JPH11352453A - Optical characteristic variable optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a structure simple, light quantity loss small, drive by liquid voltage possible and optical characteristics changeable by applying a spatially nonuniform electric field to specific liquid crystals to form a refractive index distribution and changing this refractive index distribution by changing the electric field. SOLUTION: A variable focus lens is constituted by holding the nematic liquid crystals 1 via alignment layers 6 between substrates 4, 5 respectively deposited with doughnut-shaped electrodes 3 on their inner sides and end-sealing the substrates by sealing members 2. The pitch of the twists of the nematic liquid crystals 1 is made extremely smaller than the wavelength of the light to be used. Namely, the element includes the nematic liquid crystals 1 extremely smaller in the pitch of the twists than the wavelength of the light to be used and forms the refractive index distribution by adding the spatially nonuniform electric field via the doughnut-shaped electrodes 3 to the nematic liquid crystals 1. In addition, the refractive index distribution is changed by changing the electric field by a variable resistor 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element with variable optical characteristics, and more particularly, to an optical element with variable optical characteristics 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 impossible to move the whole or a part of the lens system with an electronic endoscope or a micro-machine eye which is required to be very small. For a camera, a silver halide film camera, and the like, it is desirable that zooming and focusing can be performed without moving the lens system in order to reduce the weight and cost.

Therefore, conventionally, as means for solving these problems without moving the lens, for example, Japanese Unexamined Patent Application Publication No.
In JP-A-34656 and JP-A-4-345124, a variable focus lens has been proposed.

FIG. 31 shows a liquid crystal lens which is an example of this kind of variable focus lens. In the figure, 1 is a seal member 2
It is an obliquely aligned nematic liquid crystal sealed by a liquid crystal and sandwiched between a pair of substrates 4 and 5 provided with a donut-shaped electrode 3. Reference numeral 6 denotes an alignment film provided on the inner surfaces of the transparent substrates 4 and 5, reference numeral 7 denotes a polarizing plate provided on the front side (left side) of the substrate 4 and transmits only light vibrating in the plane of the paper, and reference numeral 8 denotes a switch 9.
And an AC power supply connected to the electrode 3 via the variable resistor 10.

In this liquid crystal lens, when the switch 9 is turned off, the liquid crystal 1 is uniformly and obliquely oriented as shown in FIG. On the other hand, when the switch 9 is turned on and a voltage is applied to the electrode 3, the direction of the electric field E becomes non-uniform as shown in FIG. 25 because the electrode 3 has a donut shape. Orient as shown. That is, since the electric field is weak near the center of the liquid crystal lens, the liquid crystal 1
Maintain the oblique orientation, but the liquid crystal 1 is perpendicular to the substrates 4 and 5 because the electric field becomes stronger as approaching the electrode 3. Therefore, the refractive index of the liquid crystal 1 with respect to the polarized light transmitted through the polarizing plate 7 is higher toward the center of the liquid crystal lens and lower toward the periphery, and has a refractive index distribution in the radial direction (y direction) of the liquid crystal lens. For this reason, the liquid crystal lens becomes an inhomogeneous lens having a convex lens function, and the incident light beam L converges.

[0007]

However, since the conventional liquid crystal lens requires the polarizing plate 7, the amount of transmitted light is less than half, the transmittance is only about 30 to 40%, and the applicable products are limited. There was such a drawback.

The present invention has been made in view of the above circumstances, and provides an optical characteristic variable optical element which has a simple structure, has a small loss of light amount, can be driven by a low voltage, and can change optical characteristics. The purpose is.

[0009]

In order to achieve the above object, an optical characteristic variable optical element according to the present invention includes a liquid crystal having a twist pitch of 60 times or less the wavelength of light used, and the liquid crystal has a spatially improper. The refractive index distribution is formed by applying a uniform electric or magnetic field or temperature, and the refractive index distribution is changed by changing the electric or magnetic field or temperature.

Further, the optical characteristic variable optical element of the present invention comprises a polymer-dispersed liquid crystal, and forms a refractive index distribution by applying a spatially non-uniform electric or magnetic field or temperature to the liquid crystal. The refractive index distribution is changed by changing the electric or magnetic field or the temperature.

Further, the optical characteristic variable optical element of the present invention comprises:
It consists of a combination of two or more liquid crystal lenses, convex and concave.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on illustrated embodiments. FIG. 1 shows a variable focus lens as one embodiment of an optical characteristic variable optical element according to the present invention. In the drawing, substantially the same members as those described in the related art are denoted by the same reference numerals. I have. The varifocal lens has a structure in which a nematic liquid crystal 2 is sandwiched between substrates 4 and 5 each having a donut-shaped electrode 3 coated on the inside thereof, with an alignment film 6 interposed therebetween, and sealed with a seal member 2. And the twist pitch P of the nematic liquid crystal 1
(FIG. 2) is much smaller than the wavelength λ of the used light. That is, P≪λ (1). As described above, when the pitch P is very small as compared with the wavelength λ of the light, the varifocal lens functions as a medium having a refractive index n ′ regardless of the polarization of the incident light.

[0013] _{n '= ne + n 0/} 2 (2) where, ne is the refractive index with respect to the liquid crystal molecular long axis direction of polarized light, n ₀ is the refractive index for polarized light of the liquid crystal molecules minor axis direction. FIG. 3 shows a refractive index ellipsoid corresponding to the liquid crystal molecules on the incident side of the nematic liquid crystal 1. Here, the x axis and the z axis are
The short axis direction and the y axis of the liquid crystal molecules are in the long axis direction of the liquid crystal molecules. It should be noted, and ne> n _0.

Next, the reason why the nematic liquid crystal 1 effectively behaves as an isotropic medium having a refractive index n 'will be described with reference to Jones' vector and matrix.

Katsumi Yoshino and Masanori Okazaki: Basics of Liquid Crystal and Display Applications According to Equations 3.10, 3.110 and 3.126 shown in P85-92 of Corona, the absolute phase change e When xp (−iα) is included, the Jones matrix w _t for the nematic liquid crystal 1 having the thickness d shown in FIG. Given by Where Φ = 2πd / P (4) Γ = 2π (ne−n ₀ ) d / λ (5) α = 2π ｛(ne + n ₀ ) / 2｝ · d / λ (6) X = (Φ ² + Γ ^{2/2) 1/2} (7) It is. Here, ordinary light is defined as polarization in the short axis direction of liquid crystal molecules, and extraordinary light is defined as polarization in the long axis direction of liquid crystal molecules, or polarization in the direction when the long axis is projected on a plane perpendicular to the optical axis. Then, Γ represents the phase difference between the ordinary light and the extraordinary light by the nematic liquid crystal 1.

Φ represents the twist angle of the liquid crystal molecules of the nematic liquid crystal 1 in radians. Also, the coordinate systems of Expressions (3) and (8) are taken as the x, y, and z axes shown in FIG. That is, the x-axis is from the front to the back of the paper, and the y-axis is the direction of the long axis of the liquid crystal molecules on the incident surface of the nematic liquid crystal 1.

Next, under the condition of equation (1), equation (3)
_Let 's look at what Wt of the _graph looks like. First, equation (1) can be modified as follows: 0 <P / λ≪1 (9) Therefore, when P / λ → 0, W in Expression (3)
_Let us find the limit value W _t L of _t . Since Γ / Φ = (ne−n ₀ ) P / λ (10), when P / λ≪1, then | Γ / Φ | ≪1 (11), and when P / λ → 0, | → / Φ | → 0.

Under the condition of equation (11) When P / λ → 0, X → Φ (16) cosX → cosΦ (17) Therefore, when P / λ → 0, Becomes This refractive index _{n '= (ne + n o} ) / 2, the thickness d, none other than isotropic medium Jones matrix along the optical axis. Therefore, since P / λ≪1, the varifocal lens of FIG. 1 functions as a medium having a refractive index of n ′.

When the switch 9 is turned on as shown in FIG. 4, an electric field as shown in FIG.
The orientation of the liquid crystal 1 changes as shown in FIG. In other words, near the optical axis of the liquid crystal lens, the orientation remains almost helical,
As the distance from the optical axis increases, the direction of the liquid crystal molecules gradually approaches perpendicular to the substrates 4 and 5, and becomes almost perpendicular to the substrates 4 and 5 in the portion sandwiched between the electrodes 3. FIG. 2 shows the orientation of the liquid crystal 1 at a position slightly away from the optical axis. Since the liquid crystal molecules are oriented in this way, the refractive index is n ′ near the optical axis and n ₀ near the periphery,
Acts as a heterogeneous lens. Equations (3) to (2)
The concept of 0) is applied to a minute portion of the liquid crystal 1. Therefore, a bright variable focus lens without a polarizing plate can be obtained.

Next, a specific configuration example of the above variable focus lens will be described. As shown in FIG. 1, the variable focus lens has a structure in which the voltage is continuously varied by a variable resistor 10, and the arrangement of the liquid crystal molecules is changed as shown in FIGS.
So that it can be brought in the middle of Thereby, a liquid crystal lens whose focal length changes continuously can be realized.

In the case of an intermediate arrangement as shown in FIG.
, The values of ne and n ₀With an intermediate value
By replacing the extraordinary light with the refractive index ne ',
Equations (3) to (20) are satisfied.

Incidentally, by configuring as shown in FIG. 1,
The method of applying the voltage is not limited to continuously variable, and a variable focus lens can be realized by selecting an applied voltage from several discrete voltage values.

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

Equation (20) shows the limit case of P / λ → 0. However, the limit value may not always be applied to an actual liquid crystal lens or varifocal lens. Let's derive an approximate expression.

Equation (3) can be approximated by considering the first order of P / λ as follows. That is, Expressions (12) to (1)
4), to the first order of P / λ, that is, from equation (10), Γ /
If the first order of Φ is left and the second order of P / λ and the second order of Γ / Φ are omitted, Get. Therefore, in order for the value of W _t N to be considered substantially equal to the Jones matrix of the isotropic medium, | i · Γ / 2Φ |
Should be close to zero. At this time, Wt N is This equation shows that the polarization direction of the liquid crystal 1 is Γ
Although it rotates by / 4 · Γ / Φ, it means that it can be regarded as an isotropic medium.

[0026] Then, a variable focus lens without blur can be obtained. From equation (10) Becomes

When the varifocal lens of the present invention is used for an actual imaging device with a lens, for example, a lens of a relatively low-cost product such as an electronic camera, a VTR camera, and an electronic endoscope, a high resolution is not required. In some cases, the condition of Equation (26) can be relaxed, and | Γ / 2Φ | <1 (28).

Since high resolution is required for a lens of an electronic imaging device having a large number of pixels, a lens of a high image quality product such as a film camera, a microscope, etc., | Γ / 2Φ | <π / 6 (29) I just need.

In the case of a lens not used for image formation, such as a lens of an optical disc, or an electronic image pickup device having a small number of pixels, the condition is further relaxed, and it is sufficient if | Γ / 2Φ | <π (30).

As can be said in common with the present embodiment, when the liquid crystal 1 has a helical arrangement, when the major axis direction of the liquid crystal molecules is not perpendicular to the optical axis, that is, when the liquid crystal molecules are oblique, ,
Ne in Expressions (1) and (26) to (30) is replaced by ne described above.
'.

Hereinafter, some design examples will be described. When the thickness d of the nematic liquid crystal 1 is small, the power of the lens is so weak that it is useless. When the thickness d is large, light is scattered and causes flare. Therefore, the thickness d is suitably about 2 μ <d <300 μ (31). As an example of the wavelength λ of light, considering visible light, 0.35μ <λ <0.7μ (32)

The value of ne−n ₀ is determined by the physical properties of the liquid crystal, but there are many substances of about 0.01 <| ne−n ₀ | <0.4 (33). Therefore, as a first design example, if d = 15 μ λ = 0.5 μ ne −n ₀ = 0.2 P = 0.05 μ φ = 60 μ (effective diameter of the varifocal lens), then Γ / 2Φ = 1 /0.2*0.2/0.05.
5 = 0.01, and the equations (26), (28), and (2)
9), Formula (30) is satisfied.

As a second design example, if d = 30 μ λ = 0.6 μ ne −n ₀ = 0.25 P = 0.3 μ φ = 180 μ, then Γ / 2Φ = 1/2 · 0.3 × 0.25 / 0.
6 = 0.0625, which satisfies Expression (26), Expression (28), Expression (29), and Expression (30).

As a third design example, if d = 50 μ λ = 0.55 μ ne −n ₀ = 0.2 P = 5 μ φ = 150 μ, then Γ / 2Φ = 1/2 · 0.2 × 5.0 / 0.5
5 = 0.909, which satisfies Expression (28) and Expression (30).

Further, as a fourth design example, consider a variable focus lens for near-infrared light, and if d = 200 μλ = 0.95 μne−n ₀ = 0.2 P = 4 μφ = 2000 μ Γ / 2Φ = 1/2 · 0.2 × 4 / 0.95 =
0.42, which is given by Expression (26), Expression (28), and Expression (2
9), Formula (30) is satisfied.

In each of the above design examples, a nematic liquid crystal has been described as an example. However, in order to make the spiral pitch of the nematic liquid crystal smaller than the wavelength of light to be used, a chiral agent may be mixed with the liquid crystal.

As the chiral agent, a cholesteric liquid crystal or a synthetic optically active compound is used. The following chemical formulas (1) and (2) show examples of nematic liquid crystals, and chemical formulas (3) and (4) show examples of chiral agents.

[0038]

In the above description, a nematic liquid crystal is used as the liquid crystal 1 used for the variable focus lens. However, the present embodiment is not limited to this, and a first modification of the variable focus lens is shown in FIG. It can be configured using a smectic liquid crystal as shown in FIG. FIG. 7 shows the arrangement of the liquid crystal molecules in the smectic C phase. FIG. 8 shows the structure of a variable focus lens using the arrangement.

When a voltage is applied to this, the liquid crystal molecules in each layer sandwiched between the pair of electrodes 3 change the z axis of the coordinate system as shown in FIG.
Aligned in the axial direction, the refractive index of the smectic liquid crystal 11 is
The refractive index n ′ on the optical axis in the state of FIG. 8 decreases to the refractive index n ₀ in the peripheral portion, and the focal length of the varifocal lens changes.

Equations (1) to (30) also apply to the first modification shown in FIGS. 7 and 8, and in particular, equations (26), (28), (29), and (30). If the condition (1) is satisfied, a variable focus lens with less blur can be obtained. FIG.
In the configuration described above, the voltage applied to the smectic liquid crystal 11 can be changed continuously, and the focal length also changes continuously. Further, by changing the sizes of the central holes of the pair of electrodes 3 as shown in FIG. 8, the change in the refractive index of the smectic liquid crystal 11 can be changed so that the aberration is reduced. This can be applied to the variable focus lens shown in FIGS.

Here, a design example of a variable focus lens using the smectic liquid crystal 11 will be described. As parameters, d = 25 μ λ = 0.55 μ ne −n ₀ = 0.3 P = 1.0 μ φ ₁ = 50 μ Assuming that φ ₂ = 70μ, Γ / 2Φ = 1/2 · 0.3 × 1.0 / 0.5
5 = 0.2725, which satisfies Expression (26), Expression (28), Expression (29), and Expression (30).

The chemical formula (5) shows that "4- (n-hexyloxy) phenyloxy-4"-(2-meterbutyl) biphenyl-4'-carboxylate, which is an example of the molecular structure of the smectic liquid crystal 11, is shown in FIG. showed that. In addition,
The pitch P is approximately 0.2 μ. As a second modification of the variable focus lens, a variable focus lens using the cholesteric liquid crystal 12 can be configured as shown in FIG.

In the cholesteric liquid crystal 12, the orientation direction of the liquid crystal molecules in each layer is parallel to the lens surface and the azimuth angle is P
Then, it changes by drawing a spiral in the z-axis direction. In this state, equations (1) to (30) apply. When a voltage is applied, the helix disappears as the orientation of the liquid crystal molecules moves toward the periphery, as shown in FIG. 9, and a convex lens action occurs. Further, in this modification, the inner surface of the substrate 5 has a convex lens shape, and is a varifocal lens having a lens effect due to the shape of the cholesteric liquid crystal 12. The shape of the inner surface of the substrate 5 may be a Fresnel lens shape.

The cholesteric liquid crystal 12 has the property of selective reflection, and totally reflects right or left circularly polarized light near the wavelength λs = P · n ′. FIG. 10 shows an example of the measured value of the reflectance of the cholesteric liquid crystal with respect to the naturally polarized light.

Therefore, it is desirable that the wavelength λs is outside the wavelength range of the light used in the variable focus lens. In other words, it is necessary that P · n ′ be outside the wavelength range of light using the variable focus lens in order to obtain a liquid crystal lens with better transmittance and no coloring. In the case of visible light, it is necessary that P · n ′ <0.4μ (34).

Note that selective reflection may occur even in the smectic C-phase liquid crystal shown in FIG. 7 which is the first modification described above, and for the above-mentioned reason, the expression (34) also applies to the example shown in FIG. Applied.

As a design example of a variable focus lens using the cholesteric liquid crystal 12, assuming that d = 15 μ ne −n ₀ = 0.4 λ = 0.45 μ P = 0.01 μ n ′ = 1.7 φ = 300 μ Γ / 2Φ = 1/2 · 0.4 × 0.01 / 0.
45 = 0.00445, and the expressions (26) and (2)
8), Equations (29) and (30) are satisfied, and P · n ′ =
Since the value is 0.017 μ, Expression (34) is also satisfied.

Chemical formula (6) is an example of cholesteric liquid crystal 12, and is a chemical formula of cholesterol benzoate. As a third modification of the variable focus lens, a discotic liquid crystal may be used instead of the cholesteric liquid crystal 12.

As can be said in common with the varifocal lens described in the present embodiment and each of the modifications and other embodiments described later, the pitch P of the spiral is determined by the wavelength λ of the light used.
It is more desirable to obtain a varifocal lens with less blur, or smaller than about 20 times the wavelength, for example, in the case of visible light, 0.4
For an optical device used with μ <λ <0.7μ, a desirable condition is 0.001μ <P <14μ (35). In order to further reduce blur, it is desired that 0.001 μ <P ≦ 5 μ (36). The lower limit of P is determined by the size of the liquid crystal molecules themselves.

In the present embodiment and each modification,
Electric fields have been used to change the orientation of each liquid crystal,
However, as shown in FIG. 11, a magnetic field H is applied to, for example, the cholesteric liquid crystal 12 using the coil 13 and the iron core 14 to change the direction of the liquid crystal due to the spatial nonuniformity of the magnetic field, thereby changing the refractive index. May be caused. Although FIG. 11 shows an example of the variable focus lens made of the cholesteric liquid crystal 12, the present invention may be applied to a variable focus lens made of the nematic liquid crystal 1 or the smectic liquid crystal 11.

In order to change the orientation of each liquid crystal, FIG.
As shown in FIG. 2, the orientation of, for example, the cholesteric liquid crystal 12 may be changed by a change in temperature using the heater 15, and the above-mentioned other liquid crystal, the nematic liquid crystal 1, or the variable focus lens such as the smectic liquid crystal 11 may be used. Also applicable to In this configuration, by changing the temperature, a phase transition occurs in the liquid crystal, and the focal length of the lens is changed. The substrates 4 and 5 may have a Fresnel lens shape.

In the above example, the pitch P of the liquid crystal is preferably smaller than the wavelength λ, but may be actually 10 to 50 times larger than the wavelength. Now, this is expressed by equations (10) and (3)
Consider using 0). That, | Γ / 2Φ | <π | 1/2 (ne -n 0) P / λ | <π where lambda = 0.5 [mu], when the _{ne -n 0 = 0.2, P <} 10πλ = 31. 4λ (37) is obtained. Equations (28), (29), (30) and the like are for the liquid crystal near the optical axis in FIG. 4, but the liquid crystal far from the optical axis in FIG. a value of ne -n ₀ is smaller than near the optical axis. Therefore, the expression (37) can be further relaxed for the whole liquid crystal lens, and P <60λ (38) may be satisfied.

For a slightly more accurate optical system, P <20λ (39) may be used in the same manner as in equation (28).

When the value of P differs depending on the location of the liquid crystal, the average value of P is taken.

FIG. 13 shows a third modification of the variable focus lens according to the present invention, in which a polymer dispersed liquid crystal layer 16 is used. That is, in this variable focus lens, the polymer dispersed liquid crystal layer 16 is disposed between the pair of substrates 4 and 5, and when the switch 9 is turned on, an electric field is applied to the polymer dispersed liquid crystal layer 16 via the electrode 3. Has been added.
As clearly shown in FIG. 14, the polymer dispersed liquid crystal layer 16 is composed of a large number of minute polymer cells 16b each having an arbitrary shape such as a sphere or a polyhedron containing liquid crystal molecules 16a.

Here, the size of the polymer cell 16b is, for example, 2 nm ≦ D ≦ λ / 5 (40) when the average diameter is D and the wavelength of light to be used is λ in the case of a spherical shape. . That is, since the size of the liquid crystal molecules 16a is about 2 nm or more, the lower limit of the diameter D is set to 2 nm or more. The upper limit of the diameter D also depends on the thickness t of the polymer-dispersed liquid crystal layer 16 in the optical axis direction of the varifocal lens, but if it is larger than the wavelength λ, the refractive index of the polymer and the liquid crystal molecules 16a Due to the difference from the refractive index of the polymer cell 16b, light is scattered at the boundary surface of the polymer cell 16b and the polymer dispersed liquid crystal layer 16 becomes opaque. The following is assumed. The transparency of the polymer-dispersed liquid crystal layer 16 becomes worse as the thickness t is larger.

As the liquid crystal molecules 16a, for example,
Uniaxial nematic liquid crystal molecules are used. Refractive index ellipsoid of the liquid crystal molecules 16a becomes a shape as shown in FIG. 15, a _{n ox = n oy = n 0} (41). However, n ₀ is the refractive index of an ordinary ray, n _ox and n _oy are refractive indices in directions perpendicular to each other in a plane including an ordinary ray.

Here, as shown in FIG.
Is off, that is, when no electric field is applied to the polymer-dispersed liquid crystal layer 16, the varifocal lens is equivalent to a parallel plane plate and does not function as a lens because the liquid crystal molecules 16a are oriented in various directions. When the focal length of the variable focus lens at this time is f _1, a f ₁ = ∞. In contrast, FIG.
When the switch 9 is turned on as shown in FIG.
Of the liquid crystal molecules 16a in the portion between the substrates 4,
5 and perpendicular to the optical axis, it becomes oblique to the substrates 4 and 5, and the direction becomes random near the optical axis. Accordingly, the arrangement near the optical axis is almost the same as that in FIG. Therefore, the refractive index of the polymer-dispersed liquid crystal layer 16 is high near the optical axis and decreases as the distance from the optical axis increases. As a result, the varifocal lens acts as a heterogeneous lens having a convex lens effect.

When the proportion of the polymer is increased, the polymer-dispersed liquid crystal layer 16 becomes closer to a solid. In this case, at least one of the substrates 4 and 5 may not be provided. This can also be applied to a liquid crystal variable focus lens shown in FIGS.

The voltage applied to the polymer-dispersed liquid crystal layer 16 can be changed stepwise or continuously by the variable resistor 10 as shown in FIG. In this way, as the applied voltage increases, the liquid crystal molecules 16a
Is oriented so that its major axis is gradually parallel to the optical axis of the varifocal lens, so that the refractive power can be changed stepwise or continuously.

Here, in the state shown in FIG. 13, that is, in a state where no electric field is applied to the polymer dispersed liquid crystal layer 16, the liquid crystal molecules 1
The average refractive index n _LC 'of 6a is approximately (n _ox + n _oy + nz) / 3≡n _LC ' (42), where nz is the refractive index in the major axis direction of the refractive index ellipsoid as shown in FIG. Become. The average refractive index n _LC when the above equation (41) is satisfied is given by (2n ₀ + ne) / 3≡n _LC (43), where nz is the refractive index of the extraordinary ray ne. At this time, the refractive index n _A of the polymer-dispersed liquid crystal layer 16 is defined as the ratio of the volume of the liquid crystal molecules 16a to the volume of the polymer-dispersed liquid crystal layer 16, where n _P is the refractive index of the polymer constituting the polymer cell 16b. Let ff be ff, and according to Maxwell Garnet's law, n _A = ff · n _LC ′ + (1−ff) n _P (44)

If the average refractive index of the ordinary ray is (n _ox + n _oy ) / 2 = n ₀ ′ (45), the state shown in FIG.
The refractive index n _B of the polymer-dispersed liquid crystal layer 16 between the electrodes 3 when an electric field is applied to 6 is given by n _B = ff · n ₀ ′ + (1-ff) n _P (46). Further, with respect to the distance y from the refractive index the optical axis of the liquid crystal layer 16 in the state shown in FIG. 16, assuming that the changes in the square, the focal length f ₂ of the variable focus lens I will ask. If the refractive index n (y) at y of the polymer-dispersed liquid crystal layer 16 is expressed as n (y) = n ₀ + n ₀₂ y ² (47), f ₂ ⁻¹ ≒ −2n ₀₂ t (48) Is represented. n (y) −n ₀ = n ₀₂ y ² (49), and at the periphery of the lens, n (y) = n _B and n ₀
= N _A , then n _B −n _A = n ₀₂ y ² (50) f ₂ = −y ² / {2 (n _B −n _A ) t} (51) Here, t is the thickness of the polymer dispersed liquid crystal layer 16.

From the above formula (51), the polymer dispersed liquid crystal layer 1
To increase the change in focal length due to | n _B −n _A
| May be increased. Here, since it is _{n B -n A = ff (n} 0 '-n LC') (52), | n 0 '-n LC' | if the large, it is possible to increase the change rate. Practically, n _B is
Since it is about 1.3 to 2, if 0.01 ≦ | n ₀ ′ −n _LC ′ | ≦ 10 (53), when ff = 0.5, the polymer dispersed liquid crystal layer 16
Can be changed by 0.5% or more, so that an effective variable focus lens can be obtained. Note that | n ₀ ′ −n _LC ′ |
Cannot be exceeded.

Next, the grounds for the upper limit of the above equation (40) will be described. `` Solar Energy Materials and Solar C
ells, Vol. 31, Wilson and Bck, 1993.Elesvier Science
Publishers B. v., Pages 197-214, `` Transmiss
ion variation using scattering / transparent switchi
“ng films” shows the change in transmittance τ when the size of the polymer-dispersed liquid crystal is changed. FIG. 6 on page 206 of this document shows that the radius of the polymer-dispersed liquid crystal is r, t = 300 μm, ff = 0.5, and n _P = 1.4.
5, when n _LC = 1.585 and λ = 500 nm, the transmittance τ is a theoretical value, r = 5 nm (D = λ / 50, D ·
When t = λ · 6 μm (where D and λ are nm and the same applies hereinafter), τ ≒ 90%, and r = 25 nm (D
= Λ / 10), it is shown that τ ≒ 50%.

Here, for example, assuming that t = 150 μm,
Assuming that the transmittance τ varies as an exponential function of t, t = 1
When estimating the transmittance τ in the case of 50 μm, r = 25
τ when nm (D = λ / 10, D · t = λ · 15 μm)
≒ 71%. Similarly, when t = 75 μm, r = 25 nm (D = λ / 10, D · t = λ · 7.5)
μm), τ ≒ 80%.

From these results, if D · t ≦ λ · 15 μm (54), τ is 70% to 80% or more, which makes the lens sufficiently practical. Therefore, for example, when τ = 75 μm, a sufficient transmittance can be obtained when D ≦ λ / 5.

The transmittance of the polymer-dispersed liquid crystal layer 16 is
The better the value of n _P is closer to the value of n _LC ′, the better. on the other hand,
When n ₀ ′ and n _P have different values, the transmittance of the polymer-dispersed liquid crystal layer 16 deteriorates. In the state shown in FIG. 13 and the state shown in FIG. 16, the average transmittance of the polymer-dispersed liquid crystal layer 16 is improved almost as follows: n _P = (n ₀ ′ + n _LC ′) / 2 (55) It is time.

Since this variable focus lens is used as a lens, even in the state shown in FIG.
Even in the state of No. 6, it is better that the transmittances are almost the same and higher. For this purpose, there are restrictions on the material of the polymer constituting the polymer cell 16b and the material of the liquid crystal molecules 16a, but practically, it is sufficient to satisfy n ₀ ′ ≦ n _P ≦ n _LC ′ (56).

If the above expression (55) is approximately satisfied, the above expression (54) is further relaxed, and D.t ≦ λ · 60 μm (57) is sufficient. Because, according to Fresnel's law of reflection, the reflectance is proportional to the square of the difference in refractive index, so that light is reflected at the boundary between the polymer constituting the polymer cell 16b and the liquid crystal molecule 16a, that is, the polymer dispersion. This is because the decrease in the transmittance of the liquid crystal layer 16 is approximately proportional to the square of the difference in the refractive index between the polymer and the liquid crystal molecules 16a. Assuming that t = 75 μm in the above equation (57), D ≦ 0.8λ is satisfied, and approximately D ≦ λ is sufficient.

The above is n₀'≒ 1.45, n_LC'≒ 1.
Although it was the case of 585, if more generally formulated, D · t ≦ λ · 15 μm · (1.585-1.45)^Two/ (N_u-N_P)^Two (58) However, (n_u-N_P)^TwoIs (n_LC'-
n_P)^TwoAnd (n₀'-N _P)^TwoThe larger of
You.

In order to increase the change in the focal length of the variable focus lens, the larger the value of ff, the better.
At -1, the volume of the polymer becomes zero and the polymer cell 16
Since b cannot be formed, 0.1 ≦ ff ≦ 0.999 (59). On the other hand, since τ increases as ff decreases, the above equation (58) can be relaxed in some cases. Preferably, 4 × 10 ⁻⁶ [μm] ² ≦ D · t ≦ λ · 45 μm · (1.585-1.45) and _{^{2 / (n u -n P)}} 2 (60). Note that the lower limit of t is t = D, as is clear from FIG. 13, and D is 2 nm or more as described above. Therefore, the lower limit of D · t is (2 × 10 ⁻³ μm). ² , that is, 4 × 10 ⁻⁶ [μm] ² .

The above is the case where a very good value is required for the light scattering and transmittance by the variable focus lens. But,
In a low-cost optical system, an illumination system of an imaging device, a signal processing system, or the like, it may not be necessary to improve light scattering and transmittance so much, and the above equation (60) can be further relaxed as follows. . 4 × 10 ^-6 [μm] ² ≦ D ・ t ≦ λ ・ 450 μm ・ (1.585-1.45) ² / (n _u −n _P ) ² (61)

It should be noted that the approximation of expressing the optical properties of a substance by a refractive index is established as described in “Iwanami Science Library 8: Asteroid Comes”, Tadashi Mukai, 1994, page 58, published by Iwanami Shoten. , D is 10 nm to 5 nm
This is the case. When D exceeds 500λ, the light scattering becomes geometrical, and the light scattering at the interface between the polymer constituting the polymer cell 16b and the liquid crystal molecules 16a increases according to the Fresnel reflection formula. Is practically 7 nm ≦ D ≦ 500λ (62).

In the configuration shown in FIG. 13, the above _nox , _ox ,
_{n oy, n 0, nz,} ne, n P, ff, D, t, λ, n
_LC ′, n _LC , n _A , n _B , f ₁ , f ₂ and the effective diameter φ of the varifocal lens are specifically set to the following values. _{n ox = n oy = n 0} = 1.5 nz = ne = 1.75 n P = 1.54 ff = 0.5 D = 50nm t = 125μm λ = 500nm n LC '= n LC = 1.5833 n _{A = 1.5617 n B = 1.52 f} 1 = ∞ f 2 = 599.5mm φ = 5mm

[0076] In this case, the right-hand side of (60) equation, λ · 45μm · (1.585 -1.45 ) 2 / (n u -n P) 2 = 50
0 nm ・ 45μm ・ (0.135) ² /(0.0433) ² ≒ 218712nm ・ μ
m. In addition, D · t is as follows: D · t = 50 nm · 125 μm = 6250 nm · μm, and certainly satisfies the above equation (60).

Further, in the above specific example, the surfaces of the substrates 4 and 5 may be curved like a normal lens.

FIG. 17 shows a configuration of an image pickup optical system for a digital camera using the variable focus lens shown in FIG. In this imaging optical system, an object (not shown)
Is formed on a solid-state imaging device 18 composed of, for example, a CCD via the variable focus lens VFL and the lens 17. In FIG. 17, illustration of the liquid crystal molecules 16a is omitted. The diaphragm of the optical system also serves as the electrode 3, and the substrates 4 and 5 have curved surfaces.

According to the imaging optical system, the variable resistor 1
0, the polymer dispersed liquid crystal layer 16 of the varifocal lens VFL
The varifocal lens VFL is adjusted by adjusting the AC voltage applied to
Variable focal lens VFL by changing the focal length of
And without moving the lens 17 in the optical axis direction, for example, for an object distance from infinity to 600 mm,
It is possible to focus continuously.

FIG. 18 shows a fourth modification of the varifocal lens using the ferroelectric liquid crystal 19. In the figure, reference numeral 20 denotes a transparent electrode. Since at least one of the substrates 4 and 5 has a curved surface, it has a lens function even when the applied electric field is uniform. The lens action can be changed by the variable resistor 10. Note that antiferroelectric liquid crystal may be used instead of the ferroelectric liquid crystal 19. In any case, the response time is shorter than that in the case of using a nematic liquid crystal, which is advantageous. In the case of a polymer dispersed liquid crystal lens using either a ferroelectric liquid crystal or an anti-ferroelectric liquid crystal, the above equations (40) to (46) and the above equations (52) to (62)
Is applied.

As can be said in common to all the liquid crystal lenses of the present invention, the Abbe number of the liquid crystal (usually represented as ν _d ) is small, and is often about 40 to 10. Therefore, since the liquid crystal lens generates strong chromatic aberration, at least one of the substrates 4 and 5 is preferably formed in a lens shape and the material thereof is preferably 50 or less in order to correct this. For example, heavy flint glass corresponds to this. If the liquid crystal lens has a convex action, it is preferable that at least one of the substrates is a concave lens, and if the liquid crystal lens has a concave action, at least one of the substrates is a convex lens.

FIG. 19 shows another embodiment of the optical characteristic variable optical element, which is an example of a variable deflection prism. In this embodiment, the polymer-dispersed liquid crystal layer 16 is sandwiched between the two substrates 4 and 5, so that the deflection of light can be changed by changing the voltage. In this case, it is preferable to use a glass material having an Acbe number of 50 or less also for the substrate 4. The liquid crystal 21 used here may be a nematic liquid crystal, a ferroelectric liquid crystal, an antiferroelectric liquid crystal, or the like.

FIG. 20 shows still another embodiment of the present invention, in which two liquid crystal variable focus lenses VFL ₁ and VFL ₂ are used in combination. One of the liquid crystal variable focus lenses VFL ₁ is composed of a polymer dispersed liquid crystal layer 16 sandwiched between substrates 4 and 5 having a donut-shaped electrode 3 and a donut-shaped transparent electrode 20. By adjusting and appropriately selecting the voltage applied between each electrode,
The aberration can be controlled by changing the distribution shape of the refractive index, and acts as a convex varifocal lens. The VFL ₂ of the liquid crystal variable focus lens is composed of the substrates 4 and 5 on which the transparent electrode 20 is formed on the nematic liquid crystal 1 via the alignment film 6, and functions as a concave variable focus lens. As described above, when the two liquid crystal variable focus lenses VFL ₁ and VFL ₂ are used, the liquid crystal is used for both, so that the Abbé number is small and the chromatic aberration can be easily corrected. If one is a convex lens, the other is a concave lens, which is necessary for correcting chromatic aberration.

FIG. 21 is a characteristic diagram showing a change in the Abbe number ν _d with a change in the refractive index n _d of the liquid crystal. Here, n _d -v _d characteristic curves of two kinds of liquid crystals are shown. In general, the Abbe number tends to decrease as the refractive index increases. Therefore, the liquid crystal variable focus lenses VFL ₁ , VFL
When the refractive index of the lens system including FL ₂ is changed, in order to reduce the fluctuation of the chromatic aberration, the liquid crystal variable focus lens VFL is required.
_1, when one of the Abbe's number [nu _d of VFL ₂ is large state, it is preferable to use the other Abbe's number [nu _d is also large. Conversely, when one of the Abbe numbers ν _d is in a small state, it is preferable to use the other Abbe number ν _{d in a} small state. Then, in order to act the lens system as a small convex lens chromatic aberration, a large Abbe's number [nu _d of the liquid crystal towards constituting a convex lens, a good pick small Abbe's number [nu _d of the liquid crystal towards constituting a concave lens. Referring to FIG. 21, a liquid crystal having characteristics as shown in the graph on the left is provided to the convex lens.
It is preferable to use a liquid crystal having characteristics as shown in the graph on the right for the concave lens. E7 and MBBA in FIG. 21 are the names of the liquid crystal. The graphs of the liquid crystal used for the convex lens and the concave lens may intersect at a position where the refractive index n _d of the liquid crystal is small. In short, the graph of the liquid crystal of the concave lens is closer to the right than the graph of the liquid crystal of the convex lens in a certain refractive index range. Good. Further, in order to remove chromatic aberration, it is desirable that the Abbe number ν _{d of the} liquid crystal does not exceed 50. Referring to FIG. 20, the focal length of VFL ₁ is f ₁ , V
Assuming that the focal length of FL ₂ is f ₂ , it is preferable to satisfy the following condition 1/2 <| f ₁ / f ₂ | <2 (63) in order to remove chromatic aberration. 20, when | f ₁ / f ₂ | exceeds the upper limit of the equation (63), chromatic aberration becomes overcorrected, and | f ₁ / f ₂ | If not, the chromatic aberration will be insufficiently corrected.

Further, as can be said for the liquid crystal optical element with variable optical characteristics of the present invention, if a tolan liquid crystal is used as the liquid crystal, the change in refractive index is large and the viscosity is small, so that the response time is short and advantageous. It is. FIG. 22 shows 4-alkylcyclohexyl-4'-alkyltolan as an example of the tolan-based liquid crystal. Here, R represents an alkyl group,
R 'represents an alkyne group. Further, in order to shorten the response time of the liquid crystal, it is preferable to always apply a low voltage to the liquid crystal. The voltage may be equal to or lower than the phase transition voltage at which the refractive index of the liquid crystal changes.

As can be said with respect to the optical characteristic variable optical element of the present invention in general, substances having an electro-optic effect, a magneto-optic effect, and a thermo-optic effect (the refractive index changes with temperature) instead of the liquid crystal, and It goes without saying that a ferroelectric material or the like may be used. Barium titanate (BaTiO ₃ ) is an example of a substance having an electro-optical effect, lead glass is an example of a substance having a magneto-optical effect, and water is a ferroelectric substance if quartz is a substance having a thermo-optical effect. Examples include barium titanate and Rochelle salt.

FIG. 23 shows an application example of the liquid crystal variable focus lens VFL, and shows an image pickup apparatus for a digital camera using free-form surface optical elements 22 and 23. The free-form surface optical elements 22 and 23 realize an image forming function by reflection and refraction of the decentered aspherical surface, and are made of plastic, glass, or the like. Is performed, there is a disadvantage that a mechanical structure for changing the distance from the solid-state imaging device 18 becomes complicated. Therefore, in this example, the liquid crystal variable focus lens V is located at a position near the stop between the two free-form surface optical elements 22 and 23.
Focusing is realized by disposing the FL and changing its refractive power. In this case, focusing can be performed without mechanically moving the free-form surface optical elements 22 and 23, so that the structure is simple and advantageous. Further, according to this configuration, one of the substrates of the liquid crystal variable focus lens VFL is replaced by the outer surface of the free-form surface optical element 22, so that
This is advantageous because the cost can be reduced.

The optical system of the present imaging apparatus can be used for a film camera or the like if the solid-state imaging device 18 is replaced with a film. Further, the free-form surface optical element and the optical characteristic variable optical element according to the present invention may be combined to form an imaging device or an optical device with a zoom lens. Also, instead of a free-form surface optical element, an uneven lens (usually GRIN
A variable focal length imaging device or optical device may be obtained by combining a diffractive optical element or an aspheric lens with the optical characteristic variable optical element according to the present invention. In this case, examples of the optical device include a pickup for an optical disk, a microscope, and the like.

If the optical characteristic variable optical element according to the present invention is configured as, for example, a variable focus lens,
The present invention can be used for a V camera, an autofocus device for an electronic endoscope, a zoom lens, and the like. Further, the present invention can also be used for a diopter adjusting device or a magnification changing device of optical equipment such as binoculars, a viewfinder of a camera, and an eyepiece of a microscope. Furthermore, it can also be used for variable focus glasses.

The following is an example of this embodiment. FIG.
26 to 26 are conceptual diagrams showing a configuration in which the optical characteristic variable optical element according to the present invention is incorporated in an objective optical system of a finder section of an electronic camera. 24 is a front perspective view showing the appearance of the electronic camera 24, FIG. 25 is a rear perspective view of the same, and FIG. 26 is a sectional view showing the internal configuration of the electronic camera 24. Electronic camera 24
In the case of this example, includes a photographic optical system 26 having a photographic optical path 25, a finder optical system 28 having a finder optical path 27, a release 29, a flash 30, a liquid crystal display monitor 31, and the like, and is disposed above the camera 24. When the release 29 is pressed, the photographing is performed through the photographing objective optical system 32 in conjunction therewith. Objective optical system for photography 3
2 is passed through a filter 33 such as a low-pass filter or an infrared cut filter.
Is formed on the imaging surface 18a. The object image received by the CCD 18 is displayed as an electronic image on the liquid crystal display monitor 31 provided on the back of the camera via the processing means 34. Also, a memory or the like is arranged in the processing means 34,
A captured electronic image can also be recorded. This memory may be provided separately from the processing means 34, or may be configured to record and write electronically using a floppy disk or the like. Further, instead of the CCD 18, a silver halide camera in which a silver halide film is disposed may be configured.

Further, on the finder optical path 27,
Objective optical system for viewfinder 35
It is arranged as. In addition, a cover lens 36 having a positive power is disposed as a cover member, and the angle of view is enlarged. The cover lens 36 and the optical characteristic variable optical element VFL on the object side of the imaging optical system aperture 37 are used to move the front group of the finder objective optical system 35 to the optical characteristics of the imaging optical system on the image side of the aperture 37. The rear group of the finder objective optical system 35 is constituted by the variable optical element VFL. Aperture 3
Each of the front group and the rear group sandwiching No. 7 has an optical characteristic variable optical element V
Zooming and focusing are performed by arranging the FL and controlling the voltage applied to the liquid crystal and the like. This control is performed by the processing means in conjunction with the zooming and focusing actions of the photographing objective optical system 32. An object image formed by the finder objective optical system 35 is formed by a field frame 39 of a Porro prism 38 which is an image erecting member.
Formed on top. In addition, the field frame 39 is the Porro prism 3
The first reflection surface 38a and the second reflection surface 38b are separated from each other and are disposed therebetween. Behind the porro prism 38, an eyepiece optical system 40 for guiding the erect image to the observer's eyeball is disposed. In the camera 24 thus configured, the finder objective optical system 35 can be configured with a small number of optical members, and high performance and miniaturization can be realized.

FIG. 27 is a conceptual diagram showing a configuration in which the optical characteristic variable optical element VFL of the present invention is incorporated in the photographing objective optical system 32 of the electronic camera 24. In the case of this example, the imaging objective optical system 32 arranged on the imaging optical path 25 uses an optical characteristic variable optical element VFL. An object image formed by the photographing objective optical system is formed on an imaging surface 18a of the CCD 18 via a filter 33 such as a low-pass filter or an infrared cut filter. The object image received by the CCD 18 is passed through a processing means 34 to a liquid crystal display element (L
(CD) 40 as an electronic image. The processing unit 34 also controls a recording unit 41 that records an object image captured by the CCD 18 as electronic information. LCD
The image displayed at 40 is guided to the observer's eyeball via the eyepiece optical system 42. The eyepiece optical system 42 is composed of an optical characteristic variable optical element VFL having the same form as that used in the objective optical system 32, and controls the voltage applied to the liquid crystal, etc., to increase the diopter of the observer. LCD4
The depth of the virtual image of 0 is adjustable. In the camera 24 configured as described above, the photographing objective optical system 32 can be configured with a small number of optical members, and high performance and miniaturization can be realized.

FIG. 28 is a conceptual diagram showing a configuration in which the optical characteristic variable optical element VFL of the present invention is incorporated in an observation objective optical system 55 of an electronic endoscope. Also in this example, the objective optical system 55 of the observation system uses an optical characteristic variable optical element for performing zooming and focusing. This electronic endoscope 4
Reference numeral 3 denotes a light source device 44 for supplying illumination light, a video processor 45 for performing signal processing corresponding to the electronic endoscope 43, and a video processor 4 as shown in FIG.
5, a monitor 46 for displaying a video signal output from the VCR 5, a VTR deck 47 and a video disk 48 connected to the video processor 45 for recording video signals and the like, and a video printer 49 for printing out the video signals as video.
The distal end portion 51 of the insertion section 50 of the electronic endoscope 43 is configured as shown in FIG. The illumination light beam from the light source device 44 passes through the light guide fiber bundle 52 and illuminates the observation site by the illumination objective optical system 53. And the light from this observation site
The image is formed as an object image by the observation objective optical system 55 via the cover member 54. This object image is formed on the imaging surface 18a of the CCD 18 via a filter 56 such as a low-pass filter and an infrared cut filter. Further, this object image is converted into a video signal by the CCD 18, and
The video signal is directly displayed on a monitor 46 by a video processor 45 shown in FIG.
The information is recorded on the TR deck 47 and the video disk 48, and is printed out as a video from the video printer 49. The endoscope thus configured can be configured with a small number of optical members despite having zooming and focusing functions, and high performance and downsizing can be realized.

FIG. 29 is a conceptual diagram showing a configuration in which the optical characteristic variable optical element VFL of the present invention is incorporated in an optical system of binoculars. Also in this example, the optical characteristic variable optical element VFL is used for the objective optical system 56. Behind the objective optical system 56, a pecan prism 57 is arranged as an image inverting optical system. Behind the pecan prism 57, an eyepiece optical system 58 for guiding the erect image to the eyeball of the observer is provided. Are located. The objective optical system 56 includes an optical characteristic variable optical element VFL having the same configuration as that of the above-described embodiment, and controls the voltage applied to the liquid crystal and the like to control the objective optical system 5.
The focal length of the zoom lens is adjustable and zooming and focusing are performed. Although only one side of the binoculars is shown in the drawing, the other side has a similar configuration. The binoculars configured as described above can be configured with a small number of optical members despite having zooming and focusing functions, and high performance and downsizing can be realized.

FIG. 30 is a conceptual diagram showing a configuration in which the optical characteristic variable optical element VFL of the present invention is incorporated in an optical system of eyeglasses. In the case of this example, the optical characteristic variable optical element VFL is used for the spectacle lens. In glasses having such a configuration,
By controlling the voltage applied to the liquid crystal, the diopter of the entire spectacle lens can be adjusted.

As described above, the optical characteristic variable optical element of the present invention has the following features in addition to the features described in the claims. (1) The optical characteristic variable optical element according to claim 1, wherein the wavelength used is a visible light wavelength region.

(2) A variable focus lens comprising the optical characteristic variable optical element according to claim 1.

(3) Equations (28), (29) and (3)
The optical characteristic variable optical element according to claim 1, wherein any one of (0), (35), (36), (37), and (39) is satisfied.

(4) The average diameter of the liquid crystal particles is 5
A refractive index distribution is formed by applying a spatially non-uniform electric field or magnetic field or temperature to a polymer-dispersed liquid crystal having a size of 00 or less and 7 nm or more, and the refractive index distribution is changed by changing the electric field or magnetic field or temperature. An optical characteristic variable optical element that is changed.

(5) A refractive index distribution is formed by applying a spatially non-uniform electric or magnetic field or temperature to a polymer-dispersed liquid crystal having an average diameter of liquid crystal particles smaller than the wavelength used and larger than the size of liquid crystal molecules. And an optical property variable optical element that changes the refractive index distribution by changing an electric field, a magnetic field, or a temperature.

(6) Formulas (53), (54), and (5)
3. The optical characteristic variable optical element according to claim 2, wherein any one of (7), (59), (60), and (61) is satisfied.

(7) An optical element with variable optical characteristics, wherein an electric field is applied to the liquid crystal by two or more electrodes having different shapes.

(8) The optical characteristic variable optical element according to claim 1 or 2, wherein an electric field is applied to the liquid crystal by two or more electrodes having different shapes.

(9) An optical element with variable optical characteristics, wherein the number of substrates of the polymer dispersed liquid crystal is one or less.

(10) An optical characteristic variable optical element using a polymer-dispersed liquid crystal using a ferroelectric liquid crystal or an antiferroelectric liquid crystal.

(11) An optical element having a variable optical characteristic, wherein a medium having an Abbe number of 50 or less is used for a liquid crystal substrate.

(12) The optical characteristic variable optical element according to claim 3, wherein the Abbe number of the liquid crystal of the convex liquid crystal lens is larger than the Abbe number of the liquid crystal of the concave liquid crystal lens in a predetermined refractive index range of the liquid crystal. .

(13) When the focal length of the convex liquid crystal lens is f ₁ and the focal length of the concave liquid crystal lens is f ₂ , the conditional expression 1/2
4. The optical characteristic variable optical element according to claim 3, wherein <| f ₁ / f ₂ | <2 is satisfied.

(14) The optical characteristic variable optical element according to the above (13), wherein a trans liquid crystal is used as the liquid crystal of the liquid crystal lens.

(15) The optical characteristic variable optical element according to any of (3) or (12) to (14), wherein a liquid crystal having an Abbe number of 50 or less is used.

(16) An optical element with variable optical characteristics using a tolan liquid crystal.

(17) The liquid crystal display according to any one of (1) to (12), wherein a substance having an electro-optical effect, a magneto-optical effect, or a thermo-optical effect is used instead of the liquid crystal. The optical property variable optical element according to the above.

(18) A non-rotationally symmetric surface, a surface having no axis of symmetry both inside and outside the surface, a surface having no rotation symmetry axis on the optical action surface,
An imaging apparatus comprising: any one of surfaces having only one plane of symmetry both inside and outside the surface; and an optical element with variable optical characteristics.

(19) An optical apparatus using the optical characteristic variable optical element according to any one of claims 1 to 3, (1) to (17).

(17) A variable focal length imaging device or optical device comprising a free-form surface and the optical characteristic variable optical element according to any one of claims 1 to 3 (1) to (17).

(18) An inhomogeneous lens, a diffractive optical element, or an aspherical lens, and the above (1) to (1)
A variable focal length imaging device or optical device comprising the optical characteristic variable optical element according to any one of 7).

(19) An autofocus device using the optical characteristic variable optical element according to any one of claims 1 to 3, (1) to (17).

(20) An autofocus device using the optical characteristic variable optical element according to any one of claims 1 to 3, (1) to (17).

(21) A diopter adjusting device using the optical characteristic variable optical element according to any one of claims 1 to 3, (1) to (17).

(22) Variable focus spectacles using the optical characteristic variable optical element according to any one of claims 1 to 3, (1) to (17).

[0121]

As described above, according to the present invention,
A bright optical property variable optical element and various optical devices and optical apparatuses using the same can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of one embodiment of an optical characteristic variable optical element according to the present invention.

FIG. 2 is an explanatory view showing a state of twisting of the nematic liquid crystal shown in FIG.

FIG. 3 is a diagram showing a refractive index ellipsoid corresponding to liquid crystal molecules on the incident side of a nematic liquid crystal.

FIG. 4 is a view showing a change in the orientation of liquid crystal when an electric field is applied to the optical property variable optical element shown in FIG.

FIG. 5 is a diagram showing a state of an electric field applied to the optical characteristic variable optical element shown in FIG.

FIG. 6 is a view showing an alignment state of the liquid crystal different from that in FIG. 4 when an electric field is applied to the optical property variable optical element shown in FIG.

FIG. 7 is a schematic diagram showing a first modified example of the optical characteristic variable optical element shown in FIG. 1 which is configured using a smectic liquid crystal.

8 is a diagram showing an alignment state when an electric field is applied to the optical property variable optical element shown in FIG.

FIG. 9 is a schematic diagram showing a second modification of the optical property variable optical element shown in FIG. 1 which is configured using cholesteric liquid crystal.

FIG. 10 is a characteristic diagram illustrating an example of an actual measurement value of a reflectance of a cholesteric liquid crystal with respect to natural polarized light with respect to a wavelength.

FIG. 11 is a schematic view of an optical characteristic variable optical element configured to generate a change in refractive index by applying a magnetic field to a cholesteric liquid crystal.

FIG. 12 is a schematic diagram of an optical characteristic variable optical element configured to generate a refractive index change by applying heat to a cholesteric liquid crystal.

FIG. 13 is a schematic diagram showing a third modification of the optical property variable optical element shown in FIG. 1 constituted by using a polymer dispersed liquid crystal layer.

FIG. 14 is a partially enlarged view of the polymer dispersed liquid crystal layer in FIG.

FIG. 15 is a diagram illustrating a refractive index ellipsoid of a uniaxial nematic liquid crystal molecule used in the modification shown in FIG. 13;

FIG. 16 is a diagram showing a change in the orientation of liquid crystal molecules when an electric field is applied to the optical property variable optical element shown in FIG.

17 is a diagram showing a configuration of an imaging optical system for a digital camera using the optical characteristic variable optical element shown in FIG.

FIG. 18 is a schematic diagram showing a fourth modification of the optical property variable optical element shown in FIG. 1 constituted by using a ferroelectric liquid crystal.

FIG. 19 is a view showing another embodiment of the optical characteristic variable optical element according to the present invention.

FIG. 20 is a view showing still another embodiment of the optical characteristic variable optical element according to the present invention.

FIG. 21 is a characteristic diagram illustrating a change in the Abbe number according to a change in the refractive index of the liquid crystal.

FIG. 22 is a diagram showing a chemical structure of a tolanic liquid crystal.

FIG. 23 is a diagram showing a configuration of an imaging device for a digital camera using the optical characteristic variable optical element according to the present invention in combination with a free-form surface optical element.

FIG. 24 is a front perspective view of an electronic camera in which the optical characteristic variable optical element according to the present invention is incorporated in a finder optical system.

25 is a rear perspective view of the electronic camera shown in FIG.

26 is a schematic sectional view showing the internal configuration of the electronic camera shown in FIG.

FIG. 27 is a schematic configuration diagram of an electronic camera in which the optical characteristic variable optical element according to the present invention is incorporated in a photographic objective optical system.

FIG. 28 is a schematic configuration diagram of an electronic endoscope apparatus in which the optical characteristic variable optical element according to the present invention is incorporated in an observation objective optical system, (a) is a configuration diagram of the entire system, and (b) is a tip of the endoscope. FIG. 3 is an internal configuration diagram of a unit.

FIG. 29 is a schematic configuration diagram of binoculars incorporating the optical characteristic variable optical element according to the present invention in an optical system.

FIG. 30 is a schematic configuration diagram of spectacles in which the optical characteristic variable optical element according to the present invention is incorporated in an optical system.

FIG. 31 is a diagram showing a basic configuration of a conventional liquid crystal lens.

FIG. 32 is a diagram showing a change in the orientation of liquid crystal when an electric field is applied to the liquid crystal lens shown in FIG. 31.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Nematic liquid crystal 2 Seal member 3 Donut-shaped electrode 4,5 Transparent substrate 6 Alignment film 7 Polarizer 8 Power supply 9 Switch 10 Variable resistor 11 Smectic liquid crystal 12 Cholesteric liquid crystal 13 Coil 14 Iron core 15 Heater 16 Polymer dispersed liquid crystal layer 16a Liquid crystal molecule 16b Polymer cell 17 Lens 18 Solid-state imaging device 19 Ferroelectric liquid crystal 20 Transparent electrode 21 Liquid crystal 22, 23 Free-form surface optical element 24 Electronic camera 25 Imaging optical path 26 Imaging optical system 27 Viewfinder optical path 28 Finder optical system 29 Release Reference Signs List 30 Flash 31 Liquid crystal display monitor 32 Objective optical system for photographing 33, 56 Filter 34 Processing means 35 Objective optical system for finder 36 Cover lens 37 Aperture 38 Porro prism 39 Field frame 40 Liquid crystal display element (LCD) 41 Recording Step 42 Eyepiece optical system 43 Electronic endoscope 44 Light source device 45 Video processor 46 Monitor 47 VTR deck 48 Video disk 49 Video printer 50 Insertion section 51 Tip end 52 Light guide fiber bundle 53 Illumination objective optical system 54 Cover member 55 For observation the objective optical system 56 the objective optical system 57 image inverting optical system 58 of the ocular optical system d nematic liquid crystal thickness E field L light P nematic liquid crystal twist pitch VFL, VFL _1, VFL ₂ varifocal lens (variable optical-property element)

Claims (3)

[Claims] 1. A liquid crystal having a twist pitch of 60 times or less the wavelength of light to be used, and a refractive index distribution is formed by applying a spatially non-uniform electric or magnetic field or temperature to the liquid crystal. An optical characteristic variable optical element in which a refractive index distribution is changed by changing an electric field, a magnetic field, or a temperature. 2. The method according to claim 1, wherein the liquid crystal includes a polymer-dispersed liquid crystal, and a spatially non-uniform electric or magnetic field or temperature is applied to the liquid crystal to form a refractive index distribution. An optical element with variable optical characteristics that changes the refractive index distribution. 3. An optical characteristic variable optical element comprising a combination of two or more convex and concave liquid crystal lenses.