Separating white light into polarized, colored light

Details Separating white light into polarized, colored light Separating white light into polarized, colored light

1999-01-28

2002-12-03

Ton, Toan (Department: 2871)

Liquid crystal cells, elements and systems

Particular structure

Having significant detail of cell structure only

C359S490020, C353S031000

Reexamination Certificate

active

06490017

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to electro-optical shutter devices, and more specifically, to methods and apparatus for separating white light into packets of polarized, colored light.
2. Description of the Related Art
FIG. 1
illustrates a cross prism or cube
10
having four component prisms
32
,
34
,
36
,
38
that fit together to give the cubic form to the cross cube
10
. The cross cube
10
is an optical device that produces colored light beams
12
,
14
,
16
from a white light beam
18
. The white light beam
18
enters the cross cube
10
through a front face
20
and the beams of red, green, and blue light
12
,
14
,
16
exit the cross cube
10
through the side faces
22
,
24
,
26
. First and second color-selective layers
28
,
30
give the cross cube
10
the above-described color-separating properties. The first and second layers,
28
,
30
are deposited along the joints or interfaces between the four components
32
,
34
,
36
, and
38
.
The selective reflectivities of the first and second layer
28
,
30
give the color-separating properties to the cross cube
10
. The first layer
28
substantially reflects only red light in a first direction. The second layer
30
substantially reflects only blue light in a direction that is opposite to the first direction. Green light passes through the cross cube
10
without either a substantial reduction in intensity or a substantial deviation in direction. To use the cross cube
10
in three-color image formation, three imagers (not shown) are generally necessary, i.e. one imager for each of the separate red, green, and blue light beams
12
,
14
,
16
. The outgoing red, green, and blue light beams
12
,
14
,
16
have substantially the same power per wavelength as the red, green, and blue components of the incoming white light beam
18
.
Referring to
FIG. 1
, the source (not shown) of the white light beam
18
may be deficient in certain color or wavelength ranges. For example, metal halide lamps are deficient in red or long wavelength visible light. Such lamps output “quasi”-white light, i.e., a white light in which one or more color components are substantially less intense than other by components. If a metal halide lamp is used with the cross cube
10
to produce the colored light beams
12
,
14
,
16
, the red light beam
12
would be substantially less intense than the other two colored light beams
14
,
16
. Similarly, a sodium lamp is deficient in blue or short wavelength visible light. Therefore, using the cross cube
10
to separate quasi-white light
18
from a sodium lamp would produce the three colored light beams
12
,
14
,
16
, but the beam of blue light
16
would be substantially less intense than the other two colored light beams
12
,
14
. In devices (not shown) that use the colored light beams
12
,
14
,
16
for color image formation, it is generally advantageous for the different colored light beams
12
,
14
,
16
to have photopically weighted intensities. Unfortunately, the simple cross prism
10
does not normally produce colored light beams of weighted intensity when the white light source is deficient in a particular wavelength or color range.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
SUMMARY OF THE INVENTION
In another aspect, embodiments of the invention feature an electro-optic shutter. The electro-optic shutter includes a color-selective layer, a liquid crystal device to receive light from the color-selective layer and a polarizer to receive light from the liquid crystal layer. The color-selective layer is adapted to transmit a first color, a first polarization of a second color, and a substantially orthogonal polarization of a third color. The liquid crystal device is adapted to rotate the polarization of light to a substantially orthogonal polarization when in a first state and to not substantially rotate the polarization of light when in a second state.


REFERENCES:
patent: 5122887 (1992-06-01), Mathewson
patent: 5404076 (1995-04-01), Dolan et al.
patent: 5571384 (1996-11-01), Pikka et al.
patent: 5606220 (1997-02-01), Dolan et al.
patent: 5627666 (1997-05-01), Sharp et al.
patent: 5686931 (1997-11-01), Fünfschilling et al.
patent: 5833360 (1998-11-01), Knox et al.
patent: 5999240 (1999-12-01), Sharp et al.
patent: 6217174 (2001-04-01), Knox
patent: WO96/37806 (1996-11-01), None
patent: WO97/43862 (1997-11-01), None

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