KR100262825B1 - Projective display device - Google Patents

Abstract

PURPOSE: A projection type display device is provided to improve the image quality by removing a bulkhead displayed on a screen using a diffraction grating, and by simultaneously preventing an adjacent pixel from being broken. CONSTITUTION: A lighting field projects a white direct light. A liquid crystal panel includes a video signal in the light projected from the lighting filed, and passes the light. A projection lens projects the light passed through the liquid crystal panel to a screen. A diffraction grating which removes a bulkhead included in a video and controls the strength of a diffraction light is arranged between the liquid crystal panel and the projection lens.

Description

Projection display device

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection display device such as a head mounted display device (HMD) or a liquid crystal display device (LCD). In particular, the present invention relates to a projection display device for improving image quality by removing a partition from appearing in an output image.

In general, a projection display device such as a head mounted display device (HMD) or a liquid crystal display device (LCD) divides an area by forming a partition wall between each pixel of the liquid crystal panel.

1 is a view showing the configuration of a general projection display device.

Referring to FIG. 1, an illumination system 110 emitting white straight light, a liquid crystal panel 120 including an image signal in the light emitted from the illumination system 110, and a liquid crystal panel 120. And a projection lens 130 to enlarge and project the light passing through the screen 140.

In the above configuration, the liquid crystal panel 120 has pixels arranged in a matrix structure, and each pixel includes R, G, and B pixels, and each pixel is separated by a partition wall. . The barrier ribs appear in an image output on the screen and cause a problem of degrading image quality.

As a method of preventing the partition wall from being output on the screen, there are a method using a microlens array and a method using a diffraction grating. Recently, a method using a diffraction grating is mainly used due to difficulties in manufacturing the microlens array. have.

As shown in FIG. 2, a diffraction grating 150 is disposed on the output side of the liquid crystal panel 120 so that light transmitted through the liquid crystal panel 120 is prevented. The diffraction grating 150 allows diffraction in various directions. At this time, the diffracted light illuminates the partition portion a as shown in FIG. 3 so that the partition wall is not visible in the output image. In this case, as shown in FIG. 4, the diffraction grating 150 is formed by forming the acrylic layer 123 on the glass plate 122 in a square shape having a size corresponding to the pixel of the liquid crystal panel 120.

In the conventional method as described above, ± 1st order diffracted light is projected to the partition wall to remove the partition wall, but diffraction light of ± 2nd order or more generated in the diffraction operation reaches another pixel to reduce the contrast of the screen. It acts as a breaking noise, causing a problem of degrading the output image quality. Particularly, when the intensity of the ± 2nd order diffracted light is too large, the brightness of the green (G) pixel is so large that the black letters in the still image impinge on adjacent pixels, causing the ± 2nd order diffracted light of adjacent green (G) pixels. The problem is broken by.

FIG. 5 is a table of experimental data showing diffraction efficiency of each diffracted light in a diffraction grating having a grating cross-sectional shape close to a sine waveform.

In the diffraction grating as shown in FIG. 5, the problem of deterioration of image quality cannot be solved because the size of the ± 2nd order diffracted light in the visible wavelength band is not negligible.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and its object is to eliminate the partition wall appearing on the screen by adopting a square diffraction grating and to suppress the intensity of ± 2nd order diffracted light to prevent adjacent pixels from breaking. It is to provide a projection display device that can improve the output image quality.

1 is a view showing the configuration of a general projection display device;

2 is a view showing a path of light propagation when the diffraction grating is used in FIG. 1;

3 is a diagram illustrating one pixel of an output image from which a partition is removed by FIG. 2;

4 is a view showing a diffraction grating according to the prior art,

5 is a table of experimental data showing the diffraction efficiency of each diffracted light in a diffraction grating having a sine wave grating cross section;

6 is a view showing the shape of a diffraction grating used in the projection display device according to the present invention;

7 is a table of experimental data showing the diffraction efficiency of each diffracted light in the diffraction grating having a square grating cross section according to the present invention.

According to a first aspect of the present invention for achieving the above object, an illumination system for emitting white straight light, a liquid crystal panel for including an image signal in the light emitted from the illumination system and pass through the liquid crystal panel A projection display device comprising a projection lens for projecting a light onto a screen,

Diffraction in the form of a square between the liquid crystal panel and the projection lens to remove the partition wall included in the image by ± 1st order diffracted light and to suppress the intensity of ± 2nd order diffracted light that may affect adjacent pixels. Provided is a projection display device in which a grid is arranged.

According to a second aspect of the present invention, the diffraction grating is formed such that the square grating has a checkered pattern arranged in a matrix structure, and the flat and concave portions are alternately alternately arranged.

According to a third aspect of the invention, the diffraction grating satisfies the formula "? = Tan-1 (d / L), Wsin? Where d is a half-pixel shift distance, L is the distance between the liquid crystal panel and the diffraction grating, W is the period width of the diffraction grating, m is the Bragg condition constant, and λ is the wavelength of the incident light.

Hereinafter, exemplary embodiments of a projection display device according to the present invention will be described in detail with reference to the accompanying drawings.

6 is a view showing the shape of the diffraction grating used in the projection display device according to the present invention, Figure 7 is an experimental data table showing the diffraction efficiency of each diffracted light in the diffraction grating having a square grating cross section according to the present invention. .

The configuration of the projection display device according to the present invention includes an illumination system 110 for emitting white straight light as shown in FIG. 1 and an image signal in the light emitted from the illumination system 110 as shown in FIG. And a projection lens 130 to enlarge and project the light passing through the liquid crystal panel 120 onto the screen 140.

At this time, between the liquid crystal panel 120 and the projection lens 130 to remove the partition wall included in the image by the ± 1st order diffracted light and to suppress the intensity of the ± 2nd order diffracted light that may affect the adjacent pixels. A diffraction grating 150 having a square shape is disposed.

The diffraction grating 150 forms a checkered pattern as shown in FIG. 6, and the flat and concave portions are alternately alternately arranged.

In the diffraction grating of the present invention as described above, the diffraction efficiency of light is determined by the refractive index of the medium, the shape of the diffraction grating, the period width of the grating, the depth of the grating, and the like. At this time, the period width of the grating is determined by the distance interval between the diffraction grating and the liquid crystal panel and the pixel size of the liquid crystal panel.

In the present invention, the diffraction efficiency of the light is determined by changing the shape and depth of the diffraction grating.

For example, when the refractive index of the medium is n = 1.5 and the distance between the liquid crystal panel and the diffraction grating is set to 8 mm, the period of the diffraction grating, that is, the width of the repeated diffraction grating, is determined between the liquid crystal panel and the diffraction grating. It is determined by the distance interval and how much of the position of the first-order diffracted light is to be reflected to remove the partition wall in the pixels of the liquid crystal panel. At this time, in order to remove the ideal partition wall, it is designed to move half a pixel with respect to the 0th order diffracted light, that is, the straight light.

When the diffraction angle θ of the ± 1st order diffracted light is obtained so that the influence of the luminance is shifted by about half a pixel at the wavelength with respect to the size of the liquid crystal panel having a width and length of 19.8 μm and 37 μm, "θ = tan-1 (d / L) ". In this case, d represents a half pixel moving distance, and L represents a distance interval between the liquid crystal panel and the diffraction grating.

In addition, the period width W of the said diffraction grating can be calculated | required by the formula of "Wsin (theta) = m (lambda)." At this time, m represents the Bragg condition constant "1", and λ represents the wavelength of the incident light. At this time, if the lambda is 555 nm, the period width W of the diffraction grating is 240 µm.

In order to minimize the effect of the ± 2nd order diffracted light under the above conditions, the grating depth is preferably 0.38 μm.

On the other hand, when the diffraction grating according to the present invention is used, the intensity of the ± 2nd order diffracted light is 1/2 to 1/3 or less in the visible wavelength range, as shown in FIG. 7. Is reduced.

Since the projection display device of the present invention uses a rectangular diffraction grating, its diffraction efficiency is suppressed so that the magnitude of the ± 2nd order diffracted light is negligible in the visible wavelength band as shown in FIG. There is an effect that can be improved.

Claims (1)

A liquid crystal panel including an image signal in light emitted from an illumination system, a projection lens for expanding and projecting the light passing through the liquid crystal panel to a screen, and a partition wall positioned between the liquid crystal panel and the projection lens and included in an image A square grating is composed of diffraction gratings arranged in a matrix structure so as to suppress the intensity of diffracted light which may affect adjacent pixels while simultaneously eliminating? The diffraction grating is formed so as to satisfy the following equation: [theta] = tan -1 (d / L), Wsin θ = mλ where d is a half pixel moving distance, L is between the liquid crystal panel and the diffraction grating Where W is the period width of the diffraction grating, m is the Bragg condition constant, and λ is the wavelength of the incident light.

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