Terahertz reconfigurable single-layer janus metasurface for directional-asymmetric wavefront manipulation

Janus metasurfaces, characterized by propagation-direction-dependent asymmetric transmission phenomena, provide an innovative design freedom for multiplexed optical systems. However, conventional approaches to asymmetric transmission typically employ three-dimensionally stacked architectures or heterogeneous material integration, exhibiting inherent limitations in fabrication complexity and intrinsic optical loss. This work presents a VO₂-based reconfigurable monolayer Janus metasurface enabling active asymmetric wavefront manipulation within the terahertz spectral range. Through synergistic utilization of VO₂'s reversible insulator-to-metal phase transition coupled with a dual-parameter modulation scheme governing incident direction, three functionally distinct optical operations are realized: an asymmetric focusing metalen, an asymmetric focusing vortex beam generator, and a Janus NOR logic gate. The proposed asymmetric wavefront modulation paradigm demonstrates advantages in fabrication cost-effectiveness and structural simplicity, thereby establishing a viable pathway toward high-efficiency, multifunctional, and chip-scale integrated photonic devices.