppermost, substrate-remote layer package 48 (or layer package 50 in the Fig. 2) be added or, if necessary, for example in the case of relatively small layer thickness, be disregarded.

[0066] The optical properties of stack 40 of layer system 10 can be simulated computationally using known calculation methods and / or optimization procedures. The layer system 10 is then fabricated with the determined layer thicknesses of the individual sublayers 60, 62 of layer packages 42, 44, 46, 48.

[0067] In the fabrication of optical layer systems 10, the optical properties of the layer system 10 are adjusted during the fabrication of the sublayers 60, 62. For example, the method known from WO 2016 / 110339 A1, which is briefly outlined below, can be used. With this known method, various optical effects such as mirroring or reflection reduction can be achieved in a material system by changing only the layer thicknesses, while keeping the material used the same. However, other methods are also possible.

[0068] By varying the layer package thicknesses with identical materials, as described in WO 2016 / 110339 A1, different reflectivities can be achieved, particularly for a reflection-reducing effect. This is achieved by minimizing or optimizing a parameter σ. The parameter σ is in turn a function of the layer thicknesses of the sublayers 60, 62, or of the ratios of the optical thicknesses t1, t2 of the sublayers 60, 62 of each of the four layer packages 42, 44, 46, 48 according to Fig. 1 or five shift packages 42, 44, 46, 48, 50 after Fig. 2 in stack 40.

[0069] At a specific wavelength λ, the optical thickness t of a layer, also called FWOT (full wave optical thickness), is determined as follows: t=dλ⋅n where d is the layer thickness, λ is the design wavelength and n is the refractive index of the sublayer 60, 62.

[0070] A reflection-reducing effect by stack 40 can be achieved for a predefinable reflectivity R. m of the stack 40 can be reached when the product of reflectivity R m and the parameter σ is set to less than 1: Rm⋅σ<1

[0071] The reflectivity R m Reflectance, also called reflectance, describes the ratio of reflected to incident intensity of a light ray as an energy quantity. The reflectivity R m It is expediently averaged over the range of light from 380 nm to 800 nm and referenced to 100%.

[0072] Such a condition R m ·σ<1 can be used as a boundary condition for an optimization process of the method for producing the layer system 10.

[0073] The optical thicknesses t1, t2 of the first and second sublayers 60, 62 of the layer packages 42, 44, 46, 48 are determined by determining the parameter σ using an optimization procedure, preferably using variational calculus.

[0074] The thicknesses of the respective sublayers 60, 62 are preferably determined by a quotient v in the case of four layer packages 42, 44, 46, 48 in the stack 40. i (with i=1, 2, 3, 4) the first optical thickness t1 of the higher refractive first sublayer 60 and the second optical thickness t2 of the lower refractive second sublayer 62 of the respective layer package 42, 44, 46, 48 are formed.

[0075] The indices i=1, 2, 3, 4 represent the sequence of the layer packages 42, 44, 46, 48 on the substrate 20. Accordingly, v1 represents the layer package 42 closest to the substrate and v4 represents the layer package 48 furthest from the substrate.

[0076] For a stack of four consecutive layer packages 42, 44, 46, 48, the parameter σ can be derived from σ=v1+v2v3+v4 be determined.

[0077] The first and second sublayers 60, 62 are produced with the parameters calculated in this way, in particular the optical thicknesses t1, t2 of the sublayers 60, 62 of the stack 40.

[0078] In an advantageous embodiment, a layer system can be 10 according to Fig. 2 of the parameters σ for a stack 40 with five consecutive layer packages 42, 44, 46, 48, 50 from the relationship σ=v1∑i=2nmaxvi to be determined, where i runs from 2 to nmax=5.

[0079] The indices i=1, 2, 3, 4, 5 represent the sequence of the layer packages 42, 44, 46, 48, 50 on the substrate 20. Accordingly, v1 represents the layer package 42 closest to the substrate and v5 represents the layer package 50 furthest from the substrate.

[0080] It is known to specify perception-related colors in the so-called CIEL*a*b* color space (simplified CIELAB color space) in Cartesian coordinates, as set out in DIN EN ISO 11664-4:2012-06 (EN ISO 11664-4:2011).

[0081] L* is the CIELab brightness, a*, b* are the CIELab coordinates, C* is the CIELab chromaticity, and h ab the CIELab hue angle.

[0082] The L* axis describes the brightness (luminance) of the color with values ​​from 0 to 100. The L* axis is perpendicular to the a*b* plane at the origin. It can also be called the neutral gray axis, since all achromatic colors (shades of gray) are contained between the endpoints black (L*=0) and white (L*=100).

[0083] Green and red are opposite each other on the a*-axis, while the b*-axis runs between blue and yellow. Complementary colors are positioned 180° apart; gray is located at their midpoint, i.e., at the origin of the coordinate system a*=0, b*=0.

[0084] The a*-axis describes the green or red component of a color, where negative values ​​represent green and positive values ​​represent red. The b*-axis describes the blue or yellow component of a color, where negative values ​​represent blue and positive values ​​represent yellow.

[0085] The a* values ​​range from approximately -170 to +100, and the b* values ​​from -100 to +150, with the maximum values ​​only being reached at medium brightness for certain hues. The CIELab color solid has its greatest extent in the mid-brightness range, but this extent varies in height and size depending on the color range.

[0086] The CIELab hue angle h ab must be between 0° and 90° if both a* and b* are positive, between 90° and 180° if b* is positive and a* is negative, between 180° and 270° if both a* and b* are negative, and between 270° and 360° if b* is negative and a* is positive.

[0087] In the CIE-L*C*h color space (simplified CIELCh color space), the Cartesian coordinates of the CIELab color space are transformed into polar coordinates. The cylindrical coordinates C* (chroma, relative color saturation, distance from the L-axis at the center) and h (hue angle, angle of the hue in the CIELab color circle) are specified. The CIELab lightness L* remains unchanged.

[0088] The hue angle h is derived from the a* and b* axes. h=arctan(b*a*)

[0089] The hue angle h here represents the color of the residual reflection of the reflection-reducing layer system 10.

[0090] The chromaticity C* results from C*=(a*)2+(b*)2

[0091] The chromaticity C* is also referred to as color depth.

[0092] In known anti-reflective coatings, the color of the residual reflection is optimized for a perpendicular incidence of light on the layer system 10 (AOI=0°) and varies greatly when the viewing angle AOI is changed.

[0093] As shown in the following figures for various residual reflection colors blue, green, yellow, red, a layer system 10 according to the invention can be formed with four layer packages 42, 44, 46, 48 or five layer packages 42, 44, 46, 48, 50, which remains largely color-stable even when the viewing angle AOI is varied in the range between 0° and 30°. In other words, the color impression of the residual reflection does not change practically when an observer views the optical element 100 at viewing angles AOI within this angular interval.

[0094] The Fig. Figures 3 to 8 show values ​​of a layer system 10 according to the invention with the residual reflection color blue.

[0095] Fig. Figure 3 shows a reflectivity R in percent of the layer system 10 according to the invention in the wavelength range between 280 nm and 1400 nm, and Fig. 4 shows a detail of the representation in Fig. 3 in the wavelength range 380 nm to 780 nm. The reflectivity R of the layer system 10 is measured in top view of the layer system 10, i.e. at small angles AOI around 0° from the surface normal 70 ( Fig. 1, Fig. 2), determined.

[0096] Fig. Figure 5 shows a gradient of chromaticity C* depending on the viewing angle AOI between 0° and 45°. Fig. Figure 6 shows a brightness L* profile depending on the viewing angle AOI between 0° and 45°. Fig. Figure 7 shows a progression of the hue angle h depending on the viewing angle AOI between 0° and 45°. Fig. Figure 8 shows a course of the photopic reflectance Rv and the scotopic reflectance Rv' depending on the viewing angle AOI between 0° and 45°.

[0097] The reflectivity R drops from about 55% at 280 nm with a small maximum around 380 nm and slowly increases again at about 730 nm ( Fig. 3) As can be seen, the reflectivity R is very low between 480 nm and 780 nm and is below 1% ( Fig. 4) Between 530 nm and 730 nm, the reflectivity R is sometimes even below 0.5%.

[0098] In the AOI interval between 0° and 45°, the chroma C* drops from about 6.5 at 0° to about 2.5 at 30°, before increasing ( Fig. 5).

[0099] In the AOI interval between 0° and 25°, the brightness L* hardly varies with a slight decrease and increases from about L*=4.5 at 30° to about L*=8 at 45° ( Fig. 6).

[0100] In the AOI interval between 0° and 45°, the hue angle h decreases slightly between 0° and 30° from about h=272° to just over h=268° and then drops more steeply to h=260° at AOI=40° ( Fig. 7).

[0101] For the residual reflection color blue, the change Δh of the hue angle h between 0° ≤ AOI ≤ 30° is preferably at most Δh = 4°, and particularly preferably at most Δh = 3.5°. The change of the hue angle h between 0° ≤ AOI ≤ 33° is preferably at most Δh = 5°, and particularly preferably at most Δh = 4.5°.

[0102] In the AOI interval between 0° and 45°, the curves of the photopic reflectance Rv and the scotopic reflectance Rv' do not vary practically and remain at 0.5 (Rv) and 0.7-0.6 (Rv') respectively, and rise to a value of 1 between AOI=30° and 45° ( Fig. 8).

[0103] The Fig. Figures 9 to 14 show values ​​of a layer system 10 according to the invention with the residual reflection color green.

[0104] Fig. Figure 9 shows a reflectivity R of the layer system 10 according to the invention in percent in the wavelength range between 280 nm and 1400 nm, and Fig. Figure 10 shows a detail of the representation in Fig. 9 in the wavelength range 380 nm to 780 nm. The reflectivity R of the layer system 10 is measured in top view of the layer system 10, i.e. at small angles AOI around 0° from the surface normal 70 ( Fig. 1, Fig. 2), determined.

[0105] Fig. Figure 11 shows a gradient of chromaticity C* depending on the viewing angle AOI between 0° and 45°. Fig. Figure 12 shows a brightness L* profile depending on the viewing angle AOI between 0° and 45°. Fig. Figure 13 shows a progression of the hue angle h depending on the viewing angle AOI between 0° and 45°. Fig. Figure 14 shows a course of the photopic reflectance Rv and the scotopic reflectance Rv' depending on the viewing angle AOI between 0° and 45°.

[0106] The reflectivity R drops from about 55% at 280 nm with a small maximum around 380 nm and slowly increases again at about 730 nm ( Fig. 9) As can be seen, the reflectivity R is very low between 430 nm and 730 nm and is below 1% ( Fig. 11). At 530 nm and between about 600 nm and about 700 nm, the reflectivity R is sometimes even below 0.5%.

[0107] In the AOI interval between 0° and 45°, the chroma C* increases from approximately C*=5 at 0° to approximately C*=6 at 30°, increases slightly further, and then drops at 40°. Fig. 11).

[0108] In the AOI interval between 0° and 30°, the brightness L* is almost constant at L*=5.5 and begins to increase at 25°, reaching L*=10 at 45° ( Fig. 12).

[0109] In the AOI interval between 0° and 45°, the hue angle h is almost constant between 0° and 20° at approximately h=147° and begins to increase slightly from 20° to just over h=155° at AOI=40° ( Fig. 13).

[0110] For the residual reflection color green, the change Δh of the hue angle h between 0° ≤ AOI ≤ 30° is preferably at most Δh = 5°, particularly preferably Δh = 2°. The change Δh of the hue angle h between 0° ≤ AOI ≤ 45° is preferably at most Δh = 5°, particularly preferably at most Δh = 4.6°.

[0111] In the AOI interval between 0° and 45°, the curves for photopic reflectance Rv and scotopic reflectance Rv' are practically identical and remain almost constant between 0° and 30°, both at 0.6 (Rv) and 0.7–0.6 (Rv'), respectively. Between AOI = 30° and 45°, the curves rise to a value of 1.5 ( Fig. 14).

[0112] The Fig. Figures 15 to 20 show values ​​of a layer system 10 according to the invention with the residual reflection color yellow.

[0113] Fig. Figure 15 shows a reflectivity R in percent of the layer system 10 according to the invention in the wavelength range between 280 nm and 1400 nm, and Fig. Figure 16 shows a detail of the representation in Fig. 9 in the wavelength range 380 nm to 780 nm. The reflectivity R of the layer system 10 is measured in top view of the layer system 10, i.e. at small angles AOI around 0° from the surface normal 70 ( Fig. 1, Fig. 2), determined.

[0114] Fig. Figure 17 shows a gradient of chromaticity C* depending on the viewing angle AOI between 0° and 45°. Fig. Figure 18 shows a brightness gradient L* depending on the viewing angle AOI between 0° and 45°. Fig. Figure 19 shows a progression of the hue angle h depending on the viewing angle AOI between 0° and 45°. Fig. Figure 20 shows a course of the photopic reflectance Rv and the scotopic reflectance Rv' depending on the viewing angle AOI between 0° and 45°.

[0115] The reflectivity R drops from about 20% at 280 nm with a slightly higher maximum of just over 30% around 330 nm, then remains low and slowly increases again at about 680° ( Fig. 15) As can be seen, the reflectivity R is very low between 430 nm and 580 nm and is below 1% ( Fig. 16).

[0116] In the AOI interval between 0° and 45°, the chroma C* slowly increases from about 6.5 at 0° to about 8 at 30°, has a maximum of 10 at about 25° and then falls again ( Fig. 17).

[0117] In the AOI interval between 0° and 25°, the brightness L* shows a slight increase of approximately L*=6.5 at 0° and L*=10 at approximately 35°, and then slowly decreases again ( Fig. 18).

[0118] In the AOI interval between 0° and 45°, the hue angle h decreases slightly between 0° and 30° from approximately h=84° to approximately h=83° and then drops more steeply from 35° onwards ( Fig. 19).

[0119] For a residual reflection color yellow, the change Δh of the hue angle h between 0° ≤ AOI ≤ 30° is preferably at most Δh = 1.5°, particularly preferably Δh = 0.9°. The change Δh of the hue angle h between 0° ≤ AOI ≤ 45° is preferably at most Δh = 5°, particularly preferably at most Δh = 4.6°.

[0120] In the AOI interval between 0° and 45°, the curves of the photopic reflectance Rv and the scotopic reflectance Rv' run parallel to each other and rise only slightly up to 20°, remaining at 0.5 (Rv') and 0.7-0.6 (Rv) respectively, and rising to a value of 2 between AOI=30° and 45° ( Fig. 20).

[0121] The Fig. Figures 21 to 26 show values ​​of a layer system 10 according to the invention with the residual reflection color red.

[0122] Fig. Figure 21 shows a reflectivity R in percent of the layer system 10 according to the invention in the wavelength range between 280 nm and 1400 nm, and Fig. 22 shows a detail of the representation in Fig. 9 in the wavelength range 380 nm to 780 nm. The reflectivity R of the layer system 10 is measured in top view of the layer system 10, i.e. at small angles AOI around 0° from the surface normal 70 ( Fig. 1, Fig. 2), determined.

[0123] Fig. Figure 23 shows a gradient of chromaticity C* depending on the viewing angle AOI between 0° and 45°. Fig. Figure 24 shows a brightness gradient L* depending on the viewing angle AOI between 0° and 45°. Fig. Figure 25 shows a progression of the hue angle h depending on the viewing angle AOI between 0° and 45°. Fig. Figure 26 shows a course of the photopic reflectance Rv and the scotopic reflectance Rv' depending on the viewing angle AOI between 0° and 45°.

[0124] The reflectivity R shows a maximum of about 20% around 330 nm, then drops to low values ​​and slowly increases again at about 530 nm ( Fig. 21). As can be seen, the reflectivity R between 430 nm and 600 nm is very low and is below 0.5% ( Fig. 22).

[0125] In the AOI interval between 0° and 45°, the chroma C* increases from approximately C*=4 at 0° to approximately C*=9 at 30°, and then remains constant between 35° and 45° ( Fig. 23).

[0126] In the AOI interval between 0° and 25°, the brightness L* hardly varies with a slight increase from about L*=3 and rises from about L*=4 at 20° to about L*=14 at 45° ( Fig. 24).

[0127] In the AOI interval between 0° and 45°, the hue angle h increases slightly between 0° and 30° from about h=10° to slightly over h=16° and then rises more steeply to h=20° at AOI=40° ( Fig. 25).

[0128] For a residual reflection color red, the change Δh of the hue angle h between 0° ≤ AOI ≤ 30° is preferably at most Δh = 6°, particularly preferably at most Δh = 5.3°. The change Δh of the hue angle h between 0° ≤ AOI ≤ 45° is preferably Δh = 20°, particularly preferably at most Δh = 16.8°.

[0129] In the AOI interval between 0° and 45°, the curves of the photopic reflectance Rv and the scotopic reflectance v' do not vary practically between 0° and 20° and both start at 0.35, while the curve (Rv) rises more sharply than the curve (Rv'). They rise to a value of 1 between AOI=30° and 45° ( Fig. 26).

[0130] Table 1 below shows, by way of example, the layer thicknesses of a layer system with four layer packages 42, 44, 46, 48: Table 1 Layer thicknesses of sublayers 60, 62 for different residual reflection colors. BlauDicke[nm] GrünDicke[nm] GelbDicke[nm] RotDicke[nm] Luft 34 Deckschicht 48 62 SiO2 81,7 70,7 62 71 64 Funktionsschicht 12 16,6 12 12 60 Ta2O5 119,2 103 136 72 46 62 SiO2 17,6 19,1 9 13,48 60 Ta2O5 27,4 24,6 72 3,5 44 62 SiO2 49,7 75,9 6,7 4 60 Ta2O5 20,1 12 62 29,4 42 62 SiO2 54,9 64,3 28,8 41 60 Ta2O5 7,5 5 20 5 32 Zwischenschicht 20 Substrat

[0131] It can be seen that, with constant layer materials of high-refractive-index sublayer 60 closer to the substrate and low-refractive-index sublayer 62 further away from the substrate, the color of the residual reflection can be achieved solely by changing the layer thicknesses of the sublayers 60 and 62. For example, Ta2O5 is used for all high-refractive-index sublayers 60 and SiO2 for the low-refractive-index sublayers 62.

[0132] Only in the layer package 48 furthest from the substrate is a preferably low-refractive-index functional layer 64 arranged between the first and second sublayers 60, 62. This serves, for example, to increase electrical conductivity and / or to equalize mechanical stresses and / or as a diffusion barrier.

[0133] The difference between the results on the inventive layer systems 10 with the residual reflection colors blue, green, yellow, red and the residual reflection color of a known layer system from the prior art for a viewing angle interval of 0° to 30° is in Fig. 27 is shown in a representation in polar coordinates. Fig. Figure 28 shows the same representation with a larger viewing angle interval from 0° to 45°.

[0134] In these two polar diagrams, the color angle h is the angle of the diagram from 0° to 360° and the hue C* is given as a radius with values ​​from 0 to 14.

[0135] Here, BL denotes the course of the residual reflection color blue, GR the course of the residual reflection color green, GE the course of the residual reflection color yellow, RO the course of the residual reflection color red and PR the course of the residual reflection color of a layer system according to the state of the art.

[0136] The small arrows next to the measurement points indicate the direction of change in the AOI viewing angle from 0° to 30° or 0° to 45°. Fig. 28. The measured values ​​of the different residual reflection colors of the layer system 10 according to the invention run practically along straight lines through the center of the diagram. In this diagram, the straight lines represent the different residual reflection colors.

[0137] For a typical residual reflection color of green at 0° of a commercially available spectacle lens with a reflection-reducing coating according to the state of the art, the change Δh of the hue angle h between 0° ≤ AOI ≤ 30° is typically Δh = 127.2°. The color of the residual reflection changes from green through blue to red.

[0138] The change in hue angle h between 0°≤AOI≤45° is typically 161.7°.

[0139] For the residual reflection color blue, the change Δh of the hue angle h between 0° ≤ AOI ≤ 30° is preferably at most Δh = 4°, and particularly preferably at most Δh = 3.5°. The change Δh of the hue angle h between 0° ≤ AOI ≤ 33° is preferably at most Δh = 5°, and particularly preferably at most Δh = 4.5°.

[0140] For a residual reflection color green, the change Δh of the hue angle h between 0° ≤ AOI ≤ 30° is preferably at most Δh = 3°, and particularly preferably at most Δh = 2°. The change Δh of the hue angle h between 0° ≤ AOI ≤ 45° is preferably at most Δh = 5°, and particularly preferably at most Δh = 4.6°.

[0141] For a residual reflection color yellow, the change Δh of the hue angle h between 0° ≤ AOI ≤ 30° is preferably at most Δh = 1.5°, and particularly preferably at most Δh = 0.9°. The change Δh of the hue angle h between 0° ≤ AOI ≤ 45° is preferably at most Δh = 5°, and particularly preferably at most Δh = 4.6°.

[0142] For a residual reflection color red, the change Δh of the hue angle h between 0° ≤ AOI ≤ 30° is preferably at most Δh = 6°, and particularly preferably at most Δh = 5.3°. The change Δh of the hue angle h between 0° ≤ AOI ≤ 45° is preferably at most Δh = 20°, and particularly preferably at most Δh = 16.8°.

[0143] Fig. Figure 29 shows a flowchart of a favorable method for designing an optical element 100 according to the invention.

[0144] In the method for designing an optical element 100 according to the invention, a layer design is defined in step S100. The layer design comprises at least a first material for high-refractive-index sublayers 60 and a second material for low-refractive-index sublayers 62, the number of desired layer packages 42, 44, 46, 48, or 42, 44, 46, 48, 50 with the sublayers 60, 62, the initial thickness values ​​of the sublayers 60, 62, and the like.

[0145] In step S102, target color values ​​are defined. These target color values ​​include brightness L*, chroma C*, and hue h, at least at their limit values ​​for an interval of an AOI viewing angle with limit values ​​of 0° and 30°. Optionally, a reflection curve can be specified as an optimization parameter; however, specifying the target color values ​​at the limit values ​​of the 0° and 30° viewing angles is preferred.

[0146] In step S104, an optimization procedure is performed to vary the individual layer thicknesses until an optimization goal is reached. The optimization procedure then continues to vary the individual layer thicknesses until the optimization goal (color stability) is achieved.

[0147] Advantageously, the target color values ​​are chosen to be the same or as similar as possible at the limits of the interval, preferably allowing only the aforementioned changes Δh of the hue angle h.

[0148] Typically, a modified simplex algorithm can be used as the computational method, but other well-known simulation methods may be equally suitable. Simulation software for such optimization methods is commercially available from various vendors, for example, the commercial simulation software "Essential MacLeod" or other well-known simulation software for the fabrication of optical layers.

Claims

[1] Optical element (100) comprising a substrate (20) and an interferometric reflection-reducing layer system (10) on at least one surface (22) of the substrate (20), wherein the layer system (10) comprises a stack (40) of at least four successive layer packages (42, 44, 46, 48), wherein each layer package (42, 44, 46, 48) comprises a first sublayer (60) with a first optical thickness (t1) and a second sublayer (62) with a second optical thickness (t2) different from the first optical thickness (t1), wherein a refractive index (n1) of the first sublayer (60) closer to the substrate is greater than a refractive index (n2) of the second sublayer (62) further away from the substrate of the stack (40), wherein the first sublayer (60) is made of Ta2O5 and the second sublayer (62) is made of SiO2, wherein the layer system (10) has a brightness (L*), a chroma (C*) and a hue angle (h) of a residual reflection color, characterized by , that the magnitude of a change (Δh) of the hue angle (h) of the residual reflection color in an interval of a viewing angle (AOI) with limit values ​​of 0° and 30° relative to a surface normal (70) to the layer system (10) is smaller than the magnitude of a change (ΔC*) of the chroma (C*) in the interval of the viewing angle (AOI), where for four layer packages (42, 44, 46, 48) with a blue residual reflection color, in the lowest, first layer package (42) the first sublayer (60) has a thickness of 7.5 nm and the second sublayer (62) has a thickness of 54.9 nm, in the following second layer package (44) the first sublayer (60) has a thickness of 20.1 nm and the second sublayer (62) has a thickness of 49.7 nm, in the following third layer package (46) the first sublayer (60) has a thickness of 27.4 nm and the second sublayer (62) has a thickness of 17.6 nm, and in the following fourth layer package (48) the first sublayer (60) has a thickness of 119.2 nm and the second sublayer (62) has a thickness of 81.7 nm, or with a green residual reflection color in the lowest, first layer package (42), the first sublayer (60) has a thickness of 5 nm and the second sublayer (62) has a thickness of 64.3 nm, in the following second layer package (44) the first sublayer (60) has a thickness of 12 nm and the second sublayer (62) has a thickness of 75.9 nm, in the following third layer package (46) the first sublayer (60) has a thickness of 24.6 nm and the second sublayer (62) has a thickness of 19.1 nm, and in the following fourth layer package (48) the first sublayer (60) has a thickness of 103 nm and the second sublayer (62) has a thickness of 70.7 nm, or with a yellow residual reflection color in the lowest, first layer package (42), the first sublayer (60) has a thickness of 20 nm and the second sublayer (62) has a thickness of 28.8 nm, in the following second layer package (44) the first sublayer (60) has a thickness of 62 nm and the second sublayer (62) has a thickness of 6.7 nm, in the following third layer package (46) the first sublayer (60) has a thickness of 72 nm and the second sublayer (62) has a thickness of 9 nm, and in the following fourth layer package (48) the first sublayer (60) has a thickness of 136 nm and the second sublayer (62) has a thickness of 62 nm, or with a red residual reflection color in the lowest, first layer package (42) the first sublayer (60) has a thickness of 5 nm and the second sublayer (62) has a thickness of 41 nm, in the following second layer package (44) the first sublayer (60) has a thickness of 29.4 nm and the second sublayer (62) has a thickness of 4 nm, in the following third layer package (46) the first sublayer (60) has a thickness of 3.5 nm and the second sublayer (62) has a thickness of 13.48 nm, and in the following fourth layer package (48) the first sublayer (60) has a thickness of 72 nm and the second sublayer (62) has a thickness of 71 nm. [2] Optical element according to claim 1, characterized by , that the hue angle (h) in the interval of the viewing angle (AOI) with the limit values ​​0° and 30° changes by a maximum of 15°. [3] Optical element according to claim 1 or 2, characterized by, that the magnitude of the change (Δh) of the hue angle (h) in a second interval of an AOI from 0° to a limiting AOI with upper limits of 30° to 45° relative to the surface normal (70) to the layer system (10) is less than the magnitude of a change (ΔC*) of the hue (C*) in the second interval of the AOI and the magnitude of the hue (C*) at the limiting AOI is at least 2. [4] Optical element according to claim 3, characterized by , that the hue angle (h) in the second interval changes by at most 20°. [5] Optical element according to any of the preceding claims, characterized by , that the photopic reflectance (Rv) in the interval of the viewing angle (AOI) with the limit values ​​0° and 30° is at most 1.5%. [6] Optical element according to any of the preceding claims, characterized by, that the scotopic reflectance (Rv') in the interval of the viewing angle (AOI) with the limit values ​​0° and 30° is at most 1.2%. [7] Optical element according to any of the preceding claims, characterized by , that at least the first sublayers (60) are formed from the same first material and the second sublayers (62) are formed at least predominantly from the same second material.

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