Abstract
This work presents an experimental study on the effects of gamma radiation on Long Period Fiber Gratings (LPFGs) in a low-dose test campaign to evaluate their eventual degradation. The study was carried out with standard single-mode fibers where the grating was inscribed using the Electric-Arc Discharge (EAD) technique. Before the gamma campaign, a detailed optical characterization was performed with repeatability tests to verify the accuracy of the setup and the associated error sources. The gamma-induced changes up to a dose of 200 krad and the recovery after radiation were monitored with the Dip Wavelength Shift (DWS). The results show that the gamma sensitivity for a total dose of 200 krad is 11 pm/krad and a total DWS of 2.3 nm has been observed with no linear dependence. Post-radiation study shows that recovery from radiation-induced wavelength shift is nearly complete in about 4000 h. Experimental results show that the changes suffered under gamma irradiation of these LPFGs are temporary making them a good choice as sensors in space applications.
Highlights
Fiber optic sensors are used in a wide range of applications in many fields of industry, engineering, and science offering alternatives to traditional sensors, based on electronic devices, thanks to their characteristics such as electromagnetic immunity, capacity of multiplexing and remote sensing, and power and weight saving; they can be used to measure several physical, chemical, and biological parameters [1,2]
The wavelength shift observed on the reflection or attenuation bands, is related to refractive index change; in the case of Fiber Bragg Gratings (FBGs), it is due to the change in the core effective refractive index and in the case of Long Period Fiber Gratings (LPFGs), it is due to the difference between core and cladding effective refractive indices [12,13,14,15,16]
7 of 14of the bars shows the irradiation time starting from zero established from the beginning of the test campaign; the circles show the LPFG1 Dip Wavelength Shift (DWS) measurements performed with the optical interrogator and the arrows show the time elapsed between irradiation and measurement moment
Summary
Fiber optic sensors are used in a wide range of applications in many fields of industry, engineering, and science offering alternatives to traditional sensors, based on electronic devices, thanks to their characteristics such as electromagnetic immunity, capacity of multiplexing and remote sensing, and power and weight saving; they can be used to measure several physical, chemical, and biological parameters [1,2]. This study is focused on sensors based on gratings written in fiber optics. In recent years, this type of sensors have been studied in applications with ionizing radiation, characterizing how radiation affects their properties and its possible application in radiation dosimetry [8]. This type of sensors have been studied in applications with ionizing radiation, characterizing how radiation affects their properties and its possible application in radiation dosimetry [8] It is well known from previous studies that the effects of radiation induce changes in fiber gratings. The most investigated effects are the Radiation Induce Attenuation (RIA) and the refractive index change [9,10,11]. The wavelength shift observed on the reflection or attenuation bands, is related to refractive index change; in the case of Fiber Bragg Gratings (FBGs), it is due to the change in the core effective refractive index and in the case of Long Period Fiber Gratings (LPFGs), it is due to the difference between core and cladding effective refractive indices [12,13,14,15,16]
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