Spatially varying polarizer for display backlight

Abstract

To provide a backlight for a display system reduced in power consumption, cost, and space requirements.SOLUTION: The invention provides systems and methods for providing a display 500 for an electronic device that includes a liquid crystal display panel assembly, a backlight assembly with a light source 524, and a spatially varying polarizer 532 that provides phase retardation that varies as a function of propagation length away from the light source. The display may also include a linear polarizer and other optical components that improve the efficiency of the backlight assembly.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present disclosure relates generally to display systems, and more particularly to backlights for display systems. [Background technology]

[0002] The demand for enhanced displays is driven by the growth of smartphones, tablets, wearable devices, high definition televisions, and other electronic devices. The growing popularity of virtual reality and augmented reality systems, especially those using head mounted displays, further increases such demand. Virtual reality systems typically completely surround the wearer's eyes and replace the actual field of view (or actual reality) in front of the wearer with a "virtual" reality, while augmented reality systems typically provide a semi-transparent or transparent overlay of one or more screens in front of the wearer's eyes so that the actual field of view is augmented with additional information. In many virtual reality and augmented reality systems, the movement of the wearer of such a head mounted display can be tracked in various ways, for example, via sensors in and / or external to the head mounted display, to enable the images shown to reflect the user's movement.

[0003] There is an increasing demand for displays that have improved performance while also being smaller or larger in size, consuming less power, and generating less heat than currently available displays. Thus, improved display panels and improved techniques for making and using display panels are needed. Summary of the Invention

[0004] The display may be summarized as comprising a non-emissive display panel assembly, a backlight assembly having a light source, and a spatially varying polarizer positioned between the non-emissive display panel assembly and the backlight assembly, the spatially varying polarizer having a polarization that varies spatially as a function of propagation length away from the light source. The spatially varying polarizer may include a multi-twist retarder. The spatially varying polarizer may provide no retardation at a proximal end near the light source and a quarter-wave retardation at a distal end opposite the proximal end. The retardation of the spatially varying polarizer may vary linearly or non-linearly between a proximal end near the light source and a distal end opposite the proximal end.

[0005] The display may further comprise a linear polarizer positioned between the space-varying polarizer and the non-emissive display panel assembly. The linear polarizer may comprise a dual brightness enhancement film (DBEF).

[0006] The display may further comprise a control circuit operably coupled to the space-varying polarizer, the control circuit operable to selectively adjust the retardation provided by the space-varying polarizer. The backlight assembly may have a light guide plate including light scattering features. The backlight assembly may have a light guide plate that does not include any light scattering features. The backlight assembly may have a wedge-shaped light guide plate. The non-emissive display panel assembly may include a liquid crystal display panel assembly. The light source may include an array of light emitting diodes.

[0007] The display may be summarized as comprising a backlight assembly having a non-emissive display panel assembly, a light guide plate, and a light source providing light to an edge of the light guide plate, a reflective polarizer positioned between the non-emissive display panel assembly and the light guide plate, and a space-varying polarizer positioned between the reflective polarizer and the light guide plate, the space-varying polarizer having a polarization that varies spatially as a function of propagation length away from the light source. The space-varying polarizer may include a multi-twist retarder. The reflective polarizer may include a dual brightness enhancement film (DBEF). The space-varying polarizer may provide no retardation at a proximal end near the light source and a quarter-wave retardation at a distal end opposite the proximal end. The light guide plate may include light scattering features. The light guide plate may not include any light scattering features. The light source may include an array of light emitting diodes. The display may be a display of a head mounted display device, a television, a laptop computer, a smartphone, a tablet computer, a computer monitor, or a wearable electronic device. [Brief description of the drawings]

[0008] In the drawings, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes and angles of various elements are not necessarily drawn to scale, and some of these elements may be arbitrarily enlarged and positioned to improve the legibility of the drawings. Furthermore, the particular shapes of the elements as drawn are not necessarily intended to convey any information regarding the actual shape of the particular elements, but may have been selected solely for ease of recognition in the drawings.

[0009] [Figure 1] A diagram of an example of a head-mounted display device with dual display panels according to one exemplary implementation.

[0010] [Diagram 2] FIG. 1 illustrates an example of a laptop with a display panel according to one exemplary implementation.

[0011] [Diagram 3] FIG. 1 is a diagram of an example of a smartphone with a display panel according to one non-limiting example implementation.

[0012] [Figure 4] FIG. 2 is a cross-sectional view of a display panel including a backlight assembly having a space-varying polarizer according to one non-limiting example implementation.

[0013] [Diagram 5] FIG. 2 is a detailed cross-sectional view of a display panel according to one non-limiting example implementation.

[0014] [Figure 6] 1 is a graph showing an example of phase delay for a space-varying polarizer as a function of propagation length away from a light source according to one non-limiting example implementation.

[0015] [Figure 7] FIG. 1 is a plan view of a space-varying polarizer according to one non-limiting example implementation, showing that the phase retardation for the space-varying polarizer varies as a function of propagation length away from the light source, from no retardation (linear) at the edge close to the light source to a quarter-wave retardation (circular) at the edge distal to the light source. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] In the following description, certain specific details are set forth to provide a thorough understanding of various disclosed implementations. However, those skilled in the art will recognize that these implementations may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, well-known structures associated with computer systems, server computers, and / or communication networks have not been shown or described in detail to avoid unnecessarily obscuring the description of these implementations.

[0017] Unless the context requires otherwise, throughout this specification and the claims which follow, the term "comprising" is synonymous with "including" and is inclusive or open-ended (i.e., does not exclude additional unrecited elements or method actions).

[0018] References throughout this specification to "one implementation" or "an implementation" mean that a particular feature, structure, or characteristic described in connection with that implementation is included in at least one implementation. Thus, the appearances of the phrase "in one implementation" or "in one implementation" in various places throughout this specification are not necessarily all referring to the same implementation. Furthermore, particular features, structures, or characteristics may be combined in any suitable manner in one or more implementations.

[0019] As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. It should also be noted that the term "or" is generally utilized to include "and / or" in its meaning unless the context clearly dictates otherwise.

[0020] The headings and abstract of the disclosure provided herein are for convenience only and do not interpret the scope or meaning of the implementations.

[0021] One or more implementations of the present disclosure are directed to displays for electronic devices such as head mounted display devices, laptop computers, tablet computers, televisions, smartphones, wearable computers, computer monitors, etc. Non-limiting examples of electronic devices that may include such displays are shown in Figures 1-3.

[0022] Liquid crystal displays (LCDs) are a common example of non-emissive displays that require a separate light source, referred to as a backlight unit or assembly. Backlight assemblies provide such displays with uniform and bright light with appropriate color characteristics. Backlight technology has become more important in recent years due to the advent of edge-lit light-emitting diode (LED) backlights, which allow displays to be much thinner than traditional displays while simultaneously reducing power consumption. It is important to make the backlight assembly as efficient as possible to meet energy regulations or other requirements. As discussed further below, the present disclosure improves the performance of backlight assemblies by providing a space-varying polarizer that provides a phase retardation that varies as a function of the propagation length away from the light source of the backlight assembly.

[0023] 1 shows a non-limiting example of an electronic device in the form of a head mounted display device 100, which may be coupled to a video rendering computing system via a wired or wireless connection to provide a virtual reality display to a human user. In operation, a user wears the HMD device 100 on his / her head, secured via one or more straps 101, and receives displayed information of a simulated environment, different from a real physical environment, from the computing system in each eye via displays 102a and 102b supported by a support structure 104 of the HMD device, which functions as an image rendering system that provides images of the simulated environment to the HMD device for display to the user, such as images generated by a game program (not shown) and / or other software programs (not shown) running on the computing system. The user is further able to move around the real physical environment in this example, and may further have one or more I / O ("input / output") devices, such as a handheld controller communicatively coupled to the computing system via a wired or wireless connection, that allow the user to further interact with the simulated environment. As the user moves location and / or changes orientation of HMD device 100, the position of the HMD device may be tracked, for example to enable a corresponding portion of the simulated environment to be displayed to the user on the HMD device, and the controller may further employ similar techniques for use in tracking the position of the controller (and optionally for using that information to assist in determining and / or verifying the position of the HMD device). After the tracked position of HMD device 100 is known, the corresponding information is transmitted to a computing system, which uses this tracked position information to generate one or more subsequent images of the simulated environment for display to the user via displays 102a and 102b.

[0024] 2 shows an example electronic device in the form of a laptop computer 200 having an upper housing 202 and a lower housing 204 coupled together via a hinge 206 that allows the housings to rotate relative to one another. The lower housing 204 includes a keyboard 208 and may include other structures (e.g., a touchpad, various ports). The upper housing 202 includes a display panel 210 that may be used to display content to a user.

[0025] 3 illustrates an example electronic device in the form of a smartphone 300. The smartphone 300 includes a housing 302 that includes a display panel 304 and a number of input components 306 (e.g., buttons). In at least some implementations, the display panel 304 may be, for example, a touchscreen display.

[0026] More generally, the displays of the present disclosure may be implemented in any type of electronic device, such as the devices shown in Figures 1-3 or other devices, including music players, gaming devices, navigation units, vehicle displays, wearable devices, kiosks, or other types of devices that include one or more displays.

[0027] 4 illustrates a cross-sectional side view of an exemplary liquid crystal display (LCD) 400 in accordance with one or more embodiments of the present disclosure. Display 400 may be implemented in any type of electronic device, such as device 100 of FIG. 1, device 200 of FIG. 2, and device 300 of FIG. 3, respectively.

[0028] The display 400 includes multiple stacked layers, each of which may be of a generally similar shape (e.g., rectangular). The display 400 may include a backlight assembly 402 that receives light 403 from a light source 404 positioned substantially adjacent an edge of the backlight assembly 402. The display 400 also includes a display module that includes an LCD panel 406 or other display layers (e.g., any non-emissive display assembly layers), other light processing layers such as optical films 408, and a linear or reflective polarizer 410 (e.g., a dual brightness enhancement film (DBEF)).

[0029] The display 400 also includes an optical retardation layer in the form of a space-varying polarizer (SVP) 412 that varies the phase retardation of the light as a function of propagation length (from left to right as shown in FIG. 4). As discussed further below, the space-varying polarizer 412 functions to increase the efficiency and uniformity of the light source 404 by increasing the amount of light that is passed upward (as shown) to the LCD panel 406.

[0030] If present, the optical film 408 may be formed as part of the backlight assembly 402 or may be formed separately therefrom. The space-varying polarizer 412 may be positioned above the optical film 408 and below the reflective polarizer 410 as shown. In other implementations, the display 400 may include a space-varying polarizer 412 but not a separate linear polarizer 410. It should be understood that the configuration shown in FIG. 4 is merely exemplary and other configurations are contemplated that may include the same layers, fewer or more layers, or different layers arranged differently. As non-limiting examples, the space-varying polarizer 412 may be positioned between one or more optical films 408, between the optical film and the backlight assembly 402, within the backlight assembly 402, etc.

[0031] 5 shows a more detailed cross-sectional view of an example display 500 that may implement features of the present disclosure. Display 500 may be implemented in any type of electronic device, such as device 100 of FIG. 1, device 200 of FIG. 2, and device 300 of FIG. 3, respectively, and may be similar to or identical to display 400 of FIG. 4.

[0032] The display 500 comprises a backlight assembly comprising a light guiding prism or plate (LGP) 502 and a reflector 504 that may be used to generate a backlight 506. In operation, the backlight 506 travels outward (upward as shown) and passes through a display pixel structure in a display layer 507, which illuminates an image generated by the display pixels for viewing by a user 508 in a direction 510. The display layer 507 may be positioned on a plastic or metal structure to form a display module that is attached to a housing of an electronic device. The display layer 507 may form a liquid crystal display panel or may be used to form other types of displays.

[0033] In the illustrated example, the display layer 507 includes a liquid crystal layer 512 positioned between display layers 514 and 516, which may be positioned between a lower polarizing layer 518 and an upper polarizing layer 520. The layers 514 and 516 may be formed from a transparent substrate layer, such as a transparent layer of plastic or glass. The layers 514 and 516 may include, for example, a color filter layer or a thin film transistor layer. Color filter elements, transistors, conductive traces, or other structures may be formed on the substrate of the layers 514 and 516 to form a color filter layer and / or a thin film transistor layer. In at least some implementations, the layers 514 or 516 or other layers may include touch sensor electrodes used to implement touch screen functionality in the display 500. As a non-limiting example, the layer 516 may include a thin film transistor layer including an array of transistors and display pixel electrodes operable to apply an electric field to the liquid crystal layer 512. In this example, layer 514 may be a color filter layer comprising an array of color filter elements that function to provide display 500 with the ability to display color images. In other implementations, layer 514 may be a thin film transistor layer and layer 516 may be a color filter layer.

[0034] During operation of the display 500, control circuitry 522, operably coupled to layer 516, which in this example includes a thin film transistor layer, may be used to generate information to be displayed on the display. The control circuitry 522 may include various circuits and components, such as display driver circuitry, flexible circuit boards, various conductive traces and couplings, etc., that drive the transistors of layer 516.

[0035] The backlight assembly may include a light-guide prism or plate 502, which may be formed from a transparent material such as glass or plastic. The light-guide prism 502 may be rectangular in shape or may have a wedge shape that is thicker toward the light source 524 and tapers away from the light source. In operation, the light source 524 generates light 526 that is directed toward the edge of the light-guide prism 502. The light source 524 may be any suitable light source, such as an array of light emitting diodes (LEDs) positioned along the edge of the light-guide prism to couple light into the light-guide prism.

[0036] Light 526 emitted from the light source 524 may be coupled into an edge surface of the light-guiding prism 502 and may be dispersed throughout the prism via total internal reflection. In at least some implementations, the light-guiding prism 502 may include light scattering features 528, which may be referred to as dots, pits, or bumps, for example. The light scattering features 528 may be located on an upper or lower surface of the light-guiding prism 502.

[0037] In other implementations, the light-guiding prism 502 may not include any light-scattering features 528, which may allow for more efficient use of the light source 524, since light-scattering features would reduce efficiency and cause loss of polarization control. In such implementations, the light 526 may be provided to the light-guiding prism 502 at a relatively wide angle (e.g., ±40 degrees, ±20 degrees), and the space-varying polarizer 532 may be adjusted to provide uniform backlighting across the length of the display 500, as discussed further below.

[0038] Light 526 scattered upward (as shown) from the light-guiding prism 502 may serve as a backlight 506 for the display 500. Light 526 scattered downward may be reflected back in the upward direction by the reflector 504, which may be formed from any suitable reflective material, such as white plastic or other reflective material.

[0039] To improve the performance of the backlight assembly, implementations of the present disclosure include one or more of an optical film 530, a space-varying polarizer 532, or a reflective polarizer 534 (eg, DBEF).

[0040] The optical film layer 530 may include one or more diffusive layers (e.g., diffusion films) to reduce hot spots, compensation films to enhance off-axis viewing, or other types of films (e.g., prism films to collimate the backlight 506).

[0041] The space-varying polarizer 532 may be positioned between the reflective polarizer 534 and the optical film 530. More generally, the space-varying polarizer 532 may be positioned anywhere between the reflective polarizer 534 and the light-guiding prism 502.

[0042] In at least some implementations, the display 500 includes a space-varying polarizer 532 and no linear reflective polarizer 534. In such implementations, the space-varying polarizer 532 may be adjusted to selectively allow light to travel therethrough such that the light is uniformly transmitted without significant loss. For example, the space-varying polarizer may provide linear polarization at a proximal end that gradually changes retardation to provide circular polarization (e.g., λ / 4 retardation) at a distal end.

[0043] The space-varying polarizer 532 may comprise a wave retarder formed from a birefringent material. Birefringence is a property of a material that has a refractive index that depends on the polarization and the direction of propagation of light. The wave retarder alters the polarization state or phase of light traveling through it. The wave retarder may have a slow axis (or extraordinary axis) and a fast axis (ordinary axis). When polarized light travels through the wave retarder, light along the fast axis travels more quickly than light along the slow axis.

[0044] As discussed above, the space-varying polarizer 532 may provide a phase delay that varies as a function of propagation length (L) from the light source 524, e.g., from left to right as shown in FIG. 5, allowing for a more uniform and efficient distribution of light from the light-guiding prism 502 to the display layer 507. FIG. 6 is a graph 600 illustrating a non-limiting example of phase delay as a function of propagation length for a space-varying polarizer of the present disclosure, such as the space-varying polarizer 412 of FIG. 4 and the space-varying polarizer 532 of FIG. 5, respectively. In this example, the space-varying polarizer provides no delay at a proximal end near the light source (e.g., light source 524) and linearly increases the delay to provide a λ / 4 delay at the distal end of the space-varying polarizer that is furthest from the light source. Specifically, in the illustrated example, the retardation of the space-varying polarizer is 0λ at ​​0L, (1 / 16)λ at (1 / 4)L, (1 / 8)λ at (1 / 2)L, (3 / 16)λ at (3 / 4)L, and (1 / 4)λ at L. Figure 7 shows a top view 700 of the space-varying polarizer 532 and illustrates that the phase retardation for the space-varying polarizer varies as a function of propagation length away from the light source 524, from no retardation (linear) at the left edge (as shown) close to the light source to a quarter wave retardation (circular) at the right edge distal to the light source.

[0045] Although the illustrated example shows a space-varying polarizer having a linearly increasing retardation that varies from 0 to λ / 4, it should be understood that numerous other configurations may be provided. In general, the space-varying polarizer may provide a retardation that varies in any manner as a function of propagation length away from the light source, and the amount of retardation may be any value (e.g., λ / 20, λ / 10, λ / 4, λ, 2λ). Furthermore, the amount of retardation may only increase, only decrease, or both increase and decrease. The amount of retardation may vary continuously or in multiple steps. The amount of retardation may vary according to any type of function, including, for example, a linear function, a polynomial function, an exponential function, a step function, other types of functions, or combinations thereof.

[0046] In at least some implementations, the space-varying polarizer may be formed from a multi-twist retarder (MTR), which is a waveplate-like retardation film that provides precise and customized levels of broadband, narrowband, or multiband retardation in a single thin film. More specifically, an MTR comprises two or more twisted liquid crystal (LC) layers on a single substrate and with a single alignment layer. Subsequent LC layers are directly aligned by the previous layer, allowing for simple fabrication and achieving automatic layer alignment, resulting in a monolithic film with a continuously varying optical axis.

[0047] 5, in at least some implementations, control circuitry 522 may be operatively coupled to space-varying polarizer 532 to selectively vary the space-dependent phase retardation of the space-varying polarizer to any desired configuration. In such implementations, display 500 may include additional layers, such as one or more additional thin film transistor layers, that allow for selective control of the space-dependent phase retardation of space-varying polarizer 532. Control circuitry 522 may control the phase retardation at any desired rate, such as, for example, one-time only, periodically, at a rate equal to or a fraction of the frame rate of display 500, etc.

[0048] The foregoing detailed description has described various implementations of devices and / or processes through the use of block diagrams, schematics, and examples. To the extent that such block diagrams, schematics, and examples include one or more functions and / or operations, those skilled in the art will appreciate that each function and / or operation within such block diagrams, flow charts, or examples may be individually and / or collectively implemented by a wide range of hardware, software, firmware, or virtually any combination thereof. In one implementation, the subject matter may be implemented via application specific integrated circuits (ASICs). However, those skilled in the art will recognize that the implementations disclosed herein can equivalently be implemented in whole or in part in standard integrated circuits, as one or more computer programs running on one or more computers (e.g., as one or more programs running on one or more computer systems), as one or more programs running on one or more controllers (e.g., microcontrollers), as one or more programs running on one or more processors (e.g., microprocessors), as firmware, or virtually any combination thereof, and that designing the circuits and / or writing the software and / or firmware code is well within the skills of those of ordinary skill in the art in light of the present disclosure.

[0049] Those skilled in the art will recognize that many of the methods or algorithms described herein may utilize additional operations, omit certain operations, and / or perform operations in an order other than that specified.

[0050] Additionally, those skilled in the art will appreciate that the mechanisms taught herein can be distributed as a program product in a variety of forms, and that the exemplary implementations apply equally regardless of the particular type of signal-bearing medium used to actually effect the distribution, including, but not limited to, the following: floppy disks, hard disk drives, CD-ROMs, digital tape, and recordable types of media such as computer memory.

[0051] The various implementations described above can be combined to provide further implementations. These and other modifications can be made to the implementations in light of the above detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific implementations disclosed in the specification and claims, but should be construed to include all possible implementations along with the full scope of equivalents to which such claims are entitled. Thus, the claims are not limited by this disclosure. (Other possible items) [Item 1] a non-emissive display panel assembly; a backlight assembly having a light source; a space-varying polarizer positioned between the non-emissive display panel assembly and the backlight assembly, the space-varying polarizer having a polarization that varies spatially as a function of propagation length away from the light source; A display comprising: [Item 2] Item 2. The display of item 1, wherein the spatially varying polarizer comprises a multi-twist retarder. [Item 3] 2. The display of claim 1, wherein the spatially varying polarizer provides no retardation at a proximal end near the light source and a quarter wave retardation at a distal end opposite the proximal end. [Item 4] 2. The display of claim 1, wherein the retardation of the spatially varying polarizer varies linearly or nonlinearly between a proximal end near the light source and a distal end opposite the proximal end. [Item 5] Item 10. The display of item 1, further comprising a linear polarizer positioned between the space-varying polarizer and the non-emissive display panel assembly. [Item 6] 6. The display of item 5, wherein the linear polarizer comprises a dual brightness enhancement film (DBEF). [Item 7] 2. The display of claim 1, further comprising a control circuit operably coupled to the spatially varying polarizer, the control circuit operable to selectively adjust the retardation provided by the spatially varying polarizer. [Item 8] Item 2. The display of item 1, wherein the backlight assembly has a light guide plate including light scattering features. [Item 9] Item 2. The display of item 1, wherein the backlight assembly has a light guide plate that does not include any light scattering features. [Item 10] Item 2. The display of item 1, wherein the backlight assembly has a wedge-shaped light guide plate. [Item 11] Item 2. The display of item 1, wherein the non-emissive display panel assembly comprises a liquid crystal display panel assembly. [Item 12] 12. The display of any one of the preceding claims, wherein the light source comprises an array of light emitting diodes. [Item 13] a non-emissive display panel assembly; a backlight assembly having a light guide plate and a light source providing light to an edge of the light guide plate; a reflective polarizer positioned between the non-emissive display panel assembly and the light guide plate; a space-varying polarizer positioned between the reflective polarizer and the light guide plate, the space-varying polarizer having a polarization that varies spatially as a function of propagation length away from the light source; A display comprising: [Item 14] Item 14. The display of item 13, wherein the spatially varying polarizer comprises a multi-twist retarder. [Item 15] Item 14. The display of item 13, wherein the reflective polarizer comprises a dual brightness enhancement film (DBEF). [Item 16] Item 14. The display of item 13, wherein the spatially varying polarizer provides no retardation at a proximal end near the light source and a quarter wave retardation at a distal end opposite the proximal end. [Item 17] Item 14. The display of item 13, wherein the light guiding plate includes light scattering features. [Item 18] Item 14. The display of item 13, wherein the light guiding plate does not include any light scattering features. [Item 19] Item 14. The display of item 13, wherein the light source comprises an array of light emitting diodes. [Item 20] 20. The display of any one of items 13 to 19, wherein the display is a display of a head mounted display device, a television, a laptop computer, a smartphone, a tablet computer, a computer monitor, or a wearable electronic device.

Claims

1. A first display and a second display, each of the first display and the second display comprising: a non-emissive display panel assembly; a backlight assembly having a light source; a space-varying polarizer positioned between the non-emissive display panel assembly and the backlight assembly, the space-varying polarizer causing polarization to vary spatially as a function of propagation length away from the light source; A head-mounted display device comprising:

2. The head mounted display device of claim 1 , wherein the spatially varying polarizer comprises a multi-twist retarder.

3. 3. A head mounted display device as described in claim 1 or 2, wherein the space-varying polarizer provides no retardation at a proximal end near the light source and a quarter wave retardation at a distal end opposite the proximal end.

4. A head mounted display device as described in any one of claims 1 to 3, wherein the retardation of the spatially varying polarizer varies linearly or nonlinearly between a proximal end near the light source and a distal end opposite the proximal end.

5. 5. A head mounted display device as described in any one of claims 1 to 4, wherein each of the first display and the second display further includes a linear polarizer positioned between the space varying polarizer and the non-emissive display panel assembly.

6. 6. The head mounted display device of claim 5, wherein the linear polarizer comprises a dual brightness enhancement film (DBEF).

7. 7. A head mounted display device as described in any one of claims 1 to 6, wherein each of the first display and the second display further includes a control circuit operably coupled to the space varying polarizer, the control circuit operable to selectively adjust the delay provided by the space varying polarizer.

8. 8. A head mounted display device as claimed in claim 1, wherein the backlight assembly comprises a light guide plate including light scattering features.

9. 8. The head mounted display device of claim 1, wherein the backlight assembly has a light guide plate that does not include any light scattering features.

10. 10. A head mounted display device as claimed in claim 1, wherein the backlight assembly comprises a wedge-shaped light guide plate.

11. 11. The head mounted display device of claim 1, wherein the non-emissive display panel assembly comprises a liquid crystal display panel assembly.

12. A head mounted display device as claimed in claim 1 , wherein the light source comprises an array of light emitting diodes.

13. the amount of retardation of the space-varying polarizer only increases as a function of propagation length away from the light source; A head mounted display device according to any one of claims 1 to 3.

14. the amount of retardation of the spatially varying polarizer varies as a function of propagation length away from the light source according to at least one of a linear function, a polynomial function, an exponential function, or a step function; A head mounted display device according to any one of claims 1 to 3.

15. A first display and a second display, each of the first display and the second display comprising: a non-emissive display panel assembly; a backlight assembly having a light guide plate and a light source providing light to an edge of the light guide plate; a reflective polarizer positioned between the non-emissive display panel assembly and the light guide plate; a space-varying polarizer positioned between the reflective polarizer and the light guide plate, the space-varying polarizer causing polarization to vary spatially as a function of propagation length away from the light source; A head-mounted display device comprising:

16. The head mounted display device of claim 15 , wherein the spatially varying polarizer comprises a multi-twist retarder.

17. 17. A head mounted display device as claimed in claim 15 or 16, wherein the reflective polariser comprises a dual brightness enhancement film (DBEF).

18. 18. A head mounted display device as described in any one of claims 15 to 17, wherein the spatially varying polarizer provides no retardation at a proximal end near the light source and a quarter wavelength retardation at a distal end opposite the proximal end.

19. 19. A head mounted display device as claimed in any one of claims 15 to 18, wherein the light guide plate includes light scattering features.

20. 19. A head mounted display device as claimed in any one of claims 15 to 18, wherein the light guide plate does not include any light scattering features.

21. 21. A head mounted display device as claimed in any one of claims 15 to 20, wherein the light source comprises an array of light emitting diodes.

22. the amount of retardation of the space-varying polarizer only increases or decreases as a function of propagation length away from the light source; A head mounted display device according to any one of claims 15 to 17.

23. the amount of retardation of the space-varying polarizer both increases and decreases as a function of propagation length away from the light source; 22. A head mounted display device according to any one of claims 15 to 21.

24. the amount of retardation of the spatially varying polarizer varies as a function of propagation length away from the light source according to at least one of a linear function, a polynomial function, an exponential function, or a step function; 22. A head mounted display device according to any one of claims 15 to 21.

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