Multilayer Optical Films

Abstract

The multilayer optical film includes a plurality of polymer layers that transmit at least 30% of substantially normally incident light having a first wavelength and polarized along a first direction in the plane of the polymer layers. Each of the polymer layers has an average thickness of less than about 500 nm. The first, second and third polymer layers in the plurality of polymer layers are disposed adjacent to one another in succession and have respective refractive indices n1, n2 and n3 along the first direction at the first wavelength and have respective average thicknesses d1, d2 and d3. n2d2 can be within about 40% of m(n1d1+n3d3), where m is a positive integer.

Description

[Background technology]

[0001] Multilayer optical films can include multiple alternating polymer layers to provide reflection bands. Summary of the Invention

[0002] This specification generally relates to optical films that include a plurality of layers, which can include a layer that provides a reflection band within a predetermined wavelength range, and can include one or more additional layers, each additional layer being substantially thicker than an adjacent layer, the one or more additional layers providing one or more transmission bands within the predetermined wavelength range.

[0003] In some aspects, the present disclosure provides a multilayer optical film comprising a plurality of polymer layers that transmit at least 30% of substantially normally incident light having a first wavelength and polarized along a first direction in the plane of the polymer layers. Each of the polymer layers has an average thickness of less than about 500 nm. The first, second and third polymer layers in the plurality of polymer layers are disposed adjacent to one another in a continuous manner and have respective refractive indices n1, n2 and n3 along the first direction at the first wavelength and respective average thicknesses d1, d2 and d3. n2d2 can be within about 40% of m(n1d1+n3d3), where m is a positive integer.

[0004] In some embodiments, the present disclosure provides a multilayer optical film comprising a first plurality of first polymer layers alternating with a second plurality of second polymer layers. In a predetermined wavelength range of about 50 nm to about 150 nm wide, the difference between the average refractive index of the first polymer layer and the average refractive index of the second polymer layer along an in-plane first direction of the multilayer optical film is sufficiently large that the thickness of the first polymer layer and the thickness of the second polymer layer vary over at least a portion of the thickness of the multilayer optical film, and the multilayer optical film has an average optical reflectance of at least 50% for substantially normally incident light polarized along the in-plane first direction in the predetermined wavelength range. In at least one group of three adjacent, consecutively arranged polymer layers in the plurality of first polymer layers and the plurality of second polymer layers, the three polymer layers have respective average thicknesses d1, d2, and d3. d2 can be within about 40% of m(d1+d3), where m is a positive integer.

[0005] In some aspects, the present disclosure provides a multilayer optical film including a plurality of optical repeat units (ORUs) totaling at least 10. Each of the ORUs includes at least two polymer layers. Each of the ORUs has an optical thickness substantially equal to half a wavelength within a predetermined wavelength range spanning from about 300 nm to about 2500 nm. At least a first ORU and a second ORU in the plurality of ORUs have an optical thickness substantially equal to half a respective wavelength L1 and L2 that are within 100 nm of each other. The first ORU and the second ORU have a single, polymeric, first layer disposed therebetween, the first layer having an optical thickness substantially equal to half a wavelength L3 disposed between L1 and L2.

[0006] In some embodiments, the present disclosure provides a multilayer optical film comprising a plurality of polymeric first layers and one or more polymeric second layers. Each of the first and second layers has an average thickness of less than about 400 nm. For each of the second layers, the second layer has an average thickness d2 and is disposed between and adjacent to two of the first layers having a maximum thickness d1, and d2≧1.3d1.

[0007] In some aspects, the present disclosure provides an optical film including a spacer layer disposed between a first optical mirror and a second optical mirror, wherein for substantially normally incident light polarized along a first direction in the same plane of the optical film, a first wavelength and a second wavelength spaced apart by about 2 nm to about 100 nm, and a third wavelength disposed between the first and second wavelengths, the first optical mirror and the second optical mirror have respective optical transmittances T1 and T2 at the first wavelength, T1' and T2' at the second wavelength, and T1" and T2" at the third wavelength, where T2>2T1, T1'>2T2', and the optical film has an optical transmittance T at the third wavelength, where T>T1" and T2".

[0008] In some embodiments, the present disclosure provides an optical film including a plurality of first layers disposed on a plurality of second layers, wherein the optical transmittance versus wavelength of each of the plurality of first layers and the plurality of second layers for substantially normally incident light polarized along the same in-plane first direction has a transmission stop band, the transmission stop band including a left band edge (LBE) on the short wavelength side of the transmission stop band where the transmission generally decreases with increasing wavelength, and a right band edge (RBE) on the long wavelength side of the transmission stop band where the transmission generally increases with increasing wavelength, the transmission stop band can be at least 20 nm wide, and the average transmission across the transmission stop band can be less than about 10%. The RBE of the plurality of first layers intersects with the LBE of the plurality of second layers by about 5% to about 50% at least at a first transmission intersection.

[0009] In some aspects, the present disclosure provides a multilayer optical film comprising a plurality of optical repeating units (ORUs) arranged sequentially along a thickness direction of the optical film and a single cavity layer, the single cavity layer being arranged between a first ORU and a second ORU in the plurality of ORUs. There are at least 30 ORUs in total. Each of the ORUs has at least two layers. Each of the at least two layers has an average thickness of less than about 500 nm. The ORUs are numbered sequentially along the thickness direction. A plot of the optical thicknesses of the sequentially numbered ORUs as a function of the corresponding number in the sequence includes a monotonic first portion, the monotonic first portion extending through at least 10 of the ORUs and including the first ORU and the second ORU, such that a best linear fit applied to the ORUs in the monotonic first portion of the sequence has an optical thickness M1 at the sequence number corresponding to the first ORU. The absolute value of the difference between M1 and the optical thickness of the single cavity layer can be less than about 10%.

[0010] In some aspects, the present disclosure provides a multilayer optical film including a resonant cavity resonating at at least one resonant wavelength. The resonant cavity is formed by disposing a polymer cavity layer between a multilayer, polymeric first optical mirror and a polymeric second optical mirror. Each of the first optical mirror and the second optical mirror includes a plurality of polymer layers, totaling at least 10. Each of the polymer layers has an average thickness of less than about 500 nm. Each of the first optical mirror and the second optical mirror can have an optical reflectivity of at least 25% for light substantially normally incident at the at least one resonant wavelength. For light incident substantially normally on the multilayer optical film at the at least one resonant wavelength, the first optical mirror and the second optical mirror reflect a portion of the incident light in substantially the same direction as a respective first reflected light and a second reflected light. The reflected lights destructively interfere with each other outside the resonant cavity.

[0011] In some aspects, provided herein is a multilayer optical film including a resonant cavity resonating at least a first resonant wavelength. The resonant cavity is formed by disposing a polymeric cavity layer between a multilayer, polymeric first optical mirror and a polymeric second optical mirror. Each of the first optical mirror and the second optical mirror includes a plurality of polymer layers totaling at least 10, each of the polymer layers having an average thickness of less than about 500 nm. Each of the first optical mirror and the second optical mirror can have an optical reflectivity of at least 25% for the first resonant wavelength for light substantially normally incident. The multilayer optical film reflects a first portion of the incident light based on destructive interference and transmits a second portion of the incident light substantially greater than the first portion of the incident light based on constructive interference for light incident substantially normally to the multilayer optical film and having the first resonant wavelength.

[0012] In some aspects, the present disclosure provides a multilayer optical film comprising a plurality of optical repeat units (ORUs) totaling at least 10. Each of the ORUs comprises at least two polymer layers, and each of the polymer layers can have an average thickness of less than about 500 nm. A single cavity layer is disposed between and adjacent a first ORU and a second ORU in the plurality of ORUs, such that for substantially normally incident light having a predetermined wavelength and polarized along a first direction in the plane of the multilayer optical film, each of the first ORU and the second ORU reflects a portion of the incident light toward the other of the first ORU and the second ORU as a respective first reflected light and a second reflected light by constructive interference. The single cavity layer constructively interferes the first reflected light and the second reflected light.

[0013] In some aspects, the present disclosure provides a multilayer optical film comprising a total of at least 10 optical repeat units (ORUs), each of the ORUs having at least two polymer layers. Each of the polymer layers can have an average thickness of less than about 500 nm. A single cavity layer is disposed between and adjacent a first ORU and a second ORU in the plurality of ORUs. Each of the first ORU and the second ORU have an optical thickness substantially equal to half the same predetermined wavelength, and the multilayer optical film reflects a first portion of the incident light based on destructive interference and transmits a second portion of the incident light that is substantially greater than the first portion of the incident light based on constructive interference for substantially normally incident light having the predetermined wavelength and polarized along a first direction in the plane of the multilayer optical film.

[0014] In some embodiments, the present disclosure provides a multilayer optical film comprising a plurality of first layers and a plurality of second layers. Each of the first layers and the second layers has an average thickness of less than about 500 nm. For each of the second layers, the second layer is disposed between and adjacent to two of the first layers and has an average thickness greater than the average thickness of each of the two first layers, and the second layer causes the multilayer optical film to have a different local peak optical transmittance of more than about 40%.

[0015] In some aspects, the present disclosure provides a multilayer optical film that includes a plurality of first layers and a plurality of second layers that are sequentially arranged and numbered along a thickness direction of the optical film, with each of the second layers being disposed between and adjacent to two of the first layers. Each of the first and second layers has an average thickness of less than about 500 nm. The second layers can be sufficiently close to each other in the sequence of layers such that the layers in combination cause the multilayer optical film to have a peak optical transmittance of greater than about 40%.

[0016] These and other aspects will become apparent from the following detailed description, but in no way should this brief summary be construed as limiting the claimed subject matter. [Brief description of the drawings]

[0017] [Figure 1A] 1 is a schematic cross-sectional view of a multilayer optical film according to some embodiments. [Figure 1B] 1B is a schematic cross-sectional view of a portion of the multilayer optical film of FIG. 1A. [Figure 2A] 1 is a schematic cross-sectional view of a multilayer optical film including a layer disposed between a first optical mirror and a second optical mirror according to some embodiments. [Figure 2B] 2B is a schematic cross-sectional view of the first optical mirror and the second optical mirror of FIG. 2A. [Figure 2C] 2B is a schematic cross-sectional view of the first optical mirror and the second optical mirror of FIG. 2A. [Figure 3A] 1 is a plot of optical transmittance versus wavelength for a first optical mirror and a second optical mirror according to some embodiments. [Figure 3B] 3B is a plot of a portion of the optical transmittance versus wavelength of FIG. 3A and a portion of the optical transmittance versus wavelength of a multilayer optical film including the first and second optical mirrors of FIG. 3A and a cavity or spacer layer therebetween, according to some embodiments. [Figure 4A] 1 is a plot of layer thickness versus layer number for a multilayer optical film according to some embodiments. [Figure 4B] 1 is a plot of layer thickness versus layer number for a multilayer optical film according to some embodiments. [Figure 4C] 1 is a plot of layer thickness versus layer number for a multilayer optical film according to some embodiments. [Figure 5A] 1 is a plot of optical repeat unit (ORU) optical thickness versus ORU number for a multilayer optical film according to some embodiments. [Figure 5B] 1 is a plot of optical repeat unit (ORU) optical thickness versus ORU number for a multilayer optical film according to some embodiments. [Figure 5C]1 is a plot of optical repeat unit (ORU) optical thickness versus ORU number for a multilayer optical film according to some embodiments. [Figure 6A] 1 is a plot of the wavelength corresponding to twice the optical thickness of the ORU versus ORU number for an optical film according to some embodiments. [Figure 6B] 1 is a plot of the wavelength corresponding to twice the optical thickness of the ORU versus ORU number for an optical film according to some embodiments. [Figure 7A] 1 is a plot of optical transmission and optical absorptance versus wavelength for light substantially normally incident on the optical film of a multilayer optical film according to some embodiments. [Figure 7B] 7B is a plot of a portion of the optical transmittance versus wavelength of FIG. 7A. [Figure 7C] 7B is a plot of a portion of the optical transmittance versus wavelength of FIG. 7A. [Figure 8A] 1 is a plot of layer thickness versus layer number for various optical films, according to some embodiments. [Figure 8B] 1 is a plot of layer thickness versus layer number for various optical films, according to some embodiments. [Figure 8C] 1 is a plot of layer thickness versus layer number for various optical films, according to some embodiments. [Figure 9A] 8A-8C are plots of optical transmission versus wavelength for substantially normally incident light for optical films having the layer thickness profiles of FIGS. 8A-8C, respectively, according to some embodiments. [Figure 9B] 8A-8C are plots of optical transmission versus wavelength for substantially normally incident light for optical films having the layer thickness profiles of FIGS. 8A-8C, respectively, according to some embodiments. [Figure 9C] 8A-8C are plots of optical transmission versus wavelength for substantially normally incident light for optical films having the layer thickness profiles of FIGS. 8A-8C, respectively, according to some embodiments. [Figure 10]1 is a plot of optical transmission versus wavelength for substantially normally incident light for films having spacer or cavity layers of different thicknesses, according to some embodiments. [Figure 11A] 1 is a plot of layer thickness versus layer number for an optical film including three spaced apart spacer or cavity layers, according to some embodiments. [Figure 11B] 1 is a plot of layer thickness versus layer number for an optical film including three spaced apart spacer or cavity layers, according to some embodiments. [Figure 11C] 1 is a plot of layer thickness versus layer number for an optical film including three spaced apart spacer or cavity layers, according to some embodiments. [Figure 11D] 1 is a plot of layer thickness versus layer number for an optical film including three spaced apart spacer or cavity layers, according to some embodiments. [Figure 12] 11A-11D are plots of optical transmission versus wavelength for substantially normally incident light for an optical film having the layer thickness profile of FIGS. 11A-11D according to some embodiments. [Figure 13A] 1 is a plot of layer thickness versus layer number for an optical film having four spacer or cavity layers, according to some embodiments. [Figure 13B] 1 is a plot of layer thickness versus layer number for an optical film having four spacer or cavity layers, according to some embodiments. [Figure 14] 13A-13B are plots of optical transmission versus wavelength for substantially normally incident light for an optical film having the layer thickness profile of FIGS. 13A-13B according to some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] In the following description, reference is made to the accompanying drawings, which form a part hereof, and in which various embodiments are shown by way of illustration. The drawings are not necessarily to scale. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. Accordingly, the following detailed description is not to be taken in a limiting sense.

[0019] Multilayer optical films including alternating polymer layers can be used to provide desired reflection and transmission in desired wavelength ranges by appropriately selecting layer thicknesses and refractive index differences, as generally described in, for example, U.S. Pat. Nos. 5,882,774 (Jonza et al.), 6,179,948 (Merrill et al.), 6,783,349 (Neavin et al.), 6,967,778 (Wheatley et al.), and 9,162,406 (Neavin et al.). The alternating polymer layers typically include alternating high and low refractive index layers, which can be described as optical layers that transmit and reflect light primarily by optical interference. Multilayer optical films including alternating high and low refractive index layers may be described as including a plurality of optical repeat units, each optical repeat unit including a high and a low refractive index layer. An optical repeat unit is generally the smallest discrete unit of an optical layer that repeats along at least a portion of the thickness of the optical film. Each optical repeat unit may include one or more layers in addition to the high and low refractive index layers, for example, as described in U.S. Pat. Nos. 5,103,337 (Schrenk et al.), 5,540,978 (Schrenk), and 6,207,260 (Wheatley et al.).

[0020] In some applications, it is desirable for the optical film to have high reflectance over a given wavelength range, such as the visible wavelength range (e.g., about 400 nm to about 700 nm, or about 420 nm to about 680 nm, or about 450 nm to about 650 nm) or the visible near infrared (NIR) wavelength range (e.g., about 400 nm to about 1200 nm, or about 400 nm to about 1000 nm, or about 400 nm to about 900 nm, or about 420 nm to about 850 nm, or about 450 nm to about 800 nm, or about 500 nm to about 800 nm, or about 550 nm to about 800 nm). However, in some cases, it is also desirable to provide transmission for one or more wavelengths within a given wavelength range. For example, the optical film can be used as a reflector for recycling light in a display, where the reflector also covers one or more transmitters or detectors (e.g., for fingerprint sensing, face recognition, or sensing of various biometric factors) that operate at a narrow wavelength range(s) within the predetermined wavelength range. According to some embodiments herein, it has been found that the optical film can provide a narrow transmission band(s) within a predetermined wavelength range such that the optical film has a desired high average reflectance (e.g., greater than about 60%, or greater than about 70%, or greater than about 80%) within the predetermined wavelength range, while providing high transmittance (e.g., greater than about 80%, or greater than about 85%, or greater than about 90%) for one or more predetermined wavelengths within the predetermined wavelength range. In some embodiments, this is achieved by utilizing a stack of optical layers to generate the reflection band, and including one or more additional optical layers within the stack, each of which has a thickness substantially greater (e.g., at least 50% greater) than the adjacent optical layers on either side of the additional optical layer.

[0021] 1A is a schematic cross-sectional view of a multilayer optical film 200 including multiple polymer layers 10, 11 according to some embodiments. Each of the polymer layers 10, 11 can have an average thickness of less than about 500 nm, or less than about 400 nm, or less than about 300 nm, or less than about 250 nm, or less than 200 nm. For example, each of the polymer layers 10, 11 can have an average thickness of more than about 30 nm, or more than about 40 nm, or more than about 50 nm. The optical film 200 can also include other layers having a thickness of more than about 500 nm. For example, the optical film 200 can include skin layers 131 and 132, with the multiple polymer layers 10, 11 disposed between the skin layers 131 and 132. Each of the skin layers 131, 132 can have an average thickness of more than about 500 nm, more than about 1 micrometer, or more than about 2 micrometers. The average thickness of each of the skin layers 131 and 132 can be, for example, up to about 20 micrometers. The optical film 200 may further include protective boundary layer(s) disposed between packets of optical layers and having an average thickness in any of the ranges described for the skin layers. The skin layer and / or protective boundary layer(s) may be formed, for example, from the polymeric material of layer 10 or of layer 11. The multiple polymer layers 10, 11 include a layer 13 having a thickness S, which is typically greater than the thickness of adjacent layers 12, 14 within the multiple polymer layers 10, 11. For example, layer 13 may be one of layers 10. Layer 13 may be referred to, for example, as a spacer layer or a cavity layer. Although only one layer 13 is shown in the schematic diagram of FIG. 1A, additional layers 13 may be included (see, for example, FIG. 11A and FIG. 13A-FIG. 13B). The multiple polymer layers 10, 11 may be described as including multiple first polymer layers (layers 10, 11 other than layer 13) and one or more second polymer layers (layer(s) 13). The multiple polymer layers 10, 11 may include more layers than are shown diagrammatically in FIG. 1A. This is shown diagrammatically, for example, in FIG. 1B. The number of layers and the refractive index difference between adjacent layers may be selected to provide a desired reflection intensity over a desired wavelength range.In some embodiments, the number of layers of the multiple polymer layers 10, 11 may be, for example, at least 10 layers in total, or at least 20 layers in total, or at least 30 layers in total, or at least 40 layers in total, or at least 50 layers in total, or at least 100 layers in total, or at least 150 layers in total, and may include, for example, up to 1000 layers in total, or up to 600 layers in total, or up to 500 layers in total, or up to 450 layers in total. The multiple first polymer layers may be described as including a plurality of optical repeat units 30, each optical repeat unit including one layer 10 and one layer 11. In some embodiments, the multilayer optical film includes a plurality of optical repeat units, each optical repeat unit including at least two layers. The two layers may be polymer layers and may have different compositions. In some embodiments, the multilayer optical film comprises a plurality of optical repeating units (ORUs) 30, e.g., at least 10 in total, or at least 20 in total, or at least 30 in total, or at least 40 in total, or at least 50 in total, or at least 75 in total, or at least 100 in total, or at least 125 in total, or at least 150 in total, and may comprise, e.g., up to 1000 in total, or up to 600 in total, or up to 400 in total, or up to 300 in total, or up to 250 ORUs in total.

[0022] In some cases, the optical transmission spectrum of the optical film 200 may be specified for light 20 incident substantially normally (e.g., within 30 degrees, or within 20 degrees, or within 10 degrees of normal incidence). The light 20 may be polarized, for example, along the x-axis, or along the y-axis, or may be unpolarized, according to the illustrated xyz coordinate system. For example, the polarization state of obliquely incident light may be described as being along a first direction in the plane, for example, if the electric field of the light projected in the plane of the film is parallel to the first direction. The light 20 may have a wavelength λ within a predetermined wavelength range λ1-λ2. λ1 may be, for example, about 300 nm, or about 350 nm, or about 380 nm, or about 400 nm, or about 420 nm, or about 450 nm. λ2 may be, for example, about 2500 nm, or about 2000 nm, or about 1600 nm, or about 1350 nm, or about 1200 nm, or about 1000 nm, or about 900 nm, or about 800 nm, or about 700 nm, or about 680 nm, or about 650 nm. In some embodiments, the optical film 200 may be an optical mirror (e.g., an optical mirror may have an optical reflectance of greater than about 60%, or greater than about 70%, or greater than about 80% for each of two mutually orthogonal polarization states for substantially normally incident light 20 and at least one wavelength within a predetermined wavelength range) or may be a reflective polarizer (e.g., a reflective polarizer may have an optical reflectance of greater than about 60%, or greater than about 70%, or greater than 80% for light having a first polarization state (e.g., polarized along the x-axis) and an optical transmittance of greater than about 60%, or greater than about 70%, or greater than about 75% for light having an orthogonal second polarization state (e.g., polarized along the y-axis) for at least one wavelength within a predetermined wavelength range for substantially normally incident light).

[0023] The multilayer optical film 200 (or optical film 210 described elsewhere herein) can be formed from polymeric materials conventionally used in multilayer optical films. Suitable materials for the various layers of the multilayer optical film 200 (or 210) include, for example, polyethylene naphthalate (PEN), coPEN (copolyethylene naphthalate terephthalate copolymer), polyethylene terephthalate (PET), polyhexylethylene naphthalate copolymer (PHEN), glycol-modified PET (PETG), glycol-modified PEN (PENG), various other copolyesters such as those described elsewhere herein, syndiotactic polystyrene (sPS), polymethyl methacrylate (PMMA), coPMMA (copolymer of methyl methacrylate and ethyl acrylate), or blends thereof. In some embodiments, the layers 10, 11 include alternating first and second layers, the first layer including, for example, PEN or PET, and the second layer including, for example, PMMA or coPMMA. Other suitable materials for the various layers in the multilayer optical film 200 include those described, for example, in U.S. Patent Nos. 5,103,337 (Schrenk et al.), 5,540,978 (Schrenk), 5,882,774 (Jonza et al.), 6,179,948 (Merrill et al.), 6,207,260 (Wheatley et al.), 6,783,349 (Neavin et al.), 6,967,778 (Wheatley et al.), 9,069,136 (Weber et al.), and 9,162,406 (Neavin et al.). Suitable sPS can be obtained, for example, from Idemitsu Kosan Co., Ltd. (Tokyo, Japan). Atactic polystyrene (aPS) can optionally be blended with sPS (e.g., at about 5 to about 30 weight percent aPS) to adjust the refractive index of the resulting layer and / or to reduce the haze of the layer (e.g., by reducing the crystallinity of the layer). Suitable PMMA can be obtained, for example, from Arkema Inc. (Philadelphia, PA).Suitable PET can be obtained, for example, from Nan Ya Plastics Corporation, America (Lake City, SC). PETG can be described as PET in which some of the glycol units of the polymer have been replaced with different monomer units, typically monomer units derived from cyclohexanedimethanol. PETG can be prepared, for example, by replacing a portion (e.g., about 15 to about 60 mole percent or about 30 to about 40 mole percent) of the ethylene glycol used in the transesterification reaction to prepare the polyester with cyclohexanedimethanol. Suitable PETG copolyesters include GN071 available from Eastman Chemical Company (Kingsport, TN). PEN and coPEN can be prepared, for example, as described in U.S. Pat. No. 10,001,587 (Liu). Glycol-modified polyethylene naphthalates (PENGs) can be described as PENs in which some of the glycol units of the polymer have been replaced with different monomer units, and can be prepared, for example, by replacing a portion (e.g., about 15 to about 60 mole percent, or about 30 to about 40 mole percent) of the ethylene glycol used in the transesterification reaction to produce the polyester with cyclohexanedimethanol. PHENs can be prepared, for example, as described for PEN in U.S. Pat. No. 10,001,587 (Liu), except that a portion (e.g., about 15 to about 60 mole percent, or about 30 to about 50 mole percent, or about 40 mole percent) of the ethylene glycol used in the transesterification reaction is replaced with hexanediol. Other suitable copolyesters include, for example, those available under the tradename TRITAN from Eastman Chemical Company (Kingsport, TN) and OKP-1 available from Osaka Gas Chemicals Co., Ltd. (Osaka, Japan).

[0024] In some embodiments, layers 10, 11 include alternating birefringent (e.g., high refractive index) and isotropic (e.g., low refractive index) layers. For example, layers 10, 11 can include alternating first and second layers, where the first layer includes, for example, PEN or PET, and the second layer includes, for example, PMMA or coPMMA, and the PEN or PET layer can be birefringent (e.g., biaxially or uniaxially oriented), and the PMMA or coPMMA can be optically isotropic. In some embodiments, layers 10, 11 include alternating high refractive index isotropic and low refractive index isotropic layers. Suitable isotropic high refractive index layers include, for example, PHEN, PENG, and OKP-1. Suitable isotropic low refractive index layers include, for example, PMMA and coPMMA. The high and low refractive indices refer to the in-plane direction, which for a reflective polarizer, may be taken along the block axis. The refractive index may be evaluated, for example, at a wavelength of about 633 nm. In the case of a reflective polarizer, the birefringent layer can be selected to define the pass and block axes of the reflective polarizer. In the case of an optical mirror, the birefringent or isotropic high index layer can be selected based on the desired reflection spectrum for obliquely incident light, for example. For example, to modify the reflection spectrum for p-polarized light at oblique incidence angles, the birefringent layer can be selected to provide a refractive index difference between different adjacent layers along the thickness direction rather than along the in-plane direction.

[0025] 1A-1B, a single cavity layer 13 is disposed adjacent to and between a first ORU 30a and a second ORU 30b in the plurality of ORUs 30. FIG. 1B illustrates a portion of light 20 reflected by ORU 30a as reflected light 24, a portion of light 20 transmitted by ORU 30a as transmitted light 22, a portion of light 22 reflected by ORU 30b as reflected light 25, a portion of light 22 transmitted by ORU 30b as transmitted light 23, a portion of light 25 reflected by ORU 30a as reflected light 26, a portion 26' of light 26 reflected by ORU 30b ... 2A and 2B, light 25', which is a combination of portions 25 and 26' reflected by ORU 30a, and a portion 25" of reflected light 25' transmitted by ORU 30a are shown. Light 20 can have a predetermined wavelength λ and can be polarized along an in-plane first direction (e.g., the x-direction) of multilayer optical film 200. Light 22, 23, 24, 25, 26, 26', 25', and 25" can have the same predetermined wavelength and can be polarized along the same in-plane first direction. In some embodiments, one of the first ORU 30a and the second ORU 30b each reflects a portion of the incident light 20 toward the other of the first ORU and the second ORU as a respective first reflected light 26 (or the first reflected light can be a sum of the portions of the incident light 20 reflected from the ORU 30a) and a second reflected light 25 (or the second reflected light can be a combination 25' of the portions of the incident light 20 reflected from the ORU 30b) by constructive interference, and the single cavity layer causes the first reflected light and the second reflected light to constructively interfere. For example, the reflected lights 26 and 25 can be reflected multiple times at the ORUs 30a and 30b, such that the portions of the reflected lights propagate substantially in phase and in the same direction within the single cavity layer 13 and constructively interfere. For example, a portion 26' of the reflected light 26 can constructively interfere with the reflected light 25.In some embodiments, the first ORU 30a and the second ORU 30b reflect a portion of the incident light 20 in substantially the same direction (e.g., nominally in the same direction, such as the negative z direction, or within 20 degrees, or 10 degrees, or 5 degrees of the same direction) as the respective first reflected light 24 and second reflected light 25' (or 25) by constructive interference, and the first reflected light and the second reflected light destructively interfere with each other outside the single cavity layer 13. For example, a portion 25" of the reflected light 25' can transmit through the ORU 30a and destructively interfere with the reflected light 24 outside the single cavity layer 13 to reduce the light reflected from the optical film. The ORU 30a may reflect another portion 26 of the incident light 20, for example, in a direction opposite to that of the reflected light 24.

[0026] Destructive interference generally occurs between light waves that are approximately 180° out of phase, resulting in a small amplitude of the combined wave compared to the individual waves. Destructive interference can be substantially perfect (e.g., for light waves that are substantially 180° out of phase and have substantially equal amplitudes), resulting in a substantially zero amplitude of the combined wave, or it can be imperfect (e.g., for light waves that are substantially 180° out of phase and have different amplitudes), resulting in a small but non-zero amplitude of the combined wave. Constructive interference generally occurs between light waves that are substantially in phase with each other, resulting in a large amplitude of the combined wave compared to the individual waves.

[0027] The predetermined wavelength λ may be about 300 nm to about 2500 nm, or may be within a predetermined wavelength range described elsewhere herein. In some embodiments, the single cavity layer 13 and the first ORU 30a and the second ORU 30b each have an optical thickness substantially equal to half the predetermined wavelength λ. For example, the single cavity layer 13 and the first ORU 30a and the second ORU 30b each can have an optical thickness within 5%, or within 3%, or within 2%, or within 1%, or within 0.8% of half the predetermined wavelength λ. In some embodiments, the first ORU 30a and the second ORU 30b each have an optical thickness substantially equal to half the predetermined wavelength λ, and the single cavity layer 13 has an optical thickness substantially equal to a positive integer multiple of half the predetermined wavelength λ. The positive integer can be within any range described elsewhere herein for a positive integer m. The optical thickness of a layer is the average thickness of the layer multiplied by the refractive index of the layer. The refractive index can be determined at a given wavelength λ and for light polarized along a first direction.

[0028] The multilayer optical film 200 may be described as including a resonant cavity 40 disposed between reflectors 43 and 44. The reflectors 43, 44 may be optical mirrors or reflective polarizers, each of which may include a plurality of optical repeat units 30. The range of the total number of polymer layers in each reflector and / or the range of the total number of optical repeat units in each reflector may be about half of any corresponding range described elsewhere herein for the optical film 200. For example, each reflector may include 5-500 polymer layers 10, 11, or may include 5-500 optical repeat units 30. In some embodiments, each reflector 43, 44 may include at least 10 polymer layers 10, 11 in total. In some embodiments, the resonant cavity 40 may be formed by disposing a polymer cavity layer 13 between a multilayer, polymeric first optical mirror and a polymeric second optical mirror.

[0029] FIG. 2A is a schematic cross-sectional view of a multilayer optical film 210 including a spacer layer 50 (e.g., a polymer cavity layer) disposed between a first optical mirror 51 and a second optical mirror 52, according to some embodiments. According to some embodiments, the optical mirrors 51, 52 can be characterized by their reflectance and / or transmittance for substantially normally incident light 54, 55, as shown generally in FIGS. 2B-2C. The reflected portion 56 and the transmitted portion 58 of the light 54 substantially normally incident on the optical mirror 51 are shown generally in FIG. 2B. Similarly, the reflected portion 57 and the transmitted portion 59 of the light 55 substantially normally incident on the optical mirror 52 are shown generally in FIG. 2C. The optical properties of the optical mirrors 51 and 52 may be characterized, for example, by the reflectance and / or transmittance of the respective light 54 and 55 substantially normally incident on the optical mirror in air.

[0030] The first optical mirror 51 and the second optical mirror 52 may include multiple polymer layers 10, 11 as further described elsewhere herein. In some embodiments, the multilayer optical film 200, 210 includes a resonant cavity 40 resonating at at least one resonant wavelength (e.g., wavelengths 41, 42 shown in Figures 7B-7C, or wavelength 63 shown in Figure 3B). The resonant cavity may be formed by disposing a polymer cavity layer 13, 50 between a multilayer, polymeric first optical mirror and a polymeric second optical mirror (e.g., 43 and 44, or 51 and 52). Each of the first optical mirror and the second optical mirror may include multiple polymer layers 10, 11, totaling at least 10, each of the polymer layers having an average thickness of less than about 500 nm. The total number of polymer layers and the average thickness of the layers may be within any of the corresponding ranges described elsewhere herein. In some embodiments, the first optical mirror and the second optical mirror each have an optical reflectivity for substantially normally incident light 54, 55 (e.g., incident in air) at at least one resonant wavelength of at least 25%, or at least 30%, or at least 35%, or at least 40%, or at least 45%, or at least 50%, or at least 55%, or at least 60% (e.g., from 25% to 80% or 70% or 65%). In some embodiments, the first optical mirror and the second optical mirror each have an optical reflectivity for substantially normally incident light at at least one resonant wavelength in the range of 25% to about 50% or about 45%. Light can be said to be at at least one resonant wavelength when the light has one of its resonant wavelength(s) or when the light has two or more wavelengths and the at least one resonant wavelength includes two or more wavelengths such that each wavelength of the light is one of the resonant wavelengths. For example, the optical reflectivity can be in any of these ranges for at least a first resonant wavelength of the at least one resonant wavelength.In some embodiments, for incident light 20 that is substantially normally incident on the multilayer optical film 200, 210 at at least one resonant wavelength, the first optical mirror and the second optical mirror reflect a portion of the incident light in substantially the same direction as respective first and second reflected lights 158 and 157 (or 24 and 25'), and the first and second reflected lights destructively interfere with each other outside the resonant cavity 40. For example, a portion 157' of the reflected light 157 can destructively interfere with the reflected light 158 ​​outside the resonant cavity 40 to result in reduced intensity light 157". In some embodiments, for incident light 20 that is substantially normally incident on the multilayer optical film 200, 210, for at least one resonant wavelength, the first optical mirror and the second optical mirror each reflect a portion of the incident light in substantially the same direction as respective first and second reflected lights 156 and 157 (or 26 and 25 or 25'). The first reflected light is reflected toward the other of the first and second optical mirrors, and the resonant cavity 40 constructively interferes with the second reflected light. In some embodiments, the multilayer optical film has an optical transmission at at least one resonant wavelength of greater than about 50%, or greater than about 60%, or greater than about 70%, or greater than about 80%, or greater than 90% for substantially normally incident light (e.g., the transmission can be in any of these ranges for at least the first of the at least one resonant wavelengths).

[0031] In some embodiments, the multilayer optical film 200, 210 includes a resonant cavity 40 resonating at least at a first resonant wavelength (e.g., at least one of 41, 42, 63). The resonant cavity can be formed by disposing a polymeric cavity layer 13, 50 between a multilayer, polymeric first optical mirror (e.g., 43, 51) and a polymeric second optical mirror (e.g., 44, 52), each of which can include a plurality of polymer layers 10, 11 totaling at least 10, each of which has an average thickness of less than about 500 nm. The number of layers 10, 11 and / or the average thickness of the layers can be within any of the ranges described elsewhere herein. Each of the first optical mirror and the second optical mirror can have an optical reflectivity for substantially normally incident light 54, 55 at the first resonant wavelength of at least 25%, or within the ranges described elsewhere herein. In some embodiments, for incident light 20, 53 substantially normally incident on the multilayer optical film 200, 201 and having a first resonant wavelength, the multilayer optical film reflects a first portion of the incident light (e.g., portion 157″ having intensity I1″) based on destructive interference of light and transmits a second portion of the incident light (e.g., portion 159 having intensity I2) that is substantially greater than the first portion of the incident light (e.g., I2 can be at least twice as large as I1) based on constructive interference of light.

[0032] In some embodiments, the multilayer optical film 200, 210 includes a plurality of optical repeat units (ORUs) totaling at least 10, each of the ORUs having at least two polymer layers 10, 11, each of the polymer layers having an average thickness of less than about 500 nm. The number of layers 10, 11 and / or the average thickness of the layers can be within any of the ranges described elsewhere herein. In some embodiments, a single cavity layer 13, 50 is disposed between and adjacent a first ORU 30a and a second ORU 30b in the plurality of ORUs, each of the first ORU and the second ORU having an optical thickness substantially equal to half the same predetermined wavelength, such that for substantially normally incident light 20, 53 having the predetermined wavelength and polarized along a first direction (x-direction) in the plane of the multilayer optical film, the multilayer optical film reflects a first portion of the incident light (e.g., 157″ having intensity I1) based on destructive interference of light and reflects a substantially greater amount of the first portion of the incident light than the first portion of the incident light. In some embodiments, the single cavity layer has an optical thickness substantially equal to a positive integer multiple of half the predetermined wavelength. The positive integer can be within any of the ranges described elsewhere herein (e.g., for m). For example, the positive integer can be less than 5 and can be 1, such that the single cavity layer has an optical thickness substantially equal to half the predetermined wavelength.

[0033] In some embodiments in which the multilayer optical film 200, 210 reflects a first portion of the incident light 20, 53 based on destructive interference and transmits a second portion of the incident light based on constructive interference, the first and second portions can have respective intensities I1 and I2, where I2 / I1>2, or I2 / I1>3, or I2 / I1>4, or I2 / I1>5, or I2 / I1>6, or I2 / I1>7, or I2 / I1>8, or I2 / I1>9, or I2 / I1>10. In some such embodiments, or in other embodiments, the incident light 20, 53 substantially normally incident on the multilayer optical film 200, 210 has an intensity I0, where I2 / I0>0.7, or I2 / I0>0.75, or I2 / I0>0.8, or I2 / I0>0.85, or I2 / I0>0.9.

[0034] 3A is a plot of optical transmittance 151 and 152 versus wavelength for a first and second mirror (e.g., 43 and 44, or 51 and 52), respectively, according to some embodiments. Optical transmittance 151 includes a transmission stop band 153 having a left band edge (LBE) 155 on the short wavelength side of transmission stop band 153 that generally decreases transmission with increasing wavelength, and a right band edge (RBE) 157 on the long wavelength side of transmission stop band 153 that generally increases transmission with increasing wavelength. Optical transmittance 152 includes a transmission stop band 154 having a left band edge (LBE) 156 on the short wavelength side of transmission stop band 154 that generally decreases transmission with increasing wavelength, and a right band edge (RBE) 158 on the long wavelength side of transmission stop band 155 that generally increases transmission with increasing wavelength. Figure 3B is a plot of the optical transmittance of Figure 3A and the optical transmittance 410 of a multilayer optical film including a first and second mirror and a cavity or spacer layer (e.g., 13 or 50) therebetween, according to some embodiments. The optical transmittance of Figures 3A-3B was calculated using standard optical modeling techniques for alternating PEN and PMMA layers having the layer thickness profile shown in Figures 4A-4C, where the cavity layer 13 was a PEN layer and the first and second mirrors included layers to the left and right, respectively, of layer 13 of Figure 4A.

[0035] In some embodiments, the optical film 200, 210 includes a spacer layer 13, 50 disposed between a first optical mirror and a second optical mirror (e.g., 43 and 44, or 51 and 52), and for substantially normally incident light (e.g., 54, 55) polarized along a first direction (e.g., the x-direction) in the same plane of the optical film, a first wavelength 60 and a second wavelength 61 separated by about 2 nm to about 100 nm (e.g., a wavelength range 62), and a third wavelength 63 between the first and second wavelengths, the first optical mirror and the second optical mirror have respective optical transmittances T1 and T2 at the first wavelength, respective optical transmittances T1' and T2' at the second wavelength, and respective optical transmittances T1" and T2" at the third wavelength, and the optical film has an optical transmittance T at the third wavelength. In some embodiments, T2>2T1, T1'>2T2', and T>T1" and T2" (i.e., T is greater than each of T1" and T2"). In some such embodiments, or in other embodiments, T2 is greater than 5T1, or 10T1, or 20T1, or 50T1, or 100T1. In some such embodiments, or in other embodiments, T1' is greater than 5T2', or 10T2', or 20T2', or 50T2', or 100T2'. In some such embodiments, or in other embodiments, T is at least 1.1 times, or 1.2 times, or 1.3 times, or 1.4 times, or 1.5 times, or 1.6 times, or 1.7 times, or 1.8 times, or 1.9 times, or 2 times as large as each of T1" and T2". In some such or other embodiments, T1" and T2" are each within a range of, for example, 10% to 60%, or 20% to 50%, or 45%. In some such or other embodiments, varying the thickness S of the spacer layer decreases T (see, e.g., FIG. 10). Varying the thickness of the spacer layer may include increasing the thickness of the spacer layer or decreasing the thickness of the spacer layer. In some embodiments, both increasing and decreasing the thickness of the spacer layer decrease T.

[0036] In some embodiments, the optical film 200, 210 includes a plurality of first layers (e.g., layers 10, 11 in the reflector 43) disposed on a plurality of second layers (e.g., layers 10, 11 in the reflector 44), and for substantially normally incident light 54, 55 polarized along the same in-plane first direction (e.g., the x-direction), the optical transmittance 151, 152 versus wavelength of each of the plurality of first layers and the plurality of second layers includes a transmission stop band 153, 154 having a left band edge (LBE) 155, 156 on the short wavelength side of the transmission stop band, where the transmission generally decreases with increasing wavelength, and a right band edge (RBE) 157, 158 on the long wavelength side of the transmission stop band, where the transmission generally increases with increasing wavelength. Each transmission stop band 153, 154 can be, for example, at least 20 nm wide, or at least 40 nm wide, or at least 60 nm wide, or at least 100 nm wide, and may be up to 500 nm wide, or up to 400 nm wide. The average transmission across the transmission stop bands 153, 154 can be, for example, less than about 10%, or less than about 7.5%, or less than about 5%, or less than about 2.5%, or less than about 2%, or less than about 1.5%, or less than about 1%. In some embodiments, the RBE of the first layers intersects with the LBE of the second layers at least at a first transmittance intersection Ta and / or Tb by about 5% to about 50%, or about 10% to about 50%, or about 10% to about 45%, or about 15% to about 45%, or about 15% to about 40%, or about 20% to about 40%, or about 15% to about 35%, or about 20% to about 35%, or about 20% to about 30%. The transmittance intersection is the optical transmittance at the point where the optical transmittance 151 and the optical transmittance 152 intersect. The at least first transmittance intersection within a particular range (e.g., about 5% to about 50%) may alternatively be described as at least a first intersection having an optical transmittance within a particular range. For example, in some embodiments, the RBE of the first plurality of layers intersects with the LBE of the second plurality of layers at at least a first intersection point having an optical transmittance (Ta, Tb) of about 5% to about 50%, or about 10% to about 45%, or within a range described elsewhere herein.In some embodiments, the optical films 200, 210 each have an optical transmittance Ta’ and / or Tb’ corresponding to at least a first transmittance intersection at wavelengths 65 and / or 64, and they are at least 10%, or 20%, or 30%, or 40%, or 50%, or 100%, or 200%, or 300% greater than at least the first transmittance intersection. For example, Tb can be about 20% and Tb’ can be about 86%, and then Tb’ is about 330% (((86 - 20) / 20)×100%) greater than Tb.

[0037] Figures 4A - 4C are plots of the total thickness against layer numbers for a multilayer optical film including a cavity or spacer layer 13 disposed between adjacent layers 12 and 14, having an average thickness d2, and having average thicknesses d1 and d3 respectively, according to some embodiments. The optical film includes a layer having a refractive index na, a layer 13 having a refractive index n2, and a layer having a refractive index nb. Each of the refractive indices may be the refractive index along the same in - plane first direction (e.g., the x - direction). In some embodiments, nb < na for at least one wavelength within a predetermined wavelength range. For example, the low - refractive - index layer (e.g., layer 10) within each optical repeating unit 30 can be made thicker than the high - refractive - index layer (e.g., layer 11) within the optical repeating unit so that the f - ratio (the ratio of the optical thickness of the high - refractive - index layer to the optical thickness of the optical repeating unit) of the optical film is 0.5. The refractive index n2 of layer 13 may be substantially equal to one of na and nb for at least one wavelength within a predetermined wavelength range. In some embodiments, the first (12), second (13), and third (14) polymer layers within the plurality of polymer layers 10, 11 are arranged adjacent to and continuously with each other, having respective refractive indices n1, n2, and n3 along the first direction at a first wavelength, and having respective average thicknesses d1, d2, and d3. The refractive indices n1 and n3 of the first layer 12 and the third layer 14 may each be one of na and nb, and the refractive index n2 may be the other of na and nb. In some embodiments, n2 is greater than each of n1 and n3. In some embodiments, n2 is less than each of n1 and n3.

[0038] In some embodiments, the difference (e.g., |na-nb|) between the average refractive index of the first polymer layer 10 and the average refractive index of the second polymer layer 11 along the first in-plane direction (e.g., x-direction) of the multilayer optical film in a given wavelength range is greater than about 0.05, or greater than about 0.1, or greater than about 0.15. The difference can be, for example, at most about 0.4, or at most about 0.35, or at most about 0.3. The given wavelength range can be from about 420 nm to about 680 nm, or any given wavelength range described elsewhere herein. The average refractive index for a number of layers and a particular wavelength range (e.g., a given wavelength range) refers to the average (e.g., unweighted average) over the layers (which may be composed of the same material) and the wavelength range.

[0039] According to some embodiments, the position and intensity of the transmission peak have been found to be less sensitive to changes in cavity thickness. For example, in some examples, the transmission peak remains above 90% and the peak wavelength shifts only about 1% when the cavity thickness shifts by about 10 to about 25%. Thus, according to some embodiments, the thickness d2 or optical thickness n2d2 of layer 13 may be specified within a substantial tolerance around a target value. In some embodiments, n2d2 is within about 40% of m(n1d1+n3d3), where m is a positive integer. For example, |n2d2-m(n1d1+n3d3)| / m(n1d1+n3d3) can be less than about 0.4. In some embodiments, n2d2 is within about 30%, or within about 20%, or within about 10%, or within about 5%, or within about 3% of m(n1d1+n3d3). In some embodiments, d2 is within about 40%, or within about 30%, or within about 20%, or within about 10%, or within about 5% of m(d1+d3), and m is a positive integer. In either case, m may be less than 15, or less than 10, or less than 5. The positive integer m can be, for example, 1, 2, 3, or 4. In some embodiments, d2 is within about 40%, or within about 30%, or within about 20%, or within about 10%, or within about 5% of m'(d1+d3), and n2d2 is within about 40%, or within about 30%, or within about 20%, or within about 10%, or within about 5%, or within about 3% of m"(n1d1+n3d3), and m' and m" can be in any of the ranges listed for m. In some embodiments, m'=m". The positive integers m' and m" may alternatively be indicated, for example, as m and m', or m' and m. In some embodiments, d2 is within about 30%, or within about 20%, of m(d1+d3) and n2d2 is within about 20%, or within about 10%, or within about 5%, or within about 3% of m(n1d1+n3d3). In some embodiments, the cavity layer 13 has an optical thickness (n2d2) within about 40%, within about 30%, within about 20%, within about 10%, within about 5%, or within about 3% of the average positive integer m times the optical thickness of the two optical repeat units 30a and 30b adjacent to the cavity layer 13.In some embodiments, the cavity layer 13 and the two optical repeat units 30a and 30b adjacent to the cavity layer 13 each have an optical thickness within about 10%, or within about 5%, or within about 3%, or within about 2%, or within about 1%, or within about 0.8% of half the same predetermined wavelength. In some embodiments, d2 is less than about 500 nm or less than about 400 nm, or d2 can be any of the thickness ranges described elsewhere herein for the polymer layers 10, 11.

[0040] In some embodiments, the multilayer optical film includes a plurality of polymeric first layers 10, 11 and one or more polymeric second layers 13, each of the first and second layers having an average thickness of less than about 400 nm or in the ranges described elsewhere herein. In some embodiments, for each of the second layers, the second layer 13 has an average thickness d2 and is disposed between and adjacent to the two first layers (12, 14) having the maximum thickness d1 (d1 being, for example, the greater of the thicknesses d1 and d2 shown in FIG. 4C), where d2≧1.3d1. In some embodiments, d2≦3d1. In some embodiments, 3≧d2 / d1≧1.3, or 2.5≧d2 / d1≧1.35, or 2.1≧d2 / d1≧1.4.

[0041] 5A-5C are plots of optical thickness versus ORU number for optical repeating units (ORUs) 30, according to some embodiments. The multiple optical repeating units (ORUs) 30 and the single cavity layer 13 are arranged consecutively along the thickness direction (z-direction) of the optical film, with the single cavity layer 13 being disposed between a first ORU 30a and a second ORU 30b in the multiple ORUs 30. According to some embodiments, the optical thickness of layer 13 is shown between the ORU numbers of ORUs 30a and 30b adjacent to layer 13 in FIGS. 5A and 5C. The ORUs 30 are numbered consecutively along the thickness direction. A plot of the optical thicknesses of the consecutively numbered ORUs as a function of the corresponding number in the sequence includes a monotonic first portion 71 extending across at least 10, or at least 20, or at least 30, or at least 40, or at least 50, or at least 60, or at least 70, or at least 80, or at least 90, or at least 100 of the ORUs 30 and including a first ORU 30a and a second ORU 30b, such that a best linear fit 72 applied to the ORUs in the monotonic first portion 71 of the sequence has an optical thickness M1 at the sequence number corresponding to the first ORU 30a (e.g., ORU number 83). The absolute value of the difference between M1 and the optical thickness 73 of a single cavity layer can be less than about 10%, or less than about 8%, or less than about 6%, or less than about 4%, or less than about 2%, or less than about 1%. The best linear fit 72 may have an optical thickness M2 at a sequence number (e.g., ORU number 84) corresponding to the second ORU 30b. The absolute value of the difference between M2 and the optical thickness 73 of the single cavity layer may be less than about 10%, or less than about 8%, or less than about 6%, or less than about 4%, or less than about 2%, or less than about 1%. The difference expressed as a percentage is the larger thickness minus the smaller thickness divided by the larger thickness multiplied by 100%. The difference may also be expressed as a length. The absolute value of the difference between M1 and the optical thickness of the single cavity layer may be, for example, 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 6 nm, or less than about 4 nm.The absolute value of the difference between M2 and the optical thickness of the single cavity layer can be, for example, 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 6 nm, or less than about 4 nm. The optical thickness of the single cavity layer can be between 0.96 times the smaller of M1 and M2 and 1.04 times the larger of M1 and M2, or between 0.98 times the smaller of M1 and M2 and 1.02 times the larger of M1 and M2, or between 0.99 times the smaller of M1 and M2 and 1.01 times the larger of M1 and M2. In some embodiments, the optical thickness of the single cavity layer is between M1 and M2.

[0042] The monotonic first portion 71 is a portion of the sequence where the optical thickness of the ORUs increases with the corresponding number in the sequence or decreases with the corresponding number in the sequence. The monotonic first portion 71 of the sequence may be a linear portion of the sequence. A plot of the optical thickness of the consecutively numbered ORUs as a function of the corresponding number in the sequence may include monotonic second and third portions 76 and 77 adjacent to both ends of the monotonic first portion 71, and / or may include non-monotonic first and second portions 78 and 79 adjacent to both ends of the monotonic first portion 71 or adjacent to the monotonic second and third portions 76 and 77. The monotonic first portion 71 can generally be any monotonic portion that extends across at least 10 ORUs 30 and includes the first ORU 30a and the second ORU 30b. In embodiments in which the linear portion extends across at least ten of the ORUs 30 and includes a first ORU 30a and a second ORU 30b, the monotonic first portion 71 may be considered to be a linear portion.

[0043] The best linear fit 72 can be a linear least squares fit. As is known in the art, such a fit minimizes the sum of the squares of the residuals, where the residuals are the difference between the data and the fitted line. Least squares analysis allows one to determine an r-squared value, sometimes referred to as the coefficient of determination. In some embodiments, the best linear fit 72 has an r-squared value that is, for example, or at least 0.9, or at least 0.95, or at least 0.98, or at least 0.99.

[0044] An optical repeat unit may be primarily reflective at a wavelength that is twice the optical thickness of the optical repeat unit. In some embodiments, each of the ORUs 30 has an optical thickness that is substantially equal to (e.g., equal to within 5%, or 3%, or 2%, or 1%, or 0.8%) half the wavelength in a predetermined wavelength range, which may extend from about 300 nm to about 2500 nm, for example, or may be at least 200 nm wide and between about 300 nm to about 2500 nm. Figures 6A-6B are plots of wavelengths that correspond to twice the optical thickness of an ORU versus ORU number, according to some embodiments. In some embodiments, at least the first ORU 30a and the second ORU 30b in the plurality of ORUs 30 have an optical thickness substantially equal to half of the respective wavelengths L1 and L2 that are within 100, or 90, or 80, or 70, or 60, or 50, or 40, or 30, or 20, or 15, or 10 nm of each other (e.g., the difference DL=L2-L1 may be 100 nm or less, or any other of these lengths), and the first ORU 30a and the second ORU 30b have a single, polymeric, first layer 13 disposed therebetween. The first layer 13 may have an optical thickness substantially equal to half of the wavelength L3 disposed between L1 and L2. The difference between L2 and L1 may be, for example, at least 1 nm, or at least 2 nm, or at least 3 nm.

[0045] In some embodiments, the multilayer optical film 200, 210 transmits at least 30%, or at least 40%, or at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90% of substantially normally incident light 20 having a first wavelength (wavelength 41 shown in FIG. 7C) between L1 and L2 and polarized along an in-plane first direction (x-direction) of the multilayer optical film. In some embodiments, the first wavelength is substantially equal to L3. In some embodiments, the multilayer optical film 200, 210 reflects at least 30%, or at least 40%, or at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90% of substantially normally incident light 20 having a second wavelength (e.g., wavelength 21) within about 100 nm of L3 and polarized along an in-plane first direction of the multilayer optical film. The second wavelength may be, for example, within about 90 nm, or within about 80 nm, or within about 70 nm, or within about 60 nm, or within about 50 nm, or within about 40 nm, or within about 30 nm, or within about 20 nm, or within about 10 nm of L3.

[0046] 7A-7C are plots of optical transmittance versus wavelength for substantially normally incident light 20 on the optical film 200, 210 according to some embodiments. Tp0 and Ts0 indicate the optical transmittance for substantially normally incident light polarized along orthogonal in-plane first and second directions (e.g., x and y directions). The optical film 200, 210 may have substantially similar optical transmittances Tp0 and Ts0 for each of the polarization states. For example, the optical film can be an optical mirror. In some embodiments, the optical film 200 is a reflective polarizer having an optical transmittance Tp0 for substantially normally incident light polarized along the in-plane first direction, for example, and a high optical transmittance (e.g., greater than about 60%) over a wavelength range of about 450 nm to about 800 nm for substantially normally incident light polarized along the second direction. The optical transmittance 177 of the reflective polarizer for substantially normally incident light polarized along the second direction is shown diagrammatically. Abs0 is the optical absorptance for substantially normally incident light. In some embodiments, the optical film 200, 210 and / or the plurality of polymer layers 10, 11 transmits at least 30%, or at least 40%, or at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90% of the substantially normally incident light 20 having a first wavelength (e.g., 41 and / or 42 and / or 63) and polarized along an in-plane first direction (e.g., x-direction) of the polymer layers. In some such embodiments, or in other embodiments, the optical film 200, 210 reflects at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90% of the substantially normally incident light 20 having a second wavelength (e.g., 21 as shown in FIG. 7B and / or 60 and / or 61 as shown in FIG. 3B) and polarized along an in-plane first direction. The second wavelength can be within about 100 nm, or within about 90 nm, or within about 80 nm, or within about 70 nm, or within about 60 nm, or within about 50 nm, or within about 40 nm, or within about 30 nm, or within about 20 nm, or within about 10 nm of the first wavelength.For example, the absolute value of the difference between the first and second wavelengths can be in the range of about 5 nm to about 40 nm or up to about 30 nm. The optical film may reflect at least 50%, or 60%, or 70%, or 80%, or 90% of the substantially normally incident light 20 having the second wavelength and polarized along an in-plane second direction orthogonal to the first direction, or the optical film may transmit at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90% of the substantially normally incident light 20 having the second wavelength and polarized along an in-plane second direction orthogonal to the first direction. The optical reflectance R1 of the optical film 200, 210 can be expressed as 100% minus the optical transmittance minus the optical absorbance. The optical films 200, 210 can have an optical reflectance of approximately 100% minus the optical transmittance when optical absorption is negligible (see, for example, FIG. 7A). The Ts0, Tp0 curves in FIG. 7A-7C and the Abs0 curve in FIG. 7A were calculated using standard optical modeling techniques for alternating PEN and PMMA layers having the layer thickness profile shown in FIG. 4A-4C, where the cavity layer 13 was a PEN layer.

[0047] In some embodiments, the resonant cavity 40 (see, e.g., FIG. 1A) resonates at at least one resonant wavelength (e.g., wavelengths 41, 42 shown in FIGS. 7B-7C or wavelength 63 shown in FIG. 3B). In some embodiments, the at least one resonant wavelength comprises a first wavelength (e.g., wavelengths 41, 42), and the multilayer optical film 200, 210 has an optical reflectivity of greater than about 50%, or greater than about 60%, or greater than about 70%, or greater than about 80%, or greater than about 90% for at least a second wavelength (e.g., wavelength 21) within about 100 nm of the first wavelength. The second wavelength can be, for example, within about 50 nm of the first wavelength, or within another range described elsewhere herein.

[0048] In some embodiments, the multilayer optical film 200, 210 includes a first plurality of first polymer layers 10 alternating with a second plurality of second polymer layers 11. Layer 13 can be, for example, one of the first polymer layers 10 or one of the polymer layers 11. In a given wavelength range of about 50 to about 150 nm wide (e.g., wavelength range 45 shown in FIG. 7B), the difference between the average refractive index of the first polymer layer and the average refractive index of the second polymer layer along the in-plane first direction (x-direction) of the multilayer optical film is sufficiently large (e.g., greater than about 0.05 or within a range described elsewhere herein), and the thickness of the first polymer layer and the thickness of the second polymer layer vary over at least a portion of the thickness of the multilayer optical film (e.g., as shown in FIGS. 4A-4B, 11A-11D, and 13A-13B), such that the multilayer optical film has an average optical reflectance of at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 85%, for substantially normally incident light 20 polarized along the in-plane first direction in the given wavelength range. The average optical reflectance Ra for wavelength range 45 is shown diagrammatically in FIG. 7B. For the optical transmittance Tp0 shown in Figures 7A-7C, the average optical reflectance Ra in the wavelength range of 590 nm to 660 nm is 88.4%. In some embodiments, the predetermined wavelength range is, for example, about 50 nm to about 100 nm wide, or about 50 nm to about 75 nm wide. In some embodiments, in at least one group of three adjacent and consecutively arranged polymer layers (e.g., layers 12-14) in the plurality of first polymer layers and the plurality of second polymer layers, the three polymer layers have respective average thicknesses d1, d2, and d3, where d2 can be related to d1 and d3 as described elsewhere herein. For example, d2 can be within about 40% of m(d1+d3), where m is a positive integer. As another example, n2d2 can be within about 40% of m(n1d1+n1d3), where m is a positive integer.

[0049] The optical film may be configured to have a desired substantial transmittance in a narrow wavelength range(s) and a desired substantial reflectance in a wavelength range adjacent to the high transmittance range(s). For example, the peak transmittance can be adjusted by adjusting the thickness of the spacer layer and / or the width of the transmittance range can be adjusted by including two or more sufficiently close spacer layers, as described in more detail elsewhere herein. The substantial transmittance, substantial reflectance, and width of the narrow wavelength range(s) may be selected as desired for a particular application. For example, the optical film may have a desired transmittance (e.g., greater than about 60%) for a first wavelength and a desired reflectance (e.g., greater than about 60%) for a second wavelength that is close to the first wavelength (e.g., within about 30 nm).

[0050] In some embodiments, for substantially normally incident light polarized along an in-plane first direction (e.g., the x-direction), the multilayer optical film 200, 210 reflects at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95% of the incident light for at least a first wavelength (e.g., wavelength 21) within a predetermined wavelength range. In some embodiments, for substantially normally incident light polarized along an in-plane second direction (e.g., the y-direction) orthogonal to the first direction, the multilayer optical film has an optical reflectivity of at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95% for at least the first wavelength. In some embodiments, for substantially normally incident light polarized along an in-plane second direction (e.g., the y-direction) orthogonal to the first direction, the multilayer optical film has an optical transmittance of at least 60%, or at least 70%, or at least 80%, or at least 90% for at least the first wavelength. In some embodiments, for substantially normally incident light 20 polarized along a first direction (e.g., the x-direction) in the plane of the multilayer optical film 200, 210, the multilayer optical film has an optical transmittance of at least 30% for a first wavelength (e.g., wavelengths 41 and 42 shown in Figures 7B-7C) and an optical reflectance of at least 50% for a second wavelength (e.g., wavelength 21 shown in Figure 7B), which can be within about 100 nm of the first wavelength, or any other range described elsewhere herein. In some embodiments, the optical transmittance is at least 40%, or 50%, or 60%, or 70%, or 80%, or 90% for the first wavelength. In some such embodiments, or in other embodiments, the optical reflectance is at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90% for the second wavelength. In some embodiments, for substantially normally incident light polarized along an in-plane first direction, the multilayer optical films 200, 210 have an optical transmittance of at least 70% for a first wavelength and an optical reflectance of at least 80% for a second wavelength, where the second wavelength is, for example, within about 30 nm of the first wavelength.

[0051] The wavelength at which the transmission peaks can be tuned by selecting the location of the layer 13 within the optical film. Figures 8A-8C are plots of layer thickness versus layer number for various optical films, according to some embodiments. In some embodiments, the polymer layers within the plurality of polymer layers are arranged consecutively along the thickness direction (z-direction) of the multilayer optical film 200 and are numbered 1-N. In some embodiments, the sequence number of the (e.g., second polymer) layer 13 is closer to 1 than to N, as shown in Figure 8A. In some embodiments, the sequence number of the (e.g., second polymer) layer 13 is closer to N / 2 than to either 1 or N, as shown in Figure 8B. In some embodiments, the sequence number of the (e.g., second polymer) layer 13 is closer to N than to 1, as shown in Figure 8C.

[0052] 9A-9C are plots of optical transmission versus wavelength for substantially normally incident light 20 for films having the layer thickness profiles of FIGS. 8A-8C, respectively, according to some embodiments. The plots can be for incident light 20 that can be polarized along an in-plane first direction. In some embodiments, the optical transmission versus wavelength is substantially similar for incident light 20 polarized along an orthogonal in-plane second direction (e.g., the optical film can be an optical mirror). In other embodiments, for incident light 20 polarized along the second direction, the optical transmission is greater than about 60%, or 70%, or 80%, or 90% over the illustrated wavelength range (e.g., the optical film can be a reflective polarizer). The optical transmissions in FIGS. 9A-9C were calculated using standard optical modeling techniques for alternating PET and coPMMA layers having the layer thickness profiles shown in FIGS. 8A-8C, where the cavity layer 13 was a coPMMA layer.

[0053] The thickness of layer 13 can be adjusted to provide a maximum peak transmittance. For example, in some embodiments, changing the thickness S of layer 13 (e.g., cavity layer) reduces the peak transmittance (e.g., corresponding to T shown in FIG. 3B). FIG. 10 is a plot of optical transmittance versus wavelength for substantially normally incident light 20 for films having layers 13 of different thicknesses, according to some embodiments. Changing the thickness from 203.4 nm to 178 nm or 228.8 nm reduces the peak transmittance. An optical film having the transmittance of FIG. 10 can be, for example, an optical mirror or a reflective polarizer for light polarized along the block axis, as further described elsewhere herein. The optical transmittance of FIG. 10 was calculated using standard optical modeling techniques for alternating high and low index layers with isotropic refractive indices of 1.65 and 1.5, respectively, and with a layer thickness profile similar to that of FIG. 8B. The refractive indices correspond approximately to those of OKP-1, PENG, or PHEN for the high index layers, and PMMA or coPMMA for the low index layers, at about 633 nm.

[0054] In some embodiments, the multilayer optical film 200, 210 includes a plurality of layers 13, each of which causes the multilayer optical film to have a different peak optical transmittance of more than about 40%, or more than about 50%, or more than about 60%, or more than about 70%, or more than about 80%, or more than about 90%. For example, the different local peak optical transmittances can be at different wavelengths, and adjacent wavelengths corresponding to adjacent local peak transmittances are spaced apart by at least about 10 nm, or at least about 20 nm, or at least about 30 nm, or at least about 40 nm. The adjacent wavelengths can be spaced apart by, for example, at most about 500 nm, or at most about 300 nm, or at most about 200 nm. Each of the layers 13 causes the optical film to have, for example, a peak transmittance of more than 40%, meaning that if the layer 13 is omitted, the film would not have a peak transmittance of more than 40%. For example, the peak transmittance can be located within the reflection band of the optical film such that if layer 13 were omitted, the transmittance at the wavelength corresponding to the local peak would be, for example, less than 30%, or less than 20%, or less than 10%, or less than 5%.

[0055] 11A-11D are plots of layer thickness versus layer number for an optical film including three spaced apart spacer or cavity layers 13a, 13b, and 13c, according to some embodiments. FIG. 12 is a plot of optical transmission versus wavelength for substantially normally incident light for an optical film having the layer thickness profile of FIGS. 11A-11D, according to some embodiments. The substantially normally incident light can be polarized along an in-plane first direction (e.g., for a mirror film, or for a reflective polarizer where the first direction is the block direction of the reflective polarizer) or unpolarized (e.g., for a mirror film). The optical transmission in FIG. 12 was calculated using standard optical modeling techniques for alternating PET and coPMMA layers having the layer thickness profile shown in FIGS. 11A-11D, where the cavity layer 13 was a PET layer.

[0056] In some embodiments, the multilayer optical film 200, 210 includes a plurality of first layers 10, 11 and a plurality of second layers 13a, 13b, 13c, each of the first and second layers having an average thickness of less than about 500 nm or in the ranges described elsewhere herein. In some embodiments, for each of the second layers, the second layer is disposed between and adjacent to two of the first layers (10a, 10b, or 10c) and has an average thickness greater than the average thickness of each of the two first layers, and the second layer causes the multilayer optical film to have a different local peak optical transmittance (Ta, Tb, Tc) of greater than about 40% or within the ranges described elsewhere herein. In some embodiments, for each of the second layers, the local peak optical transmittance is at a wavelength within about 30 nm, or within about 20 nm, or within about 10 nm, or within about 5 nm of twice the optical thickness of the second layer. In some embodiments, for each of the second layers, the local peak optical transmittance is at a wavelength substantially equal to twice the optical thickness of the second layer. In some embodiments, the different local peak optical transmittances are at different wavelengths, and the multilayer optical film 200, 210 has an optical reflectance of greater than about 50%, or greater than about 60%, or greater than about 70%, or greater than about 80%, or greater than about 90% for at least one wavelength within about 100 nm of at least one of the different wavelengths. The at least one wavelength can be within about 90 nm, or within about 80 nm, or within about 70 nm, or within about 60 nm, or within about 50 nm, or within about 40 nm, or within about 30 nm, or within about 20 nm, or within about 10 nm of at least one of the different wavelengths.

[0057] In some embodiments, the multilayer optical film 200, 210 includes multiple layers 13 that are sufficiently close to one another such that the layers 13 collectively cause the multilayer optical film to have a peak optical transmittance of, for example, greater than about 60%, or within another range described elsewhere herein. Multiple layers 13 can result in a broader transmission band within the reflection band, for example, as compared to including only one of the layers 13.

[0058] 13A-13B are plots of layer thickness versus layer number for an optical film having four adjacent spacer or cavity layers 13a-13d, according to some embodiments. FIG. 14 is a plot of optical transmittance versus wavelength for substantially normally incident light for an optical film having the layer thickness profile of FIGS. 13A-13B, according to some embodiments. The substantially normally incident light may or may not be polarized along an in-plane first direction. The optical transmittance in FIG. 14 was calculated using standard optical modeling techniques for alternating PET and coPMMA layers having the layer thickness profile shown in FIGS. 13A-13B, where the cavity layer 13 was a coPMMA layer.

[0059] In some embodiments, the multilayer optical film 200, 210 includes a plurality of first layers 10, 11 and a plurality of second layers (13a-13d) arranged and numbered consecutively along the thickness direction (z-direction) of the optical film, with each of the second layers being disposed between and adjacent to two of the first layers (10a-10d). Each of the first and second layers has an average thickness of less than about 500 nm or within another range described elsewhere herein. In some embodiments, the second layers are sufficiently close to each other in the layer sequence that in combination cause the multilayer optical film to have a peak optical transmittance TT of, for example, greater than about 40%, or greater than about 50%, or greater than about 60%, or greater than about 70%, or greater than about 80%, or greater than about 90%. In some embodiments, the plurality of second layers includes a layer (e.g., 10d) having the greatest optical thickness and a layer (e.g., 10a) having the smallest optical thickness. The peak optical transmittance can be at a wavelength between S1 times the smallest optical thickness and S2 times the largest optical thickness, where S1 can be 1.9 and S2 can be 2.1. In some embodiments, S1 is 1.9, or 1.95, or 1.98, or 1.99, or 2. In some such embodiments, or in other embodiments, S2 is 2.1, or 2.05, or 2.02, or 2.01, or 2. In some such embodiments, or in other embodiments, the peak optical transmittance is at a first wavelength, and the multilayer optical film 200, 210 has an optical reflectance of greater than about 50%, or greater than about 60%, or greater than about 70%, or greater than about 80%, or greater than about 90% for at least one second wavelength within about 100 nm of the first wavelength. The second wavelength can be, for example, within about 90 nm, or within about 80 nm, or within about 70 nm, or within about 60 nm, or within about 50 nm, or within about 40 nm, or within about 30 nm, or within about 20 nm of the first wavelength.

[0060] Terms such as "about" will be understood by those of skill in the art in the context in which they are used and described herein. Unless otherwise clear to one of skill in the art in the context in which they are used and described herein, the use of "about" as applied to quantities describing feature sizes, amounts, and physical properties will be understood to mean within 10 percent of a particular value. A quantity given as about a particular value may be exactly that particular value. For example, unless otherwise clear to one of skill in the art in the context in which they are used and described herein, a quantity having a value of about 1 means that the quantity has a value between 0.9 and 1.1, and may even be 1.

[0061] Terms such as "substantially equal" are understood by those of skill in the art in the context in which they are used and described herein. In the context in which they are used and described herein, where the use of "substantially equal" as applied to a first quantity and a second quantity describing the size, amount, and physical properties of a feature is not clear to one of skill in the art, "substantially equal" is understood to mean that the first quantity is within 5 percent of the second quantity. Quantities referred to as substantially equal may be exactly equal. For example, a first quantity substantially equal to a second quantity means that the first quantity has a value between 0.95 and 1.05 times the value of the second quantity, and that the values ​​may be equal, in the context in which they are used and described herein, where the use of "substantially equal" as applied to a first quantity and a second quantity describing the size, amount, and physical properties of a feature is not clear to one of skill in the art.

[0062] All references, patents, or patent applications referenced above are hereby incorporated by reference in their entirety. In the event of any inconsistency or contradiction between any of the incorporated references and this application, the information in the foregoing description shall prevail.

[0063] Descriptions of elements in the drawings should be understood to apply equally to corresponding elements in other drawings unless otherwise indicated. Although specific embodiments have been illustrated and described herein, those skilled in the art will appreciate that the specific embodiments illustrated and described may be replaced by various alternative and / or equivalent embodiments without departing from the scope of the present disclosure. The present application is intended to cover any adaptations, or variations, or combinations of the specific embodiments discussed herein. Accordingly, the present disclosure is intended to be limited only by the claims and the equivalents thereof.

Claims

1. 1. A multilayer optical film comprising a plurality of polymer layers that transmit at least 30% of substantially normally incident light having a first wavelength and polarized along a first direction in the plane of the polymer layers, each of the polymer layers having an average thickness of less than about 500 nm, first, second and third polymer layers in the plurality of polymer layers being disposed contiguously adjacent one another and having respective refractive indices n1, n2 and n3 at the first wavelength along the first direction and respective average thicknesses d1, d2 and d3, where n2d2 is within about 40% of m(n1d1+n3d3), where m is a positive integer.

2. 10. The multilayer optical film of claim 1 , which reflects at least 50% of the substantially normally incident light having a second wavelength and polarized along the in-plane first direction, the second wavelength being within about 100 nm of the first wavelength.

3. 1. A multilayer optical film comprising a first plurality of first polymer layers alternating with a second plurality of second polymer layers, wherein, over a predetermined wavelength range from about 50 nm to about 150 nm wide, a difference between an average refractive index of the first polymer layer and an average refractive index of the second polymer layer along an in-plane first direction of the multilayer optical film is sufficiently large, and a thickness of the first polymer layer and a thickness of the second polymer layer vary over at least a portion of a thickness of the multilayer optical film, the multilayer optical film having an average optical reflectance of at least 50% over the predetermined wavelength range for substantially normally incident light polarized along the in-plane first direction, and wherein, in at least one group of three adjacent contiguously arranged polymer layers within the plurality of first polymer layers and the plurality of second polymer layers, the three polymer layers have respective average thicknesses d1, d2 and d3, wherein d2 is within about 40% of m(d1+d3), and m is a positive integer.

4. The multilayer optical film of claim 3 , wherein d2 is less than about 400 nm.

5. 1. A multilayer optical film comprising a plurality of optical repeat units (ORUs) totaling at least 10, each of the ORUs having at least two polymer layers, each of the ORUs having an optical thickness substantially equal to half of a wavelength within a predetermined wavelength range spanning from about 300 nm to about 2500 nm, at least a first ORU and a second ORU in the plurality of ORUs having an optical thickness substantially equal to half of respective wavelengths L1 and L2 that are within 100 nm of each other, the first ORU and the second ORU having a single, polymeric, first layer disposed therebetween, the first layer having an optical thickness substantially equal to half of a wavelength L3 disposed between L1 and L2.

6. A multilayer optical film comprising a plurality of polymeric first layers and one or more polymeric second layers, wherein each of the first and second layers has an average thickness of less than about 400 nm, and for each of the second layers, the second layer has an average thickness d2 and is disposed between and adjacent to two of the first layers having the maximum thickness d1, and d2≧1.3d1.

7. 1. An optical film comprising a spacer layer disposed between a first optical mirror and a second optical mirror, for substantially normally incident light polarized along a first direction in the same plane of the optical film, for a first wavelength and a second wavelength spaced apart by about 2 nm to about 100 nm, and a third wavelength disposed between the first wavelength and the second wavelength: the first optical mirror and the second optical mirror have respective optical transmittances T1 and T2 at the first wavelength, respective optical transmittances T1' and T2' at the second wavelength, and respective optical transmittances T1" and T2" at the third wavelength, where T2>2T1 and T1'>2T2'; the optical film has an optical transmittance T at the third wavelength, T>T1″ and T2″; Optical film.

8. 1. An optical film comprising a plurality of first layers disposed on a plurality of second layers, wherein for substantially normally incident light polarized along a same in-plane first direction, the optical transmittance versus wavelength of each of the plurality of first layers and the plurality of second layers comprises a transmission stop band, the transmission stop band including a left band edge (LBE) on a short wavelength side of the transmission stop band, where the transmittance generally decreases with increasing wavelength, and a right band edge (RBE) on a long wavelength side of the transmission stop band, where the transmittance generally increases with increasing wavelength, the transmission stop band being at least 20 nm wide, and the average transmittance across the transmission stop band being less than about 10%; An optical film, wherein the RBE of the plurality of first layers intersects with the LBE of the plurality of second layers by about 5% to about 50% at least at a first transmission intersection.

9. 1. A multilayer optical film comprising a plurality of optical repeating units (ORUs) arranged consecutively along a thickness direction of the optical film and a single void layer, the single void layer being arranged between a first ORU and a second ORU in the plurality of ORUs, a total of at least 30 ORUs, each of the ORUs having at least two layers, each of the at least two layers having an average thickness of less than about 500 nm, the ORUs being consecutively numbered along the thickness direction, and the consecutively numbered ORUs as a function of corresponding number in a sequence includes a monotonic first portion, the monotonic first portion extending through at least 10 of the ORUs and including the first ORU and a second ORU, such that a best linear fit applied to the ORUs in the monotonic first portion of the sequence has an optical thickness M1 at the sequence number corresponding to the first ORU, and the absolute value of the difference between M1 and the optical thickness of the single cavity layer is less than about 10%.

10. 1. A multilayer optical film including a resonant cavity resonating at at least one resonant wavelength, the resonant cavity being formed by disposing a polymer cavity layer between a multilayer, polymeric first optical mirror and a polymeric second optical mirror, each of the first optical mirror and the second optical mirror comprising a plurality of polymer layers totaling at least 10, each of the polymer layers having an average thickness of less than about 500 nm, each of the first optical mirror and the second optical mirror having an optical reflectivity of at least 25% for light substantially normally incident at the at least one resonant wavelength, the first optical mirror and the second optical mirror reflect a portion of the incident light in substantially the same direction as respective first and second reflected lights, for light incident substantially normally incident on the multilayer optical film at the at least one resonant wavelength, and the first and second reflected lights destructively interfere with each other outside the resonant cavity.

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