Sub-terahertz (sub-THz) waves, operating in the 0.1-1 THz band, offer significant potential for next-generation 6G systems. These systems stand to benefit from photonic technologies that enable terabits-per-second communication with low latency and high throughput. This paper introduced, for the first time, a semiconductor optical amplifier (SOA) as a fast and reliable photonic-based technique for sub-THz wavelength conversion in fiber-based networks. The wavelength conversion leveraged nonlinear phenomena in the SOA, including cross-gain modulation, self-phase modulation, and four-wave mixing effects. Numerical simulations demonstrated an all-optical wavelength conversion capable of handling 100-GHz sub-THz signals with 16-ary quadrature amplitude modulation formats, achieving a data rate switching of 5 Gbps. Key system parameters were optimized, resulting in a 28.7 dB suppression ratio for the generated optical single sideband (OSSB) signal. Additionally, a proof-of-concept laboratory experiment validated the THz signal-switching concept. The proposed system incorporated a hybrid fiber/wireless channel and utilized various measures for performance evaluation.

Terahertz (THz) frequencies, spanning from 0.1 to 1 THz, are poised to play a pivotal role in the development of future 6G wireless communication systems. These systems aim to utilize photonic technologies to enable ultra-high data rates—on the order of terabits per second—while maintaining low latency and high efficiency. In this work, we present a novel photonic method for generating sub-THz vector signals within the THz band, employing a semiconductor optical amplifier (SOA) and phase modulator (PM) to create an optical frequency comb, combined with in-phase and quadrature (IQ) modulation techniques. We demonstrate, both through simulation and experimental setup, the generation and successful transmission of a 0.1 THz vector. The process involves driving the PM with a 12.5 GHz radio frequency signal to produce the optical comb; then, heterodyne beating in a uni-traveling carrier photodiode (UTC-PD) generates the 0.1 THz radio frequency signal. This signal is transmitted over distances of up to 30 km using single-mode fiber. The resulting 0.1 THz electrical vector signal, modulated with quadrature phase shift keying (QPSK), achieves a bit error ratio (BER) below the hard-decision forward error correction (HD-FEC) threshold of ${3.8 \times 10}^{-3}$. To the best of our knowledge, this is the first experimental demonstration of a 0.1 THz photonic vector THz wave based on an SOA and a simple PM-driven optical frequency comb.