Abstract
In this work, we constructed a liquid-crystal-based electrically tunable terahertz (THz) achromatic quarter-waveplate (AQWP), and demonstrated its performance in achromatism and the tunability of its achromatic range. According to the theoretical model and the simulation results, the expected performance of AQWP composed of three LC and four LC cells are compared. For better transmittance, we choose the design with three LC(MDA-00-3461) THz phase shifters. Using the Jones matrix formulism by a simple algorithm, we designed thickness and bias of each LC cell. ITO nanowhiskers (NWhs),highly transparent in the THz frequency band, is used as the transparent electrode of our LC cells. The voltage applied to each cell is estimated by the characteristic bias-phase shift curve of each cell. We demonstrated that by judiciously changing the effective birefringence of each cell, achromatic range of the AQWP can be tuned. Besides, we set up a polarization-resolved THz time-domain spectroscopy (TDS). The Stokes parameters of the THz wave can be determined. The experimental results show that our AQWP design achieve achromatism in the frequency range of 0.30~0.45 THz. Furthermore, the achromatic range can be shifted to 0.35~0.50 THz. The results are in general agreement with the theoretical predictions.