Conventional approach to change the polarization state of light is to use a birefringent crystal which can cause different phase delays along two orthogonal axes. Yet this approach may have some disadvantages such as low efficiency, bulky volume, frangibility, long propagation distance and narrow bandwidth. Controlling the polarization state of THz wave remains a big challenge due to lack of suitable natural materials. Metasurfaces, a kind of two-dimensional artificially designed materials, offer a new way to study novel terahertz devices.
Professor Jinsong Liu led graduate student Weicheng Mo and others in laser and terahertz functional laboratory of Wuhan Optoelectronics National Laboratory achieved a terahertz polarization converter working at 0.1THz based on metasurfaces. Firstly, the simulation presents a method to flexibly control the polarization of THz wave. This metasurface consists of A line arrays and B line arrays which can control Ey and Ex respectively. A and B are interlaced arrangement along y direction with an offset distance d between them in the x direction which can cause the abrupt phase delay between beam A and B, so as to tune the polarization of the reflected wave freely. Then several samples are made via the photolithography and electron beam evaporation technology. A half wave plate is obtained in the experiment, proving the feasibility of the method. Polypropylene spacer is used to make the metasurface very flexible and is more suitable for future applications.
This work ”Ultrathin flexible terahertz polarization converter based on metasurfaces” is reported on Optics Express (Vol. 24, no. 12, pp. 13621-13627, 2016) of OSA on June 16, 2016. This research is funded by National Natural Science Foundation of China(501100001809 and the Wuhan Applied Basic research project,China (20140101010009).).
（a）The structure of the terahertz polarization converter（b）The Lissajous Figure of the reflected wave