All-solution doping technique for high power fiber lasers - refractive index influence in the vicinity of Al:P = 1:1

A novel and simple solution doping technique is used to explore the refractive index behavior of Al,P-doped SiO2 in the vicinity of the Al:P-ratio of 1:1 at low doping concentrations. It is found that even if Al:P = 1:1 is matched precisely an index increase is observed. This is in contradiction to previous findings in the literature and the already sophisticated models need to be refined in this region.