JP2798554B2 - Projection type image display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection type image display apparatus having a microlens for condensing a light beam from a light source on each picture element of a display panel.

[0002]

2. Description of the Related Art Conventionally, as an optical system in a projection type image display device, a method using a parabolic reflecting mirror, a method using an elliptical reflecting mirror, and the like are known.

FIG. 3 is a schematic diagram of an optical system using a parabolic reflecting mirror. In this optical system, a light source 11a is disposed at a focal point F of a parabolic reflecting mirror 12a, and a light beam from the light source 11a is reflected by the parabolic reflecting mirror 12a to be converted into a parallel light ray as shown by a solid line in the figure. Light is incident on the panel.

FIG. 4 is a schematic diagram of an optical system using an elliptical reflecting mirror. In this optical system, the light source 11b is
b at a first focal point F1, and a condenser lens, not shown, is connected to a light source 11b at a second focal point F2 of the elliptical reflecting mirror 12b.
And the focal point of this condenser lens coincides with the second focal point F2 of the elliptical reflecting mirror 12b. In such a configuration, the light beam from the light source 11b is reflected by the elliptical reflecting mirror 12b and condensed at the second focal point F2, then converted into a parallel light beam by a condenser lens, and enters a transmission type display panel (not shown). .

[0005] The transmission type display panel used in the above-mentioned optical system usually includes a varistor or MIM in each picture element of the display panel.
A method of controlling crosstalk by adding a non-linear element such as (Metal Insulator Metal) or a method of individually driving each picture element by adding a transistor or the like as a switching element to each picture element has been adopted. . However, if a non-linear element, a switching element, or the like is added to a picture element, a portion that does not contribute to display in the picture element is increased, and the display is darkened and the aperture ratio is reduced. Here, the aperture ratio is defined by the ratio of the effective area of all picture elements to the area of the display area.

By the way, in order to provide a display panel capable of reproducing a high-definition image, which is the demand of the times, the picture element must be reduced. The aperture ratio does not change if all the constituent elements of the picture element can be reduced in a manner similar to the reduction of the picture element, but the width of the metal wiring of the electrode and the size of the additional elements such as the non-linear element and the switching element cannot be reduced below a certain level. .
This is because the accuracy of etching and the accuracy of positioning are limited in the manufacturing process. Therefore, as the size of the picture element is reduced, the ratio of the area of the metal wiring of the electrode or the area of the additional element to the picture element increases, and the aperture ratio also decreases.

[0007] A low aperture ratio means that a large percentage of light rays are blocked by opaque portions that do not contribute to display in a picture element. Therefore, a display panel having a low aperture ratio is dark even under the same illumination conditions. appear. To solve such a problem of a decrease in the amount of light contributing to display, Japanese Patent Application Laid-Open No.
-262131 and JP-A-61-11788 propose a method using a microlens array. In this method, an array of a large number of microlenses is installed on the incident side or both the incident side and the outgoing side of the light beam of the display panel, and the light beam incident on a portion that does not contribute to display is pictured by each microlens. This is a method of converging on the elemental opening. By this method, a substantial aperture ratio can be improved.

[0008]

In the case of the above-described method for improving the substantial aperture ratio using the microlenses, in order to sufficiently exert the effect of the microlenses, the parallelism of the light rays incident on the microlenses is required. Need to increase the degree. However, in the conventional method, there is a limit to the degree of parallelism of a light beam actually obtained due to the arc length of a lamp used as a light source and the accuracy of a reflecting mirror.

When a parabolic reflecting mirror is used, as shown in FIG. 3, if the light source 11a is a perfect point light source and the parabolic reflecting mirror 12a is ideal, the parabolic reflecting mirror is indicated by a solid line. The light reflected by 12a becomes perfect parallel light. However, when the arc length of the light source 11a is long, the angles α1 and α2 in the drawing become large, and light rays shown by broken lines and dashed lines are generated, and the parallelism of the light rays incident on the microlens is reduced. Further, since the accuracy of the parabolic reflector 12a is limited, even if the light source 11a is a perfect point light source, the light reflected by the parabolic reflector 12a is not completely parallel light.

The same applies to the case where an elliptical reflecting mirror is used. As shown in FIG. 4, when the light source 11b is a perfect point light source, the light reflected by the elliptical reflecting mirror 12b is, as shown by a solid line, a second focal point. Focus on one point with F2. However, in practice, due to the arc length of the light source 11b and the accuracy of the elliptical reflecting mirror 12b, the reflected light from the elliptical reflecting mirror 12b is not completely converged on the second focal point F2, and if the arc length of the light source 11b is long, it is difficult. Light rays such as those indicated by broken lines and alternate long and short dash lines are generated therein, and the focused spot becomes large. Therefore, the parallelism of the light beam after passing through the condenser lens decreases.

FIG. 5 is a schematic diagram showing a case where a light beam having low parallelism enters the microlens. As shown in the drawing, when a light beam having an angle of ± θ is incident on the microlens 14 having the focal length f, the condensed spot at a point away from the microlens 14 by the focal length f becomes (2f × t
anθ). Since the microlens 14 is provided so that its focal point is located at the opening of the picture element of the display panel, if the value of (2f × tan θ) becomes larger than the diameter of the opening of the picture element, the condensed spot is completely removed. Does not converge on the elemental opening. As a result, the effect of the micro lens 14 cannot be sufficiently exhibited.

Further, there is another problem. When the arcs of the light sources 11a and 11b are arranged so as to coincide with the optical axis as shown in FIGS. 3 and 4, the light indicated by the two-dot chain line does not reach the display panel due to the shadow of the electrodes of the light sources 11a and 11b. Hollows occur. When the light is projected on the projection screen in this state, illuminance unevenness occurs, and a uniform image cannot be obtained. In order to eliminate this hollow, the reflecting mirror 12a,
There is also a method of shifting the positions of the light sources 11a and 11b with respect to 12b. However, in this method, the reflecting mirrors 12a, 12b
As described above, the effect of the micro lens 14 cannot be exerted because the parallelism of the reflected light due to is low.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and can sufficiently exert the effect of the microlens irrespective of the arc length of the light source, and at the same time, at the same time, can hide the electrode of the light source. It is an object of the present invention to provide a projection-type image display device capable of obtaining a uniform image without illuminance non-uniformity by eliminating a hollow part of a light beam due to the above.

[0014]

According to the present invention, a projection type image display is provided.
The device comprises a light source and an axial symmetry for reflecting light from said light source.
And a micro-lens array formed
A display panel, and the light reflected by the reflecting mirror is
A tapered portion leading to a display panel; and
The size of the end face on the display panel side of the tapered portion
Larger than the size of the end face of the light source side, the light source,
Placed at a position offset from the focal point of the reflector
As a result, the above object is achieved.

[0015]

It is known that the relationship between the angle of incidence and the angle of emergence on the end face of a tapered fiber is determined by the ratio of the diameters of both end faces. According to this, if the diameter of the incident-side end face is smaller than the diameter of the emission-side end face, the outgoing angle becomes smaller than the incident angle. Therefore, the parallelism of the outgoing light beam is better than the parallelism of the light beam incident on the tapered fiber.

Further, even if the position of the light source with respect to the reflecting mirror is shifted in order to eliminate the hollow, the parallelism of the light reflected by the reflecting mirror is improved by the tapered fiber.

[0017]

Embodiments of the present invention will be described below.

(First Embodiment) FIG. 1 shows a schematic configuration diagram of an embodiment of the projection type image display apparatus of the present invention. In the projection type image display apparatus of the present embodiment, the light source 1 is disposed at the focal point of the parabolic reflector 2, and the tapered fiber 3, the microlens array 4,
The liquid crystal display panel 5 and the field lens 6 are formed so that light rays from the light source 1 pass in this order, and a projection lens 7 is formed at the focal point of the field lens 6. An image obtained by this display device is projected on a projection screen 8.

As the light source 1, for example, a metal halide lamp, a halogen lamp, a xenon lamp or the like is used.
The parabolic reflecting mirror 2 is provided to reflect the light emitted from the light source 1 to the side opposite to the tapered fiber 3 and direct the light toward the tapered fiber 3. The tapered fiber 3 may be formed of a single fiber, but usually, a plurality of fibers are bundled to obtain a desired size, and core portions having different diameters at both end surfaces are formed. The tapered fiber 3 is arranged so that the core diameter on the light source 1 side is smaller than the core diameter on the display panel 5 side, so that the reflected light from the parabolic reflecting mirror 2 can be focused on the core portion of the end surface of the tapered fiber 3 on the light source 1 side. It has become. The size of the core diameter on the light source 1 side is not limited, but is preferably about 5 mm to 100 mm in consideration of the size of a practical display panel and desired parallelism. On the other hand, it is sufficient that the core diameter of the tapered fiber 3 on the display panel 5 side is larger than the core diameter on the light source 1 side. Many can be incident. The core diameter on the display panel 5 side is 3
If the distance can be reduced to about 0 mm, the second
The present invention can be applied to the display device using the elliptical reflecting mirror described in the embodiment.

Here, the relationship between the core diameter on the entrance side and the core diameter on the exit side of the tapered fiber 3 will be described. FIG. 2 shows an optical path diagram of a light beam incident on the tapered fiber 3 having a truncated cone shape.

As shown in the figure, it is assumed that the end face of the core of the tapered fiber 3 is a circular truncated cone, the diameter of the input end face is a, and the diameter of the output end face is b (a <b). . The light beam enters the tapered fiber 3 at an incident angle θ ₁ (0 ° <
When the incident angle is θ ₁ <90 °, the output angle is θ ₂ (0 ° <
When _{θ 2 <90 °), n} 1 × a × Sinθ 1 = n 2 × b × Sinθ 2 (1) the relationship is established. Here, n ₁ and n ₂ are the refractive indexes of the substances in contact with the side surface of the core at the entrance end and the exit end of the tapered fiber 3, respectively. In the equation (1), if n ₁ = n ₂ , then a × Sin θ ₁ = b × Sin θ ₂ (2) <because it is b, Sinθ _1> a Sinθ ₂ becomes, θ _1> θ ₂ is guided. Therefore, it is understood that the parallelism of the outgoing light beam is better than the parallelism of the light beam incident on the tapered fiber 3. Further, as can be seen from equation (2), if θ ₁ is the same value, θ ₂ becomes smaller as the ratio of the diameter a of the incident side end face to the diameter b of the output side end face becomes larger. That is, if the ratio of the diameter a of the incident side end face to the diameter b of the emission side end face is increased, emitted light with better parallelism can be obtained.

The following experiment was conducted to verify the effect of this embodiment.

In the optical system shown in FIG. 1, a metal halide lamp manufactured by Ushio having an arc length of 5 mm is used as a light source 1, and the diameter of the core on the light incident side is 30 mm and the diameter of the core on the emission side is 30 mm for the tapered fiber 3. Of 80 mm was used. The aperture ratio of the used liquid crystal display panel 5 is 40
%Met.

Under the above conditions, if the parallelism of the light reflected by the parabolic reflecting mirror 2 is about ± 9 °, the parallelism of the light after passing through the tapered fiber 3 is ± 3.4 ° according to the equation (2).
It is estimated to be a degree. When the ratio of the illuminance on the projection screen 8 with and without the tapered fiber 3 was measured, the ratio was about 1.6 times higher with the tapered fiber 3 than without the tapered fiber 3, and an increase in the illuminance could be confirmed.

From the above results, it was found that the effect of the microlens array 4 can be sufficiently brought out by using the tapered fiber 3, and the illuminance on the projection screen 8 can be increased.

Further, as a result of shifting the position of the light source 1 to the side of the tapered fiber 3 in order to prevent the reflected light from being reflected by the parabolic reflecting mirror 2, even if the parallelism of the reflected light is deteriorated, the tapered fiber 3 is used. Since light beams with good parallelism are emitted, the effect of the microlens array 4 can be sufficiently exhibited. In this case, the CCR value of the image obtained on the projection screen 8 is about 50%, which is significantly improved compared to about 30% when the tapered fiber 3 is not used. The CCR value represents illuminance distribution unevenness, and is a value defined as a percentage of the minimum illuminance with respect to the maximum illuminance.

As can be seen from the above results, when the tapered fiber 3 is used, a uniform image without illuminance unevenness can be obtained, and at the same time, a bright image due to the effect of the microlens array 4 can be obtained.

(Second Embodiment) In this embodiment, the present invention is applied to an optical system using an elliptical reflecting mirror.

In the present embodiment, in the configuration of the projection type image display apparatus shown in FIG. 1, the parabolic reflecting mirror 2 is an elliptical reflecting mirror, the light source 1 is arranged at the first focal point of the elliptical reflecting mirror, and the second focal point is provided. The tapered fiber 3 is arranged at the end.

The same effect as that of the first embodiment was obtained in the above configuration.

There are several methods for forming the microlens array 4. As a typical method, a method of obtaining a gradient index lens by selective ion diffusion is known. This involves immersing a glass plate serving as a base in a molten salt, exchanging ions such as different types of alkali ions between the glass plate and the molten salt through a mask provided on the glass plate, and forming a refraction corresponding to the mask pattern. This is a method of obtaining a glass plate having a rate distribution. Since the microlens obtained by this method has no irregularities, it can be laminated to a liquid crystal display panel using a Canadian balsam or photocurable resin without passing through an air layer, and the reflection loss on the substrate surface is almost eliminated. It can be reduced to a negligible extent. This method is based on Elec
tronics Letters Vol. 17 N
o. 13p452 (1981).

The present invention is not limited to the configuration of the projection type image display device of the above two embodiments, the type of each member and the manufacturing method, but can be widely applied to the projection type image display device having a microlens array. Can be done.

[0033]

As is apparent from the above description, according to the projection type image display apparatus of the present invention, the effect of the microlens array can be sufficiently exerted regardless of the arc length of the light source, and a bright image can be provided. You can do it. In addition, a uniform image without illuminance non-uniformity can be obtained by eliminating the hollowing out of the light beam due to the shadow of the electrode of the light source.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an optical system in a projection-type image display device according to a first embodiment.

FIG. 2 is an optical path diagram of a light beam incident on a frusto-conical tapered fiber.

FIG. 3 is a schematic diagram of an optical system using a parabolic reflecting mirror.

FIG. 4 is a schematic diagram of an optical system using an elliptical reflecting mirror.

FIG. 5 is a schematic diagram when a light beam enters a microlens.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source 2 Parabolic reflector 3 Tapered fiber 4 Micro lens array 5 Liquid crystal display panel 6 Field lens 7 Projection lens 8 Projection screen

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/13 G02F 1/1335 G03B 21/14

Claims (1)

(57) [Claims] 1. A light source and a mirror having axial symmetry for reflecting light from the light source.
And a display panel on which a microlens array is formed, and guiding light reflected by the reflector to the display panel.
And a Ku tapered portion, the size of the end face of the display panel side of the tapered portion,
Larger than the size of the end face of the tapered portion on the light source side
The light source is offset from the focal point of the reflector.
A projection type image display device arranged at a different position.