Polarizing light guide plate unit and backlight unit and display device employing the same

• US 20070252923A1
• Filed: 12/14/2006
• Published: 11/01/2007
• Est. Priority Date: 04/27/2006
• Status: Abandoned Application

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: You, Jae-ho, Hwang, Seong-mo
• Application Number:
  US11/638,555
• Publication Number:
  US 20070252923A1
• Time in Patent Office: Days
• US Class Current: 349/65
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement 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

Abstract

A polarizing light guide plate (LGP) unit, a backlight unit employing the polarizing LGP unit, and a display device employing the backlight unit are provided. The polarizing LGP unit includes: an LGP which guides light emitted by a light source; a collimator that is disposed above the LGP and including a plurality of reflective patterns, each pattern having an inclined surface that reflects light exiting the LGP in an upward direction; and a polarization separating layer, disposed between the plurality of reflective patterns and the LGP, which transmits light of a first polarization and reflects light of a second polarization orthogonal to the first polarization.

Claims

1. A polarizing light guide plate (LGP) unit comprising:

an LGP which guides light emitted by a light source;

a collimator that is disposed above the LGP and comprises a plurality of reflective patterns, each pattern having an inclined surface that reflects light exiting the LGP in an upward direction; and

a polarization separating layer, disposed between the plurality of reflective patterns and the LGP, which transmits light of a first polarization and reflects light of a second polarization orthogonal to the first polarization.

2. The polarizing LGP unit of claim 1, wherein the reflective pattern has a polyhedral shape.

3. The polarizing LGP unit of claim 1, wherein the polarization separating layer comprises a plurality of thin films having different refractive indices.

4. The polarizing LGP unit of claim 3, wherein if the plurality of the thin films comprises first through m-th thin films above the LGP in this order, respective refractive indices of the plurality of the thin films satisfy following conditions:

n<sub>2k−

1</sub>>

n_2k, and n_2k+1>

n_2k,

where n<sub>2k−

1</sub>, n_2k, and n_2k+1 represents refractive indices of (2k−

1)-th, 2k-th, and (2k+1)-th thin films, respectively;

k represent a natural number; and

(2k+1) is not greater than m which is an odd number.

5. The polarizing LGP unit of claim 1, wherein the polarization separating layer comprises a plurality of alternating two thin films having different refractive indices.

6. The polarizing LGP unit of claim 1, wherein a slope of the inclined surface is adjusted such that an angle between light that is reflected from the inclined surface and exits through a top surface of the collimator and a line normal to the top surface is between about −

10° and

+10°

.

7. The polarizing LGP unit of claim 1, wherein the plurality of reflective patterns are arranged in one or two-directional arrays.

8. The polarizing LGP unit of claim 1, wherein the polarization separating layer is formed of a single thin film with a refractive index n and n satisfies tan⁻

1(n/n_i)>

90°

−

sin<sup>−

1</sup>(1/n_i) when n_i is the refractive index of the LGP.

9. The polarizing LGP unit of claim 3, wherein each of the thin films in the polarization separating layer is made of one selected from Al₂O₃, CeO₂, Ta₂O₅, TiO₂, ZnS, ZrO₂, CaF₂, and MgF₂.

10. The polarizing LGP unit of claim 1, further comprising an adhesion layer disposed between the LGP and the polarization separating layer.

11. The polarizing LGP unit of claim 10, wherein the polarization separating layer is formed of a single thin film having a refractive index n, and n satisfies tan⁻

1(n/n_a)>

sin<sup>−

1</sup>[(n_i/n_a)cos(sin<sup>−

1</sup>(1/n_i))] when n_i and n_a respectively denote refractive indices of the LGP and the adhesion layer.

12. The polarizing LGP unit of claim 2, further comprising an adhesion layer that is disposed between the LGP and the polarization separating layer and has a lower refractive index than the LGP.

13. A backlight unit comprising:

a light source;

a light guide plate (LGP) which guides light from the light source;

a collimator that is disposed above the LGP and comprises a plurality of reflective patterns, each pattern having an inclined surface that reflects light exiting the LGP in an upward direction;

a polarization separating layer, disposed between the plurality of reflective patterns and the LGP, which transmits light of a first polarization and reflecting light of a second polarization orthogonal to the first polarization; and

a reflective plate disposed on a side of the LGP.

14. The backlight unit of claim 13, wherein the polarization separating layer comprises a plurality of thin films having different refractive indices.

15. The backlight unit of claim 13, wherein the polarization separating layer comprises a plurality of alternating two thin films having different refractive indices.

16. The backlight unit of claim 13, wherein a slope of the inclined surface is adjusted such that an angle between light that is reflected from the inclined surface and exits through a top surface of the collimator and a line normal to the top surface is between about −

10° and

+10°

.

17. The backlight unit of claim 13, wherein the plurality of reflective patterns are arranged in one or two-directional arrays.

18. The backlight unit of claim 13, further comprising a polarization converting element disposed on a bottom surface of the LGP.

19. The backlight unit of claim 13, further comprising a polarization converting element disposed between the reflective plate and the LGP.

20. The backlight unit of claim 19, wherein the polarization converting element is a ¼

waveplate.

21. The backlight unit of claim 13, wherein each of the thin films of the polarization separating layer is made of one selected from Al₂O₃, CeO2, Ta₂O₅, TiO₂, ZnS, ZrO₂, CaF₂, and MgF₂.

22. The backlight unit of claim 13, further comprising an adhesion layer that is disposed between the LGP and the polarization separating layer and has a lower refractive index than the LGP.

23. A display device comprising:

the backlight unit comprising

a light source;

a light guide plate (LGP) which guides light from the light source;

a collimator that is disposed above the LGP and comprises a plurality of reflective patterns, each pattern having an inclined surface that reflects light exiting the LGP in an upward direction;

a polarization separating layer, disposed between the plurality of reflective patterns and the LGP, which transmits light of a first polarization and reflects light of a second polarization orthogonal to the first polarization; and

a reflective plate disposed on a side of the LGP; and

a display panel which produces an image using light exiting the backlight unit.

24. A display device comprising:

the backlight unit comprising;

a light source;

a light guide plate (LGP) which guides light from the light source;

a collimator that is disposed above the LGP and comprises a plurality of reflective patterns, each pattern having an inclined surface that reflects light exiting the LGP in an upward direction;

a polarization separating layer, disposed between the plurality of reflective patterns and the LGP, which transmits light of a first polarization and reflects light of a second polarization orthogonal to the first polarization;

a reflective plate disposed on a side of the LGP; and

an adhesion layer that is disposed between the LGP and the polarization separating layer and has a lower refractive index than the LGP; and

a display panel which produces an image using light exiting the backlight unit.