Optics: image projectors – Unitary plural refracting surfaces
Reexamination Certificate
1999-12-22
2001-08-14
Dowling, William (Department: 2851)
Optics: image projectors
Unitary plural refracting surfaces
C353S020000
Reexamination Certificate
active
06273569
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an illuminating optical system for virtually superimposing partial light beams onto the same illumination area after separating light emitted from a light source into partial light beams. In addition, the present invention relates to a projector which can display a uniform and bright image using the illuminating optical system.
2. Description of Related Art
In the projector, illuminating light shed upon an electro-optical device called a light valve is modulated in accordance with information of an image which one wants to display, and the modulated light is projected onto a screen to display the image. It is preferable that the image displayed by such a projector be uniform and bright, and that the efficiency with which light is used by the illuminating optical system applied to the projector be high.
As electro-optical devices, liquid crystal panels (liquid crystal light valves) of the type which modulate only one type of linearly polarized light are often used. When such liquid crystal panels are illuminated with unpolarized illuminating light, only one of the two types of linearly polarized light, perpendicular to each other, contained in the unpolarized illuminating light is used, so that the other type of linearly polarized light is not used. Therefore, when an illuminating optical system which emits unpolarized illuminating light is applied to a projector which uses the above-described liquid crystal panel, the efficiency with which illuminating light is used is reduced. To overcome this problem, there has hitherto been used an illuminating optical system using a polarization conversion optical system which converts unpolarized light emitted from the light source into one type of linearly polarized light.
Ordinarily, the intensity of light beams emitted from a light source is highest near the optical axis of the light source and tends to decrease as the distance from the optical axis increases. When such light beams are used as illuminating light beams, a non-uniform image is displayed at the projector. To overcome this problem, an integrator optical system has hitherto been used as an optical system for uniformly illuminating a liquid crystal panel acting as illumination area.
FIG. 9
is a schematic structural view of a conventional illuminating optical system. The illuminating optical system comprises a light source
4120
, a first lens array
4130
, a second lens array
4140
, a polarization conversion optical system
4150
, and a superimposing lens
4160
. The two lens arrays
4130
and
4140
, and the superimposing optical system (superimposing lens)
4160
form an integrator optical system.
The first lens array
4130
includes a plural number of small lenses
4132
. The second lens array
4140
includes a plural number of small lenses
4142
in correspondence with the plural number of small lenses
4132
of the first lens array
4130
.
The polarization conversion optical system
4150
comprises a plurality of sets of a polarization separation film
4152
and a reflective film
4154
disposed in the x-axis direction, with each polarization separation film
4152
being formed parallel to its associated reflective film
4154
. The polarization separation films
4152
and the reflective films
4154
are tilted by a certain amount with respect to the xy plane. A &lgr;/2 phase film
4156
is provided at the light-outgoing side of each polarization separation film
4152
.
The substantially parallel light beams emitted from the light source
4120
are separated into a plural number of partial light beams by the plurality of small lenses
4132
of the first lens array
4130
. By the light condensing action of the small lenses
4132
of the first lens array
4130
, the separated partial light beams are condensed near the small lenses
4142
of the second lens array
4140
and the polarization separation films
4152
of the polarization conversion optical system
4150
. Of the components of the condensed light incident upon the polarization separation films
4152
, one of the types of linearly polarized light component (for example, the p-polarized light component) is transmitted through the polarization separation films
4152
, while the other type of linearly polarized light component (for example, the s-polarized light component) is reflected by the polarization separation films
4152
. The other type of linearly polarized light component reflected by the polarization separation films
4152
is reflected by the reflective films
4154
and falls upon the superimposing optical system
4160
. On the other hand, the one type of linearly polarized light component transmitted through the polarization separation films
4152
is incident upon the &lgr;/2 phase films
4156
and is converted into a linearly polarized light component which has the same polarization direction as the other type of linearly polarized light component in order to strike the superimposing optical system
4160
. The plurality of partial light beams which have struck the superimposing optical system
4160
are each virtually superimposed on an illumination area
4180
. This allows substantially one type of linearly polarized light to illuminate the illumination area
4180
.
In the above-described conventional illuminating optical system, the substantially parallel partial light beams separated by the first lens array
4130
are condensed so that they are incident upon the polarization separation films
4152
. As a result, the partial light beams incident upon the polarization separation films
4152
are spatially separated from each other. The reflective films
4154
are disposed at locations where the partial light beams from the second lens array
4140
do not fall directly thereupon, and reflect the linearly polarized light component reflected by the polarization separation films
4152
. Accordingly, the unpolarized light emitted from the light source is separated into two types of linearly polarized light beams by the polarization separation films
4152
and the reflective films
4154
.
If the light beams emitted from the light source
4120
are ideal parallel light beams, the partial light beams to be condensed near the polarization separation films
4152
are condensed virtually at one point. However, actual light sources are not point light sources, so that the light beams emitted from the light source
4120
are not completely parallel, causing the partial light beams to form images which are spread by a certain amount. In order to convert unpolarized light emitted from the light source
4120
into virtually one type of linearly polarized light more efficiently, most of each of the partial light beams is made to fall upon its associated polarization separation film
4152
. Here, the second lens array
4140
and the polarization conversion optical system
4150
are disposed so that they are virtually in close contact with each other. Therefore, it can be said that the light-outgoing surface of the second lens array
4140
and the light-incoming surface of the polarization conversion optical system
4150
virtually coincide. Consequently, in order to cause most of each of the partial light beams to fall upon its associated polarization separation film
4152
, the x-axis direction width of each polarization separation film
4152
and each reflective film
4154
can be made equal to or greater than the x-axis direction width of its associated image formed by condensing each of the partial light beams.
For a projection lens (projection optical system) used in the projector, there is an incident angle limit value (maximum value) allowing effective projection of incident light. The incident angle limit value is called the swallow angle. The swallow angle is made large by using a lens with a small f-number. However, using a lens with a small f-number increases, for example, the size and cost of the projector, so that it is preferable to use a lens with a large f-number as projection lens. In other words, in the projector, it
Hashizume Toshiaki
Iechika Hisashi
Dowling William
Oliff & Berridg,e PLC
Seiko Epson Corporation
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