High-resolution differential-mode delay measurements in optical fibers using a frequency-domain phase-shift technique

A frequency-domain phase-shift technique, with a temporal resolution of 0.2 ps, is used to obtain differential mode delay measurements in graded-index multimode fibers. This resolution is a significant improvement over previously reported time-domain methods. As a consequence, useful results can be obtained from fibers as short as 15 m. Measurements performed at 850 nm, on 62.5-μm core diameter fibers from several different manufacturers, indicate a rich variety of mode delay profiles. Measurements on lengths ranging from 3 to 500 m, indicate that delay profiles are established in the first few meters of fiber, and the general characteristics are retained over long distances.