U.S. patent application number 13/313454 was filed with the patent office on 2012-03-29 for optical element.
This patent application is currently assigned to Sony Corporation. Invention is credited to Keita Kaifu, Yukihiro Mitsuda, Yukihiro Sano, Kazuhiro Tanaka.
Application Number | 20120075714 13/313454 |
Document ID | / |
Family ID | 40380523 |
Filed Date | 2012-03-29 |
United States Patent
Application |
20120075714 |
Kind Code |
A1 |
Tanaka; Kazuhiro ; et
al. |
March 29, 2012 |
OPTICAL ELEMENT
Abstract
An optical element includes a container including first and
second end face walls, a side face wall, and an accommodating
chamber inside the walls; first and second liquids enclosed in the
chamber; a first electrode provided on a surface of the first end
face wall; a second electrode provided on a surface of the second
end face wall; an insulating film provided on a surface of the
second electrode; and a unit configured to apply a voltage. The
shape of an interface between the liquids is changed by a voltage
application, and a light transmission path, the center of which is
a virtual axis passing through the end face walls in the thickness
direction of the container, is formed in a portion of the second
liquid. An opening having a diameter the same as or larger than the
maximum diameter of the transmission path is provided in the first
electrode.
Inventors: |
Tanaka; Kazuhiro; (Tokyo,
JP) ; Kaifu; Keita; (Tokyo, JP) ; Sano;
Yukihiro; (Tokyo, JP) ; Mitsuda; Yukihiro;
(Gifu, JP) |
Assignee: |
Sony Corporation
Tokyo
JP
|
Family ID: |
40380523 |
Appl. No.: |
13/313454 |
Filed: |
December 7, 2011 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12750845 |
Mar 31, 2010 |
8089699 |
|
|
13313454 |
|
|
|
|
12276838 |
Nov 24, 2008 |
7813049 |
|
|
12750845 |
|
|
|
|
Current U.S.
Class: |
359/665 |
Current CPC
Class: |
G02B 26/005 20130101;
G02B 3/14 20130101; G02B 26/004 20130101 |
Class at
Publication: |
359/665 |
International
Class: |
G02B 3/12 20060101
G02B003/12 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 27, 2007 |
JP |
2007-306079 |
Claims
1. An optical element comprising: a container including a first
wall and a second wall facing each other, and a chamber between the
first wall and the second wall; a first liquid having polarity or
electrical conductivity and enclosed in the chamber; a second
liquid immiscible with the first liquid and enclosed in the
chamber; a first electrode and a second electrode configured to
apply an electric field to the first liquid; an insulating film;
and a unit configured to apply a voltage between the first
electrode and the second electrode, wherein applying the voltage
changes a shape of an interface between the first liquid and the
second liquid to a curved surface, a center of which is a virtual
axis passing through the first wall and the second wall and
extending in a thickness direction of the container, which is a
direction in which the first wall and the second wall face each
other, thereby refracting light traveling in a direction of the
virtual axis and passing through the interface, the first electrode
is provided on an inner surface of the first wall, the inner
surface of the first wall facing the chamber, the second electrode
is provided on an inner surface of the second wall, the inner
surface of the second wall facing the chamber, the insulating film
is provided on a surface of the second electrode, the surface of
the second electrode facing the chamber, and when viewed from the
thickness direction of the container, an opening having a diameter
the same as or smaller than a maximum diameter of the interface is
provided in the second electrode.
2. The optical element according to claim 1, further comprising an
opening in the insulating film with a diameter the same as or
smaller than the diameter of the opening in the second
electrode.
3. The optical element according to claim 1, wherein the first
liquid comprises water and ethanol combined in a first ratio.
4. The optical element according to claim 1, wherein the second
liquid comprises at least two different types of silicone oil
combined in a second ratio.
5. An optical element comprising: a container including a first
wall and a second wall facing each other, and a chamber between the
first wall and the second wall; a first liquid enclosed in the
chamber; a second liquid immiscible with the first liquid and
enclosed in the chamber; a first electrode; a second electrode; and
an insulating film; wherein, a shape of an interface between the
first liquid and the second liquid is changed by applying a voltage
between the first electrode and the second electrode such that a
light transmission path, a center of which is a virtual axis
passing through the first wall and the second wall, is formed in a
portion of the second liquid, the second electrode is provided at
an inner surface of the second wall, the inner surface of the
second wall facing the chamber, the insulating film is provided on
a surface of the second electrode, the surface of the second
electrode facing the chamber; and when viewed along the virtual
axis, an opening having a diameter the same as or smaller than a
maximum diameter of the light transmission path is provided in the
second electrode.
6. The optical element according to claim 5, further comprising an
opening in the insulating film with a diameter the same as or
smaller than the diameter of the opening in the second
electrode.
7. The optical element according to claim 5, wherein the first
liquid comprises at least two different liquids combined in a first
ratio.
8. The optical element according to claim 5, wherein the second
liquid comprises at least two different liquids combined in a
second ratio.
9. An optical element comprising: a container including a first
wall and a second wall facing each other, and a chamber between the
first wall and the second wall; a first liquid enclosed in the
chamber; a second liquid immiscible with the first liquid and
enclosed in the chamber; a first electrode; a second electrode; and
an insulating film; wherein, a shape of an interface between the
first liquid and the second liquid is changed by applying a voltage
between the first electrode and the second electrode, such that a
light transmission path, a center of which is a virtual axis
passing through the first wall and the second wall, is formed, the
second electrode is provided at an inner surface of the second
wall, the inner surface of the second wall facing the chamber, the
insulating film is provided on a surface of the second electrode,
the surface of the second electrode facing the chamber; and when
viewed along the virtual axis, an opening having a diameter the
same as or smaller than a maximum diameter of the interface is
provided in the second electrode.
10. The optical element according to claim 9, further comprising an
opening in the insulating film with a diameter the same as or
smaller than the diameter of the opening in the second
electrode.
11. The optical element according to claim 9, wherein the first
liquid comprises at least two different liquids combined in a first
ratio.
12. The optical element according to claim 9, wherein the second
liquid comprises at least two different liquids combined in a
second ratio.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] This application is a divisional of prior application Ser.
No. 12/750,845, filed Mar. 31, 2010, which is a divisional of U.S.
Pat. No. 7,813,049, issued Oct. 12, 2010, which claims the priority
benefit of Japanese patent application number 2007-306079, filed in
the Japanese Patent Office on Nov. 27, 2007, each of which is
hereby incorporated by reference to the maximum extent allowable by
law.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an optical element.
[0004] 2. Description of the Related Art
[0005] An optical element whose optical property is changed by
changing the shape of the interface between a first liquid and a
second liquid using electrocapillarity (an electrowetting
phenomenon) has been proposed.
[0006] Such an optical element includes a container having a first
end face wall and a second end face wall facing each other, and a
side face wall connecting the first end face wall to the second end
face wall, and a hermetically sealed accommodating chamber provided
inside the end face walls and the side face wall.
[0007] A first liquid having polarity or electrical conductivity,
and a second liquid immiscible with the first liquid are enclosed
in the accommodating chamber, and a first electrode and a second
electrode for applying an electric field to the first liquid are
provided. By applying a voltage between the first electrode and the
second electrode, the shape of the interface between the first
liquid and the second liquid is changed (see Japanese Unexamined
Patent Application Publication No. 2003-177219).
SUMMARY OF THE INVENTION
[0008] In the above-described optical element, in addition to the
first and second electrodes, various types of films such as an
insulating film for providing an electric field to the first
liquid, a hydrophilic film and a water-repellent film for
increasing the moving speed of the interface between the first
liquid and the second liquid are provided. This structure is
disadvantageous from the standpoint that transparency of the
optical element is improved.
[0009] The present invention has been made in view of this
situation, and it is desirable to provide an optical element which
is advantageous in the improvement of transparency.
[0010] An optical element according to an embodiment of the present
invention includes a container including a first end face wall and
a second end face wall facing each other, a side face wall
connecting the first end face wall to the second end face wall, and
a hermetically sealed accommodating chamber provided inside the end
face walls and the side face wall; a first liquid having polarity
or electrical conductivity and enclosed in the accommodating
chamber; a second liquid immiscible with the first liquid and
enclosed in the accommodating chamber; a first electrode and a
second electrode configured to apply an electric field to the first
liquid; an insulating film; and means for applying a voltage
between the first electrode and the second electrode, wherein the
transmittance of the first liquid is lower than the transmittance
of the second liquid, the shape of an interface between the first
liquid and the second liquid is changed by the application of the
voltage with the means for applying a voltage, and a light
transmission path, the center of which is a single virtual axis
passing through the first end face wall and the second end face
wall, and extending in the thickness direction of the container,
which is a direction in which the first end face wall and the
second end face wall face each other, is formed in a portion of the
second liquid, the first electrode is provided on an inner surface
of the first end face wall, the inner surface facing the
accommodating chamber, the second electrode is provided on an inner
surface of the second end face wall, the inner surface facing the
accommodating chamber, the insulating film is provided on a surface
of the second electrode, the surface facing the accommodating
chamber, and when viewed from the thickness direction of the
container, an opening having a diameter the same as or larger than
the maximum diameter of the transmission path, the center of which
is the virtual axis, is provided in the first electrode.
[0011] An optical element according to an embodiment of the present
invention includes a container including a first end face wall and
a second end face wall facing each other, a side face wall
connecting the first end face wall to the second end face wall, and
a hermetically sealed accommodating chamber provided inside the end
face walls and the side face wall; a first liquid having polarity
or electrical conductivity and enclosed in the accommodating
chamber; a second liquid immiscible with the first liquid and
enclosed in the accommodating chamber; a first electrode and a
second electrode configured to apply an electric field to the first
liquid; an insulating film; and means for applying a voltage
between the first electrode and the second electrode, wherein the
transmittance of the first liquid is lower than the transmittance
of the second liquid, the shape of an interface between the first
liquid and the second liquid is changed by the application of the
voltage with the means for applying a voltage, and a light
transmission path, the center of which is a single virtual axis
passing through the first end face wall and the second end face
wall and extending in the thickness direction of the container,
which is a direction in which the first end face wall and the
second end face wall face each other, is formed in a portion of the
second liquid, the first electrode is provided on an inner surface
of the first end face wall, the inner surface facing the
accommodating chamber, the second electrode is provided on an inner
surface of the second end face wall, the inner surface facing the
accommodating chamber, the insulating film is provided on a surface
of the second electrode, the surface facing the accommodating
chamber, and when viewed from the thickness direction of the
container, an opening having a diameter the same as or smaller than
the maximum diameter of the transmission path, the center of which
is the virtual axis, is provided in the second electrode or in each
of the second electrode and the insulating film.
[0012] An optical element according to an embodiment of the present
invention includes a container including a first end face wall and
a second end face wall facing each other, a side face wall
connecting the first end face wall to the second end face wall, and
a hermetically sealed accommodating chamber provided inside the end
face walls and the side face wall; a first liquid having polarity
or electrical conductivity and enclosed in the accommodating
chamber; a second liquid immiscible with the first liquid and
enclosed in the accommodating chamber; a first electrode and a
second electrode configured to apply an electric field to the first
liquid; an insulating film; a film whose wettability to the second
liquid is higher than the wettability to the first liquid; and
means for applying a voltage between the first electrode and the
second electrode, wherein the transmittance of the first liquid is
lower than the transmittance of the second liquid, the shape of an
interface between the first liquid and the second liquid is changed
by the application of the voltage with the means for applying a
voltage, and a light transmission path, the center of which is a
single virtual axis passing through the first end face wall and the
second end face wall and extending in the thickness direction of
the container, which is a direction in which the first end face
wall and the second end face wall face each other, is formed in a
portion of the second liquid, the first electrode is provided on an
inner surface of the first end face wall, the inner surface facing
the accommodating chamber, the second electrode is provided on an
inner surface of the second end face wall, the inner surface facing
the accommodating chamber, the insulating film is provided on a
surface of the second electrode, the surface facing the
accommodating chamber, the film whose wettability to the second
liquid is higher than the wettability to the first liquid is
provided on a surface of the insulating film, the surface facing
the accommodating chamber, and when viewed from the thickness
direction of the container, an opening having a diameter the same
as or smaller than the maximum diameter of the transmission path,
the center of which is the virtual axis, is provided in the film
provided on the surface of the insulating film.
[0013] An optical element according to an embodiment of the present
invention includes a container including a first end face wall and
a second end face wall facing each other, a side face wall
connecting the first end face wall to the second end face wall, and
a hermetically sealed accommodating chamber provided inside the end
face walls and the side face wall; a first transparent liquid
having polarity or electrical conductivity and enclosed in the
accommodating chamber; a second transparent liquid immiscible with
the first liquid and enclosed in the accommodating chamber; a first
electrode and a second electrode configured to apply an electric
field to the first liquid; an insulating film; and means for
applying a voltage between the first electrode and the second
electrode, wherein the shape of an interface between the first
liquid and the second liquid is changed by the application of the
voltage with the means for applying a voltage to form the interface
having a curved surface, the center of which is a single virtual
axis passing through the first end face wall and the second end
face wall and extending in the thickness direction of the
container, which is a direction in which the first end face wall
and the second end face wall face each other, thereby refracting
light traveling in a direction of the virtual axis and passing
through the interface, the first electrode is provided on an inner
surface of the first end face wall, the inner surface facing the
accommodating chamber, the second electrode is provided on an inner
surface of the second end face wall, the inner surface facing the
accommodating chamber, the insulating film is provided on a surface
of the second electrode, the surface facing the accommodating
chamber, and when viewed from the thickness direction of the
container, an opening having a diameter the same as or larger than
the maximum diameter of the interface, the center of which is the
virtual axis, is provided in the first electrode.
[0014] An optical element according to an embodiment of the present
invention includes a container including a first end face wall and
a second end face wall facing each other, a side face wall
connecting the first end face wall to the second end face wall, and
a hermetically sealed accommodating chamber provided inside the end
face walls and the side face wall; a first transparent liquid
having polarity or electrical conductivity and enclosed in the
accommodating chamber; a second transparent liquid immiscible with
the first liquid and enclosed in the accommodating chamber; a first
electrode and a second electrode configured to apply an electric
field to the first liquid; an insulating film; and means for
applying a voltage between the first electrode and the second
electrode, wherein the shape of an interface between the first
liquid and the second liquid is changed by the application of the
voltage with the means for applying a voltage to form the interface
having a curved surface, the center of which is a single virtual
axis passing through the first end face wall and the second end
face wall and extending in the thickness direction of the
container, which is a direction in which the first end face wall
and the second end face wall face each other, thereby refracting
light traveling in a direction of the virtual axis and passing
through the interface, the first electrode is provided on an inner
surface of the first end face wall, the inner surface facing the
accommodating chamber, the second electrode is provided on an inner
surface of the second end face wall, the inner surface facing the
accommodating chamber, the insulating film is provided on a surface
of the second electrode, the surface facing the accommodating
chamber, and when viewed from the thickness direction of the
container, an opening having a diameter the same as or smaller than
the maximum diameter of the interface, the center of which is the
virtual axis, is provided in the second electrode or in each of the
second electrode and the insulating film.
[0015] An optical element according to an embodiment of the present
invention includes a container including a first end face wall and
a second end face wall facing each other, a side face wall
connecting the first end face wall to the second end face wall, and
a hermetically sealed accommodating chamber provided inside the end
face walls and the side face wall; a first transparent liquid
having polarity or electrical conductivity and enclosed in the
accommodating chamber; a second transparent liquid immiscible with
the first liquid and enclosed in the accommodating chamber; a first
electrode and a second electrode configured to apply an electric
field to the first liquid; an insulating film; a film whose
wettability to the second liquid is higher than the wettability to
the first liquid; and means for applying a voltage between the
first electrode and the second electrode, wherein the shape of an
interface between the first liquid and the second liquid is changed
by the application of the voltage with the means for applying a
voltage to form the interface having a curved surface, the center
of which is a single virtual axis passing through the first end
face wall and the second end face wall and extending in the
thickness direction of the container, which is a direction in which
the first end face wall and the second end face wall face each
other, thereby refracting light traveling in a direction of the
virtual axis and passing through the interface, the first electrode
is provided on an inner surface of the first end face wall, the
inner surface facing the accommodating chamber, the second
electrode is provided on an inner surface of the second end face
wall, the inner surface facing the accommodating chamber, the
insulating film is provided on a surface of the second electrode,
the surface facing the accommodating chamber, the film whose
wettability to the second liquid is higher than the wettability to
the first liquid is provided on a surface of the insulating film,
the surface facing the accommodating chamber, and when viewed from
the thickness direction of the container, an opening having a
diameter the same as or smaller than the maximum diameter of the
interface, the center of which is the virtual axis, is provided in
the film provided on the surface of the insulating film.
[0016] In the optical element according to an embodiment of the
present invention, light transmits through the opening provided in
a first electrode, a water-repellent film, an insulating film, or a
second electrode. Accordingly, the optical element is advantageous
in the improvement of transparency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1A is a view illustrating the principle of
electrocapillarity and shows a state before a voltage is
applied;
[0018] FIG. 1B is a view illustrating the principle of
electrocapillarity and shows a state after a voltage is
applied;
[0019] FIG. 2 is a longitudinal cross-sectional view showing the
basic structure of an optical element 10;
[0020] FIG. 3 is a perspective view showing the basic structure of
the optical element 10;
[0021] FIGS. 4A, 4B, and 4C are cross-sectional views illustrating
an operation when voltages V1, V2, and V3 are applied between a
first electrode 18 and a second electrode 20 of the optical element
10, respectively;
[0022] FIG. 5 is a schematic view showing an example in which the
optical element 10 is applied to an imaging optical system of an
image-pickup apparatus;
[0023] FIG. 6 is a longitudinal cross-sectional view showing the
structure of an optical element 10 according to a first
embodiment;
[0024] FIG. 7 is a longitudinal cross-sectional view showing the
basic structure of an optical element 10 according to a second
embodiment;
[0025] FIGS. 8A, 8B, and 8C are cross-sectional views illustrating
an operation when voltages V1, V2, and V3 are applied between a
first electrode 18 and a second electrode 20 of the optical element
10, respectively;
[0026] FIG. 9 is a longitudinal cross-sectional view showing the
structure of the optical element 10 according to the second
embodiment;
[0027] FIG. 10 is a plan view of a second electrode 20 of an
optical element 10 according to a third embodiment;
[0028] FIG. 11 is a plan view of the optical element 10;
[0029] FIG. 12 is a schematic perspective view showing the shape of
a second liquid 16 in FIG. 4A;
[0030] FIG. 13 is a schematic perspective view showing the shape of
the second liquid 16 in FIG. 4B;
[0031] FIG. 14 is a plan view of FIG. 4C;
[0032] FIG. 15 is a view illustrating a state in which the center
of a light transmission path 52 corresponds to a virtual axis
38;
[0033] FIG. 16 is a view illustrating a state in which the center
of the light transmission path 52 deviates from the virtual axis 38
and becomes decentered;
[0034] FIG. 17 is a perspective view of FIG. 16;
[0035] FIG. 18 is a plan view of a second electrode 20 of an
optical element 10 according to a fourth embodiment;
[0036] FIG. 19 is a plan view of a second electrode 20 of an
optical element 10 according to a fifth embodiment;
[0037] FIG. 20 is a plan view of a second electrode 20 of an
optical element 10 according to a sixth embodiment;
[0038] FIG. 21 is a plan view of a second electrode 20 of an
optical element 10 according to a seventh embodiment;
[0039] FIG. 22 is a plan view of a second electrode 20 of an
optical element 10 according to an eighth embodiment;
[0040] FIG. 23 is a plan view of a second electrode 20 of an
optical element 10 according to a ninth embodiment;
[0041] FIG. 24 is a plan view of a second electrode 20 of an
optical element 10 according to a tenth embodiment;
[0042] FIG. 25 is a plan view of a second electrode 20 of an
optical element 10 according to an eleventh embodiment;
[0043] FIG. 26 is a graph showing the relationship between a mixing
ratio of ethanol to pure water and the specific gravity, and the
relationship between the mixing ratio and the refractive index;
[0044] FIG. 27 is a graph showing the relationship between a mixing
ratio of ethylene glycol to pure water and the specific gravity,
and the relationship between the mixing ratio and the refractive
index;
[0045] FIG. 28 is a graph showing the specific gravities and the
refractive indices of pure water, ethanol, and ethylene glycol;
[0046] FIG. 29 is a graph showing the specific gravities and the
refractive indices of various types of liquids; and
[0047] FIG. 30 is a table showing numerical values of the specific
gravities and the refractive indices of various types of liquids
used.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
[0048] Before an optical element 10 of this embodiment is
described, first, the principle of electrocapillarity (an
electrowetting phenomenon) used by an optical element according to
an embodiment of the present invention will be described.
[0049] FIGS. 1A and 1B are views illustrating the principle of
electrocapillarity. FIG. 1A shows a state before a voltage is
applied and FIG. 1B shows a state after a voltage is applied.
[0050] As shown in FIG. 1A, an insulating film 2 is provided on a
substrate 1. A first liquid 3 having polarity or electrical
conductivity is disposed on a surface of the insulating film 2. A
first electrode 4 is electrically connected to the first liquid
3.
[0051] A second electrode 5 is provided between the insulating film
2 and the substrate 1.
[0052] As shown in FIG. 1A, when no voltage E is applied between
the first electrode 4 and the second electrode 5, the surface of
the first liquid 3 has a substantially spherical surface projecting
upward due to surface tension. In this case, an angle .theta.
formed by the surface of the insulating film 2 and a liquid surface
at a portion where the first liquid 3 is in contact with the
insulating film 2, i.e., the angle of contact .theta. is defined as
.theta.0. Note that the angle of contact .theta. is measured in a
state in which a liquid faces air. That is, the angle of contact
.theta. is measured at a gas-liquid interface.
[0053] In contrast, as shown in FIG. 1B, when an electric field is
applied to the first liquid 3 by applying a voltage E between the
first electrode 4 and the second electrode 5, for example, minus
charges are generated on the surface of the insulating film 2, and
thus, the electric field (electrostatic force) acts on molecules
constituting the first liquid 3. Accordingly, the molecules
constituting the first liquid 3 are attracted to each other to
improve the wettability of the first liquid 3 on the insulating
film 2. As a result, the angle of contact .theta. becomes .theta.1
that is smaller than .theta.0. The angle of contact .theta.
decreases as the value of the voltage E increases.
[0054] This phenomenon is referred to as electrocapillarity.
[0055] Next, the basic structure and operation that constitute a
prerequisite of the optical element 10 of the first embodiment will
be described.
[0056] In this embodiment, the optical element 10 constitutes a
diaphragm.
[0057] FIG. 2 is a longitudinal cross-sectional view showing the
basic structure of the optical element 10, and FIG. 3 is a
perspective view showing the basic structure of the optical element
10.
[0058] As shown in FIGS. 2 and 3, the optical element 10 includes a
container 12, a first liquid 14, a second liquid 16, a first
electrode 18, a second electrode 20, and a voltage applying unit
22.
[0059] The container 12 includes a first end face wall 24 and a
second end face wall 26 facing each other and extending in
parallel, and a side face wall 28 connecting the first end face
wall 24 to the second end face wall 26. The container 12 includes
an accommodating chamber 30 that is hermetically sealed by the
first end face wall 24, the second end face wall 26, and the side
face wall 28.
[0060] Herein, a term "thickness direction of the container 12"
means a direction in which the first end face wall 24 and the
second end face wall 26 face each other.
[0061] The first end face wall 24 and the second end face wall 26
are rectangular plates having the same shape and the same size. The
side face wall 28 is a cylindrical wall having a size that falls
within the outline of the first end face wall 24 and the second end
face wall 26. The accommodating chamber 30 has a flat circular
column shape.
[0062] The first end face wall 24, the second end face wall 26, and
the side face wall 28 are made of insulating materials.
Furthermore, the first end face wall 24 and the second end face
wall 26 are made of transparent and light-transmissive
materials.
[0063] Examples of the material constituting the first end face
wall 24 and the second end face wall 26 include transparent and
insulating synthetic resin materials, and transparent glass
materials.
[0064] The first liquid 14 has polarity or electrical conductivity,
and is enclosed in the accommodating chamber 30.
[0065] The second liquid 16 is immiscible with the first liquid 14
and is also enclosed in the accommodating chamber 30.
[0066] The first liquid 14 and the second liquid 16 have
substantially the same specific gravity. In addition, the
transmittance of the first liquid 14 is lower than the
transmittance of the second liquid 16.
[0067] Since the first liquid 14 and the second liquid 16 have
substantially the same specific gravity, an interface 48 (FIG. 2)
between the first liquid 14 and the second liquid 16 maintains a
stable shape without being affected by the gravity.
[0068] Furthermore, since the transmittance of the first liquid 14
is lower than the transmittance of the second liquid 16, a light
transmission path 52 (FIG. 4) is formed by the second liquid
16.
[0069] In this embodiment, the first liquid 14 is prepared by
mixing fine particles made of a material that does not transmit
light with a mixed liquid containing pure water, ethanol, and
ethylene glycol.
[0070] As the fine particles, for example, carbon black can be
used. When carbon black is used, it is preferable that a
hydrophilic coating treatment is performed on the surfaces of the
carbon black particles so that the carbon black particles can be
uniformly mixed with the first liquid 14. The hydrophilic coating
treatment can be performed by, for example, forming a hydrophilic
group on the surfaces of the carbon black particles.
[0071] In this embodiment, the second liquid 16 is composed of
silicone oil.
[0072] The liquid that can be used as the first liquid 14 is not
limited to the liquid used in this embodiment. Examples thereof
further include nitromethane, acetic anhydride, methyl acetate,
ethyl acetate, methanol, acetonitrile, acetone, ethanol,
propionitrile, tetrahydrofuran, n-hexane, 2-propanol, 2-butanone,
n-butyronitrile, 1-propanol, 1-butanol, dimethyl sulfoxide,
chlorobenzene, ethylene glycol, formamide, nitrobenzene, propylene
carbonate, 1,2-dichloroethane, carbon disulfide, chloroform,
bromobenzene, carbon tetrachloride, trichloroacetic anhydride,
toluene, benzene, ethylenediamine, N,N-dimethylacetamide,
N,N-dimethylformamide, tributyl phosphate, pyridine, benzonitrile,
aniline, 1,4-dioxane, and hexamethylphosphoramide.
[0073] Examples of the liquid that can be used as the second liquid
16 include silicones, decanes, octanes, nonanes, and heptanes.
[0074] Each of the first liquid 14 and the second liquid 16 may be
composed of a single liquid or a mixture of a plurality of liquids.
It is sufficient that the first liquid 14 and the second liquid 16
have substantially the same specific gravity.
[0075] Furthermore, the compositions of the first liquid 14 and the
second liquid 16 will be described.
[0076] First, the first liquid 14 will be described. The first
liquid 14 is prepared by mixing three types of liquids having
different specific gravities and different refractive indices. The
inventors of the present invention have found that, by changing the
mixing ratio of the three types of liquids, each of the specific
gravity and the refractive index of the first liquid 14 can be
changed over a wide range.
[0077] For example, first, a description will be made of a case
where the first liquid 14 is prepared using two types of
liquids.
[0078] The first liquid 14 is prepared using pure water and ethanol
as the two types of liquids, and the mixing ratio of ethanol to
pure water is changed.
[0079] As shown in FIG. 26, when the mixing ratio of ethanol to
pure water is changed, the specific gravity and the refractive
index of the first liquid 14 change linearly or follow a curve.
[0080] Alternatively, the first liquid 14 is prepared using pure
water and ethylene glycol as the two types of liquids, and the
mixing ratio of ethylene glycol to pure water is changed.
[0081] As shown in FIG. 27, when the mixing ratio of ethylene
glycol to pure water is changed, the specific gravity and the
refractive index of the first liquid 14 change linearly or follow a
curve.
[0082] Note that the specific gravity of pure water is 1.0, and the
refractive index of pure water is 1.333. The specific gravity of
ethanol is 0.789, and the refractive index of ethanol is 1.361. The
specific gravity of ethylene glycol is 1.113, and the refractive
index of ethylene glycol is 1.430.
[0083] In contrast, the first liquid 14 is prepared using three
types of liquids, and the mixing ratio of the liquids is
changed.
[0084] For example, the first liquid 14 is prepared using pure
water, ethanol, and ethylene glycol as the three types of liquids,
and the mixing ratio thereof is changed.
[0085] As shown in FIG. 28, by changing the mixing ratio of pure
water, ethanol, and ethylene glycol, the specific gravity and the
refractive index of the first liquid 14 can be changed in a large
triangle area R defined by joining three coordinates of pure water,
ethanol, and ethylene glycol.
[0086] In addition, in FIG. 28, coordinates of the specific gravity
and the refractive index of various types of commercially available
silicone oil are plotted.
[0087] Accordingly, commercially available silicone oil plotted in
the triangle area R can be used as the second liquid 16, and a
liquid prepared by mixing pure water, ethanol, and ethylene glycol
so that the specific gravity and the refractive index of the
resulting mixed liquid are the same as those of the above silicone
oil can be used as the first liquid 14.
[0088] In this embodiment, the first liquid 14 is prepared by
dissolving carbon black in a mixed liquid containing pure water,
ethanol, and ethylene glycol, and is black. The first liquid 14 is
configured so that the first liquid 14 with a thickness of about
0.1 mm can block light. This structure is advantageous in that the
thickness of the optical element can be reduced.
[0089] When the optical element 10 is configured so that the
refractive index of the first liquid 14 is the same as the
refractive index of the second liquid 16, generation of a lens
effect at the interface 48 can be prevented. This is advantageous
in that the operation of the diaphragm is reliably performed.
[0090] Furthermore, when the first liquid 14 is prepared by mixing
ethanol with water, the solidifying point (melting point) of the
first liquid 14 can be decreased, and thus, solidification in cold
climate areas can be prevented. Accordingly, the optical element 10
can be used in cold climate areas.
[0091] The solidifying point of ethanol is -114.degree. C., and the
solidifying point of ethylene glycol is -13.degree. C. Accordingly,
the solidifying point of the first liquid 14 can be reduced to
-40.degree. C. or lower.
[0092] As described above, instead of selecting two liquids having
the same specific gravity as the first liquid 14 and the second
liquid 16, a mixture of existing three types of liquids having
different specific gravities is used as the first liquid 14.
Thereby, the specific gravity of the first liquid 14 can be changed
over a wide range, as shown in the area R of FIG. 28.
[0093] More specifically, when two types of liquids having
different specific gravities are mixed with each other, the
specific gravity of the first liquid 14 obtained by changing the
mixing ratio of the two types of liquids is changed only within the
ranges represented by straight lines joining the coordinates of the
two types of liquids, as shown in FIG. 28.
[0094] In contrast, when three types of liquids are mixed with each
other, the specific gravity of the first liquid 14 can be changed
in the large triangle area R defined by joining three coordinates
of pure water, ethanol, and ethylene glycol.
[0095] Accordingly, the specific gravity of the first liquid 14 can
be easily made equal to that of the second liquid 16, and thus, the
optical element 10 having a desired property can be readily
produced.
[0096] Furthermore, as shown in FIG. 28, when the first liquid 14
is prepared by mixing at least three types of liquids having
different specific gravities and different refractive indices, for
example, pure water, ethanol, and ethylene glycol, the specific
gravity of the first liquid 14 can be easily made equal to the
specific gravity of the second liquid 16, and in addition, the
refractive index of the first liquid 14 can be easily made equal to
the refractive index of the second liquid 16 at the same time.
Accordingly, this is advantageous in that generation of a lens
effect can be prevented.
[0097] A description has been made of a case where the first liquid
14 is prepared using pure water, ethanol, and ethylene glycol as a
plurality types of liquids. The plurality types of liquids used are
not limited to pure water, ethanol, and ethylene glycol, and
various types of existing liquids can be selected.
[0098] A description will be made with reference to FIGS. 29 and
30.
[0099] FIG. 29 is a graph showing the specific gravities and the
refractive indices of various types of liquids, and FIG. 30 is a
table showing numerical values of the specific gravities and the
refractive indices of various types of liquids used.
[0100] For example, as shown in FIG. 29, examples of liquids used
include liquids classified in group A, group B, group C, and group
D. Specific compounds of the liquids used in groups A to D are
shown in FIG. 30.
[0101] As shown in a triangle area R1 of FIG. 29, by changing the
mixing ratio of three types of liquids within the large triangle
area R1 defined by joining coordinates of a liquid selected from
group A, coordinates of a liquid selected from group B, and
coordinates of a liquid selected from group C, the specific gravity
and the refractive index can be changed.
[0102] In addition, as shown in a triangle area R2 of FIG. 29, by
changing the mixing ratio of three types of liquids within the
large triangle area R2 defined by joining coordinates of a liquid
selected from group B, coordinates of a liquid selected from group
C, and coordinates of a liquid selected from group D, the specific
gravity and the refractive index can be changed.
[0103] That is, the specific gravity and the refractive index can
be easily changed by selecting various types of existing liquids
and changing the mixing ratio of the liquids.
[0104] The number of types of liquids used as the first liquid 14
is not limited to three, and may be four or more.
[0105] A description has been made of a case where the specific
gravity of the first liquid 14 is adjusted to be equal to the
specific gravity of the second liquid 16 by mixing plurality types
of liquids having different specific gravities and different
refractive indices. Alternatively, the specific gravity of the
second liquid 16 may be adjusted to be equal to the specific
gravity of the first liquid 14 by mixing plurality types of liquids
having different specific gravities and different refractive
indices.
[0106] Furthermore, in this embodiment, a case where a single type
of silicone oil is used as the second liquid 16 has been described.
However, plurality types of silicone oil having different
properties such as the refractive index and the specific gravity
are available. Accordingly, a single type of silicone oil having a
desired property may be selected and used as the second liquid 16,
or plurality types of silicone oil having different properties may
be selected and the refractive index and the specific gravity are
adjusted to desired values by changing the mixing ratio thereof,
and the resulting mixture may then be used as the second liquid
16.
[0107] The first electrode 18 and the second electrode 20 are used
for applying an electric field to the first liquid 14 to generate
electrocapillarity in the first liquid 14.
[0108] In the basic structure, as described below, a hydrophilic
film 34 is used in order to increase the operation speed of the
diaphragm. The hydrophilic film 34 is provided at a position where
the first electrode 18 faces the first liquid 14. That is, the
first electrode 18 is provided so as to face the first liquid 14
with the hydrophilic film 34 therebetween.
[0109] The second electrode 20 is provided on the inner surface of
the second end face wall 26, the inner surface facing the
accommodating chamber 30.
[0110] In this basic structure, the first electrode 18 is provided
on the entire area of the inner surface of the first end face wall
24, and the second electrode 20 is provided on the entire area of
the inner surface of the second end face wall 26.
[0111] Each of the first electrode 18 and the second electrode 20
is composed of, for example, a light-transmissive conductive
material such as an indium tin oxide (ITO) film.
[0112] The voltage applying unit 22 is provided outside the
container 12, and the voltage output from the voltage applying unit
22 is variable. A positive voltage output terminal of the voltage
applying unit 22 is electrically connected to the first electrode
18, and a negative voltage output terminal of the voltage applying
unit 22 is electrically connected to the second electrode 20.
[0113] In this basic structure, a description will be made of a
case where electrocapillarity is generated by applying a DC voltage
to the first liquid 14. However, the voltage applied to the first
liquid 14 is not limited to a DC voltage. Any voltage such as an AC
voltage, a pulse voltage, or a voltage increasing or decreasing
stepwise may be used as long as electrocapillarity is generated in
the first liquid 14.
[0114] Furthermore, in this basic structure, an insulating film 32
is provided on the entire area on the second electrode 20 provided
on the inner surface of the second end face wall 26, the inner
surface facing the accommodating chamber 30.
[0115] The insulating film 32 is also used for generating
electrocapillarity in the first liquid 14 by applying an electric
field to the first liquid 14.
[0116] More specifically, by applying a voltage between the first
electrode 18 and the second electrode 20, for example, minus
charges are generated on the surface of the insulating film 32,
thereby applying an electric field to the first liquid 14. The
electric field (electrostatic force) acts on molecules constituting
the first liquid 14, thus generating electrocapillarity.
[0117] In this basic structure, as shown in FIG. 2, in order to
increase the operation speed of the diaphragm, a
light-transmissive, transparent hydrophilic film 34 (i.e., a film
whose wettability to the first liquid is higher than the
wettability to the second liquid according to an embodiment of the
present invention) is further provided so as to cover the entire
area on the first electrode 18 and the entire area of the side face
wall 28, as described below.
[0118] This hydrophilic film 34 is configured so that the
wettability to the first liquid 14 is higher than the wettability
to the second liquid 16. That is, the hydrophilic film 34 is
configured so that the angle of contact of the first liquid 14 to
the hydrophilic film 34 is smaller than the angle of contact of the
second liquid 16 to the hydrophilic film 34.
[0119] The hydrophilic film 34 can be formed by applying, for
example, a hydrophilic polymer or a surfactant to the inner
surfaces of the first electrode 18 and the side face wall 28.
Various types of existing materials can be used as the hydrophilic
film 34.
[0120] In this basic structure, as shown in FIG. 2, in order to
increase the operation speed of the diaphragm, a
light-transmissive, transparent water-repellent film 36 (i.e., a
film whose wettability to the second liquid is higher than the
wettability to the first liquid according to an embodiment of the
present invention) is further provided so as to cover the entire
area on the insulating film 32 provided on the second electrode 20
on the second end face wall 26, as described below.
[0121] This water-repellent film 36 is configured so that the
wettability to the second liquid 16 is higher than the wettability
to the first liquid 14. That is, the water-repellent film 36 is
configured so that the angle of contact of the second liquid 16 to
the water-repellent film 36 is smaller than the angle of contact of
the first liquid 14 to the water-repellent film 36.
[0122] The water-repellent film 36 is a film having lipophilicity.
The water-repellent film 36 can be formed by baking a material
containing silicon as a main component, or by forming a film made
of an amorphous fluorocarbon resin. Various types of existing
materials can be used as the water-repellent film 36.
[0123] In FIG. 3, illustration of the hydrophilic film 34 and the
water-repellent film 36 is omitted.
[0124] According to this basic structure, as shown in FIG. 2, the
entire area of the first liquid 14 located on the inner surface of
the first end face wall 24 on which the first liquid 14 is disposed
faces the first electrode 18 with the hydrophilic film 34
therebetween. In addition, the entire area of the second liquid 16
located on the inner surface of the second end face wall 26 on
which the second liquid 16 is disposed faces the second electrode
20 with the water-repellent film 36 and the insulating film 32
therebetween.
[0125] Accordingly, when a voltage V is applied from the voltage
applying unit 22 to the first electrode 18 and the second electrode
20, for example, minus charges are generated on the surface of the
insulating film 32. Thereby, an electric field is applied to the
first liquid 14, and the electric field (electrostatic force) acts
on molecules constituting the first liquid 14, thus generating
electrocapillarity.
[0126] Next, the operation of the optical element 10 in the basic
structure will be described.
[0127] FIGS. 4A, 4B, and 4C are cross-sectional views illustrating
an operation when voltages V1, V2, and V3 are applied between the
first electrode 18 and the second electrode 20 of the optical
element 10, respectively.
[0128] As shown in FIG. 2, in a state in which no voltage V is
applied from the voltage applying unit 22 to the first electrode 18
and the second electrode 20, the shape of the interface 48 between
the first liquid 14 and the second liquid 16 is determined by a
balance between surface tensions of the first liquid 14 and the
second liquid 16 and interfacial tension on the water-repellent
film 36.
[0129] Accordingly, as the difference between the angle of contact
of the first liquid 14 to the water-repellent film 36 and the angle
of contact of the second liquid 16 to the water-repellent film 36
increases, the second liquid 16 expands on the water-repellent film
36 more flatly. As a result, the shape of the interface 48 between
the first liquid 14 and the second liquid 16 becomes a curved
surface close to a flat surface.
[0130] The first liquid 14 is disposed so as to cover the
hydrophilic film 34 provided on the first end face wall 24 and the
hydrophilic film 34 provided on the side face wall 28.
[0131] Accordingly, a part of the first liquid 14 disposed on an
annular portion near the interface between the side face wall 28
and the second end face wall 26 directly contacts the
water-repellent film 36, but the second liquid 16 is not in contact
with the hydrophilic film 34 provided on the side face wall 28.
[0132] Therefore, the annular portion in which the first liquid 14
is in contact with the water-repellent film 36 faces the second
electrode 20, with the water-repellent film 36 and the insulating
film 32 therebetween, without interposing the second liquid 16.
[0133] In this state, the first liquid 14 is disposed so as to
extend over the entire area in a direction orthogonal to the
transmission direction of light, and thus the light transmitting in
the thickness direction of the container 12 is blocked.
[0134] Next, as shown in FIG. 4A, when a voltage V1 (>0) is
applied from the voltage applying unit 22 to the first electrode 18
and the second electrode 20, the shape of the interface 48 is
changed so as to form a curved surface (spherical surface)
projecting from the second liquid 16 toward the first liquid 14 by
electrocapillarity, and the center of the interface 48 contacts the
first end face wall 24 (hydrophilic film 34).
[0135] In this state, the first liquid 14 is not present in an area
where the interface 48 is in contact with the first end face wall
24 (hydrophilic film 34). As a result, an area 50 where only the
second liquid 16 is present is formed in the accommodating chamber
30. This area 50 forms a light transmission path 52 passing through
the first end face wall 24 and the second end face wall 26 and
extending in the thickness direction of the container 12. More
specifically, the light transmission path 52 constitutes an
aperture 52A, and the diameter of the light transmission path 52
(aperture 52A) is defined as an aperture diameter D1 of the
diaphragm.
[0136] That is, by applying an electric field to the first liquid
14, the shape of the interface between the first liquid 14 and the
second liquid 16 is changed to form the light transmission path 52
composed of a part of the second liquid 16. The center of the light
transmission path 52 is a single virtual axis passing through the
first end face wall 24, the part of the second liquid 16, and the
second end face wall 26 and extending in the thickness direction of
the container 12, i.e., in the direction in which the first end
face wall 24 and the second end face wall 26 face each other.
[0137] Next, as shown in FIG. 4B, when a voltage V2 (>V1) is
applied from the voltage applying unit 22 to the first electrode 18
and the second electrode 20, the slope of the curvature of the
convex surface (spherical surface) of the interface 48 is further
increased.
[0138] Accordingly, the diameter of the area 50 which is formed in
the accommodating chamber 30 and in which only the second liquid 16
is present is increased. Consequently, the diameter of the light
transmission path 52, i.e., the aperture diameter of the diaphragm
is increased from D1 to D2.
[0139] Next, as shown in FIG. 4C, when a voltage V3 (>V2) is
applied from the voltage applying unit 22 to the first electrode 18
and the second electrode 20, the slope of the curvature of the
convex surface (spherical surface) of the interface 48 is further
increased.
[0140] Accordingly, the diameter of the area 50 which is formed in
the accommodating chamber 30 and in which only the second liquid 16
is present is further increased. Consequently, the diameter of the
light transmission path 52, i.e., the aperture diameter of the
diaphragm is increased to the maximum diameter of D3 (>D2).
[0141] Accordingly, by adjusting the voltage applied from the
voltage applying unit 22 to the first electrode 18 and the second
electrode 20, the diameter of the area 50 in which only the second
liquid 16 is present is increased or decreased to adjust the
aperture diameter of the diaphragm.
[0142] In FIGS. 4A, 4B, and 4C, .theta.1, .theta.2, and .theta.3
each represent the angle of contact of the first liquid 14. As the
electric field applied to the first liquid 14 increases, the angle
of contact decreases, i.e., .theta.1>.theta.2>.theta.3, and
the wettability of the first liquid 14 increases.
[0143] The hydrophilic film 34 and the water-repellent film 36 may
be omitted. However, it is preferable that the hydrophilic film 34
and the water-repellent film 36 are provided from the standpoint of
ensuring the performance of the optical element 10 because the
presence of the hydrophilic film 34 and the water-repellent film 36
provides the following advantages.
[0144] When a light-transmissive, transparent hydrophilic film 34
is provided so as to cover the entire area of the first electrode
18 and the entire area of the inner surface of the side face wall
28, the first liquid 14 is satisfactorily wetted with the
hydrophilic film 34. Accordingly, when the second liquid 16 once
contacts the first end face wall 24 and is then away from the first
end face wall 24, the second liquid 16 is readily separated from
the hydrophilic film 34, thus increasing the operation speed of the
diaphragm.
[0145] When a light-transmissive, transparent water-repellent film
36 is provided so as to cover the entire area of the insulating
film 32 provided on the second electrode 20 on the second end face
wall 26, the liquid surface of the first liquid 14 can smoothly
move on the water-repellent film 36, thus increasing the operation
speed of the diaphragm.
[0146] Next, a change in the shape of the interface 48 of the first
liquid 14 and the second liquid 16 will be described in detail.
[0147] When a voltage V is applied between the first electrode 18
and the second electrode 20 and an angle formed by the interface 48
between the first liquid 14 and the second liquid 16 is defined as
the angle of contact .theta., as shown in FIGS. 4A to 4C, the angle
of contact .theta. is represented by formula (1):
cos .theta.(V)=cos .theta.(V=0)+.di-elect cons.0.times..di-elect
cons.r.times.V2/2.gamma.t (1)
wherein cos .theta.(V) represents the angle of contact when an
applied voltage is V [V], cos .theta.(V=0) represents the angle of
contact when no voltage is applied, .di-elect cons.0 represents the
dielectric constant in vacuum of 8.85.times.10.sup.-12 [F/m],
.di-elect cons.r represents the relative dielectric constant of the
insulating film 32, V represents the applied voltage [V], t
represents the thickness [m] of the insulating film 32, and .gamma.
represents interfacial tension (or interfacial energy) [N/m]
between the first liquid 14 and the second liquid 16.
[0148] More specifically, the angle of contact .theta. is increased
or decreased (the wettability of the first liquid 14 is changed) by
increasing or decreasing the voltage V, thereby changing a force
for pushing the second liquid 16 by the first liquid 14. As a
result, the shape of the interface 48 is changed.
[0149] The optical element 10 is used in an imaging optical system
of an image-pickup apparatus such as a digital still camera, a
video camera, or the like.
[0150] FIG. 5 is a schematic view showing an example in which the
optical element 10 is applied to an imaging optical system of an
image-pickup apparatus.
[0151] As shown in FIG. 5, an image-pickup apparatus 100 includes
an image-pickup device 102 for capturing an image of an object, and
an imaging optical system 104 for leading the image of the object
to the image-pickup device 102.
[0152] On an optical axis L of the imaging optical system 104, from
the object to the image-pickup device 102, a first lens unit 106, a
second lens unit 108, a third lens unit 110, a fourth lens unit
112, and a filter unit 114 are arranged in that order.
[0153] In this example, the first lens unit 106 and the third lens
unit 110 are provided so as not to be movable in the optical axis
direction. The second lens unit 108 is provided as a zoom lens so
as to be movable in the optical axis direction. The fourth lens
unit 112 is provided as a focus lens so as to be movable in the
optical axis direction.
[0154] A beam of light from the object led by the first lens unit
106 is converted to a parallel beam of light by the second lens
unit 108. The parallel beam of light is led to the third lens unit
110 and converged on an image-pickup surface 102A of the
image-pickup device 102 through the fourth lens unit 112 and the
filter unit 114.
[0155] The optical element 10 is arranged at a position between the
second lens unit 108 and the third lens unit 110, through which the
parallel beam of light passes, so that the position of a virtual
axis 38 corresponds to the optical axis L of the imaging optical
system 104.
[0156] Accordingly, by expanding or contracting the light
transmission path 52 (aperture 52A) of the optical element 10, the
amount of beam of light led to the image-pickup surface 102A is
increased or decreased.
[0157] In the above-described basic structure of the optical
element 10, in addition to the first electrode 18 and the second
electrode 20, for example, the insulating film 32 for providing the
first liquid 14 with an electric field, and the hydrophilic film 34
and the water-repellent film 36 for increasing the moving speed of
the interface 48 between the first liquid 14 and the second liquid
16 are provided on the first end face wall 24 and the second end
face wall 26 through which light is transmitted. Therefore, this
basic structure is disadvantageous from the standpoint that
transparency of the optical element 10 is improved.
[0158] Consequently, in the first embodiment, transparency of the
optical element 10 is improved by forming an opening through the
first electrode 18, the second electrode 20, the insulating film
32, and the water-repellent film 36.
[0159] The first electrode 18, the second electrode 20, the
insulating film 32, and the water-repellent film 36, which include
a feature of an embodiment of the present invention will now be
described in detail.
[0160] FIG. 6 is a longitudinal cross-sectional view showing the
structure of an optical element 10 according to the first
embodiment.
[0161] In embodiments described below, the same portions and
components as the above-described basic structure are assigned the
same reference numerals, and a description thereof is omitted.
[0162] The optical element 10 of the first embodiment is the same
as the optical element having the above-described basic structure
except for the first electrode 18, the second electrode 20, the
insulating film 32, and the water-repellent film 36.
[0163] As shown in FIG. 6, when the optical element 10 is viewed
from the thickness direction of the container 12, a first electrode
opening 40 is provided in the first electrode 18, a second
electrode opening 42 is provided in the second electrode 20, an
insulating film opening 44 is provided in the insulating film 32,
and a water-repellent film opening 46 is provided in the
water-repellent film 36.
[0164] It is sufficient that the first electrode opening 40 is
formed so as to have a size with which an electric field can be
applied to the first liquid 14 using the first electrode 18.
Accordingly, the first electrode opening 40 has a diameter the same
as or larger than the maximum diameter Dmax of the transmission
path 52, the center of which is a virtual axis 38.
[0165] The first electrode 18 is provided over the entire area on
the inner surface of the first end face wall 24 except for the
first electrode opening 40.
[0166] It is sufficient that the second electrode opening 42 and
the insulating film opening 44 are formed so as to have sizes with
which an electric field can be applied to the first liquid 14 using
the second electrode 20 and the insulating film 32. Accordingly,
the second electrode opening 42 and the insulating film opening 44
are formed so as to have the same diameter as the maximum diameter
Dmax of the transmission path 52, the center of which is the
virtual axis 38.
[0167] Here, when both the second electrode opening 42 and the
insulating film opening 44 are formed, and the size of the second
electrode opening 42 is the same as the maximum diameter Dmax of
the transmission path 52, the insulating film opening 44 is formed
so as to have a size the same as or smaller than the second
electrode opening 42.
[0168] That is, in a state where the second electrode opening 42
has the maximum diameter Dmax of the transmission path 52, if the
first liquid 14 contacts the second electrode 20 through the second
electrode opening 42, the first electrode 18 and the second
electrode 20 are short-circuited via the first liquid 14. For this
reason, in order to insulate the first liquid 14 from the second
electrode 20 with the insulating film 32 therebetween even in the
case of the maximum diameter Dmax of the transmission path 52, the
insulating film opening 44 is formed so as to have a size the same
as or smaller than the second electrode opening 42.
[0169] It is sufficient that the water-repellent film opening 46 is
formed so as to have a size in which the first liquid 14 can
contact the water-repellent film 36. Accordingly, the
water-repellent film opening 46 is formed so as to have the same
diameter as the maximum diameter Dmax of the transmission path 52,
the center of which is the virtual axis 38.
[0170] Next, the operation and advantages of the optical element 10
will be described with reference to FIGS. 4A, 4B, and 4C again.
[0171] When a voltage is applied from the voltage applying unit 22
to the first electrode 18 and the second electrode 20 to change the
shape of the interface 48, thereby expanding or contracting the
aperture diameter, the diameter of the transmission path 52 formed
by a portion of the second liquid 16 also increases or decreases in
the range of D1 to Dmax.
[0172] In this case, regardless of the size of the diameter of the
transmission path 52, light incident from the incident surface of
the optical element 10 passes through the first end face wall 24,
and then passes through the first electrode opening 40, the portion
of the second liquid 16, the water-repellent film opening 46, the
insulating film opening 44, the second electrode opening 42, and
the second end face wall 26 in that order.
[0173] Accordingly, in terms of the structure, the above-described
optical element having the basic structure is disadvantageous in
that transparency of the optical element decreases because light
passes through four portions of the first electrode 18, the
water-repellent film 36, the insulating film 32, and the second
electrode 20. In contrast, in this embodiment, light passes through
the optical element without passing through the four portions of
the first electrode 18, the water-repellent film 36, the insulating
film 32, and the second electrode 20. Accordingly, this optical
element is advantageous in the improvement of transparency. It is
expected that the transmittance of the optical element 10 of this
embodiment can be improved by 3% to 10% relative to that of the
optical element having the basic structure.
[0174] In this embodiment, a description has been made of a
structure in which four openings of the first electrode opening 40,
the water-repellent film opening 46, the insulating film opening
44, and the second electrode opening 42 are provided.
Alternatively, among the following four types of structures, one
structure may be selected or two or more structures may be
combined. However, the combination of (3) and (4) is excluded.
(1) The first electrode opening 40 is provided. (2) The
water-repellent film opening 46 is provided. (3) Both the
insulating film opening 44 and the second electrode opening 42 are
provided. (4) The second electrode opening 42 is provided.
[0175] However, as in this embodiment, the structure including four
openings of the first electrode opening 40, the water-repellent
film opening 46, the insulating film opening 44, and the second
electrode opening 42 is the most advantageous from the standpoint
of improving the transparency (transmittance) of the optical
element 10.
[0176] In this embodiment, a description has been made of a case
where the diameter of the second electrode opening 42 and the
diameter of the insulating film opening 44 are the same as the
maximum diameter Dmax of the transmission path 52. However, it is
sufficient that the second electrode opening 42 and the insulating
film opening 44 are formed so as to have sizes with which an
electric field can be applied to the first liquid 14 using the
second electrode 20 and the insulating film 32. Accordingly, the
diameter of the second electrode opening 42 and the diameter of the
insulating film opening 44 may be smaller than the maximum diameter
Dmax. However, as in this embodiment, when the diameter of the
second electrode opening 42 and the diameter of the insulating film
opening 44 are the same as the maximum diameter Dmax of the
transmission path 52, this structure is more advantageous in that
transparency of the optical element 10 is ensured.
[0177] Furthermore, in this embodiment, a description has been made
of a case where the diameter of the water-repellent film opening 46
is the same as the maximum diameter Dmax of the transmission path
52. However, it is sufficient that the water-repellent film opening
46 is formed so as to have a size with which the first liquid 14
contacts the water-repellent film 36. Accordingly, the diameter of
the water-repellent film opening 46 may be smaller than the maximum
diameter Dmax. However, as in this embodiment, when the diameter of
the water-repellent film opening 46 is same as the maximum diameter
Dmax of the transmission path 52, this structure is more
advantageous in that transparency of the optical element 10 is
ensured.
[0178] In addition, in this embodiment, a case where the
water-repellent film 36 is provided has been described.
Alternatively, the water-repellent film 36 may be omitted. However,
the formation of the water-repellent film 36 is advantageous in
that the operation speed of the diaphragm is increased.
Second Embodiment
[0179] Next, a second embodiment will be described.
[0180] FIG. 7 is a longitudinal cross-sectional view showing the
basic structure of an optical element 10 according to the second
embodiment.
[0181] The second embodiment differs from the first embodiment and
third to tenth embodiments in that the optical element 10
constitutes a lens.
[0182] The basic structure of the optical element 10 of the second
embodiment is substantially the same as the first embodiment except
that the compositions of the first liquid 14 and the second liquid
16 are different from those in the first embodiment. Therefore,
structures different from the first embodiment will be mainly
described below.
[0183] In the optical element 10, an interface 48 between the first
liquid 14 and the second liquid 16 is changed by applying a voltage
with a voltage applying unit 22. Thereby, the interface 48 which
has a curved surface and the center of which is a single virtual
axis 38 passing through a first end face wall 24 and a second end
face wall 26 and extending in the thickness direction of a
container 12, which is a direction in which the first end face wall
24 and the second end face wall 26 face each other, is formed to
refract light traveling in the direction of the virtual axis 38 and
passing through the interface 48.
[0184] As in the first embodiment, the optical element 10 includes
the container 12, the first liquid 14, the second liquid 16, a
first electrode 18, a second electrode 20, and the voltage applying
unit 22.
[0185] The first liquid 14 has polarity or electrical conductivity
and is enclosed in an accommodating chamber 30.
[0186] The second liquid 16 is immiscible with the first liquid 14
and is enclosed in the accommodating chamber 30.
[0187] The first liquid 14 and the second liquid 16 are transparent
and have specific gravities substantially the same as each
other.
[0188] The refractive index of the second liquid 16 is different
from the refractive index of the first liquid 14. In this
embodiment, the optical element 10 is configured so that the
refractive index of the second liquid 16 is higher than the
refractive index of the first liquid 14.
[0189] Alternatively, the optical element 10 of this embodiment is
configured so that the Abbe number of the second liquid 16 is
different from the Abbe number of the first liquid 14.
[0190] Alternatively, the optical element 10 of this embodiment is
configured so that the refractive index of the second liquid 16 is
different from the refractive index of the first liquid 14, and in
addition, the Abbe number of the second liquid 16 is different from
the Abbe number of the first liquid 14.
[0191] Next, the operation of the optical element 10 will be
described.
[0192] FIGS. 8A, 8B, and 8C are cross-sectional views illustrating
an operation when voltages V1, V2, and V3 are applied between the
first electrode 18 and the second electrode 20 of the optical
element 10, respectively.
[0193] As shown in FIG. 7, in a state in which no voltage V is
applied from the voltage applying unit 22 to the first electrode 18
and the second electrode 20, the shape of the interface 48 between
the first liquid 14 and the second liquid 16 is determined by a
balance between surface tensions of the first liquid 14 and the
second liquid 16 and interfacial tension on a water-repellent film
36. In this state, the interface 48 forms a gradual convex surface
projecting from the second liquid 16 toward the first liquid
14.
[0194] Here, since the refractive index of the second liquid 16 is
higher than the refractive index of the first liquid 14, light
passing through the first end face wall 24 and the second end face
wall 26, traveling in the thickness direction of the container 12,
and passing through the interface 48 is refracted at the interface
48. Accordingly, the optical element 10 constitutes a lens having a
power for converging light.
[0195] Here, when the optical element 10 is viewed from the
thickness direction of the container 12, the diameter of the
interface 48, the center of which is the virtual axis 38 is a
maximum diameter DLmax.
[0196] Next, as shown in FIG. 8A, when a voltage V1 (>0) is
applied from the voltage applying unit 22 to the first electrode 18
and the second electrode 20, the slope of the curvature of the
convex surface (spherical surface) of the interface 48 is increased
by electrocapillarity.
[0197] Here, when the optical element 10 is viewed from the
thickness direction of the container 12, the diameter DL1 of the
interface 48, the center of which is the virtual axis 38, is
smaller than the maximum diameter DLmax (DL1<DLmax).
[0198] Next, as shown in FIG. 8B, when a voltage V2 (>V1) is
applied from the voltage applying unit 22 to the first electrode 18
and the second electrode 20, the slope of the curvature of the
convex surface (spherical surface) of the interface 48 is further
increased.
[0199] Here, when the optical element 10 is viewed from the
thickness direction of the container 12, the diameter DL2 of the
interface 48, the center of which is the virtual axis 38, is
smaller than DL1 (DL2<DL1).
[0200] Next, as shown in FIG. 8C, when a voltage V3 (>V2) is
applied from the voltage applying unit 22 to the first electrode 18
and the second electrode 20, the slope of the curvature of the
convex surface (spherical surface) of the interface 48 is further
increased and becomes the maximum slope.
[0201] Here, when the optical element 10 is viewed from the
thickness direction of the container 12, the diameter DL3 of the
interface 48, the center of which is the virtual axis 38, is
smaller than DL2 (DL3<DL2).
[0202] Accordingly, by adjusting the voltage applied from the
voltage applying unit 22 to the first electrode 18 and the second
electrode 20, the curvature of the interface 48 is changed, and
thus the focal length of the lens can be changed (the power of the
lens can be changed).
[0203] In addition, by adjusting the voltage applied from the
voltage applying unit 22 to the first electrode 18 and the second
electrode 20, when the optical element 10 is viewed from the
thickness direction of the container 12, the diameter of the
interface 48, the center of which is the virtual axis 38, is
increased or decreased in the range of DL3 to the maximum diameter
DLmax.
[0204] As described above, as in the first embodiment, the optical
element 10 constituting a lens can be used in an imaging optical
system of an image-pickup apparatus such as a digital still camera,
a video camera, or the like.
[0205] Next, the first electrode 18, the second electrode 20, an
insulating film 32, and the water-repellent film 36, which include
a feature of this embodiment will be described in detail.
[0206] FIG. 9 is a longitudinal cross-sectional view showing the
structure of the optical element 10 according to the second
embodiment.
[0207] As shown in FIG. 9, when the optical element 10 is viewed
from the thickness direction of the container 12, a first electrode
opening 40 is provided in the first electrode 18, a second
electrode opening 42 is provided in the second electrode 20, an
insulating film opening 44 is provided in the insulating film 32,
and a water-repellent film opening 46 is provided in the
water-repellent film 36.
[0208] It is sufficient that the first electrode opening 40 is
formed so as to have a size with which an electric field can be
applied to the first liquid 14 using the first electrode 18.
Accordingly, the first electrode opening 40 has a diameter the same
as or larger than the maximum diameter DLmax of the interface 48,
the center of which is a virtual axis 38.
[0209] The first electrode 18 is provided on the entire area of the
inner surface of the first end face wall 24 except for the first
electrode opening 40.
[0210] It is sufficient that the second electrode opening 42 and
the insulating film opening 44 are formed so as to have sizes with
which an electric field can be applied to the first liquid 14 using
the second electrode 20 and the insulating film 32. Accordingly,
the second electrode opening 42 and the insulating film opening 44
are formed so as to have the same diameter as the maximum diameter
DLmax of the interface 48, the center of which is the virtual axis
38.
[0211] Here, when both the second electrode opening 42 and the
insulating film opening 44 are formed, and the size of the second
electrode opening 42 is the same as the maximum diameter DLmax of
the interface 48, the insulating film opening 44 is formed so as to
have a size the same as or smaller than the second electrode
opening 42.
[0212] That is, in a state where the interface 48 has the maximum
diameter DLmax, if the first liquid 14 contacts the second
electrode 20 through the second electrode opening 42, the first
electrode 18 and the second electrode 20 are short-circuited via
the first liquid 14. For this reason, in order to insulate the
first liquid 14 from the second electrode 20 with the insulating
film 32 therebetween even in the case where the interface 48 has
the maximum diameter DLmax, the insulating film opening 44 is
formed so as to have a size the same as or smaller than the second
electrode opening 42.
[0213] It is sufficient that the water-repellent film opening 46 is
formed so as to have a size with which the first liquid 14 can
contact the water-repellent film 36. Accordingly, the
water-repellent film opening 46 is formed so as to have the same
diameter as the maximum diameter DLmax of the interface 48, the
center of which is the virtual axis 38.
[0214] Next, the operation and advantages of the optical element 10
will be described with reference to FIG. 7 and FIGS. 8A, 8B, and 8C
again.
[0215] When the shape of the interface 48 is changed by applying a
voltage from the voltage applying unit 22 to the first electrode 18
and the second electrode 20 from a state where no voltage is
applied, the diameter of the interface 48 also increases or
decreases in the range of DLmax to DL3.
[0216] In this case, regardless of an increase or decrease in the
diameter of the interface 48, among light components incident from
the incident surface of the optical element 10, light components
passing through the interface 48 pass through the first end face
wall 24, and then pass through the first electrode opening 40, the
portion of the second liquid 16, the water-repellent film opening
46, the insulating film opening 44, the second electrode opening
42, and the second end face wall 26 in that order.
[0217] Accordingly, in terms of the structure, the above-described
optical element having the basic structure is disadvantageous in
that transparency of the optical element decreases because light
passes through four portions of the first electrode 18, the
water-repellent film 36, the insulating film 32, and the second
electrode 20. In contrast, in this embodiment, light passes through
the optical element without passing through the four portions of
first electrode 18, the water-repellent film 36, the insulating
film 32, and the second electrode 20. Accordingly, this optical
element is advantageous in the improvement of transparency. It is
expected that the transmittance of the optical element 10 of this
embodiment can be improved by 3% to 10% relative to that of the
optical element having the basic structure.
[0218] In this embodiment, a description has been made of a
structure in which four openings of the first electrode opening 40,
the water-repellent film opening 46, the insulating film opening
44, and the second electrode opening 42 are provided.
Alternatively, among the following four types of structures, one
structure may be selected or two or more structures may be
combined. However, the combination of (3) and (4) is excluded.
(1) The first electrode opening 40 is provided. (2) The
water-repellent film opening 46 is provided. (3) Both the
insulating film opening 44 and the second electrode opening 42 are
provided. (4) The second electrode opening 42 is provided.
[0219] However, as in this embodiment, the structure including four
openings of the first electrode opening 40, the water-repellent
film opening 46, the insulating film opening 44, and the second
electrode opening 42 is the most advantageous from the standpoint
of improving the transparency (transmittance) of the optical
element 10.
[0220] In this embodiment, a description has been made of a case
where the diameter of the second electrode opening 42 and the
diameter of the insulating film opening 44 are the same as the
maximum diameter DLmax of the interface 48. However, it is
sufficient that the second electrode opening 42 and the insulating
film opening 44 are formed so as to have sizes with which an
electric field can be applied to the first liquid 14 using the
second electrode 20 and the insulating film 32. Accordingly, the
diameter of the second electrode opening 42 and the diameter of the
insulating film opening 44 may be smaller than the maximum diameter
DLmax. However, as in this embodiment, when the diameter of the
second electrode opening 42 and the diameter of the insulating film
opening 44 are the same as the maximum diameter DLmax of the
interface 48, this structure is more advantageous in that
transparency of the optical element 10 is ensured.
[0221] Furthermore, in this embodiment, a description has been made
of a case where the diameter of the water-repellent film opening 46
is the same as the maximum diameter DLmax of the interface 48.
However, it is sufficient that the water-repellent film opening 46
is formed so as to have a size with which the first liquid 14
contacts the water-repellent film 36. Accordingly, the diameter of
the water-repellent film opening 46 may be smaller than the maximum
diameter DLmax. However, as in this embodiment, when the diameter
of the water-repellent film opening 46 is same as the maximum
diameter DLmax of the interface 48, this structure is more
advantageous in that transparency of the optical element 10 is
ensured.
[0222] In addition, in this embodiment, a case where the
water-repellent film 36 is provided has been described.
Alternatively, the water-repellent film 36 may be omitted. However,
the formation of the water-repellent film 36 is advantageous in
that the operation speed of the lens is increased.
Third Embodiment
[0223] Next, a third embodiment will be described.
[0224] The third embodiment is a modification of the first
embodiment. The shape of a second electrode 20 of the third
embodiment differs from the shape of the second electrode 20 of the
first embodiment.
[0225] FIG. 10 is a plan view of the second electrode 20 of an
optical element 10 according to the third embodiment.
[0226] As shown in FIG. 10, a second electrode opening 42 includes
a circular portion 60, the center of which is a virtual axis 38,
and a plurality of projecting portions 62 projecting from portions
disposed on the outer circumference of the circular portion 60 at
intervals in the circumferential direction toward the outside in
the radial direction.
[0227] Each of the projecting portions 62 has a width in a
direction orthogonal to the direction in which the projecting
portions 62 project, and is configured so that the width tapers as
the projecting portions 62 extend toward the outside in the radial
direction.
[0228] That is, the second electrode 20 is composed of a plurality
of electrode portions 64 which extend in the radial direction and
the center of which is a single virtual axis 38 extending in the
thickness direction of a container 12.
[0229] In this embodiment, the second electrode 20 is composed of
four electrode portions 64 having the same shape and the same size,
and portions 6402 disposed outside of the electrode portions 64 are
connected to each other. Accordingly, a voltage is uniformly
applied throughout the second electrode 20 by the voltage applying
unit 22, that is, the same voltage is applied to each of the
electrode portions 64.
[0230] Each of the projecting portions 62 is disposed between
electrode portions 64 adjacent to each other in the circumferential
direction around the virtual axis 38, and each of the projecting
portions 62 constitutes a first non-electrode portion 66 in which
the electrode portion 64 is not formed.
[0231] In this embodiment, four first non-electrode portions 66
having the same shape and the same size are provided.
[0232] Each of the electrode portions 64 and each of the first
non-electrode portions 66 have a width in the circumferential
direction of the virtual axis 38. Each of the electrode portions 64
is formed so that the width of the electrode portion 64 diverges
toward the outside in the radial direction of a circle, the center
of which is the virtual axis 38. Each of the first non-electrode
portions 66 is formed so that the width of the first non-electrode
portion 66 tapers toward the outside in the radial direction.
[0233] In addition, on a single circumference, the center of which
is the virtual axis 38, the width of each of the electrode portions
64 is larger than the width of the first non-electrode portion
66.
[0234] In this embodiment, each of the electrode portions 64
extends in the form of a fan shape to the outside in the radial
direction with respect to the virtual axis 38 functioning as the
center. Each of the first non-electrode portions 66 extends in the
form of an isosceles triangle so that the width of the first
non-electrode portion 66 tapers toward the outside in the radial
direction. The end of each of the first non-electrode portions 66
is located on a single virtual circle, the center of which is the
virtual axis 38.
[0235] Furthermore, in this embodiment, the circular portion 60 is
located in a substantially circular area, the center of which is
the virtual axis 38, and the circular portion 60 constitutes a
second non-electrode portion 68 in which the electrode portion 64
is not formed.
[0236] Each of the electrode portions 64 is provided outside in the
radial direction of the second non-electrode portion 68. The inner
peripheral portion of the radial direction of each of the electrode
portions 64 extends on a single virtual circle, the center of which
is the virtual axis 38.
[0237] The first non-electrode portions 66 are provided so as to
project from portions disposed on the outer circumference of the
second non-electrode portion 68 at intervals in the circumferential
direction toward the outside in the radial direction of the second
non-electrode portion 68. Each of the first non-electrode portions
66 is connected to the outer circumference of the second
non-electrode portion 68.
[0238] Accordingly, a circular-arc portion 70 is formed at the
boundary between the inner circumference of each of the electrode
portions 64 and the outer circumference of the second non-electrode
portion 68.
[0239] Next, a change in the shape of the interface 48 between the
first liquid 14 and the second liquid 16 will be described with
reference to FIGS. 4A to 4C again.
[0240] First, as shown in FIG. 4A, a description will be made of a
case where a voltage V1 (>0) is applied from the voltage
applying unit 22 to the first electrode 18 and the second electrode
20.
[0241] FIG. 11 is a plan view of FIG. 4A. In FIG. 11, the one-dot
chain line indicates an interface 48a on the first end face wall
24, and the two-dot chain line indicates an interface 48b on the
second end face wall 26.
[0242] FIG. 12 is a schematic perspective view showing the shape of
the second liquid 16 in FIG. 4A.
[0243] As shown in FIGS. 11 and 12, on the first end face wall 24,
the interface 48a has a substantially circular shape, the center of
which is the virtual axis 38.
[0244] On the second end face wall 26, the interface 48b is
composed of four arcuate portions 48b1 and four protruding portions
48b2. The arcuate portions 48b1 extend on a circumference disposed
outside in the radial direction of the second non-electrode portion
68, the center of which is the virtual axis 38. Each of the
protruding portions 48b2 connects adjacent arcuate portions 48b1
and protrudes from the circumference formed by the arcuate portions
48b1 to the outside in the radial direction.
[0245] Next, as shown in FIG. 4B, a detailed description will be
made of a case where a voltage V2 (>V1) is applied from the
voltage applying unit 22 to the first electrode 18 and the second
electrode 20.
[0246] FIG. 13 is a schematic perspective view showing the shape of
the second liquid 16 in FIG. 4B.
[0247] As shown in FIG. 13, the second liquid 16 is pushed by the
first liquid 14. As a result, the diameter of the interface 48a on
the first end face wall 24 is increased, and the interface 48b on
the second end face wall 26 is receded to a position near the
outline of the first non-electrode portions 66 and the second
non-electrode portion 68.
[0248] Next, as shown in FIG. 4C, a detailed description will be
made of a case where a voltage V3 (>V2) is applied from the
voltage applying unit 22 to the first electrode 18 and the second
electrode 20.
[0249] FIG. 14 is a plan view of FIG. 4C.
[0250] As shown in FIG. 14, the second liquid 16 is further pushed
by the first liquid 14. As a result, the diameter of the interface
48a on the first end face wall 24 is increased to the maximum
diameter, and the interface 48b on the second end face wall 26 is
receded to a position corresponding to the outline of the first
non-electrode portions 66 and the second non-electrode portion
68.
[0251] In this case, on the second end face wall 26, the second
liquid 16 extends on the entire area of the first non-electrode
portions 66 and the second non-electrode portion 68.
[0252] Accordingly, four arms composed of the second liquid 16
project from the outer circumference of a portion of the second
liquid 16 located on the second non-electrode portion 68 to the
outside in the radial direction of the second non-electrode portion
68 along each of the first non-electrode portions 66. Therefore,
the shape of the outer periphery of the central portion (the
portion located on the second electrode opening 42) of the second
liquid 16 is changed by being pulled by the four arm portions.
[0253] As a result, the shape of the interface 48a on the first end
face wall 24 becomes a substantially rectangular shape in which
four corners are located on the first non-electrode portions
66.
[0254] As described above, the angle of contact (the wettability)
of the first liquid 14 is changed by a voltage applied to the first
liquid 14. As a result, the first liquid 14 moves to push the
second liquid 16. Accordingly, on the second end face wall 26, the
interface 48 moves only on the electrode portions 64 to which the
voltage is applied, and does not move on the first non-electrode
portions 66 or the second non-electrode portion 68 to which no
voltage is applied.
[0255] That is, on the second end face wall 26, the second liquid
16 is constantly disposed on the first non-electrode portions 66
and the second non-electrode portion 68. In addition, as the first
liquid 14 moves toward the outside in the radial direction of the
second non-electrode portion 68, the second liquid 16 moves so as
to extend from the first non-electrode portions 66 and the second
non-electrode portion 68 to the electrode portions 64.
[0256] As described above, by increasing or decreasing the voltage
applied between the first electrode 18 and the second electrode 20
in the range of V1 to V3, the shape of the interface 48 is changed
and the aperture diameter is changed from D1 to D3. In this case,
regardless of the change in the voltage applied between the first
electrode 18 and the second electrode 20, the center of the light
transmission path 52 (aperture 52A) shown in FIGS. 4A to 4C
constantly corresponds to the virtual axis 38. Even if the center
of the light transmission path 52 deviates from the virtual axis 38
and decentering occurs, the position of the center of the light
transmission path 52 is automatically recovered so as to correspond
to the position of the virtual axis 38. This phenomenon will now be
described in detail.
[0257] FIG. 15 is a view illustrating a state in which the center
of the light transmission path 52 corresponds to the virtual axis
38. FIG. 16 is a view illustrating a state in which the center of
the light transmission path 52 deviates from the virtual axis 38
and becomes decentered. FIG. 17 is a perspective view of FIG.
16.
[0258] In FIGS. 15, 16, and 17, for convenience of explanation,
four quadrants separated by two coordinate axes which are
orthogonal to the virtual axis 38 on the insulating film 32, which
is orthogonal to the virtual axis 38, and which are orthogonal to
each other are defined as a first quadrant A, a second quadrant B,
a third quadrant C, and a fourth quadrant D.
[0259] The electrode portions 64 are disposed on the first quadrant
A, the second quadrant B, the third quadrant C, and the fourth
quadrant D.
[0260] As shown in FIG. 15, in a state where decentering does not
occur in the light transmission path 52 (see FIGS. 4A to 4C), the
areas of the first liquid 14 located on the electrode portions 64
are equal to each other, and the areas of the second liquid 16
located on the electrode portions 64 are equal to each other. That
is, the lengths of the interface 48b1 between the first liquid 14
and the second liquid 16 located on the electrode portions 64 are
equal to each other.
[0261] In contrast, as shown in FIGS. 16 and 17, for example, when
the second liquid 16 moves in the direction of the second quadrant
B and decentering occurs in the light transmission path 52, the
length of the interface 48b1 located on the electrode portion 64 of
the second quadrant B is not equal to the length of the interface
48b1 located on the electrode portion 64 of the fourth quadrant
D.
[0262] More specifically, the length of the interface 48b1 located
on the electrode portion 64 of the second quadrant B is longer than
the length of the interface 48b1 located on the electrode portion
64 of the fourth quadrant D.
[0263] The reason for this is as follows. Each of the electrode
portions 64 and each of the first non-electrode portions 66 have a
width in the circumferential direction of the virtual axis 38. Each
of the electrode portions 64 is formed so that the width thereof
diverges toward the outside in the radial direction of a circle,
the center of which is the virtual axis 38. Each of the first
non-electrode portions 66 is formed so that the width thereof
tapers toward the outside in the radial direction of the
circle.
[0264] Accordingly, when the voltage applied to each of the
electrode portions 64 is uniform (when the electric potential is
uniform), a force per unit length with which the first liquid 14
pushes the second liquid 16 is uniform in each of the quadrants.
However, since the length of the interface 48b1 located on the
electrode portion 64 in the second quadrant B is long, the force
for pushing the second liquid 16 increases in proportion to the
length of the interface 48b1. Consequently, the force for pushing
the second liquid 16 in the second quadrant B acts stronger than
that in the fourth quadrant D.
[0265] Therefore, since the length of the interface 48b1 located on
the electrode portion 64 of the second quadrant B is longer than
the length of the interface 48b1 located on the electrode portion
64 of the fourth quadrant D, the force with which the first liquid
14 located on the second quadrant B pushes the second liquid 16
becomes larger than the force with which the first liquid 14
located on the fourth quadrant D pushes the second liquid 16.
[0266] As a result, the second liquid 16 is pushed back to a
position where a force with which the second liquid 16 is pushed by
the first liquid 14 is balanced. That is, as shown in FIG. 15, the
second liquid 16 is pushed back to a position at which the length
of the interface 48b1 in the second quadrant B is equal to the
length of the interface 48b1 in the fourth quadrant D. As a result,
the position of the center of the second liquid 16 corresponds to
the virtual axis 38. The shape of the interface 48 between the
first liquid 14 and the second liquid 16 is stabilized at this
position, and thus, decentering of the light transmission path 52
is prevented.
[0267] As shown in FIG. 13, four arms composed of the second liquid
16 project from the outer circumference of a portion of the second
liquid 16 located on the second non-electrode portion 68 to the
outside in the radial direction of the second non-electrode portion
68 along each of the first non-electrode portions 66. In other
words, the second liquid 16 collected on the first non-electrode
portions 66 forms the four arms.
[0268] Therefore, the outer circumference of the central portion
(the portion located on the second electrode opening 42) of the
second liquid 16 is in a state of being pulled by the four arm
portions. Thereby, the central portion of the second liquid 16 is
constantly urged so as to correspond to the virtual axis 38.
[0269] Accordingly, as shown in FIG. 17, when the second liquid 16
moves in the direction of the second quadrant B and the central
portion of the second liquid 16 is decentered from the virtual axis
38, the balance between the forces generated by the four arm
portions and acting on the central portion of the second liquid 16
is disrupted, and the forces generated by the four arm portions act
in a direction in which the center of the second liquid 16
corresponds to the virtual axis 38.
[0270] By this operation, the second liquid 16 is more reliably
recovered to a position at which the center of the second liquid 16
corresponds to the virtual axis 38. The shape of the interface 48
between the first liquid 14 and the second liquid 16 is further
stabilized at this position, and thus, decentering of the light
transmission path 52 can be prevented more effectively.
[0271] The above-described operation of the four arm portions to
control the central portion of the second liquid 16 can be
described, for example, as follows.
[0272] Specifically, when a drumskin is fixed on a barrel of a drum
with tension, the center of the drumskin is made to correspond to
the central axis of the barrel.
[0273] In this case, several points of the drumskin located in the
circumferential direction of the central axis of the barrel are
tentatively fixed, and the several points of the drumskin are then
pulled toward the outside of the barrel little by little. Thereby,
the center of the drumskin can be easily made to correspond to the
central axis of the barrel.
[0274] Similarly, forces oriented toward the outside in the radial
direction act on the second liquid 16 by means of the four arm
portions, and thus, the center of the second liquid 16 can be
easily made to correspond to the virtual axis 38.
[0275] In addition, when the voltage applied between the first
electrode 18 and the second electrode 20 is increased or decreased
in a state where the second liquid 16 is collected on each of the
first non-electrode portions 66, the second liquid 16 moves along
the four arm portions. Accordingly, this structure is advantageous
in that the second liquid 16 is moved uniformly and smoothly in the
circumferential direction of a circle, the center of which is the
virtual axis 38.
[0276] As described above, according to the third embodiment, in
addition to the same advantage as the first embodiment, the
following advantage can be achieved.
[0277] Each of the electrode portions 64 and each of the first
non-electrode portions 66 of the optical element 10 have a width in
the circumference direction of the virtual axis 38. Each of the
electrode portions 64 is formed so that the width of the electrode
portion 64 diverges toward the outside in the radial direction of a
circle, the center of which is the virtual axis 38. Each of the
first non-electrode portions 66 is formed so that the width of the
first non-electrode portion 66 tapers toward the outside in the
radial direction. Accordingly, although the same voltage is applied
to each of the electrode portions 64, the shape of the interface 48
between the first liquid 14 and the second liquid 16 is stabilized
at a position at which the center of the second liquid 16
corresponds to the virtual axis 38. Therefore, decentering of the
light transmission path 52 (aperture 52A) is prevented.
[0278] Accordingly, this structure is advantageous in that a
decrease in the optical property caused by aberration due to
decentering of the light transmission path 52 of the optical
element 10 or generation of shading due to nonuniformity of the
amount of ambient light is prevented.
Fourth Embodiment
[0279] A fourth embodiment differs from the third embodiment in
that a second electrode 20 includes three electrode portions 64 and
the number of the first non-electrode portions 66 is three.
[0280] Specifically, as shown in FIG. 18, the second electrode 20
is composed of the three electrode portions 64 having the same
shape and the same size, and portions 6402 disposed outside of the
electrode portions 64 are connected to each other.
[0281] First non-electrode portions 66 (projecting portions 62) in
which the electrode portions 64 are not formed are provided between
electrode portions 64 adjacent in the circumferential direction of
the virtual axis 38.
[0282] In this embodiment, three first non-electrode portions 66
having the same shape and the same size are provided.
[0283] The structure of the fourth embodiment is the same as the
third embodiment except that the second electrode 20 includes three
electrode portions 64 and the number of the first non-electrode
portions 66 is three.
[0284] The fourth embodiment having the above structure can also
achieve the same advantages as the third embodiment.
Fifth Embodiment
[0285] Next, a fifth embodiment will be described.
[0286] FIG. 19 is a plan view of a second electrode 20 of an
optical element 10 according to the fifth embodiment.
[0287] The fifth embodiment differs from the third embodiment in
that the second electrode 20 includes six electrode portions 64 and
the number of the first non-electrode portions 66 (projecting
portions 62) is six.
[0288] Specifically, as shown in FIG. 19, the second electrode 20
is composed of the six electrode portions 64 having the same shape
and the same size, and portions 6402 disposed at the outside of the
electrode portions 64 are connected to each other.
[0289] First non-electrode portions 66 (projecting portions 62) in
which the electrode portions 64 are not formed are provided between
electrode portions 64 adjacent in the circumferential direction of
the virtual axis 38.
[0290] In this embodiment, six first non-electrode portions 66
having the same shape and the same size are provided.
[0291] The structure of the fifth embodiment is the same as the
third embodiment except that the second electrode 20 includes six
electrode portions 64 and the number of the first non-electrode
portions 66 (projecting portions 62) is six.
[0292] The fifth embodiment having the above structure can also
achieve the same advantages as the third embodiment.
[0293] In the fifth embodiment, the number of the electrode
portions 64 and the number of the first non-electrode portions 66
(projecting portions 62) are larger than those in the third
embodiment. Therefore, the degree of nonuniformity of the force of
an electric field applied to the first liquid 14 in the
circumferential direction of a circle, the center of which is the
virtual axis 38, can be further reduced. Accordingly, the interface
48 between the first liquid 14 and the second liquid 16 also
becomes uniform in the circumferential direction. Accordingly, this
structure is advantageous in that the shape of the light
transmission path 52 (aperture 52A) of the optical element 10 is
closer to a circle.
Sixth Embodiment
[0294] Next, a sixth embodiment will be described.
[0295] FIG. 20 is a plan view of a second electrode 20 of an
optical element 10 according to the sixth embodiment.
[0296] The sixth embodiment differs from the third embodiment in
that the second electrode 20 includes eight electrode portions 64
and the number of the first non-electrode portions 66 (projecting
portions 62) is eight.
[0297] Specifically, as shown in FIG. 20, the second electrode 20
is composed of the eight electrode portions 64 having the same
shape and the same size, and portions 6402 disposed outside of the
electrode portions 64 are connected to each other.
[0298] First non-electrode portions 66 (projecting portions 62) in
which the electrode portions 64 are not formed are provided between
electrode portions 64 adjacent in the circumferential direction of
the virtual axis 38.
[0299] In this embodiment, eight first non-electrode portions 66
(projecting portions 62) having the same shape and the same size
are provided.
[0300] The structure of the sixth embodiment is the same as the
third embodiment except that the second electrode 20 includes eight
electrode portions 64 and the number of the first non-electrode
portions 66 (projecting portions 62) is eight.
[0301] The sixth embodiment having the above structure can also
achieve the same advantages as the third embodiment.
[0302] In the sixth embodiment, the number of the electrode
portions 64 and the number of the first non-electrode portions 66
(projecting portions 62) are larger than those in the third
embodiment. Therefore, the degree of nonuniformity of the force of
an electric field applied to the first liquid 14 in the
circumferential direction of a circle, the center of which is the
virtual axis 38, can become further reduced. Accordingly, the
interface 48 between the first liquid 14 and the second liquid 16
also becomes uniform in the circumferential direction. Accordingly,
this structure is advantageous in that the shape of the light
transmission path 52 (aperture 52A) of the optical element 10 is
closer to a circle.
Seventh Embodiment
[0303] Next, a seventh embodiment will be described.
[0304] FIG. 21 is a plan view of a second electrode 20 of an
optical element 10 according to the seventh embodiment.
[0305] In the seventh embodiment, the shape of each of the
electrode portions 64 constituting the second electrode 20 and the
shape of each of the first non-electrode portions 66 (projecting
portions 62) are different from those in the fifth embodiment.
[0306] Specifically, as shown in FIG. 19, the shape of each of the
first non-electrode portions 66 (projecting portions 62) in the
fifth embodiment is an isosceles triangle, whereas that in the
seventh embodiment is a substantially equilateral triangle.
[0307] In accordance with the shape of each of the first
non-electrode portions 66, the shape of each of the electrode
portions 64 located between adjacent first non-electrode portions
66 (projecting portions 62), i.e., the fan shape forming each of
the electrode portions 64 is also different from that in the fifth
embodiment.
[0308] The structure of the seventh embodiment is the same as the
fifth embodiment except for the shape of each of the electrode
portions 64 constituting the second electrode 20 and the shape of
each of the first non-electrode portions 66 (projecting portions
62).
[0309] The seventh embodiment having the above structure can also
achieve the same advantages as the fifth embodiment.
Eighth Embodiment
[0310] Next, an eighth embodiment will be described.
[0311] FIG. 22 is a plan view of a second electrode 20 of an
optical element 10 according to the eighth embodiment.
[0312] In the eight embodiment, the shape of an leading end (an end
located at the outside in the radial direction of a circle, the
center of which is the virtual axis 38) of each of first
non-electrode portions 66 (projecting portions 62), is different
from that in the fifth embodiment.
[0313] Specifically, as shown in FIG. 22, the leading end of each
of the electrode portions 64 has an arcuate shape so as to be
arranged on a circumference of a single circle, the center of which
is the virtual axis 38.
[0314] The structure of the eighth embodiment is the same as the
fifth embodiment except for the shape of the leading end of each of
the electrode portions 64.
[0315] The eighth embodiment having the above structure can also
achieve the same advantages as the fifth embodiment.
Ninth Embodiment
[0316] Next, a ninth embodiment will be described.
[0317] FIG. 23 is a plan view of a second electrode 20 of an
optical element 10 according to the ninth embodiment.
[0318] The ninth embodiment differs from the third embodiment in
that first non-electrode portions 66 (projecting portions 62) are
provided so as to be continuous to the outer circumference of a
second non-electrode portion 68.
[0319] More specifically, in the ninth embodiment, the circular-arc
portion 70 (see FIG. 10) is not provided at the boundary between
the inner circumference of each of the electrode portions 64 and
the outer circumference of the second non-electrode portion 68, and
the first non-electrode portions 66 (projecting portions 62) are
provided so as to be continuous to the outer circumference of the
second non-electrode portion 68. Accordingly, the inner portion of
each of the electrode portions 64 is arranged so as to have an
angle projecting toward the virtual axis 38.
[0320] Furthermore, the ninth embodiment differs from the third
embodiment in that the second electrode 20 includes five electrode
portions 64, and the number of the first non-electrode portions 66
(projecting portions 62) is five.
[0321] Other structures of the ninth embodiment are the same as the
third embodiment.
[0322] The ninth embodiment having the above structure can also
achieve the same advantages as the third embodiment.
Tenth Embodiment
[0323] Next, a tenth embodiment will be described.
[0324] FIG. 24 is a plan view of a second electrode 20 of an
optical element 10 according to the tenth embodiment.
[0325] As shown in FIG. 24, a second electrode opening 42 is
composed of a circular portion 60, the canter of which is the
virtual axis 38, and a plurality of projecting portions 62
projecting from portions disposed on the outer circumference of the
circular portion 60 at intervals in the circumferential direction
toward the outside in the radial direction.
[0326] Each of the projecting portions 62 has a uniform width in a
direction orthogonal to the direction in which the projecting
portions 62 project.
[0327] That is, the second electrode 20 is composed of a plurality
of electrode portions 64 which extend in the radial direction and
the center of which is a single virtual axis 38 extending in the
thickness direction of a container 12.
[0328] In this embodiment, the second electrode 20 is composed of
six electrode portions 64 having the same shape and the same size,
and portions 6402 disposed outside of the electrode portions 64 are
connected to each other. Accordingly, a voltage is uniformly
applied throughout the second electrode 20 by the voltage applying
unit 22, that is, the same voltage is applied to each of the
electrode portions 64.
[0329] First non-electrode portions 66 (projecting portions 62) in
which the electrode portions 64 are not formed are provided between
electrode portions 64 adjacent in the circumferential direction of
the virtual axis 38.
[0330] In this embodiment, six first-electrode portions 66
(projecting portions 62) having the same shape and the same size
are provided.
[0331] Each of the electrode portions 64 and each of the first
non-electrode portions 66 (projecting portions 62) have a width in
the circumferential direction of the virtual axis 38. Each of the
electrode portions 64 is formed so that the width of the electrode
portion 64 diverges toward the outside in the radial direction of
the circle, the center of which is the virtual axis 38. Each of the
first non-electrode portions 66 (projecting portions 62) has a
uniform width in the radial direction.
[0332] In addition, on a single circumference, the center of which
is the virtual axis 38, the width of each of the electrode portions
64 is larger than the width of the first non-electrode portion 66
(projecting portion 62).
[0333] In this embodiment, each of the electrode portions 64
extends in the form of a fan shape to the outside in the radial
direction with respect to the virtual axis 38 functioning as the
center. The end of each of the first non-electrode portions 66
(projecting portions 62) is located on a single virtual circle, the
center of which is the virtual axis 38.
[0334] Furthermore, in this embodiment, a second non-electrode
portion 68 in which the electrode portions 64 are not formed is
provided in a substantially circular area, the center of which is
the virtual axis 38.
[0335] Each of the electrode portions 64 is provided outside in the
radial direction of the second non-electrode portion 68. The inner
peripheral portion of the radial direction of each of the electrode
portions 64 extends on a single virtual circle, the center of which
is the virtual axis 38.
[0336] Each of the first non-electrode portions 66 (projecting
portions 62) is provided so as to project from a portion disposed
on the outer circumference of the second non-electrode portion 68
at intervals in the circumferential direction toward the outside in
the radial direction of the second non-electrode portion 68. Each
of the first non-electrode portions 66 (projecting portions 62) is
connected to the outer circumference of the second non-electrode
portion 68.
[0337] Accordingly, a circular-arc portion 70 is formed at the
boundary between the inner circumference of each of the electrode
portions 64 and the outer circumference of the second non-electrode
portion 68.
[0338] The tenth embodiment having the above structure can also
achieve the same advantages as the third embodiment.
Eleventh Embodiment
[0339] Next, an eleventh embodiment will be described.
[0340] FIG. 25 is a plan view of a second electrode 20 of an
optical element 10 according to the eleventh embodiment.
[0341] The eleventh embodiment is a modification of the second
embodiment. In this embodiment, an optical element 10 constitutes a
lens.
[0342] The structure of the optical element 10 of the eleventh
embodiment is substantially the same as the third embodiment except
that the compositions of a first liquid 14 and a second liquid 16
of the eleventh embodiment are different from the first liquid 14
and the second liquid 16 of the third embodiment. Therefore,
structures different from the third embodiment will be described
below.
[0343] In the optical element 10, the shape of the interface 48
between the first liquid 14 and the second liquid 16 is changed to
a curved surface by applying a voltage with a voltage applying unit
22. Consequently, light traveling in the thickness direction of a
container 12, which is a direction in which a first end face wall
24 and a second end face wall 26 face each other, and passing
through the interface 48 is refracted.
[0344] As in the third embodiment, the optical element 10 includes
the container 12, the first liquid 14, the second liquid 16, a
first electrode 18, a second electrode 20, and the voltage applying
unit 22.
[0345] The first liquid 14 has polarity or electrical conductivity
and is enclosed in an accommodating chamber 30.
[0346] The second liquid 16 is immiscible with the first liquid 14
and is enclosed in the accommodating chamber 30.
[0347] The first liquid 14 and the second liquid 16 are transparent
and have specific gravities substantially the same as each
other.
[0348] The refractive index of the second liquid 16 is different
from the refractive index of the first liquid 14. In this
embodiment, the optical element 10 is configured so that the
refractive index of the second liquid 16 is higher than the
refractive index of the first liquid 14.
[0349] Alternatively, the optical element 10 of this embodiment is
configured so that the Abbe number of the second liquid 16 is
different from the Abbe number of the first liquid 14.
[0350] Alternatively, the optical element 10 of this embodiment is
configured so that the refractive index of the second liquid 16 is
different from the refractive index of the first liquid 14, and in
addition, the Abbe number of the second liquid 16 is different from
the Abbe number of the first liquid 14.
[0351] The shape and the arrangement of the first electrode 18 and
the second electrode 20 are the same as those in the third
embodiment.
[0352] As shown in FIG. 25, a second electrode opening 42 includes
a circular portion 60, the center of which is a virtual axis 38,
and a plurality of projecting portions 62 projecting from portions
disposed on the outer circumference of the circular portion 60 at
intervals in the circumferential direction toward the outside in
the radial direction.
[0353] Each of the projecting portions 62 has a width in a
direction orthogonal to the direction in which the projecting
portions 62 project and is configured so that the width tapers as
the projecting portions 62 extend toward the outside in the radial
direction.
[0354] That is, the second electrode 20 is composed of a plurality
of electrode portions 64 which extend in the radial direction and
the center of which is a single virtual axis 38 extending in the
thickness direction of the container 12.
[0355] First non-electrode portions 66 (projecting portions 62) in
which the electrode portions 64 are not formed are provided between
electrode portions 64 adjacent in the circumferential direction of
the virtual axis 38.
[0356] In this embodiment, four first non-electrode portions 66
(projecting portions 62) having the same shape and the same size
are provided.
[0357] Each of the electrode portions 64 and each of the first
non-electrode portions 66 (projecting portions 62) have a width in
the circumferential direction of the virtual axis 38. Each of the
electrode portions 64 is formed so that the width of the electrode
portion 64 diverges toward the outside in the radial direction of a
circle, the center of which is the virtual axis 38. Each of the
first non-electrode portions 66 (projecting portions 62) is formed
so that the width of the first non-electrode portion 66 (projecting
portion 62) tapers toward the outside in the radial direction.
[0358] In addition, on a single circumference, the center of which
is the virtual axis 38, the width of each of the electrode portions
64 is larger than the width of the first non-electrode portion 66
(projecting portion 62).
[0359] In this embodiment, each of the electrode portions 64
extends in the form of a fan shape to the outside in the radial
direction with respect to the virtual axis 38 functioning as the
center. Each of the first non-electrode portions 66 (projecting
portions 62) extends in the form of an isosceles triangle so that
the width of the first non-electrode portion 66 (projecting portion
62) tapers toward the outside in the radial direction. The end of
each of the first non-electrode portions 66 (projecting portions
62) is located on a single virtual circle, the center of which is
the virtual axis 38.
[0360] In this embodiment, a second non-electrode portion 68 in
which the electrode portions 64 are not formed is located in a
substantially circular area, the center of which is the virtual
axis 38.
[0361] Each of the electrode portions 64 is provided outside in the
radial direction of the second non-electrode portion 68. The inner
peripheral portion of the radial direction of each of the electrode
portions 64 extends on a single virtual circle, the center of which
is the virtual axis 38.
[0362] The first non-electrode portions 66 (projecting portions 62)
are provided so as to project from portions disposed on the outer
circumference of the second non-electrode portion 68 at intervals
in the circumferential direction toward the outside in the radial
direction of the second non-electrode portion 68. Each of the first
non-electrode portions 66 (projecting portions 62) is connected to
the outer circumference of the second non-electrode portion 68.
[0363] Accordingly, a circular-arc portion 70 is formed at the
boundary between the inner circumference of each of the electrode
portions 64 and the outer circumference of the second non-electrode
portion 68.
[0364] As in FIG. 11 showing the third embodiment, the two-dot
chain line in FIG. 25 indicates an interface 48 (48b, 48b1, and
48b2) on the second end face wall 26.
[0365] Next, the operation of the optical element 10 will be
described with reference to FIG. 7 and FIGS. 8A, 8B, and 8C
again.
[0366] As shown in FIG. 7, in a state in which no voltage V is
applied from the voltage applying unit 22 to the first electrode 18
and the second electrode 20, the shape of the interface 48 between
the first liquid 14 and the second liquid 16 is determined by a
balance between surface tensions of the first liquid 14 and the
second liquid 16 and interfacial tension on the water-repellent
film 36. In this state, the interface 48 forms a gradual convex
surface projecting from the second liquid 16 toward the first
liquid 14.
[0367] Here, since the refractive index of the second liquid 16 is
higher than the refractive index of the first liquid 14, light
passing through the first end face wall 24 and the second end face
wall 26, traveling in the thickness direction of the container 12,
and passing through the interface 48 is refracted at the interface
48. Accordingly, the optical element 10 constitutes a lens having a
power for converging light.
[0368] Next, as shown in FIG. 8A, when a voltage V1 (>0) is
applied from the voltage applying unit 22 to the first electrode 18
and the second electrode 20, the slope of the curvature of the
convex surface (spherical surface) of the interface 48 is increased
by electrocapillarity.
[0369] Next, as shown in FIG. 8B, when a voltage V2 (>V1) is
applied from the voltage applying unit 22 to the first electrode 18
and the second electrode 20, the slope of the curvature of the
convex surface (spherical surface) of the interface 48 is further
increased.
[0370] Next, as shown in FIG. 8C, when a voltage V3 (>V2) is
applied from the voltage applying unit 22 to the first electrode 18
and the second electrode 20, the slope of the curvature of the
convex surface (spherical surface) of the interface 48 is further
increased.
[0371] Accordingly, by adjusting the voltage applied from the
voltage applying unit 22 to the first electrode 18 and the second
electrode 20, the curvature of the interface 48 is changed, and
thus the focal length of the lens can be changed (the power of the
lens can be changed).
[0372] As described above, as in the second embodiment, the optical
element 10 constituting a lens can be used in an imaging optical
system of an image-pickup apparatus such as a digital still camera,
a video camera, or the like.
[0373] As described above, according to the eleventh embodiment, in
addition to the same advantage as the second embodiment, the
following advantage can be achieved.
[0374] In the optical element 10, by increasing or decreasing the
voltage applied between the first electrode 18 and the second
electrode 20 in the range of V1 to V3, the shape of the interface
48 is changed and the focal length of the lens is changed. In this
case, regardless of the change in the voltage applied between the
first electrode 18 and the second electrode 20, the center of the
lens constantly corresponds to the virtual axis 38. Even if the
center of the lens deviates from the virtual axis 38 and
decentering occurs, the position the center of the lens is
automatically recovered so as to correspond to the position of the
virtual axis 38.
[0375] Specifically, as in the third embodiment, each of the
electrode portions 64 and each of the first non-electrode portions
66 (projecting portions 62) of the optical element 10 have a width
in the circumference direction of the virtual axis 38. Each of the
electrode portions 64 is formed so that the width of the electrode
portion 64 diverges toward the outside in the radial direction of a
circle, the center of which is the virtual axis 38. Each of the
first non-electrode portions 66 (projecting portions 62) is formed
so that the width of the first non-electrode portion 66 (projecting
portion 62) tapers toward the outside in the radial direction.
Accordingly, although the same voltage is applied to each of the
electrode portions 64, the shape of the interface 48 between the
first liquid 14 and the second liquid 16 is stabilized at a
position at which the center of the second liquid 16 corresponds to
the virtual axis 38. Therefore, decentering of the lens is
prevented.
[0376] Furthermore, as in the third embodiment, four arms composed
of the second liquid 16 project from the outer circumference of a
portion of the second liquid 16 located on the second non-electrode
portion 68 to the outside in the radial direction of the second
non-electrode portion 68 along each of the first non-electrode
portions 66 (projecting portions 62). Therefore, the outer
circumference of the central portion (the portion located on the
second electrode opening 42) of the second liquid 16 is in a state
of being pulled by the four arm portions. Thereby, the central
portion of the second liquid 16 is constantly urged so as to
correspond to the virtual axis 38. Accordingly, a force acting on
the central portion of the second liquid 16 and generated by the
four arm portions acts in a direction in which the center of the
second liquid 16 corresponds to the virtual axis 38.
[0377] By this operation, the second liquid 16 is more reliably
recovered to a position at which the center of the second liquid 16
corresponds to the virtual axis 38. The shape of the interface 48
between the first liquid 14 and the second liquid 16 is further
stabilized at this position, and thus, decentering of the lens can
be prevented more effectively.
[0378] In the eleventh embodiment, a description has been made of a
case where the second electrode 20 of the optical element 10 has
the same structure as that in the third embodiment. Alternatively,
the second electrode 20 may have the same structure as that in the
fourth embodiment to the tenth embodiment.
[0379] It should be understood by those skilled in the art that
various modifications, combinations, sub-combinations and
alterations may occur depending on design requirements and other
factors insofar as they are within the scope of the appended claims
or the equivalents thereof.
* * * * *