JP2003029302A - Dimmer and image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dimmer capable of further increasing the optical density ratio (contrast ratio and dynamic range) of a liquid crystal optical element and making the element small-sized and lightweight and to provide an image pickup device capable of enhancing performance, image quality and reliability by disposing the dimmer in a light path. SOLUTION: The dimmer comprises a liquid crystal optical element with a liquid crystal enclosed between opposite substrates different from each other in thickness and the liquid crystal is a guest-host type liquid crystal using a negative liquid crystal as a host material. The image pickup device has the light controller disposed in the light path of an image pickup 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 molecules 3 face the electrolysis 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 the guest-host type liquid crystal using the negative type liquid crystal as the host material is used, the ratio of the absorbance (that is, the optical density ratio) when no voltage is applied and when the voltage is applied is improved, and the contrast ratio of the dimmer is large. Therefore, it is possible to normally perform the dimming operation 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 several%, and the change in 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 (that is, the optical density ratio) when no voltage is applied and when voltage is applied is further improved, and the contrast of the light control device is improved. The ratio is further increased, and the dimming operation can be performed more normally from a bright place to a dark place.

[0015]

At present, in order to realize a high-performance image pickup device by mounting a light control device using a liquid crystal cell as described above, the light control element is made as light as possible, and In the above, it has been earnestly desired to secure the characteristics that achieve both a high response speed and a large optical density ratio (contrast ratio, dynamic range).

Therefore, an object of the present invention is to make it possible to further improve the optical density ratio (contrast ratio, dynamic range) of the liquid crystal optical element and to reduce the size and weight while making use of the features of the above-mentioned prior invention. An object of the present invention is to provide an optical device and an imaging device that can improve the performance, image quality, and reliability by arranging the optical device in the optical path.

[0017]

That is, the present invention comprises a liquid crystal optical element in which a liquid crystal is sealed between substrates facing each other having different thicknesses, and the liquid crystal is a guest-host type in which a negative type liquid crystal is used as a host material. The present invention relates to a light control device which is a liquid crystal, and also relates to an image pickup device which 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, since the counter substrates having different thicknesses are used, the light control device and the image pickup device can be made thin and lightweight.

The present inventor diligently studied to reduce the size and weight of the light control device and to further improve the light control performance. As a result, the transient response speed of the liquid crystal optical element and the optical density ratio (contrast ratio) between transparent and light shielded It has been found that the dynamic range) is greatly influenced also by the method of forming the alignment film formed on the transparent electrode surfaces of the two substrates constituting the liquid crystal optical element.

That is, in the light control device and the image pickup device according to the present invention, of the substrates having different thicknesses, the first one having the larger thickness is used.
It is desirable that the liquid crystal alignment treatment by rubbing is performed only on the substrate (the other substrate is not subjected to any rubbing treatment, the liquid crystal alignment treatment itself is not performed, or the rubbing treatment is performed). Other than liquid crystal alignment treatment such as oblique vapor deposition may be applied).

FIG. 5 shows the most general rubbing method as the liquid crystal alignment treatment. Here, only the first substrate having the large thickness is placed on the stage of the rubbing apparatus and passed through a roller. The molecules can be oriented in the direction of rotation of the roller. As an alignment treatment method using this rubbing method, as shown in FIG. 6, hybrid (one side rubbing), anti-para
-parallel) and parallel (parallel).

FIG. 7 shows the relationship between the light transmittance and the applied voltage (VT characteristic) of a liquid crystal optical element (GH cell) in which a vertical alignment film is formed by the rubbing method, depending on the alignment treatment method. As shown by comparison, the VT characteristics in the case of the parallel rubbing are based on the asymmetry of the pretilt angle due to the twist of the director between the opposing substrates and the in-plane nonuniformity thereof.
The instability of the light transmittance due to the orientation disorder is noticeable.

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

FIG. 8 compares the rising transient response when the GH cell changes from the transparent state to the light blocking state. The orientation transient treatment is performed in the falling transient response when the GH cell changes from the light blocking state to the transparent state. Almost no significant difference due to the difference in 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 light transmittance is the parallel rubbing Is the slowest
The anti-parabing responds somewhat faster than the one-sided rubbing.

From FIGS. 7 and 8, the anti-para-rubbing is excellent as a liquid crystal alignment treatment method in terms of transient response speed and light-shielding performance. In this case, the host material is the negative liquid crystal. Since the high light transmissivity at the time of transparency, which is the greatest advantage of using a liquid crystal, is reduced, a liquid crystal for producing the GH cell using the negative liquid crystal as the light control device according to the present invention. As the orientation treatment method, it has been judged that the one-sided rubbing is optimal.

When the one-side rubbing is adopted, in order to reduce the weight of the light control device as much as possible, the G
It is effective to reduce the thickness of the substrate constituting the H cell, and in consideration of the mechanical strength of the GH cell in process process work or use in finishing, the rubbing treatment is performed among the substrates having different thicknesses. The board that is not used is
It was discovered for the first time that it is possible to make it thinner than the rubbing-treated substrate.

Specifically, of the substrates having different thicknesses, the first substrate having the larger thickness has a thickness of 0.5 mm or more,
The thickness of the second substrate having a smaller thickness is more preferably 0.5 to 1.0 mm, the thickness of the second substrate is less than 0.5 mm, and more preferably 0.1 to less than 0.5 mm.
It is preferable that the ratio of the thickness of the substrate 2 to the thickness of the second substrate is 0.2 ≦ thickness ratio <1.0. According to this, both the thickness and the weight of the second substrate can be made equal to or less than half of that of the first substrate, and further miniaturization and weight saving of the light control device and the imaging device can be achieved. You can

Further, as described above, in the light control device according to the present invention, it is desirable that the liquid crystal alignment treatment is applied only to the first substrate having the large thickness. In addition to the above-mentioned rubbing (one-sided rubbing), a photo-alignment method using polarized ultraviolet rays, an oblique vapor deposition method, or the like can be applied.

Further, among the substrates having different thicknesses, at least the first substrate having a large thickness is preferably a glass substrate, but the main component of the second substrate having a small thickness is formed of a plastic material. However, this makes it possible to further reduce the thickness and weight.

The light control device and the image pickup device according to the present invention are
The transparent electrode and a first substrate having a large thickness that has been subjected to, for example, a rubbing treatment as a liquid crystal alignment treatment, and a second substrate having a small thickness that has not been subjected to the liquid crystal alignment treatment and the transparent electrode, It is preferable that the first substrate is provided with the respective lead-out portions of the respective transparent electrodes.

Further, it is preferable that the transparent electrode of the second substrate extends outside the effective optical path and is electrically connected to an electrode lead portion provided on the first substrate.
Furthermore, a space between the first and second substrates is sealed with a sealant in the peripheral portion of the liquid crystal cell, and the transparent electrode of the second substrate and the first substrate are outside the sealant. It is preferable that the electrode lead-out portion is connected.

According to this, since the electrode lead-out portion may be provided on the side of the first substrate having a large thickness, for example, it has durability against mechanical stress applied in a mounting process, and the GH The connection between the cell and the electric circuit that drives the cell can be made more compact.

In the light control device and the image pickup device according to the present invention, the dielectric constant anisotropy of the negative type liquid crystal of the liquid crystal optical element is negative, but the guest material is of positive type or negative type. It may consist of dichroic dye molecules.

FIG. 1 is a schematic sectional view of a GH cell of a light control device according to the present invention.

As shown in FIG. 1, the dimmer according to the present invention is a liquid crystal optical element (a liquid crystal optical element in which a liquid crystal mixture 34 is enclosed between a substrate 31a having a large thickness and a substrate 31b having a small thickness, which face each other. GH cell) 12 and liquid crystal mixture 3
Reference numeral 4 denotes a guest-host type liquid crystal using the negative type liquid crystal 13 as a host material and the positive type dye molecule 4 as a guest material. Further, the size of the substrate 31b having a small thickness is designed to be slightly smaller than that of the substrate 31a having a large thickness, and the sealing material 35 is provided between the substrate 31a having a large thickness and the substrate 31b having a small thickness. It is sealed.

Both the substrates 31a and 31b have a transparent electrode and an alignment film, respectively, and the substrate 3 having a large thickness is used.
1a is subjected to the liquid crystal alignment treatment such as a rubbing method, while the substrate 31b having a small thickness is not subjected to the liquid crystal alignment treatment by rubbing (for example, a vertical alignment film such as an oblique vapor deposition film is formed on a transparent electrode). However, it has not been rubbed.)

The GH cell 12 uses the negative liquid crystal 13 having a negative dielectric anisotropy (Δε) as a host material and the positive dye molecule 4 having dichroism as a guest material. When no voltage is applied, as shown in FIG.
Light is transmitted by the GH cell 12 with little absorption. On the contrary, as shown in FIG. 1B, when voltage is applied,
The direction of the director of the liquid crystal molecules changes, light is absorbed by the positive dye molecules 4, and the transmittance of the GH cell 12 decreases.
The GH cell 12 interacts with the liquid crystal molecules at the interface with the liquid crystal alignment film 33 of the GH cell 12 when no voltage is applied.
Since the raction) is very weak, light is easily transmitted when no voltage is applied, and the direction of the director of liquid crystal molecules is easily changed with the application of voltage, and the light is absorbed by the positive dye molecule.

FIG. 2A is a schematic plan view of a first substrate having a large thickness among the substrates having different thicknesses which constitute the light control device (liquid crystal optical element: GH cell 12) according to the present invention. is there. In addition, FIG. 2B is a schematic plan view of a second substrate having a smaller thickness among the substrates having different thicknesses that constitute the light control device (liquid crystal optical element: GH cell 12) according to the present invention. .

As shown in FIG. 2A, the first substrate 31a having a large thickness has an ITO (Indium tin oxide) electrode (transparent electrode) 32a and an alignment film 33a. Has been subjected to a liquid crystal alignment treatment such as a rubbing method. Further, the first substrate 31a is provided with the lead-out portions 21 of the respective transparent electrodes.

As shown in FIG. 2B, the second substrate 31b having a small thickness has an ITO (Indium tin oxide) electrode (transparent electrode) 32b, and the alignment film 33b is subjected to the liquid crystal alignment treatment. Is not applied. In addition, the ITO electrode 3
2b is extended outside the effective optical path 20.

FIG. 3 is a schematic plan view of the GH cell 12 of the light control device (liquid crystal optical element) according to the present invention. Figure 4
It is the XX sectional view taken on the line of FIG.

As shown in FIGS. 3 and 4, the GH cell 12
Means that the ITO electrode 32b extending outside the effective optical path 20 of the second substrate 31b having a small thickness is electrically connected to the electrode lead-out portion 21 provided on the first substrate 31a having a large thickness. Further, the space between the first substrate 31a and the second substrate 31b is sealed by the sealing material 35 in the liquid crystal cell peripheral portion 24. Specifically, the ITO electrode 32b of the second substrate 31b and the first substrate 3 are provided outside the sealing material 35.
The electrode lead-out portion 21 of 1a is connected by a conductive material such as carbon paste 26, and GH
It is formed so that conduction can be established between the substrates outside the effective optical path 20 of the cell 12. Here, the conductive portion made of the carbon paste 26 is generally called a common electrode.

When the light control device according to the present invention is manufactured, it is necessary to satisfy to some extent each of the characteristics that are difficult to be compatible with each other, such as the light transmittance when transparent, the light transmittance when light is blocked, and the response time of the liquid crystal optical element. There is a preferred range of cell gap lengths for the GH cell. Further, in order to realize a practical light control device using a liquid crystal optical element, it is necessary to secure a sufficient optical density ratio without lowering the response speed,
In order to achieve these objects, the gap (gap length) between the substrates of the GH cell is 2 to 4 μm, preferably 2 to 3.
It is preferably controlled to 5 μm, particularly preferably 2 to about 3 μm.

When the cell gap length of the GH cell 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 greatly increased. As a result, the optical density ratio (contrast ratio) may not be secured as a result. On the contrary, when the cell gap length of the GH cell exceeds 4 μm, a large optical density ratio (contrast ratio) can be secured,
The response speed of the light control device may be significantly deteriorated, and particularly when driving is performed such that the light transmittance is slightly changed in the halftone, it may be significantly slowed down.

Further, as shown in the sectional view taken along the line AA of FIG. 3 in FIG. 9, it is desirable that the gap at the middle portion of the liquid crystal cell corresponding to the effective optical path is smaller than the gap at the peripheral portion thereof. That is, the gap between the glass substrates facing each other of the GH cell constituting the liquid crystal optical element is controlled to 2 to 4 μm, and the cell gap length in the cell middle portion (or center portion) is made smaller than the gap length in the cell peripheral portion. It is to be.

From various studies conducted by the present inventor, it was found that the cell gap length dependency of the response speed (particularly the response speed in halftone driving) tends to be larger than that of the optical density ratio. By the length control, it becomes possible to make the liquid crystal element in the effective optical path respond at a higher speed while maintaining the optical density ratio required for the light control device.

In the present invention, in forming the cell gap as described above, as shown in FIG. 10, spacers are arranged between opposed substrates having different thicknesses, and a peripheral portion of the liquid crystal cell is sealed with a sealing material. It is preferable that the sealing material is formed to have a diameter larger than that of the spacer, or contains a hard material such as a ball shape or a fiber shape.

The dimming 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 and 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 and 19 are moved relatively in the direction indicated by the arrow 27 by using a brightness 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 output from the effective light path 20 of the light, the polarizing plate 11 is not exposed to the 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, the light control device can increase the contrast ratio of light and dark and can keep the light amount distribution substantially uniform.

[0062]

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 liquid crystal (GH) cell will be described.

As shown in FIG. 11, 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 transparent electrode 3 as shown in a schematic cross section in FIG.
Negative liquid crystal molecules (host material) 13 and positive dichroic dye molecules (guest material) are provided between two glass substrates 31a and 31b having different thicknesses on which 2a and 32b and alignment films 33a and 33b are formed. ) 4 and the mixture 34 is enclosed.

The liquid crystal molecule 13 is, for example, a negative liquid crystal having 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 made 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 which constitutes the light control device 23 is the same as the above-mentioned prior invention by the present 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 now be described. As shown in the schematic plan views of FIGS. 2 and 3, for example, a glass substrate 31a having a thickness of 0.6 mm and 0.4 m
The transparent electrode pattern 32 is formed on both the glass substrate 31b having a thickness of m.
a, 32b and alignment films 33a, 33b are formed, and 0.6 m
Only the alignment film 33a on the side of the m-thick glass substrate 31a was rubbed (rubbing on one side). Also, 0.6 mm
The thick glass substrate 31a was provided with the lead-out portions 21 of the respective transparent electrodes, and the transparent electrode of the glass substrate 31b having a thickness of 0.4 mm was extended outside the effective optical path 20.

Then, the cell peripheral portion 2 of one glass substrate
4, a sealing (sealing) material 35 made of a thermosetting epoxy resin containing glass fibers having a diameter of 3 μm, for example, is applied in a predetermined width, and then two glass substrates 31 are applied.
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 the 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 (FIG. 3).

The sealing material 3 provided in the cell peripheral portion 24
5, the transparent electrode 32 on the substrate 31b having a thickness of 0.4 mm
b and the electrode lead-out portion 21 of the substrate 31a having a thickness of 0.6 mm
In order to electrically connect the two electrodes, a carbon paste 26 was dropped between them to form a shape for establishing conduction between the substrates outside the effective optical path 20 of the cell, that is, a common electrode, as shown in FIG. However, the common electrode is not limited to the carbon paste 26, and may be appropriately selected from a paste containing conductive particles.

The cell gap of an empty cell obtained by singulating (scribing and breaking) this bonded substrate was measured by a measuring instrument utilizing light interference. As shown in FIG. The cell gap g _{c of the} cell central portion (effective optical path) 20 was about 2.7 μm, and the cell gap g _p of the cell peripheral portion 24 was about 2.9 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 a few percent. Although depending on the liquid crystal cell structure used and the constituent materials, the GH cell 12 has ± 5 V (1 k
The minimum transmittance was almost reached by applying a pulse voltage higher than (Hz).

Further, the transient response time of the light transmittance when the driving 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, the liquid crystal cell can perform a transient response operation at high speed as a light control device while sufficiently securing a difference in optical transmittance (optical density ratio) between when the liquid crystal cell is transparent and when it is light-shielded. We were able to realize even smaller and lighter dimmers.

Example 2 In this example, a liquid crystal (GH) cell 12 was manufactured.
A 0.5 mm thick glass substrate 31a and a 0.2 mm thick plastic substrate 31b are used, and transparent electrode patterns 32a and 32b and alignment films 33a and 33b are formed on both substrates,
This is an example in which only the orientation film 33a on the glass substrate 31a side having a thickness of 0.5 mm is subjected to rubbing treatment (one-side rubbing).
Further, the glass substrate 31a having a thickness of 0.5 mm is provided with the respective lead-out portions 21 of the transparent electrodes, and is 0.2 m
The transparent electrode of the m-thick plastic substrate 31b was extended outside the effective optical path 20.

Then, for example, a sealing material 35 made of a thermosetting epoxy resin containing glass fiber having a diameter of 2.5 μm is applied to the cell peripheral portion 24 of the glass substrate 31a with a predetermined width. , The other substrate 31
As an example, plastic balls 36 having a diameter of 2.5 μm are evenly dispersed on b, and the two substrates 31a and 31b are aligned and overlapped with each other, and then heat treatment is performed 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 (FIG. 3).

Here, the above-mentioned plastic ball 36
Is sprayed from above the substrate using a general method (wet spray or dry spray), and is generally 100 to 15
They were arranged almost uniformly over the entire surface of the substrate at a density of 0 / mm ² .

The sealing material 3 provided in the cell peripheral portion 24
In order to electrically connect the transparent electrode 32b of the plastic substrate 31b having a thickness of 0.2 mm and the electrode lead-out portion 21 of the glass substrate 31a having a thickness of 0.5 mm on the outer side of FIG.
As shown in FIG. 5, a carbon paste 26 was dropped between them to form a shape for establishing conduction between the substrates outside the effective optical path 20 of the cell, that is, a common electrode.

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 2.4 μm, and the cell gap of the cell peripheral portion 24 was about 2.5 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) changes from the maximum transmittance of about 75% to several% as the operating voltage is applied. Diminished.

Further, the transient response time of the light transmittance when the drive pulse was changed was 20 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 the difference in the light transmittance (optical density ratio) between when the liquid crystal cell is transparent and when the light is shielded. It was realized, and it was possible to make it even thinner and lighter.

In this embodiment, an example of spraying from above is shown as the spacer disposing method, but it is also possible to form it by using a screen printing method in order to dispose it more uniformly. The shape of the spacer is not limited to the shape shown here, and it is also possible to supply the columnar spacer 37 by printing or lithography as shown in FIG.

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 lens group 51 and the second lens group (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 based on the above-mentioned present invention 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 dimmer 23 according to the present invention, as described above,
Since it has been further reduced in size and weight, it has flexibility and can be easily put in and taken out in the optical path. 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 an algorithm of a sequence of light transmittance control by the light control device 23 in this camera system.

According to this embodiment, the second group lenses 52 and 3 are
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-mentioned 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 drive mechanism thereof, the configuration of the drive circuit and the control circuit, etc.
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).

In Example 1, the thickness is 0.6 mm and 0.4 mm.
In the second embodiment, the thick substrate is used, and the 0.5 mm thick substrate and the 0.2 mm thick substrate are used. The first substrate having a large thickness has a thickness of 0.5 mm or more, and the second substrate having a small thickness has a thickness of less than 0.5 mm, and the first substrate and the second substrate have the same thickness. The thickness ratio is preferably 0.2 ≦ thickness ratio <1.0.

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.

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

Further, although a mechanical iris is used as a means for moving the polarizing plate 11 in and out of the effective optical path 20, it 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 also 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 adjusting the light amount of various optical systems such as electrophotographic copying machines and optical communication devices, 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, other than the CCD (Charge Coupled Device) used in this embodiment,
Of course, application to a CMOS image sensor or the like is also possible.

Furthermore, 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.

[0103]

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, since the opposite substrates having different thicknesses are used, the light control device and the image pickup device can be made thin and lightweight.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a cell of a liquid crystal optical element configured by using substrates having different thicknesses according to an embodiment of the present invention.

FIG. 2 is a schematic plan view of each substrate.

FIG. 3 is a schematic plan view of a cell of the liquid crystal optical element of the same.

FIG. 4 is a partially enlarged schematic sectional view of a cell of the liquid crystal optical element of the same.

FIG. 5 is a diagram illustrating a rubbing process of a liquid crystal alignment film in cell production.

FIG. 6 is a diagram illustrating a combination of rubbing treatments as an alignment treatment method in cell production.

FIG. 7 is a graph showing the relationship between the light transmittance of the light control device and the applied drive voltage according to the embodiment of the present invention, with the difference in the liquid crystal alignment treatment.

FIG. 8 is a graph showing a state of a transient response of the light control device according to a difference in liquid crystal alignment processing.

FIG. 9 is a schematic sectional 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 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 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, 14 ... GH cell drive circuit, 15, 16 ... Lens group,
Reference numeral 17 ... Imaging surface, 18, 19 ... Iris blade, 20 ... Effective optical path, 21 ... External transparent electrode (drawing portion), 22 ... Opening portion, 23 ... Light control device, 24 ... Cell peripheral portion, 26 ... Common electrode, 31 ... Substrate, 32 ... Transparent electrode, 33 ... Alignment film, 3
4 ... Liquid crystal material (mixture), 35 ... Sealing material, 3
6 ... Spherical spacer, 37 ... Columnar spacer, 50 ... C
CD camera, 51 ... First lens group, 52 ... Second lens group, 5
3 ... 3 group lens, 54 ... 4 group lens, 55 ... CCD package, 56 ... Linear motor

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03B 9/08 G03B 9/08 GF term (reference) 2H081 AA72 2H088 HA01 HA18 HA24 JA05 JA06 MA02 MA09 2H089 LA07 LA41 QA16 RA05 RA06 TA01 TA15 TA16 2H090 HC06 JA09 JB02 JB03 JC13 KA05 KA06 LA02 LA12 MA02 MA09 MA15 MB01 2H092 GA40 MA13 NA25 PA01 PA03 PA07 PA11 QA07 QA08

Claims (11)

[Claims] 1. A light control device comprising a liquid crystal optical element in which liquid crystal is sealed between substrates facing each other having different thicknesses, and the liquid crystal is a guest-host liquid crystal using a negative liquid crystal as a host material. 2. The light control device according to claim 1, wherein among the substrates having different thicknesses, only the first substrate having a large thickness is subjected to the liquid crystal alignment treatment by rubbing. 3. A transparent electrode and a first substrate having a large thickness that has been subjected to a liquid crystal alignment treatment, and a transparent electrode and a second substrate having a small thickness that has not been subjected to a liquid crystal alignment treatment. The light control device according to claim 1, wherein each of the transparent electrodes has a lead-out portion provided on the first substrate. 4. The transparent electrode of the second substrate is extended outside the effective optical path and is electrically connected to an electrode lead portion provided on the first substrate. Light control device. 5. The first substrate having a large thickness among the substrates having different thicknesses has a thickness of 0.5 mm or more, and
The thickness of the second substrate having a smaller thickness is less than 0.5 mm, and the thickness ratio between the first substrate and the second substrate is 0.2 ≦ thickness ratio <1.0. The light control device according to claim 1. 6. The light control device according to claim 1, wherein the gap between the substrates in at least the effective optical path is controlled to be 2 μm or more and 4 μm or less. 7. The light control device according to claim 1, wherein among the substrates having different thicknesses, at least a first substrate having a large thickness is a glass substrate. 8. The light control device according to claim 1, wherein among the substrates having different thicknesses, the main component of the second substrate having the smaller thickness is formed of a plastic material. 9. The light control device according to claim 1, wherein the guest material of the liquid crystal is a dichroic dye. 10. The liquid crystal cell peripheral portion is sealed between the first and second substrates with a sealing material, and the transparent electrode of the second substrate and the first substrate are outside the sealing material. The light control device according to claim 4, wherein the electrode lead-out portion of the substrate is connected. 11. 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.