Optical Films and Polarizing Beam Splitters

Abstract

Optical films and polarizing beam splitters including the optical films are described. The optical films include a plurality of stacked first polymer interference layers disposed on a plurality of stacked second polymer interference layers, each of the first interference layer and the second interference layer primarily reflects or transmits light by optical interference for at least one wavelength within the same predetermined wavelength range, an outermost first interference layer is a first interference layer farthest from the plurality of stacked second interference layers, an outermost second interference layer is a second interference layer farthest from the plurality of stacked first interference layers, an optical thickness of the outermost first interference layer and the outermost second interference layer is equal to one-fourth of the corresponding first wavelength and second wavelength within the predetermined wavelength range, and a difference between the first wavelength and the second wavelength is less than about 40 nm.

Description

[0001] This application is a divisional application of the invention patent application filed on April 20, 2020 (international application date: October 18, 2018), with the invention name “Optical Film and Polarization Beam Splitter” and application number 201880068295.2 (international application number: PCT / IB2018 / 058100). Technical Field

[0002] The present invention relates to optical films and polarizing beam splitters. Background Art

[0003] The polarizing beam splitter may include a reflective polarizer disposed between the hypotenuses of adjacent prisms. The reflective polarizer may be a multilayer polymer film. Summary of the invention

[0004] In some aspects of the present specification, an optical film comprising a plurality of polymer interference layers is provided. Each polymer interference layer reflects or transmits light primarily by optical interference for at least one wavelength within a predetermined wavelength range extending from at least 450 nm to 1000 nm. The total number of interference layers is greater than about 100 and less than about 300. For light within the predetermined wavelength range and substantially perpendicularly incident on the optical film, for a first polarization state, the plurality of polymer interference layers has an average optical transmittance greater than about 85%, for an orthogonal second polarization state, an average optical reflectance greater than about 95%, and for the second polarization state, an average optical transmittance less than about 5%.

[0005] In some aspects of the specification, an optical film is provided, the optical film comprising a plurality of stacked first polymer interference layers disposed on a plurality of stacked second polymer interference layers. Each first interference layer and second interference layer reflects or transmits light primarily by optical interference for at least one wavelength within the same predetermined wavelength range. For the outermost first interference layer being the first interference layer farthest from the plurality of stacked second interference layers, and the outermost second interference layer being the second interference layer farthest from the plurality of stacked first interference layers, the optical thickness of the outermost first interference layer and the outermost second interference layer is equal to one quarter of the corresponding first wavelength and second wavelength within the predetermined wavelength range. The difference between the first wavelength and the second wavelength is less than about 40 nm.

[0006] In some aspects of the present specification, an optical film is provided, the optical film including a first optical stack disposed on a second optical stack and spaced from the second optical stack by one or more spacer layers. Each optical stack includes a plurality of polymer interference layers that reflect and transmit light primarily by optical interference for the same predetermined wavelength range extending from at least 450 nm to 600 nm, such that for light within the predetermined wavelength range and substantially perpendicularly incident on the optical film, the plurality of polymer interference layers in each optical stack 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. Each of the one or more spacer layers does not primarily reflect or transmit light by optical interference. Each optical stack has an interference layer that reflects longer wavelengths closer to the one or more spacer layers, and an interference layer that reflects shorter wavelengths farther away from the one or more spacer layers. The first optical stack and the second optical stack and the one or more spacer layers are formed integrally with each other.

[0007] In some aspects of the present specification, an optical film is provided that transmits at least 80% of vertically incident light having a first polarization state within a predetermined wavelength range, and reflects at least 95% of vertically incident light having an orthogonal second polarization state within a predetermined wavelength range. The optical film includes a plurality of polymer layers, wherein the average thickness of each polymer layer is less than about 200 nm. The plurality of polymer layers include a first polymer layer and a second polymer layer as two polymer layers farthest from each other in the plurality of polymer layers, the first polymer layer and the second polymer layer having respective first thicknesses and second thicknesses, and the difference between the first thickness and the second thickness is less than about 10 nm.

[0008] In some aspects of the present specification, an optical film is provided, the optical film having a first major surface and a second major surface opposite to each other, and including adjacent non-overlapping first and second optical stacks disposed between the first and second major surfaces. The first optical stack is disposed closer to the first major surface and further away from the second major surface, and the second optical stack is disposed closer to the second major surface and further away from the first major surface. For each optical stack and the major surface closest to the optical stack: the optical stack includes a plurality of first interference layers between 50 and 300; each first interference layer reflects or transmits light primarily by optical interference; each first interference layer closer to the major surface is thinner than each first interference layer further away from the major surface, each first interference layer having orthogonal in-plane refractive indices nx and ny and refractive indices nz in the thickness direction of the first interference layer, 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 stack is formed integrally with the second optical stack.

[0009] In some aspects of the present specification, a polarizing beam splitter (PBS) is provided, including 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 adhered to the first hypotenuse and the second hypotenuse. The optical film includes a plurality of alternating higher refractive index layers and lower refractive index layers disposed between opposing first and second major surfaces of the optical film. The optical film substantially transmits light having a first polarization state and substantially reflects light having an orthogonal second polarization state within a predetermined wavelength range extending from 400 nm to 700 nm. For collimated light having a second polarization state and incident on the optical film within the PBS after passing through an optical lens having an aperture number between 1.8 and 2.2 and centered on an optical axis forming an angle of approximately 30 to 60 degrees with the optical film, when the light is first incident on the first major surface of the optical film, the optical film has a total transmittance T1, and when the light is first incident on the second major surface of the optical film, the optical film has a total transmittance T2, wherein the maximum difference between T1 and T2 as a function of the wavelength of the incident light within a predetermined wavelength range is less than 0.02%.

[0010] In some aspects of the present 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 adhered to the first hypotenuse and the second hypotenuse. The optical film comprises a plurality of alternating higher refractive index layers and lower refractive index layers disposed between opposing first and second major surfaces of the optical film. The optical film substantially transmits light having a first polarization state and substantially reflects light having an orthogonal second polarization state within a predetermined wavelength range extending from 400 nm to 700 nm. When the PBS is combined in 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 aperture number in the range of 4.5 to 5.5, wherein the optical film in the PBS receives light from the imaging optical lens and reflects the received light toward an image surface, the 20% maximum full width of the point spread function of the imaging system is less than 33 microns.

[0011] In some aspects of the present 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 adhered to the first hypotenuse and the second hypotenuse. The optical film comprises a plurality of alternating higher refractive index layers and lower refractive index layers disposed between opposing first and second major surfaces of the optical film. The optical film substantially transmits light having a first polarization state and substantially reflects light having an orthogonal second polarization state within a predetermined wavelength range extending from 400 nm to 700 nm. When the PBS is combined in 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 aperture number in the range of 4.5 to 5.5, wherein the optical film in the PBS receives light from the imaging optical lens and reflects the received light toward an image surface, the 15% maximum full width of the point spread function of the imaging system is less than 60 microns.

[0012] In some aspects of the present specification, a polarizing beam splitter (PBS) is provided, including 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 hypotenuse and the second hypotenuse and adhered to the first hypotenuse and the second hypotenuse. The optical film includes a first optical stack, which is disposed on the second optical stack and is separated from the second optical stack by a light absorbing linear polarizer. The first optical stack is closer to the first hypotenuse and farther from the second hypotenuse, and the second optical stack is closer to the second hypotenuse and farther from the first hypotenuse. For each optical stack and the hypotenuse closest to the optical stack: the optical stack includes a plurality of polymer interference layers, the number of the interference layers is between 50 and 300, and mainly reflects and transmits light by optical interference in the same predetermined wavelength range extending from at least 400nm to 600nm, the interference layer closer to the hypotenuse is configured to mainly reflect shorter wavelengths in the predetermined wavelength range, and the interference layer farther from the hypotenuse is configured to mainly reflect longer wavelengths in the predetermined wavelength range. When the PBS is incorporated into an imaging system, image light entering the PBS leaves the PBS after being sequentially reflected by the first optical stack, transmitted by the optical film, and reflected by the second optical stack, and the light-absorbing linear polarizer absorbs at least 50% of the image light scattered by at least one of the first optical stack and the second optical stack, while absorbing less than 2% of the image light.

[0013] In some aspects of the present specification, a polarizing beam splitter (PBS) is provided. It includes 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 hypotenuse and the second hypotenuse and adhered to the first hypotenuse and the second hypotenuse. The optical film includes a plurality of alternating higher refractive index layers and lower refractive index layers disposed between the first and second main surfaces opposite to the optical film. The optical film substantially transmits light having a first polarization state and substantially reflects light having an orthogonal second polarization state within a predetermined wavelength range extending from at least 430 nm to 630 nm. For collimated light, the collimated light has a first polarization state and is incident on the optical film within the PBS after passing through an optical lens having an aperture number between 1.8 and 2.2 and centered on an optical axis forming an angle of about 30 to 60 degrees with the optical film, when the light is first incident on the first main surface of the optical film, the optical film has a total transmittance T3, and when the light is first incident on the second main surface of the optical film, the optical film has a total transmittance T4. The average value of each of T3 and T4 within the predetermined wavelength range is at least 92%. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1A is a schematic perspective view of a multilayer optical film;

[0015] Figure 1B yes Figure 1A A schematic perspective view of a portion of a multilayer optical film;

[0016] Figure 2 is a schematic side view of an optical film including a first optical stack and a second optical stack;

[0017] Figure 3 is a schematic diagram of the layer thickness distribution of the optical film;

[0018] Figures 4 to 5 is a schematic side view of a polarizing beam splitter;

[0019] Figures 6 to 8 is a schematic cross-sectional view of an optical system;

[0020] Fig. 9 is a schematic diagram of the point spread function of the imaging system;

[0021] Fig.10 is a schematic graph showing the transmittance of an optical film in a polarizing beam splitter for s-polarized light as a function of wavelength;

[0022] Fig.11 is a schematic graph showing the transmittance of an optical film in a polarizing beam splitter for p-polarized light as a function of wavelength;

[0023] Fig.12is a graph of the thickness of an sequential optical repeating unit (ORU) in a reflective polarizing film as a function of the number of ORUs in the film;

[0024] Fig.13 is a graph showing the transmittance of an optical film in a polarizing beam splitter for s-polarized light as a function of wavelength;

[0025] Fig.14 is a graph of the transmittance of an optical film in a polarizing beam splitter for p-polarized light as a function of wavelength;

[0026] Figures 15 to 18 is a graph showing the transmittance of an optical film in a polarizing beam splitter for s-polarized light as a function of wavelength;

[0027] Fig.19 is a graph of the transmittance of an optical film in a polarizing beam splitter for p-polarized light as a function of wavelength;

[0028] Fig. 20 is a graph of a point spread function for an imaging system utilizing a polarizing beam splitter including a reflective polarizing film; and

[0029] Figure 21 to Figure 22 is a graph of the transmission coefficient of a reflective polarizing film. DETAILED DESCRIPTION

[0030] In the following description, reference is made to the accompanying drawings, which form a part of the present invention and in which various embodiments are shown by way of example. The drawings are not necessarily drawn to scale. It should be understood that other embodiments may be conceived and carried out without departing from the scope or essence of the present description. Therefore, the following specific embodiments should not be considered to have a limiting meaning.

[0031] According to some embodiments of the present specification, an optical film having improved optical properties over conventional films is provided. In some embodiments, the optical film is a reflective polarizing film suitable for a polarizing beam splitter, which is suitable for various optical systems including head-mounted virtual reality or augmented reality displays. In some embodiments, the optical film includes a package of alternating polymer interference layers, which has a high reflectivity (e.g., greater than about 95%, 96% or 97%) within a predetermined wavelength range (e.g., 400nm to 600nm, or 450nm to 600nm or 430nm to 680nm, or 430 to 630nm, or 450nm to 1000nm) using a limited total number of interference layers (e.g., less than about 300). In some embodiments, high reflectivity over a broadband (e.g., at least 400nm or 450nm to at least 1000nm or 1050nm) is achieved using a limited total number of interference layers (e.g., less than about 300). In some cases, when the film is used in a polarizing beam splitter, a higher long wavelength band edge (e.g., at least 1000 nm or at least 1050 nm) is desired for improved performance. In some embodiments, the optical film includes two (or more) packages of alternating polymer interference layers, wherein the thicker interference layers of the first package are closer to the thicker interference layers of the second package, and the thinner interference layers of the first package are farther away from the thinner interference layers of the second package. It has been found that such optical films can simultaneously provide high-quality image reflection and very low transmission leakage (e.g., transmission in a blocking state of less than 0.05%). In some embodiments, a dichroic polarizer (light absorbing linear polarizer) is included between the two packages. It has been found that this can reduce image contamination from multiple reflections between the two packages and / or can mitigate the effects of depolarization scattering within the optical film. In some embodiments, when the optical film of the present specification is used in a polarizing beam splitter of an imaging system, an improved point spread function (e.g., a narrower 20% maximum full width) is provided compared to an otherwise equivalent imaging system utilizing a conventional optical film.

[0032] The optical films described herein can be characterized as multilayer optical films having multiple optical layers (e.g., polymer interference layers) configured to selectively transmit and reflect light within a predetermined wavelength range. In some such embodiments, the optical film acts as a reflective polarizer that selectively transmits and reflects light of different polarization states. For example, Figure 1A is a schematic perspective view of an example of a multilayer optical film 100 that includes a plurality of polymeric interference layers 102 positioned along a central axis to form an optical film 100 having a total of (N) polymeric interference layers 102 . Figure 1B is a schematic perspective view of a section of optical film 100 showing alternating interference layers 102a and 102b. Figure 1A to Figure 1BIncludes a coordinate system that defines the x, y, and z directions.

[0033] During use, light incident on a major surface (e.g., film surface 104) of optical film 100, depicted by incident light 110, may enter the first layer of optical film 100 and propagate through multiple polymer interference layers 102, undergoing selective reflection or transmission through optical interference depending on the polarization state of incident light 110. Incident light 110 may include a first polarization state (a) and a second polarization state (b) that are mutually orthogonal to each other. The first polarization state (a) may be considered a "pass" state, while the second polarization state (b) may be considered a "reflection" or "blocking" state. When incident light 110 propagates through multiple polymer interference layers 102, a portion of the light in the second polarization state (b) will be reflected by the adjacent interference layer, thereby causing the second polarization state (b) to be reflected by optical film 100, while a portion of the light in the first polarization state (a) passes entirely through optical film 100.

[0034] In some embodiments, the optical film 100 can be characterized by its reflectivity and transmittance of the first polarization state (a) and the second polarization state (b) of the incident light 110. For example, the amount of incident light 110 of a predetermined wavelength transmitted through the optical film 100 can be expressed as a percentage (Ta) of the light transmittance of the first polarization state (a) and a percentage (Tb) of the light transmittance of the second polarization state (b). The amount of incident light 110 of a predetermined wavelength range reflected by the optical film 100 can be expressed as a percentage (Ra) of the light reflectance of the first polarization state (a) and a percentage (Rb) of the light reflectance of the second polarization state (b). For a given optical film, for light within a predetermined wavelength range, the sum of the transmittance, reflectivity, and losses, such as due to absorption, will total 100%. In some embodiments, the optical film 100 has a relatively low absorptivity for light within a predetermined wavelength range. In some embodiments, the relatively low absorptivity of the optical film 100 to the incident light 110 can cause less heat to be generated within the optical film 100 and result in an overall more efficient reflective film. In other embodiments, the optical film 100 can include a dichroic absorbing layer, as further described elsewhere herein.

[0035] The predetermined wavelength range can be any suitable wavelength range, including, for example, visible light (e.g., about 400nm-700nm), a range of visible light (e.g., about 400nm or about 420nm or about 430nm, or about 450nm to about 600nm, or about 630nm, or about 635nm, or about 650nm, or about 680nm, or about 700nm), near infrared light (e.g., about 800nm-1300nm), a range based on the output of a light source such as a liquid crystal display backlight (e.g., 425nm-675nm), and a range based on providing a desired bandwidth when deviating from normal incidence (e.g., 400nm or 450nm to 1000nm or to 1050nm). In some embodiments, the optical film 100 can be configured to transmit and reflect light with different polarization states, such as visible light and near infrared light, within more than one predetermined wavelength range. For example, the predetermined wavelength ranges may include a first range from about 430 nm to about 465 nm, a second range from about 490 nm to about 555 nm, and a third range from about 600 nm to about 665 nm. In some embodiments, the optical film 100 may include a plurality of stacks / packages, each stack / package including a plurality of polymer interference layers, as further described elsewhere herein, wherein each stack / package may be directed to a different predetermined wavelength range or may be directed to the same predetermined wavelength range. In a preferred embodiment, each stack / package is configured to reflect substantially the same predetermined wavelength range.

[0036] In some embodiments, the polymer interference layer can be characterized as a series of two-layer unit cells or optical repeating units. The thickness of each unit cell can be configured to reflect a target wavelength within a predetermined wavelength range. In some examples, the center wavelength of the reflectivity of the unit cell corresponds to twice the optical thickness of the two-layer unit cell. Therefore, in order to reflect a predetermined wavelength range (e.g., 420nm to 635nm), the unit cells within the stack / package will have different thicknesses to cover wavelengths from the left band edge to the right band edge. The optical thickness of a layer refers to the refractive index of the layer multiplied by the physical thickness of the layer. In the case where the optical film is configured to reflect light polarized along the blocking axis and transmit light polarized along the orthogonal pass axis, the refractive index used to determine the optical thickness is the refractive index along the blocking axis. The two layers in the optical repeating unit can have equal or approximately equal optical thicknesses. In some cases, it is useful to characterize the optical repeating unit with an "f ratio", which is the optical thickness of the higher refractive index layer in the paired layers divided by the total optical thickness of the layer pair. In some embodiments, the f ratio is about 0.5. An f-ratio of 0.5 may be preferred because this maximizes the reflected power of the 1st order (primary) reflection band of the optical stack or envelope of the interference layer.

[0037] In some embodiments, the optical film 100 includes less than about 1200 (N) polymer interference layers 102, wherein each polymer interference layer 102 reflects or transmits incident light 110 primarily by optical interference. In some embodiments, the optical film 100 includes less than about 1000, or less than about 800, or less than about 600, or less than about 300 polymer interference layers 102. Although 1200 or more interference layers 102 may be included in the optical film 100, in some cases, it may be desirable to use fewer total layers to achieve the desired optical performance in order to reduce the overall thickness of the film, because the overall thickness of the film is reduced. In many applications, display components (e.g., LCD displays) are preferred. Additionally or alternatively, a smaller total number of interference layers 102 can reduce the complexity of the manufacturing process and reduce the possibility of introducing variability (e.g., spectral variability in blocking or passing states) or production errors (e.g., increased blocking states due to depolarization between layers, reduced passing state transmission) in the final optical film. In some embodiments, the total number N of polymeric interference layers 102 is greater than about 50, or greater than about 100, or greater than about 150, or greater than about 200.

[0038] In some embodiments, the optical film 100 or an optical stack included in the optical film 100 has an average optical transmittance (Ta) greater than about 85% for a first polarization state (a), an average optical reflectance (Rb) greater than 95% for an orthogonal second polarization state (b), and an average optical transmittance (Tb) less than about 5% for the second polarization state (b) for light 110 at substantially normal incidence 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, a total of greater than about 50, or greater than about 100 and less than about 1200, or less than about 600, or less than about 300 interference layers 102 in the optical film 100 or in an optical stack included in the optical film 100 are used to obtain the desired Ta, Tb, and Rb. By selecting materials for the interference layers and controlling the stretch ratio of the film, a high Rb (e.g., greater than about 95%) and a low Tb (e.g., less than about 5%) with a relatively small number of layers can be achieved, so that the difference in refractive index between adjacent interference layers for light having the second polarization state is small (e.g., less than 0.008), and the difference in refractive index between adjacent interference layers for light having the first polarization state is large (e.g., greater than about 0.2). If the wavelength is not specified, the refractive index or refractive index can be regarded as the refractive index at a wavelength of 550 nm.

[0039] The transmittance of an optical film generally refers to the intensity of the transmitted light divided by the intensity of the incident light (for light of a given wavelength, incident direction, etc.), but may be expressed in terms of "external transmittance" or "internal transmittance". The external transmittance of an optical film is the transmittance of the optical film when immersed in air, and no correction is required for the Fresnel reflection at the air / element interface in front of the element, or the Fresnel reflection at the element / air interface behind the element. The internal transmittance of an optical film is the transmittance of the film when the Fresnel reflection at the front and rear surfaces of the optical film has been removed. Removing the Fresnel reflection at the front and rear surfaces can be done by calculation (for example, subtracting an appropriate function from the external transmission spectrum), or by experiment. For many types of polymers and glass materials, the Fresnel reflection at each of the two external surfaces is about 4% to 6% (for normal or near normal incidence), which results in the external transmittance being shifted down by about 10% relative to the internal transmittance. If transmittance is mentioned herein without specifying whether it is internal transmittance or external transmittance, then it can be assumed that the transmittance refers to external transmittance unless the context indicates otherwise.

[0040] For example, when an optical film is used between two prisms in a polarizing beam splitter (PBS), the reflectivity and transmittance of the optical film can be expressed as the total reflectivity and total transmittance of the optical film used in the PBS, respectively. The total transmittance is the transmitted power at a given wavelength divided by the incident power of light of the given wavelength incident into the prism. Similarly, the total reflectivity is the reflected power at a given wavelength divided by the incident power of light of the given wavelength incident into the prism.

[0041] In some embodiments, the interference layer 102 of the optical film 100 includes alternating layers of two different polymeric materials that exhibit different refractive index properties (e.g., Figure 1B A and B depicted in FIG. Figure 1B As shown, the optical film 100 includes alternating layers (e.g., ABABA...) of different optical materials, which are referred to as material "(A)" and material "(B)". As further described elsewhere herein, the individual layers of the two different materials can be formed by an extrusion / lamination process, where the layers are extruded together to form a plurality of optical layers 102 (ABABA...) bonded together.

[0042] In some embodiments, during the extrusion process, the optical layer 102 can be stretched to impart various interference properties to the film. For example, the layers of A and B optical materials can be stretched along one axis (e.g., the X axis) (e.g., at a 5:1 ratio or a 6:1 ratio) without being significantly stretched along the orthogonal axis (e.g., the Y axis). For the A layer or the B layer, the refractive index along the X, Y, and Z axes are represented as nx, ny, nz, respectively. For the A layer and the B layer, respectively, along the X, Y, and Z axes, the refractive index can also be represented as n1x, n1y, n1z and n2x, n2y, n2z, respectively.

[0043] As a result of the stretching process, the choice of optical materials used to form the A and B layers can be selected to impart specific optical properties to the film. For example, the (B) material forming the optical layer 102b can have a nominal refractive index (e.g., n2 between 1.5 and 1.6) that is substantially unaltered by the stretching process. Thus, after the stretching process, the refractive index of the "B" layer 102b in the x and y directions (n2x and n2y) can be substantially the same in both directions, and can be substantially the same as the refractive index in the thickness direction (n2z). In contrast, the (A) material forming the optical layer 102a can have a refractive index that is altered by the stretching process. For example, a uniaxially stretched layer 102a of material (A) may have a higher refractive index in the X-axis or stretch direction 120 (e.g., 1.8≤n1x≤1.9), and a different refractive index associated with the Y-axis or non-stretch 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 absolute value of the difference between n1x and n1y is greater than about 0.2. Due to the increase in refractive index in the stretch direction, the layer 102a including material (A) may be considered a high refractive index (HIR) layer 102a, while the interference layer 102b including 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 embodiments, the refractive index of the alternating AB layers can be controlled by judicious material selection and processing conditions. In some embodiments, the optical properties of layer 102 cause the optical film 100 to act as a reflective polarizer that will substantially transmit a first polarization state (a) component of incident light 110 within a predetermined wavelength range oriented relative to the non-stretch axis 122, while the stretch axis 120 will correspond to a reflection axis for which a component of the incident light 110 in a second polarization state (b) within the predetermined wavelength range will be substantially reflected by optical interference.

[0044] In some embodiments, the optical film 100 can be characterized by the difference between the refractive indices between the alternating HIR layers 102a and LIR layers 102b along the stretch axis 120 (i.e., Δnx = n1x - n2x). In some such embodiments, the refractive indices between the alternating HIR layers 102a and LIR layers 102b along the non-stretch axis direction 122 can be substantially the same, such that the difference between the refractive indices in the non-stretch axis direction 122 (i.e., Δny = n1y - n2y) is approximately 0.0 (e.g., |Δny| is less than about 0.02, or less than about 0.01, or less than about 0.005). In some examples, increasing the Δnx between the HIR layers 102a and LIR layers 102b (e.g., via selection of materials and / or control of uniaxial orientation of the film) can allow for adequate transmission / reflection of polarized light for a given wavelength range with a lower total number of polymer interference layers compared to an optical film with a lower Δnx having the same optical power. For example, each packet of the reflective polarizing film of Example 1 contains 276 polymer interference layers (138 optical repeating units), and each packet has an average optical transmittance greater than 85% for normally incident light in air in the pass state, and an average optical reflectance greater than about 95% and an average optical transmittance less than 5% for normally incident light in air in the block state, wherein the average is over a wavelength range of about 400 nm or about 450 nm to about 1000 nm or about 1050 nm. Fig.21 The data shown in are for a two-packet polarizer, but since most of the reflection is caused by the packet facing the incident light, similar results are obtained for a reflective polarizer with only one of the two packets.) Thus, suitable reflectivity and transmission are obtained with a similar number of layers as some conventional reflective polarizing films, but over a significantly larger bandwidth.

[0045] Preferably, the stretch axis directions of each of the polymeric interference layers 102 will be substantially aligned (e.g., aligned or nearly aligned) such that the X-axis of each respective layer 102 represents the direction for obtaining the maximum refractive index in the XY plane of each layer. However, due to machine tolerances and the number of interference layers 102, the stretch axis 120 of each of the polymeric interference layers (e.g., representing the direction for obtaining the maximum refractive index or refraction of that layer) may be aligned within a variance of about ±2°.

[0046] In some embodiments, the optical film 100 or the optical stack included in the optical film 100 may include a total of greater than 100 (N) or less than 600 (N) or less than 300 (N) first layers 102a and second layers 102b, which reflect or transmit light primarily through optical interference. For example, the optical film 100 may include less than 300 and greater than 100 first layers 102a and less than 300 and greater than 100 second layers 102b. As another example, the optical film 100 may include between 50 and 300 first layers 102a, and may also include between 50 and 300 second layers 102b. In some embodiments, for each pair of adjacent first layers 102a and second layers 102b, the layers may define a stretch axis that represents the direction of the maximum refractive index obtained by the corresponding layer (e.g., the X-axis / direction 120 corresponding to the refractive indices n1x and n2x of the two layers). The refractive index difference between the first layer 102a and the second layer 102b of the principal axis (e.g., Δnx=n1x-n2x) can be greater than about 0.2 or greater than about 0.24. In some such embodiments, the respective stretch axis directions of each of the first optical layer 102a and the second optical layer 102b can be substantially aligned such that the interference layer 102 defines a maximum angular range of the respective stretch axis directions of less than about 2 degrees.

[0047] Any suitable technique may be used to form the optical film 100 including the plurality of polymeric interference layers 102. General techniques for forming multilayer optical films are described in U.S. Pat. No. 5,882,774 (Jonza et al.), “Optical Film,” U.S. Pat. No. 6,179,948 (Merrill et al.), “Optical Film and Process for Manufacture Thereof,” U.S. Pat. No. 6,783,349 (Neavin et al.), “Apparatus for Making Multilayer Optical Films,” and Patent Application Publication No. US 2011 / 0272849 (Neavin et al.), “Feedblock for Manufacturing Multilayer Polymeric Films.” For example, layers 102a and 102b, comprising optical materials A and B, respectively, can be manufactured using coextrusion, casting, and orientation processes to form stacks / packets of tens to hundreds of polymeric interference layers 102, and then stretching or otherwise orienting the extruded layers to form stacks / packets of interference layers 102. Depending on the desired properties of the optical film 100, each stack / packet can include between about 200 and 1000 total interference layers. As used herein, "stack / packet" is used to refer to a set of continuous interference layers 102a, 102b, which are absent any spacers or non-interference layers (e.g., arranged sequentially) formed within the stack / packet. In some embodiments, spacers, non-interference layers, or other layers can be added to the exterior of a given stack / packet to form an outer layer of the film without disrupting the alternating pattern of interference layers 102 within the stack / packet.

[0048] In some embodiments, the optical film 100 can be manufactured by coextrusion. The manufacturing method may include: (a) providing at least a first resin stream and a second resin stream, the at least first resin stream and the second resin stream corresponding to the first polymer and the second polymer to be used in the finished film; (b) using a suitable feed block to separate the first stream and the second stream into a plurality of layers, such as a feed block including (i) a gradient plate including a first flow channel and a second flow channel, wherein the cross-sectional area of ​​the first channel changes from a first position to a second position along the flow channel, (ii) a feed tube plate having a first plurality of conduits in fluid communication with the first flow channel and a second plurality of conduits in fluid communication with the second flow channel, each conduit feeding its own corresponding slot die, each conduit having a first end and a second end, the first end of the conduit being in fluid communication with the flow channel, and the second end of the conduit being in fluid communication with the slot die, and (iii) optionally an axial rod heater positioned adjacent to the conduit; (c) passing the composite material stream through an extrusion die to form a multilayer web, wherein each layer is generally parallel to a major surface of an adjacent layer; and (d) casting the multilayer web onto a chill roll (sometimes referred to as a casting wheel or casting drum) to form a cast multilayer film. The cast film may have the same number of layers as the finished film, but the layers of the cast film are generally much thicker than those of the finished film.

[0049] After cooling, the multilayer web can be reheated and drawn or stretched to produce a nearly finished multilayer optical film. Drawing or stretching achieves two goals: it thins the layer to its desired final thickness distribution; it orients the layer so that at least some of the layers become birefringent layers. Orientation or stretching can be achieved in the transverse direction (e.g., via a tenter), in the longitudinal direction (e.g., via a length orientation machine), or in any combination thereof (whether simultaneously or sequentially). If stretched in only one direction, the stretching can be "unconstrained" (where the film is allowed to relax in size in the in-plane direction perpendicular to the stretching direction) or "constrained" (where the film is constrained and thus not allowed to relax in size in the in-plane direction perpendicular to the stretching direction). If stretched in two in-plane directions, the stretching can be symmetrical (i.e., equal in the orthogonal in-plane directions) or asymmetrical. Alternatively, the film can be stretched by a batch process. In any case, subsequent or simultaneous draw reduction, stress or strain balance, heat setting, and other processing operations can also be applied to the film.

[0050] Preferably, the polymers of the various layers are selected to have similar rheological properties (e.g., melt viscosity) so that they can be coextruded without significant flow disturbance. Extrusion conditions can be selected so that the respective polymers are fully fed, melted, mixed, and pumped as a feed stream or melt stream in a continuous and stable manner. The temperature used to form and maintain each melt stream can be selected to be within the following range, which can avoid freezing, crystallization, or undue high pressure drop at the low end of the temperature range and can avoid material degradation at the high end of the range.

[0051] Examples (A) of materials suitable for optical film 100 may include, for example, polyethylene naphthalate (PEN), copolymers containing PEN and polyester (e.g., polyethylene terephthalate (PET) or dibenzoic acid), and polyethylene terephthalate modified with ethylene glycol. Examples (B) of materials suitable for optical film 100 may include, for example, copolyesters based on PEN, copolyesters based on PET, polycarbonate (PC), or a mixture of these three types of materials. In order to obtain high reflectivity through an appropriate number of layers, the difference in refractive index (Δnx) between adjacent microlayers for light polarized along the x-axis may be, for example, at least 0.2.

[0052] Although in some embodiments the optical film 100 may be described as having a total (N) interference layer 102 greater than (about 100) and less than about 600 or less than about 300, it should be understood that the total number of layers (N) may be any suitable amount configured to obtain the optical properties. In some embodiments, there may be a tradeoff between the optical properties obtained and the total number of layers (N) / thickness of the resulting film. For example, although in some embodiments, the contrast ratio (Ta / Tb) of the film can generally be increased by increasing the total number of interference layers 102 included in the optical film 100 without any of the manufacturing complexities previously discussed, the thickness of the film will also increase with the increase in the number of layers. In some embodiments, such as in modern thin optical display devices, the total thickness of the film may be a limiting factor because the space availability in such optical display units is limited. In some embodiments, the optical film 100 can provide a significant increase in one or more optical properties (e.g., contrast) while having a significantly reduced film thickness (e.g., half) compared to other film constructions (e.g., combined absorptive polarizers and reflective polarizers used in some conventional display units). Additionally, excessive film thickness may run the risk of reducing the overall contrast ratio due to depolarization of through-state light propagating through the film.

[0053] In some embodiments, the optical film 100 can have between about 100 and about 1200 total interference layers 102, wherein the total thickness of the optical film 100 is less than about 100 μm, including any optional non-interference or protective layers. In some embodiments, the total thickness of the optical film 100 over all layers of the optical film 100 is less than about 100 μm (e.g., less than 80 μm or in the range of 50 μm to 80 μm).

[0054] In some embodiments, the thickness of each polymeric interference layer 102 can be relatively thin, such that less than 30% of the interference layers 102 have a thickness greater than about 200 nm (e.g., less than 5% of the interference layers 102 have a thickness greater than 200 nm, or all interference layers 102 have a thickness less than about 200 nm), but may vary with position within the optical film 100. In some examples, the optical film 100 can be characterized according to a thickness distribution of the film. For example, the thickness of each polymeric interference layer 102 can vary, such that the thickness of each polymeric interference layer 102 generally increases (e.g., increases in thickness except for local fluctuations) as it moves from the outermost interference layers to the interference layers closer to the center of the optical film 100.

[0055] In some embodiments, the optical film includes more than one stack or package of interference layers. Figure 2 2 is a schematic side view of an optical film 200 that includes a first optical stack 202-1 and a second optical stack 202-2 disposed between opposing first major surfaces 204 and second major surfaces 214 of the optical film 200. Each of the first optical stack 202-1 and the second optical stack 202-2 includes a plurality of polymeric interference layers and can be as described for the plurality of polymeric interference layers 102. The number of interference layers included in the optical film 200 can be significantly greater than Figure 2, and may be within any of the ranges described elsewhere herein. The first optical stack 202-1 and the second optical stack 202-2 are non-overlapping in that they do not share any layers and the layers of one optical stack are not interspersed with the layers of the other optical stack. A first protection boundary layer (PBL) 205a and a second protection boundary layer 205b are included on opposite sides of the first optical stack 202-1, and a first protection boundary layer 207a and a second protection boundary layer 207b are included on opposite sides of the second optical stack 202-2. In the illustrated embodiment, the PBLs 205a and 207a are the outermost layers of the optical film 200. An intermediate layer 209 is included between the PBLs 205b and 207b. The intermediate layer 209, together with the PBLs 205b and 207b, can be described as a spacer layer between the first optical stack 202-1 and the second optical stack 202-2. Alternatively, the first optical stack 202-1 and the second optical stack 202-2 can be described as including their respective PBLs, and the intermediate layer 209 can be described as a spacer layer. In some embodiments, each of the PBLs 205a, 205b, 207a, and 207b is optically thick (i.e., the thickness is substantially greater than the wavelength in the predetermined wavelength range). In some embodiments, the thickness of the optically thick layer is greater than about 1 micron, or greater than 2 times the maximum wavelength in the predetermined wavelength range, or greater than 3 times the maximum wavelength in the predetermined wavelength range. In some embodiments, the intermediate layer 209 is optically thick.

[0056] In some embodiments, the intermediate layer 209 is a light absorbing linear polarizer. In some embodiments, the light absorbing linear polarizer has a blocking axis that is substantially aligned (e.g., within 5 degrees or within 2 degrees) with each blocking axis (second polarization state) of the first optical stack 202-1 and the second optical stack 202-2. In some embodiments, the intermediate layer 209 is 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. In some embodiments, the optical film 200 is manufactured by forming a molten stream including each layer of the optical film 200, which is a dichroic dye in the intermediate layer 209, then casting the molten stream onto a cooling roller, and then orienting the cast film substantially uniaxially. Therefore, the high refractive index layers of the first optical stack 202-1 and the second optical stack 202-2 and the dichroic dye in the intermediate layer can be oriented in substantially the same direction.

[0057] In some embodiments, the optical film 200 is integrally formed. As used herein, a first element is "integrally formed" with a second element means that the first element and the second element are manufactured together rather than being manufactured separately and subsequently joined. The integration includes manufacturing the first element and then manufacturing the second element on the first element. If the layers are manufactured together (e.g., by casting from a common molten stream and then orienting the cast layers), rather than being manufactured separately and subsequently joined, the integration includes a multilayer optical film. For example, an integrally formed optical film having more than one package can be made by forming molten streams in separate package generators, merging the packages into a common molten stream, and then casting the common molten stream to form a cast film, and then orienting the cast film (e.g., by substantially uniaxial stretching).

[0058] In some embodiments, each of the first optical stack 202-1 and the second optical stack 202-2 includes multiple polymer interference layers (e.g., polymer interference layers) that reflect and transmit light primarily by optical interference within the same predetermined wavelength range extending from at least 450nm to 600nm (e.g., 400nm to 700nm), or at least from 400nm to 600nm, or at least from 450nm to 650nm, or at least from 400nm to 700nm.

[0059] In some embodiments, the optical film 200 transmits at least 80% of the normally incident light having a first polarization state within a predetermined wavelength range, and reflects at least 95% of the normally incident light having an orthogonal second polarization state within a predetermined wavelength range. The optical film 200 may include a plurality of polymer layers (interference layers of the first optical stack 202-1 and the second optical stack 202-2), wherein the average thickness of each polymer layer is 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 farthest from each other in the plurality of polymer layers. The first layer 203a and the second layer 203b have respective first and second thicknesses (e.g., Figure 3 The thickness t1 and t N ). 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.

[0060] In some embodiments, the optical film 200 includes a plurality of stacked first polymer interference layers (interference layers of the first optical stack 202-1) disposed on a plurality of stacked second interference layers (interference layers of the second optical stack 202-2), each first interference layer and the second interference layer reflecting or transmitting light primarily by optical interference of 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 farthest from the plurality of stacked second interference layers, and the outermost second interference layer (second layer 203b) is the second interference layer farthest from the plurality of stacked first interference layers. In some embodiments, the optical thickness of the outermost first interference layer and the outermost second interference layer is equal to one-quarter of the corresponding first wavelength and second wavelength within the 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 wavelength and the second wavelength is in the range from about 420 nm to about 480 nm.

[0061] In some embodiments, the innermost first interference layer 206a is the first interference layer closest to the plurality of stacked second interference layers, the innermost second interference layer 206b is the second interference layer closest to the plurality of stacked first interference layers, and the optical thickness of the innermost first interference layer 206a and the second interference layer 206b is equal to one quarter of the corresponding third wavelength and fourth wavelength within the predetermined wavelength range. In some embodiments, the difference between the third wavelength and the fourth wavelength is less than about 120nm, or less than about 100nm, or less than about 80nm, or less than about 60nm, or less than about 40nm, or less than about 30nm, or less than about 20nm, or less than about 10nm. In some embodiments, each of the third wavelength and the fourth wavelength is in the range from about 600nm to about 635nm.

[0062] Light rays 213 reflected from the second optical stack 202-2 are shown. Other light rays may pass through the second optical stack 202-2 and be reflected by the first stack 202-1. Some of the light reflected by the first stack 202-1 may be absorbed by the intermediate layer 209, and some of the light may be reflected by or transmitted through the second optical stack 202-2. In some cases, light will be scattered by at least one of the first optical stack and the second optical stack. Scattered light typically propagates in directions other than the specular reflection direction and may be caused, for example, by impurities or defects in the optical film. Light rays 215 at higher incident angles pass through the second optical stack 202-2 and are scattered from the first optical stack 202-1 and absorbed by the intermediate layer 209. More generally, some light, particularly light at high incident angles, 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.

[0063] Various layer thickness profiles may be used in the optical films of the present specification. In some embodiments, the optical film includes two optical stacks / packages, wherein each stack / package has a substantially overlapping thickness profile such that the two optical stacks / packages reflect the same predetermined wavelength range. It has been found that arranging the optical packages so that the thinner interference layer is closer to the outermost surface of the optical film and the thicker interference layer is farther away from either outermost surface improves optical properties in various applications (e.g., in display applications utilizing polarizing beam splitters) and is therefore generally preferred, although other configurations are possible. When used, for example, in a polarizing beam splitter of an optical system, the optical film may provide one or more of a higher reflectivity of s-polarized light, a higher transmittance of p-polarized light, and a lower transmittance of s-polarized light over a wider range of incident angles than conventional reflective polarizing films.

[0064] Figure 3 2 is a schematic diagram of layer thickness profiles for an optical film including two optical stacks or packages, such as optical film 200. The first optical stack 302-1 includes a plurality of polymer interference layers having a thickness ranging from t1 at the outermost interference layer of the optical film to t2 at the outermost interference layer of the first optical stack 302-1. m , the outermost interference layer of the first optical stack 302-1 is the inner interference layer closest to the optical film of the second optical stack 302-2. The second optical stack 302-2 includes a plurality of polymer interference layers at the outermost interference layer of the second optical stack 302-2, the plurality of polymer interference layers having a thickness ranging from t at the outermost interference layer of the second optical stack 302-2 (which is the inner interference layer closest to the optical film of the first optical stack 302-1). m+1 to t at the outermost interference layer of the optical film NIn some embodiments, |t1–t N | is less than about 20 nm, or 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 m+1 |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. |

[0065] 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 including a first polymer layer and a second polymer layer as two polymer layers that are farthest from each other in the plurality of polymer layers (e.g., layers 203a and 203b), wherein the first polymer layer and the second polymer layer have respective first thicknesses t1 and second thicknesses t2. N , and the difference between the first thickness and the second thickness (the difference between thicknesses is defined herein as non-negative) is less than about 20 nm or within the range for |t1–t N | is within any of the ranges described. In some embodiments, the optical film includes a first optical stack and a second optical stack separated by one or more spacer layers, wherein the first optical stack includes a first plurality of layers of a plurality of polymer layers, the second optical stack includes a second plurality of layers of a plurality of polymer layers, the first optical stack includes a first polymer layer, and the second optical stack includes a second polymer layer. In some embodiments, the optical film includes a third polymer layer in the first plurality of layers (e.g., layer 206a in the first optical stack 202-1) and a fourth polymer layer in the second plurality of layers (e.g., layer 206b in the second optical stack 202-2) as two polymer layers in the respective first and second plurality of layers that are closest to each other, wherein the third layer and the fourth layer have respective third and fourth thicknesses, and the difference between the third thickness and the fourth thickness is less than about 40 nm or within about 10 nm for |t m –t m+1 |Within any of the described ranges.

[0066] The optical films of the present specification can be used in a variety of applications. For example, the optical films can be used to replace the reflective polarizers commonly used in display applications. In some embodiments, the optical films of the present specification are incorporated into a polarizing beam splitter (PBS).

[0067] Figure 44 is a schematic side view of a polarization 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. The optical film 400 is disposed between the first hypotenuse 432 and the second hypotenuse 442 and adhered to the first hypotenuse 432 and the second hypotenuse 442. The optical film 400 may be formed by a corresponding optically transparent adhesive layer ( Figure 4 432 and 442. Optical film 400 may be any of the optical films described herein. For example, optical film 400 may correspond to optical film 100 or 200, and may include a plurality of alternating higher refractive index layers and lower refractive index layers disposed between opposing first and second major surfaces of the optical film. In some embodiments, optical film 400 corresponds to optical film 200, wherein first optical stack 202-1 is closer to first hypotenuse 432 and farther from second hypotenuse 442, and second optical stack 202-2 is closer to second hypotenuse 442 and farther from first hypotenuse 432. In this case, layer 203a is the interference layer closest to first hypotenuse 432, and layer 203b is the interference layer closest to second hypotenuse 442.

[0068] The prism can have Figure 4 The cross-section of the prism may be an isosceles triangle as schematically shown in the figure, or 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 (entering the page) that is substantially the same as the lateral dimension or substantially different from the lateral dimension. For example, the length may be substantially greater than the lateral dimension so that the prism is substantially rod-shaped. The rod may then be cut into a plurality of prisms, which may be substantially cubic prisms.

[0069] Figure 55 is a schematic side view of a polarizing beam splitter (PBS) 550, which is similar in many respects to PBS 450. 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. Optical film 500 is disposed between and adhered to the first hypotenuse 532 and the second hypotenuse 542 by a first optically clear adhesive layer 534 and a second optically clear adhesive layer 544, respectively. Optical film 500 includes a first optical stack 502-1 disposed on and spaced apart from the second optical stack 502-2 by a light absorbing linear polarizer 509. The first optical stack 502-1 is closer to the first hypotenuse 532 and farther from the second hypotenuse 542, and the second optical stack 502-2 is closer to the second hypotenuse 542 and farther from the first hypotenuse 534. In some embodiments, for each optical stack and the hypotenuse closest to the optical stack: the optical stack includes a plurality of polymer interference layers, the number of interference layers is between 50 and 300, and the interference layers primarily reflect and transmit light by optical interference within the same predetermined wavelength range, the same wavelength range extending from at least 400nm to 600nm (e.g., from 400nm to 600nm or from 400nm to 700nm), or at least from 450nm to 600nm, or at least from 450nm to 650nm, or at least from 450nm to 1000nm (e.g., from 450nm to 1000nm or from 450nm to 1050nm). In some embodiments, for each optical stack and the hypotenuse closest to the optical stack: the interference layers closer to the hypotenuse are configured to primarily reflect shorter wavelengths within the predetermined wavelength range, and the interference layers farther from the hypotenuse are configured to primarily reflect longer wavelengths within the predetermined wavelength range. For example, the thickness distribution of the interference layers in the optical film 500 can be as follows: Figure 3 500 , where thinner layers (which reflect shorter wavelengths) are closer to the outer surface of the optical film and thicker layers (which reflect longer wavelengths) are farther from the outer surface of the optical film. In some embodiments, PBS 550 has an optical axis 555 or is used in an optical system having an optical axis 555. In some embodiments, optical axis 555 is at an angle α of about 30 to 60 degrees, or about 35 to 55 degrees, or about 40 to 50 degrees with optical film 500.

[0070] The prisms used in the PBS of the present specification can be made of any suitable material. For example, the first prism and the second prism can be independently made of glass (eg, BK7 glass) or a polymer material such as polycarbonate or polyacrylate.

[0071] The polarization beam splitter of the present specification can be used in a variety of applications. For example, the PBS can be used in an imaging or display system. The display system can be a head-mounted display, such as a virtual reality display or an augmented reality display. The use of PBS in various display applications is discussed, for example, in U.S. Patents 8,382,293 (Phillips, III et al.) and 9,535,256 (Carls et al.). The PBS of the present specification can be used in place of any of the PBSs in the optical systems described in these references. The PBS of the present specification is particularly advantageous for use in optical systems in which non-modulated light from a light source is reflected from one side of an 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 described in Figure 6 to Figure 7 Shown in.

[0072] Figure 6 670 is a schematic cross-sectional view of an optical system 675 including a PBS 650, a light source 670, a pixelated spatial light modulator 672, and a reflective component 673. PBS 650 can be any PBS of the present specification and includes an optical film 600 disposed between a first prism 630 and a second prism 640. Light source 670 produces a light output 676 that is substantially polarized in a blocking state of optical film 600. For example, referring to Figure 6 , the light source 670 may include an unpolarized light source and a linear polarizer configured to transmit light polarized along the y' axis, which may be described as a blocking state of the optical film 600. The pixelated spatial light modulator 672 may be any suitable spatial light modulator. For example, the pixelated spatial light modulator 672 may be a liquid crystal on silicon (LCoS) panel with a quarter-wave retarder between the LCoS panel and the PBS 650. The reflective component 673 is preferably a polarization-changing reflector. For example, the reflective component 673 may include a reflector and a quarter-wave retarder disposed between the reflector and the PBS 650. The light output 676 from the light source 670 is reflected from the optical film 600 and then reflected from the pixelated spatial light modulator 672 as modulated light 678 having a passing polarization state, and the modulated light is transmitted through the optical film 600 and then reflected from the reflective component 673 in a blocking polarization state and then reflected from the optical film 600. In some embodiments, light 676 first strikes the optical film 600 in an s-polarization state, which is a blocking polarization state for the optical film 600, then strikes the optical film in a p-polarization state, which is a passing polarization state, after reflecting from the pixelated spatial light modulator 672, and then strikes the optical film 600 again in an s-polarization state after reflecting from the reflective component 673.

[0073] In some embodiments, the optical film 600 includes a first optical stack and a second optical stack and optionally includes a light absorbing linear polarizer disposed between the first optical stack and the second optical stack. In some embodiments, the first optical stack faces the first prism 630 and substantially reflects the light output 676 from the light source 670, and the second optical stack faces the second prism 640 and substantially reflects the light 678 incident on the optical film 600 from the reflective component 673.

[0074] Figure 7 7 is a schematic cross-sectional view of an optical system 775 that includes a PBS 750, a light source 770, a pixelated spatial light modulator 772, and a reflective component 773. PBS 750 can be any PBS of the present specification and includes an optical film 700 disposed between a first prism 730 and a second prism 740. Light source 770 produces a light output 776 that is substantially polarized in a blocking state of optical film 700 and can be as described for light source 670. Pixelated spatial light modulator 772 can be any suitable spatial light modulator and can be as described for pixelated spatial light modulator 672. Reflective component 773 is preferably a polarization-changing reflector as described for reflective component 673. In some embodiments, reflective component 773 includes a quarter-wave retarder and a reflector disposed on a surface of a lens that can be bonded to first prism 730 or can be spaced apart from 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. Light output 776 from the light source 770 reflects from the optical film 700 and then reflects from the reflective component 773 with a passing polarization state, then transmits through the optical film 700, and then reflects from the pixelated spatial light modulator 772 as patterned light 778 with a blocking polarization state, which is then reflected from the optical film 700.

[0075] Either optical system 675 or 775 may include additional components (eg, magnification optics and / or waveguides), and may be used, for example, in a head mounted display. Optical system 675 and / or optical system 775 may be described as an imaging system.

[0076] In some embodiments, the optical film 700 includes a first optical stack disposed on a second optical stack and spaced apart from the second optical stack by a light absorbing linear polarizer, as further described elsewhere herein. Since the light output 776 can be patterned by the pixelated spatial light modulator 772 to form an image, the light output 776 can be referred to as image light. In some embodiments, the image light enters the PBS and exits the PBS after being sequentially reflected by the first optical stack, transmitted by the optical film 700, and reflected by the second optical stack, wherein the light absorbing linear polarizer absorbs at least 50%, or at least 60%, or at least 70% of the image light scattered by at least one of the first optical stack and the second optical stack, while absorbing less than 2%, or less than 1.5%, or less than 1% of the image light. When determining the absorption of the absorbing linear polarizer, the pixelated spatial light modulator 772 can be fully turned on so that the light output 776 is approximately the image light minus the light absorbed by the light absorbing linear polarizer.

[0077] Figure 8 is a schematic cross-sectional view of an optical system 875 that can be used to determine various properties of the PBS and optical films described herein. The optical system 875 includes a non-polarized point light source 870, a linear absorbing polarizer 881, a collimating optical lens 883 for collimating light emitted by the point light source 870, an optical lens 885, a PBS 850 including a first prism 830 and a second prism 840, and an optical film 800, which is disposed between the first prism 830 and the second prism 840 and receives light 876 from the optical lens 885. The point light source 870 may include light behind a screen having a pinhole (e.g., a hole having a small diameter, such as 30 microns). 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 the reflected light and thereby determine the reflectivity R. In Figure 8 The x', y', z' coordinate system is shown in . The linear absorbing polarizer 881 can be oriented to transmit light having an electric field along a particular direction in the y'-z' plane (eg, along the y' axis or along the z' axis).

[0078] In some embodiments, the optical lens 885 is an imaging optical lens. In such embodiments, the optical system 875 can be referred to as an imaging system. In some embodiments, the detector 888 is disposed at the image surface 890 (the surface where the optical system forms an image), and similarly, in some embodiments, the detector 889 is disposed at the image surface 892. In some embodiments, the optical lens 885 has an aperture number in the range of 4.5 to 5.5, or in the range of 4.9 to 5.1, or the aperture number can be nominally 5.0, but can differ from 5.0 (e.g., less than about 1%), for example due to ordinary manufacturing variations. In some embodiments, the detector 888 is configured to determine the point spread function (PSF) of the imaging system. The PSF of the imaging system describes the response of the imaging system to a point source (e.g., the spread of light output at the image surface 890). Fig. 9 The PSF for an imaging system is schematically shown. The maximum value of the PSF is Max, and has a full width at half maximum (FWHM) 991, a 30% full width at maximum (FW30% Max) 993, and a 20% full width at maximum (FW20% Max) 995. The PSF can be normalized so that Max is equal to 1 without affecting the values ​​of the various widths. In some embodiments, the 20% maximum full width of the point spread function of the imaging system is less than 33 microns, or less than 32 microns, or less than 31 microns, or less than 30.5 microns, or less than 30 microns. In some embodiments, the 20% maximum full width of the point spread function of the imaging system is greater than 15 microns or greater than 20 microns. In some embodiments, the 15% maximum full width of the point spread function of the imaging system is less than 62 microns, or less than 60 microns, or less than 58 microns, or less than 56 microns, or less than 54 microns, or less than 52 microns. In some embodiments, the 15% maximum full width of the point spread function of the imaging system is greater than 35 microns or greater than 40 microns. In some embodiments, the imaging system has a point spread function with a 30% maximum full width less than 21 microns, or less than 20 microns, or less than 19.5 microns, or less than 19.1 microns. In some embodiments, the imaging system has a point spread function with a 30% maximum full width greater than 10 microns or greater than 15 microns.

[0079] In some embodiments, the optical film 800 substantially transmits light having a first polarization state and substantially reflects light having an orthogonal second polarization state within a predetermined wavelength range extending from 400 nm to 700 nm, or from 430 nm to 630 nm, or from 450 nm to 1000 nm. Substantially reflective may be understood as a reflectivity of at least 60%, and substantially transmissive may be understood as a transmittance of at least 60%. The light having the first polarization state may be p-polarized light having an electric field in the z' direction, and the light having the second polarization state may be s-polarized light having an electric field in the y' direction. In some embodiments, the polarizer 881 is oriented so that the collimated light from the collimating lens 883 has a second polarization state. In some embodiments, the optical lens 885 has an aperture number 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 the optical axis 855, which forms an angle of about 30 to 60 degrees, or about 35 to 55 degrees, or about 40 to 50 degrees with the optical film 800. In some embodiments, when the light 876 is first incident on the first major surface of the optical film 800 (facing the first prism 830), the optical film 800 has a total transmittance T=T1. In some embodiments, the PBS 850 is positioned so that when the light 876 is first incident on the second major surface of the optical film 800 (facing the second prism 840), the second prism 840 faces the optical lens 885 and the optical film 800 has a total transmittance T=T2. When the collimated light from the collimating lens 883 has a second polarization state, a schematic diagram of the transmittance as a function of wavelength is shown in Fig.10 The predetermined wavelength range is from λ1 to λ2. In some embodiments, the maximum difference Δsmax between T1 and T2 as a function of the wavelength of light 876 within the predetermined wavelength range is less than 0.02%, or less than 0.015%, or less than 0.01%, or less than about 0.008%, or less than about 0.006%. Δsmax is the maximum value within the predetermined wavelength range of |T1-T2|. For example, the maximum difference between T1 and T2 may occur when T1 is 0.01% (or 10 -4 ) and T2 is 0.006%, so the maximum difference is 0.004%. In some embodiments, for each wavelength in the predetermined wavelength range, T1 and T2 are each less than about 0.05% (or 5×10 -4 ), or less than about 0.04%, or less than about 0.03%, or less than about 0.02%, or less than about 0.015%.

[0080] In some embodiments, polarizer 881 is oriented so that collimated light from collimating lens 883 has a first polarization state. In such embodiments, when light 876 is first incident on the first major surface of optical film 800, optical film 800 can have a total transmittance T=T3, and when light is first incident on the second major surface of optical film 800 (e.g., when PBS 850 is positioned so that second prism 840 faces optical lens 885), optical film 800 can have a total transmittance T=T4. A schematic diagram of transmittance as a function of wavelength when collimated light from collimating lens 883 has a first polarization state is shown in Fig.11 In some embodiments, the average difference Δavg between T3 and T4 as a function of the wavelength of incident light within a predetermined wavelength range is less than 3%, or less than 2%, or less than 1%, or less than 0.5%. Δavg is an unweighted average within the predetermined wavelength range of |T3-T4|. In some embodiments, the maximum difference Δpmax between T3 and T4 as a function of the wavelength of light 876 within the predetermined wavelength range is less than 5%, or less than 4%, or less than 3%. Δpmax is the maximum value within the predetermined wavelength range of |T3-T4|. In some embodiments, the average value within the predetermined wavelength range of each of T3 and T4 is at least 92%, or at least 93%, or at least 94%, or at least 95%.

[0081] Those of ordinary skill in the art will understand terms such as "about" and "substantially" in the context of use and description in this specification. If it is unclear to those of ordinary skill in the art in the context of use and description in this specification that "about" is applied to the use of quantities expressing feature sizes, quantities, and physical properties, "about" will be understood as an average value within 5% of the specified value. A quantity given as about a specified value can be exactly the specified value. For example, if it is unclear to those of ordinary skill in the art in the context of use and description in this specification, a quantity with a value of about 1 means that the quantity has a value between 0.95 and 1.05, and the value can be 1. If it is unclear to those of ordinary skill in the art in the context of use and description in this specification that "substantially vertical" is used, "substantially vertical" will refer to within 30 degrees of vertical. In some embodiments, the direction described as substantially vertical can be within 20 degrees of vertical, or within 10 degrees of vertical, or can be vertical or nominally vertical.

[0082] The following is a list of exemplary embodiments of the present specification.

[0083] Embodiment 1 is an optical film comprising a plurality of polymer interference layers, each polymer interference layer reflecting or transmitting light primarily by optical interference for at least one wavelength within a predetermined wavelength range extending from at least 450 nm to 1000 nm, the total number of the interference layers being greater than about 100 and less than about 300, such that for light within the predetermined wavelength range and substantially perpendicularly incident on the optical film, for a first polarization state, the plurality of polymer interference layers have an average optical transmittance greater than about 85%, for an orthogonal second polarization state, an average optical reflectance greater than about 95%, and for the second polarization state, an average optical transmittance less than about 5%.

[0084] Embodiment 2 is the optical film described in embodiment 1, wherein the optical film defines an x-axis along the second polarization state, a y-axis along the first polarization state perpendicular to the x-axis, and a z-axis along the thickness direction of the optical film orthogonal to the x-axis and the y-axis, and the multiple polymer interference layers include multiple alternating first-layer polymers and second-layer polymers, each of the first-layer polymer and the second-layer polymer has a refractive index of nx along the x-axis, a refractive index of ny along the y-axis, and a refractive index of 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, 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 3 is the optical film of 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, each of nx, ny, and nz is between 1.5 and 1.6.

[0086] Embodiment 4 is the optical film described in embodiment 1, and also includes a dichroic polarizer formed integrally with the multiple polymer interference layers, wherein the dichroic polarizer 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.

[0087] Embodiment 5 is the optical film of embodiment 1, wherein the first optical stack includes the plurality of polymer interference layers, and the optical film further includes a second optical stack disposed on the first optical stack, the second optical stack includes a second plurality of polymer interference layers, each polymer interference layer in the second optical stack mainly reflects or transmits light by optical interference for at least one wavelength within the predetermined wavelength range, and the total number of the interference layers in the second optical stack is greater than about 100 and less than about 300, so that for light within the predetermined wavelength range and substantially vertically incident on the optical film, for the first polarization state, the second plurality of polymer interference layers have an average optical transmittance greater than about 85%, for the orthogonal second polarization state, an average optical reflectance greater than about 95%, and for the second polarization state, an average optical transmittance less than about 5%.

[0088] Embodiment 6 is the optical film of embodiment 5, wherein the first optical stack and the second optical stack are separated by one or more spacer layers.

[0089] Embodiment 7 is the optical film described in embodiment 6, wherein each of the first optical stack and the second optical stack includes an interference layer that reflects longer wavelengths closer to the one or more spacer layers, and an interference layer that reflects shorter wavelengths farther away from the one or more spacer layers.

[0090] Embodiment 8 is an optical film of embodiment 6, wherein the one or more spacer layers include a dichroic polarizer, which transmits at least 80% of the light with the first polarization state within the predetermined wavelength range and absorbs at least 50% of the light with the second polarization state within the predetermined wavelength range.

[0091] Embodiment 9 is the optical film described in embodiment 5, wherein for the first outermost interference layer, the first outermost interference layer is the interference layer in the first optical stack that is farthest from the second optical stack, and the second outermost interference layer is the interference layer in the second optical stack that is farthest from the first optical stack, the optical thicknesses of the first outermost interference layer and the second outermost interference layer are equal to one quarter of the corresponding first and second wavelengths in the predetermined wavelength range, and the difference between the first wavelength and the second wavelength is less than about 40 nm.

[0092] Embodiment 10 is a polarization beam splitter (PBS), comprising:

[0093] a first prism including a first hypotenuse;

[0094] a second prism including a second hypotenuse facing the first hypotenuse; and

[0095] The optical film of any one of Embodiments 1 to 9, wherein the optical film is disposed between the first hypotenuse and the second hypotenuse and adhered to the first hypotenuse and the second hypotenuse.

[0096] Embodiment 11 is the PBS described in embodiment 10, wherein when the PBS is combined in an imaging system including 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 aperture number in the range of 4.5 to 5.5, wherein the optical film in the PBS receives light from the imaging optical lens and reflects the received light toward an image surface, the 20% maximum value full width of the point spread function of the imaging system is less than 33 microns, or the 15% maximum value full width is less than 60 microns.

[0097] Embodiment 12 is the PBS of embodiment 11, wherein the 20% maximum full width is less than 33 microns, and the 15% maximum full width is less than 60 microns.

[0098] Embodiment 13 is the PBS of embodiment 11, wherein the 20% maximum full width is less than 32 microns, and the 15% maximum full width is less than 56 microns.

[0099] Embodiment 14 is the PBS described in embodiment 10, wherein for collimated light, the collimated light has the second polarization state and is incident on the optical film within the PBS after passing through an optical lens with an aperture number between 1.8 and 2.2 and centered on an optical axis forming an angle of approximately 30 to 60 degrees with the optical film, when the light is first incident on a first major surface of the optical film, the optical film has a total transmittance T1, and when the light is first incident on an opposite second major surface of the optical film, the optical film has a total transmittance T2, wherein the maximum difference between T1 and T2 as a function of the wavelength of the incident light within the wavelength range of 430 nm to 630 nm is less than 0.02%.

[0100] Embodiment 15 is the PBS described in embodiment 10, wherein for collimated light, the collimated light has the first polarization state and is incident on the optical film within the PBS after passing through an optical lens having an aperture number between 1.8 and 2.2 and centered on an optical axis forming an angle of approximately 30 to 60 degrees with the optical film, when the light is first incident on a first major surface of the optical film, the optical film has a total transmittance T3, and when the light is first incident on an opposite second major surface of the optical film, the optical film has a total transmittance T4, wherein an average value of each of T3 and T4 within the wavelength range of 430 nm to 630 nm is at least 92%.

[0101] Embodiment 16 is an optical film, which includes multiple stacked first polymer interference layers arranged on multiple stacked second polymer interference layers, each first interference layer and second interference layer mainly reflects or transmits light by optical interference for at least one wavelength within the same predetermined wavelength range, the outermost first interference layer is the first interference layer farthest from the multiple stacked second interference layers, the outermost second interference layer is the second interference layer farthest from the multiple stacked first interference layers, the optical thickness of the outermost first interference layer and the outermost second interference layer is equal to one quarter of the corresponding first wavelength and second wavelength within the predetermined wavelength range, and the difference between the first wavelength and the second wavelength is less than about 40nm.

[0102] Embodiment 17 is the optical film described in 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 optical thicknesses of the innermost first interference layer and the innermost second interference layer are equal to one quarter of the corresponding third wavelength and fourth wavelength within the predetermined wavelength range, and the difference between the third wavelength and the fourth wavelength is less than about 80 nm.

[0103] Embodiment 18 is the optical film of embodiment 16, wherein for light within the predetermined wavelength range and substantially perpendicularly incident on the optical film, for a first polarization state, the plurality of stacked first polymer interference layers and the plurality of stacked second polymer interference layers have an average optical transmittance greater than about 85%, for an orthogonal second polarization state, the average optical reflectance is greater than about 95%, and for the second polarization state, the average optical transmittance is less than about 5%.

[0104] Embodiment 19 is the optical film of embodiment 18, wherein the optical film defines an x-axis along the second polarization state, a y-axis along the first polarization state perpendicular to the x-axis, and a z-axis along the thickness direction of the optical film orthogonal to the x-axis and the y-axis, each of the plurality of stacked first polymer interference layers and the plurality of stacked second interference layers comprises a plurality of alternating first and second layers, each of the first and second layers having a refractive index of nx along the x-axis, a refractive index of ny along the y-axis, and a refractive index of nz along the z-axis,

[0105] Wherein 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; 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.

[0106] Embodiment 20 is a polarization beam splitter (PBS), comprising:

[0107] a first prism including a first hypotenuse;

[0108] a second prism including a second hypotenuse facing the first hypotenuse; and

[0109] The optical film of any one of Embodiments 16 to 19, wherein the optical film is disposed between the first hypotenuse and the second hypotenuse and adhered to the first hypotenuse and the second hypotenuse.

[0110] Embodiment 21 is the PBS described in embodiment 20, wherein when the PBS is combined in an imaging system including a point light source, a collimating optical lens for collimating light emitted by the point light source, and an imaging optical lens having an aperture number in the range of 4.5 to 5.5, wherein the optical film in the PBS receives light from the imaging optical lens and reflects the received light toward an image surface, the 20% maximum value full width of the point spread function of the imaging system is less than 33 microns, or the 15% maximum value full width is less than 60 microns.

[0111] Embodiment 22 is the PBS described in embodiment 20, wherein for collimated light, the collimated light has the second polarization state and is incident on the optical film within the PBS after passing through an optical lens having an aperture number between 1.8 and 2.2 and centered on an optical axis forming an angle of approximately 30 to 60 degrees with the optical film, when the light is first incident on a first major surface of the optical film, the optical film has a total transmittance T1, and when the light is first incident on an opposite second major surface of the optical film, the optical film has a total transmittance T2, wherein the maximum difference between T1 and T2 as a function of the wavelength of the incident light within the predetermined wavelength range is less than 0.02%.

[0112] Embodiment 23 is the PBS described in embodiment 20, wherein for collimated light, the collimated light has the first polarization state and is incident on the optical film within the PBS after passing through an optical lens having an aperture number between 1.8 and 2.2 and centered on an optical axis forming an angle of approximately 30 to 60 degrees with the optical film, when the light is first incident on a first major surface of the optical film, the optical film has a total transmittance T3, and when the light is first incident on an opposite second major surface of the optical film, the optical film has a total transmittance T4, wherein an average value of each of T3 and T4 in the wavelength range from 430 nm to 630 nm is at least 92%.

[0113] Embodiment 24 is a polarization beam splitter (PBS), comprising:

[0114] a first prism including a first hypotenuse;

[0115] a second prism including a second hypotenuse facing the first hypotenuse; and

[0116] An optical film as described in any one of embodiments 16 to 19, wherein the optical film is arranged between the first hypotenuse and the second hypotenuse and adhered to the first hypotenuse and the second hypotenuse, and the optical film also includes a first optical stack and a second optical stack, the first optical stack faces the first prism and includes the multiple stacked first polymer interference layers, the second optical stack faces the second prism and includes the multiple stacked first polymer interference layers, the first optical stack is arranged on the second optical stack and is separated from the second optical stack by a light-absorbing linear polarizer, so that when the PBS is combined in an imaging system, the image light entering the PBS leaves the PBS after being reflected by the first optical stack, transmitted by the optical film, and reflected by the second optical stack in sequence, and the light-absorbing linear polarizer absorbs at least 50% of the image light scattered by at least one of the first optical stack and the second optical stack, and absorbs less than 2% of the image light.

[0117] Embodiment 25 is an optical film, which includes a first optical stack, which is arranged on a second optical stack and is separated from the second optical stack by one or more spacer layers, each optical stack includes a plurality of polymer interference layers that reflect and transmit light mainly by optical interference within the same predetermined wavelength range extending from at least 450nm to 600nm, so that for light within the predetermined wavelength range and substantially vertically incident on the optical film, the plurality of polymer interference layers in each optical stack transmit at least 80% of the light with a first polarization state, reflect at least 90% of the light with an orthogonal second polarization state, and transmit less than 5% of the light with the second polarization state, each of the one or more spacer layers does not reflect or transmit light mainly by optical interference, each optical stack has an interference layer that reflects longer wavelengths closer to the one or more spacer layers, and an interference layer that reflects shorter wavelengths farther away from the one or more spacer layers, wherein the first optical stack and the second optical stack are formed integrally with the one or more spacer layers.

[0118] Embodiment 26 is the optical film described in embodiment 25, wherein the outermost first interference layer is the polymer interference layer in the first optical stack farthest from the second optical stack, the outermost second interference layer is the polymer interference layer in the second optical stack farthest from the first optical stack, the optical thicknesses of the outermost first interference layer and the outermost second interference layer are equal to one quarter of the corresponding first wavelength and second wavelength within the predetermined wavelength range, and the difference between the first wavelength and the second wavelength is less than about 40 nm.

[0119] Embodiment 27 is an optical film as described in embodiment 25, wherein the optical film defines an x-axis along the second polarization state, a y-axis along the first polarization state perpendicular to the x-axis, and a z-axis along the thickness direction of the optical film orthogonal to the x-axis and the y-axis, wherein for each optical stack, the multiple polymer interference layers include a plurality of alternating first and second layers, each of the first and second layers 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, 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.

[0120] Embodiment 28 is a polarization beam splitter (PBS), comprising:

[0121] a first prism including a first hypotenuse;

[0122] a second prism including a second hypotenuse facing the first hypotenuse; and

[0123] The optical film of any one of embodiments 25 to 27, the optical film being disposed between and adhered to the first hypotenuse and the second hypotenuse,

[0124] Wherein, when the PBS is combined in an imaging system including a point light source, a collimating optical lens for collimating light emitted by the point light source, and an imaging optical lens having an aperture number in the range of 4.5 to 5.5, wherein the optical film in the PBS receives light from the imaging optical lens and reflects the received light toward an image surface, the 20% maximum value full width of the point spread function of the imaging system is less than 33 microns, or the 15% maximum value full width is less than 60 microns.

[0125] Embodiment 29 is a polarization beam splitter (PBS), comprising:

[0126] a first prism including a first hypotenuse;

[0127] a second prism including a second hypotenuse facing the first hypotenuse; and

[0128] An optical film according to any one of embodiments 25 to 27, wherein the optical film is disposed between and adhered to the first hypotenuse and the second hypotenuse, the first optical stack faces the first prism, the second optical stack faces the second prism, the one or more spacer layers include a light-absorbing linear polarizer, so that when the PBS is incorporated into an imaging system, image light entering the PBS leaves the PBS after being sequentially reflected by the first optical stack, transmitted by the optical film, and reflected by the second optical stack, and the light-absorbing linear polarizer absorbs at least 50% of the image light scattered by at least one of the first optical stack and the second optical stack,

[0129] At the same time, less than 2% of the image light is absorbed.

[0130] Embodiment 30 is an optical film that transmits at least 80% of vertically incident light having a first polarization state within a predetermined wavelength range, and reflects at least 95% of vertically incident light having an orthogonal second polarization state within the predetermined wavelength range, the optical film comprising a plurality of polymer layers, each polymer layer having an average thickness of less than about 200 nm, the plurality of polymer layers comprising a first polymer layer and a second polymer layer as two polymer layers farthest away from each other among the plurality of polymer layers, the first polymer layer and the second polymer layer having corresponding first thickness and second thickness, and the difference between the first thickness and the second thickness is less than about 10 nm.

[0131] Embodiment 31 is an optical film as described in embodiment 30, comprising a first optical stack and a second optical stack separated by one or more spacer layers, the first optical stack comprising a first plurality of layers among the plurality of polymer layers, the second optical stack comprising a second plurality of layers among the plurality of polymer layers, the first optical stack comprising the first polymer layer, and the second optical stack comprising the second polymer layer.

[0132] Embodiment 32 is the optical film of embodiment 31, wherein the one or more spacer layers include a dichroic polarizer that transmits at least 80% of light having the first polarization state and absorbs at least 50% of light having the second polarization state.

[0133] Embodiment 33 is a polarization beam splitter (PBS), comprising:

[0134] a first prism including a first hypotenuse;

[0135] a second prism including a second hypotenuse facing the first hypotenuse; and

[0136] The optical film described in embodiment 32 is arranged between the first hypotenuse and the second hypotenuse and adhered to the first hypotenuse and the second hypotenuse, the first optical stack faces the first prism, and the second optical stack faces the second prism, so that when the PBS is combined in an imaging system, the image light entering the PBS leaves the PBS after being reflected by the first optical stack, transmitted by the optical film, and reflected by the second optical stack in sequence, and the dichroic polarizer absorbs at least 50% of the image light scattered by at least one of the first optical stack and the second optical stack, and absorbs less than 2% of the image light.

[0137] Embodiment 34 is an optical film as described in embodiment 30, wherein the optical film defines an x-axis along the second polarization state, a y-axis along the first polarization state perpendicular to the x-axis, and a z-axis along the thickness direction of the optical film orthogonal to the x-axis and the y-axis, wherein the multiple polymer layers include multiple alternating first interference layers and second interference layers, each of the first interference layers and the second interference 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, 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, 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.

[0138] Embodiment 35 is an optical film, which includes a relative first major surface and a second major surface and adjacent non-overlapping first optical stack and second optical stack arranged between the first major surface and the second major surface, the first optical stack is arranged closer to the first major surface and farther away from the second major surface, and the second optical stack is arranged closer to the second major surface and farther away from the first major surface, for each optical stack and the major surface closest to the optical stack: the optical stack includes a plurality of first interference layers with a number between 50 and 300, each first interference layer mainly reflects or transmits light by optical interference, each first interference layer closer to the major surface is thinner than each first interference layer farther away from the major surface, each first interference layer has orthogonal in-plane refractive indices nx and ny and a refractive index nz in the thickness direction of the first interference layer, the difference between ny and nz is less than 0.008, and the difference between nx and ny is greater than 0.2, wherein the first optical stack is formed integrally with the second optical stack.

[0139] Embodiment 36 is a polarization beam splitter (PBS), comprising:

[0140] a first prism including a first hypotenuse;

[0141] a second prism including a second hypotenuse facing the first hypotenuse; and

[0142] An optical film, the optical film is disposed between the first hypotenuse and the second hypotenuse and adhered to the first hypotenuse and the second hypotenuse, and includes a plurality of alternating higher refractive index layers and lower refractive index layers disposed between opposite first and second major surfaces of the optical film, the optical film substantially transmits light having a first polarization state and substantially reflects light having an orthogonal second polarization state within a predetermined wavelength range extending from 400 nm to 700 nm, so that for collimated light, the collimated light has the second polarization state and is incident on the optical film within the PBS after passing through an optical lens having an aperture number between 1.8 and 2.2 and centered on an optical axis forming an angle of about 30 to 60 degrees with the optical film, when the light is first incident on the first major surface of the optical film, the optical film has a total transmittance T1, and when the light is first incident on the second major surface of the optical film, the optical film has a total transmittance T2, wherein the maximum difference between T1 and T2 as a function of the wavelength of the incident light within the predetermined wavelength range is less than 0.02%.

[0143] Embodiment 37 is the PBS of embodiment 36, wherein for each wavelength within the predetermined wavelength range, T1 and T2 are each less than about 0.05%.

[0144] Embodiment 38 is the PBS described in embodiment 36, such that for collimated light, the collimated light has the first polarization state and is incident on the optical film within the PBS after passing through an optical lens having an aperture number between 1.8 and 2.2 and centered on an optical axis forming an angle of approximately 30 to 60 degrees with the optical film, when the light is first incident on the first major surface of the optical film, the optical film has a total transmittance T3, and when the light is first incident on the second major surface of the optical film, the optical film has a total transmittance T4, wherein the average difference between T3 and T4 within the predetermined wavelength range is less than 3%.

[0145] Embodiment 39 is the PBS described in embodiment 36, such that for collimated light, the collimated light has the first polarization state and is incident on the optical film within the PBS after passing through an optical lens having an aperture number between 1.8 and 2.2 and centered on an optical axis forming an angle of approximately 30 to 60 degrees with the optical film, when the light is first incident on the first major surface of the optical film, the optical film has a total transmittance T3, and when the light is first incident on the second major surface of the optical film, the optical film has a total transmittance T4, wherein the maximum difference between T3 and T4 as a function of the wavelength of the incident light within the predetermined wavelength range is less than 5%.

[0146] Embodiment 40 is the PBS described in embodiment 36, wherein for collimated light, the collimated light has the first polarization state and is incident on the optical film within the PBS after passing through an optical lens with an aperture number between 1.8 and 2.2 and centered on an optical axis forming an angle of approximately 30 to 60 degrees with the optical film, when the light is first incident on the first major surface of the optical film, the optical film has a total transmittance T3, and when the light is first incident on the second major surface of the optical film, the optical film has a total transmittance T4, wherein an average value of each of T3 and T4 in the wavelength range from 430 nm to 630 nm is at least 92%.

[0147] Embodiment 41 is the PBS described in embodiment 36, wherein the optical film defines an x-axis along the second polarization state, a y-axis along the first polarization state perpendicular to the x-axis, and a z-axis along the thickness direction of the optical film orthogonal to the x-axis and the y-axis, each of the alternating higher refractive index layers and lower 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, for each higher 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, for each lower layer, the absolute value of the difference between ny and nz is less than 0.005, and the difference between nx of the higher refractive index layer and nx of the lower layer is greater than 0.2.

[0148] Embodiment 42 is a polarization beam splitter (PBS), comprising:

[0149] a first prism including a first hypotenuse;

[0150] a second prism including a second hypotenuse facing the first hypotenuse; and

[0151] An optical film, which is arranged between the first hypotenuse and the second hypotenuse and adhered to the first hypotenuse and the second hypotenuse, and includes a plurality of alternating higher refractive index layers and lower refractive index layers arranged between the opposite first major surface and the second major surface of the optical film, the optical film substantially transmits light having a first polarization state and substantially reflects light having an orthogonal second polarization state within a predetermined wavelength range extending from 400nm to 700nm, so that when the PBS is combined in an imaging system including a point light source, a collimating optical lens for collimating light emitted by the point light source, and an imaging optical lens having an aperture number in the range of 4.5 to 5.5, wherein the optical film in the PBS receives light from the imaging optical lens and reflects the received light toward an image surface, the 20% maximum value full width of the point spread function of the imaging system is less than 33 microns.

[0152] Embodiment 43 is the PBS of embodiment 42, wherein the 15% maximum full width of the point spread function is less than 60 microns.

[0153] Embodiment 44 is a polarization beam splitter (PBS), comprising:

[0154] a first prism including a first hypotenuse;

[0155] a second prism including a second hypotenuse facing the first hypotenuse; and

[0156] An optical film, which is arranged between the first hypotenuse and the second hypotenuse and adhered to the first hypotenuse and the second hypotenuse, and includes a plurality of alternating higher refractive index layers and lower refractive index layers arranged between the opposite first major surface and the second major surface of the optical film, the optical film substantially transmits light having a first polarization state and substantially reflects light having an orthogonal second polarization state within a predetermined wavelength range extending from 400nm to 700nm, so that when the PBS is combined in an imaging system including a point light source, a collimating optical lens for collimating light emitted by the point light source, and an imaging optical lens having an aperture number in the range of 4.5 to 5.5, wherein the optical film in the PBS receives light from the imaging optical lens and reflects the received light toward an image surface, the 15% maximum value full width of the point spread function of the imaging system is less than 60 microns.

[0157] Embodiment 45 is the PBS of embodiment 44, wherein the point spread function has a 20% full width maximum of less than 33 microns,

[0158] Embodiment 46 is the PBS of any one of embodiments 42 to 45, wherein the point spread function has a 30% full width maximum of less than 20 microns.

[0159] Embodiment 47 is a polarization beam splitter (PBS), comprising:

[0160] a first prism including a first hypotenuse;

[0161] a second prism including a second hypotenuse facing the first hypotenuse; and

[0162] An optical film disposed between and adhered to the first hypotenuse and the second hypotenuse, and comprising a first optical stack disposed on and spaced apart from the second optical stack by a light absorbing linear polarizer, the first optical stack being closer to the first hypotenuse and further from the second hypotenuse, the second optical stack being closer to the second hypotenuse and further from the first hypotenuse, for each optical stack and the hypotenuse closest to the optical stack: the optical stack comprising a plurality of polymer interference layers, the number of the interference layers being between 50 and 300, and being primarily formed by extending from at least 450 nm to 600 nm The PBS is configured to reflect and transmit light within the same predetermined wavelength range by optical interference of the first optical stack and the second optical stack, the interference layer closer to the hypotenuse is configured to mainly reflect shorter wavelengths within the predetermined wavelength range, and the interference layer farther from the hypotenuse is configured to mainly reflect longer wavelengths within the predetermined wavelength range, so that when the PBS is incorporated in an imaging system, image light entering the PBS leaves the PBS after being sequentially reflected by the first optical stack, transmitted by the optical film, and reflected by the second optical stack, and the light-absorbing linear polarizer absorbs at least 50% of the image light scattered by at least one of the first optical stack and the second optical stack, while absorbing less than 2% of the image light.

[0163] Embodiment 48 is the PBS described in embodiment 47, wherein the multiple polymer interference layers of the first optical stack include a first layer closest to the first hypotenuse, and the multiple polymer interference layers of the second optical stack include a second layer closest to the second hypotenuse, the first polymer layer and the second polymer layer having corresponding first thickness and second thickness, and the difference between the first thickness and the second thickness is less than about 10nm.

[0164] Embodiment 49 is a polarization beam splitter (PBS), comprising:

[0165] a first prism including a first hypotenuse;

[0166] a second prism including a second hypotenuse facing the first hypotenuse; and

[0167] An optical film, the optical film is disposed between the first hypotenuse and the second hypotenuse and adhered to the first hypotenuse and the second hypotenuse, and includes a plurality of alternating higher refractive index layers and lower refractive index layers disposed between opposite first and second major surfaces of the optical film, the optical film substantially transmits light having a first polarization state within a predetermined wavelength range extending from at least 430 nm to 630 nm, and substantially reflects light having an orthogonal second polarization state, so that for collimated light, the collimated light has the first polarization state and is incident on the optical film within the PBS after passing through an optical lens having an aperture number between 1.8 and 2.2 and centered on an optical axis forming an angle of about 30 to 60 degrees with the optical film, when the light is first incident on the first major surface of the optical film, the optical film has a total transmittance T3, and when the light is first incident on the second major surface of the optical film, the optical film has a total transmittance T4, wherein each of T3 and T4 has an average value of at least 92% within the predetermined wavelength range.

[0168] Embodiment 50 is the PBS described in embodiment 49, wherein for collimated light, the collimated light has the second polarization state and is incident on the optical film within the PBS after passing through an optical lens having an aperture number between 1.8 and 2.2 and centered on an optical axis forming an angle of approximately 30 to 60 degrees with the optical film, when the light is first incident on the first major surface of the optical film, the optical film has a total transmittance T1, and when the light is first incident on the second major surface of the optical film, the optical film has a total transmittance T2, wherein the maximum difference between T1 and T2 as a function of the wavelength of the incident light within the predetermined wavelength range is less than 0.02%.

[0169] Example

[0170] Example 1

[0171] Generally speaking Figure 2An optical film is made as depicted. The optical film includes two packages of optical repeating units (ORUs), each package including 138 ORUs. Each ORU includes a high refractive index, low melting point PEN layer (a copolymer of 90% PEN and 10% PET) and a low refractive index, approximately isotropic layer composed of 85wt% polycarbonate / 15wt% PCTg material, blended with 85wt% and 15wt% PETg. The optical film is prepared by using a conventional multilayer optical film process as described in the following patent: U.S. Patent Application Publication 2007 / 0047080 (Stover et al.). A molten stream having the desired layer is formed and then cast on a casting wheel to form a cast film. The cast film is then uniaxially oriented in the transverse direction at a stretch ratio of about 6:1 using a parabolic tenter to provide an optical film. The ORUs throughout the optical film are numbered sequentially from 1 to 276. The resulting thickness of the ORU as a function of the number of ORUs is as follows: Fig.12 The resulting refractive indices of the high refractive index layer and the low refractive index layer are given in Table 1.

[0172] Table 1

[0173]

[0174] The transmission coefficients for normally incident light in air were measured for both passing and blocking polarization states, e.g. Fig.21 shown.

[0175] A polarizing beam splitter (PBS) was prepared in which an optical film was disposed between BK7 glass prisms. For collimated light, which had a specific polarization state and was incident on the optical film in the PBS after passing through an optical lens having an aperture number of 2.04 and centered on an optical axis forming an angle of 45 degrees with the optical film, the total transmittance as a function of the wavelength of light incident on the optical film in the PBS was measured. The specific polarization state was vertically polarized or horizontally polarized, and the PBS was positioned so that vertically polarized light was incident on the optical film as s-polarized light and horizontally polarized light was incident on the optical film as p-polarized light. The pass axis of the optical film was horizontal. The transmittance was determined with an optical film oriented in which the wheel side of the film (the side cast on the casting wheel) was facing the light source (denoted as WTS), and in which the air side of the film (the side opposite to the wheel side) was facing the light source (denoted as ATS). Fig.13 and Fig.14 The transmission coefficient (total transmission) versus wavelength is shown separately for s-polarized light and p-polarized light, which are first incident on the optical film from each side of the film.

[0176] Comparative Examples C1-C4

[0177] Optical films in PBS were prepared and measured as in Example 1. The optical film of Comparative Example C1 included two packets, wherein the second packet was flipped relative to the second packet of Example 1, such that the ORU closest to one major surface was a thicker layer that reflected red wavelengths and the ORU closer to the opposite major surface was a thinner layer that reflected blue wavelengths. The optical film of C1 included approximately 750 polymer interference layers. The optical film of Comparative Example C2 had a single packet whose layer thickness varied monotonically across the optical film and had 325 polymer interference layers. The optical film of Comparative Example C3 included two packets having substantially non-overlapping thickness ranges such that one packet reflected shorter wavelengths and the other packet reflected longer wavelengths. The optical film of C3 included approximately 750 polymer interference layers. The film of Comparative Example C4 was similar to the film of Comparative Example C2, except that the total number of interference layers was 275 and a larger refractive index difference was used to obtain similar reflectivities.

[0178] For each of Comparative Examples C1-C4, the materials and processes used to make these films were substantially the same as described for Example 1, except for the total number of interference layers and their configuration as described above.

[0179] Figures 15 to 17 The total transmittance of s-polarized light first incident on each side of the optical film of Comparative Examples C1-C3 in a BK7 prism cube determined for collimated light having an s-polarization state and incident on the optical film in the PBS after passing through an optical lens having an aperture number of 2.04 and centered on an optical axis forming an angle of 45 degrees with the optical film is shown respectively. RTS and BTS respectively indicate that the side of the optical film having a red reflective layer faces the light source, or the side of the optical film having a blue reflective layer faces the light source.

[0180] Example 2

[0181] Optical films were prepared and were the same as in Example 1, except that the central spacer layer between the two ORU packets included a combination of the 4 different polarizing dichroic dyes listed in Table 2.

[0182] Table 2

[0183]

[0184] In the combinations shown in Table 3, the dichroic dye of Example 2 was added to the middle spacer layer between two ORU packets, wherein the dichroic dye was masterbatched in PEN resin at the indicated pounds per hour (pph).

[0185] Table 3

[0186] Yellow pph Red pph Blue pph Green pph LmPEN / PEN pph 0.19 0.36 0.73 0.90 67.84

[0187] The transmission coefficients for normally incident light in air were measured for both passing and blocking polarization states and are given in Fig. 22 Shown in.

[0188] Membranes were tested as in Example 1 in PBS. Fig.18 and Fig.19 The transmission coefficient (total transmission) versus wavelength for s-polarized light and p-polarized light first incident on the optical film from each side of the film of Example 2 is shown separately.

[0189] Example 3

[0190] The PBS was prepared as in Example 1. The PBS was combined in an imaging system having a point light source (modeled as a pinhole with a diameter of 30 microns), a collimating optical lens for collimating the light emitted by the point light source, and an imaging optical lens with an aperture number of 5.0 (see Figure 8 ), wherein the optical film in the PBS receives light from the imaging optical lens and reflects the received light toward the image surface. Determine the point spread function and Fig. 20 The full width at half maximum (FWHM), full width at 30% maximum (FW30%Max), full width at 20% maximum (FW20%Max), and full width at 20% maximum (FW20%Max) were determined and reported in Table 4. The measurements were repeated using the optical films of Comparative Examples C3 and C4 instead of the optical film of Example 1.

[0191] Table 4

[0192] FWHM(μm) FW30%Max(μm) FW20%Max(μm) FW15%Max(μm) C4 11.4 19.5 35.3 64 C3 8.0 23.1 49.7 80 Ex1 12.0 18.9 29.8 50

[0193] Unless otherwise indicated, the description of the elements in the drawings should be understood to apply equally to the corresponding elements in the other drawings. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that the specific embodiments shown and described may be replaced with a variety of alternative and / or equivalent implementations without departing from the scope of the present disclosure. The present application is intended to cover any modification or variation of the specific embodiments discussed herein. Therefore, the present disclosure is intended to be limited only by the claims and their equivalents.

[0194] All references, patents or patent applications cited above are incorporated herein by reference in their entirety in a consistent manner. In the event of inconsistencies or conflicts between the incorporated references and this application, the information in the foregoing description shall prevail.

Claims

1. An optical film, comprising a plurality of stacked first polymer interference layers disposed on a plurality of stacked second polymer interference layers, each of the first polymer interference layer and the second polymer interference layer reflecting or transmitting light primarily by optical interference for at least one wavelength within a same predetermined wavelength range, an outermost first polymer interference layer being the first polymer interference layer farthest from the plurality of stacked second polymer interference layers, an outermost second polymer interference layer being the second polymer interference layer farthest from the plurality of stacked first polymer interference layers, an optical thickness of the outermost first polymer interference layer and the outermost second polymer interference layer being equal to one quarter of the corresponding first and second wavelengths within the predetermined wavelength range, a difference between the first wavelength and the second wavelength being less than about 40 nm, and a thickness of each polymer interference layer of the optical film increasing moving from the outermost first polymer interference layer and the outermost second polymer interference layer to the center of the optical film.

2. An optical film that transmits at least 80% of vertically incident light having a first polarization state within a predetermined wavelength range and reflects at least 95% of vertically incident light having an orthogonal second polarization state within the predetermined wavelength range, the optical film comprising a plurality of polymer layers, each polymer layer having an average thickness of less than about 200 nm, the plurality of polymer layers comprising a first polymer layer and a second polymer layer as two polymer layers farthest from each other among the plurality of polymer layers, the first polymer layer and the second polymer layer having corresponding first thickness and second thickness, the difference between the first thickness and the second thickness being less than about 10 nm, and the thickness of each polymer layer increases from the first polymer layer and the second polymer layer farthest from each other to the polymer layer close to the center of the optical film.

3. The optical film of claim 2, wherein the optical film defines an x-axis along the second polarization state, a y-axis along the first polarization state perpendicular to the x-axis, and a z-axis along the thickness direction of the optical film orthogonal to the x-axis and the y-axis, wherein the plurality of polymer layers comprises a plurality of alternating first interference layers and second interference layers, each of the first interference layers and the 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, for each second interference layer, the absolute value of the difference between ny and nz is less than 0.005, and the difference between nx of the first interference layer and nx of the second interference layer is greater than 0.

2.

4. A polarization beam splitter, comprising: a first prism including a first hypotenuse; a second prism including a second hypotenuse facing the first hypotenuse; as well as An optical film according to claim 1, wherein the optical film is arranged between the first hypotenuse and the second hypotenuse and adhered to the first hypotenuse and the second hypotenuse, and the optical film also includes a first optical stack and a second optical stack, the first optical stack facing the first prism and including the plurality of stacked second polymer interference layers, the second optical stack facing the second prism and including the plurality of stacked first polymer interference layers, the first optical stack is arranged on the second optical stack and is separated from the second optical stack by a light-absorbing linear polarizer, so that when the polarizing beam splitter is incorporated into an imaging system, image light entering the polarizing beam splitter leaves the polarizing beam splitter after being sequentially reflected by the first optical stack, transmitted by the optical film, and reflected by the second optical stack, and the light-absorbing linear polarizer absorbs at least 50% of the image light scattered by at least one of the first optical stack and the second optical stack, while absorbing less than 2% of the image light.

5. A polarization beam splitter, comprising: a first prism including a first hypotenuse; a second prism including a second hypotenuse facing the first hypotenuse; as well as An optical film according to any one of claims 2 to 3, wherein the optical film is arranged between the first hypotenuse and the second hypotenuse and adhered to the first hypotenuse and the second hypotenuse, the predetermined wavelength range extends from 400 nm to 700 nm, so that for collimated light, the collimated light has the second polarization state, and is incident on the optical film in the polarization beam splitter after passing through an optical lens with an aperture number between 1.8 and 2.2 and centered on an optical axis forming an angle of about 30 to 60 degrees with the optical film, when the light is first incident on the first principal surface of the optical film facing the first prism, the optical film has a total transmittance T1, and when the light is first incident on the second principal surface of the optical film facing the second prism, the optical film has a total transmittance T2, wherein the maximum difference between T1 and T2 as a function of the wavelength of the incident light within the predetermined wavelength range is less than 0.02%.

6. A polarization beam splitter, comprising: a first prism including a first hypotenuse; a second prism including a second hypotenuse facing the first hypotenuse; as well as An optical film according to any one of claims 1 to 3, wherein the optical film is arranged between the first hypotenuse and the second hypotenuse and adhered to the first hypotenuse and the second hypotenuse, and the predetermined wavelength range extends from 400nm to 700nm, so that when the polarization beam splitter is combined in an imaging system including 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 aperture number in the range of 4.5 to 5.5, the optical film in the polarization beam splitter receives light from the imaging optical lens and reflects the received light toward an image surface, and the 20% maximum value full width of the point spread function of the imaging system is less than 33 microns.

7. A polarization beam splitter, comprising: a first prism including a first hypotenuse; a second prism including a second hypotenuse facing the first hypotenuse; as well as An optical film according to any one of claims 1 to 3, wherein the optical film is arranged between the first hypotenuse and the second hypotenuse and adhered to the first hypotenuse and the second hypotenuse, and the predetermined wavelength range extends from 400nm to 700nm, so that when the polarization beam splitter is combined in an imaging system including 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 aperture number in the range of 4.5 to 5.5, the optical film in the polarization beam splitter receives light from the imaging optical lens and reflects the received light toward an image surface, and the 15% maximum value full width of the point spread function of the imaging system is less than 60 microns.

8. A polarization beam splitter, comprising: a first prism including a first hypotenuse; a second prism including a second hypotenuse facing the first hypotenuse; as well as An optical film according to any one of claims 2 to 3, wherein the optical film is disposed between the first hypotenuse and the second hypotenuse and adhered to the first hypotenuse and the second hypotenuse, the predetermined wavelength range extends from at least 430 nm to 630 nm, so that for collimated light, the collimated light has the first polarization state and is incident on the optical film within the polarization beam splitter after passing through an optical lens having an aperture number between 1.8 and 2.2 and centered on an optical axis forming an angle of approximately 30 to 60 degrees with the optical film, when the light is first incident on a first principal surface of the optical film facing the first prism, the optical film has a total transmittance T3, and when the light is first incident on a second principal surface of the optical film facing the second prism, the optical film has a total transmittance T4, wherein each of T3 and T4 has an average value of at least 92% within the predetermined wavelength range.

Images