Optics: image projectors – Unitary plural refracting surfaces
Reexamination Certificate
2000-08-03
2002-12-24
Adams, Russell (Department: 2851)
Optics: image projectors
Unitary plural refracting surfaces
C353S020000, C353S031000, C353S033000, C353S034000, C353S037000, C349S005000, C349S007000, C349S008000, C349S009000
Reexamination Certificate
active
06497488
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an illumination system suitable to illuminate a rectangular object to be projected such as a liquid crystal panel, a liquid crystal projector using this illumination system, and a projector using an image forming member such as a reflection-type liquid crystal panel and a dichroic prism alone having a function as a color separation/combination device.
2. Description of the Related Art
For example, Japanese Laid-Open Patent Application No. 3-11806 discloses an integrator optical system having a combination of two sets of lens arrays as an illuminating optical system for uniformly illuminating a rectangular object to be projected such as a liquid crystal panel.
In the integrator optical system, a light flux from a light source is separated by a plurality of rectangular condenser lenses constituting a first lens array so as to form secondary light source images, which then superposedly form images on a same object to be projected through a second lens array having a plurality of condenser lenses corresponding to the plurality of condenser lenses of the first lens array. They say that, by such an integrator optical system, utilization efficiency of the light from the light source is improved, and, also, it is possible to make uniform an intensity distribution on the object to: be projected. In particular, by forming each condenser lens of the first and second lens arrays to have a rectangular shape having an aspect ratio of 4:3, for example, corresponding to the aspect ratio of the rectangular object to be projected, it is possible to improve the light utilization efficiency and make uniform the intensity distribution.
On the other hand, a liquid crystal projector using a liquid crystal panel of a type of modulating a polarized light can use only one type of a polarized light of a P-polarized component and a S-polarized component. Thereby, when a light source emits a random polarized light, approximately a half the light from the light source is not used. Accordingly, the light utilization efficiency is bad. In order to improve the light utilization efficiency, various types of polarization transformation arrangements have been proposed.
The principle thereof will now be described. After a random polarized light is separated into two orthogonal polarized components (P-polarized component and S-polarized component), one thereof is rotated by 90 degrees through a ½ phase plate or the like so as to be one having the same polarization direction as that of the other, and the optical axes of both are made coincident. Accordingly, for example, a polarization beam splitter and a rectangular prism are both provided, and a ½ phase plate is disposed on the light emitting side of the polarization beam splitter or rectangular prism. By such a polarization transformation optical system arrangement, the polarized directions can be made coincident. Japanese Laid-Open Patent Application No. 7-294906 discloses an arrangement in which light from a light source is converged onto an operation surface (dielectric multi-layer film of 45°) of the polarization beam splitter through a lens plate in order to improve a transformation efficiency in this case.
However, in an arrangement in which simply a polarization beam splitter and a rectangular prism are provided together, the lateral width or longitudinal width of the entire poetical system is approximately doubled, and, therefore, a projection lens having a small F number and a very large aperture or diameter should be used. In order to solve this problem, Japanese Laid-Open Patent Application 8-304739 discloses an example of arrangement in which the integrator optical systems disclosed in Japanese Laid-Open Patent Application 3-11806 are combined. There, in summary, a plurality of minute light fluxes (secondary light-source images) are formed through a first lens array consisting of a plurality of minute rectangular condenser lenses, these light fluxes are separated into P-polarized components and S-polarized components having different polarization directions, then, the polarized components of one polarization direction are rotated so that the polarization planes thereof are made coincident, and the thus-obtained light fluxes are emitted. That is, as a result of separating of polarized light being performed by utilizing a process of generating of minute secondary light-source images which is a feature of the integrator optical system, it is possible to control spatial expansion of light paths due to separation of the polarized light.
Further, Japanese Laid-Open Patent Application No. 10-161065 discloses to condense parallel light from a light source through a convex lens, then, transform the light into parallel light again, and, thereby, to make the beam diameter approximately half, and direct it to a polarization transformation arrangement. Thereby, the polarization transformation arrangement and integrator optical system can be substantially miniaturized.
However, these arrangements have problems in that the arrangement of the integrator optical system is complex and thereby difficult to be manufactured, efficiency in polarization alignment is not sufficient, and so forth.
For example, with regard to the integrator optical system, each of the first and second lens arrays should be formed to a special shape having many lens elements to the amount of m×n pieces like a two-dimensional array. Therefore, it is difficult to make them. Further, it is not easy to manufacture them correspond to the aspect ratio such as 4:3 of a liquid crystal panel.
Further, when, as disclosed in Japanese Laid-Open Patent Application No. 8-304739, a polarization aligning arrangement is disposed subsequent to the second lens array in order to make polarization directions coincident, the second lens array condenses light two-dimensionally (not only in the width direction of the polarization beam splitters but also in the longitudinal direction, being separated into a plurality of divisions) although polarization beam splitters and so forth of the polarization aligning arrangement are formed to be like an array. Therefore, the power in the condensing part is large and the load (stress) on the polarization beam splitters is large. Furthermore, it is difficult to make an arrangement such that correspondence is secured between the polarization beam splitter row, total reflection mirror row and one array of the second lens array.
Generally, there are various types of projectors. For example, in comparison to using a transmission-type liquid crystal panel, by using a reflection-type liquid crystal panel, it is easy to obtain high resolution and high luminance, and, also, it is possible to use a single optical component both as a color separating component and a color combining component, thereby miniaturization thereof being able to be achieved.
When such a reflection-type liquid crystal panel is used in a projector, a polarization beam splitter and a dichroic mirror as a color separation/color combining component disposed on incident and emitted light paths are used, color separation of light from a light source and color combination of modulated light reflected by the reflection-type liquid-crystal panels for respective colors are performed, the thus-obtained light is incident on a projection lens system so that a projected color image is obtained, as disclosed in Japanese Laid-Open Patent Application No. 3-249639.
FIG. 1
shows a proposed example of a liquid crystal projector using such a basic idea using reflection-type liquid-crystal panels. This liquid crystal projector includes a light source
101
, an illumination system
102
, a total reflection prism
103
, a connection prism
104
, a polarization beam splitter
105
, a color separation/color combination component
106
, three reflection-type liquid crystal panels
107
R,
107
G and
107
B, and a condenser lens
108
for each of the reflection-type liquid crystal panels
107
R,
107
G and
107
B. The light s
Kameyama Kenji
Miyagaki Kazuya
Takiguchi Yasuyuki
Yamauchi Satoshi
Adams Russell
Koval Melissa J
Ricoh & Company, Ltd.
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