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

• US 7,614,757 B2
• Filed: 02/08/2006
• Issued: 11/10/2009
• Est. Priority Date: 08/30/2005
• Status: Expired due to Fees

• Current Assignee: Samsung Display Company Limited (Samsung Electronics Co. Ltd.)
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Nesterenko, Dmitry, Choi, Hwan-young
• Primary Examiner(s): CARIASO, ALAN B
• Application Number:
  US11/349,170
• Publication Number:
  US 20070047214A1
• Time in Patent Office: 1,371 Days
• Field of Search: 362/19, 362/606, 362/609, 362/618, 362/623, 362/627, 362/617, 362/625, 362/626, 359/486
• 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 positioned 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, comprising a plurality of parallel metal wires formed on one of a top surface and a bottom surface of the light guide plate, which transmits a first polarized component of the light in a substantially perpendicular direction to the metal wires through the one of the top surface and the bottom surface of the light guide plate and reflects a second polarized component of the light in a substantially parallel direction to the metal wires;

a reflector which is disposed below the light guide plate and reflects the light emitted out from the light guide plate to an inside of the light guide plate;

a polarization converter which changes a polarization of the light not emitted through the top surface of the light guide plate into an opposite polarization; and

a micro-structured pattern, formed on a surface of a given layer in the light guide plate, which changes a proceeding direction of the light incident on the micro-structured pattern to be substantially vertical to the top surface of the light guide plate,

wherein the surface of the given layer, substantially parallel to the top surface of the light guide plate, is disposed apart from the top surface of the light guide plate, and

wherein the given layer on which the micro-structured pattern is formed is the bottom layer of the light guide plate, and the wire-grid polarizer is formed on the top surface of the light guide plate.

2. The backlight unit of claim 1, 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 to the inside of the light guide plate.

3. The backlight unit of claim 2, wherein the lateral reflection panel is sloped at a predetermined angle so that the portion of the light reflected to the inside of the light guide plate by the lateral reflection panel is totally reflected onto the bottom surface and the top surface of the light guide plate.

4. The backlight unit of claim 2, wherein the polarization converter is placed between the light guide plate and the lateral reflection panel.

5. The backlight unit of claim 1, wherein the polarization converter is placed between the bottom surface of the light guide plate and the reflector.

6. The backlight unit of claim 1,

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 an interval between the parallel metal wires is less than 200 nm so that the wire-grid polarizer functions as only a polarizer.

7. 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.

8. The backlight unit of claim 1,

wherein an interval between the parallel metal wires is 200 nm or greater, and the wire-grid polarizer further functions as a diffraction lattice to diffract the light incident on the one of the top surface and the bottom surface of the light guide plate on which the wire-grid polarizer is formed.

9. The backlight unit of claim 1, wherein the micro-structured pattern is a hologram diffraction pattern.

10. The backlight unit of claim 1, wherein the micro-structured pattern is a prism pattern.

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

12. The backlight unit of claim 1, flirt her comprising a coating layer,

formed between the top surface and the surface of the given layer in the light guide plate.

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

14. The backlight unit of claim 1, the polarization converter comprises a ¼

wave plate which delays a phase of the light which passes through the polarization converter by one fourth of a wavelength of the light.

15. 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 positioned 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, comprising a plurality of parallel metal wires formed on one of a top surface and a bottom surface of the light guide plate, which transmits a first polarized component of the light in a substantially perpendicular direction to the metal wires through the one of the top surface and the bottom surface of the light guide plate and reflects a second polarized component of the light in a substantially parallel direction to the metal wires;

a reflector which is disposed below the light guide plate and reflects the light emitted out from the light guide plate to an inside of the light guide plate;

a polarization converter which changes a polarization of the light not emitted through the top surface of the light guide plate into an opposite polarization; and

a micro-structured pattern, formed on a surface of a given layer in the light guide plate, which changes a proceeding direction of the light incident on the micro-structured pattern to be substantially vertical to the top surface of the light guide plate,

wherein the surface of the given layer, substantially parallel to the top surface of the light guide plate, is disposed apart from the top surface of the light guide plate, and

wherein the given layer on which the micro-structured pattern is formed is the bottom layer of the light guide plate, and the wire-grid polarizer is formed on the top surface of the light guide plate.

16. The LCD apparatus of claim 15, wherein an interval between the parallel metal wires is 200 nm or greater, and the wire-grid polarizer further functions as a diffraction lattice to diffract the light incident on the one of the top surface and the bottom surface of the light guide on which the wire-grid polarizer is formed.

17. The LCD apparatus of claim 15, 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 to the top surface of the light guide plate.

18. 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 polarized component of the light in a substantially perpendicular direction to a plurality of parallel metal wires of a wire-grid polarizer through one of a top surface and a bottom surface of the light guide plate and reflecting a second polarized component of the light in a substantially parallel direction to the metal wires;

reflecting the light, emitted through the light guide plate to an inside of the light guide plate; and

changing a polarization of the light not emitted through a top surface of the light guide plate into an opposite polarization so that the light with a changed polarization is emitted through the top surface of the light guide plate,

wherein the transmitting and the reflecting are performed using a micro-structured pattern, formed on a surface of a given layer in the light guide plate, which changes a proceeding direction of the light incident on the micro-structured pattern to be substantially vertical to the top surface of the light guide plate, and

wherein the surface of the given layer, substantially parallel to the top surface of the light guide plate, is disposed apart from the top surface of the light guide plate, and

wherein the given layer on which the micro-structured pattern is formed is the bottom layer of the light guide plate, and the wire-grid polarizer is formed on the top surface of the light guide plate.

19. The method of claim 18, further comprising reflecting the light, emitted through the opposite lateral side of the light guide plate, to the inside of the light guide plate.

20. The method of claim 18, further comprising changing a proceeding direction of the light, incident on the one of the top surface and the bottom surface of the light guide plate from the lateral side of the light guide plate, to be substantially vertical, using a micro-structured pattern.