operating in the terahertz frequency regions and mid-infrared regions at wavelengths of 0. 8
m to 3 mm and a method for manufacturing the same. Based on the effective medium
theorem, the effective refrac tive index is controlled by using a structure smaller than the mid-
infrared and terahertz wavelength, and a gradient can be provided for the refractive index in
a radial direction and in (Continued)