Optics: image projectors – Polarizer or interference filter
Reexamination Certificate
1998-11-19
2001-04-17
Dowling, William (Department: 2851)
Optics: image projectors
Polarizer or interference filter
C349S009000
Reexamination Certificate
active
06217173
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light source and, more particularly, to a high-efficiency polarized light source device for a liquid crystal projector.
2. Description of Prior Art
In a conventional liquid crystal (hereinafter referred to as LC) projector, the LCd is play panel is normally rectangular, but the cross-section of the projecting beam emitted from the light source is circular. Therefore, the light energy distributed in the circumferential areas is sacrificed in order to irradiate the whole LC display panel. Moreover, since an LC projector requires polarized light, half the light energy is lost while the non-polarized light emitted from the light source is being polarized.
Because of the above problems, the brightness of the display in a conventional LC projector is not sufficient for image projection. One solution is to provide a light source with a higher power. However, this causes some other problems in that this approach not only consumes much more electricity, but also generates undesirable heat that will cause further problems.
In order to overcome such problems, other optical systems have been developed in the prior art. For example, and referring to FIG. 1, U.S. Pat. No. 5,098,184 discloses an illumination system for an image projection apparatus. The illumination system comprises a radiation source
22
, a concave reflector
24
and a first and a second lens plate
26
,
28
each being provided with a matrix of lenses for forming superimposed images of the radiation source on the object to be illuminated. The first lens plate
26
and the second lens plate
28
are utilized to redistribute the light intensity. Furthermore, the shape of each lens
27
and lens
29
corresponds to the shape of the LC display panel
20
. Thus, this invention can provide a uniform brightness and efficiently make use of the light energy. However, that half the light energy is lost while converting the non-polarized light into polarized light still remains a problem.
In order to improve the efficiency of the LC projector, it is important to reduce the light energy lost while generating polarized light. A prior art entitled “Ultra-High-Efficiency LC Projector Using a Polarized Light Illuminating System” has been disclosed in SID 97 DIGEST, pp. 993 to 996, by Nakamura et al.
Referring to
FIG. 2
, the illuminating system includes a light source
30
; a reflector
31
; a first lens plate
35
; a second lens plate
38
; a polarizing beam-splitter array
140
; a plurality of half wave plates
145
; and a condenser lens
50
. The first lens plate
35
includes a plurality of rectangular lenses
36
having a geometrical shape similar to the liquid crystal panel
5
.
The second lens plate
38
includes a plurality of lenses
139
corresponding to the lenses
36
included in the first lens plate
35
.
The polarizing beam-splitter array
140
includes a plurality of beam splitters, which is placed in the rear of the second lens plate
38
for splitting and polarizing the light beams into s-polarized light beams and p-polarized light beams.
The plurality of half wave plates
145
corresponding to the polarizing beam-splitter array
140
are placed on the paths of the s-polarized light beams or the paths of the p-polarized light beams to output alight beam having the same polarization. And the condenser lens
50
projects the light beam onto the liquid crystal panel
5
.
In the illuminating system described above, the non-polarized light beam is converted into p-polarized light or s-polarized light by using a plurality of polarizing beam-splitters
140
. Each polarizing beam-splitter can optionally pass the p-polarized light or the s-polarized light. The half wave plates
145
are alternately disposed at the output of the polarizing beam-splitter. Refer to
FIG. 3
, for example, while the non-polarized light beam P+S is incident into the polarizing beam splitter
141
through the lens
139
, the p-polarized light beam P
1
is transmitted through the polarizing beam splitter
141
and the s-polarized light beam S
1
is reflected. The p-polarized light beam P
1
is then passed through the half wave plate
145
and converted into an s-polarized light beam S
2
. Thus the light beam output from the polarizing beam splitter is s-polarized light beam S
1
+S
2
. In other words, the light energy of the light source device being inputted into the polarizing beam splitter is totally converted into a light beam having the same polarization. The performance of the LC projector can be markedly raised. However, the fabrication of the illuminating system is too complex. A plurality of tiny polarizing beam splitters have to be cemented together. It is very difficult to exactly align the surfaces coated with a semi-reflecting coating for each polarizing beam splitter to be parallel with each other. Furthermore, the position of the halfwave plate has to exactly correspond to the polarizing beam splitter. That is, only one of the light beams split by the polarizing beam splitter passes through the half wave plate, while the other one does not. Moreover, the alignment of the polarizing beam splitter in the LC projector must be precise. This causes some inconvenience to make use of such an illuminating system.
SUMMARY OF THE INVENTION
Accordingly, in order to overcome the problems of the prior art, an object of the present invention is to provide a polarizing light source device for a liquid crystal projector that simplifies the fabrication and set-up of the liquid crystal projector and significantly improves its luminous efficiency.
To achieve the above object, this invention utilizes a first lens plate and a second lens plate to redistribute the light energy generated by the light source device. Furthermore, a half wave plate is utilized to make uniform the polarization of the light beams split by a beam splitter. However, in order to simplify the fabrication of the LC projector, the polarizing beam splitter mentioned above is not used in the present invention. This invention employs common polarizing beam splitting devices such as a Wallaston prism or a wedge having a polarizing semi-reflector formed thereon.
Unlike the polarizing beam splitter in the prior art, the polarizing beam-splitting device used in this invention can be placed before or after the second lens plate. That is, the configuration of the LC projector is variable.
REFERENCES:
patent: 5601351 (1997-02-01), Van Den Brandt
patent: 5764412 (1998-06-01), Suzuki et al.
patent: 5826959 (1998-10-01), Atsuchi
patent: 5865521 (1999-02-01), Hashizume et al.
patent: 5898521 (1999-04-01), Okada
patent: 6036318 (2000-03-01), Itoh
patent: 6062695 (2000-05-01), Kakuda et al.
patent: 6067193 (2000-05-01), Sekine et al.
Y. Itoh et al., “Ultra-High-Efficiency LC Projector Using a Polarized Light Illuminating System”, SID 97 Digest, 1997, pp. 993-996.
Ho Fang Chuan
Huang Junejei
Dowling William
Industrial Technology Research Institute
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