Abstract
Robust topological edge modes may evolve into complex-frequency modes when a physical system becomes non-Hermitian. We show that, while having negligible forward optical extinction cross section, a conjugate pair of such complex topological edge modes in a non-Hermitian -symmetric system can give rise to an anomalous sideway scattering when they are simultaneously excited by a plane wave. We propose a realization of such scattering state in a linear array of subwavelength resonators coated with gain media. The prediction is based on an analytical two-band model and verified by rigorous numerical simulation using multiple-multipole scattering theory. The result suggests an extreme situation where leakage of classical information is unnoticeable to the transmitter and the receiver when such a -symmetric unit is inserted into the communication channel.
Highlights
Robust topological edge modes may evolve into complex-frequency modes when a physical system becomes non-Hermitian
We show that a conjugate pair of topological complex-frequency edge modes in a PT -symmetric photonic systems can be realized through observing an anomalous sideway scattering by an array of subwavelength resonators coated with gain media
This suggests an extreme situation where leakage of classical information is unnoticeable to the transmitter and the receiver when such a PT -symmetric unit is inserted to the communication channel
Summary
The frequencies of these two topological edge modes form a complex conjugate pair, which is associated with the horizontal blue line and the red lines at Im(ω/ωp) =±0.002. The existence of these complex edge modes are due to γ =π, which is classified as the (non-trivial) regime III. Where κ = (3/d)ln[s/(d − s)], ω0 is the complex frequency of an edge mode, and pn;σ(t) represents the time-domain dipole moments in the nth unit cell. We will see that these modes can give rise to an anomalous scattering phenomenon
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