Unidirectional Thermal Emission from All‐Dielectric Metasurfaces With no Metallic Back‐Reflector

ABSTRACT Achieving unidirectional thermal emission—radiating exclusively to one side of a device without requiring a back‐reflector—is highly beneficial for many energy‐efficient optoelectronic applications. State‐of‐the‐art thermal emitters, however, typically rely on underlying metallic reflectors that complicate fabrication and increase cost. Here we show that unidirectional thermal emission can instead be realized using a simple, all‐dielectric metasurface that supports unidirectional guided resonances (UGRs). Rather than invoking topological polarization singularities in momentum space, the same effect emerges in conventional, partially etched 1D gratings, effectively reducing the architecture to a monolithic dielectric slab with a periodic surface profile. Because the UGR arises from the coupling between two guided mode resonances, the structure is intrinsically metal‐free and CMOS‐compatible, offering efficient spectral‐spatial control of the thermal emission. We fabricated the gratings using evaporated germanium on a CaF 2 substrate and experimentally verified mid‐infrared unidirectional emission directed toward either the substrate or the cladding at distinct wavelengths, aligning well with numerical predictions. Our results demonstrate a simplified route to efficient, lightweight and scalable unidirectional thermal emitters.