Abstract
In this Letter, we aim to answer the fundamental question of what will happen when two layers of Pancharatnam Berry phase elements are superimposed on each other. The different diffraction orders and their respective phase changes of this structure are investigated by Jones matrix calculations. Based on the results, we propose and demonstrate metalenses numerically that can split an incident circularly polarized beam into different helicities and focus them at different foci with controlled intensity and focal length. The decoupling of the focusing length and the relative intensity give us control to achieve an arbitrary combination of focal spot location and relative intensity. To the best of our knowledge, this is the first proposal and theoretical demonstration of bilayer Pancharatnam-Berry phase elements for metalens applications. Such a platform can be expanded to multilayers and applied to other complex functionalities such as achromatic lenses. (c) 2019 Optical Society of America