Chiral lasing via broken parity-time symmetry in bound-state-in-the-continuum metasurfaces
arXiv:2607.11235 · doi:10.1021/acsphotonics.6c00719
The paper proposes a planar metasurface design that uses spatial gain‑loss modulation to break parity‑time symmetry, enabling chiral lasing that emits nearly pure circularly polarized light without out‑of‑plane symmetry breaking.
Abstract
We propose a concept for chiral lasing from planar metasurfaces that obviates the need for traditional out-of-plane symmetry breaking by exploiting spatial gain-loss modulation to break parity-time symmetry. We explain the underlying non-Hermitian physics of this design principle using a coupled-mode model of a four-site plaquette. The symmetry requirements for such chiral emission are explained with a general symmetry analysis based on projection operator matrices, implemented algorithmically for automated evaluation. This method enables the design of planar metasurfaces capable of emitting nearly-pure circularly polarized light. We apply our analysis to simulations of both symmetric and asymmetric versions of a Fylfot metasurface design and demonstrate that the gain mode at the parity-time symmetric exceptional point exhibits chiral emission. Lastly, we present a readily manufacturable metasurface made from an InGaAs slab, showing that such a metasurface laser can be actively tuned from linear to circular polarization.
14 pages, 5 figures