Multicore optical fiber shape sensors suitable for use under gamma radiation.

David Barrera,Javier Madrigal,Salvador Sales,Sylvie Delepine-Lesoille

doi:10.1364/oe.27.029026

David Barrera, Javier Madrigal + Show 2 more

Open Access

https://doi.org/10.1364/oe.27.029026

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Abstract

We have designed and implemented a fiber optic shape sensor for high-energy ionizing environments based on multicore optical fibers. We inscribed two fiber Bragg gratings arrays in a seven-core optical fiber. One of the arrays has been inscribed in a hydrogen-loaded fiber and the other one in an unloaded fiber in order to have two samples with very different radiation sensitivity. The two samples were coiled in a metallic circular structure and were exposed to gamma radiation. We have analyzed the permanent radiation effects. The radiation-induced Bragg wavelength shift (RI-BWS) in the hydrogen-loaded fiber is near ten times higher than the one observed for the unloaded fiber, with a maximum wavelength shift of 415 pm. However, the use of the multiple cores permits to make these sensors immune to RI-BWS obtaining a similar curvature error in both samples of approximately 1 cm without modifying the composition of the fiber, pre-irradiation or thermal treatment.

Highlights

Optical fiber sensors (OFSs) have multiple advantages that make them excellent candidates for their use in extreme environmental conditions
In fiber Bragg grating (FBG) sensors, the change of the Bragg wavelength due to radiation effects is normally referred to as radiation-induced Bragg wavelength shift (RI-BWS)
We modify the FBGs sensitivities to the parameter we want to measure, i.e. curvature, strain or temperature, to encode the sensor output. This hardened by design architecture can be done in a more convenient way using multicore optical fibers (MCF) where the radiation conditions are similar in all the cores and the FBGs sensitivity can be modified bending the fiber [12]

Summary

Introduction

Optical fiber sensors (OFSs) have multiple advantages that make them excellent candidates for their use in extreme environmental conditions. Whereas RIA can reduce the signal to noise ratio, the RIRIC modifies the refractive index of the optical fiber depending on the radiation conditions and the optical fiber composition This effect can be a strong limitation for OFSs that use the wavelength as a reference, like fiber Bragg grating (FBG) sensors, limiting their accuracy. We propose to use a differential wavelength shift measurement scheme to implement sensors for high-energy ionizing environments In this scheme, two or more FBGs are needed. We modify the FBGs sensitivities to the parameter we want to measure, i.e. curvature, strain or temperature, to encode the sensor output This hardened by design architecture can be done in a more convenient way using multicore optical fibers (MCF) where the radiation conditions are similar in all the cores and the FBGs sensitivity can be modified bending the fiber [12]. The same principles described in this paper can be applied to design other sensors

Sensor fabrication

Irradiation

Experimental results

Conclusions