We propose a new technique for mitigation of nonlinear distortion
of broadband signals due to electrical/optical conversions and fibre
transmission. This technique uses memory polynomials on signals on their
original format. The performance improvement is assessed experimentally
for an orthogonal frequency division multiplexing signal, with 750 MHz of
bandwidth (centred at 1.5 GHz) and carrying 1.25 Gbps, transmitted along
a wavelength division multiplexing long-reach passive optical network. It
is shown that, in back-to-back, an error vector magnitude improvement
of 4.1 dB and 11.8 dB can be achieved with digital pre-distortion and
digital post-distortion, respectively. With 125 km of single-mode fibre
transmission,