Fig. 1. Light-energy coupling model of light-cone blackbody radiation cavity

Fig. 2. Schematic diagram of Lambertian radiant intensity at a certain distance

Fig. 3. Schematic of the end of fused-ball fiber

Fig. 4. Auxiliary light path (0≤x < r_s(1-cos θ))

Fig. 5. Auxiliary light path (r_s(1-cos θ)≤x < 0.4r_s)

Fig. 6. Relationship between coupling light intensity and curvature radius of the end face of spherical fiber

Fig. 7. Spherical fiber with different curvature radius

Fig. 8. Black-body cavity structure of spherical end-face fiber coated with black-body reinforcement

Fig. 9. Schematic of the experimental system

Fig. 10. Relationship between coupling light intensity and wavelength at different temperatures and spherical fiber diameters

Fig. 11. Relationship between curvature radius and coupling strength at different temperatures