Polarization-optimized head-up display

Abstract

The optical system includes: a display including an active display area having a maximum lateral dimension D and configured to emit an image for viewing by an eye of an observer, the active display area including a display center and a predetermined area including the display center, the predetermined area having a maximum lateral dimension d, where d / D≦0.25; a vehicle windshield; and an optical film configured to receive the image emitted by the active display area and reflect or transmit at least a portion of the received image toward the windshield, the windshield being configured to receive the image reflected or transmitted by the optical film and reflect at least a portion of the received image toward the eye, wherein for at least one first location within the predetermined area of ​​the active display area, the emitted image includes a first emitted image cone emitted from the first location, the first emitted image cone including a first emitted central image ray emitted from the first location, the optical film being oriented to polarize the first emitted central image ray substantially in the plane of incidence when incident on the windshield.

Description

Summary of the Invention

[0001] In some aspects of the present disclosure, an optical system is provided, comprising: a display having an active display area with a maximum horizontal dimension D and configured to emit an image for viewing by an eye of an observer, the active display area including a display center and a predetermined area including the display center, the predetermined area having a maximum horizontal dimension d, where d / D≦0.25; a vehicle windshield; and an optical film configured to receive the image emitted by the active display area and reflect or transmit at least a portion of the received image toward the windshield, the windshield being configured to receive the image reflected or transmitted by the optical film and reflect at least a portion of the received image toward the eye, wherein for at least one first position within the predetermined area of ​​the active display area, the emitted image includes a first emitted image cone emitted from the first position, the first emitted image cone including a first emitted central image ray emitted from the first position, the optical film being oriented to polarize the first emitted central image ray substantially in a plane of incidence when incident on the windshield. [Brief explanation of the drawings]

[0002] [Figure 1] FIG. 1 is a top schematic view of a head-up display as found in the prior art. [Figure 2A] FIG. 1 is a cross-sectional view of a polarization-optimized head-up display system according to an embodiment of the present disclosure. [Figure 2B] 1 is a front view of a display system and an optical film according to an embodiment of the present disclosure. [Figure 2C] 1A-1C illustrate various types of polarization associated with an absorbing polarizer, according to an embodiment herein. [Figure 2D]FIG. 1 is a side view of an absorbing polarizer according to an embodiment herein. [Figure 3] FIG. 1 is a cross-sectional view of a reflective polarizer according to an embodiment of the present specification. [Figure 4] FIG. 10 is a cross-sectional view of a polarization-optimized head-up display system according to an alternative embodiment herein. [Figure 5] FIG. 10 is a cross-sectional view of a polarization-optimized head-up display system according to another alternative embodiment of the present disclosure. [Figure 6A] 1 is a graphical plot illustrating the effect of a polarization-optimized head-up display, according to an embodiment herein. [Figure 6B] 1 is a graphical plot illustrating the effect of a polarization-optimized head-up display, according to an embodiment herein. DETAILED DESCRIPTION OF THE INVENTION

[0003] In the following description, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration various embodiments. 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 specification. Accordingly, the following detailed description is not to be taken in a limiting sense.

[0004] In modern head-up display (HUD) systems, a display, such as a liquid crystal display (LCD), projects an image onto a vehicle's windshield, where the image is viewable by the vehicle operator or passengers. One common problem encountered in HUD systems is "ghosting," which occurs when the projected image reflects off both the front glass-air interface (the inner surface of the windshield) and the rear glass-air interface (the outer surface of the windshield). The two reflected images "bounce" back to the viewer at different angles of incidence, creating a main image and an apparent second "ghost" image offset from the main image, which can reduce the readability of the displayed information. One common way to address this ghosting problem is for windshield manufacturers to create a wedge shape between the outer and inner surfaces of the windshield. That is, the outer glass-air interface is positioned at a slightly different angle than the inner glass-air interface, which is intended to align the two reflected images into a single image for at least one ideal viewing angle (e.g., the viewing angle of an average-height driver). Another solution to the ghosting problem is to embed a weakly reflective polarizer between two pieces of glass (i.e., sandwiched between the inner and outer glass sheets) rather than creating a wedge in the windshield, and reflect linearly polarized light from the reflective polarizer. One such example of a reflective polarizer is the 3M™ Windshield Combiner Film (3M™ WCF) manufactured by 3M Corporation. When a reflective polarizer is used, the image light from the display is linearly polarized (e.g., in a P polarization state, or P-polarized image light) and directed toward the windshield at a certain angle of, or very close to, Brewster's angle. The Brewster angle is the angle of incidence at which P-polarized light passes through the inner glass-air interface without reflection and strikes the reflective polarizer, causing at least a portion of the P-polarized light to be reflected back to the viewer as a single image (i.e., the image is reflected only by the reflective polarizer and not by the inner or outer glass-air interfaces).This technique works well to strongly reduce ghost images from the front and rear glass-to-air interfaces for angles of incidence near Brewster's angle. However, as the HUD image becomes wider, when the image is displayed at a horizontal skew angle relative to the observer (e.g., due to the inherent curve of the windshield or the driver's angle relative to the image), the P-polarized image rays defined according to the axial incidence plane are converted into a mixture of P- and S-polarized light, resulting in higher ghost image reflections.

[0005] According to some aspects of the present disclosure, optical systems are described that are based on optimizing output polarization as a function of windshield rake and skew angles. In some embodiments, the optimization can occur at the display itself. In some embodiments, the optimization can occur at any suitable point in the optical path from the display to the windshield. For example, the optimization can occur by controlling the orientation of an optical film in the optical path (such as a reflective polarizer), or the orientation of an optical reflector (e.g., a mirror used to fold the optical path), the orientation of a beamsplitter in the optical path, or the orientation of a retarder layer (e.g., a quarter-wave plate or half-wave plate) in the optical path. These examples are not intended to be limiting.

[0006] In some embodiments, an optical system (e.g., a head-up display, or HUD) includes a display, a vehicle windshield, and an optical film configured to receive an image emitted by the display and reflect or transmit at least a portion of the received image toward the windshield. In some embodiments, the display may be a liquid crystal display (LED), an organic light emitting display (OLED), a digital light processing (DLP) display, or any other suitable picture generating unit (PGU). In some embodiments, the display may have an active display area having a maximum horizontal dimension (i.e., a diagonal of the active display area) D, and the display may be configured to emit an image for viewing by the eyes of an observer, such as the eyes of an operator of a vehicle. In some embodiments, the active display area may include a display center (i.e., the physical center of the display in both the horizontal and vertical dimensions) and a predetermined area around and including the display center (i.e., the predetermined area is a subset or portion of the entire active display area). In some embodiments, the predetermined area may have a maximum lateral dimension d, and the ratio d / D is about 0.25 or less (i.e., the predetermined area may be about one-quarter of the total active display area). In some embodiments, the ratio d / D may be about 0.2 or less, about 0.15 or less, or about 0.1 or less.

[0007] In some embodiments, the optical system may be centered on an optical axis extending from the display center point to the windshield and to the viewer's eye. In some embodiments, the optical axis may be defined by a first emanating central image ray.

[0008] In some embodiments, the windshield may be a glass windshield. In some embodiments, the windshield may be curved either horizontally, vertically, or both. In some embodiments, the windshield may be rake (i.e., angled from vertical toward the operator). In some embodiments, the windshield may include a first interface (e.g., an inner glass / air interface) having a corresponding Brewster angle, where the first emanating central image ray is incident on the first interface of the windshield at the Brewster angle.

[0009] In some embodiments, the optical film may be configured to receive an image emitted by the active display area and reflect or transmit at least a portion of the received image toward the windshield. In some embodiments, the windshield may be configured to receive an image reflected or transmitted by the optical film and reflect at least a portion of the received image toward the eye. For at least one first location within a predetermined region of the active display area, the emitted image may include a first emitted image cone emanating from the first location. In some embodiments, the first emitted image cone may include a first emitted central image ray emanating from the first location. In some embodiments, the optical film may be oriented to cause the first emitted central image ray to be substantially polarized in the plane of incidence when incident on the windshield. Stated another way, the orientation of the optical film may be adjusted (e.g., rotated) so that at least the central image ray is "tuned" to have a polarization that is in the plane of incidence when the image strikes the windshield. In some embodiments, the optical film can be oriented such that at least about 90%, or at least about 95%, of the polarization of the first emerging central image light ray is in the plane of incidence when incident on the optical film.

[0010] In some embodiments, the optical film may be a reflective polarizer. In some embodiments, for substantially perpendicular incident light and for at least one visible wavelength within the visible wavelength range spanning from about 420 nm to about 670 nm, the reflective polarizer reflects about 20% to about 40% of incident light having a first polarization state (e.g., P-polarized light) and transmits at least 60% of incident light having an orthogonal second polarization state (e.g., linear S-polarized light or S-polarized light). In some embodiments, the reflective polarizer may be a multilayer optical film including a plurality of layers totaling more than about 30, a plurality of layers totaling more than about 50, or a plurality of layers totaling more than about 100. In some embodiments, the plurality of layers of the reflective polarizer includes a plurality of alternating first and second layers. In some embodiments, each of the first and second layers may have an average thickness of less than about 500 nm. In some embodiments, the difference in refractive index between the first and second layers along the first polarization state may be greater than about 0.05. In some embodiments, for substantially normally incident light and for at least one infrared wavelength within a wavelength range spanning from about 700 nm to about 1500 nm, the reflective polarizer may reflect at least 40% of the incident light for at least one of the first polarization state and the second polarization state. In other words, in some embodiments, the reflective polarizer can function to reflect heat from sunlight to prevent it from entering the HUD system.

[0011] In some embodiments, the optical film may be an absorbing polarizer. In some embodiments, for substantially normally incident light, the absorbing polarizer may transmit at least 60% of the incident light polarized along a first direction and absorb about 60% of the incident light polarized along an orthogonal second direction, wherein a first emerging central image ray, when incident on the absorbing polarizer, is polarized along a third direction, and the first and third directions form an inclination angle greater than about 5 degrees.

[0012] In some embodiments, the optical film may be an optical reflector (e.g., an optical mirror). In some embodiments, the optical reflector may be configured to receive an image emitted by the active display area and reflect at least a portion of the received image toward the windshield. In some embodiments, the windshield may be configured to receive an image reflected by the optical reflector and reflect at least a portion of the received image toward the viewer's eye. In some embodiments, the optical reflector may be oriented to substantially polarize the first emitted central image ray when incident on the windshield in the plane of incidence. In some embodiments, for substantially normally incident light and for at least one visible wavelength in the visible wavelength range spanning from about 420 nm to about 670 nm, the optical reflector may reflect at least 60% of incident light polarized along each of mutually orthogonal first and second directions (e.g., linear P-polarized light or linear S-polarized light). In some embodiments, for substantially normally incident light and for at least one infrared wavelength within a wavelength range spanning from about 700 nm to about 1500 nm, the optical reflector transmits at least 40% of incident light polarized along at least one of a first direction and a second direction that are orthogonal to each other. In some embodiments, the optical reflector can be a multilayer optical film including a plurality of alternating first and second layers, each of the first and second layers having an average thickness of less than about 500 nm.

[0013] In some embodiments, the optical system may further include a retarder layer (e.g., a quarter-wave plate or a half-wave plate) disposed between the optical film and the windshield. In some embodiments, the optical film may be an optical reflector configured to receive an image emitted by the active display area and reflect at least a portion of the received image toward the windshield. In some embodiments, the windshield may be configured to receive the image reflected by the optical reflector after the image passes through the retarder layer and reflect at least a portion of the received image toward the eye. In some embodiments, the retarder layer is oriented to polarize the first emitted central image ray substantially in the plane of incidence when incident on the windshield.

[0014] Referring now to the drawings, FIG. 1 is a top-down schematic diagram of a head-up display (HUD) as found in the prior art. As shown in FIG. 1, a typical HUD 200 projects an image onto a windshield 40, which is viewed by an observer 30 as a reflected image 22. Most windshields available today are sometimes curved, both horizontally (as shown in the top view of FIG. 1) and vertically (i.e., from top to bottom as viewed by the observer 30). For example, as shown in FIG. 1, the image projected by the HUD 200 onto the windshield 40 strikes the windshield at a horizontal skew angle of approximately 10 degrees, which is not uncommon in modern cars and can sometimes even be greater than 10 degrees. It is also important to note that the location of the HUD 200 may vary depending on the type of vehicle and may be located at a point farther away from the observer 30 than shown in FIG. 1 (imposing an even greater skew angle on the reflected image 22). When an image is projected with an axial incidence plane (i.e., relative to the optical axis) to be primarily P-polarized light, the light shifts to a mix of P- and S-polarized light due to being projected onto a surface at a significant horizontal skew angle. This increased S-polarized component can increase ghosting when viewed by observer 30.

[0015] FIG. 2A is a cross-sectional view of a polarization-optimized head-up display system according to an embodiment of the present disclosure. In some embodiments, the polarization-optimized head-up display (HUD) 300 includes a display 10, such as an LED, OLED, or other PGU. The display 10 is configured to emit an image 20 along an optical axis 60 and is projected onto a windshield 40 having a first interface 44 (e.g., an interface between the air and glass inside the windshield 40). The emitted image 20 includes an emitted light cone 23 that emanates from a first location 14 on the display, the emitted light cone 23 including an emitted central image ray 24. In some embodiments, the emitted image 20 passes through an optical film 50, at least a portion 21 of the image is transmitted therethrough and projected onto the windshield 40, and at least a portion 21 of the image is then reflected from the windshield as a reflected image 22 to the eye of the observer 30. In some embodiments, the central image ray 24 may coincide with the optical axis 60.

[0016] In some embodiments, windshield 40 may include an inner reflective polarizer layer 140 (e.g., a polymer film reflective polarizer sandwiched between inner and outer glass layers). In some embodiments, this may be a weakly reflective polarizer that reflects 20% to 40% of incident light having a first polarization state and transmits at least 60% of incident light having a second, orthogonal polarization state. Reflective polarizer 140 is discussed in more detail elsewhere herein in the discussion of FIG. 3.

[0017] FIG. 2B is a front view of display 10 and optical film 50, showing further details. The following discussion can best be viewed in conjunction with FIGS. 2A and 2B. A predetermined region 13 of active display area 11 of display 10 includes a display center 12 (the physical center of the display in both the horizontal and vertical dimensions) and a first location 14 from which emanates light cone 23. In some embodiments, first location 14 and display center 12 may be co-located (i.e., may be the same point). Emanating light cone 23 includes at least a first emanating central image ray 24 that is emitted by display 10, travels through optical film 50, is reflected from windshield 40, and continues to the eye of observer 30. In some embodiments, first emanating central image ray 24 may be coincident with or substantially parallel to optical axis 60. 2B , predetermined region 13 can have a maximum horizontal dimension d, and active display area 11 can have a maximum horizontal dimension D, with the ratio of d / D being about 0.25, or about 0.2, or about 1.5, or about 1.0. In other words, predetermined region 13 represents a central portion of active display area 11.

[0018] In some embodiments, the optical film 50 may be oriented (e.g., rotated) so that the first emanating central image light ray 24 is substantially polarized in the plane of incidence when it strikes the windshield 40. In other words, the optical film 50 may be rotated or otherwise oriented from a “conventional” orientation so that the polarization of the first emanating central image light ray 24 is substantially polarized at the point of incidence with the windshield 40, which, as discussed above, may be at a substantial skew angle relative to the observer 30 on a curved windshield 40. In this way, the system can compensate for any ghosting visible to the observer 30 due to the skew angle of the windshield.

[0019] 2B as having a rectangular shape that is physically rotated relative to display 10. However, the shape of the physical optical film 50 is arbitrary, and it is the orientation of the polarizing features within optical film 50 that is important. Also, as seen in other embodiments described herein, optimization of the polarization of image rays 24 may occur at other locations along the optical path of image rays 24.

[0020] 2C and 2D illustrate embodiments in which optical film 50 is an absorbing polarizer 70. The following discussion can best be viewed in conjunction with FIGS. 2C and 2D. When optical film 50 is an absorbing polarizer 70, for normally incident light 71 (which may include central image ray 24), absorbing polarizer 70 can transmit at least 60% of the incident light 71 polarized along a first direction (polarization direction 72, as shown in FIG. 2C) and absorb at least 60% of the incident light 71 polarized along an orthogonal second direction (polarization direction 73). In some embodiments, absorbing polarizer 70 can be oriented such that light passing through absorbing polarizer 70 is polarized along a new third direction 74. In some embodiments, first direction 72 and third direction 74 form an inclination angle α between them that is greater than about 5 degrees. 2D , central image ray 24 enters absorbing polarizer 70 with polarization direction 72, shown as 24(p72), and at least a portion of image ray 24 exits absorbing polarizer 70 with polarization direction 74, shown as 24(p74). In other words, the polarization of central image ray 24 is rotated by optical film 50 so that it is substantially polarized in the plane of incidence on the distorted windshield.

[0021] As discussed with respect to FIG. 2A, the windshield 40 may include a reflective polarizer 140 embedded therein. FIG. 3 is a cross-sectional view of one embodiment of such a reflective polarizer 140. In some embodiments, the reflective polarizer 140 may be configured as a multilayer optical film (MOF). In some embodiments, the reflective polarizer 140 includes a plurality of alternating first polymer layers 142 and second polymer layers 143. In some embodiments, the number of combined alternating first polymer layers 142 and second polymer layers 143 may be between 30 and 700. In some embodiments, the first polymer layers 142 and second polymer layers 143 may each have an average thickness of less than about 500 nm.

[0022] In some embodiments, the first polymer layer 142 may be substantially isotropic (i.e., exhibiting substantially the same refractive index when measured in different directions). In some embodiments, the second polymer layer 143 may be substantially birefringent (i.e., exhibiting two different refractive indices when measured in different orthogonal directions), with in-plane refractive indices nx and ny along the orthogonal directions, where the difference between nx and ny may be greater than about 0.05, or greater than about 0.03, or greater than about 0.01. In some embodiments, additional layers 141 (e.g., adhesive layers, other substrate layers) may be present on the outer surface of the reflective polarizer 140.

[0023] In some embodiments, the reflective polarizer 140 may be relatively weak, such that when incident light 145 strikes the film, for at least one visible wavelength within the visible wavelength range spanning from about 420 nm to about 670 nm, the reflective polarizer reflects from about 20% to about 40% of the incident light 145 having a first polarization state (e.g., P-polarized light) and transmits at least 60% of the incident light having an orthogonal second polarization state (e.g., S-polarized light).

[0024] In some embodiments, for substantially normally incident light 145 and for at least one infrared wavelength within an infrared wavelength range spanning from about 700 nm to about 1500 nm, the reflective polarizer may reflect at least 40% of the incident light for at least one of the first polarization state and the second polarization state, which in some embodiments can help reduce unwanted heat transfer (to the HUD) due to sunlight impinging on the exterior surface of the windshield.

[0025] Figures 4 and 5 are cross-sectional views of alternative embodiments of polarization-optimized head-up display systems in accordance with the present disclosure. Many of the elements of Figures 4 and 5 and Figure 2A are common. Elements of Figures 2A, 4, and 5 that share similarly numbered reference characters have identical functions, and no additional description beyond that provided above may be provided.

[0026] In FIG. 4 , polarization-optimized head-up display system 400 has a “folded” optical path (as defined by optical axis 60), where image 20′ emanates from active display area 11 of display 10 and is first reflected off optical reflector 90 (e.g., a mirror, a reflective film, etc.), after which at least a portion of image 21′ is redirected toward windshield 40. In some embodiments, retarder layer 100 (e.g., a quarter-wave plate or a half-wave plate) may be disposed on optical reflector 90. In some embodiments, one or both of optical reflector 90 and retarder layer 100 may be oriented to polarize first emanating central image ray 24 substantially in the plane of incidence when incident on windshield 40. After image 21′ is reflected from windshield 40, at least a portion of image 22′ is redirected toward observer 30 as the perceived image. In some embodiments, the optical reflector 90 may be substantially flat, curved (e.g., convex or concave to apply force), or freeform. In some embodiments, the optical reflector 90 may be a polarizing reflector (e.g., a polarizing reflective multilayer optical film) capable of rotating polarized light without a separate retarder layer 100.

[0027] In FIG. 5 , polarization-optimized head-up display system 500 adds an additional bend to the optical path represented by optical axis 60. Display 10 emits image 20′ from active display area 11. Image 20′ travels toward optical beam splitter 80. In some embodiments, optical beam splitter 80 may be a reflective polarizer that substantially reflects incident light of a first polarization state (e.g., linear S-polarized light) and substantially transmits incident light of an orthogonal second polarization state (e.g., linear P-polarized light). In one embodiment, central image light ray 24 may be emitted as light having an S-polarization state, reflected by optical beam splitter 80, and redirected toward optical reflector 90. A retarder layer 100 disposed on the optical reflector may then convert the S-polarized light to P-polarized light when at least a portion of image 21′ is redirected toward optical beam splitter 80, which then passes through. Image 21' is reflected from windshield 40, and at least a portion of image 22' is redirected toward observer 30. The orientation and rotation angle of beamsplitter 80 may be used to set the output polarization seen at the plane of incidence. In the embodiments of Figures 4 and 5, any of the elements including optical beamsplitter 80, optical reflector 90, and retarder layer 100 may be oriented so that the image (including image ray 24) is substantially polarized at the point of incidence on distorted windshield 40.

[0028] Finally, FIGS. 6A and 6B provide graphical plots illustrating the effect of a polarization-optimized head-up display according to the present disclosure. FIG. 6A provides a plot of the percentage contrast ratio of the ghost image of the P-polarized head-up display output when no polarization optimization adjustment is performed (i.e., for the embodiment of FIG. 2A , the optical film 50 is not rotated relative to the display 10). The x-axis of FIG. 6A plots the horizontal skew angle of the windshield relative to the axial plane (the angle from the axial plane at the point of incidence of the image). The y-axis plots the normal incidence angle. The dashed rectangular box represents the “eyebox” or active viewing area (approximately 5° × 12°) of the displayed image as seen by the vehicle operator. The shaded outline in FIG. 6A indicates that the contrast ratio of the ghost image increases significantly toward the right of the “eyebox,” exceeding 2 percent and approaching 3 percent.

[0029] Figure 6B shows the improved performance of the same system achieved when the HUD's output polarization is rotated by approximately 5 degrees. The entire "eyebox" in Figure 6B exhibits a ghost contrast ratio of nearly less than 1%, significantly reducing the ghost images perceived by the operator.

[0030] Terms such as "about" will be understood by those of ordinary skill in the art in the context in which they are used and described herein. Where the use of "about" as applied to quantities expressing feature sizes, amounts, and physical characteristics is not clear to those of ordinary skill in the art in the context in which it is used and described herein, "about" will be understood to mean within 10 percent of the specified value. A quantity given as about a particular value may be exactly that particular value. For example, where it is not clear to those of ordinary skill in the art in the context in which it is used and described herein, an amount having a value of about 1 means that the amount has a value between 0.9 and 1.1, and means that the value may be 1.

[0031] Terms such as "substantially" will be understood by those skilled in the art in the context in which they are used and described herein. If the use of "substantially equal" is not clear to those skilled in the art in the context in which it is used and described herein, "substantially equal" means approximately equal, where "about" is as described above. If the use of "substantially parallel" is not clear to those skilled in the art in the context in which it is used and described herein, "substantially parallel" means within 30 degrees of parallel. Directions or surfaces described as substantially parallel to one another may, in some embodiments, be within 20 degrees, or within 10 degrees, of parallel, or may be parallel or nominally parallel. If the use of "substantially aligned" is not clear to those skilled in the art in the context in which it is used and described herein, "substantially aligned" means aligned within 20% of the width of the objects being aligned. Objects described as being substantially aligned may, in some embodiments, be aligned within 10% or within 5% of the width of the objects being aligned.

[0032] All of the above-referenced references, patents, or patent applications are hereby incorporated by reference in their entirety. In the event of any inconsistency or contradiction between the portions of the incorporated references and this application, the information in the foregoing description shall prevail.

[0033] Descriptions of elements in a figure should be understood to apply equally to corresponding elements in other figures unless otherwise indicated. While specific embodiments have been illustrated and described herein, those skilled in the art will recognize that the specific embodiments illustrated and described may be replaced by various alternative and / or equivalent embodiments without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Accordingly, the present disclosure is intended to be limited only by the claims and equivalents thereof. The following are exemplary embodiments. [Item 1] 1. An optical system comprising: a display having an active display area having a maximum lateral dimension D and configured to emit an image for viewing by an eye of an observer, the active display area including a display center and a predetermined area including the display center, the predetermined area having a maximum lateral dimension d, where d / D≦0.25; Vehicle windshields and an optical film configured to receive the image emitted by the active display area and reflect or transmit at least a portion of the received image toward the windshield, the windshield being configured to receive the image reflected or transmitted by the optical film and reflect at least a portion of the received image toward the eye, wherein for at least one first location within the predetermined region of the active display area, the emitted image includes a first emitted image cone emanating from the first location, the first emitted image cone including a first emanated central image ray emanating from the first location, the optical film being oriented to polarize the first emanated central image ray substantially in a plane of incidence when incident on the windshield; An optical system comprising: [Item 2] Item 1, an optical system substantially centered on an optical axis extending from the center of the display to the eye. [Item 3] 3. The optical system of claim 2, wherein the optical axis includes the first emerging central image ray. [Item 4] Item 1, wherein the display comprises a liquid crystal display, an organic light emitting diode display, or a digital light processing display. [Item 5] Item 2. The optical system according to item 1, wherein d / D≦0.2. [Item 6] Item 10. The optical system of item 1, wherein the windshield includes a first boundary surface and a corresponding first Brewster angle, and the first emanating central image ray is incident on the first boundary surface of the windshield at the first Brewster angle. [Item 7] Item 10. The optical system of item 1, wherein the windshield comprises a reflective polarizer embedded therein. [Item 8] 8. The optical system of claim 7, wherein for substantially perpendicular incident light and for at least one visible wavelength within a visible wavelength range spanning from about 420 nm to about 670 nm, the reflective polarizer reflects from about 20% to about 40% of the incident light having a first polarization state and transmits at least 60% of the incident light having an orthogonal second polarization state. [Item 9] 9. The optical system of claim 8, wherein for the substantially perpendicular incident light and for at least one infrared wavelength in an infrared wavelength range spanning from about 700 nm to about 1500 nm, the reflective polarizer reflects at least 40% of the incident light for at least one of the first polarization state and the second polarization state. [Item 10] Item 9. The optical system of item 8, wherein the reflective polarizer comprises a plurality of layers, including a plurality of alternating first and second layers, totaling more than about 30 layers, each of the first and second layers having an average thickness less than about 500 nm, and a difference in refractive index between the first and second layers along the first polarization state being greater than about 0.05. [Item 11] Item 10. The optical system of item 1, wherein the optical film comprises an absorbing polarizer, wherein for substantially normally incident light, the absorbing polarizer transmits at least 60% of the incident light polarized along a first direction and absorbs approximately 60% of the incident light polarized along an orthogonal second direction, the first emerging central image ray is polarized along a third direction when incident on the absorbing polarizer, and the first direction and the third direction form an inclination angle greater than approximately 5 degrees. [Item 12] Item 10. The optical system of item 1, wherein the optical film comprises an optical reflector configured to receive the image emitted by the active display area and reflect at least a portion of the received image toward the windshield, the windshield configured to receive the image reflected by the optical reflector and reflect at least a portion of the received image toward the eye, and the optical reflector is oriented to polarize the first emitted central image ray substantially in the plane of incidence when incident on the windshield. [Item 13] Item 13. The optical system of item 12, wherein for substantially perpendicular incident light and for at least one visible wavelength within a visible wavelength range spanning from about 420 nm to about 670 nm, the optical reflector reflects at least 60% of the incident light polarized along each of first and second directions that are orthogonal to each other. [Item 14] Item 13. The optical system of item 12, wherein for the substantially perpendicular incident light and for at least one infrared wavelength within an infrared wavelength range spanning from about 700 nm to about 1500 nm, the optical reflector transmits at least 40% of the incident light polarized along at least one of a first direction and a second direction that are orthogonal to each other. [Item 15] Item 10. The optical system of item 1, further comprising: a retarder layer disposed between the optical film and the windshield, the optical film comprising an optical reflector configured to receive the image emitted by the active display area and reflect at least a portion of the received image toward the windshield, the windshield configured to receive the image reflected by the optical reflector after the image passes through the retarder layer and reflect at least a portion of the received image toward the eye, and the retarder layer oriented to polarize the first emitted central image ray substantially in the plane of incidence when incident on the windshield.

Claims

1. 1. An optical system comprising: a display having an active display area having a maximum lateral dimension D and configured to emit an image for viewing by an eye of an observer, the active display area including a display center and a predetermined area including the display center, the predetermined area having a maximum lateral dimension d, where d / D≦0.25; a vehicle windshield having an embedded reflective polarizer that reflects light that is substantially polarized in a plane of incidence; an optical film configured to receive the image emitted by the active display area and reflect or transmit at least a portion of the received image toward the windshield, the windshield being configured to receive the image reflected or transmitted by the optical film and reflect at least a portion of the received image toward the eye, and for at least one first location within the predetermined region of the active display area, the emitted image includes a first emitted image cone emanating from the first location, the first emitted image cone including a first emitted central image ray emanating from the first location and polarized in a direction other than a plane of incidence relative to the windshield, the optical film being oriented to rotate the polarization of the first emitted central image ray so that it is substantially polarized in the plane of incidence when incident on the windshield; the first emanating central image ray is incident on the windshield at substantially Brewster's angle; and a location at which the first emitted central image ray strikes the windshield with the optical film closer to a center of an active viewing area of ​​an image displayed on the windshield than a location at which light emitted from the display and substantially polarized in the plane of incidence strikes the windshield at substantially Brewster's angle without the optical film; Optical system.

2. The optical system of claim 1 , wherein the windshield comprises a reflective polarizer embedded therein.

3. 2. The optical system of claim 1, wherein the optical film comprises an optical reflector and a retarder layer disposed between the optical reflector and the windshield, the optical reflector configured to receive the image emitted by the active display area and reflect at least a portion of the received image toward the windshield, the windshield configured to receive the image reflected by the optical reflector after the image passes through the retarder layer and reflect at least a portion of the received image toward the eye, and the retarder layer configured to rotate the polarization of the first emitted central image ray so that it is substantially polarized in the plane of incidence when incident on the windshield.

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