JP2003084310A - Dimmer and imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dimmer which is capable of additionally improving the optical density ratio (contrast ratio, dynamic range) and the response speed of a liquid crystal optical element and an imaging device in which this dimmer is disposed in its optical path and which can realize an improvement in performance, image quality and reliability. SOLUTION: The dimmer which consists of the liquid crystal optical element with liquid crystals sealed between substrates 31a and 31b facing each other and in which the liquid crystals are guest-host type liquid crystals 34 consisting of negative type liquid crystals 13 as a host material and are subjected to a liquid crystal alignment treatment so as to attain 85 to 89 deg. pretilt angle of the liquid crystal molecules and the imaging device with the lighting controller arranged in the optical path of the imaging system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light control device for adjusting the amount of incident light and emitting the light, and an image pickup device using the same.

[0002]

2. Description of the Related Art Usually, a polarizing plate is used in a light control device using a liquid crystal optical element (liquid crystal cell). For this liquid crystal cell, for example, a TN (Twisted Nematic) type liquid crystal cell or a guest-host (GH (Guest Host)) type liquid crystal cell is used.

FIG. 16 is a schematic diagram showing the operating principle of a conventional light control device. This light control device mainly uses the polarizing plate 1 and the GH.
The GH cell 2 is not shown in the drawing,
It is enclosed between two glass substrates and has a working electrode and a liquid crystal alignment film (the same applies hereinafter). Liquid crystal molecules 3 and dichroic dye molecules 4 are enclosed in the GH cell 2.

The dichroic dye molecule 4 has anisotropy in light absorption, and is, for example, a positive type (p type) that absorbs light in the long axis direction of the molecule.
Type) dye molecule. The liquid crystal molecule 3 is a positive type (positive type) having a positive dielectric anisotropy.

FIG. 16A shows the state of the GH cell 2 when no voltage is applied (no voltage is applied). Incident light 5
Is converted into linearly polarized light by passing through the polarizing plate 1. In FIG. 16A, since the polarization direction and the molecular long axis direction of the dichroic dye molecule 4 coincide with each other, the incident light 5 is absorbed by the dichroic dye molecule 4 and the transmittance of the GH cell 2 is increased. descend.

Then, as shown in FIG. 16 (b), GH
When a voltage is applied to the cell 2, the molecular major axis direction of the dichroic dye molecule 4 becomes perpendicular to the polarization direction of the linearly polarized light as the liquid crystal molecule 3 faces the electric field direction. Therefore, the incident light 5 is G
It is almost absorbed by H cell 2 and is transmitted.

When a negative type (n-type) dichroic dye molecule that absorbs light in the minor axis direction of the molecule is used, this is the reverse of the case of the positive type dichroic dye molecule 4, and no voltage is applied. Light is not absorbed when applied, and absorbed when voltage is applied.

In the light control device shown in FIG. 16, the ratio of the absorption when the voltage is applied and when the voltage is not applied, that is, the ratio of the optical density is about 10. This has an optical density ratio that is about twice as high as that of a light control device including only the GH cell 2 without using the polarizing plate 1.

[0009]

The present applicant has proposed, in Japanese Patent Application No. 11-322186, a light control device and an image pickup device capable of further improving the optical density ratio. That is, according to Japanese Patent Application No. 11-322186 (hereinafter referred to as prior invention), a liquid crystal device and a polarizing plate arranged in an optical path of light incident on the liquid crystal device constitute a light control device. Then
Furthermore, since a guest-host type liquid crystal having a negative type liquid crystal as a host material is used, the ratio of absorbance (that is, the ratio of optical density) when no voltage is applied (transparent) and when voltage is applied (light-shielded) is improved, The contrast ratio of the light control device is increased, and the light control operation can be normally performed from a bright place to a dark place.

In the guest-host type liquid crystal cell (GH cell) 2 shown in FIG. 16, a positive type liquid crystal having a positive dielectric anisotropy (Δε) is used as the host material 3, and the guest material 4 is of two colors. A positive dye 4 having a positive light absorption anisotropy (ΔA) is used, and the polarizing plate 1 is disposed on the incident side of the GH cell 2. For this GH cell 2, a change in light transmittance when an operating voltage is applied is measured using a rectangular wave as a drive waveform.
As shown in, the average light transmittance of visible light (in air; transmittance when a polarizing plate was added in addition to the liquid crystal cell was referred to (= 100%) with application of an operating voltage: The same)
However, even if the voltage is raised to 10 V, the maximum transmittance is only about 60%, and the change in light transmittance is moderate.

This is because, when a positive type host material is used, the interaction of liquid crystal molecules at the interface with the liquid crystal alignment film of the liquid crystal cell is strong when no voltage is applied, and therefore the director of the director is applied even if a voltage is applied. Orientation does not change (or
It is considered that this is because liquid crystal molecules remain (which are difficult to change).

On the other hand, in the prior invention, as shown in FIG. 18, in the guest-host type liquid crystal cell (GH cell) 12, as the host material 13, the dielectric anisotropy (Δε) is used.
Is a negative liquid crystal of negative type MLC-6 manufactured by Merck.
608 is used as an example, and as the guest material 4, D5 manufactured by BDH, which is a positive dye having dichroism, is used as an example, so that the polarizing plate 11 is arranged on the incident side of the GH cell 12 and a rectangular wave is generated. When a change in light transmittance when an operating voltage is applied as a drive waveform is measured, as shown in FIG. 19, the average light transmittance of visible light (in air) is increased as the operating voltage is applied.
The maximum transmittance decreases from about 75% to 10% or less, and the change of the light transmittance becomes relatively sharp.

This is because when a negative-type host material is used, the interaction of liquid crystal molecules at the interface with the liquid crystal alignment film of the liquid crystal cell is very weak when no voltage is applied, so that light is not applied when no voltage is applied. It is considered that this is because the light is easily transmitted, and the direction of the director of the liquid crystal molecules is easily changed with the application of the voltage.

By thus constructing the GH cell using the negative type host material, the light transmittance (especially when transparent) is improved, and the GH cell is used by fixing the position as it is in the image pickup optical system. A compact dimming device that can be realized can be realized. In this case, by arranging a polarizing plate in the optical path of the incident light to the liquid crystal element, the ratio of the absorbance when no voltage is applied and when the voltage is applied (that is, the optical density ratio) is further improved, and The contrast ratio is further increased, and the dimming operation can be performed more normally from a bright place to a dark place.

[0015]

At the present time, in order to realize a high-performance image pickup device by mounting the light control device using the liquid crystal cell as described above, the light transmittance at the time of transparency and at the time of light shielding is required. It is desired to secure a sufficiently large optical density ratio (contrast ratio, dynamic range) that is determined by the difference between the two, and to achieve both a high response speed and a large optical density ratio, and to drive at a high transient response speed that is difficult to achieve at the same time. .

Therefore, an object of the present invention is demanded for a light control device while sufficiently securing the optical density ratio (contrast ratio, dynamic range) of the liquid crystal optical element while making use of the features of the above-mentioned prior invention. An object of the present invention is to provide a light control device capable of driving an element at a high response speed (transient response speed), and an imaging device which can be arranged in an optical path to improve performance, image quality, and reliability.

[0017]

That is, the present invention comprises a liquid crystal optical element in which liquid crystal is sealed between a plurality of substrates facing each other, and the liquid crystal is a guest-host type liquid crystal using a negative type liquid crystal as a host material. In addition, the present invention relates to a light control device in which a liquid crystal alignment process is performed so that a pretilt angle of liquid crystal molecules (an angle formed by the liquid crystal molecule director with respect to the substrate) is 85 ° to 89 °. The present invention relates to an image pickup device in which an optical device is arranged in the optical path of an image pickup system.

According to the light control device and the image pickup device of the present invention,
Since the liquid crystal element arranged in the optical path is a guest-host type liquid crystal and a negative type liquid crystal (that is, a negative dielectric anisotropy (Δε) is negative) is used as the host material, the same reason as described above is used. Therefore, the light transmittance at the time of light transmission (particularly transparent) is significantly improved as compared with the case of using a positive type (that is, positive Δε) liquid crystal,
It is possible to increase the response speed while maintaining a high optical density ratio (contrast ratio) when light is transmitted (when transparent) and when light is blocked (when light is blocked).

Further, the pretilt angle of the liquid crystal molecules is from 85 ° to
Since the liquid crystal alignment treatment is performed so as to be within the specific range of 89 °, it is possible to surely realize that the transient response speed is increased and the optical density ratio is kept large.

The present inventor has found that GH using a negative type liquid crystal material
After earnestly studying the further improvement of the performance of the cell,
Transient response speed of liquid crystal optical element and optical density ratio (contrast ratio, dynamic range) between transparent and shielded
Has been found to be greatly influenced by the pretilt angle of liquid crystal molecules in contact with the alignment films formed on the transparent electrode surfaces of the two substrates constituting the GH cell. Here, in the present specification, the “pretilt angle” is defined as the angle formed by the director of liquid crystal molecules with respect to the substrate surface.

That is, first, as shown in FIG. 1, the transient response time of the GH cell depends on the pretilt angle of liquid crystal molecules,
The response time when the drive voltage rises (transparent → light-shielded state) is shorter as the pretilt angle is smaller, and the response is faster (the change rate increases near 87 °).
It was found that the response time at the time of the fall of the drive voltage (light-shielded → transparent state) was shorter and the response was faster at the larger pretilt angle, contrary to the time of the rise.

FIG. 2 also shows the relationship between the light transmittance of the GH cell and the pretilt angle of the liquid crystal molecules, and the value of the dynamic range converted from the light transmittance when transparent and when light is blocked. The transmittance decreases as the pretilt angle decreases (the change at the time of transparency is relatively large), and the value of the dynamic range peaks at around 87 ° and decreases as the pretilt angle decreases.

From these results, when the light control device is manufactured by the GH cell using the negative type host material, the difference in the pretilt angle of the liquid crystal molecules is caused by the transient response speed of the liquid crystal optical element, the light transmittance, It was found that the GH cell must be manufactured so that the pretilt angle falls within a specific range in order to greatly affect the basic characteristics such as the dynamic range and satisfy each of the difficult characteristics to some extent. Came to do.

In particular, in order to realize a practical light control device using a liquid crystal element, it is necessary to secure a sufficient light transmittance and a dynamic range in the transparent state, and to reduce the transient response speed as much as possible. Therefore, it has been found that the pretilt angle of the liquid crystal molecules of the GH cell must be controlled to 85 ° to 89 °.

That is, if the pretilt angle of the liquid crystal molecules is less than 85 °, the transient response speed at the rise (transparent → light-shielded state) increases, but the dynamic range of light transmittance (optical density ratio, contrast ratio) is increased. It will be greatly reduced, and the decrease in transient response speed at the time of falling (light shielding → transparent state) will be noticeable. On the other hand, if the pretilt angle of the liquid crystal molecules exceeds 89 °, a relatively large dynamic range of light transmittance (optical density ratio, contrast ratio) can be secured, and the transient response speed at the time of falling (shading → transparent state) Also becomes relatively large, but the transient response speed at the time of rising (transparent → light-shielded state) becomes remarkable.

Therefore, the pretilt angle of the liquid crystal molecules, which is the angle formed by the liquid crystal director with respect to the substrate surface, is 85 ° to 8 °.
It should be 9 ° (corresponding to 1 ° to 5 ° when viewed from the substrate normal direction). The pretilt angle is preferably 86 ° to 88 °, and more preferably 87 ° or its vicinity.

Next, in the present invention, it was also found that the state of the liquid crystal alignment treatment on the substrate affects the performance of the light control device.

FIG. 5 shows the most general rubbing method as the liquid crystal alignment treatment. The substrate is placed on the stage of a rubbing apparatus and passed through the roller, so that the molecules are aligned in the direction of rotation of the roller. Can be applied. As an alignment treatment method using this rubbing method, as shown in FIG. 6, a hybrid rubbing (one side rubbing) in which only the alignment film 33 of one substrate is rubbed, and pretilts of liquid crystal molecules are parallel to each other on two substrates. Anti-parallel rubbing performed so that the pretilts of liquid crystal molecules on the two substrates are opposite to each other.
l) There are three types of rubbing.

FIG. 3 shows the difference in the relationship between the light transmittance and the applied voltage (VT characteristic) in the liquid crystal optical element (GH cell) in which the vertical alignment film is formed by using the rubbing method. In comparison, it shows. According to this, the VT characteristics in the case of parallel rubbing show that the instability of the light transmittance due to the alignment disorder is caused by the asymmetry of the pretilt angle due to the twist of the director between the opposing substrates and the in-plane nonuniformity. stand out.

The light transmittance of anti-parallel rubbing is
A low value is obtained as a whole as compared with one-sided rubbing and parallel rubbing, and anti-parallel rubbing is the best in terms of light-shielding performance with a slight difference, but the decrease in light transmittance when transparent is noticeable.

FIG. 4 compares the rising transient response when the GH cell changes from the transparent state to the light blocking state, but the falling transient response when the GH cell changes from the light blocking state to the transparent state shows the alignment treatment. Almost no significant difference due to the difference in the method has been confirmed (the relaxation time is presumed to be the dominant factor of the viscosity and elastic modulus of the liquid crystal material itself), but the transient response of the light transmittance is parallel rubbing. Is the slowest, and anti-parallel rubbing responds somewhat faster than one-sided rubbing.

From FIGS. 3 and 4, the anti-parallel rubbing is superior as a liquid crystal alignment treatment method in terms of the transient response speed and the light shielding performance. In this case, the dimming control based on the present invention is that the high light transmittance at the time of transparency, which was the greatest advantage of using the negative type liquid crystal as the host material, and the number of manufacturing processes are increased. As a liquid crystal alignment treatment method for producing a GH cell using a negative liquid crystal as a device, it is desirable to use one-side rubbing or anti-parallel rubbing. Which of these is to be adopted depends on a product set to be mounted or manufacturing. It is preferable to select from the priority characteristics required by the infrastructure and the manufacturing cost.

The liquid crystal alignment treatment is not limited to the above-mentioned rubbing, but may be any vertical alignment treatment that realizes a predetermined pretilt angle according to the present invention. For example, a photoalignment method using polarized ultraviolet rays or an oblique vapor deposition method. Etc. are also applicable.

In the present invention, as shown in FIG. 7, the optical density ratio of the liquid crystal element when it is transparent and when it is light-shielded is GH.
It was also found that it is affected by the distance (cell gap) between the two substrates forming the cell.

That is, the larger the cell gap, in other words, the larger the thickness of the liquid crystal layer, the larger the difference in light transmittance between the transparent state and the light shielding state, and the larger the optical density ratio,
The light transmittance when transparent, which is an advantage of using a negative liquid crystal as the host material, is reduced.

Further, as shown in FIG. 8, when the cell gap changes, the response speed of the GH cell as a light control device also changes significantly, and when the cell gap increases and the liquid crystal layer becomes thicker, the response speed decreases. It turns out that it will end up.

From the above, when a guest-host type liquid crystal is used to manufacture a light control device, the light transmittance when transparent, the light transmittance when light is blocked, the response time of the liquid crystal element, etc.
There is a range of cell gaps to satisfy each of the characteristics that are difficult to be compatible with each other, and in order to realize a practically advantageous light control device using a liquid crystal element, a sufficient optical density without decreasing the response speed is required. It is necessary to secure the ratio, and it is desirable to control the gap (cell gap) between the substrates enclosing the liquid crystal in the GH cell to be 2 μm or more and 4 μm or less at least in the effective optical path.

In other words, if the cell gap is less than 2 μm, the response speed as a light control device is increased, and the light transmittance when transparent is improved, but the light transmittance when shielded is also greatly increased. As a result, it becomes difficult to secure the optical density ratio (contrast ratio). On the other hand, if the cell gap exceeds 4 μm, a large optical density ratio can be secured, but the light transmittance in the transparent state decreases, and the response speed as a light control device deteriorates significantly. When driving to slightly change the transmittance,
This is extremely slow (drive a in FIG. 8). In FIG. 8, as compared with the case where the driving is switched from the transparent state to the light-shielded state, for example, 0V → 5V like the driving b, c, and d, the voltage is changed so that the halftone is generated as the driving a, eg, 2V → 3V. In such a case, the response speed becomes slow due to insufficient voltage, and it is easily affected by the size of the cell gap.

From FIGS. 7 and 8, the cell gap is preferably 2 to 4 μm, more preferably 2 to 3.5 μm, and even more preferably 2 to about 3 μm.

The dimmer according to the present invention comprises, for example, the GH cell 12 shown in FIGS. 9 and 10 (a). This GH
The cell 12 includes transparent electrodes 32a and 32b and an alignment film 33a,
Two glass substrates 31a and 3 on which 33b are respectively formed
A mixture 34 of a negative liquid crystal molecule (host material) 13 and a positive or negative dichroic dye molecule (guest material) 4 is enclosed between 1b.

The liquid crystal molecule 13 is a known negative type liquid crystal having a negative dielectric anisotropy, for example, MLC-made by Merck.
6608 is used, and the dichroic dye molecule 4 has anisotropy in light absorption, and is, for example, a known positive or negative dye that absorbs light in the long axis direction of the molecule, for example, manufactured by BDH. D
5 is used. These can be appropriately selected from known materials.

In forming the cell gap as described above in such a GH cell 12, as shown in FIG.
As shown in (c), spacers 36, 3 are provided between the opposing substrates.
7 is arranged, and the periphery of the liquid crystal cell is preferably sealed with the sealing material 35.

The light control device based on the present invention, which is composed of the above-mentioned liquid crystal optical element, has a front lens group 15 composed of a plurality of lenses such as a zoom lens as shown in FIG.
And the lens rear group 16 are arranged. Front lens group 15
The light that has passed through is linearly polarized through the polarizing plate 11 and then enters the GH cell 12. The light that has passed through the GH cell 12 is condensed by the rear lens group 16 and is displayed as an image on the imaging surface 17.

Polarizing plate 11 constituting this light control device 23
Can be put in and taken out from the effective optical path of the light incident on the GH cell 12, similarly to the above-mentioned prior invention by the present applicant. Specifically, by moving the polarizing plate 11 to a position indicated by an imaginary line, it is possible to let the light out of the effective optical path. As a means for inserting and removing the polarizing plate 11, FIG.
A mechanical iris as shown in 2 may be used.

This mechanical iris is a mechanical diaphragm device generally used in a digital still camera, a video camera, etc., and mainly comprises two iris blades 18, 19.
The polarizing plate 11 is attached to the iris blade 18.
The iris blades 18 and 19 can be moved in the vertical direction. The iris blades 18, 19 are relatively moved in the direction indicated by the arrow 27 by using a drive motor (not shown).

As a result, as shown in FIG. 12, the iris blades 18 and 19 are partially overlapped, and when this overlap becomes large, the opening 22 on the effective optical path 20 located near the center of the iris blades 18 and 19 is formed. Is covered with the polarizing plate 11.

FIG. 13 is a partially enlarged view of the mechanical iris near the effective optical path 20. At the same time that the iris blade 18 moves downward, the iris blade 19 moves upward.
Along with this, as shown in FIG. 13A, the polarizing plate 11 attached to the iris blade 18 also moves to the outside of the effective optical path 20. On the contrary, by moving the iris blade 18 upward and the iris blade 19 downward, the iris blades 18 and 19 overlap each other. According to this, FIG.
As shown in (b), the polarizing plate 11 moves onto the effective optical path 20 and gradually covers the opening 22. Iris wings 18, 1
When the mutual overlapping of 9 becomes large, the polarizing plate 11 covers all the openings 20, as shown in FIG.

Next, the dimming operation of the dimming device 23 using this mechanical iris will be described.

As the subject (not shown) becomes brighter, as shown in FIG. 13A, the iris blades 18 and 19 that have been opened in the vertical direction are driven by a motor (not shown) to start overlapping. As a result, the polarizing plate 11 attached to the iris blade 18 begins to enter the effective optical path 20 and covers a part of the opening 22 (FIG. 13B).

At this time, the GH cell 12 is in a state of not absorbing light (note that due to thermal fluctuation, surface reflection, etc.,
There is some absorption by the GH cell 12. ). For this reason,
The light passing through the polarizing plate 11 and the light passing through the opening 22 are
The intensity distributions are almost the same.

Then, the polarizing plate 11 is completely opened 22.
Is covered (FIG. 13C). Further, when the brightness of the subject increases, the voltage to the GH cell 12 is increased, and the GH cell 12 absorbs light to perform light control.

On the contrary, when the subject becomes dark,
First, by reducing or not applying the voltage to the GH cell 12, the light absorption effect by the GH cell 12 is eliminated. When the subject becomes darker, drive a motor (not shown) to move the iris blade 18 downward.
Further, the iris blade 19 is moved upward. Thus
The polarizing plate 11 is moved out of the effective optical path 20 (see FIG. 13).
(A)).

Further, as shown in FIGS. 11 to 13, since the polarizing plate 11 (transmittance, for example, 40% to 50%) can be taken out from the effective light path 20 of light, the polarizing plate 11 is not exposed to light. Not absorbed. Therefore, the maximum transmittance of the light control device can be increased to, for example, twice or more. Specifically, this dimming device is provided with a conventional fixedly installed polarizing plate and GH.
The maximum transmittance is, for example, about double when compared with the light control device including cells. The minimum transmittance is the same for both.

Further, since the polarizing plate 11 is put in and taken out by using the mechanical iris which has been put to practical use in a digital still camera or the like, the light control device can be easily realized. Further, since the GH cell 12 is used, in addition to the dimming by the polarizing plate 11, the GH cell 12 itself absorbs light, whereby dimming can be performed.

In this way, this light control device can increase the contrast ratio of light and dark and can keep the light amount distribution substantially uniform.

[0056]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

Example 1 First, an example of a light control device using a guest-host type liquid crystal (GH) cell will be described.

This light control device has a G
It is composed of an H cell 12 and a polarizing plate 11. The GH cell 12 has a negative type liquid crystal between two glass substrates 31a and 31b on which transparent electrodes 32a and 32b and alignment films 33a and 33b are respectively formed, as shown in the schematic cross section of FIG. A mixture 34 of molecules (host material) 13 and positive dichroic dye molecules (guest material) 4 is enclosed.

The liquid crystal molecule 13 is, for example, a negative liquid crystal having a negative dielectric anisotropy, MLC-660 manufactured by Merck.
8 is used as an example, and the dichroic dye molecule 4 has anisotropy in light absorption, for example, D5 manufactured by BDH, which is a positive dye that absorbs light in the long axis direction of the molecule. Using. The light absorption axis of the polarizing plate 11 was orthogonal to the light absorption axis when a voltage was applied to the GH cell 12.

A light control device 23 including the GH cell 12
Is disposed between the front lens group 15 and the rear lens group 16 including a plurality of lenses such as a zoom lens, as shown in FIG. The light that has passed through the front lens group 15 is linearly polarized through the polarizing plate 11 and then enters the GH cell 12. The light that has passed through the GH cell 12 is condensed by the rear lens group 16 and is displayed as an image on the imaging surface 17.

The polarizing plate 11 constituting the light control device 23 has the same structure as that of the above-mentioned prior application by the applicant.
It can be put into and taken out of the effective optical path of the light that enters the GH cell 12. Specifically, by moving the polarizing plate 11 to a position indicated by an imaginary line, it is possible to let the light out of the effective optical path. The mechanical iris shown in FIG. 12 may be used as a means for inserting and removing the polarizing plate 11.

A method of manufacturing the GH cell 12 will be described below. As shown in FIGS.
The transparent electrode patterns 32a and 32b and the alignment films 33a and 33b are provided on both of the two glass substrates 31a and 31b having a thickness of 5 mm.
Was formed, and only one of the alignment films 33a on the glass substrate 31a side was rubbed under the condition that the pretilt angle of the liquid crystal molecules was 87 ° (one-side rubbing).

Then, the cell peripheral portion 2 of one glass substrate
4. Sealing made of thermosetting epoxy resin containing glass fiber having a diameter of 3.5 μm as an example
After applying the material 35 with a predetermined width, the two glass substrates 31
After aligning and stacking a and 31b, heat press plate is used for appropriate conditions (for example, 150 to 170 ° C., 1 to 2 kg).
/ Cm ² : The same applies hereinafter), and heat treatment is performed while applying pressure to cure the sealing material 35 in the cell peripheral portion 24 and complete the bonding of the substrates.

The cell gap of an empty cell obtained by singulating (scribing and breaking) this bonded substrate was measured by a measuring device utilizing light interference. As a result, the cell center (effective optical path) 20 was measured. The cell gap was about 3.1 μm, and the cell gap of the cell peripheral portion 24 was about 3.4 μm.

A GH cell 12 formed by enclosing a liquid crystal material 34 composed of a negative type liquid crystal molecule (host material) 13 and a positive type dichroic dye molecule (guest material) 4 in such a cell, A rectangular wave was input as a drive waveform and the change in light transmittance when an operating voltage was applied was measured (Fig. 1
8), as shown in FIG. 19, with the application of the operating voltage,
Average transmittance of visible light (in air) is about 75% maximum transmittance
To less than 10%. The GH cell 12 is ± 5 V, although it depends on the liquid crystal cell structure and constituent materials used.
When a pulse voltage of (1 kHz) or higher was applied, the transmittance almost reached the minimum.

Further, the transient response time of the light transmittance when the drive pulse was changed was 30 ms or less for both the pulse voltage modulation and the pulse width modulation, and the high speed operation was possible.

As a result, it becomes possible to perform a transient response operation at high speed as a light control device while sufficiently securing the difference in optical transmittance (optical density ratio) between when the liquid crystal cell is transparent and when it is shielded.

Example 2 In this example, a liquid crystal (GH) cell 12 was manufactured.
Two glass substrates 31a and 31b having a thickness of 0.5 mm are used, and transparent electrode patterns 32a and 32b and alignment films 33a and 33b are formed on both the substrates, and the pretilt angle of liquid crystal molecules is different from those alignment films. This is an example in which the rubbing process is performed under the condition that the pretilt is 87 ° and the pretilts are parallel to each other after the bonding (antiparallel rubbing).

Then, for example, a sealing (sealing) material 35 made of a thermosetting epoxy resin containing a glass fiber having a diameter of 3 μm is applied in a predetermined width to the cell peripheral portion 24 of the glass substrate 31a, and the other is applied. As an example, the plastic balls 36 having a diameter of 3 μm are evenly dispersed on the substrate 31b, the two substrates 31a and 31b are aligned and superposed, and then heat-treated while applying pressure under appropriate conditions with a hot press plate. By doing so, the sealing material 35 in the cell peripheral portion 24 was cured, and the bonding of the substrates was completed.

Here, the above plastic balls 36
Is a common method (wet or dry spray)
Using, spread from above the substrate, about 100-300
/ Mm ²With a density of almost evenly distributed over the entire surface of the substrate.
It was

The cell gap of an empty cell obtained by singulating (scribing and breaking) this bonded substrate was measured by a measuring machine utilizing light interference, and it was found that the cell central portion (effective optical path) 20 The cell gap was about 2.8 μm, and the cell gap of the cell peripheral portion 24 was about 2.9 μm. Further, the arrangement of the spacers made of the plastic balls 36 could reduce the variation in the cell gap as compared with the first embodiment.

A GH cell 12 formed by enclosing a liquid crystal material 34 composed of a negative type liquid crystal molecule (host material) 13 and a positive type dichroic dye molecule (guest material) 4 in such a cell, A rectangular wave was input as a drive waveform and the change in light transmittance when an operating voltage was applied was measured (Fig. 1
8), as in the first embodiment, as shown in FIG. 19, the average light transmittance of visible light (in air) with the application of the operating voltage.
The maximum transmittance decreased from about 75% to 10% or less.

Further, the transient response time of the light transmittance when the drive pulse was changed was 15 ms or less for both the pulse voltage modulation and the pulse width modulation, and the high speed operation of Example 1 or higher was possible.

As a result, also in the present embodiment, a light control device capable of performing a transient response operation at a higher speed while sufficiently securing a difference in optical transmittance (optical density ratio) between when the liquid crystal cell is transparent and when it is shielded. Could be realized.

In this embodiment, as an example of the spacer disposing method, spraying from above is shown, but it is also possible to form the spacer by using a screen printing method so as to dispose the spacer more uniformly. The shape of the spacer is not limited to the spherical shape shown in FIG. 10 (b), but as shown in FIG. 10 (c),
It is also possible to form the columnar spacer 37 by printing or lithography.

Embodiment 3 FIG. 14 shows a case in which the light control device 23 according to the above embodiment is a CCD (Ch
arge coupled device) shows an example incorporated in a camera.

That is, in the CCD camera 50, the first group lens 51 and the second group lens (for zoom) 52 corresponding to the front lens group 15 and the rear lens group 16 are arranged along the optical axis indicated by the alternate long and short dash line. The corresponding third group lens 53, fourth group lens (for focus) 54, and CCD package 55 are arranged in this order at appropriate intervals, and the CCD package 55 has an infrared cut filter 55a and an optical low-pass filter system 55b. , CCD image pickup element 55c is housed.

Between the second group lens 52 and the third group lens 53, the G group according to the present invention described above is provided near the third group lens 53.
A light control device 23 including an H cell 12 and a polarizing plate 11 is mounted on the same optical path for adjusting the light amount (light amount stop). The focusing fourth group lens 54 is arranged so as to be movable between the third group lens 53 and the CCD package 55 along the optical path by the linear motor 57, and the zoom second group lens 52 is located in the optical path. It is arranged so as to be movable between the first group lens 51 and the dimmer 23.

FIG. 15 shows the sequence algorithm of the light transmittance control by the light control device 23 in this camera system.

According to this embodiment, the second group lenses 52 and 3
Since the dimming device 23 according to the present invention is provided between the group lenses 53, the amount of light can be adjusted by applying an electric field as described above, the system can be downsized, and the effective range of the optical path can be substantially achieved. Can be miniaturized. Therefore, CC
It is possible to achieve miniaturization of the D camera. Also,
Since the amount of light can be appropriately controlled by the magnitude of the voltage applied to the patterned electrode, it is possible to prevent the conventional diffraction phenomenon, make a sufficient amount of light incident on the image sensor, and eliminate the blurring of the image.

The embodiments and examples of the present invention have been described above, but the above examples can be variously modified based on the technical idea of the present invention.

That is, the structures and materials of the above-mentioned liquid crystal element and polarizing plate, the driving mechanism thereof, the configuration of the driving circuit and the control circuit, and the like are as follows.
Various changes are possible. In addition, the drive waveform is a rectangular wave,
Can be driven by trapezoidal wave, triangular wave, sine wave,
The tilt of the liquid crystal changes according to the potential difference between the two electrodes forming the liquid crystal cell, and the light transmittance is controlled. Therefore, normally, the transmittance is controlled by this peak value. In the above-described embodiment, the pulse voltage modulation (PH
M) Although the example using it was shown, it can be applied also when driving by pulse width modulation (PWM).

The cell gap of the above-mentioned GH cell may be changed at least in the range of 2 to 4 μm in the effective optical path, and is preferably set to 2 to 3.5 μm, particularly about 2 to 3 μm. The cell gap around the cell may be 2 to 4 μm, but may be 3.5 to 4 μm or may exceed 4 μm in some cases.

As the GH cell, a GH cell having a two-layer structure or the like can be used in addition to the above-mentioned ones. Polarizing plate 1
The position of No. 1 with respect to the GH cell 12 is between the front lens group 15 and the rear lens group 16. However, the position is not limited to this, and may be any position that is optimal from the setting conditions of the imaging lens. That is, unless an optical element such as a retardation film that changes the polarization state is used, the polarizing plate 11 may be, for example, the imaging surface 17.
It can be placed at any position on the subject side or the image pickup device side, such as between the lens rear group 16 and the like. Furthermore, the polarizing plate 1
1 may be arranged before or after a single lens (single lens) that replaces the front lens group 15 or the rear lens group 16.

The number of iris blades 18 and 19 is not limited to two, and a larger number may be used.
On the contrary, it may be one. Also, the iris blades 18 and 19 are
Although they are stacked by moving in the vertical direction, they may be moved in other directions, or may be narrowed from the periphery toward the center.

Although the polarizing plate 11 is attached to the iris blade 18, it may be attached to the iris blade 19.

As the subject becomes brighter, the dimming of the polarizing plate 11 is first performed and then the light is absorbed by the GH cell 12, but conversely, the GH cell 1 is used first.
The polarizing plate 11 may be taken in and out after the transmittance of 2 has decreased to a predetermined value.

Although the mechanical iris is used as the means for moving the polarizing plate 11 in and out of the effective optical path 20, the invention is not limited to this. For example, by directly installing the film to which the polarizing plate 11 is attached to the drive motor, the polarizing plate 1
1 may be put in and taken out.

Further, in the above example, the polarizing plate 11 is taken in and out of the effective optical path 20, but it is of course possible to fix the position in the effective optical path.

The light control device according to the present invention can also be used in combination with other known filter materials (for example, organic electrochromic materials, liquid crystals, electroluminescent materials, etc.).

Further, the light control device according to the present invention is used for various optical systems such as an electrophotographic copying machine and an optical communication device in addition to the optical aperture of the image pickup device such as the CCD camera described above. Is also widely applicable.

As the image pickup device, in addition to the CCD (Charge Coupled Device) used in this embodiment,
Of course, application to a CMOS image sensor or the like is also possible.

Further, the light control device according to the present invention can be applied to various image display elements for displaying characters, images, etc., in addition to the optical filter.

[0094]

According to the light control device and the image pickup device of the present invention, the liquid crystal element arranged in the optical path is a guest-host type, and the host material is a negative type (that is, a dielectric anisotropy (Δ
Since ε) is used as a negative liquid crystal, the light transmittance when transmitting light (especially transparent) is higher than that when a positive type (that is, Δε is positive) liquid crystal is used for the same reason as described above. Is greatly improved, and the response speed can be increased while maintaining a high optical density ratio (contrast ratio) between when light is transmitted (when transparent) and when light is blocked (when light is blocked).

Further, the pretilt angle of the liquid crystal molecules is 85 ° to
Since the liquid crystal alignment treatment is performed so as to be within the specific range of 89 °, it is possible to surely realize that the transient response speed is increased and the optical density ratio is kept large.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a pretilt angle of liquid crystal molecules and a response time in a liquid crystal optical element of a light control device according to an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a pretilt angle of liquid crystal molecules, a light transmittance, and a dynamic range in the liquid crystal optical element.

FIG. 3 is a graph showing a comparison between the light transmittance of the liquid crystal optical element and the applied drive voltage according to the type of liquid crystal alignment treatment.

FIG. 4 is a graph showing the transient response of the liquid crystal optical element for comparison according to the type of liquid crystal alignment treatment.

FIG. 5 is a diagram explaining a rubbing process of a liquid crystal alignment film in manufacturing a cell of the liquid crystal optical element.

FIG. 6 is a diagram illustrating a combination of rubbing treatments as an alignment treatment method in manufacturing cells of the liquid crystal optical element.

FIG. 7 is a graph showing the relationship between the cell gap and the light transmittance of the liquid crystal optical element.

FIG. 8 is a graph showing a comparison between the cell gap of the liquid crystal optical element and the response time according to driving conditions.

FIG. 9 is a schematic plan view of a cell of the liquid crystal optical element of the same.

FIG. 10 is a schematic cross-sectional view of each example of cells of the liquid crystal optical element.

FIG. 11 is a schematic side view of a light control device using the same liquid crystal optical element.

FIG. 12 is a front view of the mechanical iris of the light control device.

FIG. 13 is a schematic partial enlarged view showing the operation of the mechanical iris in the vicinity of the effective optical path of the light control device.

FIG. 14 is a schematic cross-sectional view of a camera system incorporating the light control device.

FIG. 15 is an algorithm of light transmittance control in the camera system.

FIG. 16 is a schematic view showing an operation principle of a conventional light control device.

FIG. 17 is a graph showing the relationship between the light transmittance of the liquid crystal optical element of the light control device and the drive applied voltage.

FIG. 18 is a schematic view showing the operation principle of the light control device of the prior invention (Japanese Patent Application No. 11-322186).

FIG. 19 is a graph showing the relationship between the light transmittance of the liquid crystal optical element of the light control device and the drive applied voltage.

[Explanation of symbols]

1, 11 ... Polarizing plate, 2, 12 ... GH cell, 3 ... Positive type liquid crystal, 4 ... Positive type dye molecule, 5 ... Incident light, 13 ... Negative type liquid crystal, 15, 16 ... Lens group, 17 ... Imaging surface, 18, 19
... iris blade, 20 ... effective optical path, 23 ... dimmer, 2
4 ... Cell peripheral part, 31a, 31b ... Substrate, 32a, 32
b ... Transparent electrode, 33a, 33b ... Alignment film, 34 ... Liquid crystal material (mixture), 35 ... Sealing material, 36 ... Spherical spacer, 37 ... Columnar spacer, 50 ... CCD camera, 51 ... First group lens, 52 ... 2 group lens, 53 ... 3 group lens, 54 ... 4 group lens, 55 ... CCD package,
56 ... Linear motor

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H088 EA32 EA33 EA34 EA37 EA61                       GA01 GA13 HA03 JA06 KA02                       KA14 LA04 LA06 MA02 MA06                       MA10 MA13                 2H090 HA03 HC13 KA06 MA01 MA11                       MB01

Claims (6)

[Claims] 1. A liquid crystal optical element in which liquid crystal is sealed between a plurality of substrates facing each other, wherein the liquid crystal is a guest-host type liquid crystal using a negative type liquid crystal as a host material, and a pretilt angle of liquid crystal molecules ( A light control device which is subjected to liquid crystal alignment treatment such that an angle formed by the liquid crystal molecular director with respect to the substrate is 85 ° to 89 °. 2. Of the pair of substrates facing each other,
Liquid crystal alignment treatment is applied to only one substrate,
The light control device according to claim 1. 3. The light control device according to claim 1, wherein the liquid crystal alignment treatment is performed such that the pretilts of the liquid crystal molecules on the respective surfaces of the pair of substrates facing each other are parallel to each other. 4. The light control device according to claim 1, wherein a gap between the pair of substrates in at least the effective optical path is controlled to be 2 μm or more and 4 μm or less. 5. The light control device according to claim 1, wherein the guest material of the liquid crystal is a dichroic dye. 6. An image pickup device in which the light control device according to claim 1 is arranged in an optical path of an image pickup system.