Multifunctional imaging enabled by optical bound states in the continuum with broken symmetry

TL;DR

This paper demonstrates how breaking symmetry in photonic crystal slabs transforms bound states in the continuum into chiral C-points, enabling multifunctional imaging and insights into topological polarization singularities.

Contribution

It introduces a method to control polarization singularities in PCS structures by symmetry breaking, enabling multifunctional imaging and topological studies.

Findings

BICs split into C-points with opposite chirality upon symmetry breaking.

The system achieves edge and bright-field imaging based on circular polarization.

The approach offers a new way to explore topological polarization singularities.

Abstract

For photonic crystal slab (PCS) structures, bound states in the continuum (BICs) and circularly polarized states (dubbed C-points) are important topological polarization singularities in momentum-space and have attracted burgeoning attention due to their novel topological and optical properties. In our work, the evolution of polarization singularities from BICs to C-points is achieved by breaking the in-plane C2 symmetry of a PCS structure of a square lattice with C4v symmetry. Correspondingly, a BIC is split into two C-points with opposite chirality, incurring distinct optical transmission responses with the incidence of right or left circular polarization (RCP or LCP). Harnessing such chirality selectivity of the C-points, we propose a multifunctional imaging system by integrating the designed PCS into a conventional 4-f imaging system, to realize both the edge imaging and conventional bright-field imaging, determined by the circular polarization state of the light source. In addition to multifunctional imaging, our system also provides a vivid picture about the evolution of the PCS platforms' singularities.