Abstract
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.
Highlights
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
Here we propose a Micro Electro Mechanical Systems (MEMS) chiral metamaterial facilitated by a deformable 3D chiral structure with the ability to switch between mirror images
When a planar Archimedean spiral is actuated in the upward vertical direction, the spiral becomes left handed (LH) (Fig. 1a)
Summary
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. Some enantiomer molecules are able to switch to the other handed isomer when subjected to stimuli such as heat or light[2,3] These features satisfy the requirements of a polarization modulator for controlling the polarization state without altering the light intensity. There remains the need for a metamaterial satisfying both of these requirements; large optical activity and enantiomeric switching ability To satisfy these requirements, here we propose a Micro Electro Mechanical Systems (MEMS) chiral metamaterial facilitated by a deformable 3D chiral structure with the ability to switch between mirror images. The 3D spirals present large optical activity, and enantiomeric switching gives rise to the symmetrical optical activity spectral shapes between the different handedness structures This technology provides new ways of manipulating polarization states of the THz electromagnetic waves
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