KR19980039530A - Optical system of liquid crystal display - Google Patents

Abstract

An optical system of the liquid crystal display device is shown. The optical system of the liquid crystal display device includes a light source for emitting light rays, pixels arranged in a matrix form, a liquid crystal plate for light modulating the light rays into an image, and separating the light rays emitted from the light sources into red, green and blue light rays. And a dichroic prism for synthesizing the respective color light rays passing through the liquid crystal plate, and color separation means for irradiating the liquid crystal plate. Since dichroic prisms are used to synthesize each color ray, the structure of the optical system can be simplified and compactly constructed.

Description

Optical system of liquid crystal display

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system of a liquid crystal display device, and more particularly, to an optical system of a liquid crystal display device (hereinafter referred to as an LCD optical system) capable of simplifying and compacting an optical system structure and improving light efficiency. .

In general, spatial light modulators, which are devices for projecting optical energy onto a screen, can be applied to various fields such as optical communication, image processing, and information display devices. Typically, such devices are classified into a direct-view image display device and a projection-type image display device according to a method of displaying optical energy on a screen.

An example of a direct-view image display device is a CRT (Cathode Ray Tube). The CRT device is called a CRT, which has excellent image quality but increases in weight and volume as the screen is enlarged, leading to an increase in manufacturing cost. There is.

Examples of the projection image display apparatus include liquid crystal displays (hereinafter referred to as LCDs), deformable mirror devices (hereinafter referred to as DMDs), and actuated mirror arrays (hereinafter referred to as AMAs). Can be. Such projection image display devices can be further divided into two groups according to their optical characteristics. That is, devices such as LCDs can be classified as Transmissive spatial light modulators, while DMD and AMA can be classified as Reflective spatial light modulators.

An LCD device is a display device that uses a liquid crystal that can electrically control the transmittance of light. A projector using the LCD (hereinafter referred to as a liquid crystal projector) has a very simple optical structure, which makes it possible to reduce the thickness of the LCD device. Can be. In addition, it is widely used as a display device for high-definition television (HDTV) and video conferencing because a large screen and high image quality can be obtained.

A liquid crystal panel used in a liquid crystal projector is commonly known as a matrix liquid crystal panel, in which pixels are arranged in a matrix in two directions perpendicular to each other, and are driven individually by a driving voltage to provide optical Change characteristics. The driving voltage can be applied to the individual pixels by a simple matrix system, and non-linear two-terminal elements such as metal-insulating metal (MIM) or three-terminal switching elements such as TFT (thin film transistor) are arranged for each pixel. It can be applied to each pixel alternately by the active matrix system.

1 is a schematic view showing the structure of a conventional LCD optical system.

Referring to FIG. 1, a conventional LCD optical system 10 includes a projection lens 24 for projecting colored light (L), and a combination of red light (R), green light (G), and blue light (B). 1, 2nd and 3rd liquid crystal plates 20a, 20b, and 20c are provided. The transmittances of the first, second and third liquid crystal plates 20a, 20b, and 20c change according to an applied image signal to transmit or block red, green, and blue lights. The transmitted light is projected by the projection lens 24 into a ray L comprising three color rays.

In addition, the conventional LCD optical system 10 includes a lamp 12 for emitting light, a condenser lens 14, first, second, third and fourth dichroic filters ( 16a, 16b, 16c, 16d, first and second mirrors 18a, 18b, and first, second, and third field lenses 22a, 22b, 22c.

A light source commonly used for the LCD optical system 10 is a metal halide lamp 12. The condenser lens 14 acts as a convex lens, and serves to focus the light emitted from the lamp 12 at its focus.

The first, second, third and fourth dichroic filters 16a, 16b, 16c, and 16d are optical filters for selectively passing light by wavelength, and the three primary colors of white light emitted from the lamp 12 are It serves to separate light, that is, red light, green light and blue light.

Hereinafter, the operating principle of the conventional LCD optical system 10 described above will be described.

After white light is emitted from the halogen metal lamp 12, this white light is focused by the condenser lens 14 and irradiated to the dichroic filter 16a. Among the white light, the green light G and the blue light B pass through the first dichroic mirror 16a, while the red light R is reflected by the first dichroic mirror 16a. This red light R is reflected by the first mirror 18a and is incident on the first field lens 22a. The red light R passing through the first field lens 22a passes through the first liquid crystal plate 20a as the transmittance of the first liquid crystal plate 20a, which is an R-liquid crystal plate, changes to a third dichroic light. Irradiated with the blade filter 16c. Since the third dichroic filter 16c is an optical filter that transmits the red light R and reflects the green light G, the red light R passes through the third dichroic filter 16c and causes a fourth dike. The loch filter 16d is irradiated.

On the other hand, the green light G and the blue light B transmitted by the first dichroic filter 16a reflect the green light G by the second dichroic filter 16b and the blue light B is transmitted. do. After the green light G passes through the second field lens 22b, the green light G passes through the second liquid crystal plate 20b as the transmittance of the second liquid crystal plate 20b, which is a G-liquid crystal plate, changes. The green light G having passed through the second liquid crystal plate 20b is reflected by the third dichroic filter 16c that transmits the red light R and reflects the green light G, and thus the fourth dichroic filter 16d. Is investigated.

After passing through the third field lens 22c, the blue light B having passed through the fourth dichroic filter 16b passes through the third field lens 22c, and as the transmittance of the third liquid crystal plate 20c, which is a B-liquid crystal plate, changes, Passes through the liquid crystal plate 20c. The blue light B passing through the third liquid crystal plate 20c is reflected by the mirror 18b and irradiated to the fourth dichroic filter 16d.

In this way, the fourth dichroic filter 16d combines three rays, i.e. red, green and blue rays, and the projection lens 24 screens the synthesized rays L (not shown). ) On the screen.

As described above, the conventional LCD optical system uses three dichroic filters to perform color separation and synthesis. Therefore, the size of the optical system is increased and it is difficult to compactly configure the optical system. In addition, since color synthesis is performed by the dichroic filter, optical axis deviation occurs due to the thickness of the filter, resulting in deterioration of image quality.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide an optical system of a liquid crystal display device capable of simplifying and compacting an optical system and improving light efficiency.

1 is a schematic view showing the configuration of an optical system of a conventional liquid crystal display element.

2 is a schematic view showing the configuration of an optical system of a liquid crystal display device according to an embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating a dichroic prism used in an optical system of the liquid crystal display shown in FIG. 2.

Explanation of symbols for main parts of the drawings

10, 100 ... LCD optics 12, 102 ... Lamp

14, 115a, 115b ... condenser lens 104 ... microlens array

16a, 16b, 16c, 16d, 106a, 106b ... dichroic filter

18a, 18b, 108a, 108b, 108c ... mirror

20a, 20b, 20c, 110a, 110b, 110c ... liquid crystal panel

22a, 22b, 22c, 112a, 112b, 112c ... field lens

114 ... color correction aperture 116 ... dichroic prism

24, 118 ... projection lens

The present invention to achieve the above object,

A light source for emitting light rays;

A liquid crystal panel in which pixels are arranged in a matrix and for light modulating the light beam into an image;

Color separation means for separating the light rays emitted from the light source into red, green, and blue light rays and irradiating the liquid crystal plate; And

It provides an optical system of a liquid crystal display device comprising a dichroic prism for synthesizing each color light beams passing through the liquid crystal plate.

As described above, the present invention focuses the light rays emitted from the light source by the microlens array and then separates them into red, green and blue light rays by color separation means such as a dichroic filter. The red, green and blue light rays thus separated are synthesized by the dichroic prism through the corresponding liquid crystal plate and then projected onto the screen by the projection lens.

Therefore, according to the optical system of the liquid crystal display device according to the present invention, since the red, green, and blue light rays separated using one dichroic prism are synthesized, the structure of the optical system can be simplified and the optical system can be compactly configured. .

In addition, since the prism is used for color synthesis, the optical axis deviation due to the thickness of the filter, which has been a problem in the conventional structure, is eliminated, thereby improving image quality.

Furthermore, a micro lens array in which each lens cell is formed to correspond to each pixel of the liquid crystal plate is disposed in front of the light source. The microlens array includes a first microlens array and a second microlens array having the same lens cell structure, and the first microlens array has a rear surface thereof in a plane and each cell has the same focal length, but a second Since the microlens array has a curvature on the back side, each lens cell has a different focal length. Accordingly, when the illumination light is 100% parallel light, illumination is possible only by the first micro lens array, but since the illumination light is not 100% parallel light, a second micro lens array is required. The light passing through the center of each lens cell of the first microlens array passes through the center of each lens cell of the second microlens array and reaches the center of the liquid crystal plate, and the edge of each lens cell of the first microlens array The passing light rays pass through the center of the second microlens array, and then reach the edge of the liquid crystal plate, and light rays incident at an angle to the center of each lens cell of the first microlens array are angles of the second microlens array. Passes the center of the liquid crystal plate past the edge of the lens cell serves to evenly illuminate the front of the liquid crystal plate. Therefore, the optical system efficiency of a liquid crystal display element can be greatly improved.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a schematic view showing the configuration of the LCD optical system 100 according to an embodiment of the present invention.

Referring to FIG. 2, the LCD optical system 100 includes a projection lens 118 for projecting color light rays, each of the first, second, and blue light rays R, green light G, and blue light B, respectively. Third liquid crystal plates 110a, 110b, and 110c are provided. The transmittances of the first, second and third liquid crystal plates 110a, 110b, and 110c change according to an applied image signal to transmit or block red, green, and blue lights. The transmitted light is projected by the projection lens 118 into a ray L comprising three color rays.

In addition, the LCD optical system 100 includes a lamp 102 for emitting light, a microlens array 104, first and second dichroic filters 106a and 106b, first, second and Third mirrors 108a, 108b, 108c, first, second and third field lenses 112a, 112b, 112c, color correction apertures 114, first and second condenser lenses 115a, 115b and dike It further includes a loic prism 116.

In general, in a liquid crystal panel in which a driving voltage is alternately applied to each pixel by an active matrix system, the pixels should be arranged at a minimum pitch, thereby opening effective holes occupied by the pixels over the entire area. The ratio of (hereinafter referred to as aperture ratio) is reduced. The transmittance of the liquid crystal plate is determined by the efficiency of the polarizer and the aperture ratio of each pixel. In the present invention, in order to increase the aperture ratio, as shown in FIG. 3, a microlens array 104 including multi-lens cells in which each lens cell is arranged at the same pitch as the pitch between pixels is provided. It arrange | positions on a light incident surface.

The microlens array 104 includes a first microlens array ML1 and a second microlens array ML2 having the same lens cell structure, and the first microlens array ML1 has a rear surface thereof in plan view. Each lens cell has the same focal length, but the second microlens array ML2 has a different focal length because each backside of the second microlens array ML2 has a curvature. Therefore, when the illumination light is 100% parallel light, illumination is possible only by the first micro lens array ML1, but since the illumination light is not 100% parallel light, the second micro lens array ML2 is required. The light passing through the center of each lens cell of the first microlens array ML1 passes through the center of each lens cell of the second microlens array ML2 to allow the first, second and third liquid crystal plates 110a and 110b to pass through. , The light rays passing through the edges of the lens cells of the first microlens array ML1 and passing through the center of the second microlens array ML2 after reaching the central portion of the first microlens array ML1. Light rays that reach the edges of the liquid crystal plates 110a, 110b, and 110c and enter an angle at the center of each lens cell of the first micro lens array ML1 are each lens cell of the second micro lens array ML2. It passes through the center of the first, second and third liquid crystal plates (110a, 110b, 110c) past the edge of the to be evenly illuminated on the front of the first, second and third liquid crystal plates (110a, 110b, 110c) It plays a role.

The first and second dichroic filters 106a and 106b are optical filters that selectively pass light by wavelength, and emit white light emitted from the halogen metal lamp 102 and passed through the microlens array 104. It serves to separate primary color light, that is, red light, green light and blue light.

The color correction opening 114 cuts the wavelength range of the light beam to narrow the color of the light beam in order to improve the purity of the light beam transmitted from the dichroic filter.

As shown in FIG. 3, the dichroic prism 116 includes a dichroic filter reflecting only red light and transmitting other light, and a dichroic filter reflecting only chuck color light and transmitting other light in an X shape. will be. Thus, by reflecting the red and blue light incident on the three perpendicular to the prism and the green light is transmitted as it is, the three color light rays are synthesized and incident to the projection lens 118.

Hereinafter, the operation principle of the LCD optical system 100 according to the present invention in detail.

After white light is emitted from the halogen metal lamp 102, the white light is focused by the microlens array 104 and irradiated to the first dichroic filter 106a. Among the white light, the green light G and the blue light B pass through the second dichroic filter 106a while the red light R is reflected on it. The red light R is reflected by the first mirror 108a and is incident on the first liquid crystal plate 110a which is the R-liquid crystal plate through the first field lens 122a. The red light R passes through the first liquid crystal plate 110a as the transmittance of the first liquid crystal plate 110a changes. Subsequently, the red light R enters the dichroic prism 116, is reflected by a dichroic filter reflecting only the red light in the dichroic prism 116, and then enters the projection lens 118.

On the other hand, the green light G and the blue light B transmitted by the first dichroic filter 106a pass through the color correction opening 114 and are irradiated to the second dichroic filter 106b. The color correction opening 114 cuts the wavelength range of each of the green light G and the blue light B to be narrowed to improve the purity of the light rays. The green light G and the blue light B irradiated to the second dichroic filter 106b through the color correction opening 114 reflect the green light G by the second dichroic filter 106b. And the blue light B is transmitted. The green light G is incident on the second liquid crystal plate 110b which is a G-liquid crystal plate through the second field lens 122b. The green light G passes through the second liquid crystal plate 110b as the transmittance of the second liquid crystal plate 110b changes. Subsequently, the green light B enters the dichroic prism 116 and passes through the dichroic prism 116 as it is to enter the projection lens 118.

The blue light B transmitted through the second dichroic filter 106b passes through the first condenser lens 115a and is then reflected by the mirror 108b to enter the second condenser lens 115b. The blue light B passing through the second condenser lens 115b is reflected by the third mirror 108c and is incident on the third liquid crystal plate 110c which is a B-liquid crystal plate through the third field lens 122c. . The blue light B passes through the third liquid crystal plate 110c as the transmittance of the third liquid crystal plate 110c changes. Subsequently, the blue light B enters the dichroic prism 116, is reflected by a dichroic filter reflecting only the blue light in the dichroic prism 116, and then enters the projection lens 118.

In this way, dichroic prism 116 synthesizes three rays, i.e. red, green, and blue rays, and projection lens 118 displays the synthesized rays L on a screen (not shown). To project on.

As described above, the present invention focuses the light rays emitted from the light source by the microlens array and then separates them into red, green and blue light rays by color separation means such as a dichroic filter. The red, green and blue light rays thus separated are synthesized by the dichroic prism through the corresponding liquid crystal plate and then projected onto the screen by the projection lens.

Therefore, according to the LCD optical system according to the present invention, since the red, green, and blue light beams are separated using one dichroic prism, the structure of the optical system can be simplified, and the optical system can be compactly configured.

In addition, since the dichroic prism is used for color synthesis, the optical axis deviation due to the thickness of the dichroic filter, which has been a problem in the conventional structure, is eliminated, thereby improving image quality.

Furthermore, a micro lens array in which each lens cell is formed to correspond to each pixel of the liquid crystal plate is disposed in front of the light source. The microlens array includes a first microlens array and a second microlens array having the same lens cell structure. The rear surface of the first microlens array is planar, and each cell has the same focal length, but the second microlens array has a different focal length for each lens cell because the rear surface of the first microlens array has a curvature. Accordingly, when the illumination light is 100% parallel light, illumination is possible only by the first micro lens array, but since the illumination light is not 100% parallel light, a second micro lens array is required. The light passing through the center of each lens cell of the first microlens array passes through the center of each lens cell of the second microlens array and reaches the center of the liquid crystal plate, and the edge of each lens cell of the first microlens array The passing light rays pass through the center of the second microlens array, and then reach the edge of the liquid crystal plate, and light rays incident at an angle to the center of each lens cell of the first microlens array are angles of the second microlens array. Passes the center of the liquid crystal plate past the edge of the lens cell serves to evenly illuminate the front of the liquid crystal plate.

Although described above with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and changed within the scope of the invention without departing from the spirit and scope of the invention described in the claims below. I can understand that you can.

Claims (6)

A light source 102 for emitting light rays; Liquid crystal panels (110a, 110b, 110c) arranged in a matrix and arranged to light modulate the light rays into an image; Color separation means for separating the light rays emitted from the light source (102) into red, green and blue light rays and irradiating the liquid crystal plate; And And a dichroic prism (116) for synthesizing each color ray passing through the liquid crystal plate. The optical system of claim 1, wherein the color separation means is a dichroic filter (106a, 106b). The microlens array (104) according to claim 1, further comprising a microlens array (104) positioned between the light source (102) and the color separation means for focusing the light rays emitted from the light source (102) on each of the pixels of the liquid crystal plate. The optical system of the liquid crystal display element characterized by the above-mentioned. The liquid crystal plate (110a, 110b, 110c) is a liquid crystal plate 110a, G-liquid crystal plate (110b) and B-liquid crystal plate for modulating the respective light rays of red, green and blue 110c), the optical system of the liquid crystal display element. The liquid crystal display of claim 1, further comprising a color correction opening (114) for cutting the transmitted light beam so that its wavelength range becomes narrow in order to improve the purity of the light beam transmitted by the color separation means. Optical system. The optical system of a liquid crystal display device according to claim 1, further comprising a projection lens (118) for forming an image by projecting light rays synthesized by the dichroic prism (116) onto a screen.