LARGE POLARIZATION MODE DISPERSION IN FIBER OPTIC CABLES

The recently observed difference in polarization mode dispersion (PMD) between spooled and cabled single-mode optical fibers is investigated experimentally. To discriminate between a large polarization mode-cou pling length or a large birefringence as a caused of high PMD, both pa rameter are measured. The results show a factor of 50 difference betwe en the mode-coupling lengths of spooled and cabled fibers, which accou nts for the larger PMD's of cabled fibers. It is suggested that cables with a loose tube design especially suffer from large polarization mo de-coupling lengths. Internal stress is shown to be the dominant sourc e of birefringence in standard telecommunication fibers by observing t he shift of the PMD spectrum over a wavelength interval as a function of temperature.