Radiation Effects on Graded Index Germanosilicate Multimode Optical Fibers

We study the nature and optical properties of room-temperature (RT)-stable defects responsible for the permanent <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula>-ray radiation-induced attenuation (RIA) in graded index (GI) multimode germanosilicate optical fibers. The two tested optical fibers conform to the OM1 and OM4 standards defining the achievable bandwidths for data transfer. The two F<sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">iber</small> samples were irradiated at doses up to 1 MGy(SiO2) at RT. Photoluminescence (PL) measurements reveal the presence of germanium lone pair centers (GLPCs) and nonbridging oxygen hole centers (NBOHCs) in both fibers. The GLPC concentration is higher in OM4 than in OM1 and decreases with increasing preirradiation dose. In contrast, the NBOHC concentration is higher in OM1, likely due to a positive impact of fluorine co-doping at the core–cladding interface of OM4, which reduces the concentration of strained bonds acting as possible NBOHC precursors. Spectral decomposition of the RIA shows that NBOHCs are the main RIA contributors in the visible range, while the GeY defect is the main contributor in the near-IR range. OM4 demonstrates greater radiation resistance than OM1, with lower permanent RIA values at 850 nm (74 dB/km) and 1310 nm (51 dB/km) compared to OM1 (100 and 88 dB/km) at 1 MGy.