9.1: Terahertz backward-wave oscillator slow-wave circuits

We have been exploring several slow-wave circuits for terahertz frequency backward-oscillators that are suitable for microfabrication. The circuits include folded waveguide circuits based on either rectangular or photonic crystal waveguides, as well as interdigital lines microfabricated either on substrates, suspended micron-scale membranes, or with entirely free-standing interdigital fingers. Beginning with numerical design studies, fabrication process development and hot circuit tests have followed when appropriate. The calculated interaction impedances, used to compare circuits, range from on-order-of one to several kilo-ohms. The free-standing interdigital lines seem to hold the most near-term promise, with testing underway.