Submillimeter-wave waveguide filters fabricated by SU-8 process and laser micromachining

For terahertz systems, rectangular waveguide is an ideal low loss medium for interconnectivity and the construction of passive circuits. A drawback when manufacturing waveguides at submillimeter wavelengths is the demanding tolerances due to small dimensions. For example, a WR-3 waveguide (operating between 220 and 325 GHz) has a cross-sectional dimension of just 864 by 432 µm, and higher frequency waveguides get proportionally smaller. An additional challenge is that whether using waveguide for passive circuits such as filters, there are additional structures inside the waveguide which are significantly smaller than the waveguide itself. Traditionally, computer numerical control (CNC) milling has been used for waveguides, however at terahertz frequencies this is difficult to utilise. Emerging technologies for terahertz waveguides are compared with conventional CNC solutions. The technologies include the photolithography-based polymer etching of waveguides using SU-8 photoresist, and the laser machining of metal. Both have shown promise, and good quality terahertz passive components have been fabricated and measured.