Analysis of core eccentricity on the long period grating in eccentric core fiber

The model of the long period fiber grating (LPFG) inscribed in the eccentric core fiber (ECF) is proposed and analyzed theoretically. The variation of the transmission spectrum is calculated under different eccentricities on the basis of the coupled-mode theory. The calculation results indicate that the order of the cladding mode that has the largest coupling efficient with the core mode changes with the change of the core eccentricity, which results in the shift of the resonant peaks. In addition, the effective refractive index of the fundamental mode increases with the core eccentricity within a certain range. The model we have proposed can provide a valid reference for designing ECF and writing LPFG in the ECF.