  In this paper it is shown that the correct mathematical framework of combined
polarization mode dispersion and polarization dependent losses (combined
PMD-PDL effects or impairments) in optical fibers is the irreducible spinor
representation of the extended Lorentz Group. Combined PMD-PDL effects are
shown to be formally identical to Lorentz Transformations acting on spin 1/2
zero mass particles. Since there are two different irreducible spinor
representations of the restricted Lorentz Group, there must also exist two
kinds of states of polarizations (SOPs) that are relevant in the description of
PMD-PDL effects. The optical process that allows to convert one kind into the
other is identified as optical phase conjugation. Optical phase conjugation
plays the same role as the time inversion operator in the Lorentz Group
representation theory. A practical and extremely important example of utility
of these ideas, a technique that significantly reduces the PMD-PDL induced
impairments, is presented. This technique allows to cancel the PDL part of the
combined PMD-PDL impairments in a very simple and straightforward way.
