Tripling the Capacity of Optical Vortices by Nonlinear Metasurface

Optical vortices have emerged as a potential approach to enhance data capacity for its extra degree of freedom of orbital angular momentum. Although linear metasurfaces have been used to generate optical vortices, their capacity can be further increased by involving nonlinear frequency conversions, providing new channels for data storage. Here, by introducing second harmonic Pancharatnam–Berry phase, one linear and two second harmonic optical vortices with different topological charges focused into different focal lengths can be generated simultaneously from the proposed metasurface, which can store threefold optical vortices compared with the conventional linear geometric metasurfaces have been demonstrated. Besides, the 2D multifocal metalens with same strength for each focus emerged from the parabolic phase factor has been experimentally observed. This nonlinear optical vortex generation process represents a new strategy for enhancing the capacity of optical communications and multi-channels integrated optical communications.