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 displays that utilize image light guides having diffractive optical elements for conveying 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, there is value in creating a virtual image that can be visually superimposed over 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 target the virtual image to the viewer's pupil and enable this superimposition function.

[0003] Although conventional image light guide arrangements have provided 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 reduction in 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 generate desired virtual image brightness and resolution while managing the volume and cost of the system. Summary of the Invention

[0004] In a first exemplary embodiment, the present disclosure provides 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 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 out of the first waveguide in an angularly decoded 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 in a second wavelength range into the second waveguide in an angularly coded manner. In accordance with the present invention, there is provided an image light guide system comprising: a first 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 diffract an image-bearing light beam in a second wavelength range into the second waveguide in an angularly coded manner; and 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 out of 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 out of 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 subject matter of the present disclosure and illustrate selected principles and teachings of the present disclosure. However, the drawings do not illustrate every possible implementation of the subject matter of the present disclosure and are not intended to limit the scope of the present disclosure in any way. [Brief description 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. [Diagram 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. [Diagram 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. [Diagram 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 illustrates a perspective view of a display system for an augmented reality display using an image light guide, according to an exemplary embodiment of the subject matter of this disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 attached drawings and described in the following specification are merely exemplary embodiments of the inventive concepts defined herein. Thus, specific dimensions, orientations, or other physical characteristics relating to the disclosed embodiments are not to be considered as limiting unless expressly stated otherwise. Also, although not applicable, similar elements in the various embodiments described herein may be generally referred to by similar reference numerals within this section of the specification.

[0009] As used herein, the terms "first," "second," and the like do not necessarily imply any order, sequential, 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 that wears a device having an imaging light guide and / or uses a device having an imaging light guide to view an image.

[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 broadly understood in elementary mathematics. As used herein, the term "subset", unless expressly stated otherwise, is used to refer to a non-empty proper subset, i.e., a subset of a larger set having 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 an optical context refer to a connection in which light travels from one optical medium or device to another optical medium or device.

[0013] As used herein, the terms "wavelength band" and "wavelength range" are equivalent and have the standard meanings 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 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 have not been 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, certain 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 a display of a virtual image. Unlike methods for forming a real image, the virtual image is not formed on the display surface. That is, when the display surface is positioned at the perceived location of the virtual image, no image is formed on the surface. Displaying a virtual image has a number of unique advantages in the presentation of augmented reality. 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 may be small, for example, a magnifying glass provides a virtual image of the object. By forming a virtual image that appears to be at some distance, a more realistic viewing experience can be provided compared to a system that projects a real image. Providing a virtual image also eliminates the need to correct screen artifacts that may be required when projecting a real image.

[0017] The 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 may be attached or formed on a surface of the planar waveguide, or embedded within the waveguide. Such a diffractive optical element may be formed as a diffraction grating, a holographic optical element (HOE), or in other known manner. For example, a diffraction grating may be formed by a surface relief. After propagating along the waveguide, the diffracted light may be redirected out of the waveguide by a similar output coupling such as an out-coupling diffractive optical element, which may be arranged to provide pupil dilation along at least one direction of the virtual image. Additionally, a rotating grating may be positioned on / in 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 type diffraction 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 type diffraction 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 rear surface 16 of the image light guide 12, or otherwise engages the front surface 14 or rear surface 16, and may be a combination of transmissive or reflective, depending on the direction in 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 the 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 a substrate S of the image light guide 12. Any real or image dimension formed by the image source 18 is first transformed into an array of overlapping, angle-related collimated beams that code for different locations within the virtual image for presentation to the incoupling diffractive optical element IDO. Typically, the light rays in each bundle that form 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 that correspond 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 surface 14 and back surface 16. Although diffracted into different combinations of angle-related beams along the boundaries set by the TIR, the image-bearing light beam WG preserves the image information in an angle-encoded form that is 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 out of the image light guide 12 as an image-bearing light beam WO (typically also by a first diffraction order) towards a nearby spatial region called the eyebox E, in which the transmitted virtual image can be seen by the viewer's eye 5 or other optical components. 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 angle-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, in order to increase one dimension of overlap between the angle-related beams injected into the eyebox E (defining the size of the area in which the virtual image can be seen), the outcoupling diffractive optical element ODO is arranged with a limited thickness T of the image light guide 12 to encounter the image-bearing light beam WG multiple times and diffract 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 enlarging or expanding 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 or fixed on 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 or 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 towards the eye box 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 the 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 the image light guide 12 toward the intermediate rotating optical element TO along its grating vector k1, which 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 will be appreciated that only a portion of the image-bearing light beam WG will be diffracted by each of multiple encounters with the intermediate rotating 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. Prior to exiting the image light guide 12 as 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 angle-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 magnitudes relative 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 incoming image-bearing light beam WI, which includes a series of angle-related beams that correspond 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 to generate a virtual image can be generated by a real display device in combination with collimating optics or other optical components, by a beam scanner to set the beam angle more directly, or by a combination such as a one-dimensional real 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 rotating optical element TO and the outcoupling diffractive optical element ODO in different orientations. In the illustrated orientation of the image light guide 12, the intermediate rotating optical element TO provides an 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 rotating optical element TO, and the outcoupling diffractive optical element ODO provide eyebox expansion in two dimensions while maintaining the intended relationships 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 rotating 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 coded by the incoupling diffractive optical element IDO into a series of different angle-related beams, but the information required to reconstruct the image is preserved by taking into account 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 coding of the image-bearing light beam WG. To that end, the outcoupling diffractive optical element ODO can be positioned symmetrically with respect to the incoupling diffractive optical element IDO, for example including diffractive features sharing 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 diffractive optical element IDO and the outcoupling diffractive optical element 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 diffractive optical element IDO and the outcoupling diffractive optical element ODO, the grating vectors k1 and k3 of the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO are also oriented at 60 degrees relative to each other. Taking the common pitch of the incoupling diffractive optical element IDO, the intermediate rotating 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, k3 (as directed line segments) form an equilateral triangle and sum to the magnitude of the zero vector, thereby avoiding asymmetric effects that may result in undesirable aberrations, including chromatic dispersion. Such asymmetric effects can also be avoided by the grating vectors k1, k2 and k3 having unequal magnitudes in the relative orientations, where the sum of the three grating vectors k1, k2 and k3 is the magnitude of the zero vector.

[0026] In a broader sense, the image-bearing light beam WI directed into the image light guide 12 is effectively coded by the incoupling diffractive optical element IDO, regardless of whether the incoupling optics IDO uses a grating, a hologram, a prism, a mirror, or some other mechanism. The reflection, refraction, and / or diffraction of light 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 rotating optical element TO, the incoupling optics IDO, and the outcoupling diffractive optical element ODO, or whether changes to the angle-related beam coding of the image-bearing light beam WI occur along the image light guide 12, the intermediate rotating 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 for generating 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 eyes positioned within the eyebox E. As shown, the orientation of the letter "R" of 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 rotation or angular orientation of the exiting light from the outcoupling diffractive optical element (ODO). From the aspect of image orientation, the intermediate rotating optical element TO simply acts as a type of optical relay, providing one dimension of eyebox expansion through a duplication of the angle-encoded beam 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 a duplication of the angle-encoded beam 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] The incoupling diffractive optical element IDO, the rotating diffractive optical element TO, and the outcoupling diffractive optical element ODO collectively 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 may be positioned and oriented relative to one another in different ways to control the overall shape of the image light guide 12 as well as the overall orientation at which the angularly related beams may 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 a waveguide stack having, among other things, a high refractive index polymer waveguide and a low refractive index polymer waveguide.

[0030] As shown in FIGS. 3-11, in an 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 an exemplary embodiment, the outcoupling diffractive optical elements ODO1, ODO2 are each a diffraction grating. In another exemplary embodiment, the outcoupling diffractive optical elements ODO1, ODO2 are each a holographic diffractive element.

[0031] Now, referring to FIG. 4 showing 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 rotated or angularly offset with respect to the x-axis 115 by a polar angle (measured from the x-axis 115) 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 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 about 30 degrees polar angle with respect to the x-axis 115, and the third set of periodic linear grating structures 110 are rotated or angularly offset by about 150 degrees polar angle with respect 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) with respect 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 more 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 that is operable to replicate and outcouple the 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, the second period, and the third period are each less than 50 nm.

[0032] As shown in FIGS. 3-10, in an exemplary embodiment, the image light guide system 50 includes a second planar waveguide 200 having a first surface 202 and a second surface 204. The first surface 202 of the waveguide is positioned generally parallel to the second surface 204 of the waveguide. A second incoupling diffractive optical element IDO2 is located on, within, or engaged with the first surface 202, and a third incoupling diffractive optical element IDO3 is located on, within, or engaged with the second surface 204. The second outcoupling diffractive optical element ODO2 is formed on / within the first surface 202, and the third outcoupling diffractive optical element ODO3 is formed on, within, or engaged with the 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] Now, referring to FIG. 5 showing 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 include 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 composed 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) of less than 30° (e.g., 25°), and the sixth plurality of periodic diffractive structures 210 may be composed 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) of more than 60° (e.g., 65°). In another embodiment, the fourth set of periodic linear grating structures 206 are generally arranged 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 (measured from the perpendicular axis) of less than 30° (e.g., 25°), while the sixth set of periodic linear grating structures 210 are rotated or angularly offset relative to the alternate axis by a polar angle (measured from the perpendicular axis) of greater than 60° (e.g., 65°). 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 in-coupling diffractive optical element IDO2. The fourth set of periodic diffractive structures 206 comprises a fourth period, the fifth set of periodic diffractive structures 208 comprises a fifth period, and the sixth set of periodic diffractive structures 210 comprises 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] Now, referring to FIG. 6 showing 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 a 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 a seventh set of periodic linear grating structures 212 rotated or angularly offset by twenty-five degrees (25°) to thirty-five degrees (30°) relative to the fourth set of periodic linear grating structures 206. The third outcoupling diffractive optical element ODO3 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 an 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 a 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, the eighth period, and the ninth period are each less than 50 nm, and the seventh period, the eighth period, and the 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, replicate, and outcouple image-bearing light in a first wavelength range via TIR. For example, the first wavelength range light path is operable to direct image-bearing light in a blue wavelength range (e.g., in the range of 440-470 nm, the range of 440-495 nm, or the range of 450-495 nm) 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 through 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., in the range of 520-560 nm or in the 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 incoupling, propagate through 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, in the range of 630-660 nm or in the range of 620-750 nm) through the waveguide 200 .

[0037] Crosstalk may be reduced between the second and third wavelength range optical paths by rotating the seventh plurality of periodic diffractive structures 212 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 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 approximately thirty degrees (30°) relative to the second incoupling diffractive optical element IDO2, and the third outcoupling diffractive optical element ODO3 is rotated approximately thirty degrees (30°) relative to the second outcoupling diffractive optical element ODO2.

[0038] In an exemplary embodiment, as shown in Figures 3, 7 and 8, the image-bearing light WI1 from the projector 18A is incident on the first incoupling diffractive optical element IDO1, and a first portion of the image-bearing light WI1 is diffracted by the first incoupling diffractive optical element IDO1 and propagates toward the outcoupling diffractive optical element ODO1 through the TIR generally as WG1. In one embodiment, the periodic linear grating structure (i.e., the first set of periodic linear grating structures 106) of the first incoupling diffractive optical element IDO1 is arranged to optimize coupling of light in a first wavelength range of the image-bearing light WI1, e.g., in the blue wavelength range of the electromagnetic spectrum. A second portion of the image-bearing light WI1 transmits through the first incoupling diffractive optical element IDO1 and the planar waveguide 100 and is incident on the 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 through the 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, e.g., in the green wavelength range.

[0039] The 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 toward the outcoupling diffractive optical element ODO2 via the TIR generally as WG3. 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 positioned to optimize coupling of a wavelength range of the image-bearing light WI2 in the red wavelength range.

[0040] 11, 12A, 12B, the 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 the first surface 202, and a second outcoupling diffractive optical element ODO2 formed on or within or engaged with the first surface 202. Of course, the second incoupling diffractive optical element IDO2 and the second outcoupling diffractive optical element ODO2 can be formed on, within, or engaged with either the first surface 202 or the 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] In an exemplary embodiment, as shown in FIG. 11 and FIG. 13A-13B, the second incoupling diffractive optical element IDO2 is located substantially coaxially with the first incoupling diffractive optical element IDO1 with respect to a virtual 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 an 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, for example including 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] In an exemplary embodiment, as shown in Figures 14 and 15, the first incoupling diffractive optical element IDO1 and the second incoupling diffractive optical element IDO2 are configured to optimize the 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 transmission type diffraction gratings, and the second incoupling diffractive optical element IDO2 and the third incoupling diffractive optical element IDO3 may be configured as reflection type 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 are configured to optimize the diffraction efficiency for the image-bearing light WI1. 1 and the seventh plurality of periodic diffractive structures 212 of the third incoupling diffractive optical element IDO3 may have a tilt angle φ 2 The periodic diffractive structures 106, 206 of the first and second incoupling diffractive optical elements IDO1, IDO2 may have a tilt angle φ that rotates 180 degrees with respect to each other.

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

[0044] The 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 range or 495-570 nm range) and the red wavelength range (e.g., 630-660 nm range or 620-750 nm range) can be transmitted to the eyebox via TIR in a single waveguide. Similarly, the 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 blending high refractive index nanoparticles into the bulk polymer material, thereby raising 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 (having a shorter wavelength than light in the green and red wavelength ranges) tends to scatter from the nanoparticles blended into the bulk polymer material, thereby adversely affecting performance. 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, light in the blue wavelength range is often attenuated. For example, the optical path of light in the blue wavelength range in a waveguide including 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 particular wavelength of light and the particular 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 convey a full-color virtual image to an eyebox having 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 possible diffraction effects in an image resulting from viewing an 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 in 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 shown as a head mounted display (HMD) with a right eye optical system 120R having a 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 pico projector or similar device, energizable to generate one or more multi-colored 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 an embodiment using right-eye optical system 120R and left-eye optical system 120L, the virtual image generated may be a stereo pair of images for a three-dimensional (3D) display. During operation by the user, the virtual image or images formed by image light guide system 50, 50A may appear to be superimposed or overlaid on real-world scene content seen by the viewer through right-eye optical system 120R and / or left-eye image light guide. 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 eye tracking of the viewer.

[0048] One or more features of the embodiments described herein may be combined to create additional embodiments not shown. Although 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 its scope, spirit, or essential characteristics. The above-described embodiments are therefore to be considered in all respects as illustrative and not restrictive. The scope of the present 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 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 out of the first waveguide in an angularly decoded manner; 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 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 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 out of the second waveguide in an angularly decoded fashion; 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 positioned 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.

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 substantially perpendicular to the first axis.

3. The image light guide system of claim 1 , 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.

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

5. 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.

6. The image light guide system of claim 1 , wherein the first refractive index is less than the second refractive index.

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

8.

8. 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 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 out of the first waveguide in an angularly decoded manner; 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 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 positioned 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 out of the second waveguide in an angularly decoded fashion.

9. 9. The image light guide system of claim 8, 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 substantially perpendicular to the first axis.

10. 9. The image light guide system of claim 8, 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.

11. 9. The image light guide system of claim 8, 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 fashion, 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 fashion.

12. The image light guide system of claim 11 , wherein the image-bearing light beam of the third wavelength range comprises a longer wavelength than the image-bearing light beam of the first wavelength range.

13. 12. The image light guide system of claim 11, 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.

14. The image light guide system of claim 8 , wherein the first refractive index is less than the second refractive index.

15. 15. The image light guide system of claim 14, wherein the first wavelength range is 440 to 495 nm.

16. 9. The image light guide system of claim 8, wherein the first refractive index is less than 1.8 and the second refractive index is greater than or equal to 1.8.

Images