Reflective liquid crystal display device with twist angle between 50.degree. and 68.degree. and the polarizer at the bisectrix

• US 5,490,003 A
• Filed: 10/21/1993
• Issued: 02/06/1996
• Est. Priority Date: 06/28/1991
• Status: Expired due to Fees

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Van Sprang, Hendrik A.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US08/141,433
• Time in Patent Office: 838 Days
• Field of Search: 359/41, 359/63, 359/64, 359/78, 359/93, 359/72, 359/102, 359/70, 359/65
• US Class Current: 349/96
• 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: G02F 1/1398 the twist being below 90°
• CPC Class Codes: G02F 2203/02 reflective

Abstract

To obtain a monotonic transmission/voltage characteristic curve in a reflective display having a small twist angle, the polarizer in a cell with crossed polarizer and analyzer is arranged parallel to the dividing line of the directions of orientation (23, 24) determining the twist angle α, the cell being optimized for α and d.Δn.

Claims

1. A projection device comprising a light source, a reflective display device of the twisted nematic type comprising a layer of liquid crystalline material between a first and a second supporting plate, said supporting plates being provided with orientation means which define a twist angle φ

for the molecules of the liquid crystalline material, means being provided for directing light from the light source onto the first supporting plate, the second supporting plate being provided with means for reflecting light which passes through the layer of liquid crystalline material, which projection device further comprises polarizing means in the light path between the light source and the first supporting plate and analyzing means in the light path after reflection at the display device characterized in that the twist angle φ

has a value between 50 and 68 degrees, in that the directions of polarization of the polarizing means and analyzing means cross each other substantially perpendicularly, said polarizing means being arranged such that the angle between the direction of polarization of the polarized light incident on the first supporting plate and the direction of orientation produced by the orientation means said first supporting plate is provided with has a value of 1/2φ

.

2. A display device as claimed in claim 1, characterized in that the substrate comprises picture electrodes which can be driven via switching elements.

3. A display device as claimed in claim 1, characterized in that the substrate is a semiconductor substrate.

4. A projection display device, characterized in that it comprises at least one light source whose light is incident on a display device as claimed in claim 1 and is reflected dependent on the optical state of pixels defined by the picture electrodes, the light thus modulated being imaged via projection means.

5. The projection device of claim 1 wherein 0.58 λ

₀ <

d.Δ

n<

0.68 λ

₀, wherein d=the thickness of the layer of liquid crystalline material, Δ

n=the difference in the refractive index of the ordinary wave and the refractive index of the extraordinary wave and λ

₀ =the central wavelength of light from the light source.

6. A projection device capable of being in a light transmissive or a light extinguished state and exhibiting a maximum transmission of light when in the extinguished stage of about 1% of the light transmission when in the transmissive state when the central wavelength of light from a light source employed in said projection device is 460-620 nm comprising said light source, a reflective display device of the twisted nematic type comprising a layer of liquid crystalline material between a first and a second supporting plate, said supporting plates being provided with orientation means which define a twist angle φ

for the molecules of the liquid crystalline material, means being provided for directing light from the light source onto the first supporting plate, the second supporting plate being provided with means for reflecting light which passes through the layer of liquid crystalline material, which projection device further comprises polarizing means in the light path between the light source and the first supporting plate and analyzing means in the light path after reflection at the display device characterized in that the twist angle φ

has a value between 50 and 68 degrees, in that the directions of polarization of the polarizing means and analyzing means cross each other substantially perpendicularly, said polarizing means being located along the bisectrix of the angle between the directions of orientation provided on said first and second supporting plates.

7. The projection device of claim 6 wherein 0.58 λ

₀ <

d.Δ

n<

0.68 λ

₀, wherein d=the thickness of the layer of liquid crystalline material, Δ

n=the difference in the refractive index of the ordinary wave and the refractive index of the extraordinary wave and λ

₀ =the central wavelength of light from the light source.