Optical block and display unit

An optical block, which may be of a small size, for applying light efficiently to a display device such as a liquid crystal panel, and a display apparatus. The optical block (1) has a polarizing beam splitter (3) mounted on baseboard (2) at a predetermined angle with respect to light applied from a light source (10), for passing a P wave toward an exit side and reflecting an S wave, reflecting device (4) mounted on the baseboard (2) for reflecting the reflected S wave toward the exit side, and plane-of-polarization rotating device (5) mounted on the baseboard (2) for rotating the plane of polarization of the S wave reflected toward the exit side. The display apparatus has a light source (10), a first multilens array (12), the optical block (1), a second multilens array (13), separating device (14, 19) for separating emitted light into red light (R), green light (G), and blue light (B), light modulating device (17, 21, 26) for generating modulated red light, modulated green light, and modulated blue light based on the separated light, and emitting device (18) for combining the modulated red light, modulated green light, and modulated blue light and emitting combined modulated light. The optical block is of a thin structure so that it may be a space saver and lightweight. Optical paths from the light source to liquid crystal panels or the like may be reduced to reduce the size of the display apparatus.

TECHNICAL FIELD 
The present invention relates to an optical block, which may be of a small 
size, for applying light efficiently to a display device such as a liquid 
crystal panel, and a display apparatus. 
BACKGROUND ART 
Recently, display apparatus such as projectors, television receivers, and 
computer display units which employ optical devices such as liquid crystal 
panels or the like are in widespread use. In a display apparatuses which 
employs a liquid crystal panel or the like, light emitted from a light 
source such as a metal halide lamp, a halogen lamp, or the like is applied 
to a liquid crystal panel having color filters (R, G, B), and the liquid 
crystal panel displays a colored video image as its output light. The 
output light from the liquid crystal panel is projected onto a screen by a 
projection lens. 
Light radiated from an ordinary light source has two planes of polarization 
that are generally referred to as a P-polarized component (hereinafter 
referred to as a P wave) and an S-polarized component (hereinafter 
referred to as an S wave). The display apparatus has polarizing means 
positioned such that light emitted from the light source is applied to the 
polarizing means before being applied to the liquid crystal panel. The 
polarizing means applies light having a plane of polarization which is 
either the P wave or the S wave depending on a polarizer disposed in front 
of the liquid crystal panel. 
If rays of randomly polarized light are applied to polarizing beam 
splitters (hereinafter referred to as a PBS) disposed in prisms, for 
example, at a given angle, then a P wave passes through the PBSs and an S 
wave is reflected by the PBSs. Both the P and S waves are refracted by end 
faces of the prisms into parallel rays of light, and only the S wave is 
converted into a P wave by being transmitted through a .lambda./2 plate. 
Alternatively, the S wave is converted into a P wave by being refracted by 
end faces of the prisms so as to be parallel to the direction of travel of 
the P wave that has passed through the PBSs, or reflected toward a 
.lambda./2 plate by a reflecting means such as a mirror or the like. 
According to the former process, one unit of optical block is employed. 
According to the latter process, one or two units of optical block are 
symmetrically arranged. 
FIG. 12 shows the structure of a conventional polarizing means and optical 
paths. A light source 40 comprises a halogen lamp, a metal halide lamp, or 
the like. Light emitted from the light source is passed through an optical 
block 50, which applies only a P wave to a liquid crystal panel (not 
shown). The optical block 50 comprises a plurality of prisms 50a-50f of 
glass which are bonded together. PBSs 52 are disposed between the prisms 
50b, 50e and between the prisms 50c, 50d, and wave plates 53 are disposed 
on front faces of the prisms 50a, 50f. P+S waves emitted from the light 
source 40 are represented by solid arrows. The path of a P wave separated 
by the optical block 50 is represented by white blank arrows, and the path 
of an S wave separated by the optical block 50 is represented by hatched 
arrows. 
P+S waves emitted from the light source 40 are separated by the PBSs 52. 
The P wave passes through the PBSs 52 and is applied to the liquid crystal 
panel. The S wave is reflected by the PBSs 52, then reflected forward by 
the prisms 50a, 50f, and converted by the wave plates 53 into a P wave, 
which is applied to the liquid crystal panel. Therefore, only the P wave 
is emitted from front faces of the prisms 50d, 50e and the wave plates 53. 
In this manner, either one of the P+S waves emitted from the light source 
40 is applied by the optical block 50 to the non-illustrated liquid 
crystal panel. 
If the optical block 50 were not employed, then the aperture of the light 
source 40 would be similar in shape to the effective area of the liquid 
crystal panel. However, a liquid crystal panel for displaying horizontally 
long images having an aspect ratio of 16:9, for example, has its side 
areas that cannot uniformly be irradiated with light, and hence cannot 
have uniform illuminance. Furthermore, since it is difficult for rays of 
light emitted from a lamp light source of a large divergent angle to be 
applied efficiently to a liquid crystal panel, it is known to use a 
multilens array composed of a number of small lenses, for example, as an 
optical means, to increase rays of light which reach a liquid crystal 
panel and uniformize a distribution of illuminance. 
If such a multilens array is used, then, as shown in FIG. 13, the multilens 
array is of a shape similar to a liquid crystal panel as a light 
modulating means and having an aspect ratio equal to the aspect ratio of 
an effective aperture of the liquid crystal panel. The multilens array 
comprises a plane multilens array 54 composed of a matrix of convex lenses 
54a and positioned closer to a light source (not shown) and a plano-convex 
multilens array 55 composed of a plurality of convex lenses 55a facing the 
convex lenses 54a of the plane multilens array 54. The multilens array 
applies rays of light from the light source efficiently and uniformly to 
the effective aperture of the liquid crystal panel. 
Rays of light emitted from the light source of a liquid crystal projector 
and applied to the multilens array 54 are converged onto the convex lenses 
55a of the multilens array 55 by the convex lenses 54a. The rays of light 
applied to the convex lenses 55a are applied to a condenser lens 56 by a 
convex lens 55b on the exit side of the multilens array 55. After the rays 
of light are modulated by a liquid crystal panel 57 associated with front 
and rear polarizers, they are applied to a cross dichroic prism 58. Before 
the rays of light are applied to the condenser lens 56 by the convex lens 
55b, they are separated into R, G, B light by optical elements such as 
dichroic mirrors. The dichroic prism 58 comprises four prisms bonded 
together by reflecting surfaces 58a, 58b in the form of thin films having 
predetermined reflecting characteristics. 
In FIG. 13, only a path of green light G is indicated by the solid lines. 
However, red light R and blue light B are similarly optically modulated by 
respective liquid crystal panels (not shown), and thereafter, as indicated 
by the arrows, applied from respective different directions to the cross 
dichroic prism 58. 
The red light R modulated by the liquid crystal panel 57 is reflected by 
the reflecting surface 58a of the dichroic prism 58 toward a projection 
lens (not shown). The blue light B is reflected by the reflecting surface 
58b of the dichroic prism 58 toward the projection lens. The green light G 
passes through the reflecting surfaces 58a, 58b. The red light R, the 
green light G, and the blue light B are combined with each other into 
light along one optical axis, generating a color video signal which is 
applied to the projection lens (not shown). As described above, the red 
light and the blue light are applied from the respective directions 
indicated by the arrows to the cross dichroic prism 58, and reflected by 
the respective reflecting surfaces 58a, 58b to the projection lens. 
With the multilens arrays 54, 55 of matrices of convex lenses 54a, 55a, the 
rays of light emitted from the light source can be applied to the 
effective aperture of the liquid crystal panel 57 more efficiently and 
uniformly than if only the condenser lens 56 were employed. 
In FIG. 14, the optical block 50 is positioned at the aperture of the light 
source 40, and the multilens arrays 54, 55 are positioned at the aperture 
of the optical block 50. This arrangement is effective to utilize rays of 
light emitted from the light source 40 more efficiently than the 
arrangements shown in FIGS. 12 and 13. 
The conventional optical block 50 has an exit surface wider than an 
entrance surface thereof, and hence tends to increase the angle of 
incidence of rays of light on the liquid crystal panel, resulting in a 
reduction in the contrast. If the light source 40 is designed for a 
smaller size in order to prevent such a reduction in the contrast, then 
the optical block 50 has to utilize rays of light having a large divergent 
angle. Moreover, since the entrance side of the conventional optical block 
is of a size proportional to the aperture of the light source 40, the exit 
side of the optical block is of a size greater than the light source 40. 
Consequently, the optical block needs a considerably large installation 
space and is costly. 
If only the multilens arrays 54, 55 are provided, then because the randomly 
polarized light emitted from the light source is applied directly to the 
polarizers, about 60% of the entire quantity of the light is blocked, and 
hence the efficiency with which the light source is utilized is poor. If 
the optical block 50 and the multilens arrays 54, 55 are combined with 
each other, then the multilens arrays 54, 55 are of an increased size 
commensurate with the exit aperture of the optical block 50, resulting in 
an increase in the length of the optical path from the multilens array 55 
to the liquid crystal panel 57, so that the overall apparatus has a large 
size. 
In order to solve the above problems, the applicant has proposed a light 
source for a display apparatus which comprises multilens arrays and an 
optical block having a plurality of joined prisms (see Japanese patent 
application No. 7-290570). FIG. 15 shows the proposed light source as 
incorporated in the optical system of a liquid crystal projector. As shown 
in FIG. 15, a light source 110 comprises a metal halide lamp 110a disposed 
at the focal point of a parabolic mirror for emitting light substantially 
parallel to the optical axis of the parabolic mirror from its aperture. An 
IR-UV blocking filter 111 blocks unwanted rays in infrared and ultraviolet 
ranges of the light emitted from the light source 110, and passes only 
effective rays of light to a next optical means. 
The optical means has a first multilens array 112 comprising a matrix of 
convex lenses 112a and a second multilens array 113 comprising a matrix of 
convex lenses 113a, two of which face each of the convex lenses 112a of 
the first multilens array 112. An optical block 101, which will be 
described later on, is disposed between the first multilens array 132 and 
the second multilens array 113. 
The optical block 101 comprises a plurality of bonded prisms. Rays of light 
converged by the first multilens array 112 are applied to a certain one of 
the prisms of the optical block 101. The optical block 101 converts 
randomly polarized light (P+S waves) into a P wave (or an S wave), which 
is applied to some of the convex lenses 113a of the second multilens array 
113. The P or S wave is then separated by various optical elements into R 
light, G light, and B light, which are applied to liquid crystal panels. 
Therefore, the first multilens array 112, the optical block 101, and the 
second multilens array 113 allow rays of light emitted from the light 
source 110 and passing through the IR-UV blocking filter 111 to be applied 
efficiently and uniformly to the effective apertures of the liquid crystal 
panels. 
Dichroic mirrors 114, 119 for separating rays of light from the light 
source 110 into red light, green light, and blue light are disposed 
between the optical block 101 and the effective apertures of the liquid 
crystal panels. In FIG. 15, the red light R reflected by the dichroic 
mirror 114 has its direction of travel bent 90.degree. by a mirror 115, 
and is applied through a condenser lens 116 to a red liquid crystal panel 
117. 
The green light G and the blue light B which have passed through the 
dichroic mirror 114 are separated from each other by the dichroic mirror 
119. The green light G is reflected by the dichroic mirror 119 so that its 
direction of travel is bent 90.degree., and is applied through a condenser 
lens 120 to a green liquid crystal panel 121. The blue light B passes 
straight through the dichroic mirror 119, and travels through a relay lens 
122, a mirror 124a, a relay lens 123, a mirror 124b, and a condenser lens 
125 to a blue liquid crystal panel 126. 
The red light, the green light, and the blue light which are optically 
modulated by the liquid crystal panels 117, 121, 126 are combined by a 
cross dichroic prism 118 as a light combining means. The red light R is 
reflected by a reflecting surface 118a toward a projection lens 130, and 
the blue light B is reflected by a reflecting surface 118b toward the 
projection lens 130. The green light G passes through the reflecting 
surfaces 118a, 118b. The R, G, B rays of light are thus combined to travel 
along one optical axis, and projected at an enlarged scale onto a screen 
(not shown) by the projection lens 130. 
FIG. 16 is a perspective view of the optical block 101 as viewed from its 
front, and FIG. 17 is a fragmentary plan view of the optical block 101. As 
shown in FIGS. 16 and 17, the optical block 101 comprises triangular 
prisms 100a, 100e and parallelogrammatic prisms 200a, 200b, 200c, 200d, 
100b, 100c, 100d which are bonded together. The randomly polarized light 
(P+S waves) emitted from the light source 110 and passing through the 
first multilens array 112 is applied to the optical block 101, as 
indicated by the solid arrows, and only a P wave is emitted from each of 
the prisms as indicated by the white blank arrows. 
PBSs 103 (103a, 103b, 103c, 103c) for reflecting an S wave and passing a P 
wave therethrough, for example, are disposed on respective slanted exit 
ends of the prisms 200 (200a, 200b, 200c, 200d). The P wave that has 
passed through the PBSs 103 are emitted forward from front surfaces of the 
prisms 100 (100a, 10b, 100c, 100d). Mirrors 104 (104a, 104b, 104c, 104d) 
for reflecting forward the S wave reflected by the PBSs 103 are disposed 
on slanted surfaces of the prisms 200 which face the PBSs 103. 1/2 
.lambda. plates 105 (105a, 105b, 105c, 105d) are disposed on front 
surfaces of the prisms 200 for rotating the plane of polarization of the S 
wave reflected by the PBSs 103 thereby to convert the S wave into a P 
wave, which is emitted forward. 
Accordingly, the prisms 200 serve as an entrance region of the optical 
block 101, and rays of light applied to the prisms 200 are separated or 
polarized by the PBSs 103 and the 1/2 .lambda. plates 105, and a P wave is 
emitted forward from the prisms 100, 200. There are as many prisms 200 as 
the number of the convex lenses 112a of the first multilens array 112. 
The optical block 101, which is composed of the prisms, the PBSs, the 
mirrors, etc., is capable of converting applied rays of randomly polarized 
light (P+S waves) into a P wave and emitting the P wave, and has entrance 
and exit sides whose areas are equal to each other. Since the optical 
block 101 is of a thinner structure than the conventional optical block, 
the optical block 101 is a space saver. 
The optical block 101 is disposed between the first multilens array 112 and 
the second multilens array 113, as shown in FIG. 18, thereby providing the 
optical system as shown in FIG. 15. 
DISCLOSURE OF THE INVENTION 
The present invention provides an optical block, which may be of a small 
size, for applying light efficiently to a display device such as a liquid 
crystal panel, and a display apparatus. 
According to the present invention, an optical block comprises a baseboard, 
a polarizing beam splitter mounted on the baseboard at a predetermined 
angle with respect to light applied from a light source, for passing a 
first polarized component of the light applied from the light source in a 
first direction and reflecting a second polarized component of the light 
applied from the light source in a second direction, reflecting means 
mounted on the baseboard, for reflecting the reflected second polarized 
component in the first direction, and plane-of-polarization rotating means 
for rotating the plane of polarization of the reflected second polarized 
component. 
A display apparatus according to the present invention uses the optical 
block. The display apparatus comprises a light source for emitting light, 
a first multilens array for being irradiated with the light emitted from 
the light source, the optical block, a second multilens array for being 
irradiated with light emitted from the optical block, separating means for 
separating light emitted from the second multilens array into red light, 
green light, and blue light, light modulating means for generating 
modulated red light, modulated green light, and modulated blue light 
corresponding to a video signal which represents a video image to be 
projected, based on the red light, the green light, and the blue light, 
and emitting means for combining the modulated red light, the modulated 
green light, and the modulated blue light outputted from the light 
modulating means, and emitting combined modulated light. 
Another display apparatus according to the present invention also uses the 
optical block. The display apparatus comprises a light source for emitting 
light, a first multilens array for being irradiated with the light emitted 
from the light source, a second multilens array for being irradiated with 
light emitted from the first multilens array, the optical block, 
separating means for separating light emitted from the second optical 
block into red light, green light, and blue light, light modulating means 
for generating modulated red light, modulated green light, and modulated 
blue light corresponding to a video signal which represents a video image 
to be projected, based on the red light, the green light, and the blue 
light, and emitting means for combining the modulated red light, the 
modulated green light, and the modulated blue light outputted from the 
light modulating means, and emitting combined modulated light. 
With the above arrangements of the optical block and the display apparatus, 
since the entrance and exit sides of the optical block can be of the same 
size as the aperture of the light source, the optical block can have a 
thin structure. Therefore, the optical block may be a space saver and 
lightweight. In the display apparatus, optical paths from the light source 
to liquid crystal panels or the like may be shortened. 
According to the present invention, an optical block comprises a first 
optical block having a first polarizing beam splitter having a first angle 
with respect to light applied from a light source, for passing a first 
polarized component of the light applied from the light source in a first 
direction and reflecting a second polarized component of the light applied 
from the light source in a second direction, first reflecting means having 
the first angle, for reflecting the reflected second polarized component 
in the first direction, and first plane-of-polarization rotating means 
having a second angle substantially perpendicularly to the first 
direction, for rotating the plane of polarization of the second polarized 
component reflected in the first direction, and a second optical block 
having a second polarizing beam splitter having a third angle at which the 
second polarizing beam splitter and the first polarizing beam splitter are 
symmetrical with respect to an optical axis of the light applied from the 
light source, for passing a first polarized component of the light applied 
from the light source in a first direction and reflecting a second 
polarized component of the light applied from the light source in a second 
direction, second reflecting means disposed at the third angle, for 
reflecting the reflected second polarized component in the first 
direction, and second plane-of-polarization rotating means disposed at the 
second angle, for rotating the plane of polarization of the second 
polarized component reflected in the first direction. A display apparatus 
comprises the above optical block and first and second multilens arrays. 
With the above arrangements of the optical block and the display apparatus, 
since the optical block comprises the first and second optical blocks 
which are symmetrical with respect to the optical axis of the light 
emitted from the light source, differences between separating 
characteristics of the polarizing beam splitters depending on the angle of 
incidence of light on the optical block can cancel each other on opposite 
sides of the optical axis. 
According to the present invention, furthermore, an optical block comprises 
a polarizing beam splitter having a predetermined angle with respect to 
light applied from a light source, for passing a first polarized component 
of the light applied from the light source in a first direction and 
reflecting a second polarized component of the light applied from the 
light source in a second direction, and reflecting and polarizing means 
having a reflecting layer for reflecting the reflected second polarized 
component in the first direction, and a plane-of-polarization rotating 
layer disposed on an upper surface of the reflecting layer, for rotating 
the plane of polarization of the second polarized component. A display 
apparatus comprises the above optical block and first and second multilens 
arrays. 
With the above arrangement of the present invention, since the 
plane-of-polarization rotating layer is disposed on the upper surface of 
the reflecting layer, the number of components of the optical block may be 
reduced, or the process of manufacturing the optical block may be 
simplified.

BEST MODE FOR CARRYING OUT THE INVENTION 
For a detailed description of the present invention, optical blocks and 
display apparatus according to embodiments of the present invention will 
be described below with reference to the accompanying drawings. 
First, an optical system of a liquid crystal projector which employs a 
display apparatus according to an embodiment of the present invention will 
be described below with reference to FIG. 7. 
As shown in FIG. 7, a light source 10 comprises a metal halide lamp 10a 
disposed at the focal point of a parabolic mirror for emitting light 
substantially parallel to the optical axis of the parabolic mirror from 
its aperture. An IR-UV blocking filter 11 blocks unwanted rays in infrared 
and ultraviolet ranges of the light emitted from the light source 10, and 
passes only effective rays of light to an optical means in front of the 
light source 10. 
The optical means has a first multilens array 12 comprising a matrix of 
convex lenses 12a and having an outer profile similar to liquid crystal 
panels 17, 21, 26 as spatial light modulating elements and having an 
aspect ratio substantially equal to the aspect ratio of an effective 
apertures of the liquid crystal panels, an optical block 1 comprising 
optical components, and a second multilens array 13 comprising a matrix of 
convex lenses 13a disposed behind the optical block 1. 
The optical block 1 comprises PBSs, mirrors, and 1/2 .lambda. plates 
mounted on a baseboard, and serves to transmit incident light in space. As 
described in detail later on with reference to FIGS. 1 and 2, light of P+S 
waves converged by the first multilens array 12 enters certain PBSs, and 
is polarized into a P wave, for example, in this embodiment. The P wave 
then travels through the second multilens array 13 and various optical 
elements such as dichroic mirrors, is separated into R light, G light, and 
B light, which are applied to the liquid crystal panels. 
Therefore, the first multilens array 12, the second multilens array 13, and 
the optical block 1 allow rays of light emitted from the light source 10 
and passing through the IR-UV blocking filter 11 to be polarized into a P 
wave, which is applied efficiently and uniformly to the effective 
apertures of the liquid crystal panels 17, 21, 26. 
The second multilens array 13 disposed behind the optical block 1 has the 
convex lenses 13a positioned on its face confronting the optical block 1, 
i.e., an entrance side thereof. The second multilens array 13 also has a 
single convex surface as a condenser lens 13X disposed on an exit side 
thereof which faces the liquid crystal panels. 
Dichroic mirrors 14, 19 for separating rays of light from the light source 
10 into red light, green light, and blue light are disposed between the 
second multilens array 13 and the effective apertures of the liquid 
crystal panels. 
In the embodiment shown in FIG. 7, the dichroic mirror 14 reflects the red 
light R and passes the green light G and the blue light B. The red light R 
reflected by the dichroic mirror 14 has its direction of travel bent 
90.degree. by a mirror 15, and is converged by a condenser lens 16 and 
applied to a red liquid crystal panel 17. 
The green light G and the blue light B which have passed through the 
dichroic mirror 14 are separated from each other by the dichroic mirror 
19. The green light G is reflected by the dichroic mirror 19 so that its 
direction of travel is bent 90.degree., and is applied through a condenser 
lens 20 to a green liquid crystal panel 21. The blue light B passes 
straight through the dichroic mirror 19, and travels through a relay lens 
22, a mirror 24a, a relay lens 23, a mirror 24b, and a condenser lens 25 
to a blue liquid crystal panel 26. 
Polarizers (not shown) for aligning the directions of polarization of light 
applied thereto are positioned in front of the liquid crystal panels 17, 
21, 26, and polarizers (not shown) for passing only emitted light having a 
certain plane of polarization are positioned behind the liquid crystal 
panels 17, 21, 26. The liquid crystal panels 17, 21, 26 modulate the 
intensity of light with voltages applied to circuits (not shown) for 
energizing the liquid crystal materials. 
The red light, the green light, and the blue light which are optically 
modulated by the liquid crystal panels 17, 21, 26 are combined by a cross 
dichroic prism 18 as a light combining means. The cross dichroic prism 18 
is of the same structure as the cross dichroic prism 58 shown in FIG. 13. 
The red light R is reflected by a reflecting surface 18a toward a 
projection lens 30, and the blue light B is reflected by a reflecting 
surface 18b toward the projection lens 130. The green light G passes 
through the reflecting surfaces 18a, 18b. The R, G, B rays of light are 
thus combined to travel along one optical axis, and projected at an 
enlarged scale onto a screen (not shown) by the projection lens 30. 
The structure of the optical block 1 will be described below with reference 
to FIGS. 1 and 2. 
FIG. 1 is a perspective view of the optical block 1 as viewed from its 
front. FIG. 2 is a view schematically showing a portion of the optical 
block 1 and illustrative of optical paths of light applied from the light 
source 10. 
The optical block 1 comprises optical components including PBSs 3 (3a, 3b, 
3c, 3d), mirrors 4 (4a, 4b, 4c, 4d), and 1/2 .lambda. plates 5 (5a, 5b, 
5c, 5d) mounted in grooves defined in an upper surface of a baseboard 2. 
The PBSs 3 comprise glass plates with TiO.sub.2 or the like evaporated on 
their surfaces, and are press-fitted in the baseboard 2 at an angle to the 
direction in which light is applied. In this embodiment, the PBSs 3 pass a 
P wave and reflect an S wave. The mirrors 4 comprise glass plates of 
elongate rectangular shape with a multilayer film of aluminum, glass, or 
the like evaporated on their surfaces, for reflecting applied light. The 
mirrors 4 are mounted on the baseboard 2 at such an angle as to reflect 
the S wave reflected by the PBSs 3 toward an exit side of the optical 
block 1. The 1/2 .lambda. plates 5 comprise glass plates of elongate 
rectangular shape with a uniaxially stretched 1/2 phase difference film of 
polycarbonate, polyvinyl alcohol, or polyethylene terephthalate, for 
example, applied thereto. The 1/2 .lambda. plates 5 are mounted on the 
baseboard 2 at a position for receiving the S wave reflected by the 
mirrors 4, polarizing the S wave into a P wave, and emitting the P wave. 
The optical block 1, which is composed of the PBSs 3, the mirrors 4, the 
1/2 .lambda. plates 5, etc., is capable of converting applied rays of 
light (P+S waves) into a P wave and emitting the P wave, and has entrance 
and exit sides whose areas are substantially equal to each other. Since 
the optical block 1 is of a thinner structure than the conventional 
optical block, the optical block 1 is a space saver. Furthermore, because 
the optical block 1 has no prisms, it is lightweight and can be 
manufactured at a reduced material cost. 
Light emitted from the metal halide lamp 10a of the light source 10 is 
radiated substantially parallel to the optical axis. Therefore, the light 
converged by the first multilens array 12 projects an electrode image (arc 
image) radially about the optical axis onto the second multilens array 13. 
If the convex lenses 13a of the second multilens array 13 are formed so as 
to correspond to the convex lenses 12a of the first multilens array 12, 
then the convex lenses 13a are divided vertically with respect to the 
longitudinal direction (horizontal direction) of the convex lenses 12a, 
and the convex lenses 13a are formed so as to minimize the difference 
between longitudinal and transverse lengths for making the aspect ratio 
closer to 1:1, so that the efficiency with which to utilize light can be 
increased. 
If the effective apertures of the liquid crystal panels are of an aspect 
ratio of 16:9, then since the convex lenses 12a are formed with an aspect 
ratio of 16:9, the convex lenses 13a are formed with an aspect ratio of 
8:9, for example. 
The convex lenses 12a of the first multilens array 12 and the convex lenses 
13a of the second multilens array 13 are arranged with their longitudinal 
direction oriented in the horizontal direction. 
The PBSs 3, the mirrors 4, and the 1/2 .lambda. plates 5 of the optical 
block 1 are mounted on the baseboard in a juxtaposed fashion parallel to 
the longitudinal direction of the convex lenses 12a of the first multilens 
array 12, i.e., horizontally as shown in FIG. 1. 
Optical paths for converging light with the first multilens array 12, the 
optical block 1, and the second multilens array 13 will be described below 
with reference to FIG. 8. The light source 10 is omitted from illustration 
in FIG. 8. The single convex lens on the exit side of the second multilens 
array 13 is omitted from illustration in FIG. 8, and the convex lenses 13a 
are shown as joined together. A condenser lens (not shown) may be disposed 
on the exit side of the second multilens array 13. 
Light emitted from the light source 10 (not shown) is converged by the 
convex lenses 12a of the first multilens array 12, and applied 
respectively to the PBSs 3 (3a, 3b, 3c, 3d) of the optical block 1. The 
optical block 1 emits a P wave which has passed through the PBSs 3 and a P 
wave converted by the 1/2 .lambda. plates 5 from an S wave which has been 
reflected by the PBSs 3 and the mirrors 4. 
The P wave emitted from the optical block 1 is applied to the convex lenses 
of the second multilens array 13 (13a, 13b, . . . , 13h). 
In the above embodiment, the optical block 1 is disposed between the first 
multilens array 12 and the second multilens array 13. However, as shown in 
FIG. 9, the first multilens array 12 and the second multilens array 13 may 
be disposed successively away from the light source 10, and followed by 
the optical block 1. 
If the convex lenses 13a of the second multilens array 13 are formed so as 
to correspond to the convex lenses 12a of the first multilens array 12, 
then there are as many convex lenses 13a of the second multilens array 13 
as the number of the convex lenses 12a of the first multilens array 12. 
For example, if the effective apertures of the liquid crystal panels are of 
an aspect ratio of 16:9, then since the convex lenses 12a are formed with 
an aspect ratio of 16:9, the convex lenses 13a are formed with an aspect 
ratio of 16:9. 
In FIG. 7, the condenser lens 13X is disposed behind the convex lenses 13a 
of the second multilens array 13. In FIG. 9, the condenser lens 13X is 
disposed behind the optical block 1 which is disposed behind the second 
multilens array 13, and converges the light emitted from the optical block 
1 onto the liquid crystal panels. 
Inasmuch as there is a difference between the length of the optical path of 
the light which has passed through the PBSs 3 and the length of the 
optical path of the light which has been reflected by the PBSs 3, they 
would be converged at different positions by the condenser lens. In view 
of this, the second multilens array 13 is positioned in front of the 
optical block 1. If the lenses of the first multilens array 12 and the 
second multilens array 13 are the same as each other, since principal rays 
of light applied to the optical block 1 are composed of parallel light, 
the light which has passed through the PBSs 3 and the light which has been 
reflected by the PBSs 3 are not converged at different positions even 
though there is a difference between the lengths of their optical paths. 
An optical block according to another embodiment of the present invention 
will be described below. 
FIG. 3 is a perspective view of an optical block 6 as viewed from its 
front, and FIG. 4 is a view schematically showing a portion of the optical 
block 6 and illustrative of optical paths of light applied from the light 
source 10. 
The optical block 6 shown in FIGS. 3 and 4 comprises PBSs 3 (3a, 3b, 3c, 
3d) mounted on a baseboard 2 for separating P+S waves into a P wave and an 
S wave, as with the optical block 1. The P wave passes through the PBSs 3, 
and the S wave is reflected by the PBSs 3 and then reaches polarizing 
mirrors 7 (7a, 7b, 7c, 7d) as polarizing mirror means. 
As shown in FIG. 4, each of the polarizing mirrors 7 comprises a mirror 
layer 7A disposed as a reflecting layer on a glass plate of elongate 
rectangular shape and a polarizer layer 7B comprising a 1/4 phase 
difference film applied as a plane-of-polarization rotating layer to an 
upper surface of the mirror layer 7A. The S wave reflected by the PBSs 3 
is applied to the polarizer layers 7B, which circularly polarize the S 
wave. The S wave then reaches the mirror layers 7A, which reflect the S 
wave toward an exit side of the optical block 6. The S wave passes the 
polarizer layers 7B, which linearly polarize the S wave. As a result, 
since the plane of polarization of the S wave is rotated 90.degree., the S 
wave is emitted as a P wave to the exit side of the optical block 6. 
In this embodiment, the number of components mounted on the baseboard 2 is 
reduced. 
The structure in which the plane-of-polarization rotating layer is mounted 
on the upper surface of the reflecting layer may be incorporated in the 
optical block 101 which employs prisms, as shown in FIGS. 16 and 17. 
As shown in FIG. 10 which schematically illustrates a portion of the 
optical block 101, PBSs 103 (103a, 103b, 103c, 103d) for reflecting an S 
wave and passing a P wave, for example, are disposed on slanted exit 
surfaces of the prisms 200 (200a, 200b, 200c, 200d), and mirror layers 107 
(107a, 107b, 107c, 107d) as reflecting layers for reflecting forward the S 
wave reflected by the PBSs 103 are disposed on slanted surfaces of the 
prisms 100 which face the PBSs 103. Polarizer layers 108 (108a, 108b, 
108c, 108d) comprising 1/4 phase difference films applied as 
plane-of-polarization rotating layers are disposed on upper surfaces of 
the mirror layers 107 closer to the prisms 200. The S wave reflected by 
the PBSs 103 is applied to the polarizer layers 108, which circularly 
polarize the S wave. The S wave then reaches the mirror layers 107 and is 
reflected thereby toward the exit side. When the S wave passes the 
polarizer layers 108 again, it is linearly polarized thereby. As a result, 
since the plane of polarization of the S wave is rotated 90.degree., the S 
wave is emitted as a P wave forward from the prisms 200. 
The process of manufacturing the optical block is simplified because the 
number of surfaces where reflecting surfaces, etc. are formed on the 
prisms 200, 100 is reduced. 
Inasmuch as the separating characteristics of the PBSs 3 depend on the 
angle of incidence, it is preferable to apply light at the same angle to 
the PBSs 3. In the optical blocks 1, 6 described with reference to FIGS. 1 
through 4, since the PBSs 3 (3a, 3b, 3c, 3d) are oriented in the same 
direction, light is applied to the PBSs 3 in right and left ends at 
different angles of incidence, and hence those PBSs 3 have different 
separating characteristics. These different separating characteristics 
appear directly in the image, tending to produce a phenomenon such as 
color variations at the right and left ends. 
To avoid such color variations, as shown in FIGS. 5 and 6 which illustrate 
optical blocks corresponding to those shown in FIGS. 2 and 4, PBSs 3L, 3R 
are arranged substantially in a V-shaped pattern spreading toward the exit 
side and symmetrical with respect to the optical axis which is indicated 
by the dot-and-dash line. Mirrors 4L, 4R shown in FIG. 5 and mirrors 7L, 
7R with plane-of-polarization rotating layers mounted thereon shown in 
FIG. 6 are also arranged substantially in a V-shaped pattern. 
With this arrangement, light is applied at the same angle to the PBSs 3L, 
3R that are mounted at the same distance from the optical axis. Since the 
dependency on the angle of incidence is canceled, any color variations 
that may appear in the image can be reduced. 
The structure in which the PBSs and the reflecting surfaces are arranged 
symmetrically with respect to the optical axis of the optical block may be 
incorporated in the optical block 101 which employs prisms, as shown in 
FIGS. 16 and 17. 
As shown in FIG. 11 which illustrates the optical block 101 and the front 
and rear multilens arrays 112, 113, the parallelogrammatic prisms 200 
(200a, 200b, 200c, 200d) and triangular prisms 100 (100a, 100b, 100c, 
100d) are arranged symmetrically with respect to the optical axis which is 
indicated by the dot-and-dash line. 
Light applied from the first multilens array 112 to the optical block 101 
is applied at the same angle on both sides of the optical axis. Therefore, 
the dependency on the angle of incidence is canceled, and hence any color 
variations that may appear in the image can be reduced. 
The optical blocks according to the embodiments shown in FIGS. 4, 5, 10, 
and 11 and others can be incorporated in the liquid crystal projectors 
shown in FIGS. 7 and 9. 
In the above embodiments, the present invention has been applied to a 
three-plate liquid crystal projector. However, the present invention may 
be applied to a single-plate liquid crystal projector, a 3D 
(3-dimensional) liquid crystal projector, or an optical system for 
converting laser beam polarization highly efficiently. 
According to the present invention, as described above, since the entrance 
and exit sides of an optical block can be of the same size as the aperture 
of a light source, the optical block can have a thin structure. Therefore, 
the optical block may be a space saver and lightweight. The cost of the 
optical block may be reduced as prisms are dispensed with. 
Because the entrance and exit sides of the optical block can be of the same 
size as the aperture of the light source, the optical paths from the light 
source to the liquid crystal panels can be shortened, and hence the 
display apparatus can be reduced in size. 
If the plane-of-polarization rotating layers are disposed on the upper 
surfaces of the reflecting layers of the optical block, then the number of 
components may be reduced, and the process of manufacturing the optical 
block may be simplified. 
If the components of the optical block are arranged symmetrically with 
respect to the optical axis of incident light, then the dependency on the 
angle of incidence can be canceled, and any color variations that may 
appear in the image can be reduced.