Waveguide, edge-lit illumination arrangement and display comprising such

• US 6,750,996 B2
• Filed: 09/23/2002
• Issued: 06/15/2004
• Est. Priority Date: 09/26/2001
• Status: Expired due to Fees

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Cornelissen, Hugo Johan, Broer, Dirk Jan, Jagt, Hendrik Johannes Boudewijn, Bastiaansen, Cees
• Primary Examiner(s): Dunn, Drew A.
• Assistant Examiner(s): BOUTSIKARIS, LEONIDAS
• Application Number:
  US10/252,974
• Publication Number:
  US 20030067760A1
• Time in Patent Office: 631 Days
• Field of Search: 359/34, 359/15, 362/31, 349/62
• US Class Current: 359/34
• 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: G03H 1/0248 Volume holograms
• CPC Class Codes: G03H 1/0408 Total internal reflection [TIR] holograms, e.g. edge lit or substrate mode holograms
• CPC Class Codes: G03H 2222/31 Polarised light

Abstract

A polarized light-emitting waveguide for use in an edge-lit lighting arrangement has polarization-selective outcoupling structure including at least a volume hologram for selectively diffracting waveguided light towards the exit surface of the waveguide with high contrast and efficiency. The light emitted by the waveguide is selectively emitted to one side thereof, highly polarized, highly collimated and may be homogeneously distributed across the exit surface. Also, light emission may be normal or near-normal to the exit surface. If combined with light recycling means the contrast, brightness and/or efficiency of the edge-lit illumination arrangement may be further increased.

Claims

1. A waveguide comprising

an entry side face for coupling light into the waveguide,

an exit surface for emission of light from the waveguide, and

polarization-selective light outcoupling means for coupling out waveguided light through the exit surface polarization selectively,

the polarization-selective outcoupling means comprising a volume hologram configured to selectively diffract waveguided light towards the exit surface with a nolarization contrast of at least a factor of five over an annular range of at least five degrees.

2. A waveguide as claimed in claim 1, wherein

the volume hologram is a volume holographic Bragg-grating.

4. A waveguide as claimed in claim 1, wherein

the volume hologram comprises a volume holographic layer having a thickness d and a refractive index modulation Δ

n, and

the product dΔ

n is selected such that waveguided light of a first polarization is diffracted more efficiently than waveguided light of a second polarization, to provide the polarization contrast.

8. A waveguide as claimed in claim 1, wherein

the polarization selective outcoupling means include a volume hologram formed from an optically anisotropic material having

a first refractive index modulation experienced by light of a first polarization and

a second refractive index modulation experienced by light of a second polarization,

the first and the second refractive index modulation being different.

12. An edge-lit illumination arrangement comprising

a waveguide as claimed in claim 1 and

a light source arranged near the entry side face thereof.

13. A reflective or transflective display device having

a front light arrangement cornpnsing an iilumination arrangement as claimed in claim 12.

14. A reflective display device as claimed in claim 13, comprising

a display cell and polarizer arranged on a viewing side of the display cell

wherein

the front light arrangement is disposed between the polarizer and the display cell.

15. A mobile phone provided with

an illumination arrangement as claimed in claim 12.

3. A waveguide comprising

an entry side face for coupling linht into the waveguide,

an exit surface for emission of light from the waveguide, and

polarization-selective light outcoupling means for coupling out waveguided light through the exit surface polarization selectively,

the polarization-selective outcoupling means comprising a volume hologram configured to selectively diffract waveguided light towards the exit surface,

wherein

the polarization selective outcoupling means include a volume hologram configured to diffract waveguided light at a Bragg-angle of about 45°

.

16. A waveguide as claimed in claim 3, wherein

the volume hologram comprises a volume holographic layer having a thickness d and a refractive index modulation Δ

n, and

the product dAn is selected such that waveguided light of a first polarization is diffracted more efficiently than waveguided light of a second polarization,

the diffraction efficiency of the first polarization being at least five times the diffraction efficicucy of the second polarization.

17. A waveguide as claimed in claim 3, wherein

the polarization-selective light outcoupling means comprises, disposed betwecn the volume hologram and the entry side face,

a polarization-selective beam splitting interface or layer for splitting waveguidcd light into light of a first polarization and light of a second polarization,

at least the light of the first polarization being directed towards the volume hologram which is configured to selectively diffract the light of the first polarization.

18. A waveguide as claimed in claim 3, wherein

the polarization selective outcoupling means include a volume hologram formed from an optically anisotropic material having

a first refractive index modulation cxperienced by light of a first polarization and

a second refractive index modulation experienced by light of a second polarization,

the first and the second refractive index modulation being different.

19. A waveguide as claimed in claim 18, comprising at least one of:

a combination of a volume hologram and an exit member integrally formed from optically anisotropic material, and

a combination of a volume hologram and a polarization-selective beam splitting layer integrally formed from optically anisotropic material.

22. An edge-lit illumination arrangement comprising

a waveguide as claimed in claim 3 and

a light source arranged near the entry side face thereof.

23. A reflective or transfiective display device having

a front light arrangement comprising an illumination arrangement as claimed in claim 22.

24. A reflective display device as claimed in claim 23, comprising

a display cell and polarizer arranged on a viewing side of the display cell

wherein

the front light arrangement is disposed between the polarizer and the display cell.

25. A mobile phone provided with

an illumination arrangement as claimed in claim 22.

5. A waveguide comprising

an entry side face for coupling light into the waveguide,

an exit surface for emission of light from the waveguide, and

polarization-selective light outcoupling means for coupling out waveauided light through the exit surface polarization selectively,

the polarization-selective outcoupling means comprising a volume hologram configured to sclectively diffract waveauided light towards the exit surface,

wherein

the polarization-selective light outcoupling means comprises, disposed between the volume hologram and the entry side face,

a polarization-selective beam splitting interface or layer for splitting waveguided light into light of a first polarization and light of a second polarization,

at least the light of the first polarization being directed towards the volume hologram which is configured to selectively diffract the light of the first polarization.

6. A waveguide as claimed in claim 5, comprising

an entry member and

an exit member,

the entry member comprising rue entry side face and

the exit member comprising the volume hologram,

the exit member and the entry member having a common interface forming the polarization-selective beam-splitting interface, and

at least the entry or the exit member being optically anisotropic having refractive indices selected such that n_entry,1/n_exit,1<

n_entry,2/n_exit,2

where

n_entry,1 is a refractive index of the entry member experienced by waveguided light of a first polarization,

n_entry,2 is a refractive index of the entry member experienced by waveguided light of a second polarization,

n_exit, 1 is a refractive index of the exit member experienced by waveguided light of a first polarization,

n_exit, 2 is a refractive index of the exit meinbcr experienced by waveguided light of a second polarization,

light of the first polarization is refracted in angular range θ

_1,min=<

θ

_r<

θ

_1,max, and light of the second polarization is refracted in angular range θ

_2,min<

θ

_r=<

_2,max, and

wherein

the volume hologram is configured to selectively diffract waveguided either light of the first polarization in the range θ

_1,min=<

θ

_r<

θ

_2,min or light of the second polarization in the range θ

_1,max<

θ

_r=<

θ

_2,max.

7. A waveguide as claimed in claim 5, comprising

an entry member and

an exit member,

the entry member comprising the entry side face and the exit member comprising the volume hologram,

the exit member and the entry member having a common interface forming the polarization-selective beam-splitting interface, and

at least the entry or the exit member being optically anisotropic having refractive indices selected such that

wavegiiided light of a first polarization incident from the entry member on the interface is at least partially transmitted into the exit member and

waveguided light of a second polarization incident from the entry member on the interface is, at least partially, totally internally reflected, and

the volume hologram is configured for diffracting the waveguided light transmitted into the exit member.

9. A waveguide as claimed in claim 5 comprising

a combination of a volume hologram and an exit member integrally formed from optically anisotropic material and/or

a combination of a volume hologram and a polarization-selective beam splitting layer integrally formed from optically anisotropic material.

20. A waveguide as claimed in claim 5, wherein

the polarization selective outcouplirig means include a volume hologram formcd from an optically anisotropic material having

a first refractive index modulation experienced by light of a first polarization and

a second refractive index modulation experienced by light of a second polarization,

the first and the second refractive index modulation being different.

26. An edge-lit illumination arrangement comprising

a waveguide as claimed in claim 5 and

a light source arranged near the entry side face thereof.

27. A reflective or transfiective display device having

a front light arrangement comprising an illumination arrangement as claimed in claim 26.

28. A reflective display device as claimed in claim 27, comprising

a display cell and polarizer arranged on a viewing side of the display cell

wherein

the front light arrangement is disposed between the polarizer and the display cell.

29. A mobile phone provided with

an illumination arrangement as claimed in claim 26.

10. A waveguide comprising

an entry side face for coupling light into the waveguide,

an exit surface for emission of light from the waveguide,

a back surface opposite the exit surface, and

a volume hologram configured to selectively couple out light to one side of the waveguide,

the one side being the exit surface side of the waveguide, and

the waveguide having a forward-to-backward contrast of at least ten at at least one emission angle.

11. A waveguide comprisina

an entry side face for coupling light into the waveguide,

an exit surface for emission of light from the waveguide,

a back surface onoosite the exit surface, and

a volume hologram configured to selectively connie out light to one side of the waveguide,

the one side being the exit surface side of the waveguide

wherein

the waveguide has an end face opposite the entry side face which end face is provided with means for reducing the amount of light reflected back into the waveguide.

21. A waveguide as claimed in claim 11, wherein

the means for reducing the amount of light reflected back into the waveguide includes at least one of:

an anti-reflecting layer, and

a light-absorbing coating.