JP2000347005A - Variable focus lens device - Google Patents

Abstract

(57) [Problem] To reduce the driving voltage of a varifocal lens device. In a variable focus lens device, a first liquid that is conductive, and a droplet of an insulating second liquid that is statically disposed in a region of a surface inside an insulating layer in a cell;
Wherein the first and second liquids have different refractive indices without mixing with each other,
The second liquid is insulating; the insulating layer is a thin film having a thickness of 1 μm or less; and the electrodes are disposed on the surfaces of the first liquid and the second liquid in the cell. To control the shape of the second liquid droplet when the voltage is applied by the voltage applying unit, and to maintain the center position of the second liquid droplet. It is characterized by including means of (1). In the variable focus lens device, the insulating layer includes a thin film of 1 micron or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a varifocal lens device, and more particularly to a varifocal lens device having a liquid lens capable of continuously controlling a focus change by a low electric field.

[0002]

2. Description of the Related Art B. Berge et al., "Electrocapillarity"
and wetting of insulator films bywater, CRAcad.Sc
i. Paris, t. 137 p. 157 (1993) ", shows a device comprising a conductive liquid droplet placed on a dielectric film placed on a plate electrode.

This document describes that when a voltage is applied between a conductive liquid droplet and an electrode, the contact angle of the droplet changes, and this phenomenon is called electro-wetting. I have.

However, it has been shown that a high voltage of about 600 V is required to realize a sufficient change in the contact angle.

A display device using the electro-wetting phenomenon is disclosed in US Pat. No. 5,659,330, but there is no suggestion that the display device is used for an optical lens.

[0006] Also, the article by Ellet, Vallet, Berge, Vovelle et al.
ectrowetting of water and aqueous solutions on pol
y (ethylene terephthalate), Polymer, Vol.37, No12p.246
5 (1996) "shows that if the voltage applied to the conductive liquid is too high, the surface of the droplet becomes unstable, and the droplet cannot maintain one shape.

[0007] These conventional techniques are not enough to stably form a variable focus lens, and furthermore, in these systems, a transparent electrode and a bonding electrode of a droplet liquid are required, and the production is difficult. , Inefficient and difficult.

No 97 12781, INP filed in France
I Grenoble, Oct. 8, 1997 discloses a lens in which the focal point of the lens can be continuously changed by electric field control using the electro-wetting phenomenon. In the variable focus lens disclosed in this patent, the applied voltage is typically a fairly high voltage AC electric field of 250 V, 50 Hz to 10 kHz.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the driving voltage of a varifocal lens device capable of varying the focal length at a high voltage.

[0010]

SUMMARY OF THE INVENTION A variable focus lens device according to the present invention includes (1) a cell filled with a first liquid and a droplet of a second liquid, and (2) the second liquid. (3) the first and second liquids have different indices of refraction without mixing with each other, The first liquid is conductive, the second liquid is insulating, the insulating layer is a thin film having a thickness of 1 μm or less, and (4) the conductive liquid in the cell and the second liquid of the insulating layer have substantially the same density. And (5) means for maintaining the center position of the droplet in order to control the shape of the droplet when a voltage is applied. It is characterized by:

According to the present invention, in a variable focus lens device, a first liquid which is conductive and a second liquid which is insulated and located in a surface region inside an insulating layer in a cell are provided. And the cell filled with
And the second liquid do not mix with each other, have different refractive indices, have substantially equal densities, the second liquid is insulative, the insulating layer is a thin film of 1 μm or less, Further comprising a voltage applying means between the first liquid and an electrode arranged on the surface of the second liquid, wherein the shape of the droplet of the second liquid when the voltage is applied by the voltage applying means is changed. In order to control, a means for maintaining a center position of the droplet of the second liquid is included.

Further, the present invention provides a variable focal length lens apparatus which changes a lens focal length by applying a voltage, wherein a transparent insulating liquid droplet forming a lens shape is provided.
A thin film insulating layer on the substrate that contacts the droplets of the insulating liquid, a transparent conductive liquid covering the droplets of the insulating liquid,
A contact area where the thin film insulating layer and the droplet of the insulating liquid are in contact, an electrode that applies a voltage that contacts the thin film insulating layer, and an electrode that conducts with the conductive liquid that applies the other voltage. A cell is formed from the transparent base material supporting the thin film insulating layer, and a plurality of cells are provided.

In order to achieve the above-mentioned object of the present invention,
By making the insulating layer supporting the droplets of the insulating liquid a thin film having a thickness of 1 μm or less, a change in the focal point of the lens can be realized with a very low driving voltage.

[0014]

Embodiments of the present invention will be described below in detail.

FIG. 1 is a sectional view of a variable focus lens device according to the present invention. In FIG. 1, reference numeral 11 denotes a droplet of an insulating liquid, which is a transparent second liquid forming a lens shape; 12, a thin film insulating layer; 13, a conductive liquid, which is a transparent first liquid;
4 is a surface treatment part, 15 is a contact area between the thin film insulating layer 12 and the droplet 11 of the insulating liquid, 16 is an electrode for applying a voltage, 17
Is an electrode to which the other voltage is applied, 18 is a transparent substrate such as transparent glass, and 19 is a cell forming one of the variable focus lens devices.

In FIG. 1, a droplet 11 of an insulating liquid is placed on the inner surface 15 of a cell 19 filled with a conductive liquid 13. Both the insulating liquid 11 and the conductive liquid 13 are transparent, do not mix with each other, have different refractive indices, and have substantially equal density values.

The thin insulating layer 12 has a hydrophobic property with respect to the conductive liquid 13, and becomes hydrophilic with respect to the conductive liquid 13 by performing the surface treatment 14. Therefore, the conductive liquid 13 exists around the insulating liquid 11 and the surface treatment 14.

Thus, the surface treatment 14 is applied to the droplet 1
1 to prevent this droplet from spreading beyond the desired contact surface.

When the system of the device is in the rest position, the droplet 11 assumes the natural form indicated by "A".

The axis indicated by "C" in FIG. 1 is perpendicular to the contact area 15 and runs through the center of this area. In the rest position, the droplet 11 is centered on the axis "C" which is the optical axis of the device. Each part of the device adjacent to axis "C" is transparent, and 18 is comprised of a transparent substrate. The electrode 16 is arranged on the surface outside the insulating layer 12, and the droplet is placed on the electrode 16 so that the area of the droplet 11 overlaps. The electrode 17 is a conductive liquid 13
And may be immersed in the conductive liquid 13, or a conductive film may be disposed on the inner wall of the cell 19.

When a voltage V is applied between the electrodes 16 and 17, the contact area 15 of the conductive liquid 13 is expanded according to the above-described principle of electro-wetting, whereby
When the insulating liquid droplet 11 is moved, the droplet 11 deforms as indicated by a broken line indicated by "B".

In this way, the focal point of the lens of the droplet 11 can be changed. In the present invention, the drive voltage V can be reduced to 10 V or less by using the thin insulating layer 12. This is an effect of the present invention, and will be quantitatively described in detail below.

In FIG. 1, the contact angle when a voltage V is applied is indicated by “θ”, and θ (V) in which θ is expressed as a function of the voltage V is expressed as follows: the dielectric constant of the insulating layer 12 epsilon, the interfacial tension of the droplet 11 gamma, when the dielectric constant of a vacuum and _{ε O, cosθ (V) -cosθ} (0) = ε O · ε · V 2 / 2d · γ (Equation 1) is shown in the above-mentioned document by Vallet, Berge, Vovelle et al. However, in the literature, the droplet 11 is a conductive liquid droplet, and the conductive liquid 13 in FIG. 1 is air, but this difference is not essential in the following quantitative consideration.

(Equation 1) quantitatively shows that θ can be changed by applying a voltage and the shape of the droplet 11 can be controlled. However, in the prior art, since the thickness d of the insulating layer 12 was on the order of microns, the drive voltage for changing the contact angle by several degrees required 100 V or more.

Therefore, according to the present invention, as the insulating layer 12, d =
When a thin film having a thickness of 1 μm or less is used, the following equation (1) is used with a view that a large change in the contact angle θ can be caused by a small voltage V. Actually, the value of the voltage V is quantitatively obtained by using the following typical value (Equation 1), θ (0) = 60 ° C. θ (V) = 0 ° C. γ = 70 mN / m , Θ are changed by approximately 60 °, d is 10 nm.
To 100 nm (0.1 μm), 5
~ 17V, and the driving voltage V is
It can be seen that the number can be reduced by one to two digits.

However, the center of the droplet 11 is O
The droplet may be moved from the axis C by the deformation of the droplet due to N and OFF. Furthermore, the contour of the contact surface 15 also
During the deformation of the droplet 11, the circle shape of the droplet may be lost. Means for maintaining the center position of the droplet 11 in order to avoid these problems are described in the above-cited patents filed in France, some of which are also applicable to the present invention.

For example, as shown in FIG. 3 of the above cited patent, three concentric electrodes 3 are used instead of the electrodes 16.
5, 36, 37. By applying these three electrodes while continuously changing the three types of electrodes V1, V2, and V3, the droplet 11 can be continuously deformed from the position A to the position B.

Another means is to arrange different surface treatment areas 14, 65, 66, 67 in the surface treatment 14, as shown in FIG. 5 of the above cited patent. In this order, the degree of hydrophilicity of the conductive liquid 13 is gradually reduced. In this way, the same result as described above can be obtained.

In another embodiment of the present invention, as shown in FIG. 6 of the above cited patent, a cylindrical shape may be used instead of a cell. In this way, a cylindrical variable focus lens is obtained.

As the thin film insulating layer 12 used in the present invention, a material having a thickness of 1 μm or less and capable of forming a uniform film without defects can be used. If necessary, a treatment for making the surface hydrophobic may be performed.

First, as the thin film insulating layer 12, Langmuir
-Blodgett (LB) method. L
The B film can obtain a uniform defect-free thin film at normal temperature and normal pressure.

Next, there is a cast coat film. As a material that can be used in the present invention, an organic or inorganic compound can be formed on a substrate by a technique such as dipping or spin coating together with a solvent. Preferably, a fluorine-based or silicon-based resin can be used. Further, a material that can be used for a film formed by sputtering is metal oxide, silicon, or the like.

The surface treatment 14 is obtained by applying a material that is hydrophilic with respect to the conductive liquid 13. The hydrophilic material is not particularly limited as long as it is a generally known material.

As the conductive liquid 13, a liquid that is itself conductive or becomes conductive by adding an ionic component, such as an aqueous solution of an inorganic salt or an organic liquid, can be used.

As the insulating liquid droplet 11, for example,
An insulating liquid that does not mix with the conductive liquid 13, such as silicon oil or paraffin oil, can be used. It is necessary to select the droplet 11 having the same density as the conductive liquid 13. Also preferably, the droplet 11 is
A liquid having a larger refractive index than the conductive liquid 13 is preferable.

Although the voltage V may be a direct current, it is more preferable to apply an AC voltage of several tens Hz to several tens kHz in order to suppress charge injection into the insulating layer 12.

The varifocal lens according to the present invention can vary and control the focal length by applying a minute voltage, so that each pixel of the photoelectric conversion device using a semiconductor device arranged one-dimensionally or two-dimensionally can be used. By adjusting the applied voltage, for example, by adjusting the applied voltage such that the autofocus is adjusted by a glass lens, the optimum focus point is detected by the appropriate distance measurement according to the target image, and the autofocus is performed. Can be.

Further, the variable focus lens according to the present invention is arranged for each element on a light emitting element or a liquid crystal element, and as a projection type projector, each image is adjusted according to the position of the screen so as to match the focus. On a display panel that forms an image by emitting light or changing the transmission angle of a liquid crystal cell, an appropriate focus can be focused on a screen by varying the voltage applied to a variable focus lens.

[0039]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the details of the variable focus lens device of the present invention will be described with reference to examples, but the present invention is not limited to the following examples.

[Examples 1 to 3] Gold electrodes 16 were formed on a glass substrate 18 by vacuum evaporation. Using this substrate with electrodes, an LB film was formed next.

FC722 (3M) which is a fluorine-based material
Was diluted 20-fold with a fluorine-based solvent FC77 (3M) to obtain a diluted solution for forming an LB film.

Next, the diluted solution was spread on the water surface of an LB film forming apparatus composed of pure water at a water temperature of 20 ° C., and the surface pressure was reduced to 10 m.
N / m. The gold / glass substrate is now L
The substrate was attached to the substrate up-down drive mechanism of the B film production apparatus, and the substrate was lowered vertically to the water surface, and stopped when the front end of the substrate was located 1 inch below the water surface. Continued
The substrate was raised and stopped at a position where the front end of the substrate was almost at the same position as the water surface. By repeating this reciprocating operation several times, a transfer rate of 0.9
In step 5, a thin film of FC722 was formed on the substrate. At this time, the substrate elevating / lowering speed was 10 mm / min.

According to such a method, the film thickness is 28 n
m, 49 nm, 1 μm, (the above examples) and 2 μm
An m (comparative example) LB film was formed.

Subsequently, a portion of the contact area 15 of the droplet is masked, and as a surface treatment of 14, a solution in which silicon oxide as a hydrophilic material is dispersed in ethanol is dip-coated.
The surface treatment 14 was performed by drying.

The droplet 11 is made of silicone oil (KF54 manufactured by Shin-Etsu Chemical Co., Ltd.) with a refractive index of 1.51 and a density of 1.1. As the conductive liquid 13, a saline solution (refractive index of 1.3) is used.
5) was used. The concentration of the saline solution was adjusted so that the density was almost the same as that of the silicon oil, and used. These were formed into transparent cells to form a lens device.

The characteristic evaluation of the varifocal lens is performed by directly measuring the focal length f (V) (m unit) of the lens by applying the driving voltage V, and using the following formula: 1 / f (V) -1 / f (0) = 60 (Expression 2) Here, 1 / f (m) is defined as the reciprocal of the focal length (unit meter) of the lens as diopter. Therefore, (Equation 2) indicates that the voltage required for the change in diopter to be 60 is V.

For example, f (V) = 0.01 (1c
m), f (0) = 0.025 (2.5 cm)
Focus is 2.5 cm to 1 cm by applying drive voltage V
(Equation 2) = 60.

The results thus obtained are shown in Table 1.

[0049]

[Table 1] From the above results, if the insulating layer is 1 μm or less, almost 5
It can be seen that a low driving voltage can be realized at 0 volt or less.

Embodiments 4 and 5 Embodiments 1 and 2 were used as insulating layers.
A lens device was formed in the same manner as in Examples 1 to 3, except that a cast coat film was prepared and used as described below instead of the LB film of No. 3.

As an insulating layer, DuPont Teflon 42 (P
TFE: Polytetrafluoroethylene 32 to 35% water dispersion) was used to form a film by a casting method.

First, the above liquid was dropped on the same gold / glass substrate as that prepared in Examples 1 to 3,
To remove the water, then PT at 380-430 ° C
The film was formed by heating until the FE particles were fused together. The film thickness is controlled by the submerged amount of the liquid.
3 μm, 0.6 μm (the above examples) and 2 μm
A cast coat film of Comparative Example was obtained.

Next, a lens device was formed in the same manner as in Examples 1 to 3, and similar characteristics were evaluated. The results shown in Table 2 were obtained.

[0054]

[Table 2] From the above results, if the insulating layer is 1 μm or less, almost 9
It can be seen that a low driving voltage can be realized at 0 volt or less.

[0055]

As described above in detail, the variable focus lens device of the present invention has a very low driving voltage by changing the focal point of the lens by making the insulating layer contained therein a thin film of 1 μm or less. , For example, 50 V or less.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a variable focus lens device according to the present invention.

[Explanation of symbols]

 Reference Signs List 11 Droplet of insulating liquid 12 Thin film insulating layer 13 Conductive liquid 14 Surface treatment 15 Contact area of droplet 16 Electrode 17 Electrode 18 Transparent base material 19 Cell A Shape of droplet at stationary position B When electric field of droplet is applied Shape C Optical axis θ Contact angle

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Atsushi Oyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Tomonari Horikiri 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inside the corporation

Claims (5)

[Claims] 1. A varifocal lens device, comprising: (1) a cell filled with a first liquid and a droplet of a second liquid; and (2) a droplet of the second liquid, the cell being filled with a droplet of the second liquid. (3) the first and second liquids have different indices of refraction and have substantially equal densities without mixing with each other; The first liquid is conductive, the second liquid is insulating, and the insulating layer is a thin film having a thickness of 1 μm or less. (4) The conductive liquid in the cell and the second liquid of the insulating layer And (5) the second liquid to control the shape of the second liquid droplet when the voltage is applied by the voltage applying means. Means for maintaining the center position of the liquid droplet of the variable focus lens device. 2. The method according to claim 1, wherein the insulating layer is a Langmuir-Blodgett (L
2. A film formed by the method (B).
7. The variable focus lens device according to 1. 3. The varifocal lens device according to claim 1, wherein the insulating layer is a cast coat film or a film formed by sputtering. 4. A varifocal lens device comprising: a first liquid that is conductive; and a droplet of an insulating second liquid that is statically disposed in a region of a surface inside the insulating layer in the cell. ,
Wherein the first and second liquids have different refractive indices without mixing with each other,
The second liquid is insulating; the insulating layer is a thin film having a thickness of 1 μm or less; and the electrodes are disposed on the surfaces of the first liquid and the second liquid in the cell. To control the shape of the second liquid droplet when the voltage is applied by the voltage applying unit, and to maintain the center position of the second liquid droplet. A varifocal lens device comprising: 5. A variable-focus lens device that changes a lens focal length by applying a voltage, wherein: a transparent insulating liquid droplet forming a lens shape; and a substrate in contact with the insulating liquid droplet. A transparent conductive liquid covering the insulating liquid droplets, a contact area where the thin film insulating layer and the insulating liquid droplet contact each other, and a voltage contacting the thin film insulating layer. An electrode for applying
A varifocal lens device comprising: a cell formed from an electrode that conducts with the conductive liquid to which the other voltage is applied, and a transparent substrate that supports the thin film insulating layer, and a plurality of the cells.