Twisted Nematic Liquid Crystal Based Terahertz Phase Shifter With Crossed Indium Tin Oxide Finger Type Electrodes

We demonstrate indium-tin-oxide (ITO) finger-type pattern (FTP) as an effective transparent conducting electrode for terahertz (THz) application. The average transmittance of ITOFTP is as high as 85% in the frequency range of 0.2-1.2 THz. A pair of fused silica substrates with ITO-FTP was employed for constructing an electrically tunable twisted nematic liquid crystal (LC) based THz phase shifter. The cross-orientation pair of ITO-FTPs served as wavelength-insensitive and transparent electrodes for the LC layer. A maximum phase shift exceeding π/2 at 1.2 THz was demonstrated for a device with a 600-μm-thick LC cell. The required driving voltage for quarter-wave operation and threshold voltage were 5.3 and 0.8 VRMS, respectively. Performance of the THz phase shifter is discussed by defining a figure of merit (FOM) for LC-based THz shifters and compared with previously reported devices.