Tungsten disulfide based anisotropic metalens for refractive index sensing applications in visible region

Studies on metalenses are rapidly developing, aiming to introduce compact optical devices with superior properties. In this study, which can contribute to the existing literature under the heading of anisotropic metamaterials, the focusing performance of the metalens using the aperture-based Pancharatnam-Berry phase method is numerically analyzed. The proposed structure is formed by coating tungsten disulfide layer on silicon nitride membrane and then etching the whole structure according to the aperture Pancharatnam-Berry phase method. The designed metalens is capable of focusing with efficiencies of 9.7 %, 6.7 %, and 8.4 % at red, green, and blue wavelengths, respectively. At all three wavelengths, the resonative behavior is provided by the anisotropic behavior. Additionally, high numerical aperture values as 0.81, 0.81, and 0.76 are obtained for all three wavelengths. Moreover, refractive index sensing performance is analyzed by immersing the structure into different types of alcohol media, and in this respect, another unique aspect of the study is revealed.