Embodiments described herein generally relate to near-eye display systems, and more specifically to near-eye display systems with reduced rainbow artifacts and methods of forming the same.
Virtual reality (VR) is generally considered to be a computer generated simulated environment in which a user has an apparent physical presence. A virtual reality experience can be generated in 3D and viewed with a head-mounted display (HMD), such as glasses or other wearable display devices that have near-eye display panels as lenses to display a virtual reality environment that replaces an actual environment.
Augmented reality (AR), however, enables an experience in which a user can still see through the display lenses of the glasses or other HMD device to view the surrounding environment, yet also see images of virtual objects that are generated for display and appear as part of the environment. AR can include any type of input, such as audio and haptic inputs, as well as virtual images, graphics, and video that enhance or augment the environment that the user experiences. As an emerging technology, there are many challenges and design constraints with augmented reality.
Typical diffractive near-eye display systems suffer from external light source diffraction, for example, a rainbow artifact, which results in the appearance of a rainbow streak of light in the user's field of view (FoV). This rainbow artifact is an unwanted diffraction to the user experience in an AR display system.
Accordingly, what is needed in the art are near-eye display systems with reduced rainbow artifact.
Embodiments described herein generally relate to near-eye display systems, and more specifically to near-eye display systems with reduced rainbow artifacts and methods of forming the same.
In one aspect, a method of manufacturing a rainbow-free waveguide display is provided. The method includes manufacturing a waveguide display assembly configured to direct image light to an eyebox plane having a length (LEyebox) and to a user's eye. The waveguide display assembly includes a waveguide combiner and an out-coupler grating. The out-coupler grating has a grating period ΛOC such that all angles of incidence θin of light from an external light source, result in diffracted angles Bout, that miss the user's eye by satisfying the following first order diffraction equation (I):
wherein λ is the wavelength of the light from the external light source.
In another aspect, a waveguide display is provided. The waveguide display is configured to direct image light to an eyebox plane having a length (LEyebox) and to a user's eye. The waveguide display includes waveguide combiner and an out-coupler grating. The out-coupler grating has a grating period
ΛOC such that all angles of incidence θin of light from an external light source, result in diffracted angles Bout, that miss the user's eye by satisfying the following first order diffraction equation (I):
wherein λ is the wavelength of the light from the external light source.
In yet another aspect, a near-eye display is provided. The near-eye display includes a frame and a display. The display includes a waveguide display configured to direct image light to an eyebox plane having a length (LEyebox) and to a user's eye. The waveguide display includes a waveguide combiner and an out-coupler grating, wherein the out-coupler grating has a grating period ΛOC such that all angles of incidence θin of light from an external light source, result in diffracted angles Bout, that miss the user's eye by satisfying the following first order diffraction equation (I):
wherein λ is the wavelength of the light from the external light source.
In another aspect, a non-transitory computer readable medium has stored thereon instructions, which, when executed by a processor, causes the process to perform operations of the above apparatus and/or method.
So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description of the implementations, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one implementation may be beneficially incorporated in other implementations without further recitation.
The following disclosure generally describes display systems for virtual reality and augmented reality. Certain details are set forth in the following description and in
Many of the details, dimensions, angles and other features shown in the Figures are merely illustrative of particular implementations. Accordingly, other implementations can have other details, components, dimensions, angles and features without departing from the spirit or scope of the present disclosure. In addition, further implementations of the disclosure can be practiced without several of the details described below.
Embodiments described herein generally relate to near-eye display systems, and more specifically to near-eye display systems with reduced rainbow artifacts and methods of forming the same. The near-eye-display system utilizes a diffractive waveguide combiner layer designed to prevent light sources from the external world from diffracting into the user's eye (commonly referred to as a rainbow artifact). A set of relationships and constraints on the waveguide combiner and optical system design are provided to ensure that no rainbow artifacts can reach the user's eye in normal operation.
Typical diffractive near-eye displays suffer from external light source diffraction (rainbow artifact), which results in the appearance of a rainbow streak of light in the user's field-of-view. Such external sources include room lights and the sun. This rainbow artifact is an unwanted distraction to the user experience in an augmented reality display system.
Current near-eye display designs either live with the issue, mitigate the issue with complex grating structures, use external films to mitigate the issue, or use visor-like mechanical features to block the undesirable light paths. In contrast, in some embodiments of the present disclosure, rainbow artifacts are eliminated by utilizing out-coupler grating periods, which do not allow diffracted orders from external light sources to reach the user's eye.
By utilizing the design relationships and constraints outlined in the present disclosure, this display system described herein does not suffer from external light source diffraction (“rainbow” artifact), in the user's field-of-view. Unlike other approaches to mitigating this artifact, some embodiments described herein do not use any external device or layers to filter the light from sources in the world which is incident on the waveguide-combiner. Additionally, some embodiments described herein do not use any visor-like mechanical blockages that extend beyond the plane of the waveguide combiner to prevent light paths that generate “rainbow” artifacts from hitting the waveguide combiner.
The appearance of rainbow artifacts is dependent on the spectrum of the light sources that generate them, as well as the location of the user's eye pupil. In order to provide a quantitative definition of “rainbow” free, a minimum wavelength of 450nm is used for the source spectrum, and it is assumes that the user's pupil is located at the nominal eye position (center) of the designed eyebox plane at the intended eye relief of the waveguide combiner display system. With this definition, the only possible rainbow artifacts that could possibly be viewed will be very blue/violet (due to the 450nm cutoff in the assumption) where human sensitivity is very low, and will be located over a small angular extent near the edges of the out-coupling grating region.
The near-eye display system 100 can include a frame 110 and a display 120. The frame 110 can be coupled to one or more optical elements. The display 120 can be configured for the user to see content presented by the near-eye display system 100. In one embodiment, which can be combined with other embodiments, the display 120 can include a waveguide display assembly for directing light from one or more images to an eye of the user.
Referring to
where θout is the angle of light 354 diffracted by the out-coupler grating 330, θin is the angle of light 352 incident on the out-coupler grating 330, 2L is the wavelength of light 354, and ΛOC is the period of the out-coupler grating 330. As the wavelength is decreased or the grating period ΛOC is increased, θout becomes closer to θin and the diffracted light 354 therefore becomes closer to the center of the user's field-of-view. However, if the out-coupler grating 330 is designed to have a grating period ΛOC small enough such that all angles of incidence, θin, result in diffracted angles θout, that miss the user's eye 230, then no rainbow artifact is viewable to the user.
Additionally, it is desirable to enable a large field-of-view (FoV) and eyebox plane 220 of the virtual content while also removing the “rainbow” artifact. The maximum FoV of the system can be determined by the substrate index. Inversely, the required minimum substrate refractive index of the waveguide combiner 320 can be determined from a requirement on the FoV.
Effective Out-Coupler Grating Period
One example of the “effective” out-coupler grating period AOCeff is as follows. There are rainbow paths which can be generated from the combination of two different physical gratings, but produce rainbow artifacts with output angles consistent with a single “effective” grating period.
If two or more out-coupler grating vectors are present, one should search for combinations of grating vectors (sums), which potentially produce a smaller magnitude grating vector to find ΛOCeff
For example, for two 1D out-coupler gratings:
Where, {right arrow over (Λ)}OC1 is the periodicity vector of the first 1D out-coupler, {right arrow over (Λ)}OC2 is the periodicity vector of second 1D out-coupler, {right arrow over (k)}OC1 is the grating vector of the first 1D out-coupler, {right arrow over (Λ)}OC2 the grating vector of the second 1D out-coupler, {right arrow over (k)}eff is the effective grating vector of the out-coupler combination, {right arrow over (Λ)}OCeff is the effective out-coupler periodicity vector, and λ is a wavelength of light which will cancel out in this calculation.
One example of this type of multiple out-coupler grating configuration is described by
A variety of options exist for the number of waveguide combiner layers utilized in the “rainbow” free system. In single waveguide layers, three display channels (red, green, blue) propagate through the same layer and diffract from the same grating structures to send the virtual image to the user's eye. In three waveguide-layer systems, each waveguide layer can be designed to support only a single display color channel. Typically, three waveguide-layer systems utilize larger effective out-coupler grating periods, λOCeff, than single waveguide layer systems because the dedicated Red layer is designed to support only red wavelengths (600-650 nm) instead of also requiring the inclusion of shorter blue wavelengths (430-470 nm).
“Rainbow” free implementations of multi-layer waveguide combiners can be made provided the requirements for the maximum allowable effective out-coupler grating periods, λOCeff, are held for all of the layers in the system. An advantage of using multiple waveguide layers is that the grating structures can be optimized for the intended display color channel they are designed to support even though the grating periods are limited by the “rainbow” free constraints, which can result in improved color uniformity, luminance uniformity, and efficiency over a single-layer implementation.
Number of Waveguide Combiner Layers
A variety of options exist for the number of waveguide combiner layers utilized in the “rainbow” free system. In single waveguide layers, three display channels (red, green, blue) propagate through the same layer and diffract from the same grating structures to send the virtual image to the user's eye. In three waveguide-layer systems, each waveguide layer can be designed to support only a single display color channel. Typically, three waveguide-layer systems utilize larger effective out-coupler grating periods, ΛOCeff, than single waveguide layer systems because the dedicated Red layer is designed to support only red wavelengths (600-650 nm) instead of also requiring the inclusion of shorter blue wavelengths (430-470 nm).
“Rainbow” free implementations of multi-layer waveguide combiners can be made provided the requirements for the maximum allowable effective out-coupler grating periods, ΛOCeff, are held for all of the layers in the system. One advantage of using multiple waveguide layers is that the grating structures can be optimized for the intended display color channel the grating structures are designed to support even though the grating periods are limited by the “rainbow” free constraints, which can result in improved color uniformity, luminance uniformity, and efficiency over a single-layer implementation.
At operation 510 of the method 500, the target FoV is determined. At operation 520 of the method 500, the eyebox dimensions are determined. At operation 530 of the method 500, the waveguide tilt is determined. The target FoV, the eyebox dimensions, and the waveguide tilt are used as inputs to calculate the out-coupler grating dimensions at operation 540, the maximum angles to the eye from the out-coupler grating at operation 550, the minimum grating vectors (maximum periods) of the out-coupler grating required to avoid the rainbow effect at operation 560, and the minimum substrate index required to support the target FoV at operation 570.
For equation (II), LOCtop is the length of the top half of the out-coupler grating region.
For equation (II), LOC
For typical system designs, θout
At operation 560, the minimum grating vectors (maximum periods) required to avoid the “rainbow” artifact are calculated using the diffraction equation (VII). From the diffraction equation (VII), the effective out-coupler grating period can be related to the maximum output angle calculated at operation 550 using equation (VI).
where λ0 is the shortest wavelength of “rainbow” artifact considered. In some embodiments, which can be combined with other embodiments, it is assumed that λ0=450 nm.
At operation 570, the minimum refractive index (n) of the substrate, for example, the waveguide combiner 320, to support the target FoV is calculated. The refractive index (n) of the substrate, for example, the waveguide combiner 320 should be large enough to allow the entire target virtual FoV to propagate in TIR. The limiting case here is the red display channel FoV, due to the longest wavelengths. The minimum refractive index (n) of the substrate is calculated using equation (VIII):
where n is the waveguide combiner substrate refractive index, and λR is the wavelength of the red display channel (assumed to be 620 nm for this example).
The following non-limiting examples are provided to further illustrate implementations described herein. However, the examples are not intended to be all inclusive and are not intended to limit the scope of the implementations described herein.
Some example system design parameters which would generate “rainbow” free systems using the equations shown above are shown in Table I below:
In some embodiments, which can be combined with other embodiments, high index of refraction substrate materials are used to maximize the field-of-view and maintain the ability to design a “rainbow” free system. Examples of these high index of refraction substrate materials include, but are not limited to, high index glasses, as well as transparent crystalline materials (SiC, LiNbO3, LiTaO3, KTaO3, etc.) are good candidates for substrates to utilize in a “rainbow” free diffractive waveguide combiner augmented reality display system.
Implementations can include one or more of the following potential advantages. Utilizing the design relationships and constraints outlined in the present disclosure, the display system described herein does not suffer from external light source diffraction (“rainbow” artifact), in the user's field-of-view. Unlike other approaches to mitigating this artifact, some embodiments described herein do not use any external device or layers to filter the light from sources in the world which is incident on the waveguide-combiner. In addition, some embodiments described herein do not use any visor-like mechanical blockages that extend beyond the plane of the waveguide combiner to prevent light paths that generate “rainbow” artifacts from hitting the waveguide combiner.
Embodiments described herein and all of the functional operations described in this specification can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structural means disclosed in this specification and structural equivalents thereof, or in combinations of thereof. Embodiments described herein can be implemented as one or more non-transitory computer program products, i.e., one or more computer programs tangibly embodied in a machine readable storage device, for execution by, or to control the operation of, data processing apparatus, e.g., a programmable processor, a computer, or multiple processors or computers.
The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).
The term “data processing apparatus” encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them. Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer.
Computer readable media suitable for storing computer program instructions and data include all forms of nonvolatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and CD ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.
When introducing elements of the present disclosure or exemplary aspects or implementation(s) thereof, the articles “a,” “an,” “the” and “said” are intended to mean that there are one or more of the elements.
The terms “comprising,” “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.
While the foregoing is directed to embodiments of the present disclosure, other and further implementations of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 63/256,083, filed Oct. 15, 2021, which is incorporated by reference herein in its entirety.
Number | Date | Country | |
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63256083 | Oct 2021 | US |