Optimization of Fiber Bragg Gratings Inscribed in Thin Films Deposited on D-Shaped Optical Fibers.

José Javier Imas,Ignacio Del Villar,Carlos R Zamarreño,Ignacio R Matías

doi:10.3390/s21124056

José Javier Imas, Ignacio Del Villar + Show 2 more

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https://doi.org/10.3390/s21124056

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Abstract

A fiber Bragg grating patterned on a SnO2 thin film deposited on the flat surface of a D-shaped polished optical fiber is studied in this work. The fabrication parameters of this structure were optimized to achieve a trade-off among reflected power, full width half maximum (FWHM), sensitivity to the surrounding refractive index (SRI), and figure of merit (FOM). In the first place, the influence of the thin film thickness, the cladding thickness between the core and the flat surface of the D-shaped fiber (neck), and the length of the D-shaped zone over the reflected power and the FWHM were assessed. Reflected peak powers in the range from −2 dB to −10 dB can be easily achieved with FWHM below 100 pm. In the second place, the sensitivity to the SRI, the FWHM, and the FOM were analyzed for variations of the SRI in the 1.33–1.4 range, the neck, and the thin-film thickness. The best sensitivities theoretically achieved for this device are next to 40 nm/RIU, while the best FOM has a value of 114 RIU−1.

Highlights

Fiber Bragg gratings (FBG) consist of periodic perturbations of the refractive index along a fiber formed by exposure of the core to an intense optical interference pattern [1,2]
A new structure consisting of a fiber Bragg grating patterned on a SnO2 thin film deposited on the flat surface of a D-shaped optical fiber was analyzed as a function of several design parameters
It was demonstrated that the position of the FBG bands for different pitches can be predicted with accuracy by adapting the Bragg–Snell law for normal incidence

Summary

Introduction

Fiber Bragg gratings (FBG) consist of periodic perturbations of the refractive index along a fiber (generally, a single mode fiber) formed by exposure of the core to an intense optical interference pattern [1,2]. These perturbations lead to the generation of resonances in the optical transmission and reflection spectrum by coupling of light from the core mode to another co-propagating or counter-propagating mode that might be guided in the core or in the cladding of the optical fiber [3]. Several different gratings can be inscribed in an optical fiber, enabling to measure strain and temperature in different points of a structure, such as aircrafts, tunnels, dams, etc. by using wavelength multiplexing of the different resonance wavelengths of the FBGs [2]

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