Symmetry Breaking Enables Direction‐Selective Power Routing Between Diffraction and Dissipation in Obliquely Metallized Opaque Metagratings

ABSTRACT

Opaque metagratings remove specular power through material dissipation and nonzero reflected diffraction, but zero‐order spectra cannot distinguish these destinations once higher orders propagate. Oblique metallization turns a reciprocal opaque metagrating into a direction‐selective power router. Cross‐sectional scanning electron microscopy identifies two one‐sided Ag/SiO ₂ morphologies. Simplified models derived from these cross sections reproduce the principal measured transverse‐magnetic zero‐order angular–spectral features using unmodified standard optical functions. Opposite incidence is tested by rotating each specimen in plane by . Order‐resolved calculations reveal that reciprocity‐enforced equality of can hide strongly different power partitions. At 606 nm and , reversing the incidence changes from 0.005 to 0.724 and from 0.936 to 0.217. Lateral mirroring reverses the routing sign, mirror‐symmetric controls suppress it, and closure of the nonzero reflected order at the Rayleigh boundary eliminates it. The framework also reproduces the zero‐order response of an Al/TiO ₂ system. Relative higher‐order measurements on an additional specimen support direction‐dependent diffraction. More broadly, this morphology‐defined, Rayleigh‐gated routing shifts opaque‐metagrating design from suppressing of specular reflection to selecting radiative or dissipative power flow, with potential for integrated beam redirection and photothermal conversion.