Fig. 1. Refractive index diagram of the fiber in the bent and straight state

Fig. 2. Equivalent model of bent fiber

Fig. 3. Optical fiber cross-sectional structure diagram

Fig. 4. Optical fiber refractive index profile

Fig. 5. Actual refractive index profile for G.657

Fig. 6. VAD deposition process

Fig. 7. Test platform for the fiber

Fig. 8. Deuterium gas treatment tank

Fig. 9. Additional attenuation value after deuterium treatment with different concentration and treatment time

Fig. 10. Additional attenuation value of optical fiber hydrogen loss without obvious over-deuterium

Fig. 11. Trace retest attenuation result of 0.9% 80 h deuterium gas formula