Three-dimensional Antimony Sulfide Based Flat Optics

Fabricating high-index materials with designed three-dimensional (3D) micro optical elements is a challenging yet exciting area of research. Here, we develop an approach to 3D print high-index nanostructures of antimony trisulfide (Sb2S3) using grayscale electron beam lithography (g-EBL). A key advantage of our approach is its simplicity compared to the conventional complex EBL-based metalens fabrication process. The refractive index of Sb2S3 films is precisely determined using a computational genetic algorithm and the transfer matrix method. The Sb2S3 structures show high fidelity and reproducibility, with the refractive index being tunable through thermal treatment. We demonstrate the fabrication and performance of 3D Fresnel Zone Plates (FZPs) and metalenses with the same design specification. Theoretical and experimental evaluation confirmed the diffraction-limited capability of as-fabricated 3D optical elements and indicates that the focusing efficiency of FZPs is higher compared to metalenses. This work advances the application of Sb2S3 in micro- and nanoscale photonics, highlighting its potential for dynamic optical devices with precise control over output properties.