Spatial distribution of the red luminescence in pristine, γ rays and ultraviolet-irradiated multimode optical fibers

In this letter, a confocal microscopy setup was used to evaluate, with a resolution of 2 μm, the nonuniform spatial distributions of the red photoluminescence (640–750 nm) in pristine, γ rays (∼1 MeV, 1.2 kGy, and 0.33 Gy/s) and ultraviolet (244 nm and 127 J/cm2) irradiated multimode optical fibers. In pristine samples, the Raman scattering is predominant and the emitting centers are only present at low concentration in the fiber cladding. However, these centers are generated by both irradiations in the whole fiber cross sections, in particular near the core–cladding interface. The spectral deconvolution of the luminescence spectra showed that the Non-Bridging Oxygen Hole Centers are mainly responsible for this red luminescence. For both irradiation types, these centers seem to be predominantly created from precursor sites: strained Si–O–Si bonds which could be induced during the fiber drawing process.