Optimum Design For All-Optical Time Domain Demultiplexing In PPLN Waveguides

The application of periodically poled lithium niobate (PPLN) waveguides in optical communication system is introduced, and all-optical time domain demultiplexing based on cascaded second-order nonlinearities of second-harmonic generation and difference-frequency generation in quasi-phase-matched periodically poled lithium niobate waveguides is discussed. The three key parameters, including the waveguide length, clock pulsewidth and clock offset, are investigated together in order to maximize conversion efficiency and control crosstalk under the given level.Crosstalk can be controlled when clock offset is controlled within a certain range, and in this range clock offset has a optimal value which can improve the conversion efficiency, but because of the GVM between the SH wave and the signal wave, this optimal value is always negative; clock pulsewidth should be maximized in the condition that crosstalk is controlled under the given level in order to maximize the conversion efficiency; waveguide length should also be maximized in the condition that crosstalk is controlled under the given level, so that the walk-off effect can be restrained.In this paper, the concepts of maximum waveguide length, maximum clock pulsewidth and optimal clock offset are defined. Their theoretical expressions are derived for the demultiplexing from 160Gbit/s to 10Gbit/s. The results calculated from the numerical simulation are well consistent with those from the theoretical expressions. Moreover, based on these analyses, for two kinds of practical situations, the waveguide length or the clock offset given, an optimum scheme is proposed to determine the other two parameters readily. The maximum conversion efficiency can therefore be achieved while the quality of the converted wave is sufficient for the practical situations.