Fig. 1. Thermal emission controls (including spectrum control, direction control, and polarization control)

Fig. 2. Thermal emission direction controls based on grating structure. (a) Coherent thermal emission source based on SiC grating structure^[18]; (b) coherent thermal emission source based on W grating structure^[19]; (c) self-focusing thermal emission source based on SiC grating structure^[20]; (d) 0° directional thermal emission based on W bull’s eye grating structure^[22]

Fig. 3. Thermal emission direction controls based on metasurfaces. (a) Narrowband directional thermal emission based on Au/SiN/Au metasurface^[23]; (b) angle-selective thermal emission based on Al/SiN/Al metasurface^[24]; (c) nonreciprocal thermal emission based on Weyl semimetal metasurface^[28]; (d) unidirectional thermal emission based on metagratings^[29]

Fig. 4. Thermal emission direction controls based on photonic crystals. (a) Narrowband directional thermal emission based on vertical-cavity enhanced resonances^[31]; (b) narrowband directional thermal emission based on SiC and one-dimensional photonic crystal^[32]; (c) narrowband directional thermal emission based on optimized Si/SiO₂ aperiodic structures^[33]; (d) narrowband directional thermal emission based on monolayer tungsten disulfide and one-dimensional photonic crystal slab^[34]

Fig. 5. Thermal emission direction controls based on epsilon-near-zero materials. (a) Narrowband directional thermal emission based on semiconductor hyperbolic metamaterials^[36]; (b) narrowband directional thermal emission from ultra-thin planar films based on polar materials^[38]; (c) broadband directional thermal emission based on gradient ENZ metamaterials^[39]; (d) whole long-wave infrared directional thermal emission based on ENZ thin films^[40]

Fig. 6. Applications of thermal emission direction controls. (a) Energy-saving windows based on broadband directional thermal emission^[43]; (b) high resolution wide-field infrared imaging^[45]; (c) infrared reflective polarizer based on epsilon-near-zero materials^[47]; (d) visible-infrared dual band information encryption with infrared information anti-snooping function^[49]