The photonic technologies have enabled the generation of THz with the photomixing technique, which is essentially a down-conversion from optical domain to the THz. Working in pulse-mode or in continuous-wave, this approach relies on an efficient optical to THz converter. Such device can be a photoconductor or an ultra-fast photodiode. At 1.55 μm, the uni-travelling carrier photodiode (UTC-PD) has been proven to be efficient and scalable to reach the THz frequencies. We report here some examples of THz communication systems enabled by InGaAs/InP UTC-emitter, in the range 200–600 GHz. Among them, first-generation (2010–2015) passive THz hotspots based on bias-free UTC-PD at 200 GHz, broadband transmission at 400 GHz and first tests conducted in the 600 GHz band are described. The second generation (2016–2020) used a high-efficiency UTC-PD for 100 Gbit/s in the 300 GHz band leveraging on GaAs technology in the receiver part.