Laser-Fabricated In ₃ SbTe ₂ Phase-Change Metasurfaces for Infrared and Terahertz Polarization Control

Phase-change materials provide nonvolatile optical tunability for programmable metasurfaces, yet their practical implementation remains fundamentally limited by their intrinsically narrow operational bandwidths. Addressing this limitation, we demonstrate broadband polarization manipulation using In3SbTe2 (IST) phase-change metasurfaces fabricated via laser direct writing of crystalline-IST grating patterns embedded within an amorphous-IST matrix. The mixed-phase architecture enables strong and continuous transmission contrast between transverse-electric and transverse-magnetic polarizations spanning the infrared to terahertz spectral regimes. As a proof of concept, an infrared quarter-wave plate is realized through geometry-controlled amplitude matching and π/2 phase retardation, achieving efficient linear-to-circular polarization conversion. Large-area (2-in.-diameter) metasurfaces are rapidly produced and successfully integrated into a terahertz imaging platform for polarization-resolved imaging. This work establishes laser-written IST metasurfaces as a scalable solution for broadband, manufacturable polarization photonics.