Performance optimization of a metasurface incorporating non-volatile phase change material.

Optical metasurface is a combination of manufactured periodic patterns of many artificial nanostructured unit cells, which can provide unique and attractive optical and electrical properties. Additionally, the function of the metasurface can be altered by adjusting the metasurface's size and configuration to satisfy a particular required property. However, once it is fabricated, such specific property is fixed and cannot be changed. Here, phase change material (PCM) can play an important role due to its two distinct states during the phase transition, referred to as amorphous and crystalline states, which exhibit significantly different refractive indices, particularly in the infrared wavelength. Therefore, a combination of metasurface with a phase change material may be attractive for achieving agile and tunable functions. In this paper, we numerically investigate an array of silicon cylinders with a thin PCM layer at their centers. The GST and GSST are the most well-known PCMs and were chosen for this study due to their non-volatile properties. This structure produces two resonant modes, magnetic dipole and electric dipole, at two different resonating wavelengths. We have numerically simulated the effect of cylinder's height and diameter on the reflecting profile, including the effect of thickness of the phase change material. Additionally, it is shown here that a superior performance can be achieved towards reduced insertion loss, enhanced extinction ratio, and increased figure of merit when a GST layer is replaced by a GSST layer.