Terahertz dielectric anisotropy enhancement in dual-frequency liquid crystal induced by carbon nanotubes

Dual-frequency liquid crystals (DFLCs), the mixture of positive and negative liquid crystal (LC) molecules, exhibit unique alternating (AC) frequency dependent anisotropic properties. Carbon nanotube (CNT), as a novel nanomaterial with strong anisotropy, has attracted much attention in recent years. Herein, we investigate the tunable terahertz birefringence and phase shift characteristics of the DFLC doped with CNT (CNT-LC) by using the terahertz time-domain polarization spectroscopy. The results show that the CNT-LC (1.5 wt%) can reach 0.5π at 0.793 THz, which can be used as a tunable THz phase shifter that is 0.12π higher than the pure DFLCs. Furthermore, through measuring the output polarization state, it is confirmed that the dielectric anisotropy enhancement mechanism of CNT-LC originates from the surface interaction between CNTs and LC molecules. Therefore, a tunable quarter-wave plate with the active polarization conversion from linearly polarized (LP) to LP or LP to circularly polarized (CP) can be realized at 0.925 THz in the CNT-LC, while the pure DFLC cannot be achieved at the same frequency. The dielectric anisotropy enhancement of CNT-LC shows its utility in the improvement of various tunable terahertz LC phase shifter and wave plate.