Digital Compensation of SSBI in Direct Detection Multicarrier System With SOA Nonlinearities

We demonstrate an efficient signal-signal beat interference (SSBI) compensation technique for a direct-detection multicarrier optical system for the first time in the presence of nonlinear transfer function introduced by a semiconductor optical amplifier (SOA). While conventional digital SSBI compensation takes into account the nonlinear effect of photo-detection due to the square-law characteristic, nonlinear wave mixing among subcarriers can also be introduced by gain saturation if the system transfer function is nonlinear, which reduces the effectiveness of digital SSBI compensation. Using the nonlinear transfer function of SOA as an example, we show that the effectiveness of SSBI compensation can be largely restored when the nonlinearity is properly modeled through digital backpropagation.