Dual projector system and image light guide

Abstract

An image light guide for conveying a virtual image includes a first surface and an opposing second surface, and a first in-coupling diffractive optic disposed along one of the first surface and the second surface, where the first in-coupling diffractive optic includes a first set of diffractive features. A second in-coupling diffractive optic disposed along one of the first surface and the second surface, wherein the second in-coupling diffractive optic includes a second set of diffractive features. The image light guide further includes an out-coupling diffractive optic disposed along at least one of the first surface and the second surface, where the out-coupling diffractive optic includes a plurality of regions, each region having a different set of diffractive features than an adjacent region, where the out-coupling diffractive optic includes a plurality of diffractive features. The plurality of regions includes a first region optimized to diffract in-coupling light from the first in-coupling diffractive optics and the second in-coupling diffractive optics.

Description

Technical Field

[0001] The present disclosure relates generally to electronic displays and, more particularly, to optical image light guide systems having diffractive optics operable to transmit image-bearing light to a viewer. Background Art

[0002] Head mounted displays (HMDs) are being developed for a range of different 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 world image located 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 to direct the virtual image to the viewer's pupil and achieve this superposition function.

[0003] In general, the optics of an HMD must meet some basic requirements for viewer acceptance, including pupil size and field of view (FOV). Pupil size requirements are based on physiological differences in the viewer's facial structure and the direction of gaze during viewing. It has been found that a minimum entrance pupil diameter of approximately 10 mm is ideal for an average viewer. A wide field of view is desirable for many tasks and operations. In addition, the generated virtual image should have sufficient brightness to ensure visibility and viewer comfort.

[0004] In addition to optical requirements, HMD design must also consider practical factors, such as the acceptable form factor expected to be reduced in size for wearing comfort, weight, cost, and ease of use. Therefore, an image light guide system is needed that provides increased FOV and brightness while maintaining a small form factor. Summary of the invention

[0005] The purpose of the present disclosure is to advance the technology of virtual image presentation using head mounted devices. Advantageously, embodiments of the present disclosure provide an optical coupling solution that is compatible with the general form factor of glasses.

[0006] These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from the following detailed description of the embodiments and the appended claims, and by reference to the accompanying drawings. In an exemplary embodiment, the present invention provides an image light guide for transmitting a virtual image, comprising a first surface and an opposing second surface, and a first in-coupling diffractive optical device arranged along one of the first surface and the second surface, wherein the first in-coupling diffractive optical device comprises a first set of diffractive features. A second in-coupling diffractive optical device arranged along one of the first surface and the second surface, wherein the second in-coupling diffractive optical device comprises a second set of diffractive features. The image light guide also includes an out-coupling diffractive optical device arranged along at least one of the first surface and the second surface, wherein the out-coupling diffractive optical device includes a plurality of regions, each region having a different set of diffractive features from an adjacent region, wherein the plurality of regions include a first region optimized to diffract in-coupled light from the first in-coupling diffractive optical device and the second in-coupling diffractive optical device.

[0007] In an exemplary embodiment, the out-coupling diffractive optical device includes a first region, a second region arranged outside the first region in a first direction, a third region arranged outside the second region in the first direction, a fourth region arranged outside the first region in the second direction, and a fifth region arranged outside the fourth region in the second direction.

[0008] In an exemplary embodiment, the second region and the fourth region are mirrored across the first region, and the third region and the fifth region are mirrored across the first region.

[0009] In an exemplary embodiment, the second region and the fourth region are straight and oriented at opposite angles relative to an imaginary axis that bisects the first region.

[0010] In an exemplary embodiment, the first region includes linear diffractive features oriented parallel to an imaginary axis arranged to bisect the first surface and is parallel to the first surface, wherein the imaginary axis extends between a first edge of the first surface adjacent to the first in-coupling diffractive optical device and the second in-coupling diffractive optical device and a second edge of the first surface adjacent to the out-coupling diffractive optical device.

[0011] In an exemplary embodiment, the third region includes linear diffractive features oriented at a first angle relative to the diffractive features of the first region, and the fifth region includes linear diffractive features oriented at a second angle relative to the diffractive features of the first region. For example, the second angle can be equal to and opposite to the first angle.

[0012] In an exemplary embodiment, the second region includes a first set of linear diffractive features parallel to the diffractive features of the first region and a second set of linear diffractive features parallel to the diffractive features of the third region.

[0013] In an exemplary embodiment, the fourth region includes a first set of linear diffractive features parallel to the diffractive features of the first region and a second set of linear diffractive features parallel to the diffractive features of the fifth region.

[0014] In an exemplary embodiment, the second region includes a diffractive feature having a first grating vector parallel to the grating vector of the first region and a second grating vector parallel to the grating vector of the third region; and wherein the fourth region includes a diffractive feature having a first grating vector parallel to the grating vector of the first region and a second grating vector parallel to the grating vector of the fifth region.

[0015] In an exemplary embodiment, the first region, the second region, the third region and the fourth region of the out-coupling diffractive optical device form a first output region, which is optimized to diffract the image-bearing light beam coupled in by the first in-coupling diffractive optical device, and the first region, the second region, the fourth region and the fifth region of the out-coupling diffractive optical device form a second output region, which is optimized to diffract the image-bearing light beam coupled in by the second in-coupling diffractive optical device.

[0016] In an exemplary embodiment, the present disclosure provides an image source for generating an angle-encoded image-bearing light beam, the image source comprising a light source system; a first beam splitter having two opposite output sides (a polarized portion of the light exits the polarization beam splitter through the two opposite output sides), wherein the polarization beam splitter is operable to polarize light from the light source system into a first light path and a second light path; a second beam splitter arranged in the first light path to receive light emitted from the first beam splitter, and a third beam splitter arranged in the second light path to receive light emitted from the first beam splitter; and a first imaging engine arranged in the first light path to receive light from the second beam splitter, and a second imaging engine arranged in the second light path to receive light from the third beam splitter.

[0017] In an exemplary embodiment, a light source system includes a first wavelength source, a second wavelength source, and a third wavelength source, wherein the first wavelength source, the second wavelength source, and the third wavelength source are operable to emit light incident on a first beam splitter.

[0018] In an exemplary embodiment, the light source system further includes lenses respectively disposed between the wavelength sources to collimate light emitted therefrom.

[0019] In an exemplary embodiment, the first beam splitter includes a polarizing beam splitter operable to split unpolarized light from the light source system into linearly polarized light.

[0020] In an exemplary embodiment, the image source includes a first prism disposed in a first optical path and a second prism disposed in a second optical path, the first prism and the second prism being operable to direct polarized light along the first optical path and the second optical path, respectively.

[0021] In an exemplary embodiment, the first imaging engine and the second imaging engine include a liquid crystal on silicon (LCOS) panel. For example, the LCOS panel is front-illuminated.

[0022] In an exemplary embodiment, the first imaging engine and the second imaging engine include digital light processing (DLP) projectors.

[0023] In an exemplary embodiment, a first wave plate is arranged to redirect polarization of light emitted by a first imaging engine, and a second wave plate is arranged to redirect polarization of light emitted by a second imaging engine. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings are incorporated herein as part of the specification. The accompanying drawings described herein illustrate embodiments of the subject matter currently disclosed and illustrate selected criteria and teachings of the present disclosure. However, the accompanying drawings do not illustrate all possible implementations of the subject matter currently disclosed and are not intended to limit the scope of the present disclosure in any way.

[0025] Figure 1 is a top view of an image light guide with exaggerated thickness to illustrate the propagation of light from an image source along the image light guide to an eyebox where a virtual image can be viewed.

[0026] Figure 2 is a perspective view of an image light guide including in-coupling diffractive optics, steering diffractive optics, and out-coupling diffractive optics for managing the propagation of an image-carrying light beam.

[0027] Figure 3A is a side view of an image light guide according to an exemplary embodiment of the presently disclosed subject matter.

[0028] Figure 3B is based on Figure 3A Side view of an embodiment of an image light guide.

[0029] Figure 4A is based on Figure 3A A top view of an embodiment of an image light guide having an exaggerated thickness.

[0030] Figure 4B is based on Figure 3A A top view of another embodiment of an image light guide having an exaggerated thickness.

[0031] Figure 4C is based on Figure 3AA top view of yet another embodiment of an image light guide having an exaggerated thickness.

[0032] Figure 5 is a side view of an image light guide including a waveguide stack according to an exemplary embodiment of the presently disclosed subject matter.

[0033] Fig. 6A is a top perspective view of an image light guide with an image source according to an exemplary embodiment of the presently disclosed subject matter.

[0034] Figure 6B is a schematic top perspective view of an image light guide with an image source according to an exemplary embodiment of the presently disclosed subject matter.

[0035] Figure 7 is a schematic top view of an image source system according to an exemplary embodiment of the presently disclosed subject matter.

[0036] Figure 8 is based on Figure 7 Image source front view of the system. DETAILED DESCRIPTION

[0037] It should be understood that, unless otherwise expressly stated, the present invention may adopt various alternative orientations and step sequences. It should also be understood that the specific components and systems shown in the drawings and described in the following specification are only exemplary embodiments of the inventive concepts defined herein. Therefore, unless otherwise expressly stated, the specific dimensions, directions or other physical characteristics associated with the disclosed embodiments should not be considered as limitations. In addition, although they may not be, in this part of the application, similar elements in the various embodiments described herein may generally be referred to by similar reference numerals.

[0038] Those skilled in the relevant art will recognize that the elements and techniques described herein can be practiced without one or more specific details, or can be practiced using other methods, components, materials, etc. In some cases, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects of the present disclosure. References to "one embodiment," "exemplary embodiments," or "embodiments" throughout the specification mean that specific features, structures, or characteristics described in conjunction with the embodiment are included in at least one embodiment of the present disclosure. Therefore, the phrases "in one embodiment," "in an exemplary embodiment," or "in an embodiment" that appear throughout the specification do not necessarily refer to the same embodiment. However, in one or more embodiments, the specific features, structures, or characteristics described may be combined in any suitable manner.

[0039] Unless otherwise stated, the terms "first", "second", etc. used herein do not necessarily indicate any sequential, order or priority relationship, but are only used to more clearly distinguish one element from another or one group of elements from another.

[0040] As used herein, the terms "viewer," "operator," "observer," "wearer," and "user" are considered equivalent and refer to a person or machine that wears and / or views images using a device with an imaging light guide.

[0041] The term "set" as used herein refers to a non-empty set, just as the concept of a series of elements or members of a set is widely understood in elementary mathematics. Unless explicitly stated otherwise, the term "subset" as used herein refers to a non-empty proper subset, i.e., a subset of a larger set that has one or more members. For a set S, a subset may include the complete set S. However, a "proper subset" of a set S is strictly contained in the set S and excludes at least one member of the set S.

[0042] As used herein, the terms "coupled," "coupler," or "coupling" in the context of optics refer to a connection through which light propagates from one optical medium or device to another optical medium or device.

[0043] As used herein, the terms "wavelength band" and "wavelength range" are equivalent and have the standard meaning used by those skilled in the color imaging arts to refer to a continuous range of wavelengths of light used to represent a multi-color image.

[0044] As used herein, the term "beam expansion" is intended to refer to replicating a beam through multiple encounters with an optical element to provide an exit pupil expansion in one or more dimensions. Similarly, "expanding" a beam or portion of a beam, as used herein, is intended to replicate the beam through multiple encounters with an optical element to provide an exit pupil expansion in one or more dimensions.

[0045] An optical system, such as an HMD, can produce a virtual image. In contrast to methods used to form 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 images have many inherent advantages over 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 a system that projects a real image. Providing a virtual image also eliminates the need to compensate for screen artifacts, which may be necessary when projecting a real image.

[0046] Figure 1is a schematic diagram showing a simplified cross-sectional view of a conventional configuration of the 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 a front surface 14 and a rear surface 16 parallel to the plane. In this example, the in-coupling diffractive optical device IDO is shown as a transmissive diffraction grating, which is arranged on, within, or otherwise engaged with the front surface 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 into the image light guide 12. The in-coupling diffractive optic IDO may be located on, within or otherwise engaged with the front surface 14 or the rear surface 16 of the image light guide 12 and may be a combination of transmissive or reflective, depending on the direction from which the image-bearing beam WI approaches the image light guide 12 .

[0047] When used as part of a near-eye or head-mounted display system, the in-coupling diffractive optical device IDO of the conventional image light guide system 10 couples an image-carrying beam 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 dimension formed by the image source 18 is first converted into an array of overlapping, angle-dependent, collimated beams encoding different positions in the virtual image for presentation to the in-coupling diffractive optical device IDO. Typically, the rays within each beam forming one of the angle-dependent beams extend in parallel, but the angle-dependent beams are tilted relative to each other by angles that can be defined in two angular dimensions corresponding to the linear dimensions of the image.

[0048] Once the angle-dependent beams are engaged with the in-coupling diffractive optical device IDO, at least a portion of the image-carrying beam WI is diffracted (typically through a first diffraction order) and thereby redirected by the in-coupling diffractive optical device IDO into the planar image light guide 12 as an angle-encoded image-carrying beam WG, which further propagates along the length dimension x of the image light guide 12 between the front surface 14 and the back surface 16 parallel to the plane by total internal reflection (TIR). 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 form of an angle encoding derivable from the parameters of the in-coupling diffractive optical device IDO. The out-coupling diffractive optical device ODO receives the encoded image-carrying beam WG and diffracts (typically also through a first diffraction order) at least a portion of the image-carrying beam WG out of the image light guide 12 (as an image-carrying beam WO) towards a nearby spatial region called the eyebox E, within which the transmitted virtual image can be seen by the eye or other optical components of the viewer. The out-coupling diffractive optical device ODO can be designed symmetrically with respect to the in-coupling diffractive optical device IDO to restore the original angular relationship of the image-bearing beam WI in the angularly related beam at the output of the image-bearing beam WO. In addition, the out-coupling diffractive optical device ODO can modify the positional angular relationship of the original field of view point to produce an output virtual image at a limited focal length.

[0049] However, in order to increase the overlap in one dimension between the angularly related 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 together with the image light guide 12 of finite thickness T 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 extending at least one dimension of the eyebox E that the replicated beams overlap. The extended eyebox E reduces sensitivity to the position of the viewer's eye viewing the virtual image.

[0050] The out-coupling diffractive optical device 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 optical device IDO, the out-coupling diffractive optical device ODO can be located on, in or otherwise engaged with the front surface 14 or the rear surface 16 of the image light guide 12, and can be a combination of transmissive or reflective types, depending on the direction through which the image-carrying beam WG is intended to be emitted from the image light guide 12. In addition, the out-coupling diffractive optical device ODO can be formed as another type of diffractive optical device, such as a volume hologram or other holographic diffractive element, which diffracts the propagating image-carrying beam WG from the image light guide 12 into an image-carrying beam WO propagating toward the eye range E.

[0051] Figure 2 A perspective view of a conventional image light guide system 10 is shown, the system being arranged to extend the eye range E in two dimensions, namely along the x-axis and the y-axis of the intended image. To achieve the eye range extension in the second dimension, the in-coupling diffractive optics IDO are oriented to diffract at least a portion of the image-carrying beam WG along the image light guide 12 along a grating vector k1 towards the intermediate steering optics TO, the grating vector k2 of the intermediate steering optics TO being oriented to diffract at least a portion of the image-carrying beam WG along the image light guide 12 in a reflective mode towards the out-coupling diffractive optics ODO. It should be understood that only a portion of the image-carrying beam WG is diffracted by each of the multiple encounters with the intermediate steering optics TO, thereby laterally replicating each angularly dependent beam of the image-carrying beam WG as they approach the out-coupling diffractive optics ODO. The intermediate steering optics TO redirect the image-carrying beam WG towards the out-coupling diffractive optics ODO (having a grating vector k3) to longitudinally replicate the angularly dependent beam of the image-carrying beam WG in a second direction before exiting 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., grooves, lines or rulings) of the diffractive optical device in 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.

[0052] like Figure 2As shown, the in-coupling diffractive optical device IDO receives an incident image-bearing beam WI, which includes a set of angle-dependent beams corresponding to individual pixels or equivalent positions within an image generated by an image source 18 (such as a projector). The full range of angle-encoded beams used to 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 one-dimensional real displays used with a scanner. In this configuration, the image light guide 12 outputs a set of replicated angle-dependent beams (replicated in two dimensions) by providing multiple encounters of the image-bearing beam WG with the intermediate steering optics TO and the out-coupling diffractive optics ODO in different orientations. In the depicted orientation of the image light guide 12, the intermediate steering optics TO provide eye range expansion in a first dimension (e.g., the y-axis direction), and the out-coupling diffractive optics ODO provide similar eye range expansion in a second dimension (e.g., the x-axis direction). The relative orientation and respective periods d of the diffractive features of the in-coupling optics IDO, the intermediate turning optics TO, and the out-coupling diffractive optics ODO provide eye range extension in two dimensions while preserving the intended relationship between the angularly related beams of the image-carrying beam WI output as the image-carrying beam WO from the image light guide system 10. It should be understood that the period d of the in-coupling diffractive optics IDO, the intermediate turning optics TO, and the out-coupling diffractive optics ODO may each include diffractive features having a common pitch d, wherein the common pitch d may be different for each optical device.

[0053] In the configuration shown, when the image-carrying beam WI input into the image light guide 12 is encoded into different angularly related sets of beams by the in-coupling diffractive optical device IDO, the information required to reconstruct the image is retained by taking into account the systematic effects of the in-coupling diffractive optical device IDO. The intermediate turning optical device TO located at an intermediate position between the in-coupling diffractive optical device IDO and the out-coupling diffractive optical device ODO can be arranged so as not to bring significant changes to the encoding of the image-carrying beam WG. Therefore, the out-coupling diffractive optical device ODO can be arranged in a symmetrical manner relative to the in-coupling diffractive optical device IDO, for example, including diffractive features sharing the same period d. Similarly, the period of the intermediate turning optical device TO can also match the common period of the in-coupling diffractive optical device IDO and the out-coupling diffractive optical device ODO. Although the grating vector k2 of the intermediate turning optics 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 turning optics TO can be oriented at 60 degrees relative to the grating vectors k1 and k3 of the in-coupling diffractive optics IDO and the out-coupling diffractive optics ODO, in this way the image beam WG is turned 120 degrees. By orienting the grating vector k2 of the intermediate turning optics TO at 60 degrees relative to the grating vectors k1 and k3 of the in-coupling diffractive optics IDO and the out-coupling diffractive optics ODO, the grating vectors k1 and k3 of the in-coupling diffractive optics IDO and the out-coupling diffractive optics ODO are also oriented at 60° relative to each other. By basing the grating vector amplitudes on a common pitch shared by the in-coupling diffractive optical device IDO, the intermediate turning diffractive optical device TO, and the out-coupling diffractive optical device ODO, the three grating vectors k1, k2, and k3 (as directed line segments) form an equilateral triangle and add to a zero vector amplitude, which avoids asymmetric effects that may introduce unwanted anomalies (including dispersion). Such asymmetric effects can also be avoided by having grating vectors k1, k2, and k3 that have unequal amplitudes in relative orientations, in which the three grating vectors k1, k2, and k3 add to a zero vector amplitude.

[0054] In a broader sense, regardless of whether the in-coupling optical device IDO uses a grating, hologram, prism, mirror or other mechanism, the image-carrying beam WI guided into the image light guide 12 is effectively encoded by the in-coupling diffractive optical device IDO. Any reflection, refraction and / or diffraction of light that occurs at the input end should be decoded accordingly by the output end to re-form the virtual image presented to the viewer. Regardless of whether any symmetry is maintained between the intermediate turning optical device TO, the in-coupling optical device IDO and the out-coupling diffractive optical device ODO, or regardless of whether any changes in the encoding of the angle-related beams of the image-carrying beam WI occur along the image light guide 12, the intermediate turning optical device TO and the in-coupling diffractive optical device IDO and the out-coupling diffractive optical device ODO can be associated so that the image-carrying beam WO output from the image light guide 12 retains or otherwise maintains the original or desired form of the image-carrying beam W1 to produce the expected virtual image.

[0055] like Figure 2 As shown, the letter "R" represents the orientation of the virtual image visible to a viewer whose eye is located 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 by the image-bearing beam WI. The change in the rotational or angular orientation of the incident image-bearing beam WI about the z-axis relative to the xy plane results in a corresponding symmetrical change in the rotational or angular orientation of the outgoing light from the outcoupling 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 angle-encoded beam of the image-bearing beam WG along one axis of the image (e.g., along the y-axis). The outcoupling diffractive optical device ODO also provides a second dimension of eye range extension by replicating 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 beam WI. The intermediate turning optic 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 rear surfaces of the image light guide 12. It will be appreciated that the representation "R" of the virtual image created by the image source consists of infinitely focused light that requires a lens (such as that in the human eye) to focus the image so that the above orientation can be detected.

[0056] The in-coupling diffractive optics IDO, the steering diffractive optics TO, and the out-coupling diffractive optics ODO together preferably preserve the angular relationship between the light beams of different wavelengths that define the virtual image when transmitted from the offset position to the near-eye position of the viewer through the image light guide 12. While doing so, the in-coupling diffractive optics IDO, the steering diffractive optics TO, and the out-coupling diffractive optics 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 of the angularly related light beams that can be guided into and out of the image light guide 12.

[0057] Figure 3A An exemplary embodiment of a waveguide 102 according to the present disclosure is shown. In the exemplary embodiment, the waveguide 102 includes an at least partially transparent substrate S (see Figures 4A-4C ), which has a front surface 104 and a rear surface 106 parallel to the plane (also Figures 4A-4C ). For example, the waveguide 102 can be made of optical glass or plastic. The waveguide 102 includes a first in-coupling diffractive optical device IDOA and a second in-coupling diffractive optical device IDOB. In one example, the first in-coupling diffractive optical device IDOA and the second in-coupling diffractive optical device IDOB can be laterally offset relative to each other (i.e., in the x or y direction) and can be arranged on the front surface 104 and / or the rear surface 106. In another example, the first in-coupling diffractive optical device IDOA and the second in-coupling diffractive optical device IDOB are laterally offset relative to each other, and at least one of the first or second in-coupling diffractive optical device IDOA, IDOB is arranged on the front surface 104, while the other of the first or second in-coupling diffractive optical device IDOA, IDOB is arranged on the rear surface 106. As shown in FIG. Figure 3A As shown, in an exemplary embodiment, the first in-coupling diffractive optical device IDOA and the second in-coupling diffractive optical device IDOB are symmetrically arranged around an imaginary axis AA that bifurcates the waveguide 102. In the example, the imaginary axis AA bisects the waveguide 102. Figure 3A As shown, the first in-coupling diffractive optical device IDOA includes a first diffraction mode 108, and the second in-coupling diffractive optical device IDOB includes a second diffraction mode 110. The first diffraction mode 108 includes a plurality of diffraction features that are periodic in at least a first direction represented by a grating vector k1. The second diffraction mode 110 includes another plurality of diffraction features that are periodic in at least a second direction represented by a grating vector k2. For example, the first diffraction mode 108 and the second diffraction mode 110 may include linear diffraction features. Although other shapes are possible, the waveguide 102 is typically formed as an inverted trapezoid, for example, where the first in-coupling diffractive optical device IDOA and the second in-coupling diffractive optical device IDOB are arranged close to the longer side of the two parallel sides of the trapezoid.

[0058] Continue to refer Figure 3A In an example embodiment, the waveguide 102 includes an out-coupling diffractive optical device ODO having a plurality of regions (e.g., a first region 112, a second region 114A, a third region 114B, a fourth region 116A, and a fifth region 116B) having diffractive features. The out-coupling diffractive optical device ODO is arranged symmetrically around the imaginary axis AA. In an example embodiment, the first region 112 defines a generally V-shaped and / or triangular region and is centrally arranged within the out-coupling diffractive optical device ODO such that the imaginary axis AA bifurcates the first region 112. The second region 114A is arranged outside the first region 112 in the -x direction (e.g., in Figure 3A 114B is arranged outside the second region 114A in the −x-axis direction (for example, Figure 3B The fourth region 116A and the fifth region 116B are mirror images of the second region 114A and the third region 114B, respectively, across a plane having a surface parallel to the imaginary axis AA. In an exemplary embodiment, the second and fourth regions 114A, 116A are generally straight in shape and are oriented at angles ±α, respectively, relative to the imaginary axis AA. The third and fifth regions 114B, 116B may include a generally triangular shape.

[0059] In an exemplary embodiment, the diffraction features of the first region 112 approximate a straight diffraction feature oriented parallel to the imaginary axis AA and having a grating vector ±k3, the diffraction features of the third region 114B approximate a straight diffraction feature oriented at an angle β relative to the diffraction features of the first region 112 and having a grating vector k4, and the diffraction features of the fifth region 116B approximate a straight diffraction feature oriented at an angle β relative to the diffraction features of the first region 112 and having a grating vector k5. The second region 114A includes diffraction features that define grating vectors k3 and k4. For example, the second region 114A includes overlapping diffraction features of the first region 112 (having grating vector k3) and the third region 114B (having grating vector k4). Similarly, the fourth region 116A includes diffraction features that define grating vectors k3 and k5. For example, the fourth region 116A includes overlapping diffraction features of the first region 112 (having grating vector k3) and the fifth region 116B (having grating vector k5).

[0060] In an exemplary embodiment, the first region 112, the second region 114A, the third region 114B and the fourth region 116A of the out-coupling diffractive optical device ODO are optimized to diffract the image-bearing beam in-coupled by the first in-coupling diffractive optical device IDOA, and the first region 112, the second region 114A, the fourth region 116A and the fifth region 116B of the out-coupling diffractive optical device ODO are optimized to diffract the image-bearing beam in-coupled by the second in-coupling diffractive optical device IDOB. Therefore, the image-bearing beam in-coupled by the first in-coupling diffractive optical device IDOA and the second in-coupling diffractive optical device IDOB utilizes at least the diffraction characteristics of the central first region 112 in its optical path to the eye range E. In other examples, the image-bearing beam in-coupled by the first in-coupling diffractive optical device IDOA and the second in-coupling diffractive optical device IDOB utilizes the diffraction characteristics of the first region 112, the second region 114A and the fourth region 116A.

[0061] Reference now Figure 3B and 6B , the first region 112, the second region 114A, the third region 114B and the fourth region 116A of the out-coupling diffractive optical device ODO may form a first output region 118A, which is optimized to diffract the image-bearing beam incoupled by the first in-coupling diffractive optical device IDOA. The first region 112, the second region 114A, the fourth region 116A and the fifth region 116B of the out-coupling diffractive optical device ODO may form a second output region 118B, which is optimized to diffract the image-bearing beam incoupled by the second in-coupling diffractive optical device IDOB.

[0062] In an example embodiment, the second region 114A of the out-coupling diffractive optical device ODO includes diffractive features including generally diamond-shaped columns, wherein each diamond-shaped column includes two sides arranged generally parallel to the diffractive features of the first region 112 (e.g., perpendicular to the grating vector k3) and two sides generally parallel to the diffractive features of the third region 114B (e.g., perpendicular to the grating vector k4). Similarly, the fourth region 116A may include diffractive features including generally diamond-shaped columns, wherein each diamond-shaped column includes two sides arranged generally parallel to the diffractive features of the first region 112 (e.g., perpendicular to the grating vector k3) and two sides generally parallel to the diffractive features of the fifth region 116B (e.g., perpendicular to the grating vector k5).

[0063] Continue to refer Figure 3AIn an exemplary embodiment, the waveguide 102 provides a first optical path for light of a first wavelength range (e.g., red light of a wavelength range of 620-750 nm) passing through the first region 112, the second region 114A, the third region 114B, and the fourth region 116A of the first in-coupling diffractive optical device IDOA and the out-coupling diffractive optical device ODO, and provides a second optical path for light of a different second wavelength range (e.g., green light of a wavelength range of 500-565 nm) passing through the first region 112, the second region 114A, the fourth region 116A, and the fifth region 116B of the second in-coupling diffractive optical device IDOB and the out-coupling diffractive optical device ODO. The partitioned out-coupling diffractive optical device ODO enables the waveguide 102 to utilize the same mode of diffraction features in the first region 112 (as well as the diffraction features in the second region 114A and the fourth region 116A) for the two optical paths. With respect to alignment of the virtual images, utilizing the same pattern of diffraction features for both optical paths in the first region 112, the second region 114A, and the fourth region 116A can prevent disconnection in the waveguide 102 where the imaged light meets in the absence of physically overlapping diffractive optical device (e.g., diffraction grating) regions.

[0064] In addition, the diffractive features in the first region and some of the diffractive features in the second region 114A and the fourth region 116A of the out-coupling diffractive optical device ODO are vertically oriented (i.e., oriented parallel to the imaginary axis AA) to prevent image noise generated by an overhead point source when in use. In other words, the vertical orientation of the diffractive features in the first region 112 (and in at least some examples the second region 114A and the fourth region 116A) prevents or mitigates "rainbows" caused by overhead point sources.

[0065] Reference now Figure 4A In an exemplary embodiment, the first in-coupling diffractive optical device IDOA, the second in-coupling diffractive optical device IDOB, and the out-coupling diffractive optical device ODO are arranged on the front surface 104 of the waveguide 102. Similarly, in another exemplary embodiment, the first in-coupling diffractive optical device IDOA, the second in-coupling diffractive optical device IDOB, and the out-coupling diffractive optical device ODO may be arranged on the rear surface 106 of the waveguide 102. In another embodiment, the first in-coupling diffractive optical device IDOA and the second in-coupling diffractive optical device IDOB are arranged on the front surface 104 of the waveguide 102, and the out-coupling diffractive optical device ODO is arranged on the rear surface 106 of the waveguide 102. Now referring to Figure 4B In an exemplary embodiment, the first in-coupling diffractive optical device IDOA is arranged on the front surface 104, and the second in-coupling diffractive optical device IDOB is arranged on the back surface 106 of the waveguide 102. Similarly, Figure 4C As shown, in an example embodiment, a first in-coupling diffractive optical device IDOA may be arranged on the rear surface 106 , while a second in-coupling diffractive optical device IDOB may be arranged on the front surface 104 of the waveguide 102 .

[0066] Reference now Figure 5 , six effective diffraction regions are formed by using two waveguides (e.g., the first waveguide 102A and the second waveguide 102B) in the waveguide stack, and are helpful to transmit a multi-color image to the eye movement range E. For example, the first waveguide 102A may include two in-coupling diffractive optical devices IDOA and IDOB, wherein the diffractive features within the two in-coupling diffractive optical devices IDOA, IDOB of the first waveguide 102A are optimized for an in-coupled image-bearing beam of a first wavelength range, such as red light, and the second waveguide 102B may include two in-coupling diffractive optical devices DOA and IDOB, wherein the diffractive features within the two in-coupling diffractive optical devices IDOA, IDOB of the second waveguide 102B are optimized for an in-coupled image-bearing beam of a different second wavelength range, such as green light and / or blue light. In these examples, the first in-coupling diffractive optical device IDOA of the first waveguide 102A and the first in-coupling diffractive optical device IDOA of the second waveguide 102B are coaxial about an imaginary axis that is arranged to pass through the two first in-coupling diffractive optical devices IDOA and pass through two planar surfaces of the first waveguide 102A (e.g., the imaginary axis is oriented perpendicular to the planar surfaces of the waveguides). Similarly, the second in-coupling diffractive optical device IDOB of the first waveguide 102A and the second in-coupling diffractive optical device IDOB of the second waveguide 102B are coaxial about an imaginary axis that is arranged to pass through the two second in-coupling diffractive optical devices IDOB and pass through two planar surfaces of the first waveguide 102A (e.g., the imaginary axis is oriented perpendicular to the planar surfaces of the waveguides). Therefore, two image sources or a single image source with a separated exit pupil can utilize six different diffractive regions or zones (e.g., diffractive optical devices) to form a full multi-color virtual image with a wide FOV using two waveguides in a single waveguide stack.

[0067] Reference now Fig. 6A and 6B In an exemplary embodiment, the image light guide system 200 including the waveguides 102, 102A, 102B, or 102A and 102B also includes two image sources 18A, 18B. Fig. 6A and 6BAs shown, one or more optical couplers 202, such as but not limited to prisms, can be used to direct the image-bearing light to the in-coupling diffractive optical devices IDOA, IDOB, respectively. The first image source 18A directs a first portion of the image-bearing light to the first in-coupling diffractive optical device IDOA, for example, via the optical coupler 202A. The second image source 18B directs a second portion of the image-bearing light to the second in-coupling diffractive optical device IDOB, for example, via the optical coupler 202B. In an exemplary embodiment, the first and second image sources 18a, 18B are arranged in a lateral orientation relative to each other. For example, the first image source 18A can be arranged to be approximately parallel to the imaginary axis AA (such as Figure 3A As shown), and the second image source 18B can be arranged to be approximately perpendicular to the first image source 18A.

[0068] In an exemplary embodiment, a first image source 18A is operable to emit image-carrying light corresponding to a first half of the field of view (FOV) of an image delivered to the eye-tracking range, and a second image source 18B is operable to emit image-carrying light corresponding to a second half of the field of view (FOV) of an image delivered to the eye-tracking range. A first in-coupling diffractive optical device IDOA is optimized to diffract the image-carrying light from the image source 18A, and a second in-coupling diffractive optical device IDOB is optimized to diffract the image-carrying light from the image source 18B. This arrangement enables each in-coupling diffractive optical device IDOA, IDOB to diffract half of the image delivered to the eye-tracking range into the waveguide 102, and when out-coupled from the out-coupling diffractive optical device ODO, these half images are combined into a single wide FOV virtual image. This provides the advantage of doubling the FOV of the image delivered to the user without compromising the brightness of the virtual image. In an exemplary embodiment, the FOV emitted by each image source 18A, 18B may be greater than half of the total FOV, such that the FOV emitted by each image source 18A, 18B overlap within the eye range.

[0069] Reference now Figure 7 and Figure 8 In an exemplary embodiment, the image light guide system 200 including the waveguide 102 includes an image source 18C having a light source system 19. The light source system 19 may include a first wavelength source 302A (e.g., a red wavelength range source), a second wavelength source 302B (e.g., a green wavelength range source), and a third wavelength source 302C (e.g., a blue wavelength range source), which are operable to emit light incident on a combiner 304 (e.g., an X-cube). Lenses 306A, 306B, 306C, respectively disposed between the wavelength sources 302A, 302B, 302C, may be used to collimate the light emitted by the wavelength sources 302A, 302B, 302C. For example, the lenses 306A, 306B, 306C may be formed of, but are not limited to, glass or plastic.

[0070] In an example embodiment, image source 18C includes polarizing beam splitter 310. Unpolarized light 308 is emitted from combiner 304 of light source system 19 and is incident on polarizing beam splitter 310. Polarizing beam splitter 310 is configured to split the light path by polarization. In an example embodiment, polarizing beam splitter 310 includes a cube beam splitter having a polarizing coating 312 arranged along a diagonal of the cube and a reflector coating paired with a quarter wave plate 314 (e.g., at 45°) arranged along a surface 316 of the cube, wherein surface 316 is arranged transverse to the path of unpolarized light 308.

[0071] For example, the polarization beam splitter 310 splits the unpolarized light 308 into S-polarized light 318A and P-polarized light 318B. Portions of the linearly polarized light 318A, 318B are emitted from opposite sides of the polarization beam splitter 310 and are incident on the first prism 320A and the second prism 320B, respectively. In an example embodiment, the first and second prisms 320A, 320B are operable to direct the linearly polarized light 318A, 318B to a desired nominal angular path. For example, the first prism 320A and the second prism 320B may be wedge prisms.

[0072] like Figure 7 As shown, in an example embodiment, image source 18C includes lenses 322A, 322B optically arranged between polarization beam splitter 310 and uniformization elements 324A, 324B. Lenses 322A, 322B are used in conjunction with lenses 306A, 306B, 306C to collimate light emitted by wavelength sources 302A, 302B, 302C. Uniformization elements 324A, 324B are configured to make the pupil more uniform. For example, uniformization elements 324A, 324B may be light pipes, lenslet arrays, or scattering elements.

[0073] Reference now Figure 8, which shows a top schematic view of an image source 18C, which in an example embodiment includes beam splitters 326A, 326B arranged in the optical path to intercept light emitted from the homogenizing elements 324A, 324B, respectively. The respective beam splitters 326A, 326B direct linearly polarized light 318A, 318B to a first liquid crystal on silicon (LCOS) panel 328A and a second LCOS panel 328B, respectively. The first and second LCOS panels 328A, 328B are front-illuminated. The collimated light leaves the first LCOS panel 328A and the second LCOS panel 328B and is incident on the in-coupling diffractive optical devices IDOA, IDOB, respectively. In other words, the image source 18C includes two imaging engines, including LCOS panels 328A, 328B, which are configured to receive light generated by a single light source system 19. In one or more example embodiments, the imaging optical device can be disposed downstream of the LCOS panels 328A, 328B. Because LCOS panels are typically polarization sensitive, in some examples, some form of retarder or wave plate may be placed between polarizing beam splitter 310 and one of the LCOS panels (e.g., 328A or 328B) to optimize the orientation of the linear polarization of a portion of the light exiting polarizing beam splitter 310. In this manner, both portions of the linearly polarized light will be oriented for optimal engagement with both LCOS panels.

[0074] Advantageously, this design provides two display panels illuminated by one (polychromatic) light source system 19 (e.g., light sources 302A, 302B, 302C), and utilizes light of each polarization by sending linearly polarized light 318A, 318B to two corresponding LCOS panels 328A, 328B, thereby improving system efficiency. In an exemplary embodiment, a quarter wave plate 330A, 330B is used to align the polarization of light emitted by one or more of the panels 328A, 328B with the diffractive features of the in-coupling diffractive optical devices IDOA, IDOB to improve the overall coupling efficiency within the waveguide 102. As described above, LCOS panels are typically polarization sensitive. This means that, when coupled with a polarizing beam splitter, most image sources utilize only half of the potential light intensity generated by the light source system, while the system does not use the other portion of the linearly polarized light. The example configuration described herein allows the use of two linearly polarized portions of light by using linearly polarized light that passes through a portion of the first LCOS panel 328A and linearly polarized light that passes through a second portion of the opposite polarization of the second LCOS panel 328B. Thus, the above-described example configuration allows for utilization of all or a majority of the light generated by the light source system 19. This example configuration enables a potential doubling of the outcoupling efficiency without doubling the power requirements of the system.

[0075] In another embodiment, the first LCOS panel 328A and the second LCOS panel 328B are replaced by a digital light processing (DLP) projector. Advantageously, this design does not require the unpolarized light 308 to be polarized by the polarizing beam splitter 310, and thus the beam splitter can be used to direct the light into two optical paths.

[0076] One or more features of the embodiments described herein may be combined to create additional embodiments that are not depicted. Although various embodiments have been described in detail above, it should be understood that they are presented by way of example and not limitation. Those skilled in the relevant art will appreciate that 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 should be considered illustrative in all respects, rather than 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 for transmitting a virtual image, comprising: a first surface and an opposing second surface; a first in-coupling diffractive optic disposed along one of the first surface and the second surface, wherein the first in-coupling diffractive optic comprises a first set of diffractive features; a second in-coupling diffractive optic disposed along one of the first surface and the second surface, wherein the second in-coupling diffractive optic comprises a second set of diffractive features, and an out-coupling diffractive optical device arranged along at least one of the first surface and the second surface, wherein the out-coupling diffractive optical device includes a plurality of regions, each region having a different set of diffractive features from an adjacent region, wherein the plurality of regions includes a first region optimized to diffract in-coupled light from the first in-coupling diffractive optical device and the second in-coupling diffractive optical device.

2. The image light guide of claim 1, wherein: The out-coupling diffractive optical device includes the first region, a second region arranged outside the first region in a first direction, a third region arranged outside the second region in the first direction, a fourth region arranged outside the first region in a second direction, and a fifth region arranged outside the fourth region in the second direction.

3. The image light guide of claim 2, wherein: The second region and the fourth region are mirrored across the first region, and the third region and the fifth region are mirrored across the first region.

4. The image light guide of claim 2 or 3, wherein the second region and the fourth region are straight and oriented at opposite angles relative to an imaginary axis bisecting the first region.

5. The image light guide according to any one of claims 1 to 4, wherein: The first region comprises linear diffractive features oriented parallel to an imaginary axis arranged to bisect the first surface, and the first region is parallel to the first surface, wherein the imaginary axis extends between a first edge of the first surface adjacent to the first in-coupling diffractive optical device and the second in-coupling diffractive optical device and a second edge of the first surface adjacent to the out-coupling diffractive optical device.

6. The image light guide of claim 5, wherein the third region comprises linear diffraction features oriented at a first angle relative to the diffraction features of the first region, and the fifth region comprises linear diffraction features oriented at a second angle relative to the diffraction features of the first region.

7. The image light guide of claim 6, wherein: The second angle is equal to and opposite to the first angle.

8. The image light guide according to claim 6 or 7, wherein: The second region includes a first set of linear diffractive features parallel to the diffractive features of the first region, and a second set of linear diffractive features parallel to the diffractive features of the third region.

9. An image light guide according to claim 6 or 7, wherein the fourth region includes a first set of linear diffraction features parallel to the diffraction features of the first region, and a second set of linear diffraction features parallel to the diffraction features of the fifth region.

10. The image light guide according to claim 6 or 7, wherein: The second region includes a diffractive feature having a first grating vector parallel to the grating vector of the first region and a second grating vector parallel to the grating vector of the third region; and wherein the fourth region includes a diffractive feature having a first grating vector parallel to the grating vector of the first region and a second grating vector parallel to the grating vector of the fifth region.

11. The image light guide of claim 2, wherein: The first region, the second region, the third region and the fourth region of the out-coupling diffractive optical device form a first output region, which is optimized to diffract the image-bearing light beam incoupled by the first in-coupling diffractive optical device, and the first region, the second region, the fourth region and the fifth region of the out-coupling diffractive optical device form a second output region, which is optimized to diffract the image-bearing light beam incoupled by the second in-coupling diffractive optical device.

12. An image source for generating an angle-coded image-bearing beam, comprising: Light source system; a first beam splitter having two opposing output sides through which polarized portions of light exit the polarizing beam splitter, wherein the polarizing beam splitter is operable to polarize light from the light source system into a first optical path and a second optical path; a second beam splitter disposed in the first optical path to receive light emitted from the first beam splitter, and a third beam splitter disposed in the second optical path to receive light emitted from the first beam splitter; as well as a first imaging engine disposed in the first optical path to receive light from the second beam splitter, and a second imaging engine disposed in the second optical path to receive light from the third beam splitter.

13. The image source of claim 12, wherein the light source system comprises: The first wavelength source, a second wavelength source, and A third wavelength source, wherein the first wavelength source, the second wavelength source, and the third wavelength source are operable to emit light incident on the first beam splitter.

14. The image source according to claim 13, wherein the light source system comprises lenses respectively arranged between the wavelength sources to collimate the light emitted by the wavelength sources.

15. The image source of claim 12, wherein the first beam splitter comprises a polarizing beam splitter operable to split unpolarized light from the light source system into linearly polarized light.

16. The image source of claim 12, further comprising a first prism disposed in the first optical path and a second prism disposed in the second optical path, wherein the first prism and the second prism are operable to direct the polarized light along the first optical path and the second optical path, respectively.

17. The image source of claim 12, wherein the first imaging engine and the second imaging engine comprise liquid crystal on silicon (LCOS) panels.

18. The image source of claim 17, wherein the LCOS panel is front-illuminated.

19. The image source of claim 12, wherein the first imaging engine and the second imaging engine comprise digital light processing (DLP) projectors.

20. The image source of claim 17, further comprising a first wave plate arranged to redirect polarization of light emitted by the first imaging engine, and a second wave plate arranged to redirect polarization of light emitted by the second imaging engine.

Images