Tunable Terahertz Filters Based on Gold-Coated Silicon Plates With Corrugations

We experimentally demonstrate a tunable terahertz (THz) filter based on parallel plate waveguides with corrugations. The filter is achieved by placing two gold-coated silicon plates with periodic grooves face to face, which are fabricated through laser ablation combined with sputtering coating process. The etched periodic corrugations attenuate certain frequencies of THz waves, leading to frequency bandgaps. When the two wider grooves are introduced, the perfect periodicity of the structure is broken, two additional transmissions with narrow linewidths appear within the bandgap, with the full width at half maximum (FWHM) of about 3 to 4 GHz and a minimum extinction ratio of 30 dB, which are attributed to the local resonances caused by defects. By changing the numbers of grooves between defects, the defect mode coupling is observed, and a broadband transmission with the FWHM of about 8 GHz is obtained. Therefore, we can achieve a tunable filtering from dual narrowband to broadband by adjusting the distance between defects. Our proposed THz tunable filters provide a very efficient method for the design and fabrication of THz waveguide devices, which can be applied to various THz systems.