Comparative study of long period and fiber Bragg gratings under gamma irradiation

In this contribution, a complete dissertation concerning the behavior of a Long Period Grating (LPG) inscribed in a B-Ge co-doped optical fiber by means of an excimer laser and exposed to proton irradiation during a recent extensive campaign performed at the European Organization for Nuclear Research (CERN) with a fluence of 4.4·10 15 p·cm −2 is provided. The experimental results have been thus combined for the first time to the best of our knowledge with numerical simulations in order to estimate the variations of the major parameters affecting the grating response during the ultra-high dose proton exposure. From the correlation between experimental and numerical analysis, the irradiation exposure was found to induce a maximal variation of the core effective refractive index of ~1.61·10 −4 , responsible of a resonance wavelength red shift of ~44 nm in correspondence of the highest absorbed radiation dose of 1.16 MGy. At the same time, a relevant decrease close to ~0.93·10 −4 in the refractive index modulation pertaining to the grating was estimated, leading to a reduction of the resonant dip visibility of ~12 dB. The effect of the proton beam on the spectral response of the LPG device and on the optical fiber parameters was assessed during the relaxation phases, showing a partial recovery only of the wavelength shift without any relevant change in the dip visibility revealing thus a partial recovery only in the refractive index of the core while the reduction of the refractive index modulation observed during the irradiation remained unchanged.www.nature.com/scientificreports www.nature.com/scientificreports/ 5 %RH, i.e. where both miniaturized capacitive sensors and polyimide coated FBGs substantially lose accuracy. Nevertheless, to assess their possible application in the new generation of detectors foreseen within the HL-LHC project, a clear understanding of the physical and optical mechanisms involved during the LPGs radiation exposure is mandatory, together with a systematic study of their behavior under realistic radiation levels with respect to those expected at HL-HLC.Certainly, massive knowledge concerning the effects of irradiation on optical fibers and optical fiber-based devices has been collected over the years, but still not all the factors involved are completely clear and known. In 2018 Girard et al. published a very interesting review about the recent advancements on the radiation hardened fiber optic-based systems 13 , highlighting the potential and the future challenges of this innovative technology for the application in harsh environments. In ref. 13 the authors also provided an overview of the main radiation-induced effects on several classes of fiber optics and fiber optic-based technology, including both point sensors and distributed sensors. It is well-assessed that radiation alters the fiber properties by creating point defects in silica-based material due to ionization or displacement damage processes leading to structural modifications in the pure or doped amorphous host silica matrix...

Section: (A)supporting

confidence: 86%

Analysis of uncoated LPGs written in B-Ge doped fiber under proton irradiation for sensing applications at CERN

Berruti

Vaiano

Quero

et al. 2020

“…Concerning the radiation sensitivities, values of 0.73 nm/kGy and 1.34 nm/kGy were recorded respectively by OZ-LPG and Nufern-LPG, for absorbed dose values of 0.5 kGy. The sensitivity of Nufern-LPG can be placed among the highest values reported in literature3136.…”

Section: Discussionmentioning

confidence: 81%

Real-time analysis of arc-induced Long Period Gratings under gamma irradiation

Esposito

Ranjan

Stăncălie

et al. 2017

In this paper, we present a comparative experimental and theoretical study on gamma radiation sensitivity of Long Period Gratings (LPGs), fabricated by electric arc discharge technique, as monitored in three single mode optical fibers supplied by different manufacturers. A real-time measurement of LPGs’ wavelength shift was performed until a total dose of 35 kGy was reached, with average dose rate of 0.18 kGy/h, the irradiation being done at room temperature. In one case, a maximum radiation sensitivity of 1.34 nm/kGy was recorded for doses up to 0.5 kGy. Moreover, by combining experimental results with numerical simulations, it was found that changes occurred in the core refractive index of the irradiated optical fibers up to 2.5 ∙ 10−5. The increase of the core thermo-optic coefficient up to 1.5 ∙ 10−8/°C was observed as well.

“…Whereas, as reported in the current paper, it was found that under mixed gamma-neutron irradiation the corresponding wavelength variations were 11.7 nm, 6.4 nm, and 10.9 nm for the same types of fibers. Tests carried out emphases that the arc-induced LPGs considered herein show a higher radiation sensitivity as compared to LPGs produced by the CO 2 laser method, as these last samples showed saturation after 60 Co gamma irradiation from 1.45 nm up to 3.5 nm, at a total dose of 34 kGy 21 .…”

Section: Discussionmentioning

confidence: 88%

“…A comparative report was presented in ref. 21 , focused on LPGs written by CO 2 , FBGs and draw tower gratings (DTGs) irradiated under the same conditions. More recently, we focused on the effects of gamma radiation on LPGs written by Electric Arc Discharge (EAD) 22 , by a comparative analysis of two LPGs in standard fibers and one in radiation resistant fibers (from Nufern).…”

Section: Introductionmentioning

confidence: 99%

Arc-induced Long Period Gratings in standard and speciality optical fibers under mixed neutron-gamma irradiation

Stăncălie

Esposito

Ranjan

et al. 2017

In this paper, for the first time, the effects of mixed neutron and gamma flux on the spectral and sensing responses of Long Period Gratings (LPGs) are thoroughly analyzed. Six LPGs written by means of Electric Arc Discharge (EAD) technique in standard and speciality fibers, including radiation-hardened ones, were tested. The EAD technique was chosen because it enables the writing of gratings both in standard and not photosensitive fibers. The experiments have been carried out in a “TRIGA” pulsed nuclear reactor and the LPGs were irradiated by a gamma-ray dose-rate of 9 Gy/s and a mean 1.2∙1012 n/(cm2s) neutron flux. Real time monitoring was performed for a comparative investigation of LPGs’ response, in terms of radiation sensitivity and wavelength shift. Experiments show that LPG in a radiation-resistant fiber exhibits resonant wavelength shift higher than LPG in standard fiber. The changes of temperature sensitivity due to radiation were experimentally established by comparison of pre- and post-radiation characterization, indicating that radiation effects induce a slight increase of the temperature sensitivity, except for the LPG in pure-silica fiber. Theoretical and numerical analysis was combined with experimental data for evaluation LPGs’ parameters changes, such as refractive index and thermo-optic coefficient, after exposure to radiation.