Full polarization and high coherence control of thermal emissions via saddle-band dispersion engineering.

Photonic engineering in metasurfaces has enabled unprecedented control over thermal emissions in recent years. Here, we present a design strategy that achieves full and simultaneous control over both polarization and coherence of thermal emission across a broad range of output angles. Our design builds upon a double-sided corrugated waveguide array that supports a unique saddle-shaped high-Q dispersion band-parabolic along the waveguide direction to ensure high spatial coherence by involving minimal wavevectors, and flat in the perpendicular direction to enhance collection efficiency through 1D spatial filters and focusing lenses. The continuous tuning of polarization states is achieved by adjusting the relative offset of corrugations along the waveguide direction. We fabricate a series of metasurfaces and demonstrate record-high temporal coherence (Q ≈ 304), spatial coherence (coherence length: 0.32 mm), spin coherence (emission circular dichroism ≈ 0.91), and multiple polarization states, with all features retained over large output angles (over 10°).