An Improved Technique for Suppression of Intrachannel Four-Wave Mixing in 40-Gb/s Optical Transmission Systems

This letter presents an efficient method for testing the efficiency of modulation techniques for countering the effects of intrachannel four-wave mixing by calculating the sum of all the contributors at a given resonance position (the position affected by the surrounding pulses). In addition to this method, we are proposing a modulation technique that shows a significant Q-factor improvement of up to 7.5 dB (depending on the number of spans and the phase sequence implemented) over the uncoded return-to-zero on-off keying. Although the implementation of this phase modulation technique is simple, it is still very efficient in extending the nonlinearity tolerance and enhancing the performance of a high-speed optical transmission system