All-optical differentiator and high-speed pulse generation based on cross-polarization modulation in a semiconductor optical amplifier

We propose an all-optical intensity differentiation scheme based on cross-polarization modulation (XPolM) in a semiconductor optical amplifier (SOA) while demonstrating the absolute value of differential signal that can be obtained by the SOA-based XPolM of two parts with relative delay from the input signal and well extracted by the polarization filter. The differentiation errors and eye diagrams versus sampling time Delta are investigated for data rate at 12.5 Gbits/s, and the minimal error approximately 0.06 is achieved at Delta=0. Owing to a much faster polarization response, our scheme bears great potential for all-optical signal processing over 100 Gbits/s. By application of the differentiator, we further obtain the 20 GHz short pulse train with a pulse width of approximately 10 ps.