Design and performance analysis of pure and hybrid WDM optical networks

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Doctoral thesis (article-based)
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Technical report / Helsinki University of Technology, Communications Laboratory. T, 50
In optical networking, information-bearing electrical signals are transported by up-converting the signals into the optical domain and then transmitting them over high-capacity low-loss optical fiber links. Furthermore, optical switching nodes with a large throughput can be used to alleviate the contention for fibers, route the optical signals and avoid failed fiber links. This guarantees a robust always-on service for entities transporting their signals via the optical network. Based on those merits, optical networking technologies are now being increasingly adapted in most operational medium and long range networks. Of the existing technologies, wavelength-division multiplexing (WDM) transmission is ubiquitous due to its ability to multiply the capacity of the installed fiber base and to enhance the flexibility of provisioning of the fiber capacity by utilizing the wavelength degree of freedom in an intelligent optical layer. This thesis focuses on flexibility improvement techniques that enable dynamic provision of bandwidth available in optical networks within acceptable cost bounds. The aforementioned nodes for optical connection provisioning are studied in detail. From the study, novel node architectures are proposed with improved scalability for handling more connections and reduced signal impairment for increased transmission range. The thesis proposes techniques for incorporating dependability enhancement during initial node design stage and the gradual node scaling after deployment by optimizing the allocation of redundant modules. Analytical comparison based on example dependability-enhanced nodes indicate significant improvements compared to corresponding nodes without redundancy. Hybrid WDM networks utilize an extra optical degree of freedom in addition to signal wavelength. The virtues of hybrid WDM as an optical layer grooming method are investigated. To that end, the thesis pays particular attention to hybrid OCDM (optical code-division multiplexing) / WDM transmission. The connection acceptance improvement due to OCDM/WDM transmission is analysed and the possible limitations of various light-path schemes are noted. The potential application of hybrid WDM for radio-over-fiber systems is explored for an urban-wide hierarchical metropolitan network. In that case, the more complex hybrid WDM scheme showed significant improvement in utilization of optical resources compared to conventional WDM implementation. Semi-hybrid WDM is proposed as a compromise solution between pure and hybrid WDM implementations. Furthermore, a 60 GHz radio-over-fiber OCDM/WDM system is proposed and guidelines are presented for possible performance improvement.
optical networking, optical layer, wavelength-division multiplexing, optical cross-connects, optical add-drop multiplexers, transmission performance, hybrid WDM, optical code-division multiplexing, radio-over-fiber
Other note
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