Principal states of polarization for an optical pulse

We propose a generalized definition of principal states of polarization for an optical pulse with arbitrary spectral components. Similar to the principal states defined by Poole et al. (see Electron. Lett. vol. 22, p. 1029, 1986) we show that regardless of the spectral components of the pulse, there exist two orthogonal input states of polarization which minimize/maximize the delay of the pulse. At the output of the fiber, these two principal states of the pulse, although depolarized, are also always orthogonal to each other.