Abstract
The energy transport properties of plasmonic waveguides can be analyzed by solving the dispersion relation for surface plasmon-polaritons (SPPs). We use this approach to derive an approximate analytical expression for SPP propagation length when the waveguide is composed of linearly arranged metallic nanoparticles, while assuming that metal losses are small or partially compensated by gain. Applied to metal-dielectric (composite) nanospheres, the obtained expression allows us to optimize the performance of the waveguide and arrive at a number of practical design rules. Specifically, we show that SPP attenuation can be minimized at a certain interparticle distance for transverse modes, but gradually grows for both longitudinal and transverse modes with the increase of particle separation. We also show that the two basic methods of supplying gain to the system, i.e., embedding the particles into a gain medium or having a metal-gain composition for the particles, do not perform equally well and the former method is more efficient, but the way the two methods affect depends on the polarization of SPPs. To investigate the role of the nanoparticles' arrangement in determining SPP characteristics, we follow a purely numerical approach and consider a two-segment bent waveguide as an example. Analyzing the waveguide's transmission shows that it behaves in an oscillatory manner with respect to the angle between the two segments and is therefore higher for certain angles than for the others. This suggests that, in the design of waveguides with bends, careful attention needs to be paid in order to avoid bend angles that yield low transmission and to choose angles that give maximum transmission.
Highlights
The demand for faster, smaller communication interconnects for on-chip information transport has resulted in enormous interest on nanoscale optical circuitry as their electronic counterparts are incapable of providing the required high level of miniaturization [1, 2]
We have investigated how surface plasmon-polaritons (SPPs) propagation in metallic nanoparticle chains are affected by different parameters of the system such as interparticle distance, material gains and chain layout
Based on the coupled-dipole method (CDM), we developed compact analytical expressions to describe SPP damping in a linear chain when the Ohmic losses are small or partially compensated by gain
Summary
The demand for faster, smaller communication interconnects for on-chip information transport has resulted in enormous interest on nanoscale optical circuitry as their electronic counterparts are incapable of providing the required high level of miniaturization [1, 2]. Various types of plasmonic structures are known to support SPPs. Thin metallic films embedded in a dielectric is one of them that is known for supporting long-distance SPP propagation of up to several millimeters, the lateral confinement it provides (about several micrometers) is rather poor [8, 9]. The dispersion equation does not lend itself to a closed-form analytical solution and requires to be solved numerically, making it difficult to intuitively evaluate the system’s parameters To this end, compact analytical descriptors to characterize SPPs are clearly in demand, as they could be translated into straightforward recipes that allow parameters to be chosen optimally.
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