Optical films and polarizing beam splitters

Abstract

To provide optical films and polarizing beam splitters including the optical films.SOLUTION: In some cases, an optical film includes a first optical stack disposed on, and spaced apart by one or more spacer layers from, a second optical stack, each optical stack comprising a plurality of polymeric interference layers reflecting and transmitting light primarily by optical interference in a same predetermined wavelength range. Each optical stack has interference layers closer to the one or more spacer layers that reflect longer wavelengths and interference layers farther from the one or more spacer layers that reflect shorter wavelengths.SELECTED DRAWING: Figure 3

Description

[Background technology]

[0001] The polarizing beam splitter may include a reflective polarizer positioned between the hypotenuses of adjacent prisms. The reflective polarizer may be a multilayer polymer film. [Overview of the project]

[0002] In some aspects of this specification, an optical film is provided comprising a plurality of polymer interference layers. Each interference layer reflects or transmits light primarily by optical interference with at least one wavelength within a predetermined wavelength range extending at least 450 nm to 1000 nm. The total number of interference layers is more than about 100 and less than about 300. With respect to light substantially incident on the optical film substantially normal to the optical film within the predetermined wavelength range, the plurality of interference layers have an average light transmittance of more than about 85% for a first polarization state, an average light reflectance of more than about 95% for an orthogonal second polarization state, and an average light transmittance of less than about 5% for the second polarization state.

[0003] In some aspects of this specification, an optical film is provided comprising a plurality of laminated first polymer interference layers disposed on a plurality of laminated second polymer interference layers. Each first and second interference layer reflects or transmits light primarily by optical interference with at least one wavelength within the same predetermined wavelength range. The outermost first interference layer, which is the first interference layer furthest from the plurality of laminated second interference layers, and the outermost second interference layer, which is the second interference layer furthest from the plurality of laminated first interference layers, have optical thicknesses equal to one-quarter of the first and second wavelengths, respectively, within the predetermined wavelength range. The difference between the first and second wavelengths is less than about 40 nm.

[0004] In some aspects of this specification, an optical film is provided, comprising a first optical laminate disposed on a second optical laminate and separated therefrom by one or more spacer layers. Each optical laminate comprises a plurality of polymer interference layers that reflect and transmit light by optical interference within the same predetermined wavelength range extending at least 450 nm to 600 nm, so that, for light substantially incident on the optical film within the predetermined wavelength range, the plurality of interference layers within each optical laminate transmit at least 80% of the light having a first polarization state, reflect at least 90% of the light having an orthogonal second polarization state, and transmit less than 5% of the light having a second polarization state. Each spacer layer within the one or more spacer layers does not reflect or transmit light primarily by optical interference. Each optical laminate has interference layers that are close to one or more spacer layers and reflect the longer wavelength, and interference layers that are farther from one or more spacer layers and reflect the shorter wavelength. The first optical laminate, the second optical laminate, and the one or more spacer layers are integrally formed with respect to each other.

[0005] In some aspects of this specification, an optical film is provided that transmits at least 80% of normally incident light having a first polarization state within a given wavelength range and reflects at least 95% of normally incident light having a second polarization state orthogonal within a given wavelength range. The optical film comprises a plurality of polymer layers, each polymer layer having an average thickness of less than about 200 nm. The plurality of polymer layers include a first polymer layer and a second polymer layer as two polymer layers in the plurality of polymer layers that are furthest apart from each other, and the first and second layers have a first thickness and a second thickness, respectively, with the difference between the first and second thicknesses being less than about 10 nm.

[0006] In some aspects of this specification, an optical film is provided comprising adjacent, non-overlapping first optical laminates and second optical laminates disposed between a first and second main surface which are opposite to each other. The first optical laminate is disposed near the first main surface and far from the second main surface, and the second optical laminate is disposed near the second main surface and far from the first main surface. For each optical laminate and the main surface closest to the optical laminate, the optical laminate includes a plurality of first interference layers ranging from 50 to 300, each first interference layer reflecting or transmitting light mainly by optical interference, each first interference layer closer to the main surface is thinner than each first interference layer farther from the main surface, each first interference layer has orthogonal plane refractive indices nx and ny, and refractive index nz in the thickness direction of the first interference layer, where the difference between ny and nz is less than 0.008 and the difference between nx and ny is greater than 0.2. The first optical laminate is formed integrally with the second optical laminate.

[0007] In some aspects of this specification, a polarizing beam splitter (PBS) is provided, comprising: a first prism having a first hypotenuse; a second prism having a second hypotenuse facing the first hypotenuse; and an optical film disposed between and bonded to the first and second hypotenuses. The optical film includes a plurality of alternating high-refractive-index and low-refractive-index layers disposed between a first main surface and a second main surface of the optical film that are opposite each other. The optical film substantially transmits light having a first polarization state in a predetermined wavelength range extending from 400 nm to 700 nm and substantially reflects light having a second polarization state that is orthogonal to it. For collimated light having a second polarization state, an f-value of 1.8 to 2.2, and passing through an optical lens centered on an optical axis at an angle of approximately 30 to 60 degrees with the optical film, before being incident on the optical film in a polarizing beam splitter (PBS), the optical film has a total transmittance T1 when the light is first incident on the first main surface of the optical film, and a total transmittance T2 when the light is first incident on the second main surface of the optical film, and the maximum difference between T1 and T2 is less than 0.02% as a function of the wavelength of the incident light within a predetermined wavelength range.

[0008] In some aspects of this specification, a polarizing beam splitter (PBS) is provided, comprising: a first prism having a first hypotenuse; a second prism having a second hypotenuse facing the first hypotenuse; and an optical film disposed between and bonded to the first and second hypotenuses. The optical film includes a plurality of alternating high-refractive-index and low-refractive-index layers disposed between a first main surface and a second main surface of the optical film that are opposite each other. The optical film substantially transmits light having a first polarization state in a predetermined wavelength range extending from 400 nm to 700 nm and substantially reflects light having a second polarization state that is orthogonal to it. A polarizing beam splitter (PBS) is incorporated into an imaging system that includes a point light source, a collimating optical lens for collimating the light emitted by the point light source, and an imaging optical lens having an f-number in the range of 4.5 to 5.5. When an optical film in the polarizing beam splitter (PBS) receives light from the imaging optical lens and reflects the received light toward the image surface, the imaging system has a point diffusion function with a 20% value total width of less than 33 μm.

[0009] In some aspects of this specification, a polarizing beam splitter (PBS) is provided, comprising: a first prism having a first hypotenuse; a second prism having a second hypotenuse facing the first hypotenuse; and an optical film disposed between and bonded to the first and second hypotenuses. The optical film includes a plurality of alternating high-refractive-index and low-refractive-index layers disposed between a first main surface and a second main surface of the optical film that are opposite each other. The optical film substantially transmits light having a first polarization state in a predetermined wavelength range extending from 400 nm to 700 nm and substantially reflects light having a second polarization state that is orthogonal to it. A polarizing beam splitter (PBS) is incorporated into an imaging system that includes a point light source, a collimating optical lens for collimating the light emitted by the point light source, and an imaging optical lens having an f-number in the range of 4.5 to 5.5. When an optical film in the polarizing beam splitter (PBS) receives light from the imaging optical lens and reflects the received light toward the image surface, the imaging system has a point diffusion function with a 15% value total width of less than 60 μm.

[0010] In some aspects of this specification, a polarizing beam splitter (PBS) is provided, comprising: a first prism having a first hypotenuse; a second prism having a second hypotenuse facing the first hypotenuse; and an optical film disposed between the first and second hypotenuses and bonded thereto. The optical film includes a first optical laminate disposed on a second optical laminate and separated therefrom by a light-absorbing linear polarizer. The first optical laminate is near the first hypotenuse and far from the second hypotenuse, and the second optical laminate is near the second hypotenuse and far from the first hypotenuse. Each optical stack and the hypotenuse closest to it contains multiple interference layers ranging from 50 to 300, which primarily reflect or transmit light by optical interference within the same predetermined wavelength range extending at least from 400 nm to 600 nm. Interference layers closer to the hypotenuse are configured to primarily reflect shorter wavelengths within the predetermined wavelength range, while interference layers further from the hypotenuse are configured to primarily reflect longer wavelengths within the predetermined wavelength range. When a polarizing beam splitter (PBS) is incorporated into the imaging system, and image light entering the polarizing beam splitter (PBS) is sequentially reflected by the first optical stack, transmitted through an optical film, reflected by the second optical stack, and then exits the polarizing beam splitter (PBS), the light-absorbing linear polarizer absorbs less than 2% of the image light, but absorbs at least 50% of the image light scattered by at least one of the first and second optical stacks.

[0011] In some aspects of this specification, a polarizing beam splitter (PBS) is provided, comprising: a first prism having a first hypotenuse; a second prism having a second hypotenuse facing the first hypotenuse; and an optical film disposed between and bonded to the first and second hypotenuses. The optical film includes a plurality of alternating high-refractive-index and low-refractive-index layers disposed between a first main surface and a second main surface of the optical film that are opposite each other. The optical film substantially transmits light having a first polarization state within a predetermined wavelength range extending at least from 430 nm to 630 nm and substantially reflects light having a second polarization state that is orthogonal to it. For collimated light having a first polarization state, an f-value of 1.8 to 2.2, and passing through an optical lens centered on an optical axis at an angle of approximately 30 to 60 degrees with the optical film, before being incident on the optical film in a polarizing beam splitter (PBS), the optical film has a total transmittance T3 when the light is first incident on the first main surface of the optical film, and a total transmittance T4 when the light is first incident on the second main surface of the optical film. The average of each of T3 and T4 over a given wavelength range is at least 92%. [Brief explanation of the drawing]

[0012] [Figure 1A] This is a schematic perspective view of a multilayer optical film. [Figure 1B] Figure 1A is a schematic perspective view of a portion of a multilayer optical film. [Figure 2] This is a schematic side view of an optical film, including a first optical laminate and a second optical laminate. [Figure 3] This is a schematic diagram of the layer thickness profile of an optical film. [Figure 4] This is a schematic side view of a polarizing beam splitter. [Figure 5] This is a schematic side view of a polarizing beam splitter. [Figure 6] This is a schematic cross-sectional view of the optical system. [Figure 7] This is a schematic cross-sectional view of the optical system. [Figure 8] This is a schematic cross-sectional view of the optical system. [Figure 9] It is a schematic graph of the point spread function of an imaging system. [Figure 10] It is a schematic plot of the transmittance of the optical film in the polarization beam splitter for s-polarization as a function of wavelength. [Figure 11] It is a schematic plot of the transmittance of the optical film in the polarization beam splitter for p-polarization as a function of wavelength. [Figure 12] It is a plot of the thickness of the ORU in the reflective polarizer film as a function of the sequential optical repetition unit number (ORU number) in the reflective polarizer film. [Figure 13] It is a plot of the transmittance of the optical film in the polarization beam splitter for s-polarization as a function of wavelength. [Figure 14] It is a plot of the transmittance of the optical film in the polarization beam splitter for p-polarization as a function of wavelength. [Figure 15] It is a plot of the transmittance of s-polarization of the optical film in the polarization beam splitter as a function of wavelength. [Figure 16] It is a plot of the transmittance of s-polarization of the optical film in the polarization beam splitter as a function of wavelength. [Figure 17] It is a plot of the transmittance of s-polarization of the optical film in the polarization beam splitter as a function of wavelength. [Figure 18] It is a plot of the transmittance of s-polarization of the optical film in the polarization beam splitter as a function of wavelength. [Figure 19] It is a plot of the transmittance of the optical film in the polarization beam splitter for p-polarization as a function of wavelength. [Figure 20] It is a plot of the point spread function of an imaging system using a polarization beam splitter including a reflective polarizer film. [Figure 21] It is a plot of the transmittance coefficient for the reflective polarizer film. [Figure 22] It is a plot of the transmittance coefficient for the reflective polarizer film. [Modes for carrying out the invention]

[0013] The following description refers to the accompanying drawings, which constitute part of this specification and illustrate various embodiments. The drawings are not necessarily to exact proportions. It should be understood that other embodiments can be conceived and implemented without departing from the scope or spirit of this disclosure. Accordingly, the embodiments for carrying out the following inventions should not be construed as restrictive.

[0014] According to several embodiments of this specification, optical films having improved optical properties compared to conventional films are provided. In some embodiments, the optical film is a reflective polarizer film suitable for use in polarizing beam splitters suitable for use in various optical systems, including head-mounted virtual reality displays or augmented reality displays. In some embodiments, the optical film comprises packets of alternating polymer interference layers having high reflectivity (e.g., more than about 95%, more than 96%, or more than 97%) over a given wavelength range (e.g., 400nm to 600nm, or 450nm to 600nm, or 430nm to 680nm, or 430nm to 630nm, or 450nm to 1000nm), and has a limited total number (e.g., less than about 300) of interference layers. In some embodiments, high reflectivity over a wide bandwidth (e.g., over at least 400nm or 450nm to at least 1000nm or 1050nm) is obtained by the limited total number (e.g., less than about 300) of interference layers. In some cases, longer wavelengths at the edge of the band (e.g., at least 1000 nm or at least 1050 nm) are desirable for improved performance when the film is used in a polarizing beam splitter. In some embodiments, the optical film comprises two (or more) packets of alternating polymer interference layers, where the interference layer of the first packet closer to the thicker interference layer of the second packet is the thicker one, and the interference layer of the first packet further from the thinner interference layer of the second packet is the thinner one. It has been found that such optical films can simultaneously achieve high-quality image reflection and very low transmission leakage (e.g., transmittance less than 0.05% in the shielded state). In some embodiments, a dichroic polarizer (light-absorbing linear polarizer) is placed between the two packets. It has been found that this can reduce image contamination from multiple reflections between the two packets and / or mitigate the effects of depolarization scattering within the optical film.In some embodiments, when the optical films of this specification are used in a polarizing beam splitter of an imaging system, they provide an improved point diffusion function (e.g., a narrower 20% value total width) compared to equivalent imaging systems using other methods that utilize conventional optical films.

[0015] The optical films described herein can be characterized as multilayer optical films having a plurality of optical layers (e.g., interference layers) configured to selectively transmit and reflect light within a given wavelength range. In some such embodiments, the optical film functions as a reflective polarizer, selectively transmitting and reflecting light in different polarization states. For example, Figure 1A is a schematic perspective view of an example of a multilayer optical film 100, which includes a plurality of interference layers 102 positioned along a central axis, forming an optical film 100 having a total of (N) interference layers 102. Figure 1B is a schematic perspective view of a segment of the optical film 100 showing alternating interference layers 102a and 102b. Figures 1A and 1B include coordinate systems defining the x, y, and z directions.

[0016] During use, light incident on the main surface (e.g., film surface 104) of the optical film 100, which is depicted as incident light 110, enters the first layer of the optical film 100 and can propagate through a plurality of interference layers 102, and depending on the polarization state of the incident light 110, it is selectively reflected or transmitted by optical interference. The incident light 110 may include a first polarization state (a) and a second polarization state (b) that are orthogonal to each other. The first polarization state (a) can be considered a "pass" state, while the second polarization state (b) can be considered a "reflection" or "blocking" state. As the incident light 110 propagates through the plurality of interference layers 102, the portion of light in the second polarization state (b) is reflected by adjacent interference layers, resulting in the second polarization state (b) being reflected by the optical film 100, while a portion of the light in the first polarization state (a) passes through the optical film 100 together.

[0017] In some embodiments, the optical film 100 can be characterized in terms of reflectance and transmittance of incident light 110 in a first polarization state (a) and a second polarization state (b). For example, the amount of incident light 110 transmitted through the optical film 100 for a predetermined wavelength can be expressed as a percentage of the light transmittance (Ta) for the first polarization state (a) and a percentage of the light transmittance (Tb) for the second polarization state (b). The amount of incident light 110 reflected by the optical film 100 for a predetermined wavelength range can be expressed as a percentage of the light reflectance (Ra) for the first polarization state (a) and a light percentage of the light reflectance (Rb) for the second polarization state (b). For a given optical film, the sum of transmittance, reflectance, and loss, such as loss due to absorption, is 100% for light in the predetermined wavelength range. In some embodiments, the optical film 100 may have a relatively low absorbance for light in the predetermined wavelength range. In some embodiments, the relatively low absorption of incident light 110 by the optical film 100 reduces the heat generated within the optical film 100, making the reflective film more efficient overall. In other embodiments, the optical film 100 may include a dichroic absorbing layer, as further described elsewhere in this specification.

[0018] The predetermined wavelength range may be any suitable wavelength range, for example, visible light (e.g., about 400 nm to 700 nm), a range of visible light (e.g., about 400 nm, or about 420 nm, or about 430 nm, or about 450 nm to about 600 nm, or about 630 nm, or about 635 nm, or about 650 nm, or about 680 nm, or about 700 nm), near-infrared light (e.g., about 800 nm to 1300 nm), a range based on the output of a light source such as a liquid crystal display backlight (e.g., 425 nm to 675 nm), and a range based on providing a desired bandwidth for out-of-normal incidence (e.g., 400 nm, or 450 nm to 1000 nm or ~1050 nm). In some embodiments, the optical film 100 may be configured to transmit and reflect light in different polarization states within two or more predetermined wavelength ranges, for example, within the range of visible light and near-infrared light. For example, the predetermined wavelength range may include a first range of about 430 nm to about 465 nm, a second range of about 490 nm to about 555 nm, and a third range of about 600 nm to about 665 nm. In some embodiments, the optical film 100 may include a number of laminates / packets, each containing a plurality of interference layers, as further described elsewhere in this specification, and each laminate / packet may target different predetermined wavelength ranges or the same predetermined wavelength range. In a preferred embodiment, each laminate / packet is configured to reflect substantially the same predetermined wavelength range.

[0019] In some embodiments, the interference layer can be characterized as a series of two-layer unit cells or optical repeating units. The thickness of each unit cell may be configured to reflect target wavelengths within a given wavelength range. In some examples, the center wavelength of reflectance for a unit cell corresponds to twice the optical thickness of the two-layer unit cell. Thus, to reflect a given wavelength range (e.g., 420 nm to 635 nm), the unit cells in the laminate / packet have different thicknesses, covering wavelengths from the left end of the band to the right end of the band. The optical thickness of a layer refers to the physical thickness of the layer multiplied by the refractive index of the layer. For an optical film configured to reflect polarization along a cutoff axis and transmit polarization along an orthogonal pass-through axis, the refractive index used to determine the optical thickness is the refractive index along the cutoff axis. Two layers within an optical repeating unit may have equal or approximately equal optical thicknesses. In some cases, it is useful to characterize the optical repeating unit in terms of the "f-ratio," which is obtained by dividing the optical thickness of the high-refractive-index layer in a pair of layers by the total optical thickness of the pair of layers. In some embodiments, the "f-ratio" is about 0.5. A frequency ratio of 0.5 may be preferable because it maximizes the reflection output in the primary reflection band of the optical laminate or packet of the interference layer.

[0020] In some embodiments, the optical film 100 includes interference layers 102 of less than about 1200(N), each interference layer 102 reflecting or transmitting incident light 110 primarily by optical interference. In some embodiments, the optical film 100 includes interference layers 102 of less than about 1000, or less than about 800, or less than about 600, or less than about 300. Interference layers 102 of 1200 or more may be included in the optical film 100. On the other hand, in some cases, since it is desirable in many applications to reduce the overall thickness of the display assembly (e.g., LCD display), it may be desirable to reduce the total number of layers to reduce the overall thickness of the film and obtain the desired optical performance. In addition, or / or by reducing the total number of interference layers 102, complexity in the manufacturing process can be reduced, the possibility of variations (e.g., spectral variations in the blocked or passed state) can be reduced, or manufacturing errors in the final optical film (e.g., increased transmittance in the blocked state, decreased transmittance in the passed state due to depolarization between layers) can be reduced. In some embodiments, the total number N of interference layers 102 is greater than approximately 50, greater than approximately 100, greater than approximately 150, or greater than approximately 200.

[0021] In some embodiments, the optical film 100, or the optical laminate contained in the optical film 100, has an average light transmittance (Ta) greater than about 85% for a first polarization state (a), an average light reflectance (Rb) greater than about 95% for an orthogonal second polarization state (b), and an average light transmittance (Tb) less than about 5% for the second polarization state (b) with respect to substantially normally incident light 110 within a predetermined wavelength range. In some embodiments, Ta is greater than about 80%, or greater than about 85%, or greater than about 87%, or greater than about 89%. In some embodiments, Rb is greater than about 90%, or greater than about 95%, or greater than about 96%, or greater than about 97%, or greater than about 98%. In some embodiments, Tb is less than about 5%, or less than about 4%, or less than about 3%, or less than about 2%, or less than about 1%, or less than about 0.5%, or less than about 0.3%, or less than about 0.2%, or less than about 0.1%, or less than about 0.05%, or less than about 0.04%, or less than about 0.03%, or less than about 0.02%, or less than about 0.01%. In some embodiments, the desired Ta, Tb, and Rb are obtained by using an interference layer 102 with a total of more than about 50, or more than about 100, and less than about 1200, or less than about 600, or less than about 300, within the optical film 100, or within an optical laminate contained within the optical film 100. High Rb (e.g., over approximately 95%) and low Tb (e.g., less than approximately 5%) with a relatively small number of layers can be achieved by selecting materials for the interference layers and controlling the stretch ratio of the film, thereby reducing the refractive index difference between adjacent interference layers for light having a second polarization state (e.g., less than 0.008) and increasing the refractive index difference between adjacent interference layers for light having a first polarization state (e.g., greater than approximately 0.2). The refractive index, or rate of refraction, may be considered as the refractive index at a wavelength of 550 nm if the wavelength is not specified.

[0022] The transmittance of an optical film generally refers to the intensity of transmitted light divided by the intensity of incident light (for light of a given wavelength and direction of incidence), but it may also be expressed as "external transmittance" or "internal transmittance." The external transmittance of an optical film is the transmittance of the optical film when the surrounding environment is air and no correction is made for Fresnel reflection at the air / element interface in front of the element or at the element / air interface behind the element. The internal transmittance of an optical film is the transmittance of the film when Fresnel reflection at its front and rear surfaces is removed. Removing the front and rear Fresnel reflections can be done either by calculation (e.g., by subtracting an appropriate function from the external transmission spectrum) or by experiment. In many types of polymer and glass materials, Fresnel reflection is about 4-6% (with respect to the normal or nearly normal angle of incidence) at each of the two external surfaces, which causes the external transmittance to decrease by about 10% compared to the internal transmittance. Whereever transmittance is referred to herein without specifying whether it is internal or external, transmittance may be considered to refer to external transmittance unless otherwise specified by the context.

[0023] The reflectance and transmittance of an optical film can be expressed, for example, in terms of the total reflectance and total transmittance of an optical film used in a polarizing beam splitter (PBS) when used between two prisms in the PBS. Total transmittance is the transmitted output at a given wavelength divided by the incident output in the prism into which light of a given wavelength is incident. Similarly, total reflectance is the reflected output at a given wavelength divided by the incident output in the prism into which light of a given wavelength is incident.

[0024] In some embodiments, the interference layer 102 of the optical film 100 includes alternating layers of two different polymer materials exhibiting different refractive index properties (e.g., A and B as shown in Figure 1B). As shown in Figure 1B, the optical film 100 includes alternating layers of different optical materials called material (A) and material (B) (e.g., ABABA...). Furthermore, as described elsewhere in this specification, the various layers of the two different materials may be formed by an extrusion / lamination process in which the layers are extruded together to form a number of optical layers 102 (ABABA...) bonded together.

[0025] In some embodiments, the optical layer 102 may be stretched during the extrusion process to impart various interference properties to the film. For example, the layers of optical materials A and B may be stretched along one axis (e.g., the X-axis) (e.g., in a 5:1 or 6:1 ratio) and less stretched along a perpendicular axis (e.g., the Y-axis). The refractive indices along the X, Y, and Z axes are denoted as nx, ny, and nz for either layer A or layer B, respectively. Alternatively, the refractive indices may be denoted as n1x, n1y, n1z and n2x, n2y, n2z for layer A and layer B, respectively, along the X, Y, and Z axes.

[0026] In selecting the optical materials used to form layers A and B, the materials may be chosen to impart specific optical properties to the film as a result of the stretching process. For example, the material (B) forming the optical layer 102b may have an apparent refractive index (e.g., n2 of 1.5 to 1.6) that is not substantially altered by the stretching process. Thus, the refractive index of layer 102b of "B" in both the x and y directions (n2x and n2y) may be substantially the same in both directions after the stretching process, and may also be substantially the same as the refractive index in the thickness direction (n2z). In contrast, the material (A) forming the optical layer 102a may have a refractive index that changes with the stretching process. For example, the uniaxially stretched layer 102a of material (A) may have a high refractive index in the X-axis or stretching direction 120 (e.g., 1.8 ≤ n1x ≤ 1.9), or a different refractive index in relation to the Y-axis or non-stretching direction 122 (e.g., 1.5 ≤ n1y ≤ 1.6), which may be substantially equal to the refractive index in the thickness direction (e.g., 1.5 ≤ n1z ≤ 1.6). In some embodiments, the absolute value of the difference between n1y and n1z is less than 0.008, and the difference between n1x and n1y is greater than approximately 0.2. Because the refractive index is high in the stretching direction, the layer 102a containing material (A) may be considered a high refractive index (HIR) layer 102a, while the interference layer 102b containing material (B) may be considered a low refractive index (LIR) layer 102b. In some embodiments, the absolute value of the difference between n2y and n2z is less than 0.005. In some embodiments, each of n2x, n2y, and n2z is between 1.5 and 1.6. In some examples, the refractive indices of the alternating A and B layers may be controlled by appropriate material selection and processing conditions. In some embodiments, due to the optical properties of layer 102, the optical film 100 acts as a reflective polarizer that substantially transmits the first polarization state (a) component of incident light 110 within a predetermined wavelength range oriented with respect to the non-stretched axis 122, while the stretched axis 120 corresponds to a reflective axis where the component of incident light 110 in a second polarization state (b) within a predetermined wavelength range is substantially reflected by optical interference.

[0027] In some embodiments, the optical film 100 can be characterized by the difference in refractive index between alternating HIR layers 102a and LIR layers 102b along the stretch axis 120 (i.e., Δnx = n1x - n2x). In some such embodiments, the refractive index between alternating HIR layers 102a and LIR layers 102b along the non-stretch axis 122 may be substantially the same, such that the difference in refractive index in the non-stretch axis 122 (i.e., Δny = n1y - n2y) is about 0.0 (e.g., less than about 0.02, or less than about 0.01, or less than about 0.005 |Δny|). In some examples, increasing Δnx between the HIR layers 102a and LIR layers 102b (e.g., by material selection and / or control of the uniaxial orientation of the film) allows for sufficient transmission / reflection of polarization over a given wavelength range using a smaller total number of interference layers compared to an optical film with a lower Δnx having the same optical output. For example, each packet of the reflective polarizing film in Example 1 contains 276 interference layers (138 optical repeating units), and each packet has an average light transmittance of over 85% for light normally incident in air in the pass-through state, an average light reflectance of over 95% and an average light transmittance of less than 5% for light normally incident in air in the blockage state, in which case the average is over a wavelength range of approximately 400 nm, or approximately 450 nm to approximately 1000 nm, or approximately 1050 nm. (The data shown in Figure 21 is for a two-packet polarizer, but similar results are retained for a reflective polarizer having only one of the two packets, since most of the reflection is due to the packet facing the incident light). Thus, suitable reflectance and transmittance were obtained with a number of layers similar to that of some conventional reflective polarizer films, but over a significantly wider bandwidth.

[0028] Preferably, the direction of each stretch axis of the interference layer 102 is substantially aligned (e.g., aligned or nearly aligned) such that the X axis of each interference layer 102 represents the direction for obtaining the maximum refractive index in the XY plane for each layer. However, depending on the mechanical tolerances and the number of interference layers 102, the stretch axis 120 for each interference layer (e.g., representing the direction for obtaining the maximum refractive index or maximum refraction for the layer) may be aligned within a variation of about ±2°.

[0029] In some embodiments, the optical film 100, or the optical laminate contained in the optical film 100, may include a first layer 102a and a second layer 102b, which reflect or transmit light primarily by optical interference, with a total refractive index greater than 100 and less than 600(N) or less than 300(N). For example, the optical film 100 may include a first layer 102a with a refractive index less than 300 and greater than 100, and a second layer 102b with a refractive index less than 300 and greater than 100. As another example, the optical film 100 may include a first layer 102a with a refractive index between 50 and 300, and a second layer 102b with a refractive index between 50 and 300. In some embodiments, for each pair of adjacent first layers 102a and second layers 102b, the layers can define a stretch axis that represents the direction in which the maximum refractive index is obtained for each layer (e.g., X-axis / direction 120 corresponding to the refractive indices n1x and n2x for the two layers). The difference in refractive index between the first layer 102a and the second layer 102b with respect to the primary axis (e.g., Δnx = n1x - n2x) may be greater than about 0.2 or greater than about 0.24. In some embodiments, the directions of the respective stretching axes for each of the first optical layer 102a and the second optical layer 102b may be substantially aligned such that the interference layer 102 defines the maximum angular range of the respective stretching axis directions to less than about 2 degrees.

[0030] An optical film 100 containing multiple interference layers 102 can be formed using any preferred technique. General techniques for forming multilayer optical films are described in U.S. Patent No. 5,882,774 (Jonza et al.) "Optical Film", U.S. Patent No. 6,179,948 (Merrill et al.) "Optical Film and Manufacturing Process Thereof", U.S. Patent No. 6,783,349 (Neavin et al.) "Apparatus for Manufacturing Multilayer Optical Film", and U.S. Patent Application Publication No. 2011 / 0272849 (Neavin et al.) "Supply Block for Manufacturing Multilayer Polymer Film". For example, layers 102a and 102b containing optical material A and optical material B, respectively, can be manufactured using co-extrusion, casting, and orientation processes to form a laminate / packet of tens to hundreds of interference layers 102, and the extruded layers can then be stretched or otherwise oriented to form a laminate / packet of interference layers 102. Each laminate / packet may contain a total of about 200 to about 1000 interference layers, depending on the desired properties of the optical film 100. As used herein, “laminated / packet” is used to refer to a continuous series of alternating interference layers 102a, 102b, which do not contain any spacers or non-interference layers formed within the laminate / packet (e.g., sequentially arranged). In some embodiments, spacers, non-interference layers, or other layers may be added to the outside of a given laminate / packet, thereby forming an outer layer of the film without disrupting the alternating pattern of the interference layers 102 within the laminate / packet.

[0031] In some embodiments, the optical film 100 can be manufactured by co-extrusion. The manufacturing method is to (a) provide at least a first stream and a second stream of resin corresponding to a first polymer and a second polymer to be used in the finished film, and (b) divide the first stream and the second stream into a plurality of layers using a suitable feed block, for example, the feed block being (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 along the flow channel from a first position to a second position, and (ii) a feed tube plate having a plurality of first conduits that are in fluid communication with the first flow channel and a plurality of second conduits that are in fluid communication with the second flow channel, wherein each conduit is The present invention comprises (iii) a supply tube plate that supplies itself to each of its own slot dies, with each conduit having a first end and a second end, the first end of the conduit being in fluid communication with a flow channel and the second end of the conduit being in fluid communication with a slot die, and (iii) optionally, an axial rod heater positioned near the conduit, dividing, (c) passing the composite stream through an extrusion die to form a multilayer web, wherein each layer is substantially parallel to the main surface of the adjacent layer, and (d) casting the multilayer web onto a chill roll, sometimes called a casting wheel or casting drum, to form a cast multilayer film. The cast film may have the same number of layers as a finished film, but the layers of the cast film are typically much thicker than the number of layers of the finished film.

[0032] After cooling, the multilayer web can be reheated, stretched, or drawn to produce a nearly finished multilayer optical film. Stretching or drawing achieves two objectives: thinning the layers to their desired final thickness profile, and oriented the layers such that at least some of them are birefringent. Orientation or drawing can be achieved simultaneously or sequentially along the width direction of the web (e.g., via a tenter), along the downstream direction of the web (e.g., via a length aligner), or in any combination thereof. When drawing along only one direction, the drawing may be "unconstrained" (the film is dimensionally relaxed in the in-plane direction perpendicular to the drawing direction) or "constrained" (the film is constrained and not dimensionally relaxed in the in-plane direction perpendicular to the drawing direction). When drawing along both in-plane directions, the drawing may be symmetrical, i.e., equal along the orthogonal in-plane directions, or asymmetrical. Alternatively, the film may be drawn in a batch process. In any case, subsequent or parallel stretching reduction, stress or strain balancing, heat setting, and other processing operations can also be applied to the film.

[0033] Preferably, the polymers of the various layers are selected to have similar rheological properties, such as melt viscosity, so that they can be co-extruded with minimal flow turbulence. The extrusion conditions may be selected to ensure that each polymer is properly fed, melted, mixed, and pumped in a continuous and stable manner as a feed stream and a melt stream. The temperature used to form and maintain each of the melt streams may be selected within a range that avoids freezing, crystallization, or excessive pressure drops at the lower end of the temperature range and avoids material degradation at the upper end of the temperature range.

[0034] The material of example (A) suitable for optical film 100 may include, for example, polyethylene naphthalate (PEN), a PEN-containing copolymer, and polyester (e.g., polyethylene terephthalate (PET) or dibenzoic acid), glycol-modified polyethylene terephthalate. The material of example (B) suitable for optical film 100 may include, for example, a PEN-based copolyester, a PET-based copolyester, polycarbonate (PC), or a blend of these three materials. To achieve high reflectivity with a reasonable number of layers, adjacent microlayers can exhibit, for example, a refractive index difference (Δnx) of at least 0.2 for light polarized along the x-axis.

[0035] In some embodiments, the optical film 100 may be described as having a total of (N) interference layers 102, more than about 100 and less than about 600 or less than about 300, although it is understood that the lower limit of the total number of layers (N) may be any suitable total configured to obtain the described optical properties. In some embodiments, there may be a cancel-out relationship between the obtained optical properties and the total number of layers (N) / the thickness of the obtained film. For example, in some embodiments, the contrast ratio (Ta / Tb) of the film may increase overall by increasing the total number of interference layers 102 contained in the optical film 100 without any of the manufacturing problems described above, but the thickness of the film also increases with increasing number of layers. In some embodiments, such as in modern thin optical display devices, the overall thickness of the film may be a limiting factor because space availability is limited in such optical display units. In some embodiments, the optical film 100 can significantly reduce the film thickness (e.g., by half) while providing a significant improvement in one or more optical properties (e.g., contrast ratio) compared to other film structures (e.g., combinations of absorbing and reflective polarizers used in some conventional display units). Furthermore, excessive film thickness can pose a risk of reducing the overall contrast ratio due to the depolarization of light passing through the film.

[0036] In some embodiments, the optical film 100 may have a total interference layer 102 of about 100 to about 1200 μm, and the overall thickness of the optical film 100 may be less than about 100 μm, including any optional non-interference or protective layers. In some embodiments, the optical film 100 has a total thickness of less than about 100 μm (e.g., less than 80 μm, or in the range of 50 μm to 80 μm) across all layers of the optical film 100.

[0037] In some embodiments, the thickness of individual interference layers 102 may be relatively thin, such that less than 30% of the interference layers 102 have a thickness greater than approximately 200 nm (for example, less than 5% of the interference layers 102 have a thickness greater than 200 nm, or all interference layers 102 have a thickness of less than approximately 200 nm), but may also vary as a function of position within the optical film 100. In some examples, the optical film 100 can be characterized in terms of the film's thickness profile. For example, the thickness of individual interference layers 102 may vary such that the thickness of individual interference layers 102 increases overall as they move from the outermost interference layers to interference layers near the center of the optical film 100 (for example, increasing independently of local variations).

[0038] In some embodiments, the optical film includes two or more laminates or packets of interference layers. Figure 2 is a schematic side view of the optical film 200, including a first optical laminate 202-1 and a second optical laminate 202-2 disposed between a first main surface 204 and a second main surface 214 on opposite sides of the optical film 200. Each of the first optical laminate 202-1 and the second optical laminate 202-2 includes a plurality of interference layers, which may be as described for the plurality of interference layers 102. The number of interference layers contained in the optical film 200 may be significantly greater than that schematically shown in Figure 2, and may be within any range described elsewhere in this specification. The first optical laminate 202-1 and the second optical laminate 202-2 are non-overlapping in that they do not share any layers and the layers of one optical laminate are not scattered across the layers of the other optical laminate. The first protective boundary layer (PBL) 205a and the second PBL 205b are included on both sides of the first optical laminate 202-1, and the first protective boundary layer 207a and the second protective boundary layer 207b are included on both sides of the second optical laminate 202-2. In the illustrated embodiment, PBLs 205a and 207a are the outermost layers of the optical film 200. The intermediate layer 209 is included between PBLs 205b and 207b. The intermediate layer 209 may be described together with PBLs 205a and 207b as a spacer layer between the first optical laminate 202-1 and the second optical laminate 202-2. Alternatively, the first optical laminate 202-1 and the second optical laminate 202-2 may be described as including their respective PBLs, and the intermediate layer 209 may be described as a spacer layer. In some embodiments, each of the PBLs 205a, 205b, 207a, and 207b is optically thick (i.e., its thickness is substantially greater than the wavelength within a given wavelength range). In some embodiments, the optically thick layer has a thickness greater than about 1 μm, or greater than twice the maximum wavelength within a given wavelength range, or greater than three times the maximum wavelength within a given wavelength range. In some embodiments, the intermediate layer 209 is optically thick.

[0039] In some embodiments, the intermediate layer 209 is a light-absorbing linear polarizer. In some embodiments, the light-absorbing linear polarizer has a cutoff axis (e.g., within 5 degrees or within 2 degrees) substantially aligned with the cutoff axis (second polarization state) of each of the first optical laminate 202-1 and the second optical laminate 202-2. In some embodiments, the intermediate layer 209 is a dichroic polarizer that transmits at least 80% of the light having the first polarization state and absorbs at least 50% of the light having the second polarization state. In some embodiments, the optical film 200 is manufactured by forming a molten stream containing each layer of the optical film 200, with the dichroic dye in the intermediate layer 209, then casting the molten stream onto a chill roll, and then substantially uniaxially oriented the cast film. The high refractive index layers of the first optical laminate 202-1 and the second optical laminate 202-2, as well as the dichroic dye in the intermediate layer, may consequently be oriented along substantially the same direction.

[0040] In some embodiments, the optical film 200 is integrally formed. As used herein, a first element “integrally formed” with a second element means that the first and second elements are manufactured together rather than separately and then joined together. “Integratedly formed” includes manufacturing the first element and then manufacturing the second element on the first element. An optical film comprising multiple layers is integrally formed if the layers are manufactured together rather than separately and then joined together (e.g., by casting from a common melt stream and then oriented the cast layers). An integrally formed optical film having two or more packets can be manufactured, for example, by forming melt streams in separate packet creators, integrating the packets into a common melt stream, then casting the common melt stream to form a cast film, and then oriented the cast film (e.g., by substantially uniaxial stretching).

[0041] In some embodiments, each of the first optical laminate 202-1 and the second optical laminate 202-2 includes a plurality of interference layers (e.g., polymer interference layers) that reflect and transmit light by optical interference within the same predetermined wavelength range extending at least 450 nm to 600 nm (e.g., 400 nm to 700 nm), or at least 400 nm to 600 nm, or at least 450 nm to 650 nm, or at least 400 nm to 700 nm).

[0042] In some embodiments, the optical film 200 transmits at least 80% of normally incident light having a first polarization state within a predetermined wavelength range and reflects at least 95% of normally incident light having a second polarization state orthogonal within a predetermined wavelength range. The optical film 200 may include a plurality of polymer layers (interference layers of a first optical laminate 202-1 and a second optical laminate 202-2), each polymer layer having an average thickness of less than about 200 nm. The plurality of polymer layers may include a first polymer layer 203a and a second polymer layer 203b as the two polymer layers furthest from each other within the plurality of polymer layers. The first layer 203a and the second layer 203b have a first thickness and a second thickness (for example, thickness t1 and thickness t, as depicted in Figure 3) N ) has. In some embodiments, the absolute value of the difference between the first thickness and the second thickness is less than about 20 nm, or less than about 10 nm, or less than about 8 nm, or less than about 7 nm.

[0043] In some embodiments, the optical film 200 includes a plurality of laminated first polymer interference layers (interference layers of the first optical laminate 202-1) disposed on a plurality of laminated second interference layers (interference layers of the second optical laminate 202-2), each first and second interference layer reflects or transmits light primarily by optical interference for at least one wavelength within the same predetermined wavelength range. In some embodiments, the outermost first interference layer (first layer 203a) is the first interference layer furthest from the plurality of laminated second interference layers, and the outermost second interference layer (second layer 203b) is the second interference layer furthest from the plurality of laminated first interference layers. In some embodiments, the outermost first and second interference layers have an optical thickness equal to one-quarter of the first and second wavelengths, respectively, within a predetermined wavelength range. In some embodiments, the difference between the first wavelength and the second wavelength is less than about 80 nm, or less than about 60 nm, or less than about 40 nm, or less than about 30 nm, or less than about 20 nm, or less than about 10 nm. In some embodiments, each of the first and second wavelengths is in the range of about 420 nm to about 480 nm.

[0044] In some embodiments, the innermost first interference layer 206a is the first interference layer closest to a plurality of stacked second interference layers, and the innermost second interference layer 206b is the second interference layer closest to a plurality of stacked first interference layers, and the innermost first interference layer 206a and the second interference layer 206b have an optical thickness equal to one-quarter of the third and fourth wavelengths, respectively, within a predetermined wavelength range. In some embodiments, the difference between the third and fourth wavelengths is less than about 120 nm, or less than about 100 nm, or less than about 80 nm, or less than about 60 nm, or less than about 40 nm, or less than about 30 nm, or less than about 20 nm, or less than about 10 nm. In some embodiments, each of the third and fourth wavelengths is in the range of about 600 nm to about 635 nm.

[0045] A ray 213 reflected from the second optical laminate 202-2 is shown. Other rays may pass through the second optical laminate 202-2 and be reflected by the first laminate 202-1. Some of the light reflected by the first laminate 202-1 may be absorbed by the intermediate layer 209, and some of this light may be reflected by the second optical laminate 202-2 or transmitted through the second optical laminate 202-2. In some cases, the light is scattered by at least one of the first optical laminate and the second optical laminate. The scattered light generally propagates in directions other than the specular reflection direction, which may result from, for example, impurities or defects in the optical film. A ray 215 at a higher angle of incidence passes through the second optical laminate 202-2, is scattered by the first optical laminate 202-1, and is absorbed by the intermediate layer 209. More generally, some light, especially light at high angles of incidence, may be scattered by at least one of the first optical stack 202-1 and the second optical stack 202-2, and the intermediate layer 209 may absorb at least a portion of the scattered light.

[0046] Various layer thickness profiles can be used in the optical films described herein. In some embodiments, the optical film comprises two optical laminates / packets, each having a substantially overlapping thickness profile such that the two optical laminates / packets reflect the same predetermined wavelength range. By arranging the optical packets such that the thinner interference layer is closer to the outermost surface of the optical film, and the thicker interference layer is further from either outermost surface, improved optical properties can be obtained in various applications (e.g., in display applications utilizing polarizing beam splitters), and this is therefore typically preferred, although other configurations are possible. The optical film can, for example, when used in a polarizing beam splitter in an optical system, provide one or more of the following compared to conventional reflective polarizer films: higher reflectivity for s-polarization, higher transmittance for p-polarization, and lower transmittance for s-polarization over a wider range of incident angles.

[0047] FIG. 3 is a schematic diagram of the layer thickness profile of an optical film, such as an optical film 200 including two optical laminates or packets. The first optical laminate 302-1 extends from t1 at the outermost interference layer of the optical film to t at the outermost interference layer of the first optical laminate 302-1, which is the innermost interference layer of the optical film closest to the second optical laminate 302-2. m The second optical laminate 302-2 includes a plurality of interference layers having a thickness ranging from t at the outermost interference layer of the second optical laminate 302-2, which is the innermost interference layer of the optical film closest to the first optical laminate 302-1, to t at the outermost interference layer of the optical film. m+1 to t at the outermost interference layer of the optical film. N In some embodiments, |t1 - t| is less than about 20 nm, less than about 15 nm, or less than about 12 nm, or less than about 10 nm, or less than about 8 nm, or less than about 7 nm, or less than about 6 nm. In some embodiments, |t - t| is less than about 40 nm, or less than about 30 nm, or less than about 20 nm, or less than about 15 nm, or less than about 12 nm, or less than about 10 nm. N | is less than about 20 nm, less than about 15 nm, or less than about 12 nm, or less than about 10 nm, or less than about 8 nm, or less than about 7 nm, or less than about 6 nm. In some embodiments, |t m - t[[ID=! m+1 | is less than about 40 nm, or less than about 30 nm, or less than about 20 nm, or less than about 15 nm, or less than about 12 nm, or less than about 10 nm.

[0048] In some embodiments, the optical film includes a plurality of polymer layers, each polymer layer having an average thickness of less than about 200 nm. The plurality of polymer layers includes a first polymer layer and a second polymer layer (e.g., layer 203a and layer 203b) as the two polymer layers farthest from each other within the plurality of polymer layers. The first polymer layer and the second polymer layer have respective first thickness t1 and second thickness t N such that the difference between the first thickness and the second thickness (the thickness difference defined herein as non-negative) is less than about 20 nm, or |t1 - t N| is within any of the ranges described. In some embodiments, the optical film comprises a first optical laminate and a second optical laminate separated by one or more spacer layers, the first optical laminate comprising a first plurality of layers within a plurality of polymer layers, the second optical laminate comprising a second plurality of layers within a plurality of polymer layers, the first optical laminate comprising a first polymer layer, and the second optical laminate comprising a second polymer layer. In some embodiments, the optical film comprises a third polymer layer within the first plurality of layers (e.g., layer 206a within the first optical laminate 202-1), and a fourth polymer layer within the second plurality of layers (e.g., layer 206b within the second optical laminate 202-2), as two polymer layers in the first plurality of layers and the second plurality of layers that are closest to each other, the third layer and the fourth layer having a third thickness and a fourth thickness, respectively, the difference between the third thickness and the fourth thickness being less than about 40 nm, or |t m -t m+1 It is located within the range described for |.

[0049] The optical films described herein can be used in a variety of applications. For example, the optical films can be used as a substitute for reflective polarizers commonly used in display applications. In some embodiments, the optical films described herein are incorporated into a polarizing beam splitter (PBS).

[0050] Figure 4 is a schematic side view of a polarizing beam splitter (PBS) 450, including a first prism 430 and a second prism 440. The first prism 430 includes a first hypotenuse 432, and the second prism 440 includes a second hypotenuse 442. An optical film 400 is disposed between the first hypotenuse 432 and the second hypotenuse 442 and is bonded to them. The optical film 400 may be bonded to the first hypotenuse 432 and the second hypotenuse 442 by optically transparent adhesive layers (not shown in Figure 4). The optical film 400 may be any of the optical films described herein. For example, the optical film 400 may correspond to optical film 100 or optical film 200, and may include a plurality of alternating high-refractive-index and low-refractive-index layers disposed between a first main surface and a second main surface on opposite sides of the optical film. In some embodiments, the optical film 400 may correspond to the optical film 200 and may have a first optical laminate 202-1 that is close to the first hypotenuse 432 and far from the second hypotenuse 442, and a second optical laminate 202-2 that is close to the second hypotenuse 442 and far from the first hypotenuse 432. In this case, layer 203a is the interference layer closest to the first hypotenuse 432, and layer 203b is the interference layer closest to the second hypotenuse 442.

[0051] The prism may have a cross-section that is a right-angled isosceles triangle, as schematically shown in Figure 4, or it may have other cross-sections. For example, one of the sides of the prism may be curved, or the cross-section may be a non-isosceles triangle. The prism may have a length (in pages) that is approximately the same as the transverse dimension, or a length that is substantially different from the transverse dimension. For example, the length may be substantially greater than the transverse dimension so that the prism is substantially rod-shaped. The rod may then be separated into a plurality of prisms, which may be substantially cubic prisms.

[0052] Figure 5 is a schematic side view of a polarizing beam splitter (PBS) 550, which is similar in many respects to the polarizing beam splitter (PBS) 450. The polarizing beam splitter (PBS) 550 includes a first prism 530 having a first hypotenuse 532, and a second prism 540 having a second hypotenuse 542 facing the first hypotenuse 532. An optical film 500 is disposed between the first hypotenuse 532 and the second hypotenuse 542 and bonded to them via a first optically transparent adhesive layer 534 and a second optically transparent adhesive layer 544. The optical film 500 includes a first optical laminate 502-1 disposed on a second optical laminate 502-2 and separated therefrom by a light-absorbing linear polarizer 509. The first optical laminate 502-1 is located near the first hypotenuse 532 and far from the second hypotenuse 542, and the second optical laminate 502-2 is located near the second hypotenuse 542 and far from the first hypotenuse 534. In some embodiments, with respect to each optical laminate and the hypotenuse closest to it, the optical laminate includes a plurality of interference layers, ranging from 50 to 300, that primarily reflect and transmit light by optical interference within the same predetermined wavelength range, extending at least 400 nm to 600 nm (e.g., 400 nm to 600 nm, or 400 nm to 700 nm), or at least 450 nm to 600 nm, or at least 450 nm to 650 nm, or at least 450 nm to 1000 nm (e.g., 450 nm to 1000 nm, or 450 nm to 1050 nm). In some embodiments, with respect to each optical laminate and the hypotenuse closest to the optical laminate, the interference layer closer to the hypotenuse is configured to reflect mainly shorter wavelengths in a predetermined wavelength range, and the interference layer further from the hypotenuse is configured to reflect mainly longer wavelengths in a predetermined wavelength range. For example, the thickness profile of the interference layer in the optical film 500 may look like that shown in Figure 3, having a thinner layer closer to the outer surface of the optical film (reflecting shorter wavelengths) and a thicker layer further from the outer surface of the optical film (reflecting longer wavelengths). In some embodiments, the polarizing beam splitter (PBS) 550 has an optical axis 555 or is used in an optical system having an optical axis 555.In some embodiments, the optical axis 555 forms an angle α with the optical film 500 of approximately 30 to 60 degrees, or approximately 35 to 55 degrees, or approximately 40 to 50 degrees.

[0053] The prisms used in the polarizing beam splitter (PBS) described herein can be made from any suitable material. For example, the first and second prisms may be made independently from glass (e.g., BK7 glass) or a polymer material such as polycarbonate or polyacrylate.

[0054] The polarizing beam splitter described herein can be used in a variety of applications. For example, the polarizing beam splitter (PBS) may be used in imaging or display systems. The display system may be a head-mounted display such as a virtual reality display or an augmented reality display. The use of polarizing beam splitters (PBS) in various display applications is described, for example, in U.S. Patent No. 8,382,293 (Phillips III et al.) and U.S. Patent No. 9,535,256 (Carls et al.). The polarizing beam splitter (PBS) described herein can be used as a substitute for any polarizing beam splitter (PBS) in the optical systems described in these references. The polarizing beam splitter (PBS) described herein is particularly advantageous for use in optical systems, where unmodulated light from a light source is reflected from one side of the optical film, and spatially modulated light from an imager is reflected from the opposite side of the optical film. Exemplary embodiments of such optical systems are shown in Figures 6 and 7.

[0055] Figure 6 is a schematic cross-sectional view of an optical system 675, including a polarizing beam splitter (PBS) 650, a light source 670, a pixelated spatial light modulator 672, and a reflective component 673. The polarizing beam splitter (PBS) 650 may be any polarizing beam splitter (PBS) as described herein and includes an optical film 600 disposed between a first prism 630 and a second prism 640. The light source 670 produces a substantially polarized light output 676 with the optical film 600 blocked. For example, the light source 670 may include a non-polarizing light source and a linear polarizer, disposed to transmit light polarized along the y' axis, with the optical film 600 blocked, referring to the x', y', z' coordinate system drawn in Figure 6. The pixelated spatial light modulator 672 may be any suitable spatial light modulator. For example, the pixelated spatial light modulator 672 may be an LCoS panel having a quarter-wavelength phase element between the silicon-based liquid crystal (LCoS) panel and the polarizing beam splitter (PBS) 650. The reflective component 673 is preferably a polarization-changing reflector. For example, the reflective component 673 may include a mirror and a quarter-wavelength phase element disposed between the mirror and the polarizing beam splitter (PBS) 650. The light output 676 from the light source 670 is reflected from the optical film 600, then reflected from the pixelated spatial light modulator 672 as modulated light 678 having a passing polarization state and passing through the optical film 600, then reflected from the reflective component 673 in a cutoff polarization state, and then reflected from the optical film 600. In some embodiments, light 676 is first incident on the optical film 600 in an s-polarized state, which is the cutoff polarization state of the optical film 600, then reflected from the pixelated spatial light modulator 672, then incident on the optical film in a p-polarized state, which is the pass-through polarization state, then reflected from the reflective component 673, and then incident on the optical film 600 again in an s-polarized state.

[0056] In some embodiments, the optical film 600 includes a first optical laminate and a second optical laminate, and optionally a light-absorbing linear polarizer disposed between them. In some embodiments, the first optical laminate faces a first prism 630 and substantially reflects the light output 676 from a light source 670, and the second optical laminate faces a second prism 640 and substantially reflects the light 678 incident on the optical film 600 from a reflective component 673.

[0057] Figure 7 is a schematic cross-sectional view of an optical system 775, including a polarizing beam splitter (PBS) 750, a light source 770, a pixelated spatial light modulator 772, and a reflective component 773. The polarizing beam splitter (PBS) 750 may be any polarizing beam splitter (PBS) described herein and includes an optical film 700 disposed between a first prism 730 and a second prism 740. The light source 770 produces a substantially polarized light output 776 when the optical film 700 is blocked and may be as described for light source 670. The pixelated spatial light modulator 772 may be any suitable spatial light modulator and may be as described for pixelated spatial light modulator 672. The reflective component 773 is preferably a polarization-changing reflector as described for reflective component 673. In some embodiments, the reflective component 773 includes a quarter-wavelength phaser and a mirror disposed on the surface of the lens, and may be coupled to or separated from the first prism 730. In other embodiments, the first prism 730 includes a curved outer surface, and the reflective component 773 is disposed on the curved outer surface of the first prism 730. The light output 776 from the light source 770 is reflected from the optical film 700, then reflected from the reflective component 773 in a passing polarization state, then transmitted through the optical film 700, then reflected from the pixelated spatial light modulator 772 as patterned light 778 having a cutoff polarization state, and then reflected from the optical film 700.

[0058] The optical system 675 or the optical system 775 may include further components (e.g., magnifying optical elements and / or waveguides) and may be used, for example, in a head-mounted display. The optical system 675 and / or the optical system 775 may be described as an imaging system.

[0059] In some embodiments, the optical film 700 includes a first optical laminate disposed on a second optical laminate and separated therefrom by a light-absorbing linear polarizer, as further described elsewhere herein. The optical output 776 is sometimes called image light because it can be patterned by a pixelated spatial light modulator 772 to form an image. In some embodiments, the image light enters a polarizing beam splitter (PBS), is sequentially reflected by the first optical laminate, transmitted through the optical film 700, reflected by the second optical laminate, and then exits the polarizing beam splitter (PBS), where the light-absorbing linear polarizer absorbs less than 2%, or less than 1.5%, or less than 1% of the image light, but absorbs at least 50%, or at least 60%, or at least 70% of the image light scattered by at least one of the first and second optical laminates. The pixel spatial light modulator 772 may be fully on when determining the absorption of the absorbing linear polarizer, so that the optical output 776 is approximately the image light minus the light absorbed by the optical absorbing linear polarizer.

[0060] Figure 8 is a schematic cross-sectional view of an optical system 875, useful for determining various properties of the polarizing beam splitter (PBS) and optical film described herein. The optical system 875 includes an unpolarized point light source 870, a linear absorbing polarizer 881, a collimating optical lens 883 for collimating the light emitted by the point light source 870, an optical lens 885, a polarizing beam splitter (PBS) 850 including a first prism 830 and a second prism 840, and an optical film 800 disposed between the first prism 830 and the second prism 840, which receives light 876 from the optical lens 885. The point light source 870 may be light behind a screen having a pinhole (e.g., a small diameter hole, e.g., 30 μm). A portion of the light 876 is reflected from the optical film 800 to a detector 888, which is configured to determine the intensity of this reflected light and thereby determine the reflectance R. The x', y', z' coordinate system is shown in Figure 8. The linear absorbing polarizer 881 may be oriented to transmit light having an electric field along a specific direction (for example, along the y' axis or along the z' axis) in the y'-z' plane.

[0061] In some embodiments, the optical lens 885 is an imaging optical lens. In such embodiments, the optical system 875 may be called the imaging system. In some embodiments, the detector 888 is located on the image surface 890 (the surface on which the optical system forms an image), and similarly, in some embodiments, the detector 889 is located on the image surface 892. In some embodiments, the optical lens 885 has an f-number in the range of, for example, 4.5 to 5.5, or 4.9 to 5.1, or the f-number may be nominally 5.0, but may differ from 5.0 due to normal manufacturing variations (e.g., by less than about 1%). In some embodiments, the detector 888 is configured to determine the point diffusion function (PSF) of the imaging system. The PSF of the imaging system describes the response of the imaging system to a point light source (e.g., the diffusion of light output at the image surface 890). Figure 9 schematically illustrates the PSF of the imaging system. The PSF has a maximum value Max, with a full width at half maximum (FWHM) of 991, a 30% full width at FW30%Max (FW30%Max) of 993, and a 20% full width at FW20%Max (FW20%Max) of 995. The PSF can be normalized so that Max equals 1 and does not affect the various width values. In some embodiments, the imaging system has a point diffusion function with a 20% full width of less than 33 μm, or less than 32 μm, or less than 31 μm, or less than 30.5 μm, or less than 30 μm. In some embodiments, the imaging system has a point diffusion function with a 20% full width of greater than 15 μm, or greater than 20 μm. In some embodiments, the imaging system has a point diffusion function with a 15% full width of less than 62 μm, or less than 60 μm, or less than 58 μm, or less than 56 μm, or less than 54 μm, or less than 52 μm. In some embodiments, the imaging system has a point diffusion function with a 15th percentile total width greater than 35 μm or greater than 40 μm. In some embodiments, the imaging system has a point diffusion function with a 30th percentile total width less than 21 μm, less than 20 μm, less than 19.5 μm, or less than 19.1 μm. In some embodiments, the imaging system has a point diffusion function with a 30th percentile total width greater than 10 μm or greater than 15 μm.

[0062] In some embodiments, the optical film 800 substantially transmits light having a first polarization state within a predetermined wavelength range extending to 400 nm to 700 nm, or 430 nm to 630 nm, or 450 nm to 1000 nm, and substantially reflects light having a second polarization state that is orthogonal to it. Substantially reflecting can be understood as meaning at least 60% reflectivity, and substantially transmitting can be understood as meaning at least 60% transmittance. The light having the first polarization state may be p-polarized with an electric field in the z' direction, and the light having the second polarization state may be s-polarized with an electric field in the y' direction. In some embodiments, the polarizer 881 is oriented such that the collimated light from the collimating lens 883 has a second polarization state. In some embodiments, the optical lens 885 has an f-value in the range of 1.8 to 2.2, or 1.9 to 2.1, or 2.0 to 2.1. In some embodiments, the optical lens 885 is centered on an optical axis 855 that forms an angle with the optical film 800 of approximately 30 to 60 degrees, or approximately 35 to 55 degrees, or approximately 40 to 50 degrees. In some embodiments, the optical film 800 has a total transmittance T=T1 when light 876 is first incident on the first main surface of the optical film 800 (facing the first prism 830). In some embodiments, the polarizing beam splitter (PBS) 850 is positioned so that the second prism 840 faces the optical lens 885, and the optical film 800 has a total transmittance T=T2 when light 876 is first incident on the second main surface of the optical film 800 (facing the second prism 840). A schematic diagram of the transmittance as a function of wavelength when the collimated light from the collimating lens 883 has a second polarization state is illustrated in Figure 10. The predetermined wavelength range is λ1 to λ2. In some embodiments, the maximum difference between T1 and T2, Δsmax, is less than 0.02%, or less than 0.015%, or less than 0.01%, or about less than 0.008%, or about less than 0.006%, as a function of the wavelength of light within a given wavelength range. Δsmax is the maximum value of |T1-T2| over a given wavelength range. For example, the maximum difference between T1 and T2 is when T1 is 0.01% (i.e., 10 -4) and may occur at wavelengths where T2 is 0.006%, resulting in a maximum difference of 0.004%. In some embodiments, T1 and T2 are each about 0.05% (i.e., about 5 × 10) for each wavelength within a given wavelength range. -4 ) is less than, or less than approximately 0.04%, or less than approximately 0.03%, or less than approximately 0.02%, or less than approximately 0.015%.

[0063] In some embodiments, the polarizer 881 is oriented such that the collimated light from the collimating lens 883 has a first polarization state. In such embodiments, the optical film 800 may have a total transmittance T=T3 when light 876 is first incident on the first main surface of the optical film 800, and a total transmittance T=T4 when light is first incident on the second main surface of the optical film (for example, when the polarizing beam splitter (PBS) 850 is positioned so that the second prism 840 faces the optical lens 885). A schematic diagram of the transmittance as a function of wavelength when the collimated light from the collimating lens 883 has a first polarization state is shown in Figure 11. In some embodiments, the average difference between T3 and T4, Δavg, is less than 3%, or less than 2%, or less than 1%, or about 0.5%, as a function of the wavelength of the light incident within a given wavelength range. Δavg is the unweighted average of |T3-T4| over a given wavelength range. In some embodiments, the maximum difference between T3 and T4, Δpmax, is less than 5%, less than 4%, or less than 3%, as a function of the wavelength of light within the given wavelength range. Δpmax is the maximum value of |T3-T4| over the given wavelength range. In some embodiments, the average of T3 and T4, each over the given wavelength range, is at least 92%, or at least 93%, or at least 94%, or at least 95%.

[0064] Terms such as “about” and “substantially” are understood by those skilled in the art in the context in which they are used and described herein. Where the use of “about” applied to the size, quantity, and physical properties of a feature is not obvious to those skilled in the art in the context in which it is used and described herein, “about” is understood to mean within 5 percent of a particular value. A quantity given as about or approximately of a particular value may be exactly that particular value. For example, where it is not obvious to those skilled in the art in the context in which it is used and described herein, a quantity having a value of about 1 means a quantity having a value between 0.95 and 1.05, and that value may be 1. Where the use of “substantially normal” is not obvious to those skilled in the art in the context in which it is used and described herein, “substantially normal” means within 30 degrees of the normal. The direction described as substantially normal may, in some embodiments, be within 20 degrees or 10 degrees of the normal, or it may be the normal or nominal normal.

[0065] The following is a list of exemplary embodiments of this specification.

[0066] Embodiment 1 is an optical film comprising a plurality of polymer interference layers, each interference layer reflecting or transmitting light mainly by optical interference with at least one wavelength within a predetermined wavelength range extending at least 450 nm to 1000 nm, the total number of interference layers being more than about 100 and less than about 300, and thereby the plurality of interference layers having an average light transmittance of more than about 85% for a first polarization state, an average light reflectance of more than about 95% for an orthogonal second polarization state, and an average light transmittance of less than about 5% for the second polarization state, with respect to light substantially incident on the optical film substantially normal to the optical film within the predetermined wavelength range.

[0067] Embodiment 2 is the optical film according to Embodiment 1, wherein the x-axis is defined along a second polarization state, the y-axis is defined along a first polarization state perpendicular to the x-axis, and the z-axis is defined along the thickness direction of the optical film perpendicular to the x-axis and y-axis, and the plurality of polymer interference layers include a plurality of alternating first and second layers, each first and second layer having a refractive index nx along the x-axis, a refractive index ny along the y-axis, and a refractive index nz along the z-axis, for each first layer the absolute value of the difference between ny and nz is less than 0.008 and the difference between nx and ny is greater than 0.2, and for each second layer the absolute value of the difference between ny and nz is less than 0.005 and the difference between nx of the first layer and nx of the second layer is greater than 0.2.

[0068] Embodiment 3 is the optical film described in Embodiment 2, wherein for each first layer, 1.8 ≤ nx ≤ 1.9, 1.5 ≤ ny ≤ 1.6, and 1.5 ≤ nz ≤ 1.6, and for each second layer, nx, ny, and nz are each between 1.5 and 1.6.

[0069] Embodiment 4 is the optical film according to Embodiment 1, further comprising a dichroic polarizer integrally formed with a plurality of polymer interference layers, wherein the dichroic polarizer transmits at least 80% of light having a first polarization state and absorbs at least 50% of light having a second polarization state.

[0070] Embodiment 5 is the optical film according to Embodiment 1, wherein the first optical laminate includes a plurality of polymer interference layers, and the optical film further includes a second optical laminate disposed on the first optical laminate, the second optical laminate includes a second plurality of polymer interference layers, each interference layer in the second optical laminate reflects or transmits light mainly by optical interference with at least one wavelength within a predetermined wavelength range, the total number of interference layers in the second optical laminate is more than about 100 and less than about 300, and so that with respect to light substantially incident on the optical film within a predetermined wavelength range, the second plurality of interference layers have an average light transmittance of more than about 85% for a first polarization state, an average light reflectance of more than about 95% for a second polarization state, and an average light transmittance of less than about 5% for a second polarization state.

[0071] Embodiment 6 is the optical film according to Embodiment 5, wherein the first optical laminate and the second optical laminate are separated by one or more spacer layers.

[0072] Embodiment 7 is an optical film according to Embodiment 6, wherein each of the first optical laminate and the second optical laminate has an interference layer that is close to one or more spacer layers and reflects longer wavelengths, and an interference layer that is far from one or more spacer layers and reflects shorter wavelengths.

[0073] Embodiment 8 is the optical film according to Embodiment 6, wherein one or more spacer layers include a dichroic polarizer that transmits at least 80% of light in a predetermined wavelength range having a first polarization state and absorbs at least 50% of light in a predetermined wavelength range having a second polarization state.

[0074] Embodiment 9 is an optical film according to Embodiment 5, wherein the first outermost interference layer is an interference layer within the first optical laminate that is furthest from the second optical laminate, the second outermost interference layer is an interference layer within the second optical laminate that is furthest from the first optical laminate, the first outermost interference layer and the second outermost interference layer have an optical thickness equal to one-quarter of the first and second wavelengths, respectively, within a predetermined wavelength range, and the difference between the first and second wavelengths is less than approximately 40 nm.

[0075] Embodiment 10 is, A first prism containing the first hypotenuse, A second prism containing the second hypotenuse facing the first hypotenuse, An optical film according to any one of embodiments 1 to 9 is disposed between the first hypotenuse and the second hypotenuse and adhered to them, It is a polarizing beam splitter (PBS) that includes [the specified component].

[0076] Embodiment 11 is a polarizing beam splitter (PBS) according to Embodiment 10, in which the polarizing beam splitter (PBS) is incorporated into an imaging system that includes a point light source, a collimating optical lens for collimating the light emitted by the point light source, and an imaging optical lens having an f-number in the range of 4.5 to 5.5, and when the optical film in the polarizing beam splitter (PBS) receives light from the imaging optical lens and reflects the received light toward the image surface, the imaging system has a point diffusion function having a 20th percentile total width of less than 33 μm or a 15th percentile total width of less than 60 μm.

[0077] Embodiment 12 is a polarizing beam splitter (PBS) according to Embodiment 11, wherein the 20% total width is less than 33 μm and the 15% total width is less than 60 μm.

[0078] Embodiment 13 is a polarizing beam splitter (PBS) according to Embodiment 11, wherein the 20% total width is less than 32 μm and the 15% total width is less than 56 μm.

[0079] Embodiment 14 is a polarizing beam splitter (PBS) according to Embodiment 10, wherein, with respect to collimated light having a second polarization state, an f-value of 1.8 to 2.2, and passing through an optical lens centered on an optical axis at an angle of approximately 30 to 60 degrees with the optical film, the optical film has a total transmittance T1 when the light is first incident on a first main surface of the optical film, and a total transmittance T2 when the light is first incident on a second main surface on the opposite side of the optical film, and the maximum difference between T1 and T2 is less than 0.02% as a function of the wavelength of the light incident within the wavelength range of 430 nm to 630 nm.

[0080] Embodiment 15 is a polarizing beam splitter (PBS) according to Embodiment 10, wherein, with respect to collimated light having a first polarization state, an f-value of 1.8 to 2.2, and passing through an optical lens centered on an optical axis at an angle of approximately 30 to 60 degrees with the optical film before being incident on the optical film in the polarizing beam splitter (PBS), the optical film has a total transmittance T3 when the light is first incident on the first main surface of the optical film, and a total transmittance T4 when the light is first incident on the second main surface on the opposite side of the optical film, and the average of each of T3 and T4 over the wavelength range of 430 nm to 630 nm is at least 92%.

[0081] Embodiment 16 is an optical film comprising a plurality of laminated first polymer interference layers disposed on a plurality of laminated second polymer interference layers, wherein each first and second interference layer reflects or transmits light mainly by optical interference with at least one wavelength within the same predetermined wavelength range, the outermost first interference layer is the first interference layer furthest from the plurality of laminated second interference layers, the outermost second interference layer is the second interference layer furthest from the plurality of laminated first interference layers, the outermost first and outermost second interference layers have an optical thickness equal to one-quarter of the respective first and second wavelengths within the predetermined wavelength range, and the difference between the first and second wavelengths is less than approximately 40 nm.

[0082] Embodiment 17 is an optical film according to Embodiment 16, wherein the innermost first interference layer is the first interference layer closest to the multiple stacked second interference layers, the innermost second interference layer is the second interference layer closest to the multiple stacked first interference layers, the innermost first interference layer and the second interference layer have an optical thickness equal to one-quarter of the third wavelength and the fourth wavelength, respectively, within a predetermined wavelength range, and the difference between the third wavelength and the fourth wavelength is less than approximately 80 nm.

[0083] Embodiment 18 is an optical film according to Embodiment 16, wherein each of the multiple laminated first polymer interference layers and the multiple laminated second polymer interference layers has an average light transmittance of more than 85% for a first polarization state, an average light reflectance of more than 95% for an orthogonal second polarization state, and an average light transmittance of less than 5% for a second polarization state, with respect to light substantially incident on the optical film within a predetermined wavelength range.

[0084] Embodiment 19 defines an x-axis along a second polarization state, a y-axis along a first polarization state perpendicular to the x-axis, and a z-axis along the thickness direction of the optical film orthogonal to the x and y axes, wherein each of the multiple laminated first polymer interference layers and the multiple laminated second polymer interference layers comprises a plurality of alternating first and second layers, each of which has a refractive index nx along the x-axis, a refractive index ny along the y-axis, and a refractive index nz along the z-axis. The optical film according to Embodiment 18 is such that, for each first layer, the absolute value of the difference between ny and nz is less than 0.008 and the difference between nx and ny is greater than 0.2; and for each second layer, the absolute value of the difference between ny and nz is less than 0.005 and the difference between nx of the first layer and nx of the second layer is greater than 0.2.

[0085] Embodiment 20 is, A first prism containing the first hypotenuse, A second prism containing the second hypotenuse facing the first hypotenuse, An optical film according to any one of embodiments 16 to 19 is disposed between the first hypotenuse and the second hypotenuse and adhered to them, It is a polarizing beam splitter (PBS) that includes [the specified component].

[0086] Embodiment 21 is a polarizing beam splitter (PBS) as described in Embodiment 20, in which the polarizing beam splitter (PBS) is incorporated into an imaging system that includes a point light source, a collimating optical lens for collimating the light emitted by the point light source, and an imaging optical lens having an f-number in the range of 4.5 to 5.5, and when the optical film in the polarizing beam splitter (PBS) receives light from the imaging optical lens and reflects the received light toward the image surface, the imaging system has a point diffusion function having a 20th percentile total width of less than 33 μm or a 15th percentile total width of less than 60 μm.

[0087] Embodiment 22 is a polarizing beam splitter (PBS) according to Embodiment 20, wherein, with respect to collimated light having a second polarization state, an f-value of 1.8 to 2.2, and passing through an optical lens centered on an optical axis at an angle of approximately 30 to 60 degrees with the optical film, the optical film has a total transmittance T1 when the light is first incident on a first main surface of the optical film, and a total transmittance T2 when the light is first incident on a second main surface on the opposite side of the optical film, and the maximum difference between T1 and T2 is less than 0.02% as a function of the wavelength of the incident light within a predetermined wavelength range.

[0088] Embodiment 23 is a polarizing beam splitter (PBS) according to Embodiment 20, wherein, with respect to collimated light having a first polarization state, an f-value of 1.8 to 2.2, and passing through an optical lens centered on an optical axis at an angle of approximately 30 to 60 degrees with the optical film before being incident on the optical film in the polarizing beam splitter (PBS), the optical film has a total transmittance T3 when the light is first incident on the first main surface of the optical film, and a total transmittance T4 when the light is first incident on the second main surface on the opposite side of the optical film, and the average of each of T3 and T4 over the wavelength range of 430 nm to 630 nm is at least 92%.

[0089] Embodiment 24 is, A first prism containing the first hypotenuse, A second prism containing the second hypotenuse facing the first hypotenuse, A polarizing beam splitter (PBS) comprising an optical film according to any one of embodiments 16 to 19, disposed between a first hypotenuse and a second hypotenuse and bonded thereto, wherein the optical film further comprises a first optical laminate comprising a plurality of laminated first polymer interference layers facing a first prism, and a second optical laminate comprising a plurality of laminated first polymer interference layers facing a second prism, the first optical laminate being disposed on the second optical laminate and separated therefrom by a light-absorbing linear polarizer, Therefore, the polarizing beam splitter (PBS) is incorporated into the imaging system, and when the image light entering the polarizing beam splitter (PBS) is sequentially reflected by the first optical stack, transmitted through the optical film, reflected by the second optical stack, and then exits the polarizing beam splitter (PBS), the light-absorbing linear polarizer absorbs less than 2% of the image light, but absorbs at least 50% of the image light scattered by at least one of the first and second optical stacks.

[0090] Embodiment 25 is an optical film comprising a first optical laminate disposed on a second optical laminate and separated therefrom by one or more spacer layers, wherein each optical laminate comprises a plurality of polymer interference layers that reflect and transmit light by optical interference in the same predetermined wavelength range extending at least 450 nm to 600 nm, thereby, with respect to light substantially incident on the optical film substantially normal to the optical film within the predetermined wavelength range, the plurality of interference layers in each optical laminate transmit at least 80% of light having a first polarization state, reflect at least 90% of light having an orthogonal second polarization state, and transmit less than 5% of light having a second polarization state, and each spacer layer in the one or more spacer layers does not reflect or transmit light mainly by optical interference, and each optical laminate has interference layers that are close to one or more spacer layers and reflect the longer wavelength, and interference layers that are farther from one or more spacer layers and reflect the shorter wavelength, and the first optical laminate, the second optical laminate and one or more spacer layers are integrally formed with respect to each other.

[0091] Embodiment 26 is an optical film according to Embodiment 25, wherein the outermost first interference layer is a polymer interference layer within the first optical laminate furthest from the second optical laminate, the outermost second interference layer is a polymer interference layer within the second optical laminate furthest from the first optical laminate, the outermost first interference layer and the outermost second interference layer have an optical thickness equal to one-quarter of the first and second wavelengths, respectively, within a predetermined wavelength range, and the difference between the first and second wavelengths is less than approximately 40 nm.

[0092] Embodiment 27 is an optical film according to Embodiment 25, wherein an x-axis is defined along a second polarization state, a y-axis is defined along a first polarization state perpendicular to the x-axis, and a z-axis is defined along the thickness direction of the optical film perpendicular to the x and y axes, and for each optical laminate, a plurality of polymer interference layers are included, comprising a plurality of alternating first and second layers, each first and second layer having a refractive index nx along the x-axis, a refractive index ny along the y-axis, and a refractive index nz along the z-axis, for each first layer, the absolute value of the difference between ny and nz is less than 0.008 and the difference between nx and ny is greater than 0.2, and for each second layer, the absolute value of the difference between ny and nz is less than 0.005 and the difference between nx of the first layer and nx of the second layer is greater than 0.2.

[0093] Embodiment 28 is, A first prism containing the first hypotenuse, A second prism containing the second hypotenuse facing the first hypotenuse, An optical film according to any one of embodiments 25 to 27 is disposed between the first hypotenuse and the second hypotenuse and adhered thereto, A polarizing beam splitter (PBS) including, A polarizing beam splitter (PBS) is incorporated into an imaging system that includes a point light source, a collimating optical lens for collimating the light emitted by the point light source, and an imaging optical lens having an f-number in the range of 4.5 to 5.5. When an optical film within the polarizing beam splitter (PBS) receives light from the imaging optical lens and reflects the received light toward the image surface, the imaging system is a polarizing beam splitter (PBS) having a point diffusion function with a 20th percentile total width of less than 33 μm or a 15th percentile total width of less than 60 μm.

[0094] Embodiment 29 is, A first prism containing the first hypotenuse, A second prism containing the second hypotenuse facing the first hypotenuse, A polarizing beam splitter (PBS) comprising an optical film according to any one of embodiments 25 to 27, disposed between a first hypotenuse and a second hypotenuse and bonded thereto, wherein the first optical laminate faces a first prism, the second optical laminate faces a second prism, and one or more spacer layers include light-absorbing linear polarizers, wherein the polarizing beam splitter (PBS) is incorporated into an imaging system and, when image light entering the polarizing beam splitter (PBS) is sequentially reflected by the first optical laminate, transmitted through the optical film, reflected by the second optical laminate, and then exits the polarizing beam splitter (PBS), the light-absorbing linear polarizers absorb less than 2% of the image light but absorb at least 50% of the image light scattered by at least one of the first optical laminate and the second optical laminate.

[0095] Embodiment 30 is an optical film that transmits at least 80% of normally incident light having a first polarization state within a predetermined wavelength range and reflects at least 95% of normally incident light having a second polarization state that is orthogonal within a predetermined wavelength range, wherein the optical film comprises a plurality of polymer layers, each polymer layer having an average thickness of less than about 200 nm, and the plurality of polymer layers comprises a first polymer layer and a second polymer layer as the two polymer layers in the plurality of polymer layers that are furthest from each other, and the first layer and the second layer have a first thickness and a second thickness, respectively, and the difference between the first thickness and the second thickness is less than about 10 nm.

[0096] Embodiment 31 is an optical film according to Embodiment 30, comprising a first optical laminate and a second optical laminate separated by one or more spacer layers, wherein the first optical laminate comprises a plurality of first layers within a plurality of polymer layers, the second optical laminate comprises a plurality of second layers within a plurality of polymer layers, the first optical laminate comprises a first polymer layer, and the second optical laminate comprises a second polymer layer.

[0097] Embodiment 32 is an optical film according to Embodiment 31, wherein one or more spacer layers include a dichroic polarizer that transmits at least 80% of light having a first polarization state and absorbs at least 50% of light having a second polarization state.

[0098] Embodiment 33 is, A first prism containing the first hypotenuse, A second prism containing the second hypotenuse facing the first hypotenuse, A polarizing beam splitter (PBS) comprising an optical film described in Embodiment 32, disposed between a first hypotenuse and a second hypotenuse and bonded thereto, wherein the first optical laminate faces a first prism and the second optical laminate faces a second prism, thereby incorporating the polarizing beam splitter (PBS) into an imaging system, and when image light entering the polarizing beam splitter (PBS) is sequentially reflected by the first optical laminate, transmitted through the optical film, reflected by the second optical laminate, and then exits the polarizing beam splitter (PBS), the dichroic polarizer absorbs less than 2% of the image light but absorbs at least 50% of the image light scattered by at least one of the first and second optical laminates.

[0099] Embodiment 34 is an optical film according to Embodiment 30, wherein an x-axis is defined along a second polarization state, a y-axis is defined along a first polarization state perpendicular to the x-axis, and a z-axis is defined along the thickness direction of the optical film perpendicular to the x-axis and y-axis, and the plurality of polymer layers include a plurality of alternating first interference layers and second interference layers, each first and second interference layer having a refractive index nx along the x-axis, a refractive index ny along the y-axis, and a refractive index nz along the z-axis, for each first interference layer, the absolute value of the difference between ny and nz is less than 0.008 and the difference between nx and ny is greater than 0.2, and for each second layer, the absolute value of the difference between ny and nz is less than 0.005 and the difference between nx of the first layer and nx of the second layer is greater than 0.2.

[0100] Embodiment 35 is an optical film comprising a first main surface and a second main surface located opposite each other, and adjacent non-overlapping first optical laminates and second optical laminates disposed between them, wherein the first optical laminate is disposed near the first main surface and far from the second main surface, and the second optical laminate is disposed near the second main surface and far from the first main surface, and for each optical laminate and the main surface closest to the optical laminate, the optical laminates are 50 to 300 The first optical laminate is an optical film comprising a plurality of first interference layers, each first interference layer reflecting or transmitting light mainly by optical interference, each first interference layer closer to the main surface being thinner than each first interference layer further from the main surface, each first interference layer having orthogonal plane refractive indices nx and ny, and refractive index nz in the thickness direction of the first interference layer, the difference between ny and nz being less than 0.008, and the difference between nx and ny being greater than 0.2, and the first optical laminate is integrally formed with the second optical laminate.

[0101] Embodiment 36 is, A first prism containing the first hypotenuse, A second prism containing the second hypotenuse facing the first hypotenuse, A polarizing beam splitter (PBS) comprising an optical film disposed between a first hypotenuse and a second hypotenuse and bonded thereto, wherein the optical film comprises a plurality of alternating high-refractive-index and low-refractive-index layers disposed between a first main surface and a second main surface on opposite sides of the optical film, the optical film substantially transmits light having a first polarization state in a predetermined wavelength range extending from 400 nm to 700 nm and substantially reflects light having a second polarization state orthogonal thereto, thereby having a second polarization state and an f-value of 1.8 to 2.2 A polarizing beam splitter (PBS) is a polarizing beam splitter (PBS) in which collimated light, after passing through an optical lens centered on an optical axis at an angle of approximately 30 to 60 degrees with the optical film, has a total transmittance T1 when the light is first incident on the first main surface of the optical film, and a total transmittance T2 when the light is first incident on the second main surface of the optical film, and the maximum difference between T1 and T2 is less than 0.02% as a function of the wavelength of the incident light within a given wavelength range.

[0102] Embodiment 37 is a polarizing beam splitter (PBS) according to Embodiment 36, wherein T1 and T2 are each less than approximately 0.05% for each wavelength within a predetermined wavelength range.

[0103] Embodiment 38 is a polarizing beam splitter (PBS) according to Embodiment 36, wherein, with respect to collimated light having a first polarization state, an f-value of 1.8 to 2.2, and passing through an optical lens centered on an optical axis at an angle of approximately 30 to 60 degrees with the optical film, the optical film has a total transmittance T3 when the light is first incident on the first main surface of the optical film, a total transmittance T4 when the light is first incident on the second main surface of the optical film, and the average difference between T3 and T4 in a predetermined wavelength range is less than 3%.

[0104] Embodiment 39 is a polarizing beam splitter (PBS) according to Embodiment 36, wherein, with respect to collimated light having a first polarization state, an f-value of 1.8 to 2.2, and passing through an optical lens centered on an optical axis at an angle of approximately 30 to 60 degrees with the optical film, the optical film has a total transmittance T3 when the light is first incident on the first main surface of the optical film, a total transmittance T4 when the light is first incident on the second main surface of the optical film, and the maximum difference between T3 and T4 is less than 5% as a function of the wavelength of the incident light within a predetermined wavelength range.

[0105] Embodiment 40 is a polarizing beam splitter (PBS) according to Embodiment 36, wherein, with respect to collimated light having a first polarization state, an f-value of 1.8 to 2.2, and passing through an optical lens centered on an optical axis at an angle of approximately 30 to 60 degrees with the optical film before being incident on the optical film in the polarizing beam splitter (PBS), the optical film has a total transmittance T3 when the light is first incident on the first main surface of the optical film, and a total transmittance T4 when the light is first incident on the second main surface on the opposite side of the optical film, and the average of each of T3 and T4 over the wavelength range of 430 nm to 630 nm is at least 92%.

[0106] Embodiment 41 is a polarizing beam splitter (PBS) according to Embodiment 36, wherein the optical film defines an x-axis along a second polarization state, a y-axis along a first polarization state perpendicular to the x-axis, and a z-axis along the thickness direction of the optical film perpendicular to the x and y axes, and each of a plurality of alternating high-refractive-index layers and low-refractive-index layers has a refractive index nx along the x-axis, a refractive index ny along the y-axis, and a refractive index nz along the z-axis, and for each high-refractive-index layer, the absolute value of the difference between ny and nz is less than 0.008 and the difference between nx and ny is greater than 0.2, and for each low-refractive-index layer, the absolute value of the difference between ny and nz is less than 0.005 and the difference between nx of the high-refractive-index layer and nx of the low-refractive-index layer is greater than 0.2.

[0107] Embodiment 42 is, A first prism containing the first hypotenuse, A second prism containing the second hypotenuse facing the first hypotenuse, A polarizing beam splitter (PBS) comprising an optical film disposed between a first hypotenuse and a second hypotenuse and bonded thereto, wherein the optical film comprises a plurality of alternating high-refractive-index and low-refractive-index layers disposed between a first main surface and a second main surface on opposite sides of the optical film, wherein the optical film substantially transmits light having a first polarization state in a predetermined wavelength range extending from 400 nm to 700 nm and substantially reflects light having a second orthogonal polarization state, thereby the polarizing beam splitter (PBS) being incorporated into an imaging system comprising a point light source, a collimating optical lens for collimating light emitted by the point light source, and an imaging optical lens having an f-number in the range of 4.5 to 5.5, wherein when the optical film in the polarizing beam splitter (PBS) receives light from the imaging optical lens and reflects the received light toward the image surface, the imaging system is a polarizing beam splitter (PBS) having a point diffusion function with a 20% value total width of less than 33 μm.

[0108] Embodiment 43 is a polarizing beam splitter (PBS) according to Embodiment 42, wherein the point diffusion function has a 15% value total width of less than 60 μm.

[0109] Embodiment 44 is, A first prism containing the first hypotenuse, A second prism containing the second hypotenuse facing the first hypotenuse, A polarizing beam splitter (PBS) comprising an optical film disposed between a first hypotenuse and a second hypotenuse and bonded thereto, wherein the optical film comprises a plurality of alternating high-refractive-index and low-refractive-index layers disposed between a first main surface and a second main surface on opposite sides of the optical film, wherein the optical film substantially transmits light having a first polarization state in a predetermined wavelength range extending from 400 nm to 700 nm and substantially reflects light having a second orthogonal polarization state, thereby the polarizing beam splitter (PBS) being incorporated into an imaging system comprising a point light source, a collimating optical lens for collimating light emitted by the point light source, and an imaging optical lens having an f-number in the range of 4.5 to 5.5, wherein when the optical film in the polarizing beam splitter (PBS) receives light from the imaging optical lens and reflects the received light toward the image surface, the imaging system is a polarizing beam splitter (PBS) having a point diffusion function with a total width of less than 60 μm at the 15th percentile.

[0110] Embodiment 45 is a polarizing beam splitter (PBS) according to Embodiment 44, wherein the point diffusion function has a 20% value total width of less than 33 μm.

[0111] Embodiment 46 is a polarizing beam splitter (PBS) according to any one of Embodiments 42 to 45, wherein the point diffusion function has a 30% value total width of less than 20 μm.

[0112] Embodiment 47 is, A first prism containing the first hypotenuse, A second prism containing the second hypotenuse facing the first hypotenuse, A polarizing beam splitter (PBS) comprising an optical film disposed between a first hypotenuse and a second hypotenuse and bonded thereto, comprising a first optical laminate disposed on a second optical laminate and separated therefrom by a light-absorbing linear polarizer, wherein the first optical laminate is close to the first hypotenuse and far from the second hypotenuse, and the second optical laminate is close to the second hypotenuse and far from the first hypotenuse, and each optical laminate and the hypotenuse closest to the optical laminate comprises a plurality of interference layers reaching 50 to 300, which mainly reflect and transmit light by optical interference within the same predetermined wavelength range extending at least 450 nm to 600 nm, and the interference layers close to the hypotenuse mainly, The polarization beam splitter (PBS) is configured to reflect the shorter wavelength within a given wavelength range, with the interference layer furthest from the hypotenuse mainly configured to reflect the longer wavelength within a given wavelength range, thereby absorbing less than 2% of the image light but absorbing at least 50% of the image light scattered by at least one of the first and second optical stacks.

[0113] Embodiment 48 is a polarizing beam splitter (PBS) according to Embodiment 47, wherein the plurality of interference layers of the first optical stack include a first layer closest to the first hypotenuse, and the plurality of interference layers of the second optical stack include a second layer closest to the second hypotenuse, and the first and second layers have a first thickness and a second thickness, respectively, and the difference between the first thickness and the second thickness is less than about 10 nm.

[0114] Embodiment 49 is, A first prism containing the first hypotenuse, A second prism containing the second hypotenuse facing the first hypotenuse, A polarizing beam splitter (PBS) comprising an optical film disposed between a first hypotenuse and a second hypotenuse and bonded thereto, comprising a plurality of alternating high-refractive-index and low-refractive-index layers disposed between a first main surface and a second main surface on opposite sides of the optical film, wherein the optical film substantially transmits light having a first polarization state within a predetermined wavelength range extending from 430 nm to 630 nm and substantially reflects light having a second polarization state orthogonal thereto, thereby having the first polarization state, 1.8 to 2. The polarizing beam splitter (PBS) is such that, with respect to collimated light having an f-number of 2 and passing through an optical lens centered on an optical axis at an angle of approximately 30 to 60 degrees with the optical film, the optical film has a total transmittance T3 when the light first incident on the first main surface of the optical film, and a total transmittance T4 when the light first incident on the second main surface of the optical film, and the average of each of T3 and T4 over a predetermined wavelength range is at least 92%.

[0115] Embodiment 50 is a polarizing beam splitter (PBS) according to Embodiment 49, wherein, with respect to collimated light having a second polarization state, an f-value of 1.8 to 2.2, and passing through an optical lens centered on an optical axis at an angle of approximately 30 to 60 degrees with the optical film, the optical film has a total transmittance T1 when the light is first incident on the first main surface of the optical film, a total transmittance T2 when the light is first incident on the second main surface of the optical film, and the maximum difference between T1 and T2 is less than 0.02% as a function of the wavelength of the incident light within a predetermined wavelength range. [Examples]

[0116] Example 1 The optical film was generally fabricated as shown in Figure 2. The optical film contained two packets of optical repeating units (ORUs), each packet containing 138 ORUs. Each ORU contained a low-refractive-index, nearly isotropic layer consisting of a high- and low-refractive-index layer of low-melt PEN (a copolymer of 90% PEN and 10% PET), and a low-refractive-index layer of 85% polycarbonate / 15% PCTg material blended with 15% PETg. The optical films were fabricated using a conventional multilayer optical film process as described in U.S. Patent Application Publication No. 2007 / 0047080 (Stover et al.). A molten stream with the desired layers was formed and then cast onto a casting wheel to form a cast film. This cast film was then uniaxially oriented transversely with a stretch ratio of approximately 6:1 using a parabolic tenter to obtain an optical film. The ORUs were sequentially numbered from 1 to 276 across the optical film. The thickness of the obtained ORUs is shown in Figure 12 as a function of the number of ORUs. The refractive indices obtained for the high-refractive-index and low-refractive-index layers are shown in Table 1. [Table 1]

[0117] The transmittance coefficient for light incident normally in air was measured for both pass-through and cut-off polarization states. This is shown in Figure 21.

[0118] A polarizing beam splitter (PBS) was fabricated using an optical film placed between BK7 glass prisms. The total transmittance as a function of wavelength of light incident on the optical film within the polarizing beam splitter (PBS) was measured for collimated light that had a specified polarization state, an f-value of 2.04, and was centered on an optical axis at a 45-degree angle to the optical film, before being incident on the optical film within the polarizing beam splitter (PBS). The specified polarization state was either vertical or horizontal polarization. By positioning the polarizing beam splitter (PBS), vertical polarization occurred on the optical film as s-polarization, and horizontal polarization occurred on the optical film as p-polarization. The axis of passage of the optical film was horizontal. Transmittance was determined by oriented the optical film, with the wheel side of the film (the side cast to the casting wheel) facing the light source (denoted as WTS) and the air side of the film (the side opposite the wheel side) facing the light source (denoted as ATS). Figures 13 and 14 show the transmission coefficients (total transmittance) for wavelengths of s-polarized and p-polarized light, respectively, that are initially incident on the optical film from each side of the film.

[0119] Comparative examples C1~C4 Optical films were prepared within a polarizing beam splitter (PBS) and measured as in Example 1. The optical film of Comparative Example C1 contained two packets, and by flipping the second packet over the second packet of Example 1, the ORU closest to one main surface became the thicker layer reflecting red wavelengths, and the ORU closer to the opposite main surface became the thinner layer reflecting blue wavelengths. The optical film of C1 contained approximately 750 interference layers. The optical film of Comparative Example C2 had a single packet with 325 interference layers whose layer thickness varied monotonically across the optical film. The optical film of Comparative Example C3 contained two packets with substantially non-overlapping thickness ranges, so that one packet reflected shorter wavelengths and the other packet reflected longer wavelengths. The optical film of C3 contained approximately 750 interference layers. The film of Comparative Example C4 was similar to that of Comparative Example C2, except that the total number of interference layers was 275 and a larger refractive index difference was used to obtain a similar reflectivity.

[0120] For each of Comparative Examples C1 to C4, the materials and processes used to manufacture these films are as described in Example 1, except that the total number of interference layers and their composition are as described above.

[0121] Figures 15 to 17 show the total transmittance for s-polarized light initially incident on each side of the optical films of Comparative Examples C1 to C3. These values ​​were determined for collimated light that has an s-polarized state, an f-value of 2.04, and passes through an optical lens centered on an optical axis at a 45-degree angle with the optical film, within a BK7 prism cube, before being incident on the optical film in the polarizing beam splitter (PBS). RTS and BTS indicate that the side of the optical film with the red-reflective layer faces the light source, or the side of the optical film with the blue-reflective layer faces the light source, respectively.

[0122] Example 2 An optical film was prepared as in Example 1, except that the center spacer layer between the two packets of ORU contained a combination of four different polarizing dichroic dyes listed in Table 2. [Table 2]

[0123] The dichroic dyes of Example 2 were added to the center spacer layer between two packets of ORU in the combinations shown in Table 3, and the dichroic dyes were masterbatched with PEN resin at the indicated pounds / hour (pph). [Table 3]

[0124] The transmittance coefficient for light incident normally in air was measured for both pass-through and cut-off polarization states. This is shown in Figure 22.

[0125] The film was tested in a polarizing beam splitter (PBS) as in Example 1. Figures 18 and 19 show the transmittance coefficients (total transmittance) for s-polarized and p-polarized wavelengths, respectively, initially incident on the optical film from each side of the film in Example 2.

[0126] Example 3 A polarizing beam splitter (PBS) was fabricated as in Example 1. The polarizing beam splitter (PBS) was incorporated into an imaging system (see Figure 8) having a point light source (modeled as a pinhole with a diameter of 30 μm), a collimating optical lens for collimating the light emitted by the point light source, and an imaging optical lens with an f-number of 5.0. The optical film within the polarizing beam splitter (PBS) received light from the imaging optical lens and reflected the received light toward the image surface. The point diffusion function was determined, which is shown in Figure 20. The full width at half maximum (FWHM), 30% full width (FW30%Max), 20% full width (FW20%Max), and 20% full width (FW20%Max) were determined. These are reported in Table 4. The measurements were repeated using the optical films of Comparative Examples C3 and C4 in place of the optical film of Example 1. [Table 4]

[0127] Unless otherwise indicated, the descriptions of elements in the figures should be understood to apply equally to corresponding elements in other figures. While specific embodiments have been illustrated and described herein, it will be understood by those skilled in the art that various alternative and / or equivalent practices can replace the illustrated and described embodiments without departing from the scope of this disclosure. This application is intended to encompass all adaptable or modified examples of the specific embodiments described herein. Therefore, this disclosure is limited only by the claims and their equivalents.

[0128] The aforementioned references, patents, and patent applications are all incorporated herein by reference in their entirety in a consistent manner. In the event of any inconsistency or contradiction between any part of the incorporated references and this application, the information in the foregoing description shall prevail.

Claims

1. An optical film comprising a first optical laminate disposed on a second optical laminate and separated therefrom by one or more spacer layers, wherein each optical laminate includes a plurality of polymer interference layers that reflect and transmit light by optical interference within the same predetermined wavelength range extending at least 450 nm to 600 nm, thereby, with respect to light substantially incident on the optical film substantially normal to the optical film within the predetermined wavelength range, the plurality of interference layers in each optical laminate have an average light transmittance of at least 80% for light having a first polarization state, an average light reflectance of at least 90% for light having an orthogonal second polarization state, and an average light transmittance of less than 5% for light having the second polarization state, and each spacer layer in the one or more spacer layers reflects or transmits light by optical interference. The optical film is not a composite, but rather each optical laminate has an interference layer that is close to one or more spacer layers and reflects the longer wavelength, and an interference layer that is far from the one or more spacer layers and reflects the shorter wavelength, the first optical laminate, the second optical laminate and the one or more spacer layers are integrally formed with respect to each other, the first outermost interference layer is a polymer interference layer in the first optical laminate that is furthest from the second optical laminate, the second outermost interference layer is a polymer interference layer in the second optical laminate that is furthest from the first optical laminate, the first outermost interference layer and the second outermost interference layer have an optical thickness equal to one-quarter of the first and second wavelengths, respectively, within a predetermined wavelength range, and the difference between the first wavelength and the second wavelength is less than 40 nm.

2. The optical film according to claim 1, wherein the first outermost interference layer and the second outermost interference layer each have a first thickness and a second thickness, and the difference between the first thickness and the second thickness is less than 10 nm.

3. The optical film according to claim 1, wherein an x-axis is defined along the second polarization state, a y-axis is defined along the first polarization state perpendicular to the x-axis, and a z-axis is defined along the thickness direction of the optical film perpendicular to the x-axis and y-axis, and for each optical laminate, the plurality of polymer interference layers include a plurality of alternating first and second layers, each first and second layer having a refractive index nx along the x-axis, a refractive index ny along the y-axis, and a refractive index nz along the z-axis, for each first layer, the absolute value of the difference between ny and nz is less than 0.008 and the difference between nx and ny is greater than 0.2, and for each second layer, the absolute value of the difference between ny and nz is less than 0.005 and the difference between nx of the first layer and nx of the second layer is greater than 0.

2.

4. The optical film according to claim 3, wherein for each first layer, 1.8 ≤ nx ≤ 1.9, 1.5 ≤ ny ≤ 1.6, and 1.5 ≤ nz ≤ 1.6, and for each second layer, nx, ny, and nz are each between 1.5 and 1.

6.

5. A first prism containing the first hypotenuse, A second prism including a second hypotenuse facing the first hypotenuse, A polarizing beam splitter (PBS) comprising an optical film disposed between a first hypotenuse and a second hypotenuse and bonded thereto, wherein the optical film comprises a first optical laminate disposed on a second optical laminate and separated therefrom by one or more spacer layers, each optical laminate includes a plurality of polymer interference layers that reflect and transmit light by optical interference within the same predetermined wavelength range extending at least 450 nm to 600 nm, thereby, with respect to light substantially incident on the optical film within the predetermined wavelength range, the plurality of interference layers in each optical laminate have an average light transmittance of at least 80% for light having a first polarization state, an average light reflectance of at least 90% for light having an orthogonal second polarization state, and an average light transmittance of less than 5% for light having the second polarization state, and each spacer layer in the one or more spacer layers does not reflect or transmit light by optical interference, and each optical laminate includes the one or more spacer layers The polarizing beam splitter (PBS) has an interference layer that is close to the pacer layer and reflects longer wavelengths, and an interference layer that is farther from the one or more spacer layers and reflects shorter wavelengths, wherein the first optical laminate, the second optical laminate and the one or more spacer layers are integrally formed with respect to each other, the first optical laminate faces the first prism, the second optical laminate faces the second prism, and the one or more spacer layers include a light-absorbing linear polarizer, wherein the polarizing beam splitter (PBS) is incorporated into an imaging system, and when image light entering the polarizing beam splitter (PBS) is sequentially reflected by the first optical laminate, transmitted through the optical film, reflected by the second optical laminate, and then exits the polarizing beam splitter (PBS), the light-absorbing linear polarizer absorbs less than 2% of the image light, but absorbs at least 50% of the image light scattered by at least one of the first optical laminate and the second optical laminate.

Images