JP2004333567A - Dimmer and image pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dimmer having a liquid crystal optical element of which the transmittance in a transparent state is high and besides which makes reservation of a high optical density ratio (contrast ratio) and realization of fast transient response motion compatible with each other and to provide an image pickup device which has improved performance, picture quality and reliability by disposing the dimmer in the optical path. <P>SOLUTION: The dimmer is constructed by sealing a liquid crystal mixture 2 between two pairs of mutually opposing substrates consisting of transparent substrates 1a, 1b, 1c composed of glass and so on and forming a first GH (Guest-Host) cell 10a and a second GH cell 10b. The liquid crystal mixture 2 consists of negative type liquid crystal molecules 3 and positive type dye molecules 4. Transparent electrodes 6a-6d are formed on the mutually opposing surfaces of the two pairs of the mutually opposing substrates and alignment layers 7a-7d are respectively laminated thereon. In the dimmer, only the alignment layers 7a and 7d on the substrates 1a and 1c are subjected to alignment treatment such as a rubbing method and so on wherein the alignment direction of the liquid crystal molecules on the alignment layer 7a and the alignment direction of the liquid crystal molecules on the alignment layer 7d are made to perpendicularly intersect with each other. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a light control device using a liquid crystal element, for example, for adjusting the light transmittance of incident light, and an imaging device using the light control device.
[0002]
[Prior art]
Usually, a polarizing plate is used for a light control device using a liquid crystal optical element (liquid crystal cell). As this liquid crystal cell, for example, a TN (Twisted Nematic) liquid crystal cell or a guest-host (GH (Guest Host)) liquid crystal cell is used.
[0003]
FIG. 16 is a schematic explanatory view showing the operation principle of a light control device using a conventional GH cell. This light control device mainly includes a polarizing plate 11 and a GH cell 12A. In the GH cell 12A, a liquid crystal mixture is sealed between two glass substrates (not shown), and an operating electrode and an alignment film (not shown) are also provided.
[0004]
The liquid crystal mixture is composed of liquid crystal molecules 13A and dichroic dye molecules 14. The liquid crystal molecules 13A as the host material are of a positive type (positive type) having a positive dielectric anisotropy. In addition, the dichroic dye molecules 14 as the guest material have anisotropy in light absorption, and may be a positive type (p type) or a negative type (n type). FIG. 16 shows an example in which the dichroic dye molecules 14 are positive (p-type) dye molecules that absorb light in the major axis direction of the molecules.
[0005]
The incident light 5 is selected when passing through the polarizing plate 11 and changes to linearly polarized light. Further, in the GH cell 12A, an alignment process is performed so that the liquid crystal molecules 13A are aligned in the same direction (vertical direction in FIG. 16) as the oscillation direction of the linearly polarized light when no voltage is applied.
[0006]
FIG. 16A shows a state of the GH cell 12A when no voltage is applied. The dichroic dye molecules 14 are also oriented in the same direction under the influence of the liquid crystal molecules 13A, and the vibration direction of the linearly polarized light coincides with the molecular long axis direction of the dichroic dye molecules 14. It is easily absorbed by the molecules 14. Therefore, the light transmittance of the GH cell 12A is low when no voltage is applied in FIG.
[0007]
On the other hand, FIG. 16B shows a state of the GH cell 12A when a voltage is applied. When a voltage is applied to the GH cell 12A, the liquid crystal molecules 13A are oriented in the direction of the electric field, and accordingly, the major axis direction of the dichroic dye molecules 14 is orthogonal to the polarization vibration direction. Therefore, the polarized light is hardly absorbed by the dichroic dye molecules 14 and is transmitted. Therefore, the light transmittance of the GH cell 12A is high under the voltage application state shown in FIG.
[0008]
Note that, as the dichroic dye molecules 14, a negative (n-type) dye molecule that absorbs light in the molecular short axis direction can also be used. In this case, the light transmittance is opposite to the case where a positive dye molecule is used. Light is hardly absorbed when no voltage is applied, and light is easily absorbed when a voltage is applied.
[0009]
In the light control device shown in FIG. 16, the ratio of the absorbance between when the voltage is applied and when no voltage is applied, that is, the ratio of the optical density is about 10. This has an optical density ratio about twice as high as that of a dimmer including only the GH cell 12A without using the polarizing plate 11.
[0010]
Average light transmittance of visible light of the dimmer shown in FIG. 16 when a rectangular wave driving pulse is applied to the GH cell 12A (value in air: when an empty liquid crystal cell and a polarizing plate are placed in the optical path) Is defined as a reference (= 100%). The same applies to the following.) Although the maximum light transmittance when the drive pulse voltage is increased to 10 V is 60, although it increases as the drive pulse voltage increases, the maximum light transmittance is 60%. %, And the light transmittance changes slowly.
[0011]
The reason is that when positive type liquid crystal molecules are used as the host material, the interaction between the liquid crystal molecules and the alignment film at the interface of the alignment film is strong when no voltage is applied. It is considered that liquid crystal molecules that do not change or hardly change are included in a relatively large amount.
[0012]
Therefore, as a result of diligent studies, the present applicant has proposed a light control device using negative liquid crystal as a host material and an imaging device using the light control device (see Patent Document 1 described below. The invention relating to No. 1 will be referred to as the prior invention.)
[0013]
FIG. 13 is a schematic diagram illustrating the operation principle of the light control device based on the prior application invention. This light control device is mainly composed of a polarizing plate 11 and a GH cell 12B, similarly to the conventional light control device of FIG. In the GH cell 12B, a negative (negative) liquid crystal molecule 13B having a negative dielectric anisotropy as a host material and a positive or negative dichroic dye molecule 14 as a guest material are enclosed. Have been. FIG. 13 shows a case where the dichroic dye molecules 14 are positive (p-type) dye molecules.
[0014]
As in the device of FIG. 16, the incident light 5 is selected when passing through the polarizing plate 11 and changes to linearly polarized light. Further, in the GH cell 12B, when a voltage is applied, an alignment process is performed so that the liquid crystal molecules 13B are aligned in the same direction (vertical direction in FIG. 13) as the vibration direction of the linearly polarized light.
[0015]
FIG. 13A shows a state of the GH cell 12B when no voltage is applied. Since the liquid crystal molecules 13B are arranged so as to be orthogonal to the substrate and the molecular long axis direction of the dichroic dye molecules 14 is orthogonal to the vibration direction of the polarized light, the polarized light is hardly absorbed by the dichroic dye molecules 14, To Penetrate. Therefore, the light transmittance of the GH cell 12B is high when no voltage is applied in FIG.
[0016]
On the other hand, FIG. 13B shows a state of the GH cell 12B when a voltage is applied. When a voltage is applied to the GH cell 12B, the liquid crystal molecules 13B are oriented so as to be orthogonal to the direction of the electric field, and accordingly, the major axis direction of the dichroic dye molecules 14 becomes coincident with the polarization direction of light. . Therefore, polarized light is easily absorbed by the dichroic dye molecules 14. Therefore, the light transmittance of the GH cell 12B is low under the voltage application state shown in FIG.
[0017]
Note that a negative (n-type) dye molecule can be used as the dichroic dye molecule. In this case, the light transmittance is opposite to the case where a positive dye molecule is used.
[0018]
FIG. 6 is a graph illustrating the light transmittance when a rectangular drive pulse is applied to the GH cell 12B of FIG. 13 with respect to the drive pulse voltage. At this time, as an example of the negative liquid crystal 13B having a negative dielectric anisotropy (Δε), MLC-6608 manufactured by Merck is used as a host material, and a positive type liquid crystal 13A having a positive light absorption anisotropy (ΔA) is used. As an example of the chromatic dye molecules 14, D5 manufactured by BDH was used as a guest material. As shown in FIG. 6, the average light transmittance of visible light decreases from the maximum light transmittance of about 75% to about 10% as the pulse voltage increases, and the change of the light transmittance is relatively steep. became.
[0019]
The reason is that when negative type liquid crystal molecules are used as the host material, the interaction between the liquid crystal molecules and the alignment film at the interface of the alignment film is very weak when no voltage is applied, so that light is easily transmitted when no voltage is applied. It is also considered that the direction of the director of the liquid crystal molecules easily changes with the application of the voltage.
[0020]
As described above, according to the invention of the prior application, by forming a guest-host type liquid crystal cell using a negative type liquid crystal as a host material, the light transmittance particularly when transparent is improved, and the GH cell can be directly used in an imaging optical system. A compact light control device that can be used with its position fixed can be realized.
[0021]
In this case, by further arranging a polarizing plate in the optical path of the incident light to the liquid crystal optical element, the ratio of the absorbance between when no voltage is applied and when a voltage is applied (that is, the ratio of optical density) is further improved, and the light control device is improved. Is further increased, and the dimming operation can be performed more normally from a bright place to a dark place.
[0022]
[Patent Document 1]
JP 2001-201769 A (FIGS. 1 and 3)
[0023]
[Problems to be solved by the invention]
The inventor of the present invention has intensively studied the further improvement of the characteristics of the light control device using such a GH cell, and as shown in FIG. 14, the optical density ratio between the transparent state and the light-shielded state of the liquid crystal optical element (see FIG. 14). It has been found that the contrast ratio and the dynamic range are greatly affected by the distance between the two glass substrates forming the GH cell (hereinafter, referred to as a cell gap).
[0024]
That is, as shown in FIG. 14, as the cell gap is larger and the thickness of the liquid crystal layer is larger, the difference in light transmittance between the transparent state and the light-shielded state is larger, and the optical density ratio is larger. However, as the cell gap increases, the light transmittance in the transparent state decreases, and the advantage of using negative liquid crystal molecules as the host material decreases.
[0025]
On the other hand, as shown in FIG. 15, when the cell gap changes, the response speed as a dimmer using the GH cells also changes greatly. For example, as the cell gap increases and the thickness of the liquid crystal layer increases, the response speed decreases. In particular, as shown as a graph a in FIG. 15, when the driving is performed such that the light transmittance is slightly changed in the halftone, the response speed is significantly reduced.
[0026]
As described above, in the light control device using the guest-host type liquid crystal optical element, the optical density ratio and the transient response speed are in a trade-off relationship with respect to the cell gap, so that a characteristic in which both are compatible is obtained. But there was a limit. Therefore, conventionally, the specification of the GH cell has been determined in such a manner that one of the characteristics is prioritized (the other characteristic must be reduced to some extent) in accordance with the set in which the GH type liquid crystal optical element is mounted.
[0027]
Under such circumstances, a dimming device using a liquid crystal optical element, which has a high light transmittance in a transparent state and can realize both a high optical density ratio and a quick transient response operation, has been desired.
[0028]
Therefore, an object of the present invention is to provide a light control device having a liquid crystal optical element which has a high light transmittance in a transparent state, and at the same time can ensure a large optical density ratio and realize a quick transient response operation, and this light control device. It is an object of the present invention to provide an imaging device in which an apparatus is arranged in an optical path and which has improved performance, image quality, and reliability.
[0029]
[Means for Solving the Problems]
That is, the present invention is a light control device in which a plurality of liquid crystal optical elements are sequentially arranged along an optical path, and each of the plurality of liquid crystal optical elements has a liquid crystal layer made of a mixture of a host material and a guest material, The present invention relates to a light control device in which at least two liquid crystal orientation directions of the plurality of liquid crystal optical elements cross each other, and relates to an image pickup device in which the light control device is disposed in an optical path of an image pickup system.
[0030]
According to the light control device and the imaging device of the present invention, since the plurality of liquid crystal optical elements each having the function of the light control device are sequentially arranged along the optical path, for each element of the liquid crystal optical element, The thickness (cell gap) of the liquid crystal layer is kept small to achieve a high response speed required for the light control device, and the plurality of liquid crystal optical elements as a whole have a sufficient thickness of the liquid crystal layer, A large optical density ratio (contrast ratio) can be achieved.
[0031]
In addition, since at least two liquid crystal orientation directions of the plurality of liquid crystal optical elements intersect each other, polarized light that has not been absorbed by one of the two liquid crystal optical elements having different liquid crystal orientation directions is Absorption by the other liquid crystal optical element is inevitably received. As a result, the light shielding performance at the time of light shielding is significantly improved, and the optical density ratio is greatly improved.
[0032]
Further, one of the two liquid crystal optical elements having different liquid crystal orientation directions can be used as a substitute for a polarizing plate, and a light control device that does not use a polarizing plate can be configured without deteriorating the light blocking performance. This dimmer has no loss due to the polarizing plate, so that the amount of light transmission when transparent is greatly improved.
[0033]
Therefore, the present invention is extremely effective for improving the performance, image quality, and reliability of a light control device and an imaging device using a liquid crystal optical element.
[0034]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, it is preferable that at least two liquid crystal orientation directions of the plurality of liquid crystal optical elements intersect with each other, particularly, intersect at right angles. Thus, the ratio of the polarized light that is not absorbed by one of the two liquid crystal optical elements having different liquid crystal orientation directions to be absorbed by the other liquid crystal optical element is maximized. The light-shielding performance of the optical element is maximized.
[0035]
The host material is preferably a positive or negative liquid crystal molecule, particularly a negative liquid crystal molecule, and the guest material is preferably a positive dichroic dye molecule. Although the guest material may be a negative type dichroic dye molecule, the effect of the present invention is that the host material is a negative type liquid crystal molecule and the guest material is a positive type dichroic dye molecule. Sometimes, it is most effective.
[0036]
In addition, it is preferable that each cell gap of the plurality of liquid crystal optical elements in at least the effective optical path is controlled to be 1 to 3 μm, whereby a more practically advantageous dimmer using the plurality of GH cells is provided. Can be realized.
[0037]
Because, when each of the above cell gaps is less than 1 μm, the response speed of the light control device becomes large, and the light transmittance in the transparent state is improved, but the light transmittance in the light-shielded state is also greatly increased. As a result, a sufficient optical density ratio (contrast ratio) may not be secured. Conversely, when each of the above cell gaps exceeds 3 μm, a large optical density ratio can be ensured, but the light transmittance in a transparent state is reduced, and the response speed as a light control device may be significantly deteriorated. In particular, when a drive that slightly changes light in the halftone is performed, the response speed may be reduced.
[0038]
As described above, according to the light control device of the present invention, the cell gaps of the plurality of liquid crystal optical elements are controlled to 1 to 3 μm, and the plurality of liquid crystal optical elements are sequentially arranged along the optical path. Since the thickness of the liquid crystal layer as a whole of the plurality of liquid crystal optical elements is sufficiently ensured, a sufficiently large optical density ratio can be achieved and a single liquid crystal optical element having a small cell gap (for example, a liquid crystal having a cell gap of 3 μm). The light control operation can be performed at high speed in the same manner as when the optical element is driven. Therefore, it is possible to achieve both a high contrast ratio and a high-speed transient response, which cannot be realized conventionally.
[0039]
At this time, at least two liquid crystal optical elements whose liquid crystal orientation directions intersect each other at the time of the light shielding operation are preferably controlled so that at least the cell gaps in the effective optical path are different from each other. The cell gap ratio is preferably 1: 1 to 1: 4, more preferably 1: 1.5 to 1: 2.5, and still more preferably 1: 2. It is desirable that the liquid crystal optical element having the larger cell gap be disposed on the light incident side.
[0040]
Alternatively, at least two liquid crystal optical elements whose liquid crystal orientation directions intersect each other at the time of the light shielding operation preferably have different concentrations of the guest material, and more specifically, have a ratio of the guest material concentration. The ratio is 1: 1 to 1: 4, more preferably 1: 1.5 to 2.5, and even more preferably 1: 2. It is desirable that the liquid crystal optical element having the higher concentration of the guest material is disposed on the light incident side.
[0041]
In this case, since the liquid crystal optical element having a high optical density is arranged on the light incident side during the light shielding operation, the main incident light is absorbed at a position as close to the incident side as possible. The light that could not be absorbed can be supplementarily absorbed by the liquid crystal optical element at the subsequent stage, and the light shielding efficiency is improved.
[0042]
Further, a polarizing plate is disposed on the light incident side, and a vibration direction of light transmitted through the polarizing plate is a direction of light absorbed by the guest material in the liquid crystal optical element on the light incident side of the plurality of liquid crystal optical elements. It is preferable that the vibration direction substantially coincides with the vibration direction of the light absorbed by the liquid crystal optical element having the larger cell gap or the liquid crystal optical element having the higher concentration of the guest material. Is good. With this configuration, the polarizing action of the polarizing plate and the light absorbing action of the plurality of liquid crystal optical elements can be most effectively combined, and a high contrast ratio can be realized in the dimming operation.
[0043]
The number of the plurality of liquid crystal optical elements may be three or more. For example, it is preferable to arrange two liquid crystal optical elements having a high optical density during the light shielding operation and one liquid crystal optical element having a low optical density during the light shielding operation in this order from the light incident side. At this time, the vibration directions of the light absorbed by the first and third liquid crystal optical elements are made to coincide with each other, and the vibration direction of the light absorbed by the second liquid crystal optical element is made orthogonal to the vibration direction. Good. In this way, the first-stage liquid crystal optical element is used as a substitute for the polarizing plate, thereby realizing a high contrast ratio in the dimming operation, and realizing a compact dimming device having a large light transmission amount when transparent. be able to.
[0044]
Alternatively, the vibration directions of the light absorbed by the three liquid crystal optical elements are made orthogonal to the first and second liquid crystal optical elements, and the main light is absorbed by the first and second liquid crystal optical elements. The third stage liquid crystal optical element supplementally absorbs the light passing through them, eliminating the need for a polarizing plate and achieving a high contrast ratio in the dimming operation, while at the same time transmitting light in the transparent state. A large-sized and compact dimmer can be realized.
[0045]
As described above, when the number of the liquid crystal optical elements, the size of the cell gap, and the concentration of the guest material are combined, a variety of dimming operations can be performed.
[0046]
Further, it is desirable that an intermediate substrate constituting the plurality of liquid crystal optical elements is shared. That is, it is preferable that a plurality of substrates are sequentially arranged side by side, and a mixture of the host material and the guest material is sealed between the plurality of adjacent substrates. Thus, the number of substrates can be reduced, the reflection at the interface between the air layer and the substrate and the absorption of light by the substrate can be reduced, and a compact light control device can be manufactured.
[0047]
At this time, in consideration of the easiness of the manufacturing process, it is preferable that an alignment process (rubbing or the like) of liquid crystal molecules is performed on an outer substrate among the substrates constituting the plurality of liquid crystal optical elements. (One side rubbing). Although it is not impossible to perform the alignment treatment of the liquid crystal molecules on the intermediate substrate, it is preferable that the alignment treatment is performed only on one surface in this case as well.
[0048]
Further, in order to make the mounting form of the plurality of liquid crystal optical elements compact and to reduce the size of the light control device, it is necessary to drive the liquid crystal optical elements on both surfaces of the peripheral portion of the intermediate substrate among the plurality of substrates. It is preferable to provide a lead-out portion for an electrode to which the operating voltage is applied.
[0049]
In addition, in order to suppress light absorption by the substrates and reduce the size and weight of the device, the thickness of each substrate constituting the plurality of liquid crystal optical elements is preferably as thin as possible, and each is preferably 0.5 mm or less. preferable.
[0050]
Further, the imaging device of the present invention is an imaging device that can effectively utilize the features of the above-described dimming device because the dimming device is arranged in the optical path of the imaging system.
[0051]
Here, an example in which the intermediate substrate is shared is described, but a structure in which a plurality of single liquid crystal optical elements having a small cell gap are simply stacked may be used. In this case, the light transmittance at the time of shading is further reduced, but if an air layer exists between the cells, light loss occurs due to light reflection at the interface between the air layer and the substrate as described above. However, it is desirable to have a device for minimizing such a loss.
[0052]
Next, a preferred embodiment of the present invention will be specifically described with reference to the drawings. The present embodiment provides a light control device having an improved optical function by disposing a GH multiplex cell including a first GH cell and a second GH cell each using a negative liquid crystal as a host material in an optical path.
[0053]
Operation principle of GH multiplex cell
This embodiment is based on the above-mentioned prior invention. According to the invention of the prior application, a guest-host comprising a liquid crystal optical element and a polarizing plate disposed in an optical path of light incident on the liquid crystal optical element, and using negative liquid crystal molecules as a host material By using the type liquid crystal, a large light transmittance in a transparent state can be achieved, and a compact dimming device can be realized in which the GH cell can be fixed and used in the imaging optical system as it is.
[0054]
FIG. 1 is a schematic sectional view showing the operation principle of a GH multiplex cell constituting a light control device according to the present embodiment, and FIG. 2A is a partially enlarged schematic sectional view of the GH multiplex cell.
[0055]
As shown in FIG. 2A, in the GH multiplex cell 10, two sets of opposing substrates made of transparent substrates 1 a, 1 b, and 1 c made of glass and the like provided at equal intervals, ie, substrates 1 a and 1 b, and The liquid crystal mixture 2 is sealed between 1b and 1c to form a first GH cell 10a and a second GH cell 10b. The substrate 1b located between the substrates 1a and 1c is shared by the two GH cells 10a and 10b. The liquid crystal mixture 2 is a guest-host type liquid crystal using the negative type liquid crystal molecules 3 as a host material and the positive type dye molecules 4 as a guest material, and between the substrates 1a and 1b and between the substrates 1b and 1c. Are sealed with a sealing material 8.
[0056]
When a glass substrate is used, the thickness of the substrates 1a, 1b, and 1c should be as thin as possible, particularly 0.5 mm or less, in order to suppress the amount of light absorbed by the glass and to reduce the size and weight of the device. Is preferred.
[0057]
Transparent electrodes 6a and 6b, and 6c and 6d are formed on the opposing surfaces of the substrates 1a and 1b and the opposing surfaces of the substrates 1b and 1c, respectively, for further controlling the alignment direction of liquid crystal molecules. Of alignment films 7a and 7b, and 7c and 7d, respectively.
[0058]
Actually, in order to control the alignment direction of the liquid crystal molecules using the alignment film, it is necessary to perform an alignment process (for example, a rubbing method) for setting the alignment direction of the liquid crystal molecules in the alignment film. Considering the easiness of the manufacturing process, it is preferable that the alignment treatment is performed only on the alignment films 7a and 7d formed on the two outer substrates 1a and 1c (single-side rubbing). The reason is that if double-sided rubbing is applied instead of the single-sided rubbing, the alignment treatment is performed on the alignment film on one surface of the intermediate substrate 1b and then on the other surface. This is because when performing the method, the alignment film which has already been subjected to the alignment treatment may be adversely affected.
[0059]
Therefore, in the present embodiment, only the alignment films 7a and 7d on the substrates 1a and 1c are subjected to an alignment treatment such as a rubbing method, and the alignment films 7b and 7c on the substrate 1b are aligned. No treatment is performed (for example, a vertical alignment film such as an oblique deposition film is formed on a transparent electrode, but a rubbing treatment is not performed). Then, the direction in which the liquid crystal molecules are aligned in the alignment film 7a is orthogonal to the direction in which the liquid crystal molecules are aligned in the alignment film 7d.
[0060]
Further, as shown in FIG. 1, an AC drive power source 34a for driving the liquid crystal cell and a counter electrode for the two GH cells 10a and 10b, that is, between the transparent electrodes 6a and 6b and between the transparent electrodes 6c and 6d, respectively. 34b is connected. In order to make the mounting form of the GH multiplex cell 10 compact and reduce the size of the light control device, an AC drive voltage is applied only to the peripheral portions on both surfaces of the intermediate substrate 1b among the three substrates 1a to 1c. It is preferable to provide electrode lead-out portions 31b and 31c for performing the operation. Further, the two GH cells 10a and 10b can be connected in parallel to the same AC drive power supply, share the power supply, and reduce the size and cost of the dimmer.
[0061]
In FIG. 1, the incident light 5 is linearly polarized by transmitting through a polarizing plate. This is not absolutely necessary, but in order to realize a high contrast ratio at the time of dimming, it is preferable that the incident light 5 is linearly polarized light. Further, similarly to the light control device of FIG. 13, in the GH cell 10a, when a voltage is applied, the liquid crystal molecules 3 are aligned in the same direction as the oscillation direction of the polarization of the incident light 5 (the vertical direction in FIG. 1). Has been made. On the other hand, in the GH cell 10b, the liquid crystal molecules 3 are oriented so that the orientation in which the liquid crystal molecules 3 are oriented when a voltage is applied is perpendicular to the liquid crystal orientation in the GH cell 10a (the direction perpendicular to the plane of FIG. 1). Has been made.
[0062]
As shown in FIG. 1A, when no voltage is applied, in the two GH cells 10a and 10b, the negative liquid crystal molecules 3 and the positive dye molecules 4 are arranged perpendicular to the substrate, and the incident light 5 (polarized light) 13) is orthogonal to the direction of the major axis of the positive dye molecules 4, so that the incident light 5 is hardly absorbed by the positive dye molecules 4 as in the case of FIG. 10b.
[0063]
On the other hand, when a voltage is applied, the direction of the director of the liquid crystal molecules changes as shown in FIG. 1B, and accordingly, the molecular major axis direction of the positive dye molecules 4 in the GH cell 10a changes the polarization direction of the incident light 5 It comes to coincide with the vibration direction. As a result, the polarized light of the incident light 5 is absorbed by the positive dye molecules 4, and the light transmittance of the GH multiplex cell 10 decreases.
[0064]
In the GH cell 10a, similarly to the prior application, since the interaction between the liquid crystal molecules 3 and the alignment film 7a at the interface of the alignment film 7a when no voltage is applied is very weak, light is easily transmitted when no voltage is applied, Further, the direction of the director of the liquid crystal molecules easily changes with the application of the voltage, and the light transmittance changes sharply with an increase in the applied operating pulse voltage.
[0065]
Here, when light whose oscillation direction is orthogonal to the polarization oscillation direction is included in the incident light 5 or is generated by depolarization while the incident light 5 travels in the GH cell 10a, this light Is not absorbed by the positive dye molecules 4 contained in the GH cell 10a but is transmitted regardless of the thickness of the liquid crystal layer of the GH cell 10a. This is one of the main causes for lowering the light shielding performance of the GH cell of the prior application.
[0066]
However, according to the present embodiment, the GH cell 10b is arranged at the subsequent stage of the GH cell 10a, and the molecular orientation of the positive dye molecules 4 in the GH cell 10b is It is controlled so as to be orthogonal to the molecular long axis direction of the positive dye molecules 4 in the GH cell 10a. As a result, light that is not absorbed by the GH cell 10a (light whose vibration direction is orthogonal to the plane of FIG. 1) is most effectively absorbed by the GH cell 10b. Is significantly improved as compared with the case of using the GH cell 10a alone.
[0067]
FIG. 3 and FIG. 4 are schematic cross-sectional views showing a GH multiplex cell which is a modification of the present embodiment. In the GH multiplex cell shown in FIG. 3, the cell gap between the GH cell 10c and the GH cell 10d is different, and the GH cell 10c is larger. In the GH multiplex cell shown in FIG. 4, the cell gap is the same, but the concentration of the positive dye molecules 4 is different, and the concentration in the GH cell 10e is higher than that in the GH cell 10f.
[0068]
In any case, a liquid crystal optical element having a higher optical density during the light-shielding operation (the GH cell 10c having a large cell gap or the GH cell 10e having a high density of the positive dye molecules 4) is disposed on the light incident side. Moreover, when a voltage is applied (during a light-shielding operation), the liquid crystal serving as the host material is so arranged that the long axis direction of the positive dye molecules 4 contained in the cell coincides with the oscillation direction of the polarized light of the incident light 5. It is controlled by the orientation of the molecule. By doing so, main incident light is absorbed at a position as close to the incident side as possible, and light that could not be absorbed by the preceding liquid crystal optical element can be supplementarily absorbed by the subsequent liquid crystal optical element. As a result, the light shielding efficiency is improved.
[0069]
The GH multiplex cell shown in FIGS. 2B and 2C is also one of the modifications, and is an example in which the spacer 9 is arranged between the opposing substrates in order to reduce the variation in the cell gap. The cell shown in FIG. 2B uses a spherical spacer, and the cell shown in FIG. 2C uses a prismatic spacer.
[0070]
GH multiplex cell
FIG. 7A is a schematic plan view of the substrates 1a and 1c arranged outside on the substrates constituting the GH multiplex cell 10 according to the present embodiment, and FIG. FIG. 4 is a schematic plan view of a substrate 1b to be formed.
[0071]
As shown in FIG. 7A, the glass substrate 1a (or 1c) disposed on the outside has a substantially square shape, and one surface (GH liquid crystal cell side) has an ITO (Indium Tin Oxide) on one surface. A transparent electrode 6a (or 6d) such as an electrode and an alignment film 7a (or 7d) are formed, and the alignment film 7a (or 7d) is subjected to an alignment process such as a rubbing method. Here, the direction in which the liquid crystal molecules are aligned in the alignment film 7a is orthogonal to the direction in which the liquid crystal molecules are aligned in the alignment film 7d. Examples of the alignment treatment method include, besides the rubbing method, a light alignment method using polarized ultraviolet light, an oblique vapor deposition method, and the like. The transparent electrode 6a (or 6d) extends outside the effective optical path 20 and is electrically connected to an electrode lead portion 31b (or 31c) provided on the glass substrate 1b as described later.
[0072]
As shown in FIG. 7B, the intermediate glass substrate 1b has a rectangular shape slightly larger than the glass substrate 1a (or 1c), and has transparent electrodes 6b and 6c such as ITO electrodes on both sides. And the alignment films 7b and 7c are formed respectively, and the alignment film 7b is not subjected to the alignment process. The substrate 1b is provided with lead portions 31b and 31c for the transparent electrode.
[0073]
FIG. 8 is a schematic plan view (a) of the GH cell 10a or 10b and a cross-sectional view taken along the line XX (b). As shown in FIG. 8, a portion between the substrates 1a and 1b (or a portion between the substrates 1b and 1c) is sealed by a sealing material 8 at a liquid crystal cell peripheral portion 32. Then, as shown in FIG. 8 (b), the transparent conductive film (transparent electrode) 6a (or 6d) extending on the substrate 1a (or 1c) and the electrode lead-out portion 31b (or 6) formed on the substrate 1b. 31c) are connected by a conductive material such as carbon paste 33 outside the sealing material 8.
[0074]
FIG. 9 is a sectional view taken along line AA shown in FIG. As described above, it is desirable that the cell gaps of the GH cells 10a and 10b are each controlled to 1 to 3 μm, and furthermore, as shown in FIG. More preferably, it is smaller than the gap at the periphery. This makes it possible to operate the light control cell 10 in the effective optical path at a higher speed while maintaining the optical density ratio required for the light control device.
[0075]
In the present embodiment, in forming the cell gap as described above, as shown in FIGS. 8B and 8C, the opposed electrodes on which the transparent electrodes 6a and 6b and the alignment films 7a and 7b are respectively formed are formed. A spacer 9 is arranged between the substrates 1a and 1b, or between the opposite substrates 1b and 1c on which the transparent electrodes 6c and 6d and the alignment films 7c and 7d are formed, respectively. It is preferable that the sealing material 8 is formed to have a larger diameter than the spacer 9 or contains a hard material such as a ball or fiber.
[0076]
Light control device
The dimming device 23 including the GH multiplex cell 10 described above is disposed between a front lens group 15 and a rear lens group 16 including a plurality of lenses like a zoom lens, for example, as shown in FIG. . The light transmitted through the front lens group 15 is linearly polarized through the polarizing plate 11 and then enters the GH multiplex cell 10. The light modulated by the GH multiplex cell 10 is condensed by the rear lens group 16 and projected on the imaging surface 17 as an image.
[0077]
The polarizing plate 11 constituting the dimmer 23 is, as previously proposed by the present applicant (see Japanese Patent Application Laid-Open No. H11-326894), with respect to the effective optical path of light incident on the GH multiplex cell 10. It can be put in and out. Specifically, by moving the polarizing plate 11 to a position indicated by a virtual line, the light can be emitted out of the effective optical path. As a means for taking the polarizing plate 11 in and out, a mechanical iris as shown in FIG. 11 may be used.
[0078]
The mechanical iris is a mechanical diaphragm device generally used for digital still cameras, video cameras, and the like, and mainly includes two iris blades 18 and 19 and a polarizing plate 11 adhered to the iris blade 18. The iris blades 18, 19 can be moved vertically. The iris blades 18 and 19 are relatively moved in the direction indicated by the arrow 21 using a drive motor (not shown).
[0079]
As a result, as shown in FIG. 11, the iris blades 18 and 19 are partially overlapped, and when this overlap increases, the opening 22 on the effective optical path 20 located near the center of the iris blades 18 and 19 becomes polarized. Covered by plate 11.
[0080]
FIGS. 11A to 11C are partially enlarged views of the mechanical iris near the effective optical path 20. At the same time as the iris blade 18 moves downward, the iris blade 19 moves upward. Along with this, as shown in FIG. 11A, the polarizing plate 11 attached to the iris blade 18 also moves out of the effective optical path 20. Conversely, by moving the iris blade 18 upward and the iris blade 19 downward, the iris blades 18 and 19 overlap each other. Accordingly, as shown in FIG. 11B, the polarizing plate 11 moves on the effective optical path 20 and gradually covers the opening 22. When the overlapping of the iris blades 18 and 19 becomes large, the polarizing plate 11 covers the entire opening 20 as shown in FIG.
[0081]
Next, the light control operation of the light control device 23 using the mechanical iris will be described.
[0082]
As the subject (not shown) becomes brighter, as shown in FIG. 11A, the iris blades 18 and 19 that have been opened in the vertical direction are driven by a motor (not shown) and start overlapping. As a result, the polarizing plate 11 attached to the iris blade 18 starts to enter the effective optical path 20 and covers a part of the opening 22 (FIG. 11B).
[0083]
At this time, the GH multiplex cell 10 is in a state of not absorbing light (the incident light is slightly attenuated by the GH multiplex cell 10 due to thermal fluctuation, surface reflection, or the like). Therefore, the light that has passed through the polarizing plate 11 and the light that has passed through the opening 22 have substantially the same intensity distribution.
[0084]
After that, the polarizing plate 11 completely covers the opening 22 (FIG. 11C). Further, when the brightness of the subject increases, the voltage applied to the GH multiplex cell 10 is increased, and the light is adjusted by absorbing the light in the GH multiplex cell 10.
[0085]
On the contrary, when the subject becomes dark, first, the voltage applied to the GH multiplex cell 10 is reduced or the voltage is not applied to reduce the light absorption effect of the GH multiplex cell 10, Or nothing. Further, when the subject becomes dark, the iris blade 18 is moved downward and the iris blade 19 is moved upward by driving the motor with a motor (not shown). Thus, the polarizing plate 11 is moved out of the effective optical path 20 (FIG. 11A).
[0086]
According to this method, as shown in FIGS. 10 and 11, when it is desired to increase the transmittance, the polarizing plate 11 (light transmittance, for example, 40% to 50%) is taken out of the effective optical path 20 of light. Therefore, the amount of incident light does not decrease due to the polarizing plate 11. Accordingly, when comparing the dimmer 23 with a conventional dimmer in which the polarizing plate is always placed in the effective optical path 20 of light, the maximum light transmittance is improved, for example, about twice. Note that the minimum light transmittance is the same for both.
[0087]
In addition, since the polarizing plate 11 is moved in and out using a mechanical iris that has been put to practical use in digital still cameras and the like, the light control device can be easily implemented. In addition, since the GH multiplex cell 10 is used, light control can be performed by controlling the light transmittance of the GH multiplex cell 10 in addition to the light control by the polarizing plate 11.
[0088]
In this manner, the light control device 23 can increase the contrast ratio between light and dark and can maintain the light amount distribution substantially uniform.
[0089]
【Example】
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
Example 1
The GH multiplex cell 10 including the two GH cells 10a and 10b having the same cell gap as shown in FIG. 1 was manufactured and incorporated in the light control device.
[0090]
As shown in FIG. 10, the light control device includes a GH multiplex cell 10 and a polarizing plate 11. Then, in the GH multiplex cell 10, as shown in cross sections in FIGS. 1 and 2 (a), the three glass substrates 1a, 1b and 1c, which are provided to face each other at equal intervals, respectively, The transparent electrodes 6a to 6d and the alignment films 7a to 7d are formed, and a negative type liquid crystal molecule 3 as a host material and a positive type as a guest material are provided in two gaps formed by two sets of opposed substrates. Mixture 2 with dichroic dye molecules 4 was encapsulated.
[0091]
Negative liquid crystal molecules 3 having a negative dielectric anisotropy include MLC-6608 manufactured by Merck, and a positive dye dichroism having anisotropy in light absorption and absorbing light in a molecular long axis direction. As the dye molecule 4, D5 manufactured by BDH was used as an example.
[0092]
Here, in the first GH cell 10c arranged on the light incident side, the liquid crystal molecules 3 contained in the first GH cell 10c are oriented such that the vibration direction of the light passing through the polarizing plate 11 is applied when a voltage is applied (during a light-shielding operation). It was configured to match the orientation.
[0093]
Then, as shown in FIG. 10, the light control device 23 is disposed between a front lens group 15 and a rear lens group 16 including a plurality of lenses such as a zoom lens. The light transmitted through the front lens group 15 is linearly polarized through the polarizing plate 11 and then enters the GH multiplex cell 10. The light modulated by the GH multiplex cell 10 is condensed by the rear lens group 16 and projected on the imaging surface 17 as an image.
[0094]
The polarizing plate 11 constituting the light control device 23 is moved into and out of an effective optical path of light incident on a plurality of GH cells 10 as previously proposed by the present applicant (Japanese Patent Laid-Open No. 11-326894). It is possible.
[0095]
Specifically, by moving the polarizing plate 11 to a position indicated by a virtual line, the light can be emitted out of the effective optical path. As a means for taking the polarizing plate 11 in and out, a mechanical iris as shown in FIG. 11 may be used.
[0096]
Here, as shown in schematic plan views in FIGS. 7 and 8A, the GH multiplex cell 10 includes, for example, both sides of a glass substrate 1b having a thickness of 0.5 mm and a glass substrate 1a having a thickness of 0.5 mm. And 1c are formed with transparent electrode patterns 6a, 6b, 6c and 6d and alignment films 7a, 7b, 7c and 7d, respectively, and are formed only on the alignment films 7a and 7d on the glass substrates 1a and 1c. Rubbing treatment was performed (single-side rubbing). Here, the rubbing directions of the alignment films 7a and 7d were orthogonalized so that the liquid crystal molecules in the first GH cell 10a and the second GH cell 10b were orthogonal to each other during the light-shielding operation (when operating voltage was applied).
[0097]
Further, on both surfaces of the glass substrate 1b, lead portions 31b and 31c for the transparent electrodes 6b and 6c are provided, respectively, and the transparent electrodes 6a and 6d of the glass substrates 1a and 1c extend outside the effective optical path 20, and They were electrically connected to the electrode lead portions 31b and 31c provided on the substrate 1b, respectively. The first GH cell 10a and the second GH cell 10b were connected to drive power supplies 34a and 34b, respectively.
[0098]
Here, the GH multiplex cell 10 is manufactured by, for example, forming a glass substrate having a diameter of 3.0 μm on the cell peripheral portion 32 of the glass substrates 1 a and 1 c having a thickness of 0.5 mm on which the transparent electrode pattern and the alignment film described above are formed in advance. After applying a sealing material 8 made of a thermosetting epoxy resin containing a fiber at a predetermined width, the three glass substrates 1a, 1b and 1c are aligned and stacked, and then a hot press plate Under moderate conditions (for example, 150 to 170 ° C., 1 to 2 kg / cm²), Heat treatment is performed while applying pressure to cure the sealing material 8 in the cell peripheral portion 32, complete the bonding of the substrates, and complete a liquid crystal cell having a two-layer structure (FIGS. 1 and 2 (a)). )).
[0099]
At this time, a transparent electrode pattern provided with a lead electrode portion was formed on both surfaces of the intermediate glass substrate among the three glass substrates to be superposed (FIGS. 1 and 7B).
[0100]
When the cell gap of an empty cell having a two-layer structure obtained by singulating (scribing and breaking) the bonded substrate was measured by a measuring device utilizing light interference, the first GH cell 10a and the second GH cell were measured. The gap at the center of the cell in 10b was about 2.2 μm, and the gap at the periphery of the cell was about 2.8 μm. Note that the thickness of the liquid crystal layer as a whole of the GH multiplex cell 10 was about 5 μm.
[0101]
The empty first GH cell 10a and the second GH cell 10b thus prepared are filled with a negative liquid crystal molecule MLC-6608 (manufactured by Merck) and a positive dichroic dye molecule D5 (manufactured by BDH). Liquid crystal mixture 2 was sealed. Then, a rectangular wave-shaped operating voltage is applied to the electrode lead portions 31b and 31c provided on the intermediate glass substrate 1b, so that an appropriate effective voltage is applied to the liquid crystal molecules of each cell. The change in transmittance was measured. The results are shown in FIGS.
[0102]
As shown in FIG. 6, the average light transmittance of visible light (in air) decreased from the maximum transmittance of about 73% to the minimum transmittance of about 2% with an increase in the applied operating voltage. The GH multiplex cell 10 almost reached the minimum transmittance when a pulse voltage of ± 5 V (1 kHz) or more was applied, although it differs depending on the liquid crystal cell structure and constituent materials used.
[0103]
As described above, in the present example, the thickness of the liquid crystal layer as a whole of the GH multiplex cell 10 was about 5 μm. Therefore, as a comparative example, a single GH cell based on the invention of the prior application was formed in which two glass substrates were provided to face each other with a cell gap of 5 μm, and the same liquid crystal mixture as in this example was sealed. In the same manner as in this example, a change in light transmittance when an operating voltage was applied was measured. The results are also shown in FIGS.
[0104]
Comparing this example with the comparative example, the minimum transmittance at the time of shading in this example was reduced to less than half of that of the comparative example, though the effective liquid crystal layer thickness was 5 μm. As a result, the dynamic range of the dimming operation could be greatly expanded.
[0105]
This is because the number of interfaces where materials having different refractive indices are in contact with each other is increased in the structure of the GH cell, and the interface reflection there reduces the amount of transmitted light as a whole. The main factor is that the number has increased on the optical path.
[0106]
Regarding the transient response time when the operating pulse voltage applied to the cell was changed, the single GH cell having a cell gap of 5 μm had a response time exceeding 100 ms when driven in halftone, High-speed operation of 20 ms or less has become possible. This realizes high-speed driving equivalent to that of a GH cell having a cell gap of about 2.5 μm and a half cell gap, although the total thickness of the liquid crystal layer is 5 μm.
[0107]
As described above, in the present embodiment, a dimming device that can achieve both the securing of a large optical density ratio and the realization of a quick transient response operation, which could not be realized conventionally, could be realized.
[0108]
In the present embodiment, the cell gaps of the first GH cell 10a and the second GH cell are each about 2.2 μm (central part) to about 2.8 μm (peripheral part) (the thickness of the liquid crystal layer as a whole is about 5 μm). And As a result, it has become possible to perform a high-speed response operation as a light control device while sufficiently ensuring a difference in light transmittance (optical density ratio) between a transparent state and a light-shielded state.
[0109]
Here, the GH multiplex cell in which the thickness of the liquid crystal layer as a whole is less than 2 μm (the cell gap of each cell is less than 1 μm) is manufactured by changing the manufacturing conditions of the cell, and the transient response speed is further increased. However, the light transmittance is increased as a whole, and the degree of increase in the light transmittance particularly when the light is shielded is so large that a sufficient optical density ratio required for the light control device may not be achieved. In addition, the variation in the gap within the cell was increased, and as the cell gap was reduced, the manufacturing yield was reduced.
[0110]
On the other hand, when the GH multiplex cell in which the thickness of the liquid crystal layer as a whole exceeds 6 μm (the cell gap of each cell exceeds 3 μm) was manufactured by changing the manufacturing conditions of the cell, the transmittance at the time of shading was suppressed low. However, the transmittance in a transparent state is greatly reduced, and a practical optical density ratio cannot be obtained in some cases. In addition, the transient response speed (especially, the response speed in halftone driving) may start to decrease, and the merit of the present embodiment does not appear much.
[0111]
Therefore, a guest-host type liquid crystal cell using a negative type liquid crystal molecule and a dichroic dye molecule is constituted by, for example, a GH multiplex cell composed of two GH cells, and a ratio of light transmittance between a transparent state and a light-shielded state (optical In order to realize a light control device capable of performing a high-speed response operation as a light control device while ensuring a sufficient concentration ratio, the cell gap of each GH cell should be 1 to 3 μm (the total cell gap should be 2 to 2 μm). 6 μm).
[0112]
Example 2
In the present embodiment, in the production of a GH multiplex cell composed of two GH cells, plastic balls having different diameters are arranged between the opposed substrates as spacers 9 in respective liquid crystal layers, and two GH cells having different cell gaps are provided. This is an example in which a GH multiplex cell 10 including 10c and 10d is formed. This embodiment is the same as the first embodiment except that a plastic ball is used as the spacer 9 and the cell gap of the two GH cells is different. Therefore, the description will be made with emphasis on the difference to avoid duplication.
[0113]
As in the first embodiment, the dimmer of the present embodiment includes a GH multiplex cell 10 including two GH cells and a polarizing plate 11, as shown in FIG. Then, in the GH multiplex cell 10, as shown in the cross section in FIG. 3, the transparent electrodes 6a to 6d are respectively provided on the opposing surfaces of the three glass substrates 1a, 1b and 1c provided to face each other at different intervals. And alignment films 7a to 7d are formed. Negative liquid crystal molecules 3 serving as a host material and positive dichroic dye molecules 4 serving as a guest material are provided in two gaps formed by two sets of opposed substrates. Mixture 2 was sealed.
[0114]
Negative liquid crystal molecules 3 having a negative dielectric anisotropy include MLC-6608 manufactured by Merck, and a positive dye dichroism having anisotropy in light absorption and absorbing light in a molecular long axis direction. As the dye molecule 4, D5 manufactured by BDH was used as an example.
[0115]
Here, in the first GH cell 10c arranged on the light incident side, the liquid crystal molecules 3 contained in the first GH cell 10c are oriented such that the vibration direction of the light passing through the polarizing plate 11 is applied when a voltage is applied (during a light-shielding operation). It was configured to match the orientation.
[0116]
Then, as shown in FIG. 10, the light control device 23 is disposed between a front lens group 15 and a rear lens group 16 including a plurality of lenses such as a zoom lens. The light transmitted through the front lens group 15 is linearly polarized through the polarizing plate 11, and then enters the GH multiplex cell 10. The light modulated by the GH multiplex cell 10 is condensed by the lens rear group 16 and is projected on the imaging surface 17 as an image.
[0117]
The polarizing plate 11 constituting the light control device 23 can be moved in and out of an effective optical path of light incident on the plurality of GH cells 10.
[0118]
Here, the GH multiplex cell 10 was produced using glass substrates 1a, 1b and 1c having a thickness of 0.5 mm as an example, as schematically shown in plan views in FIGS. 7 and 8 (a). At this time, rubbing treatment was performed only on the alignment films 7a and 7d on the glass substrates 1a and 1c (single-side rubbing). Here, in the first GH cell 10c and the second GH cell 10d, the rubbing directions in the alignment films 7a and 7d were orthogonalized so that the alignment directions of the liquid crystal molecules when the operating voltage was applied were orthogonal.
[0119]
Further, on both surfaces of the glass substrate 1b, lead portions 31b and 31c for the transparent electrodes 6b and 6c are provided, respectively, and the transparent electrodes 6a and 6d of the glass substrates 1a and 1c extend outside the effective optical path 20, and They were electrically connected to the electrode lead portions 31b and 31c provided on the substrate 1b, respectively. The first GH cell 10c and the second GH cell 10d were connected to driving power supplies 34c and 34d, respectively.
[0120]
Here, the GH multiplex cell 10 is manufactured by forming one of the two cells formed by the glass substrates 1a, 1b, and 1c having a thickness of 0.5 mm on which the transparent electrode pattern and the alignment film described above are formed in advance. A sealing material 8 made of a thermosetting epoxy resin containing glass fiber having a diameter of 2.5 μm as an example is applied with a predetermined width to the peripheral portion 32 of the glass substrate constituting As an example, a plastic ball having a diameter of 2.0 μm is evenly spread on the other substrate, and a glass fiber having a diameter of 3.5 μm is contained, for example, around the glass substrate constituting the other cell. A sealing material 8 made of a thermosetting epoxy resin is applied with a predetermined width, and is applied on the same substrate or the other opposing substrate, for example, with a 3.0 μm diameter plus. After uniformly spreading the ball, the three glass substrates 1a, 1b, and 1c are aligned and stacked, and then heat-treated while applying pressure under appropriate conditions using a hot press plate to seal the peripheral portion. The material 8 was cured to produce a liquid crystal multiplex cell composed of two GH cells having different cell gaps (FIG. 2B).
[0121]
Here, the above-mentioned plastic balls are scattered on the substrate from above using a known method, and approximately 100 to 300 pieces / mm.²It was arranged almost uniformly over the entire surface of the glass substrate at a certain density.
[0122]
When the cell gap of an empty cell having a two-layer structure obtained by singulating (scribing and breaking) the bonded substrate was measured by a measuring device utilizing light interference, one of the cells was located at the center. The gap is finished to an average of about 1.9 μm, the gap around the cell is about 2.2 μm on the average, and the other cell has an average gap of about 2.9 μm at the center and an average of about 3.9 μm at the cell periphery. It was finished to 2 μm (total cell gap is about 5 μm).
[0123]
Further, the arrangement of the spacer 9 was able to reduce the variation of each cell gap which affects the dimming characteristics in the GH cell as compared with the first embodiment.
[0124]
The GH cell 12 having the larger cell gap (approximately 3 μm) of the two cells was arranged such that the light absorption axis when voltage was applied was orthogonal to the light absorption axis of the polarizing plate 11.
[0125]
The empty first GH cell 10c and the second GH cell 10d prepared in this manner are filled with a negative liquid crystal molecule MLC-6608 (manufactured by Merck) and a positive dichroic dye molecule D5 (manufactured by BDH). Liquid crystal mixture 2 was sealed. Then, a rectangular wave-shaped operating voltage is applied to the electrode lead portions 31b and 31c provided on the intermediate glass substrate 1b, so that an appropriate effective voltage is applied to the liquid crystal molecules of each cell. The change in transmittance was measured. This result almost coincided with the result of Example 1 previously shown in FIGS. 5 and 6 (for this reason, the illustration of Example 2 is omitted). Example 1 and Example 2 exhibited almost the same characteristics when the two cells were driven so that the same effective voltage was applied to the two liquid crystal layers as a whole.
[0126]
As shown in FIG. 6, as the applied operating voltage increased, the average light transmittance of visible light (in air) decreased from the maximum transmittance of about 73% to the minimum transmittance of about 2%. The GH multiplex cell 10 almost reached the minimum transmittance when a pulse voltage of ± 5 V (1 kHz) or more was applied, although it differs depending on the liquid crystal cell structure and constituent materials used.
[0127]
Comparing this example with the comparative example, the minimum transmittance at the time of shading in this example was reduced to less than half of that of the comparative example, though the effective liquid crystal layer thickness was 5 μm. As a result, the dynamic range of the dimming operation could be greatly expanded.
[0128]
This is because the number of interfaces where materials having different refractive indices are in contact with each other is increased in the structure of the GH cell, and the interface reflection there reduces the amount of transmitted light as a whole. The main factor is that the number has increased on the optical path.
[0129]
Also in the present embodiment, a high-speed operation of 20 ms or less was possible with respect to the transient response time when the operation pulse voltage applied to the cell was changed.
[0130]
As described above, in the present embodiment, a dimming device that can achieve both the securing of a large optical density ratio and the realization of a quick transient response operation, which could not be realized conventionally, could be realized.
[0131]
In the present embodiment, as an example of the method of disposing the spacers, the example of spraying from above was shown. The present invention is not limited to the spherical shape as shown, but may be realized by supplying a columnar spacer by printing or lithography as shown in FIG. 2C.
[0132]
Furthermore, in the present embodiment, by configuring two GH cells with different cell gaps, it is possible to perform various dimming operations that are more varied than the first embodiment in which two GH cells are configured with the same cell gap. Become.
[0133]
In expectation of the same effect, as shown in FIG. 4, it is possible to configure a GH multiplex cell with two GH cells having different concentrations of dichroic dye molecules (dye molecules) as guest materials. . In this case, a cell having a high dye concentration corresponds to a cell having a large cell gap in the second embodiment, and a cell having a low dye concentration corresponds to a cell having a small cell gap in the second embodiment. And the relationship between the polarizer and the GH multiplex cell can be handled in the same manner.
[0134]
Example 3
FIG. 12 shows an example in which the light control device 23 according to the present embodiment is incorporated in a CCD (Charge Coupled Device) camera.
[0135]
That is, in the CCD camera 50, a first group lens 51 and a second group lens (for zoom) 52 corresponding to the front lens group 15 and a third group lens corresponding to the rear lens group 16 along an optical axis indicated by a chain line. 53 and a fourth group lens (for focusing) 54 and a CCD package 55 are arranged in this order at appropriate intervals, and the CCD package 55 includes an infrared cut filter 55a, an optical low-pass filter system 55b, and a CCD image sensor 55c. Is stored. Between the second group lens 52 and the third group lens 53, the light control device 23 including the plurality of GH cells 10 and the polarizing plate 11 according to the above-described present invention adjusts the light amount (light amount stop) near the third group lens 53. For the same optical path. The fourth lens group 54 for focusing is disposed so as to be movable between the third lens group 53 and the CCD package 55 along the optical path by a linear motor 57, and the second lens group 52 for zooming is disposed in the optical path. Along the first lens group 51 and the light control device 23, the first lens unit 51 and the light control device 23 are disposed so as to be movable.
[0136]
As described above, the present invention has been described with reference to the embodiments and examples, but the present invention is not limited to these examples at all, and the above-described examples can be variously modified based on the technical idea of the present invention. It goes without saying that the sample structure, the materials used, the driving method of the liquid crystal cell, the form of the light control device, and the like can be appropriately selected without departing from the gist of the invention.
[0137]
For example, in this embodiment, an example in which pulse voltage modulation (PHM) is used as a driving method of a liquid crystal cell has been described, but the present invention can be applied to a case where driving is performed by pulse width modulation (PWM).
[0138]
Further, the light control device of the present invention can be widely applied to various optical systems, for example, for adjusting the light amount of an electrophotographic copying machine or an optical communication device, in addition to the optical diaphragm of the imaging device such as the CCD camera described above. is there.
[0139]
Further, the light control device of the present invention can be applied to various image display elements for displaying characters and images, in addition to the optical filters.
[0140]
Although an example in which three glass substrates are used as substrates has been described, the light control device according to the present invention may have a configuration in which a plurality of liquid crystal optical elements are sequentially arranged along an optical path, and the number of substrates is limited to three. I can't. In particular, it is preferable that an intermediate substrate constituting a plurality of liquid crystal optical elements is shared.
[0141]
In addition, although an example in which the intermediate substrate is not subjected to the alignment process and the alignment process is performed only on the substrate disposed on the outside (one-side rubbing), the intermediate substrate is also subjected to the oblique deposition method or the like. It is of course possible to perform an orientation treatment.
[0142]
Operation and Effect of the Invention
According to the light control device and the imaging device of the present invention, a plurality of liquid crystal optical elements each having the function of the light control device are sequentially arranged along the optical path. In addition to achieving a high response speed required for the light control device by keeping the thickness (cell gap) of the liquid crystal device small, a sufficient liquid crystal layer thickness is secured in a plurality of liquid crystal optical elements as a whole, and a sufficiently large optical density ratio ( Contrast ratio) can be achieved.
[0143]
In addition, since at least two liquid crystal alignment directions of the plurality of liquid crystal optical elements intersect each other, polarized light that is not absorbed by one of the two liquid crystal optical elements having different liquid crystal alignment directions is the other. As a result, the light-shielding performance during light-shielding is significantly improved, and the optical density ratio is greatly improved.
[0144]
Further, it is possible to use one of the liquid crystal optical elements having different liquid crystal orientation directions as a substitute for a polarizing plate, and to configure a light control device without using a polarizing plate without deteriorating the light blocking performance. This dimmer has no loss due to the polarizing plate, so that the amount of light transmission when transparent is greatly improved.
[0145]
Therefore, the present invention is extremely effective for improving the performance, image quality, and reliability of a light control device and an imaging device using a liquid crystal optical element.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing an operation principle of a GH multiplex cell constituting a dimming device according to a preferred embodiment of the present invention.
FIG. 2 is a partially enlarged schematic cross-sectional view of a GH multiplex cell constituting the dimming device.
FIG. 3 is a schematic cross-sectional view showing the operation principle of another GH multiplex cell constituting the dimming device.
FIG. 4 is a schematic sectional view showing the operation principle of still another GH multiplex cell constituting the dimming device.
FIG. 5 is a graph showing the relationship between the light transmittance and the wavelength of the GH multiplex cell of Example 1 according to the present invention.
FIG. 6 is a graph showing the relationship between the light transmittance and the applied voltage in the GH multiplex cell of Example 1 according to the present invention and the GH cell according to the prior invention;
FIG. 7 is a schematic plan view of each substrate constituting a GH multiplex cell of the light control device according to the embodiment of the present invention.
FIG. 8 is a schematic plan view (a) of the first or second GH cell of the GH multiplex cell of the light control device, and a schematic cross-sectional view (b) of the XX line.
FIG. 9 is a schematic cross-sectional view taken along line AA of a first GH cell of the GH multiplex cell of the light control device.
FIG. 10 is a schematic side view of an imaging device using a light control device including GH multiplex cells.
FIGS. 11A and 11B are a front view of a mechanical iris having a polarizing plate attached thereto and partially enlarged views (a) to (c) showing a dimming operation near an effective optical path.
FIG. 12 is a schematic cross-sectional view of a camera system incorporating a dimming device including GH multiplex cells according to a third embodiment of the present invention.
FIG. 13 is a schematic diagram showing the operating principle of a light control device using a GH cell based on the prior invention (Japanese Patent Application Laid-Open No. 2001-201769).
FIG. 14 is a graph showing the relationship between the light transmittance and the cell gap of the light control device using the GH cell.
FIG. 15 is a graph showing a relationship between a response time and a cell gap of a light control device using a GH cell.
FIG. 16 is a schematic explanatory view showing the operation principle of a light control device using a conventional GH cell.
[Explanation of symbols]
1a, 1b, 1c: a transparent substrate such as a glass substrate, 2, 2e, 2f: a liquid crystal mixture,
3 ... negative liquid crystal molecules, 4 ... positive dichroic dye molecules, 5 ... incident light,
6a, 6b, 6c, 6d: transparent electrode, 7a, 7b, 7c, 7d: alignment film,
8: sealing material, 9: spacer, 10: GH multiplex cell, 10a: first GH cell,
10b: second GH cell, 11: polarizing plate,
12A: GH liquid crystal cell of positive liquid crystal molecules,
12B: GH liquid crystal cell of negative liquid crystal molecules, 13A: Positive liquid crystal molecules,
13B: negative type liquid crystal molecule, 14: positive type dye (dichroic dye molecule),
15: front lens group, 16: rear lens group, 17: imaging surface,
18, 19: iris blade, 20: effective optical path (center of cell),
21: moving direction of iris, 22: opening, 23: dimmer,
31b, 31c ... electrode lead-out part, 32 ... cell peripheral part,
33 ... Carbon paste,
34a, 34b, 34c, 34d, 34e, 34f ... power supply,
50: CCD camera, 51: 1 group lens, 52: 2 group lens (for zoom),
53 ... 3 group lens, 54 ... 4 group lens (for focus),
55: CCD package, 55a: infrared cut filter,
55b: Optical low-pass filter (LPF), 55c: CCD image sensor,
57… Linear motor

Claims (13)

A plurality of liquid crystal optical elements sequentially arranged along an optical path, wherein each of the plurality of liquid crystal optical elements has a liquid crystal layer made of a mixture of a host material and a guest material; In at least two of the above, the liquid crystal alignment directions at the time of the light shielding operation cross each other. The light control device according to claim 1, wherein the host material is a positive or negative liquid crystal molecule, and the guest material is a positive dichroic dye molecule. 2. The light control device according to claim 1, wherein at least each cell gap of the plurality of liquid crystal optical elements in the effective optical path is controlled to 1 to 3 μm. 2. The light control device according to claim 1, wherein at least two of the plurality of liquid crystal optical elements are controlled such that at least cell gaps in an effective optical path are different from each other. The light control device according to claim 5, wherein the liquid crystal optical element having the larger cell gap is arranged on the light incident side. The light control device according to claim 1, wherein at least two of the plurality of liquid crystal optical elements have different concentrations of the guest material. The light control device according to claim 7, wherein the liquid crystal optical element having the higher concentration of the guest material is disposed on the light incident side. A polarizing plate is disposed on the light incident side, and a vibration direction of light transmitted through the polarizing plate and a vibration direction of light absorbed by the guest material in the liquid crystal optical element on the light incident side of the plurality of liquid crystal optical elements. 8. The light control device according to claim 5, wherein 2. The light control device according to claim 1, wherein a liquid crystal alignment process is performed on an outer substrate among the substrates constituting the plurality of liquid crystal optical elements. 3. The light control device according to claim 1, wherein an intermediate substrate constituting the plurality of liquid crystal optical elements is shared. 13. The light control device according to claim 12, wherein an electrode lead portion of each liquid crystal optical element is provided at a peripheral portion of the intermediate substrate. 2. The light control device according to claim 1, wherein each of the substrates constituting the plurality of liquid crystal optical elements has a thickness of 0.5 mm or less. 3. An imaging device, wherein the light control device according to claim 1 is arranged in an optical path of an imaging system.

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