Concentration quenching and clustering effects in Er:YAG-derived all-glass optical fiber

A detailed investigation of concentration quenching and ion clustering effects in Er:YAG-derived all-glass optical fibers fabricated using the molten core method (MCM) is presented. Fibers are drawn from four precursor Er:YAG crystals, each possessing a different Er³⁺ concentration. The resulting fibers exhibited active ion densities ranging from 2.58 × 10²⁵ m⁻³ to 19.5 × 10²⁵ m⁻³. Compositional and refractive index profiles (RIPs) are shown to be uniformly graded across the fibers, for a given core diameter, facilitating the study of the impact of draw and host composition on rare earth spectroscopy, a first to the best of the Author’s knowledge. Measurements of the fluorescence lifetimes indicate some degree of clustering persists in all fibers; however, its reduction can clearly be correlated to an increase in sesquioxide (Al₂O₃ and Y₂O₃) concentration. Similarly, the critical quenching concentration is also revealed to increase with increasing sesquioxide concentration and ranged from 23.9 × 10²⁵ m⁻³ to 40.4 × 10²⁵ m⁻³ in the present fibers. Finally, emission and absorption spectra were found to be practically indistinguishable between the various fibers, with a zero-concentration radiative lifetime determined to be around 8.3 ms. Compared with other silica-based hosts, this lifetime is slightly lower, giving rise to proportionately higher cross-sections.