Optical film

Abstract

An optical film includes a plurality of optical repeat units where each optical repeat unit includes at least two different polymeric layers. The optical repeat units can have an f-ratio that varies along a thickness direction of the optical film to allow independent selection of bandwidths of primary and higher order reflection bands. A ratio of band edge wavelengths of a primary reflection band can be greater than a corresponding ratio of band edge wavelengths of an nth-order reflection band, where n is an integer greater than 1, by at least about 7%. A band edge wavelength of an nth-order reflection can differ from a corresponding band edge wavelength of a primary reflection band divided by n by at least about 12% of a width of the nth-order reflection band.

Description

[0001] OPTICAL FILM

[0002] TECHNICAL FIELD

[0003] The present description relates generally to optical films, and more specifically to multilayer optical films including a plurality of optical repeat units.

[0004] BACKGROUND

[0005] A multilayer optical film can include a plurality of polymeric layers arranged into optical repeat units. The multilayer optical film can be a reflective polarizer or an optical mirror.

[0006] SUMMARY

[0007] In some aspects, the present description provides an optical film including a plurality of optical repeat units where each optical repeat unit includes at least two different polymeric layers. The optical repeat units can have f-ratios (and / or layer thicknesses and / or thickness ratios) that vary along a thickness direction of the optical film to allow independent selection of bandwidths of primary and higher order reflection bands. A higher order reflection band is an nth-order reflection band where n is an integer greater than 1. A ratio of band edge wavelengths of a primary reflection band can be greater than a corresponding ratio of band edge wavelengths of an nth-order reflection band by at least about 5, 6, 7, 8, 9, 10, 11, or 12%. A band edge wavelength of an nth-order reflection band can differ from a corresponding band edge wavelength of a primary reflection band divided by n by at least about 10, 12, 15, 20, 25, or 30% of a width of the nth-order reflection band.

[0008] In some aspects, the present description provides an optical film including a plurality of optical repeat units numbering at least 10 in total, where each optical repeat unit includes at least two different polymeric layers and can have an average total thickness less than about 1500 nm, such that for a substantially normally incident light incident on the optical film and for at least one polarization state, the optical film has: a primary reflection band extending between first and second band edges; and an nth- order reflection band extending between third and fourth band edges where n is an integer greater than 1. The optical film has a reflectance generally increasing from less than about 30% to greater than about 70% with increasing wavelength along the first band edge. The reflectance generally decreases from greater than about 70% to less than about 30% with increasing wavelength along the second band edge. The first and second band edges have respective first and second band edge wavelengths where the reflectance is about 50% of a maximum reflectance of the primary reflection band. The second band edge wavelength can be greater than the first band edge wavelength by at least about 50 nm. The reflectance of the optical film generally increases from less than about 30% to greater than about 70% with increasing wavelength along the third band edge. The reflectance of the optical film generally decreases from greater than about 70% to less than about 30% with increasing wavelength along the fourth band edge. The third and fourth band edges have respective third and fourth band edge wavelengths where the reflectance is about 50% of a maximum reflectance of the nth-order reflection band. In some embodiments, a ratio of the second to the first band edge wavelengths is greater than a ratio of the fourth to the third band edge wavelengths by at least about 7%. In some such embodiments, or in other embodiments, at least one of the third or fourth band edge wavelengths differ from the respective first and second band edge wavelengths divided by n by at least about 12% of a difference between the fourth and third band edge wavelengths.

[0009] In some aspects, the present description provides an optical film including a plurality of contiguous optical repeat units numbering at least 10 in total, where each optical repeat unit includes at least different polymeric first and second layers and can have an average total thickness of less than about 1500 nm. The first and second layers have respective higher and lower average in-plane refractive indices for at least a first wavelength in a range of about 450 nm to about 1500 nm. For at least one in-plane direction and for at least the first wavelength: for each of the optical repeat units, an optical thickness of the first layer of the optical repeat unit divided by a total optical thickness of the optical repeat unit defines an f-ratio of the optical repeat unit. The plurality of contiguous optical repeat units includes first and second sub-pluralities of the optical repeat units, where the first and second sub-pluralities are stacked on one another along a thickness direction of the optical film. Each of the first and second subpluralities include at least 5 of the optical repeat units. The f-ratio can be substantially constant first and second ratios in the respective first and second sub-pluralities. An absolute value of a difference between the first and second ratios is at least about 0.05.

[0010] In some aspects, the present description provides an optical film including a plurality of optical repeat units numbering at least 15 in total, where each optical repeat unit includes at least different polymeric first and second layers and can have an average total thickness of less than about 1500 nm. The first and second layers have respective higher and lower average in-plane refractive indices for at least a first wavelength in a range of about 450 nm to about 1500 nm. For at least one in-plane direction and for at least the first wavelength: for each of the optical repeat units, an optical thickness of the first layer of the optical repeat unit divided by a total optical thickness of the optical repeat unit defines an f-ratio of the optical repeat unit. The plurality of optical repeat units include first, second, and third sub-pluralities of the optical repeat units, where the first, second, and third sub-pluralities are stacked on one another in sequence along a thickness direction of the optical film. Each of the first, second, and third sub-pluralities can include at least 5 of the optical repeat units. The f-ratio can be substantially constant first and second ratios in the respective first and third sub-pluralities. An absolute value of a difference between the first and second ratios is at least about 0.05. The f-ratio of the optical repeat units in the second sub-plurality can vary substantially continuously along the thickness direction of the optical film between the first and second ratios.

[0011] In some aspects, the present description provides an optical film including a plurality of optical repeat units numbering at least 15 in total, where each optical repeat unit includes at least two different polymeric layers and can have an average total thickness less than about 1500 nm. For each of the optical repeat units, an average thickness of a same one of the at least two different polymeric layers of the optical repeat unit divided by the average total thickness of the optical repeat unit defines a thickness ratio of the optical repeat unit. The plurality of optical repeat units includes first, second, and third subpluralities of the optical repeat units, where the first, second, and third sub-pluralities are stacked on one another in sequence along a thickness direction of the optical film. Each of the first, second, and third sub-pluralities can include at least 5 of the optical repeat units. The thickness ratio can be substantially constant first and second ratios in the respective first and third sub-pluralities. An absolute value of a difference between the first and second ratios is at least about 0.05. The thickness ratio of the optical repeat units in the second sub-plurality can vary substantially continuously along the thickness direction of the optical film between the first and second ratios.

[0012] In some aspects, the present description provides an optical film including a plurality of contiguous optical repeat units numbering at least 10 in total, where each optical repeat unit includes at least two different polymeric layers and can have an average total thickness of less than about 1500 nm. For each of the optical repeat units, an average thickness of a same one of the at least two different polymeric layers of the optical repeat unit divided by an average total thickness of the optical repeat unit defines a thickness ratio of the optical repeat unit. The plurality of contiguous optical repeat units includes first and second sub-pluralities of the optical repeat units, where the first and second subpluralities are stacked on one another along a thickness direction of the optical film. Each of the first and second sub-pluralities include at least 5 of the optical repeat units. The thickness ratio can be substantially constant first and second ratios in the respective first and second sub-pluralities. An absolute value of a difference between the first and second ratios is least about 0.05.

[0013] In some aspects, the present description provides an optical film including a plurality of optical repeat units (ORUs) coextruded and co-stretched with one another. The plurality of ORUs include opposing first and second endmost ORUs farthest from each other among the ORUs. The plurality of ORUs include first and second interior ORUs spaced apart from one another along a thickness direction of the optical film by no more than about 50 other ORUs in the plurality of ORUs. Each of the first and second interior ORUs can be spaced apart from each of the first and second endmost ORUs by at least 10 other ORUs in the plurality of ORUs. Each ORU includes at least different polymeric first and second layers and can have an average total thickness of less than about 1500 nm. The first and second layers have respective higher and lower average in-plane refractive indices for at least a first wavelength in a range of about 450 nm to about 1500 nm. The first and second layers of the first interior ORU have respective lesser and greater average layer thicknesses. The first and second layers of the second interior ORU have respective greater and lesser average layer thicknesses. The first and second interior ORUs have average total thicknesses differing by less than about 0.4 times an absolute value of a difference between the average layer thickness of the first layer of the first ORU and the average layer thickness of the first layer of the second ORU. In some aspects, the present description provides an optical film including a plurality of optical repeat units (ORUs) coextruded and co-stretched with one another and including opposing first and second endmost ORUs farthest from each other among the ORUs. The ORUs are sequentially numbered from the first endmost ORU to the second endmost ORU. The plurality of ORUs include first and second interior ORUs having respective first and second ORU numbers and spaced apart from one another along a thickness direction of the optical film by at least 5 and no more than about 50 other ORUs in the sequentially numbered ORUs. Each of the first and second interior ORUs can be spaced apart from each of the first and second endmost ORUs by at least 10 other ORUs in the plurality of ORUs. Each ORU includes at least two different polymeric layers and can have an average total thickness of less than about 1500 nm. At least a same one of the at least two different polymeric layers has an average layer thickness that varies non-monotonically with ORU number from the first to the second ORU number. The average total thickness of the ORUs varies monotonically with ORU number from the first to the second ORU number such that for each pair of adjacent ORUs having sequential ORU numbers that are each in a range from the first to the second ORU number, the average total thicknesses of the ORUs in the pair differ by less than about 2 percent.

[0014] In some aspects, the present description provides an optical film including a plurality of optical repeat units (ORUs) coextruded and co-stretched with one another. The plurality of ORUs include opposing first and second endmost ORUs farthest from each other among the ORUs. The plurality of ORUs include first and second interior ORUs spaced apart from one another along a thickness direction of the optical film by no more than about 50 other ORUs in the plurality of ORUs. Each of the first and second interior ORUs can be spaced apart from each of the first and second endmost ORUs by at least 10 other ORUs in the plurality of ORUs. Each ORU includes at least two different polymeric layers and can have an average total thickness of less than about 1500 nm. At least a same one of the at least two different polymeric layers has an average layer thickness that differs between the first and second interior ORUs by at least about 10 percent. The first and second interior ORUs have average total thickness differing by less than about 7 percent.

[0015] These and other aspects will be apparent from the following detailed description. In no event, however, should this brief summary be construed to limit the claimable subject matter.

[0016] BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 is a schematic cross-section view of an optical film 300, according to some embodiments. FIG. 2 is a schematic plot of f-ratio or thickness ratio versus optical repeat unit number for an optical film, according to some embodiments.

[0018] FIGS. 3A-3B are schematic plots of thickness versus optical repeat unit number for various optical films schematically illustrating substantially continuous layer thickness variation, according to some embodiments. FIGS. 4A-4B are schematic plots of thickness versus optical repeat unit number for various optical films, according to some embodiments.

[0019] FIGS. 5-8 are plots of layer thickness versus layer number for various optical films, according to some embodiments.

[0020] FIG. 9 is a schematic plot of reflectance versus wavelength for substantially normally incident light incident on an optical film, according to some embodiments.

[0021] FIGS. 10-11 are plots of transmittance versus wavelength for normally incident light incident on optical films, according to some embodiments.

[0022] DETAILED DESCRIPTION

[0023] In the following description, reference is made to the accompanying drawings that 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 description. The following detailed description, therefore, is not to be taken in a limiting sense.

[0024] As is known in the art, multilayer optical films including a plurality of optical repeat units (e.g., alternating first and second polymeric layers) can be used to provide desired reflection and transmission in desired wavelength ranges by suitable selection of layer thicknesses and refractive index differences. Multilayer optical films and methods of making multilayer optical films are described in U.S. Pat. Nos. 5,882,774 (Jonza et al.); 6,783,349 (Neavin et al.); 6,949,212 (Merrill et al.); 6,967,778 (Wheatley et al.); 9,162,406 (Neavin et al.); and 11,493,677 (Haag et al.), for example. An optical repeat unit of a multilayer optical film is generally the smallest distinct unit of optical layers that repeats along a thickness direction of the optical film. An optical repeat unit generally includes at least two different layers (e.g., higher index first and lower index second layers) and may optionally include additional layers as described in U.S. Pat. Nos. 5,103,337 (Schrenk et al.); 5,360,659 (Arends et al.); 5,540,978 (Schrenk); and 6,207,260 (Wheatley et al.), for example.

[0025] An optical repeat unit generally results in a first order (or primary) reflection of normally incident light at a wavelength of twice the optical thickness of the optical repeat unit while higher order harmonics (e.g., nth-order reflection) correspond to reflection at wavelengths 1 / n times this wavelength for integer n > 1. For example, a first-order reflection at a wavelength of 1000 nm could lead to a second-order reflection at a wavelength of 500 nm. The f-ratio (ratio of optical thickness of a same layer - typically the high index layer - of the optical repeat unit to a total optical thickness of the optical repeat unit), or multiple f-ratios in the case of optical repeat units that include 3 or more layers, can be chosen to suppress or enhance the nth-order reflection as generally described in U.S. Pat. Nos. 5,103,337 (Schrenk et al.); 5,360,659 (Arends et al.); 5,540,978 (Schrenk); 6,207,260 (Wheatley et al.); 9,562,996 (Kivel et al.); and 9,823,395 (Weber et al.), for example. Conventionally, for multilayer optical films that have distinct primary and nth-order reflection bands, the band edges of the n-th order band are given by about 1 / n times the band edges of the primary reflection band so that the block factor (ratio of band edge wavelengths) for the primary and nth-order bands are the same. However, for some applications it can be desired to adjust the block factor of the nth-order band independently of the block factor of the primary band, or more generally, for some applications, it can be desired to independently adjust the position of the band edges of the nth-order band and the primary band.

[0026] According to some embodiments of the present description, it has been found that the block factor, and / or the band edge wavelengths, of the nth-order band can be adjusted independently of the block factor and band edge wavelengths of the primary reflection band. It has been found, according to some embodiments, that the f-ratio can vary within a stack (or packet) of optical repeat units so that the stack produces a first order or primary reflection band resulting from the combined first-order reflection of each of the optical repeat units but only a portion of the optical repeat units in the stack substantially contribute to a given nth-order reflection band. For example, optical repeat units with an f-ratio of about i will contribute to the primary reflection band and a third order reflection band but will not substantially contribute to second and fourth order reflection bands, while optical repeat units with an f-ratio of about 2 / 3 will contribute to the first, second and fourth order reflection bands but will not substantially contribute to the third order reflection band. Since only a portion of the optical repeat units contribute to a given nth-order reflection band, the bandwidth of the nth-order reflection band can be adjusted by changing the portion of the optical repeat units that contribute to nth-order reflection band while each of the optical repeat units contributes to the primary reflection band. Useful layer thickness profiles for achieving desired nth-order reflection bands can include a substantially greater and / or non-monotonic variation in the thickness of a same layer of optical repeat units and a substantially lesser and / or monotonic variation of the total optical repeat unit thickness, according to some embodiments. Other useful thickness variations, thickness ratio variations, and f-ratio variations are described further elsewhere herein.

[0027] FIG. 1 is a schematic cross-section view of an optical film 300, according to some embodiments. The optical film 300 includes a plurality of optical repeat units 10. Each of the optical repeat units 10 can include at least two different polymeric layers 11, 12. In some embodiments, the optical film 300 includes a plurality of alternating polymeric first and second layers 11 and 12 arranged into the optical repeat units 10. The optical repeat units in the plurality of optical repeat units can number at least 10 in total. In some embodiments, the total number of the optical repeat units is at least 15, 20, 30, 40, 60, 80, 100, 120, 140, 160, 180, or 200, for example. In some embodiments, the total number of the optical repeat units is up to 1000, 800, 600, 400, 300, or 250, for example. In some embodiments, the total number of optical repeat units is in a range of 100 to 300, for example. Substantially normally incident (e.g., within about 25, 20, 15, 10, 8, or 5 degrees of normal incidence) light 100 and polarization states 101 and 102 are schematically illustrated. In some embodiments, the optical film 300 is a reflective polarizer substantially reflecting a first polarization state 101 in a predetermined wavelength range and substantially transmitting an orthogonal second polarization state 102. In some embodiments, the optical film 300 is an optical mirror substantially reflecting each of mutually orthogonal first and second polarization states 101 and 102 in a predetermined wavelength range.

[0028] In some embodiments, each optical repeat unit 10 has an average total thickness of less than about 1500, 1200, 1000, 900, 800, 700, 600, 550, 500, or 450 nm. The average total thickness of each optical repeat unit 10 can be greater than about 50, 100, 150, 200, 225, or 250 nm, for example. The total thickness of an optical repeat unit 10 is the combined thickness of all of the layers of the optical repeat unit 10. The average thickness of a layer or the average total thickness of an optical repeat unit 10 is the average of the thickness over the area of the layer or optical repeat unit 10. Average refers to unweighted mean unless indicated differently. In some embodiments, each layer 11, 12 of each optical repeat unit 10 has an average thickness less than about 500, 450, 400, 350, 300, 290, or 280 nm. The average thickness of each layer of each optical repeat unit 10 can be greater than about 20, 30, 40, 60, 80, 100, or 110 nm, for example. In some embodiments, the average total thicknesses of the optical repeat units 10 increase substantially continuously from a first major side 301 of the optical film 300 to an opposite second major side 302 of the optical film 301. In some embodiments, for each adjacent pair (e.g., 10a, 10b or 10c, lOd) of the optical repeat units, the optical repeat units of the pair have average total thicknesses that differ by less than about 2, 1.75, 1.5, 1.4, 1.3, 1.2, 1.1, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, or 0.25 percent. Thickness refers to physical thickness unless optical thickness is specified. Optical thickness of a layer is the physical thickness of the layer multiplied by a refractive index of the layer. Optical repeat units in an adjacent pair of the optical repeat units should be understood to not be separated from one another by any other optical repeat unit (e.g., the optical repeat units in an adjacent pair can be contiguous with, or immediately adjacent to, one another), unless indicated otherwise.

[0029] The layers of the optical repeat units may be referred to as optical layers, interference layers, or microlayers. The optical film 300 can optionally include one or more other layers, one or more of which may be disposed between adjacent optical repeat units 10 and / or one or more of which may be disposed such that the plurality of optical repeat units 10 is on a same side of the other layer. For example, in some embodiments, the optical film 300 includes at least one macrolayer 124, 126, where each of the at least one macrolayer has an average thickness greater than about 500, 750, 1000, 1250, 1500, 2000, or 2500 nm. Each of the at least one macrolayer can have an average thickness up to about 20, 10, 6, 5, or 4 micrometers, for example. The at least one macrolayer can include outermost skin layers 124 and 126 and / or can optionally include one or more protective boundary layers as would be appreciated by those of ordinary skill in the art (e.g., layer 125 can be a macrolayer and / or can be a protective boundary layer). In some embodiments, the optical film 300 includes a single packet of the optical repeat units such that the optical repeat units are contiguous with one another (i.e., in some embodiments, no layer separates adjacent optical repeat units in the plurality of optical repeat units). In such embodiments, the layer 125 is omitted. In some embodiments, the plurality of optical repeat units 10 is a plurality of contiguous optical repeat units (so that each optical repeat unit is immediately adjacent at least one other optical repeat unit). In some embodiments, the optical film 300 includes first and second macrolayers 124 and 126, where each of the first and second macrolayers has an average thickness greater than about 500 nm (or in a ranged described elsewhere herein), and the plurality of contiguous optical repeat units 10 is disposed between, and coextruded and co-stretched with, the first and second macrolayers 124 and 126. In some embodiments, each layer of the optical film 300 disposed between the first and second macrolayers 124 and 126 is a layer of an optical repeat unit 10 in the plurality of contiguous optical repeat units and has an average thickness less than about 500 nm (or in a range described elsewhere herein). In some embodiments, all layers of the optical film 300 are coextruded and co-stretched with one another.

[0030] Suitable materials for the various layers of the optical film 300 include, for example, polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycarbonate, polymethylmethacrylate (PMMA), copolyesters, and blends or copolymers thereof. For example, PEN can be used as a high index and / or birefringent layer (e.g., first layer 11) and PMMA can be used as a low index and / or optically isotropic layer (e.g., second layer 12). As another example, PET can be used as a high index and / or birefringent layer (e.g., first layer 11) and coPMMA can be used as a low index and / or optically isotropic layer (e.g., second layer 12). Other suitable materials are described in the multilayer optical film references provided elsewhere herein.

[0031] In some embodiments, an optical film 300 includes a plurality of (e.g., contiguous) optical repeat units 10 where each optical repeat unit includes at least two different polymeric layers. In some embodiments, the at least two different polymeric layers of each optical repeat units 10 includes first and second layers 11 and 12. In some embodiments, an optical film 300 includes a plurality of (e.g., contiguous) optical repeat units 10 where each optical repeat unit includes at least different polymeric first and second layers 11 and 12. In some embodiments, each of the first layers 11 of the plurality of optical repeat units 10 has a same first composition and each of the second layers 12 of the plurality of optical repeat units 10 has a same second composition different from the first composition. In some embodiments, the first layers 11 are substantially birefringent (e.g., a birefringence greater than about 0.05, 0.07, 0.1, 0.15, or 0.2 for at least one wavelength in a range of about 450 nm to about 1500 nm; the birefringence can be up to about 0.4, 0.35, or 0.3, for example) and the second layers 12 are substantially optically isotropic (e.g., a birefringence less than about 0.04, 0.03, 0.02, 0.015, 0.01, or 0.008 for the at least one wavelength in the range of about 450 nm to about 1500 nm). In some embodiments, the first and second layers 11 and 12 have respective higher and lower average in-plane refractive indices for at least a first wavelength in a range of about 450 nm to about 1500 nm. In-plane refractive indices are indices along directions in the plane (x-y plane) of the optical film 300. The plane of the film can be understood to be a tangent plane in the case of a curved film. The average in-plane refractive index is the average over all directions, or over two principal directions, in the plane of the layer. In some embodiments, the average in-plane refractive index can be higher for the first layers 11 than the second layers 12 by at least about 0.05, 0.07, 0. 1, 0.15, or 0.2 for the at least one wavelength in the range of about 450 nm to about 1500 nm. The difference in the average in-plane refractive indices can be up to about 0.4, 0.35, or 0.3, for example. The at least one wavelength can be or include a wavelength of about 633 nm, for example. An optical repeat unit 10 of the optical film 300 can be characterized by an f-ratio and / or by a thickness ratio. The thickness ratio is generally the average thickness of a layer of the optical repeat unit divided by the average total thickness of the optical repeat unit. Since the optical repeat units are units of layers that repeat, the same or corresponding layers between different optical repeat units can be identified. So, when thickness ratios (or f-ratios) of different optical repeat units are compared, the same or corresponding layer is chosen for the numerator in the thickness ratio (or f-ratio). For example, the layers of each of the optical repeat units can be sequentially numbered from a same side of the optical repeat unit (e.g., numbering from a top side facing major side 301 in FIG. 1, layer 11 is a first layer and layer 12 is a second layer), so that the same or corresponding layer can be identified as the layer having the same number in the sequence. In some embodiments, the optical repeat units 10 are 2-layer optical repeat units that each include different first and second layers 11 and 12 so that the plurality of optical repeat units 10 is a plurality of alternating first and second layers 11 and 12. In this case, the same or corresponding layer of the different optical repeat units can be taken to be either first layer 11 or second layer 12. The layers of each of the optical repeat units typically include a layer with a highest in-plane refractive index for a specified wavelength (e.g., 633 nm) and this high index layer may be identified as the same or corresponding layer in the optical repeat units. Similarly, the f-ratio is generally the optical thickness of a layer of the optical repeat unit divided by the total optical thickness of the optical repeat unit. When f-ratios of different optical repeat units are compared, the same or corresponding layer is chosen for the numerator in the f-ratio. Conventionally, the high index layer is chosen for the same or corresponding layer for defining the f-ratio.

[0032] Since f-ratio is defined in terms of optical thicknesses and since optical thickness of a layer is a refractive index of the layer multiplied by the thickness of the layer, a wavelength and a direction in the layer may be specified to define the refractive index used for the optical thickness. For example, for a reflective polarizer, the direction is typically chosen to be an in-plane direction along a block axis of the reflective polarizer. For an optical mirror, the refractive indices may be substantially the same for each of two mutually orthogonal in-plane directions so either of these in-plane directions may be used for defining the refractive index used in the optical thicknesses. The direction in the layer may be specified by specifying a polarization state (e.g., polarization state 101 is along the x-direction). The wavelength used for specifying the refractive index can be, for example, any visible or near-infrared wavelength. One suitable wavelength is 633 nm, for example.

[0033] In some embodiments, each optical repeat unit of the plurality of optical repeat units 10 has an f- ratio of at least about 0.1, 0.2, 0.3, 0.4, 0.45, or 0.5. In some such embodiments, or in other embodiments, each optical repeat unit of the plurality of optical repeat units 10 has an f-ratio of no more than about 0.9, 0.85, 0.8, or 0.75. In some embodiments, each optical repeat unit of the plurality of optical repeat units 10 has a thickness ratio of at least about 0.1, 0.2, 0.3, 0.4, 0.45, or 0.5. In some such embodiments, or in other embodiments, each optical repeat unit of the plurality of optical repeat units 10 has a thickness ratio of no more than about 0.9, 0.85, 0.8, or 0.75. The optical layers or optical repeat units (ORUs) of an optical film may be sequentially numbered from a first major side 301 of the optical film to and opposite second major side 302 of the optical film or sequentially numbered from a first endmost ORU (e.g., the ORU 10 closest to the first major side 301 or ORU 23a schematically illustrated in FIG. 3) to a second endmost ORU (e.g., the ORU 10 closest to the second major side 302 or ORU 23b schematically illustrated in FIG. 3). Thicknesses, thickness ratios, and / or f-ratios may then be plotted versus layer number or ORU number.

[0034] FIG. 2 is a schematic plot of f-ratio or thickness ratio versus optical repeat unit (ORU) number for an optical film 300, according to some embodiments. Ratio 362 vs ORU number shows substantially constant ratios R1 and R2 in first and second portions 321 and 322 with a substantially continuous variation in the ratio in transition portion 331 between the first and second portions 321 and 322. The ratio 362 vs ORU number shows a substantially constant ratio (which can be about Rl) in a third portion 323 with a substantially continuous variation in the ratio in the transition portion 332. Ratio 361 vs ORU number shows substantially constant ratios in portions 321, 322 and 323 with discontinuous jumps therebetween. The portions 321, 331, 332, 332, and 323 correspond to different sub-pluralities of ORUs in the plurality of ORUs 10. The discontinuous jumps in the ratio 361 occur where sub-pluralities with different ratios are contiguous with one another. In some embodiments, each of the portions 321, 331, 332, 332, and 323 include at least 5 of the ORUs. In some embodiments, one or both of the portions 331 and 332 are omitted or include fewer than 5 of the ORUs. For example, in some embodiments, portions 331 and / or 332 can include 1, 2, 3, or 4 ORUs (e.g., with f-ratio or thickness ratio between Rl and R2).

[0035] FIGS. 3A-3B and 4A-4B are schematic plots of thickness versus optical repeat unit number for various optical films, according to some embodiments. Thicknesses of the first and second layers 11 and 12 and average 20 of the thickness of the layers 11, 12 of the ORUs are shown. In some embodiments, the optical repeat units 10, which can be coextruded and co-stretched with one another, include opposing first and second endmost ORUs 23a and 23b farthest from each other among the ORUs and include first and second interior ORUs 24a and 24b. In some embodiments, each of the first and second interior ORUs 24a and 24b is spaced apart from each of the first and second endmost ORUs 23a and 23b by at least 10, 15, 20, 25, 30, 35, 40, 45, or 50 other ORUs in the plurality of ORUs. The ORUs selected as the first and second interior ORUs 24a and 24b may be such that the relatively rapid variation in layer thicknesses schematically depicted in FIGS. 3A-3B and 4A-4B occur between the ORUs 24a and 24b, or the ORUs 24a and 24b may be selected so that only a portion of the relatively rapid variation in layer thicknesses schematically depicted in FIGS. 3A-3B and 4A-4B occur between the ORUs 24a and 24b, for example. In some embodiments, the ORUs 10 are sequentially numbered from the first endmost ORU 23a to the second endmost ORU 23b. The first and second endmost ORUs 23a and 23b can have respective ORU numbers 1 and N and the first and second interior ORUs 24a and 24b can have respective first and second ORU numbers Na and Nb. In some embodiments, an absolute value of a difference between Nb and Na is in a range of 1 to about 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5. In some embodiments, an absolute value of a difference between Nb and Na is 1. For example, ORUs 24a and 24b can correspond to ORUs 10a and 10b or 10c and lOd. In some embodiments, an absolute value of a difference between Nb and Na is at least 2, 3, 4, 5, 10, 15, 20, or 25. In some embodiments, 10 < Na < Nb < N-10.

[0036] In some embodiments, the average total thickness of the optical repeat units 10 increase with increasing ORU number throughout the range from ORU number 1 to ORU number N. In other embodiments, the average total thickness of the optical repeat units 10 increase with increasing ORU number throughout the ranges from ORU number 1 to ORU number Na and from ORU number Nb to ORU number N, but decreases with increasing ORU number for at least a portion of the range from ORU number Na to ORU number Nb. This can provide an overlap of wavelength ranges of first order reflection bands provided by pluralities of ORUs having different f-ratios, for example. In some embodiments, as schematically illustrated in FIGS. 3A-3B and 4A, for example, the average total thicknesses of the optical repeat units 10 increase substantially continuously from a first major side 301 of the optical film 300 to an opposite second major side 302 of the optical film 301. In some embodiments, as schematically illustrated in FIG. 4B, for example, the average total thickness of the optical repeat units 10 can have one or more discontinuous jumps between Na and Nb, for example. The discontinuous jumps can be smaller (e.g., by a factor of at least about 1.2, 1.4, 1.6, 1.8, or 2) than differences in thicknesses of a same one of the at least two different polymeric layers 11, 12 of the ORUs 24a and 24b. In some embodiments, whether or not there are discontinuous jumps between Na and Nb, average physical thicknesses of the ORUs 24a and 24b differ by less than X%, and an average physical thickness of a same one of the at least two different polymeric layers 11, 12 of the ORUs differ between the ORUs 24a and 24b by greater than 1.5, 2, 3, 4, or 5 times X%. In some embodiments, X is in a range of about 5 to about 20.

[0037] In some embodiments, the optical film 300 includes a plurality of optical repeat units (ORUs) 10 coextruded and co-stretched with one another and including opposing first and second endmost ORUs 23a and 23b farthest from each other among the ORUs. In some embodiments, the ORUs 10 are sequentially numbered from the first endmost ORU 23a to the second endmost ORU 23b. In some embodiments, the plurality of ORUs include first and second interior ORUs 24a and 24b spaced apart from one another along a thickness direction (z -direction) of the optical film 300 by no more than about 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 4, 3, 2, 1, or 0 other ORUs in the plurality of ORU. In some embodiments, no other ORU in the plurality of ORUs 10 separate the first and second interior ORUs 24a and 24b. In some embodiments, the first and second interior ORUs 24a and 24b are spaced apart from one another along a thickness direction of the optical film 300 by at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, or 15 other ORUs the plurality of ORUs or in the sequentially numbered ORUs. For example, in some embodiments, the first and second interior ORUs 24a and 24b are spaced apart from one another along a thickness direction of the optical film 300 by at least 5 and no more than about 50, 45, 40, 35, 30, 25, or 20 other ORUs in the sequentially numbered ORUs. In some embodiments, each of the first and second interior ORUs 24a and 24b is spaced apart from each of the first and second endmost ORUs by at least 10, 15, 20, 25, 30, 35, 40, 45, 50 other ORUs in the plurality of ORUs (e.g., each of Na-1 and N-Nb can be at least 10).

[0038] In some embodiments, each ORU includes at least two different polymeric layers (e.g., each ORU can include at least different polymeric first and second layers 11 and 12) and has an average total thickness (e.g., twice the average ORU layer thickness 20) of less than about 1500 nm (or in a range described elsewhere herein). In some embodiments, the first and second layers 11 and 12 have respective higher and lower average in-plane refractive indices for at least a first wavelength in a range of about 450 nm to about 1500 nm (e.g., at a first wavelength of about 633 nm).

[0039] In some embodiments, the first and second layers 11 and 12 of the first interior ORU 24a has respective lesser and greater average layer thicknesses Tla and T2a, and the first and second layers of the second interior ORU 25b has respective greater and lesser average layer thicknesses Tib and T2b. In some embodiments, the first and second interior ORUs 24a and 24b have average total thicknesses Ta and Tb differing by less than about 0.4, 0.3, 0.2, 0.15, 0.1, 0.08, 0.06, 0.05, 0.04, 0.03, 0.02, or 0.015 times an absolute value of a difference between the average layer thickness Tla of the first layer 11 of the first ORU 24a and the average layer thickness Tib of the first layer 11 of the second ORU 24b. In some embodiments, at least 5 other ORUs in the plurality of ORUs separate the first and second interior ORUs 24a and 24b, and each of the average thicknesses of the first and second layers and the average total thickness of the ORUs varies substantially continuously along the thickness direction of the optical film between the first and second interior ORUs (see, e.g., FIG. 3). In other embodiments, no other ORUs in the plurality of ORUs separate the first and second interior ORUs 24a and 24b (e.g., the first and second interior ORUs can correspond to ORUs 10a and 10b or 10c and lOd and the jump in layer thicknesses in FIGS. 4A-4B can occur between adjacent ORUs). In some embodiments, the average total thicknesses of the first and second interior ORUs 24a and 24b differ by less than about 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1.5, 1, 0.9, or 0.8 nm. In some such embodiments, the average layer thicknesses Tla and Tib of the first layers 11 of the first and second interior ORUs 24a and 24b differ by greater than about 20, 25, 30, 35, 40, 45, or 50 nm.

[0040] In some embodiments, at least a same one of the at least two different polymeric layers (e.g., a same one of the first and second layers 11, 12 such as the first layer 11) has an average layer thickness (e.g., Tla and Tib for first layer 11 of ORUs 24a and 24b) that differs between the first and second interior ORUs 24a and 24b by at least about 10 percent, and the first and second interior ORUs 24a and 24b have average total thickness Ta and Tb differing by less than about 7, 6.5, 6, 5.5, 5, 4.5, 4, 3.5, 3, 2.5, 2, 1.5, 1.4, 1.3, 1.2, 1.1, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, or 0.25 percent. In some embodiments, at least the same one of the at least two different polymeric layers (e.g., a same one of the first and second layers 11, 12 such as the (e.g., higher average in-plane index) first layer 11) has an average layer thickness that differs between the first and second interior ORUs 24a and 24b by at least about 12, 12, 16, 18, 20, 22, 24, 26, 28, 30 percent. In some embodiments, no other ORU in the plurality of ORUs separate the first and second interior ORUs and in other embodiments, at least 5 ORUs in the plurality of ORUs separate the first and second interior ORUs. In some embodiments, the average total thicknesses Ta and Tb of the first and second interior ORUs 24a and 24b differ by less than about 0.2, 0.15, 0.1, 0.08, 0.06, 0.05, 0.04, 0.03, 0.02, or 0.015 times an absolute value of a difference between the average layer thickness Tla of the first layer 11 of the first interior ORU 24a and the average layer thickness Tib of the first layer 11 of the second interior ORU 24b. In some embodiments, the average total thicknesses Ta and Tb of the first and second interior ORUs 24a and 24b differ by less than about 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1.5, 1, 0.9, or 0.8 nm. In some such embodiments, or in other embodiments, the average layer thicknesses Tla and Tib of the first layers 11 of the first and second interior ORUs 24a and 24b differ by greater than about 20, 25, 30, 35, 40, 45, or 50 nm.

[0041] In some embodiments, as schematically illustrated in FIGS. 3A-3B and 4A-4B, at least a same one of the at least two different polymeric layers (e.g., a same one of the first and second layers 11, 12 such as the (e.g., higher average in-plane index) first layer 11) has an average layer thickness that varies non-monotonically with ORU number from the first to the second ORU number Na and Nb, and the average total thickness of the ORUs varying monotonically with ORU number from the first to the second ORU number Na and Nb such that for each pair of adjacent ORUs having sequential ORU numbers (i.e., the ORU numbers for the ORUs of the pair differ by 1) that are each in a range from the first to the second ORU number, the average total thicknesses of the ORUs in the pair differ by less than about 2, 1.75, 1.5, 1.4, 1.3, 1.2, 1.1, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, or 0.25 percent. In some embodiments, the average total thicknesses of the first and second interior ORUs 24a and 24b differ by less than about 7, 6.5, 6, 5.5, 5, 4.5, 3.5, 3, 2.5, 2, 1.5, 1.4, 1.3, 1.2, 1.1, or 1 percent. In some embodiments, for the same one of the at least two different polymeric layers (e.g., a same one of the first and second layers 11, 12), the average layer thickness include maximum and minimum thicknesses for ORU numbers in the range from the first to the second ORU number, where the maximum thickness at least about 10, 12, 12, 16, 18, 20, 22, 24, 26, 28, or 30 percent greater than the minimum thickness. For example, in FIGS. 3A-3B for the range of Na to Nb, the maximum and minimum thicknesses for second layer 12 occur just after Na and just before Nb, respectively, while the maximum and minimum thicknesses for first layer 1 loccur at Nb and Na, respectively.

[0042] FIGS. 5-8 are plots of layer thickness versus layer number for various optical films, according to some embodiments. The optical films of these figures include alternating first and second layers 11 and 12 so that the optical repeat units are 2-layer optical repeat units. The average ORU layer thickness 20 (total ORU thickness divided by the number of layers of the ORU, which is 2 in this case) versus layer number is also shown in each of these plots. The sub-pluralities 321 and 323 of the optical repeat units 10 in these figures have an f-ratio of 0.5 and a thickness ratio of 0.47. The sub-pluralities 322 of the optical repeat units 10 in these figures had an f-ratio of 0.66 and athickness ratio of 0.63. The various subpluralities can include at least 5, 7, 10, 12, 15, or 20 ORUs. In some embodiments, each of the subpluralities include less than about 90, 80, or 70 percent of the total number of ORUs of the optical film 300. In some embodiments, the sub-plurality 322 includes less than about 400, 350, 300, 250, or 200 layers in total while the sub-pluralities 321 and 323 in combination include greater than about 150, 175, 200, or 225 layers in total.

[0043] In some embodiments, a variation in f-ratio, thickness ratio, and / or layer thickness between two values or between two spaced apart ORUs is substantially continuous. In other embodiments, the variation exhibits discontinuous jumps. A substantially continuous variation is a gradual variation without abrupt jumps. For example, in FIG. 2, the ratio 362 is substantially continuous, while the ratio 361 exhibits abrupt (discontinuous) jumps (around 331 and 332) and would not be described as substantially continuous. Similarly, in FIGS. 3A-3B, the thickness variation of the first and second layers 11 and 12 and of the average ORU layer thickness 20 is substantially continuous between ORU numbers Na and Nb. In FIGS. 4A-4B, the thickness variation of the first and second layers 11 and 12 is not substantially continuous between ORU numbers Na and Nb since, for each of the first and second layers 11 and 12, there is an abrupt jump in thickness between these ORU numbers. However, in FIG. 4A, the thickness variation of the ORU average layer thickness 20 is substantially continuous at least between ORU numbers Na and Nb. Similarly, FIGS. 5 and 7 show thickness variations of the first and second layers 11 and 12 that are not substantially continuous, while FIGS. 6 and 8 show thickness variations of the first and second layers 11 and 12 that are substantially continuous. In each of FIGS. 5 to 8, the ORU average layer thickness 20 varies substantially continuously. In some embodiments, a substantially continuous variation in a quantity has no jump between adjacent layers or ORUs that is greater than about 7, 6.5, 6, 5.5, 5, 4.5, 3.5, 3, 2.5, 2.25, 2, 1.75, 1.5, 1.4, 1.3, 1.2, 1.1, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, or 0.25 percent. In some embodiments, a substantially continuous variation in a quantity has no jump between adjacent layers or ORUs that is greater than about 10, 9, 8, 7, 6, 5.5, 5, 4.5, 3.5, 3, 2.5, 2.25, 2, 1.75, 1.5, 1.4, 1.3, 1.2, 1.1, 1, 0.9, 0.8, 0.7, or 0.6 percent of a maximum variation in the quantity over the plurality of optical repeat units 10.

[0044] In some embodiments, an optical film 300 includes a plurality of (e.g., contiguous) optical repeat units 10 numbering at least 10 in total (or in a range described elsewhere herein) where each optical repeat unit 10 includes at least different polymeric first and second layers 11 and 12 and has an average total thickness of less than about 1500 nm (or in a range described elsewhere herein). In some embodiments, the first and second layers 11 and 12 have respective higher and lower average in-plane refractive indices for at least a first wavelength in a range of about 450 nm to about 1500 nm (or in a range between band edge wavelengths as described elsewhere herein). In some embodiments, for at least one in-plane direction (e.g., x-direction, referring to the x-y-z coordinate system of FIG. 1) and for at least the first wavelength: for each of the optical repeat units 10, an optical thickness of the first layer 11 of the optical repeat unit 10 divided by a total optical thickness of the optical repeat unit defines an f-ratio of the optical repeat unit. The plurality of optical repeat units 10 include first and second sub-pluralities (e.g., 321, 322) of the optical repeat units, where the first and second sub-pluralities are stacked on one another along a thickness direction of the optical film 300. Each of the first and second sub-pluralities can include at least 5, 7, 10, 12, 15, 20, 30, 40, 50, or 55 of the optical repeat units 10. The f-ratio can be substantially constant first and second ratios (e.g., Rl, R2) in the respective first and second subpluralities. In some embodiments, an absolute value of a difference between the first and second ratios is at least about 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.18, 0.20, 0.22, 0.24, 0.26, 0.28, 0.3. In some embodiments, the absolute value of the difference the first and second ratios is no more than about 0.95, 0.9, 0.8, 0.7, 0.6, 0.5, 0.45, or 0.4.

[0045] In some embodiments, the plurality of (e.g., contiguous) optical repeat units 10 includes a first transition sub-plurality (e.g., 331) of the plurality of the optical repeat units 10 that includes at least 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, or 20 of the optical repeat units 10. The first transition sub-plurality can be disposed between the first and second sub-pluralities (e.g., 321, 322). In some embodiments, the first transition sub-plurality includes no more than 70, 60, 50, 45, 40, 35, 30 or 25 of the optical repeat units 10. In some embodiments, the f-ratio of the optical repeat units 10 in the first transition sub-plurality varies substantially continuously along the thickness direction (z -direction) of the optical film 300 between the first and second ratios. For example, the ratio 362 versus ORU number in FIG. 2 shows substantially continuous variation. In some embodiments, the first and second sub-pluralities are contiguous with one another. For example, ratio 361 vs ORU number in FIG. 2 shows discontinuous jumps where sub-pluralities with different ratios are contiguous with (immediately adjacent to) one another.

[0046] The f-ratio or thickness ratio can be described as substantially constant first and second ratios in the respective first and second sub-pluralities when the maximum variation in each of the first and second ratios in the first and second sub-pluralities is substantially smaller (e.g., by at least a factor of 3, 4, 5, 7, 10, 15, or 20) than the absolute value of the difference between an average of the first ratio in the first sub-plurality and an average of the second ratio in the second sub-plurality.

[0047] In some embodiments, the plurality of (e.g., contiguous) optical repeat units 10 include first and second sub-pluralities 321, 322 of the optical repeat units 10. In some embodiments, the plurality of optical repeat units includes a third sub-plurality 323 of the plurality of the optical repeat units 10 that includes at least 5, 7, 10, 20, 30, 40, 50, or 55 of the optical repeat units 10. The second sub-plurality 322 can be disposed between the first and third sub-pluralities 321 and 323. The f-ratio may be a constant third ratio in the third sub-plurality. In some embodiments, an absolute value of a difference between the second and third ratios is at least about 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.18, 0.20, 0.22, 0.24, 0.26, 0.28, 0.3. In some embodiments, the absolute value of the difference the second and third ratios is no more than about 0.95, 0.9, 0.8, 0.7, 0.6, 0.5, 0.45, or 0.4. In some embodiments, the first and third ratios are about equal. In some embodiments, the plurality of optical repeat units 10 includes first and second transition sub-pluralities 331 and 332 of the plurality of the optical repeat units 10, where each of the first and second transition sub-pluralities 331 and 332 includes at least 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, or 20 of the optical repeat units 10. In some embodiments, each of the first and second transition sub-pluralities 331 and 332 includes no more than 70, 60, 50, 45, 40, 35, 30 or 25 of the optical repeat units 10. The first transition sub-plurality 331 can be disposed between the first and second sub-pluralities 321 and 322, and the second transition sub-plurality 332 can be disposed between the second and third sub-pluralities 322 and 323. In some embodiments, the f-ratio of the optical repeat units 10 in the first transition sub-plurality 331 varies substantially continuously along the thickness direction (z-direction) of the optical film 300 between the first and second ratios. In some embodiments, the f-ratio of the optical repeat units in the second transition sub-plurality 332 varies substantially continuously along the thickness direction (z-direction) of the optical film 300 between the second and third ratios.

[0048] The transition portion(s) or sub-plurality(ies) can be included to provide a gradual change in layer thickness between portion(s) having substantially constant f-ratios, for example, which can, according to some embodiments, result in the optical film being more robust against common manufacturing variations.

[0049] In some embodiments, the first ratio (f-ratio in first sub-plurality) is in a range of 0.45 to 0.55 and the second ratio (f-ratio in second sub-plurality) is in a range of 0.6 to 0.8. In some embodiments, one of the first and second ratios is about 0.5 and the other of the first and second ratios is at least about 0.6.

[0050] Different nomenclature may alternatively be used for the sub-pluralities 321, 331, 322, 332, and / or 323. For example, instead of referring to the sub-pluralities 321, 322, and 323 as respective first through third sub-pluralities and sub-pluralities 331 and 332 as respective first and second transition subpluralities, the sub-pluralities 321, 331, 322, 332, and 323 may be referred to as respective first through fifth sub-pluralities.

[0051] In some embodiments, the plurality of optical repeat units 10 include first, second, and third subpluralities (e.g., 321, 331, 322 or 322, 322, 323) of the optical repeat units 10, where the first, second, and third sub-pluralities are stacked on one another in sequence (i.e., the second sub-plurality is disposed between the first and third sub-pluralities) along a thickness direction (z-direction) of the optical film 300. In some embodiments, each of the first, second, and third sub-pluralities includes at least 5 of the optical repeat units 10 (or the number of ORUs can be in a respective range described elsewhere herein). In some embodiments, the f-ratio is substantially constant first and second ratios (e.g., Rl, R2) in the respective first and third sub-pluralities, where an absolute value of a difference between the first and second ratios is at least about 0.05 (or in a range described elsewhere herein), and where the f-ratio of the optical repeat units 10 in the second sub-plurality varies substantially continuously along the thickness direction of the optical film between the first and second ratios. In some embodiments, the second subplurality includes less optical repeat units 10 than included in each of the first and third sub-pluralities. In some embodiments, the plurality of optical repeat units 10 further comprises fourth and fifth subpluralities (e.g., 332, 323) of the optical repeat units stacked on the first, second, and third sub-pluralities (e.g., 321, 322, 331) with the fourth sub-plurality disposed between the third and fifth sub-pluralities. In some embodiments, each of the fourth and fifth sub-pluralities includes at least 5 (or in a range described elsewhere herein) of the optical repeat units 10. The f-ratio can be a substantially constant third ratio in the fifth sub-plurality. An absolute value of a difference between the second and third ratios can be at least about 0.05 (or in a range described elsewhere herein). In some embodiments, the f-ratio of the optical repeat units in the fourth sub-plurality varies substantially continuously along the thickness direction of the optical fdm between the second and third ratios.

[0052] The optical fdm 300 may alternatively, or in addition, be characterized by thickness ratios of the optical repeat units 10.

[0053] In some embodiments, an optical fdm 300 includes a plurality of (e.g., contiguous) optical repeat units numbering at least 10 in total (or in a range described elsewhere herein) where each optical repeat unit 10 includes at least two different polymeric layers 11 and 12 and has an average total thickness of less than about 1500 nm (or in a range described elsewhere herein). In some embodiments, for each of the optical repeat units 10, an average thickness of a same one (e.g., 11) of the at least two different polymeric layers of the optical repeat unit 10 divided by an average total thickness of the optical repeat unit 10 defines a thickness ratio of the optical repeat unit 10. In some embodiments, the plurality of optical repeat units 10 include first and second sub-pluralities (e.g., 321 and 322) of the optical repeat units 10, where the first and second sub-pluralities are stacked on one another along a thickness direction (z-direction) of the optical fdm 300. Each of the first and second sub-pluralities can include at least 5, 7, 10, 20, 30, 40, 50, or 55 of the optical repeat units 10. In some embodiments, the thickness ratio is substantially constant first and second ratios in the respective first and second sub-pluralities. In some embodiments, an absolute value of a difference between the first and second ratios is at least about 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.18, 0.20, 0.22, 0.24, 0.26, 0.28, 0.3. In some embodiments, the absolute value of the difference the first and second ratios is no more than about 0.95, 0.9, 0.8, 0.7, 0.6, 0.5, 0.45, or 0.4.

[0054] In some embodiments, the plurality of (e.g., contiguous) optical repeat units 10 includes a first transition sub-plurality (e.g., 331) of the plurality of the optical repeat units 10 that includes at least 5 (or in a range described elsewhere herein) of the optical repeat units 10. The first transition sub-plurality can be disposed between the first and second sub-pluralities (e.g., 321, 322). In some embodiments, the f- ratio of the optical repeat units 10 in the first transition sub-plurality varies substantially continuously along the thickness direction (z-direction) of the optical film 300 between the first and second ratios. For example, the ratio 362 versus ORU number in FIG. 2 shows substantially continuous variation. In some embodiments, the first and second sub-pluralities are contiguous with one another. For example, ratio 361 vs ORU number in FIG. 2 shows discontinuous jumps where sub-pluralities with different ratios are contiguous with one another.

[0055] In some embodiments, the plurality of (e.g., contiguous) optical repeat units 10 include first and second sub-pluralities 321, 322 of the optical repeat units 10. In some embodiments, the plurality of optical repeat units 10 includes a third sub-plurality 323 of the plurality of the optical repeat units 10 that includes at least 5 (or in a range described elsewhere herein) of the optical repeat units 10. The second sub-plurality 322 can be disposed between the first and third sub-pluralities 321 and 323. The thickness ratio may be a constant third ratio in the third sub-plurality. In some embodiments, an absolute value of a difference between the second and third ratios is at least about 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.18, 0.20, 0.22, 0.24, 0.26, 0.28, 0.3. In some embodiments, the absolute value of the difference the second and third ratios is no more than about 0.95, 0.9, 0.8, 0.7, 0.6, 0.5, 0.45, or 0.4. In some embodiments, the first and third ratios are about equal. In some embodiments, the plurality of optical repeat units 10 includes first and second transition sub-pluralities 331 and 332 of the plurality of the optical repeat units 10, where each of the first and second transition sub-pluralities 331 and 332 includes at least 5 (or in a range described elsewhere herein) of the optical repeat units 10. The first transition sub-plurality 331 can be disposed between the first and second sub-pluralities 321 and 322, and the second transition sub-plurality 332 can be disposed between the second and third sub-pluralities 322 and 323. In some embodiments, the thickness ratio of the optical repeat units 10 in the first transition subplurality 331 varies substantially continuously along the thickness direction (z-direction) of the optical film 300 between the first and second ratios. In some embodiments, the thickness ratio of the optical repeat units in the second transition sub-plurality 332 varies substantially continuously along the thickness direction (z-direction) of the optical film 300 between the second and third ratios.

[0056] In some embodiments, the first ratio (thickness ratio in first sub-plurality) is in a range of 0.42 to 0.52 and the second ratio (thickness ratio in the second sub-plurality) is in a range of 0.57 to 0.72.

[0057] In some embodiments, an optical film 300 includes a plurality of optical repeat units 10 numbering at least 10 (or in a range described elsewhere herein) in total, where each optical repeat unit 10 includes at least two different polymeric layers 11 and 12 and has an average total thickness less than about 1500 nm (or in a range described elsewhere herein). In some embodiments, for each of the optical repeat units 10, an average thickness of a same one (e.g., 11) of the at least two different polymeric layers of the optical repeat unit 10 divided by the average total thickness of the optical repeat unit defines a thickness ratio of the optical repeat unit. In some embodiments, the plurality of optical repeat units 10 include first, second, and third sub-pluralities (e.g., 321, 331, 322 or 322, 332, 323) of the optical repeat units 10, where the first, second, and third sub-pluralities stacked on one another in sequence along a thickness direction of the optical film. Each of the first, second, and third sub-pluralities can include at least 5 (or in a range described elsewhere herein) of the optical repeat units 10. In some embodiments, the thickness ratio is substantially constant first and second ratios in the respective first and third subpluralities. An absolute value of a difference between the first and second ratios can be at least about 0.05 (or in a range described elsewhere herein). In some embodiments, the thickness ratio of the optical repeat units 10 in the second sub-plurality varies substantially continuously along the thickness direction of the optical film between the first and second ratios. In some embodiments, the plurality of optical repeat units 10 further includes fourth and fifth sub-pluralities (e.g., 332, 323) of the optical repeat units 10 stacked on the first, second, and third sub-pluralities (e.g., 321, 331, 322) with the fourth sub-plurality disposed between the third and fifth sub-pluralities, where each of the fourth and fifth sub-pluralities including at least 5 (or in a range described elsewhere herein) of the optical repeat units 10. The thickness ratio can be a substantially constant third ratio in the fifth sub-plurality. In some embodiments, an absolute value of a difference between the second and third ratios is at least about 0.05 (or in a range described elsewhere herein). In some embodiments, the thickness ratio of the optical repeat units 10 in the fourth sub-plurality varies substantially continuously along the thickness direction (z -direction) of the optical fdm 300 between the second and third ratios.

[0058] FIG. 9 is a schematic plot of reflectance versus wavelength for substantially normally incident light incident on an optical film, according to some embodiments.

[0059] FIGS. 10-11 are plots of transmittance versus wavelength for normally incident light incident on optical films, according to some embodiments. The transmittance s of FIGS. 10-11 were calculated from the layer thickness profiles of FIGS. 5-8 (Examples 1-4) using standard optical modeling techniques where the first layers 11 were modeled as PET and the second layers 12 were modeled as coPMMA. Transmittance for a comparative (Comparative Example CE1) optical film formed from the same materials but having a constant f-ratio of 0.5 is also shown. Since optical absorption is typically negligible for these materials in visible and near-infrared wavelengths, the reflectance is given, to a good approximation, by 100% minus the transmittance. The transmittance s of FIGS. 10-11 are for a normally incident light 100 having a first polarization state 101. In some embodiments, the optical films are biaxially oriented so that the transmittance (resp., reflectance) for a normally incident light 100 having an orthogonal second polarization state 102 can be similar or about the same as the transmittance (resp., reflectance) for the first polarization state 101. In some other embodiments, the optical films are uniaxially oriented so that the transmittance for the second polarization state 102 can be high throughout a wavelength range including the illustrated reflection bands (e.g., a transmittance of at least about 75, 80, 85, or 90 percent throughout at least the wavelength range of about 400 nm to about 1500 nm). Reflectance and transmittance of an optical film should be understood to be determined for light incident on the optical film in air, unless otherwise indicated. For example, reflectance and transmittance can be measured for a substantially normally incident (e.g., an incident angle of about 8 degrees) substantially collimated light (e.g., a light beam) incident on the optical film 300 in air.

[0060] In some embodiments, an optical film 300 includes a plurality of optical repeat units 10 numbering at least 10 (or in a range described elsewhere herein) in total, where each optical repeat unit 10 includes at least two different polymeric layers 11, 12 and has an average total thickness less than about 1500 nm (or in a range described elsewhere herein), such that for a substantially normally incident light 100 incident on the optical film 300 and for at least one polarization state 101 and / or 102, the optical film has: a primary reflection band 201 extending between first and second band edges 201a and 201b; and an nth-order reflection band 205 (or 207) extending between third and fourth band edges 205a and 205b (or 207a and 207b) where n is an integer greater than 1. In some embodiments, n is no more than 8, 7, 6, 5, 4, or 3. In some embodiments, n is 2, 3, or 4. In some embodiments, n is 2 or 3.

[0061] In some embodiments, the optical film 300 has a reflectance generally increasing from less than about 30% to greater than about 70% with increasing wavelength along the first band edge 201a. In some embodiments, the reflectance generally increases from less than about 25 or 20 percent to greater than about 75 or 80 percent with increasing wavelength along the first band edge 201a. In some embodiments, the reflectance generally decreases from greater than about 70% to less than about 30% with increasing wavelength along the second band edge 201b. In some embodiments, the reflectance generally decreases from than about 75 or 80 percent to less than about 25 or 20 percent with increasing wavelength along the second band edge 201b. The first and second band edges can comprise respective first and second band edge wavelengths W1 and W2 where the reflectance is about 50% of a maximum reflectance Rm of the primary reflection band 201 (e.g., Rm can correspond to about 100% minus a minimum transmittance of the primary reflection band). In some embodiments, the second band edge wavelength is greater than the first band edge wavelength by at least about 50, 75, 100, 150, 200, 250, or 300 nm. The difference between the second and first band edge wavelengths can be up to about 1200, 1000, 800, or 600 nm, for example.

[0062] In some embodiments, the reflectance of the optical film 300 generally increases from less than about 30% to greater than about 70% with increasing wavelength along the third band edge 205a (or 207a). In some embodiments, the reflectance generally increases from less than about 25 or 20 percent to greater than about 75 or 80 percent with increasing wavelength along the third band edge 205a (or 207a). In some embodiments, the reflectance of the optical film 300 generally decreases from greater than about 70% to less than about 30% with increasing wavelength along the fourth band edge 205b (or 207b). In some embodiments, the reflectance generally decreases from greater than about 80 or 75 percent to less than about 25 or 20 percent with increasing wavelength along the fourth band edge 205b (or 207b). In some embodiments, the third and fourth band edges comprise respective third and fourth band edge wavelengths W3 and W4 (or W5 and W6) where the reflectance is about 50% of a maximum reflectance Rm' of the nth-order reflection band (e.g., Rm’ can correspond to about 100% minus a minimum transmittance of the nth-order reflection band).

[0063] In some embodiments, a ratio W2 / W1 of the second to the first band edge wavelengths is greater than a ratio W4 / W3 (or W6 / W5) of the fourth to the third band edge wavelengths by at least about 5, 6, 7, 8, 9, 10, 11, 12, 14, 16, 18, 20, 25, 30, 35, or 40% (e.g., when the ratio W2 / W1 is greater than the ratio W4 / W3 by at least 7%, the ratio W2 / W1 is greater than 1.07 times W4 / W3).

[0064] In some embodiments, at least one of the third or fourth band edge wavelengths differs from the respective first and second band edge wavelengths divided by n by at least about 10, 12 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 120, 140, 160, 180, 200, or 220 percent of a difference between the fourth and third band edge wavelengths (e.g., when the third band edge wavelength W3 differs from the first band edge wavelength W1 divided by n by at least 12% of the difference between the fourth and third band edge wavelengths W4 and W3, |W3 - Wl / n| is at least 0. 12 [W4-W3]). In some embodiments, each of the third and fourth band edge wavelengths differs from the respective first and second band edge wavelengths divided by n by at least about 10, 12, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 120, 140, 160, 180, 200, or 220 percent of the difference between the fourth and third band edge wavelengths. For example, the difference between the fourth and third band edge wavelengths can be made small by adjusting the number of layers (e.g., in sub-plurality 322) responsible for producing the nth order band so that the shift in the band edge wavelength from the corresponding primary band edge wavelength divided by n can be larger than the difference between the fourth and third band edge wavelengths. In some embodiments, the third and / or fourth band edge wavelengths differ from the respective first and second band edge wavelengths divided by n by up to about 1000, 800, 600, or 500 percent of the difference between the fourth and third band edge wavelengths.

[0065] In some embodiments, at least one of the third or fourth band edge wavelengths differs from the respective first and second band edge wavelengths divided by n by at least about 10, 12, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 100, 110, or 120 nm. In some embodiments, each of the third or fourth band edge wavelengths differs from the respective first and second band edge wavelengths divided by n by at least about 10, 12, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 100, 110, or 120 nm. In some embodiments, the third and / or fourth band edge wavelengths differ from the respective first and second band edge wavelengths divided by n by up to about 500, 400, 300, 250, 200, or 150 nm.

[0066] In some embodiments, each of the first through fourth band edge wavelengths is a range of about 350 nm to about 2500 nm, or about 380 to about 2000 nm, or about 400 to about 1500 nm. In some embodiments, the fourth band edge wavelength is greater than the third band edge wavelength by at least about 10, 12, 15, 20, 25, 30, 50, 75, 100, 125, or 150 nm.

[0067] In some embodiments, for the substantially normally incident light 100 incident on the optical film 300 and for at least one polarization state, the optical film 300 has an optical transmittance of greater than about 70, 75, 80, 85, or 90 percent for at least one wavelength between the fourth band edge wavelength W4 and the first band edge wavelength W1. In some embodiments, for the substantially normally incident light 100 incident on the optical film 300 and for each of two mutually orthogonal polarization states 101 and 102, the optical film 300 has an optical transmittance of greater than about 70, 75, 80, 85, or 90 percent for at least one wavelength between the fourth band edge wavelength W4 and the first band edge wavelength W1. In some embodiments, for the substantially normally incident light 100 incident on the optical film 300 and for the at least one polarization state of for each of two mutually orthogonal polarization states 101 and 102, the optical film 300 has an average optical transmittance of greater than about 70, 75, 80, 85, or 90 percent in at least a wavelength range disposed between the fourth and first band edge wavelength W4 and W1 and having a width of at least 50% of a difference (W1-W4) between the first and fourth band edge wavelengths.

[0068] In some embodiments, for the substantially normally incident light 100 incident on the optical film 300 and for the at least one polarization state 101 and / or 102, the optical film has: an n'th-order reflection band (e.g., 207) extending between fifth and sixth band edges (e.g., 207a and 207b), where n' is an integer greater than n. In some embodiments, n is 2 and n' is 3, for example. In some embodiments, the reflectance of the optical film 300 generally increases from less than about 30% to greater than about 70% with increasing wavelength along the fifth band edge. In some embodiments, the reflectance generally increases from less than about 25 or 20 percent to greater than about 75 or 80 percent with increasing wavelength along the fifth band edge. In some embodiments, the reflectance of the optical film 300 generally decreases from greater than about 70% to less than about 30% with increasing wavelength along the sixth band edge. In some embodiments, the reflectance generally decreases from greater than about 80 or 75 percent to less than about 25 or 20 percent with increasing wavelength along the sixth band edge. In some embodiments, the fifth and sixth band edges include respective fifth and sixth band edge wavelengths W5 and W6 where the reflectance is about 50% of a maximum reflectance of the n'th- order reflection band (e.g., the maximum reflectance can correspond to about 100% minus a minimum transmittance of the n'th-order reflection band).

[0069] In some embodiments, the ratio (W2 / W1) of the second to the first band edge wavelengths greater than a ratio (W 6 / W5) of the sixth to the fifth band edge wavelengths by at least about 5, 6, 7, 8, 9, 10, 11, 12, 14, 16, 18, 20, 25, 30, 35, or 40 percent. In some embodiments, at least one of the fifth or sixth band edge wavelengths W5, W6 differs from the respective first and second band edge wavelengths W1 and W2 divided by n' by at least about 10, 12, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 120, 140, 160, 180, 200, or 220% of a difference (W6-W5) between the sixth and fifth band edge wavelengths. In some embodiments, each of the fifth and sixth band edge wavelengths W5 and W6 differs from the respective first and second band edge wavelengths W1 and W2 divided by n' by at least about 10, 12, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 120, 140, 160, 180, 200, or 220% of the difference between the sixth and fifth band edge wavelengths W5 and W6. In some embodiments, the fifth and / or sixth band edge wavelengths differ from the respective first and second band edge wavelengths divided by n' by up to about 1000, 800, 600, or 500 percent of the difference between the sixth and fifth band edge wavelengths.

[0070] In some embodiments, each of the fifth and sixth band edge wavelengths is a range of about 350 nm to about 2500 nm, or about 380 to about 2000 nm, or about 400 to about 1500 nm. In some embodiments, the sixth band edge wavelength is greater than the fifth band edge wavelength by at least about 10, 20, 30, 40, or 50 nm.

[0071] In some embodiments, for the substantially normally incident light 100 incident on the optical film 300 and for at least one polarization state, the optical film 300 has an optical transmittance of greater than about 70, 75, 80, 85, or 90 percent for at least one wavelength between the sixth band edge wavelength W6 and the third band edge wavelength W3. In some embodiments, for the substantially normally incident light 100 incident on the optical film 300 and for each of two mutually orthogonal polarization states 101 and 102, the optical film 300 has an optical transmittance of greater than about 70, 75, 80, 85, or 90 percent for at least one wavelength between the sixth band edge wavelength W6 and the third band edge wavelength W3. In some embodiments, for the substantially normally incident light 100 incident on the optical film 300 and for the at least one polarization state or for each of two mutually orthogonal polarization states 101 and 102, the optical film 300 has an average optical transmittance of greater than about 70, 75, 80, 85, or 90 percent in at least a wavelength range disposed between the sixth and third band edge wavelength W6 and W3 and having a width of at least 50% of a difference (W3-W6) between the third and sixth band edge wavelengths.

[0072] Band edge wavelengths for the Examples of FIGS. 10-11 are provided in the following table.

[0073] The optical films having the transmittances versus wavelength illustrated in FIGS. 10-11 can have any of the layer thickness variations, f-ratio, and / or thickness ratio variations described elsewhere herein. For example, as described further elsewhere herein, in some embodiments, for each of the optical repeat units 10, an average thickness of a same one of the at least two different polymeric layers 11 and 12 of the optical repeat unit 10 divided by an average total thickness of the optical repeat unit defines a thickness ratio of the optical repeat unit. In some embodiments, the plurality of optical repeat units 10 include first and second sub-pluralities of the optical repeat units where the first and second subpluralities are stacked on one another along a thickness direction (z-direction) of the optical film 300 and where each of the first and second sub-pluralities includes at least 5 (or in a range described elsewhere herein) of the optical repeat units. In some embodiments, the thickness ratio is substantially constant first and second ratios in the respective first and second sub-pluralities, where an absolute value of a difference between the first and second ratios is at least about 0.05 (or in a range described elsewhere herein). In some embodiments, the at least two different polymeric layers of each optical repeat unit 10 includes first and second layers 11 and 12 having respective higher and lower average in-plane refractive indices for at least a first wavelength between the third and second band edge wavelengths. In some embodiments, for the at least one polarization state (e.g., polarization state 101 along the in-plane x- direction) and at least the first wavelength: for each of the optical repeat units 10, an optical thickness of the first layer of the optical repeat unit divided by a total optical thickness of the optical repeat unit defines an f-ratio of the optical repeat unit 10. In some embodiments, the plurality of optical repeat units 10 include first and second sub-pluralities of the optical repeat units where the first and second subpluralities stacked on one another along a thickness direction of the optical film and each of the first and second sub-pluralities including at least 5 of the optical repeat units 10 (or the number can be in a range described elsewhere herein). In some embodiments, the f-ratio is substantially constant first and second ratios in the respective first and second sub-pluralities where an absolute value of a difference between the first and second ratios is at least about 0.05 (or the absolute value can be in a range described elsewhere herein). Terms such as “about” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “about” as applied to quantities expressing feature sizes, amounts, and physical properties is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “about” will be understood to mean within 10 percent of the specified value. A quantity given as about a specified value can be precisely the specified value. For example, if it is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, a quantity having a value of about 1, means that the quantity has a value between 0.9 and 1. 1, and that the value could be 1.

[0074] Terms such as “substantially” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “substantially” with reference to a property or characteristic is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description and when it would be clear to one of ordinary skill in the art what is meant by an opposite of that property or characteristic, the term “substantially” will be understood to mean that the property or characteristic is exhibited to a greater extent than the opposite of that property or characteristic is exhibited.

[0075] All references, patents, and patent applications referenced in the foregoing are hereby incorporated herein by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control.

[0076] Descriptions for elements in figures should be understood to apply equally to corresponding elements in other figures, unless indicated otherwise. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and / or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations, or variations, or combinations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.

Claims

What is claimed is:

1. An optical film comprising a plurality of optical repeat units numbering at least 10 in total, each optical repeat unit comprising at least two different polymeric layers and having an average total thickness less than about 1500 nm, such that for a substantially normally incident light incident on the optical film and for at least one polarization state, the optical film has: a primary reflection band extending between first and second band edges, the optical film having a reflectance generally increasing from less than about 30% to greater than about 70% with increasing wavelength along the first band edge, the reflectance generally decreasing from greater than about 70% to less than about 30% with increasing wavelength along the second band edge, the first and second band edges comprising respective first and second band edge wavelengths where the reflectance is about 50% of a maximum reflectance of the primary reflection band, the second band edge wavelength greater than the first band edge wavelength by at least about 50 nm; and an nth-order reflection band extending between third and fourth band edges, n being an integer greater than 1, the reflectance of the optical film generally increasing from less than about 30% to greater than about 70% with increasing wavelength along the third band edge, the reflectance of the optical film generally decreasing from greater than about 70% to less than about 30% with increasing wavelength along the fourth band edge, the third and fourth band edges comprising respective third and fourth band edge wavelengths where the reflectance is about 50% of a maximum reflectance of the nth-order reflection band, a ratio of the second to the first band edge wavelengths greater than a ratio of the fourth to the third band edge wavelengths by at least about 7%.

2. The optical film of claim 1, wherein the at least two different polymeric layers of each of the optical repeat units comprises first and second layers having respective higher and lower average in-plane refractive indices for at least a first wavelength between the third and second band edge wavelengths, and wherein for the at least one polarization state and at least the first wavelength: for each of the optical repeat units, an optical thickness of the first layer of the optical repeat unit divided by a total optical thickness of the optical repeat unit defines an f-ratio of the optical repeat unit, the plurality of optical repeat units comprising first and second sub-pluralities of the optical repeat units, the first and second sub-pluralities stacked on one another along a thickness direction of the optical film, each of the first and second sub-pluralities including at least 5 of the optical repeat units, the f-ratio being substantially constant first and second ratios in the respective first and second sub-pluralities, an absolute value of a difference between the first and second ratios being at least about 0.05.

3. The optical film of claim 1, wherein for each of the optical repeat units, an average thickness of a same one of the at least two different polymeric layers of the optical repeat unit divided by an average total thickness of the optical repeat unit defines a thickness ratio of the optical repeat unit, the plurality ofoptical repeat units comprising first and second sub-pluralities of the optical repeat units, the first and second sub-pluralities stacked on one another along a thickness direction of the optical film, each of the first and second sub-pluralities including at least 5 of the optical repeat units, the thickness ratio being substantially constant first and second ratios in the respective first and second sub-pluralities, an absolute value of a difference between the first and second ratios being at least about 0.05.

4. The optical film of claim 1, wherein for the substantially normally incident light incident on the optical film and for the at least one polarization state, the optical film has: an n'th-order reflection band extending between fifth and sixth band edges, n' being an integer greater than n, the reflectance of the optical film generally increasing from less than about 30% to greater than about 70% with increasing wavelength along the fifth band edge, the reflectance of the optical film generally decreasing from greater than about 70% to less than about 30% with increasing wavelength along the sixth band edge, the fifth and sixth band edges comprising respective fifth and sixth band edge wavelengths where the reflectance is about 50% of a maximum reflectance of the n'th-order reflection band, the ratio of the second to the first band edge wavelengths greater than a ratio of the sixth to the fifth band edge wavelengths by at least about 7%.

5. An optical film comprising a plurality of optical repeat units numbering at least 10 in total, each optical repeat unit comprising at least two different polymeric layers and having an average total thickness less than about 1500 nm, such that for a substantially normally incident light incident on the optical film and for at least one polarization state, the optical film has: a primary reflection band extending between first and second band edges, the optical film having a reflectance generally increasing from less than about 30% to greater than about 70% with increasing wavelength along the first band edge, the reflectance generally decreasing from greater than about 70% to less than about 30% with increasing wavelength along the second band edge, the first and second band edges comprising respective first and second band edge wavelengths where the reflectance is about 50% of a maximum reflectance of the primary reflection band, the second band edge wavelength greater than the first band edge wavelength by at least about 50 nm; and an nth-order reflection band extending between third and fourth band edges, n being an integer greater than 1, the reflectance of the optical film generally increasing from less than about 30% to greater than about 70% with increasing wavelength along the third band edge, the reflectance of the optical film generally decreasing from greater than about 70% to less than about 30% with increasing wavelength along the fourth band edge, the third and fourth band edges comprising respective third and fourth band edge wavelengths where the reflectance is about 50% of a maximum reflectance of the nth-order reflection band, at least one of the third or fourth band edge wavelengths differing from the respective first and second band edge wavelengths divided by n by at least about 12% of a difference between the fourth and third band edge wavelengths.

6. An optical film comprising: a plurality of optical repeat units numbering at least 15 in total, each optical repeat unit comprising at least different polymeric first and second layers and having an average total thickness of less than about 1500 nm, the first and second layers having respective higher and lower average in-plane refractive indices for at least a first wavelength in a range of about 450 nm to about 1500 nm, wherein for at least one in-plane direction and for at least the first wavelength: for each of the optical repeat units, an optical thickness of the first layer of the optical repeat unit divided by a total optical thickness of the optical repeat unit defines an f-ratio of the optical repeat unit, the plurality of optical repeat units comprising first, second, and third sub-pluralities of the optical repeat units, the first, second, and third sub-pluralities stacked on one another in sequence along a thickness direction of the optical film, each of the first, second, and third sub-pluralities including at least 5 of the optical repeat units, the f-ratio being substantially constant first and second ratios in the respective first and third sub-pluralities, an absolute value of a difference between the first and second ratios being at least about 0.05, the f-ratio of the optical repeat units in the second sub-plurality varying substantially continuously along the thickness direction of the optical film between the first and second ratios.

7. The optical film of claim 6, wherein the plurality of optical repeat units further comprises fourth and fifth sub-pluralities of the optical repeat units stacked on the first, second, and third sub-pluralities with the fourth sub-plurality disposed between the third and fifth sub-pluralities, each of the fourth and fifth sub-pluralities including at least 5 of the optical repeat units, the f-ratio being a substantially constant third ratio in the fifth sub-plurality, an absolute value of a difference between the second and third ratios being at least about 0.05, the f-ratio of the optical repeat units in the fourth sub-plurality varying substantially continuously along the thickness direction of the optical film between the second and third ratios.

8. An optical film comprising: a plurality of contiguous optical repeat units numbering at least 10 in total, each optical repeat unit comprising at least different polymeric first and second layers and having an average total thickness of less than about 1500 nm, the first and second layers having respective higher and lower average inplane refractive indices for at least a first wavelength in a range of about 450 nm to about 1500 nm, wherein for at least one in-plane direction and for at least the first wavelength: for each of the optical repeat units, an optical thickness of the first layer of the optical repeat unit divided by a total optical thickness of the optical repeat unit defines an f-ratio of the optical repeat unit, the plurality of contiguous optical repeat units comprising first and second sub-pluralities of the optical repeat units, the first and second sub-pluralities stacked on one another along a thickness direction of the optical film, each of the first and second sub-pluralities including at least 5 of the optical repeat units, thef-ratio being substantially constant first and second ratios in the respective first and second subpluralities, an absolute value of a difference between the first and second ratios being at least about 0.05.

9. The optical film of claim 8, wherein the plurality of contiguous optical repeat units comprises a first transition sub-plurality of the plurality of the optical repeat units comprising at least 5 of the optical repeat units, the first transition sub-plurality disposed between the first and second sub-pluralities, the f- ratio of the optical repeat units in the first transition sub-plurality varying substantially continuously along the thickness direction of the optical film between the first and second ratios.

10. An optical film comprising: a plurality of optical repeat units (ORUs) coextruded and co-stretched with one another and comprising opposing first and second endmost ORUs farthest from each other among the ORUs and first and second interior ORUs spaced apart from one another along a thickness direction of the optical film by no more than about 50 other ORUs in the plurality of ORUs, each of the first and second interior ORUs spaced apart from each of the first and second endmost ORUs by at least 10 other ORUs in the plurality of ORUs, wherein each ORU comprises at least different polymeric first and second layers and has an average total thickness of less than about 1500 nm, the first and second layers having respective higher and lower average in-plane refractive indices for at least a first wavelength in a range of about 450 nm to about 1500 nm, the first and second layers of the first interior ORU having respective lesser and greater average layer thicknesses, the first and second layers of the second interior ORU having respective greater and lesser average layer thicknesses, the first and second interior ORUs having average total thicknesses differing by less than about 0.4 times an absolute value of a difference between the average layer thickness of the first layer of the first ORU and the average layer thickness of the first layer of the second ORU.

11. The optical film of claim 10, wherein no other ORU in the plurality of ORUs separate the first and second interior ORUs.

12. The optical film of claim 10, wherein at least 5 other ORUs in the plurality of ORUs separate the first and second interior ORUs, and each of the average thicknesses of the first and second layers and the average total thickness of the ORUs varies substantially continuously along the thickness direction of the optical film between the first and second interior ORUs.

13. An optical film comprising: a plurality of optical repeat units (ORUs) coextruded and co-stretched with one another and comprising opposing first and second endmost ORUs farthest from each other among the ORUs, theORUs sequentially numbered from the first endmost ORU to the second endmost ORU, the plurality of ORUs comprising first and second interior ORUs having respective first and second ORU numbers and spaced apart from one another along a thickness direction of the optical film by at least 5 and no more than about 50 other ORUs in the sequentially numbered ORUs, each of the first and second interior ORUs spaced apart from each of the first and second endmost ORUs by at least 10 other ORUs in the plurality of ORUs, wherein each ORU comprises at least two different polymeric layers and has an average total thickness of less than about 1500 nm, at least a same one of the at least two different polymeric layers having an average layer thickness that varies non-monotonically with ORU number from the first to the second ORU number, the average total thickness of the ORUs varying monotonically with ORU number from the first to the second ORU number such that for each pair of adjacent ORUs having sequential ORU numbers that are each in a range from the first to the second ORU number, the average total thicknesses of the ORUs in the pair differ by less than about 2 percent.

14. The optical film of claim 13, wherein for the same one of the at least two different polymeric layers, the average layer thickness comprises maximum and minimum thicknesses for ORU numbers in the range from the first to the second ORU number, the maximum thickness at least about 10 percent greater than the minimum thickness.

15. An optical film comprising: a plurality of optical repeat units (ORUs) coextruded and co-stretched with one another and comprising opposing first and second endmost ORUs farthest from each other among the ORUs and first and second interior ORUs spaced apart from one another along a thickness direction of the optical film by no more than about 50 other ORUs in the plurality of ORUs, each of the first and second interior ORUs spaced apart from each of the first and second endmost ORUs by at least 10 other ORUs in the plurality of ORUs, wherein each ORU comprises at least two different polymeric layers and has an average total thickness of less than about 1500 nm, at least a same one of the at least two different polymeric layers having an average layer thickness that differs between the first and second interior ORUs by at least about 10 percent, the first and second interior ORUs having average total thickness differing by less than about 7 percent.

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