TECHNICAL FIELD

The disclosure herein relates to technical field of display, particularly relates to a backlight assembly, a display device and a driving method thereof.

BACKGROUND

In an existing transparent display device, a light-extracting grating is arranged on a light output surface of a light guide, so that light propagates inside the light guide can be perpendicularly extracted. A liquid crystal layer is arranged at a light output side of a backlight assembly. An array of light-shielding layers is arranged at a side of the liquid crystal layer away from the backlight assembly. When display with L0 gray scale is carried out, perpendicular light beam emitted by the light-extracting grating is shielded by the light-shielding layer; when display with L255 gray scale is carried out, a driving voltage is applied to the liquid crystal layer, so that the liquid crystal layer forms a liquid crystal light grating to change direction of the perpendicular light beam, so that light rays are emitted through an interval between the light-shielding layers. By adjusting voltage in the liquid crystal layer, display with different gray scale is achieved.

However, in the transparent display device, when perpendicularly extracting light is carried out by the light-extracting grating, in addition to that light rays emitted perpendicularly, some stray light rays are generated. The stray light rays cannot be shielded by the light-shielding layer, so that the display device cannot be ensured to reach accurate L0 gray scale. Therefore, contrast of the display device is lowered.

SUMMARY

Disclosed herein is a backlight assembly, comprising: a light guide; a first grating on a first surface of the light guide, the first grating having a diffraction direction slanted relative to a thickness direction of the light guide; and a light direction adjuster on a side of the first grating away from the light guide and configured to change diffractive light coming from the first grating to a target direction.

According to an embodiment, the target direction is substantially parallel to the thickness direction of the light guide.

According to an embodiment, the light direction adjuster has a light input surface and a light output surface, the light input surface is positioned to face the first grating to receive the diffractive light, and the light output surface is slanted relative to the light input surface to receive the diffractive light received by the light input surface and output a light beam in the target direction.

According to an embodiment, the backlight assembly further comprises a first filling layer filled around the light direction adjuster. The light direction adjuster has a first refractive index and the first filling layer has a second refractive index smaller than the first refractive index, and the light output surface of the light direction adjuster is slanted relative to the thickness direction of the light guide in a direction opposite the diffraction direction.

According to an embodiment, the diffractive light has a refraction angle on the light input surface of the light direction adjuster satisfying an equation of:

0.2≤cos⁢⁢θcos[arctan(n1n2-cos⁢⁢θsin⁢⁢θ)]*cos[θ+arctan(n1n2-cos⁢⁢θsin⁢⁢θ)]≤0.8

with θ being the refraction angle, n1being the first refractive index and n2being the second refractive index, [0.2, 0.8] being a range of beam shrinkage ratio of the diffractive light.

According to an embodiment, the light direction adjuster is a trapezoid with the light input surface being a bottom surface and the light output surface being a side surface, and an angle between the side surface and bottom surface being:

θ+arctan⁡(sin⁢⁢θn1⁢/⁢n2-cos⁢⁢θ)

with θ being the refraction angle, n1being the first refractive index and n2being the second refractive index.

According to an embodiment, the backlight assembly further comprises a planarizing layer covering the first grating on a side of the first grating closer to the light direction adjuster.

According to an embodiment, a refractive index of material of the first grating and a refractive index of material of the light direction adjuster are both larger than a refractive index of material of the planarizing layer.

According to an embodiment, the backlight assembly further comprises a light emitter and a light reflector located on a light input side of the light guide. The light reflector is configured to reflect light emitted by the light emitter into the light guide for propagation inside the light guide with total reflection.

Disclosed herein is a display device, comprising any one of the above backlight assemblies, and a display panel located on a light output side of the backlight assembly.

According to an embodiment, the display panel comprises: a liquid crystal layer; a transparent substrate on a side of the liquid crystal layer away from the backlight assembly; and a second grating layer between the liquid crystal layer and the transparent substrate. The second grating layer comprises a plurality of second gratings. Each of the plurality of second gratings corresponds to a corresponding light direction adjuster and has an orthographic projection on the light guide covering an orthographic projection of a light output surface of the corresponding light direction adjuster on the light guide. The plurality of second gratings are configured to couple perpendicular incident light into the transparent substrate for propagation inside the transparent substrate with total reflection.

According to an embodiment, the display panel further comprises an electrode layer. The display panel is divided into a plurality of pixels each having one of the plurality of second gratings. The electrode layer is configured to generate an electrical field inside the liquid crystal layer to adjust a deflection direction of liquid crystal molecules inside the liquid crystal layer and control the electrical field in each pixel independently.

According to an embodiment, the electrode layer comprises a plurality of first electrodes and a second electrode, the plurality of first electrodes correspond to the plurality of pixels and the second electrode is a common electrode shared by the plurality of pixels.

According to an embodiment, the display panel further comprises a second filling layer filled between adjacent second gratings. The second filling layer has a refractive index smaller than a refractive index of the transparent substrate.

According to an embodiment, the display panel further comprises a light filter layer located at a side of the second filling layer away from the transparent substrate and the display panel contains no light-shielding layer.

Disclosed herein is a method of generating backlight for a display device. The method comprises: extracting light from a light guide by a first grating, here, the light is propagated with total reflection inside the light guide, and the light extracted from the light guide has a first direction slanted relative to a thickness direction of the light guide; adjusting, by a light direction adjuster, the light extracted from the light guide to a target direction that is different from the first direction.

According to an embodiment, the target direction is substantially parallel to the thickness direction of the light guide.

According to an embodiment, the method further comprises shrinking a cross-section of the light extracted from the light guide by the light direction adjuster.

According to an embodiment, the method further comprises passing the light extracted from the light guide through a first filling layer at a light output surface of the light direction adjuster. The light direction adjuster has a first refractive index and the first filling layer has a second refractive index smaller than the first refractive index, and the light output surface of the light direction adjuster is slanted relative to the thickness direction of the light guide in a direction opposite the first direction. The light extracted from the light guide has a refraction angle on a light input surface of the light direction adjuster satisfying an equation of:

0.2≤cos⁢⁢θcos[arctan(n1n2-cos⁢⁢θsin⁢⁢θ)]*cos[θ+arctan(n1n2-cos⁢⁢θsin⁢⁢θ)]≤0.8

with θ being the refraction angle, n1being the first refractive index and n2being the second refractive index, [0.2, 0.8] being a range of beam shrinkage ratio of the light extracted from the light guide.

According to an embodiment, the method further comprises passing the light extracted from the light guide through a planarizing layer before entering the light direction adjuster. The first grating and the light direction adjuster each have a refractive index larger than the planarizing layer.

According to an embodiment, the method further comprises: receiving light adjusted by the light direction adjuster in a liquid crystal layer; applying a control voltage to the liquid crystal layer to control a deflection direction of liquid crystal molecules inside the liquid crystal layer; and generating a backlight by passing light from the liquid crystal layer to a second grating or a second filling layer filled between adjacent second gratings.

According to an embodiment, the control voltage applied is a first level of control voltage and the deflection direction of the liquid crystal molecules inside the liquid crystal layer is controlled to direct all light received in the liquid crystal layer to the second grating.

According to an embodiment, the control voltage applied is a second level of control voltage and the deflection direction of the liquid crystal molecules inside the liquid crystal layer is controlled to direct all light received in the liquid crystal layer to the second grating.

According to an embodiment, the control voltage applied is a third level of control voltage and the deflection direction of the liquid crystal molecules inside the liquid crystal layer is controlled to direct a portion of light received in the liquid crystal layer to the second filling layer between adjacent second gratings and rest of light received in the liquid crystal layer to the second grating.

