Abstract-Enantiomeric switching of chiral metamaterial for terahertz polarization modulation employing vertically deformable MEMS spirals

• Tetsuo Kan,
• Akihiro Isozaki,
• Natsuki Kanda,
• Natsuki Nemoto,
• Kuniaki Konishi,
• Hidetoshi Takahashi,
• Makoto Kuwata-Gonokami,
• Kiyoshi Matsumoto
• & Isao Shimoyama
• http://www.nature.com/ncomms/2015/151001/ncomms9422/full/ncomms9422.html
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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.