Spectrally efficient optical coherent wavelength-division multiplexed transmission systems

Auteurs

• Markus Nölle

Paramètres

• Manuels
• Manuels universitaires

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In this thesis, three different spectrally efficient methods to multiplex individual wavelength channels in an optical coherent wavelength-division multiplexed transmission system are introduced, characterized and their performances are compared to each other. These multiplexing approaches, namely Nyquist WDM and electrical and optical OFDM, are surveyed regarding their suitability for future, flexible WDM networks using unsynchronized transmitters as well as for the generation of so-called high bitrate ‘superchannels’. In order to identify and compare the upper bounds of the achievable spectral efficiencies of the different approaches, all three systems are first compared under idealized conditions. Therefore, all practical realization issues, such as limited constellation sizes of the modulation, all transmitter and receiver hardware imperfections and also limitations regarding the digital signal processing, are ignored in this part. The maximum achievable spectral efficiencies of these idealized system configurations are estimated and compared in a commonly used legacy transmission link setup including optical dispersion compensating fibers, as well as in a future link setup without optical dispersion compensation. While the performance of the systems is found to be rather similar when considering dispersion uncompensated links, electrical OFDM shows slightly worse performance in systems applying optical dispersion compensation. To evaluate the performance of the three systems under more realistic conditions, a second analysis is performed which also considers limitations of a practical system implementation. These include reasonably-sized modulation alphabets, limited DAC and ADC resolution, limited bandwidths of the transmitter and receiver, laser phase noise and state-of-the-art signal processing routines. Consequently a variety of practical realization issues and their impact on the performance of the individual systems is addressed in this part of the thesis. This comprehensive simulative analysis allows the characterization and rating of the individual strengths and weaknesses of the particular multiplexing approaches and thus identifies the different crucial system parameters for the design of the individual systems. It is found that Nyquist WDM systems seem to cope better with most of the system limitations investigated here. In the last part of this thesis two experimental demonstrations of previously numerically investigated multiplexing approaches, namely electrical OFDM and Nyquist WDM, are described. A spectral efficiency of up to 8 bit/s/Hz in the former and a spectral efficiency times distance product of 22500 bit/s/Hz km in the latter experiment could be achieved. Although a direct comparison between the two systems is rather difficult to accomplish based on these experiments, they nevertheless show that both system approaches are basically suited to the building of highly spectrally efficient optical WDM systems, even with the electrical and optical components available today.

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• Année de publication: 2013