Broadband tunable liquid crystal terahertz waveplates driven with porous graphene electrodes

By Lei Wang, Xiao-Wen Lin, Wei Hu, G. Shao, Peng Chen, L. Liang, B. Jin, Peiheng Wu, Hao Qian, Yi Lu and 3 more. Light: Science & Applications, 2015

167 citations recorded by the source corpus.

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. A broadband, tunable terahertz wave plate with highly transparent electrodes based on porous few-layer graphene is made by a team in China. Terahertz technology holds out exciting potential for imaging, sensing and high-speed communications. However, it is proving difficult to extend liquid crystal devices to the terahertz range due to a lack of transparent electrodes in this regime. Now, researchers from Nanjing University and Tsinghua University have overcome this problem by using few-layer porous graphene to realize an electrode with a transmittance of over 98% at terahertz frequencies. By using a subwavelength metal wire grid as both the other electrode and built-in polarizer, the researchers fabricated a tunable terahertz wave plate with a phase retardation range of over π at 1.0 THz. This approach has the potential to realize various tunable terahertz liquid-crystal devices.

Subfields: Atomic and Molecular Physics, and Optics, Biomedical Engineering, Electronic, Optical and Magnetic Materials

View Paper: https://www.semanticscholar.org/paper/655207012dcc478dd03c455811bd81c26f109c0b