1 Three-Dimensional Cloaking Device Operates at Terahertz Frequencies

The invisibility cloak has been a long-standing dream for many researchers over the decades. Recently, this subject has attracted considerable interest with the introduction of transformational optics, which provides a general method to design material distributions to hide the subject from detection (1, 2). By transforming space and light propagation, a three-dimensional (3D) object is perceived as having reduced number of dimensions, in the form of points, lines, and thin sheets, making it “undetectable” judging from scattered field (2-4). Since the first experimental demonstration using resonant metamaterials (5), a variety of cloaking devices have been reported at microwave and optical frequencies (6-8) while the Terahertz (THz) domain remains unexplored. Moreover, it should be noted that all the previous experimental demonstrations are performed in a two-dimensional (2D) waveguide configuration. Although those works represent a critical step in validating the concept of the invisibility cloak, one would expect the cloaking device to be realized in 3D with the ability to cloak an object of realistic size. This requires the construction of an optically large cloaking device with features much smaller than the wavelength. Fabricating 3D structures wit