Fig. 1. (a) Configuration of the proposed fiber laser; (b) picture of low-roundness microsphere cavity; (c) picture of high-roundness microsphere cavity; (d) picture of tapered fiber-microsphere cavity coupling system observed by a horizontal microscope; (e) picture of tapered fiber-microsphere cavity coupling system observed by a vertical microscope

Fig. 2. WGM resonant spectra of incident light in different polarization states

Fig. 3. WGM resonance spectra obtained by coupling of tapered fibers-microsphere cavity with different diameters

Fig. 4. Spectra output of the fiber laser

Fig. 5. Output spectral stability of the fiber laser. (a) Spectra measured every 3 hours; (b) detailed spectra

Fig. 6. Slope efficiency of the fiber laser