Design of unidirectional energy flow film based on micro-prism structure

Unidirectional transmission optical elements are mainly designed based on metal surface microstructures, photonic crystals, etc. and the unidirectional ratio can reach 100%. These elements are mainly used in optical communications, optical switch and have unidirectional energy flow in a narrow spectral range. However, in the other cases, such as solar cells and radiative cooling, unidirectional transmission is usually required in a wide spectral range. In this paper, a unidirectional transmission film with micro-prism structure is proposed and demonstrated based on geometrical optics. When the refractive index of the used materials is about 2.0 and the bottom angle of the micro-prism is between 58-65 degrees, the unidirectional energy flow difference of the film is about 55%. Although this structure cannot achieve 100% unidirectional energy flow ratio, its working band is very wide.