Optical stack and housing for electronic device

Abstract

Optical stacks and housings for electronic devices are provided. A housing for an electronic device includes an optical film having a band edge separating a first wavelength range and a second wavelength range for optical transmittance of substantially normally incident light, where the first wavelength range extends from about 400 nm to about 700 nm, and the second wavelength range is at least about 100 nm wide and disposed between about 800 nm and about 1100 nm. The optical film has an average optical reflectance in the first wavelength range that is greater than about 90% for substantially normally incident light, and an average optical transmittance in the second wavelength range that is greater than about 80% for substantially normally incident light. The optical film transmits at least about 95% of incident radiation for at least one frequency in a range of about 0.1 Ghz to about 90 GHz and for substantially normally incident radiation. An optical stack can include the optical film.

Description

BACKGROUND

[0001] Electronic devices often include housings that can provide a desired appearance. SUMMARY

[0002] This specification generally relates to optical stacks that can be included in a housing or cover and housings for electronic devices. The housing includes an optical film bonded to an optically transparent rigid substrate. In some embodiments, the optical film has a high reflectivity (e.g., greater than about 90%) in the visible wavelength range, a high transmissivity (e.g., greater than about 80%) in the near infrared wavelength range, a large slope (e.g., greater than about 2% per nanometer (nm)) of the band edge separating the visible wavelength range and the near infrared range, and a high transmissivity (e.g., at least about 95%) for at least one frequency in a range of about 0.1 gigahertz (GHz) to about 90 GHz. Optical stacks including the optical film and at least another layer are also provided. For example, the optical layer included in the optical stack can be a tint layer or an optical diffusive layer.

[0003] In some aspects of the specification, a housing for an electronic device is provided. The housing includes an optical film bonded to an optically transparent rigid substrate. The optical film includes a band edge separating a first wavelength range and a second wavelength range for optical transmissivity of light for substantially normal incidence and for at least one polarization state, where the first wavelength range extends from about 400 nm to about 700 nm, the second wavelength range is at least about 100 nm wide and disposed between about 800 nm and about 1100 nm. The average optical reflectivity of the optical film in the first wavelength range is greater than about 90% for light for substantially normal incidence and for at least one polarization state, and the average optical transmissivity of the optical film in the second wavelength range is greater than about 80% for light for substantially normal incidence and for at least one polarization state. A best linear fit to the band edge having a slope greater than about 2% per nm of an optical transmissivity of the optical film associated with a wavelength spanning at least a range of wavelengths in which the optical transmissivity of the optical film increases from about 10% to about 70%. In some embodiments, the optical film transmits at least about 95% of the incident radiation for at least one frequency in a range of about 0.1 Ghz to about 90 GHz and for radiation for substantially normal incidence. In some embodiments, the dielectric loss tangent of the optical film is less than about 0.02 for at least one frequency in a range of about 0.1 Ghz to about 90 GHz; and the optical film reflects less than about 5% of the incident radiation for radiation for substantially normal incidence.

[0004] In some aspects of this specification, an optical stack is provided. The optical stack includes an optical film comprising a plurality of alternating polymer first layers and polymer second layers disposed on a surface layer, wherein the average thickness of each of the first and second layers is less than about 250 nm, and the average thickness of the surface layer is greater than about 2 micrometers. The first and second layers, as well as the surface layer, are integrally formed with each other. The optical transmittance of the optical film for substantially normally incident light and for at least one polarization state includes a band edge separating a first wavelength range and a second wavelength range, wherein the first wavelength range extends from about 400 nm to about 700 nm, and the second wavelength range is at least about 100 nm wide and disposed between about 800 nm and about 1100 nm. For substantially normally incident light and for at least one polarization state, the optical film has an average optical reflectance greater than about 90% in the first wavelength range, and an average optical transmittance greater than about 80% in the second wavelength range. The optimal linear fit between the optical transmittance of the optical film and the band edge, relating the optical transmittance to the wavelengths described below, has a slope greater than about 2% / nm, spanning at least a wavelength range in which the optical transmittance of the optical film increases from about 10% to about 70%. The optical stack includes an optical layer disposed on and substantially co-extended with the optical film, such that, for substantially normally incident light and for at least one polarization state, the optical layer has an optical absorption rate for a first wavelength in the first wavelength range that is at least 20% higher than the optical absorption rate for a second wavelength in the first wavelength range. The optical stack has an optical transmittance greater than about 60% for substantially normally incident light and for at least one polarization state for a third wavelength in the second wavelength range.

[0005] In some aspects of this specification, an optical stack is provided, which includes an optical film bonded to an optically transparent rigid substrate. The optical film comprises a plurality of polymer layers arranged along at least a portion of the thickness of the optical film and numbered sequentially from 1 to N, where N is an integer greater than about 100. The plurality of polymer layers includes polymer end layers at each end. A graph of the average layer thickness versus the number of layers of the plurality of polymer layers includes a first bend region separating a left region comprising at least N1 sequentially arranged polymer layers with smaller layer numbers from a middle region comprising at least N2 sequentially arranged polymer layers with larger layer numbers, where N1 is an integer greater than about 50 and N2 is an integer greater than about 10. This is such that a linear fit for the at least N1 sequentially arranged polymer layers in the left region has a positive linear slope with a value greater than about 0.04 nm per layer, where the r-squared value is greater than about 0.8, and a linear fit for the at least N2 sequentially arranged polymer layers in the middle region has a negative linear slope with a value greater than about 0.05 nm per layer, where the r-squared value is greater than about 0.8.

[0006] These and other aspects will become apparent from the detailed description that follows. However, in no way should this brief overview be construed as limiting the subject matter for which protection may be claimed. Attached Figure Description

[0007] Figure 1 It is a schematic cross-sectional view of an illustrative electronic device.

[0008] Figure 2 This is a schematic cross-sectional view of the illustrative back cover.

[0009] Figure 3 This is a schematic cross-sectional view of an illustrative optical film.

[0010] Figure 4 This is a schematic graph illustrating the optical transmittance of an illustrative optical film.

[0011] Figure 5 It is an illustrative graph of the average layer thickness versus the number of layers of multiple polymer layers, wherein the graph has a bend that separates the middle region from the right region.

[0012] Figures 6-9 It shows Figure 5 The part of the curve graph.

[0013] Figure 10 It is an illustrative graph of the average layer thickness versus the number of layers of multiple polymer layers, wherein the graph has a bend that separates the left and right regions.

[0014] Figures 11-12 It shows Figure 10 The part of the curve graph.

[0015] Figure 13 It is an illustrative graph of the average layer thickness versus the number of layers for multiple polymer layers according to some implementation schemes.

[0016] Figures 14-16 It shows Figure 13 The part of the curve graph.

[0017] Figure 17 This is a schematic illustrative graph showing the average layer thickness versus the number of layers, representing a portion of multiple polymer layers.

[0018] Figure 18 It is an illustrative graph of the optical transmittance of the optical film versus wavelength.

[0019] Figure 19 yes Figure 18 A portion of the graph.

[0020] Figure 20 It is a graph of optical transmittance versus wavelength for optical films according to some implementation schemes.

[0021] Figures 21-23 yes Figure 20 The part of the curve graph.

[0022] Figure 24 It is a graph showing the transmission of the illustrative optical film.

[0023] Figures 25A-25B This is a graph showing the return loss S11 of the illustrative optical film.

[0024] Figure 26 This is a graph showing the real part of the dielectric constant and the loss tangent of the illustrative optical film as a function of frequency.

[0025] Figure 27 This is a schematic graph illustrating the transmittance of the illustrative optical layer.

[0026] Figure 28 This is a schematic cross-sectional view of the illustrative optical layer.

[0027] Figure 29 It is a schematic graph of optical transmittance through illustrative optical stacking. Detailed Implementation

[0028] Reference is made in the following description to the accompanying drawings, which form part of the invention and illustrate various embodiments by way of example. The drawings are not necessarily drawn to scale. It should be understood that other embodiments may be conceived and practiced without departing from the scope or spirit of this specification. Therefore, the following detailed description should not be considered limiting.

[0029] Electronic devices typically include a housing. The housing is usually the outermost layer of the device and is generally visible to the user of the device. In some cases, it is desirable for the housing to be transmissive to radio waves (e.g., cell phone signals). Sometimes a metallic appearance is desired. For example, it may be desirable for the cover of an electronic device to have a metallic appearance, or for a logo or marking on an electronic device to have a metallic appearance. However, metal is not transmissive to radio waves. In some embodiments, the housing and optical stack described herein can provide a metallic appearance while substantially transmitting radio waves (e.g., at 5G wavelengths). For example, the housing may include a back cover comprising a glass layer and an optical film bonded to the glass layer, wherein the optical film may have high specular reflectivity, thereby producing a metallic appearance. In some embodiments, electronic devices such as smartphones include infrared sensors / transmitters for one or more of proximity detection (e.g., for camera autofocus), light detection and ranging (LiDAR), or temperature detection. In some embodiments, the optical film substantially transmits near-infrared wavelengths used by such sensors / transmitters while having high reflectivity in the visible wavelength range of at least 450 nm to 650 nm or 400 nm to 700 nm.

[0030] Figure 1 This is a schematic cross-sectional view of an electronic device 170 according to some embodiments. The illustrated electronic device 170 includes a display component 175 having a light output area 186 for displaying an image 455 to a viewer 460. The electronic device 170 includes a front cover 184 and a rear cover 180, and a frame 182 extending between the front cover 184 and the rear cover 180. The front cover 184 is disposed on the front side of the electronic device 170 facing the viewer 460, while the rear cover is located on the opposite rear side of the electronic device 170 facing away from the viewer 460. The housing 185 of the electronic device 170 includes the rear cover 180 and the frame 182, and may optionally be considered to include the front cover 184. In some embodiments, the housing may be a single rear cover with a curved three-dimensional design. As further described elsewhere herein, the housing 185 includes an optical film that may be included in a portion of the rear cover 180 and / or the frame 182 and / or the front cover 184. In embodiments of the electronic device having a light output area, it is generally preferred that the optical film substantially does not cover the light output area 186. For example, the optical film may cover less than 10% of the light output area 186, or in some embodiments, the optical film may not cover any of the light output area 186. The optical film may be, for example, a mirror film included to provide a desired appearance to the housing 185, and it is generally not desirable for such a film to cover a portion of the light output area 186.

[0031] In some embodiments, the electronic device includes a visible light element 166 adapted to receive or transmit light. For example, the visible light element 166 may include a camera, a camera flash, or both. In some embodiments, the housing 185 includes a window 168 for allowing visible light to pass through or out of the housing. An optical film is typically not substantially covering the window 168. In some embodiments, the electronic device includes an infrared (IR) light element 169 adapted to receive or transmit infrared light. Infrared light is typically near-infrared light (wavelengths from about 700 nm to about 2000 nm). Near-infrared (NIR) light of interest typically has wavelengths, for example, from about 800 nm to about 1500 nm, or about 1300 nm, or about 1200 nm, or about 1100 nm. In some embodiments, the housing or a portion of the housing covering the IR light element 169 is substantially transparent to NIR wavelengths. In some embodiments, an optical film included in the housing 185 covers or substantially covers the IR light element 169. In some embodiments, the optical film is substantially transparent to NIR wavelengths.

[0032] In some embodiments, electronic device 170 is configured to transmit and / or receive radiation at operating frequencies ranging from about 0.1 GHz to about 90 GHz. For example, electronic device 170 may be a 5G mobile phone. In such embodiments, it is generally desirable that at least a portion of housing 185 (e.g., back cover 180) is substantially transmissive at the operating frequency. Therefore, it is generally desirable that optical films are transmissive at the operating frequency. In some embodiments, the interior of the housing may support a signal transmitter and receiver in the form of an antenna, which is patterned or otherwise placed inside the back cover.

[0033] Figure 2This is a schematic cross-sectional view of a back cover 180 according to some embodiments. The back cover 180 includes an optically transparent rigid substrate 181. A “rigid” substrate is one that is rigid enough that when held horizontally by the edges of the substrate (the shorter edges in the case of a substantially rectangular substrate), the substrate does not deflect substantially (e.g., vertical deflection is less than about 1 / 4 the length of the longer edge). For example, a glass sheet and a sufficiently thick polymer sheet (e.g., polycarbonate, polymethyl methacrylate, or mixtures thereof) are typically rigid substrates, while flexible films are not. In some embodiments, the substrate 181 is a glass substrate with an average thickness of at least 0.5 mm. An “optically transparent” substrate is one that has an average optical transmittance greater than 50% for substantially normally incident unpolarized light. In some embodiments, this average optical transmittance is greater than about 60%, or greater than about 70%, or greater than about 80%. The back cover 180 includes an optical film 100 disposed on the substrate 181. In some embodiments, the optical film 100 is substantially co-extended with the substrate 181. For example, the optical film 100 may cover at least about 80% of the area of ​​the substrate 181. In some embodiments, the optical film 100 covers all of the substrate 181 except for optional edge portions (e.g., near the frame 182). The optical film 100 generally faces the display component 175, while the substrate 181 faces away from the display component 175. For example, the back cover 180 may be as follows: Figure 1 to Figure 2 Oriented as indicated by the xyz coordinate system.

[0034] In the illustrated embodiment, the back cover 180 includes an optional adhesive layer 183, an optional optical layer 210, and an optional optical layer 210'. For example, another adhesive layer may be optionally included between the optical layer 210 and the optical film 100. In some embodiments, the optical layers 210 and / or 210' are coatings applied to the substrate 181 or the optical film 100. The optical layers 210 or 210' may be, for example, color filters, such as dye or pigment layers or ink coatings, or may be, for example, optical diffusers. Suitable dyes or pigments for obtaining the desired color are known in the art. In some embodiments, one of the optical layers 210 and 210' is a color filter, and the other is an optical diffuser. For example, optical layer 210' may be an optical diffuser, and optical layer 210 may be a color filter, or vice versa. For example, a color filter may be included to give the housing a colored metallic appearance, and an optical diffuser layer may be included to customize the appearance of the housing. In some embodiments, one or both optical layers 210, 210' may be patterned layers (e.g., patterned optically absorptive layers). For example, the optical layer may be an ink layer that blocks a portion of the optical film 100 while other portions remain uncovered. The ink layer may have at least 20% optical absorption for at least one visible wavelength (e.g., wavelengths in the range of 400 nm to 700 nm). For layer 210, Figure 2 An optional uncovered portion 293 is schematically shown. For example, the uncovered portion 293 may define a logo or mark. In some embodiments, one of the optical layers 210, 210' is omitted. When optical layers 210 and / or 210' are included, the optical film 100 having optical layers 210 and / or 210' can be described as an optical stack 200. The back cover 180 may optionally include additional optical layers on the optical film 100 disposed opposite the substrate 181. If such additional optical layers are included, they can be considered as part of the optical stack 200. Other optical layers that may be included in the optical stack 200 include, for example, a textured layer.

[0035] Alternatively, the back cover 180 can be considered as an optical stack that can be used in other applications. For example, the optical stack can be used as a front cover for a non-display device or system. The optical stack includes an optical film 100 bonded to an optically transparent rigid substrate 181, wherein the optical film can be any optical film described herein.

[0036] In some embodiments, optical film 100 is a multilayer optical film comprising alternating polymer layers. By appropriately selecting the layer thicknesses, such multilayer optical films can be used to provide desired reflection and transmission within a desired wavelength range. Multilayer optical films and methods for manufacturing multilayer optical films are described, for example, in U.S. Patent Nos. 5,882,774 (Jonza et al.); 6,179,948 (Merrill et al.); 6,783,349 (Neavin et al.); 6,967,778 (Wheatley et al.); and 9,162,406 (Neavin et al.). The layer thickness distribution providing high reflectivity in the visible light range, high transmittance in the near-infrared range, and sharp band edges therebetween is further described elsewhere herein.

[0037] Figure 3 This is a schematic cross-sectional view of an illustrative optical film 100 comprising multiple alternating polymer first layers 101 and polymer second layers 102. In the illustrated embodiment, multiple alternating first layers 101 and second layers 102 are disposed on surface layers 105 and / or 105'. One or both of surface layers 105, 105' may optionally be omitted. The multiple alternating first layers 101 and second layers 102 reflect and transmit light primarily by optical interference and may be referred to as optical layers or interference layers. The optical film 100 may comprise a single group of first layers 101 and second layers 102, which may be referred to as interference layers, or may comprise two or more groups, wherein adjacent groups are separated by an optical thick layer 104, which may have an average thickness Tb greater than about 500 nm or greater than about 1 micrometer. An optical film or an interference layer of an optical film may be described as reflecting and transmitting light primarily by optical interference when reflection and transmission can be reasonably described by optical interference or when reflection and transmission are reasonably and correctly modeled by optical interference. When adjacent pairs of interferometer layers with different refractive indices have a combined optical thickness (refractive index multiplied by physical thickness) that is half the wavelength of light, the interferometer layer pair reflects light through optical interference. The refractive index used to determine the optical thickness can be a fixed reference wavelength (e.g., 532 nm or 633 nm). Interferometer layers typically have a physical thickness of less than about 500 nm, or less than about 300 nm, or less than about 250 nm. Surface layers typically have too large an optical thickness to primarily reflect and transmit light through optical interference, and may be referred to as non-interferometer layers, non-optical layers, or optically thick layers. However, as further described elsewhere in this document, Fresnel reflections from the primary surface of the surface layer (e.g., the outermost primary surface) can affect the transmission spectrum of the optical film.

[0038] The thicknesses of the alternating first and second layers can be selected to give the desired reflective band, and the thickness distribution can be selected to include a large number of layer pairs whose optical thicknesses correspond to the band edges, as further described elsewhere in this document. The appropriate thickness of the surface layer can be determined through optical modeling, for example, where the transmission spectrum can be determined for a range of skin thicknesses. For example, a skin thickness that produces reduced optical ringing can be selected.

[0039] The average thickness t of the interference layer is shown. In some embodiments, the average thickness of each of the first and second layers is less than about 500 nm, or less than about 250 nm, or less than about 200 nm, or less than about 180 nm, or less than about 200 nm, or in the range of 20 nm to 250 nm, or in the range of 25 nm to 200 nm, or in the range of about 30 nm to about 180 nm. The average thickness refers to the unweighted average of the thickness over the entire area of ​​the optical film 100. The thickness of the layer can be substantially constant (e.g., varying by no more than 10%, or no more than 5%, or no more than 3%), such that the average thickness is a substantially constant thickness of the layer. In some embodiments, the average thickness Ts of the surface layers 105, 105' is greater than about 2 micrometers, or greater than about 3 micrometers, or greater than about 4 micrometers, or greater than about 5 micrometers, or greater than about 6 micrometers, or greater than about 7 micrometers. In some embodiments, the thickness of the surface layers 105, 105' does not exceed about 30 micrometers, or about 20 micrometers, or about 15 micrometers, or about 10 micrometers. In some embodiments, the surface layers 105, 105' have an average thickness, for example, in the range of about 2 micrometers to about 15 micrometers or in the range of about 3 micrometers to about 10 micrometers. In some embodiments, the average thickness of the surface layer 105' is within about 20%, or about 15%, or about 10% of the average thickness of the surface layer 105.

[0040] As used herein, "integrally formed" with respect to the second element means that the first and second elements are manufactured together rather than separately and then bonded. Integrally formed includes manufacturing the first element and then manufacturing the second element on the first element. An optical film comprising multiple layers is integrally formed if the layers are manufactured together (e.g., combined into a melt flow and then cast onto a cooling roll to form a cast film having each of these layers, and then the cast film is oriented) rather than manufactured separately and then bonded thereafter. In some embodiments, at least the first layer 101 and the second layer 102, as well as the surface layer 105, are integrally formed with each other. In some embodiments, the first layer 101 and the second layer 102, the first surface layer 105, and the opposing second surface layer 105' are integrally formed with each other.

[0041] Optical film 100 may include more than Figure 3Further layers 101 and 102 are schematically shown. In some embodiments, the optical film 100 includes a plurality of alternating polymer layers 101 and 102, totaling at least 30, and transmits and reflects light primarily through optical interference. In some embodiments, the optical film 100 includes a plurality of alternating polymer first layers 101 and polymer second layers 102, the number of which is between 50 and 800, or between 400 and 800, or between 500 and 800, including endpoints. In some embodiments, the only layers in an optical film with a thickness of less than about 500 nm or less than about 250 nm are the first layer 101 and the second layer 102, and the total number of alternating polymer first layers 101 and polymer second layers 102 is in the range of 50 to 800, or between 400 and 800, or between 500 and 800.

[0042] The optical films of this specification can be made using any suitable light-transmitting material, but in many cases, the use of low-absorption polymer materials is advantageous. Using such materials, the absorption of the microlayer stack at visible and infrared wavelengths can be small or negligible, such that the sum of reflection and transmission of the stack (or a portion thereof) at any given wavelength and at any specified incident angle and polarization state is approximately 100%, i.e., R+T≈100%, or R≈100%-T. Suitable materials for alternating first and second layers 101 and surface layers 105, 105', and layer 104 include, for example, polyethylene naphthalate (PEN), copolymers containing PEN and polyester (e.g., polyethylene terephthalate (PET) or benzoic acid), glycol-modified polyethylene terephthalate, polycarbonate (PC), poly(meth)methyl methacrylate (PMMA), or mixtures of these types of materials. In some embodiments, first layer 101 comprises PEN and second layer 102 comprises PMMA. In some embodiments, the first layer 101 comprises PEN, and the second layer 102 comprises a polymer blend of ethylene glycol-modified copolyester and polycarbonate. Such polymers exhibit low absorption rates in the visible and NIR wavelength ranges of interest, as well as in the 5G frequency range of interest.

[0043] The optical transmission and reflection characteristics of an optical film can be specified for substantially normally incident light. Substantially normally incident light is light that is sufficiently close to being normally incident on the optical film, such that the difference between the transmission and reflection of substantially normally incident light and that of light typically incident on the optical film is negligible. In some embodiments, substantially normally incident light can be within 20 degrees of normal incidence, or within 10 degrees of normal incidence, or within 5 degrees of normal incidence, or can be normally incident or nominally normally incident. The transmission and reflection characteristics of the optical film can optionally or additionally be specified for substantially normally incident (e.g., radio frequency) radiation on the optical film. Substantially normally incident radiation can be understood as a line from a radiation source facing the optical film to the optical film that is substantially perpendicular to the optical film. Figure 3 The diagram schematically illustrates light or radiation 50 that is essentially normally incident. Unless otherwise stated, the radio frequency radiation can be assumed to be unpolarized. The optical transmission and reflection characteristics of the optical film can be specified for at least one polarization state. For example, optical characteristics can be specified for a first polarization state 171, or optical characteristics can be specified for an orthogonal first polarization state 171 and a second polarization state 172.

[0044] In some embodiments, the optical film 100 is reflective for at least one polarization state within a first wavelength range (e.g., at least extending from about 430 nm to about 680 nm or from about 400 nm to about 700 nm). For example, in some embodiments, the average optical reflectance of the optical film within the first wavelength range is greater than about 90%, or greater than about 95%, or greater than about 97%, or greater than about 98%, for substantially normally incident light and for at least one polarization state. The average optical transmittance (corresponding to optical reflectance) is the unweighted average of the optical transmittance (corresponding to optical reflectance) within a specified wavelength range. In some embodiments, the optical reflectance of the optical film is greater than about 90%, or greater than about 95%, or greater than about 97%, or greater than about 98%, for each wavelength within the first wavelength range, for substantially normally incident light and for at least one polarization state.

[0045] High reflectivity can be achieved by increasing the number of interference layers that reflect light within a given wavelength range. Optical films with high reflectivity are described in International Application Publication No. WO 2020 / 053832 (Fabick et al.) and U.S. Patent Application Publication No. 2020 / 0183065 (Haag et al.). In some embodiments, the optical film 100 is transmissive in a second wavelength range (e.g., at least extending from about 1000 nm to about 1200 nm; or at least about 100 nm wide and disposed between about 800 nm and about 1200 nm or between about 800 nm and about 1100 nm; or at least about 250 nm wide and disposed between about 800 nm and about 1300 nm or between about 800 nm and about 1200 nm). For example, in some embodiments, the average optical transmittance of the optical film is greater than about 75%, or greater than about 80%, or greater than about 85% for substantially normally incident light and for at least one polarization state.

[0046] Figure 4 This is a schematic graph illustrating the optical transmittance 139 of an optical film for substantially normal incident light according to some embodiments. The optical transmittance of the optical film includes a band edge 125 separating a first wavelength range 122 and a second wavelength range 126. The band edge region 124 includes at least a wavelength range in which the optical transmittance increases from about 10% to about 70% with increasing wavelength. In some embodiments, the optical transmittance of the optical film for substantially normal incident light within the band edge region 124 monotonically increases with increasing wavelength from at least about 10% to about 70%, or from at least about 10% to about 75%, or from at least about 10% to about 80%, or from at least about 5% to about 80%. In some embodiments, the first wavelength range 122 extends from at least about 450 nm to about 650 nm, or from about 400 nm to about 700 nm. In some embodiments, the second wavelength range 126 extends from about 950 nm to about 1300 nm or about 1200 nm, or is at least about 100 nm wide and situated between about 800 nm and 1100 nm (e.g., a range from about 1000 nm to about 1100 nm), or is at least about 200 nm wide and situated between about 800 nm and about 1300 nm or between about 800 nm and about 1200 nm. In some embodiments, each of the first and second wavelength ranges is at least 250 nm wide, or at least 300 nm wide. In some embodiments, the band edge region 124 is no more than 30 nm wide, or no more than 20 nm wide, or no more than 15 nm wide. The reflectivity R of at least one polarization state is schematically represented as approximately 100% minus the optical transmittance 139.

[0047] In some embodiments, the difference between the maximum value 137 and the minimum value 834 of the optical transmittance of the optical film in the second wavelength range 126 is less than about 30%, or less than about 25%, or less than about 22% (for example, the maximum value 137 of the optical transmittance in the second wavelength range 126 may be about 95%, and the minimum value 834 may be about 75%, such that the difference is about 20%).

[0048] In some embodiments, the electronic device includes a housing having an optical film and includes an infrared light element 169 adapted to emit and / or receive light at an infrared wavelength 127. In some cases, it is desirable that the optical film is transmissive to the infrared wavelength 127 and reflective for wavelengths close to the infrared wavelength 127 (e.g., about 50 nm smaller than the infrared wavelength 127). In some embodiments, at the infrared wavelength 127, the optical film transmits at least 70% of substantially normally incident light, and at a first wavelength 123 positioned between a first wavelength range 122 and the infrared wavelength 127, the optical film transmits between 40% and 60% of substantially normally incident light. In some embodiments, the first wavelength 123 is within about 60 nm, or about 50 nm, or about 40 nm, or about 30 nm, or about 20 nm of the infrared wavelength 127.

[0049] The optical transmittance 139 can be for at least one polarization state. For example, the at least one polarization state includes an orthogonal first polarization state (171) and a second polarization state (172). In this case, the optical transmittance 139 is the transmittance for each of the first and second polarization states. In some embodiments, at least one polarization state includes a first polarization state 171, and for substantially normal incident light having a second polarization state 172 orthogonal to the first polarization state 171, the average optical transmittance of the optical film is greater than about 80% in each of the first and second wavelength ranges. For example, the optical transmittance in the second polarization state can be... Figure 4 The transmittance shown schematically is 140.

[0050] In some embodiments, the slope of the best linear fit to the band edge that associates optical transmittance with the wavelengths described below is greater than about 2% / nm, or greater than about 3% / nm, or greater than about 4% / nm, or greater than about 5% / nm, where the wavelength at least spans the wavelength range in which optical transmittance increases from about 10% to about 70% (e.g., band edge region 124). The best linear fit 136 in Figure 4The optimal linear fit 136 can be determined as a linear least-squares fit of transmittance as a function of wavelengths that at least span a wavelength range where transmittance increases from about 10% to about 70% (e.g., spanning a wavelength range where transmittance increases from about 10% to about 70%, or from about 10% to about 75%, or from about 10% to about 80%). In some embodiments, the optimal linear fit for the band edge that associates optical transmittance with wavelength spans at least a wavelength range where optical transmittance increases from about 10% to about 75%, or from about 10% to about 80%. In some embodiments, the slope of the optimal linear fit for the band edge that associates optical transmittance with the wavelengths that at least spans a wavelength range where optical transmittance increases from about 10% to about 75%. In some embodiments, the slope of the best linear fit to the band edge that associates optical transmittance with the wavelengths described below is greater than about 2% / nm, greater than about 3% / nm, or greater than about 4% / nm, or greater than about 5% / nm, which at least spans the wavelength range in which optical transmittance increases from about 10% to about 80%.

[0051] The band edge slope can be adjusted by appropriately selecting the layer thickness distribution. In some embodiments, the layer thickness distribution can also be selected and combined with selection to reduce the skin thickness of the ringing to provide the desired transmission spectrum. Optical films with sharp band edges are known in the art and described in U.S. Patent No. 6,967,778 (Wheatley et al.) and International Application Publication No. WO 2020 / 053832 (Fabick et al.). A related optical film is described in co-pending U.S. Application No. 63 / 021743 entitled "Optical Film," filed May 8, 2020.

[0052] Figure 5 It is a curve showing the average layer thickness versus the number of layers for multiple polymer layers 101, 102 according to some embodiments. Figure 20 The thickness distribution can be applied to multiple polymer layers 101, 102 throughout the entire membrane or in a membrane group. Figures 6-9 It shows Figure 5 The curve is a portion of the graph. The layer thickness distribution can be selected through appropriate feed block design and processing. For example, the axial rod heater power level in a multilayer feed block described in U.S. Patent No. 6,783,349 (Neavin et al.) can be used to control the layer thickness distribution.

[0053] Atomic force microscopy (AFM) can be used to measure the average layer thickness. To reduce measurement error, the average layer thickness can be determined as a moving average. Layers can be numbered from the thinnest to the thickest, and the moving average can be averaged over 20 layers (including the 10 layers with lower layer numbers, the specified layer, and the 9 layers with higher layer numbers). Near the ends of the distribution, fewer layers are used in the moving average because fewer layers are available before or after the specified layer. For example, for a film or group with 325 layers, the average thickness of layer 1 would be the average thickness of layers 1 to 10, the average thickness of layer 2 would be the average thickness of layers 1 to 11, the average thickness of layer 101 would be the average thickness of layers 91 to 110, the average thickness of layer 325 would be the average thickness of layers 315 to 325, and the average thickness of layer 324 would be the average thickness of layers 314 to 325.

[0054] In some embodiments, the optical film 100 includes a plurality of polymer layers 101, 102 arranged along at least a portion (z-direction) of the thickness of the optical film and numbered sequentially from 1 to N, where N is an integer greater than about 100. Each of the plurality of polymer layers 101, 102 includes a polymer end layer 22, 23 or 22, 223 at each end (see example...). Figure 3 In some embodiments, the polymer end layers 22, 23 and each of the layers 101, 102 therebetween have an average thickness of less than about 300 nm. The optical film may optionally include at least one layer 104 between the polymer end layers 22, 23 (see example...). Figure 3 The polymeric end layers 101, 102, having an average thickness Tb greater than about 500 nanometers or within any thickness range described elsewhere herein, may be considered as separate layers not included in the plurality of polymeric layers 101, 102, and may be omitted in the sequential numbering from 1 to N. The numbering from 1 to N may alternatively refer to layers in a single group. For example, layers sequentially numbered from 1 to N may be layers in a first plurality of polymeric layers beginning with end layer 223 and ending with end layer 22, or beginning with end layer 223 and ending with end layer 223. In some embodiments, the polymeric end layers 22, 223 and each of the layers 101, 102 therebetween have an average thickness of less than about 300 nm.

[0055] In some embodiments, the curve shows the average layer thickness t versus the number of polymer layers 101, 102. Figure 20Including a first turning region 30, which separates a left region 31 comprising at least N1 sequentially arranged polymer layers with smaller layer numbers from a middle region 32 comprising at least N2 sequentially arranged polymer layers with larger layer numbers, such that a linear fit 41 is made for the at least N1 sequentially arranged polymer layers in the left region (e.g., see...). Figure 6 The linear slope 42 has a magnitude greater than about 0.04 nm per layer, where the r-squared value 43 is greater than about 0.8, and the linear fit 44 is for at least N2 sequentially arranged polymer layers in the intermediate region 32 (see, for example, [reference]). Figure 7 The linear slope is 45, which has a value greater than about 0.05 nm per layer, where the r-squared value is greater than about 0.8. N1 is an integer greater than about 50 (e.g., at least 47, or at least 49, or at least 50, or at least 51). In some embodiments, N1 is greater than about 100, or greater than about 150, or greater than about 180. N2 is an integer greater than about 10. In some embodiments, N2 is greater than about 15 or greater than about 20.

[0056] In some embodiments, the optical film 100 further includes a second bend region 33 that separates the intermediate region 32 from the right region 34, and includes at least N3 sequentially arranged polymer layers, wherein the polymer layers have a higher number of layers than the polymer layers in the intermediate region, such that a linear fit 47 is achieved for the at least N3 sequentially arranged polymer layers in the right region (e.g., see...). Figure 8 The structure has a positive linear slope of 48, which has a value greater than about 1.2 nm per layer, where the r-squared value of 49 is greater than about 0.6. N3 is an integer greater than about 3 (e.g., at least 3). In some embodiments, N3 is at least 3, 4, 5, or 6.

[0057] In some embodiments, the optical film 100 includes a plurality of polymer layers 101, 102, each of which includes a polymer end layer at each end. The polymer end layers and each layer therebetween may have an average thickness of less than about 300 nm. A curve showing the average layer thickness t versus the number of polymer layers is presented. Figure 20 Includes: a left region 36 comprising at least N4 sequentially arranged polymer layers; a first intermediate region 31 comprising at least N1 sequentially arranged polymer layers; a second intermediate region 32 comprising at least N2 sequentially arranged polymer layers; and a right region 34 comprising at least N3 sequentially arranged polymer layers, such that a linear fit 70 is made to the at least N4 sequentially arranged polymer layers in the left region (e.g., see...). Figure 9The linear fit 41 of at least N1 sequentially arranged polymer layers in the first intermediate region 31 has a negative linear slope 71, which has a magnitude greater than about 0.04 nm per layer, and a r-squared value 72 greater than about 0.8 (see, for example, see...). Figure 6 The linear slope 42 has a magnitude greater than about 0.04 nm per layer, where the r-squared value 43 is greater than about 0.8, and is a linear fit 44 to at least N2 sequentially arranged polymer layers in the second intermediate region 32 (see, for example, [reference needed]). Figure 5 It has a negative linear slope 45, which has a magnitude greater than about 0.05 nm per layer, where the r-squared value 46 is greater than about 0.8, and a linear fit 47 to at least N3 sequentially arranged polymer layers in the right region 34 (see, for example, [reference]). Figure 8 The linear slope 48 has a positive linear slope with a value greater than about 1.2 nm per layer, where the r-squared value 49 is greater than about 0.6. In some embodiments, N1 is an integer greater than about 50, N2 is an integer greater than about 10, N3 is an integer greater than about 3, and N4 is an integer greater than about 5 (e.g., at least 5). N1, N2, and N3 can be in any range described elsewhere. In some embodiments, N4 is at least 5, or at least 6, or at least 7. Note that, for example, depending on other elements or regions discussed, the same region may be referred to as a first region or a second region, or a middle region or a left or right region.

[0058] In some embodiments, the magnitude of the positive linear slope 42 of the linear fit 41 is greater than about 0.05 nm per layer, or greater than about 0.06 nm per layer, or greater than about 0.07 nm per layer. In some such embodiments, or in other embodiments, the r-squared value 43 of the linear fit 41 is greater than about 0.8, or greater than about 0.85, or greater than about 0.9, or greater than about 0.93, or greater than about 0.95.

[0059] In some embodiments, the magnitude of the negative linear slope 45 of the linear fit 44 is greater than about 0.06 nm per layer, or greater than about 0.07 nm per layer, or greater than about 0.08 nm per layer. In some such embodiments, or in other embodiments, the r-squared value 46 of the linear fit 44 is greater than about 0.8, or greater than about 0.85, or greater than about 0.9, or greater than about 0.93, or greater than about 0.95.

[0060] In some embodiments, the magnitude of the positive linear slope 48 of the linear fit 47 is greater than about 1.4 nm per layer, or greater than about 1.5 nm per layer, or greater than about 1.6 nm per layer. In some such embodiments, or in other embodiments, the r-squared value 49 of the linear fit 47 is greater than about 0.6, or greater than about 0.7, or greater than about 0.8, or greater than about 0.85.

[0061] In some embodiments, the magnitude of the negative linear slope 71 of the linear fit 70 is greater than approximately 0.1 nm per layer, or greater than approximately 0.5 nm per layer, or greater than approximately 0.8 nm per layer, or greater than approximately 1 nm per layer, or greater than approximately 1.2 nm per layer, or greater than approximately 1.4 nm per layer. In some such embodiments, or in other embodiments, the r-squared value of the linear fit 70 is greater than approximately 0.8, or greater than approximately 0.85, or greater than approximately 0.9, or greater than approximately 0.93, or greater than approximately 0.95.

[0062] In some embodiments, a first bend region 35 separates the left region 36 from the first intermediate region 31, wherein the polymer layers in the first intermediate region 31 have a higher number of layers than the polymer layers in the left region 36. In some such embodiments or in others, a second bend region 30 separates the first intermediate region 31 from the second intermediate region 32, wherein the polymer layers in the second intermediate region 32 have a higher number of layers than the polymer layers in the first intermediate region 31. In some such embodiments or in others, a third bend region 33 separates the second intermediate region 32 from the right region 34, wherein the polymer layers in the right region 34 have a higher number of layers than the polymer layers in the second intermediate region 32.

[0063] Figure 10 This is a graph 86 showing the average layer thickness versus the number of layers for multiple polymer layers 101, 102 according to some embodiments. The thickness distribution can be applied to multiple polymer layers 101, 102 throughout the membrane or in a membrane group. Figures 11-12 It shows Figure 10 The part of the curve graph.

[0064] In some embodiments, the optical film 100 includes a plurality of polymer layers 101, 102, which are arranged along at least a portion of the thickness (z-direction) of the optical film and are sequentially numbered from 1 to P (e.g., corresponding to layers 1 to N as described elsewhere). For example, P can be an integer greater than about 100. Each of the plurality of polymer layers 101, 102 includes a polymer end layer (e.g., layers 22, 223) at each end. Each polymer end layer and each layer between them may have an average thickness of less than about 300 nm. A graph 86 of the average layer thickness t versus the number of polymer layers 101, 102 includes: a first bend region 80 that separates a left region 81 comprising at least P1 sequentially arranged polymer layers with smaller layer numbers from a right region 82 comprising at least P2 sequentially arranged polymer layers with larger layer numbers, such that a linear fit 83 is made to the at least P2 sequentially arranged polymer layers in the right region 82 (e.g., see...). Figure 12 The linear slope has a negative linear slope of 84, which has a value greater than about 0.1 nm per layer, where the r-squared value of 85 is greater than about 0.8. In some embodiments, P1 is an integer greater than about 50, and P2 is an integer greater than about 10. In some embodiments, P1 is at least 50, or at least 100, or at least 150, or at least 200. In some such embodiments or in others, P2 is at least 10, or at least 15, or at least 18.

[0065] In some embodiments, a linear fit 87 is performed on at least P1 sequentially arranged polymer layers in the left region 81 (e.g., see...). Figure 11 The linear fit 87 has a positive linear slope 88, the magnitude of which is in the range of about 0.01 nm per layer to about 0.25 nm per layer, wherein the r-squared value 89 is greater than about 0.8. In some embodiments, the linear fit 87 has a positive linear slope 88, the magnitude of which is in the range of about 0.02 nm per layer, or about 0.03 nm per layer, or about 0.04 nm per layer to about 0.2 nm per layer or to 0.15 nm per layer. In some such embodiments or in other embodiments, the linear fit 87 has an r-squared value 89 greater than about 0.8, or greater than about 0.85, or greater than about 0.9, or greater than about 0.93, or greater than about 0.95.

[0066] In some embodiments, the magnitude of the negative linear slope 84 of the linear fit 83 is greater than about 0.15 nm per layer, or greater than about 0.2 nm per layer, or greater than about 0.22 nm per layer. In some such embodiments or in other embodiments, the r-squared value 85 of the linear fit 83 is greater than about 0.8, or greater than about 0.85, or greater than about 0.9, or greater than about 0.93, or greater than about 0.95.

[0067] In some embodiments, the optical film 100 includes a plurality of polymer layers 101, 102 arranged along at least a portion of the thickness of the optical film and numbered sequentially from 1 to N, where N is an integer greater than about 100 or greater than about 200. Each of the plurality of polymer layers includes a polymer end layer (e.g., layers 22, 223) at each end, wherein the average thickness of the polymer end layer and each layer between them is less than about 300 nm. The optical film may have, for example, […]. Figures 13-16 The layer thickness distribution is shown.

[0068] Figure 13 This is a graph 110 showing the average layer thickness versus the number of layers for multiple polymer layers 101, 102 according to some embodiments. The thickness distribution can be applied to multiple polymer layers 101, 102 throughout the membrane or in a membrane group. Figures 14-16 It shows Figure 13 The part of the curve graph.

[0069] In some embodiments, the optical film is configured such that for substantially normal incident light 50 and for at least one polarization state, the optical film has a band edge 131 with respect to wavelength optical transmittance 130 (e.g., see FIG. 20). In some embodiments, the band edge 131 is between about 800 nm and about 1100 nm. In some embodiments, the curve 110 of average layer thickness t versus the number of polymer layers 101, 102 includes a bend region 111 that separates a left region 112 comprising at least Q1 sequentially arranged polymer layers with smaller layer numbers from a right region 113 comprising at least Q2 sequentially arranged polymer layers with larger layer numbers, such that a linear fit 114 (e.g., see FIG. 20) is made to the at least Q1 sequentially arranged polymer layers in the left region 112. Figure 14 It has a positive linear slope 115, which has a magnitude greater than about 0.04 nm per layer, where the r-squared value 116 is greater than about 0.8, and a linear fit 117 to at least Q2 sequentially arranged polymer layers in the right region 113 (see, for example, [reference]). Figure 15 It has a negative linear slope of 118, which has a sufficiently large magnitude to achieve the best linear fit of 132 (see example). Figure 21The slope 133 is greater than about 3% / nm, or greater than about 4% / nm, or within any range of the edge slopes described elsewhere herein. In some embodiments, the best linear fit 132 has an r-squared value 138 greater than about 0.8, or greater than about 0.85, or greater than about 0.9, or greater than about 0.93, or greater than about 0.95. Q1 is an integer greater than about 100. In some embodiments, Q1 is at least 100, or at least 150, or at least 180. Q2 is an integer greater than about 10. In some embodiments, Q2 is at least 10, or at least 12, or at least 14.

[0070] In some embodiments, the linear fit 117 for at least Q2 sequentially arranged polymer layers in the right region 113 has a negative linear slope 118, the magnitude of which is greater than about 0.1 nm per layer, wherein the r-squared value 119 is greater than about 0.8. In some embodiments, the magnitude of the negative linear slope 118 of the linear fit 117 is greater than about 0.12 nm per layer, or greater than about 0.14 nm per layer, or greater than about 0.16 nm per layer. In some such embodiments or in other embodiments, the r-squared value 119 of the linear fit 117 is greater than about 0.8, or greater than about 0.85, or greater than about 0.9.

[0071] In some embodiments, the magnitude of the positive linear slope 115 of the linear fit 114 is greater than about 0.05 nm per layer, or greater than about 0.06 per layer, or greater than about 0.07 per layer. In some such embodiments or in other embodiments, the r-squared value 116 of the linear fit 114 is greater than about 0.8, or greater than about 0.85, or greater than about 0.9, or greater than about 0.95.

[0072] In some embodiments, the curve 110 of average layer thickness t versus the number of polymer layers includes a bend region 111 that separates a left region 112 comprising at least 100 sequentially arranged polymer layers with smaller layer numbers from a right region 113 comprising at least 10 sequentially arranged polymer layers with larger layer numbers, such that a third-order polynomial fit 120 is applied to at least 15 sequentially arranged polymer layers including the bend region 111 (see, for example...). Figure 14 The right region 113 has positive third-order coefficients 121 and negative second-order coefficients 722, where the r-squared value 723 is greater than about 0.8. In some embodiments, the r-squared value 723 is greater than about 0.85 or greater than about 0.9. In some embodiments, the left region 112 comprises at least 150 or at least 180 sequentially arranged polymer layers. In some embodiments, the right region 113 comprises at least 12 or at least 14 sequentially arranged polymer layers.

[0073] In some embodiments, the optical film 100 includes a plurality of polymer layers 101, 102 numbered sequentially from 1 to N, where N is an integer greater than about 100 or at least 150, and each of the polymer layers 101, 102 has an average thickness less than about 300 nm. The optical film 100 may also include other layers (such as 105, 105', 104) in addition to, for example, polymer layers 101, 102 greater than about 500 nm. In some embodiments, a graph 110 of the average layer thickness t versus the number of layers of the plurality of polymer layers 101, 102 includes a turning region 111 that includes the thickest polymer layer 724 of the plurality of polymer layers 101, 102 such that the optical film 100 or the plurality of polymer layers 101, 102 has the reflection and transmission characteristics described elsewhere herein.

[0074] In some embodiments, the layer thickness distribution in region 32, 82, or 113 decreases as the number of layers increases, as described by an exponential function, as further described elsewhere herein.

[0075] Figure 17 is a schematic graph of the average layer thickness 321 of the m-th layer 328 to the N-th layer 329 according to some embodiments versus the number of layers. In some embodiments, the m-th layer 328 of the plurality of polymer layers 101, 102 has an average thickness tm, where m < N, such that the average thickness of each of the plurality of polymer layers 101, 102 having a number of layers n (m ≤ n ≤ N) is within about 10% (curve 333) of, where A is a real number and d is an integer. In some embodiments, 0.01tm ≤ A ≤ 0.25tm or 0.01tm ≤ A ≤ 0.2tm. In some embodiments, 0.005N ≤ d ≤ 0.1N or 0.01N ≤ d ≤ 0.1N. In some embodiments, N - m ≥ 5 or N - m ≥ 8 or N - m ≥ 10. In some embodiments, the average thickness of the polymer layer 329 having a number of layers N is at least about 10%, or at least about 12%, or at least about 14% less than tm. In some embodiments, the average thickness of each of the plurality of polymer layers 101, 102 having a number of layers n, where m ≤ n ≤ N, is within about 5%, or about 4%, or about 3% of. In some embodiments, the average thickness of each of the plurality of polymer layers 101, 102 having a number of layers n, where m < n ≤ N, is within Within approximately 5%, or within approximately 4%, or within approximately 3%, or within approximately 2%. For curve 333 shown, d = 7, A = 20 nm, N = 330, m = 315, and tm = 124 nm. Parameter A specifies the magnitude of the apodization (the offset of the layer thickness distribution near the side of the group or film), while parameter d determines the number of layers with a significant offset in thickness.

[0076] Figure 18 It is a graph of the optical transmittance 60 of the optical film 100 versus wavelength according to some implementation schemes. Figure 19 It is a curve Figure 18 The portion near edge 61. Optical transmittance 60 can be used for substantially normally incident light 50 having a first polarization state 171. In some embodiments, the optical film is a reflective polarizer that substantially transmits light having a second polarization state 172 orthogonal to the first polarization state 171. In other embodiments, the optical film is a mirror film having an optical transmittance 60 similar to that of substantially normally incident light 50 having the second polarization state 172. The layer thickness distribution of FIG5, which also includes a group of optical films reflecting shorter wavelengths and a group of longer wavelengths, can produce optical transmittance 60. Figure 10 The layer thickness distribution can produce similar optical transmittance. In some embodiments, the optical film 100 or the plurality of polymer layers 101, 102 is substantially non-absorbent, such that the optical reflectance R of the optical film is substantially equal to 100% minus the optical transmittance of the optical film.

[0077] In some embodiments, for substantially normal incident light 50 and a first wavelength range W1 extending from about 400 nm to about 800 nm and a second wavelength range W2 extending from about 950 nm to about 1300 nm, a plurality of polymer layers 101, 102, or optical films 100: reflect more than about 80% of the incident light having a first polarization state 171 in the first wavelength range W1; and, in some embodiments, for each of the first polarization state 171 and the second polarization state 172, transmit more than about 60% of the incident light in the second wavelength range W2. In some embodiments, the plurality of polymer layers 101, 102, or optical films 100 transmit more than about 40% or more than about 50% of the incident light having a second polarization state 172 in the first wavelength range W1. In other embodiments, the plurality of polymer layers 101, 102, or optical films 100 reflect more than about 80% of the incident light having a second polarization state 172 in the first wavelength range W1. In some embodiments, for each of the first polarization state 171 and the second polarization state 172, the plurality of polymer layers 101, 102, or optical films 100 transmit more than about 70% or more than about 80% of the incident light in the second wavelength range W2. In some embodiments, for substantially normally incident light 50, for the first polarization state 171 and for the orthogonal second polarization state 172, the optical film 100 or the plurality of polymer layers 101, 102 reflect more than about 80% of the incident light 50 in the first wavelength range W1. In some such embodiments or in other embodiments, the plurality of polymer layers 101, 102, or optical films 100 transmit more than about 60%, or more than 70%, or more than about 80% of the incident light in the second wavelength range W2 for each of the first polarization state 171 and the second polarization state 172.

[0078] In some embodiments, for substantially normal incident light 50 having a first polarization state 171, the optical transmittance 60 of the optical film with respect to wavelength includes a band edge 61 between about 850 nm and about 950 nm, such that an optimal linear fit 62 is made to the band edge relating the optical transmittance to the wavelength described below (see, for example, Figure 19 The wavelength has a slope 63 greater than about 3% / nm, and the wavelength spans at least a wavelength range W3 in which the optical transmittance increases from about 10% to at least about 70% (e.g., from about 10% to about 70%, or from about 10% to about 80%, or from about 10% to at least about 80%). In some embodiments, the slope 63 is greater than about 3.5% / nm, or greater than about 4% / nm, or greater than about 4.5% / nm, or greater than about 5% / nm. In some embodiments, the best linear fit 62 has an r-squared value 64 greater than about 0.8, or greater than about 0.85, or greater than about 0.9, or greater than about 0.93, or greater than about 0.95.

[0079] Figure 20 This is a graph showing the optical transmittance of optical film 100 (130 nm) versus wavelength. Figures 21-23 yes Figure 20 The graph shows a portion of the curve. Optical transmittance 130 can be used for substantially normally incident light 50 having a first polarization state 171. In some embodiments, the optical film is a reflective polarizer that substantially transmits light having a second polarization state 172 orthogonal to the first polarization state 171. In other embodiments, the optical film is a mirror film having an optical transmittance similar to the optical transmittance 130 of substantially normally incident light 50 having the second polarization state 172. Optical films that reflect shorter wavelength groups also include those that reflect longer wavelength groups. Figure 13 The layer thickness distribution can produce an optical transmittance of 130.

[0080] In some embodiments, multiple polymer layers 101, 102, or optical films 100: reflect more than about 80% of incident light 50 having a first polarization state 171 in a first wavelength range W1; transmit more than about 40% or more than about 50% of incident light having a second polarization state 172 orthogonal to the first polarization state in the first wavelength range W1; transmit more than about 60% of incident light in a second wavelength range W2 for each of the first polarization state 171 and the second polarization state 172; and for the first polarization state 171, the optical transmittance 130 of the optical film with respect to wavelength includes a band edge 131 between about 800 nm and about 1100 nm. In some embodiments, the band edge 131 is between about 850 nm and about 950 nm. In some embodiments, an optimal linear fit 132 for the band edge 131 that associates the optical transmittance with the wavelength described below (e.g., see...) Figure 19 The wavelength has a slope of 133 within any range (e.g., greater than about 4% / nm) that is greater than about 3% / nm or described elsewhere as a band edge slope, and the wavelength spans at least across a wavelength range in which the optical transmittance increases from about 10% to about 70% along the band edge.

[0081] In some implementations, the wavelength range W5 is from a first wavelength λa with an optimal linear fit of 20% to a second wavelength λb with an optimal linear fit of 80% (see [link to implementation]). Figure 21 The wavelength range is less than about 30 nm, or less than about 20 nm, or less than about 15 nm. In some embodiments, the wavelength range from a minimum wavelength greater than about 600 nm (where the transmittance is at least about 20%) to a minimum wavelength greater than about 600 nm (where the transmittance is at least about 80%) is less than about 30 nm, or less than about 20 nm, or less than about 15 nm.

[0082] In some embodiments, a second-order polynomial fit 134 to the optical transmittance 130 is performed over a wavelength range at least 200 nm wide between the band edge and approximately 2000 nm, 1600 nm, or 1300 nm (see, for example, [link to relevant documentation]). Figure 22 The band edge has an r-squared value 739 greater than about 0.6 and a minimum optical transmittance Tmin less than about 80%. The wavelength range between the band edge and about 2000 nm, about 1600 nm, or about 1300 nm can be, for example, from about 950 nm to about 1200 nm. In some embodiments, the r-squared value 739 is greater than about 0.7 or greater than about 0.75. In some embodiments, the second-order polynomial fit 134 has positive second-order coefficients 781 and negative first-order coefficients 782. In some embodiments, the second-order polynomial fit 134 has a minimum optical transmittance Tmin less than about 75%. In some embodiments, the minimum optical transmittance Tmin is greater than about 60% or greater than about 65%.

[0083] In some embodiments, for substantially normal incident light 50 and for at least one polarization state and for a third wavelength range W4 extending from a smaller wavelength L1 to a larger wavelength L2 (e.g., see...), Figure 23 In some embodiments, 35nm ≤ L2-L1 ≤ 45nm. In some embodiments, L1 is within about 18nm or about 16nm of wavelength 135. In some embodiments, electronic device 170 includes an infrared (IR) optical element 169 adapted to receive or transmit infrared light primarily at wavelengths in the wavelength range W4 (e.g., about 940nm).

[0084] As is known in the art, the linear fit described herein can be a linear least squares fit. A polynomial fit can similarly be a least squares fit. Such a fit minimizes the sum of squared residuals, where the residuals are the differences between the data and the fitted curve (line or polynomial). Least squares analysis allows for the determination of the r-squared value (sometimes called the coefficient of determination).

[0085] It is generally desirable for optical films (and / or housings including optical films) to have high transmittance for at least one frequency in the range of about 0.1 GHz to about 90 GHz. For example, optical films can be used in 5G mobile phone housings, and it may be desirable for the optical films to be transmittant to the 5G frequencies used by the mobile phone. In addition to the transmittance of the optical film or as an alternative to the transmittance of the optical film, reflections from the film and / or the loss tangent of the film can be specified.

[0086] Transmittance and reflectance can be determined based on scattering parameters obtained using two-port free-space measurements. For example, the scattering parameter S21, which can be called insertion loss, can be determined based on two-port free-space measurements and can be defined as 10 times the base of the logarithm of the ratio of transmitted power to incident power. For example, an insertion loss of -0.1 dB (S21) means that approximately 97.7% of the incident power is emitted through the membrane. As another example, the scattering parameter S11, which can be called return loss, can be determined based on two-port free-space measurements and can be defined as 10 times the base of the logarithm of the ratio of reflected power to incident power. For example, a return loss of -20 dB (S11) means that 1% of the incident power is reflected from the membrane.

[0087] Figure 24 This is a graph showing the transmission through an exemplary optical film as a function of frequency. Low-frequency (below approximately 2.5 GHz) data were determined according to ASTM D4935-18 testing standards. Measurement errors cause some figures to be slightly above 100%. The remaining data in the graph were determined using two-port free-space measurements.

[0088] Figures 25A-25B It is a graph of the return loss S11 of the optical film in two different frequency ranges determined by using two-port free space measurements according to some implementation schemes.

[0089] The dielectric properties of optical films were determined using the split dielectric resonant cavity method. Figure 26 It is a graph of the real part of the dielectric constant as a function of frequency and the loss tangent (tanδ). For example, the IEC 61189-2-721 test standard can be used to determine the dielectric properties in the frequency range of 1 GHz to 33 GHz.

[0090] Figures 24-26 The data shown are used for membranes prepared in a manner generally as described in Example 2 of International Application Publication No. WO 2020 / 053832 (Fabick et al.).

[0091] In some embodiments, for at least one frequency in the range of about 0.1 GHz to about 90 GHz and for substantially normal incident radiation, the optical film transmits at least about 95%, or at least about 97%, or at least about 98%, or at least about 99% of the incident radiation. In some embodiments, for at least one frequency in the range of about 0.1 GHz to about 90 GHz and for substantially normal incident radiation, the dielectric loss tangent of the optical film is less than about 0.02, or less than about 0.01, or less than about 0.008, or less than about 0.006. In some embodiments, for at least one frequency in the range of about 0.1 GHz to about 90 GHz and for substantially normal incident radiation, the optical film reflects less than about 5%, or less than about 2%, or less than about 1% of the incident radiation. In some embodiments, for at least one frequency in the range of about 0.1 GHz to about 90 GHz, the real part of the dielectric constant of the optical film is not greater than about 4, or not greater than about 3.5, or not greater than about 3.2. At least one frequency referred to for any of these characteristics may include the same or multiple frequencies as at least one frequency referred to for any other of these characteristics.

[0092] In some embodiments, a combination of two or more of these characteristics falls within at least one of these ranges. For example, in some embodiments, for at least one frequency in the range of about 0.1 GHz to about 90 GHz: the dielectric loss tangent of the optical film is less than about 0.02; and for substantially normal incident radiation, the optical film reflects less than about 5% of the incident radiation; or the dielectric loss tangent of the optical film is less than 0.01; and for substantially normal incident radiation, the optical film reflects less than about 2% of the incident radiation; or the loss tangent of the optical film is less than 0.006; and for substantially normal incident radiation, the optical film reflects less than about 1% of the incident radiation.

[0093] In some implementations, at least one frequency in the range of about 0.1 GHz to about 90 GHz includes at least one frequency in the 5G bands as defined in 3GPP Release 15 or at least one frequency in the range of about 64 GHz to about 71 GHz. 3GPP refers to the Third Generation Partnership Project, a standards organization that released Release 15 in 2018 related to 5G New Radio (NR). In some implementations, at least one frequency in the range of about 0.1 GHz to about 90 GHz includes at least one frequency in the range of 0.6 to 0.7 GHz, or 2.45 to 2.55 GHz, or 3.3 to 4.2 GHz, or 4.4 to 5 GHz, or 5.9 to 7.1 GHz, or 24 to 29 GHz, or 37 to 50 GHz, or 64 to 71 GHz. In some implementations, at least one frequency in the range of about 0.1 GHz to about 90 GHz includes at least one frequency in the range of 0.5 to 1 GHz or 2.45 to 90 GHz.

[0094] In some embodiments, the optical stack includes an optical film 100 and further includes an optical layer 210 (corresponding 210') disposed on and substantially co-extended with the optical film 100. For example, the optical layer 210 (corresponding 210') may cover at least 60% or at least 80% of the area of ​​the optical film 100, and / or the optical film 100 may cover at least 60% or at least 80% of the area of ​​the optical layer 210 (corresponding 210'). The optical layer 210 or 210' may, for example, be a coloring layer (e.g., an ink coating) and / or an optical diffuser. The coloring layer may be used to provide a desired color in the reflection (e.g., to produce a colored metallic appearance), and may optionally include an optical diffuser layer to provide a greater diffuse reflectance that may be desired in some applications. In some embodiments, optical layer 210 or 210' is substantially optically absorptive for at least one visible wavelength (e.g., wavelengths in the range of 400 nm to 700 nm) (e.g., optical absorptivity of at least 20% or at least 40% for substantially normal incident light of at least one polarization state). For example, optical layer 210 or 210' may be a colored layer that absorbs more for some wavelengths than for others.

[0095] Figure 27This is a schematic graph illustrating the transmittance of substantially normally incident light for at least one polarization state through an optical layer (e.g., 210 or 210') according to some embodiments. For example, the transmittance can be substantially the same for orthogonal polarization states. The absorptivity can be approximated as 100% minus the transmittance (ignoring Fresnel reflections from the surface). In some embodiments, for substantially normally incident light and for at least one polarization state, the optical absorptivity of the optical layer for a first wavelength in the first wavelength range 122 (optical absorptivity A1 at the first wavelength λ1) is at least 20%, at least 30%, or at least 40% higher than the optical absorptivity of the optical layer for a second wavelength in the first wavelength range 122 (e.g., optical absorptivity A2 at the second wavelength λ2). Optical transmittances T1 and T2 are shown for substantially normally incident light and for at least the first polarization state at the first wavelength λ1 and the second wavelength λ2, respectively. In some embodiments, T2-T1 is at least 20%, at least 30%, or at least 40%. In some embodiments, for substantially normally incident light and for at least one polarization state: for a second wavelength λ2, the optical transmittance T2 of the optical layer is greater than about 70%, and for a first wavelength λ1, the optical absorptivity A1 of the optical layer is greater than about 40%. In some embodiments, the optical layer has an optical transmittance T3 at a third wavelength λ3 within the second wavelength range 126. In some embodiments, the third wavelength λ3 is about 850 nm or about 940 nm. The optical layer can be patterned (e.g., including patterned optically absorbing ink). In this case, the optical transmittance and optical absorptivity of the layer refer to the optical transmittance and optical absorptivity in the regions of the material in which the layer is present.

[0096] Figure 28This is a schematic cross-sectional view of an optical layer 310 (e.g., corresponding to optical layer 210 or 210') according to some embodiments. The optical layer 310 has opposing first main surfaces 311 and second main surfaces 312, and includes a plurality of particles 320 dispersed between and across the first and second main surfaces 311 and 312. The optical layer 310 (which may also be referred to as an optical diffusion layer) includes a polymer material 330 that binds the particles together to form a plurality of particle aggregates 340 defining a plurality of voids 370 therebetween. In some embodiments, the plurality of particles 320 are a plurality of nanoparticles, and the plurality of particle aggregates 340 are a plurality of nanoparticle aggregates. In some embodiments, the particles 320 are silicon dioxide or include silicon dioxide. For example, particle 20 may be a silicon dioxide nanoparticle. In some embodiments, in the plane of the cross-section of the optical layer 310 along its thickness direction (e.g., the xz plane in the illustrated cross-section): the average size of the nanoparticles 320 is between about 20 nm and about 150 nm; the average size of the nanoparticle aggregates 340 is between about 100 nm and about 1000 nm; and the voids occupy about 5% to about 50% of the area of ​​the plane of the cross-section. According to some embodiments, such optically diffused layers have been found to provide a substantially higher degree of specular transmittance in the infrared range than in the visible range. Alternatively, or further, according to some embodiments, the optically diffused layer can provide substantially higher diffuse transmittance in the visible range than in the infrared range. In some embodiments, the average thickness Td of the optical layer 310 is between about 0.1 μm and about 20 μm, or between about 1 μm and about 20 μm, or between about 1.5 μm and about 10 μm, or between about 2 μm and about 8 μm.

[0097] In some embodiments, the optical layer 310 is formed by coating a mixture of particles, monomers, and solvents, followed by curing and drying the mixture. The monomers cure into a polymer binder (polymer material 330) that binds the aggregates of particles together, and the solvent evaporates, creating voids between the aggregates. The solvent may evaporate at least partially during curing and / or a subsequent drying step may be used to complete the evaporation of the solvent. In some embodiments, curing and drying include a pre-curing step, followed by a drying step, and then a post-curing step. In some embodiments, the monomers are UV-curable and include a photoinitiator in the mixture. The size of the aggregates can be tuned by varying the UV power used to cure the monomers at higher power, generally resulting in smaller aggregate sizes. It has been found that relatively low amounts of photoinitiator with relatively high UV power produce smaller aggregate sizes and non-fragmented layers, while higher amounts of photoinitiator can produce more brittle layers. The porosity can be tuned by varying the amount of solvent used in the mixture, where higher solvent loading generally results in higher porosity. In some embodiments, the mixture comprises about 20 to about 60% by weight of solids. In some embodiments, polymer material 330 is or comprises a radiation-cured (e.g., UV-cured) polymer. In some embodiments, polymer material 330 is or comprises an acrylate. In some embodiments, polymer material 330 is or comprises pentaerythritol triacrylate. The relevant optical diffuser layer is described in co-pending U.S. Patent Application No. 63 / 021751, filed May 8, 2020, entitled "Optical Films and Stacks Including Optical Diffuser Layers".

[0098] Figure 28Light 50a and 50b, substantially normally incident on optical layer 310, are schematically shown. Light 50a has a wavelength in the visible range (e.g., corresponding to wavelength range 122), and light 50b has a wavelength in the infrared range (e.g., corresponding to wavelength range 126). For light 50a in the visible wavelength range, optical layer 310 has an average specular transmittance Vs, an average diffuse transmittance Vd, and an average total transmittance Vt (Vt = Vs + Vd). For light 50b in the near-infrared wavelength range, optical layer 310 has an average specular transmittance Is, an average diffuse transmittance Id, and an average total transmittance It (It = Is + Id). In some embodiments, for substantially normally incident light 50, 50a, 50b and the visible wavelength range of about 450 nm to about 650 nm and the infrared wavelength range of about 930 nm to about 970 nm: in the visible wavelength range, optical layer 310 has an average specular transmittance Vs; and optical layer 310 has an average total transmittance It and an average specular transmittance Is in the infrared wavelength range. In some embodiments, Is / It ≥ 0.6 and Is / Vs ≥ 2.5. In some embodiments, Is / Vs ≥ 3. In some embodiments, It / Vt > 1, or It / Vt > 2, or It / Vt > 3. In some embodiments, Is / It ≥ 0.7. If the polarization state of the incident light is not specified, it may be assumed that the incident light is unpolarized unless the context clearly indicates otherwise.

[0099] High diffuse transmittance (e.g., high Vd) corresponds to high optical haze. In some embodiments, optical layer 310 has an optical haze of at least about 5%, or at least about 10%, or at least about 20%, or at least about 30%. Optical haze is the ratio of diffuse transmittance to total transmittance and can be determined, for example, according to the ASTM D1003-13 test standard.

[0100] Figure 29 This is a schematic graph illustrating the transmittance of substantially normal-incident light for at least one polarization state through an optical stack 200 according to some embodiments. The optical stack may include optical films described elsewhere herein and, for example... Figure 27 The optical layer described in [the text]. Transmittance may be [related to the optical layer described in the text]. Figure 29 The near-infrared region, not shown in the schematic diagram, exhibits variations (see, for example...). Figure 4 In some embodiments, for a third wavelength λ3 in the second wavelength range 126, the optical stack 200 has an optical transmittance T4 greater than about 60%, or greater than about 70%, or greater than about 75% for substantially normal incident light and for at least one polarization state.

[0101] For at least one frequency in the range of about 0.1 GHz to about 90 GHz, the optical stack 200 may have transmittance, reflectance, and / or loss tangent within any range described elsewhere for the optical film 100. For example, in some embodiments, for at least one frequency in the range of about 0.1 GHz to about 90 GHz and for substantially normal incident radiation, the optical stack 200 transmits at least about 95%, or at least about 97%, or at least about 98%, or at least about 99% of the incident radiation. As another example, in some embodiments, for at least one frequency in the range of about 0.1 GHz to about 90 GHz: the dielectric loss tangent of the optical stack 200 is less than about 0.02; and for substantially normal incident radiation, the optical stack reflects less than about 5%, or less than about 2%, or less than about 1% of the incident radiation. As yet another example, in some embodiments, for at least one frequency in the range of about 0.1 GHz to about 90 GHz: the dielectric loss tangent of the optical stack is less than about 0.02; and for substantially normal incident radiation, the optical stack transmits at least about 95% of the incident radiation. The dielectric loss tangent and transmittance can be in any range described elsewhere. The reflectivity and transmittance of the optical stack 200 can be determined for radiation incident on the optical film 100 or on the optical layer 210 or 210' (if included).

[0102] Terms such as “about” will be understood in the context in which they are used and described by those skilled in the art. If it is unclear to those skilled in the art in the context of their use and description of “about” to express quantities of characteristic size, quantity, and physical properties, then “about” will be understood to mean within 10% of a specified value. A quantity given a specified value as “about” can be precisely that specified value. For example, if it is unclear to those skilled in the art in the context of their use and description of this specification, a quantity having a value of about 1 means that the quantity has a value between 0.9 and 1.1, and that the value can be 1.

[0103] All cited references, patents, and patent applications are incorporated herein by reference in their entirety in a consistent manner. In the event of any inconsistency or contradiction between the incorporated references and this application, the information in the foregoing description shall prevail.

[0104] Unless otherwise specified, the description of elements in the accompanying drawings should be understood to apply equally to corresponding elements in the other drawings. While specific embodiments have been illustrated and described herein, those skilled in the art will recognize that various alternative and / or equivalent embodiments may be used instead of the illustrated and described embodiments without departing from the scope of this disclosure. This application is intended to cover any modifications, variations, or combinations of the specific embodiments discussed herein. Therefore, this disclosure is intended to be limited only by the claims and their equivalents.

Claims

1. A housing for an electronic device, the housing being the outermost layer of the electronic device and comprising an optical film bonded to an optically transparent rigid substrate, the optical film transmitting and reflecting light primarily through optical interference, the optical film having optical transmittance for substantially normally incident light and for at least one polarization state comprising a band edge separating a first wavelength range and a second wavelength range, the first wavelength range extending from 400 nm to 700 nm, the second wavelength range being at least 100 nm wide and disposed between 800 nm and 1100 nm, such that for substantially normally incident light and for said at least one polarization state: The optical film has an average optical reflectivity greater than 90% in the first wavelength range; and The optical film has an average optical transmittance greater than 80% in the second wavelength range, wherein the best linear fit of the optical transmittance of the optical film to the band edge associated with the following wavelengths has a slope greater than 2% / nm, the wavelengths spanning at least the wavelength range in which the optical transmittance of the optical film increases from 10% to 70%, and wherein for at least one frequency in the range of 0.1 GHz to 90 GHz and for substantially normal incident radiation, the optical film transmits at least 95% of the incident radiation, wherein for at least one frequency in the range of 0.1 GHz to 90 GHz, the dielectric loss tangent of the optical film is less than 0.02, wherein the optical film comprises a plurality of polymer layers, each of the plurality of polymer layers comprising a polymer end layer at each end thereof, the average thickness of the polymer end layer and each layer therebetween being less than 300 nm, and a graph of the average layer thickness versus the number of layers of the plurality of polymer layers comprising: The left region comprises at least N4 polymer layers arranged in sequence, where N4 is an integer greater than 5; A first intermediate region, comprising at least N1 polymer layers arranged in sequence, where N1 is an integer greater than 50; The second intermediate region comprises at least N2 sequentially arranged polymer layers, where N2 is an integer greater than 10; and The right region comprises at least N3 sequentially arranged polymer layers, where N3 is an integer greater than 3. The linear fit for the at least N4 sequentially arranged polymer layers in the left region has a negative linear slope, the negative linear slope having a value greater than 0.04 nm per layer, where the r-squared value is greater than 0.8; the linear fit for the at least N1 sequentially arranged polymer layers in the first intermediate region has a positive linear slope, the positive linear slope having a value greater than 0.04 nm per layer, where the r-squared value is greater than 0.8; the linear fit for the at least N2 sequentially arranged polymer layers in the second intermediate region has a negative linear slope, the negative linear slope having a value greater than 0.05 nm per layer, where the r-squared value is greater than 0.8; and the linear fit for the at least N3 sequentially arranged polymer layers in the right region has a positive linear slope, the positive linear slope having a value greater than 1.2 nm per layer, where the r-squared value is greater than 0.

6.

2. The housing according to claim 1, wherein for at least one frequency in the range of 0.1 GHz to 90 GHz, the real part of the dielectric constant of the optical film is not greater than 4.

3. The housing according to claim 1, wherein the at least one polarization state comprises an orthogonal first polarization state and a second polarization state.

4. The housing according to claim 1, wherein the at least one polarization state includes a first polarization state, and for substantially normal incident light having a second polarization state orthogonal to the first polarization state, the optical film has an average optical transmittance greater than 80% in each of the first and second wavelength ranges.

5. The housing according to claim 1, wherein the at least one frequency in the range of 0.1 GHz to 90 GHz includes at least one frequency in the 5G band as defined by 3GPP Release 15 or at least one frequency in the range of 64 GHz to 71 GHz.

6. The housing according to claim 1, wherein the optical stack includes the optical film and further includes an optical layer disposed on and substantially co-extended with the optical film, the optical layer being substantially optically absorptive for at least one visible wavelength.

7. A housing for an electronic device, the housing being the outermost layer of the electronic device and comprising an optical film bonded to an optically transparent rigid substrate, the optical film transmitting and reflecting light primarily by optical interference, the optical film having optical transmittance for substantially normally incident light and for at least one polarization state comprising a band edge separating a first wavelength range and a second wavelength range, the first wavelength range extending from 400 nm to 700 nm, the second wavelength range being at least 100 nm wide and disposed between 800 nm and 1100 nm, such that for substantially normally incident light and for the at least one polarization state: The optical film has an average optical reflectivity greater than 90% in the first wavelength range; and The optical film has an average optical transmittance greater than 80% in the second wavelength range, wherein the best linear fit of the optical transmittance of the optical film to the band edge has a slope greater than 2% / nm, the wavelength spanning at least the wavelength range in which the optical transmittance of the optical film increases from 10% to 70%, and wherein for at least one frequency in the range of 0.1 GHz to 90 GHz: The dielectric loss tangent of the optical film is less than 0.02; and For substantially normal incident radiation, the optical film reflects less than 5% of the incident radiation, wherein the optical film comprises a plurality of polymer layers, each of which includes a polymer end layer at each end, the average thickness of the polymer end layer and each layer therebetween being less than 300 nm, and the curve of the average layer thickness versus the number of layers of the plurality of polymer layers includes: The left region comprises at least N4 polymer layers arranged in sequence, where N4 is an integer greater than 5; A first intermediate region, comprising at least N1 polymer layers arranged in sequence, where N1 is an integer greater than 50; The second intermediate region comprises at least N2 sequentially arranged polymer layers, where N2 is an integer greater than 10; and The right region comprises at least N3 sequentially arranged polymer layers, where N3 is an integer greater than 3. The linear fit for the at least N4 sequentially arranged polymer layers in the left region has a negative linear slope, the negative linear slope having a value greater than 0.04 nm per layer, where the r-squared value is greater than 0.8; the linear fit for the at least N1 sequentially arranged polymer layers in the first intermediate region has a positive linear slope, the positive linear slope having a value greater than 0.04 nm per layer, where the r-squared value is greater than 0.8; the linear fit for the at least N2 sequentially arranged polymer layers in the second intermediate region has a negative linear slope, the negative linear slope having a value greater than 0.05 nm per layer, where the r-squared value is greater than 0.8; and the linear fit for the at least N3 sequentially arranged polymer layers in the right region has a positive linear slope, the positive linear slope having a value greater than 1.2 nm per layer, where the r-squared value is greater than 0.

6.

8. An optical stack for use as a housing of an electronic device and comprising: An optical film comprising a plurality of alternating polymer first layers and polymer second layers disposed on a surface, the optical film transmitting and reflecting light primarily by optical interference, each of the first and second layers having an average thickness of less than 250 nm, the surface layer having an average thickness of greater than 2 micrometers, the first and second layers and the surface layer being integrally formed together, the optical film having optical transmittance for substantially normally incident light and for at least one polarization state comprising a band edge separating a first wavelength range and a second wavelength range, the first wavelength range extending from 400 nm to 700 nm, the second wavelength range being at least 100 nm wide and disposed between 800 nm and 1100 nm, such that for substantially normally incident light and for the at least one polarization state: The optical film has an average optical reflectivity greater than 90% in the first wavelength range; and The optical film has an average optical transmittance greater than 80% in the second wavelength range, wherein the best linear fit of the band edge relating the optical transmittance of the optical film to the following wavelengths has a slope greater than 2% / nm, the wavelengths spanning at least the wavelength range in which the optical transmittance of the optical film increases from 10% to 70%. and An optical layer disposed on and substantially co-extended with the optical film, such that, for substantially normally incident light and for the at least one polarization state, the optical layer has an optical absorptivity for a first wavelength in the first wavelength range that is at least 20% higher than the optical absorptivity for a second wavelength in the first wavelength range, wherein the optical stack has an optical transmittance for a third wavelength in the second wavelength range that is substantially normally incident light and for the at least one polarization state that is greater than 60%. The housing is the outermost layer of the electronic device. The third wavelength is 940 nm. The optical film comprises multiple polymer layers, each of which includes a polymer end layer at each end. The average thickness of the polymer end layer and each layer therebetween is less than 300 nm. The curve of the average layer thickness versus the number of layers includes: The left region comprises at least N4 polymer layers arranged in sequence, where N4 is an integer greater than 5; A first intermediate region, comprising at least N1 polymer layers arranged in sequence, where N1 is an integer greater than 50; The second intermediate region comprises at least N2 sequentially arranged polymer layers, where N2 is an integer greater than 10; and The right region comprises at least N3 sequentially arranged polymer layers, where N3 is an integer greater than 3. The linear fit for the at least N4 sequentially arranged polymer layers in the left region has a negative linear slope, the negative linear slope having a value greater than 0.04 nm per layer, where the r-squared value is greater than 0.8; the linear fit for the at least N1 sequentially arranged polymer layers in the first intermediate region has a positive linear slope, the positive linear slope having a value greater than 0.04 nm per layer, where the r-squared value is greater than 0.8; the linear fit for the at least N2 sequentially arranged polymer layers in the second intermediate region has a negative linear slope, the negative linear slope having a value greater than 0.05 nm per layer, where the r-squared value is greater than 0.8; and the linear fit for the at least N3 sequentially arranged polymer layers in the right region has a positive linear slope, the positive linear slope having a value greater than 1.2 nm per layer, where the r-squared value is greater than 0.

6.

9. A housing for an electronic device, the housing comprising an optical stack according to claim 8, the optical stack being bonded to an optically transparent rigid substrate.

10. An optical stack for use as a housing of an electronic device and comprising an optical film bonded to an optically transparent rigid substrate, the optical film transmitting and reflecting light primarily by optical interference, the optical film comprising a plurality of polymer layers arranged along at least a portion of the thickness of the optical film and sequentially numbered from 1 to N, where N is an integer greater than 100, the plurality of polymer layers including polymer end layers at each end thereof, a graph of the average layer thickness versus the number of layers of the plurality of polymer layers including a first bend region, the first bend region being a left region comprising at least N1 sequentially arranged polymer layers with smaller layer numbers and The device comprises an intermediate region consisting of at least N2 sequentially arranged polymer layers with large layer numbers, where N1 is an integer greater than 50 and N2 is an integer greater than 10, such that a linear fit of the at least N1 sequentially arranged polymer layers in the left region has a positive linear slope with a value greater than 0.04 nm per layer, where the r-squared value is greater than 0.8, and a linear fit of the at least N2 sequentially arranged polymer layers in the intermediate region has a negative linear slope with a value greater than 0.05 nm per layer, where the r-squared value is greater than 0.8, wherein the housing is the outermost layer of the electronic device.

11. The optical stack of claim 10, wherein for substantially normal incident light and a first wavelength range extending from 400 nm to 800 nm and a second wavelength range extending from 950 nm to 1300 nm, the plurality of polymer layers: The incident light with a first polarization state is reflected at a rate greater than 80% within the first wavelength range. Within the first wavelength range, more than 40% of the incident light having a second polarization state orthogonal to the first polarization state is transmitted; and For each of the first polarization state and the second polarization state, more than 60% of the incident light is transmitted within the second wavelength range.

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