All‐Dielectric Heterogeneous Metasurface as an Efficient Ultra‐Broadband Reflector

Conventional all‐dielectric metasurfaces made from high‐index and low‐loss materials (such as Si or GaAs) can achieve high optical efficiencies as well as broadband characteristics, mostly for the infrared (IR) light. However, maintaining the bandwidth and efficiency for conventional all‐dielectric metasurfaces for visible or near‐IR light becomes challenging, due to the limitations from material selection as well as fabrication techniques. In this paper, the idea of heterogeneous all‐dielectric metasurfaces is proposed for a better metasurface design in shorter‐wavelength ranges. An ultra‐broadband reflector, as a proof‐of‐principle demonstration, is presented in this paper, both numerically and experimentally. The broadband reflector demonstrates a good optical efficiency, a broadband reflectance, as well as a great manufacturability. Nanoimprint lithography patterning process and advanced etching recipes are developed for the large‐area and low‐cost heterogeneous metasurface fabrication.