Characteristics of selective and tunable wavelength converters using quasi-phase matched lithium niobate waveguide devices with dual pump configuration

We report selective and tunable wavelength converters (STWCs) from an arbitrary wavelength to another arbitrary one, which employ the cascaded second-order nonlinear effect of sum frequency mixing (SFM) and difference frequency mixing (DFM) in quasi-phase matched (QPM) lithium niobate (LN) waveguide devices. Through wavelength conversion experiments using short optical pulses for the QPM-LN waveguide devices having different crystal length, we investigate bandwidth limitation of the QPM-LN-based all-optical STWCs with dual pump configuration. We show that the critical pulse width to be wavelength-converted without waveform distortion is proportional to the length of the LN crystal, and also reveal that those ratio is 1.6 ps/cm. By utilizing this critical value as a performance metric, we successfully demonstrate highly efficient selective and tunable wavelength conversion of 40-Gbit/s data signals using the SFM-DFM cascade in a QPM-LN waveguide device with an optimum crystal length of 5 cm. The 5 cm-long device can be applied to channel-by-channel wavelength conversion in 100-GHz-spaced 40-Gbit/s dense wavelength-division multiplexed systems.