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3D optical Yagi-Uda nanoantenna array.

Dregely D, Taubert R, Dorfmüller J, Vogelgesang R, Kern K, Giessen H - Nat Commun (2011)

Bottom Line: We show that the concepts of radiofrequency antenna arrays can be applied to the optical regime proving superior directional properties compared with a single planar optical antenna, particularly for emission and reception into the third dimension.Measuring the optical properties of the structure reveals that impinging light on the array is efficiently absorbed on the subwavelength scale because of the high directivity.Moreover, we show in simulations that combining the array with suitable feeding circuits gives rise to the prospect of beam steering at optical wavelengths.

View Article: PubMed Central - PubMed

Affiliation: 4th Physics Institute and Research Center SCoPE, University of Stuttgart, D-70569 Stuttgart, Germany.

No MeSH data available.


Absorption of the incoming energy by the antenna array.(a) Absorption spectra deduced from simulated (left plot) and measured (right plot) spectra (A=1-T-R). At the resonance frequency the absorption shows the highest asymmetry for forward (red curves) and backward incidence (green curves). (b) Numerically calculated near-field intensity enhancement for forward (left plot) and backward incidence (right plot). The intensity at the tips of the feed element is significantly higher for forward incidence.
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f4: Absorption of the incoming energy by the antenna array.(a) Absorption spectra deduced from simulated (left plot) and measured (right plot) spectra (A=1-T-R). At the resonance frequency the absorption shows the highest asymmetry for forward (red curves) and backward incidence (green curves). (b) Numerically calculated near-field intensity enhancement for forward (left plot) and backward incidence (right plot). The intensity at the tips of the feed element is significantly higher for forward incidence.

Mentions: The reflected intensity of the antenna array depends on the angle of incidence of the far-field radiation. As the transmission is equal for forward and backward incidence, the absorbed energy by the array is a function of the incident angle (Supplementary Figs S3 and S4). Figure 4a compares the absorption spectra for the two opposite directions of incidence deduced from the simulated and the measured transmission and reflection spectra, following the relation A=1-T-R. At the resonance wavelength the absorption is maximally enhanced. Most of the energy is dissipated in the structure if the antenna array is excited from the +z-direction. This is confirmed by calculating the spectra with setting the imaginary part of the dielectric function, which is proportional to the specific ohmic resistance of the antenna material, to zero. In that case the reflection coefficients are equal for both incidence directions (Supplementary Figs S5 and S6). In accordance with Equation (2), the significant difference in absorption at the resonant wavelength between forward and backward illumination is a clear indication that on forward illumination the induced currents are higher and distributed unevenly between the antenna elements. From the analogy with radiowave and microwave Yagi–Uda arrays, we suspect the currents to be concentrated in the feed elements. To verify our assumption, we extract the near-field intensities from our simulations. Figure 4b shows the near-fields for plane-wave illumination at the resonance wavelength (λ=1.5 μm) from the forward direction (left plot) and the backward direction (right plot). For incidence from the forward direction, the electric near-field intensity is strongly enhanced at the feed element. For backward incidence these hot spots do not occur, which clearly confirms that the currents are distributed among the elements. In addition, the overall near-field for backward incident light is lower than that for forward incident light. This theoretical observation of the asymmetric near-field intensities matches very well with our observations in near-field experiments of planar Yagi–Uda antennas (Supplementary Figs S7 and S8). There, we find that the near-field intensity is either distributed over several elements for backward illumination (Supplementary Fig. S8, right) or concentrated on the feed element for forward incidence (Supplementary Fig. S8, left).


3D optical Yagi-Uda nanoantenna array.

Dregely D, Taubert R, Dorfmüller J, Vogelgesang R, Kern K, Giessen H - Nat Commun (2011)

Absorption of the incoming energy by the antenna array.(a) Absorption spectra deduced from simulated (left plot) and measured (right plot) spectra (A=1-T-R). At the resonance frequency the absorption shows the highest asymmetry for forward (red curves) and backward incidence (green curves). (b) Numerically calculated near-field intensity enhancement for forward (left plot) and backward incidence (right plot). The intensity at the tips of the feed element is significantly higher for forward incidence.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3104549&req=5

f4: Absorption of the incoming energy by the antenna array.(a) Absorption spectra deduced from simulated (left plot) and measured (right plot) spectra (A=1-T-R). At the resonance frequency the absorption shows the highest asymmetry for forward (red curves) and backward incidence (green curves). (b) Numerically calculated near-field intensity enhancement for forward (left plot) and backward incidence (right plot). The intensity at the tips of the feed element is significantly higher for forward incidence.
Mentions: The reflected intensity of the antenna array depends on the angle of incidence of the far-field radiation. As the transmission is equal for forward and backward incidence, the absorbed energy by the array is a function of the incident angle (Supplementary Figs S3 and S4). Figure 4a compares the absorption spectra for the two opposite directions of incidence deduced from the simulated and the measured transmission and reflection spectra, following the relation A=1-T-R. At the resonance wavelength the absorption is maximally enhanced. Most of the energy is dissipated in the structure if the antenna array is excited from the +z-direction. This is confirmed by calculating the spectra with setting the imaginary part of the dielectric function, which is proportional to the specific ohmic resistance of the antenna material, to zero. In that case the reflection coefficients are equal for both incidence directions (Supplementary Figs S5 and S6). In accordance with Equation (2), the significant difference in absorption at the resonant wavelength between forward and backward illumination is a clear indication that on forward illumination the induced currents are higher and distributed unevenly between the antenna elements. From the analogy with radiowave and microwave Yagi–Uda arrays, we suspect the currents to be concentrated in the feed elements. To verify our assumption, we extract the near-field intensities from our simulations. Figure 4b shows the near-fields for plane-wave illumination at the resonance wavelength (λ=1.5 μm) from the forward direction (left plot) and the backward direction (right plot). For incidence from the forward direction, the electric near-field intensity is strongly enhanced at the feed element. For backward incidence these hot spots do not occur, which clearly confirms that the currents are distributed among the elements. In addition, the overall near-field for backward incident light is lower than that for forward incident light. This theoretical observation of the asymmetric near-field intensities matches very well with our observations in near-field experiments of planar Yagi–Uda antennas (Supplementary Figs S7 and S8). There, we find that the near-field intensity is either distributed over several elements for backward illumination (Supplementary Fig. S8, right) or concentrated on the feed element for forward incidence (Supplementary Fig. S8, left).

Bottom Line: We show that the concepts of radiofrequency antenna arrays can be applied to the optical regime proving superior directional properties compared with a single planar optical antenna, particularly for emission and reception into the third dimension.Measuring the optical properties of the structure reveals that impinging light on the array is efficiently absorbed on the subwavelength scale because of the high directivity.Moreover, we show in simulations that combining the array with suitable feeding circuits gives rise to the prospect of beam steering at optical wavelengths.

View Article: PubMed Central - PubMed

Affiliation: 4th Physics Institute and Research Center SCoPE, University of Stuttgart, D-70569 Stuttgart, Germany.

No MeSH data available.