Efficient terahertz metasurface-based flat lens

We present a nonuniform metasurface that operates as a flat lens at 400 GHz. Efficiency is enhanced by the use of a novel, tri-layer polarization-converting nonuniform meta-surface structure. The device is fabricated and experimentally characterized. The results confirm that the flat lens is indeed capable of focusing radiation to a focal spot with ~68% efficiency. Constrained by spatial dispersion, the -3 dB bandwidth is 150 GHz.