In a twin-core optical fiber a propagating light pulse periodically transfers power between its two cores. Experiments by Tjugiarto et al. [Opt. Lett. 17, 1058 (1992)] have demonstrated that this coupling length is considerably reduced when the fiber is also spun. A coupled-mode analysis reveals a pitch resonance that couples a cladding mode with the circularly polarized core mode whose handedness matches that of the helical twist of the cores. This resonance mechanism explains the observation of enhanced coupling and cladding-mode cross coupling.
© 1996 Optical Society of America
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