Color Variation of the Up-Conversion Luminescence in Er3+-Yb3+ Co-Doped Lead Germanate Glasses and Microsphere Integrated Devices

Lead germanate glass samples co-doped with different Er
³⁺
/Yb
³⁺
concentrations were prepared and the color variation of the up-conversion emissions in these glasses was observed using a 980 nm laser pump. A practical optical integrated device based on Er
³⁺
-Yb
³⁺
co-doped lead germanate glass microsphere and a special fiber structure, consisting of single mode fiber (SMF), multimode fiber (MMF) and a suspended tri-core hollow fiber (STCHF) is described. As the pump light is coupled into the microsphere from the cores suspended inside the STCHF, the microsphere fixed in the air hole of the STCHF is excited and the up-conversion emissions are observed. Furthermore, when the pump power is increased, the luminescence output color of the microsphere can be readily tuned from yellow to green due to the change of the luminescence intensity ratio of the red to green emissions. This in-fiber microsphere resonator integrated device has the potential to be widely applied in multicolor displays, optical sensors and laser devices owing to its compact structure and excellent performance.