JPH08220531A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: To provide the small liquid crystal display device capable of being easily manufactured. CONSTITUTION: A prism sheet 5 allows light from a light source 1 to be changed in its progressing direction, and also allows it to be injected to a hologram 9 at a specified angle. A first and a second hologram element 10 and 11 are formed in the hologram 9. The first hologram element 10 allows injected light to be divided into p polarizing light and s polarizing light, allows the p polarizing light to pass through as it is, and also allows the s polarizing light to be primarily diffracted. The second hologram element 11 allows the p polarizing light to pass through as is, and also allows the s polarizing light to be primarily diffracted. A mirror 13 allows the p polarizing light progressing to the outward of the second hologram element 11 to be reflected. By these constitution, the s polarizing light is injected to the center section of a prism sheet 12, and the p polarizing light is injected to the end sections of the sheet. The prism sheet 12 converts both the p polarizing light and the s polarizing light roughly into parallel light. A λ/2 polarizing plate 29 is disposed in the light path of the p polarizing light, and converts the p polarizing light into the s polarizing light with its polarizing direction rotated by 90 deg.. Both the p polarizing light and the s polarizing light going out of a polarizing light conversion optical system 2 illuminate a liquid crystal display panel 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device having a transmissive liquid crystal display panel and a light source, and more particularly to a small size and high brightness liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, there has been known a liquid crystal display device which displays an image by allowing light from a light source to enter a transmissive liquid crystal display panel. This liquid crystal display device includes a type in which the display surface of the liquid crystal display panel is used as a screen and a type in which the image light transmitted through the liquid crystal display panel is enlarged and projected on the screen by a projection lens.

Conventionally, both of the above-mentioned types have a structure in which light from a light source is directly incident on a liquid crystal display panel. However, the above configuration has a problem that the brightness of the display image is significantly lower than the brightness of the light from the light source. This is an indefinite polarized light because the liquid crystal display panel is provided with polarizing plates on its entrance surface and exit surface, and only linearly polarized light that passes through the polarizing plate on the entrance surface side enters the liquid crystal display panel. Even if the polarizing plate on the incident surface side is ideal, the light from the light source is used for only 50% at maximum.

In order to solve the above problems, there is known a liquid crystal display device using a polarization conversion optical system for converting indefinitely polarized light of a light source into linearly polarized light with high light utilization efficiency (Japanese Patent Laid-Open No. 61-61). -90584). FIG. 11 is a configuration diagram showing the liquid crystal display device. The polarization conversion optical system 56 is the light source 5
A polarization beam splitter 5 having a polarization splitting surface 52 for splitting the projection light from 1 into p-polarized light B _p and s-polarized light B _s which are two linearly polarized lights whose polarization directions are orthogonal to each other.
5 and the total reflection surface 5 of the prism for reflecting the s-polarized light B _s
3 and the s-polarized light B _s disposed in the optical path of the s-polarized light B _s.
It is composed of a λ / 2 polarizing plate 54 for rotating the polarization direction of 90 ° into p-polarized light B ′ _p and a liquid crystal display panel 57.

With this configuration, all the projection light, which is the indefinite polarized light from the light source 51, is made into the p-polarized light, and the liquid crystal display panel 57 can be efficiently illuminated.

FIG. 12 shows the display surface 5 when the outgoing beam from the polarization conversion optical system 56 enters the liquid crystal display panel 57.
It is a figure which shows the beam shape on 7s. in this way,
The entire surface of the display surface 57s of 4: 3 or 16: 9 can be illuminated.

[0007]

The size of the liquid crystal display panel used in the liquid crystal display device is usually 3 inches to 4 inches or more because it is necessary to secure a certain resolution.

In the conventional liquid crystal display device, the area of the light incident surface 55s of the polarization beam splitter 55 of the polarization conversion optical system 56 is 1 / the area of the display surface 57s of the liquid crystal display panel 57.
It is necessary to be about 2, and even if the liquid crystal display panel 57 is 3 inches to 4 inches, it is considerably large.

When the polarization beam splitter 55 becomes large, the area of the polarization separation surface 52 becomes large, and it becomes difficult to provide uniform polarization separation performance there. For this reason,
The separation efficiency of the p-polarized light and the s-polarized light in the polarization beam splitter 55 becomes low, and the utilization efficiency of the incident light in the liquid crystal display panel 57 becomes low. Further, there is a problem that the manufacturing cost increases when the volume of the polarization beam splitter 55 increases.

Further, since the thickness of the polarization beam splitter 55 becomes large, there is a problem that the liquid crystal display device becomes large in size.

In view of the above points, an object of the present invention is to provide a high-intensity liquid crystal display device which is easy to manufacture and small in size.

[0012]

A liquid crystal display device according to claim 1, wherein a hologram for separating the incident light into p-polarized light and s-polarized light in the optical path of the incident light from the light source to the liquid crystal display panel. A polarization conversion optical system including an element is provided.

In the liquid crystal display device according to the second aspect, the traveling direction of the light from the light source is changed, and the first prism sheet which emits at a predetermined angle and the light emitted from the first prism sheet are emitted. The first hologram element for separating the polarized light and the s-polarized light to transmit the p-polarized light and diffracting the s-polarized light in the first order, and the first hologram element are arranged substantially parallel to the first hologram element. Second p-polarized light emitted from the hologram element is transmitted while s-polarized light is first-order diffracted.
Of the hologram element, a light reflecting element which is arranged substantially perpendicular to the second hologram element and which is arranged behind the second hologram element and which reflects p-polarized light traveling to the outside of the second hologram element; A second prism sheet that converts the emitted light and the light reflected by the light reflecting element into substantially parallel light and emits it to the liquid crystal display panel, and either p-polarized light or s-polarized light that enters the liquid crystal display panel. And a polarization conversion optical system including a deflecting and rotating element which is disposed in the optical path of and which rotates its polarization plane by 90 °.

[0014]

In the liquid crystal display device according to the first aspect, the hologram element is used as a means for converting the indefinite polarized light from the light source into the linearly polarized light. The hologram element can be relatively easily and uniformly manufactured by a method generally used for manufacturing ICs. Therefore, unlike the case where the conventional beam splitter is used, the conversion efficiency does not decrease due to the non-uniformity of the polarization separation surface, the liquid crystal display panel can be efficiently illuminated, and the brightness of the liquid crystal display device increases. .

According to the liquid crystal display device of the second aspect, the polarization conversion optical system for converting the indefinite polarized light from the light source into the linearly polarized light can be downsized, and the device itself can be downsized. can do.

[0016]

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

FIG. 1 is a schematic configuration diagram showing a liquid crystal display device of the present invention. The liquid crystal display device includes a light source 1, a polarization conversion optical system 2, and a liquid crystal display panel 3. The polarization conversion optical system 2 includes a first prism sheet 5, a second prism sheet 12, a first hologram element 10 on the entrance surface and an exit surface,
The hologram block 9 is formed with the second hologram element 11, the mirror 13, and the deflection rotation element (here, a λ / 2 polarizing plate is used) 29.

FIG. 2 is a partially enlarged view for explaining the operation of the polarization conversion optical system 2. The operation of the polarization conversion optical system 2 will be described below with reference to FIGS.

The first prism sheet 5 has an apex angle of 60 °, and changes the traveling direction of the incident light B ₁ from the light source 1 by the prism surfaces 5a and 5b having an apex angle of 60 °. The light is incident on the block 9 at an angle of ± 60 °. This is because the diffraction efficiency of the hologram element is generally high when the light is incident at an angle of ± 60 °.

The first hologram element 10 receives the incident light B ₁
Is split into p-polarized light B _{1 p} and s-polarized light B _{1 s} , p-polarized light B _{1 p} is transmitted as it is, and s-polarized light B _{1 s} is first-order diffracted. The light that has entered the hologram block 9 propagates at an angle different from the incident angle (± 60 °) due to the refractive index of the glass.

The p-polarized light B _{1 p} and the s-polarized light B _{1 s that} have passed through the first hologram element 10 enter the second hologram element 11, where the p-polarized light B _{1 p} is directly transmitted, The s-polarized light B _{1 s} is first-order diffracted again and emitted from the hologram block 9.

Of the p-polarized light B _{1 p} , the light that travels outward from the end of the second hologram element 11 is totally reflected by the mirror 13 (not shown in FIG. 2), and the other light travels as it is. Then, the light enters the second prism sheet 12. The second prism sheet 12 has an apex angle set to 60 °, and converts the incident light into substantially parallel light and emits it.

The s-polarized light B _{1 s} is transmitted through the λ / 2 polarizing plate 2
The polarization plane is rotated 90 ° by 9 to become p-polarized light B ′ _{1 p} , which is emitted from the polarization conversion optical system 2 together with p-polarized light B _{1 p} and illuminates the liquid crystal display panel 3. This λ / 2 polarizing plate 2
9 may be arranged in front of the second prism sheet 12.

FIG. 3A shows the polarization conversion optical system 2 having the above construction.
In a diagram showing a region X to obtain a through p-polarized light B _{1 p,} FIG. 3 (b) is a diagram showing an area Y to obtain street s-polarized light B _{1 s.} In this way, in the polarization conversion optical system 2,
On the prism sheet 12 of p-polarized light B _{1 p} and s
The region where the polarized light B _{1 s} enters is completely separated,
The p-polarized light B _{1 p} is incident on the end portion of the second prism sheet 12, and the s-polarized light B _{1 s} is incident on the central portion of the second prism sheet 12. Therefore, only the s-polarized light B _{1 s} is λ /
It can be rotated by 90 ° by the two polarizing plates 29, and the polarization direction of the emitted light can be aligned.

As described above, in this example, the polarization direction of the light from the light source 1 is converted by using the first hologram element 10 and the second hologram element 11. These hologram elements 10 and 11 can be relatively easily and uniformly manufactured by digging hologram lattice grooves on both surfaces of a glass plate by using a method generally used in IC manufacturing. Therefore, unlike the case where the beam splitter 55 of the conventional example of FIG. 11 is used, the conversion efficiency is not reduced due to the non-uniformity of the polarization separation surface, the liquid crystal display panel 3 can be efficiently illuminated, and the liquid crystal display can be displayed. The brightness of the device is increased.

Further, according to the polarization conversion optical system 2 of this example,
The beam shape on the display surface 3s of the liquid crystal display panel 3 is as shown in FIG. 4, and the incident light is used for liquid crystal display with almost no waste. Therefore, the light utilization efficiency is higher than that of the conventional one shown in FIG.

In this example, all the incident light from the light source 1 is made into p-polarized light by the polarization conversion optical system 2, but λ /
By changing the arrangement of the two polarizing plates 29, it is possible to make the light s-polarized.

FIG. 5 is a block diagram showing another example of the polarization conversion optical system of the liquid crystal display device of the present invention. This polarization conversion optical system 2'includes, instead of the hologram block 9 of the polarization conversion optical system 2 shown in FIG. 1, a first hologram plate 30 having a first hologram element formed on one surface and a second hologram plate. The second hologram plate 31 on which elements are formed is used. Therefore, the increase in the thickness of the polarization conversion optical system due to the refractive index of glass can be suppressed more than in the case of FIG. By using this polarization conversion optical system 2 ', when the incident angle is ± 60 °, the thickness of the polarization conversion optical system can be reduced to about √3 / 3 times that of the conventional example shown in FIG. .

FIG. 6 is a block diagram showing still another example of the polarization conversion optical system. The polarization conversion optical system 66 is composed of hologram plates 61, 62, 63, 64 and a λ / 2 polarizing plate 65. The hologram plates 61 and 62 are arranged so that the light from the light source is incident at an angle of ± 60 °, and there, the incident light is separated into p-polarized light B _{3 p} and s-polarized light B _{3 S.} p-polarized light B _{3 p} is as straight, lambda / 2 the polarization plane by the polarizing plate 65 is rotated 90 ° s-polarized light B _'3
s , which is emitted from the polarization conversion optical system 66. The s-polarized light B _{3 s} is first-order diffracted by the hologram plates 61 and 62, then enters the hologram plates 63 and 64, is first-order diffracted again, and is emitted from the polarization conversion optical system 66.

Also in this polarization conversion optical system 66, similarly to the polarization conversion optical systems 2 and 2'shown in FIGS. 1 and 5, the indefinite polarized light from the light source is converted into the linearly polarized light having the uniform plane of polarization. It is possible to efficiently enter the liquid crystal display panel.
However, the thickness of the polarization conversion optical system 66 is larger than that of the conventional example.

The polarization conversion optical system used in the liquid crystal display device of the present invention is not limited to the one shown in FIGS. 1, 5 and 6, and the polarization direction of incident light is aligned by using a hologram element. Anything can be used.

Further, in the above example, the case where the incident angle of light on the hologram element is 60 ° has been described, but the present invention is not limited to this, and the polarization conversion optical systems 2 and 2 shown in FIGS. In the case of ', the thickness can be made thinner by setting the incident angle larger. However, it is necessary to adjust the shape of the hologram element according to the incident angle of light so that the diffraction efficiency of the s-polarized light and the transmission efficiency of the p-polarized light with respect to the incident angle become a certain level or more.

The above is the outline of the liquid crystal display device of the present invention. The following is a concrete example of the shape of the hologram element when the incident angle of light is 60 °, and the liquid crystal display device of the present invention is a projection type liquid crystal display. An example applied to the device is shown.

As the shape of the hologram element, for example,
There are a sinusoidal shape shown in FIG. 7A and a rectangular shape shown in 7B. In the figure, d indicates the pitch and h indicates the depth.

First, the hologram element having the shape shown in FIG. 7A will be described. FIG. 8 is a graph showing the result of numerical calculation of the diffraction characteristics. This is because the refractive index of the hologram element is n = 1.66 and the Bragg incidence angle θ _B =
sin ^- a calculation result of the diffraction efficiency when diffracted by ¹ (λ / 2d) (wavelength of lambda is the incident light). The vertical axis represents the diffraction efficiency of the transmitted first-order diffracted wave, and the horizontal axis represents λ divided by d. Further, here, h / d is 1.5 (see FIG.
(A)) and 2.0 (FIG. 8 (b)) are calculated.

From FIG. 8, the diffraction efficiency of p-polarized light becomes smaller than that of s-polarized light in the region of λ / d = 1.0 to 1.2 or more, and p-polarized light and s-polarized light can be separated. You can see that. When h / d = 1.5, 1.4
In the range of 5 <λ / d <1.62, the diffraction efficiency of s-polarized light is 80% or more and the diffraction efficiency of p-polarized light is 20% or less (transmission efficiency is 80% or more), which is used in the present invention. It can be seen that the hologram element has preferable characteristics. h / d
In the case of = 2.0, it can be seen that the above-mentioned characteristics are obtained in the range of 1.55 <λ / d <1.97.

Next, the hologram element having the shape shown in FIG. 7B will be described. FIG. 9 is a graph showing the result of numerical calculation of the diffraction characteristics. The vertical axis represents the diffraction efficiency when light is incident at an incident angle of ± 60 °, and the horizontal axis is λ / d. In the calculation, the refractive index of the hologram element is 1.454, and h / d = 1.6 (see FIG. 9).
(A)), 2.0 (FIG. 9 (b)). From the figure, h / d = 2.0 and 1.62 <λ / d <
In the case of 1.85, the diffraction efficiency of s-polarized light is 80% or more, and the diffraction efficiency of p-polarized light is 20% or less (transmission efficiency is 8% or less).
It becomes 0% or more), and it can be seen that it can be used as the hologram element of the present invention.

As described above, in the hologram element having the shape shown in FIG. 7B, when the incident angle is 60 °, h / d
= 2.0 and λ / d is 1.62 to 1.85, good diffraction characteristics are obtained, but under this condition, it is difficult to efficiently diffract all light in the visible wavelength region. Therefore, it is desirable to use three types of hologram elements that match light of three types of wavelengths, red (R): 650 nm, green (G): 550 nm, and blue (B): 450 nm.

Specifically, the pitch for R is d = 0.3.
73 μm, depth h = 0.746 μm hologram element (r), pitch d = 0.318 μm for G, and hologram element (g) depth h = 0.636 μm for B, pitch d = 0. 259 μm, depth h = 0.518 μ
If the hologram element (b) of m is used, λ = 605 nm to 691 nm for R and λ = 515 for G.
nm to 588 nm, for B, λ = 420 to 480 n
In the range of m, the diffraction efficiency of s-polarized light in the hologram element is 80% or more, and the diffraction efficiency of p-polarized light is 20%.
Below (transmission efficiency is 80% or more), it can be seen that indefinite polarized light from the light source can be efficiently converted into linearly polarized light.

In the sinusoidal hologram element shown in FIG. 7A, it is desirable to use three kinds of hologram elements for the same reason.

Next, the above three types of hologram elements are replaced with the first hologram element 1 of the polarization conversion optical system 2 of FIG.
An example of a projection type liquid crystal display device applied to the 0, 2nd hologram element 11 will be described. FIG. 10 is a configuration diagram thereof.

In FIG. 10, polarization conversion optical systems 19 and 2
Reference numerals 0 and 21 denote the first hologram element 10 and the second hologram element 11 of the polarization conversion optical system 2 of FIG. 1, respectively.
The hologram elements (r), (g), and (b) described above are used.

Of the light emitted from the light source 14, the red light R
Is reflected by the first dichroic mirror 15.
The red light R has its polarization direction aligned by the polarization conversion optical system 19 including the hologram element (r), illuminates the liquid crystal panel 22, and passes through the lens 25.

The green light G of the light transmitted through the first dichroic mirror 15 is reflected by the second dichroic mirror 16 and enters the polarization conversion optical system 20 including the hologram element (g). , The liquid crystal panel 23 is illuminated with the polarization directions aligned and transmitted through the lens 26.

The blue light B transmitted through the second dichroic mirror 16 has its polarization direction aligned by the polarization conversion optical system 21 having the hologram element (b), and enters the liquid crystal panel 24, and the lens 27. Through.

The light transmitted through the lenses 25, 26 and 27 is combined by the fourth dichroic mirror 17 and the fifth dichroic mirror 18, and the projection lens 28 is used.
Image on the screen via.

Even in such a projection type liquid crystal display device, the incident light from the light source 1 can be efficiently used by the polarization conversion optical systems 19, 20, 21 and the brightness of the display screen is improved. In addition, the polarization conversion optical system 19, 20, 2
Since the thickness of 1 can be reduced, the liquid crystal display device can be downsized.

[0048]

In the liquid crystal display device according to the first aspect, since the hologram element is used in the polarization conversion optical system, the p-polarized light and the s-polarized light can be uniformly separated, and the liquid crystal display panel can be used. The amount of light that can be supplied is increased, and the brightness of the liquid crystal display device can be improved.

Further, the polarization conversion optical system can be easily manufactured at low cost.

In the liquid crystal display device according to the second aspect, since the thickness of the polarization conversion optical system can be reduced, the liquid crystal display device can be downsized.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of a liquid crystal display device of the present invention.

FIG. 2 is a partially enlarged view of the polarization conversion optical system of FIG.

FIG. 3 is a diagram showing a region where (a) p-polarized light and (b) s-polarized light can travel.

4 is a diagram showing the shape of an incident beam on the liquid crystal display panel of FIG.

FIG. 5 is a configuration diagram showing another example of a polarization conversion optical system.

FIG. 6 is a configuration diagram showing still another example of the polarization conversion optical system.

FIG. 7 is a configuration diagram showing a specific example of the shape of a hologram element.

FIG. 8 is a graph showing the diffraction efficiency of a sinusoidal hologram element.

FIG. 9 is a graph showing the diffraction efficiency of a rectangular hologram element.

FIG. 10 is a configuration diagram showing an example of a projection type liquid crystal display device.

FIG. 11 is a configuration diagram showing a conventional liquid crystal display device.

12 is a diagram showing the shape of an incident beam on the liquid crystal display panel of FIG.

[Explanation of symbols]

 1, 14 Light source 2, 2 ', 19, 20, 21, 66 Polarization converting optical system 3, 22, 23, 24 Liquid crystal display panel 5, 12 Prism sheet 10 First hologram element 11 Second hologram element 13 Mirror 29 , 65 λ / 2 polarizing plate 30 First hologram plate 31 Second hologram plate 61, 62, 63, 64 Hologram plate B1s, B3s, B'3s s polarized light B1p, B'1p, B3p p polarized light

Claims (2)

[Claims] 1. A liquid crystal display device comprising a liquid crystal display panel and a light source for illuminating the liquid crystal display panel, wherein light from the light source is p-polarized light in an optical path from the light source to the liquid crystal display panel. A liquid crystal display device comprising a polarization conversion optical system including a hologram element for separating light into s-polarized light and s-polarized light. 2. A liquid crystal display device comprising a liquid crystal display panel and a light source for illuminating the liquid crystal display panel, the first light source changing the traveling direction of the light from the light source and emitting the light at a predetermined angle. The prism sheet and the light emitted from the first prism sheet are converted into p-polarized light and s
A first hologram element that separates the polarized light into the p-polarized light and transmits the p-polarized light and diffracts the s-polarized light in the first order; and the first hologram element is arranged substantially parallel to the first hologram element. A second hologram element that transmits the light and transmits the s-polarized light in the first order; and a second hologram element that is disposed behind the second hologram element and substantially perpendicular to the second hologram element. A light-reflecting element that reflects the p-polarized light traveling outward from the second hologram element, and the light emitted from the second hologram element and the light reflected by the light-reflecting element are converted into substantially parallel light, and the liquid crystal display panel And a second prism sheet that emits light to the liquid crystal display panel, and is disposed in an optical path of one of the p-polarized light and the s-polarized light that enters the liquid crystal display panel and has a polarization plane of 90 degrees.
A liquid crystal display device comprising a polarization conversion optical system including a deflection rotation element that rotates by a degree.