Abstract-Broadband tunable liquid crystal terahertz waveplates driven with porous graphene electrodes

Lei Wang^1,*, Xiao-Wen Lin^1,*, Wei Hu¹, Guang-Hao Shao¹, Peng Chen¹, Lan-Ju Liang², Biao-Bing Jin², Pei-Heng Wu², Hao Qian³, Yi-Nong Lu³, Xiao Liang⁴, Zhi-Gang
 Zheng¹ and Yan-Qing Lu¹

http://www.nature.com/lsa/journal/v4/n2/full/lsa201526a.html

Versatile devices, especially tunable ones, for terahertz imaging, sensing and high-speed communication, are in high demand. Liquid crystal based components are perfect candidates in the optical range; however, they encounter significant challenges in the terahertz band, particularly the lack of highly transparent electrodes and the drawbacks induced by a thick cell. Here, a strategy to overcome all these challenges is proposed: Few-layer porous graphene is employed as an electrode with a transmittance of more than 98%. A subwavelength metal wire grid is utilized as an integrated high-efficiency electrode and polarizer. The homogeneous alignment of a high-birefringence liquid crystal is implemented on both frail electrodes via a non-contact photo-alignment technique. A tunable terahertz waveplate is thus obtained. Its polarization evolution is directly demonstrated. Furthermore, quarter-wave plates that are electrically controllable over the entire testing range are achieved by stacking two cells. The proposed solution may pave a simple and bright road toward the development of various liquid crystal terahertz apparatuses.