Designs of terahertz waveguides for efficient parametric terahertz generation

We show that for a slab waveguide, while pump and idler waves are weakly affected by the waveguide, their parametrically generated terahertz (THz) wave propagates in the form of multimodes. These waves may destructively interfere with one another in terms of their phases, resulting in inefficient THz parametric conversion. To avoid this problem, we designed a THz slab or rib waveguide that supports a quasi-single or single mode. Using these waveguides, the threshold powers for achieving oscillations can be significantly reduced due to the waveguide confinement of the THz waves. In addition, modal indices of refraction can be tailored for achieving phase matching without complicated periodic poling.