BACKLIGHT FOR IMAGING DEVICE COMPRISING OPTICAL CAVITY FORMED BY OPPOSED COLD AND HOT MIRRORS - Patent application

Abstract

To provide a backlight for providing illumination to an image forming device.SOLUTION: A backlight 100 includes: a front optical reflector 20 and a back optical reflector 10, which are spaced and define an optical cavity 18; and a light source 15 for emitting light into the optical cavity. The front optical reflector 20 is disposed between the image forming device and the back optical reflector 10. For normally incident light and for non-overlapping first visible light and second infrared wavelength ranges, the front optical reflector 20 transmits 80c 70% of light 80a for each wavelength in the first wavelength range, and reflects 90b 70% of light 90a for each wavelength in the second wavelength range. The back optical reflector 10 reflects 80b 70% of light for each wavelength in the first wavelength range, and transmits 90c 70% of light 90b for each wavelength in the second wavelength range. The light 80a, 90a from the light source 15 has a wavelength in the first wavelength range and a wavelength in the second wavelength range.SELECTED DRAWING: Figure 1

Description

Summary of the Invention

[0001] In some aspects herein, a backlight is provided for providing illumination to an image-forming device. In some embodiments, the backlight includes spaced-apart front and rear optical reflectors defining an optical cavity therebetween, and at least one light source that emits light into the optical cavity.

[0002] The front optical reflector may be configured to be disposed between the image forming device and the rear optical reflector. For substantially normally incident light, and for each of the orthogonal first and second polarization states, and for the non-overlapping first and second wavelength ranges, the front optical reflector may transmit at least 70% of the light for each wavelength in the first wavelength range and may reflect at least 70% of the light for each wavelength in the second wavelength range. The rear optical reflector may reflect at least 70% of the light for each wavelength in the first wavelength range and may transmit at least 70% of the light for each wavelength in the second wavelength range. The emitted light may include at least one wavelength in the first wavelength range and at least one wavelength in the second wavelength range.

[0003] In some aspects herein, a display system is provided that includes an image forming device disposed on a backlight. The backlight may include a light source, a front optical reflector disposed between the image forming device and a rear optical reflector, and a thermal management layer disposed on the rear optical reflector remote from the front optical reflector.

[0004] In some embodiments, the front optical reflector may substantially transmit visible light emitted by the light source towards the image forming device and may substantially reflect heat generated by the light source towards the rear optical reflector. In some embodiments, the rear optical reflector may substantially reflect visible light emitted by the light source towards the front optical reflector and may substantially transmit heat reflected by the front optical reflector, such that the thermal management layer may substantially absorb the heat transmitted by the rear optical reflector. [Brief description of the drawings]

[0005] [Figure 1] 1 is a cross-sectional view of a thermal management system according to one embodiment described herein. [Diagram 2] 1 is a cross-sectional view of an alternative embodiment of a thermal management system according to an embodiment described herein. [Diagram 3] 1 is a chart plotting exemplary transmittance and reflectance values ​​for a specular reflector according to one embodiment described herein. [Figure 4] 1 is a chart comparing the transmittance curve for a typical white reflector of the prior art with the transmittance curve of a specular reflector according to one embodiment described herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] In the following description, reference is made to the accompanying drawings, which 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 disclosure. Accordingly, the following detailed description is not to be taken in a limiting sense.

[0007] Ultra High Definition (UHD), High Dynamic Range (HDR) displays require unprecedented brightness and power consumption due to image quality standards, display panel inefficiencies, near instantaneous picture and data processing, and the size and number of light sources of these displays. Multilayer optical film technology allows for the management of specific portions of the electromagnetic spectrum within the display, which can result in optimal image quality and reduced heat load on the system. These UHD, HDR systems require high brightness, visible light that is directed substantially toward the viewer, and near infrared energy (i.e., heat) to be directed where it can be properly managed (e.g., dissipated through a heat sink). Typical light sources used in UHD, HDR systems emit light visible to humans in the range of about 400 nm to about 750 nm. Some systems with higher color gamuts emit light in the blue, or wavelengths centered around about 450 nm. Both types of light sources emit energy in the infrared band, which can add unwanted heat to the system.

[0008] According to some aspects of the present disclosure, a backlight is provided for providing illumination to an image-forming device. In some embodiments, the backlight includes spaced-apart front and rear optical reflectors defining an optical cavity therebetween, and at least one light source emitting light into the optical cavity. The front optical reflector may be configured to be disposed between the image-forming device and the rear optical reflector.

[0009] For substantially normally incident light, and for each of the orthogonal first and second polarization states, and for the first and second non-overlapping wavelength ranges, the front optical reflector may transmit at least 70% of the light for each wavelength in the first wavelength range and may reflect at least 70% of the light for each wavelength in the second wavelength range. The rear optical reflector may reflect at least 70% of the light for each wavelength in the first wavelength range and may transmit at least 70% of the light for each wavelength in the second wavelength range. The emitted light may include at least one wavelength in the first wavelength range and at least one wavelength in the second wavelength range.

[0010] In some embodiments, the front and rear optical reflectors include band edges separating a first wavelength range from a second wavelength range, the band edges being within 50 nm of each other. In other embodiments, the band edges are within 40 nm of each other, or within 30 nm of each other. In still other embodiments, the first and second wavelength ranges are separated by less than about 10 nm.

[0011] In some embodiments, the first wavelength range ranges from about 400 nm to about 600 nm, or from about 400 nm to about 700 nm, or from about 400 nm to about 750 nm, or from about 400 nm to about 800 nm. In some embodiments, the second wavelength range ranges from about 700 nm to about 800 nm, or from about 700 nm to about 850 nm. In some embodiments, the second wavelength range ranges from about 700 nm to about 1.7 micrometers.

[0012] In some embodiments, one or both of the front and rear optical reflectors may be multilayer optical films composed of multiple alternating layers of a first polymer layer and a second polymer layer ranging from 50 to 1000 layers, with each of the first and second polymer layers having an average thickness of less than about 500 nm. By selecting appropriate layer pairs with appropriate refractive indices, layer thicknesses, and / or number of layer pairs for each reflector, the multilayer optical film can be designed to transmit or reflect light of desired wavelengths. By selecting polymers with specific refractive indices, as well as controlling the number of pairs of alternating polymer layers, it is possible to construct an optical reflector that transmits light of wavelengths in a first set of wavelengths (e.g., corresponding to a first wavelength range) and reflects light of wavelengths in a second set of wavelengths (e.g., corresponding to a second wavelength range).

[0013] For example, in one embodiment of the first optical reflector, the first and second polymer layers may have indices of refraction nx1 and nx2 along a first polarization state, indices ny1 and ny2 along a second polarization state, and indices nz1 and nz2 along a z-axis orthogonal to the first and second polarization states, respectively, for at least one wavelength in a first wavelength range: In the first polymer layer: nx1 is about 1.60 to about 1.70 (for example, about 1.655) ny1 is about 1.60 to about 1.70 (for example, about 1.655) nz1 is about 1.45 to about 1.55 (for example, about 1.498), In the second polymer layer: nx2 is about 1.45 to about 1.55 (for example, about 1.491) ny2 is about 1.45 to about 1.55 (for example, about 1.491) nz2 is about 1.45 to about 1.55 (for example, about 1.491).

[0014] In another example, in one embodiment of a rear optical reflector, the first and second polymer layers may have refractive indices nx1 and nx2 along a first polarization state, ny1 and ny2 along a second polarization state, and nz1 and nz2 along a z-axis orthogonal to the first and second polarization states, respectively, and for at least one wavelength in a first wavelength range: In the first polymer layer: nx1 is about 1.62 to about 1.80 (for example, about 1.75) ny1 is about 1.62 to about 1.80 (for example, about 1.75) nz1 is about 1.41 to about 1.55 (for example, about 1.498), In the second polymer layer: nx2 is about 1.41 to about 1.55 (for example, about 1.491) ny2 is about 1.41 to about 1.55 (for example, about 1.491) nz2 is about 1.41 to about 1.55 (for example, about 1.491).

[0015] The refractive indices mentioned above are merely examples, and any suitable values ​​of refractive index may be used to achieve the optimum expected functionality of the optical reflector for a particular application. The examples provided are in no way limiting.

[0016] Exemplary materials for the first polymer layer may be crystalline materials including, but not limited to, polyethylene terephthalate (PET), crystalline polyethylene terephthalate (coPET), polyethylene naphthalate (PEN), or crystalline polyethylene naphthalate (coPEN). Exemplary materials for the second polymer layer may be substantially amorphous materials including, but not limited to, amorphous polyethylene terephthalate (coPET), poly(methyl methacrylate) (PMMA), and poly(methyl methacrylate) (coPMMA), as well as blends with fluorine, such as polyvinylidene difluoride (PVDF), or THV (terpolymers of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride).

[0017] In some embodiments, the backlight may also include a reflective polarizer disposed on the front optical reflector outside the optical cavity, such that for substantially normally incident light and for each wavelength in the first wavelength range, the reflective polarizer reflects at least 70% of the light having a first polarization state and transmits at least 70% of the light having a second polarization state. In some embodiments, the reflective polarizer may include a plurality of alternating first and second polymer layers ranging from 50 to 1000 layers, each of the first and second polymer layers having an average thickness of less than about 500 nm. For example, in one embodiment of the reflective polarizer, the first and second polymer layers may each have refractive indices nx1 and nx2 along the first polarization state, ny1 and ny2 along the second polarization state, and nz1 and nz2 along a z-axis orthogonal to the first and second polarization states, and for at least one wavelength in the first wavelength range: In the first polymer layer: nx1 is about 1.75 to about 1.85 (for example, about 1.810) ny1 is about 1.50 to about 1.64 (for example, about 1.574) nz1 is about 1.50 to about 1.64 (for example, about 1.570), In the second polymer layer: nx2 is about 1.50 to about 1.64 (for example, about 1.574) ny2 is about 1.50 to about 1.64 (for example, about 1.565) nz2 is about 1.50 to about 1.64 (for example, about 1.565).

[0018] For example, these values ​​can be seen at a wavelength of about 632 nm, where x is the film stretch direction for reflective polarizers (i.e., substantially uniaxial film stretch). For mirror films, the stretch direction is in both the x and y directions (in-plane) (i.e., substantially biaxial film stretch).

[0019] In some embodiments, the light source may include any suitable light source, including but not limited to a light emitting diode (LED), a laser, or a combination thereof. In some embodiments, the light source may be disposed between the front optical reflector and the rear optical reflector within the optical cavity. In some embodiments, the light source may be disposed closer to the rear optical reflector and farther from the front optical reflector. In some embodiments, the light source may be disposed along a side edge on the outside of the optical cavity.

[0020] In some embodiments, the optical cavity is a substantially hollow, air-filled cavity. In other embodiments, the optical cavity is a substantially solid volume (e.g., a filled cavity, or a solid material) that includes opposed top and bottom major surfaces, with a front optical reflector disposed on the top major surface and a rear optical reflector disposed on the bottom major surface. For example, in some embodiments, the optical cavity may be a solid light guide that distributes light received from a light source disposed outside the optical cavity via total internal reflection.

[0021] In some embodiments, the backlight may also include an optical diffuser disposed on the front optical reflector outside the optical cavity, which diffuses light that exits the optical cavity through the front optical reflector. In some embodiments, the backlight may also include one or more multilayer optical films designed to enhance the brightness of the light output from the backlight. Examples of such films include brightness enhancement films designed to collimate the output light in one or more dimensions, and reflective polarizers that can polarize light so that it can be transmitted through a display, such as a liquid crystal panel.

[0022] In some embodiments, the backlight may include a thermal management layer disposed on the rear optical reflector outside the optical cavity. The thermal management layer may include one or more of an infrared absorbing layer, a thermally conductive layer, or a combination thereof (e.g., a single layer having both thermal conductivity and infrared absorbing properties). In some embodiments, the thermal management layer may have a wavelength within the second wavelength range and may absorb at least 50% of the light transmitted by the rear optical reflector (e.g., a wavelength corresponding to the radiated thermal energy). In some embodiments, the thermal management layer may have a thermal conductivity of at least greater than 100 W / mK. In some embodiments, the thermal management layer may be or include a heat-diffusing multilayer film. Exemplary thermally conductive materials for the thermal management layer may include, but are not limited to, graphite, graphite foil, copper, and silver nanowires. In some embodiments, the backlight may also include a heat sink disposed on the thermal management layer (e.g., aluminum fins for dissipating heat).

[0023] In some embodiments, the thermal management layer may absorb at least a portion (e.g., at least 5%) of the light / energy having at least one wavelength greater than the second wavelength range. For example, in one commonly used subdivision scheme, infrared energy may be subdivided into near infrared (about 750 nm to about 1400 nm), short wavelength infrared (about 1400 nm to 3 micrometers), mid wavelength infrared (about 3 micrometers to about 8 micrometers), long wavelength infrared (about 8 micrometers to about 15 micrometers), and far infrared (about 15 micrometers to about 1000 micrometers). In some embodiments, the second wavelength range may extend across a portion of the near infrared spectrum, while the thermal management layer may absorb additional wavelengths of light / energy in a third wavelength range, which includes wavelengths greater than those in the second wavelength range (i.e., at least one wavelength greater than the second wavelength range). For example, in one embodiment, the third wavelength range may include wavelengths in the short wavelength range, the medium wavelength range, and the long wavelength range as defined herein (e.g., from about 1.5 micrometers to at least about 15 micrometers).

[0024] In some embodiments, the energy in this third wavelength range may be emitted by at least one light source, may be emitted by electronic circuitry located adjacent to or within the backlight, or may be emitted from other sources within the optical cavity. In some embodiments, the third wavelength range has a width of at least about 200 nm. In some embodiments, the rear optical reflector may transmit at least 10% of at least one wavelength in the third wavelength range.

[0025] According to some aspects herein, a display system may include an image-forming device (e.g., a liquid crystal display panel) disposed on a backlight. The backlight may include a light source (e.g., one or more LEDs), a front optical reflector disposed between the image-forming device and a rear optical reflector, and a thermal management layer disposed on the rear optical reflector distal to the front optical reflector.

[0026] In some embodiments, the front optical reflector may substantially transmit visible light emitted by the light source (i.e., light having wavelengths within the range visible to the human eye) towards the image forming device and may substantially reflect heat generated by the light source (i.e., light in the infrared range) towards the rear optical reflector. In some embodiments, the rear optical reflector may substantially reflect visible light emitted by the light source towards the front optical reflector and may substantially transmit heat reflected by the front optical reflector, such that the thermal management layer substantially absorbs the heat transmitted by the rear optical reflector. In some embodiments, a heat sink may be disposed on or near the thermal management layer to aid in dissipating heat emitted by the light source.

[0027] Referring now to the drawings, Figure 1 is a cross-sectional view of a thermal management system for a backlight 100 according to embodiments described herein. The backlight 100 includes a front optical reflector 20 and a rear optical reflector 10 spaced apart defining an optical cavity 18 therebetween, and at least one light source 15 that emits light into the optical cavity 18. In some embodiments, the front optical reflector 20 is configured to be disposed between an image-forming device 70 and the rear optical reflector 10. The image-forming device 70 may be, for example, a liquid crystal panel.

[0028] In some embodiments, an optical diffuser 40 may be disposed on the outside of the front optical reflector 20 opposite the optical cavity 18. The optical diffuser 40 may diffuse any light that exits the optical cavity 18 through the front optical reflector 20. In some embodiments, there may be one or more layers of optical enhancement layers between the front optical reflector 20 and the image forming device 70. In the embodiment shown in FIG. 1, a first brightness enhancement film 50a may be disposed above the diffuser 40, and a second brightness enhancement film 50b may be disposed above the brightness enhancement film 50a. In some embodiments, the brightness enhancement films 50a / 50b may be used to compress the output light toward the "axial" observer. By placing layers of two such brightness enhancement films (such as 50a and 50b) together rotated 90 degrees from each other, it may be possible to compress the light transmitted by the front optical reflector 20 in two separate orthogonal dimensions to substantially collimate the light before it reaches the image forming device 70. In some embodiments, a reflective polarization enhancement film 60 (e.g., 3M Dual Brightness Enhancement Film) may be used to further enhance the output light (e.g., change the polarization of the transmitted light to pass more efficiently through the image forming device 70).

[0029] In operation, the light source 15 emits light including wavelengths of light 80 visible to humans, as well as infrared energy 90, which represents heat that does not contribute to the light visible to humans, but may contribute to heat radiated from the front of the device. In FIG. 1, the light source 15 emits light 80a visible to humans and infrared energy 90a. The light 80a visible to humans and the infrared energy 90a may be emitted in various directions within the optical cavity 18. It should be noted that the arrows shown in FIG. 1 and other figures herein are exemplary and are intended to show the general movement of light throughout the backlight cavity. The light 80a visible to humans and the infrared energy 90a ultimately enter the front optical reflector 20. In some embodiments, the front optical reflector 20 transmits (passes) a substantial portion of the light 80a visible to humans (which becomes transmitted human visible light 80c) and reflects a substantial portion of the infrared energy 90a (which becomes reflected infrared energy 90b).

[0030] The reflected infrared energy 90b may be trapped within the optical cavity 18 and cause undesired heating of the backlight 100. Thus, in some embodiments, the rear optical reflector 10 may be designed to transmit (pass) a substantial portion of the reflected infrared energy (which becomes transmitted infrared energy 90c) and reflect a substantial portion of the human-visible light (including the emitted human-visible light 80a and any portion of the human-visible light 80 that did not initially pass through the front optical reflector 20). The reflected human-visible light 80b may be reflected throughout the optical cavity 18 (i.e., the light is recycled) until it re-enters the front optical reflector 20, where it may be substantially passed through as transmitted human-visible light 80c.

[0031] In some embodiments, a thermal management layer 30 may be disposed on a side of the rear optical reflector 10. This thermal management layer 30 may be designed to absorb and / or dissipate the transmitted infrared energy 90c, thereby removing unwanted heat from the backlight system 100. In some embodiments, the thermal management layer may be an infrared absorbing layer that absorbs at least a portion (e.g., at least 50%) of light / energy having wavelengths within the second wavelength range (e.g., infrared energy that may cause excess heat) that are transmitted by the rear optical reflector 10. In some embodiments, the thermal management layer 30 may include a thermally conductive layer disposed in addition to and adjacent the infrared absorbing layer for conducting heat generated as a result of infrared energy being absorbed by the infrared absorbing layer. In some embodiments, the heat may be generated by the light source 15, emitted by electronic circuitry near or within the backlight 100, or emitted from other sources within the backlight 100. In some embodiments, the thermal management layer 30 may include only a thermally conductive layer that can draw heat away from the backlight 100 and dissipate, absorb, or otherwise mitigate the heat. In some embodiments, a heat sink (not shown) may be disposed on or near the thermal management layer 30 to aid in the removal of heat from the backlight 100. In some embodiments, the heat sink may be directly coated with an infrared absorbing layer to remove heat from the backlight 100.

[0032] Figure 2 is a cross-sectional view of one embodiment of the thermal management system of Figure 1, according to an alternative embodiment described herein. Many of the components shown in Figure 2 are common to those shown in Figure 1. These components share similar reference designations and functions as similarly numbered components described in Figure 1. It should also be noted that for simplicity, image-forming device 70 and enhancing layers 50a, 50b, and 60 have been removed from Figure 2, but may be present in some embodiments.

[0033] Returning to FIG. 2, one or more light sources 15 may be disposed on one or more sides of the optical cavity 18. Light is emitted as human visible light 80a and infrared energy 90a. Human visible light 80a and infrared energy 90a enter the optical cavity 18 at various angles and are appropriately reflected and / or transmitted by the front optical reflector 20 and the rear optical reflector 10. For example, when the emitted human visible light 80a enters the rear optical reflector 10, it is substantially reflected into reflected human visible light 80b. The reflected human visible light 80b may then enter the front optical reflector 20 and be substantially transmitted (passed) into transmitted human visible light 80c. Conversely, when the emitted infrared energy 90a enters the front optical reflector 20, it is substantially reflected into reflected infrared energy 90b. The reflected infrared energy 90b may then enter the rear optical reflector 10 and be substantially transmitted (passed) into transmitted infrared energy 90c.

[0034] In other words, the front optical reflector 20 is configured to substantially transmit (e.g., at least 70%) the light 80 visible to humans and substantially reflect (e.g., at least 70%) the infrared energy 90. Conversely, the back optical reflector 10 is configured to substantially transmit (e.g., at least 70%) the infrared energy 90 and substantially reflect (e.g., at least 70%) the light 80 visible to humans. In this manner, the light 80 visible to humans is substantially transmitted towards the image-forming device (not shown in FIG. 2 ) and the infrared energy 90 is substantially transmitted away from the image-forming device and out of the optical cavity 18.

[0035] In some embodiments, a reflective polarizer 25 may be disposed on the front optical reflector 20 outside the optical cavity 18. For substantially normally incident light, and for each wavelength in the first wavelength range, the reflective polarizer substantially reflects (e.g., at least 70%) light having a first polarization state and substantially transmits (e.g., at least 70%) light having a second polarization state. In some embodiments, the reflective polarizer 25 may help increase the efficiency of light transmission through the image-forming device by changing the polarization type of the light to correspond to the type substantially transmitted by the image-forming device.

[0036] FIG. 3 is a chart plotting exemplary transmittance and reflectance values ​​for an embodiment of an infrared specular reflector, such as the embodiment of the front optical reflector 20 of FIGS. 1 and 2. Line 300T shows a transmittance profile for one anticipated embodiment of a front optical reflector that substantially transmits light with wavelengths from about 400 to about 870 nm and substantially reflects light with wavelengths corresponding to infrared energy from about 970 nm to about 1150 nm. Line 300R shows a reflectance profile for one anticipated embodiment of a front optical reflector that substantially reflects light with wavelengths from about 850 nm to about 1200 nm. The chart of FIG. 3 shows exemplary transmittance and reflectance profiles for one anticipated embodiment of a front optical reflector for purposes of illustration and not limitation. The transmittance profile 300T shows an exemplary bandpass region for light visible to humans, or a subset thereof, with an average transmittance of at least about 60%, or at least about 70%, or at least about 80%. Similarly, reflectance profile 300R illustrates an example of a region, or a subset thereof, reflective to infrared energy having an average reflectance of at least about 60%, or at least about 70%, or at least about 80%.

[0037] Finally, FIG. 4 is a chart comparing the transmission curves for a typical white light reflector of the prior art with those of a visible light specular reflector, such as the rear optical reflector 10 of FIGS. 1 and 2. Line 400W shows the percent transmission of light with wavelengths from about 700 nm to about 1200 nm for a typical white light reflector found in the prior art. For the typical white light reflector 400W, less than about 5% of all wavelengths within this range are transmitted (i.e., allowed to pass through the reflector), and thus are essentially reflected back into the optical cavity of the backlight. When combined with an infrared-reflective front optical reflector, the white optical reflector will trap infrared energy in the optical cavity, resulting in undesirable heating of the system. Line 400S shows the percent transmission of light with wavelengths in the same range (about 700 nm to about 1200 nm) for an embodiment of a visible light reflector, such as the embodiment of the rear optical reflector 10 of FIGS. 1 and 2. Profile 400S substantially reflects (i.e., does not transmit through the reflector) light having wavelengths between about 700 nm and about 1000 nm, and substantially transmits light having wavelengths between about 1000 nm and about 1200 nm. The chart in Figure 4 illustrates a non-limiting transmission profile of one embodiment of a rear optical reflector according to one embodiment described herein. The transmission profiles shown herein are examples for illustrative purposes only.

[0038] As described elsewhere herein, a blue light source (e.g., a blue LED) may be used as the light source for a display with a higher color gamut. In this case, a spectral reflector film capable of passing blue light and reflecting infrared light and a color conversion film, such as a film layer containing quantum dots or phosphor sheets, may be used prior to the diffuser. Other variations and embodiments of the front and rear optical reflectors are possible without departing from the described embodiments.

[0039] Terms such as "about" will be understood by those of skill in the art in the context in which they are used and described herein. If the use of "about" as applied to quantities expressing feature sizes, quantities, and physical properties is not clear to those of skill in the art in the context in which they are used and described herein, "about" will be understood to mean within 10 percent of the specified value. A quantity given as about a specified value may be exactly that specified value. For example, if it is not clear to those of skill in the art in the context in which they are used and described herein, a quantity having a value of about 1 means a quantity having a value between 0.9 and 1.1, and the value may be 1.

[0040] Terms such as "substantially" will be understood by those of skill in the art in the context in which they are used and described in the present description. If the use of "substantially equal" is not clear to those of skill in the art in the context in which they are used and described in the present description, "substantially equal" means approximately equal when about is as above. If the use of "substantially parallel" is not clear to those of skill in the art in the context in which they are used and described in the present description, "substantially parallel" will mean within 30 degrees of parallel. Directions or surfaces described as being substantially parallel to one another may, in some embodiments, be within 20 degrees, or within 10 degrees, or may be parallel or nominally parallel. If the use of "substantially aligned" is not clear to those of skill in the art in the context in which they are used and described in the present description, "substantially aligned" means aligned within 20% of the width of the objects being aligned. Objects described as being substantially aligned may, in some embodiments, be aligned within 10% or within 5% of the width of the objects being aligned.

[0041] Any of the above references, patents, or patent applications are incorporated herein by reference in their entirety in a consistent manner. In the event of any inconsistency or contradiction between any of the incorporated references and this application, the information in the above description shall prevail.

[0042] Descriptions of elements in the figures should be understood to apply equally to corresponding elements in other figures unless otherwise indicated. Although specific embodiments have been illustrated and described herein, those skilled in the art will appreciate that various alternative and / or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. The present application is intended to cover any adaptations or variations of the specific embodiments described herein. Accordingly, the present disclosure is to be limited only by the claims and their equivalents. Exemplary embodiments are presented below. [Item 1] 1. A backlight for providing illumination to an image forming device, comprising: a spaced-apart front optical reflector and a rear optical reflector defining an optical cavity therebetween, the front optical reflector configured to be disposed between the image-forming device and the rear optical reflector; As a result, for light at substantially normal incidence, and for each of orthogonal first and second polarization states, and for non-overlapping first and second wavelength ranges: the front optical reflector transmits at least 60% of the light for each wavelength in the first wavelength range and reflects at least 70% of the light for each wavelength in the second wavelength range; a front optical reflector and a rear optical reflector, the rear optical reflector reflecting at least 70% of the light for each wavelength in the first wavelength range and transmitting at least 70% of the light for each wavelength in the second wavelength range; at least one light source that emits light into the optical cavity, the emitted light having at least one wavelength within the first wavelength range and at least one wavelength within the second wavelength range. [Item 2] Item 2. The backlight of item 1, wherein the front optical reflector transmits at least 70% of light for each wavelength in the first wavelength range. [Item 3] Item 2. The backlight of item 1, wherein the front optical reflector and the rear optical reflector each include a plurality of polymer layers. [Item 4] 2. The backlight of claim 1, wherein the front optical reflector and the rear optical reflector each include a band edge separating the first wavelength range from the second wavelength range, the band edges being within 50 nm of each other. [Item 5] Item 5. The backlight of item 4, wherein the band edges are within 40 nm of each other. [Item 6] Item 5. The backlight of item 4, wherein the band edges are within 30 nm of each other. [Item 7] Item 2. The backlight of item 1, wherein the first wavelength range and the second wavelength range are separated by less than 10 nm. [Item 8] 2. The backlight according to item 1, wherein the first wavelength range ranges from about 400 nm to about 600 nm. [Item 9] 2. The backlight according to item 1, wherein the first wavelength range ranges from about 400 nm to about 650 nm. [Item 10] 2. The backlight according to item 1, wherein the first wavelength range ranges from about 400 nm to about 700 nm. [Item 11] 2. The backlight according to item 1, wherein the first wavelength range ranges from about 400 nm to about 750 nm. [Item 12] 2. The backlight according to item 1, wherein the first wavelength range ranges from about 400 nm to about 800 nm. [Item 13] 2. The backlight according to item 1, wherein the second wavelength range ranges from about 700 nm to about 800 nm. [Item 14] 2. The backlight according to item 1, wherein the second wavelength range ranges from about 700 nm to about 850 nm. [Item 15] Item 2. The backlight of item 1, wherein the second wavelength range extends from about 700 nm to at least about 1.7 micrometers. [Item 16] The front optical reflector includes a plurality of alternating first and second polymer layers ranging from 50 to 1000 layers, each of the first and second polymer layers having an average thickness of less than about 500 nm, and for each adjacent pair of the first and second polymer layers: In the plane of the first polymer layer and the second polymer layer, the first polymer layer and the second polymer layer respectively have refractive indices nx1 and nx2 along the first polarization state, ny1 and ny2 along the second polarization state, and nz1 and nz2 along a z-axis orthogonal to the first polarization state and the second polarization state, and for at least one wavelength in the first wavelength range: nx1 is about 1.60 to about 1.70, ny1 is about 1.60 to about 1.70, nz1 is about 1.45 to about 1.55, nx2 is about 1.45 to about 1.55, ny2 is about 1.45 to about 1.55, and 2. The backlight according to item 1, wherein nz2 is about 1.45 to about 1.55. [Item 17] nx1 is approximately 1.655, ny1 is about 1.655, nz1 is about 1.498, nx2 is approximately 1.491, ny2 is approximately 1.491, and 17. The backlight according to item 16, wherein nz2 is about 1.491. [Item 18] The rear optical reflector includes a plurality of alternating first and second polymer layers ranging from 50 to 1000 layers, each of the first and second polymer layers having an average thickness of less than about 500 nm, and for each adjacent pair of the first and second polymer layers: In the plane of the first polymer layer and the second polymer layer, the first polymer layer and the second polymer layer respectively have refractive indices nx1 and nx2 along the first polarization state, ny1 and ny2 along the second polarization state, and nz1 and nz2 along a z-axis orthogonal to the first polarization state and the second polarization state, and for at least one wavelength in the first wavelength range: nx1 is about 1.62 to about 1.80, ny1 is about 1.62 to about 1.80, nz1 is about 1.41 to about 1.55, nx2 is about 1.41 to about 1.55, ny2 is about 1.41 to about 1.55, and 2. The backlight according to item 1, wherein nz2 is about 1.41 to about 1.55. [Item 19] nx1 is about 1.75, ny1 is about 1.75, nz1 is about 1.498, nx2 is approximately 1.491, ny2 is approximately 1.491, and nz2 is approximately 1.491, Item 19. The backlight according to item 18. [Item 20] 2. The backlight of claim 1, further comprising a reflective polarizer disposed on the front optical reflector outside the optical cavity, such that for substantially normally incident light and for each wavelength in the first wavelength range, the reflective polarizer reflects at least 70% of light having the first polarization state and transmits at least 70% of light having the second polarization state. [Item 21] Item 21. The backlight of item 20, wherein the reflective polarizer comprises multiple polymer layers. [Item 22] The reflective polarizer includes a plurality of alternating first and second polymer layers ranging from 50 to 1000 layers, each of the first and second polymer layers having an average thickness of less than about 500 nm, and for each adjacent pair of the first and second polymer layers: In the plane of the first polymer layer and the second polymer layer, the first polymer layer and the second polymer layer respectively have refractive indices nx1 and nx2 along the first polarization state, ny1 and ny2 along the second polarization state, and nz1 and nz2 along a z-axis orthogonal to the first polarization state and the second polarization state, and for at least one wavelength in the first wavelength range: nx1 is about 1.75 to about 1.85, ny1 is about 1.50 to about 1.64, nz2 is about 1.50 to about 1.64, nx2 is about 1.50 to about 1.64, ny2 is about 1.50 to about 1.64, and 21. The backlight according to item 20, wherein nz2 is about 1.50 to about 1.64. [Item 23] nx1 is about 1.810, ny1 is about 1.574, nz1 is about 1.570, nx2 is approximately 1.574, ny2 is approximately 1.565, and nz2 is approximately 1.565, 23. The backlight according to item 22. [Item 24] 2. The backlight of claim 1, further comprising an optical diffuser disposed on the front optical reflector outside the optical cavity, the optical diffuser diffusing light exiting the optical cavity through the front optical reflector. [Item 25] 2. The backlight of claim 1, wherein the at least one light source is disposed within the optical cavity between the front optical reflector and the rear optical reflector. [Item 26] Item 26. The backlight of item 25, wherein the at least one light source is positioned closer to the rear optical reflector and farther from the front optical reflector. [Item 27] Item 2. The backlight of item 1, wherein the at least one light source is disposed along a side edge outside the optical cavity. [Item 28] 28. The backlight of claim 27, wherein the optical cavity comprises a solid light guide for distributing light received from the at least one light source disposed along the side edges outside the optical cavity. [Item 29] Item 2. The backlight of item 1, wherein the optical cavity is a substantially hollow air-filled cavity. [Item 30] 2. The backlight of claim 1, wherein the optical cavity is a substantially solid volume having opposed upper and lower major surfaces, the front optical reflector being disposed on the upper major surface and the rear optical reflector being disposed on the lower major surface. [Item 31] 2. The backlight of claim 1, further comprising a thermal management layer disposed on the rear optical reflector outside the optical cavity, the thermal management layer absorbing at least 50% of light having a wavelength within the second wavelength range and transmitted by the rear optical reflector. [Item 32] Item 32. The backlight of item 31, wherein the rear optical reflector is disposed between the front optical reflector and the thermal management layer. [Item 33] Item 32. The backlight of item 31, wherein the thermal management layer has a thermal conductivity of at least greater than 100 W / mK. [Item 34] Item 32. The backlight of item 31, further comprising a heat sink disposed on the thermal management layer. [Item 35] Item 32. The backlight of item 31, wherein the thermal management layer absorbs at least a portion of light having at least one wavelength greater than a wavelength in the second wavelength range. [Item 36] Item 36. The backlight of item 35, wherein the at least a portion of the light comprises at least 5% of the light. [Item 37] Item 36. The backlight of item 35, wherein the at least one wavelength includes a third wavelength range that includes wavelengths greater than the wavelengths in the second wavelength range. [Item 38] Item 38. The backlight of item 37, wherein the third wavelength range has a width of at least about 200 nm. [Item 39] Item 36. The backlight of item 35, wherein the light having the at least one wavelength greater than the second wavelength range is emitted by the at least one light source. [Item 40] Item 36. The backlight of item 35, wherein the light having the at least one wavelength greater than the second wavelength range is emitted from within the backlight. [Item 41] Item 36. The backlight of item 35, wherein the light having the at least one wavelength greater than the second wavelength range is emitted by electronic circuitry disposed adjacent to the backlight. [Item 42] Item 38. The backlight of item 37, wherein the rear optical reflector transmits at least 10% of at least one wavelength in the third wavelength range. [Item 43] Item 38. The backlight of item 37, wherein the third wavelength range extends from about 1.5 micrometers to at least about 15 micrometers. [Item 44] Item 32. The backlight of item 31, wherein the thermal management layer comprises a thermally conductive layer. [Item 45] Item 32. The backlight of item 31, wherein the thermal management layer comprises an infrared absorbing layer. [Item 46] Item 32. The backlight of item 31, wherein the thermal management layer includes a thermally conductive layer disposed adjacent to an infrared absorbing layer, the thermally conductive layer for conducting heat generated as a result of infrared light absorption by the infrared absorbing layer. [Item 47] Item 47. The backlight of item 46, wherein at least portions of the thermally conductive layer and the infrared absorbing layer are in physical contact with each other. [Item 48] Item 47. The backlight of item 46, wherein the thermally conductive layer has a thermal conductivity of at least 100 W / mK. [Item 49] A backlight according to item 1; an image forming device disposed on the front optical reflector outside the optical cavity such that light emitted by the at least one light source illuminates the image forming device after exiting the optical cavity through the front optical reflector; A display system comprising: [Item 50] 1. A display system comprising an image forming device disposed on a backlight, the backlight comprising: A light source; a front optical reflector disposed between the image forming device and a rear optical reflector; a thermal management layer disposed on the rear optical reflector distal to the front optical reflector; the front optical reflector substantially transmits visible light emitted by the light source toward the image forming device and substantially reflects heat generated by the light source toward the rear optical reflector; the rear optical reflector substantially reflects visible light emitted by the light source toward the front optical reflector and substantially transmits heat reflected by the front optical reflector; the thermal management layer substantially absorbs and conducts heat transmitted by the rear optical reflector; Display system.

Claims

1. A display system comprising an image forming device disposed on a backlight, the backlight comprising: A light source; a front optical reflector disposed between the image forming device and a rear optical reflector; a thermal management layer disposed on the rear optical reflector distal to the front optical reflector; the front optical reflector and the rear optical reflector define an optical cavity therebetween; the front optical reflector transmits visible light emitted by the light source toward the image forming device and reflects heat generated by the light source toward the rear optical reflector; the rear optical reflector reflects visible light emitted by the light source toward the front optical reflector and transmits heat reflected by the front optical reflector; the thermal management layer absorbs and conducts heat transmitted by the rear optical reflector; the light source is disposed outside the optical cavity; Display system.

2. The display system of claim 1, wherein the front optical reflector comprises a plurality of alternating first and second polymer layers ranging from 50 to 1000 layers, each of the first and second polymer layers having an average thickness of less than 500 nm.

3. The display system of claim 1, wherein the rear optical reflector comprises a plurality of alternating first and second polymer layers ranging from 50 to 1000 layers, each of the first and second polymer layers having an average thickness of less than about 500 nm.

4. The display system of claim 1, wherein the thermal management layer is configured to absorb at least 50% of light having a wavelength within a wavelength range spanning 700 nm to 850 nm.

5. The display system of claim 1, wherein the thermal management layer is configured to absorb at least a portion of light having at least one wavelength greater than a wavelength range spanning 700 nm to 850 nm.

6. The display system of claim 1, wherein the thermal management layer comprises a thermally conductive layer.

7. The display system of claim 1, wherein the thermal management layer comprises an infrared absorbing layer.

8. The display system of claim 1, wherein the thermal management layer includes a thermally conductive layer disposed adjacent to an infrared absorbing layer, the thermally conductive layer configured to conduct heat generated as a result of absorption of infrared light by the infrared absorbing layer.

9. For normally incident light, and for each of orthogonal first and second polarization states, and for non-overlapping first and second wavelength ranges, and for each pair of adjacent first and second polymer layers of the front optical reflector, In the plane of the first polymer layer and the second polymer layer, the first polymer layer and the second polymer layer respectively have refractive indices nx1 and nx2 along the first polarization state, ny1 and ny2 along the second polarization state, and nz1 and nz2 along a z-axis orthogonal to the first polarization state and the second polarization state, and for at least one wavelength in the first wavelength range: nx1 is 1.60 to 1.70, ny1 is 1.60 to 1.70, nz1 is 1.45 to 1.55, nx2 is 1.45 to 1.55, ny2 is 1.45 to 1.55, and nz2 is 1.45 to 1.55; 3. The display system of claim 2.

10. For normally incident light, and for each of orthogonal first and second polarization states, and for first and second non-overlapping wavelength ranges, and for each pair of adjacent first and second polymer layers of the rear optical reflector, In the plane of the first polymer layer and the second polymer layer, the first polymer layer and the second polymer layer respectively have refractive indices nx1 and nx2 along the first polarization state, ny1 and ny2 along the second polarization state, and nz1 and nz2 along a z-axis orthogonal to the first polarization state and the second polarization state, and for at least one wavelength in the first wavelength range: nx1 is 1.62 to 1.80, ny1 is 1.62 to 1.80, nz1 is 1.41 to 1.55, nx2 is 1.41 to 1.55, ny2 is 1.41 to 1.55, and nz2 is 1.41 to 1.55; 4. The display system of claim 3.

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