Terahertz (THz) waveguide Bragg grating is experimentally demonstrated on the basis of a mechanical assembly that includes a metal-grating sheet and a metal parallel-plate waveguide (PPWG). Bragg frequency waves, which are also called phase-matching waves, are efficiently coupled from the free space on the basis of the designed parameters of the air gap width, the metal grating thickness, and the PPWG taper angle. These optimal parameters are critical to reflect the Bragg frequency waves with a transversely resonant field across the metal grating. For other THz waves that are not phase matching to the meal grating vector, transverse resonance simultaneously occurs. However, these waves propagate forward as waveguide modes. PPWG-assembled metal grating thus performs highly distinct Bragg frequencies in the waveguide transmittance when the noisy resonance field, not following Bragg law, is exactly constrained by the waveguide scheme. Given that all components of the waveguide Bragg grating are made of metal without dielectric perturbation, a series of strong Bragg resonant modes in a wide bandwidth and a hollow-core chamber is potentially facilitated for THz gas sensors.
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