Active Terahertz Liquid Crystal Device with Carbon Nanotube Film as Both Alignment Layer and Transparent Electrodes

Liquid crystal (LC) materials are a good candidate for active phase and polarization devices. However, they also encounter significant challenges in the lack of transparent electrodes and the difficulty of LC alignment due to the thick LC cell for sub-mm wavelength in the terahertz (THz) regime. Here, we presented a strategy to overcome these difficulties, that is, using a super-aligned carbon nanotube (CNT) film with dual functions for both transparent electrodes and the aligning layer for THz LC cell. The LC molecules are uniformly aligned along the orientation direction of the CNT film because of its surface anchoring effect. The experiment results show that the active THz polarization conversions are controlled by the bias voltage tuning from 0 to 30 V between the upper and lower CNT films, and the output polarization state is converted between linear polarization and circular polarization. This work may pave a simple and flexible path toward the development of various active THz liquid crystal devices for spatial light modulation, dynamic imaging, and wavefront control.