KR100283530B1 - Projection type image display device - Google Patents

Abstract

A projection type image display apparatus capable of improving light efficiency is disclosed. The device comprises first and second dichroic filters, red, for separating the polarizations obtained by the light source, three liquid crystal plates corresponding to red, green and blue light rays, polarizers and polarizers into red, green and blue polarizations, A first polarization positioned on an optical axis of the first, second and third λ / 4 plates and the first λ / 4 plate for irradiating a corresponding liquid crystal plate with the phase difference of the green and blue polarizations being a quarter wavelength A beam splitter, a second polarization beam splitter located on the optical axis of the second λ / 4 plate, a λ / 2 plate positioned between the first and second polarization beam splitters so that the phase difference in polarization is 1/2 wavelength, and And a projection lens for projecting an image modulated from each liquid crystal plate onto a screen. The light efficiency can be greatly increased by maximizing the polarization effect.

Description

Projection type image display device

The present invention relates to a projection type image display device, and more particularly, to a projection type image display device that can improve the 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.

Projection type image display devices include a liquid crystal display (LCD), a deformable mirror device (DMD), and an actuated mirror array (AMA). 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 using a liquid crystal that can electrically control the transmittance of light. The display device using the LCD (or liquid crystal projector) has a very simple optical structure, which makes it possible to reduce light weight and shorten the size of a CRT projector. Can be. In addition, it is widely used as a display device for high-definition television (HDTV) and video conferencing because large screens and high image quality can be obtained.

Liquid crystal panels used in liquid crystal projectors are commonly known as matrix type liquid crystal plates, 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 drive voltage can be applied to 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 thin film transistors (TFTs) are placed for each pixel. Each pixel may be alternately applied by an active matrix system.

1 is a schematic view showing the configuration of a projection type image display apparatus using a conventional liquid crystal plate.

Referring to FIG. 1, the conventional projection type image display apparatus 10 includes a red light R, green light G, and blue light B, together with a projection lens 24 for projecting colored light L. FIG. Three transmissive liquid crystal plates 20a, 20b, and 20c are provided. The liquid crystal plates 20a, 20b, and 20c change their transmittances according to the applied image signal to transmit or block red, green, and blue lights. The transmitted light is projected by the projection lens 24 into a color ray L comprising three color rays.

In addition, the projection image display apparatus 10 includes a light source 12, a condenser lens 14, dichroic filters 16a, 16b, 16c, 16d, mirrors 18a, 18b), and field lenses 22a, 22b, 22c.

A light source commonly used in the projection image display device 10 is a metal halide lamp 12 that emits white light. The condenser lens 14 acts as a convex lens, and serves to focus the light emitted from the lamp 12 at its focus.

The dichroic filters 16a, 16b, 16c, and 16d are optical filters for selectively passing light by wavelength. The dichroic filters 16a, 16b, 16c, and 16d may pass white light emitted from the lamp 12 into three primary colors, that is, red light (R) and green light ( G) and blue light (B).

Hereinafter, with reference to FIG. 1, the operation principle of the conventional projection type image display apparatus 10 is demonstrated.

First, after white light is emitted from the lamp 12, this white light is focused by the condenser lens 14 and irradiated to the first dichroic filter 16a. Among the white light, the green light G and the blue light B pass through the first dichroic filter 16a, while the red light R is reflected by the first dichroic filter 16a. This red light R is reflected by the first mirror 18a and is incident on the R-field lens 22a. The red light R passing through the R-field lens 22a passes through the R-liquid crystal plate 20a as the transmittance of the R-liquid crystal plate 20a changes, and then the third dichroic filter 16c. Is investigated. 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. The green light G passes through the G-field lens 22b and then passes through the G-liquid crystal plate 20b as the transmittance of the G-liquid crystal plate 20b changes. The green light G having passed through the G-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.

The blue light B transmitted through the second dichroic filter 16b passes through the B-field lens 22c, and then, as the transmittance of the B-liquid crystal plate 20c changes, the B-liquid crystal plate 20c is used. Pass through. The blue light B passing through the B-liquid crystal plate 20c is reflected by the second 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 color rays L (not shown). ) On the screen.

2A and 2B are schematic views for explaining the structure and operating principle of the liquid crystal plate 20 shown in FIG.

2A and 2B, the liquid crystal plate 20 includes a polarizer and an analyzer spaced at regular intervals, and a liquid crystal injected into a gap between the polarizer and the analyzer. Twisted Nematic (TN) liquid crystal is mainly used as the liquid crystal, and each transmission axis of the polarizer and the analyzer is perpendicular to each other.

Looking at the operating principle of the liquid crystal plate 20, when no voltage is applied, as shown in Figure 2a, the incident light transmitted through the polarizer is linearly polarized light rotated 90 ° by the twisted nematic (TN) liquid crystal (phase difference is mπ) through the analyzer. On the other hand, when a voltage is applied to the liquid crystal plate 20, as shown in FIG. 2B, due to the dielectric anisotropy of the twisted nematic (TN) liquid crystal, the incident light transmitted through the polarizer is linearly standing upright. Not polarized Since the transmission axis of the analyzer is perpendicular to the transmission axis of the polarizer, the incident light transmitted through the polarizer is completely blocked by the analyzer and cannot be transmitted.

In general, incident light is light that is not polarized but is polarized while passing through a polarizer. Polarized light consists largely of P-polarized light and S-polarized light, where P-polarized light is a component of a wave polarized in the plane of incidence perpendicular to the interface and defined by the wave vector of the incident wave, and S-polarized light is incident The component of the wave polarized perpendicular to the plane. When no voltage is applied to the liquid crystal plate 20, when the polarization direction of the polarizer is in the P-polarization direction, as shown in FIG. 2A, the S-polarized light is absorbed from the polarizer while the P-polarized light is transmitted through the polarizer. The transmitted P-polarized light is rotated by 90 ° by the twisted nematic (TN) liquid crystal and is converted into S-polarized light, which then passes through the analyzer.

As described above, in the conventional projection type image display device, only one polarization component, that is, S-polarized light or P-polarized light, is transmitted by the polarizer of the liquid crystal plate and projected onto the screen by the projection lens. In general, the light utilization efficiency of the projection type image display apparatus using the liquid crystal plate is mainly affected by the light collimation optics and the liquid crystal plate. In the conventional projection type image display device as described above, since one polarization component, that is, S-polarized light or P-polarized light is always lost by the polarizer of the transmissive liquid crystal plate, the light efficiency is significantly reduced.

Accordingly, it is an object of the present invention to provide a projection type image display apparatus capable of improving light efficiency.

1 is a schematic diagram showing the configuration of a conventional projection image display apparatus.

2A and 2B are schematic diagrams for explaining the structure and operating principle of a liquid crystal plate used in the projection image display device shown in FIG.

3 is a schematic view showing the configuration of a projection image display device according to the present invention.

4 to 6 are schematic diagrams for explaining paths of red, green and blue light rays in the apparatus of FIG.

<Explanation of symbols for main parts of drawing>

100: projection image display device 102: lamp

104: polarizer 106, 114: dichroic filter

108, 110: polarization beam splitter 112: mirror

116: lambda / 2 plate 118, 120, 122: lambda / 4 plate

124, 126, 128: liquid crystal panel 130: projection lens

In order to achieve the above object, the present invention provides a light source for emitting light, three liquid crystal plates corresponding to red, green and blue light, a polarizer, a first dichroic filter and a second dichroic filter, and a first Provided is a projection image display device including a λ / 4 plate, a second λ / 4 plate and a third λ / 4 plate, a first polarization beam splitter, a second polarization beam splitter, a λ / 2 plate, and a projection lens.

The polarizer performs a function of polarizing light rays emitted from the light source, and the first dichroic filter and the second dichroic filter separate the polarization obtained by the polarizer into red, green, and blue polarized light. The first λ / 4 plate, the second λ / 4 plate, and the third λ / 4 plate respectively irradiate the corresponding liquid crystal plate so that the phase difference between the red, green, and blue polarizations is 1/4 wavelength, and irradiate the corresponding liquid crystal plate. A splitter is located on the optical axis of the first λ / 4 plate and a second polarizing beam splitter is located on the optical axis of the second λ / 4 plate. The λ / 2 plate is positioned between the first polarizing beam splitter and the second polarizing beam splitter so that the phase difference of the polarization is 1/2 wavelength, and the projection lens screens the image modulated from each liquid crystal plate. Function to project onto the screen.

In the projection image display device of the present invention, the white light emitted from the light source is polarized into P-polarized light or S-polarized light by a polarizer and then separated into red, green and blue polarized light by a first dichroic filter. One color polarized light reflected from the first dichroic filter is transmitted by the first polarizing beam splitter, and the phase difference is changed to 1/4 wavelength by the first λ / 4 plate, and then is reflected by the corresponding liquid crystal plate and again. Back incident to the first [lambda] / 4 plate. As a result, the one color polarization changes to 90 ° with respect to the polarization incident from the first polarization beam splitter to the first λ / 4 plate, and the one color polarization with the phase difference thus changed to the first polarization beam splitter. Reflected by the lens into the projection lens. In addition, the remaining two color polarizations passing through the first dichroic filter pass through the second polarization beam splitter, and the two color polarizations are separated by the second dichroic filter. The two color polarizations separated in this way are respectively changed in phase wavelengths by a quarter wavelength by the corresponding second and third λ / 4 plates, and then reflected by the corresponding liquid crystal plates, and thus, the second and third λ / Is back in 4th edition. As a result, the two color polarizations have a phase difference of 90 ° with respect to the polarizations incident from the second polarization beam splitter to the second and third λ / 4 plates, and thus the two color polarizations having the phase difference change are second polarizations. After being reflected by the beam splitter, the polarization component is transformed by the [lambda] / 2 plate and the converted polarization component passes through the first polarization beam splitter and enters the projection lens.

Therefore, since the polarization is irradiated to the liquid crystal panel after determining one polarization component by using a polarizer disposed in front of the light source, the light efficiency can be greatly increased by maximizing the polarization effect without the light loss caused by the liquid crystal panel.

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

3 is a schematic view showing the configuration of a projection image display device according to the present invention.

Referring to FIG. 3, the projection image display apparatus 100 according to the present invention includes a light source 102 for emitting light, a polarizer 104, a first dichroic filter 106, and a second dichroic filter ( 114, a first polarized beam splitter (PBS) 108, a second polarized beam splitter 110, a λ / 2 plate 116, a first λ / 4 plate 118, a second λ / A fourth plate 120, a third λ / 4 plate 122, a B-liquid crystal plate 124, an R-liquid crystal plate 126, a G-liquid crystal plate 128, and a projection lens 130.

The light source 102 preferably emits long wavelength infrared (LWIR) to ultraviolet (UV) light in the spectrum as a projection lamp (e.g. VIP, VHP or HTI, etc.).

The polarizer 104 is located on the optical axis of the light source 102 and preferably absorbs S-polarized light and transmits P-polarized light.

The first dichroic filter 106 and the second dichroic filter 114 are optical filters for selectively passing light by wavelength. The first dichroic filter 106 and the second dichroic filter 114 transmit white light emitted from the lamp 102 to three primary colors of light, that is, red light ( R), green light (G) and blue light (B) serves to separate. Preferably, the first dichroic filter 106 transmits the blue light (B) and reflects the red light (R) and the green light (G), and the second dichroic filter 114 receives the red light (R). It transmits and reflects green light (G).

The first polarizing beam splitter 108 and the second polarizing beam splitter 110 are designed to simultaneously perform the roles of the polarizer and the beam splitter, and the S-polarized light, which is an electric field vector perpendicular to the plane of incidence, is perpendicularly directed. Reflects and transmits P-polarized light, an electric field vector parallel to the plane of incidence.

The first [lambda] / 4 plate 118, the second [lambda] / 4 plate 120, and the third [lambda] / 4 plate 122 serve to invert the light in the polarization state so that the phase difference is 90 [deg.]. The second plate 116 serves to invert the light in the polarization state such that the phase difference is 180 °. For example, when linearly polarized light exits a λ / 4 plate, it becomes left or right polarized light due to the refractive index anisotropy of the λ / 4 plate, and when the linear S-polarized light exits a λ / 2 plate Because of the refractive index anisotropy of, it becomes linear P-polarized light. Preferably, the λ / 2 plate 116 is disposed between the first polarization beam splitter 108 and the second polarization beam splitter 110.

Three B-liquid crystal plates 124, R-liquid crystal plates 126, and G-liquid crystal plates 128 are preferably reflective liquid crystal plates. Of course, other types of reflective light modulators may be used instead of the B-liquid crystal plate 124, the R-liquid crystal plate 126, and the G-liquid crystal plate 128.

The projection lens 130 projects red, green, and blue light beams modulated by the B-liquid crystal plate 124, the R-liquid crystal plate 126, and the G-liquid crystal plate 128, respectively, on a screen (not shown). It plays a role.

Hereinafter, the operation principle of the projection image display apparatus 100 according to the present invention will be described in more detail with reference to FIGS. 3 to 6.

4 to 6 are schematic diagrams for explaining paths of red, green, and blue light rays in the projection image display apparatus 100 according to the present invention.

3 to 6, after white light is emitted from the metal halogen lamp 102, the white light is polarized by the polarizer 104. The polarizer 104 is a polarizer that converts P + S waves into P polarized light, and the P-polarized light transmitted through the polarizer 104 is incident on the first dichroic filter 106. Since the first dichroic filter 106 reflects the blue light B and transmits the red light R and the green light G, as shown in FIG. 4, the first dichroic filter 106 reflects on the first dichroic filter face 106. The blue P-polarized light Bp is transmitted to the first λ / 4 plate 118 after passing through the first polarization beam splitter 108. The linear blue P is incident on the first λ / 4 plate 118. The polarized light Bp is changed into a left or right polarized light after the phase difference is changed into a quarter wavelength and then incident on the reflective B-liquid crystal plate 124 located on the rear surface of the first λ / 4 plate 118. Left or right polarized light is reflected by the B-liquid crystal plate 124 as the reflectance of the B-liquid crystal plate 124 is changed to the right or left circular polarized light, and then to the first λ / 4 plate 118. The phase difference becomes 90 ° with respect to the linear blue P-polarized light Bp that is incident back and is incident from the first polarizing beam splitter 108 into the first λ / 4 plate 118 to linear blue S-polarized light Bs. side It is obtained in this way S- polarized blue (Bs) is directed to the projection lens 130 after being reflected from the first polarizing beam splitter 108.

As shown in FIG. 5, the red and green P-polarizations Rp and Gp transmitted through the first dichroic filter 106 are reflected by the mirror 112 and then the second polarization beam splitter 110. It penetrates and enters into the 2nd dichroic filter 114. Since the second dichroic filter 114 transmits the red light R and reflects the green light G, the red P-polarized light Rp transmitted through the second dichroic filter 114 is the second lambda / It is incident on the fourth plate 120. The linear red P-polarized light (Rp) incident on the second λ / 4 plate 120 has a phase shifted to a quarter wavelength to change to a left or right polarized light, and then a rear surface of the second λ / 4 plate 120. Is incident on the reflective R-liquid crystal plate 126 located at. The left or right polarized light is reflected by the R-liquid crystal plate 126 as the reflectance of the R-liquid crystal plate 126 changes to change to the right or left circular polarized light, and then the second λ / 4 plate 120 Is reversed to change into a linear red S-polarized light (Rs). The red S-polarized light Rs thus obtained passes through the second dichroic filter 114 and is then reflected from the second polarization beam splitter 110 to be incident on the λ / 2 plate 116. The linear red S-polarized light (Rs) incident on the λ / 2 plate 116 is changed into a linear red P-polarized light (Rp) by changing the phase difference to 1/2 wavelength, and then transmitted through the first polarizing beam splitter 108. To the projection lens 130.

The green P-polarized light Gp reflected by the second dichroic filter 114 is incident on the third λ / 4 plate 122, as shown in FIG. The linear green P-polarized light Gp incident on the third λ / 4 plate 122 is changed to a left or right polarized light after the phase difference is changed to a quarter wavelength, and then the rear surface of the third λ / 4 plate 122 is Is incident on the reflective G-liquid crystal plate 128. The left or right polarized light is reflected by the G-liquid crystal plate 128 as the reflectance of the G-liquid crystal plate 128 changes to change to the right or left circular polarized light, and then the third λ / 4 plate 122 Is reversed to change into a linear green S-polarized light (Gs). The green S-polarized light Gs thus obtained is reflected by the second dichroic filter 114 and then reflected from the second polarization beam splitter 110 and is incident on the λ / 2 plate 116. The linear green S-polarized light (Gs) incident on the λ / 2 plate 116 is changed into a linear green P-polarized light (Gp) by changing the phase difference to 1/2 wavelength, and then transmitted through the first polarizing beam splitter 108. To the projection lens 130.

In this way, the projection lens 130 projects red, green, and blue polarizations on the screen and displays corresponding color images.

As described above, according to the projection type image display apparatus of the present invention, since the polarization is irradiated to the liquid crystal panel after determining one polarization component by using a polarizer disposed in front of the light source, the polarization effect is maximized without the light loss caused by the liquid crystal panel. By doing so, the light efficiency can be greatly increased.

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 (5)

A light source 102 for emitting light rays; Three liquid crystal plates 124, 126, and 128 corresponding to red, green, and blue rays; A polarizer (104) for polarizing light rays emitted from the light source (102); A first dichroic filter (106) and a second dichroic filter (114) for separating the polarization obtained by the polarizer (104) into red, green and blue polarizations; The first λ / 4 plate 118 and the second λ / 4 plate 120 for irradiating the corresponding liquid crystal plates 124, 126, and 128 so that the phase difference between the red, green, and blue polarizations are 1/4 wavelengths. ) And third λ / 4 plate 122; A first polarization beam splitter (108) located on the optical axis of the first λ / 4 plate (118) and a second polarization beam splitter (110) located on the optical axis of the second λ / 4 plate (120); A λ / 2 plate (116) positioned between the first polarizing beam splitter (108) and the second polarizing beam splitter (110) such that the phase difference of polarization is 1/2 wavelength; And And a projection lens (130) for projecting an image modulated from the respective liquid crystal plates (124, 126, 128) on the screen. The projection type image display apparatus according to claim 1, wherein the first polarizing beam splitter 108 is positioned between the first dichroic filter 106 and the first λ / 4 plate 118. . The projection type image display according to claim 1, further comprising a mirror (112) for reflecting red, green, or blue polarized light separated by said first dichroic filter (106) to change its optical path. Device. The projection image display device according to claim 3, wherein the second polarization beam splitter (110) is located between the second λ / 4 plate (120) and the mirror (112). The dichroic filter 114 of claim 1, wherein the second dichroic filter 114 is positioned at a point where the optical axis of the second λ / 4 plate 120 and the optical axis of the third λ / 4 plate 122 are perpendicular to each other. A projection type image display device.