Optical system including light control film and Fresnel lens - Patents.com

Abstract

The optical system includes a light source, an optical film curved about a first axis, and a light control film curved about the first axis and disposed between the light source and the optical film. The optical film includes a microstructured first major surface and an opposite-facing second major surface. The microstructured first major surface defines a linear Fresnel lens including a plurality of Fresnel elements extending longitudinally along the first axis. The first major surface of the optical film faces the light control film. The light control film includes a plurality of alternating optically transmissive and optically absorbing regions extending longitudinally along the first axis, and in a cross section perpendicular to the first axis, for at least a majority of the optically transmissive regions, a centerline between adjacent optically absorbing regions is substantially perpendicular to the major surface of the light control film.

Description

[Background technology]

[0001] Light control films can contain alternating optically transmissive and optically absorbing regions and can be used to adjust the directionality of light transmitted through the film.

[0002] The display surface can be curved. Summary of the Invention

[0003] In some aspects, the present disclosure provides an optical system including a light source, an optical film curved about a first axis, and a light control film curved about the first axis and disposed between the light source and the optical film. The optical film includes a microstructured first major surface and an oppositely facing second major surface. The microstructured first major surface defines a linear Fresnel lens including a plurality of Fresnel elements extending longitudinally along the first axis. The first major surface of the optical film faces the light control film. The light control film includes a plurality of alternating optically transmissive and optically absorbing regions extending longitudinally along the first axis, and in a cross section perpendicular to the first axis, for at least a majority of the optically transmissive regions, a centerline between adjacent optically absorbing regions is substantially perpendicular to the major surface of the light control film.

[0004] In some aspects, the present disclosure provides an optical system including an optical film curved around a first axis and a light control film curved around the first axis and disposed proximate to the optical film. The optical film includes a microstructured first major surface and a second major surface facing the opposite side. The microstructured first major surface defines a linear Fresnel lens including a plurality of Fresnel elements extending longitudinally along the first axis. Each Fresnel element includes an optical facet and a sidewall intersecting the optical facet at a ridge of the Fresnel element. For at least a majority of the Fresnel elements, an optical absorption layer is disposed on and can substantially cover the sidewall. The optical absorption layer can have an average thickness t, where 100 nm < t < 1 micrometer. The first major surface of the optical film faces the light control film. The light control film includes a plurality of alternating optical transmission regions and optical absorption regions extending longitudinally along the first axis, and in a cross-section orthogonal to the first axis, for at least a majority of the optical transmission regions, a center line between adjacent optical absorption regions is substantially perpendicular to the major surface of the light control film.

Brief Description of the Drawings

[0005] [Figure 1] It is a schematic cross-sectional view of an optical system. [Diagram 2] It is a schematic cross-sectional view of an optical system. [Diagram 3] It is a schematic cross-sectional view of an optical system. [Figure 4] It is a schematic cross-sectional view of an optical laminate including an optical film and a light control film. [Diagram 5] It is a schematic cross-sectional view of an optical laminate including an optical film and a light control film. [Figure 6] It is a schematic cross-sectional view of an optical laminate including an optical film and a light control film. [Figure 7] It is a schematic cross-sectional view of an optical system schematically showing the shapes of an optical film and a light control film according to some embodiments. [Figure 8]1 is a schematic cross-sectional view of an optical system, illustrating the geometry of an optical film and a light control film according to some embodiments. [Figure 9] FIG. 2 is a schematic top view of a linear Fresnel lens. [Figure 10] FIG. 2 is a schematic top view of a light control film. [Figure 11] 1 is a schematic cross-sectional view of an optical film including a plurality of Fresnel elements. [Figure 12] 1 is a schematic cross-sectional view of a portion of an optical film including a plurality of Fresnel elements. [Figure 13] 1 is a schematic cross-sectional view of a portion of an optical film including a plurality of Fresnel elements. [Figure 14] 1 is a schematic cross-sectional view of a portion of an optical film including a plurality of Fresnel elements. [Figure 15] 1 is a schematic cross-sectional view of a portion of an optical film including a plurality of Fresnel elements. [Figure 16] 1 is a schematic cross-sectional view of a portion of an optical film including a plurality of Fresnel elements. [Figure 17] 1 is a schematic cross-sectional view of a portion of an optical film including a plurality of Fresnel elements. [Figure 18] FIG. 2 is a schematic cross-sectional view of a Fresnel element. [Figure 19] FIG. 2 is a schematic cross-sectional view of a Fresnel element. [Figure 20] FIG. 2 is a schematic cross-sectional view of a Fresnel element. [Figure 21] FIG. 2 is a schematic diagram of mean deviation surface roughness. [Figure 22] 1 is a plot of relative luminance versus position for various viewing angles. [Diagram 23] 1 is a plot of relative luminance versus position for various viewing angles. [Figure 24] 1 is a plot of relative luminance versus position for various viewing angles. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] In the following description, reference is made to the accompanying drawings which form a part hereof, and in which various embodiments are shown by way of illustration. The drawings are not necessarily to scale. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the specification. Accordingly, the following detailed description is not to be taken in a limiting sense.

[0007] Light control films, which may also be referred to as collimating films or privacy filters, can be used to adjust the directionality of the light transmitted through the film. Light control films can be placed on curved displays, for example, to filter the light output of the display. However, it is typically desirable to change the direction of the transmitted light (e.g., so that the light is directed primarily toward the viewer, rather than primarily along the normal to the display surface), as compared to using a conventional light control film placed on a curved display surface. This can be done by changing the slope of the louvers (e.g., optically absorbing regions) of the light control film, as described in U.S. Provisional Patent Application No. 62 / 865,510, entitled "Curved Display with Light Control Film," filed June 24, 2019. Alternatively, linear Fresnel lenses can be placed on conventional light control films to change the direction of the transmitted light. However, it has been found that this can result in undesirable bright bands at higher viewing angles. It has been found that, according to some embodiments herein, a Fresnel lens can be positioned in an optical system such that the Fresnel element faces the light control film, thereby reducing or substantially eliminating the bright bands at higher viewing angles.

[0008] Furthermore, it has been found that, according to some embodiments, an optically absorbing layer can be disposed on the sidewalls of the Fresnel element to reduce undesired redirection of light by the sidewalls. It has been found that by utilizing a thin optically absorbing layer, the undesired effects of the optically absorbing layer (e.g., blocking light incident on the edge of the layer that is desired to be transmitted) can be reduced. When the optically absorbing layer is thin, it is preferable that it has a relatively high extinction coefficient in order to efficiently absorb light. In some cases, a high extinction coefficient can create a reflective metal-like interface with the sidewall. It has been found that adding a cladding layer (e.g., a layer with an extinction coefficient smaller than the optically absorbing layer and larger than the sidewall material) between the high extinction coefficient absorbing layer and the sidewall can reduce reflectivity, thereby reducing undesired redirection of light by the sidewalls.

[0009] 1-3 are schematic cross-sectional views of optical systems 100, 200, and 300, respectively. Optical systems 100, 200, 300 include an optical film 110 curved about a first axis (z-axis) and a light control film 120 curved about the first axis. Optical film 110 includes a microstructured first major surface 112 and an oppositely facing second major surface 114. Microstructured first major surface 112 defines a linear Fresnel lens 111 including a plurality of Fresnel elements 115 extending longitudinally along the first axis. Light control film 120 can be disposed proximate optical film 110, with first major surface 112 of optical film 110 facing light control film 120. In some embodiments, the optical system includes a light source 130. The light control film 120 can be disposed between the light source 130 and the optical film 110, with a first major surface 112 of the optical film 110 facing the light control film 120. The light control film 120 includes a plurality of alternating optically transmissive regions 122 and optically absorbing regions 124 extending longitudinally along a first axis, and in a cross section perpendicular to the first axis (xy cross section), for at least a majority of the optically transmissive regions 122, a centerline 126 between adjacent optically absorbing regions is substantially perpendicular (e.g., within 20 degrees, or within 10 degrees, or within 5 degrees of perpendicular) to the major surfaces 128 and / or 129 of the light control film 120. The Fresnel lens 111 can be configured such that light 866 emitted from the light source 130 perpendicular to the light emitting surface of the light source is redirected by the Fresnel lens in substantially the same redirected direction (y direction).

[0010] The microstructured surface generally includes microstructures (e.g., the Fresnel elements 115 can be microstructures), which are structures having at least two orthogonal dimensions, such as width and height less than 1 mm and greater than 100 nm. The microstructures can be formed in a polymer layer. The polymer layer is a layer that includes a continuous phase of an organic polymer. The polymer layer can also include, for example, inorganic nanoparticles dispersed in the continuous phase of an organic polymer. The polymer microstructured layer can be formed on the substrate using a casting and curing process, as known in the art (see, for example, U.S. Patent Application Publication No. 2006 / 0114569 (Capaldo et al.) and U.S. Patent No. 5,175,030 (Lu et al.), and U.S. Patent No. 5,183,597 (Lu)). Other methods for making polymer structured layers include extrusion, machining, and embossing. Any suitable material can be used. For example, an acrylate (eg, polymethyl methacrylate) can be cast and cured onto a polyester (eg, polyethylene terephthalate) substrate.

[0011] The light control film 120 can be any suitable light control film, including, for example, those described in U.S. Pat. No. 8,213,082 (Gaides et al.), U.S. Pat. No. 9,335,449 (Gaides et al.), and U.S. Pat. No. 9,063,284 (Jones et al.), as well as, for example, those described in WO 2019 / 118685 (Schmidt et al.).

[0012] In some embodiments (e.g., as shown for optical system 100), light source 130 is or includes an organic light emitting diode (OLED) display 132 curved about a first axis. Alternatively, display 132 can be another type of light emitting display, such as a micro light emitting diode (microLED) display. In some embodiments (e.g., as shown for optical systems 200, 300), light source 130 includes backlight 134. In some embodiments, backlight 134 includes a light guide 136 curved about a first axis. In some embodiments, light source 130 further includes one or more light emitting elements 135 (e.g., light emitting diode(s)). Backlight 134 can be, for example, a direct-lit backlight or an edge-lit backlight. In some embodiments (e.g., as illustrated for optical system 200), the optical system can include a display panel 139 disposed between backlight 134 and light control film 120. In some embodiments (e.g., as illustrated in optical system 300), the optical system can include a display panel 139, with the optical film 110 disposed between the display panel 139 and the light control film 120.

[0013] In some embodiments, an air gap 178 separates at least a majority of the first major surface 112 of the optical film 110 from the light control film 120. The air gap can be provided, for example, by not bonding the optical film 110 and the light control film 120 together, by bonding the films together only at one or more edges, or by attaching the films together using elongated spacer members.

[0014] 4 is a schematic cross-sectional view of an optical system, or a portion of an optical system, including an optical stack 400 that includes an optical film 110 and a light control film 120. In some embodiments, the optical film 110 and the light control film 120 are taped together (e.g., with tape 176 or 177) at least along an edge 171 or 172, respectively, of the optical film 110 and a corresponding edge 181 or 182, respectively, of the light control film. In some embodiments, the optical film 110 and the light control film 120 are taped together along at least two edges 171 and 172, respectively, of the optical film 110 and a corresponding edge 181 and 182, respectively, of the light control film. Taping together along the edges should be understood to include tape being applied proximate to the edges along at least a portion (e.g., at least a majority) of the length of the edges.

[0015] FIG. 5 is a schematic cross-sectional view of an optical system, or a portion of an optical system, including an optical stack 500 including an optical film 210 and a light control film 120. The optical film 210 may correspond to the optical film 110, except that the first major surface 212 of the optical film 210 includes a plurality of elongated spacer members 142. In some embodiments, the first major surface 212 of the optical film 210 includes a plurality of elongated spacer members 142 extending toward the light control film 120 and received by an adhesive layer 144 disposed on the light control film 120. The elongated spacer members 142 may be formed together with the Fresnel elements 115, or may be deposited after the Fresnel elements 115 are formed. The elongated spacer members 142 may also be referred to as optical isolation structures, and may have any of the geometries of the optical isolation structures described, for example, in WO 2019 / 135190 (Pham et al.).

[0016] 6 is a schematic cross-sectional view of an optical system, or a portion of an optical system, including an optical stack 600 including an optical film 110 and a light control film 120. The optical system or optical stack 600 further includes a low index layer 148 disposed on and in contact with at least a majority of the first major surface 112 of the optical film 110, and an optical adhesive 144 bonding the low index layer 148 to the light control film 120. In some embodiments, the low index layer 148 has a refractive index of 1.45 or less, or 1.4 or less, or 1.35 or less, or 1.25 or less, or 1.2 or less. For example, the refractive index of the low index layer 148 can be in the range of 1.05 to 1.45, or in the range of 1.1 to 1.35, or in the range of 1.1 to 1.25, or in the range of 1.05 to 1.2. The low refractive index layer 148 can be, for example, a nanovoided polymer layer as described in U.S. Patent No. 8,808,811 (Kolb et al.). In some embodiments, the low refractive index layer 148 is an adhesive and the adhesive layer 144 is omitted.

[0017] Optical film 110, or a layer of optical film 110 including Fresnel element 115, or a Fresnel element, can have a refractive index greater than 1.5, or greater than 1.6, or greater than 1.7, for example.

[0018] In some embodiments, the optical film 110 and the light control film 120 are substantially concentric. For example, the optical film 110 and the light control film 120 can have a substantially similar shape and can be substantially coextensive with one another.

[0019] In some embodiments, an optical system (e.g., 100, 200, or 300) is adapted to display an image 888 to an observer 870 (see, e.g., FIG. 1), where in a cross section perpendicular to a first axis, optical film 110 and light control film 120 are each convex toward observer 870. Optical film 110 and light control film 120 may alternatively have different shapes as shown diagrammatically in FIGS. 7-8. FIG. 7 is a schematic cross-sectional view of an optical system 700 including optical film 810 (e.g., corresponding to optical film 110) and light control film 820 (e.g., corresponding to light control film 120) and adapted to display an image 888 to observer 870, where in a cross section perpendicular to a first axis (z-axis), optical film 810 and light control film 820 are each concave toward observer 870. FIG. 8 is a schematic cross-sectional view of an optical system 800 including an optical film 910 (e.g., corresponding to optical film 110) and a light control film 920 (e.g., corresponding to light control film 120) and adapted to display an image 888 to an observer 870, in which in a cross section perpendicular to a first axis, a first portion of each of the optical film 910 and the light control film 920 (910a and 920a, respectively) is concave toward the observer 870, and a second portion of each of the optical film 910 and the light control film 920 (910b and 920b, respectively) is convex toward the observer 870.

[0020] In the embodiments shown generally in Figures 1-10, the Fresnel elements of the optical film and / or the optically transmissive and optically absorbing regions of the light control film can extend along a first axis (z-axis). In some embodiments, the first major surface 112 of the optical film 110 defines a linear Fresnel lens 111 including Fresnel elements 115 extending longitudinally along the first axis (z-axis). Figure 9 is a schematic top view (facing the first major surface 112) of the linear Fresnel lens 111 when the optical film 110 is laid flat, according to some embodiments. Figure 10 is a schematic top view of the light control film 120 when the light control film 120 is laid flat, according to some embodiments. In some embodiments, the light control film 120 includes a plurality of alternating optically transmissive regions 122 and optically absorbing regions 124 extending longitudinally along the first axis (z-axis).

[0021] In some embodiments, each Fresnel element 115 of optical film 110 includes an optical facet 117 and a sidewall 118 that meets the optical facet 117 at a ridge 119 of the Fresnel element. In some embodiments, each Fresnel element in at least a majority of the Fresnel elements 115 includes at least a partial coating (e.g., a conformal coating) of an inorganic optically transparent layer, an optically absorbing layer, a first layer disposed between the optically absorbing layer and the sidewall, which may be less optically absorbing than the optically absorbing layer, and a second layer disposed on the optically absorbing layer opposite the sidewall, which may be less optically absorbing than the optically absorbing layer and may be one or more of a protective layer or an antireflective layer.

[0022] FIG. 11 is a schematic cross-sectional view of an optical film 310, which may correspond to optical film 110. In some embodiments, each Fresnel element 115 includes an optical facet 117 and a sidewall 118 that intersects with the optical facet 117 at a ridge 119 of the Fresnel element. In some embodiments, for each Fresnel element in at least a majority of the Fresnel elements, an optically absorbing layer 152 is disposed on and substantially covers the sidewall 118. In some embodiments, the plurality of Fresnel elements includes a plurality of polymeric Fresnel elements 334 at least partially coated (e.g., conformally coated) with an inorganic optically transparent layer 157 (see, e.g., FIG. 13). In some embodiments, for each Fresnel element in at least a majority of the Fresnel elements, an optically absorbing layer 152 is disposed on and substantially covers the inorganic optically transparent layer 157 disposed on the sidewall 118.

[0023] As further described elsewhere herein, the inorganic optically transparent layer may be used as an etch stop in a process for removing an optically absorbing layer and / or other layers from an optical facet. Suitable materials for the inorganic optically transparent layer include, for example, a-Si, SiOx, SiAlOx, SiCyOx, TiO2, and AlOx. The layer may be thin enough that, for example, more than 60% of normally incident visible light is transmitted through the layer. A layer may be considered optically transparent if it has an average optical transmission (average unweighted for unpolarized wavelengths) of visible light (wavelengths between 400 nm and 700 nm) normally incident on the layer in air that is at least 60%. In some embodiments, the average optical transmission of the inorganic optically transparent layer is greater than 60%, or greater than 70%, or greater than 80%, or greater than 85%, or greater than 90%.

[0024] In some embodiments, the optical absorption layer 152 has an average thickness t, where 100 nm < t < 2 micrometers, or 100 nm < t < 1 micrometer. In some embodiments, the average thickness t is less than 500 nm. In some embodiments, for each Fresnel element 115a in at least a majority of the Fresnel elements 115 (e.g., of the optical film 110, 210, or 310), the sidewall 118 of the Fresnel element 115a has a height H from the base 185 of the adjacent Fresnel element 115b to the ridge 119 of the Fresnel element 115a, and H / t > 10, or H / t > 15, or H / t > 18, or H / t > 20.

[0025] (For example, in some embodiments of the optical film 110, 210, or 310), for each Fresnel element in at least a majority of the Fresnel elements, the sidewall 118 of the Fresnel element is substantially perpendicular to the second major surface 114 (e.g., within 30 degrees of perpendicular, or within 20 degrees of perpendicular, or within 10 degrees of perpendicular, or within 5 degrees of perpendicular). In some embodiments, the optical film 110, 210, or 310 includes a substrate 164, and the plurality of Fresnel elements 115 are formed on the major surface 162 of the substrate 164. In some embodiments, for each Fresnel element in at least a majority of the Fresnel elements, the sidewall 118 of the Fresnel element is substantially perpendicular to the major surface 162 of the substrate 164. In some embodiments, the sidewall 118 forms an angle within the range of 85 - 90 degrees with the major surface 162 or the major surface 114 or the base of the Fresnel element, or within other ranges described elsewhere in this specification.

[0026] FIG. 12 is a schematic cross-sectional view of a portion of an optical film (corresponding to, for example, optical films 110, 210, or 310). In some embodiments, for each of at least a majority of the Fresnel elements 115, the first layer 154 is disposed between the sidewall 118 and the optical absorption layer 152. The first layer 154, which may be referred to as a cladding layer, may be included to reduce the reflection of light at the interface between the sidewall and the optical absorption layer 152. In some embodiments, the first layer 154 has an absorption coefficient k1 and the optical absorption layer 152 has an absorption coefficient k2. In some embodiments, k2>k1. In some embodiments, the plurality of Fresnel elements have an absorption coefficient k0<0.05. In some embodiments, k2>k1>k0. The absorption coefficient k0 can be understood to be the absorption coefficient of the material at the first major surface 112 that defines the Fresnel element. In some embodiments, k2 - k1 is greater than 0.05, greater than 0.1, greater than 0.15, or greater than 0.2. In some embodiments, k2 - k1 is less than 1, or less than 0.8, or less than 0.5. In some embodiments, k1 - k0 is greater than 0.001, greater than 0.005, or greater than 0.01. In some embodiments, k1 - k0 is less than 0.15, or less than 0.1, or less than 0.05. In some embodiments, k0 is less than 0.01, or less than 0.005, or less than 0.002. In some embodiments, k1 is in the range of 0.005 to 0.15, or 0.01 to 0.1. In some embodiments, k2 is in the range of 0.1 to 0.5, or 0.2 to 0.4. In some embodiments, k1<0.5×k2. In some embodiments, 0.005<k1<0.5×k2. Instead of, or in addition to, describing the first layer 154 and the optical absorption layer 152 in terms of absorption coefficient, those layers can be described in terms of the concentration of the optical absorption material, as further described elsewhere in this specification.

[0027] In some embodiments, the optical absorption layer 152 has a refractive index n1 and the first layer 154 has a refractive index n2, and |n1 - n2| is less than 0.5 or less than 0.3 or less than 0.2 or less than 0.1.

[0028] The extinction coefficient can be expressed as the imaginary part of the birefringence and the refractive index can be expressed as the real part of the birefringence. The extinction coefficient and refractive index can be understood to be evaluated at a wavelength of 550 nm unless otherwise indicated.

[0029] For example, the extinction coefficient k of a thin film coating can be determined, for example, by either ellipsometry or spectroscopy, where k can be expressed as αλ / (4π), where α is the absorption coefficient and λ is the wavelength. For a thin film coating on a transparent substrate, spectroscopy can be used to measure the absorptance A as 100%-TR, where T is the transmittance and R is the reflectance. The measured A can be appropriately corrected for the A of the substrate to obtain the A of the thin film itself. The resulting A can then be used to determine α according to the formula α=-ln[(100%-A) / 100%] / h, where h is the thickness of the thin film coating, this formula for α being an approximation used when R is relatively small and A is relatively large. The thickness h can be measured, for example, by stylus profilometry or cross-sectional scanning electron microscopy.

[0030] The light absorbing material of the optically absorbing layer 152 and / or the first layer 154 can be one or more of a dye, a pigment, or a particle (e.g., nanoparticles). Suitable light absorbing materials include carbon black nanopigments and other nanopigments such as those available from Cabot Corporation (Boston, MA) under the trade name CAB-O-JET. Other suitable light absorbing materials include those described in WO 2019 / 118685 (Schmidt et al.).

[0031] In some embodiments, first layer 154 has light absorbing material 184 with a concentration C1, and optically absorbing layer 152 has light absorbing material 182 with a concentration C2, where C2>C1. In some embodiments, C1<0.7×C2 or C1<0.5×C2.

[0032] The concentration of light absorbing material (e.g., light absorbing nanoparticles) in the optical absorbing layer can be at least 10, 15, 20, 25, 30, 35, 40, 45, or 50% by weight of the optical absorbing layer. In some embodiments, the concentration of light absorbing material in the optical absorbing layer is at least 55, 60, 65, 70, 75, 80, 85, 90, or 95% by weight of the optical absorbing layer. In some embodiments, the concentration of light absorbing material in the optical absorbing layer is 100% by weight. In some embodiments, the concentration of light absorbing material in the optical absorbing layer is 30-100% or 75-90% by weight of the optical absorbing layer.

[0033] The concentration of the light absorbing material in the first layer (cladding layer) is preferably lower than the concentration of the light absorbing material in the optically absorbing layer. The concentration of the light absorbing material in the first layer is typically at least 0.5, 1, 5, 10, 15, 20, 25, 30, 35, 40, or 45% by weight of the first layer. In some embodiments, the concentration of the light absorbing material in the first layer is no more than 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, or 75% by weight of the first layer. In some embodiments, the concentration of the light absorbing material in the first layer is 0.5-50% by weight, or 25-45% by weight of the first layer.

[0034] In some embodiments, the light control film 120 is generally as described, for example, in WO 2019 / 118685 (Schmidt et al.). In some such embodiments, the optically absorbing layer of the louver includes an optically absorbing core layer and a cladding layer on each side of the optically absorbing core layer. The optically absorbing core layer can be as described for optically absorbing layer 152, and the cladding layer can be as described for first layer 154. The use of the cladding layer can reduce the reflectivity of the louver, thereby reducing high angle light leakage and ghosting. Light control films including a core layer and a cladding layer are described in WO 2019 / 056489 (Schmidt et al.).

[0035] 13-17 are schematic cross-sectional views of a portion of an optical film (e.g., corresponding to optical film 110, 210, or 310). In some embodiments, as shown generally in FIG. 13, for example, a plurality of Fresnel elements 115 includes a microstructured polymer layer 333 conformally coated with an inorganic optically transparent layer 157. The inorganic optically transparent layer 157 can include oppositely facing first and second major surfaces 167 and 166, with the second major surface 166 facing the polymer layer 333. The polymer layer 333 has a major surface 113 facing the substrate layer 164. In some embodiments, as shown generally in FIG. 14, for example, for each Fresnel element in at least a majority of the Fresnel elements 115, an optically absorbing layer 152 is disposed on and substantially covers the inorganic optically transparent layer 157 disposed on the sidewall 118. In some embodiments, for example, for each Fresnel element in at least a majority of the Fresnel elements 115, the first layer 154 is disposed between the sidewall 118 and the optically absorbing layer 152, as shown generally in FIG. 15. In some embodiments, for example, the first layer 154 is omitted, as shown generally in FIG. 14. In some embodiments, for example, for each Fresnel element in at least a majority of the Fresnel elements 115, the second layer 156 is disposed on the optically absorbing layer 152 opposite the sidewall 118 or opposite the first layer 154, as shown generally in FIG. 16. The second layer 156 may be, for example, a protective layer and / or an anti-reflective layer. The second layer may be similar to those generally described for the first layer 154 (e.g., having an average thickness and / or extinction coefficient and / or concentration of optically absorbing material within the ranges described for the first layer 154). The inorganic optically transparent layer 157 may be optionally omitted.

[0036] In some embodiments, for example, the microstructured surface 168 is only partially coated (e.g., only on the sidewalls) with the inorganic optically transparent layer 157, as shown generally in FIG. 17. For example, the inorganic optically transparent layer may be conformally coated on the microstructured surface 168 and then removed (or at least partially removed) from the optical facets. In any of the embodiments shown in FIGS. 13-16, the inorganic optically transparent layer 157 may optionally be removed or partially removed (e.g., a thin layer may remain) from the optical facets, for example. In some embodiments, the first major surface 112 of the optical film may include a major surface of the inorganic optically transparent layer 157 (e.g., surface 167 of the plurality of sidewalls 118). In some embodiments, the Fresnel elements 115 of the at least partially coated microstructured surface may include optical facets that are part of the microstructured surface 168 of the polymer layer 333, and may include sidewalls that are part of the major surface of the inorganic optically transparent layer 157. Alternatively, the Fresnel element 115 can be considered to include optical facets and sidewalls that are part of the microstructured surface 168 of the polymer layer 333, and the inorganic optically transparent layer 157 can be considered to be a coating on the sidewalls of the polymer microstructures.

[0037] In some embodiments, the optical film includes a polymer layer 333 including a microstructured surface 168 at least partially coated with an inorganic optically transparent layer 157. The at least partially coated microstructured surface 177 (which may include the optical facets 117 and the surface 167 of the inorganic optically transparent layer 157 on the sidewalls) includes a plurality of Fresnel elements 115. Each Fresnel element 115 includes an optical facet 117 and a sidewall 118 that meets the optical facet 117 at a ridge 119 of the Fresnel element 115. The optical facet 117 and the sidewall 118 may define an oblique angle therebetween. For each Fresnel element 115 in at least a majority of the Fresnel elements, an optically absorbing layer 152 is disposed on and substantially covers the sidewall 118.

[0038] In some embodiments, the optical film includes a polymer layer 333 including a major surface 168 that includes a plurality of Fresnel elements. Each Fresnel element includes an optical facet (e.g., 117) and a sidewall (e.g., a portion of the major surface 168 facing the sidewall portion of the inorganic optically transparent layer 157) that meets the optical facet at a ridge of the Fresnel element. The optical facet and the sidewall can define an oblique angle therebetween. For each Fresnel element in at least a majority of the Fresnel elements, the inorganic optically transparent layer 157 is disposed on and substantially covers the sidewall, and an optically absorbing layer 152 is disposed on the inorganic optically transparent layer 157 opposite the sidewall, with the optically absorbing layer 152 substantially covering the inorganic optically transparent layer 157.

[0039] In some embodiments, the inorganic optically transparent layer 157 may be provided on the sidewalls along with other layer(s), such as an optically absorbing layer, as follows: the inorganic optically transparent layer may be conformally coated on the microstructured polymer layer, the optically absorbing layer (and optionally other layers) may be conformally coated on the inorganic optically transparent layer, the optically absorbing layer (and optionally other layers) may be removed from the optical facet in a first etching step, and then the inorganic optically transparent layer may be removed or partially removed from the optical facet in a second etching step. The first and second etching steps may utilize different etchants (e.g., an oxygen-only plasma for the first etching step, and a fluorinated or other halogenated gas for the second etching step), for example, to remove the desired layer(s) in the corresponding etching step.

[0040] In some embodiments, for each Fresnel element in at least a majority of the Fresnel elements 115, the first layer 154 has an average thickness t1 and the optically absorbing layer 152 has an average thickness t2. In some embodiments, t1 and t2 are each greater than 100 nm and less than 2 micrometers, or less than 1 micrometer, or less than 500 nm. In some embodiments, t1 and t2 are each less than 500 nm. In some embodiments, for each Fresnel element in at least a majority of the Fresnel elements 115, the sidewall 118 of the Fresnel element has a height H from the base of the adjacent Fresnel element to the ridge 119 of the Fresnel element. In some embodiments, H / t1>10, or H / t1>12, or H / t1>15, or H / t1>18, or H / t1>20. In some embodiments, H / t1<100. In some embodiments, H / t2>10, or H / t2>12, or H / t2>15, or H / t2>18, or H / t2>20. In some embodiments, H / t2<100. For example, in some embodiments, H / t1>15 and H / t2>15.

[0041] In some embodiments, for each Fresnel element in at least a majority of the Fresnel elements, the optical facets 117 are planar (e.g., as in a typical conventional Fresnel lens). FIG. 18 is a schematic diagram of a Fresnel element having planar optical facets 217, where the sidewalls 218 of the Fresnel element form an angle φ with the base 285 of the Fresnel element. In other embodiments, for each Fresnel element in at least a majority of the Fresnel elements 115, the optical facets 117 are curved. For example, the facets may be curved to tune various optical properties, for example, as described in U.S. Statutory Invention Registration No. H423 (Mohon et al.). The optical facets 117 may be curved, for example, as shown generally in FIG. 19 for curved optical facets 317 (concave toward sidewalls 218 and / or toward base 285 and / or toward major surface 114 (see, e.g., FIG. 1 )) or as shown generally in FIG. 20 for curved optical facets 417 (convex toward sidewalls 218 and / or toward base 285 and / or toward major surface 114). The angle φ in FIGS. 18-20 may be, for example, in the range of 80 degrees to 90 degrees or 85 degrees to 90 degrees. In some embodiments, φ is less than 90 degrees (e.g., 85 to 89.5 degrees), for example, due to manufacturing constraints.

[0042] FIG. 21 is a schematic view of the average deviation surface roughness Ra of surface 517, which can be the surface of an optical facet. The average deviation surface roughness Ra is the average of the absolute values of the deviations of the surface height from the average surface height (e.g., the average over a length in a cross-section through the facet (e.g., a cross-section orthogonal to the length of the facet)). For a curved facet, the deviation of the surface height can be defined with respect to the average or nominal curved surface. In some embodiments, for each of the at least majority of the Fresnel elements 115, the optical facet 117 has an average deviation surface roughness Ra < 250 nm. In some embodiments, Ra is less than 200 nm, less than 150 nm, less than 100 nm, less than 70 nm, less than 50 nm, less than 30 nm, or less than 20 nm. In some embodiments, Ra is greater than 50 nm, greater than 70 nm, or greater than 90 nm. For example, in some embodiments, 50 nm < Ra < 200 nm, or 70 nm < Ra < 200 nm. In some applications, it is desirable for the optical facet 117 to be optically smooth (e.g., Ra < 50 nm). In other applications, some surface roughness (e.g., 50 nm < Ra < 250 nm or 90 nm < Ra < 200 nm) may be desirable. For example, for anti-reflection, to provide (e.g., weak) optical diffusion, and / or to improve coupling, it can be useful to have some surface roughness. By using the process described in International Publication No. WO 2019 / 118685 (Schmidt et al.) to deposit and remove the optical absorption layer from the inclined facets, a surface roughness higher than desired for many applications (e.g., Ra greater than 300 nm or greater than 400 nm) can be obtained, even if the same process applied to horizontal facets results in low surface roughness. However, it has been found that the surface roughness (e.g., Ra) can be reduced (e.g., to less than 250 nm or less than 200 nm) by carefully controlling the time the optical facet is exposed to the plasma, for example, in a reactive ion etching process.Furthermore, it has been found that by applying an inorganic optically transparent layer as an etch stop before applying the optically absorbing layer (and / or other layers), the surface roughness can be further reduced and optically smooth optical facets (e.g., Ra<50 nm) can be obtained, even with long etch times. The root mean square surface roughness Rq can also be determined and can be anywhere within the ranges described for Ra.

[0043] Surface roughness can be determined from a profiled surface measured, for example, by atomic force microscopy (AFM), stylus profilometry, or optical profilometry. AFM is typically preferred for small surface roughness (e.g., less than 50 nm).

[0044] The inorganic optically transparent layer, the first layer (e.g., cladding layer), the optically absorbing layer, and / or the second layer (e.g., protective layer) can be deposited (e.g., as a conformal coating over the structured surface) using any suitable deposition technique. For example, a variety of coating methods can be used, including layer-by-layer (LbL) coating, chemical vapor deposition (CVD), sputtering, reactive sputtering, and atomic layer deposition (ALD). At least some of the deposited layers (e.g., all of the layers, or all of the layers except the optional inorganic optically transparent layer) can then be substantially removed from the optical facet (e.g., at least to the extent that any material of at least some of the deposited layers remaining on the optical facet does not significantly affect optical performance).

[0045] In some embodiments, at least one of the first layer and the optically absorbing layer comprises at least two bilayers deposited by what is commonly referred to as a "layer-by-layer self-assembly process." This process is widely used to electrostatically assemble oppositely charged polyelectrolyte films or coatings, although other functional groups such as hydrogen bond donors / acceptors, metal ions / ligands, and covalently bonded moieties can be the driving force for assembling the film. Some examples of suitable processes include those described in U.S. Pat. No. 8,234,998 (Krogman et al.) and U.S. Pat. No. 8,313,798 (Nogueira et al.), U.S. Patent Application Publication No. 2011 / 0064936 (Hammond-Cunningham et al.), and WO 2019 / 118685 (Schmidt et al.). Layer-by-layer dip coating can be performed, for example, using a StratoSequence VI (nanoStrata Inc., Tallahassee, FL) dip coating robot.

[0046] In some embodiments, the multiple bilayers deposited by layer-by-layer self-assembly are polyelectrolyte stacks that include organic polymeric polyions (e.g., cations) and counterions (e.g., anions) that include a light-absorbing material (e.g., a pigment). At least a portion of the cationic layer, anionic layer, or a combination thereof may include a light-absorbing material (e.g., a pigment) ionically bonded to the polyelectrolyte. The light-absorbing compound may be dispersed within at least a portion of the polyelectrolyte layer. A variety of polyelectrolytes may be utilized, including inorganic compounds such as silica or silicates, and various phosphonocarboxylic acids and their salts, some of which are described in U.S. Pat. No. 10,365,415 (Schmidt).

[0047] The bilayer thickness and number of bilayers can be selected to achieve the desired optical properties (e.g., optical absorptivity in the case of an optically absorbing layer, or reduced reflectivity between the sidewall and the optically absorbing layer in the case of the first layer). In some embodiments, the bilayer thickness and / or number of bilayers are selected to achieve the desired optical properties using a minimum total thickness of the self-assembled layer and / or a minimum number of layer-by-layer deposition steps. The thickness of the individual bilayers is typically in the range of about 5 nm to 350 nm. The number of bilayers is typically at least 5, 6, 7, 8, 9, or 10. In some embodiments, the number of bilayers per stack is 150 or less or 100 or less. It should be understood that the individual bilayers in the final article may not be distinguishable from one another by methods common in the art, such as scanning electron microscopy (SEM) or transmission electron microscopy (TEM). In some embodiments, the thickness of the bilayers and the total number of bilayers are selected such that the total thickness of the first layer and the optically absorbing layer is less than 2 micrometers.

[0048] After the optically absorbing layer, and optionally the first and / or second layers, and / or the inorganic optically transparent layer, are applied to the (e.g., entire) microstructured surface of the film and dried, the optically absorbing layer and the first and second layers, if present, are removed from the optical facets and may also be removed from the land areas between adjacent Fresnel elements. The inorganic optically transparent layer, which may function as an etch stop, is typically not removed, but may optionally be removed in a subsequent etching step.

[0049] Any suitable method can be used to selectively remove the layer(s) from the optical facet. In some embodiments, the layer(s) are removed by reactive ion etching. Reactive ion etching (RIE) is a directional etching process that utilizes ion bombardment to remove material. RIE systems are used to remove organic or inorganic materials by etching the surface in the direction of the ion bombardment. The most notable difference between reactive ion etching and isotropic plasma etching is the etch direction. Reactive ion etching is characterized by a ratio of vertical to lateral etch rate that is greater than 1. Systems for reactive ion etching are typically built around a durable vacuum chamber. Before starting the etching process, the chamber is evacuated to a base pressure that is typically less than 1 Torr, less than 100 mTorr, less than 20 mTorr, less than 10 mTorr, or less than 1 mTorr. Typically, an electrode holds the material to be processed and is electrically insulated from the vacuum chamber. The electrode may be a cylindrically shaped rotatable electrode. Typically, a counter electrode is also provided in the chamber, which may include the vacuum reactor wall. Gases, including etchants, typically enter the chamber through a control valve. The process pressure may be maintained by continuously evacuating the chamber gases via a vacuum pump. The type of gas used varies depending on the etching process. Etchants may include, for example, one or more of oxygen, fluorinated gases, or other halogenated gases. Etchants typically include carbon tetrafluoride (CF4), sulfur hexafluoride (SF6), octafluoropropane (C3F8), perfluorohexane (C6F 14 ), fluoroform (CHF3), boron trichloride (BCl3), hydrogen bromide (HBr), nitrogen trifluoride (NF3), chlorine, argon, and oxygen are used. Radio frequency (RF) power is applied to the electrodes to generate a plasma. Reactive ion etching is known in the art and is further described, for example, in U.S. Pat. No. 8,460,568 (David et al.) and WO 2019 / 118685 (Schmidt et al.).

[0050] The plasma may transport the sample over the electrode for a controlled period of time to achieve a particular etch depth or to limit the etch so that it does not penetrate below the layer or layers desired to be removed. For example, if it is desired to remove an optically absorbing layer and no inorganic optically transparent layers are included, the period may be adjusted to minimize the time that the optical facet may be exposed to the plasma. This may reduce the surface roughness of the optical facet (e.g., Ra<250 nm), as described elsewhere.

[0051] In some embodiments, the optically absorbing layer (and / or other layers) are removed by laser ablation, e.g., pulsed laser ablation. Pulsed laser ablation (PLA) is a directional ablation process that utilizes a photon flux to generate sufficient photon fluence to remove material by oxidation and / or sputtering. PLA systems are used to remove organic or inorganic materials by etching the surface in the direction of the photon fluence that can vaporize the target in the generation of a plasma plume. PLA depends on the wavelength of the laser and the amount of absorption present at that wavelength in the optically absorbing material. Absorption of the laser pulse creates energy for thermal, chemical, or mechanical evaporation, ablation, and / or plasma formation. The presence of oxidizing gases at the location of the laser pulse can change the amount of chemical oxidation that occurs during the PLA process. The fluence can be changed by optical configurations that change the size and position of the focal spot, as well as by power settings of the laser system. Depending on the laser fluence and the relative orientation of the sample, one skilled in the art can ablate an optically absorbing layer coated on a structured surface at an oblique angle.

[0052] An example of an optical film including microstructures, each having an optical facet and a sidewall that intersects with the optical facet at a ridge of the microstructure, with an optically absorbing layer disposed on the sidewalls but not on the optical facets, is described in U.S. patent application Ser. No. 62 / 932,578, filed Nov. 8, 2019, and entitled "OPTICAL FILM."

[0053] Below is a list of exemplary embodiments of the present specification.

[0054] A first embodiment is an optical system comprising: A light source; an optical film including a first major surface curved about a first axis and microstructured and an oppositely facing second major surface, the microstructured first major surface defining a linear Fresnel lens including a plurality of Fresnel elements extending longitudinally along the first axis; a light control film curved about a first axis and disposed between the light source and the optical film, a first major surface of the optical film facing the light control film, the light control film including a plurality of alternating optically transmissive and optically absorbing regions extending longitudinally along the first axis, wherein in a cross section perpendicular to the first axis, for at least a majority of the optically transmissive regions, a centerline between adjacent optically absorbing regions is substantially perpendicular to the major surface of the light control film; An optical system comprising:

[0055] A second embodiment is the optical system of the first embodiment, wherein the light source comprises a backlight.

[0056] A third embodiment is the optical system according to the second embodiment, wherein the backlight comprises a light guide curved about the first axis.

[0057] A fourth embodiment is the optical system according to the second or third embodiment, further comprising a display panel disposed between the backlight and the light control film.

[0058] A fifth embodiment is the optical system according to any one of the first to third embodiments, further comprising a display panel, and the optical film is disposed between the display panel and the light control film.

[0059] A sixth embodiment is the optical system of the first embodiment, wherein the light source comprises an organic light emitting diode (OLED) display curved about the first axis.

[0060] A seventh embodiment is an optical system according to any one of the first to sixth embodiments, wherein the plurality of Fresnel elements comprises a plurality of polymer Fresnel elements at least partially coated with an inorganic optically transparent layer.

[0061] An eighth embodiment is the optical system of the seventh embodiment, wherein each Fresnel element comprises an optical facet and a sidewall that intersects the optical facet at a ridge of the Fresnel element, and for each Fresnel element in at least a majority of the Fresnel elements, an optically absorbing layer is disposed on the inorganic optically transparent layer disposed on the sidewall and substantially covering the inorganic optically transparent layer.

[0062] A ninth embodiment is the optical system of any one of the first to eighth embodiments, wherein an air gap separates at least a majority of the first major surface of the optical film from the light control film.

[0063] A tenth embodiment is an optical system described in any one of the first to ninth embodiments, in which the optical film and the light control film are taped to each other at least along the edges of the optical film and the corresponding edges of the light control film.

[0064] An eleventh embodiment is an optical system described in any one of the first to ninth embodiments, in which the first main surface of the optical film has a plurality of elongated spacer members extending toward the light control film and received by an adhesive layer disposed on the light control film.

[0065] The 12th embodiment is a low refractive index layer that is disposed on and in contact with at least a majority of the first main surface of the optical film and has a refractive index of 1.45 or less; an optical adhesive that bonds the low refractive index layer to the light control film; and is the optical system according to any one of the first to ninth embodiments, further comprising

[0066] The 13th embodiment is an optical film including a first main surface that is curved around a first axis and is microstructured, and a second main surface facing the opposite side, wherein the microstructured first main surface defines a linear Fresnel lens including a plurality of Fresnel elements extending longitudinally along the first axis, each Fresnel element includes an optical facet and a side wall intersecting the optical facet at a ridge of the Fresnel element, and for each Fresnel element in at least a majority of the Fresnel elements, an optical absorption layer is disposed on and substantially covers the side wall, the optical absorption layer has an average thickness t, and 100 nm < t < 1 micrometer; a light control film that is curved around the first axis and is disposed close to the optical film, wherein the first main surface of the optical film faces the light control film, the light control film includes a plurality of alternating optical transmission regions and optical absorption regions extending longitudinally along the first axis, and in a cross section perpendicular to the first axis, for at least a majority of the optical transmission regions, a center line between adjacent optical absorption regions is substantially perpendicular to the main surface of the light control film; and is an optical system comprising

[0067] The 14th embodiment is the optical system according to the 13th embodiment, wherein for each Fresnel element in at least a majority of the Fresnel elements, the side wall of the Fresnel element has a height H from the base of the adjacent Fresnel element to the ridge of the Fresnel element, and H / t > 15.

[0068] A 15th embodiment is the optical system according to the 13th or 14th embodiment, wherein the plurality of Fresnel elements have an extinction coefficient k0<0.05, and for each Fresnel element in at least a majority of the Fresnel elements, a first layer is disposed between the sidewall and the optically absorbing layer, the first layer having an extinction coefficient k1>k0, and the optically absorbing layer having an extinction coefficient k2, where k2-k1>0.05.

[0069] Working Example Optical modeling was performed for an optical system as generally shown in Figure 1, and for a comparison optical system in which a Fresnel lens was disposed on the light control film with the Fresnel facets facing away from the light source 130. The light source surface was taken to have a parabolic shape in cross section perpendicular to the z axis, with the shape being referenced to the xyz coordinate system of Figure 1 as follows:

number

[0070] All references, patents, or patent applications referenced above are hereby incorporated by reference in their entirety. In the event of any inconsistency or contradiction between any portion of the incorporated reference and this application, the information in the foregoing description shall take precedence.

[0071] Descriptions of elements in a figure should be understood to apply equally to corresponding elements in other figures unless otherwise indicated. Although specific embodiments have been illustrated and described herein, those skilled in the art will appreciate that the specific embodiments illustrated and described may be replaced by various alternative and / or equivalent embodiments without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Accordingly, it is intended that the present disclosure be limited only by the claims and the equivalents thereof.

Claims

1. 1. An optical system comprising: A light source; an optical film including a first major surface curved about a first axis and microstructured and an oppositely facing second major surface, the microstructured first major surface defining a linear Fresnel lens including a plurality of Fresnel elements extending longitudinally along the first axis; a light control film curved about the first axis and disposed between the light source and the optical film, the first major surface of the optical film facing the light control film, the light control film including a plurality of alternating optically transmissive and optically absorbing regions extending longitudinally along the first axis, wherein in a cross section perpendicular to the first axis, for at least a majority of the optically transmissive regions, a centerline between adjacent optically absorbing regions is within 20 degrees of a normal to a major surface of the light control film; An optical system comprising:

2. The optical system of claim 1 , wherein the light source comprises a backlight.

3. The optical system of claim 2 , wherein the backlight comprises a light guide curved about the first axis.

4. The optical system of claim 2 further comprising a display panel disposed between the backlight and the light control film.

5. The optical system of claim 1 further comprising a display panel, the optical film being disposed between the display panel and the light control film.

6. The optical system of claim 1 , wherein the light source comprises an organic light emitting diode (OLED) display curved about the first axis.

7. The optical system of claim 1 , wherein the plurality of Fresnel elements comprises a plurality of polymer Fresnel elements at least partially coated with an inorganic optically transparent layer.

8. 8. The optical system of claim 7, wherein each Fresnel element comprises an optical facet and a sidewall that meets the optical facet at a ridge of the Fresnel element, and for each Fresnel element in at least a majority of the Fresnel elements, an optically absorbing layer is disposed on the inorganic optically transparent layer disposed on the sidewall and covers the inorganic optically transparent layer.

9. The optical system of claim 1 , wherein an air gap separates at least a majority of the first major surface of the optical film from the light control film.

10. The optical system of any one of claims 1 to 9, wherein the optical film and the light control film are taped together at least along an edge of the optical film and a corresponding edge of the light control film.

11. The optical system of claim 1 , wherein the first major surface of the optical film comprises a plurality of elongated spacer members extending toward the light control film and received by an adhesive layer disposed on the light control film.

12. a low refractive index layer disposed on and in contact with at least a majority of the first major surface of the optical film, the low refractive index layer having a refractive index of 1.45 or less; an optical adhesive that bonds the low refractive index layer to the light control film; The optical system of claim 1 further comprising:

13. 1. An optical system comprising: an optical film comprising a first major surface curved about a first axis and microstructured and an oppositely facing second major surface, the microstructured first major surface defining a linear Fresnel lens comprising a plurality of Fresnel elements extending longitudinally along the first axis, each Fresnel element comprising an optical facet and a sidewall that intersects the optical facet at a ridge of the Fresnel element, and for each Fresnel element in at least a majority of the Fresnel elements an optically absorbing layer is disposed on and covers the sidewall, the optically absorbing layer having an average thickness t, where 100 nm<t<1 micrometer; a light control film curved about the first axis and positioned proximate to the optical film, the first major surface of the optical film facing the light control film, the light control film including a plurality of alternating optically transmissive and optically absorbing regions extending longitudinally along the first axis, and in a cross section perpendicular to the first axis, for at least a majority of the optically transmissive regions, a centerline between adjacent optically absorbing regions is within 20 degrees of a normal to a major surface of the light control film; An optical system comprising:

14. 14. The optical system of claim 13, wherein for each Fresnel element in at least the majority of the Fresnel elements, the sidewall of the Fresnel element has a height H from a base of an adjacent Fresnel element to the ridge of the Fresnel element, where H / t>15.

15. 14. The optical system of claim 13, wherein the plurality of Fresnel elements have an extinction coefficient k0<0.05, and for each Fresnel element in at least the majority of the Fresnel elements a first layer is disposed between the sidewall and the optically absorbing layer, the first layer having an extinction coefficient k1>k0, and the optically absorbing layer having an extinction coefficient k2, where k2-k1>0.05.

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