Dual-index waveguide stack

Abstract

An image light guide system for conveying a virtual image comprising a first waveguide having a first refractive index and a second waveguide having a second refractive index, the first waveguide including a diffractive optical element arranged to in-couple and out-couple an image-bearing light beam of a first wavelength range, and the second waveguide including a diffractive optical element arranged to in-couple and out-couple an image-bearing light beam of at least a second wavelength range.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates generally to electronic display devices, and more particularly to display devices that utilize an image light guide having a diffractive optical element for transmitting image-bearing light to a viewer. [Background technology]

[0002] Head-mounted displays (HMDs) and virtual image near-eye displays are being developed for a wide range of applications, including military, commercial, industrial, firefighting, and entertainment applications. In many of these applications, it is valuable to create a virtual image that can be visually superimposed on a real-world image in the HMD user's field of view. Optical image light guides can deliver image-bearing light to the viewer in a small space to direct the virtual image toward the viewer's pupil and enable this superimposition function.

[0003] While conventional image light guide arrangements have resulted in significant reductions in the bulk, weight, and overall cost of near-eye display optics, further improvements are needed. In some instances, image resolution is constrained by the reduced bulk and cost of conventional image light guide arrangements. Similarly, diffraction and propagation of certain wavelengths of light may underperform in conventional image light guide arrangements. Thus, there is a need for an image light guide system that is operable to produce desired virtual image brightness and resolution while managing system volume and cost. Summary of the Invention

[0004] In a first exemplary embodiment, the present disclosure provides an image light guide system for conveying a virtual image, the image light guide system including: a first waveguide having a first refractive index; a first incoupling diffractive optical element formed along the first waveguide, the first incoupling diffractive optical element arranged to diffract an image-bearing light beam of a first wavelength range into the first waveguide in an angularly coded manner; and a first outcoupling diffractive optical element formed along the first waveguide, the first outcoupling diffractive optical element arranged to replicate the image-bearing light beam of the first wavelength range in at least one direction and direct the replicated image-bearing light beam from the first waveguide in an angularly coded manner. and a second incoupling diffractive optical element formed along the second waveguide, the second incoupling diffractive optical element being arranged to diffract an image-bearing light beam of a second wavelength range into the second waveguide in an angularly coded manner. Furthermore, the present invention provides an image light guide system including: an incoupling diffractive optical element; a second waveguide having a second refractive index; a second incoupling diffractive optical element formed along the second waveguide, the second incoupling diffractive optical element being arranged to replicate the image-bearing light beam of the second wavelength range in at least one direction and direct the replicated image-bearing light beam from the second waveguide in an angularly decoded manner. In one exemplary embodiment, the image light guide system includes a third incoupling diffractive optical element formed along the second waveguide, the third incoupling diffractive optical element arranged to diffract the image-bearing light beam in the third wavelength range into the second waveguide in an angularly coded manner; and a third outcoupling diffractive optical element formed along the second waveguide, the third outcoupling diffractive optical element arranged to replicate the image-bearing light beam in the third wavelength range in at least one direction and direct the replicated image-bearing light beam from the second waveguide in an angularly decoded manner.

[0005] In an exemplary embodiment, the first waveguide comprises a lower refractive index material than the second waveguide.

[0006] The accompanying drawings are incorporated herein as part of this specification. The drawings described herein illustrate embodiments of the disclosed subject matter and illustrate selected principles and teachings of the present disclosure. However, the drawings do not illustrate every possible implementation of the disclosed subject matter and are not intended to limit the scope of the present disclosure in any way. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 shows a simplified cross-sectional view of an image light guide showing the replication of the image-bearing beam along the propagation direction to extend one direction of the eyebox. [Figure 2] FIG. 2 shows a perspective view of an image light guide with a rotating grating illustrating the expansion of the image-bearing beam perpendicular to the propagation direction to expand in a second direction in the eyebox. [Figure 3] FIG. 3 shows a schematic side view of a stacked waveguide having multiple incoupling diffractive optical elements, according to an exemplary embodiment of the disclosed subject matter. [Figure 4] FIG. 4 shows a schematic top view of the first waveguide according to FIG. [Figure 5] FIG. 5 shows a schematic top view of the second waveguide according to FIG. [Figure 6] FIG. 6 shows a schematic bottom view of the second waveguide according to FIG. [Figure 7] FIG. 7 shows a schematic end view of the laminated waveguide according to FIG. [Figure 8] FIG. 8 shows a schematic end view of the laminated waveguide according to FIG. [Figure 9] 9 and 10 show schematic perspective views of the laminated waveguide according to FIG. [Figure 10] 9 and 10 show schematic perspective views of the laminated waveguide according to FIG. [Figure 11]FIG. 11 shows a schematic side view of a stacked waveguide according to an exemplary embodiment of the disclosed subject matter. [Figure 12A] FIG. 12A shows a schematic top view of the first waveguide according to FIG. [Figure 12B] FIG. 12B shows a schematic top view of the second waveguide according to FIG. [Figure 13A] FIG. 13A shows a schematic top view of the first waveguide according to FIG. [Figure 13B] FIG. 13B shows a schematic top view of the second waveguide according to FIG. [Figure 14] FIG. 14 shows a schematic side view of a portion of a reflective incoupling diffractive optical element. [Figure 15] FIG. 15 shows a schematic side view of a portion of a transmissive incoupling diffractive optical element. [Figure 16] FIG. 16 shows a perspective view of a display system for an augmented reality display using an image light guide, according to an exemplary embodiment of the disclosed subject matter. DETAILED DESCRIPTION OF THE INVENTION

[0008] It should be understood that the present invention may assume various alternative orientations and step arrangements unless expressly specified to the contrary. It should also be understood that the specific assemblies and systems illustrated in the accompanying drawings and described in the following specification are merely exemplary embodiments of the inventive concepts defined herein. Accordingly, specific dimensions, orientations, or other physical characteristics relating to the disclosed embodiments are not to be considered limiting unless expressly stated otherwise. Also, although not applicable, like elements in the various embodiments described herein may be generally referred to within this section of the specification using like reference numerals.

[0009] As used herein, terms such as "first," "second," etc. do not necessarily imply any order, sequence, or priority relationship, but are merely used to more clearly distinguish one element or set of elements from another, unless otherwise specified.

[0010] As used herein, the terms "viewer," "operator," "observer," and "user" are considered equivalent and refer to a person or machine wearing a device having an imaging light guide and / or viewing an image using a device having an imaging light guide.

[0011] As used herein, the term "set" refers to a non-empty set, as the concept of a collection of elements or members of a set is commonly understood in elementary mathematics. As used herein, the term "subset," unless explicitly stated otherwise, is used to refer to a non-empty proper subset, i.e., a subset of a larger set that has one or more members. For a set S, a subset may include the complete set S. However, a "proper subset" of set S is strictly contained in set S and excludes at least one member of set S.

[0012] As used herein, the terms "coupled," "coupler," or "coupling" in the optical context refer to a connection in which light travels from one optical medium or device to another.

[0013] As used herein, the terms "wavelength band" and "wavelength range" are equivalent and have the standard meaning used by those skilled in the art of color imaging, and refer to a continuous range of light wavelengths used to represent a multicolor image.

[0014] As used herein, the term "beam expansion" is intended to mean the duplication of a beam through multiple encounters with optical elements to provide an exit pupil expansion in one or more directions. Similarly, as used herein, "expanding" a beam or a portion of a beam is intended to mean the duplication of a beam through multiple encounters with optical elements to provide an exit pupil expansion in one or more directions.

[0015] Those skilled in the relevant art(s) will recognize that the elements and techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In some instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects of the disclosure. Throughout this specification, references to "one embodiment" or "embodiments" mean that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the disclosure. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" throughout this specification do not necessarily refer to the same embodiment. However, particular features, structures, or characteristics described may be combined in any suitable manner in one or more embodiments.

[0016] Optical systems such as HMDs can generate virtual image displays. Unlike methods for forming real images, virtual images are not formed on a display surface. That is, when a display surface is positioned at the perceived location of the virtual image, no image is formed on the surface. Displaying virtual images offers numerous unique advantages in augmented reality presentations. For example, the apparent size of the virtual image is not limited by the size or location of the display surface. Furthermore, the source object of the virtual image can be small; for example, a magnifying glass provides a virtual image of the object. Compared to systems that project real images, creating a virtual image that appears to be at a distance can provide a more realistic viewing experience. Providing a virtual image also eliminates the need to correct for screen artifacts, which may be required when projecting a real image.

[0017] An image light guide may display a virtual image using image-bearing light from a light source, such as a projector. For example, a collimated, relative angle-encoded light beam from the projector is coupled into the planar waveguide by an input coupling, such as an in-coupling diffractive optical element, which can be attached to or formed on the surface of the planar waveguide or embedded within the waveguide. Such a diffractive optical element can be formed as a diffraction grating, a holographic optical element (HOE), or in other known ways. For example, a diffraction grating can be formed by a surface relief. After propagating along the waveguide, the diffracted light can be redirected out of the waveguide by a similar output coupling, such as an out-coupling diffractive optical element, which can be configured to provide pupil dilation along at least one direction of the virtual image. Additionally, a rotation grating can be positioned on or within the waveguide to provide pupil dilation in the orthogonal direction of the virtual image. The image-bearing light output from the waveguide provides an expanded eyebox for the viewer.

[0018] FIG. 1 is a schematic diagram showing a simplified cross-sectional view of one conventional configuration of an image light guide system 10. The image light guide system 10 includes a planar image light guide 12, an incoupling diffractive optical element IDO, and an outcoupling diffractive optical element ODO. The image light guide 12 includes a transparent substrate S, which may be made of optical glass or plastic, having plane-parallel front and back surfaces 14 and 16. In this example, the incoupling diffractive optical element IDO is shown as a transmission grating disposed on, within, or otherwise engaged with the front surface 14 of the image light guide 12. However, the incoupling diffractive optical element IDO may alternatively be a reflection grating or other type of diffractive optical element (such as a volume hologram or other holographic diffractive element) that diffracts an incident image-bearing light beam WI into the image light guide 12. The incoupling diffractive optical element IDO is located on or within the front surface 14 or back surface 16 of the image light guide 12, or otherwise engages with the front surface 14 or back surface 16, and may be a combination of transmissive or reflective, depending on the direction from which the image-bearing light beam WI approaches the image light guide 12.

[0019] When used as part of a near-eye or head-mounted display system, the incoupling diffractive optical element IDO of conventional image light guide system 10 couples an image-bearing light beam WI from an image source 18 of a real, virtual, or hybrid image into the substrate S of the image light guide 12. Any real image or image dimension formed by the image source 18 is first converted into an array of overlapping, angle-related, collimated beams that encode different locations within the virtual image for presentation to the incoupling diffractive optical element IDO. Typically, the light rays in each bundle forming one of the angle-related beams extend parallel, but the angle-related beams are relatively oblique to one another through an angle that may be defined by two angular dimensions corresponding to the linear dimensions of the image.

[0020] When the angle-related beams engage the incoupling diffractive optical element IDO, at least a portion of the image-bearing light beam WI is diffracted (typically by a first diffraction order) and thereby redirected by the incoupling diffractive optical element IDO into the planar image light guide 12 as an angle-encoded image-bearing light beam WG for further propagation along the length dimension x of the image light guide 12 by total internal reflection (TIR) ​​between the plane-parallel front and back surfaces 14, 16. Although diffracted into different combinations of angle-related beams along the boundaries established by the TIR, the image-bearing light beam WG preserves the image information in an angle-encoded form derivable from the parameters of the incoupling diffractive optical element IDO. The outcoupling diffractive optical element ODO receives the encoded image-bearing light beam WG and diffracts at least a portion of the image-bearing light beam WG from the image light guide 12 as an image-bearing light beam WO (typically also by a first diffraction order) toward a nearby region of space called the eyebox E, within which the transmitted virtual image can be seen by the viewer's eye 5 or other optical component. The outcoupling diffractive optical element ODO can be designed symmetrically with respect to the incoupling diffractive optical element IDO to restore the original angular relationship of the image-bearing light beam WI from between the output angularly related beams of the image-bearing light beam WO. Furthermore, the outcoupling diffractive optical element ODO can modify the angular relationship of the original field point positions to generate an output virtual image at a finite focusing distance.

[0021] However, to increase one dimension of overlap between the angle-related beams injected into the eyebox E (which defines the size of the area in which the virtual image can be seen), the outcoupling diffractive optical element ODO is positioned with the limited thickness T of the image light guide 12 to encounter the image-bearing light beam WG multiple times, diffracting only a portion of the image-bearing light beam WG at each encounter. The multiple encounters along the length (e.g., in the first direction) of the outcoupling diffractive optical element ODO have the effect of replicating the image-bearing light beam WG and expanding or widening at least one dimension of the eyebox E where the replicated beams overlap. The expanded eyebox E reduces the sensitivity to the position of the viewer's eye 5 for viewing the virtual image.

[0022] The outcoupling diffractive optical element ODO is shown as a transmissive diffraction grating disposed on or affixed to the front surface 14 of the image light guide 12. However, like the incoupling diffractive optical element IDO, the outcoupling diffractive optical element ODO may be located on, within, or otherwise engaged with the front surface 14 or back surface 16 of the image light guide 12, and may be a combination of transmissive and reflective types, depending on the direction in which the image-bearing light beam WG is intended to exit the image light guide 12. In addition, the outcoupling diffractive optical element ODO may be formed as another type of diffractive optical element, such as a volume hologram or other holographic diffractive element, which diffracts the image-bearing light beam WG propagating from the image light guide 12 as an image-bearing light beam WO propagating toward the eyebox E.

[0023] 2 shows a perspective view of a conventional image light guide system 10 arranged to expand the eyebox E in two dimensions, i.e., along both the x-axis and y-axis of the intended image. To achieve the second dimension of eyebox expansion, the incoupling diffractive optical element IDO is oriented to diffract at least a portion of the image-bearing light beam WG along its grating vector k1, along the image light guide 12, toward the intermediate rotation optical element TO, and its grating vector k2 is oriented to diffract at least a portion of the image-bearing light beam WG in a reflective mode, along the image light guide 12, toward the outcoupling diffractive optical element ODO. It should be appreciated that only a portion of the image-bearing light beam WG is diffracted by each of its multiple encounters with the intermediate rotation optical element TO, thereby laterally replicating each of the angularly related beams of the image-bearing light beam WG as it approaches the outcoupling diffractive optical element ODO. Before exiting the image light guide 12 as the image-bearing light beam WO, the intermediate rotating optical element TO redirects the image-bearing light beam WG towards the outcoupling diffractive optical element ODO (with grating vector k3) to longitudinally replicate an angularly related beam of the image-bearing light beam WG in a second direction. The grating vectors, such as the depicted grating vectors k1, k2, and k3, extend in respective directions perpendicular to the diffractive features (e.g., grooves, lines, or rulers) of the diffractive optical element in the parallel plane of the image light guide 12 and have inverse magnitude to the period or pitch d (i.e., the center-to-center distance between the diffractive features) of the diffractive optical elements IDO, TO, and ODO, respectively.

[0024] As shown in FIG. 2, the incoupling diffractive optical element IDO receives an incident image-bearing light beam WI, which includes a series of angle-related beams corresponding to individual pixels or equivalent locations in an image generated by an image source 18, such as a projector. The full range of angle-coded beams for generating a virtual image can be generated by a physical display device in combination with collimating or other optical components, by a beam scanner to more directly set the beam angles, or by a combination of a one-dimensional physical display device used with a scanner. In this configuration, the image light guide 12 outputs a series of replicated angle-related beams (replicated in two dimensions) by providing multiple encounters of the image-bearing light beam WG with both the intermediate rotation optical element TO and the outcoupling diffractive optical element ODO at different orientations. In the illustrated orientation of the image light guide 12, the intermediate rotation optical element TO provides eyebox expansion in a first direction, e.g., the y-axis direction, and the outcoupling diffractive optical element ODO provides a similar eyebox expansion in a second direction, e.g., the x-axis direction. The relative orientations and respective periods d of the diffractive features of the incoupling optical element IDO, the intermediate rotation optical element TO, and the outcoupling diffractive optical element ODO provide eyebox expansion in two dimensions while maintaining the intended relationship between the angularly related beams of the image-bearing light beam WI that are output from the image light guide system 10 as the image-bearing light beam WO. It will be appreciated that the periods d of the incoupling diffractive optical element IDO, the intermediate rotation optical element TO, and the outcoupling diffractive optical element ODO can each include diffractive features having a common pitch d, and the common pitch d of each optical element can be different.

[0025] In the illustrated configuration, the image-bearing light beam WI input to the image light guide 12 is encoded into a series of different angle-related beams by the incoupling diffractive optical element IDO, but the information necessary to reconstruct the image is preserved by considering the systematic effects of the incoupling diffractive optical element IDO. The intermediate rotation optical element TO, located at an intermediate position between the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO, can be positioned so as not to induce any significant changes to the encoding of the image-bearing light beam WG. Therefore, the outcoupling diffractive optical element ODO can be positioned symmetrically with respect to the incoupling diffractive optical element IDO, for example, including diffractive features that share the same period d. Similarly, the period of the intermediate rotation optical element TO can also match the common period of the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO. Although the grating vector k2 of the intermediate rotation optical element TO is shown oriented at 45 degrees relative to the other grating vectors, with possible orientations maintained, the grating vector k2 of the intermediate rotation optical element TO can be oriented at 60 degrees relative to the grating vectors k1 and k3 of the incoupling and outcoupling diffractive optical elements IDO and ODO, such that the image-bearing light beam WG is rotated by 120 degrees. By orienting the grating vector k2 of the intermediate rotation optical element TO at 60 degrees relative to the grating vectors k1 and k3 of the incoupling and outcoupling diffractive optical elements IDO and ODO, the grating vectors k1 and k3 of the incoupling and outcoupling diffractive optical elements IDO and ODO are also oriented at 60 degrees relative to each other. Using the common pitch of the incoupling diffractive optical element IDO, the intermediate rotation diffractive optical element TO, and the outcoupling diffractive optical element ODO as the basis for the magnitude of the grating vectors, the three grating vectors k1, k2, and k3 (as directed line segments) form an equilateral triangle and sum to a zero vector magnitude, thereby avoiding asymmetric effects that may result in undesirable aberrations, including chromatic dispersion. Such asymmetric effects can also be avoided by having the grating vectors k1, k2, and k3 have unequal magnitudes in their relative orientations, such that the sum of the three grating vectors k1, k2, and k3 has a zero vector magnitude.

[0026] In a broader sense, the image-bearing light beam WI directed into the image light guide 12 is effectively encoded by the incoupling diffractive optical element IDO, regardless of whether the incoupling optics IDO uses a grating, hologram, prism, mirror, or some other mechanism. Light reflection, refraction, and / or diffraction occurring at the input should be decoded accordingly by the output to recreate the virtual image presented to the viewer. It may be relevant whether any symmetry is maintained between the intermediate rotation optical element TO, the incoupling optics IDO, and the outcoupling diffractive optical element ODO, or whether changes to the angle-related beam encoding of the image-bearing light beam WI occur along the image light guide 12, the intermediate rotation optical element TO, the incoupling diffractive optical element IDO, and the outcoupling diffractive optical element ODO, so that the image-bearing light beam WO output from the image light guide 12 retains or otherwise maintains the original or desired form of the image-bearing light beam WI to generate the intended virtual image.

[0027] As shown in FIG. 2 , the letter “R” represents the orientation of the virtual image as seen by a viewer with their eyes positioned within the eyebox E. As shown, the orientation of the letter “R” in the represented virtual image coincides with the orientation of the letter “R” encoded by the image-bearing light beam WI. A change in rotation about the z-axis or angular orientation of the incident image-bearing light beam WI relative to the xy plane causes a corresponding symmetric change in the rotation or angular orientation of the output light from the outcoupling diffractive optical element (ODO). From the image orientation perspective, the intermediate rotation optical element TO simply acts as a type of optical relay, providing one-dimensional eyebox expansion through angle-encoded beam replication of the image-bearing light beam WG along one axis of the image (e.g., along the y-axis). The outcoupling diffractive optical element ODO further provides a second dimension of eyebox expansion through angle-encoded beam replication along another axis (e.g., along the x-axis) while maintaining the original orientation of the virtual image encoded by the image-bearing light beam WI. The intermediate rotating optical element TO is typically a tilted or square grating, or alternatively may be a blazed grating, and is typically disposed on one of the plane-parallel front and back surfaces of the image light guide 12. Of course, the representation of the virtual image "R" created by the image source consists of light focused at infinity, which requires a lens (e.g., the lens of the human eye) to focus the image so that the orientation discussed above can be detected.

[0028] Collectively, the incoupling diffractive optical element IDO, the rotating diffractive optical element TO, and the outcoupling diffractive optical element ODO preferably preserve the angular relationships between the beams of different wavelengths that define the virtual image upon transport from an offset position to a near-eye position of the viewer by the image light guide 12. Meanwhile, the incoupling diffractive optical element IDO, the rotating diffractive optical element TO, and the outcoupling diffractive optical element ODO can be positioned and oriented relative to one another in different ways to control the overall shape of the image light guide 12 and the overall orientation at which angularly related beams can be directed into and out of the image light guide 12.

[0029] The present disclosure provides image light guide arrangements having improved output intensity of polychromatic image-bearing light across an output aperture. More specifically, the present disclosure provides waveguide stacks having, among other things, high refractive index polymer waveguides and low refractive index polymer waveguides.

[0030] As shown in FIGS. 3-11 , in one exemplary embodiment, the image light guide system 50 includes a first planar waveguide 100 having a first surface 102 and a second surface 104. The first surface 102 of the waveguide is positioned generally parallel to the second surface 104 of the waveguide. A first incoupling diffractive optical element IDO1 is disposed on or engaged with the first surface 102 or the second surface 104. Additionally, a first outcoupling diffractive optical element ODO1 is formed on or engaged with the first surface 102 or the second surface 104. In one exemplary embodiment, the outcoupling diffractive optical elements ODO1 and ODO2 are each diffraction gratings. In another exemplary embodiment, the outcoupling diffractive optical elements ODO1 and ODO2 are each holographic diffractive elements.

[0031] 4 , which shows a plan view of an exemplary embodiment of the first planar waveguide 100, the first incoupling diffractive optical element IDO1 includes a first plurality of periodic diffractive structures 106. For example, the first incoupling diffractive optical element IDO1 may include a first set of periodic linear grating structures 106 oriented generally parallel to the y-axis. The first outcoupling diffractive optical element ODO1 includes a second plurality of periodic diffractive structures 108 and a third plurality of periodic diffractive structures 110. For example, the second plurality of periodic diffractive structures 108 may be composed of a second set of periodic linear grating structures 108 that are rotated or angularly offset with respect to the x-axis 115 by a polar angle (measured from the x-axis 115) of less than 30 degrees (e.g., 25 degrees), and the third plurality of periodic diffractive structures 110 may be composed of a third set of periodic linear grating structures 110 that are rotated or angularly offset with respect to the x-axis 115 by a polar angle greater than 60 degrees (e.g., 65 degrees). In one exemplary embodiment, the second set of periodic linear grating structures 108 are rotated or angularly offset by a polar angle of approximately 30 degrees relative to the x-axis 115, and the third set of periodic linear grating structures 110 are rotated or angularly offset by a polar angle of approximately 150 degrees relative to the x-axis 115. In another embodiment, the first set of periodic linear grating structures 106 are arranged generally parallel to an alternate axis other than the y-axis, and the second set of periodic linear grating structures 108 are rotated or angularly offset by a polar angle (measured from the vertical axis) of less than 30 degrees (e.g., 25 degrees) relative to an axis perpendicular to the alternate axis, while the third set of periodic linear grating structures 110 are rotated or angularly offset by a polar angle (measured from the vertical axis) of greater than 60 degrees (e.g., 65 degrees). The second and third sets of periodic diffractive structures 108, 110 intersect and / or define different grating vectors. The second set of periodic diffractive structures 108 and the third set of periodic diffractive structures 110 form a composite diffractive optical element operable to replicate and outcouple image-bearing light incoupled by the first incoupling diffractive optical element IDO1. The first set of periodic diffractive structures 106 includes a first period, the second set of periodic diffractive structures 108 includes a second period, and the third set of periodic diffractive structures 110 includes a third period.In one exemplary embodiment, the third period is equal to the second period, and the second period is equal to the first period, hi one exemplary embodiment, the first period, second period, and third period are each less than 50 nm.

[0032] 3-10 , in an exemplary embodiment, image light guide system 50 includes a second planar waveguide 200 having a first surface 202 and a second surface 204. Waveguide first surface 202 is positioned generally parallel to waveguide second surface 204. A second incoupling diffractive optical element IDO2 is located on, within, or engaged with first surface 202, and a third incoupling diffractive optical element IDO3 is located on, within, or engaged with second surface 204. Second outcoupling diffractive optical element ODO2 is formed on / within first surface 202, and third outcoupling diffractive optical element ODO3 is formed on, within, or engaged with second surface 204. In an exemplary embodiment, the first incoupling diffractive optical element IDO1 is located substantially coaxially with the second incoupling diffractive optical element IDO2 with respect to an imaginary axis disposed through the first and second surfaces 102, 104 of the first planar waveguide 100 and through the first and second surfaces 202, 204 of the second planar waveguide 200. It will be appreciated that the second incoupling diffractive optical element IDO2, the third incoupling diffractive optical element IDO3, the second outcoupling diffractive optical element ODO2, and the third outcoupling diffractive optical element ODO3 may be formed on, on, in, or engaged with either the first surface 202 or the second surface 204.

[0033] 5 , which shows a plan view of an exemplary embodiment of the second planar waveguide 200, the second incoupling diffractive optical element IDO2 includes a fourth plurality of periodic diffractive structures 206. For example, the second incoupling diffractive optical element IDO2 may comprise a fourth set of periodic linear grating structures 206 positioned generally parallel to the y-axis. The second outcoupling diffractive optical element ODO2 includes a fifth plurality of periodic diffractive structures 208 and a sixth plurality of periodic diffractive structures 210. For example, the fifth plurality of periodic diffractive structures 208 may be comprised of a set of periodic linear grating structures rotated or angularly offset with respect to the x-axis by a polar angle (measured from the x-axis) less than 30° (e.g., 25°), and the sixth plurality of periodic diffractive structures 210 may be comprised of a set of periodic linear grating structures rotated or angularly offset with respect to the x-axis by a polar angle (measured from the x-axis) greater than 60° (e.g., 65°). In another embodiment, the fourth set of periodic linear grating structures 206 are arranged generally parallel to an alternate axis other than the y-axis, and the fifth set of periodic linear grating structures 208 are rotated or angularly offset relative to an axis perpendicular to the alternate axis by a polar angle less than 30° (e.g., 25°) (measured from the perpendicular axis), while the sixth set of periodic linear grating structures 210 are rotated or angularly offset relative to the alternate axis by a polar angle greater than 60° (e.g., 65°) (measured from the perpendicular axis). In an exemplary embodiment, the fifth set of periodic linear grating structures 208 are rotated or angularly offset relative to the x-axis by a polar angle of approximately 30°, and the sixth set of periodic linear grating structures 210 are rotated or angularly offset relative to the x-axis by a polar angle of approximately 150°. The fifth and sixth sets of periodic diffractive structures 208, 210 intersect and / or define different grating vectors. The fifth and sixth sets of periodic diffractive structures 208, 210 form a composite diffractive optical element operable to replicate and outcouple image-bearing light from the second incoupling diffractive optical element IDO2. The fourth set of periodic diffractive structures 206 includes a fourth period, the fifth set of periodic diffractive structures 208 includes a fifth period, and the sixth set of periodic diffractive structures 210 includes a sixth period.In one exemplary embodiment, the sixth period is equal to the fifth period, and the fifth period is equal to the fourth period. In one exemplary embodiment, the fourth period, the fifth period, and the sixth period are each less than 50 nm.

[0034] 6 , which shows a bottom view of the second planar waveguide 200, the third incoupling diffractive optical element IDO3 includes a seventh plurality of periodic diffractive structures 212. For example, the third incoupling diffractive optical element IDO3 may comprise the seventh set of periodic linear grating structures 212 rotated or angularly offset by approximately thirty degrees (30°), e.g., within five degrees (5°) of thirty degrees (30°), relative to the fourth set of periodic linear grating structures 206. For example, the third incoupling diffractive optical element IDO3 may include the seventh set of periodic linear grating structures 212 rotated or angularly offset by between twenty-five degrees (25°) and thirty-five degrees (30°) relative to the fourth set of periodic linear grating structures 206. The third outcoupling diffractive optical element IDO3 includes an eighth plurality of periodic diffractive structures 214 and a ninth plurality of periodic diffractive structures 216. For example, the eighth plurality of periodic diffractive structures 214 may comprise eighth set of periodic linear grating structures 214 rotated or angularly offset by approximately thirty degrees (30°), e.g., within five degrees (5°) of thirty degrees (30°), relative to the fifth set of periodic linear grating structures 208, and the ninth plurality of periodic diffractive structures 216 may comprise ninth set of periodic linear grating structures 216 rotated or angularly offset by approximately thirty degrees (30°), e.g., within five degrees (5°) of thirty degrees (30°), relative to the sixth set of periodic linear grating structures 210. In one exemplary embodiment, the eighth set of periodic linear grating structures 214 are substantially parallel to the x-axis 115 with a polar angle of approximately 0°, and the ninth set of periodic linear grating structures 216 are rotated or angularly offset relative to the x-axis 115 by a polar angle of approximately 120°. The eighth and ninth sets of periodic diffractive structures 214, 216 intersect and / or define different grating vectors. The eighth and ninth sets of periodic diffractive structures 214, 216 form a composite diffractive optical element operable to replicate and outcouple image-bearing light from the third incoupling diffractive optical element IDO3. The seventh set of periodic diffractive structures 212 includes a seventh period, the eighth set of periodic diffractive structures 214 includes an eighth period, and the ninth set of periodic diffractive structures 216 includes a ninth period.In one exemplary embodiment, the ninth period is equal to the eighth period, and the eighth period is equal to the seventh period. In one exemplary embodiment, the seventh period, eighth period, and ninth period are each less than 50 nm, and the seventh period, eighth period, and ninth period are each greater than 50 nm.

[0035] The first planar waveguide 100 includes a first wavelength range light path and a second wavelength range light path. The first wavelength range light path includes at least a first incoupling diffractive optical element IDO1 and a first outcoupling diffractive optical element ODO1. The first wavelength range light path is operable to incouple, propagate via TIR, replicate, and outcouple image-bearing light in a first wavelength range. For example, the first wavelength range light path is operable to direct image-bearing light in a blue wavelength range (e.g., 440-470 nm range, 440-495 nm range, or 450-495 nm range) through the waveguide 100.

[0036] The second planar waveguide 200 includes a second wavelength range light path and a third wavelength range light path. The second wavelength range light path includes at least a second incoupling diffractive optical element IDO2 and a second outcoupling diffractive optical element ODO2. The second wavelength range light path is operable to incouple, propagate via TIR, replicate, and outcouple image-bearing light in a second wavelength range. For example, the second wavelength range light path is operable to direct image-bearing light in a green wavelength range (e.g., a range of 520-560 nm or a range of 495-570 nm) through the waveguide 200. The third wavelength range light path includes at least a third incoupling diffractive optical element IDO3 and a third outcoupling diffractive optical element ODO3. The third wavelength range light path is operable to incouple, propagate via TIR, replicate, and outcouple image-bearing light in a third wavelength range. For example, the third wavelength range light path is operable to direct image-bearing light in the red wavelength range (eg, the 630-660 nm range or the 620-750 nm range) through the waveguide 200 .

[0037] Crosstalk can be reduced between the second and third wavelength range light paths by rotating the seventh plurality of periodic diffractive structures 212 by approximately thirty degrees (30°) relative to the fourth plurality of periodic diffractive structures 206, and by rotating the eighth and ninth plurality of grating structures 214, 216 by approximately thirty degrees (30°) relative to the fifth plurality of periodic diffractive structures 208 and the sixth plurality of periodic diffractive structures 210, respectively. In other words, the third incoupling diffractive optical element IDO3 is rotated by approximately thirty degrees (30°) relative to the second incoupling diffractive optical element IDO2, and the third outcoupling diffractive optical element ODO3 is rotated by approximately thirty degrees (30°) relative to the second outcoupling diffractive optical element ODO2.

[0038] 3, 7, and 8, image-bearing light WI1 from projector 18A is incident on first incoupling diffractive optical element IDO1, and a first portion of the image-bearing light WI1 is diffracted by first incoupling diffractive optical element IDO1 and propagates generally as WG1 through TIR toward outcoupling diffractive optical element ODO1. In one example, the periodic linear grating structure of first incoupling diffractive optical element IDO1 (i.e., the first set of periodic linear grating structures 106) is arranged to optimize coupling of light within a first wavelength range of image-bearing light WI1, e.g., the blue wavelength range of the electromagnetic spectrum. A second portion of the image-bearing light WI1 transmits through first incoupling diffractive optical element IDO1 and planar waveguide 100 and is incident on second incoupling diffractive optical element IDO2. At least a portion of the image-bearing light WI1 is diffracted by the second incoupling diffractive optical element IDO2 and propagates generally as WG2 via TIR towards the second outcoupling diffractive optical element ODO2. In one embodiment, the periodic linear grating structures of the second incoupling diffractive optical element IDO2 (i.e., the fourth set of periodic linear grating structures 206) are arranged for optimized coupling of light in a second range of wavelengths of the image-bearing light WI1, for example, in the green wavelength range.

[0039] Image-bearing light WI2 from projector 18B is incident on the second incoupling diffractive optical element IDO2, and a first portion of the image-bearing light WI2 is diffracted by the second incoupling diffractive optical element IDO2 and propagates generally via TIR as WG3 toward the outcoupling diffractive optical element ODO2. In one embodiment, the periodic linear grating structure of the third incoupling diffractive optical element IDO3 (i.e., the periodic linear grating structure 212) is arranged to optimize coupling of a wavelength range of the image-bearing light WI2 in the red wavelength range.

[0040] 11, 12A, and 12B, image light guide system 50A includes a second planar waveguide 200A having a second incoupling diffractive optical element IDO2 disposed on or within or engaged with first surface 202, and a second outcoupling diffractive optical element ODO2 formed on or within or engaged with first surface 202. It should be appreciated that second incoupling diffractive optical element IDO2 and second outcoupling diffractive optical element ODO2 may be formed on, within, or engaged with either first surface 202 or second surface 204. The second incoupling diffractive optical element IDO2 and the second outcoupling diffractive optical element ODO2 are positioned and optimized to diffract image-bearing light in both a second wavelength range (e.g., a green wavelength range in the range of 520-560 nm or a green wavelength range in the range of 495-570 nm) and a third wavelength range (e.g., a red wavelength range in the range of 630-660 nm or a red wavelength range in the range of 620-750 nm). The second outcoupling diffractive optical element ODO2 is positioned to replicate the image-bearing light in the second wavelength range and the third wavelength range in at least one direction and to outcouple the image-bearing light in the second wavelength range and the third wavelength range.

[0041] 11 and 13A-13B, the second incoupling diffractive optical element IDO2 is positioned substantially coaxially with the first incoupling diffractive optical element IDO1 with respect to an imaginary axis disposed through the first and second surfaces 102, 104 of the first planar waveguide 100 and through the first and second surfaces 202, 204 of the second planar waveguide 200A. In the exemplary embodiment, the second incoupling diffractive optical element IDO2 includes a first plurality of periodic diffractive structures 206 optimized to diffract image-bearing light in a second wavelength range into the second waveguide 200A and a second plurality of periodic diffractive structures 212 optimized to diffract image-bearing light in a third wavelength range into the second waveguide 200A. For example, the second incoupling diffractive optical element IDO2 may be a composite diffractive optical element having a plurality of periodic diffractive structures including, for example, posts. The second incoupling diffractive optical element IDO2 may also be a composite diffractive optical element having multiple intersecting or overlapping substantially linear periodic diffractive structures. In an exemplary embodiment, the second incoupling diffractive optical element IDO2 includes multiple periodic diffractive structures optimized to diffract image-bearing light in both the second and third wavelength ranges into the second waveguide 200A. For example, the second incoupling diffractive optical element IDO2 may define only one grating vector k. Of course, in an exemplary embodiment, the image light guide system 50A may be configured such that the second waveguide 200A is utilized to transmit only image-bearing light in the second wavelength range.

[0042] 14 and 15 , the first incoupling diffractive optical element IDO1 and the second incoupling diffractive optical element IDO2 are configured to optimize diffraction efficiency for the image-bearing light WI1. For example, the first incoupling diffractive optical element IDO1 and the second incoupling diffractive optical element IDO2 may be configured as transmissive diffraction gratings, and the second incoupling diffractive optical element IDO2 and the third incoupling diffractive optical element IDO3 may be configured as reflective diffraction gratings. In an exemplary embodiment, the first plurality of periodic diffractive structures 106 of the first incoupling diffractive optical element IDO1 and the fourth plurality of periodic diffractive structures 206 of the second incoupling diffractive optical element IDO2 may have a tilt angle φ1, and the seventh plurality of periodic diffractive structures 212 of the third incoupling diffractive optical element IDO3 may have a tilt angle φ2. The periodic diffractive structures 106, 206 of the first and second incoupling diffractive optical elements IDO1, IDO2 may have tilt angles φ that are rotated 180 degrees relative to each other.

[0043] In an exemplary embodiment, the first planar waveguide 100 comprises a low refractive index material (e.g., polymer, quartz, or glass) optimized to propagate image-bearing light in the blue wavelength range (e.g., 440-470 nm range or 420-495 nm range), and the second planar waveguide 200 comprises a high refractive index material (e.g., polymer, quartz, or glass) optimized to propagate image-bearing light in the green wavelength range (e.g., 520-560 nm range or 495-570 nm range) and the red wavelength range (e.g., 630-660 nm range or 620-750 nm range). For example, the low refractive index material may have a refractive index number in the range of 1.2-1.8, and the high refractive index material may have a refractive index number in the range of 1.8-2.0. In some embodiments, the low refractive index material may have a refractive index number in the range of 1.4-1.7. In some embodiments, low refractive index materials have a refractive index less than 1.8 and high refractive index materials have a refractive index greater than or equal to 1.8.

[0044] A second planar waveguide 200 including a high refractive index material has the advantage of supporting a wider spectral bandwidth, so that image-bearing light in the green wavelength range (e.g., 520-560 nm or 495-570 nm) and the red wavelength range (e.g., 630-660 nm or 620-750 nm) can be transmitted to the eyebox via TIR with a single waveguide. Similarly, a second planar waveguide 200 including a high refractive index material has the advantage of supporting a wider field of view (FOV) compared to a low refractive index material due to Snell's law.

[0045] High refractive index polymers utilized in optical waveguide substrates are traditionally achieved by incorporating high refractive index nanoparticles into the bulk polymer material, thereby increasing the overall refractive index of the bulk polymer. Waveguides fabricated with this type of high refractive index polymer generally function with acceptable performance for light in the green and red wavelength ranges, but light in the blue wavelength range (which has shorter wavelengths than light in the green and red wavelength ranges) tends to scatter from the nanoparticles incorporated into the bulk polymer material, thereby adversely affecting performance. Light in the blue wavelength range is often attenuated in other high refractive index materials, such as, but not limited to, high refractive index glass, which has a refractive index in the range of 1.9 to 2.0. For example, the optical path of light in the blue wavelength range within a waveguide containing high refractive index glass may be long enough that substantially no light in the blue wavelength range is emitted into the eyebox. The attenuation of light in the blue wavelength range in high refractive index materials is a function of the specific wavelength of light and the specific material.

[0046] In view of the foregoing, the subject matter of the present disclosure has the advantage of providing diffraction and propagation of light of multiple wavelength ranges within an image light guide under optimal conditions for each wavelength range to produce improved virtual image brightness and resolution. Furthermore, an image light guide system arranged to deliver a full-color virtual image to the eyebox with only two waveguides is superior to a system utilizing three waveguides (one waveguide for each of the red, green, and blue wavelength ranges of light) because the weight and complexity of the system is reduced, and also because potential diffraction effects in the image resulting from viewing the image through a diffractive optical element (e.g., an outcoupling diffractive optical element) are reduced compared to a three-waveguide stack.

[0047] The perspective view shown in FIG. 16 illustrates an example of an image light guide system 50, 50A within a display system for augmented reality display of virtual images. The image light guide system 50, 50A uses one or more waveguide stacks 100, 200; 100, 200A. The image light guide system 50, 50A is illustrated as a head-mounted display (HMD) with a right-eye optical system 120R having the waveguide stack 100, 200A proximate to a user's right eye. The image light guide system 50, 50A includes an image source 18, such as a picoprojector or similar device, that can be energized to generate one or more multicolor virtual images. In one embodiment, the image light guide system 50, 50A includes a left-eye optical system 120L having one or more waveguide stacks 100, 200; 100, 200A and a second image source. In embodiments using right-eye optical system 120R and left-eye optical system 120L, the generated virtual image may be a stereo pair of images for a three-dimensional (3D) display. During operation by a user, the virtual image or images formed by image light guide system 50, 50A may appear superimposed or overlaid on real-world scene content seen by a viewer through right-eye optical system 120R and / or left-eye image light guide 120R. Additional components familiar to those skilled in the art of augmented reality visualization may also be provided, such as mounting one or more cameras on the frame of the HMD for viewing scene content or tracking the viewer's gaze.

[0048] One or more features of the embodiments described herein may be combined to create additional embodiments not shown. While various embodiments have been described in detail above, it should be understood that they are presented for illustrative purposes, and not for limiting purposes. It will be apparent to those skilled in the relevant art that the subject matter of the present disclosure may be embodied in other specific forms, variations, and modifications without departing from the scope, spirit, or essential characteristics thereof. The above-described embodiments are therefore to be considered in all respects as illustrative and not restrictive. The scope of the invention is indicated by the appended claims, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.

Claims

1. 1. An image light guide system for conveying a virtual image, comprising: a first waveguide having a first refractive index; a first incoupling diffractive optical element formed along the first waveguide, the first incoupling diffractive optical element being positioned to diffract an image-bearing light beam of a first wavelength range into the first waveguide in an angularly coded manner; a first outcoupling diffractive optical element formed along the first waveguide, the first outcoupling diffractive optical element being arranged to replicate the image-bearing light beam in the first wavelength range in at least one direction and direct the replicated image-bearing light beam from the first waveguide in an angularly decoded manner; a second waveguide having a second refractive index greater than the first refractive index; a second incoupling diffractive optical element formed along the second waveguide, the second incoupling diffractive optical element being positioned to diffract an image-bearing light beam of a second wavelength range into the second waveguide in an angularly coded manner; a second outcoupling diffractive optical element formed along the second waveguide, the second outcoupling diffractive optical element being arranged to replicate the image-bearing light beam in the second wavelength range in at least one direction and direct the replicated image-bearing light beam from the second waveguide in an angularly decoded manner; a third incoupling diffractive optical element formed along the second waveguide, the third incoupling diffractive optical element being positioned to diffract an image-bearing light beam of a third wavelength range into the second waveguide in an angularly coded manner; a third outcoupling diffractive optical element formed along the second waveguide, the third outcoupling diffractive optical element being arranged to replicate the image-bearing light beam in the third wavelength range in at least one direction and direct the replicated image-bearing light beam out of the second waveguide in an angularly decoded manner; An image light guide system, wherein the image-bearing light beam of the first wavelength range comprises shorter wavelengths than the image-bearing light beam of the second wavelength range and the third wavelength range.

2. 2. The image light guide system of claim 1, wherein the first waveguide is arranged substantially parallel to the second waveguide along a first axis, and the first incoupling diffractive optical element and the second incoupling diffractive optical element are positioned substantially coaxially along a second axis that is substantially perpendicular to the first axis.

3. The image light guide system of claim 1 , wherein the image-bearing light beam in the third wavelength range comprises a longer wavelength than the image-bearing light beam in the second wavelength range.

4. 2. The image light guide system of claim 1, further comprising: a first image source operable to emit the image-bearing light beam in the first and second wavelength ranges; and a second image source operable to emit the image-bearing light beam in the third wavelength range.

5. The image light guide system of claim 1 , wherein the first refractive index is less than 1.8 and the second refractive index is 1.8 or greater.

6. 1. An image light guide system for conveying a virtual image, comprising: a first waveguide having a first refractive index; a first incoupling diffractive optical element formed along the first waveguide, the first incoupling diffractive optical element being positioned to diffract an image-bearing light beam of a first wavelength range into the first waveguide in an angularly coded manner; a first outcoupling diffractive optical element formed along the first waveguide, the first outcoupling diffractive optical element being arranged to replicate the image-bearing light beam in the first wavelength range in at least one direction and direct the replicated image-bearing light beam from the first waveguide in an angularly decoded manner; a second waveguide having a second refractive index greater than the first refractive index; a second incoupling diffractive optical element formed along the second waveguide, the second incoupling diffractive optical element being positioned to diffract an image-bearing light beam of at least a second wavelength range into the second waveguide in an angularly coded manner; a second outcoupling diffractive optical element formed along the second waveguide, the second outcoupling diffractive optical element being arranged to replicate the image-bearing light beam in the second wavelength range in at least one direction and direct the replicated image-bearing light beam from the second waveguide in an angularly decoded manner; An image light guide system, wherein the image-bearing light beam of the first wavelength range comprises shorter wavelengths than the image-bearing light beam of the second wavelength range.

7. 7. The image light guide system of claim 6, wherein the first waveguide is arranged substantially parallel to the second waveguide along a first axis, and the first incoupling diffractive optical element and the second incoupling diffractive optical element are arranged substantially coaxially along a second axis that is substantially perpendicular to the first axis.

8. 7. The image light guide system of claim 6, wherein the second incoupling diffractive optical element is arranged to diffract an image-bearing light beam of a third wavelength range into the second waveguide in an angularly coded manner, and the second outcoupling diffractive optical element is arranged to replicate the image-bearing light beam of the third wavelength range in at least one direction and direct the replicated image-bearing light beam from the second waveguide in an angularly decoded manner.

9. 9. The image light guide system of claim 8, wherein the image-bearing light beam in the third wavelength range comprises a longer wavelength than the image-bearing light beam in the first wavelength range.

10. 9. The image light guide system of claim 8, further comprising: a first image source operable to emit the image-bearing light beam in the first and second wavelength ranges; and a second image source operable to emit the image-bearing light beam in the third wavelength range.

11. 7. The image light guide system of claim 6, wherein the first wavelength range is 440 to 495 nm.

12. 7. The image light guide system of claim 6, wherein the first refractive index is less than 1.8 and the second refractive index is 1.8 or greater.

Images