Similar structures, different characteristics: optical performances of circular polarizers with single-, double-, and multi-helical metamaterials

Recently, it was demonstrated by J.K. Gansel et al. that three-dimensional single-helical metamaterials can serve as broadband circular polarizers in the infrared range. Firstly, in this paper, we used the finite difference time domain (FDTD) method to study circular polarizers with double-helical metamaterials. The results show that the operation bands are more than 50% broader than those of the single-helical structures. However, we also notice that the signal-to-noise (S/N) ratios of them are both poor (similar to 10 dB). Secondly, we analyzed the performances of triple-helical structures. It is obvious that the triple-helical circular polarizer has not only a broad operation band, but also a much higher S/N ratio (similar to 35 dB) than single- and double-helixes.