Improved design for terahertz modulation of high-speed communications

Terahertz modulation is essential for high-speed communication systems, but a long-standing trade-off between low insertion loss and high modulation depth has limited its practical use. The trade-off stems from the type of terahertz modulation structures that lead to unavoidable parasitic energy leakage and inefficient field-carrier interaction.

Bi et al. proposed a novel amplitude modulator based on a longitudinal-transverse coupled-resonance mechanism.

“We wanted to see whether this trade-off problem could be addressed more fundamentally through structural design — not simply by introducing a new material platform, such as graphene, but by rethinking how electromagnetic energy is distributed inside the device itself,” said author Sen Gong.

The modulator uses two resonant pathways: one main longitudinal modulation channel with a Schottky barrier diode and another transverse open-ended T-shaped stub. The stub allows for a coupled-resonance effect where the resonant current distribution is reshaped without disturbing the fundamental transmission mode. The researchers developed the design with simulations to study the current and field distribution, and after fabrication, they tested a prototype for high-speed modulation performance.

The results showed a 0.9 decibel insertion loss and 31 decibel modulation depth at 140 gigahertz up to 30 gigabits per second — showing low loss and strong modulation can be achieved without sacrificing speed. This suggests the design would be practical for high-speed terahertz systems. The researchers hope the results can be used for communications systems that need strong signal control with a large modulation depth.

“This design has clear potential for terahertz wireless links, particularly for on-off keying transmitters,” Gong said. “More broadly, the same idea could also be useful in terahertz sensing, imaging, and integrated wave-control devices.”

Source: “Ultralow-loss and high modulation depth terahertz amplitude modulation enabled by coupled-resonant structures,” by Chunyang Bi, Sen Gong, Jinlong You, Ziqiang Yang, Yaxin Zhang, Applied Physics Letters (2026). The article can be accessed at https://doi.org/10.1063/5.0323505 .