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Simultaneous carrier extraction from wavelength-division-multiplexed phase-conjugated twin waves by using sum-frequency generation with second-order optical nonlinear medium for phase-sensitive optical amplifier repeaters

This paper proposes and numerically investigates simultaneous carrier extraction from wavelength-division multiplexed phase-conjugated twin waves (WDM-PCTWs) in optical phase-locked loop (OPLL) for phase-sensitive optical amplifier (PSA) repeaters on optical multi-relay transmission systems. First, it is mathematically derived that the proposed scheme contributes to a signal-to-noise ratio improvement of phase error signals between WDM-PCTWs and a pump wave for PSA. As a result, the quality of the pump wave is improved. Then, the influence of chromatic dispersion in a transmission fiber on the proposed scheme is numerically investigated. When a center optical frequency of WDM-PCTWs is equal to a zero-dispersion optical frequency of an 80 km transmission fiber, the extracted carrier power increases as the number of WDM channels increase. In contrast, an optical frequency difference between the center frequency of WDM-PCTWs and the zero-dispersion optical frequency of a transmission fiber severely impairs the extracted carrier power as the number of WDM channels increase.