Multiple in-coupler waveguides and methods

Abstract

This disclosure describes techniques and waveguides for efficiently incoupling light of different optical characteristics with multiple incouplers in a waveguide, the waveguide including a first incoupler for incoupling light having a first optical characteristic, a second incoupler for incoupling light having a second optical characteristic, and a first structure at an interface of the second incoupler for reflecting light having the first optical characteristic within the waveguide.

Description

[Background technology]

[0001] In a conventional wearable head-up display (WHUD), light from an image source is coupled into a light guide 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 beam is coupled into the waveguide, it is "guided" through the substrate, typically 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, forming an exit pupil within which the virtual image generated by the image source can be viewed. Summary of the Invention

[0002] This disclosure describes embodiments for efficiently in-coupling light with different optical properties with multiple in-couplers in a waveguide while still fitting into the space-constrained form factor of a WHUD.

[0003] In one exemplary embodiment, the waveguide includes a first incoupler for incoupling light having a first optical characteristic, a second incoupler for incoupling light having a second optical characteristic, and a first structure at an interface of the second incoupler for reflecting the incoupled light having the first optical characteristic within the waveguide.

[0004] In some embodiments, for a waveguide, the first optical characteristic comprises a first wavelength range and the second optical characteristic comprises a second wavelength range different from the first wavelength range. The first structure comprises, for example, a dichroic mirror. In some embodiments, the dichroic mirror comprises a shortpass dichroic mirror having a cutoff wavelength between the first wavelength range and the second wavelength range.

[0005] In another embodiment, for a waveguide, the first optical property includes a first polarization state and the second optical property includes a second polarization state different from the first polarization state. The first structure includes, for example, a polarizing beam splitter that reflects light of the first polarization state and transmits light of the second polarization state.

[0006] In another embodiment, for a waveguide, the first optical characteristic includes a first angle of light incoupled into the waveguide at the first intercoupler grating and the second optical characteristic includes a second angle of light incoupled into the waveguide at the second intercoupler grating, the second angle being different from the first angle. The first structure may, for example, include a material with a lower refractive index than a material of a waveguide substrate of the waveguide.

[0007] In some embodiments, relative to the waveguide, the second in-coupler is positioned following the first in-coupler in a direction of light propagation towards one or more out-couplers of the waveguide.

[0008] In further embodiments, the waveguide further comprises a third incoupler for incoupling light of a third optical characteristic, and a second structure at an interface of the third incoupler for reflecting the incoupled light having the first optical characteristic and the incoupled light having the second optical characteristic within the waveguide. In some embodiments, the first optical characteristic comprises a first wavelength range, the second optical characteristic comprises a second wavelength range different from the first wavelength range, and the third optical characteristic comprises a third wavelength range different from the first wavelength range and the second wavelength range. For example, in these embodiments, the first structure comprises a first dichroic mirror and the second structure comprises a second dichroic mirror. Further, the first dichroic mirror comprises a short-pass dichroic mirror having a cutoff wavelength between the first wavelength range and the second optical wavelength range, and the second dichroic mirror comprises a second short-pass dichroic mirror having a cutoff wavelength between the third wavelength range and the first wavelength range and the second wavelength range. In some embodiments, the third incoupler is disposed following the first incoupler and the second incoupler in the light propagation direction towards one or more outcouplers of the waveguide.

[0009] In another exemplary embodiment, a method includes incoupling light having a first optical characteristic into a waveguide via a first incoupler, incoupling light having a second optical characteristic into the waveguide via a second incoupler, and reflecting the incoupled light having the first optical characteristic into the waveguide by a first structure at an interface between the second incoupler and a waveguide substrate of the waveguide.

[0010] In some embodiments, the method includes the first optical property having a first wavelength range and the second optical property having a second wavelength range different from the first wavelength range. Further, in some embodiments, the first structure includes a first dichroic mirror having a cutoff wavelength between the first wavelength range and the second wavelength range.

[0011] In some embodiments, the method includes incoupling light having a third optical property into the waveguide via a third incoupler, and reflecting the incoupled light having the first optical property and the incoupled light having the second optical property into the waveguide via a second structure at an interface between the third incoupler and a waveguide substrate of the waveguide. In some embodiments, the method includes the third optical property including a third wavelength range different from the first wavelength range and the second wavelength range, and the second structure including a second dichroic mirror having a cutoff wavelength between the third wavelength range and the first wavelength range and the second wavelength range.

[0012] In some embodiments, the method includes the first optical property having a first polarization state, the second optical property having a second polarization state different from the first polarization state, and the first structure comprising a polarizing beam splitter.

[0013] The present disclosure may be better understood, and its numerous features and advantages made apparent to those skilled in the art by referencing the accompanying drawings, in which: The use of the same reference symbols in different drawings indicates similar or identical items. [Brief description of the drawings]

[0014] [Figure 1] 1 illustrates an exemplary display system having a support structure housing a projection system configured to project an image toward a user's eye, according to some embodiments. [Diagram 2] 2 shows an example block diagram of a projection system that projects light to display an image to a user's eye through 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 separate in-coupler gratings aligned with each other in the light propagation direction, according to some embodiments. [Diagram 5] 1 illustrates an example of light being outcoupled from a waveguide according to some embodiments. [Figure 6] 13 illustrates an example of a waveguide where a dichroic mirror is located at the interface of the second inter-coupler grating and the waveguide substrate, according to some embodiments. [Figure 7] 13 illustrates an example of a waveguide with a dichroic mirror disposed at an interface of a second inter-coupler grating and a waveguide substrate, and at an interface of a third inter-coupler grating and a waveguide substrate, according to some embodiments. [Figure 8] 9 illustrates an alternative view of FIG. 8 according to some embodiments. [Figure 9] 13 illustrates an example of a waveguide where a polarizing beam splitter is located at the interface of the second inter-coupler grating and the waveguide substrate, according to some embodiments. [Figure 10] 13 illustrates an example of a waveguide having a low refractive index material disposed at the interface of the second inter-coupler grating and the waveguide substrate, according to some embodiments. [Figure 11] 1 shows an example of a flowchart illustrating a method for incoupling light into a waveguide, according to some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Inefficient transmission of received light through the waveguide of a WHUD can degrade image quality at the user's eye and generally negatively impact the user experience. For example, a source of inefficiency in an incoupler is the difference in coupling efficiency between different optical properties (e.g., wavelength / color or polarization state) of the input light and the collinear Red+Green+Blue (RGB) light that is incoupled into the waveguide and propagates as angularly separated light. Figures 1-11 show techniques for increasing the efficiency of light propagation in the waveguide while still fitting into the space-constrained form factor of a WHUD. This in turn improves the image quality provided to the user.

[0016] To illustrate, the present disclosure includes a waveguide having multiple in-couplers, each in-coupler having a grating tuned to in-couple light having one of multiple different optical properties (e.g., wavelength ranges / colors or polarization states) into the waveguide. In some cases, multiple in-couplers are arranged one after the other (i.e., behind each other) in the light propagation direction to occupy less space and better fit the space-constrained form factor of the WHUD. However, in such an arrangement, light in-coupled at one in-coupler may be reflected by the waveguide, so that at least a portion of the light is lost (e.g., out-coupled) at a different in-coupler. Using the techniques described herein, this premature out-coupling of light is prevented by selectively placing reflective structures at one or more in-couplers to reflect light having specific optical properties, such as a specified color or polarization state.

[0017] For example, in some embodiments, the waveguide includes two in-couplers. The first in-coupler is a grating configured to in-couple red light, and the second in-coupler is a grating configured to in-couple blue+green light. The second in-coupler is located relative to the first in-coupler in a direction between the first in-coupler and the out-coupler corresponding to the first and second in-couplers. With this arrangement, the red in-coupled light from the first in-coupler potentially interacts with the second in-coupler when the red in-coupled light propagates through the waveguide. Using the techniques described herein, a dichroic mirror having a cutoff wavelength value between the red light range and the blue+green light range is placed at or near the second in-coupler. Thus, the dichroic mirror reflects the red light and passes the blue+green light. This prevents (or reduces) the loss of red light at the second in-coupler, thereby improving the overall quality of the image provided by the waveguide.

[0018] 1-11 illustrate embodiments of exemplary display systems and techniques for increasing the amount of incoupled light propagated within a waveguide to an outcoupler, as described in more detail below. However, it will be 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.

[0019] FIG. 1 illustrates an exemplary display system 100 having a support structure 102 including an arm 104 housing a laser projection system configured to project an image toward a user's eye, where the user perceives the projected image displayed on one or both of lens elements 108, 110 within a field of view (FOV) area 106 of the display. In the illustrated embodiment, the display system 100 is a wearable head-up display (WHUD), which includes a support structure 102 configured to be worn on top of a user's head and has the general shape and appearance of an eyeglass (e.g., sunglasses) frame. The support structure 102 houses or otherwise includes various components to facilitate the projection of such images toward the user's eye, such as a laser projector, an optical scanner, and a wave guide. In some embodiments, the support structure 102 further includes various sensors, such as one or more forward-facing cameras, rear-facing cameras, other optical sensors, motion sensors, accelerometers, and the like. The support structure 102 may further include one or more radio frequency (RF) interfaces or other wireless interfaces, such as a Bluetooth interface, a WiFi interface, etc. 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 housed completely or partially within an interior volume of the support structure 102, such as within an arm 104 within an area 112 of the support structure 102. It should be noted 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. 1.

[0020] 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 on or otherwise provided in combination with a real-world view perceived by a user through the lens elements 108, 110. For example, laser light used to form a perceptible image or series of images may be projected to a user's eye by a laser projector of the display system 100 through a series of optical elements, such as a waveguide formed at least partially within a corresponding lens element, one or more scanning mirrors, and one or more optical relays. Thus, one or both of the lens elements 108, 110 may include at least a portion of a waveguide that routes display light received by a waveguide in-coupler to a waveguide out-coupler that outputs the display light toward a user's eye of the display system 100. In some embodiments, the waveguide includes multiple in-couplers, each of which is tuned to incouple light of one of multiple optical properties into the waveguide to increase the amount of light displayed to the user within the FOV region 106. The multiple in-couplers are, in some embodiments, arranged consecutively with one another along the light propagation path with one or more corresponding out-coupler directions to fit within the spatial dimensioning factor of the display system 100. Furthermore, in some embodiments, one or more of the in-couplers include a selectively reflective structure for reflecting light incoupled with one or more other in-couplers, so that this light is not prematurely outcoupled before being displayed to the user within the FOV region 106. The display light is modulated and scanned over the user's eye such that the user perceives the display light as an image. Additionally, each of the lens elements 108, 110 is sufficiently transparent to provide a view of the user's real-world environment such that the user can see through the lens element, and the image appears superimposed over at least a portion of the real-world environment.

[0021] 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, which may be microelectromechanical systems (MEMS)-based or piezo-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 projector's scan area size and scan area position and generates the content displayed on the display system 100. The projector scans light over a variable area of ​​the display system 100, designated by the FOV area 106. 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. Herein, the range of different user eye positions from which the display can be seen is referred to as the eyebox of the display.

[0022] In some embodiments, the projector routes the light through the first and second scan mirrors, an optical relay disposed between the first and second scan mirrors, and a waveguide disposed at the output of the second scan mirror. In some embodiments, at least a portion of the waveguide outcoupler may overlap the FOV region 106. These aspects are described in further detail below.

[0023] 2 shows a simplified block diagram of a projection system 200 that projects an image directly onto a user's eye via light. The projection system 200 includes an optical engine 202, an optical scanner 204, and a waveguide 205. The optical scanner 204 includes a first scan mirror 206, a second scan 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.

[0024] The optical engine 202 includes one or more light sources configured to generate and output light 218 (e.g., visible light, such as red, blue, and green light, and / or non-visible light, such as infrared light). In some embodiments, the optical engine 202 is coupled to a driver or other controller (not shown) that controls the timing of light emission from the light sources of the optical engine 202 according to instructions received by the controller or driver from a computer processor coupled thereto, and modulates the light 218 to be perceived as an image when output to the retina of a user's eye 216.

[0025] For example, during operation of the projection system 200, multiple light beams, each having a different wavelength, are output by the light sources of the optical engine 202 and then combined via a beam combiner (not shown) before being directed towards the user's eye 216. The 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 to the amount of color content and brightness that corresponds to the pixel being represented by the combined light at that time.

[0026] In some embodiments, one or both of the scan mirrors 206 and 208 of the optical scanner 204 are MEMS mirrors. For example, the scan mirrors 206 and 208 are MEMS mirrors that, when driven by respective actuation voltages, oscillate during active operation of the projection system 200, causing the scan mirrors 206 and 208 to scan the light 218. The oscillation of the scan mirror 206 causes the light 218 output by the optical engine 202 to be scanned across the surface of the second scan mirror 208 through the optical relay 210. 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 light directed from the scan mirror 208 toward the incoupler 212 of the waveguide 205 is separated into lights with different optical properties. That is, multiple inputs of light are directed to the incoupler 212, with each input of light having one of multiple optical properties (e.g., wavelength ranges / colors) associated with it. In some embodiments, the scan mirror 206 oscillates along a first scan axis 219 such that the light 218 is scanned only in 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 scan axis 221. In some embodiments, the first scan axis 219 is perpendicular to the second scan axis 221.

[0027] 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 corresponds to the smaller dimension of the incoupler 212) by the first scan mirror 206, routes the light 218 to the second scan mirror 208, and introduces a convergence of the light 218 to an exit pupil beyond the second scan mirror 208 in the first dimension. As used herein, "exit pupil" in an optical system refers to a location along an optical path where light beams intersect. For example, following reflection by the first scan mirror 206, the possible optical paths of the light 218 initially spread along the first scan axis, but later these paths intersect at an exit pupil beyond the second scan mirror 208 due to the convergence introduced by the optical relay 210. 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 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, which corresponds to the length dimension of the incoupler 212 of the waveguide 205. In some embodiments, the second scan mirror 208 sweeps the light 218 at the exit pupil 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 scan mirror 208 such that the second scan mirror 208 scans the light 218 as a line or row on the incoupler 212.

[0028] In some embodiments, the optical engine 202 includes an edge-emitting laser (EEL) that emits a laser beam 218 having a substantially elliptical, non-circular cross-section, and the optical relay 210 expands or minimizes the laser beam 218 along its semimajor or semiminor axis of orbit to circularize the laser beam 218 prior to focusing the laser beam 218 on the second scan mirror 208. In some such embodiments, the surface of the mirror plate of the scan mirror 206 is elliptical and non-circular (e.g., similar in shape and size to the cross-sectional area of ​​the laser beam 218). In other such embodiments, the surface of the mirror plate of the scan mirror 206 is circular.

[0029] The waveguide 205 of the projection system 200 includes an in-coupler 212 and an out-coupler 214. As used herein, the term "waveguide" will be understood to mean a combiner that transmits light from an in-coupler (such as in-coupler 212) to an out-coupler (such as out-coupler 214) using one or more of total internal reflection (TIR), special filters, and / or reflective surfaces. 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" will be 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 diffraction grating or a transmission holographic grating) such that the in-coupler or out-coupler transmits light 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 diffraction grating or a reflection holographic grating) such that the reflection grating causes the in-coupler or out-coupler to reflect light and apply a designed optical function(s) to the light during reflection. In this example, the laser light 218 received at the in-coupler 212 is relayed to the out-coupler 214 via the waveguide 205 using TIR. The laser 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.

[0030] In some embodiments, although only one in-coupler 212 is shown in FIG. 2, the waveguide 205 includes multiple in-couplers 212 to increase the amount of input light in-coupled into the waveguide 205. Each of the in-couplers is tuned to in-couple light of one of multiple optical properties into the waveguide 205, thereby increasing the overall coupling efficiency of the projection system 200, where the coupling efficiency is the amount of light propagating along the waveguide divided by the amount of input light (also called incident light). Adjustable in-coupler grating parameters include, but are not limited to, grating height, grating spacing, grating angle, and grating density. Furthermore, each in-coupler may use a different manufacturing process since it has different grating parameters. In some embodiments, the multiple optical properties are multiple wavelength ranges. In other embodiments, the multiple optical properties are multiple polarization states. In some cases, the multiple in-couplers are placed one after the other (i.e., behind each other) in the light propagation direction to occupy less space in the WHUD system. To prevent loss at the subsequent incoupler of light incoupled into the previous incoupler, reflective structures are placed at the interfaces with the waveguides or integrated into the subsequent incoupler, with reflective qualities selected to prevent light incoupled into the previous incoupler from interacting with (i.e., being outcoupled into) the subsequent incoupler, as described further herein.

[0031] The terms "incoupler" and "incoupler grating" are used in this specification and related drawings to correspond to one another unless otherwise indicated. Thus, descriptions of a "first incoupler grating," a "second incoupler grating," a "third incoupler grating," etc. (e.g., a "first grating," a "second grating," a "third grating") correspond to a "first incoupler," a "second incoupler," and a "third incoupler," respectively, unless otherwise indicated.

[0032] 2, in some embodiments, additional optical components are included in the optical path either between the optical engine 202 and the scan mirror 206, between the scan mirror 206 and the optical relay 210, between the optical relay 210 and the scan mirror 208, between the scan 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 laser light for viewing by the user's eye 216). In some embodiments, a prism is used to direct the light from the scan mirror 208 to the incoupler 212 so that the light is coupled into the incoupler 212 at the 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 positioned at an intermediate stage between the in-coupler 212 and the out-coupler 214 to receive the light coupled into the waveguide 205 by the in-coupler 212, expand the light, and redirect the light toward the out-coupler 214, which then couples the laser light out of the waveguide 205 (e.g., toward the user's eye 216).

[0033] 3 illustrates an example of light propagation within the waveguide 205 of the projection system 200 of FIG. 2, according to some embodiments. As shown, light received via the in-coupler 212 scanned along an axis 302 is directed into an exit pupil expander (EPE) 304 and then routed to the out-coupler 214 for output (e.g., toward 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 what the dimensions of the eyebox of the WHUD would be 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). It should be understood that Figure 3 illustrates a substantially ideal case, where in-coupler 212 directs light straight down in a first direction perpendicular to scan axis 302 (relative to the currently shown view), and exit pupil expander 304 directs light to the right in a second direction perpendicular to the first direction (relative to the currently shown view). Although not shown in this example, it should be understood that in some embodiments, the first direction in which in-coupler 212 directs light is not exactly perpendicular, but is slightly or substantially oblique to scan axis 302.

[0034] In some embodiments in which the waveguide 205 includes multiple in-couplers 212, the waveguide 205 also includes multiple corresponding exit pupil expanders 304 and / or out-couplers 214. For example, a first in-coupler directs light through a first exit pupil expander to a first out-coupler, and a second in-coupler directs light through a second exit pupil expander to a second out-coupler. In some embodiments, each of the in-couplers and their corresponding exit pupil expanders and out-couplers are specifically tuned to propagate light of one of the multiple optical properties through the waveguide 205 to a user.

[0035] Multiple incouplers may be applied to the waveguides positioned adjacent to each other (i.e., laterally adjacent to each other) such that the optical path incoupled by a first incoupler does not cross the optical path incoupled by a second or subsequent incoupler. In other words, each incoupler does not follow another incoupler in the optical propagation direction toward one or more outcouplers. While this prevents the light incoupled by multiple incouplers from directly interacting with each other, such an arrangement requires a thicker substrate and more space to accommodate the waveguides, so that other system parameters (e.g., optical uniformity and system complexity) are adversely affected. Furthermore, in highly space-constrained form factors, such as the WHUD 100 of FIG. 1, there is usually no space available to accommodate such a setup. The techniques described herein address this issue by arranging the incouplers in line with each other in the optical propagation direction. Furthermore, selectively reflective structures are placed on one or more of the incouplers to reflect light having a specified optical property, such as a specified color or polarization.

[0036] 4 and 5 show a side view portion 400 and a top view 500, respectively, of a portion of a waveguide substrate 405, such as corresponding to the waveguide 205 of FIG. 2. As shown, the waveguide substrate 405 has a number of incouplers, including a first incoupler 412a and a second incoupler 412b. The first incoupler 412a receives a first input light 502 in a first wavelength range (e.g., corresponding to red light) and incouples the light into the waveguide 405 as a first incoupled light 520. The second incoupler 412b receives a second input light 504 in a second wavelength range (e.g., corresponding to blue and green light) and incouples the light into the waveguide 405 as a second incoupled light 530. Each of the incouplers 412a and 412b is tuned to receive light in a corresponding wavelength range to enhance the coupling efficiency of the waveguide. Furthermore, to reduce the space required to implement a multiple incoupler setup, the second incoupler 412b is positioned following the first incoupler 412a in the light propagation direction 402 toward one or more outcouplers 550. Because the second incoupler 412b is positioned in the path of the light propagation 402 from the first incoupler 412a, a portion of the first incoupled light 520 may potentially interact with the second incoupler 412b and be lost (522), i.e., prematurely outcoupled by the second incoupler 412b. This results in a reduced amount of the first incoupled light 512 at 524 propagating toward the exit pupil expander(s) and outcoupler(s) 550. In other words, the amount of light at 524 is the first incoupled light 520 reduced by the amount of lost light 522.

[0037] Thus, as described in more detail below, in some embodiments, a reflective structure is disposed in one or more intercouplers to reflect light having one or more specified optical characteristics relative to another intercoupler, thereby preventing or reducing the amount of light loss at the intercoupler and improving the image quality provided by the waveguide.

[0038] 6 shows a top view 600 of a portion of a waveguide substrate 605, such as that corresponding to the waveguide 205 of FIG. 2, having a first in-coupler 612a and a second in-coupler 612b. The first in-coupler 612a receives a first input light 602 in a first wavelength range and in-couples the light into the waveguide 605 as a first in-coupled light 620. The second in-coupler 612b receives a second input light 604 in a second wavelength range and in-couples the light into the waveguide 605 as a second in-coupled light 634. Each of the in-couplers 612a and 612b is tuned to receive light in a corresponding wavelength range to increase coupling efficiency. Furthermore, to reduce the space required to implement a multiple in-coupler setup, the second in-coupler 612b is positioned following the first in-coupler 612a in the light propagation direction towards one or more out-couplers 650 (similar to the setup shown in Figures 4-5).

[0039] To prevent outcoupling of the first incoupled light 620 at the second incoupler 612b (i.e., as shown in FIG. 5), a reflecting structure 614 is disposed at the second incoupler 612b. For example, as shown, the reflecting structure 614 is at the interface between the waveguide substrate 605 and the second incoupler 612b. The reflecting structure 614 is a dichroic mirror, which reflects light of a first wavelength range corresponding to the first incoupled light 620 and transmits light having a second wavelength range corresponding to the input light 604 and the second incoupled light 634. This reflection of the first incoupled light 620 is shown at 622. In this way, the reflecting structure 614 prevents loss of the first incoupled light 620 at the second incoupler 612b. Thus, the amount of the first incoupled light 620 propagating to 632 towards the exit pupil expander(s) and outcoupler(s) 650 is increased. In other words, the light at 632 is the same or substantially the same as the first in-coupled light 620 because the reflecting structure 614 prevents the first in-coupled light 620 from being out-coupled at 612b, thereby improving the coupling efficiency and therefore the image quality delivered to the user.

[0040] For example, if a first incoupler 612a incouples a first input light 602 having a first wavelength range corresponding to red light and a second incoupler 612b incouples a second input light 604 having a second wavelength range corresponding to blue+green light, a dichroic mirror is used as the reflecting structure 614. The dichroic mirror has a cutoff wavelength value within the range between red and green light so as to reflect red light and transmit blue+green light. In this way, the first incoupled light 620 (red light) bypasses the second incoupler 612b by reflecting at 622 to the dichroic mirror 614. Although FIG. 6 shows a waveguide with two incouplers 612a and 612b, in some embodiments the waveguide has three or more incouplers as shown in FIGS. 7-8. Including more incouplers improves the coupling efficiency of the overall system by allowing each incoupler to be tuned to a finer range of optical properties. In some embodiments, although three in-couplers are shown in Figures 7-8, it will be appreciated that the number of in-couplers is scalable to other amounts (e.g., four or more) depending on system performance considerations. For example, a greater number of in-couplers would be utilized if a higher level of FOV multiplexing were implemented or if the in-coupling of light into the waveguides were segmented for other optical and / or performance related reasons.

[0041] 7 and 8 show a top view 700 and a side view 800, respectively, of a portion of a waveguide substrate 705, such as that corresponding to the waveguide 205 of FIG. 2. As shown, the waveguide substrate 705 has a first in-coupler grating 712a, a second in-coupler grating 712b, and a third in-coupler grating 712c. The first in-coupler 712a receives a first input light 702 in a first wavelength range and in-couples the light into the waveguide 705 as a first in-coupler in-coupled light 720. The second in-coupler 712b receives a second input light 704 in a second wavelength range and in-couples the light into the waveguide 705 as a second in-coupler in-coupled light 730. The third in-coupler 712c receives a third input light 706 in a third wavelength range and in-couples the light into the waveguide 705 as a third in-coupler in-coupled light 740. Each of the in-couplers 712a, 712b, 712c is tuned to receive light of a corresponding wavelength range to increase the coupling efficiency of the waveguides. Furthermore, to reduce the space required to implement a multiple in-coupler setup, the second in-coupler 712b is positioned following the first in-coupler 712a in the light propagation direction 802 towards one or more out-couplers 750, and the third in-coupler 712c is positioned following the second in-coupler 712b in the light propagation direction 802 towards one or more out-couplers 750.

[0042] To prevent outcoupling of light incoupled at other incouplers, the reflecting structures 714 and 716 are disposed at the second incoupler 712b and the third incoupler 712c, respectively. For example, to prevent outcoupling of the first incoupled light 720 at the second incoupler 712b, the reflecting structure 714 is disposed at the second incoupler 712b. And, to prevent outcoupling of the first incoupled light 720 and the second incoupled light 730 at the third incoupler 712c, the reflecting structure 716 is disposed at the third incoupler 712c. As shown, each of the reflecting structures 714, 716 is at the interface between the waveguide substrate 705 and the respective incoupler 712b, 712c. The reflecting structure 714 is a dichroic mirror, which reflects light in a first wavelength range corresponding to the first incoupled light 720 and transmits light in a second wavelength range corresponding to the second input light 704 and the second incoupled light 730. In other words, the dichroic mirror at 714 has a cutoff wavelength value between the first wavelength range and the second wavelength range. The reflecting structure 716 is a dichroic mirror, which reflects light in a first wavelength range corresponding to the first incoupled light 720 and light in a second wavelength range corresponding to the second incoupled light 730 and transmits light in a third wavelength range corresponding to the third input light 706 and the third incoupled light 740. In other words, the dichroic mirror at 716 has a cutoff wavelength value between the third wavelength range and the first and second wavelength ranges. Thus, the light incoupled by the incoupler can bypass the other incouplers by reflecting off the dichroic mirror.

[0043] The reflection of the first incoupled light 720 at the second incoupler 712b is shown at 722. In this way, the reflecting structure 714 prevents the loss of the first incoupled light 720 at the second incoupler 712b. Similarly, the reflecting structure 716 reflects the first incoupled light 720 at 724 and the second incoupled light 730 at 732. In this way, the reflecting structure 716 prevents the loss of the first incoupled light 720 and the second incoupled light 730 at the third incoupler 712c. Thus, the amount of the first incoupled light 720 and the amount of the second incoupled light 730 increase as they propagate to 726 and 734, respectively. This results in an improvement in the image quality delivered to the user.

[0044] Additionally, while Figures 4-8 are described with respect to incouplers that are tuned to incouple light of different wavelength ranges into the waveguide, it will be understood that in other embodiments, the incouplers are tuned to incouple light of different polarization states or other optical properties into the waveguide, and examples of these other embodiments are described in more detail below in Figures 9 and 10.

[0045] FIG. 9 shows a top view 900 of a portion of a waveguide substrate 905, such as that corresponding to the waveguide 205 of FIG. 2, with a first in-coupler 612a and a second in-coupler 912b. The first in-coupler 912a receives a first input light 902 having a first polarization state and in-couples the light into the waveguide 905 as a first in-coupled light 920. The second in-coupler 912b receives a second input light 904 having a second polarization state and in-couples the light into the waveguide 905 as a second in-coupled light 930. In some embodiments, the use of polarization techniques for in-coupling light allows the use of multiple light sources, for example of the same color. Each of the in-couplers 912a and 912b is tuned to receive light of a specific polarization state to increase the coupling efficiency of the waveguide. For example, the first polarization state is S-polarized and the second polarization state is P-polarized, or vice versa. Furthermore, to reduce the space required to implement a multiple in-coupler setup, the second in-coupler 912b is positioned following the first in-coupler 912a in the light propagation direction towards the one or more out-couplers 950.

[0046] To prevent outcoupling of the first incoupled light 920 at the second incoupler 912b, a PBS layer 914 is disposed at the second incoupler 912b. For example, as shown, the PBS layer 914 is at the interface between the waveguide substrate 905 and the second incoupler 912b. The PBS layer 914 reflects light having a first polarization state corresponding to the first incoupler coupled light 920 and transmits light having a second polarization state corresponding to the input light 904 and the second incoupled light 930. This reflection of the first incoupled light 920 is shown at 922. Thus, the PBS layer 914 prevents premature outcoupling of the first incoupled light 920 at the second incoupler 912b. Thus, the amount of the first incoupled light 920 propagating 924 towards the exit pupil expander(s) and outcoupler(s) 950 is increased, thereby improving the image quality delivered to the user.

[0047] 10 shows a top view 1000 of a portion of a waveguide substrate 1005, such as that corresponding to the waveguide 205 of FIG. 2, with a first in-coupler 1012a and a second in-coupler 1012b. The first in-coupler 1012a receives a first input light 1002 and in-couples the light into the waveguide 1005 as a first in-coupled light 1020 having a first in-coupling angle. The second in-coupler 1012b receives a second input light 1004 and in-couples the light into the waveguide 1005 as a second in-coupled light 1030 having a second in-coupling angle. Each of the in-couplers 1012a and 1012b is adjusted to in-couple light into the waveguide at a respective angle. To reduce the space required to implement a multiple in-coupler setup, the second in-coupler 1012b is positioned following the first in-coupler 1012a in the light propagation direction towards the one or more out-couplers 1050.

[0048] To prevent outcoupling of the first incoupled light 1020 at the second incoupler 1012b, a low index layer 1014 is disposed at the second incoupler 1012b. For example, as shown, the low index layer 1014 is at the interface between the waveguide substrate 1005 and the second incoupler 1012b. The low index layer 1014 reflects the first incoupled light 1020 and transmits the input light 1004 and the second incoupled light 1030. Because the angle of the first incoupled light 1020 is steeper than the input light 1004, the first incoupled light 1020 is reflected from the interface created in the low index material 1114 and the waveguide substrate 1105 by being within a critical angle such that the interface is defined by total internal reflection (TIR). For example, the refractive index of the waveguide substrate is n=2.0, and the refractive index of the low refractive index material 1014 is n=1.4. It is understood that these values ​​are examples, and that in general, the material of the low refractive index material 1014 is selected based on its refractive index being lower than that of the waveguide substrate 1005. This reflection of the first in-coupled light 1020 is shown at 1022. In this way, the low refractive index layer 1014 prevents the loss of the first in-coupled light 1020 at the second in-coupler 1012b. Thus, the amount of the first in-coupled light 1020 propagating at 1024 towards the exit pupil expander(s) and out-coupler(s) 1050 is increased, thereby improving the image quality delivered to the user.

[0049] 11 shows a method flowchart 1100 for incoupling light having different optical properties into a waveguide, according to some embodiments. The method includes incoupling light having a first optical property into the waveguide via a first in-coupler, at 1102. The method includes incoupling light having a second optical property into the waveguide via a second in-coupler, at 1104. The method includes reflecting the light having the first optical property in the waveguide by a first structure at an interface between the second in-coupler and a waveguide substrate of the waveguide, at 1106.

[0050] In some embodiments, the method further includes incoupling light having a third optical property into the waveguide via a third incoupler, hi some embodiments, the method further includes reflecting the incoupling light having the first optical property and the incoupling light having the second optical property via a second structure at an interface between the third incoupler and a waveguide substrate of the waveguide.

[0051] In some embodiments, the first, second, and if applicable third optical property of the method is a wavelength range, hi other embodiments, the optical property is a polarization state or angle of light incoupled into the waveguide.

[0052] The reflective structures described in the present disclosure reflect the light inside the waveguide. For example, the reflective structure in the second incoupler of a multiple incoupler waveguide reflects the light incoupled into the waveguide by the first incoupler. In other words, the reflective structure reflects the light already incoupled, so that the light is retained for propagation in the waveguide.

[0053] 1-11, the directions of the incident light, grating features, and propagating light are depicted in the plane of the page for clarity. However, the directions of some or all of the light paths and / or features may be within or outside the plane of the page. Additionally, the techniques and systems described above are applicable to line-scan MEMS relay systems, and 2D optical relay systems.

[0054] In some embodiments, certain aspects of the techniques described above may be implemented by one or more processors of a processing system executing software. The software includes one or more sets of executable instructions stored or otherwise tangibly embodied on a non-transitory computer-readable storage medium. The software may include instructions and specific data that, when executed by one or more processors, operate the one or more processors to perform one or more aspects of the techniques described above. 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.

[0055] 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 systems (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., a magnetic hard drive), removably attached to a computing system (e.g., an optical disk or a 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)).

[0056] In addition to the 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 variations can be made without departing from the scope of the present disclosure, as set forth in the following claims. Thus, the present specification and drawings should be regarded in an illustrative rather than restrictive sense, and all such modifications are intended to be included within the scope of the present disclosure.

[0057] 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 contemplated 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, a first incoupler for incoupling light having a first optical characteristic; a second incoupler for incoupling light having a second optical characteristic; and a first structure at an interface of the second incoupler for reflecting incoupled light having the first optical property within the waveguide; A waveguide comprising:

2. 2. The waveguide of claim 1, wherein the first optical characteristic comprises a first wavelength range and the second optical characteristic comprises a second wavelength range different from the first wavelength range.

3. The waveguide of claim 2 , wherein the first structure comprises a dichroic mirror.

4. 4. The waveguide of claim 3, wherein the dichroic mirror comprises a shortpass dichroic mirror having a cutoff wavelength between the first wavelength range and the second wavelength range.

5. 2. The waveguide of claim 1, wherein the first optical property comprises a first polarization state and the second optical property comprises a second polarization state different from the first polarization state.

6. The waveguide of claim 5 wherein the first structure comprises a polarizing beam splitter.

7. 7. The waveguide of claim 6, wherein the polarizing beam splitter reflects light of the first polarization state and transmits light of the second polarization state.

8. the first optical characteristic comprises a first angle of light incoupled into the waveguide at the first incoupler, and the second optical characteristic comprises a second angle of light incoupled into the waveguide at the second incoupler; The waveguide of claim 1 , wherein the second angle is different from the first angle.

9. The waveguide of claim 8 , wherein the first structure comprises a material with a lower refractive index than a material of a waveguide substrate of the waveguide.

10. The waveguide of claim 1 , wherein the second in-coupler is positioned following the first in-coupler in a light propagation direction towards one or more out-couplers of the waveguide.

11. a third incoupler for incoupling light of the third optical characteristic; and a second structure at an interface of the third incoupler for reflecting incoupled light having the first optical characteristic and incoupled light having the second optical characteristic within the waveguide; The waveguide of claim 1 further comprising:

12. 12. The waveguide of claim 11 , wherein the first optical characteristic comprises a first wavelength range, the second optical characteristic comprises a second wavelength range different from the first wavelength range, and the third optical characteristic comprises a third wavelength range different from the first wavelength range and the second wavelength range.

13. 13. The waveguide of claim 12, wherein the first structure comprises a first dichroic mirror and the second structure comprises a second dichroic mirror.

14. the first dichroic mirror includes a shortpass dichroic mirror having a cutoff wavelength between the first wavelength range and the second wavelength range; 14. The waveguide of claim 13, wherein the second dichroic mirror comprises a second shortpass dichroic mirror having a cutoff wavelength between the third wavelength range and the first and second wavelength ranges.

15. The waveguide of any one of claims 11 to 14, wherein the third in-coupler is positioned following the first in-coupler and the second in-coupler in a light propagation direction toward one or more out-couplers of the waveguide.

16. incoupling light having a first optical characteristic into the waveguide via a first incoupler; incoupling light having a second optical characteristic into the waveguide via a second incoupler; reflecting incoupled light having the first optical property within the waveguide by a first structure at an interface between the second incoupler and a waveguide substrate of the waveguide; A method comprising:

17. the first optical characteristic includes a first wavelength range and the second optical characteristic includes a second wavelength range different from the first wavelength range; 17. The method of claim 16, wherein the first structure comprises a first dichroic mirror having a cutoff wavelength between the first wavelength range and the second wavelength range.

18. incoupling light having a third optical characteristic into the waveguide via a third incoupler; reflecting the incoupled light having the first optical characteristic and the incoupled light having the second optical characteristic within the waveguide via a second structure at an interface between the third incoupler and the waveguide substrate of the waveguide; 20. The method of claim 17, further comprising:

19. the third optical characteristic includes a third wavelength range different from the first wavelength range and the second wavelength range; 20. The method of claim 18, wherein the second structure includes a second dichroic mirror having a cutoff wavelength between the third wavelength range and the first and second wavelength ranges.

20. the first optical characteristic comprises a first polarization state and the second optical characteristic comprises a second polarization state different from the first polarization state; The method of claim 16 , wherein the first structure comprises a polarizing beam splitter.

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