Lossless Phase-Change Material Enabled Wideband High-Efficiency Spatial Light Phase Modulation at Near-Infrared

Abstract

High-efficiency spatial light phase modulation with wide operating bandwidth is highly significant yet challenging. Dynamic metasurfaces leveraging active materials with tunable optical response provide a promising solution. Current work is generally confronted with restricted operation bandwidth and diminished modulation efficiency, constrained by the limited tunable range and inherent absorption of active materials particular at optical frequency. Recently, the emergence of lossless phase-change material Sb₂Se₃ has garnered widespread attention. Its unique characteristics, including near-zero absorption at near-infrared and a substantial refractive index contrast ≈0.93 during phase transition, enable the possibility of high-performance spatial light modulation. Pioneering studies have validated the capability of lossless phase-change metasurfaces for wavefront control, but are typically restricted to limited efficiency. Here, a hybrid phase-change metasurface utilizing over-coupled resonances supported by Sb₂Se₃ nanoholes is proposed. For the first time in optical frequency, high-efficiency 4-level phase modulation covering over π range is experimentally demonstrated with a sizable operating bandwidth of 42 nm and a minimum reflectance of exceeding 0.5. Leveraging optically driven localized phase-transition technique, dynamic beam deflection is further demonstrated. The work validates the tremendous potential of phase-change metasurfaces in achieving advanced spatial light control, signifying significant progress for the development and application of phase-change photonic devices.