By combining the advantages of both a metallic metamaterial and a dielectric interlayer, we demonstrate the general mechanism to construct the dispersion-free metastructure, in which the intrinsic dispersion of the metallic structures is perfectly cancelled out by the thickness-dependent dispersion of the dielectric spacing layer. As examples to apply this concept, a broadband quarter-wave plate and a half-wave plate are demonstrated. By selecting the structural parameters, the polarization state of light can be freely tuned across a broad frequency range, and all of the polarization states on the Poincaré sphere can be realized dispersion free.
Jiang, S. C., Xiong, X., Hu, Y. S., Hu, Y. H., Ma, G. B., Peng, R. W., … Wang, M. (2014). Controlling the polarization state of light with a dispersion-free metastructure. Physical Review X, 4(2). https://doi.org/10.1103/PhysRevX.4.021026