Fig. 1. Diagram of new inner cladding model

Fig. 2. Schematic diagram of light reflection on arbitrary surface

Fig. 3. Pump absorption characteristics of new inner cladding DCFs with different core diameters

Fig. 4. Pump absorption characteristics of DCFs with different inner cladding shapes

Fig. 5. Diagram of experimental equipments

Fig. 6. Relationship between pump current and pump power when temperature of pump source is 20 ℃

Fig. 7. Relationship between pump current and output power of thulium-doped DCF laser