Observing 0D subwavelength-localized modes at ~100 THz protected by weak topology

TL;DR

This paper demonstrates the experimental observation of zero-dimensional subwavelength light localization at around 100 THz in topological photonic crystals with weak topology, showcasing their robustness and potential for advanced nanophotonic applications.

Contribution

First experimental verification of weak topology-induced localized modes at optical frequencies in topological photonic crystals, supported by near-field microscopy and simulations.

Findings

Observation of mid-bandgap zero-dimensional light localization near 100 THz

Weak topology leads to similar strong localization at different dislocation centers

Experimental results are supported by full-field simulations

Abstract

Topological photonic crystals (TPhCs) provide robust manipulation of light with built-in immunity to fabrication tolerances and disorder. Recently, it was shown that TPhCs based on weak topology with a dislocation inherit this robustness and further host topologically protected lower-dimensional localized modes. However, TPhCs with weak topology at optical frequencies have not been demonstrated so far. Here, we use scattering-type scanning near field optical microscopy to verify mid-bandgap zero-dimensional light localization close to 100 THz in a TPhC with nontrivial Zak phase and an edge dislocation. We show that due to the weak topology, differently extended dislocation centers induce similarly strong light localization. The experimental results are supported by full-field simulations. Along with the underlying fundamental physics, our results lay a foundation for the application of TPhCs based on weak topology in active topological nanophotonics, and nonlinear and quantum optic integrated devices due to their strong and robust light localization.