Pattern-free Sb2S3–metal photonic cavity for switchable edge and bright-field imaging in reflection

We numerically investigate a lithography-free Sb2S3–metal cavity that switches between edge detection and bright-field imaging in reflection at telecom wavelengths. A (SiO2/TiO2)6 coupling mirror, a phase-change layer, an SiO2 spacer, and an optically thick Au reflector form a one-port resonator. Switching Sb2S3 shifts the near-critical-coupling resonance from 1434.1 to 1525.9 nm. At either resonance, the resonant phase state suppresses the zero spatial frequency and provides an approximately quadratic reflection transfer function over NA=0.15, whereas the off-resonant state provides an almost uniform response. Thus, changing only the nonvolatile phase state interchanges Laplacian-like edge enhancement and bright-field reproduction at a fixed wavelength. Fourier-domain simulations of orthogonal bar targets, compound symbols, and traffic signs predict approximately orientation-independent two-dimensional processing and recognizable image reconstruction within the investigated pupil. The planar, metal-backed architecture offers a compact route to reconfigurable optical preprocessing without lateral nanopatterning or mechanical motion.