Patent Description:
In some aspects of the present description, an optical film is provided, including an integral first optical stack disposed on an integral second optical stack, each integral optical stack including a plurality of polymeric interference layers reflecting and transmitting light primarily by optical interference for at least one visible wavelength in a first wavelength range extending from about <NUM> to about <NUM>, and at least one infrared wavelength in a second wavelength range extending from about <NUM> to about <NUM>, such that for substantially normally incident light: for the at least one visible wavelength, the integral first optical stack reflects at least <NUM>% of the incident light having a first polarization state and transmits at least <NUM>% of the incident light having an orthogonal second polarization state, and the second optical stack transmits at least <NUM>% of the incident light for each of the first and second polarization states; and for the at least one infrared wavelength, the second optical stack reflects at least <NUM>% of the incident light having the first polarization state and transmits at least <NUM>% of the incident light having the second polarization state.

In some aspects of the present description, a heads-up display for displaying a virtual image to a passenger of a vehicle is provided, including an exit surface through which an image substantially polarized along a first direction exits the heads-up display and a glare trap. The exit surface is configured to be disposed at or near a dashboard of the vehicle. The glare trap is disposed at the exit surface and configured to reflect at least a portion of ambient light. The glare trap may include a plurality of polymeric interference layers reflecting and transmitting light primarily by optical interference for at least one wavelength in a visible wavelength range extending from about <NUM> to about <NUM> and for at least one wavelength in an infrared wavelength range extending from about <NUM> to about <NUM>, such that for substantially normally incident light: for the at least one wavelength in the visible wavelength range, the glare trap transmits at least <NUM>% of the incident light having a first polarization state and reflects at least <NUM>% of the incident light having an orthogonal second polarization state; and for the at least one wavelength in the infrared wavelength range, the glare trap reflects at least <NUM>% of the incident light for each of the first and second polarization states.

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

According to some aspects of the present description, an optical system for displaying a virtual image to a viewer (e.g., a heads-up display in a vehicle) includes stacked integral first reflective polarizer and integral second reflective polarizer, a display, and a mirror. In some embodiments, the display may be a light emitting diode (LED) display, liquid crystal display (LCD), an organic light emitting display (OLED), a digital light processing (DLP) display, an electroluminescent (EL) display, or any other appropriate picture generating unit.

The stacked integral first reflective polarizer and integral second reflective polarizer are such that, for substantially normally incident light, and for at least one visible wavelength in a first wavelength range (e.g., human-visible light) extending from about <NUM> to about <NUM>, the first reflective polarizer may reflect at least <NUM>%, or at least <NUM>%, or at least <NUM>%, or at least <NUM>%, of the incident light having a first polarization state and may transmit at least <NUM>%, or at least <NUM>%, or at least <NUM>%, or at least <NUM>%, of the incident light having an orthogonal second polarization state, and the second reflective polarizer may transmit at least <NUM>%, or at least <NUM>%, or at least <NUM>%, or at least <NUM>%, of the incident light for each of the first and second polarization states. In some embodiments, the at least one visible wavelength may include one or more of a blue wavelength, a green wavelength, and a red wavelength.

For the purposes of this disclosure, the first and second polarization types may be any two orthogonal polarization states. For example, in some embodiments, the first and second polarization states may be two orthogonal, linear polarization types, such as p-pol and s-pol linear polarization types. In some embodiments, the first and second polarization states may be two different circular polarization types (that is, circular polarization types of opposite direction or "handedness"). Other polarization states may be used in alternate embodiments, or the types of the first and second polarization types may be swapped depending on the embodiment.

In some embodiments, for at least one infrared wavelength in a second wavelength range extending from about <NUM> to about <NUM> (e.g., infrared light), the first reflective polarizer may reflect at least <NUM>%, or at least <NUM>%, or at least <NUM>%, or at least <NUM>%, of the incident light having the first polarization state and may transmit at least <NUM>%, or at least <NUM>%, or at least <NUM>%, or at least <NUM>%, of the incident light having the second polarization state, and the second reflective polarizer may reflect at least <NUM>%, or at least <NUM>%, or at least <NUM>%, or at least <NUM>%, of the incident light having the second polarization state and transmits at least <NUM>%, or at least <NUM>%, or at least <NUM>%, of the light having the first polarization state. In some embodiments, for at least one wavelength in the infrared wavelength range, the second reflective polarizer may reflect at least <NUM>% of the incident light having the first polarization state. In some embodiments, the at least one infrared wavelength may include an infrared wavelength emitted by the sun.

In some embodiments, the stacked integral first reflective polarizer and second reflective polarizer may be a single, integral construction. In some embodiments, the first reflective polarizer and second reflective polarizer may be bonded to each other by an optical adhesive layer.

The display and mirror are disposed on a same side of, and generally facing, the stacked first and second reflective polarizers, such that for substantially normally incident light and for the at least one visible wavelength, the mirror reflects at least <NUM>%, or at least <NUM>%, or at least <NUM>%, of the incident light for each of the first and second polarization states, and such that when an image is emitted by the display, the optical system displays a virtual image of the emitted image (e.g., projected onto the windshield of a vehicle), after the emitted image is at least once reflected by the stacked first and second reflective polarizers, for viewing by a viewer (e.g., a passenger or a vehicle, such as the driver).

In some embodiments, at least one of the stacked integral first and second reflective polarizer and the mirror may be curved to provide some amount of optical power to the emitted image. In some embodiments, the curved surfaces may be spherical, aspherical, free-form (i.e., a non-rotationally symmetric surface featuring departures from a best-fit spherical surface), or any appropriate combination thereof. In some embodiments, the use of a free-form surface may provide greater control over the location, number, and size of aberrations in the emitted image projected by the optical system (e.g., improved optical transfer functions from the image on the display to the emitted image). In some embodiments, the first reflective polarizer may be disposed between the second reflective polarizer and the mirror. That is, the first and second reflective polarizers may be stacked such that the first reflective polarizer is facing the mirror.

According to some aspects of the present description, a heads-up display (HUD) may include the optical system and a windshield of a vehicle such that when an image is emitted by the display, the optical system may transmit the emitted image toward the windshield. The windshield may reflect the transmitted image toward the eye of a viewer (e.g., a driver or other passenger) in the vehicle, such that the viewer views a virtual image of the emitted image. In some embodiments, an image may be emitted by the display such that a visible image ray from the emitted image is sequentially reflected by the first reflective polarizer, reflected by the mirror, and then transmitted by the stacked first and second reflective polarizers, onto the windshield of the vehicle or a similar surface, creating a virtual image of the transmitted image display for viewing by the viewer. In some embodiments, a vehicle may include the optical system. In some embodiments, the stacked first and second reflective polarizers may be disposed at or near the dashboard of the vehicle (e.g., on the exit surface of a glare trap mounted in the dashboard).

According to some aspects of the present description, an optical film includes an integral first optical stack disposed on an integral second optical stack. In some embodiments, each integral optical stack may include a plurality of polymeric interference layers reflecting and transmitting light primarily by optical interference for at least one visible wavelength in a first wavelength range extending from about <NUM> to about <NUM> (e.g., human-visible spectrum), and at least one infrared wavelength in a second wavelength range extending from about <NUM> to about <NUM>, such that for substantially normally incident light, and for the at least one visible wavelength, the integral first optical stack reflects at least <NUM>%, or at least <NUM>%, or at least <NUM>%, of the incident light having a first polarization state and transmits at least <NUM>%, or at least <NUM>%, or at least <NUM>%, of the incident light having an orthogonal second polarization state, and the second optical stack transmits at least <NUM>%, or at least <NUM>%, or at least <NUM>%, of the incident light for each of the first and second polarization states. For normally incident light, and for the at least one infrared wavelength, the second optical stack reflects at least <NUM>%, or at least <NUM>%, or at least <NUM>%, of the incident light having the first polarization state and transmits at least <NUM>%, or at least <NUM>%, or at least <NUM>%, of the incident light having the second polarization state.

In some embodiments, the first optical stack may be spaced apart from the second optical stack by one or more spacers. In some embodiments, the spacers may each have an average thickness may be at least <NUM> times greater than the average thickness of each of the polymeric interference layers in each optical stack. In some embodiments, the optical film may further include an absorbing polarizer disposed on the stacked first and second optical stacks. For substantially normal light and for the at least one visible wavelength, the absorbing polarizer may absorb at least <NUM>%, or at least <NUM>%, or at least <NUM>%, of the incident light having the first polarization state, and transmits at least <NUM>%, or at least <NUM>%, or at least <NUM>%, of the incident light having the second polarization state.

In some embodiments, the optical film may be cut from a longitudinally continuous web, where the y-axis is along a longitudinal down-web direction and the x-axis is along a lateral cross-web direction. In some embodiments, the integral first optical stack may be integrally disposed on the integral second optical stack (e.g., formed as a larger, integral stack). In some embodiments, the integral first optical stack may be non-integrally disposed on the integral second optical stack (e.g., two separate physical stacks disposed on each other).

According to some aspects of the present description, a heads-up display (HUD) for displaying a virtual image to a passenger of a vehicle includes an exit surface through which an image substantially polarized along a first direction exits the heads-up display and a glare trap. The exit surface is configured to be disposed at or near a dashboard of the vehicle. The glare trap (i.e., a surface designed to reject at least a portion of external, incident light) is disposed at the exit surface and configured to reflect at least a portion of ambient light. The glare trap may include a plurality of polymeric interference layers reflecting and transmitting light primarily by optical interference for at least one wavelength (and, in some embodiments, each wavelength) in a visible wavelength range extending from about <NUM> to about <NUM> (e.g., human-visible light), and for at least one wavelength (and, in some embodiments, each wavelength) in an infrared wavelength range extending from about <NUM> to about <NUM>, such that for substantially normally incident light: for the at least one wavelength in the visible wavelength range, the glare trap transmits at least <NUM>%, or at least <NUM>%, or at least <NUM>%, of the incident light having the first polarization state and reflects at least <NUM>%, or at least <NUM>%, or at least <NUM>%, of the incident light having an orthogonal second polarization state; and for the at least one wavelength in the infrared wavelength range, the glare trap reflects at least <NUM>%, or at least <NUM>%, or at least <NUM>%, of the incident light for each of the first and second polarization states. In some embodiments, the glare trap may include an infrared absorbing dye, allowing the glare trap to absorb at least <NUM>%, or at least <NUM>%, or at least <NUM>%, of incident light having a wavelength from about <NUM> to about <NUM> (e.g., infrared wavelengths).

Turning now to the figures, <FIG> provides a cross-sectional view of an embodiment of a heads-up display (HUD) for displaying a virtual image, according to the present description. HUD <NUM> includes a display <NUM>, mirror <NUM>, an optical system <NUM> (e.g., an optical film stack), and a windshield <NUM>. The display <NUM> (e.g., LED display, LCD display, OLED display, DLP display, EL display, etc.) emits an image <NUM>, which travels along a path defined by representative image rays <NUM> (representing an image ray emitted at the center of image <NUM>), <NUM>, and <NUM>. Image <NUM> is first reflected from a surface of optical system <NUM>, then reflected from mirror <NUM>, before passing back through optical system <NUM> as transmitted image <NUM>. Transmitted image <NUM> is projected onto windshield <NUM> and reflected toward the eye of a passenger <NUM>, where it appears as virtual image <NUM>. That is, in some embodiments, the optical path followed by emitted image <NUM> (as represented by central image ray <NUM>) is configured such that the transmitted image <NUM> is incident on the eye of passenger <NUM> in such a way that a virtual image <NUM> appears to passenger <NUM> to be projected in the air some distance outside of windshield <NUM>. For the purposes of this disclosure, the term "passenger" shall be interpreted to include any occupant of a vehicle, including a driver. In some embodiments, optical system <NUM> may be configured to reflect at least a portion of ambient light <NUM>. For example, in some embodiments, optical system <NUM> may reflect at least a portion of sunlight (e.g., some infrared light wavelengths) incident on the optical system. This may help prevent excessive heat build-up, as well as reducing the number of visible artifacts which may obscure the virtual image <NUM>.

It should be noted that the size of components, angles of reflection, path lengths, and projected image distances shown are not intended to be to scale, and are intended only to convey general concepts.

In some embodiments, optical system <NUM> may be disposed on an exit surface <NUM>, such as a surface of a vehicle dashboard or on a glare trap for the HUD. In some embodiments, optical system <NUM> may include optical stack <NUM>, including stacked integral first reflective polarizer <NUM> and integral second reflective polarizer <NUM>. In some embodiments, optical stack <NUM> may further include an absorbing polarizer <NUM> disposed on the stacked integral first reflective polarizer <NUM> and integral second reflective polarizer <NUM>. In some embodiments, an optical adhesive (not shown in <FIG>, but discussed elsewhere herein) may be disposed between first reflective polarizer <NUM> and second reflective polarizer <NUM>. In some embodiments, first reflective polarizer <NUM> may be disposed closer to mirror <NUM> than second reflective polarizer <NUM>, as shown in <FIG>.

In some embodiments, for at least one visible (i.e., human-visible) wavelength in a first wavelength range extending from about <NUM> to about <NUM>, the first reflective polarizer may reflect at least <NUM>% of the incident light having a first polarization state and transmits (i.e., allow to pass through) at least <NUM>% of the incident light having an orthogonal second polarization state. In some embodiments, and for at least one visible wavelength in a first wavelength range extending from about <NUM> to about <NUM>, the second reflective polarizer may transmit (i.e., allow to pass through) at least <NUM>% of the incident light for each of the first and second polarization states.

In some embodiments, for at least one infrared wavelength in a second wavelength range extending from about <NUM> to about <NUM>, the first reflective polarizer <NUM> may reflect at least <NUM>% of the incident light having the first polarization state and may transmit at least <NUM>% of the incident light having the second polarization state. In some embodiments, for at least one infrared wavelength in a second wavelength range extending from about <NUM> to about <NUM>, the second reflective polarizer <NUM> may reflect at least <NUM>% of the incident light having the second polarization state and transmits at least <NUM>% of the light having the first polarization state.

In some embodiments, the effects of the combined (e.g., stacked) first reflective polarizer <NUM> and second reflective polarizer <NUM> may be to allow folding of the optical path (e.g., alternate reflecting and transmission of image rays to reflect the image rays appropriately along an intended optical path) as well as limiting the amount of unwanted light (e.g., ambient light, infrared wavelengths, etc.). In some embodiments, the optical stack <NUM> may further include absorbing polarizer <NUM>, to increase the optical efficiency of the system in transmitting primarily desired wavelengths of light.

It should be noted that other components may be present in heads-up display <NUM> which are not shown in <FIG>. These components may be necessary for the proper operation of the heads-up display <NUM>, but are omitted as they are not pertinent to the present disclosure. For example, in some embodiments, the optical system may also include one or more quarter wave plates, positioned within the system such that the polarization of the emitted and reflected image rays changes appropriately from one state to another as needed to either be transmitted by or reflected by the first reflecting polarizer <NUM>, or other components of optical stack <NUM>.

<FIG> provide graphs showing approximate percentage reflectance of various wavelength ranges for the first and second reflective polarizers, respectively, according to an embodiment described herein. <FIG> is the graph showing percentage reflectance for the first reflective polarizer <NUM>, for a first wavelength range <NUM> (e.g., human-visible wavelengths) and a second wavelength range <NUM> (e.g., infrared wavelengths). In the first wavelength range <NUM>, first reflective polarizer <NUM> may reflect at least around <NUM>% or higher of light of the first polarization state, while reflecting only around <NUM>% or less of light of the second polarization state. In the second wavelength range <NUM> (i.e., infrared wavelengths), first reflective polarizer <NUM> may reflect at least around <NUM>% or higher of light of the first polarization state, while reflecting only around <NUM>% or less of light of the second polarization state.

<FIG> is the graph showing percentage reflectance for the second reflective polarizer <NUM>, for a first wavelength range <NUM> (e.g., human-visible wavelengths) and a second wavelength range <NUM> (e.g., infrared wavelengths). In the first wavelength range <NUM>, second reflective polarizer <NUM> may reflect at least around <NUM>% or less of light of the first polarization state, while reflecting only around <NUM>% or less of light of the second polarization state. In the second wavelength range <NUM> (i.e., infrared wavelengths), second reflective polarizer <NUM> may reflect at least around <NUM>% or less of light of the first polarization state, while reflecting around <NUM>% or higher of light of the second polarization state. Combining the effects of the first reflective polarizer <NUM> and second reflective polarizer <NUM>, as shown in <FIG>, may largely reduce the transmission of infrared wavelengths in the second wavelength range <NUM> for both the first and second polarization states. It should be noted that the values shown for percent reflectance in <FIG> are exemplary only, and should not be construed to be limiting in any way.

<FIG> are cross-sectional views of layers in an optical system for displaying a virtual image, according to an embodiment of the present description. These figures illustrate what is meant by "normally incident light" as discussed in terms of each of the layers discussed herein. <FIG> shows normally incident light <NUM> in relation to first reflective polarizer <NUM> and second reflective polarizer <NUM>. <FIG> shows normally incident light <NUM> in relation to mirror <NUM>. In some embodiments, mirror <NUM> may be curved to provide power (e.g., magnification) of the reflected image rays, as shown in <FIG>. In these embodiments, normally incident light <NUM> is defined as orthogonal to a center point of mirror <NUM>. As any of the components shown in <FIG> may be curved in some embodiments, normally incident light shall be defined relative to incidence on a center point of the components (e.g., the reflective polarizers <NUM>/<NUM> of <FIG>, the absorbing polarizer <NUM> of <FIG>). Finally, <FIG> shows normally incident light <NUM> in relation to absorbing polarizer <NUM>.

<FIG> provide graphs illustrating percentage transmittance of various wavelengths of light for each of the first <NUM> and second reflective polarizers <NUM>, according to an embodiment of the present description, and <FIG> shows the combined transmission spectra of both reflective polarizers <NUM>/<NUM>. <FIG> shows the percent transmission of wavelengths for first reflective polarizer <NUM>. <FIG> depicts two lines, one representing light polarized in a first polarization state, and the other representing light polarized in a second polarization state. For the purposes of <FIG> and <FIG>, it is assumed the films are configured such that the x-axis of the film is aligned with the first polarization state, and the y-axis of the film is aligned with the second polarization state. However, alternate embodiments are possible within the scope of this disclosure which use different configurations of the films, with alternate alignments and polarization states.

As can be seen in <FIG>, the first reflective polarizer <NUM> transmits a significant portion (i.e., over <NUM> percent for much of the plot) of the light polarized to the y-axis of the film (e.g., the second polarization state of light) for both human-visible wavelengths (e.g., about <NUM> to about <NUM>) and infrared wavelengths (e.g., about <NUM> to about <NUM>). Conversely, the first reflective polarizer <NUM> reflects (i.e., does not transmit) a significant portion (i.e., over <NUM> percent for much of the plot) of the light polarized to the x-axis (e.g., the first polarization of light) for both human-visible wavelengths (e.g., about <NUM> to about <NUM>) and infrared wavelengths (e.g., about <NUM> to about <NUM>). A representative human-visible wavelength <NUM> and infrared wavelength <NUM> are shown for illustration purposes.

<FIG> shows the percent transmission of wavelengths for second reflective polarizer <NUM>. <FIG> also depicts two lines, one representing light polarized in a first polarization state (e.g., polarized to the x-axis), and the other representing light polarized in a second polarization state (e.g., polarized to the y-axis). The second reflective polarizer <NUM> transmits a significant portion (i.e., over <NUM> percent for much of the plot) of the light polarized to the y-axis for human-visible wavelengths from about <NUM> to about <NUM>, but reflects (e.g., does not transmit) infrared wavelengths from about <NUM> to about <NUM>. The second reflective polarizer <NUM> largely transmits a significant portion (i.e., over <NUM> percent for much of the plot) of the light polarized to the x-axis for both human-visible wavelengths (e.g., about <NUM> to about <NUM>) and infrared wavelengths (e.g., about <NUM> to about <NUM>). As with <FIG>, representative human-visible wavelength <NUM> and infrared wavelength <NUM> are shown for illustration and comparison purposes.

<FIG> shows the percent transmittance for an optical stack with both first reflective polarizer <NUM> and second reflective polarizer <NUM> included. The combined reflective polarizers <NUM>/<NUM> transmit a significant portion (i.e., over <NUM> percent for much of the plot) of the light polarized to the y-axis for human-visible wavelengths from about <NUM> to about <NUM>, including representative human-visible wavelength <NUM>, but substantially reflect (e.g., do not transmit) infrared wavelengths from about <NUM> to about <NUM>, including representative infrared wavelength <NUM>. For light polarized to the x-axis, the combined reflective polarizers <NUM>/<NUM> substantially reflect (e.g., do not transmit) human-visible wavelengths from about <NUM> to about <NUM> and infrared wavelengths from about <NUM> to about <NUM>.

<FIG> show cross-sectional views of an optical stack according to an embodiment of the present disclosure, including additional details on the possible construction of the layers. <FIG> illustrates that, in some embodiments, the first reflective polarizer <NUM> and the second reflective polarizer <NUM> may be bonded to each other by an optical adhesive layer <NUM>. One example of an optical adhesive layer <NUM> is a curable acrylate adhesive. However, any appropriate type of optical adhesive layer <NUM> may be used.

<FIG> illustrates an optical film <NUM> comprising an integral first optical stack <NUM> disposed on an integral second optical stack <NUM>. In some embodiments, first optical stack <NUM> may be the first reflective polarizer <NUM> of <FIG>, and second optical stack <NUM> may be the second reflective polarizer <NUM> of <FIG>. In some embodiments, integral first optical stack <NUM> may include a plurality of alternating polymeric interference layers <NUM> and <NUM>, which reflect and transmit light primarily by optical interference (e.g., alternating layers <NUM> and <NUM> may have different indices of refraction), and integral second optical stack <NUM> may include a plurality of alternating polymeric interference layers <NUM> and <NUM>, which also reflect and transmit light primarily by optical interference.

For some embodiments, polymeric interference layers <NUM> and <NUM> may be configured such that, for at least one visible wavelength in a first wavelength range extending from about <NUM> to about <NUM> (e.g., human-visible wavelengths), and at least one infrared wavelength in a second wavelength range extending from about <NUM> to about <NUM> (e.g., infrared wavelengths), for substantially normally incident light <NUM>, the integral first optical stack <NUM> reflects at least <NUM>%, or at least <NUM>%, or at least <NUM>% of the incident light having a first polarization state (x-axis) and transmits at least <NUM>%, or at least <NUM>%, or at least <NUM>% of the incident light having an orthogonal second polarization state (y-axis).

For some embodiments, polymeric interference layers <NUM> and <NUM> may be configured such that, for at least one visible wavelength in a first wavelength range extending from about <NUM> to about <NUM> (e.g., human-visible wavelengths), for substantially normally incident light <NUM>, the second optical stack <NUM> transmits at least <NUM>%, or at least <NUM>%, or at least <NUM>% of the incident light for each of the first and second polarization states, and for the at least one infrared wavelength, the second optical stack <NUM> reflects at least <NUM>%, or at least <NUM>%, or at least <NUM>% of the incident light having the first polarization state and transmits at least <NUM>%, or at least <NUM>%, or at least <NUM>% of the incident light having the second polarization state.

In some embodiments, first optical stack <NUM> may be spaced apart from the second optical stack <NUM> by one or more spacers <NUM>. In some embodiments, the average thickness of each of spacer layers may be at least <NUM> times greater than the average thickness of each polymeric interference layer (<NUM>, <NUM>, <NUM>, <NUM>) in each optical stack <NUM> and <NUM>.

<FIG> show alternate views of an optical system for displaying a virtual image as installed in a vehicle, according to an embodiment of the present description. Turning to <FIG>, transmitted image <NUM> passes through optical system <NUM> to be reflected from windshield <NUM> of vehicle <NUM> into the eyes of passenger <NUM>, creating the perception of virtual image <NUM> outside of vehicle <NUM>. <FIG> shows additional detail of the interior of the vehicle <NUM> (of <FIG>). The first reflective polarizer <NUM> and second reflective polarizer <NUM> may be disposed on an exit surface <NUM> of dashboard <NUM>, for example a glare trap <NUM>. Glare trap <NUM> may be disposed on the exit surface <NUM> for a heads-up display, configured to reduce or prevent ambient light (e.g., sunlight) from passing into the heads-up display. <FIG> illustrates that, in some embodiments, glare trap <NUM> on exit surface <NUM> may further include an infrared absorbing dye <NUM>, such that the glare trap may absorb some portion (e.g., at least <NUM>%) of an incident light having a wavelength from about <NUM> to about <NUM>, where absorbing dye <NUM> may be included in a layer designed primarily to absorb light, or added to another layer having other optical properties.

Finally, <FIG> show an optical film for use in an optical system for displaying a virtual image, as part of a web, according to an embodiment of the present description. In some embodiments, the optical film <NUM> (see <FIG>) may be cut from a longitudinally continuous web <NUM>, wherein the y-axis is along a longitudinal down-web direction <NUM> and the x-axis is along a lateral cross-web direction <NUM>. The orientation of the optical film <NUM> in relation to longitudinally continuous web <NUM> defines the optical properties of the optical film <NUM> with regard to polarization states of light as discussed herein.

Terms such as "about" will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of "about" as applied to quantities expressing feature sizes, amounts, and physical properties is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, "about" will be understood to mean within <NUM> percent of the specified value. A quantity given as about a specified value can be precisely the specified value. For example, if it is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, a quantity having a value of about <NUM>, means that the quantity has a value between <NUM> and <NUM>, and that the value could be <NUM>.

Terms such as "substantially" will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of "substantially equal" is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, "substantially equal" will mean about equal where about is as described above. If the use of "substantially parallel" is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, "substantially parallel" will mean within <NUM> degrees of parallel. Directions or surfaces described as substantially parallel to one another may, in some embodiments, be within <NUM> degrees, or within <NUM> degrees of parallel, or may be parallel or nominally parallel. If the use of "substantially aligned" is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, "substantially aligned" will mean aligned to within <NUM>% of a width of the objects being aligned. Objects described as substantially aligned may, in some embodiments, be aligned to within <NUM>% or to within <NUM>% of a width of the objects being aligned.

Claim 1:
An optical system (<NUM>) for displaying a virtual image to a viewer (<NUM>), comprising:
stacked integral first reflective polarizer (<NUM>) and integral second reflective polarizer (<NUM>), such that for substantially normally incident light:
for at least one visible wavelength in a first wavelength range extending from about <NUM> to about <NUM>, the first reflective polarizer reflects at least <NUM>% of the incident light having a first polarization state and transmits at least <NUM>% of the incident light having an orthogonal second polarization state, and the second reflective polarizer transmits at least <NUM>% of the incident light for each of the first and second polarization states; and
for at least one infrared wavelength in a second wavelength range extending from about <NUM> to about <NUM>, the first reflective polarizer reflects at least <NUM>% of the incident light having the first polarization state and transmits at least <NUM>% of the incident light having the second polarization state, and the second reflective polarizer reflects at least <NUM>% of the incident light having the second polarization state and transmits at least <NUM>% of the light having the first polarization state; and
a display (<NUM>) and a mirror (<NUM>) disposed on a same side of, and generally facing, the stacked first and second reflective polarizers, such that for substantially normally incident light and for the at least one visible wavelength, the mirror reflects at least <NUM>% of the incident light for each of the first and second polarization states, and such that when an image (<NUM>) is emitted by the display, the optical system displays a virtual image of the emitted image, after the emitted image is at least once reflected by the stacked first and second reflective polarizers, for viewing by a viewer.