INTERMODAL BEAT LENGTH MEASUREMENT WITH FABRY-PEROT OPTICAL-FIBER CAVITIES

We present a new technique for measuring the intermodal beat length of a two-mode optical fiber. We formed a Fabry-Perot fiber cavity by dep ositing reflective mirrors on the fiber tips. As the fiber is stretche d, two series of resonance peaks are observed. One series is due to th e resonance of LP01q modes and the other is due to the LP11q modes. Fr om the separation of resonance peaks as a function of cavity length, w e deduce the intermodal beat length of the fiber. The measurement prin ciple and the experimental confirmation are discussed. (C) 1997 Optica l Society of America.