Refractive index and curvature sensitivity of LPFG inscribed in few-modes fiber

A novel long period fiber grating (LPFG) is inscribed in few-mode fibers(FMFs) by CO2 laser-irradiation method. The experiment results and theoretical calculation demonstrate that the LPFGs are originated from the strong coupling between the high-order core mode LP02 and the LP04 cladding mode. The resonant wavelengths of the LPFGs is found to shift toward the lower wavelength with refractive index(RI) of surrounding or curvature increasing. For comparision, LPFGs that coupling fundamental core mode to the same cladding mode are inscribed in single-mode fibers(SMFs) by the same method. The LPFGs inscribed in FMFs have higher RI sensitivity and slight lower curvature sensitivity comparing with LPFGs inscribed in SMFs.

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