Bragg-Mirror Suppression for Enhanced Bandwidth in Terahertz Photonic Crystal Waveguides

Terahertz technology is being accelerated by photonic crystal waveguides that are implemented with an array of through-holes in an intrinsic silicon slab. Such waveguides show promise to realize compact terahertz systems. However, photonic crystal waveguides were originally developed in the infrared range, where small relative bandwidth is acceptable for communications applications. Greater relative bandwidth is desirable for the lower-frequency terahertz range, and hence our aim is to increase the bandwidth of terahertz photonic crystal waveguides. To this end, the defect-row structure of the photonic crystal waveguide track is adapted in order to suppress the Bragg-mirror effects that are typical of conventional photonic crystal waveguides. Specifically, the waveguide track is clad with semi-circular holes. The resultant structure is found to guide radiation efficiently over a bandwidth from 277 to 435 GHz-a six-fold increase in relative bandwidth over existing terahertz photonic crystal waveguides-and hence it may find applications in terahertz communications. Although simulations show that the waveguide is over-moded, experiments indicate that only the desired dominant mode is strongly excited in practice.