High-Efficiency Asymmetric Transmission of Red-Near-Infrared Light Based on Chiral Metamaterial

Designing and fabricating high-performance polarization converters that exhibit asymmetric transmission (AT), for light with different circularly/linearly polarized states with opposite propagating directions, are in high demand. The AT phenomenon leads to potential applications as isolators and circulators in information and communication systems. We propose a chiral metamaterial structure with high AT efficiency for two types of linearly orthogonal polarized red-near-IR light in two opposite incident directions. Theoretical results showed that the proposed chiral metamaterial structure achieves cross-polarization conversion where the polarization conversion ratio (PCR) is over 90%, in a broadband wavelength range from 715 to 810 nm, for both forward-propagating linearly polarized light and backward-propagating orthogonal linearly polarized light. The physical mechanisms of the polarization converter with the AT have been investigated. It was confirmed that the Fabry–Perot-like resonance and coupling between electric and magnetic dipoles lead to highly efficient asymmetric polarization conversion for two orthogonal linearly polarized light. Additionally, the conversion efficiency and bandwidth of the polarization converter are successfully optimized by adjusting the related structure parameters.

Bilayer split-ring chiral metamaterial based reconfigurable antenna for polarization conversion

A bilayer split-ring chiral metamaterial converts the linearly polarized wave, into a nearly perfect left or right-handed circularly polarized wave. The proposed antenna is intended to operate at center frequency of 5.80 GHz with switchable polarization capability. The polarization re-configurability is achieved by electronically switching of two PIN-diode pairs, which are embedded into bilayer split-ring Chiral Metamaterial. The optimized length of rectangular patch is 16 mm and width is 12.1 mm. Two types of radiation characteristics offered by the proposed antenna; left hand circularly polarized in mode 1 and right hand circularly polarized in mode 2. Measured results show that its impedance bandwidth is 155 MHz from 5.70 to 5.855 GHz for both mode 1 and mode 2. The measured axial-ratio bandwidth is 100 MHz from 5.75 to 5.85 GHz for mode 1 and 110 MHz from 5.73 to 5.84 GHz for mode 2. Antenna has LHCP gain of 2.52 dBi and RHCP gain of −23 dBi in mode 1. RHCP gain of 2 dBi and polarization purity of about −20 dBi is obtained in mode 2. The proposed antenna has simple structure, low cost and it has potential application in field of wireless communication (i.e., WiMax, WLAN etc.).