Second-order polarization mode dispersion: new expressions, induced pulse broadening, and its compensation

We derive a new expression for the polarization mode dispersion (PMD) vector including the second-order effects. An interesting interpretation of this expression is presented. The new expression is used to obtain an explicit expression for PMD-induced pulse broadening. The pulse broadening expression reveals that an increase in the first-order derivative of differential group delay (DGD) with respect to frequency always increases pulse broadening. A change of direction of the first-order PMD vector also increases pulse broadening. Further, in most cases, the second-order PMD cannot be compensated completely. The expression for minimum pulse broadening in the presence of second-order PMD is also given.