Design And Investigation Of All-Optical Logic Devices Based On PPLN Waveguides

In recent years,with the rapid development of communication services,people have gradually found that the present optical network switching capability does not match the transmission capability.Therefore,building all-optical network is an effective way to solve the problem.All-optical network has incomparable advantages compared to the traditional communication network.All-optical switching and transmission of information can be realized,which undoubtedly depends on the breakthrough of all-optical logic devices.PPLN waveguide is a kind of nonlinear optical material with rapid response low noise and miniature size.PPLN waveguide based on quasi-phase matching technology and second-order nonlinear effect is suitable for all-optical logic signal processing.Firstly,the second order nonlinear effect of PPLN waveguide based on quasi phase matching are studied,including second-harmonic generation,sum-frequency generation,difference-frequency generation,and their cascading.Secondly,the coupled mode equations are derived from the slowly varying envelope approximation with neglecting the depletion of the waveguide,and the solving method is given.Thirdly,we analyse the principles of all-optical AND,OR,XNOR gate and all-optical half-adder,all-optical half-subtracter based on a PPLN waveguide in theoretically.Finally,the research results obtained in this paper are as follows:(1)The all-optical numeric comparator is designed and implemented in quasi-phase-matched cascaded PPLN waveguides based on the theory of all-optical logic signal processing for a PPLN waveguide.In this paper,we analyze the basic principle and application conditions of cascaded PPLN waveguide.The result shows that the waveguides cascaded can be used to deal with the all-optical signal.It can not only complete the corresponding logic function of numeric comparator,but also can guarantee the transmission quality of the signal,which expand the capability of PPLN waveguide on the all-optical logic signal processing.(2)By using SFG+DFG in PPLN waveguide,all-optical 2-to-1 data selector is designed and implemented based on difference-frequency signals and remaining signals of sum-frequency generation,respectively.The waveforms and eye diagrams of data selector are obtained by numerical calculation and simulation,and the performance is analyzed.The two cases are compared by combining theoretical analysis with numerical simulation.(3)All-optical 4-2 priority encoder is proposed based quasi-phase-matched PPLN by analyzing the priority encoder in digital circuit.The simulation results agree with the theoretical derivation.The performance of the priority encoder is analyzed by the parameters such as extinction ratio,pulse width and peak power delay time.The result shows that the scheme can guarantee the coding quality of signals while completing the logic function.