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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.


Numerical directivity of the transmitting Yagi–Uda array coupled to dipole emitters.The polar plots show the numerically calculated directivity for (a) a single optical Yagi–Uda antenna, (b) a 2×2 array and (c) a 3×3 array. The calculated directivity of the xz plane is plotted in the left column and for the yz plane in the right column. Each antenna is fed by a dipole source (red spheres, 5 nm away from the feed element) with a dipole moment along the x-direction. The emitted wavelength of the dipole is 1500 nm. The black curves in the polar plots are the directivities of the corresponding emitter array without being coupled to optical antennas.
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f2: Numerical directivity of the transmitting Yagi–Uda array coupled to dipole emitters.The polar plots show the numerically calculated directivity for (a) a single optical Yagi–Uda antenna, (b) a 2×2 array and (c) a 3×3 array. The calculated directivity of the xz plane is plotted in the left column and for the yz plane in the right column. Each antenna is fed by a dipole source (red spheres, 5 nm away from the feed element) with a dipole moment along the x-direction. The emitted wavelength of the dipole is 1500 nm. The black curves in the polar plots are the directivities of the corresponding emitter array without being coupled to optical antennas.

Mentions: The angular pattern of the whole array is the product of the angular element pattern and the array factor, which is the angular radiation pattern of isotropic point sources with the same spatial distribution as the antennas in the array14. Nevertheless, in the simulations shown in Figure 2, we implement the complete array configuration into the calculation domain to account for mutual coupling effects between the Yagi–Uda antennas in the array, which are not accounted for by simple pattern multiplication. Each feed element is coupled to a dipole emitter (red sphere in Fig. 2) at a distance of 5 nm from the nanorod, emitting at λ=1.5 μm and oscillating in the direction of the nanorod axis indicated by the white rod in the schematic view. The antennas are embedded in a dielectric environment with refractive index n=1.55, taking into account the dielectric spacer used in the fabrication. In the left column of Figure 2, the directivity pattern in the xz plane is plotted, whereas the right column shows the directivity pattern in the yz plane. Figure 2a is the single Yagi–Uda antenna case. The red curve is the directivity of the antenna coupled to the dipole emitter and the black curve shows the directivity pattern of the single dipole emitter without the antenna. To obtain maximum radiation at λ=1.5 μm into the z-direction, we vary the geometrical parameters of the single Yagi–Uda antenna. First, we consider just the feed element coupled to the dipole emitter (λ=1.5 μm) and maximize the radiated power by changing the length of the gold nanorod. The coupling between dipole emitter and nanorod is strongest for a rod length of 250 nm and the symmetric far-field radiation is completely determined by the dipole mode of the feed element. As a second element, a slightly longer gold rod, the reflector, is placed underneath the feed element. As the structure symmetry is now broken along the z-axis the radiation pattern becomes asymmetric. We calculate the optimal distance between the two rods for maximum directivity in the z-direction. For this distance, we change the length of the reflector to obtain further enhancement of the radiated power in the positive z-direction. The same calculations are carried out after adding a slightly shorter element, the director, above the feed element. When excited by the dipole emitter, mutual coupling occurs between the single nanorods of the three-layer Yagi–Uda antenna. Because of the differences in length of the nanorods, the director (reflector) couples capacitively (inductively) to the feed element and the radiated power is directed into the positive z-direction (forward direction), whereas it is cancelled out in the negative z-direction (backward direction)11.


3D optical Yagi-Uda nanoantenna array.

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

Numerical directivity of the transmitting Yagi–Uda array coupled to dipole emitters.The polar plots show the numerically calculated directivity for (a) a single optical Yagi–Uda antenna, (b) a 2×2 array and (c) a 3×3 array. The calculated directivity of the xz plane is plotted in the left column and for the yz plane in the right column. Each antenna is fed by a dipole source (red spheres, 5 nm away from the feed element) with a dipole moment along the x-direction. The emitted wavelength of the dipole is 1500 nm. The black curves in the polar plots are the directivities of the corresponding emitter array without being coupled to optical antennas.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: Numerical directivity of the transmitting Yagi–Uda array coupled to dipole emitters.The polar plots show the numerically calculated directivity for (a) a single optical Yagi–Uda antenna, (b) a 2×2 array and (c) a 3×3 array. The calculated directivity of the xz plane is plotted in the left column and for the yz plane in the right column. Each antenna is fed by a dipole source (red spheres, 5 nm away from the feed element) with a dipole moment along the x-direction. The emitted wavelength of the dipole is 1500 nm. The black curves in the polar plots are the directivities of the corresponding emitter array without being coupled to optical antennas.
Mentions: The angular pattern of the whole array is the product of the angular element pattern and the array factor, which is the angular radiation pattern of isotropic point sources with the same spatial distribution as the antennas in the array14. Nevertheless, in the simulations shown in Figure 2, we implement the complete array configuration into the calculation domain to account for mutual coupling effects between the Yagi–Uda antennas in the array, which are not accounted for by simple pattern multiplication. Each feed element is coupled to a dipole emitter (red sphere in Fig. 2) at a distance of 5 nm from the nanorod, emitting at λ=1.5 μm and oscillating in the direction of the nanorod axis indicated by the white rod in the schematic view. The antennas are embedded in a dielectric environment with refractive index n=1.55, taking into account the dielectric spacer used in the fabrication. In the left column of Figure 2, the directivity pattern in the xz plane is plotted, whereas the right column shows the directivity pattern in the yz plane. Figure 2a is the single Yagi–Uda antenna case. The red curve is the directivity of the antenna coupled to the dipole emitter and the black curve shows the directivity pattern of the single dipole emitter without the antenna. To obtain maximum radiation at λ=1.5 μm into the z-direction, we vary the geometrical parameters of the single Yagi–Uda antenna. First, we consider just the feed element coupled to the dipole emitter (λ=1.5 μm) and maximize the radiated power by changing the length of the gold nanorod. The coupling between dipole emitter and nanorod is strongest for a rod length of 250 nm and the symmetric far-field radiation is completely determined by the dipole mode of the feed element. As a second element, a slightly longer gold rod, the reflector, is placed underneath the feed element. As the structure symmetry is now broken along the z-axis the radiation pattern becomes asymmetric. We calculate the optimal distance between the two rods for maximum directivity in the z-direction. For this distance, we change the length of the reflector to obtain further enhancement of the radiated power in the positive z-direction. The same calculations are carried out after adding a slightly shorter element, the director, above the feed element. When excited by the dipole emitter, mutual coupling occurs between the single nanorods of the three-layer Yagi–Uda antenna. Because of the differences in length of the nanorods, the director (reflector) couples capacitively (inductively) to the feed element and the radiated power is directed into the positive z-direction (forward direction), whereas it is cancelled out in the negative z-direction (backward direction)11.

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.