Optical electrowetting device

Abstract

The invention relates to an optical electrowetting device comprising a conductive fluid (5; 101) and a non-conductive fluid (4; 102), said fluids being non miscible, and an insulating substrate (2; 103) on which both fluids are in contact and form a triple interface, wherein the natural contact angle (105) of the non-conductive fluid (102) on the substrate (103) in presence of the conductive fluid (101) is comprised between 0° and about 20°. This device may be a variable focus liquid lens, an optical diaphragm, an optical zoom. The invention further relates to an apparatus such as a camera, a cell phone, an endoscope or a dental video camera, comprising said electrowetting device and a driver or electronic means for controlling the lens.

Description

The present invention will now be described in further details by way of non-limiting examples and by reference to the attached drawings.

FIG. 1 is a simplified cross-section view of a variable-focus liquid lens according to the invention.

FIG. 2 represents a graph illustrating undesirable focal hysteresis in a liquid lens.

FIG. 3 is a schematic description of the natural angle of a non conductive liquid on a surface in presence of a conductive liquid.

FIG. 4 is a graph showing the contact angle of numerous non conductive fluids on Parylene C, depending on the surface tension, in presence of a conductive fluid having a surface tension γ_L of 44±1 mN/m.

FIG. 5 is a graph showing the contact angle of numerous non conductive fluids on Teflon® AF depending on the surface tension, in presence of a conductive fluid having a surface tension γ_L of 44±1 mN/m.

FIG. 6 shows one example of the optical power of a liquid lens, operated at around 20 V, and comprising Parylene F as dielectric hydrophobic layer with a thickness of about 700 nm. The fluids used in this particular example are an oil phase and a conducting phase whose formulations are given below (all % are weight %):

Non-conductive fluid	Conductive fluid
T23/SIP 6827	20%	Water	39.7%
DC 702	59.4%	Na2SO4	0.2%
1,8-dichlorooctane	20%	Benzalkonium chloride	0.1%
BHT	0.6%	1,2-Propanediol	60%

FIG. 7 is a graph showing the relation between substrate polarity (mN/m) and contact angle for a non conductive fluid (γ_L=25±1 mN/m) in presence of a conductive fluid (γ_L=44±1 mN/m).

FIG. 8 is a graph showing the maximum contact angle hysteresis on Parylene C depending on natural contact angle, measured between the natural contact angle and above 60°.

FIG. 9 is a graph showing an improved focal hysteresis in a liquid lens according to the invention.

Claims

1. An optical electrowetting device comprising a conductive fluid (5; 101) and a non-conductive fluid (4; 102), said fluids being non miscible, and an insulating substrate (2; 103) on which both fluids are in contact and form a triple interface, wherein the natural contact angle (105) of the non-conductive fluid (102) on the insulating substrate (103) in presence of the conductive fluid (101) is comprised between 0° and about 20°.

2. The optical electrowetting device of claim 1, wherein the natural contact angle (105) is comprised between above 0° and about 20°, preferably between about 5° and about 16°.

3. The optical electrowetting device of claim 1, wherein the natural contact angle θn is such that 0°≦θn≦20°, preferably 0°<θn≦20°, more preferably 5°≦θn≦20°, most preferably 5°≦θn≦16°, over a range of temperature comprised between about −20° C. and about +70° C.

4. The optical electrowetting device of claim 1, wherein the difference dst between the surface tension of the non-conductive fluid and the surface energy of the insulating substrate is within the range −15≦dst≦+15 mN/m, preferably within the range −12≦dst≦+12 mN/m.

5. The optical electrowetting device of claim 1, wherein the insulating substrate surface energy has a polar component comprised between 0 mN/m and about 4 mN/m, preferably between 0 mN/m and about 2 mN/m.

6. The optical electrowetting device of claim 1, wherein the insulating substrate has a surface energy above about 30 mN/m.

7. The optical electrowetting device of claim 6, wherein the insulating substrate is made of, or comprises an upper layer which is made of, a para-xylylene linear polymer or an aromatic vinylsiloxane polymer.

8. The optical electrowetting device of claim 7, wherein the insulating substrate is made of, or comprises an upper layer which is made of, parylene, preferably Parylene C, Parylene D, Parylene N, Parylene F or AF-4, or Parylene VT-4, more preferably Parylene C, Parylene N or Parylene F.

9. The optical electrowetting device of claim 7, wherein the insulating substrate is made of, or comprises an upper layer which is made of, divinylsiloxane-benzocyclobutene (DVS-BCB) polymer.

10. The optical electrowetting device of claim 1, wherein the non-conductive fluid contains a compound of surface tension equal or above about 28 mN/m.

11. The optical electrowetting device of claim 1, wherein the insulating substrate has a surface energy below about 30 mN/m.

12. The optical electrowetting device of claim 11, wherein the insulating substrate is made of, or comprises an upper layer which is made of, a fluorinated polymer.

13. The optical electrowetting device of claim 11, wherein the insulating substrate is made of, or comprises an upper layer which is made of copolymers of tetrafluoroethylene and 2,2-bis(trifluoromethyl)-4,5-difluorodioxole.

14. The optical electrowetting device of claim 11, wherein the insulating substrate is made of, or comprises an upper layer which is made of, a perfluoropolymer obtained by cyclopolymerization of perfluoro(alkenyl vinyl ether.

15. The optical electrowetting device of claim 11, wherein the non-conductive fluid contains a compound of surface tension equal or below about 28 mN/m.

16. The optical electrowetting device of claim 1, wherein the whole of the non-conductive and the conductive fluids has a mean arithmetic cinematic viscosity of between about 1.5 cSt and about 40 cSt, within a temperature range of about −10° C. to about +60° C., preferably of about −20° C. to about +60° C., more preferably of about −20° C. to about +70° C.

17. The optical electrowetting device of claim 1, wherein the insulating substrate is made of, or comprises an upper layer which is made of, a para-xylylene linear polymer, preferably a parylene, more preferably Parylene C, Parylene D, Parylene N, Parylene F or AF-4, or Parylene VT-4, still more preferably Parylene C, Parylene N or Parylene F, the conductive fluid comprises water and an organic or inorganic salt, the non-conductive fluid comprises halogenated alkane(s) and/or siloxane oil(s).

18. The optical electrowetting device of claim 17, wherein the insulating substrate is made of, or comprises an upper layer which is made of, Parylene C, the conductive fluid comprises water and an inorganic salt, the non-conductive fluid comprises halogenated alkane(s) and siloxane oil(s).

19. The optical electrowetting device of claim 18, comprising: an insulating substrate made of, or comprising an upper layer made of, Parylene C;a conductive fluid comprising:i) from about 35 weight % to about 45 weight %, preferably from about 38 weight % to about 42 weight %, more preferably about 40 weight % of water,ii) from about 0.15 weight % to about 0.25 weight %, preferably from about 0.17 weight % to about 0.23 weight %, more preferably about 0.20 weight % of sodium sulphate,iii) from about 55 weight % to about 65 weight %, preferably from about 58 weight % to about 62 weight %, more preferably about 60 weight % of monopropylene glycol (MPG), andiv) optionally a biocide agent, up to about 0.2%; anda non-conductive fluid comprising:a) from about 15 weight % to about 25 weight %, preferably from about 18 weight % to about 22 weight %, more preferably about 20 weight % of phenyltris(trimethylsiloxy)silane,b) from about 55 weight % to about 65 weight %, preferably from about 58 weight % to about 62 weight %, more preferably about 60 weight %, of a cyclosiloxane and phenylated siloxane mixture having a Ph/Si ratio less than about 1.33 and a Ph/Me ratio less than about 1.33,c) from about 15 weight % to about 25 weight %, preferably from about 18 weight % to about 22 weight %, more preferably about 20 weight %, of 1,8-dichlorooctane, andd) from about 0.4 weight % to about 0.8 weight %, preferably from about 0.5 weight % to about 0.7 weight %, more preferably about 0.6 weight %, of a butylated hydroxyl toluene, preferably 2,6-di-tert-butyl-4-methylphenol.

20. The optical electrowetting device of claim 1, which is a variable focus liquid lens, an optical diaphragm, an optical zoom.

21. An apparatus comprising an optical electrowetting device according to claim 20, and a driver or electronic means for controlling the interface.

22. The apparatus of claim 21, wherein the driver or electronic means further comprises means to apply an A.C. voltage to the conductive fluid.

23. The apparatus of claim 22, which is a camera, a cell phone, a telemeter, an endoscope or a dental video camera.

24. An optical electrowetting device comprising a conductive fluid and a non-conductive fluid, said fluids being non miscible, and an insulating substrate on which both fluids are in contact and form a triple interface, wherein the insulating substrate comprises parylene F or AF-4 or parylene VT-4.

25. The optical electrowetting device according to claim 24, which is an optical lens driven by electrowetting.

26. An optical electrowetting device comprising a conductive fluid and a non-conductive fluid, said fluids being non miscible, and an insulating substrate on which both fluids are in contact and form a triple interface, wherein the insulating substrate comprises an aromatic vinyl siloxane type polymer, preferably divinylsiloxane-benzocyclobutene (DVS-BCB) polymer.

27. The optical electrowetting device according to claim 26, which is an optical lens driven by electrowetting.

28. An optical electrowetting device comprising a conductive fluid and a non-conductive fluid, said fluids being non miscible, and an insulating substrate on which both fluids are in contact and form a triple interface, wherein the insulating substrate comprises a perfluorinated polymer obtained by cyclopolymerisation of perfluoro(alkenyl vinyl ether).

29. The optical electrowetting device according to claim 28, which is an optical lens driven by electrowetting.