KR100277505B1 - LCD Projector Illumination System - Google Patents

Abstract

The present invention relates to a liquid crystal projector illumination system configured to increase light efficiency.

The liquid crystal projector illumination system according to the present invention includes first to third condensing lenses disposed between the second lens array and the liquid crystal panel.

Accordingly, the liquid crystal projector illumination system according to the present invention improves the light efficiency.

Description

Illumination System for Liquid Crystal Projector

The present invention relates to an illumination system using a light source, and more particularly, to a liquid crystal projector illumination system configured to increase light efficiency.

In general, projectors employing a cathode ray tube are generally used as projectors that are composed of a light source and an illumination system to enlarge a film, an image, and the like on a screen, and recently, projectors equipped with liquid crystals have been widely used. These projectors are being enlarged and high brightness to meet the needs of users. In particular, the necessity to increase the luminance level is required in order to realize a clear picture quality even in a bright surrounding environment. According to this trend, it is recognized that improving the light efficiency is a necessary problem in the liquid crystal projector.

Referring to FIG. 1, a conventional high efficiency liquid crystal projector illumination system includes a light source 2 for generating a light beam, a parabolic reflector 4 for advancing the light beam in parallel, and a light beam traveling in parallel via the parabolic reflector 4. A first lens array 6 for uniformly dividing, a second lens array 8 for focusing the light beams divided by the first lens array 6, a polarization conversion element for converting the light beams to polarization characteristics of the light beams, First to sixth condenser lenses CL1 to CL6 for advancing the light beam via the polarization conversion element toward the liquid crystal panel 12, and liquid crystal panels 12R, 12G, and 12B for controlling the amount of transmission of the light beam through the condenser lens. And a dichroic prism 14 for synthesizing the three primary color light beams propagated from the liquid crystal panel 12, and a projection lens 16 for enlarging and projecting the synthesized light beams. The light beam generated by the light source 2 is advanced to quasi-parallel light by the parabolic reflector 4. The light beam traveling from the parabolic reflector 4 to quasi-parallel light is uniformly divided by the first to nth lenses (not shown) formed in the first lens array 6. The light beam split in the first lens array 6 is focused by the first to mth lenses (not shown). In this case, the second lens array first to m-th lens is formed twice the size of the unit cross-section of the polarization conversion element. On the other hand, the polarization conversion element is composed of a polarizing beam splitter (hereinafter referred to as "PBS") array 10 and a λ / 2 plate 18 for converting the polarization characteristics of the light beam. The light beam focused by the second lens array 8 is separated into vertical linearly polarized light (P wave) and horizontal linearly polarized light (S wave) by the polarization conversion element, and the polarization characteristics of the separated light beam are converted to have the same polarization characteristics. A light beam is formed. In detail, the light beam focused by the second lens array 8 is separated into vertical linearly polarized light (P wave) and horizontally polarized light (S wave) by the polarization conversion element. Subsequently, the polarization characteristic of the horizontally polarized light (or the vertical linearly polarized light) is converted by the λ / 2 plate 18 attached to the rear surface of the PBS array 10. Accordingly, the polarization conversion element can ensure the uniformity of the screen by having the light beam has the same polarization characteristics. In addition, the light beam passing through the polarization conversion element is totally reflected by the first folding mirror FM1 to be focused on the first condenser lens CL1. The light beam focused on the first condenser lens CL1 proceeds to the first dichroic mirror DM1. The first dichroic mirror directs the red (R) light beam to the second folding mirror FM2, while the green (G) and blue (B) light beams reflect the second dichroic mirror DM2. In the second folding mirror FM2, the red (R) light beam is totally reflected toward the second condenser lens CL2. The red (R) light beam via the second condenser lens CL2 is focused on the first LCD 12R. Meanwhile, in the second dichroic mirror DM2, the blue (B) light beam is directed to the third folding mirror FM3, while the green (G) light beam is reflected toward the third condenser lens CL3. The green light beam via the third condenser lens CL3 is focused on the second LCD 12G. In addition, the third folding mirror FM3 reflects the blue (B) light beam to the fifth condenser lens CL5. The blue (B) light beam focused by the fifth condenser lens CL5 proceeds to the fourth folding mirror FM4. The fourth folding mirror FM4 totally reflects the blue light beam to the sixth condenser lens CL6. The blue (B) light beam via the sixth condenser lens CL6 is focused on the third LCD 12B. The first to third LCDs 12R, 12G, and 12B adjust the transmittances of the red (R), green (G), and blue (B) light beams in response to the image signal to advance to the dichroic prism 14. The dichroic prism 14 combines the beams of the three primary colors and advances them toward the projection lens 16. The projection lens 16 enlarges and projects the synthesized light beam to form an image on a screen (not shown) to display an image corresponding to an image signal. In the conventional liquid crystal projector, the polarization characteristics of the light beam are improved by using a polarization conversion element, and thus, the luminance level of the liquid crystal projector is increased even under bright surroundings. However, even in the large screen of 100 "or larger, the image quality can be maintained only when the brightness level is higher in the surrounding bright environment. Accordingly, there is a need for a method for improving the light efficiency to cope with the enlargement. 2 to 7 will be described with respect to the conventional illumination system.

2, an illumination system corresponding to any one color of FIG. 1 is shown. As shown in FIG. 2, an illumination system using a first lens array cell 6 ′, a second lens array cell 8 ′, two condensing lenses, and an LCD 12 is shown. The first and second lens array cells 6 ′ and 8 ′ represent unit cells of the first and second lens arrays. The shape of each cell is composed of squares to approximate the shape of LCD 12. The condenser lens uses condenser lenses CL1 and CL2 that focus the light beam. The conventional liquid crystal projector illumination system satisfies two preconditions to maintain the uniformity of the light beam and to improve the brightness. First, the illumination distribution of each cell 6 ′ of the first lens array is configured to have an image formed on the front surface of the LCD 12. Second, the light passing through each cell 8 'and the condenser lens of the second lens array should overlap the LCD 12. An imaging condition of a liquid crystal projector having the above prerequisites will be described. The light beam incident on the center of the first lens array cell 6 'is imaged at the center of the LCD 12. In addition, the light beam incident on the upper portion of the first lens array cell 6 'is formed on the lower portion of the LCD 12. In addition, the light beam incident on the lower portion of the first lens array cell 6 'is formed on the upper portion of the LCD 12. For example, the light beam incident to the center of the first lens array cell 6 'travels to the upper portion of the second lens array cell 8' disposed to face the lens beam. The second lens array cell 8 'advances the light beam introduced to the upper portion thereof in parallel. The first to second condenser lenses CL1 and CL2 focus light beams passing through the second lens array cell 8 'to the center of the LCD 12. On the other hand, the light beam incident on the upper portion (or lower portion) of the first lens array cell 6 'travels to the lower portion (or upper portion) of the second lens array cell 8' disposed opposite thereto. The second lens array cell 8 'advances the light beam introduced to its upper portion (or lower portion) in parallel. The first to second condenser lenses CL1 and CL2 focus light beams passing through the second lens array cell 8 'in parallel to the upper (or lower) portion of the LCD 12.

Referring to FIG. 3, there is shown an optical path extending the FIG. 2 illumination system. As shown in FIG. 3, an illumination system using first and second lens arrays 6, 8, two condensing lenses and LCD 12 is shown. 3 shows an optical path in which an illumination system having the first and second lens array cells 6 'and 8' of FIG. 2 is extended to an illumination system having the first and second lens arrays 6 and 8. In this case, it can be seen that the positional information at each point of the first lens array 6 is represented by the information of the angle on the output surface of the second lens array 8. In order to improve the light efficiency in the conventional illumination system, the central ray (ie, chief ray) of the light beam incident at each position of the LCD must satisfy the precondition that it should be incident perpendicularly to the LCD 12 surface. When the chief ray of the light beam incident at each point is incident perpendicularly to the LCD, the contrast, which is an important factor of image quality, is maximized as a whole. On the other hand, the efficiency of the light beam will be described in detail. In the case of using the LCD 12 with a micro lens (not shown), in order to improve the light efficiency of penetrating the LCD, the maximum angle of each beam in which the chief ray of each cell is vertically incident on the LCD surface It is preferable to limit (θ4). In this case, the maximum angle θ4 of the light beam incident on the LCD is set by the designer in consideration of the transmittance of the microlens employed in the LCD, the contrast, and the component size of the illumination system. In addition, the maximum angle θ4 of the light beam incident on the LCD has a relationship represented by Equation 1 with the height Rm from the optical axis reflected from the lamp reflector to meet the second lens array.

Here, θ2 represents the angle of the light beam focused on the second lens array, and H1 represents the horizontal length of the LCD.

On the other hand, the focusing angle θ2 of the second lens array cell represents a reference of the angle of the light beam proceeding to another cell or proceeding to the outside. That is, since the light beam traveling at an angle larger than the focusing angle θ2 of the second lens array cell is not focused on the LCD, light loss occurs. In this case, the loss of the amount of light should be minimized in order to increase the light efficiency, so that the maximum allowable angle θ t of the light beam incident on the second lens array is adjusted. That is, light larger than the maximum allowable angle θt of the light beam of the light emitted from the light source and the reflector is incident on other cells of the lens array or PBS array, thereby making it invalid. Accordingly, it is desirable to limit the maximum radius angle θm of the parabolic reflector to reduce the light loss by adjusting the maximum allowable angle θt of the light beam. In this case, the maximum allowable angle θ t of the light beam incident on the second lens array is set to be the same as the focusing angle θ 2 of the second lens array cell.

This will be described with reference to FIGS. 4 and 5. As shown in FIG. 4, the light intensity for each radiation angle emitted from the light source is simplified to a circular distribution. In this case, the light intensity is expressed in the form of a sinusoidal function Sinθ with respect to θ. Meanwhile, as shown in FIG. 5, the reflector has a form of a parabolic mirror having a predetermined focal length f and a center of a light source having a length of 2La is set at the focal point of the parabolic mirror. At this time, the smaller the maximum radius (θm) of the parabolic reflector increases the light efficiency. In this case, the light efficiency is proportional to the product of the effective transmittance of the lens cell corresponding to the amount of reflected light reflected by the parabolic reflector.

Meanwhile, as shown in FIG. 6, when the PBS array, which is a polarization conversion element, is employed, the maximum allowable angle θ t of the light beam incident on the second lens array will be described. The PBS array has a vertically striped structure and a horizontally sized half-size interval. In this case, since the light efficiency is in the correspondence relationship between each cell of the lens array and the effective radiation angle emitted and reflected from the lamp under the same conditions of the lamp and the LCD, the light of θ t ≤ θ 2 is effective, whereas in the case of employing a PBS array, Only light of θt ≦ θ2 / 2 becomes effective light. On the other hand, when the effective horizontal component angle θ t is greater than θ 2/2, some light beams may travel to other cells or to the outside, thereby reducing light efficiency. In this case, the hatched area corresponds to the area through which the effective light beam passes. Here, the angle θmp of the outgoing light beam of the reflector according to the focus of the reflector is represented by θa as shown in FIG. 5, and the proportional constant is used. θa is shown in equation (2).

Here, Y means X ² / 4f and X means (f-La) / 3.

On the other hand, the position of the optical component may be generally regarded as a fixed design variable that is managed to minimize the mechanical limitations of the optical system size and the optical system configuration and the effective light loss. Therefore, when fixing the position of the lens, the main design variables can be expressed as θ2, θ4 (or Rm), two condensing lens power f1, f3. On the other hand, in the case of employing an LCD with a microlens or limiting the angle θ4 of the light incident on the LCD, there are three main design variables. On the other hand, the above-described imaging relationship and the related design equations for managing the chief ray of the cell has four independent equations. This is interpreted as the position of the optical component that is fixed arbitrarily (particularly, the condenser lens) d0, d3, d4 has a subordinate relationship as shown in equation (3).

On the other hand, since the efficiency for the effective radiation angle has circular symmetry with respect to the axis, the light intensity for each radiation angle is proportional to the integral of the solid angle product from π to θm. Accordingly, the total amount of light is shown in equation (4).

Here, C means a constant, and X means Sin ^-1 (θt / θmp).

In this case, Hl is 14mm, d0 is 80mm, d3 is 150mm, d4 is 12mm, La is 0.7mm and θ4 is 8 as an approximation to the general configuration of a liquid crystal projector employing three 1.3 "LCDs. Table 1 shows the light intensity for each focal length of the parabolic reflector when set to °.

Light intensity incident on the LCD according to the focal length of the parabolic reflector Parabolic focus Light quantity Parabolic focus Light quantity Parabolic focus Light quantity 5 0.023013 6.7 0.014363 8.4 0.0091384 5.1 0.022354 6.8 0.013983 8.5 0.0088983 5.2 0.02172 6.9 0.013614 8.6 0.0086641 5.3 0.021108 7 0.013255 8.7 0.0084358 5.4 0.020517 7.1 0.012906 8.8 0.0082131 5.5 0.019946 7.2 0.012567 8.9 0.0079958 5.6 0.019395 7.3 0.012237 9 0.0077837 5.7 0.018862 7.4 0.011917 9.1 0.0075767 5.8 0.018346 7.5 0.0116004 9.2 0.0073746 5.9 0.017846 7.6 0.01130 9.3 0.0071773 6 0.017362 7.7 0.011005 9.4 0.0069845 6.1 0.016894 7.8 0.010717 9.5 0.0067962 6.2 0.016439 7.9 0.010436 9.6 0.006612 6.3 0.015999 8 0.010163 9.7 0.0064319 6.4 0.015571 8.1 0.009897 9.8 0.0062556 6.5 0.015156 8.2 0.009637 9.9 0.006083 6.6 0.014754 8.3 0.009385 10 0.0059137

As described above, the conventional liquid crystal projector has a problem to improve the light efficiency so that the luminance level is sufficiently high under the surrounding bright environment to meet the large screen demand of the user. In such a situation, the degree of freedom of design is reduced due to the position of the optical component as a dependent variable in the design of the illumination system, which leads to a difficulty in designing an illumination system for improving the light efficiency.

Accordingly, an object of the present invention to provide a liquid crystal projector illumination system configured to increase the light efficiency.

1 is a diagram showing a configuration of an illumination system of a conventional high efficiency liquid crystal projector.

FIG. 2 shows an illumination system corresponding to any one color of FIG. 1. FIG.

3 is an optical path diagram showing an optical path of the illumination system of FIG.

4 is a diagram showing the amount of light for each angle of a light source having a circular light distribution.

5 shows the angle of the beam by the size of the light source in the parabolic reflector.

6 is a view showing an effective maximum light beam angle in a polarization conversion element.

FIG. 7 is an enlarged view of A of FIG. 6; FIG.

8 is an optical path diagram schematically showing a liquid crystal projector illumination system according to the present invention.

9 is a characteristic diagram showing a comparison of the brightness of the liquid crystal projector illumination system.

<Description of Symbols for Main Parts of Drawings>

2: light source 4: parabolic reflector

6: first lens array 8: second lens array

10 polarization beam splitter array 12 liquid crystal panel

14 dichroic prism 16 projection lens

18: lambda / 2 plate 22: lens array

24,34: polarization changing element 26,28,30: condensing lens

36: color separation filter 38: microlens array

FM1 to FM4: first to fourth folding mirrors

CL1 to CL6: first to sixth condenser lenses

In order to achieve the above object, the liquid crystal projector illumination system according to the present invention includes first to third condensing lenses disposed between the second lens array and the liquid crystal panel.

Other objects and features of the present invention other than the above object will become apparent from the description of the embodiments with reference to the accompanying drawings.

8 to 9, a preferred embodiment of the present invention will be described.

Referring to FIG. 8, the illumination system for a liquid crystal projector according to the present invention includes first and second lens arrays 22 and 24, first to third condensing lenses 26, 28, and 30, and an LCD 12. have. Since the functions and operations of the first and second lens arrays 22 and 24 are the same as those in FIG. 3, detailed descriptions thereof will be omitted. In this case, the maximum angle θ4 of the light beam incident on the LCD, the second lens array cell focusing angle θ2, the maximum radius Rm of the parabolic reflector, etc. are applied in the same manner as in the prior art to improve the light efficiency. On the other hand, the illumination system for a liquid crystal projector according to the present invention increases the degree of freedom to design the illumination system by adding one condenser lens as compared to the conventional. Here, the mechanical conditions of the optical component were the same, and d1 was set to 10 mm and d2 to 70 mm. In this case, the light quantity is a maximum value of the light quantity with respect to the change of Rm according to the degree of freedom of the maximum radius Rm of the parabolic reflector for each focal length of the parabolic mirror. As shown in FIG. 9, the illumination system for the liquid crystal projector according to the present invention increases the degree of freedom of design by adding one condenser lens and indicates that the light efficiency is increased as compared with the conventional liquid crystal projector illumination system.

Meanwhile, the liquid crystal projector illumination system according to the present invention includes at least a color separation filter 36 for separating colors between the second condenser lens 28 and the third condenser lens 30 so as to correspond to the respective LCDs according to a designer's intention. There may be more than one. The color separation filter 36 separates the corresponding color from the white light beam and advances to each LCD.

In addition, in the liquid crystal projector illumination system according to the present invention, the polarization conversion element 34 may be disposed between the second lens array 24 and the first condenser lens 26 according to a designer's intention to improve light efficiency by using polarization characteristics. There will be. In this case, since the light efficiency is related to the correspondence between the effective radiation angle θt and the focusing angle θ2 of the lens array, which are emitted and reflected from the lamp under the same conditions of the lamp and the LCD, light of θt ≦ θ2 is effective, whereas the PBS array is effective. Is employed, only light of θt ≦ θ2 / 2 becomes effective light. In addition, the liquid crystal projector illumination system according to the present invention may be configured to increase the light efficiency by employing a microlens array 38 inside the LCD 32 according to the intention of the designer.

As described above, the liquid crystal projector illumination system according to the present invention implements an optimal optical system that can increase the light efficiency by imposing design freedom of the illumination system by using three condenser lenses.

As described above, the liquid crystal projector illumination system according to the present invention has an advantage of improving light efficiency.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (4)

A liquid crystal projector comprising a light source for generating a light beam, a liquid crystal panel for adjusting the transmission amount of the light beam in response to an image signal, and first and second lens arrays in which a plurality of lens cells are arranged to focus the light beam on the liquid crystal panel. In the illumination system, And a first to a third condensing lens disposed between the second lens array and the liquid crystal panel. The method of claim 1, Liquid crystal projector illumination system, characterized in that a micro lens is formed on the liquid crystal panel The method of claim 1, And a polarization converting element disposed between the second lens array and the first condensing lens. The method of claim 1, And a color separation filter disposed between the second condensing lens and the third condensing lens.