This work deals with the numerical analysis of an in-fiber photonic device based on multidefect micro-structured fiber Bragg gratings (MSFBGs) as in fiber refractometer. The investigated structure consists in a fiber Bragg grating where the cladding layer is stripped in different and well defined regions along the grating length. The presence of the thinned regions induces more defect states inside the spectral band-gap of the original device. The mechanism is ruled by multiple interactions of the spectra reflected by the unperturbed grating regions modulated by the phase shifts introduced by the thinned regions. The key feature of the proposed structure is the strong dependence of the defect states on the surrounding refractive indices (SRIs) in the thinned regions, leading to the possibility to realize attractive passive and active photonics devices. Here, the attention has been focused on the feasibility to use a dual defect MSFBG for multiple refractive index measurements. Numerical results reveal that by a proper choice of the thinned regions lengths, it is possible to perform multipoint measurements by a single device.

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