Liquid crystal device using a Fresnel collimating lens for improving uniformity of display contrast ratio

• US 4,756,604 A
• Filed: 07/02/1987
• Issued: 07/12/1988
• Est. Priority Date: 07/04/1986
• Status: Expired due to Term

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Nakatsuka, Hideaki, Kanazaki, Mikio
• Primary Examiner(s): Miller, Stanley D.
• Assistant Examiner(s): Phan, Trong Quang
• Application Number:
  US07/069,044
• Time in Patent Office: 376 Days
• Field of Search: 350/445, 350/452, 350/331 R, 350/334, 350/345, 350/339 R, 353/100
• US Class Current: 349/6
• CPC Class Codes: G02F 1/133526 Lenses, e.g. microlenses or Fresnel lenses
• CPC Class Codes: G03B 21/132 Overhead projectors, i.e. capable of projecting hand-writing or drawing during action epidiascopic projectors G03B21/08

Abstract

There is disclosed a liquid crystal display device having very uniform contrast ratio for use with such a projector as an overhead projector. The liquid crystal display device comprises a liquid crystal display cell having a thin film of liquid crystal material sandwiched between transparent electrodes formed on opposing transparent substrates and a Fresnel collimating lens disposed before the cell in the direction of light traveling through the cell and for collimating the light in parallel light beams from a condenser lens in the projector.

Claims

1. A liquid crystal display device for use in a projector of the type wherein light from a light source is gathered by a condenser lens, is modulated by the liquid crystal display device placed on a stage and focused on a display screen by a projection lens, said liquid crystal display device comprising a liquid crystal display cell having a thin film of liquid crystal material sandwiched between patterned transparent electrodes formed on opposing transparent substrates, and a Fresnel collimating lens disposed before said liquid crystal cell in the direction of said light traveling through said liquid crystal cell from said light source and for collimating said light in parallel light beams from said condenser lens.

2. A liquid crystal display device according to claim 1 and further comprising a Fresnel correction lens for directing light beams toward said projection lens.

3. A liquid crystal display device according to claim 1 and further comprising a pair of polarizers disposed before and behind said liquid crystal display cell in the direction of said light traveling through said liquid crystal display cell.

4. A liquid crystal display device according to claim 1 wherein said liquid crystal display cell and said Fresnel collimating lens are assembled as a unitary structure for ease of detachment from said projector.