Backlight unit using wire-grid polarizer and liquid crystal display apparatus employing the backlight unit

• US 20070047214A1
• Filed: 02/08/2006
• Published: 03/01/2007
• Est. Priority Date: 08/30/2005
• Status: Active Grant

• Current Assignee: Samsung Display Company Limited (Samsung Electronics Co. Ltd.)
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Nesterenko, Dmitry, Choi, Hwan-young
• Granted Patent: US 7,614,757 B2
• Time in Patent Office: Days
• US Class Current: 362/19
• CPC Class Codes: G02B 6/0038 Linear indentations or grooves, e.g. arc-shaped grooves or meandering grooves, extending over the full length or width of the light guide
• CPC Class Codes: G02B 6/0055 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0056 for producing polarisation effects, e.g. by a surface with polarizing properties or by an additional polarizing elements
• CPC Class Codes: G02F 1/133548 Wire-grid polarisers
• CPC Class Codes: G02F 1/13362 providing polarized light, e.g. by converting a polarisation component into another one

Abstract

A backlight unit, which can emit one of s-polarized light and p-polarized light using wire-grid polarizer, and a liquid crystal display apparatus employing the backlight unit are provided. The backlight unit includes: a light source radiating light; a light guide plate disposed with the light source at a lateral side of the light guide plate, guiding the light incident on the lateral side from the light source; a wire-grid polarizer formed on a predetermined layer of the light guide plate transmitting a first polarized component of the light through the predetermined layer and reflecting a second polarized component of light; a reflector reflecting the light to un upper surface of the light guide plate; and a polarization converter changing a polarization of the light not emitted through the upper surface of the light guide plate.

Claims

1. A backlight unit comprising:

a light source which radiates light;

a light guide plate, disposed with the light source at a lateral side of the light guide plate, which guides the light incident on the lateral side into the light guide plate;

a wire-grid polarizer, formed on a predetermined layer of the light guide plate, which transmits a first polarized component of the light through the predetermined layer and reflects a second polarized component of the light;

a reflector which reflects the light to an upper surface of the light guide plate; and

a polarization converter which changes a polarization of the light not emitted through the upper surface of the light guide plate.

2. The backlight unit of claim 1, wherein the predetermined layer comprises at least one of the upper surface and a lower surface of the light guide plate.

3. The backlight unit of claim 1, wherein the reflector comprises a lower reflection panel disposed below the light guide plate.

4. The backlight unit of claim 3, further comprising a lateral reflection panel, disposed at an opposite lateral side of the light guide plate, which reflects the light, emitted through the opposite lateral side of the light guide plate and not through the upper surface of the light guide plate, to the light guide plate.

5. The backlight unit of claim 4, wherein the lateral reflection panel is sloped at a predetermined angle so that the portion of the light reflected to the light guide plate by the lateral reflection panel is totally reflected onto the lower and upper surface of the light guide plate.

6. The backlight unit of claim 4, wherein the polarization converter is placed between the light guide plate and the lateral reflection panel.

7. The backlight unit of claim 3, wherein the polarization converter is placed between the lower surface of the light guide plate and the lower reflection panel.

8. The backlight unit of claim 1,

wherein the predetermined layer is the upper surface of the light guide plate;

wherein the light guide plate is configured such that thickness of the light guide plate decreases from the lateral side, at which the light source is disposed, to the opposite lateral side; and

wherein the wire-grid polarizer comprises a plurality of parallel wires placed side by side with an interval less than 200 nm, and functions as a polarizer to totally reflect the first and second components of the light incident on the upper surface at an angle greater than a predetermined critical angle satisfying total reflection within the light guide plate.

9. The backlight unit of claim 1, wherein the polarization converter is a diffuse reflection panel disposed at an opposite lateral side of the light guide plate.

10. The backlight unit of claim 1,

wherein the predetermined layer is the upper surface of the light guide plate;

and

wherein the wire-grid polarizer comprises a plurality of parallel wires placed side by side with an interval of 200 nm or greater, and functions as a diffraction lattice to diffract the light incident on the upper surface of the light guide plate.

11. The backlight unit of claim 1, further comprising a micro-structured pattern, formed on a predetermined layer of the light guide plate, which changes a proceeding direction of the light incident on the micro-structured pattern to be substantially vertical.

12. The backlight unit of claim 11, wherein the micro-structured pattern is a hologram diffraction pattern.

13. The backlight unit of claim 11, wherein the micro-structured pattern is a prism pattern.

14. The backlight unit of claim 11, wherein the reflector comprises a lower reflection panel disposed below the light guide.

15. The backlight unit of claim 14, further comprising a lateral reflection panel, disposed at an opposite lateral side of the light guide plate, which reflects the light, emitted through the opposite lateral side of the light guide plate and not through the upper surface of the light guide plate, to the light guide plate.

16. The backlight unit of claim 15, wherein the lateral reflection panel is sloped at a predetermined angle so that the portion of the light reflected to the light guide plate by the lateral reflection panel is totally reflected onto the lower and upper surface of the light guide plate.

17. The backlight unit of claim 15, wherein the polarization converter is placed between the light guide plate and the lateral reflection panel.

18. The backlight unit of claim 14, wherein the polarization converter is placed between the lower surface of the light guide plate and the lower reflection panel.

19. The backlight unit of claim 11, further comprising a coating layer,

wherein the predetermined layer on which the micro structured pattern is formed is the upper surface of the light guide plate;

wherein the coating layer is, formed on the micro structured pattern of the upper surface of the light guide plate; and

wherein the wire-grid polarizer is formed on the coating layer.

20. The backlight unit of claim 1, wherein the first and second polarized components of the light comprise p-polarization and s-polarization components, respectively.

21. The backlight unit of claim 1, the polarization converter comprises an 1/4 wave plate which delays a phase of the light which passes through the polarization converter by one fourth of a wavelength of the light.

22. A liquid crystal display (LCD) apparatus including an LCD panel and a backlight unit installed on a rear surface of the LCD panel, the backlight unit comprising:

a light source which radiates light;

a light guide plate, disposed with the light source at a lateral side of the light guide plate, which guides the light incident on the lateral side into the light guide plate;

a wire-grid polarizer, formed on a predetermined layer of the light guide plate, which transmits a first polarized component of the light through the predetermined layer and reflects a second polarized component of the light;

a reflector which reflects the light to an upper surface of the light guide plate; and

a polarization converter which changes a polarization of the light not emitted through the upper surface of the light guide plate.

23. The LCD apparatus of claim 22, wherein the wire-grid polarizer comprises a plurality of parallel wires placed side by side with an interval of 200 nm or greater, and functions as a diffraction lattice to diffract the light incident on the upper surface of the light guide.

24. The LCD apparatus of claim 22, further comprising a micro-structured pattern, formed on a predetermined layer of the light guide plate, which changes a proceeding direction of the light incident on the micro-structured pattern to be substantially vertical.

25. A method for generating a backlight, comprising:

guiding light into a light guide plate from a lateral side to an opposite lateral side of the light guide plate;

transmitting a first component of the light through a predetermined layer of the light guide plate and reflecting a second polarized component of the light;

reflecting the light, emitted through a lower surface of the light guide plate, to the light guide plate; and

changing a polarization of the light not emitted through an upper surface of the light guide plate so that the light with a changed polarization is emitted through the upper surface of the light guide plate.

26. The method of claim 25, further comprising reflecting the light, emitted through the opposite lateral side of the light guide plate, to the light guide plate.

27. The method of claim 25, further comprising changing a proceeding direction of the light, incident on a predetermined layer of the light guide plate from the lateral side of the light guide plate, to be substantially vertical, using a micro-structured pattern.