Liquid crystal cells – elements and systems – Particular structure
Reexamination Certificate
2000-02-17
2003-04-22
Kim, Robert H. (Department: 2371)
Liquid crystal cells, elements and systems
Particular structure
C349S005000, C353S038000, C359S641000, C359S642000, C359S721000
Reexamination Certificate
active
06552760
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a luminaire with improved light utilization efficiency, more particularly, to a polarized luminaire, an unpolarized luminaire, an illuminance distribution improving device therefore, and polarization converter each for use in a liquid crystal projection device.
2. Description of the Related Art
In projectors such as a liquid crystal projector and a movie projector, there has been a requirement for increasing light utilization efficiency of light emitted from a light source in order to obtain a brighter projected image.
FIG. 47
shows a schematic sectional view of a prior art luminaire taken along the optical axis thereof, the luminaire being employed in such projectors.
In the figure, the arc gap center of a metal halide lamp
11
coincides with a focal point of a parabolic mirror
12
, and light emitted from the metal halide lamp
11
is reflected by the parabolic mirror
12
so as to be substantially in parallel light beams. The parallel beams enter into a lens array
21
. A lens array
22
having lenses arranged in a corresponding manner to those of the lens array
21
is disposed opposite thereto. A distance between the lens arrays
21
and
22
is made equal to a focal length of the lenses of the lens array
21
so that light beams emitted from the lenses of the lens array
21
enter into the corresponding lenses of the lens array
22
efficiently. A condenser lens
23
is disposed on the lens array
22
side and between the lens array
22
and a plane
24
to be illuminated.
Parallel luminous flux incoming to any lens
211
of the lens array
21
converge at the center of a lens
221
, corresponding to the lens
211
, of the lens array
22
, pass through the condenser lens
23
and proceed to the plane
24
to be illuminated so as to illuminate the entire area thereof. That is, all images of the lenses of the lens array
21
are formed on the plane
24
in overlapping by the lens array
22
and the condenser lens
23
. An intensity distribution of light reflected from the parabolic mirror
12
has the highest in the central and is lower with going apart from the center, but if the number of lens pairs of the lens arrays is large (generally the number ranges from tens to hundreds), incident light intensities all over the plane
24
are almost uniform as shown in FIG.
48
(B) due to such workings of the lens arrays
21
and
22
and the condenser lens
23
.
In the luminaire of
FIG. 47
, manufacture error in dimension associated with constituents and mounting error thereof are varied every device. Since a liquid crystal projector or the like is an mass-produced article, as shown in FIG.
48
(A), the size of an illumination spot P on the plane
24
is necessary to be determined in consideration of a margin area MA provided outside an effective illumination area EA so as to absorb such errors. For example, in a case where the effective illumination area EA is a liquid crystal panel in rectangular shape with a longitudinal side of 15 mm and a lateral side of 20 mm, with the margin area MA having each width of 3.5 mm in the vertical direction and each width of 2.55 mm in the horizontal direction in order to cope with such errors as actually arise, 45% of the luminance light in amount is wasted in the margin area MA if considered a uniform distribution as shown in FIG.
48
(B), resulting in poor light utilization efficiency.
Now, in an unpolarized light luminaire
10
shown in
FIG. 49
, the center of an arc gap of a metal halide lamp
11
is sat to the focal point of a parabolic mirror
12
, and a UV/IR cut filter
13
is disposed on the aperture side of the parabolic mirror
12
. Unpolarized light emitted from the metal halide lamp
11
is reflected by the parabolic mirror
12
to be substantially parallel light beams, and only white light passes through the UV/IR cut filter
13
.
For example, in a liquid crystal projection device, light that has passed through a UV/IR cut filter
13
is directed to, as shown in
FIG. 50
, a lens array
21
of an polarization conversion device
20
in order to reduce heat absorption in a liquid crystal panel that uses only polarized light. A lens array
22
is of the same shape as that of the lens array
21
and arranged opposite to the lens array
21
with a distance A between the lens arrays
21
and
22
, the distance being equal to a focal length of the lens array
21
. A condenser lens
23
is disposed on the lens array
22
side and between the lens array
22
and a plane
24
to be illuminated. A focal length of the lens array
22
is not required to be equal to that of a lens array
21
.
A parallel luminous flux having being incident on a lens
210
of the lens array
21
converges at the center of a corresponding lens
220
of the lens array
22
and is passes through the condenser lens
23
to project onto the whole plane
24
to be illuminated. Likewise, a parallel luminous flux having being incident on a lens
211
of the lens array
21
converges at the center of a corresponding lens
221
of the lens array
22
and is passes through the condenser lens
23
to project onto the whole plane
24
. The emitting light from the unpolarized light luminaire
10
has an intensity distribution which is the highest in the middle and lower toward its periphery, but an almost flat illuminance distribution is obtained across an illumination spot on the plane
24
by such workings of the lens arrays
21
and
22
and the condenser lens
23
.
A polarization conversion element
25
is disposed between the lens array
22
and the condenser lens
23
.
The polarization conversion element
25
is constructed as follows. One end to the other end along X direction, arranging prisms
250
of the same shapes as one another, each having a section of a parallelogram and extending along a direction perpendicular to the drawing paper. Polarization beam splitters
251
and mirrors
252
each formed with dielectric multi-layered films are alternately inserted between the prisms
250
and formed on both end surfaces of the element facing X direction. Halfwave plates
253
are pasted on every other light emitting surfaces of the prisms
250
. In this parallelogram, widths of a pair of an incident surface and an emitting surface opposite to each other is a half of a width CX of a lens of the lens array
22
, lengths of the other pair of opposite sides are 2
−0.5
CX, and one of opposite angle is 45 degrees. The polarization conversion elements
25
are arranged such that the centers of the lenses of the lens array
22
coincide with the centers in X direction of the polarization beam splitters
251
.
For example, a p-polarized component of a light beam proceeding along the optical axis of a convex lens
211
is passes through a polarization beam splitter
251
, while an s-polarized component thereof is reflected by the polarization beam splitter
251
. The s-polarized component is further reflected by a mirror
252
, and further passes through the halfwave plate
253
to be converted to p-polarized light. Therefore, light having passed through the polarization conversion element
25
is p-polarized light.
The metal halide lamp
11
in
FIG. 49
has a light emitting part that is not a point source of light and therefore, emitted light from the unpolarized light luminaire
10
is not of perfect parallel beams. As shown in
FIG. 50
, most of non-parallel light beams, like a light beam L
1
, are reflected by the mirror
252
and s-polarized component of the reflected beams are further reflected by the polarization beam splitter
251
to be output from the polarization conversion element
25
. Part of the non-parallel light beams, like a light beam L
2
, are passes through the polarization conversion element
25
with being kept in an unpolarized state. For these reasons, light utilization efficiency is reduced, which leads to darkness of a projected picture.
In
FIG. 49
, a divergence angle &phgr; of the non-parallel beams whose intensity amount to more than half of
Gotoh Takeshi
Hamada Tetsuya
Hayashi Keiji
Kobayashi Tetsuya
Ohashi Noriyuki
Chung David
Fujitsu Limited
Greer Burns & Crain Ltd.
Kim Robert H.
LandOfFree
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