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

• US 6,981,791 B2
• Filed: 06/13/2003
• Issued: 01/03/2006
• 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): O'Shea, Sandra
• Assistant Examiner(s): Choi, Jacob Y.
• Application Number:
  US10/461,768
• Publication Number:
  US 20030231483A1
• Time in Patent Office: 935 Days
• Field of Search: 362/31, 362/26, 362/19, 349/61, 349/64, 349/65
• US Class Current: 362/600
• 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 surface light source device comprising:

a light-emitting element which generates light;

a light guide plate which has a plate-like shape and comprises an end face and two opposing plate surfaces, wherein light emitted from the light-emitting element is incident on the end face, and the light guide plate causes the light to be reflected between the plate surfaces to guide the light along the plate surfaces, causes the light to emerge from the two plate surfaces, and transmits light incident on one plate surface toward the other plate surface;

a first optical element which is placed on a side of a first said plate surface side of the light guide plate, and which transmits a part of light emerging from the first plate surface of the light guide plate toward a front side, and returns the remaining light to a rear side; and

a second optical element which is placed on a side of a second said plate surface of the light guide plate, and which transmits at least a part of light emerging from the second plate surface of the light guide plate; and

wherein the light guide plate includes a diffusion surface at the second plate surface to diffuse internally reflected light.

2. A device according to claim 1, 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.

3. A device according to claim 2, wherein the second optical element comprises a semitransparent reflective layer having white pigment added thereto.

4. A device according to claim 1, wherein the first and second optical elements comprise polarizing/separating layers, each of which reflects one of two different polarized light components of incident light and transmits the other polarized light component, and the polarizing/separating layers are arranged such that light reflected by one polarizing/separating layer is transmitted through the other polarizing/separating layer.

5. A device according to claim 4, wherein the polarizing/separating layer comprises a reflection polarizing plate which transmits one of two linearly polarized light components having orthogonal planes of polarization, and reflects the other linearly polarized light component.

6. A device according to claim 4, wherein each polarizing/separating layer comprises:

a circularly polarizing/separating element which separates light into a clockwise circularly polarized light component and a counterclockwise circularly polarized light component; and

two λ

/4 plates which sandwich the circularly polarizing/separating layer.

7. A device according to claim 1, further comprising a refracting layer which is provided outside the first optical element and refracts light, which is transmitted through the first optical element and emerging from the light guide plate, in a direction substantially parallel to a normal to a front surface of the light guide plate.

8. A device according to claim 7, wherein the refracting layer comprises a prism sheet including a plurality of oblong prism portions densely arrayed to be parallel to each other and to said end face of the light guide plate.

9. A device according to claim 1, wherein the light guide plate further comprises a reflecting/refracting surface which is formed on the second plate surface, and which retracts light internally reflected by the second plate surface in a direction in which an angle with respect to the a normal to the first plate surface of the light guide plate is smaller than an angle with respect to the normal to the first plate surface when light is reflected by a surface parallel to the first surface.

10. A surface light source device comprising:

a light-emitting element which emits light;

a light guide plate which has a platelike shape and comprises an end face and two opposing plate surfaces, wherein light emitted from the light-emitting element is incident on the end face, and the light guide plate causes the light to be reflected between the plate surfaces to guide the light to the entire plate surfaces, and causes the light to emerge from the two plate surfaces, and transmits light incident on one plate surface toward the other plate surface;

a first optical element which is placed on one a side of a first said plate surface side of the light guide plate, and which transmits a part of light emerging from one the first plate surface of the light guide plate toward a front side, and returns the remaining light to a rear side;

a second optical element which is placed on a side of a second said plate surface of the light guide plate, and which transmits at least a part of light emerging from the second plate surface of the light guide plate;

a first display element which is placed on a first plate surface side of the surface light source device, and which performs a display operation by controlling transmission of light; and

a second display element which is placed on a second plate surface side of the surface light source device, and which performs a display operation by controlling transmission of light;

wherein the light guide plate includes a diffusion surface at the second plate surface to diffuse internally reflected light.

11. A device according to claim 10, wherein the second display element has a smaller display area than the first display element.

12. A device according to claim 10, wherein at least one of the first and second display elements comprises a semitransparent reflective display element which is adapted to perform both transmission display by controlling the transmission of light emerging from the surface light source device and reflection display realized by controlling transmission of external light incident from an observation side.

13. A device according to claim 12, wherein the semitransparent reflective display element comprises a semitransparent reflective film formed from a porous metal film.

14. A device according to claim 10, 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.

15. A device according to claim 10, wherein the first and second optical elements comprise polarizing/separating layers, each of which reflects one of two different polarized light components of incident light and transmits the other polarized light component, and the polarizing/separating layers are arranged such that light reflected by one polarizing/separating layer is transmitted through the other polarizing/separating layer.

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

17. A device according to claim 10, further comprising a retracting layer which is provided outside the first optical element and refracts light, which is transmitted through the first optical element and emerging from the light guide plate, in a direction substantially parallel to a normal to a front surface of the light guide plate.

18. A device according to claim 10, wherein the refracting layer comprises a prism sheet including a plurality of oblong prism portions which are provided on said end face of the light guide plate and which extend in parallel to each other at predetermined intervals.

19. A device according to claim 10, wherein the light guide plate further comprises a reflecting/retracting surface which is formed on the second plate surface, and which refracts light internally reflected by the second plate surface in a direction in which an angle with respect to a normal to the first plate surface of the light guide plate is smaller than an angle with respect to the normal of the first plate surface when light is reflected by a surface parallel to the first surface.

20. A surface light source device comprising:

a light-emitting element which generates light;

a light guide plate which has a plate like shape and comprises an end face and two opposing plate surfaces, wherein light emitted from the light-emitting element is incident on the end face, and the light guide plate causes the light to be reflected between the plate surfaces to guide the light along the plate surfaces, causes the light to emerge from the two plate surfaces, and transmits light incident on one plate surface toward the other plate surface;

a first optical element which is placed on a side of a first said plate surface of the light guide plate, and which transmits a part of light emerging from the first plate surface of the light guide plate toward a front side, and returns the remaining light to a rear side; and

a second optical element which is placed on a side of a second said plate surface of the light guide plate, and which transmits at least a part of light emerging from the second plate surface of the light guide plate;

wherein the first and second optical elements comprise polarizing/separating layers, each of which reflects, one of two different polarized light components of incident light and transmits the other polarized light component, and the polarizing/separating layers are arranged such that light reflected by one polarizing/separating layer is transmitted through the other polarizing/separating layer.

21. A surface light source device comprising:

a light-emitting element which emits light;

a light guide plate which has a platelike shape and comprises an end face and two opposing plate surfaces, wherein light emitted from the light-emitting element is incident on the end face, and the light guide plate causes the light to be reflected between the plate surfaces to guide the light to the entire plate surfaces, and causes the light to emerge from the two plate surfaces, and transmits light incident on one plate surface toward the other plate surface;

a first optical element which is placed on a side of a first said plate surface of the light guide plate, and which transmits a part of light emerging from the first plate surface of the light guide plate toward a front side, and returns the remaining light to a rear side;

a second optical element which is placed on a side of a second said plate surface of the light guide plate, and which transmits at least a part of light emerging from the second plate surface of the light guide plate;

a first display element which is placed on a first plate surface side of the surface light source device, and which performs a display operation by controlling transmission of light; and

a second display element which is placed on a second plate surface side of the surface light source device, and which performs a display operation by controlling transmission of light;

wherein the first and second optical elements comprise polarizing/separating layers, each of which reflects one of two different polarized light components of incident light and transmits the other polarized light component, and the polarizing/separating layers are arranged such that light reflected by one polarizing/separating layer is transmitted through the other polarizing/separating layer.