Edge-lit illumination system containing cholesteric polarizer and diffuser behind waveguide

• US 5,856,855 A
• Filed: 08/23/1996
• Issued: 01/05/1999
• Est. Priority Date: 08/23/1995
• Status: Expired due to Term

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Mol, Grietje N., Broer, Dirk J., De Witz, Christianne R.M.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): Horney, Kari M.
• Application Number:
  US08/702,302
• Time in Patent Office: 865 Days
• Field of Search: 349/98, 349/115, 349/194, 349/65, 362/19, 362/31, 362/26
• US Class Current: 349/65
• CPC Class Codes: F21V 9/14 for producing polarised light
• CPC Class Codes: G02B 5/0221 the surface having an irregular structure G02B5/0226 takes precedence
• CPC Class Codes: G02B 5/0284 used in reflection
• CPC Class Codes: G02B 5/3033 in the form of a thin sheet or foil, e.g. Polaroid
• CPC Class Codes: G02B 6/0051 Diffusing 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
• CPC Class Codes: G02F 1/133536 Reflective polarizers G02F1/13362 takes precedence
• CPC Class Codes: G02F 1/133543 Cholesteric polarisers
• CPC Class Codes: G02F 1/13355 Polarising beam splitters [PBS]
• CPC Class Codes: G02F 1/13362 providing polarized light, e.g. by converting a polarisation component into another one

Abstract

An illumination system (3) comprises an optical waveguide (9) of an optically transparent material having an exit surface (19) and four end faces (13, 14, 15, 16). The light from a light source (11) is coupled into the optical waveguide (9) via at least one of the end faces (13). The illumination system, for an LCD, further has a reflective polarizer (21) in combination with a diffuser (23) for polarizing the light supplied by the light source (11). The reflective polarizer (21) is integrated with the optical waveguide and constitutes the surface (25) of the optical waveguide (9) which is located opposite the exit surface (19). The diffuser (23) is present on a surface of the polarizer (21) remote from the optical waveguide (9).

Claims

1. An illumination system comprising an optical waveguide of an optically transparent material having an exit surface and a plurality of end faces, opposite at least one of which a light source is situated, whose light can be coupled in at said end face of the optical waveguide, and polarizing means integrated with the optical waveguide for polarizing the light emitted by the light source, characterized in that the polarizing means are constituted by a reflective polarizer which is present on the surface of the optical waveguide located opposite the exit surface of the optical waveguide, a surface of the polarizer remote from the optical waveguide being provided with a diffuser.

2. An illumination system as claimed in claim 1, characterized in that a reflector is arranged at the side of the diffuser remote from the reflective polarizer.

3. An illumination system as claimed in claim 2, characterized in that the reflector is a polarization-rotating or depolarizing reflector.

4. An illumination system as claimed in claim 2, characterized in that the reflector is a foil comprising particles which reflect substantially completely.

5. An illumination system as claimed in claim 1, characterized in that a reflector which has a depolarizing effect is arranged on at least one end face remote from a light source.

6. An illumination system as claimed in claim 1, characterized in that the reflective polarizer is a cholesteric polarizer.

7. An illumination system as claimed in claim 6, characterized in that the cholesteric polarizer is implemented as a single layer of a liquid crystalline polymer material, within which layer the pitch of the molecular helix varies substantially continuously between two values which correspond to the lower limit and the upper limit, respectively, of the reflection band required to cover the full visible wavelength range.

8. An illumination system as claimed in claim 6, characterized in that the illumination system comprises an n.λ

/4 plate, in which n is an integral, odd number.

9. An illumination system as claimed in claim 8, characterized in that the n.λ

/4 plate is present on the exit surface of the optical waveguide.

10. An illumination system as claimed in claim 8, characterized in that the n.λ

/4 plate is present between the cholesteric layer and the optical waveguide.

11. An illumination system as claimed in claim 8, characterized in that the n.λ

/4 plate functions as an optical waveguide.

12. An illumination system as claimed in claim 1, characterized in that the reflective polarizer is a linear polarizer which is implemented as a stack of layers comprising a birefringent material, or as a stack of layers being alternately birefringent and non-birefringent.

13. An illumination system as claimed in claim 1, characterized in that the diffuser is a thin film which is provided on the surface of the reflective polarizer.

14. An illumination system as claimed in claim 1, characterized in that the diffuser is a light-diffusing structure provided in the surface of the reflective polarizer.

15. An illumination system as claimed in claim 14, characterized in that the light-diffusing structure is constituted by a pattern of discrete diffusing areas.

16. A flat-panel picture display device including an illumination system provided with a picture display panel for modulating the direction of polarization of light generated by the illumination system in conformity with picture information to be displayed, and an analyzer, characterized in that the illumination system is an illumination system as claimed in any one of the preceding claims.