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Demonstration of a Three-dimensional Negative Index Medium Operated at Multiple-angle Incidences by Monolithic Metallic Hemispherical Shells

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ABSTRACT

We design and construct a three-dimensional (3D) negative index medium (NIM) composed of gold hemispherical shells to supplant an integration of a split-ring resonator and a discrete plasmonic wire for both negative permeability and permittivity at THz gap. With the proposed highly symmetric gold hemispherical shells, the negative index is preserved at multiple incident angles ranging from 0° to 85° for both TE and TM waves, which is further evidenced by negative phase flows in animated field distributions and outweighs conventional fishnet structures with operating frequency shifts when varying incident angles. Finally, the fabrication of the gold hemispherical shells is facilitated via standard UV lithographic and isotropic wet etching processes and characterized by μ-FTIR. The measurement results agree the simulated ones very well.

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Transmission spectra of the single-layered 3D NIM under oblique incidence.Simulated transmission contour with respect to frequency and incident angle of a single-layered 3D NIM for (a) TE and (b) TM cases, respectively. Insets define configurations of TE and TM cases.
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f5: Transmission spectra of the single-layered 3D NIM under oblique incidence.Simulated transmission contour with respect to frequency and incident angle of a single-layered 3D NIM for (a) TE and (b) TM cases, respectively. Insets define configurations of TE and TM cases.

Mentions: The success in developing the 3D NIM under the normal incident condition by the gold hemispherical shell array encourages us to further examine the shell under oblique incident conditions. In the following, we would elaborate transmission apexes of the single-layered 3D NIM to identify the double negative identities under oblique incidence from 0° up to 85° for both TE and TM cases (see Fig. 5(a,b) for the definition of the TE and the TM cases, respectively). For the TE case, a transmission apex with double negative identities maintains its amplitude and shifts toward to the lower frequency with a frequency offset of 0.0028 THz/degree. Such a red shift corresponds to a lower resonance frequency of magnetic dipoles, stemming from a longer surface current loop at the bottom2627. On the contrary, for the electric resonance, the surface current distribution on the edge of the shell under oblique incidence remains similar so that the resonant frequency of the electric resonance is unaltered (see Fig. S1 in Supporting Information). On the other hand, for the TM case, the transmission apex preserves its amplitude as the same as the TE case but only with a slightly red-shifted operating frequency around 0.0001 THz/degree within the first 20° oblique incidence (linear region) that is much smaller compared to the TE case and indicates the double negative identities from our shell is less sensitive to the incident angle in the TM case than in the TE case. Such incident-angle insensitivity in the TM case stems from a combination of an imperceptibly lengthened current loop and a similar electric dipole profile compared to the normal incident ones when increasing incident angles (see Fig. S1). Overall, our proposed monolithic 3D NIM, composed of monolithic gold hemispherical shells, is superior to the NIM from the combination of SRRs and plasmonic wires12 and fishnet structure1328 for its less sensitivity to polarization and incident angles, respectively.


Demonstration of a Three-dimensional Negative Index Medium Operated at Multiple-angle Incidences by Monolithic Metallic Hemispherical Shells
Transmission spectra of the single-layered 3D NIM under oblique incidence.Simulated transmission contour with respect to frequency and incident angle of a single-layered 3D NIM for (a) TE and (b) TM cases, respectively. Insets define configurations of TE and TM cases.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384282&req=5

f5: Transmission spectra of the single-layered 3D NIM under oblique incidence.Simulated transmission contour with respect to frequency and incident angle of a single-layered 3D NIM for (a) TE and (b) TM cases, respectively. Insets define configurations of TE and TM cases.
Mentions: The success in developing the 3D NIM under the normal incident condition by the gold hemispherical shell array encourages us to further examine the shell under oblique incident conditions. In the following, we would elaborate transmission apexes of the single-layered 3D NIM to identify the double negative identities under oblique incidence from 0° up to 85° for both TE and TM cases (see Fig. 5(a,b) for the definition of the TE and the TM cases, respectively). For the TE case, a transmission apex with double negative identities maintains its amplitude and shifts toward to the lower frequency with a frequency offset of 0.0028 THz/degree. Such a red shift corresponds to a lower resonance frequency of magnetic dipoles, stemming from a longer surface current loop at the bottom2627. On the contrary, for the electric resonance, the surface current distribution on the edge of the shell under oblique incidence remains similar so that the resonant frequency of the electric resonance is unaltered (see Fig. S1 in Supporting Information). On the other hand, for the TM case, the transmission apex preserves its amplitude as the same as the TE case but only with a slightly red-shifted operating frequency around 0.0001 THz/degree within the first 20° oblique incidence (linear region) that is much smaller compared to the TE case and indicates the double negative identities from our shell is less sensitive to the incident angle in the TM case than in the TE case. Such incident-angle insensitivity in the TM case stems from a combination of an imperceptibly lengthened current loop and a similar electric dipole profile compared to the normal incident ones when increasing incident angles (see Fig. S1). Overall, our proposed monolithic 3D NIM, composed of monolithic gold hemispherical shells, is superior to the NIM from the combination of SRRs and plasmonic wires12 and fishnet structure1328 for its less sensitivity to polarization and incident angles, respectively.

View Article: PubMed Central - PubMed

ABSTRACT

We design and construct a three-dimensional (3D) negative index medium (NIM) composed of gold hemispherical shells to supplant an integration of a split-ring resonator and a discrete plasmonic wire for both negative permeability and permittivity at THz gap. With the proposed highly symmetric gold hemispherical shells, the negative index is preserved at multiple incident angles ranging from 0° to 85° for both TE and TM waves, which is further evidenced by negative phase flows in animated field distributions and outweighs conventional fishnet structures with operating frequency shifts when varying incident angles. Finally, the fabrication of the gold hemispherical shells is facilitated via standard UV lithographic and isotropic wet etching processes and characterized by μ-FTIR. The measurement results agree the simulated ones very well.

No MeSH data available.


Related in: MedlinePlus