Electrooptical system

• US 6,327,010 B1
• Filed: 12/19/1996
• Issued: 12/04/2001
• Est. Priority Date: 02/03/1992
• Status: Expired due to Fees

• Current Assignee: Merck Patent GmbH (Merck & Co., Inc.)
• Original Assignee: Merck Patent GmbH (Merck & Co., Inc.)
• Inventors: Baur, Günter, Fehrenbach, Waltraud, Scheuble, Bernhard, Staudacher, Barbara
• Primary Examiner(s): Parker, Kenneth
• Assistant Examiner(s): Duong, Tai V.
• Application Number:
  US08/769,517
• Time in Patent Office: 1,811 Days
• Field of Search: 349/99, 349/102, 349/103, 349/117, 349/180, 349/118, 349/120, 349/179, 349/181
• US Class Current: 349/118
• CPC Class Codes: G02F 1/133531 characterised by the arrangement of polariser or analyser axes
• CPC Class Codes: G02F 1/13363 Birefringent elements, e.g. for optical compensation
• 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

Abstract

An electrooptical system contains:

(a) a twisted nematic liquid-crystal layer, with an input side and an output side, which is positioned between a first substrate and a second substrate, each of whose inside surface is provided with an electrode coating and an alignment layer thereon, the director of said liquid crystal layer having a parallel edge alignment and a twist angle of 0°≦β≦1000,

(b) at least one compensation layer for compensating the optical path difference of the liquid-crystal layer d·Δn, and

(c) at least one device for linear polarization of light in such an arrangement that light, before entering and after exiting the liquid-crystal layer, passes through a polarization device,

I. wherein, in order to achieve high contrast, and/or high brightness, and/or high viewing angle independence of the contrast and/or the color values, the angle ψ, which the polarization device on the input side of the liquid crystal layer forms with the director of the liquid-crystal molecules on the surface of the first substrate, satisfies

I.A. condition (1) or (2)

ψ=(β+90°)/2±10°  (1)

ψ=β/2±10°  (2)

where a polarization device is present on both the light input side of the liquid crystal layer and the light output side of the liquid crystal layer, and the polarization device on the output side of the liquid crystal layer is rotated by 90°±10° with respect to the polarization device on the input side of the liquid crystal layer, and, optionally, alignment of the polarization devices on the input side and the output side of the liquid crystal layer are interchanged, or satisfies

I.B. condition (3) or (4)

30°≦ψ≦70° for 0≦β≦45°  (3)

35°≦ψ≦90° for 45≦β100°  (4),

where a polarization device is only present on the input side,

II. wherein the compensation layer comprises a material having three optical refractive indices, of which one is less than the other two, and wherein the optical axis corresponding to this lowest refractive index is essentially parallel to the surface of said second substrate or forms an angle of 2°<γ<60° with the surface of said second substrate,

as a result of which, the angle between the optical axis of the compensation layer and the optical axis of the liquid-crystal layer, upon application of a voltage, passes through a minimum, and

III. wherein the plane set up by the two other refractive indices forms an angle of between 30° and 150° with the director of the liquid-crystal at the surface of the second substrate.

Claims

1. An electrooptical system containing:

(a) a twisted nematic liquid-crystal layer having a director, with an input side and an output side, which is positioned between a first substrate and a second substrate, each of whose inside surface is provided with an electrode coating and an alignment layer thereon, the director of said liquid crystal layer having a parallel edge alignment and a twist angle of 0°

≦

β

≦

100°

,

(b) at least one compensation layer for compensating an optical path difference of the liquid-crystal layer d·

Δ

n, and

(c) at least one device for linear polarization of light in such an arrangement that light, before entering and after exiting the liquid-crystal layer, passes through a polarization device,

I. wherein, in order to achieve high contrast, and/or high brightness, and/or high viewing angle independence of the contrast and/or the color values, the angle ψ

, which the polarization device on the input side of the liquid crystal layer forms with the director of the liquid-crystal layer on the surface of the first substrate, satisfies

I.A. condition (1) or (2)

2. A system according to claim 1 wherein the liquid-crystal layer has a twist angle of 0<

β

<

90°

.

3. A system according to claim 1, wherein the twist angle is 5°

≦

β

≦

60°

.

4. A system according to claim 1, which contains only one polarization device and at least one reflector.

5. A projection device containing a system according to claim 1.

6. A system according to claim 2 which contains only one polarization device and at least one reflector.

7. An electrooptical system according to claim 6 wherein the liquid crystal has, in order to improve the viewing angle dependence of the contrast, an optical path difference d·

Δ

n of ≦

0.40 μ

m.