Optical system for displaying magnified virtual images

Abstract

The present invention provides an optical system for displaying a magnified virtual image of an image emitted by a display to a viewer. The optical system includes a first lens and a second lens, the first lens and the second lens facing each other and separated by an air gap to define an optical cavity between the first lens and the second lens. The optical cavity includes a reflective polarizer disposed on a major surface of the first lens and an optical stack disposed on a major surface of the second lens. The optical stack includes an absorbing polarizer, a first retarder layer, a partial reflector, and a second retarder layer disposed between the absorbing polarizer and the partial reflector. The first lens and / or the second lens are birefringent lenses disposed outside the optical cavity to control polarization.

Description

Technical Field

[0001] The present disclosure generally relates to optical systems for displaying magnified virtual images, and more particularly to optical systems having birefringent lenses. Background Art

[0002] Many displays, including virtual reality (VR) displays, attempt to present realistic images that replicate a real or imagined environment. In some applications, VR displays attempt to provide an immersive simulation of a three-dimensional environment. Summary of the invention

[0003] In some aspects of the present disclosure, an optical system for displaying an enlarged virtual image of an image emitted by a display to a viewer is provided. The optical system includes a first lens having a first major surface and a second major surface relative to each other. The optical system also includes a second lens having a third major surface and a fourth major surface relative to each other. The third major surface and the second major surface face each other and are separated by an air gap. The second major surface is concave toward the third major surface. Each of the first lens and the second lens has a delay greater than about 25nm at at least a first wavelength in a first wavelength range extending from about 400nm to about 700nm. The optical system also includes a reflective polarizer disposed on the second major surface and conforming to the second major surface. The reflective polarizer substantially transmits a first polarization state and substantially reflects an orthogonal second polarization state. The optical system also includes an optical stack disposed on the third major surface and conforming to the third major surface. The optical stack includes an absorbing polarizer that substantially transmits the first polarization state and substantially absorbs the second polarization state. The optical stack also includes a first retardation layer and a partial reflector disposed between the absorbing polarizer and the first retardation layer. The partial reflector has an optical reflectivity of at least 30% and an optical transmittance of at least 30% for at least one wavelength in the first wavelength range. The optical stack also includes a second retarder disposed between the absorbing polarizer and the partial reflector. Each of the first retarder and the second retarder is substantially a quarter-wave retarder at at least one wavelength in the first wavelength range. The absorbing polarizer is disposed closer to the third major surface, and the first retarder is disposed farther from the third major surface.

[0004] In some aspects of the present disclosure, an optical system for displaying a magnified virtual image of an image emitted by a display to a viewer is provided. The optical system includes a first lens and a second lens facing each other and separated by an air gap. Each of the first lens and the second lens has a delay greater than about 25 nm at at least a first wavelength in a first wavelength range extending from about 400 nm to about 700 nm. The optical system also includes a reflective polarizer disposed on a primary surface of the first lens and the second lens and conforming to the primary surface. The reflective polarizer substantially transmits a first polarization state and substantially reflects an orthogonal second polarization state. The optical system also includes a partial reflector disposed on the primary surface of the first lens and the second lens and conforming to the primary surface. The partial reflector has an optical reflectivity of at least 30% and an optical transmittance of at least 30% for at least one wavelength in the first wavelength range. The optical system also includes a first retardation layer and a second retardation layer disposed between the primary surface of the first lens and the primary surface of the second lens. The first delay layer and the second delay layer are arranged so that for each light ray emitted by the display and incident on one of the first delay layer and the second delay layer at a first incident angle and transmitted by the delay layer, wherein the transmitted light ray propagates toward the other of the first delay layer and the second delay layer, at least a first portion of the transmitted light ray is incident on the other of the first delay layer and the second delay layer at a second incident angle substantially equal to the first incident angle.

[0005] In some aspects of the present disclosure, an optical system is provided, which includes a first lens and a second lens. Each lens has a birefringence greater than about 0.02 for at least one visible wavelength. An optical cavity is defined between a first principal surface of the first lens and a second principal surface of the second lens. The optical cavity includes a reflective polarizer disposed on the first principal surface of the first lens and conforming to the first principal surface. The reflective polarizer substantially transmits a first polarization state and substantially reflects an orthogonal second polarization state. The optical cavity also includes an optical stack disposed on the second principal surface of the second lens and conforming to the second principal surface. The optical stack includes an absorbing polarizer that substantially transmits the first polarization state and substantially absorbs the second polarization state. The optical stack also includes a first retarder and a partial reflector disposed between the absorbing polarizer and the first retarder. The partial reflector has an optical reflectivity of at least 30% and an optical transmittance of at least 30% for at least one wavelength in a first wavelength range extending from about 400 nm to about 700 nm. The optical stack also includes a second retarder disposed between the absorbing polarizer and the partial reflector. Each of the first retarder and the second retarder is substantially a quarter-wave retarder at at least one wavelength in the first wavelength range. The absorbing polarizer is disposed closer to the second major surface, and the first retardation layer is disposed farther from the second major surface.

[0006] In some aspects of the present disclosure, a curved optical stack is provided. The curved optical stack includes an absorbing polarizer that substantially transmits a first polarization state and substantially absorbs an orthogonal second polarization state. The curved optical stack also includes a first retardation layer and a partial reflector disposed between the absorbing polarizer and the first retardation layer. The partial reflector has an optical reflectivity of at least 30% and an optical transmittance of at least 30% for at least one wavelength within a first wavelength range extending from about 400 nm to about 700 nm. The curved optical stack also includes a second retardation layer disposed between the absorbing polarizer and the partial reflector. At least one of the first retardation layer and the second retardation layer is substantially a quarter-wave retardation plate at at least one wavelength within the first wavelength range. The optical stack is an integrated optical stack and is curved in mutually orthogonal directions. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Various aspects of the present disclosure will be discussed in more detail with reference to the accompanying drawings, in which:

[0008] Figure 1 is a schematic diagram illustrating an optical system according to some aspects of the present disclosure; and

[0009] Figure 2 is a schematic diagram of an optical system according to some embodiments.

[0010] The figures are not necessarily drawn to scale. Like numbers used in the figures refer to like components. However, it should be understood that the use of a number to refer to a component in a given figure is not intended to limit the component labeled with the same number in another figure. DETAILED DESCRIPTION

[0011] In the following description, reference is made to the accompanying drawings, which form a part of the present invention and in which various embodiments are shown by way of example. It should be understood that other embodiments may be conceived and carried out without departing from the scope or essence of this specification. Therefore, the following specific embodiments should not be considered to have a limiting meaning.

[0012] Although the manufacturing cost of molded plastic lenses is lower than that of glass lenses, the application of molded plastics in polarized optics is limited due to its birefringence. For folded optics applications, it is desirable to control the polarization in the folded optic cavity. In addition to the quarter wave plate (QWP), the presence of birefringent materials in the folded optic cavity can complicate polarization and impair QWP performance, and can create more direct light leakage in the system.

[0013] Designing an optical system in which the birefringent lens material is disposed outside the cavity of the folded optic can help control polarization. Additionally, designing an optical system with a QWP-half-mirror-QWP structure such that direct light leakage travels through both QWPs at the same or similar angles of incidence can help control polarization and direct light leakage.

[0014] Figure 1 is a schematic diagram illustrating an optical system 200 according to some embodiments of the present specification. Optical system 200 can be described as a folded optical system in which a light beam is bent as it traverses the system so that the optical path of the light is longer than the length of the system. The optical systems disclosed herein employ folded optics and can be used, for example, in head-mounted displays such as virtual reality displays, cameras such as those included in cell phones, and smart watches. These systems can provide optical systems with high field of view, high contrast, low chromatic aberration, low distortion, and / or high efficiency in a compact configuration that can be used in a variety of applications.

[0015] The optical system (200) is configured to display a magnified virtual image (201) of an image (101). In some embodiments, the optical system includes a display (100) configured to emit an image (101), and the optical system is configured to display a magnified virtual image (201) of the emitted image for viewing by a viewer (110). The display (100) may include one or more LEDs, which in some cases include one or more laser diodes. Several such LEDs may be combined to produce a desired spectral distribution of light. The display may have red, green, and blue sub-elements to provide a full color image. For example, the outputs of red, green, and blue emitting LEDs may be combined to provide nominal white light, or white emitting LEDs may be used alternatively or additionally. In some embodiments, the display (100) may be any suitable type of display, including, for example, a liquid crystal display (LCD) and an organic light emitting diode (OLED) display. The display (100) may be substantially flat or planar, or may be curved, or may include multiple flat or planar panels disposed at obtuse angles relative to each other. In some embodiments, the image (101) emitted by the display (100) may be substantially polarized. In other embodiments, the emitted image may be substantially unpolarized.

[0016] The optical system includes a first lens (10) and a second lens (20) facing each other and separated by an air gap (30). In some embodiments, the first lens (10) includes a first principal surface (11) and a second principal surface (12) opposite to each other, and the second lens (20) includes a third principal surface (21) and a fourth principal surface (22) opposite to each other. In some aspects, the first to fourth principal surfaces (11, 12; 21, 22) may be substantially concentric with each other. In some embodiments, the third principal surface (21) of the second lens (20) and the second principal surface (12) of the first lens (10) face each other and are separated by an air gap (30). The second principal surface (12) is concave toward the third principal surface (21). In some embodiments, the third principal surface (21) of the second lens (20) is convex toward the second principal surface (12) of the first lens (10). In some embodiments, the third principal surface (21) may be substantially concentric with the second principal surface (12) and may have a diameter smaller than the second principal surface. Each of the first and second lenses (10, 20) has a retardation greater than about 25 nm at at least a first wavelength within a first wavelength range.

[0017] In some embodiments, the first wavelength range may extend from about 400 nm to about 700 nm. In some configurations, the first wavelength range may include a wavelength of about 550 nm. In some configurations, the first wavelength in the first wavelength range may be a blue primary wavelength, or a green primary wavelength, or a red primary wavelength. In some aspects, the first wavelength range may be any wavelength range in which the optical system is designed to operate. In some aspects, at least the first wavelength includes at least one of each of a blue wavelength, a green wavelength, and a red wavelength.

[0018] In some embodiments, the retardation of each of the first lens (10) and the second lens (20) at at least the first wavelength may be greater than about 50 nm. In some other embodiments, the retardation of each of the first lens and the second lens (10, 20) at at least the first wavelength may be greater than about 100 nm. In other embodiments, the retardation of each of the first lens and the second lens (10, 20) at at least the first wavelength may be greater than about 200 nm. In some aspects, within the first wavelength range, the retardation of at least one of the first lens (10) and the second lens (20) at blue wavelengths is greater than the retardation at red wavelengths.

[0019] According to some embodiments, each of the first lens (10) and the second lens (20) has a birefringence greater than about 0.02 for at least one visible wavelength. In other embodiments, each lens may have a birefringence greater than about 0.05, or greater than about 0.075, or greater than about 0.1 for at least one visible wavelength. In some embodiments, each of the first lens and the second lens (10, 20) may be made of a plastic having a high birefringence. In some embodiments, the birefringence of the first lens (10) may be less than the birefringence of the second lens (20). In some embodiments, the first lens (10) may be made of glass having a low birefringence, and the second lens (20) may be made of a plastic having a birefringence greater than the birefringence of the first lens (10).

[0020] The optical system includes a reflective polarizer (40) disposed on the major surfaces of the first lens (10) and the second lens (20) and conforming to the major surfaces. In the illustrated embodiment, the reflective polarizer (40) is disposed on the second major surface (12) of the first lens (10) and conforming to the second major surface. In other embodiments, the reflective polarizer (40) is disposed on the first major surface (11) of the first lens (10) and conforming to the first major surface. Within a first wavelength range, the reflective polarizer (40) substantially transmits light having one of the orthogonal first polarization state and the second polarization state (e.g., the first polarization state with the electric field along the x-axis), and substantially reflects light having the other of the first polarization state and the second polarization state (e.g., the second polarization state with the electric field along the y-axis). In some embodiments, for substantially normally incident light having a first wavelength, if at least 60% of the incident light having the first polarization state at the first wavelength is transmitted through the polarizer (40), then it can be said that the reflective polarizer substantially transmits light having the first polarization state at the first wavelength. In some embodiments, at least 70% or at least 80% of incident light having a first polarization state at a first wavelength is transmitted through the polarizer (40). In some embodiments, for substantially normally incident light having a first wavelength, if at least 60% of incident light having a second polarization state at the first wavelength is reflected from the reflective polarizer (40), then the reflective polarizer is said to substantially reflect light having a second polarization state at the first wavelength. In some embodiments, at least 70% or at least 80% of incident light having a second polarization state at the first wavelength is reflected from the polarizer (40).

[0021] The reflective polarizer (40) used in the optical system of the present specification can be any suitable type of reflective polarizer. The reflective polarizer can be a polymer multilayer optical film that can be substantially uniaxially oriented, as further described elsewhere. Substantially uniaxially oriented reflective polarizers can be purchased from 3M Company under the trade name Advanced Polarizing Film 5 or APF. Other types of multilayer optical film reflective polarizers (e.g., reflective polarizing brightness enhancement film or DBEF available from 3M Company) can also be used. In some embodiments, other types of reflective polarizers (e.g., wire grid polarizers) are used.

[0022] An optical system (200) according to some embodiments includes an optical stack (50) disposed on and conforming to a third major surface (21). In some embodiments, the optical stack may be an integrated optical stack and curved in mutually orthogonal directions. In some embodiments where the optical stack (50) is a curved optical stack, the optical stack includes at least an absorbing polarizer (60), a first retardation layer (70), a second retardation layer (90), and a partial reflector (80). In some configurations, the absorbing polarizer (60) is disposed closer to the third major surface (21) of the second lens (20), and the first retardation layer (70) is disposed farther from the third major surface (21) of the second lens (20). In some embodiments, each of the first retardation layer and the second retardation layer (70, 90) is substantially a quarter-wave retarder at at least one wavelength.

[0023] In some other embodiments, an optical cavity (30) is defined between the first principal surface (12) of the first lens (10) and the second principal surface (21) of the second lens (20). In some embodiments, the optical cavity may be substantially filled with air. The optical cavity (30) includes a reflective polarizer (40) disposed on and conforming to the first principal surface (12) of the first lens (10) and an optical stack (50) disposed on and conforming to the second principal surface (21) of the second lens (20). The reflective polarizer (40) substantially transmits a first polarization state (x-axis) and substantially reflects an orthogonal second polarization state (y-axis). The optical stack (50) includes an absorbing polarizer, a first retarder (70), a partial reflector (80), and a second retarder (90), as explained elsewhere in the present disclosure. In some aspects, the absorbing polarizer (60) may be disposed closer to the second principal surface (21) of the second lens (20), and the first retardation layer (70) may be disposed farther from the second principal surface (21) of the second lens (20).

[0024] In a first wavelength range, the absorbing polarizer (60) substantially transmits light having one of the orthogonal first and second polarization states (e.g., the first polarization state with the electric field along the x-axis), and substantially absorbs light having the other of the first and second polarization states (e.g., the second polarization state with the electric field along the y-axis). In some embodiments, for substantially normally incident light having a first wavelength, the absorbing polarizer is said to substantially transmit light having the first polarization state at the first wavelength if at least 60% of the incident light having the first polarization state at the first wavelength is transmitted through the absorbing polarizer (60). In some embodiments, at least 70% or at least 80% of the incident light having the first polarization state at the first wavelength is transmitted through the absorbing polarizer (60). In some embodiments, for substantially normally incident light having a first wavelength, the absorbing polarizer is said to substantially absorb light having the second polarization state at the first wavelength if at least 60% of the incident light having the second polarization state at the first wavelength is absorbed by the absorbing polarizer (60). In some embodiments, at least 70% or at least 80% of the incident light having the second polarization state at the first wavelength is absorbed by the absorptive polarizer (60).

[0025] In some embodiments, the absorbing polarizer (60) can be an iodine-doped polyvinyl alcohol (PVA) polarizer. Such polarizers include an oriented PVA layer impregnated with iodine. In other embodiments, other types of absorbing polarizers are used (e.g., oriented polymer polarizers impregnated with organic dyes).

[0026] In some embodiments, the partial reflector (80) is disposed on and conforms to the major surfaces of the first lens and the second lens (10, 20). In some aspects, the partial reflector (80) may be disposed between the absorbing polarizer (60) and the first retarder (70). The partial reflector has an optical reflectivity of at least 30% and an optical transmittance of at least 30% for at least one wavelength within the first wavelength range.

[0027] The partial reflector (80) used in the lens of the present disclosure may be any suitable partial reflector. For example, the partial reflector (80) may be constructed by coating a thin layer of metal (e.g., silver or aluminum) on a transparent substrate (e.g., a film that may then be adhered to a lens, or the substrate may be a lens). The partial reflector may also be formed, for example, by depositing a thin film dielectric coating onto the surface of a lens substrate, or by depositing a combination of metal and dielectric coatings on a surface. The partial reflector may be, for example, a half mirror.

[0028] In some embodiments, the partial reflector (80) has an average optical reflectivity and an average optical transmittance at a first wavelength or in a first wavelength range, the average optical reflectivity and the average optical transmittance are each in the range of 20% to 80%, or each in the range of 30% to 70%, or each in the range of 40% to 60%, or each in the range of 45% to 55%. Unless otherwise specified, the average optical reflectivity and the average optical transmittance in the first wavelength range refer to the unweighted averages determined at normal incidence over the predetermined wavelength range and over the polarization of the optical reflectivity and optical transmittance, respectively.

[0029] In some embodiments, for substantially normally incident light having a first wavelength, the partial reflector has an optical reflectivity of at least 30% and an optical transmittance of at least 30% for each of the first polarization state and the second polarization state. In some other embodiments, for substantially normally incident light having a first wavelength, the partial reflector has an optical reflectivity of at least 40% and an optical transmittance of at least 40% for each of the first polarization state and the second polarization state. In some other embodiments, for substantially normally incident light having a first wavelength, the partial reflector has an optical reflectivity of at least 30% and an optical transmittance of at least 30% for at least one wavelength within a second wavelength range extending from about 750 nm to about 1000 nm.

[0030] In some embodiments, the partial reflector (80) may be a reflective polarizer or may have a polarization-dependent reflectivity. However, it is generally preferred that the optical reflectivity and optical transmittance at normal incidence are independent or substantially independent of the polarization state of the incident light. For example, substantially isotropic metal layers and / or dielectric layers may be used to obtain such polarization independence.

[0031] In some configurations, the second retarder (90) may be disposed between the absorbing polarizer (60) and the partial reflector (80). In some embodiments, at least one or both of the first and second retarder layers are substantially a quarter-wave retarder at at least one wavelength within the first wavelength range. In some aspects, at least one of the first and second retarder layers (70, 90) is substantially a quarter-wave retarder at at least one wavelength within the second wavelength range extending from about 750 nm to about 1000 nm. In some other aspects, at least one of the first and second retarder layers is not a quarter-wave retarder for wavelengths of about 420 nm to about 670 nm.

[0032] In some embodiments, the first retardation layer (70) and the second retardation layer (90) are disposed between the main surface (11) of the first lens and the main surface (21) of the second lens. Figure 1 and Figure 2As best shown in , the first and second retardation layers (70, 90) are arranged so that each light ray (120) emitted by the display is incident on one of the first and second retardation layers (70) at a first angle of incidence (θ1). The incident light ray (120) is transmitted by the retardation layer (70), wherein the transmitted light ray (121) propagates toward the other of the first and second retardation layers (90). At least a first portion (121a) of the transmitted light ray (121) is incident on the other of the first and second retardation layers (90) at a second angle of incidence (θ2) substantially equal to the first angle of incidence (θ1). In some aspects, the first angle of incidence (θ1) and the second angle of incidence (θ2) are within 5 degrees of each other, or within 4 degrees or 3 degrees of each other. In some other aspects, the first angle of incidence (θ1) and the second angle of incidence (θ2) are within 2 degrees of each other. The second portion (121b) of the transmitted light (121) is incident on the other of the first retardation layer and the second retardation layer (90) at a third incident angle (θ3). After being first reflected by one of the partial reflector (80) and the reflective polarizer (40) and then reflected by the other of the partial reflector (80) and the reflective polarizer (40), the second portion (121b) of the transmitted light (121) is incident on the other of the first retardation layer and the second retardation layer (90). The third incident angle (θ3) at which the second portion (121b) of the transmitted light (121) is incident on the other of the first retardation layer and the second retardation layer (90) is different from the first incident angle (θ1) and the second incident angle (θ2). In some aspects, the difference between the third (θ3) incident angle and the first incident angle (θ1) may be greater than about 10 degrees, or greater than about 12 degrees, or greater than about 15 degrees.

[0033] In some embodiments, for each emitted light (120) transmitted from one of the first and second delay layers (70) toward the other of the first and second delay layers (90) and transmitted by the other of the first and second delay layers, one of the first and second delay layers (70) adds delay to the emitted light, and the other of the first and second delay layers (90) subtracts delay from the emitted light.

[0034] In some configurations, the optical system (200) includes a third retarder (130), and the second absorbing polarizer (140) may be disposed between the first lens (10) and the third retarder (130). In the first wavelength range, the second absorbing polarizer (140) substantially transmits light having one of the orthogonal first and second polarization states (e.g., the first polarization state with the electric field along the x-axis), and substantially absorbs light having the other of the first and second polarization states (e.g., the second polarization state with the electric field along the y-axis). The third retarder (130) may be substantially a quarter-wave retarder at at least one wavelength in the first wavelength range extending from about 400 nm to about 700 nm.

[0035] In certain embodiments, the first, second, and third retardation layers (70, 90, 130) may be laminated films or thin coatings. Suitable coatings for forming a quarter-wave retarder include, but are not limited to, for example, linear photopolymerizable polymer (LPP) materials and liquid crystal polymer (LCP) materials, as described in PCT publication WO 2018 / 178817 (Steiner et al.). In some aspects, at least one of the first and second retardation layers (70, 90) may be a multilayer retarder. In some embodiments, at least one of the first and second retardation layers may be substantially a three-quarter wavelength retarder at at least one wavelength.

[0036] In some aspects of the present disclosure, an eye tracking system may be provided in an optical system (200). The eye tracking system includes at least one light source (150) configured to emit light (151, 152) in a second wavelength range extending from about 750 nm to about 1000 nm toward an eye of a viewer (110). In some aspects, the at least one light source (150) may be disposed on one side of a combination of a first lens (10) and a second lens (20). For example, in some embodiments, the at least one light source (150) may be disposed proximate to the second lens (20). The eye reflects the emitted light as reflected emission light (153, 154), and at least one detector (160) is configured to detect the reflected emission light (153, 154). In some aspects, the at least one detector (160) may be disposed on an opposite side of the combination of the first lens and the second lens (10, 20). In some embodiments, the optical system includes a display (100) configured to emit an image (101), wherein the display includes at least one detector (160), and the optical system is configured to display a magnified virtual image (201) of the emitted image for viewing by a viewer (110).

Claims

1. An optical system for displaying to a viewer a magnified virtual image of an image emitted by a display, the optical system comprising: a first lens including first and second opposing principal surfaces; as well as a second lens including opposing third and fourth principal surfaces, the third and second principal surfaces facing each other and separated by an air gap, the second principal surface being concave toward the third principal surface, each of the first and second lenses having a retardation greater than about 25 nm at at least a first wavelength within a first wavelength range extending from about 400 nm to about 700 nm; a reflective polarizer disposed on and conformal to the second major surface, the reflective polarizer substantially transmitting a first polarization state and substantially reflecting an orthogonal second polarization state; as well as an optical stack disposed on the third major surface and conforming to the third major surface, the optical stack comprising: an absorbing polarizer that substantially transmits the first polarization state and substantially absorbs the second polarization state; First delay layer; A partial reflector disposed between the absorbing polarizer and the Between the first retarder layers, the partial reflector has an optical reflectivity of at least 30% and an optical transmittance of at least 30% for at least one wavelength within the first wavelength range; and A second delay layer, the second delay layer is arranged between the absorbing polarizer and the partial reflector, each of the first delay layer and the second delay layer is substantially a quarter-wave delay plate at at least one wavelength within the first wavelength range, wherein the absorbing polarizer is arranged closer to the third major surface and the first delay layer is arranged farther away from the third major surface.

2. The optical system of claim 1 , wherein the third principal surface is convex toward the second principal surface, wherein each of the first lens and the second lens has a retardation greater than about 100 nm at at least the first wavelength, wherein within the first wavelength range, at least one of the first lens and the second lens has a retardation at blue wavelengths greater than a retardation at red wavelengths, and wherein for substantially normally incident light having the first wavelength, the reflective polarizer transmits at least 60% of the incident light having the first polarization state and reflects at least 60% of the incident light having the second polarization state.

3. The optical system of claim 1 , wherein for substantially normally incident light having the first wavelength, the reflective polarizer transmits at least 80% of the incident light having the first polarization state and reflects at least 80% of the incident light having the second polarization state, and the absorptive polarizer transmits at least 80% of the incident light having the first polarization state and absorbs at least 80% of the incident light having the second polarization state, and wherein the third major surface is substantially concentric with the second major surface and has a diameter smaller than the second major surface.

4. An optical system according to claim 1, wherein the first major surface to the fourth major surface are substantially concentric with each other, wherein for substantially normally incident light having the first wavelength, the partial reflector has an optical reflectivity of at least 40% and an optical transmittance of at least 40% for each of the first polarization state and the second polarization state, wherein for substantially normally incident light having the first wavelength, the partial reflector has an optical reflectivity of at least 30% and an optical transmittance of at least 30% for at least one wavelength in a second wavelength range extending from about 750 nm to about 1000 nm, and wherein at least one of the first retardation layer and the second retardation layer is substantially a quarter-wave retarder at at least one wavelength in the second wavelength range extending from about 750 nm to about 1000 nm.

5. The optical system according to claim 1, further comprising: a third retarder that is substantially a quarter-wave retarder at at least one wavelength within the first wavelength range and a second absorbing polarizer that is disposed between the first lens and the third retarder and that substantially transmits the first polarization state and substantially absorbs the second polarization state; An eye tracking system, the eye tracking system comprising: at least one light source configured to emit light within a second wavelength range extending from about 750 nm to about 1000 nm toward an eye of the viewer, the eye reflecting the emitted light as reflected emitted light; and at least one detector configured to detect the reflected emission light, wherein the at least one light source is disposed on one side of a combination of the first lens and the second lens, and the at least one detector is disposed on an opposite side of the combination of the first lens and the second lens, wherein the at least one light source is disposed proximate to the second lens; and A display is configured to emit an image, the optical system is configured to display a magnified virtual image of the emitted image for viewing by a viewer, wherein the display includes the at least one detector.

6. An optical system for displaying to a viewer a magnified virtual image of an image emitted by a display, the optical system comprising: a first lens and a second lens, the first lens and the second lens facing each other and separated by an air gap, each of the first lens and the second lens having a retardation greater than about 25 nm at at least a first wavelength within a first wavelength range extending from about 400 nm to about 700 nm; a reflective polarizer disposed on and conforming to a major surface of one of the first lens and the second lens, the reflective polarizer substantially transmitting a first polarization state and substantially reflecting an orthogonal second polarization state; a partial reflector disposed on and conforming to another major surface of the other of the first lens and the second lens opposite to the major surface, the partial reflector having an optical reflectivity of at least 30% and an optical transmittance of at least 30% for at least one wavelength within the first wavelength range; as well as A first delay layer and a second delay layer, wherein the first delay layer and the second delay layer are arranged between the main surface and the other main surface, one of the first delay layer and the second delay layer is arranged between the reflective polarizer and the partial reflector and the partial reflector is arranged between the first delay layer and the second delay layer, so that for each light emitted by the display and incident on one of the first delay layer and the second delay layer at a first incident angle and transmitted by the delay layer, wherein the transmitted light propagates toward the other of the first delay layer and the second delay layer, at least a first part of the transmitted light is incident on the other of the first delay layer and the second delay layer at a second incident angle substantially equal to the first incident angle.

7. An optical system according to claim 6, wherein the first incident angle and the second incident angle are within 5 degrees or 2 degrees of each other, wherein the second portion of the transmitted light is incident on the other of the first retardation layer and the second retardation layer at a third incident angle different from the first incident angle and the second incident angle, wherein the difference between the third incident angle and the first incident angle is greater than about 10 degrees, and wherein the second portion of the transmitted light is incident on the other of the first retardation layer and the second retardation layer after first being reflected by one of the partial reflector and the reflective polarizer and then reflected by the other of the partial reflector and the reflective polarizer.

8. An optical system according to claim 6, wherein at least one of the first delay layer and the second delay layer is not a quarter-wave delay plate for wavelengths of about 420 nm to about 670 nm, and wherein for each emitted light transmitted from one of the first delay layer and the second delay layer toward the other of the first delay layer and the second delay layer and transmitted by the other of the first delay layer and the second delay layer, one of the first delay layer and the second delay layer adds delay to the emitted light and the other of the first delay layer and the second delay layer subtracts delay from the emitted light.

9. An optical system comprising a first lens and a second lens, each lens having a birefringence greater than about 0.02 for at least one visible wavelength, a first principal surface of the first lens and a second principal surface of the second lens defining an optical cavity therebetween, wherein the optical cavity is substantially filled with air and comprises: a reflective polarizer disposed on and conforming to the first major surface of the first lens, the reflective polarizer substantially transmitting a first polarization state and substantially reflecting an orthogonal second polarization state; as well as an optical stack disposed on and conforming to the second principal surface of the second lens, the optical stack comprising: an absorbing polarizer that substantially transmits the first polarization state and substantially absorbs the second polarization state; First delay layer; A partial reflector disposed between the absorbing polarizer and the The partial reflector has an optical reflectivity of at least 30% and an optical transmittance of at least 30% for at least one wavelength within a first wavelength range extending from about 400 nm to about 700 nm between the first retarder layers; and A second delay layer, the second delay layer is arranged between the absorbing polarizer and the partial reflector, each of the first delay layer and the second delay layer is substantially a quarter-wave delay plate at at least one wavelength within the first wavelength range, wherein the absorbing polarizer is arranged closer to the second major surface and the first delay layer is arranged farther away from the second major surface.

10. A curved optical stack, comprising: an absorbing polarizer that substantially transmits a first polarization state and substantially absorbs an orthogonal second polarization state; First delay layer; a partial reflector disposed between the absorbing polarizer and the first retarding layer, the partial reflector having an optical reflectivity of at least 30% and an optical transmittance of at least 30% for at least one wavelength within a first wavelength range extending from about 400 nm to about 700 nm; as well as a second delay layer, the second delay layer is arranged between the absorbing polarizer and the partial reflector, at least one of the first delay layer and the second delay layer is substantially a quarter-wave delay plate at at least one wavelength within the first wavelength range, wherein the optical stack is an integrated optical stack and is curved in mutually orthogonal directions in a convex manner toward the first delay layer.

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