Distributed sensors based on Brillouin dynamic grating in specialty fibers

Abstract

Brillouin dynamic grating (BDG) represents an acoustic phonon generated by stimulated Brillouin scattering (SBS) of pump waves in one polarization which plays a role of reflection grating for probe wave at different optical frequency orthogonally polarized to the pump. Since the optical frequency offset between the pump and probe waves, called BDG frequency, is determined by the birefringence of the medium the operation of BDG has been conducted on the basis of polarization maintaining fibers (PMF's). In this talk we present theoretical and experimental results of distributed fiber sensors based on the BDG in specialty fibers such as an elliptic-core two-mode fiber (e-core TMF), a PM photonic crystal fiber (PM-PCF), and a conventional single mode fiber (SMF). First, the mapping of modal birefringence between LP 01 and LP 11 modes, and polarization birefringence between x- and y-polarization for each mode is demonstrated with 1.5m spatial resolution by the BDG operation in the 75m e-core TMF. We show that there are large difference in temperature and strain dependence of the BDG generated by different mode pairs (LP 01x or y -LP 11x or y ). Discussion on possible applications of the spatial-mode-based BDG in future space-division multiplexed (SDM) communication system is also briefly provided. In BDG experiments based on the PM-PCF we show the BDG spectrum has unique dependence on the ambient temperature change, which can be used for implementation of distributed sensors with special functionality. Finally the BDG operation in a bent or twisted SMF is presented with the comparison of the theoretical and experimental results.