Experimental Characterization of Photodiode Transmitters for Probabilistically Shaped High-Speed THz Wireless Transmission

Terahertz (THz) wireless communication is a key enabler for 6G networks, offering ultra-high data rates and broad bandwidth scalability. Photonic generation of THz signals using photodiodes has emerged as a promising approach, yet a systematic performance comparison between different architectures remains largely unexplored. This paper presents an experimental investigation of two distinct THz transmitter architectures. One is based on a WR3.4 waveguide-coupled photodiode, while the other employs a quasi-optically coupled photodiode with a silicon lens. Both architectures are evaluated using probabilistic constellation shaping with high-order quadrature amplitude modulation (QAM). We evaluate output power, bit error rate (BER), and system linearity across both photodiode-based architectures under standardized conditions. The results reveal key trade-offs between transmitter design choices, nonlinearities, and achievable performance, offering critical insights for optimizing next-generation THz wireless systems.