Illumination optical system with reflecting light valve

Details Illumination optical system with reflecting light valve Illumination optical system with reflecting light valve

2002-02-07

2003-05-13

Dowling, William (Department: 2851)

Optics: image projectors

Reflector

C353S020000

Reexamination Certificate

active

06561656

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an illumination optical system using a reflecting light valve such as a digital micromirror device (referred to as “DMD” hereinafter) or a reflecting liquid crystal display. It also relates to a projection display (e.g., projector) including the illumination optical system.
2. Description of the Background Art
FIG. 14
is a schematic diagram of an illumination optical system applied to a conventional projection display disclosed in Japanese Patent Application Laid-open No. 2000-241755. In
FIG. 14
, reference numeral
31
designates a light source and reference numeral
32
designates a parabolic mirror that reflects light from the light source
31
and makes the reflected light generally parallel to an optical axis of illumination. Reference numeral
33
designates a first lens array, reference numeral
34
designates a convex lens constituting the first lens array
33
, reference numeral
35
designates a second lens array, and reference numerals
36
and
37
designate convex lenses constituting the second lens array
35
. Further, reference numeral
38
designates a collective lens and reference numeral
39
designates a to-be-illuminated surface.
Light emitted from the light source
31
and then reflected by the parabolic mirror
32
is generally made parallel; however, in the open end of the parabolic mirror
32
, the light intensity distribution in the periphery is higher than that in the center because of the influences of optical properties of the light source
31
such as light emission and light distribution. The illumination optical system of
FIG. 14
has the functions of reducing such a deviation of the illumination light distribution and illuminating the central portion of the to-be-illuminated surface more brightly than the peripheral portion. Now, the operation of the illumination optical system in
FIG. 14
will be briefly described.
The first lens array
33
is formed of an array of a plurality of convex lenses
34
having the same focal length. The second lens array
35
, on the other hand, is formed of an array of alternate convex lenses
36
and
37
having two different focal lengths. The focal length of the convex lenses
36
is determined so as to adjust, in combination with the condenser lens
38
, the focus of their corresponding convex lenses
34
in the first lens array
33
on the to-be-illuminated surface
39
. From this, light passing through half of the convex lenses
34
in the first lens array
33
is superimposed on the to-be-illuminated surface
39
, and even if the light intensity distribution in the open end of the parabolic mirror
32
is not uniform, the to-be-illuminated surface
39
can be provided with a uniform illuminance distribution.
The focal length of the convex lenses
37
, on the other hand, is determined to be greater than that of the convex lenses
36
; therefore, even in combination with the condenser lens
38
, the focus of their corresponding convex lenses
34
in the first lens array
33
cannot be adjusted on the to-be-illuminated surface
39
. That is, light passing through the convex lenses
37
has a convexly curved illuminance distribution on the to-be-illuminated surface
39
, with the central portion being higher in illuminance than the peripheral portion.
As above described, the illuminance distribution on the to-be-illuminated surface
39
is formed by a combination of (i) the uniform illuminance distribution of the light passing through the convex lenses
36
and (ii) the convexly curved illuminance distribution of the light passing through the convex lenses
37
. That is, the illuminance distribution on the to-be-illuminated surface
39
gently changes within an effective illuminated area on the to-be-illuminated surface
39
, with the central portion being higher in illuminance than the peripheral portion. This achieves a projection display capable of making improvement on uniform illumination that is not suitable for TV image display, for example.
In the above conventional projection display illustrated in
FIG. 14
, however, the light passing through the convex lenses
37
, which account for one half of the total lenses in the second lens array
35
, is not focused on the to-be-illuminated surface
39
. Accordingly, a light source image to be formed on the pupil of a projection lens (not shown) is out of focus as well. Considering efficiency of light utilization, the light source image on the pupil should be in sharp focus. From this, the conventional projection display in
FIG. 14
has a problem that the positive provision of the convex lenses
37
causes defocusing as above described, thereby resulting in unavoidable energy loss.
SUMMARY OF THE INVENTION
A first aspect of the present invention is directed to an illumination optical system comprising: a light source; a light mixing element mixing light emitted from the light source; a reflecting light valve having a plurality of pixels; a transmission optical system located between the light mixing element and the reflecting light valve and bringing a light exit surface of the light mixing element into optical conjugation with a to-be-illuminated surface of the reflecting light valve; and a field lens located between the transmission optical system and the reflecting light valve, wherein a focal length of the field lens is determined so that an illuminance distribution which varies according to the application of the illumination optical system can be achieved on the to-be-illuminated surface.
According to a second aspect of the present invention, in the illumination optical system of the first aspect, the focal length of the field lens is determined so that an illumination margin takes on a value in the neighborhood of 1.0, and a diagonal dimension of a to-be-illuminated area on the to-be-illuminated surface is equivalent to the product of a diagonal dimension of the to-be-illuminated surface and the illumination margin.
According to a third aspect of the present invention, in the illumination optical system of the first aspect, the focal length of the field lens is determined by obtaining at least one of a radius of curvature of the field lens and the type of a glass material forming the field lens on the basis of the illuminance distribution which varies according to the application of the illumination optical system.
According to a fourth aspect of the present invention, in the illumination optical system of the first aspect, the light exit surface of the light mixing element and the to-be-illuminated surface of the reflecting light valve are generally similar in shape.
According to a fifth aspect of the present invention, in the illumination optical system of the first aspect, the plurality of pixels in the reflecting light valve each are configured of a micromirror having a variable angle of inclination.
According to a sixth aspect of the present invention, in the illumination optical system of the first aspect, the light mixing element is formed in the shape of a hollow rod, using its inner surface as a reflecting surface.
According to a seventh aspect of the present invention, the illumination optical system of the first aspect further comprises: a rotary color filter located either in front of or behind the light mixing element to pass the light emitted from the light source.
According to an eighth aspect of the present invention, in the illumination optical system of the first aspect, the field lens is a planoconvex lens having a plane surface on the side of the to-be-illuminated surface of the reflecting light valve.
According to a ninth aspect of the present invention, in the illumination optical system of the first aspect, the field lens has at least one aspherical surface.
According to a tenth aspect of the present invention, in the illumination optical system of the first aspect, the field lens is a Fresnel lens.
An eleventh aspect of the present invention is directed to a projection display comprising: the illumination optical system of the first aspect

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