Surface light source for emitting light from two surfaces and double-sided display device using the same

• US 7,156,546 B2
• Filed: 11/19/2005
• Issued: 01/02/2007
• Est. Priority Date: 06/17/2002
• Status: Expired due to Fees

• Current Assignee: Casio Computer Company Limited
• Original Assignee: Casio Computer Company Limited
• Inventors: Higashiyama, Hiroshi
• Primary Examiner(s): Alavi, Ali
• Assistant Examiner(s): Choi, Jacob Y.
• Application Number:
  US11/282,521
• Publication Number:
  US 20060077687A1
• Time in Patent Office: 409 Days
• Field of Search: 362/31, 362/26, 362/19, 362/600, 362/561, 362/602, 362/612, 349/61, 349/64, 349/65
• US Class Current: 362/561
• CPC Class Codes: F21Y 2115/10 Light-emitting diodes [LED]
• 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 6/0051 Diffusing sheet or layer
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer
• CPC Class Codes: G02F 1/133342 for double-sided displays
• CPC Class Codes: H04M 1/0214 Foldable telephones, i.e. with body parts pivoting to an open position around an axis parallel to the plane they define in closed position combined with translation movement H04M1/0235
• CPC Class Codes: H04M 1/0266 for a display module assembly
• CPC Class Codes: H04M 2250/16 including more than one display unit

Abstract

A surface light source device includes a light-emitting element which generates light, and a light guide plate which, causes light emitted from the light-emitting element to be incident from an end face, causes the light to be reflected between opposite plate surfaces to guide the light along the plate surfaces and make the light emerge from the plate surfaces, and transmits light incident from one plate surface toward the other plate surface. A first optical element is placed on one plate surface side of the light guide plate, transmits part of light emerging from one plate surface of the light guide plate toward a front side, and returns the remaining light to a rear side. A second optical element is placed on the other plate surface side and transmits at least part of light emerging from the other plate surface side.

Claims

1. A display apparatus comprising:

a flat backlight including a light source which emits light and a light guide plate having an end face facing the light source and two opposing surfaces, wherein the light from the light source is incident on the end face, and is partially guided in the light guide plate while being internally reflected by the two opposing surfaces, so as to partially emerge from the two opposing surfaces;

a first optical element, which is disposed on a side of a first one of the two opposing surfaces, and which partially transmits the light emerged from the first opposing surface toward a front side, and partially returns the light to a rear side;

a second optical element, which is disposed on a side of a second one of the two opposing surfaces, and which transmits at least a part of the light emerged from the second opposing surface;

a first liquid crystal display which has a front side and a back side and two polarizing plates disposed on the front side and the back side, respectively, and which is disposed on a side of the first optical element; and

a second liquid crystal display which has a front side and a back side and two polarizing plates disposed on the front side and the back side, respectively, and which is disposed on a side of the second optical element.

2. The display apparatus according to claim 1, wherein the second liquid crystal display has a smaller display area than a display area of the first liquid crystal display.

3. The display apparatus according to claim 2, wherein at least one of the first and second liquid crystal displays comprises a semitransparent reflective film.

4. The display apparatus according to claim 3, wherein the semitransparent reflective film is formed from a porous metal film.

5. The display apparatus according to claim 2, wherein the first liquid crystal display comprises a color image display and the second liquid crystal display comprises a mono-chrome image display.

6. The display apparatus according to claim 2, wherein at least one of the first and second liquid crystal displays comprises an STN type liquid crystal display.

7. The display apparatus according to claim 2, wherein the first optical element comprises a diffusion layer which diffuses incident light and causes the diffused light to emerge from both surfaces thereof, and the second optical element comprises a semitransparent reflective layer.

8. The display apparatus according to claim 2, wherein a diffusion layer is disposed between one of the first and second liquid crystal displays and the light guide plate.

9. The display apparatus according to claim 2, wherein the first and second optical elements comprise polarizing/separating layers, each of which reflects a first one of two different polarized light components of incident light and transmits a second one of the two polarized light components, and wherein the polarizing/separating layers are arranged such that light reflected by one polarizing/separating layer is transmitted through the other polarizing/separating layer.

10. A device according to claim 9, wherein each polarizing/separating layer comprises a reflection polarizing plate which transmits a first one of two linearly polarized light components having orthogonal planes of polarization, and reflects a second one of the two linearly polarized light components.

11. The display apparatus according to claim 9, wherein the light guide plate comprises a diffusion surface formed on at least of one of the two opposing surfaces.

12. The display apparatus according to claim 11, wherein a diffusion layer is disposed between one of the first and second liquid crystal displays and the light guide plate.

13. The display apparatus according to claim 1, further comprising a retracting layer which is provided outside the first optical element and refracts light, which emerges from the light guide plate and is transmitted through the first optical element, in a direction substantially parallel to a normal to a front surface of the light guide plate.

14. The display apparatus according to claim 3, wherein the refracting layer comprises a prism sheet including a plurality of oblong prism portions which are provided in parallel to the end face of the light guide plate and which extend in parallel to each other at predetermined intervals.

15. The display apparatus according to claim 1, wherein the light guide plate further comprises a reflecting/refracting surface which is formed on one of the two opposing surfaces, and which refracts light internally in a direction at which an angle with respect to a normal to the other one of the two opposing surfaces is smaller than an angle with respect to a normal of said one of the opposing surfaces when light is reflected by the other one of the two opposing surfaces.

16. The display apparatus according to claim 1, wherein the first optical element comprises a transmission axis and a reflection axis.

17. The display apparatus according to claim 16, wherein one of the polarizing plates of the first liquid crystal display which faces the first optical element comprises a transmission axis which is substantially parallel to the transmission axis of the first optical element.

18. The display apparatus according to claim 17, wherein the second optical element comprises a transmission axis and a reflection axis.

19. The display apparatus according to claim 18, wherein one of the polarizing plates of the second liquid crystal display which faces the second optical element comprises a transmission axis which is substantially parallel to the transmission axis of the second optical element.

20. The display apparatus according to claim 18, wherein the light guide plate comprises a diffusion surface formed on at least of one of the two opposing surfaces.

21. A display apparatus comprising:

a flat backlight including a light source which emits light and a light guide plate having an end face facing the light source, a front surface, and a back surface opposed to the front surface, wherein the light from the light source is incident on the end face, and is partially guided in the light guide plate while being internally reflected by the front and back surfaces, so as to partially emerge from the front and back surfaces;

a first optical element, which includes a polarizing/separatinq layer, and which is disposed on a side of the front surface of the light guide plate to partially transmit the light emerged from the front surface of the light guide plate toward an outside and to partially return the light to the light guide plate;

a second optical element, which includes a polarizing/separating layer, and which is disposed on a side of the back surface of the light guide plate to partially transmit the light emerged from the back surface of the light guide plate toward an outside and to partially return the light to the light guide plate;

a first liquid crystal display, which has a front side and a back side opposed to the front side and two polarizing plates disposed on the front side and the back side, respectively, and which is disposed on a side of the first optical element such that the back side faces the first optical element; and

a second liquid crystal display, which has a front side and a back side opposed to the front side and two polarizing plates disposed on the front side and the back side, respectively, and which is disposed on a side of the second optical element such that the back side faces the second optical element.

22. The display apparatus according to claim 21, wherein the polarizing/separating layer of the first optical element comprises a transmission axis and a reflection axis.

23. The display apparatus according to claim 22, wherein the polarizing plate disposed on the back side of the first liquid crystal display comprises a transmission axis which is substantially parallel to the transmission axis of the polarizing/separating layer of the first optical element.

24. The display apparatus according to claim 23, wherein the polarizing/separating layer of the second optical element comprises a transmission axis and a reflection axis.

25. The display apparatus according to claim 24, wherein the polarizing plate disposed on the back side of the second liquid crystal display comprises a transmission axis which is substantially parallel to the transmission axis of the polarizing/separating layer of the second optical element.

26. The display apparatus according to claim 21, wherein the light guide plate comprises a diffusion surface formed on the back surface thereof.

27. The display apparatus according to claim 26, wherein the first optical element comprises a diffusion layer.

28. A display apparatus comprising:

a flat backlight including a light source which emits light and a light guide plate having an end face facing the light source, a front surface, and a back surface opposed to the front surface, wherein the light from the light source is incident on the end face, and is partially guided in the light guide plate while being internally reflected by the front and back surfaces, so as to partially emerge from the front and back surfaces;

a first optical element, which has a transmission axis and reflection axis, and which is disposed on a side of the front surface of the light guide plate to partially transmit the light emerged from the front surface of the light guide plate toward an outside and to partially return the light to the light guide plate;

a second optical element, which has a transmission axis and reflection axis, and which is disposed on a side of the back surface of the light guide plate to partially transmit the light emerged from the back surface of the light guide plate toward an outside and to partially return the light to the light guide plate;

a first liquid crystal display, which has a front side and a back side opposed to the front side and two polarizing plates that include a transmission axis and are disposed on the front side and the back side of the first liquid crystal display, respectively, and which is disposed on a side of the first optical element such that the back side faces the first optical element; and

a second liquid crystal display, which has a front side and a back side opposed to the front side and two polarizing plates that include a transmission, axis and are disposed on the front side and the back side of the second liquid crystal display, respectively, and which is disposed on a aide of the second optical element such that the back side faces the second optical element.

29. The display apparatus according to claim 28, wherein the transmission axis of the polarizing plate disposed on the back side of the first liquid crystal display is substantially parallel to the transmission axis of the first optical element.

30. The display apparatus according to claim 29, wherein the transmission axis of the polarizing plate disposed on the back side of the second liquid crystal display is substantially parallel to the transmission axis of the second optical element.

31. The display apparatus according to claim 30, wherein the light guide plate comprises a diffusion surface formed on the back surface thereof.

32. The display apparatus according to claim 31, wherein the first optical element comprises a diffusion layer.