Patent Application
20230176380
The present disclosure relates to tunable optical devices, and in particular to lightguides usable in visual displays, as well as components, modules, and methods for lightguides and visual displays.
Visual displays provide information to viewer(s) including still images, video, data, etc. Visual displays have applications in diverse fields including entertainment, education, engineering, science, professional training, advertising, to name just a few examples. Some visual displays such as TV sets display images to several users, and some visual display systems such s near-eye displays (NEDs) are intended for individual users.
An artificial reality system generally includes an NED (e.g., a headset or a pair of glasses) configured to present content to a user. The near-eye display may display virtual objects or combine images of real objects with virtual objects, as in virtual reality (VR), augmented reality (AR), or mixed reality (MR) applications. For example, in an AR system, a user may view images of virtual objects (e.g., computer-generated images (CGIs)) superimposed with the surrounding environment by seeing through a “combiner” component. The combiner component including its light routing optics may be transparent to external light.
An NED is usually worn on the head of a user. Consequently, a large, bulky, unbalanced, and heavy display device with a heavy battery would be cumbersome and uncomfortable for the user to wear. Head-mounted display devices can benefit from a compact and energy-efficient configuration, including efficient light sources and illuminators providing illumination of a display panel, high-throughput combiner components and ocular lenses, and other optical elements in the image forming train that can provide an image to a user’s eye with minimal image distortions and artifacts.
Exemplary embodiments will now be described in conjunction with the drawings, in which:
While the present teachings are described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives and equivalents, as will be appreciated by those of skill in the art. All statements herein reciting principles, aspects, and embodiments of this disclosure, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.
As used herein, the terms “first”, “second”, and so forth are not intended to imply sequential ordering, but rather are intended to distinguish one element from another, unless explicitly stated. Similarly, sequential ordering of method steps does not imply a sequential order of their execution, unless explicitly stated.
Near-eye displays may use pupil-replicating lightguides to carry images to user’s eyes. Pupil-replicating lightguides have an advantage of not requiring ocular lenses for viewing the image. Pupil-replicating lightguides can transmit the outside light without refocusing or redirection, allowing their use as combiner elements in augmented reality (AR) display systems.
Pupil-replicating lightguides may have a drawback of low optical throughput, in part due to having to spread the input image light beam over a large area of an eyebox of the display. Since a user’s eye, more precisely user’s eye pupil, occupies only a small portion of a total eyebox area, most of the light out-coupled by a pupil-replicating lightguide is lost. Most of the broadly spread light does not enter the eye pupil, instead illuminating outer areas of the user’s eyes and user’s face. Another source of optical throughput loss is related to having to optimize the out-coupling grating of the pupil-replicating lightguide to operate in a uniform manner over the entire eyebox. Such parameters as grating strength, grating fringes slant angles, etc., need to be optimized to account for losses of optical power as the image light propagates through the waveguides while being out-coupled, for the purpose of providing a uniform distribution of the image light over the entire eyebox area. The optimization of grating parameters for uniformity may result in a drop of overall optical throughput.
In accordance with this disclosure, an overall effective throughput of a pupil-replicating lightguide may be increased by providing an out-coupling grating structure having a switchable distribution of out-coupling efficiency. The switchable out-coupling efficiency may be provided by a grating having structure a variable or switchable slant angle of the grating fringes. The slant angle of the grating fringes that out-couple the image light may be varied to direct more light energy towards a particular location of the eye pupil. The current eye pupil location may be determined by an eye tracking system.
In some embodiments, a switchable out-coupling grating structure may include a plurality of diffraction gratings having different local slant angles of grating fringes. The diffraction gratings of the grating structure may be made switchable between a high-efficiency state where a percentage of the image light out-coupled from the slab is above a first threshold, and a low-efficiency state where a percentage of the image light out-coupled from the slab is below a second threshold lower than the first threshold, e.g. 10 times or even 100 times lower.
The gratings may be physically switched ON and OFF. In some embodiments, the gratings may have a wavelength-selective refractive index contrast, and the switching may be achieved by quickly switching the illuminating wavelength causing one grating to diffract the light being guided by the pupil-replicating lightguide and another grating to be transparent to such light.
In accordance with the present disclosure, there is provided a pupil-replicating lightguide for expanding image light. The pupil-replicating lightguide includes a slab of transparent material for guiding the image light in the slab by a series of internal reflections from opposed surfaces of the slab, and an out-coupling grating structure supported by the slab for out-coupling portions of the image light from the slab. The portions are laterally offset from one another along a path of the image light in the slab. The out-coupling grating structure has a switchable distribution of out-coupling efficiency.
The out-coupling grating structure may include a plurality of diffraction gratings having different local slant angles of grating fringes. The diffraction gratings are switchable between a high-efficiency state, in which a percentage of the image light out-coupled from the slab is above a first threshold, and a low-efficiency state, in which a percentage of the image light out-coupled from the slab is below a second threshold lower than the first threshold. The second threshold may be e.g. at least 10 times, or at least 100 lower than the first threshold. The plurality of switchable diffraction gratings may include switchable gratings with spatially varying slant angle of the grating fringes along the path of the image light. The switchable gratings may be disposed in a stack configuration parallel to the opposed surfaces of the slab. The plurality of diffraction gratings may include a polarization volume hologram (PVH) grating, a tunable liquid crystal (LC) surface-relief grating, a fluidic grating, etc. The out-coupling grating structure may include a grating having a wavelength-dependent refractive index contrast.
In accordance with the present disclosure, there is provided a near-eye display comprising a projector for providing image light, and an above described pupil-replicating lightguide coupled to the projector. The near-eye display may further include an eye tracker for determining a position of a pupil of a user’s eye at an eyebox of the near-eye display, and a controller operably coupled to the projector, the eye tracker, and the pupil-replicating lightguide, and configured to cause the eye tracker to determine the position of the pupil, and, responsive to the determined position of the pupil, switch the angular distribution of diffraction efficiency to increase an amount of the image light illuminating the pupil at the determined position.
In some embodiments, the near-eye display may further include an eye tracker for determining a position of a pupil of the user’s eye at an eyebox of the near-eye display, and a controller operably coupled to the projector, the eye tracker, and the pupil-replicating lightguide, and configured to cause the eye tracker to determine the position of the pupil; and, responsive to the determined position of the pupil, switch a diffraction grating of the plurality of diffraction gratings to the high-efficiency state. The controller may be further configured to switch the remaining diffraction gratings of the plurality of diffraction gratings to the low-efficiency state.
In accordance with the present disclosure, there is further provided a method for displaying an image. The method includes providing image light to a pupil-replicating lightguide comprising a slab of transparent material, guiding the image light in the slab by a series of internal reflections from opposed surfaces of a slab of transparent material, out-coupling portions of the image light from the slab by an out-coupling grating structure, wherein the portions are laterally offset from one another along a path of the image light in the slab, and switching angular distribution of out-coupling efficiency of a plurality of grating fringes of the out-coupling grating structure. The switching of the angular distribution of the out-coupling efficiency may include switching a plurality of diffraction gratings having different local slant angles of grating fringes, where the diffraction gratings are switched between a high-efficiency state, in which a percentage of the image light out-coupled from the slab is above a first threshold, and a low-efficiency state, in which a percentage of the image light out-coupled from the slab is below a second threshold lower than the first threshold. The method may further include using an eye tracker to determine a position of a pupil of a user’s eye at an eyebox of the near-eye display; and, responsive to the determined position of the pupil, switching the angular distribution of diffraction efficiency to increase an amount of the image light illuminating the pupil at the determined position.
Referring now to
The out-coupling grating structure 108 has a switchable or tunable distribution of out-coupling efficiency, enabling the control of locations and/or distribution of angles of out-coupling the image light portions 114 with high efficiency at the account of other locations and angles where the image light portions 114 are out-coupled with a lesser efficiency. In other words, the distribution of the out-coupling efficiency in XY plane and/or out-coupling angle direction may be tuned or switched. Herein and throughout the rest of the specification, the terms “tunable” and “switchable” are used interchangeably.
For example, at a first location 121, the image light portions 114 can be out-coupled with maximum light energy converging at locations A, B, or C, as required. At a second location 122, the image light portions 114 can be out-coupled with maximum light energy converging at locations D, E, or F, as needed. It is further noted that, while the out-coupling angles depend on the in-coupling angles and the grating pitch of the in-coupler 106 and the out-coupling gratings structure 108, the maximum flow of energy in a particular direction or location on the out-coupling grating structure 108 depends on refractive index contrast and the local grating slant angle.
Referring to
The diffraction gratings 201 and 202 of
Turning to
The pupil-replicating lightguide 100 carries the image light 304 generated by the microdisplay 354 to an eyebox 360 by delivering portions of the image light 304 to the eyebox 360, enabling a user’s eye 362 to directly view the image. The image can be viewed in superposition with, or overlaid upon, a view of external environment of the user, because external light 364 can propagate through the pupil-replicating lightguide 100 without being refocused or redirected. Thus, the pupil-replicating lightguide 100 functions as an effective combiner element superimposing the display-generated imagery with views of surrounding real-life environment.
The near-eye display 350 may utilize an eye tracker 366 for determining a position of a pupil of the user’s eye 362 at the eyebox 360 of the near-eye display 350, and a controller 368 operably coupled to the projector 352, the eye tracker 366, and the pupil-replicating lightguide 100. The controller 368 may be suitably configured, e.g. programmed via software and/or firmware, hardwired, etc., to cause the eye tracker 366 to determine the position of the eye pupil. Responsive to the determined position of the eye pupil, the controller 368 may switch the angular distribution of diffraction efficiency of the out-coupling grating structure 108 as explained above with reference to
For example, in embodiments where the pupil-replicating lightguide 100 of
Referring now to
As explained above with reference to
Non-limiting illustrative examples of switchable diffraction gratings usable in lightguides and displays of this disclosure will now be presented.
Referring first to
A second substrate 502 is spaced apart from the first substrate 501. The second substrate 502 supports a second conductive layer 512. A cell is formed by the first 511 and second 512 conductive layers. The cell is filled with a LC fluid, forming an LC layer 508. The LC layer 508 includes nematic LC molecules 510, which may be oriented by an electric field across the LC layer 508. The electric field may be provided by applying a voltage V to the first 511 and second 512 conductive layers.
The surface-relief grating structure 504 may be polymer-based, e.g. it may be formed from a polymer having an isotropic refractive index np of about 1.5, for example. The LC fluid has an anisotropic refractive index. For light polarization parallel to a director of the LC fluid, i.e. to the direction of orientation of the nematic LC molecules 510, the LC fluid has an extraordinary refractive index ne, which may be higher than an ordinary refractive index no of the LC fluid for light polarization perpendicular to the director. For example, the extraordinary refractive index ne may be about 1.7, and the ordinary refractive index no may be about 1.5, i.e. matched to the refractive index np of the surface-relief grating structure 504.
When the voltage V is not applied (left side of
In some embodiments of the LC surface-relief grating 500, the surface-relief grating structure 504 may be formed from an anisotropic polymer with substantially the same or similar ordinary no and extraordinary ne refractive indices as the LC fluid itself. When the LC director aligns with the optic axis of the birefringent polymer, the refractive index contrast is close to zero at any polarization of impinging light, and there is no diffraction. When the LC director is misaligned with the optic axis of the birefringent polymer e.g. due to application of an external electric field, the refractive index contrast is non-zero for any or most polarizations of the impinging light, and accordingly there is diffraction and beam deflection.
Turning to
Boundary LC molecules 607b at the top surface 605 of the LC layer 604 may be oriented at an angle to the top surface 605. The boundary LC molecules 607b may have a spatially varying azimuthal angle, e.g. linearly varying along X-axis parallel to the top surface 605, as shown in
The boundary LC molecules 607b define relative phases of the helical structures 608 having the helical period p. The helical structures 608 form a volume grating comprising helical fringes 614 tilted at an angle ϕ, as shown in
The helical nature of the fringes 614 of the volume grating makes the PVH grating 600 preferably responsive to light of polarization having one particular handedness, e.g. left- or right- circular polarization, while being substantially non-responsive to light of the opposite handedness of polarization. Thus, the helical fringes 614 make the PVH grating 600 polarization-selective, causing the PVH grating 600 to diffract light of only one handedness of circular polarization. This is illustrated in
Referring now to
At least one of the first 721 and second 722 electrode structures may be patterned for imposing a spatially variant electric field onto the first 701 and second 702 fluids. For example, in
The application of the spatially variant electric field causes the inter-fluid boundary 703 to distort as illustrated in
Portions of a patterned electrode may be individually addressable. In some embodiments, the patterned electrode 721 may be replaced with a continuous, non-patterned electrode coupled to a patterned dielectric layer for creating a spatially nonuniform electric field across the first 701 and second 702 fluids. Also in some embodiments, the backplane electrode is omitted, and the voltage is applied between the segmented electrodes themselves.
The thickness of the first 721 and second 722 electrodes may be e.g. between 10 nm and 50 nm. The materials of the first 721 and second 722 electrodes besides ITO may be e.g. indium zinc oxide (IZO), zinc oxide (ZO), indium oxide (IO), tin oxide (TO), indium gallium zinc oxide (IGZO), silver nanowires, carbon nanotubes, indium tin oxide (ITO), ITO/Ag/ITO trilayer film, etc. The first 701 and second 702 fluids may have a refractive index difference of at least 0.1, and may be as high as 0.2 and higher. One of the first 701 or second 702 fluids may include polyphenylether, 1,3-bis(phenylthio)benzene, etc. The first 711 and/or second 712 substrates may include e.g. fused silica, quartz, sapphire, etc. The first 711 and/or second 712 substrates may be straight or curved, and may include vias and other electrical interconnects. The applied voltage may be varied in amplitude and/or duty cycle when applied at a frequency of between 100 Hz and 100 kHz. The applied voltage can change polarity and/or be bipolar. Individual first 701 and/r second 702 fluid layers may have a thickness of between 0.5-5 micrometers, more preferably between 0.5-2 micrometer.
To separate the first 701 and second 702 fluids, surfactants containing one hydrophilic end functional group and one hydrophobic end functional group may be used. The examples of a hydrophilic end functional group are hydroxyl, carboxyl, carbonyl, amino, phosphate, sulfhydryl. The hydrophilic functional groups may also be anionic groups such as sulfate, sulfonate, carboxylates, phosphates, for example. Non-limiting examples of a hydrophobic end functional group are aliphatic groups, aromatic groups, fluorinated groups. For example, when polyphenyl thioether and fluorinated fluid may be selected as a fluid pair, a surfactant containing aromatic end group and fluronirated end group may be used. When phenyl silicone oil and water are selected as the fluid pair, a surfactant containing aromatic end group and hydroxyl (or amino, or ionic) end group may be used. These are only non-limiting examples.
Referring to
Some switchable gratings include a material with tunable refractive index. By way of a non-limiting example, a holographic polymer-dispersed liquid crystal (H-PDLC) grating may be manufactured by causing interference between two coherent laser beams in a photosensitive monomer/liquid crystal (LC) mixture contained between two substrates coated with a conductive layer. Upon irradiation, a photoinitiator contained within the mixture initiates a free-radical reaction, causing the monomer to polymerize. As the polymer network grows, the mixture phase separates into polymer-rich and liquid-crystal rich regions. The refractive index modulation between the two phases causes light passing through the cell to be scattered in the case of traditional PDLC or diffracted in the case of H-PDLC. When an electric field is applied across the cell, the index modulation is removed and light passing through the cell is unaffected. This is described in an article entitled “Electrically Switchable Bragg Gratings from Liquid Crystal/Polymer Composites” by Pogue et al., Applied Spectroscopy, v. 54 No. 1, 2000, which is incorporated herein by reference in its entirety.
Tunable or switchable gratings with a variable grating period may be produced e.g. by using flexoelectric LC. For LCs with a non-zero flexoelectric coefficient difference (e1-e3) and low dielectric anisotropy, electric fields exceeding certain threshold values result in transitions from the homogeneous planar state to a spatially periodic one. Field-induced grating is characterized by rotation of the LC director about the alignment axis with the wavevector of the grating oriented perpendicular to the initial alignment direction. The rotation sign is defined by both the electric field vector and the sign of the (e1-e3) difference. The wavenumber characterizing the field-induced periodicity is increased linearly with the applied voltage starting from a threshold value of about π/d, where d is the thickness of the layer. A description of flexoelectric LC gratings may be found e.g. in an article entitled “Dynamic and Photonic Properties of Field-Induced Gratings in Flexoelectric LC Layers” by Palto in Crystals 2021, 11, 894, which is incorporated herein by reference in its entirety.
Tunable gratings with a variable grating period or a slant angle may be provided e.g. by using helicoidal LC. Tunable gratings with helicoidal LCs have been described e.g. in an article entitled “Electrooptic Response of Chiral Nematic Liquid Crystals with Oblique Helicoidal Director” by Xiang et al. Phys. Rev. Lett. 112, 217801, 2014, which is incorporated herein by reference in its entirety.
For gratings exhibiting strong wavelength dependence of grating efficiency, several gratings, e.g. several volumetric Bragg grating (VBG) gratings, may be provided in the lightguide. The gratings that diffract light at any given moment of time may be switched by switching the VBG grating on and off, and/or by switching the wavelength of the light propagating in the waveguide.
Referring now to
The purpose of the eye trackers 904 is to determine position and/or orientation of both eyes of the user to enable steering the output image light to the locations of the user’s eyes as disclosed herein. The eyebox illuminators 906 illuminate the eyes at the corresponding eyeboxes 912, to enable the eye trackers 904 to obtain the images of the eyes, as well as to provide reference reflections i.e. glints. The glints may function as reference points in the captured eye image, facilitating the eye gazing direction determination by determining position of the eye pupil images relative to the glints images. To avoid distracting the user with the light of the eyebox illuminators 906, the light illuminating the eyeboxes 912 may be made invisible to the user. For example, infrared light may be used to illuminate the eyeboxes 912.
Turning to
In some embodiments, the front body 1002 includes locators 1008 and an inertial measurement unit (IMU) 1010 for tracking acceleration of the HMD 1000, and position sensors 1012 for tracking position of the HMD 1000. The IMU 1010 is an electronic device that generates data indicating a position of the HMD 1000 based on measurement signals received from one or more of position sensors 1012, which generate one or more measurement signals in response to motion of the HMD 1000. Examples of position sensors 1012 include: one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects motion, a type of sensor used for error correction of the IMU 1010, or some combination thereof. The position sensors 1012 may be located external to the IMU 1010, internal to the IMU 1010, or some combination thereof.
The locators 1008 are traced by an external imaging device of a virtual reality system, such that the virtual reality system can track the location and orientation of the entire HMD 1000. Information generated by the IMU 1010 and the position sensors 1012 may be compared with the position and orientation obtained by tracking the locators 1008, for improved tracking accuracy of position and orientation of the HMD 1000. Accurate position and orientation is important for presenting appropriate virtual scenery to the user as the latter moves and turns in 3D space.
The HMD 1000 may further include a depth camera assembly (DCA) 1011, which captures data describing depth information of a local area surrounding some or all of the HMD 1000. The depth information may be compared with the information from the IMU 1010, for better accuracy of determination of position and orientation of the HMD 1000 in 3D space.
The HMD 1000 may further include an eye tracking system 1014 for determining orientation and position of user’s eyes in real time. The obtained position and orientation of the eyes also allows the HMD 1000 to determine the gaze direction of the user and to adjust the image generated by the display system 1080 accordingly. The determined gaze direction and vergence angle may be used to adjust the display system 1080 to reduce the vergence-accommodation conflict. The direction and vergence may also be used for displays’ exit pupil steering as disclosed herein. Furthermore, the determined vergence and gaze angles may be used for interaction with the user, highlighting objects, bringing objects to the foreground, creating additional objects or pointers, etc. An audio system may also be provided including e.g. a set of small speakers built into the front body 1002.
Embodiments of the present disclosure may include, or be implemented in conjunction with, an artificial reality system. An artificial reality system adjusts sensory information about outside world obtained through the senses such as visual information, audio, touch (somatosensation) information, acceleration, balance, etc., in some manner before presentation to a user. By way of non-limiting examples, artificial reality may include virtual reality (VR), augmented reality (AR), mixed reality (MR), hybrid reality, or some combination and/or derivatives thereof. Artificial reality content may include entirely generated content or generated content combined with captured (e.g., real-world) content. The artificial reality content may include video, audio, somatic or haptic feedback, or some combination thereof. Any of this content may be presented in a single channel or in multiple channels, such as in a stereo video that produces a three-dimensional effect to the viewer. Furthermore, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof, that are used to, for example, create content in artificial reality and/or are otherwise used in (e.g., perform activities in) artificial reality. The artificial reality system that provides the artificial reality content may be implemented on various platforms, including a wearable display such as an HMD connected to a host computer system, a standalone HMD, a near-eye display having a form factor of eyeglasses, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers.
The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments and modifications, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Further, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.
This application claims priority from U.S. Provisional Pat. App. No. 63/286,381 entitled “Display Applications of Switchable Gratings”, and U.S. Provisional Pat. App. No. 63/286,230 entitled “Active Fluidic Optical Element”, both filed on Dec. 6, 2021 and incorporated herein by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| 63286381 | Dec 2021 | US | |
| 63286230 | Dec 2021 | US |
