The control of polarization state, as well as a control of all states of polarization of a light signal travelling through a singlemode optical fiber, is performed using different schemes. The polarization control of the signal in a DWDM channel is performed using reference signals in lateral channels in real time. A polarization encoded quantum key distribution scheme is discussed and performed in the central channel through the control system polarization. The influence of the PMD and the spectral distance between channels in control is also investigated theoretically and experimentally. Two prototypes were built, a full polarization control system and a PMD compensator is shown and totally described, as well their test results. Measurements of PMD compensation on a link at 43Gb / s were performed in different modulation formats and in different situations of polarization scrambling, with and without the use of FEC in order to evaluate the efficiency of modulation formats, and PMD compensation with single or multiple section delay lines.