Meta Patent | Phase plate and fabrication method for color-separated laser backlight in display systems
Patent: Phase plate and fabrication method for color-separated laser backlight in display systems
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Publication Number: 20230244185
Publication Date: 2023-08-03
Assignee: Meta Platforms Technologies
Abstract
According to examples, a method for phase plate fabrication may be described herein. The method may include providing an interferometer configuration to generate a hologram of a plurality of pinholes. In some examples, the interferometer configuration includes a substrate for photopolymer attachment, a photopolymer having a predetermined thickness, and an exposure mask with a plurality of pinholes. The method may also include exposing the photopolymer with collimated light, via a laser source, through the exposure mask with a plurality of pinholes, wherein the collimated light passes through the exposure mask itself to create a collimated beam, and the plurality of pinholes of the exposure mask to create a spherical wavefront. The collimated beam and the spherical wavefront may help generate the hologram on the photopolymer for use as a phase plate for improved light transmissivity in display systems.
Claims
1.A method for phase plate fabrication, comprising: providing an interferometer configuration to generate a hologram of a plurality of pinholes, wherein the interferometer configuration comprises at least a photopolymer and an exposure mask; exposing the photopolymer to collimated light through the exposure mask with a plurality of pinholes, by passing the collimated light through: the exposure mask to create a collimated beam; and the plurality of pinholes to create a spherical wavefront, wherein the collimated beam and the spherical wavefront generate the hologram of the plurality of pinholes; and iteratively shifting pinhole placement for additional wavelengths to repeat exposure of the photopolymer to the collimated light.
2.The method of claim 1, wherein the interferometer configuration comprises: a substrate for photopolymer attachment; the photopolymer having a predetermined thickness; and the exposure mask with the plurality of pinholes;
3.The method of claim 1, wherein the collimated light is laser light.
4.The method of claim 1, wherein the plurality of pinholes in the exposure mask have a periodic structure.
5.The method of claim 4, wherein any two pinholes of the plurality of pinholes have about 18 micrometer separation.
6.The method of claim 1, wherein each of the plurality of pinholes has about 1 micrometer diameter.
7.The method of claim 1, further comprising: selecting a placement of the photopolymer between 100 micrometers and 200 micrometers away from a Talbot self-imaging plane generated by the exposure mask.
8.The method of claim 7, further comprising: adding a random phase to at least a portion of the plurality of pinholes in the exposure mask; or randomizing a location of at least a portion of the pinholes in the exposure mask.
9.The method of claim 1, wherein the interferometer configuration comprises at least two exposure masks.
10.A method for configuring an exposure mask, comprising: determining a size of an exposure mask with a plurality of pinholes for phase plate fabrication; determining a relative transmission for the mask region relative to the pinholes; determining a size and location for the plurality of pinholes within the exposure mask based on the relative transmission; and fabricating the exposure mask with the plurality of pinholes.
11.The method of claim 10, further comprising: determining the relative transmission using the following expression:
12.The method of claim 10, wherein the plurality of pinholes in the exposure mask have a periodic structure.
13.The method of claim 12, wherein any two pinholes of the plurality of pinholes have about 18 micrometer separation.
14.The method of claim 10, wherein each of the plurality of pinholes has about 1 micrometer diameter.
15.The method of claim 10, further comprising: adding a random phase to at least a portion of the plurality of pinholes in the exposure mask.
16.The method of claim 10, further comprising: randomizing a location of at least a portion of the pinholes in the exposure mask.
17.An interferometer configuration for phase plate fabrication, the interferometer configuration comprising: a substrate; a photopolymer having a predetermined thickness attached to the substrate; and an exposure mask with a plurality of pinholes to expose the photopolymer to collimated light by passing the collimated light through: the exposure mask to create a collimated beam; and the plurality of pinholes to create a spherical wavefront, wherein the collimated beam and the spherical wavefront generate the hologram of the plurality of pinholes. iteratively shifting pinhole placement for additional wavelengths to repeat exposure of the photopolymer to the collimated light.
18.The interferometer configuration of claim 17, wherein pinhole placement is iteratively shifted for additional wavelengths to repeat exposure of the photopolymer to the collimated light.
19.The interferometer configuration of claim 17, wherein the plurality of pinholes in the exposure mask have a periodic structure.
20.The interferometer configuration of claim 17, wherein the photopolymer is placed between 100 micrometers and 200 micrometers away from a Talbot self-imaging plane generated by the exposure mask.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This patent application claims the benefit of U.S. Provisional Patent Application Ser. No. 63/305,090 filed on Jan. 31, 2022. The disclosures of the above application are hereby incorporated by reference for all purposes.
TECHNICAL FIELD
This patent application relates generally to display systems, and more specifically, to phase plate and fabrication method for color-separated laser backlight in display systems.
BACKGROUND
With recent advances in technology, prevalence and proliferation of content creation and delivery has increased greatly in recent years. In particular, interactive content such as virtual reality (VR) content, augmented reality (AR) content, mixed reality (MR) content, and content within and associated with a real and/or virtual environment (e.g., a “metaverse”) has become appealing to consumers.
To facilitate delivery of this and other related content, service providers have endeavored to provide various forms of wearable display systems. One such example may be a head-mounted device (HMD), such as a wearable headset, wearable eyewear, or eyeglasses. In some examples, the head-mounted device (HMD) may employ a first projector and a second projector to direct light associated with a first image and a second image, respectively, through one or more intermediary optical components at each respective lens, to generate “binocular” or “stereoscopic” vision for viewing by a user. However, providing a head-mounted device (HMD) that is compact, lightweight with sufficiently bright and high-resolution images remains a constant challenge.
BRIEF DESCRIPTION OF DRAWINGS
Features of the present disclosure are illustrated by way of example and not limited in the following figures, in which like numerals indicate like elements. One skilled in the art will readily recognize from the following that alternative examples of the structures and methods illustrated in the figures can be employed without departing from the principles described herein.
FIG. 1 illustrates a block diagram of an artificial reality system environment including a near-eye display, according to an example.
FIG. 2 illustrates a perspective view of a near-eye display in the form of a head-mounted display (HMD) device, according to an example.
FIGS. 3A-3D illustrate cross-sectional views of a color-separated liquid crystal display (LCD) with laser backlight, according to an example.
FIGS. 4A-4D illustrate a cross-sectional pixel-level view of a color-separated liquid crystal display (LCD) with laser backlight with a phase plate, according to examples.
FIG. 5 illustrates an interferometer configuration for creating hologram of pinholes for phase plate fabrication, according to an example.
FIG. 6 illustrates a configuration using a phase plate with conjugate beam to generate illumination patterns at a liquid crystal display (LCD), according to an example.
FIGS. 7A-7B illustrates views of an exposure mask for phase plate fabrication, according to an example.
DETAILED DESCRIPTION
For simplicity and illustrative purposes, the present application is described by referring mainly to examples thereof. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. It will be readily apparent, however, that the present application may be practiced without limitation to these specific details. In other instances, some methods and structures readily understood by one of ordinary skill in the art have not been described in detail so as not to unnecessarily obscure the present application. As used herein, the terms “a” and “an” are intended to denote at least one of a particular element, the term “includes” means includes but not limited to, the term “including” means including but not limited to, and the term “based on” means based at least in part on.
Some display systems, such as, VR-based head-mounted devices (HMDs) and/or eyewear devices, provide an immersive, stereoscopic visual experience. In some conventional displays, however, light transmissivity (or lack thereof) may present issues. For instance, in a traditional liquid crystal display (LCD), such as those used in such VR-based HMDs, a significant amount of light may be lost through the various optical layers that form the overall display. In many ways, this may be referred to as “wall-plug efficiency” of an LCD. The systems and methods described herein may provide phase plate solution and fabrication method for color-separated laser backlight in a display system, such as VR-based head-mounted devices (HMDs).
FIG. 1 illustrates a block diagram of an artificial reality system environment 100 including a near-eye display, according to an example. As used herein, a “near-eye display” may refer to a device (e.g., an optical device) that may be in close proximity to a user's eye. As used herein, “artificial reality” may refer to aspects of, among other things, a “metaverse” or an environment of real and virtual elements, and may include use of technologies associated with virtual reality (VR), augmented reality (AR), and/or mixed reality (MR). As used herein a “user” may refer to a user or wearer of a “near-eye display.”
As shown in FIG. 1, the artificial reality system environment 100 may include a near-eye display 120, an optional external imaging device 150, and an optional input/output interface 140, each of which may be coupled to a console 110. The console 110 may be optional in some instances as the functions of the console 110 may be integrated into the near-eye display 120. In some examples, the near-eye display 120 may be a head-mounted display (HMD) that presents content to a user.
In some instances, for a near-eye display system, it may generally be desirable to expand an eye box, reduce display haze, improve image quality (e.g., resolution and contrast), reduce physical size, increase power efficiency, and increase or expand field of view (FOV). As used herein, “field of view” (FOV) may refer to an angular range of an image as seen by a user, which is typically measured in degrees as observed by one eye (for a monocular HMD) or both eyes (for binocular HMDs). Also, as used herein, an “eye box” may be a two-dimensional box that may be positioned in front of the user's eye from which a displayed image from an image source may be viewed.
In some examples, in a near-eye display system, light from a surrounding environment may traverse a “see-through” region of a waveguide display (e.g., a transparent substrate) to reach a user's eyes. For example, in a near-eye display system, light of projected images may be coupled into a transparent substrate of a waveguide, propagate within the waveguide, and be coupled or directed out of the waveguide at one or more locations to replicate exit pupils and expand the eye box.
In some examples, the near-eye display 120 may include one or more rigid bodies, which may be rigidly or non-rigidly coupled to each other. In some examples, a rigid coupling between rigid bodies may cause the coupled rigid bodies to act as a single rigid entity, while in other examples, a non-rigid coupling between rigid bodies may allow the rigid bodies to move relative to each other.
In some examples, the near-eye display 120 may be implemented in any suitable form-factor, including a HMD, a pair of glasses, or other similar wearable eyewear or device. Examples of the near-eye display 120 are further described below with respect to FIGS. 2 and 3. Additionally, in some examples, the functionality described herein may be used in a HMD or headset that may combine images of an environment external to the near-eye display 120 and artificial reality content (e.g., computer-generated images). Therefore, in some examples, the near-eye display 120 may augment images of a physical, real-world environment external to the near-eye display 120 with generated and/or overlayed digital content (e.g., images, video, sound, etc.) to present an augmented reality to a user.
In some examples, the near-eye display 120 may include any number of display electronics 122, display optics 124, and an eye-tracking unit 130. In some examples, the near eye display 120 may also include one or more locators 126, one or more position sensors 128, and an inertial measurement unit (IMU) 132. In some examples, the near-eye display 120 may omit any of the eye-tracking unit 130, the one or more locators 126, the one or more position sensors 128, and the inertial measurement unit (IMU) 132, or may include additional elements.
In some examples, the display electronics 122 may display or facilitate the display of images to the user according to data received from, for example, the optional console 110. In some examples, the display electronics 122 may include one or more display panels. In some examples, the display electronics 122 may include any number of pixels to emit light of a predominant color such as red, green, blue, white, or yellow. In some examples, the display electronics 122 may display a three-dimensional (3D) image, e.g., using stereoscopic effects produced by two-dimensional panels, to create a subjective perception of image depth.
In some examples, the display optics 124 may display image content optically (e.g., using optical waveguides and/or couplers) or magnify image light received from the display electronics 122, correct optical errors associated with the image light, and/or present the corrected image light to a user of the near-eye display 120. In some examples, the display optics 124 may include a single optical element or any number of combinations of various optical elements as well as mechanical couplings to maintain relative spacing and orientation of the optical elements in the combination. In some examples, one or more optical elements in the display optics 124 may have an optical coating, such as an anti-reflective coating, a reflective coating, a filtering coating, and/or a combination of different optical coatings.
In some examples, the display optics 124 may also be designed to correct one or more types of optical errors, such as two-dimensional optical errors, three-dimensional optical errors, or any combination thereof. Examples of two-dimensional errors may include barrel distortion, pincushion distortion, longitudinal chromatic aberration, and/or transverse chromatic aberration. Examples of three-dimensional errors may include spherical aberration, chromatic aberration field curvature, and astigmatism.
In some examples, the one or more locators 126 may be objects located in specific positions relative to one another and relative to a reference point on the near-eye display 120. In some examples, the optional console 110 may identify the one or more locators 126 in images captured by the optional external imaging device 150 to determine the artificial reality headset's position, orientation, or both. The one or more locators 126 may each be a light-emitting diode (LED), a corner cube reflector, a reflective marker, a type of light source that contrasts with an environment in which the near-eye display 120 operates, or any combination thereof.
In some examples, the external imaging device 150 may include one or more cameras, one or more video cameras, any other device capable of capturing images including the one or more locators 126, or any combination thereof. The optional external imaging device 150 may be configured to detect light emitted or reflected from the one or more locators 126 in a field of view of the optional external imaging device 150.
In some examples, the one or more position sensors 128 may generate one or more measurement signals in response to motion of the near-eye display 120. Examples of the one or more position sensors 128 may include any number of accelerometers, gyroscopes, magnetometers, and/or other motion-detecting or error-correcting sensors, or any combination thereof.
In some examples, the inertial measurement unit (IMU) 132 may be an electronic device that generates fast calibration data based on measurement signals received from the one or more position sensors 128. The one or more position sensors 128 may be located external to the inertial measurement unit (IMU) 132, internal to the inertial measurement unit (IMU) 132, or any combination thereof. Based on the one or more measurement signals from the one or more position sensors 128, the inertial measurement unit (IMU) 132 may generate fast calibration data indicating an estimated position of the near-eye display 120 that may be relative to an initial position of the near-eye display 120. For example, the inertial measurement unit (IMU) 132 may integrate measurement signals received from accelerometers over time to estimate a velocity vector and integrate the velocity vector over time to determine an estimated position of a reference point on the near-eye display 120. Alternatively, the inertial measurement unit (IMU) 132 may provide the sampled measurement signals to the optional console 110, which may determine the fast calibration data.
The eye-tracking unit 130 may include one or more eye-tracking systems. As used herein, “eye tracking” may refer to determining an eye's position or relative position, including orientation, location, and/or gaze of a user's eye. In some examples, an eye-tracking system may include an imaging system that captures one or more images of an eye and may optionally include a light emitter, which may generate light that is directed to an eye such that light reflected by the eye may be captured by the imaging system. In other examples, the eye-tracking unit 130 may capture reflected radio waves emitted by a miniature radar unit. These data associated with the eye may be used to determine or predict eye position, orientation, movement, location, and/or gaze.
In some examples, the near-eye display 120 may use the orientation of the eye to introduce depth cues (e.g., blur image outside of the user's main line of sight), collect heuristics on the user interaction in the virtual reality (VR) media (e.g., time spent on any particular subject, object, or frame as a function of exposed stimuli), some other functions that are based in part on the orientation of at least one of the user's eyes, or any combination thereof. In some examples, because the orientation may be determined for both eyes of the user, the eye-tracking unit 130 may be able to determine where the user is looking or predict any user patterns, etc.
In some examples, the input/output interface 140 may be a device that allows a user to send action requests to the optional console 110. As used herein, an “action request” may be a request to perform a particular action. For example, an action request may be to start or to end an application or to perform a particular action within the application. The input/output interface 140 may include one or more input devices. Example input devices may include a keyboard, a mouse, a game controller, a glove, a button, a touch screen, or any other suitable device for receiving action requests and communicating the received action requests to the optional console 110. In some examples, an action request received by the input/output interface 140 may be communicated to the optional console 110, which may perform an action corresponding to the requested action.
In some examples, the optional console 110 may provide content to the near-eye display 120 for presentation to the user in accordance with information received from one or more of external imaging device 150, the near-eye display 120, and the input/output interface 140. For example, in the example shown in FIG. 1, the optional console 110 may include an application store 112, a headset tracking module 114, a virtual reality engine 116, and an eye-tracking module 118. Some examples of the optional console 110 may include different or additional modules than those described in conjunction with FIG. 1. Functions further described below may be distributed among components of the optional console 110 in a different manner than is described here.
In some examples, the optional console 110 may include a processor and a non-transitory computer-readable storage medium storing instructions executable by the processor. The processor may include multiple processing units executing instructions in parallel. The non-transitory computer-readable storage medium may be any memory, such as a hard disk drive, a removable memory, or a solid-state drive (e.g., flash memory or dynamic random access memory (DRAM)). In some examples, the modules of the optional console 110 described in conjunction with FIG. 1 may be encoded as instructions in the non-transitory computer-readable storage medium that, when executed by the processor, cause the processor to perform the functions further described below. It should be appreciated that the optical console 110 may or may not be needed or the optional console 110 may be integrated with or separate from the near-eye display 120.
In some examples, the application store 112 may store one or more applications for execution by the optional console 110. An application may include a group of instructions that, when executed by a processor, generates content for presentation to the user. Examples of the applications may include gaming applications, conferencing applications, video playback application, or other suitable applications.
In some examples, the headset tracking module 114 may track movements of the near-eye display 120 using slow calibration information from the external imaging device 150. For example, the headset tracking module 114 may determine positions of a reference point of the near-eye display 120 using observed locators from the slow calibration information and a model of the near-eye display 120. Additionally, in some examples, the headset tracking module 114 may use portions of the fast calibration information, the slow calibration information, or any combination thereof, to predict a future location of the near-eye display 120. In some examples, the headset tracking module 114 may provide the estimated or predicted future position of the near-eye display 120 to the virtual reality engine 116.
In some examples, the virtual reality engine 116 may execute applications within the artificial reality system environment 100 and receive position information of the near-eye display 120, acceleration information of the near-eye display 120, velocity information of the near-eye display 120, predicted future positions of the near-eye display 120, or any combination thereof from the headset tracking module 114. In some examples, the virtual reality engine 116 may also receive estimated eye position and orientation information from the eye-tracking module 118. Based on the received information, the virtual reality engine 116 may determine content to provide to the near-eye display 120 for presentation to the user.
In some examples, the eye-tracking module 118 may receive eye-tracking data from the eye-tracking unit 130 and determine the position of the user's eye based on the eye tracking data. In some examples, the position of the eye may include an eye's orientation, location, or both relative to the near-eye display 120 or any element thereof. So, in these examples, because the eye's axes of rotation change as a function of the eye's location in its socket, determining the eye's location in its socket may allow the eye-tracking module 118 to more accurately determine the eye's orientation.
In some examples, a location of a projector of a display system may be adjusted to enable any number of design modifications. For example, in some instances, a projector may be located in front of a viewer's eye (i.e., “front-mounted” placement). In a front-mounted placement, in some examples, a projector of a display system may be located away from a user's eyes (i.e., “world-side”). In some examples, a head-mounted display (HMD) device may utilize a front-mounted placement to propagate light towards a user's eye(s) to project an image.
FIG. 2 illustrates a perspective view of a near-eye display in the form of a head-mounted display (HMD) device 200, according to an example. In some examples, the HMD device 200 may be a part of a virtual reality (VR) system, an augmented reality (AR) system, a mixed reality (MR) system, another system that uses displays or wearables, or any combination thereof. In some examples, the HMD device 200 may include a body 220 and a head strap 230. FIG. 2 shows a bottom side 223, a front side 225, and a left side 227 of the body 220 in the perspective view. In some examples, the HMD device 200 may also include external cameras on the top/bottom/left/right/front exterior, such as bottom right camera 228, top left camera 229, and front camera 231, as shown. In some examples, the head strap 230 may have an adjustable or extendible length. In particular, in some examples, there may be a sufficient space between the body 220 and the head strap 230 of the HMD device 200 for allowing a user to mount the HMD device 200 onto the user's head. In some examples, the HMD device 200 may include additional, fewer, and/or different components.
In some examples, the HMD device 200 may present to a user, media or other digital content including virtual and/or augmented views of a physical, real-world environment with computer-generated elements. Examples of the media or digital content presented by the HMD device 200 may include images (e.g., two-dimensional (2D) or three-dimensional (3D) images), videos (e.g., 2D or 3D videos), audio, or any combination thereof. In some examples, the images and videos may be presented to each eye of a user by one or more display assemblies (not shown in FIG. 2) enclosed in the body 220 of the HMD device 200.
In some examples, the HMD device 200 may include various sensors (not shown), such as depth sensors, motion sensors, position sensors, and/or eye tracking sensors. Some of these sensors may use any number of structured or unstructured light patterns for sensing purposes. In some examples, the HMD device 200 may include an input/output interface 140 for communicating with a console 110, as described with respect to FIG. 1. In some examples, the HMD device 200 may include a virtual reality engine (not shown), but similar to the virtual reality engine 116 described with respect to FIG. 1, that may execute applications within the HMD device 200 and receive depth information, position information, acceleration information, velocity information, predicted future positions, or any combination thereof of the HMD device 200 from the various sensors.
In some examples, the information received by the virtual reality engine 116 may be used for producing a signal (e.g., display instructions) to the one or more display assemblies. In some examples, the HMD device 200 may include locators (not shown), but similar to the virtual locators 126 described in FIG. 1, which may be located in fixed positions on the body 220 of the HMD device 200 relative to one another and relative to a reference point. Each of the locators may emit light that is detectable by an external imaging device. This may be useful for the purposes of head tracking or other movement/orientation. It should be appreciated that other elements or components may also be used in addition or in lieu of such locators.
It should be appreciated that in some examples, a projector mounted in a display system may be placed near and/or closer to a user's eye (i.e., “eye-side”). In some examples, and as discussed herein, a projector for a display system shaped liked eyeglasses may be mounted or positioned in a temple arm (i.e., a top far corner of a lens side) of the eyeglasses. It should be appreciated that, in some instances, utilizing a back-mounted projector placement may help to reduce size or bulkiness of any required housing required for a display system, which may also result in a significant improvement in user experience for a user.
As mentioned above, light transmissivity (or lack thereof) may present issues in some display systems, such as VR-based head-mounted devices (HMDs) and/or eyewear devices. Loaw light transmissivity may limit brightness and minimize a user's desired immersive visual experience. Thus, the systems and methods described herein may help improve “wall-plug efficiency” of an LCD in such displays.
FIGS. 3A-3D illustrate cross-sectional views of a color-separated liquid crystal display (LCD) with laser backlight, according to an example. FIG. 3A illustrates the various layers that form an LCD stack 300A. As shown, the LCD stack may include a white LED 302 backlight that transmits light through any number of optical components, such as a light guide plate (LGP) 303, one or more polarizers 312, 304, a thin film transistor (TFT) 306, a liquid crystal (LC) layer 308, a color filter (CF) 310, etc. As depicted, when light 314 passes through the LCD stack, each of these layers may cut the amount of light passing through it in some capacity, as indicated by the percentages. When calculated, the amount of light that actually gets transmitted at the end by at least the portion of the LCD stack comprising the LGP, polarizer, and TFT, may be only a small fraction of light. By some estimates, the light transmissivity is approximately 0.0945 transmissivity (9.45%) or less than 10%.
Accordingly, one of the primary goals of the systems and methods described herein is to improve light transmissivity in the LCD stack and to provide increased brightness, visual acuity, and higher quality images in ARNR HMDs. One way to help minimize light loss may be to use an alternative light source or configuration.
FIG. 3B illustrates a cross-sectional views of a color-separated liquid crystal display (LCD) with laser backlight, according to an example. Here, rather than the white LED and LGP of FIG. 3A, the LCD stack 300B uses a laser backlight configuration that includes, for example, an RBG laser 322, a grating light guide (LG) 323, and a micro lens array (MLS) 325. In this example, transmissivity of light 324 of this portion of the LCD stack 300B may be estimated to be just under approximately 0.1575 (15.75%) or around 16%, which represents a significant improvement. FIG. 3C illustrates close-up cross-sectional view of a color-separated liquid crystal display (LCD) 348 with laser backlight using MLAs, according to an example. Here, the micro lens array (MLA) 346 may focus the light beam 350 through the aperture, thus boosting the overall transmission. Light from a light source 342 may be provided through a waveguide 344 to the color-selective micro lens array (MLA) 346.
Further still, FIG. 3D illustrates a cross-sectional views of a color-separated liquid crystal display (LCD) with laser backlight using a phase plate, according to another example. Here, rather than the micro lens array (MLA) of FIG. 3B, the LCD stack 300D uses a laser backlight configuration that includes, for example, an RBG laser 322, a grating light guide (LG) 323, and a phase plate 335. The MLA of FIG. 3B may have less than 50% transmissivity, but the transmissivity of the phase plate in FIG. 3D may be greater than 60%, by some calculations. As a result, light transmissivity of this portion of the LCD stack 300C using the phase plate may be estimated to be greater than 0.2268 (22.68%) or around 22%, which represents an even more significant improvement. In many ways, the use of a phase plate may also focus the light beam through the aperture, thereby boosting the overall transmission at even greater efficiency than the MLA layer.
In order for the phase plate to help provide improved transmission, there may be several parameters to optimize these results. FIGS. 4A-4D illustrate a cross-sectional pixel-level view of a color-separated liquid crystal display (LCD) with laser backlight with a phase plate, according to examples. For instance, diagram 400A in FIG. 4A shows source light 402 being adjusted by a phase plate 404. As mentioned herein, the phase plate 404 may change the relative phase of the components of polarized light passing through the phase plate and also focus the light. Thus, adjusted light 406 may be focused on selected pixels 408 such that blue light components focus on a blue subpixel, red light components focus on a red subpixel, and green light components focus on a green subpixel. Here, there may be a red, green, and blue pixel (e.g., pixel 410) measured with a width of approximately 18 microns (μm) (e.g., within a range of 10-25 μm), with each of the holes associated with each of the colors may be approximately 3.5 microns (e.g., within a range of 2-5 μm). For this configuration to operate with high efficiency, it may be desirable for the light to pass in a cone-like shape at approximately 40 degrees, as shown. Furthermore, in some examples, the overall height may be in the range of 200-500 μm. Using these parameters, the LCD with laser backlight using the phase plate may provide the design responses for wavelengths associated with each of the three colors (red, green, and blue), as shown in the views 400B, 400C, and 400D of FIGS. 4B, 4C, and 4D with pixels 422, pixel substrate 405 and phase plate 404.
As a result, the systems and methods described herein may provide phase plate fabrication method for color-separated laser backlight in a display system, such as an VR-based head-mounted devices (HMDs). Specifically, the phase plate fabrication method described herein may use an interferometer setup to make a hologram of pinholes. The phase plate fabrication method described herein may also repeat the process any number of times with shifted pinhole for other wavelengths. The phase plate fabrication method described herein may also play the hologram with conjugate beam to generate desired illumination pattern(s). Other various examples may also be considered or provided.
FIG. 5 illustrates an interferometer configuration 500 for creating hologram of pinholes for phase plate fabrication, according to an example. As shown, the interferometer configuration 500 may include a substrate 510 to which a photopolymer 508 may be attached. In some examples, the photopolymer 508 may be 3 μm or greater (or generally <50 μm). A mask 504 with pinholes 506 may also be provided at a distance of approximately 200-500 μm from the photopolymer 508. In this step of the phase plate fabrication method, a collimated laser light 507 may come from the bottom of the configuration 500 and pass through a 1% mask as a collimated beam. It should be appreciated that light may pass through the 1 μm pinholes 506 to create a spherical wavefront. In some examples, the collimated beam may interfere with the spherical wavefront at the photopolymer layer. This interference may help form a desired hologram pattern on the photopolymer for use as a phase plate in a display as described above. It should be appreciated that the 1 um pinhole may produce a full width at half maximum (FWHM) cone angle of 40° degrees:
Sin(FFOV/2)=wavelength/pinholeDiameter, (1)
where FFOV represents the full field of view. In addition, during this step, exposure time may vary between 0.5-6 seconds, depending on laser power. In most cases, a 10 mW/cm2 laser may be used for approximately 1 second.
As mentioned above, this process may be repeated with shifted pinholes for other wavelengths. In some examples, depending on the thickness (e.g., 3-50 μm) and photopolymer properties (e.g., index dynamic), the configuration 500 may be used to expose the different wavelength response to a different photopolymer. In other words, a red laser may be used to expose, then shift the pinhole and use a green laser, and then shift the pinhole again for a blue laser, etc. Depending on how many how many exposures are to be performed, the thickness of the photopolymer may vary. For example, the more exposures to be performed, the thicker the photopolymer should be. This is generally because the index dynamic of the material usually is typically higher for thicker material. One reason for additional exposure is to capture more than one wavelength, as described above. In an RBG example, the process involves multiplexing the response of the three wavelengths. In some examples, it may be desirable to have off axis exposure or other variation. In these scenarios, the process may involve additional beam steering, e.g., to expose at any number of different angles as well.
In some examples, more than one photopolymer layer may also be provided. For example, three films may be used. For instance, after exposure for each of these films (red, green, and blue), each of these films may be laminated on top of each other using any number of lamination processing techniques to form a singular component as well.
FIG. 6 illustrates a configuration 600 using a phase plate with conjugate beam to generate illumination patterns at a liquid crystal display (LCD) 608, according to an example. As shown, the phase plate, formed from the above fabrication steps, may be used in the configuration 600. Specifically, the configuration 600 may position the phase plate and hologram with conjugate beam to generate a desire illumination pattern for the LCD. Thus, RGB light 602 may pass through a transparent substrate, photopolymer 604 with pinholes and arrive as adjusted light 606 on the liquid crystal display (LCD) 608. It should be appreciated that in some examples, the position between the phase plate and the TFT (e.g., 1st surface of the LCD) should be relatively the same as the exposure distance (200-500 um), as shown in FIG. 5. Other various examples, however, may also be considered or provided.
FIGS. 7A-7B illustrates views 700A-700B of an exposure mask for phase plate fabrication, according to an example. As described above, the exposure mask 702 may include a plurality of pinholes 710, as shown in FIG. 7A. In some examples, each of these pinholes may have a diameter 706 of approximately 1 μm. There may also be a patterned across the entirety of the mask, and in some examples, the pinholes 710 may be spaced with a distance 704 of 18 μm apart. In some examples, the mask may also be coated, e.g., with chrome. The size of the mask 702 may range from 5×5 cm or 8×8 cm, or any other pertinent size or dimension (see below for calculation). It should also be appreciated that the actual shape of the pinholes 710 need not be entirely circular. Slightly elliptically shaped pinholes may also be provided. It should be appreciated that the pinhole may be configured with 100% light transmission while the chrome (other portions) of the mask may be configured with 0.4% light transmission. That said, the hole transmission may likely be lower than 100% in actual operation and therefore the chrome transmission may be scaled accordingly.
FIG. 7B illustrates a potential calculation 700B for exposure mask dimensions, according to an example. As shown, forgiven mask having a pinhole with radius r (½ of pinhole diameter 706) and distance 704 between pinholes p=18 μm, the following expression may be used to calculate:
where T is the relative transmission for the mask region (black) relative to the pinholes (white), and arcsin (λ/2r)=20° results in 2r=1.3 μm for 450 nm to have 20° angles. As shown, other calculations may also be provided. Ultimately, these calculations may be used to maximize the fringe contrast for interference exposure, having about the same light/area between the collimated and spherical wavefront.
It should be appreciated that the above process may experience what may be referred to as a “Talbot image plane” issue. In short, when collimated light passes through periodic pinhole structure, a phenomenon known as “Talbot self-imaging plane” may occur at several distances away from the pinhole mask. In other words, when a plane wave is incident upon a periodic diffraction grating, the image of the grating may be repeated at regular distances away from the grating plane. In this scenario, the regular distance may be referred to as a Talbot length, and the repeated images may be referred to as “self-images” or “Talbot images.”
In order to avoid reference beam interfering with Talbot plane (replication of pinhole), the systems and methods described herein may provide at least one of the following solutions: (1) Shifting the interference plane 100-200 μm away from Talbot plane (e.g., Talbot plane at 500 μm, then place photopolymer at 600-700 μm); (2) Adding random phase to pinhole to break the periodic phase; (3) Randomizing the 1 μm pinhole location by couple um offset to avoid periodic pattern, and/or (4) Using two or more sets of masks, where each mask increases the period which changes the Talbot distance.
In addition to the methods, processes, and/or techniques described above, there may be any number of ways to create the phase masks for the phase plate solution for improved light transmissions in a display system. These may include photolithography (binary or grayscale), nanoimprint, meta- or nano-structure (e.g., nanopillars), or other similar methods, processes, and/or techniques. Depending on cost, speed, and ease of use, these and/or other methods, processes, and/or techniques may be incorporated into the systems and methods described herein.
In the foregoing description, various inventive examples are described, including devices, systems, methods, and the like. For the purposes of explanation, specific details are set forth in order to provide a thorough understanding of examples of the disclosure. However, it will be apparent that various examples may be practiced without these specific details. For example, devices, systems, structures, assemblies, methods, and other components may be shown as components in block diagram form in order not to obscure the examples in unnecessary detail. In other instances, well-known devices, processes, systems, structures, and techniques may be shown without necessary detail in order to avoid obscuring the examples.
The figures and description are not intended to be restrictive. The terms and expressions that have been employed in this disclosure are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof. The word “example” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment or design described herein as “example’ is not necessarily to be construed as preferred or advantageous over other embodiments or designs.
Although the methods and systems as described herein may be directed mainly to digital content, such as videos or interactive media, it should be appreciated that the methods and systems as described herein may be used for other types of content or scenarios as well. Other applications or uses of the methods and systems as described herein may also include social networking, marketing, content-based recommendation engines, and/or other types of knowledge or data-driven systems.
