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 o f 0.2 ps, is used to obtain differential mode delay measurements in gr aded-index multimode fibers. This resolution is a significant improvem ent over previously reported time-domain methods. As a consequence, us eful results can be obtained from fibers as short as 15 m. Measurement s performed at 850 nm, on 62.5-mu m core diameter fibers from several different manufacturers, indicate a rich variety of mode delay profile s. Measurements on lengths ranging from 3 to 500 m, indicate that dela y profiles are established in the first few meters of fiber, and the g eneral characteristics are retained over long distances.