Spectral evolution of cooperative luminescence in an Yb3+-doped silica optical fiber

We have analyzed the cooperative luminescence of an ytterbium-doped silica fiber in which the ytterbium concentration is quite large, i.e., ∼1021 cm−3. The presence of a fast decaying component in a decay profile of 2F5/2→2F7/2 transition indicates the formation of ytterbium pairs in the fiber. The ytterbium cooperative luminescence spectrum is characterized by two peaks at 488 nm and at ∼512 nm, respectively. Overall intensity of the visible cooperative upconversion luminescence is proportional to excitation power at 980 nm. However, as fiber length increases, intensity of the shorter-wavelength side of the cooperative luminescence spectrum becomes smaller than the other portion, which results in a narrower spectral bandwidth.