Optical: systems and elements – Single channel simultaneously to or from plural channels – By surface composed of lenticular elements
Reexamination Certificate
2001-07-02
2003-10-14
Mack, Ricky (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By surface composed of lenticular elements
C359S626000, C362S268000
Reexamination Certificate
active
06633435
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an illumination optical system to be used for providing increased service efficiency of light and a sharp image, and to a projector including the illumination optical system.
2. Description of the Related Art
FIG. 9
is a perspective external view illustrating a typical projector. Referring to
FIG. 9
, a rectangular parallelepiped projector
501
includes an upper case
503
which defines the upper surface thereof and is provided with operating buttons
502
, a lower case
504
which defines the lower surface of the projector
501
, and a front case
505
which defines the front surface of the projector
501
. There is a projection lens
506
, the front-end portion of which protrudes from the front case
505
.
For example, such a projector as mentioned above includes a known optical system configured as shown in FIG.
10
.
That is, the projector
501
includes a light source
510
, and an illumination optical system
520
for providing a uniform illumination distribution of light emitted from the light source
510
and for allowing the light to impinge upon liquid crystal panels
550
R,
550
G,
550
B with the same polarization. The projector
501
also includes a color beam splitting optical system
530
for splitting a beam W launched from the illumination optical system
520
into red, green, and blue beams R, G, B, and a relay optical system
540
for introducing the blue beam B in the beams R, G, B, which have been split by the color beam splitting optical system
530
, into the liquid crystal panel
550
B associated with the blue beam B. The projector
501
further includes the three liquid crystal panels
550
R,
550
G,
550
B as light modulating means for modulating each color beam in accordance with given image information, a cross dichroic prism
560
as a color beam combining optical system for combining modulated respective color beams, and the projection lens
506
for expanding combined beams and projecting the beams onto a projection screen.
FIG. 11
is a schematic view illustrating the action of the illumination optical system
520
. As shown in
FIG. 11
, the illumination optical system
520
allows a first lens array
521
to split the light emitted from the light source
510
into a plurality of sub-beams, then the sub-beams to impinge upon a polarization conversion element array
523
via a second lens array
522
, and then the polarization conversion element array
523
to provide the respective sub-beams with the same polarization direction. Thereafter, the illumination optical system
520
allows a superimposing lens
524
to superimpose the sub-beams on the image forming area of the liquid crystal panels
550
R,
550
G,
550
B.
The illumination optical system
520
functions as described above to allow polarized light of one type to illuminate uniformly all parts of the respective liquid crystal panels
550
R,
550
G,
550
B. Therefore, when displaying an image with a projector, the system contributes to providing a sharp and high contrast image all over the display area.
Below, the process of providing the same polarization direction (of converting polarization) in the aforementioned illumination optical system
520
will be explained in more detail with reference to
FIGS. 11 and 12
.
FIG. 11
is an enlarged view illustrating part of the illumination optical system
520
. The polarization conversion element array
523
is configured to have a polarization splitting film
523
b
and a reflective film
523
c,
which are alternately disposed between a plurality of light transmissive members
523
a.
There is also provided a half-wave plate
523
d
on the transmission side corresponding to the polarization splitting film
523
b.
The first lens array
521
splits the light emitted from the light source
510
into a plurality of sub-beams and then condenses the respective sub-beams near the polarization splitting film
523
b
of the polarization conversion element array
523
. Accordingly, condensed images of the respective sub-beams are formed near the polarization splitting film
523
b.
The condensed images are derived from the light-emitting portion of the light source
510
. The incident light upon the polarization splitting film
523
b
is split into p- and s-polarized beams, and the p-polarized beam which is a transmitted beam is converted into an s-polarized beam with the half-wave plate
523
d.
On the other hand, the s-polarized beam which is a reflected beam is directed substantially in the same direction as the p-polarized beam at the reflective film
523
c
and then launched from the polarization conversion element array
523
without any change. As described above, the respective sub-beams that have been split with the first lens array are provided with the same polarization. To achieve such an ideal polarization conversion, it is necessary to allow the incident light upon the polarization conversion element array
523
to impinge only upon the polarization splitting film
523
b.
This is because incidence of light upon the reflective film
523
c
would cause the light to be converted reversely in polarization direction. Incidentally,
FIG. 11
shows the incidence portion corresponding to the polarization splitting film
523
b
as an effective incidence portion
523
e.
Now, suppose the light-emitting portion of the light source
510
is an ideal point light source and the illumination optical system
520
is an ideal one that has no errors in its design and fabrication. In this case, a condensed point image would be formed near the polarization splitting film
523
b.
It would be therefore possible in this case to allow the incident light upon the polarization conversion element array
523
to impinge only upon the polarization splitting film
523
b.
However, in practice, the light-emitting portion of the light source
510
has a given size, thereby providing a given size to the condensed image formed near the polarization splitting film
523
b.
The size of the condensed image often exceeds that of the effective incident portion
523
e
in the ideal system. In such a case, as schematically shown in
FIG. 12
, the effective incident portion
523
e
may be made larger than that of the ideal system in order to allow the light to impinge only upon the effective incident portion
523
e.
At this time, it is necessary for the first lens array
521
to direct the sub-beams outwardly except for the central portion thereof. In some cases, some lenses constituting the first lens array
521
are decentered (i.e., the optical axis of the lenses is shifted from their geometric center).
The lenses that constitute the first lens array and are decentered for service have step differences at their boundaries due to differences in shape of their surfaces. The presence of a step difference often produces a portion with a rounded edge (i.e., the edge on the periphery of a lens is not formed at a specified angle but in a curved shape) during the manufacture of the lens array. Incident light upon the rounded edge cannot reach an illuminated area or the image forming area of the liquid crystal panels
550
R,
550
G,
550
B, so that the peripheral portion of the illuminated area becomes dark. Consequently, the portion corresponding to the rounded edge appears as a display shadow in the projected area as shown in
FIG. 13
when projecting the light onto the screen, conventionally, it has been obliged to provide an excess illumination margin at the expense of brightness in order to avoid the display shadow.
SUMMARY OF THE INVENTION
The present invention was developed to solve the aforementioned problems without sacrificing brightness, employing the following configurations.
An illumination optical system according to the present invention includes a lens array with a plurality of lenses for splitting light emitted from a light source into a plurality of sub-beams, at least some of the lenses of the lens array being decentered. The illumination optical system is characterized i
Akiyama Koichi
Hashizume Toshiaki
Ladas & Parry
Mack Ricky
LandOfFree
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