Parallel-chain optical transmission line for a low-loss ultraconfined light beam

Coupling and guided propagation along parallel chains of plasmonic nanoparticles

“…This implies that for a correct evaluation of the modal properties and the field distribution generated in this forward-leaky mode regime, the formulas of Eq. operation, whose interesting properties we have already highlighted in details in [12], may lead to ultra-confined low-loss optical guidance in terms of optical nanotransmission-lines. These properties are not only limited to the modes operating near the light line, but they are also valid for higher frequencies and more confined modes.…”

“…This geometry has been preliminarily analyzed in [12] for its longitudinally polarized guided modes, where it was shown that the coupling between the chains, limited in that analysis to its dominant contribution coming from the averaged current density on the chain axes, would generate the splitting of the regular longitudinal mode into two coexisting longitudinal modes, respectively, with symmetric and antisymmetric field distributions. The antisymmetric mode is the one corresponding to transmission-line operation [12], as outlined in the introduction, for which two antiparallel displacement current flows are supported by the parallel chains. A similar modal propagation has been analyzed in [9] for a related distinct geometry, consisting of longitudinal dipoles placed over a perfectly conducting plane.…”

“…As we have underlined in [12], a naked conducting wire at low frequencies has analogous limitations: although metals are much more conductive and less lossy in radio frequencies, connecting two points in a regular circuit with a single wire would still produce unwanted spurious radiation and sensitivity to metal absorption. This problem, which is much amplified at optical frequencies due to the poorer conductivity and higher loss of metals in the visible, is simply approached at low frequencies by closely pairing two parallel wires (or, which is the same, placing a ground plane underneath the conducting trace), forming the well known concept of a transmission-line that provides a return path for the conduction current.…”

“…Analogously, applying the nanocircuit concepts [13]- [14], we have recently put forward ideas to realize optical nanotransmission-line waveguides in different geometries [15]- [16], which have been proven to be more robust to material and radiation losses and may provide wider bandwidth of operation. In particular, as we introduced in [12], one such idea consists in pairing together two parallel arrays of plasmonic nanoparticles, suggesting that the coupling among the guided modes may improve the guidance performance. In [12] we have shown that this is indeed the case: operating with the antisymmetric longitudinal mode, such parallel chains indeed may confine the beam in the background region between the chains, leading to confined propagation that is combined with robustness to material absorption and radiation losses.…”

Subwavelength waveguides composed of dielectric nanoparticles

“…A new type of optical waveguide, drastically different from conventional waveguides involving either the Bragg scattering or total internal reflection, is based on the guiding properties of an array of coupled high-Q optical resonators [1]. Recent realizations of such novel waveguides include chains of microresonators or microcavities [2][3][4], magnetoinductive waveguides [5][6][7][8][9][10][11] with magnetic resonators coupled by induced voltages, and chains of metallic nanoparticles with subwavelength localized waves guided due to the excitation of surface plasmon polaritons [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. Very small sizes of plasmonic nanoparticles and the ability of such waveguides to bend without any significant reduction of a signal propagation suggest their use as building blocks for photonic integrated circuits [14].…”