Meanwhile, metasurface design can enable more functionality and performance of CPs by enhancing the light-matter interaction and increase spectral tunability at a wide range of wavelengths that are not possible with the conventional simple thin films. With rationally designed optical modes, the far-field electromagnetic wave characteristics can be fully controlled. With the tunable optical properties, multiple states of unconventional optical functionality can be achieved in one device . For thermal and IR applications, Kirchhoff's law is employed to equate absorptivity and emissivity, providing directional emission control and increase emissivity contrast to thermal emitters and radiative coolers.