The giant optical activity of chiral metamaterials (CMMs) holds great potential for tailoring the polarization state of an electromagnetic (EM) wave. In controlling the polarization state, the aspect of asymmetric transmission (AT), where a medium allows the EM radiation to pass through in one direction while restricting it in the opposite direction, adds additional degrees of freedom such as one-way channelling functionality. In this work, a CMM formed by a pair of mutually twisted slanted complementary metal strips is realized for broadband AT accompanied with cross-polarization (CP) conversion for linearly polarized EM waves. Numerically, the proposed ultra-thin (∼λ/42) CMM shows broadband AT from 8.58 GHz to 9.73 GHz (bandwidth of 1.15 GHz) accompanied with CP transmission magnitude greater than 0.9. The transmission and reflection spectra reveal the origin of the asymmetric transmission as the direction sensitive cross polarization conversion and anisotropic electric coupling occurring in the structure which is then elaborated with the surface current analysis and electric field distribution within the structure. An experiment is carried out to verify the broadband AT based CP conversion of the proposed CMM at microwave frequencies, and a reliable agreement between numerical and experimental results is obtained. Being ultra-thin, the reported broadband AT based CP conversion of the proposed CMM is useful for controlling radiation patterns in non-reciprocal EM devices and communication networks.

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 =4 Â =4 Â =9 at the far-infrared operating waveband. The CP conversion and filtering functionalities of the proposed FSCMM are ensured for oblique incidences up to 20 with an optical isolation of more than 25 dB for both x -and 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.

Controlling of the lineshape of Fano resonance attracts much attention recently due to its wide capabilities for lasing, biosensing, slow-light applications and so on. However, the controllable Fano resonance always requires stringent alignment of complex symmetry-breaking structures and thus the manipulation could only be performed with limited degrees of freedom and narrow tuning range. Furthermore, there is no report so far on independent controlling of both the bright and dark modes in a single structure. Here, we semi-analytically show that the spectral position and linewidth of both the bright and dark modes can be tuned independently and/or simultaneously in a simple and symmetric metal-slit superlattice, and thus allowing for a free and continuous controlling of the lineshape of both the single and multiple Fano resonances. The independent controlling scheme is applicable for an extremely large electromagnetic spectrum range from optical to microwave frequencies, which is demonstrated by the numerical simulations with real metal and a microwave experiment. Our findings may provide convenient and flexible strategies for future tunable electromagnetic devices.

The ever-increasing interest towards metamaterial absorbers owes to its remarkable features such as ultra-thin nature and design flexibility. Subduing the inherent narrow bandwidth of such absorbers is the prime goal in metamaterial absorber research, as this can widen the applications areas. A greater challenge is to construct bidirectional absorber, which provides direction-insensitive absorption, as most of the existing designs exhibit single sided absorption due to the complete metal film used in the design. This work presents the realization of a bidirectional, bandwidth-enhanced metamaterial absorber with basic elements such as strips and squares optimized to have adjacent resonances leading to a bandwidth-enhanced absorption. The structural evolution of the constituent metallic components towards the formation of bandwidth-enhanced absorption is described. The bidirectional absorber exhibits more than 90% absorption between 13.40 GHz and 14.25 GHz from the two incident directions. The mechanism of absorption is studied with the surface current analysis and the effective parameters of the structure. The choice of the metallic components with four-fold rotation symmetry renders the proposed design to be polarization independent and wide-angle receptive. The numerical studies are verified experimentally at microwave frequencies, which shows a good agreement between them.

Articles you may be interested inComplementary chiral metasurface with strong broadband optical activity and enhanced transmission Appl. Phys. Lett. A frequency-tunable 90°-polarization rotation device using composite chiral metamaterials Dual-band asymmetric transmission of linear polarization in bilayered chiral metamaterial Appl. Phys. Lett. 102, 191905 (2013); 10.1063/1.4805075 Intensity modulation and polarization rotation of visible light by dielectric planar chiral metamaterials