arXiv subjects

Ehsan Saei Ghareh Naz

Publications and source records attributed to Ehsan Saei Ghareh Naz.

5 recordsLinked to original sources

arXiv2023

Symmetry induced selective excitation of topological states in SSH waveguide arrays

The investigation of topological state transition in carefully designed photonic lattices is of high interest for fundamental research, as well as for applied studies such as manipulating light flow in on-chip photonic systems. Here, we report on topological phase transition between symmetric topological zero modes (TZM) and antisymmetric TZMs in Su-Schrieffer-Heeger (SSH) mirror symmetric waveguides. The transition of TZMs is realized by adjusting the coupling ratio between neighboring waveguide pairs, which is enabled by selective modulation of the refractive index in the waveguide gaps. Bi-directional topological transitions between symmetric and antisymmetric TZMs can be achieved with our proposed switching strategy. Selective excitation of topological edge mode is demonstrated owing to the symmetry characteristics of the TZMs. The flexible manipulation of topological states is promising for on-chip light flow control and may spark further investigations on symmetric/antisymmetric TZM transitions in other photonic topological frameworks.

physics.optics↗

arXiv2018

Topological phase transition in a stretchable photonic crystal

We design a setup to realize tunable topological phases in elastic photonic crystals. Using the Su-Schrieffer-Heeger (SSH) model as a canonical example, we show how a system can be continuously tuned across its topological phase transition by stretching. We examine the setup both analytically and numerically, showing how the phase transition point may be identified from the behavior of bulk modes. Our design principle is generic as it can be applied to a variety of systems, and enables multiple new theoretical predictions to be experimentally tested by continuously strain-tuning system properties, such as the shape of the bandstructure and the topological invariant. In addition, it allows for cost-effective device fabrication, since a wide range of parameter space can be accessed on a single photonic crystal chip.

cond-mat.mes-hall↗

arXiv2016

Topology induced anomalous plasmon modes in metallic Mobius nanorings

We report on the investigation of plasmonic resonances in metallic Möbius nanorings. Half-integer numbers of resonant modes are observed due to the presence of an extra phase π provided by the topology of the Möbius nanostrip. Anomalous plasmon modes located at the non-orientable surface of the Möbius nanoring break the symmetry that exist in conventional ring cavities, thus enable far-field excitation and emission as bright modes. The far-field resonant wavelength as well as the feature of half-integer mode numbers is invariant to the change of charge distribution on the Möbius nanoring due to the nontrivial topology. Owing to the ultra-small mode volume induced by the remaining dark feature, an extremely high sensitivity as well as a remarkable figure of merit is obtained in sensing performance. The topological metallic nanostructure provides a novel platform for the investigation of localized surface plasmon modes exhibiting unique phenomena in plasmonic applications such as high sensitive detection and plasmonic nanolasers.

physics.optics↗

arXiv2016

Hybridization of photon-plasmon modes in metal-coated microtubular cavities

The coupling of resonant light and surface plasmons in metal layer coated optical microcavities results in the formation of hybrid photon-plasmon modes. Here, we comprehensively investigate the hybridization mechanism of photon-plasmon modes based on opto-plasmonic microtubular cavities. By changing the cavity structure and the metal layer thickness, weakly, moderately and strongly hybridized resonant modes are demonstrated depending on the photon-plasmon coupling strength. An effective potential approach is applied to illustrate the hybridization of photon-plasmon modes relying on the competition between light confinement by the cavity wall and the potential barrier introduced by the metal layer. Our work reveals the basic physical mechanisms for the generation of hybrid modes in metal-coated whispering-gallery-mode microcavities, and is of importance for the study of enhanced light-matter interactions and potential sensing applications.

physics.optics↗

arXiv2016

Localized surface plasmons selectively coupled to resonant light in tubular microcavities

Vertical gold-nanogaps are created on microtubular cavities to explore the coupling between resonant light supported by the microcavities and surface plasmons localized at the nanogaps. Selective coupling of optical axial modes and localized surface plasmons critically depends on the exact location of the gold-nanogap on the microcavities which is conveniently achieved by rolling-up specially designed thin dielectric films into three dimensional microtube ring resonators. The coupling phenomenon is explained by a modified quasi-potential model based on perturbation theory. Our work reveals the coupling of surface plasmon resonances localized at the nanoscale to optical resonances confined in microtubular cavities at the microscale, implying a promising strategy for the investigation of light-matter interactions.

physics.optics↗