Optical: systems and elements – Polarization without modulation – By relatively adjustable superimposed or in series polarizers
Reexamination Certificate
2001-06-13
2003-04-08
Chang, Audrey (Department: 2872)
Optical: systems and elements
Polarization without modulation
By relatively adjustable superimposed or in series polarizers
C359S506000, C359S246000, C353S020000, C348S742000
Reexamination Certificate
active
06545804
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a projection display, more particularly to a projection display with two reflective light valves.
2. Description of the Related Art
In a conventional projection display, primary color components, such as red, green and blue color components, are processed before projecting the same so as to form an image on a projection screen. During the processing of light, the issue of light leakage must be addressed in order to achieve optimum image quality.
Referring to
FIG. 1
, a conventional projection display
1
is shown to comprise a polarization beam splitter prism
11
which reflects S-polarization light in a transverse direction and which allows P-polarization light to pass directly therethrough. The polarization beam splitter prism
11
has a light input side
111
, a first split-light side
112
adjacent to the light input side
111
, a second split-light side
113
opposite to the light input side
111
, and a light output side
114
opposite to the first split-light side
112
. A P-state polarizer
12
is disposed adjacent to the light input side
111
, allows P-polarization light to pass directly therethrough, and absorbs S-polarization light. A first light polarization selector
13
is disposed between the P-state polarizer
12
and the light input side
111
, and converts the polarization state of red light that passes therethrough. A first reflective light valve
14
is disposed adjacent to the first split-light side
112
, whereas a second reflective light valve
15
is disposed adjacent to the second split-light side
113
. A color switch
16
is disposed between the second split-light side
113
and the second reflective light valve
15
, and allows color components to pass therethrough in accordance with a predetermined color sequence. A second light polarization selector
17
is disposed adjacent to the light output side
114
. An S-state polarizer
18
is disposed adjacent to one side of the second light polarization selector
17
opposite to the light output side
114
, and prevents P-polarization light from passing therethrough. A projection lens
19
receives the light that passes through the S-state polarizer
18
. When the first and second reflective light valves
14
,
15
are in an active (ON) state, they modulate and convert the polarization state of light that is incident thereon, and reflect the modulated light in an opposite direction. In the following paragraphs, the operation of the conventional projection display
1
will be described in greater detail with the first and second reflective light valves
14
,
15
in the active (ON) state. In addition, each of a pair of quarter wavelength plates is disposed between the polarization beam splitter prism
11
and a respective one of the first and second reflective light valves
14
,
15
for enhancing the image contrast quality.
In use, when input white light
10
is provided to the P-state polarizer
12
, only P-polarization first, second and third color components
101
,
102
,
103
(such as red, blue and green color components) will pass therethrough and reach the first light polarization selector
13
. The first light polarization selector
13
changes the polarization state of the first color component
101
to S-polarization, and maintains the polarization state of the second and third color components
102
,
103
at P-polarization. When the polarization beam splitter prism
11
receives the first, second and third color components
101
,
102
,
103
from the first light polarization selector
13
, the S-polarization first color component
101
will be reflected toward the first reflective light valve
14
, whereas the P-polarization second and third color components
102
,
103
will be allowed to pass directly through the polarization beam splitter prism
11
. The second and third color components
102
,
103
from the polarization beam splitter prism
11
will be controlled by the color switch
16
so as to pass sequentially therethrough and reach the second reflective light valve
15
. Because the paths of the second and third color components
102
,
103
and the processing procedure therefor are essentially the same, processing of the third color component
103
will not be described herein for the sake of brevity.
When the first and second reflective light valves
14
,
15
are in the active (ON) state, the S-polarization first color component
101
will be modulated by the first reflective light valve
14
, and the polarization state of the first color component
101
will be changed to P-polarization. The P-polarization first color component
101
will then be reflected by the first reflective light valve
14
back to the polarization beam splitter prism
11
, and will be allowed by the polarization beam splitter prism
11
to pass directly therethrough so as to reach the second light polarization selector
17
. The second light polarization selector
17
will convert the polarization state of the P-polarization first color component
101
to S-polarization, and the S-polarization first color component
101
will pass through the S-state polarizer
18
before reaching the projection lens
19
for projecting the same on a projection screen (not shown). On the other hand, the P-polarization second color component
102
will be modulated by the second reflective light valve
15
, and the polarization state of the P-polarization second color component
102
will be changed to S-polarization. The S-polarization second color component
102
will then be reflected by the second reflective light valve
15
back to the polarization beam splitter prism
11
, and will be further reflected by the polarization beam splitter prism
11
to pass in sequence through the second light polarization selector
17
and the S-state polarizer
18
so as to reach the projection lens
19
. When the second color component
102
is projected by the projection lens
19
, it cooperates with the first color component
101
to form an image on the projection screen (not shown).
In the aforesaid conventional projection display
1
, white light is separated into color components, which are modulated by reflective light valves and which are subsequently recombined to form images on a projection screen. However, due to current manufacturing constraints and the characteristics of polarized light, P-polarization light will be unable to pass through the polarization beam splitter prism with very high transmission efficiency. As such, when P-polarization light passes directly through the polarization beam splitter prism, a small portion of the P-polarization light will be reflected to form light leakage components, as indicated by the phantom lines in FIG.
1
. While a portion of the S-polarization light will pass through the polarization beam splitter prism to result in corresponding light leakage components, the amount of the light leakage components attributed to the S-polarization light is much less than that attributed to the P-polarization light. In the conventional projection display
1
of
FIG. 1
, it is assumed that 10% of the P-polarization light will be reflected by the polarization beam splitter prism
11
to form light leakage components, and that 2% of the S-polarization light will be allowed by the polarization beam splitter prism
11
to pass directly therethrough to form light leakage components. Therefore, when the S-polarization first color component
101
is reflected by the polarization beam splitter prism
11
, about 2% of the first color component
101
will form a first light leakage component
101
′ that passes directly through the polarization beam splitter prism
11
and that reaches the second reflective light valve
15
. The second reflective light valve
15
will change the polarization state of the first light leakage component
101
′ to P-polarization, and the P-polarization first light leakage component
101
′ will be reflected back to the polarization beam splitter prism
11
. At this time, about 10
Chang Audrey
Curtis Craig
Prokia Technology Co., Ltd.
Trop Pruner & Hu P.C.
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