JP2003107475A - Liquid crystal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a device which can stably hold high linear polarizability and rotates the polarization direction by voltage impression. SOLUTION: This liquid crystal device 100 has a liquid crystal cell 110 which is a liquid crystal cell 110 in which a liquid crystal layer 1 is held between translucent substrates 5 and 6 with transparent electrodes 3 and 4 attached thereto and changes a retardation value of the incident linearly polarized light of a wavelength λ according to the magnitude of the voltage impressed between the transparent electrodes 3 and 4 and a phase plate which is a phase plate 120 having a thin organic matter film to generate a phase difference to make the retardation value of he incident linearly polarized light into λ/4 and has the orientation direction of the molecules constituting the thin organic matter film parallel with the surface of the phase plate, in which the phase advance axial direction of the liquid crystal cell 110 and the phase advance axial direction of the phase plate 120 forms an angle of nearly 45 deg..

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the magnitude of an applied voltage while maintaining the linearity of incident light that is linearly polarized light.
The present invention relates to a liquid crystal element that rotates the polarization direction of outgoing incident light.

[0002]

2. Description of the Related Art FIG. 4 shows an example of a conventional liquid crystal element that rotates the polarization direction of incident light that is linearly polarized light according to the magnitude of an applied voltage. The liquid crystal element is a nematic liquid crystal in which the alignment direction of liquid crystal molecules is parallel to the substrate surface between the transparent substrates 5 and 6 on which the transparent electrodes 3 and 4 are formed, and is aligned in a direction forming an angle of 45 degrees with the X axis. The liquid crystal layer 1 composed of the
A liquid crystal cell 110 sealed by and a phase plate 140 made of a birefringent crystal having a fast axis or a slow axis aligned in the X-axis direction are arranged on the light emitting surface side thereof. here,
An AC power supply 9 for generating a rectangular wave is connected to the transparent electrodes 3 and 4,
When no voltage is applied, the retardation value R of the liquid crystal cell 110 with respect to the linearly polarized incident light in the Y-axis direction at the wavelength λ is approximately λ.
The thickness of the liquid crystal layer 1 is set to be / 2, and the retardation value of the phase plate 140 is λ / 4.

In this liquid crystal element, when no voltage is applied between the transparent electrodes 3 and 4, the light transmitted through the liquid crystal layer becomes linearly polarized light in the X-axis direction and coincides with the slow axis or the fast axis of the phase plate 140. Therefore, the light is transmitted through the phase plate while maintaining the linearly polarized state in the X-axis direction. As the applied voltage increases, the alignment direction of the liquid crystal molecules tilts in the thickness direction of the liquid crystal layer, so that the retardation value R of the liquid crystal layer decreases, and the light transmitted through the liquid crystal cell 110 becomes elliptically polarized light, but transmits through the phase plate 140. By doing so, rotation of the polarization direction according to the retardation value R of the liquid crystal layer occurs while maintaining the linearly polarized state.

[0004]

The phase plate 140 used in such a liquid crystal device is made of a birefringent crystal such as quartz.
It is generally processed into a plate thickness of 3 mm or more, but in the case of a birefringent crystal, the retardation value strongly depends on the incident angle which is the angle between the traveling direction of the incident light and the normal line of the phase plate. There is a problem in that the retardation value of light or divergent light is distributed in the plane of the element, and the polarization state of the emitted light is not constant. Further, since the retardation value has wavelength dependence, there is a problem that linearity is deteriorated when incident light of linearly polarized light is emitted when the wavelength of incident light has a width.

In view of the above situation, it is an object of the present invention to provide a liquid crystal element that rotates the polarization direction while maintaining high linearity when incident light of linearly polarized light is emitted.

[0006]

SUMMARY OF THE INVENTION The present invention is a liquid crystal cell in which a liquid crystal layer is sandwiched between substrates with electrodes, and an incident straight line of wavelength λ is generated according to the magnitude of the voltage applied between the electrodes. A phase plate having a liquid crystal cell that changes the retardation value of polarized light and an organic thin film that generates a phase difference that makes the retardation value of incident linearly polarized light substantially λ / 4. And a phase plate parallel to the surface of the phase plate, and the fast axis direction of the liquid crystal cell and the fast axis direction of the phase plate form an angle of about 45 degrees. provide.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is a liquid crystal element comprising a liquid crystal cell in which a liquid crystal layer is sandwiched between substrates with electrodes. The liquid crystal element has a liquid crystal cell that changes the retardation value of the incident linearly polarized light of wavelength λ in accordance with the magnitude of the voltage applied between the electrodes, and the retardation value of the incident linearly polarized light is substantially λ / 4. And a phase plate having an organic thin film that generates a phase difference. Then, in the phase plate, the orientation direction of the molecules forming the organic thin film is parallel to the phase plate surface. Further, in the liquid crystal element, the fast axis direction of the liquid crystal cell and the fast axis direction of the phase plate form an angle of about 45 degrees.

With this structure, the retardation value of the phase plate changes little even when the incident angle of the incident light changes or when the incident light has a distributed incident angle. This has the effect that the polarization direction of the emitted light can be rotated according to the magnitude of the voltage applied between the transparent electrodes without deteriorating the linearity.

FIG. 1 is a side view showing an example of the structure of the liquid crystal element of the present invention. FIG. 2 is a diagram showing a coordinate system that constitutes the liquid crystal element of the present invention and shows the relationship between the fast axis / slow axis of the liquid crystal and the phase plate and the polarization direction. Transparent electrodes 3 and 4 are formed on one surface of the translucent substrates 5 and 6, respectively, and a film for an alignment film is applied thereon, and then each film is subjected to an alignment treatment in the same direction to form an alignment film (not shown). No.) and the seal material 8 is used to form cells. Furthermore, the ordinary refractive index n _o (l
c) and the extraordinary light refractive index n _e (lc) (n _o (lc) <n _e
A nematic liquid crystal of (lc)) is injected to form a liquid crystal layer 1 to obtain a liquid crystal cell 110 in which the alignment direction of liquid crystal molecules is aligned parallel to the substrate surface in the cell.

Further, after coating a film for an alignment film on one surface of each of the transparent substrates 6 and 7 facing each other, each film is subjected to an alignment treatment in the same direction to form an alignment film (not shown). -Make into cells by using ruthenium material. Furthermore, by injecting a liquid crystal monomer solution into the cell to form a liquid crystal monomer layer in which the alignment direction of the liquid crystal molecules is aligned parallel to the substrate surface in the cell, the alignment of the liquid crystal molecules is performed by irradiating with ultraviolet light to solidify and solidify. The phase plate 120 including the polymer liquid crystal layer 2 whose direction is fixed is obtained.

[0011] In this case, the fast axis direction of the liquid crystal cell comprising a liquid crystal layer 1 (ordinary refractive index _n o (lc) direction), the ordinary refractive index _n o (plc) and extraordinary refractive index _n e (plc) ( n _o
(Plc) <n e (plc) fast axis of the phase plate made of a polymer liquid crystal layer 2) (ordinary refractive index _n o (plc) direction) are formed at an angle of, but for example, 45 degrees There is. In FIG. 1, the fast axis direction of the liquid crystal layer 1 is set at 135 degrees with respect to the X axis which is the polarization direction of the incident light, and the liquid crystal cell 1 is arranged so that the light enters from the liquid crystal cell 110 side. The angle between the fast axis direction of the phase plate and the fast axis direction of the phase plate is
It may deviate from 45 degrees as long as it has the effect of the present invention, and may be from 40 degrees to 50 degrees.

Here, the thickness d (l) of the liquid crystal layer 1 is set so that the retardation value of the liquid crystal cell 110 becomes, for example, λ / 2 when no voltage is applied to the incident linearly polarized light of the wavelength λ in the X-axis direction.
The c) and _{0.5λ / (n e (lc)} -n o (lc)), the retardation value of the phase plate 120 is substantially lambda / 4
I am trying. Here, the retardation value of the phase plate 120 may deviate from λ / 4 as long as it has an effect of maintaining the linearity of the outgoing linearly polarized light of the liquid crystal element. Further, it may be an odd multiple of λ / 4.

When a rectangular wave AC voltage is applied from the AC power supply 9 to the transparent electrodes 3 and 4 of the liquid crystal cell 110 thus obtained, the retardation value R of the liquid crystal cell 110 is λ / 2 when no voltage is applied. Change to zero.

In the polymer liquid crystal, since the alignment directions of liquid crystal molecules are aligned parallel to the substrate surface, the incident angle, which is the angle between the traveling direction of the incident light and the normal line of the phase plate, is from 0 degree to 20 degrees. Even if tilted, the variation in retardation value is small and the wavelength λ
It functions as a stable λ / 4 phase plate against the incident light.

In the liquid crystal element shown in FIG. 1, since the rotation angle θ of the polarization direction of the outgoing light with respect to the incident light is expressed by θ = 180 × R / λ with respect to the retardation value R of the liquid crystal cell 110, the liquid crystal cell As the voltage applied to 110 increases, θ decreases from 90 degrees to 0 degrees.

As described above, the liquid crystal used in the liquid crystal element is a nematic liquid crystal, the alignment directions of the liquid crystal molecules when no voltage is applied are aligned in parallel between the substrates with electrodes, and the phase plate is a polymer liquid crystal. It is preferable that the liquid crystal cell and the phase plate are integrated. The reason is that the liquid crystal element is downsized and the angle formed between the fast axis direction of the liquid crystal cell and the fast axis direction of the phase plate is fixed, so that the stability of optical performance is improved.

When light having a wavelength at the central wavelength λ is incident, it is preferable to use a phase plate in which two polymer liquid crystal layers having different retardation values and fast axis directions are laminated. By stacking the layers, the wavelength dependence of the retardation value can be reduced, and the deterioration of the linearity of outgoing linearly polarized light can be improved.

FIG. 3 is a side view showing another example of the structure of the liquid crystal element of the present invention using such a phase plate 130.
The liquid crystal cell 110 has the same structure as that of FIG. 1, and the phase plate 130 has a polymer liquid crystal layer 11 having a retardation value of, for example, λ / 2 and a high retardation value of, for example, λ / 4 on one surface of each of the transparent substrates 6 and 7. After forming the molecular liquid crystal layer 12, the polymer liquid crystal layer is sandwiched and bonded using a translucent adhesive 13. The other reference numerals in FIG. 3 that are the same as those in FIG. 1 indicate the same elements.

Here, in the coordinate system shown in FIG. 2, the polymer liquid crystal layer 11 is oriented with respect to the polarization direction of incident light along the X axis.
The alignment direction of the liquid crystal molecules of the polymer liquid crystal is aligned such that the fast axis of the polymer liquid crystal layer 12 has an angle of 30 degrees and the fast axis of the polymer liquid crystal layer 12 has an angle of, for example, -30 degrees. Is preferred. It should be noted that the positive and negative angles have positive signs of the rotation angle from the + X axis direction to the + Y axis direction. Where λ /
The values of 2 and λ / 4 may deviate from these values as long as the output linearly polarized light of the liquid crystal element has an effect of maintaining the linearity, and 30 ° and −30 ° are about ± 5 °. There may be width.

Further, the angle formed by the slow axis of the polymer liquid crystal layer 11 with respect to the polarization direction of the incident light along the X axis is approximately 30.
The alignment direction of the liquid crystal molecules of the polymer liquid crystal may be aligned such that the angle formed by the slow axis of the polymer liquid crystal layer 12 is approximately −30 degrees. By forming the liquid crystal element 200 in which the phase plate 130 is integrated with the liquid crystal cell 110, high linearity of outgoing linearly polarized light can be maintained even when light having a wavelength width is incident.

In the above-mentioned example, an example in which a polymer liquid crystal is used as an organic thin film of a phase plate having a phase difference generating function, but another organic thin film such as polycarbonate is uniaxially stretched to form a composite film. You may use what gave the refractive property. The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

[0022]

EXAMPLE A liquid crystal device of the present invention will be described with reference to FIG. A nematic liquid crystal having an ordinary light refractive index n _o (lc) = 1.50 and an extraordinary light refractive index n _e (lc) = 1.66 was used, and the thickness d (lc) of the liquid crystal layer 1 was set to 4.5 μm.
The alignment treatment was performed on the alignment film formed on the substrate so that the fast axis direction of the liquid crystal cell forming the liquid crystal element was 135 degrees with respect to the X axis in FIG.

Further, the polymer liquid crystal layers 11 and 12 which are phase plates each have an ordinary light refractive index n _o = 1.55 and an extraordinary light refractive index n _e = 1.65, and each polymer liquid crystal layer has a thickness. To be 7.7 μm and 3.85 μm respectively, and 1.4 μm
To the center wavelength of incident light in the wavelength band from 1.
The retardation values for 55 μm were set to λ / 2 and λ / 4, respectively. Here, the polymer liquid crystal layer 1
The fast axis directions of 1 and 12 were bonded with the translucent adhesive 13 so that the directions of the fast axes were 30 ° and −30 ° with respect to the X-axis which was the incident polarization direction, that is, the directions were at an angle of 60 °.

The polymer liquid crystal layer 11 thus obtained
The phase plate 130 in which 12 and 12 are laminated is a phase plate whose retardation value is substantially λ / 4 with respect to the incident light, and the fast axis direction and the fast axis direction of the liquid crystal cell are 45. Forming an angle of degrees.

The liquid crystal element has a wavelength of 1.4 μm to 1.
Linearly polarized light having a polarization direction in the X-axis direction up to 7 μm is incident. When no voltage is applied, the retardation value R of the liquid crystal cell 110 is 0.72 μm, and the polarization direction of the emitted light of the liquid crystal element 200 is about 150 with respect to the polarization direction of the incident light.
The light became linearly polarized light rotated by 30 degrees (the angle formed by both directions is 30 degrees). Further, the retardation value of the liquid crystal cell 110 when a rectangular wave AC voltage having a voltage amplitude of 10 V or more is applied is 0.
When the thickness is 05 μm or less, the polarization direction of the emitted light of the liquid crystal element 200 becomes a linearly polarized light which is rotated by about 60 degrees with respect to the polarization direction of the incident light.

At this time, the ellipticity (the ratio a / b of the short axis amplitude a to the long axis amplitude b of the outgoing elliptical polarized light) representing the linearity of the outgoing linearly polarized light has a wavelength from 1.4 μm to 1.7 μm. It was 0.01 or less in the band, and showed high linearity.

[0027]

As described above, by using the liquid crystal element of the present invention, the state of linearly polarized light is maintained regardless of the incident angle and the wavelength of the linearly polarized light incident on the liquid crystal element, and the liquid crystal element is maintained. A liquid crystal element in which the polarization direction rotates according to the magnitude of the voltage applied to the constituent liquid crystal cells is realized.

[Brief description of drawings]

FIG. 1 is a side view showing an example of the configuration of a liquid crystal element of the present invention.

FIG. 2 is a diagram showing a coordinate system showing a relationship between a fast axis / slow axis of a liquid crystal and a phase plate, and a polarization direction, which constitutes a liquid crystal element of the present invention.

FIG. 3 is a side view showing another example of the configuration of the liquid crystal element of the present invention.

FIG. 4 is a side view showing a configuration example of a conventional liquid crystal element.

[Explanation of symbols]

1: Liquid crystal layer 2, 11, 12: Polymer liquid crystal layer 3,4: Transparent electrode 5, 6, 7: Translucent substrate 8: Seal material 9: AC power supply 13: Translucent adhesive 100, 200: Liquid crystal element 110: Liquid crystal cell 120, 130, 140: Phase plate

Claims (4)

[Claims] 1. A liquid crystal cell in which a liquid crystal layer is sandwiched between electrodes-attached substrates, wherein the retardation value of incident linearly polarized light of wavelength λ is changed according to the magnitude of voltage applied between the electrodes. A phase plate having a cell and an organic thin film that generates a phase difference such that the retardation value of incident linearly polarized light is substantially λ / 4, and the orientation direction of the molecules constituting the organic thin film is parallel to the phase plate surface. A liquid crystal element, wherein the phase axis of the liquid crystal cell and the phase axis of the phase plate make an angle of about 45 degrees. 2. The liquid crystal used in the liquid crystal device is a nematic liquid crystal, the alignment directions of liquid crystal molecules when no voltage is applied are aligned in parallel between the electrodes-attached substrates, and the phase plate is an organic thin film. 2. The liquid crystal cell and the phase plate are integrated as a polymer liquid crystal as a component.
The liquid crystal device according to item 1. 3. The phase plate comprises at least two polymer liquid crystal layers, wherein the two polymer liquid crystal layers have different retardation values, and the two polymer liquid crystal layers have a fast axis direction or a slow phase direction. The liquid crystal element according to claim 2, wherein the liquid crystal elements have different axial directions. 4. A liquid crystal element in which the liquid crystal cell, the first polymer liquid crystal layer and the second polymer liquid crystal layer are arranged in this order from the incident light side, and the liquid crystal element has a center wavelength λ of incident light. On the other hand, the first polymer liquid crystal layer has a retardation value of substantially λ / 2, and the second polymer liquid crystal layer has a retardation value of substantially λ / 4, which corresponds to the polarization direction of incident light. On the other hand, the fast axis direction of the first polymer liquid crystal layer and the fast axis direction of the second polymer liquid crystal layer are approximately 30 degrees and approximately -30 degrees, respectively, or the first polymer liquid crystal layer 4. The liquid crystal device according to claim 3, wherein the slow axis direction and the slow axis direction of the second polymer liquid crystal layer are approximately 30 degrees and approximately -30 degrees, respectively.