Radiation Effects on Long Period Fiber Gratings: A Review

Abstract

Over the last years, fiber optic sensors have been increasingly applied for applications in environments with a high level of radiation as an alternative to electrical sensors, due to their: high immunity, high multiplexing and long-distance monitoring capability. In order to assess the feasibility of their use, investigations on optical materials and fiber optic sensors have been focusing on their response depending on radiation type, absorbed dose, dose rate, temperature and so on. In this context, this paper presents a comprehensive review of the results achieved over the last twenty years concerning the irradiation of in-fiber Long Period Gratings (LPGs). The topic is approached from the point of view of the optical engineers engaged in the design, development and testing of these devices, by focusing the attention on the fiber type, grating fabrication technique and properties, irradiation parameters and performed analysis. The aim is to provide a detailed review concerning the state of the art and to outline the future research trends.

A New Setup for Real-Time Investigations of Optical Fiber Sensors Subjected to Gamma-Rays: Case Study on Long Period Gratings

“…The results are reported in Figure 6, and the industrial SVST Co-60 irradiator (Figure 6a) is compared to the currently proposed setup based on the customized GC-5000 ( Figure 6b). As can be observed, in both cases the LPG resonance wavelength associated to the 3rd order cladding mode shifted to higher wavelengths as a consequence of an increase in the core refractive index due to the radiation, which is in agreement with the literature [23]. The shift was equal to 3.7 nm after a total dose of 35 kGy in the case of the SVST Co-60 irradiator, whereas for the GC-5000 setup it was 4.7 nm after a total dose of 52.6 kGy.…”

“…The test was performed at a dose rate of 0.18 kGy/h up to a total dose of 35 kGy, at around 23 • C temperature, and it lasted around 300 h, as seen in the irradiation profile (i.e., dose versus time) reported in Figure 7b. The grating attenuation band shifted to higher wavelengths, in agreement with the literature [23]: the response showed an approximate linear trend at lower doses, subsequently the slope decreased until it reached a saturation level at about 15 kGy. Several breaks in the irradiation can be observed in Figure 7b, which resulted in a partial recovery of the wavelength shift in Figure 7a due to bleaching mechanisms [32], as the source had to be periodically retracted in the water tank.…”

“…A residual refractive index change after recovery of 1.4 × 10 −5 was estimated for this wavelength shift by means of our approach based on numerical simulations [22]. Finally, the GC-5000 proposed setup was also used to observe the recovery phase at room temperature after the irradiation, as reported in Figure 8, where part of the radiation induced effects fades due to bleaching mechanisms [23]. Here, the wavelength shift is normalized to the value measured at the end of the irradiation and the time is reported as starting at the same instant.…”

“…Various experimental setups have been implemented for the real-time monitoring of optical fiber induced attenuation and optical fiber sensor response, as a consequence of gamma irradiation. The on-line recording of the results allows a proper evaluation of the temporary effects as well as insights into the cumulative effects [ 22 , 23 ]. For example, the evaluation of combined radiation and temperature effects on single-mode Ge-doped and F-doped optical fibers was performed at the IRMA 60-Co facility, Institute de Radioprotection et de Sûreté Nucléaire (France) [ 14 ].…”

Effect of Low-Doses of Gamma Radiation on Electric Arc-Induced Long Period Fiber Gratings

“…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]. It is well known from previous studies that the effects of radiation induce changes in fiber gratings.…”