JPH09243806A - Optical characteristic variable optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical hydrophilic variable optical element which is simple in structure, is low in light quantity loss, is derivable by a low voltage and obviates the occurrence of unhappiness by using liquid crystals having a twist pitch smaller than the wavelength of the light transmitted through the liquid crystals. SOLUTION: A variable forces lens 1 is constituted by holding chiral nematic liquid crystals 2 between flat plate glass 4 and lens 5 respectively formed with transparent electrode film 3 on the inner side via oriented film 6 and is sealed with a sealant 7. The pitch of the twists of the liquid crystals 2 is made extremely smaller than the wavelength of the light. The lens 5 acts as a lens having a refractive index n' without depending on the polarization of incident light where n' is defined as n'=(ne +n0 )/2 (ne is refractive index to the polarization in the major axis direction of the liquid crystal molecules, n0 is refractive index to the polarization in the minor axis direction of the liquid crystal molecules). When an electronic field is impressed between the oriented films 6, the arrangement of the liquid crystal molecules changes and the liquid crystals 2 turn to isotropic media having the refractive index n0 .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable-optical-characteristic optical element, and more particularly to a variable-optical-characteristic optical element for changing optical characteristics.

[0002]

2. Description of the Related Art In focusing a zoom lens or an image pickup apparatus, the lens is usually moved mechanically.

However, it is not possible to move the whole or a part of the lens system with an electronic endoscope or a micromachine eye, which is required to be very small, and
For a television camera, an electronic still camera, a silver salt film camera, or the like, it is desirable that zooming and focusing can be performed without moving the lens system in order to reduce weight and cost.

Therefore, conventionally, as a means for solving these problems without moving the lens, a variable focus lens has been proposed, for example, in Japanese Patent Laid-Open Nos. 5-34656 and 4-345124. .

For example, as shown in FIG. 29, a varifocal lens 201 proposed in Japanese Unexamined Patent Publication No. 5-34656 has a chiral nematic liquid crystal 202 in which the major axis of liquid crystal molecules is twisted by 360 ° and a transparent electrode is provided inside. A flat glass 204 coated with the film 203 and a Fennenels substrate 205 are sandwiched by an alignment film 206 and sealed by a sealing material 207.

In the varifocal lens 201 having such a structure, when the power source 208 is turned on by the switch 209 and an electric field is applied between the alignment films 206, the chiral nematic liquid crystal 202 becomes homeotropic alignment as shown in FIG. The chiral nematic liquid crystal 202, which is isotropic with respect to the polarization of incident light, has a lower refractive index than the state of FIG. 29, or has the same state depending on the polarization direction.

In the state of FIG. 29, when the polarization direction of incident light and the major axis of the liquid crystal molecule 210 of the chiral nematic liquid crystal 202 on the incident side (long direction of ellipsoid of FIG. 29) are the same,
The chiral nematic liquid crystal 202 has a high refractive index, and when the polarization direction of incident light and the minor axis direction of the liquid crystal molecules on the incident side match, the chiral nematic liquid crystal 202 has a low refractive index.

This is because, in this example, the pitch P of twist of the chiral nematic liquid crystal 202 is 10 μm to 30 μm, and the wavelength λ of light (about 0.4 μm to 0.7 μm for visible light).
Since it is much larger than that of μ), the light incident from the left will follow the twist of the liquid crystal molecules and the polarized light will proceed. The reason for this is shown, for example, in “Katsumi Yoshino, Masanori Ozaki; Basics of Liquid Crystal and Display Applications P91 to P93; Corona Publishing Co., Ltd.” (hereinafter referred to as Document 1), and therefore description thereof is omitted.

[0009]

Therefore, the varifocal lens 201 shown in FIG. 29 has a short focal length for polarized light in the long axis direction of the liquid crystal molecules on the incident side, and the short axis of the liquid crystal molecules on the incident side. The variable focus lens 2 of FIG.
Since the focal length of 01 becomes long, the conventional variable focus lens 201 becomes a double focus lens, and only a blurred image is formed, so that the target variable focus lens cannot be realized.

The present invention has been made in view of the above circumstances, and has a simple structure, can be driven by a low voltage with little loss of light quantity, can be driven by a low voltage, and can change optical characteristics without changing the optical characteristics. Is intended to provide.

[0011]

In the variable optical-characteristic element of the present invention, liquid crystal is enclosed in a space formed by a pair of members, and the alignment state of the liquid crystal molecules of the liquid crystal is changed by a physical action from the outside. In the optical characteristic variable optical element for controlling and changing the optical characteristic of the liquid crystal, the liquid crystal is configured to have a twist pitch smaller than the wavelength of light transmitted through the liquid crystal.

In the optical-property variable optical element of the present invention, the liquid crystal has a twist pitch smaller than the wavelength of the light transmitted through the liquid crystal, so that the structure is simple and the loss of the light amount is small. It is possible to drive by voltage and it is possible to change optical characteristics without causing blurring.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

1 to 17 relate to the first embodiment of the present invention. FIG. 1 is a configuration diagram showing a basic configuration of a variable focus lens, and FIG. 2 is a refractive index of molecules of the chiral nematic liquid crystal of FIG. FIG. 3 is a diagram showing an ellipsoid, FIG. 3 is an explanatory diagram for explaining the operation of the variable focus lens of FIG. 1, FIG. 4 is a configuration diagram showing a specific configuration of the variable focus lens of FIG. 1, and FIG. 5 is a variable focus of FIG. FIG. 7 is a diagram showing a liquid crystal molecular arrangement of a chiral smectic C phase of a chiral smectic liquid crystal used in a first modification of the lens, FIG. 6 is a configuration diagram showing a configuration of a varifocal lens using the chiral smectic liquid crystal of FIG. 5, and FIG. 6 is an explanatory view for explaining the operation of the variable focus lens of FIG. 6, FIG. 8 is a configuration diagram showing a configuration of a second modification of the variable focus lens of FIG. 1 using a chiral cholesteric liquid crystal, and FIG. 9 is a variable diagram of FIG. Explain the action of the focusing lens FIG. 10 is a diagram showing the actual measurement value of the reflectance of the chiral cholesteric liquid crystal of FIG. 8, and FIG. 11 is a configuration diagram showing the configuration of the second modification of the variable focus lens of FIG. 1 using discotic liquid crystal. 12 is an explanatory view for explaining the action of the varifocal lens of FIG. 11, FIG. 13 is a view showing a refractive index ellipsoid of molecules of the discotic liquid crystal of FIG. 11, and FIG. 14 is a view of the discotic liquid crystal of FIG. FIG. 15 is the first view when viewed, and FIG. 15 shows the discotic liquid crystal of FIG.
FIG. 16 is a second diagram when viewed from the direction, FIG. 16 is a configuration diagram showing a configuration of a varifocal lens that uses a magnetic field to change the orientation of the chiral nematic liquid crystal of FIG. 1, and FIG. It is a block diagram which shows the structure of the variable focus lens which used the temperature change for changing the orientation of the Matek liquid crystal.

As shown in FIG. 1, a varifocal lens 1 as a variable-optical-characteristic optical element of the first embodiment is a flat glass having a chiral nematic liquid crystal 2 and a transparent electrode film 3 coated inside. 4 and the lens 5 between the alignment film 6
The basic structure is a structure in which the chiral nematic liquid crystal 2 is sandwiched between and sealed by a sealing material 7, and the twist pitch P of the chiral nematic liquid crystal 2 is extremely smaller than the wavelength λ of light.
That is,

## EQU1 ## P << λ (1). In this way, when the pitch P is much smaller than the wavelength λ of light, the lens 5 acts as a lens having a refractive index n ′ regardless of the polarization of incident light.

[0016]

[Equation 2] Here, ne is a refractive index for polarized light in the major axis direction of the liquid crystal molecule, and no is a refractive index for polarized light in the minor axis direction of the liquid crystal molecule, and in FIG. 2, a refractive index ellipse corresponding to the incident side liquid crystal molecule of the chiral nematic liquid crystal 2 Show the body. Here, the x-axis and the z-axis are the minor axis directions of the liquid crystal molecules, and the y-axis is the major axis direction of the liquid crystal molecules. Note that ne> no.

Next, the reason why the chiral nematic liquid crystal 2 of this embodiment behaves effectively as an isotropic medium having a refractive index n ′ will be described below based on the Jones vector and matrix.

As shown in P85-92 of the above-mentioned document 1,
According to Equation 3.107, Equation 3.110, and Equation 3.126, when the absolute phase change exp (-iα) is included,
The Jones matrix Wt for the chiral nematic liquid crystal 2 of thickness d shown in FIG.

(Equation 3) Given in. However,

(Equation 4)

(Equation 5)

(Equation 6)

(Equation 7)

(Equation 8) It is.

Here, ordinary light is defined as polarized light in the short axis direction of liquid crystal molecules, and extraordinary light is polarized light in the long axis direction of liquid crystal molecules, or
If the long axis is defined as the polarized light in the direction when projected on a plane perpendicular to the optical axis, Γ represents the phase difference between the ordinary ray and the extraordinary ray by the chiral nematic liquid crystal 2.

Φ represents the twist angle of the liquid crystal molecules of the chiral nematic liquid crystal 2 in radians. Further, the coordinate systems of the equations (3) and (8) are represented by x,
It should be taken like the y and z axes. That is, the x-axis is directed from the front side to the back side of the paper, and the y-axis is the direction of the liquid crystal molecule long axis on the incident surface of the chiral nematic liquid crystal 2.

Now, under the condition of the equation (1), the equation (3)
Let's find out what Wt looks like.

First, the equation (1) is

[Equation 9] And can be transformed. Therefore, when P / λ → 0, W in equation (3)
Let's find the limit value WtL of t.

[0023]

(Equation 10) Therefore, when P / λ << 1

[Equation 11] Therefore, when P / λ → 0, | Γ / Φ | → 0.

Under the condition of equation (11)

(Equation 12)

(Equation 13)

[Equation 14]

(Equation 15) When P / λ → 0,

[Expression 16] X → Φ (16)

[Expression 17] cosX → cosΦ (17)

(Equation 18)

[Equation 19] Therefore, when P / λ → 0

(Equation 20) Becomes This has a refractive index n '= (ne + no) / 2 and a thickness d.
, None other than the Jones matrix of an isotropic medium along the optical axis.

Therefore, since P / λ << 1, the varifocal lens 1 in FIG. 1 acts as a lens having a refractive index n ', and it is possible to form an image without blurring.

Further, in the variable focus lens 1 shown in FIG.
When the AC power supply 8 is turned on by the switch 9 and an electric field is applied between the alignment films 6, the chiral nematic liquid crystal 2 is arranged as shown in FIG. 3, and the liquid crystal becomes an isotropic medium having a refractive index no. Compared with the state of 1, the liquid crystal lens has a different focal length, and a variable focus lens without blur can be realized.

Next, a specific structural example of the variable focus lens 1 will be described with reference to FIG. As shown in FIG. 4, the varifocal lens 1 has a configuration in which the voltage is continuously variable by a variable resistor 21, and the liquid crystal molecules are arranged in the middle of the above FIGS. 1 and 3. Configure it so that you can bring it. As a result, a liquid crystal lens whose focal length changes continuously can be realized.

Even in the case of the intermediate arrangement as shown in FIG. 4, by replacing the value of ne with the refractive index ne 'of extraordinary light which is an intermediate value between ne and no, the above equation (3) ) -Equation (20) is satisfied.

With the configuration shown in FIG. 4, the method of applying the voltage is not limited to the continuous variable, but the variable focus can be selected even if the applied voltage is selected from several discrete voltage values. A lens can be realized.

Here, a practical example of the variable focus lens 1 configured as shown in FIG. 4 will be described in detail.

Although the limit case of P / λ → 0 is shown in the formula (20), the limit value may not always be true in an actual liquid crystal lens or varifocal lens. Let's derive an approximate expression.

When the equation (3) is approximated by considering up to the first order of P / λ, it becomes as follows. That is, equations (12) to (1
In 4), up to the first order of P / λ, that is, from equation (10),
Remaining up to the 1st order of Γ / Φ, 2nd order or more of P / λ, 2 of Γ / Φ
If you omit the following items,

(Equation 21)

(Equation 22) Next

(Equation 23) Get. Therefore, in order to consider that the value of WtN is almost equal to the Jones matrix of the isotropic medium, | i · Γ / 2Φ | should be close to 0. At this time, WtN is

(Equation 24) This equation shows that the liquid crystal has a polarization direction of incident light of Γ /
Although it rotates by 4 · Γ / Φ, it means that it can be regarded as an isotropic medium.

[0033]

(Equation 25) That is,

(Equation 26) If so, a variable focus lens without blur can be obtained. From equation (10)

[Equation 27] Becomes

When the varifocal lens of the present invention is used for a lens of a relatively low-cost product such as an actual imaging device with a lens, for example, an electronic camera, a VTR camera, an electronic endoscope, etc., the number of pixels of a solid-state imaging device Since there are few cases and a high resolution may not be required, the condition of the equation (26) can be relaxed,

[Equation 28] Is fine.

Since a high resolution is required for a lens of an electronic image pickup device having a large number of pixels, a lens of a high quality product such as a film camera, a microscope, etc.,

(Equation 29) Should be fine.

In the case of a lens such as a lens of an optical disk which is not used for image formation, the condition is further relaxed,

[Equation 30] Should be fine.

It should be noted that, as is common to all of the present embodiments, when the liquid crystal has a helical arrangement, when the long axis direction of the liquid crystal molecules is not perpendicular to the optical axis, that is, when the liquid crystal molecules are oblique,
The ne of the formulas (1) and (26) to (30) is replaced with the above ne ′
You can replace it with.

The following are some design examples.

If the thickness d of the chiral nematic liquid crystal 2 is thin, the power of the lens is weak and is not useful, and if it is thick, light is scattered and flare is caused.

Approximately 2 μ <d <300 μ (31) is appropriate. Considering visible light as an example of the wavelength λ of light,

[Expression 32] 0.35μ <λ <0.7μ (32)

The value of ne-no is determined by the physical properties of the liquid crystal,

[Equation 33] There are many substances with 0.01 <| ne-no | <0.4 (33). Therefore, as a first design example, if d = 15μ λ = 0.5μ ne-no = 0.2 P = 0.05μ, then Γ / 2Φ = π · 0.2 × 0.05 / 0.5 = 0.02π, formula (26), formula (28), formula (29), formula (3
0) is satisfied.

As a second design example, if d = 30 μ λ = 0.6 μ ne-no = 0.25 P = 0.3 μ, then Γ / 2Φ = π · 0.3 × 0.25 / 0. 6 = 0.125
becomes π, and formula (26), formula (28), formula (29), formula (3
0) is satisfied.

As a third design example, if d = 50 μ λ = 0.55 μ ne-no = 0.2 P = 0.6 μ, then Γ / 2Φ = π · 0.2 × 0.6 / 0 .55 = 0.218
becomes π, and Expressions (28) and (30) are satisfied.

Further, as a fourth design example, considering a varifocal lens for near infrared light, and d = 200 μ λ = 0.95 μ ne-no = 0.2 P = 0.7 μ, Γ / 2Φ = Π ・ 0.2 × 0.7 / 0.95 = 0.145
8π, and equation (26), equation (28), equation (29), and equation (3
0) is satisfied.

In each of the above design examples, the chiral nematic liquid crystal has been described as an example. However, in order to make the pitch of the helix of the chiral nematic liquid crystal smaller than the wavelength of the light used, it is advisable to mix the chiral agent with the liquid crystal.

As the chiral agent, a cholesteric liquid crystal or a synthetic optically active compound is used. Examples of the chiral nematic liquid crystal are shown in the following chemical formulas (1) and (2), and examples of the chiral agent are shown in the chemical formulas (3) and (4).

[0046]

Embedded image

Embedded image

Embedded image

Embedded image In the above description, the chiral nematic liquid crystal 2 is used as the liquid crystal used for the varifocal lens 1, but the present embodiment is not limited to this, and as a first modification of the varifocal lens, FIG. It can be configured using a chiral smectic liquid crystal 31 as shown. This figure 5
6 shows an arrangement of liquid crystal molecules of a chiral smectic C phase, and FIG. 6 shows the structure of a varifocal lens 1a using the same.
Shown in

As shown in FIG. 6, in the chiral smectic liquid crystal 31, when no voltage is applied, the liquid crystal molecules are oriented in a specific direction for each layer 31a, and the direction rotates at a constant period P.

When a voltage is applied to this, the liquid crystal molecules of each layer are aligned in the Z-axis direction of the coordinate system as shown in FIG. 7, and the refractive index of the chiral smectic liquid crystal 31 is n ′ in the state of FIG.
To no, the focal length of the varifocal lens 1 changes.

Equations (1) to (30) also apply to the first modified example shown in FIGS. 5 to 7, particularly equation (2).
By satisfying 6), formula (28), formula (29), and formula (30), a varifocal lens with less blur can be obtained. Also in the configuration of FIG. 6, the voltage applied to the chiral smectic liquid crystal 31 can be continuously changed, and accordingly, the focal length also continuously changes.

Here, an example of designing the varifocal lens 1a using the chiral smectic liquid crystal 31 will be described. As parameters, d = 25 μ λ = 0.55 μ ne-no = 0.3 P = 0.1 μ Γ / 2Φ = π · 0.3 × 0.1 / 0.55 = 0.054
5π, and the formula (26), the formula (28), the formula (29), and the formula (3
0) is satisfied.

In the chemical formula (5), "4- (n-hexyloxy) phenyloxy-4"-(2-meterbutyl) biphenyl-4'-carboxylate "which is an example of the molecular structure of the smectic liquid crystal 31 is shown. showed that. The pitch P is about 0.2 μ.

[0052]

Embedded image As a second modification of the variable focus lens, a variable focus lens 1b using a chiral cholesteric liquid crystal 41 can be configured as shown in FIG.

In the chiral cholesteric liquid crystal 41, the alignment direction of the liquid crystal molecules is parallel to the lens surface in each layer, the azimuth angle is the period P, and changes in a spiral in the Z-axis direction. Equations (1) to (30) apply in this state.

When a voltage is applied, the orientation of the liquid crystal molecules disappears as shown in FIG. 9, and the focal length changes.

The chiral cholesteric liquid crystal has the property of selective reflection, and totally reflects the right or left circularly polarized light near the wavelength λs = Pn ′. FIG. 10 shows an example of the actual measurement value of the reflectance of the chiral cholesteric liquid crystal with respect to natural polarized light.

Therefore, the wavelength λs is the variable focus lens 1b.
It is desirable to be outside the wavelength range of the light used in. That is, it is necessary for Pn ′ to be outside the wavelength range of light using the varifocal lens 1b in order to obtain a liquid crystal lens with higher transmittance and no coloring.

If it is visible light,

It is necessary that Pn '<0.4μ (34).

Selective reflection may occur even in the liquid crystal of the chiral smectic C phase shown in FIG. 5, which is the first modification example described above, and therefore the formula (34) is also applied to the example shown in FIG. 5 for the above reason. It

As a design example of the varifocal lens 1b using the chiral cholesteric liquid crystal 41, if d = 15 μ ne-no = 0.4 λ = 0.45 μ P = 0.01 μ n ′ = 1.7, then Γ / 2Φ = π ・ 0.4 × 0.01 / 0.45 = 0.00
It becomes 89π, and formula (26), formula (28), formula (29), formula (3
0) is satisfied and Pn ′ = 0.017 μ, and therefore the expression (34) is also satisfied.

The chemical formula (6) is an example of a chiral cholesteric liquid crystal and is a chemical formula of cholesterol benzoate.

[0061]

[Chemical 6] As a third modification of the variable focus lens, a discotic liquid crystal 51 may be used as shown in FIG. 11, and when a voltage is applied, the discotic liquid crystal 51 as shown in FIG.
Changes its orientation, and the focal length as a convex lens becomes longer.
That is, since the discotic liquid crystal 51 is a negative uniaxial crystal like the refractive index ellipsoid shown in FIG. 13, the focal length as a convex lens becomes long.

In this case, when FIG. 12 is viewed from the Z direction, if the molecular arrangement of the discotic liquid crystal 51 is not oriented in one direction as shown in FIG. 14 or FIG.
In the state of 2, the alignment of the liquid crystal need not draw a spiral.
Therefore, the expressions (1) to (30) may not be satisfied.

It can be said that the pitch P of the helix is smaller than the wavelength λ of the light used, which is common to the variable focus lenses described in the present embodiment, each of the modifications and other embodiments described later. Is more desirable in order to obtain a varifocal lens with less blurring. For example, in the case of visible light, in an optical device used with 0.4μ <λ <0.7μ,

[Equation 35] 0.0001μ <P <0.4μ (35) is a desirable condition. To further reduce the blurring

It is desired that 0.0001μ <P ≦ 0.2μ (36). The lower limit of P is determined by the size of the liquid crystal molecule itself.

Further, in the present embodiment and each modification,
Electric fields have been used to change the orientation of each liquid crystal,
Not limited to this, as shown in FIG. 16, a coil 55 and an iron core 56 are used, for example, a chiral cholesteric liquid crystal 4
The magnetic field H may be applied to 1 and changed. In addition,
Although FIG. 16 shows an example of the variable focus lens of the chiral cholesteric liquid crystal 41, it may be applied to the variable focus lens of the chiral nematic liquid crystal 2 or the chiral smectic liquid crystal 31.

To change the orientation of each liquid crystal, a heater 58 may be used to change the orientation of, for example, the chiral cholesteric liquid crystal 41 by changing the temperature as shown in FIG. In addition, the present invention can be applied to other liquid crystal, a chiral nematic liquid crystal 2, a chiral smectic liquid crystal 31, and the like, as well as a variable focus lens. In this configuration, by changing the temperature, a phase transition is caused in the liquid crystal and the focal length of the lens is changed. The lens is the Fresnel lens 60, and the power of the variable focus lens is obtained without increasing the thickness of the liquid crystal. Here, the Fresnel lens 60 and the lens 5 may have an aspherical shape depending on the application.

FIG. 18 is a structural diagram showing the structure of a variable focus lens according to the second embodiment of the present invention.

Since the second embodiment is almost the same as the first embodiment, only different points will be described, the same components will be denoted by the same reference numerals, and description thereof will be omitted.

In the second embodiment, the diffractive optical element (DO
(Also called E or HOE) is made of liquid crystal to form a variable focus lens.

As shown in FIG. 18, the variable focus lens 61 of the second embodiment uses the chiral nematic liquid crystal 2,
It is configured such that it is sandwiched between a lens 62 and a parallel glass 63, each of which has a transparent electrode film 3 coated on the inside, with an alignment film 6 interposed therebetween, and is sealed by a sealing material 7.

The lens 62 has a Fresnel lens shape,
The uneven portion is at the level of the wavelength of light, and the width W of one ring zone of the lens 62 is

[Equation 37] W · θ = m · λ It is determined by (37). Here, θ is the refraction angle of the light ray in the ring zone, and m is the diffraction order.

When the refractive index of the chiral nematic liquid crystal 2 is changed by applying a voltage, the order of diffraction is changed, so that the focal length of the varifocal lens 61 can be discontinuously changed.

That is, if the notched height of a certain ring zone is h and the refractive index of the lens 62 is ng,

(38)

[Equation 39]

[Expression 40] m1 ≠ m2 (40).

However, when m1 and m2 are different integers from each other, h, m1, m2, n ', no and ng are expressed by the formula (38).
If the expression (40) is satisfied, the varifocal lens 61 becomes a diffractive optical element whose diffraction efficiency is optimized by the orders m1 and m2.

The focal length changes to f1 / m1 and f1 / m2 when the switch 9 is turned on and off. Where f1
Is the focal length of the first-order diffractive optical element. Note that, practically, the expressions (38) and (39) may be approximately satisfied.

Hereinafter, application examples of the above-described embodiments and their modifications will be described.

As shown in FIG. 19, an electronic endoscope 71 as a first device using the variable focus lens of each of the above-described embodiments and its modifications transmits illumination light for illuminating a subject. The illumination light from the light guide 72 is illuminated by the illumination lens 7.
The subject is irradiated with light from the subject 3 and the subject image is made incident through the objective lens 74. Then, the varifocal lens 75 is stopped down 7
It is arranged in the vicinity of 6, and an image is formed on the image forming surface of the CCD 78 by the optical lens 77, signal processing is performed by the signal processing device 79, and a subject image is displayed on the monitor 80. In this configuration, the variable focus lens 75 is used for focus adjustment and realizes an electronic endoscope having an autofocus function.

In the second device using the variable focus lens of the above-mentioned embodiment and each modification thereof, as shown in FIG. 20, the CCD 82 picks up the subject image by the objective lens 81, and the signal processing device. An image pickup device 89 for processing a signal by 83 and displaying a subject image on a monitor 84. Two variable focus lenses 85, 86 are provided between an objective lens 81 and a CCD 83 via a diaphragm 88, and the focal lengths are interlocked. Then, both zooming and focusing are realized. These are actually electronic cameras,
Used in a TV camera or the like, the variable focus lenses 85 and 86 are driven by a control circuit 87 so as to focus and zoom.

In FIG. 20, variable focus lenses 85 and 8 are used.
6 shows the case of a concave lens and a convex lens, respectively, but a convex and convex lens or a combination of convex and concave lenses and a concave and convex lens may be used.

FIG. 21 shows another application example of the liquid crystal satisfying the expression (1), which is used for the diaphragm 91 of the optical system.

The diaphragm 91 has a structure sandwiched by transparent members 92 and 93 made of a transparent material which seals the chiral nematic liquid crystal 2 which is a liquid crystal satisfying the formula (1). Has a saw-toothed shape or a triangular shape in cross-section at the portion in contact with the liquid crystal. Further, the diaphragm 91 has a rotationally symmetrical shape with respect to the optical axis.

In FIG. 21, the ray a incident on the center of the diaphragm 91 from the left and right passes through as it is, while the ray b incident on the peripheral portion is the chiral nematic liquid crystal 2 and the transparent member 93.
It is in a state in which the diaphragm 91 is narrowed down because it is totally reflected at the boundary surface of and and is bent to the side and cannot pass through the diaphragm 91.

In FIG. 22, when the voltage is applied to the diaphragm 91, the chiral nematic liquid crystal 2 is homeotropically oriented, so that the light ray b is totally reflected at the boundary surface between the transparent member 93 and the chiral nematic liquid crystal 2. Without going straight, Figure 2
Compared with No. 1, the effective diameter of the diaphragm is wider. When the refractive index of the transparent member 93 is n93,

## EQU00004 ## If 0.8no <n93 <1.3no (41), the light ray b travels substantially straight in the state of FIG.

The condition for total reflection of the light ray a in the state of FIG. 21 is that when the illustrated angle is β,

(Equation 42) It is.

Further, the chiral nematic liquid crystal 2 is practically replaced by the formula (26) or the formula (2) instead of the formula (1).
8) or the formula (29) or the formula (30) may be satisfied.

As the liquid crystal, in addition to the chiral nematic liquid crystal 2, the above-mentioned chiral smectic liquid crystal 3 is used.
1, a chiral cholesteric liquid crystal 41, a discotic liquid crystal 51, a polymer dispersed liquid crystal in which liquid crystal is dispersed in a polymer, a polymer liquid crystal, or the like can also be used. In the case of the chiral smectic liquid crystal 31 or the chiral cholesteric liquid crystal 41, it is more preferable that the formula (34) is also satisfied. Also,
As is common to all liquid crystals, the formula (35) and the formula (3
It is even better if 6) is satisfied.

FIG. 23 shows an example of the second diaphragm 101 using the chiral nematic liquid crystal 2. 21 is different from the diaphragm 91 in FIG. 21 in that the periphery of the transparent member 102 that replaces the transparent member 93 is a DOE (diffractive optical element), and the periphery of the transparent member 102 has a height λ of light used. To the extent of
It is in the shape of a saw blade.

In the state of FIG.

[Mathematical formula-see original document] Since no <n102 (43), the light beams b1 and b2 in the peripheral portion are bent outward by diffraction, are absorbed by the light absorbing substance 103, and are not transmitted backward from the diaphragm 101. Note that n102 is the refractive index of the transparent member 102.

Since FIG. 23 shows the state when the voltage is turned off, the liquid crystal has a chiral nematic arrangement.

## EQU00004 ## Since 0.9n '<n102 <1.2n' (44), b1 and b2 go straight about, and operate as if the diaphragm is substantially open.

As the shape of the DOE, the refraction angle θ is determined by the expression (37), and in order to increase the diffraction efficiency and further improve the operation as the diaphragm, the expressions (38) to (40) are satisfied. Even better (but replace ng with n102).

As the liquid crystal, chiral nematic liquid crystal 2 is used.
Besides, the above-mentioned chiral smectic liquid crystal 31, chiral cholesteric liquid crystal 41, and discotic liquid crystal 5
1, and further, polymer dispersed liquid crystal in which liquid crystal is dispersed in polymer, polymer liquid crystal and the like can be used. Chiral smectic liquid crystal 31 or chiral cholesteric liquid crystal 4
In the case of 1, it is even better if the expression (34) is also satisfied.

The liquid crystal needs to satisfy the formula (1), but in practice, instead of the formula (1), the formula (26) or the formula (2) is used.
8) or the formula (29) or the formula (30) may be satisfied.

If the transparent member 92 is also DOE, a larger refraction angle can be obtained, and a high-performance diaphragm can be obtained.

The voltage applied to the diaphragm 101 may be continuously variable. In this case, the diaphragm in which the transmittance of the peripheral portion of the diaphragm 101 continuously changes is convenient.

The diaphragms 91 and 101 are the diaphragm 76 of the electronic endoscope 71 of FIG. 19 and the diaphragm 8 of the image pickup apparatus 80 of FIG.
8 can be used. Since the electronic endoscope 71 and the imaging device 80 always include a power source, the power source can be used also for the liquid crystal element, which is convenient.

Further, in the diaphragm 101, the transparent member 102
If the central part A is eliminated and the entire surface is made into a saw-tooth shape, a diaphragm capable of changing the light quantity can be obtained although the luminous flux diameter does not change. In order to have an effect similar to that of the optical element capable of varying the amount of transmitted light, equation (38) or equation (39)
It is better that one of the two is approximately satisfied, and it is better that equations (38) and (39) are not simultaneously satisfied (note that equation (4)
0) needs to be satisfied).

This is because, for example, if the equation (38) is completely satisfied and the equation (39) is incomplete, the light amount of the order m1 is different in both states of FIGS.
Since it exists, the diaphragm 101 operates as a density variable filter for the light of the following formula m1.

When both equations (38) and (39) are satisfied, the diaphragm 101 operates as an optical shutter for the light of the following equation m1 or m2. Even in this case, if the voltage is continuously changed from the state of FIG. 23 to the state of FIG. 24, the ne in the equations (38) and (39) can be replaced by the continuously changing ne ′, so that the transmitted light amount It can be operated as a variable optical element (it is necessary to consider equation (2)).

FIG. 25 shows equations (1), (26) and (2).
8), the equation (29), or the equation (30), which is an example of the variable prism (or variable light deflector) 111 using a liquid crystal.

In this variable prism 111, as shown in FIG. 25, a wedge-shaped or saw-toothed transparent member 1 is used.
12 and the transparent member 113 between the chiral nematic liquid crystal 2
Is arranged. For example, if the refractive index of the transparent member 112 is made equal to the refractive index n ′ of the chiral nematic liquid crystal 2, the light from the left and right in FIG. 25 goes straight.

When a voltage is applied to the variable prism 111, the alignment of the liquid crystal becomes homeotropic as shown in FIG. 26, and the refractive index of the chiral nematic liquid crystal 2 drops to no, so that the light is refracted to the upper right. . It is convenient to make the voltage continuously variable because the refraction angle of light continuously changes.

As the liquid crystal, a chiral nematic liquid crystal 2
Besides, the above-mentioned chiral smectic liquid crystal 31, chiral cholesteric liquid crystal 41, discotic liquid crystal 51,
Further, a polymer dispersed liquid crystal in which a liquid crystal is dispersed in a polymer, a polymer liquid crystal or the like can also be used. In the case of the chiral smectic liquid crystal 31 or the chiral cholesteric liquid crystal 41, it is more preferable that the formula (34) is also satisfied.

The shape of the saw blade is finely divided to make the transparent member 1
A variable prism can be obtained by using 12 as a diffractive optical element.
At this time, it is preferable to satisfy the formula (37), and further the formula (38),
If the expressions (39) and (40) are satisfied, the diaphragm effect is high.
An optical element is obtained (however, ng represents the refractive index of the transparent member 112 at this time).

The variable prism 111 can be used in electronic cameras, TV cameras, film cameras, binoculars, etc. for preventing blurring.

By the way, the principle of spatial modulation of light rays used in the diaphragms 91 and 101 and the variable prism 111 can be applied to a display.

FIG. 27 shows an example of a display 121 using a liquid crystal satisfying any one of formula (1) or formula (26), formula (28), formula (29), and formula (30).

In this display 121, as shown in FIG. 27, a liquid crystal 124 is arranged between a transparent member 122 having a saw blade-shaped cross section and a transparent member 123. The refractive index of the transparent member 122 is substantially equal to n '. The liquid crystal 124 is configured such that a variable voltage is applied to a desired pixel by the individual electrode 125.
The light of No. 6 is transmitted through the color filter 127 to the transparent member 12
3, the liquid crystal 124, and the transparent member 122 are sequentially transmitted.

In the display 121 thus constructed, for example, in a pixel to which no voltage is applied, such as the pixel of A, the liquid crystal 124 has a twisted nematic orientation, and the light of the lamp 125 goes straight. Looks bright.

Further, in a pixel to which a high voltage is applied, such as the B pixel, the liquid crystal 124 is homeotropic, so the light of the lamp 125 is strongly refracted by the transparent member 122 and is dark to the human eye. Can see

When an intermediate voltage is applied like the pixel of C,
Since the light of the lamp 125 is refracted between A and B,
It looks a little bright to human eyes. It is bright because it does not use a polarizing plate like ordinary displays.

FIG. 28 shows a reflector 1 instead of the lamp 125.
It is an example of a reflective display 130 using 31.

In the reflection type display 130, FIG.
As shown in, the incident light is reflected and appears bright in a pixel such as the pixel A to which no voltage is applied. Also, pixel B
Since a voltage is applied to the incident light, the incident light is refracted and is eventually absorbed and scattered to appear dark. Pixel C is in the middle.

In addition to the display in which the refracting power of these lights is variable, in order to realize the brightness of pixels, the diaphragm 91 described above is used.
A type using total reflection as described above and a type using a diffractive optical element like the diaphragm 101 are also conceivable.

In the above display examples, the liquid crystal used is, in addition to the chiral nematic liquid crystal 2, a chiral smectic liquid crystal 31, a chiral cholesteric liquid crystal 41, a discotic liquid crystal 51, or a polymer dispersion in which liquid crystal is dispersed in a polymer. Liquid crystals and polymer liquid crystals can also be used.

The liquid crystal used for the display should satisfy any one of formula (1), formula (26), formula (28), formula (29) and formula (30). In the case of the chiral smectic liquid crystal 31 or the chiral cholesteric liquid crystal 41, the formula (34)
It's even better to meet

In the diaphragm optical element, the prism, and the display device using the liquid crystal described above, when the wavelength of the light used is visible light, the formula (35) or the formula (36) is satisfied, Higher performance can be obtained.

The liquid crystal used in each of the above embodiments is
When a substance that absorbs infrared rays is mixed to give an infrared cut filter effect, the infrared cut filter can be omitted when used in an electronic imaging system that uses visible light, which is advantageous in cost reduction and space reduction. In the case of an imaging system in which the light used is not visible light, if a substance that cuts non-observation light is mixed with the liquid crystal, the filter can be omitted and the same effect can be obtained.

It is ideal that the optical element having the variable characteristic using the liquid crystal in each of the above-mentioned embodiments should satisfy the expression (1). However, when it is used in an actual product, the expression (1) is used. Does not necessarily have to be satisfied, and if you do not require high precision,

It is sufficient if P <λ (45).

If a slightly higher accuracy is desired,

It is even better if P <λ / 2 (46) is satisfied.

For illumination systems, low-cost optical devices, etc.,

Even if P <2λ (47), it may be practical.

When the discotic liquid crystal 51 is used, the formula (45) or the formula (46) or the formula (47) may not be satisfied in some cases.

For all of the above-described embodiments,
As the liquid crystal, in addition to the chiral nematic liquid crystal 2, a chiral smectic liquid crystal 31, a chiral cholesteric liquid crystal 41, a discotic liquid crystal 51, a polymer dispersed liquid crystal in which a liquid crystal is dispersed in a polymer, a polymer liquid crystal, or the like can be used. .

[Additional remarks] (Additional remark 1) A liquid crystal is enclosed in a space formed by a pair of members, and an alignment state of liquid crystal molecules of the liquid crystal is controlled by a physical action from the outside to obtain an optical characteristic of the liquid crystal. In the variable optical-characteristic element for changing the optical characteristic, the liquid crystal has a twist pitch smaller than a wavelength of light passing through the liquid crystal.

(Additional Item 2) The variable optical characteristic optical element according to Additional Item 1, wherein the variable optical characteristic optical element is a variable focus lens that varies the focal length of the liquid crystal.

(Additional Item 3) The variable optical characteristic optical element according to Additional Item 1, wherein the variable optical characteristic optical element is a diaphragm for varying the amount of transmitted light of the liquid crystal.

(Additional Item 4) The variable optical characteristic optical element according to Additional Item 1, wherein the variable optical characteristic optical element is a prism for varying the transmission direction of the transmitted light of the liquid crystal.

(Additional Item 5) One of the pair of members is a diffractive member, and the variable optical-characteristic element changes the focal length of the liquid crystal to change the diffraction efficiency of the diffractive member. 2. The variable optical characteristic optical element according to item 1, which is an element.

(Additional Item 6) A liquid crystal is enclosed in a space formed by a pair of members, and the alignment state of the liquid crystal molecules of the liquid crystal is controlled by a physical action from the outside to change the optical characteristics of the liquid crystal. A display device including an optical property variable optical element, wherein the liquid crystal has a twist pitch smaller than a wavelength of light passing through the liquid crystal.

(Additional Item 7) Formula (28), Formula (29),
7. The variable optical-property element or display device according to any one of appendices 1 to 6, which satisfies at least one of formula (30), formula (45), formula (46), and formula (47). .

(Additional Item 8) As the liquid crystal, any one of a chiral nematic liquid crystal, a chiral cholesteric liquid crystal, a chiral smectic liquid crystal, a polymer liquid crystal, a liquid crystal dispersed in a polymer, and a discotic liquid crystal is used. 7. The variable optical property optical element or display device according to any one of Supplementary Notes 1 to 7.

(Additional Item 9) P.n 'is shorter than the wavelength of the light used, and the liquid crystal is a chiral cholesteric liquid crystal or a chiral smectic liquid crystal. Variable optical element or display device.

(Additional Item 10) Formula (35) or Formula (3)
6) The variable optical characteristic optical element or display device according to any one of appendices 1 to 9 characterized by satisfying 6).

(Additional Item 11) A diffractive optical element including the variable optical-characteristic optical element according to Additional Item 6, which satisfies the expression (37).

(Additional Item 12) Equation (37), Equation (3)
8), the formula (39), and the diffractive optical element including the variable optical-property element according to item 6 satisfying the equation (40).

(Additional Item 13) Formula (41) or Formula (4)
A diaphragm comprising the variable optical-property element according to any one of appendices 3 or 7 to 10 that satisfies 2).

(Additional Item 14) A diaphragm comprising the variable optical-property element according to any one of additional items 6 to 10, which satisfies the expression (37).

(Additional Item 15) Expression (37), Expression (3
8), the formulas (39) and (40) are satisfied.
A diaphragm comprising the variable optical characteristic optical element described in any one of 0.

(Additional Item 16) Formula (43) or Formula (4)
4) A diffractive optical element including the variable optical-property element according to any one of items 6 to 10 which satisfies 4).

(Additional Item 17) Optical Element of Variable Characteristic Made of Discotic Liquid Crystal (Additional Item 18) The physical action from the outside is an electric field,
11. The variable optical-property element or display device according to any one of appendices 1 to 10, which has an action of changing at least one of a magnetic field and a temperature.

(Additional Item 19) Equation (28), Equation (2)
9), formula (30), formula (45), formula (46), formula (4)
An optical element capable of varying the amount of transmitted light that satisfies at least one of 7).

(Additional Item 20) Formula (38) or Formula (3)
Additional item 1 that satisfies at least one of 9) and Expression (40).
9. An optical element according to item 9, wherein the transmitted light amount is variable.

(Additional Item 21) An electronic image pickup device using the optical element according to additional items 1 to 20.

(Additional Item 22) A reflective display device using the optical element according to Additional Items 6 to 10.

[0143]

As described above, according to the optical-property variable optical element of the present invention, the liquid crystal has a twist pitch smaller than the wavelength of light passing through the liquid crystal, so that the structure is simple and the light amount loss is small. There is an effect that the optical characteristics can be changed without causing blurring due to a small amount of light emission, which can be driven by a low voltage.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a basic configuration of a variable focus lens according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a refractive index ellipsoid of molecules of the chiral nematic liquid crystal of FIG.

FIG. 3 is an explanatory diagram illustrating the operation of the variable focus lens of FIG.

FIG. 4 is a configuration diagram showing a specific configuration of the variable focus lens shown in FIG.

5 is a diagram showing a liquid crystal molecular arrangement of a chiral smectic C phase of a chiral smectic liquid crystal used in a first modification of the varifocal lens of FIG.

6 is a configuration diagram showing a configuration of a variable focus lens using the chiral smectic liquid crystal of FIG.

FIG. 7 is an explanatory diagram illustrating an operation of the variable focus lens of FIG.

FIG. 8 is a configuration diagram showing a configuration of a second modification of the varifocal lens of FIG. 1 using a chiral cholesteric liquid crystal.

FIG. 9 is an explanatory view explaining the operation of the variable focus lens of FIG.

FIG. 10 is a diagram showing measured values of reflectance of the chiral cholesteric liquid crystal of FIG.

11 is a configuration diagram showing a configuration of a second modification of the variable focus lens of FIG. 1 using a discotic liquid crystal.

FIG. 12 is an explanatory diagram illustrating the operation of the variable focus lens of FIG. 11.

13 is a diagram showing an index ellipsoid of molecules of the discotic liquid crystal of FIG.

FIG. 14 is a first diagram of the discotic liquid crystal of FIG. 12 when viewed from the Z direction.

FIG. 15 is a second view of the discotic liquid crystal of FIG. 12 seen from the Z direction.

16 is a configuration diagram showing the configuration of a varifocal lens that uses a magnetic field to change the orientation of the chiral nematic liquid crystal of FIG.

FIG. 17 is a configuration diagram showing a configuration of a varifocal lens that uses temperature change to change the orientation of the chiral nematic liquid crystal of FIG. 1.

FIG. 18 is a configuration diagram showing a configuration of a variable focus lens according to a second embodiment of the present invention.

FIG. 19 is a first diagram that includes the variable focus lens according to each embodiment.
Diagram showing the configuration of the device

FIG. 20 is a second view including the variable focus lens according to each embodiment.
Diagram showing the configuration of the device

FIG. 21 is a configuration diagram showing a configuration of a first application example to which the variable focus lens of each embodiment is applied.

FIG. 22 is an explanatory view explaining the operation of the first application example of FIG. 21.

FIG. 23 is a configuration diagram showing a configuration of a second application example to which the variable focus lens of each embodiment is applied.

FIG. 24 is an explanatory view explaining the operation of the second application example of FIG. 23.

FIG. 25 is a configuration diagram showing a configuration of a third application example to which the variable focus lens of each embodiment is applied.

FIG. 26 is an explanatory view explaining the operation of the third application example of FIG. 25.

FIG. 27 is a configuration diagram showing a configuration of a fourth application example to which the variable focus lens of each embodiment is applied.

FIG. 28 is a configuration diagram showing a configuration of a fifth application example to which the variable focus lens of each embodiment is applied.

FIG. 29 is a configuration diagram showing a configuration of a conventional variable focus lens.

FIG. 30 is an explanatory view explaining the operation of the variable focus lens shown in FIG. 29.

[Explanation of symbols]

 1 ... Variable focus lens 2 ... Chiral nematic liquid crystal 3 ... Transparent electrode film 4 ... Flat glass 5 ... Lens 6 ... Alignment film 7 ... Sealing material 8 ... AC power supply 9 ... Switch 21 ... Variable resistance agent Attorney Susumu Ito

Claims (1)

[Claims] 1. A variable optical characteristic for enclosing a liquid crystal in a space formed by a pair of members, controlling an alignment state of liquid crystal molecules of the liquid crystal by an external physical action, and changing an optical characteristic of the liquid crystal. In the optical element, the variable optical characteristic element is characterized in that the liquid crystal has a twist pitch smaller than a wavelength of light transmitted through the liquid crystal.