Mechanically Reconfigurable Polarization Converter for Terahertz Waves

In terahertz systems, polarization conversion is usually carried out using conventional waveplates. However, limitations in these waveplates arise from inadequate material accessibility, relatively narrow bandwidth, low efficiency, and bulkiness. To overcome these limitations, a transmissive terahertz metasurface with mechanically reconfigurable polarization conversion is proposed. The separation between two identical metasurface plates is varied to switch between quarter-wave plate and half-wave plate functionalities. Measurement results verify that with no separation, the device can perform as a quarter-wave plate providing better than 3-dB axial ratio and an efficiency of over 75% from 246 to 320 GHz. With a separation of 150 $\bm {\mu }$ m between the two units, the transmission output becomes a cross-polarized wave with a 18-dB extinction ratio and an efficiency of over 74% across the same band. Altogether, the proposed polarization conversion device provides the advantage of reconfigurability and can be simply installed into existing terahertz systems to achieve multiple functionalities.