HK1088400B - Lens of variable focal length and manufacture method - Google Patents

Description

Variable focus lens and method of manufacturing the same

Technical Field

The present invention relates to variable focus lenses and more particularly to lenses that take advantage of the deformation of liquid droplets caused by the phenomenon of electrowetting.

Background

In european patent 1166157, which is the applicant of the present company, various embodiments of variable focus lenses are disclosed. Fig. 1 in the present application is basically drawn according to fig. 12 in the patent. A chamber is defined by two transparent insulating plates 1 and 2 and side walls (not shown). The non-planar lower plate 2 comprises a conical or cylindrical recess or recess 3 having an axis Δ, which contains an insulating liquid droplet 4. The remaining part of the chamber is filled with a conducting liquid 5 which is immiscible with the insulating liquid and has a different refractive index and approximately the same density. A ring electrode 7 having an opening facing the recess 3 is disposed on the back surface of the lower plate 2. The other electrode 8 is in contact with the conducting liquid 5. By the electrowetting phenomenon, the curvature of the interface between the two liquids can be adjusted according to the voltage V applied between the electrodes 7 and 8, for example changing from an initial concave shape indicated by reference sign a to a convex shape indicated by reference sign B and shown in dashed lines. Thus, depending on the applied voltage, light passing through the chamber perpendicular to the plates 1 and 2 in the area of the droplet 4 will be focused to a greater or lesser extent. The conductive liquid is substantially an aqueous liquid, and the insulating liquid is an oily liquid.

The lens holder formed by the transparent plates 1, 2 and the side walls connecting the transparent plates constitutes a substantially rigid structure. The lens has a higher expansion coefficient than that of the material from which the lens holder is made, and the pressure of the liquid in the lens holder may rise significantly when the temperature of the liquid in the lens is increased, for example during the operation of assembling the components making up the lens holder or after the lens holder is assembled.

Excessive pressure of the liquid contained in the lens causes a risk of deformation of said upper and lower transparent plates 1, 2, and at the same time undesired optical distortions. Worst case, if the liquid pressure increases too much, the transparent plates 1, 2 may be caused to crack. Thus, it is necessary to take precautions when assembling the lens and/or to limit the allowable temperature range for storage and use of such lenses.

Disclosure of Invention

The present invention is directed to a variable focus lens whose characteristics are not disturbed by pressure variations of the liquid contained within the lens when the lens is assembled and used.

Another object of the invention is a method of manufacturing such a variable focus lens.

To achieve the above object, according to a first aspect, the present invention proposes a variable focus lens having an optical axis Δ, said lens comprising two transparent windows facing each other and parallel to each other, at least partially facing each other and parallel to each other, and said windows at least partially delimiting an interface comprising two immiscible and optically different liquids, wherein said lens comprises: a cover connected to one of the transparent windows and including a first cylindrical sidewall; a body having rotational symmetry about an axis defining the optical axis of the lens, said body being connected to the other of said transparent windows and said body including a second cylindrical sidewall having a smaller diameter than said first cylindrical sidewall; a gasket compressed between the first and second cylindrical sidewalls; and an elastic means deformable in accordance with a pressure change of the liquid.

According to another aspect, the invention proposes a method of manufacturing a variable focus lens having an optical axis, said lens comprising two transparent windows facing each other at least partially and parallel to each other and at least partially delimiting an inner volume containing an immiscible conducting liquid and an insulating liquid having different optical indices and defining an interface, said lens further comprising elastic means deformable in response to a variation of the pressure of said conducting liquid and insulating liquid, wherein said method comprises the steps of: providing a cover having rotational symmetry about said optical axis, a cylindrical opening passing through a central portion of said cover and said cover extending to form a first cylindrical sidewall, a transparent window sealing said cover to cover said cylindrical opening; providing a body with a second cylindrical opening through a central portion of the body and extending to form a second cylindrical sidewall having a smaller diameter than the first cylindrical sidewall, another of the transparent windows sealing the body to cover the second cylindrical opening; disposing a gasket between the first and second cylindrical sidewalls; after the inner volume is filled with the conductive liquid and the insulating liquid, the cover is placed and sealed onto the body.

Drawings

The objects, features and advantages of the present invention, as well as others, will be understood in detail by the following description of certain exemplary embodiments, given without limitation, in conjunction with the accompanying drawings, in which:

figure 1 is a cross-sectional view, as already mentioned above, showing a conventional exemplary embodiment of a variable focus lens; and is

Figures 2 and 3 are cross-sectional views showing an exemplary embodiment of a variable focus lens according to the invention in two sequential steps of manufacturing the variable focus lens;

FIG. 4 is a cross-sectional view showing another embodiment of a lens according to the present invention;

figure 5 is a schematic view of a mobile phone comprising an optical device comprising a variable focus lens according to the invention.

Detailed Description

According to an embodiment of the invention, a lens arrangement is provided having resilient means which is preferably deformable in response to a change in pressure of a liquid contained in the lens, and whose deformation has no or little effect on the optical properties of the lens. Thus, any deformation of the components that has an effect on the optical performance of the lens is limited, thus ensuring that the lens retains its optical performance when the lens holder is assembled and the lens is used.

Fig. 2 shows an exemplary embodiment of a variable focus lens holder according to the present invention in an intermediate step of manufacturing the lens holder. The variable focus lens holder 10 according to the invention comprises an upper part 12 and a lower part 14, which are made separately from each other and which, when assembled, define an inner volume 15 containing an insulating liquid and a conducting liquid (not shown). The lower part 14 comprises a body 16 with symmetry of revolution about an axis Δ, for example made of steel, which comprises a base 17 through which a central opening 18 passes and which continues to a cylindrical side wall 20, which terminates in a frustoconical flange 22. The base 17 of the body 16 comprises a corrugated portion 23 with symmetry of revolution about the axis Δ and which has an "S" shape in section in a plane containing the axis Δ. A cylindrical plate 24 made of a transparent material, such as glass, is fixed to the body 16 by means of a fixing material 22, such as frit glass or any other type of adhesive, while covering the opening 18 on the same side of the inner volume 15 of the lens holder 10.

The upper part 12 of the lens holder 10 comprises a cover 30, through the central part of which a cylindrical opening 32 passes, and which extends to form a cylindrical side wall 34, the diameter of which is greater than the diameter of the cylindrical side wall 20 of the body 16. The cap 30 includes a resilient portion 36 disposed between the opening 32 and the cylindrical sidewall 34.

In the embodiment shown in fig. 2, said elastic portion 36 comprises a wave-shaped portion having symmetry of revolution about said axis Δ and having an "S" shape in section in a plane containing said axis Δ.

Advantageously, the cover comprises an upper wall (31) connected to the transparent plate and to the cylindrical side wall 34, and the upper wall comprises a curved portion 36 having symmetry of revolution about the axis (Δ) of the lens. For example, the cover is made of stamped metal, such as stainless steel. The thickness of the upper wall of the hood will be determined according to the desired volume change to compensate for the swelling effect of the liquid. For example, a thickness of typically about 0.1 to 0.25mm has a good effect on lenses having an outer diameter below 20 mm.

A cylindrical plate 38 made of a transparent material, such as glass, is fixed to the cover 30 by a fixing material 40, such as glass or an adhesive, while covering the opening 32 on the same side of the inner volume 15 of the lens holder 10.

The cylindrical plate 38 is used as a window covering the opening 32. According to a variant of the invention, the window may be a fixed lens made of transparent optical material.

On the same side of the internal volume 15, an intermediate piece 42 is seated on the seat 17 of said body 16. The intermediate member 42 includes a flat surface 44 that abuts the glass sheet 24 and an opening 46 through the intermediate member that defines a conical surface 48 adjacent the glass sheet 24. The intermediate piece 42 is made of, for example, stainless steel and is coated with an insulating layer at least on its surface in contact with the conductive liquid contained in the lens holder 10. During use of the lens, the edges of the interface between the conducting liquid and the insulating liquid, both contained within the inner volume 15, move along the frustoconical surface 48, the insulating liquid wetting the glass plate 24. Advantageously, for good control of the movement of the interface between the two liquids, the roughness of the conical surface 48 is defined by a roughness parameter Ra (arithmetic mean deviation) which is less than 0.1 μm. To achieve such roughness values, the manufacture of the conical surface 48 may involve abrasive polishing (friction finishing), electrolytic polishing, or diamond tooling type surface finishing processes.

A gasket 50 is disposed between the body 16 and the cap 30 on the outer periphery of the body 16 and the cap 30. The gasket 50 includes an annular surface portion 52 that extends to form a skirt portion 54. By way of example, the gasket 50 is made of fluorinated silicone (fluorosiloxane), or ethylene propylene terpolymer (EPDM), or FKM, FKM being the standard name for Viton (Viton) type fluorinated polymers, and Viton being the trade name of Dupont Dow Elastomer. More generally, the gasket 50 is made of a material that has a low absorption of the liquid contained in the internal volume 15 of the lens holder 10, and this also helps to maintain the dielectric properties of the lens.

In manufacturing the lens holder 10 according to the present invention, the upper member 12 and the lower member 14 are first manufactured separately. The intermediate piece 42 is fixed to the body 16, for example by a crimping fitting, so as to obtain a good electrical contact between the intermediate piece 42 and the body 16. Furthermore, a sealing device is provided between the intermediate piece 42 and the glass pane 24. This may involve pre-depositing a polymer layer on the flat surface 44 of the intermediate member 42 or on the glass plate 24, for example by means of a curable adhesive. The washer 50 is seated on the body 16 with the ring surface portion 52 abutting the intermediate piece 42 and the skirt portion 54 surrounding the cylindrical sidewall 20 of the body 16. The frustoconical flange 22 of the body 16 helps to retain the gasket 50 on the body 16 prior to assembly of the cap 30. The second component 14, in contact with the gasket 50, is then immersed in the conductive liquid. A droplet of insulation is placed in contact with glass sheet 24 and conical surface 48. The placement of the insulating liquid may be facilitated by providing a layer of material on the surface of the glass plate 24 to be contacted by the insulating liquid that preferentially tends to be wetted by the insulating liquid rather than the conductive liquid. The cap 30 is then placed over the gasket 50 with the skirt portion 54 of the gasket 50 sandwiched between the sidewall 34 of the cap 30 and the sidewall 20 of the body 16. In this way, a lens holder 10 as shown in fig. 2 is produced in principle. The step of placing the upper part 12 on the lower part 14 is advantageously done in a liquid environment, limiting the risk of air entering the inner volume 15 of the lens holder 10.

In the embodiment shown in fig. 2, the portion 52 of the gasket compressed between the cover and the intermediate piece 42 is toroidal, but other shapes are possible for this portion 52. For example, the cross-section of the portion of the gasket may be rectangular or any other shape.

In the final step of manufacturing the lens holder 10, the free flange of the side wall 34 of the cover 30 is crimped onto the body 16 while the annular portion 52 of the gasket 50 is compressed between the cover 30 and the intermediate piece 42. By way of example, the cap 30 is crimped onto the body 16 under controlled compressive forces acting on the gasket 50. This then results in the structure shown in fig. 3, wherein the side 34 of the cap 30 includes an end 56 that is crimped onto the body 16. Thus, the skirt 54 of the gasket 50 is compressed between the sidewall 34 of the cap 30 and the sidewall 20 of the body 16. Thus, the internal volume 15 of the lens holder 10 can be sealed by compression of the annular surface portion 52 and compression of the side edge portion 54 of the gasket 50.

By contrast with the structure shown in fig. 1, the upper electrode of the lens comprises said cap 30 and the lower electrode comprises the body 16 in electrical contact with said intermediate piece 42. Thus, the gasket 50 also provides electrical insulation of the cap 30 relative to the body 16.

According to this exemplary embodiment of the lens holder 10 according to the present invention, the aforementioned elastic means are the elastic portions 36 of the cover 30. Specifically, if the pressure in the internal volume 15 of the lens holder 10 rises, the elastic portion 36 provided on the cover 30 deforms preferentially with respect to the other portions of the lens holder 10. The stresses acting on the transparent cylindrical plates 24, 38 are therefore reduced, thus avoiding any risk of deformation or breakage of said plates 24, 38. Since the plates 24, 38 are not deformed, the optical power of the lens remains constant. And thus the focal length of the lens is unchanged.

The transparent plate 38 may have some relative movement with respect to the transparent plate 24 when the resilient portion 36 is deformed. However, due to the symmetry of revolution of the elastic portion 36, this movement of the transparent plate 38 occurs substantially only along the axis Δ. The parallelism of the two transparent plates 24, 38 is thus maintained, thus avoiding any offset of the optical axis of the lens.

The wavy portion 23 provided on the body 16 may also serve as an elastic means if the thickness of the body 16 exceeds the thickness of the cover 30, but has a smaller range of action than the elastic portion 36. However, the wavy portion 23 may be deformed in a case where, for example, a liquid contained in the lens holder 10 swells significantly.

According to a variant of the invention, the elastic means comprise an air-filled cavity formed, for example, on the intermediate piece 42 and which is separated from the inner volume 15 of the lens holder 10 containing the insulating and conducting liquid by a water-impermeable elastic membrane. The change in pressure within the internal volume 15 then causes a deformation of the membrane.

According to another variant of the invention, the sealing layer provided between the glass pane 24 and the intermediate piece 42 and the layer provided on the glass pane 24 on the same side of the inner volume 15, which is intended to be wetted by an insulating liquid rather than by an electrically non-conductive liquid, are one and the same monolayer.

According to another variant of the invention, the material used to fix the glass plates to the cover 30 and to the body 16, respectively, is protected by a protective layer, preventing the fixing means from deteriorating in the presence of the liquid contained in the internal volume 15 of the lens holder 10. This relates, for example, to a protective layer based on an organic material.

According to another variant of the invention, after the intermediate piece 42 has been fitted on the body 16 in contact with the transparent plate 24, the side designed to face the internal volume 15 of the lens holder 10 is covered as a whole by an insulating layer.

According to another variant of the invention, the intermediate piece 42 and the body 16 are formed in a single piece, on which the cap 30 is crimped. The single piece may include a shoulder for receiving the transparent plate 24.

Fig. 4 shows a cross-sectional view of another embodiment of a lens according to the invention. According to this embodiment, and similar to the embodiment shown in fig. 2 and 3, the lens 10 according to the invention comprises two transparent windows 24, 38 facing each other and parallel to each other and which at least partially delimit an inner volume (15) containing two liquids of different optical indices and immiscible with each other, while the two liquids define an optical interface (not shown in fig. 4). In fig. 4, the window is a transparent plate made of a light-transmitting material such as glass. According to one variant, at least one window has a fixed optical length and is centered on the optical axis (Δ) of the variable focusing lens.

As previously described with reference to fig. 2 and 3, the lens includes a cover 30 connected to a transparent window 38 and including a first cylindrical sidewall 34. It also comprises a body 16 with rotational symmetry with the optical axis (Δ) of the lens as the axis of rotation. The body is connected to another transparent window (24) and includes a second cylindrical sidewall 20 having a smaller diameter than the first cylindrical sidewall. As previously described, the upper electrode includes the cap 30 and the lower electrode includes the body 16. The gasket 50 is provided to ensure compactness of the lens holder. Which is compressed between the first and second cylindrical sidewalls. In the embodiment of fig. 4, the gasket comprises a skirt 54 compressed between the first and second cylindrical side walls and a portion 52 compressed between the cap and the intermediate part 42, which in this example is formed in one piece with the body, and comprises an opening defining a conical or cylindrical critical surface 48 at which the interface between the two liquids can move. According to the invention, the lens further comprises elastic means 36 deformable in response to the pressure of the liquid. In this embodiment, the elastic means comprise a bend 36 formed on the upper wall 31 of the cover, said bend having a symmetry of revolution about the optical axis (Δ) of the lens. For example, the curved portion includes at least one annular curved portion centered on an optical axis (Δ) of the lens. Also in this example, the cover may be made of stamped metal, such as stainless steel. The thickness of the upper wall of the hood will be determined according to the desired volume change to compensate for the swelling effect of the liquid. For example, a thickness of typically about 0.1 to 0.25mm has a good effect on lenses having an outer diameter below 20 mm.

Other resilient means may be provided. For example, an air-filled cavity may be inserted into the lens to compensate for the swelling effect of the liquid. In fig. 4, the first sidewall 34 includes a flange 56 crimped onto the body 16 for sealing the closure to the body. Other methods of sealing the cover to the body are possible, for example the cover may be glued to the body.

The method used to manufacture a lens according to the invention as shown in figure 4 may be similar to the method described previously.

Advantageously, the method includes the step of providing a cap 30 and a body 16, respectively, to which windows 38 and 24 have been sealed, respectively. A gasket 50 is then positioned between the first and second cylindrical sidewalls, and the cap is positioned and sealed to the body after the internal volume has been filled with both liquids.

According to a variant, the step of filling said inner volume comprises immersing the body and the transparent window connected thereto in a solution of said conductive liquid, placing a drop of an insulating liquid in contact with said transparent window, and placing the gasket and the side walls of the cap in a state in which said body remains immersed in said conductive solution at the same time. Advantageously, the sealing of the side walls of the cap to the body is done while the body is kept immersed in the conductive dissolver, thus avoiding any air bubbles from being introduced into the lens.

Due to the elastic means provided in the lens, a deformation of the window due to an increase in pressure of the liquid during manufacturing of the lens will not occur.

Advantageously, as shown in fig. 4, the cap is provided with a bend having symmetry of revolution about the axis (Δ) to form the elastic means.

According to a variant, during the manufacture of the lens, a cavity filled with air is inserted into the lens, which cavity is deformable as a function of the pressure of the liquid.

Advantageously, the sealing of the cover to the body is achieved by crimping the side walls of the cover onto the body, so that the lens holder obtains very good mechanical strength.

The invention is, of course, susceptible to modifications and changes in various ways, which will be obvious to a person skilled in the art. In particular, the above-described steps of the method may be modified. As an example, the insulating liquid droplets may be directed onto the lower part 14 of the lens holder 10 before the lens holder is immersed in a conducting liquid.

Fig. 5 is a schematic diagram of an example of an optical device 60 employing a variable focus lens 10 according to the present invention. According to this example, the optical device comprises a lens holder 61 for holding the variable focal length lens 10 and a set of fixed lenses 62. It further comprises a driver 64 for driving the lens, which driver is connected to the electrodes of the lens via leads 65, 66.

The optical device may be used in many systems where miniaturized variable focus optical devices are required, such as mobile phones, endoscope systems, etc.

Claims (24)

1. A variable focus lens (10) having an optical axis (Δ), comprising two transparent windows (24, 38) facing each other at least partially and parallel to each other and at least partially delimiting an inner volume (15) containing two immiscible and optically different liquids defining an interface, wherein the lens comprises:

a cover (30) connected to one of said transparent windows (38) and comprising a first cylindrical side wall;

a body (16) having rotational symmetry about an axis defining a lens optical axis (Δ), said body being connected to the other of said transparent windows (24) and comprising a second cylindrical sidewall (20) having a smaller diameter than said first cylindrical sidewall;

a gasket (50) compressed between the first and second cylindrical sidewalls; and

an elastic device (36) deformable in response to a change in pressure of the liquid.

2. Lens (10) according to claim 1, characterized in that said elastic means have a symmetry of revolution about the optical axis (Δ) of said lens.

3. The lens of claim 1, further comprising:

an intermediate piece (42) connected to or formed in one piece with the body, the intermediate piece comprising an opening defining a conical or cylindrical critical surface (48) at which the interface between the two liquids is movable.

4. The lens of claim 3, wherein the gasket (50) includes a first portion (52) compressed between the cover and the intermediate piece and a skirt (54) compressed between the first and second cylindrical sidewalls.

5. The lens of claim 4, wherein the first portion compressed between the cover and the intermediate piece is toroidal.

6. Lens according to claim 1, characterized in that said cover comprises an upper wall (31) connected to one of said transparent windows (38) and extending to form said first cylindrical side wall, and in that said elastic means comprise a curved portion (36) formed on the upper wall of said cover with symmetry of revolution about the optical axis (Δ) of said lens.

7. Lens according to claim 6, characterized in that said curvature comprises at least one circular curvature centered on the optical axis (Δ) of the lens.

8. The lens of claim 6, wherein the cover is made of stamped metal.

9. The lens of claim 8, wherein the upper wall of the cover has a thickness of 0.1 to 0.25 mm.

10. A lens according to claim 3, characterized in that the roughness of said surface is defined by a roughness parameter Ra, which is less than 0.1 μm.

11. The lens of claim 1, wherein the first cylindrical sidewall (34) includes a flange (56) crimped onto the body (16).

12. A lens according to claim 3, further comprising a sealing layer between the intermediate piece (42) and the other transparent window (24) and/or between the body (16) and the other transparent window (24).

13. Lens according to claim 1, characterized in that the body (16) and/or the cover (30) are connected to the respective transparent window (24, 38) by means of a frit glass (22, 40) covered with a protective layer based on an organic compound.

14. Lens according to claim 1, characterized in that the window (24, 38) is a transparent plate.

15. The lens of claim 1, wherein at least one of the windows is a fixed lens.

16. An optical device comprising a variable focus lens as claimed in any of claims 1 to 15.

17. A mobile phone comprising the optical device of claim 16.

18. A method of manufacturing a variable focus lens having an optical axis (Δ), said lens comprising two transparent windows which at least partially face each other and are parallel to each other and which at least partially delimit an inner volume (15) containing an immiscible, electrically conductive liquid and an insulating liquid having different optical indices, and which define an interface, said lens further comprising elastic means (36) deformable in response to a variation in pressure of said electrically conductive liquid and insulating liquid, wherein said method comprises the steps of:

providing a cover (30) having rotational symmetry about said optical axis (Δ), a cylindrical opening passing through a central portion of said cover and said cover extending to form a first cylindrical sidewall, said cover being sealed to cover said cylindrical opening by a transparent window;

providing a body (16) with a second cylindrical opening through a central portion of the body and extending to form a second cylindrical sidewall (20) having a smaller diameter than the first cylindrical sidewall, another of the transparent windows sealing the body to cover the second cylindrical opening;

disposing a gasket (50) between the first and second cylindrical sidewalls;

after the inner volume is filled with the conductive liquid and the insulating liquid, the cover is placed and sealed onto the body.

19. The method according to claim 18, characterized in that it comprises:

an intermediate piece (42) is disposed on the body, the intermediate piece including an opening defining a conical or cylindrical surface at which the interface is movable.

20. The method of claim 18, wherein the step of filling the internal volume comprises:

immersing the body and the other transparent window connected with the body in a dissolved body of the conductive liquid;

placing an insulating droplet in contact with the other transparent window;

the gasket and the side wall of the cap are placed in a state where the body is kept immersed in a dissolved body of the conductive liquid.

21. The method of claim 20, wherein sealing the side wall of the cap to the body is achieved while the body is maintained immersed in a dissolved body of the conductive liquid.

22. Method according to claim 18, characterized in that the cover is provided with a bend having rotational symmetry about the optical axis (Δ) for forming the resilient means.

23. The method of claim 22, wherein the cover is made of stamped metal.

24. The method of claim 18, wherein sealing the cover to the body is accomplished by crimping a sidewall of the cover to the body.