Aberration-free aspherical tunable liquid lenses by regulating local curvatures

Aberration is a long-standing problem of fixed focal lenses and usually requires a complicated lens set to compensate. It becomes more challenging for tunable lenses. This paper reports an original design of in-plane optofluidic lens that enables to compensate the spherical aberration during the tuning of focal length. The key idea is to use two arrays of electrode strips to symmetrically control the two air/liquid interfaces by dielectrophoretic effect. The strips work together to define the global shape of the lens interface and thus the focal length, whereas each strip regulates the local curvature of interface to focus the paraxial and peripheral arrays to the same point. Experiments using a silicone oil droplet demonstrate the tuning of focal length over 500 – 1400 µm and obtain the longitudinal spherical aberration (LSA) of ~3.5 µm, which is only 1/24 of the LSA 85 µm of the spherical lens. Fine adjustment of the applied voltages of strips allows to even eliminate the LSA and enable the aberration-free tunable lenses. It is the first time that local curvature regulation is used to compensate the aberration within one in-plane lens. This simple and effective method will find potential applications in lab-on-a-chip systems.