Rapid starting, high-speed liquid crystal variable optical retarder

• US 4,566,758 A
• Filed: 05/09/1983
• Issued: 01/28/1986
• Est. Priority Date: 05/09/1983
• Status: Expired due to Fees

• Current Assignee: Tektronix Incorporated (Fortive Corp.)
• Original Assignee: Tektronix Incorporated (Fortive Corp.)
• Inventors: Bos, Philip J.
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): Lewis, David
• Application Number:
  US06/493,107
• Time in Patent Office: 995 Days
• Field of Search: 350/340, 350/341, 350/334, 350/346, 350/347 R, 350/347 E, 350/350 R
• US Class Current: 349/128
• CPC Class Codes: G02F 1/1395 Optically compensated birefringence [OCB]- cells or PI- cells

Abstract

A liquid crystal cell (100) includes a chiral additive in the liquid crystal material (106) to operate the cell as a rapid starting, high-speed variable optical retarder. The cell is fabricated so that the surface noncontacting directors (116 and 118) of the opposed surfaces of the director alignment layers (112 and 112'"'"') of the electrode structures (102 and 104) are tilt-biased in opposite directions. This surface contacting director configuration induces rapid surface noncontacting director (120a, 120b, 120c, 120d, 120e) relaxation without optical bounce when the cell is switched from the field aligned ("ON") state to the partly relaxed ("OFF") state. The chiral additive prevents an inactive cell from relaxing to the splayed topological state, thereby enabling switching operation without a warm-up delay and preventing the surface of the cell from having a mottled appearance when it remains unused.

Claims

1. A rapid starting, high-speed liquid crystal variable optical retarder comprising:

a liquid crystal cell which includes a pair of generally parallel electrode structures that contain a mixture of a chiral agent and a nematic liquid crystal material which has directors, the inner surface of each electrode structure including a director alignment layer which has been conditioned so that the directors of the liquid crystal material in contact therewith become substantially uniformly aligned to form tilt bias angles with the conditioned surface, the tilt bias angles of the directors in contact with the conditioned surface of one electrode structure being defined in a rotational sense opposite to the tilt bias angles of the directors in contact with the other conditioned surface of the other electrode structure and the projections of the directors in contact with the conditioned surfaces being aligned so that the projections onto one of the conditioned surfaces are parallel to the projections onto the other conditioned surface; and

the liquid crystal cell being operable in response to an applied electric field to cause a substantial number of the surface noncontacting directors to align in substantially end-to-end relation in a direction generally normal to the conditioned surfaces to provide a first amount of optical retardation through the cell of light incident to one of the surfaces of the electrode structures, in rapid response to a substantial diminution of the magnitude of the electric field to cause at least some of the surface noncontacting directors within the interior of the cell to rotate about axes that are perpendicular to the normal to the conditioned surfaces to provide a second amount of optical retardation of light incident to one of the surfaces of the electrode structures, and in response to a relatively prolonged absence of the electric field to inhibit director relaxation to a splayed state.

2. The variable optical retarder of claim 1 in which the second amount of retardation is substantially half-wave optical retardation.

3. The variable optical retarder of claim 1 in which the electrode structure are separated by a distance, d, and the chiral additive is mixed with the liquid crystal material in an amount which causes the directors of the liquid crystal material prior to its inclusion between the electrode structures to have a pitch, p, that satisfies the expression ##EQU4##

4. The variable optical retarder of claim 1 in which the first amount of retardation is essentially zero optical retardation.

5. The variable optical retarder of claim 1 in which the second amount of retardation is determined by the quantity Δ

nd, where Δ

n represents the effective birefringence and d represents the thickness, of the cell.