Manipulation of Terahertz Waves with a Right- or Left-handed Metasurface for Directivity Enhancement

The manipulation of terahertz waves based on flat optics with metasurfaces is being employed in terahertz continuous-wave (CW) sources, such as resonant tunneling diodes (RTD) and quantum cascade lasers (QCL) for 6G wireless communications and terahertz imaging. However, two-dimensional optical components in terahertz flat optics are strongly subject to the distance from CW sources because metaatoms with different dimensions optimize the gradient distribution of the refractive indices, such as in gradient-refractive-index (GRIN) metalenses. Here we demonstrate that an original terahertz metasurface with identical double-sided meta-atoms on a dielectric substrate enhances the directivity of terahertz waves. Terahertz time-domain spectroscopy (THz-TDS) measures that the metasurface has right- or left-handed dispersion characteristics, resulting in transmittance enhancement with 177% at 0.47 THz. The metasurface could be mounted on terahertz CW sources without considering the design of the distance between the metasurafce and sources to enhance the directivity. Our findings suggest that the manipulation of terahertz waves has the potential to significantly accelerate the growth of terahertz industrial applications.