We theoretically evaluate the performance of tunable channel-selective wavelength shift based on cascaded sum- and difference-frequency generation by the use of two pump lights in periodically poled lithium niobate waveguides. In double-pass configurations, the functions of wavelength add/drop and wavelength shift are easy to integrate in the same waveguide. Analysis shows that a longer waveguide more competently adapts narrower channel spacing in wavelength-division-multiplexed (WDM) systems. This wavelength shifter is flexible due to the almost separable operations of the two pumps: The channel is selected by setting the first pump, and the wavelength-shifting value is tuned by adjusting the second pump. This wavelength shifter has a very large dynamic region. For a 2.56-cm-long waveguide, the maximum dynamic region is as broad as 67 nm in a 0.4-nm channel-spacing WDM system. The dynamic region is mainly dominated by the limitation of multiple-channel crosstalk in a dense WDM system. However, it is dominated by the limitation of single-channel efficiency fluctuation in a coarse one.
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