Extremely lower lasing threshold in Er3+/Yb3+ co-doped phosphate dual glass microspheres

Erbium-doped glass microsphere laser systems hold significant promise in the applications of bio-medicine and optical fiber sensing. However, their development has been hindered by the relatively high laser pump threshold. In this study, we proposed a unique dual microsphere system where two microspheres are affixed to a single-mode fiber taper and achieved a remarkably low lasing threshold of 19 μW for single-mode laser emission at 1544 nm. This is in sharp contrast with the lasing threshold of 56 μW observed in single microspheres. Our findings represent a significant achievement in the development of low-threshold, compact infrared laser sources for emerging applications in photonics.