Abstract
We propose a complementary split-ring resonator (CSRR) for a directional coupling of surface plasmon polaritons. An air-slot split-ring in a gold film is investigated using the finite-difference time-domain method. The normally incident light couples to either a monopole or a dipole SPP depending on the polarization of light. Adjusting the angle of the linear polarization of the incident light enables a one-way propagation of SPPs on the gold film. Theoretical analysis based on the propagation of cylindrical waves from the SPP point source is provided with Hankel function. The propagated power in one direction is obtained to be 30 times higher than the opposite direction with a coupling efficiency of 18.2% from the simulation for an array of the CSRRs. This approach to the directional coupling of SPPs will be advantageous for miniaturizing photonic and plasmonic circuits and devices.
Highlights
Surface plasmon polaritons (SPPs) are the collective oscillations of electrons which propagate along the interface between a metal and a dielectric[1]
An array of nanorods which support localized surface plasmons can be arranged as an antenna array to realize unidirectional coupling of the desired linear polarization[20,21,22,23]
We propose a different approach of using the interference of a monopole and a dipole SPPs excited at a complementary split-ring resonator (CSRR)
Summary
The resonant SPP modes were numerically investigated by the finite-difference time-domain (FDTD) method[32] using a homemade code. The plasmonic modes excited by x- and y-polarized sources have Ez-field profiles which are anti-symmetric and symmetric about the symmetric axis of the CSRR, respectively, as shown in the insets of Fig. 1(b). Ez-field amplitude at the source point, and k and ω are the wavevector and the frequency of the wave, respectively It is a radially travelling cylindrical wave described by the zeroth order Hankel function of the first kind H0(1) whose amplitude decreases by 1/ ρ when ρ 1 which obeys the law of conservation of energy[34]. As Ez(ρ, φ, t) = Ezm(ρ, t)e−iδ + Ezd(ρ, φ, the dipole modes due to the off-resonance t) where δ is the temporal phase difference between the monopole excitation
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