Optical sampling system using a PPLN crystal and wavelength-tunable soliton pulse

A high temporal-resolution optical sampling system has been produced by using sum-frequency generation in a periodically-poled lithium niobate crystal and using wavelength-tunable soliton pulses generated by the self-frequency shift effect as optical sampling pulses. The system achieved high temporal resolution using a 2-mm-thick periodically poled lithium niobate crystal and wavelength-tunable soliton pulses which were generated by mode-locked fiber laser pulses and a highly nonlinear fiber. Analysis of system jitter, both theoretically and experimentally, clearly revealed optical intensity fluctuations in the fiber laser pulses and chromatic dispersion in the fiber used to generate the wavelength-tunable soliton pulses. System jitter was kept below 70 fs by using a short fiber. Clear eye diagrams for a 640-Gbit/s optical signal were successfully observed with this system.