A Design of a Slow-group-velocity and Low-loss Bragg Waveguide in Terahertz

We propose a design of small-core multiple-layer Bragg waveguide for guiding the THz signal by TE01 mode, which is composed of alternating un-doped silicon (high refractive index) and high-density polyethylene (low refractive index). The group velocity of the THz wave traveling inside this small-core waveguide slows down to below 0.5c, while the propagation loss is less than 0.3 dB per centimeter ranging from 0.95 THz to 1.2 THz, which is better than the traditional metallic tube. Furthermore, a novel scheme is proposed to excite and retrieve the very high-purity TE01 mode in a Bragg waveguide by employing additional Y-type TE01 mode converters. Based on this scheme, for the first time, one is possible to characterize the Bragg TE01 mode in experiment or further apply such wave-guiding system in THz communication or beam-wave interaction for THz generation.