MULTIMODE OPTICAL FIBERS WITH NONCIRCULAR CROSS SECTION.

An experimental investigation is presented to verify some theoretical results on the existence of two classes of modes (whispering and bouncing modes) in elliptical step index fibers. By utilizing a technology previously developed, silica plastic fibers with quasi elliptical cross section have been fabricated. The used noncircular preforms have been obtained by machining the circular cross section rods with a CO//2 laser. The near field measurements performed on fibers with different ellipticity are interpreted on the basis of the theoretical results.