Polarized light illuminator and projecting type image display

Details Polarized light illuminator and projecting type image display Polarized light illuminator and projecting type image display

1999-06-30

2002-04-16

Spyrou, Cassandra (Department: 2872)

Optical: systems and elements

Polarization without modulation

Polarizarion by dichroism

C359S485050, C362S019000, C353S020000, C349S005000, C349S009000

Reexamination Certificate

active

06373629

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a polarized-light illumination unit that illuminates a rectangular area uniformly using-polarized light whose polarization directions have been aligned. The present invention also relates to a projection-type image display unit that magnifies and projects images onto a screen by modulating polarized light emitted from the polarized-light illumination unit using a light valve.
BACKGROUND ART
Projection-type image display units using a liquid crystal panel as a light valve are excellent particularly in their small size, light weight, and ease of installation, and therefore have been forming a market rapidly as presentation tools. The projection-type image display units also are expected to become widespread in a consumer field, since they are excellent in their small size, light weight, and uniformity in image quality from the center to the periphery compared to a conventional CRT projection TV.
In the market of these projection-type image display units (hereafter referred to as “liquid crystal projectors”) using a liquid crystal panel as a light valve, there are two needs, namely the increase in luminance and the reduction in cost.
With respect to the increase in luminance, it also is conceivable to handle it by replacing a light source with one that consumes a larger amount of electricity. However, this is a temporary countermeasure. Obviously, it is most desirable to handle it by further improving the utilization efficiency of light from the light source. A conventional liquid crystal light valve can utilize only one of two polarization directions, thus wasting half of the incident light as heat. However, based on the above-mentioned backgrounds, illumination units employing a system according to Publication of Japanese Unexamined Patent Application Tokkai Hei
8-304739
or a system to which said system is applied have been developed recently, thus improving the light utilization efficiency greatly. This configuration will be described with reference to
FIG. 23
as follows.
A light source section
910
comprises a light-source lamp
911
and a reflector
912
. Randomly polarized light emitted from the lamp
911
is reflected in one direction by the reflector
912
and enters a first lens plate
920
in an integrator optical system. The first lens plate
920
is a compound lens member in which many rectangular minute lenses
921
are arranged. The light that has entered there is gathered by respective minute lenses
921
. Illuminant images are formed on a second lens plate
930
by the minute lenses
921
. The second lens plate
930
comprises a condenser-lens array
931
that is placed in the vicinity of the position where the illuminant images are formed, a polarization-separation prism array
933
formed of an aggregate of polarization beam splitters
934
, a &lgr;/2 phase-difference plate
935
, and a lens
937
at the outgoing side. The illuminant images are formed on the array
931
by respective minute lenses
921
in the first lens plate
920
. Then, a ray of light is separated by the polarization beam splitters
934
depending on its polarization direction. The polarization directions of the rays of light that have been separated are aligned by the &lgr;/2 phase-difference plate
935
. After that, the rays of light pass through the lens
937
and illuminate an illumination area
940
. Thus, the polarization directions of the randomly polarized light from the light-source lamp
911
can be aligned efficiently.
On the other hand, with respect to the reduction in cost, in order to reduce the cost of the liquid crystal panel, which has the highest proportion of cost in the entire costs, the effort for decreasing a panel size has been made. Concretely, the cost reduction is targeted by increasing the number of panels obtained at one time through changing panels with a diagonal length of 1.3 inches, which were the conventional majority, into those with a diagonal length of 0.9 inch and further into those with a diagonal length of 0.5 inch.
However, when seeking to maintain the same resolution as that in a conventional unit while decreasing panel size, damping of light increases in an effective image display area on a panel. Particularly, when a transmission light valve is used, apertures of pixels are decreased in size considerably, thus decreasing light transmittance.
As described above, the high luminance and the low costs have been very difficult to attain at the same time. Methods for tackling this include a method of improving an apparent numerical aperture by providing microlenses for respective pixels on a panel with a decreased size. In this method, however, the microlenses narrow down incident light once, but then a ray of light spreads. Therefore, an illumination unit that can provide light with a small spread angle, in other words, with a large illumination f-number, as incident light is required.
On the other hand, when actually manufacturing products using the method in the Publication of Japanese Unexamined Patent Application Tokkai Hei 8-304739, it is advantageous in practice to form the polarization beam splitters
934
using prisms with a parallelogramatic cross-sectional shape. Therefore, the prisms with this shape are mounted in current products. Further, in order to process the prisms at low cost, it is desirable that all the aforementioned polarization beam splitters
934
have the same thickness in the direction of the system optical axis
952
(a distance between two opposed planes orthogonal to the system optical axis). As a result, all the prisms forming the polarization beam splitters have the same shape. Consequently, when the shape of the prisms is designed to correspond to the biggest illuminant image in the vicinity of the central portion (in the vicinity of the system optical axis) in the illuminant images formed on the condenser lens array
931
, the prisms have a useless portion for relatively small illuminant images formed at the periphery. Therefore, the second lens plate
930
itself is increased in size, and thus illumination light comes to have a small illumination f-number and a wide incidence angle, which has been a problem.
Thus, in the conventional technique, high luminance and the low costs have been difficult to attain at the same time.
DISCLOSURE OF THE INVENTION
The present invention seeks to solve the above-mentioned conventional problems. It is an object of the present invention to provide a polarized-light illumination unit in which illumination light spreads a little (the illumination f-number is large) and the polarization directions of randomly polarized light from a light source can be converted to a desired polarization direction.
It is another object of the present invention to provide a low-cost pojection-type image display unit that has high light utilization efficiency thus enables images with high luminance to be obtained.
In order to attain the above-mentioned objects, the present invention employs the following configurations.
A polarized-light illumination unit according to a first configuration of the present invention comprises: a light source for emitting randomly polarized light; an integrator optical system having a first lens plate formed of an aggregate of a plurality of rectangular lenses, a second lens plate formed of an aggregate of a plurality of minute lenses corresponding to the rectangular lenses one to one, and a condenser lens; a polarization separation section for separating the light emitted from the light source into two polarized lights whose polarization directions are orthogonal to each other and whose optical axes are substantially parallel to each other; and a polarization conversion section for aligning the polarization directions of the two polarized lights. The respective rectangular lenses are formed to have shifted centers of aperture and curvature so that illuminant images are formed in a plurality of rows on the second lens plate by the rectangular lenses in the first lens plate. The minute lenses in the second lens plate are arrang

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