Summary

In some aspects of the present description, an optical system is provided, including an extended illumination source configured to emit light from an extended emission surface thereof, and an optical stack disposed on the extended emission surface and including a first reflective polarizer disposed on a first light redirecting layer. The extended illumination source includes at least one light source, and a reflecting layer spaced apart from, and substantially co-extensive with, the extended emission surface. The reflecting layer may be configured to reflect incident light that is emitted from the at least one light source toward the extended emission surface. For substantially normally incident light and for a first wavelength range extending from about 450 nm to about 650 nm, and a second wavelength range extending from about 750 nm to about 1100 nm, the first reflective polarizer may transmit at least 40% of the incident light for a first polarization state for each wavelength in the first wavelength range, and may reflect at least 70% of the incident light for an orthogonal second polarization state for each wavelength in the first wavelength range, and may transmit at least 40% of the incident light for each of the first and second polarization states for at least one wavelength in the second wavelength range. For each of the first and second polarization states, the reflecting layer may reflect at least 70% of the incident light for each wavelength in the first wavelength range, and may transmit at least 70% of light for the at least one wavelength in the second wavelength range. For the first wavelength range and for light incident at an incident angle Q with respect to a direction normal to the first reflective polarizer, the first reflective polarizer may have an average optical transmission TO when the incident angle is about zero degree, and an average optical transmittance T60 when the incident angle is about 60 degrees. In some embodiments, the first light redirecting layer may be disposed between the first reflective polarizer and the extended emission surface, and may include a plurality of first truncated structures, each first truncated structure having opposing side surfaces making an angle a between about 60 degrees to about 120 degrees with each other, and a substantially planar top surface joining the opposing side surfaces. The top surfaces of the first truncated structures may have an average width Wl, such that W1 is greater than or equal to 2 microns, such that the optical stack has an on-axis effective transmission Tl, and a comparative optical stack of the same construction except that Wl for the comparative optical stack is less than about 0.2 microns, has an on-axis effective transmission T2, and the ratio of T60/T0 is sufficiently small so that Tl and T2 are within about 20% of each other. In some aspects of the present description, an optical system is provided, including an extended illumination source configured to emit light from an extended emission surface thereof, and an optical stack disposed on the extended emission surface and including a first reflective polarizer disposed on a first light redirecting layer. The extended illumination source includes at least one light source, and a reflecting layer spaced apart from, and substantially co-extensive with, the extended emission surface. The reflecting layer may be configured to reflect incident light that is emitted from the at least one light source toward the extended emission surface. For substantially normally incident light and for a first wavelength range extending from about 450 nm to about 650 nm, and a second wavelength range extending from about 750 nm to about 1100 nm, the first reflective polarizer may transmit at least 40% of the incident light for a first polarization state for each wavelength in the first wavelength range, and may reflect at least 70% of the incident light for an orthogonal second polarization state for each wavelength in the first wavelength range, and may transmit at least 40% of the incident light for each of the first and second polarization states for at least one wavelength in the second wavelength range. For each of the first and second polarization states, the reflecting layer may reflect at least 70% of the incident light for each wavelength in the first wavelength range, and may transmit at least 70% of light for the at least one wavelength in the second wavelength range. For the first wavelength range and for light incident at an incident angle Q with respect to a direction normal to the first reflective polarizer, the first reflective polarizer may have an average optical transmission TO when the incident angle is about zero degree, and an average optical transmittance T60 when the incident angle is about 60 degrees. In some embodiments, the first light redirecting layer may be disposed between the first reflective polarizer and the extended emission surface, and may include a plurality of peaked structures and a plurality of substantially planar gaps between at least a subset of the plurality of peaked structures, each peaked structure comprising opposing side surfaces making an angle between about 60 degrees to about 120 degrees with each other, the opposing side surfaces meeting at a peak, the plurality of substantially planar gaps having an average width Wl, W1 > 2 microns, such that the optical stack has an on-axis effective transmission Tl, and a comparative optical stack that comprises a same construction except that Wl for the comparative optical stack is less than about 0.2 microns, has an on-axis effective transmission T2, and wherein T60/T0 is sufficiently small so that Tl and T2 are within 20% of each other.

Brief Description of the Drawings

FIG. 1 is a side, cutaway view of an optical system with truncated structures, in accordance with an embodiment of the present description; FIGS. 2A and 2B illustrate incident light striking various layers of an optical system, in accordance with an embodiment of the present description;

FIG. 3 illustrates incident light striking the reflective layer of an optical system, in accordance with an embodiment of the present description;

FIG. 4 is a chart plotting percentage transmission of an optical fdm, in accordance with an embodiment of the present description;

FIG. 5 illustrates the light transmitted by an optical stack, in accordance with an embodiment of the present description;

FIG. 6 is a side, cutaway view of a light redirecting layer, in accordance with an embodiment of the present description; and

FIGS. 7A-7C illustrate side, cutaway views of light redirecting layers with various alternate profdes, in accordance with an embodiment of the present description.

Detailed Description

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. 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 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 includes an extended illumination source (e.g., a backlight system for a display) configured to emit light from an extended emission surface thereof, and an optical stack disposed on the extended emission surface and including a first reflective polarizer disposed on a first light redirecting layer. For example, the optical system may represent a display assembly on a portable computing device, such as a smart phone or tablet computer.

The extended illumination source includes at least one light source, and a reflecting layer spaced apart from, and substantially co-extensive with, the extended emission surface. In some embodiments, the light source may include, but not be limited to, one or more of the following: light-emitting diode, electroluminescent panel, cold cathode fluorescent lamps, hot cathode fluorescent lamps, and/or incandescent bulbs.

In some embodiments, the extended illumination source may further include a lightguide for propagating light along a length and a width of the lightguide (e.g., via internal reflection). In some embodiments, the lightguide may be disposed between the reflecting layer and the first light redirecting layer. In some embodiments, the lightguide may include the extended emission surface. In some embodiments, the extended illumination source may include a first optically diffusive layer for scattering light and including the extended emission surface. The first optically diffusive layer and the reflecting layer may be substantially co-extensive with each other and defining an optical cavity therebetween.

In some embodiments, the light source may be disposed proximate an edge surface of the light guide (i.e., positioned near one end of the lightguide, rather than between the lightguide and the reflecting layer). In some embodiments, the light source may be disposed in an optical cavity between the lightguide and the reflecting layer.

In some embodiments, the reflecting layer may be configured to reflect incident light that is emitted from the at least one light source toward the extended emission surface. In some embodiments, the reflecting layer may be configured to reflect light that exits the lightguide toward the reflecting layer, such that the reflected light propagates toward the first light redirecting layer.

In some embodiments, and for substantially normally incident light and for a first wavelength range extending from about 450 nm to about 650 nm (e.g., human-visible light), and a second wavelength range extending from about 750 nm to about 1100 nm (e.g., near infrared light), the first reflective polarizer may transmit at least 40% of the incident light for a first polarization state for each wavelength in the first wavelength range, and may reflect at least 70% of the incident light for an orthogonal second polarization state for each wavelength in the first wavelength range, and may transmit at least 40% of the incident light for each of the first and second polarization states for at least one wavelength in the second wavelength range.

In some embodiments, and for each of the first and second polarization states, the reflecting layer may reflect at least 70% of the incident light for each wavelength in the first wavelength range and may transmit at least 70% of light for the at least one wavelength in the second wavelength range. In some embodiments, the at least one wavelength may be one or more wavelengths in a range from about 850 nanometers (nm) to about 940 nm. For the first wavelength range and for light incident at an incident angle Q with respect to a direction normal to the first reflective polarizer, the first reflective polarizer may have an average optical transmission TO when the incident angle is about zero degree, and an average optical transmittance T60 when the incident angle is about 60 degrees.

In a typical operating scenario, the optical system may allow at least a portion of at least one wavelength in the second wavelength range (i.e., an infrared wavelength) to pass through the reflective layer, the first light redirecting layer, the extended illumination source, and the reflecting layer, such that the transmitted infrared light may be used to detect features on an object disposed above the optical system (e.g., to be able to detect ridges of a fingerprint on a finger held close to the optical system.) In some embodiments, the first light redirecting layer may be disposed between the first reflective polarizer and the extended emission surface, and may include a plurality of first truncated structures, each first truncated structure having opposing side surfaces making an angle a between about 60 degrees to about 120 degrees with each other, and a substantially planar top surface joining the opposing side surfaces. In some embodiments, the first truncated surfaces may form a regular array. In some embodiments, the first truncated surfaces may form an irregular array. In some embodiments, the first truncated structures may be first linear truncated structures extending along a first direction (e.g., along an y-axis) and arranged along an orthogonal second direction (e.g., along an x-axis).

In some embodiments, the top surfaces of the first truncated structures may have an average width Wl, such that W1 is greater than or equal to 2 microns, such that the optical stack has an on-axis effective transmission Tl, and a comparative optical stack of the same construction except that Wl for the comparative optical stack is less than about 0.2 microns, has an on-axis effective transmission T2, and the ratio of T60/T0 is sufficiently small so that Tl and T2 are within about 20% of each other. Stated another way, the optical system is configured such that, as the ratio of T60/T0 decreases, the more the light passing through the optical stack becomes collimated. In some embodiments, the ratio of T60/T0 may be less than about 0.5, or less than about 0.4, or less than about 0.3. In some embodiments, at least two of the first truncated structures may have different width values for their top surfaces (i.e., different top surface widths which contribute to the average width, Wl).

In some embodiments, the first light redirecting layer may further include a plurality of second truncated structures including opposing side surfaces making an angle between about 60 degrees to about 120 degrees with each other. In some embodiments, the plurality of second truncated structures may have a substantially planar top surface joining the opposing side surfaces, the top surfaces of the second truncated structures may have an average width W2, where W2 is less than or equal to about 2 microns. In some embodiments, the first light redirecting layer may further include a plurality of untruncated second structures including opposing side surfaces making an angle between about 60 degrees to about 120 degrees with each other and meeting at a peak. In some embodiments, the peaks of the untruncated second structures and the substantially planar top surfaces of the first truncated structures may he substantially in a same plane, as shown in FIG. 6. FIG. 6 shows the peaks 69’ of the untruncated second structures 67’ and the substantially planar top surfaces 63 ’ of the first truncated structures 6 G of the first light redirecting layer 60’ lying substantially in a same plane PI.

In some embodiments, the optical stack may further include a second light redirecting layer including a plurality of truncated structures with opposing side surfaces making an angle between about 60 degrees to about 120 degrees with each other, and a substantially planar top surface joining the opposing side surfaces. In some embodiments, the top surfaces of the truncated structures may have an average width, Wl, such that W1 is greater than or equal to about 2 microns.

In some embodiments, the inclusion of truncated features in the light redirecting layers allows at least a portion of the light entering the optical system (e.g., one or more wavelengths of infrared light) to pass through the optical system without being distorted (e.g., reflected into a new direction) so that the light can be used to detect features external to the optical system (e.g., such as the ridges of a fingerprint.)

In some embodiments, the optical system may further include a liquid crystal display panel disposed on the first reflective polarizer for forming an image signal which may be seen by a viewer. In some embodiments, the optical system may further include an infrared detector configured to sense at least one infrared wavelength in the second wavelength range. In some embodiments, the extended illumination source may be disposed between the first light redirecting layer and the infrared detector. In some embodiments, the optical system may further include an infrared light source for illuminating an object (e.g., a finger with fingerprint) disposed proximate the optical system. In some embodiments the infrared light source may emit light in the second wavelength range, such that the infrared detector may detect at least one wavelength emitted by the infrared light source and reflected by the object.

Turning now to the figures, FIG. 1 is a side, cutaway view of an optical system according to the present description. In some embodiments, optical system 400 may include an extended illumination source 300, and an optical stack 200. In some embodiments, optical system 400 may further include a display (e.g., a liquid crystal display) 110 and an infrared detector 130. In some embodiments, the extended illumination source 300 may include at least one light source 30, 31, which may be disposed within an optical cavity 90 defined between a reflecting layer 40 and a lightguide 70, or may be disposed at an edge 71 of lightguide 70, or both. For an edge light source 30, light 10b may enter lightguide 70 through edge 71 and may be reflected from an upper internal surface of lightguide 70, toward reflecting layer 40 and be reflected up through lightguide 70. Similarly, light 10a may enter lightguide 70 through edge 71 and may be reflected from a lower internal surface of lightguide 70 and reflected up through lightguide 70 to exit extended emission surface 20. Light lOa/lOb may be reflected multiple times from internal surfaces of lightguide 70, as long as the angle of incidence of the light impinging on the internal surfaces is greater than the critical angle (i.e., the angle above which light is entirely reflected back into the lightguide 70). In some embodiments, light 10c emitted by a light source 31 located beneath lightguide 70 (i.e., within optical cavity 90) may impinge on lightguide 70 at an angle of incidence less than the critical angle and may consequently be transmitted through lightguide 70 substantially without reflection.

In some embodiments, extended illumination source 300 may further include an optically diffusive layer 80, configured to scatter light. When diffusive layer 80 is present, the top layer 21 may become the extended emission surface 21 (instead of external surface 20 of lightguide 70). A diffusive layer 80 may be used to remove artifacts introduced as light passes through lightguide 70 (e.g., bright spots or uneven brightness from light exiting lightguide 70).

Light exiting extended illumination source 300 (e.g., light 10a, 10b, 10c) impinges on optical stack 200. In some embodiments, optical stack 200 includes a first light redirecting layer 60 and a first reflective polarizer 50. In some embodiments, optical stack 200 may further include a second light redirecting layer 100. In some embodiments, first light redirecting layer 60 may include a plurality of first truncated structures 61. Each truncated structure 61 may include opposing side surfaces 62a and 62b which make an angle a with each other. In some embodiments, the angle a may be between about 60 degrees and about 120 degrees. In some embodiments, each truncated structure 61 may have a substantially planar top surface 63 joining side surfaces 62a and 62b. In some embodiments, the top surfaces of the first truncated structures 61 may have an average width, Wl, suchthatWl is greater than or equal to about 1.5 microns, or about 2.0 microns, or about 2.5 microns, or about 3.0 microns.

In some embodiments, the first light redirecting layer 60 may further include a plurality of untruncated second structures 67. Each untruncated second structure 67 may have opposing side surfaces 68a and 68b making an angle d with each other and meeting at a peak 69. In some embodiments, the angle d may be between about 60 degrees and about 120 degrees.

In some traditional systems, light redirecting films with peaked or pyramidal shaped structures are often used as a means of enhancing the brightness of light emitted by the light redirecting films. That is, the use of pyramidal structures can have a collimating effect on light passing through the light redirecting films, causing light rays to either emerge from the film in a substantially collimated form, or to be reflected back into the illumination source to be recycled (e.g., reflected by lightguide and/or reflecting layer at a different angle, potentially resulting in a light ray at an angle which will now pass through the light redirecting film). While these light redirecting films with peaked, pyramidal features may increase the brightness of the transmitted light rays, they can also distort images created by light reflected from an external object and entering into the optical system (e.g., infrared light reflected from a finger placed on or near a display surface for security and identification purposes). However, by configuring at least some of the features on the light redirecting film 60 (e.g., the first truncated structures 61) such that they have a substantially planar top surface 63, incoming light rays that pass through the substantially planar top surface 63 may be transmitted through light redirecting fdm 60 substantially unaltered.

For example, in some embodiments, optical system 400 may include an infrared light source 140 internal to the optical system 400 which emits infrared light 13. At least a portion of infrared light 13 is allowed to pass through optical stack 200 and other layers of the system to impinge on object 150 (e.g., a finger touching or adjacent to an external surface of optical system 400). Infrared light 13 illuminates object 150 and is reflected back into optical system 400 as reflected infrared light 14, of which at least a portion is transmitted by the optical system 400, including reflecting layer 40, where it is detected by infrared detector 130. At least a portion of the transmitted, reflected infrared light 14 will pass through the substantially planar top surfaces 63 of one or more of the first truncated structures 61, such that it is substantially unaltered through reflection, refraction, distortion, and other processes. Infrared detector 130 receives the infrared light 14, creating an image of object 150. Although infrared light source 140 is depicted in FIG. 1 as located within optical cavity 90, it may be located in other locations within optical system 400 (e.g., above first light redirecting layer 60, on an edge of lightguide 70, etc.) without deviating from the concepts described herein.

As the use of substantially planar top surfaces 63 on at least a portion of the structures on the light redirecting film 60 may reduce the overall gain produced by the light redirecting film, it is important that the light redirecting film 60 (as well as other elements/layers of optical stack 200) be configured such that the on-axis light transmission level (Tl) of optical stack 200 is sufficient to at least partially compensate for any perceived reduction in brightness.

In some embodiments, the top surfaces 63 of the first truncated structures 61 may have an average width Wl, such that W1 is greater than or equal to about 1.5 microns, or about 2.0 microns, or about 2.5 microns, or about 3.0 microns. Let Tl represent the on-axis effective transmission for optical stack 200 (with first truncated structures 61, and let T2 represent the on- axis effective transmission for a comparative optical stack of the same construction except that W 1 for the comparative optical stack is less than about 0.2 microns (i.e., the structures in the comparative optical stack are effectively untruncated). Further, for the first wavelength range and for light 42 (see FIG. 3) incident at an angle of incidence, Q, with respect to a direction 43 (see FIG. 3) normal to the first reflective polarizer 50, the first reflective polarizer 50 may have an average optical transmission TO (see FIG. 5) when Q is about zero degrees, and an average optical transmission T60 (see FIG. 5) when Q is about 60 degrees.

In some embodiments, the optical stack 200 may be configured such that the ratio of T60/T0 is sufficiently small so that Tl and T2 are within about 20% of each other. Stated another way, the optical system is configured such that, as the ratio of T60/T0 decreases, the more the light passing through the optical stack becomes collimated. In some embodiments, the ratio of T60/T0 may be less than about 0.5, or less than about 0.4, or less than about 0.3. In some embodiments, at least two of the first truncated structures 61 may have different width values for their top surfaces (i.e., different top surface widths which contribute to the average width, Wl).

In some embodiments, the first light redirecting layer 60 may further include a plurality of substantially planar gaps 66 between other structures (e.g., first truncated structures 61 and/or untruncated second structures 67). In the embodiments when the first light redirecting layer 60 includes substantially planar gaps 66, the substantially planar gaps 66 may serve the same function as the substantially planar top surfaces 63 of first truncated structures 61. That is, the substantially planar gaps 66 may allow infrared wavelengths to pass through first light redirecting layer 60 with minimized distortion, such that they may be used by infrared detector 130 to create an image of object 150. In some embodiments, the substantially planar gaps 66 may have an average width, Wl, such that Wl is greater than or equal to about 1.5 microns, or about 2.0 microns, or about 2.5 microns, or about 3.0 microns.

As with the embodiments utilizing the substantially planar top surfaces 63 of first truncated structures 61, embodiments utilizing substantially planar gaps 66 (instead of, or in combination with, planar top surfaces 63 of first truncated structures 61) may provide similar transmission levels. In some embodiments, substantially planar gaps 66 may have an average width Wl, such that Wl is greater than or equal to about 1.5 microns, or about 2.0 microns, or about 2.5 microns, or about 3.0 microns. Let T1 represent the on-axis effective transmission for optical stack 200 (with substantially planar gaps 66, and let T2 represent the on-axis effective transmission for a comparative optical stack of the same construction except that W 1 for the comparative optical stack is less than about 0.2 microns (i.e., the structures in the comparative optical stack effectively have zero planar gap between them). Further, for the first wavelength range and for light 42 (see FIG. 3) incident at an angle of incidence, Q, with respect to a direction 43 (see FIG. 3) normal to the first reflective polarizer 50, the first reflective polarizer 50 may have an average optical transmission TO (see FIG. 5) when Q is about zero degrees, and an average optical transmission T60 (see FIG. 5) when Q is about 60 degrees.

In some embodiments, the optical stack 200 may be configured such that the ratio of T60/T0 is sufficiently small so that T1 and T2 are within about 20% of each other. Stated another way, the optical system is configured such that, as the ratio of T60/T0 decreases, the more the light passing through the optical stack becomes collimated. In some embodiments, the ratio of T60/T0 may be less than about 0.5, or less than about 0.4, or less than about 0.3. In some embodiments, at least two of the substantially planar gaps 66 may have different width values (i.e., different widths for the planar surfaces which contribute to the average width, Wl). The first light redirecting layer 60 may use various combinations of structures, including but not limited to truncated structures 61, untruncated structures 67, and substantially planar gaps 66 to achieve the improvements described herein. FIGS. 7A through 7C illustrate the profiles of three possible embodiments of light redirecting layer 60. In the embodiment of FIG. 7A, first light redirecting layer 60 includes a plurality of untruncated structures 67 and a plurality of substantially planar gaps 66. Although the arrangement of structures shown in FIG. 7A appears to be regularly spaced and alternating between untruncated structures 67 and substantially planar gaps 66, the spacing may be irregular, as well, and may use a different order or combination of structure types without deviating from the concepts described herein.

FIG. 7B illustrates a second alternate embodiment of first light redirecting layer 60, featuring a combination of truncated structures 61, untruncated structures 67 and substantially planar gaps 66. FIG. 7C illustrates a third alternate embodiment of first light redirecting layer 60, featuring an alternating pattern of truncated structures 61 and untruncated structures 67. In other embodiments, the ratio between truncated structures 61, untruncated structures 67, and/or substantially planar gaps 66 may be equal or unequal. For example, in some embodiments, the ratio of untruncated structures 67 to truncated structures 61 may be 1 to 3, 1 to 2, 1 to 1, 2 to 1, or 3 to 1, or 4 to 1, or any other appropriate ratio.

FIG. 4 provides a chart plotting an example percentage transmission for optical stack 200, with lines showing typical transmission percentage values for light at an incidence angle of about 0 degrees and light at an incidence angle of about 60 degrees. Based on this chart, average transmission values from about 450 nm to about 650 nm are TO around 28.3%, and a T60 of about 6.38%, providing a ratio T60/T0 of about 0.23. The chart of FIG. 4 is provided for illustration purposes only and not meant to be limiting in any way.

Returning to FIG. 1, in some embodiments, second light redirecting layer 100 may include a plurality of second truncated structures 61 (not shown on second light redirecting layer 100 but similar to truncated structures on first light redirecting layer 60). In some embodiments, each second truncated structure 61 may have opposing side surfaces 62a and 62b making an angle between about 60 degrees to about 120 degrees with each other and a substantially planar top surface 63 joining opposing side surfaces 62a and 62b. In some embodiments, the top surfaces of the second truncated structures 61 may have an average width greater than or equal to about 2 microns. In some embodiments, second light redirecting layer 100 may be disposed adjacent to first light redirecting layer 60 but rotated such that the second truncated features 61 are substantially orthogonal to the first truncated features 61. In other words, in some embodiments, two light redirecting films with truncated features may be combined to enhance the overall brightness of the transmitted light (e.g., due to collimation of the transmitted light) while still allowing a portion of infrared light to pass through the optical system 400 to an infrared detector 130.

In some embodiments, optical stack 200 may further include a first reflective polarizer 50 disposed on the first light redirecting layer 60 (or, when present, on second light redirecting layer 100). In some embodiments, first reflective polarizer 50 may transmit at least 40% or at least 45% or at least 50% of incident light 51 (see FIG. 2B) for a first polarization state for each wavelength in a first wavelength range, and may reflect at least 70% or at least 75% or at least 80% of incident light 51 for an orthogonal second polarization state for each wavelength in the fire wavelength range. In some embodiments, the first wavelength range may be from about 450 nm to about 650 nm (e.g., a human-visible range). The first and second polarization states may be any two orthogonal polarization states for light, such as, for example, linear p-polarized (p-pol) light and linear s-polarized (p-pol) light.

In some embodiments, first reflective polarizer 50 may transmit at least 40% or at least 45% or at least 50% of incident light 51 for each of the first and second polarization states for at least one wavelength in a second wavelength range. In some embodiments, the second wavelength range may be between about 750 nm and about 1100 nm (e.g., infrared wavelengths).

In some embodiments, optical system 400 may include a liquid crystal display panel 110 disposed on the first reflective polarizer 50, for forming an image 111 viewable by a viewer 120 in response to an image signal input 112, as finally transmitted light lOd passes through the display.

In some embodiments, the reflecting layer 40 may reflect at least 70% or at least 75% or at least 80% of incident light 41 (see FIG. 2A) for each wavelength in the first wavelength range and for each of the first and second polarization states. In some embodiments, the reflecting layer 40 may transmit at least 70% or at least 75% or at least 80% of incident light 41 for at least one wavelength in the second wavelength range (e.g., an infrared wavelength) for each of the first and second polarization states. Stated another way, reflecting layer 40 will substantially reflect wavelengths of human-visible light in the first wavelength range, and substantially transmit at least one wavelength of infrared light in the second wavelength range.

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 10 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 1, means that the quantity has a value between 0.9 and 1.1, and that the value could be 1.

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 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 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 20% of a width of the objects being aligned. Objects described as substantially aligned may, in some embodiments, be aligned to within 10% or to within 5% of a width of the objects being aligned.

All references, patents, and patent applications referenced in the foregoing are hereby incorporated herein by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control.

Descriptions for elements in figures should be understood to apply equally to corresponding elements in other figures, unless indicated otherwise. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations can be substituted for the specific embodiments shown and described 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. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.