Slot waveguide bypasses need for tapered spikes for terahertz communication

Occupying the frequencies between microwaves and infrared light, terahertz radiation has shown potential for future telecommunications standards. Most existing terahertz silicon waveguides work by confining electromagnetic waves within a silicon-based core. However, connecting two parallel silicon beams of the slot waveguide on a single wafer requires a low-index medium composed of silicon and air, which introduces large impedance mismatches and signal loss, requiring fragile tapered spike structures.

Ngo et al. have developed and tested a slot waveguide that can support ultra-high-speed communication with a simpler, more robust alignment. The group’s tapered spike-free device features a slot channel formed from a subwavelength air-hole array. The resulting device allows terahertz waves to directly couple from a metallic hollow waveguide without requiring dielectric insertion.

“This work is expected to facilitate robust interconnection solutions for terahertz integrated systems, particularly in the context of 6G and beyond,” said author Nguyen Ngo. “As operating frequencies increase, the footprint of silicon devices shrinks, making precise alignment of conventional tapered spike structures increasingly challenging.”

Conventional designs demand a substrate to support the beams. The group drew on effective medium theory, which examines heterogeneous material properties as though they were homogeneous, to assemble with a single wafer.

The device exhibited ultra-high data transmission up to 0.8 terabits per second across 14 channels from 330 to 600 gigahertz while maintaining reduced sensitivity to misalignment, making it well suited for scalable fabrication and practical waveguide packaging.

The effective-medium slot also could tailor refractive indices to allow other components, such as filters and resonators, to be integrated into a single fabrication process — a crucial feature in multifunctional terahertz circuits.

The group next looks to integrate their waveguides with compact terahertz transceivers.

Source: “Terahertz communications using effective-medium-slot waveguides,” by Nguyen H. Ngo, Weijie Gao, Guillaume Ducournau, Hadjer Nihel Khelil, Rita Younes, Pascal Szriftgiser, Hidemasa Yamane, Yoshiharu Yamada, Shuichi Murakami, Withawat Withayachumnankul, and Masayuki Fujita, APL Engineering Physics (2026). The article can be accessed at https://doi.org/10.1063/5.0322259 .