Magnetically tunable optical bound states in the continuum with arbitrary polarization and intrinsic chirality

TL;DR

This paper theoretically demonstrates magnetically tunable optical bound states in the continuum with arbitrary polarization and intrinsic chirality, enabling advanced control of light-matter interactions for potential optical applications.

Contribution

It introduces a method to achieve magnetically tunable BICs with arbitrary polarization and intrinsic chirality in magneto-optical photonic crystals, advancing control over topological photonic states.

Findings

Achieved magnetically tunable BICs with full polarization control.

Generated intrinsic chiral BICs with high circular dichroism (>0.99).

Observed high quality factor (Q=46000) due to symmetry preservation.

Abstract

Optical bound states in the continuum (BICs), which are exotic localized eigenstates embedded in the continuum spectrum and topological polarization singularity in momentum space, have attracted great attentions in both fundamental and applied physics. Here, based on magneto-optical photonic crystal slab placed in external magnetic fields to break the time-reversal symmetry, we theoretically demonstrate magnetically tunable BICs with arbitrary polarization covering the entire Poincar\'e sphere and efficient off-{\Gamma} chiral emission of circularly polarized states. More interestingly, by further breaking the in-plane inversion symmetry of the magneto-optical photonic crystal slab to generate a pair of circularly polarized states (C point) spawning from the eliminated BICs and tuning the external magnetic field strength to move one C point to the {\Gamma} point, one at-{\Gamma} intrinsic chiral BICs with near-unity circular dichroism exceeding 0.99 and a high quality factor of 46000 owning to the preserved out-of-plane mirror symmetry can be observed. These findings may lead to a plethora of potential applications in chiral-optical effects, structured light, and tunable optical devices.