Two dimensional subdiffraction focusing beyond the near-field diffraction limit via metasurface

Abstract

Near-field plates with the capabilities of modulating the near-field pattern and forcing the incident wave to a subwavelength spot have been experimentally investigated at microwave wavelengths. Their superlensing prop-erties result from the radiationless electromagnetic interference. However, the material’s loss and limitations of state-of-the-art nanofabricating technology pose great challenges to scale down the microwave near-field plates to the infrared or optical region. In this paper, a related but alternative approach based on metasurface is introduced which breaks the near-field diffraction limit at mid-infrared region (10.6 μm). The metasurface consists of periodic arrangement of chromium dipolar antennas with the same geometry but spatially varying orientations, which plays the dual roles in achieving the prescribed amplitude modulation and the abrupt π phase change between the subwavelength neighboring elements. As a result, a two dimensional subdiffraction focus as small as 0.037λ2 at ~0.15λ above the metasurface is presented. In addition, the broadband response and ease fabrication bridge the gap between the theoretical investigation and valuable applications, such as near-field data storage, subdiffraction imaging and nanolithography.