Geo2 concentration dependence of nonlinear refractive index coefficients of silica‐based optical fibers

Abstract

AbstractThe nonlinear refractive index coefficient n2 dependence on the GeO2 concentration in optical fibers is quantitatively shown for SiO2 core fibers and GeO2‐SiO2 core/SiO2 clad fibers with Δ = 0.35–2.2% using an XPM measurement method where the phase change in the fiber of a probe signal caused by a pump signal is found from the delay self‐heterodyne spectrum. The GeO2 concentration distribution which determines the n2 distribution in the fiber is not uniform, and the measured n2 is the average of the product of the local n2 and the fourth power of the electric field in the fiber. In this work, this relationship of the measured n2, the cross sectional distribution of n2, and the electric field distribution in the fiber is used to define an effective GeO2 concentration, ηeff. This effective GeO2 concentration level is used to evaluate n2. The measured n2 increases proportionally to ηeff by the relationship n2[x 10–20 m2/W] = 0.0552°eff[mol%] + 2.44. Furthermore, the measured n2 in the fiber agrees well with the n2 of bulk glass obtained a semiempirically for the nonlinear refractive index coefficient derived from linear refractive index data.