Anomalous reflection focusing metasurface based on a dendritic structure

In this study, we designed a metasurface based on dendritic model structures. This metasurface consists of three branches, which rotate symmetrically around the z-axis. In accordance with the principle of optical resonator, the dendritic metasurface achieved distinct anomalous reflection and refraction in the infrared spectrum at an incidence angle range of 0-90°. On the basis of this phenomenon, the structure of an asymmetric dendritic metasurface unit was designed, with each unit consisting of two branches. This metasurface unit could achieve abnormal reflection and refraction for a normal incident plane wave. An opposite phenomenon would occur when the metasurface was rotated 180° around the z-axis. We used this feature to design a metasurface that could achieve a prominent reflective plane focusing effect at the mid-wave infrared band as a result of anomalous reflection. The dendritic metasurface had a uniform structure that could be adjusted flexibly. The anomalous phenomenon could be realized over a wide range of wavebands and angles at the mid-wave infrared band. In addition, the focusing effect was evident, and the reflection efficiency was higher than those of other structures.