in [20]. (From Eyal, A. et al., Electron. Lett., 35(17), 1658, 1999.) (d) PMDC described by [18]. (From Heismann, F., IEEE Photon. Technol. Lett., 17(5), 1016, 2005.) (e) PMDC formed by two concat- enated First Order-PMDCs, wherein the first introduces a fixed DPD equal to the mean DGD in the fiber and the second a continuously variable DPD [21]. (From Yu, Q. et al., IEEE Photon. Technol. Lett., 13(8), 863, 2001.) (f) PMDC described by [19,21]. (From Yu, Q. et al., IEEE Photon. Technol. Lett., 13(8), 863, 2001; Kogelnik, H. et al., Opt. Lett., 25(1), 19, 2000.) Next Generation Transmission Systems EOP=14-10 EOP = (9.6) where 1 and oo are the overall noise variance corresponding to the two transmitted bits. Assuming that the noise does not change, the following equation is immediately derived: (9.7) The PMD compensators considered in Figure 9.15 are Conventional first order-polarization mode dispersion compensation (FO-PMDC) with variable differential phase delay PMDC based on the Kogelnik-Bruyere model described in [19] PMDC based on the truncated exponential expansion form (EEF) described in [20] PMDC described by [18] PMDC formed by two concatenated First Order-PMDCs, wherein the first intro- duces a fixed differential phase detector (DPD) equal to the mean DGD in the fiber and the second a continuously variable DPD [21] PMDC described by [19,21] The performance of second order compensators depends in an important measure on the control algorithm and on the effectiveness of the compensation device, but it is in any case quite better than the performance of a single order compensator. The number of stages of the PMD compensator can be increased to three or more in order to achieve high order compensation and target better performances. More compen- sation stages however also mean a more complex control algorithm and a more expensive device (keeping in mind that PMDCs are per channel devices). The performance improvement and the control complexity of high order compensation devices have been studied in several pa