Light color filter and incoupler for incoupling light into waveguide

Abstract

An eyewear display includes a light engine to emit display light and a waveguide with an incoupler to incouple the display light emitted from the light engine. The eyewear display includes a light filter with a gradient along a first direction that transmits different wavelengths of light through the light filter. Thus, the light filter outputs a light gradient with colors that vary along the first direction. The incoupler includes grating features, such as grating height or fill factor, which vary along an incoupling direction that is aligned with the first direction of the light filter. The grating features of the incoupler are tuned to incouple wavelength ranges of light corresponding to the light gradient that is output by the light filter.

Description

LIGHT COLOR FILTER AND INCOUPLER FOR INCOUPLING LIGHT INTO WAVEGUIDEBACKGROUND

[0001] In an eyewear display, display light beams from a light engine are initially coupled into a waveguide by an incoupler which can be formed as an optical grating on a surface, or multiple surfaces, of the waveguide or disposed within the waveguide. Once the display light beams have been coupled into the waveguide, the incoupled display light beams are “guided” through the waveguide, typically by multiple instances of total internal reflection (TIR), to then be directed out of the waveguide by an outcoupler, which can also be formed as an optical grating on or within the waveguide. The outcoupled display light beams overlap at an eye relief distance from the waveguide forming an exit pupil within which a virtual image generated by the light engine can be viewed by the user of the eyewear display.

[0002] In some cases, some of the display light beams emitted from the light engine reflect off of the incoupler and back toward the light engine instead of being incoupled into the waveguide. The light engine or other optical components between the light engine and the incoupler may then redirect these reflected light beams back toward the incoupler which are then incoupled into the waveguide. The display light beams that bounce back and forth between the incoupler and the light engine before being subsequently incoupled can generate mirrored ghost artifacts that appear as inverted duplicate virtual images when observed by a user of the eyewear display.SUMMARY

[0003] In a first embodiment, an eyewear display includes a light filter and a waveguide. The light filter includes a color gradient along a first direction that transmits different wavelength ranges of light. The waveguide includes an incoupler to incouple light into the waveguide in an incoupling direction, wherein the first direction is aligned with the incoupling direction.

[0004] In some aspects of the first embodiment, the color gradient includes a plurality of regions distributed along the first direction, each region of the plurality of regions to transmit light having a different wavelength range. In some aspects, a first region of the plurality of regions is positioned along the first direction nearest to the incoupling direction, and the first region transmits light in a red wavelength range, a blue wavelength range, and a green wavelength range. Additionally, in some aspects, a second region of the plurality of regions is arranged next to the first region along the first direction, and the second region transmits light in the red wavelength range and the green wavelength range and blocks light in the blue wavelength range. Furthermore, in some aspects, a third region of the plurality of regions is arranged next to the second region on a side opposite to the first region along the first direction. The third region transmits light in the red wavelength range and blocks light in the blue wavelength range and the green wavelength range. In some aspects, a fourth region of the plurality of regions is arranged next to the third region on a side opposite to the second region along the first direction. The fourth region blocks light in the blue wavelength range, the green wavelength range, and the red wavelength range.

[0005] In some aspects of the first embodiment, the incoupler includes a plurality of incoupler segments distributed along the incoupling direction. For example, in some aspects, each incoupler segment of the plurality of incoupler segments has one or more grating features that are different from grating features in other ones of the plurality of incoupler segments. The one or more grating features includes one or more of a grating height, a grating fill factor, a grating angle, or a grating material. These different grating features, in some embodiments, are tuned to diffract light having a particular wavelength range incident thereon at a higher diffraction efficiency. For example, the particular wavelength range may correspond to the light gradient output by the light filter.

[0006] In a second embodiment, an eyewear display includes a light engine, a light filter, and a waveguide. The light engine emits light having a plurality of wavelength ranges (i.e., a variety of colors such as red, green, and blue light). The light filterincludes a color gradient along a first direction that transmits different wavelength ranges of light. The light engine emits light through the light filter to an incoupler of the waveguide. The incoupler incouples light into the waveguide after it is incident on (e.g., passes through) the light filter. The incoupler incouples the light into the waveguide in an incoupling direction, where the first direction is aligned with the incoupling direction.

[0007] In some aspects of the second embodiment, the color gradient includes a plurality of regions. Each region of the plurality of regions transmits light having a different wavelength range of the plurality of wavelength ranges. For example, in some aspects, a first region of the plurality of regions is positioned along the first direction nearest to the incoupling direction, a second region of the plurality of regions is arranged next to the first region along the first direction, and a third region of the plurality of regions is arranged next to the second region on a side opposite to the first region along the first direction. The first region transmits light in a red wavelength range, a blue wavelength range, and a green wavelength range. The second region transmits light in the red wavelength range and the green wavelength range and blocks light in the blue wavelength range. The third region transmits light in the red wavelength range and blocks light in the blue wavelength range and the green wavelength range.

[0008] In some aspects of the second embodiment, the incoupler includes a plurality of incoupler segments distributed along the incoupling direction. In some aspects, each incoupler segment of the plurality of incoupler segments has one or more grating features that are different from grating features in other ones of the plurality of incoupler segments. These different grating features, in some embodiments, are tuned to diffract light having a particular wavelength range incident thereon at a higher diffraction efficiency. For example, the particular wavelength range may correspond to the light gradient output by the light filter.

[0009] In some aspects of the second embodiment, the light engine includes a micro-LED display panel.

[0010] In a third embodiment, a method includes emitting, by a light engine, light having a plurality of wavelength ranges. In some aspects, the method includes receiving, by a light filter including a color gradient that varies along a first direction, the light emitted from the light engine and transmitting light having different ones of the plurality of wavelength ranges along the first direction to generate a light gradient with varying wavelength ranges. In some aspects, the method includes incoupling, at an incoupler of a waveguide, the light gradient into the waveguide in an incoupling direction, where the incoupling direction is aligned with the first direction.

[0011] In some aspects of the third embodiment, the color gradient includes a plurality of regions, each region of the plurality of regions to transmit light having a different wavelength range of the plurality of wavelength ranges. In some aspects, the incoupler includes a plurality of incoupler segments distributed along the incoupling direction. Each incoupler segment of the plurality of incoupler segments has one or more grating features that are different from grating features in other ones of the plurality of incoupler segments. These different grating features, in some embodiments, are tuned to diffract light having a particular wavelength range incident thereon at a higher diffraction efficiency. For example, the particular wavelength range may correspond to the light gradient output by the light filter.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] 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. The use of the same reference symbols in different drawings indicates similar or identical items.

[0013] FIG. 1 shows an example eyewear display in accordance with some embodiments.

[0014] FIG. 2 shows an example of a projection system with a light filter arranged between the light engine and an incoupler of a waveguide of an eyewear display, such as that shown in FIG. 1 , in accordance with some embodiments.

[0015] FIG. 3 shows an example of light propagation within a waveguide of a projection system, such as the projection system of FIG. 2, in accordance with some embodiments.

[0016] FIG. 4 shows light propagation from a light engine to a user in an eyewear display, such as that of FIGs. 1 and 2, in accordance with some embodiments.

[0017] FIG. 5 shows an example view of a light filter, such as the light filters of FIGs. 2 and 4, in accordance with various embodiments

[0018] FIG. 6 shows an example of a cross section view of a light filter and incoupler system of an eyewear display, such as the eyewear display of FIG. 1 , in accordance with various embodiments.

[0019] FIG. 7 shows different areas of an incoupler with the number of interactions (n) a light beam will experience with the incoupler based on its initial position of incidence on the incoupler, in accordance with some embodiments.

[0020] FIG. 8 shows a series of diagrams illustrating different color dependent high coupling efficiency regions of an incoupler and two examples of light filters that output light with a color gradient corresponding to the different color dependent high coupling efficiency regions of the incoupler, in accordance with various embodiments.

[0021] FIG. 9 shows examples of light filters being implemented as a series of stacked color filters in accordance with various embodiments.

[0022] FIG. 10 shows several example top views of a red color filter positioned with respect to an incoupler in accordance with various embodiments.

[0023] FIG. 11 shows an example of a cross section view of a light filter and incoupler system of an eyewear display with the light filter applied to the backside of a waveguide, in accordance with various embodiments.

[0024] FIG. 12 shows a method flowchart creating a color gradient of light for incoupling into a waveguide, in accordance with some embodiments.DETAILED DESCRIPTION

[0025] Conventional techniques for reducing mirrored ghost artifacts include tilting the waveguide to redirect the reflected light away from reflective surfaces (e.g., surfaces of the light engine), reducing the size of the exit pupil by adding an aperture or otherwise redesigning the light projection source, or reducing the size of the incoupler so that it has a comparable dimension to the waveguide thickness in the incoupling direction. While these conventional techniques are sometimes effective in reducing the generation of mirrored ghost artifacts, they also have disadvantages. For instance, tilting the waveguide increases the total product volume, which may be limited in the restricted form factor of an eyewear display, and reducing the size of the exit pupil or of the incoupler can negatively affect the performance of the eyewear display. FIGs. 1-12 provide techniques for reducing or eliminating mirrored ghost artifacts by inserting a light color filter in the eyewear display and tuning the incoupler grating features to correspond to the light received via the light color filter. In this manner, the techniques described herein implement a light engine-to-incoupler optical path that has different exit apertures for different colors. This effectively minimizes the amount of light (e.g., blue light) that is reflected back and forth between the incoupler and the light engine, thereby reducing or eliminating mirrored ghost artifacts and improving the quality of the virtual image delivered to the user.

[0026] To illustrate, in some embodiments, an eyewear display includes a light engine to emit display light and a waveguide with an incoupler to incouple the display light emitted from the light engine. The eyewear display also includes a light filter, such as a spatially varying color filter, with a gradient along a first direction that transmits different wavelengths of light through the light filter. According to some embodiments, in a first region at one end of the light filter, the light filter allows all light to pass through (i.e. , the first region transmits all light). In a second region next to the first region along the first direction, the light filter absorbs blue light and allows other colors of light such as red light and green light to pass through (i.e., the second region transmits red and green light and absorbs blue light). In a third region next to the second region along the first direction, the light filter absorbs blue light and green light and allows red light to pass through (i.e., the third region transmits red light). In afourth region next to the third region along the first direction, the light filter does not allow any color of light to pass through. Therefore, the light filter outputs a light gradient with colors (i.e., wavelength ranges) that vary along the first direction. Additionally, in some embodiments, the incoupler includes grating features, such as grating height or fill factor, which vary along an incoupling direction that is aligned with the first direction of the light filter. The grating features of the incoupler are tuned to incouple wavelength ranges of light corresponding to the light gradient that is output by the light filter. As such, the light filter and incoupler are together designed and implemented in the eyewear display such that the highest diffraction efficiency is achieved for the light incident at each position along the incoupler. This configuration reduces or eliminates the light that is reflected off of the incoupler back toward the light engine, thereby minimizing the appearance of mirrored ghost artifacts and improving the quality of the virtual image observed by the user of the eyewear display.

[0027] FIG. 1 illustrates an example eyewear display 100 in accordance with various embodiments. The eyewear display 100 (also referred to as a wearable heads up display (WHLID), head-mounted display (HMD), near-eye display, or the like) has a support structure 102 that includes an arm 104, which houses a microdisplay projection system configured to project images toward the eye of a user, such that the user perceives the projected images as being displayed in a field of view (FOV) area 106 of a display at one or both of lens elements 108, 110. In the depicted embodiment, the support structure 102 of the eyewear display 100 is configured to be worn on the head of a user and has a general shape and appearance (i.e., “form factor”) of an eyeglasses frame. The support structure 102 contains or otherwise includes various components to facilitate the projection of such images toward the eye of the user, such as a light engine and a waveguide (shown in FIG. 2, for example). In some embodiments, the support structure 102 further includes various sensors, such as one or more front-facing cameras, rear-facing cameras, other light sensors, motion sensors, accelerometers, and the like. The support structure 102 further can include one or more radio frequency (RF) interfaces or other wireless interfaces, such as a Bluetooth™ interface, a WiFi interface, and the like. Further, insome embodiments, the support structure 102 includes one or more batteries or other portable power sources for supplying power to the electrical components of the eyewear display 100. In some embodiments, some or all of these components of the eyewear display 100 are fully or partially contained within an inner volume of support structure 102, such as within the arm 104 in region 112 of the support structure 102. It should be noted that while an example form factor is depicted, it will be appreciated that in other embodiments the eyewear display 100 may have a different shape and appearance from the eyeglasses frame depicted in FIG. 1.

[0028] One or both of the lens elements 108, 110 are used by the eyewear display 100 to provide an augmented reality (AR) or mixed reality (MR) display in which rendered graphical content can be superimposed over or otherwise provided in conjunction with a real-world view as perceived by the user through the lens elements 108, 110. In some embodiments, one or both of lens elements 108, 110 serve as optical combiners that combine environmental light (also referred to as ambient light) from outside of the eyewear display 100 and light emitted from a light engine in the eyewear display 100. For example, light used to form a perceptible image or series of images may be projected by the light engine of the eyewear display 100 onto the eye of the user via a series of optical elements, such as a waveguide formed at least partially in the corresponding lens element, a light filter (e.g., a spatially varying color filter that has discrete color filter regions), one or more scan mirrors, one or more optical relays, and / or one or more prisms. In some embodiments, the light engine is configured to emit light having a plurality of wavelength ranges, e.g., red light, green light, and blue light (collectively referred to as RGB light). As the light passes through the light filter, the light is converted into a color gradient of light that had varying wavelengths along a first direction. An incoupler of the waveguide receives this light and incouples it into the waveguide. In some embodiments, the incoupler has a wavelength-dependent (i.e., color-dependent) diffraction efficiency that incouples light into the waveguide based on the color gradient of light output by the polarization gradient layer. One or both of the lens elements 108, 110 thus includes at least a portion of a waveguide that routes display light received by the incoupler of the waveguide to an outcoupler of the waveguide, which outputs the display light towardan eye of a user of the eyewear display 100. The display light is modulated and projected onto the eye of the user such that the user perceives the display light as an image in FOV area 106. In addition, in some embodiments, each of the lens elements 108, 110 is sufficiently transparent to allow a user to see through the lens elements to provide a field of view of the user’s real-world environment such that the image appears superimposed over at least a portion of the real-world environment.

[0029] In some embodiments, the light engine 202 is a digital light processingbased projector, a scanning laser projector, a liquid crystal on silicon (LCoS) light engine, or any combination of a modulative light source such as a laser or one or more light-emitting diodes (LEDs) or organic light-emitting diodes (OLEDs) (e.g., a micro-LED display panel or the like) located in region 112. In some embodiments, the light engine is configured to emit RGB light. In some embodiments, the light engine includes multiple laser diodes (e.g., a red laser diode, a green laser diode, and / or a blue laser diode) and at least one scan mirror (e.g., two one-dimensional scan mirrors, which may be micro-electromechanical system (MEMS)-based or piezobased). The light engine is communicatively coupled to the controller (not shown) and a non-transitory processor-readable storage medium or memory storing processorexecutable instructions and other data that, when executed by the controller, cause the controller to control the operation of the light engine. In some embodiments, the controller controls a scan area size and scan area location for the light engine and is communicatively coupled to a light engine (not shown) that generates content to be displayed at the eyewear display 100. The light engine scans light over a variable area, designated the FOV area 106, of the eyewear display 100. The scan area size corresponds to the size of the FOV area 106, and the scan area location corresponds to a region of one of the lens elements 108, 110 at which the FOV area 106 is visible to the user. Generally, it is desirable for a display to have a wide FOV area 106 to accommodate the outcoupling of light across a wide range of angles.

[0030] As previously mentioned, a waveguide is integrated into one or both of lens elements 108, 110. In some configurations, the waveguide includes a single waveguide substrate and in other configurations, the waveguide includes multiplewaveguide substrates stacked on top of one another (referred to as a waveguide stack). The waveguide is separated from the light engine by a first distance that is restricted by the form factor of the eyewear display 100 and, according to some aspects of the present disclosure, a light filter is located within this first distance, i.e., between the waveguide and the light engine. The light filter receives the light emitted from the light engine and outputs a color gradient of light that varies along a first direction. For example, the first direction is aligned with an incoupling direction in which the light is incoupled into the waveguide. In some embodiments, the incoupler of the waveguide includes incoupler grating features that vary along the incoupling direction to incouple different wavelengths of light at different diffraction efficiencies. For example, the incoupler is aligned with the light filter such that light including blue light is incident on the incoupler at or near an edge of the incoupler that lies closest to the path of light propagation within the waveguide.

[0031] FIG. 2 illustrates a diagram of a projection system 200 that projects images onto the eye 216 of a user in accordance with various embodiments. The projection system 200, which may be implemented in the eyewear display 100 in FIG. 1 , includes one or more of a light engine 202, an optical scanner 204, a light filter 230, and / or a waveguide 205. In this example, the optical scanner 204 includes a first scan mirror 206, a second scan mirror 208, and an optical relay 210. The waveguide 205 includes one or more incouplers 212 and one or more outcouplers 214, with the one or more outcouplers 214 being optically aligned with an eye 216 of a user. For example, the one or more outcouplers 214 substantially overlap with the FOV area 106 shown in FIG. 1 .

[0032] The light engine 202 includes one or more light sources configured to generate and project display light 218 (e.g., visible light such as RGB light and, in some embodiments, non-visible light such as infrared light). In some embodiments, the light engine 202 is coupled to a driver or other controller (not shown), which controls the timing of emission of display light from the light sources of the light engine 202 in accordance with instructions received by the controller or driver from a computer processor coupled thereto to modulate the display light 218 to be perceivedas images when output to the retina of an eye 216 of a user. For example, during operation of the projection system 200, one or more beams of display light 218 are output by the light source(s) of the light engine 202 and then directed into the waveguide 205 before being directed to the eye 216 of the user. The light engine 202 modulates the respective intensities of the light beams so that the combined light reflects a series of pixels of an image, with the particular intensity of each light beam at any given point in time contributing to the amount of corresponding color content and brightness in the pixel being represented by the combined light at that time.

[0033] In some embodiments, the light engine 202 projects the display light 218 to an optical scanner 204. In some embodiments, one or both of the scan mirrors 206 and 208 in the optical scanner 204 are MEMS mirrors that are driven by respective actuation voltages to oscillate during active operation of the projection system 200, causing the scan mirrors 206 and 208 to scan the light 218. Oscillation of the scan mirror 206 causes light 218 output by the light engine 202 to be scanned through the optical relay 210 and across a surface of the second scan mirror 208. The second scan mirror 208 scans the light 218 received from the scan mirror 206 toward the incoupler 212 of the waveguide 205. In some embodiments, the scan mirror 206 oscillates along a first scanning axis 219, such that the light 218 is scanned in only one dimension (i.e., in a line) across the surface of the second scan mirror 208. In some embodiments, the scan mirror 208 oscillates or otherwise rotates along a second scanning axis 221. In some embodiments, the first scanning axis 219 is perpendicular to the second scanning axis 221.

[0034] In some embodiments, the optical relay 210 is a line-scan optical relay that receives the light 218 scanned in a first dimension by the first scan mirror 206 (e.g., the first dimension corresponding to the small dimension of the incoupler 212), routes the light 218 to the second scan mirror 208, and introduces a convergence to the light 218 in the first dimension to an exit pupil beyond the second scan mirror 208. Herein, an “exit pupil” in an optical system refers to the location along the optical path where beams of light intersect. For example, the possible optical paths of the light 218, following reflection by the first scan mirror 206, are initially spread along the firstscanning axis, but later these paths intersect at an exit pupil beyond the second scan mirror 208 due to convergence introduced by the optical relay 210. For example, the width (i.e. , smallest dimension) of a given exit pupil approximately corresponds to the diameter of the light corresponding to that exit pupil. Accordingly, the exit pupil can be considered a “virtual aperture.” According to various embodiments, the optical relay 210 includes one or more collimation lenses that shape and focus the light 218 on the second scan mirror 208 or includes a molded reflective relay that includes two or more spherical, aspheric, parabolic, and / or freeform lenses that shape and direct the light 218 onto the second scan mirror 208. The second scan mirror 208 receives the light 218 and scans the light 218 in a second dimension, the second dimension corresponding to the long dimension of the incoupler 212 of the waveguide 205. In some embodiments, the second scan mirror 208 causes the exit pupil of the light 218 to be swept along a line along the second dimension.

[0035] In some embodiments, the light engine 202 projects display light 218 directly to the light filter 230. That is, in some embodiments, the optical scanner 204 is absent from projection system 200. Accordingly, in such embodiments, the light engine 202 is arranged such that the optical path of the light 218 emitted from the light engine 202 is in line with the incoupler 212 and the light filter 230 is arranged therebetween. In other embodiments, the light filter 230 is included in the optical relay 210 of the optical scanner 204.

[0036] In some embodiments, the light filter 230 is positioned between the light engine 202 and incoupler 212 without making contact with either one. In other embodiments, the light filter 230 is optically bonded to the light engine 202 or to the incoupler 212.

[0037] In any case, the display light 218 emitted from the light engine 202 towards the incoupler 212 passes through the light filter 230. The light filter 230, in some embodiments, the light filter 230 includes a spatial color filter gradient that varies along a first direction 232 of the light filter 230. The spatial color filter of the light filter 230 transmits or absorbs different colors (i.e., wavelength ranges) of light along the first direction 232. For example, at a first side 230-1 of the light filter 230, all of theRGB light in the display light that is incident on the light filter 230 passes through. At a second side 230-2 of the light filter 230, all the display light that is incident thereon is absorbed. In between the first side 230-1 and the second side 230-2, the light filter 230 allows different colors of light to pass through along the first direction 232. Thus, after passing through the light filter 230, the display light 218 ranges from light having a wide range of wavelengths to light having a more specific wavelength range along the first direction 232 when it is incident on the incoupler 212.

[0038] The incoupler 212 is configured to receive the display light 218 after it passes through the light filter 230 and direct the display light 218 into the waveguide 205. In some embodiments, the incoupler 212 is defined by a smaller dimension (i.e. , width) and a larger orthogonal dimension (i.e., length) with a first edge 212-1 that is closest to the incoupling direction 240 and a second edge 212-2 that is farthest from the incoupling direction 240. In some embodiments, the “incoupler region” is defined as the region of the waveguide 205 between the first edge 212-1 and the second edge 212-2 of the incoupler 212. In some aspects, the incoupling direction 240 is defined as the direction in which the incoupled light is propagated within the waveguide 205. The term “waveguide,” as used herein, is understood to mean a combiner using one or more of total internal reflection (TIR), specialized filters, or reflective surfaces, to transfer light from an incoupler (such as incoupler 212) to an outcoupler (such as the outcoupler 214). In some display applications, the light is a collimated image, and the waveguide 205 transfers and replicates the collimated image to the eye. In general, the terms “incoupler” and “outcoupler” will be understood to refer to any type of optical grating structure, including, but not limited to, reflective facets, diffraction gratings, holograms, holographic optical elements (e.g., optical elements using one or more holograms), volume diffraction gratings, volume holograms, surface relief diffraction gratings, and / or surface relief holograms. In some embodiments, a given incoupler or outcoupler is configured as a transmissive grating (e.g., a transmissive diffraction grating or a transmissive holographic grating) that causes the incoupler or outcoupler to transmit light and to apply designed optical function(s) to the light during the transmission. In some embodiments, a given incoupler or outcoupler is a reflective grating (e.g., a reflectivediffraction grating or a reflective holographic grating) that causes the incoupler or outcoupler to reflect light and to apply designed optical function(s) to the light during the reflection. In the present example, the light 218 received at the incoupler 212 is propagated to the outcoupler 214 via the waveguide 205 using TIR. A portion of the light 218 is then output to the eye 216 of a user via the outcoupler(s) 214. Also, in some embodiments, one or more exit pupil expanders (not shown), such as a fold grating, are arranged in an intermediate stage between incoupler 212 and outcoupler 214 to receive light that is coupled into waveguide 205 by the incoupler 212, expand the light in one dimension, and redirect the light towards the outcoupler 214. As described above, in some embodiments the waveguide 205 is implemented in an optical combiner as part of an eyeglass lens, such as the lens element 108, 110 (FIG. 1) of the display system having an eyeglass form factor and employing projection system 200.

[0039] The waveguide 205 includes two major surfaces 220 and 222, with major surface 220 being world-side (i.e., the surface farthest from the user) and major surface 222 being eye-side (i.e., the surface closest to the user). In some embodiments, the waveguide 205 is between a world-side lens and an eye-side lens, which form lens elements 108, 110 shown in FIG. 1 , for example. In some embodiments, the incoupler 212 and the outcoupler 214 are located, at least partially, at major surface 220. In another embodiment, the incoupler 212 and the outcoupler 214 are located, at least partially, at major surface 222. In further embodiments, the incoupler 212 is located at one of the major surfaces, while the outcoupler 214 is located at the other of the major surfaces.

[0040] FIG. 3 shows an example of light propagation within the waveguide 205 of the projection system 200 of FIG. 2. As shown, light is received via the incoupler 212, scanned along the axis 302, directed into an exit pupil expander (EPE) 304, and then directed to the outcoupler 214 to be output from the waveguide 205 (e.g., toward the eye of the user). In some embodiments, EPE 304 expands one or more dimensions of the eyebox of an eyewear display that includes the projection system 200 (e.g., with respect to what the dimensions of the eyebox of the eyewear display would bewithout the EPE 304). In some embodiments, the incoupler 212 and the EPE 304 each include respective one-dimensional diffraction gratings (i.e. , diffraction gratings that extend along one dimension). It should be understood that FIG. 3 shows a case in which the incoupler 212 directs light straight down (with respect to the presently illustrated view) in a first direction that is perpendicular to the scanning axis 302 and the EPE 304 directs light to the right (with respect to the presently illustrated view) in a second direction that is perpendicular to the first direction. While not shown in the present example, in other embodiments, the first direction in which the incoupler 212 directs light is slightly or substantially diagonal, rather than perpendicular, with respect to the scanning axis 302.

[0041] Also shown in FIG. 3 is a cross-section 306 of the incoupler 212 illustrating features of the grating (also referred to as grating features) that can be configured to tune the efficiency of the incoupler 212. The period p of the grating is shown having two regions, with transmittances t1 and t2 and widths d1 and d2, respectively. The grating period is constant p=d1+d2, but the relative widths d1 , d2 of the two regions may vary. In some embodiments, the relationship between the relative widths and the period is indicated by a fill factor such that d1=xp and d2=(1-x)p. In addition, while the profile shape of the grating features in cross-section 306 is generally shown as being square or rectangular with a height h, the shape can be modified based on the wavelength of light that the incoupler 212 is intended to receive. For example, in some embodiments, the shape of the grating features is triangular, rather than square, to create a more “saw-toothed” profile. In some embodiments, the incoupler 212 is configured as a grating with a constant period but different fill factors, heights, and slant angles (9) based on the desired efficiency of the respective incoupler 212 or the desired efficiency of a region of the respective incoupler 212. Although shown as being at or near 90° in FIG. 3, in some embodiments, the slant angles (9) can be acute or obtuse angles. For example, slanted or blazed gratings include slant angles (9) other than 90°. In some embodiments, the grating features of the incoupler 212 vary along the incoupling direction to incouple different wavelength ranges of light at different diffraction efficiencies.

[0042] FIG. 4 illustrates a portion of an eyewear display 400 in accordance with various embodiments. In some embodiments, the eyewear display 400 represents the display 100 of FIG. 1 and includes the components of the projection system 200 of FIG. 2. The light engine 202, the optical scanner 204, the incoupler 212, the light filter 230, and a portion of the waveguide 205 are included in an arm 402 of the eyewear display 400, in the present example.

[0043] The eyewear display 400 includes an optical combiner lens 404, which includes a first lens 406, a second lens 408, and the waveguide 205, with the waveguide 205 disposed between the first lens 406 and the second lens 408. Light exiting through the outcoupler 214 travels through the second lens 408 (which corresponds to, for example, the lens element 110 of the eyewear display 100). In use, the light exiting second lens 408 enters the pupil of an eye 410 of a user wearing the eyewear display 400, causing the user to perceive a displayed image carried by the laser light output by the light engine 202. The optical combiner lens 404 is substantially transparent, such that light from real-world scenes corresponding to the environment around the eyewear display 400 passes through the first lens 406, the second lens 408, and the waveguide 205 to the eye 410 of the user. In this way, images or other graphical content output by the projection system 200 are combined (e.g., overlayed) with real-world images of the user’s environment when projected onto the eye 410 of the user to provide an AR experience to the user. The eyebox of eyewear display 400 corresponds to the region (or volume) in which the eye 410 of the user can perceive images associated with light projected from light engine 202.

[0044] In some embodiments additional optical elements are included in any of the optical paths between the light engine 202 and the incouplers 212, in between the incouplers 212 and the outcoupler(s) 214, and / or in between the outcoupler(s) 214 and the eye 410 of the user (e.g., in order to shape the display light from light engine 202 for viewing by the eye 410 of the user). As an example, the light filter 230 is used to generate a color gradient in the light that is incident on the incoupler 212. In some embodiments, the light filter 230 is located in the hinge of the eyewear display 400, and in other embodiments, it is located before the hinge of the eyewear display 400(as shown in FIG. 4). In some embodiments, the grating features of the incoupler(s) 212 are designed such that the incoupler 212 receives light from the light filter 230 and incouples it into the waveguide 205 at an appropriate angle to allow propagation of the light in waveguide 205 by TIR.

[0045] FIG. 5 shows an example top view of a light filter 500, such as one corresponding to light filter 230 in FIGs. 2 and 4, in accordance with various embodiments. In some embodiments, the light filter 500 is a single layer, spatially varying color filter. That is, the light filter 500 includes multiple adjacent regions where each region is configured to transmit (i.e., allow corresponding light to pass through) or block (e.g., absorb) different wavelength ranges of light. In other embodiments, the light filter 500 is a series of stacked absorptive color filters in which each absorptive color filter in the stack implements one of various regions that are configured to absorb different colors (i.e., wavelength ranges) of light. When viewed from a top view as shown in FIG. 5, the series of stacked absorptive color filters resembles a single layer, spatially varying color filter due to the overlapping absorptive color filters covering different regions.

[0046] In either embodiment (i.e., in the embodiment with the single layer, spatially varying color filter or in the embodiment with the series of stacked absorptive color filters), the light filter 500 has a plurality of regions 502-508 that are arranged adjacent to one another along a first direction 510. In some cases, the first direction 510 is aligned with the incoupling direction in which light is incoupled by the incoupler into the waveguide (e.g., referring to FIGs. 2 and 5, first direction 510 corresponds to first direction 232 that is aligned with incoupling direction 240). The first region 502 is closest to a first edge 512-1 of the light filter and is configured to allow all of the display light incident thereon to pass through. For example, the first region 502 is a substantially optically clear material that transmits red, green, and blue light. A second region 504 is arranged next to the first region 502 along the first direction 510. In some embodiments, the second region 504 is a color filter that blocks (e.g., absorbs) blue light and allows red and green light to pass through. A third region 506 is arranged next to the second region 504 along the first direction 510. In someembodiments, the third region 506 is a color filter that blocks (e.g., absorbs) blue light and green light and allows red light to pass through. In some embodiments, a fourth region 508 is arranged next to the third region 506. In some embodiments, the fourth region 508 blocks all light (e.g., absorbs RGB light) such that no display light passes through. In this manner, the light filter 500 begins to block (e.g., absorb) increasingly larger wavelengths of light as the distance from the first edge 512-1 increases. For example, first, the light filter 500 begins to block blue light at region 504, then blocks both blue and green light at region 506, then blocks red, green, and blue light at region 508. In other words, as the distance from the first edge 512-2 increases, the light filter’s cutoff wavelength also increases. As such, the light filter 500 generates a light gradient at its output that includes light with different wavelength ranges along the first direction 510.

[0047] Although shown as having four regions 502-508 in FIG. 5, in other embodiments, the light filter 500 has a different number of regions (e.g., 2, 3, or 5). For example, in a light filter with three regions instead of the four regions illustrated in FIG. 5, the first region closest to the edge 512-1 transmits all light, the second region adjacent to the first region transmits only red light (and block blue and green light), and the third region adjacent to the second region on the opposite side of the first region blocks all of the display light. In addition, although shown as having distinct edges in FIG. 5, the transition between the regions 502-508 may not be as well defined and instead may be implemented as a gradual transition from one region to the next. Also, FIG. 5 shows an embodiment in which the light filter 500 has a flat color gradient (i.e., regions 502-508 are defined by chords of the circle). In other embodiments, the color gradient has a different geometry (e.g., see light filters 850 and 860 of FIG. 8).

[0048] Thus, in accordance with various of the embodiments described herein, the light filter 500 includes a gradient implemented by the various regions 502-508 that transmits different wavelength ranges of light along the first direction 510. The light filter 500 is positioned in the optical path of light between the light engine (such as light engine 202 in FIG. 2) and the point of being incoupled into the waveguide via theincoupler (such as incoupler 212 in FIG. 2). As such, the light filter 500 receives the display light emitted from the light engine and generates light with a light gradient at the light filter’s 500 output for incoupling into the waveguide via the incoupler.

[0049] FIG. 6 shows an example of a cross section view of a light filter and incoupler system 600 of an eyewear display, such as eyewear display 100 of FIG. 1 , in accordance with various embodiments. The light filter and incoupler system 600 includes the light filter 610 (e.g., such as light filter 500 of FIG. 5) and an incoupler 620 (e.g., such as incoupler 212 of FIG. 2) of a waveguide 630. Incoupling direction 640 shows the direction in which light is propagated within the waveguide 630 after being incoupled via the incoupler 620. The light filter and incoupler system 600 receives display light 650 emitted from a light engine (e.g., such as light engine 202 of FIG. 2) in the eyewear display.

[0050] As illustrated in this example, the light filter 610 is a single layer, spatially varying color filter with multiple regions 612-618. The multiple regions 612-618 are adjacent to one another along a first direction 642 and implement a gradient that transmits different wavelength ranges of light along the first direction 642. In some embodiments, each of the regions 612-618 correspond to the regions 502-508, respectively, described with respect to FIG. 5. That is, region 612 is an optically transparent region that transmits all light (i.e. , region 612 allows red, green, and blue light to pass through), region 614 is a color filter that blocks blue light and transmits red and green light, region 616 is a color filter that blocks blue and green light and transmits red light, and region 618 blocks red, green, and blue light. In this manner, the light output from region 612 toward the incoupler 620 includes light having wavelength ranges corresponding to red, green, and blue light, the light output region 614 toward the incoupler 620 includes light having wavelength ranges corresponding to red and green light (but not blue light), and the light output from region 616 toward the incoupler 620 includes light having a wavelength range corresponding to red light (but not blue and green light).

[0051] The incoupler 620 includes a number of incoupler segments 622-628 adjacent to one another along the incoupling direction 640. In some embodiments,the incoupling direction 640 is aligned with the first direction 642. For example, the incoupling direction 640 is parallel or substantially parallel (e.g., having an angle of difference of 10° or less) to the first direction 642. The incoupler segments 622-628 include one or more grating features that vary across the incoupler segments 622- 628. For example, incoupler segment 622 includes a grating of height hi , incoupler segment 624 includes a grating of height h?, incoupler segment 626 includes a grating of height hs, and incoupler segment 628 includes a grating of height , where each of the grating heights hi to h4 are different. In some embodiments, each one of the grating heights in the corresponding incoupler segments 622-628 is selected to correspond with the wavelength range of display light that passes through the light filter 610. For example, the grating height of the gratings in incoupler segment 622 is selected to have a high diffraction efficiency for all wavelengths of light (e.g., RGB light), the grating height of the gratings in incoupler segment 624 is selected to have a high diffraction efficiency for red and green light, and the grating height of the gratings in incoupler segment 626 is selected to have a high diffraction efficiency for red light. In some embodiments, incoupler segment 628 (e.g., the last incoupler segment further from the incoupling direction that corresponds to region 618 that blocks all light) includes a recycling grating. The recycling grating receives light that is incoupled into the waveguide in the opposite direction of the incoupling direction 640 back toward the incoupling direction. That is, the recycling grating “recycles” the light that is diffracted into the waveguide at an m=-1 order back into the m=+1 order, where the m=+1 order corresponds to the light incoupled to the incoupling direction 640. In some cases, the recycling grating has a smaller period than the period of the incoupler grating, e.g., half the period of the incoupler grating, and has the same orientation as the incoupler grating. In other embodiments, an additional or alternative grating feature (i.e., in addition to or other than the grating height) may vary from one incoupler segment to the next. For example, each incoupler segment 622-628 may additionally or alternatively have different fill factors, different grating angles, be made of different materials, or be coated with different materials to accomplish the varying diffraction efficiencies for the different wavelength ranges of light that are output from the light filter 610.

[0052] In some embodiments, when implemented as a single layer, spatially varying color filter as illustrated in FIG. 6, the light filter 610 includes different regions 612-618 in a single layer that are adjacent to one another. In these embodiments, the light filter 610 is made by lithographic, inkjet, or similar processes, for example, such that the regions 612-618 are adjacent to one another as shown in FIGs. 5 and 6, for example.

[0053] FIG. 7 shows an example top view of an incoupler 700 with an arrow 720 illustrating the incoupling direction in accordance with some embodiments. Incoupling direction 720 corresponds to the direction in which the display light beams incident on incoupler 700 are propagated within the waveguide (not shown). The incoupler 700 includes a first edge 712-1 (also referred to as the incoupling edge) arranged closest to the path of the incoupling direction 720 and a second edge 712-2 arranged farthest from the path of the incoupling direction 720. The number of interactions that a display light beam has with the incoupler is denoted at FIG. 7 as “n,” where “n=1” corresponds to the display light beam having one interaction with the incoupler, “n=2” corresponds to the display light beam having two interactions with the incoupler (the initial interaction in which the display light beam is incoupled into the waveguide and one rebounce), and so on. As shown in FIG. 7, the incoupler includes an n=1 area 702, an n=2 area 704, an n=3 area 706, and an n=4 area 708. Thus, display light incident in area 702 experiences the fewest number of interactions (only one) with the incoupler 700 and display light incident on area 708 experiences the highest number of interactions (in this case, four) with the incoupler 700.

[0054] Areas of the incoupler 700 further from the first edge 712-1 have lower coupling efficiency and contribute more to generation of mirrored ghost artifacts. In some embodiments, for diffractive incoupler grating designs that have exit pupil diameter larger than the waveguide thickness, it is typical for a small region of the exit pupil to have high coupling efficiency and low possibility of generating mirror ghost artifact (i.e. , corresponding to the n=1 region 702). The size of this region is wavelength dependent as the bounce spacing of light has a strong effect on rebounce loss. Thus, by controlling the color of light that is incident on the incouplerat the different areas 702-708 of the incoupler 700 via a light filter as described herein, the amount of light that is reflected off of the incoupler is reduced, thereby minimizing the type of light that is responsible for generating image ghost artifacts.

[0055] FIG. 8 shows a first column 800 illustrating top views of an incoupler. Each top view 800-1 , 800-2, 800-3 represents the same incoupler indicating different color dependent high coupling efficiency regions of the incoupler. FIG. 8 also shows example top views of two light filters 850, 860 implementing different color gradient schemes (also referred to as color masking schemes) to output a light color gradient corresponding to the high coupling efficiency regions illustrated in the first column 800 in accordance with various embodiments.

[0056] The first column 800 shows three example diagrams 800-1 to 800-3 of an incoupler illustrating the multiple high coupling efficiency regions for different colors. As such, the example diagrams 800-1 to 800-3 correspond to the same incoupler (e.g., such as an incoupler in any of the previous Figures). The incoupling direction 820 is also shown for the incoupler is also shown. In the first example diagram 800-1 , incoupler region 802 corresponds to the high coupling efficiency for blue light and incoupler region 812 corresponds to the low coupling efficiency for blue light. That is, blue light that is incident on incoupler region 802 is more likely to be incoupled and retained within the waveguide than blue light that is incident on incoupler region 812. For example, blue light that is incoupled in incoupler region 812 is more likely to be incident on the incoupler a second time, and therefore be prematurely extracted from the incoupler. In the second example diagram 800-2, incoupler region 804 corresponds to the high coupling efficiency for green light and incoupler region 814 corresponds to the low coupling efficiency for green light. That is, green light that is incident on incoupler region 804 is more likely to be incoupled and retained within the waveguide than green light that is incident on incoupler region 814. For example, green light that is incoupled in incoupler region 814 is more likely to be incident on the incoupler a second time, and therefore be prematurely extracted from the incoupler. As illustrated, the incoupler region 804 that has a high coupling efficiency for green light includes the incoupler region 802 that has a high coupling efficiency forblue light. In the third example diagram 800-3, incoupler region 806 corresponds to the high coupling efficiency for red light and incoupler region 816 corresponds to the low coupling efficiency for red light. That is, red light that is incident on incoupler region 806 is more likely to be incoupled and retained within the waveguide than red light that is incident on incoupler region 816. For example, red light that is incoupled at incoupler region 816 is more likely to be incident on the incoupler a second time, and therefore be prematurely extracted from the incoupler. As illustrated, the incoupler region 806 that has a high coupling efficiency for red light includes the incoupler regions 802, 804 that have a high coupling efficiency for blue light and green light, respectively. The different sizes of the regions of high coupling efficiency for the different colors of light are attributed to the different wavelengths, and thus the different angles at which the light is diffracted into the waveguide. Blue light has a shorter wavelength and is thus diffracted at a sharper angle into the waveguide, thereby increasing the number of times that it can potentially interact (i.e., bounce on) the incoupler again. The corresponding incoupler regions 812, 814, 816 for each color of light are the regions that will likely contribute to the generation of mirrored ghost artifacts. Thus, a light filter is implemented in the optical path between the light engine and the incoupler to reduce the amount of light of a corresponding color that is incident on each of these low coupling efficiency regions since this light contributes more to the generation of mirror ghost artifacts than light that is incident on the high coupling regions. For example, the light filter blocks blue light so that it is less likely to be incident on incoupler region 812, blocks green light so that it is less likely to be incident on incoupler region 814, and blocks red light so that it is less likely to be incident on incoupler region 816. Two examples of light filters 850, 860 are illustrated on the right side of FIG. 8.

[0057] Light filter 850 shows an embodiment with four light masking regions 852, 854, 856, 858. In some embodiments, the light filter 850 is similar to the light filter 500 of FIG. 5 with a difference in that the regions of light filter 850 are designed to follow the incoupler geometries discussed in diagrams 800-1 to 800-3. The first light masking region 852 transmits all light (e.g., allows red, green, and blue light to pass through). The second light masking region 854 transmits red light and green light butblocks blue light. The third light masking region 856 transmits red light but blocks blue light and green light. The fourth light masking region 858 blocks all light. Thus, the light passing through the light filter 850 has a color gradient corresponding to the high coupling efficiency regions discussed above. As such, the light filter 850 minimizes or eliminates the different light colors incident on the corresponding lower coupling efficiency regions of the incoupler, thereby reducing the amount of light that is reflected off of the incoupler. This diminishes or eliminates the appearance of mirrored ghost artifacts.

[0058] Light filter 860 shows an alternative embodiment with three light masking regions 862, 864, 866. In some embodiments, since the light filter 860 has fewer masking regions, it may facilitate manufacturing of the light filter 860. The first light masking region 862 transmits all light (e.g., allows red, green, and blue light to pass through). The second light masking region 864 transmits red light and green light but blocks blue light. The third light masking region 866 transmits red light but blocks blue light and green light. As such, some red light may be incident on incoupler region 816. However, since this region is relatively small, the impact on the generation of mirrored ghost artifacts may be insignificant. That is, the light filter 860 minimizes the different light colors incident on the corresponding lower coupling efficiency regions of the incoupler, thereby reducing the amount of light that is reflected off of the incoupler. This diminishes or eliminates the appearance of mirrored ghost artifacts.

[0059] FIG. 9 shows examples of light filters 900, 910, 920, 930, 940, 950 being implemented as a series of stacked color filters in accordance with various embodiments. In the illustrations shown in FIG. 9, each light filter 900, 910, 920, 930, 940, 950 receives light emitted by the light engine from the top of the respective light filter (i.e., above layers 902, 912, 922, 932, 942, 952, respectively) and outputs a light having a color gradient from the bottom of the respective light filter (i.e., below layers 906, 916, 926, 936, 946, 956, respectively). Thus, although the incoming light and output light color gradient is only shown for the first light filter 900 for clarity purposes, it is appreciated that the other light filters 910, 920, 930, 940, 950 also receive light from the light engine and output light having a color gradient in a similar manner.

[0060] In some embodiments, the light filter is positioned parallel or substantially parallel to the waveguide surface. Three such embodiments are shown in light filters 900, 910, 920.

[0061] Light filter 900 includes multiple stacked color filters 902, 904, 906. Each color filter 902, 904, 906 includes a non-shaded region that transmits all light (i.e., allows all light to pass through) and a shaded region that blocks a specific wavelength range (i.e., color or colors) of light. For example, color filter 902 includes region 902-1 that blocks (e.g., absorbs) all colors of light. Color filter 904 includes region 904-1 that allows red light to pass through but blocks (e.g., absorbs) blue light and green light. Color filter 906 includes a region 906-1 that allows red light and green light to pass through but blocks (e.g., absorbs) blue light.

[0062] In this manner, light filter 900 outputs a light gradient of different light colors based on incoming light 901 received from the light engine. In some embodiments, the incoming light 901 includes red, green, and blue light. The light gradient output from the light filter 900 includes multiple components: a first component 901 includes red, green, and blue light; a second component 903 includes red light and green light; a third component 905 includes red light; and a fourth component 907 includes no red, blue, or green light. Thus, from right to left, the light filter 900 at first absorbs no wavelengths of light, then begins to absorb shorter wavelengths of light (e.g., blue light) then additionally begins to absorb longer wavelengths of light (e.g., green light then also red light).

[0063] Although shown as being spaced apart in light filter 900, in some embodiments, the color filters 902, 904, 906 are stacked directly on top of one another and adhered to one another with an optically appropriate adhesive.

[0064] Light filter 910 includes multiple stacked color filters 912, 914, 916. Color filter 912 is implemented as a prism that blocks (e.g., absorbs) all light. By implementing color filter 912 as a prism, any light that is reflected off of it is reflected at a non-zero angle. In some embodiments, this helps to further reduce the light associated with the generation of mirrored ghost artifacts. Each color filter 914, 916includes a non-shaded region that transmits all light (i.e., allows all light to pass through) and a shaded region that blocks a specific wavelength range (i.e., color or colors) of light. Color filter 914 includes region 914-1 that allows red light to pass through but blocks (e.g., absorbs) blue light and green light. Color filter 916 includes a region 916-1 that allows red light and green light to pass through but blocks (e.g., absorbs) blue light. Although shown as being spaced apart in light filter 910, in some embodiments, the color filters 912, 914, 916 are stacked directly on top of one another and adhered to one another with an optically appropriate adhesive.

[0065] Light filter 920 includes multiple stacked color filters 922, 924, 926. Color filter 922 is implemented as a Fresnel prism that blocks (e.g., absorbs) all light. In some embodiments, this helps to further reduce the light associated with the generation of mirrored ghost artifacts and occupies less volume than the prism 912 shown in light filter 910. Each color filter 924, 926 includes a non-shaded region that transmits all light (i.e., allows all light to pass through) and a shaded region that blocks a specific wavelength range (i.e., color or colors) of light. Color filter 924 includes region 924-1 that allows red light to pass through but blocks (e.g., absorbs) blue light and green light. Color filter 926 includes a region 926-1 that allows red light and green light to pass through but blocks (e.g., absorbs) blue light. Although shown as being spaced apart in light filter 920, in some embodiments, the color filters 922, 924, 926 are stacked directly on top of one another and adhered to one another with an optically appropriate adhesive.

[0066] In some embodiments, the light filter can be arranged tilted with respect to the incoming light from the light engine to redirect any light that reflects off of the light filter away from the light engine. Three such embodiments are shown in light filters 930, 940, 950. In some of these configurations, the tilted filter embodiments shown in 930, 940, 950 are used in combination with a light trap that absorbs the light reflected by the tilted surface. For example, this light trap may be a dark surface positioned to the upper left (as illustrated in FIG. 9) of any one of light filters 930, 940, 950. One such example of a light trap 939 is shown for light filter 930.

[0067] Light filter 930 includes multiple stacked color filters 932, 934, 936. Each color filter 932, 934, 936 includes a non-shaded region that transmits all light (i.e., allows all light to pass through) and a shaded region that blocks a specific wavelength range (i.e., color or colors) of light. For example, color filter 932 includes region 932-1 that blocks (e.g., absorbs) all colors of light. Color filter 934 includes region 934-1 that allows red light to pass through but blocks (e.g., absorbs) blue light and green light. Color filter 936 includes a region 936-1 that allows red light and green light to pass through but blocks (e.g., absorbs) blue light. Although shown as being spaced apart in light filter 930, in some embodiments, the color filters 932, 934, 936 are stacked directly on top of one another and adhered to one another with an optically appropriate adhesive.

[0068] Light filter 940 includes multiple stacked color filters 942, 944, 946. Each color filter 942, 944, 946 includes a non-shaded region that transmits all light (i.e., allows all light to pass through) and a shaded region that blocks a specific wavelength range (i.e., color or colors) of light. For example, color filter 942 includes region 942-1 that blocks (e.g., absorbs) all colors of light. Color filter 944 includes region 944-1 that allows red light to pass through but blocks (e.g., absorbs) blue light and green light. Color filter 946 includes a region 946-1 that allows red light and green light to pass through but blocks (e.g., absorbs) blue light. In some embodiments, the color filters 942, 944, 946 are adhered to one another with an optically appropriate adhesive. Light filter 940 also includes a base prism 948 on which the stack of color filters 942, 944, 946 is positioned. In some embodiments, the base prism 948 ensures that the stack of color filters 942, 944, 946 retains its position or angle relative to other optical components in the eyewear display. In some embodiments, the base prism 948 is made of an optically transparent material that transmits red, green, and blue light.

[0069] Light filter 950 includes multiple stacked color filters 952, 954, 956. Each color filter 952, 954, 956 includes a non-shaded region that transmits all light (i.e., allows all light to pass through) and a shaded region that blocks a specific wavelength range (i.e., color or colors) of light. For example, color filter 952 includesregion 952-1 that blocks (e.g., absorbs) all colors of light. Color filter 954 includes region 954-1 that allows red light to pass through but blocks (e.g., absorbs) blue light and green light. Color filter 956 includes a region 956-1 that allows red light and green light to pass through but blocks (e.g., absorbs) blue light. In some embodiments, the color filters 952, 954, 956 are adhered to one another with an optically appropriate adhesive. Light filter 950 also includes two prisms 958, 960 between which the stack of color filters 942, 944, 946 is positioned. In some embodiments, the two prisms 958, 960 ensure that the stack of color filters 942, 944, 946 retains its position or angle relative to other optical components in the eyewear display. In some embodiments, the two prisms 958, 960 are made of an optically transparent material that transmits red, green, and blue light.

[0070] In some embodiments, the different features discussed above with respect to light filters 900, 910, 920, 930, 940, 950 can be combined with one another. For example, in some embodiments, one or more prisms such as those shown for light filters 940 and 950 are integrated into one or more of light filters 900, 910, 920, 930.

[0071] FIG. 10 shows several example top views of a red color filter positioned with respect to an incoupler in accordance with various embodiments. As such, FIG. 10 illustrates simplified embodiments in which a single color filter that is shaped and positioned with respect to an incoupler that is separated into two regions: a first region optimized for incoupling broadband light (e.g., RGB light) and a second region optimized for incoupling red light. In this manner, the overall design can be simplified while removing regions that contribute more to the generation of mirrored ghost artifacts (e.g., the regions where blue light and green light are incoupled at a low coupling efficiency).

[0072] One example of an incoupler 1000 and a correspondingly positioned light filter 1012 is shown at the top of FIG. 10. Incoupler 1000 is shaped optimized and binary segmented according to the incoupling direction 1006. For example, as shown in FIG. 10, the incoupler 100 includes two crescent shaped sections: incoupler section 1002 has grating features that are designed for optimizing the incoupling of broadband light (e.g., RGB light) and incoupler section 1004 has grating features thatare designed for optimizing the incoupling of red light. Diagram 1010 shows the positioning of a red color filter 1012 with respect to incoupler 1000 (the outline of incoupler 1000 is shown as a dashed line). As illustrated, the area 1002-1 in diagram 1010 corresponds to incoupler section 1002 that incouples broadband light. In some embodiments, the red color filter 1012 is implemented as an optically transparent red film on a clear substrate or as a single, optically transparent red sheet (e.g., a plastic or polymer sheet).

[0073] Another example of an incoupler 1050 and a correspondingly positioned light filter 1062 is shown at the bottom of FIG. 10. Incoupler 1050 is shaped optimized and binary segmented according to the incoupling direction 1056. For example, as shown in FIG. 10, the incoupler 100 includes two rectangular shaped sections: incoupler section 1052 has grating features that are designed for optimizing the incoupling of broadband light (e.g., RGB light) and incoupler section 1054 has grating features that are designed for optimizing the incoupling of red light. Diagram 1060 shows the positioning of a red color filter 1062 with respect to incoupler 1050 (the outline of incoupler 1050 is shown as a dashed line). As illustrated, the area 1052-1 in diagram 1060 corresponds to incoupler section 1052 that incouples broadband light. In some embodiments, the red color filter 1062 is implemented as an optically transparent red film on a clear substrate or as a single, optically transparent red sheet (e.g., a plastic or polymer sheet).

[0074] FIG. 11 shows an example of a cross section view of a light filter and incoupler system 1100 of an eyewear display with the light filter applied to the backside of a waveguide, in accordance with various embodiments. The light filter and incoupler system 1100 includes the light filter 1120 and an incoupler 1110 (e.g., such as incoupler 212 of FIG. 2) of a waveguide 1130. Incoupling direction 1180 shows the direction in which light is propagated within the waveguide 1130 after being incoupled via the incoupler 1110. Similar to the previously described embodiments, the light filter and incoupler system 1100 receives display light 1150- 1174 emitted from a light engine (e.g., such as light engine 202 of FIG. 2) in the eyewear display.

[0075] In the embodiment shown in FIG. 11 , the light filter 1100 is directly applied to the surface of the waveguide 1130 opposite to the incoupler 1110. The light filter 1100 includes multiple regions 1122, 1124, 1126. Each of the multiple regions 1122, 1124, 1126 of the light filter 1120 reflect or absorb different wavelengths of light. For example, light filter region 1122 absorbs red, blue, and green light; light filter region 1124 absorbs blue light and green light and reflects red light; and light filter region 1126 absorbs blue light and reflects red light and green light. The light filter 1120 is positioned such that its regions 1122, 1124, 1126 absorb light that would otherwise bounce off the incoupler 1110 and be prematurely extracted from the waveguide to the different bounce spacings of red, green, and blue light. For example, red light 1150, 1152 has a larger bounce spacing. Thus, red light reflects off both light filter regions 1124, 1126 since it will not bounce off of the incoupler 1110 due to its larger angle bounce. Green light 1160, 1162 has an intermediate bounce spacing (relative to red light and blue light). Light filter region 1124 absorbs green light since any subsequent reflections would be incident on the incoupler 1110 due to its bounce angle. However, light filter region 1126 reflects green light since any reflections will not be incident again (i.e. , bounce again) on the incoupler 1110. Blue light 1170, 1172, 1174 has the smallest bounce spacing. Thus, light filter regions 1124, 1126 absorb blue light since any subsequent reflections would be incident on the incoupler 1110 due to its small bounce angle. Thus, by positioning the light filter 1120 directly to the backside of a waveguide 1130, the light filter and incoupler system 1100 is more compact and may facilitate implementation into a limited eyewear display form factor.

[0076] FIG. 12 shows a method flowchart for creating a color gradient of light for incoupling into a waveguide, in accordance with some embodiments. At 1202, a light engine (such as light engine 202 of FIG. 2) emits display light having a variety of wavelength ranges such as RGB light. At 1204, a light filter (such as any one of the light filters described in FIGs. 2, 4, 5, 6, 8, 9, and 10) generates a light gradient along a first direction. In some embodiments, the light gradient has different sections that include light having different wavelength ranges or colors. For example, a first section of the light gradient to be incident closest to the incoupling edge of an incouplerincludes light having a wavelength range corresponding to RGB light. A second section adjacent to the first section along the incoupling direction includes light having a smaller wavelength range corresponding to red and green light. A third section adjacent to the second section along the incoupling direction includes light having an even smaller wavelength range corresponding to red light. At 1206, an incoupler (such as any one of the incoupler described in FIGs. 2, 3, 4, 6, 7, 8, and 10) incouples the light output from the light filter into the waveguide. In some embodiments, the incoupler incouples the light into the waveguide in an incoupling direction that is aligned with the first direction that the light gradient is generated by the light filter at block 1204.

[0077] Note that not all of the activities or elements described above in the general description are required, that a portion of a specific activity or device may not be required, and that one or more further activities may be performed, or elements included, in addition to those described. Still further, the order in which 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, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present disclosure as set forth in the claims below. Accordingly, the specification and figures are to 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.

[0078] Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any feature(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature of any or all the claims. Moreover, the particular embodiments disclosed above are illustrative only, as the disclosed 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 asdescribed in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope of the disclosed subject matter. Accordingly, the protection sought herein is as set forth in the claims below.

Claims

WHAT IS CLAIMED IS:1 . An eyewear display comprising: a light filter comprising a color gradient along a first direction that transmits different wavelength ranges of light; and a waveguide comprising an incoupler to incouple light into the waveguide in an incoupling direction, wherein the first direction is aligned with the incoupling direction.

2. The eyewear display of claim 1 , wherein the color gradient comprises a plurality of regions distributed along the first direction, each region of the plurality of regions to transmit light having a different wavelength range.

3. The eyewear display of claim 2, wherein a first region of the plurality of regions is positioned along the first direction nearest to the incoupling direction, wherein the first region transmits light in a red wavelength range, a blue wavelength range, and a green wavelength range.

4. The eyewear display of claim 3, wherein a second region of the plurality of regions is arranged next to the first region along the first direction, wherein the second region transmits light in the red wavelength range and the green wavelength range and blocks light in the blue wavelength range.

5. The eyewear display of claim 4, wherein a third region of the plurality of regions is arranged next to the second region on a side opposite to the first region along the first direction.

6. The eyewear display of claim 5, wherein the third region transmits light in the red wavelength range and blocks light in the blue wavelength range and the green wavelength range.

7. The eyewear display of claim 6, wherein a fourth region of the plurality of regions is arranged next to the third region on a side opposite to the second region along the first direction.

8. The eyewear display of claim 7, wherein the fourth region blocks light in the blue wavelength range, the green wavelength range, and the red wavelength range.

9. The eyewear display of claim 1 , wherein the incoupler comprises a plurality of incoupler segments distributed along the incoupling direction.

10. The eyewear display of claim 9, wherein each incoupler segment of the plurality of incoupler segments has one or more grating features that are different from grating features in other ones of the plurality of incoupler segments.11 . The eyewear display of claim 10, wherein the one or more grating features comprise one or more of a grating height, a grating fill factor, a grating angle, or a grating material.

12. An eyewear display comprising: a light engine to emit light having a plurality of wavelength ranges; a light filter comprising a color gradient along a first direction that transmits different wavelength ranges of light; and a waveguide comprising an incoupler to incouple light from the light filter in an incoupling direction, wherein the first direction is aligned with the incoupling direction.

13. The eyewear display of claim 12, wherein the color gradient comprises a plurality of regions, each region of the plurality of regions to transmit light having a different wavelength range of the plurality of wavelength ranges.

14. The eyewear display of claim 13, wherein a first region of the plurality of regions is positioned along the first direction nearest to the incoupling direction, asecond region of the plurality of regions is arranged next to the first region along the first direction, and a third region of the plurality of regions is arranged next to the second region on a side opposite to the first region along the first direction.

15. The eyewear display of claim 14, wherein the first region transmits light in a red wavelength range, a blue wavelength range, and a green wavelength range, wherein the second region transmits light in the red wavelength range and the green wavelength range and blocks light in the blue wavelength range, and wherein the third region transmits light in the red wavelength range and blocks light in the blue wavelength range and the green wavelength range.

16. The eyewear display of claim 12, wherein the incoupler comprises a plurality of incoupler segments distributed along the incoupling direction.

17. The eyewear display of claim 16, wherein each incoupler segment of the plurality of incoupler segments has one or more grating features that are different from grating features in other ones of the plurality of incoupler segments.

18. The eyewear display of claim 12, wherein the light engine comprises a microLED display panel.

19. A method comprising: emitting, by a light engine, light having a plurality of wavelength ranges; receiving, by a light filter comprising a color gradient that varies along a first direction, the light emitted from the light engine and transmitting light having different ones of the plurality of wavelength ranges along the first direction to generate a light gradient with varying wavelength ranges; and incoupling, at an incoupler of a waveguide, the light gradient into the waveguide in an incoupling direction, the incoupling direction aligned with the first direction.

20. The method of claim 19, wherein the color gradient comprises a plurality of regions, each region of the plurality of regions to transmit light having a different wavelength range of the plurality of wavelength ranges.

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