Optics: image projectors – Unitary plural refracting surfaces
Reexamination Certificate
1999-07-19
2001-09-11
Metjahic, Safet (Department: 2858)
Optics: image projectors
Unitary plural refracting surfaces
C353S031000
Reexamination Certificate
active
06286961
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an illumination system that divides a light flux emitted from a light source into a plurality of partial light fluxes and causes the plurality of partial light fluxes to be superimposed on an identical illumination area. The present invention also pertains to a projection display apparatus that produces substantially uniform, bright projected images using such an illumination system.
2. Discussion of the Background
A projection display apparatus uses a light modulator, or ‘light valve’, to modulate illumination light, illuminating the light modulator, responsive to image information, and projects the modulated light flux on a screen to display an image. A typical example of the light modulator is a liquid-crystal panel. It is naturally desirable that the image displayed by the projection display apparatus is substantially uniform and bright. For that purpose, the illumination light emitted from an illumination device (illumination system) incorporated in the projection display apparatus should have a high utilization efficiency of light. One proposed technique to enhance the utilization efficiency of the illumination light disposes a plurality of micro lenses corresponding to the respective pixels of the liquid-crystal panel on the light-entering side of the liquid-crystal panel.
FIGS.
15
(A) and
15
(B) show light fluxes entering a liquid-crystal panel in the case where micro lenses are disposed on the light-entering side of the liquid-crystal panel. More concretely FIGS.
15
(A) and
15
(B) show the cross section of a liquid-crystal panel
1000
and a micro lens array
1100
including a plurality of micro lenses
1110
. The liquid-crystal panel
1000
includes liquid-crystal layers
1010
that are surrounded by light shielding layers
1020
, which are referred to as the ‘black matrixes’, in a lattice configuration. The micro lens array
1100
is disposed on the light-entering side of the liquid-crystal panel
1000
in such a manner that the center of one liquid-crystal layer
1010
corresponding to each pixel of the liquid-crystal panel
1000
substantially coincides with the optical axis of one micro lens
1110
. As shown in FIG.
15
(A), the light flux, which enters the micro lens
1110
substantially in parallel with the optical axis of the micro lens
1110
, is condensed by the micro lens
1110
to pass through the liquid-crystal layer
1010
. This arrangement ensures the utilization of such light fluxes that would be shielded by the light shielding layers
1020
in the structure without the micro lenses
1110
. The micro lenses accordingly work to enhance the utilization efficiency of light.
The micro lens
1110
also condenses the light flux that enters the micro lens
1110
obliquely to the optical axis of the micro lens
1110
as shown in FIG.
15
(B). Part of this light flux, however, does not pass through the liquid-crystal layer
1010
but is shielded by the light shielding layer
1020
. In this case, the use of the micro lenses worsens the utilization efficiency of light. This phenomenon is more significant in the case of the greater angle of the light flux to the optical axis (that is, the incident angle).
The smaller incident angle of light into the liquid-crystal panel relieves the above problem and improves the utilization efficiency of light. In the structure without micro lenses, the smaller incident angle of light into an optical element other than the liquid-cystal panel (for example, a projection lens for causing the modulated light flux emitted from the liquid-crystal panel to be projected on a screen) would improve the utilization efficiency of light in the optical element and thereby improves the utilization efficiency of light in the whole projection display apparatus.
One possible method of decreasing the incident angle of light into an illumination area is to lengthen the optical path between a light source and the illumination area (especially the optical path between the light source and an optical element immediately before the illumination area). This method, however, undesirably increases the size of the whole illumination system.
In an optical integrator system, a light flux emitted from the light source is divided into a plurality of partial light fluxes, and the plurality of partial light fluxes are superimposed on the illumination area. It is accordingly difficult to decrease the incident angle of light into the illumination area without significantly lengthening the optical path in the illumination system including the optical integrator system.
SUMMARY OF THE INVENTION
The object of the present invention is to solve the above problem arising in the prior art and provide a technique that decreases the incident angle of a light flux into an illumination area without significantly lengthening an optical path between a light source and the illumination area in an illumination system including an optical integrator system.
In order to attain the above object, the present invention is directed to an illumination system that divides a light flux emitted from a light source into a plurality of partial light fluxes and causes the plurality of partial light fluxes to be substantially superimposed on an illumination area, so as to enable a light-entering face of a specific optical apparatus to be illuminated as the illumination area. The illumination system has a light flux contraction section having a function of an afocal optical system that changes an incident light flux to an emitting light flux, the emitting light flux having a width narrower than the incident light flux. The light flux contraction section has a light condensing function and a light parallelizing function to actualize the afocal optical system.
The width of the light flux emitted from the illumination system is contracted by the light flux contraction section having the function of the afocal optical system. This arrangement decreases the incident angle of the light flux that irradiates the illumination area without significantly lengthening the optical path between the light source and the illumination area. The smaller incident angle of the light flux entering an optical element generally results in the better utilization efficiency of light in the optical element. The illumination system of the present invention accordingly improves the utilization efficiency of light.
In accordance with one preferable application of the present invention, the illumination system further includes: a light source that emits a substantially parallel light flux; and a dividing and superimposing section that divides the light flux emitted from the light source into a plurality of partial light fluxes and causes the plurality of partial light fluxes to be substantially superimposed on the illumination area, wherein the light flux contraction section is included in the dividing and superimposing section.
In this preferable structure, the dividing and superimposing section changes the substantially parallel light flux emitted from the light source to a plurality of partial light fluxes having a contracted total width as a whole and causes the plurality of partial light fluxes to be substantially superimposed on the illumination area. This arrangement decreases the incident angle of each partial flux into the illumination area and thereby improves the utilization efficiency of light emitted from the illumination system.
In the illumination system of the above structure, it is preferable that the dividing and superimposing section includes: a first light flux dividing section having the light condensing function and a function of a first lens array having a plurality of small lenses to divide the substantially parallel light flux into the plurality of partial light fluxes; a second light flux dividing section having the light parallelizing function and a function of a second lens array having a plurality of small lenses corresponding to the plurality of small lenses included in the first lens array; and a superi
LeRoux Etienne
Metjahic Safet
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Seiko Epson Corporation
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