Broadband localization of light at the termination of a topological photonic waveguide

Localized optical field enhancement enables strong light-matter interactions necessary for efficient manipulation and sensing of light. Specifically, tunable broadband energy localization in nanoscale hotspots offers a wide range of applications in nanophotonics and quantum optics. We experimentally demonstrate a novel principle for the local enhancement of electromagnetic fields, based on strong suppression of backscattering. This is achieved at a designed termination of a topologically non-trivial waveguide that nearly preserves the valley degree of freedom. The symmetry origin of the valley degree of freedom prevents edge states to undergo intervalley scattering at waveguide discontinuities that obey the symmetry of the crystal. Using near-field microscopy, we reveal that this can lead to strong confinement of light at the termination of a topological photonic waveguide, even without breaking time-reversal symmetry. We emphasize the importance of symmetry conservation by comparing di..., The transversal electric-field components are collected by a near-field probe in a raster scan 20 nm above a photonic crystal. Two detectors pick up the Ex and Ey components and are read-out by two lock-in amplifers that retrieve the real and imaginary part. Custom software reads out all the electric-field components as a function of position of the probe and frequency of our laser in stores it separated files which are later combined in a multi-dimensional array using python., , # Broadband localization of light at the termination of a topological photonic waveguide

[https://doi.org/10.5061/dryad.kd51c5bg4](https://doi.org/10.5061/dryad.kd51c5bg4)

We provide all datasets and code that generate the figures of the paper \"Broadband localization of light at the termination of a topological waveguide\". Scripts are titled to the figures they refer to in the paper. Some scripts generate multiple panels. Parameter choices are included and should be adjusted accordingly.

## Description experimental datasets

Experimental datasets are available as .npz files. These files contain data points of the electric field.

Naming conventions:

* \_*xy*_: Dependency on position (xy).
* \_*f_vs_xy*_: Dependency on frequency (f) and position (xy).
* \_*armchair*\_ or \_*zigzag*_: Type of termination.
* \_*surface*_: Type of interface: between VPCs and trivial PhC. (Blank for VPC-VPC interface)
* \_*s1.0*_: Scaling factor of the lattice constant a0. Scaling 1.0 refers to a0 = 449 ...