Pump–probe measurement of metastable state lifetime reduced by cooperative upconversion in a high-concentration erbium-doped fiber

We report measurements of the metastable state lifetime in a high-concentration erbium-doped fiber. We use a single-wavelength pump–probe technique that allows us to measure the average lifetime over the entire fiber length. A reduction in the lifetime of approximately 20% caused by a cooperative upconversion effect is clearly observed when the input power is increased up to 10 mW. The input power dependence of the lifetime is analyzed using a simple model. The cooperative upconversion coefficient is determined based on this analysis.