Reconfigurable photoinduced terahertz wave modulation using hybrid metal-silicon metasurface

We present a photoinduced reconfigurable metasurface to enable high spatial resolution terahertz (THz) wave modulation. Conventional photoinduced THz wave modulation uses optically induced conductive patterns on a semiconductor substrate to create programmable passive THz devices. The technique, albeit versatile and straightforward, suffers from limited performance resulting from the severe lateral diffusion of the photogenerated carriers that undermines the spatial resolution and conductivity contrast of the photoinduced conductive patterns. The proposed metasurface overcomes the limitation using a metal-jointed silicon mesa array with subwavelength-scaled dimensions on an insulator substrate. The structure physically restrains the lateral diffusion of the photogenerated carriers while ensuring the electrical conductivity between the silicon mesas , which is essential for THz wave modulation. The metasurface creates high-definition photoconductive patterns with dimensions smaller than the diffusion length of photogenerated carriers. The metasurface provides a modulation depth of -20 to -10 dB for the THz waves between 0.2 to 1.2 THz and supports a THz bandpass filter with a tunable central frequency. The new, to the best of our knowledge, design concept will benefit the implementation of reconfigurable THz devices.