Bias-free nonreciprocal image processing via reconfigurable metasurface

In this work, we demonstrate a bias-free, nonreciprocal, and reconfigurable image-processing platform with rapid modulation speed using a silicon metasurface integrated with an underlying vanadium dioxide (VO2) thin film. A silicon photonic crystal, supporting resonant modes with tailored optical dispersion, enables high-resolution edge differentiation (~11µm). Meanwhile, the photothermal-induced nonlinearity (i.e., insulator-to-metal transition) of VO2 combined with direction-dependent asymmetric absorption, produces a nonreciprocal response free of bias—the input image itself acts as a bias. Our experimental findings reveal the steady-state nonreciprocal edge-detected and bright-field imaging modalities under forward and backward illumination within a power window. We further show that the same device acts as a fast reconfigurable metasurface under high illumination: it enables rapid switching between the two modalities in under 100 ms. This approach overcomes the limitations of reciprocal imaging, advancing photonic techniques for secure and high-resolution imaging.