Projection-type display device

• US 4,995,702 A
• Filed: 10/30/1987
• Issued: 02/26/1991
• Est. Priority Date: 10/31/1986
• Status: Expired due to Term

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Aruga, Shuji
• Primary Examiner(s): Miller, Stanley D.
• Assistant Examiner(s): MAI, HUY KIM
• Application Number:
  US07/114,996
• Time in Patent Office: 1,215 Days
• Field of Search: 350/174, 350/173, 350/331 R, 350/337, 350/339 F, 350/333, 350/408, 350/401, 350/402, 350/334, 350/347 R, 350/379
• US Class Current: 349/8
• CPC Class Codes: G02F 1/1396 the liquid crystal being selectively controlled between a twisted state and a non-twisted state, e.g. TN-LC cell G02F1/141 takes precedence
• CPC Class Codes: H04N 9/3105 for displaying all colours simultaneously, e.g. by using two or more electronic spatial light modulators simultaneous projection in colour photography G03B33/10; beam splitting or combining systems per se G02B27/10

Abstract

A projection-type display device using twisted nematic liquid crystal light valves in which the photoelectric transfer characteristics of three light valves for selectively transmitting red, green and blue light to a synthesizing device are matched. The product of the birefrigence Δn and thickness d of the twisted nematic liquid crystal and thickness of cell is selected to fall within a predetermined optimal range of values depending upon the wavelength of light which travels therethrough. The thickness d or birefrigence Δn of the twisted nematic liquid crystal material of each light valve may be the same.

Claims

1. A projection-type display device in which light representative of the image to be projected is produced by a plurality of light valves, comprising:

a first light valve having a first twisted nematic liquid crystal cell with a birefringence Δ

n₁ and a thickness d₁, the value of Δ

n₁ being selected for controlling the red wavelength of light incident thereto;

a second light value having a second twisted nematic liquid crystal cell with a birefringence Δ

n₂ and a thickness d₂, the value of Δ

n₂ being selected for controlling the green wavelength of light incident thereto;

a third light valve having a third twisted nematic liquid crystal cell with a birefringence Δ

n₃ and a thickness d₃, the value of Δ

n₃ being selected for controlling the blue wavelength of light incident thereto; and

synthesizing means for adding the red, green and blue wavelengths of light transmitted through the respective first, second and third light valves prior to projection by the device;

wherein the values of Δ

n₁, Δ

n₂ and Δ

n₃ are unequal.

2. The projection-type display device of claim 1, in which Δ

n₁ ×

d₁ /λ

₁ for the first light valve, Δ

n₂ ×

d₂ /λ

₂ for the second light valve and Δ

n₃ ×

d₃ /λ

₃ for the third light valve each have values between 2.2 and 2.6 wherein λ

₁, λ

₂ and λ

₃ represent the red wavelength, green wavelength and blue wavelength, respectively.

3. The projection type display device of claim 2, where Δ

n₁ ×

d₁ /λ

₁ =Δ

n₂ ×

d₂ /λ

₂ =Δ

n₃ ×

d₃ /λ

₃.

4. The projection-type display device of claim 2, value of Δ

n₁ ×

d₁ is greater than the value of Δ

n₂ ×

d₂ is greater than the value of Δ

n₃ ×

d₃.

5. The projection-type display device of claim 4, wherein Δ

n₁ ×

d₁ has a value between 1.4 and 1.6 microns, Δ

n₂ ×

d₂ has a value between 1.2 and 1.4 microns and Δ

n₃ ×

d₃ has a value between 1.0 and 1.2 microns.

6. The projection-type display device of claim 1, wherein the thicknesses d₁, d₂ and d₃ are substantially equal.

7. The projection-type display device of claim 1 wherein each light valve includes a pair of transparent substrates spaced apart having a thin film transistor formed on the interior surface of one of the substrates and a light shielding layer formed on the interior surface of the other of the substrates.

8. The projection-type display device of claim 7, wherein the thin film transistor is selected from the group consisting of polysilicon, amorphous silicon and compound semiconductor.

9. The projection-type display device of claim 7, further including a pair of polarizers, each polarizer disposed adjacent to and on the exterior surface of one of the substrates.

10. The projection-type display device of claim 1, in which each of the light valves includes a pair of stripe-type transparent electrodes.

11. The projection-type display device of claim 1, wherein Δ

n₁ >

Δ

n₂ >

n₃.

12. A method of manufacturing a projection-type display device having three light valves comprising:

producing a first liquid crystal cell serving as a first light valve having a first twisted nematic liquid crystal material with a birefringence Δ

n₁ and a thickness d₁ ;

producing a second liquid crystal cell serving as a second light valve having second twisted nematic liquid crystal material with a birefringence Δ

n₂ and a thickness d₂ ;

producing a third liquid crystal cell serving as a third light valve having a third twisted nematic liquid crystal material with a birefringence Δ

n₃ and a thickness d₃ ; and

producing a synthesizer for adding the wavelengths of light produced by the first, second and third light valves;

wherein the value of Δ

n₁ is greater than the value of Δ

n₂ is greater than the value of Δ

n₃.

13. The method of claim 12, wherein the light valves are produced such that Δ

n₁ ×

d₁ has a value between 1.4 microns and 1.6 microns, Δ

n₂ ×

d₂ has a value between 1.2 and 1.4, and Δ

n₃ ×

d₃ has a value between 1.0 and 1.2 microns.

14. The method of claim 12, further including the step of manufacturing each light valve with twisted nematic liquid crystal material of the same thickness.

15. A method of manufacturing a projection-type display having three light valves comprising:

producing a first liquid crystal cell serving as a first light valve having first twisted nematic liquid crystal material with a first birefringence;

producing a second liquid crystal cell serving as a second light valve having second twisted nematic liquid crystal material with a second birefringence;

producing a third liquid crystal cell serving as a third light valve having a third twisted nematic liquid crystal material with a third birefringence;

wherein each of the light valves has twisted nematic liquid crystal material of the same birefringence.

16. A method of projecting an image, comprising:

projecting light from a light source towards color separating means for separating the image into red, green and blue components;

directing each of the red, green and blue components toward a different one of three transparent twisted nematic liquid crystal light valves, each light valve having a birefringence Δ

n and a thickness d for controlling the respective light component incident thereto, a different value of birefringence Δ

n than the value of birefringence Δ

n of each of the other two light valves and having a product of birefringence Δ

n and thickness d which is constant throughout the light valve; and

selectively transmitting the red, blue and green components through the light valves to synthesizing means for combining the red, green and blue components to form the desired image prior to projecting the image blue components to form the desired image and projecting the image.

17. The method of claim 16, wherein

the first light valve is selected to have a first twisted nematic liquid crystal with a birefrigence Δ

n₁ and a thickness d₁, the value of the product Δ

n₁ ×

d₁ is selected for controlling the red wavelength of light incident thereto;

the second light valve is selected to have a second twisted nematic liquid crystal with a birefrigence Δ

n₂ and a thickness d₂, the value of the product Δ

n₂ ×

d₂ is selected for controlling the green wavelength of light incident thereto; and

the third light valve is selected to have a third twisted nematic liquid crystal with a birefrigence Δ

n₃ and a thickness d₃, the value of the product Δ

n₃ ×

d₃ is selected for controlling the blue wavelength of light incident thereto.

18. The method of claim 17 wherein the thicknesses d₁, d₂ and d₃ are substantially equal.