Topological polarization singular enables multiple-system excellent circular dichroism via chiral bound states in the continuum with all-dielectric metasurfaces

The advancements in chiroptics have propelled applications beyond traditional optics, expanding its reach into domains such as heat and fluid mechanics. The current research predominantly focused on utilizing plasmonic materials in the photothermal and photofluidic systems. However, these systems face limitations in circular dichroism due to inherent Ohmic loss associated with plasmonic materials. Herein, we introduce the concept of topological polarization singularity in an all-dielectric structure, which supports chiral bound states in the continuum. The introduction of topological polarization singularity gives the structure an impressive chiral light absorption response. The BICs resonant mode achieves a 147-fold field enhancement, significantly improving the photothermal conversion efficiency of dielectric material. Moreover, the g factors of photothermal and optical fluids reach 1.9, approaching the theoretical limit value. Consequently, an exceptionally high degree of circular dichroism is realized in multiple systems including light absorption, photothermal, and photofluidic systems. Our proposed structures can potentially be used in chiral photothermal and chiral nanoparticle capture, as well as photofluidic applications related to biochemistry and clinical biology.