Chirp compensating in long haul optical links by means of self-phase modulation and real-time feedback

A new method for chromatic dispersion compensation based on a real-time chirp feedback is presented. The method makes use of an optical channel modulated at 10 Gbits/s by an external modulated transmitter using a nonreturn to zero (NRZ) in the nonlinear regime. The signal undergoes self-phase modulation (SPM) effect. An optical filter, which is used as an optical frequency discriminator, is located at the end of the link and serves for measuring the time-resolved frequency chirp in the transmitter. We show that by measuring the chirp in real time and controlling the SPM effect, we can manage the amount of chromatic dispersion to be compensated. This control process enables us to reduce the system path penalty to a value close to 0 dB and thus achieve a dramatic improvement in the system bit error rate (BER).