Optics: image projectors – Prism in light path
Reexamination Certificate
1997-05-14
2001-08-21
Dowling, William (Department: 2851)
Optics: image projectors
Prism in light path
C353S038000
Reexamination Certificate
active
06276803
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention relates to optical path converting optical elements, optical converters, as well as optical projectors and image display apparatuses using such optical elements.
b) Related Art
(First example)
A structure of an example of a liquid crystal projector
1
is shown in FIG.
1
. This liquid crystal projector
1
employs an integrator lens
5
to provide a uniform luminance distribution. The principle of this luminance distribution adjustment is shown in FIGS.
2
(
a
) to
2
(
c
).
This liquid crystal projector
1
is constructed as follows. An integrator lens (lens array)
5
, a field lens
6
, and a condenser lens
7
are arranged ahead of a subsurface illuminator
4
that is constructed of a lamp
2
and a parabolic reflector
3
. A liquid crystal display panel
8
is arranged ahead of the condenser lens
7
, and a projector lens
10
is arranged ahead of the liquid crystal display panel
8
.
Thus, in the liquid crystal projector
1
that is constructed as shown in
FIG. 1
, light rays r that have been injected rearward from the lamp
2
and reflected by the reflector
3
enter into the integrator lens
5
as substantially parallel rays. As shown in FIG.
2
(
b
), a luminous intensity distribution in a direction (X-axis direction) perpendicular to the optical axis of the light rays r before entering into the integrator lens
5
becomes maximum on the optical axis and drastically reduces as the light rays deviates from the optical axis. That is, it is bright in the middle and dark in the periphery. The field lens
6
is arranged slightly ahead of the focal points of the respective lens element regions of the integrator lens
5
, and the condenser lens
7
is arranged at the focal point of the field lens
6
. As a result, the light rays r that have passed through the respective lens element regions of the integrator lens
5
are condensed by the respective lens element regions of the integrator lens
5
, then enter into the field lens
6
as dispersed light rays, and are irradiated onto the entire part of the condenser lens
7
as shown in FIG.
2
(
a
). Then, the light rays r that have been collimated by the condenser lens
7
pass through the liquid crystal display panel
8
, and an image generated by the liquid crystal display panel
8
is projected onto a screen
11
via the projector lens
10
.
Since the light rays r having different luminous intensities which have passed through the different lens element regions of the integrator lens
5
are synthesized by the condenser lens
7
this way, the light rays r having an ununiform luminous intensity distribution are converted into light rays having a uniform luminous intensity distribution by passing through the optical system including the integrator lens
5
, the field lens
6
, and the condenser lens
7
as shown in FIG.
2
(
c
), and thereafter enter into the liquid crystal display panel
8
. As a result, the luminance distribution of an image projected onto the screen
11
becomes also uniform.
(Second example)
FIG. 3
shows an example of an image display apparatus
16
which uses a microlens to improve luminance. As shown in
FIG. 3
, this image display apparatus
16
has a microlens array
17
arranged so as to confront the liquid crystal display panel
8
. The liquid crystal display panel
8
is formed by sealing a liquid crystal material
23
between a glass substrate
21
and a glass substrate
22
. The glass substrate
21
has a black matrix region
19
having wirings and the like for driving TFTs
18
, transparent electrodes
20
, and the like formed thereon. The glass substrate
22
has a total surface common electrode formed thereon. The transparent electrode (
20
) portions surrounded by the black matrix region
19
serves as pixel holes
24
. Lenses
25
forming the microlens array
17
are arranged so as to confront the pixel holes
24
, respectively.
Thus, if the microlens array
17
is not employed, part of light rays r that have entered into the liquid crystal display panel
8
are shielded by the black matrix region
19
as shown in FIG.
4
. Therefore, light utilization efficiency is reduced, which in turn reduces the luminance of the image display apparatus
16
. In contrast thereto, if the microlens array
17
is employed, light rays r that have entered into the respective lenses
25
of the microlens array
17
are condensed onto the respective pixel holes
24
of the liquid crystal display panel
8
as shown in FIG.
5
. That is, all the light rays having entered into the liquid crystal display panel
8
can be transmitted through the pixel holes
24
. As a result, light utilization efficiency can be improved by utilizing the microlens array
17
, and the luminance of the image display apparatus
16
can be improved.
In view of the aforementioned examples, it is conceivable to manufacture an image display apparatus
16
having a high luminance distribution as well as a uniform luminance distribution if the microlens array
17
is interposed between the optical system and the liquid crystal display panel
8
such as shown in FIG.
2
(
a
).
However, when the optical system constructed of the integrator lens
5
, the field lens
6
, and the condenser lens
7
is used, the diffusing angle &thgr; of the light that has passed through the condenser lens
7
becomes wide (see FIG.
2
(
a
)). Therefore, light rays r such as indicated by broken lines in
FIG. 5
are shielded by the black matrix region
19
, so that the light rays cannot be condensed onto the pixel holes
24
by the microlens array
17
effectively.
Moreover, if the optical system such as shown in FIG.
2
(
a
) is employed, the optical system becomes complicated. Since the field lens
6
must be arranged, the image display apparatus
16
becomes expensive.
SUMMARY OF THE INVENTION
The present invention has been made in view of the aforementioned circumstances. An object of the present invention is therefore to provide an optical element that can make luminous intensity distribution uniform without increasing the light diffusing angle. Another object of the present invention is to propose important applications using such optical element.
An optical path converting optical element is characterized by comprising two prism arrays, each prism array having a plurality of prisms arrayed thereon, both prism arrays being disposed in such a manner that prism arraying directions thereof are substantially parallel to each other.
A mode of embodiment is characterized in that in the optical path converting optical element the two prism arrays are formed on front and back surfaces of a plate.
A mode of embodiment is characterized in that in the optical path converting optical element a shape of a prism array disposed on a light entering side and a refractive index of the plate are set in such a manner that a light ray whose optical path has been converted by the prism array disposed on the light entering side is totally reflected on a side surface of the plate.
A mode of embodiment is characterized in that in the optical path converting optical element one of the prism arrays is constructed of an interface between a first portion having a first refractive index and a second portion having a second refractive index; and the other prism array is constructed of a surface of the second portion.
A mode of embodiment is characterized in that in the optical path converting optical element a shape of a prism array disposed on a light entering side and a refractive index of the second portion are set in such a manner that a light ray whose optical path has been converted by the prism array disposed on the light entering side is totally reflected on a side surface of the second portion.
A mode of embodiment is characterized in that in the optical path converting optical element two plates are included, each plate having one surface thereof being flat and the other surface being formed into the prism array; a flat surface side of one of the plates is arranged so as to confront a prism array side o
Aoyama Shigeru
Kitajima Hiroshi
Shinohara Masayuki
Yamashita Tsukasa
Dowling William
Foley & Lardner
Omron Corporation
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