Polarization mode dispersion is the limiting factor in todays large capacity photonic network systems since it
causes intersymbol interference especially at high data rates. When polarization multiplex is employed to increase
spectral efficiency, the distortions caused by polarization mode dispersion get even stronger due to the
additional polarization crosstalk. Employing coherent detection these mitigations can be fully compensated with
linear filters, since coherent detection delivers amplitude, phase and polarization information of the electrical
field. As a drawback we have to take into account a high complexity of the receiver, causing high overall cost.
At the other hand we have direct detection systems where the receiver complexity can be kept low. Furthermore
maximum likelihood sequence estimation detection has been successfully demonstrated for standard direct detection
systems. In a first step an advanced maximum likelihood sequence estimation detector, which is able to
work in an intensity modulated polarization multiplex direct detection system, is developed. The performance of
the detector is assessed by simulations and it is shown that it is capable to significantly reduce system outages.
The method then is compared with a least mean squares based equalizer which is employed to compensate for
signal distortions in an intensity modulated polarization multiplex coherent detection transmission system.
The still increasing demand for data bandwidth in short-haul transmission as well as in long- haul transmission
implicates the development of optical high-speed communication systems that carry 40 Gbit/s and higher. This
step is limited mainly by the polarization mode dispersion (PMD) of the fiber infrastructure. Direct detection
transmission systems are state of the art. At this the square-law detection of the photo diode transforms linear
distortions into nonlinear effects, which makes linear equalization principles less effective. Coherent detection on
the other hand delivers amplitude, phase and polarization information of the field and thus enables advanced
PMD-compensation in the electrical domain. We realize PMD-compensation by means of least mean squares
based adaptive electronic equalizers. The drawback of adaptive equalization principles is the setting of the
adaption step-size. Small step-sizes lead to very accurate results, but are very time-consuming. By contrast
large step-sizes can accelerate the adaption process but lead to inaccurate equalizer settings. Accordingly, it
is desirable to resize the step-size during the adaption process. For these reasons different step-size control
algorithms are implemented, analyzed and adapted to the requirements of an optical PMD affected transmission
system. It shows that step-size control algorithms are able to accelerate the adaption-process significantly.
Due to the growing demand of bandwidth in optical communication systems, the step towards 40 Gbit/s is inevitable. This step is limited mainly by the polarization mode dispersion of the fiber infrastructure. To extend the usability of the infrastructure it is necessary to employ PMD-compensation. The On/Off-keying modulation format in conjunction with direct detection is state of the art in high bitrate optical communication systems. But as a drawback, direct detection only provides an output signal which is proportional to the square of the absolute value of the electrical field and therefore transforms linear effects such as PMD into the nonlinear domain, which makes linear compensation schemes less effective. Coherent detection on the other hand delivers amplitude, phase and polarization information of the field and thus enables advanced PMD-compensation in the electrical domain. In our work, we employ optical coherent detection to receive two orthogonal components of the complex valued electrical field of an On/Off-keying modulated optical carrier. This single input multiple output system delivers us up to four output signals, i.e. real and imaginary part of the two detected polarization planes, which can be fed to feed forward equalizers or other electronic processing methods for an effective compensation of signal distortions caused by PMD. The required feed forward equalizer settings and their performance are presented.
The most common model used for PMD simulations visualizes the fiber as a concatenation of a large number of birefringent elements. This system's DGD has the same Maxwellian PDF for each frequency. By measurement of certain links it is shown that the PDF of the DGD is not equal for all of the frequency bands. This behavior could be traced back to the fact that fiber links consist of a certain number of stable buried sections, with nearly no PMD changes over weeks and months. These sections are connected by sections exposed to strong temperature variations, acting as polarization rotators. This new model of a fiber link is known as the hinge model. To characterize these hinges, the temperature dependent behavior of several DCM and patch cords commonly used in WDM systems have been investigated. Measurements showed that DCM are the most active hinges. They produce approximately a full rotation in Stokes space when heated 1°C. This rotation is both reproducible and reversible. An novel model of the analyzed DCM has been developed in Matlab, which is able to reproduce the described measured behavior in simulations. The frequency dependency of the DGD's PDF leads from overall systems outage probability to frequency selective outage probability. That means instead of having a system outage at a certain outage probability, outage probabilities are connected to a number of outage channels.
The opportunity to address special future client interfaces, i.e. IP router interfaces, and to reduce CapEx and OpEx in network domains with highly aggregated traffic are arguments for network operators to insist on the principal option to employ 40G in their backbone network. The fiber infrastructure of most network operators is adequate for a 40G introduction if parameters such as chromatic dispersion, fiber attenuation, nonlinear fiber effects are considered. Already the transition from 2.5Gbit/s to 10Gbit/s per channel the Polarization Modem Dispersion (PMD) for many operators
proved to be a limiting factor. The heterogeneous distribution of PMD of cable and fiber segments enabled the operators to install 10 G systems by measuring and selecting the fibers. The migration towards 40G is limited mainly by the PMD of the fiber infrastructure. Again the heterogeneous distribution of PMD values means that only fraction of the possible links are feasible for 40G transmission. To extend the usable part of the infrastructure it is very important to define accurately the PMD limit which is acceptable for 40 G transmission.
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