Topologically protected interface mode in plasmonic waveguide arrays

Abstract

Recent realization of nontrivial topological phases in photonic systems has provided unprecedented opportunities in steering light flow in novel manners. Based on the Su-Schriffer-Heeger (SSH) model, a topologically protected optical mode was successfully demonstrated in a plasmonic waveguide array with a kinked interface that exhibits a robust nonspreading feature. However, under the same excitation conditions, another antikinked structure seemingly cannot support such a topological interface mode, which appears to be inconsistent with the SSH model. Theoretical calculations are carried out based on the coupled-mode theory, in which the mode properties, excitation conditions, and the robustness are studied in detail. It is revealed that under the exact eigenstate excitations, both kinked and antikinked structures do support such robust topological interface modes; however, for a realistic single-waveguide input only the kinked structure does so. It is concluded that the symmetry of interface eigenmodes plays a crucial role, and the odd eigenmode in a kinked structure offers the capacity to excite the nonspreading interface mode in the realistic excitation of a one-waveguide input. Our finding deepens the understanding of mode excitation and propagation in coupled waveguide systems, and could open a new avenue in optical simulations and photonic designs.

Nonlinear topological states in the Su–Schrieffer–Heeger model

“…In the latter case, α m denotes electric field amplitude in m th cavity. Such correspondence allows one to investigate the physics of the SSH model in fully classical setups, including electronic [11,12], photonic [13][14][15][16][17][18][19], plasmonic [20][21][22][23], polaritonic [24] and mechanical [25] systems. The bulk energy spectrum of the SSH model is found from Eqs.…”

“…Possibly the simplest model of the topological states in one-dimensional systems is provided by the wellcelebrated Su-Schrieffer-Heeger model (SSH) [11,12], which was investigated and realized in various contexts including electronic [11,12], photonic [13][14][15][16][17][18][19], plasmonic [20][21][22][23], polaritonic [24] and mechanical [25] systems. Though initially the SSH model was applied to explain charge transfer in polymer molecules, it can be also used for describing the physics of artificial photonic and plasmonic structures.…”

“…1(a). Plasmonic realization of the SSH model [21][22][23] allows one to achieve a nanoscale confinement of the edge mode which, however, is subject to the losses inherent to metals. On the contrary, the SSH model based on the all-dielectric platform [15,16,18] is almost loss-free but has worse confinement of light.…”

Optical Isolation with Nonlinear Topological Photonics

“…In the linear regime, the κ parameters are constants independent of n. The linear SSH model has been extensively investigated in photonics, including in femtosecond-laser-written waveguide arrays [48,49] and plasmonic waveguide arrays [50]. It has a phase transition at κ 1 = κ 2 ; when κ 1 < κ 2 , there is an edge state with zero eigenvalue localized to the left edge of the lattice.…”

Robust Light State by Quantum Phase Transition in Non-Hermitian Optical Materials

“…By increasing the gain/loss contrast, the eigen spectra become complex and the system can transit into PT broken phase [3][4][5][6] . Recent investigations of PT symmetric metamaterials have enabled a variety of intriguing optical phenomena, including effective manipulation of cavity oscillating modes [7][8][9] and unidirectional light transport [10][11][12][13][14][15][16] , which promise new functionalities for integrated photonics information processing.To secure fault-tolerant light transport for optical communications, robust optical interface states, inspired by topological insulators and quantum Hall systems in condensed-matter physics, have been developed [17][18][19][20][21][22][23] . From a topological perspective, a system can acquire a non-negligible geometric phase (also called Berry phase) under a cyclic and adiabatic variation in a parameter space, which classifies the topological orders of matter 24 .…”