Investigation of spectral properties and lateral confinement of THz waves on a metal-rod-array-based photonic crystal waveguide

Terahertz (THz) waves laterally confined in a 1 mm-thick microstructured planar waveguide are demonstrated on a free-standing metal rod array (MRA), and one apparent rejection band of a transmission spectrum, resembling the bandgap of a photonic crystal, is found in 0.1–0.6 THz. The visibility of the photonic bandgap in the spectral width and power distinction can be manipulated by changing the MRA geometry parameters, including the rod diameter, the interspace between adjacent rods, and the propagation length based on an interactive MRA-layer number. THz transmission ratio enhanced by a large interactive length is verified in 30 MRA layers due to the longitudinally resonant guidance of transverse-magnetic-polarized waveguide modes along the MRA length, which is critical to the interspace width of adjacent rods and the metal coating of the rod surface. For an MRA with respective rod diameter and interspace dimensions of about 0.16 and 0.26 mm, the highest transmission of the guided resonant THz waves are performed at 0.505–0.512 THz frequency with strong confinement on the metal rod tips and a low scattering loss of 0.003