Methods for identifying optical fibers which exhibit elevated levels of polarization mode dispersion

A method for detecting an elevated level of polarization mode dispersion in an optical fiber comprising:

• a) applying light to a first end of the optical fiber using an optical time domain reflectometer (OTDR);
• b) after step a), detecting the light reflected back to the OTDR from the fiber and generating a first set of values which comprise the amplitude of the detected reflected light as a function of distance along the length of the fiber from the first end of the fiber;
• c) applying light to a second end of the optical fiber using an OTDR;
• d) after step c), detecting the light reflected back to the OTDR from the fiber and generating a second set of values which comprise the amplitude of the detected reflected light as a function of distance along the length of the fiber from the second end of the fiber;
• e) forming a third set of values from the first and second sets of values, variations in said third set of values being indicative of variations, if any, of the fiber's mode field diameter along its length;
• and
• f) detecting in said third set of values a cyclical pattern having at least one predetermined characteristic as a function of distance along the length of the fiber, the presence of said cyclical pattern being indicative of an elevated level of PMD.