Chiral spectral singularities spawning from quasi-bound states in the continuum in PT-symmetric dielectric metasurfaces

We investigate the chiral spectral singularities, i.e., laser threshold modes, in PT-symmetric dielectric metasurfaces originating from quasi-bound states in the continuum. The poles, referred to as the quasi-bound states in the continuum, of scattering matrix can move to the upper complex frequency plane from the lower half-plane by increasing the balanced gain and loss. The maximal intrinsic optical chirality of laser threshold mode has been theoretically demonstrated via the large transmission circular dichroism spectra. Our work paves the way for studying the enhanced optical chirality in non-Hermitian nanophotonics empowered by quasi-bound states in the continuum, together with various intriguing applications, such as chiral coherent perfect absorber and laser.

Automated summary

We investigate the chiral spectral singularities, known as laser threshold modes, in PT-symmetric dielectric metasurfaces produced through quasi-bound states in the continuum. By increasing balanced gain and loss, the poles, referred to as the quasi-bound states in the continuum, of the scattering matrix can transition from the lower half-plane to the upper complex frequency plane. Theoretical demonstration of the maximal intrinsic optical chirality of the laser threshold mode is achieved through large transmission circular dichroism spectra. Our work lays the foundation for studying enhanced optical chirality in non-Hermitian nanophotonics enabled by quasi-bound states in the continuum, along with various intriguing applications such as chiral coherent perfect absorber and laser.