Fig. 1. Schematic diagram of experimental setup

Fig. 2. Resonance absorption spectra of microspheres coupled out of tapered fiber with 1550 nm ASE light source as pump source

Fig. 3. Schematic of Q factor testing. (a) Schematic of Q factor test setup; (b) oscilloscope display

Fig. 4. Yb³⁺ doped and Yb³⁺-Zr⁴⁺ co-doped self-stimulated Raman scattering spectrum under same pump wavelength but different pump powers(inset: a partial detail view of the highest order self-stimulated Raman scattering laser). (a) First-order self-stimulated Raman output spectrum of Yb³⁺ doped microsphere obtained under pump power of 18.5 dBm; (b) third-order self-stimulated Raman output spectrum of Yb³⁺ doped microsphere under pump power of 24.3 dBm; (c) third-order self-stimulated Raman spectrum of Yb³⁺-Zr⁴⁺ co-doped microsphere under pump power of 18.5 dBm, with third-order wavelength of 1295 nm

Fig. 5. Comparison of third-order Stokes laser threshold and conversion efficiency of Yb³⁺-doped and Yb³⁺-Zr⁴⁺ co-doped microsphere