Abstract
A bidirectional electromagnetically induced transparency (EIT) arising from coupling of magnetic dipole modes is demonstrated numerically and experimentally based on nanoscale a-Si cuboid-bar metasurface. Analyzed by the finite-difference time-domain (FDTD) Solutions, both the bright and dark magnetic dipole mode is excited in the cuboid, while only the dark magnetic dipole mode is excited in the bar. By breaking the symmetry of the cuboid-bar structure, the destructive interference between bright and dark magnetic dipole modes is induced, resulting in the bidirectional EIT phenomenon. The position and amplitude of simulated EIT peak is adjusted by the vertical spacing and horizontal spacing. The EIT metasurface was fabricated by Electron-Beam Lithography and deep silicon etching technique on the a-Si film deposited by Plasma-Enhanced Chemical Vapor Deposition. Measured by a convergent spectrometer, the fabricated sample achieved a bidirectional EIT peak with transmission up to 65% and 63% under forward and backward incidence, respectively. Due to the enhanced magnetic field induced by the magnetic dipole resonance, the fabricated bidirectional EIT metasurface provides a potential way for magnetic sensing and magnetic nonlinearity.
Highlights
Induced transparency (EIT) has attracted enormous interest due to its unique characteristics, including extreme dispersion and enhanced nonlinear effect
The impact of spacing between cuboid and bar on the Electromagnetically induced transparency (EIT) peak is investigated by numerical simulations, and the results indicate that the EIT peak is tuned by the coupling separations and structural asymmetry, which is the spacing between cuboid and bar in different direction, respectively, arising from the shift of the dark mode and change of coupling effect
Under forward incidence, the dip at 803 nm remains unchangeable while the dip at 722 nm reduces significantly in the simulated transmission spectrum of sole-cuboid nanostructure metasurface shown by the black curve in Figure 3a, indicating that the magnetic dipole mode is bidirectional but the electric dipole mode is not
Summary
Induced transparency (EIT) has attracted enormous interest due to its unique characteristics, including extreme dispersion and enhanced nonlinear effect. Graphene-based metamaterials have been proposed to induce tunable EIT effect by adjusting the applied bias on the graphene [21,22,23,24,25,26], which serve as building blocks for adjustable optical devices. EIT dielectric metamaterials based on Mie-resonance, where the displacement current replaces the conduction current, feature greatly reduced non-radiative loss compared with plasmonic counterparts, providing a promising platform for application in low-loss, slowlight devices [27,28,29], high-efficiency optical sensors [30,31], polarization convertors [32], and high-modulation optical switches [33,34]
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