All-optical modulation format conversion from OOK to DP-QPSK based on fiber nonlinearity

In this paper we propose and demonstrate by simulation an all-optical modulation format conversion from non-return-tozero on-off keying (NRZ-OOK) at 10 Gb/s to dual-polarization quadrature-phase-shift keying(DP-QPSK) at 20 Gb/s for each channel, by cross phase modulation (XPM) in a polarization-maintaining highly nonlinear fiber (PM-HNLF). The obtained results show a constellation diagram with an error vector magnitude (EVM), 17.26% and 18.79%, for each channel. The input powers of the two NRZ-OOK channels were 16.9dBm and 13.9dBm for a 3km fiber length. We also studied the impact of the nonlinear fiber length in the conversion of the signal and analyzed the system performance based on error vector magnitude (EVM) for different fiber lengths.