Kan Tetsuo, Isozaki Akihiro, Kanda Natsuki, Nemoto Natsuki, Konishi Kuniaki, Takahashi Hidetoshi, Kuwata-Gonokami Makoto, Matsumoto Kiyoshi, Shimoyama Isao
Department of Mechano-Informatics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
IRT Research Initiative, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
Nat Commun. 2015 Oct 1;6:8422. doi: 10.1038/ncomms9422.
Active modulation of the polarization states of terahertz light is indispensable for polarization-sensitive spectroscopy, having important applications such as non-contact Hall measurements, vibrational circular dichroism measurements and anisotropy imaging. In the terahertz region, the lack of a polarization modulator similar to a photoelastic modulator in the visible range hampers expansion of such spectroscopy. A terahertz chiral metamaterial has a huge optical activity unavailable in nature; nevertheless, its modulation is still challenging. Here we demonstrate a handedness-switchable chiral metamaterial for polarization modulation employing vertically deformable Micro Electro Mechanical Systems. Vertical deformation of a planar spiral by a pneumatic force creates a three-dimensional spiral. Enantiomeric switching is realized by selecting the deformation direction, where the polarity of the optical activity is altered while maintaining the spectral shape. A polarization rotation as high as 28° is experimentally observed, thus providing a practical and compact polarization modulator for the terahertz range.
太赫兹光偏振态的主动调制对于偏振敏感光谱至关重要，在非接触霍尔测量、振动圆二色性测量和各向异性成像等重要应用中发挥着作用。在太赫兹波段，缺乏类似于可见光范围内光弹性调制器的偏振调制器阻碍了此类光谱技术的拓展。太赫兹手性超材料具有自然界中无法获得的巨大光学活性；然而，对其进行调制仍然具有挑战性。在此，我们展示了一种利用垂直可变形微机电系统实现用于偏振调制的手性可切换超材料。通过气动力使平面螺旋垂直变形可形成三维螺旋。通过选择变形方向实现对映体切换，在此过程中光学活性的极性发生改变，同时保持光谱形状不变。实验观察到高达28°的偏振旋转，从而为太赫兹波段提供了一种实用且紧凑的偏振调制器。
