Improving the Performance of 40-Gbit/s CPFSK by Using XPM-Based Format Converter

We propose and simulate a novel all-optical modulation format converter to produce continuous-phase frequency-shift keying (CPFSK) at 40 Gb/s. The conversion is performed by an asymmetric semiconductor optical amplifier-based Mach-Zehnder interferometer. The converted CPFSK format is detected using an optical frequency discriminator demodulator. We show that as a result of the chirp imposed on the converted CPFSK format during the conversion, it offers more tolerance against positive and negative residual dispersion relative to the directly generated CPFSK. By considering a 2-dB power penalty, more than twice the positive dispersion tolerance of the directly generated CPFSK can be attained.