An adaptive liquid lens with a reciprocating movement in a cylindrical hole.

We demonstrate a liquid droplet which can do a reciprocating movement in a cylindrical hole. The droplet in the hole exhibits a lens character. By applying a voltage, the border of the droplet is stretched to expand by the generated dielectric force. Due to the fixed volume, the dome of the droplet in the hole has to move toward the substrate without changing its surface profile. Therefore, the focal length of the droplet remains unchanged although the focal point is shifted. Once the voltage is removed, the droplet can return to its original state. The droplet with such a movement functions as an adaptive lens. Our lens can provide a high resolution (~114 lp/mm) whether or not it is actuated. The dynamic response time is reasonably fast. Integrating with a solid lens, the compound lens can provide a variable focal length.