Linearity Enhancement of a Directly Modulated Uncooled DFB Laser in a Multi-Channel Wireless-over-Fibre Systems

We present the first experimental demonstration of two 3.5 MSymb/s QPSK modulated wireless channels over fibre in a 2.2 km fibre ring architecture using feed-forward linearisation at the base station to improve the dynamic range of a directly modulated uncooled DFB laser. A reduction of 10 dB is observed in the spectral re-growth caused due to strong input from the adjacent channel together with reduction from 25% to <10% in the error vector magnitude at input level of −25 dBm of the weaker channel. Intermodulation distortion is reduced by 10 dB when two strong channels are at +12 dBm input level.