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

Abstract

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 tricore 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.

Recent progress of in-fiber WGM microsphere resonator

“…In addition, due to the diverse and flexible structures of the in-fiber resonator, a variety of optical mechanisms such as EIT [ 53 ] and Fano resonance [ 49 ] can be utilized to improve the properties or functionalities of photonic devices, such as optimize optical filtering [ 55 ] and realize optical switching [ 54 ]. The adoption of an active microsphere in the in-fiber resonator breaks the application limitation of the passive microsphere and further expands the application fields, including tunable luminescence colors [ 46 ], laser [ 28 , 48 ], self-reference biosensing [ 47 ], etc.…”

“…Color variation of the Er 3+ -Yb 3+ co-doped lead germanate glass microsphere was also investigated [ 46 ]. Glass samples were prepared by the above-mentioned melt-quenching method and the chemical compositions of the host media were 45 mol % PbO, 45 mol % GeO 2 , and 10 mol % Ga 2 O 3 .…”

“…As the two peaks around 547 and 659 nm are dominant while the peak around 524 nm is weak, the former two peaks was mainly considered in ref. [ 46 ]. The intensity ratio of the red emission around 659 nm to the green emission around 547 nm was found to be different for glass samples with different Er 3+ /Yb 3+ concentration ratios, and this difference induced variations of the luminescence color, as shown in the insets of Fig.…”

“…As the counterpart of passive microspheres, active microspheres are of great interest for in-fiber resonators because they provide the possibilities of remote excitation and breaking the limitations of passive microspheres. For example, color-tunable luminescence and self-referenced biosensing have been demonstrated by using active microspheres [ 46 , 47 ]. Additionally, in-fiber laser is a current hot spot and many efforts are being made to optimize the structure of optical fiber and to improve the coupling efficiency of in-fiber coupler [ 48 ].…”