An experimental investigation on ultralow threshold laser and blue shift cooperative luminescence (CL) in a Yb3+ doped silica microsphere (YDSM) with continuous-wave 976 nm laser diode pumping is reported. The experimental results show that the YDSM emits laser oscillation with ultralow threshold of 2.62 μW, and the laser spectrum is modulated by the microsphere morphology characteristics. In addition, blue emission of YDSM is also observed with the increase of pump power, which is supposed to be generated by CL of excited Yb ion-pairs with the absorption of 976 nm photons and Si-O vibration phonons, and the process is explained with an energy level diagram. This property of the blue shift CL with phonons absorption in the Yb3+doped microcavity makes it attractive for the application of laser cooling based on anti-Stokes fluorescence emission, if the Yb3+doped microcavity made from with low phonon energy host materials.

A fiber-taper-microsphere-coupled system was used to research the characteristics of laser oscillation and upconversion luminescence of Yb3+:Er3+ co-doped phosphosilicate (YECP) microspheres. The YECP microspheres were fabricated by melting the end of phosphosilicate filaments. Single- and multimode laser oscillation at 1535-1565 nm within the C-band were obtained. In addition, the output power of the single-mode laser at 1545.5 nm can be as high as 48.98 μW, which was achieved under pump power of 9.63 mW, and the side-mode suppression ratio was 51.49 dB. Upconversion fluorescence of Er3+ at 521, 532, and 544 nm also were measured, and the pump power dependence was studied. The fluorescence intensity was lower than that of Yb3+:Er3+ co-doped silica and oxyfluoride glass ceramic microspheres. Moreover, the physical mechanism of upconversion suppression and laser oscillation enhancement observed in our experiment was presented, which is beneficial to the preparation of rare-earth-doped microcavity lasers.

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High-quality-factor microspheres with smooth surface are fabricated through surface tension by heating and fusing a single tapered fiber using arc of electrodes discharge. Stimulated Raman scattering of the third order nonlinear phenomena of microspheres with high power density whispering gallery modes was studied by coupling 976 nm laser into microspheres through tapered fiber as evanescent wave. The total six cascaded Raman lasers were observed in the experiment. At each order, single longitudinal mode and multi longitudinal mode Raman lasers were observed. The Raman laser at around 1200 nm was measured with pump power less than 582.6 μW. The sixth-order Raman laser at around 1287.04 nm was observed when pump power is 3.014 mW.