Abstract
Because of the strong inherent resonances, the giant optical activity obtained via chiral metamaterials generally suffers from high dispersion, which has been a big stumbling block to broadband applications. In this paper, we propose a type of planar chiral metamaterial consisting of interconnected metal helix slat structures with four-fold symmetry, which exhibits nonresonant Drude-like response and can therefore avoid the highly dispersive optical activity resulting from resonances. It shows that the well-designed chiral metamaterial can achieve nondispersive and pure optical activity with high transmittance in a broadband frequency range. And the optical activity of multi-layer chiral metamaterials is proportional to the layer numbers of single-layer chiral metamaterial. Most remarkably, the broadband behaviors of nondispersive optical activity and high transmission are insensitive to the incident angles of electromagnetic waves and permittivity of dielectric substrate, thereby enabling more flexibility in polarization manipulation.
Highlights
Manipulating the polarization states of electromagnetic waves has been a long-time interest in realms of life sciences, photoelectrons, telecommunications, etc
Metamaterials enable numerous of extraordinary electromagnetic phenomena that do not exist in natural materials, for instance, abnormal refraction or reflection[1,2,3,4,5,6], super-resolution imaging[7, 8], cloaking[9,10,11], and perfect absorption of electromagnetic waves[12,13,14]
Owing to the inherent Lorentz-like resonances, the giant optical activity of the previous chiral metamaterials (CMMs) is generally accompanied by high losses, high dispersion, narrow transmission bandwidths, and strong polarization distortion because of large ellipticity[18,19,20, 36, 41,42,43], which is exceedingly detrimental for designing broadband and efficient polarization rotators
Summary
Manipulating the polarization states of electromagnetic waves has been a long-time interest in realms of life sciences, photoelectrons, telecommunications, etc. Materials with chirality, which can rotate the polarization plane of electromagnetic waves, are very suitable for designing polarization converters. Owing to the inherent Lorentz-like resonances, the giant optical activity of the previous CMMs is generally accompanied by high losses, high dispersion, narrow transmission bandwidths, and strong polarization distortion because of large ellipticity[18,19,20, 36, 41,42,43], which is exceedingly detrimental for designing broadband and efficient polarization rotators. Three-dimensional off-resonant or nonresonant types of CMMs were demonstrated to achieve nondispersive optical activity[47, 48]. It is found that the frequency of the transmission peak of our CMM presents dynamical tunability by altering the permittivity of dielectric substrate, indicating that the CMM is suitable for designing frequency-tunable polarization manipulation devices for telecommunication applications
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