Optical element and imaging device

An optical element includes a first liquid; a second liquid that is immiscible with the first liquid and that has polarity or electrical conductivity; a first substrate portion; a second substrate portion; a sidewall portion; a second electrode disposed on one of the second substrate portion and the sidewall portion; and an accommodating portion constituted by the first substrate portion, the second substrate portion, and the sidewall portion and sealing the first liquid and the second liquid therein. The optical element further includes a first film disposed on the first substrate portion side of the accommodating portion and having high affinity with the first liquid, a second film disposed on the second substrate portion side of the accommodating portion and having high affinity with the second liquid, and a third film disposed at the center of the second film and having high affinity with the first liquid.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application claims priority to Japanese Priority Patent Application JP 2008-249240 filed in the Japan Patent Office on Sep. 26, 2008, the entire content of which is hereby incorporated by reference.

BACKGROUND

The present application relates to an optical element and an imaging device. More specifically, the present application relates to an optical element utilizing an electrowetting phenomenon and an imaging device including the same.

In imaging optical systems used in imaging devices such as a still camera and a video camera, it is necessary for such imaging optical systems to have functions of adjusting the focus and adjusting the amount of light, to realize natural defocusing, to make the distribution of the amount of light on an image surface to be uniform etc. Among these requirements, in general, the requirement for adjusting the amount of light is met by a mechanical aperture mechanism including a plurality of movable blades.

However, such a mechanical aperture mechanism has the following problems: A mechanical driving unit for driving the movable blades is necessary, and thus the size of the device increases. In addition, in a small aperture state in which an opening of the aperture mechanism is small, diffraction of a light beam occurs, thereby decreasing the resolution of an acquired image. Furthermore, a sound is generated during the operation of the aperture mechanism.

To solve the above problems in such a mechanical aperture mechanism, optical elements using an electrocapillarity (electrowetting phenomenon) have been proposed (refer to, for example, Japanese Unexamined Patent Application Publication No. 2000-356792 (document '792)).FIG. 18is a schematic view of an optical element disclosed in document '792. An optical element100described in document '792 is an optical element configured to control the amount of light beam30passing through the element (the amount of transmitted light).

The optical element100is configured so that a transparent substrate102and a transparent cover plate106are liquid-tightly sealed on a lower opening and an upper opening, respectively, of a cylindrical container105by adhesion or the like. A transparent electrode103, an insulating layer104, and a water-repellent film111are provided on the inner surface of the transparent substrate102in that order. A hydrophilic film113is provided on the inner surface of the transparent cover plate106. A rod-shaped electrode125is provided so as to penetrate through the container105, and an end of the rod-shaped electrode125is in contact with a first liquid121. The first liquid121and a second liquid122are hermetically sealed in a space constituted by the hydrophilic film113, the water-repellent film111, and the inner wall of the container105. The first liquid121is a liquid having electrical conductivity or polarity, and the second liquid122is a liquid that is immiscible with the first liquid121. The refractive index of the first liquid121is substantially the same as the refractive index of the second liquid122, but the transmittance of the first liquid121is different from the transmittance of the second liquid122.

According to the optical element100described in document '792, a voltage is applied between the transparent electrode103and the rod-shaped electrode125, and thus the shape of the interface between the two liquids is changed through the electrowetting phenomenon. As a result, a part of the surface of the second liquid122on the hydrophilic film113side contacts the hydrophilic film113to form on the hydrophilic film113an opening through which light can be transmitted (to form an optical path in the optical element100). In this optical element100, the size of the opening formed on the hydrophilic film113is changed by changing the voltage applied, thus adjusting the amount of light beam30passing through the optical element100. That is, according to this optical element100, the amount of light can be electrically controlled, and thus it is possible to solve the shortcomings of the mechanical aperture mechanism described above.

SUMMARY

In the optical element using an electrowetting phenomenon, decentration of an opening provided on the light-incident side readily occurs, and the amount of decentration is also large. In such a case, a problem of decreasing the resolution occurs. To solve this problem, in document '792, the transparent electrode103is formed such that the shape of the transparent electrode103is a concave shape when viewed from the liquid side. However, this structure causes a problem that it is difficult to reduce the thickness of the optical element100. Furthermore, in the optical element100described in document '792, since the transparent electrode103is formed so as to have a concave shape viewed from the liquid side, the structure of the optical element100becomes complex and it is difficult to make the optical element100and to reduce the size of the optical element100.

In an optical element using an electrowetting phenomenon, it is desirable to suppress decentration of an opening with a simpler structure.

An optical element according to an embodiment includes a first liquid and a second liquid that is immiscible with the first liquid and that has polarity or electrical conductivity. The optical element according to an embodiment further includes a first substrate portion, a second substrate portion, a sidewall portion, a second electrode disposed on one of the second substrate portion and the sidewall portion, and an accommodating portion constituted by the first substrate portion, the second substrate portion, and the sidewall portion and sealing the first liquid and the second liquid therein. The first substrate portion includes a first substrate having optical transparency, a first electrode disposed on a surface of the first substrate and having optical transparency, and an insulating film disposed on the first electrode and having optical transparency. Furthermore, the first substrate portion includes a first film disposed on the insulating film and having higher affinity with the first liquid than with the second liquid and optical transparency. The second substrate portion includes a second substrate having optical transparency, a second film disposed on a surface of the second substrate and having higher affinity with the second liquid than with the first liquid and optical transparency, and a third film disposed at the center of the second film and having higher affinity with the first liquid than with the second liquid and optical transparency. The sidewall portion connects the first substrate portion to the second substrate portion so that the first film and the second film face each other.

An imaging device according to an embodiment includes the optical element according to an embodiment, a power supply unit configured to apply a voltage between the first electrode and the second electrode of the optical element, a lens unit configured to focus incident light, and an imaging element on which the light is focused through the optical element and the lens unit.

In an embodiment, the third film having higher affinity with the first liquid than with the second liquid is provided at the center of the second film of the second substrate portion. Therefore, in the case where no voltage is applied, the first liquid is fixed by being in contact with not only the first film of the first substrate portion but also the third film of the second substrate portion. Accordingly, a contact area between the first liquid and a film on the second substrate portion side of the accommodating portion is formed on the third film or in an area centering on the third film.

In an embodiment, the third film having higher affinity with the first liquid than with the second liquid is provided at the center of the second film of the second substrate portion. This structure can suppress a shift of the center of a contact area between the first liquid and a film of the accommodating portion on the second substrate portion side from the optical axis. That is, according to the embodiment, decentration of the contact area between the first liquid and the film of the accommodating portion on the second substrate portion side can be suppressed with a simpler structure.

When the optical element according to an embodiment is applied to an aperture mechanism (iris) of an imaging device or the like, the above-mentioned contact area functions as an opening through which light is transmitted. Accordingly, in such a case, decentration of the opening can be suppressed with a simpler structure.

DETAILED DESCRIPTION

The present application will now be described with reference to the drawings according to an embodiment. As described below, optical elements according to embodiments will be described using an aperture mechanism (iris) used in an imaging device as an example. Note that embodiments are not limited to examples described below.

First Embodiment

Structure of Imaging Device

FIG. 1shows an example of the schematic structure of an imaging device to which an aperture mechanism (hereinafter referred to as “liquid iris”) of this embodiment is applied.FIG. 1shows an example of an imaging device including a zoom mechanism.FIG. 1mainly shows the structure of an optical system of the imaging device, and the structures of a portion configured to process an acquired image and a portion configured to perform a control process of the optical system are omitted. The embodiment can be applied also to an imaging device that does not include a zoom mechanism.

An optical system of an imaging device20includes a first lens unit1, a second lens unit2, a liquid iris10, a third lens unit3, a fourth lens unit4, a filter5, and an imaging element6. The first lens unit1, the second lens unit2, the liquid iris10, the third lens unit3, the fourth lens unit4, the filter5, and the imaging element6are arranged in that order from the incident side of a light beam30.

Among the first lens unit1to the fourth lens unit4for focusing incident light, the first lens unit1and the third lens unit3are attached so as to be fixed in a lens barrel (not shown). The second lens unit2is a lens unit for zooming and is attached to the lens barrel so as to move in a direction of an optical axis7. The fourth lens unit4is a lens unit for focusing and is attached so as to move in the direction of the optical axis7. The movement of the second lens unit2(for zooming) and the fourth lens unit4(for focusing) in the direction of the optical axis7is controlled by a control unit (not shown) in the imaging device20.

The liquid iris10(optical element) adjusts an opening diameter (aperture diameter) of the liquid iris10at the light-incident side by utilizing an electrowetting phenomenon, whereby adjusting the amount of light beam30passing through the liquid iris10. The opening diameter (aperture diameter) of the liquid iris10at the light-incident side is adjusted by changing the value of voltage applied to the liquid iris10, and this adjustment is controlled by the control unit (not shown) in the imaging device20. The specific structure and the operation of the liquid iris10will be described in detail below.

The filter5is constituted by an infrared cut filter, a low-pass filter, or the like. The imaging element6is constituted by, for example, charge coupled devices (CCD) or complementary metal oxide semiconductors (CMOS).

In the imaging device20of this embodiment, as shown inFIG. 1, the light beam30incident from the first lens unit1side is focused on an imaging surface6aof the imaging element6through the above-mentioned various optical elements. An image data acquired in the imaging element6is subjected to a predetermined process by an image-processing unit (not shown) in the imaging device20.

FIGS. 2A and 2Bshow the schematic structure of the liquid iris10of this embodiment.FIG. 2Ais a schematic cross-sectional view of the liquid iris10when no voltage is applied (hereinafter, this state is also referred to as “static state”), andFIG. 2Bis a top view of the liquid iris10viewed from the light-incident side at that time.

The liquid iris10includes a first substrate portion11, a second substrate portion21, and a sidewall portion31connecting the first substrate portion11to the second substrate portion21. A first liquid41and a second liquid42are hermetically enclosed in an accommodating chamber40(accommodating portion) constituted by the first substrate portion11, the second substrate portion21, and the sidewall portion31.

As the first liquid41, a liquid that has an insulating property or nonpolarity, and that has optical transparency is used. Any liquid having such properties can be used as the first liquid41. For example, silicone oil is used as the first liquid41. There are various types of commercially available silicone oil having different specific gravities and refractive indices. Accordingly, when silicone oil is used as the first liquid41, among various types of commercially available silicone oil, silicone oil having substantially the same specific gravity and refractive index as those of the second liquid42described below is selected and used as the first liquid41.

On the other hand, as the second liquid42, a liquid that is immiscible with the first liquid41, that has substantially the same specific gravity and refractive index as those of the first liquid41, and that has polarity or electrical conductivity is used. Any liquid having such properties can be used as the second liquid42. For example, when silicone oil is used as the first liquid41, water (specific gravity: 1, refractive index: 1.333) can be used as the second liquid42. In this case, instead of water, a mixed liquid of water and ethanol, a mixed liquid of water, ethanol, and ethylene glycol, a mixed liquid prepared by adding common salt to a mixed liquid of water and ethanol, or the like can also be used. In this embodiment, in order to make optical transparency of the second liquid42lower than that of the first liquid41(in order to decrease optical transparency of the second liquid42), the second liquid42(e.g., water) is colored by mixing carbon black or the like. A dye other than carbon black may be used as a colorant.

Furthermore, in order to make the specific gravity and the refractive index of the second liquid42to be closer to those of the first liquid41, for example, a liquid prepared by mixing ethanol, ethylene glycol, common salt etc. with water is used as the second liquid42, and the specific gravity and the refractive index of the second liquid42may be controlled by adjusting the mixing ratio of these. By adjusting the refractive index of the second liquid42to be substantially the same as the refractive index of the first liquid41, refraction of light (lens effect) at the interface between the first liquid41and the second liquid42can be prevented or sufficiently decreased, thereby performing the operation of an aperture of the liquid iris10more reliably. Furthermore, by adjusting the specific gravity of the second liquid42to be substantially the same as the specific gravity of the first liquid41, a change in the shape of the interface between the first liquid41and the second liquid42can be suppressed when the whole device is vibrated or tilted. Note that it is sufficient that the values of the specific gravity and refractive index of the second liquid42are close to those of the first liquid41to an extent that optical properties, a vibration resistance property etc. of the device are within allowable tolerances of the device.

The first substrate portion11includes a first substrate12, a first electrode13disposed on the first substrate12, an insulating film14disposed on the first electrode13, and a first water-repellent film15disposed on the insulating film14.

The first substrate12is a square plate-shaped member composed of a light-transmissive material such as transparent glass and having a thickness of, for example, about 0.2 to 0.3 mm. Alternatively, a transparent synthetic resin material may be used as the material of the first substrate12. The first electrode13is a transparent electrode composed of indium tin oxide (ITO) or the like. The first electrode13is connected to a terminal of a power supply8of the imaging device20. The insulating film14is a dielectric film composed of polyvinylidene chloride, polyvinylidene fluoride, or the like.

The first water-repellent film15(first film) is a thin film (hydrophobic or lipophilic thin film) having higher affinity with the first liquid41(nonpolar liquid) than with the second liquid42(polar liquid). That is, the wettability of the first liquid41on the first water-repellent film15is larger than the wettability of the second liquid42on the first water-repellent film15. In this embodiment, a fluorocarbon resin or the like is used as a material of the first water-repellent film15. Any thin film having lipophilicity and optical transparency may be used as the first water-repellent film15.

The second substrate portion21includes a second substrate22, a second electrode23disposed on the second substrate22, a hydrophilic film24disposed on the second electrode23, and a second water-repellent film25disposed at the center of the hydrophilic film24.

As in the first substrate12, the second substrate22is a square plate-shaped member composed of a light-transmissive material such as transparent glass and having a thickness of, for example, about 0.2 to 0.3 mm. As in the first electrode13, the second electrode23is a transparent electrode composed of ITO or the like. The second electrode23is connected to another terminal of the power supply8of the imaging device20.

The hydrophilic film24(second film) is a thin film having higher affinity with the second liquid42(polar liquid) than with the first liquid41(nonpolar liquid). That is, the wettability of the second liquid42on the hydrophilic film24is larger than the wettability of the first liquid41on the hydrophilic film24. In this embodiment, a polyvinyl alcohol resin, a polyacrylic acid resin, or the like is used as a material of the hydrophilic film24. Any thin film having hydrophilicity and optical transparency may be used as the hydrophilic film24.

As in the first water-repellent film15, the second water-repellent film25(third film) is a thin film (lipophilic thin film) having higher affinity with the first liquid41(nonpolar liquid) than with the second liquid42(polar liquid). In this embodiment, the same material as the first water-repellent film15is used as a material of the second water-repellent film25. Note that the material constituting the second water-repellent film25may be the same as or different from the material constituting the first water-repellent film15.

The surface of the second water-repellent film25at the accommodating chamber40side is circular in shape (seeFIG. 2B). The embodiment is not limited thereto, and the surface of the second water-repellent film25may have a shape other than a circular shape. However, as described below, in this embodiment, an opening50that transmits light expands centering on the second water-repellent film25. In this case, the planar shape of the opening50is preferably a circular shape in consideration of the resolution. Therefore, in order to maintain the planar shape of the opening50to be a circular shape, the surface of the second water-repellent film25is preferably circular in shape.

In this embodiment, since the second water-repellent film25having higher affinity with the first liquid41than with the second liquid42is provided at the center of the hydrophilic film24, as shown inFIG. 2A, a part of the first liquid41contacts the second water-repellent film25even in the static state. As a result, as shown inFIG. 2B, the opening50is formed at the light-incident side even in the static stare. Accordingly, in order to increase the range of a change in the diameter of the opening50, the diameter of the opening50in the static state is preferably as small as possible. That is, the diameter of the second water-repellent film25is preferably as small as possible.

Furthermore, preferably, the thickness of the second water-repellent film25is substantially the same as the thickness of the hydrophilic film24. Specifically, it is preferable that a surface of the second water-repellent film25on the accommodating chamber40side be flush with a surface of the hydrophilic film24on the accommodating chamber40side. The reason for this is as follows. If the thickness of the second water-repellent film25is different from the thickness of the hydrophilic film24, and a difference in level is generated on the surface at the accommodating chamber40side, optical properties are changed by the portion including the difference in level and thus it is difficult to obtain desired optical properties. Furthermore, from the standpoint of the optical properties of the liquid iris10, materials of the hydrophilic film24and the second water-repellent film25are preferably selected so that the refractive index of the hydrophilic film24is as close to the refractive index of the second water-repellent film25as possible. Note that it is sufficient that the values of the thickness and the refractive index of the hydrophilic film24are close to those of the second water-repellent film25to an extent that optical properties of the device are within allowable tolerances of the device.

The sidewall portion31includes a cylindrical sidewall member32and a hydrophilic film33provided on the inner wall surface of the sidewall member32.

The sidewall member32is a cylindrical member composed of an insulating material (such as glass). In this embodiment, the sidewall member32has an inner diameter of about 9 mm, an outer diameter of about 11 mm, and a height of about 1 mm. The sidewall member32includes an inlet32afor injecting the first liquid41and the second liquid42into the liquid iris10. The inlet32ais sealed from the outside of the sidewall member32using an adhesive member34.

The hydrophilic film33(fourth film) is a thin film having higher affinity with the second liquid42(polar liquid) than with the first liquid41(nonpolar liquid). In this embodiment, as in the hydrophilic film24of the second substrate portion21, a polyvinyl alcohol resin, a polyacrylic acid resin, or the like is used as a material of the hydrophilic film33. Any thin film having hydrophilicity and optical transparency may be used as the hydrophilic film33.

An alternating-current power supply is used as the power supply8(power supply unit) of the imaging device20to which the first electrode13and the second electrode23are connected. A direct-current power supply may also be used as the power supply8. However, in such a case, when the power supply is set to the off-state from a voltage-applied state, electrical charges are somewhat left on the insulating film14. Accordingly, the speed of an operation for which the first liquid41is returned to the original static state becomes somewhat lower than the case where an alternating-current power supply is used. Therefore, an alternating-current power supply is more preferably used as the power supply8.

[Principle of Suppression of Decentration]

A description will be made of the principle of suppressing decentration of the opening50in the liquid iris10of this embodiment. In the liquid iris10of this embodiment, in the case where no voltage is applied between the first electrode13and the second electrode23(in the static state), the interface between the first liquid41and the second liquid42is in the state shown inFIG. 2A.

More specifically, the first water-repellent film15is provided over the entire surface of the accommodating chamber40on the first substrate portion11side, and thus the first liquid41having higher wettability on the first water-repellent film15spreads over and contacts the first water-repellent film15. In addition, the second water-repellent film25is provided at the center of the surface of the accommodating chamber40on the second substrate portion21side. Accordingly, a part of the surface of the first liquid41on the second substrate portion21side contacts the second water-repellent film25. Specifically, in this embodiment, in the accommodating chamber40, the first liquid41is fixed to the first water-repellent film15on the first substrate portion11side and the second water-repellent film25on the second substrate portion21side.

On the other hand, the second liquid42is disposed so as to contact the hydrophilic film24provided on the second substrate portion21side of the accommodating chamber40and the hydrophilic film33provided on the sidewall portion31side thereof and to surround the first liquid41.

The interface between the first liquid41and the second liquid42has a spherical shape. This shape is determined by the balance of the surface tensions of the first liquid41and the second liquid42, and the interfacial tensions on the first water-repellent film15. The first liquid41spread on the first water-repellent film15close to the sidewall portion31as shown inFIG. 2A. However, since the hydrophilic film33is provided on the sidewall portion31side of the accommodating chamber40, the first liquid41does not contact the sidewall portion31.

As described above, a part of the first liquid41is fixed to the second water-repellent film25provided on the second substrate portion21side. Since the second water-repellent film25is disposed at the center of the hydrophilic film24, the center of the second water-repellent film25is located at substantially the same position as the optical axis. Accordingly, the center position of a contact area between the first liquid41and the second water-repellent film25, i.e., the center position of the opening50formed on the light-incident side (second substrate portion21side) of the liquid iris10is substantially disposed on the optical axis, thus suppressing decentration.

As described above, in this embodiment, by utilizing not only the affinity between the first water-repellent film15and the first liquid41but also the affinity between the second water-repellent film25and the first liquid41, decentration of the first liquid41, i.e., decentration of the opening50is suppressed. More specifically, a three-dimensional control of decentration suppression can be performed in this embodiment.FIGS. 3A and 3Billustrate this feature.

FIG. 3Ais a schematic cross-sectional view of the liquid iris10in the static state, andFIG. 3Bis a top view of the liquid iris10in the static state viewed from the light-incident side. InFIG. 3A, a concept of the three-dimensional control of decentration suppression of the liquid iris10of this embodiment is represented by the black dots.

For comparison,FIGS. 4A and 4Bshow a concept of decentration suppression in a liquid iris90(comparative example) that does not include the second water-repellent film25.FIG. 4Ais a schematic cross-sectional view of the liquid iris90of the comparative example in the static state, andFIG. 4Bis a top view of the liquid iris90of the comparative example in the static state, viewed from the light-incident side. In the comparative example, decentration is suppressed by utilizing only the affinity between the first water-repellent film15and the first liquid41, and thus a two-dimensional control of decentration suppression is performed (see black dots inFIG. 4A). Accordingly, in the liquid iris90of the comparative example, the effect of suppressing decentration is smaller than that of the present embodiment.

As described above, in this embodiment, the second water-repellent film25having higher affinity with the first liquid41than with the second liquid42is provided at the center of the hydrophilic film24on the light-incident side of the liquid iris10. Accordingly, decentration suppression can be three-dimensionally controlled to increase the effect of suppressing decentration.

Furthermore, in this embodiment, since the second water-repellent film25having higher affinity with the first liquid41than with the second liquid42is provided at the center of the hydrophilic film24, the second liquid42is repelled by the second water-repellent film25. Accordingly, a black residue (stain) is eliminated in the opening50, thus increasing the light transmittance.

Furthermore, in this embodiment, decentration is suppressed by a simple structure in which the second water-repellent film25is provided at the center of the hydrophilic film24. In addition, the electrode in the liquid iris10of this embodiment is flat, which is different from the concave electrode of the optical element (seeFIG. 18) disclosed in document '792. Accordingly, the liquid iris10of this embodiment has a simple structure as compared with that disclosed in document '792, and thus the thickness of the liquid iris10can be reduced.

[Method of Making Liquid Iris]

Next, a method of making the liquid iris10of this embodiment will now be described with reference toFIG. 5.FIG. 5is a flowchart showing a procedure for making the liquid iris10.

First, a first substrate12composed of a light-transmissive material such as transparent glass is prepared. Next, a first electrode13composed of a light-transmissive electrically conductive material (e.g., ITO) is formed on a surface of the first substrate12by a vapor deposition method or the like so as to have a film thickness of about 30 nm (Step S1). Next, a dielectric film composed of polyvinylidene chloride, polyvinylidene fluoride, or the like and having a thickness in the range of, for example, about 1 to 5 μm is, for example, bonded onto the first electrode13with an adhesive to form an insulating film14(Step S2).

Next, a fluorocarbon resin or the like is applied onto the insulating film14by a spin-coating method or the like and baked at, for example, 150° C. to form a first water-repellent film15having a thickness in the range of about 10 to 30 nm (Step S3). A first substrate portion11is prepared by Steps S1to S3described above.

In addition, a second substrate portion21and a sidewall portion31are prepared as follows in parallel with Steps S1to S3. First, a second substrate22composed of a light-transmissive material such as transparent glass is prepared. Next, a second electrode23composed of a light-transmissive electrically conductive material (e.g., ITO) is formed on a surface of the second substrate22by a vapor deposition method or the like so as to have a film thickness of about 30 nm (Step S4).

Next, a sidewall member32is bonded onto the second electrode23using, for example, a UV-curable adhesive (Step S5). Next, a polyvinyl alcohol resin, a polyacrylic acid resin, or the like is applied onto the second electrode23and the inner wall of the sidewall member32by a spin-coating method or the like to form a hydrophilic film24and a hydrophilic film33, respectively, each having a thickness in the range of about 300 to 600 nm (Step S6).

Next, a second water-repellent film25is formed at the center of the hydrophilic film24(Step S7). In this step, the thickness of the second water-repellent film25is controlled to be substantially the same as the thickness of the hydrophilic film24. The second water-repellent film25can be formed by the following method. First, the hydrophilic film24is formed on the entire surface of the second electrode23. Next, an area of the hydrophilic film24other than a portion where the second water-repellent film25is to be formed is masked. Next, the portion of the hydrophilic film24where the second water-repellent film25is to be formed is removed by an etching method or the like. A fluorocarbon resin or the like is then applied onto the portion from which the hydrophilic film24has been removed, thus forming the second water-repellent film25. Alternatively, the following method may be employed. First, a portion of the second electrode23where the second water-repellent film25is to be formed is masked, and a polyvinyl alcohol resin, a polyacrylic acid resin, or the like is applied thereon by a spin-coating method or the like to form the hydrophilic film24. Next, the hydrophilic film24is masked, and a fluorocarbon resin or the like is then applied thereon to form the second water-repellent film25.

The second substrate portion21and the sidewall portion31, and a member produced by connecting the second substrate portion21to the sidewall portion31are prepared by Steps S4to S7described above.

Next, the first substrate portion11and the member produced by connecting the second substrate portion21to the sidewall portion31, which are prepared as described above, are bonded to each other using, for example, a UV-curable adhesive (Step S8). In this step, the first substrate portion11is bonded to the member such that the first water-repellent film15faces the hydrophilic film24(and second water-repellent film25). In this step, an accommodating chamber40for enclosing a first liquid41and a second liquid42is formed in the liquid iris10.

Next, an antireflection film (not shown) is formed on a desired surface (surface on the light-incident side or the light-emitting side) of the liquid iris10by a vapor deposition method or the like (Step S9). For example, a multilayered antireflection film in which low-refractive index layers and high-refractive index layers are alternately stacked may be used as the antireflection film. For example, the antireflection film is formed of LaTiO3/SiO2films or the like, and the thickness thereof is, for example, about 400 nm.

Next, the first liquid41and the second liquid42are injected into the accommodating chamber40from an inlet32aprovided through the sidewall member32using a syringe or the like (Step S10). In this step, first, a predetermined amount of second liquid42is injected into the accommodating chamber40, and the first liquid41is then filled in the remaining space in the accommodating chamber40. In this step, the first liquid41and the second liquid42are filled so that air does not remain in the accommodating chamber40. The ratio of the amount of first liquid41injected to the amount of second liquid42injected is appropriately adjusted in accordance with the degree of wettability of the second liquid42on the hydrophilic films24and33, the degree of wettability of the first liquid41on the first water-repellent film15and the second water-repellent film25, the diameter of the second water-repellent film25etc.

Next, the first electrode13and the second electrode23are connected to the power supply8(Step S11). Lastly, for example, a UV-curable adhesive (adhesive member34) is applied onto the sidewall member32, and the adhesive is then cured by ultraviolet irradiation to seal the inlet32aof the sidewall member32(Step S12). Accordingly, the accommodating chamber40is hermetically sealed to seal the first liquid41and the second liquid42therein. As described above, the liquid iris10is produced in this embodiment.

Before a description of an operation of the liquid iris10of this embodiment when a voltage is applied thereto, an electrowetting phenomenon (electrocapillarity) will be briefly described.

FIGS. 6A and 6Bare views showing the principle of the electrowetting phenomenon.FIG. 6Ais a view showing a state of a polar liquid80when no voltage is applied to the polar liquid80, andFIG. 6Bis a view showing a state of the polar liquid80when a voltage is applied to the polar liquid80.

In the example shown inFIGS. 6A and 6B, a member includes a substrate81, an electrode82disposed on the substrate81, an insulating film83disposed on the electrode82, and a water-repellent film84(hydrophobic film) disposed on the insulating film83. It is assumed that a polar liquid80(e.g., water) is dropped on the water-repellent film84. The polar liquid80is connected to a terminal of a power supply85through a switch86, and another terminal of the power supply85is connected to the electrode82. In this example, as shown inFIG. 6A, positive ion-molecules80aand negative ion-molecules80bare present in the polar liquid80.

When no voltage is applied to the polar liquid80(when the switch86is in the off-state), the surface of the polar liquid80becomes spherical (the state shown inFIG. 6A) because of the surface tension. In this case, the angle formed by the surface of the water-repellent film84and the portion of the liquid surface of the polar liquid80that is in contact with the water-repellent film84, that is, the contact angle is represented by θ0.

When the switch86is closed and a voltage is applied to the polar liquid80, positive charges83aare generated on a surface of the insulating film83and negative charges83bare generated on another surface thereof. In the example shown inFIGS. 6A and 6B, the positive charges83aare generated on the polar liquid80side of the insulating film83, and the negative charges83bare generated on the electrode82side of the insulating film83. In this case, an electrostatic force acts on the negative ion-molecules80bof the polar liquid80, and the negative ion-molecules80bare attracted to the water-repellent film84on the insulating film83. As a result, the polar liquid80adheres to the water-repellent film84in a spread-out manner (the state shown inFIG. 6B), as compared with the case where no voltage is applied (the state shown inFIG. 6A). The contact angle θ of the polar liquid80at that time becomes smaller than the contact angle θ0when no voltage is applied. Specifically, the wettability of the polar liquid80on the water-repellent film84(i.e., affinity between the polar liquid80and the water-repellent film84) is increased by applying the voltage. This phenomenon is referred to as an electrowetting phenomenon.

In this embodiment, the shape of the interface between the first liquid41and the second liquid42enclosed in the liquid iris10is changed by utilizing the above-described electrowetting phenomenon to perform the aperture operation of the liquid iris10.

FIGS. 7A and 7Bshow the state of the operation of the liquid iris10when a voltage V1is applied between the first electrode13and the second electrode23.FIG. 7Ais a cross-sectional view of the liquid iris10when the voltage V1is applied, andFIG. 7Bis a top view of the liquid iris10viewed from the light-incident side at that time. When the voltage V1is applied between the first electrode13and the second electrode23, the first liquid41is further pressed onto films on the second substrate portion21side through an electrowetting phenomenon. Consequently, a contact area between the first liquid41and the films on the second substrate portion21side, i.e., the diameter of a circular opening50formed on the light-incident side of the liquid iris10increases. For example, in the example shown inFIGS. 7A and 7B, when the voltage V1is applied, the diameter of the opening50becomes T1, which is larger than the diameter of the opening50in the static state (seeFIG. 2B).

With reference toFIG. 8, a description will be made of the principle that when a voltage is applied between the first electrode13and the second electrode23, the contact area between the first liquid41and the films on the second substrate portion21side increases.FIG. 8is a view showing the principle of an operation when a voltage is applied to the liquid iris10. InFIG. 8, a description will be made of an example in which positive charges14aare generated on the liquid side of the insulating film14, and negative charges14bare generated on the first electrode13side of the insulating film14.

When a voltage is applied between the first electrode13and the second electrode23, positive charges14aare generated on the liquid side of the insulating film14. In this case, an electrostatic force acts on the negative ion-molecules42bin the second liquid42, which is a polar liquid, and the negative ion-molecules42bare attracted to the first water-repellent film15side (as shown by the white arrows inFIG. 8). In this case, the second liquid42is made to spread over the first water-repellent film15through the electrowetting phenomenon. Consequently, a pushing force (shown by the black arrows inFIG. 8) acts to the first liquid41from the second liquid42, which is present around the first liquid41. Accordingly, the surface shape of the first liquid41on the hydrophilic film24side is changed so as to be pushed toward the hydrophilic film24side (as shown by the hatched arrow inFIG. 8). As a result, a part of the surface of the first liquid41on the hydrophilic film24side is pressed onto the films on the hydrophilic film24side. As a result, the contact area between the first liquid41and the films on the second substrate portion21side increases, thus increasing the diameter of the opening50formed on the light-incident side (hydrophilic film24side) of the liquid iris10.

Furthermore, when the voltage applied between the first electrode13and the second electrode23is increased, the second liquid42is made to further spread over the first water-repellent film15through the electrowetting phenomenon. Accordingly, the pushing force (shown by the black arrows inFIG. 8) acting from the second liquid42to the first liquid41further increases, and the shape of the surface of the first liquid41on the hydrophilic film24side is changed so as to be further pushed to the hydrophilic film24side. Specifically, an angle of inclination formed between the first water-repellent film15and the interface of the first liquid41and the second liquid42further increases. In this case, the contact area between the first liquid41and the films on the hydrophilic film24side further increases, thereby further increasing the diameter of the opening50.FIGS. 9A and 9Bshow this state.

FIG. 9Ais a cross-sectional view of the liquid iris10when a voltage V2(>V1) is applied between the first electrode13and the second electrode23, andFIG. 9Bis a top view of the liquid iris10viewed from the light-incident side at that time. When the voltage applied between the first electrode13and the second electrode23is increased from V1to V2, the diameter of the opening50formed on the light-incident side of the liquid iris10is also increased from T1to T2.

As described above, in the liquid iris10of this embodiment, a part of the first liquid41is fixed to the second water-repellent film25provided at the center of the hydrophilic film24in the static state. Accordingly, the opening50formed during the application of a voltage expands centering on the second water-repellent film25. That is, even during the application of a voltage, a shift (decentration) of the center of the opening50formed on the light-incident side from the optical axis does not occur. Consequently, according to this embodiment, decentration can be suppressed even during the application of a voltage, thus suppressing a decrease in the resolution.

Second Embodiment

In a second embodiment, a description will be made of an example in which the structure of the first electrode is changed in the structure of the liquid iris10of the first embodiment.

FIGS. 10A and 10Bare schematic views of a liquid iris of this embodiment.FIG. 10Ais a cross-sectional view of a liquid iris60when no voltage is applied.FIG. 10Bis a top view of the liquid iris60viewed from the incident side of a light beam30at that time. In the liquid iris60shown inFIGS. 10A and 10B, the same components as those of the liquid iris10(shown inFIGS. 2A and 2B) of the first embodiment are assigned the same reference numerals.

The liquid iris60includes a first substrate portion61, a second substrate portion21, and a sidewall portion31that connects the first substrate portion61to the second substrate portion21. A first liquid41and a second liquid42are hermetically sealed in an accommodating chamber40constituted by the first substrate portion61, the second substrate portion21, and the sidewall portion31.

The structure of the liquid iris60of this embodiment is the same as that of the liquid iris10of the first embodiment except that the structure of a first electrode63of the first substrate portion61is changed. Therefore, a description of the structure other than the first electrode63is omitted here.

FIG. 11shows a schematic structure of the first electrode63used in this embodiment. An electrode opening63bis provided at the center of an electrode portion63aof the first electrode63. The electrode portion63aof the first electrode63is composed of the same material as the first electrode13of the first embodiment and has the same thickness as that of the first electrode13thereof. A first substrate12on which the first electrode63is provided is exposed at the electrode opening63b.

The electrode opening63bis a star-shaped opening. The electrode opening63bin this embodiment includes a circular portion63cdisposed at the center of the first electrode63and four projecting portions63d. The projecting portions63dare separately disposed around the circumference of the circular portion63cat intervals of 90 degrees, and each project from the circumference toward the outside in the shape of an inverted-V character.

The electrode opening63bcan be formed (patterned) as follows. First, the first electrode63is formed over the entire surface of the first substrate12as in the first embodiment (Step S1inFIG. 5). Next, a portion of the first electrode63corresponding to the electrode opening63bis removed by a wet-etching method or the like to form the electrode opening63b. Alternatively, a portion of the first substrate12corresponding to the electrode opening63bis masked, and the first electrode63may then be formed on the first substrate12. The liquid iris60of this embodiment can be prepared as in the first embodiment except that the electrode opening63bis formed as described above.

FIG. 12is a view showing the principle of suppressing decentration of an opening when the star-shaped electrode opening63bis formed at the center of the first electrode63. When the position of the first liquid41(insulating transparent liquid) is shifted (decentered) from the center of the first electrode63on the first electrode63as shown inFIG. 12, an area where the first liquid41overlaps the electrode portion63abecomes nonuniform (i.e., the symmetry of the area is lost).

When a voltage is applied to the liquid iris60in such a state, the balance of the pushing forces acting from the second liquid42to the first liquid41due to an electrowetting phenomenon is disrupted. In this case, a force to balance the pushing forces, i.e., a restoration force (shown by the white arrow inFIG. 12) for returning the first liquid41to the center of the first electrode63acts on the first liquid41. Accordingly, in this embodiment, the restoration force acts during application of a voltage so that the first liquid41is located at the center of the first electrode63, and thus decentration of the opening can be suppressed. Accordingly, in this embodiment, the effect of suppressing decentration on the first electrode63(on the first water-repellent film15) can be further increased.

[Other Examples of First Electrode]

The shape of the electrode opening63bof the first electrode63is not limited to the star shape shown inFIG. 11. As for the star shape of the electrode opening, a plurality of projections projecting from the center to the outside are arranged in a direction around the center of the first electrode at substantially the same distance from each other (substantially the same interval).FIGS. 13 to 17show examples of an electrode opening having a star shape other than the shape shown inFIG. 11.

In the example shown inFIG. 13, an electrode opening70bincludes a circular portion70cdisposed at the center of a first electrode70and six projecting portions70d. The projecting portions70dare separately disposed around the circumference of the circular portion70cat intervals of 60 degrees, and each project from the circumference toward the outside in the shape of an inverted-V character.

In the example shown inFIG. 14, an electrode opening71bincludes a circular portion71cdisposed at the center of a first electrode71and eight projecting portions71d. The projecting portions71dare separately disposed around the circumference of the circular portion71cat intervals of 45 degrees, and each project from the circumference toward the outside in the shape of an inverted-V character.

In the example shown inFIG. 15, an electrode opening72bincludes a circular portion72cdisposed at the center of a first electrode72and six projecting portions72d. The projecting portions72dare separately disposed around the circumference of the circular portion72cat intervals of 60 degrees, and each project from the circumference toward the outside in the shape of an inverted-V character. In this example shown inFIG. 15, the leading end of each of the projecting portions72dhas a circular arc shape concentric with the circular portion72c.

In the example shown inFIG. 16, an electrode opening73bincludes a circular portion73cdisposed at the center of a first electrode73and three projecting portions73d. The projecting portions73dare separately disposed around the circumference of the circular portion73cat intervals of 120 degrees, and each project from the circumference toward the outside in the shape of an inverted-V character.

In the example shown inFIG. 17, an electrode opening74bincludes a circular portion74cdisposed at the center of a first electrode74and six rectangular projecting portions74deach having a uniform width. The projecting portions74dare separately disposed around the circumference of the circular portion74cat intervals of 60 degrees, and each project from the circumference toward the outside.

The electrode opening of the first electrode may have any shape as long as when the first liquid41is located at the center of the first electrode, an area where the first liquid41overlaps the electrode portion is symmetric with respect to the center of the first electrode.

In the embodiments described above, examples in which a second electrode23composed of a transparent electrode film is provided on a second substrate22have been described, but the present application is not limited thereto. For example, as in document '792, a rod-shaped electrode may be used as the second electrode. In such a case, the rod-shaped electrode is inserted from the sidewall portion, and an end of the rod-shaped electrode is directly in contact with the second liquid42. In such a case, the hydrophilic film24and the second water-repellent film25are formed directly on the second substrate22.

In the embodiments described above, a description has been made of examples in which the present application is applied to a liquid iris, but the present application is not limited thereto. The present application can be applied also to an optical element such as a shutter or a lens. However, when the present application is applied to a lens, both the first liquid41and the second liquid42are constituted by transparent liquids, and liquids having refractive indices different from each other are used as the first liquid41and the second liquid42.