JP2003057689A - Optical element and image display device using the optical element - Google Patents

Abstract

(57) [Summary] PROBLEM TO BE SOLVED: To provide a leakage light component in a conventional pixel shift element.
Of image quality and image quality
You. SOLUTION: Incident linearly polarized light is first polarized plane rotation means.
Polarized plane of 0 ° or 90 ° in time when passing through 2.
Receive rotation. At 0 °, the incident linearly polarized light is birefringent
The light goes straight on the crystal 3 and enters the second polarization plane rotating means 4,
In synchronization with the polarization plane switching timing of the polarization plane rotation means 2
It receives a polarization plane rotation of 0 ° or 90 ° with respect to time. 0
The light that has been rotated by the angle .theta.
Outgoing light l ₁And emitted. On the other hand, the incident linear light
Of 90 ° rotation by the polarization plane rotating means 2
Travels as extraordinary light in the birefringent crystal 3 and the second polarized light
The plane rotation means 4 receives a 90 ° polarization plane rotation. Obedience
Therefore, the light incident on the linear polarization means 5 has its polarization plane adjusted again.
It is. After passing through the linear polarization means 5, the second outgoing light in the figure
l_TwoAnd emitted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element that changes the traveling direction of light by an electric signal, and more specifically, when switching the traveling direction of light, a component of light that appears as light leakage at a position different from the original traveling position. And an image display device using the optical element.

[0002]

2. Description of the Related Art (Optical Element for Changing Optical Path) An optical element for changing an optical path (hereinafter referred to as an optical deflecting element) deflects an optical path of light by an external signal, that is, shifts outgoing light in parallel to incident light, or It is an element that can switch the optical path by rotating it at a certain angle or by combining both. In this description, the magnitude of the shift is called "shift amount" for the light deflection by the parallel shift, and the rotation amount is called "rotation angle" for the light deflection by the rotation.

Conventionally, KH ₂ PO has been used as an optical deflection element.
₄ (KDP), NH ₄ H ₂ PO ₄ (ADP), LiNb
O ₃ , LiTaO ₃ , GaAs, CdTe, and other materials having a large primary electro-optical effect (Pockels effect), KTN,
Electro-optical devices using materials having a large secondary electro-optical effect such as SrTiO ₃ , CS ₂ and nitrobenzene, and acousto-optical devices using materials such as glass, silica, and TeO ₂ are known (for example, Shoji Aoki). Edited by "Opto-Electronic Device", Shokodo). In general, an electro-optical device changes the refractive index by applying a high voltage to modulate an optical path or light intensity, and an acousto-optical device applies an ultrasonic wave to induce a standing wave to cause optical diffraction. To control. However, in order to obtain a sufficiently large light deflection amount by these methods, the optical path length needs to be long, but the use is limited because the material is expensive.

On the other hand, an optical element using a liquid crystal material has been proposed, and one of the following is given as an example. (1-1) "Light Beam Shifter" in Japanese Patent Laid-Open No. 6-18940 A light beam shifter made of an artificial birefringent plate is provided for the purpose of reducing the light loss of an optical space switch.
Here, two wedge-shaped transparent substrates are arranged in opposite directions, and a light beam shifter in which a liquid crystal layer is sandwiched between the transparent substrates,
And a light beam shifter in which the light beam shifter is connected to the rear surface of the matrix type deflection control element. In addition, two wedge-shaped transparent substrates are arranged in opposite directions, and a light beam shifter sandwiching a liquid crystal layer capable of matrix driving and shifting the incident light beam by half a cell is connected in multiple stages by shifting by half cells. A light beam shifter is provided.

(1-2) "Optical Deflection Switch" of Japanese Unexamined Patent Publication No. 9-133904 A light capable of obtaining large deflection, high in deflection efficiency, and capable of arbitrarily setting deflection angle and deflection distance. A deflection switch is provided. Here, two transparent substrates are arranged facing each other at a predetermined interval, and the surfaces facing each other are subjected to vertical alignment treatment, and a smectic A-phase ferroelectric liquid crystal is sealed between the transparent substrates to form a transparent substrate on the transparent substrate. It is a liquid crystal element including a drive device that is vertically aligned with respect to the electrodes, has electrodes arranged in parallel with the smectic layer so that an AC electric field can be applied, and applies an AC electric field to the electrodes. By using the electroclinic effect of the smectic A-phase ferroelectric liquid crystal, the refraction angle of polarized light incident on the liquid crystal layer and the direction of displacement can be changed by birefringence due to the tilt of the liquid crystal molecules.

However, the above-mentioned (1-1) Japanese Patent Laid-Open No.
In Japanese Patent Laid-Open No. 18940, since nematic liquid crystal is used as the liquid crystal material, it is difficult to increase the response speed to sub-millisecond, and it cannot be used for applications requiring high-speed switching. Further, in the above-mentioned (1-2) Japanese Patent Laid-Open No. 9-133904, a smectic A phase ferroelectric liquid crystal is used. However, since the smectic A phase does not have spontaneous polarization, it appears to be found in the chiral smectic C phase. After all, I can not expect high speed operation.

(Related to Pixel Shift) The pixel shift element mentioned here is an image display element in which a plurality of pixels capable of controlling light at least according to image information are two-dimensionally arranged, and a light source for illuminating the image display element. An optical member for observing an image pattern displayed on the image display element, and a light deflection device for deflecting an optical path between the image display element and the optical member for each of a plurality of subfields obtained by temporally dividing the image field. Means for displaying an image pattern in which the display position is displaced according to the deflection of the optical path for each subfield, thereby displaying the image by multiplying the apparent number of pixels of the image display element. The light deflecting means or the light deflecting element in the apparatus. Therefore, it is basically possible to apply the above-mentioned "light deflection element". Here, the technology conventionally proposed as a pixel shift element will be described.

(2-1) "Projection Display Device" of Japanese Patent No. 2939826 The above-mentioned publication is a projection display device for enlarging and projecting an image displayed on a display element onto a screen by a projection optical system. A means for shifting a projected image, comprising at least one optical element capable of turning the polarization direction of transmitted light and at least one transparent element having a birefringence effect in the optical path from the element to the screen; Means for effectively reducing the aperture ratio of the display element and projecting the projection area of each pixel of the display element discretely on the screen is a projection display device.

In the above-mentioned Japanese Patent No. 2939826, an optical element capable of rotating the polarization direction (called an optical rotation element).
The pixel shift is performed by the projection image shift means (pixel shift means) having at least one and at least one transparent element having a birefringence effect (referred to as a birefringent element). As a problem, the plane of polarization of the light entering the optical element from the projection optical system should be adjusted so as to ideally form a predetermined angle (0 ° or 90 °) with the optical crystal axis of the transparent element. This relationship is not always satisfied due to the installation error, and in that case, due to the pixel shift, an image due to the leaked light component appears at a position different from the screen position where the projection light reaches and forms an image at a certain moment. In this case, the image due to the leaked light component deteriorates the contrast and deteriorates the image quality. Even if the plane of polarization of the light entering the optical element from the projection optical system is adjusted so as to form a predetermined angle (0 ° or 90 °) with the optical crystal axis of the transparent element, the projection light itself may have a certain spread. Since the light is incident on the optical element, the light ray obliquely incident on the optical element also causes leakage light.

(2-2) "Image display device, method for improving resolution of image display device, imaging method, recording device and reproducing device" disclosed in Japanese Patent Laid-Open No. 6-324320. The number of pixels of an image display device such as an LCD is increased. Without apparently improving the resolution of the displayed image. Each of a plurality of pixels arranged in the vertical direction and the horizontal direction emits light in accordance with a display pixel pattern, and an optical path is provided for each field between an image display device displaying an image and an observer or a screen. The optical member to be changed is arranged. In addition, the display pixel pattern in which the display position is displaced according to the change of the optical path is displayed on the image display device for each field. The optical path is changed by alternately making the portions having different refractive indexes appear in the optical path between the image display device and the observer or the screen for each field of the image information.

In the above-mentioned JP-A-6-324320, as a means for changing the optical path, a combination mechanism of an electro-optical element and a birefringent material, a lens shift mechanism, a vari-angle prism, a rotating mirror, a rotating glass, etc. are described. In addition to the method of combining the optical rotatory element and the birefringent element, a lens, a reflector, a voice coil, a piezoelectric element, etc.
We have proposed a method of displacing (translating, tilting) an optical element such as a birefringent plate to switch the optical path. The former method using a birefringent element has the same problem as that of the above-mentioned Japanese Patent No. 2939826, and the latter method has a problem that the structure is complicated and the cost is increased because the optical element is driven. .

(2-3) "Optical wobbling display device by rotation of polarized light" disclosed in Japanese Patent Laid-Open No. 8-29779, which enables a high-definition image to be displayed by a low-resolution display element and is used as a polarizing screen for improving contrast. On the other hand, the invention provides an optical wobbling display device that uses polarization rotation to obtain a contrast improving effect.

FIG. 12 is a diagram showing a configuration example of the display device disclosed in Japanese Patent Laid-Open No. 8-29779. Figure 1
In FIG. 2, the polarization plane of the display light from the LCD 101 is rotated by the first polarization plane rotation element 103 for each field, passed through the birefringence optical element 102, and the optical path of one field is shifted with respect to the other. And apparently double the number of pixels. Further, by disposing the second polarization plane rotation element 104 after the birefringence optical element 102, the polarization plane of the display light of one field whose polarization plane emitted from the birefringence optical element 102 is rotated is reversed. Rotate. This fixes the polarization plane of that field (usually vertical)
Then, the polarization planes of the respective fields are aligned in one polarization direction, so that the contrast improving effect on the polarizing screen 105 is obtained.

In the display device disclosed in the above-mentioned Japanese Patent Laid-Open No. 8-29779, a second polarization plane rotating element 104 is provided for the purpose of combining with a polarizing screen, and the above-mentioned Japanese Patent No. 2939826. The problem indicated by is not taken into consideration. The polarization plane is fixed by the second polarization plane rotation element 104, and the polarization screen 105
When projected onto the screen, improvement in contrast can be expected, but the polarizing screen 105 has a large area and it is not easy to match the polarization plane of the projection light with the polarization plane of the polarization screen, which is convenient for installation. I had a problem. Further, since the polarizing screen 105 is basically a reflection type screen, it cannot be used in combination with a transmission type projection device.

[0015]

To summarize the problems in the prior art described above, regarding the conventional pixel shift element, the angle between the plane of polarization of the light incident on the optical element from the projection optical system and the optical crystal axis of the transparent element. Due to adjustment error, chromatic aberration, error due to thermal expansion, or spread of projection light, etc., the image due to the leaked light component may appear at the moment when there is an image due to the leak light component at a position different from the screen position where the projection light originally arrives and forms an image due to pixel shift. This leakage light component may deteriorate the contrast and the image quality.

Further, the polarizing screen has a large area, and it is not easy to make the plane of polarization of the projection light coincide with the plane of polarization of the polarizing screen, which makes it difficult to install the polarizing screen. In addition, since it is a reflection type screen, it cannot be used in combination with a transmission type projection device.

The present invention has been made in view of the above situation, and the invention of claim 1 is an optical element for suppressing deterioration of contrast and deterioration of image quality due to leakage light components in a conventional pixel shift element. The purpose is to provide.

According to a second aspect of the present invention, in order to perform a pixel shift, first polarization plane rotating means for temporally switching the polarization plane of the light incident on the birefringent crystal, and the polarization plane synchronizing with this switching. It is an object of the present invention to provide an optical element capable of efficiently removing the leaked light in the pixel shift element by the second polarization plane rotating means including.

It is an object of the invention of claim 3 to provide an optical element in which the material necessary for realizing high-speed switching in the second polarization plane rotating means is embodied.

It is an object of the invention of claim 4 to provide an optical element embodying a driving method necessary for realizing high-speed switching in the second polarization plane rotating means.

The inventions of claims 5 and 6 provide an optical element embodying the structure of the linear polarization means necessary for realizing highly efficient leakage light removal in the second polarization plane rotation means. With the goal.

It is an object of the present invention to provide an optical element for suppressing deterioration of contrast and deterioration of image quality due to leakage light components in a conventional pixel shift element.

It is an object of the present invention to provide an optical element embodying the constitution of the polarization control means for suppressing the deterioration of the contrast and the deterioration of the image quality.

It is an object of the present invention to provide an optical element configured to perform pixel shift (optical path shift) at a plurality of places.

It is an object of the present invention to provide an optical element which does not deteriorate its performance even when the temperature changes.

It is an object of the present invention to provide an image display device in which the deterioration of contrast at the time of pixel shift, which is a conventional image deterioration factor, is suppressed.

[0027]

According to a first aspect of the present invention, there is provided a first polarization plane rotating means capable of temporally switching the polarization plane of incident linearly polarized light, and the first polarization plane rotating means. Birefringent crystal that switches the traveling direction of the incident light according to the polarization plane of the incident light, and polarized light that is temporally switched by the first polarization plane rotating means with respect to the light from the birefringent crystal. It has a second polarization plane rotating means for aligning the planes to substantially the same polarization plane, and a linear polarization means for transmitting only the light of a specific polarization plane with respect to the light passing through the second polarization plane rotating means. It is characterized by.

According to a second aspect of the present invention, in the first aspect of the invention, the second polarization plane rotating means is provided with a pair of transparent substrates provided to face each other, and in the vicinity of the facing surfaces of the pair of transparent substrates. It has a pair of electrodes provided and a liquid crystal layer for switching the polarization plane by an electric field generated by the electrodes in synchronization with the polarization plane switching timing of light in the first polarization plane rotating means. is there.

According to a third aspect of the present invention, in the second aspect, the liquid crystal layer is a chiral smectic C liquid crystal.

According to a fourth aspect of the present invention, in the second or third aspect of the present invention, there is provided a voltage applying means for applying a voltage to the liquid crystal layer, and the voltage applied to the liquid crystal layer by the voltage applying means is at least It is characterized in that it is an AC voltage having two or more types of frequencies.

The invention of claim 5 is characterized in that, in the invention of any one of claims 1 to 4, the linear polarization means is made of a birefringent crystal.

According to a sixth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the linear polarization means is a dichroic polarizing element.

According to a seventh aspect of the present invention, the first polarization plane rotating means capable of temporally switching the polarization plane of the incident linearly polarized light, and the traveling direction of the light from the first polarization plane rotating means. A birefringent crystal that is switched according to the polarization plane of the incident light, and a polarization plane that is temporally switched by the first polarization plane rotation means for the light from the birefringent crystal to be substantially equal polarization planes. It has a polarization control means for allowing only a specific polarization plane to pass while aligning.

According to an eighth aspect of the present invention, in the invention of the seventh aspect, the polarization control means includes a pair of transparent substrates provided to face each other, and a pair of transparent substrates provided on opposite sides of the pair of transparent substrates. And a liquid crystal layer composed of a chiral smectic C phase filled between the transparent substrates, and either or both of the pair of transparent substrate surfaces facing each other across the liquid crystal layer are It is characterized in that it is configured to be inclined with respect to the plane orthogonal to the incident optical axis in correspondence with the deflection direction.

The invention of claim 9 is characterized in that, in the invention of any one of claims 1 to 8, a plurality of pairs of the first polarization plane rotating means and the birefringent crystal are provided. It is a thing.

According to a tenth aspect of the present invention, in the invention according to any one of the first to ninth aspects, a transparent electric resistance material is provided in the vicinity of the liquid crystal layer, and Joule heat generated by applying a current to the transparent electric resistance material. Is provided with a temperature control means for controlling the liquid crystal layer to a predetermined temperature.

According to an eleventh aspect of the present invention, an image display element in which a plurality of pixels capable of controlling light according to image information are two-dimensionally arranged, a light source for illuminating the image display element, and display on the image display element are provided. 11. An optical member for making an image pattern observable, and an optical path between the image display element and the optical member is deflected for each of a plurality of subfields obtained by temporally dividing the image field. And a light deflection unit including the optical element according to the first aspect, and displaying an image pattern in which the display position is displaced according to the deflection of the optical path for each of the subfields, the apparent image of the image display element is displayed. The feature is that the number of pixels is multiplied and displayed.

[0038]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an optical element and an image display device of the present invention will be specifically described below with reference to the accompanying drawings. In all the drawings for explaining the embodiments, the parts having the same functions are designated by the same reference numerals, and the repeated description thereof will be omitted. (Embodiment 1) FIG. 1 is a schematic view for explaining an embodiment of an optical element of the present invention. In FIG. 1, 1 is an optical element of the present invention, 2 is a first polarization plane rotating means, 3 is a birefringent crystal, 4 is a second polarization plane rotating means, and 5 is a linear polarization means. By using the optical element of the present invention, the leaked light component can be efficiently removed, so that a high-contrast image can be obtained. Further, it contributes not only to the pixel shift technology in the image display device but also to improvement of switching reliability in optical communication, for example.

The following description corresponds to claim 1. The incident light is set in advance as linearly polarized light, and its polarization plane is determined by the relationship with the optical crystal axis direction of the birefringent crystal 3. Specifically, assuming that the orthogonal coordinate system is as shown in FIG. 1, a uniaxial optical crystal material is used as the birefringent crystal 3, and its optical crystal axis is (X, Y, Z) = (1, 0, -1). ), The polarization plane of the incident light (electric field vector plane) is selected so as to coincide with the XY plane or the XZ plane. Hereinafter, a case where the polarization plane of incident light is in the XY plane will be described. When passing through the first polarization plane rotating means 2, the incident light undergoes a polarization plane rotation of 0 ° or 90 ° in terms of time.

When the rotation of the polarization plane is 0 °, that is, when the rotation is not received, the linearly polarized light enters the birefringent crystal 3 while keeping the polarization plane in the XY plane. Since the polarization direction (Y-axis direction) is perpendicular to the optical crystal axis, the light behaves as ordinary light, goes straight without being rotated, and enters the second polarization plane rotating means 4. In the second polarization plane rotation means 4, the incident light is synchronized with the polarization plane switching timing of the first polarization plane rotation means 2 and is also 0 ° or 90 ° in terms of time.
Undergoes polarization plane rotation. Here, it is assumed that the light beam advances by being rotated by 0 ° (that is, the polarization plane is kept as it is in the XY plane without rotating). Although this light passes through the linear polarization means 5, the linear polarization means 5 is installed so that only the light on the XY plane is transmitted and the other light is not transmitted. The light transmitted through the linear polarization means 5 is the first light in FIG.
Is emitted to the position indicated as the emitted light l ₁ .

On the other hand, when the incident light is rotated by 90 ° in the first polarization plane rotating means 2, the incident linearly polarized light is incident on the birefringent crystal 3 with its polarization plane rotated to the XZ plane.
The principle of 90 ° rotation will be described later. In this case, since the polarization direction (Z-axis direction) is not perpendicular to the optical crystal axis, the light behaves as extraordinary light, rotates in a predetermined direction, and travels (travels obliquely downward in the figure), It is incident on the polarization plane rotating means 4. The second polarization plane rotation means 4 receives the polarization plane rotation of 90 ° in synchronization with the polarization plane switching timing of the first polarization plane rotation means 2. Therefore, the plane of polarization of the incident light on the linear polarization means is adjusted to the XY plane again.
After passing through the linear polarization means 5, the second outgoing light l ₂ in the figure
To the position indicated by.

In any case, the incident light to the linear polarization means 5 has a plane of polarization in the XY plane, but in the process reaching this point, strictly speaking, not only the linear polarization in the XY plane but also light in other directions are mixed. It becomes a state. The cause is that the polarization plane of the light entering the optical element from the projection optical system contains an XZ component due to an installation error, and the projection light itself enters the optical element with a certain spread, That the obliquely incident light rays similarly generate light other than the XY plane, and further, the first and second polarization plane rotating means 2 and 4.
Depending on the characteristics of the above, it is impossible to completely perform polarization rotation of a predetermined angle depending on the incident light wavelength. These lights are leaked light, for example, the second emitted light l ₂ is generated when the first emitted light l ₁ is emitted.

FIG. 2 is a diagram showing an example of the result of calculation of the relationship between the incident angle and the amount of leaked light when light is obliquely incident. Leakage light generated when the light is obliquely incident on the first polarization plane rotation means 2 and the polarization plane is rotated by 90 ° and deviated from the required optical path is calculated. As is clear from FIG. 2, the leakage light significantly increases as the incident angle increases. When this optical element is used for an optical switch, this leaked light causes an erroneous switching operation, and in the case of an image display device, it causes a reduction in contrast, which is not preferable. Therefore, it is an important subject of the present invention to remove such leaked light.

As the first polarization plane rotating means 2, a conventionally used polarization plane rotating means using liquid crystal can be used. However, when used for the pixel shift of the image display device, high-speed switching is required according to the number of pixel shifts. Since the structure and function of the first polarization plane rotation means 2 are common to the second polarization plane rotation means 4, the details thereof will be described later in the description of the second polarization plane rotation means.

As the birefringent crystal 3, a uniaxial optical crystal is preferably used. As an optical crystal, KH ₂ PO ₄
(KDP), NH ₄ H ₂ PO ₄ (ADP), LiNbO ₃ ,
Materials such as LiTaO ₃ , GaAs, and CdTe that have a large primary electro-optic effect (Pockels effect), KTN, and Sr.
Materials having a large secondary electro-optical effect such as TiO ₃ , CS ₂ and nitrobenzene, and materials such as glass, silica and TeO ₂ can be used.

FIG. 3 shows LiNbO ₃ as the optical crystal.
It is a figure which shows an example of the result of having calculated the light shift amount when is used. The optical axis is set as shown in FIG. 1, and the refractive index of the optical crystal is that when the wavelength is 633 nm (no =
2.286, ne = 2.200) is used.

The second polarization plane rotating means 4 is composed of a liquid crystal layer. FIG. 4 is a diagram showing an example of a specific structure of the second polarization plane rotating means 4. In FIG. 4, reference numeral 51 denotes a pair of transparent substrates, and a pair of transparent electrodes 52 is formed on the surface side where the pair of transparent substrates 51 face each other. The transparent substrate 51 is connected to a voltage applying means 55 for applying an AC voltage. The application of the AC voltage is controlled so that the voltage is applied to the liquid crystal at a predetermined timing in synchronization with the first polarization plane rotating means. An alignment film 54 is formed on at least one side of the transparent electrode pair 52 on the opposite surface side of the electrode pair, and a liquid crystal material 53 is filled between the alignment film 54 and the other transparent substrate. 2). With such a configuration, an optical element structure capable of efficiently removing leaked light is provided. The above optical element has no mechanical moving parts and is excellent in reliability.

The liquid crystal material is selected such that the difference Δn in refractive index between ordinary light and extraordinary light satisfies the relationship Δn · d = λ / 2 (λ is a predetermined wavelength of visible light) with the thickness d. Further, as the response speed, if it is used for pixel shift of the image processing apparatus, the following conditions are selected.

The image field (time t _Field ) is temporally divided into n, and the optical path between the image display element and the optical member is deflected for each of the n sub-fields to set the pixel shift position to n. In this case, the time t _SF of one subfield is represented by t _SF = t _Field / n. Light is deflected during the period of t _SF , but if the time is t _shift , display cannot be performed during the period of t _shift , and thus the light use efficiency is reduced by an amount corresponding to this period. The light use efficiency E is represented by the following formula. E = (t _SF −t _shift ) / t _SF

If the pixel shift position n is n = 4 and the image field t _Field is 16.7 ms, 0.9 <(16.7 / 4-t _shift ) is required to secure the light use efficiency E of 90% or more. /(16.7/4) t _shift <0.42 (ms), and it is necessary to perform light deflection in 0.42 ms. Since the response speed is several ms or more in the driving by the normal voltage On / Off for the nematic liquid crystal, it is not suitable for use in the optical element for pixel shift shown here, and the chiral smectic C phase is not suitable. A ferroelectric liquid crystal consisting of is preferably used (corresponding to claim 3). With the above configuration, an optical element having a high-speed response sufficient for pixel shift can be obtained. Even in the system in which the nematic liquid crystal and the driving system by the voltage applying means 55 as described in claim 4 are combined, the speed can be increased, but in claim 3, there is no problem of heat generation at the time of applying high frequency in claim 4, and the consumption is reduced. There is an effect that the electric power is small.

The smectic liquid crystal is a liquid crystal molecule in which the long axis direction of the liquid crystal molecule is arranged in layers. A liquid crystal in which the normal direction of the layer (the normal direction of the layer) and the long axis direction of the liquid crystal molecules are coincident with each other is referred to as a smectic A phase, and a liquid crystal not in coincident with the normal direction is referred to as a chiral smectic C phase. The chiral smectic C-phase ferroelectric liquid crystal generally has a so-called spiral structure in which the liquid crystal director direction is spirally rotated in each layer in a state where an external electric field does not work. Peel the facing direction of the liquid crystal director. The liquid crystal composed of these chiral smectic C phases has an asymmetric carbon in the molecular structure,
Because of this, the spontaneous polarization is Ps.
By rearranging the liquid crystal molecules in a direction determined by the external electric field E, the optical characteristics are controlled. Here, an optical element will be described by taking a ferroelectric liquid crystal as an example, but an antiferroelectric liquid crystal can be similarly used.

The structure of the chiral smectic C-phase ferroelectric liquid crystal is composed of a main chain, a spacer, a skeleton, a bonding part, a chiral part and the like. As the main chain structure, polyacrylate, polymethacrylate, polysiloxane, polyoxyethylene, etc. can be used. The spacer is for connecting the skeleton responsible for molecular rotation, the bonding part, and the chiral part to the main chain, and a methylene chain or the like having an appropriate length is selected. In addition, a —COO— bond or the like is selected for the bonding portion that connects the chiral portion and the rigid skeleton such as the biphenyl structure. Chiral smectic C
The rotation axis of the molecular spiral rotation of the ferroelectric liquid crystal is oriented horizontally to the substrate surface by the alignment film 54, and so-called homogeneous alignment is formed.

FIG. 5 is a view showing an alignment state of an element using a chiral smectic C liquid crystal applicable to the first and second polarization plane rotating means and an element structure including the liquid crystal, and is a schematic side view of an optical element. 5 (A) and A- in FIG. 5 (A).
A sectional view taken along the line A ′ is shown in FIG. On both sides of the liquid crystal phase (liquid crystal material 53), transparent electrode pairs 52 are formed by solid electrodes.
Is formed and the electric field is applied in a direction perpendicular to the homogeneously aligned liquid crystal director, that is, in the light traveling direction. Cross-sectional view of liquid crystal surface (AA ')
As shown in the sectional view, the liquid crystal director is a transparent electrode 5.
It is oriented in either of two directions corresponding to the electric field direction from 2. That is, it is possible to take the first alignment state and the second alignment state. In this configuration, the plane of polarization of the incident light is x
Given the z-plane, the incident light travels in the liquid crystal as ordinary light in the first alignment state, and as light including both ordinary light and extraordinary light in the second alignment state. Therefore, the difference between ne and no, that is, the difference in refractive index Δn is felt, and the polarization plane is rotated by 90 ° under the condition of Δn · d = λ / 2.

In order to regulate the liquid crystal orientation to a predetermined angle, the alignment film 54 formed on the surfaces of both transparent substrates 51 is rubbed in the direction corresponding to the liquid crystal orientation, and the orientation depending on the rubbing direction is applied. The direction of the liquid crystal director is strongly regulated. In the chiral smectic C liquid crystal, the tilt angle θ changes depending on the temperature T, and when the phase transition point is Tc, there is a relation of θ∝ (T−Tc) ^β . β varies depending on the material, but takes a value of about 0.5. In order to prevent the polarization plane rotation from taking a desired value due to this temperature dependence, it is desirable to provide a temperature adjusting means for monitoring the temperature and adjusting the temperature to a predetermined temperature.

The temperature control may be performed by monitoring the temperature of the optical element and providing feedback to activate a heating source or a cooling source for reducing the difference from the set temperature. Further, instead of monitoring the temperature, the light deflection position may be monitored to operate the heating / cooling source so as to reduce the difference from the normal position. As the heating source, a heating source may be provided outside the element, but for miniaturization, it is preferable to use Joule heat obtained by forming a resistance wire inside the element and passing an electric current through it. A Peltier element or the like is preferably used as the cooling source (corresponding to claim 10). With the above configuration, since the temperature can be kept constant, stable operation is possible even in an environment where the temperature changes greatly.

As a driving method which has a smaller temperature dependence than the ferroelectric liquid crystal and can be speeded up in each stage as compared with the above-mentioned AC voltage On / Off driving, a high frequency is used for the nematic liquid crystal. It is also possible to use a dual-frequency driving method in which a voltage and a low-frequency voltage are combined to act (corresponding to claim 4). Thereby, an optical element having a high-speed response sufficient for pixel shift can be obtained. Claim 3
Even if the chiral smectic C liquid crystal material as shown in (1) is used, the speed can be increased, but by applying the dual frequency driving method to the nematic liquid crystal, uniform alignment control is easier than in the case of the chiral smectic C liquid crystal. There is an advantage that the manufacturing process can be relatively simplified.

In the above dual frequency driving method, basically, control can be performed by applying a voltage to the transparent electrode pair 52 formed on the opposing surfaces of the pair of transparent substrates 51. An appropriate value for the frequency of the applied voltage is obtained from the dielectric anisotropy of the liquid crystal, and for example, a combination of a high frequency AC voltage of 100 kHz and a low frequency AC voltage of 1 kHz may be alternately applied. As an advantage of adopting the dual-frequency driving method, nematic liquid crystal can be selected as a material to be used, alignment defects are less likely to occur and defect generation can be suppressed to a low level as compared with ferroelectric liquid crystals.

A commercially available polarizing element can be used as the linear polarization means 5, and a calcite prism (corresponding to claim 5) obtained by processing a birefringent crystal such as calcite as a gran type prism is preferable. Can be used for. For example, when a Glan-Taylor prism, which is one of the Calcite-made prisms, is used, the extinction ratio is 10 ⁻⁵ or less (for example, Melles Glio-made Glan-Taylor polarizing prism),
Almost all leaked light due to the incident light angle shown in FIG. 2 can be cut. It is also possible to use liquid crystal instead of crystalline as the above-mentioned polarizing element. With this structure, an extremely high extinction ratio can be obtained, which greatly contributes to the improvement of contrast. The conventional method combined with a polarizing screen could not be applied to a transmission type display device, but this can be achieved by adopting this optical element.

On the other hand, when it is used for light having a relatively wide area, a dichroic sheet polarizing plate can be used as the linear polarizing means 5. This polarizing plate is cheaper than the above-mentioned birefringent crystal and has an extinction ratio of 10 ⁻⁴ (for example, a dichroic sheet polarizing plate manufactured by Melles Griot Co., Ltd.), so that extremely excellent leakage light can be removed. Yes (corresponding to claim 6). With the above configuration, a practical extinction ratio is obtained, which contributes to the improvement of contrast. Compared with using the birefringent crystal of claim 5, the cost can be reduced. Therefore, it is particularly effective when the effective diameter of light is relatively large. Similarly to the fifth aspect, the conventional method combined with the polarizing screen could not be applied to the transmission type display device, but this can be achieved by adopting the present optical element.

(Embodiment 2) FIG. 6 illustrates an example of an optical element having a structure in which two pairs of the first polarization direction rotating means and the birefringent crystal of the optical element shown in FIG. 1 are provided. In the figure, 2a and 2b are first polarization direction rotating means, 3a and 3b.
Is a birefringent crystal. Here, it is possible to shift the light shift to four positions (l _{1 to} l ₄ ) on a straight line (in the Z direction in the figure) by appropriately selecting the thicknesses of the respective birefringent crystals 3a and 3b. . Or two birefringent crystals 3
By changing the crystal axis directions of a and 3b, it is possible to two-dimensionally select _four shift positions l _{1 to} l 4 in the YZ plane. In the configuration in which the pixel shift in the image display device is set at two vertical and horizontal positions in the YZ plane, the crystal axis direction of the birefringent crystal is set, for example, in the (X, Y, Z) = (1,1,0) direction. Can be realized with. In the case where the polarization direction rotating means / birefringent crystal pairs are provided in a multi-pair multi-stage manner in order to set the light shifts at a large number of positions, including the case of this embodiment, the polarization control means 6 is arranged at the final stage. One may be provided (corresponding to claim 9). With the above configuration, by providing a plurality of pairs of the first polarization plane rotating means and the birefringent crystal that are responsible for the pixel shift, it is possible to shift the pixel to a plurality of positions (three or more), but leak light is prevented. For removal, only one "second polarization plane rotation means and linear polarization means" (corresponding to claim 1) or "polarization control means" (corresponding to claim 7) is provided in the final stage. Is enough,
Even if there are multiple stages, there is no increase in cost.

(Embodiment 3) FIG. 7 is a view for explaining another structure of the optical element of the present invention. In FIG.
1 is the optical element of the present invention, 2 is the first polarization plane rotating means, 3
Is a birefringent crystal, 6 is a polarization control means, and the second polarization plane rotation means 4 and linear polarization means 5 shown in FIG. 1 need not be provided in this embodiment, and the polarization control means 6 is required. Become.

In FIG. 7, the structure and function of the first polarization plane rotating means 2 and the birefringent crystal 3 are similar to those of the embodiment shown in FIG. Polarization planes of 0 ° (that is, in the XY plane according to the description of the first embodiment) and 90 ° (the same XZ plane) are incident on the polarization control unit 6 while temporally switching, but the polarization characteristics are As described above, the linearly polarized light is not good. Therefore, the polarization control means 6 has a function of switching the polarization plane of the transmitted light between 0 ° and 90 ° in synchronism with the first polarization plane rotation means 2 and preventing the transmission of light other than its linear polarization component. By using this configuration, the leaked light component can be efficiently removed, so that a high-contrast image can be obtained. Further, it contributes not only to the pixel shift technology in the image display device but also to improvement of switching reliability in optical communication, for example. When compared with the configuration of claim 1, since the portion configured by using the second polarization plane rotation means 2 and the linear polarization means 5 can be configured by one polarization control means, the number of parts is reduced and the light quantity loss is suppressed. To be

FIG. 8 is a view for explaining an example of the structure of the polarization control means 6 (corresponding to claim 8). A side view of the polarization control means is shown in FIG. 8 (A) and FIG. 8 (A). 8B is an enlarged schematic view of the liquid crystal sealing side surfaces of the transparent substrates 61a and 61b in FIG. The polarization control means 6 is composed of a pair of transparent substrates 61a and 61b, an alignment film (not shown), a transparent electrode (not shown), and a chiral smectic C liquid crystal as the liquid crystal layer 62. The surface of the transparent substrate 61a on the liquid crystal sealing side has a predetermined angle ψ with respect to the plane orthogonal to the incident optical axis.
₁ (≠ 0) There is a tilted relationship. In addition, it is preferable in terms of optical design that the refractive index of the transparent substrate is matched with the refractive index ne or no of the liquid crystal.

In order to keep the gap within a desired range while maintaining the above inclination angle ψ ₁ , as shown in FIG. 8B, inclined portions having inclined surfaces t are formed in a saw blade shape at a certain interval. Is also good. As a method for forming the sawtooth shape, a glass substrate may be etched or a transparent plastic material may be processed by injection molding or the like. In any of the forming methods, the portion corresponding to the edge of the saw blade is likely to have disordered liquid crystal alignment, and therefore it is desirable to control the incident light so that the light does not pass through this portion. The liquid crystal layer 62 is substantially homogeneously aligned with respect to the substrate surface, and the alignment is controlled by a transparent electrode (not shown) formed near both interfaces of the liquid crystal.

The feature of the configuration of this embodiment is that only the light of a desired polarization plane can be transmitted by switching the alignment direction of the liquid crystal in accordance with the polarization plane of the incident light. That is, by controlling the orientation of the liquid crystal, only ordinary light or extraordinary light may be made to go straight without changing the incident light direction, and the other light may be rotated to be guided to the outside of the optical system. By adopting this configuration, leaked light can be guided to the outside of the optical path and can be effectively removed.

To determine the traveling direction of light in the configuration of FIG. 8, strictly speaking, as described above, the refractive index in each direction based on the liquid crystal director direction with respect to the incident light traveling direction and both no and ne based on the refractive index ellipsoid. Is obtained, and the traveling direction of light is obtained based on it. Here, the traveling direction of light, that is, the rotation angle is obtained according to Snell's law, assuming that no and ne are switched depending on the alignment state of the liquid crystal. .

The refractive index of the liquid crystal in the long axis direction is ne = 1.8,
The refractive index in the minor axis direction is set to no = 1.6, and an angle ψ ₁ formed by the normal direction of the front side interface of the liquid crystal (interface between the transparent substrate 61a and the liquid crystal layer 62) to the light traveling direction with respect to the light traveling direction. Is 30
The transparent substrate 61 is arranged so that the angle formed by the normal line of the rear interface (interface between the transparent substrate 61b and the liquid crystal layer 62) and the incident light direction is 0 °. The optical member that comes into contact with the liquid crystal has a refractive index of no. According to Snell's law, the rotation angle ψ ₂ from the interface normal direction at the front side liquid crystal interface is sin ψ
_{From 2} = (no / ne) sin ψ ₁ , ψ ₂ = 26.4 (°). Further, the rotation angle ψ ₃ of the light beam incident on the counter substrate (transparent substrate 61b) sandwiching the liquid crystal from the counter substrate normal direction is ψ ₃ = ψ ₁ −
ψ ₂ = 3.6.

[0068] rotation angle in the substrate of the light beam incident on the counter substrate, than _{sinψ 4 = (ne / no)} sinψ 3, ψ 4 = 4.05 (°)
Becomes Assuming that the effective diameter of the optical path is 10 mm, when an optical element such as a lens is provided in the subsequent stage, it is necessary to eliminate the leaked light outside the optical axis outside the effective diameter when the distance from this optical element to the lens is L. L becomes L = 142 (mm) from L · sin ψ ₄ = 10 (mm).

(Embodiment 4) FIG. 9 is a diagram for explaining another example (corresponding to claim 10) of the configuration of the optical element of the present invention, which serves as a heating source for the optical element shown in FIG. 3 shows an element structure provided with an electric resistance material 7. Electric resistance material 7
Is preferably a material that is transparent in the visible light range, has an appropriate electric resistance, and is excellent in heat resistance (room temperature to about 70 ° C.).
Here, ITO is used as the electric resistance material 7. ITO
Are formed in the vicinity of the second polarization plane rotating means 4.

In the temperature control means 71, the temperature of the optical element 1 is monitored by a temperature sensor (not shown) such as a thermistor, and a current is applied to the ITO so as to reduce the difference from the set temperature. Temperature control is performed. It is desirable that the set temperature is equal to or higher than the ambient temperature around the optical element 1 and within a range where an appropriate θ can be obtained.
Usually, it is preferable to set the temperature in the range of 40 to 70 ° C.

(Embodiment 5) FIG. 10 is a schematic view for explaining an embodiment (corresponding to claim 11) of the image display device of the present invention. In FIG. 10, 11 is an illumination light source in which LED lamps are arranged in a two-dimensional array, 12 is a diffusion plate, 1
3 is a condenser lens, 14 is a transmissive liquid crystal panel as an image display element, 15 is a projection lens, 16 is a screen, 17 is a light source drive section, 18 is a drive section of a transmissive liquid crystal panel, and 19 is the optical element according to the present invention. An optical deflecting unit composed of an element, and 20 is a drive unit of the optical deflecting unit.

The illumination light emitted from the illumination light source 11 under the control of the light source drive unit 17 becomes uniform illumination light by the diffusion plate 12, and the condenser lens 13 controls the liquid crystal drive unit 18 in synchronization with the illumination light source. Then, the liquid crystal panel 14 is critically illuminated. The illumination light spatially modulated by the liquid crystal panel 14 is converted into image light by the light deflector 19.
The image light is shifted by an arbitrary distance in the pixel arrangement direction by the light deflecting means 19. Light deflection means 1
The light emitted from 9 is enlarged by the projection lens 15 and projected on the screen 16. The amount of light shift is half the pixel pitch because image multiplication is performed twice in the pixel arrangement direction.
Is set to. By correcting the image signal for driving the liquid crystal panel 14 by the shift amount in accordance with the shift amount, an apparently high-definition image can be displayed.

As the light deflecting means 19, an optical element of the type described in the above embodiment can be appropriately selected and used. Since the conventional light deflecting means does not include the linear polarization means 5 described in the present invention, the image projected on the screen 16 using the conventional light deflecting means contains leaked light and the image quality in terms of contrast is high. Was not good. On the other hand, the optical element of the present invention can eliminate image deterioration factors due to the leaked light as described above, and thus has good image quality. By using the optical element of the present invention as the light deflecting means, it is possible to suppress the contrast reduction due to the leaked light generated at the time of pixel shift, and thus it is possible to provide a high quality image.

(Embodiment 6) FIG. 11 is a view for explaining another embodiment (corresponding to claim 10) of the image display apparatus of the present invention, which is a light polarization means using the optical element shown in FIG. 19
2 shows an image display device having a configuration in which a temperature sensor 22 and a polarization beam splitter 21 are installed. The optical element 1 shown in FIG. 9 has been described in Example 4 above. A thermistor is used as the temperature sensor 22, but any device that can monitor the temperature such as a thermocouple can be used. The temperature information from the temperature sensor 22 is sent to the drive unit 20 of the light deflecting means to detect the difference from the set temperature. In accordance with this difference, the transparent resistance material made of ITO provided in the optical element is energized to generate Joule heat by applying a current, thereby reducing the difference from the set temperature.

It is desirable that the above-mentioned set temperature is equal to or higher than the ambient temperature around the optical element and within a range where an appropriate θ can be obtained. Usually, it is better to set the temperature in the range of 40 to 70 ° C. Further, the light deflection position control is performed by controlling the electric field application direction by the electrode pair in the optical element and the temperature control for the optical element, so that an appropriate pixel shift amount is held and a good image can be obtained.

[0076]

As is apparent from the above description, according to the optical element of the present invention, the leaked light component can be efficiently removed, so that a high-contrast image can be obtained. Further, it contributes not only to the pixel shift technology in the image display device but also to improvement of switching reliability in optical communication, for example. Further, according to the image display device configured by using the above optical element, it is possible to suppress the contrast reduction due to the leaked light generated at the time of pixel shift, and thus it is possible to provide a high quality image.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining an example of an optical element of the present invention.

FIG. 2 is a diagram showing an example of a result of calculating a relationship between an incident angle and a leaked light amount when light is obliquely incident.

FIG. 3 Li as an optical crystal applied to a birefringent crystal
NbO ₃ is a diagram showing an example of a result of the light shifting amount is calculated when using.

FIG. 4 is a diagram showing an example of a specific structure of a second polarization plane rotating means.

FIG. 5 is a diagram showing an alignment state of a device using a chiral smectic C liquid crystal applicable to the first and second polarization plane rotating means and a device structure including the liquid crystal.

FIG. 6 is a diagram for explaining an example of an optical element having a structure in which two pairs of the first polarization direction rotating means and the birefringent crystal of the optical element shown in FIG. 1 are provided.

FIG. 7 is a diagram for explaining another embodiment of the optical element of the present invention.

FIG. 8 is a diagram for explaining an example of a structure of polarization control means.

FIG. 9 is a diagram for explaining another embodiment of the optical element of the present invention.

FIG. 10 is a schematic view for explaining an embodiment of the image display device of the present invention.

FIG. 11 is a diagram for explaining another embodiment of the image display device of the present invention.

FIG. 12 is a diagram showing a configuration example of a conventional display device.

[Explanation of symbols]

1 ... Optical element of the present invention, 2 ... First polarization plane rotating means, 2
a, 2b ... First polarization direction rotating means, 3 ... Birefringent crystal, 3a, 3b ... Birefringent crystal, 4 ... Second polarization plane rotating means, 5 ... Linear polarization means, 6 ... Polarization control means , 7 ... Electric resistance material, 11 ... Illumination light source, 12 ... Diffusion plate, 13 ... Condenser lens, 14 ... Transmissive liquid crystal panel as image display element, 15 ... Projection lens, 16 ... Screen, 17
... light source drive section, 18 ... transmissive liquid crystal panel drive section, 19 ... light deflecting means, 20 ... light deflecting means drive section, 21 ... polarization beam splitter, 22 ... temperature sensor,
51 ... Pair of transparent substrates, 52 ... Transparent electrode pair, 53 ... Liquid crystal material, 54 ... Alignment film, 55 ... Voltage applying means, 61a, 6
1b ... Transparent substrate, 62 ... Liquid crystal layer, 71 ... Temperature control means,
101 ... LCD, 102 ... Birefringent optical element, 103 ... First polarization plane rotating element, 104 ... Second polarization plane rotating element,
105 ... Polarizing screen.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Emura Nimura             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh (72) Inventor Yumi Matsuki             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh (72) Inventor Masanori Kobayashi             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh (72) Inventor Yasuyuki Takiguchi             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh F-term (reference) 2H049 BA05 BA08 BA42 BB00 BB03                       BB62 BC22                 2H091 FA07X FA07Z FA10Z FA26X                       FA26Z FA45Z FB06 KA10                       LA04 LA12 LA17                 2H099 AA11 BA09 CA05                 2K002 AB04 BA06 CA14 DA14 EA11                       EA30 HA03                 5G435 AA02 BB12 BB15 DD11 FF05

Claims (11)

[Claims] 1. A first polarization plane rotation means capable of temporally switching the polarization plane of incident linearly polarized light, and the first polarization plane rotation means.
Of the birefringent crystal for switching the traveling direction of the incident light from the polarization plane rotating means according to the polarization plane of the incident light, and the light from the birefringent crystal by the first polarization plane rotating means. Second polarization plane rotation means for aligning polarization planes that can be switched in time to substantially equal polarization planes, and linearly polarized light that allows only light of a specific polarization plane to pass through the light passing through the second polarization plane rotation means And an optical element. 2. The optical element according to claim 1, wherein the second polarization plane rotating means is provided in a pair of transparent substrates facing each other, and in the vicinity of the facing surfaces of the pair of transparent substrates. An optical element, comprising: a pair of electrodes; and a liquid crystal layer that switches polarization planes by an electric field generated by the electrodes in synchronization with the polarization plane switching timing of light in the first polarization plane rotation means. 3. The optical element according to claim 2, wherein the liquid crystal layer is a chiral smectic C liquid crystal. 4. The optical element according to claim 2, further comprising a voltage applying unit that applies a voltage to the liquid crystal layer, and the voltage applying unit applies at least two types of voltage to the liquid crystal layer. An optical element having an alternating voltage having the above frequencies. 5. The optical element according to claim 1, wherein the linear polarization means is made of a birefringent crystal. 6. The optical element according to claim 1, wherein the linear polarization means is a dichroic polarization element. 7. A first polarization plane rotating means capable of temporally switching the plane of polarization of incident linearly polarized light, and the first polarization plane rotating means.
Of the birefringent crystal for switching the traveling direction of the light from the polarization plane rotating means according to the polarization plane of the incident light and the light from the birefringent crystal by the first polarization plane rotating means. And a polarization control means that allows only a specific polarization plane to pass while aligning the polarization planes that can be switched to substantially the same polarization plane. 8. The optical element according to claim 7, wherein the polarization control means comprises a pair of transparent substrates provided so as to face each other, and a pair of electrodes provided at opposing sides of the pair of transparent substrates. And a liquid crystal layer composed of a chiral smectic C phase filled between the transparent substrates, and either or both of the pair of transparent substrate surfaces facing each other with the liquid crystal layer sandwiched between the transparent substrate and the liquid crystal layer. An optical element characterized by being inclined with respect to a plane orthogonal to the incident optical axis in accordance with. 9. The optical element according to claim 1, wherein a plurality of pairs of the first polarization plane rotating means and the birefringent crystal are provided. . 10. The optical element according to claim 1, wherein a transparent electric resistance material is provided in the vicinity of the liquid crystal layer, and Joule heat generated by applying a current to the transparent electric resistance material acts. An optical element comprising a temperature control means for controlling the liquid crystal layer to a predetermined temperature by performing the above. 11. An image display device in which a plurality of pixels capable of controlling light according to image information are two-dimensionally arranged, a light source for illuminating the image display device, and an image pattern displayed on the image display device can be observed. The optical member according to any one of claims 1 to 10, wherein the optical path between the image display element and the optical member is deflected for each of a plurality of subfields obtained by temporally dividing the image field. And a light deflecting unit formed of an element, and displaying an image pattern in which the display position is displaced according to the deflection of the optical path for each subfield, thereby multiplying the apparent number of pixels of the image display element. An image display device characterized by displaying the image.