Sub-Second Switching Speed Polarization-Independent 2 pi Terahertz Phase Shifter

This study develops a 2 pi terahertz (THz) phase shifter that stacks three layers of cholesteric liquid crystal (CLC) cells. Each CLC cell in the focal conic state with randomly helical structures exhibits isotropic properties for a THz wave and enables polarization independence. An external vertical electric field is applied to modulate the refractive index of the CLC cells by switching the liquid crystals between focal conic and homeotropic states. The driving voltage and response time were significantly improved by the multi-stacking technique relative to that of a 5-mm-thick CLC-based 2 pi THz phase shifter, whose critical voltage is as high as 1200 V and response time is tens of seconds. The proposed multilayer device has a relatively small critical voltage of 400 V and a short response time of less than 1 s.