Optical systems

Abstract

The present invention provides optical assemblies and optical systems for forming images. [Solution] The optical assembly 400 includes an integrated lens assembly 100 having one or more lenses bonded to each other, with spaced-apart first and second lens main surfaces 11, 21. The first and second optical films 30, 40 are bonded to the first and second lens main surfaces 11, 21, respectively. The first and second optical films 30, 40 include a plurality of polymer layers. Each polymer layer has an average thickness of less than about 500 nm. For substantially perpendicularly incident light and in the visible wavelength range, the plurality of polymer layers in the first optical film have an average light transmittance and average light reflectance of more than about 70% for a first polarization state and an orthogonal second polarization state, respectively. The plurality of polymer layers in the second optical film have an average light transmittance of more than about 70% for at least one of the first and second polarization states.

Description

Technical Field

[0001] The present disclosure generally relates to the field of optics, and more specifically, to an optical system for forming an image.

Background Art

[0002] Optical systems that can form an image from an illuminated object find numerous and important applications in areas such as advertising, marketing, and product displays. The optical system may also be included in a head-mounted display to provide an image to an observer. Such an optical system may include a display panel and various optical components between the display panel and the observer's eye. In such a system, it is advantageous to be small in size, have a wide viewing angle and high contrast, and be observable under any ambient lighting conditions.

Summary of the Invention

[0003] Some aspects of the present disclosure relate to an optical assembly including an integrated lens assembly having one or more lenses joined to each other with spaced-apart first and second lens principal surfaces. First and second optical films are joined to the first and second lens principal surfaces, respectively. Each of the first and second optical films includes a plurality of polymer layers totaling at least 10 layers, and each polymer layer has an average thickness of less than about 500 nm. For substantially normal incident light and in the visible wavelength range extending from about 420 nm to about 680 nm, the plurality of polymer layers in the first optical film have an average light transmittance of more than about 70% for the first polarization state in the visible wavelength range and an average light reflectance of more than about 70% for the orthogonal second polarization state. The plurality of polymer layers in the second optical film have an average light transmittance of more than about 70% for at least one of the first and second polarization states in the visible wavelength range.

[0004] Some other aspects of the present disclosure relate to an optical assembly including a polymer optical lens having first and second lens main surfaces facing opposite directions, wherein at least one of the first and second lens surfaces is curved. The first and second polymer optical films are bonded to the first and second lens main surfaces, respectively. The first and second polymer optical films have respective average thicknesses T1 and T2, respective elastic stiffness moduli Q1 and Q2 in the same first direction, and respective thermal strains E1 and E2 in the same second direction, and the products Q1T1E1 and Q2T2E2 are within 20% of each other.

[0005] Some other aspects of the present disclosure relate to an optical assembly including a polymer optical lens having first and second lens main surfaces facing opposite directions, wherein at least one of the first and second lens surfaces is curved. The first and second polymer optical films are bonded to the first and second lens main surfaces, respectively. The first and second polymer optical films have respective average thicknesses T1 and T2, respective elastic moduli Q1 and Q2 in the same first direction, and respective coefficients of thermal expansion A1 and A2 in the same second direction, and the products Q1T1A1 and Q2T2A2 are within 20% of each other.

[0006] Some aspects of this disclosure relate to an optical assembly including an integrated lens assembly having one or more lenses bonded to each other, each having a spaced-apart first and second lens main surface. A polymer reflective polarizer is bonded to the first lens main surface, and an optical film is bonded to the second lens main surface. The optical film includes a first optical layer having refractive indices nx1 and ny1 along the x and y directions in mutually orthogonal planes, respectively, and a refractive index nz1 along the thickness direction of the optical layer, which is orthogonal to the x and y directions. For at least one wavelength in the visible wavelength range from about 420 nm to about 650 nm, the magnitude of the difference between nx1 and ny1 is greater than about 0.02, and the magnitude of the difference between nz1 and one of nx1 and ny1 is less than about 0.02. For substantially perpendicular incident light in the visible wavelength range, a reflective polarizer has an average light transmittance of over 70% for incident light polarized along one of the x and y directions, and an average light reflectance of over 70% for incident light polarized along the other of the x and y directions. A polymer reflective polarizer exhibits transmittance variation depending on the azimuth angle, with the maximum reflectance corresponding to one direction defining the principal optical axis. This can alternatively be called the cutoff state. Transmittance is maximized in the direction perpendicular to the cutoff state, which is generally called the pass-through state of the polarizer. These pass-through and cutoff states define the principal optical axis of the reflective polarizer. The first optical layer of the optical film has an average light transmittance of over 70% for incident light polarized along each of the x and y directions.

[0007] Some aspects of this disclosure relate to optical assemblies including an integrated lens assembly having one or more lenses bonded to each other, each having spaced-apart first and second lens main surfaces. A polymer reflective polarizer is bonded to the first lens main surface, and an optical film is bonded to the second lens main surface. The optical film includes a first optical layer having refractive indices nx1 and ny1 along the x and y directions in mutually orthogonal planes, respectively, and a refractive index nz1 along the thickness direction of the optical layer, which is orthogonal to the x and y directions. For at least one wavelength in the visible wavelength range from about 420 nm to about 650 nm, nx1 > ny1 > nz1, and each of nx1-ny1 and ny1-nz1 is greater than about 0.02. For substantially perpendicular incident light and in the visible wavelength range, the reflective polarizer has an average light transmittance of greater than about 70% for incident light polarized along one of the x and y directions, and an average light reflectance of greater than about 70% for incident light polarized along the other of the x and y directions. The first optical layer of the optical film has an average light transmittance of over 70% for incident light polarized along the x and y directions, respectively.

[0008] Some other aspects of the present disclosure relate to an optical assembly including a polymer optical lens having first and second lens main surfaces facing opposite directions, wherein at least one of the first and second lens surfaces is curved. The first and second polymer optical films are bonded to the first and second lens main surfaces, respectively. Each of the first and second polymer optical films has an average thickness T, an elastic stiffness Q along the same first direction, and a thermal strain E along the first direction, wherein the product QTE of the first polymer optical film is within 20% of the product QTE of the second polymer optical film.

[0009] In some cases, thermal strain can be governed by reversible thermal expansion behavior. In these cases, thermal strain can be adequately defined as the product of the temperature change and the thermal expansion coefficients A1 and A2, defined in the same second direction. In other embodiments, thermal strain can be governed by irreversible or contraction behavior. In other embodiments, thermal strain can arise from a combination of both reversible and irreversible effects.

[0010] Some other aspects of the present disclosure relate to an optical assembly including a polymer optical lens having first and second lens main surfaces facing opposite directions, wherein at least one of the first and second lens surfaces is curved. The first and second polymer optical films are bonded to the first and second lens main surfaces, respectively. Each of the first and second polymer optical films has an average thickness T, an elastic stiffness modulus Q along the same first direction, and a coefficient of thermal expansion A along the first direction, wherein the product QTA of the first polymer optical film is within 20% of the product QTA of the second polymer optical film.

[0011] Other embodiments of the present disclosure relate to an optical system for displaying an image to an observer, comprising a display adapted to emit an image and an optical assembly according to one or more embodiments described herein. A first retarder layer is disposed between the optical assembly and the display. A display lens is disposed between the first retarder layer and the display. A partial reflector is disposed on and conforms to the main surface of the first optical lens and has an average light reflectance of at least 30% in the visible wavelength range. [Brief explanation of the drawing]

[0012] Various aspects of this disclosure will be discussed in more detail with reference to the accompanying drawings.

[0013] [Figure 1A] This figure schematically shows optical assemblies according to several embodiments. [Figure 1B] This figure schematically shows an integrated lens assembly according to several embodiments. [Figure 2] This figure schematically shows the structure of an optical film according to several embodiments. [Figure 3A] This figure schematically illustrates a lens assembly comprising one or more lenses having concave and / or convex lens surfaces according to different embodiments. [Figure 3B]This figure schematically illustrates a lens assembly comprising one or more lenses having concave and / or convex lens surfaces according to different embodiments. [Figure 3C] This figure schematically illustrates a lens assembly comprising one or more lenses having concave and / or convex lens surfaces according to different embodiments. [Figure 4] This figure schematically illustrates an optical system for displaying an image to an observer, according to several embodiments. [Figure 5] This figure schematically illustrates an optical assembly equipped with a polymer optical lens according to several embodiments.

[0014] These diagrams are not necessarily on a constant scale. Similar numbers used in the diagrams indicate similar components. However, it should be understood that the use of a number to indicate a component in a particular diagram is not intended to limit the component to another diagram bearing the same number. [Modes for carrying out the invention]

[0015] The following description refers to the accompanying drawings, which constitute part of this specification and illustrate various embodiments. It should be understood that other embodiments can be conceived and implemented without departing from the scope or spirit of this disclosure. Therefore, the following embodiments for carrying out the invention should not be construed as restrictive.

[0016] Without considering the balance of the mechanical system, particularly regarding thermal expansion mismatches in layered composite materials, insert molding of lenses with optical films can result in changes in optical form that may no longer meet the optical specifications of the lens. If the in-plane mechanical properties are unbalanced, changes in curvature due to temperature or time may occur. Mechanically unbalanced composite polymer optical lenses containing optical functional films (uniaxial / biaxially oriented optical films whose material is similar or dissimilar to the polymer resin) on the lens surface(s) may not be able to maintain shape accuracy and may fail reliability tests. In layered composite materials, mechanical balance is achieved by ensuring a symmetrical distribution of material properties from a central "plane".

[0017] While it may be possible to reduce the bending effect by making one layer thicker than the other, it cannot eliminate the effect entirely. The initial curvature can be altered so that the structure bends to a desired shape at the end of the process, but the desired shape may only occur at one temperature and may be prone to change over time due to creep. It may be advantageous to balance both the elastic (reversible) properties and the residual stresses within the structure. Furthermore, bending in one direction can be reduced by balancing the mechanical properties in that direction, but in practice, this balancing must generally be done simultaneously along two separate orthogonal axes, which are preferably aligned with the axes of the maximum and minimum stress generation within the film, also referred herein as the principal directions of stress generation.

[0018] Embodiments disclosed herein provide solutions for fabricating insert-molded optical lenses having a reliable form. Other embodiments disclosed herein describe composite optical lenses having a balanced uniaxial / biaxially stretched optical film on the lens surface(s) to maintain and improve shape accuracy.

[0019] An optical system (600) for displaying an image (111) to an observer (113) is schematically shown in Figure 4. The optical system includes an optical assembly (400) and a display (110) adapted to emit an image (112). A first retarder layer (120) may be positioned between the optical assembly (400) and the display (110), and a display lens (130) may be positioned between the first retarder layer (120) and the display (110). A partial reflector (140) may be positioned on the display lens (130) and, in some embodiments, may be fabricated to fit the main surface (131) of the display lens (130). The partial reflector (140) may have an average light reflectance of at least 30% in the visible wavelength range.

[0020] Figures 1A and 1B schematically show an optical assembly (400) including a one-piece lens assembly (100). In some embodiments, the one-piece lens assembly may include a single lens (10, 20). In other embodiments, the lens assembly (100) may include one or more bonded lenses (10, 20) having a spaced-out first lens main surface (11) and a second lens main surface (21), as is best seen in Figure 1B. A first optical film (30) may be bonded to the first lens main surface (11), and a second optical film (40) may be bonded to the second lens main surface (21).

[0021] In some embodiments, as shown in Figure 3A, one or more lenses (10, 20) of an integrated lens assembly (100') may be joined to each other via an adhesive layer (60). As shown in Figures 3A to 3C, both the first main lens surface (11) and the second main lens surface (21) of the lenses (10, 20) may be convex, or both the first main lens surface (11') and the second main lens surface (21') may be concave. In other embodiments, one of the first and second main lens surfaces (11'') may be concave, and the other of the first and second main lens surfaces (21'') may be convex.

[0022] In some embodiments, each of the first optical film (30) and the second optical film (40) may be a multilayer optical film (MOF) including a plurality of polymer layers (31, 32), as shown in FIG. 2. In some examples, the plurality of polymer layers (31, 32) may have a total number of layers of at least 10. In some examples, the plurality of polymer layers (31, 32) may have a total number of layers of at least 50, at least 100, at least 200, at least 300, at least 400, or at least 500. Each of the polymer layers (31, 32) may have an average thickness of less than about 500 nm, less than about 400 nm, or less than about 200 nm. In some embodiments, the number of layers of the optical film (30) may be selected to achieve the desired optical properties using a minimum number of layers for reasons of film thickness, flexibility, and economy. For example, at least one of the first optical film (30) and the second optical film (40) may include less than 10 polymer layers. At least one of the first optical film (30) and the second optical film (40) may include at least one skin layer (33). The average thickness of the at least one skin layer (33) may be greater than about 500 nm, and in some examples, greater than 700 nm or greater than 1 micron. For the first and second optical films including the plurality of polymer layers described herein, the principal directions are selected such that the x-axis and the y-axis are in the plane of the layer and the z-axis corresponds to the thickness of the layer. The principal axes of elasticity of the film are the directions in which the elastic modulus, the coefficient of thermal expansion, and the refractive index reach their extreme values (maximum or minimum). These should also be aligned with the light passing direction and the light blocking direction in the film. When the thermal strain is dominated by the reversible thermal expansion behavior, the principal direction of stress generation will be aligned with the principal direction of elasticity of the film. However, when non-reversible effects such as shrinkage dominate the thermal strain, the principal direction of stress generation may be significantly different from the principal direction of elasticity.

[0023] Multilayer polymer films can exhibit a wide range of optical and physical properties and may be utilized for various optical and non-optical applications. The optical and physical properties of the multilayer films can depend on many variables, including the type of polymer materials used in the individual layers, the total number of the individual layers of the film, and / or the layer thickness profile of the film. As a result, the properties of the multilayer films can be adjusted by precisely controlling one or more of these variables during the film manufacturing process. A multilayer polymer film may include a plurality of individual layers each formed from one or more types of polymer materials. For example, a particular multilayer optical film may include hundreds of individual polymer layers alternating between a high refractive index polymer material and a low refractive index polymer material. The formation of such polymer layers can generally be accomplished via a feedblock device that receives a suitable polymer material in the form of a polymer melt stream and orientates the polymer material into a multilayer polymer flow stream including a stack of the individual layers. After exiting the feedblock, the multilayer flow stream can be further processed within the film line to produce a multilayer optical film. Examples of feedblocks and film lines configured to manufacture multilayer optical films are described, for example, in U.S. Patent No. 6,783,349 to Neavin et al.

[0024] Various MOFs are generally known. MOFs generally include alternating first polymer layers (31) and second polymer layers (32) comprising at least one birefringent polymer (e.g., an oriented semicrystalline polymer) and one second polymer. In some embodiments, the optical film (30) may be a multilayer stack having alternating first optical layers (31) and second optical layers (32) of at least two materials. In one embodiment, the materials of the first layer (31) and second layer (32) may consist of polymers such as polyester. For example, an exemplary polymer useful as the first birefringent layer (31) in a multilayer optical film (30) may be polyethylene naphthalate (PEN). Other semicrystalline polyesters suitable as birefringent polymers for the first birefringent layer (31) in a multilayer optical film (30) may include, for example, polybutylene 2,6-naphthalate (PBN) and polyethylene terephthalate (PET). The second layer (32) of the multilayer optical film (30) can be made from a variety of polymers having a glass transition temperature compatible with that of the first birefringent polymer layer (31) and a refractive index similar to that of the isotropic polymer layer (31). Examples of other polymers suitable for use in optical films, particularly the second polymer layer (32), include vinyl polymers and copolymers made from monomers such as vinylnaphthalene, styrene, maleic anhydride, acrylates, and methacrylates. Examples of such polymers include polyacrylates, polymethacrylates such as poly(methyl methacrylate) (PMMA), and isotactic or syndiotactic polystyrenes. Other polymers include condensation polymers such as polysulfones, polyamides, polyurethanes, polyamic acids, and polyimides. In addition, the second polymer layer (32) can be formed from polyester, polycarbonate, fluoropolymer, and homopolymers and copolymers of polydimethylsiloxane, as well as mixtures thereof. The layer is selected to achieve reflection of a specific bandwidth of electromagnetic radiation. In one embodiment, the materials of the multiple layers (31, 32) may have different refractive indices.In some embodiments, one of the first optical film (30) and the second optical film (40) may include PET as the first optical layer (31) and any other polymer having a low refractive index, including a copolymer of PMMA (coPMMA), or a copolyester, a fluorinated polymer, or a combination thereof, as the second optical layer (32). The transmission and reflection properties of the optical films (30, 40) are based on the difference in refractive index between layer (31) and layer (32) and the coherent interference of light caused by the thickness of the layers (31, 32).

[0025] In some embodiments, for substantially perpendicularly incident light (50) and in the visible wavelength range of about 420 nm to about 680 nm, the multiple polymer layers (31, 32) within the first optical film (30) may have an average light transmittance of more than about 70% with respect to a first polarization state (x axis) and an average light reflectance of more than about 70% with respect to a second orthogonal polarization state (y axis) in the visible wavelength range. In some examples, the average light transmittance of the first optical film (30) may be more than about 80%, more than about 85%, more than about 90%, more than about 95%, or more than about 99% with respect to the first polarization state (x axis), and the light reflectance of the first optical film (30) may be more than about 80%, more than about 85%, more than about 90%, more than about 95%, or more than about 99% with respect to a second orthogonal polarization state (y axis) in the visible wavelength range. Multiple polymer layers within the second optical film (40) may have an average light transmittance of more than about 70%, and in some examples more than about 80%, more than about 85%, more than about 90%, more than about 95%, or more than about 99% for at least one or each of the first and second polarization states in the visible wavelength range.

[0026] In some embodiments, in the ultraviolet wavelength range, for example, for at least one wavelength less than about 400 nm, the multiple polymer layers (31, 32) in the second optical film (40) may have an average light transmittance of more than about 60%, more than about 70%, or more than about 80% for a first polarization state (x axis) and an average light reflectance of more than about 60%, more than about 70%, or more than about 80% for a second polarization state (y axis).

[0027] According to some embodiments, in the infrared wavelength range, for example, for at least one wavelength greater than about 750 nm, the multiple polymer layers (31, 32) in the second optical film (40) may have an average light transmittance of more than about 60%, more than about 70%, or more than about 80% for a first polarization state (x axis) and an average light reflectance of more than about 60%, more than about 70%, or more than about 80% for a second polarization state (y axis).

[0028] In another embodiment, the second optical film (40) may be fabricated to be substantially transparent for at least one wavelength greater than about 750 nm in the infrared wavelength range. For example, multiple polymer layers within the second optical film (40) may have average light transmittances of more than about 60%, more than about 70%, or more than about 80% for each of the first (x-axis) and second (y-axis) polarization states.

[0029] In another embodiment, the second optical film (40) may be fabricated to be substantially reflective for at least one wavelength greater than about 750 nm in the infrared wavelength range. For example, multiple polymer layers within the second optical film (40) may have average light reflectances of more than about 60%, more than about 70%, or more than about 80% for each of the first (x-axis) and second (y-axis) polarization states.

[0030] In another embodiment, at least one of the first optical film (30) and the second optical film (40) may be fabricated to be substantially non-absorbent in the visible wavelength range of about 420 nm to about 680 nm. For example, for at least one of the first (x-axis) and second (y-axis) polarization states, at least one of the polymer layers of the first optical film (30) and the second optical film (40) may have an average light absorption rate of less than about 20%, less than about 15%, less than about 10%, or less than about 5% in the visible wavelength range.

[0031] In other embodiments, the optical assembly may include multiple layers of orthotropic material that can bend to a small extent due to either an external or internal load (e.g., thermal mismatch). Each layer may have an average thickness, a set of orthotropic elastic stiffness properties, and a set of orthotropic thermal strain. For example, as best shown in Figure 5, an optical assembly (500) having multiple layers may include a polymer optical lens (70) having a first lens main surface (71) and a second lens main surface (72) facing the opposite direction, a first polymer optical film (80) bonded to the first lens main surface (71), and a second polymer optical film (90) bonded to the second lens main surface (72). At least one of the first lens surface (71) and the second lens surface (72) may be curved. Each of the first polymer optical film (80) and the second polymer optical film (90) may have an average thickness T, an elastic stiffness Q along the same first direction (101), and a thermal strain E along the first direction. In some embodiments, the product QTE of the first polymer optical film (80) may be within 20%, 15%, 10%, 5%, 2%, or 1% of the product QTE of the second polymer optical film (90). If the thickness of the polymer optical lens (70) is greater than the average thickness of the first polymer optical film (80) and the second polymer optical film (90), the thermal strain along the neutral plane located at half the total thickness of the optical assembly may be dominated by the lens material. In some cases, in order to prevent thermal bending of the optical lens, both the layer stiffness moduli of the first polymer optical film (80) and the second polymer optical film (90), and the product of the layer stiffness moduli and the thermal strain of the first polymer optical film (80) and the second polymer optical film (90) may be canceled out.

[0032] In other embodiments, the first polymer optical film (80) bonded to the first main lens surface (71) may have an average thickness T1, and the second polymer optical film (90) bonded to the second main lens surface (72) may have an average thickness T2. At least one of the first lens surface (71) and the second lens surface (72) may be curved. In some examples, the first polymer optical film (80) may be a mechanically balanced film (MBF), and the second polymer optical film (90) may be a reflective polarizing film (RPF). The thickness profiles of the first polymer optical film (80) and the second polymer optical film (90) can generally be selectively obtained, for example, as described in U.S. Patent No. 5,882,774 (Jonza et al.), No. 6,179,948 (Merrill et al.), No. 6,783,349 (Neavin et al.), No. 6,967,778 (Wheatley et al.), and No. 9,162,406 (Neavin et al.). In some examples, at least one of the first polymer optical film (80) and the second polymer optical film (90) may contain a total of at least 10 polymer layers. In other examples, at least one of the first polymer optical film (80) and the second polymer optical film (90) may contain fewer than 10 polymer layers.

[0033] For example, as shown in Figure 5, the first polymer optical film (80) may have an elastic stiffness modulus Q1 in the first direction (101), and the second polymer optical film (90) may have an elastic stiffness modulus Q2 in the same first direction (101). The first polymer optical film (80) may have a thermal strain E1 in the second direction (102), and the second polymer optical film (90) may have a thermal strain E2 in the same second direction (102). The first direction (101) and the second direction (102) may be within 20 degrees of each other, and in some examples, they may be within 15 degrees, 10 degrees, 5 degrees, or 2 degrees of each other.

[0034] In some embodiments, the product Q1T1E1 and Q2T2E2 may be within 20% of each other. In some other embodiments, the product Q1T1E1 and Q2T2E2 may be within 15%, 10%, 5%, 2%, or 1% of each other. By canceling out the product of the elastic stiffness modulus, thickness, and thermal strain of the first polymer optical film (80) and the second polymer optical film (90), changes in lens curvature can be prevented.

[0035] Changes in lens curvature can also occur in optical lenses as a result of simple thermal expansion of the lens material. In some embodiments, each of the first polymer optical film (80) and the second polymer optical film (90) may have an average thickness T, an elastic stiffness modulus Q along the same first direction (101), and a coefficient of thermal expansion A along the same first direction. The product QTA of the first polymer optical film (80) may be within 20% of the product QTA of the second polymer optical film (90). In some examples, the product QTA of the first polymer optical film (80) may be within 15%, 10%, 5%, 2%, or 1% of the product QTA of the second polymer optical film (90).

[0036] In most cases, the principal axis of A will coincide with the principal axis of Q within 5 degrees. In contrast, the principal axis of E can be completely independent of the principal axes of Q and A. In some cases, the difference between the principal axes of A and Q and the principal axis of E may be greater than 20 degrees. In other cases, the difference between the principal axes of A and Q and the principal axis of E may be greater than 30 degrees. In other cases, the difference between the principal axes of A and Q and the principal axis of E may be greater than 40 degrees. In such cases, the principal axis or direction of thermal stress generation will be defined as the direction in which the product of the elastic modulus Q and the thermal strain E achieves their extreme values ​​(maximum or minimum), in contrast to the principal directions of the individual properties. In such cases, the principal direction of thermal stress may not align with the light transmission and light blocking directions within the film. Furthermore, bending in one direction can be reduced by balancing the mechanical properties in that direction. In practice, this balancing generally has to be done simultaneously along two separate orthogonal axes, which are preferably aligned with the axes of the maximum and minimum stress generation within the film.

[0037] When the lens thickness is much greater than the film thickness and the lens curvature is small, the above design criteria can be applied very strictly, especially when the film expansion is governed by reversible behavior. However, for thinner lenses and / or higher lens curvature, the mechanisms governing both the magnitude and direction of mechanical balancing become more complex and may require some corrections. For example, for thinner lenses, the elastic and flexural stiffness moduli of the lens may also need to be considered. The mathematical equations covering the precise balance become more complex but have been well studied over time in the composite materials industry and are adequately described in composite materials textbooks such as Vinson and Sier Akowski (The Behavior of STRUCTURES Composed of ComposiTe MATeriAls, M.A. Tinus Nijhoff Publishers, Dordrech T, 1987). Higher lens curvature can further complicate these relationships. However, while the mathematical equations describing the precise balancing can become more complex, in many of the cases covered within this application, the results of the precise calculations still fall within the aforementioned conditions for Q, T, and E for each film, and / or the product of Q, T, and A, and are in the same direction and within 20% of each other.

[0038] Furthermore, if one side of the lens surface has a very high curvature relative to the other side, the formation of an orthotropic film on the curved surface may cause the principal directions of the film, and even the projection of those principal directions onto a low-curvature (or flat) side, to vary depending on the position and with respect to a substantially uniform film on the low-curvature side. In such cases, it may only be possible to achieve perfect balance at a single point or along a pair of transverse axes. In such cases, balancing becomes a matter of optimization, and the selection of the best balancing region is determined by which one results in the smallest deviation from the desired lens shape. However, in many of the subjects of this application, the directional difference between the principal directions of the two films at any point projected onto a low-curvature surface remains within 20 degrees of each other.

[0039] In some embodiments, the first polymer optical film (80) and the second polymer optical film (90) may have thermal expansion coefficients A1 and A2, respectively, in the same third direction (103), as shown in Figure 5. In some examples, changes in lens curvature can be prevented by canceling out the products of the elastic stiffness modulus, thickness, and thermal expansion of the first polymer optical film (80) and the second polymer optical film (90). For example, in some embodiments, the products Q1T1A1 and Q2T2A2 may be within 20% of each other. In other examples, the products Q1T1A1 and Q2T2A2 may be within 15%, 10%, 5%, 2%, or 1% of each other. The first direction (101) and the third direction (103) may be within 20 degrees of each other, and in some examples, they may be within 15, 10, 5, or 2 degrees of each other.

[0040] In some other embodiments, each of the first polymer optical film (80) and the second polymer optical film (90) may have an average thickness T, an elastic shear modulus Q', and a thermal strain E' with respect to the same second direction (102) perpendicular to the first direction. The product Q'TE' of the first polymer optical film (80) may be within 20% of the product Q'TE' of the second polymer optical film (90). In some examples, the product Q'TE' of the first polymer optical film (80) may be within 15%, 10%, 5%, 2%, or 1% of the product Q'TE' of the second polymer optical film (90). In other embodiments, each of the first polymer optical film (80) and the second polymer optical film (90) may have a coefficient of thermal expansion A' along the second direction (102). The product Q'TA' of the first polymer optical film (80) may be within 20%, 15%, 10%, 5%, 2%, or 1% of the product Q'TA' of the second polymer optical film (90).

[0041] In some embodiments, the first direction may be substantially the in-plane direction of the first polymer optical film (80) and the second polymer optical film (90), respectively. The second direction may be substantially the in-plane direction of the first polymer optical film (80) and the second polymer optical film (90), respectively. For first and second polymer optical films comprising a plurality of polymer layers as described herein, the principal direction is selected such that the x and y axes are in the plane of the layer and the z axis corresponds to the thickness or height of the layer. In some embodiments, the first and second directions may be selected to be within 10 degrees or 5 degrees of the principal in-plane direction (x,y) of the film.

[0042] In some embodiments, for substantially perpendicularly incident light (51, 52), each of the first polymer optical film (80) and the second polymer optical film (90) may have an average light transmittance of more than 70%, more than 80%, or more than 90% with respect to at least a first polarization state (x axis) in the visible wavelength range of about 420 nm to about 650 nm. For substantially perpendicularly incident light (51, 52), at least one of the first polymer optical film (80) and the second polymer optical film (90) may have an average light transmittance of more than 70%, more than 80%, or more than 90% with respect to a second polarization state (y axis) orthogonal to the first polarization state in the visible wavelength range of about 420 nm to 650 nm.

[0043] Referring back to Figures 1A and 1B, in some embodiments, the first optical film (30) may be a polymer reflective polarizer (30) bonded to the first lens main surface (11), and the second optical film (40) may be a uniaxially oriented optical film (40) bonded to the second lens main surface (21). In some embodiments, the optical film may include a birefringent material. The term "birefringent" means that the refractive indices in the orthogonal x, y, and z directions are not all the same. For the optical films described herein, the principal directions may be selected such that the x and y axes are in the plane of the film and the z axis corresponds to the thickness or height of the film. The principal directions of the film are the directions in which the modulus of elasticity, coefficient of thermal expansion, and refractive index achieve their extreme values ​​(maximum or minimum values). These should also be aligned with the light transmission and light blocking directions within the reflective polarizer film.

[0044] In some examples, the optical film (40) may include a first optical layer having refractive indices nx1 and ny1 along the x and y directions in mutually orthogonal planes, respectively, and a refractive index nz1 along the thickness direction of the optical layer, which is orthogonal to the x and y directions. In the visible wavelength range extending from about 420 nm to about 650 nm, for at least one wavelength, the in-plane birefringence, which is the magnitude of the difference between the maximum in-plane refractive index nx1 and the minimum in-plane refractive index ny1 of the first optical layer, may be greater than about 0.02. In some examples, the magnitude of the difference between nx1 and ny1 may be greater than about 0.05, greater than about 0.10, greater than about 0.15, greater than about 0.20, or greater than about 0.22. The out-of-plane birefringence, which is the magnitude of the difference between one of the in-plane refractive indices of the first optical layer (e.g., nx1 or ny1) and the out-of-plane refractive index nz1, may be less than about 0.02. In some examples, the magnitude of the difference between nz1 and one of nx1 and ny1 may be less than about 0.015, less than about 0.01, less than about 0.007, or less than about 0.005. The optical film (40) may also include a second optical layer which may be an isotropic layer. The second optical layer includes refractive indices nx2, ny2, and nz2 along the x, y, and z directions, respectively. In some examples, in the visible wavelength range from about 420 nm to about 650 nm, the in-plane birefringence, which is the magnitude of the maximum difference between the refractive indices nx2, ny2, and nz2 of the second optical layer for at least one wavelength, may be less than about 0.02. In some examples, the out-of-plane birefringence, which is the magnitude of the difference between the refractive indices nx2, ny2, and nz2 of the second optical layer, may be less than about 0.015, less than about 0.01, less than about 0.007, or less than about 0.005.

[0045] In some other embodiments, in the visible wavelength range from about 420 nm to about 650 nm, nx1 > ny1 > nz1 for at least one wavelength. In other embodiments, the magnitude of the difference between each of nx1-ny1 and ny1-nz1 may be greater than about 0.02. In some examples, the magnitudes of each of nx1-ny1 and ny1-nz1 may be greater than about 0.03, greater than about 0.04, or greater than about 0.05.

[0046] For substantially perpendicularly incident light in the visible wavelength range, the reflecting polarizer (30) may have an average light transmittance of more than about 70% for incident light polarized along one of the x and y directions. In some examples, the average light transmittance may be more than about 80% or more than about 90% for incident light polarized along one of the x and y directions. For substantially perpendicularly incident light in the visible wavelength range, the average light reflectance of the reflecting polarizer (30) may be more than about 70% for incident light polarized along the other of the x and y directions. In some examples, the average light reflectance may be more than about 80% or more than about 90% for incident light polarized along the other of the x and y directions. The first optical layer of the optical film (40) may have an average light transmittance of more than about 70% for incident light polarized along each of the x and y directions. In some examples, the average light transmittance may be more than about 80% or more than about 90% for incident light polarized along each of the x and y directions.

Claims

1. An integrated lens assembly comprising one or more lenses joined together, each having a first and second lens main surface spaced apart, The first and second optical films are bonded to the first and second main surfaces of the lens, respectively, and each of the first and second optical films comprises a total of at least 10 polymer layers, each of which has an average thickness of less than about 500 nm, thereby, in the case of substantially normally incident light and a visible wavelength range of about 420 nm to about 680 nm, The plurality of polymer layers in the first optical film have an average light transmittance of more than 70% for a first polarization state and an average light reflectance of more than 70% for a second orthogonal polarization state in the visible wavelength range. The plurality of polymer layers in the second optical film have an average light transmittance of more than 70% for at least one of the first and second polarization states in the visible wavelength range. First and second optical films, An optical assembly comprising:

2. The optical assembly according to claim 1, wherein the plurality of polymer layers in the second optical film have an average light transmittance of more than 70% for each of the first and second polarization states in the visible wavelength range.

3. The optical assembly according to claim 1, wherein, for at least one wavelength less than about 400 nm, the plurality of polymer layers in the second optical film have an average light transmittance of more than about 60% for the first polarization state and an average light reflectance of more than about 60% for the second polarization state, and for at least one wavelength greater than about 750 nm, the plurality of polymer layers in the second optical film have an average light transmittance of more than about 60% for the first polarization state and an average light reflectance of more than about 60% for the second polarization state.

4. The optical assembly according to claim 1, wherein, for at least one of the first and second polarization states, the plurality of polymer layers of at least one of the first and second optical films have an average light absorption rate of less than 20% in the visible wavelength range.

5. An optical system for displaying an image to an observer, A display adapted to emit images, The optical assembly described in claim 1, A first retarder layer disposed between the optical assembly and the display, A display lens disposed between the first retarder layer and the display, A partial reflector is disposed on the main surface of the display lens and conforms to the main surface, and has an average light reflectance of at least 30% in the visible wavelength range. An optical system equipped with [the necessary components].

6. A polymer optical lens comprising first and second main lens surfaces facing opposite directions, wherein at least one of the first and second lens surfaces is curved, The first and second polymer optical films are bonded to the first and second main lens surfaces, respectively, and each has an average thickness T1 and T2, elastic stiffness moduli Q1 and Q2 in the same first direction, and thermal strains E1 and E2 in the same second direction, and the products Q1T1E1 and Q2T2E2 are within 20% of each other. An optical assembly comprising:

7. The optical assembly according to claim 6, wherein the first and second polymer optical films have the same coefficients of thermal expansion A1 and A2 in the same third direction, the products Q1T1A1 and Q2T2A2 are within 20% of each other, and the first direction and the third direction are within 20 degrees of each other.

8. A polymer optical lens comprising first and second main lens surfaces facing opposite directions, wherein at least one of the first and second lens surfaces is curved, The first and second polymer optical films are bonded to the first and second main lens surfaces, respectively, and each has an average thickness T1 and T2, elastic moduli Q1 and Q2 in the same first direction, and thermal expansion coefficients A1 and A2 in the same second direction, and the products Q1T1A1 and Q2T2A2 are within 20% of each other. An optical assembly comprising:

9. The optical assembly according to claim 8, wherein, in the case of substantially perpendicularly incident light, each of the first and second polymer optical films has an average light transmittance of at least more than 70% for at least a first polarization state in the visible wavelength range of about 420 nm to about 650 nm.

10. The optical assembly according to claim 8, wherein the first and second polymer optical films have the same thermal strains E1 and E2 in the same third direction, the products Q1T1E1 and Q2T2E2 are within 20% of each other, and the first direction and the third direction are within 20 degrees of each other.

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