Backward propagation is the most effective way of
performing digital post-compensation in an optical system. In this
work we exploit a simple optimization procedure based on finding
the optimal fraction of nonlinearities that must be compensated
in order to achieve the best performance. Using a 40 Gb/s
NRZ-QPSK signal, propagated over 20x80 km of standard
single-mode fiber, we present compensation results employing
nonlinear optimization and we compare its performance with
non-optimized backward propagation. Finally, we analyze the
impact of both temporal and space resolution on the optimum
nonlinear operator and on the overall compensation performance.