Optics: image projectors – Unitary plural refracting surfaces
Reexamination Certificate
2000-06-01
2002-05-14
Dowling, William (Department: 2851)
Optics: image projectors
Unitary plural refracting surfaces
C353S102000
Reexamination Certificate
active
06386709
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a display unit for projecting a small-sized display element on an enlarged scale, such as a liquid crystal projector.
2. Description of the Related Art
FIG. 14
shows an optical system of a liquid crystal projector in a related art. A light pencil emitted from a lamp
1
is reflected by a reflecting mirror
2
to form a roughly collimated light pencil
3
. This collimated light pencil
3
is incident on a multilens array A
4
and is divided into a plurality of light pencils. The provided light pencils are incident on a corresponding multilens array B
5
and guide to a polarization conversion element
6
for making polarized light uniform. The light pencil with the polarized light made uniform is emitted through a condenser
7
as a condensed light pencil. The light pencil emitted through the condenser
7
changes in direction 90 degrees through a lens
8
and is incident on a dichroic mirror
20
. The dichroic mirror
20
allows red light to pass through and reflects blue light and green light. The passing-through red light has an optical path bent through a reflecting mirror
22
, undergoes a light beam angle correction through a collimator lens
9
R, and illuminates a liquid crystal panel
10
R. The green light and blue light reflected by the dichroic mirror
20
are incident on a dichroic mirror
21
, which then reflects the green light and allows the blue light to pass through. The reflected green light undergoes a light beam angle correction through a collimator lens
9
G and illuminates a liquid crystal panel
10
G. The blue light passing through the dichroic mirror
21
has an optical path bent through a reflecting mirror
23
, passes though a lens
18
, and again has an optical path bent through a reflecting mirror
24
. Then, the blue light passes through a collimator lens
9
B and illuminates a liquid crystal panel
10
B.
The liquid crystal panel
10
R modulates the projected light by a red video signal and displays an image. Thus, the light is allowed to pass through or is shielded selectively on the liquid crystal panel. The passing-through light is incident on a dichroic prism
11
, has an optical path bent by a reflection face
11
R, and is incident on a projection lens
12
. The liquid crystal panel
10
G modulates the projected light by a green video signal and the light passing through the liquid crystal panel
10
G is incident on the dichroic prism
11
and is incident on the projection lens
12
as it is. Likewise, the light incident on the liquid crystal panel
10
B is incident on the dichroic prism
11
, has an optical path bent by a reflection face
11
B, and is incident on the projection lens
12
. The red light, green light, and blue light incident on the projection lens
12
are combined and projected on an enlarged scale as a full-color image.
FIG. 15
shows a part of the optical path of the projection display unit in the related art.
FIG. 15
shows a state in which the optical path from the lamp
1
through the liquid crystal panel
10
G to the projection lens
12
is extracted from the optical path in FIG.
14
and is aligned on a line without showing the mirrors for changing the light beam directions. However, the dichroic prism
11
is not shown.
The light pencil emitted from the lamp
1
is reflected by the reflecting mirror
2
to form the collimated light pencil
3
. The collimated light pencil
3
is divided into a plurality of light pencils through the multilens array A
4
for narrowing the light pencil toward the corresponding multilens array B
5
. The multilens array B
5
has a role of maintaining the corresponding multilens array A
4
and the display element
10
in conjugate relation. The light pencils passing through the multilens array B
5
are incident on the polarization conversion element
6
and are divided into two linearly polarized light pencils orthogonal to each other. One of the light pencils rotates the vibration face of the polarized light 90 degrees by means of a phase difference plate
13
disposed on the emission face of the polarization conversion element
6
. Therefore, all light incident on the condenser
7
becomes linearly polarized light with the vibration face made uniform. The condenser
7
has a role of superposing images of the multilens array A
4
formed on the multilens array B
5
on the display element
10
. The collimator lens
9
before the display element
10
has a role of making even incidence angles of light beams in the display element
10
plane.
In
FIG. 15
, attention is focused on a light beam angle
14
toward the center of the display element
10
. The magnitude of the light beam angle
14
is almost inversely proportional to the distance from the condenser
7
to the display element and is almost proportional to the light pencil diameter passing through the condenser
7
. Since the light passing through the display element
10
is input to the projection lens
12
and is projected on an enlarged scale, the light incidence angle
14
on the display element
10
needs to be made equal to an input angle
19
to the projection lens
12
.
The projection display unit in the related art is thus configured, wherein the projection lens
12
is limited by the magnitude of the input angle
19
and the outer dimensions of projection lens
12
are determined. The characteristics of the resolution, distortion of a projection screen, and uniformity of brightness in a projection screen, performance proper to the projection lens
12
make it difficult to design and manufacture as the input angle
19
grows; this is a problem.
Further, if the length from the condenser
7
to the display element
10
is lengthened, as shown in
FIG. 16
, to lessen the light beam angle
14
or the input angle
19
, the placement space of the parts needs to be taken larger than that in FIG.
15
and thus the outside shape of the projection display unit becomes large; this is a problem.
Alternatively, if a method of lessening the light pencil diameter passing through the condenser
7
for lessening the light beam angle
14
or the input angle
19
is adopted as shown in
FIG. 17
, the following problems arise: A sufficient amount of light does not arrive at the display element
10
, heat is generated due to light lost by lessening the light pencil diameter, stray light is produced due to scattering of light, etc.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a small-sized system comprising a lens for correcting a light pencil incident on a display element or the light beam angle of the light pencil. It is another object of the invention to provide a system good in light use efficiency by placing the numbers of lens cells and the lens cell sizes of two multilens arrays used with a projection display unit in appropriate relationship.
In order to achieve the above objects, according to a first aspect of the invention, there is provided a projection display unit comprising: a light source for projecting an image; a reflecting mirror for reflecting a light pencil emitted from the light source; a first multilens array for dividing a light pencil gathered by the reflecting mirror into a plurality of light pencils; a second multilens array for forming an image of light pencil emitted from the first multilens array; a polarization conversion element for converting light pencils in an irregular polarization state emitted from the second multi lens array into linearly polarized light; a condenser having positive power for superposing the light pencils provided through the second multilens array; a collimator lens having positive power for correcting the angle of a light beam; a display element for forming an image by electric modulation; a projection lens for enlarging and projecting the image formed on the display element; and a correction lens being disposed between the condenser and the collimator lens for correcting a light pencil incident on the display element.
According to a second aspect of the invention, there is provided a
Dowling William
Mitsubishi Denki & Kabushiki Kaisha
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