Flat optical transparent window: mechanism and realization based on metasurfaces

Abstract

A material exhibiting a wide-band optical transparent window (OTW) with negligible transmittance fluctuation is highly desired in various applications, but the conventional approach of stacking multiple transmission-resonant metasurfaces creates undesired amplitude fluctuations within the OTW. In this article, we first establish a coupled-mode theory to understand the inherent physics governing the transmission properties in such systems, based on which we then propose a criterion that can help researchers design structures exhibiting wide-band OTWs with diminished transmittance fluctuations. Compared to a brute-force optimization method, our approach is much faster and physically intuitive. As an illustration of our theory, we design a four-layer structure (with a total thickness of 36 mm) through solving the proposed criterion, and experimentally demonstrate that it exhibits a flat OTW within the 3.7–5 GHz range, with transmittance fluctuations smaller than 10 percent. Our findings can stimulate the design of artificial structures exhibiting the desired shapes of transmission windows fitting applications in different frequency regimes.