Head-up display system

Abstract

The optical system includes an image projector having a light source. The reflective polarizer receives light emitted by the light source at a first angle of incidence greater than 30 degrees and reflects a portion of the light as a first reflected light. The spatial light modulator receives the first reflected light at a second angle of incidence greater than 5 degrees and transmits a portion of the first reflected light as projected image light. The first mirror receives the projected image light at a third angle of incidence and reflects a portion of the projected image light as a second reflected image light that is received by a second mirror at a fourth angle of incidence and reflects a portion of the second reflected image light as a third reflected image light having a visible image. The light source and the spatial light modulator are disposed on the same side of the reflective polarizer.

Description

[Technical Field]

[0001] The present disclosure relates generally to optical systems, and more particularly to optical systems for head-up display systems. [Background technology]

[0002] Electronic displays are provided in many applications to render digital information to an observer. Head-up displays (HUDs), due to their transparent nature, allow the observer to observe not only the information but also the view through the HUD. Thus, the observer can observe the displayed information without losing the ability to observe the real world through the HUD. While HUD systems have been developed for use in high-speed vehicles, particularly aircraft, they are now increasingly being considered as a feature of other vehicles, including automobiles. On a smaller scale, HUD systems are used as goggle lenses or helmet visors, or in a variety of other virtual reality (VR) applications. HUDs can be implemented on various surfaces and windows, such as vehicle windshields. Therefore, vehicle operation information, such as vehicle speed and / or navigation direction, can be displayed to the vehicle occupant, for example, on the windshield. HUD systems may be positioned behind the vehicle steering wheel, for example, on or near the vehicle dashboard, to generate information that carries an image that is projected onto the windshield. Summary of the Invention

[0003] Some aspects of the present disclosure relate to an optical system including an image projector for projecting substantially collimated image light having an image. The image projector includes at least one light source emitting substantially collimated light. A first reflective polarizer receives the substantially collimated emitted light at a first angle of incidence and reflects at least a portion of the emitted light as a first reflected light. A spatial light modulator having a plurality of pixels for forming an image receives the first reflected light at a second angle of incidence and transmits at least a portion of the first reflected light as at least a portion of substantially collimated projected image light having the image. The projected image light has a first polarization state. The optical system includes a first mirror receiving the substantially collimated projected image light at a third angle of incidence and reflecting at least a portion of the projected image light as a second reflected image light having the image. A second mirror receives the second reflected image light having the image at a fourth angle of incidence and reflects at least a portion of the second reflected image light as a third reflected image light having the image for viewing by a viewer. The at least one light source and the spatial light modulator are disposed on the same side of the first reflective polarizer, the first angle of incidence being greater than about 30 degrees, and the second angle of incidence being greater than about 5 degrees.

[0004] Some aspects of the present disclosure relate to a head-up display (HUD) for forming a virtual image of a projected image for observation by a vehicle occupant. The HUD includes an image projector for projecting image light having an image. The image projector includes at least one light source emitting substantially collimated light. A first reflective polarizer receives the substantially collimated emitted light at a first incident angle and reflects at least a portion of the emitted light as a first reflected light. A spatial light modulator including a plurality of pixels for forming an image receives the first reflected light at a second incident angle and transmits at least a portion of the first reflected light as substantially collimated projected image light having the image. The projected image light has a first polarization state. The image projector includes a first folding angle greater than approximately 30 degrees, substantially centered on a first folding optical axis extending from the at least one light source to the spatial light modulator. The HUD includes projection optics for projecting and forming a virtual image of the projected image. The projection optical system includes a first mirror for receiving the substantially collimated projection image light at a third angle of incidence and reflecting at least a portion of the projection image light as second reflected image light having an image. The second mirror receives the second reflected image light having the image at a fourth angle of incidence and reflects at least a portion of the second reflected image light as third reflected image light having an image for viewing by an observer. The vehicle windshield is configured to receive the third reflected image light and reflect a portion of the received image toward the observer so that the observer can view a virtual image of the reflected image. The image projector includes a second folding angle greater than approximately 90 degrees substantially centered on a second folding optical axis extending from the spatial light modulator to at least the windshield. [Brief explanation of the drawings]

[0005] Various aspects of the present disclosure will be discussed in more detail with reference to the accompanying drawings.

[0006] [Figure 1] 1 illustrates a schematic diagram of a head-up display system according to some embodiments of the present disclosure. [Figure 2]10 illustrates a schematic diagram of an optical system for a head-up display system according to another embodiment of the present disclosure.

[0007] The drawings are not necessarily to scale. Like numbers used in the drawings refer to like components. However, it will be understood that the use of a number to refer to a component in a particular drawing is not intended to limit the component in another drawing bearing the same number. DETAILED DESCRIPTION OF THE INVENTION

[0008] In the following description, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration various embodiments. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. Accordingly, the following detailed description is not to be taken in a limiting sense.

[0009] The term head-up display (HUD) is used herein to refer to such display systems, whether used on the windows or windshields of vehicles such as aircraft, watercraft, or motor vehicles such as automobiles, trucks, and motorcycles, in smaller systems such as goggle lenses or helmet visors, or in a variety of other applications.

[0010] For example, a HUD system projects an image onto a vehicle's windshield, allowing an observer (e.g., a driver) to observe information in the form of a virtual image. The HUD system may be configured to display one or more of vehicle operation information such as vehicle speed, navigation information such as directions and / or maps, ambient information such as temperature, radio stations, or track listings, communication information such as caller information, and road sign information or restrictions such as effective speed limits. The HUD system may be positioned behind the vehicle's steering wheel, e.g., on or near the vehicle's dashboard, to generate an image that is projected onto the windshield and then reflects light, e.g., toward the driver.

[0011] A HUD system includes an image generating unit (PGU) that projects from the bottom corners of the HUD onto a cold mirror, which reflects the image toward a main focusing mirror and out onto the windshield, creating a z-shaped beam path. Most PGU projection sources include an array of LEDs with a lenslet-type collimator that projects toward a display system (such as an LCD), which has a diffusing element on the side facing the PGU. A specific throw distance between the LEDs and the diffuser / LCD may be desirable to achieve uniform illumination across the image plane. This throw distance, along with a heat sink behind the LED array for thermal management, creates an extended PGU geometry that can increase the HUD volume, which can extend downward into the vehicle's dashboard area. The embodiments described herein address these and other challenges.

[0012] Some embodiments of the present disclosure describe a HUD system that more effectively utilizes the available space within the HUD, addressing thermal management, volume reduction, and optical efficiency of the system.

[0013] An optical system (300) according to some aspects of the present disclosure is shown in FIG. 1. In some embodiments, the optical system (300) may be a HUD system for forming a virtual image (102) of a projected image (11) for viewing by an occupant (70) of a vehicle (110). The optical system (300) includes an image projector (200) that projects image light (10) having the image (11) for viewing by the eye of the observer (70). In some aspects, the image light (10) may be substantially collimated image light (10). The optical system is configured such that the observer views the virtual image (102) of the projected image, allowing the observer to observe various types of information, such as speed, fuel level, temperature, warnings, direction, etc., on the windshield (100). The image projector (200) includes at least one light source (20) for emitting substantially collimated light (21). In some aspects, the light source may include an organic light-emitting display (OLED), an electroluminescent panel, an incandescent or phosphorescent light source, a CRT, an LED, as well as lenses, collimators, reflectors, and / or polarizers. In some embodiments, the image projector (200) may include a heat sink (80) thermally coupled to at least one light source (20). The heat sink (80) may be configured as a cooling body thermally coupled to the light source (20) to dissipate heat emitted from the light source (20).

[0014] In some embodiments, the divergence angle of the substantially collimated light (21) emitted by the at least one light source (20) may be less than about 10 degrees, or less than about 7.5 degrees, or less than about 5 degrees.

[0015] The image projector (200) further includes a spatial light modulator (40) having a plurality of pixels (41) for forming an image (11). In some embodiments, a first reflective polarizer (30) may be disposed between the at least one light source (20) and the spatial light modulator (40). The first reflective polarizer (30) receives substantially collimated radiation light (21) emitted by the at least one light source (20) at a first angle of incidence (θ1) and reflects at least a portion of the radiation light as first reflected light (31) toward the spatial light modulator (40). The spatial light modulator (40) receives the first reflected light (31) at a second angle of incidence (θ2) and transmits at least a portion of the first reflected light as substantially collimated projected image light (10) comprising an image and having a first polarization state, or as at least a portion of the substantially collimated projected image light (10) comprising an image and having a first polarization state.

[0016] In some embodiments, the first reflective polarizer (30) can generally comprise a material that transmits light of a first polarization and reflects light of a second, different polarization. Reflective polarizers include, but are not limited to, diffusely reflective polarizers, multilayer reflective polarizers, and cholesteric reflective polarizers. The first reflective polarizer (30) can be a broadband reflective polarizer or a notch reflective polarizer. In other examples, the first reflective polarizer (30) can be one or more of an absorbing linear polarizer, a multilayer polymeric reflective polarizer, or a stack of reflective polarizers, which substantially transmits light having a first polarization state and substantially reflects light having an orthogonal second polarization state. Substantially uniaxially oriented reflective polarizers are available from 3M Company under the trade names Advanced Polarizing Film 5 or APF. Other types of multilayer optical film reflective polarizers (e.g., Dual Brightness Enhancement Film or DBEF, available from 3M Company) can also be used. Other types of reflective polarizers (e.g., wire grid polarizers) can also be used.

[0017] In some embodiments, the first reflective polarizer (30) can be said to substantially reflect incident light if the average reflectivity of the first reflective polarizer (30) for the first polarization state (x-axis) is greater than about 60%, or greater than 70%, or greater than 80%, for substantially normally incident light and over the visible range spanning from about 420 nm to about 680 nm.

[0018] In some embodiments, the at least one light source (20) and the spatial light modulator (40) may be located on the same side of the first reflective polarizer (30). In some aspects, the first angle of incidence (θ1) may be greater than about 30 degrees, or greater than about 35 degrees, or greater than about 40 degrees, or greater than about 50 degrees. The second angle of incidence (θ2) may be greater than about 5 degrees, or greater than about 10 degrees, or greater than about 15 degrees, or greater than about 20 degrees.

[0019] In some embodiments, the image projector may include a light diffuser (90) disposed between the first reflective polarizer (30) and the spatial light modulator (40) to diffuse the reflected light (31) and ensure light uniformity. In some aspects, the light diffuser (90) may be one of a diffusion film or a microlens array.

[0020] The optical system (300) includes a first mirror (50) for receiving substantially collimated projected image light (10) at a third angle of incidence (θ3). The first mirror (50) reflects at least a portion of the projected image light as a second reflected image light (51) having an image (11). In some embodiments, the first mirror (50) may be a high-reflectivity mirror having a reflectivity greater than 99.5%. In some examples, the third angle of incidence (θ3) may be approximately 20-60 degrees. In some examples, the third angle of incidence (θ3) may be approximately 25-50 degrees or approximately 30-45 degrees.

[0021] The optical system (300) may also include a second mirror (60) for receiving the second reflected image light (51) having the image (11) at a fourth angle of incidence (θ4). The second mirror (60) reflects at least a portion of the second reflected image light as third reflected image light (61) having the image for viewing by the observer (70). In some embodiments, the second mirror (60) may be a high-reflectivity mirror having a reflectivity greater than 99.5%. In some examples, the fourth angle of incidence (θ4) may be approximately 20 to 60 degrees. In some examples, the fourth angle of incidence (θ4) may be approximately 25 to 50 degrees or approximately 30 to 45 degrees. In some embodiments, the windshield (100) of the vehicle (110) may be configured to receive the third reflected image light (61). A portion (101) of the image received by the windshield (100) may be reflected toward the observer (70) so that the observer (70) can see a virtual image (102) of the reflected image.

[0022] According to the embodiment shown in FIG. 2, the image projector (200′) includes a third mirror (120). A first reflective polarizer (30) may be disposed between the at least one light source (20) and the third mirror (120). In some aspects, the first reflective polarizer (30) reflects a portion of the emitted light as a first reflected light (31) having a first polarization state and transmits a portion of the emitted light as a first transmitted light (32) having an orthogonal second polarization state. The third mirror (120) receives the first transmitted light (32) at a fifth angle of incidence (θ5) and reflects at least a portion of the first transmitted light as a fourth reflected light (121). In some aspects, the fifth angle of incidence (θ5) may be greater than about 30 degrees, or greater than about 35 degrees, or greater than about 40 degrees, or greater than about 50 degrees.

[0023] According to the embodiment shown in FIG. 2 , the spatial light modulator (40) can be configured to receive the first reflected light (31) at a second angle of incidence (θ2). The spatial light modulator (40) transmits at least a portion of the first reflected light as a substantially collimated first projected image light (12) having at least a first portion of the image (11) and a first polarization state (x-axis). The spatial light modulator (40) may be further configured to receive the fourth reflected light (121) at a sixth angle of incidence (θ6). In some cases, the sixth angle of incidence (θ6) may be greater than about 5 degrees, or greater than about 10 degrees, or greater than about 15 degrees, or greater than about 20 degrees. The spatial light modulator (40) transmits at least a portion of the fourth reflected light as a substantially collimated second projected image light (13) having at least a second portion of the image (11) and a first polarization state (x-axis). The first and second projected image lights (12, 13) combine to form a substantially collimated projected image light (10) (FIG. 1) having an image (11) and a first polarization state (x-axis).

[0024] In some embodiments, the first angle of incidence (θ1) and the fifth angle of incidence (θ5) may be within about 5 degrees of each other, or within 2 degrees of each other. In some other embodiments, the second angle of incidence (θ2) and the sixth angle of incidence (θ6) may be within about 5 degrees of each other, or within 2 degrees of each other.

[0025] In some embodiments, the image projector (200′) may include a retarder layer (130) disposed between the first reflective polarizer (30) and the third mirror (120). In some examples, the retarder layer (130) may be a quarter-wave retarder. In some aspects, the retarder layer (130) may be a film laminated on the first reflective polarizer (30) or a coating applied to the first reflective polarizer (30). For example, the retarder layer (130) may be an oriented polymer film laminated on the first reflective polarizer (30) or a liquid crystal polymer coating on the first reflective polarizer (30). Suitable coatings for forming a quarter-wave retarder include, but are not limited to, linear photopolymerizable polymer (LPP) materials and liquid crystal polymer (LCP) materials, as described elsewhere.

[0026] In some embodiments, the third mirror (120) may be a highly reflective mirror having a reflectivity of greater than 99.5%. The light reflected by the third mirror (120) passes through a retarder layer (130) that converts light polarized in the second direction (y-axis) to light polarized in the first direction (x-axis).

[0027] Another embodiment, as shown in Figure 1, illustrates a head-up display (HUD) (300) that forms a virtual image (102) of a projected image (11) for viewing by an occupant 70 of a vehicle (110). The HUD (300) may include an image projector (200) for projecting image light (10) bearing the image (11) and projection optics (140) for projecting and forming a virtual image of the projected image.

[0028] The image projector (200) of the HUD projects image light (10) having an image (11) for viewing by the eyes of the occupant (70). In some aspects, the image light (10) may be substantially collimated. The image projector (200) includes at least one light source (20) for emitting substantially collimated light (21). In some aspects, the light source may include an organic light-emitting display (OLED), an electroluminescent panel, an incandescent or phosphorescent light source, a CRT, an LED, and lenses, collimators, reflectors, and / or polarizers. In some embodiments, the image projector (200) may include a heat sink (80) thermally coupled to the at least one light source (20). The heat sink (80) may be configured as a cooling body thermally coupled to the light source (20) to dissipate heat emitted from the light source (20).

[0029] In some embodiments, the divergence angle of the substantially collimated light (21) emitted by the at least one light source (20) may be less than about 10 degrees, or less than about 7.5 degrees, or less than about 5 degrees.

[0030] The image projector (200) of the HUD includes a spatial light modulator (40) having a plurality of pixels (41) for forming an image (11). In some embodiments, a first reflective polarizer (30) may be disposed between the at least one light source (20) and the spatial light modulator (40). The first reflective polarizer (30) receives substantially collimated radiation light (21) emitted by the at least one light source (20) at a first angle of incidence (θ1) and reflects at least a portion of the radiation light as first reflected light (31) toward the spatial light modulator (40). The spatial light modulator (40) receives the first reflected light (31) at a second angle of incidence (θ2) and transmits at least a portion of the first reflected light as substantially collimated projected image light (10) comprising an image and having a first polarization state.

[0031] In some embodiments, the first reflective polarizer (30) can generally comprise a material that transmits light of a first polarization and reflects light of a second, different polarization. Reflective polarizers include, but are not limited to, diffusely reflective polarizers, multilayer reflective polarizers, and cholesteric reflective polarizers. The first reflective polarizer (30) can be a broadband reflective polarizer or a notch reflective polarizer. In other examples, the first reflective polarizer (30) can be one or more of an absorbing linear polarizer, a multilayer polymeric reflective polarizer, or a stack of reflective polarizers, which substantially transmits light having a first polarization state and substantially reflects light having an orthogonal second polarization state. Substantially uniaxially oriented reflective polarizers are available from 3M Company under the trade names Advanced Polarizing Film 5 or APF. Other types of multilayer optical film reflective polarizers (e.g., Dual Brightness Enhancement Film or DBEF, available from 3M Company) can also be used. Other types of reflective polarizers (e.g., wire grid polarizers) can also be used.

[0032] In some embodiments, a first reflective polarizer (30) can be said to substantially reflect incident light if the average reflectance of the first reflective polarizer (30) for a first polarization state (x-axis) can be greater than about 60%, or greater than 70%, or greater than 80% for substantially normally incident light and in the visible range spanning about 420 nm to about 680 nm. In other embodiments, a first reflective polarizer (30) can be said to substantially transmit incident light if the average transmittance of the first reflective polarizer (30) for a second, orthogonal polarization state (y-axis) can be greater than about 60%, or greater than 70%, or greater than 80% for substantially normally incident light and in the visible range spanning about 420 nm to about 680 nm.

[0033] In another embodiment, the reflective polarizer (30) may be a narrow tri-band notched reflector that produces a higher output color gamut. The high color gamut narrow-band PGU output can be matched with a similar notched CMF-type reflective polarizer that can reduce the load on the spatial light modulator by rejecting IR, a significant amount of visible energy with polarization, and some of the remaining light with the correct polarization through wavelength filtering.

[0034] In some embodiments, the projection optical system includes a first mirror (50), a second mirror (60), and a windshield (100) of the vehicle. The first mirror (50) receives the substantially collimated projection image light (10) at a third angle of incidence (θ3) and reflects at least a portion of the projection image light as a second reflected image light (51) having an image (11). In some embodiments, the first mirror (50) may be a high-reflectivity mirror having a reflectivity greater than 99.5%. In some aspects, the third angle of incidence (θ3) may be approximately 20 to 60 degrees. In some aspects, the third angle of incidence (θ3) may be approximately 25 to 50 degrees or approximately 30 to 45 degrees.

[0035] The second mirror (60) receives the second reflected image light (51) having the image (11) at a fourth angle of incidence (θ4) and reflects at least a portion of the second reflected image light (51) as a third reflected image light (61) having the image for viewing by the observer (70). In some embodiments, the second mirror (60) may be a high-reflectivity mirror having a reflectivity greater than 99.5%. In some examples, the fourth angle of incidence (θ4) may be approximately 20-60 degrees. In other examples, the fourth angle of incidence (θ4) may be approximately 25-50 degrees or approximately 30-45 degrees. In some embodiments, the windshield (100) of the vehicle (110) may be configured to receive the third reflected image light (61), and a portion (101) of the image received by the windshield (100) may be reflected toward the observer (70). The observer (70) may be configured to view a virtual image (102) of the reflected image.

[0036] In some embodiments, the image projector (200) may be substantially centered on a first folded optical axis extending from the at least one light source (20) to the spatial light modulator (40) and, in some aspects, may include a first folding angle (α1) that is greater than about 30 degrees, or greater than about 40 degrees, or greater than 50 degrees. In some other embodiments, the image projector may be substantially centered on a second folded optical axis extending from the spatial light modulator (40) to at least the windshield (100) and, in some aspects, may include a second folding angle (α2) that is greater than about 90 degrees, or greater than about 100 degrees, or greater than 110 degrees. The desired throw distance between the light source (20) and the spatial light modulator (40) to achieve uniform illumination across the image plane can be maintained while simultaneously folding or bending the image projector (200) in different directions to reduce the overall HUD volume without compromising brightness uniformity across the image.

[0037] Below is a list of exemplary embodiments:

[0038] Embodiment 1. An optical system, an image projector for projecting substantially collimated image light having an image, the image projector including at least one light source emitting substantially collimated light; a first reflective polarizer receiving the substantially collimated emitted light at a first angle of incidence and reflecting at least a portion of the emitted light as a first reflected light; and a plurality of pixels for forming an image, receiving the first reflected light at a second angle of incidence and transmitting at least a portion of the first reflected light as at least a portion of substantially collimated projected image light having the image, 1. An optical system comprising: a spatial light modulator, wherein image light has a first polarization state; a first mirror that receives the substantially collimated projected image light at a third angle of incidence and reflects at least a portion of the projected image light as second reflected image light having an image; and a second mirror that receives the second reflected image light having the image at a fourth angle of incidence and reflects at least a portion of the second reflected image light as third reflected image light having the image for viewing by an observer; wherein the at least one light source and the spatial light modulator are positioned on the same side of the first reflective polarizer, and the first angle of incidence is greater than about 30 degrees and the second angle of incidence is greater than about 5 degrees.

[0039] Embodiment 2. The optical system of embodiment 1, wherein the image projector further comprises a heat sink thermally coupled to the at least one light source.

[0040] Embodiment 3. The optical system of embodiment 1, wherein the image projector further includes a light diffuser disposed between the first reflective polarizer and the spatial light modulator.

[0041] Embodiment 4. The optical system of embodiment 1, further comprising a vehicle windshield, the windshield configured to receive the third reflected image light and reflect a portion of the received image toward an observer so that the observer can view a virtual image of the reflected image.

[0042] Embodiment 5. An image projector includes a first reflective polarizer disposed between at least one light source and a third mirror, the first reflective polarizer reflecting a portion of the emitted light as a first reflected light having a first polarization state and transmitting a portion of the emitted light as a first transmitted light having an orthogonal second polarization state; the third mirror receiving the first transmitted light at a fifth angle of incidence and reflecting at least a portion of the first transmitted light as a fourth reflected light; and the spatial light modulator receiving the first reflected light at the second angle of incidence and reflecting at least a portion of the first reflected light. 10. The optical system of claim 1, further comprising: receiving a fourth reflected light at a sixth incident angle; transmitting at least a portion of the fourth reflected light as a substantially collimated first projected image light having at least a first portion of the image and having a first polarization state; receiving a fourth reflected light at a sixth incident angle; and transmitting at least a portion of the fourth reflected light as a substantially collimated second projected image light having at least a second portion of the image and having the first polarization state; wherein the first and second projected image lights combine to form a substantially collimated projected image having the image and having the first polarization state.

[0043] Embodiment 6. The optical system of embodiment 5, wherein the fifth angle of incidence is greater than about 30 degrees and the sixth angle of incidence is greater than about 5 degrees.

[0044] Embodiment 7. The optical system of embodiment 5, wherein the image projector further includes a retarder layer disposed between the first reflective polarizer and the third mirror.

[0045] Embodiment 8. The optical system of embodiment 5, wherein the first and fifth angles of incidence are within about 5 degrees of each other.

[0046] Embodiment 9. The optical system of embodiment 5, wherein the second and sixth angles of incidence are within about 5 degrees of each other.

[0047] Embodiment 10. An optical system as described in embodiment 1, wherein the divergence angle of the substantially collimated light emitted by the at least one light source is less than about 10 degrees.

[0048] Embodiment 11. The optical system of embodiment 1, wherein the third incident angle is approximately 20 to 60 degrees.

[0049] Embodiment 12. The optical system of embodiment 1, wherein the fourth angle of incidence is approximately 20 to 60 degrees.

[0050] Embodiment 13. An optical system as described in embodiment 1, wherein the first angle of incidence is greater than about 35 degrees.

[0051] Embodiment 14. An optical system as described in embodiment 1, wherein the second angle of incidence is greater than about 10 degrees.

[0052] Embodiment 15. A head-up display (HUD) forming a virtual image of a projected image for observation by an occupant of a vehicle, the image projector including: an image projector that projects image light having an image, the image projector including at least one light source that emits substantially collimated light; a first reflective polarizer that receives the substantially collimated emitted light at a first angle of incidence and reflects at least a portion of the emitted light as first reflected light; and a spatial light modulator including a plurality of pixels for forming the image, the spatial light modulator that receives the first reflected light at a second angle of incidence and transmits at least a portion of the first reflected light as at least a portion of substantially collimated projected image light having the image, the projected image light having a first polarization state; the image projector including a first folding angle greater than about 30 degrees substantially centered on a first folding optical axis extending from the at least one light source to the spatial light modulator. a projection optical system for projecting and forming a virtual image of the projected image, the projection optical system including: a first mirror that receives substantially collimated projection image light at a third angle of incidence and reflects at least a portion of the projection image light as second reflected image light having an image; and a second mirror that receives the second reflected image light having the image at a fourth angle of incidence and reflects at least a portion of the second reflected image light as third reflected image light having the image for viewing by an observer; and a windshield for the vehicle configured to receive the third reflected image light and reflect a portion of the received image toward the observer so that the observer can view the virtual image of the reflected image, wherein the image projector includes a second folding angle greater than about 90 degrees substantially centered about a second folding optical axis extending from the spatial light modulator to at least the windshield.

[0053] Embodiment 16. A HUD as described in embodiment 15, wherein the first reflective polarizer has an average reflectance of greater than about 70% for a first polarization state and an average transmittance of greater than about 70% for an orthogonal second polarization state for substantially normally incident light and in the visible range spanning from about 420 nm to about 680 nm.

[0054] Embodiment 17. The image projector includes a first reflective polarizer disposed between at least one light source and a third mirror, the first reflective polarizer reflecting a portion of the emitted light as a first reflected light having a first polarization state and transmitting a portion of the emitted light as a first transmitted light having an orthogonal second polarization state; the third mirror receiving the first transmitted light at a fifth incident angle and reflecting at least a portion of the first transmitted light as a fourth reflected light; and the spatial light modulator: receiving the first reflected light at a second angle of incidence and transmitting at least a portion of the first reflected light as substantially collimated first projected image light having a first polarization state, the first projected image light including at least a first portion of the image; 16. A HUD as described in embodiment 15, receiving fourth reflected light at a sixth incident angle and transmitting at least a portion of the fourth reflected light as second substantially collimated projected image light comprising at least a second portion of the image and having a first polarization state, the first and second projected image lights combining to form second substantially collimated projected image light comprising the image and having the first polarization state.

[0055] Embodiment 18. A HUD as described in embodiment 17, wherein the first and fifth angles of incidence are within about 5 degrees of each other.

[0056] Embodiment 19. A HUD as described in embodiment 17, wherein the second and sixth angles of incidence are within about 5 degrees of each other.

Claims

1. 1. An optical system comprising:

1. An image projector for projecting substantially collimated image light containing an image, comprising: at least one light source that emits substantially collimated light; a first reflective polarizer that receives the substantially collimated radiation at a first angle of incidence and reflects at least a portion of the radiation as a first collimated reflected light; a spatial light modulator including a plurality of pixels for forming the image, the spatial light modulator receiving the first collimated reflected light as collimated incident light at a second angle of incidence and transmitting at least a portion of the first collimated reflected light as at least a collimated portion of the substantially collimated projected image light comprising the image, the projected image light having a first polarization state; an image projector including: a first mirror that receives the substantially collimated projected image light at a third angle of incidence and reflects at least a portion of the projected image light as a second reflected image light that includes the image; a second mirror that receives the second reflected image light including the image at a fourth incident angle and reflects at least a portion of the second reflected image light as third reflected image light including the image for observation by a viewer; the at least one light source and the spatial light modulator are disposed on the same side of the first reflective polarizer; the first angle of incidence is greater than 30 degrees; The optical system wherein the second angle of incidence is greater than 5 degrees.

2. 10. The optical system of claim 1, further comprising a vehicle windshield configured to receive the third reflected image light and reflect a portion of the received image toward the observer so that the observer can view a virtual image of the reflected image.

3. the image projector comprises the first reflective polarizer disposed between the at least one light source and a third mirror, the first reflective polarizer reflecting a portion of the emitted light as the first reflected light having the first polarization state and transmitting a portion of the emitted light as a first transmitted light having an orthogonal second polarization state; the third mirror receiving the first transmitted light at a fifth angle of incidence and reflecting at least a portion of the first transmitted light as a fourth reflected light; and the spatial light modulator comprising: receiving the first reflected light at the second angle of incidence and transmitting at least a portion of the first reflected light as substantially collimated first projected image light having the first polarization state and including at least a first portion of the image; 2. The optical system of claim 1, receiving the fourth reflected light at a sixth angle of incidence and transmitting at least a portion of the fourth reflected light as a substantially collimated second projected image light comprising at least a second portion of the image and having the first polarization state, the first projected image light and the second projected image light combining to form the substantially collimated projected image light comprising the image and having the first polarization state.

4. 4. The optical system of claim 3, wherein the fifth angle of incidence is greater than 30 degrees, the sixth angle of incidence is greater than 5 degrees, the first angle of incidence and the fifth angle of incidence are within 5 degrees of each other, and the second angle of incidence and the sixth angle of incidence are within 5 degrees of each other.

5. The optical system of claim 1 , wherein the divergence angle of the substantially collimated light emitted by the at least one light source is less than 10 degrees.

6. 2. The optical system of claim 1, wherein the third angle of incidence is between 20 and 60 degrees, and the fourth angle of incidence is between 20 and 60 degrees.

7. The optical system of claim 1 , wherein the first angle of incidence is greater than 35 degrees and the second angle of incidence is greater than 10 degrees.

8. 1. A head-up display (HUD) for forming a virtual representation of a projected image for observation by an occupant of a vehicle, comprising: an image projector for projecting image light containing the image, at least one light source that emits substantially collimated light; a first reflective polarizer that receives the substantially collimated radiation at a first angle of incidence and reflects at least a portion of the radiation as a first collimated reflected light; an image projector including a spatial light modulator including a plurality of pixels for forming the image, the spatial light modulator receiving the first collimated reflected light as collimated incident light at a second angle of incidence and transmitting at least a portion of the first collimated reflected light as at least a collimated portion of the substantially collimated projected image light comprising the image, the projected image light having a first polarization state; and an image projector including a first folding angle greater than 30 degrees across the first reflective polarizer substantially centered on a first folding optical axis extending from the at least one light source to the spatial light modulator. a projection optical system for projecting and forming the virtual image of the projected image, a first mirror that receives the substantially collimated projected image light at a third angle of incidence and reflects at least a portion of the projected image light as a second reflected image light that includes the image; a second mirror that receives the second reflected image light including the image at a fourth incident angle and reflects at least a portion of the second reflected image light as third reflected image light including the image for observation by a viewer; and a windshield for the vehicle configured to receive the third reflected image light and reflect a portion of the received image toward the observer so that the observer can view the virtual image of the reflected image; the image projector includes a second folding angle of greater than 90 degrees across the first mirror substantially centered on a second folding optical axis extending from the spatial light modulator to at least the windshield.

9. 9. The HUD of claim 8, wherein the first reflective polarizer has an average reflectance of greater than 70% for a first polarization state and an average transmission of greater than 70% for an orthogonal second polarization state for substantially normally incident light and in the visible range spanning 420 nm to 680 nm.

10. the image projector comprises the first reflective polarizer disposed between the at least one light source and a third mirror, the first reflective polarizer reflecting a portion of the emitted light as the first reflected light having the first polarization state and transmitting a portion of the emitted light as a first transmitted light having an orthogonal second polarization state; the third mirror receiving the first transmitted light at a fifth angle of incidence and reflecting at least a portion of the first transmitted light as a fourth reflected light; and the spatial light modulator comprising: receiving the first reflected light at the second angle of incidence and transmitting at least a portion of the first reflected light as substantially collimated first projected image light having the first polarization state and including at least a first portion of the image; 10. The HUD of claim 8, wherein the HUD receives the fourth reflected light at a sixth angle of incidence and transmits at least a portion of the fourth reflected light as a substantially collimated second projected image light that includes at least a second portion of the image and has the first polarization state, the first projected image light and the second projected image light combining to form the substantially collimated projected image light that includes the image and has the first polarization state.

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