Large-gap cascaded Moiré metasurfaces enabling switchable bright-field and phase-contrast imaging compatible...

Bright-field and phase-contrast imaging represent two of the most essential modes for target recognition and feature extraction, offering broad applicability in fields such as biomedicine and autonomous driving. In this work, we propose a cascaded Moiré metasurfaces system with a large interlayer spacing, which enables switchable bright-field and phase-contrast imaging at a wavelength of 532 nm by adjusting the illumination conditions between coherent and incoherent light sources. By employing an optimized phase-iterative algorithm, the stringent spacing requirement of conventional cascaded Moiré metasurfaces is relaxed from the subwavelength scale (∼100 nm) to beyond 1 mm, while maintaining robust imaging performance under spacing deviations of ±0.1 mm. Through controlled relative rotation of the two metasurfaces by an angle θ, the system dynamically switches between a focused solid Airy disk (θ = 0°) and vortex beams with tunable topological charges ranging from -5 to +5 (θ = ±20° to ±100°). The design achieves a focusing efficiency of 82 % and vortex beam purities up to 99 %. Owing to its versatile switching capability, the system supports multi-order edge extraction for both phase-type and amplitude-type objects, reaching a spatial frequency of 228 lp/mm. This approach overcomes the limitation of existing edge-detection metasurfaces, which operate only under either coherent or incoherent illumination. Our findings provide a new technical pathway toward compact, multifunctional, and integrated imaging devices.