Patent Application
20240094456
The present disclosure relates generally to electronic displays and more particularly to displays utilizing image light guides with diffractive optics to convey image-bearing light to a viewer.
Head-Mounted Displays (HMDs) and virtual image near-eye displays are being developed for a range of diverse uses, including military, commercial, industrial, firefighting, and entertainment applications. For many of these applications, there is value in forming a virtual image that can be visually superimposed over the real-world image that lies in the field of view of the HMD user. An optical image light guide may convey image-bearing light to a viewer in a narrow space for directing the virtual image to the viewer's pupil and enabling this superposition function.
Although conventional image light guide arrangements have provided significant reduction in bulk, weight, and overall cost of near-eye display optics, further improvements are needed. In some instances, the size of the eyebox is constrained, forcing HMD designs to limit tolerances for movement and device placement. Additionally, light can often be unevenly distributed over the visual field, leading to hot spots, such as higher levels of light within the center of the visual field and lower light levels within the visual field periphery. Another difficulty with conventional image light guide arrangements relates to beam management functions within the waveguide. For example, beam expansion and light distribution functions can increase the size of waveguides as well as their manufacturing cost and complexity.
In a first exemplary embodiment, an image light guide for conveying a virtual image includes a substrate operable to propagate image-bearing light beams along a length thereof. An in-coupling diffractive optic is formed along the substrate and is operable to diffract image-bearing light beams into the substrate in an angularly encoded form. An out-coupling diffractive optic is formed along the substrate, wherein the out-coupling diffractive optic is operable to diffract the image-bearing light beams from the substrate in an angularly decoded form. The in-coupling diffractive optic has three pluralities of periodic diffractive structures, and the out-coupling diffractive optic has at least two pluralities of periodic diffractive structures. The two pluralities of periodic diffractive structures of the out-coupling diffractive optic are parallel with two of the three pluralities of periodic diffractive structures of the in-coupling diffractive optic.
The accompanying drawings are incorporated herein as part of the specification. The drawings described herein illustrate embodiments of the presently disclosed subject matter and are illustrative of 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.
It is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific assemblies and systems illustrated in the attached drawings and described in the following specification are simply exemplary embodiments of the inventive concepts defined herein. Hence, specific dimensions, directions, or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting, unless expressly stated otherwise. Also, although they may not be, like elements in various embodiments described herein may be commonly referred to with like reference numerals within this section of the application.
Where they are used herein, the terms “first”, “second”, and so on, do not necessarily denote any ordinal, sequential, or priority relation, but are simply used to more clearly distinguish one element or set of elements from another, unless specified otherwise.
Where used herein, the term “exemplary” is meant to indicate “an example of”, and is not intended to suggest any preferred or ideal embodiment.
Where used herein, the terms “viewer”, “operator”, “observer”, and “user” are considered equivalents and refer to the person or machine who wears and/or views images using a device having an imaging light guide.
Where used herein, the term “set” refers to a non-empty set, as the concept of a collection of elements or members of a set is widely understood in elementary mathematics. The term “subset”, unless otherwise explicitly stated, is used herein to refer to a non-empty proper subset, that is, to a subset of the larger set, having one or more members. For a set S, a subset may comprise the complete set S. A “proper subset” of set S, however, is strictly contained in set S and excludes at least one member of set S.
Where used herein, the terms “coupled,” “coupler,” or “coupling” in the context of optics refer to a connection by which light travels from one optical medium or device to another optical medium or device.
Where used herein, the term “beam expansion” is intended to mean replication of a beam via multiple encounters with an optical element to provide exit pupil expansion in one or more directions. Similarly, as used herein, to “expand” a beam, or a portion of a beam, is intended to mean replication of a beam via multiple encounters with an optical element to provide exit pupil expansion in one or more directions.
An optical system, such as a HMD, can produce a virtual image. In contrast to methods for forming a real image, a virtual image is not formed on a display surface. That is, if a display surface were positioned at the perceived location of a virtual image, no image would be formed on that surface. Virtual images have a number of inherent advantages for augmented reality presentation. For example, the apparent size of a virtual image is not limited by the size or location of a display surface. Additionally, the source object for a virtual image may be small; for example, a magnifying glass provides a virtual image of an object. In comparison with systems that project a real image, a more realistic viewing experience can be provided by forming a virtual image that appears to be some distance away. Providing a virtual image also obviates the need to compensate for screen artifacts, as may be necessary when projecting a real image.
An image light guide may utilize image-bearing light from a light source such as a projector to display a virtual image. For example, collimated, relatively angularly encoded, light beams from a projector are coupled into a planar waveguide by an input coupling such as an in-coupling diffractive optic, which can be mounted or formed on a surface of the planar waveguide or buried within the waveguide. Such diffractive optics can be formed as diffraction gratings, holographic optical elements (HOEs) or in other known ways. For example, the diffraction grating can be formed by surface relief. After propagating along the waveguide, the diffracted light can be directed back out of the waveguide by a similar output coupling such as an out-coupling diffractive optic, which can be arranged to provide pupil expansion along one dimension of the virtual image. In addition, a turning grating can be positioned on/in the waveguide to provide pupil expansion in an orthogonal dimension of the virtual image. The image-bearing light output from the waveguide provides an expanded eyebox for the viewer.
As illustrated in
When used as a part of a near-eye display system, the in-coupling diffractive optic IDO couples the image-bearing light WI from a real, virtual or hybrid image source 18 into the substrate S of the planar waveguide 22. Any real image or image dimension is first converted into an array of overlapping angularly related beams encoding the different positions within an image for presentation to the in-coupling diffractive optic IDO. Typically, the rays within each bundle forming one of the angularly related beams extend in parallel, but the angularly related beams are relatively inclined to each other through angles that can be defined in two angular dimensions corresponding to linear dimensions of the image.
The image-bearing light WI is diffracted (generally through a first diffraction order) and thereby redirected by in-coupling diffractive optic IDO into the planar waveguide 22 as angularly encoded image-bearing light beams WG for further propagation along a length dimension X of the planar waveguide 22 by Total Internal Reflection (“TIR”) from the plane parallel front and back surfaces 12, 14. Although diffracted into a generally more condensed range of angularly related beams in keeping with the boundaries set by TIR, the image-bearing light WG preserves the image information in an angularly encoded form that is derivable from the parameters of the in-coupling diffractive optic IDO. The out-coupling diffractive optic ODO receives the encoded image-bearing light WG and diffracts (also generally through a first diffraction order) the image-bearing light WG out of the planar waveguide 22 as the image-bearing light WO toward a region of space referred to as an eyebox E, within which the transmitted virtual image can be seen by a viewer's eye. Generally, the out-coupling diffractive optic ODO is designed symmetrically with respect to the in-coupling diffractive optic IDO to restore the original angular relationships of the image-bearing light WI among outputted angularly related beams of the image-bearing light WO. However, to increase one dimension of overlap among the angularly related beams populating the eyebox E within which the virtual image can be seen, the out-coupling diffractive optic ODO is arranged, together with a limited thickness T of the planar waveguide 22, to encounter the image-bearing light WG multiple times and to diffract only a portion of the image-bearing light WG on each encounter. The multiple encounters along the length of the out-coupling diffractive optic ODO have the effect of enlarging one dimension of each of the angularly related beams of the image-bearing light WO (i.e., beam expansion) thereby expanding one dimension of the eyebox E within which the beams overlap. The expanded eyebox E decreases sensitivity to the position of a viewer's eye for viewing the virtual image. Embodiments of the out-coupling diffractive optic ODO can modify the original field points' positional angular relationships producing an output virtual image at a finite focusing distance.
As described above, out-coupling diffractive optics with refractive index variations along a single dimension can expand one dimension of the eyebox by replicating the individual angularly related beams in their direction of propagation along the waveguide between encounters with the out-coupling diffractive optic. In addition, out-coupling diffractive optics with refractive index variations along a second dimension can expand a second dimension of the eyebox and provide two-dimensional expansion of the eyebox. The refractive index variations along a first dimension of the out-coupling diffractive optic can be arranged to diffract a portion of each beam's energy out of the waveguide upon each encounter therewith through a desired first order of diffraction, while another portion of the beam's energy is preserved for further propagation in its original direction through a zero order of diffraction. The refractive index variations along a second dimension of the out-coupling diffractive optic can be arranged to diffract a portion of each beam's energy upon each encounter therewith through a desired first order of diffraction in a direction angled relative to the beam's original direction of propagation, while another portion of the beam's energy is preserved for further propagation in its original direction through a zero order of diffraction.
The out-coupling diffractive optic ODO is shown as a transmissive-type diffraction grating arranged on the back surface 14 of the planar waveguide 22. However, like the in-coupling diffractive optic IDO, the out-coupling diffractive optic ODO can be located on the front surface 12 or the back surface 14 of the planar waveguide 22 and be of a transmissive or reflective-type in a combination that depends, at least in part, upon the direction through which the image-bearing light WG is intended to exit the planar waveguide 22.
As illustrated in
As illustrated in
While the image-bearing light WI input into the image light guide 10 is encoded into a different set of angularly related beams by the in-coupling diffractive optic IDO, the information required to reconstruct the image is preserved by accounting for the systematic effects of the in-coupling diffractive optic IDO. The intermediate optic TO, located in an intermediate position between the in-coupling and out-coupling diffractive optics IDO, ODO, is typically arranged so that it does not induce any significant change on the encoding of the image-bearing light WG. The out-coupling diffractive optic ODO is typically arranged in a symmetric fashion with respect to the in-coupling diffractive optic IDO, e.g., including diffractive features sharing the same period. Similarly, the period of the intermediate optic TO also typically matches the common period of the in-coupling and out-coupling diffractive optics IDO, ODO. As illustrated in
The image-bearing light WI that is diffracted into the planar waveguide 22 is effectively encoded by the in-coupling diffractive optic IDO, whether the in-coupling diffractive optic IDO uses gratings, holograms, prisms, mirrors, or some other mechanism. Any reflection, refraction, and/or diffraction of light that takes place at the in-coupling diffractive optic IDO must be correspondingly decoded by the out-coupling diffractive optic ODO to re-form the virtual image that is presented to the viewer. The intermediate optic TO, placed at an intermediate position between the in-coupling and out-coupling diffractive optics IDO, ODO, is typically designed and oriented so that it does not induce any change on the encoded light. The out-coupling diffractive optic ODO decodes the image-bearing light WG into its original or desired form of angularly related beams that have been expanded to fill the eyebox E.
Whether any symmetries are maintained or not among the intermediate optic TO and the in-coupling and out-coupling diffractive optics IDO, ODO or whether any change to the encoding of the angularly related beams of the image-bearing light WI takes place along the planar waveguide 22, the intermediate optic TO and the in-coupling and out-coupling diffractive optics IDO, ODO are related so that the image-bearing light WO that is output from the planar waveguide 22 preserves or otherwise maintains the original or desired form of the image-bearing light WI for producing the intended virtual image.
The letter “R” represents the orientation of the virtual image that is visible to the viewer whose eye is in the eyebox E. As shown, the orientation of the letter “R” in the represented virtual image matches the orientation of the letter “R” as encoded by the image-bearing light WI. A change in the rotation about the z axis or angular orientation of incoming image-bearing light WI with respect to the x-y plane causes a corresponding symmetric change in rotation or angular orientation of outgoing light from out-coupling diffractive optic ODO. From the aspect of image orientation, the intermediate optic TO typically acts as a type of optical relay, providing expansion of the angularly encoded beams of the image-bearing light WG along one axis (e.g., along the y-axis) of the image. The out-coupling diffractive optic ODO further expands the angularly encoded beams of the image-bearing light WG along another axis (e.g., along the x-axis) of the image while maintaining the original orientation of the virtual image encoded by the image-bearing light WI. As illustrated in
The present disclosure provides for an image light guide having improved diffraction efficiency and image-bearing light output intensity across the output aperture. More specifically, the present disclosure provides for, inter alia, a waveguide having a compound in-coupling diffractive optic and a compound out-coupling diffractive optic operable to expand image-bearing light beams in two-dimensions and output the expanded image-bearing light beams toward an eyebox.
As illustrated in
In an embodiment, the out-coupling diffractive optic ODO comprises first and second sets of periodic out-coupling diffractive structures 110, 112. The first and second sets of periodic out-coupling diffractive structures 110, 112 form a compound diffractive optic operable to expand and out-couple image-bearing light from the out-coupling diffractive optic ODO. In an embodiment, the first and second sets of periodic out-coupling diffractive structures 112 comprise diffraction gratings (e.g., linear rulings) and the diffraction gratings of the first set of periodic out-coupling diffractive structures 110 are crossed with the diffraction gratings of the second set of periodic out-coupling diffractive structures 112. In an embodiment, as illustrated in
The first and second sets of periodic out-coupling diffractive structures 110, 112 have fourth and fifth grating vectors k4, k5 extending normal to the periodic diffractive structures 110, 112, respectively. In an embodiment, the grating vector k4 is offset from the in-coupling grating vector k1 and from the x-axis by sixty-degrees (+60°), and the grating vector k5 is offset from the in-coupling grating vector k1 and the x-axis by negative sixty-degrees (−60°).
In operation, at least a portion of image-bearing light beams incident upon the first, second, and third sets of periodic in-coupling diffractive structures 104, 106, 108 undergo diffraction and are directed into the image light guide 100 as image-bearing light WG for further propagation within the image light guide 100 by TIR and/or by diffraction reflection. To illustrate one or more properties of the presently disclosed embodiments, the image light guide 100 is described below, inter alia, in terms of the optical paths of one or more portions of a beam of image-bearing light WI that is arranged normal to the plane of the in-coupling diffractive optic IDO when incident thereon, unless otherwise stated. However, persons skilled in the art will recognize that these descriptions are not limiting, and that the image-bearing light WI incident upon the in-coupling diffraction optic IDO may be arranged at any angle for which the system is optimized.
For example, where a central ray of a beam of image-bearing light WI is incident upon the in-coupling diffractive optic IDO along the normal to the in-coupling diffractive optic IDO, a portion of the image-bearing light WI is incident upon each of the first, second, and third sets of periodic in-coupling diffractive structures 104, 106, 108. In this example, portions of the image-bearing light WI are directed parallel to the directions of the first grating vector k1, the second grating vector k2, and the third grating vector k3 towards the out-coupling diffractive optic ODO. The second set of periodic in-coupling diffractive structures 106 and the third set of periodic in-coupling diffractive structures 108 direct portions of the image-bearing light toward the outer regions (in the y-axis direction) of the out-coupling diffractive optic ODO. Directing portions of the image-bearing light incident upon the in-coupling diffractive optic IDO toward the outer regions (in the y-axis direction) of the out-coupling diffractive optic ODO reduces the intensity of the image-bearing light out-coupled from the center (in the y-axis direction) of the out-coupling diffractive optic ODO. This configuration reduces or eliminates a so-called hotspot in the eyebox.
As illustrated in the detail view of
Referring back to
With continued reference to
In an embodiment, the depth of the periodic diffractive structures 106, 108, 110, 112 in the in-coupling diffractive optic IDO and the out-coupling diffractive optic ODO is the same. In another embodiment, the depth of periodic diffractive structures 104, 106, 108, 110, 112 are varied to increase the efficiency of selected orders of diffraction. For example, the second and third sets of periodic in-coupling diffractive structures 106, 108 may have a greater depth than the first set of periodic in-coupling diffractive structures 104 and the first and second sets of periodic out-coupling diffractive structures 110, 112.
As illustrated in
With continued reference to
A portion of the image-bearing light incident upon the first and second sets of periodic intermediate diffractive structures 122, 124 may be out-coupled from the image light guide 100. However, this image-bearing light that is out-coupled at the intermediate diffractive optic TDO is outside of the eyebox, and therefore does not affect the formation of the virtual image.
As illustrated in
The image light guide 100 includes a first intermediate diffractive optic TDO1 located at least partially within the path of a portion of in-coupled image-bearing light WG. In an embodiment, where the image-bearing light is incident upon the in-coupling diffractive optic IDO generally perpendicular to the plane thereof, the first intermediate diffractive optic TDO1 is located at least partially within the path of image-bearing light propagating generally parallel with the first grating vector k2. The portion 116A of the first intermediate diffractive optic TDO1 extends at least partially about the in-coupling diffractive optic IDO such that image-bearing light diffracted generally parallel with the first grating vectors k2 is incident upon the portion 116A of the first intermediate diffractive optic TDO1. The image light guide 100 also includes a second intermediate diffractive optic TDO2 located at least partially within the path of a portion of in-coupled image-bearing light WG. In an embodiment, where the image-bearing light is incident upon the in-coupling diffractive optic IDO generally perpendicular to the plane thereof, the second intermediate diffractive optic TDO2 is located at least partially within the path of image-bearing light propagating generally parallel with the second grating vector k3. The portion 116B of the second intermediate diffractive optic TDO2 extends at least partially about the in-coupling diffractive optic IDO such that image-bearing light diffracted generally parallel with the second grating vectors k3 is incident upon the portion 116B of the second intermediate diffractive optic TDO2.
As illustrated in
In embodiments of the present disclosure, the periodic structures may be, but are not limited to, straight line diffractive features, circular posts, or elliptical posts. For example,
Persons skilled in the art will recognize that in one or more embodiments of the diffractive patterns illustrated in
As illustrated in
Blue light from the projector 18 that is incident upon the stacked image light guide assembly 400 transmits through the in-coupling diffractive optic IDO1 of the first image light guide 402 and is diffracted at the in-coupling diffractive optic IDO2 of the second image light guide 404. The diffracted blue light is then conveyed via TIR through the second image light guide substrate S2 and directed to the out-coupling diffractive optic ODO2 of the second image light guide 404. Red light from the projector 18 that is incident upon the stacked image light guide assembly 400 is diffracted at the in-coupling diffractive optic IDO1 of the first image light guide 402. The diffracted red light is then conveyed via TIR through the first image light guide substrate S1 and directed to the out-coupling diffractive optic ODO1 of the first image light guide 402.
The perspective view of
One or more features of the embodiments described herein may be combined to create additional embodiments which are not depicted. While various embodiments have been described in detail above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant arts that the disclosed subject matter may be embodied in other specific forms, variations, and modifications without departing from the scope, spirit, or essential characteristics thereof. The embodiments described above are therefore to be considered in all respects as illustrative, and not restrictive. The scope of the invention is indicated by the appended claims, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2022/013329 | 1/21/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63140432 | Jan 2021 | US |
