Fig. 1. Light propagation mode in the tapered fiber

Fig. 2. Fiber diameter changes with operating wavelength

Fig. 3. System of KF-FBT

Fig. 4. Optics electronic eyepiece image of tapered fiber

Fig. 5. Waist diameter and length of tapered fiber changes with stretching time

Fig. 6. Waist diameter of tapered fiber changes with stretching length

Fig. 7. Energy distributions in tapered fiber with 2.475 μm tapered waist diameter. (a) Chart of energy distribution; (b) profile of normalized energy

Fig. 8. Normalized output optical power changes with wavelength when the tapered waist diameter is 2.475 μm

Fig. 9. Transmission spectrum of tapered fiber with 2.475 μm tapered waist diameter

Fig. 10. Tunable fiber laser based on tapered fiber

Fig. 11. Gain spectrum of erbium-doped fiber at 47 mW pump power

Fig. 12. Power of tunable laser and dual-wavelength laser when the tapered waist diameter is 2.475 μm