Additive manufacturing of planar waveguides for terahertz applications.

The emerging planar photonic crystal (PC) and effective medium (EM) waveguides are considered promising technical platforms for terahertz communications. Beyond short-scale connections and various signal processing functionalities, versatile terahertz on-chip systems could be achievable by their physical integration; however, the inefficient coupling poses challenges. In this work, we propose an interface design between planar PC and EM waveguides with minimal insertion loss. Stereolithography 3D printing was validated as a cost-effective alternative to the microfabrication technologies for the demonstration of these two waveguide designs. Experiments found that optimized PC and EM waveguides in photosensitive resin exhibited transmission losses of 3.4 dB/cm and 2.1 dB/cm at 140 GHz, respectively. Furthermore, by adjusting the radius and positioning of certain air holes adjacent to the waveguide core, we reduced the insertion loss associated with the waveguide interface to 0.4 dB; significantly lower compared with direct butt coupling without transitions. The ∼30% increase in power coupling efficiency enabled terahertz signal transmission with higher data rates and lower bit error rate for terahertz communications. We believe that the proposed terahertz planar waveguide fabrication routes and structural designs could hold huge potential to offer efficient rapid-prototyping and inter-waveguide integration solutions for multifunctional terahertz circuits.