Optical device with focal length variation

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.