Ultralow-loss and high-modulation depth terahertz amplitude modulation enabled by coupled-resonant structures

Efficient amplitude modulation of terahertz (THz) waves is essential for high-speed communication systems. However, the long-standing trade-off between low insertion loss (IL) and high-modulation depth (MD) in THz modulators is fundamentally constrained by parasitic energy leakage and inefficient field–carrier interaction. Here, we propose a THz amplitude modulator based on a longitudinal–transverse coupled-resonance mechanism. By introducing a transverse open-ended T-shaped stub, the resonant current distribution is effectively tailored, and parasitic leakage along the device edges and feeding paths is strongly suppressed, enabling large MD under low-loss operation. The proposed modulator exhibits an IL of only 0.9 dB and a MD of 31 dB at 140 GHz, while supporting high-speed modulation of up to 30 Gbps. This work provides a compact and scalable structural approach for realizing low-loss, high-modulation depth, and high-speed THz amplitude modulation.