Finite-Size Effect Induced Spatial-Spectral Mode Splitting in Membrane Metasurfaces

This work reports the spatial-spectral engineering and finite-size quantization of optical modes within a triangular-lattice silicon nitride membrane metasurface.

Truncating the lattice into a finite square cavity breaks translational symmetry and lifts modal degeneracy, splitting optical modes into discrete cavity-envelope sub-modes.

High-resolution photoluminescence (PL) scanning reveals distinct spatial field distributions.

The corner-localized sub-mode features the highest Q-factor due to multipolar far-field destructive interference, whereas the core-localized sub-mode exhibits strong radiative coupling.

PL mapping reveals a symmetric, four-fold clover-like wavelength arrangement.

These results demonstrate that boundary-induced deterministic symmetry can override underlying lattice characteristics, offering a robust strategy for precise spatial-spectral tailoring of light-matter interactions at the nanoscale.