TW202340791A - Lightguides with color- and time-sequential gratings - Google Patents

Abstract

A lightguide for conveying image light to an eyebox of a display device includes a tunable grating, e.g. an out-coupling grating for out-coupling the image light from the lightguide. The tunable grating may be tuned or switched to effectively diffract light of a color channel of a color-sequential display. In augmented reality display systems, a lightguide combiner element may include a switchable grating to out-couple the image light only during short time intervals and to not out-couple the image light in between these time intervals. Effectively, the out-coupling grating is present only a portion of overall operation time of the display, which improves the transparency of the combiner element to the outside light and reduces rainbow effects.

Description

Light guides with color-sequential and time-sequential gratings

The present invention relates to tunable optical devices and, in particular, to light guides that may be used in visual display systems, as well as components, modules, and methods for use in light guides and visual display systems. References to related applications

The claims in this application originate from U.S. Provisional Patent Application No. 63/286,349, titled "Active Gratings in Pupil-Replicated Displays and Illuminators" filed on December 6, 2021. , the priority of U.S. Provisional Patent Application No. 63/286,230 filed on December 6, 2021 and U.S. Non-Provisional Patent Application No. 17/581,303 filed on January 21, 2022, and are incorporated by reference in full. into this article.

Visual displays provide information including still images, videos, data, etc. to viewers. 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 televisions, display images to several users, and some visual display systems, such as near-eye displays (NED), are intended for individual users.

Artificial reality systems typically include an NED (eg, a head-mounted device or a pair of glasses) configured to present content to a user. Near-eye displays can display virtual objects or images that combine real objects and virtual objects, such as in virtual reality (VR), augmented reality (AR) or mixed reality (MR). . For example, in an AR system, a user can view images of virtual objects (e.g., computer-generated images (CGI)) overlaid with the surrounding environment by viewing through a "combiner" component. The combiner assembly, including its light routing optics, can be transparent to external light.

NEDs are usually worn on the user's head. Therefore, a large, bulky, unbalanced and/or heavy display device with a heavy battery would be cumbersome and uncomfortable for the user to wear. Head-mounted display devices can benefit from compact and efficient configurations, including efficient light sources and illuminators that provide illumination of the display panel, high-throughput combiner components and eye lenses, and image forming series that can minimize image distortion and artifacts to the user. Other optical components of the eye that provide images.

One aspect of the invention refers to a light guide for transmitting light, the light guide comprising at least one of a plurality of color channels, the light guide comprising: a plate of transparent material for passing light from one of the opposing surfaces of the plate a series of internal reflections to guide the light therein; an in-coupling grating structure supported by the plate for coupling the light into the plate; and an out-coupling grating structure supported by the plate for coupling light from the plate The panel couples out a portion of the light, wherein at least one of the in-coupling grating structure or the out-coupling grating structure is tunable in at least one of grating spacing or grating efficiency for the plurality of color channels with the light The light of a particular person operates together.

In the light guide of the foregoing aspects, at least one of the coupling-in grating structure or the coupling-out grating structure includes a polarizing volume hologram (PVH) grating.

In the lightguide of the foregoing aspects, at least one of the in-coupling grating structure or the out-coupling grating structure includes a tunable panning Ratnum-Berry phase (PBP) liquid crystal (LC) grating.

In the light guide of the aforementioned aspects, at least one of the coupling-in grating structure or the coupling-out grating structure includes a tunable liquid crystal (LC) surface relief grating.

In the light guide of the aforementioned aspect, at least one of the coupling-in grating structure or the coupling-out grating structure includes a fluid surface relief grating.

In the lightguide of the previous aspect, the at least one of the coupling-in grating structure or the coupling-out grating structure includes a switchable volume Bragg grating (VBG) according to each of the plurality of color channels.

In the light guide of the aforementioned aspect, the light guide is a pupil replica light guide; and the plurality of color channels include a red channel, a green channel and a blue channel; wherein the coupling-out grating structure has a spatially variable tunable grating spacing so as to be predefined The angular distribution couples out the portions of the light from the light guide.

In the light guide of the aforementioned aspect, the light guide is a pupil replica light guide; and the plurality of color channels include a red channel, a green channel and a blue channel; wherein the coupling-out grating structure has a spatially varying tunable grating efficiency to improve the coupling efficiency. The grating structure provides spatial uniformity of the portions of light coupled from the plate.

Another aspect of the present invention refers to a display device for transmitting an image including a first color channel and a second color channel to an eye movement area. The display device includes: a light engine configured to provide a light engine including: Light from at least one of the first beam and the second beam of the first color channel and the second color channel; a light guide coupled to the light engine for receiving the light, the light guide comprising: a transparent material plate , for guiding the light therein by a series of internal reflections from opposing surfaces of the plate; a coupling grating structure supported by the plate for coupling the light into the plate; and An out-coupling grating structure is supported by the plate for coupling out a portion of the light from the plate; wherein at least one of the in-coupling grating structure or the out-coupling grating structure has at least one of a grating pitch or a grating efficiency. Tunable for operation with light from a particular one of the first color channel or the second color channel; and a controller operatively coupled to the light engine and the light guide and configured to: cause the The light engine provides the first light beam carrying the first color channel; at least one of the coupling-in grating structure or the coupling-out grating structure is tuned in at least one of grating pitch or grating efficiency to increase the first the flux of the light beam; causing the light engine to provide the second light beam carrying the second color channel; and tuning the in-coupling grating structure or the out-coupling grating structure in at least one of grating pitch or grating efficiency. At least one is used to increase the flux of the second light beam.

In the display device of the aforementioned aspect, at least one of the in-coupling grating structure or the out-coupling grating structure includes a polarization volume hologram (PVH) grating.

In the display device of the aforementioned aspect, at least one of the in-coupling grating structure or the out-coupling grating structure includes a tunable Pan-Pertnum-Berry phase (PBP) liquid crystal (LC) grating.

In the display device of the aforementioned aspect, at least one of the coupling-in grating structure or the coupling-out grating structure includes a tunable liquid crystal (LC) surface relief grating.

In the display device of the aforementioned aspect, at least one of the coupling-in grating structure or the coupling-out grating structure includes a fluid surface relief grating.

In the display device of the aforementioned aspect, at least one of the coupling-in grating structure or the coupling-out grating structure includes a switchable volume Bragg grating (VBG) according to each of the first color channel and the second color channel. .

In the display device of the aforementioned aspect, the light guide is a pupil replica light guide, and the coupling-out grating structure has at least one of a spatially varying tunable grating spacing or a spatially varying tunable grating efficiency, so as to distribute at a predefined angle and Predefined spatial uniformity couples the portions of the first beam and the second beam from the plate.

In the display device of the aforementioned aspect, the light further includes a third color channel of the image; the light engine is further configured to provide a third light beam carrying the third color channel; and the controller is further programmed to The light engine is caused to provide the third beam and at least one of the coupling-in grating structure or the coupling-out grating structure is tuned in at least one of grating spacing or grating efficiency to increase the flux of the third beam.

Yet another aspect of the invention is a method for transmitting an image to an eye movement zone, the method comprising: providing a first light beam carrying a first color channel of the image; coupling the first light beam to a light guide The coupling grating structure, the light guide includes a coupling grating structure for coupling out part of the first light beam; at least one of the grating spacing or the grating efficiency is tuned in the coupling grating structure or the coupling grating structure. At least one to increase the flux of the first beam; provide a second beam carrying a second color channel of the image; couple the second beam to the coupling grating of the light guide; and at the grating pitch or The at least one of the grating efficiency tunes the at least one of the coupling-in grating structure or the coupling-out grating structure to increase the flux of the second light beam.

The method of the foregoing aspect further includes: providing a third light beam carrying a third color channel of the image; coupling the third light beam to the coupling grating of the light guide; and in the grating spacing or the grating efficiency. The at least one tunes the at least one of the coupling-in grating structure or the coupling-out grating structure to increase the flux of the third light beam.

In the method of the aforementioned aspect, the outcoupling grating structure has a spatially variable tunable grating spacing so as to couple out the portions of the first beam and the second beam from the light guide in a predefined angular distribution.

In the method of the aforementioned aspect, the outcoupling grating structure has a spatially varying tunable grating efficiency so as to couple out the portions of the first beam and the second beam from the light guide with predefined spatial uniformity.

Although the present teachings are described in connection with various specific examples and examples, the present teachings are not intended to be limited to such specific examples. On the contrary, as one of ordinary skill in the art will appreciate, this teaching encompasses various alternatives and equivalents. All statements herein reciting principles, aspects, and specific examples of the invention, 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, that is, any elements developed that perform the same function, regardless of structure.

As used herein, the terms "first," "second," etc. are not intended to imply a sequential ordering, but are intended to distinguish one element from another element unless expressly stated otherwise. Similarly, the sequential ordering of method steps does not imply a sequential order of their performance unless expressly stated.

Near-eye displays use light guides to carry images to the viewer's eyes and/or to illuminate the display panels that produce the images to be displayed. The light guide may include a grating structure for coupling light into the light guide and a portion for coupling out the light along the surface of the waveguide. According to the present invention, the grating structure of the light guide may include a tunable/switchable grating with variable efficiency, period, blaze angle, etc. The terms "switchable," "tunable," and "variable" are used interchangeably herein and mean that grating parameters, such as grating intensity, blaze angle, grating spacing, etc., can be controlled by applying external control signals. At least one. The specific parameters that are controlled depend on the type of tunable grating used.

The tunability of the grating parameters enables optimization of light guide performance parameters such as luminous flux, eye zone size, artifact suppression, etc. For example, for a color-sequential near-eye display, luminous flux may be optimized individually for light in each of the red, green, and blue color channels. In addition, for AR displays, the combiner element can be further improved by turning on the outcoupling grating for a brief moment to display an AR image, enabling better viewing of the surrounding environment through AR glasses while suppressing unwanted image artifacts, rainbow effects, etc. transparency.

According to the present invention, there is provided a light guide for transmitting light, which includes at least one color channel of a plurality of color channels. A light guide consists of a flat plate of transparent material that is used to guide light therein by a series of internal reflections from opposing surfaces of the flat plate. The coupling grating structure is supported by the flat plate for coupling light into the flat plate. The decoupling grating structure is supported by the flat plate and is used for coupling out light from the flat plate. At least one of the coupling-in grating structure or the coupling-out grating structure is tunable in at least one of a grating pitch or a grating efficiency for operation with light from a particular one of a plurality of color channels of the light. At least one of the coupling-in grating structure or the coupling-out grating structure may include, for example, a polarizing volume hologram (PVH) grating, a tunable Panchalanma-Berry phase (PBP) liquid crystal (LC) grating, a tunable liquid crystal (LC) grating, LC) surface relief gratings, fluid gratings, and switchable volumetric Bragg gratings (VBG) based on each of a plurality of color channels.

The light guide may include, for example, a pupil replica light guide. The plurality of color channels may include, for example, a red channel, a green channel, and a blue channel. The outcoupling grating structure may have a spatially varying tunable grating spacing to couple out a portion of the light from the light guide in a predefined angular distribution, and/or a spatially varying tunable grating efficiency to improve the efficiency of the light outcoupling from the plate by the outcoupling grating structure. Partial spatial uniformity.

According to the present invention, a display device for transmitting an image including a first color channel and a second color channel to an eye movement area is provided. The display device includes a light engine for providing light including at least one of a first light beam and a second light beam carrying a first color channel and a second color channel, respectively, of an image. The light guide is coupled to the light engine for receiving the first light beam and the second light beam. The controller is operably coupled to the light engine.

The light guide includes: a flat plate of transparent material for guiding light therein by a series of internal reflections from opposing surfaces of the flat plate; a coupling grating structure supported by the flat plate for coupling light into the flat plate; and The coupling grating structure is supported by a flat plate and is used to couple light from the flat plate. At least one of the coupling-in grating structure or the coupling-out grating structure is tunable in at least one of grating spacing or grating efficiency for operation with light from a particular one of the first color channel or the second color channel. Coupling-in and/or out-coupling gratings may include any of the grating structures mentioned above, namely polarizing volume hologram (PVH) gratings, tunable Pan-Ratnam-Berry phase (PBP) liquid crystals (LC) gratings, tunable liquid crystal (LC) surface relief gratings, fluid gratings, switchable volume Bragg gratings (VBG) based on each of a plurality of color channels.

The controller is configurable to cause the light engine to provide a first light beam carrying a first color channel; to tune at least one of a coupling into the grating structure or a coupling out of the grating structure at at least one of a grating pitch or a grating efficiency. to increase the flux of the first light beam; to cause the light engine to provide a second light beam carrying a second color channel; and to tune at least one of the grating spacing or the grating efficiency to couple into the grating structure or to couple out of the grating structure. To increase the flux of the second beam. The light engine may be further configured to provide a third light beam carrying a third color channel of the image to be displayed. The controller may be further configured to cause the light engine to provide the third beam and to tune at least one of coupling into or out of the grating structure at at least one of grating spacing or grating efficiency to increase flux of the third beam. The controller can tune individual light grids in a chronological manner.

In specific examples where the light guide is a pupil replica light guide, the outcoupling grating structure may have at least one of a spatially varying tunable grating spacing or a spatially varying tunable grating efficiency to provide a predefined angular distribution and/or a predefined Parts of the first beam and the second beam are uniformly coupled in space from the flat plate.

According to the present invention, a method for transmitting an image to a glaucoma zone is further provided. The method includes providing a first light beam carrying a first color channel of the image. The first light beam is coupled to the coupling grating structure of the light guide, and the light guide includes an outcoupling grating structure for coupling out a portion of the first light beam. At least one of the grating pitch or the grating efficiency is tuned to at least one of the coupling-in grating structure or the coupling-out grating structure to increase the flux of the first light beam. A second light beam carrying a second color channel of the image is provided. The second light beam is coupled to the coupling grating of the light guide. At least one of the coupling-in grating structure or the coupling-out grating structure is tuned at least one of the grating pitch or the grating efficiency to increase the flux of the second light beam. A third light beam carrying a third color channel of the image may be provided. At least one of the coupling-in grating structure or the coupling-out grating structure can be tuned in at least one of the grating pitch or the grating efficiency to increase the flux of the second light beam.

In some embodiments, the outcoupling grating structure has a spatially varying tunable grating spacing to couple out portions of the first beam and the second beam from the light guide in a predefined angular distribution. The outcoupling grating structure may have a spatially varying tunable grating efficiency to couple out portions of the first and second beams from the light guide with predefined spatial uniformity.

Referring now to FIG. 1 , light guide 100 transmits light 102 from input location 104 to output location 106 . The light guide 100 includes a flat plate 108 of transparent material for guiding light 102 in the flat plate 108 by a series of internal reflections from opposing surfaces 111 , 112 of the flat plate 108 . Light 102 may be reflected from opposing surfaces 111, 112 via total internal reflection (TIR). The light guide 100 further includes a coupling grating structure 114 supported by the plate 108 for coupling light 102 into the plate 108 , and an outcoupling grating structure 116 supported by the plate 108 for coupling light out of the plate 108 . The coupling-in grating structure 114 and the coupling-out grating structure 116 may be disposed in the plate 108 (as shown) or on the plate 108 . The outcoupling grating structure 116 may, but need not, provide multiple laterally offset portions of the light 102 at the output location 106, in which case the lightguide 100 is referred to as a pupil replica lightguide.

In some embodiments, light 102 may be used to illuminate a display panel or another optical element at output location 106 . In some embodiments, light 102 may carry an angular domain image to be viewed at output location 106 . Light 102 includes a plurality of color channels, such as red, green, and blue channels. Individual color channel lights can be provided in chronological order. For example, during a first time interval, the light 102 may carry a red channel (i.e., a red light beam); during a subsequent second time interval, the light 102 may carry a green channel (i.e., a green light beam); and during a subsequent third time interval, the light 102 may carry a green channel (i.e., a green light beam). Time interval, light 102 can carry the blue channel (ie, blue light beam). The first time interval, the second time interval and the third time interval may be repeated in a chronological manner while the display is in operation to provide RGB images.

In the specific example where the light 102 carries several color channels simultaneously, the in-coupling grating structure 114 and the out-coupling grating structure 116 need to be configured to operate with all color channels of the light simultaneously, that is, the grating structures 114 and 116 need to be optimized to For operation with polychromatic light. This optimization often requires a tradeoff in which the diffraction efficiency of grating structures 114 and 116 at specific wavelengths of individual color channels is reduced while diffracting light at all wavelengths or color channels with substantially similar efficiency. However, this is no longer necessary when the light for the individual color channels is provided in a time-sequential manner as explained above. At least one of the in-coupling grating structure 114 or the out-coupling grating structure 116 may be tunable in at least one of a grating spacing or a grating efficiency for use with light from a particular one of a plurality of color channels of the light 102 operate. The tunability of the in-coupling grating structure 114 and/or the out-coupling grating structure 116 allows one to individually optimize the grating performance of each color channel, thereby increasing the overall diffraction efficiency and improving the flux of the light guide 100 .

In the specific example where the lightguide 100 is a pupil replica lightguide and the light 102 carries a plurality of color channels (eg, a red channel, a green channel, and a blue channel), the outcoupling grating structure 116 can have independent features for each of the color channels. A spatially varying grating pitch that is tuned to a preconfigured spatial pitch distribution to couple out a portion of the light from the light guide in a predefined angular distribution. This enables the spatial pitch distribution to be optimized individually for each color channel. In this other pupil replica lightguide embodiment, the outcoupling grating structure 116 may have spatially varying grating efficiency. The spatially varying grating efficiency can be independently tuned for each of the color channels to improve the spatial uniformity of the portion of light coupled out of the panel by the coupling out grating structure 116.

Referring to Figure 2, the color selective performance of the light guide 100 is schematically illustrated for three consecutive time intervals (ie, the first, second, and third intervals discussed above). During the first time interval, the light 102 includes a red channel beam, and the in-coupling grating structure 114 and/or the out-coupling grating structure 116 are tuned to improve or maximize the luminous flux of the red channel light (long dashed line at the top of Figure 2 ). During the second time interval, the light 102 includes a green channel beam, and the in-coupling grating structure 114 and/or the out-coupling grating structure 116 are tuned to improve or maximize the luminous flux of the green channel light (the solid line in the middle of Figure 2 ). Finally, during the third time interval, the light 102 includes a blue channel beam, and the in-coupling grating structure 114 and/or the out-coupling grating structure 116 are tuned to improve or maximize the luminous flux of the blue channel light (bottom of FIG. 2 short dashed line at ). Of course, the display order of the red, green and blue channels can be changed if necessary.

Returning to FIG. 3 , the display device 350 includes a light engine 352 coupled to the pupil replica lightguide 300 , and a controller 305 operably coupled to the light engine 352 and the pupil replica lightguide 300 . Light engine 352 provides image light at eye movement zone 360 that carries the angular domain image to be viewed by user's eyes 362 . To this end, the light engine 352 may emit a first light beam 321 and a second light beam 322 carrying first color channels and second color channels of image light, respectively. There may be more than two color channels, such as three or even more color channels, and corresponding three or more light beams, each carrying its own color channel. In the illustrated example, light engine 352 includes display panel 354 coupled to projector lens 356 for converting linear domain images displayed by display panel 354 into angular domain images. In some embodiments, light engine 352 may include a beam scanner for rasterizing angular domain images.

Pupil replicating lightguide 300 is based on lightguide 100 of Figure 1 and includes similar components. Any suitable embodiment of light guide 100 may be used. Briefly, the pupil replica light guide 300 of FIG. 3 includes a flat plate 308 of transparent material such as glass, metal oxide, crystal, plastic, etc. The plate 308 guides the first light beam 321 (solid line) and the second light beam 322 (dashed line) in the plate 308 by a series of internal reflections from the first opposing surface 311 and the second opposing surface 312 of the plate 308 . For convenience of illustration, the first beam 321 and the second beam 322 are shown offset from each other.

The first surface 311 and the second surface 312 extend parallel to each other, and in some embodiments may be straight (as shown) or curved. The pupil replica light guide 300 includes a coupling grating structure 314 supported by the flat plate 308 for coupling the first light beam 321 and the second light beam 322 into the flat plate 308 . The pupil replica light guide 300 further includes an outcoupling grating structure 316 supported by the flat plate 308 for coupling out portions 321A, 322A of the first beam 321 and the second beam 322 from the flat plate 308, respectively. At least one of the in-coupling grating structure 314 or the out-coupling grating structure 316 of the pupil replica light guide 300 is tunable in at least one of the grating pitch or the grating efficiency for use with the first color channel or the second color channel. Operates with a specific person's light.

The controller 305 may be appropriately configured, such as programmed with software, firmware, and/or hardware, to cause the light engine 352 to provide the first light beam 321 carrying the first color channel. The controller 305 tunes at least one of the coupling-in grating structure 314 or the coupling-out grating structure 316 at at least one of the grating pitch or the grating efficiency to increase the distance of the first beam 321 from the light engine 352 to the eye movement area 360 flux. In other words, the grating pitch and/or the grating efficiency are selected so that the light of the first color channel (eg, red light) is transmitted to the eye movement zone 360 with high efficiency. Next, the controller 305 causes the light engine 352 to provide the second light beam 322 carrying the second color channel. The controller 305 tunes at least one of the in-coupling grating structure 314 or the out-coupling grating structure 316 at at least one of the grating pitch or the grating efficiency to increase the flux of the second light beam. In other words, the grating pitch and/or the grating efficiency are selected by the controller 305 so that the light of the second color channel (eg, green light) is transmitted to the eye movement area 360 with higher efficiency.

Controller 305 may cause light engine 352 to provide a third light beam carrying a third color channel (not shown in Figure 3 for simplicity). The controller 305 then tunes at least one of the in-coupling grating structure 314 or the out-coupling grating structure 316 at at least one of the grating pitch or the grating efficiency to increase the flux of the third light beam (eg, the blue light beam).

During successive time intervals, beams of individual color channels may be provided in a time-sequential manner. At each of these time intervals, the in-coupling 314 and/or out-coupling grating 316 parameters are tuned for optimal transmission of the particular one of the color channels. Displays with sequential presentation of color channels are referred to herein as color-sequential displays. In some embodiments of color sequential displays, the outcoupling grating structure 316 may have at least one of a spatially varying tunable grating spacing or a spatially varying tunable grating efficiency to predetermine the specific construction and viewing requirements of the display device 350 . Portions 321A, 322 of the first beam 321 and the second beam 322 are coupled from the plate 308 with a defined angular distribution and a predefined spatial uniformity.

Referring now to FIG. 4 and further to FIG. 3 , a method 400 for transmitting an image to an eye movement zone of a display device includes providing ( 402 ) a first light beam carrying a first color channel (eg, a red channel) of the image. The first light beam is coupled (404) to the coupling grating structure of the light guide, such as the coupling grating 314 of the light guide 300 of Figure 3. Tuning (FIG. 4; 406) the grating pitch and/or the grating efficiency of at least one of the coupling-in grating structure 314 or the coupling-out grating structure 316 to increase the flux of the first light beam, for example, to optimize transmission of the display to be displayed The light grating structure 314, 316 of the red channel of the image.

A second beam is then provided (408). The second beam carries a second color channel of the image, such as the green channel. Couple (410) the second beam to the coupling grating of the light guide. Coupling into and/or out of the grating structure during grating pitch and/or grating efficiency tuning (412) to increase the flux of the second light beam, for example, to optimize the grating structures 314, 316 to transmit the green color of the image to be displayed. Channel light.

A third beam may then be provided (414). The third beam carries a third color channel of the image, such as the blue channel. Couple (416) the third beam to the coupling grating of the light guide. The grating pitch and/or grating efficiency tuning (418) is coupled into and/or out of the grating structure to increase the flux of the third light beam, for example, to optimize the grating structures 314, 316 to transmit the blue color of the image to be displayed. The light of the color channel. As explained above, the outcoupling grating structure 316 may have a spatially varying tunable grating spacing to couple portions of the first and second beams from the plate 308 in a predefined angular distribution. The decoupling grating structure 316 may also have a spatially varying tunable grating efficiency to couple portions of the first and second beams from the plate 308 with predefined spatial uniformity.

Steps 402, 404, 406 associated with the first color channel may be performed within a first time interval. Steps 408, 410, 412 associated with the second color channel may be performed during a second time interval following the first time interval. Steps 414, 416, 418 associated with the third color channel may be performed during a third time interval following the second time interval. Next, steps 402 to 418 of method 400 may be repeated. Thus, the different color channels of the image can be displayed in a time-sequential manner, with the in-coupling grating structure 314 and/or the out-coupling grating structure 316 being optimized for displaying a particular color channel at a time.

Example implementations of the in-coupling grating structure 314 and/or the out-coupling grating structure 316 will be further considered below with reference to Figures 8-13. Each of the coupling-in grating structure 314 and/or the coupling-out grating structure 316 may include an individually tunable grating per grating structure or multiple gratings per grating structure, one grating per color channel. The light barrier can be switched on and off depending on whether a particular channel is displayed at any given moment.

Returning to FIG. 5 , the near-eye display 550 includes: a light engine 552 for providing image light 521 carrying an angular domain image; a pupil replicating light guide 500 coupled to the light engine 552 for expanding the image light 521 ; and a controller 505 operatively coupled to the light engine 552 and the pupil replicating lightguide 500 . In the illustrated example, light engine 552 includes display panel 554 coupled to projector lens 556 for converting linear domain images displayed by display panel 554 into angular domain images. In some embodiments, light engine 552 may include a beam scanner for rasterizing angular domain images.

Pupil replicating light guide 500 includes a plate 508 of transparent material, such as glass, metal oxide, crystal, plastic, etc., which is used to transmit external visible light 564 through plate 508 by a signal from opposing surfaces 511, 512 of plate 508. A series of internal reflections are used to guide the image light 521 in the flat plate 508. Opposing surfaces 511, 512 may be exterior surfaces of plate 508, or alternatively, in some embodiments, additional layers may be provided. Pupil replica light guide 500 may further include a coupling grating 514 supported by plate 508 for coupling image light 521 into plate 508 . The decoupling grating 516 may be supported by the flat plate 508 for coupling out the portion 521A of the image light 521 from the flat plate 508 to propagate toward the eye movement area 560 so that the user's eyes 562 can see the image. Portions 521A are laterally offset from each other along the path of image light 521 in plate 508, as illustrated. The decoupling grating 516 has a diffraction efficiency that can be switched between a high-efficiency state and a low-efficiency state. In the high-efficiency state, the percentage P ₁ of image light coupled out from the flat plate 508 is higher than the first threshold value L ₁ , and in this low efficiency state, the percentage P ₂ of the image light coupled out from the plate 508 is lower than the second threshold value L 2 which is lower than the first threshold value L _{1 .} The high efficiency state may correspond to the maximum diffraction efficiency of the outcoupling grating 516, and the low efficiency state may correspond to a state when the outcoupling grating 516 diffracts little or no light.

With reference to Figure 6 and further reference to Figure 5, the controller 505 (Figure 5) may be suitably configured, such as programmed with software, firmware and/or hardware to cause the light engine 552 to operate during the first time interval T ₁ (Figure 6 ) during which the image light 521 is provided, and the outcoupling grating 516 is switched to a high-efficiency state during the first time interval T ₁ . During the subsequent second time interval T ₂ , the controller 505 switches the decoupling grating to a low efficiency state. The second time interval T ₂ may immediately follow the first time interval T ₁ . The next first time interval T ₁ may immediately follow the second time interval T ₂ , and so on. Pupil replica lightguide 500 may be configured to transmit external visible light 564 therethrough during first time interval T ₁ and second time interval T ₂ or only during first time interval T ₁ . In order to save power, the controller 505 may be configured so that the light engine 552 does not provide image light during the second time interval T ₂ , that is, the light engine 552 is turned off during the second time interval T ₂ .

One benefit of only switching the outcoupling grating 516 to a high efficiency state during the first time interval T ₁ is better transmission of external visible light 564 via the pupil replica lightguide 500 . When the decoupling grating 516 is in an inefficient state, the flux of external visible light 564 is improved and possible artifacts such as rainbow artifacts are reduced. The second threshold value L ₂ may be at least three times lower than the first threshold value L ₁ , or at least ten times lower than the first threshold value L ₁ , or even at least a hundred times lower than the first threshold value L 1 . In order to further improve the flux of the external visible light 564 of the pupil replicating light guide 500, the second time interval _T2 may be at least two times larger than the first time interval _T1 , or in some embodiments nine times larger, or even larger than the first time interval T1. The interval T ₁ is at least a hundred times larger.

Returning to FIG. 7 and with further reference to FIGS. 5 and 6 , a method 700 for utilizing a generated image (eg, a real view augmented image or a virtual image) to augment a view of an external environment includes placing an image light (eg, a real view augmented image or a virtual image) carrying the generated image. Image light 521) generated by light engine 552 (FIG. 5) is coupled (702) to a plate of transparent material, such as plate 508. By allowing external visible light 564 to propagate through the plate 508 of the pupil replica lightguide 500 and the outcoupling grating 516, the external environment can be observed through the plate 508.

Image light 521 is directed (Fig. 7; 704) in plate 508 by a series of internal reflections from opposing surfaces 511, 512 of plate 508. During the first time interval T ₁ , the outcoupling grating 516 is switched ( 706 ) to a high-efficiency state and remains in the high-efficiency state, wherein the outcoupling grating 516 couples out the laterally offset portion 521A of the image light 521 from the plate. As described above, the percentage of image light 521 coupled out from the plate 508 as portion 521A is higher than the first threshold L ₁ . During a second time interval T ₂ after the first time interval T ₁ , the outcoupling grating 516 is switched ( 708 ) to a high-efficiency state in which the percentage of image light 521 outcoupled from the plate 508 is less than the first threshold. The second threshold L ₂ is lower than L ₁ . The second threshold value L ₂ may be at least ten times lower than the first threshold value L ₁ . The second time interval T ₂ may be at least nine times greater than the first time interval T ₁ .

The two final steps 706 and 708 may then be repeated one after the other in a loop. During the third time interval after the second time interval (ie, the first interval of repetition), the decoupling grating 516 can be switched to a high efficiency state again. Then, during a fourth time interval following the third time interval (ie, the repeated second time interval), the decoupling grating 516 may be switched to a low efficiency state again, and so on. Image light 521 may be coupled to plate 508 only during the intervals when outcoupling grating 516 is switched to a high efficiency state to maintain power. The decoupling grating 516 may have less rainbow effect in a low efficiency state than in a high efficiency state. Switching the outcoupling grating 516 to a low efficiency state for a substantial portion of the viewing time results in a reduction of the overall rainbow effect and other image and/or viewing artifacts, and may also improve the overall transparency of the pupil replicating lightguide 500 to external visible light 564.

Non-limiting examples of switchable/tunable gratings that may be used in the light guides and displays of the present invention will now be presented. Referring first to Figure 8, a tunable liquid crystal (LC) surface relief grating 800 can be used, for example, in the coupling grating structure 114 and/or the coupling out grating structure 116 in Figures 1 and 2, and in the coupling grating structure 314 and/or the coupling out in Figure 3. The grating structure 316, the in-coupling grating structure 514 and/or the out-coupling grating structure 516 of FIGS. 5 and 6. The tunable LC surface relief grating 800 includes a first substrate 801 supporting a first conductive layer 811 and a surface relief grating structure 804 having a plurality of ridges 806 extending from the first substrate 801 and/or the first conductive layer 811 .

The second substrate 802 is spaced apart from the first substrate 801 . The second substrate 802 supports the second conductive layer 812. The unit is formed of a first conductive layer 811 and a second conductive layer 812 . The cells are filled with LC fluid, forming LC layer 808. LC layer 808 includes nematic LC molecules 810 that can be oriented by an electric field across LC layer 808 . The electric field may be provided by applying voltage V to the first conductive layer 811 and the second conductive layer 812.

For example, surface relief grating structure 804 may be formed from a polymer having an isotropic refractive index n _p of approximately 1.5. LC fluids have anisotropic refractive index. For light polarization parallel to the guide of the LC fluid (that is, parallel to the orientation direction of the nematic LC molecules 810), the LC fluid has an extraordinary refractive index n _e , which can be higher than perpendicular to the guide. The ordinary refractive index of the LC fluid for the polarization of light n _o . For example, the extraordinary refractive index n _e may be about 1.7, and the ordinary refractive index n _o may be about 1.5, that is, matching the refractive index n _p of the surface relief grating structure 804 .

When no voltage V is applied (left side of FIG. 8 ), the LC molecules 810 are aligned substantially parallel to the grooves of the surface relief grating structure 804 . In this configuration, a linearly polarized beam 821 with an e-vector oriented along the grooves of the surface relief grating structure 804 will undergo diffraction because the surface relief grating structure 804 will have a non-zero refractive index contrast. When a voltage V is applied (right side of FIG. 8 ), the LC molecules 810 are aligned generally perpendicular to the grooves of the surface relief grating structure 804 . In this configuration, a linearly polarized beam 821 with an e-vector oriented along the grooves of the surface relief grating structure 804 will not experience diffraction because the surface relief grating structure 804 will appear to be index matched and therefore will Has essentially zero refractive index contrast. For a linearly polarized beam 821 with an e-vector oriented perpendicular to the grooves of the surface relief grating structure 804, no diffraction will occur in either case (i.e., when a voltage is applied and when no voltage is applied) because Under this polarization of linearly polarized beam 821, surface relief grating structure 804 is index matched. Thus, the tunable LC surface relief grating 800 can be turned on and off (for polarized light) by controlling the voltage on the LC layer 808. Several such gratings with different spacing/tilt angles/refractive index contrasts can be used to switch between several grating configurations.

Referring now to FIG. 9A , a Ratnum-Berry phase (PBP) LC switchable grating 900 may be used, for example, in the coupling-in grating structure 114 and/or the coupling-out grating structure 116 of FIGS. 1 and 2 , the coupling-in grating of FIG. 3 structure 314 and/or the coupling-out grating structure 316, the coupling-in grating structure 514 and/or the coupling-out grating structure 516 of FIGS. 5 and 6 . The PBP LC switchable grating 900 of Figure 9A includes LC molecules 902 in an LC layer 904. LC molecules 902 are positioned in the XY plane with different in-plane orientations depending on the X coordinate. The orientation angle ϕ ( x ) of the LC molecules 902 in the PBP LC switchable grating 900 is given by:

ϕ ( x ) = π x /T = π x sin θ / λ _o (1)

where λ _o is the wavelength of the illuminating light, T is the 900 pitch of the PBP LC switchable grating, and θ is the diffraction angle given by:

θ = sin ^-1 (λ _o /T) (2)

The azimuthal angle ϕ varies continuously across the surface of the LC layer 904 parallel to the XY plane, as illustrated in Figure 9B. This change has a constant period equal to T. The optical phase retardation P in the PBP LC grating 900 of Figure 9A is attributed to the PBP effect, which exhibits P(x) = 2 ϕ (x) when the optical retardation R of the LC _layer 904 is equal to λ /2.

Figures 10A and 10B illustrate the operation of the PBP LC switchable grating 900 of Figure 9A. PBP LC switchable grating 900 includes an LC layer 904 (Fig. 9A) disposed between parallel substrates configured to apply an electric field on the LC layer 904. LC molecules 902 are oriented substantially parallel to the substrate in the absence of an electric field and are oriented substantially perpendicular to the substrate in the presence of an electric field.

In Figure 10A, the PBP LC switchable grating 900 is in an off state such that its LC molecules 902 (Figures 9A, 9B) are positioned primarily parallel to the substrate plane (ie, parallel to the XY plane in Figure 10A). When the incident beam 1015 is left-circular polarized (LCP), the PBP LC switchable grating 900 redirects the beam 1015 upward to a predetermined non-zero angle, and the beam 1015 becomes right-circular polarized (RCP) ). The RCP deflected beam 1015 is shown in solid lines. When the incident beam 1015 is right circularly polarized (RCP), the PBP LC switchable grating 900 redirects the beam 1015 downward at a predetermined non-zero angle, and the beam 1015 becomes left circularly polarized (LCP). The LCP deflected beam 1015 is shown in dashed lines. Applying voltage V to the PBP LC switchable grating 900 reorients the LC molecules along the Z-axis (ie, perpendicular to the plane of the substrate as shown in Figure 10B). With this position down on the LC molecule 902, the PBP structure is erased and the beam 1015 maintains its original direction, whether it is LCP or RCP. Therefore, the active PBP LC grating 900 is a tunable grating, that is, it has variable beam steering properties. Additionally, the operation of active PBP LC grating 900 can be controlled by controlling the polarization state of illumination beam 1015.

Returning to Figure 11A, the polarization volume hologram (PVH) grating 1100 can be used, for example, in the coupling grating structure 114 and/or the coupling out grating structure 116 in Figures 1 and 2, and in the coupling grating structure 314 and/or the coupling out grating in Figure 3. In the structure 316, or in the coupling grating structure 514 and/or the coupling grating structure 516 of Figures 5 and 6. The PVH grating 1100 of Figure 11A includes an LC layer 1104 defined by parallel surfaces opposite top 1105 and bottom 1106. The LC layer 1104 may include an LC fluid containing rod-shaped LC molecules 1107 (ie, nematic LC molecules) with positive dielectric anisotropy. Chiral dopants can be added to the LC fluid so that the LC molecules in the LC fluid self-organize into periodic helical configurations, including helical structures 1108 extending between the top 1105 and bottom 1106 parallel surfaces of the LC layer 1104 . This configuration of LC molecules 1107 (referred to herein as a cholesterol-type configuration) includes a plurality of helical periods p , such as at least two, at least five, at least ten, between the top 1105 and bottom 1106 parallel surfaces of the LC layer 1104 At least twenty or at least fifty spiral periods p .

Boundary LC molecules 1107b at the top surface 1105 of the LC layer 1104 may be oriented at an angle to the top surface 1105. Boundary LC molecules 1107b may have spatially varying azimuth angles, such as linearly varying along the X-axis parallel to top surface 1105, as shown in Figure 11A. To this end, the alignment film 1112 may be disposed at the top surface 1105 of the LC layer 1104. Alignment film 1112 may be configured to provide a desired orientation pattern of boundary LC molecules 1107b, such as a linear dependence of azimuth angle on the X-coordinate. The pattern of spatially varying polarization directions of UV light can be selected to match the desired orientation pattern of boundary LC molecules 1107b at the top surface 1105 and/or the bottom surface 1106 of the LC layer 1104. When the alignment film 1112 is coated with a cholesteric LC fluid, the boundary LC molecules 1107b are oriented along the photopolymerized chains of the alignment film 1112, thus adopting the desired surface orientation pattern. Adjacent LC molecules adopt a spiral pattern extending from top surface 1105 to bottom surface 1106 of LC layer 1104, as shown.

Boundary LC molecules 1107b define the relative phases of the helical structure 1108 with helical period p . The spiral structure 1108 forms a volume grating containing spiral stripes 1114 tilted at an angle ϕ , as shown in Figure 11A. The steepness of the tilt angle ϕ depends on the rate of change of the azimuthal angle of the boundary LC molecules 1107b at the top surface 1105 and p . Therefore, the tilt angle ϕ is determined by the surface alignment pattern of the boundary LC molecules 1107b at the alignment film 1112. The volume grating has a period Λ _x along the X-axis and a period Λ _y along the Y-axis. In some embodiments, the periodic helical structure 1108 of the LC molecules 1107 can be polymer stabilized by mixing the stabilizing polymer into the LC fluid and curing (polymerizing) the stabilizing polymer.

The helical nature of the volume grating's stripes 1114 allows the PVH grating 1100 to respond better to polarized light with one specific handedness (e.g., left or right circular polarization), and essentially to light with the opposite handedness of polarization. No response. Therefore, the spiral stripes 1114 make the PVH grating 1100 polarization selective, so that the PVH grating 1100 diffracts only one handedness of circularly polarized light. This is illustrated in Figure 11B, which shows a light beam 1120 striking a PVH grating 1100. The beam 1120 includes a left circularly polarized (LCP) beam component 1121 and a right circularly polarized (RCP) beam component 1122 . LCP beam component 1121 propagates through PVH grating 1100 with substantially no diffraction. As used herein, the term "substantially no diffraction" means that even though an insignificant portion of the light beam (in this case, the LCP beam component 1121 ) may diffract, the portion of the diffracted light energy is so small that it does not affect the PVH grating 1100 expected performance. The RCP beam component 1122 of the beam 1120 is diffracted, thereby producing a diffracted beam 1122'. The polarization selectivity of the PVH grating 1100 results from the effective refractive index of the grating, which depends on the relationship between the handedness or chirality of the illuminating beam and the handedness or chirality of the grating stripes 1114 . Changing the handedness of the illuminating light can be used to switch the performance of the PVH grating 1100. The PVH grating 1100 can also be made tunable by applying a voltage to the LC layer 1104, which distorts or erases the helical structure described above. It should further be noted that the sensitivity of PVH 1100 to right-hand circularly polarized light is specifically meant only as an illustrative example. When the handedness of the spiral stripes 1114 is reversed, the PVH 1100 can be made sensitive to left circularly polarized light. Therefore, the operation of the PVH 1100 can be controlled by controlling the polarization state of the illumination beam 1120. Additionally, in some embodiments, the PVH 1100 can be made tunable by applying an electric field on the LC layer 1104, which erases the periodic helical structure 1108.

Referring now to Figures 12A and 12B, the fluid surface relief grating 1200 can be used, for example, in the coupling grating structure 114 and/or the coupling out grating structure 116 in Figures 1 and 2, and in the coupling grating structure 314 and/or the coupling out grating structure 316 in Figure 3. , and in the coupling grating structure 514 and/or the coupling grating structure 516 of FIGS. 5 and 6 . Fluid surface relief grating 1200 includes a first immiscible fluid 1201 and a second immiscible fluid 1202 separated by an inter-fluid boundary 1203 . One of the fluids may be a hydrophobic fluid, such as an oil, for example silicone oil, while the other may be a water-based fluid. In some embodiments, one of the first fluid 1201 and the second fluid 1202 may be a gas. The first fluid 1201 and the second fluid 1202 may be included in a unit formed by the first and second substrates 1211 and 1212 supporting the first and second electrode structures 1221 and 1222. The first electrode structure 1221 and/or the second electrode structure 1222 may be at least partially transparent, absorptive and/or reflective.

At least one of the first electrode structure 1221 and the second electrode structure 1222 may be patterned for imposing a spatially varying electric field onto the first fluid 1201 and the second fluid 1202 . For example, in 12A and 12B, the first electrode 1221 is patterned, and the second electrode 1222 is not patterned, that is, the second electrode 1222 is a backplane electrode. In the specific example shown, both first electrode 1221 and second electrode 1222 are substantially transparent. For example, the first electrode 1221 and the second electrode 1222 may be indium tin oxide (ITO) electrodes. Individual portions of the patterned electrodes can be individually addressable. In some embodiments, patterned electrode 1221 may be replaced with a continuous, non-patterned electrode coupled to the patterned dielectric layer for generating spatially non-uniform electric fields on first fluid 1201 and second fluid 1202 .

Figure 12A shows the fluid surface relief grating 1200 in a non-actuated state when no electric field is applied across the inter-fluid boundary 1203. When no electric field is present, the inter-fluid boundary 1203 is straight and smooth; therefore, a light beam 1205 striking the fluid surface relief grating 1200 does not diffract and propagates directly through as illustrated. 12B shows the fluid surface relief grating 1200 in the driven state when voltage V is applied between the first electrode 1221 and the second electrode 1222, so that the first fluid 1201 and the second fluid are separated by the inter-fluid boundary 1203. 1202 produces a spatially variable electric field. Applying a spatially varying electric field causes the interfluid boundary 1203 to distort, as illustrated in Figure 12B, thereby forming a periodic change in the effective refractive index, ie, a surface relief diffraction grating. The light beam 1205 irradiated on the fluid surface relief grating 1200 will be diffracted, thereby forming a first diffraction sub-beam 1231 and a second diffraction sub-beam 1232. By changing the amplitude of the applied voltage V , the intensity of the fluid surface relief grating 1200 can be changed. By applying an electric field to different patterns, such as with individually addressable sub-electrodes or pixels of the first electrode 1221, the grating period, and therefore the diffraction angle, can be changed. More generally, changing the effective voltage between individual sub-electrodes or pixels of the first electrode 1221 can lead to three-dimensional conformal changes in the fluid interface (ie, the inter-fluid boundary 1203 inside the fluid volume) to impart a fluid surface relief grating 1200 desired optical response. The applied voltage pattern may be pre-biased to compensate or counteract the effects of gravity, ie, the distortion of the boundary 1203 between fluids caused by gravity.

The thickness of the first electrode 1221 and the second electrode 1222 may be, for example, between 10 nm and 50 nm. In addition to ITO, the materials of the first electrode 1221 and the second electrode 1222 may be, for example, indium zinc oxide (IZO), zinc oxide (ZO), indium oxide (IO), tin oxide (TO), indium gallium zinc oxide (IGZO) wait. The first fluid 1201 and the second fluid 1202 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 fluid 1201 or the second fluid 1202 may include polyphenylene ether, 1,3-bis(phenylthio)benzene, or the like. The first substrate 1211 and/or the second substrate 1212 may include, for example, fused silica, quartz, sapphire, etc. The first substrate 1211 and/or the second substrate 1212 may be straight or curved, and may include through holes and other electrical interconnections. The applied voltage may vary in amplitude and/or duty cycle when applied at a frequency between 100 Hz and 100 kHz. The applied voltage may change polarity and/or be bipolar. Each of the first fluid layer 1201 and/or the second fluid layer 1202 may have a thickness between 0.5 and 5 microns, more preferably between 0.5 and 2 microns.

To separate the first fluid 1201 and the second fluid 1202, a surfactant containing a hydrophilic terminal functional group and a hydrophobic terminal functional group may be used. Examples of hydrophilic terminal functional groups are hydroxyl, carboxyl, carbonyl, amine, phosphate, sulfhydryl. For example, the hydrophilic functional group can also be an anionic group, such as sulfate, sulfonate, carboxylate, and phosphate. Non-limiting examples of hydrophobic terminal functional groups are aliphatic groups, aromatic groups, and fluorinated groups. For example, when polyphenylene sulfide and fluorinated fluid may be selected as a fluid pair, a surfactant containing aromatic end groups and fluorinated end groups may be used. When phenyl silicone oil and water are selected as the fluid pair, surfactants containing aromatic end groups and hydroxyl (or amine or ionic) end groups can be used. These are non-limiting examples only.

Referring to Figure 13A, a pupil replica lightguide 1300A of the present invention includes a body 1306A having two parts, a substrate 1328 for propagating image light 1304, and a mechanical coupling at a side of the substrate 1328 joining its top surface 1315 and bottom surface 1316. Connected volume wave acoustic actuator 1330A. In the specific example shown, volume wave acoustic actuator 1330A includes an electroresponsive layer 1332A, such as a piezoelectric layer, disposed between electrodes 1307A, 1308A. In operation, electrical signals at high frequencies, typically in the range of 1 MHz to 100 MHz or higher, are applied to electrodes 1307A, 1308A, causing electrically responsive layer 1332A to generally oscillate at the frequency of the mechanical resonance of electrically responsive layer 1332A. The oscillating thickness of electroresponsive layer 1332A generates volume acoustic waves 1334A propagating in substrate 1328 in direction 1335 (ie, along the X-axis). Volume acoustic wave 1334A modulates the refractive index of substrate 1328 due to the photoelastic effect. The modulated refractive index creates diffraction gratings that couple portions 1312, 1313 of the image light 1304 out of the pupil replica light guide 1300A. By changing the strength of the electrical signal applied to volume wave acoustic actuator 1330A, the strength of the outcoupling grating can be changed. The decoupling grating can be switched on and off by switching on and off the oscillating electrical signal. The grating period can be changed by changing the frequency of the oscillating electrical signal. In some embodiments, acoustic wave terminator 1336A may be coupled to an opposite side of substrate 1328 to absorb volume acoustic wave 1334A and thereby prevent standing acoustic waves from forming in substrate 1328 .

Returning to Figure 13B, the pupil replica waveguide 1300B of the present invention includes a waveguide body 1306B having two parts, a substrate 1328 for propagating the image beam 1304, and a surface wave acoustic actuator 1330B mechanically coupled at the top surface 1315. Alternatively, surface wave acoustic actuator 1330B may also be coupled at bottom surface 1316. In the specific example shown, surface wave acoustic actuator 1330B includes an electroresponsive layer 1332B, such as a piezoelectric layer, disposed between electrodes 1307B, 1308B. In operation, electrical signals at high frequencies, typically in the range of 1 MHz to 100 MHz or higher, are applied to electrodes 1307B, 1308B, causing electroresponsive layer 1332B to oscillate. Oscillation of electroresponsive layer 1332A generates surface acoustic waves 1334B propagating in substrate 1328 in direction 1335 (ie, along the X-axis). Surface acoustic wave 1334B forms a diffraction grating that couples portions 1312, 1313 of image light 1304 out of pupil replica lightguide 1300B. By varying the intensity of the electrical signal applied to surface wave acoustic actuator 1330B, the intensity of the surface grating can be varied. The surface grating can be switched on and off by switching on and off an oscillating electrical signal. The grating period can be changed by changing the frequency of the oscillating electrical signal. In some embodiments, acoustic wave terminators 1336B may be coupled to opposite sides of substrate 1328 at the same surface (ie, at top surface 1315 in FIG. 13B ) to absorb surface acoustic waves 1334B and thus prevent standing acoustic waves from forming.

Some switchable gratings include materials with tunable refractive index. By way of non-limiting example, a holographic polymer-dispersed liquid crystal (H-PDLC) grating can be formed by a photosensitive monomer/liquid crystal contained between two substrates coated with a conductive layer. (LC) mixture is produced by inducing interference between two coherent laser beams. Upon irradiation, the photoinitiator contained in the mixture initiates a free radical reaction, resulting in polymerization of the monomers. 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 conventional PDLC or diffracted in the case of H-PDLC. When an electric field is applied to the cell, the refractive index modulation is removed and light passing through the cell is unaffected. This is described in Pogue et al., "Electrically Switchable Bragg Gratings from Liquid Crystal/Polymer Composites", Applied Spectroscopy, Vol. 54, No. 1, 2000 /Polymer Composites), which is incorporated by reference in its entirety.

Tunable or switchable gratings with variable grating period can be produced, for example, by using flexoelectric LC. For LCs with non-zero flexoelectric coefficient differences ( e 1- e 3) and low dielectric anisotropy, electric fields exceeding a certain threshold cause a transition from a homogeneous planar state to a spatially periodic state. Field-sensing gratings are characterized by rotation of the LC director about an alignment axis, where the wave vector of the grating is oriented perpendicular to the initial alignment direction. The sign of rotation is defined by the sign of the electric field vector and ( e 1- e 3) difference. The wavenumber characterizing the periodicity of the field induction increases linearly with the applied voltage starting from a critical value of approximately π/ d , where d is the thickness of the layer. A description of flexoelectric LC gratings can be found, for example, in Palto's Crystals 2021, 11, 894 titled "Dynamic and Photonic Properties of Field-Induced Gratings in Flexoelectric LC" Layers), which is incorporated by reference in its entirety.

Tunable gratings with variable grating period or tilt angle can be provided, for example, by using spiral LCs. Tunable gratings with helical LCs have been described, for example, by Xiang et al., Phys. Rev. Lett. 112, 217801, 2014 under the title "Electrical response of chiral nematic liquid crystals with oblique helical directors" (Electrooptic Response of Chiral Nematic Liquid Crystals with Oblique Helicoidal Director)", which is incorporated into this article by full text citation.

For gratings that exhibit strong wavelength dependence of grating efficiency, several gratings may be provided in the light guide, such as several volumetric Bragg gratings (VBG) gratings. The grating diffracting light at any given moment can be switched by turning the VBG grating on and off and/or by switching the wavelength of light propagating in the waveguide.

Referring now to Figure 14, an augmented reality (AR) near-eye display 1400 includes a frame 1401 that supports the following for each eye: a light engine 1430 for providing an image beam carrying an angular domain image; a pupil replicating light guide 1406 that includes Any of the waveguides disclosed herein for providing multiple offset portions of the image beam to spread the angular domain image over the eye zone 1412; and a plurality of eye zone illuminators 1410, shown as black dots , replicating the clear aperture spread of light guide 1406 around the pupil on the surface facing eye movement zone 1412. Eye tracking cameras 1404 may be provided for each eye zone 1412.

The purpose of the eye tracking camera 1404 is to determine the position and/or orientation of the user's two eyes. The eye zone illuminator 1410 illuminates the eye corresponding to the eye zone 1412, thereby allowing the eye tracking camera 1404 to obtain an image of the eye and provide a reference reflection, ie, a flash. The flash can serve as a reference point in the captured image of the eye, thereby facilitating eye gaze direction determination by determining the position of the eye's pupil image relative to the flash image. In order to avoid distracting the user's attention due to the light of the eye zone illuminator 1410, the eye zone illuminator can be made to emit light that is invisible to the user. For example, infrared light may be used to illuminate eye movement zone 1412.

Returning to Figure 15, HMD 1500 is an example of an AR/VR wearable display system. In order to immerse oneself in the AR/VR environment to a greater extent, the AR/VR wearable display system encloses the user's face. HMD 1500 can produce fully virtual 3D images. HMD 1500 may include a front body 1502 and straps 1504 that may be secured around a user's head. The front body 1502 is configured for secure and comfortable placement in front of the user's eyes. The display system 1580 may be disposed in the front body 1502 to present AR/VR images to the user. Display system 1580 may include any of the display devices and waveguides disclosed herein. The sides 1506 of the front body 1502 may be opaque or transparent.

In some embodiments, the front body 1502 includes a positioner 1508 and an inertial measurement unit (IMU) 1510 for tracking the acceleration of the HMD 1500 , and a position sensor 1512 for tracking the position of the HMD 1500 . IMU 1510 is an electronic device that generates data indicative of the position of HMD 1500 based on measurement signals received from one or more of position sensors 1512 that generate a or Multiple measurement signals. Examples of position sensors 1512 include: one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor to detect motion, error correction for IMU 1510 A type of sensor, or a combination thereof. Position sensor 1512 may be located external to IMU 1510, internal to IMU 1510, or some combination thereof.

The locator 1508 is tracked by an external imaging device of the virtual reality system, so that the virtual reality system can track the position and orientation of the entire HMD 1500 . The information generated by the IMU 1510 and the position sensor 1512 may be compared with the position and orientation obtained by the tracking locator 1508 to improve the tracking accuracy of the position and orientation of the HMD 1500 . As the user moves and rotates in 3D space, accurate position and orientation are crucial to presenting appropriate virtual scenery to the user.

HMD 1500 may further include a depth camera assembly (DCA) 1511 that captures data describing depth information surrounding some or all of the local areas in HMD 1500 . For better accuracy in determining the position and orientation of the HMD 1500 in 3D space, the depth information may be compared with information from the IMU 1510.

The HMD 1500 may further include an eye tracking system 1514 for instantly determining the orientation and position of the user's eyes. The acquired position and orientation of the eyes also allows HMD 1500 to determine the direction of the user's gaze and adjust the image produced by display system 1580 accordingly. The determined gaze direction and vergence angle may be used to adjust the display system 1580 to reduce vergence adjustment conflicts. Direction and vergence may also be used for exit pupil steering of displays as disclosed herein. In addition, the determined convergence and gaze angles can be used to interact with the user, highlight objects, bring objects to the foreground, generate additional objects or indicators, etc. An audio system may also be provided that includes, for example, a set of small speakers built into the front body 1502.

Specific examples of the invention may include or may be implemented with artificial reality systems. The artificial reality system adjusts the sensory information about the external world obtained through sensing in a certain way before presenting it to the user, such as visual information, audio, contact (somatosensory) information, acceleration, balance, etc. By way of non-limiting example, artificial reality may include virtual reality (VR), augmented reality (AR), mixed reality (MR), composite reality, or some combination and/or derivative thereof. Artificial reality content may include fully generated content or generated content combined with captured (eg, real-world) content. Artificial reality content may include video, audio, physical or tactile feedback, or some combination thereof. Any of this content may be presented in a single channel or in multiple channels, such as in stereoscopic video, which creates a three-dimensional effect on the viewer. Additionally, in some embodiments, artificial reality may also be used with applications such as creating content in the artificial reality and/or otherwise being used in the artificial reality (e.g., performing activities in the artificial reality), products, accessories, services, or a combination thereof. Artificial reality systems that provide artificial reality content can be implemented on a variety of platforms, including wearable displays such as HMDs connected to host computer systems, stand-alone HMDs, near-eye displays with the appearance of glasses, mobile devices or computing systems, or any other hardware platform capable of delivering artificial reality content to one or more viewers.

The scope of the invention is not limited by the specific examples described herein. Indeed, various other specific examples and modifications in addition to those described herein will be apparent to those skilled in the art from the foregoing description and accompanying drawings. Accordingly, such other specific examples and modifications are intended to be within the scope of this invention. Furthermore, although the invention has been described herein for a particular purpose and in the context of a particular implementation in a particular environment, one of ordinary skill in the art will recognize that its usefulness is not so limited and that the invention may be practiced in other fields. Any number of purposes may be beneficially implemented in any number of environments. Accordingly, the patent claims set forth below should be construed in view of the full scope and spirit of the invention as described herein.

100: Light guide 102: Light 104: Input position 106: Output position 108: Flat plate 111: Opposite surface 112: Opposite surface 114: Coupling grating structure 116: Coupling grating structure 300: Pupil replication light guide 305: Controller 308: Flat plate 311: First opposite surface 312: Second opposite surface 314: Coupling grating structure 316: Coupling grating structure 321: First light beam 321A: Part 322: Second light beam 322A: Part 350: Display device 352: Light engine 354: Display panel 356: projector lens 360: eye movement area 362: user's eyes 400: method 402: step 404: step 406: step 408: step 410: step 412: step 414: step 416: step 418: step 500: light Pupil copy light guide 505: Controller 508: Flat plate 511: Opposite surface 512: Opposite surface 514: Coupling grating 516: Coupling grating 521: Image light 521A: Part 550: Near-eye display 552: Light engine 554: Display panel 556: Projection Machine lens 560: eye movement area 562: user's eyes 564: external visible light 700: method 702: step 704: step 706: step 708: step 800: tunable liquid crystal surface relief grating 801: first substrate 802: second substrate 804 : Surface relief grating structure 806: Ridges 808: LC layer 810: LC molecules 811: First conductive layer 812: Second conductive layer 821: Linearly polarized beam 900: Interrogated Ratnum-Berry phase LC switchable grating 902: LC molecules 904: LC layer 1015: incident beam 1100: polarized volume holographic grating 1104: LC layer 1105: top surface 1106: bottom surface 1107: LC molecules 1107b: boundary LC molecules 1108: spiral structure 1112: alignment film 1114: spiral stripes 1120: Beam 1121: Left circularly polarized beam component 1122: Right circularly polarized beam component 1122': Diffraction beam 1200: Fluid surface undulation grating 1201: First fluid 1202: Second fluid 1203: Boundary between fluids 1205: Beam 1211: No. One substrate 1212: second substrate 1221: first electrode structure 1222: second electrode structure 1231: first diffraction sub-beam 1232: second diffraction sub-beam 1300A: pupil replica light guide 1300B: pupil replica waveguide 1304: image Light 1306A: Body 1306B: Waveguide body 1307A: Electrode 1307B: Electrode 1308A: Electrode 1308B: Electrode 1312: Part 1313: Part 1315: Top surface 1316: Bottom surface 1328: Substrate 1330A: Volume acoustic actuator 1330B: Surface acoustic Actuator 1332A: Electroresponsive layer 1332B: Electroresponsive layer 1334A: Volume acoustic wave 1334B: Surface acoustic wave 1335: Direction 1336A: Acoustic wave terminator 1336B: Acoustic wave terminator 1400: Augmented reality near-eye display 1401: Frame 1404: Eye tracking Camera 1406: Pupil copy light guide 1410: Eye zone illuminator 1412: Eye zone 1430: Light engine 1500: HMD 1502: Front body 1504: Strip 1506: Side 1508: Positioner 1510: Inertial measurement unit 1511: Depth Camera assembly 1512: position sensor 1514: eye tracking system 1580: display system L ₁ : first threshold value L ₂ : second threshold value P ₁ : percentage P ₂ : percentage T ₁ : first time interval T ₂ : second time interval V : voltage ϕ : angle Λ _x : period Λ _y : period

Illustrative specific examples will be described in connection with the drawings, wherein:

[Fig. 1] is a side cross-sectional view of the light guide of the present invention;

[Fig. 2] is a schematic diagram of the light guide of Fig. 1 including a tunable grating configured to diffract image light of the red, green, and blue channels in a time-sequential manner;

[Fig. 3] is a schematic diagram of a display device using the light guide of Fig. 1;

[Fig. 4] is a flow chart of the method of the present invention for transmitting images to the eye movement area;

[Fig. 5] is a schematic diagram of a display device using a pupil replicating light guide with a switchable decoupling grating;

[Fig. 6] A sequence diagram illustrating the operation of the display device of Fig. 5;

[Fig. 7] is a flow chart of the method of the present invention for using artificially generated images to augment a view of the external environment;

[Figure 8] shows a side cross-sectional view of the tunable liquid crystal (LC) surface relief grating of the present invention;

[Fig. 9A] is a front view of an active pancharatnam-Berry phase (Pancharatnam-Berry phase; PBP) liquid crystal (LC) grating that can be used in the light guide of the present invention;

[Figure 9B] is an enlarged schematic diagram of the LC molecules in the LC layer of the active PBP LC grating in Figure 9A;

[Figures 10A and 10B] are side views of the active PBP LC grating in Figures 9A and 9B, showing the light propagation in the off (Figure 10A) and on (Figure 10B) states of the active PBP LC grating;

[Fig. 11A] is a side cross-sectional view of a polarization volumetric grating (PVH) that can be used in the light guide of the present invention;

[Figure 11B] is a diagram illustrating the optical performance of the PVH of Figure 11A;

[Fig. 12A] is a side cross-sectional view of a fluid grating that can be used in the light guide of the present invention in a disconnected state;

[Fig. 12B] is a side cross-sectional view of the fluid grating of Fig. 12A in a switched-on state;

[Fig. 13A] is a side cross-sectional view of the light guide of the present invention including an acoustic actuator for generating volumetric acoustic waves in the light guide;

[Fig. 13B] is a side cross-sectional view of the light guide of the present invention including an acoustic actuator for generating surface acoustic waves in the light guide;

[Fig. 14] is a view of the augmented reality (AR) display of the present invention having the appearance size of a pair of glasses; and

[Fig. 15] is a three-dimensional view of the head-mounted display (HMD) of the present invention.

100:Light guide

102:Light

104:Input location

106:Output position

108: Tablet

111: Relative surface

112: Relative surface

114: Coupling grating structure

116: Coupling grating structure

Claims (20)

A light guide for transmitting light, which includes at least one of a plurality of color channels, the light guide including: A flat plate of transparent material for directing the light therein by a series of internal reflections from opposite surfaces of the flat plate; A coupling grating structure supported by the plate for coupling the light into the plate; and a coupling grating structure supported by the flat plate for coupling out a portion of the light from the flat plate, wherein at least one of the coupling-in grating structure or the coupling-out grating structure is tunable in at least one of a grating pitch or a grating efficiency for operating with a particular one of the plurality of color channels of the light . The light guide of claim 1, wherein the at least one of the coupling-in grating structure or the coupling-out grating structure includes a polarizing volume hologram grating. The light guide of claim 1, wherein the at least one of the coupling-in grating structure or the coupling-out grating structure includes a tunable disk Ratnam-Berry phase liquid crystal grating. The light guide of claim 1, wherein the at least one of the coupling-in grating structure or the coupling-out grating structure includes a tunable liquid crystal surface relief grating. The light guide of claim 1, wherein the at least one of the coupling-in grating structure or the coupling-out grating structure includes a fluid surface relief grating. The lightguide of claim 1, wherein the at least one of the coupling-in grating structure or the coupling-out grating structure includes a switchable volume Bragg grating according to each of the plurality of color channels. Such as the light guide of claim 1, wherein: The light guide is a pupil replica light guide; and The plurality of color channels include a red channel, a green channel and a blue channel; The outcoupling grating structure has a spatially varying tunable grating spacing to couple out the portions of the light from the light guide in a predefined angular distribution. Such as the light guide of claim 1, wherein: The light guide is a pupil replica light guide; and The plurality of color channels include a red channel, a green channel and a blue channel; The outcoupling grating structure has a spatially varying tunable grating efficiency to improve the spatial uniformity of the portions of light coupled out from the plate by the outcoupling grating structure. A display device for transmitting an image including a first color channel and a second color channel to an eye movement area. The display device includes: a light engine configured to provide light including at least one of a first light beam and a second light beam carrying the first color channel and the second color channel respectively; A light guide coupled to the light engine for receiving the light, the light guide comprising: A flat plate of transparent material for directing the light therein by a series of internal reflections from opposite surfaces of the flat plate; A coupling grating structure supported by the plate for coupling the light into the plate; and A coupling grating structure supported by the flat plate for coupling out part of the light from the flat plate; wherein at least one of the coupling-in grating structure or the coupling-out grating structure is tunable in at least one of grating spacing or grating efficiency for use with a specific one of the first color channel or the second color channel. operate together with light; and A controller operably coupled to the light engine and the light guide and configured to: causing the light engine to provide the first light beam carrying the first color channel; Tuning the at least one of the coupling-in grating structure or the coupling-out grating structure at at least one of the grating pitch or the grating efficiency to increase the flux of the first light beam; causing the light engine to provide the second light beam carrying the second color channel; and The at least one of the coupling-in grating structure or the coupling-out grating structure is tuned in at least one of the grating pitch or the grating efficiency to increase the flux of the second light beam. The display device of claim 9, wherein the at least one of the coupling-in grating structure or the coupling-out grating structure includes a polarizing volume holographic grating. The display device of claim 9, wherein the at least one of the coupling-in grating structure or the coupling-out grating structure includes a tunable disk Ratnam-Berry phase liquid crystal grating. The display device of claim 9, wherein the at least one of the coupling-in grating structure or the coupling-out grating structure includes a tunable liquid crystal surface relief grating. The display device of claim 9, wherein the at least one of the coupling-in grating structure or the coupling-out grating structure includes a fluid surface relief grating. The display device of claim 9, wherein the at least one of the coupling-in grating structure or the coupling-out grating structure includes a switchable volume Bragg grating according to each of the first color channel and the second color channel. The display device of claim 9, wherein the light guide is a pupil replica light guide, and wherein the outcoupling grating structure has at least one of a spatially varying tunable grating spacing or a spatially varying tunable grating efficiency to distribute at a predefined angle and coupling out the portions of the first beam and the second beam from the plate with predefined spatial uniformity. Such as the display device of claim 9, wherein: The light further includes a third color channel of the image; The light engine is further configured to provide a third light beam carrying the third color channel; and The controller is further programmed to: causing the light engine to provide the third light beam; and The at least one of the coupling-in grating structure or the coupling-out grating structure is tuned in at least one of the grating pitch or the grating efficiency to increase the flux of the third light beam. A method for transmitting images to the eye movement zone, which method includes: providing a first light beam carrying a first color channel of the image; coupling the first light beam to a coupling grating structure of the light guide, the light guide including an outcoupling grating structure for coupling out a portion of the first light beam; Tuning at least one of the coupling-in grating structure or the coupling-out grating structure at at least one of the grating pitch or the grating efficiency to increase the flux of the first light beam; providing a second light beam carrying a second color channel of the image; coupling the second light beam to the coupling grating of the light guide; and The at least one of the coupling-in grating structure or the coupling-out grating structure is tuned at at least one of the grating pitch or the grating efficiency to increase the flux of the second light beam. For example, the method of request item 17 further includes: providing a third light beam carrying a third color channel of the image; coupling the third beam to the coupling grating of the light guide; and The at least one of the coupling-in grating structure or the coupling-out grating structure is tuned at at least one of the grating pitch or the grating efficiency to increase the flux of the third light beam. The method of claim 17, wherein the outcoupling grating structure has a spatially varying tunable grating spacing to couple out the portions of the first beam and the second beam from the light guide in a predefined angular distribution. The method of claim 17, wherein the outcoupling grating structure has a spatially varying tunable grating efficiency to couple out the portions of the first beam and the second beam from the light guide with predefined spatial uniformity.