A Simple NRZ-OOK to PDM RZ-QPSK Optical Modulation Format Conversion by Bidirectional XPM

We proposed and experimentally demonstrated an all-optical modulation format conversion mechanism by applying bidirectional cross-phase modulation in a single highly nonlinear fiber. In our experiment, four individual 12.5 Gb/s nonreturn to zero ON-OFF keying signals are successfully converted to a 50-Gb/s polarization division multiplexed return to zero quadrature-phase shift keying signal within a satisfactory power penalty. The performance and feasibility of the proposed converter are both numerically and experimentally investigated. Moreover, the timing-mismatch tolerance among all the signals in the proposed format converter is also analyzed.