Parikshit Moitra1,Yunzheng Wang2,3,Xinan Liang1,Li Lu2,Alyssa Poh2,Tobias Mass1,Robert Simpson2,Arseniy Kuznetsov1,Ramon Paniagua Dominguez1
Institute of Materials Research and Engineering1,Singapore University of Technology and Design2,Shandong University3
Parikshit Moitra1,Yunzheng Wang2,3,Xinan Liang1,Li Lu2,Alyssa Poh2,Tobias Mass1,Robert Simpson2,Arseniy Kuznetsov1,Ramon Paniagua Dominguez1
Institute of Materials Research and Engineering1,Singapore University of Technology and Design2,Shandong University3
Recent advances in wavefront shaping, by complete control of amplitude and phase of the propagating light waves, have been explored with the application of resonant all-dielectric metasurfaces, composed of high-index nano-resonators. However, there is a major limitation, in terms of lack of post-fabrication tunability of their optical responses, as these metasurfaces are commonly fabricated from passive materials. To circumvent this issue, chalcogenide phase change materials (PCMs) have been incorporated to the design, to bestow a fast and non-volatile tunability of the optical responses. Most of these tunable metasurfaces have been demonstrated in the mid infrared spectrum using Germanium-Antimony-Telluride (GST) PCMs. To lower the absorption loss of GST in the near infrared, selenium (Se) is doped with GST to form Ge-Sb-Se-Te (GSST) to achieve lossless optical properties in the wavelength range longer than 1 μm. However, there have been no demonstrations in the visible frequencies showing complete wavefront control with high efficiency using PCMs due to the lack of lossless and high-index PCMs in the same spectral range. Antimony trisulfide (Sb<sub>2</sub>S<sub>3</sub>) fits the requirement very well based on its low-loss and high refractive index optical properties in the visible frequencies, along with a sharp index contrast (~0.5) between its amorphous and crystalline phases. Here, we demonstrated nanofabrication process development of this novel material using conventional methods to realize high resolution metasurfaces. Having equipped with this fabrication capability, we realized Huygens’ metasurfaces with nanoholes etched on to 160 nm thick as-deposited amorphous-Sb<sub>2</sub>S<sub>3 </sub>film and further demonstrated tunability of transmission resonance by 60 nm and close to 2π optical phase shift upon non-volatile and reversible switching between its amorphous and crystalline phases. With the design based on phase-only manipulation, we further realized reversibly switchable beam steering, tunable holograms and bound-states-in-the-continuum (BIC). We strongly believe that these demonstrations pave the way towards future metasurface devices with dynamic wavefront control viz. high resolution spatial light modulators for AR/ VR applications, tunable flat optics, LiDAR and optical holography.