JP2001272687A - Liquid crystal device for control of polarized light - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device in which the direction of linearly polarized light can be electrically fast rotated and controlled in a simple structure. SOLUTION: The liquid crystal device has a liquid crystal layer 3 sealed between a transparent substrate 2 and a substrate 4 having a punched pattern electrode divided into a plurality of parts by slits. The inner face of one substrate is subjected to intense alignment treatment to align the liquid crystal molecules parallel in one direction to the substrate while the inner face of the other substrate is subjected to the aligning treatment to give weak alignment controlling force. By adding a voltage on divided electrodes such as electrode pairs 4a, 4b or 4c, 4d along the diameter direction of the punched pattern electrode, an effect to twist the alignment of the liquid crystal molecules is induced. Thereby, rotation of the polarization direction of the incident linearly polarized light can be electrically controlled for the incident linearly polarized light having the polarization direction in the uniaxial alignment direction of the liquid crystal molecules.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a polarization controller for electrically controlling the direction of polarization of linearly polarized light without using a mechanical movable device.

[0002]

2. Description of the Related Art Polarization characteristics related to polarization corresponding to the direction of the electric field of light are one of the important properties of light, and devices capable of variably controlling the polarization direction are used in optical engineering and optoelectronics, which are applied fields of light. Very important.

Conventionally, linearly polarized light polarized in one direction is extracted by combining incident light from a light source containing polarized light components in all directions, such as incandescent lamps and sunlight, or incident light having circular polarization characteristics with a linear polarizing plate. By rotating the linear polarizing plate, linearly polarized light polarized in an arbitrary direction can be extracted.

The liquid crystal molecules are oriented parallel to the surfaces of the two substrates, and the orientation is gradually twisted between the two substrates.
In a twisted nematic liquid crystal cell (hereinafter, referred to as a “TN cell”) that is twisted by 0 degrees, when no voltage is applied to the liquid crystal cell, the polarization direction of incident light rotates 90 degrees along the alignment direction of liquid crystal molecules. effective. On the other hand, when a voltage equal to or higher than the threshold value is applied to the liquid crystal cell, the twist of the liquid crystal molecule alignment is eliminated, so that the polarization direction of the incident light is transmitted through the liquid crystal cell without rotating. By utilizing this effect, the polarization direction of the incident light can be controlled by 90 degrees by varying the voltage applied to the TN liquid crystal cell. Furthermore, by configuring a liquid crystal cell in which the twist angle of the molecular orientation is set to various values other than 90 degrees, it is possible to control the polarization direction corresponding to the set angle.

When a half-wave plate called an optical retardation called a retardation having a half of the wavelength is used, the polarization direction of the incident light can be rotated by 90 degrees.
Based on this principle, the same rotation control of the polarization direction can be performed using the electric field control birefringence effect of the liquid crystal. In other words, by adjusting the voltage applied to a homogeneously aligned liquid crystal cell in which liquid crystal molecules of a nematic liquid crystal having a positive dielectric anisotropy are aligned parallel to each other between two substrates, the birefringence generated in the liquid crystal cell and the liquid crystal By setting the value of the retardation, which is the product of the cell thickness, to be half the wavelength of the incident light, the polarization direction of the incident light can be electrically rotated by 90 degrees.

Further, as a method for forcibly aligning the liquid crystal molecules in a specific direction parallel to the substrate surface, there is a method of applying an electric field in the in-plane direction of the substrate, as described in Appl.
s. Lett. (Vol. 26, p. 603) and "Liquid Crystals and Their Applications (Sangyo Tosho Co., Ltd.)" (p. 195). In addition, a driving method of a liquid crystal cell called “in-plane switching” for performing display by applying a voltage between electrodes provided on the same substrate to reorient liquid crystal molecules is also known.

Further, a liquid crystal layer is inserted between a pair of opposing cutout divided pattern electrodes which have been subjected to an alignment treatment having a strong alignment control force such that liquid crystal molecules are aligned in one direction parallel to the substrate. A liquid crystal microlens that changes the position of a focal point in a plane perpendicular to the optical axis by applying different voltages to the portions has been devised.
304.

Similarly, a liquid crystal layer is inserted between a pair of opposing cutout divided pattern electrodes which have been treated so that liquid crystal molecules are oriented perpendicular to the substrate surface, and the hole pattern is formed in the diameter direction. A method of forming a wave plate or a phase plate having an optical axis in an arbitrary direction by applying a voltage to an electrode portion to incline and orient liquid crystal molecules in that direction is referred to as “I.
EEE Photonics Technology
Letters "(Vol. 8, No. 3, page 390)
Is disclosed.

[0009]

However, in the above-mentioned conventional method, when linearly polarized light is incident, when the linearly polarizing plate is mechanically rotated, the intensity of the light transmitted through the polarizing plate changes greatly. Therefore, it is not possible to control the polarization direction of the incident light so that the output light intensity becomes constant. When a TN liquid crystal cell is used, a polarization control effect at an angle corresponding to the twist angle of the molecular alignment can be performed, but the polarization direction cannot be controlled at an arbitrary angle. Further, when the change in the retardation of the liquid crystal, that is, the electric field control birefringence effect is used, only the effect that the polarization direction is simply rotated by 90 degrees is obtained, and the 90 degree rotation effect is applied to the incident light having a specific wavelength. However, since the polarization state of the light transmitted through the liquid crystal cell is generally elliptically polarized light, there is a problem that the polarization direction cannot be controlled over a wide wavelength range.

Furthermore, when a voltage is applied between the hole-dividing divided pattern electrodes, it is not possible to control the three-dimensional light-collecting characteristics of the microlens effect or to operate as an electric field control wave plate. However, there is a problem that the rotation of the plane of polarization in the direction of linear polarization cannot be controlled.

An object of the present invention is to solve each of the above problems,
It is an object of the present invention to provide a polarization control device capable of extremely quickly rotating and controlling the polarization direction of incident light with a simple configuration without a mechanically movable part.

[0012]

According to a first aspect of the present invention, there is provided a slit provided with a circular or elliptical hole, and provided with a hole continuous with the hole. A liquid crystal element in which a liquid crystal layer is sealed between a substrate having a hole pattern electrode divided into a plurality of portions and a transparent substrate, wherein liquid crystal molecules are parallel to the substrate on a surface in contact with the liquid crystal of one of the substrates. An alignment process having a strong alignment control force such that the alignment is performed in one direction is performed, and an alignment process having a weak alignment control force is performed on a surface of the other substrate that is in contact with the liquid crystal. A liquid crystal polarization controller which forms a potential distribution.

In the liquid crystal polarization controller, a plurality of portions of the electrode divided by the slit are independently applied with a voltage.

It is preferable that the alignment regulating force of the alignment film is 10 μJ / m 2 or more for an alignment film having a strong alignment regulating force, and 1 μJ / m 2 or less for an alignment film having a weak alignment regulating force.

Furthermore, the liquid crystal layer may be a liquid crystal in which a dichroic dye is dissolved.

According to such a configuration, by applying a voltage to a pair of electrodes corresponding to the diameter direction of the hole-shaped pattern electrode to form a potential distribution, the liquid crystal molecules are polarized in a direction in which the liquid crystal molecules are aligned in one direction. The direction of polarization of the linearly polarized incident light can be controlled to rotate in the diameter direction where the potential distribution is formed.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of a liquid crystal polarization conversion device according to one embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a linear polarizing plate (or called a polarizer), and reference numeral 2 denotes a transparent substrate made of glass, plastic, or the like. Reference numeral 3 denotes a liquid crystal layer, and reference numeral 4 denotes a substrate provided with hole-shaped pattern division electrodes 4a, 4b, 4c, 4d and the like. This is a structure in which a liquid crystal layer 3 is provided between the two substrates 2 and 4 which are kept at a fixed interval by a spacer (not shown).

Further, on one of the substrates 2 and 4 which is in contact with the liquid crystal layer 3, that is, on the opposite surface, an alignment film such as a polyimide (not shown) having a strong alignment regulating force or a polyvinyl alcohol having a high degree of polymerization and high saponification degree. And an alignment film formed by rubbing (friction) in one direction, and a film of polymethyl acrylate or the like (not shown) having a weak alignment control force is formed on the other opposing surface.
The liquid crystal layer 3 is made of a liquid crystal material such as a nematic liquid crystal (in this embodiment, K15 or BL007 manufactured by Merck) is used.
Is sealed between the two alignment films and sealed by a sealing means (not shown).

Reference numeral 5 denotes an analyzer which is used to measure the characteristics of the polarization conversion device according to the present invention.

Hereinafter, the principle of the liquid crystal polarization controller shown in FIG. 1 will be described in connection with a case where an alignment film having a strong alignment control force is provided on the opposing surface of the transparent substrate 2 and rubbing (friction) is performed in one direction. explain.

In the liquid crystal polarization converter having the structure described above, the polarization direction of the linear polarizer 1 is set so as to match the rubbing direction of the substrate 2. Here, when no voltage is applied to any of the electrodes, almost all of the liquid crystal molecules including the vicinity of the alignment film of the substrate 4 provided with the alignment film having a weak alignment regulating force are in the liquid crystal layer 3. And 3 are oriented parallel to the rubbing direction of the alignment film having a strong alignment regulating force, there is no rotation effect of the incident linearly polarized light, and the incident linearly polarized light passes through the liquid crystal layer 3 without changing the polarization direction. I do.

On the other hand, when a voltage is applied between the hole-shaped pattern dividing electrodes 4a and 4b provided on the substrate 4, the liquid crystal molecules in the hole-shaped portion between the electrodes 4a and 4b are parallel to the substrate and have an electric field. Most of the liquid crystal molecules in the liquid crystal layer 3 including the liquid crystal molecules on the alignment film surface having a weak alignment regulating force by applying a sufficiently large voltage to receive the force for the alignment in the direction of the electric field, that is, the direction of the electric field, that is, the electrode 4a. There is an effect that the hole-shaped pattern corresponding to 4b is oriented in the diameter direction.

However, since the liquid crystal molecules in the vicinity of the substrate provided with the alignment film having a strong alignment regulating force are kept aligned in the rubbing direction, the liquid crystal molecules of the liquid crystal layer 3 have an alignment film having a strong alignment regulating force. The substrate 2 is gradually twisted in the direction of the electric field from the rubbing direction of the substrate 2 toward the substrate 4. When the two substrates 2 and 4 are subjected to an alignment treatment having a strong alignment regulating force, the alignment effect of the liquid crystal molecules due to the electric field generated by the voltage applied between the divided electrodes is reduced.
In this case, it is difficult to obtain good polarization control characteristics. Therefore, it is necessary to perform an alignment treatment on one of the substrate surfaces, which has a weak alignment control force such that the liquid crystal molecules can be easily aligned in the direction of the electric field.

Since the direction of polarization of the linear polarizing plate 1 on the incident side is arranged so as to coincide with the rubbing direction of the alignment film having a strong alignment regulating force, the linearly polarized light incident on the liquid crystal polarization conversion device is The liquid crystal layer is twisted along the alignment direction of the liquid crystal molecules and transmits through the liquid crystal layer, and transmits through the liquid crystal layer 3 under the effect of rotating the polarization direction in the direction of the electric field, that is, in the diameter direction having a potential gradient. Next, when a voltage is applied between the electrodes 4c and 4d so that an electric field is generated in the diameter direction corresponding to the electrodes 4c and 4d, the incident linearly polarized light
The light passes through the liquid crystal layer 3 under the effect of rotating in the diameter direction of c and 4d. Even if a voltage is applied between the other pair of electrodes, linearly polarized light polarized in the diameter direction corresponding to the electrode to which the voltage is applied can be similarly extracted. Furthermore, by applying a voltage smaller than the voltage applied between the pair of electrodes to the adjacent electrodes so that the potential gradient changes smoothly,
The proportion of the region where the polarization control effect occurs in the hole-shaped pattern can be increased, and the occurrence of disclination caused by the disorder of the alignment of the liquid crystal molecules can be suppressed. It is to be noted that the above-described polarization control effect is characterized in that it does not depend on the wavelength of the incident light. Further, the same polarization control effect can be obtained even if the polarization direction of the linear polarizing plate on the incident side is set to a direction orthogonal to the rubbing direction of the substrate 2. However, when the polarization direction of the incident light is set to an arbitrary angle other than the rubbing direction or the angle at which the rubbing direction is 90 degrees, a sufficient polarization control effect cannot be obtained because the birefringence of the liquid crystal layer works.

When a liquid crystal called a host in which a dye called a dichroic guest is dissolved is used for the liquid crystal layer 3, a guest-host effect occurs in which a polarized component corresponding to the orientation direction of the liquid crystal molecules is absorbed. Only the polarization component orthogonal to the alignment direction of the liquid crystal molecules, which is not affected by the absorption effect by the host effect, can pass through the liquid crystal layer 3. Therefore, when the alignment state of the liquid crystal molecules is twisted, the polarization direction of the transmitted light is similarly affected by the twisting effect, so that the above-described rotation control effect of the polarization direction can be similarly exerted. When liquid crystal to which a guest dye is added is used, the linear polarizing plate 1 can be omitted because the absorption effect of the guest dye in the liquid crystal layer 3 has the same effect as the function of the polarizing plate.

In FIG. 1 of the embodiment, the case where the alignment film having a strong alignment regulating force is provided on the transparent substrate 2 has been described.
The same effect of controlling the rotation of polarized light can be obtained even when it is attached on top of. In this case, the incident light enters from the side of the substrate provided with the alignment film having a strong alignment regulating force, that is, from the side of the substrate 4.

FIG. 1 shows a case where the hole-shaped pattern electrode is divided into eight, but if the number of divided electrodes is further increased, the polarization direction can be controlled with higher definition.

Next, the polarization control effect when a voltage is applied to the electrodes of the liquid crystal polarization control device according to the present invention will be described.

A polyimide film SE-2170 on a glass substrate
Is applied to a thickness of about 150 nm, heat-treated and stabilized, and then subjected to a rubbing treatment in one direction to give approximately 100 μJ /
A substrate 2 having a strong alignment regulating force of m2 was prepared. On the other hand, an aluminum thin film having a thickness of about 150 nm is formed on a glass substrate by a vacuum evaporation method, and an 8-divided circular hole pattern electrode having a diameter of 100 μm and a width of a slit for dividing each electrode of 10 μm is formed by a photolithography method. The attached substrate 4 was produced. Polymethyl acrylate was applied as an alignment film having a weak alignment control force of about 0.01 μJ / m 2 on the opposing surface of the divided pattern electrode. The surface of the substrate coated with the polymethyl acrylate does not need to be particularly subjected to rubbing or the like, but may be subjected to rubbing. As the alignment film having the alignment regulating force, a polyvinyl alcohol film having a low degree of polymerization and a low degree of saponification may be used.

In order to satisfy the Morgan condition necessary for the polarization direction of the linearly polarized light incident on the liquid crystal layer to be twisted along the twist of the liquid crystal molecular alignment, a material having a large birefringence of the liquid crystal is used. 3 also needs to be thickened to some extent. Therefore, in this embodiment, spherical polymer particles having a particle size of 20 μm are used as spacers to keep the distance between the substrates 2 and 4 constant, and a nematic liquid crystal K15 having a positive dielectric anisotropy is enclosed as the liquid crystal 3, and polarization conversion is performed. The device was configured. When BL009, which is a nematic liquid crystal having a larger birefringence value than K15, is used, the particle diameter is 11 μm.
Was used. In these cases, the thickness of each liquid crystal layer is set so as to satisfy Morgan conditions.

As a light source for measuring the characteristics of the liquid crystal polarization converter in the present invention, monochromatic light obtained by combining a white light source using a tungsten lamp with an interference filter transmitting a wavelength band of 488 nm or 622 nm was used.
In FIG. 1, the angle between the polarization direction of the analyzer 5 and the rubbing direction of the transparent substrate 2, that is, the azimuthal angle of the analyzer 5 is defined as θ, and the change in the transmittance of the liquid crystal polarization converter with respect to the change in θ is measured. FIG. 2 shows characteristics when no voltage is applied to the electrodes and when a voltage of 8 volts (1 kilohertz) is applied to a pair of split electrodes corresponding to a direction parallel to the rubbing direction. In addition,
In FIG. 2 and FIGS. 3 and 4 described below, a solid line is obtained from theoretical calculation, and a white circle represents 632n.
The measured value is when the monochromatic light having the wavelength of m is incident, and the black circle is the measured value when the monochromatic light having the wavelength of 488 nm is incident. FIG. 2 shows that the transmittance becomes maximum when the azimuth angle θ of the analyzer 5 is 0 degree and 180 degrees, and becomes minimum when the azimuth angle is 90 degrees. In other words, when no voltage is applied to the electrodes and when a voltage that generates an electric field in the rubbing direction is applied, the effect of the twist on the liquid crystal molecule alignment does not occur, so that the linearly polarized light incident on the liquid crystal polarization conversion device changes its polarization direction. This means that the light is transmitted without change.
The frequency of the voltage applied between the electrodes may be several tens hertz to several tens kilohertz.

Next, 8 volts (1 volt) is similarly applied to the pair of divided electrodes so that the direction of the electric field is 45 degrees with respect to the rubbing direction.
FIG. 3 shows the characteristics when a voltage of (kilohertz) is applied.
From FIG. 3, the azimuth angle θ of the analyzer 5 having the maximum transmittance is 45 degrees, and the minimum angle is 1 degree obtained by rotating this angle by 90 degrees.
The angle is 35 degrees, indicating that the direction of the incident linearly polarized light is rotated by 45 degrees. FIG. 4 shows the characteristics when the direction of the electric field is 90 degrees with respect to the rubbing direction. FIG. 4 also confirms that the polarization direction of the incident linearly polarized light is rotated by 90 degrees. In each of these cases, the measured values agreed with the theoretical values irrespective of the wavelength, indicating that the liquid crystal polarization conversion device according to the present invention had good characteristics. Also, when a voltage was applied to another combination of electrode pairs, similar polarization control characteristics could be obtained. The speed at which the polarization direction changes when a voltage of 8 volts (1 kilohertz) is applied is about 0.1 seconds or less, but the speed of polarization control can be further increased by applying a larger voltage. it can.

As the liquid crystal layer 3 in FIG. 1, a liquid crystal obtained by adding 1% by weight of a blue dichroic guest dye LCDR1 (manufactured by Nippon Kayaku) to a nematic liquid crystal K15 was used. Using a monochromatic light source having a wavelength of 632 nm, which is the absorption wavelength range of the blue dichroic guest dye, omitting the linear polarizing plate 1 and similarly applying a voltage between a pair of divided pattern electrodes corresponding to the diameter direction of the circular pattern to control polarization. As a result of measuring the effect, the result obtained by shifting the transmittance characteristics shown in FIGS. 2 to 4 by 90 degrees was obtained. This result is that the molecules of the dichroic guest dye are twisted in the direction of the electric field from the rubbing direction of the substrate having a strong alignment regulating force together with the molecules of the liquid crystal as the host by the guest-host effect, and as a result, the liquid crystal layer 3 Since the polarized light component of the transmitted light corresponding to the electric field direction is strongly absorbed, an effect is shown in which the polarized light component orthogonal to the electric field direction passes through the liquid crystal layer 3. Here, since the dichroic ratio and order parameter of the dichroic guest dye used were not sufficiently large values, the contrast ratio defined as the ratio between the maximum value and the minimum value of the transmittance was a small value. By using a material having a large dichroic ratio of the guest dye, a polarization conversion device having more excellent characteristics can be configured.

[0034]

According to the present invention, by applying a voltage to the divided pattern electrodes, the direction of the linearly polarized light can be very quickly controlled with a simple structure without requiring any mechanical action.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of a liquid crystal polarization control device according to the present invention.

FIG. 2 is a diagram showing the relationship between the transmittance and the azimuth angle θ of the analyzer when no voltage is applied to the electrodes and when a voltage of 8 volts (1 kilohertz) is applied between a pair of electrodes corresponding to the rubbing direction. is there.

FIG. 3 is a diagram showing the relationship between the transmittance and the azimuth angle θ of the analyzer when a voltage of 8 volts (1 kilohertz) is applied between a pair of electrodes corresponding to a direction at 45 degrees to the rubbing direction. .

FIG. 4 is a diagram showing the relationship between the transmittance and the azimuth angle θ of the analyzer when a voltage of 8 volts (1 kilohertz) is applied between a pair of electrodes corresponding to a direction at 90 degrees to the rubbing direction. .

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Linear polarizing plate (polarizer) 2 Transparent substrate 3 Liquid crystal layer 4 Substrate provided with hole type pattern division electrode 4a, 4b, 4c, 4d Hole type pattern division division electrode 5 Analyzer

Claims (4)

[Claims] 1. A circular or elliptical hole is provided,
And a substrate having a hole pattern electrode divided into a plurality of portions by a slit provided continuously with the hole portion,
A liquid crystal element having a liquid crystal layer sealed between transparent substrates,
On one surface of the substrate that contacts the liquid crystal, an alignment process is performed that has a strong alignment control force so that the liquid crystal molecules are aligned in one direction parallel to the substrate. On the other surface of the other substrate that contacts the liquid crystal, a weak alignment control force is applied. A liquid crystal polarization control device which performs an alignment treatment having the following characteristics and forms a potential distribution in the diameter direction of the hole-shaped pattern electrode. 2. The liquid crystal polarization control device according to claim 1, wherein a voltage is independently applied to a plurality of portions of the electrode divided by the slit. 3. The liquid crystal according to claim 1, wherein the alignment film has a strong alignment control force of 10 μJ / m 2 or more and the alignment film has a weak alignment control force of 1 μJ / m 2 or less. Polarization controller. 4. A liquid crystal polarization controller according to claim 1, wherein said liquid crystal layer is a liquid crystal in which a dichroic dye is dissolved.