JPH03192320A - Projection type display device - Google Patents

Abstract

PURPOSE:To multiply the quantity of light transmitted through an incident side polarizing plate and to realize high-brightness image display by providing an optical means for converting non-polarized illuminating luminous flux emitted from a light source to linearly polarized light and constituting the device so that the axis of polarization of the incident side polarizing plate of a liquid crystal light valve may conform with the direction of the linearly polarized light of the illuminating luminous flux. CONSTITUTION:The illuminating luminous flux 2 emitted from the light source 1 is in a non-polarized state and is separated to reflected S polarized light 30 and transmitted P polar ized light 33a by the joint surface 20a of a polarizing and separating means. The reflected S polarized light is made incident on a polarizing rotating means 21. The S polarized light 30 made incident on the polarizing rotating means is emitted as the P polarized light 31, transmitted through the means 20 still as the P polarized light, reflected by an optical path conversion means 23 and passes through a condenser lens 10 as the linearly polarized light 33b in the same polarizing and advancing directions as those of the transmitted P polarized light 33a to be made incident on the liquid crystal light valve 3. The axis of polarization is arranged on the incident side polarizing plate 8 of the liquid crystal light valve 3 so as to conform with the direction of the incident linearly polarized light 33a and 33b. As a result, light energy which is about twice as much as in conventional practice is made incident on a liquid crystal layer and contributes the image display.

Description

Detailed Description of the Invention [1i Field of Industrial Application] The present invention relates to a projection type display device that enlarges and projects an image formed on a liquid crystal light valve onto a screen, and particularly relates to a projection type display device that enlarges and projects an image formed on a liquid crystal light valve onto a screen. The present invention relates to a projection display device using a lamp that emits polarized light.

[Prior Art] FIG. 5 is an explanatory diagram of an optical system of a conventional projection display device. In the figure, (1) is a light source, (120) is a lamp, (
130) is a reflecting mirror, (2) is an illumination beam emitted from the light source (1), (3) is a liquid crystal light valve, (8) and (9) are polarizing plates placed before and after the liquid crystal light valve, (4) is a projection lens, (5) is a screen, and (10) is a condenser lens.

Next, the operation will be explained. The light source (1) is a lamp (12
It consists of a liquid crystal light valve (
3) is irradiated with the illumination light beam (2). As the lamp, for example, a metal halide lamp, a discharge lamp such as a xenon lamp, a halogen lamp, etc. are used. An image is displayed on the surface of the liquid crystal light valve (3) as described later, and the in-plane transmittance changes depending on the shading and color of the image.

The light flux that has passed through the liquid crystal light valve (3) further passes through a projection lens (4) and becomes projection light (110), which is enlarged and imaged on a screen (5) for viewing. Note that the condenser lens (lO) is provided to make the illumination light flux enter the projection lens with high efficiency to obtain a high-brightness projected image.

Next, regarding the configuration and operation of the liquid crystal light valve (3),
This will be explained with reference to FIG. The liquid crystal (6) is sandwiched between two glass substrates (7), and polarizing plates (8) and (9) are placed on both sides.
are arranged. When no voltage is applied V=O (Fig. 6(a)), linearly polarized light (2a
) is an output side polarizing plate (9) arranged so that the polarization direction is rotated by 90'' due to the optical rotation of the liquid crystal when transmitted through the liquid crystal (6), and the polarization axis is orthogonal to the input side polarizing plate (8). On the other hand, when a voltage V higher than the threshold voltage vth is applied (Fig. 6(b)), the optical rotation of the liquid crystal decreases, and the amount of light transmitted through the transmission side polarizing plate (9) becomes smaller than the voltage. It decreases as the transmittance increases.Using this kind of transmittance control effect,
By configuring electrodes in a dimensional array, a two-dimensional image display element can be formed. The above liquid crystal has an optical rotation angle of 90
We have explained an example of using a T However, since it is not directly related to the subject matter of the present invention, the explanation will be omitted.

Furthermore, as a second conventional device, FIG. 7 shows an optical system of a device using three liquid crystal light valves. In the figure,
(1) is a light source, which specifically includes a lamp (120) that generates white light, such as a metal halide lamp, xenon lamp, or halogen lamp, and a reflecting mirror (130). (
2) is the illumination light flux emitted from the light source (1), (14R),
(14B) is a dichroic mirror for color separation, (15B)
), (15G) is a guichroic mirror for color synthesis, (1
1), (12) are mirrors, (3R), (3G)
.

(3B) is a liquid crystal light valve, (8R), (8G)
, (8B) is the incident side polarizing plate, (9R), (9G)
, (9B) are output side polarizing plates, (IOR), (IOG
), (10B) are condenser lenses.

Next, the operation of the second conventional device will be explained.

After the illumination light flux (2) is emitted from the white light source lamp (120),
The light is reflected by a reflecting mirror (130) and is emitted from a light source (1). The dichroic mirror (14R) reflects red light and transmits blue and green light. In addition, dichroic mirror (14B
) reflects blue light and transmits green light. Therefore, the liquid crystal light valves (3G), (3B), and (3R) are irradiated with green, blue, and red illumination light beams, respectively.

Images corresponding to green, blue, and red color light are formed on the liquid crystal light valves (3G), (3B), and (3R) by an external circuit (not particularly shown), and the irradiated light is transmitted and modulated within the light valve surface. LCD light bulb (3G), (3B
).

The emitted light (3R) enters the projection lens (4) as a composite light beam (100) by a dichroic mirror (15B) that reflects blue light, a dichroic mirror (15G) that reflects green light, and a reflection mirror (12). , is imaged on the screen (5) as a projected light beam (110),
The enlarged color image is presented for viewing. In addition, condenser lenses (IOR), (IOC), (IOB) are
They are used to make red, green, and blue light enter the projection lens (4) with high efficiency. In addition, each LCD light valve (
The configuration and operation of 3R), (3G), and (3B) are the same as those described above with reference to FIG.

[Problems to be Solved by the Invention] Since the conventional projection display device is configured as described above, the light flux used for image display by the liquid crystal light valve is transmitted through the incident side polarizing plate (8) or ( 8R), (8G
), (8B). On the other hand, the lamps used in conventional equipment (
120) are metal halide lamps, xenon lamps,
It was a non-polarized (naturally polarized) light source such as a halogen lamp, and the illumination light (2) was also non-polarized.

As a result, the incident side polarizing plate (8) or (8R), (s
G).

(8B), only about half of the illumination light flux (2) entered the liquid crystal layer. The remaining half of the light energy is mainly transmitted through the polarizing plate (8) or (8R) or (8G) on the incident side.
.

It is absorbed by (8B) and becomes heat, and the polarization characteristics deteriorate due to the temperature increase of the incident side polarizing plate (8) or (8R), (8G), (8B), and the liquid crystal operating characteristics change due to the temperature increase of the adjacent liquid crystal layer. etc., was the cause.

The present invention has been made to solve the above-mentioned problems, and it is possible to effectively utilize the energy of the illumination light flux and prevent the temperature rise of the incident side polarizing plate (8), resulting in a high-brightness image. The purpose is to develop a projection display device that can display images.

[Means for Solving the Problems] A projection type display device according to the present invention includes a polarization separation means for separating an unpolarized light beam into a first and a second linearly polarized light beam, and two first and second linearly polarized light beams that are orthogonal to each other. a total reflection prism having a total reflection surface and an inclined surface, the intersection line of the total reflection surface is the direction of a reference angle that forms 45@ with the polarization direction of the second linearly polarized light beam, and the intersection line of the inclined surface A reflection mirror is formed on a half surface with a boundary of The light beam is reflected in the order of the reflecting surface and guided to the reflecting mirror, and the light beam reflected by the reflecting mirror is reflected in the order of the second total reflection surface and the first total reflection surface to become the second linearly polarized light beam. On the other hand, the polarization direction is 90
``polarization rotation means for making the rotated third linearly polarized light beam re-enter the polarization separation means; an optical path converting means for converting the liquid crystal light beam into a fourth linearly polarized beam having the same traveling direction and polarization direction as the first linearly polarized beam; It illuminates the bulb.

In other words, it has an optical means for converting the unpolarized illumination light beam emitted from the light source into linearly polarized light, and is configured so that the direction of the linearly polarized light of the illumination light beam matches the polarization axis of the polarizing plate on the input side of the liquid crystal light valve. It is something.

[Function] By linearly polarizing the illumination light beam as described above, the amount of light transmitted through the incident-side polarizing plate can be doubled, and absorption by the polarizing plate can also be reduced.

Furthermore, if the extinction ratio of the illumination light beam linearly polarized by the optical means is good, the apparatus can be configured without a polarizing plate on the incident side.

[Example] FIG. 1 is an explanatory diagram showing an optical system of a projection type display device in Example 1 of the present invention.

In the figure, (20) is a polarization separation means (polarization beam splitter), (21) is a polarization rotation means, and two total reflection mirror surfaces (21a) and (21b) are orthogonal to each other.
It consists of a total reflection prism consisting of a slope and a slope. (
21C) is a reflection mirror formed on a part of the slope of the polarization rotation means (21), and (23) is an optical path conversion means (mirror).

Next, the operation of the embodiment will be explained.

The illumination light beam (2) emitted from the light source (1) is in a non-polarized state as in the conventional example, and is separated into reflected S-polarized light (30) and transmitted P-polarized light (33a) by the joint surface (20a) of the polarization separation means. . The reflected S-polarized light enters the polarization rotation means (21).

The polarization rotation means (21) is arranged so that the intersection line (22) is rotated by 45@ as a reference angle around two axes from the X direction in the figure, and the polarization direction of the incident light is changed by 90 degrees as described later. @Rotates and emits light. Therefore, the S-polarized light (30) incident on the polarization rotation means becomes the P-polarized light (31
), passes through the polarization separation means (20) as P-polarized light, is reflected by the optical path conversion means (23), and becomes linearly polarized light (with the same polarization direction and traveling direction as the transmitted P-polarized light (33a)). 33b), the light enters the liquid crystal light valve (3) through the condenser lens (lO). The polarization axis of the incident-side polarizing plate (8) of the liquid crystal light valve (3) is aligned with the direction of the incident linearly polarized light (33a) and (33b). As a result, approximately twice as much light energy enters the liquid crystal layer as compared to the case where a conventional non-polarized light beam enters, contributing to image display. The light emitted from the liquid crystal light valve (3) is projected by the projection lens (4) as in the conventional example.
10) and is enlarged and projected onto the screen (5).

Next, the operation of the polarization rotation means (21), which is characteristic of the present invention, will be explained in detail with reference to FIG.

FIG. 2(a) is an explanatory diagram of the polarization rotation function, FIG. 2(b) is a plan view of the polarization separation means and polarization rotation means, and FIG. 2(C) is a front view.

The polarization rotation means (21) includes total reflection surfaces (2
1a), (21b) and slopes (21c), (21d)
It is in the form of a total reflection prism composed of Of the slope, the right half (21
In c), a reflective optical path conversion means is formed as shown by diagonal lines. The light ray (30) that enters the polarization rotation means (21) from the half surface (21d) on which the optical path conversion means is not formed of the slope is 4
5'' linearly polarized light (amplitude E,), and is divided into equal amplitude orthogonal components Xy, as shown in the circle at the bottom left of the figure.However, the direction of y is The incident light beam (30) is parallel to the total reflection surface (21a), as shown in the figure.
(21b) and reflected light path converting means (21C).
). The light beam reflected by the optical path conversion means (21c) is sequentially reflected by the total reflection surface (21b) and (21a), and exits from the left half surface (21d) of the slope, and becomes the light beam (31).
becomes. Here, the conditions for total reflection are: ■ The reflectance of x and y polarized light is almost equal. ■ The phase difference when total reflection of polarized light in x and y directions is determined by the total reflection surface (21a) and (21b). It becomes 180@ by 4 reflections.

When these two conditions are satisfied, the polarized light E2 of the emitted light beam (31) becomes linearly polarized light orthogonal to El as shown. The above condition (2) is necessarily satisfied if total reflection occurs at the surfaces (21a) and (21b). As shown in Fig. 2(a), the light ray (30) is incident on the surface (21a) at an angle of 45'', and the surface (21a) is
21b), the conditions for total reflection are (1) where the refractive index of the prism is n.
) is given by the formula.

n＞r d　　　・・・・・・(I) However, it was assumed that the medium outside the prism was air.

Next, the above condition (2) will be explained.

X caused by a single total internal reflection at 45″ incidence.

The phase difference Δ between y-polarized light is expressed as Δ□2 (tan −' (n digits)) −tan−' where n is the refractive index of the prism glass material.
(n-' 1-7]))...(n). As mentioned above, total reflection occurs a total of four times due to reflection by the optical path converting means (21C), so the output light beam (
31), the phase difference between the x and y polarized light is 4Δ. When calculating 4Δ by substituting n-1,55378 into equation (■), it becomes 4Δ=A (m). Therefore, in the vicinity of n-1,55378, Figure 2 (
A phase difference of 180 @ occurs between the x and y components of the reflected light (31) shown in a) compared to the state of the incident light (30). Therefore, as shown in the lower right circle of Fig. 2(a), the polarization direction (E,) of the emitted light (3I) is 90° with respect to E.
"rotates. Note that the slope of the polarization rotation means (21) (or the second
As shown in Figures (b) and (C), one half of the surface above the polarization separation means (20) is the transmitting surface, and the other half is the reflective optical path conversion means surface, with the intersection line (22) as the boundary. (shown with diagonal lines).

In FIG. 1, S reflected by the polarization separation means (20)
Since the polarized light (30) is linearly polarized light making an angle of 45° with respect to the intersection line (22), it is reflected in the direction of travel opposite to the incident light with the polarization direction rotated by 90@ by the polarization rotation means (21). The light enters the polarization separation means (20) again as P-polarized light (31), and exits the polarization separation means (20) as transmitted P-polarized light (32). In addition, the polarization rotation means (21)
As a prism glass material whose refractive index n is around 1°55378, P CD 3 (n
a”1.55232), Sb F l (n
n=1.55115), BaL manufactured by 5CHOTT
F8 (na=1.55361), P S K'
3 (n, = 1.55232, etc.) is suitable.

However, other glass materials such as HOY A or S Cl-10TT BK7 (n n=1
．． 5168) can also be used in the present invention, although the degree of improvement is lower than that of the above-mentioned glass materials. This is because the light ray (31), which is slightly elliptically polarized because the given phase difference is not 180', passes through the polarizing beam splitter (20) and is converted into P-polarized light (32), and the light ray (33a), (33b
) 0) This is because the polarization directions are the same.

[Other Embodiments] Next, a second embodiment of the present invention will be described with reference to FIG. 3. In the figure, (23a) and (23b) are reflective optical path changing means. The unpolarized illumination light (2) emitted from the light source (1) is separated into reflected S-polarized light (33a) and transmitted P-polarized light (30) by the polarization separation means (20).

The transmitted P-polarized light enters the polarization rotation means (21). Similar to the first embodiment, the polarization rotation means (21) includes orthogonal total reflection surfaces (21a), (21b) and It is constituted by a total reflection prism with reflective optical path conversion means (21C) provided on one half of the slope. The transmitted P-polarized light (30) is the intersection line (
22), the polarization direction is rotated by 90'' by the polarization rotation means (21), resulting in S-polarized light (31) traveling in the opposite direction to the light beam (30). (20) becomes reflected S-polarized light (32),
It is reflected by the optical path conversion means (23a) and (23b) to become linearly polarized light (33b) having the same polarization direction and traveling direction as the above-mentioned reflected S-polarized light (33a), and passes through the condenser lens (10) to the liquid crystal light valve. (3). The polarization axis of the incident-side polarizing plate (8) is aligned with the direction of the incident linearly polarized light (33a), (33b), and compared to the conventional case where non-polarized illumination light is incident, Approximately twice as much light energy enters the liquid crystal layer and contributes to image display. As in the conventional example, the light emitted from the liquid crystal light valve is converted into a projection light (110) by a projection lens (4).
The image is enlarged and projected onto the screen (5).

Next, a third embodiment of the present invention will be described with reference to FIG.

This embodiment uses the same polarization separation means (20) and polarization rotation means (21) as in FIG. 1 showing the first embodiment.

This is an example in which the optical path conversion means (23) is applied to the optical system shown in FIG. 7, which shows the second conventional example. Similarly to the first embodiment, the light beam (
33a) and (33b) are linearly polarized lights having the same polarization direction and traveling direction. In addition, the incident side polarizing plate (8
The polarization axes of R), (8G), and (8B) are rays (33a
), (33b) are arranged in the same direction as the polarization direction. With the above configuration, as in the first embodiment, it is possible to reduce optical energy loss due to the polarizing plate on the incident side of the liquid crystal light valve.

In each of the above embodiments, the direction of the reference angle in which the intersection line of the orthogonal reflecting surfaces forms 45'' has been described, but it goes without saying that this angle has a degree of freedom. ) or (3R), (3G), (
3B) entrance side polarizing plate (8) or (8R).

We have explained the case where (8G>, (8B) is used in the same way as in the conventional configuration. However, since the light beams (33a) and (33b) generated from the light beam (2) are linearly polarized,
LCD light valve (3) or (3R), (3G),
(3B) is the incident side polarizing plate (8) or (8R),
Image formation is possible without using (8G) and (8B). In addition to optical loss due to polarization selection characteristics, the polarizing plate has absorption loss due to the material itself, but as described above, the incident side polarizing plate (8) or (8R).

If (8G) and (8B) are omitted, absorption loss of the material is eliminated, so a projection display device with higher brightness can be realized.In addition, each embodiment of the present invention can be used as a transmissive type liquid crystal light valve. However, projection type display devices using reflective liquid crystal light valves are also known.Polarization separation means (20) and polarization rotation means (21), which are the core of the present invention, are
), optical path conversion means (23) or (23a), (23
The linearly polarized optical system consisting of b) can be applied without problems to devices using reflective liquid crystal or light valves. moreover,
In the above embodiments, the liquid crystal light valve has been explained using a method that utilizes the optical rotation of the liquid crystal as an example, but there are also methods that electrically control the birefringence of the liquid crystal, such as E C
B (electrically control
d birefringence) form etc. are also known,
It goes without saying that the present invention can also be applied to projection display devices that use liquid crystal light valves that require these incident-side polarizing plates. Further, the number of light valves is not limited to three, but three or more, or even one or two light valves may be used (applicable).

[Effects of the Invention] As detailed above, according to the projection display device of the present invention, the unpolarized (naturally polarized) illumination light beam emitted from the light source is directed into a straight line having a polarization direction in which it should be incident on the liquid crystal light valve. Since it is equipped with an optical means for converting into polarized light, the amount of light that passes through the polarizing plate on the incident side of the liquid crystal light valve is doubled, making it possible to realize a high-brightness projected image. Furthermore, it is possible to reduce deterioration of polarization characteristics due to heat generation of the polarizing plate on the incident side and fluctuations in operating characteristics of the liquid crystal, which have been problems in the past. Furthermore, by omitting the polarizing plate on the incident side of the liquid crystal light valve, which was conventionally necessary, there is no absorption loss in the material of the polarizing plate itself, so a simpler projection display device with higher brightness can be realized.

[Brief explanation of drawings]

1.3.4 are explanatory diagrams showing the optical system of the projection type display device in Examples 1 and 2.3 of the present invention, respectively, and FIG. 2 is an illustration of the polarization rotation means used in the projection type display device of the present invention. Explanatory diagram of operating principle and configuration 1. 5.7 is an explanatory diagram of the optical system of a conventional projection display device, and FIG. 6 is an explanatory diagram of the operating principle of a liquid crystal light valve. In the figure, <3
), (3R), (3G), (3B) are liquid crystal light valves, (4) are projection lenses, (1) are light source means, (2
0) is a polarization separation means, (21) is a polarization rotation means, (21
a), (21b) are total reflection surfaces in the polarization rotation means, (2
1C) is a reflective optical path conversion means in the polarization rotation means (21);
(23), (23a), and (23b) are optical path changing means. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] An optical system comprising a liquid crystal light valve for forming an image, a projection lens for enlarging and projecting the image formed on the liquid crystal light valve, and a light source means for emitting a non-polarized light flux to illuminate the light valve. a projection type display device having a polarization separation means for separating the unpolarized light beam into first and second linearly polarized light beams;
a total reflection prism having a total reflection surface and an inclined surface, the intersection line of the total reflection surface is the direction of a reference angle that forms 45 degrees with the polarization direction of the second linearly polarized light beam, and the intersection line of the inclined surface A reflection mirror is formed on a half surface with a boundary of The light beam is reflected in the order of the reflecting surfaces and guided to the reflecting mirror, and the light beam reflected by the reflecting mirror is guided to the second total reflecting surface,
Polarization rotation means for causing a third linearly polarized light beam, which is reflected in the order of the first total reflection surface and whose polarization direction has been rotated by 90 degrees with respect to the second linearly polarized light beam, to be re-injected into the polarization separation means;
an optical path in which a light beam obtained by the third linearly polarized light beam re-entering the polarization separation means and then exiting is a fourth linearly polarized light beam having the same traveling direction and polarization direction as the first linearly polarized light beam; A projection type display device, comprising: a conversion means, and illuminates the liquid crystal light valve with the first linearly polarized light beam and the fourth linearly polarized light beam.