Optical Amplification with Large Goos-H$\ddot{a}$nchen Shift Driven by Non-Hermitian Bilayer Meta-Grating Under Lasing State

The coexistence of gain and loss in parity-time symmetric bilayer meta-gratings enables the transformation of bound states in the continuum into a ring of lasing threshold modes. Under lasing state, gain saturation drives the contraction of this mode ring into a single discrete lasing point. Additio