WO2014051623A1

WO2014051623A1 - Directional waveguide-based backlight for use in a multivew display screen

Info

Publication number: WO2014051623A1
Application number: PCT/US2012/058022
Authority: WO
Inventors: David Fattal; Raymond G Beausoleil; Marco Fiorentino; James A Brug
Original assignee: Hewlett Packard Development Co LP
Current assignee: Hewlett Packard Development Co LP
Priority date: 2012-09-28
Filing date: 2012-09-28
Publication date: 2014-04-03
Anticipated expiration: 2015-03-28
Also published as: TW201418845A

Description

DIRECTIONAL WAVEGUIDE-BASED BACKLIGHT FOR USE IN A MULTIVEW

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, and PCT Patent Application Serial No.

(Attorney Docket No. ), entitled "Directional Waveguide-Based

Backlight with Integrated Hybrid Lasers for Use in a Multiview Display Screen", concurrently filed herewith, 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.

[0003] 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. 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:

[0006] FIG. 1 illustrates a schematic diagram of a top view of a waveguide-based directional backlight in accordance with various examples;

[0007] FIG. 2 illustrates a schematic diagram of a 3D view of an example backlight;

[0008] FIGS. 3A-B illustrate top views of a directional backlight according to FIG.

1;

[0009] FIG. 4 illustrates an example of a waveguide having geometrically distinct regions;

[0010] FIG. 5 illustrates a schematic diagram of a directional backlight having multiple waveguide arrays with the waveguides of FIG. 4; and

[0011] FIG. 6 is a flowchart for generating a 3D image with a directional waveguide-based backlight in accordance with various examples.

DETAILED DESCRIPTION

[0012] A directional waveguide-based backlight for use in a multiview display screen is disclosed. The directional backlight uses a plurality of light sources to generate a plurality of input planar lightbeams for a plurality of waveguide arrays. Each waveguide array is composed of a set of waveguides. Each waveguide is composed of a plurality of directional pixels to guide the input planar lightbeams and scatter a fraction of them into output directional lightbeams. The input planar lightbeams propagate in substantially the same plane as the directional backplane, which is designed to be substantially planar.

[0013] In various examples, the directional pixels have patterned gratings of substantially parallel and slanted grooves arranged in or on top of the waveguide. The waveguides may be, for example, dielectric or polymer waveguides, among others. The patterned gratings can consist of grooves etched in the waveguides or grooves made of material deposited on top of the waveguides (e.g., any material that can be deposited and etched or lift-off, including any dielectrics or metal).

[0014] In various examples, the plurality of light sources comprises a plurality of narrow-bandwidth light sources with a spectral bandwidth of approximately 30 nm or less. For example, the narrow-bandwidth light sources may include Light Emitting Diodes ("LEDs"), lasers, and so on. As described in more detail herein below, each directional pixel may be specified by a grating length (i.e., dimension along the propagation axis of the input planar lightbeams), a grating width (i.e., dimension across the propagation axis of the input planar lightbeams), a groove orientation, a pitch, and a duty cycle. Each directional pixel may emit a directional lightbeam 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 gratings vanishes thereby preventing the scattering of light in additional unwanted directions. This insures that only one directional lightbeam emerges from each directional pixel regardless of the output angle.

[0015] As further described in more detail herein below, a directional backlight can be designed with directional pixels that have a certain grating length, a grating width, a groove orientation, a pitch and a duty cycle. Each directional pixel can generate a directional lightbeam having a given view such that the plurality of directional pixels in the plurality of waveguides provides multiple views that form a multiview 3D image. The multiview 3D image can be a red, blue, and green multiview 3D image generated from the directional lightbeams emitted by the directional pixels in the backlight.

[0016] It is appreciated that, in the following description, numerous specific details are set forth to provide 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.

[0017] Referring now to FIG. 1, a schematic diagram of a top view of a waveguide- based directional backlight in accordance with various examples is described. Directional backlight 100 includes light sources lOSa-d to generate coUimated input planar lightbeams 1 lOa-d for a waveguide array 115 composed of waveguides 120a-d. As generally described herein, a planar lightbeam refers to a beam of light wherein the directions of the light rays in the beam are substantially parallel to each other. The waveguides 120a-d may be dielectric or polymer waveguides having a plurality of directional pixels arranged thereon, such as, for example, directional pixels 125a-c arranged on waveguide 120a. The directional pixels 125a- c scatter a fraction of the input planar lightbeam 110a into output directional lightbeams 130a-c.

[0018] In various examples, each directional pixel 125a-c has patterned gratings of substantially parallel grooves, e.g., grooves 135a for directional pixel 125a. The thickness of the grating grooves can be substantially the same for all grooves resulting in a substantially planar design. The grooves can be etched in the waveguides or be made of material deposited on top of the waveguides (e.g., any material that can be deposited and etched or lift-off, including any dielectrics or metal).

[0019] Each directional lightbeam 130a-c has a given direction and an angular spread that is determined by the patterned gratings in its corresponding directional pixel 12Sa-c. In particular, the direction of each directional lightbeam 130a-c is determined by the orientation and the grating pitch of the patterned gratings. The angular spread of each directional lightbeam is in turn determined by the grating length and width of the patterned gratings. For example, the direction of directional lightbeam 130a is determined by the orientation and the grating pitch of patterned gratings 135a.

[0020] It is appreciated that this substantially planar design and the formation of directional lightbeams 130a-c upon an input planar lightbeam 110a requires a grating with a substantially smaller pitch than traditional diffraction gratings. For example, traditional diffraction gratings scatter light upon illumination with lightbeams that are propagating substantially across the plane of the grating. Here, the gratings in each directional pixel 125a-c are substantially on the same plane as the input planar lightbeam 110a when generating the directional lightbeams 130a-c. This planar design enables illumination with the light sources lOSa-d.

[0021] In various examples, the light sources 105a-d can be narrow-bandwidth light sources such as LEDs. Light source 105a may be, for example, a red LED, light source 105b may be a green LED, light source 105c may be a blue LED, and light source 105d may be a white LED. Accordingly, directional lightbeams 130a-d coming out of waveguide 120a may be red lightbeams, the directional lightbeams coming out of waveguide 120b may be green lightbeams, the directional lightbeams coming out of waveguide 120c may be blue lightbeams, and the directional lightbeams coming out of waveguide 120d may be white lightbeams. As described below, the directional pixels may be designed to provide for precise control of the direction and angular spread of the directional lightbeams, enabling multiple views to be formed.

[0022] The directional lightbeams 130a-c are precisely controlled by characteristics of the gratings in directional pixels 125a-c 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 grating 135a controls the angular spread ΔΘ of the directional lightbeam 130a along the input light propagation axis and the grating width W controls the angular spread ΔΘ of the directional lightbeam 130a across the input light propagation axis, as follows:

where λ is the wavelength of the directional lightbeam 130a. 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 lightbeam 130a.

[0023] The grating length L and the grating width W can vary in size in the range of 0.1 to 200 um. The groove orientation angle Θ and the grating pitch Λ may be set to satisfy a desired direction of the directional lightbeam 130a, 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.

[0024] It is appreciated that directional backlight 100 is shown with a waveguide array 115 of four waveguides 120a-d for illustration purposes only. A directional backlight in accordance with various examples can be designed with many such waveguide arrays (e.g., higher than 100), depending on how the directional backlight 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 directional pixels may have any shape, including for example, a circle, an ellipse, a polygon, or other geometrical shape. Further, it is appreciated that any narrow-bandwidth light source may be used to generate the input planar lightbeams 110a-d (e.g., a laser or LED).

[0025] FIG. 2 shows a 3D view of an example backlight Backlight 200 is shown with a waveguide array composed of waveguides 205a-c. Each waveguide has multiple directional pixels arranged thereon, such as, for example, directional pixel 210a in waveguide 205a, directional pixel 210b in waveguide 205b, and directional pixel 210c in waveguide 205c. The directional pixels 210a-c may be designed to have a different grating pitch and orientation. Each directional pixel 210a-c receives an input planar lightbeam (e.g., lightbeams 215a-c) and scatters them into a directional lightbeam (e.g., directional lightbeams 220a-c) according to the grating pitch and orientation of each directional pixel. The directional lightbeams 220a-c, as described above, therefore enable multiple views to be generated into a 3D image. Each directional lightbeam can be precisely controlled by the characteristics of its corresponding directional pixel.

[0026] Attention is now directed to FIGS. 3A-B, which illustrate top views of a directional backlight according to FIG. 1. In FIG. 3A, directional backlight 300 is show with light sources 30Sa-d (e.g., LEDs) generating input planar lightbeams 310a-d, and waveguides 315a-d consisting of a plurality of polygonal directional pixels arranged thereon (e.g., directional pixel 320 in waveguide 315a). Each directional pixel is able to scatter a portion of an input planar lightbeam into an output directional lightbeam (e.g., directional lightbeam 325 scattered by directional pixel 320 from input planar lightbeam 310a). The directional lightbeams scattered by all the directional pixels in the waveguides 315a-d can represent multiple image views that when combined form a 3D image, such as, for example, 3D image 330.

[0027] Similarly, in FIG. 3B, directional backlight 335 is shown with light sources 340a-d (e.g., LEDs) generating input planar lightbeams 345a-d, and waveguides 350a-d consisting of a plurality of polygonal directional pixels arranged thereon (e.g., directional pixel 355 in waveguide 350a). Each directional pixel is able to scatter a portion of an input planar lightbeam into an output directional lightbeam (e.g., directional lightbeam 360 scattered by directional pixel 355 from input planar lightbeam 345a). The directional lightbeams scattered by all the directional pixels in the waveguides 350a-d can represent multiple image views that when combined form a 3D image, such as, for example, 3D image 365.

[0028] In various examples, the waveguides in a waveguide array can be designed with geometrically distinct regions. Each geometrically distinct region has a directional pixel that is perpendicular to the region's orientation, thus enabling the directional lightbeams to have different vertical orientations in each region. FIG. 4 shows an example of a waveguide having geometrically distinct regions. Waveguide 400 has geometrically distinct waveguide regions 405a-405e. Each waveguide region may have a single horizontal section such as waveguide region 405a or multiple sections having different orientations such as waveguide regions 405b-e. Waveguide regions 405b-e have an angular section placed between two horizontally oriented sections. For example, waveguide region 405e has angular section 410 placed between horizontal sections 415a-b.

[0029] Each waveguide region has a single directional pixel arranged thereon, such as directional pixels 420a-e. The directional pixels 420a-e placed in each waveguide region are oriented perpendicularly to the orientation of the region as shown in the figure. In the case of waveguide regions (e.g., regions 405b-e) having an angular section between two horizontal sections, the directional pixels (e.g., pixels 420b-e) are arranged perpendicularly to the orientation of the angular section. This enables the directional lightbeams scattered out of each directional pixel to have different vertical orientations in each region.

[0030] Attention is now directed to FIG. 5, which illustrates a schematic diagram of a directional backlight having multiple waveguide arrays with waveguides of FIG. 4. Directional backlight 500 is shown with multiple waveguide arrays 505a-c, with each waveguide array having four waveguides (e.g., one for red light, one for green, one for blue light, and another for white light). The waveguide arrays SOSa-c can be designed to form different viewing sections, such as, for example, viewing section 510. Each viewing section may have directional pixels designed to scatter directional lightbeams into a given image view to generate a 3D image.

[0031] A flowchart for generating a 3D image with a directional backlight in accordance with various examples is illustrated in FIG. 6. First, the characteristics of the directional pixels of the directional backlight are specified (600). The characteristics may include characteristics of the patterned gratings in the directional pixels, such as, for example, a grating length, a grating width, an orientation, a pitch, and a duty cycle. As described above, each directional pixel in the directional backlight can be specified with a given set of characteristics to generate a directional lightbeam having a direction and an angular spread that is precisely controlled according to the characteristics. Next, a directional backlight is fabricated with the plurality of directional pixels arranged on a plurality of waveguides (60S). The waveguides may be dielectric or polymer waveguides, among others. The directional pixels may be etched in the waveguides or be made of patterned gratings with material deposited on top of the waveguides (e.g., any material that can be deposited and etched or lift-off, including any dielectrics or metal). In various examples, the waveguides may also have geometrically distinct regions as shown in FIGS. 4-5. Light from a plurality of light sources is input into the directional backlight in the form of input planar lightbeams (610). Lastly, a 3D image is generated from the directional lightbeams that are scattered by the directional pixels in the directional backlight (615).

[0032] Advantageously, the precise control that is achieved with the directional pixels in the directional backlight enables a 3D image to be generated with an easy to fabricate substantially planar structure. Different configurations of directional pixels can generate different 3D images. The directional backlights 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.

[0033] 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 limited to the examples shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

WHAT IS CLAIMED IS:

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

a plurality of light sources to generate a plurality of input planar lightbeams; and a plurality of waveguide arrays, each waveguide array having a set of waveguides, each waveguide having a plurality of directional pixels with patterned gratings to scatter the plurality of input planar lightbeams into a plurality of directional lightbeams, each directional lightbeam having a direction and angular spread controlled by characteristics of a directional pixel in the plurality of directional pixels.

2. The directional waveguide-based backlight of claim 1 , wherein the plurality of light sources comprises a plurality of narrow-bandwidth light sources.

3. The directional waveguide-based backlight of claim 1 , wherein the plurality of waveguide arrays are substantially planar.

4. The directional waveguide-based backlight of claim 1 , wherein the patterned gratings comprise a plurality of substantially parallel and slanted grooves.

5. The directional waveguide-based backlight of claim 4, wherein the characteristics of a directional pixel comprise a grating length, a grating width, a grating orientation, a grating pitch, and a duty cycle.

6. The directional waveguide-based backlight of claim 5, wherein the pitch and orientation of a directional pixel control the direction of a directional lightbeam scattered by the directional pixel.

7. The directional waveguide-based backlight of claim 6, wherein the length and width of a directional pixel control the angular spread of a directional lightbeam scattered by a directional pixel.

8. The directional waveguide-based backlight of claim 1, wherein a waveguide in the set of waveguides comprises a plurality of geometrically distinct regions, each region having a plurality of sections and a single directional pixel.

9. A method for generating a multiview 3D image with a waveguide-based directional backlight, comprising:

specifying a plurality of characteristics for a plurality of directional pixels, each directional pixel composed of a patterned grating having substantially parallel and slanted grooves;

fabricating a directional backlight with the plurality of directional pixels arranged on a plurality of waveguides;

illuminating the plurality of waveguides with light from a plurality of light sources; and

generating the multiview image with directional lightbeams scattered by the plurality of directional pixels in the directional backlight.

10. The method of claim 9, wherein each directional lightbeam is controlled by the characteristics of a directional pixel.

11. The method of claim 10, wherein the characteristics of a directional pixel comprise a grating length, a grating width, a grating orientation, a grating pitch, and a duty cycle.

12. The method of claim 11 , wherein the pitch and orientation of a directional pixel control the direction of a directional lightbeam scattered by the directional pixel.

13. The method of claim 11 , wherein the length and width of a directional pixel control the angular spread of a directional lightbeam scattered by the directional pixel.

14. The method of claim 11 , wherein fabricating a directional backlight comprises fabricating a waveguide having a plurality of geometrically distinct regions, each region having a plurality of sections and a single directional pixel.

15. A waveguide, comprising:

a plurality of geometrically distinct regions, each region having a plurality of sections; and

a plurality of directional pixels arranged on the plurality of geometrically distinct regions to scatter an input planar lightbeam into a plurality of directional lightbeams, each directional lightbeam having a direction and angular spread controlled by characteristics of a directional pixel in the plurality of directional pixels.

16. The waveguide of claim 15, wherein the plurality of sections comprises an angular section placed between two horizontally oriented sections.