Nonuniform distribution of oxygen hole centers in silica optical fibers

This letter reports spatially variant distributions of nonbridging oxygen hole centers (NBOHCs) in pure synthetic silica core optical fibers with fluorine doped silica claddings. Results of low‐temperature x‐band electron spin resonance (ESR) etchback measurements have established the presence of NBOHCs in increased concentration at the core‐clad interfacial region. The observations on a low‐OH content silica core fiber are contrasted with that on a high‐OH fiber. The correlation between the ESR results and the spatially variant luminescent patterns observed in these fibers during excimer laser irradiation is also discussed.