Efficient light focusing through tunable spiralized Fresnel zone plate

Here we present a structure based on a tunable spiralized Fresnel zone plate, engineered to turn dark zones into additional emission zones by properly rephasing the crossing light. The choice of a suitable configuration allows us to reduce the inherent linear anisotropy related to wire structures. The spiral design permits us to sweep the focus point along the three orthogonal coordinate directions and also provides some degree of frequency tunability, all desirable characteristics for modern applications of this type of lenses, such as modern micro-lensing devices. (C) 2019 Optical Society of America