  Chiral response is of tremendous importance to many fields, such as
analytical chemistry, polarization manipulation and biological sensing. Here, a
chiral metasurface based on rectangular holes is systematically investigated.
The results show that the chirality is closely related to the size and the
orientation of resonance unit. It is found that the period of the structure is
always smaller than the wavelength at which chirality appears, which will
provide a good basis for the design of chiral structures. More importantly, the
CD is highly sensitive to the orientation of resonance unit. By adjusting the
rotation angle, it is not only possible to invert the CD, but also to change
the symmetry of the structure to realize the regulation of chirality. The
chirality can be significantly enhanced in the proposed structure, and the
maximum of circular dichroism (CD) can reach 0.76. To better understand the
physical mechanism, the distributions of electric field for LCP and RCP waves
are also discussed as well. This work will not only deepen the understanding of
chiral metasurfaces, but also provide guidance for the design of similar chiral
structures.
