Lens tinting for integrated lenticular displays

Abstract

The present disclosure describes tinting techniques in a lens stack assembly for a wearable head mounted display (WHMD). The lens stack assembly includes a waveguide disposed between two lenses, the two lenses including tinting to selectively reduce the amount of ambient light transmitted to a user without reducing the amount of display light in the WHMD. Additionally, the tinting techniques described herein reduce or eliminate the generation of ghost images caused by light outcoupled from the waveguide away from the user reflecting back toward the user.

Description

[Background technology]

[0001] Wearable head-mounted displays (WHMDs) use a projector to emit a light pattern to display images or videos. For example, the projector typically emits this light pattern (called display light) into a waveguide, which incouples the display light with an incoupler, guides the display light back to the waveguide via one or more instances of total internal reflection (TIR), and outcouples the display light toward the user via an outcoupler. WHMDs, such as those used in augmented reality (AR) or mixed reality (MR), not only project display light toward the user but also allow the user to observe the surrounding environment through the WHMD's optical see-through lenses. For example, ambient light from sources external to the WHMD (i.e., light not generated by the WHMD's projector) passes through the WHMD's lenses to reach the user. Conventional WHMDs apply tinting to the WHMD's lenses to reduce the amount of ambient light reaching the user and improve the ratio of display light to ambient light. However, conventional tinting technologies can interfere with the display light, degrading the quality of the displayed image and negatively impacting the user experience. Summary of the Invention

[0002] In a first exemplary embodiment, the lens stack assembly includes a waveguide disposed between a first lens and a second lens, the waveguide configured to incouple display light at an input incoupler and outcouple display light at an outcoupler, and a tint applied to the second lens having a first optical transmission level for light having a first optical characteristic associated with the display light and a second, lower optical transmission level for light having a second optical characteristic.

[0003] In some aspects of the first exemplary embodiment, the first optical characteristic comprises a first wavelength range and the second optical characteristic comprises a wavelength outside the first wavelength range.

[0004] In some aspects of the first exemplary embodiment, the first optical property comprises a first polarization state, the second optical property comprises a second polarization state different from the first polarization state, and the tint is polarization selective, transmitting light of the first polarization state and blocking light of the second polarization state.

[0005] In some aspects of the first exemplary embodiment, the tint is a bulk tint incorporated into the substrate of the first lens.

[0006] In some aspects of the first exemplary embodiment, the tint is a surface coating tint applied to a major surface of the first lens.

[0007] In some aspects of the first exemplary embodiment, the tinting is a gradient tint having a gradient along a first direction on a major surface of the first lens or a gradient along a second direction across a thickness of the first lens.

[0008] In some aspects of the first exemplary embodiment, the coloring is photochromic or electrochromic. For example, in some aspects, the coloring changes based on one or more environmental factors to alter the second light transmission level.

[0009] In some aspects of the first exemplary embodiment, the first lens is a world-side lens and the second lens is an eye-side lens that is closer to the user than the first lens.

[0010] In some aspects of the first exemplary embodiment, the second optical characteristic is associated with ambient light from a source external to a wearable head mounted display (WHMD) that includes the lens stack assembly.

[0011] In a second exemplary embodiment, the lens stack assembly includes a waveguide disposed between a first lens and a second lens, the waveguide configured to incouple display light at an incoupler and outcouple display light at an outcoupler, the first lens being a world-side lens and the second lens being a user's eye-side lens, and the first lens including a tint that absorbs light received from the waveguide.

[0012] In some aspects of the second exemplary embodiment, the tinting absorbs light having a first optical characteristic associated with the display light, hi some aspects of the second exemplary embodiment, the first optical characteristic is a first wavelength range.

[0013] In some aspects of the second exemplary embodiment, the tinting at least partially blocks light having a second optical characteristic unrelated to the display light. In some aspects of the second exemplary embodiment, the at least partial blocking of light having the second optical characteristic includes reflection or absorption. In some aspects of the second exemplary embodiment, the second optical characteristic is associated with ambient light entering the lens stack assembly through the first lens.

[0014] In some aspects of the second exemplary embodiment, the tinting comprises a bulk tint incorporated into the substrate of the first lens.

[0015] In some aspects of the second exemplary embodiment, the tint comprises a surface coating tint applied to a major surface of the first lens.

[0016] In some aspects of the second exemplary embodiment, the tinting includes a gradient tint having a gradient along a first direction on a major surface of the first lens or a gradient along a second direction across a thickness of the first lens.

[0017] In some aspects of the second exemplary embodiment, the coloring comprises photochromic coloring or electrochromic coloring; Optical absorption of light received from the waveguideLevels vary based on one or more environmental factors.

[0018] In a third exemplary embodiment, a method for controlling light in a WHMD with a lens stack assembly including a waveguide disposed between a world-side lens and an eye-side lens is described, the method including incoupling display light with an incoupler of the waveguide, outcoupling a first portion of the incoupled display light to a user through the eye-side lens, and absorbing a second portion of the incoupled display light with the world-side lens.

[0019] In some aspects of the third exemplary embodiment, the tinting of the world-side lens absorbs light having a first optical characteristic associated with the display light.

[0020] In some aspects of the third exemplary embodiment, the first optical characteristic is a wavelength range, and the tinting is further configured to at least partially block light having a second optical characteristic that includes a second wavelength range associated with ambient light from a source external to the WHMD.

[0021] In a fourth exemplary embodiment, a method for controlling light in a WHMD including a lens stack assembly including a waveguide disposed between a world-side lens and an eye-side lens is described. The method includes incoupling display light having a first optical characteristic with an incoupler and outcoupling the incoupled display light to a user through an eye-side lens, wherein the eye-side lens is tinted to have a first light transmission level for the first optical characteristic, the eye-side lens at least partially blocks ambient light from a light source external to the WHMD, and the eye-side lens is tinted to have a second light transmission level for a second optical characteristic associated with the ambient light, the second light transmission level being lower than the first light transmission level.

[0022] The present disclosure may be better understood, and its numerous features and advantages made apparent, to those skilled in the art by referencing the accompanying drawings, in which: The use of the same reference symbols in different drawings indicates similar or identical items. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a diagram of an exemplary display system having a support structure housing a projection system configured to project images toward a user's eyes, according to some embodiments. [Figure 2] FIG. 2 illustrates an example of a portion of a WHMD displaying display light from a projector and ambient light from the surrounding environment, according to some embodiments. [Figure 3] FIG. 1 is a diagram of a lens stack assembly, according to some embodiments. [Figure 4] FIG. 1 illustrates a lens stack assembly with selective tinting applied to the eye-side lens, according to some embodiments. [Figure 5] FIG. 10 is a diagram illustrating the occurrence of a ghost image. [Figure 6] FIG. 10 illustrates a lens stack assembly with absorptive tinting applied to the world-facing lens to reduce or eliminate ghost images, according to some embodiments. [Figure 7] FIG. 10 illustrates a lens stack assembly with polarization-selective tinting applied to the world-facing lenses to reduce or eliminate ghost images, according to some embodiments. [Figure 8] 10 is a flowchart illustrating a method by which a WHMD controls light to eliminate the creation of ghost images in a WHMD, according to some embodiments. [Figure 9] 10 is a flowchart illustrating a method for a WHMD to selectively block ambient light, according to some embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0024] The lenses of conventional WHMDs may be tinted to reduce the amount of ambient light reaching the user's eyes and increase the relative proportion of display light to the total light, including display light and ambient light, that the user can observe. However, when implemented in a lens stack assembly with an integrated optical see-through display such as a waveguide, the tint of the tinted lenses may interfere with the display light. For example, conventional tinting applied to the eye-side lens of the lens stack assembly (e.g., the lens between the waveguide and the user) not only reduces the brightness or intensity of the ambient light, but also the brightness or intensity of the display light, potentially adversely affecting the quality of the displayed image. While the effects of tinting can be overcome by increasing the brightness of the display light, this approach increases the power consumption of the WHMD. Furthermore, conventional reflective tinting applied to the world-side lens (i.e., the lens between the waveguide and the outside world) to reflect incoming ambient light may reflect a portion of the display light outcoupled from the waveguide away from the user back toward the user. This results in ghost images and degraded image quality presented to the user. 1-9 illustrate techniques for applying tinting to a lens stack assembly to selectively block ambient light without adversely affecting the quality of the image produced by the display light, thereby improving the user experience.

[0025] To illustrate, in some embodiments, the lens stack assembly includes a waveguide disposed between a first lens and a second lens. The first lens is configured as a world-side lens facing the user's external environment, and the second lens is configured as an eye-side lens facing the user. In some embodiments, the eye-side lens includes a tint having a first optical transmission level for a first optical property related to the display light and a second, lower optical transmission level for another optical property not related to the display light. For example, the tint does not block light in a first wavelength range related to the display light and at least partially blocks light in a second wavelength range related to ambient light. Thus, the quality (e.g., brightness) of the display light is largely unaffected, ambient light reaching the user's eyes is reduced, and the visibility of images generated by the display light is improved. In some embodiments, the world-side lens includes an absorptive tint to absorb light outcoupled from the waveguide away from the user. Thus, the generation of ghost images is reduced or completely eliminated, improving the quality of the images provided to the user.

[0026] 1-9 illustrate embodiments of tinted lens stack assemblies and corresponding tinting techniques for providing WHMD that selectively block ambient light and reduce ghost images. In this disclosure, the term "tinting" or similar terms generally refers to some type of light attenuation method. This includes, for example, adding a colorant to a white color, adding black to a colorant to darken (i.e., shade), adding a polarizing filter such as a grid polarizer to selectively filter light based on its polarization state, etc. However, it will be understood that the disclosed apparatus and techniques are not limited to implementation in this particular display system and can be implemented in any of a variety of display systems using the guidelines provided herein.

[0027] FIG. 1 illustrates an exemplary display system 100 having a support structure 102. The support structure 102 includes an arm 104 that houses a projection system configured to project an image toward a user's eyes, which the user perceives as being displayed in a field of view (FOV) area 106 of the display via one or both lens elements 108, 110. In the illustrated embodiment, the display system 100 is a WHMD that includes the support structure 102 configured to be worn on the user's head and has the general shape and appearance of a frame of eyeglasses (e.g., sunglasses, etc.). The support structure 102, including the lens elements 108, 110, includes or encompasses various components to facilitate projecting such an image toward the user's eyes, such as a laser projector, an optical scanner, a waveguide, etc. In some embodiments, the support structure 102 further includes one or more front-facing cameras, a rear-facing camera, and various sensors, such as other light sensors, motion sensors, and accelerometers. In some embodiments, support structure 102 further includes one or more radio frequency (RF) interfaces or other wireless interfaces, such as a Bluetooth™ interface, a WiFi interface, etc. Additionally, in some embodiments, support structure 102 also includes one or more batteries or other portable power sources for powering the electrical components of display system 100. In some embodiments, some or all of these components of display system 100 are housed completely or partially within an interior volume of support structure 102, such as within arms 104 within region 112 of support structure 102. Note that while an exemplary form factor is illustrated, it will be understood that in other embodiments, display system 100 may have a different shape and appearance than the eyeglass frames illustrated in FIG. 1 .

[0028] One or both of lens elements 108, 110 may be used by display system 100 to provide an augmented reality (AR) display that can provide rendered graphical content overlaid on or otherwise combined with a real-world view perceived by a user through lens elements 108, 110. For example, a projected light beam (i.e., display light) used to form a perceptible image or series of images may be projected to a user's eye by a projector of display system 100 via a series of optical elements, such as a waveguide, one or more scanning mirrors, and one or more optical relays, formed at least partially within the corresponding lens element. Thus, one or both of lens elements 108, 110 includes at least a portion of a waveguide that routes display light received by a waveguide incoupler to a waveguide outcoupler, which outputs the display light toward the eye of a user of display system 100. In some embodiments, the outcoupler at least partially overlaps FOV region 106. The display light is modulated and scanned onto the user's eye, and the user perceives the display light as an image. Additionally, each lens element 108, 110 is sufficiently transparent so that a user can see through the lens element, providing a view of the user's real-world environment, with the image being superimposed on at least a portion of the real-world environment.

[0029] In some embodiments, one or both of the lens elements 108, 110 includes a lens stack assembly with a waveguide disposed between a first lens and a second lens. For example, the first lens is a world-side lens, and the second lens is an eye-side lens facing the user. In some embodiments, the second (i.e., eye-side) lens includes a tint having a first light transmission level for a first optical property related to display light and a tint having a second lower light transmission level for other optical properties unrelated to display light, such as ambient light from real-world viewing. In this manner, the lens stack assembly reduces the amount of ambient light provided to the user, while leaving the display light (i.e., from the projection system) largely unaffected. In some embodiments, the first lens (i.e., world-side lens) includes a tint to absorb light outcoupled from the waveguide in a direction away from the user. In this manner, the lens stack assembly reduces or eliminates the generation of ghost images, thereby improving the quality of the image provided to the user.

[0030] In some embodiments, the projector is a digital light processing-based projector, a scanning laser projector, or any combination of a modulated light source, such as a laser or one or more LEDs, and a dynamic reflector mechanism, such as one or more dynamic scanners or a digital light processor. In some embodiments, the projector includes multiple laser diodes (e.g., red, green, and / or blue laser diodes) and at least one scan mirror (e.g., two one-dimensional scan mirrors that may be microelectromechanical systems (MEMS)-based or piezoelectric-based). The projector is communicatively coupled to a controller and a non-transitory processor-readable storage medium or memory that stores processor-executable instructions and other data that, when executed by the controller, cause the controller to control operation of the projector. In some embodiments, the controller is communicatively coupled to a processor (not shown) that controls the size of the projector's scan area and the position of the scan area and generates the content displayed on the display system 100. The projector scans light over a variable area designated as the FOV area 106 of the display system 100. The size of the scan region corresponds to the size of the FOV region 106, and the location of the scan region corresponds to the area on one of the lens elements 108, 110 where the FOV region 106 is visible to the user. It is generally desirable for a display to have a wide FOV to accommodate light outcoupling over a wide range of angles. The range of different user eye positions from which the display can be viewed is referred to herein as the display's eyebox.

[0031] 2 shows a portion of a display system 200 including a projection system having a projector 206 and a waveguide 212 disposed within an optical combining lens 218 and including an in-coupler 214 and an out-coupler 216. In some embodiments, the display system 200 represents the display system 100 of FIG. 1. In this example, an arm 204 of the display system 200 houses the projector 206, which includes an optical engine 208 (e.g., a laser or a display panel), one or more optical elements 210, the in-coupler 214, and a portion of the waveguide 212.

[0032] The optical coupling lens 218 includes a lens stack assembly including an eye-side lens 220, a world-side lens 222, and a waveguide 212. The waveguide 212 is embedded or disposed between the eye-side lens 220 and the world-side lens 222. Display light 228 is incoupled into the waveguide 212 at the incoupler 214, exits through the outcoupler 216 as display light 230, and passes through the eye-side lens 220 (e.g., corresponding to some embodiments of the lens element 110 of the display system 100). In use, the display light 230 exiting the ES lens 220 enters the pupil of the eye 224 of a user wearing the display system 200, causing the user to perceive a display image carried by light output by the optical engine 208. The optical coupling lens 218 is substantially transparent, allowing light from the real world 232 corresponding to the environment surrounding the display system 200 (i.e., ambient light) to pass through the world-side lens 222, the waveguide 212, and the eye-side lens 220 to reach the user's eye 224. In this way, images or other graphical content output by the projector 206, when projected onto the user's eye 224, are combined (e.g., overlaid) with real-world images of the user's environment, providing the user with an AR experience.

[0033] In some embodiments, one or more tints (e.g., surface coating tints or bulk constant density tints) are applied to one or both of the world-side lens 222 and the eye-side lens 220. In some embodiments, the tint applied to the world-side lens 222 is absorptive, reducing or preventing light outcoupled from the waveguide 212 from reflecting back toward the user's eye 224 and reducing or eliminating the creation of ghost images. In some embodiments, the tint applied to the eye-side lens 220 is selectively transmissive, used to display images in the display system 200, such that wavelengths of light, such as those corresponding to the display light 230 (e.g., wavelengths of green, red, and blue light), are transmitted through the tint, while other wavelengths of light, such as those corresponding to the ambient light 232, are blocked (i.e., reflected or absorbed) by the tint.

[0034] The waveguide 212 of the display system 200 includes an in-coupler 214 and an out-coupler 216. In some embodiments, one or more exit pupil expanders, such as a diffraction grating, are positioned intermediate between the in-coupler 214 and the out-coupler 216 to receive light coupled into the waveguide 212 by the in-coupler 214, expand the received light at each exit pupil expander, and redirect the light toward the out-coupler 216, which couples the light 230 out of the waveguide 212 (e.g., toward the user's eye 224). In some embodiments, the waveguide 212 is configured to have a peak frequency response at a wavelength of green light, such as about 575 nm, thereby improving the perceptibility of the projected image output by the waveguide 212.

[0035] As used herein, the term "waveguide" is understood to mean a combiner that transfers light from an incoupler (such as incoupler 214) to an outcoupler (such as outcoupler 216) using one or more of total internal reflection (TIR), special filters, or reflective surfaces. In some display applications, the light is a collimated image, and the waveguide transfers and replicates the collimated image to the eye. In general, the terms "incoupler" and "outcoupler" are understood to refer to any type of optical grating structure, including, but not limited to, a diffraction grating, a hologram, a holographic optical element (e.g., an optical element using one or more holograms), a volume diffraction grating, a volume hologram, a surface-relief diffraction grating, or a surface-relief hologram. In some embodiments, a given incoupler or outcoupler is configured as a transmission grating (e.g., a transmission diffraction grating or a transmission holographic grating) that transmits light through the incoupler or outcoupler and applies a designed optical function(s) to the light during transmission. In some embodiments, a given in-coupler or out-coupler is a reflective grating (e.g., a reflective diffraction grating or a reflective holographic grating) that reflects light back to the in-coupler or out-coupler, applying a designed optical function(s) to the light during reflection. In this example, in-coupler 214 relays light 228 received via one or more optical paths through waveguide 212 to out-coupler 216. The light propagates through waveguide 212 via TIR. Out-coupler 216 then outputs light 230 to the user's eye 224.

[0036] In some embodiments, projector 206 is connected to a driver or other controller (not shown), which controls the timing of light emission from light sources (e.g., LEDs, etc.) of optical engine 208 according to instructions received from a computer processor (not shown) connected thereto, and modulates the output light so that it is perceived as an image when output to the retina of a user's eye 224. For example, during operation of display system 200, the light sources of optical engine 208 output light of selected wavelengths, and the output light is directed to user's eye 224 via optical elements 210 and waveguides 212. Optical engine 208 modulates the intensity of each of its respective light sources such that the output light represents a pixel of the image. For example, the intensity of a given light source or group of light sources of optical engine 208 corresponds to the brightness of a corresponding pixel of an image projected by projector 206 of display system 200.

[0037] 3 shows a top view 300 of a lens stack assembly 302 according to some embodiments and a world-side or eye-side view 350 of the world-side lens 222 or the eye-side lens 220. In some embodiments, the lens stack assembly 302 corresponds to the optical coupling lens 218 of FIG. 2 or the lens elements 108, 110 of FIG. 1.

[0038] The lens stack assembly 302 includes a waveguide 212 disposed between a first lens 222 and a second lens 220. The first lens 222 is a world-side lens facing a world-side direction 304, and the second lens 220 is an eye-side lens facing a user direction 306. The first lens 222 includes a first major surface 312 facing the world-side direction 304 and a second major surface 314 facing the waveguide 212. The waveguide 212 includes a first major surface 316 facing the first lens 222 and a second major surface 318 facing the second lens 220. The second lens 220 includes a first major surface 320 facing the waveguide 212 and a second major surface 322 facing the user direction 306. For purposes of this disclosure, major surfaces 312, 314, 316, 318, 320, and 322 are referred to as S1, S2, S3, S4, S5, and S6, respectively. For example, first major surface 312 of first lens 222 is S1, second major surface 322 of second lens 220 is S6, and corresponding major surfaces therebetween are numbered increasing from S2 to S5. The thickness of each of first lens 222 and second lens 220 is also referred to as the distance between their respective major surfaces.

[0039] Regarding the coloring of the second lens 220, in some embodiments, the second lens 220 is colored so that light associated with a first optical characteristic has a first light transmission level (i.e., transmits a first amount of light corresponding to the first level) and light associated with the other optical characteristic has a second, lower light transmission level (i.e., transmits a second amount of light corresponding to the second, lower level). In some embodiments, the light associated with the first optical characteristic is light associated with the display light. In some embodiments, the first optical characteristic corresponds to a specific wavelength range, such as a specific wavelength of red, green, or blue light associated with the display light. For example, in some embodiments, the coloring is a wavelength-selective gray, purple, blue, green, amber, yellow, orange, or other type of color coloring. In other embodiments, the first optical characteristic corresponds to a polarization state. For example, the first optical characteristic is a vertical polarization state, and the display light is vertically polarized. Thus, in some embodiments, the coloring is a polarization-selective coloring, applied, for example, as a surface coating. In some embodiments, the first light transmission level corresponds to allowing nearly all light of that optical property to pass through. For example, the first light transmission level corresponds to a high visible light transmittance (VLT) value, such as 80% or greater. A second, lower light transmission level means that less light passes through than the first light transmission level. In other words, the second light transmission level corresponds to a lower VLT value than the first light transmission level. For example, this lower VLT value corresponds to a value between 43% and 80%, or between 18% and 43%, or less than 18%. In some embodiments, the light associated with the other optical property corresponds to ambient light, e.g., light entering the lens stack assembly from the worldside direction 304.

[0040] In some embodiments, the coloring of the second lens 220 is more absorptive of light associated with the other optical property than light associated with the first property. That is, the coloring has a high absorption rate for light not associated with the first optical property. For example, the coloring transmits (i.e., does not absorb) light in a first wavelength range associated with the display light and at least partially absorbs light in a second wavelength range different from the first wavelength range. In other embodiments, the coloring of the second lens 220 is more reflective of light associated with the other optical property than light associated with the first property. That is, the coloring has a high reflection rate for light not associated with the first optical property. For example, the coloring transmits (i.e., does not reflect) light in a first wavelength range associated with the display light and at least partially reflects light in a second wavelength range different from the first wavelength range.

[0041] In some embodiments, the tint is applied to the second lens 220 as a surface coating, i.e., the tint is applied to either or both of the first major surface 320 (i.e., S5) or the second major surface 322 (i.e., S6). In other embodiments, the tint is applied to the second lens 220 as a bulk density tint, i.e., the tint is incorporated into the substrate of the second lens 220.

[0042] In some embodiments, the tinting of the second lens 220 is applied as a gradient tint. For example, in the case of a surface coating tint, the gradient tint varies gradually along a first direction of the major surface of the second lens 220. In some embodiments, the first direction corresponds to a vertical direction 354 or a horizontal direction 352 of the corresponding major surface of the second lens 220. In other embodiments, the first direction corresponds to a diagonal direction, for example, from the upper left corner to the lower right corner, as shown in the eye-side view 350 of the second lens 220. For example, as shown in the eye-side view 350 of the second lens 220, the gradient tint is applied in the vertical direction 354, becoming darker from top to bottom. In another example, in the case of a bulk density tint, the gradient tint varies gradually along a thickness direction 330 of the second lens 220. This thickness direction 330 corresponds to the direction between the first major surface 320 and the second major surface 322 of the second lens 220.

[0043] In some embodiments, the tint of the second lens 220 is photochromic or electrochromic. In some embodiments, the second light transmission level changes based on one or more environmental factors. For example, in the case of photochromic tinting, the tint darkens (i.e., becomes less transmissive) to light in bright conditions relative to other optical properties. For example, the tinting characteristics change to block higher levels of ambient light outdoors on a sunny day and block lower levels of ambient light indoors.

[0044] Regarding the tinting of the first lens 222, in some embodiments, the first lens 222 is tinted such that light outcoupled from the waveguide 212 is absorbed by the first lens 222. During operation, the waveguide 212 outcouples a first portion (and a majority) of the display light toward the user 306, but can also outcouple a second portion (and a smaller portion) of the display light in a direction away from the user, e.g., toward the worldward direction 304. Thus, the first lens 222 is tinted to absorb rather than reflect this light. For example, the display light has a particular wavelength or range of wavelengths, and the tinting of the first lens 222 absorbs light associated with this particular wavelength or range of wavelengths. Thus, reflection of this second portion of the display light toward the user 306 is reduced or completely eliminated, thereby reducing or eliminating ghost images projected to the user. In some embodiments, the tinting applied to the second lens 222 also at least partially blocks ambient light incident from the worldward direction 304. Therefore, the tint applied to the first lens 222 also further reduces the amount of ambient light transmitted to the user.

[0045] In some embodiments, the tint is applied to the first lens 222 as a surface coating. That is, the tint is applied to either or both of the first major surface 312 (i.e., S1) or the second major surface 314 (i.e., S2). In other embodiments, the tint is applied to the first lens 222 as a bulk density tint. That is, the tint is incorporated into the substrate of the first lens 222.

[0046] In some embodiments, the tint of the first lens 222 is applied as a gradient tint. For example, in the case of a surface coating tint, the gradient tint varies gradually along a first direction of the major surface of the first lens 222. In some embodiments, the first direction corresponds to the vertical direction 354 or horizontal direction 352 of the corresponding major surface of the first lens 222. In other embodiments, the first direction corresponds to a diagonal direction, for example, from the upper left corner to the lower right corner as shown in the eye-side view 350. In another example, in the case of bulk density tint, the gradient tint varies gradually along a thickness direction 332 of the first lens 222. This thickness direction 332 corresponds to the direction between the first major surface 312 and the second major surface 314 of the first lens 222. For example, the tint is more concentrated (e.g., less transparent to light of the respective characteristics) at the major surface 314 than at the major surface 312.

[0047] In some embodiments, the tint applied to the first lens 222 is a photochromic or electrochromic tint, and the level of light absorption of light received from the waveguide 212 changes based on one or more environmental factors. For example, in the case of a photochromic tint, in conditions where ghost images are likely to occur, the tint becomes more absorbing of light associated with the display light. For example, in a dark room, the tint changes to absorb more of the display light.

[0048] 4 illustrates an embodiment of a lens stack assembly 400 that illustrates the effect of selective transmission tinting of the second lens 220. In some embodiments, the lens stack assembly 400 corresponds to the lens stack assembly 302 of FIG. 3, the optical coupling lens 218 of FIG. 2, and / or one or both of the lens elements 108, 110 of FIG. 1.

[0049] The selective transmission coloring of the second lens 220 at least partially blocks (e.g., absorbs or reflects) ambient light 232 passing through the second lens 220, resulting in a reduced amount of ambient light 232a being observed by the user, while the display light (229-230) outcoupled from the outcoupler 216 is transmitted. In some embodiments, the selective transmission coloring of the second lens 220 has a first light transmission level for light having a first optical characteristic associated with the display light and a second, lower light transmission level for light having other optical characteristics. For example, the selective transmission coloring of the second lens 220 is substantially transmissive to a first set of wavelengths of light (e.g., wavelengths associated with the display light, such as certain red, green, and / or blue wavelengths) and at least partially blocks other wavelengths. In another example, the selective transmission coloring of the second lens 220 is substantially transmissive to a first polarization state (e.g., vertically polarized light) and blocks other polarization states (e.g., horizontally polarized light). In either case, the display light 229, 230 is substantially unaffected by the tinting of the second lens 220, while the ambient light passing through the second lens 220 is reduced (232a).

[0050] In some embodiments, the tint of the second lens 220 shown in the lens stack assembly 400 is a bulk constant density tint or a surface coating. In some embodiments, the tint of the second lens 220 shown in the lens stack assembly 400 is a gradient tint. In some embodiments, the tint of the second lens 220 shown in the lens stack assembly 400 is a photochromic or electrochromic tint.

[0051] During operation of an exemplary display system 100, such as a WHMD, including the lens stack assembly 400, the waveguide 212 receives display light 228 at the incoupler 214 and redirects it through the waveguide via one or more TIR instances toward the outcoupler 216. The outcoupler 216 redirects display light 229 out of the waveguide 212. This display light 229 passes through the second lens 220 toward the eye 224 and is observed by the user as display light 230. Ambient light 232 passes through the lens stack assembly 400, including the first lens 222, the waveguide 212, and the second lens 220, and toward the eye 224 as ambient light 232a. Because the tinting of second lens 220 is configured to transmit light of a first optical characteristic (e.g., wavelength range) associated with the display light (e.g., 228, 229), the intensity of display light 229 before and after passing through the lens is substantially the same. However, the tinting of second lens 220 reduces the intensity of ambient light, as shown at 232a. This reduction in intensity is indicated by the thinner dashed line in 232a after passing through second lens 220. Because the tinting of second lens 220 is substantially transparent to the display light and at least partially blocks the ambient light, the intensity (i.e., brightness) of the display light passing through second lens 220 is largely unaffected while the intensity of the ambient light is reduced. Therefore, the quality of the image associated with the display light is improved.

[0052] Figure 5 illustrates the effect of a ghost image scenario in a lens arrangement 500. Figure 6 illustrates the effect of a lens stack assembly 600 in mitigating or minimizing the creation of ghost images, according to some embodiments.

[0053] 5 , the first lens 522 of the lens stack assembly 500 includes conventional reflective tinting for reflecting at least a portion 544 of ambient light 540 at the first lens 522. For example, ambient light 540 is received at the first lens 522, a first portion 542 of which is transmitted, and a second portion 544 of which is reflected. Thus, the first lens 522 with the reflective tinting reduces the amount of ambient light transmitted to the user's eye 224. However, the conventional reflective tinting of the first lens 522 also reflects the portion 502 of the outcoupled light from the outcoupler 516 toward the eye 224 as reflected outcoupled light 504.

[0054] During operation of a system including the lens arrangement 500, the waveguide 512 receives display light 528 at the incoupler 514 and outcouples a first portion 530 of the light toward the user 224 at the outcoupler 516. However, a second portion 502 of the outcoupled light is outcoupled away from the user 224. In a conventional system in which the first lens 522 has a reflective color, the second portion 502 of the outcoupled light is reflected toward the user as reflective outcoupled light 504. This reflective outcoupled light 504 causes the user to perceive a ghost image, which adversely affects the quality of the image perceived by the user. The lens stack assembly 600 shown in FIG. 6 reduces or eliminates the occurrence of ghost images.

[0055] 6 illustrates an embodiment of a lens stack assembly 600 illustrating the effect of tinting the first lens 222 to absorb light outcoupled from the waveguide 212. In some embodiments, the lens stack assembly 600 corresponds to the lens stack assembly 302 of FIG. 3, the optical coupling lens 218 of FIG. 2, and / or one or both of the lens elements 108, 110 of FIG. 1.

[0056] The absorptive tint of the first lens 222 absorbs light having a first optical characteristic associated with the display light 228. For example, the first optical characteristic includes a particular wavelength or range of wavelengths. In this manner, the portion 602 of light outcoupled by the outcoupler 216 in a direction away from the user 224 is absorbed rather than reflected by the first lens 222 (e.g., compare to FIG. 5 , where the portion 502 of outcoupled light is reflected as reflected outcoupled light 504). This reduces or completely eliminates the generation of ghost images. In some embodiments, the absorptive tint of the first lens 222 also at least partially blocks (e.g., absorbs) ambient light 640, reducing the intensity or brightness of the ambient light (shown at 642) transmitted to the user.

[0057] In some embodiments, the tint of the first lens 222 of the lens stack assembly 600 is a bulk constant density tint or a surface coating. In some embodiments, the tint of the first lens 222 of the lens stack assembly 600 is a gradient tint. In some embodiments, the tint of the first lens 222 of the lens stack assembly 600 is a photochromic or electrochromic tint.

[0058] During operation of an exemplary display system 100, such as a WHMD, including the lens stack assembly 600, display light 228 is incoupled into the waveguide 212 at the incoupler 214 and redirected through the waveguide 212 via multiple TIR instances toward the outcoupler 216. The display light 228 has a first optical characteristic, such as a specific wavelength or range of wavelengths. At the outcoupler 216, a first portion 230 of the display light is outcoupled directly toward the user's eye 224. However, a second portion 602 of the display light may be outcoupled in the wrong direction, i.e., away from the user's eye 224. Instead of reflecting this outcoupled light 602, the absorptive coloring of the first lens 222 absorbs this second portion 602 of the outcoupled light. Therefore, the absorptive coloring of the first lens 222 eliminates the occurrence of ghost images. Therefore, degradation of the quality of the image displayed through the lens assembly due to ghost images is reduced or eliminated.

[0059] 7 illustrates an embodiment of a lens stack assembly 700 illustrating the effect of polarization-selective tinting of the first lens 222 to transmit light 702 outcoupled from the waveguide 212 and block at least a portion of ambient light 740. In some embodiments, the lens stack assembly 700 corresponds to the lens stack assembly 302 of FIG. 3, the optical coupling lens 218 of FIG. 2, and / or one or both of the lens elements 108, 110 of FIG. 1.

[0060] The polarization-selective tinting of the first lens 222 transmits light of a first polarization state associated with the display light 228 and blocks light of other polarization states. For example, if the display light is vertically polarized, the polarization-selective tinting of the first lens 222 transmits vertically polarized light and blocks light of other polarization states, such as horizontally polarized light. Thus, the generation of ghost images caused by reflection of the second portion 702 of the outcoupled light is eliminated, while also reducing (742) the amount of ambient light 740 passing through the first lens 222.

[0061] During operation of an exemplary display system 100, such as a WHMD including the lens stack assembly 700, display light 228 is incoupled into the waveguide 212 at the incoupler 214 in a first polarization state (e.g., vertical polarization) and redirected through the waveguide 212 via multiple TIR instances toward the outcoupler 216. At the outcoupler 216, a first portion 230 of the display light is outcoupled directly toward the user's eye 224. However, a second portion 702 of the display light may be outcoupled in the wrong direction, i.e., away from the user's eye 224. The polarization-selective coloring of the first lens 222 transmits the second portion 702 of the outcoupled light (i.e., the light passes through unaffected) because the second portion 702 of the outcoupled light is vertically polarized. Thus, reflection of the second portion 702 of the outcoupled light toward the user's eye 224 is reduced or eliminated. However, the polarization-selective tinting of the first lens 222 blocks at least a portion of the ambient light 740, reducing the amount of ambient light 742 that passes through the first lens 222. Thus, the incorporation of polarization-selective tinting in the first lens 222, along with the selective polarization of the display light 228, reduces or entirely avoids ghost image degradation of images displayed through the lens assembly 700. Additionally, the amount of ambient light 740 that is transmitted to the user's eye 224 is also reduced, thereby improving the quality of the images displayed to the user.

[0062] FIG. 8 is a flowchart 800 illustrating an example of a method for controlling light in a WHMD, according to some embodiments. In some embodiments, the WHMD includes a lens stack assembly with a waveguide disposed between a world-side lens and an eye-side lens. At 802, the method includes incoupling display light with an incoupler of the waveguide. At 804, the method includes outcoupling a first portion of the incoupled display light to a user through the eye-side lens. At 806, the method includes absorbing a second portion of the incoupled display light with the world-side lens. For example, in some embodiments, the absorptive coloring of the world-side lens is wavelength-specific to correspond to a particular wavelength associated with the display light. Thus, the generation of ghost images is reduced or completely eliminated. In some embodiments, the absorptive coloring also at least partially blocks (e.g., absorbs) ambient light. Thus, the amount of ambient light observed by the user is reduced.

[0063] FIG. 9 is a flowchart 900 illustrating an example of a method for controlling light in a WHMD, according to some embodiments. In some embodiments, the WHMD includes a lens stack assembly with a waveguide disposed between a world-side lens and an eye-side lens. At 902, the method includes incoupling display light having a first optical characteristic with an incoupler. At 904, the method includes outcoupling the incoupled display light to a user through an eye-side lens, the tint of the eye-side lens having a first light transmission level for the first optical characteristic. At 906, the method includes partially blocking ambient light from a light source external to the WHMD with the eye-side lens, the tint of the eye-side lens having a second, lower light transmission level for a second optical characteristic associated with the ambient light. For example, in some embodiments, the first optical characteristic is a specific wavelength or wavelength range. In other embodiments, the first optical characteristic is a polarization state. Thus, the amount of ambient light transmitted to the user is reduced, while the display light is unaffected.

[0064] In some embodiments, the coloring described in this disclosure is applied as a surface coating coloring, a bulk density coloring, or any combination thereof. In some embodiments, the coloring described in this disclosure is applied as a gradient coloring. In some embodiments, the coloring described in this disclosure is a photochromic or electrochromic coloring.

[0065] In some embodiments, certain aspects of the techniques described above may be implemented by one or more processors of a processing system executing software. The software includes one or more sets of executable instructions stored or otherwise tangibly embodied on a non-transitory computer-readable storage medium. The software may include instructions and specific data that, when executed by one or more processors, operate the one or more processors to perform one or more aspects of the techniques described above. Non-transitory computer-readable storage media may include, for example, magnetic or optical disk storage devices, solid-state storage devices such as flash memory, cache, random access memory (RAM), or other single or multiple non-volatile memory devices, and the like. The executable instructions stored on the non-transitory computer-readable storage medium may be source code, assembly language code, object code, or other instruction formats that are interpreted or otherwise executable by one or more processors.

[0066] A computer-readable storage medium may include any storage medium, or combination of storage media, that is accessible by a computer system during use to provide instructions and / or data to the computer system. Such storage media may include, but are not limited to, optical media (e.g., compact discs (CDs), digital versatile discs (DVDs), Blu-ray discs), magnetic media (e.g., floppy disks, magnetic tape, or magnetic hard drives), volatile memory (e.g., random access memory (RAM) or cache), non-volatile memory (e.g., read-only memory (ROM) or flash memory), or microelectromechanical systems (MEMS)-based storage media. A computer-readable storage medium may be embedded in a computing system (e.g., system RAM or ROM), fixedly attached to a computing system (e.g., a magnetic hard drive), removably attached to a computing system (e.g., an optical disk or universal serial bus (USB)-based flash memory), or coupled to a computer system via a wired or wireless network (e.g., network-accessible storage (NAS)).

[0067] In addition to those described, it should be noted that not all activities or elements described above in the general description are required, and that some of the specific activities or devices may not be required, and that one or more additional activities may be performed or one or more additional elements may be included. Furthermore, the order in which the activities are listed is not necessarily the order in which they are performed. Also, the concepts have been described with reference to specific embodiments. However, those skilled in the art will recognize that various modifications and variations can be made without departing from the scope of the present disclosure, as set forth in the claims below. Accordingly, the specification and drawings should be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present disclosure.

[0068] Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, any feature or features that may cause or enhance any benefit, advantage, or solution to a problem should not be construed as critical, necessary, or essential features of any or all claims. Moreover, the specific embodiments disclosed above are illustrative only, as the disclosed inventive subject matter may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. No limitations are intended to the details of construction or design herein shown, other than as set forth in the claims below. It is therefore apparent that the specific embodiments disclosed above may be altered or modified, and that all such variations are contemplated within the scope of the disclosed inventive subject matter. Consequently, the protection sought herein is as set forth in the claims below.

Claims

1. a waveguide disposed between the first lens and the second lens, the waveguide configured to incouple the display light at an incoupler and outcouple the display light at an outcoupler; the tint of the second lens has a first light transmission level for light having a first optical characteristic associated with the display light and a second, lower light transmission level for ambient light having a second optical characteristic; the first lens is configured as a world-side lens, and the second lens is configured as an eye-side lens that is closer to the user than the first lens, A lens stack assembly for use in a wearable head-mounted display (WHMD).

2. The lens stack assembly of claim 1 , wherein the first optical characteristic comprises a first wavelength range and the second optical characteristic comprises wavelengths outside the first wavelength range.

3. the first optical property comprises a first polarization state, and the second optical property comprises a second polarization state different from the first polarization state; 10. The lens stack assembly of claim 1, wherein the tint is polarization selective to transmit light of the first polarization state and block light of the second polarization state.

4. The lens stack assembly of claim 1 , wherein the tint comprises a bulk tint incorporated into a substrate of the first lens.

5. The lens stack assembly of any one of claims 1 to 4, wherein the tint comprises a surface coating tint applied to a major surface of the first lens.

6. 6. The lens stack assembly of claim 5, wherein the tinting comprises a gradient tint having a gradient along a first direction on the major surface of the first lens or a gradient along a second direction across a thickness of the first lens.

7. The lens stack assembly of any one of claims 1 to 4, wherein the tinting comprises a photochromic tinting or an electrochromic tinting.

8. The lens stack assembly of claim 7 , wherein the tinting varies based on one or more environmental factors to alter the second light transmission level.

9. The lens stack assembly of any one of claims 1 to 4, wherein the second optical property is associated with the ambient light from a source external to the WHMD that includes the lens stack assembly.

10. The first lens includes a coloration for absorbing or transmitting light received from the waveguide. The lens stack assembly of claim 1 .

11. A lens stack assembly as described in claim 10, wherein the coloring of the first lens absorbs light having a first optical characteristic associated with the display light.

12. The lens stack assembly of claim 11 , wherein the first optical property is a first wavelength range.

13. A lens stack assembly as described in any one of claims 10 to 12, wherein the coloring of the first lens at least partially blocks light having the second optical property that is not related to the display light.

14. The lens stack assembly of claim 13 , wherein the at least partial blocking of light having the second optical property comprises reflection or absorption.

15. The lens stack assembly of claim 13 , wherein the second optical property is associated with ambient light entering the lens stack assembly through the first lens.

16. A lens stack assembly as described in any one of claims 10 to 12, wherein the coloring of the first lens includes bulk coloring incorporated into the substrate of the first lens.

17. A lens stack assembly as described in any one of claims 10 to 12, wherein the coloring of the first lens includes a surface coating coloring applied to a major surface of the first lens.

18. A lens stack assembly as described in claim 17, wherein the coloring of the first lens includes a gradient coloring having a gradient along a first direction on the main surface of the first lens or a gradient along a second direction across the thickness of the first lens.

19. A lens stack assembly described in any one of claims 10 to 12, wherein the coloring of the first lens includes photochromic coloring or electrochromic coloring, and the optical absorption level of light received from the waveguide varies based on one or more environmental factors.

20. A lens stack assembly described in any one of claims 1 to 4, 10 to 12, wherein the surface of the first lens facing the waveguide has a concave shape.

21. 1. A method for controlling light in a wearable head-mounted display (WHMD) including a lens stack assembly with a waveguide disposed between a world-side lens and an eye-side lens, comprising: The method comprises: incoupling display light having a first optical characteristic with an incoupler; and outcoupling the incoupled display light to a user through the eye-side lens, wherein a tint of the eye-side lens has a first light transmission level for the first optical characteristic, and the method further comprises: a method comprising at least partially blocking ambient light from a light source external to the WHMD with the eye-side lens, wherein the tinting of the eye-side lens has a second light transmission level for a second optical property associated with the ambient light, the second light transmission level being lower than the first light transmission level.

22. The method of claim 21, comprising absorbing a second portion of the incoupled display light with the world-side lens.

23. 22. The method of claim 21, wherein the tint of the world-side lens absorbs light having the first optical characteristic associated with the display light.

24. the first optical property is a wavelength range; 24. The method of claim 23, wherein the tinting of the world-side lens is further configured to at least partially block light having the second optical characteristic that includes a second wavelength range associated with the ambient light from a source external to the WHMD.

25. A method described in any one of claims 21 to 24, wherein the waveguide side surface of the world side lens has a concave shape.

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