Reflective display device and a light source for a display device

• US 6,483,613 B1
• Filed: 04/30/2001
• Issued: 11/19/2002
• Est. Priority Date: 08/04/1998
• Status: Expired due to Fees

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Woodgate, Graham John, Khazova, Marina Vladimirovna
• Primary Examiner(s): Spyrou, Cassandra
• Assistant Examiner(s): Juba, Jr., John
• Application Number:
  US09/762,339
• Time in Patent Office: 568 Days
• Field of Search: 359/15, 359/19, 359/20, 359/565, 349/65, 349/95, 349/104, 349/61, 349/62, 349/63, 349/64
• US Class Current: 359/19
• CPC Class Codes: G02B 27/0018 with means for preventing ghost images anti-reflection coatings G02B1/11
• CPC Class Codes: G02B 5/1876 Diffractive Fresnel lenses; Zone plates; Kinoforms G02B5/1842, G02B5/1847 take precedence; optical systems having diffractive correction means G02B27/0037; Fresnel lenses operating by refraction G02B3/08
• CPC Class Codes: G02B 5/32 Holograms used as optical elements
• CPC Class Codes: G02F 1/133504 Diffusing, scattering, diffracting elements associated to illuminating devices G02F1/133606
• CPC Class Codes: G02F 1/133526 Lenses, e.g. microlenses or Fresnel lenses
• CPC Class Codes: G02F 1/133553 Reflecting elements associated to illuminating devices G02F1/133605
• CPC Class Codes: G02F 1/1336 Illuminating devices
• CPC Class Codes: G02F 1/133616 Front illuminating devices

Abstract

A reflective liquid crystal display device (LCD) (40) includes: a substrate (60), a reflecting layer (61), a liquid crystal layer (62), an electrode layer (63), a color filter layer (64), an upper substrate (65), and a polarizer (66). The reflective liquid crystal display device further includes a holographic field lens (67). By providing the holographic field lens, the LCD can be used with a closely placed, offset light source (41), since the holographic field lens simultaneously concentrates light incident on the LCD and redirects it in a preferred direction. The holographic field lens can be provided within the structure of the LCD.

Claims

1. A display device comprising:

a spatial light modulator having an optical modulation layer;

a reflector disposed behind the optical modulation layer with respect to a display direction; and

a holographic field lens,

wherein for a given angle of incidence, the diffraction efficiency of the holographic field lens varies in a gradient manner over the holographic field lens.

2. A display device as claimed in claim 1, wherein the reflector is disposed within the spatial light modulator.

3. A display device as claimed in claim 1, wherein the reflector is a non-Lambertian reflector.

4. A display device as claimed in claim 1, wherein the holographic field lens is adapted to collimate diverging light incident on the holographic field lens.

5. A display device as claimed in claim 4, wherein the collimated light is directed at an angle θ

to the normal axis to the display device, wherein θ

is greater half the acceptance angle of the holographic field lens.

6. A display device as claimed in claim 5, wherein θ

≧

3°

.

7. A display device as claimed in claim 1, wherein the holographic field lens is a holographic microlens array.

8. A device as claimed in claim 7, further comprising color filters, wherein the pitch of the holographic microlens array is substantially three times the pitch of the color filters.

9. A display device as claimed in claim 1, wherein the holographic field lens is disposed in front of the optical modulation layer.

10. A display device as claimed in claim 1, wherein the holographic field lens includes the reflector so as to form a single element.

11. A display device as claimed in claim 1, wherein the holographic field lens is disposed within the spatial light modulator.

12. A display device as claimed in claim 1, wherein the holographic field lens is positioned close to the optical modulation layer.

13. A display device as claimed in claim 12, wherein the holographic field lens is separated from the optical modulation layer.

14. A display device as claimed in claim 1, further comprising a light source arranged to illuminate the spatial light modulator with diverging light.

15. A display device as claimed in claim 14, wherein the light source is offset with respect to the spatial light modulator.

16. A display device as claimed in claim 15, wherein the diffraction efficiency of the holographic field lens is lower at the offset side of the light source with respect to the spatial light modulator and is higher at a side away said offset side of the light source.

17. A display device as claimed in claim 14, further comprising a homogenizer disposed in the optical path between the light source and the spatial light modulator.

18. A display device as claimed in claim 17, wherein the homogenizer is a holographic homogenizer.

19. A display device as claimed in claim 18, wherein the homogenizer is a reflective homogenizer.

20. A display device as claimed in claim 19, wherein the homogenizer is a reflective volume holographic homogenizer.

21. A display device as claimed in claim 14, wherein the light source is substantially monochromatic.

22. A display device as claimed in claim 21, wherein the light source is a light-emitting diode.

23. A display device as claimed in claim 14, wherein the light source is a white light source.

24. A display device as claimed in claim 14, wherein the light source comprises at least:

a first light source emitting light at a first wavelength; and

a second light source emitting light at a second wavelength.

25. A display device as claimed in claim 24, wherein the first light source comprises a first light emitting diode for emitting light of the first wavelength, and the second light source comprises a second light emitting diode for emitting light of the second wavelength.

26. A display device as claimed in claim 25,

wherein the holographic field lens is chromatic,

and wherein the first and second light sources are disposed at the respective foci of the holographic field lens for the light of the first wavelength and the light of the second wavelength respectively.

27. A display device as claimed in claim 24,

wherein the holographic field lens is chromatic,

and wherein the first and second light sources are disposed at the respective foci of the holographic field lens for the light of the first wavelength and the light of the second wavelength respectively.

28. A display device as claimed in claim 14, further comprising a cover member, wherein the light source is disposed on the cover member.

29. A display device as claimed in claim 14, further comprising a support member for supporting the light source.

30. A display device as claimed in claim 29, wherein the support member is movable between a stowed position and a position in which the light source is able to illuminate the spatial light modulator.

31. A display device as claimed in claim 1, wherein the optical modulation layer is a liquid crystal layer.

32. An illumination system for illuminating the display device claimed in claim 1, comprising at least one light source, and a holographic homogenizer disposed in the path of light from said at least one light source.

33. An illumination system as claimed in claim 32, wherein the holographic homogenizer is a reflective holographic homogenizer.

34. An illumination system as claimed in claim 32, wherein the holographic homogenizer is a transmissive holographic homogenizer.

35. An illumination system as claimed in claim 34, further comprising a reflector, wherein the transmissive holographic homogenizer is disposed between said at least one light source and the reflector.

36. An illumination system as claimed in claim 32, further comprising first, second and third light sources for emitting light at a first wavelength, a second wavelength and a third wavelength, respectively, wherein the first, second and third light sources are disposed in a linear array.

37. An illumination system as claimed in claim 36, wherein the linear array of light sources is disposed at an achromatic angle to the holographic homogenizer.

38. An illumination system as claimed in claim 36, wherein each of said at least one light source is a light-emitting diode.

39. An illumination system as claimed in claim 32, further comprising first, second and third light sources for emitting light of a first wavelength, a second wavelength and a third wavelength respectively, wherein the first, second and third light sources are arranged in a substantially triangular configuration.

40. An illumination system as claimed in claim 39, wherein each of said at least one light source is a light-emitting diode.

41. An illumination system as claimed in claim 32, wherein each of said at least one light source is a light-emitting diode.