Computer graphics processing and selective visual display system – Plural physical display element control system – Optical means interposed in viewing path
Reexamination Certificate
2001-06-22
2003-01-14
Luu, Matthew (Department: 2672)
Computer graphics processing and selective visual display system
Plural physical display element control system
Optical means interposed in viewing path
C345S048000, C345S036000, C359S292000, C359S490020, C359S587000, C359S634000, C349S008000, C349S009000, C348S744000, C348S750000, C353S008000, C353S031000
Reexamination Certificate
active
06507326
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to color projection apparatus. More specifically, this invention pertains to color projection apparatus operable to separate an illumination-light flux into multiple colors of light, create color images, combine such color images, and project the combined color images onto a viewing surface.
BACKGROUND OF THE INVENTION
A prior-art color projection device using reflection-type light valves, shown in
FIG. 5
, is disclosed in Japanese Unexamined Patent Publication No. 63-39294. In the
FIG. 5
apparatus, a white illumination-light flux is emitted from a light source
223
that comprises, for example, a halogen lamp. The illumination-light flux typically passes through a collimating lens
222
operable to make parallel the rays comprising the illumination-light flux. The illumination-light flux then enters a polarizing beam splitter (PBS)
221
disposes along the optical axis O of a color separation optical system
211
.
S-polarized light of the illumination-light flux is reflected by the PBS
221
and is incident on the color-separation optical system
211
. The s-polarized light incident on the color-separation optical system
211
is separated into the three primary colors, red (R), blue (B), and green (G), as follows.
The color separation optical system
211
includes a first prism
211
A, a second prism
211
B, and a third prism
211
C, each disposes as shown in
FIG. 5. A
surface
211
e
of the first prism
211
A is coated with an evaporated, thin dichroic film which reflects blue light but transmits light with longer wavelengths (i.e., red and green light). There is a gap between the first prism
211
A and the second prism
211
B. A thin, dichroic film, which reflects red light but transmits green light, is coated on a surface
211
f
of the second prism
211
B, between the second prism
211
B and the third prism
211
C.
As the illumination-light flux reflected from the PBS
221
enters through surface
211
a
of the first prism
211
A, blue light is reflected by the surface
211
e
and is then reflected inwardly by the surface
211
a
toward an emergence surface
211
b
of the first prism. Red light that passes through the surface
211
e
of the first prism
211
A is reflected by the surface
211
f
and is then reflected inwardly by the surface of the second prism
211
B between the first and second prisms. The inwardly reflected red light then exits through an emergence surface
211
c
of the second prism
211
B. Green light that passes through the surface
211
e
of the first prism
211
A and through the surface
211
f
of the second prism
211
B travels toward an emergence surface
211
d
of the third prism
211
C.
Reference numerals
212
,
213
, and
214
denote two-dimensional reflection-type liquid crystal light valves (LCLVs) for displaying a blue light image, a red light image, and a green light image, respectively. Each of the reflective-type LCLVs have dielectric reflecting layers
215
,
216
, and
217
, respectively, formed on the back of transmission-type LCLVs so that the LCLVs operate as reflection-type LCLVs. As each color of light enters a respective LCLV, the light is modulated by the respective LCLV. Hence, each color's video signal is converted into an image that has a transmission-rate distribution at the respective LCLV.
The modulated color light is then reflected and changed in polarization state by 90°. That is, the s-polarized light is converted by the LCLV to p-polarized light. The modulated and reflected color lights travel along reverse paths through the first, second and third prisms
211
A,
211
B,
211
C, respectively, to be combined into a single light flux. The resultant combined, single light flux emerges from the incidence plane of the first prism
211
A. The light flux whose polarization state has been converted is passed through the PBS
221
and projected on a screen
235
by a projection lens
224
.
A problem with the conventional example shown in
FIG. 5
is its inability to provide sufficiently high-contrast projected images. The conventional projection device example described herein does not project an idea “black” image on the screen for the following reasons.
As linearly polarized light fluxes are incident on the dichroic films, after being passed through the PBS
221
, the light flux is in part transmitted and in part reflected by the dichroic films. The s-polarized light and p-polarized light of the transmitted and reflected light fluxes are determined by a vector n normal to each dichroic film surface and a propagation vector T of the incident light flux. The vectors s of the s-polarized light is determined by s=n×T. Whenever a light flux is incident on a dichroic film in a manner such that the linear polarization plane is not in a plane defined by a line normal to the dichroic film surface and the propagation direction of the incident light, the light flux is separated into s-polarized light and p-polarized light, and a phase difference is imposed between the s-polarized light and p-polarized light. As a result, the resultant light flux typically behaves as elliptically polarized light. Hence, the light flux traveling through the PBS
221
includes light of undesirable polarization. The PBS
221
then directs the undesirable polarized light toward the screen
225
. Accordingly, an ideal black image is not projected on the screen
225
. Additionally, the contrast of the projected image is poor.
One known technique to solve the above problem has been disclosed in Japanese Unexamined Patent Publication No. 6-175123 wherein a special compensation plate is utilized to compensate for the light-flux polarization phase difference. In this technique, however, it is required to precisely control the light flux state of polarization at both the dichroic films and the compensation plate.
Another prior-art color projection device, shown in
FIG. 6
, is disclosed in Japanese Examined Patent Publication No. 5-82793. In the
FIG. 6
apparatus, a plurality of dichroic films are operable to separate a white illumination-light flux emitted from a light source into the three primary light colors of red (R), green (G), and blue (B). The separated color lights are directed to respective LCLVs that modulate the color lights. Each color light, including the modulated color light, is reflected or emitted according to signals associated with the color light. Dichroic films are used to combine the color light and the resulting combined color light is projected on a screen by a projection lens.
The prior art color projection device of
FIG. 6
includes a white illumination-light source comprising a lamp
20
and an elliptical mirror
21
. Light rays comprising the illumination-light flux emitted from the light source
20
are made substantially parallel by a collimator lens
22
. The light flux then passes through an opening
23
a,
defined by a light-interceptive plate
23
, and a filter
24
operable to allow only visible light to pass therethrough. The light flux is directed toward a polarizing beam splitter (PBS)
16
. The light flux incident on the PBS
16
is separated into s-polarized light, which is reflected by the PBS
16
, and p-polarized light which is transmitted by the PBS
16
and subsequently discarded.
The s-polarized light is separated into blue light, red light, and green light by a blue-light reflection dichroic prism
17
and a red-light reflection dichroic prism
18
. The separated color lights are routed to respective LCLVs
1
B,
1
G, and
1
R. The color lights are modulated by the LCLVs
1
B,
1
G, and
1
R to p-polarized light. Hence, each color's video signal is converted into an image that has a transmission-rate distribution at the respective LCLV. The modulated color lights are reflected from the respective LCLVs
1
B,
1
G, and
1
R, back to the corresponding dichroic prisms
17
and
18
.
The color lights are then combined by the dichroic prisms
17
and
18
and directed to the PBS
16
. The PBS
16
transmits p-polarized light (i.e., signal light
Hattori Tetsuo
Manabe Yuji
Klarquist & Sparkman, LLP
Luu Matthew
Nikon Corporation
Sajous Wesner
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