We propose an d simul ate an all - optical tunable notch filter base d on a sum-frequency generation process in a periodically poled lithium niobate(PPLN) waveguide.The central wavelength of t he filter can be tuned by adjusting the wavel ength of in put pump light. The maximum signal suppression at the central wavelength can be also changed by varying the power of input pump light. A maximum signal depletion of up to 34.4 dB is achieved when the central wavelength is tuned at 1545 nm. The simul
