Abstract
Abstract Radiation-induced attenuation (RIA) of light and radiation-induced shift (RIS) of the resonant wavelength in fiber Bragg gratings (FBGs) during reactor irradiation up to a neutron fluence of 4.8 × 1020 neutron/cm2 (flux density 2.87 × 1014 neutron cm–2 s–1) and gamma dose of 2.3 × 109 Gy (dose rate 1.4 kGy/s) are studied. The FBGs were fabricated by femtosecond writing in radiation-resistant optical fibers (OFs) with an undoped silica glass core, as well as by UV writing in a standard germanosilicate OFs (SMF-28). The RIS of the resonant wavelength of the grating was 2.5–3.4 nm for all studied samples (except FBGs with a polyimide coating), which, apparently, is due to radiation-induced compaction of the silica glass matrix. In FBGs written through a polyimide coating, an anomalously large RIS was found in the short-wavelength spectral region (by ~1.5%), which linearly depended on the neutron fluence. Such a large shift, apparently, is due to the shrinkage of the polyimide coating under exposure to intense gamma-neutron radiation at high temperature in vacuum, which, even at a small coating thickness (~10 μm), leads to a significant compression of the region of the OF with the grating. Experiments have shown that, under such intense radiation, FBGs written in radiation-resistant optical fibers with a protective copper coating are preferable for practical use; FBGs with a polyimide coating can presumably be regarded as dosimeters; and germanosilicate fibers with FBGs are unsuitable due to significant RIS (~2 dB/cm).