Multilayer partial reflector, backlight and display system

Abstract

A multilayer partial reflector includes a plurality of alternating first and second polymer layers, a total number of which is at least 50, and disposed between and integrally formed with opposing first and second polymer skin layers. For a visible wavelength range extending from about 420 nm to about 680 nm and for incident light propagating in an incidence plane including an x-direction, and for s-polarized incident light, the multilayer partial reflector has an average reflectivity Rsl for a first incidence angle of less than about 10 degrees and an average reflectivity Rs2 for a second incidence angle of greater than about 45 degrees, and for p-polarized incident light, the multilayer partial reflector has an average reflectivity Rpl for the first incidence angle and an average reflectivity Rp2 for the second incidence angle. Each of Rs2 / Rsl and Rp2 / Rpl is greater than about 1.15.

Description

Technical Field

[0001] This disclosure relates generally to multilayer partial reflectors. Specifically, this disclosure relates to multilayer partial reflectors for backlights of display panels. Background Technology

[0002] Collimated reflective polarizers are typically used in display devices to eliminate optical artifacts, such as reflected moiré fringes. However, such collimated reflective polarizers can reduce the axial brightness of the display device. Summary of the Invention

[0003] In a first aspect, this disclosure provides a multilayer partial reflector. The multilayer partial reflector includes a plurality of alternating first and second polymer layers, totaling at least 50. The plurality of alternating first and second layers are disposed between and integrally formed with opposite first and second polymer layers. Each of the first and second polymer layers has an average thickness greater than about 0.5 micrometers. The first and second polymer layers include corresponding refractive indices nx1 and nx2 along an x-direction in the same plane, corresponding refractive indices ny1 and ny2 along a y-direction in a plane orthogonal to the x-direction, and corresponding refractive indices nz1 and nz2 along a z-direction orthogonal to the x and y directions of the polymer layer. For at least one wavelength in the visible light wavelength range extending from about 420 nanometers (nm) to about 680 nm, nx1 and ny1 differ from each other by about 0.05. For the at least one wavelength in the visible light wavelength range, nz1 is at least 0.06 smaller than each of nx1 and nx2. For the at least one wavelength within the visible light wavelength range, and for each of the first polymer surface layer and the second polymer surface layer, the refractive indices of the polymer surface layer and one of the first polymer layer and the second polymer layer differ from each other by approximately 0.05 along each of the x-direction, y-direction, and z-direction. For the visible light wavelength range and incident light propagating in an incident plane including the x-direction, and for s-polarized incident light, the plurality of alternating first polymer layers and the second polymer layers have an average reflectivity Rs1 for a first incident angle less than approximately 10 degrees and an average reflectivity Rs2 for a second incident angle greater than approximately 45 degrees. Furthermore, for the visible light wavelength range and incident light propagating in the incident plane, and for p-polarized incident light, the plurality of alternating first polymer layers and the second polymer layers have an average reflectivity Rp1 for the first incident angle and an average reflectivity Rp2 for the second incident angle. Each of Rs2 / Rs1 and Rp2 / Rp1 is greater than approximately 1.15.

[0004] In a second aspect, this disclosure provides a backlight source for illuminating a display panel configured to form an image. The backlight source includes an extended light source configured to emit light through an emitting surface. The extended light source also includes a back reflector. The backlight source further includes a multilayer partial reflector, as described in the first aspect. The multilayer partial reflector is disposed on the emitting surface and configured to receive the emitted light and transmit a portion of the received light through the multilayer partial reflector. The multilayer partial reflector and the back reflector form a circulating optical cavity therebetween.

[0005] In a third aspect, this disclosure provides a display system including a display panel disposed on a backlight source of the second aspect.

[0006] In a fourth aspect, this disclosure provides a multilayer partial reflector. The multilayer partial reflector includes at least 50 alternating first and second polymer layers. Each of the first and second polymer layers has an average thickness of less than about 500 nm. Furthermore, the first and second polymer layers include corresponding refractive indices nx1 and nx2 along an x-direction in the same plane, corresponding refractive indices ny1 and ny2 along a y-direction in a plane orthogonal to the x-direction, and corresponding refractive indices nz1 and nz2 along a z-direction orthogonal to both the x and y directions. For at least one wavelength in the visible light wavelength range extending from about 420 nm to about 680 nm, nz1 is at least 0.06 smaller than each of nx1 and nx2. For the at least one wavelength in the visible light wavelength range, the difference between nx2 and ((nx1+nz1) / 2) is less than about 0.05. Additionally, for the at least one wavelength in the visible light wavelength range, nx2 and nz2 differ from each other by about 0.05. For the visible light wavelength range, the infrared wavelength range from about 800 nm to about 1300 nm, incident light propagating in an incident plane including the x-direction, and for a first incident angle less than about 10 degrees, a plurality of alternating first polymer layers and second polymer layers have an average reflectivity Rp1 for incident light polarized along the x-direction and an average reflectivity Rs1 for incident light polarized along the y-direction. Each of Rp1 and Rs1 is less than about 85% for the visible light wavelength range and less than about 50% for the infrared wavelength range. Additionally, for the visible light wavelength range, the infrared wavelength range, the incident light propagating in the incident plane, and for a second incident angle greater than about 45 degrees, a plurality of alternating first polymer layers and second polymer layers have average reflectivities Rp2 and Rs2 for the corresponding p-polarized and s-polarized incident light. Each of Rp2 and Rs2 is greater than about 70% for the visible light wavelength range.

[0007] In a fifth aspect, this disclosure provides a multilayer partial reflector. The multilayer partial reflector includes a plurality of alternating first and second polymer layers, totaling between about 50 and 600. The plurality of alternating first and second polymer layers are disposed between integrally formed opposing first and second polymer surface layers. Each polymer layer disposed between the first and second polymer surface layers has an average thickness of less than about 500 nm. For at least one wavelength in the visible light wavelength range extending from about 420 nm to about 680 nm, each of the first and second polymer layers has an in-plane birefringence of less than about 0.05. For the at least one wavelength in the visible light wavelength range, the first polymer layer has an out-of-plane birefringence of greater than about 0.06. Additionally, for the at least one wavelength in the visible light wavelength range, the second polymer layer has an out-of-plane birefringence of less than about 0.02. For the visible light wavelength range and incident light propagating in an incident plane including a first direction in the same plane, and at a first incident angle of less than about 10 degrees, the multilayer partial reflector has an average reflectivity Rs1 for the s-polarized incident light and an average reflectivity Rp1 for the p-polarized incident light. Rp1 / Rs1 is between about 0.8 and about 1.2. For the first incident angle and for each of the p-polarized and s-polarized incident light, the optical reflectivity of the multilayer partial reflector as a function of wavelength includes a reflection band edge between about 760 nm and about 980 nm. Attached Figure Description

[0008] The exemplary embodiments disclosed herein can be more fully understood in light of the following detailed description in conjunction with the figures below. The figures are not necessarily drawn to scale. Similar numbers used in the figures refer to similar parts. However, it should be understood that the use of numbers to refer to parts in a given figure is not intended to limit parts labeled with the same numbers in another figure.

[0009] Figure 1 The illustration shows a detailed schematic cross-sectional view of a multi-layer partial reflector according to one embodiment of the present disclosure;

[0010] Figure 2A The figure illustrates a graph depicting the thickness variations of a plurality of alternating first and second polymer layers in a multilayer partial reflector according to an embodiment of the present disclosure.

[0011] Figure 2B The illustration shows one embodiment according to this disclosure. Figure 2A A magnified view of a portion of the graph;

[0012] Figure 3A and Figure 3BThe illustration shows a schematic cross-sectional view of a multi-layer partial reflector according to one embodiment of the present disclosure;

[0013] Figure 4A The figure illustrates a graph depicting the relationship between the optical reflectivity of a multilayer partial reflector according to an embodiment of the present disclosure and wavelength for s-polarized incident light incident at a first incident angle.

[0014] Figure 4B The figure illustrates a graph depicting the relationship between the optical reflectivity of a multilayer partial reflector according to an embodiment of the present disclosure and wavelength for p-polarized incident light incident at a first incident angle.

[0015] Figure 4C The figure illustrates a graph depicting the relationship between the optical reflectivity of a multilayer partial reflector according to an embodiment of the present disclosure and wavelength for s-polarized incident light incident at a second incident angle.

[0016] Figure 4D The figure illustrates a graph depicting the relationship between the optical reflectivity of a multilayer partial reflector according to an embodiment of the present disclosure and wavelength for p-polarized incident light incident at a second incident angle.

[0017] Figure 5A The illustration shows a detailed schematic cross-sectional view of a display system including multiple partial mirrors according to one embodiment of the present disclosure;

[0018] Figure 5B The figure shows a schematic diagram of a reflective polarizer of a display system according to one embodiment of the present disclosure;

[0019] Figure 5C The illustration depicts an embodiment according to this disclosure. Figure 5B A graph showing the optical characteristics of a reflective polarizer;

[0020] Figure 6A The illustration shows a detailed schematic cross-sectional view of an optical system including multiple partial mirrors according to one embodiment of the present disclosure;

[0021] Figure 6B The illustration shows one embodiment according to this disclosure. Figure 6A A schematic diagram of the reflective polarizer of the optical system;

[0022] Figure 6C The illustration shows a departure according to one embodiment of this disclosure. Figure 6A The light emission distribution of the optical system;

[0023] Figure 6D The illustration shows a departure according to one embodiment of this disclosure. Figure 6A A graph showing the relative intensity of light in an optical system;

[0024] Figure 7A The illustration shows exemplary graphs of the layer thickness of a conventional collimating multilayer optical film (CMOF) and samples A, B, and C.

[0025] Figure 7B The diagram shows Figure 7A An enlarged view of a portion of an exemplary graph;

[0026] Figure 8A The figure shows an exemplary graph depicting the relationship between the optical reflectance of sample A and CMOF and wavelength for s-polarized incident light incident at a first incident angle.

[0027] Figure 8B The figure shows exemplary graphs depicting the relationship between the optical reflectivity of samples B and C and wavelength for s-polarized incident light incident at a first incident angle.

[0028] Figure 9A The figure illustrates another exemplary graph depicting the relationship between the optical reflectance of sample A and CMOF and wavelength for p-polarized incident light incident at a first incident angle.

[0029] Figure 9B The figure illustrates another exemplary graph depicting the relationship between the optical reflectance of samples B and C and wavelength for p-polarized incident light incident at a first incident angle.

[0030] Figure 10A The figure illustrates another exemplary graph depicting the relationship between the optical reflectance of sample A and CMOF and wavelength for s-polarized incident light incident at a second incident angle.

[0031] Figure 10B Another exemplary graph depicting the relationship between the optical reflectance of samples B and C and wavelength for s-polarized incident light incident at a second incident angle is shown.

[0032] Figure 11A The figure illustrates another exemplary graph depicting the relationship between the optical reflectance of samples A and CMOF and wavelength for p-polarized incident light incident at a second incident angle; and

[0033] Figure 11B Another exemplary graph depicting the relationship between the optical reflectivity of samples B and C and wavelength for p-polarized incident light incident at a second incident angle is shown. Detailed Implementation

[0034] In the following description, reference is made to the accompanying drawings, which form a part thereof, and various embodiments are illustrated therein. It should be understood that other embodiments are contemplated and made without departing from the scope or spirit of this disclosure. Therefore, the following detailed description should not be considered limiting.

[0035] In the following disclosure, the following definitions are used.

[0036] As used herein, all numbers should be regarded as being modified by the term “about”. As used herein, “a,” “an,” “the,” “at least one,” and “a or more” are used interchangeably.

[0037] As used herein, as a modifier of a characteristic or attribute, unless otherwise specifically defined, the term “approximately” means that the characteristic or attribute will be easily identifiable by a person skilled in the art without requiring absolute precision or a perfect match (e.g., within + / - 20% for quantifiable characteristics).

[0038] Unless otherwise specifically defined, the term “substantially” means a high degree of approximation (e.g., within + / -10% for quantifiable properties), but also does not require absolute precision or a perfect match.

[0039] Unless otherwise specifically defined, the term “about” means a high degree of approximation (e.g., within + / -5% for quantifiable properties), but also does not require absolute precision or a perfect match.

[0040] As used herein, the terms “first” and “second” are used as identifiers. Therefore, such terms should not be construed as limiting the scope of this disclosure. Throughout the embodiments of this disclosure, the terms “first” and “second” are used interchangeably when used in conjunction with a feature or element.

[0041] As used herein, when a first material is referred to as “similar” to a second material, at least 90% by weight of the first material and the second material are identical, and any variation between the first material and the second material accounts for less than about 10% by weight of each of the first material and the second material.

[0042] As used in this article, "at least one of A and B" should be understood as meaning "only A, only B, or both A and B".

[0043] As used herein, the term "membrane" generally refers to a material having a very high length or width-to-thickness ratio. A membrane has two main surfaces defined by its length and width. Membranes typically exhibit good flexibility and can be used in a wide variety of applications, including displays. Membranes may also have a certain thickness or material composition, making them semi-rigid or rigid. The membranes described in this disclosure can be composed of various polymeric materials. Membranes can be single-layered, multilayered, or blends of different polymers.

[0044] As used herein, the term "layer" generally refers to the thickness of a material within a membrane that has a relatively uniform chemical composition. A layer can be any type of material, including polymers, cellulose, metals, or blends thereof. A given polymer layer may comprise a single polymer type or a blend of polymers and may include additives. A given layer may be combined with or bonded to other layers to form a membrane. A layer may be partially continuous or completely continuous compared to adjacent layers or membranes. A given layer may be partially or completely co-extended with adjacent layers. A layer may contain sublayers.

[0045] As used herein, unless otherwise specifically defined, the term "about...in between" generally refers to a range that includes the endpoints or is closed. For example, if the parameter X is about A and B, then A ≤ X ≤ B.

[0046] As used herein, unless otherwise specifically defined, the term "refractive index" generally refers to the refractive index of a material or layer. Similarly, unless otherwise specifically defined, the term "refractive index" generally refers to the refractive index of multiple materials or layers.

[0047] This disclosure relates to multi-layer partial reflectors and backlights including the multi-layer partial reflectors. Backlights including multi-layer partial reflectors can be used in display systems or optical systems. For example, multi-layer partial reflectors can be used in the backlight of a display device. The display device can be integrated into electronic devices such as computer monitors, televisions, mobile phones, personal digital assistants (PDAs), wearable devices, and other portable devices. Some other examples may include optical biometric scanners, such as fingerprint scanners, retinal scanners, etc.

[0048] In some examples, the display device including the liquid crystal display (LCD) panel also includes a backlight, because the LCD panel is not self-emissive. Light emitted by the backlight passes through the LCD panel to reach the viewer. In some other examples, the display device may include an organic light-emitting display (OLED). In other examples, the display device may include a display, such as a liquid crystal on silicon (LCoS) display or a micro light-emitting diode (LED) display. In some examples, the display device can be used for augmented reality (AR) applications or virtual reality (VR) applications. Typically, the light emitted by the display is circulated to reduce the power consumption of the display device. To circulate the light, a collimated reflective polarizer, such as a collimated multilayer optical film (CMOF), can be used.

[0049] Display devices can also be susceptible to optical artifacts such as reflected moiré fringes. Collimated reflective polarizers can be used in display devices to eliminate these optical artifacts. Specifically, a collimated reflective polarizer can be positioned between the diffuser and the display panel of the display device to eliminate such optical artifacts. However, the diffuser can depolarize light polarized by the collimated reflective polarizer. In such cases, an additional collimated reflective polarizer (APF) is typically used to repolarize the light. However, this can reduce the axial brightness of the display device. Additionally, a collimated reflective polarizer (CMOF) typically collimates light polarized in one direction and essentially reflects light polarized in another direction orthogonal to that direction. Therefore, light polarized in the other direction is not collimated, resulting in reduced axial brightness. In some cases, increasing the axial brightness can increase the power consumption of the display device. This can adversely affect the battery life of electronic devices, including the display device.

[0050] In one aspect, this disclosure provides a multilayer partial reflector. The multilayer partial reflector includes at least 50 alternating first and second polymer layers. The alternating first and second layers are disposed between and integrally formed with opposite first and second polymer layers. Each of the first and second polymer layers has an average thickness greater than about 0.5 micrometers. The first and second polymer layers include corresponding refractive indices nx1 and nx2 along an x-direction in the same plane, corresponding refractive indices ny1 and ny2 along a y-direction in a plane orthogonal to the x-direction, and corresponding refractive indices nz1 and nz2 along a z-direction orthogonal to the x and y directions of the polymer layer. For at least one wavelength in the visible light wavelength range extending from about 420 nanometers (nm) to about 680 nm, nx1 and ny1 differ from each other by about 0.05. For at least one wavelength in the visible light wavelength range, nz1 is at least 0.06 smaller than each of nx1 and nx2. For at least one wavelength in the visible light wavelength range, for each of the first and second polymer layers, the refractive indices of the polymer layer and the first and second polymer layers differ from each other in the x, y, and z directions by approximately 0.05. For the visible light wavelength range and incident light propagating in an incident plane including the x-direction, and for s-polarized incident light, the plurality of alternating first and second polymer layers have an average reflectivity Rs1 for a first incident angle less than approximately 10 degrees and an average reflectivity Rs2 for a second incident angle greater than approximately 45 degrees. Additionally, for the visible light wavelength range and incident light propagating in an incident plane, and for p-polarized incident light, the plurality of alternating first and second polymer layers have an average reflectivity Rp1 for a first incident angle and an average reflectivity Rp2 for a second incident angle. Each of Rs2 / Rs1 and Rp2 / Rp1 is greater than approximately 1.15.

[0051] Therefore, for the visible light wavelength range, and for each of s-polarized and p-polarized light, multilayer partial reflectors have a higher average optical reflectivity for light incident at a second incident angle greater than about 45 degrees (i.e., off-axis light) compared to light incident at a first incident angle less than about 10 degrees (i.e., substantially perpendicular incident light or axial light). In other words, for the visible light wavelength range, and for each of s-polarized and p-polarized light, multilayer partial reflectors have greater optical transmittance for axial light compared to off-axis light. Since multilayer partial reflectors can substantially collimate both s-polarized and p-polarized light off-axis for the visible light wavelength range, they provide improved collimation compared to conventional collimators that typically reflect only one of s-polarized and p-polarized light incident at a second incident angle. Furthermore, for the visible light wavelength range, multilayer partial reflectors can have a lower average optical reflectivity for axial light compared to conventional collimators that even substantially block axial light (one of s-polarized and p-polarized light) polarized in one direction. Optical reflectivity for axial light is generally undesirable because it reduces axial brightness. Therefore, a smaller average optical reflectivity for axial light in the visible light wavelength range can improve the axial brightness of display systems that include multiple partial mirrors.

[0052] In addition, the reflective strip edge of the multi-layer partial reflector can be adjusted to allow light in the infrared wavelength range to pass through, thereby enabling the display device including the multi-layer partial reflector to be used for fingerprint sensing applications.

[0053] Now refer to the attached diagram, Figure 1 A detailed schematic cross-sectional view of a multi-layer partial reflector 10 according to one embodiment of the present disclosure is illustrated. The multi-layer partial reflector 10 is interchangeably referred to as "reflector 10". Reflector 10 defines mutually orthogonal x-directions, y-directions, and z-directions. The x-directions and y-directions correspond to in-plane axes of reflector 10, while the z-direction is a transverse axis disposed along the thickness of reflector 10. In other words, the x-directions and y-directions are along the plane of reflector 10 (i.e., the xy plane), and the z-direction is perpendicular to the plane of reflector 10, i.e., along the thickness of reflector 10. The z-direction is interchangeably referred to as the "thickness direction". Reflector 10 further defines a first direction and a second direction that are mutually orthogonal. In some embodiments, the first direction and the second direction are along in-plane axes of reflector 10. In other words, the first direction and the second direction correspond to the x-direction and the y-direction, respectively.

[0054] In some embodiments, the reflector 10 includes a first primary surface 101 and a second primary surface 102, which are opposite to each other. In some embodiments, the first primary surface 101 and the second primary surface 102 of the reflector 10 are exposed to an external environment. In such embodiments, the first primary surface 101 and the second primary surface 102 of the reflector 10 may form a first reflector-environment interface and a second reflector-environment interface with the external environment, respectively. In some embodiments, the external environment includes air.

[0055] The reflector 10 includes a plurality of alternating first polymer layers 11 and second polymer layers 12. The plurality of alternating first polymer layers 11 and second polymer layers 12 may be interchangeably referred to as "alternating first polymer layers 11 and second polymer layers 12" or "first polymer layers 11 and second polymer layers 12" or "polymer layers 11, 12".

[0056] The total number of alternating first polymer layers 11 and second polymer layers 12 is at least 50. In some embodiments, the total number of alternating first polymer layers 11 and second polymer layers 12 is at least 100, at least 200, at least 300, or at least 400. In some embodiments, the total number of alternating first polymer layers 11 and second polymer layers 12 is between about 50 and about 600. In some embodiments, the total number of alternating first polymer layers 11 and second polymer layers 12 is between about 100 and about 500, between about 200 and about 450, or between about 300 and about 450. Figure 1 As shown, multiple alternating first polymer layers 11 and second polymer layers 12 are stacked in an alternating configuration along the thickness direction of the reflector 10.

[0057] In some embodiments, the multilayer partial reflector (such as reflector 10) can be a multilayer optical film (MOF), which has previously been demonstrated by co-extrusion of alternating polymer layers. See, for example, U.S. Patents 3,610,729 (Rogers), 4,446,305 (Rogers et al.), 4,540,623 (Im et al.), 5,448,404 (Schrenk et al.), and 5,882,774 (Jonza et al.). In these polymer multilayer optical films, the polymer material is primarily or exclusively used in the composition of the individual layers (such as the first polymer layer 11 and the second polymer layer 12). Furthermore, such multilayer optical films are compatible with high-volume manufacturing processes and can be manufactured and stored as large sheets and rolls.

[0058] Multilayer optical films comprise multiple layers with different refractive index characteristics, such that at least some of the light incident on these layers is reflected at the interfaces between adjacent layers. These layers are typically thin enough that the light reflected at the multiple interfaces between adjacent layers undergoes constructive or destructive interference to impart the desired reflective or transmissive properties to the multilayer optical film. For multilayer optical films designed to reflect light at ultraviolet, visible, or near-infrared wavelengths, each of these layers typically has an optical thickness of less than about 1 μm (the physical thickness of the layer multiplied by its corresponding refractive index). Layers with higher optical thicknesses may be included, such as surface layers at the outer surface of the multilayer optical film, or protective boundary layers (PBLs) disposed within the multilayer optical film to separate coherent groups of these layers (referred to herein as “layer groups”).

[0059] For polarization applications, such as reflective polarizers, at least some of these layers may comprise a birefringent polymer, wherein the refractive index of the layers has different values ​​along the orthogonal Cartesian axis of the polymer. Birefringent polymers can also be used in non-polarization applications.

[0060] In some cases, these layers have thicknesses and refractive indices corresponding to quarter-wave stacking, i.e., arranged in optical repeating units or cells, each comprising two adjacent layers having substantially equal optical thicknesses (f-ratio = 50%). Such optical repeating units reflect light with wavelengths λ twice the total optical thickness of the optical repeating units through constructive interference. Other layer arrangements are also known, such as multilayer optical films with two optical repeating units having f-ratios different from 50%, or multilayer optical films where the optical repeating units comprise more than two layers. Multilayer optical films with such optical repeating units can be configured to reduce or increase certain higher-order reflections, see, for example, U.S. Patents 5,360,659 (Arends et al.) and 5,103,337 (Schrenk et al.). Thickness gradients along the thickness direction (such as the z-direction) of multilayer optical films can be used to provide broadened reflective bands, such as those extending over a significant portion of the visible wavelength range and potentially including the near-infrared wavelength range, such that these layers have reflectivity in the visible wavelength range for light incident at an oblique angle of incidence, as the reflective bands shift to shorter wavelengths. Thickness gradients modulated to sharpen band edges (i.e., wavelength transitions between high reflectivity and high transmittance) are discussed in U.S. Patent 6,157,490 (Wheatley et al.).

[0061] Further details regarding multilayer optical films and their related designs and constructions can be discussed in U.S. Patents 5,882,774 (Jonza et al.) and 6,531,230 (Weber et al.), PCT Publications WO 95 / 17303 (Ouderkirk et al.) and WO 99 / 39224 (Ouderkirk et al.), and the March 2000 issue of Science, Volume 287, entitled “Giant Birefringent Optics in Multilayer Polymer Mirrors” (Weber et al.). Multilayer optical films and related articles may include additional layers and coatings selected to suit their optical, mechanical, and / or chemical properties. For example, an ultraviolet (UV) absorbing layer may be added to one side of the multilayer optical film where light is incident to protect components of the multilayer optical film from degradation caused by UV light. Multilayer optical films may be attached to mechanically reinforcing layers using UV-curable acrylate adhesives or other suitable materials. Such reinforcing layers may comprise polymers such as polyethylene terephthalate (PET) or polycarbonate, and may also include structured surfaces that provide optical functions such as light diffusion or collimation, for example, by using beads or prisms. Multilayer optical films may also include additional layers and coatings, such as scratch-resistant layers, tear-resistant layers, and hardeners, see, for example, U.S. Patent 6,368,699 (Gilbert et al.). Methods and apparatus for preparing multilayer optical films are discussed in U.S. Patent 6,783,349 (Neavin et al.).

[0062] Typically, the reflection and transmission properties of a multilayer optical film (such as mirror 10) can be determined based on the refractive indices (such as nx1, ny1, nz1, nx2, ny2, nz2) of the corresponding layers (such as the first polymer layer 11 and the second polymer layer 12) and the average thickness (such as the average thickness t) and thickness variations (such as...) of these layers. Figure 2A and Figure 2B The refractive index of each layer can be varied at least locally within the multilayer optical film by an in-plane refractive index (such as nx1, ny1, nx2, ny2) and a refractive index associated with the thickness direction of the multilayer optical film (such as nz1, nz2). These refractive indices can represent the corresponding refractive indices of the layers of the multilayer optical film for light polarized along mutually orthogonal x- and y-directions, respectively.

[0063] In some cases, the layers of a multilayer optical film can be oriented along the x-direction of the multilayer optical film such that the magnitude of the difference (Δnx) between nx1 and nx2 can be maximized. For ease of explanation in this patent application, unless otherwise specified, the x, y, and z directions are assumed to be local Cartesian coordinates applicable to any point of interest on the multilayer optical film, wherein these layers extend parallel to the xy plane, and wherein the x-axis is oriented in the plane of the multilayer optical film to maximize the magnitude of Δnx. In such cases, the magnitude of the difference (Δny) between ny1 and ny2 can be equal to or less than, but not greater than, the magnitude of Δnx. Furthermore, the material of the first layer of the multilayer optical film can be specified by requiring Δnx to be non-negative. In other words, the material used for these layers can be selected such that nx1 is equal to or greater than nx2, thereby making Δnx ≥ 0. In practice, the refractive index of the layers of the multilayer optical film can be controlled through prudent material selection and processing conditions.

[0064] Multilayer optical films can be fabricated by co-extruding multiple (e.g., tens or hundreds) layers of alternating polymers A and B, sometimes followed by passing the multilayer extrudate of alternating polymers A and B through one or more multipliers, and then stretching or otherwise oriented the multilayer extrudate to form the final film. The resulting film typically consists of multiple alternating layers whose thickness and refractive index are modulated to provide one or more reflective bands in desired regions of the electromagnetic spectrum, such as the visible or near-infrared range.

[0065] In some cases, to achieve a target reflectivity for light polarized in one direction (such as the x-direction), multiple alternating layers can be modulated to exhibit a difference in refractive index (such as Δnx) of at least about 0.04 for light polarized in that direction. In such cases, to further achieve a target reflectivity for light polarized in a direction orthogonal to that direction (such as the y-direction), multiple alternating layers can be modulated to exhibit a difference in refractive index (such as Δny) of at least about 0.05 for light polarized in a direction orthogonal to that direction. Among other things, the '774 patent (Jonza et al.) referenced above describes a manner in which the difference (Δnz) between nz1 and nz2 can be modulated to achieve a desired reflectivity for obliquely incident p-polarized light. In some cases, to maintain a high reflectivity for obliquely incident p-polarized light, the alternating layers can be modulated such that Δnz can be substantially less than the maximum in-plane refractive index difference (i.e., Δnx). In some cases, Δnz ≤ 0.5 * Δnx, or Δnz ≤ 0.25 * Δnx. In some cases, Δnz can have a value of zero or near zero, which creates interfaces between alternating layers whose reflectivity for p-polarized light remains substantially constant depending on the incident angle of the p-polarized light. In other cases, Δnz can be less than 0, which creates interfaces whose reflectivity for p-polarized light increases with increasing incident angle of the p-polarized light. In some cases, the values ​​of Δnx, Δny, and Δnz can be similarly modulated to achieve the target reflectivity for s-polarized light.

[0066] Patent '774 (Jonza et al.) also discusses certain design considerations related to multilayer optical films that can be configured as polarizers (referred to as multilayer reflective or reflective polarizers). In many applications, an ideal reflective polarizer has substantially high reflectivity along one axis (“extinction” or “blocking” axis) and substantially zero reflectivity along another axis (“transmission” or “light transmission” axis). For the purposes of this patent application, light whose polarization state is substantially aligned with the transmission axis is referred to as transmitted light, and light whose polarization state is substantially aligned with the blocking axis or extinction axis is referred to as blocking light. Unless otherwise specified, transmitted light at a 60° incident angle is measured in p-polarized transmitted light. If some reflectivity appears along the transmission axis, the efficiency of the polarizer at angles deviating from the normal may decrease, and if the reflectivity varies for each wavelength, color may be introduced into the transmitted light. Furthermore, in some multilayer systems, it may be impossible to accurately match the two y-axis refractive indices and the two z-axis refractive indices, and when the z-axis refractive index mismatch occurs, a slight mismatch may be expected with respect to the in-plane refractive indices n1y and n2y. Specifically, by arranging the y-axis refractive index mismatch to have the same sign as the z-axis refractive index mismatch, a Brewster effect is generated at the microlayer interface to minimize the off-axis reflectivity along the transmission axis of the multilayer reflective polarizer, and thus minimize the off-axis color.

[0067] In some examples, a manufacturing method for multilayers may include: (a) providing at least a first resin stream and a second resin stream, the first resin stream and the second resin stream corresponding to a first polymer A and a second polymer B to be used in a finished film; (b) dividing the first stream and the second stream into multiple layers using a suitable feed block, the feed block such as including: (i) a gradient plate including a first flow channel and a second flow channel, wherein the first channel has a cross-sectional area that changes from a first position to a second position along the flow channel; (ii) a feed tube sheet having a first plurality of conduits in fluid communication with the first flow channel and a second conduit in fluid communication with the second flow channel. A plurality of conduits, each of the first plurality of conduits and the second plurality of conduits feeding into its own corresponding slot die, each of the first plurality of conduits and the second plurality of conduits having a first end and a second end, the first end of the conduits being in fluid communication with the flow channels, and the second end of the conduits being in fluid communication with the slot die; and (iii) optionally an axial rod heater located proximal to the conduits; (c) causing the composite material flow through an extrusion die to form a multilayered spoke, wherein each layer is substantially parallel to the corresponding main surface of the adjacent layer; and (d) casting the multilayered spokes onto a cooling roller (sometimes called a casting wheel or casting drum) to form a cast multilayered film. The cast film may have the same number of layers as the finished film, but the layers of the cast film are typically much thicker than those of the finished film.

[0068] After cooling, the multilayer web can be preheated and drawn or stretched to prepare a near-finished multilayer optical film. Drawing or stretching achieves two objectives: it thins the layers to their desired final thickness distribution; and it orients the layers such that at least some of them become birefringent. Orientation or stretching can be achieved along the horizontal direction (e.g., via a tenter frame), along the vertical direction (e.g., via a length orientation machine), or any combination thereof (whether simultaneously or sequentially). If stretching is performed in only one direction, the stretching can be “unconstrained” (where the film is allowed to relax dimensionally in a direction perpendicular to the stretching direction) or “constrained” (where the film is constrained and therefore not allowed to relax dimensionally in a direction perpendicular to the stretching direction). If stretching is performed in two in-plane directions, the stretching can be symmetrical (i.e., equal in orthogonal in-plane directions) or asymmetrical. Alternatively, the film can be stretched using a batch method. In any case, subsequent or simultaneous drawing reduction, stress or strain balancing, heat setting, and other processing operations can be applied to the film.

[0069] The polymers in the alternating layers can be selected to have similar rheological properties (e.g., melt viscosity) so that they can be co-extruded without significant flow disturbance. Extrusion conditions can be selected to adequately feed, melt, mix, and pump the respective polymers as feed streams or melt streams in a continuous and stable manner. The temperatures used to form and maintain each melt stream can be selected within a range that avoids freezing, crystallization, or undue pressure drops at the lower end of the range and material degradation at the higher end of the range.

[0070] Multilayer optical films can be made from any suitable light-transmitting material, but in many cases, the use of low-absorption polymer materials is advantageous. Using such materials, the absorption rates of these layers for visible and infrared wavelengths can be small or negligible, such that at any given wavelength and for any specified angle of incidence and polarization state of incident light incident on the multilayer optical film, the sum of the reflectivity (R) and transmittance (T) of the multilayer optical film is approximately 100%, i.e., R + T ≈ 100%, or R ≈ 100% - T. Exemplary multilayer optical films can be made from polymer materials and can be manufactured using co-extrusion, casting, and orientation processes. References were made to U.S. Patent 5,882,774 (Jonza et al.) "Optical Film", U.S. Patent 6,179,948 (Merrill et al.) "Optical Film and Process for Manufacture Thereof", U.S. Patent 6,783,349 (Neavin et al.) "Apparatus for Making Multilayer Optical Films", and patent application publication US2011 / 0272849 (Neavin et al.) "Feedblock for Manufacturing Multilayer Polymeric Films".

[0071] In some embodiments, polymer layers 11, 12 may comprise one or more polymer materials, such as polyethylene hexyl naphthalate (PHEN), polyethylene naphthalate (PEN), copolymers comprising PHEN, PEN and / or other polyesters (e.g., polyethylene terephthalate (PET) or polyesters comprising dibenzoic acid), ethylene glycol-modified polyethylene terephthalate, polycarbonate (PC), poly(methyl methacrylate) (PMMA), or blends of these classes of materials.

[0072] In some embodiments, the first polymer layer 11 may include a high refractive index optical (HIO) layer. In some examples, the first polymer layer 11 may contain a PHEN copolymer, wherein the hexanediol in the final polymer is present in a diol-based proportion between about 30 mol% and about 70 mol%.

[0073] In some embodiments, the second polymer layer 12 may include a low-refractive-index (LIO) optical layer. In some examples, the second polymer layer 12 may comprise a PHEN copolymer, wherein the hexanediol in the final polymer is present in a diol-based proportion between about 30 mol% and 70 mol%. In some examples, the second polymer layer may comprise a blend of PHEN copolymer and PET, wherein the PET level is between 30% and 70% by weight of the final polymer.

[0074] The first polymer layer 11 and the second polymer layer 12 include corresponding refractive indices nx1 and nx2 along the x-direction in the same plane. Specifically, the first polymer layer 11 includes a refractive index nx1 along the x-direction in the plane, and the second polymer layer 12 includes a refractive index nx2 along the x-direction in the same plane. In other words, each first polymer layer 11 includes a refractive index nx1 along the x-direction, and each second polymer layer 12 includes a refractive index nx2 along the x-direction.

[0075] In some implementations, the refractive index nx1 is between about 1.6 and about 1.76, i.e., 1.6 ≤ nx1 ≤ 1.76. In some examples, the refractive index nx1 may be about 1.690, about 1.739, or about 1.740.

[0076] In some implementations, the refractive index nx2 is between about 1.55 and about 1.75, i.e., 1.55 ≤ nx2 ≤ 1.75. In some examples, the refractive index nx2 may be about 1.620, about 1.628, or about 1.629.

[0077] The first polymer layer 11 and the second polymer layer 12 include corresponding refractive indices ny1 and ny2 in the y-direction of a plane orthogonal to the x-direction. Specifically, the first polymer layer 11 includes a refractive index ny1 in the y-direction, and the second polymer layer 12 includes a refractive index ny2 in the y-direction. In other words, each first polymer layer 11 includes a refractive index ny1 in the y-direction, and each second polymer layer 12 includes a refractive index ny2 in the y-direction.

[0078] In some implementations, the refractive index ny1 is between about 1.6 and about 1.76, i.e., 1.6 ≤ ny1 ≤ 1.76. In some examples, the refractive index ny1 may be about 1.695, about 1.739, or about 1.740.

[0079] In some implementations, the refractive index ny2 is between about 1.55 and about 1.75, i.e., 1.55 ≤ ny2 ≤ 1.75. In some examples, the refractive index ny2 may be about 1.620, 1.628, or about 1.629.

[0080] The first polymer layer 11 and the second polymer layer 12 also include corresponding refractive indices nz1 and nz2 along the thickness directions orthogonal to the x and y directions of the polymer layers 11 and 12. Specifically, the first polymer layer 11 includes a refractive index nz1 along the thickness direction, and the second polymer layer 12 includes a refractive index nz2 along the thickness direction. In other words, each first polymer layer 11 includes a refractive index nz1 along the z direction. Each second polymer layer 12 includes a refractive index nz2 along the z direction.

[0081] In some implementations, the refractive index nz1 is between about 1.5 and about 1.55, i.e., 1.5 ≤ nz1 ≤ 1.55. In some examples, the refractive index nz1 may be about 1.510, about 1.513, or about 1.514.

[0082] In some implementations, the refractive index nz2 is between about 1.6 and about 1.7, i.e., 1.6 ≤ nz2 ≤ 1.7. In some examples, the refractive index nz2 may be about 1.620, about 1.623, or about 1.624.

[0083] In some implementations, for the visible light wavelength range of 95 nm extending from about 420 nm to about 680 nm... Figures 4A to 4D At least one wavelength within the visible light wavelength range 95 (shown), nx1 and ny1 differ from each other by about 0.05. In some embodiments, at least one wavelength within the visible light wavelength range 95 is a red wavelength. In some embodiments, at least one wavelength within the visible light wavelength range 95 is about 633 nm. In other words, for at least one wavelength within the visible light wavelength range 95, the magnitude of the difference between nx1 and ny1 may be less than or equal to about 0.05, i.e., |nx1-ny1|≤0.05. Therefore, in some cases, nx1 and ny1 may be substantially equal to each other. In other words, the first polymer layer 11 may have an in-plane birefringence of less than about 0.05. Generally speaking, birefringence is a measure of optical anisotropy in a material. Furthermore, birefringence is measured as the difference between two refractive indices of a material along two mutually perpendicular directions (e.g., the x-direction and the y-direction). In some implementations, for at least one wavelength within the visible light wavelength range of 95, nx1 and ny1 differ from each other within about 0.02, about 0.015, about 0.01, about 0.0075, about 0.005, about 0.004, about 0.003, or about 0.002.

[0084] In some embodiments, for at least one wavelength within the visible light wavelength range 95, nz1 is at least 0.06 smaller than each of nx1 and nx2. In other words, the difference between nx1 and nz1 may be greater than or equal to 0.06, i.e., (nx1-nz1)≥0.06, and the difference between nx2 and nz1 may be greater than or equal to 0.06, i.e., (nx2-nz1)≥0.06. In some embodiments, for at least one wavelength within the visible light wavelength range 95, nz1 is at least 0.08, at least 0.1, at least 0.12, at least 0.14, at least 0.16, at least 0.18, at least 0.20, at least 0.21, or at least 0.22 smaller than each of nx1 and nx2. Therefore, for at least one wavelength within the visible light wavelength range 95, the first polymer layer 11 has an out-of-plane birefringence greater than about 0.06.

[0085] In some embodiments, for at least one wavelength within the visible light wavelength range of 95, nx2, ny2, and nz2 differ from each other within about 0.05. In other words, the magnitude of the difference between nx2 and ny2 may be less than or equal to about 0.05, i.e., |nx2-ny2|≤0.05; the magnitude of the difference between ny2 and nz2 may be less than or equal to about 0.05, i.e., |ny2-nz2|≤0.05; and the magnitude of the difference between nz2 and nx2 may be less than or equal to about 0.05, i.e., |nz2-nx2|≤0.05. In some embodiments, for at least one wavelength within the visible light wavelength range of 95, nx2, ny2, and nz2 differ from each other within about 0.02, about 0.015, about 0.01, about 0.0075, about 0.005, or about 0.0025. Therefore, in some cases, nx2, ny2, and nz2 may be substantially equal to each other. Additionally, in some examples, the second polymer layer 12 may be isotropic.

[0086] In some embodiments, for at least one wavelength within the visible light wavelength range of 95, the magnitude of the difference between nx2 and ((nx1+nz1) / 2) is less than about 0.05. In other words, the magnitude of the difference between nx2 and the average of nx1 and nz1 is less than about 0.05, i.e., |nx2-((nx1+nz1) / 2)|<0.05. In some embodiments, for at least one wavelength within the visible light wavelength range of 95, the magnitude of the difference between nx2 and ((nx1+nz1) / 2) is less than about 0.045, less than about 0.04, less than about 0.035, less than about 0.03, less than about 0.025, less than about 0.02, less than about 0.015, or less than about 0.01. Therefore, in some cases, nx2 may be substantially equal to the average of nx1 and nz1.

[0087] In some embodiments, for at least one wavelength within the visible light wavelength range 95, each of the first polymer layer 11 and the second polymer layer 12 has an in-plane birefringence of less than about 0.05. Specifically, for at least one wavelength within the visible light wavelength range 95, each of the first polymer layers 11 has an in-plane birefringence of less than about 0.05, i.e., |nx1-ny1| < 0.05, and each of the second polymer layers 12 has an in-plane birefringence of less than about 0.05, i.e., |nx2-ny2| < 0.05. In some embodiments, for at least one wavelength within the visible light wavelength range 95, each of the first polymer layer 11 and the second polymer layer 12 has an in-plane birefringence of less than about 0.4, less than about 0.03, less than about 0.02, or less than about 0.01. In some examples, |nx1-ny1| may be about 0.005. In some examples, |nx2-ny2| may be about 0.

[0088] In some embodiments, the first polymer layer 11 has an out-of-plane birefringence greater than about 0.06 for at least one wavelength within the visible light wavelength range 95. Specifically, for at least one wavelength within the visible light wavelength range 95, the first polymer layer 11 has an out-of-plane birefringence greater than about 0.06 relative to the z-direction, i.e., |nx1-nz1| > 0.6 and |ny1-nz1| > 0.6. In some embodiments, the first polymer layer 11 has an out-of-plane birefringence greater than about 0.08, greater than about 0.12, greater than about 0.14, or greater than about 0.16 for at least one wavelength within the visible light wavelength range 95. In some examples, |nx1-nz1| may be about 0.18. In some examples, |ny1-nz1| may be about 0.185.

[0089] In some embodiments, the second polymer layer 12 has an out-of-plane birefringence of less than about 0.02 for at least one wavelength within the visible light wavelength range 95. Specifically, for at least one wavelength within the visible light wavelength range 95, the second polymer layer 12 has an out-of-plane birefringence of less than about 0.02 relative to the z-direction, i.e., |nx²-nz²| < 0.02 and |ny²-nz²| < 0.02. In some embodiments, the second polymer layer 11 has an out-of-plane birefringence of less than about 0.015, less than about 0.01, less than about 0.005, or less than about 0.002 for at least one wavelength within the visible light wavelength range 95. In some examples, |nx²-nz²| may be about 0. In some examples, |ny²-nz²| may be about 0. In some examples, the second polymer layer 12 may be isotropic.

[0090] The reflector 10 also includes opposing first polymer surfaces 13 and 14. The first polymer surfaces 13 and 14 may be collectively referred to as "polymer surfaces 13, 14". Each of the first polymer layer 11 and the second polymer layer 12 is disposed between the first polymer surface 13 and the second polymer surface 14. In other words, the first polymer surface 13 and the second polymer surface 14 comprise opposing main surfaces of the reflector 10. In some embodiments, the first polymer surface 13 and the second polymer surface 14 comprise corresponding first main surface 101 and second main surface 102. Thus, in some embodiments, the first polymer surface 13 and the second polymer surface 14 form corresponding first and second reflector-environment interfaces with the external environment. In some cases, the reflector 10 comprises integrally formed opposing first polymer surfaces 13 and 14. A plurality of alternating first polymer layers 11 and second polymer layers 12 are disposed between integrally formed opposing first polymer surfaces 13 and 14. In some cases, multiple alternating first polymer layers 11 and second polymer layers 12 are disposed between opposite first polymer surface layers 13 and second polymer surface layers 14, and are integrally formed with the first polymer surface layer and the second polymer surface layer.

[0091] Each of the polymer surface layers 13 and 14 has an average thickness “ts”. Each of the polymer surface layers 13 and 14 defines an average thickness “ts” along the z-direction. As used herein, the term “average thickness” refers to the average thickness along a plane of the layer (i.e., the xy-plane). Each of the polymer surface layers 13 and 14 has an average thickness “ts” greater than about 0.5 micrometers. In some embodiments, each of the polymer surface layers 13 and 14 has an average thickness “ts” greater than about 0.75 micrometers, greater than about 1 micrometer, greater than about 2 micrometers, greater than about 5 micrometers, greater than about 6 micrometers, greater than about 7 micrometers, greater than about 8 micrometers, greater than about 9 micrometers, greater than about 10 micrometers, greater than about 12 micrometers, or greater than about 15 micrometers.

[0092] In some embodiments, the first polymer surface layer 13 and the second polymer surface layer 14 comprise substantially the same material composition. In some embodiments, at least one of the first polymer layer 11 and the first polymer surface layer 13 and the second polymer surface layer 14 comprises substantially the same material composition. In some embodiments, at least one of the second polymer layer 12 and the first polymer surface layer 13 and the second polymer surface layer 14 comprises substantially the same material composition.

[0093] In some embodiments, the first polymer surface layer 13 and the second polymer surface layer 14 may comprise one or more polymer materials, such as PHEN, PEN, copolymers containing PHEN, PEN and / or other polyesters (e.g., PET or polyesters containing benzoic acid), ethylene glycol-modified polyethylene terephthalate, PC, PMMA, or blends of these types of materials.

[0094] In some embodiments, for at least one wavelength within the visible light wavelength range of 95, and for each of the first polymer surface layer 13 and the second polymer surface layer 14, the corresponding refractive indices of polymer surface layers 13, 14 and one of the first polymer layer 11 and the second polymer layer 12 differ from each other in the x, y, and z directions by approximately 0.05. In some embodiments, for at least one wavelength within the visible light wavelength range of 95, and for each of the first polymer surface layer 13 and the second polymer surface layer 14, the corresponding refractive indices of polymer surface layers 13, 14 and one of the first polymer layer 11 and the second polymer layer 12 differ from each other in the x, y, and z directions by approximately 0.02, approximately 0.015, approximately 0.01, approximately 0.0075, approximately 0.005, or approximately 0.0025.

[0095] As discussed above, in some embodiments, at least one of the first polymer layer 11 and the first polymer surface layer 13 and the second polymer surface layer 14 comprises substantially the same material composition. Therefore, in some embodiments, for each of the first polymer surface layer 13 and the second polymer surface layer 14, the corresponding refractive indices of polymer surface layers 13, 14 and the first polymer layer 11 along the x, y, and z directions are substantially similar. Specifically, for each of the first polymer surface layer 13 and the second polymer surface layer 14, the corresponding refractive indices of polymer surface layers 13, 14 and the first polymer layer 11 along the x, y, and z directions differ from each other by approximately 0.05. In some embodiments, for each of the first polymer surface layer 13 and the second polymer surface layer 14, the corresponding refractive indices of the polymer surface layers 13, 14 and the first polymer layer 11 in the x, y and z directions differ from each other by about 0.02, about 0.015, about 0.01, about 0.0075, about 0.005 or about 0.0025.

[0096] As discussed above, in some embodiments, at least one of the second polymer layer 12 and the first polymer surface layer 13 and the second polymer surface layer 14 comprises substantially the same material composition. Therefore, in some embodiments, for each of the first polymer surface layer 13 and the second polymer surface layer 14, the corresponding refractive indices of polymer surface layers 13, 14 and the second polymer layer 12 along the x, y, and z directions are substantially similar. Specifically, for each of the first polymer surface layer 13 and the second polymer surface layer 14, the corresponding refractive indices of polymer surface layers 13, 14 and the second polymer layer 12 along the x, y, and z directions differ from each other by approximately 0.05. In some embodiments, for each of the first polymer surface layer 13 and the second polymer surface layer 14, the corresponding refractive indices of the polymer surface layers 13, 14 and the second polymer layer 12 along the x, y and z directions differ from each other by about 0.02, about 0.015, about 0.01, about 0.0075, about 0.005 or about 0.0025.

[0097] In some embodiments, the reflector 10 may include at least one intermediate layer 16. In some embodiments, the at least one intermediate layer 16 has an average thickness greater than about 500 nm. In some embodiments, the at least one intermediate layer 16 is disposed between a plurality of polymer first layers 11 and polymer second layers 12. Specifically, the at least one intermediate layer 16 may be disposed between two stacks of polymer first layers 11 and polymer second layers 12. Figure 1 In the illustrated embodiment, at least one intermediate layer 16 is disposed between the first polymer layer 11a and the second polymer layer 12a. In some embodiments, the material composition of at least one intermediate layer 16 may be substantially similar to the material composition of at least one of the first polymer surface layer 13 and the second polymer surface layer 14.

[0098] In some embodiments, polymer surface layers 13, 14, polymer layers 11, 12, and at least one intermediate layer 16 may extend substantially together with each other, or have comparable in-plane dimensions (i.e., length and width). In other words, polymer surface layers 13, 14, polymer layers 11, 12, and at least one intermediate layer 16 may extend substantially together with each other in the xy plane.

[0099] In some embodiments, the reflector 10 may include additional or intermediate layers, such as an adhesive layer, a substrate layer, etc. The reflector 10 may have any suitable thickness based on the desired application properties.

[0100] Figure 2AA graph 150 is illustrated, depicting the thickness variations of a plurality of alternating first polymer layers 11 and second polymer layers 12 of a mirror 10 according to one embodiment of the present disclosure. The thicknesses of the plurality of alternating first polymer layers 11 and second polymer layers 12 are depicted in nanometers (nm) on the vertical axis, and the number of layers is depicted on the horizontal axis. Specifically, graph 150 illustrates the average layer thickness in nm on the vertical axis and the number of layers on the horizontal axis. Figure 2A In the illustrated embodiment, graph 150 depicts the thickness variation of a plurality of alternating first polymer layers 11 and second polymer layers 12 of the reflector 10 from layer 1 to layer 420. Graph 150 includes a thickness curve 155, which depicts the thickness variation of the plurality of alternating first polymer layers 11 and second polymer layers 12 of the reflector 10. Figure 2B The diagram shows an enlarged view of portion A of graph 150, depicting the thickness variation of multiple alternating first polymer layers 11 and second polymer layers 12 of the reflector 10 from layer 100 to layer 150.

[0101] Now for reference Figure 1 , Figure 2A and Figure 2B Each of the first polymer layer 11 and the second polymer layer 12 has an average thickness “t”. Specifically, each of the first polymer layer 11 and the second polymer layer 12 defines an average thickness “t” along the z-direction. Each of the first polymer layer 11 and the second polymer layer 12 is interchangeably referred to as “each polymer layer 11, 12”. Each of the first polymer layer 11 and the second polymer layer 12 has an average thickness “t” of less than about 500 nm. Specifically, each polymer layer 11, 12 disposed between the first polymer surface layer 13 and the second polymer surface layer 14 has an average thickness “t” of less than about 500 nm. In some embodiments, each of the first polymer layer 11 and the second polymer layer 12 has an average thickness “t” of less than about 400 nm, less than about 300 nm, or less than about 200 nm.

[0102] As can be seen from graph 150, in some embodiments, the difference between the maximum and minimum thicknesses of the alternating first polymer layer 11 and the second polymer layer 12 is between about 45% and 65%. In some embodiments, the difference between the maximum and minimum thicknesses of the alternating first polymer layer 11 and the second polymer layer 12 may be between about 50% and about 60%.

[0103] exist Figure 2AIn the illustrated embodiment, the maximum and minimum thicknesses of the alternating first polymer layer 11 and second polymer layer 12 are 126.7 nm and 57.6 nm, respectively. Therefore, the difference between the maximum and minimum thicknesses of the alternating first polymer layer 11 and second polymer layer 12 is approximately 54.5%.

[0104] Additionally, in some embodiments, the thickness of the first polymer layer 11 and the second polymer layer 12 typically increases with the number of layers until a threshold number of layers between 350 and 400 is reached. Furthermore, the thickness of the first polymer layer 11 and the second polymer layer 12 typically decreases with the number of layers beyond the threshold number.

[0105] In some embodiments, the maximum difference in thickness between adjacent polymer layers in the alternating first polymer layer 11 and second polymer layer 12 is less than about 25%. In some embodiments, the maximum difference in thickness between adjacent polymer layers in the alternating first polymer layer 11 and second polymer layer 12 is less than about 20%, less than about 15%, or less than about 10%. Figure 2A and Figure 2B In the illustrated embodiment, the maximum difference between the thicknesses of adjacent polymer layers in the alternating first polymer layer 11 and second polymer layer 12 is approximately 10%.

[0106] The difference in thickness between adjacent polymer layers 11 and 12 is in Figure 2B The optimal map is shown in the figure. Specifically, the thickness curve 155 has multiple V-shaped segments that indicate the corresponding values ​​of the thickness of the alternating first polymer layer 11 and second polymer layer 12.

[0107] The thickness of each of the alternating first polymer layer 11 and second polymer layer 12 is a discrete value indicated by the peaks or valleys of the corresponding V-shaped segments. Figure 2B The illustration shows the thicknesses of exemplary polymer layers 211, 212, 213, 214, and 215 (211-215). Polymer layers 211, 212, 213, 214, and 215 may correspond to... Figure 2B The layers shown are 105, 106, 107, 108, and 109. Polymer layers 211-215 have corresponding thicknesses 201, 202, 203, 204, and 205 (201-205). In this example, polymer layers 211, 213, and 215 with corresponding thicknesses 201, 203, and 205 can be first polymer layers 11, and polymer layers 212 and 214 with corresponding thicknesses 202 and 204 can be second polymer layers 12, such that the thickness of each second polymer layer in the second polymer layers 12 is less than the thickness of the adjacent subsequent first polymer layer 11.

[0108] However, in some examples, polymer layers 211, 213, 215 with corresponding thicknesses 201, 203, 205 may be second polymer layers 12, and polymer layers 212, 214 with corresponding thicknesses 202, 204 may be first polymer layers 11, such that the thickness of each first polymer layer in the first polymer layer 11 is less than the thickness of the adjacent subsequent second polymer layer 12.

[0109] Figure 3A and Figure 3B A schematic cross-sectional view of a reflector 10 according to one embodiment of the present disclosure is shown. Figure 3A and Figure 3B The incident light beams 20 and 21 propagating in the incident plane 22 are illustrated respectively.

[0110] The incident plane 22 includes the x-direction. The incident plane 22 may also include the normal N of the mirror 10. The normal N is substantially orthogonal to the plane of the mirror 10 (i.e., the xy-plane). In other words, the normal N is substantially along the z-direction of the mirror 10. The incident plane 22 substantially corresponds to the xz-plane of the mirror 10. In some embodiments, the incident plane 22 includes a first direction within the same plane. In some embodiments, the same plane is the xz-plane of the mirror 10, and the first direction within the same plane is the x-direction.

[0111] like Figure 3A and Figure 3B As shown, each of the incident beams 20 and 21 is incident on the mirror 10 at an angle θ relative to the normal N. Specifically, each of the incident beams 20 and 21 is incident on the mirror 10 at the first main surface 101 (i.e., at the first mirror-environment interface). However, in some embodiments, at least one of the incident beams 20 and 21 may be incident on the mirror 10 at the second main surface 102 (i.e., at the second mirror-environment interface).

[0112] In some cases, the angle of incidence θ can be a first angle of incidence less than about 10 degrees. In some implementations, the first angle of incidence is less than about 9 degrees, less than about 8 degrees, less than about 7 degrees, less than about 6 degrees, less than about 5 degrees, less than about 4 degrees, less than about 3 degrees, less than about 2 degrees, or less than about 1 degree. In some examples, the first angle of incidence is about 0 degrees.

[0113] In some cases, the second angle of incidence θ can be greater than about 45 degrees. In some embodiments, the second angle of incidence is greater than about 50 degrees or greater than about 55 degrees. In some embodiments, the second angle of incidence is about 60 degrees.

[0114] Now for reference Figure 3AThe incident light 20 is s-polarized light. Incident light 20 can also be interchangeably referred to as "s-polarized incident light 20" or "s-polarized incident light 20". The incident light 20 is polarized along a second direction. In some embodiments, the second direction may be along the y-direction. Therefore, the incident light 20 is polarized along the y-direction. Incident light 20 can also be interchangeably referred to as "sunlight 20 polarized along the y-direction".

[0115] Now for reference Figure 3B The incident light 21 is p-polarized light. The incident light 21 can also be interchangeably referred to as "p-polarized incident light 21" or "p-polarized incident light 21". Specifically, when the incident light 21 is incident at a first incident angle, the incident light 21 is polarized along a first direction. In some embodiments, the first direction may be along the x-direction. Therefore, when the incident light 21 is incident at a first incident angle, the incident light 21 may be polarized along the x-direction. The incident light 21 can be interchangeably referred to as "x-polarized incident light 21".

[0116] Figure 4A The figure illustrates a multi-layered partial reflector 10 according to one embodiment of the present disclosure. Figure 1 As shown) for s-polarized incident light 20 (incident at the first incident angle) Figure 3A The graph 400 shows the relationship between optical reflectance and wavelength. Specifically, graph 400 depicts the relationship between the optical reflectance of multiple alternating first polymer layers 11 and second polymer layers 12 and wavelength for s-polarized incident light 20 incident at a first incident angle of less than about 10 degrees. Wavelength is expressed in nanometers (nm) on the horizontal axis. Optical reflectance is expressed as a percentage of reflectance on the left vertical axis. Optical transmittance is expressed as a percentage of transmittance on the right vertical axis. The percentage of transmittance and percentage of reflectance are approximately complementary, i.e., percentage of transmittance = (100 - percentage of reflectance).

[0117] Graph 400 includes a curve 30 corresponding to the relationship between the optical reflectivity of the multilayer partial reflector 10 and wavelength for s-polarized incident light 20 incident at a first incident angle. In some cases, for graph 400, the first incident angle is approximately 0 degrees. Curve 30 is interchangeably referred to as "relationship between optical reflectivity and wavelength 30". Optical reflectivity is interchangeably referred to as "reflectivity".

[0118] refer to Figure 1 , Figure 3A , Figure 3B and Figure 4AFor visible light wavelength range 95, infrared wavelength range 96 from about 800 nm to about 1300 nm, incident light 20 propagating in an incident plane 22 including the x-direction, and for a first incident angle less than about 10 degrees, a plurality of alternating first polymer layers 11 and second polymer layers 12 have an average reflectivity Rs1 for incident light 20 polarized in the y-direction. Specifically, for visible light wavelength range 95, infrared wavelength range 96, incident light 20 propagating in an incident plane 22 including the first direction (i.e., the x-direction) in the same plane, and at a first incident angle less than about 10 degrees, the reflector 10 has an average reflectivity Rs1 for s-polarized incident light 20. In other words, for visible light wavelength range 95, infrared wavelength range 96 and incident light 20 propagating in incident plane 22 including the x-direction, and for s-polarized incident light 20, a plurality of alternating first polymer layers 11 and second polymer layers 12 have an average reflectivity Rs1 for a first incident angle of less than about 10 degrees.

[0119] In some embodiments, Rs1 is less than about 85% for the visible light wavelength range of 95. In some embodiments, Rs1 is less than about 80%, less than about 75%, less than about 70%, or less than about 65% for the visible light wavelength range of 95.

[0120] Additionally, in some embodiments, Rs1 is greater than about 50% for the visible light wavelength range of 95. In some embodiments, Rs1 is greater than about 55%, greater than about 60%, greater than about 65%, or greater than about 70% for the visible light wavelength range of 95. Therefore, in some embodiments, Rs1 is between about 50% and about 85% for the visible light wavelength range of 95. In some examples, Rs1 is about 64% or about 71.7% for the visible light wavelength range of 95.

[0121] Additionally, in some embodiments, for the infrared wavelength range 96, for s-polarized incident light 20 propagating in the incident plane 22 including the x-direction and for the first incident angle, the plurality of alternating first polymer layers 11 and second polymer layers 12 have an average transmittance Ts1 greater than about 50%. In some embodiments, for the infrared wavelength range 96, for s-polarized incident light 20 propagating in the incident plane 22 including the x-direction and for the first incident angle, the plurality of alternating first polymer layers 11 and second polymer layers 12 have an average transmittance Ts1 greater than about 60%, greater than about 70%, greater than about 75%, or greater than about 80%. In some examples, Ts1 is about 81% or about 83.7%.

[0122] Additionally, as depicted in graph 400, for the first incident angle and for s-polarized incident light 20, the relationship 30 of optical reflectivity as a function of wavelength includes a reflection band edge 32 between approximately 760 nm and approximately 980 nm. In some embodiments, for the first incident angle and for s-polarized incident light 20, the relationship 30 of optical reflectivity as a function of wavelength includes a reflection band edge 32 between approximately 780 nm and approximately 960 nm or between approximately 800 nm and approximately 940 nm.

[0123] Figure 4B The figure illustrates a multi-layered partial reflector 10 according to one embodiment of the present disclosure. Figure 1 As shown) for p-polarized incident light 21 incident at the first incident angle Figure 3B The graph 410 shows the relationship between optical reflectance and wavelength (as shown). Specifically, graph 410 depicts the relationship between the optical reflectance of multiple alternating first polymer layers 11 and second polymer layers 12 and wavelength for p-polarized incident light 21 incident at a first incident angle of less than about 10 degrees. Wavelength is expressed in nanometers (nm) on the horizontal axis. Optical reflectance is expressed as a percentage of reflectance on the left vertical axis. Optical transmittance is expressed as a percentage of transmittance on the right vertical axis. The percentage of transmittance and percentage of reflectance are approximately complementary, i.e., percentage of transmittance = (100 - percentage of reflectance).

[0124] Graph 410 includes curve 31 corresponding to the relationship between the optical reflectivity of the multilayer partial reflector 10 and the wavelength for p-polarized incident light 21 incident at a first incident angle. In some cases, for graph 410, the first incident angle is approximately 0 degrees. Curve 31 may be interchangeably referred to as "relationship between optical reflectivity and wavelength 31".

[0125] refer to Figure 1 , Figure 3A , Figure 3B and Figure 4BFor incident light 21 propagating in the visible light wavelength range 95, the infrared wavelength range 96, and the incident light 21 propagating in the incident plane 22 including the x-direction, and for a first incident angle of less than about 10 degrees, the plurality of alternating first polymer layers 11 and second polymer layers 12 have an average reflectivity Rp1 for incident light 21 polarized in the x-direction. Specifically, for incident light 21 propagating in the visible light wavelength range 95, the infrared wavelength range 96, and the incident light 21 propagating in the incident plane 22 including the first direction in the same plane, and for a first incident angle of less than about 10 degrees, the reflector 10 has an average reflectivity Rp1 for p-polarized incident light 21. In other words, for incident light 21 propagating in the visible light wavelength range 95, the infrared wavelength range 96, and the incident light 21 propagating in the incident plane 22 including the x-direction, and for p-polarized incident light 21, the plurality of alternating first polymer layers 11 and second polymer layers 12 have an average reflectivity Rp1 for the first incident angle.

[0126] In some embodiments, Rp1 is less than about 85% for the visible light wavelength range of 95. In some embodiments, Rp1 is less than about 80%, less than about 75%, less than about 70%, or less than about 65% for the visible light wavelength range of 95.

[0127] Additionally, in some embodiments, Rp1 is greater than about 50% for the visible light wavelength range of 95. In some embodiments, Rp1 is greater than about 55%, greater than about 60%, greater than about 65%, or greater than about 70% for the visible light wavelength range of 95. Therefore, in some embodiments, Rp1 is between about 50% and about 85% for the visible light wavelength range of 95. In some examples, Rp1 is about 64% or about 71.7% for the visible light wavelength range of 95.

[0128] Additionally, in some embodiments, for the infrared wavelength range 96, for p-polarized incident light 21 propagating in the incident plane 22 including the x-direction and the first incident angle, the plurality of alternating first polymer layers 11 and second polymer layers 12 have an average transmittance Tp1 greater than about 50%. In some embodiments, for the infrared wavelength range 96, for p-polarized incident light 21 propagating in the incident plane 22 and the first incident angle, the plurality of alternating first polymer layers 11 and second polymer layers 12 have an average transmittance Tp1 greater than about 60%, greater than about 70%, greater than about 75%, or greater than about 80%. In some examples, Tp1 is about 81% or about 83.7%.

[0129] Additionally, as depicted in graph 410, for the first incident angle and for p-polarized incident light 21, the optical reflectivity versus wavelength relationship 31 includes a reflection band edge 33 between approximately 760 nm and approximately 980 nm. In some embodiments, for the first incident angle and for p-polarized incident light 21, the optical reflectivity versus wavelength relationship 31 includes a reflection band edge 33 between approximately 780 nm and approximately 960 nm or between approximately 800 nm and approximately 940 nm.

[0130] Now for reference Figure 4A and Figure 4B For the visible light wavelength range 95, each of Rp1 and Rs1 is less than about 85%. In some embodiments, for the visible light wavelength range 95, each of Rp1 and Rs1 is less than about 80%, less than about 75%, less than about 70%, or less than about 65%. Additionally, for the infrared wavelength range 96, each of Rp1 and Rs1 is less than about 50%. In some embodiments, for the infrared wavelength range 96, each of Rp1 and Rs1 is less than about 45%, less than about 35%, less than about 30%, or less than about 25%.

[0131] Therefore, for the infrared wavelength range 96, for each of the s-polarized incident light 20 and the p-polarized incident light 21, and for the first incident angle, the plurality of alternating first polymer layers 11 and second polymer layers 12 can be substantially transmissive. Thus, the multilayer partial reflector 10 is suitable for IR fingerprint sensing applications.

[0132] In some embodiments, for the visible light wavelength range 95, Rp1 / Rs1 is between about 0.8 and about 1.2. In other words, for the visible light wavelength range 95, the ratio of Rp1 to Rs1 is between about 0.8 and about 1.2. In some embodiments, for the visible light wavelength range 95, Rp1 / Rs1 is between about 0.85 and about 1.15, between about 0.90 and about 1.10, or between about 0.95 and about 1.05. In some examples, for the visible light wavelength range 95, Rp1 / Rs1 is about 1.

[0133] In some embodiments, for the visible light wavelength range of 95, Rp1 and Rs1 differ from each other within 10%. In some embodiments, for the visible light wavelength range of 95, Rp1 and Rs1 differ from each other within 9%, 8%, 7%, 6%, 5%, 4%, 3%, or 2%.

[0134] Therefore, for the visible light wavelength range 95, the multiple alternating first polymer layers 11 and second polymer layers 12 can have substantially similar average optical reflectivity for each of the s-polarized incident light 20 and the p-polarized incident light 21 and for the first incident angle.

[0135] For each of the p-polarized incident light 21 and the s-polarized incident light 20, the optical reflectivity versus wavelength relationship 31, 30 includes the reflection band edge 33, 31 between about 760 nm and about 980 nm.

[0136] The corresponding optical reflectivity of the multilayer partial reflector 10 in relation to wavelength 31, 30, and the reflection band edges 32, 33 can be adjusted based on the desired application attributes of the IR fingerprint sensing application.

[0137] Figure 4C The figure illustrates a multi-layered partial reflector 10 according to one embodiment of the present disclosure. Figure 1 As shown, for s-polarized incident light 20 incident on mirror 10 at the second incident angle (as shown) Figure 3A The graph 420 shows the relationship between optical reflectance and wavelength (as shown). Specifically, graph 420 depicts the relationship between the optical reflectance of multiple alternating first polymer layers 11 and second polymer layers 12 and wavelength for s-polarized incident light 20 incident at a second incident angle greater than approximately 45 degrees. Wavelength is expressed in nanometers (nm) on the horizontal axis. Optical reflectance is expressed as a percentage of reflectance on the left vertical axis. Optical transmittance is expressed as a percentage of transmittance on the right vertical axis. The percentage of transmittance and percentage of reflectance are approximately complementary, i.e., percentage of transmittance = (100 - percentage of reflectance).

[0138] Graph 420 includes curve 35 corresponding to the relationship between the optical reflectivity of the multilayer partial reflector 10 and the wavelength for s-polarized incident light 20 incident at a second incident angle. In some cases, for graph 420, the second incident angle is approximately 60 degrees. Curve 35 is interchangeably referred to as "relationship between optical reflectivity and wavelength 35".

[0139] refer to Figure 1 , Figure 3A , Figure 3B and Figure 4C For incident light 20 propagating in the visible light wavelength range 95, the infrared wavelength range 96, and the incident light 20 propagating in the incident plane 22 including the x-direction, and for a second incident angle greater than approximately 45 degrees, a plurality of alternating first polymer layers 11 and second polymer layers 12 have an average reflectivity Rs2 for incident light 20 polarized in the y-direction. Specifically, for incident light 20 propagating in the visible light wavelength range 95, the infrared wavelength range 96, and the incident light 20 propagating in the incident plane 22, and for s-polarized incident light 20, a plurality of alternating first polymer layers 11 and second polymer layers 12 have an average reflectivity Rs2 for a second incident angle greater than approximately 45 degrees.

[0140] In some embodiments, Rs2 is less than about 97% for the visible light wavelength range of 95. In some embodiments, Rs2 is less than about 96%, less than about 95%, or less than about 94% for the visible light wavelength range of 95.

[0141] Additionally, in some embodiments, Rs2 is greater than about 70% for the visible light wavelength range of 95. In some embodiments, Rs2 is greater than about 75%, greater than about 80%, greater than about 85%, or greater than about 90% for the visible light wavelength range of 95. Therefore, in some embodiments, Rs2 is between about 70% and about 97% for the visible light wavelength range of 95. In some examples, Rs2 is about 92.4% or about 94.8%.

[0142] Additionally, in some embodiments, for the infrared wavelength range 96, for s-polarized incident light 20 propagating in the incident plane 22 including the x-direction and for the second incident angle, the plurality of alternating first polymer layers 11 and second polymer layers 12 have an average transmittance Ts2 greater than about 40%. In some embodiments, for the infrared wavelength range 96, for s-polarized incident light 20 propagating in the incident plane 22 and for the second incident angle, the plurality of alternating first polymer layers 11 and second polymer layers 12 have an average transmittance Ts2 greater than about 45%, greater than about 50%, greater than about 55%, or greater than about 60%. In some examples, Ts2 is about 64.2% or about 64.6%.

[0143] Figure 4D The figure illustrates a multi-layered partial reflector 10 according to one embodiment of the present disclosure. Figure 1 As shown) for p-polarized incident light 21 incident on mirror 10 at the second incident angle ( Figure 3B The graph 430 shows the relationship between optical reflectance and wavelength. Specifically, graph 430 depicts the relationship between the optical reflectance of multiple alternating first polymer layers 11 and second polymer layers 12 and wavelength for p-polarized incident light 21 incident at a second incident angle greater than approximately 45 degrees. Wavelength is expressed in nanometers (nm) on the horizontal axis. Optical reflectance is expressed as a percentage of reflectance on the left vertical axis. Optical transmittance is expressed as a percentage of transmittance on the right vertical axis. The percentage of transmittance and percentage of reflectance are approximately complementary, i.e., percentage of transmittance = (100 - percentage of reflectance).

[0144] Graph 430 includes curve 36 corresponding to the relationship between the optical reflectivity of the multilayer partial reflector 10 and the wavelength for p-polarized incident light 21 incident at a second incident angle. In some cases, for graph 430, the second incident angle is approximately 60 degrees. Curve 36 is interchangeably referred to as "relationship between optical reflectivity and wavelength 36".

[0145] refer to Figure 1 , Figure 3A , Figure 3B and Figure 4D For visible light wavelength range 95, infrared wavelength range 96 and incident light 21 propagating in incident plane 22 including the x-direction, and for p-polarized incident light 21, a plurality of alternating first polymer layers 11 and second polymer layers 12 have an average reflectivity Rp2 with respect to the second incident angle.

[0146] In some embodiments, Rp2 is less than about 98% for the visible light wavelength range of 95. In some embodiments, Rp2 is less than about 97%, less than about 96%, less than about 95%, less than about 94%, or less than about 93% for the visible light wavelength range of 95.

[0147] Additionally, in some embodiments, Rp2 is greater than about 70% for the visible light wavelength range of 95. In some embodiments, Rp2 is greater than about 75%, greater than about 80%, greater than about 85%, or greater than about 90% for the visible light wavelength range of 95. Therefore, in some embodiments, Rp2 is between about 70% and about 98% for the visible light wavelength range of 95. In some examples, Rp2 is about 93.3% or about 94.8% for the visible light wavelength range of 95.

[0148] Additionally, in some embodiments, for the infrared wavelength range 96, for p-polarized incident light 21 propagating in the incident plane 22 including the x-direction and the second incident angle, the plurality of alternating first polymer layers 11 and second polymer layers 12 have an average transmittance Tp2 greater than about 70%. In some embodiments, for the infrared wavelength range 96, for p-polarized incident light 21 propagating in the incident plane 22 and the second incident angle, the plurality of alternating first polymer layers 11 and second polymer layers 12 have an average transmittance Tp2 greater than about 75%, greater than about 80%, greater than about 85%, greater than about 90%, or greater than about 95%. In some examples, Tp2 is about 99.5% or about 99.7%.

[0149] Now for reference Figure 4C and Figure 4D For incident light 20 and 21 propagating in the visible light wavelength range 95, the infrared wavelength range 96, and in the incident plane 22 including the x-direction, and for a second incident angle greater than about 45 degrees, the plurality of alternating first polymer layers 11 and second polymer layers 12 have average reflectivities Rp2 and Rs2 for the corresponding p-polarized incident light 21 and s-polarized incident light 20. Furthermore, for the visible light wavelength range 95, each of Rp2 and Rs2 is greater than about 70%. In some embodiments, for the visible light wavelength range 95, each of Rp2 and Rs2 is greater than about 75%, greater than about 80%, greater than about 85%, or greater than about 90%.

[0150] Therefore, for each of Rp2 and Rs2 and for the visible light wavelength range 95, mirror 10 can substantially reflect off-axis light incident at an angle of incidence greater than about 45 degrees. Specifically, for the visible light wavelength range 95, mirror 10 can substantially reflect each of s-polarized incident light 20 and p-polarized incident light 21, as well as the second angle of incidence.

[0151] Now for reference Figures 4A to 4D For the visible light wavelength range of 95, each of Rs2 / Rs1 and Rp2 / Rp1 is greater than about 1.15. In some embodiments, for the visible light wavelength range of 95, each of Rs2 / Rs1 and Rp2 / Rp1 is greater than about 1.2, greater than about 1.25, greater than about 1.3, greater than about 1.35, greater than about 1.4, or greater than about 1.45.

[0152] Therefore, for the visible light wavelength range 95, and for each of the s-polarized incident light 20 and p-polarized incident light 21, the mirror 10 has a higher average optical reflectivity for light incident at the second incident angle (i.e., off-axis light) compared to light incident at the first incident angle (i.e., substantially perpendicular incident light or axial light). In other words, for the visible light wavelength range 95, and for each of the s-polarized incident light 20 and p-polarized incident light 21, the mirror 10 has greater optical transmittance for axial light compared to off-axis light. Since the mirror 10 can substantially collimate the off-axis light of both the s-polarized incident light 20 and the p-polarized incident light 21 for the visible light wavelength range 95, it provides improved collimation compared to conventional collimating films that typically reflect only one of the s-polarized and p-polarized light incident at the second incident angle. Furthermore, for the visible light wavelength range 95, mirror 10 can have a smaller average optical reflectivity for axial light compared to conventional collimating films that even essentially block axial light polarized in one direction (either s-polarized light 20 or p-polarized light 21). Therefore, for the visible light wavelength range 95, the smaller average optical reflectivity for axial light provides improved axial brightness.

[0153] Furthermore, for the infrared wavelength range 96, the plurality of alternating first polymer layers 11 and second polymer layers 12 are substantially transmissive to each of the s-polarized incident light 20 and p-polarized incident light 21 incident at the first and second incident angles. In other words, for the infrared wavelength range 96, the reflector 10 can be substantially transparent. Therefore, the reflector 10 is suitable for IR fingerprint sensing applications.

[0154] In some cases, the display system (not shown) used to sense the user's finger may include a reflector 10. Figure 1(As shown). One embodiment of such a display system may be as described herein. The display system may include a display panel configured to generate an image for a user to view and a backlight source including a light guide for illuminating the display panel. The backlight source may also include a reflector 10 disposed adjacent to the light guide and opposite to the display panel. The reflector 10 may serve as a back reflector of the backlight source and may be used to circulate light from the light guide toward the display panel. The display system may also include an optical construct disposed between the display panel and the light guide, wherein the optical construct includes a reflective polarizer comprising a plurality of polymer layers and having a first structured main surface disposed between the display panel and the plurality of polymer layers. The display system may also include an infrared sensor disposed near the backlight source and opposite to the reflective polarizer. The display system may also include an infrared light source configured to emit infrared light toward the display panel. A user's finger may be placed on the display panel, and a portion of the infrared light may be reflected from the finger and transmitted through the backlight source and the reflector 10, such that the infrared sensor may detect at least a portion of the infrared light transmitted through the reflector 10. In some cases, the display system may also include a structured mirror disposed between the mirror 10 and the infrared sensor and including an optical mirror and an array of discretely spaced optical bumps formed on the optical mirror and facing the light guide. For substantially perpendicular incident light, for at least a first polarization state, the optical mirror may have an average optical reflectivity greater than about 30% in the visible light wavelength range, and for each of the first polarization state and an orthogonal second polarization state, the optical mirror may have a specular transmittance greater than about 20% for at least one wavelength in the infrared wavelength range.

[0155] Figure 5A A detailed schematic cross-sectional view of a display system 60 including a reflector 10 according to one embodiment of the present disclosure is illustrated. Specifically, the display system 60 includes a display panel 41 disposed on a backlight 40. The backlight 40 provides illumination to the display panel 41. The display panel 41 is configured to form an image 42.

[0156] In some embodiments, the display panel 41 includes a liquid crystal display (LCD) panel. The backlight 40 includes an extended light source 43 configured to emit light 44 through an emitting surface 45 of the extended light source. The light 44 is interchangeably referred to as "emitted light 44".

[0157] The backlight 40 also includes a reflector 10. The reflector 10 is disposed on the emitting surface 45. The reflector 10 and the back reflector 46 form a circular optical cavity 47 between them.

[0158] Extended light source 43 also includes a back reflector 46. In some embodiments, the back reflector 46 may be highly reflective. For example, the back reflector 46 may have an axial average reflectivity of at least 90%, 95%, 98%, 99%, or greater. Such reflectivity values ​​can reduce losses in the circulating optical cavity 47. Additionally, such reflectivity values ​​may include both specular and diffuse reflection. In some embodiments, the back reflector 46 may be primarily a specular reflector, a diffuse reflector, or a combination of specular and diffuse reflectors, whether spatially uniformly distributed or patterned. In some embodiments, the back reflector 46 may be a semi-specular reflector. In some cases, the back reflector 46 may comprise a rigid metal substrate with a high-reflectivity coating or a high-reflectivity film laminated to a supporting substrate. In some embodiments, the back reflector 46 may comprise one or more elements, such as silver, aluminum, a white coating, a non-conductive coating, etc.

[0159] The reflector 10 is configured to receive the emitted light 44. The reflector 10 is further configured to allow a portion of the received light to be transmitted through the reflector. In other words, the reflector 10 is configured to receive the emitted light 44 incident on the reflector 10, and the light exiting the reflector 10 includes the portion of the emitted light 44 that has been transmitted through the reflector 10.

[0160] In some embodiments, the backlight 40 further includes a first optical diffuser 48 disposed between the reflector 10 and the emitting surface 45. The first optical diffuser 48 diffuses the light 44 emitted by the extended light source 43.

[0161] In some embodiments, the backlight 40 also includes a second optical diffuser 49. The second optical diffuser 49 is disposed on the reflector 10 opposite to the emitting surface 45. The second optical diffuser 49 is configured to diffuse the light transmitted by the reflector 10.

[0162] Each of the first optical diffuser 48 and the second optical diffuser 49 may include any suitable diffuser film or plate configured to diffuse or scatter light. For example, the first optical diffuser 48 and the second optical diffuser 49 may diffuse light by using a textured surface of a substrate or by other means such as incorporating light-diffusing particles within the matrix of the film.

[0163] In some embodiments, the backlight 40 also includes a reflective polarizer 50 disposed on the reflector 10 and opposite to the emitting surface 45. Figure 5A In the illustrated embodiment, the reflective polarizer 50 is arranged adjacent to the second optical diffuser 49, such that the second optical diffuser 49 is located between the reflector 10 and the reflective polarizer 50. Therefore, in Figure 5A In the illustrated embodiment, the reflective polarizer 50 is arranged to receive transmitted light diffused by the second optical diffuser 49.

[0164] In some embodiments, the reflective polarizer 50 may be a collimated multilayer optical film (CMOF). However, the reflective polarizer 50 may be any suitable reflective polarizer. In some embodiments, the reflective polarizer 50 may include one or more of a multilayer polymer reflective polarizer, a wire grating reflective polarizer, and a diffuse reflective polarizer. A reflective polarizer relies on the difference in refractive indices between at least two materials (typically polymer materials) to selectively reflect light in one polarization state while transmitting light in an orthogonally polarized state.

[0165] Figure 5B The illustration shows one embodiment according to this disclosure. Figure 5A A schematic diagram of the reflective polarizer 50 of the display system 60 shown. Figure 5B The illustration also shows substantially perpendicular incident light 501 incident on the reflective polarizer 50, i.e., substantially perpendicular incident light 501 incident at an angle of approximately 0 degrees relative to the normal N1 of the reflective polarizer 50. In some embodiments, the normal N1 may be substantially parallel to the normal N ( Figure 3A and Figure 3B (As shown). Basically, the perpendicularly incident light 501 can be interchangeably referred to as "incident light 501".

[0166] In some cases, the incident light 501 may be polarized along a first direction. In some embodiments, the first direction may be the x-direction. Additionally, in some other cases, the incident light 501 may be polarized along a second direction orthogonal to the first direction. In some embodiments, the second direction may be the y-direction.

[0167] Figure 5C A graph 510 depicting the optical characteristics of a reflective polarizer 50 according to one embodiment of the present disclosure is shown. Specifically, graph 510 depicts the optical reflectivity and optical transmittance of the reflective polarizer 50. Wavelength is expressed in nanometers (nm) on the horizontal axis. Optical reflectivity is expressed as a percentage of reflectivity on the left vertical axis. Optical transmittance is expressed as a percentage of transmittance on the right vertical axis. The percentage of transmittance is approximately complementary to the percentage of reflectivity, i.e., percentage of transmittance = (100 - percentage of reflectivity).

[0168] Now for reference Figure 5B and Figure 5C The graph 510 includes a reflectance curve 505. The reflectance curve 505 depicts the optical reflectance of the reflective polarizer 50 for substantially perpendicular incident light 501 polarized along a first direction.

[0169] Graph 510 also includes a reflectance curve 506. The reflectance curve 506 depicts the optical transmittance of the reflective polarizer 50 for substantially perpendicular incident light 501 polarized along a second direction orthogonal to the first direction.

[0170] As depicted in reflectance curve 505, for the visible light wavelength range 95 and substantially perpendicular incident light 501, when the incident light 501 is polarized along the first direction, the reflective polarizer 50 has an average optical reflectance greater than about 60%. In some embodiments, for the visible light wavelength range 95 and substantially perpendicular incident light 501, when the incident light 501 is polarized along the first direction, the reflective polarizer 50 has an average optical reflectance greater than about 70%, greater than about 80%, or greater than about 90%.

[0171] As depicted in reflectivity curve 506, for the visible light wavelength range 95 and substantially perpendicular incident light 501, when the incident light 501 is polarized along a second direction orthogonal to the first direction, the reflective polarizer 50 has an average optical transmittance greater than about 60%. In some embodiments, for the visible light wavelength range 95 and substantially perpendicular incident light 501, when the incident light 501 is polarized along a second direction orthogonal to the first direction, the reflective polarizer 50 has an average optical transmittance greater than about 70%, greater than about 80%, or greater than about 90%.

[0172] Figure 6A A detailed schematic cross-sectional view of an optical system 70 according to one embodiment of the present disclosure is illustrated. In some embodiments, the optical system 70 is formed by providing a substantially Lambertian light source 71, which includes a back reflector 72 and emits substantially unpolarized light 73 through an extended emitting surface 74 of the substantially Lambertian light source.

[0173] A Lambertian light source is a light source that obeys Lambertian cosine law I = I0cosα, where α is the viewing angle and I0 is the light intensity normal to the light source at a viewing angle α of approximately 0 degrees. For a Lambertian light source, the light intensity at a viewing angle α close to 90 degrees is very low. Light-emitting diodes (LEDs) approximate Lambertian sources because they tend to have large beam divergence and a near-spherical radiation pattern. In some cases, a Lambertian light source can achieve a Lambertian or Lambertian-like effect by providing an externally coupled photometric diffuser (e.g., composed of or containing acetal, silica, etc.) close to a non-Lambertian light source.

[0174] In some embodiments, the back reflector 72 has a total reflectivity greater than about 90% at at least one wavelength within the visible light wavelength range 95. In some embodiments, the back reflector 72 has a total reflectivity greater than about 92%, greater than about 94%, greater than about 96%, greater than about 98%, or greater than about 99% at at least one wavelength within the visible light wavelength range 95. The optical system 70 is further formed by distributing the reflective mirror 10 between the reflective polarizer 75 and the emitting surface 74.

[0175] Light 78 leaves the optical system 70. Light 78 can leave the optical system 70 through the reflective polarizer 75.

[0176] In some implementations, the back reflector 72 may be substantially similar to Figure 5A 46. ​​Back reflector.

[0177] Figure 6B The figure shows a schematic diagram of a reflective polarizer 75 of an optical system 70 according to one embodiment of the present disclosure. Figure 6B The illustration also shows substantially perpendicular incident light 76 incident on the reflective polarizer 75, i.e., substantially perpendicular incident light 76 incident at an angle of approximately 0 degrees relative to the normal N2 of the reflective polarizer 75. In some embodiments, the normal N2 may be substantially parallel to the normal N ( Figure 3A and Figure 3B (As shown). Basically, the perpendicularly incident light 76 can be interchangeably referred to as "incident light 76".

[0178] In some cases, the incident light 76 may be polarized along a first direction. In some embodiments, the first direction may be the x-direction. Additionally, in some cases, the incident light 76 may be polarized along a second direction orthogonal to the first direction. In some embodiments, the second direction may be the y-direction. In some cases, the incident light 76 may be partially polarized light. Furthermore, in some cases, the incident light 76 may be unpolarized light with an unknown or arbitrary polarization state or a distribution of polarization states.

[0179] In some implementations, the reflective polarizer 75 may be substantially similar to the reflective polarizer 50. Figure 5A and 5B As shown). Specifically, the optical characteristics of the reflective polarizer 75 can be substantially similar to those of the reflective polarizer 50, as shown in Figure 510. Figure 5C (As shown). Therefore, in some embodiments, for the visible light wavelength range 95 and substantially perpendicular incident light 76, when the incident light 76 is polarized along the x-direction, the reflecting polarizer 75 has an average optical reflectivity greater than about 60%. In some embodiments, for the visible light wavelength range 95 and substantially perpendicular incident light 76, when the incident light 76 is polarized along the x-direction, the reflecting polarizer 75 has an average optical reflectivity greater than about 70%, greater than about 80%, or greater than about 90%.

[0180] Furthermore, for the visible light wavelength range 95 and substantially perpendicular incident light 76, when the incident light 76 is polarized along the y-direction, the reflective polarizer 75 has an average optical transmittance greater than about 60%. In some embodiments, for the visible light wavelength range 95 and substantially perpendicular incident light 76, when the incident light 76 is polarized along the y-direction, the reflective polarizer 75 has an average optical transmittance greater than about 70%, greater than about 80%, or greater than about 90%.

[0181] Figure 6C The illustration shows an exit optical system 70 according to one embodiment of the present disclosure. Figure 6A Shown) of light 78( Figure 6A The luminescence distribution (shown in Figure 77) is shown.

[0182] Figure 6D The illustration shows the optical system 70 when viewed at different angles relative to the z-direction according to one embodiment of the present disclosure. Figure 6A Shown) of light 78( Figure 6A The graph 600 shows the relative intensity of the light 78 (as shown). Specifically, the graph 600 plots the relative intensity of the light 78 on the left vertical axis and the different angles relative to the z-direction on the horizontal axis. The graph 600 includes intensity curves 601, 602, and 603 that depict the relative intensity of the light 78 leaving the optical system 70.

[0183] Now for reference Figures 6A to 6D The emission distribution 77 of light 78 exiting the optical system 70 via the reflective polarizer 75 includes at least one global peak at an angle 79 to the normal (i.e., normal N2) of the reflective polarizer 75. In some embodiments, the at least one global peak forms an angle 79 greater than about 5 degrees with respect to the normal of the reflective polarizer 75. In some embodiments, the normal of the reflective polarizer 75 is along the z-direction. Therefore, the emission distribution 77 of light 78 exiting the optical system 70 via the reflective polarizer 75 includes at least one global peak at an angle 79 greater than about 5 degrees with respect to the z-direction of the reflective polarizer 75. Figure 6D In the illustrated embodiment, angle 79 is approximately 13 degrees. In some embodiments, the emission distribution 77 of the light 78 exiting the optical system 70 via the reflective polarizer 75 includes at least one global peak at an angle 79 greater than approximately 7 degrees, greater than approximately 10 degrees, or greater than approximately 12 degrees with respect to the normal of the reflective polarizer 75.

[0184] In some embodiments, at least one global peak lies in a plane at an angle β to the x-direction. In some embodiments, the angle β is between about 30 degrees and about 60 degrees. In some embodiments, the angle β is between about 35 degrees and about 55 degrees, or between about 40 degrees and about 50 degrees. Figure 6CIn the illustrated embodiment, the tilt angle β is approximately 45 degrees. The emission distribution 77 of light 78 includes four global peaks at an angle 79 greater than approximately 5 degrees to the normal of the reflective polarizer 75. Specifically, the emission distribution 77 includes a first global peak P1, a second global peak P2, a third global peak P3, and a fourth global peak P4. The first global peak P1 and the third global peak P3 are located on a plane 80 at a tilt angle β to the x-direction. The second global peak P2 and the fourth global peak P4 are located on a plane 81 at a tilt angle β to the x-direction.

[0185] Now for reference Figures 6A to 6D Intensity curves 601, 602, and 603 depict the variations or distributions of light 78 exiting the optical system 70 at tilt angles β of 0 degrees, 45 degrees, and 90 degrees, respectively. From Figure 6D As can be observed in graph 600, curve 602 includes peaks in the relative intensity of light 78 exiting optical system 70. Additionally, it can be observed that the peaks form an angle 79 greater than approximately 5 degrees relative to the z-direction. This corresponds to the location of at least one global peak in the emission distribution 77.

[0186] In some implementations, the first global peak P1, the second global peak P2, the third global peak P3, and the fourth global peak P4 may have substantially similar relative intensities.

[0187] Examples and Data

[0188] The multilayer partial reflector (“reflector 10”) disclosed herein is constructed and compared with a conventional collimating multilayer optical film (CMOF). The CMOF includes multiple first and second layers, as well as a first surface layer and a second surface layer. The CMOF comprises 650 layers.

[0189] Table 1 below provides the refractive indices of different layers of CMOF.

[0190] Table 1

[0191] First layer 1.840 1.625 1.490 Second floor 1.570 1.570 1.570 First surface layer 1.570 1.570 1.570 Second surface layer 1.570 1.570 1.570

[0192] The reflector is constructed similarly to reflector 10, such as... Figure 1 The mirror comprises 420 layers.

[0193] Table 2 below provides exemplary refractive indices for different layers of the mirror.

[0194] Table 2

[0195]

[0196]

[0197] The mirror is constructed using alternating high-refractive-index (HIO) and low-refractive-index (LIO) films. Both HIO and LIO films contain polymeric materials, including polyethylene hexyl naphthalate (PHEN) copolymers, polyethylene terephthalate (PET), and blends thereof. The materials used for the HIO and LIO films are selected based on the desired refractive indices along the x, y, and z directions. A series of PHEN copolymers were prepared using the following components: dimethyl naphthalate (NDC), hexanediol (HD), ethylene glycol (EG), cobalt acetate (CoAc), and tetrabutyl titanate (TBT). These components were added to a 10-gallon stainless steel reactor at room temperature, equipped with hot oil temperature control, a top separation column, and a vacuum pump, and heated under a nitrogen atmosphere at a pressure of approximately 138 kPa and mixed at approximately 125 revolutions per minute (rpm). The transesterification reaction was driven at approximately 257 degrees Celsius (°C) for approximately 2 hours. Methanol generated during the reaction is distilled off through a separation column and collected in a receiver. Once the reaction is complete, the pressure in the reactor is gradually reduced to atmospheric pressure, and then the reactor is evacuated, with the vacuum level increased as much as possible within the limits allowed by the batch viscosity. Any excess EG is distilled off. The reaction proceeds to the desired endpoint after approximately 2 hours at a temperature of approximately 285°C and a vacuum level of approximately 1 mmHg. The desired endpoint is equivalent to a viscosity of approximately 0.48 dL / g for PEN. The reactor is then emptied, and the resin is allowed to cool and further ground into smaller pieces. The mol% of HD is determined. Five exemplary batches of PHEN copolymers (PHEN 30, PHEN 35, PHEN 40, PHEN 50, and PHEN 70) were prepared by varying the proportions of the components used in the reaction. For example, PHEN 30 has 30 mol% HD.

[0198] Table 3 below provides exemplary ingredient ratios for these five batches of PHEN.

[0199] Table 3

[0200] NDC(#) 40 40 40 40 40 HD(#) 5.81 6.78 7.74 9.68 13.55 EG(#) 20.33 19.83 19.32 18.30 16.27 CoAc(g) 2.72 2.72 2.72 2.72 2.72 TBT(g) 0.91 1.36 1.36 1.29 1.73

[0201] A series of bilayer films were prepared using exemplary PHEN copolymers. A first extruder was configured to supply a series of PHEN copolymers, and a second extruder was configured to supply 0.64V polyester resin. These materials were extruded and cast onto cooling rollers to prepare 24-mil castable sheet films. The castable sheet films were biaxially oriented at a ratio of 350% × 350% of the initial film size. Stretching was performed at approximately 100°C to approximately 105°C, with a preheating time of approximately 45 seconds (s). The oriented films were then annealed at approximately 225°C for approximately 15 seconds. The refractive index of the top layer of each of these oriented films was measured.

[0202] Table 4 below provides the refractive indices of the oriented film along the x, y, and z directions (nx, ny, and nz, respectively).

[0203] Table 4

[0204] PHEN 30 1.6985 1.6985 1.552 PHEN 35 1.6395 1.6395 1.622 PHEN 40 1.629 1.629 1.624 PHEN 50 1.628 1.628 1.626 PHEN 70 1.625 1.625 1.623

[0205] The results show that 40% or higher HD is suitable for isotropic LIO membranes.

[0206] The PHEN copolymer was further blended with different levels of PET. These were cast into films and then stretched, oriented, and annealed. The refractive index of the top layer of each of these oriented films was measured.

[0207] Table 5 below provides the refractive indices (nx, ny, nz) of oriented films of PHEN 40 blends with different levels of PET along the x, y, and z directions, respectively.

[0208] Table 5

[0209] 0 1.629 1.629 1.624 20 1.617 1.617 1.614 40 1.6065 1.6065 1.605 50 1.6045 1.6045 1.602 60 1.6225 1.6225 1.577 70 1.61 1.61 1.607 80 1.646 1.646 1.529

[0210] Based on the desired refractive index of the HIO and LIO layers (e.g., the films in Table 2), PHEN or a blend of PHEN and PET copolymer is selected.

[0211] Three samples A, B, and C of the reflector disclosed herein were constructed, each sample having a different thickness profile.

[0212] Figure 7A An exemplary graph 700 depicts the thickness variations of different layers in a CMOF and samples A, B, and C. Sample A is substantially similar to the "mirror 10" of this disclosure. Thickness is depicted in nanometers (nm) on the vertical axis, and the number of layers is depicted on the horizontal axis. Graph 700 includes a thickness curve 701 depicting the thickness variations of adjacent layers in the CMOF. Graph 700 also includes thickness curves 705, 706, and 707 depicting the thickness variations of adjacent layers in samples A, B, and C, respectively. Figure 7B A magnified view of part B of graph 700 is further illustrated.

[0213] Table 6 provides exemplary thickness profiles of CMOF and samples A, B, and C.

[0214] Table 6

[0215]

[0216] refer to Figure 7A and Figure 7BFor CMOF, the maximum and minimum thicknesses of the first and second layers are 131.2 nm and 47.1 nm, respectively. Therefore, the difference between the maximum and minimum thicknesses of the first and second layers in CMOF is approximately 64.1%. Furthermore, the maximum difference in thickness between the first and second layers in CMOF is approximately 31.1%. The difference in thickness between the first and second layers in CMOF is... Figure 7B The best map in the middle.

[0217] For sample A, the maximum and minimum thicknesses of the first and second layers are 126.7 nm and 57.6 nm, respectively. Therefore, for sample A, the difference between the maximum and minimum thicknesses of the first and second layers is approximately 54.5%. Additionally, for sample A, the maximum difference in thickness between the first and second layers is approximately 10.1%. The difference in thickness between the first and second layers of sample A is... Figure 7B The best map in the middle.

[0218] For sample B, the maximum and minimum thicknesses of the first and second layers are 131.1 nm and 55.6 nm, respectively. Therefore, for sample B, the difference between the maximum and minimum thicknesses of the first and second layers is approximately 57.6%. Additionally, for sample B, the maximum difference in thickness between the first and second layers is approximately 6.6%. The difference in thickness between the first and second layers of sample B is... Figure 7B The best map in the middle.

[0219] For sample C, the maximum and minimum thicknesses of the first and second layers are 132.2 nm and 56.3 nm, respectively. Therefore, for sample C, the difference between the maximum and minimum thicknesses of the first and second layers is approximately 57.4%. Furthermore, for sample C, the maximum difference in thickness between the first and second layers is approximately 6.6%. The difference in thickness between the first and second layers of sample C is... Figure 7B The best map in the middle.

[0220] refer to Figure 7A and Figure 7B It was observed that each of curves 701, 705, 706, and 707 has multiple V-shaped segments indicating corresponding values ​​of the thickness of the first and second layers. The peaks and valleys of the V-shaped segments represent the thickness of each layer.

[0221] The changes in thickness curves 705, 706, and 707 (corresponding to samples A, B, and C, respectively) were observed to be roughly equivalent, while the change in thickness curve 701 (corresponding to CMOF) was greater than that in thickness curves 705, 706, and 707. This means that the thickness variation between adjacent layers in CMOF is greater than that between adjacent layers in samples A, B, and C.

[0222] Figure 8AAn exemplary graph 800 illustrates the optical characteristics of sample A and the CMOF. (Reference) Figure 1 , Figure 3A , Figure 3B and Figure 8A Graph 800 includes a reflectance curve 805 depicting the relationship between the optical reflectance of sample A and wavelength for s-polarized light incident at a first incident angle of less than about 10 degrees. Additionally, graph 800 includes a reflectance curve 806 depicting the relationship between the optical reflectance of the CMOF and wavelength for s-polarized light incident at a first incident angle of less than about 10 degrees. The s-polarized light can be light polarized along a second direction (e.g., the y-direction) orthogonal to a first direction (e.g., the x-direction). In this example, the s-polarized incident light can be incident on the corresponding mirror-environment interface of the CMOF and sample A, where the external environment can include air. Wavelength is expressed in nanometers (nm) on the horizontal axis. Optical reflectance is expressed as a percentage of reflectance on the left vertical axis. Optical transmittance is expressed as a percentage of transmittance on the right vertical axis. The percentage of transmittance is approximately complementary to the percentage of reflectance, i.e., percentage of transmittance = (100 - percentage of reflectance).

[0223] As depicted in reflectivity curve 805, for the incident plane 22 including the first direction ( Figure 3A As shown, for an s-polarized incident light propagating in the sample A, and for a first incident angle of less than about 10 degrees, the multiple alternating first and second polymer layers of sample A have an average optical reflectivity of about 64% in the visible wavelength range 95 and an average optical transmittance of about 84% in the infrared wavelength range 96.

[0224] As depicted in reflectance curve 806, for s-polarized incident light propagating in the same incident plane 22 including the first direction, and for a first incident angle of less than about 10 degrees, the multiple alternating first and second layers of the CMOF have an average optical reflectance of about 48% in the visible light wavelength range 95 and an average transmittance of about 88% in the infrared wavelength range 96.

[0225] Figure 8B An exemplary graph 810 illustrates the optical characteristics of samples B and C. Graph 810 includes reflectance curves 815 and 816, respectively, depicting the relationship between the optical reflectance of samples B and C and wavelength for s-polarized light incident at a first incident angle of less than approximately 10 degrees. In this example, s-polarized incident light may be incident on the respective mirror-environment interfaces of samples B and C. Wavelength is expressed in nanometers (nm) on the horizontal axis. Optical reflectance is expressed as a percentage of reflectance on the left vertical axis. Optical transmittance is expressed as a percentage of transmittance on the right vertical axis. The percentage of transmittance is approximately complementary to the percentage of reflectance, i.e., percentage of transmittance = (100 - percentage of reflectance).

[0226] As depicted in reflectivity curve 815, for the incident plane 22 including the first direction ( Figure 1 As shown, for an s-polarized incident light propagating in the sample B at a first incident angle of less than about 10 degrees, the multiple alternating first and second polymer layers of sample B have an average optical reflectivity of about 71% in the visible wavelength range 95 and an average optical transmittance of about 82% in the infrared wavelength range 96.

[0227] As depicted in reflectance curve 816, for s-polarized incident light propagating in the incident plane 22 including the first direction, and for a first incident angle of less than about 10 degrees, the multiple alternating first and second polymer layers of sample C have an average optical reflectance of about 72% in the visible light wavelength range 95 and an average optical transmittance of about 81% in the infrared wavelength range 96.

[0228] Figure 9A An exemplary graph 900 illustrates the optical characteristics of sample A and the CMOF. Graph 900 includes a reflectance curve 905 depicting the relationship between the optical reflectance of sample A and wavelength for p-polarized light incident at a first incident angle of less than about 10 degrees. Additionally, graph 900 includes a reflectance curve 906 depicting the relationship between the optical reflectance of the CMOF and wavelength for p-polarized light incident at a first incident angle of less than about 10 degrees. The p-polarized light incident at the first incident angle of less than about 10 degrees can be light polarized along a first direction. In this example, the p-polarized incident light can be incident on the respective mirror-environment interface of the CMOF and sample A, where the external environment can include air. Wavelengths are expressed in nanometers (nm) on the horizontal axis. Optical reflectance is expressed as a percentage of reflectance on the left vertical axis. Optical transmittance is expressed as a percentage of transmittance on the right vertical axis. The percentage of transmittance is approximately complementary to the percentage of reflectance, i.e., percentage of transmittance = (100 - percentage of reflectance).

[0229] As depicted in reflectivity curve 905, for the incident plane 22 including the first direction ( Figure 3B P-polarized incident light propagating in the sample (shown), and for a first incident angle of less than about 10 degrees, the multiple alternating first and second polymer layers of sample A have an average optical reflectivity of about 64% in the visible light wavelength range 95 and an average optical transmittance of more than about 84% in the infrared wavelength range 96.

[0230] As depicted in reflectance curve 906, for p-polarized incident light propagating in the same incident plane 22 including the first direction, and for a first incident angle of less than about 10 degrees, the multiple alternating first and second layers of the CMOF have an average optical reflectance of about 98% in the visible wavelength range 95 and an average transmittance of about 71% in the infrared wavelength range 96.

[0231] Figure 9B An exemplary graph 910 illustrates the optical characteristics of samples B and C. Graph 910 includes reflectance curves 915 and 916, respectively, depicting the relationship between the optical reflectance of samples B and C and wavelength for p-polarized light incident at a first incident angle of less than approximately 10 degrees. In this example, p-polarized incident light may be incident on the respective mirror-environment interfaces of samples B and C, where the external environment may include air. Wavelength is expressed in nanometers (nm) on the horizontal axis. Optical reflectance is expressed as a percentage of reflectance on the left vertical axis. Optical transmittance is expressed as a percentage of transmittance on the right vertical axis. The percentage of transmittance is approximately complementary to the percentage of reflectance, i.e., percentage of transmittance = (100 - percentage of reflectance).

[0232] As depicted in reflectivity curve 915, for the incident plane 22 including the first direction ( Figure 3B As shown, for a first incident angle of less than about 10 degrees, the multiple alternating first and second polymer layers of sample B have an average optical reflectivity of about 71% in the visible wavelength range 95 and an average optical transmittance of about 82% in the infrared wavelength range 96.

[0233] As depicted in reflectance curve 916, for p-polarized incident light propagating in the incident plane 22 including the first direction, and for a first incident angle of less than about 10 degrees, the multiple alternating first and second polymer layers of sample C have an average optical reflectance of about 72% in the visible light wavelength range 95 and an average optical transmittance of about 81% in the infrared wavelength range 96.

[0234] As from Figures 8A to 9B It is evident that, for the visible light wavelength range, the CMOF essentially transmits s-polarized light incident at the first incident angle while essentially blocking p-polarized light incident at the same angle. On the other hand, each of samples A, B, and C essentially transmits both s-polarized and p-polarized light incident at the first incident angle. Therefore, for the visible light wavelength range, each of samples A, B, and C has a lower average optical reflectivity for axial light compared to the CMOF. This lower average optical reflectivity for axial light provides improved axial brightness for the visible light wavelength range.

[0235] Figure 10AAn exemplary graph 1000 illustrates the optical characteristics of sample A and the CMOF. Graph 1000 includes a reflectance curve 1005 depicting the relationship between the optical reflectance of sample A and wavelength for s-polarized light incident at a second incident angle greater than approximately 45 degrees. Additionally, graph 1000 includes a reflectance curve 1006 depicting the relationship between the optical reflectance of the CMOF and wavelength for s-polarized light incident at a second incident angle greater than approximately 45 degrees. S-polarized light can be light polarized along a second direction. In this example, s-polarized incident light can be incident on the respective mirror-environment interface of the CMOF and sample A. Wavelength is expressed in nanometers (nm) on the horizontal axis. Optical reflectance is expressed as a percentage of reflectance on the left vertical axis. Optical transmittance is expressed as a percentage of transmittance on the right vertical axis. The percentage of transmittance is approximately complementary to the percentage of reflectance, i.e., percentage of transmittance = (100 - percentage of reflectance).

[0236] As depicted in reflectivity curve 1005, for the incident plane 22 including the first direction ( Figure 3A As shown, for s-polarized incident light propagating in the sample A, and for a second incident angle greater than about 45 degrees, the multiple alternating first and second polymer layers of sample A have an average optical reflectivity of about 92% in the visible light wavelength range 95 and an average optical transmittance of about 65% in the infrared wavelength range 96.

[0237] As depicted in reflectance curve 1006, for s-polarized incident light propagating in an incident plane 22 including the first direction, and for a second incident angle greater than about 45 degrees, the multiple alternating first and second layers of the CMOF have an average optical reflectance of about 86% in the visible wavelength range 95 and an average optical transmittance of about 67% in the infrared wavelength range 96.

[0238] Figure 10B An exemplary graph 1010 illustrates the optical characteristics of samples B and C. Graph 910 includes reflectance curves 1015 and 1016, respectively, depicting the relationship between the optical reflectance of samples B and C and wavelength for s-polarized light incident at a second incident angle greater than approximately 45 degrees. In this example, s-polarized incident light can be incident on the respective mirror-environment interfaces of samples B and C. Wavelength is expressed in nanometers (nm) on the horizontal axis. Optical reflectance is expressed as a percentage of reflectance on the left vertical axis. Optical transmittance is expressed as a percentage of transmittance on the right vertical axis. The percentage of transmittance is approximately complementary to the percentage of reflectance, i.e., percentage of transmittance = (100 - percentage of reflectance).

[0239] As depicted in reflectivity curve 1015, for the incident plane 22 including the first direction ( Figure 3AAs shown, for s-polarized incident light propagating in the sample B, and for a second incident angle greater than about 45 degrees, the multiple alternating first and second polymer layers of sample B have an average optical reflectivity of about 94% in the visible light wavelength range 95 and an average optical transmittance of about 64% in the infrared wavelength range 96.

[0240] As depicted in reflectance curve 1016, for s-polarized incident light propagating in an incident plane 22 including the first direction, and for a second incident angle greater than about 45 degrees, the multiple alternating first and second polymer layers of sample C have an average optical reflectance of about 93% in the visible wavelength range 95 and an average optical transmittance of about 64% in the infrared wavelength range 96.

[0241] Figure 11A An exemplary graph 1100 illustrates the optical characteristics of sample A and the CMOF. Graph 1100 includes a reflectance curve 1105 depicting the relationship between the optical reflectance of sample A and wavelength for p-polarized light incident at a second incident angle greater than approximately 45 degrees. Additionally, graph 1100 includes a reflectance curve 1106 depicting the relationship between the optical reflectance of the CMOF and wavelength for p-polarized light incident at a second incident angle greater than approximately 45 degrees. In this example, p-polarized incident light can be incident on the respective mirror-environment interfaces of the CMOF and sample A. Wavelengths are expressed in nanometers (nm) on the horizontal axis. Optical reflectance is expressed as a percentage of reflectance on the left vertical axis. Optical transmittance is expressed as a percentage of transmittance on the right vertical axis. The percentage of transmittance is approximately complementary to the percentage of reflectance, i.e., percentage of transmittance = (100 - percentage of reflectance).

[0242] As depicted in reflectance curve 1105, for p-polarized incident light propagating in the incident plane 22 including the first direction, and for a second incident angle greater than about 45 degrees, the multiple alternating first and second polymer layers of sample A have an average optical reflectance of about 93% in the visible light wavelength range 95 and an average optical transmittance of about 99% in the infrared wavelength range 96.

[0243] As depicted in reflectance curve 1106, for p-polarized incident light propagating in an incident plane 22 including the first direction, and for a second incident angle greater than about 45 degrees, the multiple alternating first and second layers of the CMOF have an average optical reflectance of about 99% in the visible light wavelength range 95 and an average optical transmittance of about 99% in the infrared wavelength range 96.

[0244] Figure 11BAn exemplary graph 1110 illustrates the optical characteristics of samples B and C. Graph 1110 includes reflectance curves 1115 and 1116, respectively, depicting the relationship between the optical reflectance of samples B and C and wavelength for p-polarized light incident at a second incident angle greater than approximately 45 degrees. In this example, p-polarized incident light can be incident on the respective mirror-environment interfaces of samples B and C. Wavelength is expressed in nanometers (nm) on the horizontal axis. Optical reflectance is expressed as a percentage of reflectance on the left vertical axis. Optical transmittance is expressed as a percentage of transmittance on the right vertical axis. The percentage of transmittance is approximately complementary to the percentage of reflectance, i.e., percentage of transmittance = (100 - percentage of reflectance).

[0245] As depicted in reflectivity curve 1115, for the incident plane 22 including the first direction ( Figure 3B As shown, for p-polarized incident light propagating in the sample (and for a second incident angle greater than about 45 degrees), the multiple alternating first and second polymer layers of sample B have an average optical reflectivity of about 95% in the visible light wavelength range 95 and an average optical transmittance of about 99% in the infrared wavelength range 96.

[0246] As depicted in reflectance curve 1116, for p-polarized incident light propagating in an incident plane 22 including the first direction, and for a second incident angle greater than about 45 degrees, the multiple alternating first and second polymer layers of sample C have an average optical reflectance of about 94% in the visible light wavelength range 95 and an average optical transmittance of greater than about 99% in the infrared wavelength range 96.

[0247] As from Figures 8A to 11B It is evident that, for the visible light wavelength range, and for both s-polarized and p-polarized light, samples A, B, and C exhibit higher average optical reflectivity for light incident at a second incident angle greater than approximately 45 degrees (i.e., off-axis light) compared to light incident at a first incident angle less than approximately 10 degrees (i.e., substantially perpendicular incident light or axial light). In other words, for the visible light wavelength range, and for each of s-polarized and p-polarized light, samples A, B, and C have greater optical transmittance for axial light compared to off-axis light. Since samples A, B, and C substantially collimate the off-axis light of both s-polarized and p-polarized light for the visible light wavelength range, they provide improved collimation compared to a CMOF that substantially reflects axially p-polarized light. Therefore, for the visible light wavelength range, samples A, B, and C have lower average optical reflectivity for axial light compared to a CMOF. Optical reflectivity for axial light is generally undesirable as it reduces axial brightness. Therefore, for the visible light wavelength range, the smaller average optical reflectivity for axial light improves the axial brightness provided by samples A, B, and C.

[0248] Unless otherwise stated, all figures used in the specification and claims to indicate feature dimensions, quantities, and physical properties should be understood to be modified by the term "about". Therefore, unless stated to the contrary, the numerical parameters listed in the foregoing specification and appended claims are approximations and can vary according to the desired properties sought by those skilled in the art using the teachings disclosed herein.

[0249] 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 in place of the illustrated and described embodiments without departing from the scope of this disclosure. This application is intended to cover any modifications or variations of the specific embodiments discussed herein. Therefore, this disclosure is intended to be limited only by the claims and their equivalents.

Claims

1. A multi-layered partial reflector, the multi-layered partial reflector comprising: A plurality of alternating first and second polymer layers, the total number of first and second polymer layers being at least 50, are disposed between and integrally formed with opposing first and second polymer surface layers. Each of the first and second polymer layers has an average thickness of less than 500 nm, and each of the polymer surface layers has an average thickness of greater than 0.5 μm. The first and second polymer layers include corresponding refractive indices nx1 and nx2 along the x-direction in the same plane, corresponding refractive indices ny1 and ny2 along the y-direction in a plane orthogonal to the x-direction, and corresponding refractive indices nz1 and nz2 along the z-direction of the polymer layer orthogonal to the x and y directions, such that for at least one wavelength in the visible light wavelength range extending from 420 nm to 680 nm: nx1 and ny1 differ from each other by less than 0.05; nz1 is at least 0.06 smaller than each of nx1 and nx2; nx2, ny2, and nz2 differ from each other by less than 0.05; and For each of the first polymer surface layer and the second polymer surface layer, the corresponding refractive index of the polymer surface layer and one of the first polymer layer and the second polymer layer differs from each other by within 0.05 along the x-direction, the y-direction and the z-direction; Specifically, for the visible light wavelength range and incident light propagating in the incident plane including the x-direction: For s-polarized incident light, the multiple alternating first and second polymer layers have an average reflectivity Rs1 for a first incident angle less than 10 degrees and an average reflectivity Rs2 for a second incident angle greater than 45 degrees; and For p-polarized incident light, multiple alternating first and second polymer layers have an average reflectivity Rp1 for the first incident angle and an average reflectivity Rp2 for the second incident angle, with each of Rs2 / Rs1 and Rp2 / Rp1 being greater than 1.

15.

2. The multilayer partial reflector of claim 1, wherein for each of the first polymer surface layer and the second polymer surface layer, the corresponding refractive indices of the polymer surface layer and the first polymer layer along each of the x-direction, the y-direction and the z-direction differ from each other by within 0.

05.

3. The multilayer partial reflector according to claim 1, wherein the second polymer layer and at least one of the first polymer surface layer and the second polymer surface layer comprise the same material composition.

4. The multi-layered partial reflector according to claim 1, wherein: The difference between the maximum and minimum thicknesses of the alternating first and second polymer layers is between 45% and 65%; and The maximum difference in thickness between adjacent polymer layers in the alternating first and second polymer layers is less than 25%.

5. The multilayer partial reflector according to claim 1, wherein Rp2 is less than 98% and greater than 70%.

6. The multilayer partial reflector according to claim 1, wherein Rp1 and Rs1 differ from each other by less than 10%.

7. The multilayer partial reflector of claim 1, wherein for an infrared wavelength range from 800 nm to 1300 nm, for s-polarized incident light propagating in the incident plane including the x-direction and the first incident angle, a plurality of alternating first polymer layers and second polymer layers have an average transmittance Ts1 greater than 50%.

8. The multilayer partial reflector of claim 1, wherein for an infrared wavelength range from 800 nm to 1300 nm, for s-polarized incident light propagating in the incident plane including the x-direction and the second incident angle, a plurality of alternating first polymer layers and second polymer layers have an average transmittance Ts2 greater than 40%.

9. The multilayer partial reflector of claim 1, wherein for an infrared wavelength range from 800 nm to 1300 nm, for p-polarized incident light propagating in the incident plane including the x-direction and the first incident angle, a plurality of alternating first polymer layers and second polymer layers have an average transmittance Tp1 greater than 50%.

10. The multilayer partial reflector of claim 1, wherein for an infrared wavelength range from 800 nm to 1300 nm, for p-polarized incident light propagating in the incident plane including the x-direction and the second incident angle, a plurality of alternating first polymer layers and second polymer layers have an average transmittance Tp2 greater than 70%.

11. The multilayer partial reflector of claim 1, wherein the optical system is formed in the following manner: A Lambertian light source is provided, the Lambertian light source including a back reflector and emitting unpolarized light through an extended emitting surface of the Lambertian light source, the back reflector having a total reflectivity greater than 90% at at least one wavelength in the visible light wavelength range; and The multilayer partial reflector according to claim 1 is disposed between the reflective polarizer and the emitting surface, such that for the visible light wavelength range and perpendicular incident light, the reflective polarizer has an average optical reflectivity greater than 60% when the incident light is polarized along the x-direction and an average optical transmittance greater than 60% when the incident light is polarized along the y-direction. Therefore, the emission distribution of light leaving the optical system through the reflective polarizer includes at least one global peak at an angle greater than 5 degrees to the normal of the reflective polarizer.

12. The multilayer partial reflector of claim 11, wherein the at least one global peak is located in a plane at an angle to the x-direction.

13. A backlight source for providing illumination to a display panel configured to form an image, the backlight source comprising: An extended light source, the extended light source being configured to emit light through an emitting surface and including a back reflector; as well as According to claim 1, the multi-layer partial reflector is disposed on the emitting surface and configured to receive emitted light and transmit a portion of the received light through the multi-layer partial reflector, wherein the multi-layer partial reflector and the back reflector form a circulating optical cavity therebetween.

14. A multi-layered partial reflector, the multi-layered partial reflector comprising: A plurality of alternating first and second polymer layers, the total number of first and second polymer layers being at least 50, are disposed between and integrally formed with the first and second polymer layers, each of the first and second polymer layers having an average thickness of less than 500 nm, the first and second polymer layers comprising corresponding refractive indices nx1 and nx2 along the x-direction in the same plane, corresponding refractive indices ny1 and ny2 along the y-direction in a plane orthogonal to the x-direction, and corresponding refractive indices nz1 and nz2 along the z-direction of the polymer layer orthogonal to the x and y directions, such that for at least one wavelength in the visible light wavelength range extending from 420 nm to 680 nm: nz1 is at least 0.06 smaller than each of nx1 and nx2; The magnitude of the difference between nx2 and ((nx1+nz1) / 2) is less than 0.05; and nx2, ny2, and nz2 differ from each other within 0.05; Specifically, for the visible light wavelength range, the infrared wavelength range from 800 nm to 1300 nm, and incident light propagating in the incident plane including the x-direction: For a first incident angle less than 10 degrees, multiple alternating first and second polymer layers have an average reflectivity Rp1 for incident light polarized along the x-direction and an average reflectivity Rs1 for incident light polarized along the y-direction, each of Rp1 and Rs1 being less than 85% for the visible light wavelength range and less than 50% for the infrared wavelength range; and For a second incident angle greater than 45 degrees, the plurality of alternating first and second polymer layers have average reflectivities Rp2 and Rs2 for the corresponding p-polarized and s-polarized incident light, each of Rp2 and Rs2 being greater than 70% of the visible light wavelength range.

15. A multi-layered partial reflector, the multi-layered partial reflector comprising: A plurality of alternating first and second polymer layers, the total number of the first and second polymer layers being between 50 and 600, are disposed between integrally formed opposing first and second polymer surface layers. Each polymer layer disposed between the first and second polymer surface layers has an average thickness of less than 500 nm, such that for at least one wavelength in the visible light wavelength range extending from 420 nm to 680 nm: Each of the first polymer layer and the second polymer layer has an in-plane birefringence of less than 0.05; The first polymer layer has an out-of-plane birefringence greater than 0.06; and The second polymer layer has an out-of-plane birefringence of less than 0.02; Wherein, for the visible light wavelength range and incident light propagating in an incident plane including a first direction in the same plane, and at a first incident angle of less than 10 degrees, the multilayer partial reflector has an average reflectivity Rs1 for s-polarized incident light and an average reflectivity Rp1 for p-polarized incident light, wherein Rp1 / Rs1 is between 0.8 and 1.2; and Wherein, for the first incident angle and for each of the p-polarized incident light and the s-polarized incident light, the optical reflectivity of the multilayer partial reflector in relation to wavelength includes a reflection band edge between 760 nm and 980 nm.

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