Multifunctional terahertz metasurface devices based on 3D-printed low refractive index meta-gratings

Metasurface optical devices have shown a tendency to gradually supersede the conventional bulk devices in applications requiring compactness and light weight. Typical metasurface-based flat lenses that manipulate the wavefront rely on phase mapping using a limited number of subwavelength structures. However, this approach greatly reduces the efficiency when limited structures are mapped for a high numerical aperture (NA). Here, we theoretically and experimentally propose low refractive index meta-grating-based multifunctional devices fabricated by three-dimensional printing technology. The meta-grating arrays effectively bend the incident polarized terahertz wave to the designed diffraction angle of 67 degrees, with transmission efficiencies of 74.1% (S-dimer) and 54.2% (P-dimer) at the frequency of 0.1 THz. Then, the meta-lens based on the proposed meta-grating arrays achieves the measured focus efficiency of 32.1% with NA = 0.902, corresponding to a maximum collection angle of 64.5 degrees. The designed flat devices with excellent characteristics in terms of efficiency and NA represent a new paradigm in high efficiency, low-cost and multifunctional terahertz devices.