Application of vector diffraction theory in geometric phase based metasurfaces

Abstract

In geometric phase based metasurfaces, phase modulation of the output light can be achieved by designing the shape and layout of the subwavelength structure. For traditional electromagnetic simulation software, the operating principle is often based on finite-difference time-domain, finite element method, or finite integration technique (FIT). Their disadvantages include, for example, the time-consuming simulation and the complicated modeling process. In addition, the computational accuracy may be affected by the size of divided grids. In this paper, an improved vector diffraction theory is investigated to calculate the distribution of the transmitted light field when the incident circular polarization light (CPL) passes through the geometric phase based metasurfaces. The structure acts as a diffraction screen when using the method to calculate the diffraction field. When CPL is incident, the geometric phase is imparted to the output light, and the transmission light field is calculated by normal vector diffraction theory. Three kinds of structures, which can be seen as nano-object arrays, have been designed and characterized to validate our method. The first and second devices realized the separation of cross-polarization and co-polarization components, and the third one realized the function of the focusing lens with a subwavelength catenary array. The transmission fields calculated by the refined vector diffraction theory are in good agreement with the FIT method. We believe this simple yet generalized method can be employed for efficient design of geometric phase based metasurfaces, such as Bessel beam generators, focusing lenses, holographic coding, etc.