JPH09258328A - Projector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a projector capable of easily achieving high contrast by compensating a phase difference between normal light and abnormal light caused in a spatial optical modulator on an optical path for optical modulation. SOLUTION: This projector 100 is provided with a projecting light source 10, a polarizer 16, a half mirror 18, a liquid crystal compensating cell 20, the liquid crystal spatial optical modulator 22, an image write device 24 and an analyzer 30. The phase difference between the normal light and the abnormal light caused in the parallel oriented liquid crystal type spatial optical modulator 22 is compensated by the cell 20, so that the wavelength dispersion of the phase difference between the normal light and the abnormal light is restrained. Thus, leakage light in the off-state of the projector 100 is reduced and the high contrast is obtained. Since temperature characteristic concerning optical modulation is nearly coincident between the cell 20 and the modulator 22, the high contrast is maintained even when the operation temperature of the cell 20 and the modulator 22 is changed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projector using a liquid crystal spatial light modulator.

[0002]

2. Description of the Related Art Conventionally, several types of large-screen projectors have been developed. At present, the most widely used method is simple matrix drive T
This is a system using a matrix type liquid crystal TV such as an N liquid crystal TV or a TFT active matrix drive TN liquid crystal TV. However, the projector using the simple matrix drive TN liquid crystal TV has a problem that the high speed display cannot be achieved because the response becomes insufficient when the number of pixels is increased due to the problem of operating speed. Further, in a projector using a TFT active matrix drive TN liquid crystal TV, since there is a drive element for each pixel, the aperture ratio of the modulation unit for one pixel is low, and as a result, the projection light intensity is low and it is possible to support high resolution. However, in that case, since the area ratio of the driving element occupies one pixel becomes large, there is a problem that the aperture ratio becomes lower and the projection light intensity also decreases.
Further, as a common problem of projectors using these matrix-type liquid crystal TVs, when the projection screen is enlarged, the pixel matrix becomes visible, and the display quality deteriorates.

As another type of projector, there is a projector using a liquid crystal spatial light modulator as a product that overcomes the above problems. Since this spatial light modulator is a high resolution device having an aperture ratio of 100% instead of a matrix system, it can handle a large number of pixels and high projection light intensity.

The liquid crystal spatial light modulator used here is a combination of amorphous silicon and birefringence control (ECB) liquid crystal. The ECB liquid crystal includes parallel alignment liquid crystal and vertical alignment liquid crystal. Here, the parallel alignment liquid crystal is a liquid crystal having a positive relative dielectric anisotropy Δε, and all liquid crystal molecules are arranged in parallel with the substrate surface in the same direction. On the other hand, the vertically aligned liquid crystal is a liquid crystal in which Δε is negative, and all liquid crystal molecules are aligned perpendicularly to the substrate surface and in the same direction.

The advantage of the projector provided with the spatial light modulator using the vertically aligned liquid crystal is that the liquid crystal molecules are vertical in the OFF state (the state in which no image to be projected is input to the spatial light modulator). Therefore, since the birefringence Δn is small, the wavelength dispersion with respect to the projection light is small, and as a result,
The black level of the projected image in the OFF state is low and the contrast is high. However, in order to produce an alignment film, a very troublesome process of applying a vertical alignment film on two layers of obliquely vapor-deposited films such as SiO is required, and it is necessary to mass-produce a large area liquid crystal. Has the disadvantage that it is not suitable.

On the other hand, the parallel alignment liquid crystal can be produced by aligning the liquid crystal by a simple method of rubbing polyimide or the like, and has an advantage that it can be easily applied to a large area and mass production.

[0007]

A color projector using a parallel alignment liquid crystal spatial light modulator includes a three-plate type one in which one spatial light modulator is used for each color of RGB, and
There is a single-panel type that projects a color image by displaying each component image of RGB in time series with one spatial light modulator.

However, any type of projector has a problem based on the characteristic of the parallel alignment liquid crystal that the birefringence Δn is large, the change of Δn with temperature and the wavelength dispersion are large. That is, in either method,
Since the phase difference between the ordinary light and the extraordinary light caused by the birefringence of the liquid crystal part of the spatial light modulator depends on the wavelength of the projected light, chromatic dispersion occurs, which increases the leaked light. The contrast in the OFF state is low. Also, in the case of the three-plate type, when the temperature of the liquid crystal part changes due to the heat of the projected light, etc., the black level in the OFF state is lowered at the initial drive voltage due to the temperature dependence of the Δn value of the liquid crystal, and the screen Since it becomes brighter, there is a problem that it is necessary to adjust the drive voltage and it takes several hours to warm up until the temperature of the device becomes stable. Further, in the single plate type, there is a problem of temperature change of the liquid crystal as in the case of the three plate type. In addition, due to the wavelength dispersion property of the phase modulation generated in the liquid crystal, the optimum driving voltage for each of RGB is Since it is different, complicated driving is required, and the response speed of the spatial light modulator is R
There is a problem that it may not be possible to follow the GB switching. Further, since the RGB projection light has a wider wavelength width than the three-plate type, the influence of wavelength dispersion is large,
It is more difficult to obtain good black in the OFF state, and there is also a problem that the contrast tends to be low.

The present invention has been made to solve the above-mentioned problems, and comprises a parallel alignment liquid crystal type spatial light modulator,
An object of the present invention is to provide a projector that can easily achieve high contrast.

[0010]

In order to solve the above-mentioned problems, the projector of the present invention comprises (a) a projection light source,
(B) a polarizer installed on the output optical path of the projection light from this projection light source, and (c) installed on the path of the projection light that has passed through this polarizer, and at least part of the light from the polarizer An optical path adjuster for outputting on the optical path for light modulation, and for outputting at least a part of the light traveling on the optical path for light modulation and incident on the optical path for detection, and (d) the light A parallel alignment ECB liquid crystal type spatial light modulator installed on the optical path for modulation;
(E) An image writing device for sending a projection image to the spatial light modulator for recording, and (f) an analyzer installed on the optical path for analysis, and (g) on the optical path for light modulation. At
It is characterized in that a compensating element for compensating the phase difference between the ordinary light and the extraordinary light generated in the spatial light modulator is provided between the optical path adjuster and the spatial light modulator.

Here, the compensating element may be a liquid crystal cell or a retardation plate. A beam splitter or the like can be used as the optical path adjuster.

In the projector of the present invention, since the phase difference between the ordinary light and the extraordinary light generated in the parallel alignment liquid crystal type spatial light modulator is compensated by the compensating element, the wavelength dispersion of the phase difference between the ordinary light and the extraordinary light is suppressed. To be As a result, leakage of light when the projection image is not input from the image writing device, that is, when the projector is in the OFF state is reduced, and high contrast is obtained.

The compensating element is preferably a liquid crystal cell provided with a parallel-aligned ECB liquid crystal having substantially the same material and substantially the same thickness as the liquid crystal portion of the spatial light modulator. In this case, since the temperature characteristics relating to the light modulation substantially match between the compensation element and the spatial light modulator, high contrast is maintained even when the operating temperature of the compensation element or the spatial light modulator changes.

Further, in the projector of the present invention in which the compensating element is the above-mentioned liquid crystal cell, (h) an optical sensor for detecting the projection light passing through the analyzer, and (i) an image writing device for projecting the light onto a spatial light modulator. A drive voltage control controller that applies a drive voltage having a value that minimizes the light intensity detected by the optical sensor when no application image is transmitted, to the liquid crystal cell or the spatial light modulator. Good to have. In this case, the driving voltage of the compensating liquid crystal cell is automatically set to an appropriate value, so that a high contrast can be easily obtained.

In the projector of the present invention,
The compensating element may be capable of compensating for the phase difference under at least one operating temperature. When using an element that can be compensated only under a certain temperature, it is advisable to provide a temperature adjusting device for maintaining the operating temperature of the compensation element and the spatial light modulator at the certain temperature.

Next, the projector of the present invention is a projector provided with a single spatial light modulator,
(J) a wavelength tunable filter installed on the optical path between the projection light source and the optical path adjuster for extracting light of a predetermined wavelength from the projection light; and (k) switching the wavelength extracted by the wavelength tunable filter, A wavelength control controller that controls the image writing device to cause the spatial light modulator to record the component image of the projection image having the extraction wavelength of the wavelength tunable filter may be further provided.

According to this projector, for example, light of each color of RGB (red, green, blue) is sequentially extracted at a predetermined time interval by a wavelength tunable filter, and RGB component images are switched at a predetermined time interval. By outputting while outputting a color image.

Next, the projector of the present invention is provided with a projection light source that outputs projection light in a wavelength band including the visible region, and extracts one of red, green, and blue light on the optical path for light modulation. The optical system including the color selection element, the compensation element, and the spatial light modulator described above may be installed in three sets for each color of red, green, and blue.

In this case, the phase difference between the ordinary light and the extraordinary light of the projected light is compensated for each of the colors red, green and blue. A color image can be projected by combining and outputting the compensated projection lights of the respective colors.

[0020]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. Also, the dimensional ratios in the drawings do not always match those described.

FIG. 1 shows a projector 10 according to this embodiment.
FIG. The projector includes a projection light source 10, a polarizer 16, a half mirror 18, a liquid crystal compensation cell 20, a liquid crystal spatial light modulator 22, an image writing device 24, and an analyzer 30 as main components.

FIG. 2 shows a polarizer 16, a liquid crystal compensation cell 20,
It is a figure for demonstrating the axial arrangement of the liquid crystal spatial light modulator 22 and the analyzer 30. The arrow A indicates the axial direction of the polarizer 16, the arrow B indicates the axial direction of the analyzer 30, and the arrow C indicates the liquid crystal spatial light modulator 2.
The liquid crystal alignment direction 2 and the arrow D indicate the liquid crystal alignment direction of the liquid crystal compensation cell 20, respectively. Here, the axial directions of the polarizer and the analyzer represent the polarization direction of the linearly polarized light extracted by the polarizer and the analyzer (the vibration direction of the electric field).

As shown in FIGS. 1 and 2, the projector of the present embodiment has a parallel orientation ECB (birefringence control).
A projector using a liquid crystal spatial light modulator, comprising a liquid crystal layer of the same type, the same layer thickness, and the same molecular arrangement as the liquid crystal layer in the spatial light modulator, on the projection light source side of the spatial light modulator. The compensation cell is arranged so that the major axis direction of the liquid crystal in the compensation cell and the major axis direction of the liquid crystal in the spatial light modulator are orthogonal to each other. This projector is classified as a single plate projector because it has a single spatial light modulator.

White projection light is output from the projection light source 10 and sequentially passes through a collimating lens 12 and a color filter 14 arranged on the optical path between the light source 10 and the polarizer 16. The white projection light is collimated by the collimating lens 12 and then extracted in the predetermined wavelength range by the color filter 114. Then
The projected light enters the polarizer 16, and linearly polarized light in which an electric field oscillates in the axial direction of the polarizer 16 is extracted.

The projection light that has passed through the polarizer 16 passes through the half mirror 18, and is then subjected to modulation as described later by the liquid crystal compensation cell 20. A power supply 26 is connected to the liquid crystal compensation cell 20, and a drive voltage is applied to the liquid crystal compensation cell 20.

As shown in FIG. 2, this liquid crystal compensation cell 20
Intersects with the polarization direction selected by the polarizer 16, that is, the axial direction of the polarizer at an angle of −45 °. In FIG. 2, the direction of A → C → B → D, that is, the clockwise angle is defined as a positive azimuth angle.

The projection light that has passed through the liquid crystal compensation cell 20 is parallel aligned liquid crystal spatial light modulator (ParallelAligned Liquidcrys).
tal-Spatial Light Modulator (PAL-SLM) 22. FIG. 3 is a sectional view showing the structure of the PAL-SLM 22. The PAL-SLM 22 is composed of a liquid crystal cell having a parallel alignment ECB (birefringence control) liquid crystal 40. This liquid crystal cell is a sandwich type in which two substrates are processed so that the long axis direction of liquid crystal molecules is aligned parallel to the substrate surface, and the liquid crystal is changed in the vertical direction by applying a driving voltage. It is a liquid crystal cell.

The parallel alignment liquid crystal 40 is obtained by aligning a liquid crystal having a positive dielectric anisotropy Δε in parallel homogeneous alignment, that is, so that the major axis direction of the liquid crystal molecules is substantially parallel to the surfaces of the glass substrates 47 and 48. And functions as the optical modulator of the PAL-SLM 22. Alignment layers 41 and 42 are formed on both sides of the liquid crystal 40. Glass substrate 47 and alignment layer 41
Between the amorphous silicon (aS
i) A layer 49 is provided. a-Si layer 49 and orientation layer 41
A dielectric multilayer mirror 45 is provided between the a-Si layer 49 and the dielectric mirror 45 because it is difficult to completely reflect the projection light incident on the PAL-SLM 22. A light-shielding layer 46 is provided between and.
ITO electrodes 43 and 44 are formed between the substrate 47 and the a-Si layer 49, and between the substrate 48 and the alignment layer 42, respectively, and an AC voltage is applied from the power supply 28 (FIG. 1) between these ITO electrodes. By doing so, the PAL-SLM 22 is driven. AR coats 50 and 51 are formed on the outer surfaces of the substrates 47 and 48, respectively.

As shown in FIG. 2, the PAL-SLM 22 is
It is arranged so that the axial direction of the polarizer 16 and the alignment direction of the liquid crystal 40 intersect at an angle of 45 °.

Image data to be projected on the screen 34 is distributed on the a-Si layer 49 of the PAL-SLM 22 by being irradiated with the writing light from the image writing device. a-
When the writing light enters the Si layer 49, the impedance of a-Si decreases in the area illuminated by the writing light (bright area) according to the intensity distribution of the writing light. As a result, the voltage applied to the liquid crystal 40 increases in accordance with the intensity distribution of the writing light, and the tilt state of the liquid crystal changes, so the apparent birefringence Δn changes and I = I ₀ from the phase difference δ. sin ²
According to the equation (δ / 2), the light transmitted through the liquid crystal 40 is modulated according to the intensity distribution of the writing light. Thus, PAL-
The projection light incident on the SLM 22 is modulated according to the written image when passing through the liquid crystal 40.
This point is similar to the conventional projector.

The projected light passes through the liquid crystal 40, is then reflected by the dielectric mirror 45, passes through the liquid crystal 40 again, is modulated, and then is output from the PAL-SLM 22. After that, the projected light passes through the compensation cell 20 again to be modulated, is then reflected by the half mirror 18 and passes through the analyzer 30, is enlarged by the projection lens 32, and is projected onto the screen 34. As a result, the image written in the PAL-SLM 22 is displayed on the screen 34.

Next, the structure and function of the liquid crystal compensation cell 20 will be described. FIG. 4 is a sectional view showing the structure of the liquid crystal compensation cell 20. The liquid crystal compensating cell 20 is formed by aligning a liquid crystal of the same material as the liquid crystal 40 of the PAL-SLM 22 with the same layer thickness as the liquid crystal 40 and in parallel homogeneous alignment. An ITO electrode 63 and an alignment layer 61 are provided between the glass substrate 65 and the liquid crystal 60, and an ITO electrode 64 and an alignment layer 62 are provided between the glass substrate 66 and the liquid crystal 60. Boards 65, 66
An AR coat is formed on the outer surface of the.

In the case where there is no compensation cell, PAL-SLM2
If there is no image written in 2 (OF of the projector
In the F state), the projection light incident on the PAL-SLM 22 has a birefringence Δn ₁ (= n _1e −n _1o ; n _1e is the liquid crystal 40) of the liquid crystal 40.
The ordinary refractive index n _1o of the liquid crystal is modulated according to the extraordinary refractive index of the liquid crystal 40. In this case, the phase difference δ ₁ between the ordinary ray and the extraordinary ray of the projected light that travels back and forth through the liquid crystal 40 is expressed by the following equation.

Δ ₁ = (2π / λ) · Δn ₁ · 2d ₁ (1) where λ is the wavelength of the projection light transmitted through the color filter 14, and Δn ₁ is the compound of the liquid crystal portion 40 of the PAL-SLM 22. Refractive index, d
₁ represents the thickness of the liquid crystal 40 of the PAL-SLM 22.

As shown in the equation (1), it can be seen that the phase difference δ ₁ has different values depending on the wavelength λ of the projected light, so that wavelength dispersion occurs. When such wavelength dispersion occurs, the light component leaking from the analyzer 30 and emitted in the OFF state becomes large, so that the contrast decreases.

On the other hand, in the present projector provided with the liquid crystal compensation cell 20, the projection light incident on the liquid crystal compensation cell 20 has a birefringence Δn ₂ (= n _2e −n _2o ; n _2e) of the liquid crystal 6
The ordinary light refractive index of 0 and n _2o are modulated according to the extraordinary light refractive index of the liquid crystal 60. When no image is written in the PAL-SLM 22, the phase difference δ ₂ between the ordinary ray and the extraordinary ray of the projected light that has reciprocated through the liquid crystal compensation cell 20 is expressed by the following equation.

Δ ₂ = − (2π / λ) · Δn ₂ · 2d ₂ (2) Here, λ is the same as in the formula (1), and Δn ₂ is the birefringence of the liquid crystal 60 in the compensation cell 22. , D ₂ represent the thickness of the liquid crystal 60 in the compensation cell 22. The negative sign on the right side of the equation (2) indicates the alignment direction of the liquid crystal 40 of the PAL-SLM 22 and the compensation cell 20.
This is due to the fact that the liquid crystal alignment direction is orthogonal to.

As can be seen from the above equations (1) and (2), the phase difference δ between the ordinary ray and the extraordinary ray of the projected light that reciprocates through the liquid crystal parts of the compensation cell 20 and the PAL-SLM 22 is given by the following equation. expressed.

Δ = (2π / λ) · (Δn ₁ · 2d ₁ −Δn ₂ · 2d ₂ ) (3) As is apparent from the equation (3), the compensation cell 20 and the PAL-SL are
If the birefringence Δn and the thickness d are the same between both liquid crystals of M22, the phase difference δ ₁ due to the PAL-SLM 22 and the phase difference δ ₂ due to the liquid crystal compensation cell 20 cancel each other out, resulting in a phase difference. No chromatic dispersion occurs.

As described above, the present projector 10
At 0, both liquid crystals have the same thickness d (d ₁ = d ₂ ). Further, the birefringence of the liquid crystal 60 in the compensation cell 20 is Δ.
In order to make n ₂ equal to the birefringence Δn ₁ of the liquid crystal 40 in the PAL-SLM 22, when the tilt of the liquid crystal 60 is not written in the compensation cell 20 from the image writing device 24 (O
A voltage is applied from the power supply 26 so as to be the same as the inclination of the liquid crystal 40 in the PAL-SLM 22 in the FF state). PAL-SL
Birefringence of the liquid crystal 40 in the M22 [Delta] n ₁ and the birefringence index of the liquid crystal 60 of the compensation cell 20 △ n ₂ and a by the same, PAL-SLM
The phase modulated by the liquid crystal 40 of 22 can be canceled by the compensation cell to eliminate the phase difference. As a result, all the problems due to the wavelength dispersion of δ are eliminated.

In the projector 100, the PAL-
Since the liquid crystal 40 of the SLM 22 and the liquid crystal 60 of the compensation cell 20 are made of the same material, even if the operating temperature of the projector changes, the PAL-SLM 22 and the compensation cell 20
The characteristics of change similarly. Therefore, the effect of canceling the phase difference δ between the ordinary light and the extraordinary light is maintained, and the problem of the change in the operating state due to the temperature change is also eliminated.

When the writing light is incident on the PAL-SLM 22, the PAL-SLM 22 is written in the portion where the projection image is written.
Δn ₁ of the liquid crystal 40 in 22 and the liquid crystal 60 in the compensation cell 22
Since there is a difference between Δn ₂ and Δn ₂ , the projection light remains modulated by the phase difference according to the written image. Therefore, in this case, the written image is projected on the screen 34.

The inventor of the present invention has proposed the case of the present projector including the compensation cell 20 and the compensation cell 2 from the present projector.
The OFF state (PAL-
The spectral characteristics of the projection output light (light emitted from the projection lens) in the state where no image was written in the SLM 22 were measured.
This measurement, as shown in FIG.
Instead of the above, a spectroscope 36 is arranged. At the time of measurement, a tungsten lamp that outputs white light is used as the projection light source 10 and a center wavelength of 63 is used as the color filter 14.
Use a 0 nm narrow band transmission filter to
It was made incident on the AL-SLM22. Drive waveform of PAL-SLM22 is 1kH
z and 2.5v, and the driving waveform of the compensation cell 20 was 1kHz and 1.2v.

FIG. 6 shows the spectral characteristics of the projection output light in the OFF state of the present projector including the compensation cell 20 (solid line), and the spectral characteristics of the projection output light in the OFF state of the projector in which the compensation cell 20 is removed from the configuration of the present projector. (Dashed line), and the spectral characteristics (dashed line) of the projection light emitted from the projection light source 10 after passing through the color filter are shown. Further, FIG. 7 is an enlarged view of a solid line and a wavy line in FIG.

As shown in these figures, and in particular in FIG.
When the compensation cell 20 is not used (broken line), the PAL-SLM22
Due to the wavelength dispersion based on the birefringence of the parallel alignment liquid crystal 40 provided in, the light intensity becomes large at wavelengths around the wavelength of 600 nm, and the leakage light (projection light output in the OFF state) becomes large. On the other hand, in the present projector including the compensation cell 20, since the phase modulation in the PAL-SLM 22 is canceled, the chromatic dispersion can be suppressed and the leakage light can be reduced. In fact, FIG. 7 shows that the light intensity is reduced at the wavelength where the light intensity is large when the compensation cell 20 is not used, and the leak light can be reduced.

Further, the present inventor arranged a photodetector at the position of the spectroscope 36 in FIG. 5 and maintained the temperature of the entire optical system at 0 ° C., 20 ° C. and 40 ° C. while maintaining the PAL-SL.
The temperature characteristic was measured by changing the drive voltage of M22 and measuring the transmittance of the projected light in the OFF state (the intensity of the projected output light / the intensity of the output light of the light source 10). The driving voltage of the compensation cell 20 during the measurement was 1.2v.

FIG. 8 shows the temperature characteristics of the projector made up of the PAL-SLM 22 alone (without the compensation cell 20), and FIG. 9 shows the temperature characteristics of the present projector provided with the compensation cell 20. From the viewpoint of reducing leakage light in the OFF state, it can be said that the drive voltage at which the transmittance of the projected light in the OFF state is minimal is the optimum drive voltage. As shown in Fig. 8, in the case of PAL-SLM alone, the change in operating temperature (0 ° C →
The optimum drive voltage of the PAL-SLM22 has changed according to 20 ° C → 40 ° C. On the other hand, in the case of the present projector including the compensation cell 20, as shown in FIG.
Even if the operating temperature changes, the optimum driving voltage hardly changes. Therefore, according to the present projector including the compensation cell 20, high contrast can be realized without the need to adjust the drive voltage of the PAL-SLM according to the operating temperature.

In this embodiment, the compensation cell 20 is used as a means for canceling the phase difference between the ordinary light and the extraordinary light generated in the PAL-SLM, but the phase difference for canceling the phase difference in the PAL-SLM is projected. Other elements can be applied as long as they are elements that impart light. As such a compensating element, for example, a retardation plate represented by a retardation film can be mentioned. The retardation film is a film in which polymers such as polycarbonate and polyvinyl alcohol are uniaxially stretched and superposed on each other to give a desired birefringence. Even such a retardation film can be applied as a compensating element in the projector of the present invention, because the retardation that cancels the retardation in PAL-SLM can be imparted to the projection light.

Further, in this embodiment, as the liquid crystal in the compensation cell, a parallel alignment liquid crystal having the same material and the same layer thickness as the liquid crystal in the PAL-SLM is used so that the compensation cell and the PAL-SLM exhibit the same temperature characteristic. However, the compensating element in the present invention is the PAL-SL
It does not have to have the same temperature characteristics as M. That is, the compensating element in the present invention is only required to be able to give the projection light a phase difference that cancels the phase difference in the PAL-SLM under at least one certain temperature. When using a compensating element that cancels the phase difference in PAL-SLM only under a single temperature, store this compensating element and PAL-SLM in a temperature control tank and adjust the operating temperature of the compensating element to PAL-SLM. -The temperature should be maintained at a temperature that cancels the phase difference in SLM. Also in this case, high contrast can be realized without the need for complicated adjustment work.

[0050]

【Example】

(Example 1) FIG. 10 is a diagram showing the configuration of this example corresponding to the above embodiment. This projector 100a
Is a single-panel type projector that projects a color image on the screen 34.

This projector 100a includes a xenon lamp 10a as a projection light source, a UV filter 14a, an IR filter 14b as a color filter, and a variable wavelength filter 14c for switching RGB.
It has. The white light emitted from the xenon lamp 10a is the UV filter 14a and the IR filter 14b.
After the infrared and ultraviolet components have been cut by, the wavelength tunable filter 14c selects one of the wavelength components corresponding to RGB.

A beam splitter 72 is arranged on the optical path between the polarizer 16 and the liquid crystal compensation cell 20.
As the beam splitter 72, in addition to the half mirror 18 used in the above embodiment, a diffraction grating, a diffusion plate, a Fresnel zone plate, or the like can be used.

A fiber optical plate (FOP) is used as a substrate on the input side of the PAL-SLM 22 here, and is coupled with a projection image writing CRT 70 using a FOP 71 as a face plate. This FOP7
1 and the CRT 70 constitute one image writing device 24a. Variable wavelength filter 14c and CRT7
Both 0s are connected to the controller 74. The controller 74 selects the color (wavelength) to be transmitted by the wavelength tunable filter 14c and causes the CRT 70 to display the component image of this color (wavelength) in the projection image. Specifically, the controller 74 causes the CRT 70 to display a red component image when transmitting red through the filter 14c. Similarly, a green component image is displayed on the CRT 70 when transmitting green through the filter 14c, and a blue component image is displayed when transmitting blue. As a result, on the screen 34,
A color image in which images of RGB colors are overlapped is projected. By switching RGB every 5 msec, one frame of color display can be performed in 15 msec.

The inventor of the present invention is
In the case where the image writing device 24a does not write an image (OFF state) by using the projector in which the compensation cell 20 is removed from the projector 100a, the PA
The change in the transmittance of the projected light (the intensity of the projected output light / the intensity of the output light of the light source 10a) according to the drive voltage of the L-SLM 22 was measured. A voltage of 1.2v was applied to the compensation cell 20. 11 is a projector in which the compensation cell 20 is removed from the projector 100a, and FIG.
It is a figure which shows the measurement result in the case of 00a. Since it is preferable that the screen 34 is darker when there is no image writing,
The voltage at which the transmittance is minimal is the optimum drive voltage. FIG.
As shown in 1, when the compensation cell is not used,
The optimum drive voltage for each of RGB is R (630nm)
= 2.2v, G (530nm) = 2.6v, B (450nm) = 2.3v, and different values for each color. In contrast, FIG.
As shown in FIG. 2, when the compensation cell is used, RG
B. A single drive voltage of 2.5v for all wavelengths can be adopted as the optimum value. As can be seen from this result, in the single-plate color projector, by using the compensation cell as in the present invention, high contrast can be obtained without the need to control the drive voltage of the PAL-SLM.

Example 2 Projector 1 of Example 1
In 00a, the driving voltage of the compensation cell 20 had to be adjusted in advance so that the projection output light when the writing light was OFF was detected and the intensity of this projection output light was minimized. Therefore, an optical sensor is arranged at a position where a part of the projection light output from the compensation cell 20 is incident, and a drive voltage control controller that controls the drive voltage of the compensation cell 20 according to the output signal of the optical sensor is installed. By doing so, the optimum projected image can be automatically obtained.

FIG. 13 is a diagram showing a configuration of a projector 100b including the drive voltage control controller 78, and FIG. 14 is a plan layout view of the optical sensor 76. As shown in FIG. As shown in FIG. 13, the controller 78 is
It is connected to the power supply 26 of the compensation cell 20 and the optical sensor 76 arranged between the analyzer 30 and the projection lens 32, respectively. As shown in FIG. 14, the optical sensor 76 is arranged such that the light receiving surface of the sensor is located in a portion (black portion) in the projected light where an image is not displayed, and the controller 78 controls the sensor output so that the sensor output becomes the lowest. , The voltage applied to the compensation cell 20 is controlled at any time. Therefore, according to the projector of this embodiment, it is not necessary to adjust the drive voltage of the compensation cell 20. Although almost all of the projected light is transmitted through the compensation cell 20, the PAL-SLM 22 is absorbed by the light-shielding layer or the like, so that the temperature of the compensation cell 20 may differ from that of the PAL-SLM 22. In this case, the drive voltage of the compensation cell is automatically adjusted by the controller 78 to obtain the optimum light output. Therefore, according to this embodiment, a high contrast can be obtained more easily.

(Third Embodiment) FIG. 15 is a diagram showing the configuration of a projector 101 according to the third embodiment. The projector 101 includes three PAL-SLMs 22d (for blue) and 22e.
It is a three-plate type projector equipped with (for red) and 22f (for green). The white projection light emitted from the xenon lamp 10a is cut into infrared and ultraviolet components by the UV filter 14a and the IR filter 14b, then passes through the polarizer 16, and then enters the beam splitter 72. The projection light reflected by the beam splitter 72 is
The red component incident on the red transmission bandpass filter 14e and transmitted therethrough is incident on the red compensation cell 20e.
The green component of the projection light that has passed through the beam splitter 72 is reflected by the green reflector 80 and enters the green compensation cell 20f. The components other than green of the projection light transmitted through the beam splitter 72 are transmitted through the green reflection plate 80 and are incident on the blue transmission bandpass filter 14d, and the blue component transmitted therethrough is incident on the blue compensation cell 20d. The projection light of each color that has entered and returned to each compensation cell and PAL-SLM is combined via the beam splitter 72, and then passes through the analyzer 30 and the projection lens 32 to form a color image on the screen 34. To do. Even in the case of such a three-plate type projector, each PAL-SLM
By installing a compensating element that cancels the phase difference between ordinary and extraordinary light in PAL-SLM for each, wavelength dispersion of the phase difference in the wavelength width of each R, G, B filter is suppressed, and high contrast is easily achieved. Obtainable.

[0058]

As described above in detail, according to the projector of the present invention, the phase difference between the ordinary light and the extraordinary light generated in the parallel alignment liquid crystal spatial light modulator is compensated by the compensating element. Further, it is possible to suppress the wavelength dispersion of the phase difference between the extraordinary lights, reduce the leaked light in the OFF state of the projector, and easily obtain a high contrast.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a projector according to an embodiment.

FIG. 2 is a diagram for explaining an axial arrangement of a polarizer, a liquid crystal compensation cell, a liquid crystal spatial light modulator, and an analyzer.

FIG. 3 is a cross-sectional view showing the structure of PAL-SLM.

FIG. 4 is a sectional view showing a structure of a liquid crystal compensation cell.

FIG. 5 is a diagram showing an arrangement of spectroscopes when measuring the spectral characteristics of the projection output light in the OFF state of the projector.

FIG. 6 is a spectral characteristic of projection output light in an OFF state of a projector including a compensation cell (solid line), a spectral characteristic of projection output light in an OFF state of a projector in which the compensation cell is removed from the configuration of the projector (broken line),
FIG. 3 is a diagram showing spectral characteristics (dashed line) of the projection light emitted from the projection light source.

FIG. 7 is an enlarged view of a solid line and a wavy line in FIG.

FIG. 8 is a diagram showing a temperature characteristic of a projector having no compensation cell.

FIG. 9 is a diagram showing a temperature characteristic of a projector including a compensation cell.

FIG. 10 is a diagram illustrating a configuration of a projector according to the first exemplary embodiment.

FIG. 11 is a PAL-SLM when a compensation cell is not used.
FIG. 6 is a diagram showing a change in transmittance of projection light according to the driving voltage of FIG.

FIG. 12 is a diagram showing a change in transmittance of projection light according to a driving voltage of PAL-SLM when a compensation cell is used.

FIG. 13 is a diagram showing a configuration of a projector according to a second embodiment.

FIG. 14 is a diagram showing an arrangement of optical sensors.

FIG. 15 is a diagram showing a configuration of a projector according to a third embodiment.

[Explanation of symbols]

10 ... Projection light source, 12 ... Collimating lens, 14 ... Color filter, 16 ... Polarizer, 18 ... Half mirror, 2
0 ... Compensation cell, 22 ... PAL-SLM, 24 ... Image writing device, 26 ... Compensation cell drive power supply, 28 ... PAL-SLM drive power supply, 30 ... Analyzer, 32 ... Projection lens, 34 ... Screen.

Claims (6)

[Claims] 1. A projection light source, a polarizer installed on the output optical path of the projection light from the projection light source, and a light from the polarizer installed on the path of the projection light passing through the polarizer. And an optical path adjuster for outputting at least a part of the light on the optical path for optical modulation, and for outputting at least a part of the light traveling on the optical path for optical modulation and incident on the optical path for detection. A parallel alignment ECB liquid crystal type spatial light modulator installed on the light modulating optical path, an image writing device for sending a projection image to the spatial light modulator for recording, and an optical writing optical path on the detecting optical path. An installed analyzer, wherein, on the optical path for light modulation, between the optical path adjuster and the spatial light modulator, between ordinary light and extraordinary light generated in the spatial light modulator. The feature is that a compensating element that compensates for the phase difference of Projector to be. 2. The projector according to claim 1, wherein the compensation element is a liquid crystal cell including a parallel-aligned ECB liquid crystal having substantially the same material and substantially the same thickness as the liquid crystal portion of the spatial light modulator. . 3. An optical sensor for detecting the projection light that has passed through the analyzer, and a detection by the optical sensor when a projection image is not sent from the image writing device to the spatial light modulator. The projector according to claim 2, further comprising: a controller for controlling a drive voltage that applies a drive voltage having a value that minimizes the light intensity to the liquid crystal cell or the spatial light modulator. 4. The temperature adjusting device according to claim 1, further comprising a temperature adjusting device that maintains operating temperatures of the compensation element and the spatial light modulator at a temperature at which the compensation element can compensate the phase difference. projector. 5. A wavelength tunable filter comprising a single spatial light modulator, which is installed on an optical path between the projection light source and the optical path adjuster and extracts light of a predetermined wavelength from the projection light. A controller that switches the wavelengths extracted by the wavelength tunable filter and controls the image writing device to write a component image of the projection image having the extraction wavelength of the wavelength tunable filter into the spatial light modulator. The projector according to claim 1, further comprising: 6. The color selection element, wherein the projection light source outputs projection light in a wavelength band including a visible region, and extracts one of red, green, and blue light on the optical path for light modulation. The projector according to claim 1, wherein three sets of optical systems including the compensation element and the spatial light modulator are installed for each color of red, green, and blue.