108 Gbit/s, 64 QAM fully-coherent mobile-fronthaul transmission over 10 km SMF and 70 m wirelessly in the 125 GHz band

We report a 108 Gbit/s fully coherent optical-wireless transmission in the 125 GHz band for 6G mobile fronthaul. Using an injection-locked heterodyne detection scheme, we generated a 125 GHz-IF signal with a single-sideband phase noise of 3.2 degrees, which was sufficiently low for the demodulation of a 64 QAM data signal. By applying a digital pre-equalization scheme, we successfully transmitted an 18 Gbaud 64 QAM signal over a 10 km single-mode fiber and over 70 m wirelessly with a spectral efficiency of 5.71 bit/s/Hz.