High-Accuracy Dispersion Surfaces Measurement Unlocks Photonic Crystal Slabs Topology

TL;DR

This paper introduces a highly accurate, diffraction-free spectral mapping technique for measuring dispersion surfaces in photonic crystal slabs, enabling detailed topological analysis and identification of bound states in the continuum.

Contribution

A novel high-precision, aberration-free method for dispersion surface measurement in photonic crystals, surpassing previous optical imaging limitations.

Findings

Achieved angular accuracy of 3 x 10^(-4) radians

Spectral accuracy of 0.2 nm within the Brillouin zone

Enabled distinction of anisotropic and isotropic BICs

Abstract

Characterization of dispersion surfaces (DS) in photonic crystals (PhCs) can predict striking topological features, such as bound states in the continuum (BICs). Precise measurement of dispersion, particularly near the {\Gamma}-point, is crucial since even subtle geometric deviations significantly impact the distribution of topological charges and associated polarization singularities. Here, we propose a novel technique to measure DS of PhC slabs with high angular accuracy of up to 3 x 10^(-4) radians, and spectral accuracy of 0.2 nm within an expanded region of the Brillouin zone. Remarkably, our technique is diffraction- and aberration-free as it does not rely on optical imaging but rather on spectral mapping. The analysis of DS presented in this work demonstrates the robustness of our technique, and enables us to distinguish anisotropic BICs along a specific symmetry axis from isotropic states around the {\Gamma}-point. Moreover, the experimental DS obtained supply the information necessary to study and identify super-BICs.