Far-Infrared Circular Polarization and Polarization Filtering Based on Fermat's Spiral Chiral Metamaterial

A bilayered-twisted Fermat's spiral chiral metamaterial (FSCMM) is proposed for the realization of circular polarization of far-infrared waves and polarization filters. It is demonstrated through full-wave simulations that the proposed FSCMM can convert waves from linear to circular polarization (CP) around 2.5 THz. The reported FSCMM is sensitive to the handedness of circularly polarized light, where it can filter out either righthanded or left-handed CP light with an optical isolation of 35 dB around 2.5 THz. The proposed FSCMM is compact with a dimension of λ/4 × λ/4 × λ/9 at the far-infrared operating waveband. The CP conversion and filtering functionalities of the proposed FSCMM are ensured for oblique incidences up to 200 with an optical isolation of more than 25 dB for both xand y-oriented linear polarized excitations. The operation bandwidth of the proposed system is enhanced in the level of 0.058 THz to 0.11 THz for twoand three-unit-cell composite systems, respectively. Due to the strong circular dichroism, compactness, wide-angle functionalities, and appreciable bandwidth, the proposed FSCMM is useful for the development of integrated far-infrared spectroscopic and imaging devices.