JPH0915534A - Polarization separation / synthesis device and liquid crystal display device - Google Patents

Abstract

(57) [Abstract] [Purpose] To improve the effective use efficiency of light in the liquid crystal panel. [Structure] White light having mixed polarization directions is used as a light source 1, and light emitted from the light source 1 is separated by a polarization beam splitter 3 into two linearly polarized light components P1 and S having different polarization directions. The polarized component light S is transmitted through the half-wave plate 4 to rotate its polarization direction by 90 ° to match the other polarization direction (P2), and then guide these two lights to the combining prism 6. In combining and taking out, the light incident on the polarization beam splitter 3 is shaped into an elliptical shape by the optical shape shaping means 9, and the minor axis direction of the elliptical shape coincides with the combining direction of the light 7 at the time of emission from the combining prism 6. As a result, the effective light utilization efficiency in the liquid crystal panel section is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization splitting / synthesizing device for extracting light with mixed polarization directions by aligning the polarization directions, and a liquid crystal display device equipped with the polarization splitting / synthesizing device.

[0002]

2. Description of the Related Art Optical systems using liquid crystals such as liquid crystal projectors have recently attracted attention as alternatives to conventional CRTs. As the light, light that is linearly polarized in a certain polarization direction is often used. In order to obtain such light linearly polarized in a certain direction, a method of combining a light source such as a metal halide lamp having a mixed polarization direction with a polarizing plate is generally used. In this case, of the light incident on the polarizing plate, the polarized component light having a polarization plane perpendicular to the light passing through the polarizing plate is removed. It will be reduced to less than half of what it was, resulting in a large loss of light.

Therefore, there has been proposed a method of obtaining light linearly polarized in a certain direction while suppressing the loss of light quantity (for example, Japanese Patent Application No. 6-237587). In this proposed method, a light beam from a light source is split into two linearly polarized light components, P-polarized light and S-polarized light, by a polarization beam splitter, and one of the light components is transmitted through a wave plate to make its polarization plane 90 °. This is a method in which the light is rotated to match the polarization direction of the other light and then combined with the other light again.

FIG. 10 shows an apparatus disclosed in Japanese Patent Application No. 6-237587. The light emitted from the light source 1 becomes parallel light reflected by the curved mirror 2, and is split into P-polarized light and S-polarized light by the polarization beam splitter 3. The S-polarized light reflected by the polarization beam splitter 3 has a polarization plane of 9 by passing through the ½ wavelength plate 4 as a polarization direction rotating means.
After being rotated by 0 ° and converted into P-polarized light (P2), it is incident on the combining prism 6. On the other hand, the polarization beam splitter 3
The P-polarized light that has passed through is reflected by the mirror 5 (P
1), the light is incident on the combining prism 6. The two lights P1 and P2 incident on the combining prism 6 are combined into one light by the function of the combining prism 6, and are extracted as outgoing light 7.

As described above, in this conventional technique, the light emitted from the light source in which the two polarized component lights of P-polarized light and S-polarized light coexist is converted from S-polarized light to P-polarized light to obtain a straight line of only P-polarized light. It can be extracted as polarized component light.

[0006]

By the way, the light emitted from the light source 1 is reflected by the curved mirror 2 and enters the polarization beam splitter 3, and the shape of the light at that time is generally as shown in FIG.
It has a circular shape as shown in FIG. On the other hand, the shape of the light emitted from the synthesizing prism 6 is the emitted light 7 obtained by synthesizing the P-polarized light (P1) separated by the polarization beam splitter 3 and the P-polarized light (P2) converted from the S-polarized light as described above. Therefore, as shown in FIG. 11B, the two light beams are combined into an elliptical shape having a ratio of the short diameter to the long diameter of approximately 1: 2.

In a liquid crystal display device such as the above-mentioned liquid crystal projector, light emitted from a liquid crystal light valve including a liquid crystal panel and a polarizing plate is projected on a screen to display an image. At this time, in terms of the effective use efficiency of light, the larger the ratio of the light that can enter the liquid crystal panel to the total light, the higher the effective use efficiency of light.

FIG. 12 shows the outer shape of the liquid crystal panel 16 and the shape of the emitted light 7 with which the liquid crystal panel 16 is irradiated. This figure is
The size is such that the elliptical light 7 having a ratio of the minor axis to the major axis of about 1 to 2 comes into contact with the liquid crystal panel 16 having a ratio of the length in the horizontal direction to the length in the longitudinal direction of 4 which is commonly used. This is the case when irradiation is performed at. The ratio of actually taking in and using the light 7 in the liquid crystal panel 16 is the ratio of the area occupied by the liquid crystal panel 16 to the area irradiated with the light 7, and here only about 59% of the light is used. There will be no.

Further, the light transmitted through the liquid crystal panel projects an image on the screen through the projection lens. The brighter the image on the screen, the easier it is to see the image. For example, if the screen illuminance is high, a sufficiently bright image can be viewed without darkening the room. The brightness of the image on the screen is largely related to how much light can be taken into the liquid crystal panel, and improvement of the light utilization efficiency in the liquid crystal panel is required.

However, when the effective utilization efficiency of light in the liquid crystal panel portion is considered simply as the area ratio of the incident light area of the light to the liquid crystal panel and the occupied area of the liquid crystal panel, the light incident on the polarization beam splitter 3 is considered. In the case of a circular shape, there is a problem that the brightness on the screen is insufficient due to the low light utilization efficiency of about 59% as described above.

The present invention has been made to solve the problems of the prior art, and it is an object of the present invention to provide a polarization splitting / combining device and a liquid crystal display device capable of improving the effective light utilization efficiency in a liquid crystal panel section. To aim.

[0012]

A polarization separation / combination device of the present invention allows white light emitted from a light source to enter a polarization separation means for separating a P polarization component and an S polarization component, and the polarization separation means separates the white light. In the polarization splitting / synthesizing device, in which the polarization directions of the respective polarized component lights thus obtained are matched by the polarization direction rotating means, and then the light is combined and extracted by being incident on the light combining means,
The white light emitted from the light source is shaped into an elliptical shape by the light shape shaping means, and the minor axis direction of the elliptical shape is made to coincide with the direction in which light is emitted from the polarization splitting means. Is achieved.

The liquid crystal display device of the present invention is a liquid crystal display device in which light emitted from a polarization splitting / combining device is incident on a liquid crystal light valve in which the ratio of the horizontal length to the vertical length of the liquid crystal panel is M: N. In claim 1, the light incident on the polarization splitting means of the polarization splitting / combining device according to claim 1 is elliptical, and the ratio of the major axis length to the minor axis length is N: M / 2. The purpose is achieved.

[0014]

According to the present invention, white light having mixed polarization directions is used as the light source, and the light emitted from the light source is separated into two linearly polarized light components having different polarization directions by the polarization separating means, and the separated one is separated. By passing the polarized component light of (1) through the polarizing plate, its polarization direction is rotated by 90 ° and matched with the light of the other polarization direction. After that, these two lights are guided to the photosynthesis means to be synthesized and taken out. In this process, the light shape shaping means shapes the light incident on the polarization splitting means into an elliptical shape, and the minor axis direction of the elliptical shape is made to coincide with the direction in which the light is emitted from the polarization splitting means. As a result, the efficiency of effective use of light in the liquid crystal panel portion of the liquid crystal display device is improved.

In this case, if the ratio of the length in the horizontal direction to the length in the vertical direction of the liquid crystal panel is M to N, the light incident on the polarized light separating means has a ratio of the major axis length to the minor axis length of N. Vs. M /
It has an elliptical shape of 2.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a plan view of a liquid crystal projector incorporating the polarization splitting / synthesizing device of this embodiment. The polarization splitting / combining device includes a light source 1 that emits white light such as a metal halide lamp, a halogen lamp, or a xenon lamp, an elliptical mirror 8, an optical shape shaping unit 9 including a cylindrical lens 10 and a plano-convex lens 11, and a polarization splitting unit. It comprises a polarization beam splitter 3, a half-wave plate 4 as a polarization direction rotating means, a mirror 5, and a combining prism 6. The emitted light 7 obtained by this polarization separation / combination device is a liquid crystal light valve 12 including a liquid crystal panel and a polarizing plate, a field lens 13 and a projection lens 14.
Then, the light is irradiated onto the screen 15 via the.

The light emitted from the light source 1 is elliptic mirror 8
After being converted into convergent light having a substantially circular beam shape by being reflected by, the light beam shape is converted into parallel light having a substantially elliptical shape when passing through the light shape shaping unit 9.

The optical shape shaping means 9 is composed of a cylindrical lens 10 and a plano-convex lens 11 for reducing only one direction of a light beam. Further, the cylindrical lens 10 is configured so that the light is shaped in the same direction as the direction in which the light is emitted from the synthesizing prism 6, and the circular convergent light incident on the light shape shaping means 9 is The cylindrical lens 10 converts the light into elliptical light in only one direction, and then the plano-convex lens 11 converts the light into parallel light.

When the light emitted from the light shaping means 9 passes through the polarization beam splitter 3, it is divided into P-polarized light (P1) as transmitted light and S-polarized light (S) as reflected light according to the polarization direction. . The separated S-polarized light (S) is 1 /
By passing through the two-wave plate 4, the plane of polarization is rotated by 90 ° and converted into P-polarized light (P2), which is then incident on the combining prism 6. One P-polarized light (P1) is reflected by the mirror 5 and then is incident on the combining prism 6. The two lights that have entered the combining prism 6 are extracted as outgoing light 7 whose polarization directions match. The emitted light 7 is guided to a liquid crystal light valve 12 including a liquid crystal panel and a polarizing plate, and then passes through a field lens 13 and a projection lens 14 and then to the screen 1.
5 is illuminated.

FIG. 2 (a) shows a case where the shape of the incident light on the polarization beam splitter 3 is an elliptical shape in which the ratio of the minor axis length to the major axis length is 1: 2. Here, the minor axis direction of the elliptical shape shaped by the light shape shaping means 9 is a direction that coincides with the direction in which light is emitted from the synthetic prism 6. Therefore, the light 7 emitted from the combining prism 6 has a substantially circular shape as shown in FIG.

FIG. 3 shows the outer shape of the liquid crystal panel 16 and the shape of the light 7 irradiated on the liquid crystal panel 16 when the light 7 emitted from the synthesizing prism 6 is circular. This FIG.
This is a case where the circular light 7 is radiated in such a size that it comes into contact with the liquid crystal panel 16 having a ratio of the length in the horizontal direction to the length in the vertical direction which is generally 4/3. The effective light use efficiency of the liquid crystal panel 16 is about 61% when the ratio of the area of the liquid crystal panel 16 to the area irradiated with the light 7 is about 61%, and the incident light to the polarization beam splitter 3 is shaped by the optical shape shaping means 9. The effective light utilization efficiency is slightly improved compared to the case without shaping.

Further, FIG. 4A shows the shape of the incident light on the polarization beam splitter 3, in which the ratio of the minor axis length to the major axis length is 2: 3. FIG. 4B shows the outer shape of the liquid crystal panel 16 and the shape of the light 7 with which the liquid crystal panel 16 is irradiated.
That is, in FIG. 4, with respect to the liquid crystal panel 16 in which the ratio of the horizontal length and the vertical length of the liquid crystal panel is M: N, the incident light to the polarization beam splitter 3 is changed to the long axis length and the short axis length. This is a case of an elliptical shape having a height ratio of N to M / 2. Here, it corresponds to M = 4 and N = 3. The effective light utilization efficiency in terms of the ratio of the area occupied by the liquid crystal panel 16 to the area irradiated with the light 7 is about 64%. By optimizing the elliptical shape of the incident light to the polarization beam splitter 3, the effective light utilization efficiency is improved. Further improvement can be achieved.

By the way, in order to further improve the light effective use efficiency, a method of moving light outside the region of the liquid crystal panel into the region of the liquid crystal panel can be considered. For example, there is a case where light outside the liquid crystal panel area A as shown in FIG. 4 is moved to the liquid crystal panel area B and used. At this time, the problem is the incident angle of the light 7 on the liquid crystal panel 16. There is a limit to the angle of light that passes through the liquid crystal panel 16, and an allowable incident angle according to the characteristics of the liquid crystal panel 16 is provided. If light with a poor incident angle is used, problems such as color bleeding and color mixing occur on the screen 15. For this reason,
A light incident angle limiting means (not shown) is provided on the light incident surface of the liquid crystal panel 16, and limits the incident light so that light exceeding the allowable incident angle does not enter the liquid crystal panel 16. When the light exceeding the allowable incident angle, that is, the incident light containing a large amount of light with poor parallelism is used, the amount of light kicked by the light incident angle limiting means is increased and the light effective utilization efficiency is not improved. Moving the light outside the liquid crystal panel area A to the liquid crystal panel area B means that the outgoing light 7 from the combining prism 6 originally entered the liquid crystal panel 16 as parallel light, whereas The part is incident on the liquid crystal panel 16 at an angle according to the amount of movement. The larger the amount of movement, the more the liquid crystal panel 16
The incident angle to the liquid crystal panel 16 becomes large, and there is a possibility that it cannot be taken into the liquid crystal panel 16 beyond the allowable incident angle according to the characteristics of the liquid crystal panel 16. Therefore, it is required to reduce the movement amount in order to reliably take in light into the liquid crystal panel 16. In the case of the liquid crystal panel 16 which has a ratio of the length in the horizontal direction to the length in the vertical direction of 4: 3, which is commonly used, FIG.
2 and 4, the movement amounts for moving the light outside the liquid crystal panel area A to the liquid crystal panel area B are M and L, respectively. At this time, since the length of L is about 0.5 times the length of M, the incident light on the polarization beam splitter 3 has an elliptical shape in which the ratio of the major axis length to the minor axis length is 2: 3. Compared with the case where the incident light to the polarization beam splitter 3 has a circular shape, the incident angle of the moved light with respect to the liquid crystal panel is smaller and the possibility of being taken into the liquid crystal panel is higher. become.

(Embodiment 2) FIG. 5 is a diagram showing a part of a polarization splitting / combining apparatus according to another embodiment of the present invention. In the second embodiment, a parabolic curved mirror 17 is used instead of the elliptical mirror 8 of the first embodiment, and a concave column lens 18 is used instead of the plano-convex lens 11 of the first embodiment. The light emitted from the light source 1 that emits white light is reflected by the parabolic curved mirror 17 to be substantially parallel light having a substantially circular light flux shape. Then, in the cylindrical lens 10 that reduces only one direction of the light flux, the light is converged in only one direction, so that the light is converted into a substantially elliptical shape. The direction of the cylindrical lens 10 is configured such that the minor axis direction of this elliptical shape coincides with the direction in which light is emitted from the combining prism 6.
The direction of light converged by the concave lens 18 is returned to parallel light again to be elliptical parallel light, which is then incident on the polarization beam splitter 3.

(Third Embodiment) FIG. 6 is a diagram showing a part of still another polarization separation / combination device of the present invention. In the third embodiment, the members forming the optical shape shaping means 9 are replaced with those in the first embodiment. That is, the plano-concave lens 19 and the shaping prism 20 are used. The light emitted from the light source 1 that emits white light is reflected by the elliptical mirror 8 to be converged light having a substantially circular luminous flux shape, and then is converted into parallel light of a predetermined size by the plano-concave lens 19. . Then, the light beam is shaped into an elliptical shape by the shaping prism 20 that reduces only one direction of the light beam, and then enters the polarization beam splitter 3. The shaping direction by the shaping prism 20 is such that the minor axis direction of the shaped elliptical shape coincides with the synthesis direction of the light emitted from the synthesis prism 6.

(Embodiment 4) FIG. 7A is a plan view of a liquid crystal projector incorporating a polarization splitting / combining device using a prism type polarization beam splitter 21. FIG.
(B) is an enlarged plan view showing the prism type polarization beam splitter 21. The prism type polarization beam splitter 21 is configured as follows. The parallel light flux emitted from the light source 1 and transmitted through the light shape shaping means 9 is 4
The two incident lights B25, B26, B27, B28 are split and incident on the mirrors 25, 26 and the polarization beam splitters 27, 28. Among them, the lights B27 and B28 incident on the polarization beam splitters 27 and 28 are P-polarized lights Bp2 which are transmitted.
7, Bp28 and the reflected S polarized light Bs27, Bs28 are separated. The transmitted P-polarized light Bp27, Bp28 is converted into S-polarized light Bs27 ', Bs28' by the λ / 2 plate 33.
And is emitted to the right on the paper surface. Reflected S-polarized light B
The mirrors 29 and 30 change the directions of s27 and Bs28 to the right on the paper surface. Next, the light B incident on the mirrors 25 and 26
25 and B26 are incident on the polarization beam splitters 31 and 32, and S which is reflected by the P-polarized light Bp25 and Bp26 that is transmitted therethrough is reflected.
It is separated into polarized lights Bs25 and Bs26. S reflected
The polarized lights Bs25 and Bs26 are emitted as they are toward the right side of the drawing, and the transmitted P-polarized lights Bp25 and Bp26 are reflected by the mirror 2
3, 23 'can be turned to the right in the plane of the drawing, and the λ / 2 plates 24, 24' can be used for S-polarized light BS25 ', Bs26'.
It is configured to be converted into and output.

FIG. 8A shows the shape of a light beam incident on the prism type polarization beam splitter 21, which is a circular shape. FIG. 8B shows a prism type polarization beam splitter 21.
3 shows the shape of the outgoing light flux of. The shape of the emitted light beam can be regarded as a substantially elliptical shape in which the ratio of the major axis length to the minor axis length indicated by the broken line T is 2: 1.

FIG. 9A shows the shape of an incident light beam to the prism type polarization beam splitter 21, which is an elliptical shape of approximately 1: 2. FIG. 9B shows the shape of the light flux emitted from the prism type polarization beam splitter 21. Here, the minor axis direction of the elliptical shape shaped by the light shape shaping means 9 is a direction that coincides with the combined direction of the light when it is emitted from the prism type polarization beam splitter 21, and at this time, the emitted light 7 Has a substantially circular shape as indicated by a broken line Q.

As described above, even when the polarization splitting / combining means is changed, the relationship between the incident light flux shape and the outgoing light flux shape can be regarded as almost the same, and therefore, the incident light flux shape is an ellipse adapted to the liquid crystal panel shape. The same applies to the effect of improving the effective use efficiency of light due to the shape. Instead of the prism type polarization beam splitter 21, the prism type polarization beam splitter 40 shown in FIG.
The plate type polarization beam splitter 50 shown in FIG. 4 can be used.

The prism type polarization beam splitter 40 shown in FIG. 13 employs two types of compound prisms 45 and 46, and mirrors 23, 23 ', 25 and 2 shown in FIG. 7B.
Instead of 6, 29, 30 prism surfaces 47, 47 ', 4
Use 8, 48 ', 49, 49' total reflection surfaces (at this time, since the surfaces 47, 48, 47 ', 48' are to be total reflection surfaces, they should be placed slightly apart so that a thin air layer can be formed between them. It is desirable that the reflectance on these surfaces be approximately 10
It is a structure with 0%. In addition, 43,44,44 'is λ
/ 2 plate.

The plate type polarization beam splitter 50 shown in FIG. 14 includes a polarization beam splitter 52 and a mirror 5.
3 and a λ / 2 plate 54 are combined to perform polarization conversion of light similar to that of FIG. 7B or 13.

In each of the above embodiments, as the optical shape shaping means, a combination of an elliptical mirror, a cylindrical lens and a plano-convex lens, or a combination of a parabolic curved mirror, a cylindrical lens and a concave column lens, or an elliptical mirror, a plano-concave lens and a shaping lens. Although the case of the combination of prisms is shown, the present invention is not limited to this, and any means may be used as long as it is a means for converting a light shape from a circular shape to an elliptical shape. Further, although the half-wave plate is used as the polarization direction rotating means, it is also possible to use a 90 ° twist TN type liquid crystal element or the like. Further, the same effect can be obtained whether the emitted light is matched with P-polarized light or S-polarized light.

[0034]

In the polarization splitting / synthesizing device of the present invention, when white light having mixed polarization directions is used as a light source and the light emitted from the light source is shaped into an elliptical shape by the optical shape shaping means, the minor axis of the elliptical shape is used. The direction is made to coincide with the direction in which light is emitted from the polarized light separating / combining means. Furthermore, when the ratio of the horizontal length to the vertical length of the liquid crystal panel is M to N, the ratio of the major axis length to the minor axis length of the elliptical shape is N to M / 2. Then, the polarization direction of the shaped light is made incident on the polarization separation means for separating the two linear polarization components of the P polarization component and the S polarization component, and the polarization direction rotation means divides the polarization direction of each polarization component light. Are output as matched emission light. As a result, when the emitted light is applied to the liquid crystal light valve, the incident light is shaped into a light flux shape that takes into account the shape of the liquid crystal panel and the angle of incidence of the light on the liquid crystal panel. The efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a plan view of a liquid crystal projector incorporating a polarization splitting / synthesizing device according to an embodiment.

FIG. 2A is a diagram showing a shape of light incident on a polarization beam splitter, and FIG. 2B is a diagram showing a shape of light emitted from a combining prism.

FIG. 3 is a diagram showing an outer shape of a liquid crystal panel and a shape of light applied to the liquid crystal panel.

FIG. 4A is a diagram showing an incident light shape on a polarization beam splitter, and FIG. 4B is a diagram showing an outer shape of a liquid crystal panel and a shape of light irradiated on the liquid crystal panel.

FIG. 5 is a diagram showing a part of a polarization splitting / synthesizing device according to another embodiment of the present invention.

FIG. 6 is a diagram showing a part of a polarization splitting / synthesizing device according to still another embodiment of the present invention.

7A is a plan view of a liquid crystal projector incorporating a polarization splitting / combining device using a prismatic polarization beam splitter, and FIG. 7B is an enlarged view showing the prismatic polarization beam splitter.

FIG. 8A is a diagram showing an incident light shape of a prism type polarization beam splitter, and FIG. 8B is a diagram showing an emission light shape of the prism type polarization beam splitter.

9A is a diagram showing the shape of incident light on a prism type polarization beam splitter, and FIG. 9B is a diagram showing the shape of light emitted from a prism type polarization beam splitter.

FIG. 10 is a plan view of a conventional polarization splitting / synthesizing device.

FIG. 11A is a diagram showing the shape of light incident on the polarization beam splitter, and FIG. 11B is a diagram showing the shape of light emitted from the combining prism.

FIG. 12 is a diagram showing an outer shape of a conventional liquid crystal panel and a shape of light applied to the liquid crystal panel.

FIG. 13 is a view showing a prism type polarization beam splitter having another configuration used in the polarization splitting / combining device of the present invention.

FIG. 14 is a diagram showing a plate-type polarization beam splitter used in the polarization splitting / combining device of the present invention.

[Explanation of symbols]

 1 Light Source 2 Curved Mirror 3 Polarizing Beam Splitter 4 1/2 Wave Plate 5 Mirror 6 Synthetic Prism 7 Emitted Light from Polarization Separation / Synthesis Device 8 Elliptical Mirror 9 Optical Shape Shaping Device 10 Cylindrical Lens 11 Plano-Convex Lens 12 Liquid Crystal Light Valve 13 Field Lens 14 Projection Lens 15 Screen 16 Liquid Crystal Panel 17 Parabolic Curved Mirror 18 Concave Column Lens 19 Plano-Convex Lens 20 Shaping Prism 21 Prism Type Polarizing Beam Splitter

Claims (2)

[Claims] 1. The white light emitted from a light source is made incident on a polarization separation means for separating a P polarization component and an S polarization component, and the polarization direction of each polarization component light separated by the polarization separation means is rotated. In the polarization splitting / combining device that is combined by the means and then is incident on the light combining means to extract the white light emitted from the light source, the white light emitted from the light source is shaped into an elliptical shape by the optical axis shaping means. A polarization splitting / combining device that matches the direction of light emitted from the polarization splitting means. 2. A liquid crystal display device in which light emitted from a polarization splitting / combining device is incident on a liquid crystal light valve in which the ratio of the horizontal length to the vertical length of a liquid crystal panel is M: N.
A liquid crystal display device in which the light incident on the polarization separation means of the polarization separation / combination device according to claim 1 is elliptical, and the ratio of the major axis length to the minor axis length is N: M / 2.