All-optical logic signal processing is a key technology in optical communication network

which has the potential to realize all-optical network.The all-optical numeric comparator is proposed based on Sum-Frequency Generation and DifferenceFrequency Generation（SFG+DFG）in quasi-phase-matched cascaded Periodically Poled Lithium Niobate（PPLN）waveguides.The waveforms are obtained by numerical calculation and simulation

and the performance of all-optical numeric comparator is analyzed by the parameters such as eye diagrams

pulse width

extinction ratio and peak power delay time.The results show that the cascaded waveguides can be used to deal with the all-optical signal.It can realize the corresponding logic function and guarantee the transmission quality of the signal

which expand the capability of PPLN waveguide on the all-optical logic signal processing.