ABSTRACT Chalcogenide phase‐change photonics has revolutionized reconfigurable optics by enabling nonvolatile light‐matter control. While low‐loss phase‐change materials (PCMs) with near‐zero extinction coefficients ( k ≈ 0) unlock ideal phase‐only modulation, their growing compositional complexity hinders uniform fabrication and switching stability. Here, we introduce an elemental solution: wafer‐scale (8‐inch) selenium (Se) thin films achieving unprecedented uniformity, full near‐infrared transparency, and ultralow losses across the visible range, meanwhile sustaining one million (10 6 ) reversible cycles without degradation. First‐principles calculations reveal that the giant refractive index switching (Δ n ≈ 0.6) stems from the unique fracture‐reconfiguration dynamics of Se helical chains. Furthermore, we demonstrate a manufacturable, etch‐free platform with laser‐reconfigurable patterns for dynamic image generation and Gaussian‐vortex beam conversion. By harmonizing atomic simplicity with device‐grade scalability, this elemental PCM establishes a new paradigm for high‐performance programmable photonics.
Huang et al. (Tue,) studied this question.