Fig. 1. Schematic diagrams of highly Tm³⁺-doped silica fiber prepared by coating on inner wall of silica capillary and tapering.(a) Coating; (b) heat treatment; (c) secondary fused tapering

Fig. 2. Spectral performance of highly Tm³⁺-doped high-silica glass. (a) Absorption cross section; (b) emission spectrum (inset is infrared transmission spectrum)

Fig. 3. Simplified energy level diagram of Tm³⁺ and cross relaxation between Tm³⁺ ions

Fig. 4. Physical properties of highly Tm³⁺-doped silica optical fiber. (a) Element distribution at end face of optical fiber (inset is end face of optical fiber) ; (b) refractive index distribution of optical fiber

Fig. 5. Images of fusion splicing between highly Tm³⁺ -doped silica optical fiber and passive silica optical fiber

Fig. 6. 1947 nm fiber laser based on all-fiber linear cavity structure

Fig. 7. Laser performance of highly Tm³⁺-doped silica optical fiber. (a) Slope efficiency for different fiber length; (b) laser spectrum of 4.6-cm highly Tm³⁺-doped silica optical fiber (inset is laser spectrum in range of 1944-1951 nm)

Fig. 8. 1947 nm signal source and Tm³⁺-doped fiber amplifier

Fig. 9. Gain characteristics of 2.3-cm highly Tm³⁺-doped silica optical fiber. (a) Output signal intensity for different pump power; (b) gain coefficient curve