JPH0862564A - Projection type liquid crystal display device - Google Patents

Abstract

PURPOSE: To provide a projection type liquid crystal display device where the maintenance of the brightness of a projected picture is made compatible with the high contrast of the picture. CONSTITUTION: This projection type liquid crystal display device including a polarization beam splitter 12 transmitting bundle of rays emitted from a light source 13 is composed of a photoconductive liquid crystal light valve 1 having a liquid crystal layer, a reflecting film, and a photoconductive film laminated sequentially from a side near to the beam splitter 12 between a pair of transference electrodes provided on the opposed surface of a pair of transparent substrates, a driving means impressing a driving voltage on the pair of transference electrodes, and a writing means forming a picture by horizontal scanning and making the picture incident on the photoconductive film from a photoconductive film side. This device is provided with a phase difference compensating element 17 arranged between the beam splitter 12 and the light valve 1 so that the oscillating surfaces of an electric vector on the linearly polarized component of reflection light transmitted through the liquid crystal layer in the case of a specified driving voltage may be perpendicular to each other and the phase difference caused by double refractivity is compensated by means of the liquid crystal on the liquid crystal layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a cathode ray tube (hereinafter referred to as CR
T) and photoconductive liquid crystal light valve (hereinafter LC)
A projection type liquid crystal display device (hereinafter, also referred to as a projector) having a projection light output unit composed of an LV), and in particular, a projector for projecting reflected light by a projection lens system while imparting a projection image to an incident light flux to the LCLV. Regarding

[0002]

2. Description of the Related Art FIG. 1 shows an example of LCLV1. LC
The LV 1 includes transparent electrodes 4 and 5, a photoconductive film 6 made of amorphous silicon (a-Si), a light-shielding film 7, and a reflective film 8 made of a dielectric, which are arranged between the substrates 2 and 3, respectively.
It has a structure including liquid crystal alignment films 9 and 10 and a liquid crystal 11 arranged between the liquid crystal alignment films. LCLV liquid crystal layer 1
1 is defined by the spacer and the alignment film. A transparent electrode 4 is arranged on the reading side glass substrate 2, and a photoconductive film 6 is formed.
An electrode 5 is arranged on the writing side glass substrate 3.
The LCLV 1 is formed by forming the transparent electrode 4 and the liquid crystal alignment film 9 on the inner surface to be opposed on one read side substrate 2, and forming the electrode 5, a- on the other write side glass substrate 3.
A Si film 6, a light-shielding film 7, a reflective film 8 and a liquid crystal alignment film 10 are sequentially formed, and a liquid crystal 11 is sealed between the liquid crystal alignment films 9 and 10. The light-shielding film 7 receives a-Si from the incident light from the projection light source.
The reflection film 8 is a film that prevents leakage to the film 6, and the reflection film 8 plays a role of efficiently reflecting the incident light from the projection light source. L
CLV1 basically converts an optical signal into an electrical signal a
A light-to-light conversion element in which a photoconductive film 6 made of a material such as -Si and a liquid crystal layer 11 made of a material such as liquid crystal for converting an electric signal into an optical signal are combined.

FIG. 2 shows an example of a projector having a projection light output means composed of a CRT 14 and an LCLV 1 for writing an image on the a-Si film 6. CRT14 and LC
Fiber optic plate 1 between LV1
4a is arranged so as to efficiently write the image displayed on the front face of the CRT 2 to the photoconductive film of the LCLV 1. The polarization beam splitter 12 splits parallel light from a projection light source 13 such as a metal halide lamp into S and P polarized light.

Next, the operating principle of the LCLV1 will be described. The operation of the LCLV is as shown in FIG.
When an AC voltage is applied between the transparent electrodes 4 and 5 by 0, when an image is drawn on the photoconductive film 6 by the incident light from the writing side glass substrate 3, the internal resistance of the photoconductive film 6 causes the brightness of the image to change. It locally changes in accordance with (change in received light amount). An AC voltage between the transparent electrodes 4 and 5 is applied to a portion of the adjacent liquid crystal layer 11 corresponding to the variable resistance portion of the photoconductive film,
The liquid crystal molecules are spatially modulated according to the brightness of the image, and a birefringence is generated.

When there is a change in the birefringence of the projected image of the liquid crystal layer 11 of the LCLV, a substantially parallel light flux from the light source 13 is incident on the polarization beam splitter 12 as shown in FIG. It is carried out by injecting the S-polarized light component into the glass substrate 2 on the reading side of the LCLV 1.
Here, when the birefringence change of the liquid crystal layer of the LCLV1 occurs, the S-polarized component is converted into the P-polarized component in the reflected light reflected by the LCLV according to the birefringence of the liquid crystal layer. Then, this P-polarized component is the polarization beam splitter 1
By passing 2 as it is, the P-polarized component, that is, the projection light, is projected on the screen 16 via the projection lens 15.

Applied voltage (VOLTAGE) in LCLV1
The basic relationship between the brightness (OUTPUT LEVEL) is shown by the curves A and B in FIG. 3A shows a state in which the CRT 14 for writing to the a-Si film 6 is not illuminated (dark state), and FIG.
B is a state (bright state) in which the CRT 14 for writing in the a-Si film 6 is illuminated. Here, the liquid crystal 11 is a nematic liquid crystal having a negative dielectric anisotropy, and the liquid crystal alignment films 9 and 10 are films in which liquid crystal molecules are aligned substantially vertically.

When the AC voltage applied to the transparent conductive films 4 and 5 is gradually increased from 0 V, there is no writing to the a-Si film 6 by the CRT 14 in the dark state of FIG. The impedance of 6 is high, and the applied voltage is divided into both the a-Si film 6 and the liquid crystal 11, and the apparent threshold voltage of the liquid crystal becomes high. On the other hand, when the applied voltage is similarly varied, the light of the CRT 14 is irradiated to the a-Si film 6 in the bright state of FIG.
Impedance will decrease. As a result, the voltage is
Since most of them are applied to 1, the threshold voltage of the liquid crystal becomes low.

Therefore, in the dark state of FIG. 3A, the threshold voltage of the apparent liquid crystal (about 10 V in the figure) is applied to the transparent conductive films 4 and 5 as a drive voltage to write to the a-Si film 6. The impedance of the a-Si film 6 changes by turning on and off the CRT 14 for performing the above, and a voltage corresponding to the amount of change is applied to the liquid crystal 11 and the liquid crystal 11 responds.
That is, the light which the projection light source 13 has passed through the polarization beam splitter 12 to make it linearly polarized and incident on the LCLV 1 is CR.
When T14 is off, the liquid crystal 11 does not respond and birefringence does not occur. Therefore, the incident linearly polarized light cannot pass through the polarization beam splitter 12, and a black image is obtained on the screen 16.

On the other hand, when the CRT 14 is on, a voltage is applied to the liquid crystal 11, so that the emitted light becomes elliptically polarized light due to the phase difference caused by the birefringence of the liquid crystal 11 in response. Therefore, a bright image is obtained on the screen 16 after passing through the polarization beam splitter 12. The brightness is about 50% at a threshold voltage of about 10V.

[0010]

FIG. 4 shows an enlarged view of the liquid crystal near the threshold value (7 to 12 V) in FIG. From FIG. 4, in the actual LCLV1, even if the dark state is about 8V from the liquid crystal 1
It can be seen that 1 gradually responds and causes a phase difference.
Therefore, if the drive voltage is set to about 9 V in the dark state of C in FIG. 4, the brightness of black can be darkened to about 0.1%.
When the light of 14 is applied to the a-Si film 6, the amount of light that can be modulated by the liquid crystal 11 in response is as small as about 18% as can be seen from the bright state of FIG. 3B. As a result, the contrast (18% / 0.1%) can be as high as about 180 to 1, but a dark projected image is obtained as a whole.

On the other hand, when the drive voltage is set to a voltage of 10 V which gives about 1% of the brightness of black in the dark state of D in FIG. 4, when the light of the CRT 14 is irradiated on the a-Si film 6, the liquid crystal 11 is emitted. As can be seen from the dark state of FIG. 3, the amount of light that can be modulated in response to is about 50%, but the contrast (50% / 1%) is about 50: 1, which is a low projected image.

It is an object of the present invention to provide a projection type liquid crystal display device having an LCLV for maintaining both the brightness of a projected image and a high contrast.

[0013]

A projection type liquid crystal display device according to the present invention comprises a polarizing beam splitter through which a light beam emitted from a light source is transmitted, and a pair of transparent electrodes provided on opposing surfaces of a pair of transparent substrates. A photoconductive liquid crystal light valve having a liquid crystal layer, a reflective film, and a photoconductive film, which are sequentially stacked between the polarization beam splitters, a drive unit for applying a drive voltage to the pair of transparent electrodes, and a horizontal drive unit. A projection type liquid crystal display device comprising a writing means for forming an image by scanning and for making the image incident on the photoconductive film from the photoconductive film side, wherein the reflected light transmitted from the liquid crystal layer at a predetermined driving voltage It is arranged between the polarization beam splitter and the photoconductive liquid crystal light valve so that the planes of oscillation of the electric vectors of the linearly polarized light components are perpendicular to each other, and the birefringence of the liquid crystal in the liquid crystal layer. Characterized in that it has a retardation compensation element to compensate for the resulting phase difference.

[0014]

According to the present invention, the phase difference compensating element is installed so that the vibrating planes of the linearly polarized electric vectors of the reflected light transmitted from the liquid crystal layer of the LCLV at the predetermined driving voltage of the projector are perpendicular to each other. That is, the phase difference compensating element and the liquid crystal layer at a predetermined driving voltage of the LCLV are configured to be in the crossed Nicols.

In general, when two elements each of which causes a phase difference, for example, a polarizer and an analyzer having phase differences R1 and R2, respectively, are placed in an overlapping manner, the total phase difference is calculated by comparing the optical axes of the two elements. When the axes in the direction in which refraction does not occur: liquid crystal molecular axes) are aligned (parallel Nicols), R1 + R2
And when the optical axes of the two elements are orthogonal (orthogonal Nicols)
Is represented by R1-R2. That is, the phase difference caused by the LCLV drive voltage is R1, the phase difference caused by the phase difference compensating element is R2, the optical axes of these two elements are orthogonal to each other, and the values of R1 and R2 are equal, The phase difference at can be made zero.

Therefore, even if the driving voltage to which the LCLV liquid crystal slightly responds is set in order to obtain the brightness, the phase difference compensating element for compensating the phase difference caused by the driving voltage is provided in the LCLV.
By providing it on the front surface of, the phase difference in the dark state of the projected light can be zero, that is, black can be obtained, and a bright, high-contrast projected image can be obtained.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. The projector of this embodiment is shown in FIG. The projector of this embodiment has the same structure as the projector shown in FIG. 2 except that it has a phase difference compensation element 17 provided between the polarization beam splitter 12 and the LCLV 1. That is, the projector according to the present embodiment has the polarization beam splitter 1 through which the light flux emitted from the light source 13 is transmitted.
2, a LCLV1, a drive power source 20 for applying a drive voltage to a pair of transparent electrodes, an image is formed by horizontal scanning, and the image is incident on the photoconductive film from the photoconductive film side.
And T14. The LCLV 1 is sequentially laminated between the pair of transparent electrodes 4 and 5 provided on the opposing surfaces of the pair of transparent substrates 2 and 3 from the side closer to the polarization beam splitter 12.
It has a liquid crystal layer 11, a reflective film 8 and a photoconductive film 6.

The phase difference compensating element 17 is arranged so that the vibrating planes of the electric vectors of the linearly polarized components of the reflected light transmitted from the liquid crystal layer 11 at a predetermined driving voltage are perpendicular to each other, and the birefringence by the liquid crystal of the liquid crystal layer is provided. The phase difference caused by is compensated. FIG. 6 shows the specifically manufactured phase difference compensating element 17
The perspective view including the partial cross section of FIG. In FIG. 6, the transparent electrodes 2 are formed on the inner surfaces of the two substrates 18 and 19 that should face each other.
0 and 21 and the liquid crystal alignment films 22 and 23 are formed, and the liquid crystal 24 is sealed between the liquid crystal alignment films 22 and 23 to form the phase difference compensation element 17.

The liquid crystal used for the phase difference compensating element 17 is a nematic liquid crystal, and its physical property value is that the dielectric anisotropy is about −.
2, the refractive index anisotropy is 0.2. The cell thickness is 2
In μm, the pretilt angle was about 1 ° from the substrate normal direction. First, the alignment directions (arrows X and Y in FIG. 6) of the phase difference compensating element 17 and the liquid crystal alignment film of the LCLV1 are at an angle of 90 degrees to each other.
The phase difference compensating element 17 is installed on the front surface of the LCLV 1 so that the angle becomes °. After that, an AC voltage was applied to the phase difference compensating element 17 by the variable voltage power source so that the brightness was minimized. As a result, the vibration planes of the electric vectors of the linearly polarized light components of the reflected light transmitted from the liquid crystal layer at the time of driving voltage can be made perpendicular to each other. The voltage at this time is 3.3.
The voltage was 7V. Then, the applied voltage (VO
The curve of (LTAGE) vs. brightness (OUTPUT LEVEL) was measured.

The results are shown in FIG. 7, and an enlarged view thereof is shown in FIG. 7A is a state in which the CRT 14 for writing to the a-Si film 6 is not illuminated (dark state), and FIG. 7B is a state in which the CRT 14 for writing to the a-Si film 6 is illuminated (bright state). Is. LCLV from A (dark state) in FIG.
When the applied voltage of 1 was 10 V, the minimum value at which the brightness was about 0.1% was obtained. As a result, the phase difference compensation element 17 is
It can be seen that the phase difference of LCLV1 can be compensated by providing it on the front surface of LV1 and applying a voltage to this phase difference compensating element 17.

This state (LCLV1 drive voltage: 10
V, the drive voltage of the phase difference compensation element 17: 3.37 V),
Writing to the a-Si film 6 (writing wavelength 660 nm,
16 pulses were performed at a period of 60 Hz with an average writing light intensity of about 150 μW / cm ² and a writing light waveform EXP of a writing light intensity of 1/10 for 15 milliseconds. FIG. 9 shows the time change (TIME (ms: millisecond)) of the brightness (OUTPUT LEVEL (%)) at that time. As a result, the average brightness of the projected light obtained by one light pulse is about 50%, and the brightness of the projected light is about 0.1% when writing is not performed (in the dark state). It can be seen that it can be obtained at about 500 to 1.

As a comparative example, in a projector from which the phase difference compensating element 17 has been removed, a voltage of 9.1 V with a brightness of about 0.1% that produces the same black as that of the example is used as the driving voltage of the LCLV1 as in the example. I wrote. FIG. 10 shows the time change (TIME) of the brightness (OUTPUT LEVEL) of the comparative example. From this, the brightness obtained by one light pulse is about 27%,
The contrast was about 250: 1, and the brightness and the contrast were about half of those of the example.

Further, the result of measuring the response characteristics with the driving voltage of the LCLV1 of the comparative example being 10 V, which is the same as that of the embodiment, is shown in FIG.
It is shown in FIG. From FIG. 11, the brightness obtained by one light pulse was obtained at about 60%, but since the brightness of black when writing is not performed is about 1%, the contrast is about 60%. I only get 1. According to this embodiment, an LCLV using a nematic liquid crystal having a negative dielectric anisotropy is used.
In the above, by providing the phase difference compensating element between the polarization beam splitter and the LCLV, it is possible to obtain a projector capable of obtaining a high-contrast projected image without impairing the brightness. Further, it is apparent that a nematic liquid crystal having a positive dielectric anisotropy oriented substantially horizontally can be used as the liquid crystal layer of the phase difference compensating element.

Further, in the above embodiment, the phase difference compensating element 1 is used.
Although a voltage was applied to 7 to cause the liquid crystal molecules to respond and a phase difference was generated, it was possible to prepare a liquid crystal element in which the liquid crystal molecules were tilted by a predetermined angle in advance, without applying a voltage to the phase difference compensation element. Also, the phase difference can be compensated. Further, as the phase difference compensating element for compensating the phase difference as described above, a nematic liquid crystal having a positive dielectric anisotropy may be used, and further, a uniaxial polymer film such as polystyrene or polycarbonate film may be used. A phase plate or a wave plate may be used.

[0025]

As described above, according to the present invention, in the projection type liquid crystal display device having the polarization beam splitter and the photoconductive type liquid crystal light valve, the linearly polarized electric vector of the reflected light transmitted from the liquid crystal layer is A phase difference that is provided between the polarization beam splitter and the photoconductive liquid crystal light valve so that the oscillating planes are perpendicular to each other, and that compensates for the phase difference caused by the birefringence of the liquid crystal of the liquid crystal layer at a predetermined driving voltage. Since it has a compensating element, it is possible to achieve a high-contrast projected image in which the brightness can be maintained.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a conventional LCLV.

FIG. 2 is a schematic configuration diagram of a conventional projector.

FIG. 3 is a graph showing characteristics of applied voltage of LCLV vs. brightness in a conventional projector.

FIG. 4 is a partially enlarged view of FIG.

FIG. 5 is a schematic configuration diagram of a projector of the present invention.

FIG. 6 is a schematic partially cutaway perspective view of a phase difference compensating element and an LCLV of the present invention.

FIG. 7 is a graph showing characteristics of applied voltage vs. brightness of LCLV in the projector of the present invention.

FIG. 8 is a partially enlarged view of FIG. 3;

FIG. 9 is a graph showing a temporal change in brightness when projection display is actually performed using the projector of the present invention.

FIG. 10 is a graph showing a temporal change in brightness when projection display is actually performed using the projector of the comparative example.

FIG. 11 is a graph showing a temporal change in brightness when projection display is actually performed using the projector of the comparative example.

[Explanation of symbols for main parts]

 1 LCLV 2,3 Substrate (glass plate) 4,5 Transparent conductive film 6 a-Si film 7 Light-shielding film 8 Dielectric reflective film 9,10 Liquid crystal alignment film 11 Liquid crystal 12 Polarization beam splitter 13 Projection light source 14 CRT 15 Projection lens 16 Screen 17 Phase difference compensator 18, 19 Substrate (glass) 20, 21 Transparent conductive film 22, 23 Liquid crystal alignment film 24 Liquid crystal

Claims (6)

[Claims] 1. A polarizing beam splitter, through which a light beam emitted from a light source passes, and a pair of transparent electrodes provided on opposite surfaces of a pair of transparent substrates, which are sequentially stacked from a side closer to the polarizing beam splitter. A photoconductive type liquid crystal light valve having a liquid crystal layer, a reflective film and a photoconductive film, a driving means for applying a drive voltage to the pair of transparent electrodes, an image is formed by horizontal scanning, and the image is formed from the photoconductive film side. A projection type liquid crystal display device including a writing means that is incident on the photoconductive film, wherein vibration planes of electric vectors of linearly polarized light components of reflected light transmitted from the liquid crystal layer at a predetermined drive voltage are perpendicular to each other. A phase difference compensating element disposed between the polarization beam splitter and the photoconductive liquid crystal light valve and compensating for a phase difference caused by birefringence of the liquid crystal of the liquid crystal layer. Projection type liquid crystal display device which is characterized in that. 2. The phase difference compensating element has a liquid crystal layer, and has a desired liquid crystal alignment processing direction of a liquid crystal alignment film of the liquid crystal layer and a liquid crystal alignment processing direction of a liquid crystal alignment film of the photoconductive liquid crystal light valve. The projection type liquid crystal display device according to claim 1, wherein an angle is given and an angle formed by the liquid crystal alignment treatment directions between the respective liquid crystal alignments is 90 degrees or in the vicinity thereof. 3. The projection type liquid crystal display device according to claim 2, wherein the liquid crystal layer of the phase difference compensating element comprises a nematic liquid crystal having a negative dielectric anisotropy oriented substantially vertically. 4. The projection type liquid crystal display device according to claim 2, wherein the liquid crystal layer of the phase difference compensating element comprises a nematic liquid crystal having a positive dielectric anisotropy oriented substantially horizontally. 5. The projection type liquid crystal display device according to claim 2, wherein a voltage is applied to the liquid crystal layer of the phase difference compensating element to compensate for the phase difference. 6. The projection type liquid crystal display device according to claim 1, wherein the phase difference compensating element is a phase plate or a wave plate.