Apparatus and method for directing light to multiple in-coupler waveguides - Patents.com

Abstract

This disclosure describes techniques and configurations for directing light from an optical engine to one of multiple incouplers of a multiple incoupler waveguide system. For example, this disclosure describes multiple reflective and transmissive elements for selectively directing light to a first incoupler or a second incoupler based on multiple optical properties.

Description

[Background technology]

[0001] In a conventional wearable head-up display (WHUD), light beams from an image source are coupled into a light-guiding substrate, commonly referred to as a waveguide, by an input optical coupling, such as an in-coupling grating (i.e., an in-coupler), which may be formed on the surface of the substrate or embedded within the substrate. Once the light beams are coupled into the waveguide, they are typically "guided" through the substrate by multiple instances of total internal reflection (TIR), and then directed out of the waveguide by an output optical coupling (i.e., an "out-coupler"), which may also take the form of a diffractive optic. The light beams emitted from the waveguide overlap at an eye relief distance from the waveguide to form an exit pupil, within which a virtual image generated by the image source can be viewed. Summary of the Invention

[0002] This disclosure describes techniques and apparatus that utilize multiple transmissive and reflective elements to selectively direct light to multiple in-couplers based on the optical properties of the light.

[0003] In an exemplary embodiment, the apparatus includes a waveguide including a first intercoupler and a second intercoupler, and a plurality of reflective and transmissive elements that selectively direct light to the first intercoupler or the second intercoupler based on a plurality of optical properties.

[0004] In certain embodiments of the apparatus, the plurality of reflective and transmissive elements separate the light into a portion of the light having a first optical characteristic of the plurality of optical characteristics and a portion of the light having a second optical characteristic of the plurality of optical characteristics, and in some embodiments, the plurality of reflective and transmissive elements selectively direct the portion of the light having the first optical characteristic to a first incoupler and the portion of the light having the second optical characteristic to a second incoupler.

[0005] In certain embodiments of the apparatus, the plurality of optical properties are a plurality of wavelength ranges, and each of the incouplers is tuned to incouple light in one of the plurality of wavelength ranges. In some embodiments, the plurality of reflective and transmissive elements include mirrors. In some embodiments, the plurality of reflective and transmissive elements include beam splitters, and the beam splitters are dichroic beam splitters that separate the light into two or more of the plurality of wavelength ranges. In certain embodiments, the plurality of reflective and transmissive elements include an optical relay element for focusing a first pupil plane associated with a first wavelength range of the plurality of wavelength ranges onto the first incoupler, or for focusing a second pupil plane associated with a second wavelength range of the plurality of wavelength ranges onto the second incoupler. For example, the optical relay element includes one or more of a lens group, a reflector, a metasurface, a prism assembly with a total internal reflection (TIR) ​​gap having a plurality of reflective and transmissive elements, or any combination thereof.

[0006] In certain embodiments of the apparatus, the plurality of optical properties are a plurality of polarization states, and each of the incouplers is tuned to incouple light of one of the plurality of polarization states. In some embodiments, the plurality of reflective and transmissive elements include a polarizing beam splitter and one or more wave plates.

[0007] In certain embodiments of the apparatus, the plurality of reflective and transmissive elements include a plurality of lenses having different focal lengths. In some embodiments, the plurality of reflective and transmissive elements include optical clean-up filters including color-selective or polarization-selective filters to remove light having undesirable optical characteristics from being directed to the first incoupler or the second incoupler. In some embodiments, the plurality of reflective and transmissive elements receive light from a single optical engine and selectively direct the received light to the first incoupler or the second incoupler.

[0008] In another exemplary embodiment, an apparatus includes a waveguide stack including a first waveguide substrate including a first incoupler and a second waveguide substrate including a second incoupler offset from the first incoupler, and the apparatus also includes a plurality of reflective and transmissive elements for selectively directing light to the first incoupler or the second incoupler based on a plurality of optical properties.

[0009] In certain embodiments of the apparatus, the plurality of reflective and transmissive elements direct light of a first optical characteristic of the plurality of optical characteristics to a first intercoupler and light of a second optical characteristic of the plurality of optical characteristics to a second intercoupler.

[0010] In certain embodiments, the apparatus further includes one or more additional waveguide substrates stacked on the second waveguide substrate, each of the one or more additional waveguide substrates including a respective additional incoupler, each of the one or more additional incouplers being laterally offset relative to the first incoupler, the second incoupler, and each of the other respective additional incouplers. Further, the plurality of reflective and transmissive elements are configured to selectively direct light to a respective one or more additional incouplers based on a plurality of optical properties.

[0011] In some embodiments of the apparatus, the plurality of reflective and transmissive elements include a beam splitter. For example, in certain embodiments, the beam splitter is a dichroic beam splitter and the plurality of optical properties are a plurality of distinct wavelength ranges. In this example, the dichroic beam splitter separates the light into a plurality of distinct wavelength ranges for transmission to one of the incouplers. As another example, in other embodiments, the beam splitter is a polarizing beam splitter and the plurality of optical properties are a plurality of distinct polarization states. In this example, the polarizing beam splitter separates the light into a plurality of distinct polarization states for transmission to one of the incouplers.

[0012] In some embodiments of the apparatus, the plurality of reflective and transmissive elements includes one or more optical focusing elements for focusing light towards one or more of the in-couplers.

[0013] Another exemplary embodiment includes a plurality of reflective and transmissive elements that receive input light from a single optical engine, separate the input light into at least two portions of light based on one or more optical properties, and selectively direct each of the at least two portions of light to one of a plurality of in-couplers of the waveguide. In some embodiments, the plurality of reflective and transmissive elements include elements and features described within this disclosure.

[0014] The present disclosure may be better understood, and its numerous features and advantages made apparent to those skilled in the art by reference to the accompanying drawings, in which: The use of the same reference symbols in different drawings indicates similar or identical items. [Brief description of the drawings]

[0015] [Figure 1] 1 illustrates 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. [Diagram 2] 2 shows an example block diagram of a projection system that projects light representing an image to a user's eye via a display system, such as the display system of FIG. 1, according to some embodiments. [Diagram 3] 3 illustrates an example of light propagation within a waveguide of a projection system, such as the projection system of FIG. 2, according to some embodiments. [Figure 4] 1 illustrates an example of a close-up view of a waveguide stack, according to some embodiments. [Diagram 5] 1A-1D show example top and side views of a portion of a waveguide stack and a portion of an optical scanner, according to some embodiments. [Figure 6] 1 illustrates an example of a top view of a portion of a waveguide stack and a portion of an optical scanner, according to some embodiments. [Figure 7] 1 illustrates another example of a top view of a portion of a waveguide stack and a portion of an optical scanner in accordance with some embodiments. [Figure 8]1 illustrates an example of a top view of a portion of a waveguide stack having three waveguides and a portion of an optical scanner, according to some embodiments. [Figure 9] 1 illustrates an example of a top view of a portion of an optical scanner having a MEMS mirror and a portion of a waveguide stack, according to some embodiments. [Figure 10] 10 shows a zoomed view of FIG. 9 according to some embodiments. [Figure 11] 1 illustrates an example of a top view of a portion of an optical scanner having a portion of a waveguide stack and an optical focusing element, according to some embodiments. [Figure 12] 1 illustrates an example of a portion of a waveguide having multiple in-couplers in a common waveguide and a portion of an optical scanner according to some embodiments. [Figure 13] 1 illustrates an example of multiple in-couplers in a pupil plane and a waveguide according to some embodiments. [Figure 14] 1 illustrates an example of a pupil walk at an intercoupler, according to some embodiments. [Figure 15] 1 illustrates an example of a lens as a secondary optical relay element in an optical scanner, according to some embodiments. [Figure 16] 14 illustrates an example of a metasurface as a secondary optical relay element in an optical scanner, according to some embodiments. [Figure 17] 1 illustrates an example of an optical scanner having multiple reflective elements including mirrors, beam splitters, air gaps, and multiple prisms, according to some embodiments. [Figure 18] 1 illustrates an example of an optical scanner having multiple reflective elements, including mirrors and beam splitters, according to some embodiments. [Figure 19] 1 illustrates an example of separating red light from blue+green light according to some embodiments. [Figure 20] 1 illustrates an example of an optical scanner utilizing multiple in-couplers and polarization of a waveguide, according to some embodiments. [Figure 21]1 illustrates another example of an optical scanner utilizing multiple in-couplers and polarization of a waveguide, according to some embodiments. [Figure 22] 1 illustrates an example of an optical scanner including multiple waveguide in-couplers and optical focusing elements, according to some embodiments. [Figure 23] 1 illustrates an example of filtering light in a color-selective manner according to some embodiments. [Figure 24] 1 illustrates an example of filtering light in a polarization-selective manner according to some embodiments. [Diagram 25] 1 illustrates examples of a waveguide with multiple in-couplers, an optical scanner, and a display light source as an optical engine, according to some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] In a WHUD, a waveguide with multiple incouplers offers the advantage of higher incoupling efficiency because each incoupler can be tuned to incouple light of a particular optical characteristic, such as a particular wavelength range. However, multiple incoupler waveguides typically require separate projectors and / or optical scanners for each incoupler, and the spatially constrained form factor of a WHUD may not have enough space to accommodate such a configuration. Figures 1-25 show techniques for selectively directing light from a single projector to multiple incouplers via an optical scanner with multiple transmissive and reflective elements based on the optical characteristics of the light. Thus, the advantage of multiple incoupler waveguides is that they can be realized in a smaller form factor WHUD, thereby improving the overall user experience.

[0017] To illustrate, in the case of a waveguide with multiple incouplers, a first incoupler is tuned to incouple light of a first optical characteristic (e.g., a first wavelength range) and a second incoupler is tuned to incouple light of a second optical characteristic (e.g., a second wavelength range). In some embodiments, the multiple incouplers are arranged through a waveguide stack, with each waveguide of the waveguide stack having a corresponding incoupler. In other embodiments, the multiple incouplers are applied to a common waveguide. In either case, the optical scanner includes multiple reflective and transmissive elements, such as mirrors, beam splitters, prisms, lenses, wave plates, or metasurfaces, or any combination thereof, that are designed and arranged to selectively direct light having one or more specified optical characteristics to a corresponding one of the multiple incouplers. Additionally, the optical scanner equalizes (within a margin of difference) the optical path length of the light directed to each incoupler. Thus, the pupil planes of each optical path are highly coincident with each incoupler, effectively incoupling and increasing the amount of received light guided through the waveguide, thereby improving the quality of the image delivered by the waveguide while still using a single projector.

[0018] To further illustrate, in some embodiments, the waveguide has two incouplers designated as a first incoupler and a second incoupler. The first incoupler is tuned to incouple red light, and the second incoupler is tuned to incouple blue and green light. Using the techniques described herein, the optical scanner's multiple reflective and transmissive elements receive light from a single optical engine (i.e., a projector) and direct a red light portion of the received light to the first incoupler and a blue and green light portion of the received light to the second incoupler. Specifically, the multiple reflective and transmissive elements include a dichroic mirror that reflects the red light portion to the first incoupler and transmits the blue and green light portions. The multiple reflective and transmissive elements further include a mirror that receives the transmitted blue and green light portions from the dichroic mirror and reflects the blue and green light portions to the second incoupler. Furthermore, the multiple reflective and transmissive elements may include additional elements, such as lenses and / or prisms, to equalize (within a margin of difference) the optical path length of the red light portion directed to the first incoupler and the optical path lengths of the blue and green light portions directed to the second incoupler, such that the pupil plane of each light portion coincides with its respective incoupler, thereby increasing the amount of incoupled light that is effectively propagated in the waveguide.

[0019] 1-25 show an embodiment of a display system having an optical scanner for directing light to multiple inter-couplers, as described in more detail below, however, it is understood that the apparatus and techniques of the present disclosure are not limited to implementation in this particular display system, but instead may be implemented in any of a variety of display systems using the guidelines provided herein.

[0020] FIG. 1 illustrates an exemplary display system 100 having a support structure 102 including an arm 104 housing a projection system configured to project images toward a user's eye such that the user perceives the projected image as being displayed within a field of view (FOV) region 106 of the display on one or both of lens elements 108, 110. In the illustrated embodiment, the display system 100 is a wearable head-up display (WHUD) including a support structure 102 configured to be worn on a user's head and having the general shape and appearance of an eyeglass (e.g., sunglasses) frame. The support structure 102 contains or otherwise includes various components that facilitate the projection of such images toward the user's eye, such as a projector, an optical scanner, and a wave guide. In some embodiments, the support structure 102 further includes various sensors, such as one or more front-facing cameras, rear-facing cameras, other optical sensors, motion sensors, accelerometers, and the like. The support structure 102 can further include one or more radio frequency (RF) interfaces or other wireless interfaces, such as a Bluetooth interface, a WiFi interface, and the like. Additionally, in some embodiments, the support structure 102 further includes one or more batteries or other portable power sources for powering the electrical components of the display system 100. In some embodiments, some or all of these components of the display system 100 are contained completely or partially within an interior volume of the support structure 102, such as within the arms 104 of the region 112 of the support structure 102. It is understood that while an exemplary form factor is shown, in other embodiments, the display system 100 may have a different shape and appearance than the eyeglass frames shown in FIG.

[0021] One or both of the lens elements 108, 110 may be used by the display system 100 to provide an augmented reality (AR) display, in which rendered graphical content may be superimposed or otherwise provided in conjunction with a real world view as perceived by a user through the lens elements 108, 110. For example, light used to form a perceptible image or series of images may be projected by a projector of the display system 100 to a user's eye through a series of optical elements, such as a waveguide, one or more scanning mirrors, and one or more optical relays, formed at least partially in the corresponding lens element. Thus, one or both of the lens elements 108, 110 may include at least a portion of a waveguide that transmits display light received by a waveguide in-coupler to a waveguide out-coupler, which outputs the display light toward the eye of a user of the display system 100. The display light is modulated and scanned to the user's eye such that the user perceives the display light as an image. In addition, each of the lens elements 108, 110 is sufficiently transparent to allow a user to look through the lens element to provide a view of the user's real-world environment such that the image appears superimposed on at least a portion of the real-world environment.

[0022] 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 digital light processors. In some embodiments, the projector includes multiple laser diodes (e.g., red laser diodes, green laser diodes, and / or blue laser diodes) and at least one scanning mirror (e.g., two one-dimensional scanning 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 the operation of the projector. In some embodiments, the controller is communicatively coupled to a processor (not shown) that controls the scanning area size and scanning area position of the projector and generates the content displayed on the display system 100. The projector scans light over a variable area designated by the FOV area 106 of the display system 100. The scan region size corresponds to the size of the FOV region 106, and the scan region position corresponds to the area of ​​one of the lens elements 108, 110 where the FOV region 106 is visible to the user. In general, it is desirable for a display to have a wide FOV to accommodate outcoupling of light 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 eyebox of the display.

[0023] In some embodiments, the projector sends light through a first scanning mirror and a second scanning mirror, an optical relay disposed between the first scanning mirror and the second scanning mirror, and a waveguide disposed at the output of the second scanning mirror. In some embodiments, the optical scanner, including one or more of the first scanning mirror, the second scanning mirror, or the optical relay, includes a plurality of reflective and transmissive elements that selectively direct light to a particular incoupler of a waveguide having a plurality of incouplers based on one of a plurality of different optical properties (e.g., wavelength range or polarization state). The multiple incouplers provide the advantage of a higher incoupling efficiency of light, thereby increasing the amount of light propagated through the waveguide to a corresponding outcoupler for outcoupling to the FOV region 106, and at least a portion of the outcoupler (or multiple outcouplers) overlaps with the FOV region 106. Additionally, the optical scanner allows for a multiple incoupler configuration within the form factor of the support structure 102, as described in more detail below.

[0024] 2 shows a simplified block diagram of a projection system 200 that projects an image directly onto a user's eye via light, e.g., laser light or microdisplay light. The projection system 200 includes an optical engine 202, an optical scanner 204, and a waveguide 205. In some embodiments, the optical scanner 204 includes a first scanning mirror 206, a second scanning mirror 208, and an optical relay 210. The waveguide 205 includes an in-coupler 212 and an out-coupler 214, which in this example is optically aligned with the user's eye 216. In some embodiments, the projection system 200 is implemented in a wearable head-up display or other display system, such as the display system 100 of FIG. 1.

[0025] In some embodiments, the optical engine 202 (also referred to as a projector) includes one or more light sources configured to generate and output light 218 (e.g., visible laser light, such as red, blue, and green laser light, and / or non-visible laser light, such as infrared laser light). In some embodiments, the optical engine 202 is coupled to a driver or other controller (not shown) and controls the timing of emission of light from the light sources of the optical engine 202 according to instructions received from a computer processor coupled thereto by the controller or driver to modulate the light 218 to be perceived as an image when output to the retina of the user's eye 216. In some embodiments, the optical engine 202 includes one or more laser light sources. In other embodiments, the optical engine 202 includes one or more light emitting diode (LED) light sources, or other types of LED displays (e.g., micro LED displays), liquid crystal displays (LCDs), or dot matrix displays (DMDs).

[0026] For example, during operation of projection system 200, multiple light beams, each having a different wavelength, are output by light sources in optical engine 202, then combined via a beam combiner (not shown) and directed to a user's eye 216. Optical engine 202 modulates the intensity of each of the light beams such that the combined light reflects off a series of pixels of an image, with the particular intensity of each light beam at any given time contributing an amount of corresponding color content and brightness of the pixel represented by the combined light at that time.

[0027] In some embodiments, one or both of the scanning mirrors 206 and 208 of the optical scanner 204 are MEMS mirrors. For example, the scanning mirrors 206 and 208 are MEMS mirrors that are driven by respective actuation voltages to oscillate during active operation of the projection system 200, causing the scanning mirrors 206 and 208 to scan the light 218. The oscillation of the scanning mirror 206 causes the light 218 output by the optical engine 202 to pass through the optical relay 210 and across the surface of the second scanning mirror 208. The second scanning mirror 208 scans the light 218 received from the scanning mirror 206 towards the incoupler 212 of the waveguide 205. In some embodiments, the scanning mirror 206 oscillates along a first scanning axis 219 such that the light 218 is scanned only in one dimension (i.e., linearly) across the surface of the second scanning mirror 208. In some embodiments, the scanning mirror 208 oscillates or otherwise rotates along the second scanning axis 221. In some embodiments, the first scanning axis 219 is perpendicular to the second scanning axis 221.

[0028] In some embodiments, the incoupler 212 has a substantially rectangular profile and is configured to receive the light 218 and direct the light 218 into the waveguide 205. The incoupler 212 is defined by a smaller dimension (i.e., width) and a larger orthogonal dimension (i.e., length). In one embodiment, the optical relay 210 is a line-scan optical relay that receives the light 218 scanned in a first dimension (e.g., the first dimension corresponding to the smaller dimension of the incoupler 212) by the first scanning mirror 206, sends the light 218 to the second scanning mirror 208, and introduces a convergence of the light 218 in the first dimension at an exit pupil beyond the second scanning mirror 208. As used herein, "exit pupil" in an optical system refers to a location along an optical path where light beams intersect. For example, the possible optical paths of the light 218 following reflection from the first scan mirror 206 initially diverge along the first scan axis, but later, due to the convergence introduced by the optical relay 210, these paths intersect at an exit pupil beyond the second scan mirror 208. For example, the width (i.e., smallest dimension) of a given exit pupil corresponds approximately to the diameter of the light corresponding to that exit pupil. Thus, 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 onto the second scan mirror 208, or includes a shaped reflecting 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 scanning mirror 208 receives the light 218 and scans the light 218 in a second dimension, which corresponds to the dimension of the length of the incoupler 212 of the waveguide 205. In some embodiments, the second scanning mirror 208 causes the exit pupil of the light 218 to sweep along a line along the second dimension. In some embodiments, the incoupler 212 is positioned at or near the sweep line downstream from the second scanning mirror 208 such that the second scanning mirror 208 scans the light 218 as a line or row on the incoupler 212.

[0029] In some embodiments, the optical engine 202 includes an edge-emitting laser (EEL) that emits laser light 218 having a substantially elliptical and non-circular cross-section, and the optical relay 210 expands or minimizes the laser light 218 along its major and minor axes to circularize the laser light 218 before it is focused onto the second scanning mirror 208. In some such embodiments, the surface of the mirror plate of the scanning mirror 206 is elliptical and non-circular (e.g., similar shape and size to the cross-sectional area of ​​the laser light 218). In other such embodiments, the surface of the mirror plate of the scanning mirror 206 is circular.

[0030] The waveguide 205 of the projection system 200 includes an in-coupler 212 and an out-coupler 214. As used herein, the term "waveguide" is understood to mean a combiner that uses one or more of total internal reflection (TIR), specialized filters, and / or reflective surfaces to transmit light from an in-coupler (such as in-coupler 212) to an out-coupler (such as out-coupler 214). In some display applications, the light is a collimated image, and the waveguide transmits and replicates the collimated image to the eye. In general, the terms "in-coupler" and "out-coupler" 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 that uses one or more holograms), a volume diffraction grating, a volume hologram, a surface relief diffraction grating, and / or a surface relief hologram. In some embodiments, a given in-coupler or out-coupler is configured as a transmission grating (e.g., a transmission grating or a transmission holographic grating) that transmits light to the in-coupler or out-coupler and applies a designed optical function(s) to the light during transmission. In some embodiments, a given in-coupler or out-coupler is a reflection grating (e.g., a reflection grating or a reflection holographic grating) that reflects light to the in-coupler or out-coupler and applies a designed optical function(s) to the light during reflection. In this example, light 218 received at the in-coupler 212 is relayed to the out-coupler 214 via the waveguide 205 using TIR. The light 218 is then output to the user's eye 216 via the out-coupler 214. As mentioned above, in some embodiments, the waveguide 205 has a form factor of glasses and is implemented as part of a glasses lens, such as lens 108 or lens 110 (FIG. 1) of a display system using the projection system 200.

[0031] In some embodiments, the waveguide 205 includes multiple incouplers 212, although shown in FIG. 2 as a single incoupler 212. The multiple incouplers are arranged either in a common waveguide, such as the waveguide 205, or in a stack of waveguides (multiple waveguides 205 stacked together) with an incoupler in each waveguide. In some embodiments, each of the multiple incouplers is tuned to incouple light of a particular optical characteristic to improve the overall incoupling efficiency of the projection system 200. Adjustable incoupler grating parameters include, but are not limited to, grating height, grating spacing, grating angle, and grating density. To effectively implement multiple incoupler waveguides in a single optical engine 202, the optical scanner 204 includes multiple reflective and transmissive elements that separate the light 218 based on one or more optical characteristics and direct each portion of the light to a respective incoupler. Additionally, the multiple reflective and transmissive elements of the optical scanner are designed and positioned to equalize (within a margin of difference) the optical path length of the light directed to each incoupler. It is understood that the optical path length is the product of the geometric length of the optical path and the refractive index and geometry of the medium through which the light propagates. Optical scanners including multiple reflective and transmissive elements are described in further detail below.

[0032] The terms "intercoupler" and "intercoupler grating" are used in this specification and related drawings to correspond to one another unless otherwise indicated. Thus, descriptions of "first intercoupler grating," "second intercoupler grating," "third intercoupler grating," etc. (e.g., "first grating," "second grating," "third grating") correspond to "first intercoupler," "second intercoupler," and "third intercoupler," respectively, unless otherwise indicated.

[0033] 2, in some embodiments, multiple reflective and transmissive elements are included in the optical path between the optical engine 202 and the scanning mirror 206, between the scanning mirror 206 and the optical relay 210, between the optical relay 210 and the scanning mirror 208, between the scanning mirror 208 and the incoupler 212, between the incoupler 212 and the outcoupler 214, and / or between the outcoupler 214 and the eye 216 (e.g., to shape the light for viewing by the user's eye 216). For example, in some embodiments, a prism or prism assembly is used to direct the light from the scanning mirror 208 into the corresponding incoupler 212 such that the light is coupled into the corresponding incoupler 212 at an appropriate angle to facilitate propagation of the light in the waveguide 205 by TIR. Also, in some embodiments, an exit pupil expander such as a folding grating (e.g., exit pupil expander 304 in FIG. 3 , described below) is disposed at an intermediate stage between in-coupler 212 and out-coupler 214 to receive light coupled into waveguide 205 by in-coupler 212, expand the light, and redirect the light towards out-coupler 214, which then couples the light out of waveguide 205 (e.g., towards the user's eye 216). In some embodiments, projection system 200 includes multiple exit pupil expanders, each optically coupling a respective in-coupler with a respective out-coupler of the multiple in-coupler system.

[0034] FIG. 3 illustrates an example of light propagation in the waveguide 205 of the projection system 200 of FIG. 2, according to some embodiments. Although shown with one in-coupler 212, one exit pupil expander 304, and one out-coupler 214, this is for clarity, with the understanding that in some embodiments the waveguide includes multiple instances of each. In such a configuration, for example, each in-coupler 212 is tuned to incoupled light of a particular optical characteristic (e.g., wavelength range or polarization state) for proceeding to a corresponding exit pupil expander 304 and a corresponding out-coupler 214. An optical scanner with multiple reflective and transmissive elements receives the light, separates the light, and directs each portion of the light to one of the respective in-couplers. As shown, the light received through the in-coupler 212, scanned along axis 302, is directed into an exit pupil expander (EPE) 304 and then sent to the out-coupler 214 for output (e.g., towards the user's eye). In some embodiments, the exit pupil expander 304 expands one or more dimensions of the eyebox of the WHUD that includes the projection system 200 (e.g., relative to the dimensions of the eyebox of the WHUD without the exit pupil expander 304). In some embodiments, the in-coupler 212 and the exit pupil expander 304 each include a respective one-dimensional diffraction grating (i.e., a diffraction grating that extends along one dimension). In the example of FIG. 3, the in-coupler 212 directs all or a substantial portion of the incoming light straight down (with respect to the currently shown view) in a first direction perpendicular to the scan axis 302, and the exit pupil expander 304 directs it to the right (with respect to the currently shown view) in a second direction that is perpendicular to the first direction. Although not shown in this example, it is understood that in some embodiments, the first direction in which the in-coupler 212 directs light is not strictly perpendicular to the scan axis 302, but is slightly or substantially oblique.

[0035] FIG. 4 shows a close-up view 400 of a waveguide stack 402 having multiple waveguides 405A, 405B. In some embodiments, the waveguide stack including the waveguides 405A, 405B corresponds to the waveguide 205 of FIGS. 2 and 3. Each of the waveguides 405A, 405B of the waveguide stack has an in-coupler 412A, 412B, respectively, an exit pupil expander (EPE) 404A, 404B, respectively, and an out-coupler 414A, 414B, respectively. The in-couplers 412A, 412B of the waveguide stack 400 are offset from each other, i.e., they do not completely overlap with respect to each other in the waveguide stack 400. This offset in-coupler position allows light of a particular optical characteristic to be directed to a respective in-coupler tuned to in-couple light of that particular optical characteristic. For example, in-coupler 412A is tuned to incouple light in a first wavelength range (e.g., corresponding to red light) and in-coupler 412B is tuned to incouple light in a second wavelength range (e.g., corresponding to blue and green light). By tuning in-couplers 412A, 412B to incouple light in a particular wavelength range and include the aforementioned offset, the overall in-coupling efficiency of the waveguide stack is increased, thereby increasing the amount of light transmitted to the user.

[0036] 5 illustrates a top view 500 and a side view 550 of a portion of a waveguide stack, such as that corresponding to the waveguide stack 402 including a first waveguide 405A and a second waveguide 405B. As shown, the in-coupler 412A of the first waveguide 405A is offset from the in-coupler 412B of the second waveguide 405B. Thus, light 502 entering the in-coupler 412A is incoupled and propagated within the first waveguide 405A, and light 504 entering the in-coupler 412B is incoupled and propagated within the second waveguide 405B. Light propagating in the first waveguide 405A from the in-coupler 412A is directed to and through the corresponding EPE 404A to the corresponding out-coupler 414A, and light propagating in the second waveguide 405B from the in-coupler 412B is directed to and through the corresponding EPE 404B to the corresponding out-coupler 414B. In this figure, the out-couplers 414A, 414B are shown as substantially overlapping to output light to a similar FOV of the WHUD, although it will be understood that other configurations, e.g., out-couplers dedicated to specific portions of the overall FOV of the WHUD, are likewise contemplated and covered by this disclosure.

[0037] In some embodiments, each of the incouplers 412A, 412B is tuned to incouple light of a particular optical characteristic, such as a particular wavelength range or polarization state. For example, the light 502 directed to the first incoupler 412A has a wavelength range corresponding to red light, and the light 504 directed to the second incoupler 412b has a wavelength range corresponding to blue and green light. Techniques by which the optical scanner effectively separates the light based on its wavelength range (i.e., color) and directs each portion of the light to the respective incoupler 412A, 412B are described in detail below. These techniques include the use of beam splitters to separate the light and reflective surface(s) to direct the portions of the light to the corresponding incoupler. Additionally, additional elements such as prisms and / or lenses can, for example, equalize the optical path length of each portion of the light to improve the quality of the image provided to the user.

[0038] 6 shows a top view 600 of a portion of a waveguide stack having two waveguides 405A, 405B and a portion of an optical scanner having multiple reflective and transmissive elements 620, 622, 634, 636. In some embodiments, the waveguide stack having the waveguides 405A, 405B corresponds to the waveguide stack 402 of FIG.

[0039] In some embodiments, the plurality of reflective and transmissive elements 620, 622, 634, 636 include folding mirrors that receive the input light 601 and separate the input light 601 into portions of light based on one or more optical properties and deliver them to the incoupler 412A of the waveguide 405A and the incoupler 412B of the waveguide 404B. For example, the incoupler 412B is tuned to incouple red light, and the incoupler 412A is tuned to incouple blue and green light. In this case, the plurality of reflective and transmissive elements include a prism assembly having two prisms 620, 622, a first selectively transmissive layer 634, such as a dichroic mirror, that transmits the blue and green light toward the incoupler 412A and reflects the red light toward the incoupler 412B, and a reflective surface 636, such as a mirror, for reflecting the blue and green light from the selectively transmissive layer 634 toward the incoupler 412A. Furthermore, the multiple reflective and transmissive elements 620, 622, 634, 636 are configured such that the pupil plane of each portion of the separated light coincides with the location of the respective in-coupler (i.e., in-coupler 412A, 412B) in a different plane (i.e., waveguide 405A, 405B). The optical path lengths satisfy (or fall within a specified margin of difference in the relationship) a+b=c, in other words, the optical path length along which each portion of the separated light reaches the corresponding in-coupler is the same. In this example, optical path portion "a" corresponds to the portion from the reflecting surface 636 to the in-coupler 412A, optical path portion "b" corresponds to the portion from the selectively reflecting surface 634 to the reflecting surface 636, and optical path portion "c" corresponds to the portion from the selectively reflecting surface 634 to the in-coupler 412B. In some embodiments, the dimensions and materials of the prisms 620, 622 are selected to satisfy the optical path length equations given above. For example, the material may be selected from one or more types of glass, one or more types of plastic, or any combination thereof. Additionally, as shown in Figure 6 and subsequent figures, the optical path length is based in part on the thickness of the waveguide substrates 405A, 405B. Thus, the optical scanner shown in Figure 6 effectively directs each portion of light to the respective in-coupler 412A, 412B while equalizing the optical path length (within the margin of difference).This increases the amount of light incoupled into the waveguides 405A, 405B, improving the quality of the image delivered to the user.

[0040] 7 shows a top view 700 of a portion of a waveguide stack having two waveguides 405A, 405B and a portion of an optical scanner having multiple reflective and transmissive elements 720, 722, 734, 736. In some embodiments, the waveguide stack having the waveguides 405A, 405B corresponds to the waveguide stack 402 of FIG.

[0041] The plurality of reflective and transmissive elements includes a beam splitter 734 disposed between a prism assembly having two prisms 720, 722. In some embodiments, the beam splitter 734 is a polarizing beam splitter, a dichroic beam splitter (i.e., a dichroic mirror), or a proportional (i.e., 50T / 50R, 90T / 10R, 33T / 67R, 90R / 10T, etc.) beam splitter. In general, the beam splitter 734 splits the input light into light of two or more optical characteristics. For example, a dichroic mirror is used to split the light into light of different wavelengths (i.e., colors) by reflecting red light to the incoupler 412B, transmitting blue and green light, and then reflecting the blue and green light from a reflective surface 736, such as a mirror, to the incoupler 412A. In some embodiments, the dimensions and materials of the prisms 720, 722 are selected to satisfy (or be within a specified margin of difference in) the optical path length relationship expressed as a+b=c, i.e., the optical path length along which each portion of the separated light reaches the corresponding incoupler is the same. In this example, optical path portion "a" corresponds to the portion from the reflective surface 736 to the incoupler 412A, optical path portion "b" corresponds to the portion from the beam splitter 734 to the reflective surface 736, and optical path portion "c" corresponds to the portion from the beam splitter 734 to the incoupler 412B. For example, the materials may be selected from one or more types of glass, one or more types of plastic, or any combination thereof. As shown in FIG. 7, the light 701 received by the first prism 720 includes "n" optical paths (in this example, n=3), but the multiple reflective and transmissive elements 720, 722, 734, 736 of the optical scanner are each selected to have the same optical path length, i.e., a n +b n =c n While maintaining the same optical characteristic, the light of each optical characteristic can still be effectively separated and guided to its respective in-coupler, thereby increasing the amount of light incoupled into the waveguide and improving the quality of the image delivered to the user.

[0042] Although two waveguides 405A, 405B are shown in the waveguide stack in Figures 4-7, in some embodiments the waveguide stack includes three or more waveguides, with the in-couplers of the waveguides offset from one another so as not to completely overlap. Such a configuration is described in further detail in Figure 8. Furthermore, it is understood that the concepts discussed herein are extendable to other quantities, such as four or more waveguides in a waveguide stack, depending on the level of optical resolution required based on optical considerations.

[0043] 8 shows a top view 800 of a portion of a waveguide stack having three waveguides 405A, 405B, and 405C along with their corresponding in-couplers 412A, 412B, and 412C, respectively, and a portion of an optical scanner having multiple reflective and transmissive elements 820-830. In some embodiments, the multiple reflective and transmissive elements include a prism assembly having three prisms 820, 822, 824, two beam splitters 826, 828, and one reflective surface 830, such as a mirror. The beam splitters 826, 828 are one or more of a polarizing beam splitter, a dichroic beam splitter (i.e., a dichroic mirror), or a proportional (i.e., 50T / 50R, 90T / 10R, 33T / 67R, 90R / 10T, etc.) beam splitter. In general, the beam splitters 826, 828 split the light 801 input into the system into three optical properties. For example, when splitting the light into different wavelength ranges, the first dichroic mirror 826 reflects the light in the first wavelength range (e.g., red) to the in-coupler 412C and transmits the light in the second wavelength range (e.g., green) and the third wavelength range (e.g., blue). The second dichroic mirror 828 reflects the light in the second wavelength range (e.g., green) to the in-coupler 412B and transmits the light in the third wavelength range (e.g., blue), which is then reflected by a reflective surface 830, such as a mirror, to the in-coupler 412A. In some embodiments, the dimensions and materials of prisms 820, 822, 824 are selected to satisfy (or fall within a specified margin of difference in) the optical path length relationship expressed as a+b+d=c+d=e, i.e., the optical path length along which each portion of separated light reaches its corresponding incoupler is the same. In this example, optical path portion "a" corresponds to the portion from reflective surface 830 to incoupler 412A, optical path portion "b" corresponds to the portion from beam splitter 828 to reflective surface 830, optical path portion "c" corresponds to the portion from beam splitter 828 to incoupler 412B, optical path portion "d" corresponds to the portion from beam splitter 826 to beam splitter 828, and optical path portion "e" corresponds to the portion from beam splitter 826 to incoupler 412C.For example, the material may be selected from one or more types of glass, one or more types of plastic, or any combination thereof, which increases the amount of light incoupled into the waveguides 405A, 405B, and 405C, improving the quality of the image delivered to the user.

[0044] The embodiment shown in FIG. 8 provides the additional advantage that each of the in-couplers can be more precisely tuned to in-couple light of a narrower range of optical properties. For example, if two in-couplers are used, each of the in-couplers can be more precisely tuned to in-couple light of one of three wavelength ranges instead of only one of two wavelength ranges. This improves the coupling efficiency of each in-coupler and further improves the coupling efficiency of the entire waveguide, resulting in a higher quality image being delivered to the user.

[0045] FIG. 9 shows a top view 900 of a block diagram of an optical scanner having an optical relay system such as that shown in FIG. 2 with optical focusing elements 912, 914 disposed in the light path from a scanning MEMS mirror 902 to the plurality of reflective and transmissive elements 720, 722, 734, 736, for example as shown in FIG. 7. In some embodiments, the MEMS mirror 902 corresponds to one of the mirrors 206 or 208 of FIG. 2. In some embodiments, the MEMS mirror 902 corresponds to 206, and the plurality of reflective elements 720, 722, 734, 736 are included (in this example) in place of the mirror 208 of FIG. 2. The optical focusing elements 912, 914 of the optical relay (such as those corresponding to 210) are lenses that direct light toward the plurality of reflective and transmissive elements 720, 722, 734, 736. FIG. 10 shows a zoomed view 1000 of a portion of FIG. 9. As shown in FIG. 10, an optical focusing element 904 is positioned in front of the multiple transmitting and reflective elements 720, 722, 734, 736 to direct light into the first element, ie, the prism 720 in this example.

[0046] 11 shows a top view 1000 of a portion of a waveguide stack having two waveguides 405A, 405B and a portion of an optical scanner. In some embodiments, the waveguide stack having the waveguides 405A, 405B corresponds to the waveguide stack 402 of FIG. 2. The optical scanner includes a plurality of transmitting and reflecting elements 1120, 1122, 1124, 1126 including an optical focusing element 1120, 1122 disposed between a beam splitter 1124 and a reflective surface 1126, and stacked waveguides 405A, 405B. In this embodiment, the two optical focusing elements 1120, 1122 are disposed in the optical path after the beam splitter 1124, the optical focusing element 1120 is disposed between the beam splitter 1124 and the in-coupler 412B, and the optical focusing element 1122 is disposed between the beam splitter 1124 and the reflective surface 1126. As shown in FIG. 11, the optical focusing elements 1120, 1122, together with the beam splitter 1124 and the reflective surface 1126, split the received light 1101 into two portions and direct each portion so that it coincides with one of the two in-couplers 412A, 412B, respectively. The dimensions and materials of the optical focusing elements 1120 and 1122 are designed and selected so that the light beams coincide (within a margin of difference) with the respective in-couplers 412A, 412B. The multiple transmissive and reflective elements 1120, 1122, 1124, 1126 are a n +b n =c n The optical path lengths of the separated light portions are arranged and designed so that the optical path length relationship expressed as n " corresponds to the portion from the reflecting surface 1126 to the inter-coupler 412a, and the optical path portion "b n " corresponds to the portion from the beam splitter 1124 to the reflecting surface 1126, and the optical path portion "c n" corresponds to the portion from the beam splitter 1124 to the in-coupler 412B, where in this example n=3 (corresponding to three optical paths). For example, the materials may be selected from one or more types of glass, one or more types of plastic, or any combination thereof. The configuration shown in FIG. 11 improves the coupling efficiency of each in-coupler as well as the overall coupling efficiency of the waveguides, resulting in more light propagating in the waveguides 405A, 405B and delivering a higher quality image to the user.

[0047] Figure 12 shows a top view 1200 of a waveguide 1205, such as a portion of the waveguide 205 of Figure 2, with multiple in-couplers 1212A, 1212B and a portion of an optical scanner. As shown in Figure 12, multiple in-couplers 1212A and 1212B are disposed on a common waveguide substrate 1205. The optical scanner includes multiple reflective and transmissive elements 1220-1226, including a prism assembly having prisms 1220 and 1222, a beam splitter 1224, and a reflective surface 1226, that receive light 1201, split the light 1201 into two portions based on its optical properties, and direct each portion to a respective in-coupler. However, unlike the waveguide stack of the previous figure, the optical path lengths along which each portion of light is directed to each incoupler are not equal, i.e., the optical path relationship in this case is represented by a+b≠c, where optical path portion "a" corresponds to the portion from the reflecting surface 1226 to the incoupler 1212A, optical path portion "b" corresponds to the portion from the beam splitter 1224 to the reflecting surface 1226, and optical path portion "c" corresponds to the portion from the beam splitter 1224 to the incoupler 1212B. Thus, the pupil plane of the optical relay does not coincide with both incouplers 1212A and 1212B simultaneously. This is further illustrated by way of example in FIG. 13. As shown in 1300, when the pupil plane of the second portion of light coincides with the second incoupler (shown at 1302), the pupil plane of the first portion of light corresponding to the first incoupler is beyond the first incoupler (shown at 1304). Or, as shown at 1350, when the pupil plane of a first portion of light coincides with a first incoupler (shown at 1352), the pupil plane of a second portion of light corresponding to a second incoupler occurs in front of the second incoupler (shown at 1354). The scenario shown at 1350 results in a pupil walk 1402 at the second incoupler 1354, and is shown in more detail in FIG. 14 where arrows 1405 indicate the light propagation direction. In some embodiments, to minimize double bounce losses, the system typically allows colors with large bounce spacing (i.e., red light) to have pupil walk 1402.As described in more detail below, in some embodiments, the multiple reflective and transmissive elements include secondary optical relay elements for refocusing a secondary pupil plane at the respective incouplers, thereby preventing or reducing pupil walk and improving the quality of the image provided by the waveguide.

[0048] For example, this secondary optical relay element is included in the optical path of the light entering the incoupler 1212A, as shown in FIGS. 15 and 16. In some embodiments, the secondary optical relay element is one of a lens group, a reflector, a metasurface, or a combination thereof. Although shown in the optical path to the incoupler 1212A, in alternative embodiments, the secondary optical relay element is included in the optical path to the incoupler 1212B, for example, to address the scenario shown in 1300. The secondary optical relay element refocuses the light beam, so that the secondary pupil plane is focused at each incoupler. This improves the quality of the image provided to the user. Furthermore, since multiple incouplers are placed on a common waveguide substrate as opposed to a waveguide stack, the thickness of the waveguide components is reduced.

[0049] FIG. 15 shows a top view 1500 corresponding to the plurality of reflective and transmissive elements with the addition of a lens 1528 as a secondary optical relay element 1350. In some embodiments, the optical scanner also includes a plurality of reflective and transmissive elements 1220-1226 including a prism assembly having prisms 1220 and 1222, a beam splitter 1224, and a reflective surface 1226, which collectively receive the light 1501, separate the light 1501 into two portions based on its optical properties, and direct each portion to a respective in-coupler 1212A, 1212B. As shown, the lens 1528 refocuses a portion of the second portion of the light beam passing through the beam splitter 1224, so that the secondary pupil surface 1534 coincides with the in-coupler 1212A. The original pupil surface 1354 is also shown. The dimensions and material of the lens 1528 are designed and selected such that the secondary pupil surface 1534 coincides with the in-coupler 1212A. For example, the material may be selected from one or more types of glass, one or more types of plastic, or any combination thereof, and thus pupil walk is minimized or avoided entirely.

[0050] FIG. 16 shows a top view 1600 of a configuration similar to that shown in FIG. 15, but with a metasurface 1628 as a secondary optical relay element instead of the lens 1528 shown in FIG. 15. The metasurface 1628 refocuses the light beam directed to the in-coupler 1212A so that the secondary pupil plane 1634 coincides with the in-coupler 1212A. The material and / or design of the metasurface are artificially designed so that the secondary pupil plane 1634 coincides with the in-coupler 1212A. For example, the metasurface is composed of a thin film that includes a series of elements specifically designed to provide the desired refractive quality. Thus, pupil walk is minimized or avoided entirely, and the waveguide improves the quality of the image delivered to the user.

[0051] FIG. 17 shows a top view 1700 of a portion of a waveguide 1205, such as that corresponding to the waveguide 205 of FIG. 2, with multiple in-couplers 1212A, 1212B and a portion of an optical scanner with multiple transmission and reflection elements 1740, 1742, 1744, 1746, 1748, 1750, according to some embodiments. Similar to FIGS. 15-16, the waveguide 1205 includes multiple in-couplers 1212A, 1212B. In this example, an additional prism 1740 and an air gap 1742 in the multiple reflection and transmission elements 1740-1750 solves the pupil walk problem. The optical scanner also includes a prism assembly with prisms 1744 and 1748, a beam splitter 1746, and a mirror 1750 in the multiple reflection and transmission elements. The plurality of reflective and transmissive elements 1740-1750 equalize (within a margin of difference) the optical path lengths of the portions of light directed to the incouplers 1212A, 1212B. That is, the optical path lengths satisfy (or fall within a specified margin of difference of) the relationship expressed by a+b=c+d, i.e., the optical path lengths at which each portion of separated light arrives at the corresponding incoupler are the same. In this example, optical path portion "a" corresponds to the portion from mirror 1750 to incoupler 1212A, optical path portion "b" corresponds to the portion from beam splitter 1746 to mirror 1750, optical path portion "c" corresponds to the portion from beam splitter 1746 to the interface of prism 1744 and air gap 1742, and optical path portion "d" corresponds to the portion from the interface of prism 1744 and air gap 1742 to incoupler 1212B. Specifically, input light 1701 enters prism 1740. The input angle and prism material are designed and selected so as not to exceed the TIR critical angle at the exit face / air gap 1742. The light continues until it interacts with beam splitter 1746, located between prism 1744 and prism 1748. A second portion of the light continues through the beam splitter and reflects off mirror surface 1750 towards incoupler 1212A, while a first portion of the light reflects off beam splitter 1746 back towards air gap 1742 and reflects off the interface of prism 1744 and air gap 1742 towards incoupler 1212B.In some embodiments, the mirror surface 1750 is a TIR reflective surface, a metallic mirror, or a dielectric mirror.

[0052] The angles of the prisms shown in 1700 are designed so that the reflected light meets the TIR condition and is directed towards the respective incoupler, e.g., incoupler 1212B. As with the multiple substrate example above, beam splitter 1746 is a polarizing beam splitter, a dichroic beam splitter (i.e., a dichroic mirror), or a proportional (i.e., 50T / 50R, 90T / 10R, 33T / 67R, 90R / 10T, etc.) beam splitter. For example, a dichroic beam splitter is used to direct light of different wavelengths (i.e., colors) to incouplers 1212A and 1212B. The dimensions and / or materials of the multiple reflective and transmissive elements 1740-1750 are selected such that the optical path lengths a, b, c, and d meet (or are within a margin of difference) the equation a+b=c+d. Thus, pupil walk is minimized or avoided entirely, improving the quality of the image delivered to the user.

[0053] FIG. 18 illustrates a top view 1800 of a portion of a waveguide 1205, such as that corresponding to the waveguide 205 of FIG. 2, with a plurality of in-couplers 1212A, 1212B and a portion of an optical scanner. The optical scanner includes a plurality of reflective and transmissive elements 1844-1850, including a beam splitter 1846 and a mirror 1850, and a prism assembly with prisms 1844, 1846. In some embodiments, the optical scanner illustrated in FIG. 18 is substantially similar to that illustrated in FIG. 17, except for the presence of prism 1740 and the absence of air gap 1742. The dimensions and materials of the plurality of reflective and transmissive elements 1844-1850 are selected such that the optical path lengths a, b, c, and d satisfy the relationship expressed as a+b=c+d (or fall within a specified margin of difference in the relationship), i.e., the optical path lengths by which each portion of the separated light reaches the corresponding in-coupler are the same. In this example, optical path portion "a" corresponds to the portion from mirror 1850 to incoupler 1212A, optical path portion "b" corresponds to the portion from beam splitter 1846 to mirror 1850, optical path portion "c" corresponds to the portion from beam splitter 1846 to interface 1860 of prism 1844, and optical path portion "d" corresponds to the portion from interface 1860 of prism 1844 to incoupler 1212B. Thus, pupil walk is minimized or avoided altogether, thereby improving the quality of the image delivered to the user.

[0054] FIG. 19 shows diagrams 1900A-1900D illustrating an example of splitting a red light beam and a blue+green light beam from an incident light 1901. As shown in 1900A, the optical scanner's multiple reflective and transmissive elements include a TIR prism 1940, an air gap 1942, a dichroic mirror 1934, a mirror surface 1936, and a MEMS structure 1908. The area marked 1912B indicates the area where the blue+green light beams go to their respective incouplers, and the area marked 1912A indicates the area where the red light beam goes to their respective incouplers. 1900B shows the blue+green light beams splitting from the red light beam, 1900C focuses the path of the red light beam, and 1900D focuses the path of the blue+green light beam.

[0055] FIG. 20 shows a top view of a portion of a waveguide 1205, such as the waveguide 205 of FIG. 2, with multiple in-couplers 1212A and 1212B and a portion of an optical scanner. In this embodiment, the optical scanner includes multiple reflective and transmissive elements 2002-2014 that receive an input light 2001, split the input light 2001 into two portions based on a polarization technique, and direct each portion of light to one of the two in-couplers 1212A, 1212B. For example, the in-coupler 1212A is tuned to in-couple light of a first polarization state, and the in-coupler 1212B is tuned to in-couple light of a second polarization state. In some embodiments, depending on the system configuration, a polarization separation technique is selected over a color separation technique to reduce the number of components or space. Depending on the type of coupler, for example, the response of the coupler as a function of polarization versus color, a polarization separation technique is selected as opposed to a color separation technique.

[0056] The plurality of reflective and transmissive elements 2002-2014 includes a prism assembly having prisms 2002, 2006, 2012, a polarizing beam splitter (PBS) 2004, a wave plate 2008, a beam splitter 2010, and a mirror 2014. In some embodiments, the wave plate 2008 is a fractional wave plate, e.g., a quarter wave plate (QWP) or a half wave plate, the mirror 2414 is a TIR reflective, metallic mirror, or a dielectric mirror, and the beam splitter 2010 is a dichroic beam splitter or a proportional (i.e., 50T / 50R, 90T / 10R, 33T / 67R, 90R / 10T, etc.) beam splitter that separates the light.

[0057] For example, P polarized light 2001 enters prism 2002 and is transmitted through PBS 2004. The light passes through wave plate 2008 and is converted to circularly polarized light. A portion of the light continues through beam splitter 2010 and reflects off mirror surface 2014 toward incoupler 1212A, while the remaining light reflects off beam splitter 2010 and passes back through wave plate 2008. The second pass through wave plate 2008 converts the polarization state from P polarized light to S polarized light. The S polarized light continues to PBS 2004 and reflects off PBS 2004 toward incoupler 1212B. The dimensions and materials of the multiple reflecting and transmitting elements 2002-2014 are selected and designed such that the optical path lengths a, b, c, and d satisfy the relationship expressed by a+b=c+d (or fall within a specified margin of difference in the relationship), i.e., the optical path lengths along which each portion of the separated light reaches the corresponding incoupler are the same. In this example, optical path portion "a" corresponds to the portion from mirror 2014 to incoupler 1212A, optical path portion "b" corresponds to the portion from beam splitter 2010 to mirror 2014, optical path portion "c" corresponds to the portion from beam splitter 2010 to PBS 2004, and optical path portion "d" corresponds to the portion from PBS 2004 to incoupler 1212B. Thus, the waveguide improves the quality of the image delivered to the user.

[0058] Although Fig. 20 shows multiple reflective and transmissive elements such as PBS 2004, wave plate 2008, beam splitter 2010, and mirror 2014 implemented in a structure such as a prism assembly, in some embodiments the same functionality is achieved using separate components. In Fig. 21, PBS 2104, wave plate 2108, beam splitter 2110, and mirror 2114 correspond to the similar components of Fig. 20, except that they are implemented without the prism assembly shown in Fig. 20. In other words, multiple reflective and transmissive elements 2104, 2108, 2110, 2114 are separate components designed and positioned such that the optical path lengths a, b, c, and d satisfy the relationship expressed by a+b=c+d (or fall within a specified margin of difference in the relationship), i.e., the optical path length that each portion of the separated light takes to reach the corresponding in-coupler is the same. In this example, optical path portion "a" corresponds to the portion from mirror 2114 to incoupler 1212A, optical path portion "b" corresponds to the portion from beam splitter 2110 to mirror 2114, optical path portion "c" corresponds to the portion from beam splitter 2110 to PBS 2104, and optical path portion "d" corresponds to the portion from PBS 2104 to incoupler 1212B. Thus, multiple reflective and transmissive elements include fewer components than shown in FIG. 20, but can still improve the quality of the image delivered by the waveguide.

[0059] FIG. 22 shows a top view of a waveguide 1205, such as that corresponding to the waveguide 205 of FIG. 2, with multiple in-couplers 1212A and 1212B and a portion of an optical scanner. In this embodiment, the optical scanner includes multiple reflective and transmissive elements 2204-2212 that direct light from a scanning MEMS mirror 2202 to one of two in-couplers 1212A, 1212B using multiple optical lenses 2204, 2210, 2212 with different magnifications in the optical path to each in-coupler. For example, the focal length of lens 2210 is not equal to the focal length of lens 2212. Thus, the magnification of each optical path of light to each in-coupler 1212A, 1212B is different. This allows a fixed diameter spot size (i.e., limited by the size of the mirror aperture) at the MEMS mirror 2202 to be magnified by different amounts for different wavelength ranges / colors. For example, a system such as that shown in Figure 22 may be configured to output a blue spot with a diameter of 1.0 mm and a red spot with a diameter of 1.4 mm. In some embodiments, this feature is also achieved by secondary optical relay elements, including additional lenses, reflectors, and / or metasurfaces.

[0060] In any of the above configurations, a potential concern is that unwanted light will reach an unintended in-coupler, for example red light being directed into an in-coupler tuned to in-couple blue and green light. In some embodiments, clean-up filters on both sides of the light path prevent unwanted light from reaching the unintended in-coupler. The filters can be either color-selective (dichroic), as shown in FIG. 23, or polarization-selective, as shown in FIG. 24.

[0061] FIG. 23 shows a top view 2300 of an optical scanner that uses optical clean-up filters 2302-2306 in separating incoming light 2301. As shown, dielectric mirror 2302 reflects red light and transmits green light, dielectric mirror 2304 reflects red light and transmits green light, and dielectric mirror 2306 reflects green light and transmits red light. Thus, green light is exclusively directed to an incoupler via dielectric mirror 2304, and red light is exclusively directed to another incoupler via dielectric mirror 2306. While this example shows separation of green and red light, similar techniques can be used for other colors, e.g., blue light. In some embodiments, blue light is also transmitted through dielectric mirror 2304 along with the green light.

[0062] 2 shows a top view of a waveguide 1205, such as the waveguide 205 of FIG. 2, with multiple in-couplers 1212A and 1212B and an optical scanner. The optical scanner includes multiple reflective and transmissive elements 2402-2414 that use polarization techniques to direct received light 2401 to one of the two in-couplers 1212A, 1212B. The multiple reflective and transmissive elements 2402-2414 include a prism assembly of prisms 2402, 2406, 2412, a PBS 2404, a wave plate 2408, a beam splitter 2410, and a mirror 2414. For example, the waveplate 2408 is a fractional waveplate, e.g., a QWP, the mirror 2414 is a TIR reflective, metallic, or dielectric mirror, and the beamsplitter 2410 is a dichroic beamsplitter or a proportional (i.e., 50T / 50R, 90T / 10R, 33T / 67R, 90R / 10T, etc.) beamsplitter. In some embodiments, the plurality of reflective and transmissive elements 2402-2414 correspond to the plurality of reflective and transmissive elements 2002-2014 of FIG. 20. Waveplate / filter 2440 and waveplate / filter 2442 are also included to change the polarization state of the light coming into each of the in-couplers 1212A, 1212B, respectively. The waveplate / filter 2440, 2442 include one or more QWPs, one or more half waveplates, or any combination thereof.

[0063] In some embodiments, the parallel output at the incoupler is achieved by angular separation between the colors of the optical relay by changing the angles of the multiple reflective and transmissive elements, such as beam splitters and / or mirrors. In other words, the different types of light input to the multiple reflective and transmissive elements do not all need to be collinear. That is, the light paths from the multiple reflective elements to the incoupler are parallel, but the light paths entering the multiple reflective and transmissive elements are not parallel. Thus, in some embodiments, no optical components are required to make the individual color light beams collinear in front of the MEMS mirror.

[0064] In some embodiments, the separation of light into lights with different optical properties for directing to one of multiple incouplers (e.g., common waveguide incouplers 1212A, 1212B or waveguide stack incouplers 412A, 412B) is performed based on different wavelength ranges / colors of light. For example, red and green light enter the waveguide at a first incoupler and blue light enters the waveguide at a second incoupler. In another example, blue and green enter the waveguide at a first incoupler while red enters the waveguide at a second incoupler. In another example, red and blue light enter the waveguide at a first incoupler while green enters the waveguide at a second incoupler.

[0065] The above-mentioned technique for equalizing the optical path length can be extended to other display light sources such as micro LED, LCD, and DMD. This is illustrated in FIG. 25 with a display light source 2552. An optical scanner including an optical relay 2554 having two lenses and multiple reflective and transmissive elements 2502-2514 directs light from the display light source 2552 to two in-couplers 1212A, 1212B. The multiple reflective and transmissive elements 2502-2514 include a prism assembly having three prisms 2502, 2506, 2512, a PBS 2504, a wave plate 2508, a beam splitter 2510, and a reflective surface 2514 such as a mirror. Thus, the multiple reflective and transmissive elements direct light to each of the in-couplers to improve the quality of the image delivered by the waveguide.

[0066] Within this disclosure, the margin of difference in optical path length discussed is in the range of 15% or less, and in some embodiments, 5% or less. In some embodiments, it is understood that the margin of difference is a function of the thickness of the waveguide substrate (or waveguide stack), and the optical scanner described herein minimizes the margin of difference in optical path length of light directed to each in-coupler such that the margin of difference is less than the thickness of the waveguide.

[0067] 1-25, the directions of the incident light, grating features, and propagating light are shown in the plane of the page for clarity. However, the directions of some or all of the light paths and / or features may be in or out of the plane of the page. Additionally, the techniques and systems described above are applicable to linear scanning MEMS relay systems, and 2D optical relay systems.

[0068] 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 in 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. The non-transitory computer-readable storage medium may include, for example, magnetic or optical disk storage devices, solid-state storage devices such as flash memory, caches, 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.

[0069] 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 tapes, 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 system (MEMS)-based storage media. A computer-readable storage medium may be incorporated into a computing system (e.g., system RAM or ROM), fixedly attached to a computing system (e.g., magnetic hard drives), removably attached to a computing system (e.g., optical disks 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)).

[0070] In addition to those mentioned above, 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, or 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 appreciate that various modifications and changes can be made without departing from the scope of the present disclosure, as set forth in the following claims. Thus, 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.

[0071] Benefits, other advantages, and solutions to problems have been described above with respect to specific embodiments. However, the benefits, advantages, and solutions to problems, as well as any feature or features that may cause or make any benefit, advantage, or solution more pronounced, 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 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 to the details of construction or design shown herein are intended, other than as set forth in the claims that follow. It is therefore apparent that the specific embodiments disclosed above may be altered or modified, and all such variations are considered to be within the scope of the disclosed subject matter. The protection sought herein is therefore as set forth in the claims that follow.

Claims

1. a waveguide including a first inter-coupler and a second inter-coupler; a plurality of reflective and transmissive elements for selectively directing light to the first intercoupler or the second intercoupler based on a plurality of optical characteristics; 13. An apparatus comprising:

2. 2. The apparatus of claim 1 , wherein the plurality of reflective and transmissive elements separate light into a portion of light having a first optical characteristic among the plurality of optical characteristics and a portion of light having a second optical characteristic among the plurality of optical characteristics, and selectively direct the portion of light having the first optical characteristic to the first intercoupler and the portion of light having the second optical characteristic to the second intercoupler.

3. 3. The apparatus of claim 1, wherein the plurality of optical properties are a plurality of wavelength ranges, and each of the in-couplers is tuned to in-couple light in one of the plurality of wavelength ranges.

4. The apparatus of claim 3 , wherein the plurality of reflective and transmissive elements comprises mirrors.

5. The apparatus of any one of claims 3 to 4, wherein the plurality of reflective and transmissive elements includes a beam splitter, the beam splitter being a dichroic beam splitter that separates light into two or more of the plurality of wavelength ranges.

6. 6. The apparatus of claim 5, wherein the plurality of reflective and transmissive elements include an optical relay element for focusing a first pupil plane associated with a first wavelength range of the plurality of wavelength ranges onto the first intercoupler or for focusing a second pupil plane associated with a second wavelength range of the plurality of wavelength ranges onto the second intercoupler.

7. 7. The apparatus of claim 6, wherein the optical relay element comprises one or more of a lens group, a reflector, a metasurface, a prism assembly with a total internal reflection (TIR) ​​gap having the plurality of reflective and transmissive elements, or any combination thereof.

8. The apparatus of any one of claims 1 to 7, wherein the plurality of reflective and transmissive elements comprises a plurality of lenses with different focal lengths.

9. 3. The apparatus of claim 1, wherein the plurality of optical properties are a plurality of polarization states, and each of the incouplers is adjusted to incouple light of one of the plurality of polarization states.

10. The apparatus of claim 9 , wherein the plurality of reflective and transmissive elements includes a polarizing beam splitter and one or more wave plates.

11. The apparatus of any one of claims 1 to 10, wherein the plurality of reflective and transmissive elements include optical clean-up filters including color-selective or polarization-selective filters to remove light having undesirable optical characteristics from being directed to the first intercoupler or the second intercoupler.

12. 12. The apparatus of claim 1, wherein the plurality of reflective and transmissive elements receive light from a single optical engine and selectively direct the received light to the first intercoupler or the second intercoupler.

13. a waveguide stack, the waveguide stack comprising: a first waveguide substrate including a first inter-coupler; a second waveguide substrate including a second inter-coupler offset from the first inter-coupler; a plurality of reflective and transmissive elements for selectively directing light to the first intercoupler or the second intercoupler based on a plurality of optical characteristics; The apparatus further comprising:

14. 14. The apparatus of claim 13, wherein the plurality of reflective and transmissive elements direct light of a first optical characteristic of the plurality of optical characteristics to the first intercoupler and light of a second optical characteristic of the plurality of optical characteristics to the second intercoupler.

15. The waveguide stack comprises: one or more additional waveguide substrates stacked on the second waveguide substrate, each of the one or more additional waveguide substrates including a respective additional incoupler, each of the respective additional incouplers being laterally offset relative to the first incoupler, the second incoupler, and each of the other respective additional incouplers, the waveguide stack further comprising:

15. The apparatus of claim 13, comprising a plurality of reflective and transmissive elements configured to selectively direct light to the respective one or more additional in-couplers based on the plurality of optical properties.

16. The apparatus of any one of claims 13 to 15, wherein the plurality of reflective and transmissive elements comprises a beam splitter.

17. 17. The apparatus of claim 16, wherein the beam splitter is a dichroic beam splitter, the plurality of optical properties are a plurality of distinct wavelength ranges, and the dichroic beam splitter separates light into the plurality of distinct wavelength ranges for transmission to one of the in-couplers.

18. 17. The apparatus of claim 16, wherein the beam splitter is a polarizing beam splitter, the plurality of optical properties are a plurality of distinct polarization states, and the polarizing beam splitter separates light into the plurality of distinct polarization states for transmission to one of the in-couplers.

19. The plurality of reflective and transmissive elements include:

19. Apparatus according to claim 13 to 18, comprising one or more optical focusing elements for focusing light towards one or more of the in-couplers.

20. receiving input light from a single optical engine; splitting the input light into at least two light portions based on one or more optical characteristics; selectively directing each of the at least two portions of light to one of a plurality of in-couplers of a waveguide; A plurality of reflective and transmissive elements.

Images