Enhanced off-axis viewing performance of liquid crystal display employing a fiberoptic faceplate in conjunction with dual negative retarders and a brightness enhancing film on the illumination source

• US 5,751,390 A
• Filed: 12/12/1996
• Issued: 05/12/1998
• Est. Priority Date: 12/12/1996
• Status: Expired due to Term

• Current Assignee: Thomson Licensing (Vantiva SA)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Silverstein, Louis D., Crawford, Gregory P., Fiske, Thomas G.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): TON, MINH TOAN T
• Application Number:
  US08/764,542
• Time in Patent Office: 516 Days
• Field of Search: 349/118, 349/119, 349/120, 349/159, 349/64
• US Class Current: 349/120
• CPC Class Codes: G02F 1/133526 Lenses, e.g. microlenses or Fresnel lenses
• CPC Class Codes: G02F 1/133634 the refractive index Nz perpendicular to the element surface being different from in-plane refractive indices Nx and Ny, e.g. biaxial or with normal optical axis

Abstract

A transmissive, backlit color twisted-nematic or super-twisted-nematic liquid crystal display employing a front fiber-optic faceplate or optical equivalent as a front retaining element of a liquid crystal cell that increases viewing angle between the display and a viewer while minimizing or eliminating undesirable variations in luminance, contrast ratio and chromaticity is described. The fiber-optic faceplate or optical equivalent includes cylindrical optical features and interstitial cladding material of greater optical index than the cylindrical optical features. The interstitial cladding material may include an opaque mask blocking layer to prevent the interstitial apertures from diffracting off-axis light into an observer'"'"'s viewing cone. In particular the liquid crystal display includes dual negative retarders, and a light shaping element such as a brightness enhancing film on the illumination source that increase the effective viewing angle between the display and a viewer while minimizing undesirable variations in display chromaticity, luminance, and contrast ratio. The front fiber-optic faceplate or optical equivalent works in conjunction with the dual negative retarders and the light shaping element to provide an improved contrast ratio with a perfectly symmetric viewing angle and to eliminate grey scale inversions.

Claims

1. A direct-view, rear-illuminated liquid crystal display device, comprising in sequential order:

A) a backlight source;

B) a rear diffuser layer;

C) a light shaping film,

D) a rear linear polarizer;

E) a liquid crystal cell including

i) a rear glass layer with addressing elements and pixel ITO electrodes,

ii a liquid crystal layer,

iii) a common ITO electrode,

iv) a front polarizer, and

v) a front fiber-optic faceplate as a front containing element substantially adjacent to said front polarizer, said front fiber-optic faceplate including optical fibers and cladding material, said front fiber-optic faceplate having a plurality of fibers, and

F) wherein said liquid crystal cell is constructed to produce a highly anisotropic light distribution possessing extremely high contrast around a narrow meridian of the display viewing volume and is comprised of;

i) a first negative retardation film located between the front polarizer and the liquid crystal layer,

ii) a second negative retardation film located between the rear polarizer and the liquid crystal layer,

iii) said first negative retardation film has indices of refraction n_x1 and n_y1, on the plane of the first retardation film and an index of refraction n_z1 in a thickness direction, a distance dri which is the thickness of the first retardation film, the indices of refraction of the first retardation film are described by the equation nz₁ <

n_x1 =n_y1, and an optical path length of the first retardation film is approximately described by the equation Δ

nd=(n_z1 -n_x1)d_r1,

iv) said second negative retardation film has indices of refraction n_x2 and n_y2 on the plane of the second retardation film and an index of refraction n_z2 in a thickness direction, a distance d_r which is the thickness of the second retardation film, the indices of refraction of the second retardation film are described by the equation n_z2 <

n_x2 =n_y2, and an optical path length of the second retardation film is approximately described by the equation Δ

nd=(n_z2 -n_x2)d_r2,

v) said liquid crystal layer, in an homeotropically aligned state, has indices of refraction n_e and n_o where index of refraction n_e extends in a thickness direction of the liquid crystal layer and the index of refraction n_o is perpendicular to the index of refraction n_e and extends in the direction in the plane of the liquid crystal layer, the index of refraction n_e is always greater than the index of refraction n_o, for a positive optically anisotropic liquid crystal material, said liquid crystal layer has a distance d_c which is the thickness of the liquid crystal layer, and an optical path length of the liquid crystal layer is approximately described by the equation Δ

nd=(n_e -n_o)d_c, and

vi) a sum of the optical path lengths of the two retardation films must be substantially equal to an absolute value of the optical path length of the liquid crystal layer and is opposite in sign to the value of the optical path length of the liquid crystal layer.

2. The direct-view, rear-illuminated liquid crystal display device of claim 1 wherein the optical path lengths of the first and second negative retardation films and the liquid crystal layer are approximately described by the equation (n_z1 -n_x1)d_r1 +(n_z2 -n_x2)d_r2 =˜

-(n_e -n_o)d_c.

3. The direct-view liquid crystal display device of claim 1, wherein said liquid crystal layer is composed of twisted nematic material.

4. The direct-view liquid crystal display device of claim 1, wherein said liquid crystal layer is composed of super-twisted nematic material.

5. The direct-view liquid crystal display device of claim 1, further comprising said front fiber-optic faceplate wherein the cladding material is so constructed to substantially prevent the cladding material from diffracting off-axis light into an observer'"'"'s viewing cone.

6. The direct-view liquid crystal display device of claim 5, further comprising said front fiber-optic faceplate having opaque cladding apertures on at least a front face.

7. The direct-view liquid crystal display device of claim 6 wherein the opaque cladding apertures on at least the front face comprise an opaque anti-reflective coating on the front face of said fiber-optic faceplate.

8. The direct-view liquid crystal display device of claim 6 wherein the opaque cladding apertures on at least the front face comprise substantially completely opaque cladding.

9. The direct-view liquid crystal display device of claim 1 wherein the light shaping element is a brightness enhancing film.

10. The direct view liquid crystal display device of claim 1 wherein the light shaping element is a holographic diffuser film.

11. The direct view liquid crystal display device of claim 1 wherein the light shaping element comprises a brightness enhancing film and a holographic diffuser film.