JP3230377B2 - Optical wobbling display by polarization rotation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device for improving resolution by combining a mosaic display device such as an LCD and an optical system for rotating a polarization and an optical path.

[0002]

2. Description of the Related Art Using an LCD (Liquid Crystal Display),
LCD to display on the screen with backlight
Projectors are known. Current LCD projectors use a polarizing screen to improve contrast deficiency because they are difficult to see in a bright room. The principle is as follows. The display light emitted from the LCD is a linearly polarized wave. Therefore, when the display light is projected and displayed on a polarizing screen having a polarization direction corresponding to the polarization plane of the display light,
The display light appears to be totally reflected, but the disturbance light is reduced because only one of the vertical and horizontal polarized waves is reflected, and the contrast of the display light is increased.

On the other hand, in order to perform interlaced display on an LCD, the number of pixels in the vertical direction is required to be twice that in non-interlaced display. However, LCD
When the number of pixels is increased to increase the resolution, the aperture ratio is deteriorated, and the production yield is deteriorated due to the occurrence of a bright spot defect, so that the cost is increased.

Accordingly, the present applicant has filed an earlier application (Japanese Patent Application No. Hei.
No. 16955) proposed a resolution improving method and apparatus capable of increasing the apparent number of pixels optically without increasing the number of pixels. The principle is as follows. A light path changing means is provided between the LCD and the viewer or the screen. For example, when the light path is changed for each field in the vertical direction, the image information of the odd field and the image information of the even field are changed according to the change of the light path. Display on LCD. The image information of these odd and even fields is displayed on the same pixel on the LCD. However, since the optical path is changed and shifted in the vertical direction, the image position is apparently shifted between the odd and even fields. And an image equivalent to an interlaced display image is obtained. That is, apparently, the number of pixels appears to be doubled in the vertical direction. Such an approach is called an optical wobbling system.

FIG. 1 shows the principle of an optical wobbling system in which a polarization plane rotating element using a ferroelectric liquid crystal (hereinafter, FLC) and a birefringent optical element are used as an optical path changing means.

Reference numeral 1 denotes L using a TFT (thin film transistor).
It is a CD, and a light beam from a backlight light source is transmitted toward a viewer or a screen to be displayed light. The transmitted light (display light) becomes a linearly polarized wave by the action of the liquid crystal. Reference numeral 2 denotes a birefringent optical element, which is composed of, for example, a quartz plate, calcite, a liquid crystal plate, or the like, has a different refractive index depending on the rotation angle of the plane of polarization of incident light, and refracts normal light and abnormal light. 3 is π
This is a polarization plane rotation element also called a cell.
And the birefringent optical element 2. The polarization plane rotation element 3 is a glass plate 3 with a transparent electrode on both sides of the FLC 31.
2, 33 are attached. A drive circuit 4 is provided between the transparent electrodes of the glass plates 32, 33 with transparent electrodes.
, A liquid crystal driving voltage is applied, and the polarization plane is rotated and changed for each field.
And the polarization planes of the normal light and the extraordinary light. A phase compensation film 34 is provided on the outer surface of the glass plate 33 with a transparent electrode.

When the normal light of the birefringent optical element 2 is, for example, vertical polarization (= 90 ° of polarization) and the extraordinary light is horizontal polarization (= 0 ° of polarization), the polarization plane rotation element 3 The plane of polarization is rotated by 90 ° and 0 ° for each field. The liquid crystal drive voltage for this is formed by the drive circuit 4. In other words, the drive circuit 4 adjusts the amplitude of the frame synchronization signal, which is phase-synchronized with the discrimination signal of the odd field and the even field, to obtain a liquid crystal drive voltage, which is applied between the transparent electrodes of the polarization plane rotation element 3. Thereby, the polarization plane rotation element 3
Is, for example, to change the plane of polarization from 0 ° to 90 ° in an odd field.
In the even field, the polarization plane is changed from 90 ° to 0 °,
Rotate each.

[0008] In the prior art as described above, the LCD
The linearly polarized wave from the display surface of No. 1 is converted by the polarization plane rotation element 3 into
By changing the plane of polarization for each field, the birefringent optical element 2
To the polarization planes of the normal light and the extraordinary light. In this way, the display light rays from the same pixel position of the LCD 1 are also refracted by the birefringent optical element 2 with different refractive indexes for each field, and are incident on the viewer or the screen. As a result, the display light beam emitted from the same pixel is viewed or displayed on the screen as if emitted from a position shifted by Δx every field, and the pixel pattern is optically shifted. The relational expression at this time is as follows: When the thickness of the birefringent optical element 2 is d, the shift amount Δ
x becomes Δx = d * tan θ. Where θ is the separation angle,
* Indicates multiplication. Therefore, this shift amount ΔX is 1
If it is set so as to be の of the scanning line interval of the field, it becomes possible to perform interlaced display with the apparently doubled number of pixels while maintaining the number of pixels of the LCD 1 as the number of pixels of one field.

[0009]

However, in the pixel doubling optical wobbling system (FIG. 5) described in the earlier application (Japanese Patent Application No. 5-16955), the polarization plane of the display output light is set to 0/90 degrees. When a polarizing screen is used to alternately rotate and project both horizontal and vertical polarized wave images, the field image of one polarized wave that does not match the polarization direction of the polarizing screen becomes invisible and flicker occurs. As it is, the benefits of improving the resolution and improving the contrast as in the prior art cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to eliminate flicker from a conventional contrast improving polarizing screen or to improve contrast as compared with the conventional screen. It is an object of the present invention to provide an optical wobbling display device that uses polarization rotation and can double the number of pixels.

[0011]

In order to achieve the above object, an optical wobbling display device using polarization rotation according to the present invention comprises a mosaic display device which emits linearly polarized display light, and a polarization mosaic display device. A first polarization plane rotation element that rotates the wavefront by 0 and 90 degrees for each field of the video signal, a birefringent optical element that generates an optical path shift between the 0-degree polarization wave and the 90-degree polarization wave, In the optical wobbling display device, the display light emitted from the birefringent optical element, whose polarization plane rotates for each field, passes the 0-degree polarized wave at 0 degree and transmits the 90-degree polarized light. The wave is provided after the birefringent optical element with a second polarization plane rotation element for rotating the polarization plane to 0 degree, and the display light emitted from the second polarization plane rotation element is polarized when the polarization direction is 0 degree. Polarized light that matches the polarized light A mosaic display device which is configured to project and display cleanly or emits linearly polarized display light, and a first mosaic display device which rotates the plane of polarization of the display light to 0 ° and 90 ° for each field of a video signal. , And a birefringent optical element that generates an optical path shift between the 0-degree polarized wave and the 90-degree polarized wave, in each of the fields emitted from the birefringent optical element. A second polarization plane rotating element is provided for the display light whose polarization plane is rotated to rotate the polarization plane of 0 degree to 90 degrees and pass the 90 degree polarization wave at 90 degrees. The display device is provided after the birefringent optical element, and the display light emitted from the second polarization plane rotation element is projected and displayed on a polarizing screen whose polarization direction matches the 90-degree polarized light. .

In the above-described optical wobbling display device, the electrodes of the first polarization plane rotation element and the second polarization plane rotation element are divided into the same plurality of electrodes, and the divided electrodes in the first polarization plane rotation element are divided. The polarization plane rotation control of each electrode is performed in synchronization with the scanning of the mosaic display device, and the polarization plane rotation control of the divided electrodes in the second polarization plane rotation element is interlocked with the first polarization plane rotation element. Performing at the set timing is suitable when a mosaic display device having an afterimage effect is used.

In another optical wobbling display device according to the present invention, a mosaic display device that emits linearly polarized display light, and the polarization plane of the display light is set to 0 degree and 90 degrees for each field of a video signal. An optical wobbling display device comprising: a rotating first polarization plane rotation element; and a birefringent optical element that generates an optical path shift between the 0-degree polarized wave and the 90-degree polarized wave, the light emitted from the birefringent optical element. The second polarization plane rotates the polarization plane of the 90-degree polarized wave to 0 degree while passing the 0-degree polarized wave at 0 degree with respect to the display light whose polarization plane is rotated for each field. A rotation element is provided after the birefringent optical element, and the display light emitted from the second polarization plane rotation element is projected and displayed on a polarization screen whose polarization direction matches the 0-degree polarization light. I do.

[0014]

In the optical wobbling display device using the polarization rotation of the present invention, the polarization plane of the display light is rotated by 0/90 degrees for each field by the first polarization plane rotation element, and is passed through the birefringent optical element. The light path of this field is shifted with respect to the light path of the other field, and apparently the number of pixels is doubled. Further, a second optical element provided after the birefringent optical element is provided.
The polarization plane rotation element rotates the polarization plane of the display light of one of the rotated fields of the polarization plane emitted from the birefringent optical element in the opposite direction, and returns the polarization plane of the field to fixed (usually vertical). By aligning the polarization plane of each field with the polarization direction of the polarizing screen, the same contrast improving effect as that of the conventional contrast improving polarizing screen can be obtained. Further, by using a circular polarization conversion element or a depolarization element instead of the second polarization plane rotation element, when the display light is depolarized and projected and displayed on a screen having different reflection in the polarization direction. In addition, the screens of any fields are made to appear to be reflected, thereby obtaining the above-described effect of doubling the pixels and preventing the occurrence of flicker.

[0015]

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

FIG. 1 is a block diagram of one embodiment of the present invention.
This embodiment is an example in which the same polarization plane rotation element (π cell) that rotates by 0/90 degrees after passing through the birefringent optical element of the conventional optical wobbling display device of FIG. 5 is mounted.

Reference numeral 1 denotes an LCD using, for example, a TFT (thin film transistor), which transmits a light beam from a backlight light source to generate display light. The transmitted light (display light) becomes a linearly polarized wave by the action of the liquid crystal. 2 is a birefringent optical element,
For example, it is composed of a quartz plate, calcite, a liquid crystal plate, or the like, has a different refractive index depending on the rotation angle of the plane of polarization of incident light, and is refracted into normal light and extraordinary light. 3 is a first polarization plane rotation element (π
Cell), which is disposed between the LCD 1 and the birefringent optical element 2. The first polarization plane rotator 3 is configured such that glass plates 32 and 33 with transparent electrodes are adhered to both surfaces of the FLC 31, and a liquid crystal drive from the drive circuit 4 is provided between the transparent electrodes of the glass plates 32 and 33 with both transparent electrodes. A voltage is applied, and the plane of polarization is rotated and changed for each field, so that the plane of polarization of the normal light and the plane of abnormal light of the birefringent optical element 2 match. A phase compensation film 34 is provided on the surface of the glass plate 33 with a transparent electrode. As the polarization plane rotation element,
In addition to the FLC, for example, a configuration using a nematic liquid crystal or the like can be used.

In the present embodiment, a polarizing screen 5 is disposed in front of the birefringent optical element 2, and after the birefringent optical element 2, a second polarization plane rotation element having the same configuration as the first polarization plane rotation element 3 is provided. The element 6 is arranged. That is, in the second polarization plane rotation element 6 as well, the glass plates 62 and 63 with transparent electrodes are attached to both surfaces of the FLC 61, and the outer glass plate 6 with transparent electrodes 6 is formed.
3 is provided with a phase compensation film 64. The liquid crystal drive voltage is applied from the drive circuit 4 in the same manner as the first polarization plane rotation element 3.

When the normal light of the birefringent optical element 2 is, for example, vertical polarization (= 90 ° of polarization) and the extraordinary light is horizontal polarization (= 0 ° of polarization), the first polarization plane rotation element is used. 3 is 1
The polarization plane is rotated between 90 ° and 0 ° for each field.
The liquid crystal drive voltage for this is formed by the drive circuit 4. That is, the drive circuit 4 adjusts the amplitude of the frame synchronization signal, which is phase-synchronized with the discrimination signal of the odd field and the even field, as a liquid crystal driving voltage, and applies the liquid crystal driving voltage between the transparent electrodes of the polarization plane rotation element 3. Thereby, the polarization plane rotation element 3 sets the polarization plane to 0 ° in an odd field, for example.
From 90 ° to 0 °, and in even fields from 90 ° to 0 °. On the other hand, the second polarization plane rotation element 6 is synchronized with the first polarization plane rotation element 3 to
The polarization plane is rotated between 90 ° and 0 ° for each field.
For this purpose, the liquid crystal driving voltage formed by the drive circuit 4 is applied with the same polarity as that of the first polarization plane rotation element 3.

With the above configuration, when the first polarization plane rotation element 3 rotates the polarization plane by 90 degrees, the second polarization plane rotation element 6 is also rotated by 90 degrees so that the display output light can be returned to the original polarization plane. Can be returned to. Conversely, if the second polarization plane rotation element is driven in the opposite phase, the display light in the fixed polarization direction is obtained by rotating the original polarization plane by 90 degrees. In this case, the connection between the second polarization plane rotation element 6 and the drive circuit 4 has a polarity opposite to that of FIG. By matching the polarization direction of the display light that has returned to a constant value with the polarization direction of the polarizing screen 5, the display light of each field is totally reflected by the polarizing screen 5, and the same contrast improving effect as in the related art is obtained.

In the polarizing screen 6, the optical path of one field is shifted by the first polarization plane rotating element 3 and the birefringent optical element 2, and the interlaced full line display can be performed without increasing the number of panel pixels of the LCD 1. . Therefore, the aperture ratio does not decrease because the number of pixels is not increased,
High brightness display is possible. In addition, high-resolution display can be performed by a low-cost mosaic display device such as an LCD having a small number of pixels.

Since the number of pixels in the horizontal direction can be increased, the total number of pixels can be quadrupled. Furthermore, if this method is applied to full interlaced NTSC, HDTV display with 1125 vertical scanning lines is also possible.

When an LCD is used as in the above embodiment, the liquid crystal screen usually has an afterimage function, and the written pixels hold the written state (information) until the next field. In other words, the information of the odd field and the information of the even field are simultaneously stored in one screen. In the above embodiment, since the entire screen is shifted at the same time, a field screen to be shifted and a field screen not to be shifted are shifted together. Even when a mosaic display device having such an afterimage effect is used, the effect is actually recognized on about half of the screen. However, in such a case, in order to improve the resolution, it is desirable that only the same field of the screen is shifted as much as possible in synchronization with the vertical scanning. A preferred embodiment in such a case will be described below.

FIG. 2 shows an example in which only the same field is shifted as much as possible in synchronization with vertical scanning.

In this embodiment, instead of the transparent electrodes for the entire screen of the glass plates 33 and 63 with transparent electrodes of the polarization plane rotating elements 3 and 6 in FIG. 1, they correspond to a plurality of horizontal scanning lines. A scanning line electrode TDk (transparent electrode) in a state where the screen is divided into a plurality (five in this example) is provided. The rest is the same as the configuration of the polarization plane rotation element of FIG. Then, the scanning line electrodes T are synchronized with the vertical scanning of the LCD 1.
By controlling the scan line voltage Ek between Dk (k = 1, 2,..., 5) and the transparent electrodes of the glass plates 32 and 62 with opposed transparent electrodes, the polarization of linearly polarized waves from the pixels of each scan line is controlled. The wavefront is scanned from 0 ° to 90 ° or from 90 ° to 0 ° so as to sequentially rotate in the vertical direction.

FIG. 3 shows the scanning line voltage Ek at this time.
FIG. 9 is a diagram illustrating an example of (k = 1, 2,..., 5). That is, each field section is divided into five sections, and at the timing when writing in the divided section is started, the scan line voltage E
k is 0 ° to 90 ° of the polarization plane or 90 ° to 0 ° of the polarization plane
To the control voltage.

FIG. 2 shows the state of the first scanning line electrode TD1.
And the portion of the second scanning line electrode TD2 is the writing area of the current field, the polarization plane is 90 °, and the area below the third scanning line electrode TD3 is the previous field display area, and the polarization plane is 0 °.

It is ideal that the scanning line electrodes are provided for the number of scanning lines (for example, 218). Even if the entire screen is shifted as described above, the effect of optical deflection is about half of the screen. Therefore, the transparent electrode is divided into a plurality of lines (for example, the whole is divided into five) as in the above example without dividing into the number of scanning lines, so that a sufficient effect can be obtained while simplifying the constitution. Obtainable.

FIG. 4 shows the principle when a ferroelectric liquid crystal is used as a polarization plane rotating element (π cell).

First, if the optical axis of the liquid crystal and the incident polarization plane (Y axis) are made to coincide with each other when an electric field is applied in the same direction as the light traveling direction, the polarization plane of the emitted light does not change. Next, when an electric field is applied in a direction opposite to the traveling direction, the liquid crystal optical axis is inclined by 45 degrees in a locus where the cone rotates. When light polarized in the Y-axis direction enters in this state, it is divided into a liquid crystal optical axis component and a vertical component.
The speed of light in each direction component differs from the difference in the refractive index (birefringence) in each direction. Here, a thickness d (2πd (ne−no) / λ = π, where ne is an extraordinary light refractive index, such that the phase of light perpendicular to the optical axis direction is different from the phase of parallel light by 180 degrees on the emission side. , No: calculated from the refractive index of the normal light), the combined wave rotates 90 degrees as compared with the incident light.

In the case where the optical wobbling system performs projection display on a polarizing screen, in order to prevent flicker, the second polarization plane rotating element of the above embodiment is replaced with a circular polarization conversion element or a depolarizing plate. You can take measures. These circular polarization conversion elements and depolarizing plates are each formed of an element having a different refractive index depending on the polarization direction, and have different thicknesses in the transmission direction. In the case of a circular polarization conversion element, a 波長 wavelength plate is typical, and its thickness is １ ／ of the wavelength of light. Further, the depolarizing plate has a thickness several times or more the wavelength of light. The slow axis (axis in the direction of higher refractive index) of such an element is set at 0 ° of the display light emitted from the birefringent optical element in the above embodiment.
Alternatively, it is mounted at an angle of 45 ° with respect to the axis in the polarization direction of 90 °. As a result, the display light emitted from the birefringent optical element is depolarized, and regardless of the polarization direction of the polarizing screen, the screen in any field is slightly darkened but appears to be reflected, so that a pixel doubling effect is obtained. And flicker can be prevented. This embodiment is simple because it does not require driving, and has an advantage as a measure against flicker when the screen is somewhat polarized even on a normal screen.

[0032]

As is apparent from the above description, according to the optical wobbling display device using the polarization rotation of the present invention, the polarization plane is rotated with respect to the display light whose polarization plane rotates for each field emitted from the birefringent optical element. Since the polarization plane rotation element for rotating the polarization plane in reverse to return to the fixed (usually vertical) is provided after the birefringent optical element, the display light of each field can be totally reflected by the polarizing screen, The contrast can be improved as compared with the conventional contrast improving polarizing screen, and the number of pixels can be doubled.

When a circular polarization conversion element or a depolarizing plate is used instead of the above-mentioned polarization plane rotation element, display light of each field can be reflected on a screen having a polarization function. And the flicker can be prevented.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention.

FIG. 2 is a diagram showing an example of the structure of a polarization plane rotation element having divided electrodes.

FIG. 3 is a diagram showing drive voltage timing of the polarization plane rotation element.

FIG. 4 is a diagram illustrating the principle when a ferroelectric liquid crystal is used as the polarization plane rotation element.

FIG. 5 is a configuration diagram of a conventional wobbling display device.

[Explanation of symbols]

 Reference Signs List 1 LCD 2 Birefringent optical element 3 First polarization plane rotation element (π cell) 4 Drive circuit 5 Polarizing screen 6 Second polarization plane rotation element (π cell) 31, 61 FLC 32 33, 62, 63: Glass plate with transparent electrode 34, 64: Phase compensation filter

Claims (4)

(57) [Claims] 1. A mosaic display device that emits linearly polarized display light, a first polarization plane rotation element that rotates a polarization plane of the display light by 0 degrees and 90 degrees for each field of a video signal, A birefringent optical element that generates an optical path shift between the 0-degree polarized wave and the 90-degree polarized wave, wherein the polarization plane rotates for each field emitted from the birefringent optical element. The 0 degree polarization wave is 0
The second polarization plane rotation element for passing the 90 degree polarization wave and rotating the polarization plane to 0 degree is provided after the birefringent optical element, and the display emitted from the second polarization plane rotation element is passed. An optical wobbling display device by polarization rotation, wherein light is projected and displayed on a polarizing screen whose polarization direction coincides with the 0-degree polarized light. 2. A mosaic display device that emits linearly polarized display light, a first polarization plane rotation element that rotates the plane of polarization of the display light by 0 degrees and 90 degrees for each field of a video signal, A birefringent optical element that generates an optical path shift between the 0-degree polarized wave and the 90-degree polarized wave, wherein the polarization plane rotates for each field emitted from the birefringent optical element. The 0 degree polarization wave is 9
A second polarization plane rotation element is provided after the birefringent optical element for rotating the polarization plane to 0 degree and passing the 90 degree polarization wave as it is at 90 degrees, and the second polarization plane rotation element is emitted from the second polarization plane rotation element. An optical wobbling display device using polarization rotation, wherein display light is projected and displayed on a polarizing screen whose polarization direction coincides with the 90-degree polarized light. 3. The first polarization plane rotation element and the second polarization plane rotation element are divided into the same plurality of electrodes, and the polarization plane rotation control of each of the divided electrodes in the first polarization plane rotation element is performed. Is performed in synchronization with the scanning of the mosaic display device, and the polarization plane rotation control of each of the divided electrodes in the second polarization plane rotation element is performed at a timing linked to the first polarization plane rotation element. 3. The optical wobbling display device according to claim 1, wherein 4. A mosaic display device that emits linearly polarized display light, a first polarization plane rotation element that rotates the polarization plane of the display light by 0 degrees and 90 degrees for each field of a video signal, A birefringent optical element that generates an optical path shift between the 0-degree polarized wave and the 90-degree polarized wave, wherein the polarization plane rotates for each field emitted from the birefringent optical element. For the incoming polarized display light, a circular polarization conversion element or depolarization element for depolarizing is provided after the birefringent optical element, and the display light emitted from the circular polarization conversion element or depolarization element is An optical wobbling display device using polarization rotation, wherein projection display is performed on a screen having different reflection in the polarization direction.