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

• US 20030231483A1
• Filed: 06/13/2003
• Published: 12/18/2003
• Est. Priority Date: 06/17/2002
• Status: Active Grant

• Current Assignee: Casio Computer Company Limited
• Original Assignee: Casio Computer Company Limited
• Inventors: Higashiyama, Hiroshi
• Granted Patent: US 6,981,791 B2
• Time in Patent Office: Days
• US Class Current: 362/610
• 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 having one end face and two opposing plate surfaces, causes light emitted from the light-emitting element to be incident from one end face, causes the light to be reflected between the plate surfaces to guide the light along the plate surfaces and make the light emerge from the two plate surfaces, and transmits light incident from one plate surface toward the other plate surface;

a first optical element which 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; and

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

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 one surface and the other surface, and

the second optical element has a semitransparent reflective layer.

3. A device according to claim 2, wherein the second optical element has a semitransparent reflective layer to which white pigment is added.

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 has 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 the polarizing/separating layer includes 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 placed to sandwich the circularly polarizing/separating layer.

7. A device according to claim 1, wherein the light guide plate has, on the other plate surface, a diffusion surface which diffuses internally reflected light.

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

9. A device according to claim 8, wherein the refracting layer includes a prism sheet on which oblong prism portions parallel to one end face of the light guide plate at which the light-emitting element is placed are densely arrayed parallel to each other.

10. A device according to claim 1, wherein the light guide plate includes a reflecting/refracting surface which is formed on the other plate surface and refracts light, internally reflected by the plate surface, in a direction in which an angle with respect to the normal to the plate surface of the light guide plate becomes smaller than that when the light is regularly reflected by a surface parallel to the front surface.

11. A surface light source device comprising:

a light-emitting element which emits light;

a light guide plate which has a plate-like shape having one end face and two opposing plate surfaces, causes light emitted from the light-emitting element to be incident from one end face, causes the light to be reflected between the plate surfaces to guide the light to the entire plate surfaces and make the light emerge from the two plate surfaces, and transmits light incident from one plate surface toward the other plate surface;

a first optical element which 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 the front side, and returns the remaining light to a rear side;

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

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

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

12. A device according to claim 11, wherein the first and second display elements have different display areas, and the second display element has a smaller display area than the first display element.

13. A device according to claim 11, wherein at least one of the first and second display elements includes a semitransparent reflective display element which can perform both transmission display realized by controlling 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.

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

15. A device according to claim 11, wherein

the first optical element comprises a diffusion layer which diffuses incident light and causes the diffused light to emerge from both one surface and the other surface, and

the second optical element has a semitransparent reflective layer.

16. A device according to claim 11, 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.

17. A device according to claim 11, wherein the polarizing/separating layer has 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.

18. A device according to claim 11, further comprising a refracting layer which is provided outside the first optical element and refracts light emerging from the light guide plate and transmitted through the first optical element in a direction substantially parallel to the normal to the front surface of the light guide plate.

19. A device according to claim 11, wherein the refracting layer includes a prism sheet having a . plurality of oblong prism portions which are provided on one end face of the light guide plate at which the light-emitting element is placed and extend parallel to each other at predetermined intervals.

20. A device according to claim 11, wherein the light guide plate includes a reflecting/refracting surface which is formed on the other plate surface and refracts light, internally reflected by the plate surface, in a direction in which an angle with respect to the normal to the plate surface of the light guide plate becomes smaller than that when the light is regularly reflected by a surface parallel to the front surface.