JPH05249408A - Projection type liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain the projection type liquid crystal display device which has a small and simple outside shape, displays bright and high-purity images and has high-resolution image quality drastically decreased in astigmatisms. CONSTITUTION:The incident angle of light on dichroic mirrors 2, 3, 8, 9 and a reflection mirror 4 is set at 20 to 40 deg.. A light source 1 is disposed on the incident side thereof and a projection lens 10 on the exit side. Aberration compensating glass 11 optically equiv. to the dichroic mirrors 8, 9 is inserted between liquid crystal light valves 5B, G, R and the projection lens 10 in the position twisted from the dichroic mirrors 8, 9 in such a manner that the same incident angles of light are obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection type liquid crystal display device for enlarging and projecting an image formed by a liquid crystal light valve by a projection lens. Further, it relates to a projection type liquid crystal display device using an optical system for correcting astigmatism.

[0002]

2. Description of the Related Art In conventional projection type liquid crystal display devices, as is the case with those already commercialized, the incident angle of light to the light separating means and the light combining means was about 45 degrees. This was the smallest and most space-efficient optical system except the light source and projection lens.

Further, as an optical system for correcting astigmatism of a conventional projection type liquid crystal display device, there are known structures such as the actual open-air plane 3-73910 and Japanese Patent Laid-Open No. 3-170925. The former is to adjust astigmatism to the worse one so that all three lenses are the same, and the latter is to reduce astigmatism by using a lens.

[0004]

However, in the prior art,
In the 45-degree incident optical system, the projection lens and the light source were projected, and the size was increased and a convex portion was formed. In addition, in terms of optics, color purity deterioration and optical axis shift occur.

The former of the astigmatism correction optical system does not reduce the astigmatism, and the latter increases other aberrations.
Therefore, the image quality on the screen is deteriorated.

The projection type liquid crystal display device of the present invention solves the above problems, and its purpose is to display a bright and high color purity image while having a small and simple outer shape. It is an object of the present invention to provide a projection type liquid crystal display device having a high resolution and high image quality with drastically reduced aberrations.

[0007]

In order to solve the above-mentioned problems, a projection type liquid crystal display device of the present invention includes a light source, a light separating means for separating light from the light source, and a light separating means for modulating the light. A liquid crystal light valve, a light combining means for combining the modulated light from the liquid crystal light valve, and a projection lens for projecting the light from the light combining means, in the light separating means and the light combining means. The incident angle of light is between 20 degrees and 40 degrees, and an aberration correction glass optically equivalent to the light combining means is twisted with respect to the light combining means between the liquid crystal light valve and the projection lens. It is characterized in that it is inserted at the position so that the incident angles of light are the same.

Further, the aberration correcting means is inserted such that the incident angle of the light on the aberration correcting glass is different from the incident angle of the light on the light combining means.

Further, the optical path that passes through the light combining means closest to the projection lens is an optical path for green, and the aberration correction glass is inserted between the liquid crystal light valve and the projection lens in the optical path for green. Is characterized by.

[0010]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view of an optical system showing an embodiment of the present invention.

Light emitted from the light source 1 is separated into three primary colors of red, green and blue by the wavelength selection characteristics of the dichroic mirrors 2 and 3. For example, the dichroic mirror 2 reflects yellow light (light of about 500 nm or more) and transmits blue light (light of about 500 nm or less). In addition, the dichroic mirror 3 allows green light (from about 500 nm to about 6 nm).
It reflects light of wavelengths between 00 nm) and transmits red light (light of about 600 nm or more). That is, it is separated into three primary colors of red, green and blue.

At this time, the optical axis is designed to have an incident angle of 30 degrees, and the wavelength characteristics are designed to satisfy the above characteristics when the incident angle is 30 degrees.

The light source 1 is used by combining a light source such as a halogen lamp, a xenon lamp, a metal halide lamp, etc., a reflection optical system such as a spherical reflector, a parabolic reflector, an ellipsoidal reflector and a condensing optical system such as a condenser lens. .. Although not shown, a heat ray cut filter, an ultraviolet ray cut filter, a cooling unit, etc. are arranged to prevent deterioration of image quality due to heat.

Of the separated primary color lights, the red and green lights go straight as they are, and the blue light is reflected by the reflection mirror 4 and goes straight, and the corresponding liquid crystal light valves 5R and 5R, respectively.
It is incident on 5G and 5B.

The respective primary color lights that have entered the liquid crystal light valve 5
R, 5G, 5B and the polarizing plates 6 arranged before and after them
7, light modulation corresponding to each primary color, that is, an image is formed and emitted for each primary color according to the magnitude of the applied signal voltage.

Generally, when the TN type liquid crystal display element is used as the liquid crystal light valves 5R, 5G and 5B, since the polarizing plates 6 and 7 are used, the polarization axis of the liquid crystal light valves 5R, 5G and 5B of the light splitting optical means and the light synthesizing optical means is used. By arranging so as to correspond to the P-polarization axis or the S-polarization axis and using either polarized light, a sharp color separation characteristic can be obtained and the color purity is improved.

However, depending on the structure of the photosynthetic optical means, only one liquid crystal light valve is displayed horizontally or vertically upside down, and it is necessary to match the clear viewing direction and the liquid crystal twisting direction with each other. Productivity is poor because we have to manufacture different types of liquid crystal light valves. Further, when the same liquid crystal light valve is used, image quality deterioration such as color unevenness and color shift in halftone occurs.

Further, the configuration becomes difficult even in tilted projection in which the projected image is displayed above or below the main body of the projection type liquid crystal display device.

Therefore, as a method for solving these problems, P polarized light + S polarized light is used. This makes the polarization axis the intermediate direction between the P polarization axis and the S polarization axis. FIG. 2 shows the spectral characteristics of a general 45-degree incident blue reflection dichroic mirror. The broken line indicates P polarization, the alternate long and short dash line indicates S polarization, and the solid line indicates P + S polarization. As can be seen from the figure, the spectral characteristics deteriorate and the color purity deteriorates.

The dichroic mirror has a structure in which transparent dielectrics having different refractive indexes are laminated to have a film thickness of about the light wavelength. The dichroic mirror hardly receives light absorption loss and reflects light in the transmission wavelength range by the optical multiple interference phenomenon. It has the function of dispersing light in the wavelength range. In the dichroic mirror using such a dielectric multilayer film, as the incident angle of light increases from 0, the difference between the spectral characteristics of the P-polarized component and the S-polarized component becomes remarkable.

The dichroic mirror will be described in more detail.

The dielectric multilayer film that determines the spectral characteristics of the dichroic mirror is n when the optical film thickness nd of the dielectric film is the central wavelength λ of the reflection band and the incident angle of light is θ.
It satisfies the relationship of d · cos θ = λ / 4 and is formed by alternately laminating a plurality of high refractive index films and low refractive index films.

Here, the characteristics such as the inclination of the boundary wavelength band between the reflection band and the transmission band, the reflectance, the half-value width of the reflection band, etc. depend on the number of layers N of the multilayer film, the high refractive index n _H , and the low refractive index n _L. To do. The full width at half maximum of the reflection band is given by the following equation.

Δg = 2 / π * sin ⁻¹ ((η _H −η _L ) / (η _H + η _L )) However, in the case of P polarized light η _H = n _H / cos θ _H η _L = n _L / cos θ _L In the case of S polarization η _H = n _H · cos θ _H η _L = n _L · cos θ _L Let θ be the incident angle of light and n _{0 be} the refractive index of air, then θ _H ,
θ _L satisfies the following equation.

N ₀ · sin θ = n _H · sin θ _H = n _L · sin θ _L As described above, the spectral characteristic of the dichroic mirror is P.
The difference between polarized light and S-polarized light is explained by the above formula.

As the incident angles of the effective refractive indices η _H and η _L of the dielectric multilayer film increase from 0 ° to 90 °, P
The difference between the polarized light and the S-polarized light becomes remarkable, and the full width at half maximum Δg of the reflection band also largely changes depending on the polarized light. The larger the incident angle, the larger the difference between the P-polarized light and the S-polarized light.

Therefore, as compared with the structure in which the dichroic mirrors are arranged with the incident angle of 45 degrees, as in the present invention, 2
By making the light incident from 0 degree to 40 degrees,
The polarization dependence is greatly reduced, and the color separation characteristics are significantly improved even when using P polarization + S polarization. FIG. 3 shows the spectral characteristics of the dichroic mirror when the incident angle of light is 30 degrees. Similar to FIG. 2, the solid line indicates the P + S polarization, the dotted line indicates the P polarization, and the alternate long and short dash line indicates the S polarization. P + compared to Fig. 2
It can be seen that the light separation characteristic of the S-polarized component is steep.

Here, the greater the angle of incidence on the dichroic mirror, the longer the length of the dichroic mirror. That is, the area becomes large. The larger the area of the dichroic mirror, the lower the productivity in terms of the flatness of the substrate and the uniformity of the film thickness of the dielectric multilayer film. Further, the deviation of the optical path caused by the thickness of the substrate of the dichroic mirror becomes large.

Assuming that the length of the dichroic mirror is L and the deviation of the optical path is w, the following equation is obtained for the incident angle θ. Here, 1 is the length of the liquid crystal light valve, and D and n are the thickness and the refractive index of the substrate of the dichroic mirror.

L = 1 / cos θ w = D * sin θ (1− (cos θ / √ (n ² −sin ² θ))) As is clear from this equation, the incident angle of light to the dichroic mirror is 20 to 40. By setting the degree, the deviation of the length and the optical path can be reduced.

On the other hand, conversely, the smaller the angle of incidence on the dichroic mirror, the smaller the length and area of the dichroic mirror, but the problem of increasing the optical path length from the light source to the liquid crystal light valve remains. As the optical path length increases, the volume of the projection liquid crystal display device increases and
The amount of effective light decreases and the output light flux decreases.

However, regarding the volume, considering that the light source is arranged on the light incident side of the light separating optical system, and the projection lens is arranged on the light emitting side of the light combining optical system, the structure is as shown in FIG. Then, the projection like the conventional projection lens is eliminated, the appearance is rather clean and the volume hardly increases.

Further, as a result of detailed examination of the incident angle θ of light from 45 ° to 5 °, when comparing the volumes including the projection lens and the light source, the minimum volume is obtained when the incident angle of light is 30 °. Became. However, for the projection lens and the light source, numerical values of general size were used.

Of the color light modulated by the liquid crystal light valves 5R, 5G and 5B, the red light is reflected by the reflection mirror 4 and then transmitted through the aberration correction glass 11 and the dichroic mirror 9 to reach the projection lens 10. To do. The green light is reflected by the dichroic mirrors 8 and 9,
Reach the projection lens 10. Blue light is aberration correction glass 1
After passing through 1 and the dichroic mirror 8, it is reflected by the dichroic mirror 9 and reaches the projection lens 10.

Here, the aberration correction glass 11, which is an optical system for correcting astigmatism, will be described in detail.

It is currently most common to use a dichroic mirror as the light combining optical means. However, this causes astigmatism because an object that is non-rotationally symmetric with respect to the optical axis of the projection lens and has a different refractive index from the surroundings is inserted into the imaging optical system. This astigmatism is caused by the difference in the optical path length of the light passing through the dichroic mirror between the image plane in the radial direction (meridional image plane) and the image plane in the annular line direction (sagittal image plane), and the astigmatism is caused by the projection lens. There are two image positions, an image forming position in the radial direction and an image forming position in the annular line direction.

Therefore, the optimum image in this optical system is a blurred image because the least circle of confusion of both is observed. Further, it is practically impossible to correct the astigmatism due to this by the projection lens, and the image in which this astigmatism occurs must be observed as it is.

FIG. 4 is a diagram for explaining that astigmatism can be removed by the present invention, (a) is a perspective view,
(B) is a plan view.

In FIG. 4A, the light travels along the X axis, passes through the aberration correction glass 11 tilted by the angle θ in the XZ plane, and passes through the dichroic mirror 9 tilted by the angle θ in the XY plane. .. That is, the aberration correction glass 11 and the dichroic mirror 9 have a twisted positional relationship, and light incident planes are orthogonal to each other. . The angle θ is an incident angle of light with respect to the aberration correction glass 11 and the dichroic mirror 9, and is an angle between 20 degrees and 40 degrees.

FIG. 4 is a plan view showing the behavior of light rays at this time.
It is (b) and represents the imaging state of the light ray in a radial direction and a circular line direction. In the figure, the broken line represents the optical path of the light beam when the aberration correction glass 11 and the dichroic mirror 9 are not present, and the light beam is imaged on the plane 41, and astigmatism naturally does not occur.

On the other hand, the solid line in the figure shows the optical path of the light beam when the aberration correction glass 11 and the dichroic mirror 9 are inserted. As is apparent from the figure, by inserting the aberration correction glass 11 optically equivalent to the dichroic mirror 9 into the dichroic mirror 9 in a twisted relationship and at the same incident angle, the radiation direction and the annular line direction are In this case, the light rays form an image on the flat surface 42, and astigmatism does not occur.

Since there is the above-mentioned effect in the paraxial region, if the projection lens is made to be telecentric, the above-mentioned image forming state is maintained at all points on the liquid crystal light valve. By matching the surface with the flat surface 42, it is possible to completely eliminate astigmatism, which has been conventionally caused by the transmission of the dichroic mirror.

The three primary color lights recombined in this way are projected as an enlarged image on the screen in front by the projection lens 10. The dichroic mirrors 2, 3,
The liquid crystal light valves may be arranged differently by changing the wavelength selection characteristics of 8 and 9.

(Embodiment 2) As described above, the present invention is
Completely corrects astigmatism for a telecentric imaging optical system, but the diagonal length of the liquid crystal light valve becomes large as the projection type liquid crystal display device becomes finer in recent years. Therefore, it is difficult to form a telecentric image forming optical system. Further, as large screen projection is desired, an optical system in which the optical axis of the projection lens and the center of the screen are displaced, that is, a so-called tilt optical system is required.

For such an optical system, it is difficult to completely correct the astigmatism because the light rays are inclined, but according to the present invention, a remarkable difference can be confirmed by the presence or absence of the aberration correction glass. ..

In FIG. 5, the incident angle of light on the dichroic mirror and the aberration correction glass is 30 degrees, and F = 4.
5 is a simulation result using a projection lens having a maximum chief ray tilt angle of 7 degrees, where (a) represents the chief ray tilt angle versus defocus amount, and (b) represents the chief ray tilt angle versus MTF.
In FIG. 5, the solid line is the case with the aberration correction glass according to the present invention, and the broken line is the case without it. Further, each of the four graphs represents a meridional (M) image and a sagittal (S) image at points of symmetry with respect to the optical axis of the projection lens.

As shown in FIG. 5A, according to the present invention, the defocus amount is 0 at the principal ray tilt angle, that is, the central portion of the projection lens is 0, and the peripheral portion thereof has no aberration correction, as compared with the case where no aberration correction is performed. It can be seen that the defocus amount is extremely small. This means that the projected image is almost in the focused state at the center of the projection lens and its peripheral portion. Further, since the defocus amount is small overall, the depth of focus of the projection lens can be reduced, so that the F value of the projection lens can be reduced to brighten the projected image. These are highly effective in a high-definition projection liquid crystal display device, particularly in a high-definition projection liquid crystal display device.

Further, as shown in FIG. 5 (b), there is a clear difference in the MTF at the central portion of the projection lens with and without the aberration correction glass, and there is a difference in the variation as the principal ray tilt angle increases. I understand. Therefore, when the aberration correction glass according to the present invention is used, the resolution increases on the projected image as it approaches the center of the projection lens, and the uniformity of the resolution can be improved even in the peripheral portion.

[0049]

[Table 1]

Table 1 shows the incident angle of the light beam to the dichroic mirror under the same conditions as in the simulation of FIG.
It is a result of calculating the defocus amounts for M and S at the four corners of the liquid crystal light valve when the incident angle of the light beam on the aberration correction glass is changed while being fixed to 4 degrees. From this, by changing the incident angle of the light ray to the dichroic mirror and the incident angle of the light ray to the aberration correction glass,
It can be seen that the balance operation of the defocused state in the projected image is possible.

In this case, a well-balanced defocus state can be realized by setting the incident angle of the light ray on the aberration correction glass from 28 degrees to 29 degrees. This angular relationship is a condition for changing the angle state of the light ray. It changes depending on (incident angle of light beam on dichroic mirror, maximum tilt angle of principal ray, amount of tilt, etc.).

(Embodiment 3) FIG. 6 shows another embodiment of the present invention. The same parts as those in FIG. 1 are designated by the same reference numerals. The basic operation is the same as in the case of FIG.

In this embodiment, as described above, the liquid crystal light valves 5R, 5G, 5B are operated by operating the wavelength selection characteristics of the dichroic mirrors 61, 62, 63, 64.
The optical path for transmitting the dichroic mirror 64 closest to the projection lens 10 is defined as the green optical path 65, and the green liquid crystal light valve 5G is provided on the optical path.
Are arranged. Further, the aberration correction glass 11 is not provided on the blue optical path 66, and the aberration correction glass 11 is arranged only on the green optical path 65.

This embodiment realizes the downsizing of the projection type liquid crystal display device with the above-mentioned structure.
Since blue has a relatively low relative luminous efficiency, the astigmatism caused thereby has a relatively small effect on the resolution of the projected image. Therefore, the astigmatism is corrected only in green, which has a relatively high relative luminous efficiency. At this time, the liquid crystal light valve 5G for green is used.
6, the presence or absence of the aberration correction glass 11 does not affect the size of the projection type liquid crystal display device.

FIG. 7 is an explanatory diagram for proving this, and shows the relationship between the incident angle of the light beam to the dichroic mirror and the pitch P between the mirrors (shown in FIG. 6). The pitch P between the mirrors is a factor that determines the size of the projection type liquid crystal display device. In the figure, the solid line shows the relationship when the aberration correction glass 11 is inserted, and the broken line shows the relationship when the aberration correction glass 11 is not inserted.

That is, when the aberration correction glass 11 is inserted, the pitch P between the mirrors should be set to a value above both graphs for each incident angle. It can be seen that the pitch P between the mirrors becomes minimum at an angle of 30 degrees. In other words, in an optical system with an incident angle of 30 degrees, the presence or absence of the aberration correction glass 11 and the pitch P between the mirrors are irrelevant, that is, the size of the projection type liquid crystal display device.

Therefore, according to this embodiment, it is possible to obtain a good projection image in which astigmatism is corrected without increasing the size of the projection type liquid crystal display device. Further, with the configuration of this embodiment, the plate thickness of the reflection mirror 4 for reflecting green light can be increased. This allows
Since the flatness of the reflection mirror 4 can be improved and even the deterioration of image quality due to the warp of the reflection mirror can be improved, the projected image is further improved.

[0058]

As described above, in the projection type liquid crystal display device of the present invention, since the light is incident on the light separating means and the light combining means at an incident angle of 20 to 40 degrees, the projection lens and the light source are arranged. The dead space generated by the can be eliminated, and the appearance becomes very simple and downsized. Especially, if the angle is set to 30 degrees, the space is most efficient, and the dichroic mirror can be downsized.

Further, since the deviation of the optical path is reduced, the optical axis can be easily adjusted, astigmatism can be reduced, and the brightness and the color purity can be improved, so that the remarkable image quality can be obtained. ..

Furthermore, since the aberration correction glass is inserted at a twisted position with respect to the light combining optical system at the same angle as the incident angle of light to the light combining optical system or at a different angle,
Astigmatism can be completely removed for the telecentric optical system and can be drastically reduced for the non-telecentric optical system. Therefore, it is possible to realize a projection type liquid crystal display device which is compact but has high resolution.

The higher the definition of the projection type liquid crystal display device in the future, the greater the effect of the present invention is, particularly in the projection type liquid crystal display device corresponding to the high definition.

[Brief description of drawings]

FIG. 1 is a plan view of an optical system that represents an embodiment of the present invention.

FIG. 2 is a diagram showing spectral characteristics of a blue reflection dichroic mirror that is incident at 45 degrees.

FIG. 3 is a diagram showing spectral characteristics of a blue reflection dichroic mirror that is incident at 30 degrees.

4A and 4B are explanatory views of astigmatism removal, in which FIG. 4A is a perspective view and FIG. 4B is a plan view.

FIG. 5 is a simulation result at 30 ° incidence,
FIG. 7A is a diagram showing a principal ray tilt angle versus defocus amount, and FIG. 9B is a diagram showing a principal ray tilt angle versus MTF.

FIG. 6 is a plan view of an optical system that represents an embodiment of the present invention.

FIG. 7 is an explanatory diagram of a projection type liquid crystal display device size with respect to an incident angle.

[Explanation of symbols]

 1 Light source 2,3 Dichroic mirror 4 Reflection mirror 5 Liquid crystal light valve 6,7 Polarizing plate 8,9 Dichroic mirror 10 Projection lens 11 Aberration correction glass 61,62 Dichroic mirror 63,64 Dichroic mirror

Claims (4)

[Claims] 1. A light source, a light separating means for separating the light from the light source, a liquid crystal light valve for modulating the light from the light separating means, and a photosynthesis for combining the modulated light from the liquid crystal light valve. And a projection lens for projecting light from the light combining means, wherein an incident angle of light to the light separating means and the light combining means is between 20 degrees and 40 degrees, and Between the liquid crystal light valve and the projection lens, an aberration correction glass that is optically equivalent to the light combining means is inserted at a twisted position with respect to the light combining means so that the incident angles of light are the same. Characteristic projection type liquid crystal display device. 2. The incident angle of light on the aberration correction glass is different from the incident angle of light on the light combining means,
The projection type liquid crystal display device according to claim 1, wherein the aberration correction glass is inserted. 3. An optical path that passes through a light combining means closest to the projection lens is an optical path for green, and the aberration correction glass is inserted between the liquid crystal light valve and the projection lens in the optical path for green. Claim 1 or 2 characterized
The projection type liquid crystal display device described in. 4. The projection type liquid crystal display device according to claim 1, wherein the liquid crystal light valve for modulating light is a liquid crystal light valve using TN type liquid crystal.