HK1205793B - Directional backlight with a modulation layer - Google Patents

Description

Directional backlight with modulation layer

Cross Reference to Related Applications

The present application relates to PCT patent application serial No. PCT/US2012/035573 (attorney docket No.82963238) entitled "Directional Pixel for Use in a display Screen" filed on day 27, 2012 and filed on day 31, ___ (attorney docket No.83011348), both assigned to the assignee of the present application and incorporated herein by reference.

Background

The ability to reproduce a light field in a display screen is an important requirement in imaging and display technology. A light field is the set of all light rays that travel through each point in space in each direction. Any natural, real-world scene can be characterized entirely by its light field if information is provided about the intensity, color, and direction of all light rays passing through the scene. The goal is to enable viewers of the display screen to experience the scene as if they were personally experiencing the scene.

Currently available display screens in televisions, personal computers, laptop computers, and mobile devices are still mostly two-dimensional and therefore are not able to reproduce the light field accurately. Three-dimensional ("3D") displays have recently emerged, but they also have angular and spatial resolution that is not high, except to provide a limited number of views. Examples include 3D displays based on holography, parallax barriers or lenticular lenses.

One common theme between these displays is the difficulty in generating a light field that is precisely controlled at the pixel level to achieve good image quality for a wide range of viewing angles and spatial resolutions.

Drawings

The present application may be more completely understood in consideration of the following detailed description in connection with the accompanying drawings, in which like reference numerals refer to like parts throughout, and in which:

fig. 1 illustrates a schematic diagram of a directional backlight (directional backlight) according to various examples;

2A-B illustrate exemplary top views of the directional backlight of FIG. 1;

3A-B illustrate additional top views of the directional backlight according to FIG. 1;

FIG. 4 illustrates a directional backlight having a triangular shape;

FIG. 5 illustrates a directional backlight having a hexagonal shape;

FIG. 6 illustrates a directional backlight having a circular shape; and

fig. 7 is a flow diagram for generating a 3D image with a directional backlight in accordance with various examples.

Detailed Description

Directional backlights having modulation layers are disclosed. As generally used herein, a directional backlight is a layer in a display screen (e.g., an LCD display screen) for providing a light field in the form of a directional beam of light. The directional lightbeams are scattered by a plurality of directional pixels in the directional backlight. Each directional beam originates from a different directional pixel and has a given direction and angular spread based on the characteristics of that directional pixel. This specified directionality enables the directional beam to be modulated (i.e., turned on, off, or varied in brightness) using multiple modulators. The modulator may be, for example, a liquid crystal display ("LCD") unit (with or without a polarizer). Other types of modulators may be used, such as modulators based on different mechanisms including micro-electromechanical ("MEMS"), fluidic, magnetic, electrophoretic, or other mechanisms that modulate light intensity when an electrical signal is applied.

In various examples, the directional pixels are arranged in a directional backplane illuminated by a plurality of input planar beams. The directional pixels receive the input planar light beams and scatter a portion of them as directional light beams. A modulation layer is placed over the directional pixels to modulate the directional beams as desired. The modulation layer includes a plurality of modulators (e.g., LCD cells), where each modulator modulates a single directional lightbeam from a single directional pixel or a set of directional lightbeams from a set of directional pixels. The modulation layer enables the generation of 3D images with many different views, each view being provided by a set of directed light beams.

In various examples, the directional pixels in the directional backplane have a patterned grating of substantially parallel trenches arranged in or on top of the directional backplane. The directional backplane may be, for example, a plate (slab) of transparent material such as silicon nitride ("SiN"), glass or quartz, plastic, indium tin oxide ("ITO"), or other material that directs the input planar beam to the directional pixels. The patterned grating may be comprised of trenches etched directly into the directional backplane or waveguide, or may be comprised of trenches made of a material deposited on top of the directional backplane or waveguide (e.g., any material that can be deposited and etched or stripped, including any dielectric or metal). The grooves may also be slanted.

As described in greater detail herein below, each directional pixel may be determined by a grating length (i.e., a dimension along the propagation axis of the input planar beam), a grating width (i.e., a dimension across the propagation axis of the input planar beam), a trench orientation, a pitch, and a duty cycle. Each directional pixel may emit a directional beam having a direction determined by the trench orientation and the grating pitch and an angular spread determined by the grating length and width. By using a duty cycle of 50% or around 50%, the second fourier coefficient of the patterned grating becomes zero, thereby preventing scattering of light in other unwanted directions. This ensures that only one directional beam of light emanates from each directional pixel, regardless of its output angle.

As described in further detail herein below, a directional backlight may be designed with directional pixels having a certain grating length, grating width, trench orientation, pitch, and duty cycle selected to produce a given 3D image. The 3D image is generated from directional beams emitted by the directional pixels and modulated by the modulation layer, wherein the modulated directional beams from a set of directional pixels generate a given image view.

It should be understood that in the following description, numerous specific details are set forth in order to provide a thorough understanding of the embodiments. However, it is understood that the embodiments may be practiced without limitation to these specific details. In other instances, well-known methods and structures may not have been described in detail so as not to unnecessarily obscure the description of the embodiments. In addition, the embodiments may be used in combination with each other.

Referring now to fig. 1, a schematic diagram of a directional backlight according to various examples is depicted. The directional backlight 100 includes a directional back plate 105 that receives a set of input planar light beams 110 from a plurality of light sources. The plurality of light sources may include, for example, one or more narrow bandwidth light sources, such as light emitting diodes ("LEDs"), lasers, etc., having a spectral bandwidth of about 30nm or less. The input planar beam 110 propagates in substantially the same plane as the directional backplane 105, which directional backplane 105 is designed to be substantially planar.

The orientation back-plate 105 may be composed of a plate of transparent material (e.g., SiN, glass or quartz, plastic, ITO, etc.) having a plurality of orientation pixels 115a-d arranged in the orientation back-plate 105 or on top of the orientation back-plate 105. Directional pixels 115a-d scatter a portion of input planar beam 110 into directional beams 120 a-d. In various examples, each orientation pixel 115a-d has a patterned grating of substantially parallel trenches (e.g., trench 125a for orientation pixel 115 a). The thickness of the grating trenches may be substantially the same for all trenches, resulting in a substantially planar design. The trenches may be etched in the directional backplane or made of a material (e.g., any material that can be deposited and etched or stripped, including any dielectric or metal) deposited on top of the directional backplane 105.

Each directional beam 120a-d has a given direction and angular spread determined by the patterned grating forming the corresponding directional pixel 115 a-d. Specifically, the direction of each directional beam 120a-d is determined by the orientation of the patterned grating and the grating pitch. The angular spread of each directed beam is determined by the grating length and width of the patterned grating. For example, the direction of the directed beam 115a is determined by the orientation of the patterned grating 125a and the grating pitch.

It will be appreciated that this substantially planar design and the formation of the directed beams 120a-d from the input planar beam 110 requires a grating having a much smaller pitch than conventional diffraction gratings. For example, conventional diffraction gratings scatter light when illuminated with a light beam that propagates substantially through the plane of the grating. Here, the grating in each directional pixel 115a-d is substantially in the same plane as the input planar beam 110 when generating the directional beams 120 a-d.

The directed beams 120a-d are precisely controlled by the characteristics of the gratings in the directed pixels 115a-d, including the grating length L, the grating width W, the trench orientation θ, and the grating pitch Λ. Specifically, the grating length L of the grating 125a controls the angular spread Δ Θ of the directional beam 120a along the input light propagation axis, and the grating width W controls the angular spread Δ Θ of the directional beam 120a intersecting the input light propagation axis as follows:

where λ is the wavelength of the directed beam 120 a. The orientation of the grooves, determined by the grating orientation angle theta, and the grating pitch or period, determined by Λ, control the direction of the directed beam 120 a.

The grating length L and the grating width W may vary in size in the range of 0.1 to 200 μm. The trench orientation angle theta and the grating pitch lambda may be set to meet the desired direction of the directed beam 120a, where for example the trench orientation angle theta is on the order of-40 to +40 degrees and the grating pitch lambda is on the order of 200-700 nm.

In various examples, modulation layer 130 with multiple modulators (e.g., LCD cells) is positioned over directional pixels 115a-d to modulate directional lightbeams 120a-d scattered by directional pixels 115 a-d. Modulation of the directional beams 120a-d includes controlling their brightness (e.g., turning them on, off, or changing their brightness) with a modulator. For example, modulators in modulation layer 130 may be used to turn on directional beams 120a and 120d and turn off directional beams 120b and 120 c. The ability to provide modulation to the directional beams 120a-d enables the production of many different image views.

Modulation layer 130 may be placed on top of spacer layer 135, which spacer layer 135 may be made of a material or simply be composed of space (i.e., air) between directional pixels 115a-d and the modulators of modulation layer 130. The spacer layer 135 may have a width on the order of 0-100 μm, for example.

It should be understood that the directional backplane 105 is shown with four directional pixels 115a-d for illustration purposes only. Depending on how the directional backplane is used (e.g., in a 3D display screen, in a 3D table, in a mobile device, etc.), the directional backplane according to various examples may be designed to have many directional pixels (e.g., more than 100). It should also be understood that the directional pixels may have any shape, including, for example, circular, elliptical, polygonal, or other geometric shapes.

Referring now to fig. 2A-B, top views of the directional backlight according to fig. 1 are illustrated. In fig. 2A, a directional backlight 200 is shown having a directional backplane 205, where the directional backplane 205 includes a plurality of polygonal directional pixels (e.g., directional pixels 210) arranged in a transparent plate. Each directional pixel is capable of scattering a portion of the input planar beam 215 into an output directional beam (e.g., directional beam 220). Each directional beam is modulated by a modulator (e.g., LCD cell 225 for directional beam 220). The directional lightbeams scattered by all the directional pixels in the directional backplane 205 and modulated by the modulator (e.g., LCD cell 225) may represent multiple image views that, when combined, form a 3D image.

Similarly, in FIG. 2B, a directional backlight 230 is shown having a directional backplane 235, the directional backplane 235 comprising a plurality of circular directional pixels (e.g., directional pixels 240) arranged in a transparent plate. Each directional pixel can scatter a portion of the input planar beam 245 into an output directional beam (e.g., directional beam 250). Each directional beam is modulated by a modulator (e.g., LCD cell 255 for directional beam 250). The directional lightbeams scattered by all the directional pixels in the directional backplane 235 and modulated by the modulator (e.g., LCD cell 255) may represent multiple image views that, when combined, form a 3D image.

In various examples, a single modulator may be used to modulate a set of directional light beams from a set of directional pixels. That is, a given modulator may be placed over a set of directional pixels, rather than having one modulator per directional pixel as shown in FIGS. 2A-B.

Referring now to fig. 3A-B, top views of a directional backlight according to fig. 1 are depicted. In fig. 3A, a directional backlight 300 is shown having a directional backplane 305, the directional backplane 305 comprising a plurality of polygonal directional pixels (e.g., directional pixels 310a) arranged in a transparent plate. Each directional pixel is capable of scattering a portion of input planar beam 315 into an output directional beam (e.g., directional beam 320 a). A set of directional beams (e.g., directional beams 320a-d scattered by directional pixels 310 a-d) is modulated by a modulator (e.g., LCD cell 325a that modulates directional beams 320 a-d). For example, LCD unit 325a is used to turn on directional pixels 310a-d while LCD unit 325d is used to turn off directional pixels 330 a-d. The directional lightbeams scattered by all the directional pixels in the directional backplane 305 and modulated by the LCD cells 325a-D may represent multiple image views that, when combined, form a 3D image.

Similarly, in fig. 3B, a directional backlight 340 is shown having a directional backplane 345, where the directional backplane 345 comprises a plurality of circular directional pixels (e.g., directional pixel 350a) arranged in a transparent plate. Each directional pixel is capable of scattering a portion of input planar light beam 355 into an output directional light beam (e.g., directional light beam 360 a). A set of directional beams (e.g., directional beams 360a-d scattered by directional pixels 350 a-d) is modulated by a modulator (e.g., LCD unit 370a modulates directional beams 360 a-d). For example, LCD unit 370a is used to turn on directional pixels 350a-d while LCD unit 370d is used to turn off directional pixels 365 a-d. The directional beams scattered by all directional pixels in the directional backplane 345 and modulated by modulators such as LCD cells 370a-D may represent multiple image views that, when combined, form a 3D image.

It should be understood that the directional backplane may be designed to have different shapes, such as, for example, triangular (as shown in fig. 4), hexagonal (as shown in fig. 5), or circular (as shown in fig. 6). In FIG. 4, the directional backplane 405 receives input planar beams from three different spatial directions, e.g., input planar beam 410 and 420. This configuration may be used when the input planar light beams represent different colors of light, for example, red for input planar light beam 410, green for input planar light beam 415, and blue for input planar light beam 420. Each of the input planar light beams 410-420 is disposed on one side of the triangular shaped directional backplane 405 to converge its light on a set of directional pixels. For example, the input planar beam 410 is scattered as a directional beam by a set of directional pixels 425 and 435. The subset of directional pixels 425-435 may also receive light from the input planar light beam 415-420. However, by design, this light is not scattered into the intended viewable area of the directional backlight 400.

For example, assume that input planar beam 410 is directed to a subset G of pixels 425 and 435_AScattered into the desired visible area. The desired viewing area may be defined by a maximum ray angle θ measured from a normal to the directional backlight 400_maxAnd (4) determining. Input planar beam 410 may also be directed to pixel G_B440-450, but those unwanted rays are outside the expected viewing area as long as the following equations are satisfied:

wherein λ_AIs the wavelength, n, of the input planar beam 410_eff ^AIs the effective index (λ) of horizontal propagation of the input planar beam 410 in the directional backplane 405_BIs the wavelength of the input planar light beam 420 (scattered by directional pixel 440-450), and n_eff ^BIs the effective index of refraction for the input planar beam 420 to propagate horizontally in the directional backplane 405. Is effective thereinIn the case where the refractive index and the wavelength are substantially the same, equation 2 is simplified as:

for a directional backplane with an index of refraction n greater than 2 and input plane beams propagating near the grazing angle, it can be seen that the intended viewing area of the display can be extended to the entire space (n)_effSin θ is not less than 2_max1). For lower index directional backplanes such as glass (e.g., n-1.46), the expected viewable area is limited to about θ_max<arcsin (n/2) (. + -. 45 ℃ for glass).

It should be understood that each directional beam may be modulated by a modulator, such as, for example, LCD unit 455. Because precise directional and angular control of the directional lightbeams can be achieved by each directional pixel in the directional backplane 405, and the directional lightbeams can be modulated by a modulator, such as an LCD cell, the directional backlight 405 can be designed to produce multiple different views of a 3D image.

It should also be appreciated that the directional backplane 405 shown in fig. 4 may be formed into a more compact design by implementing that the top corners (vertices) of the triangular plates may be cut away to form a hexagonal shape as shown in fig. 5. The directional backplane 505 receives input planar beams from three different spatial directions, e.g., input planar beam 510-. Each of the input planar beams 510 and 520 is arranged on a separate side of the hexagonal-shaped directional backplane 505 to converge its rays on a subset of the directional pixels (e.g., directional pixels 525 and 535). In various embodiments, the hexagonal-shaped directional backplane 505 has side lengths that may range on the order of 10-30mm, with directional pixel sizes on the order of 10-30 μm.

It should be understood that the directional backlight 500 is shown with multiple configurations of modulators. For example, a single modulator may be used to modulate a directional beam from a group of directional pixels, such as LCD cell 540 for directional pixel 525 and 535, or a single modulator may be used to modulate a single directional pixel, such as LCD cell 555 for directional pixel 560. It will be appreciated by those skilled in the art that any modulator configuration for the directional pixels may be used to modulate the directional light beams scattered by the directional pixels.

It should also be understood that directional backlights for use with color input plane beams can also have any geometry other than triangular (fig. 4) or hexagonal (fig. 5) as long as light from the three primary colors is introduced from three different directions. For example, the directional backlight may be polygonal, circular, elliptical, or another shape capable of receiving light from three different directions. Referring now to FIG. 6, a directional backlight having a circular shape is illustrated. The directional backplane 605 in the directional backlight 600 receives input planar light beams 610 and 620 from three different directions. Each directional pixel has a circular shape, e.g., directional pixel 620, and scatters a directional light beam modulated by a modulator, e.g., LCD cell 625. Each LCD cell has a rectangular shape and the circular orientation backplane 605 is designed to accommodate rectangular LCD cells for circular orientation pixels (or polygonal orientation pixels if desired).

A flow chart for generating a 3D image with a directional backlight according to the present application is illustrated in fig. 7. First, characteristics of directional pixels of a directional backlight are determined (700). The characteristics may include characteristics of the patterned grating in the orientation pixel, such as, for example, grating length, grating width, orientation, pitch, and duty cycle. As described above, each directional pixel in a directional backlight may be determined with a given set of characteristics to produce a directional lightbeam having a direction and angular spread precisely controlled according to the characteristics.

Next, a directional backplane with directional pixels is fabricated (705). The directional backplane is made of a transparent material and may be manufactured using any suitable manufacturing technique such as optical lithography (lithography), nanoimprint lithography, roll-to-roll imprint lithography, direct embossing using an imprint mold, and other techniques. The directional pixels may be etched in the directional backplane or made of a patterned grating using a material deposited on top of the directional backplane (e.g., any material that can be deposited and etched or stripped, including any dielectric or metal).

A modulation layer (e.g., an LCD-based modulation layer) is then added to the directional backplane (710). The modulation layer comprises a plurality of modulators (e.g., LCD cells) placed on top of a spacer layer (as shown in fig. 1) over a directional backplane. As described above, the modulation layer may be designed such that a single directional pixel has a single modulator or a group of directional pixels has a single modulator. As further described above, the directional backplane (and directional pixels) may have different shapes (e.g., polygonal, triangular, hexagonal, circular, etc.) to accommodate modulation layers comprised of rectangular shaped modulators.

Light from a plurality of narrow bandwidth light sources is input to a directional backplane (715) in the form of an input planar beam. Finally, the 3D image is generated from the modulated directional beam, which is scattered by the directional pixels in the directional backplane (720).

Advantageously, the precise control achieved by the modulation and orientation pixels in the directional backlight enables the generation of 3D images with ease of fabrication of substantially planar structures. Different configurations of the orientation pixels produce different 3D images. Furthermore, the directional beams produced by the directional pixels may be modulated to produce any desired effect in the generated image. The directional backlights described herein can be used to provide 3D images in display screens (e.g., in TVs, mobile devices, tablet computers, video game devices, etc.) as well as other applications such as 3D watches, 3D artistic devices, 3D medical devices, and others.

It is to be understood that the description of the disclosed embodiments above is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (24)

1. A directional backlight, comprising:

a directional backplane comprising a sheet of transparent material configured to direct a plurality of input planar light beams, the directional backplane having a plurality of directional pixels configured to scatter a portion of the directed input planar light beams out of a surface of the sheet of transparent material into a plurality of directional light beams corresponding to directions of different views of a three-dimensional (3D) image, each directional light beam having a direction and angular spread controlled by characteristics of a directional pixel of the plurality of directional pixels; and

a modulation layer having a plurality of modulators configured to modulate a plurality of directional light beams,

wherein each of the plurality of orientation pixels comprises a patterned grating in, on, or in and on a surface of the sheet of transparent material.

2. The directional backlight of claim 1, further comprising a spacer layer over the directional backplane.

3. The directional backlight according to claim 2, wherein the modulation layer is located over the spacer layer.

4. The directional backlight of claim 1, wherein the sheet of transparent material of the directional backplane is substantially planar, the plurality of input planar optical beams being configured to propagate within the plane of the sheet of substantially planar transparent material.

5. The directional backlight of claim 1, wherein the patterned grating comprises a plurality of substantially parallel grooves.

6. The directional backlight of claim 1, wherein the characteristics of directional pixels comprise a grating length, a grating width, a grating orientation, a grating pitch, and a grating duty cycle of the patterned grating.

7. The directional backlight of claim 6, wherein a grating pitch and a grating orientation of the patterned grating control a direction of a directional beam scattered by the directional pixel.

8. The directional backlight of claim 6, wherein a grating length and a grating width of the patterned grating control an angular spread of directional light beams scattered by directional pixels.

9. The directional backlight of claim 1, wherein a single modulator from the plurality of modulators modulates a directional lightbeam from a single directional pixel.

10. The directional backlight of claim 1, wherein a single modulator from the plurality of modulators modulates a directional lightbeam from a group of directional pixels.

11. The directional backlight of claim 1, wherein the directional backplane comprises a polygonal sheet of transparent material.

12. The directional backlight of claim 1, wherein the directional backplane comprises a circular sheet of transparent material.

13. The directional backlight of claim 1, wherein the plurality of directional pixels comprises a plurality of polygonal directional pixels.

14. The directional backlight of claim 1, wherein the plurality of directional pixels comprises a plurality of circular directional pixels.

15. The directional backlight of claim 1, wherein the modulation layer comprises an LCD-based modulation layer and the plurality of modulators comprises a plurality of LCD cells.

16. A method of generating a 3D image with a directional backlight having a modulation layer, comprising:

determining a plurality of characteristics for a plurality of directional pixels, each directional pixel comprising a patterned grating;

fabricating an orientation backplane comprising a sheet of transparent material configured to direct a beam of light, on which the plurality of orientation pixels are arranged;

adding a modulation layer having a plurality of modulators over the directional backplane;

illuminating the directional backplane with a plurality of input planar light beams, the input planar light beams being directed within a sheet of transparent material and scattered out of the sheet of transparent material by the plurality of directional pixels into a plurality of directional light beams; and

the plurality of directional beams are modulated with the plurality of modulators to produce a plurality of views of the 3D image.

17. The method of claim 16, wherein each directional beam is controlled by characteristics of a directional pixel.

18. The method of claim 16, wherein the characteristics of the directional pixels include a grating length, a grating width, a grating orientation, a grating pitch, and a grating duty cycle of the patterned grating.

19. The method of claim 16, wherein a single modulator from the plurality of modulators modulates a directional lightbeam from a single directional pixel.

20. The method of claim 16, wherein a single modulator from the plurality of modulators modulates a directional lightbeam from a set of directional pixels.

21. The method of claim 16, wherein the modulation layer comprises an LCD-based modulation layer and the plurality of modulators comprises a plurality of LCD cells.

22. A 3D imaging directional backlight, comprising:

a directional backplane comprising a layer of material configured to direct light within the layer of material as planar light beams, the directional backplane having a plurality of directional pixels configured to scatter a portion of a plurality of input planar light beams directed within the layer of material out as a plurality of directional light beams directed as a light field away from a surface of the directional backplane, each directional pixel comprising a patterned grating, each directional light beam having a direction and angular spread controlled by a characteristic of a directional pixel of the plurality of directional pixels; and

a modulation layer having a plurality of modulators configured to modulate the plurality of directional beams, the modulation layer adjacent to a surface of the directional backplane,

wherein the modulated set of directional beams from the corresponding set of directional pixels represents one of a plurality of different views forming the 3D image.

23. The 3D imaging directional backlight of claim 22, wherein each modulator of the modulation layer is configured to modulate a single light beam from a single directional pixel.

24. The 3D imaging directional backlight of claim 22, wherein a grating pitch and a grating orientation of the patterned grating of directional pixels controls a direction of a directional lightbeam scattered by the directional pixels.