Optical system of liquid crystal projector

Details Optical system of liquid crystal projector Optical system of liquid crystal projector

2001-11-30

2003-10-28

Fuller, Rodney (Department: 2851)

Optics: image projectors

Composite projected image

Multicolor picture

C353S020000, C353S081000, C349S009000

Reexamination Certificate

active

06637891

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal projector, and more particularly, to an optical system for a liquid crystal projector enabling to minimize a size of the optical system and a count of optical parts constructing the optical system using three pieces of reflective type liquid crystal displays.
2. Background of the Related Art
Lately, a projector, which magnifies and projects a small image to a large screen, attracts attention as a flat display enabling to realize a large-sized screen with a slim design instead of a cathode ray tube having a large volume and a limited screen size. The projector as a display constructing a small screen image uses a cathode ray tube or a liquid crystal display(hereinafter abbreviated LCD), and particularly, a liquid crystal projector using LCD prevails for the trend of slim size. The liquid crystal projector generally uses a backlit or reflective LCD. Such a liquid crystal display has been developed on the basis of small size, lightness, and high brightness, while an LCD panel has been developed on the basis of high opening ratio and high resolution. In order to cope with the trends of the liquid crystal projector such as high resolution, small size, and low price, a reflective type LCD panel is widely used for the liquid crystal projector.
The liquid crystal projector realizes an image on an LCD panel using light emitted from a light source and images a video pf the LCD panel on a screen using a projecting optical system, whereby the video imaged on the screen is appreciated. When the projector is constructed in a manner that the image of the LCD panel is directly projected to a rear screen, a projection distance between the screen and the projecting optical system should be provided so that a sufficient space behind the screen is essential. Hence, the projector becomes thickened so as to make it difficult to reduce the volume of the projector. In order to settle such a problem, a total reflection mirror is inserted between the screen and projecting optical system so as to fold a light path. Thus, a thickness of the projector is reduced. Although it is also able to reduce the thickness of the projector further by decreasing an arranged angle of the total reflection mirror, there is a limit to reduce the arranged angle of the total reflection mirror and the projecting optical system so as to project the image on the rear screen without distortion. Besides, there is a limitation to reducing the thickness of the optical system including an illumination system, LCD, and a projecting lens system due to the natural span length of the system itself.
FIG. 1
illustrates a diagram of an optical system for a liquid crystal projector according to a related art.
Referring to
FIG. 1
, a liquid crystal projector according to a related art includes first and second fly eye lenses (hereinafter abbreviated FEL)
6
and
8
arranged between a light source
4
and a total reflection mirror
14
, a polarizing beam split array(hereinafter abbreviated PBS array)
10
, a first light-concentrating lens
12
, and a second light-concentrating lens
16
arranged between the total reflection mirror
14
and a first dichroic mirror
18
. A white light irradiated from a lamp of the light source
4
is reflected by an elliptical mirror so as to proceed toward the first FEL
6
. The first FEL
6
divides the incident light into cell units so as to be focused on the respective lens cells of the second FEL
8
. The second FEL
6
transforms the incident light into the parallel light in parallel with a specific part so as to transmit toward the PBS array. The PBS array
10
separates the incident light into linear polarized lights having specific optical axes respectively, i.e. a P polarized light and an S polarized light, and a ½ wavelength plate(not shown in the drawing) attached to a rear of the PBS array
10
in part transforms the transmitted P polarized light into the S polarized light. Hence, the incident light is entirely transformed into the S polarized light by the PBS array
10
so that the light irradiated from the light source
4
becomes incident on liquid crystal panels
26
R,
26
G, and
26
B mostly. The first light-concentrating lens
12
concentrates the incident light from the PBS array
10
on the total reflection mirror
14
, and the total reflection mirror
14
totally reflects the incident light from the first light-concentrating lens
12
so as to make the reflected light proceed toward the second light-concentrating lens
16
. The second light-concentrating lens
16
concentrates the incident light from the total reflection mirror
14
upon the first dichroic mirror
18
. The first dichroic mirror
18
transmits a blue area of the incident light as well as reflects green and red areas of the incident light of which wavelengths are longer than that of the blue light.
The optical system for the liquid crystal projector includes a second dichroic mirror
20
arranged between the first dichroic mirror
18
and the red liquid crystal panel
26
R, a first polarizing film
22
R, a first polarizing beam split prism (hereinafter abbreviated PBSP)
24
R, a second polarizing film
22
G and a second PBSP
24
G arranged between the second dichroic mirror
20
and the green liquid crystal panel
26
G, a first relay lens
27
arranged between the first dichroic mirror
18
and the blue liquid crystal panel
26
B, a second total reflection lens
28
, a second relay lens
29
, a third polarizing film
22
B, a third PBSP
24
B, a dichroic prism
30
arranged between the first to third PBSPs
24
R,
24
G, and
24
B, and a projecting lens
32
installed to confront a light-projecting surface of the dichroic prism
30
. The second dichroic mirror
20
reflects a green region light of the incident light reflected on the first dichroic mirror
18
so as to make the reflected green region light proceed toward the second polarizing film
22
G and transmits a red region light to proceed toward the first polarizing film
22
R. The second total reflection mirror
28
reflects an incident blue region light transmitted through the first dichroic mirror
18
to proceed toward the third polarizing film
22
B. In this case, the first and second relay lens
27
and
29
as field lenses relay an imaging point of the blue region light so as to make the imaging point re-imaged on the blue liquid crystal panel
26
B. The first to third polarizing films
22
R,
22
G, and
22
B transmit just the S polarized lights in parallel with the corresponding optical axes of the polarizing films to make the S polarized lights proceed to the first to third PBSPs
24
R,
24
G, and
24
B, respectively. The first to third PBSPs
24
R,
24
G, and
24
B reflect the red, green, and blue S polarized lights, which are transmitted through the first to third polarized films
22
R,
22
G, and
22
B and then become incident, to proceed toward the red, green, and blue liquid crystal panels
26
R,
26
G, and
26
B, respectively. Moreover, the first to third PBSPs
24
R,
24
G, and
24
B acquires image information from the red, green, and blue liquid crystal panels
26
R,
26
G, and
26
B respectively so as to transmit the red, green, and blue lights transformed into the P polarized lights to proceed toward the dichroic prism
30
. The red, green, and blue liquid crystal panels
26
R,
26
G, and
26
B as reflective type liquid crystal panels transform the incident S polarized lights reflected upon the first to third PBSPs
24
R,
24
G, and
24
B into the P polarized lights respectively in accordance with the image signal, thereby realizing an image. The dichroic prism
30
composes the incident red, green, and blue lights by acquiring the image information form the red, green, and blue liquid crystal panels
26
R,
26
G, and
26
B respectively so as to project the composed light through the projecting surface toward the projecting lens
32
. First and second polarizing transform films(not shown in the drawing) are arranged between the first and

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