Mapping of intermodal beat length distribution in an elliptical-core two-mode fiber based on Brillouin dynamic grating

Distributed measurement and characterization of the intermodal beat length between LP01 and LP11 modes in an elliptical-core (e-core) two-mode fiber (TMF) are demonstrated by the analysis of Brillouin dynamic grating (BDG) spectra. The BDG is generated by the stimulated Brillouin scattering (SBS) of the LP01 mode and probed by the LP11 mode, with four different pairs of the spatial and polarization modes in the e-core TMF applied for the pump and the probe (LP01x-LP11y, LP01y-LP11y, LP01x-LP11x, and LP01y-LP11x). A mode selective coupler (MSC) is used for selective launch and retrieval of the LP01 and the LP11 modes in the BDG operation, and the local reflection spectra from the BDG are obtained by an optical time-domain analysis. A distribution map of the intermodal beat length is acquired for each pair of the pump-probe modes with a 1.5 m spatial resolution along a 75 m e-core TMF. Temperature-and strain-dependence of the BDG spectrum is also evaluated for each case. (C)2014 Optical Society of America