Optical stack including inversely formed polarizers

Abstract

An optical stack includes curved first and second polarizers disposed along a same first axis. For substantially normally incident light and for a same predetermined wavelength range, each of the first and second polarizers substantially transmits the incident light having a first polarization state and substantially blocks the incident light having a second polarization state orthogonal to the first polarization state. One of the first and second polarizers is thinner closer to the first axis and thicker farther from the first axis, and the other of the first and second polarizers is thicker closer to the first axis and thinner farther away from the first axis.

Description

[0001] PA103049W002

[0002] OPTICAL STACK INCLUDING INVERSELY FORMED POLARIZERS

[0003] TECHNICAL FIELD

[0004] The present description relates generally to curved polarizers such as thermoformed polarizers, and more specifically, to optical stacks including two curved polarizers.

[0005] BACKGROUND

[0006] Reflective or absorbing polarizers can be thermoformed into a curved shape.

[0007] SUMMARY

[0008] In some aspects, the present description provides an optical stack including first and second polarizers disposed along a same first axis. Each of the first and second polarizers can be curved about second and third axes, where the first, second, and third axes are mutually orthogonal to one another, such that for substantially normally incident light and for a same predetermined wavelength range, each of the first and second polarizers substantially transmits the incident light having a first polarization state and substantially blocks the incident light having a second polarization state orthogonal to the first polarization state. One of the first and second polarizers is thinner closer to the first axis and thicker farther from the first axis; and the other of the first and second polarizers is thicker closer to the first axis and thinner farther away from the first axis.

[0009] In some aspects, the present description provides an optical stack including spaced apart curved first and second polarizers disposed along a same first axis, such that for incident light substantially along the first axis and for a same predetermined wavelength range: each of the first and second polarizers has a maximum average transmittance for the incident light having a first polarization state and a minimum average transmittance for the incident light having a second polarization state orthogonal to the first polarization state; one of the first and second polarizers has a lower minimum average transmittance closer to the first axis and a higher minimum average transmittance farther from the first axis; and the other of the first and second polarizers has a higher minimum average transmittance closer to the first axis and a lower minimum average transmittance farther away from the first axis.

[0010] In some aspects, the present description provides an optical stack including spaced apart first and second polarizers disposed along a same first axis and having different respective first and second curvatures at respective first and second locations where the first axis intersects the respective first and second polarizers, such that for incident light substantially along the first axis and for a same predetermined wavelength range, each of the first and second polarizers has a maximum average transmittance for the incident light polarized along a pass axis and a minimum average transmittance for the incident light polarized along a block axis orthogonal to the pass axis. In a plan view along the first axis: for a same first distance away from the first axis along a same first direction, the pass axes of thefirst and second polarizers are rotated in opposite directions from a substantially same pass axis of the first and second polarizers at the respective first and second locations.

[0011] 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.

[0012] BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional view of an optical stack including first and second polarizers, according to some embodiments.

[0013] FIGS. 2A-2C are schematic cross-sectional views of optical stacks, according to some other embodiments.

[0014] FIGS. 3A-3C are schematic plots of thickness versus position for polarizers, according to some embodiments.

[0015] FIGS. 4A-4B are schematic contour plots of minimum transmittance for polarizers, according to some embodiments.

[0016] FIG. 5A-5C are plots of minimum transmittance versus position for various polarizers, according to some embodiments.

[0017] FIG. 6 is a schematic plan view of an optical stack illustrating pass axes of two polarizers, according to some embodiments.

[0018] FIGS. 7A-7B are schematic contour plots of pass axis orientation for polarizers, according to some embodiments.

[0019] FIG. 8A-8C are plots of polarization axis orientation versus position for various polarizers, according to some embodiments.

[0020] FIG. 9 is a schematic cross-sectional view of a multilayer optical film reflective polarizer, according to some embodiments.

[0021] FIG. 10 is a schematic cross-sectional view of an absorbing polarizer, according to some embodiments.

[0022] FIG. 11 is a schematic cross-sectional view of an optical stack including reflective and absorbing polarizers, a retarder and a partial reflector, according to some embodiments.

[0023] DETAILED DESCRIPTION

[0024] 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.

[0025] According to some embodiments of the present description, it has been found that an optical stack can include first and second polarizers where the polarizers are formed (shaped) using different firstand second processes such that variations in properties of one polarizer are at least partially balanced or compensated by variations in properties of the other polarizer. Each of the first and second processes can be a pressurization process where a concave mold is used for one of the first and second processes and a convex mold is used for the other of the first and second processes. Alternatively, one of the first and second processes can be a pulldown process and the other of the first and second processes can be a pressurization processes, for example. Pulldown and pressurization processes are described in U.S. Pat. No. 11,543,572 (Jennings et al.), for example. Using a convex mold in a pressurization process or pulldown process can result in the thermoformed polarizer being thickest near a center of the polarizer (since the polarizer can be pinned to the mold near the center of the polarizer and this can limit how much the polarizer stretches near the center during the thermoforming process) while using a concave mold in a pressurization process can result in the polarizer being thinnest near a center of the polarizer (since the polarizer can stretch more near the center location than locations away from the center when the polarizer is pushed into the cavity of the concave mold. The process of forming a polarizer into a curved shape using a convex mold in a pressurization or pulldown process and the process of forming a polarizer into a curved shape using a concave mold in a pressurization process may be referred to as inverse forming processes.

[0026] In some embodiments, at least one of the first and second polarizers is a reflective polarizer. A reflective polarizer can be a cholesteric reflective polarizer including a liquid crystal layer or can be a multilayer optical film reflective polarizer including a plurality of interference layers (layers that reflect or transmit light primarily by optical interference), for example. Cholesteric reflective polarizers are known in the art and are described in U.S. Pat. No. 5,793,456 (Broer et al.), for example. Optical films including interference layers are known in the art and 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. Interference layers may be described as reflecting or transmitting light primarily by optical interference when the reflectance and transmittance of the interference layers can be reasonably described by optical interference or reasonably accurately modeled as resulting from optical interference. Useful reflective polarizers include, for example, Image Quality Polarizer Enhanced (IQPE), Advanced Polarizing Film (APF), and Dual Brightness Enhancement Film (DBEF), all available from 3M Company (St. Paul, MN).

[0027] In some embodiments, at least one of the first and second polarizers is an absorbing polarizer. An absorbing polarizer can include a conventional iodine-stained polyvinyl alcohol layer, such as those available from Sanritz Corporation (Tokyo, Japan), or can include an oriented polymer layer with dye dispersed therein, such as a uniaxially oriented polyester layer with uniaxially oriented dichroic dye dispersed therein. When an optical stack includes a linear reflective polarizer and a linear absorbing polarizer, a block axis of the polarizers may be substantially aligned (e.g., to within about 6, 5, 4, 3, 2, or 1 degrees). When an optical stack includes a circular reflective polarizer (e.g., a cholesteric polarizer) anda linear absorbing polarizer, the optical stack may include a retarder (e.g., a quarter-wave retarder) disposed between the reflective and absorbing polarizers.

[0028] According to some embodiments, the optical stack may be useful in head mounted display applications such as those described in U.S. Pat. No. 10,678,052 (Ouderkirk et al.), for example. For example, the optical stack can include a reflective polarizer as a portion of a folded optical system as described in Ouderkirk et al. and can further include an absorbing polarizer which may be a pre-polarizer or a clean-up polarizer, for example.

[0029] FIG. 1 is a schematic cross-sectional view of an optical stack 100 including first and second polarizers 110 and 120, according to some embodiments. The first and second polarizers 110 and 120 are disposed along the first axis 150. In some embodiments, the first and second polarizers 110 and 120 are spaced apart along the first axis 150. In some embodiments, the optical stack 100 includes an optical lens 205 having opposing first and second major surfaces 207 and 209 where the first and second polarizers 110 and 120 are disposed on the respective first and second major surfaces 207 and 209. The optical lens 205 can be made from any suitable lens material known in the art. For example, the optical lens 205 may be made of polymethylmethacrylate (PMMA). The optical lens 205 can have any suitable lens shape such as convex-concave, biconvex, positive meniscus, negative meniscus, or biconcave. FIGS. 2A-2C are schematic cross-sectional views of optical stacks 100, according to various embodiments. In some embodiments, the first polarizer 110 is concave towards the second polarizer 120. In some embodiments, the first polarizer 110 is convex towards the second polarizer 120. In some embodiments, the second polarizer 120 is convex towards the first polarizer 110. In some embodiments, the second polarizer 120 is concave towards the first polarizer 110.

[0030] In some embodiments, an optical stack 100 includes first and second polarizers 110 and 120 disposed along a same first axis 150. In some embodiments, each of the first and second polarizers 110 and 120 is curved about second and third axes (x- and y-axes), where the first, second, and third axes are mutually orthogonal to one another, such that for substantially normally incident light 170 and for a same predetermined wavelength range (e.g., about 420 to 680 nm, or about 400 to 700 nm), each of the first and second polarizers substantially transmits (e.g., an average transmittance in the predetermined wavelength range of at least 60, 70, 80, 85, or 90 percent) the incident light having a first polarization state 171 and substantially blocks (e.g., an average transmittance in the predetermined wavelength range of no more than 40, 30, 20, 15, or 10 percent) the incident light having a second polarization state 172 orthogonal to the first polarization state 171. The polarizer can block the incident light by reflecting and / or absorbing the incident light.

[0031] In some embodiments, the first and second polarizers 110 and 120 are spaced apart along the first axis 150 and have different respective first and second curvatures at respective first and second locations 112 and 114 where the first axis 150 intersect the respective first and second polarizers 110 and 120. For example, in FIG. 1 the curvature of the first polarizer 110 and the first location 112 is greater than the curvature of the second polarizer 120 and the second location 114. Here, curvature can be understood tobe gaussian curvature, unless indicated differently. In some embodiments, the first polarizer 110 is a reflective polarizer and the second polarizer 120 is an absorbing polarizer. In some embodiments, the reflective and absorbing polarizers have different curvatures at the respective first and second locations 112 and 114. In some embodiments, the reflective and absorbing polarizers have respective higher and lower curvatures at the respective first and second locations 112 and 114. It may be preferred that the reflective and absorbing polarizer have respective higher and lower curvatures as this has been found to better maintain a low block-state transmittance, for example, according to some embodiments. In some other embodiments, the reflective and absorbing polarizers have respective lower and higher curvatures at the respective first and second locations 112 and 114. In some embodiments, each of the first and second polarizers 110 and 120 is substantially centered on the first axis 150 (e.g., for each polarizer, a distance between a centroid of the polarizer and the first axis can be less than 15, 10, 5, 3, or 2 percent of a largest dimension of the polarizer).

[0032] In some embodiments, the optical stack 100 further includes an optical lens 205 having opposing first and second major surfaces 207 and 209, with the first and second polarizers 110 and 120 disposed on, and substantially conforming (e.g., conforming, or nominally conforming, or conforming up to variations small (e.g., less than 10, 7, 5, 3, or 2 percent compared to a largest dimension of the major surface) to, the respective first and second major surfaces 207 and 209. In some embodiments, each of the optical lens and the first and second polarizers is substantially centered on the first axis 150. In some such embodiments, or in other embodiments, the first polarizer 110 is a reflective polarizer and the second polarizer 120 is an absorbing polarizer. In some embodiments, the reflective and absorbing polarizers have different average curvatures. In some embodiments, the reflective polarizer has an average curvature higher than an average curvature of the absorbing polarizer. In some embodiments, the reflective polarizer has an average curvature smaller than an average curvature of the absorbing polarizer. The average curvature of a polarizer can be understood to be the unweighted mean of the gaussian curvature over a total area of the polarizer, unless indicated differently.

[0033] FIGS. 3A-3C are schematic plots of thickness versus position for polarizers 105a and 105b, according to some embodiments. The polarizer 105a can be thermoformed via pressurization against a convex mold while the polarizer 105b can be thermoformed via pressurization against a concave mold, for example. The position where the polarizers intersect the first axis 150 is schematically indicated. One of the polarizers 105a and 105b can correspond to one of the polarizers 110 and 120, and the other of the polarizers 105a and 105b can correspond to the other of the polarizers 110 and 120. In FIG. 3A, the polarizer 105a is thicker than the polarizer 105b. In FIG. 3B, the polarizer 105a is thicker than the polarizer 105b near the first axis 150, and the polarizer 105b is thinner than the polarizer 105b away from the first axis 150. In FIG. 3C, the polarizer 105a is thinner than the polarizer 105b.

[0034] In some embodiments, one (e.g., corresponding to polarizer 105a) of the first and second polarizers 110 and 120 is thinner closer to the first axis and thicker farther from the first axis (e.g., thicknesses hl at position dl and h2 at position d2, where hl < h2 and dl is closer to the first axis 150than d2); and the other (e.g., corresponding to polarizer 105b) of the first and second polarizers 110 and 120 is thicker closer to the first axis and thinner farther away from the first axis (e.g., thicknesses h3 at position dl and h4 at position d2, where h3 > h4 and dl is closer to the first axis 150 than d2). In some embodiments, the one of the first and second polarizers 110 and 120 has a thickness hl at a distance dl from the first axis along a first direction (e.g., y-direction) and a thickness h2 at a distance d2 from the first axis along the first direction, where dl < 0.7 d2 and hl < 0.98 h2. In some such embodiments, or in other embodiments, hl is less than 0.96, 0.94, 0.92, 0.9, 0.88, 0.85, or 0.8 times h2. In some such embodiments, or in other embodiments, dl is less than 0.6, 0.5, 0.4, 0.3, 0.2, or 0.1 times d2. In some such embodiments or in other embodiments, dl is 0 and d2 is at least 80% of a maximum distance along the polarizer from the first axis along the first direction. In some such embodiments, or in other embodiments, the other of the first and second polarizers has a thickness h3 at the distance dl from the first axis along the first direction and a thickness h4 at the distance d2 from the first axis along the first direction, where h4 < 0.98 h3 or h4 is less than 0.96, 0.94, 0.92, 0.9, 0.88, 0.85, or 0.8 times h3.

[0035] In some embodiments, an optical stack 100 includes spaced apart curved first and second polarizers 110 and 120 disposed along a same first axis 150, such that for incident light 170 substantially along the first axis 150 and for a same predetermined wavelength range (e.g., about 420 nm to about 680 nm): each of the first and second polarizers 110 and 120 has a maximum average transmittance for the incident light having a first polarization state 171 and a minimum average transmittance (Tmin) for the incident light having a second polarization state 172 orthogonal to the first polarization state 171. Here, the minimum and maximum of the average transmittance is taken over polarization states so that the minimum and maximum transmittance s correspond to transmittances for respective block and pass polarization states. The light 170 substantially along the first axis can be substantially collimated light beam (e.g., having a divergence / convergence angle of less than about 5, 3, 2 or 1 degree) propagating substantially parallel (e.g., within 20, 15, 10, 8, or 5 degrees of parallel) to the first axis 150 and covering the first and second locations 112 and 114 when incident on the respective first and second polarizers 110 and 120.

[0036] FIGS. 4A and 4B are schematic contour plots of Tmin for differently thermoformed polarizers, according to some embodiments. Regions of high (H) and low (L) Tmin are schematically indicated. The polarizer of FIG. 4A can be thermoformed via pressurization against a convex mold and can correspond to polarizer 105a while the polarizer of FIG. 4B can be thermoformed via pressurization against a concave mold and can correspond to polarizer 105b, for example. In some embodiments, an optical stack 100 includes both polarizers such that in a plan view, the high Tmin region H of one polarizer at least partially overlaps the low Tmin region L of the other polarizer. Optical artifacts of the variation in Tmin can be at least partially compensated by having the high and low Tmin regions H and L of the two polarizers at least partially overlap.

[0037] In some embodiments, one (see, e.g., FIG. 4A) of the first and second polarizers 110 and 120 has a lower minimum average transmittance closer to the first axis 150 and a higher minimum averagetransmitance farther from the first axis 150 (e.g., minimum average transmitances T1 at position dl and T2 at position d2, where T1 < T2 and dl is closer to the first axis 150 than d2); and the other (see, e.g., FIG.4B) of the first and second polarizers 110 and 120 has a higher minimum average transmitance closer to the first axis 150 and a lower minimum average transmitance farther away from the first axis 150 (e.g., minimum average transmittances T3 at position dl and T4 at position d2, where T3> T4 and dl is closer to the first axis 150 than d2). In some embodiments, for incident light 10 substantially along the first axis 150 and for the same predetermined wavelength range: the one of the first and second polarizers 110 and 120 has a minimum average transmitance T1 at a first location 331 (i.e., Tmin at the first location 331 is Tl) a distance dl from the first axis 150 along a first direction (e.g., y-direction) and a minimum average transmitance T2 at a second location 332 a distance d2 from the first axis 150 along the first direction, where dl < 0.7 d2 and Tl < 0.9 T2. In some such embodiments, or in other embodiments, dl is less than 0.6, 0.5, 0.4, 0.3, 0.2, or 0.1 times d2. In some such embodiments, or in other embodiments, Tl is less than 0.85, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, or 0.2 times T2. In some such embodiments, or in other embodiments, for incident light 170 substantially along the first axis 150 and for the same predetermined wavelength range: the other of the first and second polarizers 110 and 120 has a minimum average transmittance T3 at a third location 333 at the distance dl from the first axis 150 along the first direction and a minimum average transmitance T4 at a fourth location 334 at the distance d2 from the first axis along the first direction, where T4 < 0.95 T3. In some such embodiments, or in other embodiments, T4 is less than 0.925, 0.9, 0.875, 0.85, 0.8, 0.7, 0.6, 0.5, or 0.4 times T3.

[0038] FIG. 5A-5C are plots of Tmin versus position for various polarizers, according to some embodiments.

[0039] In FIG. 5A, the polarizer was a multilayer optical film reflective polarizer available under the tradename of Image Quality Polarizer Enhanced (IQPE) from 3M Company (St. Paul, MN). Results are shown for thermoforming in a pressurization process using concave and convex molds having a 38.6 mm radius of curvature and a 40 mm aperture (curves 38.6 ConcaveTD and 38.6 ConvexTD) or having a radius of curvature of 65 mm and a 48 mm aperture (curves 65 ConcaveTD and 65 ConvexTD). The polarizers were thermoformed using an infrared (IR) heater temperature of 400 to 450 deg. F ( 204 to 232 deg. C) for 40 seconds resulting in a film temperature of approximately 125 to 150 deg. C. Tmin is ploted as a function of position along a transverse direction (TD, corresponding to y-direction) orthogonal to a machine direction (MD) used in orienting a multilayer extruded web in making the polarizer. Examples of the minimum transmittances Tl through T4 are indicated in FIG. 5A.

[0040] In FIGS. 5B-5C, the polarizer was an absorbing polarizer useful in virtual reality applications and denoted VRAP. The absorbing polarizer was made by coextruding and substantially uniaxially costretching a polyethylene naphthalate (PEN) layer) between substantially amorphous outer layers formed of a blend of polycarbonate and polyesters (e.g., as described for PCcoPET in U.S. Pat. No. 10,288,789 (Johnson et al.)) with dichroic die dispersed in the PEN layer (e.g., as described in U.S. Pat. Appl. Pub. No. 2021 / 0033766 (Haag et al.)) as described further elsewhere herein. The polarizers werethermoformed using an IR heater temperature of 450 deg. F (232 deg. C) for 40 seconds. Results are shown for thermoforming in a pressurization process using a convex mold (FIG. 5B) or using a concave mold (FIG. 5C), with each mold having a 38.6 mm radius of curvature and a 40 mm aperture. Tmin is plotted as a function of position along a transverse direction (TD), a machine direction (MD), and at angles of plus or minus 45 degrees relative to the machine direction. In some embodiments, an optical stack includes a reflective polarizer formed using a convex mold (e.g., corresponding to 38.6 ConvexTD) and an absorbing polarizer formed using a concave mold (e.g., corresponding to VRAP 38.6 ConcaveTD). For example, in FIG. 5A, the curve 38.6 ConvexTD is mostly convex upward while in FIG.

[0041] 5C, the curve VRAP 38.6 ConcaveTD is mostly concave downward so that the shapes of the Tmin versus position curves at least partially compensates for the variations of Tmin with position. As an alternative to VRAP, a conventional absorbing polarizer (e.g., a Sanritz polarizer) may be used. It has been found that conventional absorbing polarizers show a similar overall pattern of Tmin and polarization axis variation as a VRAP absorbing polarizer, but with an overall lower value of Tmin (e.g., less than 2 or 1 percent at least near the first axis 150 for convex forming) but often exhibited regions of high Tmin (e.g., greater than 20 or 40 percent away from the first axis 150) unless a low forming temperature (e.g., a film temperature of less than about 125 deg. C) was utilized. In some embodiments, VRAP is preferred over conventional iodine-stained absorbing polarizers due to its stability under higher thermoforming temperatures.

[0042] In some embodiments (e.g., in the case of a reflective polarizer), each of T1 to T4 is in a range of 0.1 to 2 percent, or 0.2 to 1.5 percent, or 0.3 to 1.3 percent, or 0.4 to 1.2 percent. In some embodiments (e.g., in the case of an absorptive polarizer such as VRAP), each of T1 to T4 is in a range of 1 to 25 percent, or 5 to 22 percent, or 9 to 19 percent, or 11 to 16 percent.

[0043] In some embodiments, an optical stack 100 includes spaced apart first and second polarizers 110 and 120 disposed along a same first axis 150 and having different respective first and second curvatures at respective first and second locations 112 and 114 where the first axis 150 intersects the respective first and second polarizers 110 and 120, such that for incident light substantially along the first axis 150 and for a same predetermined wavelength range (e.g., about 420 nm to about 680 nm), each of the first and second polarizers 110 and 120 has a maximum average transmittance for the incident light polarized along a pass axis (e.g., x-axis) and a minimum average transmittance for the incident light polarized along a block axis (e.g., y-axis) orthogonal to the pass axis.

[0044] FIG. 6 is a schematic plan view of an optical stack 100 along a first axis 150 illustrating pass axes of first and second polarizers 110 and 120, according to some embodiments. The first and second polarizers 110 and 120 can have a substantially same pass axis 261 at the first axis 150. One (e.g., corresponding to polarizer 105a) of the first and second polarizers has a pass axis 305a at a distance d3 from the first axis 150 along a first direction 253 (e.g., a direction making an angle in a range of 40 to 50 degrees with the x-axis) and the other (e.g., corresponding to polarizer 105b) of the first and second polarizers has a pass axis 305b at the distance d3 from the first axis 150 along the first direction 253. Thepass axes 305a and 305b are rotated in respective counterclockwise and clockwise directions relative to the pass axis 261.

[0045] FIGS. 7A-7B are schematic contour plots of pass axis orientation for polarizers, according to some embodiments. The polarizer of FIG. 7A can be thermoformed via pressurization against a convex mold and can correspond to polarizer 105a while the polarizer of FIG. 7B can be thermoformed via pressurization against a concave mold and can correspond to polarizer 105b, for example. The pass axis is close to parallel to the pass axis 261 near the first axis 150 and is rotated clockwise (indicated by a “+”) or counterclockwise (indicated by a

[0046]

[0047] relative to the pass axis 261 in regions at about plus or minus 45 degrees from the x-axis. Patterns similar to those of FIGS. 7A-7B have been found for thermoformed IQPE, VRAP and conventional iodine-stained absorbing polarizers. However, in some cases, there may be regions (not shown in FIGS. 7A-7B) adjacent to a “+” or region showing the opposite behavior of the “+” or region (e.g., such behavior has been found for some directions when thermoforming absorbing polarizers via convex pressurization). In some embodiments, an optical stack 100 includes the first and second polarizers such that in a plan view, the high clockwise rotated regions “+” of one polarizer at least partially overlaps the high counterclockwise rotated regions of the other polarizer. Optical artifacts of the variation in the pass axis can be at least partially compensated by having the “+” and regions of the two polarizers at least partially overlap.

[0048] In some embodiments, in a plan view along the first axis 150: for a same first distance d3 away from the first axis 150 along a same first direction 253, the pass axes of the first and second polarizers 110 and 120 are rotated in opposite directions from a substantially same pass axis 261 of the first and second polarizers at the respective first and second locations 112 and 114. In some such embodiments, in the plan view along the first axis 150 and for the same first distance d3 away from the first axis along a same first direction 253, the pass axes of the first and second polarizers 110 and 120 are each rotated by an angle in a range of about 0.05 to 10 degrees from the substantially same pass axis 261 of the first and second polarizers at the respective first and second locations 112 and 114. In some such embodiments, or in other embodiments, for each of the first and second polarizers 110 and 120, the angle is at least about 0.06, 0.08, 0.1 0.12, 0.15, 0.2, 0.25, 0.5, 0.75, or 1 degree. In some such embodiments, or in other embodiments, for each of the first and second polarizers 110 and 112, the angle is no more than about 8, 6, 5, 4, 3, 2.5, 2, or 1.5 degrees. The pass axes of the first and second polarizers 110 and 120 at the first and second locations 112 and 114 are substantially the same in the plan view when an angle between these axes is substantially smaller (e.g., at least a factor of 3, 5, 10, or 20) than each of the angles (e.g., each of the angles between the x-axis and the axes 305a and 305b in FIG. 6) at the distance d3 along the direction 253.

[0049] FIG. 8A-8C are plots of polarization axis orientation (relative to the x-axis) versus position for various polarizers made as described for FIGS. 5A-5C, according to some embodiments. In FIG. 8 A, the polarizer was a multilayer optical film reflective polarizer available under the tradename of IQPE from 3M Company (St. Paul, MN). Results are shown for thermoforming in a pressurization process usingconcave and convex molds having a 38.6 mm radius of curvature and a 40 mm aperture (curves 38.6 Concave45 and 38.6 Convex45) and or having a radius of curvature of 65 mm and a 48 mm aperture (curves 65 Concave45 and 65 Convex45). The polarization axis is plotted as a function of position along a direction making a 45-degree angle with the x- and y-axes. An example d3 is indicated in FIG. 8A. In FIGS. 8B-8C, the polarizer was an absorbing polarizer denoted VRAP as described further elsewhere herein. Results are shown for thermoforming in a pressurization process using a convex mold (FIG. 8B) or using a concave mold (FIG. 8C), with each mold having a 38.6 mm radius of curvature and a 40 mm aperture. The polarization axis is plotted as a function of position along a transverse direction (TD), a machine direction (MD), and at angles of plus or minus 45 degrees relative to the machine direction. In some embodiments, an optical stack includes a reflective polarizer formed using a convex mold (e.g., corresponding to 38.6 Convex45) and an absorbing polarizer formed using a concave mold (e.g., corresponding to VRAP 38.6 Concave45). For example, in FIG. 8A, the curve 38.6 Convex45 has dips at lateral positions and in FIG. 8C, the curve VRAP 38.6 Concave45 has peaks at lateral positions so that the shapes of the polarization axis versus position curves at least partially compensates for the variations of the polarization axis with position.

[0050] FIG. 9 is a schematic cross-sectional view of a multilayer polymeric reflective polarizer 50, according to some embodiments. The polymeric reflective polarizer 50 can correspond to one of the polarizers 110 or 120, for example. In some embodiments, the polymeric reflective polarizer 50 includes a plurality of polymeric layers 51, 52, 53. In some embodiments, the polymeric reflective polarizer 50 includes a plurality of alternating first and second polymeric layers 51, 52, where each first and second polymeric layer 51, 52 has an average thickness of less than about 500, 450, 400, 350, or 300 nm. In some embodiments, the average thickness of each of the first and second polymeric layers 51, 52 is at least 5, 10, 20, 30, 40, or 50 nm. In some embodiments, the plurality of alternating first and second polymeric layers 51, 52 number at least 10, 20, 30, 40, or 50 in total. In some embodiments, the total number of first and second polymeric layers 51, 52 is no more than 3000, 2000, or 1000. In some embodiments, the plurality of alternating first and second polymeric layers 51, 52 is disposed between skin layers 53. In some embodiments, each skin layer 53 has an average thickness greater than about 500, 750, 1000, or 1500 nm. The average thickness of each skin layer 53 may be up to about 50, 40, 30, 20, or 10 micrometers, for example. In some embodiments, the first layers 51 are substantially optically isotropic, and the second layers 52 are birefringent. For example, for at least one wavelength in a wavelength range from about 400 nm to about 700 nm, a maximum birefringence of the first layers 51 can be less than about 0.03, 0.025, 0.02, 0.015, or 0.01 while the maximum birefringence of the second layers 52 can be greater than about 0.05, 0.075, 0.1, 0.125, or 0.15.

[0051] In some embodiments, for a substantially normally incident light 170 and a predetermined wavelength range (e.g., about 400 nm to about 700 nm or about 420 nm to about 680 nm), the reflective polarizer 50 substantially reflects (e.g., average optical reflectance greater than about 60, 70, 80, or 90 percent) the incident light for a first polarization state 171 and substantially transmits (e.g., averageoptical transmittance greater than about 60, 70, 80, or 85 percent) the incident light for an orthogonal second polarization state 172.

[0052] FIG. 10 is a schematic cross-sectional view of an absorbing polarizer 60, according to some embodiments. The absorbing polarizer 60 can correspond to one of the polarizers 110 or 120, for example. The absorbing polarizer 60 include an inner layer 71 disposed between outer layers 72 and 73. In some embodiments, the absorbing polarizer 60 includes an iodine-stained polyvinyl alcohol layer. For example, layer 71 may be an iodine -stained polyvinyl alcohol layer (in which case, optional oriented dye molecules 74 may be omitted from the volume of the layer and oriented iodine molecules may be present at or near a major surface of the layer) while layers 72 and 73 may be protective layers. Absorbing polarizers including an iodine-stained polyvinyl alcohol layer are known in the art and include those available from Sanritz Corporation (Tokyo, Japan). An alternative to utilizing a polyvinyl alcohol layer is to use an extruded polymer layer that includes a dye (e.g., 74) dispersed therein and that is stretched to orient the polymer molecules and the dye. The polymer may be any strain hardening polymer (e.g., polyester polymers or copolymers) such as those commonly used for the birefringent layers of a multilayer optical fdm. The polymer is typically a thermoplastic and is typically water insoluble, in contrast to polyvinyl alcohol which is water soluble. A polymer with a water solubility so low at room temperature (e.g., about 23 deg. C) that a fdm cannot practically be formed from the polymer via deposition from a water-based solution of the polymer will be considered to be water insoluble. The dye can be dichroic dye such as those described in U.S. Pat. Appl. Pub. No. 2021 / 0033766 (Haag et al.), for example, and those available from Mitsui Fine Chemicals, Inc. (Tokyo, Japan), for example. Haag et al. describes an absorbing polarizer layer comprising dichroic dye dispersed in a layer of polyethylene naphthalate (PEN). Other useful strain hardening polyesters include polyethylene terephthalate (PET), for example.

[0053] In some embodiments, an absorbing polarizer 60 includes a water-insoluble thermoplastic polymer layer 71 comprising substantially uniaxially oriented (e.g., nominally uniaxially oriented or oriented more or substantially more along a same first axis than along any other axis) optically absorptive dye 74 dispersed therein. In some embodiments, the absorbing polarizer 60 includes co-extruded and costretched first and second polymeric outer layers 72 and 73 and a polymeric inner layer 71 disposed therebetween, where the inner layer 71 includes substantially uniaxially oriented optically absorptive dye 74 dispersed therein. In some embodiments, each of the first and second polymeric outer layers 72 and 73 and the polymeric inner layer 71 comprises water-insoluble thermoplastic polymer. In some embodiments, each of the first and second polymeric outer layers 72 and 73 comprise a substantially optically isotropic polymer (e.g., a blend of polycarbonate and polyesters, or glycol-modified PET (PETG), or other substantially isotropic polyesters, or PMMA or coPMMA) and the polymeric inner layer comprises a birefringent polyester (e.g., PET or PEN). In some embodiments, each of the first and second polymeric outer layers 72 and 73 comprise respective first and second polymers having respective first and second compositions, and the polymeric inner layer 71 comprises a third polymer having a thirdcomposition different from each of the first and second compositions. In some embodiments, the first and second compositions are substantially same compositions (e.g., nominally the same or the same up to minor variations that do not substantially affect the physical or optical properties of the layers).

[0054] In some embodiments, for a substantially normally incident light 170 and a predetermined wavelength range (e.g., about 420 nm to about 680 nm), the absorbing polarizer 60 substantially absorbs (e.g., average optical absorption greater than about 60, 70, 80, or 85 percent) the incident light for a first polarization state 171 and substantially transmits (e.g., average optical transmittance greater than about 60, 70, 80, or 85 percent) the incident light for an orthogonal second polarization state 172.

[0055] In some embodiments, the absorbing polarizer 60 has a contrast ratio of no more than about 500, 250, 100, 50, 25, or 10. In some such embodiments, or in other embodiments, the absorbing polarizer 60 has a contrast ratio of at least 1.5, 2, 3, 4, or 5. The contrast ratio is generally the ratio of the average pass state (second polarization state 172) transmittance to average block state (first polarization state 171) transmittance for a substantially normally incident light 170 and a wavelength range of about 420 nm to about 680 nm.

[0056] In some embodiments, an optical stack includes reflective and absorbing polarizers. In some embodiments, the optical stack is incorporated into an optical system that further includes a partial reflector, and a retarder disposed between the partial reflector and the reflective polarizer of the optical stack as generally described in U.S. Pat. No. 10,678,052 (Ouderkirk et al.), for example. The absorbing polarizer can be disposed on an opposite side of the reflective polarizer from the retarder (e.g., the absorbing polarizer can be a clean-up polarizer). In some embodiments, the optical stack further includes the retarder and partial reflector.

[0057] FIG. 11 is a schematic cross-sectional view of an optical stack 200, according to some embodiments. In some embodiments, optical stack 200 includes optical stack 100 (including reflective and absorbing polarizers 110 and 120 and first optical lens 205) and further includes retarder 280 and partial reflector 290. The optical stack 200 further includes second and third optical lenses 245 and 285 where the partial reflector 290 and the retarder 280 are disposed on opposite major surfaces of the third optical lens 285 and the second optical lens is disposed between, and attached to, the reflective polarizer 110 and the retarder 280. An optional protective lens 215 may be disposed on the absorbing polarizer 120 opposite the first optical lens 205. In some embodiments, for a first wavelength in a range of about 400 nm to about 700 nm, the retarder has a retardance of about a quarter of the first wavelength. In some embodiments, for each of orthogonal first and second polarization states 171 and 172 and for a wavelength range of about 420 nm to about 680 nm, the partial reflector 290 has an average transmittance and an average reflectance that are each in a range of about 30 to 70 percent, or about 40 to 60 percent, or about 45 to 55 percent.

[0058] 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 quantitiesexpressing 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.

[0059] 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.

[0060] 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.

[0061] 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 stack comprising first and second polarizers disposed along a same first axis, each of the first and second polarizers curved about second and third axes, the first, second, and third axes being mutually orthogonal to one another, such that for substantially normally incident light and for a same predetermined wavelength range, each of the first and second polarizers substantially transmits the incident light having a first polarization state and substantially blocks the incident light having a second polarization state orthogonal to the first polarization state, wherein:one of the first and second polarizers is thinner closer to the first axis and thicker farther from the first axis; andthe other of the first and second polarizers is thicker closer to the first axis and thinner farther away from the first axis.

2. The optical stack of claim 1, wherein the first and second polarizers are spaced apart along the first axis and have different respective first and second curvatures at respective first and second locations where the first axis intersects the respective first and second polarizers.

3. The optical stack of claim 1, wherein the first polarizer is a reflective polarizer and the second polarizer is an absorbing polarizer.

4. The optical stack of claim 1 further comprising an optical lens having opposing first and second major surfaces, the first and second polarizers disposed on, and substantially conforming to, the respective first and second major surfaces.

5. The optical stack of claim 4, wherein each of the optical lens and the first and second polarizers is substantially centered on the first axis.

6. The optical stack of claim 4, wherein the first polarizer is a reflective polarizer and the second polarizer is an absorbing polarizer, the reflective and absorbing polarizers having different average curvatures.

7. The optical stack of claim 1, wherein the one of the first and second polarizers has a thickness hl at a distance dl from the first axis along a first direction and a thickness h2 at a distance d2 from the first axis along the first direction, dl < 0.7 d2, hl < 0.98 h2.

8. The optical stack of claim 7, wherein the other of the first and second polarizers has a thickness h3 at the distance dl from the first axis along the first direction and a thickness h4 at the distance d2 from the first axis along the first direction, h4 < 0.98 h3.

9. An optical stack comprising spaced apart curved first and second polarizers disposed along a same first axis, such that for incident light substantially along the first axis and for a same predetermined wavelength range:each of the first and second polarizers has a maximum average transmittance for the incident light having a first polarization state and a minimum average transmittance for the incident light having a second polarization state orthogonal to the first polarization state;one of the first and second polarizers has a lower minimum average transmittance closer to the first axis and a higher minimum average transmittance farther from the first axis; andthe other of the first and second polarizers has a higher minimum average transmittance closer to the first axis and a lower minimum average transmittance farther away from the first axis.

10. The optical stack of claim 9, wherein for incident light substantially along the first axis and for the same predetermined wavelength range:the one of the first and second polarizers has a minimum average transmittance T1 at a first location a distance dl from the first axis along a first direction and a minimum average transmittance T2 at a second location a distance d2 from the first axis along the first direction, dl < 0.7 d2, T1 < 0.9 T2.

11. The optical stack of claim 10, wherein for incident light substantially along the first axis and for the same predetermined wavelength range:the other of the first and second polarizers has a minimum average transmittance T3 at a third location at the distance dl from the first axis along the first direction and a minimum average transmittance T4 at a fourth location at the distance d2 from the first axis along the first direction, T4 < 0.95 T3.

12. The optical stack of claim 9, wherein for incident light substantially along the first axis and for the same predetermined wavelength range:the other of the first and second polarizers has a minimum average transmittance T3 at a third location at a distance dl from the first axis along a first direction and a minimum average transmittance T4 at a fourth location a distance d2 from the first axis along the first direction, dl < 0.7 d2, T4 < 0.9 T3.

13. An optical stack comprising spaced apart first and second polarizers disposed along a same first axis and having different respective first and second curvatures at respective first and second locations where the first axis intersects the respective first and second polarizers, such that for incident light substantially along the first axis and for a same predetermined wavelength range, each of the first and second polarizers has a maximum average transmittance for the incident light polarized along a pass axis and aminimum average transmitance for the incident light polarized along a block axis orthogonal to the pass axis, wherein in a plan view along the first axis:for a same first distance away from the first axis along a same first direction, the pass axes of the first and second polarizers are rotated in opposite directions from a substantially same pass axis of the first and second polarizers at the respective first and second locations.

14. The optical stack of claim 13, wherein in the plan view along the first axis and for the same first distance away from the first axis along the same first direction, the pass axes of the first and second polarizers are each rotated by an angle in a range of 0.05 to 10 degrees from the substantially same pass axis of the first and second polarizers at the respective first and second locations.

15. The optical stack of claim 13, wherein in the plan view along the first axis and for the same first distance away from the first axis along the same first direction, the pass axes of the first and second polarizers are each rotated by an angle in a range of 0.1 to 5 degrees from the substantially same pass axis of the first and second polarizers at the respective first and second locations.

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