WO2014081415A1

WO2014081415A1 - Directional waveguide-based pixel for use in a multiview display screen

Info

Publication number: WO2014081415A1
Application number: PCT/US2012/066063
Authority: WO
Inventors: James A Brug; Patricia A. Beck; David A Fattal; Zhen PENG; Yoocharn Jeon
Original assignee: Hewlett-Packard Development Company, Lp
Priority date: 2012-11-20
Filing date: 2012-11-20
Publication date: 2014-05-30

Abstract

A directional waveguide-based pixel for use in a mutliview display screen is disclosed. The directional waveguide-based pixel has a liquid crystal layer interposed between the waveguide layer and a substrate layer. The waveguide layer has a waveguide and a patterned grating to scatter an input light beam into a plurality of directional light beams, each directional light beam having a direction and angular spread controlled by characteristics of the patterned grating. An active matrix with individually addressable electrodes may be integrated in the substrate layer or in the waveguide layer to modulate the directional light beams.

Description

DIRECTIONAL WAVEGUIDE-BASED PIXEL FOR USE IN A MULTIVIEW

DISPLAY SCREEN

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to PCT Patent Application Serial No. PCT/US2012/035573 (Attorney Docket No. 82963238), entitled "Directional Pixel for Use in a Display Screen", filed on April 27^th, 2012, PCT Patent Application Serial No. PCT/US2012/058022 (Attorney Docket No. 82963252), entitled "Directional Waveguide- Based Backlight for Use in a Multiview Display Screen", filed on September 28^th, 2012, and PCT Patent Application Serial No. PCT/US2012/058026 (Attorney Docket No. 82963246), entitled "Directional Waveguide-Based Backlight with Integrated Hybrid Lasers for Use in a Multiview Display Screen", filed on September 28^th, 2012, and assigned to the assignee of the present application and incorporated by reference herein.

BACKGROUND

[0002) The ability to reproduce a light field in a display screen has been a key quest in imaging and display technology. A light field is a set of all light rays traveling in every direction through every point in space. Any natural, real-world scene can be fully characterized by its light field, providing information on the intensity, color, and direction of all light rays passing through the scene. The goal is to enable viewers of a display screen to experience a scene as one would experience it in person.

[0003J Currently available display screens in televisions, personal computers, laptops, and mobile devices remain largely two-dimensional and are thus not capable of accurately reproducing a light field. Three-dimensional ("3D") displays have recently emerged but suffer from inefficiencies in angular and spatial resolution in addition to providing a limited number of views. Examples include 3D displays based on holograms, parallax barriers, or lenticular lenses.

[0004] A common theme among these displays is the difficulty to fabricate displays for light fields that are controlled with precision at the pixel level in order to achieve good image quality for a wide range of viewing angles and spatial resolutions.

-i- HP 82963260 PATENT

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The present application may be more fully appreciated in connection with the following detailed description taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:

10006] FIG. 1 illustrates a schematic diagram of a waveguide-based directional pixel platform in accordance with various examples;

[0007] FIG. 2 illustrates the waveguide-based directional pixel platform of FIG. 1 with an additional layer;

[0008] FIG. 3 illustrates a schematic diagram of a waveguide-based directional pixel platform in accordance with various other examples; and

[0009] FIG. 4 illustrates a schematic diagram of a waveguide-based directional pixel platform in accordance with yet other examples.

DETAILED DESCRIPTION

[0010] A directional waveguide-based, pixel platform for use in a multiview display screen is disclosed. The directional waveguide-based pixel platform enables multiple views of a 3D image to be generated from incoming light rays with a substantially planar structure. The pixel structure closely integrates a photonic waveguide (used to steer the direction of the incoming light rays) with a liquid crystal layer (used to modulate the intensity of the light rays) to achieve large viewing angles with a natural and continuous change of view.

[0011] In various examples, the directional waveguide-based pixel platform has a waveguide layer composed of a waveguide and a plurality of patterned gratings to guide an input light beam into output directional light beams. The input light beam propagates in the waveguide in substantially the same plane as the waveguide, which is designed to be substantially planar. Each patterned grating may be formed, of substantially parallel and slanted grooves. The waveguide may be formed of a dielectric or a polymer material, among others, that is sufficiently different in index from adjacent layers to allow light to propagate in a controlled manner.

[0012] As described in more detail herein below, each patterned grating may be specified by a grating length (i.e., dimension along the propagation axis of the input light beams), a grating width (i.e., dimension across the propagation axis of the input light beams), a groove orientation, a pitch, and a duty cycle (e.g., the ratio of width of the formed grooves HP 82963260 PATENT

to the period.) Each patterned grating may emit a directional light beam with a direction that is determined by the groove orientation and the grating pitch, and with an angular spread that is determined by the grating length and width. By using a duty cycle of or around 50%, the second Fourier coefficient of the patterned grating vanishes, thereby preventing the scattering of light in additional unwanted directions and ensuring that only one directional light beam emerges from a patterned grating regardless of the output angle.

[0013] As further described in more detail herein below, the directional light beam scattered by each patterned grating is modulated by a liquid crystal layer placed above the waveguide layer. Various configurations of active matrices and electrodes may be designed to control the liquid crystal layer. One configuration may include a liquid crystal layer interposed between an active matrix substrate and the waveguide layer. Another configuration may include a liquid crystal layer interposed between a transparent electrode substrate layer and the waveguide layer, with a transparent patterned electrode controlled by an active matrix placed between each patterned grating and the waveguide.

[0014] It is appreciated that, in the following description, numerous specific details are set forth to pro vide a thorough understanding of the examples. However, it is appreciated that the examples may be practiced without limitation to these specific details. In other instances, well known methods and structures may not be described in detail to avoid unnecessarily obscuring the description of the examples. Also, the examples may be used, in combination with each other.

[0015] Referring now to FIG. 1, a schematic diagram of a waveguide-based directional pixel platform in accordance with various examples is described. Directional pixel platform 100 is shown with directional pixels lQ5a-e. Each directional pixel lQ5a-c includes a liquid crystal layer 110 interposed between an active matrix substrate 115 and a waveguide layer 120, The thickness of the liquid crystal layer 110 is determined by the spacing between the active matrix substrate 115 and. the waveguide layer 120 and is kept small, ranging from 1-10 μηι. This enables the direction of the light emitted from the patterned grating to be at a large angle, allowing a wide field of view for the 3D image. A typical field of view would be 90°, though larger angles approaching 180° are possible. The waveguide layer 120 is composed of a waveguide 125, an electrode layer 130, and patterned gratings 135a-e placed on top of the electrode layer 130. An input light beam 140 propagates HP 82963260 PATENT

in the waveguide 125 and is scattered by the patterned gratings 135a-c into directional light beams 145a-c.

[0016] The directional light beams 145a-c are modulated by the active matrix substrate 1 15 which may be composed of a thin film transistor ("TFT") active matrix (or other such active matrix) and individually addressable electrodes 150a-c. The patterned gratings 135a-c are formed of substantially parallel grooves (e.g., groove 155) with about the same thickness, resulting in a substantially planar design. The grooves can be formed from the material of the electrode layer 130 or made of any material formed and patterned (or patterned and formed) on top of the electrode layer 130 with suitable index properties to steer the input light beam in a desirable fashion, by for instance, causing the total internal reflection to be interrupted. Suitable materials may be dielectrics, polymers and metals, among others. The electrode layer 130 provides a first electrode for the individually addressable electrodes I SOa-e in the active matrix substrate 1 15.

[0017] Each directional fight beam 145a-c has a direction and angular spread that depends on characteristics of its corresponding patterned grating 135a-c. In particular, the direction of each directional light beam 145a-c is determined by the in plane orientation and the grating pitch of its corresponding patterned grating 135a-c. The angular spread of each directional light beam 145a-c is in turn determined by the grating length and width of its corresponding patterned grating 135a-e. For example, the direction of directional light beam 145a is determined by the in plane orientation and the grating pitch of patterned grating 135a, and. the angular spread, of directional light beam 145b is determined by the grating length and width of the patterned grating 135b.

[0018] It is appreciated that the substantially planar design of pixel platform 100 and the formation of directional light beams 145a-c upon an input light beam 140 require that the patterned, gratings 135a-c be designed, with a substantially smaller pitch than traditional diffraction gratings. For example, traditional diffraction gratings scatter light upon illumination with light beams that are propagating substantially across the plane of the grating. Here, each patterned grating ! 35a-e is substantially on the same plane as the input light beam 140 when generating the directional light beams 145a-c.

[0019] It is also appreciated that the directional pixels 105a-c are designed to provide for precise control of the direction and angular spread of the directional light beams 145a-c, enabling multiple image views to be formed. The directional light beams 145a-e are HP 82963260 PATENT

precisely controlled by characteristics of their corresponding patterned gratings 135a-e, including a grating length L, a grating width W, a groove orientation Θ, and a grating pitch Λ. In particular, the grating length L of a given patterned grating (e.g., patterned grating 135a, patterned grating 135b, or patterned grating 135c) controls the angular spread ΔΘ of the directional light beam scattered by the patterned grating (e.g., directional light beams 140a-c respectively scattered by patterned gratings 135a-e) along the input light propagation axis. The grating width W of the given patterned, grating also controls the angular spread ΔΘ of the directional light beam scattered by the given patterned grating across the input light propagation axis, as follows:

4,ί ί^' 4,ί ^λ!

\C-> — ! ! (Eq. 1) πί πΨ )

where λ is the wavelength of the directional light beam scattered by the patterned grating. The groove orientation, specified by the grating orientation angle θ, and the grating pitch or period, specified by Λ, control the direction of the directional light beam scattered, by the patterned grating.

[0020] The grating length L and the grating width W can vary in size in the range of 1 to 200 μτη. The groove orientation angle Θ and the grating pitch Λ may be set to satisfy a desired direction of a directional light beam, with, for example, the groove orientation angle Θ on the order of -40 to +40 degrees and the grating pitch Λ on the order of 200-700 nm.

[0021] It is appreciated that pixel platform 100 is shown with three directional pixels lOSa-e for purposes of illustration only. A pixel platform in accordance with various examples can be designed to achieve a very high density of directional pixels (e.g., in the order of many thousands), depending on how the pixel platform 100 is used (e.g., in a 3D display screen, in a 3D watch, in a mobile device, etc.) It is also appreciated that the patterned grating in each directional pixel may have any shape, including for example, a circle, an ellipse, a polygon, or other geometrical shape.

[0022] Further, it is appreciated that any narrow-bandwidth light source (not shown) may be used to generate the input light beam 140 (e.g., a laser or LED) for waveguide 125. One skilled in the art appreciates that a backlight or other similar structure may be integrated with the pixel platform 100 to provide the light source needed to generate the directional light beams 145a-e scattered from each directional pixel l lQa-c. Additionally, it is appreciated HP 82963260 PATENT

that other layers may be integrated with the pixel platform 100, including, for example, one or more polarizers and alignment layers.

[0023] FIG. 2 shows the waveguide-based directional pixel platform of FIG. 1 with an additional layer. Directional pixel platform 200 is shown with directional pixels 205a-c. In this case, a thin (e.g., 20 - 100 μηι) transparent substrate layer with a thin transparent substrate 260 and an electrode layer 265 is interposed between the liquid crystal layer 210 and the waveguide layer 220 composed of waveguide 225, electrode 230, and gratings 235a- c. This thin transparent substrate layer enables the liquid crystal layer 210 and the active matrix 215 to be fabricated in part or as a foil liquid crystal display (shuttering layers) independently from the photonic layers. The shutter layei s) would then be assembled at a later stage of manufacturing to the patterned gratings 235a-e. This simplifies the fabrication and retains the ability of the directional light beams 245 a-c to be scattered from input light beam 240 at large viewing angles. It is appreciated that by adding electrode layer 265, electrode 230 may be removed from the waveguide layer 220,

[0024] Attention is now directed to FIG. 3, which shows another example of a waveguide-based directional pixel platform. In this case, an electrode layer 330 is placed on top of patterned gratings 335a-c rather than below as seen in FIG. 1 . Directional pixel platform 300 is shown with directional pixels 305a-c. Each directional pixel 305a-c includes a liquid, crystal layer 310 interposed between an active matrix substrate 315 and a waveguide layer 320. The waveguide layer 320 is composed of a waveguide 325, an electrode layer 330, and patterned gratings 335a-c placed below the electrode layer 330. An input light beam 340 propagates in the waveguide 325 and is scattered by the patterned, gratings 335a-c into directional light beams 345a-c.

[0025] The directional light beams 345a-c are modulated by the active matrix substrate 31 and individually addressable electrodes 350a-c. The patterned gratings 335a-c are formed of substantially parallel grooves. The grooves can be formed from the material of the electrode layer 330 or can be made of any material formed and patterned (or patterned and formed) on top of the electrode layer 330 with suitable index properties to steer the input light beam in a desirable fashion, by for instance, causing the total internal reflection to be interrupted. Suitable materials may be dielectrics, polymers and metals, among others.

[0026] The electrode layer 330 provides a first electrode for the individually addressable electrodes 350a-c in the active matrix substrate 315. Similar to FIG. 1 , each HP 82963260 PATENT

directional light beam 345a-c has a direction and. angular spread that depends on characteristics of its corresponding patterned grating 335a-c. The angular spread of each directional light beam 345a-c is in turn determmed by the grating length and width of its corresponding patterned, grating 335a-c.

10027] Referring now to FIG. 4, a waveguide-based directional pixel platform in accordance with various other examples is described. In this case, an active matrix with individually addressable electrodes is integrated directly into a waveguide layer. Directional pixel platform 400 is shown with directional pixels 4G5a-e. Each directional pixel 405a-c includes a liquid crystal layer 410 interposed between a transparent electrode substrate layer 415 and a waveguide layer 420. The transparent electrode substrate layer 415 is composed of a transparent substrate 425 and an electrode 430.

[0028] The waveguide layer 420 is composed of a waveguide 425, an active matrix with individually addressable electrodes 440a-e, and patterned gratings 435a-c placed directly on top of the active matrix and electrodes 440a-c. An input light beam 445 propagates in the waveguide 425 and. is scattered by the patterned gratings 435a-c into directional light beams 45Qa-c. The directional light beams 450a-c are modulated by the acti ve matrix and electrodes 440a-c. Similar to FIGS. 1-3, each directional light beam 450a-c has a direction and angular spread that depends on characteristics of its corresponding patterned grating 435a-c. The angular spread of each directional light beam 450a-c is in turn determmed by the grating length and width of its corresponding patterned grating 435a-c.

[0029] Advantageously, the precise control that is achieved with the directional pixels in the directional waveguide-based pixels shown in FIGS. 1-4 enables a 3D image to be generated with a substantially planar structure. Different configurations of directional pixels can generate different 3D images. The directional pixels described herein can be used to provide 3D images in display screens (e.g., in TVs, mobile devices, tablets, video game devices, and so on) as well as in other applications, such as, for example, 3D watches. 3D art devices, 3D medical devices, among others.

[0030] It is appreciated that the previous description of the disclosed examples is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to these examples will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other examples without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be IIP 82963260 PATENT

limited to the examples shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

HP 82963260 PATENT WHAT IS CLAIMED IS:

1. A directional waveguide-based pixel for use in a multiview display screen, comprising:

an active matrix substrate;

a waveguide layer comprising a waveguide and a patterned grating to scatter an input light beam into a plurality of directional light beams, each directional light beam having a direction and angular spread controlled by characteristics of the patterned grating; and

a liquid crystal layer interposed between the active matrix substrate and the waveguide layer.

2. The directional waveguide-based pixel of claim 1 , wherein the liquid crystal layer interposed between the active matrix substrate and the waveguide layer is a thin layer with thickness ranging from 1 - ΙΟμτη.

3. The directional waveguide-based pixel of claim 1 , wherein the active matrix substrate comprises a transparent active matrix substrate.

4. The directional waveguide-based pixel of claim 1 , further comprising an individually- addressable electrode formed on a first surface of the active matrix substrate, the first surface facing the liquid crystal layer.

5. The directional waveguide-based pixel of claim 1 , further comprising a first electrode layer interposed between the patterned grating and the waveguide.

6. The directional waveguide-based pixel of claim 1 , wherein the patterned grating is formed directly on the waveguide.

7. The directional waveguide- based pixel of claim 6, further comprising a first electrode layer placed on top of the patterned grating. HP 82963260 PATENT

8. The directional waveguide- based pixel of claim 5, further comprising an electrode substrate layer interposed between the liquid crystal layer and the waveguide layer.

9. The directional waveguide-based pixel of claim 8, wherein the electrode substrate layer comprises an electrode placed at a first surface of a thin transparent substrate, the first surface facing the liquid crystal layer.

10. The directional waveguide- based pixel of claim 1 , wherein the characteristics of the patterned grating comprise a grating length, a grating width, a grating orientation, a grating pitch, and a duty cycle.

1 1. The directional waveguide-based pixel of claim 10, wherein the pitch and orientation of the patterned grating control the direction of a directional light beam scattered by the patterned grating.

12. The directional waveguide-based pixel of claim 10, wherein the length and width of the patterned grating control the angular spread of a directional light beam scattered by the patterned grating,

13. A directional waveguide-based pixel for use in a multiview display screen, comprising:

a transparent electrode substrate layer;

a liquid crystal layer interposed between the transparent electrode substrate layer and the waveguide layer.

14. The directional waveguide- based pixel of claim 13, wherein the liquid crystal layer interposed between the transparent electrode substrate layer and the waveguide layer is a thin layer, ranging from 1-10 μηι in thickness. HP 82963260 PATENT

15. The directional waveguide- based pixel of claim 13, wherein the transparent electrode substrate layer comprises an electrode placed on a first surface of a transparent substrate, the first surface facing the liquid crystal layer.

16. The directional waveguide-based pixel of claim 13, wherein the waveguide layer further comprises ars active matrix and an electrode interposed between the patterned grating and the waveguide.

17. The directional waveguide-based pixel of claim 13, wherein the characteristics of the patterned grating comprise a gratmg length, a grating width, a grating orientation, a gratmg pitch, and a duty cycle,

18. The directional waveguide-based pixel of claim 17, wherein the pitch and orientation of the patterned grating control the direction of a directional light beam scattered by the patterned grating.

19. The directional waveguide-based pixel of claim 17, wherein the length and width of the patterned grating control the angular spread of a directional light beam scattered by the patterned grating.