Study on all optical signal regeneration technology in ultrafast optical communication system

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All-optical nonlinear interferometric switches (NIS) are very attractive devices to realize the all optical 2R/3R function. The Mach-Zehnder interferometer (MZI) using semiconductor optical amplifiers and the nonlinear optical loop mirror (NOLM) using dispersion-shifted fibers are good candidates for practical NIS configurations.When these NIS 's are periodically inserted in a long-distance transmission system using optical amplifiers, we can expect that the NIS's prevent the degradation of the SNR induced by the accumulation of the optical amplifier noise.We derive a simple formula for calculating the SNR in the transmission system where NIS's are periodically inserted. Prom this formula, we clearly see that the SNR can be maintained at a certain value even after the signal traveling over an infinite distance. This formula also predicts that there exists a critical level of the optical amplifier noise. When the optical amplifier noise is larger than the critical level, the improvement of the SNR can no longer be achieved.We also construct a NOLM composed of a 50-m highly-nonlinear dispersion-shifted fiber, and succeed in switching of 0.5-ps optical pulses. In addition, the polarization diversity scheme for the NOLM is demonstrated.