Realization of spinning mode with maximum chirality in photonic-crystal defect cavity at exceptional point

Abstract

Optical modes spinning with maximum chirality in cavities at the chip level are essential for quantum and biomedical applications. The coalescent chiral mode at the exceptional point (EP) due to non-Hermicity is the one in demand. Yet, approaching EPs require fine balances between the loss/gain and the dielectric perturbation, which are typically nontrivial. In this paper, by elevating the reliability of fine-tuning, we realize circularly-polarized-like lasing modes with maximum chirality at the EP of photonic-crystal one-hole cavities. Such an EP is of intracavity type in the subwavelength scale and reaching it requires more reliable strategies than those for its forerunners. We adopt the in-plane tunneling loss that is well controlled with the layer number of air holes in the photonic-crystal slab. By removing and relocating holes in blocks, we systematically elevate the chirality of the radiation field. The collective variations of holes render the EP robust against the uncertainty in fabrications. Without auxiliary non-Hermitian and chiral structures, our works promote coherent chiral light sources at the chip level.