Theoretical design of eight‐band linear‐to‐circular converter in reflection and transmission modes based on self‐complementary metasurfaces

Multiband linear‐to‐circular (LTC) metamaterial converters have promising applications in modern optical system. However, it is challenging to design a converter with conversion bands of more than four and the axial ratio of less than 3 dB due to the coupling interaction of different resonant structures in a unit cell. In this article, we demonstrate a broad class of self‐complementary THz infinite thin metasurfaces composed of supercells of fractal metal rectangular patches and holes dimers of spanning 1 THz octave in bandwidth, while still being highly efficient. The advantages of this converter are as follows. The device is theoretically nonthickness; the LTC polarization conversion can be achieved in both the reflected and transmitted fields; the phase difference between two orthogonal linear polarization components is theoretically 90° in any frequency. Therefore, an eight‐band LTC converter is achieved in reflection and transmission modes. This new nonthickness multiband device will demonstrate a major advance toward an LTC synthetic metasurface in the THz band.