Electrical PMD equalization methods for intensity modulated optical polarization multiplex transmission systems

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.