Online Tests of an Optical Fiber Long-Period Grating Subjected to Gamma Irradiation

Abstract

This paper reports the outcomes of the tests that we conducted as online measurements for the evaluation of one optical fiber long-period grating produced by a fusion technique in a single-mode radiation-hardened optical fiber, and subjected to gamma irradiation. During the irradiation, the grating temperature was monitored. Before the irradiation, the temperature sensitivity of the grating was 27.7 pm= C, while the value of this parameter postirradiation was found to be 29.3 pm= C. The spectral characteristics of the grating were measured (i) in the laboratory with an ANDO AQ6317C optical spectrum analyzer and (ii) online, for the first time, with a LUNA OBR 4600 backscatter reflectometer, operating in the frequency acquisition mode. Such online measurement enables the study of recovery effects during the irradiation. The wavelength dip of the grating shifted under gamma irradiation, with 16 pm/kGy for the maximum total dose of 45 kGy. At room temperature, the recovery of the irradiation-induced shift of the wavelength dip was almost complete in about 120 h, at a rate of 6.7 pm/h. Postirradiation heating of the sensor produced the reversing of the recovery effect. The investigation indicated that, up to 45 kGy, the grating is more sensitive to radiation than other optical fiber sensors.

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

“…In principle, the fabrication of EAD-induced LPGs is possible in all kinds of optical fibers, and it was successfully demonstrated in boron co-doped fibers 18 , pure-silica core fibers 19 , photonic crystal fibers 20 21 , hollow core fibers 22 23 24 , cladding-etched fibers 25 26 . Moreover, the authors have recently successfully applied the technique to Fluorine-doped fibers 15 27 28 , which are fundamental for applications in radiation environments 29 30 31 , since they are significantly less sensitive to radiation as compared to standard Ge-doped fibers 19 32 .…”

“…About Long Period Gratings, there are only few reports concerning their behaviour under gamma ray irradiation. A detailed state-of-art concerning LPGs under gamma irradiation can be found in refs 30 and 31 . Briefly, tests on LPGs inscribed by CO 2 laser in N-doped optical fiber and by UV radiation in Ge-doped optical fiber are reported in ref.…”

“…A LPG manufactured in F-doped fiber, being produced by CO 2 method was studied in ref. 30 . Some other works dealing with specially designed long period gratings report their sensitivity to gamma radiation.…”

Gamma Radiation Measurements using an Optical Fiber Laser

“…After analyzing these IEDFs into lasers with ring cavities, the fibers were extracted from the cavities and characterized by means of an Optical Backscatter Reflectometer (OBR) LUNA OBR 4600, operating in the time domain acquisition mode with a spatial resolution of 4 mm, as it has been done in previous studies [5]. This instrument is used for component testing, enabling ultra-high resolution reflectometry with backscatter level sensitivity.…”

Arc-Induced Long Period Gratings from Standard to Polarization-Maintaining and Photonic Crystal Fibers

“…In particular, the high radiation sensitivity of P-doped fibers, with respect to standard Ge-doped fibers, makes them suitable for radiation dosimetry [ 74 , 75 , 76 ]. On the contrary, pure-silica core fibers have been proven to show very low radiation sensitivity and thus the devices written in these fibers have been studied for applications in ionizing radiation environments [ 62 , 67 , 77 ]. These are just few of the examples remarking how the fabrication of sensors in fibers having different physical properties, represents a fundamental step for further success of fiber optic sensing technology.…”