Resonant and thermal changes of refractive index in a heavily doped erbium fiber pumped at wavelength 980nm

We report a theoretical and experimental study of the refractive index variation in a heavily doped erbium silica fiber within the spectral range 1500–1580nm under the pumping at the wavelength 980nm. The two main contributions in the refractive index change are addressed—the resonant part determined by the saturation effect in the fiber and the thermal part stemming from the fiber heating due to the excited-state absorption and Stokes losses. We demonstrate that the thermal contribution in the resultant refractive index change is a notable value, which is the feature of erbium fibers with a high concentration of erbium ions.