Optics: image projectors – Polarizer or interference filter
Reexamination Certificate
2001-12-27
2004-10-12
Dowling, William C. (Department: 2851)
Optics: image projectors
Polarizer or interference filter
C102S200000
Reexamination Certificate
active
06802610
ABSTRACT:
This application claims the benefit of the Korean Application No. P2000-84712 filed on Dec. 28, 2000, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image projector.
2. Background of the Related Art
The projector enlarges, and projects a small picture formed on a small display inside of the image projector by using a projection lens to a large sized screen, to display a large sized picture. In the image projector, there are a front projection type in which the picture is displayed on a front face of the screen, and a rear projection type in which the picture is displayed on a rear face of the screen. As a typical example of the latter, there is the projection television. As the small display in the image projector that displays the small picture, LCD (Liquid Crystal Display) and DMD (Digital Micromirror Device), and the like are employed. The LCD is provided with a polarized beam converter for displaying the picture by using a linearly polarized light.
FIG. 1
illustrates a related art image projector,
FIG. 2
illustrates an operation of the polarization beam sprite array in the image projector in
FIG. 1
,
FIGS. 3A and 3B
illustrate operation of the image projector in
FIG. 1
,
FIGS. 4A and 4B
illustrate operation of the polarization beam sprite prism in the image projector in
FIG. 1
, and
FIG. 5
illustrates a lamp with an elliptic reflector.
Referring to
FIG. 1
, the related art image projector is provided with a lamp
1
for emitting beams of lights, a parabolic reflector
2
for reflecting the beams to forward of the lamp
1
, and a polarized beam converter for transmitting an ‘S’ wave, and converting ‘P’ wave into ‘S’ wave and transmitting the converted ‘S’ wave among the beams from the parabolic reflector
2
.
The related art image projector also provided with first to third illumination lenses
10
,
12
, and
14
for focusing the beams polarized into a particular pole (i.e., the S wave) at the polarized beam converter, a color switch
16
for transmitting only a particular beam among the beams from the third illumination lens
14
, and a polarization beam sprite prism
18
for supplying a particular color beam from the color switch
16
to a display
22
, and the beam reflected at the display
22
to a projection lens
20
.
The display
22
displays a picture by reflecting the color beam from the polarization beam sprite prism
18
in response to a video signal, and the projection lens
20
enlarging the beam of the picture from the display
22
, and projects to a screen at a distance.
The beams of lights from the lamp
1
are incident on the polarized beam converter by the parabolic reflector
2
. The polarized beam converter transmits the S wave, and converts and transmits P wave among the beams from the parabolic reflector
2
. To do this, the polarized beam converter is provided with a first lens array
4
, a second lens array
6
, and a polarization beam sprite array
8
facing a light output surface of the second lens array
6
.
The first lens array
4
, or the second lens array
6
focuses the beams of light including the P wave and the S wave to a plurality of focusing points. To do this, the first, or second lens array
4
, or
6
has a matrix of a plurality of lenses.
The polarization beam sprite array
8
transmits ‘S’ wave, and converts the P wave into the S wave, and transmits the converted S wave, both from the second lens array
6
. To do this, the polarized beam sprite array
8
is provided with polarized beam split planes
24
and reflection planes
26
both sloped with respect to the optical output surface, and half wavelength plates
28
attached to optical output surface of the polarized beam split planes
24
as shown in FIG.
2
.
The polarized beam split plane
24
transmits only the P wave and reflects the S wave among the white beams from the second lens array
6
. The P wave transmitted through the polarized beam split plane is converted into an S wave by the half wavelength plate
28
. On the other hand, the S wave reflected at the polarized beam split plane
24
is reflected at the reflection plane
26
and forwarded as it is. That is, the entire beam of light including the P wave and the S wave passed through the polarization beam sprite array
8
is converted into the S wave.
The beam converted into the S wave at the polarized beam converter are incident on the first to third illumination lenses
10
,
12
, and
14
in succession. The first to third illumination lenses
10
,
12
, and
14
focus the beams converted into the S wave onto the color switch
16
.
The color switch
16
splits red, green, and blue colors in succession so that one display cell has red, green, and blue colors in common. To do this, the color switch
16
filters a particular color beam according to a change of a voltage signal supplied from a voltage supply part (not shown). In this instance, the color beams passed through the color switch
16
are converted into the P wave from the S wave, and incident on the polarization beam sprite prism
18
.
The P wave color beam from the color switch
16
to the polarization beam sprite prism
18
transmits a split plane
30
in the polarization beam sprite prism
18
, and incident on the display
22
.
The display
22
reflects the P wave color beam transmitted through the polarization beam sprite prism
18
according to a video signal, to produce a picture beam with picture information. In this instance, as shown in
FIG. 3A
, the P wave color beam reflected at the display
22
is converted into the S wave.
The picture beam converted into the S wave at the display
22
is reflected at the split plane
30
of the polarization beam sprite prism
18
, and directed to the projection lens
20
. To do this, the split plane
30
of the polarization beam sprite prism
18
transmits the P wave, and reflects the S wave as shown in
FIGS. 4A and 4B
. Accordingly, the polarization beam sprite prism
18
transmits the P wave from the color switch
16
, and reflects the S wave from the display
22
toward the projection lens
20
.
In the meantime, as shown in
FIG. 3B
, the display
22
transmits the P wave color beam from the polarization beam sprite prism
18
, as it is if there is an electrical signal applied thereto. Therefore, no beam of light is directed to the projection lens
20
when the electrical signal is applied to the display
22
. The projection lens
20
enlarges the picture beam from the polarization beam sprite prism
18
, and projects onto a screen at a distance therefrom.
However, the color switch
16
for splitting the color beam from the beams of lights in the related art image projector has a poor light efficiency caused by poor light transmission. For compensating such a disadvantage, a color wheel may be employed in place of the color switch
16
.
However, for employing the color wheel in the related art image projector, an optical system that converges the beam of light and an optical system that diverges the beam of light again are required, additionally.
Moreover, the polarized beam converter in the related art image projector requires lens arrays each having a plurality of lenses. However, the lens arrays with the plurality of lenses cause optical losses between the lenses. The number of the lenses in the lens arrays may be reduced for reducing the optical loss, but that increases a thickness of the polarization array to push the cost up. Moreover, since an optical conversion efficiency is significantly dependent on an alignment of the lens arrays, assembly of the image projector requires much time.
In addition to this, the related art image projector has the lamp with the parabolic reflector for providing parallel beams to the polarized beam converter. The lamp with the parabolic reflector has an optical efficiency poorer than a lamp with an elliptic reflector as shown in FIG.
5
.
The poor optical efficiency will be explained in detail assuming that a diameter of the parabolic reflector is Dp and a diameter of the e
Dowling William C.
Fleshner & Kim LLP
LG Electronics Inc.
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