High-efficiency multiband UTC-PD modules for photonic-assisted wireless communications

The terahertz (THz) frequency range provides a wide bandwidth for future high-capacity wireless links. However, compact THz sources that combine high conversion efficiency, flat frequency response, and multiband adaptability remain a major challenge. We propose a unified architecture of a photomixer module for multiband THz signal generation. To overcome the intrinsic bandwidth-efficiency trade-off, the proposed photomixer modules incorporate ultra-high-speed evanescently coupled waveguide unitraveling carrier photodetectors (UTC-PDs). Specially designed integrated passive circuits allow flexible adaptation to different frequency bands in the THz range while ensuring low loss and efficient mode conversion. Based on this architecture, we demonstrate photomixer modules covering the W-, F-, and D-bands, which deliver high-power, low-noise THz signals with flat frequency response within ±2.5 dB. Photonic-assisted THz wireless communication experiments confirm the high performance of the proposed photomixer modules. Without resorting to power amplifiers and lenses, the W-band module supports error-free 34-Gbaud 16-QAM (136 Gbps) transmission, whereas the D-band module achieves 32-Gbaud 16-QAM (128 Gbps) transmission, meeting the forward error correction threshold. Furthermore, thanks to its high saturation power, the D-band module can sustain a data rate of 120 Gbps over extended distances by simply increasing the input optical power. These results highlight a highly efficient and flexible photonic THz transmitter architecture, paving the way for compact, multiband, and high-capacity wireless backhaul and fiber-wireless convergence.