Fast response optical devices by double liquid crystal cells structure

Patent metadata

Field	Value
Publication number	US-9261745-B2
Application number	US-201313892895-A
Country	US
Kind code	B2
Filing date	May 13, 2013
Priority date	May 13, 2013
Publication date	Feb 16, 2016
Grant date	Feb 16, 2016

Abstract

A phase retarder comprises first and second π-cells or other tunable birefringent devices arranged optically in series. The phase retardation value of the phase retarder is a difference between the phase retardation values of the first and second π-cells. Driving circuitry drives the phase retarder to generate a target phase retardation value by: (1) prior to a relaxation period, biasing the π-cells to produce the target phase retardation value; (2) during the relaxation period, biasing the first π-cell at a constant bias value; and (3) during the relaxation period, lowering the bias value of the second π-cell continuously or stepwise to maintain the target phase retardation value for the phase retarder throughout the relaxation period. In some embodiments the operation (2) comprises applying zero bias to the first π-cell throughout the relaxation period. In some embodiments the operation (1) comprises applying a maximum operational bias to the second π-cell.

First claim

The invention claimed is:

1. An apparatus comprising:
a phase retarder comprising a first tunable birefringent device and a second tunable birefringent device arranged optically in series wherein each of the first tunable birefringent device and the second tunable birefringent device has a maximum-bias phase retardation φ max — drive at steady state for a maximum bias value and a relaxed phase retardation φ relaxed at steady state for a minimum bias value; and
driving circuitry configured to drive the phase retarder to generate a target phase retardation φ target for the phase retarder over the relaxation period of a time frame comprising a transition period followed by a relaxation period by operations including:
(1) biasing the second tunable birefringent device at the maximum bias value during the transition period yielding the maximum-bias phase retardation φ max — drive for the second tunable birefringent device at the beginning of the relaxation period,
(2) biasing the first tunable birefringent device during the transition period at a bias value determined based on the target phase retardation φ target ,
(3) biasing the first tunable birefringent device at the minimum bias value during the relaxation period yielding the relaxed phase retardation φ relaxed for the first tunable birefringent device at the end of the relaxation period, and
(4) biasing the second tunable birefringent device during the relaxation period at a bias value determined based on the target phase retardation φ target ,

wherein the driving circuitry is configured to perform the biasing operations (2) and (4) at bias values between the minimum bias value and the maximum bias value.

2. The apparatus of claim 1 wherein the minimum bias value is zero volts.

3. The apparatus of claim 1 wherein the first tunable birefringent device is a first π-cell and the second tunable birefringent device is a second π-cell having its rubbing directions oriented tranverse to the rubbing directions of the first π-cell.

4. The apparatus of claim 1 wherein:
the first tunable birefringent device is a first π-cell and the second tunable birefringent device is a second π-cell having its rubbing directions oriented tranverse to the rubbing directions of the first π-cell;
the first π-cell provides an additive phase retardation contribution to the total phase retardation of the phase retarder;
the second π-cell provides a subtractive phase retardation contribution to the total phase retardation of the phase retarder; and
the biasing operations (1), (2), (3), and (4) respectively comprise:
(1) biasing the second π-cell at the maximum bias value during the transition period yielding the maximum-bias phase retardation φ max — drive for the second π-cell at the beginning of the relaxation period,
(2) biasing the first π-cell during the transition period at a bias value yielding phase retardation φ max — drive +φ target for the first π-cell at the beginning of the relaxation period;
(3) biasing the first π-cell at the minimum bias value during the relaxation period yielding the relaxed phase retardation φ relaxed for the first π-cell at the end of the relaxation period, and
(4) biasing the second π-cell during the relaxation period at a bias value yielding phase retardation φ relaxed −φ target for the second π-cell at the end of the relaxation period.

5. The apparatus of claim 4 wherein the biasing operation (4) comprises reducing the bias of the second π-cell continuously or in multiple voltage decrease steps over the relaxation period from the maximum bias value at the beginning of the relaxation period to the bias value yielding phase retardation φ relaxed −φ target at the end of the relaxation period.

6. The apparatus of claim 5 wherein reducing of the bias of the second n-cell continuously or in multiple voltage decrease steps over the relaxation period is configured to maintain the total phase retardation of the phase retarder at the target phase retardation φ target throughout the relaxation period.

7. The apparatus of claim 1 wherein the biasing operations (2) and (4) are configured to yield

1
T

⁢

∫
i
f

⁢

ϕ
A

⁡

(
t
)

-

ϕ
B

⁡

(
t
)

⁢

⁢

ⅆ
t

=

ϕ
target

where T is the duration of the relaxation period, the integral ∫ i f . . . dt is over the relaxation period, φ A (t) is the phase retardation of the first tunable birefringent device over the relaxation period, and φ B (t) is the phase retardation of the second tunable birefringent device over the relaxation period.

8. The apparatus of claim 1 wherein the biasing operation (4) is configured to maintain φ A (t)−φ B (t)=φ target throughout the relaxation period where t denotes time, φ A (t) is the phase retardation of the first tunable birefringent device over the relaxation period, and φ B (t) is the phase retardation of the second tunable birefringent device over the relaxation period.

9. The apparatus of claim 1 wherein the biasing operation (4) comprises reducing the bias of the second tunable birefringent device from the maximum bias value at the beginning of the relaxation period to a bias value yielding phase retardation φ relaxed −φ target for the second tunable birefringent device at the end of the relaxation period.

10. The apparatus of claim 9 wherein the biasing operation (4) reduces the bias of the second tunable birefringent device continuously or in multiple voltage decrease steps over the relaxation period.

11. The apparatus of claim 10 wherein the biasing operation (4) reduces the bias of the second tunable birefringent device continuously or in multiple voltage decrease steps over the relaxation period to maintain the total phase retardation of the phase retarder at φ A (t)−φ B (t)=φ target over the relaxation period where t denotes time, φ A (t) is the phase retardation of the first tunable birefringent device over the relaxation period, and φ B (t) is the phase retardation of the second tunable birefringent device over the relaxation period.

12. The apparatus of claim 1 further comprising:
a first polarizer and a second polarizer disposed on opposite sides of the phase retarder.

13. A display comprising an array of pixels wherein each pixel includes:
the apparatus of claim 1 ;
polarizers disposed on both sides of the phase retarder of the apparatus of claim

Assignees

• Cheng Hsienhui
• Bhowmik Achintya
• Bos Philip J
• Univ Kent State Ohio

Inventors

• Cheng Hsienhui
• Bhowmik Achintya
• Bos Philip J

Classifications

• G02F1/13471 Primary

  in which all the liquid crystal cells or layers remain transparent, e.g. FLC, ECB, DAP, HAN, TN, STN, SBE-LC cells (G02F1/13475 takes precedence) · CPC title

• G02F1/13363

  Birefringent elements, e.g. for optical compensation · CPC title

• G02F1/1393

  the birefringence of the liquid crystal being electrically controlled, e.g. ECB-, DAP-, HAN-, PI-LC cells (G02F1/1396, G02F1/141 take precedence) · CPC title

• G02B27/286

  for controlling or changing the state of polarisation, e.g. transforming one polarisation state into another (G02B5/3083 takes precedence; light guide coupling means utilising polarising elements G02B6/34) · CPC title