Broadband terahertz linear cross-polarization conversion in transmission mode using planar coupled metamaterials

Abstract

We demonstrate a metamaterial (MM) design capable of showing linear broadband polarization conversion over the terahertz (THz) frequency range. The building block of the proposed MM structure is composed of a strip and four split ring resonators (SRRs), which are coupled through their near fields. To examine co- and cross-polarization transmission amplitudes, we gradually increase the distance between the strip and SRRs. When the SRRs are near (S = 2 μm) the strip, maximum cross-polarization conversion is attained with a resonance mode hybridization effect in the co-polarization transmission due to strong near-field coupling between the strip and SRRs. When the SRRs moved away from the strip (S = 22 μm), minimum cross-polarization conversion is attained due to weak coupling between the strip and SRRs. This MM system exhibits a transition from a strongly coupled state to a weakly coupled state with the rise in displacement between the strip and SRRs. The ability to tune the linear polarization conversion can be useful in the improvement of efficient THz polarization rotation devices. The proposed MM structure can be used in other frequency domains, like the microwave and visible range, by scaling up/down the structure.