© 1995-2012 IEEE. The authors demonstrate single-polarisation WDM transmission with capacities higher than 400 Gb/s and 1 Tb/s, and show the possibility of obtaining capacity in excess of 4 Tb/s for interconnect applications within and between data centres, based on a single laser source. Quantum Dash (Q-Dash) passively mode-locked lasers (PMLLs), with free spectral ranges of 82.8, 44.7, and 10.2 GHz, were used for the generation of a large number of carriers, enabling high data rate transmission. The terabit per second transmission using Q-Dash MLLs was demonstrated in this paper, and was enabled using intensity modulated and directly detected (IM/DD) single-side band orthogonal frequency-division multiplexed signals. The system performance was investigated for a propagation distance of 3 and 50 km of standard single mode fibre indicating the potential for interconnect applications within and between data centres. The relative intensity noise (RIN) of all Q-Dash devices was characterised, and the effect of RIN on the system performance was investigated by examining the error-vector magnitude of OFDM subcarriers over the desired frequency range.