Light valve having reduced reflected light, high brightness and high contrast

• US 5,737,050 A
• Filed: 01/16/1996
• Issued: 04/07/1998
• Est. Priority Date: 08/25/1992
• Status: Expired due to Term

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Takahara, Hiroshi, Ohmae, Hideki
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): DUDEK, JAMES A
• Application Number:
  US08/586,421
• Time in Patent Office: 812 Days
• Field of Search: 359/72, 359/82, 359/83, 359/40, 359/41, 359/51, 359/68, 359/74, 359/580, 359/588, 359/79, 349/5, 349/10, 349/58, 349/60, 349/122, 349/158
• US Class Current: 349/122
• CPC Class Codes: G02F 1/1333 Constructional arrangements; Manufacturing methodsG02F1/135, G02F1/136 take precedence
• CPC Class Codes: G02F 1/1334 based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals
• CPC Class Codes: G02F 1/133502 Antiglare, refractive index matching layers
• CPC Class Codes: G02F 1/133512 Light shielding layers, e.g. black matrix G02F1/136209 takes precedence
• 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

Abstract

In a light valve, a liquid crystal layer made of liquid crystal/resin composite is interposed between a transparent substrate with a counterelectrode and a reflection substrate with reflection electrodes. The size of the transparent substrate is designed so that the light modulated by the liquid crystal layer is prevented from again entering into the liquid crystal layer after reflected at an interface of the transparent substrate with air. The transparent substrate may be combined with a transparent plate or flat concave lens with a transparent coupling material. Each pixel has a reflection electrode and liquid crystal molecules above the reflection electrode are aligned according to the signals supplied to thin film transistors. The counterelectrode is formed as a multi-layer film of dielectric films and a transparent electrically conductive film. The dielectric films are made of a material having a refractive index of 1.6-1.8, and the optical thickness of the dielectric films is λ/4 while that of the transparent electrically conductive film is λ/2. Thus, the reflection of light is prevented by the interference in the multi-layer film. By using the light valve apparatus, the incident light entering from the side of the counterelectrode is scattered or it is transmitted through the liquid crystal layer, reflected by the reflection electrodes and leaves through the counterelectrode. By using the light valve apparatus in a projection display system, an image of high brightness and high contrast can be realized.

Claims

1. A light valve apparatus comprising:

a first transparent substrate on which a counter electrode is formed;

a second substrate having electrodes formed on the surface of the second substrate;

a third transparent substrate, wherein said first and third transparent substrates comprise a non-image forming portion that is adapted to be substantially free from light for forming an image being transmitted therethrough;

a first optical-coupling layer coupling the first and third substrates optically;

an optical modulation layer interposed between the first and second substrates, said optical modulation layer forming an image according to a change in optical scattering state;

a first light-absorbing member formed on a side of at least one of the first and third substrates, wherein said first light-absorbing member is located at said non-image forming portion; and

a first anti-reflection member formed on a surface of the first transparent substrate facing said optical modulation layer.

2. The light valve apparatus according to claim 1, wherein at least one of the refractive indices of said first and second substrates differs from that of the light modulation layer under no electric field within 0.15.

3. The light valve apparatus according to claim 1, wherein a following relationship holds:

##EQU15## where "t" denotes the total thickness of said first and third substrate between the optical modulation layer and air, "n" denotes the refractive index of said third substrate and "d" denotes a diagonal length of an image display area of said optical modulation layer to be modulated to display an image.

4. The light valve apparatus according to claim 1, further comprising:

a fourth substrate;

a second optical-coupling layer connecting said second and fourth substrates; and

a second light-absorbing member formed on a side of one of said third and fourth substrates.

5. The light valve apparatus according to claim 1, further comprising a second light-absorbing member formed on a surface of said second substrate opposite to the surface on which the electrodes are formed.

6. The light valve apparatus according to claim 1, further comprising a second anti-reflection member formed on the surface of said first transparent electrode, and wherein said counter electrode is interposed between said first and second anti-reflection members.

7. The light valve apparatus according to claim 6, said anti-reflection film comprising:

a first dielectric film of optical thickness of about λ

/4, a transparent electrically conducting film of optical thickness of about λ

/2 applied to the first dielectric film and a second dielectric film of optical thickness of about λ

/4 applied to the transparent electrically conducting film;

wherein λ

denotes wavelength of incident light, the refractive index n₁ of the two dielectric films is between 1.6 and 1.8.

8. The light valve apparatus according to claim 7, wherein said optical modulation layer comprises a liquid crystal/resin composite including a liquid crystal component and a resin component.

9. The light valve apparatus according to claim 8, wherein the thickness of the optical modulation layer is between 5 and 25 μ

m.

10. The light valve apparatus according to claim 8, wherein said liquid crystal/resin composite is a polymer dispersion liquid crystal with droplets of an average size between 0.5 and 3 μ

m or a polymer network liquid crystal with pores of an average pore size between 0.5 and 3 μ

m.

11. The light valve apparatus according to claim 7, wherein the first and second dielectric thin films are made of one of aluminum oxide (Al₂ O₃), yttrium oxide (Y₂ O₃), silicon oxide (SiO), tungsten oxide (WO₃), cerium fluoride (CeF₃), magnesium oxide (MgO), and lead fluoride (PbF₂).

12. The light valve apparatus according to claim 7 wherein the refractive indices n₁ of the dielectric films and n₂ of the electrically conducting film satisfies a relationship n₂ >

n₁ >

n₃ wherein n₃ denotes the refractive index of the optical modulation layer when an electric field is not applied.

13. The light valve apparatus according to claim 6, said anti-reflection film comprising:

a dielectric film of optical thickness of about λ

/4 and a transparent electrically conducting film of optical thickness of about λ

/2 applied to the dielectric film;

wherein λ

denotes wavelength of incident light, the refractive index n₁ of the dielectric film is between 1.5 and 1.7.

14. The light valve apparatus according to claim 13, wherein the dielectric thin film is made of one of aluminum oxide (Al₂ O₃), silicon oxide (SiO), tungsten oxide (WO₃), cerium fluoride (CeF₃), lanthanum fluoride (LaF₃), and neodium fluoride (NdF₃).

15. The light valve apparatus according to claim 6, wherein said anti-reflection film comprises a transparent electrically conducting film of optical thickness of λ

/2 wherein λ

denotes the wavelength of light.

16. The light valve apparatus according to claim 15, wherein the refractive index of said transparent electrically conducting material is 1.9 or less.

17. The light valve apparatus according to claim 6, said anti-reflection film comprising:

a first transparent dielectric film of optical thickness of about λ

/4, a transparent electrically conducting film of optical thickness of about λ

/2 applied to the first dielectric film and a second transparent dielectric film of optical thickness of about λ

/4 applied to the transparent electrically conducting film, wherein λ

denotes wavelength of incident light;

one of said first and second transparent dielectric films comprising a multi-layer film, which multi-layer film comprising first films of low refractive index between 1.3 and 1.7 and second films of high refractive index between 1.7 and 2.3, the first films and the second films being layered alternately, the other of said first and second transparent dielectric films comprising a single layer of refractive index between 1.6 and 1.8;

said first films being made of one of magnesium fluoride (MgF₂), silicon oxide (SiO₂), aluminum oxide (Al₂ O₃), cerium fluoride (CeF₃) and silicon oxide (SiO);

said second films being made of one of yttrium oxide (Y₂ O₃), zirconium oxide (ZrO₂), hafnium oxide (HfO₂), tantalum oxide (Ta₂ O₅), cerium oxide (CeO₂), titanium oxide (TiO₂) and zinc sulfide (ZnS);

said the other of said first and second transparent dielectric films being made of one of aluminum oxide (Al₂ O₃), silicon oxide (SiO), yttrium oxide (Y₂ O₃), magnesium oxide (MgO), lead fluoride (PbF₂) and tungsten oxide (WO₃).

18. The light valve apparatus according to claim 6, said anti-reflection film comprising:

a first transparent dielectric film of optical thickness of about λ

/4, a transparent electrically conducting film of optical thickness of about λ

/2 applied to the first dielectric film and a second transparent dielectric film of optical thickness of about λ

/4 applied to the transparent electrically conducting film, wherein λ

denotes wavelength of incident light;

said first and second transparent dielectric films comprising a multi-layer film, which multi-layer film comprising first films of low refractive index between 1.3 and 1.7 and second films of high refractive index between 1.7 and 2.3, the first films and the second films being layered alternately, the other of said first and second transparent dielectric films comprising a single layer of refractive index between 1.6 and 1.8;

said first films being made of one of magnesium fluoride (MgF₂), silicon oxide (SiO₂), aluminum oxide (Al₂ O₃), cerium fluoride (CeF₃) and silicon oxide (SiO);

said second films being made of one of yttrium oxide (Y₂ O₃), zirconium oxide (ZrO₂), hafnium oxide (HfO₂), tantalum oxide (Ta₂ O₅), cerium oxide (CeO₂), titanium oxide (TiO₂) and zinc sulfide (ZnS).

19. The light Valve apparatus according to claim 6, further comprising another anti-reflection film formed on said third substrate on a surface in contact with air, the another anti-reflection film comprising a multi-layer film made of transparent dielectric materials.

20. The light valve apparatus according to claim 1, wherein said electrodes comprise a plurality of reflection electrodes arranged as a matrix.

21. The light valve apparatus according to claim 1, wherein said third substrate has a curved plane at an interface with air.

22. The light valve apparatus according to claim 1, further comprising a film formed between two adjacent reflection electrodes of said reflection electrodes, the film being made of a material of a dielectric index smaller than that of said optical modulation layer.

23. A projection display system comprising:

a light valve, said light valve comprising;

a first transparent substrate on which a counter electrode is formed;

a second transparent substrate having electrodes formed on the surface of the second transparent substrate;

a third transparent substrate, wherein said first and third transparent substrates comprise a non-image forming portion adapted to be substantially free from light for forming an image being transmitted therethrough;

a first optical-coupling layer connecting the first and third substrates optically;

an optical modulation layer interposed between the first and second substrates, said optical modulation layer forming an image according to an optical modulation layer forming an image according to a change in optical scattering state; and

a first light-absorbing member formed on a side of at least one of the first and third substrates, wherein said first light-absorbing member is located at said non-image forming portion; and

an anti-reflection member formed on a surface of the first transparent substrate at a side opposing said optical modulation layer;

a light source for generating a light beam;

an optical system for guiding the light beam generated by the light source to the light valve;

a projection device for projecting the light modulated by the display panel.

24. The projection display system according to claim 23, wherein a following relationship holds:

##EQU16## where "t" denotes the total thickness of the third substrate between said optical modulation layer and a surface of said third transparent substrate in contact with air, "n" denotes the refractive index of said third substrate and "d" denotes a diagonal length of an image display area of the optical modulation layer.

25. A projection display system according to claim 23, wherein said light valve further comprises:

a fourth transparent substrate;

a second optical-coupling layer connecting said second and fourth substrates; and

a light-absorbing member formed on a side of one of said third and fourth substrates.

26. The light valve apparatus according to claim 23, said first transparent substrate comprising an anti-reflection member formed on a surface thereof.

27. The projection display system according to claim 26, further comprising another anti-reflection film formed on said third substrate in an image display area on a surface in contact with air, said another anti-reflection film comprising a multi-layer film made of transparent dielectric materials.

28. The projection display system according to claim 26, wherein said anti-reflection film comprises:

a first dielectric film of optical thickness of about λ

/4 of refractive index between 1.6 and 1.8, a transparent electrically conducting film of optical thickness of about λ

/2, the transparent electrically conducting film being layered on the first anti-reflection member, and a second dielectric film of optical thickness of about λ

/4 of refractive index between 1.6 and 1.8, the second dielectric film being layered on the transparent electrically conducting film, wherein λ

denotes a wavelength of incident light, and wherein the refractive index n₁ of the first and second dielectric films and the refractive index n₂ of the transparent electrically conducting film satisfy a relationship n₂ >

n₁ >

n₃ wherein n₃ denotes the refractive index of the optical modulation layer when an electric field is not applied.

29. The projection display system according to claim 23, further comprising a second light-absorbing film formed on said second substrate on a surface different from the surface on which said electrodes are formed.

30. The projection display system according to claim 23, wherein said optical modulation member comprises a liquid crystal/resin composite including a liquid crystal component and a resin component.

31. The projection display system according to claim 23, wherein said electrodes comprises a plurality of reflection electrodes arranged as a matrix and wherein switching elements for applying signals to the reflection electrodes are formed below the reflection electrodes.

32. The projection display according to claim 23, wherein said anti-reflection film comprises a transparent electrode, and the optical thickness of said transparent electrode is substantially equal to one half the wavelength of light modulated by said optical modulation layer.

33. The projection display system according claim 23, wherein said third substrate has a flat plane and a curved plane and the flat plane thereof is connected optically with said first substrate with the optical coupling layer.

34. The projection display system according to claim 23, wherein said optical coupling layer is made of a photosetting adhesive, a thermosetting adhesive or a silicone resin.

35. The projection display system according to claim 23, wherein said projection device comprises a plurality of lenses and a mirror arranged between the lenses, wherein the light generated by said optical source is converged by the mirror to lead towards said light valve.

36. A light valve apparatus comprising:

a first transparent substrate on which a transparent counter electrode is formed;

a second substrate comprising a plurality of pixel electrodes arranged as a matrix;

an optical modulation layer interposed between the first and second substrates, said optical modulation layer forming an image according to a change in optical scattering state; and

a film formed between a first pixel electrode in the pixel electrodes and a second pixel electrode therein adjacent to the first pixel electrode on said second substrate, said film being made of a material of a relative dielectric constant smaller than that of said optical modulation layer.

37. The light valve apparatus according to claim 36, further comprising another dielectric film formed on said transparent electrode for reflecting light.

38. A light valve apparatus comprising:

a first transparent substrate on which a transparent counter electrode is formed;

a second substrate comprising a plurality of pixel electrodes arranged as a matrix;

an optical modulation layer interposed between the first and second substrates, said optical modulation layer forming an image according to a change in optical scattering state;

a third transparent substrate, wherein said first and third transparent substrates comprise a non-image forming portion adapted to be substantially free from light for forming an image being transmitted therethrough;

an optical coupling layer coupling said first and third substrates optically;

a first light-absorbing member formed on a side of at least one of the first and third substrates, wherein said first light-absorbing member is located at said non-image forming portion; and

a film made formed between first pixel electrode in the pixel electrodes and a second pixel electrode therein adjacent to the first pixel electrode on said second substrate, said film being made of a dielectric material of relative dielectric constant smaller than that of said optical modulation layer;

wherein said first transparent substrate comprises an anti-reflection member formed on a surface of the first transparent substrate at a side opposing said optical modulation layer.

39. A projection display system comprising:

a light valve apparatus comprising;

a first transparent substrate on which a transparent electrode is formed;

a second substrate comprising a plurality of pixel electrodes arranged as a matrix;

an optical modulation layer interposed between the first and second substrates, said optical modulation layer forming an image according to a change in optical scattering state; and

a film formed between a first pixel electrode in the pixel electrodes and a second pixel electrode therein adjacent to the first electrode, said film being made of a material of dielectric index smaller than that of said optical modulation layer;

a light source for generating a light beam;

an optical system for guiding the light beam generated by the light source to the light valve apparatus; and

a projection device for projecting the light modulated by the light valve apparatus.

40. The light valve apparatus according to claim 39, wherein a following relation holds:

##EQU17## where "t" denotes a thickness of said first substrate, "n" denotes the refractive index of said first substrata and "d" denotes a diagonal length of an image display area of said optical modulation layer.

41. A projection display system comprising:

a light valve apparatus comprising;

a first transparent substrate;

a second substrate comprising a plurality of pixel electrodes arranged as a matrix;

an optical modulation layer interposed between the first and second substrates, said optical modulation layer forming an image according to a change in optical scattering state;

a third transparent substrate, wherein said first and third transparent substrates comprise a non-image forming portion adapted to be substantially free from light for forming an image being transmitted therethrough;

an optical coupling layer coupling said first and third substrates optically;

a first light-absorbing member formed on a side of at least one of the first and third substrates, wherein said first light-absorbing member is located at said non-image forming portion; and

a film formed between a first pixel electrode in the pixel electrodes and a second pixel electrode therein adjacent to the first pixel electrode on said second substrate, said film being made of a material of relative dielectric constant smaller than that of said optical modulation layer;

a light source for generating a light beam;

an optical system for guiding the light beam generated by the light source to the light valve apparatus; and

a projection device for projecting the light modulated by the display panel.