Birefringence waveguide stack

Abstract

An image light guide system for delivering a virtual image includes a first waveguide having a first refractive index and a second waveguide having a second refractive index. The first waveguide includes a diffractive optic arranged to couple in and out an image-carrying beam of a first wavelength range. The second waveguide includes a diffractive optic arranged to couple in and out an image-carrying beam of at least a second wavelength range.

Description

Technical Field

[0001] The present disclosure relates generally to electronic displays and, more particularly, to displays that utilize image light guides having diffractive optics to deliver image-bearing light to a viewer. Background Art

[0002] Head mounted displays (HMDs) and virtual image near-eye displays are being developed for a wide variety of uses, including military, commercial, industrial, firefighting, and entertainment applications. For many of these applications, it is valuable to form a virtual image that can be visually superimposed on a real image that is present in the field of view of the HMD user. Optical image light guides can deliver image-bearing light to a viewer in a confined space in order to direct the virtual image to the viewer's pupil and enable this superposition functionality.

[0003] Although conventional image light guide arrangements have significantly reduced the volume, weight, and overall cost of near-eye display optics, further improvements are needed. In some cases, image resolution is constrained by the reduction in volume and cost of conventional image light guide arrangements. Similarly, diffraction and propagation of certain wavelengths of light do not perform well in conventional image light guide arrangements. Therefore, there is a need for an image light guide system that is operable to produce a 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 invention provides an image light guide system for delivering a virtual image, the system comprising: a first waveguide having a first refractive index; a first coupling-in diffractive optical device formed along the first waveguide, wherein the first coupling-in diffractive optical device is arranged to diffract an image-bearing beam of a first wavelength range into the first waveguide in an angularly coded form; a first coupling-out diffractive optical device formed along the first waveguide, wherein the first coupling-out diffractive optical device is arranged to replicate the image-bearing beam of the first wavelength range in at least one direction and guide the replicated image-bearing beam from the first waveguide in an angularly decoded form; a second waveguide having a second refractive index; a second coupling-in diffractive optical device formed along the second waveguide, wherein the second coupling-in diffractive optical device is arranged to diffract the image-bearing beam of a second wavelength range into the second waveguide in an angularly coded form; and a second coupling-out diffractive optical device formed along the second waveguide, wherein the second coupling-out diffractive optical device is arranged to replicate the image-bearing beam of the second wavelength range in at least one direction and guide the replicated image-bearing beam from the second waveguide in an angularly decoded form. In an exemplary embodiment, the image light guide system comprises: a third coupling-in diffractive optical device formed along a second waveguide, wherein the third coupling-in diffractive optical device is arranged to diffract an image-bearing beam of a third wavelength range into the second waveguide in an angularly coded form; and a third coupling-out diffractive optical device formed along the second waveguide, wherein the third coupling-out diffractive optical device is arranged to replicate the image-bearing beam of the third wavelength range in at least one direction and guide the replicated image-bearing beam from the second waveguide in an angularly decoded form.

[0005] In an exemplary embodiment, the first waveguide comprises a material having a lower refractive index than the second waveguide. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0007] FIG. 1 shows a simplified cross-sectional view of an image light guide, illustrating one direction of replication of the image-bearing beam along the direction of propagation to extend the eye range.

[0008] FIG. 2 shows a perspective view of an image light guide with a steering grating, illustrating the expansion of the image-bearing beam perpendicular to the propagation direction to expand the second direction of the eye.

[0009] Figure 3 A schematic side view of a stacked waveguide having multiple coupled-in diffractive optics according to an exemplary embodiment of the presently disclosed subject matter is shown.

[0010] Figure 4Shown according to Figure 3 Schematic top view of a first waveguide.

[0011] Figure 5 Shown according to Figure 3 Schematic top view of the second waveguide.

[0012] Figure 6 Shown according to Figure 3 Schematic bottom view of the second waveguide.

[0013] Figure 7 Shown according to Figure 3 Schematic end view of a stacked waveguide.

[0014] Figure 8 Shown according to Figure 3 Schematic end view of a stacked waveguide.

[0015] Fig. 9 and 10 Shown according to Figure 3 Schematic perspective view of a stacked waveguide.

[0016] Fig.11 A schematic side view of a stacked waveguide according to an exemplary embodiment of the presently disclosed subject matter is shown.

[0017] Fig. 12A Shown according to Fig.11 Schematic top view of a first waveguide.

[0018] Fig. 12B Shown according to Fig.11 Schematic top view of the second waveguide.

[0019] Fig.13A Shown according to Fig.11 Schematic top view of a first waveguide.

[0020] Fig. 13B Shown according to Fig.11 Schematic top view of the second waveguide.

[0021] Fig.14 A schematic side view of part of a reflective in-coupling diffractive optic is shown.

[0022] Fig.15 A schematic side view of part of a transmissive coupling into a diffractive optical device is shown.

[0023] Fig.16 A perspective view of a display system for augmented reality viewing using an imaging light guide is shown according to an exemplary embodiment of the presently disclosed subject matter. DETAILED DESCRIPTION

[0024] It is to be understood that the present invention may assume a variety of different orientations and step sequences, unless expressly specified to the contrary. It is also to be understood that the specific components and systems shown in the drawings and described in the following specification are merely exemplary embodiments of the inventive concepts defined herein. Therefore, unless otherwise expressly stated, specific dimensions, directions, or other physical characteristics associated with the disclosed embodiments should not be considered limiting. In addition, although they may not be, in this section of this application, similar elements in the various embodiments described herein may generally be referenced by similar reference numerals.

[0025] The terms "first", "second", etc. used herein do not necessarily indicate any order, sequence or priority, but are only used to more clearly distinguish one element or a group of elements from another element, unless otherwise stated.

[0026] As used herein, the terms "viewer," "operator," "observer," and "user" are considered equivalent and refer to a person or machine wearing and / or using a device having an imaging light guide to view an image.

[0027] The term "set" as used herein refers to a non-empty set, as the concept of a set of elements or members of a set is widely understood in elementary mathematics. The term "subset" as used herein, unless explicitly stated otherwise, refers to a non-empty proper subset, i.e., a subset of a larger set with one or more members. For a set S, a subset may include the complete set S. A "proper subset" of a set S is strictly contained in the set S and does not contain at least one member of the set S.

[0028] As used herein, the terms "coupling," "coupler," or "coupling" in an optical context refer to a connection through which light is transmitted from one optical medium or device to another optical medium or device.

[0029] 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 wavelengths of light used to represent a multi-color image.

[0030] As used herein, the term "beam expansion" refers to replicating a beam via multiple encounters with an optical element to provide an exit pupil expansion in one or more directions. Similarly, "expanding" a beam or a portion of a beam as used herein refers to replicating a beam via multiple encounters with an optical element to provide an exit pupil expansion in one or more directions.

[0031] Those skilled in the relevant art will recognize that the elements and techniques described herein may be practiced without one or more specific details, or may be practiced using other methods, components, materials, etc. In some cases, in order to avoid obscuring certain aspects of the present disclosure, well-known structures, materials, or operations are not shown or described in detail. References to "one embodiment" or "embodiment" throughout the specification mean that the specific features, structures, or characteristics described with respect to the embodiment are included in at least one embodiment of the present disclosure. Therefore, the appearance of the phrase "in one embodiment" or "in an embodiment" throughout the specification does not necessarily refer to the same embodiment. However, the specific features, structures, or characteristics described may be combined in any suitable manner in one or more embodiments.

[0032] An optical system, such as an HMD, can produce a virtual image display. In contrast to methods of forming a real image, a virtual image is not formed on a display surface. That is, if the display surface is located at the perceived location of the virtual image, no image is formed on the surface. Virtual image displays have many inherent 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. In addition, the source object of the virtual image may be small; for example, a magnifying glass provides a virtual image of an object. By forming a virtual image that appears to be at a distance, a more realistic viewing experience can be provided compared to systems that project real images. Providing a virtual image also avoids the need to compensate for screen artifacts, which may be necessary when projecting a real image.

[0033] 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, relatively angle-coded light beam from a projector is coupled to a planar waveguide via an input coupling such as an in-coupling diffractive optical device, which may be mounted or formed on the surface of the planar waveguide or buried within the waveguide. Such a diffractive optical device may be formed as a diffraction grating, a holographic optical element (HOE), or in other known ways. For example, the diffraction grating may be formed by surface relief. After propagating along the waveguide, the diffracted light may be directed back out of the waveguide via a similar output coupling such as an out-coupling diffractive optical device, which may be arranged to provide pupil expansion along at least one direction of the virtual image. In addition, a steering grating may be placed on or in the waveguide to provide pupil expansion in an orthogonal direction to the virtual image. The image-bearing light output from the waveguide provides an extended eyebox for the viewer.

[0034] 1 is a simplified cross-sectional view showing a conventional configuration of an image light guide system 10. The image light guide system 10 includes a planar image light guide 12, an in-coupling diffractive optical device IDO, and an out-coupling diffractive optical device 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 in-coupling diffractive optical device IDO is shown as a transmissive diffraction grating disposed on, in, or otherwise engaged with the front face 14 of the image light guide 12. However, the in-coupling diffractive optical device IDO may alternatively be a reflective diffraction grating or other type of diffractive optical device, such as a volume hologram or other holographic diffractive element, which diffracts the incident image-bearing light beam WI to the image light guide 12. The coupled-in diffractive optical device IDO can be located on, in or otherwise engaged with the front surface 14 or the back surface 16 of the image light guide 12, and can be a combination of transmissive or reflective types, depending on the direction from which the image-bearing beam WI approaches the image light guide 12.

[0035] When used as part of a near-eye or head-mounted display system, the coupled-in diffractive optical device IDO of the conventional image light guide system 10 couples image-bearing beams WI from a real, virtual or hybrid image source 18 into the substrate S of the image light guide 12. Any real image or image size formed by the image source 18 is first converted into an array of overlapping, angularly correlated, collimated beams encoding different positions in the virtual image for presentation to the coupled-in diffractive optical device IDO. Typically, the rays within each bundle forming one of the angularly correlated beams extend in parallel, but the angularly correlated beams are relatively inclined to each other by angles that can be defined as two angular dimensions corresponding to the linear dimensions of the image.

[0036] Once the angle-dependent beams are coupled to the coupling-in diffractive optical device IDO, at least a portion of the image-carrying beam WI is diffracted (typically through the first diffraction order) and thereby redirected by the coupling-in diffractive optical device IDO into the planar image light guide 12 as an angle-coded image-carrying 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 and 16. Despite being diffracted into different combinations of angle-dependent beams consistent with the boundaries set by TIR, the image-carrying beam WG retains the image information in the angle-coded form derivable from the parameters of the coupling-in diffractive optical device IDO. The coupling-out diffractive optical device ODO receives the encoded image-carrying beam WG and diffracts (typically also through the first diffraction order) at least a portion of the image-carrying beam WG out of the image light guide 12 (as image-carrying beam WO) towards an adjacent spatial region called the eyebox E, within which the transmitted virtual image can be seen by the eye 5 or other optical components of the viewer. The coupled-out diffractive optical device ODO can be designed symmetrically with respect to the coupled-in diffractive optical device IDO to restore the original angular relationship of the image-bearing beam WI in the output angularly dependent beam of the image-bearing beam WO. In addition, at a finite focusing distance, the coupled-out diffractive optical device ODO can modify the positional angular relationship of the original field of view points to produce an output virtual image.

[0037] However, in order to increase one dimension of overlap in the angularly dependent beams that fill the eyebox E (defining the size of the area in which the virtual image can be seen), the out-coupling diffractive optic ODO is arranged with the image light guide 12 of finite thickness T so as to encounter the image-carrying beam WG multiple times and diffract only a portion of the image-carrying beam WG at each encounter. The multiple encounters along the length (e.g., first direction) of the out-coupling diffractive optic ODO have the effect of replicating the image-carrying beam WG and enlarging or expanding at least one dimension of the eyebox E in which the replicated beam overlaps. The expanded eyebox E reduces sensitivity to the position of the viewer's eye 5 viewing the virtual image.

[0038] The out-coupling diffractive optic ODO is shown as a transmissive diffraction grating arranged on or fixed to the front surface 14 of the image light guide 12. However, like the in-coupling diffractive optic IDO, the out-coupling diffractive optic ODO may be located on, in or otherwise engaged with the front or back surface 14 or 16 of the image light guide 12, and may be a combination of transmissive or reflective types, depending on the direction through which the image-bearing beam WG is intended to leave the image light guide 12. Furthermore, the out-coupling diffractive optic ODO may form another type of diffractive optic, such as a volume hologram or other holographic diffractive element, which diffracts the propagating image-bearing beam WG from the image light guide 12 to propagate towards the eye range E as the image-bearing beam WO.

[0039] FIG2 shows a perspective view of a conventional image light guide system 10 for extending the eye range E in two dimensions, i.e., along the x-axis and y-axis of the intended image. To achieve the eye range extension in the second dimension, the coupling-in diffractive optics IDO are oriented to diffract at least a portion of the image-carrying beam WG along a grating vector k1 of the image light guide 12 toward the intermediate turning optics TO, and the grating vector k2 of the intermediate turning optics TO are oriented to diffract at least a portion of the image-carrying beam WG in a reflective mode along the image light guide 12 toward the coupling-out diffractive optics ODO. It should be appreciated that only a portion of the image-carrying beam WG is diffracted by each of the multiple encounters with the intermediate turning optics TO, thereby laterally replicating each angularly dependent beam of the image-carrying beam WG as the angularly dependent beam of the image-carrying beam WG approaches the coupling-out diffractive optics ODO. The intermediate turning optics TO redirect the image-carrying beam WG toward the coupling-out diffractive optics ODO (having a grating vector k3), which is used to longitudinally replicate the angularly dependent beam of the image-carrying beam WG in the second direction before leaving the image light guide 12 as the image-carrying beam WO. Grating vectors, such as the depicted grating vectors k1, k2 and k3, extend in respective directions perpendicular to the diffractive features (e.g., groove, line or ruling) of the diffractive optical device within parallel planes of the image light guide 12 and have respective amplitudes that are the inverse of the period or pitch d (i.e., the center distance between the diffractive features) of the diffractive optical devices IDO, TO and ODO.

[0040] As shown in FIG2 , the coupled-in diffractive optical device IDO receives an incident image-bearing beam WI, which includes a set of angularly dependent beams corresponding to individual pixels or equivalent positions in an image generated by an image source 18 such as a projector. The full range of angularly coded beams that produce a virtual image can be generated by a real display in conjunction with collimating optics or other optical components, by a beam scanner that more directly sets the angle of the beam, or by a combination of a one-dimensional real display such as used with a scanner. In this configuration, the image light guide 12 outputs a replicated set of angularly dependent beams (replicated in two dimensions) by providing multiple encounters of the image-bearing beam WG with the intermediate steering optics TO and the coupled-out diffractive optical device ODO in different orientations. In the depicted orientation of the image light guide 12, the intermediate steering optics TO provide an eye range extension in a first dimension (e.g., the y-axis direction), while the coupled-out diffractive optical device ODO provides a similar eye range extension in a second dimension (e.g., the x-axis direction). The relative orientation and respective periods d of the diffractive features of the coupling-in optics IDO, the intermediate turning optics TO, and the coupling-out diffractive optics ODO provide eye range extension in two dimensions while preserving the desired relationship between the angularly dependent beams of the image-bearing beam WI output as the image-bearing beam WO from the image light guide system 10. It should be appreciated that the periods d of the coupling-in diffractive optics IDO, the intermediate turning optics TO, and the coupling-out diffractive optics ODO may each include diffractive features having a common spacing d, wherein the common spacing d may be different for each optical device.

[0041] In the configuration shown in the figure, when the image-carrying beam WI input into the image light guide 12 is coupled into the diffractive optical device IDO and encoded into another set of angularly related beams, the information required for reconstructing the image is retained due to the systematic effect of coupling into the diffractive optical device IDO. The intermediate steering optical device TO is located in an intermediate position between the coupling-in and coupling-out diffractive optical devices IDO and ODO, and it can be arranged so as not to bring significant changes to the encoding of the image-carrying beam WG. Therefore, the coupling-out diffractive optical device ODO can be arranged in a symmetrical manner with respect to the coupling-in diffractive optical device ODO, for example including diffractive features sharing the same period d. Similarly, the period of the intermediate steering optical device TO can also match the common period of the coupling-in and coupling-out diffractive optical devices ODO and ODO. Although the grating vector k2 of the intermediate steering optical device TO is shown as being oriented at 45 degrees relative to the other grating vectors that maintain possible orientations, the grating vector k2 of the intermediate steering optical device TO can be oriented at 60 degrees relative to the grating vectors k1 and k3 of the coupling-in and coupling-out diffractive optical devices IDO and ODO, thereby rotating the image-carrying beam WG by 120 degrees. By orienting the grating vector k2 of the intermediate turning optic TO at 60 degrees relative to the grating vectors k1 and k3 of the coupling-in and coupling-out diffractive optics IDO and ODO, the grating vectors k1 and k3 of the coupling-in and coupling-out diffractive optics IDO and ODO are also oriented at 60 degrees relative to each other. By basing the grating vector magnitudes on a common spacing shared by the coupling-in, intermediate turning and coupling-out diffractive optics IDO, TO and ODO, the three grating vectors k1, k2 and k3 (as directed line segments) form an equilateral triangle that sums to a zero vector magnitude, which avoids asymmetric effects that could introduce unwanted anomalies including dispersion. Such asymmetric effects can also be avoided by having the grating vectors k1, k2 and k3 have unequal magnitudes in relative orientation, with the sum of the three grating vectors k1, k2 and k3 being a zero vector magnitude.

[0042] In a broader sense, regardless of whether the coupling into the diffractive optical device IDO uses a grating, hologram, prism, mirror or other mechanism, the image-bearing beam WI directed into the image light guide 12 is effectively encoded by the coupling into the diffractive optical device IDO. Any reflection, refraction and / or diffraction of the light at the input end should be decoded accordingly at the output end to re-form the virtual image presented to the viewer. Regardless of whether the symmetry between the intermediate steering optical device TO, the coupling-in optical device IDO and the coupling-out diffractive optical device ODO is maintained, or whether the encoding of the angularly related beams of the image-bearing beam WI changes along the image light guide 12, the intermediate steering optical device TO can be associated with the coupling-in and coupling-out diffractive optical devices IDO and ODO so that the image-bearing beam WO output from the image light guide 12 retains or otherwise maintains the original or desired form of the image-bearing beam WI used to produce the intended virtual image.

[0043] As shown in FIG. 2 , the letter “R” represents the orientation of a virtual image visible to a viewer whose eye is within the eye range E. As shown, the orientation of the letter “R” in the represented virtual image matches the orientation of the letter “R” encoded in the image-bearing beam WI. A change in the rotation or angular orientation of the incident image-bearing beam WI about the z-axis relative to the xy plane causes a corresponding symmetrical change in the rotation or angular orientation of the outgoing light coupled out of the diffractive optical device (ODO). From the perspective of image orientation, the intermediate steering optical device TO simply acts as an optical relay, providing a one-dimensional eye range extension by replicating the angularly encoded beam of the image-bearing beam WG along one axis of the image (e.g., along the y-axis). Coupling out of the diffractive optical device ODO further provides a second dimension of eye range extension by replicating the angularly 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 beam WI. The intermediate steering optical device TO is typically a tilted grating or a square grating, or may alternatively be a blazed grating, and is typically arranged on one of the plane-parallel front and back surfaces of the image light guide 12. It should be appreciated that the representation "R" of the virtual image created by the image source consists of infinitely focused light which requires a lens (eg, a lens in a human eye) to focus the image so that the orientation discussed above can be detected.

[0044] Taken together, the coupling-in, steering and coupling-out diffractive optical devices IDO, TO and ODO preferably preserve the angular relationship between the light beams of different wavelengths that define the virtual image when passing from the offset position to the near-eye position of the viewer through the image light guide 12. At the same time, the coupling-in, steering and coupling-out diffractive optical devices IDO, TO and ODO can be relatively positioned and oriented in different ways to control the overall shape of the image light guide 12 and the overall orientation with which the angularly related light beams can be guided into and out of the image light guide 12.

[0045] The present disclosure provides an image light guide arrangement that improves multi-color image-bearing light output intensity across an output aperture. More specifically, the present disclosure provides, among other things, a waveguide stack having a high refractive index polymer waveguide and a low refractive index polymer waveguide.

[0046] like Figure 3-11As shown, 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 waveguide first surface 102 is generally positioned parallel to the waveguide second surface 104. A first coupling-in diffractive optical device ID01 is located on, in, or joined to the first surface 102 or the second surface 104. In addition, a first coupling-out diffractive optical device ODO1 is formed on, in, or joined to the first surface 102 or the second surface 104. In an exemplary embodiment, the coupling-out diffractive optical devices ODO1, ODO2 are both diffraction gratings. In another exemplary embodiment, the coupling-out diffractive optical devices ODO1, ODO2 are both holographic diffractive elements.

[0047] Reference now Figure 4, shows a top view of an example embodiment of a first planar waveguide 100, a first coupling-in diffractive optical device ID01 including a first plurality of periodic diffractive structures 106. For example, the first coupling-in diffractive optical device ID01 may include a first group of periodic linear grating structures 106 oriented generally parallel to the y-axis. The first coupling-out diffractive optical device 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 include a second group of periodic linear grating structures 108 rotated or angularly offset relative to an x-axis 115 at 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 include a third group of periodic linear grating structures 110 rotated or angularly offset relative to the x-axis 115 at a polar angle greater than 60 degrees (e.g., 65 degrees). In an exemplary embodiment, the second group of periodic linear grating structures 108 are rotated or angularly offset relative to the x-axis 115 at a polar angle of about 30 degrees, and the third group of periodic linear grating structures 110 are rotated or angularly offset relative to the x-axis 115 at a polar angle of about 150 degrees. In another embodiment, the first group of periodic linear grating structures 106 are positioned generally parallel to an alternative axis other than the y-axis, and the second group of periodic linear grating structures 108 are rotated or angularly offset relative to an axis perpendicular to the alternative axis at a polar angle (measured from the vertical axis) of less than 30 degrees (e.g., 25 degrees), and the third group of periodic linear grating structures 110 are rotated or angularly offset relative to the alternative axis at a polar angle (measured from the vertical axis) of greater than 60 degrees (e.g., 65 degrees). The second and third groups of periodic diffractive structures 108 and 110 intersect and / or define different grating vectors. The second and third groups of periodic diffractive structures 108 and 110 form a composite diffractive optical device operable to replicate and couple out image-bearing light coupled in by the first coupling-in diffractive optical device IDO1. The first group of periodic diffractive structures 106 includes a first period, the second group of periodic diffractive structures 108 includes a second period, and the third group of periodic diffractive structures 110 includes a third period. In an example embodiment, the third period is equal to the second period, and the second period is equal to the first period. In an example embodiment, the first period, the second period, and the third period are all less than 50 nm.

[0048] like Figure 3-10As shown, in an example embodiment, the image light guide system 50 includes a second planar waveguide 200 having a first surface 202 and a second surface 204. The waveguide first surface 202 is positioned generally parallel to the waveguide second surface 204. A second coupling-in diffractive optical device ID02 is located on, in, or joined to the first surface 202, and a third coupling-in diffractive optical device ID03 is located on, in, or joined to the second surface 204. A second coupling-out diffractive optical device ODO2 is formed on / in the first surface 202, and a third coupling-out diffractive optical device ODO3 is formed on, in, or joined to the second surface 204. In an example embodiment, the first coupling-in diffractive optical device ID01 is substantially coaxial with the second coupling-in diffractive optical device ID01 relative to an imaginary axis arranged 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 should be appreciated that the second coupling-in diffractive optical device IDO2, the third coupling-in diffractive optical device IDO3, the second coupling-out diffractive optical device ODO2 and the third coupling-out diffractive optical device ODO3 may be formed on, in or bonded to the first surface 202 or the second surface 204.

[0049] Reference now Figure 5, shows a top view of an example embodiment of a second planar waveguide 200, the second coupling-in diffractive optical device IDO 2 includes a fourth plurality of periodic diffractive structures 206. For example, the second coupling-in diffractive optical device IDO2 may include a fourth group of periodic linear grating structures 206 positioned generally parallel to the y-axis. The second coupling-out diffractive optical device 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 include a group of periodic linear grating structures rotated or angularly offset relative to the x-axis at a polar angle (measured from the x-axis) of less than 30 degrees (e.g., 25 degrees), and the sixth plurality of periodic diffractive structures 210 may include a group of periodic linear grating structures rotated or angularly offset relative to the x-axis at a polar angle (measured from the x-axis) of greater than 60 degrees (e.g., 65 degrees). In another embodiment, the fourth group of periodic linear grating structures 206 are positioned generally parallel to an alternative axis other than the y-axis, and further the fifth group of periodic linear grating structures 208 are rotated or angularly offset relative to an axis perpendicular to the alternative axis at a polar angle (measured from the perpendicular axis) less than 30 degrees (e.g., 25 degrees), and the sixth group of periodic linear grating structures 210 are rotated or angularly offset relative to the alternative axis at a polar angle (measured from the perpendicular axis) greater than 60 degrees (e.g., 65 degrees). In an exemplary embodiment, the fifth group of periodic linear grating structures 208 are rotated or angularly offset relative to the x-axis at a polar angle of about 30 degrees, and the sixth group of periodic linear grating structures 210 are rotated or angularly offset relative to the x-axis at a polar angle of about 150 degrees. The fifth and sixth groups of periodic diffractive structures 208 and 210 intersect and / or define different grating vectors. The fifth and sixth groups of periodic diffractive structures 208, 210 form a composite diffractive optical device operable to replicate and couple out image-bearing light from the second coupling-in diffractive optical device IDO2. The fourth group of periodic diffractive structures 206 includes a fourth period, the fifth group of periodic diffractive structures 208 includes a fifth period, and the sixth group of periodic diffractive structures 210 includes a sixth period. In an exemplary embodiment, the sixth period is equal to the fifth period, and the fifth period is equal to the fourth period. In an exemplary embodiment, the fourth period, the fifth period, and the sixth period are all less than 50 nm.

[0050] Reference now Figure 6, showing a bottom view of the second planar waveguide 200, the third coupled-in diffractive optical device IDO3 includes a seventh multiple period diffractive structure 212. For example, the third coupled-in diffractive optical device IDO3 may include a seventh group of periodic linear grating structures 212, which is rotated or angularly offset by about thirty degrees (30 degrees) relative to the fourth group of periodic linear grating structures 206, for example, within 5 degrees (5 degrees) of 30 degrees (30 degrees). For example, the third coupled-in diffractive optical device IDO3 may include a seventh group of periodic linear grating structures 212, which is rotated or angularly offset by between 25 degrees (25 degrees) and 35 degrees (30 degrees) relative to the fourth group of periodic linear grating structures 206. The third coupled-out diffractive optical device ODO3 includes an eighth multiple period diffractive structure 214 and a ninth multiple period diffractive structure 216. For example, the eighth plurality of periodic diffractive structures 214 may include an eighth plurality of periodic linear grating structures 214 rotated or angularly offset by about thirty degrees (30 degrees), e.g., within five degrees (5 degrees) of thirty degrees (30 degrees), relative to the fifth plurality of periodic linear grating structures 208, and the ninth plurality of periodic diffractive structures 216 may include a ninth plurality of periodic linear grating structures 216 rotated or angularly offset by about thirty degrees (30 degrees), e.g., within five degrees (5 degrees) of thirty degrees (30 degrees), relative to the sixth plurality of periodic linear grating structures 210. In an example embodiment, the eighth plurality of periodic linear grating structures 214 are substantially parallel to the x-axis 115 at a polar angle of about 0 degrees, and the ninth plurality of periodic linear grating structures 216 are rotated or angularly offset by a polar angle of about 120 degrees relative to the x-axis 115. The eighth and ninth plurality of periodic diffractive structures 214, 216 intersect and / or predefine different grating vectors. The eighth and ninth groups of periodic diffractive structures 214, 216 form a composite diffractive optical device operable to replicate and couple out image-bearing light from the third coupled-in diffractive optical device IDO3. The seventh group of periodic diffractive structures 212 includes a seventh period, the eighth group of periodic diffractive structures 214 includes an eighth period, and the ninth group of periodic diffractive structures 216 includes a ninth period. In an example embodiment, the ninth period is equal to the eighth period, and the eighth period is equal to the seventh period. In an example embodiment, the seventh period, the eighth period, and the ninth period are all less than 50 nm, and the seventh period, the eighth period, and the ninth period are all greater than 50 nm.

[0051] The first planar waveguide 100 includes a first wavelength range optical path and a second wavelength range optical path. The first wavelength range optical path includes at least a first coupling-in diffractive optical device ODO1 and a first coupling-out diffractive optical device ODO1. The first wavelength range optical path is operable to couple in, propagate via TIR, replicate, and couple out image-bearing light of the first wavelength range. For example, the first wavelength range optical path is operable to guide image-bearing light in a blue wavelength range (e.g., in the range of 440-470nm, in the range of 440-495nm, or in the range of 450-495nm) through the waveguide 100.

[0052] The second planar waveguide 200 includes a second wavelength range optical path and a third wavelength range optical path. The second wavelength range optical path includes at least a second coupling-in diffractive optical device ODO2 and a second coupling-out diffractive optical device ODO2. The second wavelength range optical path is operable to couple-in, propagate via TIR, replicate, and couple-out image-bearing light of the second wavelength range. For example, the second wavelength range optical path is operable to guide image-bearing light in a green wavelength range (e.g., in the range of 520-560nm or in the range of 495-570nm) through the waveguide 200. The third wavelength range optical path includes at least a third coupling-in diffractive optical device ODO3 and a third coupling-out diffractive optical device ODO3. The third wavelength range optical path is operable to couple-in, propagate via TIR, replicate, and couple-out image-bearing light of the third wavelength range. For example, the third wavelength range optical path is operable to guide image-bearing light in a red wavelength range (e.g., in the range of 630-660nm or in the range of 620-750nm) through the waveguide 200.

[0053] Crosstalk between the optical paths of the second and third wavelength ranges can be reduced by rotating the seventh multiple period diffractive structure 212 by approximately thirty degrees (30°) relative to the fourth multiple period diffractive structure 206, and rotating the eighth and ninth multiple period grating structures 214 and 216 by approximately thirty degrees (30°) relative to the fifth and sixth multiple period diffractive structures 208 and 210, respectively. In other words, the third coupling-in diffractive optical device IDO3 is rotated by approximately thirty degrees (30°) relative to the second coupling-in diffractive optical device IDO2, and the third coupling-out diffractive optical device ODO3 is rotated by approximately thirty degrees (30°) relative to the second coupling-out diffractive optical device ODO2.

[0054] like Figure 3 , 7and 8. In an exemplary embodiment, image-carrying light WI1 from projector 18A is incident on a first coupling-in diffractive optical device IDO1, a first portion of the image-carrying light WI1 is diffracted by the first coupling-in diffractive optical device IDO1, and propagates toward a coupling-out diffractive optical device ODO1 as WG1, typically via TIR. In one example, the periodic linear grating structure (i.e., a first group of periodic linear grating structures 106) of the first coupling-in diffractive optical device IDO1 is arranged to optimize the coupling of image-carrying light WI1 of a first wavelength range (e.g., light in the blue wavelength range of the electromagnetic spectrum). A second portion of the image-carrying light WI1 is transmitted through the first coupling-in diffractive optical device IDO1 and the planar waveguide 100, and is incident on a second coupling-in diffractive optical device IDO2. At least a portion of the image-carrying light WI1 is diffracted by the second coupling-in diffractive optical device IDO2, and propagates toward a second coupling-out diffractive optical device ODO2 as WG2, typically via TIR. In one example, the second periodic linear grating structure coupled into the diffractive optical device IDO2 (ie, the fourth group of periodic linear grating structures 206) is arranged to optimize coupling of image-bearing light WI1 of a second wavelength range (eg, light in the green wavelength range).

[0055] The image-carrying light WI2 from the projector 18B is incident on the second coupling-in diffractive optical device IDO2, a first portion of the image-carrying light WI2 is diffracted by the second coupling-in diffractive optical device IDO2, and propagates toward the coupling-out diffractive optical device ODO2 typically via TIR as WG3. In one example, the periodic linear grating structure (i.e., the periodic linear grating structure 212) of the third coupling-in diffractive optical device IDO3 is arranged to optimize the coupling of the image-carrying light WI2 in the wavelength range within the red wavelength range.

[0056] In an example embodiment, if Figure 11-12BAs shown in , the image light guide system 50A includes a second planar waveguide 200A having a second coupling-in diffractive optical device ODO2 located on, in, or joined to a first surface 202, and a second coupling-out diffractive optical device ODO2 formed on, in, or joined to the first surface 202. It should be appreciated that the second coupling-in diffractive optical device ID02 and the second coupling-out diffractive optical device ODO2 may be formed on, in, or joined to the first surface 202 or the second surface 204. The second coupling-in diffractive optical device ID02 and the second coupling-out diffractive optical device ODO2 are arranged and optimized to diffract image-bearing light of a second wavelength range (e.g., a green wavelength range in the range of 520-560 nm or 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 in the range of 620-750 nm). The second out-coupling diffractive optical device ODO2 is arranged to replicate the image-bearing light of the second and third wavelength ranges in at least one direction and to couple out the image-bearing light of the second and third wavelength ranges.

[0057] In an example embodiment, if Fig.11 and 13A -13B, the second coupling-in diffractive optical device IDO1 is substantially coaxial with the first coupling-in diffractive optical device IDO1 about an imaginary axis, which passes through the first and second surfaces 102, 104 of the first planar waveguide 100 and the first and second surfaces 202, 204 of the second planar waveguide 200A. In an exemplary embodiment, the second coupling-in diffractive optical device IDO2 includes a first plurality of periodic diffractive structures 206 optimized to diffract image-bearing light of a second wavelength range to the second waveguide 200A and a second plurality of periodic diffractive structures 212 optimized to diffract image-bearing light of a third wavelength range to the second waveguide 200A. For example, the second coupling-in diffractive optical device IDO2 may be a composite diffractive optical device having a plurality of periodic diffractive structures including, for example, columns. The second coupling-in diffractive optical device IDO2 may also be a composite diffractive optical device having a plurality of crossed or overlapped generally linear periodic diffractive structures. In an example embodiment, the second in-coupling diffractive optical device ID02 includes a plurality of periodic diffractive structures optimized to diffract image-bearing light of the second and third wavelength ranges into the second waveguide 200A. For example, the second in-coupling diffractive optical device ID02 may define only one grating vector k. It should be appreciated that in an example embodiment, the image light guide system 50A may be configured such that the second waveguide 200A is used to transmit only image-bearing light of the second wavelength range.

[0058] In an example embodiment, if Fig.14 and 15As shown, the first coupled-in diffractive optical device IDO1 and the second coupled-in diffractive optical device IDO2 are configured to optimize the diffraction efficiency of the image-bearing light WI1. For example, the first coupled-in diffractive optical device IDO1 and the second coupled-in diffractive optical device IDO2 may be configured as transmission-type diffraction gratings, and the second coupled-in diffractive optical device IDO2 and the third coupled-in diffractive optical device IDO3 may be configured as reflection-type diffraction gratings. In an exemplary embodiment, the first multiple periodic diffractive structure 106 of the first coupled-in diffractive optical device IDO1 and the fourth multiple periodic diffractive structure 206 of the second coupled-in diffractive optical device IDO2 may have an inclination angle φ1, and the seventh multiple periodic diffractive structure 212 of the third coupled-in diffractive optical device IDO3 may have an inclination angle φ2. The periodic diffractive structures 106, 206 of the first and second coupled-in diffractive optical devices IDO1, IDO2 may have an inclination angle φ, and they are rotated 180 degrees relative to each other.

[0059] In an example embodiment, the first planar waveguide 100 includes a low refractive index material (e.g., polymer, quartz, or glass) optimized for propagating image-bearing light in a blue wavelength range (e.g., in a range of 440-470 nm or in a range of 420-495 nm), and the second planar waveguide 200 includes a high refractive index material (e.g., polymer, quartz, or glass) optimized for propagating image-bearing light in a green wavelength range (e.g., in a range of 520-560 nm or in a range of 495-570 nm) and a red wavelength range (e.g., in a range of 630-660 nm or in a range of 620-750 nm). For example, the refractive index number of the low refractive index material may be in a range of 1.2-1.8, and the refractive index number of the high refractive index material may be in a range of 1.8-2.0. In some examples, the refractive index number of the low refractive index material may be in a range of 1.4-1.7. In some examples, the low refractive index material has a refractive index less than 1.8, and the high refractive index material has a refractive index greater than or equal to 1.8.

[0060] The second planar waveguide 200 comprising 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., in the range of 520-560 nm or in the range of 495-570 nm) and the red wavelength range (e.g., in the range of 630-660 nm or in the range of 620-750 nm) can be delivered to the eye range in a single waveguide via TIR. Similarly, the second planar waveguide 200 comprising 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.

[0061] High refractive index polymers used in optical waveguide substrates are traditionally achieved by mixing high refractive index nanoparticles into the bulk polymer material, thereby increasing the overall refractive index of the bulk polymer. While waveguides made from this type of high refractive index polymer generally function with acceptable performance for light in the green and red wavelength ranges, light in the blue wavelength range (which has a shorter wavelength than light in the green and red wavelength ranges) tends to disperse the nanoparticles mixed in the bulk polymer material, thereby negatively affecting performance. In other high refractive index materials, such as unrestricted high refractive index glass, which has a refractive index in the range of 1.9-2.0, light in the blue wavelength range tends to attenuate. For example, in a waveguide comprising high refractive index glass, the optical path of light in the blue wavelength range can be long enough that essentially no light in the blue wavelength range is emitted into the eye movement range. In a high refractive index material, the attenuation of light in the blue wavelength range is a function of the specific wavelength of light and the specific material.

[0062] In summary, the presently disclosed subject matter has the advantages of providing diffraction and propagation of light of multiple wavelength ranges in an image light guide under optimal conditions for each wavelength range to produce improved virtual image brightness and resolution. In addition, an image light guide system arranged to deliver a full color virtual image to an eye range with only two waveguides is superior to a system using three waveguides (one waveguide for each of the red, green, and blue wavelength ranges of light) because of the reduced weight and complexity of the system and because of the reduced potential diffraction effects of the image caused by viewing the image through a diffractive optic (e.g., coupled out of a diffractive optic) relative to a three waveguide stack.

[0063] Fig.16The perspective view shown illustrates an example of an image light guide system 50, 50A in a display system for viewing virtual images in augmented reality. 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 the user's right eye. The image light guide system 50, 50A includes an image source 18, such as a micro-projector or similar device, which can be activated to generate one or more multi-color virtual images. In one example, 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 example using the right eye optical system 120R and the left eye optical system 120L, the generated virtual image can be a stereoscopic image pair for three-dimensional (3D) viewing. During operation by the user, the virtual image or images formed by the image light guide system 50, 50A may appear to be superimposed or overlaid on the real scene content seen by the viewer through the right eye optical system 120R and / or the left eye image light guide system. In addition, additional components familiar to those skilled in the art of augmented reality visualization may be provided, such as one or more cameras mounted on the HMD frame for viewing the scene content or tracking the viewer's gaze.

[0064] One or more features of the embodiments described herein may be combined to create other embodiments not described. Although various embodiments have been described in detail above, it should be understood that they are presented by way of example rather than limitation. For those skilled in the relevant art, the disclosed subject matter may be embodied in other specific forms, variations and modifications without departing from its scope, spirit or essential characteristics. Therefore, the above-described embodiments are considered to be illustrative in all aspects and not restrictive. The scope of the present invention is indicated by the appended claims, and all changes within their equivalent meanings and scopes are intended to be included therein.

Claims

1. An image light guide system for delivering a virtual image, comprising: a first waveguide having a first refractive index; a first in-coupling diffractive optic formed along the first waveguide, wherein the first in-coupling diffractive optic is arranged to diffract the image-bearing beam of the first wavelength range into the first waveguide in an angularly coded manner; a first out-coupling diffractive optical device formed along the first waveguide, wherein the first out-coupling diffractive optical device is arranged to replicate the image-bearing beam of the first wavelength range in at least one direction and to guide the replicated image-bearing beam from the first waveguide in an angularly decoded form; a second waveguide having a second refractive index; a second in-coupling diffractive optic formed along the second waveguide, wherein the second in-coupling diffractive optic is arranged to diffract the image-bearing beam of the second wavelength range into the second waveguide in an angularly coded manner; a second out-coupling diffractive optic formed along the second waveguide, wherein the second out-coupling diffractive optic is arranged to replicate the image-bearing beam of the second wavelength range in at least one direction and to direct the replicated image-bearing beam from the second waveguide in an angularly decoded form; a third in-coupling diffractive optic formed along the second waveguide, wherein the third in-coupling diffractive optic is arranged to diffract the image-bearing beam of a third wavelength range into the second waveguide in an angularly coded manner; as well as A third out-coupling diffractive optical device is formed along the second waveguide, wherein the third out-coupling diffractive optical device is arranged to replicate the image-bearing beam of the third wavelength range in at least one direction and to guide the replicated image-bearing beam from the second waveguide in an angularly decoded form.

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 wherein the first coupling-in diffractive optic and the second coupling-in diffractive optic are substantially coaxial along a second axis substantially orthogonal 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 a shorter wavelength 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. The image light guide system of claim 1, further comprising a first image source operable to emit image-bearing light beams of first and second wavelength ranges, and a second image source operable to emit image-bearing light beams of a 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. 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. An image light guide system for delivering a virtual image, comprising: a first waveguide having a first refractive index; a first in-coupling diffractive optic formed along the first waveguide, wherein the first in-coupling diffractive optic is arranged to diffract the image-bearing beam of the first wavelength range into the first waveguide in an angularly coded manner; a first out-coupling diffractive optical device formed along the first waveguide, wherein the first out-coupling diffractive optical device is arranged to replicate the image-bearing beam of the first wavelength range in at least one direction and to guide the replicated image-bearing beam from the first waveguide in an angularly decoded form; a second waveguide having a second refractive index; a second in-coupling diffractive optic formed along the second waveguide, wherein the second in-coupling diffractive optic is arranged to diffract the image-bearing beam of at least a second wavelength range into the second waveguide in an angularly coded manner; A second out-coupling diffractive optical device is formed along the second waveguide, wherein the second out-coupling diffractive optical device is arranged to replicate the image-bearing beam of the second wavelength range in at least one direction and to guide the replicated image-bearing beam from the second waveguide in an angularly decoded form.

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 wherein the first coupled-in diffractive optical device and the second coupled-in diffractive optical device are substantially coaxial along a second axis substantially orthogonal to the first axis.

10. The image light guide system of claim 8, wherein the image-bearing light beam of the first wavelength range comprises a shorter wavelength than the image-bearing light beam of the second wavelength range.

11. The image light guide system of claim 8, wherein the second in-coupling diffractive optic is arranged to diffract the image-bearing beam of the third wavelength range into the second waveguide in an angularly coded manner; and wherein, The second out-coupling diffractive optical device is arranged to replicate the image-bearing beam of the third wavelength range in at least one direction and to guide the replicated image-bearing beam from the second waveguide in an angularly decoded form.

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. The image light guide system of claim 11, further comprising a first image source operable to emit image-bearing light beams of first and second wavelength ranges, and a second image source operable to emit image-bearing light beams of a 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. The image light guide system of claim 14, wherein the first wavelength range is between 440-495 nanometers.

16. 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