Optical: systems and elements – Polarization without modulation – Polarizarion by dichroism
Reexamination Certificate
1999-11-30
2002-06-11
Chang, Audrey (Department: 2872)
Optical: systems and elements
Polarization without modulation
Polarizarion by dichroism
C359S292000, C359S301000, C359S586000, C359S587000, C359S589000, C359S629000, C359S634000, C359S638000, C359S640000, C359S833000, C359S834000, C359S835000, C359S836000, C359S837000
Reexamination Certificate
active
06404552
ABSTRACT:
This application claims the benefit of Japanese Application No.10-339759 which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a full-color projection type display device having such a construction that reflection type light valves for R-, G- and B-light beams are disposed, beams of polarized light in individual colors which enter the respective light bulbs are modulated and exit, the modulated beams of light assuming the respective colors from the light valves are synthesized of colors, an analyzing optical system analyzes and takes out the synthesized beams of light, and the analyzed beams of light are projected through a projection lens, and more particularly to a projection type display device capable of reducing a projection of a ghost image.
2. Related Background Art
What is known as a prior art projection type display device is a full-color projection type display device disclosed in, e.g., Japanese Patent Application Publication No.2505758.
FIG. 18
shows the projection type display device disclosed in
FIG. 1
of the above Patent Application Publication, and this display device will hereinafter be briefly explained.
Light beams emitted from a light source
23
travel through a shaping lens
22
, then are converted into. substantially collimated beams of light and enter a polarization beam splitter
21
. The light source beams entering the polarization beam splitter
21
are separated in polarization into beams of S-polarized light reflected by a polarization separator of the polarization beam splitter, and beams of P-polarized light penetrating through this polarization separator. The former beams of S-polarized light exit from the polarization beam splitter
21
and enter a color separating/synthesizing composite prism constructed of prisms
11
A,
11
B,
11
C. Note that in this color separating/synthesizing composite prism, a surface
11
e
of the prism
11
A is formed with a B-light reflection dichroic film, and a bonded surface between the prisms
11
B and
11
C is formed with an R-light reflection dichroic film. Further, an air gap is formed between the prisms
11
A and
11
B.
The light beams entering the prism
11
A from the surface
11
a
travel through the prism, then impinge upon the B-light reflection dichroic film formed on the surface
11
e
, and are separated of colors into beams of B-light reflected therefrom and mixed beams of R- and G-light penetrating through the B-light reflection dichroic film, entering the prism
11
B and traveling therethrough. The beams of B-light reflected by this film travel through the prism
11
A, then are totally reflected by the surface
11
a
, further travel and exit from an outgoing surface
11
b
. Subsequently, the beams of B-light enter a B-light oriented reflection light valve
12
disposed in the vicinity of the outgoing surface. On the other hand, the mixed beams of R- and G-light having penetrated therethrough are incident upon the R-light reflection dichroic film. The beams of R-light reflected from this film travel through the prism
11
B, then are totally reflected by an incident surface of the prism
11
B, subsequently exit from an outgoing surface
11
C and enter the R-light oriented light valve
13
. The beams of G-light having traveled through the prism
11
C travel further as they are, then exit from a surface
11
d
, and enter the G-light oriented light valve
14
.
The beams of S-polarized light entering the respective color light oriented light valves receive modulating action by color signals and are thereby converted into beams of P-polarized light. Then, the light beams are reflected and exit as mixed beams of light of the thus modulated P-polarized light defined as the modulated light and the S-polarized light defined as the non-modulated light. The mixed beams of light exiting from the respective color light oriented light valves travel back along the above light paths, and exit as the color-synthesized beams of light from the surface
11
a
of the prism
11
A. The color-synthesized beams of light are again made incident upon the polarization beam splitter
21
, whereby only the P-polarized light as the modulated light is analyzed and taken out as the light of transmission through the polarization beam splitter. The color-synthesized light beams which have been analyzed enter the projection lens
24
, thereby forming a desired full-color projected image on a screen
25
.
In the projection type display device described above, however, it has proven that there might be a case where a ghost image is formed on the screen.
What has hitherto been known as a method of preventing the ghost image from appearing in the projected image on the projection type display device using the reflection type light valves may be a method disclosed in Japanese Patent Application Laid-Open Publication No.5-93887. A quarter-wave phase plate is disposed on the light path between the polarization beam splitter and the projection lens, the light beams among the projected beams of light entering the projection lens, which are reflected from the surfaces of some lens elements constituting the projection lens and travel back, are again incident on the light valves and reflected therefrom, and the ghost image is formed when these reflected beams of light reenter the projection lens. The above method was contrived to prevent this ghost image from being thus formed. Namely, the light beams conceived as a cause of the ghost image pass through the quarter-wave phase plate twice, thereby changing oscillating directions of the polarization thereof. With this being utilized, the light beams of the cause are cast away by the polarization beam splitter before reentering the light valves.
The ghost image described above could not, however, be prevented by disposing the quarter-wave phase plate between the projection lens and the polarization beam splitter. That is, in the projection type display device described above, the reflected light beams from the surfaces of the constructive lens elements of the projection lens are not the cause of the ghost image.
As a result of having studied the ghost image that occurred on the projection type display device and pursued the cause thereof, the present inventor has discovered that factors which will hereinafter be mentioned may be principal causes for forming the ghost image.
(1) The light beams, entering the prism member
11
A, of the beams of S-polarized light exiting from the S-polarized light outgoing surface of the polarization beam splitter
21
of the projection type display device disclosed in the example of the prior art, partially receive the reflecting action from the incident surface
11
a
of the prism member
11
A, thus travel back, then enter the polarization beam splitter
21
, penetrate through a polarization separator, then enter the projection lens, and are projected as the ghost image.
(2) The beams of S-polarized light separated in polarization by the polarization beam splitter
21
are partially reflected by the S-polarized light outgoing surface, thus travel back, then penetrate through the polarization separator, and are projected as the ghost image:
(3) The beams of P-polarized light entering the polarization beam splitter, separated in polarization by the polarization separator and penetrating therethrough, are partially reflected by the P-polarized light outgoing surface, thus travel back, reflected by the polarization separator etc., then travel further, fall upon the projection lens, and are projected as the ghost image.
As explained above, it has proven that the cause of the ghost image is not single, and the ghost image is formed due to a plurality of factors overlapped.
For eliminating those causes, to start with, it might be considered that the reflected light be reduced by forming anti-reflection films on both of the polarization outgoing surfaces of the polarization beam splitter.
Based on this method, however, though capable of reducing the reflected light to some extent, it is im
Chang Audrey
Curtis Craig
Miles & Stockbridge P.C.
Nikon Corporation
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