Frequency synchronization in dence FDM optical networks

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We studied device and system technologies for future FDM optical networks. Tunable, lascrs, frequency conversion devices, and FDM transmission technologies were focused on, and main results are summarized in the followings.(1) Tunable lasersWe developed two types of frequency tunable laser at 1,5mum region. One is the external ring-cavity semiconductor laser. The mode-hop free operation has been achieved in this laser. The other is the Erbium-doped fiber laser, whose polarization and single mode are stabilized by a specially designed cavity structure.(2) Dense FDM transmission technologiesWe proposed a novel design method of dispersion management for long-distance dense FDM transmission systems. To increase the transmission capacity further, the midway phase conjugation was found to be effective.(3) All optical signal processing for FDM systemsWe developed an intra-cavity four-wave mixing device by using an external ring-cavity semiconductor laser. The high conversion efficiency and high signal-to-noise ratio have been achieved. This device can be used as a frequency converter and an optical phase conjugator.