Illumination device and application thereof to the illumination of a transmissive screen

• US 6,014,192 A
• Filed: 07/16/1997
• Issued: 01/11/2000
• Est. Priority Date: 07/16/1996
• Status: Expired due to Term

• Current Assignee: Thonson-Csf
• Original Assignee: Thomson-CSF (Thales SA)
• Inventors: Joubert, Cecile, Lehureau, Jean-Claude, Loiseaux, Brigitte
• Primary Examiner(s): Kim, Robert H.
• Application Number:
  US08/895,449
• Time in Patent Office: 909 Days
• Field of Search: 362/31, 362/32, 349/61, 349/62, 349/69
• US Class Current: 349/62
• CPC Class Codes: F21V 9/14 for producing polarised light
• CPC Class Codes: G02B 6/0033 Means for improving the coupling-out of light from the light guide
• CPC Class Codes: G02B 6/0046 Tapered light guide, e.g. wedge-shaped light guide
• 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: G02B 6/0076 Stacked arrangements of multiple light guides of the same or different cross-sectional area
• CPC Class Codes: G02F 1/13362 providing polarized light, e.g. by converting a polarisation component into another one

Abstract

An illumination device comprises a light source coupled to a waveguide. the waveguide comprises a diffracting element capable of diffracting emergent light rays coming from the source, in a direction substantially perpendicular to the surface of the waveguide. A device of this kind is particularly well-suited to transmissive display screens of the liquid crystal display screen type. It can generate a highly collimated, polarized light.

Claims

1. An illumination device comprising:

a light source outputting light rays at a plurality of angles; and

a light waveguide coupled with said light source, wherein the light waveguide comprises a diffracting element located within the waveguide to diffract emergent ones of said light rays having angles of incidence between 90° and

a limit angle of reflection at an output of said waveguide to provide output light rays which are in a direction substantially perpendicular to a surface of the waveguide.

2. An illumination device according to claim 1, wherein the diffracting element is a holographic element.

3. An illumination device according to claim 1, wherein the waveguide has an optical index grating organized in strata oriented in a direction forming an angle substantially equal to 45°

with the normal to the plane of the waveguide.

4. An illumination device according to claim 1, wherein the diffracting element comprises:

an etched grating, the etchings having flanks with refraction indices at about 45°

to the normal to the surface of the waveguide and flanks parallel to the normal to the plane of the waveguide;

a resonant cavity into which the etched grating is integrated.

5. An illumination device according to claim 4, wherein the etched grating is covered with a layer of material having a refraction index n2, the entire unit being integrated into a material having the same refraction index n1 as that of the grating.

6. An illumination device according to one of the claims 1 to 5, wherein the diffracting element transmits a s polarized light defined perpendicularly to the plane of incidence and diffracts a p polarized light defined perpendicularly to the plane of incidence and wherein said diffracting element comprises means to convert the s polarized light into p polarized light.

7. An illumination device according to claim 6 comprising, at the end of the waveguide opposite the light source, a quarter-wave plate and a mirror parallel to said quarter-wave plate, and also comprising a mirror located in a plane parallel to the surface of the waveguide and opposite the plane of extraction of light.

8. An illumination device for a display screen, comprising a superimposition of three illumination devices according to claim 1, a first device comprising a light source emitting in the red, a second device comprising a light source emitting in the green and a third device comprising a light source emitting in the blue.