Liquid crystal panel having micro-lens array with extended focal length and display apparatus having the same

According to a liquid crystal panel of the present invention, the focal length of micro-lenses is set to be longer than the distance between the micro-lens array and the first substrate, while light collected by each micro-lens is arranged to focus inside the first substrate. Thus, the divergence angle after focusing can be reduced. Therefore, the maximum light-emerging angle from the LCD panel can be reduced, and eclipse of the light which causes chrominance or luminance non-uniformity does not occur even when a lens having a high F number is used as a projection lens.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to liquid crystal panels, which have 
collecting micro-lenses opposing pixel electrodes driving liquid crystal 
pixels so as to achieve higher luminance, and projection type display 
devices using such liquid crystal panels. 
2. Description of the Related Art 
Recently, liquid crystal projectors and liquid crystal projection TVs, in 
which an image on a liquid crystal panel is projected onto a screen by a 
magnifying optical projection system utilizing a liquid crystal panel as 
an optical switching element, have been popularly developed. These 
apparatuses are advantageous in that they are thin and lightweight, have 
sharp images, are not affected by earth's magnetic field, and do not 
require registration adjustment. 
Such liquid crystal display devices are classified into single-panel 
systems composed of a liquid crystal panel having color filters for three 
colors, i. e., B (blue), R (red), and G (green), and three-panel systems 
having monochrome liquid crystal panels for the B, R, and G optical paths. 
According to the single-panel systems, a compact and lightweight liquid 
crystal device can be readily formed at a lower cost because of its simple 
structure. However, since the color filters absorb a large amount of 
light, it is difficult to achieve higher luminance and efficient cooling. 
To solve such problems, for example, Japanese Patent Laid-Open No. 4-60538 
(hereinafter referred to as "document (i)") and "ASIA DISPLAY '95, p 887" 
(hereinafter referred to as "document (ii)") disclose color liquid crystal 
display devices in which collecting micro-lenses are arranged as follows: 
one collecting micro-lens opposes every three pixel electrodes driving 
liquid crystal pixels, and light beams of three colors, i. e., B, R, and 
G, enter each of the micro-lenses from mutually different directions so as 
to be collected, and the resultant emerging light beam of each color 
enters a pixel electrode corresponding to the color of the emerging light 
beam. In this color liquid crystal display device, light beams which would 
normally enter the regions between the pixels (the matrix of opaque 
regions in which thin-film transistors (TFTs) are formed as pixel driving 
elements) can be effectively utilized so that the effective aperture ratio 
increases, thereby achieving a higher luminance. 
According to such color liquid crystal display devices, the focal points of 
the micro-lenses opposing the pixel electrodes are positioned near the 
corresponding pixel portions. In other words, collimated light entering 
the micro-lens is collected to focus near the pixel portion, and then, 
diverges again. 
Although data projectors and rear projection TVs based on the liquid 
crystal projection system have already been put into practical use, it is 
supposed that with the development of multi-media, these devices are 
required to display computer and AV (audio.multidot.video) images on the 
same panel at a resolution as high as that of high-definition televisions. 
In such a case, the optical system including the liquid crystal display 
elements must have higher resolution, higher image quality, and higher 
luminance as compared with conventional optical systems. For example, a 
liquid crystal display panel employed in presently used rear-projection 
TVs uses TFTs made of amorphous silicon (a-Si), and the total number of 
pixels is approximately 1,300,000 or less in a picture size of 3 to 5 
inches. However, to achieve thinner and lighter devices according to the 
liquid crystal projection system, it is necessary to increase the pixel 
density to approximately 1,500,000 to 2,000,000 pixels in a picture size 
of 2 inches. Moreover, such compact high-resolution LCD panels, including 
their optical system, are advantageous in reducing prices. Thus, a further 
increase in consumer demand is expected in the future. Concerning process 
techniques, it is supposed that high-temperature polysilicon 
(polycrystalline silicon) TFT techniques or low-temperature polysilicon 
TFT techniques become important for producing such high-resolution liquid 
crystal panels. 
As mentioned above, there is a greater necessity to reduce the area of 
pixel portions in liquid crystal projectors to achieve higher resolution. 
Thus, from now on, the TFTs, as the pixel driving elements, are required 
to be formed from polysilicon instead of amorphous silicon. This is 
because in the case of a-Si having low carrier-mobility, the size of the 
TFTs must increase to some extent for providing a certain amount of 
electric current for driving the pixels. Meanwhile in the case of 
polysilicon having high carrier-mobility, the size of the TFTs can be 
reduced. Practically, the pixel pitch is limited to approximately 100 
.mu.m in the case of a-Si, while a small pixel pitch of 20 .mu.m can be 
employed in the case of polysilicon. 
With such a reduction in the pixel area, the collecting diameter of the 
micro-lenses is required to be correspondingly smaller. Although, it is 
ideal that the light beams entering the micro-lenses from the projection 
optical system are completely parallel to the optical axis, in practice, 
the light beams are shifted from the parallel state by a small angle. 
Thus, light beams which should enter only one pixel reach the opaque 
regions between adjacent pixels, thereby reducing transmission efficiency. 
Consequently, the luminance of the display image decreases and the effects 
of the micro-lenses decline. Additionally, when a light beam, which should 
enters only one pixel for a certain color (e. g., the pixel for G), enters 
an adjacent pixel for another color (e. g., the pixel for R), so-called 
color mixing occurs and deteriorates the color image quality. For example, 
the incident light intensity and the shift between the original incident 
angle and the light beam entering a pixel of a certain color (e. g., the 
pixel for G) has the relationship shown in FIG. 5. The incident light 
intensity reaches its maximum value at angles slightly shifted from the 
original incident angle, as is shown in FIG. 5. Therefore, it is 
understood that the shift of the incident angle greatly affects the 
luminance and color mixing of the displayed images. 
The larger the distance between each pixel portion and the corresponding 
micro-lens, the more significant the trend becomes. Therefore, with an 
increasing demand for high resolution, the distance between each pixel and 
the corresponding micro-lens must be correspondingly reduced. For 
achieving the above, the following methods can be employed: a method for 
reducing the focal length by decreasing the size of the micro-lenses while 
retaining their shape, and a method for reducing the focal length alone 
without changing the size of the micro-lenses. According to the former 
method, the aperture angle (the angle subtended by the lens diameter at 
the focal point) in the light-emerging side does not alter because the 
shape of the micro-lenses is retained. However, to design and produce such 
fine micro-lenses is not easy. Furthermore, it is not practical to reduce 
the size of the micro-lenses while retaining the shape, considering the 
relationship between the display-element format and other optical parts. 
Therefore, the focal length is required to decrease without greatly 
changing the lens diameter. 
In such a case, the aperture angle can be raised by positioning the focal 
points at the pixel portion, as is mentioned above. The divergence angle 
of the emerging light beams from the micro-lens is thereby enlarged. Thus, 
to effectively utilize the entire light beams emerging from the liquid 
crystal panel without eclipsing, the F number of the projection lens 
positioned behind the liquid crystal panel must be considerably reduced, 
in other words, it is necessary to employ a bright lens system. This is 
because eclipses of light beams result in luminance or chrominance 
non-uniformity in images projected on a screen. However, it is generally 
difficult and costly to design and produce a lens system having a low F 
number, and thus the cost for the device as a whole increases. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide liquid 
crystal panels at a low cost, which achieve high-resolution images without 
deteriorated image quality such as luminance or chrominance 
non-uniformity, and projection type display device using such liquid 
crystal panels. 
A liquid crystal panel of the present invention comprises: a first 
substrate having pixel electrodes arranged in a matrix pattern; a second 
substrate opposing the first substrate, the second substrate having a 
transparent substrate, an opposing electrode opposing the pixel 
electrodes, and a micro-lens array provided between the transparent 
substrate and the opposing electrode; and a liquid crystal layer 
sandwiched between the first and second substrates; in which the focal 
length of micro-lenses composing the micro-lens array is set to be longer 
than the distance between the micro-lens array and the first substrate, 
and light collected by each of the micro-lenses is allowed to pass through 
the pixel electrodes and to focus inside the first substrate. The 
micro-lenses may be arranged such that each of the micro-lenses opposes 
each of the pixel electrodes or each micro-lens opposes a plurality of 
pixel electrodes in the first substrate. The liquid crystal panel may have 
a color filter provided between the opposing electrode and micro-lenses. 
A projection type display device of the present invention comprises: a 
light source; a means for separating light emerging from the light source 
into a plurality of light beams having mutually different wavelength 
ranges; a liquid crystal panel in which the light beams enter, the liquid 
crystal panel having: a first substrate having pixel electrodes arranged 
in a matrix pattern; a second substrate opposing the first substrate, the 
second substrate comprising a transparent substrate, an opposing electrode 
opposing the pixel electrodes, and a micro-lens array provided between the 
transparent substrate and the opposing electrode; and a liquid crystal 
layer sandwiched between the first substrate and the second substrate; in 
which the focal length of micro-lenses composing the micro-lens array is 
set to be longer than the distance between the micro-lens array and the 
first substrate, and the light collected by each of the micro-lenses is 
allowed to pass through the pixel electrodes and to focus inside the first 
substrate; and a means for synthesizing each of the light beams, which 
have been transmitted through the liquid crystal panel and modulated 
therein, on a display screen. The micro-lenses may be arranged such that 
each micro-lens opposes a plurality of pixel electrodes in the first 
substrate. The means for separating the emerging light may be composed of 
dichroic mirrors, a hologram element, a diffraction grating, or a prism. 
A projection type display device of the present invention comprises: a 
light source; a means for separating light emerging from the light source 
into a plurality of light beams having mutually different wavelength 
ranges; a plurality of liquid crystal panels in which the light beams 
enter, respectively, each of the liquid crystal panels comprising: a first 
substrate having pixel electrodes arranged in a matrix pattern; a second 
substrate opposing the first substrate, the second substrate having a 
transparent substrate, an opposing electrode opposing the pixel 
electrodes, and a micro-lens array provided between the transparent 
substrate and the opposing electrode; and a liquid crystal layer 
sandwiched between the first and second substrates; in which the focal 
length of micro-lenses composing the micro-lens array is set to be longer 
than the distance between the micro-lens array and the first substrate, 
and light collected by each of the micro-lenses is allowed to pass through 
the pixel electrodes and to focus inside the first substrate; and a means 
for synthesizing the light beams emerging from the corresponding liquid 
crystal panels on a display screen. The micro-lenses may be arranged such 
that each of the micro-lenses is allowed to oppose each of the pixel 
electrodes in the first substrate. Light beams of the primary colors R, G, 
and B may be incident on the corresponding liquid crystal panels. 
According to a liquid crystal panel of the present invention, the focal 
length of the micro-lenses is set to be longer than the distance between 
the micro-lens array and the first substrate, while light collected by 
each micro-lens is arranged to focus inside the first substrate; thus the 
divergence angle after focusing can be reduced.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The above and other objects, features and advantages of the present 
invention will be better understood from the following detailed 
description of the preferred embodiment taken in conjunction with the 
accompanying drawings. 
FIG. 1 shows the main structure of a color liquid crystal projector of an 
embodiment incorporated in the present invention. This device has: 
dichroic mirrors 12B, 12R, and 12G color-separating the parallel white 
light 11, coming from a white-light source (not shown in the figure), into 
a plurality of light beams having mutually different wavelength ranges, i. 
e., a B light beam, a R light beam, and a G light beam, respectively; an 
LCD panel 20 modulating the intensity of the B light beam, the R light 
beam, and the G light beam in response to color image signals; and a 
projection lens 30 collecting the light emerging from the LCD panel 20 for 
projection and color-synthesizing on a screen 40. 
The parallel white light 11 is color-separated into light beams of B, R, 
and G having mutually different wavelength ranges by the dichroic mirrors 
12B, 12R, and 12G, respectively. The dichroic mirrors 12B, 12R, and 12G 
are adjusted to have a small angle between each other so that these light 
beams enter the LCD panel 20 at mutually different angles. In this 
embodiment, the R light beam is allowed to perpendicularly enter the LCD 
panel 20, and the B light beam and the G light beam are arranged to enter 
the LCD panel 20 at angles of [+.theta.] and [-.theta.], respectively, 
with respect to the R light beam. The LCD panel 20, which will be 
explained in detail with reference to FIG. 2, has a first substrate 21 on 
which numerous pixel electrodes are arranged according to a matrix 
pattern, a second substrate 22 having an opposing electrode and 
micro-lenses (both are not shown in this figure), and a liquid crystal 
layer 23 sandwiched between the first substrate 21 and the second 
substrate 22. 
The three types of light beams entering the LCD panel 20 perpendicularly, 
at [+.theta.] to the perpendicular direction, and at [-.theta.] to the 
perpendicular direction may be assigned to the B, R, and G light beams in 
any manner. 
Although dichroic mirrors are used in this embodiment for color-separating 
the light into different wavelength ranges, holograms, diffraction 
gratings, prisms, etc. may be employed instead. 
FIG. 2 is an enlarged diagram showing the cross-sectional structure of the 
LCD panel 20 of FIG. 1. As is shown in this figure, the first substrate 21 
is composed of: a glass substrate 21a; a plurality of pixel electrodes 
21B, 21R, and 21G arranged regularly from the bottom to the top of the 
figure on one side (light-incident side in this figure) of the glass 
substrate 21a according to a matrix pattern; and opaque regions 21b 
composed of TFTs (not shown in the figure) which are used as switching 
elements for applying a voltage to each of the pixel electrodes in 
response to the image signals. Each of the TFTs has a gate electrode, a 
drain electrode, and a source electrode (none of these is shown in the 
figure) made of, for example, polysilicon. The gate electrode is connected 
to an address line (not shown in the figure) running from the top to the 
bottom of the figure, the source electrode is connected to a data line 
(not shown in the figure) running in the direction perpendicular to the 
plane of the figure, and the drain electrode is connected to the 
corresponding pixel electrode 21B, 21R, or 21G. The alignment of the 
liquid crystal molecules in the portion of the liquid crystal layer 23 
between a pixel electrode and an opposing electrode 22d is changed by 
selectively applying an image signal voltage to the pixel electrode which 
is chosen by the address line and the data line. The polarization 
direction of the light beams passing through the portion of the liquid 
crystal layer 23 is thereby altered. 
Meanwhile, the second substrate 22 is composed of: a glass substrate 22a; a 
micro-lens array 22b formed on one side of the glass substrate 22a (the 
light-emerging side in the figure); cover glass 22c closely placed on the 
micro-lens array 22b; and the opposing electrode 22d formed on the cover 
glass 22c. 
The opposing electrode 22d is a transparent electrode formed on the entire 
surface or required regions (i. e., at least the regions opposing the 
pixel electrodes 21B, 21R, and 21G of the first substrate 21) of the cover 
glass 22c. The electric potential of the opposing electrode 22d is fixed 
at a constant value. 
The micro-lens array 22b can be formed as gradient index lenses by a 
selective ion diffusion method, however, it may be formed by other 
methods. Although each micro-lens ML composing the micro-lens array 22b is 
generally formed as a plano-convex lens whose axis is perpendicular to the 
plane of the figure, it may be a general spherical lens or nearly 
spherical lens having a curved face. Furthermore, although the 
light-incident side of the micro-lenses MLs is convex and the 
light-emerging side is flat in this embodiment, alternatively, the 
light-incident side of the micro-lenses MLs may be flat and the 
light-emerging side may be convex. 
The micro-lens array 22b is formed such that one micro-lens is arranged for 
every three pixel electrodes 21B, 21R, and 21G of the first substrate 21. 
The light beams B, R, and G entering the micro-lenses from three different 
directions are collected, pass through the liquid crystal layer 23, and 
then, enter the pixel electrodes 21B, 21R, and 21G, respectively. For 
example, concerning the R light beam, the focal point F.sub.R of the 
micro-lens array 22b is positioned deep inside the glass substrate 21a, 
but not on or near the pixel electrode 21R. In other words, the focal 
length f of the micro-lens is set longer than the distance d between the 
pixel electrode 21R and the principal point A of the micro-lens. 
Therefore, the R light beam emerging from the micro-lens passes through 
the pixel electrode 21R while not being completely focused. Light beams of 
other colors (the B and G light beams) behave similarly to the above. This 
is a notable feature of the present invention. 
The operation of a liquid crystal display device having the above structure 
will be explained. 
As shown in FIG. 1, the parallel white light 11 coming from a light source 
(not shown in the figure) is color-separated into the three light beams B, 
R, and G having mutually different wavelength ranges by the dichroic 
mirrors 12B, 12R, and 12G, respectively. The three light beams B, R, and G 
are linearly polarized by a polarizer not shown in the figure, and then, 
enter the micro-lens array 22b of the LCD panel 20 from mutually different 
directions. Explanation will be made of light beams entering one 
micro-lens ML of the micro-lens array 22b. Since the R light beam 
perpendicularly enters the glass substrate 22a, it focuses inside the 
glass substrate 21a after passing through the pixel electrode 21R through 
which the optical axis of the micro-lens Ml passes. The B light beam 
enters the glass substrate 22a at an incident angle .theta., is refracted 
at a refractive angle .psi. enters the micro-lens ML at an incident angle 
.psi., is transmitted through the pixel electrode 21B through which the 
line making an angle .psi. with the optical axis of the micro-lens Ml 
passes (not shown in the figure), and focuses at a focal point F.sub.B 
inside the glass substrate 21a. Similarly, the G light beams enters the 
glass substrate 22a at an incident angle .theta., is refracted at a 
refractive angle .psi., enters the micro-lens ML at an incident angle 
.psi., is transmitted through the pixel electrode 21G through which the 
line making an angle .psi. with the optical axis of the micro-lens Ml 
passes (not shown in the figure), and focuses at a focal point F.sub.G 
inside the glass substrate 21a. 
At this time, the voltage applied to the pixel electrodes 21B, 21R, and 21G 
varies in response to the pixel signals, and correspondingly, the 
polarization directions of the B, R, and G light beams are modulated, 
while passing through the liquid crystal layer 23. 
The B, R, and G light beams then focus inside the glass substrate 21a of 
the first substrate 21, diverge again at divergence angles of .phi..sub.B, 
.phi..sub.R, and .phi..sub.G, respectively, emerge form the glass 
substrate 21a, selectively pass through the polarizer not shown in the 
figure, and are collected by the projection lens 30 to be 
color-synthesized on the screen 40. 
With the distance between the principal point A of the micro-lens ML and 
the pixel electrodes 21B, 21R, and 21G being d and the pixel pitch (the 
pitch of the pixel electrodes 21B, 21R, and 21G) being p, d and p must 
satisfy the following equation (1): 
EQU d.multidot.tan.psi.=p (1) 
According to Snell's law, .psi. and .theta. have the following relationship 
of equation (2): 
EQU n.sub.Air .multidot.Sin.theta.=n.sub.SUB .multidot.sin.psi.(2) 
wherein n.sub.Air and n.sub.SUB are the refractive index of air and the 
refractive index of the glass substrate 22a, respectively. 
The advantages of this embodiment will be explained as compared with a case 
in which the focal points of the micro-lens ML are positioned on or near 
the pixel electrodes 21B, 21R, and 21G of the first substrate 21. 
FIG. 3 is a diagram showing the case in which the focal points of the 
micro-lens ML are positioned on or near the pixel electrodes while the 
distance between the micro-lens ML and the pixels is the same as that of 
FIG. 2, in other words, the structure of an inside opposing-substrate type 
in which micro-lenses are arranged on the light-emerging surface of the 
second substrate, as is described in the document (ii). In this figure, 
the numerals identify substantially identical parts in FIG. 2, and 
detailed explanations thereof are omitted. 
As is shown in this figure, the B, R, and G light beams entering the 
micro-lens ML from different directions are respectively collected and 
focused on the pixel electrodes 21B, 21R, and 21G of the first substrate 
21. At this time, with the focal length of the micro-lens ML in air being 
f' and the pixel pitch (the pitch of the pixel electrodes 21B, 21R, and 
21G) being p, the incident angles (i. e., the angles made with the R light 
beam) .theta. satisfy the following equation (3), as is mentioned in the 
above documents: 
EQU tan.theta.=p/f' (3) 
In such a case, the divergence angles of the B, R, and G light beams after 
focusing are .phi..sub.B ', .phi..sub.R ', and .phi..sub.G ', 
respectively, which are considerably larger than the divergence angles 
.phi..sub.B, .phi..sub.R, and .phi..sub.G of the present embodiment (FIG. 
2). In other words, the divergence angles .phi..sub.B, .phi..sub.R, and 
.phi..sub.G can be reduced by setting the focal length f of the micro-lens 
ML longer than the distance d between the micro-lens ML and the pixel 
electrodes 21B, 21R, and 21G while setting the focal points inside the 
glass substrate 21a of the first substrate 21. As a result, according to a 
liquid crystal display device of this embodiment, the divergence angles of 
the emerging light beams from the LCD panel 20 decrease, and thus, 
eclipses do not occur even if the projection lens 30 has a small effective 
diameter (i. e., has a high F number). Therefore, low-cost lenses having a 
high F number can be used as the projection lens 30, which constitutes a 
large part of the cost of the liquid crystal display device. 
A preferred example incorporated in this embodiment will be described. 
In FIG. 2, the focal point F.sub.R is at a position approximately 120 .mu.m 
inside the glass substrate 21a from the pixel electrode 21R, with the 
pixel pitch p being 20 .mu.m, the focal length f of the micro-lens ML in 
air being 230 .mu.m (336 .mu.m in a quartz substrate having a refractive 
index of 1.46), the distance d between the micro-lens ML and the pixel 
electrodes 21B, 21R, and 21G being 217 .mu.m, and the incident angle .psi. 
at the micro-lens ML being 5.3.degree. (.psi.=7.7.degree.). In such a 
case, although the collected diameter projected on the pixels (i. e., the 
diameter of the light beam at the position where the R light beam passes 
through the pixel electrode 21R) is approximately 21.2 .mu.m, color mixing 
does not readily occur, since the sum of the pixel pitch 20 .mu.m and the 
opaque region width of 4.5 .mu.m is 24.5 .mu.m. Thus, according to this 
embodiment, the collected diameter projected on the pixels is required to 
not exceed the sum of the pixel pitch and the opaque region width. 
Since color mixing depends on not only the collected diameter but also the 
angular distribution of the incident light, it is necessary to use a lamp 
having the shortest possible arc length as the white light source to 
obtain uniformly collimated light. For example, when a metal halide lamp 
having an arc length of 1.4 mm is employed, the incident light from the 
lamp has an angular distribution of from -3.5.degree. to +3.5.degree., as 
is shown in FIG. 5. However, color mixing does not cause a practical 
problem because the incident angle having the peak intensity is around 
1.degree.. 
According to this example (FIG. 2), the maximum light-emerging angle from 
the LCD panel 20 is approximately 18.7.degree. with respect to the normal 
line of the LCD panel 20. Thus, the F number of the projection lens 30 is 
set to approximately 1.5 so as to collect all the emerging light. 
When light beams are allowed to focus on the pixel electrodes 21B, 21R, and 
21G, as is shown in FIG. 4, and the focal length of the micro-lens ML in 
air is set to 150 .mu.m, the maximum light-emerging angle from the LCD 
panel 20 is approximately 22.7.degree.. Thus, the F number of the 
projection lens 30 must be lower than 1.5, approximately 1.3, for 
collecting all the emerging light, increasing the production cost of the 
projection lens 30. 
The possibility of reducing the maximum light-emerging angle from the LCD 
panel 20 by other methods including conventional methods will be 
investigated below. 
First, the maximum light-emerging angle from the LCD panel 20 can be 
reduced by decreasing the refractive angle .psi. in the glass substrate 
22a. Although the refractive angle .psi. can be reduced by decreasing the 
incident angle .theta. with respect to the glass substrate 22a, it is 
necessary to further improve the collimation of the incident light of each 
color to prevent color mixing. However, when the collimation of the 
incident light is improved to decrease the distribution range of the light 
divergence angle, the total amount of the incident light entering the LCD 
panel 20 is reduced in the optical system, as is shown in FIG. 5. 
Brightness is thereby reduced, in other words, improvement of luminance, 
which is the essential object of the usage of micro-lens, cannot be 
achieved. 
Secondly, a case will be discussed in which micro-lenses are positioned on 
the light-incident surface of a second substrate of a LCD panel, as is 
described in the above-mentioned document (i). In such a case, the 
thickness of the second substrate is approximately 1.1 to 0.7 mm. Assuming 
that the thickness of the second substrate is 0.7 mm, which is the lower 
limit, the focal length of the micro-lenses is approximately 0.7 mm (700 
.mu.m). Therefore, the incident angle .theta. satisfying equation (3) is 
1.8.degree.. However in practice, when the angles between the incident 
light beams are set within 1.8.degree., the total amount of light in the 
optical system is disadvantageously reduced similarly to the above. 
Furthermore, the angles made between two successive mirrors of the three 
dichroic mirrors must be 0.9.degree. (=.theta./2), which is practically 
very difficult and unrealistic to adjust. Assuming that the thickness of 
the second substrate is 1.1 mm, which is the upper limit, the incident 
angle .theta. must be reduced further, resulting in more difficult 
adjustment. 
As is mentioned above, considering the prevention of color mixing and 
luminance reduction, the focal points of the micro-lenses are set on the 
pixels in the documents (i) and (ii). However, the focal points of the 
micro-lenses are not always required to be positioned on the pixels 
because of the following reasons: color mixing can be practically 
prevented by reducing the arc length of light source lamps or optimizing 
the light-separation properties of the dichroic mirrors; and with respect 
to the luminance reduction, no problem occurs when light beams are allowed 
to pass through the aperture portion of each pixel. The present invention 
aims at achieving this point, and accordingly, the focal points of the 
micro-lenses are positioned inside the first substrate but not on the 
pixels. 
In the prior arts including documents (i) and (ii), TFTs made of amorphous 
silicon are employed, with the pixel pitch being approximately 100 .mu.m. 
Therefore, the eclipse problem in the projection lens does not occur in 
conventional systems in which the focal points of the micro-lenses are set 
on the pixels, and such a problem has not been recognized. However, in the 
trend of requiring higher image quality, the F number of the projection 
lens must decrease to a considerably low value according to conventional 
methods when the pixel pitch is reduced to approximately 20 .mu.m or less 
for achieving higher resolution with the TFTs made of polysilicon. Thus, 
the difficulty and cost for producing projection lenses inevitably 
increase. The present invention is extremely effective in solving such 
problems and can sufficiently cope with the demand for higher resolution, 
which is supposed to be more intense in the future. 
Another embodiment of the present invention will be explained below. 
FIG. 4 shows an enlarged cross-sectional structure of an LCD panel in a 
projection type liquid crystal display device of another embodiment 
incorporated in the present invention. In this embodiment, 
color-separation by dichroic mirrors, as is shown in FIG. 1, is not 
employed. A micro-lens and a color filter are arranged for every pixel so 
as to achieve color display. As is shown in FIG. 4, the LCD panel has: a 
first substrate 121 on which numerous pixel electrodes are arranged 
according to a matrix pattern; a second substrate 122 having an opposing 
electrode, micro-lenses, and color filters; and a liquid crystal layer 123 
sandwiched between the first substrate 121 and the second substrate 122. 
The first substrate 121 is composed similarly to the first substrate 21 of 
FIG. 2 and has: a glass substrate 121a; pixel electrodes 121B, 121R, and 
121G regularly arranged on the light-incident side of the glass substrate 
121a according to a matrix pattern; and opaque regions 121b composed of 
TFTs (not shown in the figure) which are used as switching elements for 
applying a voltage to the pixel electrodes in response to the image 
signals. Since the system of applying signal voltage to each pixel 
electrode (i. e., the structure and switching drive system of the TFTS) is 
similar to that of FIG. 2, the explanation is omitted. 
Meanwhile, the second substrate 122 has: a glass substrate 122a; a 
micro-lens array 122b formed on the light-emerging side of the glass 
substrate 122a; cover glass 122c closely placed on the micro-lens array 
122b; color filters 122e, for the B, R, and G light beams, formed on the 
cover glass 122c corresponding to the pixels; and an opposing electrode 
122d formed on the color filters 122e. The color filters 122e are not 
always required for three-panel system projectors. 
The structure and operation of the opposing electrode 122d is similar to 
those of the opposing electrode 22d of FIG. 2. The micro-lens array 122b 
is formed such that one micro-lens is arranged for each of the pixel 
electrodes 121B, 121R, and 121G of the first substrate 121. The collimated 
light coming from a light source (not shown in the figure) enters and is 
collected by all the micro-lenses MLs, passes through the corresponding 
color filters 122e to form color light beams B, R, and G, and after 
passing through the liquid crystal layer 123, the color beams enter the 
pixel electrodes 121B, 121R, and 121G, respectively. In other words, 
differently from the case of FIG. 2, the optical axes of color light beams 
B, R, and G are parallel to each other in this embodiment. 
Concerning the R light beam, the focal point F.sub.R of the micro-lens 
array 122b is positioned deep inside the glass substrate 121a but not on 
or around the pixel electrode 121R. In other words, the focal length f of 
the micro-lenses is set longer than the distance d between the pixel 
electrode 121R and the principal point A of the micro-lens array 122b. 
Therefore, the R light beam emerging from the micro-lens passes through 
the pixel electrode 121R while not being completely focused. Light beams 
of other colors behave similarly to the above. 
In this embodiment, the focal points of the micro-lenses are positioned in 
the first substrate 121 but not on the pixel electrodes, as is similar to 
the case of FIG. 2, thus even when the distance d between the micro-lens 
array 122b and the first substrate 121 decreases with the reduction in the 
pixel pitch, the focal length of the micro-lenses can be set to a larger 
value than d. Therefore, the divergence angle .phi..sub.R of this case is 
smaller than the divergence angle .phi..sub.R ' of the case in which the 
focal points of micro-lenses are positioned on the pixel electrodes (shown 
by dashed lines in the figure). As a result, the emerging angle from the 
LCD panel is reduced. Thus, it is not necessary to significantly decrease 
the F number of the projection lens (not shown in the figure) used for 
synthesizing the color image on the screen. Production costs are thereby 
reduced. 
For example, the focal point of the micro-lenses is at a position 
approximately 128 .mu.m inside the glass substrate 121a from the pixel 
electrode 121R, when the pixel pitch p is 32 .mu.m, the focal length f of 
the micro-lenses in air is 180 .mu.m, and the distance d between the 
principal point of the micro-lenses and the pixel electrodes is 135 .mu.m. 
In this case, the maximum light-emerging angle from the LCD panel is 
approximately 13.8.degree. with respect to the normal line of the LCD 
panel (when a light beam having a divergence angle of +/-8.degree. 
enters). Thus, the F number of the projection lens is approximately 2.3. 
Meanwhile, in the case of setting the focal point on the pixels similarly 
to prior art, the maximum light-emerging angle is approximately 18.10, and 
thus the F number of the projection lens must be set to lower than 2.3. 
Therefore, according to the present embodiment, a projection lens which 
can be more readily produced at lower cost as compared with prior art can 
be used, thereby achieving cost reduction of the device as a whole. 
Although the present invention has been explained with reference to 
embodiments in the above, the present invention is not restricted to those 
embodiments and various modifications can be effected within the spirit 
and scope of the invention. For example, although the pixel driving TFTs 
are placed on the pixel-electrode side in the above embodiments, they may 
be positioned on the second-substrate side. In addition, with respect to 
the central light, the incident angles of the other two color light beams 
are the same .theta. as in the embodiment shown in FIGS. 1 and 2, however 
these incident angles may be different from each other. In such a case, 
the pixel pitch must be changed correspondingly. 
In addition, although the color filters 122e are positioned on the 
light-emerging side of the cover-glass substrate 122c in the embodiment 
shown in FIG. 4, they may be arranged on the light-incident side 
(micro-lens side). Moreover, the color filters can be omitted in the case 
of a monochrome type liquid crystal display device. Furthermore, the 
present invention can be applied to a system, such as three-panel system 
projectors and projection TVs, in which micro-lenses are fixed to 
monochrome liquid crystal panels arranged in the corresponding optical 
paths of B, R, and G light so as to also achieve higher luminance. 
Large screen displays by a magnifying optical projection system utilizing a 
liquid crystal panel are classified into single-panel systems composed of 
a single liquid crystal panel having color filters and three-panel systems 
not having color filters. According to the three-panel systems, light 
beams separated into the primary colors R, G, and B having mutually 
different wavelength ranges are collected to display dots in a liquid 
crystal panel so as to reproduce a color image, as is shown in FIG. 1. In 
other words, separate liquid crystal panels are provided for each of the 
primary colors R, G, and B, and light beams modulated by the corresponding 
liquid crystal panels are synthesized and projected on a screen by one 
projection lens. 
FIG. 6 is a cross-sectional diagram showing the structure of an optical 
system of an LCD panel of an embodiment, in which a dichroic prism is 
employed in the optical system for color synthesis. Light from a light 
source 60 passes through an interference filter 61. A dichroic mirror 62B 
reflects the B light such that the direction of the B light changes by 
90.degree. directing it towards a liquid crystal panel 63B, and transmits 
light of the other colors (R and G). The transmitted light impinges on a 
second dichroic mirror 62G which reflects the G light directing it towards 
a liquid crystal panel 63G, and transmits the R light which is directed 
towards a liquid crystal panel 63R by mirrors 67. As is mentioned above, 
the separated light beams of R, G, and B are allowed to enter three liquid 
crystal panels 63R, 63G, and 63B, respectively. In each of the liquid 
crystal panels 63R, 63G, and 63B, an image corresponding to the color of 
the panel is reproduced and the incident light beam of each color is 
modulated. The modulated incident light beams enter a dichroic prism 64 
from mutually different directions. A color image is synthesized in the 
dichroic prism 64, and then, projected on a screen 66 by a projection lens 
65. In the liquid crystal panels of such a projection display device, a 
micro-lens and a pixel electrode are arranged for each pixel. Simpler 
design and lower costs for projection lenses can be achieved by 
positioning the focal points of the micro-lenses inside the pixel 
substrate so as to increase the F number of the projection lens. 
As explained above, according to a liquid crystal panel of the present 
invention, the focal length of micro-lenses is set to be longer than the 
distance between the micro-lens array and the first substrate, while light 
collected by each micro-lens is arranged to focus inside the first 
substrate. Thus, the divergence angle after focusing can be reduced. 
Therefore, the maximum light-emerging angle from the LCD panel can be 
reduced, and eclipse of the light which causes chrominance or luminance 
non-uniformity does not occur even when a lens having a high F number is 
used as a projection lens. Thus, difficulty and costs for producing 
projection lenses can be reduced, thereby advantageously reducing the cost 
of the device as a whole.