Optical device with focal length variation

1. An optical device with focal length variation comprising:

a first deformable membrane,

a second deformable membrane,

a support to which a respective peripheral anchoring area of each of said membranes is connected,

a constant volume of fluid enclosed between the first and the second membrane, said fluid producing mechanical coupling of said first and second membranes,

an actuation device of a region of the first membrane located between the anchoring area and a central part of the first membrane, configured to deform by application of electrical actuation voltage in a single direction of deflection to displace at least a portion of the fluid volume, wherein said displacement of fluid is to cause deformation of the central part of the first membrane,

wherein, based at least in part on a stiffness of the central part of the first membrane:

from a rest position in which the actuation device is inactive, the first membrane deforms only in a first direction when electrical actuation voltage less than a threshold is applied to the actuation device and the second membrane deforms to absorb the fluid displacement caused by deformation of the first membrane to minimize the pressure of the fluid on the first membrane, and

the actuation region of the first membrane remaining deformed in said first direction, the central part of the first membrane deforms in a second direction opposite the first direction under the effect of the pressure of the fluid displaced by the actuation device when electrical actuation voltage greater than said threshold is applied to the actuation device.

2. The device according to claim 1 , wherein the second membrane exhibits stiffness less than the central part of the first membrane.

3. The device according to claim 1 , further comprising an actuation device of an actuation region of the second membrane located between the anchoring area and a central part of said membrane, configured to deform by application of electrical actuation voltage.

4. The device according to claim 3 , wherein the actuation device of the second membrane is capable of deforming in two opposite directions as a function of the electrical actuation voltage applied to said device.

5. The device according to claim 1 , wherein, in a rest configuration, the central part of the first membrane is planar.

6. The device according to claim 5 , further comprising a substrate extending between both membranes and comprising at least one fluid passage opening, such that the fluid pressure is identical on either side of said substrate.

7. The device according to claim 1 , wherein the material of the first and/or the second membrane is a siloxane resin or mineral material comprising silicon.

8. The device according to claim 1 , wherein the actuation device of the first membrane comprises at least one piezoelectric actuator.

9. The device according to claim 1 , wherein the first or the second membrane is reflecting.

10. The device according to claim 1 , wherein the stiffness of the first membrane is selected so that in the absence of fluid pressure exerted on said membrane, application of electrical actuation voltage to the actuation device causes deformation of the actuation region and of the central part of the membrane, the tangents to the membrane on either side of the junction between the actuation region and the central part being combined.

11. The device according to claim 1 , wherein the diameter of the deformable part of the first membrane is different from the diameter of the deformable of the second membrane.

12. The device according to claim 1 , characterized in that the diameter of the deformable part of the first membrane is identical to the diameter of the deformable part of the second membrane.

13. The device of claim 1 , wherein the device is included in an imaging device.

14. A method for variation of the focal length of an optical device comprising:

applying, to an actuation device of a region of a first deformable membrane, a first electrical actuation voltage less than a threshold, causing a deformation of the first deformable membrane in a first direction while a second deformable membrane deforms to absorb displacement of fluid enclosed between the first deformable membrane and the second membrane caused by deformation of the first deformable membrane to minimize the pressure of fluid on the first deformable membrane; and

applying, to the actuation device, a second electrical actuation voltage greater than said threshold, causing a deformation of a central part of the first deformable membrane in a second direction opposite the first direction under the effect of pressure of the fluid displaced by the actuation device, the actuation region of the first membrane remaining deformed in the first direction.

15. The method according to claim 14 , wherein:

at rest, the first and the second membrane each form a plane diopter,

the first electrical actuation voltage is applied to deform the actuation region and the central part towards the fluid, the second membrane deforming in the direction opposite the fluid, such that the central part of the first membrane forms a divergent diopter and the second membrane forms a convergent diopter,

the second electrical voltage is applied to deform the actuation region towards the fluid, displacement of the fluid causing deformation of the central part in the direction opposite the fluid, such that the central part of each of the two membranes forms a convergent diopter.

16. The method according to claim 14 , wherein the diameter of the deformable part of the first membrane is less than the diameter of the deformable part of the second membrane, and wherein:

at rest, the first and the second membrane each form a plane diopter,

the first electrical actuation voltage is applied to deform the actuation region and the central part towards the fluid, the second membrane deforming in the direction opposite the fluid, such that the optical device forms a divergent meniscus.

17. The method according to claim 14 , wherein the diameter of the deformable part of the first membrane is greater than the diameter of the deformable part of the second membrane, and wherein:

at rest, the first and the second membrane each form a plane diopter,

the first electrical actuation voltage is applied to deform the actuation region and the central part towards the fluid, the second membrane deforming in the direction opposite the fluid, such that the optical device forms a convergent meniscus.

18. The method according to claim 14 , wherein the optical device comprises an actuation device of an actuation region of the second membrane located between the anchoring area and a central part of said membrane, configured to deform by application of electrical actuation voltage, and wherein:

at rest, the first and the second membrane each form a plane diopter,

the first electrical actuation voltage is applied to the actuation device of the first membrane to deform the actuation region and the central part towards the fluid without applying electrical actuation voltage of the actuation device of the second membrane, the second membrane deforming in the direction opposite the fluid such that the central part of the first membrane forms a divergent diopter and the second membrane forms a convergent diopter,

the second electrical actuation voltage is applied to the actuation device of the first membrane to deform the actuation region towards the fluid and electrical actuation voltage is applied to the actuation device of the second membrane towards the fluid to increase convergence of the diopter formed by the central part of the second membrane.