Large and active circular dichroism in a photosensitive silicon based metasurface

Active circular dichroism (CD) is highly required for flexible polarization control in modern terahertz (THz) systems. In this work, we numerically achieve large and active CD in THz region by optically controlling photosensitive silicon in a gold/silicon hybrid cross-shape metasurface. At the incident angle of 75 degrees, the proposed metasurface exhibits large CD. By tuning the conductivity of photosensitive silicon with an optical pump, the large CD (0.89) can be dynamically switched to 0.06 and the peak frequency is blue shifted around 0.09 THz. The simultaneous switching of CD strength and peak frequency is attributed to the variation of resonance modes between electric and magnetic dipole resonances. Our proposed active metasurface with dynamic CD has profound potential in the fields of reconfigurable THz devices.