Abstract
Parity-time (PT) symmetric photonic systems have attracted much attention due to their intriguing properties and asymmetric behaviors. In this paper, we propose a plasmonic nanoantenna with PT-symmetric potential for unidirectional scattering functionality. The studied plasmonic nanoantenna is comprised of three metallic layers separated by two dielectric layers. Such kind of system, with the same coefficient of loss and gain in each of the two dielectric layers, holds the characteristic of PT symmetry. We show that the unidirectional scattering is obtained for the passive structure (i.e. κ=0, ), and the switching between forward and backward directionality can be achieved with a single element by changing the excitation wavelength, when the induced electric dipole (ED) and magnetic dipole (MD) modes satisfy the first or second Kerker conditions, respectively. In addition, we find that the forward-to-backward ratio spectra can be strongly affected by the non-Hermiticity parameter κ. In particular, it is possible to reverse the radiation direction at the same wavelength in a wide spectra band by adjusting κ. Moreover, putting the nanoantennas in an array of transverse configuration can efficiently narrow the main lobe angular beam width to be less than 6 degrees . These results contribute to the basic understanding of the optical properties of active-passive finite nanostructures with potential applications for the design of novel nanostructures displaying asymmetric and tunable responses.
Highlights
Surface plasmon polaritons (SPPs) refer to collective oscillations of conductive electrons at metal and dielectric interface [1]
From the evolution of the magnetic dipole (MD) and electric dipole (ED) spectra based upon different κ in Figure 2, we can see that the MD mode shows strong dependence on κ, whereas the ED mode is almost unchanged
We showed that the nonHermiticity parameter has strong influences on the total cross sections and the scattering directionality of the antenna
Summary
Surface plasmon polaritons (SPPs) refer to collective oscillations of conductive electrons at metal and dielectric interface [1]. The interest in PT-symmetry of photonic systems relies on the exotic properties including, to cite some [3], asymmetric propagation [33, 34], reflection [35], scattering [36], unidirectional invisibility [37, 38], switching [39, 40], and extraordinary non-linear behaviors [41, 42] These intriguing phenomena have been already observed in dielectric waveguides [43] and cavities [44] or photonic lattices [45, 46], among other realizations [3]. We find that the beam-width of the scattered light can be further narrowed when the antenna multilayers are arranged in a chain
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