JPH02311887A - Projection type liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent moire fringe from occurring by making the extending direction of plural projecting lines of a phase grating coincide with the ridge direction of the lenticular lens of a transmission type screen. CONSTITUTION:The phase grating 4 having plural projecting lines 16 arranged in parallel with a direction perpendicular to an optical axis is provided between a liquid crystal cell 1 and the transmission type screen 6, and the extending direction of the plural projecting lines 16 is made to coincide with the ridge direction of the lenticular lens 12 of the screen 6. Therefore, the spatial frequency having the intensity distribution of light projected from the lenticular lens 12 is made lower than either of the spatial frequency corresponding to the pitch of the electrode of the liquid crystal cell 1 and the spatial frequency corresponding to the pitch of the lenticular lens 12 by the phase grating 4. Thus, the moire fringe caused by the difference of the spatial frequency between the component that the intensity distribution of the light projected from the lenticular lens 12 corresponds to the pitch of the electrode of the liquid crystal cell 1 and the component that it corresponds to the pitch of the lenticular lens 12 is prevented from occurring.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a liquid crystal cell as a light valve.
The present invention relates to a rear projection type liquid crystal projection display device used as a rear projection type liquid crystal projection display device.

Background Art This type of display device uses an active matrix method in which a nonlinear element such as a thin film transistor is incorporated in each pixel as a drive method for the liquid crystal cell, which increases the amount of display information, making it difficult to display TV images. There is something that made it possible. However, in active matrix liquid crystal cells, the nonlinear element and pixel electrodes for driving the liquid crystal are opaque, so when enlarged and projected onto a transmissive screen, the shadows of these electrodes appear on the screen. It will be projected.

On the other hand, as a transmission screen, a two-panel screen in which a Fresnel lens 6 and a lenticular lens 7 are combined is generally used, as shown in FIG.

However, when an image from an active matrix liquid crystal cell is enlarged and projected onto a transmission screen containing this lenticule 2-lens, the shadow of the electrode part of the liquid crystal cell is projected onto the screen as described above. There is a problem in that a beat occurs due to the pitch of the projected image and the pitch of the lenticular lens of the screen, resulting in a so-called moiré image, which significantly deteriorates the image quality.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a liquid crystal projection display device that can prevent the occurrence of moiré images.

In the liquid crystal projection display device according to the present invention, a phase grating having a plurality of protrusions arranged parallel to each other in a direction perpendicular to the optical axis is provided between the liquid crystal cell and the transmission screen, and The extending direction is made to match the ridgeline direction of the lenticular lens of the transmission screen.

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 to 5.

In FIG. 1, reference numeral 1 denotes an active matrix type liquid crystal cell, and light emitted from a light source 2 is converted into parallel light by a condenser lens 3 and irradiated onto this liquid crystal cell 1. This irradiation light passes through the liquid crystal cell 1, passes through the rectangular wave phase grating 4 and the magnifying projection lens 5, and then is irradiated onto the transmission screen 6.

As the transmission screen 6, as shown in FIG. 2, a two-panel screen in which a Fresnel lens 11 and a lenticular lens 12 are combined is used. In this two-panel screen, by arranging the lenticular lens 12 on the incident surface side, it is possible to widen the angle of view and reduce color shift, and furthermore, by the action of the black stripe 13 along the ridgeline direction of the exit surface, external light Images with good contrast can be obtained even under illumination. Furthermore, the concentric Fresnel lens 11 allows the light to be macroscopically converged in the direction of the observer in front, and the diffusion layer 14 allows appropriate vertical directivity characteristics to be obtained.

Further, the rectangular wave phase grating 4 is formed similarly to the phase grating disclosed in Japanese Patent Publication No. 49-20105, and acts as an optical low-pass filter. That is,
As shown in FIG. 3, the rectangular wave phase grating 4 consists of a transparent substrate portion 15 and a grating portion 16 consisting of a plurality of protrusions formed parallel to each other on the entire surface of the substrate portion 15. . This rectangular wave phase grating 4 is designed such that the main surface of the substrate portion 15 is perpendicular to the optical axis, and the extending direction of the plurality of protrusions forming the grating portion 16 coincides with the ridgeline direction of the lenticular lens 12. It is located in

Here, the width in the direction perpendicular to the optical axis of each of the plurality of protrusions forming the lattice portion 16 is a1, the pitch of the plurality of protrusions is p1, the length of each of the plurality of protrusions in the optical axis direction That is, the optical height of the grating portion 16 is assumed to be δ. At this time, if the following equation holds true, the performance of the rectangular wave phase grating 4 as a low-pass filter is sufficiently within a practically acceptable range.

δ≧−1・・・・・・(1) p/a≧2・・・・・・(2
) Surroundings δ≦1-0.35p/a (3)
A δ≧1−0.65p/a (4) Also, if the distance between the surfaces of the liquid crystal cell 1 and the substrate portion 15 of the rectangular wave phase grating 4 is g, then the rectangular wave phase grating 4 The cut-off spatial frequency Sc is expressed by the following equation.

5c-a/1λ (5) Here, λ is the wavelength of the irradiated light.

Since the spatial frequency of the image projected onto the lenticular lens 12 is lower than the cut-off spatial frequency Sc, this cut-off spatial frequency Sc is projected onto the spatial frequency corresponding to the pitch of the electrodes of the liquid crystal cell 1 and the liquid crystal surface of the liquid crystal cell 1. By setting the spatial frequency to a value lower than one of the spatial frequencies corresponding to the pitch of the lenticular lens 12, the spatial frequency of the intensity distribution of the light emitted from the lenticular lens 12 can be adjusted to the pitch of the electrodes of the liquid crystal cell 1. The component corresponding to the pitch of the electrodes of the liquid crystal cell 1 of the intensity distribution of light emitted from the lenticular lens 12 is lower than either one of the corresponding spatial frequency and the spatial frequency corresponding to the pitch of the lenticular lens 12, and the lenticular This makes it possible to prevent moire fringes from occurring due to differences in spatial frequencies between components corresponding to the pitch of the lens 12.

FIG. 4 is a block diagram showing another embodiment of the present invention, in which each part is the same as the first embodiment except that the rectangular wave phase grating 4 is disposed between the magnifying projection lens 5 and the transmission screen 6. It is configured similarly to the device.

In such a configuration, if the distance between the entire surface of the substrate portion 15 of the rectangular wave phase grating 4 and the transmission screen 6 is g', then
The cutoff spatial frequency Sc of the rectangular wave phase grating 4 is expressed by the following equation.

5c-a/g'λ (6) Therefore, in the device shown in FIG. 4, the cut-off spatial frequency Sc expressed by equation (6) is set to By setting a value lower than either the frequency or the spatial frequency corresponding to the pitch of the lenticular lens 12 projected onto the liquid crystal surface of the liquid crystal cell 1, the occurrence of moire fringes is prevented in the same way as in the device shown in FIG. can do.

FIG. 5 is a configuration diagram showing still another embodiment of the present invention, in which irradiation light emitted from a light source 21 is converted into parallel light by a reflector 22 and then incident on a dichroic mirror 23. The dichroic mirror 23 is formed to selectively reflect only the blue component of the irradiated light.

A blue component is separated from the irradiated light by this dichroic mirror 23 and reflected by a reflecting mirror 24, and then enters a dichroic prism 27 via a liquid crystal cell 25 and a rectangular wave phase grating 26.

On the other hand, the component transmitted through the dichroic mirror 23 is incident on the dichroic mirror 29.

The dichroic mirror 29 is formed to selectively reflect only the green component of the irradiated light.

The dichroic mirror 29 separates the green component from the irradiated light, and the liquid crystal cell 30 and the rectangular wave phase grating 31
The light then enters the dichroic prism 27.

Further, the component transmitted through the dichroic mirror 29, that is, the red component, is reflected by the reflecting mirrors 32 and 33, and then enters the dichroic prism 27 via the liquid crystal cell 34 and the rectangular wave phase grating 35.

In the dichroic prism 27, the blue component is reflected by the reflective surface 27a, the green component is transmitted through the reflective surfaces 27a and 27b, and the red component is reflected by the reflective surface 27b. The dichroic prism 27 causes each of the blue, green, and red components to enter the magnifying projection lens 37 . The magnifying projection lens 37 irradiates each of the blue, green, and red components onto the transmission screen 38 to form a color image.

In the above configuration, blue, green,
The occurrence of moire fringes in each of the red components can be prevented, and a good color image can be obtained.

In the above embodiment, the rectangular wave phase grating 4 is provided between the liquid crystal cell 4 and the magnifying projection lens 5 and between the magnifying projection lens 5 and the transmission screen 6. It may be formed on the pupil of the projection lens 5. However, in that case, if the focal length of the magnifying projection lens 5 is f, the cutoff spatial frequency Sc of the rectangular wave phase grating 4 is expressed by the following equation.

S c -a / fλ (7) Effects of the Invention As detailed above, in the liquid crystal projection display device according to the present invention, there is a gap in the direction perpendicular to the optical axis between the liquid crystal cell and the transmission screen. A phase grating having a plurality of protrusions arranged parallel to each other is provided, and the extending direction of the plurality of protrusions is made to coincide with the ridgeline direction of the lenticular lens of the transmission screen. Therefore, in the liquid crystal projection display device according to the present invention, the spatial frequency of the intensity distribution of light emitted from the lenticular lens is adjusted by the phase grating into the spatial frequency corresponding to the pitch of the electrodes of the liquid crystal cell and the spatial frequency corresponding to the pitch of the lenticular lens. The spatial frequency between the component corresponding to the pitch of the electrodes of the liquid crystal cell and the component corresponding to the pitch of the lenticular lens 12 of the intensity distribution of the light emitted from the lenticular lens can be made lower than either one of the frequencies. This makes it possible to prevent moiré fringes caused by the difference.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
FIG. 3 is a schematic perspective view showing the configuration of the transmission screen.
FIG. 4 is a cross-sectional view showing the shape of a rectangular wave phase grating, FIG. 4 is a block diagram showing another embodiment of the present invention, and FIG. 5 is a block diagram showing still another embodiment of the present invention. Explanation of symbols of main parts 1...Liquid crystal cell 2...Light source 4...Square wave phase grating 6...Screen

Claims (2)

[Claims] (1) A liquid crystal projection display device that irradiates a light source light onto an active matrix liquid crystal cell, and enlarges and projects the light passing through the liquid crystal cell onto a transmissive screen including a lenticular lens, the liquid crystal cell and the transmissive screen A phase grating having a plurality of protrusions arranged parallel to each other in a direction perpendicular to the optical axis is provided between the lenses, and the extending direction of the plurality of protrusions matches the ridgeline direction of the lenticular lens. A liquid crystal projection display device featuring: (2) The cutoff spatial frequency of the phase grating is set to a value lower than either one of the spatial frequency corresponding to the pitch of the electrodes of the liquid crystal cell and the spatial frequency corresponding to the pitch of the lenticular lens. 2. A liquid crystal projection display device according to claim 1.