Binocular alignment of rigid frames for near-eye displays

Abstract

A method of aligning images in a near-eye binocular display system, comprising: providing a substantially rigid binocular frame operable to receive two or more planar waveguides, each of the two or more planar waveguides including an in-coupling diffractive optical element operable to diffract an image-bearing light beam from an image source into the waveguide, and an out-coupling diffractive optical element operable to diffract the image-bearing light beam from the waveguide towards the eyebox, the in-coupling diffractive optical element operable to in-couple light incident from a first direction and the out-coupling diffractive optical element operable to out-couple light in the first direction, fixing the binocular frame to a fixed alignment mount, positioning a first projector to the right of the frame to project a first image, and projecting the first image onto a screen without the one or more planar waveguides in place.

Description

[Technical Field]

[0001] The present disclosure relates generally to electronic display devices worn by a viewer to form virtual images for the left and right eyes, and more particularly to binocular alignment in a head-mounted display (HMD).

[0002] HMDs are being developed for a wide range of applications, including military, commercial, industrial, firefighting, and entertainment applications. In many of these applications, it is particularly valuable to form a virtual image that can be visually superimposed on a real-world image formed within the eye of the HMD user's field of view. An image light guide transmits image-bearing light along a transparent waveguide from a location outside the viewer's field of view to a location aligned with the viewer's pupil, while preserving the viewer's view of the environment through the waveguide.

[0003] In some image light guides, a collimated, relative angle-encoded light beam from an image source is coupled into a plate-shaped waveguide by an input coupling, such as an incoupling diffractive optical element, which can be attached to or formed on the surface of the plate-shaped waveguide or embedded within the waveguide. Such a diffractive optical element can be formed as a diffraction grating, a holographic optical element, or by other known methods. After propagating along the waveguide, the diffracted light can be redirected out of the waveguide by a similar output grating, which can be configured to provide pupil dilation along at least one dimension of the virtual image. Additionally, a turning diffractive optical element can be positioned along the waveguide between the input and output gratings to provide pupil dilation in a second, orthogonal dimension of the virtual image. The two dimensions of pupil dilation define an expanded eyebox within which the viewer's pupil can be positioned to view the virtual image transmitted by the light guide.

[0004] Image light guides and diffractive optical elements can create a virtual image focused at optical infinity by delivering a collimated, angle-coded light beam to the viewer's eyebox. However, the virtual image may also be focused at a somewhat closer distance, such as in the 1 m to 1.5 m range. Using a near-focused solution can enable viewers to enjoy the benefits of augmented reality imaging in applications where having real-world scene content at a closer distance is useful, such as manufacturing and warehousing applications. Summary of the Invention

[0005] The present disclosure provides systems and methods for consistently generating stereoscopic presentations of properly aligned virtual images in near-eye display systems. Reducing or eliminating virtual image misalignment and undesirable optical effects such as inaccurate color matching, blurring, and optical noise can, for example, reduce eye fatigue (i.e., eye strain).

[0006] In a first exemplary embodiment, the present disclosure provides a method for aligning images in a near-eye binocular display system, comprising providing a substantially rigid binocular frame operable to receive two or more planar waveguides, each of the two or more planar waveguides including an incoupling diffractive optical element operable to diffract an image-bearing light beam from an image source into the waveguide and an outcoupling diffractive optical element operable to diffract the image-bearing light beam from the waveguide toward the eyebox. The incoupling diffractive optical element is operable to incouple light incident from a first direction, and the outcoupling diffractive optical element is operable to outcouple light in the first direction. The binocular frame is fixed to a fixed alignment mount, and a first projector is positioned on the right side of the frame to project a first image onto a screen where one or more planar waveguides are not in place. A second projector is positioned on the left side of the frame to project a second image onto a screen where one or more planar waveguides are not in place. The first image and the second image are compared to the respective targets, and the positioning of the first projector and / or the second projector is adjusted to align the first image and the second image with the respective targets.

[0007] In a second exemplary embodiment, the present disclosure provides a system for alignment of a virtual image in a near-eye binocular display system, including a substantially rigid frame, a fixed alignment mount operable to fix the frame, and a screen having a photodetector operable to measure characteristics of a calibration image. The system further includes a first projector connected to the right side of the frame, the first projector operable to project a first image, and a second projector connected to the left side of the frame, the second projector operable to project a second image. The system further includes one or more objective lenses operable to receive the first image at afocality and refocus the afocal image as a calibration image on a performance screen, the screen operable to compare pixel orientations of the one or more calibration images.

[0008] In a third exemplary embodiment, the present disclosure provides a method for aligning a rigid frame and projectors in a head-mounted display system independently of waveguide alignment, comprising: fixing a generally rigid binocular frame to a fixed alignment mount, the binocular frame operable to support a waveguide; positioning a first projector proximate to a right side of the frame, the first projector having no fixed waveguide and operable to project a right image to a first location in space; positioning a second projector proximate to a left side of the frame, the second projector having no fixed waveguide and operable to project a left image to a second location in space; positioning a screen at a first and second position relative to the frame, the screen having a photodetector operable to receive and measure characteristics of the left and right images; comparing the measured image characteristics of the left and right images; and adjusting the positioning of at least the first projector or the second projector.

[0009] In certain embodiments of the present invention, alignment may be achieved in a factory setting prior to the installation of the waveguide. [Brief explanation of the drawings]

[0010] The accompanying drawings are incorporated herein as part of this specification. The drawings described herein illustrate embodiments of the disclosed subject matter and illustrate selected principles and teachings of the present disclosure. However, the drawings do not illustrate every possible implementation of the disclosed subject matter and are not intended to limit the scope of the present disclosure in any way.

[0011] [Figure 1A] FIG. 1A is a simplified cross-sectional view of an image light guide showing replication of an image-bearing beam along the propagation direction to expand one direction of the eyebox, according to an exemplary embodiment of the disclosed subject matter. [Figure 1B] FIG. 1B is a schematic side view of an image light guide illustrating a consistent angular relationship between the incoupling ray vector and the light rays emitted by the outcoupling diffractive optical element, according to an exemplary embodiment of the disclosed subject matter. [Figure 1C] FIG. 1C is a schematic side view of an image light guide positioned at a non-perpendicular angle to the incoupling ray, showing a consistent angular relationship between the incoupling ray vector and the ray emitted by the outcoupling diffractive optical element. [Figure 2A] FIG. 2A is a schematic top view of a binocular image light guide showing the consistent angular relationship between the incoupling ray vectors and the light rays emitted by the outcoupling diffractive optical element. [Figure 2B] FIG. 2B is a schematic top view of a binocular image light guide showing the consistent angular relationship between the incoupling ray vectors and the light rays emitted by the outcoupling diffractive optical element. [Figure 3A] FIG. 3A is a top-elevation perspective view of an image light guide having a rear-facing projector that conveys a virtual image that appears at infinity within the viewer's field of view, according to an embodiment of the present disclosure. [Figure 3B] FIG. 3B is a top-elevation perspective view of an image light guide having a forward-facing projector that conveys a virtual image that appears at infinity within the viewer's field of view, according to an embodiment of the present disclosure. [Figure 4] FIG. 4 is a simplified top view schematic diagram of a head mounted display device transmitting outcoupled light to a viewer's field of view. [Figure 5] FIG. 5 shows a head-mounted near-eye display system worn by a viewer. [Figure 6A] FIG. 6A is a top-elevation perspective view of a projector that forms an image on a screen some distance from the viewer. [Figure 6B] FIG. 6B is a simplified top view schematic diagram of a head mounted display device that projects light from a rear-facing projector onto a screen. [Figure 6C]FIG. 6C is a simplified top view schematic diagram of a head mounted display device projecting light from misaligned rear-facing projectors onto two screens. [Figure 6D] FIG. 6D is a simplified top view schematic diagram of a head mounted display device according to FIG. 6C with rear-facing projectors aligned. [Figure 7] FIG. 7 is a top-elevation perspective view of an image projector that forms an image on an intermediate adjustment element that is operable to refocus the image on another screen positioned at a distance. [Figure 8] FIG. 8 is a top-elevation perspective view of a pair of image projectors forming a stereoscopic image that refocuses from an intermediate adjustment element onto an alignment screen positioned at a distance. [Figure 9] FIG. 9 is a schematic top view of a binocular imaging light guide in which a rear-facing projector emits light onto two cameras. [Figure 10] FIG. 10 is a process diagram illustrating the projector calibration procedure. [Figure 11A] FIG. 11A is a waveguide stack module according to an exemplary embodiment of the disclosed subject matter. [Figure 11B] FIG. 11B is an exploded view of the waveguide stack module according to FIG. 11A. [Figure 12] FIG. 12 shows an exploded view of a waveguide stack according to an exemplary embodiment of the disclosed subject matter. [Figure 13] FIG. 13 is a schematic side view of a calibration device according to an exemplary embodiment of the presently disclosed subject matter. [Figure 14] FIG. 14 is a schematic perspective view of a calibration device according to an exemplary embodiment of the presently disclosed subject matter. [Figure 15] FIG. 15 is a schematic perspective view of a calibration device according to another exemplary embodiment of the presently disclosed subject matter. DETAILED DESCRIPTION OF THE INVENTION

[0012] It should be understood that the present invention may assume various alternative orientations and step arrangements unless expressly specified to the contrary. It should also be understood that the specific assemblies and systems illustrated in the accompanying drawings and described in the following specification are merely exemplary embodiments of the inventive concepts defined herein. Accordingly, specific dimensions, orientations, or other physical characteristics relating to the disclosed embodiments are not to be considered limiting unless expressly stated otherwise. Also, although not applicable, like elements in the various embodiments described herein may be generally referred to within this section of the specification using like reference numerals.

[0013] As used herein, terms such as "first," "second," etc. do not necessarily imply any order, sequence, or priority relationship, but are merely used to more clearly distinguish one element or set of elements from another, unless otherwise specified.

[0014] 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 near-eye display device to view images.

[0015] As used herein, the terms "coupling" and "coupler" in the optical context refer to a connection where light travels from one optical medium or device to another.

[0016] As used herein, the term "about" as applied to a value is intended to mean within the tolerance of the device used to generate the value, or in some examples, ±10%, or ±5%, or ±1%, unless expressly specified otherwise.

[0017] As used herein, the term "substantially" is intended to mean within the tolerances of the device used to generate the value, or in some examples, ±10%, or ±5%, or ±1%, unless expressly specified otherwise.

[0018] As used herein, the terms "optical infinity" and "infinity" correspond to their conventional use in cameras and imaging technology and refer to imaging using substantially collimated light such that the focal length is at least greater than about four meters (4 m).

[0019] As used herein, the term "beam expansion" is intended to mean the duplication of a beam through multiple encounters with optical elements to provide an exit pupil expansion in one or more directions. Similarly, as used herein, "expanding" a beam or a portion of a beam is intended to mean the duplication of a beam through multiple encounters with optical elements to provide an exit pupil expansion in one or more directions.

[0020] Optical systems such as HMDs can generate virtual image displays. Unlike methods for generating real images, virtual images are not generated on a display surface. That is, when a display surface is positioned at the perceived location of the virtual image, no image is generated on the surface. Displaying virtual images offers numerous unique advantages in augmented reality presentations. For example, the apparent size of the virtual image is not limited by the size or location of the display surface. Furthermore, the source object of the virtual image can be small; for example, a magnifying glass can provide a virtual image of the object. Compared to systems that project real images, creating a virtual image that appears to be at a distance can provide a more realistic viewing experience. Providing a virtual image also eliminates the need to correct for screen artifacts, which may be required when projecting a real image.

[0021] An image light guide may display a virtual image using image-bearing light from a light source, such as a projector. For example, a collimated, relative angle-encoded light beam from the projector is coupled into a planar waveguide by an input coupling, such as an in-coupling diffractive optical element, which can be attached to or formed on the surface of the planar waveguide or embedded within the waveguide. Such a diffractive optical element can be formed as a diffraction grating, a holographic optical element (HOE), or by other known methods. For example, a diffraction grating can be formed by a surface relief. After propagating along the waveguide, the diffracted light can be redirected out of the waveguide by a similar output coupling, such as an out-coupling diffractive optical element, which can be positioned to provide pupil dilation along at least one direction of the virtual image. Additionally, a turning grating can be positioned on or within the waveguide to provide pupil dilation in the orthogonal direction of the virtual image. The image-bearing light output from the waveguide provides an expanded eyebox for the viewer.

[0022] 1A is a schematic diagram showing a simplified cross-sectional view of one conventional configuration of an image light guide system 10. The image light guide system 10 includes a planar image light guide 12, an incoupling diffractive optical element IDO, and an outcoupling diffractive optical element ODO. The image light guide 12 includes a transparent substrate S, which may be made of optical glass or plastic, for example, having plane-parallel front and back surfaces 14 and 16. In this example, the incoupling diffractive optical element IDO is shown as a transmission grating disposed on, within, or otherwise engaged with the front surface 14 of the image light guide 12. However, the incoupling diffractive optical element IDO may alternatively be a reflection grating or other type of diffractive optical element (such as a volume hologram or other holographic diffractive element) that diffracts an incident image-bearing light beam WI into the image light guide 12. The incoupling diffractive optical element IDO is located on or within the front surface 14 or back surface 16 of the image light guide 12, or otherwise engages the front surface 14 or back surface 16, and may be a combination of transmissive or reflective, depending on the direction in which the image-bearing light beam WI is intended to approach the image light guide 12.

[0023] When used as part of a near-eye display system or a head-mounted display, the incoupling diffractive optical element IDO of a conventional image light guide system 10 couples an image-bearing light beam WI from an image source 50 of a real, virtual, or hybrid image into the substrate S of the image light guide 12. Any real image or image dimension formed by the image source 50 is first converted into an array of overlapping, angle-related, collimated beams that encode different locations within the virtual image for presentation to the incoupling diffractive optical element IDO. Typically, the light rays in each bundle forming one of the angle-related beams extend parallel, but the angle-related beams are relatively oblique to one another through an angle that may be defined by two angular dimensions corresponding to the linear dimensions of the image.

[0024] When the angle-related beams engage the incoupling diffractive optical element IDO, at least a portion of the image-bearing light beam WI is diffracted (typically by a first diffraction order) and thereby redirected by the incoupling diffractive optical element IDO into the planar image light guide 12 as an angle-encoded image-bearing light beam WG for further propagation along the length dimension x of the image light guide 12 by total internal reflection (TIR) between the plane-parallel front and back surfaces 14, 16. Although diffracted into different combinations of angle-related beams along the boundaries established by the TIR, the image-bearing light beam WG preserves the image information in an angle-encoded form derivable from the parameters of the incoupling diffractive optical element IDO. The outcoupling diffractive optical element ODO receives the encoded image-bearing light beam WG and diffracts at least a portion of the image-bearing light beam WG from the image light guide 12 as an image-bearing light beam WO (typically also by a first diffraction order) toward a nearby spatial region referred to as the eyebox E, within which a transmitted virtual image can be seen by a viewer's eye or other optical component. The outcoupling diffractive optical element ODO can be designed symmetrically with respect to the incoupling diffractive optical element IDO to restore the original angular relationship of the image-bearing light beam WI from between the output angularly related beams of the image-bearing light beam WO. Furthermore, the outcoupling diffractive optical element ODO can modify the angular relationship of the original field point positions to generate an output virtual image at a finite focusing distance.

[0025] However, to increase one dimension of overlap between the angle-related beams injected into the eyebox E (which defines the size of the area in which the virtual image can be seen), the outcoupling diffractive optical element ODO is positioned with the limited thickness T of the image light guide 12 to encounter the image-bearing light beam WG multiple times, diffracting only a portion of the image-bearing light beam WG at each encounter. The multiple encounters along the length (e.g., in the first direction) of the outcoupling diffractive optical element ODO have the effect of replicating the image-bearing light beam WG and expanding or widening at least one dimension of the eyebox E where the replicated beams overlap. The expanded eyebox E reduces the sensitivity to the position of the viewer's eye 5 for viewing the virtual image.

[0026] The outcoupling diffractive optical element ODO is shown as a transmissive diffraction grating disposed on or affixed to the front surface 14 of the image light guide 12. However, like the incoupling diffractive optical element IDO, the outcoupling diffractive optical element ODO may be located on, within, or otherwise engaged with the front surface 14 or back surface 16 of the image light guide 12 and may be a combination of transmissive and reflective types, depending on the direction in which the image-bearing light beam WG is intended to exit the image light guide 12. In addition, the outcoupling diffractive optical element ODO may be formed as another type of diffractive optical element, such as a volume hologram or other holographic diffractive element, which diffracts the image-bearing light beam WG propagating from the image light guide 12 as an image-bearing light beam WO propagating toward the eyebox E.

[0027] When the image source 50 is positioned to emit the image-bearing light beam WI toward the image light guide 12 from a position opposite the front surface 14 through which the image-bearing light beam WO is transmitted, i.e., when the angle-related image-bearing light beam WI approaches the surface 16, the image-bearing light beam WO is emitted through the outcoupling diffractive optical element ODO on the surface 14 with a vector equal to the angle of incidence, rendering the image-bearing light beam WI and the image-bearing light beam WO parallel in angle space. FIG. 1A shows that the image-bearing light beam WI incident on the surface 16 at an angle of incidence 30 normal to the surface 16 generates the image-bearing light beam WO that emits from the surface 14 at an exit angle 32 normal to the surface 14. As shown in FIG. 1A, the angle of incidence 30 and the exit angle 32 are equal relative to the surfaces 16 and 14.

[0028] 1B shows a non-normally incident image-bearing light beam WI having an incident angle 34, and an image-bearing light beam WO emerging from surface 14 at a non-normal exit angle 36. The exit angle 36 of the exit beam WO is equal to the incident angle 34.

[0029] In one embodiment, as shown in FIG. 1C , the incidence angle 34 of the image-bearing light beam WI and the exit angle 40 of the image-bearing light beam WO are changed, but the relationship between the incidence angle 34 and the exit angle 40 is maintained. The incidence angle 34 and the exit angle 40 are equal to and independent of the roll, pitch, and yaw of the waveguides 12, 12a. The relationship between the incidence angle 34 and the exit angle 40 is a function of the image-bearing light beam WI being incident on the incoupling diffractive optical element IDO from the waveguide 12 on the opposite side of the eyebox E. When the image-bearing light beam WI is incident on the incoupling diffractive optical element IDO from the waveguide 12 on the same side as the eyebox E, the relationship between the incidence angle 34 and the exit angle 40 is not independent of the pitch, roll, and yaw of the waveguide 12. As described in detail herein, this angular relationship enables methods for aligning and calibrating a projector in the rigid frame binocular systems disclosed herein.

[0030] 2A and 2B show that the relationship between the entrance angle 34 and the exit angle 40 is maintained (when the image-bearing light beam WI enters the incoupling diffractive optical element IDO from the waveguide 22 on the opposite side of the eyebox E) even if the alignment of one or more of the waveguides 12, 12a with respect to one or more of the respective projectors 50, 50a is changed. In other words, the alignment of the waveguides 12, 12a with respect to the projectors 50, 50a does not affect the alignment virtual image V at optical infinity.

[0031] 3A shows a waveguide 12 positioned to diffract a projected image-bearing light beam WI at a preconfigured angle of incidence, with the waveguide 12 optimized to present a virtual image V fixed in angular space to a viewer 60. A rear-facing projector 50 is operable to transmit the image-bearing light beam WI to an incoupling diffractive optical element IDO, and may do so without mechanical contact with the waveguide 12. A mounting device, such as an eyeglass lens frame, a helmet mount, a waveguide case, or other mounting, may be utilized to secure the projector 50 and / or the waveguide 12.

[0032] 3B , in an exemplary embodiment, projector 50 is positioned facing front / forward relative to viewer 60. To achieve angular matching between image-bearing light beam WI and image-bearing light beam WO, optical element 54, including but not limited to a combination of mirrors, dove prisms, folding prisms, pentaprisms, or the like, is positioned to direct image-bearing light beam WI as image-bearing light beam WI2 toward incoupling diffractive optical element IDO from the required direction away from eyebox E (facing rearward). Mounting devices may be positioned to fix optical element 54 and projector 50 relative to one another, regardless of the presence or orientation of waveguide 12.

[0033] FIG. 4 illustrates an embodiment of a head-mounted near-eye display system 80 having a mountain-shaped configuration. In other embodiments, the head-mounted near-eye display system 80 may have a variety of shapes, including, but not limited to, wrap frames, sports and swim goggles, traditional eyeglass frames, and protective eyewear. The head-mounted near-eye display system 80 may include multiple bending points, including arm hinges 76, 76a, nose bridge 72, temple frames 74, 74a, and lens frame 70. To maintain separation of the waveguides 12, 12a from the projectors 50, 50a, the lens frame 70 is operable to function as a mount for the rear-facing projectors 50, 50a. This configuration offers several advantages. With the angle-encoded exit beam WO exiting the waveguides 12, 12a at an angle equal to the incident beam WI relative to the position of the viewer's eye 62, 62a, the lens frame 70 provides the most stable position possible for mounting the projectors 50, 50a. Given the general stiffness and limited flexure available in lens frame 70, stereoscopic vergence of output beam WO can be more reliably achieved. Waveguide 12 is operable to be moved or misaligned within head-mounted near-eye display system 80 without affecting the factory-calibrated alignment of fixedly mounted projectors 50, 50a and without affecting the presentation of virtual image V as noted in FIG. 3B. Returning to FIG. 4, waveguide swap ports 78, 78a allow waveguides 12, 12a to be removed from head-mounted near-eye display system 80 and replaced without affecting the factory-calibrated alignment of fixedly mounted projectors 50, 50a.

[0034] In one embodiment, the waveguides 12, 12a interface with the head-mounted near-eye display system 80 via an input mechanism that is easily accessible by sliding them into place through waveguide swap ports 78, 78a on the side of the lens frame 70, as shown in FIG. 5 . The waveguide swap port 78 may secure the installed waveguides 12, 12a using rubber seals, plastic clips, or machine screws 84. In another embodiment, the waveguide swap port 78 may be located on or within the top or bottom of the lens frame 70. The waveguides 12 are operable for insertion into the waveguide swap port 78 by inserting the side of the waveguide 12 having the outcoupling diffractive optical element (ODO) first, the side having the incoupling diffractive optical element (IDO) first, or the top or bottom side, depending on the orientation of the waveguide swap port 78 relative to the head-mounted near-eye display system 80. Once inserted, the waveguides 12, 12a are locked in place by a tensioning mechanism which may be engaged through spring pressure clips, snap clamps, spring clips, or the like.

[0035] When replaced, the waveguides 12, 12a do not require fine-tuning of their position after insertion. Rather, controlled focal convergence is achieved by factory alignment of the projectors 50, 50a. Referring now to FIG. 6A, the projector 50 is operable to generate an image at infinity and a full set of image-bearing light beams 90 corresponding to individual pixels in the image. As shown in FIG. 6A, in one embodiment, during alignment of a rear-facing / projecting projector 50, 50a, the projector 50, 50a is mounted on the lens frame 70 without the waveguides 12, 12a in place. The set of image-bearing light beams 90 generates an image M that can be displayed without the need for the waveguides 12, 12a to decode the image-bearing light. The image-bearing light beams 90 transmitted by the projectors 50, 50a are operable to generate the intended image M on a surface, such as a performance screen 96, without the presence of the waveguides 12. In one embodiment, performance screen 96 includes a digital sensor array comprising photodetectors in communication with controller 97 operable to receive and measure various characteristics of the calibration image. For example, the digital sensor array may include area charge-coupled devices (CCDs), complementary metal-oxide semiconductors (CMOSs), and / or photodiodes. In another embodiment, performance screen 96 includes a generally flat surface without a digital sensor array.

[0036] 6B shows a generally top-down perspective view of an embodiment of an image calibration scheme. When mounted on lens frame 70, left projector 50 and right projector 50a are operable to project image-bearing light beam 90 onto performance screen 96 set at a predetermined distance. Image-bearing light beam 90 generates a real image M. When both left projector 50 and right projector 50a are utilized, two images M are generated on performance screen 96. Image M may be further adjusted according to a projector alignment method described below. The projector alignment method may be implemented in a manufacturing environment.

[0037] In one embodiment, projector alignment is performed manually by a human operator. For example, the operator may project an image-bearing light beam 90 from each projector 50, 50a onto a projector screen 96 and align the image M on the projector screen 96 by eye to effect projector alignment.

[0038] As shown in FIGS. 6C and 6D, in one embodiment, a performance screen 96 is utilized during calibration of the projectors 50, 50a. In another embodiment, two performance screens 96, one for each projector 50, 50a, may be utilized during calibration. As shown in FIG. 6C, the projector 50a is misaligned such that the non-normal incident beam WI has an angle of incidence 34A on the performance screen 96, thus causing distortion of the virtual image V (the virtual image V is shown for reference but would not be generated without the waveguides 12, 12a). In FIG. 6D, the projector 50a is aligned such that the non-normal incident beam WI has an angle of incidence 34B on the performance screen 96, such that the stereoscopic virtual image V generated when the waveguides 12, 12a are installed is aligned. In one embodiment, the performance screen 96 includes a target T to which the image-bearing light beam 90 is aligned. If the performance screen 96 does not utilize a sensor array, the target T may be an image, such as a reticle. When the performance screen 96 utilizes a sensor array, the target T may be a selection of pixels.

[0039] 7, in one embodiment, to accommodate projector 50 transmitting image-bearing light beam 90 at afocality, an intermediate adjustment element is utilized to achieve focus on performance screen 96. In one embodiment, intermediate adjustment element is an objective lens 94 or similar optical system (e.g., a diopter correction lens) operable to receive image-bearing light beam 90 at afocality and focus afocal image M1 on performance screen 96 as calibration image M2. In one embodiment, intermediate adjustment element 94 is operable to magnify afocal image M1 on the performance screen as calibration image M2.

[0040] In one embodiment, performance screen 96 includes a photodetector device in communication with controller 97 operable to receive and measure various characteristics of calibration image M2. Performance screen 96, constructed using photodetectors responsive to timing accuracy and pulse frequency, spectral range, lumens or light intensity, and pixel orientation, enables a method for ensuring that the light output of projector 50 meets desired or preset requirements. In one embodiment, performance screen 96 also includes pixel grid 100 operable to compare pixel orientation of calibration image M2 to a reference pixel or factory-set alignment scheme. In one embodiment, the reference pixel is displayed at the center of calibration image M2. In another embodiment, the reference pixel is located in various regions of the image. For example, pixel alignment may be defined as the visual angle of one pixel on a device with a pixel density of 96 dots per inch ("96 dpi") and a visual angle of 0.0213 degrees, with a tolerance of 0.005 degrees.

[0041] In one embodiment, performance screen 96 is operable to account for undesirable effects on image-bearing light beam 90 caused by objective lens 94, including chromatic aberrations and other wavelength-dependent optical distortions seen in image M2. In certain aspects, such undesirable effects are anomalies and / or distortions known to be present in objective lens 94. Methods for more fine-grained calibration of projector 50, such as to correct for peripheral pixel alignment, color adjustment, and the like, include the use of alignment system software that implements image processing algorithms. Software alignment may occur before or after course alignment, as described in the example of FIG. 10.

[0042] In one embodiment, alignment mounts and mounting bracket 56 (shown in FIGS. 7, 8, and 13-15) are operable to provide a mechanical means for aligning the projection of image M1 about the X, Y, and Z axes. Projector 50, 50a may be aligned manually and / or electronically. In one embodiment, mounting bracket 56 includes adjustment screws 57 operable to adjust the roll, pitch, and yaw of projector 50, 50a.

[0043] As shown in FIG. 8 , in one embodiment, the right projector 50 and the left projector 50a of a head-mounted near-eye display system 80 are aligned without installing waveguides 12, 12a. This configuration includes a second projector, projector 50a, operable to deliver a stereoscopic viewing experience to a viewer 60. Projector 50 is operable for initial coarse alignment via a reference pixel alignment scheme and factory calibration of image area M2 using a performance screen 96. Once projector 50 achieves image display quality and accuracy specifications, second projector 50a may be similarly aligned to ensure that the image-bearing light beam 90 transmitted by second projector 50a converges with the image-bearing light beam 90 transmitted by projector 50.

[0044] 9, in one embodiment, projector alignment may be performed with waveguides 12, 12a installed. In this embodiment, cameras 500, 500A are located within eyebox E. The real images captured by cameras 500, 500A are then used to calibrate the alignment of projectors 50, 50a.

[0045] 13 and 14 , in one embodiment, calibration of the projector 50, 50a is performed utilizing a calibration apparatus 600. In one embodiment, the calibration apparatus 600 includes a stand 602 operable to hold the near-eye display system 80 in a fixed position. The stand 602 may also be referred to herein as a fixed alignment mount. For example, the stand 602 may include a clamping mechanism 604. The clamp 604 has an upper finger 606 and a lower finger 608. The lower finger 608 may be operable to move up and down on the stand 602 via a clamping screw 610 to open and close on the nose bridge 72. In one embodiment, the calibration apparatus 600 includes an objective lens 94 and a performance screen 96. As shown in FIGS. 13 and 14 , in one embodiment, the stand 602, the objective lens 94, and the performance screen 96 are mounted on a platform 620. The platform 620 maintains the relative positions of the stand 602, objective lens 94, and performance screen 96 so that the only elements adjusted during calibration are the projectors 50, 50a.

[0046] As shown in FIG. 15, in one embodiment, the calibration device includes cameras 500, 500A for calibration of projectors 50, 50a when waveguides 12, 12a are installed as described in FIG.

[0047] FIG. 10 is a flow chart illustrating a method 200 for aligning and calibrating a projector in a rigid frame binocular system. In step 210, an operator powers on the near-eye display system 80. Next, in step 220, the near-eye display system 80 may be connected to a local area network (LAN) or wide area network (WAN), such as a WiFi network, and transition to a standby state operable to receive system updates. In another embodiment, the near-eye display system 80 may bypass the network connection. In step 230, the operator may verify that the near-eye display system software is running the latest (i.e., most recently updated) operating system (“OS”) and calibration software. The operator initiates system updates, if necessary. After verification, the operator initiates a general test preparation procedure in step 240. Step 240 may include several actions depending on the test lab conditions and equipment needs.

[0048] In one embodiment, the pre-test procedure actions may be performed in sequence before proceeding with the remainder of the method for aligning and calibrating a projector in a rigid-frame binocular system. In another embodiment, any of the pre-test procedure actions may be repeated individually, out of sequence, any number of times, or omitted. Typical pre-test procedure actions in step 240 include, but are not limited to, functional checks to ensure basic component functionality, such as LED lights, touchpad input sensors, and projectors, is operational. Additionally, the operator may check for mechanical defects that affect the alignment test, such as warping of the temple arms 74, 74a, tolerance issues, or detecting physical discrepancies within the near-eye display system. The presence of such defects would require a review of the near-eye display system at hand and a halt to the calibration process. The operator may also check the ambient temperature range for optimal conditions and verify that airborne cleanliness specifications meet Class 100 as specified in Federal Standard 209c Particulate Contaminants or Class 5 as specified in ISO standards. Additionally, the surface cleanliness of the objective lens 94 and projectors 50, 50a may also be verified as meeting Class 100 as specified by Federal Standard 209c Particulate Contaminant Rating or Class 5 as specified by ISO Standard. In another embodiment, the particulate contaminant standard may allow for Class 6 or higher under ISO Standard. Further verifications included in step 240 may determine the operability of the performance screen 96, including screen sensor verification and positioning of operational image reference pixels for projector alignment.

[0049] Moving to step 250, the operator secures the near-eye display system 80 to a fixed mounting system located within the test environment. In step 260, the operator or a mechanical arm may make fine adjustments to the position of the first projector 50. In one embodiment, the first projector 50 refers to only the right-side projector, where only one projector is aligned at a time for purposes of the projector calibration scheme. In one embodiment, the left-side projector may be the first projector. In another embodiment, both projectors 50, 50a may be calibrated in series. Electronic calibration software may be used to further calibrate the projector positioning. In step 270, the mounted near-eye display system projects an image onto the performance screen 96 using the first projector 50. In step 280, image values are captured by the performance screen 96 and measured by the calibration software. In one embodiment, the performance screen 96 is photosensitive and has a photodetector operable to measure various characteristics of the calibration image. In certain embodiments, this step may include calibration with respect to a reference pixel or factory-default alignment scheme, as described above.

[0050] In step 290, the system and / or test operator evaluates the image data against accuracy specifications, such as the exemplary accuracy specifications described above. If the specifications are not met, the near-eye display system alignment method returns to step 260 for further mechanical and / or electronic adjustments based on the performance data. If the specifications are met, the calibration process proceeds to step 300, where an operator, or a similar mechanical element attached to a mechanical arm or frame, may perform fine adjustments to the position of the second projector 50a prior to adjustment by the first projector 50. Electronic adjustment software may be used to further calibrate the positioning of the projector 50a. Data received through the performance screen test of the first projector 50 may additionally be used to inform the calibration of the second projector 50a.

[0051] In step 310, the attached near-eye display system 80 projects an image onto the performance screen 96 using its second projector 50a. In step 320, image values are captured by the performance screen 96 and measured by the calibration software as described above. In step 330, a system and / or test operator evaluates the image data against accuracy specifications to ensure the projectors 50, 50a are properly aligned with each other. If the specifications are not met, the near-eye display system alignment method returns to step 300 for further mechanical and / or electronic adjustments of the second projector 50a based on the performance data. If the specifications are met, a pairing sequence is initiated to fix and record the position of each projector 50, 50a as part of the system values in step 340. The system values may be used in future internal system alignment procedures. In step 350, the successful alignment of the projectors of the near-eye display system 80 is recorded in a calibration certificate. The waveguide may be added to the frame after the above-described embodiment of the method is completed, but may also be added or inserted earlier in the alignment process.

[0052] 11A-12 , in one embodiment, the waveguides 12, 12a are included in a waveguide stack module 400. The waveguide stack module 400 may be utilized in a head-mounted near-eye display system 80 by connecting the waveguide stack module 400 to a lens frame 70. The waveguide stack module 400 may be environmentally sealed to prevent moisture, dirt, and any other particles from entering the interior of the waveguide stack module 400. In one embodiment, the waveguide stack module 400 includes a waveguide housing 402, a blackening material 404, a waveguide assembly 406, an outer cover 408, and an inner cover 410.

[0053] In one embodiment, there is a perimeter seal between the outer cover 408 and the housing 402 to prevent debris from entering the enclosed system. Additionally, the outer cover 408 may include an anti-reflective coating thereon to reduce unwanted reflections. The inner cover 410 may also include an anti-reflective coating and / or an anti-"smudge" coating thereon. The outer cover 408, inner cover 410, and waveguide housing 402 seal the waveguide assembly 406 within the waveguide stack module 400.

[0054] Waveguide assembly 406 includes one or more waveguides 12, 22a (as described herein). As shown in Figure 12, in one embodiment, waveguide assembly 406 also includes a second waveguide 422. Waveguides 12, 12a and second waveguide 422 may be separated by UV photoactive material 412 while maintaining suitable parallelism for optical performance.

[0055] One or more features of the embodiments described herein may be combined to create additional embodiments not shown. While various embodiments have been described in detail above, it should be understood that they are presented for illustrative purposes, and not for limiting purposes. It will be apparent to those skilled in the relevant art that the subject matter of the present disclosure may be embodied in other specific forms, variations, and modifications without departing from the scope, spirit, or essential characteristics thereof. The above-described embodiments are therefore to be considered in all respects as illustrative and not restrictive. The scope of the present invention is indicated by the appended claims, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.

Claims

1. 1. A method for alignment of images in a near-eye binocular display system, comprising:

1. A substantially rigid binocular frame operable to support two or more waveguides, each of said two or more waveguides comprising: an incoupling diffractive optical element operable to diffract an image-bearing light beam from an image source into said waveguide; an outcoupling diffractive optical element operable to diffract the image-bearing light beam from the waveguide towards an eyebox; providing the incoupling diffractive optical element operable to incouple light incident from a first direction and the outcoupling diffractive optical element operable to outcouple light in the first direction; securing the binocular frame to a fixed alignment mount; positioning a first projector to the right of the binocular frame to project a first image; projecting the first image onto a screen without supporting the two or more waveguides in the binocular frame; positioning a second projector to the left of the binocular frame for projecting a second image; projecting the second image onto the screen without supporting the two or more waveguides in the binocular frame; and comparing the first image and the second image to respective targets; adjusting the positioning of at least the first projector or the second projector to align the first image and the second image with the respective targets.

2. 10. The method of claim 1, further comprising providing an intermediate adjustment element operable to receive the first image from the first projector and the second image from the second projector and to focus the images on the screen.

3. 3. The method of claim 2, further comprising: refocusing the first image and the second image on the screen; and comparing the refocused images with the respective targets to verify that the first projector and the second projector are aligned.

4. The method of claim 2 , wherein the intermediate adjustment element is an objective lens.

5. The method of claim 1 , wherein the screen is positioned more than 1 meter and less than 4 meters from the binocular frame.

6. The method of claim 1 , wherein the binocular frame comprises a waveguide exchange port adapted for removable insertion of a waveguide.

7. The method of claim 6 further comprising removably inserting a waveguide into the waveguide exchange port.

8. 10. The method of claim 1, further comprising: positioning the first projector to emit image-bearing light in a direction away from the screen; and providing optics to direct the image-bearing light toward the screen.

9. the screen comprises a photodetector in communication with a controller operable to measure image characteristics, the method comprising: measuring image characteristics of the first image on the screen and comparing the measured image characteristics with desired image characteristics; measuring image characteristics of the second image on the screen and comparing the measured image characteristics with the desired image characteristics; 10. The method of claim 1, further comprising: comparing the measured image characteristics from the first image and the second image to verify that the first projector and the second projector are aligned.

10. The method of claim 9 , wherein the controller is operable to detect misalignment of the first image and the second image.

11. The method of claim 1 , further comprising placing one or more waveguides within the binocular frame.

12. 1. A system for alignment of a virtual image in a near-eye binocular display system, comprising: a substantially rigid binocular frame configured to support two or more waveguides; a fixed alignment mount operable to fix the binocular frame; a screen having a photodetector in communication with a controller operable to measure characteristics of a calibration image, the controller operable to compare pixel orientations of one or more calibration images; a first projector connected to a right side of the binocular frame, the first projector operable to project a first image; a second projector connected to a left side of the binocular frame, the second projector operable to project a second image; and one or more objective lenses operable to receive the first image and the second image at afocality and refocus the afocal images as first and second calibration images on the screen without supporting the two or more waveguides in the binocular frame.

13. The system of claim 12 , wherein the controller is operable to compare a position of the first image with a position of the second image.

14. The system of claim 12 , wherein the controller is operable to compare pixel orientations of the calibration image to a reference pixel or a factory default alignment scheme.

15. The system of claim 12 , wherein the binocular frame comprises a waveguide exchange port adapted for removable insertion of a waveguide.

16. 13. The system of claim 12, wherein the fixed alignment mount, the screen, and the one or more objective lenses are coupled to a platform, the platform operable to maintain relative positions of the fixed alignment mount, the screen, and the one or more objective lenses such that only the first projector and the second projector are movable during alignment.

17. 13. The system of claim 12, wherein the screen comprises a pixel grid operable to compare pixel orientations of the first image with reference pixels.

18. 13. The system of claim 12, further comprising a mechanical alignment element attached to the binocular frame operable to align the first image and the second image with one or more reference pixels.

19. The system of claim 12 , further comprising a mechanical alignment element attached to the binocular frame, the mechanical alignment element operable to move the first projector.

20. 20. The system of claim 19, wherein the mechanical alignment elements include adjustment screws operable to adjust roll, pitch, and yaw of the first projector.

21. 1. A method for aligning a rigid frame and a projector in a head mounted display system independent of waveguide alignment, comprising: securing a generally rigid binocular frame to a fixed alignment mount, said binocular frame operable to support a waveguide; positioning a first projector proximate to a right side of the binocular frame, the first projector operable to project a right image at a first location in space where a waveguide is not in place; positioning a second projector proximate to the left side of the binocular frame, the second projector operable to project a left image to a second location in space where a waveguide is not in place; positioning a screen at the first position and the second position relative to the binocular frame, the screen having a photodetector operable to receive and measure characteristics of the left image and the right image; comparing the measured image characteristics of the left and right images; and adjusting the positioning of at least the first projector or the second projector.

22. 22. The method of claim 21, wherein the screen is in communication with a controller operable to compare pixel orientations of the left and right images.

23. 22. The method of claim 21, wherein the screen is in communication with a controller operable to compare pixel orientation of the left image with a reference pixel or factory default alignment scheme.

24. 22. The method of claim 21, further comprising: providing an intermediate adjustment element operable to receive the right image from the first projector and the left image from the second projector and refocus the right and left images on the screen; refocusing the left and right images on the screen; and comparing the refocused images to confirm that the first and second projectors are aligned.

25. 22. The method of claim 21, further comprising disposing a waveguide within the binocular frame.

26. 22. The method of claim 21, wherein comparing the measured image characteristics is completed before placing a waveguide within the binocular frame.

Images