Phase-modulated GST metasurfaces: Polarization-independent ultra-broadband absorbers and switchable photonic devices beyond amplitude modulation

We demonstrate a phase-modulation paradigm for metasurface perfect absorbers that fundamentally differs from conventional amplitude-control approaches. By strategically arranging crystalline germanium–antimony–tellurium (c-GST) disk meta-atoms with π-phase-shifted reflection characteristics in a fourfold rotational symmetry configuration, we achieve polarization-insensitive ultra-broadband absorption averaging 96.6% (peaking >99%) across the 1000–1600 nm spectrum. Capitalizing on the dramatic optical contrast between amorphous and crystalline GST phases, we further develop dual-mode photonic switches: (1) a polarization-independent switch maintaining >2.5 contrast ratio throughout the band, reaching a record 43.6 at specific wavelengths; (2) a polarization-tunable switch, enabling dynamic spectral control, where peak contrast ratios shift from 36@1278 nm (TM) to 14@1090 nm (TE). The subwavelength thickness (300 nm) of all meta-atoms ensures CMOS-compatible fabrication potential, while the phase-reconfiguration mechanism provides more degrees of freedom for multifunctional photonic integration.