Enhanced THz Transmission through Micromachined Sub-wavelength Annular Apertures

In this paper we report on the development of THz filters based on sub-wavelength apertures. We demonstrate the applicability of both bulk and surface micromachined approaches to the fabrication of these structures. In particular, a surface micromachined electroplated copper process has been developed which enables the fabrication of coaxial, or annular, apertures surrounded by periodic concentric grooves. To the best of our knowledge this is the first time this structure has been fabricated for operation at THz frequencies.