Polarization-induced pulse spreading in birefringent optical fibers with zero differential group delay

The polarization properties of concatenations of trunks of birefringent fib ers and elements with polarization-dependent losses are analyzed. We show b oth theoretically and experimentally that the concatenation can have zero d ifferential group delay over a whole range of wavelengths but that a pulse propagating down the concatenation can still experience significant pulse s preading. In this example the two main methods used for characterizing pola rization mode dispersion in optical fiber systems, i.e., Jones matrix eigen analysis and the interferometric method, give different results. This count erintuitive example underlines the need for a careful assessment of the bas ic concepts related to polarization effects in the presence of polarization -dependent losses. (C) 1999 Optical Society of America.