Experimental Investigation of Wavelength Conversion Using Highly-Nonlinear Fiber and Two-Stage-Comb-Generated Pump With High Frequency Precision

All-optical wavelength conversion, using four-wave mixing in highly nonlinear fiber for different wavelengths at GHz resolution, was experimentally investigated with two-stage-comb-generated pump light for 10 Gbaud RZ-QPSK signals. The pump light was generated using a mode-locked fiber laser followed by a LiNbO
₃
phase modulator, or by using a tunable laser followed by two-stage LiNbO
₃
phase modulators (LN-PMs). The performance of the generated pumps was compared with the electrical spectrum, and eye patterns of the wavelength converted signals. It is confirmed that the quality of the generated pump light could be evaluated from the measured power spectrum within the GHz frequency range, and that the suppression of the noise level of the pump light affects the time waveform of the idler signal. In our experiments, clear eye openings could be obtained in case of the pump generation scheme using two-stage phase modulators. The pump lights with frequency shifts from the original continuous waveform light carrier of −10 GHz at the 1st-LN-PM, ±5 GHz at the 2nd-LN-PM, +10 GHz at the 1st-LN-PM, and −5 GHz at the 2nd-LN-PM were generated, and a frequency difference of the pump of less than the resolution of an optical spectrum analyzer, compared with the ideal one, was confirmed. In addition, wavelength converted signals with different wavelengths were obtained according to the different wavelengths of the pump lights. Clear eye openings of the wavelength converted signals were observed, and a bit error rate of <10
⁻¹⁰
for converted idlers was achieved in case of ±5 GHz frequency shift from the original light carrier.