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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal light valve which is used
for a projection type display device, a spatial light modulating element
and a coherent light operating element.
2. Description of the Related Art
The inventors of the present invention know of other addressing systems for
forming an image on a liquid crystal valve according to a signal standing
for an image (referred to as an image signal) which include an electric
addressing system, a laser head addressing system or a light addressing
system.
As to the electric addressing system, a liquid crystal light valve of a
simple multiplexing driving system is arranged to have a plurality of
scanning electrodes and signal electrodes formed in a matrix manner. This
liquid crystal light valve is arranged to selectively apply an electric
voltage on any of the pixels consisting of scanning electrodes X1, X2, . .
. Xn and signal electrodes Y1, Y2, . . . Ym ranged in the X direction and
the Y direction, respectively and transmit a scanning signal and a data
signal through electric wires.
As to the light addressing system, a liquid crystal light valve is arranged
so that a liquid crystal layer and a photoconductive layer are laid
between both of the glass substrates and provide transparent electrodes
for directly addressing the liquid crystal through the effect of
irradiated light.
Typical examples of the light addressing type liquid crystal light valve
have been disclosed in J. Grinberg, A. Jacobson, W. Bleha, L. Miller, L.
Frasss, D. Boswell and G. Myer "A New Real-time Noncoherent To Coherent
Write Image Converter" and "The Hybrid Field Effect Liquid Crystal Light
Valve", Optical Engineering Volume 14, 217 (1975).
In these examples, the liquid crystal light valve of a light addressing
type is arranged to have a pair of glass substrates, two transparent
electrodes, a photoconductive layer, a dielectric mirror, two orientation
films, a sealing member, a liquid crystal layer, and an A. C. power
source. The A. C. power source serves to apply a voltage between the
transparent electrodes. When an addressing (writing) ray of light is
incident to one glass substrate, the impedance of the photoconductive
layer is made smaller on the light-hit area (bright state) so that the
voltage is applied from the A. C. power source to the liquid crystal
layer. On the other hand, on the other area where no light impinges (dark
state), the impedance of the photoconductive layer is kept constant so
that no voltage may be applied to the liquid crystal layer.
The difference between the bright state and the dark state leads to forming
an image data corresponding to the addressing light. The image data is
allowed to be read by a reading ray of light.
This type of liquid crystal light valve may apply to a projection type
display device, a coherent operating element, and so forth.
As another example, there has been proposed an addressing type liquid
crystal light valve having a combination of the electric addressing system
and the light addressing system. As disclosed in Japanese Lying Open No.
2-134617, a data signal in the electric addressing system is allowed to be
transmitted by using a light signal.
The above-described electric addressing system liquid crystal light valve
of a simple multiplex driving type is arranged to apply divided voltages
on the pixels except display pixels. This known light valve hence has a
disadvantage of lowering a display contrast. The time when a data signal
used for controlling a display state is applied to the display pixels is a
constant time defined by a duty ratio. For the remaining time, the data
signal having no concern with the control of the display state is applied
onto the display pixels. Hence, the liquid crystal disadvantageously
responds to the data signal sent at a non-selecting time. To overcome
these disadvantages, a method referred to as a voltage averaging method is
generally used for the simple multiplex driving system having matrix
electrodes.
However, the margin of an operating voltage in the voltage averaging method
is made lower as the number n of scanning electrodes is increasing. In a
case that the used liquid crystal material has constant electro-optical
characteristics, the number n of scanning electrodes for holding a
practical display quality is defined. Hence, the use of the voltage
averaging method disadvantageously makes it possible to provide a higher
resolution or a larger screen than that arranged for the held scanning
electrodes.
Further, in the known electric addressing type liquid crystal valve, the
resistance of wire and the capacitance cause a signal waveform to be
delayed, resulting in being unable to realize a large device or a
high-density device.
On the other hand, the known liquid crystal light valve of a light
addressing system needs a CRT or an addressing light source such as a
liquid crystal panel. This brings about a disadvantage that the overall
device cannot be made reduced in size.
In the addressing system having a combination of the known electric
addressing system and the known light radiation addressing system (see
Japanese Lying Open No. 2-134617), the waveform of the data signal is
converted into the change of light intensity and is written on the
photoconductive layer. Hence, disadvantageously, it is necessary to
provide a higher sensitive photoconductive layer which will be sensitive
to a minute change of light intensity. And, the photoconductive layer has
to have a quite uniform sensitivity distribution for uniformly displaying
an image on the screen.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a liquid
crystal light valve which is capable of forming a high-contrast image and
is reduced in size.
In carrying out the object, a liquid crystal light valve includes a first
substrate having a transparent electrode formed thereon, a second
substrate, a liquid crystal provided between the first and second
substrates, a photoconductive layer formed between the liquid crystal
layer and the first substrate, the photoconductive layer being adapted to
change impedance thereof in response to an incident ray of light thereto,
and a light waveguide for emitting light from the first substrate side to
the photoconductive layer.
According to another aspect of the invention, the light waveguide is formed
as stripes on the first substrate. The transparent electrode formed on the
second substrate is patterned as stripes.
According to another aspect of the invention, the light waveguide is formed
of a high-molecular waveguide.
According to another aspect of the invention, the light waveguide is formed
of an electro-luminescent element.
According to another aspect of the invention, the first substrate contains
two small substrates. The light waveguide contains a first light waveguide
formed on one of the two small substrates and a second light waveguide
formed on the other small substrate.
According to another aspect of the invention, one small substrate formed on
the liquid crystal layer is formed of a fiber plate.
According to another aspect of the invention, at least one of the first and
the second light waveguides is formed of an electro-luminescent element.
In operation, when a ray of light is applied to the photoconductive layer
from the first substrate, the impedance of the photoconductive layer is
changed so as to select the proper scanning lines. The impedance of the
photoconductive layer on the selected portion to which is applied the
light from the light waveguide is smaller than the impedance of the liquid
crystal. This makes it possible to apply most of a data signal applied on
the transparent electrode provided on the first substrate onto the liquid
crystal layer. On the other hand, on the non-selecting part of the
photoconductive where no light is applied from the light waveguide, the
impedance of the photoconductive layer is larger than that of the liquid
crystal layer. Hence, the data signal having no concern with controlling a
display state is not allowed to be applied on the liquid crystal layer.
Since the scanning signal is transmitted with the light sent from the light
waveguide, as mentioned above, this liquid crystal light valve does not
apply the data signal onto the liquid crystal corresponding to the
non-selecting part of the photoconductive layer constantly, unlike the
known liquid light valve of the simple multiplex driving system for
transmitting the scanning signal through electric wires. Hence, a bias
ratio of a voltage applied from the selected part of the photoconductive
layer to the liquid crystal layer to a voltage applied from the
non-selecting part of the photoconductive layer to the liquid crystal
layer becomes larger. The liquid crystal light valve is capable of forming
an image at a higher contrast accordingly.
The overall device is reduced in size, because only one light source, that
is, the liquid crystal light valve is needed.
Further, the scanning signal (pulse waveform) is converted into an on/off
state of light before it is written in the photoconductive layer. Hence,
what the photoconductive layer requires is only to indicate a larger
impedance than a certain threshold value. The photoconductive layer is not
required to have a high performance unlike the technique of converting the
data signal into a variable light intensity when it is written on the
photoconductive layer. This is advantageous in manufacturing the device.
According to the present invention, the scanning signal is transmitted
through the light sent from an electro-luminescent element served as a
light signal source for scanning. Hence, the light valve of this invention
does not apply the data signal onto the liquid crystal corresponding to
the non-selecting part of the photoconductive layer, unlike the known
liquid crystal light valve of the simple matrix driven system arranged
which matrix electrodes for transmitting the scanning signal through
electric wires. It means that a bias ratio of a voltage applied from the
selected part of the photoconductive layer to the liquid crystal layer to
a voltage applied from the non-selecting part of the photoconductive layer
to the liquid crystal layer is made larger. This results in the light
valve of this invention forming an image at a higher contrast.
The light waveguides are formed on the two substrates contained in the
first substrate. This results in eliminating a gap between the adjacent
scanning lines and increasing the scanning lines in number, thereby
improving the resolution and the numerical aperture.
Of the two substrates contained in the first substrate, the substrate
formed on the side of the liquid crystal layer is formed of a fiber plate
for the purpose of preventing a crosstalk caused by leakage of light.
Further objects and advantages of the present invention will be apparent
from the following description of the preferred embodiments of the
invention as illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view schematically showing a liquid crystal light
valve according to a first embodiment of the present invention;
FIG. 2 is a schematic view showing a driving unit included in the liquid
crystal light valve shown in FIG. 1;
FIG. 3 is a perspective view showing a connection of an LED array shown in
FIG. 2;
FIG. 4 is a schematic view showing an embodiment of a projective type image
display device to which the liquid crystal light valve shown in FIG. 1
applies;
FIG. 5 is a sectional view schematically showing a liquid crystal light
valve according to a second embodiment of the present invention;
FIG. 6 is a sectional view showing a substrate where a light waveguide and
an LED unit included in a liquid crystal light valve according to a third
embodiment of the present invention;
FIG. 7 is a sectional view schematically showing a liquid crystal light
valve according to a fourth embodiment of the present invention;
FIG. 8 is a perspective view schematically showing a liquid crystal light
valve according to a fourth embodiment of the present invention;
FIG. 9 is a sectional view cut on the line 9--9 of FIG. 8;
FIG. 10 is a schematic view showing a driving unit included in the liquid
crystal light valve shown in FIGS. 8 and 9;
FIG. 11 is a sectional view schematically showing a liquid crystal light
valve according to a sixth embodiment of the present invention;
FIG. 12 is a schematic view showing a driving unit included in the liquid
crystal light valve shown in FIG. 11;
FIG. 13 is a perspective view showing a connection of an LED array shown in
FIG. 12 in detail;
FIG. 14 is a sectional view schematically showing a liquid crystal light
valve according to a seventh embodiment of the present invention; and
FIG. 15 is a schematic view showing a two-dimensional light-operating
element to which applied is a liquid crystal light valve according to an
eighth embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Herein, the description will be directed to a liquid crystal light valve
according to a first embodiment of the invention as referring to FIGS. 1
and 4. FIG. 1 is a sectional view schematically showing the liquid crystal
light valve.
As shown, 10 denotes a liquid crystal light valve, which is arranged to
have a light waveguide 11, glass substrates 12a and 12b, a transparent
electrode 13, a clad layer 14, a metal film 15, a photoconductive layer
16, a dielectric mirror 17, a data-transmitting electrode 19, orientation
films 20a and 20b, and a liquid crystal layer 21.
The light waveguide 11 is formed as stripes (thin wires) on the glass
substrate 12a by means of a heat- or electric-field-based ion-exchanging
technique. A scanning light signal is transmitted along the light
waveguide 11.
According to this embodiment, in order to guide even light of inferior
directivity sent from a light-emitting diode, for example, as the light
waveguide 11, a multi-mode light waveguide is formed by exchanging
thallium (Tl) ion. In place, a silver (Ag) ion may be used.
The transparent electrode 13 is formed of tin-doped indium oxide (ITO:
Indium Tin Oxide). The transparent electrode 13 is formed on the light
waveguides 11 and the glass substrate 12a through the clad layer 14
located therebetween by means of a sputtering technique. The transparent
electrode 13 may be patterned as stripes in a manner to be overlapped with
the light waveguide 11.
The clad layer 14 is evaporated between the transparent electrode 13 and
both of the glass substrate 12a and the light waveguide 11 by means of a
sputtering technique. This is formed because the transparent electrode 13
has a larger index of refraction than the light waveguide 11. The material
of the clad layer 14 is silicon oxide (SiO.sub.2) which is a
low-refractive dielectric. The SiO.sub.2 film is required to have a
thickness so as to allow a proper quantity of light to be leaked out of
the light waveguide 11 serving as a light source. The preferable thickness
is in the range of 500 angstrom to 5000 angstrom. In this embodiment, the
thickness of SiO.sub.2 is 3000 angstrom.
On the back surface of the glass substrate 12a, that is, an opposite
surface to the surface where the light waveguides 11 are formed, a metal
film 15 is deposited for cutting off the light applied from any place
except the light waveguides 11.
The material of the metal film 15 is aluminium (Al) or molybdenum (Mo), for
example. Alternatively, a pigment-dispersed type light-shielding film,
which is often used for a color filter of the liquid crystal panel, may be
used in place of the metal film 15.
On the transparent electrode 13, the photoconductive layer 16 is formed to
receive light from the light waveguide 11. The photoconductive layer 16 is
formed of amorphous silicon hydride (a-Si:H) by means of a plasma CVD
(Chemical Vapor Deposition) technique.
In place of the material a-Si:H, the photoconductive layer 16 may be formed
to have a characteristic of varying its impedance according to the
quantity of irradiated light. Another material of the layer 16 may be
bismuth silicon oxide (Bi.sub.12 SiO.sub.20), cadmium sulfide (CdS),
amorphous silicon carbide hydride (a-SiC:H), amorphous silicon oxide
hydride (a-SiO:H) and amorphous silicon nitride hydride (a-SiN:H).
As a technique of suppressing a dark current in the photoconductive layer
16, it is possible to form an inhibitive electrode structure by utilizing
selective transparency of carriers. For example, if the photoconductive
layer 16 is formed of a-Si, a thin phosphorus (P)-doped n-type layer and a
thin boron (B)-doped p-type layer, both made of a-Si, are combined to have
a pin type diode structure or a pinip type back-to-back diode structure.
Alternatively, the inhibitive electrode structure may be formed by using a
Schottky junction or a hetero junction with a material having a wide-gap
characteristic. A quite thin film (50 angstrom to 300 angstrom) of
SiO.sub.2 or silicon nitride (SiN.sub.x) film may be deposited on one
surface or both surfaces of the photoconductive layer 16 if necessary.
On the photoconductive layer 16, there is formed the dielectric mirror 17
by means of an electron-beam evaporation technique. The dielectric mirror
17 is made of a multilayered film consisting of one layer of titanium
oxide (TiO.sub.2) and the other layer of silicon oxide (SiO.sub.2)
alternately laminated.
To prevent reading light 18 from being leaked out to the photoconductive
layer 16 through the dielectric mirror 17, a light-shielding layer may be
formed between the dielectric mirror 17 and the photoconductive layer 16.
As the light-shielding layer, it is possible to use a carbon-dispersed
organic film, cadmium telluride (CdTe) and aluminum oxide (Al.sub.2
O.sub.3) on which Ag is electroless-plated.
On the glass substrate 12b opposite to the glass substrate 12a, there is
deposited on an data-transmitting electrode 19, which is made of ITO
evaporated on the substrate 12b and is patterned as stripes by the
sputtering technique.
On the dielectric mirror 17 and the data-transmitting electrode 19, the
orientation films 20a and 20b are respectively formed by spin-coating a
polyimide film and sintering the coated film. The molecular orientation is
performed on the orientation films 20a and 20b by means of a rubbing
technique.
Then, the glass substrates 12a and 12b are pasted through a spacer(s) (not
shown) so that the data-transmitting electrode 19 may be located
vertically with respect to the light waveguide for scanning 11. Liquid
crystal is injected into the space defined by the orientation films 20a
and 20b and the spacer(s) in order to form the liquid crystal layer 21.
The liquid crystal to be used should be selected so that its impedance is
larger than that of a part of the photoconductive layer 16 selected as a
scanning line but smaller than that of the other part of the
photoconductive layer 16 not selected as the scanning line.
In the liquid crystal light valve arranged as above, the liquid crystal
layer 21 has a far larger impedance than the part of the photoconductive
layer 16 selected as the scanning line by irradiated light, so that most
of the data signal applied between the electrodes may be applied into the
liquid crystal layer 21. The liquid crystal layer 21 has a smaller
impedance than the other part of the photoconductive layer 16 where no
light impinges, so that no data signal may be applied onto the liquid
crystal layer 21.
According to this embodiment, therefore, the scanning signal is transmitted
with the light from the light waveguide. The data signal is not allowed to
be constantly applied onto the non-selected part of the photoconductive
layer, unlike the known liquid crystal light valve of a simple multiplex
driving system having a matrix electrodes for transmitting the scanning
signal through electric wires.
As a result, a bias ratio of an voltage applied from the selected part of
the photoconductive layer to the liquid crystal layer to an voltage
applied from the non-selected part of the photoconductive layer to the
liquid crystal layer is made larger. Hence, the light valve of this
embodiment enables forming a high-contrast image and contributes to
implementing a large device or a high-density device because the wire
resistance or capacitance does not cause any delay to take place in a
signal waveform.
Further, the light valve of this embodiment operates to increase a margin
of an operating voltage used in a voltage averaging method, which voltage
is defined by the normal number of scanning lines. This results in
allowing the light valve to offer a higher resolution or a larger screen.
In addition, a gradation may be represented by modifying the waveform of
the data signal.
In the above-described embodiment, the light waveguide 11 is formed on the
same level as one surface of the glass substrate 12a. Alternatively, the
light waveguide may be formed completely inside of the glass substrate.
FIG. 2 schematically showing a driving unit of the liquid crystal light
valve 10 shown in FIG. 1. A signal or timing generating unit is not
illustrated for simplifying the description.
As shown, the driving unit of the light valve 10 is constructed to have an
LED (Light-Emitting Diode) array 25 for a scanning signal and a driving
circuit 26 for driving the transparent electrodes 19. In place of the LED
array 25, a semiconductor laser (LD) may be used.
The LED array 25 is connected to the liquid crystal light valve 10 so that
a light pulse signal may be guided from the LED array 25 to the light
valve 10.
FIG. 3 is a perspective view showing a connection of the LED array 25 shown
in FIG. 2 in detail.
As shown, the light emitted from the LED array 25 is guided to the light
waveguide of the light valve 10 through an optical lens array 27. As an
alternative connection, without using the optical lens array 27, the end
of the light waveguide may be directly connected with the phosphor surface
of the LED array 25.
28 denotes a reflective mirror, which serves to reflect the light leaked to
the end of the light waveguide so that the light may be efficiently guided
to the photoconductive layer. The reflective mirror is formed of Al or Ag
and corresponds to the metal film 15 shown in FIG. 1.
FIG. 4 is a view schematically showing one embodiment of a projection type
display device to which the liquid crystal light valve 10 shown in FIG. 1
applies.
As shown, the projection type display device is constructed to have the
liquid crystal light valve 10, a lamp 31, a lens 32, a polarizing beam
splitter 33, a lens 34, and a screen 35. The lamp 31 applies light through
the lens 32 and the polarizing beam splitter 33 into the liquid crystal
light valve 10 on which an image is formed. When the light transmits
through the part of the liquid crystal layer where the molecular
orientation is changed, the polarization of the light is changed through
an electric-optical effect. Hence, the light reflected on the light valve
10 is allowed to transmit through the polarizing beam splitter 33. The
reflected light is expanded through the lens 34 so that the image formed
on the light valve 10 is allowed to be projected on the screen 25.
The liquid crystal light valve according to this embodiment, therefore,
does not need an addressing light source for a CRT or a liquid crystal
display unlike the known liquid crystal light valve of an optical
addressing system which needs such a light source. Hence, the liquid
crystal light valve of this embodiment makes great contribution to
reducing the overall device in size.
The operation mode of the liquid crystal used in this embodiment is a
hybrid field-effect mode of a nematic liquid crystal. As another operation
mode, a twisted nematic mode, a supertwisted nematic mode or an
electrically controlled birefringent mode may be used.
In addition, a ferroelectric liquid crystal, an antiferroelectric liquid
crystal and a smectic liquid crystal providing an electro-clinic effect
may be used. Further, a phase-change mode, a dynamic-scattering mode or a
guest-host mode of the nematic liquid crystal, or a guest-host mode of a
liquid crystal compound film or a smectic liquid crystal may result in
removing the polarizing beam splitter 33.
In turn, the description will be directed to a liquid crystal light valve
according to a second embodiment of the present invention.
FIG. 5 is a sectional view schematically showing the liquid crystal light
valve of the second embodiment. As shown, the liquid crystal light valve
40 is formed to have a light waveguide 41, glass plates 42a and 42b, a
transparent electrode 43, a clad layer 44, a metal film 45, a
photoconductive layer 46, a dielectric mirror 47, a data-transmitting
electrode 49, orientation films 50a and 50b, and a liquid crystal layer
51.
The light waveguide 41 is formed as stripes (thin lines) on the glass
substrate 42a by means of an ion exchanging technique. A scanning light
signal travels along the light waveguide 41. In this embodiment, a
multi-mode waveguide formed by a Tl ion exchanging technique is used so
that it may guide even light having inferior directivity such as the light
emitted from an LED. Alternatively, an Ag ion may be used.
The transparent electrode 43 is formed of tin-doped indium oxide (ITO). The
transparent electrode 43 is formed on the light waveguides 41 and the
glass substrate 42a through the clad layer 44 located therebetween by
means of the sputtering technique.
The patterns of ITO forming the transparent electrode 43 are located in
parallel to and shifted by 1/2 pitch from the stripes of the light
waveguide 41. The other portion of the transparent electrode 43 except the
ITO is formed of an insulating material 52 such as SiO.sub.2 for the
purpose of preventing the short of the transparent electrodes 43. Hence,
the light waveguide 41 and the insulating material 52 are overlapped with
each other with the clad layer 44 being located therebetween.
The clad layer 44 is evaporated between the transparent electrode and the
glass substrate 42a and the light waveguides 41 formed in the substrate
42a by means of the sputtering technique. This clad layer 44 is provided,
because the transparent electrode 43 has a larger index of refraction than
the light waveguide 41.
The clad layer 44 is formed of SiO.sub.2 which is a low refractive
dielectric. The SiO.sub.2 film is required to have such a thickness as
allowing proper light to be leaked out of the light waveguide 41 served as
a light source. The preferable thickness is in the range of 500 angstrom
to 5000 angstrom. In this embodiment, the thickness of SiO.sub.2 is 3000
angstrom.
On the back surface of the glass substrate 42a, that is, an opposite
surface to the surface where the light waveguides 41 are formed, a metal
film 45 is deposited for cutting off the light applied from any place
except the light waveguides 41.
The material of the metal film 45 may be Ag, Al or Mo. Alternatively, an
pigment-dispersed type light-shielding film, which is often used for a
color filter of the liquid crystal panel, may be used in place of the
metal film 45.
On the transparent electrode 43, the photoconductive layer 46 is deposited
to receive light from the light waveguide 41. The photoconductive layer 46
is formed of amorphous silicon hydride (a-Si:H) by means of the plasma CVD
technique.
In place of the material a-Si:H, the photoconductive layer 46 may be formed
to have a characteristic of varying its impedance according to the
quantity of irradiated light. As another material, the layer 46 may be
formed of Bi.sub.12 SiO.sub.20, CdS, a-SiC:H, a-SiO:H and a-SiN:H.
As a technique of suppressing a dark current in the photoconductive layer
46, it is possible to form an inhibitive electrode structure by utilizing
selective transparency of carriers. For example, if the photoconductive
layer 46 is formed of a-Si:H, a thin phosphorus (P)-doped n-type layer and
a thin boron (B)-doped p-type layer, both made of a-Si, are combined to
have a pin type diode structure or a pinip type back-to-back diode
structure. Alternatively, the inhibitive electrode structure may be formed
by using a Schottky junction or a hetero junction with a material having a
wide-gap characteristic. A quite thin film (50 angstrom to 300 angstrom)
SiO.sub.2 or SiN.sub.x film may be deposited on one surface or both
surfaces of the photoconductive layer 46 if necessary.
On the photoconductive layer 46, there is formed the dielectric mirror 47
by means of the EB evaporation technique. The dielectric mirror 47 is made
of a multilayered films consisting of one layer TiO2 and the other layer
of SiO2 alternately laminated.
To prevent reading light 48 from being leaked out to the photoconductive
layer 46 through the dielectric mirror 47, a light-shielding layer may be
formed between the dielectric mirror 47 and the photoconductive layer 46.
As the light-shielding layer, it is possible to use a carbon-dispersed
organic film, cadmium telluride (CdTe) and aluminium oxide (Al.sub.2
O.sub.3) on which Ag is electroless-plated. On the glass substrate 42b
opposite to the glass substrate 42a, there is deposited on an
data-transmitting electrode 49, which is made of ITO evaporated on the
substrate 42b and is patterned as stripes by the sputtering technique.
On the dielectric mirror 47 and the data-transmitting electrode 49, the
orientation films 50a and 50b are respectively formed by spin-coating a
polyimide film and sintering the coated film. The molecular orientation is
performed on the orientation films 50a and 50b by means of the rubbing
technique.
The glass substrates 42a and 42b are pasted through a spacer(s) (not shown)
so that the data-transmitting electrode 49 is located vertically with the
light waveguides for scanning 41. Liquid crystal is injected into the
space defined by the orientation films 50a and 50b and the spacer(s) in
order to form the liquid crystal layer 51. The liquid crystal to be used
should be selected so that its impedance is larger than that of a part of
the photoconductive layer 46 selected as a scanning line but smaller than
that of another part of the photoconductive layer 46 not selected as the
scanning line.
In the liquid crystal light valve arranged as above, the liquid crystal
layer 51 has a far larger impedance than the part of the photoconductive
layer 46 selected as the scanning line by irradiated light, so that the
almost of the data signal applied between the electrodes may be applied
into the liquid crystal layer 51. The liquid crystal layer 51 has a
smaller impedance than the other part of the photoconductive layer 46
where no light impinges, so that no data signal may be applied onto the
liquid crystal layer 51.
The liquid crystal light valve 40 is arranged so that one photoconductive
layer 46 selected as a scanning line by irradiated light comes into
contact with two scanning transparent electrodes 43 and the synchronous
scanning is performed so as to apply a data signal onto only one scanning
transparent electrode 43 in a manner that the scanning line is divided
into two. The liquid crystal light valve according to this embodiment
provides a high-contrast image and twice as large a resolution as the
light valve according to this embodiment.
In the above-described embodiment, the light waveguides 41 are formed on
the same level as one surface of the glass substrate 42a. In place, the
light waveguide may be formed completely inside of the glass substrate.
The liquid crystal light valve according to the second embodiment has the
same driving unit as that according to the first embodiment. The
construction of a connection of an LED array included in the second
embodiment is the same as that included in the first embodiment. The
construction of a projection type display unit having the liquid crystal
light valve 40 applied thereto and the operation mode of the liquid
crystal are the same as those of the first embodiment shown in FIG. 4.
In turn, the description will be directed to a liquid crystal light valve
according to a third embodiment of the present invention.
As described above, the liquid crystal light valve of the first embodiment
has the driving unit containing the LED array 25 served as a scanning
light signal source shown in FIG. 2. In this arrangement, however, it is
necessary to quite accurately position the end of the light waveguide to
the LED array. In order to make this troublesome work easier, the liquid
crystal light valve according to the third embodiment is formed so that
the LED unit having an LED array may be located on the same substrate as
and adjacent to the light waveguide.
FIG. 6 is a sectional view showing a substrate on which the light waveguide
and the LED unit are formed in the liquid crystal light valve of this
embodiment.
As shown, the LED unit 62 and the light waveguide 63 are formed on the
substrate 61 made of silicon monocrystalline so as to locate the
components 62 and 63 adjacent to each other. The LED unit 62 is formed of
a-Si.sub.x C.sub.1-x :H and has a pin structure. This material makes it
possible to form the LED unit 62 at a relatively low temperature and to
provide the resulting LED unit with high luminance. In addition, if a
buffer layer made of GaP may be provided and the used substrate contains
no silicon, an LED made of a Al.sub.x GA.sub.1-x As system material is
allowed to be used.
In this case, the LED contained in the LED unit 62 provides a phosphor
wavelength range to be varied by adjusting a composition ratio X of the
Al.sub.x GA.sub.1-x As system. Hence, the LED enables to change its
luminous wavelength according to a sensitivity of the photoconductive
layer, which is advantageous in improving its performance.
A light waveguide 63 is formed to have a core layer 65 made of SiO.sub.2
-GeO.sub.2 and a clad layer 66 made of SiO.sub.2. The light waveguide 63
made of an SiO.sub.2 system material is formed by means of the CVD
technique based on an oxidation of a SiC.sub.14 gas and a GeC.sub.14 gas.
As another means, a flame deposition technique may be used. With this
technique, in place of the GeC.sub.14 gas, an SiO.sub.2 -TiO.sub.2 formed
by a TiC.sub.14 gas may be used as the core layer.
On the top and the bottom are provided LED electrodes 64a and 64b,
respectively. In a case of using the LED made of a-Si.sub.x C.sub.1-x, a
transparent electrode or a metal electrode can be used as those electrodes
64a and 64b. In a case of using the LED made of Al.sub.x Ga.sub.1-x As, a
substrate 61 made of monocrystalline silicon can be used as an electrode.
As shown, the LED unit 62 and the light waveguide 63 are formed on the same
substrate 61 in a manner to allow those components 62 and 63 to locate
adjacent to each other. Hence, the light emitted from the LED unit 62 is
guided into the light waveguide 63 located on the side of the LED unit 62.
That is, in place of the glass substrates 12a and 42a having the light
waveguides 11 and 41 formed thereon according to the first and the second
embodiments, the light valve according to the third embodiment provides
the substrate on which the LED unit 62 and the light waveguide 63 are
formed as mentioned above. The other construction of the light valve
according to the third embodiment is the fundamentally same as that of the
light valve according to the first or the second embodiment.
According to the third embodiment, like the first or the second embodiment,
the liquid crystal light valve enables to offer a high contrast image and
reduce the overall device in size.
The positioning of the LED unit 62 to the light waveguide 63 is implemented
by a photolithography technique. The easy and accurate positioning is
allowed.
In the third embodiment, the substrate 61 serves as a layer for cutting off
a visible light. Hence, unlike the first and the second embodiments
needing the metal films 15 and 45, no metal film is required.
In turn, the description will be directed to a liquid crystal light valve
according to a fourth embodiment of the present invention.
FIG. 7 is a sectional view schematically showing the liquid crystal light
valve of the fourth embodiment. As shown, the liquid crystal light valve
80 is arranged to have a light waveguide 81, a pair of glass substrates
82a and 82b, a transparent electrode 83, a clad layer 84, a metal film 85,
a photoconductive layer 86, a dielectric mirror 87, a data-transmitting
electrode 89, orientation films 90a and 90b, and a liquid crystal layer
91.
The light waveguide 81 is a high-molecular waveguide made of
photo-polymerized polycarbonate Z. The striped patterns of the light
waveguide 81 are allowed to be formed by means of a photo-lithography
technique. As another material of the high-molecular waveguide,
polyurethane, epoxy, photosensitive plastic or photoresist may be used.
Between the light waveguide 81 and the dielectric mirror 87, a clad layer
84 is provided for preventing light from being leaked from the light
waveguide 81 to the dielectric mirror 87.
The clad layer 84 is formed by coating a resin having a smaller index of
refraction than the light waveguide 81.
The glass substrates 82a and 82b, the transparent electrode 83, the metal
film 85, the photoconductive layer 86, the dielectric mirror 87, the
data-transmitting electrode 89, the orientation films 90a and 90b and the
liquid crystal layer 91 have the same composition and mater | | |
