Fabrication and characterization of variable-focus liquid lens based on coil

This paper presents a coil-based liquid lens (CLL) with a mature and simple fabrication process. A tunable focal length is achieved by changing the liquid–liquid interface curvature using electrowetting on dielectric (EWOD). The lens cavity is a coil wound or stacked by a particular structure named EWOD wire, which is made by coating a soft insulating dielectric layer on a flexible conductive core. As a result, requirements for different lens designs can be achieved, and coating an insulating dielectric layer in complex cavities is not required. The optical performance of the CLL is measured with a clear aperture of 8 mm, which shows that the tunable range for the focal length is (−∞, −35 mm] ∪ [78 mm, +∞) at a voltage of 0–235 V, and the response time is less than 40 ms.