Head-Mounted Display (HMD) with Spatially Varying Retarder Optical System

Abstract

Head-mounted displays, or other near-to-eye displays, incorporate optical systems that include spatially varying retarders (SVRs). The SVRs can be manufactured with correction factors applied to them to compensate for one or more manufacturing errors present in molded lenses and / or polarizing beam splitters included in the system's optical system.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This is a PCT application which claims priority to U.S. patent application Ser. No. 16 / 692,823, entitled "HEAD-MOUNTED DISPLAY (HMD) WITH SPATIALLY-VARYING RETARDER OPTICS," filed November 22, 2019, which claims priority under 35 U.S.C. § 120 as a continuation-in-part of pending U.S. patent application Ser. No. 16 / 101,333, entitled "HEAD-MOUNTED DISPLAY (HMD) WITH SPATIALLY-VARYING RETARDER OPTICS," filed August 10, 2018, now U.S. Patent No. 10,778,963, all of which are incorporated herein by reference in their entireties. [Background technology]

[0002] Near-eye display technology can be used to present information and images to a user as part of a virtual reality ("VR") or augmented reality ("AR") system. Such near-eye displays can be incorporated into a head-mounted display ("HMD") device or headset. While these near-eye information displays can be oriented as direct-view, in many cases the information displays are combined with one or more lenses in the HMD. The lens system can include a lens, various optical elements, an aperture stop, and a lens housing for housing various components optically aligned with one another. While such lenses can enhance the VR or AR experience, the performance of the lens system depends in part on the design of each of the elements of the system, as well as the overall design of the system that defines the optical interactions between the elements.

[0003] Conventional information displays, such as liquid crystal displays, typically emit light over a wide cone or field of view. The angular divergence of these conventional displays can range over more than 160 degrees and even approach 180 degrees. When viewed directly, this angularly wide light may not cause undesirable effects. However, when a conventional information display is used in an HMD, such as in a VR or AR system, the angularly wide emission can lead to undesirable results. This is the case when the light emitted by the information display strikes the lens of the HMD at an angle of incidence that exceeds the imaging capability of the lens. Such light is not properly imaged into the user's eye, at least in part, due to the fact that off-axis light presents a polarization that is somewhat elliptical. That is, while on-axis light is linearly polarized, off-axis light presents some degree of elliptical polarization. Thus, light at angles that exceed the focusing capability of the lens of the HMD can result in undesirable visual effects such as flood lighting, ghosting, glare, scattering, and other stray light effects. This non-imaged stray light can result in users of VR or AR headsets experiencing undesirable visual artifacts. [Brief description of the drawings]

[0004] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The detailed description is described with reference to the accompanying drawings, in which the leftmost digit(s) of a reference number identifies the figure in which the reference number first appears. The same reference numbers in different figures indicate similar or identical items.

[0005] [Figure 1] FIG. 1 is a schematic diagram showing a user and a wearable device in which the techniques and configurations described herein may be implemented.

[0006] [Diagram 2] FIG. 2 is a schematic cross-sectional view of a portion of an exemplary wearable device positioned relative to a user's eye.

[0007] [Diagram 3]1 is a schematic cross-sectional view of a system including a display and an optical subsystem including a spatially varying retarder (SVR) according to some embodiments.

[0008] [Figure 4] 1 is a schematic cross-sectional view of a system including a display and an optical subsystem including a spatially varying retarder (SVR) according to some embodiments.

[0009] [Diagram 5] 1 is a schematic cross-sectional view of a system including a display and an optical subsystem including a spatially varying retarder (SVR) according to some embodiments.

[0010] [Figure 6] 1 is a schematic diagram of an exemplary spatially varying retarder (SVR) in accordance with some embodiments.

[0011] [Figure 7] 1 is a schematic cross-sectional view of a system including a display and an optical subsystem including a spatially varying retarder (SVR) according to some embodiments.

[0012] [Figure 8] 1 is a flow diagram illustrating a process for providing a focused image to an eye of a user of a display device, according to some exemplary embodiments.

[0013] [Figure 9] 1 is a flow diagram illustrating a process for applying correction factors during manufacturing of a spatially varying retarder (SVR) to compensate for known or determined manufacturing errors in molded lenses and / or polarizing beam splitters. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] In various embodiments described herein, techniques and architectures can be used to generate images focused on the eye (s) of a user of a wearable device. Examples of wearable devices include display devices worn on the user's head or as part of a helmet, such as a head-mounted display ("HMD") device or headset, and may include position and / or motion sensors to measure the inertial position or orientation of the wearable device. The display device may include a display in front of one eye, each eye, or both eyes. Display devices may include liquid crystal displays (LCDs), organic light-emitting diodes (OLEDs), liquid crystal on silicon (LCOS), or cathode ray tubes (CRTs), just to name a few. The wearable device may display computer-generated images, referred to as virtual images. For example, a processor of the wearable device may render and display a synthetic (virtual) scene, as described below, such that a viewer (the wearer of the wearable device) perceives the scene as reality (or augmented reality).

[0015] In some embodiments, an LCD display device comprises several components. Two of the components are a display matrix, which blocks light in a granular or pixelated manner to create an image, and a light source or backlight. The light source is usually positioned behind the display matrix and illuminates the image. For color displays, the backlight usually emits a broad spectrum of light, e.g., white light.

[0016] Near-eye display technology may be used to present information and images to a user as part of a virtual reality ("VR") or augmented reality ("AR") system, which may be in the form of a wearable device such as those introduced above. A VR or AR HMD may use one or more lenses to direct light associated with images displayed on one or more information displays (e.g., pixelated LCD display devices) to the user's eyes. Among other things, lenses are used to bend light from an information display to make the information display appear to the user to be farther away than it actually is. This provides the user with a greater depth of field in the virtual environment, allowing the user to more easily focus on the displayed image. Lenses may also be used within a VR or AR headset to increase the field of view of the information display relative to the user. A wider field of view may increase the immersive effect of the VR or AR system. Lenses may furthermore be used within a VR or AR headset to shape light from a single display such that the light received by the user is separately adjusted for the user's left and right eyes. The use of images separately adjusted for each eye may allow the user to perceive, for example, a stereoscopic or three-dimensional image. The lenses are further designed with the constraints of a near-eye environment, where the user's eyes are relatively close to the information display.

[0017] In various embodiments, the optical system of the wearable device incorporates a spatially varying retarder (SVR). In particular, the system, which also includes an information display, enables near-to-eye applications that involve focusing an image onto a user's eye relatively close to the information display. The SVR is used to modify the phase of light (of the image generated by the information display) by different amounts for different parts of the SVR. Thus, the SVR provides an appropriate level of phase difference for various angles of incidence, which reduces undesirable visual effects such as flood lighting, ghosting, glare, scattering, and other stray light effects present in conventional optical system designs. Such phase modification by the SVR works in concert with various optical elements in the optical system, as described below.

[0018] Also described herein are spatially varying retarders (SVRs), which may be manufactured using correction factors to correct for manufacturing errors that may occur within components of the systems described herein. One exemplary manufacturing error that may be corrected during the fabrication of the SVRs described herein is stress birefringence in a molded lens, which may be a by-product of molding the lens during fabrication. Another exemplary manufacturing error that may be corrected during the fabrication of the SVRs described herein is polarization variation across a polarizing beam splitter (sometimes referred to herein as a "reflective polarizer" or "reflective film"). In an exemplary process, an extent of manufacturing error in at least one of the molded lens or the polarizing beam splitter may be determined. Based at least in part on the extent of the manufacturing error, a correction factor for the spatially varying retarder (SVR) may be determined. The SVR may then be formed by applying a correction factor during fabrication of the SVR to compensate for (or correct for) the manufacturing error. Also described herein are systems including SVRs manufactured using correction factors to compensate for manufacturing errors in at least one of the molded lens or the polarizing beam splitter, as described herein. When this correction factor is applied during the fabrication of the SVR, the overall performance of the optical system may be improved, for example, an optical subsystem including an SVR may further mitigate undesirable visual effects that may be caused by manufacturing defects in other component parts of the optical subsystem.

[0019] Those skilled in the art will recognize that the following description is illustrative only and is in no way limiting. Other embodiments will readily suggest themselves to those skilled in the art having the benefit of this disclosure. Reference will now be made in detail to specific implementations as illustrated in the accompanying drawings. The same reference numerals are used throughout the drawings and the following description to refer to the same or similar parts.

[0020] 1 is a schematic diagram showing a user 102 and a wearable device 104, according to some embodiments. A computing device associated with the wearable device 104 may provide rendering data associated with individual virtual content items to the wearable device 104, causing the individual virtual content items to be presented on a display associated with the wearable device 104. The rendering data may include instructions for rendering a graphical representation of the virtual content items via the device's display. For example, the rendering data may include instructions describing the geometry, perspective, textures, lighting, shading, etc. associated with the virtual content items. In an illustrative example, the virtual content items may be presented on the display of the wearable device 104 as part of a game that the user 102 may play using the wearable device 104.

[0021] In some examples, the computing device may be located remotely from the wearable device 104 within a network, such as the Internet. In other embodiments, the computing device may be collocated with the wearable device 104 (e.g., embedded within the wearable device 104). Additionally, the wearable device 104 may be communicatively coupled to the network in any manner, such as by a global or local wired or wireless connection (e.g., a local area network (LAN), an intranet, Bluetooth, etc.). The network may facilitate communication between the computing device and the wearable device 104 associated with one or more users, such as user 102.

[0022] 2 is a schematic cross-sectional view of a portion 202 of a wearable device 204 positioned relative to a user's eye 206. For example, the wearable device 204 may be the same as or similar to the wearable device 104. In certain embodiments, the wearable device 204 may be configured to display images seen by both the left and right eyes of the user. This may be accomplished using separate left and right LCD displays, or may be accomplished using a single LCD display. Similarly, the wearable device 204 (e.g., in the form of a VR or AR headset) may include a single lens assembly or may use individual left and right lens assemblies.

[0023] Exemplary light rays 208 and 210 illustrate possible light paths from the wearable device 204 to the cornea 212 of the eye 206. The cornea 212 may be treated as having a substantially spherical shape. The wearable device 204 may include a near-to-eye display such that the paths of the light rays 208 and 210 are relatively short, for example to provide an eye relief of about 20 millimeters. In this case, the optics of the wearable device 204 are configured to focus light onto a surface (e.g., the cornea 212) that is relatively close to the wearable device. Such a configuration may involve a pancake optical system having a relatively thin profile that allows the pancake optical system to fit within the wearable device 204 while allowing physical clearance from the user's eye 206.

[0024] 3 is a schematic cross-sectional view of a system 300 including a display and an optical subsystem including a spatially varying retarder (SVR) according to some embodiments. The system 300 may be incorporated into a head-mountable device, such as a wearable device 104 / 204. However, it should be understood that the system 300 may be incorporated into other types of devices, including, but not limited to, cameras, binoculars, office equipment, scientific equipment, and the like. The system 300 may include a pixelated display device 302, sometimes referred to as an information display 302, a backlight assembly 304, and an optical subsystem 306. A schematic diagram of a user's eye 308 is also illustrated. Such elements are aligned along an optical axis 310.

[0025] The light-emitting backlight assembly 304 may include light sources such as one or more light-emitting diodes (LEDs), one or more OLEDs, one or more cold cathode fluorescent lamps (CCFLs), one or more lasers, one or more quantum dots, or any combination of these exemplary light sources. The light sources in the backlight assembly 304 may emit light across a broad spectrum (e.g., white light) such that the information display 302 can generate color images across the visible spectrum. The backlight assembly 304 may emit light uniformly across its entire front surface, for example, over a range of about 160-180 degrees.

[0026] The information display 302, in conjunction with the backlight assembly 304, may emit light (light approximately parallel to the face of the backlight assembly 304) over an angle range of up to approximately 180 degrees. This range of emission angles may also be referred to as the field of view of the backlight assembly 304, or the light cone of the backlight assembly 304. In some embodiments, the information display 302 may be an LCD matrix including one or more polarizing layers, liquid crystal layers, and thin film transistor layers. The LCD matrix creates images by obscuring portions of the backlight in a pixelated fashion. When light 312 is emitted from the backlight assembly 304 and passes through the information display 302 (e.g., the LCD matrix), an image is displayed. For clarity, FIG. 3 shows a separation between the backlight assembly 304 and the information display 302. However, these two components may be sandwiched together with little, if any, space between them.

[0027] The optical subsystem 306 may include a lens assembly for directing light from the information display 302 toward the user's eye 308. The optical subsystem 306 may have, for example, a pancake configuration. In this case, the optical subsystem 306 may include an assembly of optical elements configured to direct light from the information display 302 toward the user's eye 308 using on-axis optical folding based at least in part on the polarization of the light, as described below. In some embodiments, the lens assembly of the optical subsystem 306 includes various optical elements other than lenses. For example, the optical subsystem 306 may include at least one polarizing beam splitter 338 and a spatially varying retarder (SVR) 316. The polarizing beam splitter 338 may be located between the SVR 316 and the exit face (or side) 314 of the optical subsystem 306. The SVR 316 is configured to change the phase of light passing through the SVR 316 by different amounts for different portions of the SVR 316. For example, light emitted from the periphery of the display toward the user's eyes may enter the optical subsystem 306 at a relatively large angle of incidence. The SVR 316, when configured to vary the degree of phase modification across the SVR 316, may provide an appropriate level of phase difference for light from all angles to mitigate undesirable visual effects (e.g., eliminate undesirable stray light from reaching the user's eyes 308).

[0028] Polarizing beam splitter 338 may represent a beam splitter that passes only linearly polarized light, thereby reflecting all other light that is not linearly polarized. Polarizing beam splitter 338 may be considered a linear polarizer reflector, or a reflective linear polarizer. That is, polarizing beam splitter 338 may combine the functionality of a linear polarizer and a beam splitter in a single element.

[0029] In some embodiments, the polarizing beam splitter 338 may be replaced with a partially reflective mirror (e.g., a 50 / 50 mirror). That is, according to some embodiments, the optical subsystem 306 may include at least one partially reflective mirror located between the SVR 316 and the output face (or side) 314 of the optical subsystem 306 (e.g., the partially reflective mirror may be at the position of reference number 338 in FIG. 3).

[0030] 3 illustrates an exemplary optical path 318 of light for an image produced by information display 302. For simplicity, optical subsystem 306 is illustrated generally as including at least one lens-shaped element. However, optical subsystem 306 may include any of several types of optical elements that need not be lenses. Specific examples of optical subsystem 306 are now described.

[0031] The optical subsystem 306 may include a first quarter-wave plate 326 having a front surface 322 and a back surface 324. The front surface 322 may be considered an entrance side of the optical subsystem 306 (e.g., a lens assembly) where light enters the optical subsystem 306. The front surface 322 of the first quarter-wave plate 326 may be disposed on the information display 302. As used herein, "disposed on" may mean "in contact" or "adjacent" such that there may be a space between a layer disposed on another layer. Thus, the first quarter-wave plate 326 may be in contact with the information display 302 or may be spaced a distance away from the information display 302, but is interposed between the information display and the lens 330. It should also be understood that "disposed on" may mean directly disposed on or indirectly disposed on (e.g., with one or more intermediate layers). The lens 330 may be interposed between the first quarter-wave plate 326 and the SVR 316. The SVR 316 may be disposed on a polarizing beam splitter 338 (or, alternatively, the SVR 316 may be disposed on a partially reflecting mirror at reference number 338 in FIG. 3).

[0032] In one example, the SVR 316 can be part of a second quarter-wave plate. In this aspect, the second quarter-wave plate (interposed between the lens 330 and the polarizing beam splitter 338 (or a partially reflective mirror)) can include a material, feature, or another suitable mechanism that changes the phase of light passing through the SVR 316 by different amounts for different portions of the SVR 316. Although the SVR 316 is shown and described in FIG. 3 as being interposed between the lens 330 and the polarizing beam splitter 338 (or a partially reflective mirror), it should be understood that, alternatively, the SVR 316 can be part of the first quarter-wave plate 326 instead. In this alternative embodiment, the SVR 316 shown in FIG. 3 can be replaced with a standard quarter-wave plate (i.e., a quarter-wave plate without an SVR). That is, the optical subsystem 306 may include two quarter wave plates (one at position 326 and one at position 316) and the SVR may be part of either of the two quarter wave plates. In some embodiments, when the optical subsystem 306 includes two quarter wave plates (one at position 326 and one at position 316), the SVR may be part of both quarter wave plates.

[0033] To illustrate the principle of operation of the optical subsystem 306, light path 318 enters the first quarter-wave plate 326 polarized (e.g., linearly polarized in one orientation p) at the front surface 322 of the first quarter-wave plate 326. The light exiting the back surface 324 of the first quarter-wave plate 326 may be circularly polarized. This light passes through lens 330. The light emerging from lens 330 then passes through SVR 316 and is reflected off a polarizing beam splitter 338 (or alternatively, the light passing through SVR 316 is reflected off a partially reflecting mirror at 338 in FIG. 3). This reflected light passes through SVR 316 in the opposite direction, causing the light to change its handedness while remaining circularly polarized and oriented at 45 degrees. The light that passes through the SVR 316 in the reverse direction is again reflected by lens 330, causing the light to make a third pass through the SVR 316 in the forward direction (i.e., toward the user's eye 308). This reflected light passes through a polarizing beam splitter 338 (or, alternatively, the light passes through a partially reflective mirror located at 338 in FIG. 3) and emerges from the output side (or face) 314 of the optical subsystem 306.

[0034] The SVR 316 alters the phase of light passing through the SVR 316 with an appropriate level of phase difference as a function of the location on the SVR 316 where the incoming light enters the SVR 316. In this embodiment, the light emerging from the SVR 316 is horizontally polarized. Because the polarizing beam splitter 338 allows horizontally polarized light to pass toward the user's eye 308 and blocks otherwise vertically polarized light, the SVR 316 performs a late stage phase change to allow the light to pass through the polarizing beam splitter 338. In the example of FIG. 3, the exemplary light path 318 is off-axis, so that the light path 318 entering the SVR 316 is elliptically polarized, and the location on the SVR 316 where the light path 318 enters the SVR 316 includes materials (e.g., birefringent materials) and / or features that alter the phase of the light by an appropriate amount to cause the incoming elliptically polarized light to appear as horizontally polarized light. This can be contrasted with an on-axis light path (not shown) that enters the optical subsystem 306 at an angle of incidence equal to zero. Such an on-axis light path will not have its polarization state altered by the SVR 316 because the amount that the phase is altered varies across the area of ​​the SVR 316, with little or no phase change at the center of the SVR 316. However, for incident light that is further off-axis, the SVR 316 is configured to alter the phase of that off-axis incoming light by an appropriate amount as a function of the angle of incidence, and therefore the position on the SVR 316. Although the example illustrates that the polarizing beam splitter 338 allows horizontally polarized light to pass toward the user's eye 308 and reflects all other light that is not otherwise horizontally polarized, it should be understood that the polarizing beam splitter 338 may allow vertically polarized light to pass toward the user's eye 308 and reflect all other light that is not otherwise vertically polarized.

[0035] 4 is a schematic cross-sectional view of a system 400 including a display and an optical subsystem including a spatially varying retarder (SVR) according to some embodiments. The system 400 may be incorporated into a head-mountable device, such as a wearable device 104 / 204. However, it should be understood that the system 400 may be incorporated into other types of devices, including, but not limited to, cameras, binoculars, office equipment, scientific equipment, and the like. The system 400 may include a pixelated display device 402, sometimes referred to as an information display 402, a backlight assembly 404, and an optical subsystem 406. A schematic diagram of a user's eye 408 is also illustrated. Such elements are aligned along an optical axis 410.

[0036] The light-emitting backlight assembly 404 may include light sources such as one or more light-emitting diodes (LEDs), one or more OLEDs, one or more cold cathode fluorescent lamps (CCFLs), one or more lasers, one or more quantum dots, or any combination of these exemplary light sources. The light sources in the backlight assembly 404 may emit light across a broad spectrum (e.g., white light) such that the information display 402 can generate color images across the visible spectrum. The backlight assembly 404 may emit light uniformly across its entire front surface, for example, over a range of about 160-180 degrees.

[0037] The information display 402, in conjunction with the backlight assembly 404, may emit light (light approximately parallel to the face of the backlight assembly 404) over an angle range of up to approximately 180 degrees. This range of emission angles may also be referred to as the field of view of the backlight assembly 404, or the light cone of the backlight assembly 404. In some embodiments, the information display 402 may be an LCD matrix including one or more polarizing layers, liquid crystal layers, and thin film transistor layers. The LCD matrix creates images by obscuring portions of the backlight in a pixelated fashion. When light 412 is emitted from the backlight assembly 404 and passes through the information display 402 (e.g., the LCD matrix), an image is displayed. For clarity, FIG. 4 shows a separation between the backlight assembly 404 and the information display 402. However, these two components may be sandwiched together with little, if any, space between them.

[0038] The optical subsystem 406 may include a lens assembly for directing light from the information display 402 toward the user's eye 408. The optical subsystem 406 may have, for example, a pancake configuration. In this case, the optical subsystem 406 may include an assembly of optical elements configured to direct light from the information display 402 toward the user's eye 408 using on-axis optical folding based at least in part on the polarization of the light, as described below. In some embodiments, the lens assembly of the optical subsystem 406 includes various optical elements other than lenses. For example, the optical subsystem 406 may include at least one linear polarizer 438 and a spatially varying retarder (SVR) 416. The linear polarizer 438 may be located between the SVR 416 and the exit face 414 of the optical subsystem 406. The SVR 416 is configured to change the phase of light passing through the SVR 416 by different amounts for different portions of the SVR 416. For example, light emitted from the periphery of the display toward the user's eyes may enter the optical subsystem 406 at a relatively large angle of incidence. The SVR 416, when configured to vary the degree of phase modification across the SVR 416, may provide an appropriate level of phase difference for light from all angles to mitigate undesirable visual effects (e.g., eliminate undesirable stray light from reaching the user's eyes 408).

[0039] 4 illustrates an exemplary optical path 418 of light for an image produced by information display 402. For simplicity, optical subsystem 406 is illustrated generally as including at least one lens-shaped element. However, optical subsystem 406 may include any of several types of optical elements that need not be lenses. Specific examples of optical subsystem 406 are now described.

[0040] The optical subsystem 406 may include a reflective and refractive element 430 (sometimes referred to as “element 430”). The reflective and refractive element 430 may include a 50 / 50 mirror that allows approximately 50 percent of the incoming light to pass through the element 430 while approximately 50 percent of the incoming light is reflected away by the element 430. The optical subsystem 406 may further include a first quarter-wave plate 426 having a front surface 422 and a back surface 424. The first quarter-wave plate 426 may be disposed on a beam splitter 436 having a front surface adjacent the back surface 424 of the first quarter-wave plate 426 and a back surface 428. The beam splitter 436 may be disposed on the SVR 416. The SVR 416 may be disposed on a linear polarizer 438. It should be understood that "disposed on" can mean directly disposed on or indirectly disposed on (e.g., with one or more intermediate layers). In addition, it should be understood that "disposed on" can mean "in contact with" or "adjacent" such that there may be a space between a layer disposed on another layer.

[0041] In one example, the SVR 416 can be part of a second quarter wave plate. In this aspect, the second quarter wave plate (interposed between the polarizing beam splitter 436 and the linear polarizer 438) can include a material, feature, or another suitable mechanism that changes the phase of light passing through the SVR 416 by different amounts for different portions of the SVR 416. Although the SVR 416 is shown and described in FIG. 4 as being interposed between the beam splitter 436 and the linear polarizer 438, it should be understood that, alternatively, the SVR 416 can be part of the first quarter wave plate 426 instead. In this alternative embodiment, the SVR 416 shown in FIG. 4 can be replaced with a standard quarter wave plate. That is, the optical subsystem 406 can include two quarter wave plates (one at 426 and one at 416), and the SVR can be part of either of the two quarter wave plates. In some embodiments, if the optical subsystem 406 includes two quarter-wave plates (one at position 426 and one at position 416), the SVR can be part of both quarter-wave plates.

[0042] To illustrate the principle of operation of the optical subsystem 406, light path 418 enters the optical subsystem 406 polarized (e.g., linearly polarized in one orientation p) at the entrance side (or face) of the optical subsystem 406 (e.g., at the entrance side of element 430). A portion of the light passes through the reflective and refractive element 430 while the remainder of the light is reflected away by the element 430. Light path 418 emerging from the exit side of element 430 represents the portion of the light passing through element 430. The light emerging from element 430 then passes through a first quarter wave plate 426 and becomes circularly polarized. This circularly polarized light reflects off of beam splitter 436 and passes back through the first quarter wave plate 426, causing the light to change its handedness while remaining circularly polarized and oriented at 45 degrees. In some embodiments, beam splitter 436 includes another 50 / 50 mirror. The light that passes through the first quarter-wave plate 426 in the reverse direction is reflected again, causing the light to pass through the first quarter-wave plate 426 a third time in the forward direction (i.e., toward the user's eye 408). This reflected light passes through a beam splitter 436, then through an SVR 416 (e.g., a second quarter-wave plate that includes an SVR 416), and then through a linear polarizer 438 before emerging from the output side (or face) 414 of the optical subsystem 406.

[0043] The SVR 416 alters the phase of light passing through the SVR 416 with an appropriate level of phase difference as a function of the location on the SVR 416 where the incoming light enters the SVR 416. In this embodiment, the light emerging from the SVR 416 is horizontally polarized. Because the linear polarizer 438 allows horizontally polarized light to pass toward the user's eye 408 and blocks otherwise vertically polarized light, the SVR 416 performs a late stage phase change to allow the light to pass through the linear polarizer 438. In the example of FIG. 4, the exemplary light path 418 is off-axis, so that the light path 418 entering the SVR 416 is elliptically polarized, and the location on the SVR 416 where the light path 418 enters the SVR 416 includes materials (e.g., birefringent materials) and / or features that alter the phase of the light by an appropriate amount to cause the incoming elliptically polarized light to appear as horizontally polarized light. This can be contrasted with an on-axis light path (not shown) that enters the optical subsystem 406 at an angle of incidence equal to zero. Such an on-axis light path does not have its polarization state altered by the SVR 416 because the amount that the phase is altered varies across the area of ​​the SVR 416, with little or no phase change at the center of the SVR 416. However, for incident light that is further off-axis, the SVR 416 is configured to alter the phase of that off-axis incoming light by an appropriate amount as a function of the angle of incidence, and therefore the position on the SVR 416.

[0044] 5 is a schematic cross-sectional view of a system 500 including a display and an optical subsystem, according to some embodiments. The system 500 may be incorporated into a head-mountable device, such as the wearable device 104 / 204. However, it should be understood that the system 500 may be incorporated into other types of devices, including, but not limited to, cameras, binoculars, office equipment, scientific equipment, and the like. The system 500 may include a pixelated display device 502, sometimes referred to as an information display 502, a backlight assembly 504, and an optical subsystem 506. A schematic view of a user's eye 508 is also illustrated. Such elements are aligned along an optical axis 510.

[0045] The light-emitting backlight assembly 504 may include light sources such as one or more light-emitting diodes (LEDs), one or more OLEDs, one or more cold cathode fluorescent lamps (CCFLs), one or more lasers, one or more quantum dots, or any combination of these exemplary light sources. The light sources in the backlight assembly 504 may emit light across a broad spectrum (e.g., white light) such that the information display 502 can generate color images across the visible spectrum. The backlight assembly 504 may emit light uniformly across its entire front surface, for example, over a range of about 160-180 degrees.

[0046] The information display 502, in conjunction with the backlight assembly 504, may emit light (light approximately parallel to the face of the backlight assembly 504) over an angle range of up to about 180 degrees. This range of emission angles may also be referred to as the field of view of the backlight assembly 504, or the light cone of the backlight assembly 504. In some embodiments, the information display 502 may be an LCD matrix including one or more polarizing layers, liquid crystal layers, and thin film transistor layers. The LCD matrix creates an image by obscuring portions of the backlight in a pixelated fashion. When light 512 is emitted from the backlight assembly 504 and passes through the information display 502 (e.g., the LCD matrix), an image is displayed. For clarity, FIG. 5 shows a separation between the backlight assembly 504 and the information display 502. However, these two components may be sandwiched together with little, if any, space between them.

[0047] The optical subsystem 506 may include a lens assembly for directing light from the information display 502 toward the user's eye 508. The optical subsystem 506 may have, for example, a pancake configuration. In this case, the optical subsystem 506 may include an assembly of optical elements configured to direct light from the information display 502 toward the user's eye 508 using on-axis optical folding based at least in part on the polarization of the light, as described below. In some embodiments, the lens assembly of the optical subsystem 506 includes various optical elements other than lenses. For example, the optical subsystem 506 may include at least one linear polarizer 538 and a spatially varying retarder (SVR) 516. The linear polarizer 538 may be located between the SVR 516 and the exit face 514 of the optical subsystem 506. The SVR 516 is configured to change the phase of light passing through the SVR 516 by different amounts for different portions of the SVR 516. For example, if a backlight / display emits light at a variety of angles, light emitted from the periphery of the display toward the user's eyes may enter the optical subsystem 506 at a relatively large angle of incidence. The SVR 516, when configured to vary the degree of phase modification across the SVR 516, may provide an appropriate level of phase difference for light from all angles to mitigate undesirable visual effects (e.g., eliminate undesirable stray light from reaching the user's eyes 508).

[0048] 5 illustrates an exemplary optical path 518 of light for an image produced by information display 502. For simplicity, optical subsystem 506 is illustrated generally as a block including at least one lens-shaped element. However, optical subsystem 506 may include any of several types of optical elements that need not be lenses. A specific embodiment of optical subsystem 506 will now be described.

[0049] The optical subsystem 506 may include a linear polarizer 520 having a front surface 522 and a back surface 524. The linear polarizer 520 may be disposed on a quarter wave plate 526 having a front surface adjacent the back surface 524 of the linear polarizer 520 and a back surface 528. The quarter wave plate 526 may be disposed on a lens doublet 530. In an embodiment, the lens doublet 530 may comprise a plano-concave singlet having a planar surface 532 and a concave surface 534. The curvature of the concave surface 534 may establish the focal length of the optical subsystem 506. A first reflective polarizing beam splitter, which may comprise an optical coating (e.g., a thin metal film or a multilayer dielectric film), may be located at (e.g., disposed on) the concave surface 534 of the lens doublet 530. The lens doublet 530 may be disposed on the SVR 516. The SVR 516 may be disposed on the second reflective polarizing beam splitter 536. The second reflective polarizing beam splitter 536 may be disposed on the optional second linear polarizer 538. It should be understood that "disposed on" can mean directly disposed on or indirectly disposed on (e.g., with one or more intermediate layers). In addition, it should be understood that "disposed on" can mean "in contact with" or "adjacent" such that there may be a space between a layer disposed on another layer.

[0050] To illustrate the principle of operation of the optical subsystem 506, light path 518 enters the optical subsystem 506 unpolarized at the entrance side (or face) of the optical subsystem 506, and the light path 518 is polarized in one orientation, for example, p, by a linear polarizer 520. After passing through the quarter wave plate 526, the light becomes right-handed circularly polarized. After passing through the lens doublet 530 and subsequently through the SVR 516, the resulting s-polarized light reflects off the second reflective polarizing beam splitter 536, passes back through the SVR 516, reflects again off the first reflective polarizing beam splitter at the concave surface 534 of the lens doublet 530, passes through the SVR 516 a third time, and emerges from the exit side (or face) 514 of the optical subsystem 506 as p-polarized light. Any stray s-polarized light can be removed by an optional second linear polarizer 538 , so that pure p-polarized light reaches the eye 508 .

[0051] 6 is a schematic diagram of an exemplary spatially varying retarder (SVR) 600, according to some embodiments. The SVR 600 can be the same as or similar to the SVR 316 / 416 / 516 illustrated in FIGS. 3 / 4 / 5, for example.

[0052] In some embodiments, the SVR 600 may be a monolithic structure comprising a substrate 602, a matching layer 604, and M twisted birefringent layers 606A, 606B, ... 606M of liquid crystal elements, where M is an integer equal to or greater than 1. Such layers may include polymerizable liquid crystals. The cylinder in FIG. 6 corresponds to the optical axis (and nematic director field). Subsequent twisted birefringent layers 606 are aligned by preceding twisted birefringent layers 606. Ellipses 608 and 610 diagrammatically indicate the polarization of the incoming light 612 and the outgoing light 614, respectively.

[0053] The SVR600 offers many benefits, such as effective control of broadband polarization transformation. Because the SVR600 includes a subsequent liquid crystal layer that is directly aligned by the previous layer, fabrication of the SVR600 is relatively simple, achieving automatic layer alignment and resulting in a monolithic film with a continuously varying optical axis. The SVR600 is generally well suited for patterned achromatic retarders, and can achieve broadband and / or low variation retardance within wavelengths from visible to infrared. For example, the SVR600 can operate with relatively high achromaticity over bandwidths of 450-650 nanometers (nm) and 400-800 nm.

[0054] It should be understood that the exemplary SVR 600 shown in FIG. 6 is just one example type of SVR 416 / 516 that is suitable for implementation in the techniques and systems described herein. In some embodiments, the exemplary SVR 416 / 516 can comprise one or more layers of birefringent material, such as a polymer, that acts as a mechanism to change the polarization state of light passing through the SVR by different amounts for different portions of the SVR. In some embodiments, the exemplary SVR 416 / 516 can comprise a thin film dichroic material (e.g., a stack) that acts as a mechanism to change the polarization state of light passing through the SVR by different amounts for different portions of the SVR. In some embodiments, the exemplary SVR 416 / 516 can comprise a substrate having nano-features that act as a mechanism to change the polarization state of light passing through the SVR by different amounts for different portions of the SVR. In any of these exemplary configurations, the SVR416 / 516 alters polarization to different degrees / amounts as a function of position on the SVR416 / 516 (e.g., altering the polarization state by a greater amount toward the periphery of the SVR416 / 516 and altering the polarization state by a lesser amount toward the center of the SVR416 / 516).

[0055] 7 is a schematic cross-sectional view of a system 700 including a display and an optical subsystem, according to some embodiments. The system 700 may be incorporated into a head-mountable device, such as the wearable device 104 / 204. The system 700 may include an information display 702, a backlight assembly 704, and an optical subsystem 706. A schematic view of a user's eye 708 is also illustrated. Such elements are aligned along an optical axis 710.

[0056] The system 700 may be similar to the system 500 illustrated in Fig. 5 with the addition of a Fresnel lens 712 disposed on an entrance side (or face) 714 of the optical subsystem 706 or a Fresnel lens 716 on an exit side (or face) 718 of the optical subsystem 706. For example, the Fresnel lens 712 may be disposed on the front surface 422 of the first quarter-wave plate 426 as described with reference to Fig. 4 or on the front surface 522 of the linear polarizer 520 as described with reference to Fig. 5. Alternatively, the polarizing beam splitter 338, the second reflective polarizing beam splitter 536, or the linear polarizer 438 / 538 (as described with reference to Figs. 3 / 4 / 5) may be disposed on the Fresnel lens 716. 7 shows both Fresnel lenses 716 and 718 as part of the optical subsystem 706, it should be understood that the optical subsystem 706 could include Fresnel lens 712 without Fresnel lens 716, or the optical subsystem 706 could include Fresnel lens 716 without Fresnel lens 712. Such addition of a Fresnel lens (712 or 716) to the optical subsystem 706 could be used to change the focal length of the light exiting the optical subsystem 706. Additionally or alternatively, other types of lenses could be used on side 714 and / or side 718 of the optical subsystem 706.

[0057] FIG. 8 is a flow diagram illustrating a process 800 for providing a focused image to an eye of a user of a display device, according to some exemplary embodiments. For example, such a display device may be included in an HMD that is the same as or similar to the wearable device 104. In block 802, the display device may generate an image using, for example, a pixelated display device, such as an LCD display. Such generation may be in conjunction with, for example, an illumination backlight. In block 804, the display device may direct light of the image to a lens assembly, such as the optical subsystem 506, to change the focal length of the image to a modified focal length. For example, the lens assembly may include a spatially varying retarder (SVR) 316 / 416 / 516 / 600, which is configured to change the phase of light passing through the SVR 316 / 416 / 516 / 600 by different amounts for different portions of the SVR 316 / 416 / 516 / 600. In block 806, the display device may project an image having a modified focal length to the eye of the user.

[0058] In some embodiments, the spatially varying retarders (SVRs) 316 / 416 / 516 / 600 described herein may be manufactured with correction factors to correct for manufacturing errors that may occur in the components of the systems described herein. One exemplary manufacturing error that may be corrected during fabrication of the SVRs 316 / 416 / 516 / 600 described herein is stress birefringence in molded lenses, which may be a by-product of molding the lenses during manufacturing. To illustrate, stress birefringence occurs when an isotropic material is stressed or deformed (i.e., stretched or bent), causing a loss of physical isotropy and, as a result, a loss of isotropy in the material's permittivity tensor. Thus, when the lens is molded, this may result in stress birefringence in the molded lens. For example, referring to FIG. 3, the optical subsystem 306 may include a lens 330 interposed between the first quarter-wave plate 326 and the SVR 316. This lens 330 may be a molded lens manufactured using a molding technique in which the material of the lens 330 is stressed or deformed to create the desired properties (e.g., shape) of the final part. As a result of this manufacturing process, the manufactured lens 330 may exhibit stress birefringence, as described herein. This stress birefringence in the molded lens 330 can be compensated for during the manufacturing of the SVR 316 described herein, which can effectively return the polarization of the light emerging from the lens 330 to the state that would have been present if the stress birefringence had not been present in the molded lens 330. Stated another way, a molded lens 330 that includes stress birefringence (as a result of manufacturing the lens 330) may polarize light passing through it in an undesired way, and these undesired polarization effects can be effectively "undone" by manufacturing the SVR 316 with a correction factor that compensates for the undesired polarization effects. For example, during manufacture of the SVR 316 (e.g., during the manufacturing process of laying out a sheet of material for the SVR 316), a correction factor can be applied to the SVR 316 to take into account a known or determined amount of stress birefringence in the molded lens 330 that has been manufactured or will be manufactured.The correction factor may include, but is not limited to, adjusting the type of birefringent material used to fabricate the SVR 316, adjusting the number M of birefringent layers 606 (see FIG. 6) included in the SVR 316, adjusting the features (e.g., nanofeatures) included in the SVR 316 (e.g., by changing the type, number, and / or density of the features), etc. In some embodiments, if the stress birefringence is localized, the correction factor may be applied to the SVR 316 at locations on the SVR 316 that correspond to the local stress birefringence in the molded lens 330. In some embodiments, the SVR 316 may be applied as a film having a correction factor to correct or compensate for manufacturing errors in the molded lens 330. Thus, the manufactured SVR 316 may provide an appropriate level of retardation as a function of the extent and / or location of manufacturing defects in the molded lens 330.

[0059] Another exemplary manufacturing error that may be corrected during fabrication of the SVR 316 / 416 / 516 / 600 described herein is polarization variation across the polarizing beam splitter (sometimes referred to herein as a "reflective polarizer" or "reflective film"). To illustrate, a roll-to-roll process may be used to manufacture the polarizing beam splitter. In such a manufacturing process, material for the polarizing beam splitter may be rolled out (e.g., into a sheet), stretching the material as it is rolled out, and then a layer of film may be applied to the rolled out material to create the final part. By way of example, and referring again to FIG. 3, the optical subsystem 306 may include a polarizing beam splitter 338 located between the SVR 316 and the exit face (or side) 314 of the optical subsystem 306. This polarizing beam splitter 338 may be manufactured using roll-to-roll techniques, in which the material of the polarizing beam splitter 338 is stretched or deformed to create the final part, as described herein. As a result of this manufacturing process, the manufactured polarizing beam splitter 338 may have manufacturing errors, which may include undesired variations in polarization across the polarizing beam splitter 338. These manufacturing errors in the polarizing beam splitter 338 may also be compensated for during formation of the SVR 316 described herein. For example, during fabrication of the SVR 316 (e.g., the manufacturing process of laying out a sheet of material for the SVR 316), a correction factor may be applied to the SVR 316 to account for a known or determined amount of polarization variation in the manufactured or to-be manufactured polarizing beam splitter 338. This correction factor may include, but is not limited to, adjusting the type of birefringent material used to fabricate the SVR 316, adjusting the number M of birefringent layers 606 (see FIG. 6) included in the SVR 316, adjustments to the features (e.g., nano-features) included in the SVR 316 (e.g., by changing the type, number, and / or density of the features), etc. In some embodiments, if the undesired polarization within the polarizing beam splitter 338 is local, a correction factor may be applied to the SVR 316 at a location on the SVR 316 that corresponds to the local undesired polarization within the polarizing beam splitter 338.In some embodiments, the SVR 316 may be applied to the polarizing beam splitter 338 as a film having a correction factor to correct or compensate for known or determined manufacturing errors in the polarizing beam splitter 338. In some embodiments, this correction factor (applied while forming the SVR 316) may be applied directly to the polarizing beam splitter 338 during the manufacturing process, which may benefit the overall performance of the polarizing beam splitter 338, and thus the overall performance of the systems including these components, as described herein.

[0060] Although a first manufacturing error in the molded lens 330 and a second manufacturing error in the polarizing beam splitter 338 are discussed separately above, it should be understood that the SVR 316 / 416 / 516 / 600 may be manufactured with correction factors to correct or compensate for the manufacturing errors in both the molded lens 330 and the polarizing beam splitter 338, as described herein. That is, the correction factor applied to the SVR 316 / 416 / 516 / 600 during its manufacture may be based on both the first manufacturing error in the molded lens 330 and the second manufacturing error in the polarizing beam splitter 338. In this manner, the SVR 316 / 416 / 516 / 600 may be manufactured in a manner that compensates for both manufacturing errors.

[0061] 9 is a flow diagram illustrating a process 900 for applying correction factors to compensate for known or determined manufacturing errors in molded lenses and / or polarizing beam splitters during manufacturing of the spatially varying retarder (SVR) 316 / 416 / 516 / 600. Process 900 may be implemented during the manufacturing process of an optical subsystem of a display system that will be included in an HMD, such as an HMD that is the same as or similar to wearable device 104.

[0062] In block 902, the degree of manufacturing error in the manufactured components of the optical subsystem may be determined. For example, in sub-block 904, the amount of stress birefringence in the molded lens may be determined. This may be measured using polarimetry techniques, such as by measuring the change in polarization of light passing through the material of the molded lens. In some embodiments, the difference in the refractive index of the components in the material of the molded lens may be measured to determine the amount of stress birefringence. In some embodiments, if the stress birefringence is non-uniform in the molded lens, the locations on the molded lens where the stress birefringence is presented may be determined in sub-block 904. As another example, in sub-block 906, the polarization variation in the polarizing beam splitter may be determined. This may be measured in terms of extinction ratio, laser induced damage threshold (LIDT), wavelength range, and / or thickness across the polarizing beam splitter. In some embodiments, if the undesired / unwanted polarization is localized in the polarizing beam splitter, the locations on the polarizing beam splitter where the undesired polarization is presented may be determined in sub-block 906.

[0063] In block 908, a correction factor may be determined that is applied during the manufacturing process (e.g., during formation or fabrication) of the spatially varying retarder (SVR) 316 / 416 / 516 / 600. The correction factor determined in block 908 is configured to compensate for the manufacturing errors determined in block 902. For example, the correction factor may be determined to correct a first manufacturing error of the molded lens, to correct a second manufacturing error of the polarizing beam splitter, or to correct manufacturing errors of both the molded lens and the polarizing beam splitter. In some embodiments, the correction factor is a factor of correction for adjusting the type of birefringent material used to fabricate the SVR 316 / 416 / 516 / 600, adjusting the number M (see FIG. 6) of birefringent layers 606 included in the SVR 316 / 416 / 516 / 600, adjusting the features (e.g., nano-features) included in the SVR 316 / 416 / 516 / 600 (e.g., by changing the type, number, and / or density of the features), and the like. In some embodiments, if the manufacturing defect to be corrected is localized to the defect, a correction factor may be applied to the SVR316 / 416 / 516 / 600 at a location on the SVR316 / 416 / 516 / 600 that corresponds to the localized manufacturing defect at the defect.

[0064] In block 910, the SVR316 / 416 / 516 / 600 may be manufactured (e.g., formed) by applying the correction factor determined in block 908. Many variations and modifications may be made to the above-described embodiments, elements of which should be understood to be among the other acceptable embodiments. All such variations and modifications are intended to be included herein within the scope of this disclosure. The invention as originally claimed in the present application is set forth below. [Appendix 1] 1. A method comprising: Determining a degree of manufacturing error in at least one of a molded lens or a polarizing beam splitter to be included in the lens assembly; determining a correction factor for a spatially varying retarder (SVR) to be included in the lens assembly based at least in part on the extent of the manufacturing error; and forming the SVR by applying the correction factor. [Appendix 2] 2. The method of claim 1, wherein the extent of the manufacturing error includes an amount of stress birefringence in the molded lens, and the correction factor is determined based on the amount of stress birefringence in the molded lens. [Appendix 3] 2. The method of claim 1, wherein the extent of the manufacturing error includes polarization variation in the polarizing beam splitter, and the correction factor is determined based on the polarization variation in the polarizing beam splitter. [Appendix 4] 2. The method of claim 1, wherein determining the extent of the manufacturing errors includes determining a degree of a first manufacturing error in the molded lens and determining a degree of a second manufacturing error in the polarizing beam splitter, and wherein the correction factor is determined based on the first manufacturing error and the second manufacturing error. [Appendix 5] determining a location of the manufacturing error in the at least one of the molded lens or the polarizing beam splitter; 2. The method of claim 1, wherein forming the SVR by applying the correction factor includes applying the correction factor to a location on the SVR that corresponds to the location of the manufacturing error in the at least one of the molded lens or the polarizing beam splitter. [Appendix 6] The correction coefficient is Adjusting the type of birefringent material used to fabricate the SVR; Adjustment of several birefringent layers included in said SVR; or 2. The method of claim 1, wherein the SVR includes an adjustment to one or more features, and the adjustment is a correction factor for at least one of the adjustments. [Appendix 7] 2. The method of claim 1, wherein the lens assembly is to be incorporated into a head mounted display (HMD). [Appendix 8] 1. A method comprising: Determining a degree of manufacturing error in at least one of a lens or a reflective polarizer to be included in an optical subsystem of a head mounted display (HMD); determining a correction factor to be applied during manufacturing of a spatially varying retarder (SVR) to be included in the optical subsystem; and producing the SVR by applying the correction factor. [Appendix 9] 9. The method of claim 8, wherein the extent of the manufacturing error includes an amount of stress birefringence in the lens, and the correction factor is determined based on the amount of stress birefringence in the lens. [Appendix 10] 9. The method of claim 8, wherein the extent of the manufacturing error includes polarization variation in the reflective polarizer, and the correction factor is determined based on the polarization variation in the reflective polarizer. [Appendix 11] 9. The method of claim 8, wherein determining the extent of the manufacturing errors includes determining a degree of a first manufacturing error in the lens and determining a degree of a second manufacturing error in the reflective polarizer, and wherein the correction factor is determined based on the first manufacturing error and the second manufacturing error. [Appendix 12] The correction coefficient is Adjusting the type of birefringent material used to fabricate the SVR; Adjustment of several birefringent layers of polymerizable liquid crystals in the SVR; or 9. The method of claim 8, wherein the SVR includes an adjustment to at least one of the type, number, or density of features included in the SVR. [Appendix 13] 9. The method of claim 8, wherein the SVR is fabricated as part of a quarter-wave plate. [Appendix 14] 9. The method of claim 8, wherein the correction factor is applied to a location on the SVR that corresponds to a location of the manufacturing error. [Appendix 15] 1. A system comprising: an information display including pixels configured to collectively form an image; a backlight assembly for illuminating the pixels of the information display; an optical subsystem for directing light of the image from the information display towards an eye of a user, the optical subsystem comprising: A molded lens; a polarizing beam splitter positioned between the shaping lens and an output face of the optical subsystem; a spatially varying retarder (SVR) interposed between the lens and the polarizing beam splitter, the SVR configured to compensate for manufacturing errors in at least one of the molded lens or the polarizing beam splitter. [Appendix 16] 16. The system of claim 15, wherein the SVR is configured to compensate for an amount of stress birefringence in the molding lens. [Appendix 17] 16. The system of claim 15, wherein the SVR is configured to compensate for polarization variations in the polarizing beam splitter. [Appendix 18] 16. The system of claim 15, wherein the SVR is configured to compensate for an amount of stress birefringence in the molded lens and polarization variation in the polarizing beam splitter. [Appendix 19] The SVR includes a characteristic that compensates for the manufacturing error in at least one of the molded lens or the polarizing beam splitter, the characteristic comprising: the particular type of birefringent material used to fabricate the SVR; a particular number of birefringent layers included in said SVR; or 16. The system of claim 15, including at least one of a particular type, a particular number, or a particular density of features included in the SVR. [Appendix 20] 16. The system of claim 15, wherein the SVR is part of a quarter-wave plate.

Claims

1. 1. A method comprising: determining an extent of manufacturing error in at least one of a molded lens or a polarizing beam splitter to be included in the lens assembly, wherein the extent of manufacturing error comprises at least one of an amount of stress birefringence in the molded lens or a polarization variation in the polarizing beam splitter; determining a correction factor for a spatially varying retarder (SVR) to be included in the lens assembly, wherein the correction factor is determined based on at least one of the amount of stress birefringence in the molded lens or polarization variation in the polarizing beam splitter; forming the SVR by applying the correction factor.

2. 2. The method of claim 1 , wherein the determining the extent of the manufacturing error comprises determining the amount of stress birefringence in the molded lens and determining a polarization variation in the polarizing beam splitter, and the correction factor is determined based on the amount of stress birefringence in the molded lens and the polarization variation in the polarizing beam splitter.

3. determining a location of the manufacturing error in the at least one of the molded lens or the polarizing beam splitter; 2. The method of claim 1 , wherein the forming of the SVR by applying the correction factor comprises applying the correction factor to a location on the SVR that corresponds to the location of the manufacturing error in the at least one of the molded lens or the polarizing beam splitter.

4. The correction coefficient is Adjusting the type of birefringent material used to fabricate the SVR; Adjusting the number of birefringent layers included in the SVR; or 10. The method of claim 1, wherein the factor of correction is for at least one of an adjustment to at least one of the type, number, or density of one or more nanofeatures included in the SVR.

5. The method of claim 1 , wherein the lens assembly is to be incorporated into a head mounted display (HMD).

6. 1. A method comprising: determining an extent of manufacturing tolerances in at least one of a lens or a reflective polarizer to be included in an optical subsystem of a head mounted display (HMD), wherein the extent of manufacturing tolerances comprises at least one of an amount of stress birefringence in the lens or a polarization variation in the reflective polarizer; determining a correction factor to be applied during manufacturing of a spatially varying retarder (SVR) to be included in the optical subsystem, wherein the correction factor is determined based on at least one of the amount of stress birefringence in the lens or the polarization variation in the reflective polarizer. and producing the SVR by applying the correction factor.

7. 7. The method of claim 6, wherein determining the extent of the manufacturing error comprises determining the amount of the stress birefringence in the lens and determining the polarization variation in the reflective polarizer, and the correction factor is determined based on the amount of the stress birefringence in the lens and the polarization variation in the reflective polarizer.

8. The correction coefficient is Adjusting the type of birefringent material used to fabricate the SVR; Adjusting the number of birefringent layers of polymerizable liquid crystal included in the SVR; or 7. The method of claim 6, wherein the factor of correction is for at least one of an adjustment to at least one of the type, number, or density of nanofeatures included in the SVR.

9. The method of claim 6 , wherein the SVR is fabricated as part of a quarter wave plate.

10. The method of claim 6 , wherein the correction factor is applied to a location on the SVR that corresponds to a location of the manufacturing error.

11. 1. A system comprising: an information display including pixels configured to collectively form an image; a backlight assembly for illuminating the pixels of the information display; an optical subsystem for directing light of the image from the information display towards an eye of a user, the optical subsystem comprising: A molded lens; a polarizing beam splitter positioned between the shaping lens and an output face of the optical subsystem; a spatially varying retarder (SVR) interposed between the molded lens and the polarizing beam splitter, the SVR configured to compensate for manufacturing errors in at least one of the molded lens or the polarizing beam splitter.

12. The system of claim 11 , wherein the SVR is configured to compensate for an amount of stress birefringence in the molded lens.

13. The system of claim 11 , wherein the SVR is configured to compensate for polarization variations in the polarizing beam splitter.

14. 12. The system of claim 11, wherein the SVR is configured to compensate for an amount of stress birefringence in the molded lens and polarization variation in the polarizing beam splitter.

15. The SVR includes a feature that compensates for the manufacturing error in at least one of the molded lens or the polarizing beam splitter, the feature comprising: The particular type of birefringent material used to fabricate the SVR; a particular number of birefringent layers included in said SVR; or The system of claim 11 , comprising at least one of a particular type, a particular number, or a particular density of nano-features included in the SVR.

16. The system of claim 11 , wherein the SVR is a portion of a quarter wave plate.

17. The system of claim 11 , wherein the optical subsystem is part of a head mounted display (HMD).

18. The method of claim 1 , wherein the SVR is fabricated as part of a quarter wave plate.

19. The method of claim 4 , wherein the birefringent layer comprises a layer of polymerizable liquid crystal.

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